Patent Grant
7144664
Herein is described photosensitive members, imaging members, photoreceptors, or photoconductors useful in electrostatographic apparatuses, including printers, copiers, other reproductive devices, and digital apparatuses. In specific embodiments, described herein are photosensitive members having deletion control additives. In embodiments, the deletion control additives comprise a 3,4,9,10 perylenetetracarboxylic diimide compound. The deletion control additive provides, in embodiments, a better resistance to corona effluence and a more electrically sensitive device, hence increasing image quality.
Electrophotographic imaging members, including photoreceptors, photosensitive members, or photoconductors, typically include a photoconductive layer formed on an electrically conductive substrate or formed on layers between the substrate and photoconductive layer. The photoconductive layer is an insulator in the dark, so that electric charges are retained on its surface. Upon exposure to light, the charge is dissipated, and an image can be formed thereon, developed using a developer material, transferred to a copy substrate, and fused thereto to form a copy or print.
Many advanced imaging systems are based on the use of small diameter photoreceptor drums. The use of small diameter drums places a premium on photoreceptor life. A major factor limiting photoreceptor life in copiers and printers is wear. The use of small diameter drum photoreceptors exacerbates the wear problem because, for example, 3 to 10 revolutions are required to image a single letter size page. Multiple revolutions of a small diameter drum photoreceptor to reproduce a single letter size page can require up to 1 million cycles from the photoreceptor drum to obtain 100,000 prints, a desirable goal for commercial systems.
For low volume copiers and printers, bias charging rolls (BCR) are desirable because little or no ozone is produced during image cycling. However, the microcorona generated by the BCR during charging, damages the photoreceptor, resulting in rapid wear of the imaging surface, for example, the exposed surface of the charge transport layer. More specifically, wear rates can be as high as about 16 microns per 100,000 imaging cycles. Similar problems are encountered with bias transfer roll (BTR) systems.
One approach to achieving longer photoreceptor drum life is to form a protective overcoat on the imaging surface, for example, the charge transporting layer of a photoreceptor. This overcoat layer must satisfy many requirements, including transporting holes, resisting image deletion, resisting wear, and avoidance of perturbation of underlying layers during coating.
Various overcoats employing alcohol soluble polyamides have been proposed in the prior art. One of the earliest ones is an overcoat comprising an alcohol soluble polyamide without any methyl methoxy groups (Elvamide 80630®) containing N,N′-diphenyl-N,N′-bis(3-hydroxyphenyl)-(1,1′-biphenyl)-4,4′-diamine. This overcoat is described in U.S. Pat. No. 5,368,967, the entire disclosure thereof being incorporated herein by reference. Although this overcoat had very low wear rates in machines employing corotrons for charging, the wear rates were higher in machines employing BCR.
A crosslinked polyamide overcoat overcame this shortcoming. This overcoat comprised a crosslinked polyamide, referred to as Luckamide®, containing N,N′-diphenyl-N,N′-bis(3-hydroxyphenyl)-(1,1′-biphenyl)-4,4′-diamine. In order to achieve crosslinking, a polyamide polymer having N-methoxymethyl groups (Luckamide®) was employed along with a catalyst such as oxalic acid. This tough overcoat is described in U.S. Pat. No. 5,702,854, the entire disclosure thereof being incorporated herein by reference. With this overcoat, very low wear rates were obtained in machines employing bias charging rolls (BCR) and bias transfer rolls (BTR). Durable photoreceptor overcoatings containing crosslinked polyamide (i.e., Luckamide®) containing N,N′-diphenyl-N,N′-bis(3-hydroxyphenyl)-(1,1′-biphenyl)-4,4′-diamine (DHTPD) (Luckamide®-DHTPD) have been prepared using oxalic acid and trioxane to improve photoreceptor life by at least a factor of 3 to 4. Such improvement in the bias charging roll wear resistance involved crosslinking of Luckamide® under heat treatment, for example, 110° C.–120° C. for 30 minutes.
However, adhesion of this overcoat to certain photoreceptor charge transport layers, containing certain polycarbonates (e.g., Z-type 300) and charge transport materials such as bis-N,N-(3,4-dimethylphenyl)-N-(4-biphenyl)amine and N,N′-diphenyl-N,N′-bis(3-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine, is greatly reduced under some drying conditions. Polyvinyl butyral (PVB) was added to the formulation to promote the poor adhesion between the overcoat layer and the charge transport layer. The addition of PVB to the Luckamide overcoat formulation is described in U.S. Pat. No. 6,207,334, the entire disclosure thereof being incorporated herein by reference.
