DEVELOPER ROLLER FOR LIQUID ELECTROPHOTOGRAPHIC PRINTING
1. A developer roller for liquid electrophotographic printing, comprising:
- a conductive cylinder;
a compliant exterior around the cylinder to present a film of liquid electrophotographic ink to a photoconductor during printing; and
rigid conductive plastic sandwiched between the cylinder and the exterior.
In one example, a developer roller for liquid electrophotographic printing includes a cylindrical metal inner core, a rigid conductive plastic outer core surrounding the inner core, and a compliant exterior surrounding the outer core.
- 1. A developer roller for liquid electrophotographic printing, comprising:
a conductive cylinder; a compliant exterior around the cylinder to present a film of liquid electrophotographic ink to a photoconductor during printing; and rigid conductive plastic sandwiched between the cylinder and the exterior.
- View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
- 9. A developer roller for liquid electrophotographic printing, comprising:
a multi-part rigid conductive core that includes a cylindrical metal inner core and a rigid conductive plastic outer core surrounding the inner core; and a resistive compliant exterior surrounding the outer core.
- View Dependent Claims (10, 11, 12, 13)
- 14. A developer unit for a liquid electrophotographic printer, comprising:
a developer roller to present LEP ink to a photoconductor; and a squeegee roller to squeegee ink on the developer roller; the developer roller including a multi-part rigid conductive core that includes; a cylindrical metal inner core and a rigid conductive plastic outer core surrounding the inner core; and a compliant exterior surrounding the outer core.
- View Dependent Claims (15)
Liquid electro-photographic (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. Some LEP printers use a developer roller that includes an aluminum or steel core covered by a polyurethane exterior. Polyurethane formed around an aluminum or steel core is susceptible to depolymerization caused by unwanted ion migration. Electroless nickel plating may be used to minimize the risk of depolymerization. Even with nickel plating, however, the polyurethane exterior is still susceptible to depolymerization, particularly in hot, humid environments. Also, polyurethane does not adhere well to electroless nickel plating, making the polyurethane exterior sensitive to detaching from the core. Consequently, for better adhesion the polyurethane exterior is wrapped around the ends of the core. The corner at each of end of the metal core is rounded to accommodate the polyurethane wrap. The rounded corners weaken the electric field at the ends of the roller, which shortens the usable length of the roller.
A new developer roller for liquid electrophotographic printing has been developed in which a layer of rigid conductive plastic is sandwiched between a metal core and a polyurethane exterior to improve adhesion and to reduce depolymerization of the polyurethane, without degrading the mechanical or electrical characteristics of the roller. In one example, a carbon fiber filled polyphenylene sulfide (PPS) or other suitably rigid plastic is formed directly on a metal core and then a polyurethane exterior is applied directly to the plastic. The plastic provides good adhesion for the polyurethane exterior without the risk of ion migration that can cause depolymerization, and the carbon fiber fill and intimate contact of the plastic with the metal core provides good core conductivity and mechanical strength. Also, the better adhesion of the polyurethane to the plastic allows a sharper corner at the ends of the core, extending the usable length of the roller.
This 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, “conductive” means having a resistivity below 1 kΩ-cm; and “resistive” means having a resistivity of at least 10 kΩ-cm.
A conductive core 12 provides the operating voltage to exterior 14 during printing. Thus, the resistivity of outer core 18 should be low and the electrical conductivity between inner core 16 and outer core 18 should be high. Outer core 18 should also provide a good adhesive base for exterior 14. Although any suitably rigid conductive plastic may be used, it is expected that a carbon filled plastic cast, molded or otherwise formed directly on core 12 will provide the desired conductivity and mechanical rigidity for many liquid electrophotographic printing applications. In the example shown in
A hard plastic shell 28 formed around a cylindrical inner core 16 allows a comparatively sharp corner 30 at each end 24, 26 of inner core cylinder 20. For example, a polyurethane exterior 14 may be formed securely on a carbon fiber filled polyphenylene sulfide (PPS) outer core 18 around a corner 30 with a radius of 0.5 mm, as shown in
Although any suitably compliant resistive material may be used for exterior 14, it is expected that a polyurethane exterior 14 exhibiting a resistivity of at least 0.5 MΩ-cm will be suitable for many liquid electrophotographic printing applications to match the properties of the exterior on existing developer rollers. Similarly, although any suitable rigid conductive plastic may be used for outer core 16, it is expected that a carbon filled PPS, polycarbonate, polyamide, or polyetherimide exhibiting a resistivity below 1.0 kΩ-cm will enable performance comparable to existing developer rollers, for seamless integration into existing LEP printers and LEP printing processes. For example, testing shows that an outer core 18 made of PPS filled with about 50% carbon fibers by weight, exhibiting a resistivity below 1000-cm, cast directly around a solid cylindrical aluminum inner core 14 provides the mechanical and electrical characteristics that enable performance comparable to existing developer rollers with a solid metal core.
The interface between a rigid plastic carbon filled core 18 and a polyurethane exterior 14 is more stable than a metal-to-polyurethane interface, reducing the risk of depolymerization that can cause reversion spots or staining during storage. A plastic core 18 also reduces or eliminates the need for electroless nickel plating a metal core 16, thus lowering cost, while improving adhesion between the polyurethane exterior and the core.
Referring specifically to
The now more concentrated ink film 50 on developer roller 10 is presented to photoconductor 54 where some of the ink is transferred in the pattern of a latent electrostatic image on the photoconductor, as the desired ink image 74. A charged cleaner roller 46 rotates along developer roller 10 to electrically remove residual ink from roller 10. In the example shown, cleaner roller 46 is rotated counterclockwise (arrow 76) so that the surfaces move in the same direction at the interface between rollers 10 and 46. In this example, cleaner roller 46 is scrubbed with a so-called “sponge” roller 48 that is rotated against cleaner roller 46. In the example shown, sponge roller 48 is rotated counterclockwise (arrow 78) so that the surfaces move in opposite directions at the interface between rollers 46 and 48. Some of the ink residue may be absorbed into sponge roller 48 and some may fall away. Ink is removed from sponge roller 48 through contact with the chamber wall and/or with a squeezer roller (not shown). Excess carrier liquid and ink drains to return chamber 62, as indicated by flow arrows 80, where it can be recycled to reservoir 58.
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.