MXPA96001070A - Explosive in resistant emulsion to laprecompres - Google Patents

Abstract

The present invention relates to an emulsion explosive consisting of a density less than 0.95 g / cc, comprising an explosive emulsion matrix and at least 4% by weight of low resistance microspheres wherein the microspheres consist essentially of microspheres with a crushing strength of less than 2.8 Kg / cm2 (400 psi)

Description

EXPLOSIVE EMULSION RESISTANT TO PRECOMPRESSION D E S C R I P C I O N FIELD OF THE INVENTION This invention relates to the field of emulsion explosives and in particular to an emulsion explosive which is resistant to pre-compression desensitization.

DESCRIPTION OF THE RELATED TECHNIQUE The use of water-in-oil emulsion explosives has come to have an increased importance in the mining industry. One of the serious problems that remain which hinders the use of these explosives in a certain number of applications is their lack of resistance to precompression. This term refers to the phenomenon where an emulsion explosive becomes insensitive to initiation by the action of a gas pressure pulse or shock from a previously detonated attached hole. The existence of this phenomenon significantly restricts the usefulness of these types of explosives.

Emulsion explosives are well known in the explosives industry. These explosives can generally be described as the emulsion of an aqueous or molten solution of an oxidizing salt, such as ammonium nitrate, which forms a discontinuous phase, in a continuous organic fuel phase. Typically the emulsion is stabilized by the addition of an emulsifier to the continuous phase. In order to provide sensitivity to this type of explosives, gas voids are added or formed within the emulsion and are usually introduced using glass or plastic microspheres (also called "icrolobes") or by gasification. Unfortunately, it is the premature collapse of these holes, under pressure with the shock wave generated by the detonation of the attached blast holes, which is the main cause of pre-compression desensitization. One of the most commercially important solutions to this problem has been the use of so-called 'high strength microspheres. These microspheres are able to withstand the pressures typically encountered during precompression in the hole environment without breaking. However, there are disadvantages to using these high strength microspheres. First, there is the economic disadvantage in that it is necessary to use a relatively large amount of these microspheres in order to obtain a sufficiently low density that will provide adequate sensitization. Furthermore, it is extremely difficult to formulate an explosive that has both sufficient explosive strength and is sufficiently sensitive for normal applications, using these high strength microspheres. One method to overcome these resulting problems has been to use additional sensitization agents. Adopting this strategy, the sensitivity of the emulsion explosive is less dependent on the use of hollow materials and therefore these emulsions are less prone to pre-compression desensitization. However, these additional sensitizing agents are typically added to the emulsion after it has been formed. Accordingly, it is necessary to handle generally solid sensitizers and mix them in a hot emulsion. The security referred to with this solution is obvious. A second method to overcome these problems has been to include "cushioning" agents within the formulation of the emulsion. Unfortunately, these cushioning agents are mainly carbonaceous materials that add additional fuel to the emulsion. This can cause considerable difficulties for the formulator attempting to produce a product having specific detonation characteristics, such as providing a high-energy Fume Class 1 material (class I smoke). Therefore, the addition of these materials can cause serious restrictions in the scale of applications for emulsion explosives. In addition to the resistance to precompression, it is necessary that there is a low density explosive in the mining industry. The prior art has attempted to solve this problem by adding a combination of high strength microspheres as well as gasificationThat solution, unfortunately, leads to additional problems. In addition to the aforementioned problems related to high strength microspheres, it is difficult to obtain a high quality explosive using gasification technology. If both technologies are used in combination, it becomes more difficult to achieve a high quality explosive. Therefore, it is desirable to provide an emulsion explosive with improved resistance to precompression desensitization without the need to resort to high strength microspheres, or to resort to a combination of high strength microspheres and gasification technology.

