Patent Publication Number: US-8538286-B2

Title: Air duct and toner cartridge using same

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This patent application is a continuation application of U.S. patent application Ser. No. 12/421,725, filed Apr. 10, 2009, entitled “Air Duct and Toner Cartridge Using Same,” now U.S. Pat. No. 8,078,079, issued Dec. 13, 2011. Cross-reference is made to copending U.S. patent application Ser. No. 11/959,016, entitled “Upper Seal for Inhibiting Doctor Blade Toner Leakage,” filed Dec. 18, 2007, U.S. patent application Ser. No. 11/959,058, entitled “Developer Roll Lip Seal”, filed Dec. 18, 2007, and U.S. patent application Ser. No. 12/421,725, entitled “Air Duct and Toner Cartridge Using Same” filed Apr. 10, 2009, all assigned to the assignee of the present invention. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     None. 
     REFERENCE TO SEQUENTIAL LISTING, ETC 
     None. 
     BACKGROUND 
     1. Field of the Invention 
     The present invention relates generally to image-forming devices, and more particularly, to the cooling of a toner cartridge in an image-forming device. 
     2. Description of the Related Art 
     Image forming devices such as laser printers utilize a light beam that is focused to expose a discrete portion of a photoreceptive or image transfer drum in order to attract printing toner to these discrete portions. One component of a laser printer is the photoreceptive drum assembly. The photoreceptive drum assembly is made out of photoconductive material that is discharged by light photons, typically emitted by a laser. The drum is initially given a charge by a charge roller. As the photoreceptive drum revolves, the printer directs a laser beam across the surface to discharge certain points. In this way, the laser “draws” the letters and images to be printed as a pattern of electrical charges—an electrostatic latent image. The system can also work with either a more positively charged electrostatic latent image on a more negatively charged background, or on a more negatively charged electrostatic latent image on a more positively charged background. 
     The printer&#39;s laser or laser scanning assembly draws the image to be printed on the photoreceptive drum. A known laser scanning assembly may include a laser, a movable mirror, and a lens. The laser receives the image data defined by pixels that make up the text and images one horizontal line at a time. As the beam moves across the drum, the laser emits a pulse of light for every pixel to be printed. Typically, the laser does not actually move the beam. Instead, the laser reflects the light beam off a movable mirror. As the mirror moves, the light beam passes through a series of lenses. This system compensates for the image distortion caused by the varying distance between the minor and points along the drum. The laser assembly moves in one plane horizontally as the photoreceptor drum continuously rotates, so the laser assembly can draw the next line. A print controller synchronizes this activity. In the process of forming the latent image on the photoreceptive drum, the laser discharges those areas where the latent image is formed. 
     When the toner becomes electrostatically charged, the toner is attracted to exposed portions of the image transfer drum. After the data image pattern is set, charged toner is supplied to the photoconductive drum. Because of the charge differential, the toner is attracted to and clings to the discharged areas of the drum, but not to the similarly charged “background” portions. Toner is an electrostatically charged powder with two main ingredients, pigment, and plastic. The pigment provides the coloring, such as black in a monochrome printer, or cyan, magenta, yellow, and black in a color printer, and forms the text and images. The pigment is blended with plastic particles so the toner will melt when passing through the heat of a fuser assembly. The toner is stored in a toner cartridge housing, a small container built into a removable casing. The printer gathers the toner from a sump within the housing and supplies it to a developer unit using paddles and transfer rollers. The developer roll is a charged rotating roller, typically with a conductive metal shaft and a polymeric conductive coating, which receives toner from a toner adder roll positioned adjacent the developer roll. Due to electrical charge and mechanical scrubbing, the developer roll collects toner particles from the toner adder roll. A doctor blade assembly engages the developer roll to provide a consistent coating of toner along the length and surface of developer roll by scraping or “doctoring” excess toner from the developer roll. The doctor blade may also induce a charge on the toner. This, in turn, provides a consistent supply of toner to the photoconductive drum. When the coating of toner on the developer roll is inconsistent, too thick, too thin, or bare, the coating of the photoconductive drum is inconsistent, and the level of darkness of the printed image may vary due to these inconsistencies. This condition is considered a print defect. 
