Stock material or miscellaneous articles – Hollow or container type article – Polymer or resin containing
Reexamination Certificate
2001-12-21
2004-03-30
Chen, Vivian (Department: 1773)
Stock material or miscellaneous articles
Hollow or container type article
Polymer or resin containing
C428S034200, C428S034300, C428S035700, C428S036900, C428S480000, C428S481000, C428S483000, C428S332000, C428S339000, C428S475500, C428S500000, C428S507000, C428S511000, C428S514000, C428S522000, C428S532000, C428S533000, C428S537500, C442S394000, C442S395000, C442S396000, C442S398000
Reexamination Certificate
active
06713140
ABSTRACT:
BACKGROUND
For numerous applications it is desired to contain and/or temporarily prevent passage of aqueous waste or other aqueous materials and at some later time dispose of the barrier material in a clean and environmentally friendly manner. To be effective, the material used to temporarily prevent passage must provide a barrier to leakage and at the appropriate time desirably break up into components that facilitate suitable disposal while minimizing adverse effects on the environment. Uses for such latently separable barrier materials include bags or other containers for biological waste, agricultural mats of various kinds, and disposable items like single use beverage containers and the like. Prior attempts to provide such materials have included laminates of film barriers with water sensitive layers of, for example, polyvinyl alcohol. In use, the barrier contacts the liquid contents and prevents passage until the water sensitive layer is exposed to an aqueous environment. At that point the water sensitive layer dissolves, breaks up or otherwise separates to facilitate disposal. Disposal by flushing in conventional toilets is possible with some of these combinations. Difficulties have been identified with these prior materials because many water sensitive materials like polyvinyl alcohol become dimensionally unstable when exposed to conditions of moderate to high humidity and tend to weaken or stretch. In use as a container, for example, the material can stretch out of shape and/or weaken to the point of rupture. Attempts to add stability by increasing the barrier film thickness, for example, add unacceptable cost and/or increase the issues to be addressed upon disposal. The thicker films have a greater tendency to remain intact on flushing, for example, and clog toilets or downstream systems. The need continues, therefore, for a temporary barrier, latently dispersible material that is stable under use conditions but also easily disposable under aqueous conditions as by flushing, for example. The present invention addresses this and similar needs.
SUMMARY OF THE INVENTION
The present invention includes a latently dispersible barrier composite using a low strength barrier layer of water insoluble composition combined with a water sensitive, low strength carrier and on the opposing side of the carrier an inextensible, dispersible support layer. The layers are bonded and provide a barrier to aqueous liquid contact from one side but the combination disperses when contacted by aqueous liquid from the other side. In use as a container, cover, or the like, convenient and environmentally sensitive disposal may be achieved. Examples of barrier layers include films or fine fibers of very lightweight construction using polymers such as polylactic acid or polycaprolactone. Examples of water sensitive carrier webs include films of polyvinyl alcohol with or without other components. Examples of inextensible support materials include higher modulus or low stretch toilet tissue grades.
Where all component layers are biodegradable and/or dispersible, disposal is facilitated. For many applications it will be desirable to maintain component layers as light or low basis weight as is compatible with the intended use. In particular, the barrier layer may not be readily dispersible if it is of increased thickness. Cost will provide an incentive to reduce the weight of the component layers, particularly for single use applications. Many such applications will use a barrier layer of polylactic acid having a thickness in the range of from about 0.5 to about 2.0 microns, polyvinyl alcohol film carrier layer having a thickness in the range of from about 10 to about 50 microns, and a tissue support layer in the range of from about 10 to about 30 gsm, for example. As a result the composite will desirably have a hydrohead property of at least about 15 mbar, for some applications at least about 25 mbar, for more demanding applications at least about 50 mbar, and in some cases at least about 75 mbar. Bonding of the layers may be by a variety of means that preserve desired properties, including thermal (such as coextrusion or extrusion coating, for example) and adhesive, pattern and smooth bonding means.
DEFINITIONS
As used herein unless the context requires a different meaning, the following terms have the meanings set forth below:
As used herein and in the claims, the term “comprising” is inclusive or open-ended and does not exclude additional unrecited elements, compositional components, or method steps.
As used herein the term “nonwoven fabric or web” means a web having a structure of individual fibers or threads which are interlaid, but not in an identifiable manner as in a knitted fabric. Nonwoven fabrics or webs have been formed from many processes such as for example, meltblowing processes, spunbonding processes, and bonded carded web processes. The basis weight of nonwoven fabrics is usually expressed in ounces of material per square yard (osy) or grams per square meter (gsm) and the fiber diameters useful are usually expressed in microns. (Note that to convert from osy to gsm, multiply osy by 33.91).
As used herein the term “meltblown fibers” means fibers formed by extruding a molten thermoplastic material through a plurality of fine, usually circular, die capillaries as molten threads or filaments into converging high velocity, usually hot, gas (e.g. air) streams which attenuate the filaments of molten thermoplastic material to reduce their diameter, which may be to microfiber diameter. Thereafter, the meltblown fibers are carried by the high velocity gas stream and are deposited on a collecting surface to form a web of randomly dispersed meltblown fibers. Such a process is disclosed, for example, in U.S. Pat. No. 3,849,241 to Butin et al. Meltblown fibers are microfibers that may be continuous or discontinuous, are generally smaller than 10 microns in average diameter, and are generally tacky when deposited onto a collecting surface.
“Bonded carded web” refers to webs made from staple fibers which are sent through a combing or carding unit, which breaks apart and aligns the staple fibers in the machine direction to form a generally machine direction-oriented fibrous nonwoven web. Such fibers are usually purchased in bales that are placed in a picker that separates the fibers prior to the carding unit. Once the web is formed, it then is bonded by one or more of several known bonding methods. One such bonding method is powder bonding, wherein a powdered adhesive is distributed through the web and then activated, usually by heating the web and adhesive with hot air. Another suitable bonding method is pattern bonding, wherein heated calender rolls or ultrasonic bonding equipment are used to bond the fibers together, usually in a localized bond pattern, though the web can be bonded across its entire surface if so desired. Another suitable and well-known bonding method, particularly when using bicomponent staple fibers, is through-air bonding.
“Airlaying” is a well-known process by which a fibrous nonwoven layer can be formed. In the airlaying process, bundles of small fibers having typical lengths ranging from about 6 to about 19 millimeters (mm) are separated and entrained in an air supply and then deposited onto a forming screen, usually with the assistance of a vacuum supply. The randomly deposited fibers then are bonded to one another using, for example, hot air or a spray adhesive. Examples of airlaying technology can be found in U.S. Pat. Nos. 4,494,278, 5,527,171, 3,375,448 and 4,640,810.
As used herein, through-air bonding or “TAB” means a process of bonding a nonwoven web containing adhesive polymeric component fibers, particles or the like in which air sufficiently hot to melt one of the polymers of which the fibers or particles of the web are made is forced through the web. The air velocity often is between 100 and 500 feet per minute and the dwell time may be as long as 6 seconds. The melting and resolidification of the polymer provides the bonding. Through air bonding has relatively r
McCormack Ann Louise
Shick Richard Lee
Chen Vivian
Herrick William D.
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