Abstract:
A method for manufacturing a roll. The method includes positioning a shaft for the roll within a mold, introducing flowable material into the mold from a first end thereof, rotating the shaft at least about 20 revolutions, and following introducing the flowable material into the mold and rotating the shaft, curing the material at an elevated temperature. The method substantially reduces or otherwise eliminates weld lines and flow lines in the manufactured roll.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present application relates generally to injection molding techniques for the manufacture of rolls, and particularly to injection molding techniques for the manufacture of developer rolls for electrophotographic imaging devices. 
         [0003]    2. Description of the Related Art 
         [0004]    Monochrome laser printers often utilize a polyurethane developer roll. The developer roll is typically created using a reactive injection molding process that uses a roll mold having a substantially cylindrical shape. Examples of prior developer roll and mold injection techniques may be found in U.S. Pat. Nos. 5,874,172 and 6,767,489, the content of which are hereby incorporated by reference herein in their entirety. 
         [0005]      FIGS. 1-3  illustrate the known processing steps for and injection molding process for creating a developer roll. Flowable material enters the mold  1  through a side injection port  3  and flows into the main cavity  5  ( FIG. 2 ) where the flow front is split evenly by the developer roll shaft  7  into two separate, substantially parabolic-shaped flow fronts, as shown in  FIG. 3 . The parabolic flow fronts continue their path around shaft  7  and meet directly opposite the side injection port  3 , creating what is referred to as a “weld line” or “knit line.” Once these flow fronts have contacted each other, the flowable material continues to move upwardly within main cavity  5  so as to fill the cavity. In the process of filling cavity  5 , the weld line is seen to continue along the direction of the longitudinal axis of shaft  7  until the weld line is stretched along the entire length of the created developer roll. 
         [0006]    Because the viscosity of the base materials of the developer roll is relatively high and the fact that mold systems have been seen to only withstand about 40 psi of pressure before their mix head seals leak, there is relatively little chance to create turbulent mixing to eliminate the weld line. In fact, the Reynolds number, which is a dimensionless number generally used to define laminar and turbulent flow regimes, for a typical cylindrical mold system is approximately 3, whereas a minimum Reynolds number of 2100 defines the onset of turbulent mixing. In order to reach the turbulent mixing regime, one would need to reduce the base materials viscosities by a factor of about 700, which is near physically impossible, or increase the flow rate of the system by the same factor, which would result in pressures well above the mix head pressure rating. 
         [0007]    From a mechanical standpoint, a developer roll having a weld line has not been seen to pose a serious problem. However, from an electrical uniformity perspective, a weld line of a developer roll is seen to result in electrical property variation around the circumference of the developer roll during use in an electrophotographic imaging device, which in turn produces print defects. The defect is replicated a number of times on a sheet of media corresponding to the number of revolutions of the developer roll per sheet. 
         [0008]    Besides weld lines, injecting material directly at shaft  7  may also produce flow line patterns in a common formation at the gate location. Although these lines are very subtle when looking at the roll, they are very distinct when considering a voltage map of the surface of the developer roller and in some cases printed sheets. 
         [0009]    The weld line and flow line patterns are believed to be the result of shear induced phase separation since the formulation components of the developer roller are not completely miscible. If the developer roll formulation materials separate such that a thin layer of one component is at the air interface of the flow front within the mold  1 , material property differences are believed likely to exist, such as material density, electrical resistivity, microhardness, etc. 
         [0010]    Based upon the foregoing, there is a need for an improved process for manufacturing rolls, and particularly developer rolls, which is relatively simple and inexpensive to implement. 
       SUMMARY 
       [0011]    Example embodiments overcome shortcomings experienced in prior roll processing techniques and thereby satisfy a need for a process for manufacturing rolls and rolls resulting therefrom. 
