Production of plastic-bonded explosive substances

A process for the production of plastic-bonded explosive substances wherein the binder is applied from aqueous dispersion is characterized in that polyurethanes applied in the absence of organic solvents are used as binder and in that the granulates obtained are dried and then compressed. Explosive substances obtained by the process are also provided.

This invention relates to a process for the production of plastic-bonded 
explosive substances of crystalline explosives and/or crystalline 
inorganic oxidizers, energy-generating additives and a polyurethane binder 
applied from aqueous dispersion without the use of organic solvents, and 
to the explosive substances obtained by this process. 
It is known, for example from German Offenlegungsschrift No. 2,709,949, 
that polyurethanes can be used in plastic-bonded explosive substances. The 
advantage of polyurethanes is that, in addition to good mechanical 
properties, they impart above-average resistance to shock and impact and 
minimal mechanical sensitivity to the explosive substances. Thus, 
explosive substances containing from 2.5 to 10% of polyurethane are 
described for example in the Encyclopedia of Explosives and Related Items. 
In the known process, the crystalline explosive substances are minerally 
mixed with the polyurethane binder by the slurry technique in which the 
polyurethane binder is dissolved in a solvent and the resulting solution 
is added to an aqueous dispersion of the explosive substance provided with 
protective colloids. By applying a complicated process, in which the 
solvent is distilled off from the mixture, it is possible to produce 
granulate in the required size. 
However, processes are also known in which the polyurethane binder is 
applied using the dry explosive with the sole assistance of organic 
solvents. In this case, too, the solvent is distilled off until granulates 
are formed. The polyurethanes used in these known processes are solid 
polymers of relatively high molecular weight, the binding process being 
physical, i.e. no reaction takes place. 
The reactive processes are known to start with liquid, hydroxy-terminated 
polyesters, ethers and butadienes which are crosslinked with isocyanates. 
The latter process is predominantly used when it is desired to obtain 
pourable mixtures of explosive substances. 
Between the slurry process and the reactive process there are a variety of 
different intermediate stages. The disadvantage of the slurry process in 
the described versions, apart from the use of organic solvents, is that it 
is difficult and expensive to carry out both technically and in terms of 
energy consumption. In addition, the recovery of large quantities of 
solvents is problematical. In the reactive processes, binder contents of 
less than 6% are difficult to disperse. Added to this is the disadvantage 
of having to operate under strictly anhydrous conditions to avoid any 
porosity in the explosive substance. 
U.S. Pat. No. 3,173,817 describes explosive substances which are produced 
from aqueous dispersion using a polyacrylate. In this case, the plastics 
dispersion is coagulated by the addition of inorganic salts and the 
explosive granulates formed are mechanically separated from the water and 
dried. 
The advantage of solvent-free processing is offset by the disadvantage of 
the poor thermal stability of the acrylates and the danger of inorganic 
coagulating agents being included to the detriment of the stability of the 
explosive. In addition, reproducible granulate formation, i.e. the 
production of a defined granulate, for compression-molding purposes is 
very difficult. 
In the same way as the known polyurethane-bond explosive substances from 
the slurry process, the granulates have to be compression-molded under 
heat to ensure that the pressing obtained has the desired properties. 
However, compression-molding under heat is technically difficult and 
expensive. 
Accordingly, the object of the present invention is to provide a process 
for the production of plastic-bonded explosive substances in which the 
disadvantages referred to above do not arise. More particularly, the 
object of the invention is to provide a process in which 
1. polyurethane binders are used, 
2. the explosive substances are produced from aqueous dispersions without 
any need to use organic solvents, 
3. the granulates obtained in the process can be cold-pressed and extruded, 
4. both processes may be varied and explosive substances differing in their 
properties may be obtained. 
Accordingly, the present invention relates to a process for the production 
of plastics-bonded explosives, the binder being applied from aqueous 
dispersions, characterised in that polyurethanes applied in the absence of 
organic solvents are used as binder and the granulates obtained are dried. 
According to the invention, novel, aqueous aliphatic and/or aromatic 
polyurethane dispersions having a solids content of from 30 to 40% are 
used. Polyurethane dispersions of this type are commercially available. 
They have particle sizes in the range from 0.1 to 0.4 .mu.m and specific 
gravities of the order of 0.9 to 1.2, preferably 1.1. The pH-value of 
these dispersions may vary and is generally in the range from 5 to 8. 
However, the pH-value of the polyurethane dispersions depends upon their 
production and is of no significance to the process according to the 
invention. Transparent, approximately 0.1 to 0.2 mm thick films produced 
from commercially available aqueous dispersions of this type have breaking 
elongations, as determined in accordance with DIN 53504, of more than 500% 
and in addition show high tensile strengths. 
Aqueous polyurethane dispersions of this type dry irreversible to form 
highly elastic films which adhere excellently to the crystals of 
explosives. The thermal stability and compatibility with blasting 
explosives of the polymers according to the invention is comparable with 
that of hitherto used polyurethanes so that the advantages of the 
polyurethanes may be exploited without being offset by the disadvantages 
of complicated processing. 
