Abstract:
A catalytic converter unit for pre-filtering dirt particles from a gas discharge containing an ozone-laden gas discharge from electrographic copy machines, in advance of the passage of the gas discharge through a gas-neutralizing catalyst bed, to exclude the passage of the dirt particles which can cause contamination and degradation of the catalyst, and plugging of the catalyst bed resulting in reduced gas-permeability and the creation of a significant pressure drop thereacross which interferes with or substantially reduces the rate of gas flow through the unit. The catalytic converter units incorporate an easily-removable, cleanable and/or replaceable dirt filter screen which is supported for simple removal from the unit for periodic cleaning or replacement.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to the well-known problem of generation of objectionable toxic or dangerous gases by equipment, particularly ozone gas generation by electrostatic imaging machines, and provides a convenient filter/catalytic converter unit which facilitates the simple cleaning or replacement of a dirt pre-filter element, as necessary, to protect the gas-neutralizing catalyst for the life of the machine. 
     As is well known, ozone gas is generated in electrostatographic copying equipment as a result of corona discharge during sensitization of the recording surface of the photosensitive member. This is also true of other stations within the copier which employ corona discharge devices. Ozone emissions into the surrounding machine environment are controlled by catalytic “filtering” devices capable of conversion of the ozone to relatively harmless substances and are located in the copier exhaust stream. These filters are generally characterized as fixed-bed devices; that is, the catalyst is impregnated into a porous substrate which is integrated within the copier exhaust housing or is incorporated into the corona discharge electrode structure itself. Each type of ozone control system described hereinabove is limited in its ability to neutralize the ozone due to the physical constraints placed upon the catalysts containing element. 
     As will be appreciated, the amount of exposure of the ozone laden vapors to the catalyst determines the capacity and efficiency of ozone neutralization by the catalyst-containing element. Where the catalyst is entrained within or coated upon a porous or fibrous support, ozone laden vapors must be capable of penetration of this structure for contact with the catalyst. This presents problems since ozone laden exhaust produced by electrostatic copiers also contains numerous “dirt” particulates or contaminants (e.g. toner, paper fragments, etc.) These particulates can pass with the ozone laden exhaust to the catalyst support and, after a relatively brief period, impregnate the support material thereby diminishing the porosity of the catalyst- containing element. As the porosity of the support decreases, so too does the amount of catalyst accessible to the ozone-laden vapors. This can require frequent replacement of the catalyst-containing element or some sacrifice in the completeness of exhaust treatment in order to extend catalytic activity of the “filtering” device. 
     These considerations also apply to the neutralizing of other objectionable, toxic and dangerous gases such as carbon monoxide, nitrogen oxides and similar gases by known catalyst beds whereby it is desirable to filter dirt contaminants from the discharge before it contacts the catalyst bed. 
     2. State of the Art 
     U.S. Pat. No. 4,143,118 discloses an electrographic apparatus incorporating a catalyst-impregnated filter screen associated with a corotron and heater element to achieve in-situ ozone pre-neutralization prior to the transmission of the exhaust gas to an ozone-neutralization unit having a granular catalyst bed filter. Back-flushing is required to remove entrapped particles from blocking the outlet end of the unit and creating a substantial pressure drop. 
     U.S. Pat. No. 4,315,837 discloses an electrographic apparatus incorporating a composite support matrix, such as glass beads, coated with ozone-neutralizing catalyst to form a filter element within the exhaust conduit of the apparatus. The catalyst matrix is held in place, at each end, by a foraminous member which permits passage of the exhaust gas and retention of the composite catalyst matrix without appreciable pressure drop thereacross. The foraminous member is in contact with the composite catalyst matrix, not easily separable therefrom for cleaning or replacement, and not indicated to be a dirt filter. 
     U.S. Pat. No. 4,388,274 discloses an electrographic copying machine incorporating an exhaust system for transporting the ozone-laden gas from each of the corona stations to an ozone-neutralizing filter unit containing a thin layer of ozone-decomposing catalyst retained between foraminous screens. The screens confine the catalyst bed and are not separable therefrom for cleaning or replacement nor are they disclosed to function as dirt filters. 
     SUMMARY OF THE INVENTION 
     The present invention provides a novel, convenient catalytic converter unit for pre-filtering dirt particles from a gas discharge containing an objectionable, neutralizable gas component, such as the ozone-laden gas discharge from electrographic copy machines in advance of the passage of the gas discharge through a gas-neutralizing catalyst bed, to exclude the passage of the dirt particles onto or into the catalyst bed where they can cause contamination and degradation of the catalyst, and plugging of the catalyst bed resulting in reduced gas-permability and the creation of a significant pressure drop thereacross which interferes with or substantially reduces the rate of gas flow through the unit. 
     The present catalytic converter units incorporate an easily-removable, cleanable and/or and replaceable dirt filter element having a dirt-trapping mesh which is upstream of, closely-spaced from, the catalyst bed and is supported for simple removal from the unit for periodic cleaning or replacement without interfering with the catalyst bed. 
