The present invention relates to elastomeric films laminated to nonelastomeric materials, such as fabrics, where the resulting laminates are elastomeric without mechanical activation. The present invention also relates to methods of making laminates of elastomeric films and nonelastomeric materials, where the resulting laminates are elastomeric without mechanical activation.
Elastomeric materials have long been prized for their ability to expand to fit over or around larger objects, and then retract to provide a snug fit around the objects. Elastomeric materials are often used in garments to provide a snug fit, such as in active wear. Elastomers can also form resilient but effective barriers, such as in the cuffs of thermal garments intended to retain body heat.
One example of a type of garment where both fit and barrier properties are important is hygienic products such as diapers. Elastomeric materials are used in the waist, around the leg openings, and in the fasteners (for a diaper) or sides (for an underpants-type garment). The elastomeric materials in these regions improve the overall fit of the garment, and also make it much easier to both don and remove the garment. The elastomeric materials also act as resilient barriers, improving the containment capabilities of the garment while still allowing comfort and free movement to the wearer.
In a hygienic product, the elastomeric material used can be in the form of threads, fabrics, or films. Using elastomeric threads can pose challenges in assembling the garment, since the threads must be applied as one component of many in the manufacturing process. These threads can also be weak and they tend to break, which could lead to the elastic failing even if there are redundant threads present. Elastomeric fabrics are somewhat easier to work with in a manufacturing process, but the fabrics themselves tend to be expensive both in raw materials and in the cost of manufacturing the fabric itself. Elastomeric films are easier to use in manufacturing than threads and are less expensive than elastomeric fabrics to produce. Elastomeric films also tend to be stronger than threads or fabrics, and less likely to fail in use.
However, elastomeric materials may be irritating or damaging if exposed directly to the skin. Many people are allergic to latex or synthetic rubber compounds if these compounds are in contact with the skin. Elastomeric materials that directly touch the skin can also rub, pinch, or ‘burn’ the skin, creating painful red marks.
To avoid direct contact between the elastomeric materials and the wearer's skin, and also to give the elastomeric material a more pleasant, cloth-like feel and appearance, it is known in the art to cover the elastomeric material with fabric or fabric-like material. For instance, elastomeric films used in limited-use or disposable garments may be bonded or laminated to layers of nonwoven, woven, or knitted fabric, so the fabric covers the elastomer and contacts the wearer's skin. This bonding or lamination of the elastomeric film to fabrics is done by various known means, including extrusion lamination, adhesive lamination, thermal lamination, and ultrasonic lamination. The fabrics used for disposable items are typically nonwoven materials made from inexpensive but non-elastomeric materials such as polypropylene or polyethylene.
However, once typical elastomeric films are bonded to one or more layers of fabric, the resulting laminate is usually no longer elastomeric, unless the fabric itself is also made of elastomeric materials. Nonwoven fabrics made from elastomeric polymers are known, but these materials are typically too expensive for limited-use or disposable articles. If a non-elastomeric fabric is bonded to an elastomeric film, the fabric will bond to the elastomer in such a way as to restrain the elastomer, and the resulting laminate will be no more elastomeric than the fabric component.
Many approaches have been taken to form a laminate of elastomeric film and fabric which remains elastomeric once the laminate layers are bonded together. One approach is to fold, corrugate, crepe, or otherwise gather the fabric layer prior to bonding it to the elastomeric film. The gathered fabric is bonded to the film at specified points or lines, not continually across the surface of the film. While the film is in a relaxed state, the fabric remains corrugated or puckered on the film; once the elastomeric film is stretched, the fabric layer flattens out until the puckered material is essentially flat, at which point the elastomer stretching ceases.
Another approach is to stretch the elastomeric film, then bond the fabric to the film while the film is stretched. Again, the fabric is bonded to the film at specified points or lines rather than continually across the surface of the film. When the stretched film is allowed to relax, the fabric corrugates or puckers over the unstretched elastomeric film.
