Paper making and fiber liberation – Apparatus – Web creping or crinkling type
Reexamination Certificate
2002-03-19
2003-04-01
Chin, Peter (Department: 1731)
Paper making and fiber liberation
Apparatus
Web creping or crinkling type
C162S113000, C162S281000
Reexamination Certificate
active
06540879
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to creped paper. More particularly, the invention relates to creped paper having desirable bulk, appearance, and softness characteristics, such that the paper is capable of being used for at least one of tissues, towels, and napkins. The invention also relates to a notched creping blade for use in a creped paper manufacturing process and a system including such a blade. The invention further relates to improved methods of manufacturing paper.
2. Description of Related Art
Paper is generally manufactured by dispersing cellulosic fiber in an aqueous medium and then removing most of the liquid. In particular, cellulosic fibers suspended in water are deposited on a moving foraminous support to form a nascent web. Water is removed from the nascent web, and the de-watered web is adhered to a heated cylindrical dryer (e.g., Yankee dryer). The web is then removed from the dryer.
Paper derives some of its strength from the mechanical interlocking of the cellulosic fibers in the web, but most of the strength is derived from hydrogen bonds that link the cellulosic fibers to one another. With paper intended for use as bathroom tissue, the degree of strength imparted by this inter-fiber bonding, while necessary to the utility of the product, can result in a lack of perceived softness by consumers. One common method of increasing the perceived softness and cushion of bathroom tissue is to crepe the paper.
Creping is a process that typically includes fixing the cellulosic web to a cylindrical dryer (e.g., with an adhesive and release agent), and then scraping the web off of the dryer with a creping blade. Creping the paper advantageously breaks inter-fiber bonds, thereby increasing the perceived softness of the paper. However, creping with a conventional blade may not be sufficient to impart desired combinations of softness, bulk (i.e., thickness or caliper), and appearance to the paper. Therefore, creped paper for use as bathroom tissue generally requires additional processing after creping, particularly when produced using conventional wet pressing technology.
Paper produced using through air drying techniques normally have sufficient caliper, but may have an unattractive appearance. To overcome this shortcoming, an overall pattern can be imparted to the web during the forming and drying process by use of a patterned fabric having proprietary designs to enhance appearance. However, such patterned fabrics are not available to all producers. Moreover, through air dried tissues can be deficient in surface smoothness and softness, unless they are further processed using techniques such as calendering, embossing, and/or stratification of low coarseness fibers on the tissue's outer layers.
Conventional tissues produced by wet pressing also generally require post-creping processes to impart softness and bulk. For example wet-pressed tissues are often calendered and/or embossed to bring softness and bulk parameters into acceptable ranges for premium quality products. Calendering, however, adversely affects caliper (i.e., thickness) and may raise the tensile modulus of the paper, which is inversely related to tissue softness. Embossing increases product caliper and can reduce the tensile modulus, but lowers strength and can decrease the surface softness of the paper. Accordingly, it can be appreciated that various combinations of calendering and/or embossing can have adverse effects on strength, appearance, surface smoothness, and thickness perception of the paper. In particular, there is a fundamental conflict between the use of calendering and the desire to increase the caliper of paper.
Conventional processes for creping paper using patterned or non-uniform creping blades are known. These processes, however, are suited for production of wadding, insulating papers, and other extremely coarse papers, but are not acceptable for production of premium quality bath tissue, facial tissue, and/or kitchen toweling.
Three references of interest are U.S. Pat. No. 3,507,745 to Fuerst, U.S. Pat. No. 3,163,575 to Nobbe, British Pat. No. 456,032 to Pashley. Fuerst teaches the use of a highly beveled blade having square shouldered notches formed into the blade. The Fuerst blade is suitable for producing very high bulk for cushioning and insulation purposes, but is not generally suitable for premium quality towel and tissue products.
Nobbe discloses a doctor blade for differentially creping sheets from a drum to produce a product that is quite similar to the product described in the Fuerst patent. Nobbe teaches a flat blade having cut notches. The portions of the sheet that contact the notched portions of the blade will have a coarse crepe or no crepe, while the areas of the sheet that contact the unnotched blade portions will have a fine crepe.
The blade disclosed in Fuerst has a large bevel angle with portions of the creping edge being flattened to produce a surface that results in fine crepe in the portions of the sheet that contact this surface. The portions of the sheet that contact the unmodified sections of the blade will have very coarse crepe, thus giving an appearance of having almost no crepe. Our experience suggests that neither the Nobbe nor the Fuerst blades are suitable for the manufacture of commercially acceptable premium quality tissue and towel products.
The Pashley reference teaches creping a sheet from a cylinder using a creping blade having an edge serrated in a sawtooth pattern. The teeth are disclosed as being about one-eighth (0.125) inch deep and having a frequency of about 8 per inch. The paper disclosed in Pashley is much coarser and more irregular than the crepe of a product made using conventional creping technology, and therefore not acceptable for use in premium tissue and towel products.
In light of the foregoing, there is a need in the art for an improved creped paper, creping blade, creping system, and method of producing paper.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to creped paper, a creping blade, a creping system, and methods of producing paper that substantially obviate one or more of the limitations of the related art. To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention includes creped paper capable of being used for at least one of tissues, towels, and napkins. The creped paper includes a cellulosic web including crepe bars and undulations. Preferably, the cellulosic web includes recycled material. The crepe bars extend in a direction transverse to a machine direction and preferably have a spatial frequency of about 5 to about 150 crepe bars per inch. The undulations include ridges, furrows, crests, and sulcations extending longitudinally in the machine direction. The ridges and furrows are interspersed on the air side of the web, and the crests and sulcations are interspersed on a Yankee side of the web. The ridges preferably have a spatial frequency of about 5 to about 50 ridges per inch. A basis weight of the web is preferably about 7 to about 40 pounds per 3,000 square foot ream of the web. The undulations and crepe bars intersect to form a reticulum. The creped paper is preferably at least one of one-ply, multi-ply, embossed, calendered, wet-pressed, and through air dried.
In another aspect, the invention includes a creping blade for creping a cellulosic web from a rotatable cylinder in a creping process. The creping blade includes first and second side faces. The first side face is at least substantially opposite to the second side file. The blade also includes an upper surface adjacent to the first and second side faces. Preferably, the upper surface is not perpendicular to at least one of the first and second side faces. A plurality of notches are provided along the upper surface. Each of the notches has a bottom portion and an open end defined by at least a portion of the upper surface. The notches are configured to increase the caliper of the cell
Awofeso Anthony O.
Harper Frank D.
Marinack Robert J.
Chin Peter
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Fort James Corporation
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