Respirator and filter cartridge

Details Respirator and filter cartridge Respirator and filter cartridge

1995-01-20

2001-08-21

Spitzer, Robert H. (Department: 1724)

Gas separation: apparatus

Solid sorbent apparatus

Plural diverse separating means

C096S153000, C055SDIG003, C128S206120, C128S206170, C128S206280

Reexamination Certificate

active

06277178

ABSTRACT:

TECHNICAL FIELD
This invention pertains to respirators and filter cartridges that protect against gases or vapors and that have a bonded sorbent filter element, a sleeve that houses the filter element, and a folded edge of the sleeve retaining the filter element in position.
BACKGROUND OF THE INVENTION
Sorbent particles such as activated carbon are commonly used in respirators as gas or vapor filters. The filters generally are classified according to the manner in which the sorbent material is supported in the filter and include packed bed filters, loaded nonwoven filters, loaded foam filters, and bonded sorbent filters.
In packed bed filters, the sorbent particles are constrained in a container by compressive forces imposed on and transmitted through the particle bed by rigid grids and screens that cover the inlet and outlet areas. Virtually all packed bed filters are cylindrical, have constant thickness or bed depth, and have a planar inlet and outlet. To fill the cartridge, the adsorbent particles typically are poured through screens that scatter the particles as they fall, creating a level bed packed substantially to maximum density. The compressive forces from the constraining grids and screens restrain particle movement to minimize flow channeling through the packed bed.
An example of a packed bed filter is shown in U.S. Pat. No. 4,543,112. This patent discloses a sorbent filter assembly made by sequentially placing a first resilient perforated plate, a first retention filter, a sorbent bed, a second retention filter, a second resilient perforated plate, and a cover within the cylindrical portion of a canister shell. The cover is forced downwardly to compress the sorbent bed and to resiliently spring bias or stress the first resilient perforated plate. While the parts are held together under compression, an annular edge portion of the cylindrical shell is rolled into a circumferentially extending groove on the canister cover to hermetically seal and mechanically hold the parts together in their assembled and compressed relationship.
The necessity for this number of parts and processing steps introduces complexity as well as weight, bulk, and cost. A further problem is experienced when a packed bed respirator is combined in series with a particulate filter for use in environments containing particulates as well as vapor hazards such as in paint spray applications. In this situation, the retaining grids and screens create nonuniform airflow pathways within the particulate filter resulting in reduced utilization of the filter media and increased pressure drop therethrough.
Loaded nonwoven webs have been disclosed that contain sorbent particles in the interstices between the fibers forming the web. An example is shown in U.S. Pat. No. 3,971,373. Loaded foams also have been disclosed that contain adsorbent particles dispersed within and bonded in the foam structure. U.S. Pat. No. 4,046,939 describes a carbon impregnated foam for protective clothing against noxious chemicals. Both loaded nonwoven webs and loaded foam structures must be edge sealed to the respirator component to prevent unfiltered air from bypassing the filter. Known sealing means include adhesives, such as disclosed in U.S. Pat. No. 5,063,926, and gaskets or sealing rings, such as disclosed in U.S. Pat. No. 5,222,488. Loaded structures generally suffer from having a lower sorbent particle density than the packed beds.
A significant advance over the packed beds technology and loaded webs and foams was the invention of bonded sorbents. In bonded sorbent technology, the sorbent particles are molded into a unitary structure using polymer particles that bind the sorbent particles together. Bonded sorbent structures eliminate the need for additional supporting structures, as are necessary in packed beds. An example of a bonded sorbent structure is disclosed in U.S. Pat. No. 5,033,465. Bonded sorbent structures have been sealed to the respirator using an adhesive—see, for example, U.S. Pat. No. 5,078,132; or by injection molding—see, for example, U.S. Pat. No. 4,790,306. The filter elements in these respirators are not able to be readily replaced, and thus when the filter's service life has met its limit, the respirator is discarded as waste.
SUMMARY OF THE INVENTION
The present invention provides a new filter cartridge and a new respirator that overcome some of the disadvantages of known respirators and filter cartridges.
Briefly, the filter cartridge of the invention comprises:
(a) a housing that includes a sleeve that has an inner surface and has a folded edge extending from the sleeve; and
(b) a filter element that includes a bonded sorbent filter element, the filter element being pressed against the sleeve's inner surface to form an interference therewith and is held in the sleeve by the folded edge. The respirator of the invention, in brief summary, comprises a respirator face piece and the filter cartridge summarized above.
The filter cartridge and respirator of the invention have a bonded sorbent filter element, a sleeve housing the filter element, and a folded edge of the sleeve retaining the filter element in position. The interface between the bonded sorbent filter element and the housing sleeve prevents channeling (that is, passage of unfiltered air around the filter element) by having the filter element compressed at the interface with the sleeve. When air passes through the filter element in channels, it avoids contact with the sorbent particles, causing a premature break-through of contaminants. The sleeve may be provided with an annular groove of decreased wall thickness that defines a fold line for forming a folded edge. When the sleeve is folded radially inward at the fold line, the resulting folded edge holds the filter element in position in the sleeve. Optionally, a particulate filter may be juxtaposed against the bonded sorbent filter element before the sleeve is folded.
Filter cartridges and respirators of this invention contain few components and can be assembled with relatively few manufacturing steps. The sleeve, which can be easily and inexpensively injection molded in essentially a single step, can provide a housing for the filter element, a sealing means for ensuring that all inhaled air passes through the filter element, and a retaining means for securing the filter element to the housing. The result is a filter cartridge and a respirator that are relatively light in weight, possess minimal parts, and are relatively easy to manufacture.
These and other advantages of the invention are more fully shown and described in the drawings and detailed description of this invention, where like reference numerals are used to represent similar parts. It is to be understood, however, that the drawings and description are for the purposes of illustration only and should not be read in a manner that would unduly limit the scope of this invention.


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