Patent Application
20150111137
The present embodiments pertain to a novel imaging member, namely, an imaging member or photoreceptor comprising an overcoat layer which exhibits both low surface energy and wear resistance. The overcoat layer comprises a soluble filler material which disperses much readily in the overcoat layer coating solution than polytetrafluoroethylene (PTFE) particles, conventionally used to provide low surface energy and wear resistance. In embodiments, the soluble filler material is a silicone poly(ethylene glycol) ester (silicone PEG ester).
In 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 is 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 or ionographic 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. The contact type charging device includes a conductive member which is supplied a voltage from a power source with a D.C. voltage superimposed with a 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 contact type charging device charges the image bearing member to a predetermined potential. Typically the contact type charger is in the form of a roll charger such as that disclosed in U.S. Pat. No. 4,387,980, the relative portions thereof incorporated herein by reference.
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 (sometimes referred to as an “interfacial 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 optional 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 “electrostatographic” includes “electrophotographic” and “xerographic.” The terms “charge transport molecule” are generally used interchangeably with the terms “hole transport molecule.”
Low surface energy fillers are known to be desirable for overcoat layers. A commonly used filler is PTFE particle, which imparts low surface energy and wear resistance to the overcoat layers. However, PTFE particles are difficult to disperse in the overcoat layer because the overcoat layer coating solution has very low viscosity. Thus, there is a need for a low surface energy filler which can be easy to incorporate into overcoat layers.
According to aspects illustrated herein, there is provided an imaging member, comprising: a substrate; a charge generation layer disposed on the substrate; a charge transport layer disposed on the charge generation layer; and an overcoat layer disposed on the charge transport layer, wherein the overcoat layer comprises a silicone poly(ethylene glycol) ester.
In another embodiment, there is provided an imaging member, comprising: a substrate; a charge generation layer disposed on the substrate; a charge transport layer disposed on the charge generation layer; and an overcoat layer disposed on the charge transport layer, wherein the overcoat layer comprises silicone poly(ethylene glycol) ester.
Yet another embodiment, there is provided an image forming apparatus for forming images on a recording medium comprising: a) an imaging member having a charge retentive-surface for receiving an electrostatic latent image thereon, wherein the imaging member comprises a substrate, a charge generation layer disposed on the substrate, a charge transport layer disposed on the charge generation layer, and an overcoat layer disposed on the charge transport layer, wherein the overcoat layer comprises silicone poly(ethylene glycol) ester; b) a development component for applying a developer material to the charge-retentive surface to develop the electrostatic latent image to form a developed image on the charge-retentive surface; c) a transfer component for transferring the developed image from the charge-retentive surface to a copy substrate; and a fusing component for fusing the developed image to the copy substrate.
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.
The presently disclosed embodiments generally pertain to a novel imaging member or photoreceptor which comprises a silicone poly(ethylene glycol) ester (silicone PEG ester) and exhibits both low surface energy and wear resistance. As compared to the conventional overcoat layer without any silicone PEG ester, the improved overcoat layer exhibits good print quality and has little negative impact on overall electrical performance of the photoreceptor. Moreover, silicone PEG esters are soluble in alcohols, and thus can be readily incorporated into the overcoat coating solution.
The present embodiments provide an overcoat layer that is made by incorporating into a crosslinking overcoat coating solution a silicone PEG ester for low surface energy and wear resistance. The disclosed silicone PEG ester is represented by the following structure
wherein a, b, and c are the number of the corresponding repeating units, and R is an alkyl. In an embodiment, a ranges from about 4 to about 200, or from about 6 to about 100; b ranges from about 1 to about 30, or from about 2 to about 10; and c ranges from about 1 to about 40, or from about 2 to about 20. R may be an alkyl having from about 4 to about 24 carbon atoms.
The disclosed silicone PEG ester is formed through the esterification of a corresponding fatty acid with dimethicone copolyol. Specific examples of the silicone PEG esters include SILSENSE® IW-12 silicone, a dimethicone PEG-7 cocoate with the following structure
wherein a ranges from about 6 to about 100; b ranges from about 2 to about 10; and R is derived from cocoa fatty acid; SILSENSE® DW-18 silicone, a dimethicone PEG-7 isostearate with the following structure
wherein a ranges from about 6 to about 100; b ranges from about 2 to about 10; and R is derived from isostearic acid; or Ultrabee™ WD Silicone, a dimethicone PEG-8 Beeswax with the following structure
wherein a ranges from about 6 to about 100; b ranges from about 2 to about 10; and R is derived from beeswax fatty acids; and the like, and mixtures thereof, all commercially available from Lubrizol Corporation (Walnut Creek, Calif.). Incorporation of such soluble fillers into the overcoat layer provides low surface energy and reduced wear.
