LAMINATE HAVING IMPROVED BARRIER
This application is a continuation-in-part of U.S. patent application Ser. No. 08/929,432 filed Sep. 15, 1997 now U.S. Pat. No. 5,997,981 entitled "Breathable Barrier Composite Useful as an Ideal Loop Fastener Component", now U.S. Pat. No. 5,997,981, which is incorporated herein in its entirety by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention is directed to laminates that have clothlike attributes and that act as barriers to passage of liquids and have improved resistance to viral passage. There are numerous uses for such laminates including disposable and limited use apparel such as surgeon's gowns and industrial workwear. Other applications include components of personal care products like disposable diapers, training pants, incontinence wear and feminine hygiene products. Barrier needs vary for such products, but are critical for medical products such as surgical drapes and gowns, for example. Film components can provide absolute barrier properties but are often uncomfortable and lack the ability to pass moisture vapor, i.e. breathe, while conventional nonwovens do not provide adequate protection for many applications. Laminates of breathable, lightweight films with nonwovens can meet the needs of many applications but, when bonded conventionally, compromise barrier protection for the most demanding medical applications. The field includes laminates having improved barrier properties especially adapted for such medical and other uses where improved barrier is especially important.
The art is replete with references to laminates of films and nonwovens for medical and other applications. For example, coassigned U.S. Pat. No. 4,379,192 to Wahlquist and Shultz describes such laminates formed by a patterned application of heat and pressure to combined layers of a melfblown nonwoven and a polymeric film. The laminate is both an absorbent and an impervious barrier for medical applications. It is also known, for example, as taught in coassigned U.S. Pat. No. 5,695,868 to McCormack, to form laminates including breathable films for use as backing components of, e.g. disposable diapers. Particularly for medical applications demanding a high barrier level to viral penetration, it remains desired to provide a breathable material having improved barrier properties at a cost consistent with disposability and single use applications.
SUMMARY OF THE INVENTION
The present invention is directed to a laminate of a pattern prebonded nonwoven and a film as well as to the process for making such a laminate and applications for the laminate as a high barrier material that can have breathable, clothlike attributes. In accordance with the invention, the film preferentially bonds to the nonwoven in the pattern prebond areas and bonding can be achieved without deleteriously affecting the integrity of the film in the bond areas. In a preferred aspect for medical applications, the film is thin and microporous while maintaining the desired barrier levels to viral penetration. Bonding may be achieved thermally by smooth calendering without requiring added adhesive wherein the smooth roll bonding will generally maintain substantially uniform film thickness in the laminate. Advantageous embodiments include polyolefin spunbonded non
wovens bonded to a coextruded film of mLLDPE (metallocene or "single site" catalyzed polyethylene) or conventional LLDPE (linear low density polyethylene) using a bonding layer containing an amorphous polymer (for
5 example, less than 30% crystallinity) of a "single site" (or metallocene) catalyzed LLDPE and/or other amorphous polymer(s) in face-to-face contact with the spunbond nonwoven. The amorphous bonding layer may, and for most applications will, include up to 75%, frequently between about 45% to about 70% of a filler as described in more detail below. The polymer component of the bonding layer may also include a crystalline component, frequently in the amount of from about 45% to 75%, and may also include other polymers for reduced cost or to impart desired properties or improve processing so long as such additional
15 components do not result in a laminate peel strength, as described below, of less than about 25 grams, desirably not less than about 45 grams. The nonwoven layer contains a bond pattern of either uniform or nonuniform bond impressions that result in an unbonded area of at least about 80%
20 taken over any 100 cm square of nonwoven surface. In addition, the bond frequency provides a pattern density in the range of from about 100 to about 600 bonds/in.2, advantageously about 200 to about 500 bonds/in2. The film layer is either a multilayer or coextruded structure with an
25 exposed layer of a soft, amorphous polymer as previously described, or a monolayer that is amorphous as described, having adhesive properties and, in either case, can be a microporous liquid barrier that is conformable and compatible with the nonwoven component. To enhance clothlike
3Q aesthetics, a retracted laminate can be formed by stretching the film prior to lamination to the nonwoven and subsequently allowing the laminate to relax or retract producing a textured surface of unbonded inter-bond filaments or fibers between bond areas where the film and nonwoven remain
35 securely attached. The invention also includes the method for making the laminate which desirably is carried out as an inline process to avoid the need to store rolls of the amorphous-layer film.
As used herein the following terms have the specified meanings unless the context demands a different meaning or a different meaning is expressed; also, the singular generally includes the plural, and the plural generally includes the
45 singular unless otherwise indicated.
"Nonwoven" means a web of fibers or filaments that is formed by means other than knitting or weaving and that contains bonds between some or all of the fibers or filaments; such bonds may be formed, for example, by thermal,
50 adhesive or mechanical means such as entanglement.
"Fiber" means an elongated strand of defined length, such as staple fibers formed by cutting a continuous strand into lengths of, for example, 2 to 5 cm. Collections of fibers may have the same or different lengths.
55 "Filament" means a generally continuous strand that has a very large ratio of length to diameter, for example, 1000 or more.
"Spunbond" means a nonwoven of filaments formed by melt extrusion of a polymer into strands that are quenched
60 and drawn, usually by high velocity air, to strengthen the filaments which are collected on a forming surface and bonded, often by the patterned application of heat and pressure. Spunbonded processes are described, for example, in the following patents to which reference may be made for
65 additional details: U.S. Pat. No. 4,340,563 to Appel et al, U.S. Pat. No. 3,802,817 to Matsuki et al., and U.S. Pat. No. 3,692,618 to Dorschner et al.