A charge transport layer for a photoreceptor includes at least a bisphenol A-phthallic acid dichloride ester copolymer polycarbonate binder and at least one charge transport material. The charge transport layer exhibits excellent wear resistance, excellent electrical performance, and delivers superior print quality.

1. Field of the Invention
This invention relates to a novel charge transport layer composition of a photoreceptor used in electrophotography. More in particular, the invention relates to a polycarbonate binder for use in a charge transport layer.
2. Description of Related Art
In the art of electrophotography, an electrophotographic plate comprising a photoconductive insulating layer on a conductive layer is imaged by first uniformly electrostatically charging the surface of the photoconductive insulating layer. The plate is then exposed to a pattern of activating electromagnetic radiation such as light, which selectively dissipates the charge in the illuminated areas of the photoconductive insulating layer while leaving behind an electrostatic latent image in the non-illuminated areas. This electrostatic latent image may then be developed to form a visible image by depositing finely divided electroscopic toner particles, for example from a developer composition, on the surface of the photoconductive insulating layer. The resulting visible toner image can be transferred to a suitable receiving member such as paper.
Electrophotographic imaging members are usually multilayered photoreceptors that comprise a substrate support, an electrically conductive layer, an optional hole blocking layer, an optional adhesive layer, a charge generating layer, a charge transport layer, and optional protective or overcoating layer(s). The imaging members can take several forms, including flexible belts, rigid drums, etc. For most multilayered flexible photoreceptor belts, an anti-curl layer is usually employed on the back side of the substrate support, opposite to the side carrying the electrically active layers, to achieve the desired photoreceptor flatness. One type of multilayered photoreceptor comprises a layer of finely divided particles of a photoconductive inorganic compound dispersed in an electrically insulating organic resin binder.
U.S. Pat. No. 4,265,990 discloses a layered photoreceptor having a separate charge generating (photogenerating) layer (CGL) and charge transport layer (CTL). The charge generating layer is capable of photogenerating holes and injecting the photogenerated holes into the charge transport layer. The photogenerating layer utilized in multilayered photoreceptors include, for example, inorganic photoconductive particles or organic photoconductive particles dispersed in a film forming polymeric binder. Inorganic or organic photoconductive materials may be formed as a continuous, homogeneous photogenerating layer.
Examples of photosensitive members having at least two electrically operative layers including a charge generating layer and diamine containing transport layer are disclosed in U.S. Pat. Nos. 4,265,990, 4,233,384, 4,306,008, 4,299,897 and 4,439,507. The disclosures of these patents are incorporated herein in their entirety.
Charge transport layers are known to be comprised of any of several different types of polymer binders that have a charge transport material dispersed therein. For example:
U.S. Pat. No. 6,242,144 describes a charge transport layer including an electrically inactive resin binder such as polycarbonate resin, polyester, polyarylate, polyacrylate, polyether, polysulfone, and the like, with weight average molecular weights varying from about 20,000 to about 150,000. It is further indicated that preferred binders include polycarbonates such as poly(4,4xe2x80x2-isopropylidene-diphenylene)carbonate (bisphenol-A-polycarbonate), poly(4,4xe2x80x2-cyclohexylidinediphenylene) carbonate (referred to as bisphenol-Z polycarbonate), and the like.
U.S. Pat. No. 6,020,096 similarly describes that a photoreceptor includes a charge transport layer including any suitable electrically inert film forming polymeric binder such as poly(4,4xe2x80x2-isopropylidene-diphenylene)carbonate, poly(4,4xe2x80x2-isopropylidene-diphenylene)carbonate, poly(4,4xe2x80x2-diphenyl-1,1xe2x80x2-cyclohexane carbonate), polyaryl ketones, polyester, polyarylate, polyacrylate, polyether, polysulfone, and the like.
U.S. Pat. No. 6,171,741 describes that a photoreceptor includes a charge transport layer including an electrically inactive resin material, preferably polycarbonate resins having a weight average molecular weight from about 20,000 to about 150,000. The most preferred polycarbonate resins are poly(4,4xe2x80x2-dipropylidene-diphenylene carbonate) with a weight average molecular weight of from about 35,000 to about 40,000, available as LEXAN 145 from General Electric Company; poly(4,4xe2x80x2-isopropylidene-diphenylene carbonate) with a weight average molecular weight of from about 40,000 to about 45,000, available as LEXAN 141 from the General Electric Company; a polycarbonate resin having a weight average molecular weight of from about 50,000 to about 120,000, available as MAKROLON from Bayer Corp.; and a polycarbonate resin having a weight average molecular weight of from about 20,000 to about 50,000 available as MERLON from Mobay Chemical Company. It is also described that methylene chloride solvent is a desirable component of the charge transport layer coating mixture for adequate dissolving of all the components and for its low boiling point.
In addition, U.S. Pat. No. 5,728,498 describes a flexible electrophotographic imaging member including a supporting substrate coated with at least one imaging layer comprising hole transporting material containing at least two long chain alkyl carboxylate groups dissolved or molecularly dispersed in a film forming binder.
What is still desired is an improved binder for a charge transport layer of an imaging member (photoreceptor) that exhibits excellent performance properties the same as or better than existing binder materials discussed above, and has a further advantage of being coated using a solvent that is more environmentally friendly than methylene chloride.
It is therefore one object of the invention to develop a novel binder resin for use as a charge transport layer binder.
It is a still further object of the present invention to develop a charge transport layer binder that performs as well as or better than existing charge transport layer binders and is additionally capable of being coated from a solution containing an environmentally friendly solvent.
These and other objects are obtained by the present invention. In a first aspect, the present invention relates to a charge transport layer material for a photoreceptor comprising at least a bisphenol A-phthallic acid dichloride ester copolymer polycarbonate binder and at least one charge transport material dispersed in a solvent comprised of at least tetrahydrofuran.
In a second aspect of the invention, the invention relates to a charge transport layer of a photoreceptor comprising at least a bisphenol A-phthallic acid dichloride ester copolymer polycarbonate binder and at least one charge transport material.
In a third aspect of the invention, the invention relates to an image forming device comprising at least a photoreceptor and a charging device which charges the photoreceptor, wherein the photoreceptor comprises an optional anti-curl layer, a substrate, an optional hole blocking layer, an optional adhesive layer, a charge generating layer, a charge transport layer comprising at least a bisphenol A-phthallic acid dichloride ester copolymer polycarbonate binder and at least one charge transport material, and an optional overcoat layer.
By the use of the preferred polycarbonate resin binder as the charge transport layer binder in the present invention, a charge transport layer of an imaging member is achieved that has excellent hole transporting performance and wear resistance, and that is able to be coated onto the imaging member structure with an environmentally friendly solvent such as tetrahydrofuran.
In the present invention, the charge transport layer material for a photoreceptor comprises at least a bisphenol A-phthallic acid dichloride ester copolymer polycarbonate binder and at least one charge transport material dispersed in a solvent comprised of at least tetrahydrofuran.
The bisphenol A-phthallic acid dichloride ester copolymer polycarbonate binder is believed to most preferably be comprised of a copolymer of bisphenol A (i.e., 4,4xe2x80x2-isopropylidenediphenol) and a phthallic acid dichloride ester. Preferably, the copolymer polycarbonate has a weight average molecular weight, as measured by Gel Permeation Chromatography using dichloromethane as eluent and polystyrene standards of, for example, about 150,000 to about 500,000, more preferably from about 150,000 to about 300,000, more preferably from about 1 75,000 to about 225,000, most preferably of about 200,000. This type of copolymer polycarbonate resin is commercially available from General Electric under the name LEXAN ML5273 and is identified as a copolymer(bisphenol-A/phthallic acid dichloride ester carbonate)(PCE), CAS Registry number 71519-80-7.
The charge transport layer of a photoreceptor must be capable of supporting the injection of photo-generated holes and electrons from a charge generating layer and allowing the transport of these holes or electrons through the organic layer to selectively discharge the surface charge. If some of the charges are trapped inside the transport layer, the surface charges will not completely discharged and toner image will not be fully developed on the surface of the photoreceptor.
The charge transport layer thus must include at least one charge transport material. Any suitable charge transport molecule known in the art may be used, and the charge transport molecules may either be dispersed in the polymer binder or incorporated into the chain of the polymer. Suitable charge transport materials are very well known in the art, and any such charge transport material may be used herein without limitation.
For example, a preferred charge transport molecule comprises an aromatic amine compound of one or more compounds having the general formula:
wherein R1 and R2 are an aromatic group selected from the group consisting of a substituted or unsubstituted phenyl group, naphthyl group, and polyphenyl group and R3 is selected from the group consisting of a substituted or unsubstituted aryl group, alkyl group having from 1 to 18 carbon atoms and cycloaliphatic compounds having from 3 to 18 carbon atoms. The substituents should be free form electron withdrawing groups such as NO2 groups, CN groups and the like.
Examples of charge transporting aromatic amines represented by the structural formulae above for charge transport layers capable of supporting the injection of photogenerated holes of a charge generating layer and transporting the holes through the large transport layer include, for example, triphenylmethane, bis(4-diethylamine-2-4xe2x80x2-4xe2x80x3-bis(diethylamino)-2xe2x80x2,2xe2x80x3-dimethyltriphenylmethane, N,Nxe2x80x2-bi{1,1xe2x80x2-biphenyl}-4,4xe2x80x2-diamine wherein the alkyl is, for example, methyl, ethyl, propyl, n-butyl, etc., N,Nxe2x80x2-diphenyl-N,Nxe2x80x2-bis(chlorophenyl)-{1,1xe2x80x2-biphenyl}-4,4xe2x80x2-diamine, N,Nxe2x80x2-di(1,1xe2x80x2-biphenyl)-4,4xe2x80x2-diamine, and the like dispersed in an inactive resin binder.
More preferably, the charge transport layer comprises an arylamine small molecule dissolved or molecularly dispersed in the binder. Typical aromatic amine compounds include triphenyl amines, bis and poly triarylamines, bis arylamine ethers, bis alkyl-arylamines and the like. Most preferably, the charge transporting material is the aromatic amine TPD, which has the following formula:
An especially preferred charge transport layer employed herein comprises from about 20 to about 80 percent by weight of at least one charge transport material and about 80 to about 20 percent by weight of the polymer binder. The dried charge transport layer preferably will contain between about 30 percent and about 70 percent by weight of a small molecule charge transport molecule based on the total weight of the dried charge transport layer.
The charge transport layer material may also include additional additives used for their known conventional functions as recognized by practitioners in the art. Such additives may include, for example, antioxidants, leveling agents, surfactants, wear resistant additives such as polytetrafluoroethylene (PTFE) particles, light shock resisting or reducing agents, and the like.
