Anisotropic film

Details Anisotropic film Anisotropic film

1998-04-03

2001-08-07

Thibodeau, Paul (Department: 1773)

Stock material or miscellaneous articles

Composite

Of addition polymer from unsaturated monomers

C428S474400, C428S480000, C525S240000

Reexamination Certificate

active

06270910

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to anisotropic films having a continuous phase and a discontinuous phase.
BACKGROUND
Elastic film materials, nonwovens, and other similar films have many industrial and consumer uses. Among other uses, such materials are frequently used, for example, in the disposable or personal use garment product area, garment meaning a product used on or in association with a body (human or animal). Specific such uses include disposable diapers, training pants, incontinence articles, sanitary napkins, bandages, surgical drapes and gowns, medical nonwovens, face masks, sport wraps and the like.
Generally, elastic films and materials can be formed from materials which exhibit elastic properties in substantially all directions. However, for some applications it is desirable to have materials which are primarily elastic in only a single direction, i.e., materials that are anisotropically elastic. A large amount of work, and a large number of patent applications and patents have been directed toward providing such anisotropically elastic materials, with a wide variety of solutions being provided.
A number of approaches have been successful in providing anisotropic elastic films. One common approach has been to laminate an elastic web material to a second web material that is easily stretched in one direction but not in the transverse direction. To produce these “stretch-bonded laminates,” an elastic film or nonwoven materials, or a similar type of elastic web, is elongated in one direction. While elongated, the elastic web is either continuously-bonded or point-bonded to an inelastic web material. Afterwards, tension is released and the elastic web is allowed to recover from its elongation. The attached inelastic web material then puckers making the stretch-bonded laminate readily extensible in the direction of the elastic web's elongation but not in the transverse direction. The laminate can then be restretched up to the point of previous elongation of the elastic web. This is not a universal solution, however, because the described puckering can be undesirable for some applications.
In order to eliminate puckering, inelastic nonwoven web materials have been prepared with a large number of substantially parallel slits. This slit nonwoven web material can be attached to an untensioned elastic web material. When the laminate is stretched in a direction perpendicular to the direction of the slits the laminate stretches and recovers without the formation of puckers or gathers in the inelastic nonwoven web.
Some approaches to preparing anisotropic materials do not involve bonding an elastic material to a non-elastic material. For example, anisotropic behavior can be obtained in an elastomeric nonwoven fibrous web of meltblown elastomeric fibers by aligning the fibers with an airstream to produce a web with a higher peak load tension in the direction of fiber orientation.
Even with the existence of the above-described solutions, as well as others, there still exists a continuing need for new constructions of such films. Preferably the films should be easy to manufacture, form readily into a roll, can be subsequently easily unwound without substantial blocking, and can be handled and converted into a final form for use, e.g., on a limited-use garment.
SUMMARY OF THE INVENTION
The present inventors have identified films that exhibit useful anisotropic properties. The anisotropic films can be useful in various applications where elastic film properties are desired, and are particularly useful in applications where anisotropic film properties are desired; e.g., where elasticity in one direction is desirable with relatively higher tensile strength desired in a perpendicular direction. Relatively higher tensile strength can be desirable, for example, when it is necessary for processing to roll a film onto a core to form a larger roll, where winding, unwinding, and any further processing can preferably be accomplished with little or no stretching of the film.
An aspect of the invention relates to anisotropic film having a continuous elastic phase comprising a polyolefin elastomer, and a discontinuous phase within the continuous phase. The film can be used by itself or in combination with other materials as a laminate material, e.g., for personal use garments.
As used herein, the term “anisotropic,” refers to a film that exhibits elasticity and strength properties that are different when measured in one direction than in a second direction. The directions of measurement are conventionally referred to, e.g., as a “machine direction,” “MD,” or “inelastic direction,” and a direction perpendicular to the machine direction, referred to as a “cross direction,” “CD,” or “elastic direction.” Elasticity and strength properties can be measured by a number of different physical properties of a film, including one or more of tensile strength, permanent set or set, and elastic force, etc. These properties are referred to herein as “film properties.”
The term “elastic” as used within the present description will be given meaning as generally accepted in the elastic materials art, not inconsistent with the following: in terms of permanent set, an elastic material can be defined to recover at least about 80 percent of its stretched length after extension of 100% strain (double its initial length).


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