Patent Publication Number: US-10775715-B2

Title: Roller seal for a developer unit in a liquid electrophotographic printer

Description:
BACKGROUND 
     Liquid electrophotographic (LEP) printing uses a special kind of ink to form images on paper and other print substrates. LEP ink usually includes charged polymer particles dispersed in a carrier liquid. The polymer particles are sometimes referred to as toner particles and, accordingly, LEP ink is sometimes called liquid toner. LEP ink may also include a charge control agent to help control the magnitude and polarity of charge on the particles. An LEP printing process involves placing an electrostatic pattern of the desired printed image on a photoconductor and developing the image by presenting a thin layer of LEP ink to the charged photoconductor. The ink may be presented to the photoconductor with a roller that is commonly referred to as a “developer roller.” Charged toner particles in the ink adhere to the pattern of the desired image on the photoconductor. The ink image is transferred from the photoconductor to a print substrate, for example through a heated intermediate transfer member that evaporates much of the carrier liquid to dry the ink film, and then to the print substrate as it passes through a nip between the intermediate transfer member and a pressure roller 
    
    
     
       DRAWINGS 
         FIG. 1  is an isometric, partially exploded view illustrating one example of a developer unit for liquid electrophotographic printing. 
         FIGS. 2 and 3  are elevation and isometric views, respectively, showing rollers and seals from the developer unit in  FIG. 1 . 
         FIG. 4  illustrates one example of a section along the line  4 - 4  in  FIG. 1 . 
         FIG. 5  illustrates one example of a section along the line  5 - 5  in  FIG. 1 . 
         FIGS. 6 and 7  are details from  FIG. 5 . The outboard seal is omitted in  FIG. 7  to more clearly show the inboard seal. 
         FIGS. 8 and 9  are isometric views illustrating the example seals and end cap in the developer unit shown in  FIG. 1 . The seals are omitted in  FIG. 9  to more clearly show the end cap. 
         FIG. 10  is an isometric detail of the outboard seal shown in  FIG. 9 . 
         FIG. 11  is an isometric detail of the inboard seal shown in  FIG. 9 . 
     
    
    