         [0012]    In accordance with an example embodiment, there is disclosed a process by which flow lines and weld lines are substantially reduced. The example process includes injecting flowable material into a mold; following the flowable material being injected into the mold, rotating one of the shaft and the mold relative to the other; and following the rotating, curing the flowable material. During the rotating, weld lines and flow lines are stretched, thereby reducing their width to the point that the width of any remaining electrical non-uniformities are much less than a single pel dot. In a first embodiment, the shaft is rotated relative to the mold. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The above-mentioned and other features and advantages of the various embodiments, and the manner of attaining them, will become more apparent and will be better understood by reference to the accompanying drawings, wherein: 
           [0014]      FIG. 1  is a side cross sectional view of an existing mold apparatus illustrating the flow of material therein; 
           [0015]      FIGS. 2 and 3  are top cross sectional views of the mold apparatus of  FIG. 1 ; 
           [0016]      FIG. 4  is a side, cross sectional view of a mold apparatus in accordance with an example embodiment of the present disclosure; 
           [0017]      FIGS. 5 ,  6  and  7  are top cross sectional views of the mold apparatus of  FIG. 4  at various stages during the injection of flowable material therein; and 
           [0018]      FIGS. 8A-8C  are images of cross sectional views of roll portions created according to an example embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    The following description and drawings illustrate embodiments sufficiently to enable those skilled in the art to practice it. It is to be understood that the subject matter of this application is not limited to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. The subject matter is capable of other embodiments and of being practiced or of being carried out in various ways. For example, other embodiments may incorporate structural, chronological, electrical, process, and other changes. Examples merely typify possible variations. Individual components and functions are optional unless explicitly required, and the sequence of operations may vary. Portions and features of some embodiments may be included in or substituted for those of others. The scope of the application encompasses the appended claims and all available equivalents. The following description is, therefore, not to be taken in a limited sense, and the scope of the present application as defined by the appended claims. 
         [0020]    Also, it is to be understood that the phraseology and terminology used herein is 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. 
         [0021]    With reference to  FIGS. 4-7 , there is shown a process for manufacturing a roll member according to a first example embodiment. A mold  41  may have an inlet  43  for receiving the mold material and a main mold cavity  45  in communication with inlet  43 . The flowable mold material may be, for example, a polyurethane rubber composition. Inlet  43  may be disposed along a bottom portion of mold  41 , as shown in  FIG. 4 . Like in the existing mold system of  FIGS. 1-3 , material flowing into cavity  45  ( FIG. 5 ) is split substantially evenly by developer roll shaft  47  into two separate, substantially parabolic flow fronts, as shown in  FIG. 6 . Such flow fronts flow around developer roll shaft  47  and eventually meet along a portion of cavity  45  that is substantially opposite inlet  43 . Once contact is made between the flow fronts, the flowable material continues to fill cavity  45 , moving upwardly towards the top thereof. As a result of the flow of material as described, weld and flow lines are formed along the longitudinal length of the developer roll, for substantially the entire length thereof. 
         [0022]    Relatively soon after completion of the flow of material being injected into cavity  45 , in accordance with an example embodiment, developer roll shaft  47  is rotated before the created developer roll is cured. Rotation of shaft  47  causes the weld line (exaggerated in  FIG. 7 ) and flow lines to stretch in a substantially spiral pattern about the axis of shaft  47 . Using existing roll processing techniques, weld lines are on the order of about 1 to about 2 mm wide run substantially the full length of the developer roller, which is about 230 mm. In order to reduce the width of a weld line to less than one half of its original width, thereby corresponding to the diameter of a single pel dot (about 40 microns), shaft  47  may be rotated at least about 20 rotations. Assuming that shaft  47  is about 9.5 mm in diameter and mold cavity  45  is about 22 mm in diameter, 20 rotations will result in a weld line that is approximately 20 microns wide. It is understood that 20 rotations of shaft  47  is a substantially minimum guideline, and rotating shaft  47  more than 20 revolutions will improve the effectiveness of the rotating by reducing the thickness of the weld line further. However, it is further understood that continuing to rotate shaft  47  beyond a certain number of shaft rotations will not result in a noticeable improvement in either weld line width or in reducing electrical property (voltage) variation along the circumference of the developer roll produced. 
