Embossed Stretchable Elastic Laminate and Method of Production
A stretchable embossed elastic laminate including at least one nonwoven fabric layer, and at least one elastomeric material extruded as a melt onto a major surface of the nonwoven fabric to form an elastic layer bonded to the surface of the nonwoven fabric. The elastic laminate is embossed with a deep embossing pattern to provide an embossed laminate having good tensile strength and excellent resistance to delamination. Also disclosed is a method of forming a stretchable embossed laminate wherein at least one melted elastic material is extruded onto a major surface of the nonwoven fabric, and the elastic material and the nonwoven fabric are conveyed through a nip formed by a layon roll and an embossing roll having a deep embossing pattern.
This application claims the benefit of U.S. Provisional Application Ser. No. 60/818,066, filed on Jun. 30, 2006. The disclosure of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTIONThe presently described technology relates generally to stretchable elastic laminates. More specifically, the present technology relates to embossed stretchable elastic laminates formed from an elastic melt layer and a non-woven layer and having a deep emboss pattern that allows for improved resistance to delamination of the nonwoven from the elastic layer.
Disposable absorbent articles (e.g., disposable diapers for children or adults) often include elastic features designed to provide enhanced and sustainable comfort and fit to the wearer by conformably fitting to the wearer over time. Examples of such elastic features may include, for example, elastic waistbands, elastic leg cuffs, elastic side tabs, or elastic side panels so that the absorbent article can expand and contract to conform to the wearer in varying directions. Additionally, such elastic features are often required to be breathable to provide a desired level of comfort to the wearer's skin.
Further, the elastic features of disposable absorbent articles may be made of stretchable elastic laminates. A stretchable elastic laminate typically includes an elastic film and a non-woven fabric. More particularly, the elastic film is typically bonded to the non-woven fabric to form the stretchable elastic laminate.
A nonwoven elastomeric laminate is disclosed, for example, in U.S. published application No. 2005/0287892 A1. According to the disclosure, the nonwoven web is one in which the fibers are thermally bonded to form the web material (see paragraph 0054). An elastomeric film is directly bonded to the nonwoven web layer by feeding the elastomeric film and the nonwoven web to the nip between two calender rollers. Pressure between the calender rollers ranges from about 0.25 to about 5 bar. Pressures at the lower end of the range are stated as being preferred, in order to insure that the elastomeric material does not become deeply embedded in the nonwoven web (see paragraph 0042).
Bonding the elastic film to the non-woven fabric typically requires a secondary bonding operation. For example, U.S. Pat. No. 6,069,097 (the '097 patent) describes a composite elastic material comprising a non-woven fabric secured to an elastic member, wherein the elastic member and the non-woven fabric are secured together at a plurality of points in the stretchable direction of the non-woven fabric (see Abstract). The '097 patent discloses using a heated embossing roller and a chilled roller to bond a co-extruded elastic film to a spunlace non-woven fabric to form the composite elastic sheet, (see col. 14, lines 7-20). Further, the '097 patent discloses that the composite sheet should be bonded in a particular pattern, namely that the composite should be bonded in an approximately perpendicular direction to the direction of elongation, and also that the bond sites should be positioned on either side of the elastic sheet so as not to overlap with bond sites on the other side of the elastic sheet, (see col. 5, lines 60-65).
Additionally, for example, U.S. Pat. App. Pub. No. 2004/0121687 (the '687 publication) describes forming an extensible laminate by laminating an extensible nonwoven web to an elastomeric sheet to form a laminate and mechanically stretching the laminate in a cross direction (see Abstract). The '687 publication discloses that an extensible laminate can be formed using nip rolls 46, 48 to bond an elastomeric sheet 14 to an extensible nonwoven web 12 (paragraph 0088). According to the '687 publication, “the extensible nonwoven web 12 may be laminated to the elastomeric sheet by a variety of processes including, but not limited to adhesive bonding, thermal bonding, point bonding, ultrasonic welding and combinations thereof” (paragraph 0090).
Furthermore, the '687 publication also describes the extensible nonwoven web 12 as “a necked spunbonded web, a necked meltblown web or a necked bonded carded web” (paragraph 0065). Stretching the nonwoven web in one direction not only causes necking in the other direction, but may also cause the nonwoven web to become thicker. A variation in thickness may require more complicated set-up procedures and additional processing equipment when utilizing the nonwoven web in different manufacturing operations, thus resulting in increased manufacturing costs. Moreover, necking of the nonwoven web may cause orientation of the fibers which may result in a striated appearance that may not be aesthetically pleasing.
Employing a secondary bonding operation, such as those described in the '097 patent and the '687 publication, to form the stretchable laminate typically increases the production cost of the stretchable elastic laminate.
Improving the elasticity of the stretchable elastic laminate typically requires stretch activation, which typically requires a secondary stretching operation. For example, U.S. Pat. No. 6,313,372 (the '372 patent) relates to a stretch-activated plastic composite. According to the '372 patent, “it may be desirable that such stretch activation be done either prior to or during production of a product using the composite” (col. 4, lines 37-39).
Additionally, for example, the '687 publication describes stretching a non-woven fabric with two pairs of rollers, each pair of rollers operating at a different speed. More particularly, the '687 publication describes necking an extensible nonwoven web 12 using a first nip 30, including nip rolls 32, 34 turning at a first surface velocity, and a second nip 36, including nip rolls 38, 40 turning at a second surface velocity that is higher than the first surface velocity (see paragraph 0085). The '687 publication also describes mechanically stretching the laminate 50 using grooved rolls 58, 60 (extensible paragraph 0091) or a tenter frame 66 (extensible paragraph 0092).
