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
The same part numbers designate the same or similar parts throughout the figures. The figures are not necessarily to scale.
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.
Referring to
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
In this example, developer roller 14 includes an anti-friction ring 78 at each end 74A, 74B to reduce friction between roller 14 and face seals 72A, 72B. Anti-friction rings 78 may be desirable, for example, where friction between the ends of developer roller 14 and face seals 72A, 72B 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
Outboard, squeegee and cleaner roller face seal 62A is omitted in
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
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 (
Seals 62A, 62B and 72A, 72B 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 62A/72A and 62B/72B will help maintain a good seal without taking a set, and while still maintaining acceptable lateral stability. Although shown as separate parts, seals 62A/72A and 62B/72B 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.
Filing Document | Filing Date | Country | Kind |
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PCT/EP2017/052072 | 1/31/2017 | WO | 00 |
Publishing Document | Publishing Date | Country | Kind |
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WO2018/141369 | 8/9/2018 | WO | A |
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