     The electrostatic image on the photoconductive drum is charged such that the toner particles move from the developer roll onto the latent image on the photoconductive drum to create a toned image on the photoconductive drum. The toned image is transferred from the photoconductive drum to a printable medium such as paper or onto an intermediate transfer belt which then transfers the toned image onto the printable medium. The paper or transfer belt is oppositely charged to the toner, causing it to transfer to the paper or transfer belt. This charge is stronger than the charge of the electrostatic image, so the paper or belt pulls the toner particles away from the surface of the photoconductive drum. Since it is moving at the same speed as the drum, the paper or transfer belt picks up the image pattern exactly. 
     One problem that often occurs in a laser printer or other image-forming device is toner leakage. Toner from the sump can leak into the toner cartridge and interfere with the proper operation of the unit. One significant area of toner leakage is a path along portions of the developer roll where a J-seal, positioned proximate both ends of the developer roll, slidably engages the developer roll, particularly where the developer roll, doctor blade, and J-seal all meet. These locations are difficult to seal due to the tolerances, stiffness, and deflections of the aforementioned components. Observations of operational toner pressure as well as vibration and drop testing have demonstrated that the areas around the surface of the developer roll and the J-seal are a frequent toner leak path, especially in higher volume housings. 
     The interface between the developer roll and the J-seal, identified on the developer roll as the “clean band,” creates heat inside the toner cartridge when the developer roll turns. Friction is unavoidable with current designs because the J-seal must contact the developer roll around its periphery at all times. The J-seal interface is a source of high friction because the J-seal must be made from a pliable material in order to securely contain the toner in the cartridge. The J-seal interface contacts the developer roll, which is frequently covered by a polymeric or rubberized material with a high coefficient of friction. It will be appreciated that the temperature of the developer roll along its length is significantly higher at the clean bands than it is at intermediate positions due to friction with the J-seal. 
     One solution to excessive heat from the J-seal interface has been to apply a lubricant to the clean band area in an attempt to decrease the coefficient of friction. However, such an approach has significant drawbacks. Any lubricant applied to the J-seal or to the ends of the developer roll can potentially contaminate the toner and ruin any printed image. Additionally, the lubricant can seep into other areas of the cartridge or printer, causing unwanted damage and interfere with the proper operation of the unit. 
     Another solution to excessive heat from the J-seal has been to utilize directed airflow, such as from a fan, to blow air across the entire length of the developer roll. However, this had been found to be ineffective in lowering the temperature of the developer roll by any significant amount. 
     In addition, the heat created by the friction at the J-seal interface causes further problems with the proper operation of a laser printer or other image-forming device as print speed increases. Since it is essential to maintain pressure between the J-seal and the developer roll, more heat is created as the print speed increases. In known printers, a print speed of 35 pages per minute (ppm) is slow enough that, even with continuous printing, the heat created at the J-seal can be dissipated into the surrounding cartridge parts and into the atmospheric air to prevent heat related failure. In such an instance, the toner cartridge can reach a thermal equilibrium and still operate properly with undirected machine airflow as a cooling method. However, printing at higher speeds such as at or above 50 ppm causes extreme overheating, which is localized at the ends of the developer roll around the J-seal interface. Low thermal conductivity of the developer roll worsens the heating condition, and a large temperature gradient can be created around the clean bands in the axial direction of the developer roll. 
     It will be appreciated that high temperatures negatively affect the ability of the J-seal to seal toner inside the cartridge. As heat from the clean band areas increases, the temperature of the surface of the developer roll increases, and the temperature of the toner in the immediate region also increases. Temperatures of up to 70° C. around the J-seal interface have been measured when a printer was operated at 50 ppm. For some toners, fusing can occur at approximately 46° C. Thus, it will be appreciated that toner fusing may occur in the area of contact between the J-seal and the developer roll when the image forming device is operated at speeds of 50 ppm or higher. In such an instance, the J-seal contacts an irregular layer of fused toner on the developer roll, and not an extremely smooth surface, which is the most desirable condition in order to achieve a consistent and reliable seal. This condition allows toner to escape past the J-seal and out of the toner cartridge. 
     Once toner leakage at the J-seal begins, toner loss almost always continues at a rapid rate, permitting several grams of toner per minute to escape into the printer. Such large amounts of toner losses are substantial enough to severely affect cartridge yield, and may result in yields of several thousand pages fewer than expected. In addition, major print defects occur, as the escaped toner from the toner cartridge can spill directly onto the transfer belt near the location of the first transfer or onto the print media. 
