Method for detecting fingerprints

Abstract

Process for producing powdered polycyanoacrylate polymer by charging a reaction vessel with an aqueous mist, dripping a 2-cyanoacrylate into the reaction vessel, allowing the resulting reaction mass (polycyanoacrylate polymer) to cool, removing the polycyanoacrylate polymer from the reaction vessel, drying it, and pulverizing the dry solid into a powder. Powdered polycyanoacrylate polymer having a particle diameter in the range of from 1 to 200 microns. The particle size and shape herein contribute to uniform distribution of fumes during fingerprint capture. A high level of accuracy in fingerprint detection is provided among three distinct levels which include: (a) first level detection from ridge flow patterns such as whorl or loop; (b) second level detection from ridge flow singularities such as ridge endings and bifurcations; (c) and third level detection from pore configuration.

Claims

1. A method for detecting fingerprints, said method comprising: vaporizing a powdered polycyanoacrylate polymer wherein more than 95% of the particle mass comprises particles having a particle diameter in the range of from 1 to 200 microns in the vicinity of a substrate suspected of containing fingerprints; and allowing the vaporized polycyanoacrylate to settle onto the substrate suspected of containing the fingerprints.

2. A method for detecting fingerprints, said method comprising: vaporizing a powdered polycyanoacrylate polymer having one or more of the following particle size characteristics: (i) at least 50 weight-% of the powder particles have a feret length of from 20 to 80 nanometers; (ii) at least 50 weight-% of the powder particles have a feret width of from 10 to 40 nanometers; and (iii) at least 50 weight-% of the powder particles have a rectangularity ranging from 60 to 75 in the vicinity of a substrate suspected of containing fingerprints; and allowing the vaporized polycyanoacrylate to settle onto the substrate suspected of containing the fingerprints.

3. A method for detecting fingerprints, said method comprising: vaporizing a powdered polycyanoacrylate produced by a process comprising: (a) charging a reaction vessel with a mist comprising water; (b) adding methyl or ethyl 2-cyanoacrylate to the reaction vessel by dripping it into the water mist, thereby producing an exothermic reaction, while decreasing the rate of addition of methyl or ethyl 2-cyanoacrylate or temporarily halting addition of the methyl or ethyl 2-cyanoacrylate if the temperature in the reaction vessel becomes too high for uniform polymerization; (c) once all of the methyl or ethyl 2-cyanoacrylate has been added, allowing the reaction mass to cool; (d) removing the polycyanoacrylate polymer from the reaction vessel; (e) drying the polycyanoacrylate polymer to provide a dry solid polycyanoacrylate polymer; and (f) pulverizing the dry solid into a powder in the vicinity of a substrate suspected of containing fingerprints; and allowing the vaporized polycyanoacrylate to settle onto the substrate suspected of containing the fingerprints.

4. The method for detecting fingerprints of claim 1, wherein said powdered polycyanoacrylate polymer has a median particle diameter of approximately 20 microns and a mean particle diameter of approximately 60 microns.

5. The method for detecting fingerprints of claim 2, wherein said powdered polycyanoacrylate polymer has all three of characteristics (i), (ii), and (iii).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1A, 1B, and 1C are graphical depictions of feret length, feret width, and rectangularity of a sample of particles produced in accordance with the invention.

(2) FIG. 2 is a graph of incremental volume percent versus particle diameter of a sample of the particles of the invention.

(3) FIG. 3A is a photograph of a fingerprint developed with a composition of the present invention, showing first, second, and third level (pores) detection. FIG. 3B is a photograph of a different fingerprint developed with a composition of the present invention, showing first, second, and third level (pores) detection.

