Stock material or miscellaneous articles – Composite – Of silicon containing
Reexamination Certificate
2000-11-30
2002-09-17
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Composite
Of silicon containing
C106S287110, C106S287120, C361S221000, C399S176000, C399S279000, C399S313000, C524S413000, C524S435000, C528S028000, C528S025000, C528S038000, C492S053000
Reexamination Certificate
active
06451438
ABSTRACT:
TECHNICAL FIELD
This invention relates to conductive, soft urethane rollers, e.g., developer rollers, charge rollers, or toner transfer rollers, for use in an electrophotographic printer, e.g., a laser printer. The invention also relates to an electrophotographic printer containing such a roller.
BACKGROUND
A laser printer often includes a digital light emitter photoconductor drum, a charge roller, a developer roller, a developer blade, a transfer roller, and a toner storage unit. During printing, the transfer roller supplies toner to the developer roller, and the developer blade forms the toner into a thin, even layer on the surface of the developer roller. The charge roller, which is in contact with the surface of the photoconductive drum, receives a high voltage from a power supply, and charges the photoconductive drum with a positive or negative charge. After the photoconductive drum has been exposed a light emitter, the surface of the photoconductor drum forms an electrostatic latent image. The voltage difference between the developer roll and the photoconductive drum allows the former to transfer toner to the drum surface. Areas of the drum surface that are discharged by the laser attract the toner, whereas areas that are more highly charged repel the toner. The discharged and charged areas thus form toner images. The laser printer may also include a toner-removal wiper that removes excess toner from the surface of the developer roller after the developer roller has contacted the photoconductor drum. The toner on the drum subsequently is transferred to paper, and then fuses to form the print.
Many different designs of laser printers are known. They include Shiraki et al., U.S. Pat. No. 5,768,668; Sato, U.S. Pat. No. 5,752,146; Park, U.S. Pat. No. 5,727,022; Okada et al., U.S. Pat. Nos. 5,669,047 and 5,655,197; Sakaguchi, U.S. Pat. No. 5,602,631; Iguchi et al., U.S. Pat. No. 5,600,417; Ikeda et al., U.S. Pat. No. 5,367,367; Kogo et al., U.S. Pat. Nos. 5,324,885 and 5,214,239; Kinoshita et al., U.S. Pat. Nos. 5,311,264 and 5,287,150; Nishio, U.S. Pat. Nos. 5,241,343, 5,076,201, and 5,062,385; and Goyert et al., U.S. Pat. No. 4,521,582; all of which are incorporated herein by reference.
The charge roller and developer roller are usually cylindrical in shape and typically include a central shaft surrounded by a synthetic rubber or urethane elastomer portion. Many charge rollers for use in electrophotographic printing contain multiple layers of rubber coating or foam coating with carbon black filler inside. Due to the need to coat the surface with multiple layers, low production and high cost result.
Coating a charge roller of high conductivity and soft durometer with one layer of rubber/foam (specifically, urethane) has been a challenging task. Most soft charge rollers having high conductivity (typically, 5E5-5E7) need to contain plasticizer to maintain the right hardness (typically, 25 Shore A-50 Shore A). The use of plasticizer, however, may lead to tackiness on the surface of the roller, which can result in poor print quality.
Having the right hardness is also important for proper functioning of a developer roller. Typically, a developer roller has a durometer ranging from about 50 Shore A to 65 Shore A. For use in a high speed, high resolution printer, rollers are typically required to have lower durometer (e.g., 30-50 Shore A). When the hardness drops to below 50 Shore A, the surface of the roller can become too tacky for the toner powder to be properly transferred from the developer roller to the drum, resulting in poor print quality. On the other hand, a hardness of more than 50 Shore A may lead to partial melting of the toner for high speed, high resolution printers.
SUMMARY OF INVENTION
In general, the invention features a conductive roller (e.g., a developer roller or charge roller) for use in laser printers or other electrophotography printers such as photocopier or thermal printer. The roller includes an inner shaft surrounded by a single layer of conductive solid or foam thermoset copolymer formed of reactive silicone and urethane precursors. A roller containing solid thermoset copolymer means that the thermoset urethane portion contains no void. In contrast, a roller containing foam thermoset copolymer contains void, e.g., a microcellular roller. The rollers generally have a uniform volume resistivity ranging from about 1E5 to about 5E10 ohm-cm; preferably, from about 5E5 to about 5E9 ohm-cm, and a hardness of between about 25 Shore A and about 50 Shore A; preferably, between about 30 Shore A and about 45 Shore A.
The thermoset copolymer exhibits a stable volume resistivity even when the humidity changes from about 10% to about 90% and the temperature changes from about 10° C. to about 40° C. By “stable volume resistivity ” is meant that the ratio of volume resistivity at 10° C., 20% relative humidity (LL) to the volume resistivity at 40° C., 90% relative humidity (HH) is less than 50. The thermoset copolymer also exhibits low tackiness under the same conditions (i.e., from LL to HH). The entire copolymer displays uniform conductivity. A roller has low tackiness if it does not adhere to another identical roller during storage, i.e., no pressure is applied to the rollers, and the coefficient of friction is less than 2.0.
In one aspect, the conductive roller contains a metal salt evenly or homogeneously distributed in a copolymer formed of the precursors: (i) a diisocyanate, (ii) a reactive silicone containing an amine group, and (iii) a polyol or a polyamine. The incorporation of silicone into the backbone of the copolymer generally allows the resulting copolymer to have low tackiness property and better resistance to change in humidity and temperature. The roller preferably is substantially free of plasticizer and non-reactive silicone oil. As used herein, a copolymer that is “substantially free ” of a material means that the amount of the material is negligible in the composition, i.e., less than about 0.001 wt % of the total weight of the copolymer. By “non-reactive ” is meant the silicone oil does not incorporate into the backbone of the copolymer.
In another aspect, the conductive roller has a volume resisitivity of between about 1E5 ohm-cm and about 5E10 ohm-cm and contains a metal salt completely dissolved and evenly or homogeneously distributed in a copolymer formed of the precursors: (i) a diisocyanate, (ii) a reactive silicone containing a hydroxyl group or an amine group, and (iii) a polyol or a polyamine.
The invention also features methods of preparing the roller including the thermoset copolymer, as well as laser printers including the roller.
Other features and advantages will be apparent from the description of the preferred embodiments thereof, and also from the claims.
DETAILED DESCRIPTION
A preferred conductive roller contains a shaft surrounded by a single layer of solid conductive silicone-containing thermoset copolymer. The outer surface of the roller may be uncoated, or may be coated with, e.g., a rubber such as a urethane rubber, nitrile rubber or silicone rubber. The thickness of the coating may be, e.g., between 1.5 and 10 mil. The shaft can be made of steel, aluminum, a conductive plastic, pultrusion conductive rod, or any other material commonly used for the shaft of a conductive roller.
The conductive roller can be used in photographic printing or electrophotographic printing; preferably, the roller is used in electrophotographic printers, e.g., laser printers, thermal printers, and photocopiers.
In one embodiment, the preferred silicone-containing thermoset copolymer is formed of precursors such as a diisocyanate, a polyol or a polyamine, and a reactive silicone containing an amine group. In another embodiment, the preferred silicone-containing thermoset copolymer, which has a volume resistivity of between about 5E5 ohm-cm and about 5E9 ohm-cm, is formed of precursors such as a diisocyanate, a polyol or a polyamine, and a reactive silicone containing a hydroxyl group and/or an amine group.
The silicone-containing thermoset copolyme
Chiang Albert C.
Roderick John A.
Dawson Robert
Mearthane Products Corporation
Zimmer Marc S
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