ENCAPSULATED VAPOR-DETECTION AND IDENTIFICATION TAGS In view of the alarming increase in terrorist acts in recent years, the government is revisiting technological countermeasures to combat terrorism. Accordingly, the terrorism bill signed by President Clinton in April of 1996 includes provisions to study the incorporation into explosives of: a) post-blast identification tags, which identify the source of the explosive; and b) pre-blast vapor-detection tags (referred to as"detecting agents"in The Congressional Record, H3325, April 15,1996) which could be detected by sniffing machines or dogs. The specific detecting agents listed in H3325 include ethylene glycol dinitrate (EGDN), 2,3-dimethyl-2, 3-dinitrobutane (DMNB), para-mononitrotoluene (p-MNT), and ortho-mononitrotoluene (o-MNT).

Post-blast identification tags for explosives identification have been known since the 1970s. U. S. Patent 3,772,200 describes code-bearing microparticles containing tagging elements in various combinations and concentrations to provide codes which can be interpreted using an electron microscope. U. S. Patent 4,053,433 discloses multilayered microparticles of color-coded melamine resins. Since the color sequence is designed to be unique to each manufacturer, the post-blast identification tag can be used to identify the explosive's manufacturer, a specific batch number, and even a production date. U. S. Patent 4,390,452 discloses microparticles having flat surfaces bearing repetitive identifying indicia such as alphanumerics, which can be visually interpreted under magnification.

In addition to color-coded post-blast identification tags, combinations of fluorescent rare earth compounds bound together into a ceramic-like particle have also been evaluated.

A scanning monochronometer can be used to read the wavelength of the rare earth compounds, thereby identifying the post-blast identification tag code. These ceramic post- blast identification tags have also been incorporated with a spotting phosphor (which fluoresces in the visible range when illuminated by shortwave radiation) and magnetic particles, both of which assist in the identification tag recovery process.

Curie point post-blast identification tags, which consist of a collection of five distinct ferrites packaged with an ultraviolet sensitive spotting phosphor in a binder of potassium silicate, have also been evaluated for use in post-blast identification. Ferromagnetism disappears when the temperature of the ferrite is raised above a specific temperature, designated as the Curie point temperature. Identification of a recovered post-blast

identification tag is accomplished by placing it in a temperature-controlled chamber and recording the magnetism as a function of temperature.

In view of the obvious need for incorporating identification tags and/or vapor- detection tags into explosives or explosive precursors such as ammonium nitrate, it would be desirable to incorporate, with controlled metering, either or both of the identification tag and the vapor-detection tag into the explosive or explosive precursor. In view of the fact that some post-blast identification tags have been shown to sensitize explosives, it would be further desirable to improve the safe handling of the post-blast identification tag.

The present invention addresses the deficiencies of the prior art. In one aspect, the present invention is a composition comprising: a) a nitro group-containing pre-blast vapor- detection tag and/or a post-blast identification tag; and b) a coating material which is a solid at about 25°C, wherein the vapor-detection tag and/or the identification tag are microencapsulated in the coating material.

In a second aspect, the present invention is a method of preparing microspheres or microparticles containing a post-blast identification tag and/or a nitro group-containing vapor- detection tag encapsulated in a coating material comprising the steps of: a) forming a dispersion or a solution by dispersing the identification tag and/or dispersing or dissolving the vapor-detection tag in the coating material at a temperature above the melting point of the coating material but below a temperature at which either the coating material or the vapor- detection tag decomposes; b) pouring the dispersion or solution onto a rotating disk maintained at a sufficiently high temperature and rotated at a sufficient velocity to fling microparticles from the disk so that at least a portion of the microparticles contains an identification tag and or a vapor-detection tag microencapsulated in the coating material ; and c) cooling and collecting the microparticles.

In a third aspect, the present invention is a composition comprising a plurality of microparticles that contain a post-blast identification tag encapsulated in a first coating material, and a plurality of microspheres that contain a second coating material and a nitro group-containing vapor-detection tag, with the proviso that the first and the second coating materials each are solids at about 25°C.

In a fourth aspect, the present invention is a composition comprising a nitro group- containing vapor-detection tag, and/or a post-blast identification tag, and a coating material

which is a solid at about 25°C ; wherein the vapor-detection tag and/or the identification tag are microencapsulated in the coating material to form microparticles and/or microspheres; and c) a medium in which the microparticles and/or microspheres are dispersed, the medium being either explosives or explosive precursors.