DETAILED DESCRIPTION OF THE INVENTION

(4) Methyl or ethyl 2-cyanoacrylate is generally used as the sole or primary monomer which is polymerized to make the polymer that is powdered in accordance with the present invention. Methyl cyanoacrylate has a boiling point of 48-49° C. Ethyl 2-cyanoacrylate has a flash point of 83° C. and a boiling point of 54-56° C. However, other 2-cyanoacrylates and 2-cyanomethacrylates, such as methyl 2-cyanomethacrylate, propyl 2-cyanoacrylate, isopropyl 2-cyanoacrylate, butyl 2-cyanoacrylate, isopropyl 2-cyanomethacrylate, cyclohexyl 2-cyanoacrylate, allyl 2-cyanoacrylate, and benzyl 2-cyanomethacrylate, may be used. These 2-cyano(meth)acrylates can be used alone or in combinations of two or more. In a preferred embodiment of the invention, the polymerizable monomer is ethyl 2-cyanoacrylate. Another preferred monomer is methyl 2-cyanoacrylate (cyanoacrylic acid methyl ester), also known as Coapt, Adhere, Cyanolit, Mecrilat, Mecrilate, mecrylate, and so on. It is commercially available from a number of suppliers in the U.S. and abroad. Unless the context indicates otherwise, the term “polycyanoacrylate” refers to a polymer formed from one or more of the above monomers.

Example 1—Process for Making Polycyanoacrylate Polymer

(5) A mist of water droplets is created in a stainless steel-lined reaction chamber having a volume of approximately 8 cubic feet. Then, 500 grams of ethyl 2-cyanoacrylate is slowly dripped into the mist, producing an exothermic reaction. Polymer created by the reaction coats the inner walls of the reaction chamber. The rate of addition of the ethyl 2-cyanoacrylate is decreased or temporarily halted if the temperature in the reaction vessel reaches 50° C. After all of the ethyl 2-cyanoacrylate has been added, the reaction mass is allowed to cool for about 10 minutes to ensure that the final product temperature remains below 50° C. Any condensed water is then poured out, leaving a gummy or taffy-like substance adhering to the walls of the reaction chamber. The substance is scraped out of the container and pressed between two stainless steel plates each having an area of approximately 2 square feet to express water from the substance (polymeric mass). Subsequently, the polymeric mass is placed into an environmentally-controlled chamber for approximately 1 to 2 days at about 60° C., resulting in a dry solid polymeric mass.

Example 2—Process for Producing Powdered Polycyanoacrylate Product

(6) The polymeric mass is then transferred into a burr grinder, where it reduced to a powder having a particle diameter in the range of from 1 to 200 microns, with a median particle diameter of approximately 20 microns and a mean particle diameter of approximately 60 microns.

(7) Samples of product of the invention produced in accordance with the above method were analyzed by Microbac Laboratories (Hauser Division, Boulder, Colo., USA) via the following processes to determine various parameters of the particles, including the feret lengths and widths of the particles and the rectangularity of the particles:

(8) 1. Particle size distribution was measured using laser light scattering;

(9) 2. Skeletal density was determined via gas displacement density analysis;

(10) 3. Particle shape analysis was conducted using a dynamic image analyzer.

(11) Results of feret length and width analysis and rectangularity determination were as follows:

(12) TABLE-US-00001 FERET LENGTH (sizes in microns) particle count 12417 number percentiles minimum 8.0 10% 17.1 maximum 260.3 25% 21.5 mean 35.9 50% 29.1 std. dev. 21.9 75% 43.9 mode 25.2 90% 62.6

(13) TABLE-US-00002 FERET WIDTH (sizes in microns) particle count 12417 number percentiles minimum 5.7 10% 10.6 maximum 158.2 25% 13.4 mean 23.4 50% 18.1 std. dev. 15.5 75% 27.8 mode 16.0 90% 43.4

(14) TABLE-US-00003 RECTANGULARITY particle count 12416 number percentiles minimum 0.335 10% 0.662 maximum 1.000 25% 0.692 mean 0.718 50% 0.720 std. dev. 0.051 75% 0.747 mode 0.710 90% 0.774

(15) FIGS. 1A, 1B, and 1C are graphical depictions of, respectively, the above data relating to feret length, feret width, and rectangularity of the sample of particles produced in accordance with the invention.

(16) An embodiment of the present invention is a powdered polycyanoacrylate polymer having the following particle size characteristics: (i) at least 50 weight-% of the powder particles have a feret length of from 20 to 80 nanometers; (ii) at least 50 weight-% of the powder particles have a feret width of from 10 to 40 nanometers; and (iii) at least 50 weight-% of the powder particles have a rectangularity ranging from 60 to 75.

