Surgery – Means and methods for collecting body fluids or waste material – Absorbent pad for external or internal application and...
Reexamination Certificate
2001-08-24
2002-12-24
Chapman, Jeanette (Department: 1772)
Surgery
Means and methods for collecting body fluids or waste material
Absorbent pad for external or internal application and...
C604S317000, C604S367000
Reexamination Certificate
active
06497691
ABSTRACT:
TECHNICAL FIELD
The present invention is directed to a thermoplastic film composition, and more particularly, to a thermoplastic film consisting essentially of a vinyl copolymer, which exhibits structural durability and enhanced drapeability suitable for application as a breathable barrier layer in absorbent disposable hygiene and medical/industrial protective end-use articles.
BACKGROUND OF THE INVENTION
This invention is directed to breathable barrier films, or films capable of transmitting moderate levels of water vapor but are generally resistant to the passage of water in a liquid form. Breathable films have been known and used for many years in the production of, for example, water-proof clothing, to allow for the escape of water vapor from the surface of the skin of the wearer while improving long-term comfort. Such breathable films can be broadly classified as being of a microporous or monolithic nature.
A microporous film has a large number of pores formed in the film using special processing conditions. One method of obtaining microporsity in films is described in U.S. Pat. No. 3,870,593, wherein a quantity of powdered inert material, such as calcium carbonate, is incorporated as a pore nucleating agent into a thermoplastic matrix prior to extrusion in film form. After extrusion, the loaded film is drawn, thus extending the thermoplastic matrix away from the pore-nucleating agent and inducing the formation of small pores. As described in U.S. Pat. No. 4,308,303 after production of the microporous film, the film may be subsequently coated with fibers to produce a laminate. The lamination of microporous films to fabrics is practicable by a number of well-known and acceptable methods, including adhesive and thermal bonding.
Due to the mode of pore formation in microporous films creating a pathway through the protective film, such films are not suitable for certain applications. The indiscriminate passing of dangerous gases, vapors and biological agents, such as viral pathogens, would be contraindicated in end-uses whereby protection from such dangerous material is desirable, if not critical.
A second class of breathable films is referred to as monolithic films, in which the film offers a generally uniform construction which is free of pores. Monolithic breathable films are capable of allowing the transfer of certain gases and liquid vapors due to chemical absorption into the film matrix and subsequent transfer through the film thickness and release on the opposite film facing. For films, a high rate of moisture transmission is driven by the relatively high concentration and pressure of vapor on one side of the film. This mechanism of transfer is described in U.S. Pat. No. 5,445,874, which discloses thin films of certain polyurethanes that possess inherently water vapor transmission rates higher than the human skin, allowing the film to be used as an outer layer in burn dressings.
As practiced monolithic films require a change in the thickness of the film in order to modify the water vapor transfer rate (WVTR) performance, with thinner films providing higher WVTR's. As the thickness of a monolithic film is modified in order to adjust the WVTR, and particular when such films are reduced in caliper, the risk increases that a tear or imperfection may occur which will compromise the effectiveness of the barrier properties. Also, these breathable films tend to be harsh and noisy when combined with substrate materials and do not have an attractive visual appearance or a favorable fit to the user.
An unmet need exists for a breathable barrier film, with good WVTR properties, which exhibits sufficient structural durability necessary to maintain barrier performance and improved drapeability for enhanced fit and user comfort.
SUMMARY OF THE INVENTION
In accordance with the present invention, a thermoplastic film composition, and more particularly, a monolithic thermoplastic film comprising of a vinyl copolymer which exhibits sufficient structural durability and enhanced drapeability suitable for application as a breathable barrier layer in disposable end-use articles such as disposable hygiene and protective medical/industrial products. The film exhibits a WVTR of at least about 140 and no more than about 450.
The film is composed primarily of an vinyl copolymer, which can optionally be formed into a homogeneous and uniform blend with at least one melt additive. The film exhibits enhanced drapeability and strength for structurally durable breathable barrier performance with the additional benefit of favorable adhesion to a broad number of component polymers and substrate materials when utilized in laminate constructs.
Suitable vinyl copolymers include those families of polymers as well as acetates and acrylates. A preferred form of the vinyl copolymer are those selected from the ethylenic acrylates, with ethylene methyl acrylate being most preferred. Melt additives that can be optionally compounded with the ethylene methyl acrylate prior to extrusion include colorants, softening agents, UV stabilizers, and surface energy modifiers such as anti-static, hydrophobic and hydrophilic compounds and the mixtures thereof.
Advantageously, the film of the present invention can be in cast sheet form that can be used either individually or in conjunction with other separately formed materials, or preferably, can be continuously and directly applied to a substrate material while the film is in a molten or semi-molten state. When the film is applied directly to a substrate material, such as a woven or nonwoven fabric, the film exhibits useful adhesion properties without the necessary addition of other adhesives.
It has also been found that the film of the present invention can be loaded with elevated concentrations of melt additive without undue determent to the performance of the structurally durable, drapeable barrier properties. Of particular benefit, higher concentrations of titanium dioxide can be used to significantly improve the opacity of the resultant breathable barrier film. An improvement in opacity is of particular importance in the fabrication of personal hygiene articles, whereby the increased opacity reduces the printing through of organic exudates expressed into the article during its use.
DETAILED DESCRIPTION
While the present invention is susceptible of embodiment in various forms, hereinafter is described a presently preferred embodiment of the invention, with the understanding that the present disclosure is to be considered as an exemplification of the invention, and is not intended to limit the invention to the specific embodiment illustrated.
As used herein, the term water vapor transmission rate or WVTR is a value expressed in terms of grams of transmitted moisture per square meter of film over a 24 hour or one day period as determined by the protocol and teachings of U.S. Pat. No. 5,843,056, hereby incorporated by reference.
The present invention contemplates the use of a vinyl copolymer thermoplastic resin, which can optionally be admixed with one or more melt additives and extruded or cast into thin films either as an individual film, or as a film layer applied directly upon a substrate material.
In the preferred embodiment, the vinyl copolymer thermoplastic resin is incorporated into a film in the amount of at least 80% by weight, with the remainder of the film weight comprising one or more aesthetic or performance modifying melt additives. Within the blend parameters set forth above, practical consideration must be made as to the film formation including the structural durability of the film when used alone or as a layer with a fabric, and the minimum thickness at which a film can be formed using conventional equipment. The minimum thickness is on the order of 0.1 to 0.2 thousandths of an inch, and the maximum thickness can extend up to about 2 thousandths of an inch. A thin film having a higher amount of colorant might be used, for example, as an outer barrier for a hygiene product such as diapers. Thicker films might be employed in articles where structural d
Bevins Errette
Santisteban Jorge
Chapman Jeanette
Polymer Group Inc.
Wood Phillips Katz Clark & Mortimer
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