Explosive composition

Abstract

 The invention relates to an emulsion explosive composition comprising a discontinuous phase comprising at least one oxygen-releasing salt; a continuous organic phase; an emulsifying agent; and at least one polymer soluble in the organic phase and wherein the polymer comprises associative functional groups.
The explosive is especially advantageous for use in wet boreholes.

Description

[0001] The invention relates to emulsion explosive compositions having a discontinuous phase comprising an oxygen- releasing salt and a continuous liquid organic phase and in particular to emulsion explosives compositions containing an oil-soluble polymer having associative groups.

[0002] Emulsion explosive compositions have been widely accepted in the explosives industry because of their excellent explosive properties and ease of handling. The emulsion explosive compositions now in common use in the industry are of the water-in-oil type first disclosed by Bluhm in US Patent No. 3 447 978 and comprise as components:

(a) a discontinuous aqueous phase comprising discrete droplets of an aqueous solution of inorganic oxygen- releasing salts;

(b) a continuous water-immiscible organic phase throughout which the droplets are dispersed; and

(c) an emulsifier which forms an emulsion of the droplets of oxidizer salt solution throughout the continuous organic phase.

[0003] For some applications, water content of the oxidizer phase of the emulsion may be eliminated or reduced to a low level, for example, to less than 4% by weight of the total emulsion composition. Such compositions are conveniently referred to as melt-in-oil or melt-in-fuel emulsion explosives and have been described, for example, in US Patent 4 248 644.

[0004] The term "emulsion explosive" is used herein to embrace compositions of both the water-in-oil and the melt-in-oil types.

[0005] Emulsion explosives may be handled in bulk and are easily loaded into boreholes for large-scale blasting operations. A particular problem however arises where boreholes contain water, for example, after rain. In such cases, and in particular where boreholes become completely or partially filled with water, the explosive performance of emulsion explosives is severely reduced. This is a particular problem when using blends of emulsion explosive and a solid adjuvant such as ammonium nitrate prills or ANFO.

[0006] Indeed, in many cases it is difficult to detonate an emulsion explosive charge which has been loaded into a borehole containing water.

[0007] Due to these problems it has generally been the practice to drain water from a borehole before loading the explosive. This is both time consuming and labour intensive.

[0008] If emulsion explosives are carefully loaded into the bottom of a borehole via a hose, it is sometimes possible to displace water from the bore-hole. However, this again is a time consuming procedure and unsatisfactory for deep boreholes.

[0009] We have now developed an emulsion explosive composition which is highly elastic and which may be loaded into wet boreholes without using such procedures.

[0010] Further advantages of the composition of the present invention will become evident on considering the physical properties of the emulsion explosive composition.

[0011] Accordingly we provide an emulsion explosive composition comprising a discontinuous phase comprising at least one oxygen-releasing salt; a continuous organic phase; an emulsifying agent; and at least one polymer soluble in the organic phase and wherein the polymer comprises associative functional groups.

[0012] Generally the associative functional groups are polar groups capable of entering into specific association with other associative groups.

[0013] Examples of associative functional group may be selected from a group of : ionmeric functional groups; functional groups which are capable of protolytic reactions; and groups capable forming hydrogen bonds.

[0014] Examples of functional groups capable of association through hydrogen bond formation may be selected from the group consisting of hydroxyl, carboxyl and carboxamide functional groups.

[0015] Examples of ionomeric functional groups include those selected from the groups of salts of sulphonic and carboxylic acids such as metal and ammonium ion salts thereof, and quaternary ammonium salts.

[0016] Examples of groups capable of undergoing protolytic reaction include acid groups such as carboxylic, sulphonic and phosphoric acid groups and basic groups such as nitrogen-containing basic groups.

[0017] Examples of nitrogen-containing basic groups may be chosen from the groups of formula I

where R¹ and R² may be aryl, aralkyl, alkyl cycloalkyl or hydrogen and R¹ and R² may together form a 5 or 6 membered heteocyclic ring by a linking group of 4 or 5 members; and nitrogen containing heteroaromatic group such as pyridyl, picolinyl, quinolinyl, isoquinolinyl and quinoxalinyl groups and the salts thereof. Preferred acid and basic groups include the carboxylic acid group, sulphonic acid group and pyridyl group.

[0018] Examples of the group of formula I wherein R¹ and R² form a heterocycle include pyrazolinyl, pyrrolidinyl, peperazinyl and morpholinyl.

