Patent Grant
8649704
The disclosure herein relates to overcoat layers, and more specifically, to an outer surface layer of carbon black and polycarbonate for xerographic members such as bias charging members.
In a conventional charging step included in electrophotographic processes using an electrophotographic photosensitive member, in most cases a high voltage (DC voltage of about 5-8 KV) is applied to a metal wire to generate a corona, which is used for the charging. In this method, however, a corona discharge product such as ozone and NOx is generated along with the generation of the corona. Such a corona discharge product deteriorates the photosensitive member surface and may cause deterioration of image quality such as image blurring or fading or the presence of black streaks across the copy sheets. Further, ozone contamination may be harmful to humans if released in relatively relatively large quantities. In addition, a photosensitive member that contains an organic photoconductive material is susceptible to deterioration by the corona products.
Also, as the power source, the current directed toward the photosensitive member is only about 5 to 30% thereof. Most of the power flows to the shielding plate. Thus, the efficiency of the charging means is low.
For overcoming or minimizing such drawbacks, methods of charging have been developed using a direct charging member for charging the photosensitive member. For example, U.S. Pat. No. 5,017,965 to Hashimoto et al., uses a charging member having a surface layer which comprises a polyurethane resin. Another approach, European Patent Application 0 606 907 A1, uses a charging roller having an elastic layer comprising epichlorohydrin rubber, and a surface layer thereover comprising a fluorine containing bridged copolymer.
These and other known charging members are used for contact charging a charge-receiving member (photoconductive member) through steps of applying a voltage to the charging member and disposing the charging member being in contact with the charge-receiving member. Such bias charging members require a resistivity of the outer layer within a desired range. Specifically, materials with resistivities which are too low will cause shorting and/or unacceptably high current flow to the photoconductor. Materials with too high resistivities will require unacceptably high voltages. Other problems which can result if the resistivity is not within the required range include nonconformance at the contact nip, poor toner releasing properties and generation of contaminant during charging. These adverse affects can also result in bias charging members having non-uniform resistivity across the length of the contact member. It is usually the situation that most of the charge is associated at or near the center of the charge member. The charge seems to decrease at points farther away from the center of the charge member. Other problems include resistivity that is susceptible to changes in temperature, relative humidity, running time, and leaching out of contamination to photoconductors.
Due to its contact, the direct charging apparatus also causes more wear and tear to itself, imaging members and any other components with which it comes in contact. Failure modes in a bias charge roller (BCR) show up in prints such as dark streaks, and white and dark spots, which are associated with surface damages on BCR. These defects are usually derived from degradation or debris build-up on the BCR surface along the circumference, i.e. the process direction. The degradations can be scratches, abrasion, or pothole-like damages to the BCR surface. Another known deficiency is toner filming on the BCR surface that can also show up as print streaks. All these failures will reduce BCR life and therefore limit usage life.
There is described a bias charging member that includes a conductive core, and an outer surface layer disposed on the conductive core. The outer surface layer includes a conductive additive and polycarbonate.
There is further described a method of refurbishing a bias charging member. The method includes obtaining a bias charging member having a conductive core and an outer surface. A dispersion of a carbon black and polycarbonate is coated on the outer surface. The coating is heated to form a conductive overcoat.
There is further described a bias charging member that includes a conductive core and an outer surface layer on the conductive core. The surface layer includes carbon black and a polymer, wherein the outer surface layer has a surface resistivity of equal to or greater than about 1×1013 ohm/, an average modulus of from about 3.50 to about 5.00 GPa and an average hardness of from about 250 to about 500 MP.
Referring to
The protective overcoat layer or outer surface layer 7 contains semiconductive carbon black in polycarbonate. The density of the carbon black was about 264 kg/m3.
The electro-conductive core 4 serves as an electrode and a supporting member of the charging roll, and is composed of an electro-conductive material such as a metal or alloy of aluminum, copper alloy, stainless steel or the like; iron coated with chromium or nickel plating; an electro-conductive resin and the like. The diameter of the electro-conductive core is, for example, about 1 mm to about 20 cm, or from about 5 mm to about 2 cm.
The base materials can be isoprene rubber, chloroprene rubber, epichlorohydrin rubber, butyl rubber, polyurethane, silicone rubber, fluorine rubber, styrene-butadiene rubber, butadiene rubber, nitrile rubber, ethylene propylene rubber, epichlorohydrin-ethylene oxide copolymer rubber, epichlorohydrin-ethylene oxide-allyl glycidyl ether copolymer rubber, ethylene-propylene-diene terpolymer copolymer rubber (EPDM), acrylonitrile-butadiene copolymer rubber (NBR), natural rubber, and blends thereof. Among these, polyurethane, silicone rubber, EPDM, epichlorohydrin-ethylene oxide copolymer rubber, epichlorohydrin-ethylene oxide-allyl glycidyl ether copolymer rubber, NBR, and blends thereof are preferably used.