     SUMMARY OF THE INVENTION 
     In accord with the present invention, a cartridge for containing toner material used in an image forming device comprises a developer roll, a seal providing an interface with the developer roll and the toner, and an air duct for conducting air flow across the interface to cool the developer roll. 
     Further in accord with the present invention, an air duct in a cartridge for containing toner material, a developer roll, and a seal providing an interface with the developer roll, the developer roll having a distal end and a proximal end, with one seal located at each of the distal and proximal ends, comprises an elongated hollow body, a pair of nozzles in fluid communication with the hollow body, one of the nozzles being disposed at the distal end of the developer roll and the other of the nozzles being disposed at the proximal end of the developer roll. 
     Still further in accord with the present invention, in an image forming device having a cartridge for containing toner material, a developer roll, and a J-seal providing an interface therebetween, the improvement comprises an air duct disposed adjacent the developer roll for conducting air flow across the J-seal interface to cool the developer roll and J-seal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a perspective view of an exemplary electrophotographic printer; 
         FIG. 2  is a perspective view of a toner cartridge used in the electrophotographic printer of  FIG. 1 ; 
         FIG. 3  is a partially exploded perspective view of a developer assembly; 
         FIG. 4  is an exploded perspective view of a developer seal assembly; 
         FIG. 5  is a perspective view of an exemplary air duct and a developer roll in the toner cartridge of the present invention; 
         FIG. 6  is a perspective view of the air duct of  FIG. 5 ; 
         FIG. 7  is a bottom plan view of the air duct of  FIG. 6 ; 
         FIG. 8  is a cross-section taken along the lines  8 - 8  of the air duct of  FIG. 5 ; 
         FIG. 9  is a cross section taken along the lines  9 - 9  of the air duct of  FIG. 5 ; 
         FIG. 10  is a perspective view of an exemplary toner cartridge cutaway to reveal the air duct of  FIG. 6 ; 
         FIG. 11  is a graph illustrating the temperature of a seal used in the toner cartridge of the present invention; 
         FIG. 12  is a graph illustrating air speed versus temperature as measured in the toner cartridge of the present invention; and 
         FIG. 13  is a perspective view of an alternate embodiment of the toner cartridge of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     It is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless limited otherwise, the terms “connected,” “coupled,” and “mounted,” and variations thereof herein are used broadly and encompass direct and indirect connections, couplings, and mountings. In addition, the terms “connected” and “coupled” and variations thereof are not restricted to physical or mechanical connections or couplings. 
     Referring now to  FIG. 1 , a perspective view of a peripheral device  10  having a laser printing mechanism is depicted in perspective view. Although the peripheral device  10  is depicted as a laser printer, one skilled in the art should realize that the present design may alternatively be used with an all-in-one device, copier, fax, stand-alone device or the like having an electrophotographic (laser) print engine. The exemplary peripheral device embodied by the laser printer  10  comprises a housing  12  including a primary access door  14  positioned on the top-front of the housing  12 . The housing  12  generally comprises a front surface, first and second side surfaces, a rear surface (not shown) and a bottom surface to enclose the laser printer operating mechanisms. On the front of the housing  12 , the primary access door  14  is pivotally mounted to allow opening and access for installation or removal of a developer assembly  40  ( FIG. 3 ). The front panel of the primary access door  14  comprises an operations panel  16  that includes a display  18 , an alpha numeric keypad  20 , a plurality of selection buttons  22 , as well as a flash memory slot  24 . The operations panel  16  is in electronic communication with a controller (not shown), which may be embodied by one or more microprocessors, in order to operate the laser printer  10 . Beneath the primary access door  14  is a secondary access door  26  that allows access to the developers or toner cartridges  112  (see  FIG. 2 ). The printer  10  may operate in both monochrome and color. In the latter instance, for example, three additional toner colors may be utilized to provide the color printing, comprising the toner colors cyan, yellow, or magenta, although other colors may be utilized. 
