Creped towel and tissue incorporating high yield fiber

#The present invention relates generally to creped towel and tissue products prepared with an undulatory creping blade and including tubular, high coarseness fibers such as lignin-rich, high yield fibers. In a preferred embodiment, the products are made from furnish incorporating at least about 15% BCTMP.

#The use of recycled cellulosic furnish to make towel and tissue products is increasingly desirable in view of the rising costs of virgin fibers, especially for facilities which use large volumes of absorbent products. Products made from recycle furnish tend to be relatively stiff, having relatively high tensiles and relatively low bulk leading to poor absorbency and properties. Moreover, these products tend to have relatively low wet/dry strength ratios. Various methods have been employed to increase the bulk and softness of products made from recycle furnish, including the use of softeners, debonders and the like as well as anfractuous fibers and/or new processing techniques; some of which require significant capital investment and cannot be readily adapted to existing production capacity such as conventional wet-press paper machines with Yankee dryers.

#There is disclosed in U.S. Pat. No. 5,607,551 to Farrington, Jr. et al. throughdried tissues made without the use of a Yankee dryer. The typical Yankee functions of building machine direction and cross-machine direction stretch are replaced by a wet end rush transfer and the throughdrying fabric design, respectively. According to the '551 patent it is particularly advantageous to form the tissue with chemi-mechanically treated fibers in at least one layer. Resulting tissues are reported to have high bulk and low stiffness. Furnishes enumerated in connection with the Farrington, Jr. et al. process include virgin softwood, hardwood as well as secondary or recycle fibers. Col. 4, lines 28-31. In the '551 patent it is further taught to incorporate high-lignin content fibers such as groundwood, thermomechanical pulp, chemimechanical pulp, and bleached chemithermomechanical pulp. Generally these pulps have lignin contents of about 15 percent or greater, whereas chemical pulps (Kraft and sulfite) are low yield pulps have a lignin content of about 5 percent or less. The high-lignin fibers are subjected to a dispersing treatment in a disperser in order to introduce curl into the fibers. The temperature of the fiber suspension during dispersion can be about 140° F. or greater, preferably about 150° F. or greater and preferably about 210° F. or greater. The upper limit on the temperature is dictated by whether or not the apparatus is pressurized, since the aqueous fiber suspensions within an apparatus operating at atmosphere cannot be heated above the boiling point of water. Interestingly, it is believed that the degree of permanency of the curl is greatly impacted by the amount of lignin in the fibers being subjected to the dispersing process, with greater effects being attainable for fibers having higher lignin content. Col. 5, lines 43 and following. Lignin-rich, high coarseness, generally tubular fibers are further described in U.S. Pat. No. 6,254,725 of Lau et al. as well as U.S. Pat. No. 6,074,527 of Hsu et al. See also U.S. Pat. Nos. 6,287,422; 6,162,961; 5,932,068; 5,772,845; 5,656,132. The so-called uncreped, through-dried process of the '551 patent requires a relatively high capital investment and is expensive to operate inasmuch as thermal dewatering of the web is energy intensive and is sensitive to fiber composition.

#The present invention is described in detail below with reference to the various Figures wherein like numerals designate similar parts and wherein:

#FIG. 1 is a schematic diagram of a papermaking machine useful for the practice of the present invention;

#FIG. 2 is a schematic diagram illustrating various characteristic angles of a creping process;

#The invention is described in detail below for purposes of description and exemplification only. Modifications within the spirit and scope of the present invention, set forth in the appended claims, will be readily apparent to those of skill in the art.

#In general, the invention is directed to a creped absorbent cellulosic sheet incorporating from about 15% to about 40% by weight of high coarseness, generally tubular and lignin-rich cellulosic fiber based on the weight of cellulosic fiber in the sheet prepared by way of a process comprising applying a dewatered web to a heated rotating cylinder and creping the web from the heated rotating cylinder with an undulatory creping blade. When a lignin-rich, high coarseness and generally tubular cellulosic fiber is used, it typically comprises at least about 10% by weight lignin based on the weight of the lignin-rich cellulosic fiber, and preferably at least about 15% by weight lignin based on the weight of the lignin-rich cellulosic fiber. In preferred embodiments, the lignin-rich, high coarseness generally tubular fiber comprises from about 15% to about 25% by weight lignin based on the weight of the lignin-rich, high coarseness and generally tubular cellulosic fiber in the sheet. The lignin-rich, high coarseness and generally tubular fiber typically has an average fiber length of at least about 2.25 mm and usually from about 2.25 to about 2.75 mm as well as a coarseness of from about 20-30 mg/100 m.

#Suitable lignin-rich, high coarseness and generally tubular cellulosic fibers include fibers selected from the group consisting of: APMP, TMP, CTMP, BCTMP, and mixtures thereof, as defined herein. The sheet may be an embossed absorbent sheet, and in some embodiments a perforate embossed sheet. These fibers are typically present from about 20 to about 40 percent by weight. BCTMP is a particularly suitable fiber for many products and may have a lignin content of at least 15%, at least 20% or at least 25% by weight. BTCMP with a lignin content of 25-35% may be employed.