(17) FIG. 2 is a graph of incremental volume percent versus particle diameter of a sample of the particles of the invention. The particles were made into a paste by mixing them with water and immersing the mixture in a Triton X ultrasonic bath for 2 minutes. Analysis conditions were as follows: flow rate 12.0 liters per minute, ultrasonic intensity 100%, ultrasonic time 240 seconds, and circulation time 240 seconds. The mean particle diameter was 58.269 microns. However, the median particle diameter was 21.783 microns.

Example 3—Method of Using the Powdered Polycyanoacrylate Product to Detect Fingerprints

(18) An example of a method of using the powdered polycyanoacrylate polymer is as follows:

(19) 1. Weigh out 0.04-0.12 grams of powder per cubic foot of fuming space and place it in an aluminum fuming dish;

(20) 2. Place the fuming dish on the a plate within the fuming chamber;

(21) 3. Set the fuming chamber relative humidity to 80%;

(22) 4. Turn the hot plate to 220° C. and set the run time to between 13 and 30 minutes; and

(23) 5. When the run is completed, photograph, lift, or otherwise process prints using standard fingerprint collection methods.

(24) The powdered form of polycyanoacrylate made available by the present invention facilitates significant improvement in accurate weighing and measuring by the user when the product is used to detect fingerprints. The powder can more effectively be measured by weight using conventional methods, while posing little or no threat of exposure to fumes for the user. In its powdered form, the inventive product is unreactive at ambient temperatures, posing no handling exposure risks and emitting no discernable odors.

(25) Due to its efficiency in dissipation of fumes, the invention allows for using only about one tenth the amount by volume during processing as compared to liquid cyanoacrylate processing. Additionally, once the heat source is removed and the temperature drops below 220° C., fuming stops immediately and all remaining polycyanoacrylate material can be collected and reused at a later date, further reducing waste.

(26) FIGS. 3A and 3B are photographs of two different fingerprints, each of which was developed with a composition of the present invention. The photographs contain enlarged insets that serve to elucidate the fact that compositions of the present invention facilitate the visualization of pores (some of which are indicated by directional arrows in the insets) in the fingerprint ridges. Directional arrows 1 and 2 indicate pores in the fingerprint ridges in FIG. 3A. Directional arrows 3 and 4 indicate pores in the fingerprint ridges in FIG. 3B. Applicants' invention when used in accordance with the method outlined above consistently enables visualization of the pores as well as the ridges, thus enabling greater accuracy in fingerprint matching.

Example 4—Process for Producing Powdered Polycyanoacrylate Product from Methyl 2-Cyanoacrylate Monomer

(27) A mist of water droplets is created in a stainless steel-lined reaction chamber having a volume of approximately 8 cubic feet. Then, 500 grams of methyl 2-cyanoacrylate is slowly dripped into the mist, producing an exothermic reaction. Polymer created by the reaction coats the inner walls of the reaction chamber. The rate of addition of the methyl 2-cyanoacrylate is decreased or temporarily halted if the temperature in the reaction vessel approaches the boiling point of the methyl 2-cyanoacrylate. After all of the methyl 2-cyanoacrylate has been added, the reaction mass is allowed to cool for about 10 minutes to ensure that the final product temperature remains below the boiling point of the methyl 2-cyanoacrylate. Any condensed water is then poured out, leaving a gummy or taffy-like substance adhering to the walls of the reaction chamber. The substance is scraped out of the container and pressed between two stainless steel plates each having an area of approximately 2 square feet to express water from the substance (polymeric mass). Subsequently, the polymeric mass is placed into an environmentally-controlled chamber for approximately 1 to 2 days at about 60° C., resulting in a dry solid polymeric mass. The polymeric mass is then transferred into a burr grinder, where it reduced to a powder having a particle diameter in the range of from 1 to 200 microns, with a median particle diameter of approximately 20 microns and a mean particle diameter of approximately 60 microns.

(28) Particular embodiments of the present invention have been described in detail above. However, it will be apparent that variations and modifications of the described embodiments are possible. Accordingly, the scope of the present invention is not limited to the embodiments described but instead is limited only by the appended claims.