Optics: measuring and testing – By dispersed light spectroscopy – With raman type light scattering
Reexamination Certificate
2001-10-23
2004-06-01
Font, Frank G. (Department: 2877)
Optics: measuring and testing
By dispersed light spectroscopy
With raman type light scattering
C356S326000
Reexamination Certificate
active
06744500
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method of and apparatus for utilization of Laser Raman Spectroscopic technology for identification of material inclusions in a cellulose matrix, particularly the identification and quantification of sclereids, shives and/or stickies that may be present in pulp or paper.
BACKGROUND
Sclereids are dense cellulosic inclusions or stone cells occurring in both hardwood and softwood fibers. When embodied in papermaking pulp in sufficient numbers, sizes and/or concentrations, they can cause a variety of problems in papermaking, calendering, coating and converting operations. In the finished paper, they may produce blemishes, reduce the visual quality of the paper, result in non-uniform reception of printing inks, etc. There are few tests available for measuring sclereid inclusions in pulp and paper and they are mainly empirical, based on human observation and manual count.
Shives are undesireable wood fiber particles that are occasionally present in a finished paper product. Shives can have disadvantageous effects on the appearance, surface smoothness, ink receptivity and other aspects of a finished paper product. Few, if any, tests are available for accurate and efficient detection of shives in pulp and paper.
Stickies are encountered in the manufacture of papers made in whole or in part from recycled paper stock due to the presence of material inclusions in the recycled stock, for example, thermoplastics, pressure-sensitive adhesives, hot melts and wax. Under the heat and pressure of the papermaking process, these materials become tacky and adhere to various components of the papermaking machinery, such as wires, felts, dryers, calendars and coaters; thus the name stickies. Stickies impair paper machine runnability, cause web breaks, are one cause of coater blade streaks, and necessitate down-time for cleaning. They also create problems in converting operations and reduce the visual quality of the finished sheet of paper. With regard to the finished sheet, it is important for recycled-paper producers and merchants to identify and quantify these materials and to characterize the quality of the recovered paper.
Several methods have been proposed for quantifying stickies in the pulp slurry at the wet end of the paper machine. Generally, these involve screening a sample of the pulp through a laboratory-screening device under controlled screening conditions to screen out macro stickies, namely stickies of a size greater than 0.10 millimeters (mm) or 0.004 inches. Smaller stickies, i.e., micro stickies, which are not deemed particularly deleterious, pass through the screen with the cellulose fibers in the pulp. The filtrate or rejects from the screen are transferred to a black filter paper. A coated paper is placed on top of the filter paper, and together they are heated and pressed under controlled conditions. When the coated paper is removed from the filter paper, the coating will be picked up by the stickies and create a contrast on the black filter paper, which allows measurement, visually or with an image analyzer, of the area and the number of the heat-set stickies. See, e.g., TAPPI Journal, Vol. 82, No. 2, February 1999, pages 143-151.
U.S. Pat. No. 5,823,677 discloses a method of detecting and identifying stickies based on infrared (IR) radiation. According to the disclosure, a temperature gradient will exist between the stickies and a reference, e.g., ambient temperature or a substrate containing the stickies, when a sample containing the stickies and the reference are allowed to cool or to warm from a first temperature to a second temperature over a controlled period of time. The temperature gradient or difference is determined by measurement of the infrared radiation of the stickies and the reference, preferably by use of a thermographic camera. Also according to the disclosure, a characteristic gradient exists for each type of stickie when allowed to lose or gain heat for the same amount of time. These characteristic gradients allow for identification of the type of stickie by the surface temperature. This gradient is a function of the rate of heat loss or gain that is uniquely associated with each type of stickie.
The method disclosed in U.S. Pat. No. 5,823,677 comprises the steps of providing a sample which contains both at least one stickie and a reference material at a first temperature; allowing the sample to change from the first temperature to a second temperature; scanning the sample with a means for measuring infrared radiation after the sample has reached the second temperature so as to sense the temperatures of said at least one stickie and the reference material; determining the temperature difference between said at least one stickie and the reference material; and identifying said at least one stickie by the temperature differential.
While the above-described methods of stickies detection are widely used in the paper industry, they do not provide adequate accuracy, precision, speed, or specific identification and quantification of material inclusions.
U.S. Pat. No. 5,842,150 discloses a method for qualitative and quantitative determination of the organic content in pulp, paper and effluents from pulp and paper mills using ultraviolet, visible, near-infrared and infrared energy techniques, including Raman Spectroscopy. Laser Raman Spectroscopy has also been used for quantifying lignin content in pulp samples.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method of and apparatus for detecting the presence of contaminant materials in pulp and paper with accuracy, speed and precision, and with specific identification and quantification of all or selected ones of the constituents, contaminants in the pulp or paper. It is noted that as used herein the term “contaminants” is intended to broadly refer to substances whose presence are undesirable in paper or pulp products, with examples including but not limited to sclereids, shives, stickies, foreign substances, and the like.
It is in particular an object of the invention to provide a method of and apparatus for detecting the presence of sclereids, shives, and the like in pulp and paper, and the presence of stickies and the like in pulp and paper made in whole or in part from recycled stock, and to do so with greatly enhanced speed, accuracy and precision, and with specific identification and quantification of each stickie, sclereid, and shive substance present in the pulp or paper.
A further object of the invention is to utilize laser Raman spectroscopic technology, in combination with computer science, to provide precise identification and quantification of the constituents and contaminants in pulp or paper, especially pulp and paper made from or containing recycled stock.
A further object of the invention is to provide for high-speed laser Raman spectroscopic scanning of pulp and paper samples, transmission of Raman images of the constituents and/or contaminants in the samples to a computer, comparison of the transmitted images to a library of Raman fingerprints in computer memory, and communication to paper-making personnel of the identity, quantity and location in the sample of all and/or selected ones of the constituents and/or contaminants present in the sample.
Raman spectroscopic technology is capable of producing a distinctive “image” of each substance submitted for spectroscopic examination and each image is different from the images of all other substances. It is noted that as used herein, the term “image” as used with respect to spectroscopic technology is intended to broadly refer to data output from a spectrometer with or without subsequent processing. By way of example, an “image” may comprise a spectrum or other imagery, fingerprint, vector data, attribute identifier or other signal by which one substance may be distinguished from another by Raman technology. In effect, the technology produces a fingerprint individual to each substance, just as the fingerprint of each human being is distinctive and different from the fing
Bradbury James E.
Grant Edward R.
Kukura Philipp
Smith Donald R.
Font Frank G.
Greer Burns & Crain Ltd.
Lauchman Layla
Stora Enso North America Corporation
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