GB2305994A - An explosive device - Google Patents

Abstract

An explosive device comprises a casing; a projectile which is releasably held within the casing; an activatable explosive contained within the casing for projecting the projectile from the casing when the explosive is activated; and a sealant 25 for at least a portion of any gap in the explosive device, such as any gap in the casing and/or any gap between the projectile and the casing, and in a sufficient amount to substantially prevent ingress of moisture into the casing and onto the explosive wherein the sealant is prepared by the polymerisation of a sealant composition comprising (i) at least one polymerisable hydroxy monomer; and (ii) at least one plasticising polymerisable co-monomer. The hydroxy monomer may be hydroxy propyl methacrylate and the co-monomer may be lauryl methacrylate or propylene glycol monomethacrylate and the curing process may be anaerobic.

Description

AN EXPLOSIVE DEVICE The present invention relates to an explosive device that has been sealed by use of an anaerobic sealant composition. The sealant composition is used to seal an explosive contained within the explosive device to prevent moisture ingressing onto or into the explosive.

Anaerobic sealant compositions are known. An example of an anaerobic sealant composition is described in GB-A-1345939. This sealant composition comprises polymerisable acrylic esters.

As indicated the present invention relates to an explosive device. In this regard, typically the term "explosive device" as used herein includes a projectile releasably held within a casing wherein the projectile is expelled from the casing upon activation (e.g. explosion) of an explosive contained within the casing.

Examples of explosive devices include ammunition, devices that inflate air bags and devices that activate seat belt tensioners.

Until now, the most commonly used sealing composition used to seal gaps in explosive devices - such as gaps in the casing and the gap between the casing and the projectile - was solvent-based bitumen. Bitumen suffers from many disadvantages. For example, it is solvent based and therefore the sealing process is slow. Secondly, after the bitumen has hardened on evaporation of the solvent it often flakes upon firing of the explosive device. This is disadvantageous as when, for example, an explosive device, such as ammunition, is fired from a gun, it fouls the gun barrel. Also, the flaking leads to inaccuracy when firing the ammunition. Thirdly, bitumen does not form a moisture-proof seal. This causes problems with the new class of explosives which are substantially lead-free and which are water sensitive - which are described later.Hence, the bitumen does not form a water tight seal between the gaps in the casing or between the projectile and the casing. Thus, any ingress of water into the casing renders the explosive device less effective or inoperative.

Traditionally, explosives have been lead based. Recently, however. a new class of explosives has been used in explosive devices. These explosives are lead-free.

An example of a lead-free explosive is described in US-A-541,7160.

However, despite reducing the levels of lead in the atmosphere of for example shooting ranges, where ammunition is fired, in practice these explosives have a disadvantage in that, unlike the leaded explosives, they are moisture-sensitive and to such an extent that ammunition containing such explosive is unacceptable for use in the tropics where the atmosphere tends to be very humid. It is therefore even more important that these lead free explosives must be maintained in a water free environment. Thus. traditional use of sealants such as bitumen. which do not form a moisture-proof seal, is therefore unsuitable for sealing explosive devices such as ammunition containing such explosive.

The present invention therefore seeks to overcome the problems associated with the sealing compositions of the prior art.

According to a first aspect of the present invention there is provided an explosive device comprising: a casing; a projectile which is releasably held within the casing; an activatable explosive contained within the casing for projecting the projectile from the casing when the explosive is activated; and a sealant for sealing at least a portion of any gap in the explosive device and in a sufficient amount to substantially prevent ingress of moisture into the casing and onto the explosive; wherein the sealant is prepared by the polymerisation of a sealant composition comprising: (i) at least one polymerisable hydroxy monomer; and (ii) at least one plasticising polymerisable co-monomer.

According to a second aspect of the present invention there is provided a method of preparing an explosive device comprising a casing; a projectile which is releasably held within the casing; and an activatable explosive contained within the casing for projecting the projectile from the casing when the explosive is activated; the method comprising contacting at least a part of the explosive device with a sealant composition comprising: (i) at least one polymerisable hydroxy monomer; and (ii) at least one plasticising polymerisable co-monomer; and allowing the anaerobic cure thereof to substantially prevent moisture ingressing into the casing and onto the explosive.

According to the third aspect of the present invention there is provided the use of a sealant composition as defined above for sealing an explosive contained in an explosive device.

According to the fourth aspect of the present invention there is provided the combination of a sealant composition as defined above and a lead free explosive.