The use of such secondary stretching operations typically increases the production cost of the stretchable elastic laminate.
BRIEF SUMMARY OF THE INVENTIONThe presently described technology is directed to a stretchable laminate that has improved stretch properties such as improved elongation to break and low permanent deformation, as well as high tensile strength, high delamination resistance and aesthetic appeal.
In one aspect, the present technology is directed to an embossed stretchable laminate that includes a nonwoven fabric that is stretchable in at least one direction and an elastic material extruded or otherwise applied as a melt onto a major surface of the non-woven fabric such that the melt forms an elastic layer bonded to the surface of the nonwoven fabric.
In another aspect, the present technology is directed to an embossed stretchable laminate that includes a nonwoven fabric that is stretchable in at least one direction, and an elastic material applied as a melt to a major surface of the nonwoven fabric via a roll having a deep embossing pattern which is utilized during formation of a laminate to give the laminate an improved resistance to delamination.
For example, in at least one preferred embodiment, the present technology provides an embossed stretchable elastic laminate comprising at least one nonwoven fabric that is stretchable in at least one direction, and an elastic material applied as a melt onto a major surface of said nonwoven fabric. In preferred embodiments, the melt forms an elastic layer bonded to said surface of said nonwoven fabric. Additionally, it is preferred that the nonwoven fabric has an embossing pattern applied to a major surface of said nonwoven fabric opposite the major surface receiving the elastic material, said embossing pattern comprising discontinuous discrete shapes having a depth of at least about 0.008 inches.
In another aspect, the present technology is directed to a method of making an embossed stretchable laminate which includes heating an elastic material to form an elastic melt and applying the melt to a major surface of at least one nonwoven fabric layer wherein the fabric is stretchable in at least one direction, to form an elastic layer bonded to the surface of the nonwoven fabric, and applying a deep embossing pattern to the nonwoven fabric. For example, in at least one embodiment, a method of forming an embossed stretchable elastic laminate is provided that comprises the steps of: (a) providing a nonwoven fabric that is stretchable in at least one direction; (b) heating an elastic material to form an elastic melt; (c) applying said elastic melt to a major surface of said nonwoven fabric; (d) applying a compressive force to at least one of said elastic melt and said nonwoven fabric to form an elastic layer bonded to said surface of said nonwoven fabric; and (e) during the step of applying a compressive force with a roller having a deep embossing pattern to form a deep embossing pattern on a major surface of said nonwoven fabric opposite the major surface receiving the elastic melt.
In another aspect, the present technology is directed to a method of perforating the laminate or film within the laminate to improve its breathability.
In another aspect, the present technology is directed to a method of minimizing the stretch in selected zones of the laminate to facilitate a secure attachment to nonstretchy films, laminates or hooks in a disposable garment.
In another aspect, the present technology is directed to a method of increasing the elongation of the elastic laminate.
In a further aspect, the present technology is directed to a component for an absorbent article, or an absorbent article comprised of a component (for example, a side tab, a side panel, a waistband or an elastic belt substrate), that comprises an embossed stretchable laminate that includes a nonwoven fabric that is stretchable in at least one direction, and an elastic material applied as a melt to a major surface of the nonwoven fabric, by a roll with a deep embossing pattern. In at least one such embodiment, a component for an absorbent article is provided that comprises at least one nonwoven fabric that is stretchable in at least one direction, and an elastic material applied as a melt onto a major surface of said nonwoven fabric, wherein the melt forms an elastic layer bonded to said surface of said nonwoven fabric, and wherein said nonwoven fabric has an embossing pattern applied to a major surface of said nonwoven fabric opposite the major surface receiving the elastic material via a roller having a deep embossing pattern. The embossing pattern preferably comprises discontinuous, discrete shapes having a depth of at least about 0.008 inches.
BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGSWhile the specification concludes with claims particularly pointing out and distinctly claiming the subject matter which is regarded as the presently described technology of the present invention; it is believed that the presently described technology will be more fully understood from the following description taken in conjunction with the accompanying figures, in which:
The stretchable elastic laminates, methods of producing such laminates, and articles incorporating the stretchable elastic laminates of the presently described technology are suited for a variety of uses and applications, in particular for use in garments, such as a disposable absorbent article.
As used herein, the term “absorbent article” refers to a device which absorbs and contains body exudates, and more specifically, refers to a device which is placed against the skin of a wearer to absorb and contain the various exudates discharged from the body. Examples of absorbent articles include diapers, pull-on pants, training pants, incontinence briefs, diaper holders, feminine hygiene garments, and the like.
The term “disposable” is used herein to describe absorbent articles, which generally are not intended to be laundered or otherwise restored or reused as absorbent articles, but rather discarded after use by the wearer.
The term “elastic” refers herein to any material that upon application of a force to its relaxed, initial length can stretch or elongate without substantial rupture and breakage by at least 50% of its initial length, and which can recover at least 30% of its initial length upon release of the applied force.
The term “spunlace nonwoven fabric” as used herein refers to a structure of individual fibers or threads which are physically entangled, without thermal bonding. Physical entanglement may be achieved using a water entanglement process or alternatively, a needling process or a combination of both processes. Spunlace nonwoven fabric is distinguishable from “spun-bonded nonwoven fabric” in that spun-bonded nonwoven fabric has thermal bonding points between individual fibers in the nonwoven fabric, such that the fibers are thermally bonded into a cohesive web.