The solvent system is a further aspect of the present charge transport layer material. As noted above, conventional polycarbonate binder resins for charge transport layers have required the use of methylene chloride as a solvent in order to form a coating solution, for example that renders the coating suitable for application via dip coating. However, methylene chloride has environmental concerns that require this solvent to have special handling and results in the need for more expensive coating and clean-up procedures. The copolymer polycarbonate of the present invention, however, can be dissolved in a solvent system that is more environmentally friendly than methylene chloride, thereby enabling the charge transport layer to be formed less expensively than with conventional polycarbonate binder resins. A most preferred solvent system for use with the charge transport layer material of the present invention is tetrahydrofuran (THF). Other solvents may also be present, if desired, such as toluene and the like.
Of course, as the copolymer polycarbonate resin of the invention is also soluble in methylene chloride, this solvent may also be used with the copolymer polycarbonate if desired. As such, it is not required that the charge transport layer of the invention be formed from a solution containing tetrahydrofuran.
The total solid to total solvents of the coating material may preferably be around about 10:90 wt % to about 30:70 wt %, more preferably between about 5:85 wt % to about 25:75 wt %.
To form the charge transport layer material of the present invention, the components of the composition of the material are added to a vessel, for example a vessel equipped with a stirrer. The components may be added to the vessel in any order without restriction, although the solvent system is most preferably added to the vessel first. The transport molecule and copolymer polycarbonate binder polymer may be dissolved together, although each is most preferably dissolved separately and then combined with the solution in the vessel.
Once all of the components of the charge transport layer material have been added to the vessel, the solution may be mixed to form a uniform coating composition. The mixing may be done under high shear conditions, for example stirring at a rate exceeding at least about 1,000 rpm.
The charge transport layer solution is applied to the photoreceptor structure (which is detailed below). More in particular, the layer is formed upon a previously formed layer of the photoreceptor structure. Most preferably, the charge transport layer may be formed upon a charge generating layer. Any suitable and conventional technique may be utilized to apply the charge transport layer coating solution to the photoreceptor structure. Typical application techniques include, for example, spraying, dip coating, extrusion coating, roll coating, wire wound rod coating, draw bar coating and the like.
The dried charge transport layer preferably has a thickness of between, for example, about 10 micrometers and about 50 micrometers. In general, the ratio of the thickness of the charge transport layer to the charge generating layer is preferably maintained from about 2:1 to about 200:1, and in some instances as great as about 400:1. The charge transport layer of the invention possesses excellent wear resistance.
The other layers of the photoreceptor will next be explained. It should be emphasized that it is contemplated that the invention covers any photoreceptor structure, regardless of additional layers present and regardless of the ordering of the layers within the structure, so long as the charge transport layer includes the copolymer polycarbonate of the invention as described above.
Any suitable multilayer photoreceptors may be employed in the imaging member of this invention. The charge generating layer and charge transport layer as well as the other layers may be applied in any suitable order to produce either positive or negative charging photoreceptors. For example, the charge generating layer may be applied prior to the charge transport layer, as illustrated in U.S. Pat. No. 4,265,990, or the charge transport layer may be applied prior to the charge generating layer, as illustrated in U.S. Pat. No. 4,346,158, the entire disclosures of these patents being incorporated herein by reference. Most preferably, however, the charge transport layer is employed upon a charge generating layer, and the charge transport layer may optionally be overcoated with an overcoat and/or protective layer.
A photoreceptor of the invention employing the charge transport layer may comprise an optional anti-curl layer, a substrate, an optional hole blocking layer, an optional adhesive layer, a charge generating layer, the charge transport layer, and one or more optional overcoat and/or protective layer(s).
The photoreceptor substrate may comprise any suitable organic or inorganic material known in the art. The substrate can be formulated entirely of an electrically conductive material, or it can be an insulating material having an electrically conductive surface. The substrate is of an effective thickness, generally up to about 100 mils, and preferably from about 1 to about 50 mils, although the thickness can be outside of this range. The thickness of the substrate layer depends on many factors, including economic and mechanical considerations. Thus, this layer may be of substantial thickness, for example over 100 mils, or of minimal thickness provided that there are no adverse effects on the system. Similarly, the substrate can be either rigid or flexible. In a particularly preferred embodiment, the thickness of this layer is from about 3 mils to about 10 mils. For flexible belt imaging members, preferred substrate thicknesses are from about 65 to about 150 microns, and more preferably from about 75 to about 100 microns for optimum flexibility and minimum stretch when cycled around small diameter rollers of, for example, 19 millimeter diameter.
The substrate can be opaque or substantially transparent and can comprise numerous suitable materials having the desired 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. Typical 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, 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. The conductive layer can vary in thickness over substantially wide ranges depending on the desired use of the electrophotoconductive member. Generally, the conductive layer ranges in thickness from about 50 Angstroms to many centimeters, although the thickness can be outside of this range. When a flexible electrophotographic imaging member is desired, the thickness of the conductive layer typically is from about 20 Angstroms to about 750 Angstroms, and preferably from about 100 to about 200 Angstroms for an optimum combination of electrical conductivity, flexibility, and light transmission. When the selected substrate comprises a nonconductive base and an electrically conductive layer coated thereon, the substrate can be of any other conventional material, including organic and inorganic materials. Typical substrate materials include insulating non-conducting materials such as various resins known for this purpose including polycarbonates, polyamides, polyurethanes, paper, glass, plastic, polyesters such as MYLAR or MELINEX 442 (available from Du Pont) and the like. The conductive layer can be coated onto the base layer by any suitable coating technique, such as vacuum deposition or the like. If desired, the substrate can comprise a metallized plastic, such as titanized or aluminized MYLAR, wherein the metallized surface is in contact with the photogenerating layer or any other layer situated between the substrate and the photogenerating layer. The coated or uncoated substrate can be flexible or rigid, and can have any number of configurations, such as a plate, a cylindrical drum, a scroll, an endless flexible belt, or the like. The outer surface of the substrate may comprise a metal oxide such as aluminum oxide, nickel oxide, titanium oxide, or the like.
Most preferably, the photoreceptor of the invention employing the charge transport layer is in the form of a belt or a drum. If a drum, the drum is most preferably in the form of a small diameter drum of the type used in copiers and printers.
A hole blocking layer may then optionally be applied to the substrate. Generally, electron blocking layers for positively charged photoreceptors allow the photogenerated holes in the charge generating layer at the top of the photoreceptor to migrate toward the charge (hole) transport layer below and reach the bottom conductive layer during the electrophotographic imaging processes. Thus, an electron blocking layer is normally not expected to block holes in positively charged photoreceptors such as photoreceptors coated with a charge generating layer over a charge (hole) transport layer. For negatively charged photoreceptors, any suitable hole blocking layer capable of forming an electronic barrier to holes between the adjacent photoconductive layer and the underlying zirconium or titanium layer may be utilized. A hole blocking layer may comprise any suitable material. Typical hole blocking layers utilized for the negatively charged photoreceptors may include, for example, polyamides such as Luckamide (a nylon-6 type material derived from methoxymethyl-substituted polyamide), hydroxy alkyl methacrylates, nylons, gelatin, hydroxyl alkyl cellulose, organopolyphosphazenes, organosilanes, organotitanates, organozirconates, silicon oxides, zirconium oxides, and the like. Preferably, the hole blocking layer comprises nitrogen containing siloxanes. Typical nitrogen containing siloxanes are prepared from coating solutions containing a hydrolyzed silane. Typical hydrolyzable silanes include 3-aminopropyl triethoxy silane, (N,Nxe2x80x2-dimethyl 3-amino) propyl triethoxysilane, N,N-dimethylamino phenyl triethoxy silane, N-phenyl aminopropyl trimethoxy silane, trimethoxy silylpropyldiethylene triamine and mixtures thereof.
During hydrolysis of the amino silanes described above, the alkoxy groups are replaced with hydroxyl group. An especially preferred blocking layer comprises a reaction product between a hydrolyzed silane and the zirconium and/or titanium oxide layer which inherently forms on the surface of the metal layer when exposed to air after deposition. This combination reduces spots and provides electrical stability at low RH. The imaging member is prepared by depositing on the zirconium and/or titanium oxide layer of a coating of an aqueous solution of the hydrolyzed silane at a pH between about 4 and about 10, drying the reaction product layer to form a siloxane film and applying electrically operative layers, such as a photogenerator layer and a hole transport layer, to the siloxane film.
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 layers are preferably 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. This siloxane coating is described in U.S. Pat. No. 4,464,450, the disclosure thereof being incorporated herein in its entirety. After drying, the siloxane reaction product film formed from the hydrolyzed silane contains larger molecules. The reaction product of the hydrolyzed silane may be linear, partially crosslinked, a dimer, a trimer, and the like.
The siloxane 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 blocking layer of between about 0.005 micrometer and about 0.3 micrometer (50 Angstroms to 3,000 Angstroms) is preferred 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 preferred for zirconium and/or titanium oxide layers for optimum electrical behavior and reduced charge deficient spot occurrence and growth.
An adhesive layer may optionally be applied to the hole blocking layer. The adhesive layer may comprise any suitable film forming polymer. Typical adhesive layer materials include, for example, copolyester resins, polyarylates, polyurethanes, blends of resins, and like.
A preferred copolyester resin is a linear saturated copolyester reaction product of four diacids and ethylene glycol. The molecular structure of this linear saturated copolyester in which the mole ratio of diacid to ethylene glycol in the copolyester is 1:1. The diacids are terephthalic acid, isophthalic acid, adipic acid and azelaic acid. The mole ratio of terephthalic acid to isophthalic acid to adipic acid to azelaic acid is 4:4:1:1. A representative linear saturated copolyester adhesion promoter of this structure is commercially available as 49,000 (available from Rohm and Haas Inc., previously available from Morton International Inc.). The 49,000 is a linear saturated copolyester which consists of alternating monomer units of ethylene glycol and four randomly sequenced diacids in the above indicated ratio and has a weight average molecular weight of about 70,000. This linear saturated copolyester has a Tg of about 32xc2x0 C. Another preferred representative polyester resin is a copolyester resin derived from a diacid selected from the group consisting of terephthalic acid, isophthalic acid, and mixtures thereof and diol selected from the group consisting of ethylene glycol, 2,2-dimethyl propanediol and mixtures thereof; the ratio of diacid to diol being 1:1, where the Tg of the copolyester resin is between about 50xc2x0 C. and about 80xc2x0 C. Typical polyester resins are commercially available and include, for example, VITEL PE-100, VITEL PE-200, VITEL PE-200D, and VITEL PE-222, VITEL 1750B all available from Bostik, Inc. More specifically, VITEL PE-100 polyester resin is a linear saturated copolyester of two diacids and ethylene glycol where the ratio of diacid to ethylene glycol in this copolyester is 1:1. The diacids are terephthalic acid and isophthalic acid. The ratio of terephthalic acid to isophthalic acid is 3:2. The VITEL PE-100 linear saturated copolyester consists of alternating monomer units of ethylene glycol and two randomly sequenced diacids in the above indicated ratio and has a weight average molecular weight of about 50,000 and a Tg of about 71xc2x0 C.