One of the most noticeable problems in current organic photoreceptors is lateral charge migration (LCM), which results in the deletion of electrophotographic images. The primary cause of LCM is the increased conductivity of the photoreceptor surface, which results in charge movement of the latent electrostatic image. The development of charge pattern results in toned images that are less precise than the originals. The increase in surface conductivity is believed to be primarily due to oxidation of the charge transport molecule by nitrous oxides effluents from bias charging roll and corona charging devices. The problem is particularly evident in some machines, wherein there are several charging corotrons, and in photoreceptors where there is little surface wear on the photoreceptor and the conductive oxidized species are not worn away. The latter is the case with crosslinked polyamide overcoats.
To eliminate LCM, tetrakis methylene(3,5-di-tert-butyl-4-hydroxy hydrocinnamate)methane(Irganox 1010), butylated hydroxytoluene (BHT), bis(4-diethylamino-2-methylphenyl)phenylmethane(BDETPM), bis-[2-methyl-4-(N-2-hydroxyethyl-N-ethyl-aminophenyl)]-phenylmethane (DHTPM), and the like, have been added to the charge transport layer of organic photoreceptors with arylamine charge transporting species. To eliminate gross macroscopic deletions of Kanji characters in the A zone, BDETPM or DHTPM has been added to the polyamide overcoat formulations. However, in the case of the polyamide overcoat, all these known deletion control additives have been shown to be inadequate.
It appears that deletion is most apparent in the polyamide overcoat because of its extreme resistance to wear (10 nm/kilocycle with bias charging rolls and 4 nm/kilocycle with scorotron charging). Because the oxidized surface does not wear off appreciably, deletion from the polyamide overcoat is more apparent than in polycarbonate charge transport layers where the greater wear rates continually refresh the photoconductor surface. Therefore, new and improved deletion control additives are needed to preserve image quality in polyamide overcoated photoreceptor drums and belts, by reducing or eliminating lateral charge migration and the resultant print defects caused by corona effluents on photoreceptor surfaces. It is further desired to provide an overcoat for photoreceptors that accelerates hole transport through the overcoat layer to eliminate or reduce lateral charge migration. In addition, it is also desired to provide a photoreceptor coating that allows the preservation of half-toned and high frequency print features of 300 dots per inch and less to be maintained for more than 2,000 continuous prints (or at least 8,000 photoreceptor cycles) in the A, B and C zones.
Embodiments include: an imaging member comprising a substrate; a charge transport layer comprising charge transport materials dispersed therein; and thereover, an overcoat layer comprising a deletion control additive.
Embodiments further include an imaging member comprising a substrate; a charge transport layer comprising charge transport materials dispersed therein; and thereover, an overcoat layer comprising a deletion control additive, a crosslinking agent, and polyamide.
In addition, embodiments include an image forming apparatus for forming images on a recording medium comprising a) a photoreceptor member having a charge retentive surface to receive an electrostatic latent image thereon, wherein the photoreceptor member comprises a substrate, a charge transport layer comprising charge transport materials therein, and thereover, an overcoat layer comprising a deletion control additive, wherein the charge retentive surface is on the overcoat layer; b) a development component to apply 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 another member or a copy substrate; and d) a fusing member to fuse the developed image to the copy substrate.
For a better understanding, reference may be had to the accompanying figure.
Herein are described deletion control additives to preserve image quality in overcoated photoreceptor drums and belts. In embodiments, the deletion control additive comprises a deletion control additive.
Referring to
After the toner particles have been deposited on the photoconductive surface, in image configuration, they are transferred to a copy sheet 16 by transfer means 15, which can be pressure transfer or electrostatic transfer. In embodiments, the developed image can be transferred to an intermediate transfer member and subsequently transferred to a copy sheet.