The blasting explosives obtained with the polymers according to the 
invention may be cold-pressed very effectively under pressures of less 
than 2000 bars. If necessary, the mechanical properties of the polymers 
may readily be adjusted by using high-polymer, water-soluble plasticizers 
or reinforcing resins which may be dissolved in the water of the 
dispersion in accordance with the invention, forming a film with the 
polyurethane. 
Polymeric plasticizers are used because the migration phenomena of the 
plasticizer observed in the case of polymers plasticized with low 
molecular weight plasticizers have to be avoided. 
The plasticizers used in accordance with the invention are, for example, 
polyethylene glycols, polypropylene glycols, polyvinyl pyrrolidone and 
polyvinyl methyl ether, but preferably polyethylene glycols having a 
molecular weight of at least 5000, which although soluble in water are not 
hygroscopic, and polyvinylethers. Water-soluble reinforcing resins are 
epoxide resins such as 3,4-epoxycyclohexyl methyl- and 
3,4-epoxycyclohexane carboxylate and the reaction product of 
pentaerythritol and epichlorhydrin, polymethoxy melamines, 
polyethylene/maleic acid anhydride copolymers, polyacrylamide and phenolic 
resins. The reinforcing resins work in different ways. Whereas the epoxide 
resins are hardened with a water-soluble hardener parallel to the physical 
drying and film-forming process of the polyurethane, the 
polyethylene/maleic acid anhydride copolymer films together with the 
polyurethane to form films characterised by increased mechanical strength. 
The polymethoxy melamines, phenolic resins and the polyacrylamide are 
dissolved in the dispersion, but change at the temperatures prevailing in 
the process during drying in the range from 40.degree. to 50.degree. C. 
into soluble, crosslinked products which produce an increase in strength. 
Table I shows both some plasticizers and also reinforcing resins and their 
effect on one of the polyurethane dispersions according to the invention. 
TABLE I 
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Pro- 
portion 
in the Tensile Breaking 
binder strength elongation 
Substance (%) (N/mm.sup.2)* 
(%) 
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1. Polyurethane binder 
100 40 300 
from dispersion 
2. Polyethylene glycol 
5 27.5 600 
20,000 
3. Polyethylene glycol 
10 11 720 
20,000 
4. Polyvinyl methyl ether 
15 34 520 
5. 3,4-epoxycyclohexylmethyl 
5 59 350 
and 3,4-epoxycyclohexane 
carboxylate + polyol- 
silane hardener 
6. Polyacrylamide 10 68 220 
7. Polymethoxy melamine 
15 84 200 
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*as measured on films 0.1 mm thick 
It has been found that the proportion of plasticizer in the binder should 
amount to between 0 and 30% and preferably to between 5 and 15% and that, 
within these limits, it is possible to produce extrudable, elastoplastic 
explosive compositions. The proportion of reinforcing resin is determined 
above all by its compatibility with the polyurethane and by its solubility 
in water. It should amount to between 0 and 50% and preferably to between 
2 and 20%. 
Crystalline explosives which may be processed with the binder according to 
the invention must above all be insoluble in water. Accordingly, it is 
possible to use any crystalline, water-insoluble primary and secondary 
blasting explosives such as, for example RDX, HMX, nitroguanidine, 
potassium and guanidine picrate, tetryl, diamino- and 
triaminotrinitrobenzene, benzotrifuroxane, diaminohexanitrobiphenyl, 
hexanitrostilbene and pentaerythritol tetranitrate, this list being by no 
means complete. 
In the process according to the invention, the proportion of crystalline 
explosive in the composition as a whole may amount to between 50 and 
99.8%, i.e. even the smallest quantities of binder may be applied without 
difficulty. 
The explosive substances according to the invention may be produced by two 
methods. Either the aqueous polyurethane dispersion is initially 
introduced with the plasticizers or reinforcing resins and the water-moist 
explosive substance is mixed in using a suitable mixer. This process is 
suitable for binder contents of up to 8%, the water content being 
controlled by the addition of water where the binder content is smaller. 
The moist explosive composition may then be safely granulated and dried. 
This process is known per se. With higher binder contents, the mass 
becomes so pasty that mechanical granulation is impossible. In this case, 
a dispersion of the binder and blasting explosive is prepared in a 
relatively large quantity of water and the binder is coagulated. 
Granulates are formed, being separated from the water and dried. 
According to the invention, coagulation is carried out with the 
polyvinylmethyether already described as plasticizer to avoid 
contamination by inorganic salts. This material has the property of 
precipitating from the aqueous solution in finely divided form on heating 
and thus breaking the polyurethane dispersion. 
Another possible method according to the invention of coagulating the 
binder is to add the phenolic resins described as reinforcing resins. In 
this case, the coagulation time may be precisely set through the 
proportion of phenolic resin, thus enabling controlled granulate formation 
to be obtained. It is a particular advantage that the grain size of the 
crystalline explosive substances and additives is not critical. Thus, 
nitroguanidine for example with a grain size of from 1 to 2 .mu.m may 
readily be processed into compression-moldable granulate so that there is 
no need to use expensively recrystallised nitroguanidine. 
