Patent Application
20060093933
This invention relates to organophotoreceptors suitable for use in electrophotography and, more specifically, to organophotoreceptors including a polymeric charge transport material having a plurality of silanyl units, some of which comprising an active, physically and/or chemically, pendant group. This invention further relates to a method 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.
Organophotoreceptors may be used for both dry and liquid electrophotography. There are many differences between dry and liquid electrophotography. A significant difference is that a dry toner is used in dry electrophotography, whereas a liquid toner is used in liquid electrophotography. A potential advantage of liquid electrophotography is that it can provide a higher resolution and thus sharper images than dry electrophotography because liquid toner particles can be generally significantly smaller than dry toner particles. As a result of their smaller size, liquid toners are able to provide images of higher optical density than dry toners.
In both dry and liquid electrophotography, the charge transport material used for the organophotoreceptor should be compatible with the polymeric binder in the photoconductive element. The selection of a suitable polymeric binder for a particular charge transport material can place constraints on the formation of the photoconductive element. If the charge transport material is not compatible with the polymeric binder, the charge transport material may phase-separate or crystallize in the polymeric binder matrix, or may diffuse onto the surface of the layer containing the charge transport material. If such incompatibility occurs, the organophotoreceptor can cease to transport charges.
Furthermore, liquid electrophotography faces an additional issue. In particular, the organophotoreceptor for liquid electrophotography is in contact with the liquid carrier of a liquid toner while the toner dries or pending transfer to a receiving surface. As a result, the charge transport material in the photoconductive element may be removed by extraction by the liquid carrier. Over a long period of operation, the amount of the charge transport material removed by extraction may be significant and, therefore, detrimental to the performance of the organophotoreceptor.
This invention provides organophotoreceptors having good electrostatic properties such as high Vacc and low Vdis. This invention also provides polymeric charge transport materials having reduced extraction by liquid carriers and reducing the need for a polymeric binder.
In a first aspect, an organophotoreceptor comprises an electrically conductive substrate and a photoconductive element on the electrically conductive substrate, the photoconductive element comprising:
where n and m are each a distribution of integers between 1 and 50,000 with an average value of greater than one, and the n units of R1—Si—X1—Ar1 and m units of R2—Si—X2—Ar2—X3-Z form a random copolymer, an alternative copolymer, or a block copolymer comprising at least two different blocks, each of which having the same repeating silanyl units;
A1 and A2 are each a terminal group such as a hydroxyl group, an alkoxyl group, a phenoxy group, an alkylsulfanyl group, a thiol group, and an amino group;
Ar1 and Ar2 comprise, each independently, an aromatic group; and
Z comprises a functional group such as a hydrazone group, an azine group, a fluorenyl group, a fluorenylidene group, an aromatic heterocyclic group, an acyl group such as formyl and acetyl, a carboxyl group, a hydroxyl group, a thiol group, an amino group such as —NH2, an N-arylamino group, an N-alkylamino group, an N,N-diarylamino group, an N-alkyl-N-arylamino group, and an N,N-dialkylamino group, a reactive ring group such as an oxiranyl group, an oxetanyl group, a thiiranyl group, and an aziridinyl group, an alkenyl group such as a vinyl group and a 2-phenylethenyl group, an acrylate group, a methacrylate group, and combinations thereof; and
(b) a charge generating compound.
The A1 and A2 groups are 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 and/or the terminating step. Non-limiting examples of the terminal group include a hydroxyl group, an alkoxyl group, a phenoxy group, an alkylsulfanyl group, a thiol group, and an amino group.
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 polymeric 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 polymeric charge transport material having Formula (I) above. The Z group of the polymeric charge transport material having Formula (I) may react with each other or other functional groups that are reactive toward the Z group to form cross-linked polymeric charge transport materials.
