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; No. 5,226,992; No. 5,336,545; and No. 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/m2 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:
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:
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/m2. 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 for tensioning as may be required for normal web processing). The preferred extrusion coating of the film onto the non-woven web results in a final fabric having a smooth, ungathered or puckered surface, as all components are joined in an effectively relaxed configuration. Further, extrusion coating provides for large bonding interface area between layers, so that a coherent final laminate fabric results. Other means of attachment comprise bonding with an adhesive or thermal bonding by calendering.
The fabric of the invention has a CD elongation of at least 120% and preferably greater than 150% that is superior to that of elastic non-woven laminates of the prior art. Further, the elastic recovery of the fabric of the invention, which is 85% or greater after several cycles of 100% elongation, is also superior to that of any prior art elastic non-woven laminate fabric.
A preferred embodiment of the laminate elastic fabric of the invention comprises an elastic layer sandwiched in between two non-woven outer layers. A first non-woven web is as described above, with a CD elongation of at least 120%, with at least 150% most preferred, and a basis weight of between about 10-50 gm/m2. An elastic vinylidene isoprene film, with a thickness of between about 0.5-3.5 mils, is laminated onto the web. Finally, a second non-woven web having a CD elongation of at least 120% as well as other physical properties and characteristics that may be substantially similar to the first web, including basis weight, is thermally bonded to the exposed side of the film with the film thereby sandwiched between the two non-woven layers. The temperature and pressure used to perform the lamination having a pronounced effect on physical performance.
The method of the invention generally comprises the steps of providing a non-woven fabric web having a CD elongation of at least 120% and a basis weight of between 10-50 gm/m2, attaching an elastic film to the non-woven web with both the web and the film in substantially relaxed, unstretched states. The film comprises a vinylidene isoprene polymer with a thickness of between about 0.5 and 3.5 mils. The preferred means of attachment of the film to the non-woven web is by extrusion coating. As both the elastic and non-woven layers are in substantially relaxed, unstretched states when joined, the final laminate fabric of the invention has a smooth surface free from the puckering and/or gathering of non-woven elastic laminates of the prior art.
The preferred non-woven web provided in the method of the invention is as generally described above in relation to the preferred fabric of the invention. It has a CD elongation of at least 150% and a basis weight of between about 10-100 gm/m2. The web may comprise spunbond or meltblown continuous filaments, or more preferably hydroentangled, or highly randomized, carded staple fiber webs. The web may be prepared in line with the joining of the layers, or may be prepared separately. Preferred materials of composition include polyolefins, and polyesters (PET), polyamides, and the blends thereof.
The preferred vinylidene isoprene polymer film of the method of the invention is also as described above in association with the preferred fabric of the invention. Most preferably the film has a thickness in range of about 2.0 to 2.5 mils.
A preferred embodiment of the method of the invention comprises the steps of providing a first non-woven web having a CD elongation of at least 120%, with at least 150% most preferred, and a basis weight of between about 10-50 gm/m2. Next, an elastic vinylidene isoprene film is extrusion coated onto the web in a thickness as described above, including preferred ranges. A second non-woven web having physical properties and characteristics similar to the first web, including basis weight and CD elongation, is then thermally bonded to the exposed side of the film with both the second web and the first web and film laminate in substantially relaxed, unstretched states. The film is thereby sandwiched between the two non-woven layers.
The thermal point bonding of the second layer to the exposed side of the film can be carried out at a temperature in the range of the melting temperature of the film, to result in an intimate co-mingled bond between both outer non-woven layers and the film layer therebetween.
It has been found that subtle variations in the bonding temperature and pressure during the lamination process yield constructs of differing performance. Two particularly preferred sets of bonding temperatures and pressures are referred to those yielding a “high-bond” and a “low-bond”. Both high-bond and low-bond materials are formed by the application of an engraved calender roll having a discontinuous bond pattern with no greater than about 15% land area. The high bond materials incorporate the use of the engraved calender roll at a temperature in the range of about 360° F. to 390° F. The low-bond materials incorporate the use of the engraved calender roll at a temperature in the range of about 340° F. to 360° F. The pressure of the engraved calender roll for the manufacture of the high-bond material versus the low-bond is increased by no more than about 10%.
An optional, additional step in the method of the invention further comprises tensioning the laminated fabric of the invention in the machine direction after joining of the layers in a calender nip and before winding the fabric onto a winder. The tension is released before winding, so that the fabric is wound in a relaxed state. The tensioning causes some bonds to break in the nonwoven fabric layers. This breakage increases the overall elongation capacity of the laminate fabric, and decreases the stretch force of the laminate fabric.
The method of the invention thereby provides an improved process for making an elastic non-woven laminate fabric that does not require applying unusual tension to or otherwise stretching either the non-woven layer(s) or the elastic layer, instead allowing fabrication while the layers are in a substantially relaxed, un-extended state. The present invention therefore avoids the additional efforts and expenses associated with the stretching of one or all of the layers during processing, specifically the specialized equipment and process controls required to provide and maintain a tensioning station in the production line.
Further, the method of the invention is a simpler and more efficient method than those of the prior art. Also, the method of the invention results in a fabric having CD elongation of at least 120%, and elastic recovery of at least 85% after 3 cycles of 100% elongation.
The above brief description sets forth rather broadly the more important features of the present disclosure so that the detailed description and examples that follow may be better understood, and so that the present contributions to the art may be better appreciated. There are, of course, additional features of the disclosure that will be described hereinafter which will form the subject matter of the claims appended hereto. In this respect, before explaining the several embodiments of the disclosure in detail, it is to be understood that the disclosure is not limited in its application to the details of the construction and the arrangements set forth in the following description or illustrated in the drawings. The present invention is capable of other embodiments and of being practiced and carried out in various ways, as will be appreciated by those skilled in the art. Also, it is to be understood that the phraseology and terminology employed herein are for description and not limitation.