A key advantage of the sealant composition of the present invention is that it protects the explosive from water - such as from moisture in the air - by forming a durable and, in some cases, a flexible seal.

The sealant composition of the present invention is easy to apply. Also the components of the composition can be selected so that the composition can cure very rapidly. These are two important advantages for manufacturing explosive devices on a large scale.

Another key advantage is that the sealant composition of the present invention is compatible with the new class of explosives which are lead free.

In addition, it has been found that, when the explosive device is, for example, ammunition, upon firing the ammunition no residues are left from the sealant composition. In some cases accuracy of firing is improved by use of ammunition that has been prepared by use of the sealant composition of the present invention.

The term "explosive device" includes ammunition such as projectiles that are fired s from guns ins the like such as, for example, cartridges containing bullets. The term also covers any other explosive or non-explosive weapons such as rockets and artillery shells. The term also includes projectiles together with their fuses, propelling charges and primers. Also included are explosively activated devices such as those which cause seat belt tensioners to be activated and which cause air bags to inflate.

The term "projectile" as used herein includes any suitable body which can be projected by a force and can then continue in motion. Examples of suitable projectiles include a missile or a bullet or a firing pin (such as for a seat belt tensioner or air bag inflating device). The term also includes self-propelling weapons such as rockets, torpedoes or guided missiles.

The term "explosive" includes any explosive used for propelling projectiles. The explosive may be lead based or lead free. Preferably the explosive is lead free.

The term "monomer mix" as used herein includes any suitable polymerisable hydroxy monomer and any plasticising polymerisable co-monomer which forms a suitable anaerobic sealant and which is compatible with either or both of the lead based or lead free explosives.

Preferably, the at least one plasticising co-monomer contains a hydroxy group.

Preferably, the hydroxy monomer is a hydroxy Cm 20 alkyl (meth)acrylate, preferably a hydroxy C, ,0 alkyl (meth)acrylate, and more preferably a hydroxy Cl 5 alkyl (meth)acrylate. Preferably, the hydroxy monomer is hydroxy propyl methacrylate.

Preferably, the composition comprises two plasticising co-monomers.

Preferably, the at least one plasticising co-monomer is a monomer which is capable of.giving rise to a low glass transition temperature polymer.

Preferably, the at least one plasticising co-monomer is selected from lauryl methacrylate and\or polypropylene glycol monomethacrylate.

Preferably, the composition comprises two plasticising co-monomers.

Preferably, the composition further comprises a cross-linking agent.

Preferably, the cross-linking agent is triethylene glycol dimethacrylate.

Preferably, the sealant composition further comprises an initiator.

The term "initiator" includes any species which is able to aid the onset of the polymerisation reaction.

Preferably, the initiator comprises at least one or more of: (i) saccharin; (ii) cumene hydroperoxide; and (iii) NN dimethyl p-toluidine.

Preferably, the sealant composition further comprises an inhibitor.

The term "inhibitor" includes any species which stabilises the sealing composition by stopping or slowing down the reaction thereby reducing to a minimum the polymerisation of the monomer before application to the explosive device.

Preferably, the inhibitor comprises at least one or more of: (i) phenothiazine; (ii) oxalic acid; (iii)' EDTA solution; and (iv) 1,4 naphthaquinone.

Preferably, the curing process is a substantially anaerobic process.

Preferably, at least one of the casing and projectile are formed of a non-metallic material.

Preferably, the curing process is catalysed by heat or radiation.

Preferably, at least one of the casing and projectile are formed of metal.

Preferably, the metal of the casing and/or projectile catalyses the curing process.

Preferably, the explosive is a lead-free explosive.

Preferably, the sealant seals at least a portion of any gap in the casing and/or at least any gap between the projectile and the casing. Preferably, the sealant seals at least a portion of any gap between the projectile and the casing.

The sealant composition is an anaerobic sealant. Preferably, the sealant composition is a single part adhesive, unlike the sealants of the prior art which are generally two part systems.

The curing reaction is preferably a redox-type reaction. Preferably, where at least one of the casing and projectile are formed from metal, the reaction is influenced by the type or types of metal from which the casing and/or projectile are formed thereby permitting one to tailor different rates of catalysis. Where at least one of the casing and projectile are formed from a non-metallic material, the reaction is preferably catalysed by means of heat or radiation.