Another polyester resin is VITEL PE-200 available from Bostik, Inc. This polyester resin is a linear saturated copolyester of two diacids and two diols where the ratio of diacid to diol in the copolyester is 1:1. The diacids are terephthalic acid and isophthalic acid. The ratio of terephthalic acid to isophthalic acid is 1.2:1. The two diols are ethylene glycol and 2,2-dimethyl propane diol. The ratio of ethylene glycol to dimethyl propane diol is 1.33:1. The VITEL PE-200 linear saturated copolyester consists of randomly alternating monomer units of the two diacids and the two diols in the above indicated ratio and has a weight average molecular weight of about 45,000 and a Tg of about 67xc2x0 C.
The diacids from which the polyester resins of this invention are derived are terephthalic acid, isophthalic acid, adipic acid and/or azelaic acid acids only. Any suitable diol may be used to synthesize the polyester resins employed in the adhesive layer of this invention. Typical diols include, for example, ethylene glycol, 2,2-dimethyl propane diol, butane diol, pentane diol, hexane diol, and the like.
Alternatively, the adhesive interface layer may comprise polyarylate (ARDEL D-100, available from Amoco Performance Products, Inc.), polyurethane or a polymer blend of these polymers with a carbazole polymer. Adhesive layers are well known and described, for example in U.S. Pat. Nos. 5,571,649, 5,591,554, 5,576,130, 5,571,648, 5,571,647 and 5,643,702, the entire disclosures of these patents being incorporated herein by reference.
Any suitable solvent may be used to form an adhesive layer coating solution. Typical solvents include tetrahydrofuran, toluene, hexane, cyclohexane, cyclohexanone, methylene chloride, 1,1,2-trichloroethane, monochlorobenzene, and the like, and mixtures thereof. Any suitable technique may be utilized to apply the adhesive layer coating. Typical coating techniques include extrusion coating, gravure coating, spray coating, wire wound bar coating, and the like. The adhesive layer is applied directly to the charge blocking layer. Thus, the adhesive layer of this invention is in direct contiguous contact with both the underlying charge blocking layer and the overlying charge generating layer to enhance adhesion bonding and to effect ground plane hole injection suppression. Drying of the deposited coating may be effected by any suitable conventional process such as oven drying, infra red radiation drying, air drying and the like. The adhesive layer should be continuous. Satisfactory results are achieved when the adhesive layer has a thickness between about 0.01 micrometer and about 2 micrometers after drying. Preferably, the dried thickness is between about 0.03 micrometer and about 1 micrometer. At thickness of less than about 0.01 micrometer, the adhesion between the charge generating layer and the blocking layer is poor and delamination can occur when the photoreceptor belt is transported over small diameter supports such as rollers and curved skid plates. When the thickness of the adhesive layer of this invention is greater than about 2 micrometers, excessive residual charge buildup is observed during extended cycling.
The photogenerating layer may comprise single or multiple layers comprising inorganic or organic compositions and the like. One example of a generator layer is described in U.S. Pat. No. 3,121,006, the disclosure of which is totally incorporated herein by reference, wherein finely divided particles of a photoconductive inorganic compound are dispersed in an electrically insulating organic resin binder. Multiphotogenerating layer compositions may be utilized where a photoconductive layer enhances or reduces the properties of the photogenerating layer.
The charge generating layer of the photoreceptor may comprise any suitable photoconductive particle dispersed in a film forming binder. Typical photoconductive particles include, for example, phthalocyanines such as metal free phthalocyanine, copper phthalocyanine, titanyl phthalocyanine, hydroxygallium phthalocyanine, vanadyl phthalocyanine and the like, perylenes such as benzimidazole perylene, trigonal selenium, quinacridones, substituted 2,4-diamino-triazines, polynuclear aromatic quinones, and the like. Especially preferred photoconductive particles include hydroxygallium phthalocyanine, chlorogallium phthalocyanine, benzimidazole perylene and trigonal selenium.
Examples of suitable binders for the photoconductive materials include thermoplastic and thermosetting resins such as polycarbonates, polyesters, including polyethylene terephthalate, polyurethanes, polystyrenes, polybutadienes, polysulfones, polyarylethers, polyarylsulfones, polyethersulfones, polycarbonates, polyethylenes, polypropylenes, polymethylpentenes, polyphenylene sulfides, polyvinyl acetates, polyvinylbutyrals, polysiloxanes, polyacrylates, polyvinyl acetals, polyamides, polyimides, amino resins, phenylene oxide resins, terephthalic acid resins, phenoxy resins, epoxy resins, phenolic resins, polystyrene and acrylonitrile copolymers, polyvinylchlorides, polyvinyl alcohols, poly-N-vinylpyrrolidinone)s, vinylchloride and vinyl acetate copolymers, acrylate copolymers, alkyd resins, cellulosic film formers, poly(amideimide), styrene-butadiene copolymers, vinylidenechloride-vinylchloride copolymers, vinylacetate-vinylidenechloride copolymers, styrene-alkyd resins, polyvinylcarbazoles, and the like. These polymers may be block, random or alternating copolymers.
When the photogenerating material is present in a binder material, the photogenerating composition or pigment may be present in the film forming polymer binder compositions in any suitable or desired amounts. For example, from about 10 percent by volume to about 60 percent by volume of the photogenerating pigment may be dispersed in about 40 percent by volume to about 90 percent by volume of the film forming polymer binder composition, and preferably from about 20 percent by volume to about 30 percent by volume of the photogenerating pigment may be dispersed in about 70 percent by volume to about 80 percent by volume of the film forming polymer binder composition. Typically, the photoconductive material is present in the photogenerating layer in an amount of from about 5 to about 80 percent by weight, and preferably from about 25 to about 75 percent by weight, and the binder is present in an amount of from about 20 to about 95 percent by weight, and preferably from about 25 to about 75 percent by weight, although the relative amounts can be outside these ranges.
The particle size of the photoconductive compositions and/or pigments preferably is less than the thickness of the deposited solidified layer, and more preferably is between about 0.01 micron and about 0.5 micron to facilitate better coating uniformity.
The photogenerating layer containing photoconductive compositions and the resinous binder material generally ranges in thickness from about 0.05 micron to about 10 microns or more, preferably being from about 0.1 micron to about 5 microns, and more preferably having a thickness of from about 0.3 micron to about 3 microns, although the thickness can be outside these ranges. The photogenerating layer thickness is related to the relative amounts of photogenerating compound and binder, with the photogenerating material often being present in amounts of from about 5 to about 100 percent by weight. Higher binder content compositions generally require thicker layers for photogeneration. Generally, it is desirable to provide this layer in a thickness sufficient to absorb about 90 percent or more of the incident radiation which is directed upon it in the imagewise or printing exposure step. The maximum thickness of this layer is dependent primarily upon factors such as mechanical considerations, the specific photogenerating compound selected, the thicknesses of the other layers, and whether a flexible photoconductive imaging member is desired.
The photogenerating layer can be applied to underlying layers by any desired or suitable method. Any suitable technique may be utilized to mix and thereafter apply the photogenerating layer coating mixture. 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 technique, such as oven drying, infra red radiation drying, air drying and the like.
Any suitable solvent may be utilized to dissolve the film forming binder. Typical solvents include, for example, tetrahydrofuran, toluene, methylene chloride, monochlorobenzene and the like. Coating dispersions for charge generating layer may be formed by any suitable technique using, for example, attritors, ball mills, Dynomills, paint shakers, homogenizers, microfluidizers, and the like.
Optionally, an overcoat layer and/or a protective layer can also be utilized to improve resistance of the photoreceptor to abrasion. In some cases, an anticurl back coating may be applied to the surface of the substrate opposite to that bearing the photoconductive layer to provide flatness and/or abrasion resistance where a web configuration photoreceptor is fabricated. These overcoating and anticurl back coating layers are well known in the art, and can comprise thermoplastic organic polymers or inorganic polymers that are electrically insulating or slightly semiconductive. Overcoatings are continuous and typically have a thickness of less than about 10 microns, although the thickness can be outside this range. The thickness of anticurl backing layers generally is sufficient to balance substantially the total forces of the layer or layers on the opposite side of the substrate layer. An example of an anticurl backing layer is described in U.S. Pat. No. 4,654,284, the disclosure of which is totally incorporated herein by reference. A thickness of from about 70 to about 160 microns is a typical range for flexible photoreceptors, although the thickness can be outside this range. An overcoat can have a thickness of at most 3 microns for insulating matrices and at most 6 microns for semi-conductive matrices. The use of such an overcoat can still further increase the wear life of the photoreceptor, the overcoat having a wear rate of 2 to 4 microns per 100 kilocycles, or wear lives of between 150 and 300 kilocycles.
The photoreceptor of the invention is utilized in an electrophotographic image forming device for use in an electrophotographic imaging process. As explained above, such image formation involves first uniformly electrostatically charging the photoreceptor, then exposing the charged photoreceptor to a pattern of activating electromagnetic radiation such as light, which selectively dissipates the charge in the illuminated areas of the photoreceptor while leaving behind an electrostatic latent image in the non-illuminated areas. This electrostatic latent image may then be developed at one or more developing stations to form a visible image by depositing finely divided electroscopic toner particles, for example from a developer composition, on the surface of the photoreceptor. The resulting visible toner image can be transferred to a suitable receiving member such as paper. The photoreceptor is then typically cleaned at a cleaning station prior to being re-charged for formation of subsequent images.
The photoreceptor of the present invention may be charged using any conventional charging apparatus. Such may include, for example, an AC bias charging roll (BCR) as known in the art. See, for example, U.S. Pat. No. 5,613,173, incorporated herein by reference in its entirety. Charging may also be effected by other well known methods in the art if desired, for example utilizing a corotron, dicorotron, scorotron, pin charging device, and the like.
The novel copolymer polycarbonate resin binder of the charge transport layer of the present invention achieves formation of a charge transport layer that performs at least as well as conventional polycarbonate binder resins in terms of adhesion, wear resistance and electrical performance of the charge transport layer, while offering the additional advantage of being soluble in environmentally friendly solvents such as tetrahydrofuran.
The invention will now be further described by the following examples and comparative examples, which are intended to further illustrate the invention but not necessarily limit the invention. All parts and percentages are by weight unless otherwise indicated.