         [0023]    Rotation of shaft  47  may be for a predetermined time duration. For a polyurethane rubber composition having a viscosity in the range between about 5000 cP and about 8000 cP when entering mold cavity  45 , the minimum time duration may be between about three seconds and about 15 seconds, and in particular between about ten seconds and about 15 seconds. This time duration may correspond to the rotation of shaft  47  being between about 80 rpm and about 300 rpm. 
         [0024]    The time duration for rotating shaft  47 , as well as the rate of shaft rotation, may vary depending upon the viscosity of the flowable material. For example, a flowable material having a relatively higher viscosity may allow for rotating shaft  47  for a longer period of time and/or at a lower rate of rotation. A flowable material having a relatively lower viscosity, on the other hand, may allow for a shorter period of time for rotating shaft  47  and/or a higher rate of shaft rotation. 
         [0025]    Another factor which may affect the number of revolutions of shaft  47  may be the diameter of mold cavity  45 . In particular, a mold cavity  45  having a diameter that is greater than about 22 mm may allow for less revolutions of shaft  47  to suitably stretch the flowable material. 
         [0026]    The total duration of shaft rotation may be, for example, about 60 seconds. The shaft rotating is completed prior to the flowable material reaching its gel point. Continuing to rotate shaft  47  after the flowable material reaches its gel point may undesirably introduce mechanical defects in the produced roll. 
         [0027]    It is further understood of a need to refrain from setting the speed of rotation of shaft  47  at such a relatively high rate so as to cause shaft  47  to slip, relative to the flowable material. Spinning shaft  47  too fast may result in the weld line not being sufficiently stretched. 
         [0028]    Shaft  47  may be rotated by any of a number of mechanisms. For instance, the end portion of shaft  47  opposite the end to which inlet  43  is associated may be mechanically coupled to the shaft of a motor such that the motor&#39;s shaft and shaft  47  are substantially coaxial. Alternatively, the longitudinal axis of shaft  47  and the longitudinal axis of the shaft of the motor may be substantially parallel to each other. The motor may, for example, be an electric drill. 
         [0029]    An alternative molding method, according to another example embodiment, is to spin shaft  47  during the time the flowable material is injected into mold cavity  45  through inlet  43 . Rotating shaft  47  while the flowable material is being injected into mold cavity  45  can result in substantially the same result, but more rotations will be required as compared to spinning shaft  47  only after mold injection is complete. It is estimated that under the same shaft and mold dimensions, it would take more than about ten times the number of rotations of shaft  47  compared to spinning after injection is complete. The reason that more rotations may be required is that spinning shaft  47  during injection requires the weld line to be stretched in two dimensions instead of one. Basically, the weld line would follow a substantial corkscrew type pattern, similar in shape to a barber shop pole, about the axis of shaft  47 . The weld line is thus being stretched circumferentially about the axis and parallel to the axis of shaft  47 . 
         [0030]    In another example embodiment, shaft  47  is rotated both during the injection of flowable material in mold  41  and following completion of such injection. 
         [0031]    In yet another example embodiment, mold  41  is rotated while shaft  47  is held stationary. This may occur using a similar mechanism for rotating shaft  47 . For example, an axle may extend from a top portion of mold  41  to which a motor or the like may be mechanically coupled. The rotation of mold  41  may occur only following the completion of flowable material being injected into mold cavity  45 , only during the injection of the flowable material into mold cavity  45 , or both during the injection of flowable material and thereafter. 
         [0032]    In another embodiment, shaft  47  is rotated in one direction and mold  41  is rotated in another direction. This dual rotation may occur only following completion of flowable material being injected into mold cavity  45 , only during the injection of the flowable material into mold cavity  45 , or both during the injection and thereafter. 
