CA1110074A - Water resistant high explosive - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A particulate high explosive material characterized in that said particulate high explosive mate-rial has been treated with an alkyl ester of an aromatic or an aliphatic acid, the ester being characterized in that it has a melting point no higher than a temperature of -10°c.

Description

1~1~74 ~ 2 -This invention rela~es ~o particulate l~ expLosi~ematerial treated to impro~e its resistance to water desensiti~
.sat-on, to methods for the manufacture of the treated par~iculate hi.gh explosive material and to de-tonating cord contalning ~aid treated particulate high explosive material.
Particulate high explosive materials such as, for example, pentaerythritol tetranitrate ~PETN) are widely used as a base charge in commercial detonators and as the core ma~erial in detonating fusecord. Fusecord of tllis kind, commonly and hereinafter referred to as detonating cord, is widely used for detonation transmission lines for blasting and for g~nerating seismic waves in land ~nd marine seis~.ic prospecting. One form of detonating cord may ~e made by - locating dry discrete solid high explosive particles in an encasing~ thermoplastic tube as described i.n Australian Patent Specification No 221 849. Generally the detonating corcl com-prises a core consisting of dry compacted high explosive particles such as, for example PETN or cyclotrimethylcne-trinitramine (RDX) surrounded by non-explosive wrapping ma~erials. The core is often encased in an envelope of paper or plastics film reinforced with wrapping materials usually co~-prising one or more spun layers of textile yarns surrounded by a watcrproof sheath of thermo~las~ics material. ~n the manu-facture of cords of tllis cons~ruction a lon~ituclinal tape is contillually convoluted to form a thin tube by pass:in~ jt thr~ugi~

