WATER-IN-OIL TYPE EMULSION EXPLOSIVE

Abstract: Thermostability, age stability, and ignition property at low temperatures of a W/O type emulsion explosive, containing an auxiliary sensitizer, are improved by incorporating a chelating agent in the W/O type emulsion explosive.

Description: The present invention relates to a water in oil type emulsion explosive, particularly a water in oil type emulsion explosive composed of a continuous phase consisting of a carbonaceous fuel, a dispersive phase consisting of an aqueous solution of an inorganic oxidative salt, an emulsifier, a foam retainer, and an auxiliary sensitizer. Recently, many studies on water in oil type emulsion explosive have been reported. Among such reports, there are known water in oil type (to be referred to as "W/O type", hereinafter) emulsion explosive not containing an explodent sensitizer such as trinitrotoluene or trimethylenetrinitramine, etc. and containing an auxiliary sensitizer such as mono-methylamine nitrate or hydrazine nitrate, etc. and having improved detonability by a blasting cap and an improved sympathetic detonation property, as disclosed by Japanese Patent Application Laid-open Nos. 60-51,685 and 60-90,887. AW/O type emulsion explosive which comprises a decomposition inhibitor, such as formic acid, odalic acid or tartaric acid, in a conventional W/O type emulsion explosive, for preventing decomposition of the explosive in a high temperature atmosphere is known from Japanese Patent Application Laid-open No. 59-13,690. Though the W/O type emulsion explosive disclosed by the above Official gazettes 60-51,685 and 60-90,887 do not contain an explodent sensitizer, they contain an auxiliary sensitizer. Therefore, in cases when they are used for blasting rocks which are at high temperature or in a high temperature atmosphere caused by a pressurized state of a blasting hole, the explosives are liable to be decomposed. Such decomposition at the time of blasting is likely to lead to accidental detonation, and has a risk of causing a gas explosion if a combustible gas is present in the environmental atmosphere of a coal mine drift or the like. Hence, there is a need for W/O type emulsion explosives to be improved. The above Japanese Patent Application Laid-open No. 59-13,690 does not disclose a concrete example of a thermally stable W/O type emulsion explosive containing an auxiliary sensitizer. Though 59-13,690 discloses a slurry explosive containing monomethylaminenitrate as an auxiliary sensitizer, the addition of monomethylaminenitrate to a W/O type emulsion explosive will not improve aging stability significantly nor the heat resistant property sufficiently. Therefore, an object of the present invention is to provide a W/O type emulsion explosive containing a specific auxiliary sensitizer, which does not decompose even under the kind of high temperature conditions mentioned above, and which remains stable for a long period of time under normal conditions. Another object of the present invention is to provide a W/O type emulsion explosive of remarkably improved thermostability, age stability and ignition sensitivity at low temperatures. Now, the above objects can be achieved by the present invention. The present invention is a W/O type emulsion explosive composed of a continuous phase consisting of a carbonaceous fuel, a dispersive phase consisting of an aqueous solution of an inorganic oxidative salt, an emulsifier, a foam retainer, and 1-40 wt% of an auxiliary sensitizer, comprising further 0.1-10 wt% to a chelating agent, said auxiliary sensitizer being a nitric acid salt of a compound of the general formula X-NH₂ wherein X represents CH₂CH₂NH₂, CH₂CH₂OH or NH₂ group and said chelating agent being at least one or two selected from the group consisting of sodium citrate, sodium ethylenediaminetetraacetate and nitrilotriacetic acid. The carbonaceous fuel which forms the continuous phase in the W/O type emulsion explosive of the present invention includes all the carbonaceous fuels that are conventionally used in producing the prior W/O type emulsion explosive. Illustrative examples thereof are hydrocarbons, such as paraffin series hydrocarbons, olefin series hydrocarbons, naphthene series hydrocarbons, aromatic hydrocarbons, saturated or unsaturated hydrocarbons, petroleum purified mineral oils, lubricants, and liquid paraffin, etc.; hydrocarbon derivatives, such as nitrohydrocarbons, etc.; derivatives