     Referring now to  FIG. 3 , a developer assembly  40  is depicted in perspective view. The developer assembly  40  comprises a housing  42 , formed of a first housing portion  44  and a second housing portion  46 . Along at least one side of the housing  42  is a lid  43 . Within the first housing portion  44 , toner is stored, and at least one paddle is located therein on a rotating shaft to move the toner from the first housing portion  44  toward the second housing portion  46 . A toner adder roll  56  is located within or adjacent to the second housing portion  46 , and receives toner therefrom. The toner adder roll  56  coats the developer roll D with toner, which is scraped or “doctored” by the doctor blade  54  to form an even layer of toner on the developer roll D, and in turn supplies toner to the imaging or photoreceptive drum. A seal assembly  38  inhibits leakage of toner between the developer housing  46  and the corner  59  formed by the doctor blade bracket  52  and the doctor blade  54  when it is dropped, and also during operation when the developer assembly  40  vibrates and creates internal pressures. 
     The developer assembly  40  includes J-seals  70  at the ends of the developer roll D. The developer roll D is exploded in  FIG. 3  for clarity, so that the J-seals  70  may be seen. The J-seals  70  are substantially J-shaped to receive the developer roll D, although other curvilinear shapes may be utilized. The J-seals  70  are as described U.S. patent application Ser. No. 11/959,016, entitled UPPER SEAL FOR INHIBITING DOCTOR BLADE TONER LEAKAGE, and U.S. patent application Ser. No. 11/959,058, entitled DEVELOPER ROLL LIP SEAL, both filed Dec. 18, 2007, all assigned to the assignee of this application, and incorporated herein by reference. The upper portion of the J-seal  70  is slightly curved substantially to match the deflected shape of the blade  54 . The lower portion of the J-seal  70  is curved to receive the developer roll D. Disposed above the J-seal  70  is a doctor blade seal  60 , which extends in a length that is parallel to the axial dimension of the developer roll D. Also disposed above the J-seal  70  is a doctor blade bracket assembly  50  comprising at least one first bracket  52  and the doctor blade  54 . Like the doctor blade seal  60 , the doctor blade bracket assembly  50  also extends in a direction that is substantially parallel to the axial dimension of both the toner adder roll  56  and developer roll D. The doctor blade seal  60  is captured between the doctor blade bracket assembly  50  and the J-seal  70  or the lid  43 . The doctor blade  54  engages the developer roll D to scrape excess toner from the surface of the developer roll D, which provides a consistent level of toner to the imaging or photoreceptive drum of the printer  10 . The doctor blade seal  60  is seated on the J-seals  70  to inhibit leakage of toner near the ends of the developer roll D and between the lid  43  and the developer housing  42 . The doctor blade bracket assembly  50  compresses the doctor blade seal  60  to improve sealing in this area. 
     Referring now to  FIG. 4 , an exploded perspective view of the seal assembly  38  is depicted. The doctor blade bracket assembly  50  and the doctor blade seal  60  are cut in section for purpose of clarity. As previously indicated, the doctor blade bracket assembly  50  is disposed above the doctor blade seal  60  that is positioned above the J-seal  70 . The doctor blade bracket assembly  50  comprises a bracket  52  and a blade  54  connected to the bracket  52 . The blade  54  is welded to the bracket  52 . However, the bracket  52  may be connected to the blade  54  by a fixative such as epoxy, cement, glue, or the like. The blade  54  may also be connected to the bracket  52  by a fastener, or the blade  54  may be captured or sandwiched between first and second bracket members. The bracket  52  includes an aperture  58  for connection of the doctor blade bracket assembly  50  to the housing  42 . The aperture  58  is oval in shape so as to provide an adjustment for the blade  54  toward or away from the developer roll D. The bracket  52  is generally a stiff material such as steel and rectangular in shape extending from one side of the housing  42  to an opposed side of the housing  42 . The bottom surface of the bracket  52  is generally smooth so as to engage the upper surface of the doctor blade seal  60 . 
     The blade  54  extends from the bracket  52  toward a peripheral surface of the developer roll D in order to scrape excess toner from the outer surface of the developer roll D. The blade  54  is generally rectangular in shape, having a long or width-wise dimension substantially parallel to the direction of the axial dimension of the developer roll D. The blade  54  includes a front surface  55  and a rear surface  57 . The blade  54  is straight in its natural state, but, in order to provide a “doctoring” force on the developer roll D, has a slight curvature due to interference with the developer roll D upon installation. In addition, the blade  54  has notches N near ends of the blade for removing all toner from the ends of the developer roll D where printing does not occur. The blade  54  may also receive an electrical potential in order to charge the developer roll D with a desired polarity during operation. The lower surface of the bracket  52  engages an upper surface  62  of the doctor blade seal  60 , so as to capture the seal  60  between the doctor blade assembly  50  and the J-seal  70 . The blade  54  may be formed of phosphor bronze to provide the desired elasticity and electrical conductivity, or alternatively, may be formed of a hardened stainless steel to provide a desired elasticity and also withstand corrosion that might damage the developer roll D. Other materials may also be utilized. 