After the transfer of the developed image is completed, copy sheet 16 advances to fusing station 19, depicted in
Electrophotographic imaging members are well known in the art. Electrophotographic imaging members may be prepared by any suitable technique. Referring to
The substrate may be opaque or substantially transparent and may comprise any suitable material having the required mechanical properties. Accordingly, the substrate may comprise a layer of an electrically non-conductive or conductive material such as an inorganic or an organic composition. As electrically non-conducting materials, there may be employed various resins known for this purpose including polyesters, polycarbonates, polyamides, polyurethanes, and the like which are flexible as thin webs. An electrically conducting substrate may be any metal, for example, aluminum, nickel, steel, copper, and the like or a polymeric material, as described above, filled with an electrically conducting substance, such as carbon, metallic powder, and the like or an organic electrically conducting material. The electrically insulating or conductive substrate may be in the form of an endless flexible belt, a web, a rigid cylinder, a sheet and the like. The thickness of the substrate layer depends on numerous factors, including strength desired and economical considerations. Thus, for a drum, this layer may be of substantial thickness of, for example, up to many centimeters or of a minimum thickness of less than a millimeter. Similarly, a flexible belt may be of substantial thickness, for example, about 250 micrometers, or of minimum thickness less than 50 micrometers, provided there are no adverse effects on the final electrophotographic device.
In embodiments where the substrate layer is not conductive, the surface thereof may be rendered electrically conductive by an electrically conductive coating 2. The conductive coating may vary in thickness over substantially wide ranges depending upon the optical transparency, degree of flexibility desired, and economic factors. Accordingly, for a flexible photoresponsive imaging device, the thickness of the conductive coating may be between about 20 angstroms to about 750 angstroms, or from about 100 angstroms to about 200 angstroms for an optimum combination of electrical conductivity, flexibility and light transmission. The flexible conductive coating may be an electrically conductive metal layer formed, for example, on the substrate by any suitable coating technique, such as a vacuum depositing technique or electrodeposition. Typical metals include aluminum, zirconium, niobium, tantalum, vanadium and hafnium, titanium, nickel, stainless steel, chromium, tungsten, molybdenum, and the like.
An optional hole blocking layer 3 may be applied to the substrate 1 or coating. Any suitable and conventional blocking layer capable of forming an electronic barrier to holes between the adjacent photoconductive layer 8 (or electrophotographic imaging layer 8) and the underlying conductive surface 2 of substrate 1 may be used.
An optional adhesive layer 4 may be applied to the hole-blocking layer 3. Any suitable adhesive layer well known in the art may be used. Typical adhesive layer materials include, for example, polyesters, polyurethanes, and the like. Satisfactory results may be achieved with adhesive layer thickness between about 0.05 micrometer (500 angstroms) and about 0.3 micrometer (3,000 angstroms). Conventional techniques for applying an adhesive layer coating mixture to the hole blocking layer include spraying, dip coating, roll coating, wire wound rod coating, gravure coating, Bird applicator coating, and the like. Drying of the deposited coating may be effected by any suitable conventional technique such as oven drying, infrared radiation drying, air drying and the like.
At least one electrophotographic imaging layer 8 is formed on the adhesive layer 4, blocking layer 3 substrate 1. The electrophotographic imaging layer 8 may be a single layer (7 in
The charge generating layer 5 can be applied to the electrically conductive surface, or on other surfaces in between the substrate 1 and charge generating layer 5. A charge blocking layer or hole-blocking layer 3 may optionally be applied to the electrically conductive surface prior to the application of a charge generating layer 5. If desired, an adhesive layer 4 may be used between the charge blocking or hole-blocking layer 3 and the charge generating layer 5. Usually, the charge generation layer 5 is applied onto the blocking layer 3 and a charge transport layer 6, is formed on the charge generation layer 5. This structure may have the charge generation layer 5 on top of or below the charge transport layer 6.
Charge generator layers may comprise amorphous films of selenium and alloys of selenium and arsenic, tellurium, germanium and the like, hydrogenated amorphous silicon and compounds of silicon and germanium, carbon, oxygen, nitrogen and the like fabricated by vacuum evaporation or deposition. The charge-generator layers may also comprise inorganic pigments of crystalline selenium and its alloys; Group II–VI compounds; and organic pigments such as quinacridones, polycyclic pigments such as dibromo anthanthrone pigments, perylene and perinone diamines, polynuclear aromatic quinones, azo pigments including bis-, tris- and tetrakis-azos; and the like dispersed in a film forming polymeric binder and fabricated by solvent coating techniques.
Phthalocyanines have been employed as photogenerating materials for use in laser printers using infrared exposure systems. Infrared sensitivity is required for photoreceptors exposed to low-cost semiconductor laser diode light exposure devices. The absorption spectrum and photosensitivity of the phthalocyanines depend on the central metal atom of the compound. Many metal phthalocyanines have been reported and include, oxyvanadium phthalocyanine, chloroaluminum phthalocyanine, copper phthalocyanine, oxytitanium phthalocyanine, chlorogallium phthalocyanine, hydroxygallium phthalocyanine magnesium phthalocyanine and metal-free phthalocyanine. The phthalocyanines exist in many crystal forms, and have a strong influence on photogeneration.