The exemplary embodiments of this disclosure are described below with reference to the drawings. The specific terms are used in the following description for clarity, selected for illustration in the drawings and not to define or limit the scope of the disclosure. The same reference numerals are used to identify the same structure in different figures unless specified otherwise. The structures in the figures are not drawn according to their relative proportions and the drawings should not be interpreted as limiting the disclosure in size, relative size, or location. In addition, though the discussion will address negatively charged systems, the imaging members of the present disclosure may also be used in positively charged systems.
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, 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 to 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 considerations.
The substrate 10 may have a number of many 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 5×10−5 psi (3.5×10−4 Kg/cm2) and about 7×10−5 psi (4.9×10−4 Kg/cm2).
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 undercoat or 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 may 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 4-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 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 potential. 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 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) carbonate, 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 0.2 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 generation 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 in 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 through. 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 Cl 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™ BHT-R, MDP-S, BBM-S, WX-R, NW, BP-76, BP-101, GA-80, GM and 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, 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 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 weight percent of the antioxidant in at least one of the charge transport layer is from about 0 to 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 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 Overcoat Layer
To provide an overcoat layer 32 that exhibits both low surface energy and wear resistance as compared to conventional overcoat layers employed in organic photoreceptors, the present embodiments employ an overcoat layer 32 incorporates a soluble filler 36. In the present embodiments, the overcoat layer formulation comprises a silicone PEG ester 36 of the following formula/structure:
wherein a, b, and c are the number of the corresponding repeating units, and R is an alkyl. In an embodiment, a ranges from about 4 to about 200, or from about 6 to about 100; b ranges from about 1 to about 30, or from about 2 to about 10; and c ranges from about 1 to about 40, or from about 2 to about 20; R is an alkyl having from about 4 to about 24 carbon atoms. In specific embodiments, R is an alkyl derived from cocoa fatty acid, isostearic acid or beeswax fatty acids and the like.
The disclosed silicone PEG ester is formed through the esterification of a corresponding fatty acid with dimethicone copolyol. Specific examples of the silicone PEG esters include SILSENSE® IW-12 silicone, a dimethicone PEG-7 cocoate with the following structure
wherein a ranges from about 6 to about 100; b ranges from about 2 to about 10; and R is derived from cocoa fatty acid; SILSENSE® DW-18 silicone, a dimethicone PEG-7 isostearate with the following structure
wherein a ranges from about 6 to about 100; b ranges from about 2 to about 10; and R is derived from isostearic acid; or Ultrabee™ WD Silicone, a dimethicone PEG-8 Beeswax with the following structure
wherein a ranges from about 6 to about 100; b ranges from about 2 to about 10; and R is derived from beeswax fatty acids, and the like, and mixtures thereof, all commercially available from Lubrizol Corporation (Walnut Creek, Calif.). Incorporation of such soluble fillers into the overcoat layer provides low surface energy and reduced wear. In embodiments, the silicone PEG ester is present in an amount of from about 0.1 to about 40, or from about 1 to about 30, or from about 5 to about 20 weight percent of the total overcoat layer. In embodiments, the overcoat layer of the present embodiments has a wear rate of from about 1 to about 30, or from about 2 to about 25, or from about 3 to about 20 nm/kcycle. In embodiments, the wear of the present overcoat layer is reduced by of from about 5 to about 50 percent, or from about 10 to about 45 percent, or from about 15 to about 40 percent as compared to the wear of an overcoat layer without the silicone PEG ester.
In embodiments, the overcoat layer is formed from a formulation or solution comprising a small transport molecule or plurality of transport molecules, a crosslinker compound, an optional resin, an optional acid catalyst, and one or more optional surface additives in a solvent or a solvent mixture. To facilitate the crosslinking process, the combination of the small transport molecule and the crosslinker compound takes place in the presence of a strong acid solution.