Where the casing and projectile are formed of metal, the metal catalyses the curing reaction when the sealing composition is applied to the gap. Where the casing and projectile are formed from non-metallic material, the sealing reaction is catalysed by means of heat or radiation when the sealing composition is applied to the gap. Preferably, the casing of the explosive device is preferably formed from brass. Preferably, the projectile is formed from a tin leaded material or steel or is formed from acetal. Preferably, the metal of the projectile is harder relative to the casing.

The gaps in the explosive device, such as any gap in the casing and any gap between the casing and the projectile, may be preferably sealed in a very short amount of time and in some instances can be sealed in approximately ten seconds when a rapid production rate is required. However, it may be advantageous in some instances for the sealing reaction to be slower if, for example, joints of the explosive device need to be readjusted. It is therefore preferable that the curing time can be adjusted to suit the required need and the composition of the present invention can be tailored to that required need.

The sealing composition of the present invention therefore comprises a monomer mix, and preferably, further comprises an inhibiting system and an initiating system. The monomer mix produces a sealant which is effective at preventing the ingression of moisture onto explosive such as that contained in ammunition casing. The inhibiting system stabilises the sealant composition and the initiating system activates the polymerisation step. In some instances the initiator activates the polymerisation step when it comes into contact with the metal of the casing and the projectile.

The monomer mix comprises a polymerisable hydroxy monomer and at least one plasticising co-monomer. Optionally the plasticising co-monomer contains hydroxy groups. Preferably, the monomer mix comprises two plasticising comonomers.

The polymerisable hydroxy monomer is preferably present in an amount of about 20% to 60% by weight, more preferably 30% to 50% by weight, more preferably 35% to 45% by weight, more preferably about 41 % by weight of the composition.

The plasticising co-monomer is preferably present in an amount of about 20% to 70% by weight, more preferably 30% to 60% by weight, more preferably 40% to 60% by weight, more preferably 45% to 55% by weight, more preferably about 50% by weight of the composition. If there are two co-monomers present in the composition, they may be present in equal quantities or one may be present in a greater amount than the other. For example, one co-monomer can be present in an amount of about 10% by weight and the other co-monomer can be present in amount of about 40% by weight.

The hydroxy monomer is preferably one or more of a hydroxy C1.20 alkyl methacrylate or a hydroxy Cm.20 alkyl acrylate (i.e. C, 20 alkyl (meth)acrylate), preferably a hydroxy C, l0 alkyl methacrylate or a hydroxy Cl l0 alkyl acrylate, more preferably a hydroxy C1.s alkyl methacrylate or a hydroxy C1.5 alkyl acrylate. Typical examples include hydroxy ethyl methacrylate, hydroxy propyl methacrylate, or hydroxy propyl acrylate. Preferably, the monomer is hydroxy propyl methacrylate.

The plasticising co-monomer is preferably a monomer which is capable of giving rise to a low glass temperature polymer i.e. a soft polymer. Two preferred plasticising co-monomers are polypropylene glycol monomethacrylate and lauryl methacrylate. Examples of other co-monomers that may be used include polyethylene glycol monomethacrylate, 2-ethyl-hexyl-methacrylate and polypropylene glycol acrylate. Other examples of suitable plasticising comonomers are known to those skilled in the art.

It is thought that the presence of polypropylene glycol monomethacrylate in the composition counteracts the acidity of the methacrylate, thereby making the hydroxy monomer compatible with the explosive.

The monomer mix may optionally include a cross-linking agent. The addition of a cross-linking agent controls the flexibility of the sealant and stops the sealant cracking when the projectile is being handled. The cross-linking agent is preferably present in about less than 10% by weight of the composition, preferably from 3 % to 7% by weight, preferably 5 % by weight of the composition. The cross-linking agent is preferably triethylene glycol dimethacrylate. Examples of other cross-linking agents which may be used in this invention include tetra-ethylene glycol diacrylate and trimethylol propane trimethacrylate. Other examples of suitable cross-linking agents are known to those skilled in the art.

The inhibiting system is preferably present in an amount of less than 2% by weight, preferably less than 1% by weight, preferably less than 0.5 % by weight.

Preferably the inhibiting system is present in an amount of about 0.005 % to 0.1 % by weight of the composition.

The inhibiting system can comprise one or more components. Preferably, the inhibiting system comprises more than one component. Preferably, the components are phenothiazine, oxalic acid, the tetra sodium salt of EDTA and 1,4 naphthoquinone which may be taken singly or in combination. Other components which may be included in the inhibiting system include hydroquinine, stearically hindered phenols and nitroxides.