Any suitable polymeric film forming binder material may be employed as the matrix in the charge-generating (photogenerating) binder layer. Typical polymeric film forming materials include those described, for example, in U.S. Pat. No. 3,121,006, the entire disclosure of which is incorporated herein by reference. Thus, typical organic polymeric film forming binders include thermoplastic and thermosetting resins such as polycarbonates, polyesters, polyamides, polyurethanes, polystyrenes, polyarylethers, polyarylsulfones, polybutadienes, polysulfones, polyethersulfones, polyethylenes, polypropylenes, polyimides, polymethylpentenes, polyphenylene sulfides, polyvinyl acetate, polysiloxanes, polyacrylates, polyvinyl acetals, polyamides, polyimides, amino resins, phenylene oxide resins, terephthalic acid resins, phenoxy resins, epoxy resins, phenolic resins, polystyrene and acrylonitrile copolymers, polyvinylchloride, vinylchloride and vinyl acetate copolymers, acrylate copolymers, alkyd resins, cellulosic film formers, poly(amideimide), styrenebutadiene copolymers, vinylidenechloride-vinylchloride copolymers, vinylacetate-vinylidenechloride copolymers, styrene-alkyd resins, polyvinylcarbazole, and the like. These polymers may be block, random or alternating copolymers.
The photogenerating composition or pigment is present in the resinous binder composition in various amounts. Generally, however, from about 5 percent by volume to about 90 percent by volume of the photogenerating pigment is dispersed in about 10 percent by volume to about 95 percent by volume of the resinous binder, or from about 20 percent by volume to about 30 percent by volume of the photogenerating pigment is dispersed in about 70 percent by volume to about 80 percent by volume of the resinous binder composition. In one embodiment, about 8 percent by volume of the photogenerating pigment is dispersed in about 92 percent by volume of the resinous binder composition. The photogenerator layers can also fabricated by vacuum sublimation in which case there is no binder.
Any suitable and conventional technique may be used to mix and thereafter apply the photogenerating layer coating mixture. Typical application techniques include spraying, dip coating, roll coating, wire wound rod coating, vacuum sublimation and the like. For some applications, the generator layer may be fabricated in a dot or line pattern. Removing of the solvent of a solvent coated layer may be effected by any suitable conventional technique such as oven drying, infrared radiation drying, air drying and the like.
The charge transport layer 6 may comprise a charge transporting small molecule 22 dissolved or molecularly dispersed in a film forming electrically inert polymer such as a polycarbonate. The term “dissolved” as employed herein is defined herein as forming a solution in which the small molecule is dissolved in the polymer to form a homogeneous phase. The expression “molecularly dispersed” is used herein is defined as a charge transporting small molecule dispersed in the polymer, the small molecules being dispersed in the polymer on a molecular scale. Any suitable charge transporting or electrically active small molecule may be employed in the charge transport layer. The expression charge transporting “small molecule” is defined herein as a monomer that allows the free charge photogenerated in the transport layer to be transported across the transport layer. Typical charge transporting small molecules include, for example, pyrazolines such as 1-phenyl-3-(4′-diethylamino styryl)-5-(4″-diethylamino phenyl)pyrazoline, diamines such as N,N′-diphenyl-N,N′-bis(3-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine, hydrazones such as N-phenyl-N-methyl-3-(9-ethyl)carbazyl hydrazone and 4-diethyl amino benzaldehyde-1,2-diphenyl hydrazone, and oxadiazoles such as 2,5-bis (4-N,N′-diethylaminophenyl)-1,2,4-oxadiazole, stilbenes and the like. However, to avoid cycle-up in machines with high throughput, the charge transport layer should be substantially free (less than about two percent) of di- or tri-amino-triphenyl methane. As indicated above, suitable electrically active small molecule charge transporting compounds are dissolved or molecularly dispersed in electrically inactive polymeric film forming materials. A small molecule charge transporting compound that permits injection of holes from the pigment into the charge generating layer with high efficiency and transports them across the charge transport layer with very short transit times is N,N′-diphenyl-N,N′-bis(3-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine. If desired, the charge transport material in the charge transport layer may comprise a polymeric charge transport material or a combination of a small molecule charge transport material and a polymeric charge transport material.