[0019] The said polymer may comprise more than one type of functional group. For example said polymer may comprise a plurality of different monomers capable of undergoing dipole-dipole interaction or protolytic reaction with one another.

[0020] Polymers suitable for use in preparation of compositions of the invention may be prepared by conventional polymerization techniques. Suitable polymers may be prepared by addition polymerization reactions using at least one main monoethylenically unsaturated monomer and at least one associative monomer comprising a functional group chosen from associative functional groups as hereinbefore described, and groups capable of conversion to said associative functional groups.

[0021] Examples of main monoethylenically unsaturated monomers (hereinafter referred to as main monomer) may be selected from the group consisting of: alkenes, preferably comprising from 2 to 6 carbon atoms such as ethylene and propylene; higher alkyl acrylates and methacrylates, in which the alkyl group contains from 4 to 18 carbon atoms, for example 2-ethyl hexylacrylate, stearyl methacrylate and lauryl 30 methacrylate; styrenes; alkyl styrenes in which the alkyl group contains from 1 to 12 carbon atoms, for example tertiarybutyl styrene; and vinyl esters of fatty acids, such as vinyl stearate.

[0022] Particularly preferred main monomers are lauryl methacrylate, styrene and tert-­butylstyrene.

[0023] Examples of associative monomers may be chosen from the groups consisting of:
vinyl substituted nitrogen containing heteroaromatic compounds such as vinyl pyridines, vinylpicolines, vinyl quinolines, vinylisoquinolines and vinyl quinoxalines, hydroxy(C₁ to C₆)alkyl acrylates and methacrylates, such as hydroxyethyl acrylate and hydroxy propyl methacrylate; acrylic acid, methacrylic acid and their metal or amine salts; acrylamide; methacrylamide; acids selected from the group of styrene sulfonic acid, vinyl sulfonic acid, 2-acrylamides, propane sulfonic acid, acrylic acid, methacrylic acid; and the metal salts of these acids; halide salts of quaternary ammonium compounds selected from the group consisting of dimethylammonium methacrylate, diethylammonium ethyl-methacrylate; diethylammonium ethyl-methacrylate; and precursors of these monomers. Particularly preferred associative monomers are methacrylic acid and metal and amine salts thereof, and vinylpyridines such as 2-vinylpyridine and 4-vinylpyridine.

[0024] Where the associative monomer comprises an associative group precursor, the precursor will be capable of conversion to an associative group following polymerization.

[0025] For example, dienes such as norbornene and butadiene may be used in the preparations of polymers, and the monmeric units derived therefrom may be converted to sulfonic acids and thence to salts of sulfonic acids by procedures known to those in the art.

[0026] Emulsion polymerization is a particularly convenient technique for preparation of copolymers for use in the present composition However, the method of preparation is not narrowly critical and the skilled artisan will be well acquainted with a wide variety of techniques for preparation of suitable polymers.

[0027] The polymers can conveniently be obtained by aqueous emulsion copolymerisation of the constituent monomers employing if necessary a minor proportion of a water-miscible organic co-solvent, such as acetone, in order to enhance the solubility of the monomer mixture in the aqueous continuous phase (the main monomers described above will inherently have very low solubilites in water and a measurable degree of solubility in the continuous phase is necessary if the polymerisation is to proceed at an acceptable rate). The polymerisation is generally carried out at a temperature in the range 0 - 70°C, preferably 10 - 60°C, in an inert gas atmosphere and in the presence of a water-soluble free radical initiator system, such as ammonium persulphate or potassium persulphate in combination with sodium dithionite optimally, sodium sulphite, sodium thiosulphate or ascorbic acid. There may be added to the polymerisation mixture water-soluble surfactants such as sodium dodecylbenzenesulphonate, sodium dioctylsulpho­succinate, sodium lauryl sulphate or salts of sulphated nonylphenol-ethylene oxide condensates. The amount of initiator (or initiator combination) used may typically lie in the range 0.05% to 1%, and the amount of surfactant in the range 1% to 15%, based on the weight of the monomer mixture. The polymerisation may be effected by a "one-shot" procedure, in which all the monmer required is introduced into the reaction mixture at once, or by a "seed and feed" procedure in which a small proportion of the total monomer mixture is polymerised initially to form a "seed" polymer dispersion and the remainder of the monomer is then added gradually. Chain transfer agents, such as n-octyl mercaptan, dodecyl mercaptan or chloroform, may also be added during the course of the polymerisation, especially in the later stages when more than 75% of the monomer has beeen polymerised, in order to regulate the formation of the polymer.

