Patent Application
20140295333
Reference is made to commonly owned and co-pending, U.S. patent application Ser. No. ______ (not yet assigned) entitled “Image Forming System” to Richard A. Klenkler et al., electronically filed on Mar. 29, 2013 (Attorney Docket No. 20120863-419914).
The presently disclosed embodiments relate generally to image forming systems comprising imaging apparatus members and components, and toner compositions for use with those members and components. Furthermore, the present embodiments relate to toner compositions used with the imaging apparatus members and components to form images. In particular, the present embodiments pertain to a specific toner composition for use with an electrophotographic imaging member comprising an overcoat layer protecting the imaging member surface and a contact type charging device, such as a “bias charge roll” (BCR). The toner composition comprises a combination of additives that provide an image forming system that does not suffer from the commonly observed deletion and imaging member wear issues. Deletion is a print defect in which the printed image appears blurry and fine features (e.g., a 1 bit line) disappear.
In electrophotography or electrophotographic printing, the charge retentive surface, typically known as a photoreceptor, is electrostatically charged, and then exposed to a light pattern of an original image to selectively discharge the surface in accordance therewith. The resulting pattern of charged and discharged areas on the photoreceptor form an electrostatic charge pattern, known as a latent image, conforming to the original image. The latent image is developed by contacting it with a finely divided electrostatically attractable powder known as toner. Toner is held on the image areas by the electrostatic charge on the photoreceptor surface. Thus, a toner image is produced in conformity with a light image of the original being reproduced or printed. The toner image may then be transferred to a substrate or support member (e.g., paper) directly or through the use of an intermediate transfer member, and the image affixed thereto to form a permanent record of the image to be reproduced or printed. Subsequent to development, excess toner left on the charge retentive surface cleaned from the surface. The process is useful for light lens copying from an original or printing electronically generated or stored originals such as with a raster output scanner (ROS), where a charged surface may be imagewise discharged in a variety of ways.
The described electrophotographic copying process is well known and is commonly used for light lens copying of an original document. Analogous processes also exist in other electrophotographic printing applications such as, for example, digital laser printing and reproduction where charge is deposited on a charge retentive surface in response to electronically generated or stored images.
To charge the surface of a photoreceptor, a contact type charging device has been used, such as disclosed in U.S. Pat. No. 4,387,980 and U.S. Pat. No. 7,580,655, which are incorporated herein by reference. The contact type charging device, also termed “bias charge roll” (BCR) includes a conductive member which is supplied a voltage from a power source with a D.C. voltage superimposed with an A.C. voltage of no less than twice the level of the D.C. voltage. The charging device contacts the image bearing member (photoreceptor) surface, which is a member to be charged. The outer surface of the image bearing member is charged at the contact area. The contact type charging device charges the image bearing member to a predetermined potential.
Electrophotographic photoreceptors can be provided in a number of forms. For example, the photoreceptors can be a homogeneous layer of a single material, such as vitreous selenium, or it can be a composite layer containing a photoconductive material in a mechanically robust matrix. In addition, the photoreceptor can be layered. Multilayered photoreceptors or imaging members have at least two layers, and may include a substrate, a conductive layer, an optional undercoat layer (sometimes referred to as a “charge blocking layer” or “hole blocking layer”), an optional adhesive layer, a photogenerating layer (sometimes referred to as a “charge generation layer,” “charge generating layer,” or “charge generator layer”), a charge transport layer, and an overcoating layer in either a flexible belt form or a rigid drum configuration. In the multilayer configuration, the active layers of the photoreceptor are the charge generation layer (CGL) and the charge transport layer (CTL). Enhancement of charge transport across these layers provides better photoreceptor performance. Multilayered flexible photoreceptor members may include an anti-curl layer on the backside of the substrate, opposite to the side of the electrically active layers, to render the desired photoreceptor flatness.
Conventional photoreceptors are disclosed in the following patents, a number of which describe the presence of light scattering particles in the undercoat layers: Yu, U.S. Pat. No. 5,660,961; Yu, U.S. Pat. No. 5,215,839; and Katayama et al., U.S. Pat. No. 5,958,638. The term “photoreceptor” or “photoconductor” is generally used interchangeably with the terms “imaging member.” The term “electrophotographic” includes “electrophotographic” and “xerographic.” The terms “charge transport molecule” are generally used interchangeably with the terms “hole transport molecule.”
To further increase the service life of the photoreceptor, use of overcoat layers has also been implemented to protect photoreceptors and improve performance, such as wear resistance. However, these low wear overcoats are associated with poor image quality due to deletion print defects that are exacerbated in a humid environment. In addition, high torque associated with low wear overcoats under BCR charging also causes severe issues, such as photoreceptor drive motor failure and photoreceptor cleaning blade damage. As a result, use of a low wear overcoat with BCR charging systems is still a challenge, and there is a need to find a way to achieve the life target with overcoat technology in such systems.
According to aspects illustrated herein, there is provided an image forming system comprising: an image forming apparatus for forming images further comprising an imaging member having a charge retentive-surface for developing an electrostatic latent image thereon, wherein the imaging member comprises: a substrate, one or photoconductive layers disposed on the substrate, and an overcoat layer disposed on the one or more photoconductive layers, and a charging unit comprising a charging roller disposed within charging distance of the surface of the imaging member; and toner composition for use in the image forming apparatus to form the images further comprising toner parent particles, and one or more additives comprising zinc stearate having a particle size about 4 to about 8 μm.
In another embodiment, there is provided an image forming system comprising an image forming system comprising: an image forming apparatus for forming images further comprising an imaging member having a charge retentive-surface for developing an electrostatic latent image thereon, wherein the imaging member comprises: a substrate, one or more photoconductive layers disposed on the substrate, and an overcoat layer disposed on the one or more photoconductive layers, wherein the overcoat layer comprises a charge transport molecule, an acrylic polyol, a melamine formaldehyde compound, and an acid catalyst, and a charging unit comprising a charging roller disposed within charging distance of the surface of the imaging member; and toner composition for use in the image forming apparatus to form the images further comprising toner parent particles, and one or more additives comprising zinc stearate having a particle size about 4 to about 8 μm.
