Patent Application
20060046172
This invention relates to organophotoreceptors suitable for use in electrophotography and, more specifically, to organophotoreceptors including a polymeric charge transport material having repeating units comprising at least two carbazolyl groups and an aromatic group. This invention also relates to methods of making the polymeric charge transport material.
In electrophotography, an organophotoreceptor in the form of a plate, disk, sheet, belt, drum or the like having an electrically insulating photoconductive element on an electrically conductive substrate is imaged by first uniformly electrostatically charging the surface of the photoconductive layer, and then exposing the charged surface to a pattern of light. The light exposure selectively dissipates the charge in the illuminated areas where light strikes the surface, thereby forming a pattern of charged and uncharged areas, referred to as a latent image. A liquid or solid toner is then provided in the vicinity of the latent image, and toner droplets or particles deposit in the vicinity of either the charged or uncharged areas to create a toned image on the surface of the photoconductive layer. The resulting toned image can be transferred to a suitable ultimate or intermediate receiving surface, such as paper, or the photoconductive layer can operate as an ultimate receptor for the image. The imaging process can be repeated many times to complete a single image, for example, by overlaying images of distinct color components or effect shadow images, such as overlaying images of distinct colors to form a full color final image, and/or to reproduce additional images.
Both single layer and multilayer photoconductive elements have been used. In single layer embodiments, a charge transport material and charge generating material are combined with a polymeric binder and then deposited on the electrically conductive substrate. In multilayer embodiments, the charge transport material and charge generating material are present in the element in separate layers, each of which can optionally be combined with a polymeric binder, deposited on the electrically conductive substrate. Two arrangements are possible for a two-layer photoconductive element. In one two-layer arrangement (the “dual layer” arrangement), the charge-generating layer is deposited on the electrically conductive substrate and the charge transport layer is deposited on top of the charge generating layer. In an alternate two-layer arrangement (the “inverted dual layer” arrangement), the order of the charge transport layer and charge generating layer is reversed.
In both the single and multilayer photoconductive elements, the purpose of the charge generating material is to generate charge carriers (i.e., holes and/or electrons) upon exposure to light. The purpose of the charge transport material is to accept at least one type of these charge carriers and transport them through the charge transport layer in order to facilitate discharge of a surface charge on the photoconductive element. The charge transport material can be a charge transport compound, an electron transport compound, or a combination of both. When a charge transport compound is used, the charge transport compound accepts the hole carriers and transports them through the layer with the charge transport compound. When an electron transport compound is used, the electron transport compound accepts the electron carriers and transports them through the layer with the electron transport compound.
This invention provides organophotoreceptors having good electrostatic properties such as high Vacc and low Vdis.
In a first aspect, an organophotoreceptor comprises an electrically conductive substrate and a photoconductive element on the electrically conductive substrate, the photoconductive element comprising:
(a) a polymeric charge transport material having the formula
where n is a distribution of integers between 1 and 100,000 with an average value of greater than one;
Y comprises an aromatic group;
X is a bond or a linking group such as a —(CH2)n— group, where n is an integer between 1 and 20, inclusive, and one or more of the methylene groups is optionally replaced by O, S, N, C, B, Si, P, C═O, O═S═O, a heterocyclic group, an aromatic group, an NRa group, a CRb group, a CRcRd group, a SiReRf group, a BRg group, or a P(═O)Rh group, where Ra, Rb, Rc, Rd, Re, Rf, Rg, and Rh are, each independently, a bond, H, a hydroxyl group, a thiol group, a carboxyl group, an amino group, a halogen, an alkyl group, an acyl group, an alkoxy group, an alkylsulfanyl group, an alkenyl group, such as a vinyl group, an allyl group, and a 2-phenylethenyl group, an alkynyl group, a heterocyclic group, an aromatic group, or a part of a ring group, such as cycloalkyl groups, heterocyclic groups, and a benzo group; and
(b) a charge generating compound.
The organophotoreceptor may be provided, for example, in the form of a plate, a flexible belt, a flexible disk, a sheet, a rigid drum, or a sheet around a rigid or compliant drum. In one embodiment, the organophotoreceptor includes: (a) a photoconductive element comprising the charge transport material, the charge generating compound, a second charge transport material, and a polymeric binder; and (b) the electrically conductive substrate.
In a second aspect, the invention features an electrophotographic imaging apparatus that comprises (a) a light imaging component; and (b) the above-described organophotoreceptor oriented to receive light from the light imaging component. The apparatus can further comprise a toner dispenser, such as a liquid toner dispenser. The method of electrophotographic imaging with photoreceptors containing the above noted charge transport materials is also described.
In a third aspect, the invention features an electrophotographic imaging process that includes (a) applying an electrical charge to a surface of the above-described organophotoreceptor; (b) imagewise exposing the surface of the organophotoreceptor to radiation to dissipate charge in selected areas and thereby form a pattern of at least relatively charged and uncharged areas on the surface; (c) contacting the surface with a toner, such as a liquid toner that includes a dispersion of colorant particles in an organic liquid, to create a toned image; and (d) transferring the toned image to a substrate.
In a fourth aspect, the invention features a charge transport material having Formula (I) above.
In a fifth aspect, the invention features a method of preparing a polymeric charge transport material comprising the steps of
(a) providing a reaction mixture of a dicarbazolyl compound having the formula:
where X is a bond or a linking group and a dihalo-aromatic compound having the formula of Ha-Y-Ha′ where Y comprises an aromatic group and Ha and Ha′ are, each independently, a halide;
(b) dissolving the reaction mixture in a solvent to form a solution; and
(c) refluxing the solution in the presence of a mixture of copper powder, potassium carbonate, and a crown ether.
In a sixth aspect, the invention features a polymeric charge transport material prepared by reacting a mixture of a dicarbazolyl compound having the formula:
a dihalo-aromatic compound having the formula of Ha-Y-Ha′, copper powder, potassium carbonate, and a crown ether; where X is a bond or a linking group; Y comprises an aromatic group; and Ha and Ha′ are, each independently, a halide.
The invention provides suitable charge transport materials for organophotoreceptors featuring a combination of good mechanical and electrostatic properties. These photoreceptors can be used successfully with toners, such as liquid toners, to produce high quality images. The high quality of the imaging system can be maintained after repeated cycling.
Other features and advantages of the invention will be apparent from the following description of the particular embodiments thereof, and from the claims.
An organophotoreceptor as described herein has an electrically conductive substrate and a photoconductive element including a charge generating compound and a polymeric charge transport material having repeating units comprising at least two carbazolyl groups and an aromatic group. These polymeric charge transport materials have desirable properties as evidenced by their performance in organophotoreceptors for electrophotography. In particular, the polymeric charge transport materials of this invention have high charge carrier mobilities and good compatibility with various binder materials, and possess excellent electrophotographic properties. The organophotoreceptors according to this invention generally have a high photosensitivity, a low residual potential, and a high stability with respect to cycle testing, crystallization, and organophotoreceptor bending and stretching. The organophotoreceptors are particularly useful in laser printers and the like as well as fax machines, photocopiers, scanners and other electronic devices based on electrophotography. The use of these charge transport materials is described in more detail below in the context of laser printer use, although their application in other devices operating by electrophotography can be generalized from the discussion below.
To produce high quality images, particularly after multiple cycles, it is desirable for the charge transport materials to form a homogeneous solution with the polymeric binder and remain approximately homogeneously distributed through the organophotoreceptor material during the cycling of the material. In addition, it is desirable to increase the amount of charge that the charge transport material can accept (indicated by a parameter known as the acceptance voltage or “Vacc”), and to reduce retention of that charge upon discharge (indicated by a parameter known as the discharge voltage or “Vdis”).
Charge transport materials may comprise monomeric molecules (e.g., N-ethyl-carbazole-3-aldehyde N-methyl-N-phenyl-hydrazone), dimeric molecules (e.g., disclosed in U.S. Pat. Nos. 6,140,004, 6,670,085 and 6,749,978), or polymeric molecules (e.g., poly(vinylcarbazole)). The charge transport materials may also be classified as a charge transport compound or an electron transport compound. There are many charge transport compounds and electron transport compounds known in the art for electrophotography. Non-limiting examples of charge transport compounds include, for example, pyrazoline derivatives, fluorene derivatives, oxadiazole derivatives, stilbene derivatives, enamine derivatives, enamine stilbene derivatives, hydrazone derivatives, carbazole hydrazone derivatives, (N,N-disubstituted)arylamines such as triaryl amines, polyvinyl carbazole, polyvinyl pyrene, polyacenaphthylene, and the charge transport compounds described in U.S. Pat. Nos. 6,689,523, 6,670,085, and 6,696,209, and U.S. patent application Ser. Nos. 10/431,135, 10/431,138, 10/699,364, 10/663,278, 10/699,581, 10/449,554, 10/748,496, 10/789,094, 10/644,547, 10/749,174, 10/749,171, 10/749,418, 10/699,039, 10/695,581, 10/692,389, 10/634,164, 10/663,970, 10/749,164, 10/772,068, 10/749,178, 10/758,869, 10/695,044, 10/772,069, 10/789,184, 10/789,077, 10/775,429, 10/775,429, 10/670,483, 10/671,255, 10/663,971, 10/760,039. All the above patents and patent applications are incorporated herein by reference.
Non-limiting examples of electron transport compounds include, for example, bromoaniline, tetracyanoethylene, tetracyanoquinodimethane, 2,4,7-trinitro-9-fluorenone, 2,4,5,7-tetranitro-9-fluorenone, 2,4,5,7-tetranitroxanthone, 2,4,8-trinitrothioxanthone, 2,6,8-trinitro-indeno[1,2-b]thiophene-4-one, and 1,3,7-trinitrodibenzo thiophene-5,5-dioxide, (2,3-diphenyl-1-indenylidene)malononitrile, 4H-thiopyran-1,1-dioxide and its derivatives such as 4-dicyanomethylene-2,6-diphenyl-4H-thiopyran-1,1-dioxide, 4-dicyanomethylene-2,6-di-m-tolyl-4H-thiopyran-1,1-dioxide, and unsymmetrically substituted 2,6-diaryl-4H-thiopyran-1,1-dioxide such as 4H-1,1-dioxo-2-(p-isopropylphenyl)-6-phenyl-4-(dicyanomethylidene)thiopyran and 4H-1,1-dioxo-2-(p-isopropylphenyl)-6-(2-thienyl)-4-(dicyanomethylidene)thiopyran, derivatives of phospha-2,5-cyclohexadiene, alkoxycarbonyl-9-fluorenylidene)malononitrile derivatives such as (4-n-butoxycarbonyl-9-fluorenylidene)malononitrile, (4-phenethoxycarbonyl-9-fluorenylidene)malononitrile, (4-carbitoxy-9-fluorenylidene)malononitrile, and diethyl(4-n-butoxycarbonyl-2,7-dinitro-9-fluorenylidene)malonate, anthraquinodimethane derivatives such as 11,11,12,12-tetracyano-2-alkylanthraquinodimethane and 11,11-dicyano-12,12-bis(ethoxycarbonyl)anthraquinodimethane, anthrone derivatives such as 1-chloro-10-[bis(ethoxycarbonyl)methylene]anthrone, 1,8-dichloro-10-[bis(ethoxy carbonyl) methylene]anthrone, 1,8-dihydroxy-10-[bis(ethoxycarbonyl)methylene]anthrone, and 1-cyano-10-[bis(ethoxycarbonyl)methylene)anthrone, 7-nitro-2-aza-9-fluroenylidene-malononitrile, diphenoquinone derivatives, benzoquinone derivatives, naphtoquinone derivatives, quinine derivatives, tetracyanoethylenecyanoethylene, 2,4,8-trinitro thioxantone, dinitrobenzene derivatives, dinitroanthracene derivatives, dinitroacridine derivatives, nitroanthraquinone derivatives, dinitroanthraquinone derivatives, succinic anhydride, maleic anhydride, dibromo maleic anhydride, pyrene derivatives, carbazole derivatives, hydrazone derivatives, N,N-dialkylaniline derivatives, diphenylamine derivatives, triphenylamine derivatives, triphenylmethane derivatives, tetracyano quinodimethane, 2,4,5,7-tetranitro-9-fluorenone, 2,4,7-trinitro-9-dicyanomethylene fluorenone, 2,4,5,7-tetranitroxanthone derivatives, 2,4,8-trinitrothioxanthone derivatives, 1,4,5,8-naphthalene bis-dicarboximide derivatives as described in U.S. Pat. Nos. 5,232,800, 4,468,444, and 4,442,193 and phenylazoquinolide derivatives as described in U.S. Pat. No. 6,472,514. In some embodiments of interest, the electron transport compound comprises an (alkoxycarbonyl-9-fluorenylidene)malononitrile derivative, such as (4-n-butoxycarbonyl-9-fluorenylidene)malononitrile, and 1,4,5,8-naphthalene bis-dicarboximide derivatives.
Although there are many charge transport materials available, there is a need for other charge transport materials to meet the various requirements of particular electrophotography applications.
In electrophotography applications, a charge-generating compound within an organophotoreceptor absorbs light to form electron-hole pairs. These electrons and holes can be transported over an appropriate time frame under a large electric field to discharge locally a surface charge that is generating the field. The discharge of the field at a particular location results in a surface charge pattern that essentially matches the pattern drawn with the light. This charge pattern then can be used to guide toner deposition. The charge transport materials described herein are especially effective at transporting charge, and in particular holes from the electron-hole pairs formed by the charge generating compound. In some embodiments, a specific electron transport compound or charge transport compound can also be used along with the charge transport material of this invention.
The layer or layers of materials containing the charge generating compound and the charge transport materials are within an organophotoreceptor. To print a two dimensional image using the organophotoreceptor, the organophotoreceptor has a two dimensional surface for forming at least a portion of the image. The imaging process then continues by cycling the organophotoreceptor to complete the formation of the entire image and/or for the processing of subsequent images.
The organophotoreceptor may be provided in the form of a plate, a flexible belt, a disk, a rigid drum, a sheet around a rigid or compliant drum, or the like. The charge transport material can be in the same layer as the charge generating compound and/or in a different layer from the charge generating compound. Additional layers can be used also, as described further below.
In some embodiments, the organophotoreceptor material comprises, for example: (a) a charge transport layer comprising the charge transport material and a polymeric binder; (b) a charge generating layer comprising the charge generating compound and a polymeric binder; and (c) the electrically conductive substrate. The charge transport layer may be intermediate between the charge generating layer and the electrically conductive substrate. Alternatively, the charge generating layer may be intermediate between the charge transport layer and the electrically conductive substrate. In further embodiments, the organophotoreceptor material has a single layer with both a charge transport material and a charge generating compound within a polymeric binder.
The organophotoreceptors can be incorporated into an electrophotographic imaging apparatus, such as laser printers. In these devices, an image is formed from physical embodiments and converted to a light image that is scanned onto the organophotoreceptor to form a surface latent image. The surface latent image can be used to attract toner onto the surface of the organophotoreceptor, in which the toner image is the same or the negative of the light image projected onto the organophotoreceptor. The toner can be a liquid toner or a dry toner. The toner is subsequently transferred, from the surface of the organophotoreceptor, to a receiving surface, such as a sheet of paper. After the transfer of the toner, the surface is discharged, and the material is ready to cycle again. The imaging apparatus can further comprise, for example, a plurality of support rollers for transporting a paper receiving medium and/or for movement of the photoreceptor, a light imaging component with suitable optics to form the light image, a light source, such as a laser, a toner source and delivery system and an appropriate control system.
An electrophotographic imaging process generally can comprise (a) applying an electrical charge to a surface of the above-described organophotoreceptor; (b) imagewise exposing the surface of the organophotoreceptor to radiation to dissipate charge in selected areas and thereby form a pattern of charged and uncharged areas on the surface; (c) exposing the surface with a toner, such as a liquid toner that includes a dispersion of colorant particles in an organic liquid to create a toner image, to attract toner to the charged or discharged regions of the organophotoreceptor; and (d) transferring the toner image to a substrate.
As described herein, an organophotoreceptor comprises a charge transport material having the formula:
where n is a distribution of integers between 1 and 100,000 with an average value of greater than one;
Y comprises an aromatic group;
X is a bond or a linking group such as a —(CH2)n— group, where n is an integer between 1 and 20, inclusive, and one or more of the methylene groups is optionally replaced by O, S, N, C, B, Si, P, C═O, O═S═O, a heterocyclic group, an aromatic group, an NRa group, a CRb group, a CRcRd group, a SiReRf group, a BRg group, or a P(═O)Rh group, where Ra, Rb, Rc, Rd, Re, Rf, Rg, and Rh are, each independently, a bond, H, a hydroxyl group, a thiol group, a carboxyl group, an amino group, a halogen, an alkyl group, an acyl group, an alkoxy group, an alkylsulfanyl group, an alkenyl group, such as a vinyl group, an allyl group, and a 2-phenylethenyl group, an alkynyl group, a heterocyclic group, an aromatic group, or a part of a ring group, such as cycloalkyl groups, heterocyclic groups, and a benzo group.
A heterocyclic group includes any monocyclic or polycyclic (e.g., bicyclic, tricyclic, etc.) ring compound having at least a heteroatom (e.g., O, S, N, P, B, Si, etc.) in the ring.
An aromatic group can be any conjugated ring system containing 4n+2 pi-electrons. There are many criteria available for determining aromaticity. A widely employed criterion for the quantitative assessment of aromaticity is the resonance energy. Specifically, an aromatic group has a resonance energy. In some embodiments, the resonance energy of the aromatic group is at least 10 KJ/mol. In further embodiments, the resonance energy of the aromatic group is greater than 0.1 KJ/mol. Aromatic groups may be classified as an aromatic heterocyclic group which contains at least a heteroatom in the 4n+2 pi-electron ring, or as an aryl group which does not contain a heteroatom in the 4n+2 pi-electron ring. The aromatic group may comprise a combination of aromatic heterocyclic group and aryl group. Nonetheless, either the aromatic heterocyclic or the aryl group may have at least one heteroatom in a substituent attached to the 4n+2 pi-electron ring. Furthermore, either the aromatic heterocyclic or the aryl group may comprise a monocyclic or polycyclic (such as bicyclic, tricyclic, etc.) ring.
Non-limiting examples of the aromatic heterocyclic group include furanyl, thiophenyl, pyrrolyl, indolyl, carbazolyl, benzofuranyl, benzothiophenyl, dibenzofuranyl, dibenzothiophenyl, pyridinyl, pyridazinyl, pyrimidinyl, pyrazinyl, triazinyl, tetrazinyl, petazinyl, quinolinyl, isoquinolinyl, cinnolinyl, phthalazinyl, quinazolinyl, quinoxalinyl, naphthyridinyl, acridinyl, phenanthridinyl, phenanthrolinyl, anthyridinyl, purinyl, pteridinyl, alloxazinyl, phenazinyl, phenothiazinyl, phenoxazinyl, phenoxathiinyl, dibenzo(1,4)dioxinyl, thianthrenyl, and a combination thereof. The aromatic heterocyclic group may also include any combination of the above aromatic heterocyclic groups bonded together either by a bond (as in bicarbazolyl) or by a linking group (as in 1,6 di(10H-10-phenothiazinyl)hexane). The linking group may include an aliphatic group, an aromatic group, a heterocyclic group, or a combination thereof. Furthermore, the linking group may comprise at least one heteroatom such as O, S, Si, and N.
Non-limiting examples of the aryl group include phenyl, naphthyl, benzyl, tolanyl group, sexiphenylene, phenanthrenyl, anthracenyl, coronenyl, tolanylphenyl, fluorenyl, fluorenylidenyl, and a combination thereof. The aryl group may also include any combination of the above aryl groups bonded together either by a bond (as in biphenyl group) or by a linking group (as in stilbenyl, diphenyl sulfone, an arylamine group). The linking group may include an aliphatic group, an aromatic group, a heterocyclic group, or a combination thereof. Furthermore, the linking group may comprise at least one heteroatom such as O, S, Si, and N.
Substitution is liberally allowed on the chemical groups to affect various physical effects on the properties of the compounds, such as mobility, sensitivity, solubility, stability, and the like, as is known generally in the art. In the description of chemical substituents, there are certain practices common to the art that are reflected in the use of language. The term group indicates that the generically recited chemical entity (e.g., alkyl group, aryl group, alkylene group, arylene group, phenyl group, aromatic group, heterocyclic group, etc.) may have any substituent thereon which is consistent with the bond structure of that group. For example, where the term ‘alkyl group’ or ‘alkenyl group’ is used, that term would not only include unsubstituted linear, branched and cyclic alkyl group or alkenyl group, such as methyl, ethyl, ethenyl or vinyl, isopropyl, tert-butyl, cyclohexyl, cyclohexenyl, dodecyl and the like, but also substituents having heteroatom(s), such as 3-ethoxylpropyl, 4-(N,N-diethylamino)butyl, 3-hydroxypentyl, 2-thiolhexyl, 1,2,3-tribromoopropyl, and the like, and aromatic group, such as phenyl, naphthyl, carbazolyl, pyrrole, and the like. However, as is consistent with such nomenclature, no substitution would be included within the term that would alter the fundamental bond structure of the underlying group. For example, where a phenyl group is recited, substitution such as 2- or 4-aminophenyl, 2- or 4-(N,N-disubstituted)aminophenyl, 2,4-dihydroxyphenyl, 2,4,6-trithiophenyl, 2,4,6-trimethoxyphenyl and the like would be acceptable within the terminology, while substitution of 1,1,2,2,3,3-hexamethylphenyl would not be acceptable as that substitution would require the ring bond structure of the phenyl group to be altered to a non-aromatic form. Where the term moiety is used, such as alkyl moiety or phenyl moiety, that terminology indicates that the chemical material is not substituted. Where the term alkyl moiety is used, that term represents only an unsubstituted alkyl hydrocarbon group, whether branched, straight chain, or cyclic.
Organophotoreceptors
The organophotoreceptor may be, for example, in the form of a plate, a sheet, a flexible belt, a disk, a rigid drum, or a sheet around a rigid or compliant drum, with flexible belts and rigid drums generally being used in commercial embodiments. The organophotoreceptor may comprise, for example, an electrically conductive substrate and on the electrically conductive substrate a photoconductive element in the form of one or more layers. The photoconductive element can comprise both a charge transport material and a charge generating compound in a polymeric binder, which may or may not be in the same layer, as well as a second charge transport material such as a charge transport compound or an electron transport compound in some embodiments. For example, the charge transport material and the charge generating compound can be in a single layer. In other embodiments, however, the photoconductive element comprises a bilayer construction featuring a charge generating layer and a separate charge transport layer. The charge generating layer may be located intermediate between the electrically conductive substrate and the charge transport layer. Alternatively, the photoconductive element may have a structure in which the charge transport layer is intermediate between the electrically conductive substrate and the charge generating layer.
The electrically conductive substrate may be flexible, for example in the form of a flexible web or a belt, or inflexible, for example in the form of a drum. A drum can have a hollow cylindrical structure that provides for attachment of the drum to a drive that rotates the drum during the imaging process. Typically, a flexible electrically conductive substrate comprises an electrically insulating substrate and a thin layer of electrically conductive material onto which the photoconductive material is applied.
The electrically insulating substrate may be paper or a film forming polymer such as polyester (e.g., polyethylene terephthalate or polyethylene naphthalate), polyimide, polysulfone, polypropylene, nylon, polyester, polycarbonate, polyvinyl resin, polyvinyl fluoride, polystyrene and the like. Specific examples of polymers for supporting substrates included, for example, polyethersulfone (STABAR™ S-100, available from ICI), polyvinyl fluoride (Tedlar™, available from E.I. DuPont de Nemours & Company), polybisphenol-A polycarbonate (MAKROFOL™, available from Mobay Chemical Company) and amorphous polyethylene terephthalate (MELINAR™, available from ICI Americas, Inc.). The electrically conductive materials may be graphite, dispersed carbon black, iodine, conductive polymers such as polypyrroles and Calgon® conductive polymer 261 (commercially available from Calgon Corporation, Inc., Pittsburgh, Pa.), metals such as aluminum, titanium, chromium, brass, gold, copper, palladium, nickel, or stainless steel, or metal oxide such as tin oxide or indium oxide. In embodiments of particular interest, the electrically conductive material is aluminum. Generally, the photoconductor substrate has a thickness adequate to provide the required mechanical stability. For example, flexible web substrates generally have a thickness from about 0.01 to about 1 mm, while drum substrates generally have a thickness from about 0.5 mm to about 2 mm.
The charge generating compound is a material that is capable of absorbing light to generate charge carriers (such as a dye or pigment). Non-limiting examples of suitable charge generating compounds include, for example, metal-free phthalocyanines (e.g., ELA 8034 metal-free phthalocyanine available from H.W. Sands, Inc. or Sanyo Color Works, Ltd., CGM-X01), metal phthalocyanines such as titanium phthalocyanine, copper phthalocyanine, oxytitanium phthalocyanine (also referred to as titanyl oxyphthalocyanine, and including any crystalline phase or mixtures of crystalline phases that can act as a charge generating compound), hydroxygallium phthalocyanine, squarylium dyes and pigments, hydroxy-substituted squarylium pigments, perylimides, polynuclear quinones available from Allied Chemical Corporation under the trade name INDOFAST™ Double Scarlet, INDOFAST™ Violet Lake B, INDOFAST™ Brilliant Scarlet and INDOFAST™ Orange, quinacridones available from DuPont under the trade name MONASTRAL™ Red, MONASTRAL™ Violet and MONASTRAL™ Red Y, naphthalene 1,4,5,8-tetracarboxylic acid derived pigments including the perinones, tetrabenzoporphyrins and tetranaphthaloporphyrins, indigo- and thioindigo dyes, benzothioxanthene-derivatives, perylene 3,4,9,10-tetracarboxylic acid derived pigments, polyazo-pigments including bisazo-, trisazo- and tetrakisazo-pigments, polymethine dyes, dyes containing quinazoline groups, tertiary amines, amorphous selenium, selenium alloys such as selenium-tellurium, selenium-tellurium-arsenic and selenium-arsenic, cadmium sulphoselenide, cadmium selenide, cadmium sulphide, and mixtures thereof. For some embodiments, the charge generating compound comprises oxytitanium phthalocyanine (e.g., any phase thereof), hydroxygallium phthalocyanine or a combination thereof.
The photoconductive layer of this invention may optionally contain a second charge transport material which may be a charge transport compound, an electron transport compound, or a combination of both. Generally, any charge transport compound or electron transport compound known in the art can be used as the second charge transport material.
An electron transport compound and a UV light stabilizer can have a synergistic relationship for providing desired electron flow within the photoconductor. The presence of the UV light stabilizers alters the electron transport properties of the electron transport compounds to improve the electron transporting properties of the composite. UV light stabilizers can be ultraviolet light absorbers or ultraviolet light inhibitors that trap free radicals.
UV light absorbers can absorb ultraviolet radiation and dissipate it as heat. UV light inhibitors are thought to trap free radicals generated by the ultraviolet light and after trapping of the free radicals, subsequently to regenerate active stabilizer moieties with energy dissipation. In view of the synergistic relationship of the UV stabilizers with electron transport compounds, the particular advantages of the UV stabilizers may not be their UV stabilizing abilities, although the UV stabilizing ability may be further advantageous in reducing degradation of the organophotoreceptor over time. The improved synergistic performance of organophotoreceptors with layers comprising both an electron transport compound and a UV stabilizer are described further in copending U.S. patent application Ser. Number 10/425,333 filed on Apr. 28, 2003 to Zhu, entitled “Organophotoreceptor With A Light Stabilizer,” incorporated herein by reference.
Non-limiting examples of suitable light stabilizer include, for example, hindered trialkylamines such as Tinuvin 144 and Tinuvin 292 (from Ciba Specialty Chemicals, Terrytown, N.Y.), hindered alkoxydialkylamines such as Tinuvin 123 (from Ciba Specialty Chemicals), benzotriazoles such as Tinuvan 328, Tinuvin 900 and Tinuvin 928 (from Ciba Specialty Chemicals), benzophenones such as Sanduvor 3041 (from Clariant Corp., Charlotte, N.C.), nickel compounds such as Arbestab (from Robinson Brothers Ltd, West Midlands, Great Britain), salicylates, cyanocinnamates, benzylidene malonates, benzoates, oxanilides such as Sanduvor VSU (from Clariant Corp., Charlotte, N.C.), triazines such as Cyagard UV-1 164 (from Cytec Industries Inc., N.J.), polymeric sterically hindered amines such as Luchem (from Atochem North America, Buffalo, N.Y.). In some embodiments, the light stabilizer is selected from the group consisting of hindered trialkylamines having the following formula:
where R1, R2, R3, R4, R6, R7, R8, R10, R11, R12, R13, R14, R15 are, each independently, hydrogen, alkyl group, or ester, or ether group; and R5, R9, and R14 are, each independently, alkyl group; and X is a linking group selected from the group consisting of —O—CO—(CH2)m—CO—O— where m is between 2 to 20.
The binder generally is capable of dispersing or dissolving the charge transport material (in the case of the charge transport layer or a single layer construction), the charge generating compound (in the case of the charge generating layer or a single layer construction) and/or an electron transport compound for appropriate embodiments. Examples of suitable binders for both the charge generating layer and charge transport layer generally include, for example, poly(styrene-co-butadiene), poly(styrene-co-acrylonitrile), modified acrylic polymers, poly(vinyl acetate), styrene-alkyd resins, soya-alkyl resins, poly(vinyl chloride), poly(vinylidene chloride), polyacrylonitrile, polycarbonates, poly(acrylic acid), polyacrylates, polymethacrylates, styrene polymers, poly(vinyl butyral), alkyd resins, polyamides, polyurethanes, polyesters, polysulfones, polyethers, polyketones, phenoxy resins, epoxy resins, silicone resins, polysiloxanes, poly(hydroxyether) resins, poly(hydroxystyrene) resins, novolak, poly(phenylglycidyl ether-co-dicyclopentadiene), copolymers of monomers used in the above-mentioned polymers, and combinations thereof. Specific suitable binders include, for example, poly(vinyl butyral), polycarbonate, and polyester. Non-limiting examples of poly(vinyl butyral) include BX-1 and BX-5 from Sekisui Chemical Co. Ltd., Japan. Non-limiting examples of suitable polycarbonate include polycarbonate A which is derived from bisphenol-A (e.g. Iupilon-A from Mitsubishi Engineering Plastics, or Lexan 145 from General Electric); polycarbonate Z which is derived from cyclohexylidene bisphenol (e.g. Iupilon-Z from Mitsubishi Engineering Plastics Corp, White Plain, N.Y.); and polycarbonate C which is derived from methylbisphenol A (from Mitsubishi Chemical Corporation). Non-limiting examples of suitable polyester binders include ortho-poly(ethylene terephthalate) (e.g. OPET TR-4 from Kanebo Ltd., Yamaguchi, Japan).
Suitable optional additives for any one or more of the layers include, for example, antioxidants, coupling agents, dispersing agents, curing agents, surfactants, and combinations thereof.
The photoconductive element overall typically has a thickness from about 10 microns to about 45 microns. In the dual layer embodiments having a separate charge generating layer and a separate charge transport layer, charge generation layer generally has a thickness from about 0.5 microns to about 2 microns, and the charge transport layer has a thickness from about 5 microns to about 35 microns. In embodiments in which the charge transport material and the charge generating compound are in the same layer, the layer with the charge generating compound and the charge transport composition generally has a thickness from about 7 microns to about 30 microns. In embodiments with a distinct electron transport layer, the electron transport layer has an average thickness from about 0.5 microns to about 10 microns and in further embodiments from about 1 micron to about 3 microns. In general, an electron transport overcoat layer can increase mechanical abrasion resistance, increases resistance to carrier liquid and atmospheric moisture, and decreases degradation of the photoreceptor by corona gases. A person of ordinary skill in the art will recognize that additional ranges of thickness within the explicit ranges above are contemplated and are within the present disclosure.
Generally, for the organophotoreceptors described herein, the charge generation compound is in an amount from about 0.5 to about 25 weight percent, in further embodiments in an amount from about 1 to about 15 weight percent, and in other embodiments in an amount from about 2 to about 10 weight percent, based on the weight of the photoconductive layer. The charge transport material is in an amount from about 10 to about 80 weight percent, based on the weight of the photoconductive layer, in further embodiments in an amount from about 35 to about 60 weight percent, and in other embodiments from about 45 to about 55 weight percent, based on the weight of the photoconductive layer. The optional second charge transport material, when present, can be in an amount of at least about 2 weight percent, in other embodiments from about 2.5 to about 25 weight percent, based on the weight of the photoconductive layer, and in further embodiments in an amount from about 4 to about 20 weight percent, based on the weight of the photoconductive layer. The binder is in an amount from about 15 to about 80 weight percent, based on the weight of the photoconductive layer, and in further embodiments in an amount from about 20 to about 75 weight percent, based on the weight of the photoconductive layer. A person of ordinary skill in the art will recognize that additional ranges within the explicit ranges of compositions are contemplated and are within the present disclosure.
For the dual layer embodiments with a separate charge generating layer and a charge transport layer, the charge generation layer generally comprises a binder in an amount from about 10 to about 90 weight percent, in further embodiments from about 15 to about 80 weight percent and in some embodiments in an amount from about 20 to about 75 weight percent, based on the weight of the charge generation layer. The optional charge transport material in the charge generating layer, if present, generally can be in an amount of at least about 2.5 weight percent, in further embodiments from about 4 to about 30 weight percent and in other embodiments in an amount from about 10 to about 25 weight percent, based on the weight of the charge generating layer. The charge transport layer generally comprises a binder in an amount from about 20 weight percent to about 70 weight percent and in further embodiments in an amount from about 30 weight percent to about 50 weight percent. A person of ordinary skill in the art will recognize that additional ranges of binder concentrations for the dual layer embodiments within the explicit ranges above are contemplated and are within the present disclosure.
For the embodiments with a single layer having a charge generating compound and a charge transport material, the photoconductive layer generally comprises a binder, a charge transport material, and a charge generation compound. The charge generation compound can be in an amount from about 0.05 to about 25 weight percent and in further embodiment in an amount from about 2 to about 15 weight percent, based on the weight of the photoconductive layer. The charge transport material can be in an amount from about 10 to about 80 weight percent, in other embodiments from about 25 to about 65 weight percent, in additional embodiments from about 30 to about 60 weight percent and in further embodiments in an amount from about 35 to about 55 weight percent, based on the weight of the photoconductive layer, with the remainder of the photoconductive layer comprising the binder, and optionally additives, such as any conventional additives. A single layer with a charge transport composition and a charge generating compound generally comprises a binder in an amount from about 10 weight percent to about 75 weight percent, in other embodiments from about 20 weight percent to about 60 weight percent, and in further embodiments from about 25 weight percent to about 50 weight percent. Optionally, the layer with the charge generating compound and the charge transport material may comprise a second charge transport material. The optional second charge transport material, if present, generally can be in an amount of at least about 2.5 weight percent, in further embodiments from about 4 to about 30 weight percent and in other embodiments in an amount from about 10 to about 25 weight percent, based on the weight of the photoconductive layer. A person of ordinary skill in the art will recognize that additional composition ranges within the explicit compositions ranges for the layers above are contemplated and are within the present disclosure.
In general, any layer with an electron transport layer can advantageously further include a UV light stabilizer. In particular, the electron transport layer generally can comprise an electron transport compound, a binder, and an optional UV light stabilizer. An overcoat layer comprising an electron transport compound is described further in copending U.S. patent application Ser. No. 10/396,536 to Zhu et al. entitled, “Organophotoreceptor With An Electron Transport Layer,” incorporated herein by reference. For example, an electron transport compound as described above may be used in the release layer of the photoconductors described herein. The electron transport compound in an electron transport layer can be in an amount from about 10 to about 50 weight percent, and in other embodiments in an amount from about 20 to about 40 weight percent, based on the weight of the electron transport layer. A person of ordinary skill in the art will recognize that additional ranges of compositions within the explicit ranges are contemplated and are within the present disclosure.
The UV light stabilizer, if present, in any one or more appropriate layers of the photoconductor generally is in an amount from about 0.5 to about 25 weight percent and in some embodiments in an amount from about 1 to about 10 weight percent, based on the weight of the particular layer. A person of ordinary skill in the art will recognize that additional ranges of compositions within the explicit ranges are contemplated and are within the present disclosure.
For example, the photoconductive layer may be formed by dispersing or dissolving the components, such as one or more of a charge generating compound, the charge transport material of this invention, a second charge transport material such as a charge transport compound or an electron transport compound, a UV light stabilizer, and a polymeric binder in organic solvent, coating the dispersion and/or solution on the respective underlying layer and drying the coating. In particular, the components can be dispersed by high shear homogenization, ball-milling, attritor milling, high energy bead (sand) milling or other size reduction processes or mixing means known in the art for effecting particle size reduction in forming a dispersion.
The photoreceptor may optionally have one or more additional layers as well. An additional layer can be, for example, a sub-layer or an overcoat layer, such as a barrier layer, a release layer, a protective layer, or an adhesive layer. A release layer or a protective layer may form the uppermost layer of the photoconductor element. A barrier layer may be sandwiched between the release layer and the photoconductive element or used to overcoat the photoconductive element. The barrier layer provides protection from abrasion to the underlayers. An adhesive layer locates and improves the adhesion between a photoconductive element, a barrier layer and a release layer, or any combination thereof. A sub-layer is a charge blocking layer and locates between the electrically conductive substrate and the photoconductive element. The sub-layer may also improve the adhesion between the electrically conductive substrate and the photoconductive element.
Suitable barrier layers include, for example, coatings such as crosslinkable siloxanol-colloidal silica coating and hydroxylated silsesquioxane-colloidal silica coating, and organic binders such as poly(vinyl alcohol), methyl vinyl ether/maleic anhydride copolymer, casein, poly(vinyl pyrrolidone), poly(acrylic acid), gelatin, starch, polyurethanes, polyimides, polyesters, polyamides, poly(vinyl acetate), poly(vinyl chloride), poly(vinylidene chloride), polycarbonates, poly(vinyl butyral), poly(vinyl acetoacetal), poly(vinyl formal), polyacrylonitrile, poly(methyl methacrylate), polyacrylates, poly(vinyl carbazoles), copolymers of monomers used in the above-mentioned polymers, vinyl chloride/vinyl acetate/vinyl alcohol terpolymers, vinyl chloride/vinyl acetate/maleic acid terpolymers, ethylene/vinyl acetate copolymers, vinyl chloride/vinylidene chloride copolymers, cellulose polymers, and mixtures thereof. The above barrier layer polymers optionally may contain small inorganic particles such as fumed silica, silica, titania, alumina, zirconia, or a combination thereof. Barrier layers are described further in U.S. Pat. No. 6,001,522 to Woo et al., entitled “Barrier Layer For Photoconductor Elements Comprising An Organic Polymer And Silica,” incorporated herein by reference. The release layer topcoat may comprise any release layer composition known in the art. In some embodiments, the release layer is a fluorinated polymer, siloxane polymer, fluorosilicone polymer, silane, polyethylene, polypropylene, polyacrylate, or a combination thereof. The release layers can comprise crosslinked polymers.
The release layer may comprise, for example, any release layer composition known in the art. In some embodiments, the release layer comprises a fluorinated polymer, siloxane polymer, fluorosilicone polymer, polysilane, polyethylene, polypropylene, polyacrylate, poly(methyl methacrylate-co-methacrylic acid), urethane resins, urethane-epoxy resins, acrylated-urethane resins, urethane-acrylic resins, or a combination thereof. In further embodiments, the release layers comprise crosslinked polymers.
The protective layer can protect the organophotoreceptor from chemical and mechanical degradation. The protective layer may comprise any protective layer composition known in the art. In some embodiments, the protective layer is a fluorinated polymer, siloxane polymer, fluorosilicone polymer, polysilane, polyethylene, polypropylene, polyacrylate, poly(methyl methacrylate-co-methacrylic acid), urethane resins, urethane-epoxy resins, acrylated-urethane resins, urethane-acrylic resins, or a combination thereof. In some embodiments of particular interest, the release layers are crosslinked polymers.
An overcoat layer may comprise an electron transport compound as described further in copending U.S. patent application Ser. No. 10/396,536, filed on Mar. 25, 2003 to Zhu et al. entitled, “Organoreceptor With An Electron Transport Layer,” incorporated herein by reference. For example, an electron transport compound, as described above, may be used in the release layer of this invention. The electron transport compound in the overcoat layer can be in an amount from about 2 to about 50 weight percent, and in other embodiments in an amount from about 10 to about 40 weight percent, based on the weight of the release layer. A person of ordinary skill in the art will recognize that additional ranges of composition within the explicit ranges are contemplated and are within the present disclosure.
Generally, adhesive layers comprise a film forming polymer, such as polyester, poly(vinyl butyral), poly(vinyl pyrrolidone), polyurethane, poly(methyl methacrylate), poly(hydroxy amino ether) and the like. Barrier and adhesive layers are described further in U.S. Pat. No. 6,180,305 to Ackley et al., entitled “Organic Photoreceptors for Liquid Electrophotography,” incorporated herein by reference.
Sub-layers can comprise, for example, poly(vinyl butyral), organosilanes, hydrolyzable silanes, epoxy resins, polyesters, polyamides, polyurethanes, cellulosics, and the like. In some embodiments, the sub-layer has a dry thickness between about 20 Angstroms and about 20,000 Angstroms. Sublayers containing metal oxide conductive particles can be between about 1 and about 25 microns thick. A person of ordinary skill in the art will recognize that additional ranges of compositions and thickness within the explicit ranges are contemplated and are within the present disclosure.
The charge transport materials as described herein, and photoreceptors including these compounds, are suitable for use in an imaging process with either dry or liquid toner development. For example, any dry toners and liquid toners known in the art may be used in the process and the apparatus of this invention. Liquid toner development can be desirable because it offers the advantages of providing higher resolution images and requiring lower energy for image fixing compared to dry toners. Examples of suitable liquid toners are known in the art. Liquid toners generally comprise toner particles dispersed in a carrier liquid. The toner particles can comprise a colorant/pigment, a resin binder, and/or a charge director. In some embodiments of liquid toner, a resin to pigment ratio can be from 1:1 to 10:1, and in other embodiments, from 4:1 to 8:1. Liquid toners are described further in Published U.S. patent applications 2002/0128349, entitled “Liquid Inks Comprising A Stable Organosol,” and 2002/0086916, entitled “Liquid Inks Comprising Treated Colorant Particles,” and U.S. Pat. No. 6,649,316, entitled “Phase Change Developer For Liquid Electrophotography,” all three of which are incorporated herein by reference.
Charge Transport Material
As described herein, an organophotoreceptor comprises a charge transport material having the formula
where n is a distribution of integers between 1 and 100,000 with an average value of greater than one;
Y comprises an aromatic group;
X is a bond or a linking group such as a —(CH2)n— group, where n is an integer between 1 and 20, inclusive, and one or more of the methylene groups is optionally replaced by O, S, N, C, B, Si, P, C═O, O═S═O, a heterocyclic group, an aromatic group, an NRa group, a CRb group, a CRcRd group, a SiReRf group, a BRg group, or a P(=O)Rh group, where Ra, Rb, Rc, Rd, Re, Rf, Rg, and Rh are, each independently, a bond, H, a hydroxyl group, a thiol group, a carboxyl group, an amino group, a halogen, an alkyl group, an acyl group, an alkoxy group, an alkylsulfanyl group, an alkenyl group, such as a vinyl group, an allyl group, and a 2-phenylethenyl group, an alkynyl group, a heterocyclic group, an aromatic group, or a part of a ring group, such as cycloalkyl groups, heterocyclic groups, and a benzo group.
In some embodiments, the organophotoreceptors as described herein may comprise an improved charge transport material of Formula (I) where Y comprises an arylamine group, such as an (N,N-disubstituted)arylamine group (e.g., triarylamine group, alkyldiarylamine group, and dialkylarylamine group), a carbazolyl group, and a julolidinyl group. In other embodiments of interest, Y is selected from the group consisting of the following formulae:
where m is an integer between 1 and 30; and R1, R2, R3, and R4 comprise, each independently, H, a hydroxyl group, a carboxyl group, an amino group, an alkyl group, an acyl group, an alkoxy group, an alkenyl group, such as a vinyl group, an allyl group, and a 2-phenylethenyl group, an alkynyl group, a heterocyclic group, or an aromatic group. In further embodiments of interest, the formulae for the Y group above may comprise at least a substituent selected from the group consisting of a hydroxyl group, a thiol group, a carboxyl group, an amino group, a halogen, a hydrazone group, an azine group, an enamine group, a stilbenyl group, an enamine stilbenyl group, an arylamine group, an alkyl group, an acyl group, an alkoxy group, an alkylsulfanyl group, an alkenyl group, an alkynyl group, a heterocyclic group, an aromatic group and a ring group such as cycloalkyl groups, heterocyclic groups, and a benzo group. In additional embodiments of interest, X is a bond or a —CH═N-Z-N═CH— group where Z is a bond, an alkylene group, an alkenylene group, an alkynylene group, or an arylene group.
Specific, non-limiting examples of suitable charge transport materials within Formula (I) of the present invention have the following structures:
where n is a distribution of integers between 1 and 100,000 with an average value of greater than one.
Synthesis Of Charge Transport Materials
The charge transport materials of this invention may be prepared by one of the following multi-step synthetic procedure, although other suitable procedures can be used by a person of ordinary skill in the art based on the disclosure herein.
General Synthetic Procedures for Charge Transport Materials of Formula (I)
The charge transport material of Formula (I) may be prepared by heating at an elevated temperature or refluxing a reaction mixture of a dicarbazolyl compound of Formula (II), where X is a bond or a linking group, and a dihalo-aromatic compound having the formula Ha-Y-Ha′, where Y comprises an aromatic group; and Ha and Ha′ are, each independently, a halide, such as fluoride, chloride, bromide, and iodide, in the presence of a mixture of copper powder, potassium carbonate, and a crown ether. The reaction mixture may further comprise a solvent such as ethers, alcohols, hydrocarbons, and ketones. Some examples of the reaction are described in the article by S. Grigalevicius et al., Polymer, Vol. 43, p. 2603 (2002), which is incorporated herein by reference.
The asterisks (*) indicate terminal groups on the polymer, which may vary between different polymer units depending on the state of the particular polymerization process at the end of the polymerization step. Non-limiting examples of the terminal group include H and Ha where Ha is a halide. The n in Formula (I) is a distribution of integers between 1 and 100,000 with an average value of greater than one. In some embodiments of interest, n is a distribution of integers between 5 and 10,000. In other embodiments of interest, n is a distribution of integers between 10 and 5,000.
In some embodiments of interest, the X group of the dicarbazolyl compound of Formula (II) is a bond. Such dicarbazolyl compound may be prepared by oxidative coupling of the corresponding carbazole in the presence of ferric chloride (FeCl3) according to a similar procedure as described in the article by D. B. Romero et al., Synth. Met., Vol. 80, p. 271 (1996), which is incorporated herein by reference.
In other embodiments of interest, the X group of the dicarbazolyl compound is a linking group, such as a —(CH2)n— group where n is an integer between 1 and 20, inclusive, and one or more of the methylene groups is optionally replaced by O, S, N, C, B, Si, P, C═O, O═S═O, a heterocyclic group, an aromatic group, an NRa group, a CRb group, a CRcRd group, a SiReRf group, a BRg group, or a P(═O)Rh group, where Ra, Rb, Rc, Rd, Re, Rf, Rg, and Rh are, each independently, a bond, H, a hydroxyl group, a thiol group, a carboxyl group, an amino group, a halogen, an alkyl group, an acyl group, an alkoxy group, an alkylsulfanyl group, an alkenyl group, such as a vinyl group, an allyl group, and a 2-phenylethenyl group, an alkynyl group, a heterocyclic group, an aromatic group, or a part of a ring group, such as cycloalkyl groups, heterocyclic groups, and a benzo group. In other embodiments of interest, the X linking group is a —CR5═N-Z-N═CR5-group where Z is a bond, an alkylene group, an alkenylene group, an alkynylene group, or an arylene group; and R5 comprises H, an alkyl group, an alkenyl group, an alkynyl group, or an aromatic group. In further embodiments of interest, the Z group is a bond, a phenylene group, a methylene group, an ethylene group, a propylene group, or a butylene group. In additional embodiments of interest, the X linking group may be. In general, a person of ordinary skill in the art can select the appropriate functional group of the crosslinking agent to react with the binder, or similarly, a person of ordinary skill in the art can select appropriate functional groups of the binder to react with the functional group of the crosslinking agent
The dicarbazolyl compound of Formula (II) where X group is a —CR5═N-Z-N═CR5— group may be prepared by reacting a carbazoyl compound of Formula (III) having an acyl group (—COR5), where R5 comprises H, an alkyl group, an alkenyl group, an alkynyl group, or an aromatic group; and R6 comprises H or a protecting group for the N—H bond, with a diamine compound having the formula H2N-Z-NH2 where Z is a bond, an alkylene group, an alkenylene group, an alkynylene group, or an arylene group. The acyl group may be in either the 1, 2, 3, or 4 position of the carbazolyl ring. Non-limiting examples of H2N-Z-NH2 include hydrazine, arylene diamines such as phenylene diamine, and alkylene diamines such as ethylene diamine and methylene diamine. In some embodiments of interest, R6 may be H where such 9H-carbazole derivatives of Formula (III) are stable. Otherwise, R6 may be a protecting group for the N—H bond. Non-limiting examples of protecting group for the N-H bond include acyl derivatives, urea and urethane-type derivatives, alkyl and aryl derivatives, azomethine derivatives, 1,3-dicarbonyl derivatives, N-nitroso derivatives, N-nitro derivatives, phosphoryl derivatives, sulfenyl derivatives, sulfonyl derivatives, N-sulfonic acid derivatives, and trialkylsilyl derivatives. The formations and removals of the above N—H protection groups are described by J. W. Barton in Chapter two of “Protective Groups in Organic Chemistry,” edited by J. F. W. McOmie (1975), which is incorporated herein by reference.
In general, a person of ordinary skill in the art can replace the —C(═O)R5 group of Formula (III) with a first functional group, such as a carboxylic acid group and an acid anhydride group, that can react with the H2N groups in H2N-Z-NH2. Similarly, the H2N groups in H2N-Z-NH2 can be replaced with a second functional group and a third functional group respectively, both of which can react with the —C(═O)R5 group of Formula (III). The second functional group and the third functional group may be the same or different. Non-limiting examples of the second functional group and the third functional group include a hydroxyl group, a thiol group, a carbanion group or its precursors, a carbene group or its precursors, an enamine group or its precursors, and a nitrene group or its precursors. Furthermore, a person of ordinary skill in the art can replace both the —C(═O)R5 group of Formula (III) and the H2N groups in H2N-Z-NH2, with a first functional group, a second functional group, and a third functional group respectively, where the first functional group is reactive toward both the second functional group and the third functional group.
The dihalo-aromatic compound having the formula Ha-Y-Ha′ may be prepared by halogenating an aromatic compound Y. Any conventional halogenating reagents may be used for halogenating the aromatic compound Y. In some embodiments of interest, Y comprises an arylamine, such as (N,N-disubstituted)arylamines, substituted and unsubstituted carbazoles, and substituted and unsubstituted julolidines, and the halogenating reagent comprises a mixture of potassium iodide, potassium iodate, and acetic acid. Such halogenation reaction is described in the article by S. Grigalevicius et al., Polymer, Vol. 43, p. 2603 (2002), citing S. Tucker, J. Chem. Soc., p. 548 (1926), both of which are incorporated herein by reference.
In further embodiments of interest, Y is selected from the group consisting of the following formulae:
where m is an integer between 1 and 30; and R1, R2, R3, and R4 comprise, each independently, H, a hydroxyl group, a carboxyl group, an amino group, an alkyl group, an acyl group, an alkoxy group, an alkenyl group, an alkynyl group, a heterocyclic group, or an aromatic group. In other embodiments of interest, Formulae (III)-(VI) may further comprise at least a substituent selected from the group consisting of a hydroxyl group, a thiol group, a carboxyl group, an amino group, a halogen, an alkyl group, an acyl group, an alkoxy group, an alkylsulfanyl group, an alkenyl group, an alkynyl group, a heterocyclic group, an aromatic group, and a ring group.
In general, aromatic compounds having Formula (III) or (IV) may be obtained commercially from a supplier such as Aldrich. Aromatic compounds having Formula (V) may be prepared by refluxing a mixture of the corresponding carbazole and dihaloalkane in a solvent in the presence of a phase transfer catalyst, such as tetrabutylammonium hydrogensulfate, and a base such as potassium hydroxide. Aromatic compounds having Formula (VI) may be prepared by oxidative coupling of the corresponding carbazole in the presence of ferric chloride (FeCl3) according to a similar procedure as described in the article by D. B. Romero et al., Synth. Met., Vol. 80, p. 271 (1996), which is incorporated herein by reference.
The invention will now be described further by way of the following examples.
This example describes the synthesis of Compounds (1)-(5) in which the numbers refer to formula numbers above.
Preparations of Precursors for Compounds (1)-(5)
3,3′-Bicarbazole. 3,3′-Bicarbazole was obtained by the oxidative coupling of carbazole in the presence of ferric chloride (FeCl3) according to a similar procedure as described in the article by D. B. Romero et al., Synth. Met., Vol. 80, p. 271 (1996), which is incorporated herein by reference. Anhydrous iron(III) chloride (available from Acros) (20 g, 0.12 mol) was added to a magnetically stirred solution of 9H-carbazole (5 g, 0.03 mol, available from Aldrich) in 100 ml of chloroform placed in a 250 ml threeneck round bottom flask equipped with a reflux condenser. The reaction mixture was stirred at the ambient temperature for 30 minutes and then poured into a large excess of methyl alcohol. The precipitated material was isolated by filtration and the crude product was purified by column chromatography using silica gel with an eluant mixture of hexane and ethyl acetate in a volume ratio of 1:1. The yield of 3,3′-bicarbazole (FW=332.397) was 62% (3.13 g). The mass spectrum of the product was characterized by the following m/z peak: 333.6 (95%, M+1).
3,6-Diiodo-9-(2-ethylhexyl)carbazole. 3,6-Diiodo-9-(2-ethylhexyl)carbazole was prepared by the alkylation reaction of 3,6-diiodo-9H-carbazole with 2-ethylhexyl bromide in the presence of a phase transfer catalyst according to a similar procedure as described in the article by C. Beginn, et al., Macromol. Chem. Phys., Vol. 195, p. 2353 (1994), which is incorporated herein by reference. 3,6-Diiodo-9H-carbazole was prepared by reacting 9H-carbazole with a mixture of potassium iodide, potassium iodate, and acetic acid according to the procedure described in the article by S. Grigalevicius et al., Polymer, Vol. 43, p. 2603 (2002), citing S. Tucker, J. Chem. Soc., p. 548 (1926), both of which are incorporated herein by reference.
A mixture of 3,6-diiodocarbazole (4.19 g, 0.01 mol), 2-ethylhexyl bromide (2.89 g, 0.015 mol) and tetrabutylammonium hydrogen sulfate (0.1 g, 0.003 mol) was dissolved in 20 ml of acetone in a 100 ml round bottom flask equipped with a magnetic stirrer and a reflux condenser. The mixture was refluxed and powdered sodium hydroxide (1.2 g, 0.03 mol) was added. After the reaction mixture was refluxed for 4 hours, the acetone solvent was removed and the reaction product was dissolved in 100 ml of diethyl ether. The suspension obtained was filtered and the precipitate was washed with diethyl ether. After the removal of the diethyl ether solvent, the product was purified by two recrystallizations from a mixture of methanol and toluene in a volume ratio of 3:1. The yield of 3,6-diiodo-9-ethylhexylcarbazole (FW=531.21) was 2.16 g (41% of yellowish crystals). The melting point of the product was found to be 99-100.5° C. The mass spectrum of the product was characterized by the following m/z peak: 531.3 (M+1).
1,6-Di(3-iodo-9-carbazolyl)hexane. 1,6-Di(3-iodo-9-carbazolyl)hexane may be prepared according to the procedure described in the article by S. Grigalevicius et al., “Synthesis and properties of the polymers containing 3,3′-dicarbazyl units in the main chain and their model compounds,” Polymer, Vol. 43, p. 5693 (2002), which is incorporated herein by reference.
1,12-Di(3-iodo-9-carbazolyl)dodecane. 1,12-Di(3-iodo-9-carbazolyl)dodecane may be prepared according to the procedure described in the article by S. Grigalevicius et al., “Synthesis and properties of the polymers containing 3,3′-dicarbazyl units in the main chain and their model compounds,” Polymer, Vol. 43, p. 5693 (2002), which is incorporated herein by reference.
Di(4-iodophenyl)ethylamine. Di(4-iodophenyl)ethylamine may be prepared by the reaction of diphenylethylamine (available from Aldrich, Milwaukee, Wis.) with a mixture of potassium iodide, potassium iodate, and acetic acid according to the procedure described in the article by S. Grigalevicius et al., Polymer, Vol. 43, p. 2603 (2002), which is incorporated herein by reference.
3,3′-Bi(9-ethyl-carbazole). 3,3′-Bi(9-ethyl-carbazole) may be obtained by the oxidative coupling of 9-ethyl-carbazole (available from Aldrich, Milwaukee, Wis.) in the presence of ferric chloride (FeCl3) according to a similar procedure as described in the article by D. B. Romero et al., Synth. Met., Vol. 122, p. 271 (1996), which is incorporated herein by reference.
Compound (1)
A mixture of 3,3′-bicarbazole (0.91 g, 2.74 mmol) and 3,6-diiodo-9-(2-ethylhexyl)carbazole (1.45 g, 2.74 mmol) was dissolved in 20 ml of dry 1,2-dichlorobenzene to form a solution. Then a mixture of copper powder (0.69 g, 11 mmol), potassium carbonate (3.0 g, 21.7 mmol) and 18-crown-6 ether (0.14 g, 0.53 mmol) was added to the solution. After the reaction mixture was heated to 170° C. and stirred for 72 hours, the inorganic components were filtered off while the reaction mixture was still hot. The crude product was purified by precipitating a purer product from a dichlorobenzene solution of the crude product with a mixture of hexane and methanol in a volume ratio of 1:1. The precipitation process was repeated several times. The precipitated product was filtered and extracted with hot methanol for 120 hours to remove the residue of 18-crown-6 and low molecular weight fractions. The yield of Compound (1) was 29% (0.49 g). The 1H-NMR spectrum (100 MHz) of the product in CDCl3 was characterized by the following chemical shifts (δ, ppm): 0.75-1.16 (m, 6H, CH3); 1.22-1.61 (m, 8H, CH2); 2.1-2.34 (m, 1H, CH), 4.06-4.43 (m, N—CH2), 7.19-7.46 (m, Ar). The infrared absorption spectrum of the product was characterized by the following wave numbers (KBr window, cm−1): 3047 (C—H, Ar); 2955, 2927, 2871 (C—H, Alk); 1493, 801 (C═C, Ar).
Compound (2)
Compound (2) may be prepared according to the procedure for Compound (1) except that 1,6-di(3-iodo-9-carbazolyl)hexane replaces 3,6-diiodo-9-(2-ethylhexyl)carbazole.
Compound (3)
Compound (3) may be prepared according to the procedure for Compound (1) except that 1,12-di(3-iodo-9-carbazolyl)dodecane replaces 3,6-diiodo-9-(2-ethylhexyl)carbazole.
Compound (4)
Compound (4) may be prepared according to the procedure for Compound (1) except that di(4-iodophenyl)ethylamine replaces 3,6-diiodo-9-(2-ethylhexyl)carbazole.
Compound (5)
Compound (5) may be prepared according to the procedure for Compound (1) except that 3,3′-bi(9-ethyl-carbazole) replaces 3,6-diiodo-9-(2-ethylhexyl)carbazole.
This example describes the measurement of charge mobility for samples formed with the charge transport materials described in Example 1.
Sample 1
A mixture of 0.1 g of Compound (1) and 0.1 g of polycarbonate Z was dissolved in 2 ml of tetrahydrofuran. The solution was coated on a polyester film with a conductive aluminum layer by a dip roller. After the coating was dried for 1 hour at 80° C., a clear 10 μm thick layer was formed. The hole mobility of the sample was measured and the results are presented in Table 1.
Mobility Measurements
The mobility of a charge transport material of Formula (I) may be measured by the following procedure. Each sample was corona charged positively up to a surface potential U and illuminated with 2 ns long nitrogen laser light pulse. The hole mobility μ was determined as described in Kalade et al., “Investigation of charge carrier transfer in electrophotographic layers of chalkogenide glasses,” Proceeding IPCS 1994: The Physics and Chemistry of Imaging Systems, Rochester, N.Y., pp. 747-752, incorporated herein by reference. The hole mobility measurement was repeated with appropriate changes to the charging regime to charge the sample to different U values, which corresponded to different electric field strength inside the layer E. This dependence on electric field strength was approximated by the formula
μ=μ0eα√{square root over (E)}
Here E is electric field strength, μ0 is the zero field mobility and α is Pool-Frenkel parameter. Table 1 lists the mobility characterizing parameters μ0 and α values and the mobility value at the 6.4×105 V/cm field strength as determined by these measurements for the four samples.
The ionization potential of a charge transport material of Formula (I) may be measured by the following procedure. To perform the ionization potential measurements, a thin layer of a charge transport material about 0.5 μm thickness was coated from a solution of 2 mg of the charge transport material in 0.2 ml of tetrahydrofuran on a 20 cm2 substrate surface. The substrate was an aluminized polyester film coated with a 0.4 μm thick methylcellulose sub-layer.
Ionization potential was measured as described in Grigalevicius et al., “3,6-Di(N-diphenylamino)-9-phenylcarbazole and its methyl-substituted derivative as novel hole-transporting amorphous molecular materials,” Synthetic Metals 128 (2002), p. 127-131, incorporated herein by reference. In particular, each sample was illuminated with monochromatic light from the quartz monochromator with a deuterium lamp source. The power of the incident light beam was 2-5·10−8 W. A negative voltage of −300 V was supplied to the sample substrate. A counter-electrode with the 4.5×15 mm2 slit for illumination was placed at 8 mm distance from the sample surface. The counter-electrode was connected to the input of a BK2-16 type electrometer, working in the open input regime, for the photocurrent measurement. A 10−15−10−12 amp photocurrent was flowing in the circuit under illumination. The photocurrent, I, was strongly dependent on the incident light photon energy hv. The I0.5=f(hv) dependence was plotted. Usually, the dependence of the square root of photocurrent on incident light quanta energy is well described by linear relationship near the threshold (see references “Ionization Potential of Organic Pigment Film by Atmospheric Photoelectron Emission Analysis,” Electrophotography, 28, Nr. 4, p. 364 (1989) by E. Miyamoto, Y. Yamaguchi, and M. Yokoyama; and “Photoemission in Solids,” Topics in Applied Physics, 26, 1-103 (1978) by M. Cordona and L. Ley, both of which are incorporated herein by reference). The linear part of this dependence was extrapolated to the hv axis, and the Ip value was determined as the photon energy at the interception point. The ionization potential measurement has an error of ±0.03 eV. The ionization potential values are given in Table 1 above.
As understood by those skilled in the art, additional substitution, variation among substituents, and alternative methods of synthesis and use may be practiced within the scope and intent of the present disclosure of the invention. The embodiments above are intended to be illustrative and not limiting. Additional embodiments are within the claims. Although the present invention has been described with reference to particular embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.