[0028] Typically, the polymers are prepared using 0.001 to 30% associative monomer by weight of total monomer and preferably 0.01 to 20% w/w.

[0029] Typically, the total amount of said polymer will comprise in the range of 0.001 to 10% by weight of the emulsion composition. However, we have found that particularly good results are obtained by using in the range of 0.01 to 2% of the total emulsion composition. Generally, the amount of polymer will be in the range of 0.001 to 20% w/w based on the organic phase and preferably in the range 0.1 to 10%. However, higher or lower quantities may be used if desired, the amount of polymer being determined without undue experimentation based on the required properties of the emulsion.

[0030] As hereinbefore stated the polymer is soluble in the organic phase. Generally, the polymer will be soluble in the organic phase at the polymer/organic phase weight ratio to be usd in the emulsion explosive.

[0031] Hence the polymer will generally be soluble in the organic phase at a concentration of at least 0.001% w/w and preferably at least 0.1% w/w.

[0032] One polymer particularly useful for the preparation of composition of the invention is a polymer of styrene, lauryl methacrylate and methacrylic acid.

[0033] An example of such a polymer may be derived by emulsion polymerization from a mixture of 10-80% w/w styrene, 10-80% w/w lauryl methacrylate and 0.1-10% w/w methacrylic acid. A particularly preferred composition comprises 50-60% lauryl methacrylate, 40-50% styrene and 1-4% methacrylic acid.

[0034] As hereinbefore discussed, the emulsion explosive compositions of the present invention have advantages over conventional explosives, making them more suitable for loading in wet boreholes.

[0035] Without wishing to be bound by theory, we believe that the better wet borehole performance of the emulsions of the invention may be due to their elastic and cohesive nature. Unlike conventional emulsion explosives which tend to break up when loaded into water, the emulsions of the present invention pass easily through water. The cohesive properties and resilience also make the emulsion explosive composition particularly useful in packaged products.

[0036] Emulsion explosives of the invention typically have an elastic modulus in the range 100-1000 Pa at 20°C. Typically, the viscosity is in the range 120,000 to 800,000 cp at 20°C.

[0037] The advantages of the emulsion explosive compositions are particularly apparent when the polymer has an average weight molecular weight of at least 1 x 10⁵. Preferably the polymer has an average molecular weight in the range 5 X 10⁵ to 1 X 10⁷, more preferably 1 x 10⁶ to 1 x 10⁷. This is particularly surprising as it was expected that the bulk of high molecular weight polymer molecules may disrupt the stability of an emulsion explosive.

[0038] For example, in the case of water-in-oil emulsion explosives. it is generally believed that droplets of oxidizer solution in an emulsion explosive are separated by bilayers of oil phase which are 5 to 20 nm thick, hence bulky polymer molecules of molecular weight 1 x 10⁶ and higher that are typically 100 to 200 nm in diameter were not expected to be compatible with an emulsion explosive.

[0039] Suitable oxygen-releasing salts for use in the discontinuous phase component of the composition of the present invention include the alkali and alkaline earth metal nitrates, chlorates and perchlorates, ammonium nitrate, ammonium chlorate, ammonium perchlorate and mixtures thereof. The preferred oxygen-releasing salts include ammonium nitrate, sodium nitrate and calcium nitrate. More preferably, the oxygen-releasing salt comprises ammonium nitrate or a mixture of ammonium nitrate and sodium or calcium nitrates.

[0040] Typically, the oxygen-releasing salt component of the compositions of the present invention comprises from 45 to 95% and preferably from 60 to 90% by weight of the total composition. In compositions wherein the oxygen-releasing salt comprises a mixture of ammonium nitrate and sodium nitrate, the preferred composition range for such a blend is from 5 to 80 parts of sodium nitrate for every 100 parts of ammonium nitrate. Therefore, in the preferred compositions of the present invention, the oxygen-releasing salt component comprises from 45 to 90% by weight (of the total composition) ammonium nitrate from 0 to 40% by weight (of the total composition) sodium or calcium nitrates.

[0041] The discontinuous phase may be entirely devoid of water, in the case of a melt-in-oil emulsion or may contain water in the case of a water-in-oil emulsion. In the latter case, the amount of water employed in the compositions of the present invention is typically in the range of from 1 to 30% by weight of the total composition. Preferably the amount employed is from 5 to 25%, and more preferably from 6 to 20%, by weight of the total composition.