An electro-conductive agent, an electronic electro-conductive agent or an ionic electro-conductive agent may be used in the base material 5. Examples of the electronic electro-conductive agent include fine powder of: carbon black such as Ketjen Black and acetylene black; pyrolytic carbon, graphite; various kinds of electro-conductive metal or metal alloy such as aluminum, copper, nickel and stainless steel; various kinds of electro-conductive metal oxide such as tin oxide, indium oxide, titanium oxide, tin oxide-antimony oxide solid solution, and tin oxide-indium oxide solid solution; insulating materials having a surface treated by an electro-conductive process; and the like. Furthermore, examples of the ionic electro-conductive agent include perchlorates or chlorates of tetraethylammonium, lauryltrimethyl ammonium and the like; perchlorates or chlorates of alkali metal such as lithium and magnesium, and alkali earth metal; and the like. These electro-conductive agents may be used alone, or in combination of two or more kinds thereof.
Furthermore, the amount of addition to the base material 5 is not particularly limited. For example, the amount of the electronic electro-conductive agent to be added is from about 1 to about 30 parts by weight, or from about 5 to about 25 parts by weight with respect to 100 parts by weight of the rubber material. The amount of the ionic electro-conductive agent to be added is in the range of about 0.1 to about 5.0 parts by weight, or from about 0.5 to about 3.0 parts by weight with respect to 100 parts by weight of the rubber material. The layer thickness of the base material is from about 10 mm to about 20 cm, or from about 50 mm to about 3 cm.
The protective overcoat layer is composed of polycarbonate and a conductive agent such as carbon black. The carbon black loading is directly correlated to the surface resistivity of the material. The amount of the electro-conductive agent to be added is not particularly limited. For example, the amount of electro-conductive agent can be in the range of about 0.1 to about 40 by weight, or from about 4 to about 9 parts by weight, or in the range of about 6 to 7 parts by weight with respect to 100 parts by weight of the total weight of the coating. The layer thickness of the protective overcoat layer is from about 0.1 μm to about 500 μm, or from about 1 μm to about 50 μm.
The structure of the polycarbonate in the outer surface layer 7 may include but is not limited to derivatives of bisphenol A polycarbonate (PCA), bisphenol C polycarbonate (PCC), bisphenol F polycarbonate (PCF), bisphenol Z polycarbonate (PCZ) and the like. The polycarbonate has a weight average molecular weight (Mw) in the range from about 100,000 to about 500,000. The outer surface layer has an average modulus of from about 3.50 to about 5.00 GPa and an average hardness of from about 250 to about 500 MPa. Surprisingly, a higher resistivity is possible using polycarbonate, a material that possesses a high surface hardness, than with softer materials.
There may be present a conductive filler in any one of the substrate layers, intermediate layers or overcoat layers. Conductive fillers include those listed previously as electroconductive agents and particles and carbon fillers such as carbon black, graphite, fluorinated carbon, and the like; conductive polymer fillers such as polyaniline, polypyrrole, polythiophene, polyacetylene and the like; metal fillers such as silver, copper, antimony and the like; metal oxide fillers such as titanium oxides, zinc oxides antimony tin oxides and the like
There may be present non-conductive fillers in the substrate layers or intermediate layers.
The protective overcoat 7 also allows for refurbishing of the BCR 2. By applying a protective overcoat 7 to a BCR 2 having a damaged surface, either the base material 5 or the outer surface, a BCR can be used multiple times. When the outer surface of the BCR 2 becomes too damaged to provide acceptable prints, it is returned for refurbishing. Refurbishing involves applying a protective overcoat 7 as described herein. After application of the surface layer, the BCR is typically heated to remove any residual solvent.
Since BCRs usually can last in machine for many thousand cycles, accelerated testing was performed with a print cartridge wear test fixture. The protocol for the testing involves initial screening (time=0), which involves resistance and charge uniformity measurements, and print test. The BCR was subjected to wear for 50,000 cycles in the wear fixture, followed by a screening under the same procedures as the time=0 screening. The same process continued, i.e. screening at successive 50 thousand intervals in the wear fixture, until significant print streaks appeared.
The overcoat dispersion was prepared by ball milling a sample of PcZ 400, a polycarbonate available from Mitsubishi Gas Chemical Co., with 5 wt % Vulcan XC72 carbon black (Cabot) in THF. The sample was ball milled for 3 days, after which the dispersion was filtered. The resistivity of the material was measured to be 1013 Ω/□. The sample was then coated on a BCR using a Tsukiage coater giving a 6 μm overcoat. The BCR was then dried in a convection oven at 135° C. for 15 min to remove any solvent.