     An end portion  61  of the doctor blade seal  60  is shown above one of the J-seals  70 . The doctor blade seal  60  has first and second ends  61  ( FIG. 3 ). As previously described, the doctor blade seal  60  extends between the ends  61  in a direction generally parallel to the axial dimension of the developer roll D and the toner adder roll  56 . The doctor blade seal  60  is formed of a foam material to act as a deformable seal between the bracket assembly  50  and the J-seal  70  or the lid  43 , as well as around the housing  42  adjacent the J-seal  70  and between the bracket  52  and the blade  54 . The ends  61  are positioned on an upper seat surface  73  of the J-seal  70 . The portion of the doctor blade seal  60  between the ends  61  is supported by the lid  43  of the housing  42  ( FIG. 3 ). 
     The doctor blade seal  60  has the upper surface  62 , a lower surface  63  and a plurality of sides extending between the upper and lower surfaces  62 ,  63 . Along the front of the doctor blade seal  60 , toward the doctor blade  54 , a tongue  64  is integrally formed with and extends from the doctor blade seal end  61 . On an outer end of the tongue  64  is a tongue end surface  65  of the doctor blade seal  60 . Perpendicular to tongue end surface  65  of the tongue  64  near the blade  54  is a tongue-extending surface  66 . Angled from the tongue-extending surface  66  is an angled or tapered surface  68 . The angled surface  68  joins the tongue-extending surface  66  and a front seal surface  69 , which extends the distance of the doctor blade seal  60  to the opposite end  61  (not shown) of the doctor blade seal  60 . Therefore, the tongue  64  generally extends from the angled surface  68  in a direction substantially perpendicular to the front seal surface  69 . In combination, the surfaces  69 ,  68 ,  66  define a recess wherein an upper seat inner seal wall  78  of the J-seal  70  is received. An end wall  67  is indented and is received against upper seat outer seal wall  82 . As previously indicated, the doctor blade seal  60  extends in a width-wise direction, which corresponds to the width of a media sheet, and perpendicular to the media feed path direction to an opposite end of seal  60 . 
     Beneath the doctor blade seal  60 , the J-seal  70  comprises an upper seat portion  72 , and a developer roll leg  74 , which is substantially j-shaped and depends from the upper seat portion  72 . The J-seal  70  may be formed in a molding process, such as injection molding, compression molding, or other known processes for forming a plastic, such as a thermoplastic rubber having the trade name SANTOPRENE. The leg  74  has a front surface  75  comprising a plurality of grooves  76 , which provide several functions. The grooves  76  “snowplow” the toner on the developer roll D and capture toner between the grooves to inhibit leakage. The grooves  76  also direct the toner toward a storage area via rotation of the developer roll D ( FIG. 3 ). The grooves  76  are disposed at an angle, which may be from about zero to about forty-five degrees from the sidewall of the leg  74 . 
     The upper seat portion  72  comprises a seating surface  73 , the upper seat inner seal or seal wall  78 , and an upper seat outer seal or seal wall  80 . A gap  86  is disposed between the upper seat inner seal  78  and the upper seat outer seal  80 , wherein the tongue  64  may be closely received within the upper seat portion  72  to interlock the J-seal  70  and the doctor blade seal  60 . The seating surface  73  also comprises an aperture  73   a  made for receiving an alignment pin for proper positioning of the J-seal  70  to the housing  42 . 
     The upper seat inner seal wall  78  extends upwardly from the upper seat surface  73 . The upper seat inner seal  78  is disposed at an acute angle with respect to the outer seal  80 , which corresponds to that of the angled surface  68 , so that the upper seat inner seal  78  and angled surface  68  engage one another in sealing fashion. Further, the upper seat inner seal  78  is received within the recess defined by the surfaces  66 ,  68 ,  69 . 
     As is known, the laws of heat transfer provide three basic ways to move heat from one location to another: convection, conduction, and radiation. In the case of a laser printer  10  such as the one depicted in  FIG. 1 , convection is the most efficient way to remove heat. The limited space inside the laser printer  10  eliminates many possibilities to conduct heat away from the developer roll D. The developer roll D is relatively thick and a relatively poor conductor of heat, so the developer roll D supports very little heat transfer. The matching components of the developer roll D are, in the preferred embodiment, made of plastic molded parts, which are also relatively poor conductors of heat. Since the space allotted inside the laser printer  10  is reduced in an effort to produce a compact size, there is little room inside the toner cartridge  112  for additional components. Cooling by radiation inside the cartridge  112  is not feasible because the highest operating temperature inside the toner cartridge  112  is generally not high enough to realize a measurable benefit. 
     Turning now to  FIG. 5 , an air duct  128  is disposed within toner cartridge  112  adjacent the developer roll D and directs air onto proximal and distal clean bands  130 ,  132  of the developer roll D through proximal and distal nozzles  140 ,  142 . The equation giving the heat transferred by convection is
 