of fuel oils and/or petroleum, such as unpurified or purified microcrystalline wax, paraffin wax, etc.; mineral waxes, such as montan wax, etc.; animal waxes, such as whale wax, etc.; insect waxes, such as bees wax, etc.; and other waxes. These are used alone or in admixture. Preferable carbonaceous fuels from the aspect of age stability are microcrystalline wax and petrolactam, particularly microcystalline wax. The carbonaceous fuel may also include a polymer of low molecular hydrocarbons, such as petroleum resin, low molecular polyethylene, or low molecular polypropylene, etc. The carbonaceous fuel is usually used in an amount of 1-10 wt% in the emulsion explosive. The aqueous solution of the inorganic oxidative salt, which constitutes the dispersive phase of the W/O type emulsion explosive of the present invention, includes all the aqueous solutions of the inorganic oxidative salt that are conventionally used in producing the prior W/O type emulsion explosive. As the inorganic oxidative salt, use is made of, for example, ammonium nitrate; nitrates of alkali metal or alkaline earth metal, such as sodium nitrate, or calcium nitrate, etc.; and inorganic perchlorates, such as ammonium perchlorate, or sodium perchlorate, etc. Usually, ammonium nitrate is used alone or in admixture with other inorganic oxidative salt. The inorganic oxidative salt is generally used in an amount of 5-90 wt%, usually 40-80 wt%, in the aqueous solution thereof. The aqueous solution of the inorganic oxidative salt is used in an amount of 3-30 wt%, preferably 5-25 wt%, in the emulsion explosive. The emulsifier used in the present invention includes all the emulsifiers that are conventionally used in producing the prior W/O type emulsion explosive. For example, use is made of fatty acid esters of sorbitan, such as sorbitan monolaurate, sorbitan monooleate, sorbitan monopalmitate, sorbitan monostearate, sorbitan sesquioleate, sorbitan dioleate, or sorbitan trioleate, etc.; mono- or di-glycerides of fatty acid, such as monoglyceride of stearic acid, etc.; fatty acid esters of polyoxyethylenesorbitan; oxazoline derivatives; imidazoline derivatives; phosphoric acid esters; alkali metal salts or alkaline earth metal salts of fatty acids; or primary, secondary or tertiary amine salts, etc. These are used alone or in admixture of at least two. Among these emulsifiers, fatty acid esters of sorbitan are preferable. The emulsifier is used in an amount of 0.1-10 wt%, preferably 1-5 wt%, in the emulsion explosive. The foam retainer used in the present invention includes all the foam retainers that are conventionally used or proposed in producing the prior W/O type emulsion explosive. For example, various minute hollow spheric bodies, and foamed bodies containing a plurality of foams can be used. Illustrative examples of such minute hollow spheric bodies are inorganic minute hollow spheric bodies obtained from glass, alumina, shale, sirasu (Japanese volcano ash), silicon sand, volcanic rock, sodium silicate, borax, pearl stone or obsidian, etc.; carbonaceous minute hollow spheric bodies obtained from pitch or coal, etc.; and synthetic resin series minute spheric bodies obtained from phenol resin, polyvinylidenechloride, epoxy resin or urea resin, etc. Illustrative examples of such foamed bodies containing a plurality of foams are particles of foamed synthetic high molecular substances or particulates obtained by grinding such foamed synthetic high molecular substances. The foamed synthetic high molecular substances are prepared by incorporating foams into synthetic high molecular materials, e.g., polymers, copolymers, modified polymers, blend polymers of olefin, such as ethylene or propylene, etc., vinylidene chloride, vinyl alcohol, vinyl acetate, acrylic acid, acrylic acid ester, methacrylic acid, or methacrylic acid ester, etc.; polyurethanes, polyesters, polyamides, urea resins, epoxy resins, phenol resins, or the like, by various means, such as mechanical foaming, chemical foaming, microcapsulation, or incorporation of easily volatile matter. Preferably, particles of preliminarily foamed synthetic high molecular substances of polystyrene, polyurethane, polyethylene or polypropylene, etc. are used, viewed from availability and economical cost. The foam retainer is used alone or in admixture. The selection of the foam retainer and the mixing recipe of the foam retainers are properly selected depending