The term “machine direction” for a nonwoven fabric, web or laminate refers to the direction in which it was produced. The terms “cross direction” or “transverse direction” refer to the direction perpendicular to the machine direction.
The terms “stretchable” or “extensible” refer herein to a material that can be stretched, without substantial breaking, by at least 50% of its relaxed, initial length in at least one direction. The term can include elastic materials, as well as nonwovens that are inherently extensible, but do not recover. Such nonwovens can be made to behave in an elastic manner by bonding them to elastic films.
The term “delamination” refers to a failure of the bond between the nonwoven and film after some amount of stretching. Delamination typically is evident as a raised section of nonwoven over 10 mm of the laminate in any direction.
The stretchable laminate of the present technology comprises at least one nonwoven fabric and an elastic material extruded as a melt onto a major surface of the nonwoven fabric, wherein the melt forms an elastic layer bonded to the surface of the nonwoven fabric. In a preferred embodiment, the laminate is a 3-layer laminate in which an elastic layer is sandwiched between two nonwoven fabric layers, with at least one of the nonwoven fabric layers being formed from a spunlace nonwoven fabric.
The spunlace nonwoven fabric used herein is made from a material having a melting point or softening point that is greater than the temperature of the elastic melt at the time the elastic melt contacts the spunlace nonwoven fabric. Selecting a spunlace nonwoven fabric with a melting point or softening point greater than the temperature of the elastic melt at the time of contact insures that melting of the fibers in the spunlace nonwoven fabric does not occur when the elastic melt is extruded onto the surface of the nonwoven fabric.
Suitable materials for the spunlace nonwoven fabric include high melting temperature materials, such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polypropylene terephthalate (PPT), polyacrylonitrile (PAN), polyamides, including polyamide 6 and polyamide 6.6, and polyacrylate (PAC). Other suitable materials for the spunlace nonwoven fabric include materials that do not have a true melting point, but have a high softening temperature range or a high decomposition temperature. Such materials include viscose, aramide (known commercially as Nomex™), polyvinylalcohol (PVA) (known commercially as Vinylon™), and rayon. Other polymeric materials, such as polypropylene, may also be used for the spunlace nonwoven fabric. A preferred material for the spunlace nonwoven fabric is PET having a melting point of approximately 260° C. A suitable PET spunlace nonwoven fabric is commercially available from Tomen America Inc. of New York, N.Y., under the product name Tomiace PET. Other suppliers of PET spunlace nonwoven fabric include Sandler Vliesstoffe of Germany and BBA Group of Brentwood, Tenn.
The spunlace nonwoven fabric may have a basis weight of about 20 to about 80 gsm and is stretchable in an amount of about 50% to about 200% of its initial length. In general, spunlace nonwoven fabrics having a basis weight at the upper end of the range have better strength and are more stretchable than lower basis weight spunlace nonwovens, but are also more expensive. A suitable spunlace nonwoven fabric for use herein has a basis weight of about 30 grams per square meter (gsm) and is stretchable in the cross-direction.
Use of a spunlace nonwoven fabric made from a material having a high melting or decomposition temperature provides a surprisingly high level of laminate elongation compared to other nonwoven fabrics having thermal bonding points. Without wishing to be bound by a particular theory, it is believed that there are three attributes that help create the high level of elongation. First, the high melting or decomposition temperature of the nonwoven (for a PET nonwoven around 260° C.) allows it to retain its fiber integrity even when in contact with the melted elastic material. Second, the relative incompatibility of the nonwoven fabric with the polymers used to form the elastic layer keeps the elastic melt from wetting out the nonwoven fibers and causes the attachment of the nonwoven fabric to the melted elastic material to be a physical trapping of the surface fibers rather than a full chemical bond. This physical trapping helps to allow some sliding of the nonwoven fibers, thereby contributing to the level of elongation. Third, the spunlace nonwoven, being a physically entangled nonwoven rather than a thermally bonded nonwoven, may allow some fiber sliding without requiring much physical separation between the nonwoven fabric and the elastic layer.
The use of a spunlace nonwoven fabric in a stretchable laminate provides additional advantages. For example, the spunlace fabric lends itself to the addition of liquid absorbing natural fibers to the spunlace fabric. Since manufacture of the present laminate does not depend on nonwoven melting to achieve attachment between the elastic layer and the nonwoven fabric, natural fibers that are nonmelting can be added to the spunlace fabric without detrimentally affecting the attachment between the elastic layer and the spunlace fabric. Suitable natural fibers that may be added include cellulose, cotton, wool, flax and hemp. Such added natural fibers contribute to a level of comfort in hygiene applications that cannot be achieved by other nonwoven materials. In addition, natural fibers are biodegradable. By incorporating such fibers into the spunlace nonwoven, or indeed, utilizing a spunlace nonwoven fabric manufactured entirely from natural fibers, and selecting an elastic material that is also biodegradable, the entire elastic laminate structure may be made to be biodegradable, a desirable property for disposable articles to have. A further advantage of the spunlace technology is the furrowed appearance that it creates in the finished elastic laminate. The furrows generally corresponding to the channels created by the hydraulics creates an aesthetically appealing laminate with a look that simulates the appearance of incrementally stretched elastic laminates that are popular in disposable absorbent garments.
The high temperature resistance of the spunlace fabric may also be used to advantage for high speed “welding” applications where the spunlace nonwoven layer of the laminate is in close proximity to a hot bar or hot wire, and a more delicate, lower melting temperature material on the opposite surface of the laminate could be kept relatively cool. In such applications, the spunlace fabric can withstand the heat from the hot bar or wire without melting and can transfer some of the heat to the lower layers.
