Patent Application
20120190518
1. Technical Field
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.
2. Description of the Related Art
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.
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.
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.
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.
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.
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.
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.
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.
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:
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.
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.
With reference to
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
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.
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.
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.
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.
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.
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'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.
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.
In another example embodiment, shaft 47 is rotated both during the injection of flowable material in mold 41 and following completion of such injection.
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.
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.
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
The role in which the above-mentioned middle region in the left-most image of
The left-most images of
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.