Any suitable electrically inactive resin binder insoluble in the alcohol solvent used to apply the overcoat layer may be employed in the charge transport layer. Typical inactive resin binders include polycarbonate resin, polyester, polyarylate, polyacrylate, polyether, polysulfone, and the like. Molecular weights can vary, for example, from about 20,000 to about 150,000. Examples of binders include polycarbonates such as poly(4,4′-isopropylidene-diphenylene)carbonate (also referred to as bisphenol-A-polycarbonate, poly(4,4′-cyclohexylidinediphenylene) carbonate (referred to as bisphenol-Z polycarbonate), poly(4,4′-isopropylidene-3,3′-dimethyl-diphenyl)carbonate (also referred to as bisphenol-C-polycarbonate) and the like. Any suitable charge transporting polymer may also be used in the charge transporting layer. The charge transporting polymer should be insoluble in the alcohol solvent employed to apply the overcoat layer. These electrically active charge transporting polymeric materials should be capable of supporting the injection of photogenerated holes from the charge generation material and be capable of allowing the transport of these holes therethrough.
Any suitable and conventional technique may be used to mix and thereafter apply the charge transport layer coating mixture to the charge generating layer. Typical application techniques include spraying, dip coating, roll coating, wire wound rod coating, and the like. Drying of the deposited coating may be effected by any suitable conventional technique such as oven drying, infrared radiation drying, air drying and the like.
Generally, the thickness of the charge transport layer is between about 10 and about 50 micrometers, but thicknesses outside this range can also be used. The hole 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. In general, the ratio of the thickness of the hole transport layer to the charge generator layers can be maintained from about 2:1 to 200:1 and in some instances as great as 400:1. The charge transport layer, is substantially non-absorbing 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, i.e., 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 embodiments, an overcoat is coated on the charge-generating layer. In embodiments, a polyamide resin is used as the resin in the overcoat layer. In embodiments, the polyamide is an alcohol-soluble polyamide. In embodiments, the polyamide comprises pendant groups selected from the group consisting of methoxy, ethoxy and hydroxy pendant groups. In embodiments, the pendant groups are methylene methoxy pendant groups. In embodiments, the polyamide has the following formula III:
wherein R1, R2 and R3 are alkyl groups having from about 1 to about 15 carbons, or from about 1 to about 10 carbons, or from about 1 to about 5 carbons, such as methyl, ethyl, propyl, butyl, and the like, and n is a number of from about 50 to about 1,000, or from about 150 to about 500, or about 270. Typical commercially available alcohol-soluble polyamide polymers suitable for use herein include those sold under the trade names LUCKAMIDE® 5003 from Dai Nippon Ink, NYLON® 8, CM4000® and CM8000® both from Toray Industries, Ltd., and other polyamides such as those prepared according to the method described in Sorenson and Campbell, “Preparative Methods of Polymer Chemistry,” second edition, pg. 76, John Wiley & Sons, Inc., 1968, and the like, and mixtures thereof. In embodiments, the polyamide has methoxy, ethoxy and hydroxy groups, including N-methoxymethyl, N-ethoxymethyl, and N-hydroxymethyl pendant groups.
The polyamide is present in the overcoat in an amount of from about 20 to about 90 percent, or from about 40 to about 60 percent by weight of total solids.
A deletion control agent (9 and/or 18 in
However, the above known deletion control agents do not allow for effective deletion control when used with polyamide-based hold transporting layers. The problem is escalated when the photoreceptor is used in a high-speed machine that uses charging corotrons, and when a highly wear resistant layer allows the buildup of the conductive oxidized species. IRGANOX 1010, BHT, BDETPM, DHTPM, and the like, have been added to the charge transport layer with arylamine charge transporting species. However, in the case of the polyamide based overcoat, these known deletion control additives have proven inadequate. Deletion is most apparent in the polyamide overcoat because of its extreme resistance to wear (10 nm/kilocycle with BCR and 4 nm/kilocycle with scorotron charging). Because the oxidized surface does not wear off appreciably, deletion from polyamide overcoats is more apparent than in polycarbonate charge transport layers, where the greater wear rates continually refresh the photoconductor surface.
A new deletion control agent can be added to the outer layer. In embodiments, the deletion control agent is a 3,4,9,10 perylenetetracarboxylic dimide. Examples of 3,4,9,10 perylenetetracarboxylic dimide include those having the following formula I:
wherein R1 and R2 and R3 can be the same or different and can be a straight or branched alkyl group of from about 1 to about 25 carbons, or from about 1 to about 10 carbons, or from about 1 to about 5 carbons, such as methyl, ethyl, propyl, butyl, pentyl, and the like.
