Chemistry: analytical and immunological testing – Tracers or tags
Reexamination Certificate
1998-02-24
2002-08-13
Alexander, Lyle A. (Department: 1743)
Chemistry: analytical and immunological testing
Tracers or tags
C436S027000, C436S172000
Reexamination Certificate
active
06432715
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an improved method for marking individual microparticles of a substance for the purpose of subsequent identification. A further aspect of the invention relates to the microparticles themselves which include therein a near infrared fluorophore.
There has long been interest in methods for identifying various substances by incorporating materials which provide, possibly in coded form, information about the source, date, and lot or batch number of the material. Although there are other obvious applications for such “taggants”, the need for identification of explosives and certain bulk chemicals which can be used to make explosives has become increasingly urgent with the increase in the use of explosives in terrorism. It is desirable for the manufacturer to be able to incorporate small particles (“microtaggants”) into an explosive, some of which will survive the explosion, and which upon recovery from the debris of the explosion will provide information about the manufacturer, as well as the date of manufacture and the particular lot of the explosive. Reference to the manufacturer's records would make it possible to trace the explosive to the final seller and possibly to the ultimate purchaser.
There are many occasions on which it is necessary or desirable to mark items or materials so that ownership or the original manufacturer can be established. It is also frequently desired to include in the identification information such as the date of manufacture and, in case the items are made in different batches or lots, the particular lot with which the item is associated.
A color code of some sort is, of course, an obvious method of identification and a system of this sort has been used for many years for indicating the resistance value of small electrical resistors and capacitors. For resistors, colored bands corresponding to the first and the second significant figures of the resistance value, followed by a third band corresponding to a decimal multiplier provide a simple code. The color of each band further provides a multiplier for that band. Additional bands may be used to indicate the percent tolerance, or accuracy, of the indicated resistance value, and the percent change in resistance value per 1000 hours of use.
U.S. Pat. Nos. 4,053,433 and 4,390,452 (Minnesota Mining & Manufacturing Co.) contain reviews of a number of methods for identifying units of production of bulk substances with identifying microparticles having properties different from the properties of particles previously determined to be present in the bulk material. Analytical methods used to identify such particles include microscopy (for size, shape, color, phosphorescence, or fluorescence); determination of density, hardness, or trace ingredients; or spectrometry to measure light absorption; fluorimetry; or reflectance. More specific examples include tagging with refractory microparticles containing low levels of elements such as manganese, cobalt, zinc, etc. The identity and amount of each of which may be varied to provide an identification code. It is obvious that these methods are not adaptable to coding for more than a very small amount of information.
Isotopes of the various elements may be used in the same way. However, complicated equipment not readily available to law enforcement personnel is required for identification.
U.S. Pat. No. 4,053,433 describes the use of microparticles which are encoded with an orderly sequence of visually distinguishable colored segments. Decoding of the microparticles can be accomplished with the aid of a microscope or other magnifying device. According to this patent, identification is provided by incorporating the encoded microparticles into the substance and subsequently examining the substance for encoded microparticles. In practice, the microparticles consist of refractory particles containing bands of various colors, which are ordered in the polymer to provide a code which may be read under a microscope. By using this technique, it is possible to provide up to C*(C−1)
n−1
uniquely coded batches, where C is the number of available colors and n is the number of segments in the color sequence. According to this formula, if a library of 12 colors is used in an eight-layered sequence, with no color adjacent to itself, a total of 233,846,052 codes are possible if the code is read in one direction. Half that number of codes is possible if the colors are arranged so that the same code may be read in either direction. The broadest dimension across the color sequence of the particles is between 1 and 1000 microns, and preferably between 50 microns to 250 microns.
Although this method is extremely flexible and provides a large number of codes, the desired size of the particles requires that the coding colors be laid down with great accuracy and in extremely thin layers. Since each layer can contain only one visible color, the maximum number of layers for a very small particle is four. Assuming that seven different colors are available for use, the number of possible codes is 756.
U.S. Pat. No. 4,390,452 describes an improvement over U.S. Pat. No. 4,053,433 in which the microparticles contain at least one flat surface which bears identifying indicia selected from alphanumerics and symbols which can be visually interpreted under magnification. According to this patent, this top layer is photosensitive, so that the identifying indicia may be applied to the surface by exposing it to an ultraviolet light.
The prior art cited in U.S. Pat. Nos. 4,053,433 and 4,390,452 is included herein by reference.
Taggants have been used in Switzerland for the identification of explosives since about 1980. These include “microtaggants” such as those described in U.S. Pat. Nos. 4,053,433 and U.S. 4,390,452; and those available commercially, such as “HF-6” (Swiss Blasting AG), which has a code consisting of several layers of color, each of which represents a distinctive feature of this particular product; and “Explotracer” (Societe Suisse des Explosifs), which consists of a basic polymer marked with fluorescent pigments and rare earth elements. The code is based upon the melting point of the polymer and the identity of the elements which are included in it.
It is necessary not only for the taggant particles to be identifiable, but they must also be isolated for identification. Especially in the case of an explosion, the very small particles are widely scattered and must be separated and isolated from a large amount of extraneous debris. This has been done by incorporating finely divided iron or other magnetic particles in the micro taggants, or by incorporating ultraviolet dyes or pigments which render them visible when illuminated by ultraviolet light. However, magnetic material is almost universally dispersed in the environment, and a large amount of extraneous material is inevitably recovered with the microtaggant.
The incorporation of ultraviolet fluorescent material as an aid to locating the microtaggants is also subject to a great deal of interference. Many materials which are present in the environment also fluoresce in the UV region so that, again, isolating the microtaggant from extraneous material is complicated. UV fluorescence is also easily quenched or masked by other materials which may be present in the debris from an explosion. Another disadvantage of using a UV fluorescent compound is that it must be place on one of the exposed surfaces of the microtaggant since most pigments and dyes used to make a layered microtaggant would interfere with the UV fluorescent material by absorbing the fluorescent light. (
The Physics and Chemistry of Color The Fifteen Causes of Color
, Kurt Nassau, pp. 4-19, U.S. (1983)). Finally, materials which fluoresce in the visible region are difficult or impossible to detect during examination of debris in daylight or artificial light.
Accordingly, there is a need for a microparticle taggant that can readily be identified and that overcomes the above described disadvantages.
SUMMARY
Krutak, Sr. James John
Nelson Gregory Wayne
Alexander Lyle A.
Isotag Technology, Inc.
Schultz George R.
LandOfFree
Method for marking items for identification does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for marking items for identification, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for marking items for identification will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2971618