Stock material or miscellaneous articles – Structurally defined web or sheet – Including components having same physical characteristic in...
Reexamination Certificate
1998-09-30
2001-08-21
Copenheaver, Blaine (Department: 1771)
Stock material or miscellaneous articles
Structurally defined web or sheet
Including components having same physical characteristic in...
C428S218000, C428S315700, C428S316600, C428S319700, C428S913000, C442S370000
Reexamination Certificate
active
06277479
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to breathable microporous films. More particularly, the present invention relates to breathable microporous films having zoned breathability and methods of making the same.
BACKGROUND OF THE INVENTION
Microporous films are “breathable” barriers in the sense that the film acts as a barrier to liquids and particulate matter but allows water vapor and air to pass therethrough. In addition, by achieving and maintaining high breathability it is possible to provide an article that is more comfortable to wear since the migration of water vapor through the fabric helps reduce and/or limit discomfort resulting from excess moisture trapped against the skin. Thus, such an article can potentially contribute to an overall improved skin wellness.
Accordingly, microporous films have become an important article of commerce, finding a wide variety of applications. For example, microporous films have been used as outer covers for personal care products such as diapers, training pants, incontinence garments, feminine hygiene products and the like. In addition, microporous films have likewise found use in protective apparel and infection control products such as surgical gowns, surgical drapes, protective workwear, wound dressings and bandages. Often microporous films are utilized as multilayer laminates in such applications. The films can provide the desired barrier properties to the article while other materials laminated thereto can provide additional characteristics such as strength, abrasion resistance and/or good hand. For example, fibrous webs such as nonwoven fabrics allow the laminate to retain its breathability and can provide additional strength as well as an article having a cloth-like feel. Thus, microporous film laminates can be used in a variety of applications including, for example, those described above.
Although the breathability provided by microporous films and/or laminates thereof is advantageous in many articles, there exist some situations where high breathability can be undesirable. For example, in personal care articles such as diapers or incontinence garments the breathable barrier and absorbent core generally work together to retain bodily fluids discharged into the garment. However, when fluid is retained within the absorbent core, significantly higher levels of water vapor begin to pass through the breathable barrier. The increased levels of water vapor passing through the outer cover can form condensate on the outer surface of the garment. The condensate is simply water but can be perceived by the wearer as leakage. In addition, the condensate can create a damp uncomfortable feel to the outer portion of the garment which is unpleasant for those handling the article. It is believed that the skin wellness and/or improved comfort benefits of breathable outer covers are often not achieved at areas directly adjacent to the portion of the absorbent core which retains considerable amounts of liquid (e.g. typically those areas of the central or crotch region of the garment). Providing a breathable barrier which has less or limited breathability in such regions, while providing good breathability in the remaining regions, would provide a garment with excellent wearer comfort yet which limits the potential for outer cover dampness. Thus, a breathable barrier that provides either zoned or controlled regional breathability is highly desirable.
Therefore, there exists a need for a breathable microporous film having regions with varied levels of breathability. In addition, there exists a need for such films which retain the desired barrier properties and which are capable of lamination to additional materials. Further, there exists a need for methods of making such films and in particular methods of reliably obtaining the desired levels of breathability in distinct regions of a film.
SUMMARY OF THE INVENTION
The aforesaid needs are fulfilled and the problems experienced by those skilled in the art overcome by the film of present invention which, in one aspect, comprises a first microporous region having a thickness less than 50 &mgr; and a WVTR of at least 800 g/m
2
/24 hours and a second region having a thickness substantially equal to or less than that of the first region wherein the WVTR of the second region is at least 15% less than the WVTR of the first region. Desirably the second region has decreased porosity relative to that of the first region. Despite the existence of variations in film structure, the film can have a hydrohead of at least about 50 mbar. The second region desirably has minimum dimensions of 3 cm by 5 cm and still more desirably comprises from about 5% to about 75% of the area of said film. In one embodiment, the first region can have a WVTR in excess of about 2500 g/m
2
/24 hours and the second region a WVTR less than about 1500 g/m
2
/24 hours. Additionally, the second region can have a thickness less than about 95% of the thickness of the first region. Further, the film can comprise a third region having a WVTR intermediate to that of the first and second regions. The film can be a monolayer film or part of a multilayer film structure and can also be laminated with one or more additional materials as desired.
In a further aspect of the invention, methods of making films having-regions of varied breathability are provided and can comprise providing a microporous film having a hydrohead of at least 50 mbars and a WVTR of at least 800 g/m
2
/24 hours and then selectively applying heat and/or pressure to a portion of said film thereby creating first and second regions therein. The porosity and the WVTR is decreased within the second region of the microporous film, i.e. the region to which heat and/or pressure has been selectively applied, relative to the WVTR and porosity of the first region. In one embodiment, the film can be heated prior to and/or simultaneously with application of pressure. The second region can have a minimum dimensions of at least 3 cm by 5 cm and desirably the second region comprises from about 5% to about 75% of the area of said film. In a particular embodiment, pressure is selectively applied to the microporous film by a pair of rollers wherein at least one of the rollers is a patterned roller having a raised surface. Optionally, one or both of the rollers can be heated. Monolayer or multilayer films having at least one microporous layer can be utilized in conjunction with the methods of the present invention.
In still a further aspect of the invention, methods of making film laminates having varied regional breathability are provided and can comprise providing a breathable thermoplastic polymer microporous film having a WVTR of at least 800 g/m
2
/24 hours and a hydrohead of at least 50 mbars and bonding the breathable film to a breathable fibrous material thereby forming a multilayer laminate. The fibrous material can comprise a resilient polymeric material having a melting point at least 10° C. greater than the thermoplastic polymer comprising said film. A selected region of the microporous film can then be treated with sufficient energy wherein the porosity within that region of the microporous film is decreased a desired amount. In a particular embodiment, a selected region of the film laminate can be treated to reduce its WVTR by selectively exposing the region to sufficient heat, such as by focused hot air, capable of causing a significant melt fraction in the film polymer. With the onset of a significant melt fraction the porosity of the film can be decreased, i.e. the density increased, within the selected region of the film.
DEFINITIONS
As used herein the term “nonwoven” fabric or web means a web having a structure of individual fibers or threads which are interlaid, but not in an identifiable manner as in a knitted or woven fabric. Nonwoven fabrics or webs have been formed by many processes such as for example, meltblowing processes, spunbonding processes, hydroentangling, air-laid and bonded carded web processes.
As used herein the term “spunbond fibers” refers to sm
Barnett, Jr. Larry Ned
Blaney Carol Ann
Campbell Stephen Michael
Fell David Arthur
Freiburger Sarah Jane Marie
Copenheaver Blaine
Kimberly--Clark Worldwide, Inc.
Robinson James B.
Tulley Douglas H.
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