In yet further embodiments, there is provided an image forming system comprising: an image forming apparatus for forming images further comprising an imaging member having a charge retentive-surface for developing an electrostatic latent image thereon, wherein the imaging member comprises: a substrate, one or more photoconductive layers disposed on the substrate, and an overcoat layer disposed on the one or more photoconductive layers, and a charging unit comprising a charging roller disposed in contact with the surface of the imaging member; and toner composition for use in the image forming apparatus to form the images further comprising toner parent particles comprising polystyrene, polymethylmethacrylate, and zinc stearate having a particle size of from about 4 to about 8 μm.
For a better understanding, reference may be made to the accompanying figures.
In the following description, reference is made to the accompanying drawings, which form a part hereof and which illustrate several embodiments. It is understood that other embodiments may be used and structural and operational changes may be made without departure from the scope of the present disclosure.
Integration of photoreceptors having overcoat layers into image forming machines using bias charge roll (BCR) charging presents two major challenges. One is reducing the friction between the cleaning blade and photoreceptor surface to a level that is compatible with the nominal torque level of photoreceptor drive motor and photoreceptor cleaning blade mechanical stability and life cycle, and another is mitigating the deletion print defect. In fact, high torque and deletion have always commonly been observed with organic based overcoated photoreceptors in image forming machines using BCR charging. A known trade-off dependence between wear rate and image deletion imposes a limit on photoreceptor overcoat layer wear rate and, therefore, prevents wear rate reduction to reach the low levels required for significant improvement in photoreceptor life. In BCR charging systems, overcoat layers are associated with a trade-off between deletion and photoreceptor wear rate. For example, most organic photoconductor (OPC) materials sets require a certain level of wear rate in order to suppress deletion, thus limiting the life of a photoreceptor.
The present embodiments provide a toner additive-based solution to the problem of high torque and deletion print defects observed with overcoated photoreceptors under BCR charging. Specifically, polymethylmethacrylate (PMMA) was demonstrated to mitigate torque and zinc stearate was demonstrated to mitigate deletion. While additives such as PMMA and zinc stearate are generally used for lubrication, it is unexpected and unknown that use of zinc stearate would also address deletion problems in image forming apparatuses. Thus, the disclosed embodiments are directed generally to an improved electrophotographic imaging system that uses a toner composition comprising a combination of additives with an image forming apparatus comprising an overcoated photoreceptor and a contact type charging device to address the poor image quality and high torque associated with overcoat layers and the problems these layers cause in BCR charging systems, such as motor failure and blade damage. The toner composition mitigates the deletion and torque issues and, as such, the present embodiments provide a system in which both low wear photoreceptors are achieved and in which deletion and/or high torque is not an issue.
The present embodiments provide a specific toner composition comprising polymethylmethacrylate (PMMA) and zinc stearate to be used in a system with an image forming apparatus comprising an overcoated photoreceptor and a contact type charging device. Specifically, PMMA and zinc stearate are blended with the parent toner particle. The toner particle may comprise polyester, polystyrene matrix, and the like. In embodiments, the zinc stearate comprises fine particle sizes of from about 1 to about 20 μm, or from about 3 μm to about 10 μm, or from about 4 μm to about In a specific embodiment, the particle size is about 6 μm. In specific embodiments, the zinc stearate is ZnPF, obtained from Nippon Oil and Fats Co. Ltd. (Tokyo, Japan). In embodiments, the zinc stearate is present in the toner composition in an amount of about 5.00 weight percent to about 0.01 weight percent, or from about 2.00 weight percent to about 0.05 weight percent, or from about 1.00 weight percent to about 0.10 weight percent by the total weight of the toner composition. In further embodiments, zinc stearate is present in a weight ratio to the toner parent particle of from about 5.00:100 to about 0.01:100, or from about 2.00:100 to about 0.05:100, or from about 1.00:100 to about 0.10:100. The PMMA, in embodiments, has a particle size of from about 1.0 μm to about 0.1 μm, or from about 1.0 μm to about 0.3 μm, or from about μm to about 0.2 μm, or from about 0.35 μm to about 0.2 μm. In embodiments, the PMMA is present in the toner composition in an amount of from about 2.00 weight percent to about 0.01 weight percent, or from about 1.00 weight percent to about 0.05 weight percent, or from about 0.75 weight percent to about 0.20 weight percent by the total weight of the toner composition. In further embodiments, the PMMA is present in weight ratio to the toner parent particle of from about 2.00:100 to about 0.01:100, or from about 1.00:100 to about 0.05:100, or from about 0.75:100 to about 0.20:100. In embodiments, the PMMA may have a molecular weight of from about 300,000 to about 700,000, or from about 250,000 to about 500,000, or from about 100,000 to about 300,000. Other properties of the PMMA may include a glass transition temperature of 105° C. to a 128° C. or a blow-off charge of −500 μC/g to +500 μC/g. The PMMA may or may not be surface treated. Suitable PMMA may be available from Esprix Technologies (Sarasota, Fla.).
The charge generation layer 18 and the charge transport layer 20 forms an imaging layer described here as two separate layers. In an alternative to what is shown in the figure, the charge generation layer may also be disposed on top of the charge transport layer. It will be appreciated that the functional components of these layers may alternatively be combined into a single layer.