Another approach is to ‘neck’ the fabric prior to bonding it to the elastomer. Necking is a process by which the fabric is pulled in one direction, which causes the fibers in the fabric to slide closer together, and the width of the fabric in the direction perpendicular to the pulling direction is reduced. Necking is very effective with knitted and nonwoven fabrics, although it is less effective with woven fabrics. If the necked fabric is point-bonded to an elastomeric film, the resulting laminate will stretch somewhat in a direction perpendicular to the direction in which the fabric was pulled during the necking process, because the fibers of the necked fabric can slide away from one another as the laminate stretches.
Yet another approach is to activate the elastomeric laminate once it has been formed. Activation is a process by which the elastomeric laminate is rendered easy to stretch. Most often, activation is a physical treatment, modification or deformation of the elastomeric laminate, said activation being performed by mechanical means. For example, the elastomeric laminate may be incrementally stretched by using intermeshing rollers, as discussed in U.S. Pat. No. 5,422,172, to render the laminate stretchable and recoverable. However, the mechanical activation process can weaken or tear the underlying film, fabric, or the laminate as a whole, which creates a risk of the laminate tearing and failing while the material is in use. Laminates that undergo post-lamination mechanical activation are often made of heavier-gauge materials in order to correct for potential failures due to the laminate being damaged during mechanical activation.
Some of these methods are limited by the need for complicated manufacturing techniques. For instance, corrugating or gathering a fabric layer prior to bonding the fabric to the elastomeric film requires machinery to gather and hold the fabric prior to bonding. In addition, an excess amount of fabric must be used relative to the amount of elastomeric film, since there must be extra fabric to corrugate or pucker over the unstretched film. Stretching the elastomeric film or necking the fabric prior to bonding the stretched or necked layer to the unstretched layer also requires additional machinery to pre-stretch or pre-neck one layer, then hold that layer in a stretched or necked condition. These processes are slow ways to manufacturing elastomeric materials. Mechanically activating an already-formed elastomeric laminate is much faster, but still requires additional capital for mechanical activation machinery to manipulate the laminate in order to activate it.
There remains a need to effectively manufacture a laminate of an elastomeric film and fabric that is stretchable without complicated processing methods or capital-intensive mechanical activation techniques. Such a laminate should be easy, inexpensive, and fast to manufacture, without using excessive amounts of material.
In one embodiment, the present invention is directed to a laminate of an elastomeric film and one or more layers of fabric, said laminate being stretchable and recoverable without mechanical activation. By controlling the elastomeric film composition, the type of fabric used in the laminate, and the bond strength between the film and fabric layers, an elastomeric laminate that does not require excessive material can be made using high-speed machinery without requiring mechanical activation to make the laminate stretchable. In other embodiments of the present invention, methods of making such elastomeric laminates requiring no mechanical activation are given.
Other embodiments of the invention will be apparent in view of the following detailed description of the invention.
The invention will be more fully understood in view of the drawings, in which:
a-1d illustrate several possible structures for the inventive multilayer elastomeric laminate;
The inventors have discovered that, by careful selection of the elastomeric film composition, the physical properties of the laminated fabric, and the bonding conditions and bond strength of the resulting elastomeric laminate, stretchable and recoverable laminates of elastomeric film and one or more layers of fabric can be manufactured that do not require that one or more layers of the laminate be gathered or stretched prior to lamination. The elastomeric laminate of the present invention also does not require mechanical activation after it is formed in order to be stretchable and recoverable. The inventive elastomeric laminate and methods of making such elastomeric laminate are disclosed herein.