The present invention addresses the aforementioned deficiencies in the art by providing a simple means of controlling the addition of the identification tag and/or the vapor- detection tag into an explosive or explosive precursor. The present invention also provides improvement in the safety of handling the post-blast identification tag as well as the vapor- detection tag. Moreover, the present invention provides a way to increase the lifetime of the vapor-detection tag by increasing the shelf stability of the agent.

The composition of the present invention comprises an identification tag and/or a vapor-detection tag, and a coating material, wherein the post-blast identification tag or detecting agent is microencapsulated in the coating material to form microspheres or microparticles. The coating material preferably has a melting point or a glass transition temperature in the range of from 35°C to 200°C and is preferably a petroleum-derived alkane hydrocarbon wax, a polyethylene wax, a polyethylene-alkene copolymer, a polyterpene resin, an oxidized hydrocarbon wax containing hydroxyl or carboxyl groups, a polyester, a polyamide, or a combination thereof. More preferably, the coating material is a petroleum-derived alkane hydrocarbon wax, a polyethylene-alkene copolymer, a polyethylene wax, or a polyterpene resin. Most preferably, the coating material is a polyterpene resin. Preferred coating materials have a weight average molecular weight in the range of from 500 Daltons, more preferably from 1000 Daltons, to 3000 Daltons, more preferably 2000 Daltons. These waxes are exemplified by Bolero"^ 1426 polyterpene wax (available from International Group, Inc.), Polywax 500, Polywax 1000, and PolywaxT"' 2000, or blends thereof. (Polywax is a trademark of Petrolite Corporation.) For the purposes of this invention, microspheres are spherical particles having a diameter of not greater than 1500 microns. For the purposes of this invention, microspheres are formed when just the vapor-detection tag is encapsulated in the coating material.

Preferably, the size of the microspheres is preferably not greater than 750 microns, more preferably not greater than 500 microns, and most preferably not greater than 350 microns in diameter. The microspheres preferably have a diameter of not less than 25 microns, more

preferably not less than 50 microns, and most preferably not less than 75 microns in diameter.

An identification tag that is coated with the coated material does not necessarily form a microsphere, but instead tends to conform to the shape of the post-blast identification tags. Coated materials that contain the post-blast identification tags or the post-blast identification tags and the vapor-detection tags are referred to as"microparticles". The size of a microparticle formed varies depending on the size of the identification tag, but is preferably not greater than 750 microns, more preferably not greater than 500 microns, and most preferably not greater than 350 microns in diameter. The microparticle preferably has a diameter of not less than 25 microns, more preferably not less than 50 microns, and most preferably not less than 75 microns in diameter.

The post-blast identification tag is any particle which is coded for retrospective identification. The broadest dimension of the post-blast identification tag, which is insoluble in the coating material, is typically in the range of from 1 micron to 500 microns, but upper limits of 250 microns to 350 microns are preferred to provide large numbers of the post-blast identification tag per unit weight of the bulk material, namely the explosive. The preferred post-blast identification tag for use in the present invention range from 50 microns to 250 microns at the broadest dimension. The shape of the post-blast identification tag is preferably cylindrical, spherical, or polyhedral so as to be readily recognizable and retrievable from common particulate substances. The post-blast identification tag may be incorporated with any number of readily detectable species such as a fluorescent material or magnetic iron oxide pigments or iron powder, any of which serve to aid in the retrieval of the post-blast identification tag after an explosion. Although in principle, a plurality of post-blast identification tags can exist in a single microsphere, it is preferred that there be only one post-blast identification tag that is encapsulated per microsphere.

The vapor-detection tag is any compound that contains a nitro group and has a vapor pressure sufficiently high to be detected by a vapor-detecting means. Such vapor-detecting means include"high tech"methods (for example, gas chromatography, mass spectrometry, and chemiluminescence), as well as"low tech"methods (for example, specially-trained dogs). The vapor-detection tag may be a solid or a liquid at ambient temperature, and is preferably soluble in the coating material when the coating material is molten. Examples of

preferred vapor-detection tags include ethylene glycol dinitrate, 2,3-dimethyl-2,3- dinitrobutane, para-mononitrotoluene, and ortho-mononitrotoluene.

It is also possible to prepare compositions comprising a plurality of microparticles that contain identification tags encapsulated in a first coating material, and a plurality of microspheres that contain a vapor-detection tag and a second coating material. Preferably, but not essentially, the first coating material is the same as the second coating material.

The concentration of the vapor-detection tag in the microsphere can vary substantially, and depends on the nature of the coating material and the vapor-detection tag, as well as on whether the vapor-detection tag is soluble or insoluble in the molten coating material. The concentration of the vapor-detection tag in the microsphere is preferably not greater than 75 weight percent, more preferably not greater than 50 weight percent, and most preferably not greater than 25 weight percent based on the weight of the coating material and the vapor-detection tag; and preferably not less than 1 weight percent, more preferably not less than 5 weight percent, and most preferably not less than 10 weight percent, based on the weight of the coating material and the vapor-detection tag.

Any suitable microencapsulation method may be used to form the compositions of the present invention. Examples of such means include a centrifugal method for forming high quality capsules having a diameter as large as 1500 microns, as disclosed by Somerville in U. S. Patents 3,015,128 and 3,310,612.

In a preferred method, a composition containing the identification tag and/or the vapor-detection tag, preferably a molten vapor-detection tag, and the coating material are combined at a temperature sufficiently above the melting point of the coating material to form a dispersion of the identification tag in a solution of the coating material and, optionally, the vapor-detection tag, or a solution of the pre-blast-detecting agent in the coating material.

This dispersion or solution is then poured onto a heated rotating disk. The rotation causes the dispersion or solution to be flung off the disk as microspheres, wherein the identification tag and/or the vapor-detection tag is/are encapsulated in the coating material. The microspheres or microparticles preferably solidify by the cooling effect of air. The velocity of rotation, the temperature of the disk, the rate at which the dispersion or solution is poured onto the disk, and the type of apparatus all influence the size of the microspheres or microparticles formed.

In the case where the post-blast identification tag is used, at least a portion of the microparticles contain the identification tag. Preferably, at least 90 percent, more preferably at least 95 percent, most preferably 100 percent by weight of the identification tag is encapsulated in the coating material. In the event that some of the identification tag is not microencapsulated in the coating material in the course of the process to form microcapsules, a means for separating particles by size such as a sieve, is advantageously used to remove such uncoated post-blast identification tag, particularly in the case where the size distribution of the pre-coated post-blast identification tag is narrow (for example, 250 to 350 microns). A particle size separator could also be effective in separating microspheres that do not contain the identification tag from those that do.

The present invention addresses a need in the art by providing a means for controlling the amounts of identification tag material and vapor-detection tag in a material such as an explosive. Moreover, microencapsulation of a vapor-detection tag increases the efficacy of the agent by effectively reducing the vapor pressure of the agent without substantially affecting the detectability of the agent.

The following examples are for illustrative purposes only and are not intended to limit the scope of this invention.

Example 1 A post-blast identification tag, which is a cross-linked melamine/alkyd resin (120 g), and molten p-nitrotoluene (60 g, 70°C) were added to molten BolerT" 1426 paraffin wax (240 g, 70°C, a trademark of International Group, Inc.), in which the p-nitrotoluene was miscible. The hot mixture was then poured at the rate of 100 g/minute onto the center of a disk maintained at 70°C, and rotating at 3000 rpm. Microparticles of the post-blast identification tag encapsulated in the wax and the p-nitrotoluene were flung off the rotating disk and into a collection area. The resultant solid microparticles (290 g) had a diameter in the range of from 75 microns to 500 microns. Analysis of representative microparticles indicated that all of the post-blast identification tags were encapsulated. The microparticles were air-dried and then stored until they needed to be formulated with an explosive.

Example 2 BolerT" 1426 polyterpene wax was melted and held in a container at 70°C. p-Nitrotoluene (melting point 52°C to 54°C) was melted and mixed with the wax to form a

homogeneous blend that contained 60 percent wax and 40 percent p-nitrotoluene. The blend was fed onto a rotating disk maintained at 70°C and rotating at 3000 rpm.

Microcapsules containing the p-nitrotoluene encapsulated in the wax were flung from the disk and allowed to fall on butcher paper. The particle size of the microcapsules (determined by light microscopy) were in the range of from 75 microns to 350 microns.

Example 3 The experiment was the same as Example 2 except that the blend that was fed onto the rotating disk contained 80 percent wax and 20 percent p-nitrotoluene.