However, the main advantage of the process according to the invention lies 
in the fact that it is easy to carry out using simple machinery, safety 
being guaranteed by the fact that processing is carried out in the aqueous 
phase. 
Another very considerable advantage lies in the very good cold-pressability 
of the granulates which may be controlled through the proportion of 
plasticizer. Thus, it is possible to produce elastomeric pressings in the 
pressure range from 800 to 2500 bars with the same binder content, but 
with a different plasticiser content. 
One advantage over the equally cold-pressable explosive substances 
containing liquid two-component polyurethanes is that there are no pot 
lives to be observed nor any thermal after-treatments required for 
hardening, in addition to which the granulated blasting explosive may be 
indefinitely stored. By virtue of the good flow properties of the binder, 
the duty times of the presses may be kept short, i.e. of the order of 2 to 
3 s. 
Finally, a major advantage is that the mechanical properties of the charges 
produced from the explosive substances according to the invention may be 
adapted to meet particular requirements--for the same performance data--by 
modifying the binder in the manner described. 
It is obvious that the process is not limited to the production of the 
described binder/explosive mixtures, instead explosive substances may also 
be produced from the binder according to the invention, organic 
crystalline explosives and inorganic salts as well as energy-generating 
metal powders. These salts known per se may be perchlorates, such as 
potassium perchlorate, nitrates, such as barium nitrate, heavy metal 
oxides, such as lead, iron and copper oxides. Metal powders may be 
aluminum, aluminum-magnesium alloys, silicon, titanium, zirconium and 
tungsten. Finally, it is also obvious that the explosive substances 
according to the invention may also be used as porpellent charge powders 
instead of conventional nitrocellulose powders. 
In this connection, it is a considerable advantage that the binder may be 
formulated in such a way that the mixtures may be extruded cold or at 
moderately elevated temperature and no solvents are required. 
The invention is illustrated but in no way limited by the following 
Examples.

EXAMPLE 1 
142.5 g of an aqueous polyurethane dispersion, 3 g of polyethylene glycol 
(molecular weight 20,000) and 1034 g of RDX (average grain size 60 .mu.m, 
10% water) were mixed for 15 minutes in a vertical kneader. The most 
friable mass was passed through a mechanical granulator. The granulates 
obtained were dried for 24 h at 50.degree. C. Thereafter the blasting 
explosive had a water content of 0.1%. 
EXAMPLE 2 
The granulates of Example 1 were compression-molded at 20.degree. C. under 
pressures of 1500, 2000 and 2500 bars to form pressings 30 mm in diameter. 
The densities of the resulting pressings amounted to 1.68, 1.71 and 1.735 
g/cc (98% of the theoretical density). 
EXAMPLE 3 
The granulates of Example 1 were subjected to a stability test at 
120.degree. C. (amount weighed in 2.5 g). 
______________________________________ 
Evolution of gas 
Time (h) ml/2.5 g 
______________________________________ 
2 0.2 
4 0.25 
6 0.25 
8 0.3 
10 0.3 
20 0.3 
______________________________________ 
The blasting explosive shows high thermal stability. 
EXAMPLE 4 
The detonation rate of pressings obtained in accordance with Example 3 was 
measured. A value of 8360 +40/-20 m/sec was obtained for a density of 
1.735 g/cc. 
EXAMPLE 5 
A nitroguanidine having an average grain size of 1.8 .mu.m was processed in 
accordance with Example 1. On account of its poor bulk density, the 
nitroguanidine was mixed in three portions and 6% of water (based on the 
total quantity) was additionally introduced. 
The mass obtained granulated excellently. At 1.6 g/cc, the the pressing 
density of the blasting explosive reached at 2000 bars amounted to 95% of 
the theoretical. 
EXAMPLE 6 
800 g of RDX, 150 g of aluminium (92% metal) and 125 g (5%) of an aqueous 
polyurethane dispersion were suspended in a stirrer-equipped vessel. After 
the addition of 20 g of a 50% phenolic resin/formaldehyde condensate, the 
dispersion coagulated in 60 s. Granulates varying from 3 to 4 mm in 
diameter were formed. After drying, the granulate could be pressed at 2500 
bars/20.degree. C. into pressings having a density of 1.86 g/cc. 
EXAMPLE 7 
A suspension of 820 g of RDX, 18 g of PEG 20,000 and 405 g (16.2%) of the 
aqueous polyurethane dispersion according to the invention was prepared in 
accordance with Example 1. Following the addition of 50 g of a 10% aqueous 
solution of polyvinyl methyl ether, the temperature was raised to 
45.degree. C. The dispersion coagulated and granulates having a grain size 
of from 1 to 2 .mu.m were formed. The dried, highly elastic granulates 
could be extruded at 50.degree. C. into dimensionally stable shapes. 
The compositions according to the invention may be used as smokeless 
propellants.