     The same part numbers designate the same or similar parts throughout the figures. The figures are not necessarily to scale. 
     DESCRIPTION 
     In liquid electrophotographic printing, a thin film of LEP ink is applied to the exterior of a developer roller and then presented to a photoconductor at a nip between the developer roller and the photoconductor. A squeegee roller rotates against the developer roller to squeegee excess carrier liquid from the ink film before the ink is presented to the photoconductor. A cleaner roller rotates against the developer roller to remove residual ink after ink has been transferred to the photoconductor. The ends of each roller are sealed to help prevent ink leaking away from the rollers. 
     A new sealing system has been developed for the developer, squeegee, and cleaner rollers in an LEP developer unit to help contain ink at the ends of the rollers. In one example, the sealing system includes a first pair of face seals to seal the ends of the squeegee roller and the cleaner roller and a second pair of face seals to seal the ends of the developer roller. Each of the face seals for the developer roller is located inboard from the corresponding face seal for the squeegee and cleaner rollers and includes an annular sealing surface to contact the end face of the developer roller. Each of the seals for the developer roller also includes a guide surface intersecting the sealing surface near the nip between the developer roller and the cleaner roller. This guide surface helps guide any ink that does leak past the seal toward the cleaner roller where it can be removed along with ink cleaned from the surface of the developer roller. Each of the seals for the developer roller may also include radial sealing surfaces that partially surround the outboard ends of the squeegee roller and the cleaner roller. 
     These and other examples shown in the figures and described below illustrate but do not limit the scope of the patent, which is defined in the Claims following this Description. 
     As used in this document, “annular” means fully ring shaped like an annulus, or partially ring shaped like an annulus sector. 
       FIG. 1  is an isometric, partially exploded view illustrating one example of a developer unit  10  for a liquid electrophotographic printer.  FIGS. 2 and 3  are elevation and isometric views, respectively, showing rollers and seals from developer unit  10  in  FIG. 1 .  FIG. 4  illustrates one example of a section along line  4 - 4  in  FIG. 1 . Hatching is omitted and some of the parts are simplified in  FIG. 4  for clarity.  FIG. 5  illustrates one example of a section along line  5 - 5  in  FIG. 1 . A developer unit for an LEP printer is commonly referred to as a “binary ink developer” or a “BID.” An LEP printer may include multiple BIDs, one for each color ink for example. 
     Referring to  FIGS. 1-5 , developer unit  10  includes a housing  12  housing a developer roller  14 , a squeegee roller  16 , a cleaner roller  18 , and a sponge roller  20 . Referring specifically to  FIG. 4 , developer roller  14  is exposed outside housing  12  to present a film  22  of LEP ink  24  to a photoconductor  25 . LEP ink  24  may be pumped to a local supply chamber  26  in developer unit  10  from an external reservoir  28  through an inlet  30 , as shown diagrammatically in  FIG. 4 . Also, excess ink  24  may be reclaimed and collected in a local return chamber  32  and returned to reservoir  28  through an outlet  34 . In operation, according to one example, supply chamber  26  is pressurized to force ink  24  up through a channel  36  to the electrically charged developer roller  14 , as indicated by flow arrow  38 . A thin layer of ink is applied electrically to the surface of a rotating developer roller  14  along an electrode  40 . A voltage difference between developer roller  14  and electrode  40  causes charged particles in the LEP ink to adhere to roller  14 . Squeegee roller  16  rotates along developer roller  14  to squeegee excess carrier liquid from the ink on roller  14  while charged particles in the ink continue to adhere developer roller  14 . In the example shown, developer roller  14  is rotated clockwise and squeegee roller  16  is rotated counterclockwise so that the surfaces move in the same direction at the nip  42  between rollers  14  and  16   
     The now more concentrated ink film  22  on developer roller  14  is presented to photoconductor  25  where some of the ink is transferred in the pattern of a latent electrostatic image on the photoconductor at the nip  44  between roller  14  and photoconductor  25 , as the desired ink image  46 . A charged cleaner roller  18  rotates along developer roller  14  to electrically remove residual ink from roller  14 . In the example shown, cleaner roller  18  is rotated counterclockwise so that the surfaces move in the same direction at the nip  48  between rollers  14  and  18 . In this example, cleaner roller  18  is scrubbed with a so-called “sponge” roller  20  that is rotated against cleaner roller  18 . In the example shown, sponge roller  20  is rotated counterclockwise so that the surfaces move in opposite directions at the nip between rollers  18  and  20 . Some of the ink residue may be absorbed into sponge roller  20  and some may fall away. Excess carrier liquid and ink drains to return chamber  32 , as indicated by flow arrows  50 , where it can be recycled to reservoir  28 . 
     Referring again to  FIGS. 1-5 , developer unit  10  also includes end caps  52 A,  52 B attached to housing  12  to support each roller  14 - 20  on its respective shaft  54 - 60 . A roller sealing system  61  includes a pair of first face seals  62 A,  62 B between end caps  52 A,  52 B and the ends  64 A,  64 B of squeegee roller  16  and the ends  66 A,  66 B of cleaner roller  18 , to help prevent ink from leaking off the circular outer surfaces  68 ,  70  past the ends of rollers  16 ,  18 . Sealing system  61  also includes a pair of second face seals  72 A,  72 B between end caps  52 A,  52 B and the ends  74 A,  74 B of developer roller  14 , to help prevent ink from leaking off the circular outer surface  76  past the ends of roller  14 . In this example, as best seen in  FIGS. 2 and 3 , developer roller  14  is shorter than squeegee roller  16  and cleaner roller  14 , and each developer roller face seal  72 A,  72 B is located inboard from each squeegee/cleaner roller face seal  62 A,  62 B. 