Although a spunlace nonwoven is preferred for the nonwoven layer or layers, other nonwoven fabrics are also suitable for use in the present technology. Such nonwoven fabrics include, for example, those formed by meltblowing processes, spunbonding processes, air laying processes and bonded carded web processes. One example of a suitable nonwoven fabric is a spunbond nonwoven fabric made from fibers containing an elastic core and a polylethylene or polypropylene sheath, which is available from BBA Group under the trade name Dreamex™.
The elastic layer which is extruded onto the nonwoven fabric is formed from one or more thermoplastic materials. Thermoplastic materials suitable for use in the elastic layer or layers in the laminates of the present technology are generally materials that flow when heated sufficiently above their glass transition temperature and become solid when cooled.
Thermoplastic materials that have elastomeric properties are typically called elastomeric materials. Thermoplastic elastomeric materials are generally defined as materials that exhibit high resilience and low creep as though they were covalently crosslinked at ambient temperatures, yet process like thermoplastic nonelastomers and flow when heated above their softening point. Thermoplastic elastomeric materials, in particular block copolymers, useful in practicing the presently described technology can include, for example, linear, radial, star, and tapered block copolymers such as styrene block copolymers, which may include, for example, Kraton® or Kraton®-based styrene block copolymers available from Kraton Polymers, Inc., located in Houston, Texas; styrene-isoprene block copolymers, styrene-(ethylene-butylene) block copolymers, styrene-(ethylene-propylene) block copolymers, and styrene-butadiene block copolymers; polyether esters such as that available under the trade designation HYTREL™ G3548 from E.I. DuPont de Nemours; and polyether block amides such PEBAX™ available from Elf Atochem located in Philadelphia, Pa. Preferably, styrene block copolymers are utilized in practicing the presently described technology. Styrene-ethylene butylene block copolymers are most preferred.
Non-styrene block copolymers (elastomers or plastomers) suitable for use in accordance with the presently described technology include, but are not limited to, ethylene copolymers such as ethylene vinyl acetates, ethylene octane, ethylene butene, and ethylene/propylene copolymer or propylene copolymer elastomers, such as those available under the trade designation VISTAMAXX® available from ExxonMobil, located in Irving, Texas, or ethylene/propylene/diene terpolymer elastomers, and metallocene polyolefins such as polyethylene, poly (1-hexane), copolymers of ethylene and 1-hexene, and poly(1-octene); thermoplastic elastomeric polyurethanes such as that available under the trade designation MORTHANE™ PE44-203 polyurethane from Morton International, Inc., located in Chicago, Ill. and the trade designation ESTANE™ 58237 polyurethane from Noveon Corporation, Inc., located in Cleveland, Ohio; polyvinyl ethers; poly-α-olefin-based thermoplastic elastomeric materials such as those represented by the formula —(CH2CHR)x where R is an alkyl group containing about 2 to about 10 carbon atoms; poly-α-olefins based on metallocene catalysis such as ENGAGE™ 8200, ethylene/poly-α-olefin copolymer available from Dow Plastics Co., located in Midland, Mich.; polybutadienes; polybutylenes; polyisobutylenes such as VISTANEX NM L-80, available from Exxon Chemical Co.; and polyether block amides such PEBAX™ available from Elf Atochem located in Philadelphia, Pa. A preferred elastomer or plastomer of the presently described technology is an ethylene/propylene copolymer or polypropylene copolymer. It is also preferable that the non-styrene block copolymer elastomer or plastomer of the presently described technology comprise from about 10% to about 95% by weight of the elastomeric layer based upon the total weight of the composition. For example, one embodiment of the elastomer or plastomer of the presently described technology may be comprised of a polypropylene copolymer containing from about 50% to about 95% of propylene content.
Additional elastomers which can be utilized in accordance with presently described technology also include, for example, natural rubbers such as CV-60, a controlled viscosity grade of rubber, and SMR-5, a ribbed smoked sheet rubber; butyl rubbers, such as EXXON™ Butyl 268 available from Exxon Chemical Co., located in Houston, Texas; synthetic polyisoprenes such as CARIFLEX™, available from Shell Oil Co., located in Houston, Texas, and NATSYN™ 2210, available from Goodyear Tire and Rubber Co., located in Akron, Ohio; and styrene-butadiene random copolymer rubbers such as AMERIPOL SYNPOL™ 1101 A, available from American Synpol Co., located in Port Neches, Texas.
The elastic layer can be extruded as a single layer onto the surface of the nonwoven fabric. Alternatively, the elastic layer can comprise a plurality of elastic layers which are formed by co-extruding the melted elastic materials through a suitable co-extrusion die. For example, the elastic layer can comprise a three layer structure, which allows for a core layer sandwiched between two outer layers.
The elastic material used for each of the different layers of the co-extruded elastic layer can be selected from the elastomeric materials described above in order to vary the level of adhesion between the elastic layer and the nonwoven fabric. Adjusting the level of adhesion between the elastic layer and the nonwoven allows one to obtain a desired balance between laminate stretch and delamination resistance. In one embodiment, the multi-layer elastic layer comprises a KRATON™ styrene block copolymer core layer sandwiched between two outer layers formed from VISTAMAXX™ elastomer. Alternatively, the outer layers of the multi-layer elastic layer may be tie layers formed from a material that promotes adhesion between the elastic layer and the nonwoven layer or layers. Such tie layers may be formed from compositions known in the art to promote adhesion between incompatible materials. For example, tie layers may be formed from maleic anhydride grafted polyolefins, such as BYNEL® from DuPont or PLEXAR® from Equistar.
