Patent Publication Number: US-7899357-B2

Title: Reinforced doctor blade assembly seal and printer cartridge employing the reinforced seal

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     None. 
     BACKGROUND 
     1. Field of the Invention 
     The present invention relates generally to an image forming device and, more particularly, to a reinforced doctor blade assembly seal and a printer cartridge employing the reinforced seal. 
     2. Description of the Related Art 
     An image forming device, such as a laser printer and the like, includes a drum having a photoconductive outer cylindrical surface charged to a uniform electrical potential and then selectively exposed to light in a pattern corresponding to an original image. Those areas of the photoconductive surface exposed to light are discharged thus forming a latent electrostatic image thereon. A developer material, such as toner, having an electrical charge such that the toner is attracted to the discharged area of the photoconductive surface operates in contact with the photoconductive surface. The drum developed image then rotates toward a transfer station. A recording sheet is then brought into contact with the photoconductor and the toner thereon is transferred to the recording sheet in the form of the latent electrostatic image. The recording sheet is then heated, permanently fusing the toner to the sheet. In preparation for the next image forming cycle, the photoconductive surface of the drum is cleaned of residual toner and recharged. U.S. Pat. No. 6,990,308, assigned to the assignee of the present invention, discloses an image forming device having the aforementioned configuration. The disclosure of this patent is hereby incorporated herein by reference thereto. 
     Typically, as seen in the cited patent, the toner is stored in a toner well or reservoir of a printer cartridge located adjacent to the drum. A doctor blade assembly and a developer roll of a developer unit, which is part of the printer cartridge, are positioned between the toner reservoir and the drum for controlling the amount of toner delivered to the drum. A nip created between the doctor blade of the doctor blade assembly and the developer roll controls the thickness of the toner layer formed on the developer roll. To be able to print correctly, toner must be evenly distributed, or doctored, out in a thin uniform layer onto the developer roll in the proper thickness. This function is performed by the doctor blade. 
     Referring to  FIGS. 1 ,  2 A and  2 B herein, there is partially shown in  FIGS. 2A and 2B  the printer cartridge  10  in which a seal  12  in the form of an elongated strip of a flexible plastic film is positioned between the doctor blade assembly  14  and a portion of a housing  16  of the printer cartridge  10 . The housing portion is in the form of a corner  16   a  on the housing  16 . The strip of film comprising the seal  12 , shown by itself in  FIG. 1 , is a bi -axially-oriented PET (boPET) polyester film material, marketed under the trademark Mylar. It is positioned in a space or gap  18  between the doctor blade assembly  14  and the corner  16   a  on the cartridge housing  16  in order to prevent leaking of toner from between these components through this gap  18 . Referring to  FIG. 1  herein, this seal, generally designated  12 , is shown by itself. In  FIG. 2A  the seal  12  is shown correctly installed and positioned in the printer cartridge  10 , closing the gap  18  between a bracket  20  of the doctor blade assembly  14  and the housing  16  of the printer cartridge  10 . 
     The developer roll  22 , a toner adder roll  24  and the doctor blade assembly  14 , with the doctor blade  26  mounted by the bracket  20 , make up the developer unit  28  and are mounted on the housing  16  of the printer cartridge  10 , as shown in  FIGS. 2A and 2B . The quantity of toner in the toner reservoir of the printer cartridge  10  is depleted through use in the printing operation. Thus the printer cartridge  10  is a consumable item which must be replaced periodically in the image forming device. Being a consumable, the printer cartridge  10  must be designed and manufactured to withstand rough handling during shipping, separate from the printer, through the supply chain to a customer and installation into an image forming device. The printer cartridge  10  has the potential to be dropped and thus exposed to large shock forces during shipping separate from the printer. 