Charge uniformity measurements of the BCR with polycarbonate/carbon black overcoat and regular BCRs with no overcoat at time equal zero and after 50,000 cycles were compared. The charge uniformity of overcoated BCRs was comparable to the standard BCR without any overcoats before and after the wear test, suggesting there is no internal electric build-up in the overcoat layers and no deterioration in the charging capability with the addition of the overcoat.
Start and running torques of the overcoated BCRs were comparable with standard BCRs and the results are consistent with print and wear test, as no noticeable torque issues were detected.
Print testing of the BCR with the polycarbonate overcoat showed significant improvement over prints obtained from the BCR with no overcoat.
In summary, an overcoat for a BCR composed of a polycarbonate polymer doped with carbon black significantly improves print quality compared to a BCR with no overcoat. The overcoated BCR displays excellent charge uniformity, which is comparable to a BCR with no overcoat. After subjecting the overcoated BCR to 50,000 cycles wear on a Hodaka fixture, no black streaks were observed, which is in contrast to prints obtained from a BCR with no overcoat as shown in
It will be appreciated that a variety of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art, which are also intended to be encompassed by the following claims.
| Number | Name | Date | Kind |
|---|---|---|---|
| 4899689 | Takeda et al. | Feb 1990 | A |
| 4966675 | Steininger | Oct 1990 | A |
| 5017965 | Hashimoto et al. | May 1991 | A |
| 5068063 | Tremper, III | Nov 1991 | A |
| 5678140 | Fuei et al. | Oct 1997 | A |
| 5702812 | Bracken et al. | Dec 1997 | A |
| 5804309 | Itoh et al. | Sep 1998 | A |
| 5822169 | Yoshioka et al. | Oct 1998 | A |
| 6203855 | Tarnawskyj et al. | Mar 2001 | B1 |
| 6376594 | Sasagawa et al. | Apr 2002 | B1 |
| 6458883 | Takashima et al. | Oct 2002 | B1 |
| 6728502 | Hara | Apr 2004 | B2 |
| 6807389 | Facci et al. | Oct 2004 | B2 |
| 6889023 | Suda et al. | May 2005 | B2 |
| 6915095 | Longhenry et al. | Jul 2005 | B2 |
| 6962746 | Taniguchi et al. | Nov 2005 | B2 |
| 8465893 | Grabowski et al. | Jun 2013 | B2 |
| 8483591 | Lin et al. | Jul 2013 | B2 |
| 20030113650 | Suwabe et al. | Jun 2003 | A1 |
| 20030175045 | Hara | Sep 2003 | A1 |
| 20040057749 | Saito et al. | Mar 2004 | A1 |
| 20060034636 | Kosuge et al. | Feb 2006 | A1 |
| 20070224404 | Finley et al. | Sep 2007 | A1 |
| 20070230975 | Yamazaki et al. | Oct 2007 | A1 |
| 20070271792 | Kagawa et al. | Nov 2007 | A1 |
| 20080232853 | Law | Sep 2008 | A1 |
| 20090180806 | Oshima et al. | Jul 2009 | A1 |
| 20110045305 | Gilmartin et al. | Feb 2011 | A1 |
| 20110207872 | Schinkel et al. | Aug 2011 | A1 |
| 20120301818 | Gilmartin et al. | Nov 2012 | A1 |
| 20130004205 | Gilmartin et al. | Jan 2013 | A1 |
| 20130236721 | Law, Kock-Yee | Sep 2013 | A1 |
| Number | Date | Country |
|---|---|---|
| 0606907 | Jul 1994 | EP |
| 2006163059 | Jun 2006 | JP |
| Entry |
|---|
| U.S. Appl. No. 12/548,522, Office Action dated Oct. 20, 2011. |
| U.S. Appl. No. 12/548,522, Office Action dated Apr. 26, 2012. |
| Wenderoth, U.S. Appl. No. 12/622,682, Office Action, Apr. 17, 2013, 32 pages. |
| Wenderoth, U.S. Appl. No. 12/548,522, Notice of Allowance & Fees Due, Mar. 13, 2013, 9 pages. |
| Wenderoth: U.S. Appl. No. 12/548,522, Office Action Nov. 26, 2012, 19pgs. |
| Wenderoth, U.S. Appl. No. 12/622,682, Office Action Communication, Aug. 22, 2013, 21 pages. |
| Wenderoth, U.S. Appl. No. 12/622,682, Office Action Communication, Dec. 13, 2013. |
| Number | Date | Country | |
|---|---|---|---|
| 20110123220 A1 | May 2011 | US |