The level of adhesion between the elastic layer and the nonwoven may also be adjusted through the use of adhesive fibers, which can provide adhesive bonding between the nonwoven fabric and the elastic layer where a low level of stretch is desired. Such adhesive fibers may include, for example, polyvinyl alcohol fibers, alginic fibers, fibers made from hot melt adhesives, or fibers made from thermoplastic materials having a low softening or melting point.
It will be appreciated by those skilled in the art that additives may be added to the one or more layers of the presently described laminates in order to improve certain characteristics of the particular layer. Preferred additives include, but are not limited to, color concentrates, neutralizers, process aids, lubricants, stabilizers, hydrocarbon resins, antistatics, antiblocking agents and fillers. It will also be appreciated that a color concentrate may be added to yield a colored layer, an opaque layer, or a translucent layer. A suitable neutralizer may include, for example, calcium carbonate, while a suitable processing aid may include, for example, calcium stearate.
Suitable antistatic agents may include, for example, substantially straight-chain and saturated aliphatic, tertiary amines containing an aliphatic radical having from about 10 to about 20 carbon atoms that are substituted by ω-hydroxy-(C1-C4)-alkyl groups, and N,N-bis-(2-hydroxyethyl)alkylamines having from about 10 to about 20 carbon atoms in the alkyl group. Other suitable antistatics can include ethoxylated or propoxylated polydiorganosiloxanes such as polydialkylsiloxanes and polyalkylphenylsiloxanes, and alkali metal alkanesulfonates.
Antiblocking agents suitable for use with the presently described laminates include, but are not limited to, calcium carbonate, aluminum silicate, magnesium silicate, calcium phosphate, silicon dioxide, and diatomaceous earth. Such agents can also include polyamides, polycarbonates, and polyesters.
Additional processing aids that may be used in accordance with the presently described technology include, for example, higher aliphatic acid esters, higher aliphatic acid amides, metal soaps, polydimethylsiloxanes, and waxes. Conventional processing aids for polymers of ethylene, propylene, and other α-olefins are preferably employed in the present technology. In particular, alkali metal carbonates, alkaline earth metal carbonates, phenolic stabilizers, alkali metal stearates, and alkaline earth metal stearates can be used as processing aids.
Fillers may be added to the elastic material to promote a microporous structure within the elastic layer when the layer is stretched. Examples of useful fillers include, but are not limited to, alkali metal and alkaline earth metal carbonates, such as sodium carbonate (Na2CO3), calcium carbonate (CaCO3), and magnesium carbonate (MgCO3), nonswellable clays, silica (SiO2), magnesium sulfate, magnesium oxide, calcium oxide, alumina, mica, talc, titanium dioxide, zeolites, aluminum sulfate, barium sulfate, and aluminum hydroxide.
Turning now to
It has been found that improved resistance to delamination can be achieved in the stretchable laminates if the embossing roll is provided with a deep embossing pattern that imparts discontinuous, discrete dots, dashes, crosses, or other discontinuous discrete shapes. By a deep embossing pattern it is meant that the engraving depth of the embossing roll is at least about 0.008 inches. Preferably the engraving depth of the embossing roll is in the range of about 0.008 inches to about 0.5 inches, alternatively in the range of about 0.008 inches to about 0.4 inches, alternatively in the range of about 0.008 inches to about 0.3 inches, alternatively in the range of about 0.008 inches to about 0.2 inches, alternatively in the range of about 0.008 inches to about 0.1 inches, alternatively in the range of about 0.008 inches to about 0.060 inches. The depth of the pattern can vary depending upon the shape selected. For example, if the dot pattern is selected (illustrated in
Without being bound by a particular theory, it is believed that the deep embossing pattern imparted to the nonwoven fabric concentrates the compressive force in a small area to create discrete bonding sites. These discrete bonding sites provide improved resistance to delamination compared to typical shallow embossing patterns, having substantially greater bonding areas, such as male fine square taffeta (MFST) embossing patterns, which are about 0.0013 inches in depth.
An elastic material 30 is extruded through a die tip 32 at a temperature above the melting point of the elastic material so that the elastic material is melted. The melted elastic material drops down to the nip 16 between the layon roll 14 and the embossing roll 18 where it contacts the nonwoven fabric 12 and the nonwoven fabric 22. As the nonwoven fabrics 12 and 22 and the elastic material 30 travel through the nip 16, compressive force at the nip 16 causes the nonwoven fabric 22 to be embossed by the embossing roll 18 and causes the elastic material to physically entrap the fibers at the surfaces of the nonwoven fabrics, resulting, upon cooling of the elastic material, in an embossed stretchable laminate having an elastic layer bonded to the surfaces of the nonwoven fabrics but not embedded within them. A suitable compressive force at the nip may be from about 10 to about 150 pounds per lineal inch (PLI). It should also be appreciated by those skilled in the art that the embossing can also be accomplished by lay on roll 14.
It will be appreciated by those skilled in the art that, although a three-layer stretchable laminate is illustrated in
It will also be appreciated by those skilled in the art that the compressive force used to bond the elastic layer to the nonwoven fabric may be generated using techniques other than conveying the elastic melt and the nonwoven fabric through a nip. Such alternative techniques may include, for example, using an air knife to blow the nonwoven fabric into the elastic melt, using a vacuum box to draw the elastic melt down into the nonwoven fabric, using nonwoven web tension to pull the nonwoven fabric into the elastic melt, using a static bar (static electric pressure), or combinations of these alternative techniques.
