Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Reexamination Certificate
2001-09-06
2004-04-27
Singh, Arti R. (Department: 1771)
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
C428S198000, C442S328000, C442S381000, C442S394000, C442S396000, C442S409000
Reexamination Certificate
active
06726983
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to laminate elastic fabrics, and more particularly to elastic fabrics that are comprised of a non-woven layer laminated to an elastic layer, the laminate being formed by a controlled combination of temperature and pressure to render the laminate with a specific elastic performance.
The prior art contains a number of examples of laminate elastic fabrics comprised of a non-woven layer and an elastic layer. Such fabrics are useful for applications such as garments, disposable medical products, personal hygiene products, industrial products, and diapers. Depending on the particular application, the fabric may require particular properties such as a desired degree of elongation/recovery, porosity, softness, etc. These properties may be influenced by the selection of the particular non-woven component layer and the elastic component layer.
To construct the non-woven laminate elastic, the non-woven layer may be laminated to the elastic component layer with a chemical bond, mechanical bond, or by thermal bonding. Tension may be applied to either the elastic member or the non-elastic member prior to laminating to provide the final fabric with its elastic elongation capability. In these various methods of fabrication, the recovery capability of the laminate is a function only of the recovery of the elastic member.
When the elastic layer is stretched prior to joining the layers, the non-woven layer then “gathers” between the bond points when the laminate is relaxed, with the laminate surface disadvantageously showing “puckering”. Also, this method of fabricating an elastic laminate results in only a limited elongation potential, as an effect called “positive stop” limits laminate extension to the physical limits of the non-woven gathered between the bonded points. Such a process is disclosed in U.S. Pat. No. 4,720,415, and U.S. Pat. No. 4,842,596, incorporated herein by reference.
Alternatively, the non-woven layer can be tensioned prior to joining a tensioned or relaxed elastic member. When relaxed, the laminate fabric again shows a puckered surface with “gathers” of the non-woven between bond points. The previously described “positive stop” feature is also again manifested by the extension of the gathers in the non-woven layer when tension is applied. Also, this method produces a dimensional distortion in the non-woven layer referred to as “necking” or “necking in”. Several variations of this process are disclosed in U.S. Pat. Nos. 4,981,747; 5,226,992; 5,336,545; and 5,514,470; incorporated herein by reference.
These methods produce laminates that exhibit stretch and recovery primarily oriented in the direction of the applied tension, the machine direction (“MD”). Little or no stretch and recovery is induced in the cross tension direction (“CD”). Achieving a degree of elastic stretch and recovery in the CD has been significantly more difficult than the MD.
U.S. Pat. No. 5,114,781, incorporated herein by reference, discloses a method for producing a laminate, which has CD elastic stretch and recovery. The process disclosed is based on laminating a ‘reversibly necked’ substrate under tension to a tensioned elastic member. The provided definition of a ‘reversibly necked’ fabric is one that has been treated in some way while in a tensioned, necked-in state to impart memory to the material. The effect of this memory is to induce the fabric to return to its necked-in configuration after tension is applied in the CD. The fabric and method disclosed, however, result in a fabric surface that is puckered and gathered as the necked-in fabric is bonded to a tensioned elastic layer. Also, the reversible necking of the non-elastic layer requires an additional process step with associated costs and efforts.
Thus it is made apparent that the tensioning processes generally disclosed in the prior art have associated shortcomings. The practice has resulted in fabrics generally having only MD elasticity, at the expense of elasticity in the CD. Among other factors, this has resulted from the requirement of tensioning either the elastic or non-elastic layers or both when the layers are bonded together. While significant tensioning may be achieved in the MD, it is much more difficult to achieve in the CD, particularly simultaneously with the MD tensioning as MD tensioning in the MD may cause the CD dimension to be reduced or “necked in”, and to thereby lose CD elongation capacity.
Further, tensioning results in fabrics having a disadvantageously gathered or puckered surface, and limited elongation. Equipment and process controls are required for tensioning that are far more complex, expensive, and difficult to maintain than a standard lamination processing line. Finally, the fabrics of the prior art have offered only limited elastic recovery, particularly after multiple elongation cycles.
A heretofore unresolved need therefore exists for an improved process for making an elastic laminate non-woven fabric, and likewise for an improved elastic laminate non-woven fabric.
OBJECTS OF THE INVENTION
It is an object of the invention to provide a process for making a non-woven elastic laminate fabric having a high degree of CD elongation.
It is a further object of the invention to provide a process for making a non-woven elastic laminate fabric having a high degree of elastic recovery, the laminate being formed by a controlled combination of temperature and pressure to render the laminate with a specific elastic performance.
It is a further object of the invention to provide a non-woven elastic laminate fabric having a high degree of CD elongation.
It is a still further object of the invention to provide a non-woven elastic laminate fabric having a high degree of elastic recovery, the laminate being formed by a controlled combination of temperature and pressure to render the laminate with a specific elastic performance.
SUMMARY OF THE INVENTION
The present invention comprises a method for making a non-woven elastic laminate fabric, as well as the elastic laminate fabric produced thereby, the laminate being formed by a controlled combination of temperature and pressure to render the laminate with a specific elastic performance.
The elastic non-woven laminate fabric of the invention comprises a non-woven fabric web having a CD elongation of at least 120% and a basis weight of between about 10-100 gm/m
2
laminated to an elastic film layer comprised of a vinylidene isoprene polymer having a thickness of between 0.5 to 3.5 mils. The resulting elastic laminate non-woven fabric of the invention has CD elongation of at least 120%, MD elongation of 25-70%, and a CD elastic recovery of at least 85% after multiple cycles of 100% elongation.
It is noted that % elongation as used herein may be defined as:
elongation
%
=
100
×
[
(
elongation
.
length
-
original
.
length
original
.
length
)
]
Thus if a fabric is 10 in. long in a relaxed original state, and may be stretched to 25 in, then it shows 150% elongation. Further, as used herein % recovery may be defined as:
recovery
%
=
100
×
[
(
elongated
.
length
-
final
/
relaxed
.
length
elongated
.
length
-
original
.
length
)
]
Thus if the above fabric returned to a relaxed final state of 15 in., then it shows 67% recovery.
Preferably, the non-woven web component of the fabric of the invention has a CD elongation of at least 150% and a basis weight of between about 15-50 gm/m
2
. The preferred non-woven web may comprise spunbond or meltblown filament webs, or hydroentangled, carded staple fibers. Preferred materials of composition for the non-woven web of the invention include poly(ethylene terephthalate) (“PET”) and polyolefins.
The use of the preferred film also provides advantages over the use of elastic net-like structures or reticulated films in that more uniform elongation and a more uniform, wrinkle free surface appearance result. The film is preferably extrusion coated onto the non-woven web, while the web is in a relaxed, un-tensioned state (except
Erdos Valeria Griep
Mosley Ellen
Polymer Group
Pratt Christopher C
Singh Arti R.
Wood Phillips Katz Clark & Mortimer
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