    
    
     THE DRAWINGS 
     FIG. 1 is a schematic view of a representative electrographic copying machine incorporating an ozone catalytic converter unit according to the present invention; 
     FIG. 2 is an elevational view of a catalytic converter unit according to the present invention. 
     FIG. 3 is an end view of the unit of FIG. 2, taken along the line  3 — 3  thereof, and 
     FIG. 4 is an axial cross-sectional view of the ozone catalytic converter unit of FIGS.  2  and  3 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 schematically depicts the various components of an illustrative electrostatographic copying machine incorporating the present filter/catalytic converter apparatus for the collection and removal of dirt as well as ozone and other noxious gases. However, it will become evident from the following discussion that the apparatus for the collection and removal of dirt, ozone and other noxious gases is equally suited for use in a wide variety of devices and is not necessarily limited in its application to the particular embodiment shown herein. 
     As shown in FIG. 1, the electrostatographic copying machine employs a belt  10  having a photoconductive surface  12  deposited on a conductive substrate  14 . Preferably, photoconductive surface  12  is made from a selenium alloy with conductive substrate  14  being made from an aluminum alloy. Belt  10  moves in the direction of arrow  16  to advance successive portions of photoconductive surface  12  sequentially through the various processing stations disposed about a path of movement thereof. Belt  10  is entrained about stripping roller  18 , tension roller  20  and drive roller  22  which is itself driven by motor  24 . 
     The various processing stations employed in the illustrated copying machine will be now briefly described. Initially, a portion of the belt  10  passes through a charging station A. At charging station A, a corona generating or discharging device, indicated generally by the reference  28 , charges photoconductible surface  12  of belt  10  to a relatively high, substantially uniform potential. The corona discharging device  28  will be described in detail in connection with FIGS. 2 to  4  below. 
     Next, the charged portion of photoconductive surface  12  is advanced through exposure station B. At exposure station B, an original document  30  is positioned face down upon transparent platen  32 . Lamps  34  flash light rays onto original document  30 . The light rays reflected from original document  30  are transmitted through lens  36  forming a light image thereon. The light image is projected onto the charged portion of photoconductive surface  12  to selectively dissipate the charge thereon. This records an electrostatic latent image on photoconductive surface  12  which corresponds to the informational areas contained within original document  30 . 
     Thereafter, belt  10  advances the electrostatic latent image recorded on photoconductive surface  12  to development station C. At development station C, a magnetic brush developer roller  38  advances a developer mix into contact with the electrostatic latent image. The latent image attracts the toner particles from the carrier granules forming a toner powder image on photoconductive surface  12  of belt  10 . 
     Belt  10  then advances the toner powder image to transfer station D. At transfer station D, a sheet of support material  40  is moved into contact with the toner powder image. The sheet of support material is advanced to transfer station D by a sheet feeding apparatus  42 . Preferably, sheet feeding apparatus  42  includes a feed roller  44  contacting the upper sheet of stack  46 . Feed roller  44  rotates so as to advance the upper most sheet from stack  46  into chute  48 . Chute  48  directs the advancing sheet of support material into contact with the photoconductive surface  12  of belt  10  in a timed sequence so that the toner powder image developed thereon contacts the advancing sheet of support material at transfer station D. 
     Transfer station D includes a corona discharging device  50  which sprays ions onto the back side of sheet  40 . This attracts the toner powder image from photoconductive surface  12  to sheet  40 . After transfer, the sheet  40  advances to detack station E. At detack station E, a corona discharging device  26  charges the back side of the sheet  40  so as to facilitate the separation of the sheet  40  and the toner powder image thereon from the photoconductive surface  12 . After the detack station E, the sheet continues to move in the direction of arrow  52  onto a conveyor (not shown) which advances the sheet to fusing station F. 
     Fusing station F includes a fuser assembly, indicated generally by  54 , which permanently affixes the transferred toner powder image to sheet  40 . Preferably, fuser assembly  54  includes a heated fuser roller  56  and a backup roller  58 . Sheet  40  passes between fuser roller  56  and backup roller  58  with the toner powder image contacting fuser roller  56 . In this manner, the toner powder image is permanently affixed to sheet  40 . After fusing, chute  60  guides the advancing sheet  40  to catch tray  62  for removal from the copying machine by the operator. 
     Invariably after the sheet of support material is separated from photoconductive surface  12  of belt  10 , some residual particles remain adherent thereto. These residual particles are removed from photoconductive surface  12  at cleaning station G. Cleaning station G includes a preclean corona discharging device  64  and a rotatably mounted fibrous brush  66  in contact with photoconductive surface  12 . The preclean corona discharging device  64  neutralizes any remaining electrostatic charge carried by the residual particles and they are then removed or cleaned from photoconductive surface  12  by the rotation of brush  66  in contact therewith. Subsequent to cleaning, a discharge lamp (not shown) floods photoconductive surface  12  with light to dissipate any residual electrostatic charge remaining thereon prior to the charging thereof from the next successive imaging cycle. 