Photoreceptor charge transport layer with a polycarbonate binder


A vehicle seat having a seat surface and a seatback is tiltable about a transversely extending pivot axis. The seatback is arranged to be tiltable from an upright seat position into a tilted resting position. In order to achieve a comfortable setting of the headrest in all seat positions and resting positions, the seatback has an automatically driven height adjustment apparatus and an automatically driven tilt adjustment apparatus, each positioned within the seatback.

The present application claims priority to Application No. 102 09 189.7, filed in the Federal Republic of Germany on Mar. 4, 2002, which is expressly incorporated herein in its entirety by reference thereto.
The present invention relates a vehicle seat.
German Published Patent Application No. 196 44 021 describes a vertically adjustable headrest for a vehicle seat. The headrest has a cushion carrier that engages from above into the back of the vehicle seat and is adjustable vertically by an electric linear drive. It is disadvantageous here that the adjustment capability of the headrest is not sufficient to achieve comfortable support of the head in all seat positions.
German Published Patent Application No. 31 16 208 describes a surgical chair having a headrest, the position of which is manually adjustable. The operation of this adjustment apparatus is very complex. Adjustment of the headrest can be performed only with difficulty by the seat occupant alone.
German Published Patent Application No. 100 22 441 describes a seatback for a vehicle seat having a so-called active headrest. The headrest height can be set manually. By a two-armed lever positioned in the seatback, in the event of a rear-end crash the headrest is accelerated toward the occupant""s head because the seat occupant""s body presses on the lever. This headrest as well is insufficiently adjustable, so that comfortable head support is not ensured.
It is an object of the present invention to provide a vehicle seat, having an adjustable seatback, which has a headrest that may ensure comfortable and secure head support in every possible seat position, may have a compact configuration, and may be as easy as possible to operate.
The above and other beneficial objects of the present invention may be achieved by providing a vehicle seat as described herein.
In an example embodiment, the vehicle seat has a height adjustment apparatus and a tilt adjustment apparatus. By the height adjustment apparatus, the height of the headrest is set in preselectable fashion so that good head support may be ensured for short and tall persons. In addition, the vehicle seat has a tilt adjustment apparatus that sets and/or modifies the tilt of the headrest and/or the spacing of the headrest from the seat occupant. The tilt adjustment apparatus is automatically driven and may be controlled such that the headrest may be moved into a freely preselectable position. To ensure a maximally compact and, in particular, robust arrangement of the tilt adjustment apparatus, the latter may be positioned in integrated fashion in the seatback. The tilt adjustment apparatus is joined to a cushion carrier of the headrest and acts on the latter to pivot the headrest about a pivot axis located in the seatback and extending transversely, so that the tilt adjustment apparatus modifies and/or adapts the spacing of the headrest from the seat occupant.
The placement of the pivot axis in the seatback may be selected so that upon adjustment of the headrest tilt, no vertical motion relative to the head may occur. The pivot axis may be positioned in a region corresponding approximately to the rotation point of head when sitting up into the reading position. Optimum adjustment of the headrest may thereby be achieved. Especially in the case of a vehicle seat having a pivotable backrest that may be pivoted between an upright seat position and a tilted reclining position, it is possible to ensure an optimum and/or comfortable setting of the headrest for all possible seat positions. With the seatback pivoted back, it is possible for the seat occupant to assume a resting position and for the headrest also to pivot back correspondingly. It is also possible, with the seatback pivoted back, to assume a relaxed reading position by swinging the headrest farther forward. Comfortable head support may therefore be guaranteed in every seat position, and the seat occupant may relax his or her neck muscles.
For convenient operation, provision may be made for the height adjustment device and/or tilt adjustment device to have a drive motor, e.g., an electric or pneumatic drive motor, etc. A preselected position may be easily arrived at, and/or a pleasant seating position for the seat occupant may be established, by activating the tilt adjustment device and/or height adjustment device, for example, by pressing a button.
An example embodiment provides for the height adjustment device to have a slide that may be moved up and down by a drive motor in the seatback. The slide may be arranged to retain the headrest cushion carrier by having a receptacle into which the cushion carrier of the headrest may be inserted, e.g., may be snap-locked, from above. The height of the headrest is thus varied as the slide moves up and/or down.
An example embodiment provides for the height adjustment apparatus to be mounted on the tilt adjustment apparatus, e.g., for the height adjustment apparatus to be joined by the tilt adjustment apparatus to a part of the seatback frame or to the seatback frame itself. In order to modify the tilt and/or the position of the headrest, the tilt adjustment apparatus pivots the height adjustment apparatus about a pivot axis. Since the headrest and the cushion are mounted on the height adjustment apparatus, the tilt adjustment apparatus acts indirectly, via the height adjustment apparatus, on the headrest in order to adjust the tilt and/or position.
The placement of the tilt adjustment apparatus and the height adjustment apparatus in the seatback may provide that the headrest may be adjusted with very little noise. In addition, the tilt adjustment apparatus and/or the height adjustment apparatus may have low-noise drives, e.g., an electric geared motor or spindle drive, etc., in each case, in order to ensure low-noise adjustment of the headrest.
It may be possible to use the vehicle seat according to the present invention in passenger cars, in buses, and in watercraft or rail vehicles, etc. Use of the vehicle seat according to the present invention as a comfortable passenger seat in aircraft is also provided.
Further features and example embodiments of the present invention are described below with reference to the Figures. The features and feature combinations described above and described below are usable not only in the particular combination indicated but also in other combinations or in isolation, without departing from the scope of the present invention.
Further example embodiments of the present invention are illustrated in and explained with reference to the Figures.