q=hAΔT  (Equation 1)
 
     where 
     q=heat transfer rate 
     h=heat transfer coefficient 
     A=surface area 
     ΔT=temperature difference between surface and ambient air 
     As is evident from Equation 1, greater heat transfer occurs with increasing temperature difference. In the case of the developer roll D, the temperature difference between ambient air and the surface of the developer roll D is much greater at the clean bands  130 ,  132  than across the other portions of the developer roll D. Also, the heat transfer coefficient, h, increases with air velocity. It will thus be appreciated that the most effective cooling of developer roll D occurs when the air blown onto the clean bands  130 ,  132  occurs at the highest possible velocity. 
     The air duct  128  carries ambient air through the toner cartridge  112  and directs it onto the proximal and distal ends  146 ,  144  of the developer roll D, without obstructing the laser path through the printer  10 , in order to maximize the air velocity at the clean bands  130 ,  132 . The equation determining the flow through the air duct  128  is known as the Bernoulli equation, and describes the operating conditions at any point in a straight duct where the flow is steady and friction is neglected. 
     
       
         
           
             
               
                 
                   
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                         1 
                         2 
                       
                       ⁢ 
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                       ⁢ 
                       
                         v 
                         2 
                       
                     
                     + 
                     
                       ρ 
                       ⁢ 
                       
                           
                       
                       ⁢ 
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                   = 
                   const 
                 
               
               
                 
                   ( 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     2 
                   
                   ) 
                 
               
             
           
         
       
     
     where
         p=pressure at any point in the duct   ρ=density of the material inside duct (in this case, air)       

     v=velocity inside the duct at the point in question 
     g=gravitational force at the point 
     h=height of the point in question 
     Since the Bernouilli Equation (Equation 2) describes any point in the air duct  128 , the density of the air inside the air duct  128  is approximately constant, and the height at every point inside the air duct  128  is approximately zero. The Bernoulli Equation (Equation 2) can thus be simplified to relate the air velocity at the inlet and exit of the air duct  128  for a given pressure difference, and the resulting equation is 
     
       
         
           
             
               
                 
                   
                     v 
                     2 
                   
                   = 
                   
                     
                       
                         v 
                         1 
                         2 
                       
                       + 
                       
                         
                           2 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           Δ 
                           ⁢ 
                           
                               
                           
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                           p 
                         
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                   ( 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
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                     3 
                   