The initiating system is preferably present in an amount of less than 10% by weight, preferably less than 5% by weight, preferably less than 4% by weight.

Preferably the inhibiting system is present in an amount of about 0.3% to 4% by weight of the composition. The initiating system can comprise one or more components. Preferably, the initiating system comprises more than one component. Preferably, the components are saccharin, cumene hydroperoxide and NN dimethyl p-toluidine which may be taken singly or in combination. Other components which may be included in the initiating system include tertiary butyl perbenzoate, 2,2dimethyoxy-1 ,2-diphenylethane-lone and copper naphthenate.

Other additives may also be incorporated into the sealant composition. Examples include accelerators, viscosity modifiers, fillers, tackifiers, dyes, fluorescein agents and external plasticisers.

Surprisingly, we have now found that the combination of the above-mentioned components is particularly useful for sealants for explosive devices such as ammunition and also for explosively activated devices such as those which are used in seat belt tensioners and air bag devices.

The projectile can be releasably held within all or a part of the casing.

Preferably, the projectile is releasably held within a part of the casing.

In a preferred embodiment of the present invention, the explosive device is a cartridge having a bullet releasably held therein. However, the explosive device may be any other kind of suitable ammunition, such as a cartridge for a cannon or an explosive device such as those which cause airbags to inflate and those which are found in seat belt tensioners.

The present invention therefore relates to the use of a low modulus anaerobic adhesive to seal explosive devices.

Thus, in accordance with a highly preferred embodiment of the present invention there is provided an explosive device comprising: a casing; a projectile which is releasably held within the casing; an activatable explosive contained within the casing for projecting the projectile from the casing when the explosive is activated; and a sealant for sealing any gap in the explosive device (such as at least a portion of any gap in the casing and/or at least a portion of any gap between the projectile and the casing) wherein the sealant is in a sufficient amount to substantially prevent ingress of moisture into the casing and onto the explosive; and further wherein the sealant is prepared by the polymerisation of a composition comprising: % weight hydroxy propyl methacrylate 41 lauryl methacrylate 40 polypropylene glycol monomethacrylate 10 triethylene glycol dimethacrylate 5 phenothiazine 0.01 oxalic acid 0.005 EDTA solution* 0.1 1,4 naphthoquinone 0.005 saccharin 1 cumene hydroperoxide 2 NN dimethyl p-toluidine 0.3 dyestuff 0.05 fluorescing agent 0.1 reodorant 0.005 *5% solution of the tetrasodium salt of EDTA in a 1:1 by volume water:propan-2-ol mixture.

The present invention will now be described only by way of example with reference to accompanying drawings in which: Figure 1 is a schematic diagram of a preferred explosive device according to the present invention, namely a cartridge having a bullet releasably held therein; Figure 2 is a schematic diagram showing the application of the sealing composition to a cartridge; and Figure 3 is a schematic diagram showing the position of the sealant when cured.

As mentioned a preferred explosive device is a cartridge (1) such as that shown in Figure 1. The cartridge (1) comprises a casing (5), a projectile (10), such as a 9 mm bullet, and an explosive (15). At end (7) of the casing is usually a percussion cap (not shown) which may also contain explosive and which in use is struck by a gun hammer or the like (not shown). Striking of the percussion cap activates the explosive therein which in turn activates the main explosive inside the casing which causes ejection of the projectile from the casing.

The projectile (10) is releasably held within the casing (5) by way of an interference fit resulting in a gap (18) between the casing and the projectile through which moisture from the air is able to enter the ammunition. In this regard, if there were no sealant moisture would be able to ingress onto the explosive by passage along the gap thereby causing the ammunition to be unusable. It is therefore necessary to apply a sealant between the projectile casing and the projectile portion to prevent the ingression of moisture.

A typical sealing composition for the use according to the present invention comprises: % weight hydroxy propyl methacrylate 41 lauryl methacrylate 40 polypropylene glycol monomethacrylate 10 triethylene glycol dimethacrylate 5 phenoth iazine 0.01 oxalic acid 0.005 EDTA solution* 0.1 1,4 naphthoquinone 0.005 saccharin 1 cumene hydroperoxide 2 NN dimethyl p-toluidine 0.3 dyestuff 0.05 fluorescing agent 0.1 reodorant 0.005 *5 % solution of the tetrasodium salt of EDTA in a 1:1 by volume water:propan-2-ol mixture.