The Overcoat Layer
Other layers of the imaging member may include, for example, an optional over coat layer 32. An optional overcoat layer 32, if desired, may be disposed over the charge transport layer 20 to provide imaging member surface protection as well as improve resistance to abrasion. In embodiments, the overcoat layer 32 may have a thickness ranging from about 0.1 micrometer to about 15 micrometers or from about 1 micrometer to about 10 micrometers, or in a specific embodiment, about 3 micrometers to about 10 micrometers. These overcoating layers typically comprise a charge transport component and an optional organic polymer or inorganic polymer. These overcoating layers may include thermoplastic organic polymers or cross-linked polymers such as thermosetting resins, UV or e-beam cured resins, and the likes. The overcoat layers may further include a particulate additive such as metal oxides including alumina and silica, or low surface energy materials including polytetrafluoroethylene (PTFE), and combinations thereof.
Any known or new overcoat materials may be included for the present embodiments. In embodiments, the overcoat layer may include a charge transport component or a cross-linked charge transport component. In particular embodiments, for example, the overcoat layer comprises a charge transport component comprised of a tertiary arylamine containing substituent capable of self cross-linking or reacting with polymer resin to form a cured composition. Specific examples of charge transport component suitable for overcoat layer comprise the tertiary arylamine with a general formula of
wherein Ar1, Ar2, Ar3, and Ar4 each independently represents an aryl group having about 6 to about 30 carbon atoms, Ar5 represents aromatic hydrocarbon group having about 6 to about 30 carbon atoms, and k represents 0 or 1, and wherein at least one of Ar1, Ar2, Ar3 Ar4, and Ar5 comprises a substituent selected from the group consisting of hydroxyl (—OH), a hydroxymethyl (—CH2OH), an alkoxymethyl (—CH2OR, wherein R is an alkyl having 1 to about 10 carbons), a hydroxylalkyl having 1 to about 10 carbons, and mixtures thereof. In other embodiments, Ar1, Ar2, Ar3, and Ar4 each independently represent a phenyl or a substituted phenyl group, and Ar5 represents a biphenyl or a terphenyl group.
Additional examples of charge transport component which comprise a tertiary arylamine include the following:
and the like, wherein R is a substituent selected from the group consisting of hydrogen atom, and an alkyl having from 1 to about 6 carbons, and m and n each independently represents 0 or 1, wherein m+n>1. In specific embodiments, the overcoat layer may include an additional curing agent to form a cured, crosslinked overcoat composition. Illustrative examples of the curing agent may be selected from the group consisting of a melamine-formaldehyde resin, a phenol resin, an isocyalate or a masking isocyalate compound, an acrylate resin, a polyol resin, or mixtures thereof. In embodiments, the crosslinked overcoat composition has an average modulus ranging from about 3 GPa to about 5 GPa, as measured by nano-indentation method using, for example, nanomechanical test instruments manufactured by Hysitron Inc. (Minneapolis, Minn.).
The Substrate
The photoreceptor support substrate 10 may be opaque or substantially transparent, and may comprise any suitable organic or inorganic material having the requisite mechanical properties. The entire substrate can comprise the same material as that in the electrically conductive surface, or the electrically conductive surface can be merely a coating on the substrate. Any suitable electrically conductive material can be employed, such as for example, a metal or metal alloy. Electrically conductive materials include copper, brass, nickel, zinc, chromium, stainless steel, conductive plastics and rubbers, aluminum, semitransparent aluminum, steel, cadmium, silver, gold, zirconium, niobium, tantalum, vanadium, hafnium, titanium, nickel, niobium, stainless steel, chromium, tungsten, molybdenum, paper rendered conductive by the inclusion of a suitable material therein or through conditioning in a humid atmosphere ensure the presence of sufficient water content to render the material conductive, indium, tin, metal oxides, including tin oxide and indium tin oxide, and the like. It could be single metallic compound or dual layers of different metals and/or oxides.
The substrate 10 can also be formulated entirely of an electrically conductive material, or it can be an insulating material including inorganic or organic polymeric materials, such as MYLAR, a commercially available biaxially oriented polyethylene terephthalate from DuPont, or polyethylene naphthalate available as KALEDEX 2000, with a ground plane layer 12 comprising a conductive titanium or titanium/zirconium coating, otherwise a layer of an organic or inorganic material having a semiconductive surface layer, such as indium tin oxide, aluminum, titanium, and the like, or exclusively be made up of a conductive material such as, aluminum, chromium, nickel, brass, other metals and the like. The thickness of the support substrate depends on numerous factors, including mechanical performance and economic operations. The substrate 10 may have a number of different configurations, such as for example, a plate, a cylinder, a drum, a scroll, an endless flexible belt, and the like. In the case of the substrate being in the form of a belt, as shown in
The thickness of the substrate 10 depends on numerous factors, including flexibility, mechanical performance, and economic considerations. The thickness of the support substrate 10 of the present embodiments may be at least about 500 micrometers, or no more than about 3,000 micrometers, or be at least about 750 micrometers, or no more than about 2500 micrometers.
An exemplary substrate support 10 is not soluble in any of the solvents used in each coating layer solution, is optically transparent or semi-transparent, and is thermally stable up to a high temperature of about 150° C. A substrate support 10 used for imaging member fabrication may have a thermal contraction coefficient ranging from about 1×10−5 per ° C. to about 3×10−5 per ° C. and a Young's Modulus of between about 4.5×105 PSI (3 GPa) and about 7.5×105 (5 GPa).
The Ground Plane
The electrically conductive ground plane 12 may be an electrically conductive metal layer which may be formed, for example, on the substrate 10 by any suitable coating technique, such as a vacuum depositing technique. Metals include aluminum, zirconium, niobium, tantalum, vanadium, hafnium, titanium, nickel, stainless steel, chromium, tungsten, molybdenum, and other conductive substances, and mixtures thereof. The conductive layer may vary in thickness over substantially wide ranges depending on the optical transparency and flexibility desired for the electrophotoconductive member. Accordingly, for a flexible photoresponsive imaging device, the thickness of the conductive layer may be at least about 20 Angstroms, or no more than about 750 Angstroms, or at least about 50 Angstroms, or no more than about 200 Angstroms for an optimum combination of electrical conductivity, flexibility and light transmission.