Vehicle seat having an adjustable-tilt headrest


A method for minimizing feedback responses in an ARQ protocol is disclosed, whereby different mechanisms can be used to indicate erroneous D-PDUs and construct S-PDUs. The S-PDUs are constructed so as to optimize performance in accordance with certain criteria. One such criterion used is to minimize the size of the S-PDUs. A second such criterion used is to maximize the number of SNs included in an S-PDU of limited size.

1. Technical Field of the Invention
The present invention relates in general to the telecommunications field and, in particular, to a method for minimizing feedback responses in Automatic Repeat Request (ARQ) protocols, such as, for example, selective-repeat ARQ protocols.
2. Description of Related Art
When data is conveyed between nodes in a telecommunication network, certain algorithms are used to recover from the transmission of erroneous data and the loss of data on the transmission links between the nodes. An algorithm commonly used to recover from the transmission of erroneous data is referred to as an ARQ protocol.
The existing ARQ protocols (i.e., algorithms) include two peer entities that communicate with each other over transmission links. Each such entity includes a receiver and a sender. The units of data conveyed between the peer entities are commonly referred to as Protocol Data Units (PDUs). The ARQ protocols include certain rules for sending and receiving PDUs, as well as rules for the structure of the PDUs. As such, the name xe2x80x9cAutomatic Repeat Requestxe2x80x9d indicates the basic function of the protocol: the receiver requests the sender to retransmit those PDUs that were lost or contained errors during transmission.
The receiver can inform the sender about which PDUs were correctly received (i.e., receiver acknowledges correctly-received PDUs) and/or which PDUs were incorrectly received. When the sender receives this information, it retransmits the xe2x80x9clostxe2x80x9d PDUs. In other words, an ARQ protocol is a set of rules that allow the use of efficient retransmission mechanisms between a sending side and receiving side in a communication system. These rules specify, for example, how and in what form the PDUs are to be constructed so that the receiving side can interpret the conveyed PDUs correctly and respond to them accordingly.
Three main types of information elements (PDUs) can be transferred between two ARQ peer entities: user data; error recovery control data; and common control data. These three types of PDUs can be found in all of the existing ARQ protocols. A user data PDU contains at least user data and a sequence number. An error recovery control data PDU contains various control information needed for error recovery and control functions such as positive and negative acknowledgments. A common control data PDU contains common control data.
In the known High Level Data Link Control (HDLC) protocol, which forms the basis for many existing ARQ protocols, the three types of PDUs are called, respectively, information frames (I-frames), supervisory frames (S-frames), and unnumbered frames (U-frames). Examples of HDLC-derived ARQ protocols are the Radio Link Protocol (RLP) used in the Global System for Mobile Communications (GSM), the Radio Link Control (RLC) and Logical Link Control (LLC) protocols used in the General Packet Radio Service (GPRS), the Infrared Link Access Protocol (IrLAP) used in IrDA systems, and the LAP-B protocol used in X.25 systems. Notably, PDUs that include user data and at least a sequence number are denoted herein as Data-PDUs (D-PDUs), and PDUs that include control data needed for error control/recovery are denoted herein as Status-PDUs (S-PDUs).
In most communication systems, user data information is conveyed in both directions between the peer entities. A common feature included in an ARQ protocol is the possibility of including error control information in the user data PDUs. This capability is known as xe2x80x9cpiggybackingxe2x80x9d. For example, an acknowledgment is included in all I-frames (i.e., D-PDUs) of HDLC-derived protocols. The acknowledgment informs the peer entity about the sequence number of the last (in-sequence) correctly received PDU.
The most common existing ARQ protocols implement one or more mechanisms to recover from errors on a transmission link, such as a Stop-and-Wait ARQ, Go-back-N ARQ, and Selective-Repeat ARQ. The use of these mechanisms and ARQs in general is well known.
FIG. 1 is a sequence diagram that illustrates the use of ARQ protocols. As shown, two ARQ peer entities 10, 12 are communicating with each other. The arrows in FIG. 1 indicate the transmission of PDUs between the two entities, and the content of each PDU is described directly above the respective arrow. Referring to FIG. 1, a sequence of transmitted D-PDUs and S-PDUs is shown. A D-PDU includes user data, a sequence number (SN), and possibly piggybacked error control information. An S-PDU includes status information but no user information. A sequence number (SN=x) is associated with a D-PDU to identify that specific D-PDU. An acknowledgment (ACK=x) is used to acknowledge any PDU with a SN less than x. A negative acknowledgment (NAK=x) is used to acknowledge that a PDU (with an SN=x) has not been correctly received.
Two types of error control feedback responses are shown in FIG. 1. For one of the feedback responses (e.g., S-PDU, ACK=2) 14, the second ARQ peer entity 12 has acknowledged that it has received the PDUs with the SN=0 and SN=1. For the second type of feedback response (e.g., S-PDU, NAK=3) 16, the second peer entity 12 has indicated that the PDU with the SN=3 was corrupted and should be retransmitted by the first peer entity 10.
As discussed above, the S-PDUs are special PDUs which are transmitted between peer entities. An S-PDU includes information about the SNs of corrupted PDUS. Two main methods are currently used for coding the SNs within S-PDUs. One such method is to use a list of SNs to be retransmitted. The second method is to use a bitmap to represent the SNs to be retransmitted. As such, apart from representing SNs, an S-PDU also includes a format identifier which can be used by a receiver to distinguish between the different PDU formats (i.e., D-PDUs and S-PDUs).
The list method used for coding SNs includes the SNs of the erroneous PDUs in the S-PDU. If the length of the list is not predefined and thereby known, this length information is indicated in the S-PDU. For example, a length field can be included in the S-PDU. FIG. 2 shows such an S-PDU, which can be created by a receiver using a list method for coding SNs.
Referring to FIG. 2, a receiver can create an S-PDU with the contents shown, if the sender has transmitted a sequence of D-PDUs with SNs=0-15, and the PDUs with SNs=3, 5, 6, 7 and 8 have failed (not been correctly received). For example, the first two elements in the list (after the length field) indicate that the D-PDU with SN=3 was erroneous. The third and fourth elements in the list indicate that the D-PDUs with SNs=5-8 were erroneous. The final element is included to acknowledge the remaining PDUs (SNs up to 15).
The size of the S-PDU depends on the number of bits used to represent the PDU format identifier field, the length field and the SN field. As such, the size of an S-PDU can be calculated by the expression:
DU.SIZELIST=size(pdu.format.field)+size(length.field)+no.listelements*size(seq.no.field).xe2x80x83xe2x80x83(1)
For example, this list method is used in the SSCOP protocol, wherein two S-PDU formats exist and are denoted by the term xe2x80x9cSTATxe2x80x9d for a variable list length, and xe2x80x9cUSTATxe2x80x9d for a list with a limited number of elements (e.g., 2 elements).
FIG. 3 shows an S-PDU which can be created by a receiver using a bitmap method for coding SNs. When a bitmap is used to indicate SNs, the receiver creates the S-PDU from the SN of the last in-sequence correctly received D-PDU and a bitmap. This SN is referred to as a Start SN (SSN). Consequently, this S-PDU implicitly acknowledges all D-PDUs received up to the value of the SSN. Each location in the bitmap is used to address a specific S-PDU relative to the SSN. Typically, the size of the bitmap is fixed to the size of the ARQ receiver window and does not have to be explicitly indicated. If the bitmap is not fixed, the length has to be indicated.
The bitmap shown in FIG. 3 shows an S-PDU created from the example described above with respect to FIG. 2, and a window size of 16. As such, each location in the bitmap can have one of the two values, 0 or 1: A xe2x80x9c1xe2x80x9d means that SN=(SSN+bit_position) has been correctly received; and a xe2x80x9c0xe2x80x9d value means that SN=(SSN+bit_position) has not been correctly received. Of course, the meaning of the xe2x80x9c0xe2x80x9d and xe2x80x9c1xe2x80x9d values can be interchanged. The size of an S-PDU when using such a bitmap can be derived from the following expression:
PDU.SIZEBITMAP=size(pdu.format.field)+size(SSN.field)+size(bitmap.field).xe2x80x83xe2x80x83(2)
Both the RLC and LLC protocols in the GPRS system use such an expression and convey bitmaps between peer entities for error control purposes.
A significant problem with existing ARQ protocols is that they are static in construction (e.g., fixed length messages are used). In certain situations, this approach leads to a waste of bandwidth resources, because a great deal of overhead information is transmitted unnecessarily. For example, such situations can occur in systems having a large number of D-PDUs being transmitted between two ARQ peer entities, and these D-PDUs have to be acknowledged and selectively requested for retransmission. For some error control situations, the existing solutions introduce a significant amount of unnecessary overhead. The following example illustrates such a situation.
In the Wideband-Code Division Multiple Access (WCDMA) system currently being standardized for the so-called 3rd Generation Cellular Communication System, one ARQ protocol used is an RLC protocol. The,SN set includes the values 0-4095, which means that each SN is coded with 12 bits. An assumption can be made that for high data rates, a relatively large set of SNs will have to be addressed in some S-PDUs. Also, assume that the status of 100 D-PDUs (SN=1-100) needs to be communicated between the RLC peer entities in an S-PDU.
Table 1 below shows the number of bits needed to code an S-PDU using the list and bitmap methods described above. Different error circumstances are provided to highlight the large difference in the number of bits required for the two methods. Assume that the following element sizes are used: bitmap=128 bits; length=5 bits; and one PDU format identifier=1 bit (for distinguishing between a D-PDU and an S-PDU). As such, the different S-PDU sizes shown in Table 1 are calculated in accordance with Equations (1) and (2) above, respectively.
As illustrated by rows 2-5 in Table 1, both of the existing solutions have problems with efficiently building small S-PDUs for error circumstances shown. The length of the LIST does not depend so much on the number of erroneous D-PDUs, but rather on the distribution of the errors within the window used. This fact becomes evident by comparing rows 1 and 2 in Table 1.
A general statement of the problem to be solved is to determine how to efficiently represent (encode) in a message the status of an arbitrary amount and distribution of n numbers from a set of m numbers. As such, a significant need exists for a method that can be used to minimize the size of S-PDUs in an ARQ protocol Also, a significant need exists for a method that can be used to maximize the number of SNs in an S-PDU with limited size, if it is not possible to fit all potential SNs into a single S-PDU. As described in detail below, the present invention successfully resolves the above-described problems and other related problems.
In accordance with an embodiment of the present invention, a method for minimizing feedback responses in an ARQ protocol is provided, whereby different mechanisms can be used to indicate erroneous D-PDUs and construct S-PDUs. In particular, these different mechanisms can be combined in a single S-PDU. The S-PDUs are constructed so as to optimize system performance in accordance with certain criteria. One such criterion used is to minimize the size of the S-PDUs. A second such criterion used is to maximize the number of SNs included in an S-PDU of limited size.
An important technical advantage of the present invention is that radio interface bandwidth resources can be saved.
Another important technical advantage of the present invention is that protocol overhead can be minimized.
Still another important technical advantage of the present invention is that system capacity can be increased.
Yet another important technical advantage of the present invention is that the number of feedback responses in a selective-repeat ARQ protocol can be minimized.

