Paper making and fiber liberation – Processes and products – Non-uniform – irregular or configured web or sheet
Reexamination Certificate
1999-12-21
2001-04-03
Chin, Peter (Department: 1731)
Paper making and fiber liberation
Processes and products
Non-uniform, irregular or configured web or sheet
C162S109000, C162S117000, C162S205000, C428S153000, C156S183000, C264S283000
Reexamination Certificate
active
06210528
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to wet-creped webs for towel and tissue and, more particularly to methods for making wet-creped webs having an imprinted pattern.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a low density paper base web for towels and tissues from a wet-creped web as well as a process for making such a web.
It is a further object of the present invention to provide a low density paper based web with improved tensile strength, tear strength and thickness as well as a process for making such a web.
It is a feature of the present invention to provide a low density paper base web having a pattern of densifications therein wherein fines are concentrated in the densifications as well as a process for making such a web.
Another feature of the present invention is to provide a low density paper base web for towels and tissues having a pattern of densifications therein wherein chemicals added to the furnish are concentrated on one surface of the finished web and particularly, on one surface of the densifications. It is also a feature of the present invention to provide a process for drying a low density paper base web for towels and tissues having a pattern of densifications therein wherein chemicals added to the furnish are caused to migrate and thereby concentrate on one surface of the finished web and particularly, on one surface of the densifications.
Briefly stated, these and numerous other features, objects and advantages of the present invention will become readily apparent upon a reading of the detailed description, claims and drawings set forth herein.
According to the invention, a wet-creped paper web is removed from a Yankee dryer at a dryness of between 45 and 65%. Desirably, the wet-creped paper web is removed at a dryness ranging from about 50 to about 60%. The web is then passed to the after dryer section of the paper machine.
A feature of the invention is to press an after dryer fabric into the wet base web to transfer the topography of the after dryer fabric to the web and to generate improved tensile strength, tear strength and thickness.
The wet base web is pressed into the drying fabric utilizing a nip before the web is 70% dry. Desirably, this pressing step occurs at a web dryness ranging from about 45 to about 65%. More desirably, this pressing step occurs at a web dryness ranging from about 50 to about 60%.
Pressing the wet base web into the drying fabric may be accomplished utilizing a hard press roll such as a steel roll which is backed by a soft roll such as a rubber roll. That is, the steel roll contacts the after dryer fabric and presses the after dryer fabric into the base web which is backed or supported by the rubber roll. Alternatively, a soft press roll (e.g., rubber press roll) may contact the after dryer fabric and press the after dryer fabric into the base web which is backed or supported by a hard roll (e.g., steel roll). In yet another alternative, a soft press roll (e.g., rubber press roll) may be used to contact the after dryer fabric and press the after drying fabric into the base web which is supported by a drying can such as, for example, a Yankee dryer, heated drum and/or steam can. In such an embodiment, the drying can will need to be sufficiently robust to support the load of the press roll. The load on the rolls may be varied to obtain the desired conformation of the web to the wire so that the topography of the wire is transferred to the web. Desirably, this transfer of the wire topography to the web will be substantial.
As an example, the load on the rolls may be sufficient to produce a pressure at the nip of from about 10 to about 400 pounds per square inch. As a further example, the load on the rolls may be sufficient to produce a pressure at the nip of from about 15 to about 100 pounds per linear inch. As a further example, the load on the rolls may be sufficient to produce a pressure at the nip of from about 20 to about 50 pounds per linear inch.
According to the invention, once the wet base web initially contacts the drying fabric, it should remain on the drying fabric without any change in the registration between the wet base web and the drying fabric until the base web is at least about 80% dry. Desirably, the wet base web should remain on the drying fabric until it is about 95% dry.
In one embodiment of the invention, a drying can or series of drying cans may be used to dry the wet base web. The terms “can drying” and “drying cans” are used herein to refer to and include Yankee dryers and other rotating, solid surface, heated drums such as, for example, steam cans, gas fired or electrically heated drums. An after drying fabric is used to hold the web against the drying cans. The after drying fabric may be threaded in a mode or configuration wherein the web and fabric contact and registration are maintained until the web is substantially dry (e.g., at least about 80% dry). Generally speaking, the term “dry” or “dryness” refers to an average dryness of the web at the point of measurement and is a ratio of the bone dry fiber weight to the total web weight (fibers and water) at the point of measurement. Desirably, a single drying fabric may be used to carry the web. In such an embodiment, the fabric may traverse the drying cans in a serpentine pattern such that the web contacts the drying fabric and stays in contact with the drying fabric until the web is substantially dry.
The present invention encompasses a low density, wet-creped paper web having improved levels of tensile strength, tear strength and thickness made according to the process described above.
In an embodiment, the low density, wet-creped paper web has a distribution of densified regions corresponding to the distribution of knuckles on the drying fabric. Generally speaking, these densified regions should be distributed so that the distance between at least a portion of the densified regions is less than or equal to the length of the longest fiber in the furnish (e.g., pulp fibers and/or other fibers) used to make the paper web. Desirably, these densified regions should be distributed so that the distance between at least a portion of the densified regions is less than the average fiber length of the furnish (e.g., pulp fibers and/or other fibers) in the furnish used to make the paper web.
The densified regions will generally have improved strength and will enhance the overall strength of the paper web. The portions of the paper web outside the densified regions will generally have lower to much lower densities. Such low density regions generally provide good water or liquid absorption.
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Chin Peter
Fortuna Jos'e A.
Kimberly--Clark Worldwide, Inc.
Sidor Karl V.
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