Regardless of the technique employed to form the metal layer, a thin layer of metal oxide forms on the outer surface of most metals upon exposure to air. Thus, when other layers overlying the metal layer are characterized as “contiguous” layers, it is intended that these overlying contiguous layers may, in fact, contact a thin metal oxide layer that has formed on the outer surface of the oxidizable metal layer. Generally, for rear erase exposure, a conductive layer light transparency of at least about 15 percent is desirable. The conductive layer need not be limited to metals. Other examples of conductive layers may be combinations of materials such as conductive indium tin oxide as transparent layer for light having a wavelength between about 4000 Angstroms and about 9000 Angstroms or a conductive carbon black dispersed in a polymeric binder as an opaque conductive layer.
The Hole Blocking Layer
After deposition of the electrically conductive ground plane layer, the hole blocking layer 14 may be applied thereto. Electron blocking layers for positively charged photoreceptors allow holes from the imaging surface of the photoreceptor to migrate toward the conductive layer. For negatively charged photoreceptors, any suitable hole blocking layer capable of forming a barrier to prevent hole injection from the conductive layer to the opposite photoconductive layer may be utilized. The hole blocking layer include polymers such as polyvinylbutryral, epoxy resins, polyesters, polysiloxanes, polyamides, polyurethanes and the like, or may be nitrogen containing siloxanes or nitrogen containing titanium compounds such as trimethoxysilyl propylene diamine, hydrolyzed trimethoxysilyl propyl ethylene diamine, N-beta-(aminoethyl)gamma-amino-propyl trimethoxy silane, isopropyl 4-aminobenzene sulfonyl, di(dodecylbenzene sulfonyl)titanate, isopropyl di(4-aminobenzoyl)isostearoyl titanate, isopropyl tri(N-ethylamino-ethylamino)titanate, isopropyl trianthranil titanate, isopropyl tri(N,N-dimethylethylamino)titanate, titanium-4-amino benzene sulfonate oxyacetate, titanium aminobenzoate isostearate oxyacetate, [H2N(CH2)4]CH3Si(OCH3)2, (gamma-aminobutyl)methyl diethoxysilane, and [H2N(CH2)3]CH3Si(OCH3)2 (gamma-aminopropyl)methyl diethoxysilane, as disclosed in U.S. Pat. Nos. 4,338,387, 4,286,033 4,286,033 and 4,291,110.
General embodiments of the undercoat layer may comprise a metal oxide and a resin binder. The metal oxides that can be used with the embodiments herein include, but are not limited to, titanium oxide, zinc oxide, tin oxide, aluminum oxide, silicon oxide, zirconium oxide, indium oxide, molybdenum oxide, and mixtures thereof. Undercoat layer binder materials may include, for example, polyesters, MOR-ESTER 49,000 from Morton International Inc., VITEL PE-100, VITEL PE-200, VITEL PE-200D, and VITEL PE-222 from Goodyear Tire and Rubber Co., polyarylates such as ARDEL from AMOCO Production Products, polysulfone from AMOCO Production Products, polyurethanes, and the like.
The hole blocking layer should be continuous and have a thickness of less than about 0.5 micrometer because greater thicknesses may lead to undesirably high residual voltage. A hole blocking layer of between about 0.005 micrometer and about 0.3 micrometer is used because charge neutralization after the exposure step is facilitated and optimum electrical performance is achieved. A thickness of between about 0.03 micrometer and about 0.06 micrometer is used for hole blocking layers for optimum electrical behavior. The hole blocking layers that contain metal oxides such as zinc oxide, titanium oxide, or tin oxide, may be thicker, for example, having a thickness up to about 25 micrometers. The blocking layer may be applied by any suitable conventional technique such as spraying, dip coating, draw bar coating, gravure coating, silk screening, air knife coating, reverse roll coating, vacuum deposition, chemical treatment and the like. For convenience in obtaining thin layers, the blocking layer is applied in the form of a dilute solution, with the solvent being removed after deposition of the coating by conventional techniques such as by vacuum, heating and the like. Generally, a weight ratio of hole blocking layer material and solvent of between about 0.05:100 to about 0.5:100 is satisfactory for spray coating.
The Charge Generation Layer
The charge generation layer 18 may thereafter be applied to the undercoat layer 14. Any suitable charge generation binder including a charge generating/photoconductive material, which may be in the form of particles and dispersed in a film forming binder, such as an inactive resin, may be utilized. Examples of charge generating materials include, for example, inorganic photoconductive materials such as amorphous selenium, trigonal selenium, and selenium alloys selected from the group consisting of selenium-tellurium, selenium-tellurium-arsenic, selenium arsenide and mixtures thereof, and organic photoconductive materials including various phthalocyanine pigments such as the X-form of metal free phthalocyanine, metal phthalocyanines such as vanadyl phthalocyanine and copper phthalocyanine, hydroxy gallium phthalocyanines, chlorogallium phthalocyanines, titanyl phthalocyanines, quinacridones, dibromo anthanthrone pigments, benzimidazole perylene, substituted 2,4-diamino-triazines, polynuclear aromatic quinones, enzimidazole perylene, and the like, and mixtures thereof, dispersed in a film forming polymeric binder. Selenium, selenium alloy, benzimidazole perylene, and the like and mixtures thereof may be formed as a continuous, homogeneous charge generation layer. Benzimidazole perylene compositions are well known and described, for example, in U.S. Pat. No. 4,587,189, the entire disclosure thereof being incorporated herein by reference. Multi-charge generation layer compositions may be used where a photoconductive layer enhances or reduces the properties of the charge generation layer. Other suitable charge generating materials known in the art may also be utilized, if desired. The charge generating materials selected should be sensitive to activating radiation having a wavelength between about 400 and about 900 nm during the imagewise radiation exposure step in an electrophotographic imaging process to form an electrostatic latent image. For example, hydroxygallium phthalocyanine absorbs light of a wavelength of from about 370 to about 950 nanometers, as disclosed, for example, in U.S. Pat. No. 5,756,245.
