Fabric (woven – knitted – or nonwoven textile or cloth – etc.) – Scrim – Woven scrim
C442S035000, C442S046000, C442S049000, C442S149000, C442S150000, C442S328000, C428S131000, C428S134000, C428S136000, C428S137000, C428S192000, C428S194000
FIELD OF THE INVENTION
The invention relates to laminated structures that are useful in the construction of disposable articles, e.g. diapers, etc. In particular, the invention relates to a high strength, through-bonding technique that enhances the strength and durability of stretchable laminates.
BACKGROUND OF THE INVENTION
Many commercially available disposable articles include laminated components which are breathable and stretchable, for example absorbent articles like disposable diapers for infants and undergarments for incontinent adults use stretchable side panels. Many, if not most, of these disposable articles use layers of nonwoven material. Other products which use nonwoven laminates include bandages, body wraps, and the like.
Several types of nonwoven fabrics are known in the art. In general, nonwoven fabrics contain fibers of polyethylene, polypropylene, polyethylene terephalate, nylon, or rayon and are joined in any number of ways for example adhesives, thermal bonding, felting, or other methods known in the art. Thermally bonded nonwoven polypropylene is particularly prevalent in disposable articles. Thermally bonded nonwoven polypropylene is breathable and has a soft, cloth-like feel which is particularly suitable for these applications.
The assignee of this application has been involved in the development of various adhesives for use in nonwoven laminated structures, e.g. see copending U.S. patent application Ser. No. 08/632,117 entitled “Oil Resistant Polybutylene Based Hot Melt Adhesive” filed on Apr. 15, 1996 by Bonnie M. Harris and Monina Kanderski; and U.S. patent application Ser. No. 08/914,523 entitled “Hot Melt Adhesive Having a High Acid Number for Disposable Soft Goods”, filed on Aug. 9, 1997 by Mark D. Alper and Diane Strelow, both incorporated herein by reference. As discussed in the above incorporated patent applications, it is difficult to find adhesives that are effective for bonding nonwoven material to the elastomeric films or meshes which are desirable for use in nonwoven laminate structures. Some elastomeric films or mesh webs (e.g., oil resistant materials or materials embodying incompatible process aids) are simply difficult to laminate with nonwoven fabric. In addition, effective and durable bonding to elastomeric film or mesh is particularly difficult because of the mechanical stresses put on the bonds when the laminated structure is repeatedly stretched.
The following discussion regarding elastomeric films and meshes is added to provide a more complete explanation of some of the difficulties encountered when fabricating laminated structures with commercially available elastomeric films or meshes.
Commercially available elastomeric films and meshes are typically manufactured from A-B-A block copolymers such as styrene-butadiene-styrene (SBS), styrene-isoprene-styrene (SIS), styrene-ethylene/butylene-styrene, as well as other polyolefins such as, but not limited to, ethylene vinyl acetate (EVA), and low density polyethylene (LDPE). These elastomeric materials typically include about 20% to about 30%, by weight, of the elastomeric block copolymers, and about 20% to about 30%, by weight, of other polyolefins, or ethylene vinyl acetate. An example of these films and the specifics of their composition can be found in U.S. Pat. No. 4,476,180. Once these elastomeric webs are formulated and extruded, the webs can be very tacky. The tackiness makes it difficult to process the web on the extrusion line, and in subsequent converting equipment. To address problems associated with the tackiness of the elastomeric web, manufacturers of the elastomeric webs usually incorporate a relatively high amount of slip agent into their formulations. For example, fatty acid amides having the formula CH
are commonly used as slip agents. The letter R is a chain of repeating—CH
—units typically about 12 to 24 carbon atoms in length. The most commonly used fatty acid amide is Erucamide. It is commercially available under the trade name Kemamide B from the Humko-Sheffield Chemical Company. This particular slip agent has a carbon chain which is 22 units long, a molecular weight of about 337.6, and a capillary melting point of about 82° C.
The slip agents incorporated into the elastomeric films and meshes have caused significant problems for prior art hot melt adhesives which are commonly used in the production of nonwoven laminates. In particular, it is believed that the slip agents become mobile, under specific environmental circumstances, or are otherwise incompatible with the polymers used in the elastomeric films or meshes; and, these two factors combine to cause the slip agents to migrate to, or otherwise to become deposited on, or “bloom” to, the exterior surface of the film or mesh. The slip agents have a waxy nature, and they act as a lubricant once they bloom to the surface of the film or mesh. For the manufacturers of elastomeric film and meshes, this provides two valuable benefits. The first benefit is that the presence of the waxy layer on the exterior surface of the film or mesh helps prevent adjacent layers of film from adhering thereto (known in the industry as “blocking”) when it is placed into a roll form. The second benefit is that the waxy layer acts as a lubricant, thereby facilitating the use of the film when it is unwound, and later processed over rollers, guides, etc. during subsequent converting and/or processing.
While the slip agents referred to above facilitate and even enhance the use of these synthetic films and meshes in manufacturing, the slip agents which migrate to the exterior surface of the film or mesh appear to destroy, or substantially weaken bonds of prior art adhesives. The amount of slip agent present in the films currently in commercial production ranges from about 0.1% to 1%, by weight, although some films currently in production have as much as 4.5%, by weight. A further disclosure of the use of slip agents in films or meshes can be found in U.S. Pat. Nos. 4,476,180, 4,977,014 and 4,714,735, all of which are incorporated by reference herein.
In view of the difficulty surrounding the application of hot melt adhesives to elastomeric films and meshes, the industry has long sought a hot melt adhesive composition which would effectively bind these elastomeric films and meshes to breathable materials, such as nonwoven webs.
SUMMARY OF THE INVENTION
In contrast to prior attempts to develop improved adhesives, the invention involves the use of a high strength through-bonding fabrication technique for elastomeric laminates. In its preferred embodiment, the laminated structure includes two outer layers of nonwoven material and an inner elastomeric layer laminated between the outer nonwoven layers. The inner elastomeric layer is preferably a mesh, and in accordance with the invention, must provide openings therethrough so that a bonding side of the first nonwoven outer layer is exposed through the openings to a bonding side of the second nonwoven outer layer. An A important aspect of the invention involves the use of through-bond adhesive to directly bond the first and second outer layers of nonwoven material to each other through at least some of the openings in the inner layer. The direct bonds between the nonwoven layers that occur through the openings in the elastomeric mesh mechanically secure the elastomeric mesh within the trilaminate structure. In many applications, it may also be desirable to provide adhesive for bonding the outer nonwoven layers directly to the elastomeric mesh. It is the direct bond, however, between the nonwoven layers that occurs through the openings in the elastomeric mesh that is primarily responsible for enhancing the durability of the nonwoven trilaminate structure.
In some nonwoven/elastomeric mesh trilaminates or like structures, the nonwoven layers are not stretchable in the machine direction, but are spreadable in the cross direction. The elastomeric mesh allows the trilaminate to stretch in the cross direction when the trilaminate is stretched, and returns the trilaminate to the re
Carper James D.
Strelow Diane M.
Stuczynski Russell P.
Andrus Sceales Starke & Sawall LLP
Ato Findley Inc.
Cole Elizabeth M.
Ruddock Ula C.
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