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  Chemically stiffened fibers in sheet formUSPTO Application #: 20070270070Title: Chemically stiffened fibers in sheet form Abstract: A method for making stiffened cellulosic fiber in sheet form, and the resultant stiffened cellulosic fiber. The method of making the stiffened fibers involves impregnating a cellulosic base fiber in sheet form with a treatment composition solution, drying and curing the impregnated sheet, and thereafter adding water or an aqueous solution of odor removing agent to the cured sheet to produce a sheet of stiffened cellulosic fiber having a moisture content of at least about 6.0 weight %. When defiberized, the stiffened fiber has a low content of fines and knots and nits. The stiffened fiber also exhibits a low degree of yellowing and is substantially free of a burnt-like odor. The stiffened fiber may be used in an absorbent article, such as in a liquid acquisition layer or absorbent core of a baby diaper. (end of abstract) Agent: Hunton & Williams LLP Intellectual Property Department - Washington, DC, US Inventor: Othman A. Hamed USPTO Applicaton #: 20070270070 - Class: 442414 (USPTO) The Patent Description & Claims data below is from USPTO Patent Application 20070270070. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND [0001]1. Field [0002]The embodiments relate, in general to stiffened cellulosic fibers and a process for manufacturing stiffened fibers. More particularly, the embodiments relate to a process that provides stiffened fibers in sheet form useful for making a liquid acquisition layer suitable for use in absorbent products. The stiffened fibers of the embodiments can be described as having rapid liquid absorption and acquisition, high liquid absorbent capacity, low liquid retention capacity, and low contents of fines and knots and nits. In addition, the fiber is substantially free of a burnt-like odor. The embodiments also relate to personal care products that use the stiffened fibers. The personal care products have improved acquisition and reduced rewet. [0003]2. Description of Related Art [0004]Absorbent articles intended for personal care products, such as adult incontinent pads, feminine care products, and infant diapers typically are comprised of at least a top sheet, a back sheet, a storage core disposed between the top sheet and back sheet, and an optional liquid acquisition layer disposed between the top sheet and the storage core. The liquid acquisition layer usually is incorporated in the absorbent articles to provide better distribution of liquid, increased rate of liquid absorption, reduced gel blocking, and improved surface dryness. A wide variety of fibers useful for making acquisition layers are known in the art. Included among these are synthetic fibers, a composite of cellulosic fibers and synthetic fibers, and cellulosic fibers. A cellulosic fiber is preferred because it is made from a natural fiber that is abundant, biodegradable, and relatively inexpensive. Preferably, the cellulosic fiber is cross-linked cellulosic fiber, because cross-linked cellulosic fibers provide a bulky low-density acquisition structure that allows the layer to quickly absorb fluid and then quickly release it to the core. [0005]Cross-linked cellulosic fibers and processes for making them have been described in the literature for many years (see, for example, G. C. Tesoro, Cross-Linking of Cellulosics, in Vol. II of Handbook of Fiber Science and Technology, pp. 1-46 (M. Lewin and S. B. Sello eds., Mercel Dekker, New York, 1983)). The cross-linked cellulosic fibers typically are prepared by reacting cellulose with polyfunctional agents that are capable of covalently bonding to at least two hydroxyl groups of the anhydroglucose repeat unit of cellulose in neighboring chains simultaneously. [0006]Cellulosic fibers typically are cross-linked in individualized form. Processes for making cross-linked fiber in individualized form comprise dipping swollen or non-swollen fiber in an aqueous solution of cross-linking chemicals and a catalyst. The fiber so treated usually is cross-linked by heating it at elevated temperature in the swollen state, as described in U.S. Pat. No. 3,241,553, or in the collapsed state after defiberizing it, as described in U.S. Pat. No. 3,224,926, and European Patent No. 0,427,316 B1, the disclosures of each of which are incorporated by reference herein in their entirety. [0007]Cellulosic fiber also can be cross-linked in non-aqueous solution. A process for making cross-linked fiber in non-aqueous solution is shown in U.S. Pat. No. 4,035,147 by Sangenis, et al. (this disclosure of which is incorporated by reference herein in its entirety). The patent discloses that cellulosic fibers can be cross-linked by contacting dehydrated, non-swollen fibers with crosslinking agent and a catalyst in a substantially non-aqueous solution that contains an insufficient amount of water to cause the fiber to swell. [0008]Despite the commercial availability and practicality, cross-linked cellulosic fibers have not been widely adopted in absorbent products, seemingly because of the difficulty of successfully cross-linking cellulosic fibers in sheet form. More specifically, it has been found that cross-linked fiber in sheet form tends to become more difficult to defiberize without causing substantial problems with the fibers. These problems include severe fiber breakage and increased amounts of knots and nits (hard fiber clumps). Another short-coming is that upon wetting, the cross-linked fiber tends to emit a strong, burnt-like odor that is objectionable to most manufacturers of personal care products. This odor has been found to be common in fibers that have been heated to relatively