Any suitable inactive resin materials may be employed as a binder in the charge generation layer 18, including those described, for example, in U.S. Pat. No. 3,121,006, the entire disclosure thereof being incorporated herein by reference. Organic resinous binders include thermoplastic and thermosetting resins such as one or more of polycarbonates, polyesters, polyamides, polyurethanes, polystyrenes, polyarylethers, polyarylsulfones, polybutadienes, polysulfones, polyethersulfones, polyethylenes, polypropylenes, polyimides, polymethylpentenes, polyphenylene sulfides, polyvinyl butyral, polyvinyl acetate, polysiloxanes, polyacrylates, polyvinyl acetals, polyamides, polyimides, amino resins, phenylene oxide resins, terephthalic acid resins, epoxy resins, phenolic resins, polystyrene and acrylonitrile copolymers, polyvinylchloride, vinylchloride and vinyl acetate copolymers, acrylate copolymers, alkyd resins, cellulosic film formers, poly(amideimide), styrene-butadiene copolymers, vinylidenechloride/vinylchloride copolymers, vinylacetate/vinylidene chloride copolymers, styrene-alkyd resins, and the like. Another film-forming polymer binder is PCZ-400 (poly(4,4′-dihydroxy-diphenyl-1-1-cyclohexane) which has a viscosity-molecular weight of 40,000 and is available from Mitsubishi Gas Chemical Corporation (Tokyo, Japan).
The charge generating material can be present in the resinous binder composition in various amounts. Generally, at least about 5 percent by volume, or no more than about 90 percent by volume of the charge generating material is dispersed in at least about 95 percent by volume, or no more than about 10 percent by volume of the resinous binder, and more specifically at least about 20 percent, or no more than about 60 percent by volume of the charge generating material is dispersed in at least about 80 percent by volume, or no more than about 40 percent by volume of the resinous binder composition.
In specific embodiments, the charge generation layer 18 may have a thickness of at least about 0.1 μm, or no more than about 2 μm, or of at least about μm, or no more than about 1 μm. These embodiments may be comprised of chlorogallium phthalocyanine or hydroxygallium phthalocyanine or mixtures thereof. The charge generation layer 18 containing the charge generating material and the resinous binder material generally ranges in thickness of at least about 0.1 μm, or no more than about 5 μm, for example, from about 0.2 μm to about 3 μm when dry. The charge generation layer thickness is generally related to binder content. Higher binder content compositions generally employ thicker layers for charge generation.
The Charge Transport Layer
In a drum photoreceptor, the charge transport layer comprises a single layer of the same composition. As such, the charge transport layer will be discussed specifically in terms of a single layer 20, but the details will be also applicable to an embodiment having dual charge transport layers. The charge transport layer 20 is thereafter applied over the charge generation layer 18 and may include any suitable transparent organic polymer or non-polymeric material capable of supporting the injection of photogenerated holes or electrons from the charge generation layer 18 and capable of allowing the transport of these holes/electrons through the charge transport layer to selectively discharge the surface charge on the imaging member surface. In one embodiment, the charge transport layer 20 not only serves to transport holes, but also protects the charge generation layer 18 from abrasion or chemical attack and may therefore extend the service life of the imaging member. The charge transport layer 20 can be a substantially non-photoconductive material, but one which supports the injection of photogenerated holes from the charge generation layer 18.
The layer 20 is normally transparent in a wavelength region in which the electrophotographic imaging member is to be used when exposure is affected there to ensure that most of the incident radiation is utilized by the underlying charge layer 18. The charge transport layer should exhibit excellent optical transparency with negligible light absorption and no charge generation when exposed to a wavelength of light useful in xerography, e.g., 400 to 900 nanometers. In the case when the photoreceptor is prepared with the use of a transparent substrate 10 and also a transparent or partially transparent conductive layer 12, image wise exposure or erase may be accomplished through the substrate 10 with all light passing through the back side of the substrate. In this case, the materials of the layer 20 need not transmit light the wavelength region of use if the charge generation layer 18 is sandwiched between the substrate and the charge transport layer 20. The charge transport layer 20 in conjunction with the charge generation layer 18 is an insulator to the extent that an electrostatic charge placed on the charge transport layer is not conducted in the absence of illumination. The charge transport layer 20 should trap minimal charges as the charge passes through it during the discharging process.
The charge transport layer 20 may include any suitable charge transport component or activating compound useful as an additive dissolved or molecularly dispersed in an electrically inactive polymeric material, such as a polycarbonate binder, to form a solid solution and thereby making this material electrically active. “Dissolved” refers, for example, to forming a solution in which the small molecule is dissolved in the polymer to form a homogeneous phase; and molecularly dispersed in embodiments refers, for example, to charge transporting molecules dispersed in the polymer, the small molecules being dispersed in the polymer on a molecular scale. The charge transport component may be added to a film forming polymeric material which is otherwise incapable of supporting the injection of photogenerated holes from the charge generation material and incapable of allowing the transport of these holes. This addition converts the electrically inactive polymeric material to a material capable of supporting the injection of photogenerated holes from the charge generation layer 18 and capable of allowing the transport of these holes through the charge transport layer 20 in order to discharge the surface charge on the charge transport layer. The high mobility charge transport component may comprise small molecules of an organic compound which cooperate to transport charge between molecules and ultimately to the surface of the charge transport layer. For example, but not limited to, N,N′-diphenyl-N,N-bis(3-methyl phenyl)-1,1′-biphenyl-4,4′-diamine (TPD), other arylamines like triphenyl amine, N,N,N′,N′-tetra-p-tolyl-1,1′-biphenyl-4,4′-diamine (TM-TPD), and the like. A number of charge transport compounds can be included in the charge transport layer, which layer generally is of a thickness of from about 5 to about 75 micrometers, and more specifically, of a thickness of from about 15 to about 40 micrometers. Examples of charge transport components are aryl amines of the following formulas/structures:
wherein X is a suitable hydrocarbon like alkyl, alkoxy, aryl, and derivatives thereof; a halogen, or mixtures thereof, and especially those substituents selected from the group consisting of C1 and CH3; and molecules of the following formulas
wherein X, Y and Z are independently alkyl, alkoxy, aryl, a halogen, or mixtures thereof, and wherein at least one of Y and Z are present.
