Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2002-02-08
2003-04-15
Watkins, III, William P. (Department: 1772)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S160000, C156S163000, C156S164000, C156S229000, C156S290000, C156S291000, C156S209000, C156S292000, C156S324000, C156S308200
Reexamination Certificate
active
06547915
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to a process for making a composite elastic material and articles formed therefrom, having creep resistance, improved aesthetics, dimensional stability and inherent latency. The material is formed from an elastic fibrous web which is joined with at least one gatherable layer using the nip between an anvil calender roller and a point un-bonded calender roller having recessed areas on its surface.
BACKGROUND OF THE INVENTION
Composite elastic materials and laminates thereof are known in the art as are methods for compression embossing fibrous webs. Composite elastic materials are gaining popularity for use especially in the areas of absorbent articles and disposable items because of the flexibility and conformability such materials provide the articles. The term “composite elastic material” means a multicomponent or multilayer elastic material in which at least layer has an elastic component. As used herein, the term “laminate” means a composite material made from two or more layers or webs of material which have been attached or bonded to one another. The term “absorbent articles” refers to devices which absorb and contain body exudates and, more specifically, refers to devices that are placed against or in proximity to the body of the wearer to absorb and contain the various exudates discharged from the body, and is intended to include diapers, training pants, absorbent underpants, incontinence products, medical applications such as surgical drapes, gowns and facemasks, articles of clothing or portions thereof including workwear and lab coats, and the like. Specific examples of such uses include, for instance, waistbands of diapers and training pants, side panels of training pants, and cuffs of surgical gowns. The term “disposable” is used herein to describe absorbent articles not intended to be laundered or otherwise restored or reused as an absorbent article.
Research in this area tends to be focused on utilizing elastic materials in such absorbent articles to achieve a better fit for the wearer (more conformability to the user's body), while continually searching for ways to improve the overall appearance and physical properties of the article. It is generally accepted by those in the field, that although elastic materials provide articles with better conformability, such articles generally do not have an attractive appearance or feel. The ultimate goal for such disposable items is to achieve a “cloth-like” appearance and feel, without compromising physical properties such as strength, elongation, and the like.
Another important property, known especially by those having skill in elastics, is a property known as inherent latency. As used herein, the term “inherent latency” means the internal elasticity of a material, which is dormant until the material has been subjected to an activation process, for example, to elevated temperatures, as for instance, the temperature of the body of a wearer of the article. Furthermore, the process of converting these materials into such items as diapers, is usually conducted at elevated temperatures. Shrinkage of the material, due to the activation of the inherent latency, causes production problems as well. To quantify inherent latency, a test has been described in more detail below wherein percent shrinkage has been measured at an elevated temperature over a given period of time. When the temperature increases, e.g. to body temperature, the inherent latency is activated to improve the fit and conformability of the article. Controlling inherent latency has proved complex, however, because too much inherent latency may create too much elasticity, which may, for instance, cause over-tightening, resulting in “red marking” or irritation to the skin of the wearer. As an example, an article such as a diaper, having an appropriate amount of inherent latency, will neither tend to sag or droop while being worn (and subsequently saturated with body wastes), nor will it cause red marking. (As will be understood by those skilled in the art, there are many properties which contribute to red marking, such as adjustment of the basis weight of the material. For purposes of the present invention, the inherent latency is the property controlled to improve the materials). Such sagging or drooping is a result of too little inherent latency and has typically been quantified as stress relaxation and creep. The term “stress relaxation” is defined as the decreasing load required to hold a constant elongation over a period of time. The term “creep” is defined as the loss of shape or dimension of an article due to some reversible and/or irreversible flow or structural breakdown under a constant load or force. There are two kinds of creep: (1) the time-dependent component, in which the shape changes because of the irreversible flow or structural breakdown under a constant load or force and does not recover when the force is removed; and (2) the time-independent component, wherein some of the shape recovers when the force is removed. Of course, one skilled in the art would understand that reversible loss of shape or dimension may also occur. Such is the case for materials having properties similar to a metal spring, in which case the deformation is totally reversible. As used herein, “creep resistant” means that the material resists the tendency to creep, through for instance, chemical structure, physical structure, and the like.
To make such composite materials, at least one layer of a fibrous web is laminated to at least one facing layer. Lamination may occur, for instance, by passing the layers through the nip between two rolls, one roll being a calender roll, and the other roll being an anvil roll, to compression bond and laminate the layers together. The calender and/or anvil rolls have traditionally been patterned in some way, otherwise known as point bonding, so that the resulting laminate material was not bonded across its entire surface. As a specific example, a fibrous web of an elastic continuous filament and meltblown fiber has been point bonded to a facing layer while the continuous filament web was in a stretched state as described in commonly assigned European Patent Application 0 548 609 A1 to Wright. Upon release of the tension, the laminate would retract, thereby “gathering up” the facing layer. The two-fold advantage of this was that 1) a more “cloth-like” appearance resulted, and 2) the inelastic layer could return to its pre-gathered dimension, thereby capitalizing on the elasticity of the continuous filament web.
One disadvantage of this method of lamination, though, was that the patterned (e.g. Ramisch) rolls used in point bonding can damage the elastic filaments as can be seen, for instance, in FIG.
4
.
FIG. 4
is a scanning electron micrograph of an elastomeric continuous filament layer
118
which has been attached to an elastomeric meltblown fiber layer
126
and bonded using patterned rolls. Several of the continuous filament strands have been torn, nicked, cut and the like as exemplified by
118
′. Such damage affects the elastic properties and, thus, the performance of the material and laminates thereof by causing the fibers to completely break during use, at body temperature, and under stretched conditions as can be seen in FIG.
5
.
FIG. 5
is a scanning electron micrograph of the material of
FIG. 4
after being subjected to use conditions. If the filament is broken, then the inherent latency of that particular filament will have little or no affect on the material and thus will not contribute to the product conformability to the body.
Commonly assigned PCT publication number WO 98/29251 to Thomas et al., describes a means of solving this problem by utilizing two smooth calender rolls to bond the layers together. Smooth roll calendering resulted in improved dimensional stability (e.g., less stress relaxation and creep) because the continuous filaments were not broken during calendering as can be seen in FIG.
6
. In
FIG. 6
, a material as described above for
FIG
Dunkerly, II Cedric Arnett
Fitts, Jr. James Russell
Singletary Jennifer Leigh
Taylor Jack Draper
Thomas Oomman Painumoottil
Flack Steven D.
Kimberly--Clark Worldwide, Inc.
Watkins III William P.
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