[0042] The organic phase component of the composition of the present invention comprises the continuous "oil" phase of the emulsion explosive and is a fuel. Preferably the organic phase is water-immiscible. Suitable organic fuels include aliphatic, alicyclic and aromatic compounds and mixtures thereof which are in the liquid state at the formulation temperature. Suitable organic fuels may be chosen from fuel oil, diesel oil, distillate, kerosene, naphtha, waxes, (eg. microcrystalline wax), paraffin oils, benzene, toluene, xylenes, asphaltic materials, polymeric oils such as the low molecular weight polymers of olefins, animal oils, fish oils, and other mineral, hydrocarbon or fatty oils, and mixtures thereof. Preferred organic fuels are liquid hydrocarbons generally referred to as petroleum distillates such as gasoline, kerosene, fuel oils and paraffin oils.

[0043] Typically, the organic fuel or continuous phase of the emulsion explosive composition of the present invention comprises from 2 to 15% by weight and preferably 3 to 10% by weight of the total composition.

[0044] The emulsifying agent component of the composition of the present invention may be chosen from the wide range of emulsifying agents known in the art for the preparation of emulsion explosive compositions. Examples of such emulsifying agents include alcohol alkoxylates, phenol alkoxylates, poly(oxyalkylene) glycols, poly(oxyalkylene) fatty acid esters, amine alkoxylates, fatty acid esters of sorbitol and glycerol, fatty acid salts, sorbitan esters, poly(oxyalkylene) sorbitan esters, fatty amine alkoxylates, poly(oxyalkylene) glycol esters, fatty acid amides, fatty acid amide alkoxylates, fatty amines, quaternary amines, alkyloxazolines, alkenyloxazolines, imidazolines, alkyl­sulfonates, alkanoylsulfonates, allkylsulfo­succinates, alkylphosphates, alkenylphosphates, phosphate esters, lecithin, copolymers of poly(oxyalkylene) glycols and poly(12-hydroxy­stearic acid) polyalkylene succinic acid and derivatives thereof, and mixtures thereof. Among the preferred emulsifying agents are the 2-alkyl- and 2-alkenyl-4,4ʹ-bis (hydroxymethyl) oxazoline, the fatty acid esters of sorbitol, lecithin, copolymers of poly(oxyalkylene) glycols and poly(12-hydroxystearic acid), and mixtures thereof, and particularly sorbitan mono-oleate, sorbitan sesquioleate, 2-oleyl- 4,4ʹ-bis (hydroxymethyl) oxazoline, mixture of sorbitan sesquioleate, lecithin and a copolymer of poly(oxyalkylene glycol and poly (12-hydroxystearic acid), polyisobutylene succinic acid and derivatives thereof, and mixtures thereof.

[0045] Typically, the emulsifying agent component of the composition of the present invention comprises up to 5% by weight of the total composition. Higher proportions of the emulsifying agent may be used and may serve as a supplemental fuel for the composition but in general it is not necessary to add more than 5% by weight of emulsifying agent to achieve the desired effect. One of the advantages of the compositions of the present invention is that stable emulsions can be formed using relatively low levels of emulsifying agent, and for reasons of economy it is preferable to keep to amount of emulsifying agent in the range from 0.1 to 2.0% by weight of the total composition.

[0046] If desired, other optional fuel materials, hereinafter referred to as secondary fuels, may be incorporated into the compositions of the present invention in addition to the water-immiscible organic fuel phase. Examples of such scondary fuels include finely- divided solids, and water-miscible organic liquids which can be used to partially replace water as a solvent for the oxygen-releasing salts or to extend the aqueous solvent for the oxygen-releasing salts. Examples of solid secondary fuels include finely divided materials such as: sulfur; aluminum; and carbonaceous materials such as gilsonite, comminuted coke or charcoal, carbon black, resin acids such as abietic acid, sugars such as glucose or dextrose and other vegetable products such as starch, nut meal, grain meal and wood pulp. Examples of water-miscible organic liquids include alcohols such as methanol, glycols such as ethylene glycol, amides such as formamide and amines such as methylamine.

[0047] Typically, the optional secondary fuel component of the compositions of the present invention comprise from 0 to 30% by weight of the total composition.