Alkyl and alkoxy contain, for example, from 1 to about 25 carbon atoms, and more specifically, from 1 to about 12 carbon atoms, such as methyl, ethyl, propyl, butyl, pentyl, and the corresponding alkoxides. Aryl can contain from 6 to about 36 carbon atoms, such as phenyl, and the like. Halogen includes chloride, bromide, iodide, and fluoride. Substituted alkyls, alkoxys, and aryls can also be selected in embodiments.
Examples of specific aryl amines that can be selected for the charge transport layer include N,N′-diphenyl-N,N′-bis(alkylphenyl)-1,1-biphenyl-4,4′-diamine wherein alkyl is selected from the group consisting of methyl, ethyl, propyl, butyl, hexyl, and the like; N,N′-diphenyl-N,N′-bis(halophenyl)-1,1′-biphenyl-4,4′-diamine wherein the halo substituent is a chloro substituent; N,N′-bis(4-butylphenyl)-N,N′-di-p-tolyl-[p-terphenyl]-4,4″-diamine, N,N′-bis(4-butylphenyl)-N,N′-di-m-tolyl-[p-terphenyl]-4,4″-diamine, N,N′-bis(4-butylphenyl)-N,N′-di-o-tolyl-[p-terphenyl]-4,4″-diamine, N,N′-bis(4-butylphenyl)-N,N′-bis-(4-isopropylphenyl)-[p-terphenyl]-4,4″-diamine, N,N′-bis(4-butylphenyl)-N,N′-bis-(2-ethyl-6-methylphenyl)-[p-terphenyl]-4,4″-diamine, N,N′-bis(4-butylphenyl)-N,N′-bis-(2,5-dimethylphenyl)-[p-terphenyl]-4,4′-diamine, N,N′-diphenyl-N,N′-bis(3-chlorophenyl)-[p-terphenyl]-4,4″-diamine, and the like. Other known charge transport layer molecules may be selected in embodiments, reference for example, U.S. Pat. Nos. 4,921,773 and 4,464,450, the disclosures of which are totally incorporated herein by reference.
Examples of the binder materials selected for the charge transport layers include components, such as those described in U.S. Pat. No. 3,121,006, the disclosure of which is totally incorporated herein by reference. Specific examples of polymer binder materials include polycarbonates, polyarylates, acrylate polymers, vinyl polymers, cellulose polymers, polyesters, polysiloxanes, polyamides, polyurethanes, poly(cyclo olefins), and epoxies, and random or alternating copolymers thereof. In embodiments, the charge transport layer, such as a hole transport layer, may have a thickness of at least about 10 μm, or no more than about 40 μm.
Examples of components or materials optionally incorporated into the charge transport layers or at least one charge transport layer to, for example, enable improved lateral charge migration (LCM) resistance include hindered phenolic antioxidants such as tetrakis methylene(3,5-di-tert-butyl-4-hydroxy hydrocinnamate) methane (IRGANOX® 1010, available from Ciba Specialty Chemical), butylated hydroxytoluene (BHT), and other hindered phenolic antioxidants including SUMILIZER™ SUMILIZER™ BHT-R, MDP-S, BBM-S, WX-R, NR, BP-76, BP-101, GA-80, GM and GS GS (available from Sumitomo Chemical Co., Ltd.), IRGANOX® 1035, 1076, 1098, 1135, 1141, 1222, 1330, 1425WL, 1520L, 245, 259, 3114, 3790, 5057 and 565 (available from Ciba Specialties Chemicals), and ADEKA STAB™ AO-20, AO-30, AO-40, AO-50, AO-60, 60, AO-70, AO-80 and AO-330 (available from Asahi Denka Co., Ltd.); hindered amine antioxidants such as SANOL™ LS-2626, LS-765, LS-770 and LS-744 (available from SANKYO CO., Ltd.), TINUVIN® 144 and 622LD (available from Ciba Specialties Chemicals), MARK™ LA57, LA67, LA62, LA68 and LA63 (available from Asahi Denka Co., Ltd.), and SUMILIZER® TPS (available from Sumitomo Chemical Co., Ltd.); thioether antioxidants such as SUMILIZER® TP-D (available from Sumitomo Chemical Co., Ltd); phosphite antioxidants such as MARK™ 2112, PEP-8, PEP-24G, PEP-36, 329K 329K and HP-10 (available from Asahi Denka Co., Ltd.); other molecules such as bis(4-diethylamino-2-methylphenyl)phenylmethane (BDETPM), bis-[2-methyl-4-(N-2-hydroxyethyl-N-ethyl-aminophenyl)]-phenylmethane (DHTPM), and the like. The percent of the antioxidant in at least one of the charge transport layer is from about 0 about 20, from about 1 to about 10, or from about 3 to about 8 weight percent.
The charge transport layer should be an insulator to the extent that the electrostatic charge placed on the hole transport layer is not conducted in the absence of illumination at a rate sufficient to prevent formation and retention of an electrostatic latent image thereon. The charge transport layer is substantially nonabsorbing to visible light or radiation in the region of intended use, but is electrically “active” in that it allows the injection of photogenerated holes from the photoconductive layer, that is the charge generation layer, and allows these holes to be transported through itself to selectively discharge a surface charge on the surface of the active layer.