     Dropping the printer cartridge  10  can lead to excessive toner leaks from behind the doctor blade assembly bracket  20  due to internal pressure forcing the doctor blade assembly seal  12  to blow out and dislocate from its correct sealing position, as seen in  FIG. 2A , to the blown-out position, as seen in  FIG. 2B . A photograph of the blown-out position of the seal  12  replicated by a drop test is shown in  FIG. 2C . This blow out and dislocation of the seal  12  causes two problems. First, when the seal  12  is pushed out over the doctor blade assembly  14  as shown in  FIG. 2C , its sealing integrity is lost and toner can easily leak from the printer cartridge  10 . Second, as shown in  FIG. 2B  the seal  10  may assume a wedged condition upstream of the gap  18  and on top of the doctor blade assembly  14  where it applies increased downward force onto the doctor blade  26 , adversely affecting the doctoring performance of the doctor blade  26 . 
     One proposed solution for avoidance of the blow out problem has been to use a seal in the form of a strip of foam material, rather than of the boPET polyester material, behind the doctor blade assembly. However, the presence of the foam tends to prevent the doctor blade  26  from translating smoothly against the developer roll  22 . Also, the foam causes more leak paths to propagate than the boPET polyester seal, requiring the application of wax to fill the anticipated leak paths. 
     Thus, there is a continuing need for an innovation that will provide effective sealing between the doctor blade assembly and the housing of the printer cartridge. 
     SUMMARY OF THE INVENTION 
     The present invention meets this need by employing an innovation involving the reinforcement of the prior art seal through its partial lamination with a supplemental strip of smaller size to provide a reinforced seal. The robustness of the printer cartridge incorporating the reinforced seal of the present invention is increased to withstand shock from rough shipping and handling of the printer cartridge to a customer, with no compromise of its sealing function. Partial lamination with the smaller size supplemental strip provides the reinforced seal with laminated and non-laminated portions having different thicknesses which improves printer cartridge robustness and provides extra rigidity allowing for easier and more accurate installation of the reinforced seal. 
     Accordingly, in an aspect of the present invention, a doctor blade assembly seal includes a base strip of a flexible plastic film having a thickness and a surface of predetermined area bounded by multiple edges, and a supplemental strip of a flexible plastic film having a thickness and a surface of predetermined area bounded by multiple edges. The base strip also has a foldable or flexible region extending length-wise of the base strip between one pair of the multiple edges and spaced from and located intermediately between another pair of the multiple edges. The flexible plastic film of the supplemental strip is laminated onto the flexible plastic film of the base strip offset from and along one side of the foldable region such that the base strip has laminated and non-laminated portions with different thicknesses along opposite sides of the foldable region on the base strip. The reinforced seal also includes an attaching mechanism, such as an adhesive coating, on at least a section of the non-laminated portion of the base strip extending between the one pair of multiple edges of the base strip. The thickness of the supplemental strip is within a range of from three to four times greater than the thickness of the base strip. The multiple edges of the base strip correspond to and are longer than the multiple edges of the supplemental strip such that the surface of the base strip is substantially U-shaped and borders the supplemental strip along a plurality of the multiple edges of the supplemental strip. At least a portion of the U -shaped surface on the base strip has the adhesive coating thereon. 
     In another aspect of the present invention, a printer cartridge includes a housing having a reservoir for holding toner, a developer roll supported by the housing and operable to receive toner from the reservoir and transfer the toner to a photoconductive drum, a doctor blade assembly supported by the housing adjacent to the developer roll and having a doctor blade and a bracket for positioning the doctor blade to form a nip with the developer roll to control the amount of toner metered onto the developer roll, the bracket also disposed adjacent a portion of the housing such that a gap is defined between the bracket and the housing portion, and the above-described reinforced seal disposed through the gap to provide sealing of the gap between the bracket and the housing portion to prevent potential leakage of toner in a predetermined direction of flow through the gap and from the printer cartridge. The adhesive coating on the non-laminated portion of the base strip adapts the reinforced seal at the non-laminated portion for attachment to the housing at least downstream of the gap. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale and in some instances portions may be exaggerated in order to emphasize features of the invention, and wherein: 
         FIG. 1  is a perspective view of a prior art doctor blade assembly seal. 