.. ~

a die~ particl~late explosive material is con~inuously ~ed throu~h the die lnto the tubc thus formed and consolida-ted ~ passing tlle tube through compacting dies, te~tile yarns on bobbins rotating around the tube are continuously he7ically S wound around the tube and the thermoplastics sheath is extrnded around the yarns. In order to assist the flow of the partic~ te explosive material into the tube one or more central yarns may be contiruously drawn throug'n the die as the detonating cord is formed and remain in the finished cord.
I'he explosive core of con~ercial detonating cord is rcadily desensitised by water and if an open end of the cord is immersed in water sufficient water may permeate through the particulate explosive material to cause the cord to fail to propagate detonation. In blasting operations, for example in q~arrying and opencast mining, it is common practice to conncct blasting charges in deep water-fillerl shotholes with detonation transmission llnes of detonating cord which ~ay be r~uired to remain in~ersed in the water for sc~eral days be-f'orc the charges are fired. Therefore, a detonating cord having an improved resistance to water perme~tion is of considera~le importance in quarrying, mining and in application3 such as mar3ne seismic prospecting. In attempts to reduce the desensitisation of the cores of detonating cords it hls been proposed to treat the high explosive component with solid materials ~ihich prevent the ingress of moisture into and on to the higll explosive material. Typical examples of such solid materials includc salts or ester3 of long chain saturated carboxylic acids such as calcium stearate which has a melting point of about 179C or butyl stearate which has a melting S point of about 16C. Again in the specification of USA Patent 3, 884, 735 it is taught that PETN or RDX may be rendered water r~si~tant by treating the high explosive with a solid polymeric material such as an epoxyhydroxypolyester typified by the material available commercially under the re~istered tra,de name of "Araldite" 6020. Whilst the use of .solid waterproof~ng agcnts has provided some improvement in water resistance, it has usually been at the expense of other desirable attributes of the explosive core. Thus for example the use of solid materials such as calcium stearate tends to reduc~ the flow rate of the core material in comparison with the flow rate of untreated high explosive core materials; furthermore the use of solid waterproofing agents in conjunction with the high explosive component can lead to uneven distribution of the solid agent in the core and the local concerl~ration of such agents may lead to uneven detonation rates or may e~en cause a cessation of the detonation of the core. Detonating cord is used under a wide range of conditions and en~ironments such as in hot tropical regions, wet temperate regions or in cold sub-polar or polar regions and it is highly desira~le tl~at ~odif~ing ~5 agents in cvntac~, with the core of high explosive ma~erial should * Registered Trade Mark }74 bc a~fccted as little as possible by the range of temperatures of the enviror~en.t.s in whi.ch it may ~e used. Thus it would be advantageous that the modifying agent ~e relatively non-volatile in situ.ations where elevated temperatures are likely S to be encountered, and likewise the agent should not be trans-formed to a solid state under cold conditions. We have now found a class of ma-terials which are eminently suitable as modifyi.ng agents for use in admixture with high explosive core material. The members of this class of material ha~e~ in general terms, high boilin.g points, low vapour pressures at ambient temperatures and low melting points and include es~ers which ha~e hitherto been used as plasticizer~ in t,le preparat;ion of plastics composi.tions. Not only are the~- relatively stable over a wide range of temperatures but surprisingly they impart a degree of ~ater resistance to particulate high explosive materials. From within this class of esters we have found that a useful. subclass comprises esters of aromatic or aliphatic carboxylic acids, and more particularly compr;ses e~ters selected from thc group consisting of alkyl esters of unsaturated fatty caids or hydroxy derivatives thereo~, alkyl es~ers of saturated dicarboxylic acids and alkyl esters of aromatic dicar~oxylic aci.ds. A preferred subclass of estel-s is the class wherein the aromatic dicarboxylic acid moiety is phthalic acid. So as to ensure that the difficulties of the pri.or art relating ~o the use of solid modifying agel2ts are reduced it is desirahl~ that t;lle modifying agents of the invention have melting points belo~J a temperature o~ abcut -10C and preferably l)elow a ~emper;ature of about ~25C.
Accordingly in one embodiment of the invention there is provided a particulate ~gh e~plosive composition comprislng particulale h;~h explosive material and a modifying water-resisting agent, said agent being eharaeterised in that it eom-prises an esGer of an acid selected from the group eonsisting o~
aliphatie and aromatic aeids, and being characterised further in that the said agent has a melting point no higher than a temperature of -10C. In a preferred embodiment of theinvention ~here is provided a high expl~sive eomposition as deseribed above wherein the said ~gent has a melting point no higher than a temperature of -25C. In ar~ther embodiment of the invention there is provided a high explssive composition as deseribed above wherein the said ester is an ester selected from thc group eonsisting of alkyl ester~ of unsaturated aliphatie aeids~
~ypieally maleie acicl,oleis aeid, or hydroxy derivatives thereof~
typieally rieinoleic acid; alkyl esters of saturated aliphatie dicarboxylic aeids, typieally oxalic, suecinie aeid, adipic acid, sebacie aeid or azelaic acid; and alkyl esters o~ aromatic d~carboyxlie acids,typicall~Y a phthal}c acid. In the instances wherein the ~aid agent is an alkyl ester the alkyl groups ~hereo may be straight or branched chain al~yl groups and eonveniently containing from 1 to 18 carbon atoms in the chain. Optionally ~he alkyl groups may be substituted, ancl thus provide, for example~ alkoxyalkyl groups or alkylacetyl groups. In the instances where the acld component of the est;er is a dicarboxylic acid the ester may contain two alk~l groups wllich may be the sa.ne or different. One preferred group of modifying agents is a group derived from a phthalic acid and alkyl moieties containing from 4 to 12 carbon atoms in a straight or branched alkyl chain. Typical examples of thiæ group include di-n-octylphthalate, di-iso-octylphthalate, dinonylphthalate, di-2-ethylhexyl isophthalate, diisodecyl phthalate or kutyl ethylhexylphthalate.
So as to facilitate the understanding of the i.nventi.on there is set out below in Takle 1 a list of typical esters w~ich are useful as modifying agents in the invention. Table 1 also includes published appro~imate melting points of the com-pounds and such information is included to provide a basis forthe choice of an a~ent for use under environmental conditions likely to be encountered when the compositions of the in-vention are used. It will be appreciated that variations in the purity of the ester may cause variations from the listed melting points, and furtllermore when mixtures o f such esters are used to form the modify7ng agent the melting point of the mixture will nrobably di.ffcr from thc melting points o the indivi.dual ester componei1ts.