         [0033]    An experiment was conducted to determine the effectiveness of the above-identified processes. About 10 cc of white, slow setting epoxy was injected into the bottom of mold cavity  45  of a number of molds  41  prior to the reactive injection of the polyurethane rubber composition having a viscosity between about 5000 and about 8000 cP. In this particular case, the flowable polyurethane rubber composition included a black pigment to help provide adequate contrast between the weld line area and the bulk rubber. Substantially immediately after injecting the epoxy into cavity  47  of a mold  41 , the black polyurethane rubber composition was injected via inlet  43 . Following completion of the injection of the rubber composition into molds  41 , shaft  47  of about one third of the molds  41  was spun at relatively low rotational speeds (i.e., between about 100 rpm and about 200 rpm), shaft  47  of another third of molds  41  were spun at relatively high rotational speeds (i.e., between about 1000 rpm and about 1200 rpm), and shaft  47  of the final one third of molds  41  were not rotated. The shaft rotations were carried out in the order that the parts were molded using a coupling adapter and a cordless drill. The shaft spinning was carried out for about ten seconds for each mold  41 . The results of the experiment are shown in  FIGS. 8A-8C . 
         [0034]      FIG. 8A  shows photographs of cross sections located about 17 mm from inlet  43  of molds  41 .  FIG. 8B  shows photographs of cross sections about 35 mm from inlet  43  of molds  41 , and  FIG. 8C  shows photographs of cross sections located near the middle of mold cavity  45  of molds  41 . In each of  FIGS. 8A-8C , the left-most image is of a roll that was not spun, the middle and right images are of rolls that had their shaft  47  spun at relatively low speed (about 100 rpm to about 200 rpm) and relatively high speed (about 1000 rpm to about 1200 rpm), respectively. In looking at the left image in each of  FIGS. 8A-8C , a weld line resulting from the inability of the flow fronts to intimately mix is clearly visible. Each of the weld lines has three distinct regions, circled in the images. The middle region represents the bulk of the weld line, is about 1 mm to about 2 mm in width and spans approximately one third of the radius of the created roll, i.e., between shaft  47  and the outer surface of the roll. The inner and outer regions, located on either end of the middle region proximal to shaft  47  and to the outer surface of the created roll, respectively, are substantially triangular shaped regions. All of these regions are believed to pose problems in that they represent stagnant flow regions and result in electrical non-uniformities being formed around the circumference of the created roll at the region locations. 
         [0035]    The role in which the above-mentioned middle region in the left-most image of  FIGS. 8A-8C  plays in created electrical non-uniformities depends upon the diameter of the created roll. When the mold diameter is relatively large, such as about 22 mm, the middle region has a higher probability of being a major cause for electrical non-uniformities being formed. However, as the mold diameter decreases, such as to about 17 mm, the center region shrinks in size, thereby leaving the inner and outer triangular regions to dictate the occurrence of electrical non-uniformities. If the triangular regions are more dominate relative to the middle region, the weld lines are likely to be noticeably wider and more pronounced in print samples. In other words, smaller diameter rolls will have weld lines that are noticeably worse than larger diameter rolls. The reason for the mold diameter effect is due to the parabolic velocity profile of the two flow fronts and the fact that the molded parts also undergo a grinding process that removes about 1 mm of the diameter from the roll. The images in  FIGS. 8A-8C  are as molded without grinding being performed. 
         [0036]    The left-most images of  FIGS. 8A-8C  make clear the issue concerning weld lines. As can be seen in the middle and right-most images of  FIGS. 8A-8C , i.e., the images of the rolls created as a result of the additional act of rotating shaft  47 , there are no perceivable weld lines. Even at the interface with shaft  47  and outer (air) interface, virtually no sign of white epoxy is visible. Further, there are little if any visible artifacts in the created rolls at the intersection of the flow fronts. Additional experiments have shown that electrical uniformities at or near the regions of the flow fronts are substantially reduced or eliminated. 
         [0037]    The foregoing description of multiple embodiments has been presented for purposes of illustration. It is not intended to be exhaustive or to limit the application to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. It is understood that the subject matter of the present application may be practiced in ways other than as specifically set forth herein without departing from the scope and essential characteristics. It is intended that the scope of the application be defined by the claims appended hereto.