         FIG. 2A  is a side elevational view of a portion of a printer cartridge depicting correct positioning of the prior art seal of  FIG. 1  in a gap between a doctor blade assembly and a corner on a housing of the printer cartridge. 
         FIG. 2B  is a view similar to that of  FIG. 2A  but now showing the prior art seal of  FIG. 1  dislocated to a blown-out position in which it assumes a wedged condition on top of the doctor blade assembly. 
         FIG. 2C  is a photograph of a blown-out doctor blade assembly seal. 
         FIG. 3  is a perspective view an exemplary embodiment of a reinforced seal of the present invention. 
         FIG. 4  is an enlarged cross-sectional view of the reinforced seal taken along line  4 - 4  of  FIG. 3 . 
         FIG. 5  is an enlarged fragmentary cross-sectional view of the reinforced seal extending in the sealing relationship in the gap between the doctor blade assembly and a corner portion on the printer cartridge housing. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the invention are shown. Indeed, the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numerals refer to like elements throughout the views. 
     Referring now to  FIGS. 3-5 , there is illustrated an exemplary embodiment of a reinforced seal of the present invention, generally designated  30 , for sealably closing the gap  18  between the doctor blade assembly  14  and the housing  16  of the printer cartridge  10 . The reinforced seal  30  basically has partially a single layered construction and partially a two layered, laminated construction, comprised of an elongated base strip  32  of a flexible plastic film and an elongated supplemental strip  34  of a flexible plastic film smaller in size than the base strip  32  and laminated, such as by being adhesively attached, on the base strip  32 . The material comprising the flexible plastic film of both strips  32 ,  34 , while not necessarily so limited, may be the same, a bi-axially-oriented polyethylene terephthalate (PET) polyester, or boPET polyester, which is also the same material used in the prior art seal of  FIG. 1 . 
     Both the base and supplemental strips  32 ,  34  of the reinforced seal  30  have polygonal configurations, preferably each rectangular in shape. The strips  32 ,  34  have respective surfaces  32   a ,  34   a  of predetermined areas bounded by multiple edges  32   b - 32   e ,  34   b - 34   e , respectively, correspondingly adjacently positioned in spaced apart relationship to each other. In the exemplary embodiment illustrated in  FIG. 3 , the multiple edges  32   b - 32   e  and  34   b - 34   e  on the respective base and supplemental strips  32 ,  34  preferably are four in number. The area of the surface  32   a  of the base strip  32  is larger than the area of the surface  34   a  of the supplemental strip  34  such that the surface  32   a  of the base strip  32  has a U-shaped configuration and borders the supplemental strip  34  at a plurality, namely three, of its edges  34   c - 34   e . The base strip  32  is thus provided with adjacent laminated and non-laminated portions, generally designated  36 ,  38 , along opposite sides of a foldable region F (as represented by a dashed line) extending between one pair of edges  32   c ,  32   d  of the base strip  32  and spaced from and intermediately between another pair of edges  32   b ,  32   e  of the base strip  32 . The base and supplemental strips  32 ,  34  are substantially aligned with one another along their respective one edges  32   b ,  34   b.    
     The supplemental strip  34  is shorter in length and width than the base strip  32 . The strips  32 ,  34  are relatively narrow in configuration with their respective lengths being much longer or larger than their widths. The U-shaped surface  32   a  of the base strip  32  further has a U-shaped outer portion  40  and a U-shaped inner portion  42  such that the U-shaped inner portion  42  bounds the plurality, namely three, of the multiple edges  34   b - 34   e  of the supplemental strip  34 . The U-shaped outer portion  40  has an attaching mechanism, such as an adhesive coating  44 , thereon and contains the foldable region F which is aligned with the gap  18  when the reinforced seal  30  is installed as shown in  FIG. 5 . The foldable or flexible region F per se is at approximately the same position as it was on the prior art seal shown in  FIG. 1 . 