It should be further appreciated by those skilled in the art that according to the present technology, the elastic material 30, nonwoven fabrics 12 and 22 and resultant embossed stretchable laminate can be perforated. Such materials, nonwoven fabrics and laminates of the present technology can be perforated by any conventional means or processes known or utilized to perforate such materials. Thus, those skilled in art will appreciate that the step of perforation is included within the spirit and scope of the present technology.
The stretchable laminate resulting from the extrusion lamination and embossing process has sufficient adhesion between the elastic layer and the nonwoven fabric that delamination of the layers does not occur, yet the adhesion is not so strong that it negatively impacts the stretch properties of the laminate. The adhesion between the elastic layer and the nonwoven is such that no additional downstream bonding steps are necessary to insure that delamination between the layers does not occur.
An additional property achieved by the stretchable laminates of the presently described technology is improved resistance to stretching in the machine direction. This is an important property because it allows the laminate to be easily converted on a manufacturing line. Resistance to stretching is determined by measuring the tensile force required to stretch the laminate 5% in the machine direction. The greater the tensile force, the greater the laminate resists stretching in the machine direction as the laminate is processed through manufacturing equipment.
The improved tensile forces for the stretchable elastic laminates made in accordance with the present technology are achieved without utilizing additional processing techniques, such as necking. The tensile forces at 5% machine direction stretch (tensile at 5% MD) for the stretchable laminates of the presently described technology may be as high as 150 grams, preferably 200 grams, more preferably 250 grams, and most preferably 300 grams or higher, without necking.
For some applications, it may be desirable to have a low stretch zone on the elastic laminate in order to assure a secure bond or attachment between the elastic laminate and a nonstretchy substrate. Such a low stretch zone or area can be achieved in the present elastic laminate in a variety of ways. For example, a tie layer coating can be applied to the surface of the nonwoven fabric where a low level of stretch is desired prior to lamination with the elastic melt. The tie layer would not cause appreciable stiffening, but would assure such a complete bond between the nonwoven fabric and the elastic layer that little stretch could occur in the tie layer region. Alternatively, a heavy bonding pattern could be applied to those areas of the laminate where a low level of stretch is desired to insure that there is a complete bond between the nonwoven fabric and the elastic layer. Alternatively, heat could be applied to the nonwoven in zones which will at least partially fuse the nonwoven or create a greater degree of bonding to the elastic material. The heat could be applied to the nonwoven before lamination. One particularly preferred approach is heating the nonwoven web with IR heat directed to specific areas of the nonwoven, but other approaches with hot contact rollers would also achieve the desired result. Another approach to create the low stretch areas would be to use selective prestretching of the nonwoven in the zones where a low level of stretch is desired in the finished elastic laminate. These prestrained regions of the nonwoven would resist further elongation after being applied to the nonwoven. The prestraining could be accomplished with bowing techniques known to the industry. Approaches would include the use of small casters or wide rollers a contoured surface or a fixed rod or plate with a contoured surface. This prestraining approach would have the additional benefit of creating areas of nonwoven between the prestrained zones having a greater level of potential stretch than it had originally. This would increase the level of final laminate stretch. Another approach for creating low stretch zones would be the use of heat after the laminate is formed by the application of heat in lanes to partially fuse the nonwoven and/or increase its bond with the elastic film. This heat could be applied with radiative, convective or conductive heat. One particularly preferred approach would the use of hot rollers applied to the web at or close to the slitting station. With this approach the increased fusion could be more precisely positioned with respect to the edges of a slit laminate roll so that is positioned more exactly where the end customer would desire it. The heated fusion is not necessarily continuously applied along the machine direction of the laminate as any fusion pattern that is generally aligned in the transverse direction of the web would reduce the laminate stretch. Particularly preferred patterns would include transverse oriented line segments, bands or curved bands. Other approaches known in the art for creating low stretch zones, which are also known in the art as “deadened lanes,” may also be utilized. One such approach is to add strips of conventional polypropylene nonwoven fabric in lanes where little stretch is desired. This could be done on one or both sides of the stretchable laminate.
For some applications it may be desirable for the elastic laminate to be perforated in at least some regions so that it has improved porosity. This is especially useful in garment applications where the porosity contributes to the wearer's comfort. Since the nonwoven webs are inherently porous the desired laminate porosity can be achieved even if only the film is perforated. Approaches known in the art for creating perforations include among others needle perforation (hot or cold), die cutting, laser, water jet or hot air pulsing. Additional perforation techniques are envisioned for use with the present technology. One preferred method would be the use of fiber ends or segments lifted out of the plan of the nonwoven web (in the z-direction) to perforate the elastic melt upon contact. The number of the protruding nonwoven ends or segments can be increased by techniques such roughening the nonwoven with a sanding or abrasion action or by perforating the nonwoven web with a spiked roll such as the pinned shells produced by Robert A. Main & Sons, Inc., located in Wyckoff, N.J. Another preferred method would be creation of perforations during the lamination process while the elastic material is quiescent and more easily perforated. The perforation at this stage could be created by raised elements on one of the lamination rolls and this impact could be enhanced if desired by heating these raised elements. The perforation of the elastic melt at the lamination stage of the process could also be created by selective introduction of water or air with either of the lamination rollers to disrupt the continuity of the elastic melt. If desired the perforation could be accomplished subsequent to lamination. Another preferred technique for this would be spark induced perforation such as that developed in corona treatment. Another preferred technique would be die cutting of the laminate. The cutting could be accomplished with or without material removal. A preferred die cutting approach would be use of cutting segments generally aligned with the machine direction of the web which would also increase the cross direction stretch capability of the laminate. If desired these cutting segments may include smaller cross direction elements that could blunt any tearing propagation of the laminate when stretched in the cross direction. One example cutting pattern would be an I-beam shaped cut repeated across the web wherever porosity is desired.