     In this example, developer roller  14  includes an anti-friction ring  78  at each end  74 A,  74 B to reduce friction between roller  14  and face seals  72 A,  72 B. Anti-friction rings  78  may be desirable, for example, where friction between the ends of developer roller  14  and face seals  72 A,  72 B creates an unacceptable risk of damaging the seals without anti-friction rings. Each ring  78  is constructed as a thin flat disk made of polytetrafluoroethylene (PTFE) or another suitably low friction material. The outer diameter of rings  78  may be slightly smaller than the diameter of outer surface  76  so that the rings do not interfere with roller nips  42  and  48 . Low friction rings  78  may be secured in place, for example, with push-on retainers  80  on shaft  54 . Push-on retainers  80  may be desirable, for example, to secure rings  78  pre-flexed with a concave shape (bowed out at the center of the ring) to help keep the rings flat when installed. A push-on retainer takes advantage of the outboard force at the center of the ring for a more secure fit. 
     Referring to the detail views of  FIGS. 6 and 10 , each outboard seal  62 A,  62 B is constructed as a single part to seal the ends of both the squeegee roller  16  and the cleaner roller  18 . Also in this example, each seal  62 A,  62 B encircles shafts  56 ,  58  with a continuous face  82  to seal around the full circumference of roller ends  64 A,  64 B and  66 A,  66 B. In one example, the radius  83  of each face  82  is greater than the diameter of the corresponding roller  16 ,  18  to block ink from leaking outboard over the edge of the seal. The generally circular sealing faces  82  are joined by a web  84 . Each seal  62 A,  62 B may also include lobes  86  and  88 , for example to help seal a splash guard  90  and a doctor blade  92 , respectively. Splash guard  90  and doctor blade  92  are called out in  FIG. 7 . 
     Outboard, squeegee and cleaner roller face seal  62 A is omitted in  FIG. 7  to more clearly show inboard, developer roller face seal  72 A. Referring to the detail views of  FIGS. 7 and 11 , in this example each seal  72 A,  72 B is constructed as an arcuate body  94  that includes an inboard face  96  defining an annular sealing surface  98  along the arc  100  of body  94 , to contact the end face  74 A,  74 B of roller  14  ( FIGS. 2 and 3 ). Although it is expected that body arc  100  usually will be a circle, corresponding to a circular roller  14 , other suitable curves are possible. As noted above, in the example shown in the figures, the face on each end  74 A,  74 B of roller  14  is formed by an anti-friction ring  78 . In other examples, there are no anti-friction rings on the ends of developer roller  14 . In one example, the outer radius  102  of sealing surface  98  is greater than the outer radius of the end of the developer roller  14 , to help block ink from leaking outboard over the edge of the seal. 
     Seal body  94  also includes a guide surface  104  to help guide any ink that does leak past face  96  toward cleaner roller  18  where it can be removed along with ink residue cleaned from the surface of developer roller  14 . Guide surface  104  is oriented across body arc  100  at one end of annular sealing surface  98  near nip  48  between rollers  14  and  18 . Guide surface  104  is oriented along a chord  106  of body arc  100  that intersects body arc  100  at an obtuse interior angle  108 . As shown in  FIG. 7 , guide surface  104  intersects a line  107  between the center points (axes of rotation) of developer roller  14  and cleaner roller  18  at an acute angle  109  greater than 0°. Also in this example, as best seen in  FIG. 11 , guide surface  104  intersects annular sealing surface  98  at a right angle. While the length of guide surface  104  along chord  106  may vary, guide surface  104  should extend inward (toward the interior of body arc  100 ) further than any other part of seal body  94 . With this configuration, any ink encountering guide surface  104  is guided outward toward the circular outer surface of developer roller  14  and on to cleaner roller  18 . Testing shows that a guide surface  104  significantly reduces the accumulation of ink at the ends of the developer roller compared to a face seal  72 A,  72 B that does not include a guide surface  104 . 
     Developer roller seal body  94  may also include a sealing surface  110  at the end of annular sealing surface  98  near nip  48 . Sealing surface  110  conforms to the shape of the outer surface  70  ( FIG. 3 ) of cleaner roller  18 . As best seen in  FIG. 7 , surface  110  is pressed against roller surface  70  to form a radial seal  112  near each end of cleaner roller  18 . Seal body  94  may also include a sealing surface  114  at the end of annular sealing surface  98  near nip  42 . Sealing surface  114  conforms to the shape of the outer surface  68  ( FIG. 3 ) of squeegee roller  16 . As best seen in  FIG. 7 , surface  114  is pressed against roller surface  68  to form a radial seal  116  near each end of squeegee roller  16 . 
       FIGS. 8 and 9  are isometric views illustrating seals  62 B,  72 B and end cap  52 B in developer unit  10  shown in  FIG. 1 . The seals are omitted in  FIG. 8  to more clearly show the end cap. The configuration of seals  62 A,  72 A and end cap  52 A in developer unit  10  in  FIG. 1  is the same as that shown in  FIGS. 8 and 9  for seals  62 B,  72 B and end cap  52 B. Referring to  FIGS. 8 and 9 , outboard seal  62 B fits into a pocket  118  in end cap  52 B to help keep the seal in the desired position against the spinning rollers  16  and  18 . Seal  62 B may be glued to the end cap for additional stability. A mortise  120  on inboard seal  72 B fits over a tenon  122  on end cap  52 B to help keep the seal in the desired position against the spinning rollers  14  and  18 . In this example, a fixture  124  on endcap  52 B is fitted to the inside curvature at the less bulky end of the seal  72 B near radial seal  116  for added support to resist the motion of developer roller  14  and squeegee roller  16 . Inboard seal  72 B may be glued to outboard seal  62 B for additional stability. 
     Seals  62 A,  62 B and  72 A,  72 B may be made of a closed cell foam or another suitably resilient material that is compressible between an end cap and a roller. For a replaceable developer roller  14 , there can be some variation in the length and position of the roller, and so the sealing system should be able to accommodate a corresponding variation in seal compression. For a closed cell foam, at least 0.5 mm of foam compression is desired to form an effective face seal while the foam tends to take a set when compressed 10% or more. Thus, for an installation in which the position of the ends of the developer roller may vary ±0.5 mm, an overall combined thickness of 10.5 mm to 12.5 mm for the two seals  62 A/ 72 A and  62 B/ 72 B will help maintain a good seal without taking a set, and while still maintaining acceptable lateral stability. Although shown as separate parts, seals  62 A/ 72 A and  62 B/ 72 B could be molded or otherwise formed as a single part. 
     As noted above, the examples shown in the figures and described herein illustrate but do not limit the scope of the patent, which is defined in the following Claims. 
     “A”, “an” and “the” used in the claims means one or more.