Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1999-10-27
2002-04-09
Sells, James (Department: 1734)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S324000, C156S496000, C264S288800
Reexamination Certificate
active
06368444
ABSTRACT:
FIELD OF THE INVENTION
The present invention is generally directed to an apparatus and method for biaxially stretching extensible polymeric films and nonwoven webs in the cross-machine and machine directions, and the material produced therefrom. More particularly, the present invention relates to an apparatus and methods for biaxially stretching films and nonwoven webs in the cross-machine and machine directions while reducing the levels of variability in stretch.
BACKGROUND OF THE INVENTION
Polymeric nonwoven webs, films and laminates made therefrom exhibit properties which make them especially suitable for use in personal care products. For example, such materials may be used as outer covers for personal care products such as diapers, training pants, incontinence garments, and feminine hygiene products. Additionally, such materials are particularly suited for use in protective outer wear such as coveralls, surgical garments, and face masks.
In particular, film laminates have become an important article in commerce, finding a wide variety of uses. Such laminates have been used in personal care products to create soft, barriers that provide stretch. The ability to “give without rupture” and in some instances “stretch,” allows for body conformance by these products.
While a variety of film laminates are known in the art, a particularly useful film laminate includes a breathable barrier. Breathable barriers can comprise stretch-filled microporous film or non-filled microporous film layers. Stretch-filled microporous films are typically filled with particles or other matter and then crushed or stretched to form a fine pore network throughout the film. The pores result when the polymers in the film separate from the particle filler. This film-pore network allows gas and water vapor to pass through the film while acting as a barrier to liquids and particulate matter. The amount of filler within the film and the degree of stretching is controlled so as to create a network of micropores of a size and frequency to impart the desired level of breathability to a fabric. An exemplary stretched filled film is described in commonly assigned WO Patent Application 95/16562 to McCormack. The McCormack reference discloses a stretched filled film comprising a predominantly linear polyolefin polymer, a bonding agent and about 30 to 80% by weight calcium carbonate which can be stretched to impart breathability to the film. The stretched film may then be laminated to a nonwoven web to create a laminate that takes advantage of the strength, integrity and cloth-like aesthetics of the nonwoven web and the barrier properties of the stretched film.
Providing a low cost film lamination method that achieves both a desired level of conformance and breathability is problematic, particularly when laminating stretch-filled films. In order to achieve acceptable body conformance, the lamination method should impart good stretch (that is effective stretch with limited variability) properties, and must also be able to allow for the formation and retention of the micropores upon processing. The pores must be capable of being stretched to an extent that they remain open and yet are not enlarged to the level that would allow liquid or particulate matter to pass.
Another particularly useful laminate including a breathable barrier includes a non-filled microporous film. While a nonwoven web can be laminated to a non-filled microporous film, in order to obtain a laminate with cross-directional stretch (CD) and machine direction stretch (MD), the nonwoven web must often be separately stretched in each direction.
In order to achieve MD and CD stretch in laminates including monolithic films (that is nonporous films), the film must be separately stretched in each direction during the manufacturing process.
It has been recognized that to enhance a personal care product's ability to conform to the body, nonwoven webs and films (and laminates thereof) which make up the personal care product are separately stretched in the CD and MD directions during manufacture, to create breathable low density/low basis weight fabric with stretch in multiple directions. A technique which has been used to stretch nonwoven webs and films in multiple directions, includes passing these sheet materials through multiple sets of intermeshing rolls. In this regard, a sheet of nonwoven web or film is fed through a series of nips formed between multiple sets of intermeshing rolls. The rolls typically have intermeshing peaks and troughs along their respective surfaces or are made of removable intermeshing disks stacked laterally along the length of axles. As the nonwoven web or film is coursed between the sets of rotating rolls, the rolls are brought together in a mating fashion, thereby forcing the surfaces of the rolls to intermesh. As a result, the material is clamped by multiple incremental nips formed between the intermeshing regions of the two rolls. The rotation of one or both of the intermeshing rolls (in opposing directions) pulls the material through the set of rolls.
As the nonwoven web or film travels between the intermeshed areas on the rolls, it is stretched by the increments between the peaks (or disks, as the case may be). This incremental stretching, as shown in
FIG. 1
, produces zones of variable stretch on the nonwoven web or film sheet. A machine direction, partial cross-sectional view of a nonwoven web
20
being coursed through prior art intermeshed rolls is shown in FIG.
1
. The nonwoven web
20
has discrete stretch points
21
between unstretched regions
22
. The stretch points
21
occur at the extended points
23
on the peaks of the rolls' surfaces. The material is held taut between each of these peaks and stretched. This variable stretching often leads to weakening of the nonwoven material in these regions, and ultimately to material failure. In many instances, the surface of the rolls act as slitters if they are operated at high speed, with the edges of the peaks or disks piercing the nonwoven material.
Rolls with intermeshing surface troughs perpendicular to the rolls' longitudinal axis, or that are made of stacked disks, will stretch nonwoven material in the CD direction. Rolls with intermeshing surface troughs that are parallel to the rolls' longitudinal axis will stretch this material in the MD direction. In order to stretch biaxially, that is in both the CD and MD directions, the nonwoven material must be coursed through consecutive pairs of rolls with a first pair of rolls having troughs perpendicular to those of the second set. Therefore, biaxial stretching has heretofore required an extended production line.
In using intermeshed rolls to stretch microporous film, the film pores may not sufficiently be opened to maintain their porosity through a later lamination step. In elastic films, the pores often collapse. As a result, it is often difficult to obtain adequate stretching or pore formation over the entire width of a film sheet without rupturing the sheet. If less variability in stretch is desired to achieve high breathability, the film sheet must be run through sets of rolls multiple times. Even with repetitive rolling however, such rolls fail to allow for targeted stretching in discrete regions on the film material.
Other methods for stretching an impregnated film to produce a microporous product include the concomitant controlling of the velocity of the film introduction into a nip of troughed rolls to substantially the identical velocity of the surface velocity of the rolls. This technique, disclosed in U.S. Pat. No. 4,153,751 to Schwarz for the creation of microporous film, is best accomplished by numerous runs to achieve a desired draw. If only one pass of film is run, it is likely that the pores formed around the film filler will be oblong in shape. As a result, such pores may collapse during a later lamination step.
In order to create a nonwoven web with enhanced stretch, softness and drapability, and with lower basis weight, the shapes and sizes of the troughs on intermeshing roll
Clark Darryl Franklin
Estey Paul Windsor
Fitts, Jr. James Russell
Jameson Lee Kirby
Kilpatrick Diane Leilani
Flack Steven D.
Kimberly--Clark Worldwide, Inc.
Sells James
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