For the purpose of this disclosure, the following terms are defined:
The elastomeric polymers used in the polymer film layer of the elastomeric laminates and methods of this invention may comprise any extrudable elastomeric polymer resin. Examples of such elastomeric polymer resins include block copolymers of vinyl arylene and conjugated diene monomers, natural rubbers, polyurethane rubbers, polyester rubbers, elastomeric polyolefins and polyolefin blends, elastomeric polyamides, or the like. The elastomeric film may also comprise a blend of two or more elastomeric polymers of the types previously described. For instance, one useful group of elastomeric polymers are the block copolymers of vinyl arylene and conjugated diene monomers, such as AB, ABA, ABC, or ABCA block copolymers where the A segments comprise arylenes such as polystyrene and the B and C segments comprise dienes such as butadiene, isoprene, or ethylene butadiene. Suitable block copolymer resins are readily available from KRATON® Polymers of Houston, Tex. or Dexco™ Polymers LP of Planquemine, La. Another useful group of elastomeric polymers are polyolefinic elastomers (POEs) which are elastomeric copolymers of polyethylene or polypropylene. Suitable POEs are available from The Dow Chemical Company of Midland, Mich. or ExxonMobil Chemical Company of Houston, Tex.
The elastomeric film of the present invention comprise greater than or equal to about 50% of one or more elastomeric resins in the film composition. The use of POEs is particularly preferred, because the elastomeric film will have a greater affinity for a polyolefinic fabric in the laminate. The elastomeric film of the present invention may comprise other components to modify the film properties, aid in the processing of the film, or modify the appearance of the film. For example, polymers such as polystyrene homopolymer or high-impact polystyrene may be blended with the elastomeric polymer in the film in order to stiffen the film and improve the strength properties. Low-molecular-weight polyolefins or mineral oil may be added to the elastomeric film to reduce the elastic modulus and improve the stretchability of the film. Viscosity-reducing polymers and plasticizers may be added as processing aids. Other additives such as pigments, dyes, antioxidants, antistatic agents, slip agents, foaming agents, heat and/or light stabilizers, and inorganic and/or organic fillers may be added.
The basis weight of the elastomeric film in the nonactivated elastomeric laminate must be controlled. It has been found that the elastomeric film should have a basis weight less than about 70 gsm, more preferably less than about 50 gsm, more preferably less than about 30 gsm. A lower basis-weight film allows the extruded polymer film to cool and solidify more rapidly, which gives the manufacturer more control over the strength of the bond between the elastomeric film and the fabric layers in the laminate. A lower basis-weight film also has the distinct advantage of being less expensive to manufacture. Because the inventive laminate is not activated after lamination, however, the resulting nonactivated elastomeric laminate is as strong and resists tearing as well as heavier elastomeric laminates that require mechanical activation.
The nonactivated elastomeric laminate also includes a substrate layer which is laminated to the elastomeric film by known lamination means. The substrate layer may be an extensible sheet-like material, such as another polymer film or a fabric. The substrate layer must comprise extensible materials, such that the substrate layer has a tensile strain at break of more than about 100%. However, the substrate material must not have a strong internal bond, such that the substrate material has a tensile stress at break of about 4 N/inch or less.
In one embodiment, the substrate layer is a nonwoven fabric. Examples of suitable nonwoven fabrics include spunbond, carded, meltblown, and spunlaced nonwoven webs. For the present invention, carded nonwovens are particularly preferred. These fabrics may comprise fibers of polyolefins such as polypropylene or polyethylene, polyesters, polyamides, polyurethanes, elastomers, rayon, cellulose, copolymers thereof, or blends thereof or mixtures thereof. The nonwoven fabrics may also comprise fibers that are homogenous structures or comprise bicomponent structures such as sheath/core, side-by-side, islands-in-the-sea, and other known bicomponent configurations. For a detailed description of nonwovens, see “Nonwoven Fabric Primer and Reference Sampler” by E. A. Vaughn, Association of the Nonwoven Fabrics Industry, 3d Edition (1992). Such nonwoven fabrics typically have a weight of about 5 grams per square meter (gsm) to 75 gsm. In a preferred embodiment, the nonwoven fabric should have a basis weight of about 5 to 30 gsm.