     As can be gathered from the above description, there are four separate stations where corona discharging devices are employed in this illustrative electrostatographic copying machine, and where there is a need for the collection and removal of ozone and; other noxious gases generated by such corona discharge devices. In accordance with the present invention, the ozone and other noxious gases, as well as any dirt particles or contaminants, are collected at these corona discharge devices, and are passed on through conduits (shown as dotted lines in FIG. 1) to a dirt pre-filter/ozone catalytic converter unit  68  according to the present invention, as more fully illustrated by FIGS. 2 to  4  of the drawings. 
     Referring to FIGS. 2 and 3, the unit  68  illustrated thereby is a cylindrical housing  70  having an inlet fitting  72  for receiving dirty ozoned air from the corona discharge stations of the copy machine, and a discharge outlet  74  at the downstream end of the unit for discharging the air exiting the interior surface  93  of the catalyst bed  90  after it has been freed of dirt and ozone and other impurities. 
     The unit  68  is mounted on the frame of the copy machine in a convenient location, such as by means of a rear bracket  76 , and the outlet  74  may be connected to a vent means. 
     Referring to the cross-sectional view of FIG. 4, the housing  70  of the present catalytic converter unit  68  comprises a shell or casing  70 A which is easily removable and which encloses a filter/catalyst cylindrical member  80  which is fixed to an end cap  82  of the unit  68 , or otherwise supported with its outer surface closely spaced from the inner surface of the housing  70  of unit  68  to form an annular space or passage  86  therebetween. The end of the filter catalyst member  80 , adjacent the unit inlet fitting  72 , is sealed by a domed cap  84  having an aerodynamic outer surface which uniformly distributes the dirty inlet gas radially-outwardly into the annular passage  86  where its only escape to outlet  74  is through the filter/catalyst member  80 . The outer shell or casing  70 A of the housing  70  has an inner surface  70 B, and may be threadably or frictionally engaged on the end cap  82  so as to be easily removable, without tools, to provide access to the filter/catalyst member  80 . 
     The preferred novel filter/catalyst member  80  comprises an outer dirt filter screen sleeve  88  which completely surrounds the inner tubular bed  90  of granular catalyst confined between an enclosure unit comprising inner and outer air-permeable sleeves  92 . The filter screen sleeve  88  is removably supported in spaced relation to the outer retaining sleeve  92  of the catalyst bed  90 , such as by means of confinement between end bushings  94 , so that the filter screen sleeve  88  can be removed for periodic cleaning or replacement, as necessary. 
     A preferred dirt filter screen sleeve  88  is a fine mesh screen of polytetrafluoroethylene (PTFE) which filters out and traps dirt and contaminant particles of 1 micron size or larger and precludes them for contacting and poisoning the catalyst, which is widely known to be the principal cause of failure of catalytic converters. The present design enables the catalyst bed to be effective for the life of the apparatus by shielding it against contact with dirt and other contaminants, and by enclosing the filter/catalyst member  80  within an outer cylindrical housing shell or casing  70 A which is easily removable from the housing base or end cap  82  to facilitate the removal of the dirt filter sleeve  88  for periodic cleaning and replacement, to preserve the useful life of the catalyst. 
     According to a preferred embodiment of the invention, the present catalyst bed  90  comprises a compacted bed of fine granular ozone-decomposing catalyst particles which convert ozone gas to harmless oxygen gas upon contact. The granular bed is confined in an enclosure unit or retaining screen assembly  91  comprising the inner and outer gas-permeable sleeves  92 , such as stainless steel woven wire cloth of 16×16 mesh, 0.023″ diameter wire, 0.04″ width openings, 39.9% open area. 
     Filling of the catalyst screen assembly  91  is accomplished by filling the space between the screen sleeves  92  with catalyst granules, vibrating at 100 to 200 cycles/min. for about 30 seconds at 1.3 to 1.6 amplitude to cause compacting or settling of the granules, and repeating the process until no further settling occurs. 
     The catalytically active granular material suitable for use in the apparatus and method of the instant invention can be virtually any material disclosed in the art which is capable of conversion of ozone or other dangerous gas to relatively innocuous products. Typical catalytically active ozone-neutralizing materials which are suitable for this purpose include those substances which have been historically termed “hopcalites”. 
     Briefly, these catalysts comprise metal oxides or basic sulfates, acetates or carbonates of the more common metals, either alone or in admixture. These substances are prepared under conditions intended to produce a finely divided granular material. Among the metals whose oxides, basic carbonates, basic acetates and basic sulfates have been found to be catalytically active are: manganese, cobalt, copper, iron, nickel, bismuth, lead and silver. In practice, mixtures of two or more of the above materials are preferable to a single compound acting alone. Moreover, catalytic activity of these compounds or mixtures of these compounds can be further enhanced by the addition of very minor quantities of finely divided metals, particularly metals of the platinum group, (these metals being regarded as promoters). 
     While the preferred two-stage filter device is an ozone gas catalytic converter, it should be understood that the present design can be used with any two-stage air/gas treatment device in which it is desirable to pre-filter the air/gas in advance of catalytic treatment to remove odor, poisonous gases and/or other objectionable or unwanted gases. 
     While the invention has been described in detail with reference to specific preferred embodiments, it will be appreciated that various modifications may be made from the specific details without departing from the spirit and scope of the invention.