Gas separation: apparatus – Solid sorbent apparatus – Layered or laminated
Reexamination Certificate
2000-07-17
2001-10-16
Smith, Duane S. (Department: 1724)
Gas separation: apparatus
Solid sorbent apparatus
Layered or laminated
C055S524000, C055SDIG005
Reexamination Certificate
active
06302946
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an air filter for residential or industrial use, which has the ability to substantially reduce odors in the airstream passing therethrough.
Air filters for residential or industrial use are commonly fabricated by forming a filtering media which is composed of a non-woven web of randomly arranged fibers which are held together at their crossing points by a cured latex or other suitable binder which is applied to the web by spraying, bath, roller, etc. The binder may also incorporate a coloring agent, a fire retardant, and other components, as may be desired.
It has previously been proposed to apply carbon (or charcoal) particles to the filtering media for the purpose of adding an odor removing capability to the media. In one such process, carbon particles are sprinkled onto the media which has been coated with a tacky adhesive, so that the particles are anchored to the fibers of the media when the adhesive dries. While such carbon impregnated filters are reasonably effective in removing odors from gases having an inorganic source, such as gasoline or toluene, they are not particularly effective in removing odors from gases having an organic source, such as cooking or other household odors.
Sodium bicarbonate is recognized for its ability to remove odors from gases having an organic source, but prior attempts to add sodium bicarbonate to an air filtering media have not been totally satisfactory. For example, in one previously proposed process, powdered sodium bicarbonate is first suspended in an aqueous solution which includes a suitable binder, and the solution is then sprayed onto the surface of the previously formed filter media. However, as far as the applicants are aware, this proposal has not been commercially successful since the odor removing component is deposited only on the surface of the non-woven web, and its ability to effectively remove odors is thus diminished. The spraying process also is inefficient, since the powdered sodium bicarbonate remains is suspension and does not dissolve, and it tends to rapidly clog the nozzles.
As opposed to spraying a solution containing sodium bicarbonate onto the surface of the filter media, it has also been proposed to add the sodium bicarbonate to the binder which is applied to the web as part of the initial fabrication of the media. However, this proposal has also proven to be unworkable, since the sodium bicarbonate is alkaline and it changes the pH of the binder solution toward the base side. Apparently, the resulting raising of the pH in turn significantly limits the ability of the binder to cure and set up, and the resulting media does not possess sufficient integrity to serve its intended function.
It is accordingly an object of the present invention to provide a method of fabricating a filtering media composed of a web of non-woven fibers, which is able to effectively remove household and other odors from the airstream passing therethrough.
It is a more particular object of the invention to provide a method of the described type and wherein the ability of the binder to cure and set up, and thereby anchor the crossing points of the fibers, is not diminished by the addition of an alkaline odor removing component such as sodium bicarbonate, to the binder.
It is still another object of the invention to provide an air filtering media composed of a web of non-woven fibers, which has discrete particles of an alkaline odor removing component dispersed through the entire thickness of the web, so as to permit a highly effective removal of odors passing through the media.
SUMMARY OF THE INVENTION
The above and other objects and advantages of the present invention are achieved by the discovery that when the deodorizing component, and particularly a particulate sodium bicarbonate, is added to an aqueous solution containing a conventional binder, such as a vinyl acrylic copolymer, in a relatively low solids concentration, the binder is not degraded by the raising of the pH and it is able to effectively cure and anchor the sodium bicarbonate particles to the fibers of the web. This finding permits the solution to be added to the media by a post treatment process as described herein. The post treatment process of the invention also achieves a complete dispersal of the deodorizing component throughout the thickness of the web.
More particularly, the method of the present invention includes the steps of forming an air permeable web of randomly arranged fibers, and then saturating the web with a first aqueous solution which includes a binder in a relatively high solids concentration. The web is then dried so as to at least substantially cure the binder and anchor the crossing points of the fibers in the web.
The dried web, which is substantially self-sustaining, is then saturated with a second aqueous solution which includes a binder in a relatively low solids concentration, together with a particulate deodorizing compound, such as sodium bicarbonate, suspended therein in an amount which is sufficient to impart odor removing properties in the completed air filter media. The web is then again dried to at least substantially cure the binder added with the second solution to thereby anchor the particulate deodorizing component to the fibers of the web.
The process as described above can be conducted as a batch process, wherein the web resulting from the initial saturation and drying steps is wound into a roll for shipment or storage, and then later unwound to conduct the second saturation and drying steps. The process can also be conducted continuously, wherein the web advances to the second saturation step immediately after the first drying step.
Preferably, each of the saturating steps includes passing the web through the nip of a pair of rollers, so as to force the solution into the interior of the web from both sides. Complete dispersal of the particles of the deodorizing component throughout the thickness of the web can thereby be achieved.
It is also preferred to add a foaming agent to each of the solutions, and foaming the solution prior to application of the solution to the web.
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Cronia Forrest E.
Montgomery Kenneth Dale
Alston & Bird LLP
Flanders Corporation
Smith Duane S.
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