[0048] It lies within the invention that there may also be incorporated into the emulsion explosive compositions hereinbefore described other substances or mixtures of substances which are oxygen-releasing salts or which are themselves suitable as explosive materials. As a typical example of such a modified emulsion explosive composition, reference is made to compositions wherein there is added to and mixed with an emulsion explosive composition as hereinbefore described up to 90% w/w of a solid oxidizing salt such as ammonium nitrate or an explosive composition comprising a mixture of a solid oxidizing salt such as ammonium nitrate and fuel oil and commonly referred to by those skilled in the art as "Anfo". The compositions of "Anfo" are well known and have been described at length in the literature relating to explosives.

[0049] Mixtures of solid ammonium nitrate or "Anfo" and the emulsion explosive of the invention are suited to use in wet bore holes and water containing bore holes. Mixtures of "Anfo" (or solid ammonium nitrate) and conventional emulsion explosive generally give poor performance when loaded into bore holes containing water. The mixture tends to break up on impact with water and this tends to result in the dissolution of the ammonium nitrate. In contrast, mixtures of "Anfo" with the emulsion explosive of the present invention may be used in bore holes containing water without significant loss of performance.

[0050] Accordingly there is provided an explosive composition comprising a emulsion as hereinbefore described and up to 90% w/w of a composition comprising an ammonium nitrate fuel oil mixture.

[0051] Typically, the proportion of ammonium nitrate or "Anfo" in such compositions will be in the range 20-80% w/w.

[0052] It also lies within the invention to have as a futher explosive component of the composition well known explosive materials comprising one or more of, for example, trinitrotoluene, nitroglycerine or pentaerythritol tetranitrate.

[0053] Accordingly there is provided an explosive composition comprising as a first component an emulsion explosive composition as hereinbefore described and as a second component an amount of material which is an oxidizing salt or which is in its own right an explosive material.

[0054] Generally it is not necessary to use thickening agents in the discontinuous phase of the present composition as the amount of polymer may be varied according to the properties desired. However, if desired, the discontinuous phase of the compositions of the present invention may comprise thickening agents which optionally may be cross-linked. The thickening agents, when used in the compositions of the present invention, are suitably polymeric materials, especially gum materials typified by the galactomannan gums such as locust bean gum or guar gum or derivatives thereof such as hydroxypropyl guar gum. Other useful but less preferred gums are the so-called biopolymeric gums such as the heteropolysaccharides prepared by the microbial transformation of carbohydrate material, for example the treatment of glucose with a plant pathogen of the genus Xanthomonas typified by Xanthomonas campestris.

[0055] Typically, where used, the optional thickneing agent component of the compositions of the present invention comprises from 0 to 2% by weight of the total composition.

[0056] As indicated above, when used in the compositions of the present invention, the thickening agent optionally may be cross-linked. It is convenient for this purpose to use conventional cross-linking agents such as zinc chromate or dichromate either as a separate entity or as a component of a conventional redox system such as a mixture of potassium dichromate and potassium antimony tartrate.

[0057] Typically, the optional cross-linking agent component of the compositions of the present invention comprises from 0 to 0.5% and preferably from 0 to 0.1% by weight of the total composition.

[0058] The emulsion explosive compositions of the present invention may additionally comprise a discontinuous gaseous component.

[0059] The methods of incorporating a gaseous component and the enhanced sensitivity of emulsion explosive compositions comprising such gaseous components have been previously reported. Typically, where used the said gaseous component will be present in an amount required to reduce the density of the composition to with in the rane 0.8 to 1.4 gm/cc.

[0060] The gaseous component may, for example, be incorporated into the composition of the present invention as fine gas bubbles dispersed through the composition, as hollow particles which are often referred to as microballoons or microspheres, as porous particles, or as mixtures thereof.

[0061] A discontinuous phase of fine gas bubbles may be incorporated into the compositions of the present invention by mechanical agitation, injection or bubbling the gas through the composition, or by chemical generation of the gas in situ.

[0062] Suitable chemicals for the in situ generation of gas bubbles include peroxides, such as hydrogen peroxide, peroxide nitrates, such as sodidum nitrite, nitrosoamines, such as N, Nʹ-dinitrosopentamethylene tetramine, alkali metal borohydrides, such as sodium borohydride, and carbonates, such as sodium carbonate. Catalytic agents such as thiocyanate or thiourea may be used to accelerate the decomposition of a nitrite gassing agent. Suitable small hollow particles include small hollow microspheres of glass or resinous materials, such as phenol-formaldehyde and urea-formaldehyde. Suitable porous materials include expanded minerals, such as perlite.

[0063] Where used, the gaseous agent is preferably added during cooling, after preparation of the emulsion, and typically comprises 0.05 to 50% by volume of the total emulsion explosive composition at ambient temperature and pressure. More preferably, where used, the gaseous component is present in the range 10 to 30% by volume of the emulsion explosive composition and preferably the bubble size of the occluded gas is below 200 µm. More preferably,at least 50% of the gas component will be in the form of bubbles or microspheres of 20 to 90 µm internal diameter.

[0064] The pH of the emulsion explosive compositions of the present invention is not narrowly critical. However, in general the pH is between 0 and 8, preferably between 0.5 and 6.

[0065] The emulsion explosive composition of the present invention may be prepared by a number of methods.

[0066] The polymer may be mixed with the oil phase before preparation of the emulsion. Alternatively, it may be more convenient to prepare the emulsion composition of the invention by mixing of a composition comprising at least one polymer with an emulsion explosive composition comprising: a discontinuous phase comprising at least one oxygen releasing salt; a continuous organic phase; and an emulsifying agent.

[0067] If desired, the polymer may be added using both methods, that is adding the polymer to the oil phase before preparation of the emulsion and also to the emulsion once prepared.

[0068] When a composition comprising the polymer is added to the prepared emulsion, the polymer may, for example, be in the form of a solid such as a powder, a solution in a suitable solvent such as a hydrocarbon solvent or as an aqueous dispersion.

[0069] Aqueous dispersions of polymer may be prepared by methods well known to those skilled in the art. For example, such a dispersion may be formed by mixing a fine powder of polymer with an aqueous composition in the presence of a surfactant.

[0070] In a particularly preferred embodiment of the process of the invention we therefore provide a process comprising mixing an aqueous dispersion of said polymer with an explosive composition comprising (a) an emulsion explosive comprising a discontinuous aqueous phase comprising an oxygen releasing salt, a continuous organic phase and an emulsifying agent and optionally (b) solid ammonium nitrate or a mixture of solid ammonium nitrate and fuel oil. Generally, the composition is mixed for a period following additive of the polymer so as to facilitate dispersion within the emulsion explosive.

[0071] One preferred method of preparing suitable polymers involves an emulsion polymerization technique which produces a latex of the product (i.e., an aqueous dispersion of small polymer particles). We have found it to be particularly convenient in many instances to use such composition in preparation of the emulsion explosive composition of present invention.

[0072] In an embodiment of the invention there is thus provided a process for the preparation of an emulsion explosive composition, the process comprising:
dissolving said oxygen-releasing salt in water at a temperature above the fudge point of the salt solution, preferably at a temperature in the range of 25 to 110°C, to give an aqueous salt solution;
optionally mixing said polymer with said water immiscible organic phase;
combining said salt solution, said water-immiscible organic phase, said water-in-oil emulsifying agent.
Mixing until the emulsion is uniform and if said polymer has not been added, adding a said polymer.

[0073] The invention is now demonstrated by but in no way limited to the following examples in which all proportions are on a weight basis unless otherwise specified.

Example 1

[0074] A high molecular weight (average molecular weight in excess of 1 x 10⁶) copolymer of tert-butyl styrene and 4-vinyl pyridine (97:3 by weight) was prepared by emulsion polymerization.

Emulsion Polymerization Method - (preparation of polymer latex)

[0075] The surfactant AEROSOL OT (AEROSOL is a trade mark) (available from American Cyanamid), (0.3 g) and initiator ammonium persulfate, (0.10 g) were dissolved in acetone (10.0 g) and water (50.0 g) the monomers (tert-butyl styrene, and 4-vinylpyridine; 20 g) were added, and the mixture emulsified by stirring. The mixture was flushed with nitrogen for ten minutes, sealed, and the temperature raised to 50°C and maintained at that temperature for 24 hours, with gentle stirring. The resulting product was a latex of polymer. The polymer was found to have an average molular weight of approx. 1.19 x 10⁶ g mol⁻¹. Powder To prepare the polymer as a powder a small amount of latex (10 g) was added dropwise to a large excess of methanol (100 g), and the polymer isolated by filtration. The polymer was dried in air and ground to a fine powder.

Examples 2 and 3 and Comparative Example A

[0076] These examples demonstrate the effect on the viscosity of an emulsion explosive composition of the addition of a polymer powder prepared according to Example 1.

Example 2

[0077] A diesel solution for use as the organic phase was prepared by dissolving copolymer powder prepared according to Example 1 in diesel oil at a temperasture of 80°C to give a concentration of 1% w/w of diesel solution.