When the sealing composition of the present invention is applied in drop wise manner near to or over the gap (18), which is represented in Figure 2 by way of drop (20), the composition flows around the gap and in addition penetrates inwards in a capillary-type action - sometimes referred to as "wicking". After a short period of time the composition cures, thus producing a seal (25) - such as that shown in Figure 3. Typically, with the above composition the curing reaction takes about ten seconds to form a suitable seal but this may be adjusted if required.

Tests on the ammunition thus prepared revealed that the sealant composition protects the explosive from water, the sealant composition is compatible with the new class of explosives which are lead free, no residues are left from the sealant composition upon firing the ammunition.

It should be noted that the explosive device according to the present invention may take the form of any explosive device as defined above and is not limited to a cartridge.

Other modifications of the present invention will be apparent to those skilled in the art.

Claims (24)

1. An explosive device comprising: a casing; a projectile which is releasably held within the casing; an activatable explosive contained within the casing for projecting the projectile from the casing when the explosive is activated; and a sealant for sealing at least a portion of any gap in the explosive device and in a sufficient amount to substantially prevent ingress of moisture into the casing and onto the explosive wherein the sealant is prepared by the polymerisation of a sealant composition comprising: (i) at least one polymerisable hydroxy monomer; and (ii) at least one plasticising polymerisable co-monomer;

2. An. explosive device according to claim 1 wherein the at least one plasticising co-monomer contains a hydroxy group.

3. An explosive device according to claim 1 or claim 2 wherein the hydroxy monomer is one or more of a hydroxy C1.20 alkyl (meth)acrylate, preferably a hydroxy C1.10 alkyl (meth)acrylate, more preferably, a hydroxy C1.3 alkyl (meth)acrylate.

4. An explosive device according to claim 3 wherein the hydroxy monomer is hydroxy propyl methacrylate.

5. An explosive device according to any one of the preceding claims wherein the least one plasticising co-monomer is capable of giving rise to a low glass transition temperature polymer.

6. An explosive device according to any one of the preceding claims wherein the at least one plasticising co-monomer is selected from lauryl methacrylate and\or polypropylene glycol monomethacrylate.

7. An explosive device according to any one of claims 1 to 4 wherein the composition comprises two plasticising co-monomers.

8. An explosive device according to any one of the preceding claims wherein the composition further comprises a cross-linking agent.

9. An explosive device according to claim 8 wherein the cross-linking agent is triethylene glycol dimethacrylate.

10. An explosive device according to any one of the preceding claims wherein the sealant composition further comprises an initiator.

11. An explosive device according to any one of the preceding claims wherein the initiator comprises at least one or more of: (i) saccharin; (ii) cumene hydroperoxide; and (iii) NN dimethyl p-toluidine.

12. An explosive device according to any one of the preceding claims wherein the sealant composition further comprises an initiator.

13. An explosive device according to any one of the preceding claims wherein the inhibitor comprises at least one or more of : (i) phenothiazine; (ii) oxalic acid; (iii) EDTA solution; and (iv) 1,4 naphthaquinone.

14. An explosive device according to any one of the preceding claims wherein the curing process is substantially anaerobic.

15. An explosive device according to any one of the preceding claims wherein at least one of the casing and projectile are formed of a non-metallic material.

16. An explosive device according to claim 15 wherein the curing process is catalysed by heat or radiation.

17. An explosive device according to any one of the preceding claims wherein at least one of the casing and projectile are formed of metal.

18. An explosive device according to claim 17 wherein the metal of the casing and/or projectile catalyses the curing process.

19. An explosive device according to any one of the preceding claims wherein the explosive is a lead-free explosive.

20. An explosive device according to any one of the preceding claims wherein the sealant seals at least a portion of any gap between the projectile and the casing.

21. A method of preparing an explosive device comprising a casing; a projectile which is releasably held within the casing; and an activatable explosive contained within the casing for projecting the projectile from the casing when the explosive is activated; the method comprising contacting at least a part of the explosive device with a sealant composition as defined in any one claims 1 to 20; and allowing the anaerobic cure thereof to substantially prevent moisture ingressing into the casing and onto the explosive.

22. Use of a sealant composition as defined in any one of claims 1 to 20 for sealing an explosive device explosive.

23. The combination of a sealant composition as defined in any one of claims 1 to 20 and a lead free explosive.

24. An explosive device substantially as hereinbefore described.