In embodiments, R1 and R2 and R3 can be the same or different and can be straight or branched carbon chain having from about 1 to about 25 carbons, such as methyl, ethyl, propyl, butyl, pentyl, and the like. In embodiments, R1 and R3 are the same and are both straight or branched carbon chains having from about 1 to about 25 carbons, such as methyl, ethyl, propyl, butyl, pentyl, and the like. In embodiments, R1 and R3 are both straight pentyl chains. In embodiments, R1 and R3 are both branched pentyl chains. In embodiments, R1 and R3 are different. In embodiments, one of R1 and R3 is a straight chain having from about 1 to about 25 carbons, and the other of R1 and R3 is a branched chain having from about 1 to about 25 carbons. In embodiments, one of R1 and R3 is a straight pentyl chain, and the other of R1 and R3 is a branched pentyl chain. In embodiments, R2 is a straight carbon chain having from about 1 to about 25 carbons such as methyl, ethyl, propyl, butyl, pentyl, and the like. In embodiments, R2 is a straight pentyl chain.
The deletion control compound is present in the polyamide overcoat in an amount of from about 0.1 to about 1 percent, or from about 1 to about 10 percent, or from about 5 to about 15 percent by weight of total solids.
A second deletion control agent 22 or a charge control agent 22, can be present in the outer overcoat layer in addition to the(4-N,N-diethylamino-2-methylphenyl)-4-N,N-diethylaminophenylmethane [TEA-TPM]. Examples include those deletion control agents listed above, such as tetrakis[ methylene(3,5-di-tert-butyl-4-hydroxy hydrocinnamate)]methane [Irganox 1010], butylated hydroxytoluene [BHT], bis(4-diethylamino-2-methylphenyl)phenylmethane [BDETPM], bis-[2-methyl-4-(N-2-hydroxyethyl-N-ethyl-aminophenyl)]-phenylmethane [DHTPM], and the like. The charge transport molecules or second deletion control agents are present in the overcoat layer in an amount of from about 50 to about 99 percent, or from about 60 to about 90 percent or from about 70 to about 80 percent by weight of total solids.
Crosslinking agents can be used in combination with the overcoat to promote crosslinking of the polymer, such as the polyamide, thereby providing a strong bond. Examples of suitable crosslinking agents include oxalic acid, p-toluene sulfonic acid, phosphoric acid, sulfuric acid, and the like, and mixtures thereof. In embodiments, the crosslinking agent is oxalic acid. The crosslinking agent can be used in an amount of from about 1 to about 20 percent, or from about 5 to about 10 percent, or about 8 to about 9 percent by weight of total polymer content.
The thickness of the continuous overcoat layer selected depends upon the abrasiveness of the charging (e.g., bias charging roll), cleaning (e.g., blade or web), development (e.g., brush), transfer (e.g., bias transfer roll), etc., in the system employed and can range up to about 10 micrometers. In embodiments, the thickness is from about 1 micrometer and about 5 micrometers.
Any suitable and conventional technique may be used to mix and thereafter apply the overcoat layer coating mixture to the charge-generating layer. Typical application techniques include spraying, dip coating, roll coating, wire wound rod coating, and the like. Drying of the deposited coating may be effected by any suitable conventional technique such as oven drying, infrared radiation drying, air drying, and the like. The dried overcoating should transport holes during imaging and should not have too high a free carrier concentration. Free carrier concentration in the overcoat increases the dark decay. In embodiments, the dark decay of the overcoated layer should be about the same as that of the unovercoated device.
All the patents and applications referred to herein are hereby specifically, and totally incorporated herein by reference in their entirety in the instant specification.
The following Examples further define and describe embodiments herein. Unless otherwise indicated, all parts and percentages are by weight.