TA~lE L

C~.b~ cid Alkyl mo~ety Meltong Point _ .____ ._ ____. _ Adipic acid Di~et,hyl -14 Di-isobutyl -20 Di-2-ethylh~exyl .~75 Di-.iso-nonyl Rangingb from -70 Di-nonyl ~65 Di-deeyl Ranging from -84 . Di-m~thoxyethyl -16 Di-butoxyethyl ~34 _ ____ .
Azelaie aeid Di-2-ethylhexyl Below 65 Di-n-hexyl -24 Di-iso-oetyl -68 Isophthalic aeid Di~2-ethylhcxyl -46 _ _ Maleic aeid Di-~rthyl -19 Oleie acid Amyl -4o Butyl Below -10 Methyl -16 n-propyl 20 ~_~ _ ____ Oxalie aeid Di-pIopyl ~44 Di-butyl -3o ~ _ _ Phthalic aci.d Di-amyl Below -55 Di-butyl -4~
Di-iso-butyl _50 Di-iso-de~yl -37 Di-2-ethylhexyl -46 ~ ._ ~'ABL~ 1 (Continued) __ _ :

moiety Alkyl moiety C
_ _ , .
Phthalic acid Di-methoxyethyl ~40 Di-i,so-nony~l -48 Di~n-octyl -25 Di~iso-octyl -46 Butyl ethylhexyl ~3~
Butyl isohexyl -5o Butyl octyl Below -5 . Decyl ethyl hexyl -48 ~ . .
Ricinoleic acid Butyl -10 n-butyl acetylRanging from -65 to -30 Methyl -3o Methyl acetyl ~ . _ Sebacic acid Di-~utyl -12 Di-octyl -4o . Di-i.so-octyl Ranging from -50 to ~4 _ _ . . Di-butoxyethyl _~_ Succinic acid Di-butyl ~ -19 The higII ex~losive material component of the co~position of the invention is suitahly a material which has been used conventlonally to form high explosive cores in detonating cords of the prior art. Suitable materials include, fOI' examplc, nitramines such as cyclotrimethylenetrinitramine (RDX? or cyclotetramethylenetetranitramine (H~IX), nitrates o~ po]yhydric l~'g~74 alcvhols such as pentaerythritol tetranit,rate ~PE~Nj, mannitol hexanitrate or erythrityl tetranitrate, nitroaromatic compounds sueh a,5 trinitrotolnene or nitroglycols such as ethylene glycol mononitrate. Pentaerythritol tetranitrate is a particularly preferred material. If desired, mixtures of high explo$ive materials may be used.
The proportions of modifying agent and highexplosive material in the compositions of the invention will vary de-pendent on thc nature of the individual components and the use to which tlle composition is to be put. Thus for example the modifying agent May constitute as much as 5% w/w of the composition and it has been found that as little as 0.005% W/~l of the modifying agent imparts some resistance to the dele.,erious action of aqueous media on the high explosive material. More usually, amounts of modi~ing agent whi~h con,stitute from 0.01 to 1% w/w of the composition provide adequate water resistance without unduly affecting the detonating ch~racteristics of the composition and excellent detonating cord can be made ~y a conventional dry spinning process when the modifying agent constitutes from 0.05 to 0.~% w/w of the composition used to make the core of the detonating cord.
In a further aspect the invention provides methods of preparlng the high explosive compositions o the invention.
The high explosive material is conveniently treated with