The inventive nonactivated elastomeric laminate may also comprise two or more such substrate layers, as described above. Also, within the scope of this invention are other types of substrate layers, such as woven fabrics, knitted fabrics, scrims, netting, etc. However, because of cost, availability, and ease of processing, nonwoven fabrics are usually preferred for the inventive nonactivated elastomeric laminates.
Controlling the bond strength between the elastomeric film and the fabric layers of the nonactivated elastomeric laminate is an important aspect of the present invention. Bond strength is typically measured by a method such as ASTM D-1876. The inventors have discovered that the bond between the elastomeric film layer and the fabric layer of the elastomeric laminate should be equal to or less than about 50 N/in to achieve the inventive nonactivated elastomeric laminate. In another embodiment, the bond between the elastomeric film layer and the fabric layer should be no more than about 40 N/in. In yet another embodiment, the bond between the elastomeric film layer and the fabric layer should be not more than about 25 N/in. Bond strength between the layers can be achieved by a number of ways, depending on the lamination method. If the layers are laminated by an adhesive method, the choice of adhesive and the amount of adhesive applied to bond the layers can be adjusted to achieve the desired bond strength. If the layers are laminated by an extrusion lamination process, the temperature of the extruded molten elastomeric web can be controlled to optimize the bond strength. The temperature of the extruded molten web can be controlled by a cooling device such as the device described in U.S. Pat. No. 6,740,184 and U.S. Pat. No. 6,951,591.
Any film-forming process can prepare the elastomeric film of the present invention. Known film-forming processes include cast extrusion and blown-film extrusion. In a specific embodiment, a coextrusion process, such as cast coextrusion or blown-film coextrusion, is used to form the elastomeric film. Coextrusion of multilayer films by cast or blown processes are well known.
The elastomeric film must be bonded to one or more nonwoven fabric layers to form the inventive elastomeric laminate. There are many known bonding methods that may be used to bond the elastomeric polymer film layer to the fabric layer(s). Such methods include extrusion lamination, vacuum lamination, adhesive bonding, thermal bonding, ultrasonic bonding, calender bonding, point bonding, and laser bonding. Combinations of bonding methods are also within the scope of the present invention.
One method of forming the inventive elastomeric laminate is adhesive bonding, illustrated in
In another embodiment, an extrusion lamination process is used to form the nonactivated elastomeric laminate. Such extrusion lamination processes are well known.
It is to be understood that additional processing steps such as aperturing the elastomeric laminate, printing the laminate, slitting the laminate, laminating additional layers to the laminate, and other such processes may be added to the inventive process and are within the scope of this invention.
The following example is presented to illustrate one embodiment of the present invention. This example is not intended to limit the invention in any way.
An elastomeric laminate of the present invention was prepared by extrusion laminating an elastomeric film layer between two nonwoven fabric layers. The elastomeric film comprised about 95% VISTAMAXX® polyolefinic elastomer from ExxonMobil Chemical Company, about 4% white masterbatch compound from Shulman Company, and about 1% process aid from Lehmann & Voss. The elastomeric film was extruded to form a film basis weight of about 40 gsm. The nonwoven fabric layers comprised carded polypropylene nonwoven at a basis weight of 24 gsm per layer. This nonwoven fabric had an internal bond of about 3.6 N/in. The extrusion laminated elastomeric laminate was not mechanically activated in any way. No pinholes or tears were observed in the resulting laminate. This laminate could easily be manually stretched to about 150% or more of its original width by adults of normal strength, and the laminate did not develop pinholes, tears, or other damage after being repeated stretched by hand.
This application claims priority under 35 U.S.C. §119 of U.S. Application Ser. No. 60/886,567 filed Jan. 25, 2007.
Number | Date | Country | |
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60886567 | Jan 2007 | US |
Number | Date | Country | |
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Parent | 13165239 | Jun 2011 | US |
Child | 13485217 | US | |
Parent | 12019835 | Jan 2008 | US |
Child | 13165239 | US |