Paper making and fiber liberation – Processes and products – Multi-layer waterlaid webs or sheets
Reexamination Certificate
2002-05-23
2004-11-23
Chin, Peter (Department: 1731)
Paper making and fiber liberation
Processes and products
Multi-layer waterlaid webs or sheets
C162S130000, C162S109000
Reexamination Certificate
active
06821387
ABSTRACT:
BACKGROUND OF THE INVENTION
Strength and softness are important attributes in consumer tissue products such as bathroom tissue, towels, and napkins. Strength and softness are strongly influenced by the sheet structure of a tissue product. The type and arrangement of fibers employed in the manufacture of tissue products are important factors in determining the strength and softness of products made from such fibers.
Strength and softness usually are inversely related. That is, the stronger a given sheet, the less softness that sheet is likely to provide. Likewise, a softer sheet is usually not as strong. Thus, this inverse relationship between strength and softness results in a constant endeavor in the industry to produce a sheet having a strength that is at least as high as conventional prior art sheets, but with improved softness. Also, a sheet that is at least as soft as known sheets, but with improved strength, is desirable.
It is common in the manufacture of tissue products to provide two furnishes (or sources) of fiber. Sometimes, a two-furnish system is used in which the first furnish is comprised of hardwood eucalyptus wood fibers, and the second furnish is made of Northern softwood fibers. Eucalyptus hardwood fibers tend to be softer and more “fuzzy” to the touch, and therefore often these fiber types are provided on outer surfaces of a tissue product.
As a general rule fibers having better softness are provided in outer layers of tissue products—which routinely contact the skin of consumers. The inner layers of tissue products often may comprise fibers, which provide strength. Thus, in this way the desirable properties of tissue products can be maximized at a minimal cost in raw materials. Further, debonding agents have also traditionally be utilized to further soften the tissue product.
Unfortunately, however, sloughing sometimes is increased by the use of debonding agents. Sloughing may be described generally as the loss of paper particles from the surface of the paper due to surface abrasion. Many consumers react negatively to paper that exhibits a high degree of sloughing.
Thus, it would be desirable to provide a process and product that can provide a high level of softness, strength, and absorbent capacity for good handfeel, but with reduced sloughing.
SUMMARY OF THE INVENTION
In accordance with one embodiment of the present invention, a method of making a tissue product (single- or multi-ply) is disclosed. The method comprises (a) providing a first furnish of softwood fibers; (b) providing a second furnish of hardwood fibers; (c) fractionating the first furnish of softwood fibers into a long fiber fraction and a short fiber fraction; (d) diverting the short fiber fraction to the second furnish to form a third furnish; (e) forming a first layer using the long fiber fraction of the first furnish; (f) forming a second layer using the third furnish; and (g) incorporating the first layer and the second layer into a first ply.
For example, in some embodiments, the first layer can be placed adjacent to the second layer and crimped therewith to form the ply. If desired, the first layer and the second layer can also define outer surfaces of the first ply.
In addition, the method can also comprise combining the first ply with a second ply. In one embodiment, the second ply is comprised of at least two layers. For example, one layer of the second ply may be formed from the long fiber fraction of the first furnish and another layer may be formed from the third furnish. Optionally, the layer of the second ply formed of the long fiber fraction of the first furnish can be positioned adjacent to the first layer of the first ply.
The hardwood and/or softwood fibers may generally be used in the tissue product in any desired amount. For example, in some embodiments, the weight percentage of hardwood fibers in the tissue product is from about 50 and about 80 percent, and in some embodiments, from about 60 to about 70 percent. Likewise, the weight ratio of hardwood fibers to softwood fibers in the tissue product can, in one embodiment, be about 2:1.
Thus, it is possible to product a layered structure in which at least one layer employs hardwood fibers enhanced with the short fiber fraction of a softwood furnish, while at least one additional layer employs the long fiber fraction of the softwood furnish. A one ply, two-layered tissue may be constructed. Also, a two-ply, two-layered tissue or a three-ply, two-layered tissue may be constructed. Regardless of the construction utilized, the tissue of the present invention can have reduced levels of slough, with about the same or comparable levels of softness.
Other features and aspects of the present invention are discussed in greater detail below.
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Chin Peter
Paper Technology Foundation Inc.
LandOfFree
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