2~ the modifying agen~ when the high explosive material is in solution or suspended in solvent or damp with solvent. For example, PETN ls usually purified by crystallizatioll from acetone solution and it is convenient to ~dd the mod.ifying agent either to the solutiorl of PETN in acetone or~ after the PETN has crystallised, to the agitated mixture of PETN crystals in the acetone mother liquor. Alternati.vely, if desired the .
modifying agent may be added to the filter cake of P~TN crystals before drying. The modifying agent may be added without dilution to the solution of PETN in acetone or to the agitat;ed mixture of PET~ crystals in th~ acetone mother 3iquor. If desired the modifying agent may be added to the PETN solution, or suspension of PETN crys~als, in diluted form in an appopriate solvent. In the preparation of modifying a~ent - treated YETN
it has been found convenient to add the liquid agent~ prefera~ly a di-C6-C12 al~yl phthalate~ isophthalate or terephthalate, after the PETN has crystallised, to the continuously agitated mi.xture of P~TN crystals in the acetone mother liquor. The treated P~TN is readily separated and dried by cor.ventional methods.
In general we have found that the compositions of the invention may be used to manuracture detonating cord in the plant normally used for the manufacturc of detonating cord.
In yet a further aspect the invention pro~ides detonating fusecord comprising a detonable core component located within a casing component said csre component being characterised i.n that it comprises a particulate high explosi~e ~ ~;lQ~74 compo.sition of thc invention as hereinbefore described.
The particle size of the higll e;piosive composition suitahly may be similar to the particle size of high explosi~e material which is normally used in the preparation of detonating cord. Thus particles havin~ a surface area of about 400 s~ua-re centimetres per gram are useful. However~ the efficacy of the detonating cords of the invention is increased as the surfaces -area of the particles is increased and it is preferred that the particles have a surface area of at least about 500 square centimetres per gram and particles having a surface area in the range from 1000 to 6000~ for example from about 1500 to 2500 square centimetres pcr gram, are rnore preferred or most practical purposes.
The ca~sing component in which the core component is enclosed may be formed in situ as the detonating cord is being made or it may be a preformed component. Thus~ for example, the casing component may he of a type wherein the core is fed into a casing made in situ an~ comprisin~ an envelope of paper or plastics film around which is applied reinforced yarns Z0 and over which is then extruded an abrasion resistant sheath o thermoplastic material. Alternatively the casing component may be in the form of ~ preformed tube which suitably may be of soft metal such as lead or an alloy thereof or of a thermo-plastics composition comprising material such as polyamides, for example a nylon, polyolefins such as polypropylene, poly-

3 --et;hylene or copo~.ymerfi ~hcr~of such as may be derived fromethy;'ene and viny]. esters typi.cally vinyl acetate, polyesters sucl- as polyethylene terephthalate~ or poly~inylchloride.
Rub~er compositions derived. from natural or synthetic rubbers are also useful. Such tubes iP desired may be of the rigid type~ for example they may he fabricated from nonplasticized or li.ghtly plasti.ci.zed polyvin.yl chloride compositions~ but it i~ preferred that they be reasonably flexible~ for example they may be made from plastlcized polyvinylchloride composi.tions.
Flexible tubular casing components made from polyolefins, typically polyethylene or polypropylene are especially preferrefi.
Suitably the internal diameter of the casing component may be in thc range from about 1/8 inch to about one inch~ but casings of an internal diameter beyond this range may be used if ~sired.
S The casing components may ~!ave a plain outer surface, but it is often advantageous to provide them with an exterior braiding or with a foamed exterior or with an exterior wherei~ the surface is not smooth5 for example it may be ribbed or fluted, to provide the casing component with enhanced resistance to abrasion, tear ~0 and impact as well as providJng the detonating cord with good flexure or knot ho].dlng properties. Dependent to some extcnt on the flow properties of the core component and the natllre of the casing component~ the core component may be fed to the casing component by pouring, injection or extrusion or by appli-cat~on of suction.

t74

4 --The construction and manufacture of a detonating cordin accordanc:e with the invention is hereinafter described, by way of exarnple on3.y, with reference to the accompanying drawing ~owin~ diagrammatically a length of fuse-cord with one end dissected to illustrate the manufacturing sequencer In the manufacture of the detonating cord a central core 1 of particulate explosive material is fed from a hopper exit into a thin tube 2 formed by convolution of a tape. A
yarn 3 is trained through the hopper exit and along the axi~
of the tube 2 to remain within the core 1. The tube 2 is s~rrounded by a spun layer of textile yarn 4 and a counterspun layer of textile yarn 5 and the layer 5 is coated with an extruded. layer of thermoplastics material.
We have found that detonating cord having a core of particulate high explosive material which has been treated with a liquid agent as hereinbefore described is markedly superior to similar cord using the untreated high explosive material in it.s ab~lity to resist the migration of water along the core, and that such cord is much less liable to failure through water de-sensitisation. Surprisingly we have found that PETN or tri-ni.troto~uene (TNT), for example, needs to be treated with only a small percentage by weight of such an agent,for example diisooctyl phthalate~to significantly improve its water r~sistance. Furthermore, PETN tre~ted with a small percentage of diisooctyl phthalate according to thi.s in~ention has no noti.ceable loss i.n sensiti,vity to detonation.
, We ha~e al.so found that the high cxplosive compositions of the invention may bc used in the conventional manne~ to manufacture detonati.ng cord without the additi.on o specific anti-static agen,ts to the compositions. However, if d,esired one or more of the anti-static agents known in the art, may be added to the high explosive composition of the in~renti.on.