Photoreceptor Outer Coatings using Known Deletion Control Additives
Electrophotographic imaging members were prepared by applying by dip coating, a charge blocking layer on a rough surface of 17 aluminum drums having a diameter of 3 cm and a length of 31 cm. The blocking layer coating mixture was a solution of 8 weight percent polyamide (nylon 6) dissolved in a 92 weight percent butanol, methanol and water solvent mixture. The butanol, methanol and water mixture percentages were 55, 36 and 9 percent by weight, respectively. The coating was applied at a coating bath withdrawal rate of about 30 cm/minute. After drying in a forced air oven, each blocking layer had a thickness of about 1.5 micrometers. The dried blocking layers were coated with a charge generating layer containing about 2.5 weight percent hydroxyl gallium phthalocyanine pigment particles, about 2.5 weight percent polyvinylbutyral film forming polymer, and about 95 weight percent cyclohexanone solvent. The coatings were applied at a coating bath withdrawal rate of about 30 cm/minute. After drying in a forced air oven, each charge-generating layer had a thickness of about 0.2 micrometer. The drums were subsequently coated with charge transport layers containing N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1; -biphenyl-4,4′-diamine dispersed in polycarbonate binder (PcZ400). The charge transport coating mixture consisted of 8 weight percent N,N′-diphenyl-N,N′-bis(3 -mehtylphenyl)-1,1;-biphenyl-4,4′-diamine, 12 weight percent binder and 80 weight percent monochlorobenzene solvent. The dried thickness of each transport layer was 20 micrometers.
One drum from Example 1 was overcoated with a protective layer coating solution. Its composition was prepared as followed: 0.7 grams polyamide containing methoxymethyl groups (Luckamide® 5003 available from Dai Nippon Ink), 0.3 grams ELVAMIDE® 8063 (available from E.I. Dupont), methanol (3.5 grams) and 1-propanol (3.5 grams) were all combined in a 2 ounce amber bottle and warmed with magnetic stirring in a water bath at about 60° C. A solution formed within 30 minutes. This solution was then allowed to cool to 25° C. Next, 0.08 grams oxalic acid was added and the mixture was warmed to 40° C. Subsequently, 0.9 grams N,N′-diphenyl-N, N′-bis(3-hydroxyphenyl)-[1,1′-biphenyl]-4,4′-diamine (DHTPD) was added and stirred until a complete solution was formed. A separate solution containing 0.08 grams Cymel®303 (hexamethoxymethylmelamine available from the Cytec Industries Inc.) and 0.2 grams bis(4-diethylamino-2-methylphenyl)-4-methoxyphenylmethane and one gram tetrahydrofuran was formed and added to the polymer solution. The solution was allowed to set overnight to insure mature viscosity properties.
A 6 micrometer thick overcoat was applied in the dip coating apparatus with a pull rate of 250 millimeters/min. The overcoated drum was dried at 120° C. for 35 minutes. The photoreceptor was print tested in a Xerox Docucolor 12/50 copy machine for 4,000 consecutive prints. There were significant reductions in image sharpness and color intensity, resulting from the print deletions caused by the overcoat.
An un-overcoated drum of Comparative Example 1 and the overcoated drum of Comparative Example 2 above were tested in a wear fixture that contained a bias charging roll for charging. Wear was calculated in terms of nanometers/kilocycles of rotation (nm/Kc). Reproducibility of calibration standards was about ±2 nm/Kc. The wear of the drum without the overcoat of Comparative Example 1 was greater than 80 nm/Kc. Wear of the overcoated drums of Comparative Example 2 was about 20 nm/Kc.
One drum from Comparative Example 1 was overcoated with a protective layer coating solution as prepared in Comparative Example 2, except that the following substitutions were made.
An amount of 0.8 grams N,N′-diphenyl-N,N′-bis(3-hydroxyphenyl)-(1,1′-biphenyl)-4,4′-diamine (DHTPD) was used instead of 0.9 grams. An amount of 0.2 grams tetrakis[methylene(3,5-di-tert-butyl-4-hydroxy hydrocinnamate)]methane (Irganox 1010) was substituted for 0.2 grams bis (4-diethylamino-2-methylphenyl)-4-methoxyphenylmethane. The drum was tested in accordance with Comparative Example 2. Its wear rate was about 33 nm/Kc.
One drum from Comparative Example 1 was overcoated with a protective layer coating solution as prepared in Comparative Example 2, except that the following substitutions were made.
An amount of 0.2 grams butylated hydroxytoluene (BHT) was substituted for 0.2 grams bis (4-diethylamino-2-methylphenyl)-4-methoxyphenylmethane. The drum was tested in accordance with Comparative Example 2. Its wear rate was about 20 nm/Kc.
Compositions of these comparative overcoated solutions using known deletion control additives are described in Table 1 below. Their corresponding wear rates are listed in Table 2 below. All values in Table 1 are expressed in grams.
