Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Composite having voids in a component
Reexamination Certificate
2003-10-15
2004-11-02
Tarazano, D. Lawrence (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Composite having voids in a component
C428S318400, C428S304400, C428S515000, C428S523000, C428S910000, C525S240000, C524S427000
Reexamination Certificate
active
06811865
ABSTRACT:
FIELD OF THE INVENTION
This invention is directed to breathable films and laminates containing them. Most of the moisture vapor breathability is induced by stretching the films by a small amount in the cross direction.
BACKGROUND OF THE INVENTION
Laminates which are breathable to water vapor but substantially impermeable to liquid water are known in the art, and are commonly used in diaper backings, other personal care absorbent garments, medical and industrial protective garments, and the like. These laminates may be composed of a breathable, stretch-thinned filled film and a spunbond web. The breathable film can be formed by blending one or more polyolefins with an inorganic particulate filler, forming a film from the mixture, and stretching the film to cause void formation around the filler particles. The resulting film may have thin polymer membranes around the filler particles which permit molecular diffusion of water vapor, while the overall film substantially blocks transmission of liquid water, or may have micropores going through the film. The breathable film can be laminated to a nonwoven web, for instance, a spunbond web, by thermal or adhesive bonding. The spunbond web adds abrasion resistance, strength and integrity to the breathable laminate, and provides a soft, cloth-like feel.
One trend affecting the personal care absorbent garment industry, and the protective garment industry, involves the demand and need for products with higher breathability to water vapor, which retain or increase the barrier to water, blood and other liquid substances. This trend reflects the demand for increased wearer comfort without loss of barrier performance. Another trend affecting these industries involves the demand and need for products having better fit, which conform to the contours of the wearer's body.
Still another trend involves the demand and need for products which are less expensive to produce, and which use less materials without sacrificing desirable product characteristics. Still another trend involves the demand and need for laminates having higher breathability to moisture vapor in selected regions of the laminates. In diapers and other pant-like absorbent articles, liquid can accumulate in the crotch region. When this happens, heat from the wearer's body can cause the space between garment and the wearer to become saturated with water vapor, facilitating the occurrence of diaper rashes and other skin irritations. The best way to effectively vent the water vapor is through other regions of the garment which are not affected by the pool of liquid in the crotch.
SUMMARY OF THE INVENTION
The present invention is directed to a breathable film, and a breathable laminate including the film and at least one nonwoven web. The film has a first state in which it has not been extended in the cross-direction, and a second state in which it has been extended by 25% in the cross-direction. The film has a first water vapor transmission rate (WVTR) of at least 500 grams/m
2
-24 hours in the first state, and a second WVTR in the second state, determined from the WVTR test procedure described below. The second WVTR in the second state is at least about 225% of the first WVTR, and is not less than about 4000 grams/m
2
-24 hours. The large increase in WVTR between the first state and the second state occurs solely as a result of stretching the film by about 25% in the cross-direction.
The present invention is also directed to a breathable laminate which exhibits similar properties. The nonwoven web is selected, and is bonded to the breathable film, so as not to substantially impair the breathability of the film. In essence, the breathability of the laminate is determined by the breathability of the film, although the WVTR values may be somewhat lower for the laminate depending on the bonding technique employed. The laminate has a first state in which it has not been extended in the cross-direction, and a second state in which the laminate (including the film) has been extended by about 25% in the cross-direction of the film. The laminate has a first WVTR in the first state which is at least 500 grams/m
2
-24 hours, determined from the WVTR test procedure described below. The laminate has a second WVTR in the second state which is at least 225% of the first WVTR, and is not less than about 4000 grams/m
2
-24 hours.
The breathable laminate can be used in a wide variety of personal care absorbent articles and protective garments. In one embodiment, the laminate is used as a backsheet in a disposable diaper or other pant-like absorbent garment. The diaper or other pant-like garment is initially undersized, representing a material savings. To don the garment on a wearer, the front and back regions in the garment (including the laminate) are stretched by about 25% of the original width of the laminate, in the cross-direction of the film. This stretching causes the front and back regions to have substantially higher WVTR than the crotch region, which is not significantly stretched during donning.
With the foregoing in mind, it is a feature and advantage of the invention to provide a breathable film, and a corresponding film
onwoven web laminate, to which high moisture vapor breathability can be induced by only minor stretching in the cross-direction of the film.
It is also a feature and advantage of the invention to provide a garment, such as a pant-like absorbent garment, to which selected regions of high breathability can be induced by minor stretching occurring during donning of the garment.
The foregoing and other features and advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments.
Definitions
The term “extendible” is used herein to mean a material which upon application of a stretching force, can be extended in a particular direction (e.g., the cross-direction), to a stretched dimension (e.g., width) which is at least 25% greater than an original, unstretched dimension. When the stretching force is removed after a one-minute holding period, the material preferably does not retract, or retracts by not more than 30% of the difference between the stretched dimension and the original dimension. Thus, a material having a width of one meter, which is extendible in the cross direction, can be stretched to a width of at least 1.25 meters. When the stretching force is released, after holding the extended width for one minute, a material stretched to a width of 1.25 meters will preferably not retract, or will retract to a width of not less than 1.175 meters. Extendible materials are different from elastic materials, the latter tending to retract most of the way to their original dimension when a stretching force is released. The stretching force can be any force sufficient to extend the material to between 125% of its original dimension, and its maximum stretched dimension in the selected direction (e.g., the cross direction) without rupturing it.
The “percent retraction” is determined when an extended material is relaxed to where the retractive force drops below 10 grams for a 3-inch wide sample. “Percent permanent set” is 100 minus “percent retraction.”
The term “inelastic” refers both to materials that do not stretch by 25% or more and to materials that stretch by that amount but do not retract by more than 30%. Inelastic materials include extendible materials, as defined above, as well as materials that do not extend, e.g., which tear when subjected to a stretching force.
The term “machine direction” as applied to a nonwoven web, refers to the direction of travel of a conveyor passing beneath the spinnerette or similar extrusion or forming apparatus for the filaments, which causes the filaments to have primary orientation in the same direction. While the filaments may appear wavy, or even randomly oriented in a localized section of a nonwoven web, they usually have an overall machine direction of orientation which was parallel to the movement of the conveyor that carried them away from the extrusion or
Conyer Sjon-Paul Lee
Daley Michael Allen
Hwang Patricia Hsiaoyin
Morell Charles John
Morman Michael Tod
Kimberly--Clark Worldwide, Inc.
Pauley Petersen & Erickson
Tarazano D. Lawrence
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