For some applications it may be desirable to increase the level of the elongation of the elastic laminate in the cross direction. One preferred technique for increasing the elongation of the laminate would be the addition of available stretch in the nonwoven by creating a greater path length for regions of the nonwoven by extending the nonwoven out of the plane of the nonwoven web (in the z-direction) in lanes or discrete zones. These lanes or zones can preferably be created by allowing the nonwoven to conform to the pattern roll before the nonwoven makes contact with the elastic melt in the lamination process. The additional loft is expected to create channels where air flow is permitted to enhance the comfort of the user. In applications where the loft is not desired for aesthetic reasons it can be available on one side of the laminate and not on the other and the lofty side can be positioned so that it is hidden from view in use. In an especially preferred embodiment of this approach the flat surface would be comprised of a nonwoven having higher inherent elongation than the nonwoven used for the lofty surface of the web.
Although it is generally recognized in the art that higher elongation is an advantage for elastic laminates, it is not generally recognized that there is an advantage to a laminate with two stages of elongation. The first stage could be nonrecoverable or less recoverable and the second stage elastically recoverable. With a nonrecoverable first stage it is possible to reduce the amount of elastic laminate employed in a garment. A shorter segment of elastic laminate could be utilized to save cost. The user would extend the laminate through its first nonrecoverable stage of elongation till it is close to the desired minimum length for its fit function. The second stage of recoverable elongation for the laminate would correspond more closely with the desired fit range of the garment. An elastic laminate with this desired two stages of elongation could be created with the invented process through the removal of laminate material or the selected rupturing of the elastic sheet such that the initial elongation of the laminate is directed toward partially closing up the voids created in the laminate. One preferred technique would be the use of die cutting to produce open spots in the laminate through material removal. A preferred pattern for this approach would be an array of ovals or parallelograms or the like with the long axis generally aligned in the machine direction of the web. Another preferred technique would be the use of die cutting to cut the web without removal. A preferred pattern for this approach would be an array of slits generally aligned with the machine direction of the web. The slits would preferentially be interrupted with cross direction elements designed to blunt any tear propagation in the machine direction as the laminate is stretched in the cross direction. A die cut resembling an I-beam is particularly preferred for this purpose.
One skilled in the art will recognize that modifications may be made in the presently described technology without deviating from the spirit or scope of the invention. Various embodiments of the presently described technology are also described in the following illustrative examples, which are not to be construed as limiting the invention or scope of the specific procedures or compositions described herein.
EXAMPLE 1 (COMPARATIVE) A three layer extrusion laminate was prepared by extruding a melt of an elastic resin from a die, such as die 32 shown in
BYNEL® E418 5% by weight outer layer/KRATON G1657 90% by weight core/BYNEL® E418 5% by weight outer layer.
A first nonwoven web made from a PET spunlace material having a basis weight of about 30 gsm and available from Tomen America, Inc. of N.Y., travels over the layon roll to the nip and a second, nonwoven web made of the PET spunlace material travels over the embossing roll to the nip where the first and second nonwoven webs each make contact with the elastic melt. Pressure at the nip causes the elastic melt to bond to the surfaces of the first and second nonwoven webs, and cause the embossing roll to form the MFST embossed pattern on the outer surface of the second nonwoven web, thus forming a three layer embossed laminate in which the elastic layer is sandwiched between the first and second nonwoven webs.
EXAMPLE 2A three layer extrusion laminate was prepared in the same manner, using the same elastic resin melt and the same PET spunlace nonwoven material for the first and second nonwoven layers as the laminate made in comparative Example 1, except that the embossing roll is provided with a rectangular deep embossing pattern.
EXAMPLE 3A three layer extrusion laminate was prepared in the same manner as Example 2, using the same elastic resin melt and the same PET spunlace nonwoven material for the first and second nonwoven layers. Except that the embossing roll is provided with a dot deep embossing pattern.
Each of the laminates made in Examples 1-3 have overall thicknesses of about 2 mils and have approximately the same basis weight. The laminates were tested to determine the extent of delamination as a function of number of loading cycles using an Instron mechanical testing machine. The test geometry is a 4″×1″ strip with a 2″ gauge length. The crosshead speed was 20″/minute to 100% strain for 20 cycles. Three specimens of each laminate were tested. After 20 cycles, pictures of the grip boundary showing the untested region in the grip and a region that was tested for 20 cycles were taken under a microscope. The results for Examples 1-3 are illustrated in
As can be seen from
The laminate made in accordance with Example 2, which was embossed with the rectangular deep embossing pattern, showed improved resistance to delamination compared to Example 1. As can be seen from
The laminate made in accordance with Example 3, which was embossed with the dot deep embossing pattern, showed superior resistance to delamination compared to Example 1. As can be seen from
First cycle hysteresis curves for each of the laminates made in accordance with Examples 1-3 are illustrated in
The invention has now been described in such full, clear, concise and exact terms as to enable any person skilled in the art to which it pertains, to practice the same. It is to be understood that the foregoing describes preferred embodiments and examples of the invention and that modifications may be made therein without departing from the spirit or scope of the invention as set forth in the claims.
