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United States Patent [w]
Krutak, Sr. et al.
US006036885A [ii] Patent Number: 6,036,885  Date of Patent: Mar. 14,2000
 METHOD FOR MAKING CELLULOSE ESTERS INCORPORATING NEARINFRARED FLUOROPHORES
 Inventors: James John Krutak, Sr.; Thomas
Vernon McCray; Edwin Taylor Boyd;
Fred Dewey Barlow, Jr.; Melvin
Glenn Mitchell; Lee Reynolds Partin,
all ol Kingsport, Tenn.
 Assignee: Eastman Chemical Company, Kingsport, Tenn.
 Appl. No.: 09/153,742  Filed: Sep. 15, 1998
 Int. CI.7 C09K 11/02; D06P 3/60
 U.S. CI 252/301.34; 106/170.1;
106/161.01; 106/171.1; 8/518; 8/519; 8/528;
 Field of Search 252/301.34; 106/170.1,
106/168.01, 171.1; 8/518, 519, 528, 527,
 References Cited
U.S. PATENT DOCUMENTS
3,759,947 9/1973 Pugin et al 8/661
4,504,084 3/1985 Jauch 283/94
4,992,204 2/1991 Kluger et al 252/301.16
5,123,999 6/1992 Honnorat et al 162/140
5,292,855 3/1994 Krutak et al 528/289
5,298,584 3/1994 Blanchard et al 527/300
5,336,714 8/1994 Krutak et al 524/608
5,397,819 3/1995 Krutak et al 524/88
5,423,432 6/1995 Krutak et al 209/577
5,461,136 10/1995 Krutak et al 528/289
5,525,516 6/1996 Krutak et al 436/56
5,553,714 9/1996 Cushman et al 209/577
5.555,508 9/1996 Mitchell et al 264/138
5,614,008 3/1997 Escano et al 106/23
5,662,773 9/1997 Frederick et al 162/4
5.665,151 9/1997 Escano et al 106/31.15
5,703,229 12/1997 Krutak et al 540/140
FOREIGN PATENT DOCUMENTS
55-122100 9/1980 lapan .
64-30788 2/1989 lapan .
2-293500 12/1990 lapan .
5-98599 4/1993 lapan .
7-196782 8/1995 lapan .
Primary Examiner—C. Melissa Koslow
Attorney, Agent, or Firm—Bernard J. Graves; Harry J.
A cellulosic ester has associated with the ester at least one near infrared fluorophore. A method for incorporating the near inlred fluorophore into the cellulosic ester is also provided. In the method, the near infrared fluorophore is dissolved in a strong acid and precipitated to form an acid paste. The paste is then added to an activated cellulose, such as a hydrolyzed cellulose acetate, in the presence ol at least one acid and acid anhydride. Advantageously, such marked cellulosic materials can be solvent spun into staple fibers which may be lurther utilized in known materials, webs and articles.
14 Claims, 1 Drawing Sheet
METHOD FOR MAKING CELLULOSE
ESTERS INCORPORATING NEAR-
The present invention relates to materials having a fluorescent marker. More particularly, the invention relates to a synthetic polymer having a near infrared fluorophore associated with the polymer. Another aspect of the present invention is a method for incorporating a thermally stable 10 fluorescing marker into cellulose acetate.
The incorporation of an invisible marker into or onto a natural or synthetic material has recently acquired an elevated awareness due to a variety of reasons. Primarily, such markers have found great utility in security measures 15 for documents, such as checks, passports, negotiable instruments, stock certificates and the like, and labels for pharmaceuticals, health care and cosmetics. Markers have also been incorporated into fibers and threads for woven, nonwoven and knitted materials, as well as being placed on 20 a garment as a means for verifying its authenticity. For example, in the clothing industry, the prevention of counterfeited articles is necessary to protect profitability, assure the customer of the quality of the goods sold, and protect the brand name and loyalty of the customer. The marking of 25 authentic articles is only one means used to achieve these, as well as other, goals of the producer.
Use of fluorescent agents for the tracing and identification of articles such as monitoring the integrity of the yarn or 3Q fiber during slashing, warping or weaving is described in U.S. Pat. No. 4,992,204. The patent discloses tagging a material with a luminophore that is cross-linked with at least one poly(oxyalkylene). The tagging compound has an absorbance within the range of about 300 nm to 400 nm. 35
U.S. Pat. No. 4,504,084 issued to Miehe et al. on Nov. 12, 1991 discloses a method for marking originals so that copies can be distinguished from the originals. The method includes using a ribbon having a printing medium for printing the original. The ribbon includes a substance in the 40 form of a marking which, when used, produces an invisible distinguishable marking which is recognizable only by using a special scanner.
Fluorescing markers have also been used in the petroleum and plastics industry as a means for identifying the material 45 and/or separating marked materials from non-marked materials. For example, U.S. Pat. No. 5,525,516 teaches a method for marking or tagging petroleum products such as diesel fuel, gasoline, and the like with a near infrared fluorescing marker. Such marked petroleum products may then be 50 readily identified.