[0078] An emulsion composition was then prepared using the following components

The method used was as follows:
The ammonium nitrate and calcium nitrate were dissolved in the water at a temperature of about 80°C to give the oxidizer phase. The oxidizer phase was combined with a mixture of the diesel solution and emulsifier and the resulting mixture was stirred rapidly to form an emulsion.

Example 3

[0079] The procedure of Example 2 was repeated except that the diesel solution was prepared using 2% w/w of copolymer prepared according to Example 1.

Comparative Example A

[0080] The procedure of Example 2 was repeated except that copolymer was not used in the organic phase.

[0081] The viscosities of the emulsions of Examples 2, 3 and Comparative Example A were measured at room temperature (20°C) with a BROOKFIELD instrument using spindle #7 on speed 5 rpm and the results are shown in the Table 1 below.

Example 4 and Comparative Example B

[0082] This example demonstrates a method of preparation of an emulsion of the invention by addition of a polymer powder to a preformed emulsion.

[0083] An emulsion having the following components was prepared according to Example 2, the organic phase not containing dissolved polymer.

[0084] * The emulsifier was a 1:1 molar condensate of poly(isobutylene) succinic anhydride and ethanolamine and had an average molecular weight in the range of 800 to 1200.

[0085] A sample of the composition was set aside for comparison (Comparative Example B). NITROPRIL is a trade mark.

Example 4

[0086] To a sample of the prepared emulsion (200 g) at 80°C was added polymer powder (0.24 g, 2% w/w on diesel) prepared according to Example 1. The composition was heated at 80° for four hours with occasional stirring, then allowed to cool. The composition was stored at room temperature overnight.

Examples 5 to 7 and Comparative Examples C and D

[0087] The following examples demonstrate the highly viscoelastic nature of the explosives of the invention.

Comparative Example C

[0088] An emulsion composition having the following components was prepared according to Example 2, the organic phase being free of polymer.

[0089] * The emulsifier was a 1:1 molor condensate of poly(isobutylene)succinic anhydride and ethanolamine and had an average molecular weight in the range 800 to1200.

[0090] A sample of emulsion was set aside for comparison and the bulk of the emulsion was used in preparation of the following compositions.

Examples 5 to 7

[0091] To three samples of emulsion prepared above were added polymer latexes prepared according to the procedure of example 1 using the monomer compositions shown in Table 3 below (numbers in brackets show the proportion of each monomer based on the total monomer composition). The average molecular weight of polymers used in Examples 6 and 7 was measured and found to be 1.23 x 16⁶ g mol⁻¹ for example 6 and 0.82 x 10⁶ g mol⁻¹ for example 7.

[0092] In each case the appropriate latex was added to the emulsion to give a polymer concentration of approx. 6% w/w on the organic phase and the latex was thoroughly mixed with the emulsion.

Comparative Example D

[0093] An emulsion explosive composition was prepared using the above procedure except that the polymer added in Examples 5 to 7 was omitted.

[0094] The viscosity of the emulsion compositions was measured at room temperature using a BROOKFIELD instrument spindle #7 at speed 5.

[0095] The yield stress and elastic modulus of the compositions was measured using a BOHLIN Rheometer.

[0096] * Elongation is a comparative measure of viscoelasticity of the emulsion compositions and was determined using the following method:-
A spatula having a 1 cm width blade was inserted into a bulk sample of emulsion at an angle of about 45° to the surface to a depth of about 1 cm. The spatula was raised vertically from the emulsion at a rate of about 1 cm S⁻¹ until the thread of emulsion between the spatula and bulk sample broke or became less than 1 mm in thickness. The height of the spatula above the bulk emulsion was measured at this stage.
Compositions of the invention typically have an elongation in the range 2 to 30 cm (preferably 4 to 20 cm).

Examples 8 to 10 and Comparative Example E

[0097] These examples demonstrate the advantage of using explosives of the present invention when loading into wet boreholes.

Comparative Example E

[0098] An emulsion explosive prepared according to Comparative Example C (7.5 kg) was mixed with "ANFO" (ammonium nitrate fuel oil mixture) (7.5 kg). The mixture was gassed using an in-situ nitrite gassing agent.

Example 8

[0099] An emulsion explosive prepared according to Comparative Example C was (7.5 kg) was throughly mixed with polymer latex (37.5 g latex containing 9.38 g of *polymer) to give a polymer concentration of 0.13% w/w on total emulsion. This emulsion mixture was combined and mixed with 7.5 kg of "ANFO" and the composition was gassed using an in-situ nitrite gassing agent.

Example 9

[0100] An emulsion/ANFO mix was prepared according to Example 8 except that 75 g of latex containing 18.75 g *polymer was added.

[0101] * The polymer latex used in Examples 8 and 9 was prepared according to the procedure of Example 1 using the monomers styrene (47%), lauryl methacrylate (50%) and methacrylic acid (3%) [percentages based on w/w of total monomer]

Example 10

[0102] An emulsion/ANFO mix was prepared according to Example 8 except that the quantity of Latex was adjusted to provide a polymer concentration of 0.5% w/w on total emulsion prior to addition of ANFO.

[0103] The performance of the explosives prepared in Examples 8, 9 and Comparative Example E on loading into wet boreholes was tested using the following procedure:-

[0104] The explosive sample was dropped 3 metres into water 2 metres deep. The explosive was allowed to settle and was then removed from the water. After 2 hours the total detonation energy of the explosive was tested.

[0105] Results of the tests are shown in Table 4.

[0106] The above results clearly show the 25 superiority in performance of the compositions of the present invention over corresponding compositions devoid of polymer.

Claims

1. An emulsion explosive composition comprising a discontinuous phase comprising at least one oxygen-releasing salt; a continuous organic phase; an emulsifying agent; and at least one polymer soluble in the organic phase and wherein the polymer comprises associative functional groups.

2. An emulsion explosive composition according to claim 1 wherein said associative functional groups are selected from the group consisting of ionomeric functional groups, functional groups which are capable of protolytic reactions and groups capable of forming hydrogen bonds.

3. An emulsion explosive composition according to claim 1 or claim 2 wherein said associative functional groups are selected from one or more of the members of the group consisting of carboxylic acid group, sulphonic acid group, phosphoric acid group, nitrogen containing basic groups of formula I


wherein R¹ and R² are independently selected from aryl, aralkyl, alkyl, cycloalkyl and hydrogen and R¹ and R² may together form a 5 or 6 membered heterocycle by a linking group of 4 or 5 constituent members; and nitrogen containing heteroaromatic groups.

4. An emulsion explosive according to any one of claims 1 to 3 wherein the polymer is a copolymer of at least one monomer selected from the group consisting of C₂ to C₆ alkenes, (C₄ to C₁₈ alkyl) - acrylates, styrenes, (C₁ to C₁₈ alkyl)styrenes, and vinyl esters of fatty acids with at least one comonomer selected from the group consisting of vinyl substituted nitrogen containing heteromatic compounds, hydroxy(C₁ to C₆ alkyl) acrylates, hydroxy(C₁ to C₆ alkyl)methacrylates, acrylic acid, methacrylic acid, the metal and amine salts of acrylic and methacrylic acid, styrene sulphonic acid, vinyl sulfonic acid, 2-acrylamidopropane sulphonic acid, and the halid salts of quaternary ammonium compounds selected from the group consisting of dimethylammonium methacrylate and diethylammonium ethylmethacrylate.

5. An emulsion explosive composition according to claim 4 wherein said polymer is a copolymer of at least one monomer selected from the group consisting of styrene, (C₁ to C₆ alkyl)styrene, (C₄ to C₁₈ alkyl)acrylates and (C₄ to C₁₈ alkyl)methacrylates with at least one comonomer selected from the group consisting of vinyl pyridines, acrylic acid and methacrylic acid.

6. An emulsion explosive according to claim 4 or claim 5 wherein said polymer is a copolymer of 10 to 80% by weight styrene, 10-80% by weight lauryl methacrylate and 0.1 to 10% by weight methacrylic acid.

7. An emulsion explosive according to claim 4 or claim 5 wherein said polymer comprises in the range of 0.01 to 20% w/w of said comonomer.

8. An emulsion explosive according to any one of claims 1 to 3 inclusive wherein the average molecular weight of said polymer is in the range of from 5 x 10⁵ to 1 x 10⁷.

9. An emulsion explosive composition according to any one of claims 1 to 8 comprising in the range of from 0.01 to 10% by weight of said polymer.

10. A process for preparing an emulsion explosive according to any one of claims 1 to 9 comprising mixing a composition comprising said polymer with an explosive composition comprising
(a) an emulsion explosive comprising a discontinuous aqueous phase comprising an oxygen releasing salt, a continuous organic phase and an emulsifying agent and optionally (b) solid ammonium nitrate or a mixture of solid ammonium nitrate and fuel oil.