on the use of the W/O type emulsion explosive. If the explosive is to be used in a use field of thinking much of the dead pressure property of the explosive, the foam retainer is used advantageously in the explosive. The foam retainer is usually used in an amount of adjusting the apparent specific gravity or bulk density of the W/O type emulsion explosive to 0.80-1.35. In the present invention, the term "auxiliary sensitizer" is used to differentiate it from explodent sensitizer, such as trinitrotoluene, trimethylenetrinitramine, or the like explosives. The auxiliary sensitizer is the nitrate of the compound of the formula X-NH₂ wherein X represents CH₂CH₂NH₂, CH₂CH₂OH or NH₂ group. Examples thereof are hydrazine nitrate, ethylene-diamine nitrate and ethanolamine nitrate. These specific auxiliary sensitizers are used alone or in admixture. The auxiliary sensitizers may also include a metal powder, such as aluminum powder, in addition to the auxiliary sensitizer. The auxiliary sensitizer is used in an amount of 1-40 wt% in the W/O type emulsion explosive. If the amount is too high, the production of the emulsion explosive becomes hazardous and disadvantageous economically. If the amount is too low, then age stability and ignition sensitivity at low temperatures are not improved significantly. The chelating agent which is simultaneously used with the auxiliary sensitizer is sodium citrate, sodium ethylenediaminetetraacetate or nitrilotriacetic acid The chelating agent is used alone or in admixture. The chelating agent is used in an amount of 0.1-10 wt% relative to the amount of the auxiliary sensitizer, depending on the type and the mixing amount of the auxiliary sensitizer. If the amount of the chelating agent is less than 0.1 wt%, the function of the chelating agent of preventing the decomposition of the W/O type emulsion explosive is small, while, if it exceeds 10 wt%, the function of the chelating agent is not improved and the explosion property of the W/O type emulsion explosive is adversely influenced. The W/O type emulsion explosive of the present invention may also contain an emulsion stabilizer, such as a heretofore known metallic salt of a higher fatty acid, e.g., zinc stearate, zinc myristate, aluminum stearate, or the like. Further, the W/O type emulsion explosive may also contain a publicly known reducer or cooling agent, such as sodium chloride, potassium chloride, or the like, for the use in coal mines. In such case, the other components are determined, considering the explosion rate and the post gases, etc. The W/O type emulsion explosive of the present invention can be produced, for example, as follows. The inorganic oxidative salt, the auxiliary sensitizer and the chelating agent are dissolved in warm water of about 60-100°C, to prepare an aqueous solution of the inorganic oxidative salt, etc. Meanwhile, the carbonaceous fuel, and the emulsifier are melt mixed at a liquefying temperature of generally 70-90°C, to obtain a combustible mixture. Then, the aqueous solution of the inorganic oxidative salt, etc., and the combustible mixture are mixed at 60-90°C under agitation of about 600-6,000 rpm, to obtain a W/O type emulsion. Subsequently, the foam retainer, and the W/O type emulsion are mixed in a vertical blender at about 30 rpm, to obtain a W/O type emulsion explosive. In the above procedures, the auxiliary sensitizer and the chelating agent may be omitted in preparing the aqueous solution of the inorganic oxidative salt, and they may be added directly in preparing the W/O type emulsion prior to the production of the W/O type emulsion explosive. The W/O type emulsion explosive of the present invention is stable even at high temperatures by the function of the chelating agent, even though it contains a specific auxiliary sensitizer. Also, it can ignite well at low temperatures after held at high temperatures. Hereinafter, the present invention will be explained in more detail with reference to examples. In the examples, all parts are represented by weight basis. Example 1 W/O type emulsion explosive of the compositions as shown in the following Table 1 are produced in the following way. 73.1 parts of ammonium nitrate, 4.0 parts of hydrazine nitrate, and 5.6 parts of sodium nitrate, are added to 11.2 parts of water. The mixture is added with 0.3 part of zinc stearate as the emulsion stabilizer, and 0.1 part of sodium citrate as the chelating agent. The