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     where 
     v1=velocity at duct inlet 
     v2=velocity at duct exit 
     ρ=density of air 
     Δp=pressure difference between inlet and exit (operating pressure difference provided by the fan) 
     From Equation 3, one of skill in the art will recognize that increasing the pressure difference across the air duct  128  increases the exit velocity. However, increasing the pressure difference across the air duct  128  provides a lower flow rate. 
     Referring now to  FIGS. 5 to 10 , the air duct  128  in the toner cartridge  112  is a unitary structure that comprises a hollow elongated body portion  138  and a pair of nozzles in fluid communication with the interior of body portion  138 , the distal nozzle  142  and the proximal nozzle  140 . It will be appreciated from  FIG. 5  that the distal nozzle  142  is located adjacent a distal end  144  of the developer roll D, while the proximal nozzle  140  is located adjacent a proximal end  146  of the developer roll D. The elongated body portion  138  of the air duct  128  has an inlet that is in fluid communication with a plenum/manifold  152  via neck portion  148 . The plenum/manifold  152  is in fluid communication with air from a fan or other air blower  150  located in the laser printer  10 . The fan  150  provides air at a predetermined velocity to the elongated body portion  138  and to the proximal and distal nozzles  140 ,  142 . Air from the proximal and distal nozzles  140 ,  142  flows across proximal and distal clean bands  130 ,  132  of the developer roll D adjacent the distal and proximal ends  144 ,  146  thereof. The plenum/manifold  152 , in the illustrated embodiment, has only a single developer roll D and a single air duct  128 , such as would be found in a monochrome laser printer  10 . In the alternate embodiment of  FIG. 13 , as discussed more fully hereinbelow, the plenum/manifold  152  connects multiple developer rolls D via neck portions  148 , and provides fluid communication with the fan or air blower  150 . In  FIG. 10 , the air duct  128  is shown positioned and inserted within the toner cartridge  112 . Proximal and distal nozzles  140 ,  142 , are directed at distal and proximal ends  144 ,  146  of developer roll D and seals  70  when developer assembly  40  (see  FIG. 3 ) is installed in toner cartridge  112 . 
     With reference to  FIGS. 5 and 8 , the proximal and distal nozzles  140 ,  142  generally taper in an axial manner in a direction away from the elongated body portion  138 . A cross section of the distal nozzle  142  has an irregular quadrilateral shape. It will be appreciated that the cross section of the proximal nozzle  140  is a mirror image of the cross section of the distal nozzle  142 . With reference to  FIGS. 5 and 9 , the elongated body portion  138  has a generally substantially regular rectangular cross section along its axial length. It will be appreciated that the air duct  128  provides airflow from the fan  150  across the distal and proximal clean bands  130 ,  132  to cool the developer roll D. As illustrated in  FIG. 7 , the proximal and distal  140 ,  142  have openings  156 ,  154  for the air from the fan  150  to exit across the clean bands  130 ,  132 . The tips of the proximal and distal nozzles  140 ,  142 , where the openings  156 ,  154  are located, do not contact clean bands  130 ,  132  of the developer roll D, but are in close proximity thereto so that the air therefrom may blow across the developer roll D. 
     Referring now to  FIGS. 11 to 13 , a test was conducted by blowing a narrow stream of air, approximately the same width as the proximal and distal clean bands  130 ,  132 , onto the developer roll D as it is configured in a developer unit from a model C782 color printer available from Lexmark International, Inc., turning at a rate corresponding to a speed of 50 ppm. This test, as illustrated in  FIGS. 11 and 12 , verified that the surface temperature of the developer roll D drops with increasing air speed. The developer roll D was enclosed so that no ambient air was allowed to pass over the developer roll D. All temperature differences achieved were the direct result of the airflow exiting from the air duct  128 . The results of the test are depicted in the graph of  FIG. 12 , which illustrates that for increasing air speeds, the temperature of the developer roll D cools with increasing air velocity. 
       FIG. 13  illustrates an embodiment of the present invention in a color laser printer that was used in the test, and included four air ducts  200 ,  202 ,  204 ,  206  with the same geometry and spacing as depicted in  FIGS. 5 to 9 . The air ducts  200 ,  202 ,  204 ,  206  were in fluid communication with the fan  150 . In  FIG. 11 , curve  208  represents the temperature of the J-seal  70  at 750 feet per minute (fpm); curve  210  represents the temperature at 1000 fpm; curve  212  represents the temperature at 1500 fpm; and curve  214  represents the temperature at 2000 fpm.  FIG. 12  illustrates that the air flow from the air ducts  200 ,  202 ,  204 ,  206  asymptotically reduced the operating temperature of the developer roll D from 68° C. to 46° C., when measured 2 mm from the end of the back of the blade  54  as the air speed increased to 1500 fpm and higher with only a slight decrease in temperature occurring at higher air speeds. 
     The foregoing description of embodiments of the invention has been presented for purposes of illustration. It is not intended to be exhaustive or to limit the invention to the precise steps and/or forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be defined by the claims appended hereto.