SUMMARY OF THE INVENTION According to the above, the present invention provides an emulsion explosive comprising an explosive emulsion matrix in combination with a high level of low resistance microspheres. This is in direct contrast to the prior knowledge of the use of microspheres in explosive compositions. Prior to the present invention, it was conventional desire that the microspheres that are used provide a resistance to precompression desensitization and that the microspheres should be of high strength. This solution led to the formulation of difficulties described here in the foregoing. Preferred microspheres of the present invention are glass or resin materials, such as phenol-formaldehyde, urea-formaldehyde and copolymers of vinylidene chloride and acrylonitrile. In general, these materials are graded for their crushing strength when subjected to an external force, low resistance microspheres typically have a crush resistance of approximately 250 psi, intermediate strength microspheres have a crush resistance of approximately 500 psi. and the high strength microspheres have a crush resistance of about 2000 psi In accordance with the above, the preferred microspheres of interest in the practice of the present invention are those microspheres that have a crush strength of less than 400 psi, more preferably having a crush resistance of between 100 and 400 psi, and more preferably having a crush resistance of between 200 and 300 psi.The resistance to crushing or crushing is measured, according to the method described by 3M in its Guide to Scotchlite glass bubble user (trademark regis trada) by the following procedure. Isostatic strength values are obtained by applying isostatic pressures according to ASTM D3102 (Edition 1982) to cause a 10% volume loss in glycerol. In typical applications of the prior art, low resistance microspheres are typically used at levels below 4% by weight of the total formulation (ie explosive matrix in emulsion and microspheres). More typically, low strength microspheres are generally used at levels of approximately 2.5% by weight. In the practice of the present invention, the microspheres are preferably used at levels greater than 4%, more preferably at levels between 4 and 15% and more preferably at levels between 6 and 8% by weight of the total formulation. The use at these levels of microspheres results in emulsion explosives which preferably have a density of less than about 0.95 g / cc and more preferably have a density of less than 0.90 g / cc. According to the foregoing, in a preferred embodiment, the present invention provides an emulsion explosive having improved resistance to compression desensitization (as compared to typical emulsion explosives) comprising from 85 to 96% by weight of a matrix explosive in emulsion and between 4 and 15% by weight of microspheres having a crushing strength of between 100 and 400 psi and having a density less than 0.95 g / cc. As discussed hereinbefore the term compression desensitization is well known in the explosives industry and the degree of resistance to this phenomenon is readily determined by those skilled in the art. However, preferably, the degree of improvement in resistance to pre-compression desensitization is evaluated according to the test procedure indicated in the examples that follow here. When tested for precompression resistance, common emulsion explosives having typical levels of low resistance microspheres have a precompression resistance value of approximately 20 cm or greater. Preferred emulsion explosives prepared according to the present invention have a precompression strength value of less than 18 cm, more preferably less than 15 cm and greater preference less than 10 cm. The term "explosive emulsion matrix" is used to describe the explosive emulsion composition before the addition of the microspheres and generally comprises the discontinuous oxidative salt phase and the invisible organic fuel phase in continuous water, with emulsifier. The explosive emulsion matrix used in the practice of the present invention can be based on any of the typical emulsion explosives known in the industry. The oxidizing salt for use in the discontinuous phase of the emulsion explosives is preferably selected from the group consisting of alkali metal and alkaline earth nitrates, chlorates and perchlorates, ammonium nitrate, ammonium chlorates, ammonium perchlorates and mixtures thereof . It is particularly preferred that the oxidizing salt be ammonium nitrate or a mixture of ammonium nitrate and sodium nitrate. A preferred oxidizing salt mixture may comprise, for example, a solution of 77% ammonium nitrate, 11% sodium nitrate and 12% water. Typically, the oxidizing salt is a concentrated aqueous solution of the salt or mixture of salts. However, the oxidizing salt can also be a molten, molten solution of the oxidizing salt when a low water content is desired. It may be desirable for the discontinuous phase of the emulsion explosive to be a eutectic composition. By eutectic composition it is indicated that the melting point of the composition is eutectic or is in the eutectic region of the components of the composition. The oxidizing salt for use in the discontinuous phase of the emulsion may comprise a melting point reducer. Suitable melting point reducers for use with ammonium nitrate in the discontinuous phase include organic salts such as lithium nitrate, silver nitrate, lead nitrate, sodium nitrate, potassium nitrate; alcohols such as methyl alcohol, ethylene glycol, glycerol, mannitol, sorbitol, pentaerythritol; carbohydrates, such as sugars, starches and dextrins; aliphatic carboxylic acids and their salts such as formic acid, acetic acid, ammonium formate, sodium formate, sodium acetate and ammonium acetate; glycine; chloroacetic acid; Glycolic Acid; succinic acid; tartaric acid, adipic acid; lower aliphatic amides such as formamide, acetamide and urea; Urea nitrate; nitrogenous substances such as nitroguanidine, guanidine nitrate, methylamine, methylamine nitrate and ethylene diamine dinitrate; and mixtures thereof. Typically, the discontinuous phase of the emulsion comprises from 60 to 97% by weight of the explosive emulsion matrix and preferably more than about 70% by weight of the emulsion explosive matrix. The phase of invisible organic fuel in continuous water of the emulsion explosive comprises an organic fuel. Suitable organic fuels for use in the continuous phase include aliphatic, alicyclic and aromatic compounds and mixtures thereof which are in the liquid state at the temperature of the formulation. Suitable organic fuels can be selected from fuel oil, diesel oil, distillate, furnace oil, kerosene, naphtha, waxes (eg nitrocrystalline wax, paraffin wax and paraffin wax (50% mixture of paraffin wax and 50% petroleum) ), paraffinic oils, benzene, toluene, xylenes, asphalt