In embodiments the small transport molecule can be selected from the group consisting of N,N′-diphenyl-N—N′-bis(hydroxyphenyl)[1,1′-terphenyl]-4,4′-diamine (DHTER), N,N′-diphenyl-N,N′-bis(3-hydroxyphenyl)-[1,1′-biphenyl]-4,4′-diamine (DHTBD), and the like, and mixtures thereof. In embodiments, the optional resin can be selected from the group consisting of polyester polyols, polyacrylate polyols, and the like, and mixtures thereof. One specific resin used is JONCRYL®, an acrylic polyol, available from BASF Corp. (Florham Park, N.J. The crosslinker compound may be, in embodiments, selected from the group consisting of methylated formaldehyde-melamine resin, methoxymethylated melamine resin, ethoxymethylated melamine resin, propoxymethylated melamine resin, butoxymethylated melamine resin, hexamethylol melamine resin, alkoxyalkylated melamine resins such as methoxymethylated melamine resin, ethoxymethylated melamine resin, propoxymethylated melamine resin, butoxymethylated melamine resin and the like, and mixtures thereof. In one example, the melamine formaldehyde crosslinker compound is CYMEL® 303, available from Cytec Corporation (West Paterson, N.J.). An acid catalyst may be selected from the group consisting of toluenesulfonic acid, amine-protected toluenesulfonic acid, and the like, and mixtures thereof. In embodiments, the acid catalyst used is NACURE® XP-357 available from King Industries (Norwalk, Conn.). The surface additives may be selected from the group consisting of alkylsilanes, perfluorinated alkylalcohols, and the like, and mixtures thereof. In specific embodiments, the surface additive is SILCLEAN® 3700, a solution of a silicone modified polyacrylate (OH-functional) which can be crosslinked into a polymer network due to its —OH functionality. SILCLEAN® 3700 is available from BYK-Chemie GmbH (Wesel, Germany). The solvent may be selected from the group consisting of alcohols, ethers, esters, ketones, and the like and mixtures thereof. In one embodiment, the solvent used is a glycol ether and is available at about 20 percent solids (DOWANOL® PM), available from The Dow Chemical Co. (Midland, Mich.).
In embodiments, the silicone PEG ester is present in an amount of from about 1 percent to about 30 percent, or from about 2 percent to about 25 percent, or from about 3 percent to about 20 percent of the overcoat solution. In further embodiments, the small transport molecule is present in an amount of from about 40 percent to about 95 percent, or from about 45 percent to about 90 percent of the overcoat solution. In other embodiments, the optional resin is present in an amount of from about 1 percent to about 50 percent, or from about 10 percent to about 40 percent of the overcoat solution. In embodiments, the crosslinker compound is present in an amount of from about 1 percent to about 50 percent, or from about 4 percent to about 40 percent of the overcoat solution. In the present embodiments, the acid catalyst is present in an amount of from about 0.5 percent to about 3 percent, or from about 1 percent to about 2 percent of the overcoat solution. In the present embodiments, one or more surface additives are present in an amount of from about 0.1 percent to about 6 percent, or from about 0.5 percent to about 2 percent of the overcoat solution. In yet further embodiments, the solvent is present in an amount of from about 50 percent to about 80 percent, or from about 55 percent to about 75 percent of the overcoat solution.
The prepared overcoat solution is subsequently coated and dried onto the photoreceptor. The average thickness of the dried overcoat layer after being dried at a temperature of from about 120 to about 200° C. for a period of from about 20 to about 120 minutes is from about 1 micron to about 15 microns, or from about 3 microns to about 10 microns.
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.
Experimentally, the control overcoat layer solution was prepared by mixing the following: N,N′-diphenyl-N,N′-bis(3-hydroxyphenyl)-[1,1′-biphenyl]-4,4′-diamine (DHTBD) (11.38 grams), CYMEL® 303LF (5.71 grams), NACURE® XP-357 (0.96 gram), SILCLEAN® 3700 (0.91 gram), 1-methoxy-2-propanol (40 grams), and bis(4-diethylamino-2-methylphenyl)-(4-diethylaminophenyl)-methane (TrisTPM) (0.85 gram) pre-dissolved in cyclopentanone (4.4 grams). The disclosed silicone PEG ester incorporated overcoat layer solution was prepared by adding about 7.5 wt % or 15 wt % of the silicone PEG ester, SILSENSE® IW-12 silicone, into the above controlled solution. The silicone PEG ester was completely soluble in the solution.
Three photoconductors were prepared comprising 3 component UCL, hydroxyl phthalocyanine Type V CGL, about 27-micron thick PCZ-400/mTBD/BHT=60/40/1 CTL, and the corresponding 3.5-micron thick overcoat layer (cured at 160° C./40 minutes). Both the controlled and disclosed overcoat layer solutions were filtered through a 1-micron glass filter before coating.
The t=0 photo-induced discharge curve (PIDC) are shown in
The deletion test in A zone was conducted in-house with a printer. The disclosed OCL photoconductors showed comparable deletion resistance to the controlled OCL photoconductor. Preliminary printing evaluation after 500 prints in A and J zone from a printer showed comparable image quality (IQ) characteristics in every category for the above controlled and disclosed OCL photoconductors.
The wear rate was tested using an in-house bias charge roller (BCR) wear fixture at ambient conditions (for example, from about 23 to about 25° C.). The disclosed OCL photoconductor comprising about 15 wt % of the silicone PEG ester possessed a wear rate of about 19 nm/kcycle, while the controlled OCL photoconductor possessed a wear rate of about 28 nm/kcycle—about 30% wear reduction.
In summary, the present embodiments disclose the incorporation of a soluble silicone PEG ester additive into a crosslinked overcoat layer for low surface energy and wear without sacrifices of other key photoreceptor characteristics. The additive can be applied to any crosslinked overcoat layer platform for further property improvements.
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.