Method for minimizing feedback responses in ARQ protocols


An inkjet printhead with thermal bend actuators for ejecting ink from the nozzle apertures and drive circuitry for operating each thermal bend actuator in a normal mode wherein drive signals to the actuator ejects ink from the chamber, or a pre-heat mode wherein drive signals to the actuator heats ink in the chamber but does not eject ink from the chamber. The invention uses the drive signal to the bend actuator to generate heat to raise the temperature of the ink in the chamber, but controls the signal so that the actuator will not respond in a manner that will eject ink. After a brief pre-heat cycle, the drive circuitry can switch to normal operating mode and the bend actuators will eject ink for printing. With the ink temperature and viscosity within normal operating range, the print quality is not compromised.

In a portable system utilized for the control of ink flow to an inkjet printhead, it is necessary to ensure that the printhead continues to function and receive an ink supply in the presence of movement of the printhead due to its portability. Examples of portable systems include the recently filed PCT Application Nos. PCT/AU98/00550 and PCT/AU98/00549 filed by the present applicant.
For example, when utilized in a camera system with an internal printer, it is desirable to provide for proper operation and ink flow and the presence of movement of the portable camera system. Further, it is desirable to provide for such a system as cheaply and efficiently as possible. This is particularly the case where the camera is utilized in a portable manner whilst printing.
Most commercially used inks have properties similar to water. Accordingly the viscosity of ink will substantially fluctuate with temperature. When the printer is not in use, the ink in the nozzle chambers will cool to ambient and its viscosity is higher than during printer operation. When the printer first activates after a period of inactivity, the viscous ink is more difficult to eject. Many printers will compensate for this by briefly operating the actuators in an overdrive mode until the printhead is at its normal operating temperature. However, reducing the power consumption of printheads is an overriding consideration because removing the heat generated by the actuators is a fundamental issue for inkjet printing. A low power printhead will have little or no need for a cooling system but has a reduced ability for overdrive. As the power consumption of the printhead is reduced, the operating range of the ejection actuators needs to increase in order to overdrive. Such a broad operating range is difficult and impractical.

Thermal bend actuated inkjet with pre-heat mode


A beam combiner for combining a plurality of light beams onto an optical path, comprising: a first dichroic element having a dichroic coating that is disposed to transmit light of a first wavelength band along the optical path and to reflect light of a second wavelength band onto the optical path, and a second dichroic element having a dichroic coating that is disposed to transmit the light of the first and second wavelength bands along the optical path and to reflect light of a third wavelength band onto the optical path. The beam combiner further includes a phase difference compensation multilayer thin-film stack that provides at least one reflectance edge transition that lies outside any of the first, second, and third wavelength bands and which provides compensation for an accumulated phase difference for polarization states of the transiting in at least one of the first, second, and third wavelength bands.

Electronic projection systems have been developed or commercialized using a wide range of modulation technologies. The various light modulation approaches used include deflection, diffraction, blocking or absorption, scattering, and rotation of polarization states, for example. Imaging devices using Liquid Crystal Devices (LCDs), for example, directly modulate the polarization state of incident light within each color channel in a pixel-by-pixel fashion. Imaging devices that use digital micro-mirror devices, include Digital Light Processor (DLP) devices from Texas Instruments Inc., Dallas, Tex., for example, consisting of micro-mirror arrays that deflect light in a pixel-by-pixel fashion.
Each particular light modulation technology has characteristic strengths and weaknesses. For example, in systems that modulate polarization, contamination can occur between on- and off-states due to inadvertent phase shifting, skew ray or large angle cross-talk, or stress birefringence. In alternate systems that modulate light by deflection or diffraction, angular scattering can cause re-direction of light beams into the imaging path. Often, the characteristic disadvantages of one type of light modulation are not factors with another type.
Polarization effects, however, impact numerous light modulation approaches. Polarization is used, for example, to enable 3D or stereo projection in high-end DLP-based systems. DLP projectors adapted for stereo projection using Real-D (Beverly Hills, Calif.) technology use a polarization rotator to switch between polarization states for right- and left-eye images, as perceived by viewers wearing polarization discriminating glasses. The polarization contrast required for 3D projection in DLP based systems is relatively modest (˜400:1), but ghost images can occur if the contrast is too low. Polarized light sources such as visible light emitting lasers are also being used for image projection systems, with or without 3-D projection. Taken together, the polarization sensitivity of a projector, relative to color or contrast artifacts, even in cases where the light modulation components themselves relatively insensitive to polarization, has increased compared to prior art systems.
Color combiners, and other types of optical components for separating and recombining spectral components and for redirecting and conditioning light within the projection apparatus, typically rely on multilayer thin-film optical coatings. Conventional coating designs provide various types of spectral filters with needed levels of reflectivity or transmission at selected wavelengths. However, conventional multilayer coating designs do not provide a highly uniform response to light having different polarization states. In the case of conventional reflective multilayer coatings, for example, there is higher reflectivity for light whose electric field vector oscillates perpendicularly to the plane of incidence (s-polarization) relative to the reflectivity for p-polarized light whose electric field vector oscillates parallel to the plane of incidence over the entire range of incidence angles. The reflectivity for p-polarized light reaches its minimum at the layer-specific Brewster angle. Consequently, noticeable amplitude splits for s- and p-polarized light can occur, particularly in the region about the Brewster angle. At lesser angles, spanning on-axis light, specular light, full-field light, or skew rays, the light efficiency varies with polarization and angle. As another example, if circularly polarized light falls onto a conventional, obliquely-positioned deflecting mirror formed from thin-film coatings, the p-component of the light is more strongly attenuated than the s-component of the light after the reflection. In a polarization sensitive projector, having a polarization analyzer such as a MacNeille prism or a wire grid polarizer, these light efficiency differences can introduce significant contrast or color shading errors. In nominally polarization-sensitive systems lacking a polarization analyzer, on the other hand, image artifacts from these polarization efficiency differences may go largely unnoticed.
Color combiners or other types of dichroic filters can also introduce phase changes for each polarization (Δφs and Δφp), as well as relative phase differences between the various polarization directions (Δφsp=Δφs−Δφp), meaning that the transiting light experiences differing amounts of rotation according to polarization and angle. As a result, the outgoing polarization state of the light is different from the incoming polarization state. These effects can be compounded in an optical system in which there are multiple reflections for polarized light, so that even slight phase shifts for polarized light on each of a number of surfaces can have an additive effect. Linear polarized light can easily become circularly or elliptically polarized, changing the polarization response as the light then transits downstream optics. For example, with conventional beam combiners, designed for optimal spectral efficiency performance, phase differences Δφsp between s- and p-polarized light often exceed ±20 degrees or more. Phase difference Δφsp as large as ±100 degrees or more can often be measured near edge transitions. By comparison, for polarization maintenance, best performance would be achieved with phase differences Δφsp at or near 0 degrees, or at least within no more than about ±10 degrees, without compromising image quality or brightness while attaining the phase performance.
Where thin-film surfaces handle the p- and s-polarized light differently, the effective contrast of a digital imaging system can be compromised due to light leakage; throughput also suffers accordingly. In systems that use polarized light for left- and right-eye image separation in stereoscopic (3D) imaging, light leakage due to non-uniform handling of polarized light can lead to cross-talk that degrades the stereoscopic viewing effect. Various solutions have been proposed to compensate for known differences in how coatings respond to s- and p-polarized light. In image projection systems, for example, the use of various types of compensating components, such as quarter-wave retarders, has been taught for correcting the de-polarization of thin-film surfaces.
For projection or display systems that depend inherently on polarization manipulation, such as LCD- or LCOS (liquid crystal on silicon)-based systems, the problem is more acute, since undesired polarization differences and consequent light leakage can directly cause image artifacts. LCDs, of course, modulate polarization orientations temporally and spatially, in a pixel-wise fashion, which means that image quality depends on polarization fidelity. Polarization contributes directly to image contrast (>2000:1 for digital cinema), contrast uniformity, and contrast uniformity with color. There are numerous examples of polarization compensators developed to enhance the polarization performance with LCDs, including those designed for vertically aligned or nematic LCDs. These compensators typically use polymer films to provide angular varying birefringence, structured in a spatially variant fashion, to affect polarization states in portions (that is, within certain spatial and angular areas) of the transiting light beam, without affecting the polarization states in other portions of the light beam. Birefringence is a directional variation of refractive index (Δn=ns−np=nx−ny), that can be provided by intrinsic material properties or by form birefringent sub-wavelength structures. Retardance is the phase change Δφ expressed as distance, where the phase change Δφ(x, t, λ)=2πt(Δn/λ). For example a π/2 (or 90°) phase change Δφ can be provided by a properly oriented compensator having a quarter wave λ/4 of retardance, which, at 550 nm, equals ˜138 nm retardance.
As one example, U.S. Pat. No. 4,701,028 to Clerc et al. describes birefringence compensation designed for a vertically aligned LCD with restricted thickness. U.S. Pat. No. 5,298,199 to Hirose et al. describes the use of a biaxial film compensator correcting for optical birefringence errors in the LCD, used in a package with crossed sheet polarizers, where the LCD dark state has a non-zero voltage (a bias voltage). Additionally, U.S. Pat. No. 5,619,352 to Koch et al. describes compensation devices, usable with twisted nematic LCDs, where the compensators have a multi-layer construction, using combinations of A-plates, C-plates, and O-plates, as needed.
Likewise, in such systems, compensators have also been developed to correct for polarization performance variations of other components, such as the polarization beam splitters or analyzers, either individually or in combination with the LCDs. For example, U.S. Pat. No. 5,576,854 to Schmidt et al. describes a compensator constructed for use in projector apparatus using an LCD with the conventional MacNeille prism type polarization beam splitter. The Schmidt compensator provides 0.27 waves (λ's) of compensation, where 0.25λ's compensate for the MacNeille prism and 0.02λ's of retardance (A-plate) compensate for thermally induced stress birefringence in the counter electrode substrate of the LCD.
In some LCD based projector designs, the color combiner or splitter has its coatings positioned between the LCD panels and the polarization beam splitter. This, in turn, means that system polarization performance is dependent on the design and fabrication of these components, A detailed analysis of this problem is given, for example, by A. E. Rosenbluth et al. in "Correction of Contrast in Projection Systems By Means of Phase-Controlled Prism Coatings and Band-Shifted Twist Compensators" (SPIE Proc., Vol. 3954, pp. 63-90, 2000). Rosenbluth et al. describe a conventional projection architecture in which a "Plumbicon" or "Philips" prism is used in a double-pass configuration to provide both color splitting and recombination. The projector described uses twisted nematic LC panels. The "Plumbicon" tri-prism, described in U.S. Pat. No. 3,202,039 by DeLang, was originally developed for splitting light in TV cameras.
Rosenbluth et al. observe that tilted dichroics are usually polarizing, in that they exhibit a differential phase shift (Δφps=Δφp−Δφs), in both reflection and transmission, which causes polarization mixing, or compound angle depolarization, to transiting light beams. In particular, when oblique or skew light traverses color splitting coatings, which tend to be thick, there are generally differences between the effective penetration depths of the s- and p components, giving the coating a differential phase change Δφps between the two polarizations. Rosenbluth et al. observe that tilted dichroic coatings are usually strong amplitude polarizers at the edges of the band, which in turn implies a strong differential phase shift throughout the band, because of the dispersion integrals that link phase shift with intensity performance. Thus, as s- and p-polarizations transit the coatings at compound incidence angles, they experience different amplitude and phase responses. The most significant polarization cross-talk occurs when skew rays pass through the tilted beam-dividing coatings of the optical system.
Rosenbluth et al. seek to suppress depolarization from the coatings of the tri-prism assembly by designing the prism coatings to collectively remove the rotational component of depolarization rather than designing the coatings to be individually non-phase shifting. While the dispersion integrals link the phase performance and the light throughput efficiency, substantial changes in phase can be provided with marginal effect on throughput. The design of Rosenbluth et al., exploits the double pass geometry of the Philips prism. That is, individual coatings are not designed to be non-phase shifting (zero phase difference, Δφps=0), nor are the coatings designed to be collectively phase corrected in single pass, but they are designed to be collectively phase corrected in double pass. The optimization does not emphasize minimizing amplitude de-polarization effects. Rosenbluth et al. basically designed prism coatings so that skew rays experience elliptical polarization without rotation, while the double-pass symmetry of light passing through the prism assembly advantageously cancels the ellipticity. This symmetry and inherent cancellation only holds if the intensity losses in the dichroic coatings are essentially equal for s- and p-polarizations; thus, correction is imperfect near the band edges. Rosenbluth et al. provide examples in which coating depolarization is optimized in combination with the polarization beam splitter (PBS), with or without the benefit of polymeric film compensators that compensate for PBS or light valve depolarization effects.
Aside from Rosenbluth, the phase implications of multilayer thin-film optical coatings are not widely understood by those who specify and design optical thin-film coatings and have been only briefly explored or noted in the literature. However, few if any of the conventional approaches to this problem achieve satisfactory results.
Because de-polarization can degrade the signal-to-noise (S/N) ratio or contrast in telecommunications and other data signal handling optical systems, there have been a number of proposed solutions for compensating for polarization phase shift Δφ where thin-film surfaces are used for narrow-band optical signals. For example, U.S. Pat. No. 4,373,782 to Thelen entitled "Non-Polarizing Thing Film Edge Filter" describes forming an edge filter having the same s- and p-polarization performance on either the rising or falling edge. This provides a polarization-neutral effect for a single, narrow range of frequencies or wavelengths, but does not compensate for polarization effects beyond this narrow range. Similarly, U.S. Pat. No. 5,579,159 entitled "Optical Multilayer Thin Film and Beamsplitter" to Ito describes coatings design approaches that achieve s- and p-polarized light reflectances that are "substantially close to each other over a predetermined wavelength". However, the Ito solution is intended for beam splitter use with a single laser beam in the IR range and this method is also not readily extendible beyond a narrow range of wavelengths.
U.S. Pat. No. 6,014,255 entitled "Polarizing Beam Splitter and Magneto-Optic Reading Device Using the Same" to Van Der Wal et al. describes a magneto-optic reader that is optimized to direct light over a single, narrow IR wavelength, with phase difference Δφ reduced by thickening the top and bottom layers over a multilayer thin film design. Again, this method does not address the larger problem of polarization compensation applicable to color-combining optics.
With the increasing use of lasers and other narrow-band light sources, some of the conventional strategies and approaches to the problem of combining modulated light beams, originally developed for more broadband illumination, prove unsatisfactory. Optical filters designed for imaging applications using arc lamp and other broadband sources are typically designed to optimize spectral efficiency, maximize bandwidth, and reject IR or UV light. These components are simply not designed to provide the needed performance over the narrow wavelength bands typical of lasers and other solid state light sources, and are generally designed without regard for polarization phase response.
Conventional approaches to reducing phase differences that affect how multilayer thin-film optical coatings handle polarization may work well enough with narrow-range optical signals for telecommunications. However, these conventional solutions fall short of what is needed to compensate for phase- and polarization-shifting effects of dichroic surfaces in image projection. Thus, there is need for an improved method for design of multilayer thin-film optical coatings for phase difference compensation to provide coatings that exhibit reduced polarization-specific response.

Phase-compensated thin-film beam combiner


A frame panel apparatus for the ready presentation of flat media therein. The apparatus includes a flexible frame arranged to define a peripheral support for a display. An upper transparent panel having a periphery entirely enclosed by the flexible frame and a lower support panel having a periphery with a only a portion thereof supported by a shoulder member of the flexible frame support a display media therebetween.

1. Field of the Invention
This invention relates to horizontally displayed media presentations, and more particularly to a flat, maintainable, floor mountable, frame arrangement for displaying a readily changeable marketing message.
2. Prior Art
Successful marketing requires the ability to get people""s attention. Media presentations and retail displays are often presented on the items themselves, hung on walls and from ceilings, or from some sort of a vertical stand in close proximity to the item on sale.
An area that has been basically overlooked by the people in the marketing and sales field, is that of floor presentations and displays. A concern of such floor presentation or display, however, is the requirement that such floor display be kept neat and clean, free from the obvious dirt and debris infiltration that would be indigenous to a floor disposed marketing arrangement. One such floor display arrangement may be seen in U.S. Pat. No. 6,022,599 to Rietveld et al. This ""599 patent discloses a display unit, which however, is somewhat cumbersome to utilize and which maintains certain peripheral frame and panel portions open and susceptible to grime because of incomplete peripheral framing or support.
Further prior art is found in the form of a placemat having a clear plastic topmost sheet with a rubber lower layer. A three sided cut adjacent the periphery of the lower rubber layer permits a central flap to open downwardly, to receive an advertisement. The advertisement thus be seen through the top sheet. The lower sheet of rubber material is very flexible and will not support an inexpensive thin poster sheet of paper as an advertisement by itself. This is because this mat lacks a stiff backing-sheet and a protective peripheral frame edge for the back sheet support and for maintenance of cleanliness of the panel. Its display ad itself must be thick and stiff to make up for the flexible backing sheet, the changeable display ad therefore being expensive to produce because of its required thickness.
It is an object of the present invention to provide a floor panel and display arrangement that overcomes the disadvantages of the prior art.
It is a further object of the present invention to provide a floor panel and display arrangement that permits a simple and clean method of changing a paper-thin display poster within that frame arrangement.
It is a still further object of the present invention to provide a method of manufacturing a frame display arrangement, which is simpler and more convenient than the prior art.
The frame panel display apparatus of the present invention comprises a preferably rectangular or square shaped peripheral frame molded of a soft, flexible, resilient material, such as rubber or the like.
The peripheral frame has a first end and a parallel second end. The peripheral frame also has a first side and a second side generally parallel to one another. The peripheral frame has an inner surface which includes a first inner peripheral slot. The first inner peripheral slot extends around the entire inner periphery of the frame. A transparent upper panel is preferably molded into the first peripheral slot during fabrication of the frame. The upper panel is of rectangular or square configuration and has its entire periphery supportively engaged in that first peripheral slot within the frame.
The frame, at its first end, has a shoulder portion, which includes a stepped groove, extending only along its first end, adjacent the inner periphery of the first slot thereat. The shoulder portion of the frame at its first end of the frame has an extended web disposed inwardly of the uppermost lip of the peripheral notch of the frame at the first end.
A lower back or support panel is disposed adjacent and is hingedly supported upon and by the shoulder portion of the frame only at its first end of the lower panel. The lower back support panel is narrower than the upper panel and is shorter than the upper panel so as to be readily arcuately displaceable therefrom, while the upper panel is supported within its peripheral inner groove of the frame.
The bottom back or support panel has a second end that is in close fitting but not engaging contact with the second end of the peripheral frame. The first side and the second side of the peripheral frame are also not in contacting engagement with the respective sides of the lower support panel, to permit that ready arcuate swinging of the lower support panel away from the upper panel, about their common first end thereof.
A plurality of anti-skid support pads are preferably arranged between the lowermost side of the bottom or lower panel so as to provide support to both the lower panel and the upper panel when they are disposed within the peripheral frame. Such support is necessary inasmuch as the frame panel assembly is intended to be placed on a floor or walking surface and actually stepped or walked upon. A further embodiment contemplates the panel assembly in use as a desk or countertop display.
A paper poster or thin display media may be inserted between the upper panel and the lower panel to present to pedestrians a marketing message beneath their feet within a commercial establishment.
In order to change the message, the second end of the peripheral frame may be lifted from the floor (or horizontal desk/counter) surface, while the bottom or lower panel remains in place against the floor. The initial poster or display may be removed and a new display sheet inserted therein. The stiff lower panel remains securely in place within the first end of the frame assembly by virtue of the extended web portion comprising the receiving shoulder at the first end of the frame assembly in which the lower panel is received and secured thereat.
During manufacture of the frame assembly, the upper transparent panel and the lower support panel are juxtaposed together, and placed in a mold so that the first end of the peripheral frame encapsulates the first transverse end of the lower support panel and it encapsulates and seals therewith, the entire periphery of the upper transparent panel therearound. A spacer element may be integral with the mold or placed around the second end and sides of the lower panel in the mold to maintain that slight second end and side gap between the lower panel and the inner edge of the soft frame.
A further embodiment of the present invention contemplates the embedding of magnets within the lower periphery of the peripheral frame during the molding process to permit such a frame display apparatus to be more securely utilized on a metal surface, such as a desk, floor, or wall.
Thus, what has been shown is a novel panel assembly, particularly suited for a floor display presentation wherein the thin inexpensive media presented for display may be readily changed and maintained in a cleaner and more secure frame environment than the prior art. A mop or other wiper and fluid may readily be applied to clean the present frame panel apparatus because of the fully sealed nature of the peripheral frame and the upper panel supported therein, a feature not found in the prior art.
The invention thus comprises a frame panel apparatus for the ready presentation of flat media therein, comprising a flexible frame arranged to define a peripheral support for a display, an upper transparent panel having a periphery entirely enclosed by the flexible frame, and a lower support panel having a periphery with a only a portion thereof supported by a shoulder member of the flexible frame. The frame is of rectilinear configuration. The shoulder member extends across a first end only, of the flexible frame. The upper panel is disposed in a sealing slot on an inner surface of the frame. The lower panel is shorter and narrower than the upper panel to permit ready arcuate separation therebetween. The lower panel is hingedly supported at a first end thereof, to a first end of the frame. The lower panel has a lower surface with an arrangement of support pads thereon, the support pad arrangement providing support for both the lower and the upper panel. The upper panel and the lower panel are in close juxtaposition with respect to one another. The flat media is pressed snugly between the upper panel and the lower panel for visual presentation therefrom, and for cleanliness of appearance.
The invention also includes a method of presenting a visual display as a floor assembly, comprising the steps of: arranging a flexible peripheral frame about the entire periphery of a transparent upper panel; securing a first end of a lower support panel in a first end of the frame, beneath the upper frame; placing support pads on a bottom side of the lower support panel to support both the lower and the upper panel; pivotably lifting up the frame and the upper panel about a first end of the frame; inserting a display media between the upper and lower panels; and lowering the upper panel and frame onto the lower panel to secure the upper and lower panels in a snug sealed display presenting relationship. The method may include the steps of: arranging an extended web on the first end of the frame to support the first end of the lower panel; placing an arrangement of magnets in the frame for improving securement thereof the a metal surface; and wherein the frame is molded from rubber.