In addition, in the present embodiments using a belt configuration, the charge transport layer may consist of a single pass charge transport layer or a dual pass pass charge transport layer (or dual layer charge transport layer) with the same or different transport molecule ratios. In these embodiments, the dual layer charge transport layer has a total thickness of from about 10 μm to about 40 μm. In other embodiments, each layer of the dual layer charge transport layer may have an individual thickness of from 2 μm to about 20 μm. Moreover, the charge transport layer may be configured such that it is used as a top layer of the photoreceptor to inhibit crystallization at the interface of the charge transport layer and the overcoat layer. In another embodiment, the charge transport layer may be configured such that it is used as a first pass charge transport layer to inhibit microcrystallization occurring at the interface between the first pass and second pass layers.
Any suitable and conventional technique may be utilized to form and thereafter apply the charge transport layer mixture to the supporting substrate layer. The charge transport layer may be formed in a single coating step or in multiple coating steps. Dip coating, ring coating, spray, gravure or any other drum coating methods may be used.
Drying of the deposited coating may be effected by any suitable conventional technique such as oven drying, infra-red radiation drying, air drying and the like. The thickness of the charge transport layer after drying is from about 10 μm to about 40 μm or from about 12 μm to about 36 μm for optimum photoelectrical and mechanical results. In another embodiment the thickness is from about 14 μm to about 36 μm.
The Adhesive Layer
An optional separate adhesive interface layer may be provided in certain configurations, such as for example, in flexible web configurations. In the embodiment illustrated in
Any suitable solvent or solvent mixtures may be employed to form a coating solution of the polyester for the adhesive interface layer. Solvents may include tetrahydrofuran, toluene, monochlorobenzene, dichloromethane, cyclohexanone, and the like, and mixtures thereof. Any other suitable and conventional technique may be used to mix and thereafter apply the adhesive layer coating mixture to the hole blocking layer. Application techniques may include spraying, dip coating, roll coating, wire wound rod coating, and the like. Drying of the deposited wet coating may be effected by any suitable conventional process, such as oven drying, infra-red radiation drying, air drying, and the like.
The adhesive interface layer may have a thickness of at least about 0.01 micrometers, or no more than about 1 micrometers after drying. In embodiments, the dried thickness is from about 0.03 micrometers to about 0.07 micrometer.
The Ground Strip
The ground strip may comprise a film forming polymer binder and electrically conductive particles. Any suitable electrically conductive particles may be used in the electrically conductive ground strip layer 19. The ground strip 19 may comprise materials which include those enumerated in U.S. Pat. No. 4,664,995. Electrically conductive particles include carbon black, graphite, copper, silver, gold, nickel, tantalum, chromium, zirconium, vanadium, niobium, indium tin oxide and the like. The electrically conductive particles may have any suitable shape. Shapes may include irregular, granular, spherical, elliptical, cubic, flake, filament, and the like. The electrically conductive particles should have a particle size less than the thickness of the electrically conductive ground strip layer to avoid an electrically conductive ground strip layer having an excessively irregular outer surface. An average particle size of less than about 10 micrometers generally avoids excessive protrusion of the electrically conductive particles at the outer surface of the dried ground strip layer and ensures relatively uniform dispersion of the particles throughout the matrix of the dried ground strip layer. The concentration of the conductive particles to be used in the ground strip depends on factors such as the conductivity of the specific conductive particles utilized.
The ground strip layer may have a thickness of at least about 7 micrometers, or no more than about 42 micrometers, or of at least about 14 micrometers, or no more than about 27 micrometers.
The Anti-Curl Back Coating Layer
The anti-curl back coating 1 may comprise organic polymers or inorganic polymers that are electrically insulating or slightly semi-conductive. The anti-curl back coating provides flatness and/or abrasion resistance.
Anti-curl back coating 1 may be formed at the back side of the substrate 2, opposite to the imaging layers. The anti-curl back coating may comprise a film forming resin binder and an adhesion promoter additive. The resin binder may be the same resins as the resin binders of the charge transport layer discussed above. Examples of film forming resins include polyacrylate, polystyrene, bisphenol polycarbonate, poly(4,4′-isopropylidene diphenyl carbonate), 4,4′-cyclohexylidene diphenyl polycarbonate, and the like. Adhesion promoters used as additives include 49,000 (du Pont), Vitel PE-100, Vitel PE-200, Vitel PE-307 (Goodyear), and the like. Usually from about 1 to about 15 weight percent adhesion promoter is selected for film forming resin addition. The thickness of the anti-curl back coating is at least about 3 micrometers, or no more than about 35 micrometers, or about 14 micrometers.
Various exemplary embodiments encompassed herein include a method of imaging which includes generating an electrostatic latent image on an imaging member, developing a latent image, and transferring the developed electrostatic image to a suitable substrate.
While the description above refers to particular embodiments, it will be understood that many modifications may be made without departing from the spirit thereof. The accompanying claims are intended to cover such modifications as would fall within the true scope and spirit of embodiments herein.
The presently disclosed embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, the scope of embodiments being indicated by the appended claims rather than the foregoing description. All changes that come within the meaning of and range of equivalency of the claims are intended to be embraced therein.
The example set forth herein below and is illustrative of different compositions and conditions that can be used in practicing the present embodiments. All proportions are by weight unless otherwise indicated. It will be apparent, however, that the embodiments can be practiced with many types of compositions and can have many different uses in accordance with the disclosure above and as pointed out hereinafter.
During experimentation, the present inventors tested different toners composed of different parent particles blended with different additive combinations. The objective was to test the impact that the parent particle and additive package has on deletion and high torque image forming machines that use overcoated photoreceptors and BCR charging. Two different parent particles, polystyrene-based versus polyester-based (disclosed in U.S. Pat. No. 7,691,552 and U.S. Pat. Application No. 20120189955, which are hereby incorporated by reference), and two different additive packages, package A and package B, were examined. The additive package formulations are shown in Table 1, where the constituent quantities are given in weight ratio to toner parent particle. The two parent particles and two additive packages were blended to make four different toners: polyester parent with package B, polyester parent with package A, polystyrene parent with package B, and polystyrene parent with package A. These toners were tested in a Xerox X700i multi-function printer in the BCR charged magenta housing with an overcoated photoreceptor (made according to the Examples shown in U.S. patent application Ser. No. 13/246,109, which is hereby incorporated by reference in its entirety) in an environment at 28 C and 80% relative humidity.
