Abstract:
Developer roller ( 5 ) is rotated rapidly for high speed printing, which can cause excessive heating at end seal ( 1 ). Heat damage to toner ( 24 ) is avoided by providing gaps ( 30   a,    30   b ) under the seals ( 1 ) which reduce the stiffness of roller ( 5 ) and thereby reduce frictional heating.

Description:
TECHNICAL FIELD  
       [0001]     This invention relates to xerographic imaging by interaction between a developer roller and a photoconductor roller having an electrostatic image rotating at high speeds, the developer roller having an end seal subject to frictional heating.  
       BACKGROUND OF THE INVENTION  
       [0002]     A common method of development with toner of an electrostatic image on a photoconductor roller (typically termed a drum) is by a developer roller moved in contact with the drum. The developer roller has toner applied to it and holds a layer of toner by electrostatic attraction. The developer roller rotates past a doctor blade, which may also have an electrical charge, and then contacts the rotating photoconductor roller.  
         [0003]     In this configuration a source of toner is located on the side of the developer roller opposite the photoconductor roller. Seals of various kinds are employed to prevent this toner from escaping from the sides of the developer roller. Typically the seal is a member that is shaped to fit the contour of the developer roller and is resilient so that it can be firmly pressed between the end of the developer roller and a frame member. Some such seals take the form of a letter J and are often termed J-seals.  
         [0004]     The friction of the developer roller moving against such a seal, which is essentially stationary, creates increased temperatures as printing speeds are increased by rotating the developer roller and the photoconductor drum faster. The temperatures become a serious technical concern when they rise to the point of melting or otherwise degrading the toner. The melting of toner will cause catastrophic failure of imaging.  
         [0005]     This problem has apparently not been addressed in the prior art. However, as printing speeds increase, an avoidance of the unacceptable temperatures from seal friction is needed.  
       DISCLOSURE OF THE INVENTION  
       [0006]     This invention employs the recognition that the developer roller exists under the seal only to contain toner, not for development purposes. That being true, an internal weakening of the developer roller immediately under the seal will not degrade the imaging operation.  
         [0007]     In accordance with this invention the developer roller immediately under the seal is reduced in stiffness. In an embodiment, a void area is located on the developer roller between a supporting shaft of the developer roller and an outer part of the developer roller. Since that outer part will flex inward somewhat during use, friction between the developer roller and the seal is reduced. In a typical implementation of this invention, the difference in temperature between a developer roller of standard configuration and a developer roller having a gap under the seal was 13.5%. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     The details of this invention will be described in connection with the accompanying drawings, in which  
         [0009]      FIG. 1  shows front and back isometric views of a seal employed in a representative embodiment of this invention, which are not novel in themselves and which are therefore labeled as prior art.  
         [0010]      FIG. 2  is a cross-sectional view of the seal of  FIG. 1  taken at line  2 - 2 , also labeled prior art.  
         [0011]      FIG. 3  is a is a cut away sectional view showing the placement of the seal in a process cartridge, which is not novel in itself and is therefore labeled as prior art.  
         [0012]      FIG. 4  is a side view of the developer roller seal, the developer roller, and the photoconductor drum, cross-sectioned through the seal to show the internal gap under the seal, with arrows showing motion.  
         [0013]      FIG. 5  shows the developer roller with dotted outlines illustrating the weakened portions or gaps under seals at each end. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0014]     Although only pertinent parts are shown in the drawings, it will be readily understood that the other parts complete a standard laser printer imaging device, such as described in U.S. Pat. No. 6,487,383 B2 assigned to the same assignee to which this invention is assigned. That patent is prior art with respect to this invention. For added clarity,  FIGS. 1 through 4  of this specification are based on figures of that patent.  
         [0015]     A representative seal  1  employed in this invention is shown in  FIG. 1 . The front side of seal I has a curved portion  3 , which conforms to the surface of the developer roller  5  (see  FIG. 3 ) and a flat surface  7  which conforms to the surface of a doctor blade  9  (see  FIG. 4 ). The front side of seal has region  11  with ridges to guide toner as described in detail in the foregoing 6,487,383. The region  11  contacts developer roller  5   
         [0016]     As shown in  FIG. 2 , the back side of the seal  13  forms a cantilever configuration with region  11  of side  3  and with flat surface  7  ( FIG. 1 ). This provides a spring effect to press the font side against the developer roller  5  and the doctor blade  9 .  