From the results above, it is clear that deletion occurred by use of a mixture of polyamides in combination with known charge transport materials such as DHTBD. So far, no known deletion control additive can prevent such a print deletion when using a polyamide overcoat. Without the overcoat layer, the device is more resistance to deletion. However, its wear rate is much higher than that with the overcoat, hence reducing the life of the device.
The following example describes the overcoat compositions of embodiments herein.
Two drums from Comparative Example 1 were overcoated with a protective layer coating solution as prepared in Comparative Example 2, except that the following substitutions were made.
An amount of 0.2 grams 1,3-bis(n-pentylimidoperyleneimido)propane pigmented particles was substituted for 0.2 grams bis(4-diethylamino-2-methylphenyl)-4-methoxyphenylmethane.
One drum from Example 6 was print tested in a Xerox Docucolor 12/50 copy machine for 4,000 consecutive prints. The print tests were carried out in 3 different environmental zones, e.g. A zone (hot and humid), B zone (ambient condition) and C zone (cold and dry). There were no significant reductions in image sharpness, color intensity, and no other problems like background defects or print defects resulting from the overcoats. The 300 dpi and 600 dpi print resolutions were preserved during the 4,000 consecutive prints. The print target consists of a series of isolated lines with the widths of 1 pixel with a pattern of 1 pixel on and 1 pixel off. At 600 dpi resolution, the distance between the centers of 2 consecutive 1 on-pixels is 84 microns and the width of each pixel is 42 microns. How well a sample withstands against corona is determined by the visibility of those lines or can be computed using the contrast function, which is the ratio of the difference between the color intensities of 2 off- and on- pixels and the sum between these color intensities. The color intensity of 1 pixel ranges from 0 known as black to 255 known as pure white. The contrast values also known as the real print resolutions of 1 pixel lines were computed at every 1000 print interval and are displayed in Table 3.
The key message from Table 3 is that by the end of 4,000 continuous prints, the print resolution of 1 bit lines has been reduced by a factor of 2 for Comparative Example 2 (overcoat layer without pigments) and by a factor of 1.5 for both Comparative Example 1 (device without any overcoat) and Example 6 (device with pigmented overcoat layer). Print quality of the device from Example 6 is much better than that of Comparative Example 2 in which there were no pigments.
The second drum of Example 6 was tested for electrical characteristics. It was charged by a corotron mounted along the circumference of the drum. The surface potentials were measured as a function of time by several capacitively coupled probes placed at different locations around the shaft. The probes were calibrated by applying known potentials to the drum substrate. The films on the drum were exposed and erased by light sources located at appropriate positions around the drum. The measurements were accomplished charging the photoconductor devices in a constant current or voltage mode. As the drum rotated, the initial charging potential was measured. Further rotation leads to the exposure station, where the photoconductor devices were exposed to monochromatic radiation of known intensity. The surface potential after exposure was also measured. The devices were then exposed to an erase lamp of appropriate intensity and any residual potentials are measured. A photo induced discharge characteristics curve was obtained by plotting the potentials as a function of exposure. Most printers with drum-type photoreceptor such as DocuColor 50/12 printer develop images at the exposures ranging between 3 to 5 ergs/cm2, the slope region of the photo induced discharge characteristics (PIDC) curve. Thus, the device's electrical sensitivity (often called the slope of the PIDC curve) is crucial to the image quality. Since pigments were added to the overcoat, the device's sensitivity increased significantly while its residual voltage was not affected at all. At 3 ergs/cm2, the surface potential of Comparative Example 2 was 370 V and that of the device herein (Example 6) was 230 V. Therefore, the presently described device is considered a fast device and is suitable for a drum-type photoreceptor printer.
The drum tested in Example 7 was then tested in a wear fixture that contained a bias charging roll for charging. The average wear rate after 100,000 cycles was 20 nm /kcyles, which is in the same range of wear rates of other non-pigmented overcoated devices listed in Comparative Example 5. Therefore, addition of 1,3-bis(n-pentylimidoperyleneimido)propane pigments to the overcoat suggested herein does not appear to affect the device's wear life.
While devices have been described in detail with reference to specific and embodiments, it will be appreciated that various modifications and variations will be apparent to the artisan. All such modifications and embodiments as may readily occur to one skilled in the art are intended to be within the scope of the appended claims.
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| Number | Date | Country |
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| 0 156 514 | Oct 1985 | EP |
| Number | Date | Country | |
|---|---|---|---|
| 20050181290 A1 | Aug 2005 | US |