The print test was designed to probe photoreceptor cleaning blade torque, deletion image quality defects, and overall image quality. Photoreceptor cleaning blade torque has been found to rise to unacceptable levels with overcoated photoreceptors under BCR charging. This can lead to excessive blade edge wear or even blade chatter, which severely reduces cleaning efficiency resulting in the rapid buildup of toner contamination on the BCR. When this happens the BCR can no longer charge the photoreceptor uniformly resulting in a streaky appearance to printed images, severely affecting image quality. It was in this indirect, image quality and BCR contamination based manner that photoreceptor cleaning blade torque was evaluated.
Deletion image quality defects have also been found to occur at unacceptable levels with overcoated photoreceptors under BCR charging, particularly in high humidity. The deletion image defect arises from excessive dissipation of static charge on the surface of the photoreceptor after the generation of the latent electrostatic image in the xerographic process. Image quality becomes unacceptable when the severity of the dissipation reaches a threshold where fine features in the image are no longer developed. In this test the severity of deletion was qualitatively evaluated by examining printed test patterns of fine lines. If all lines were printed as intended then there was no observed deletion and deletion was judged as ‘good’, and if any of the lines did not print as intended then the deletion was judged as quality was judged based on fidelity of reproduction of several different print test patterns. If there was any observable defect in the prints of these test patterns then the overall image quality was judged as ‘unacceptable’, otherwise the image quality was judges as ‘good’.
The torque, deletion, and overall image quality performance of the four toners that were tested is shown in Table 2. The results indicate that the polyester parent particle helps lubricate to reduce high torque while additive package B helps lubricate and reduce deletion. Given the improved performance of additive package B over additive package A, the individual components of each package were compared to help isolate which specific additive or combination of additives provided the observed improvements
As can be seen in Table 1, there are several different constituents between package A and B. Namely, different titania, silica, and zinc stearate materials, as well as a difference in ceria loading and the inclusion of PMMA in package B but not in package A. To isolate the effect of each difference, additional additive packages were formulated, changing one constituent for each iteration. Each of these additive packages was then blended with polystyrene parent particle and tested as before in the X700i magenta housing. Through this iterative process it was determined that inclusion of 0.5% MP116CF PMMA, which is comprised of primary spherical particles in the size range of from about 0.36 to about 0.5 microns, in either additive package A or B resulted in the elimination of excessively high torque, and that the inclusion of 0.18% ZnPF zinc stearate in either additive package resulted in the elimination the deletion print defect.
This result was confirmed by both adding MP116CF PMMA and replacing ZnSt-S with ZnPF in additive package A then blending with polystyrene-parent particle and again testing as before in the X700i magenta housing. The test result confirmed that the combination of PMMA and ZnPF eliminated the high torque and deletion problems. The results of these print tests are summarized in Table 3.
In further experimentation, three variant types of zinc stearate: ZnSt-S from Asahi Denka Kogyo Co., Ltd.; ZnSt-L from Ferro Corp.; and ZnPF from Nippon Oil and Fat Corp., were substituted for the standard zinc stearate in additive package A, and PMMA was added to address photoreceptor/cleaning blade torque. These variant additive packages labelled C, D, and E are shown in Table 4.
The additive packages made with these 3 variant types of zinc stearate were blended with polystyrene parent particle to make 3 toners. These toners were tested as before for torque, deletion, and overall image quality performance. The results of these tests are shown in Table 5. The results indicate a difference among the 3 variant zinc stearates at mitigating deletion print defects. The ZnSt-S had no effect at mitigating deletion; the ZnSt-L had some effect, noticeably reducing deletion; and the ZnPF had the greatest effect, completely eliminating deletion. From these results it is clear that the various zinc stearates have differing effectiveness at mitigating deletion, even though they are not obviously different from one another.
The various zinc stearates were analyzed to understand the characteristic difference that impacts effectiveness at mitigating deletion. Analysis included gas chromatography/mass spectroscopy to measure stearic acid alkyl chain length, differential scanning calorimetry to measure melting temperature and latent heat of fusing, elemental analysis and acidity to measure the amount of free stearic acid, and particle size distribution. The characterization revealed no significant distinguishable chemical difference among the various zinc stearates, however, there was a significant difference in particle size, as shown in Tables 6, 7 and 8, and
Based on the above analysis, it was proposed that the ZnPF, because of its smaller particle size, is more apt to spread out as a thin and uniform monolayer on the photoreceptor surface. To test this theory, water contact angle measurements were used to measure hydrophobicity (higher contact angle) of the overcoated photoreceptor before and after running as before in the BCR charged magenta housing of an X700i multifunction printer in an environment at 28 C and 80% RH. For each toner blend of polystyrene parent with additive package A, C, D, and E water contact angle was measured on the surface of a fresh overcoated photoreceptor that had been run for 10 Kcycles. For comparison, the contact angle on the surface of a virgin overcoated photoreceptor was measured, as well. Results, shown in Table 9, indicate that when the overcoated photoreceptor is run with additive package E (ZnPF and PMMA) it retains a contact angle closest to the virgin state and when run with additive package A (ZnSt-S) the water contact angle decreases by the largest amount. The trend continues as a function of zinc stearate particle size and the inclusion of PMMA.
The high contact angle observed with the additive package containing ZnPF suggests the presence of a layer or hydrophobic material on the surface of the photoreceptor, lending support to the proposed mono-layer theory.
All the patents and applications referred to herein are hereby specifically, and totally incorporated herein by reference in their entirety in the instant specification.
It will be appreciated that several of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also that 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. Unless specifically recited in a claim, steps or components of claims should not be implied or imported from the specification or any other claims as to any particular order, number, position, size, shape, angle, color, or material.
