Wet-resilient webs and disposable articles made therewith

Details Wet-resilient webs and disposable articles made therewith Wet-resilient webs and disposable articles made therewith

1997-08-15

2002-08-20

Morris, Terrel (Department: 1771)

Paper making and fiber liberation

Processes and products

Non-uniform, irregular or configured web or sheet

C162S009000, C442S385000, C442S389000, C442S412000, C442S413000, C428S153000, C428S156000

Reexamination Certificate

active

06436234

ABSTRACT:

BACKGROUND OF THE INVENTION
In the manufacture of absorbent paper products such as facial tissue, bath tissue, paper towels, napkins and the like, many different sheet properties influence the performance of the particular product being made. Softness, strength, absorbency, bulk and the like are often the subject of improvements. However, a property of tissue-related products is that when wetted and crumpled in the hand, they essentially collapse into a dense wet mass. Stated another way, such tissue products have a low wet compressive modulus, low bending modulus and low wet resiliency. These properties are undesirable for such products when used to wipe up liquids because, once saturated, they lose their designed structure and thus much of their functionality.
Similar problems can be found with some disposable absorbent articles. Generally, disposable absorbent articles include, in their construction, an absorbent core positioned between a liquid-permeable cover or topsheet layer and a liquid-impermeable baffle or backsheet layer. The cover material is generally designed to allow body exudates to permeate through the cover so that the absorbent core can absorb the fluids. The baffle or backsheet material is generally fluid impermeable and is positioned so that it is away from the body. The absorbent core serves to store fluid that contacts the article. An additional layer of material, termed a transfer layer or surge layer, may also be present between the absorbent core and the liquid-permeable cover. This layer serves to manage the transfer or distribution of the liquid to the absorbent core. Examples of such absorbent articles include products such as diapers, sanitary napkins, training pants, incontinent garments, overnight pads, panty liners, underarm shields, as well as other absorbent devices used for medical purposes such as surgical absorbents. Such articles are designed to absorb body fluids, such as urine, menses, blood, perspiration and other excrement discharged by the body.
One continuing problem with some disposable absorbent articles is that the bodily excretions are usually directed at one portion of the absorbent, whereas the absorptive capacity of the product is spread over a greater area. Localized insults of body fluid may cause a failure of the product because the fluid handling characteristics of the liquid-permeable cover, transfer layer and the absorbent core are inadequate to quickly distribute the fluid throughout the absorbent core material. Such failures are often in part due to the collapse of the low density structure of the various components when wetted. This is a particular problem for cellulosic materials.
Accordingly, there is a need for a wet-resilient web material that can more effectively transfer and/or absorb fluids for use in tissues, towels and absorbent products.
SUMMARY OF THE INVENTION
It has been discovered that papermaking fibers containing high-yield fibers, such as chemithermomechanical pulp fibers, when combined with wet strength additives, can be made into a low-density, three-dimensional sheet or web followed by or incorporating largely noncompressive drying means such that the resulting low density cellulosic sheet has remarkable wet resiliency properties, showing great resistance to wet collapse.
“Noncompressive drying refers to drying methods such as through-air drying; air jet impingement drying; non-contacting drying such as air flotation drying, as taught by E. V. Bowden, Appita Journal, 44(1): 41 (1991); through-flow or impingement of superheated steam; microwave drying and other radiofrequency or dielectric drying methods; water extraction by supercritical fluids; water extraction by nonaqueous, low surface tension fluids; infrared drying; drying by contact with a film of molten metal; and other methods for drying cellulosic webs that do not involve compressive nips or other steps causing significant densification or compression of a portion of the web during the drying process. (Standard dry creping technology is viewed as a compressive drying method since the web must be mechanically pressed onto part of the drying surface, causing significant densification of the regions pressed onto the heated Yankee cylinder.) The three-dimensional sheets of the present invention could be dried with any of the above mentioned noncompressive drying means without causing significant web densification or a significant loss of their three-dimensional structure and their wet resiliency properties.
Preferably, the low-density three-dimensional structure is created in substantial part before the sheet reaches a solids level (dryness level) of about 80% or higher. Creating the low-density three-dimensional structure can be achieved in part through a variety of means, including but not limited to the use of specially treated high-bulk fibers such as curled or chemically treated fibers as an additive in the furnish, including the fibers taught by C. C. Van Haaften in “Sanitary Napkin with Cross-linked Cellulosic Layer,” U.S. Pat. No. 3,339,550, issued Sep. 5, 1967, which is hereby incorporated by reference; mechanical debonding means such as differential velocity (“rush”) transfer between fabrics or wires, hereafter described; mechanical straining or “wet straining” of the moist web, including the methods taught by M. A. Hermans et al. in U.S. Pat. No. 5,492,598, “Method for Increasing the Internal Bulk of Throughdried Tissue,” issued Feb. 20, 1996, herein incorporated by reference, and M. A. Hermans et al. in U.S. Pat. No. 5,411,636, “Method for Increasing the Internal Bulk of Wet-Pressed Tissue,” issued May 2, 1995, herein incorporated by reference; molding of the fiber onto a three-dimensional wire or fabric, such as the fabrics disclosed by Chiu et al. in U.S. Pat. No. 5,429,686, “Apparatus for Making Soft Tissue Products,” issued Jul. 4, 1995, which is hereby incorporated by reference, including differential velocity transfer onto or from said three-dimensional wire or fabric; wet embossing of the sheet; wet creping; and the optional use of chemical debonding agents.
Products of the present invention have surprisingly high wet resiliency. For example, when the products of this invention are saturated with water and crumpled in one's hand into a ball about the size of a golf ball, and thereafter released, they quickly open up to mostly uncrumple themselves. By contrast, current commercially-available products such as bath tissues and paper towels remain substantially wadded up in a wet ball. It has been further discovered that such sheets, when properly made, can have unexpectedly good fluid handling properties, such as high intake rate, high in-plane permeability, high absorption capacity, and rapid in-plane distribution of liquid, making these materials ideally suited for use in tissues, paper towels and numerous absorbent articles. As used herein, unless otherwise stated, absorbent articles include sanitary napkins and other feminine care products; disposable diapers and related personal care products; training pants; incontinence products; breast pads; poultry pads and meat pads for absorbing blood and meat juices; bed pads for home and hospital use; sweat bands and other perspiration absorbing articles; odor and sweat absorbing pads for use in shoes or garments; and the like. The materials of the present invention can be utilized in numerous articles where fluid is absorbed or entrapped, functioning as fluid surge webs, transfer layers, distribution webs, absorbent cores, absorbent composites, and so forth. The high wet strength and significant large-scale texture of the materials also can serve effectively in preventing the breakup or loss of integrity of weaker, adjacent materials such as fluff pulp or tissue in absorbent articles, allowing the materials of the present invention to serve effectively as means for maintaining or improving the integrity of the absorbent core (superabsorbent/fluff mixture) of absorbent articles such as diapers and the like. Further, the combination of high wet strength, high absorption capac

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