l'he invention is now illustrated by, but is in no way limited to, the following examplcs wherein all parts and percentages are on a weight basi~ unless otherwise specified.
Examplcs 4 to 6 are not ac_ording to the invention and are S included for the purposes of comparison.
Example 1 Diisooctyl phthalate (2 parts was added to an agitated slurry of pentaerythritol tetranitrate (1000 parts) in aqueous acetone and the mix-ture was agitated until the diisooctyl phthalate was uniformly mixed into the slurry. The diisooctyl phthalate (DIOP) treated PETN was separated and dried.
For the purpose of comparison PETN treated with 1.5%
by weight calciw,n stearate (a solid additive known in the ar~
for waterproo~ing particulate exp'.osives~ was prepared by a similar method to that described for the preparation of ~IOP
treated PET~.
For the purpose of comparison PETN treated with 0,05%
o~ nonylphenol condensed wi-~h an average of 8 moles of ethylene oxide (a surfactant kno~ in the art as an anti-static additive) was prepared by a similar me-thod to that descri,bed for the preparation of DIOP treated ~ETN.
Examp:les 2-6 Detonating cvrds were prepared ~rom the DIOP treatcd PETN~ calcium stearate (CaSt) treated PETN and surfactant (Ng3 treated PET~ of Example 1 according to the process dc,scribcd 1~0~74 in the specifi-ation with reference to the accompanying drawing.
The explosi.ve core 1 was the treated PET~ loaded at a char~e rate of 10 g per metre into a tube 2 for.~ed from a 16 mm wide polyethylene transport tape. The wrapping yarns in the layers 4 and 5 were either 1260 denier nylon or 1100 denier poly--propylene, the layer 4 consisting of 8 yarns helically wound at 30 turns per metre and the layer 5 consisting of 10 yarns helically wound at 30 turns per metre. The sheath 6 was ex-truded polyethylene.
Each of the detonating cords produced was tested for water penetration. For this test 1 metre lengths of the cord were suspen~ed vertically in a tank containing a 3 metre depth of water so that each end of the PETN core of the cord was exposed to the water and the bottom end of the cord was under a 3 metre head of water. After- immersion for 24 hrs the cords were with~rawn from the tank, and the lower half (50 cm) of the cord was cut into 5 cm lengths and each len~th analysed for water content. The results are presented in Table 2 wherein the 50 cm lcngth is measured from tile lower immersed end (0 cmj to the point halfway along the cord (50 cm) and the water conten~ is given as ~ by weight.
The upper 50 cm half of the test detonating cord was t~stcd for sensitivity by firing a test detonator applied to the upper end of the cord (i.e. thc end exposed to the water in the immersion test). The test detonating cords of EYamples ~SlOQ74 18 ~ r 2 and 3 were fired by a test detonator after the :immersion test indicating that the immersion in water had not desensitised the PETN.

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The general procedure of Example 3 was repeated except that the DIOP of that Example was leplaced by 1 part of di-n-octylphthalate (DOP). The results of the water penetration test are set out in Table 2. The cord so produced was detonab~e after being subjected to the immersion test.
Exam~le 8 The general procedure of Example 3 was repeated except that the DIOP of that Example was replaced by 1 part of di-isodecylphthalate (DIDP). The results of the water penetrationtest are set out in Tab3.e 2. The cord so produced was ~etonable after being subjected to the immersion test.
Examples 9 to 1~
In these examples detonable explosive compositions accordin~ to the invention were prepared ~y the metllod of Example 1 except that in these examples the diisooctyl rhthalate of Example 1 was replaced by differing amounts of various modifying agents selected from the agents listed in Table 1.

