An electrophotographic photoreceptor essentially comprises a charge generation layer (CGL) and charge transport layer (CTL) coated on a suitable substrate. The substrate may be an aluminized MYLAR polyester terephthalate or an anodized aluminum drum. An aluminum drum can be coated with a suitable sub-layer and/or a barrier layer, derived by dispersing metal oxides in a polymer binder.
The charge generation layer comprises pigments or dyes selected from phthalocyanines, squaraines, azo compounds, perylenes etc. The pigment or dye may be dispersed or dissolved in a suitable solvent, with or without a polymer binder.
The charge transport layer usually comprises a charge transport material or multiple charge transport materials in a polymer matrix. Additives such as silicone oils, silicone resins, fluoropolymers or inorganic oxides may also be used. An overcoat layer comprising only a polymer layer or a charge transport material-polymer composite may also be used.
An area of active interest is to increase the life of the photoconductor drum or member. As the photoconductor or photoreceptor life is increased significantly, it is possible to have the photoconductor as a part of a printer rather than as a component in a cartridge with toner which is periodically replaced. This helps lower the cost of the laser toner cartridge.
However, as the photoconductor becomes part of the printer, rather than the cartridge, the probability of the photoconductor coating being touched and the subsequent attack of the coating due to finger-based oils, can result in surface deterioration of the coating by cracking or crazing. The cracks or craze thus developed on the photoconductor coating can result in a print defect, resulting in a failure. Also, as the cracks develop on the point of contact, these cracks or crazing can propagate and result in the entire photoconductor coating being cracked or crazed. This invention is directed to improving the resistance of a photoconductor to cracking or crazing as caused by accidental touching of the photoconductor coating.
This invention will discuss the merits and de-merits of prior art, and outline the best mode of operation.
JP 60-225161 patent application (Sato et al., Sony Corp.), U.S. Pat. No. 6,183,921 B1(Yu et al., Xerox Corp) and JP 05-323633 patent application (Kawakami, Ricoh KK) discuss the use of plasticizers that are either dialkylterephthalates (Sony Corp.) or linear or branched esters that may be either aliphatic or aromatic based systems to prevent crack formation and be curl-resistant.
The foregoing JP 05-323633 discloses a photosensitive layer that contains a charge generating agent, a charge transporting agent, a dialkylterephthalate (C1-8) hydrocarbon chain and a polycarbonate binder.
DE 314840 A1 discusses the use of ferrocene as a plasticizer to prevent cracking (Baumgartner et al., Standard Elektrik Lorenz AG).
EP 0 447 078 A2 patent application et al, Thomson Consumer Electronics, Inc. and RCE Licensing Corp. describes the use of an n-propylphthalate, dioctylphthalate or diundecylphthalate as a plasticizer in a photoconducting layer. The photoconductive layer comprises an organic polymer, a photoconductive dye, and a plasticizer.
The foregoing JP 05-323633 is to a single-layer photoreceptor. The foregoing U.S. Pat. No. 6,183,921 is based on polymeric charge transport material, and in particular polymeric tetraaryl-substituted biphenyldiamine. Also, U.S. Pat. No. 6,183,921 specifically discusses the benefit of using diethyl phthalate at 4% to about 8% concentration (by weight) in the charge transport layer. However the charge transport layer cracking studied was induced when the charge transport layer is in contact with a solvent. U.S. Pat. No. 6,189,921 does not discuss the cracking phenomenon in small molecule (non-polymeric) charge transport material based layers. Hence, it is not clear that the cracking is inherently related to the polymeric charge transport material.
The inventors also believe that a Japanese reference, specific details apparently lost, describes the use of an n-propylcarbazol as a plasticizer, to help prevent crack formation.