         [0017]     Seals are typically resilient material, although they may take many forms. Ridges  11  improve sealing action but may not be necessary in many instances. A preferred seal as illustrated is made from artificial rubber.  
         [0018]     As shown in  FIG. 3 , seal  1  is mounted between an edge of frame  20 , to which the backside  13  of seal  1  conforms, and developer roller  5  and doctor blade  9 . Frame  20  is part of a laser printer imaging device (not fully shown), and, more specifically, part of a toner cartridge (not fully shown) installed in a laser printer. Shown is one side wall  22  of a toner cartridge that forms a chamber for toner  24  (suggested by the dotted area) along with other walls of the cartridge (not shown).  
         [0019]     Toner  24  is pushed out of the region opposite side wall  22  into contact with a toner adder roller (not shown) to thereby continuously be applied as a layer of toner  24  to developer roller  5 , as is conventional. Doctor blade  9  controls further the layer of toner  24  on developer roller  5  as it rotates to bring toner to developer roller  24  (see  FIG. 4 )  
         [0020]      FIG. 4  is a cross-sectional view through the seal  1 . Developer roller  5  has a center support shaft  5   a , which typically is steel. As the view is of that region under seal  1 ,  FIG. 4  shows a circular gap  30   a  surrounding shaft  5   a . The core material  5   b  mounted on shaft  5   a  forms the body of developer roller  5 .  FIG. 4  also shows known flap elements, upper element  32  and lower element  34 , which are part of the sealing of toner  24  from escaping past the sides of developer roller  5  and doctor blade  9 .  
         [0021]     As is standard the two rollers  5  and  26  are rotated through a motor, shown illustratively an element M, in the laser printer imaging device. The two rollers  5  and  26  contact one another while moving in the same direction at the location of contact, as shown by arrows in  FIG. 4 . Typically developer roller  5  is rotated marginally faster than the speed of photoconductor roller  26  to provide some rubbing action. This speed differential does not cause detrimental frictional heating.  
         [0022]     When the speed of developer roller  5  is relatively high to achieve higher speed printing (more pages per minute), the frictional heating between seal  1  and roller  5  can be sufficient to melt toner  24  or otherwise seriously degrade toner  24 . It is that effect which this invention mitigates.  
         [0023]      FIG. 5  shows just the developer roller  5  in accordance with this embodiment. Except for gaps  30   a  and  30   b  on each end, roller  5  may be essentially as described in U.S. Pat. No. 5,874,172 to Beach et al., which is assigned to the assignee of this invention. That roller has a core material that is a polycaprolactone ester polyurethane, having some polydiol with an outer layer, more-electrically-resistive-layer of oxidized polydiene. (The drawings of this application do not separately illustrate the outer layer of oxidized polydiene).  
         [0024]     In accordance with this invention each end of roller  5  has a gap between shaft  5 a and the outer body of core  5   b . These gaps  30   a  and  30   b  are only at the ends, which is location where development by roller  5  is not employed.  
         [0025]     Although a gap is employed, it will be recognized that the air in the gap is not necessary to functioning so long as material in the gap is soft enough to allow added flexibility to the part of body  5   b  located under the seal  1  or other seal. For example, gaps  30   a  and  30   b  might be filled with a foam or a soft rubber-like insert.  
         [0026]     Similarly, the configuration of the gaps can take many shapes, all of which regulate the resulting stiffness of the core  5   b  when it contacts a seal  1 . Gaps increased in the longitudinal direction (in the direction of shaft  5   a ) have reduced stiffness because the cantilever effect is enhanced. Gaps increased laterally (i.e., reducing the thickness of core  5   b  under the seal  1 , have reduced stiffness because of the reduced support material.  
         [0027]     Accordingly, the interaction of heat produced and toner during operation can essentially define this invention. The invention requires areas of reduced support under the seal or seals. If during normal operation of an identical roller without the areas of reduced support the toner is damaged significantly by heat, then the roller with reduced support under the seal or seals is an implementation of this invention.