. .
Example Modifying agent the composition ~_ .~ ~
9 Di-ni-butyl phthalate O. o6 Di-n-isobutylphthalate O. o6 11 Decyl ethylhe~ylphthalate 1.3 12 Dimethoxyethyl adipate O. oo8 13 Di-n-hexyl azealate 0.25 14 Butyl oleate 0.03 Butyl acetyl ricinoleate 2.0 16 Dioctyl sebacate ` 0.15 17 ~ibutyl succinate ______ ___~___ ___ ___ _ E~ample 18 11 parts of di-iso-octyl phthalate was added to a ~lurry of 240 parts of recrystallized trinitrotoluene in an aqueo~s acetone mother liquor and the mixture was agitated to provide a uniform dispersion. The DIOP~treated trinitro-toluene was separated from the dispersion and dried, to give a detonable, water-resistant composition according to the invention.
Example_19 To a crystallizer containing 270 kilograms of crysta3.1i~ed P~TN i~ an a~itated acetone mother liquor there was added 270 grams of DIOP to provide treated PET~ which was separated and dr~.ed to remove the mother liquor. The resultant com--position ob~ained from the drying pan contained o.o89% of DIOP.

Exam3~1e "O
__ A moist fi.lter cake containing 270 parts of PETN was washed with successive small amounts of mixture cf DIOP, acetone an,d water until 27 parts of DIOP had been added to the filter cake, and thereafter the treatcd filter cake was dri.ed to re-move the aqueous acetone therefrom. The treated filter cake contained 3.1,3% of DIOP.

Claims (17)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. A particulate high explosive composition suitable for use as a core in detonating cord and having improved resistance to water desensitization, said composition comprising particles of high explosive material treated with a modifying water-resisting agent, said agent being characterized in that it comprises an ester of an acid selected from the group consisting of aliphatic and aromatic acids and being characterized further in that the said agent has a melting point no higher than a temperature of -10°C.

2. A composition according to Claim 1 wherein the said agent has a melting point no higher than a temperature of -25°C.

3. A composition according to Claim 1 wherein the said ester is an alkyl ester in which the alkyl moiety contains from 1 to 18 atoms in a chain which is selected from the group consisting of straight chains and branched chains and which optionally may be substituted.

4. A composition according to Claim 1 wherein the said ester is derived from an acid selected from the group consisting of unsaturated fatty acids, hydroxy-substituted unsaturated fatty acids, alphatic dicarboxylic acid and aromatic dicarboxylic acids.

5. A composition according to Claim 4 wherein the said ester is derived from an acid selected from the group consisting of maleic acid, oleic acid and ricinoleic acid.

6. A composition according to Claim 4 wherein the said ester is derived from an acid selected from the group consisting of adipic acid, oxalic acid, azelaic acid, sebacic acid and succinic acid.

7. A composition according to Claim 4 wherein the said ester is derived from an acid selected from the group consisting of phthalic acid and isophthalic acid.

8. A composition according to Claim 7 wherein the said ester is derived from phthalic acid and alkyl moieties which may be the same or different and contain from 4 to 12 carbon atoms.

9. A composition according to Claim 8 wherein the said ester is di-isooctyl phthalate.

10. A composition according to Claim 1 wherein the high explosive material is selected from the group consisting of nitramines, nitrates of polyhydric alcohols and nitro-aromatic compounds.

11. A composition according to Claim 10 wherein the said high explosive material is pentaerythritol tetranitrate.

12. A composition according to Claims 1, 2 or 3 wherein the said modifying agent constitutes from 0,005 to 5% w/w of the composition.

13. A composition according to Claims 1, 2 or 3 wherein the said modifying agent constitutes from 0.01 to 1% w/w of the composition.

14. A composition according to Claim 1 wherein the said modifying agent constitutes from 0.05 to 0.2% w/w of the composition.

15. A composition according to Claim 14 wherein the said modifying agent is di-isooctyl phthalate and the said high explosive material is pentaerythritol tetranitrate.

16. A process for manufacturing a composition according to Claims 1, 2 or 3 which process comprises treating a particulate high explosive material, optionally in the presence of a liquid damping medium, with an amount of a modifying water-resisting agent having a melting point no higher than -10°C and comprising an ester of an acid selected from the group consisting of aliphatic and aromatic acids in a manner such that said high explosive material is provided with a coating of said agent sufficient to inhibit the ingress of an aqueous medium on to the said high explosive material.

17. A detonating cord comprising a detonable core component located within a casing component, said core component being characterized in that it comprises a particulate high explosive composition according to Claims 1, 2 or 3.