admixture is completely dissolved at 90°C to obtain an aqueous solution of the inorganic oxidative slat, etc. In the meantime, 3.2 parts of microcrystalline wax (produced by Mobile Petroleum Co. and sold under the trade name of "Waxrex 602") as the carbonaceous fuel, and 1.6 parts of sorbitan monooleate as the emulsifier, are dissolved at 90°C, to obtain a combustible mixture. The combustible mixture is added slowly with 94.3 parts of the above aqueous solution of the inorganic oxidative salt, at 90°C under agitation of 650 rpm, to obtain 99.1 parts of a W/O type emulsion. The W/O type emulsion is added with 0.9 part of prefoamed particles of foamed styrol (produced by Mitsubishi Yuka Badische K.K.) as the foam retainer, mixed and blended at 60-80°C. Each 100 g of the blended mixture is weighed out, shaped into a column of a diameter of 25 mm, and wrapped in a laminated paper. Thus obtained wrapped W/O type emulsion explosive are tested on the following tests; namely, (a) measurement of apparent specific gravity after 1 day of the production, (b) age stability test of ignition sensitivity, wherein the wrapped explosive is subjected to a storage test under forced deterioration consisting of repetition of a temperature cycle of holding the wrapped explosive at -40°C for 2 hours and then at +30°C for 22 hours, and then to an ignition test at -15°C using a No. 6 detonator, in order to determine a number of the temperature cycles that can ignite the explosive fully, (c) test of ignition sensitivity at low temperatures, wherein the wrapped explosive is held at 50°C for 72 hours, then left under storage at an ambient temperature (0-30°C) for 1 year, and ignited at a low temperature, in order to determine the lowest value of such low temperature that can ignite the explosive, and (d) stability of the W/O type emulsion, wherein the wrapped explosive is held at 50°C for 15 days, then left at 20°C for 1 day, and measured on its breakage voltage after held at an isothermal and isohumid condition of a temperature of 20±2°C and a humidity of 60-65% for 30 minutes by means of a device for measuring a breakage voltage at a discharge gap of 3 mm. The results are shown also in Table 1. Examples 2 and 3 The procedures of Example 1 are repeated using the mixing recipes of the components as shown in Table 1, to obtain respective W/O type emulsion explosive corresponding to the mixing recipes. Each W/O type emulsion explosive is tested on the same items as in Example 1. The results are shown in Table 1. Comparative Examples 1-5 The procedures of Example 1 are repeated using the mixing recipes of the components as shown in Table 1, to obtain respective W/O type emulsion explosive corresponding to the mixing recipes. Each W/O type emulsion explosive is tested on the same items as in Example 1. The results are shown in Table 1. In Table 1, the carbonaceous fuels represent the followings: In Table 1, the foam retainers represent the followings: As clearly seen from the comparison of Examples and Comparative Examples shown in Table 1, the W/O type emulsion explosive of the present invention (Examples 1-3) containing the chelating agent in addition to the auxiliary sensitizer exhibit less destruction at high temperatures, excellent age stability, and splendid ignition property at low temperatures, as compared to the prior W/O type emulsion explosive (Comparative Examples 1-5) containing the auxiliary sensitizer without containing the chelating agent.

Claims: 1. A water in oil type emulsion explosive composed of a continuous phase consisting of a carbonaceous fuel, a dispersive phase consisting of an aqueous solution of an inorganic oxidative salt, an emulsifier, an auxiliary sensitizer, and a foam retainer, characterised in comprising 1-40 wt% of the auxiliary sensitizer in the emulsion, and 0.1-10 wt% of a chelating agent, the amount of chelating agent being relative to the amount of the auxiliary sensitizer, said auxiliary sensitizer being a nitric acid salt of a compound of thegeneral formula X-NH₂ wherein X represents CH₂CH₂NH₂, CH₂CH₂OH or NH₂ group and said chelating agent being at least one or two selected from the group consisting of sodium citrate, sodium ethylenediaminetetraacetate and nitrilotriacetic acid.

Inventors: AMANO, TOMOYUKI, EDAMURA, KOJI, KUROKAWA, KOICHI
Applicants: NIPPON OIL AND FATS COMPANY, LIMITED
Application year: 1988
Main classification: C06B47
IPC codes: C06B23, C06B47