Paper making and fiber liberation – Processes and products – Non-uniform – irregular or configured web or sheet
Reexamination Certificate
1997-11-14
2002-09-10
Fortuna, Jose (Department: 1731)
Paper making and fiber liberation
Processes and products
Non-uniform, irregular or configured web or sheet
C162S100000, C162S111000, C162S117000, C162S123000, C162S158000, C162S181100, C428S537500
Reexamination Certificate
active
06447641
ABSTRACT:
FIELD OF THE INVENTION
This invention generally relates to the field of paper making, and more specifically, to a fibrous web produced by a transfer system.
BACKGROUND
In a paper making machine, paper stock is fed onto traveling endless belts or “fabrics” that are supported and driven by rolls. These fabrics serve as the papermaking surface of the machine. In many paper making machines, at least two types of fabrics are used: one or more “forming” fabrics that receive wet paper stock from a headbox or headboxes, and a “dryer” fabric that receives the web from the forming fabric and moves the web through one or more drying stations, which may be through dryers, can dryers, capillary dewatering dryers or the like. In some machines, a separate transfer fabric may be used to carry the newly formed paper web from the forming fabric to the dryer fabric.
Generally speaking, the term “first transfer” refers to the transfer of the wet paper stock from a headbox to the forming fabric, which will be referred to as the “first carrier fabric”. The term “second transfer” may be understood as the transfer of the paper web that is formed on the first carrier fabric to a transfer fabric or a dryer fabric, which will be referred to as a “second carrier fabric”. These terms may be used in connection with twin wire forming machines, Fourdrinier machines and the like.
At or near the second transfer, the first carrier fabric and the second carrier fabric are guided to converge so that the paper web is positioned between the two fabrics. Generally speaking, centripetal acceleration, centrifugal acceleration and/or air pressure (which is typically applied as either a positive pressure or a negative pressure from a “transfer head” that is adjacent to the fabrics) causes the web to separate from the forming fabric and attach to the dryer fabric.
While the second carrier fabric is often run at the same speed as the first carrier fabric, it is known that the second carrier fabric may be run at a speed that is less than the speed of the first carrier fabric. This difference in speed between the fabrics is typically expressed in terms of a ratio of fabric velocities (i.e., velocity ratio) to describe what is known in the industry as “negative draw.” As described in U.S. Pat. No. 4,440,597, to Wells et al., the speed differential between the fabrics in the region of the second transfer bunches the web and creates microfolds that enhance the web's bulk and absorbency. This increases the bulk and absorbency of the web, and also increases stretch or extensibility in the machine direction (MD) of the web. Too much negative draw, however, will create undesirable “macrofolding” in which part of the web buckles and folds back on itself.
FIG. 1
depicts a cross-sectional representation (not to scale) of an exemplary macrofold in a paper sheet. Generally speaking, macrofolds occur in such a manner that adjacent machine direction spaced portions of the web become stacked on each other in the Z-direction of the web. The risk of macrofolding appears to impose a limitation on the amount of negative draw (i.e., the velocity ratio) that can be applied at the second transfer.
Generally speaking, it has been thought that the amount of MD foreshortening and subsequent extensibility (i.e., MD stretch) imparted to the web at the second transfer is very closely proportional to or essentially the same as the velocity ratio of the second carrier fabric to that of the first carrier fabric. Thus, attempts to increase the MD stretch or foreshortening of a web by increasing the velocity ratio (i.e., negative draw) were thought to also increase the likelihood of macrofolding.
Accordingly, a need exists for an improved process of making a fibrous web with desirable machine direction stretchability while avoiding macrofolding. For example, such a need extends to a process of making a paper web with desirable machine direction stretch while avoiding macrofolding.
There is also a need for an improved second transfer system for use in a paper making machine that allows greater MD extensibility (i.e., MD stretch) to be achieved at the same, or even lower, levels of negative draw than heretofore thought possible. Meeting this need is important because it is highly desirable to achieve greater MD extensibility (i.e., MD stretch) at the same, or even lower, levels of negative draw. It is also highly desirable to achieve even the same amount of MD extensibility (i.e., MD stretch) at lower levels of negative draw. Meeting this need would provide the positive benefits of creating MD-oriented extensibility or stretch in the web while avoiding or lowering the risk of macrofolding. Meeting this need could also allow more MD-oriented extensibility or stretch to be built into the web without increasing the risk of macrofolding.
Furthermore, webs produced by a conventional transfer process using a convex transfer head surface, for example the process described in U.S. Pat. No. 4,440,597, and issued Apr. 3, 1984, may lack sufficient toughness, particularly when wet. Generally, a towel incorporating a web produced by a transfer process with improved toughness provides more durability during scrubbing. In addition, a transfer process produced web with improved toughness may resist deformation and breaking during processing, thereby improving manufacturing efficiencies. Generally moreover, improved toughness permits manufacture of a towel with less strength, but with comparable toughness of a conventional towel. Generally, lowering the strength requirements permits the manufacture of a towel with a softer feel.
Accordingly, a web that is manufactured by a transfer process and has greater toughness will improve over conventional webs.
DEFINITIONS
As used herein, the term “nonwoven web” refers to a web that has a structure of individual fibers or filaments which are interlaid forming a matrix, but not in an identifiable repeating manner. Nonwoven webs have been, in the past, formed by a variety of processes known to those skilled in the art such as, for example, meltblowing, spunbonding, wet-forming and various bonded carded web processes.
As used herein, the term “spunbonded web” refers to a web of small diameter fibers and/or filaments which are formed by extruding a molten thermoplastic material as filaments from a plurality of fine, usually circular, capillaries in a spinnerette with the diameter of the extruded filaments then being rapidly reduced, for example, by non-eductive or eductive fluid-drawing or other well known spunbonding mechanisms. The production of spunbonded nonwoven webs is illustrated in patents such as Appel, et al., U.S. Pat. No. 4,340,563.
As used herein, the term “meltblown fibers” means fibers formed by extruding a molten thermoplastic material through a plurality of fine, usually circular, die capillaries as molten threads or filaments into a high-velocity gas (e.g. air) stream which attenuates the filaments of molten thermoplastic material to reduce their diameters, which may be to microfiber diameter. Thereafter, the meltblown fibers are carried by the high-velocity gas stream and are deposited on a collecting surface to form a web of randomly disbursed meltblown fibers. The meltblown process is well-known and is described in various patents and publications, including NRL Report 4364, “Manufacture of Super-Fine Organic Fibers” by V. A. Wendt, E. L. Boone, and C. D. Fluharty; NRL Report 5265, “An Improved Device for the Formation of Super-Fine Thermoplastic Fibers” by K. D. Lawrence, R. T. Lukas, and J. A. Young; and U.S. Pat. No. 3,849,241, issued Nov. 19, 1974, to Buntin, et al.
As used herein, the term “microfibers” means small diameter fibers having an average diameter not greater than about 100 microns, for example, having a diameter of from about 0.5 microns to about 50 microns, more specifically microfibers may also have an average diameter of from about 1 micron to about 20 microns. Microfibers having an average diameter of about 3 microns or less are commonly referred to as ultra-fine microfibers. A description
Kaufman Kenneth
Wolkowicz Richard Ignatius
Dority & Manning P.A.
Fortuna Jose
Kimberly--Clark Worldwide, Inc.
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