Claims
1. An embossed stretchable elastic laminate comprising:
- at least one nonwoven fabric that is stretchable in at least one direction; and
- an elastic material applied as a melt onto a major surface of said nonwoven fabric;
- wherein the melt forms an elastic layer bonded to said surface of said nonwoven fabric; and
- wherein said nonwoven fabric has an embossing pattern applied to a major surface of said nonwoven fabric opposite the major surface receiving the elastic material, said embossing pattern comprising discontinuous discrete shapes having a depth of at least about 0.008 inches.
2. The embossed stretchable elastic laminate of claim 1, wherein the nonwoven fabric comprises a material selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate, polypropylene terephthalate, polyamides, polyacrylates, polyacrylonitrile, viscose, aramide, polyvinylalcohol and rayon.
3. The embossed stretchable elastic laminate of claim 1, wherein the elastic material comprises a styrene block copolymer.
4. The embossed stretchable elastic laminate of claim 3, wherein the styrene block copolymer comprises SEBS.
5. The embossed stretchable elastic laminate of claim 1, wherein the elastic layer is comprised of a plurality of layers formed by co-extruding the elastic material and at least one other material.
6. The embossed stretchable elastic laminate of claim 5, wherein the at least one other material is a second elastic material.
7. The embossed stretchable elastic laminate of claim 5, wherein the at least one other material is a tie layer material.
8. The embossed stretchable elastic laminate of claim 1, wherein said laminate comprises a second nonwoven fabric and said elastic material is applied to a major surface of said second nonwoven fabric so that the elastic layer is sandwiched between and bonded to said major surfaces of the nonwoven fabric and the second nonwoven fabric.
9. The embossed stretchable laminate of claim 1, wherein the at least one nonwoven fabric is a spunlace nonwoven fabric.
10. The embossed stretchable laminate of claim 8, wherein the second nonwoven fabric is a spunlace nonwoven fabric.
11. The embossed stretchable laminate of claim 1, wherein the embossing pattern comprises a series of discrete dots having a depth in the range of about 0.010 to about 0.060 inches.
12. The embossed stretchable laminate of claim 1, wherein the embossing pattern comprises a series of discrete perpendicular rectangles having a depth in the range of about 0.008 to about 0.060 inches.
13. The embossed stretchable laminate of claim 1, wherein the embossing pattern is imparted by a roll having embossing pattern depth of about 0.008 inches to about 0.5 inches.
14. The embossed stretchable elastic laminate of claim 1, wherein the at least one nonwoven fabric comprises natural fibers selected from the group consisting of cellulose, cotton, hemp, wool and flax.
15. The embossed stretchable elastic laminate of claim 5, wherein the elastic layer comprises first and second outer layers and at least one core layer.
16. The embossed stretchable elastic laminate of claim 15, wherein the first and second outer layers are tie layers.
17. A method of forming an embossed stretchable elastic laminate comprising the steps of:
- (a) providing a nonwoven fabric that is stretchable in at least one direction;
- (b) heating an elastic material to form an elastic melt;
- (c) applying said elastic melt to a major surface of said nonwoven fabric;
- (d) applying a compressive force to at least one of said elastic melt and said nonwoven fabric to form an elastic layer bonded to said surface of said nonwoven fabric; and
- (e) during the step of applying a compressive force with a roller having a deep embossing pattern to form a deep embossing pattern on a major surface of said nonwoven fabric opposite the major surface receiving the elastic melt.
18. The method of claim 17, wherein a single elastic material is applied to the surface of said nonwoven to form a single elastic layer.
19. The method of claim 17, wherein the applying step comprises co-extruding at least two materials, at least one of which is an elastic material, onto the surface of the nonwoven fabric.
20. The method of claim 17, wherein the elastic melt and the nonwoven fabric are conveyed through a nip formed by a layon roll and an embossing roll to form the elastic layer bonded to the surface of the nonwoven fabric.
21. The method of claim 17, wherein the compressive force is generated by using at least one of an air knife, a vacuum box, nonwoven web tension, or a static bar.
22. The method of claim 17, wherein the deep embossing pattern comprises a series of discrete dots having a depth in the range of about 0.010 to about 0.060 inches.
23. The method of claim 17, wherein the deep embossing pattern comprises a series of discrete perpendicular rectangles having a depth in the range of about 0.008 to about 0.060 inches.
24. A component for an absorbent article comprising;
- at least one nonwoven fabric that is stretchable in at least one direction; and
- an elastic material applied as a melt onto a major surface of said nonwoven fabric, wherein the melt forms an elastic layer bonded to said surface of said nonwoven fabric;
- wherein said nonwoven fabric has an embossing pattern applied to a major surface of said nonwoven fabric opposite the major surface receiving the elastic material via a roller having a deep embossing pattern, said embossing pattern comprising discontinuous, discrete shapes having a depth of at least about 0.008 inches.
25. An absorbent article comprising the component of claim 24.
Type: Application
Filed: Jun 29, 2007
Publication Date: Jan 3, 2008
Inventors: Amiel Sabbagh (Williamsburg, VA), Martin Hoenigmann (Chippewa Falls, WI), Jeffrey Middlesworth (Wauconda, IL)
Application Number: 11/771,572
International Classification: D04H 13/00 (20060101); D04H 1/00 (20060101);