     The base strip  32  has a thickness of approximately 0.051 mm, the same as the prior art seal  12 . The supplemental strip  34  has a thickness of approximately 0.19 mm which is within a range of from three to four times the thickness of the base strip  32 . The thickness of the base strip  32  provides sufficient flexure stiffness needed to press the non -laminated portion  38  of the base strip  32  of the reinforced seal  30  and the adhesive coating  44  thereon against an outside surface  16   b  of the housing  16  above the gap  18  with the supplemental strip  34  located below the gap  18  so as to prevent potential leakage of toner along the path of flow as represented by arrow  46  through the gap  18 , as best seen in  FIG. 5 . The adhesive coating  44  on the base strip  32  enables it, the same as in the case of the prior art seal  12 , to stick to the outside surface  16   b  of the housing  16 , as shown in  FIG. 2A . 
     Thus, the supplemental strip  34  is laminated on the base strip  32  as described above such that when the reinforced seal  30  is installed on the outside surface  16   b  of the housing  16  the adhesively-coated area of the base strip  32  alone extends above the corner  16   a on the housing  16  where the base strip  32  adheres to the housing  16  while the supplemental strip  34  is located below the housing corner  16   a . The foldable region F defined on the base strip  32  of the reinforced seal  30  is contiguous with the corner  16   a  of the housing  16  where the seal  30  is bent when in its installed position, as depicted in  FIG. 5 . Thus, the supplemental strip  34  does not come into any significant contact, if any, with the corner  16   a  nor cause any unintended repositioning of the doctor blade assembly  14 . The supplemental strip  34  being laminated to the base strip  32  sufficiently stiffens and reinforces the partially laminated seal  30  of the present invention such that the shock load needed to cause a seal failure is now higher than the printer cartridge  10  is likely to experience during handling and shipping. The thickness of the reinforced seal  30  through the base and supplemental strips  32 ,  34  of the laminated portion  36  is greater than the width of the gap  18  which deters blow out of the reinforced seal  30  outward through the gap  18 . As a result, the reinforced seal  30  is much more resistant to blowing out over the doctor blade assembly  14 . Also, with this added stiffness or rigidity, the ease of installation of the reinforced seal  30  is also increased. Before the rigidity of the laminated construction was added, the entire length of the prior art seal  12  deflected under its own weight. Now, with the reinforced seal  30  being partially laminated construction, once the non-laminated portion  38  of the reinforced seal  30  is properly placed onto the housing  16 , with the adhesive-covered opposite end portions  30   a  of the seal  30  overlapping J-seals  48  located at the opposite ends of the doctor blade assembly  14  and the developer roll  22 , the middle unsupported laminated portion  36  of the reinforced seal  30  holds its generally planar shape due to the reinforcing presence of the supplemental strip  34  allowing for more precise placement of the reinforced seal  30  when being secured to the housing  16  of the printer cartridge  10 . 
     The reinforced seal  30  tailors the solution provided by the present invention to meet the constraints of the problem that is faced. For example, merely increasing the thickness of the entire prior art seal  12  would not alleviate the problem. While a thicker boPET polyester film of the prior art seal  12  would be less prone to flexing when exposed to shock loads, it must not be so thick that the seal would yield and crease, as the thicker seal would do, when it is placed behind the doctor blade assembly. Just using a thicker seal is also not feasible because opposite end portions that overlap the J-seals  48  must remain thinner than the remainder of the seal to prevent a leak path across the J-seals  48  located adjacent the opposite end portions of the seal and so as not to dislocate the positioning of the doctor blade nip. In order to prevent the prior art seal  12  from creasing while positioned behind the doctor blade assembly  14 , the prior art seal  12  to be effective would have to be provided with a variable thickness like the reinforced seal  30 . Thus, it can be readily understood that the partial laminated construction of the reinforced seal  30  is tailored to address and satisfy all these design constraints without causing unintended adverse consequences. 
     The foregoing description of several 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 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.