Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2000-10-06
2004-02-17
Ball, Michael W. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S242000, C156S244170, C156S245000, C156S272200, C264S257000, C604S366000, C604S374000, C604S385010
Reexamination Certificate
active
06692603
ABSTRACT:
SUMMARY OF THE INVENTION
It has been discovered that airlaid webs comprising heat-sensitive binder material (thermoplastic or thermally curable) can be molded into useful, three-dimensional shapes providing improved body fit and flow control by means of an online process in which a flat airlaid web comprising binder material is held against a molding substrate after or during application of energy to the web, causing the web to conform to the molding substrate and form bonds that lock the web into the shape of the molding substrate. The web can be held against the molding substrate by pneumatic forces, tension in the web itself, tension applied by a belt or wire, restraining forces from a backing surface such as a second surface that conforms to the molding substrate, and the like. The molding substrate can be metal (e.g., aluminum, steel, copper, brass, titanium, and the like), glass, ceramic, plastic, a composite material, and the like, and can be gas permeable or impermeable.
The methods of the present invention can enable production at industrial speeds of molded absorbent structures shaped to provide both body fit and flow control in absorbent articles.
Molded airlaid structures within the scope of the present invention include those having slotted vertical gaps that offer an entranceway for gushes of body fluids, as well as anatomically conforming shapes adapted to not only receive and direct flowing fluids, but to also guide the flexure of the article in use to better conform to the body. Articles according to the latter concept can, for example, have a central elongated hump, one or more longitudinal flow channels, and a plurality of transverse flexure zones (hereafter described) away from the central hump to cause the article to flex toward the body when compressed from the sides. Such articles can adapt to fit the body of the wearer during the dynamic conditions of use, thereby providing both comfort and leakage prevention.
The energy can be applied by microwave radiation, radiofrequency energy, or other electromagnetic radiation sources, as well as by heated air or by conduction with heated surfaces. When microwave energy is applied, the web can incorporate binder materials such as thermoplastic binder fibers or curable resins that are relatively sensitive to microwave radiation (compared to pure cellulose itself) by virtue of a high dipole moment. In one embodiment, microwave energy is applied to the moving web as it passes through an opening in a microwave resonance chamber, where microwave energy is focused into the web. In another embodiment, microwave energy is applied to the web through a rotating microwave horn terminating in a microwave-transparent window having a three-dimensional structure suitable for molding the web. The rotating horn moves with the web while the web is near or in contact with the horn. A wide variety of other embodiments are also within the scope of the present invention, as set forth hereafter.
Alternatively, the energy can be applied in the form of heated gas passing through the web, or by conduction from one or more heated molding surfaces, or by application of ultrasonic energy, infrared energy, and the like. The energy heats the binder material, promoting fusion of a portion of the binder material to join fibers in the airlaid in the case of a thermoplastic binder, or promoting curing in the case of thermosetting materials or heat-curable crosslinking agents. The resulting molded airlaid web can be cut into discrete sections suitable for incorporation into an absorbent article. The section of airlaid web can have any one or more of the following characteristics: a substantially uniform density, an apparent thickness at least 50% greater than the original thickness of the unmolded web, an Overall Surface Depth (hereafter defined) of at least 0.5 mm, a Surface Height of at least 1 mm, a wet compressed bulk at least 50% greater than that of the unmolded web, a longitudinally elongated central hump and one or more transverse flexure zones between the hump and one or more of the longitudinal ends of the section of the airlaid web, and one or more longitudinal flow channels formed by elevated structures on the section of the airlaid web.
As used herein, an “airlaid web” is a fibrous structure formed primarily by a process involving deposition of air-entrained fibers onto a mat, typically with binder fibers present, and typically followed by densification and thermal bonding. In addition to traditional thermally bonded airlaid structures (those formed with non-tacky binder material present and substantial thermally bonded), the scope of the term “airlaid” according to the present invention can also include coform, which is produced by combining air-entrained dry, dispersed cellulosic fibers with meltblown synthetic polymer fibers while the polymer fibers are still tacky. Further, an airformed web to which binder material is subsequently added can be considered within the scope of the term “airlaid” according to the present invention. Binder can be added to an airformed web in liquid form (e.g., an aqueous solution or a melt) by spray nozzles, direction injection or impregnation, vacuum drawing, foam impregnation, and so forth. Solid binder particles can also be added by mechanical or pneumatic means.
As used herein, an “airformed web” refers to a mat comprising cellulosic fibers such as those from fluff pulp that have been separated, such as by a hammermilling process, and then deposited on a porous surface without a substantial quantity of binder fibers present. Airfelt materials used as the absorbent core in many diapers, for example, are a typical example of an airformed material.
In one embodiment, the absorbent article of the present invention has an upper absorbent layer comprising a three-dimensional molded cellulosic airlaid web having a portion of water-resistant thermoplastic binder material therein. The molded airlaid web can have a substantially uniform basis weight and thickness prior to molding, but is molded to have a plurality of elevated regions offering a distinctive profile well suited for conforming to the body of the wearer. The molded web can also be adapted for providing significant void volume beneath the upper absorbent layer and preventing leakage to the sides of the article. In some embodiments, the molded airlaid web has a body-side surface topography comprising a central hump having an oval shape elongated in the longitudinal direction, and a plurality of molded flexure zones having a component extending in the transverse direction and disposed between the central hump and at least one longitudinal end of the molded airlaid web. The molded flexure zones assist in permitting an initially flat article to readily conform to the shape of the wearer's body along the longitudinal axis of the article.
In one embodiment, thermal molding is achieved as hot gas passes through the web in the region to be molded, causing the binder material to become activated (e.g., for thermoplastic material such as binder fibers to at least partially melt and bond cellulosic fibers together) to hold the web in the shape defined by the mold. Heat transfer may further be assisted by providing an oscillatory flow of heated gas with a reverse flow component, such as is found in the heated gases produced from pulsed combustion systems, wherein acoustic waves enhance the heat transfer of the gases. An exemplary system for providing oscillatory flow of heated gases suitable for the present invention is disclosed in U.S. Pat. No. 6,085,437, issued Jul. 1, 1998 to G. K. Stipp, herein incorporated by reference.
When shaping of the web comprises application of mechanical pressure from a solid surface, as opposed to pneumatic pressure, the web can be heated before the mechanical forces for shaping are fully applied in order reduce damage to the web and achieve higher strength and molding definition. Such preheating can be achieved with any known method, such as steam impregnation, heated air passing through the web, application of radiative
Bednarz Julie Marie
Chen Fung-jou
Lindsay Jeffrey Dean
Makoui Kambiz Bayat
Sun Tong
Ball Michael W.
Haran John T.
Kimberly--Clark Worldwide, Inc.
Pauley Petersen & Erickson
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