Stock material or miscellaneous articles – Structurally defined web or sheet – Including components having same physical characteristic in...
Reexamination Certificate
1998-12-28
2001-07-17
Copenheaver, Blaine (Department: 1771)
Stock material or miscellaneous articles
Structurally defined web or sheet
Including components having same physical characteristic in...
C428S315500, C428S316600, C442S370000, C442S372000, C442S374000, C442S375000
Reexamination Certificate
active
06261674
ABSTRACT:
TECHNICAL FIELD
This invention generally relates to polymer films, and more particularly relates to breathable polymer films for use in making disposable absorbent products.
BACKGROUND OF THE INVENTION
Polymer films are useful in making a variety of disposable articles because polymer films are relatively inexpensive to manufacture, and can be made to be strong, durable, flexible, soft, and a barrier to aqueous liquids such as water. For example, polymer films are used to make disposal personal care items such as diapers, adult incontinence products, feminine care absorbent products, training pants, and the like. In particular, polymer films are suitable outer covers for personal care items and health care products. Polymer films are also useful in making some types of garments and coverings for a variety of articles.
Disposable personal care and health care items, and the like, are often desirably breathable, a barrier to liquids, and strong enough to endure handling in normal use. Breathable means gas or water vapor permeable, liquid barrier means impermeable to liquid, and strength relates to tensile properties. While it is possible to enhance each of these properties of polymer films separately, enhancing the breathability of polymer films, without diminishing the barrier or strength properties of the film, is difficult. For example, certain polymers are more breathable than others, but have unsatisfactory barrier and tensile properties. Other polymers have superior barrier or tensile properties, but are not sufficiently breathable. Accordingly, there is a need for a polymeric film with enhanced breathability and desirable barrier and strength properties for use in making personal care items, health care items, and the like.
SUMMARY OF THE INVENTION
This invention satisfies the above-described need by providing a breathable microlayer polymer film comprising a plurality of coextruded microlayers including a first layer comprising a first melt-extrudable polymer and a second layer comprising a second melt-extrudable polymer, wherein the first melt-extrudable polymer has a first water vapor transmission rate and the second melt-extrudable polymer has a second water vapor transmission rate less than the first water vapor transmission rate. The microlayer film of this invention is breathable, but also has sufficient strength and liquid barrier properties for use in applications such as disposable absorbent personal care and health care products, garments, and other covering materials. The breathability of the film is illustrated by the water vapor transmission rate of the film. The water vapor transmission rate of the microlayer polymer film of this invention is desirably within the range from about 500 to about 15,000 g/m
2
/24 hrs per 1 mil of film thickness. While the first polymer is chosen to be more breathable than the second polymer, the second polymer can be chosen so that second polymer imparts to the microlayer film properties which the first polymer does not have. For example, the second polymer can have different tensile properties or barrier properties than that of the first polymer. Specifically, the second polymer can be chosen so as to impart greater elongation, tensile strength, toughness, reduce modulus, improve flexibility, higher barrier to liquids, microbial organisms, organic toxins, blood, and the like. Therefore, the microlayer polymer film of this invention is particularly suitable for making personal care items such as diapers, feminine care products, adult incontinence products, and training pants, and health care products such as wound dressings or surgical gowns.
The first and second layers can include a particulate filler material, and preferably a hydrophilic surfactant, to enhance the breathability of the microlayer film. The particulate filler material is particularly useful for enhancing the breathability of the second layer which comprises a less breathable polymer.
More particularly, the microlayer polymer film of this invention includes a plurality of first layers comprising first melt-extrudable polymer and a plurality of second layers comprising second melt-extrudable polymer. The plurality of first layers and plurality of second layers are arranged in a series of parallel repeating laminate units, each laminate unit comprising at least one of the first layers and at least one of the second layers.
Generally, the individual microlayers of the film of this invention have a thickness small enough so that the first and second layers of the microlayer film adhere to one another to form a laminate and do not delaminate. Each microlayer in the polymer film of this invention has a thickness from about 10 angstroms to about 150 microns. Desirably, each microlayer has a thickness which does not exceed 50 microns and preferably does not exceed 10 microns. More particularly, each microlayer has a thickness which is not less than 100 angstroms and preferably not less than 500 angstroms. Broadly described, the film of this invention has first and second layers totaling 8 to 17,000 in number, and preferably 60 to 8000 in number. Thinner microlayer films, such as for personal care product covers, have a total of 60 to 4000 total microlayers. Preferably, such film has 120 to 1000 total microlayers.
More particularly, desirable first (more breathable) melt-extrudable polymers include those having a water vapor transmission rate of at least about 500 g/m
2
/24 hrs per 1 mil of film thickness and desirable second (less breathable) melt-extrudable polymers include those a water vapor transmission rate of not more than about 100 g/m
2
/24 hrs per 1 mil of film thickness. For example, suitable first or more breathable polymers for use in this invention include polyethylene oxide (PEO), polycaprolactone and polybutylene succcinate. Suitable second or less breathable polymers include polyolefins such as linear low density polyethylene and polypropylene. It should be understood, however, that the foregoing ranges describe desirable polymers for use in this invention, which is not limited to polymers with such water vapor transmission rates. The first and second polymers can both be polymers with high water vapor transmission rates or can both be polymers with low water vapor transmission rates, but the first and second polymers should have different water vapor transmission rates.
According to a particular embodiment of the present invention, each laminate unit of the microlayer film can include a tie layer positioned between the first layer and the second layer for modifying or enhancing properties of the microlayer film. The tie layer can be formed from a variety of polymers. Suitable polymers are chosen depending on the desired properties of the microlayer film. For example, the tie layer polymer can be selected to have an affinity to the first layer or second layer, or both, for improving adhesion and interaction between those layers. The tie layer polymer can also be selected to enhance other properties of the microlayer film such as toughness and barrier.
The microlayer polymer film of this invention desirably has a dry tensile strength of at least about 5 MPa in the machine direction and a hydrostatic burst strength of at least about 1 mbar.
According to another aspect of this invention, a method for making a breathable microlayer polymer film is provided. This method includes coextruding a first melt-extrudable polymer and second melt-extrudable polymer to form a laminate comprising a first layer including the first melt-extrudable polymer and a second layer including the second melt-extrudable polymer, wherein the first melt-extrudable polymer has a first water vapor transmission rate and the second melt-extrudable polymer has a second water vapor transmission rate less than the first water vapor transmission rate. The method further includes separating the laminate while the laminate is in a melt-extrudable state to form a pair of laminate halves each including a portion of the first layer and a portion of the second layer. After separation, the lamina
Branham Kelly Dean
Soerens Dave A.
Topolkaraev Vasily
Copenheaver Blaine
Kilpatrick & Stockton LLP
Kimberly--Clark Worldwide, Inc.
Ruddock Ula C.
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