high temperatures. The odor becomes stronger when the fiber is heated while in contact with a conventional cross-linking agent such as, for example, citric acid. It is believed that the odor may be related to compounds formed from cellulose and cross-linking agents during the heating process. These compounds can include aldehydes, ketones, acids, and some other organic materials. These disadvantages render cross-linked fiber unsuitable for applications in absorbent articles intended for body waste management. [0009]Efforts to make cross-linked fibers in sheet form have met with limited success. For example, Chatterjee, et al., showed in U.S. Pat. No. 3,932,209 (the disclosure of which is incorporated herein by reference in its entirety) that fiber with modified morphology and having low contents of hemicellulose and lignin, such as mercerized fibers, can be cross-linked in sheet form without substantial formation of knots and nits. Unfortunately, the use of mercerized fiber to produce cross-linked fiber in sheet form is relatively expensive. [0010]In previous work, (e.g., U.S. patent application Ser. No. 10/683,164 (Publication No. 2005-0079361 A1) entitled "Materials Useful In Making Cellulosic Acquisition Fibers In Sheet Form" filed Oct. 10, 2003, the disclosure of which is incorporated herein by reference in its entirety) it was shown that conventional fibers in sheet form can be successfully cross-linked using modified cross-linking agents. The modified cross-linking agent acted as a cross-linking agent and as a wedge that lowered the inter-fiber bonding and increases fiber bulkiness. This minimized the formation of knots and nits during fiber cross-linking. The resultant cross-linked fibers showed similar or better performance characteristics than conventional cellulose fibers cross-linked in individualized from. [0011]The description herein of certain advantages and disadvantages of known cellulosic fibers, treatment compositions, and methods of their preparation, is not intended to limit the scope of the embodiments. Indeed, the embodiments may include some or all of the methods, fibers and compositions described above without suffering from the same disadvantages. SUMMARY [0012]In view of the difficulties presented by methods for making cross-linked fibers, there remains a need for a simple, commercially feasible process suitable for making cross-linked or stiffened fiber in sheet form. A need also exists for stiffened fibers in sheet form that, upon defiberizing, produce fiber having low contents of fines, and knots and nits. In addition, a need exists for a stiffened fiber that is substantially free of a burnt-like odor and that is capable of neutralizing the odor released from body fluid. The stiffened fiber preferably has high liquid absorbent capacity and low liquid retention capacity. The embodiments described herein desire to fulfill these needs and to provide further related advantages. [0013]It is therefore a feature of an embodiment to provide a method for making stiffened fibers in sheet form. The method involves providing a treatment composition, providing a cellulosic base fiber in sheet form, impregnating the sheet with the treatment composition, drying and curing the impregnated sheet to produce stiffened fiber in sheet form, and thereafter adding water to the cured sheet to increase the moisture content of the fiber to over 6.0 weight %. The moisture content represents the amount of moisture contained in the fiber, expressed as parts by weight of water per 100 parts of stiffened fibers. [0014]An alternative method of making stiffened cellulosic fibers in sheet form involves providing cellulosic base fiber, providing a treatment composition, forming a suspension of the cellulosic base fibers in the treatment composition, converting the suspension into a wet-laid sheet, pressing the wet-laid sheet until it has a wet pick-up of about 50 weight % to about 200 weight %, drying and curing the wet-laid sheet to form a sheet of stiffened cellulosic fibers, and then applying water to the sheet of stiffened cellulosic fibers to increase its moisture content to no more than about 6.0 weight %. [0015]It also is a feature of an embodiment to provide a stiffened fiber made by one of the above-described methods. It also is a feature of an embodiment to provide an airlaid structure, and an absorbent article comprising the stiffened fiber. [0016]These and other objects, features and advantages will appear more fully from the following detailed description of the preferred embodiments of the invention. BRIEF DESCRIPTION OF THE DRAWINGS [0017]FIG. 1 is a photograph at 1000.times. magnification of a commercially available cross-linked cellulosic fiber. [0018]FIG. 2 is a photograph at 500.times. magnification of a cellulosic fiber cross-linked in sheet form. [0019]FIG. 3 shows the absorbent capacity and centrifuge retention capacity (CRC) values of stiffened cellulosic fiber (SF), conventional un-crosslinked cellulosic fluff pulp (Rayfloc-J-LDE), mechanically-treated conventional cellulosic fluff pulp (CTMP), and commercially-available cross-linked cellulosic fibers (STCC). [0020]FIG. 4 shows the acquisition time and rewet for diaper samples having various acquisition layers, after a second fluid insult, as described in Example 4. [0021]FIG. 5 shows the acquisition time and rewet for diaper samples having various acquisition layers, after a third fluid insult, as described in Example 4. Continue reading... Full patent description for Chemically stiffened fibers in sheet form Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Chemically stiffened fibers in sheet form patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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