materials, polymeric oils such as polymers and low molecular weight olefins, animal oils, fish oils, vegetable oils and other mineral or fatty hydrocarbon oils and mixtures thereof. preferred organic are liquid hydrocarbons, generally referred to as petroleum distillates, such as gasoline, kerosene, fuel oils and paraffin oils Typically, the continuous invisible organic fuel phase of the explosive emulsion matrix comprises from 3 to 30% by weight. weight of the emulsion explosive and preferably 5 to 15% by weight of the emulsion explosive matrix. The emulsion comprises an emulsifying component to aid in the formation of the emulsion and to improve the stability of the emulsion. The emulsifying component can be selected from the wide range of agents and ulsifiers known in the art suitable for the preparation of explosive emulsion 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, salts of fatty acids, esters 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, alkyl sulphonates, alkylarylsulfonates, alkyl sulfosuccinates, alkyl phosphates, alkenyl phosphates, phosphate esters, lecithin, copolymers of poly (oxyalkylene) glycols and poly (12-hydroxystearic acid), condensation products of compounds comprising at least one primary amine and polyfalq acid or anhydride (in ) il] succinic and mixtures thereof. Among the preferred emulsifying agents are 2-alkyl and 2-alkenyl-4,4'-bis (hydroxymethyl) oxazolines, the fatty acid esters of sorbitol, lecithin, copolymers of poly (oxyalkylene) glycols and poly (12-hydroxystearic acid) , condensation products of compounds comprising at least one primary amine and poly [alk (en) yl] succinic acid or anhydride and mixtures thereof. More preferably the emulsifying component comprises a condensation product of a compound comprising at least one primary amine and poly [alk (en) yl] succinic acid or anhydride. A preferred emulsifier is a surfactant based on a polyisobutylene succinic anhydride (PIBSA). This emulsifier can generally be described as condensation products of a polyfalq (en) yl] succinic anhydride and an amine such as ethylene diamine., diethylene triamine and ethanoamine. Typically, the emulsifying component of the emulsion explosive comprises up to 5% by weight of the emulsion explosive matrix. Higher proportions of the emulsifier component can be used and can serve as a supplemental fuel for the composition, but in general it is not necessary to add more than 5% by weight of the emulsifying component to achieve the desired effect. Stable emulsions can be formed using relatively low levels of emulsifying component and for reasons of economy, it is preferred to maintain minimal amounts of emulsifier necessary to achieve the desired effect. The preferred level of emulsifying component used is in the range of 0.4 to 3.0% by weight of the emulsion explosive matrix. If desired, further fuel materials, hereinafter referred to as secondary fuels, may be incorporated in the emulsion explosives Examples of such secondary fuels include finely divided solids Examples of solid secondary fuels include finely divided materials such as sulfur, aluminum, carbonaceous materials such as gilsonite, coke or crushed coal, carbon black, resin acids such as abietic acid, sugars such as glucose or dextrose and other plant products such as starch, nutmeat, grain meal and wood pulp and mixtures thereof Typically, the optional secondary fuel component of the emulsion explosive comprises from 0 to 30% by weight of the emulsion explosive matrix, preferably the emulsion explosives of the present invention are oxygen balanced; they have an oxygen balance that typically provides a more efficient explosive which, when denoted, leaves very few components unreacted. Additional components can be added to the explosive to control the oxygen balance. Although the present invention provides an emulsion explosive having adequate sensitivity, density and strength for precompression desensitization, additional gasification may be desirable. Therefore, the explosive may additionally comprise an additional discontinuous gaseous component, which gaseous component may be used to vary the density and / or the sensitivity of the explosive composition. In addition, other suitable porous materials including expanded minerals such as perlite and expanded polymers such as polystyrene can be added to the emulsions of the present invention. Traditional methods for incorporating a gaseous component and increasing the sensitivity of explosive compositions comprising gaseous components are well known to those skilled in the art. The gaseous components can, for example, be incorporated into the explosive composition as fine gas bubbles dispersed in the composition. A discontinuous phase of fine gas bubbles can also be incorporated into the explosive composition by mechanical agitation, injection or bubbling of the gas through the composition or by chemical generation of the gas in situ. Chemicals suitable for in situ chemical generation of gas bubbles include peroxides, such as hydrogen peroxide, nitrites, such as sodium nitrite, nitrous acids, such as N, N'-dinitroso-pentamethylene-tetramine, alkali metal borohydrides, such as sodium borohydride and carbonates such as sodium carbonate. Preferred chemicals for in situ generation of gas bubbles are nitrous acid and its salts that decompose under acid pH conditions to produce gas bubbles. Preferred nitrous acid salts include alkali metal nitrites, such as sodium nitrite. Catalyst agents such as thiocyanate or thiourea can be used to accelerate the decomposition of a nitrite gasifying agent. The emulsion explosives prepared according to the present invention can be used in any of those applications where the most traditional emulsion explosives are currently used. When used in accordance with the present invention, the emulsion explosive preferably has formulations according to the guide lines indicated hereinafter: Ingredient% by weight Oxidizing salts (nitrates, perchlorates) > approx. 70% Water 4 - 20 Sensitizers 0 - 40 Additional fuels, densifiers 0 - 50 Low resistance microgrels 4 - 15 Invisible fuel component in water, emulsifiable 0 - 10 Emulsifier 0.5 - 6 Emulsion explosives prepared in accordance with the present invention may allow the formulation of emulsion explosive products resistant to pre-compression desensitization that do not require, or that minimize the use of, special high-strength microspheres, cushioning agents or sensitizing agents. Therefore, they allow the explosives formulator to prepare explosives in emulsion using more traditional and less expensive components. In addition, it allows the explosives formulator more flexibility to provide emulsion explosives resistant to precompression. The invention will now be described as an example only, with reference to the following examples.

EXAMPLES A number of different emulsion explosives were prepared and the properties of each explosive were measured with respect to the density and resistance to precompression. The resistance to precompression of each formulation was measured using the following test procedure. In this test a donor charge containing 2 g of PETN (pentaerythritol tetranitrate) and a receiving cartridge (a 32 mm x 200 mm paper cartridge containing the explosive test material) was placed under the water at a known distance. . The receiving cartridge was primed with a number 8 EB detonator that was delayed 75 milliseconds after the donor charge detonator. The detonation results were determined either by inspection or by detonation velocity measurements or both. The smaller the distance between the donor and the receiver cartridge in which the receiver will remain detonable; The precompression of the sample material will be greater. The formulations of the emulsions used to prepare the packaged products tested are presented in a Table 1, together with the density of the resulting emulsion and the result of a precompression test conducted on the single emulsion formulation.

Table 1; Formulation of emulsions * - KIGMB Microglobes that have a resistance to crushing and approximately 250 psi.

From Table 1, it can be seen that formulations B, C and E containing high levels of low resistance microspheres are more resistant to compression desensitization than formulations A and D containing more typical levels of microspheres. Therefore, it is demonstrated that both low resistance microsphere levels can be used to provide improved precompression resistance. Furthermore, when compared to the test results obtained using an NG (nitroglycerin) high performance non-emulsion based explosive, the emulsion prepared in the "E" example compared favorably with the 8 CM prcompression value obtained for the explosive NG Having described specific embodiments of the present invention, it will be understood that modifications suggested to those skilled in the art can be made and that it is intended to cover all modifications that fall within the scope of the attached clauses.

Claims (7)

R E I V I N D I C A C I O N S

1. - An emulsion explosive consisting of a density less than 0.95 g / cc, comprising an explosive emulsion matrix and at least 4% by weight of low resistance microspheres wherein the microspheres consist essentially of microspheres with a crushing strength less than 2.8 Kg / cm (400 psi). 2.- Explosive emulsion according to the clause 1, wherein the low strength microspheres have a crushing strength of between 0.7 and 2.8 Kg / cm (100 to 400 psi). 3. Explosive emulsion according to clause 1, comprising from 85 to 96% by weight of an explosive emulsion matrix and from 4 to 15% by weight of low resistance microspheres. 4.- Explosive emulsion according to the clause 3, which comprises 92 to 94% by weight of an emulsion explosive matrix and between 6 to 8% by weight of low resistance microspheres 5.- Emulsion explosive according to the clause 4, which has a density less than 0.90 g / cc. 6. Explosive emulsion according to clause 1, which has a value of precompression resistance of less than 15 cm. 7. Explosive emulsion according to clause 1, which has a value of precompression resistance of less than 10 cm. SUMMARY An explosive emulsion composition having improved resistance to compression desensitization comprising an explosive emulsion matrix and a high level of low resistance microspheres. Preferably, the microspheres have a crushing strength of between 100 and 400 psi and are present at at least 4% by weight of the formulation, accordingly, the present invention allows the use of more common microspheres (and usually less costly) in the production of an emulsion explosive resistant to pre-compression desensitization. In addition, the emulsion explosives of the present invention will allow emulsion explosives to be used, in general, in a wide range of applications. Under protest to tell the truth, the best known method for putting the present invention into practice is the one described in the description of this application. In testimony of which we sign the present in: Mexico, D.F., to March 22, 1996. ICI EXPLOSIVES USA INC.