U.S. Pat. Nos. 5,397,819, 5,553,714 and 5,461,136 teach incorporating a near infrared fluorescing compound into thermoplastic materials. The general concept of tagging various thermoplastic materials with near infrared fluoro- 55 phores for identification purposes is disclosed in U.S. Pat. No. 5,397,819. This patent relates to a method for marking or tagging a thermoplastic polymeric material using conventional techniques such as those employed to incorporate other additives in similar resins, such as, by admixing, dry 60 or melt blending as powders or pellets, or copolymerizing one or more thermally stable, near infrared fluorescing compounds therein. A wide range of thermoplastic polymers are suitable for blending with the near infrared fluorophore including polyesters such as poly(ethylene terephthalate) 65 and poly(butylene terephthalate); polyolefins such as polypropylene, polyethylene, linear low density
polyethylene, polybutylene and copolymers made from ethylene, propylene and butylene; polyamides such as nylon 6 and nylon 66; polycarbonates; cellulose esters such as cellulose acetate, propionate, butyrate, or mixed ester; polyacrylates such as poly(methyl methacrylate); polyimides; polyester-amides; polystyrene; ABS (acrylonitrile-butadinestyrene) type polymers, and thermoplastic oligomers, and the like.
When the near infrared fluorophore is melt blended into the polymer, these operations are conducted at temperatures in excess of 200° C, frequently in excess of 250° C. At such high temperatures, the near infrared fluorophores are readily blended in the molten polymer melt during preparation or processing or just prior to molding or spinning into a fiber and remain in the polymer as true a true blend after processing.
However, it has been discovered that the thermally stable near infrared fluorophores used for this purpose do not readily associate with cellulose esters under the mild conditions required for processing these materials. Most cellulose esters are relatively thermally unstable, requiring them to be processed at temperatures below about 200° C. Under these relatively mild process conditions, the near infrared fluorophores do not dissolve or disperse in the material, nor do the near infrared fluorophores dissolve or disperse into the ordinary plasticizers or solvents used in manufacturing cellulosic esters. The result can be dispersed pockets of fluorescing compounds. These undistributed compounds can further adversely affect the properties of the thermoplastic or articles made from them. Consequently, it has not been possible heretofore to feasibly and acceptably incorporate these thermally stable near infrared fluorophores in cellulosic esters.
Accordingly, there is a need for a cellulosic ester having at least one near infrared fluorophore associated with the thermoplastic. There is also a need for a method of associating a thermally stable near infrared fluorophore with a cellulosic ester.
SUMMARY OF THE INVENTION
Broadly, the present invention relates to a cellulosic ester having at least one near infrared fluorophore associated with the cellulosic ester. Also provided is a method for incorporating the near infrared fluorophore into the cellulosic ester by providing a paste comprising a near infrared fluorophore admixed into a sufficient amount of an acid catalyst system suitable for esterification of the cellulose, and adding the paste to a portion of the cellulose esterification catalyst system.
It is an object of the invention to provide a cellulosic ester having a near infrared fluorophore associated with the ester.
It is another object of the invention to provide a method for preparing a cellulosic ester containing a near infrared fluorophore.
It is another object of the invention to provide a method wherein a near infrared fluorophore is incorporated into a cellulosic ester by acid pasting.
Numerous other objects and advantages of the present invention will become readily apparent from the following detailed description of the preferred embodiments and the appended claims.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a graph illustrating the relationship between the acid used for acylation, the degree of substitution of the OH
groups by acyl groups, and the degree of polymerization for the production of a cellulosic ester. As is readily apparent by the area inside of the box, there is a wide range of acyl substitution which may be achieved.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Cellulose acetate is prepared industrially by adding activated cellulose to a strong acid such as sulfuric acid. 15 Activated cellulose acetate may be prepared by using methods well known in the art, such as, by contacting the cellulose acetate with acetic acid, acetic anhydride, propionic anhydride, butyric anhydride, and the like. A description of making activated cellulose acetate is described in greater detail in S. Gedon, R. Fengl, "Organic Cellulose Ester", Kirk-Othmer Encyclopedia of Chemical Technology, 5th ed., vol. 5, John Wiley & Sons, Inc., p. 510 et seq., (1993), the disclosure of which is incorporated herein by 25 reference. Suitable sources of cellulose include, but not limited to wood pulp and cotton linters. The cellulose dissolves as it becomes esterified. When esterification is completed, the mixture is treated with aqueous acetic acid and part of the strong acid is neutralized to produce a cellulose dope. The mixture is held for 10 to 12 hours to effect partial hydrolysis of the ester. When the desired degree of hydrolysis of the cellulose ester has been attained, the remaining sulfuric acid is neutralized, the dope is concentrated, filtered, and the cellulose ester is precipitated in dilute acetic acid. Cellulose esters other than the cellulose acetate are made by suitable variations of this procedure.
In one embodiment of the invention a method is provided for associating a near infrared fluorophore with a cellulosic ester. Desirably, the near infrared fluorophore is admixed with the cellulosic ester during preparation of the cellulosic ester. The near infrared fluorophores are incorporated into the cellulosic esters in an amount to produce a detectable fluorescence, using an appropriate detection device, when exposed to electromagnetic radiation having wavelengths of about 670 nm to 2500 nm. The preferred near infrared fluorophore compounds useful in the practice of the invention are selected from the classes of phthalocyanines, naphthalocyanines and squaraines corresponding to the Formulae I, II and III: