Paper making and fiber liberation – Processes and products – Non-uniform – irregular or configured web or sheet
Reexamination Certificate
1995-05-05
2001-03-20
Chin, Peter (Department: 1731)
Paper making and fiber liberation
Processes and products
Non-uniform, irregular or configured web or sheet
C162S112000, C162S113000, C162S116000, C162S123000, C162S126000, C162S129000, C162S130000
Reexamination Certificate
active
06203663
ABSTRACT:
BACKGROUND OF THE INVENTION
Tissue products such as facial tissue, bath tissue, kitchen towels, dinner napkins and the like are often aesthetically enhanced by printing or embossing the surface of the tissue with decorative designs. Both printing and embossing are basesheet post treatments which increase operational costs and require additional capital equipment. An economical method of enhancing the aesthetic appeal of tissues which does not require additional equipment and additional web handling would be advantageous.
SUMMARY OF THE INVENTION
It has now been discovered that tissue sheets can be provided with decorative patterns by forming the tissue sheet on a forming fabric having a decorative pattern superposed thereon or incorporated therein. As a result of the different drainage characteristics of the portions of the forming fabric having the decorative pattern, the resulting tissue sheet exhibits a subtle, yet distinctive, translucent decorative pattern corresponding to the decorative pattern of the forming fabric. More particularly, areas of the forming fabric having a more restrictive flow (or no flow) will not retain the same quantity and type of fibers as the areas of the forming fabric having a less restrictive flow. As a consequence, by using a papermaking furnish containing relatively long fibers and relatively short fibers, a decorative pattern can be imparted into the newly-formed sheet in which the decorative pattern in the tissue is delineated by areas of different fiber composition (different fiber length) corresponding to areas of differing forming fabric drainage.
Hence, in one aspect, the invention resides in a tissue sheet having a distinct decorative pattern cast into the sheet during the initial formation of the sheet on a forming fabric, said tissue sheet comprising long papermaking fibers and short papermaking fibers, wherein the decorative pattern is defined by areas having a greater average fiber length and/or a lower basis weight than the surrounding adjacent area of the tissue sheet. For purposes herein, “long” fibers are fibers having an average fiber length greater than 0.7 millimeters, a weighted average fiber length of greater than 2.0 millimeters, and less than 8 million fibers per gram as measured using a Kajaani FS200 Fiber Analyzer. Virgin softwood fibers are typically long fibers. “Short” fibers are fibers and fines having an average fiber length of less than 0.7 millimeters, a weighted average fiber length of less than 1.2 millimeters, and greater than 15 million fibers per gram as measured using a Kajaani FS200 Fiber Analyzer. With some exceptions, virgin hardwood fibers are typically short fibers. However, secondary softwood fibers and refined softwood fibers can include a population of short fibers if the fiber length distribution of that population falls within the foregoing definition. In such instances, the decorative effect can be achieved with solely softwood fibers. All Kajaani measurements include the presence of fines.
In another aspect, the invention resides in a method of forming a tissue sheet comprising depositing an aqueous suspension of short fibers and long fibers onto a decorative forming fabric which contains areas of relatively slow drainage, the shapes of which areas define distinct decorative designs, wherein the forming fabric retains the fibers of the aqueous suspension of fibers as the water passes through the forming fabric, and wherein the long fibers are preferentially retained on the surface of the forming fabric in the decorative areas of relatively slow drainage. The newly-formed paper sheet is then further dewatered and dried.
More specifically, the invention resides in a method of making a tissue sheet comprising: (a) depositing a first aqueous suspension of papermaking fibers having a consistency of less than 5 weight percent onto a decorative forming fabric to form a first embryonic web, said first suspension of papermaking fibers containing at least about 50 dry weight percent short fibers; (b) depositing a second aqueous suspension of papermaking fibers onto a forming fabric of uniform appearance to form a second embryonic web, said second suspension of papermaking fibers containing at least about 50 dry weight percent long fibers; (c) dewatering and combining the first and second embryonic webs at a consistency of from about 20 to about 50 percent; and (d) drying the combined web to form a unitary, layered, decorative tissue sheet.
In a further aspect, the invention resides in a woven papermaking forming fabric having multiple spaced-apart areas of relatively slow drainage, the shapes of which areas define visually distinct decorative patterns.
The aqueous suspension of papermaking fibers can be introduced to the decorative forming fabric in several different ways. In all cases the consistency of the aqueous fiber suspension is 5 weight percent or less, more specifically from about 0.05 to about 2 weight percent, and still more specifically about 0.2 weight percent. For example, if using a single headbox, the aqueous fiber suspension can be layered or blended (non-layered). If blended, the papermaking fibers preferably comprise at least about 50 dry weight percent short fibers and at least about 20 dry weight percent long fibers. This combination of fibers provides a large number of short fibers which flow around the decorative design areas of the fabric having impeded drainage flow rates, thereby concentrating the short fibers in the high flow rate areas of the forming fabric to form corresponding areas in the resulting paper sheet of relatively higher basis weight and opacity. At the same time, there are a sufficient number of long fibers to bridge the decorative areas of slow drainage in the forming fabric and provide sufficient continuity and strength to the resulting web, even though the basis weight in the decorative areas of the sheet is relatively low.
If a layered headbox is used to deposit a layered aqueous suspension of fibers onto the forming fabric, a short fiber layer, or a layer containing predominantly short fibers, is advantageously deposited directly onto the decorative forming fabric to enable the relatively short fibers to follow the relatively fast drainage flows without the drainage of the fabric being altered by the collection of long fibers. The remaining layer(s) have greater amounts of long fibers, or can contain predominantly long fibers or consist entirely of long fibers. Some of the longer fibers end up bridging the slower-draining decorative areas of the forming fabric, while other long fibers cover the areas occupied by the short fiber layer.
If more than one headbox is used, such as when couch forming by combining two independently-formed wet webs, a predominantly short fiber-containing web can be formed on a decorative forming fabric while the other web containing a greater percentage of long fibers can be formed on a conventional forming fabric to provide a strength layer for the resulting layered paper sheet.
As used herein, a “decorative” forming fabric is a forming fabric having spaced-apart decorative (aesthetically pleasing) areas which are visually recognizable and distinct relative to the balance or continuum of the forming fabric. Each decorative area of the forming fabric is constructed to adorn and embellish the tissue or paper sheet formed thereon with a corresponding distinct, visually-discernable, aesthetically pleasing decorative indicia. These decorative indicia comprise straight and/or curvilinear lines on the surface of the fabric which are of relatively low or no drainage and which collectively form representations of things such as flowers, butterflies, leaves, animals, toys, monograms, words, fleur de lis, and the like. Alternatively, the decorative areas can be of other shapes such a lace, geometries, and the like. The decorative areas can be incorporated into the forming fabric by a variety of means which impart relatively slow removal of water within the decorative areas of the forming fabric. Such means include, but are not limited to, sil
Behnke Janica Sue
Chen Fung-Jou
Kamps Richard Joseph
Radtke Darnell Clarence
Chin Peter
Croft Gregory E.
Kimberly--Clark Worldwide, Inc.
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