In a fifth aspect, the invention features a method of preparing a polymeric charge transport material comprising the steps of:
(a) forming a polysilane having acyl groups by reacting an acylating agent with a polysilane having a chemical composition represented by the following formula:
where n and m are each a distribution of integers between 1 and 50,000 with an average value of greater than one, and the n units of R1—Si—X1—Ar1 and m units of R2—Si—X2—Ar2 form a random copolymer, an alternative copolymer, or a block copolymer comprising at least two different blocks, each of which having the same repeating silanyl units;
R1 and R2 comprise, each independently, an alkyl group, an alkoxy group, an alkenyl group, an alkynyl group, a heterocyclic group, an aromatic group, or a combination thereof;
X1 and X2 comprise, each independently, a bond or a linking group, such as a —(CH2)m— group, where m 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 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, a part of a ring group, such as cycloalkyl groups, heterocyclic groups, and a benzo group, or an alkyl group where one or more of the hydrogens of the alkyl group is optionally replaced by an aromatic group, a hydroxyl group, a thiol group, a carboxyl group, an amino group, or a halogen;
A1 and A2 are each a terminal group;
Ar1 and Ar2 comprise, each independently, an aromatic group; and
(b) forming a polysilane having hydrazone groups by reacting the polysilane having acyl groups with a hydrazine having the formula H2N—NR4R5 where R4 and R5 comprise, each independently, H, an alkyl group, an alkenyl group, an alkynyl group, a heterocyclic group, an aromatic group, or a combination thereof.
In a sixth aspect, the invention features a polymeric charge transport material prepared by the steps of:
(a) providing a reaction mixture of at least a chlorosilane monomer, an alkali metal, and an aromatic solvent;
(b) heating the mixture to form a polysilane having chloro end groups;
(c) reacting the chloro end groups with a chemical having at least an active hydrogen that is reactive towards the chloro end groups;
(d) forming a polysilane having acyl groups by reacting an acylating agent with the polysilane from step (c); and
(e) forming a polysilane having hydrazone groups by reacting the polysilane having acyl groups with a hydrazine having the formula H2N—NR4R5 where R4 and R5 comprise, each independently, H, an alkyl group, an alkenyl group, an alkynyl group, a heterocyclic group, an aromatic group, or a combination thereof.
In a seven aspect, the invention features a polymeric charge transport material prepared by the steps of:
(a) providing a reaction mixture of at least a chlorosilane monomer, an alkali metal, and an aromatic solvent;
(b) heating the mixture to form a polysilane having chloro end groups;
(c) reacting the chloro end groups with a chemical having at least an active hydrogen that is reactive towards the chloro end groups;
(d) forming a polysilane having acyl groups by reacting an acylating agent with the polysilane from step (c);
(e) converting the polysilane having acyl groups into a polysilane having imine groups by reacting the polysilane having acyl groups with a primary amine;
(f) reducing polysilane having imine groups to a polysilane having secondary amine groups; and
(g) reacting the polysilane having secondary amine groups with a chemical having the formula Z2-Y2-L2 where Z2 comprises a vinyl group, a methacrylate group, an acrylate group, or a reactive ring group; L2 comprises a leaving group, such as mesylate, tosylate, iodide, bromide, and chloride; and Y2 comprises a bond or 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 NRi group, a CRj group, a CRkRl group, a SiRmRn group, a BRo group, or a P(═O)Rp group, where Ri, Rj, Rk, Rl, Rm, Rn, Ro, and Rp are, each independently, a bond, H, a hydroxyl group, a thiol group, a carboxyl group, an amino group, a halogen, 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, a part of a ring group, such as cycloalkyl groups, heterocyclic groups, and a benzo group, or an alkyl group where one or more of the hydrogens of the alkyl group is optionally replaced by an aromatic group, a hydroxyl group, a thiol group, a carboxyl group, an amino group, or a halogen.
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 and dry 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 a plurality of silanyl units. Some of the silanyl units may comprise an active, physically and/or chemically, pendant group. The pendant group is selected from the group consisting of a hydrazone group, an azine group, a fluorenyl group, a fluorenylidene group, an aromatic heterocyclic group, an acyl group, a carboxyl group, a hydroxyl group, a thiol group, an amino group, a reactive ring group, an alkenyl group, an acrylate group, and a methacrylate 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-carbazolo-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 compositions (e.g., poly(vinylcarbazole)). The charge transport materials can 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, 6,696,209, 6,749,978, and 6,768,010, and U.S. patent application Ser. Nos. 10/431,135, 10/431,138, 10/699,364, 10/663,278, 10/699,581, 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, 10/749,164, 10/772,068, 10/749,178, 10/758,869, 10/695,044, 10/772,069, 10/789,184, 10/789,077, 10/775,429, 10/670,483, 10/671,255, 10/663,971, 10/760,039, 10/815,243, 10/832,596, 10/836,667, 10/814,938, 10/834,656, 10/815,118, 10/857,267, 10/865,662, 10/864,980, 10/865,427, 10/883,453, 10/929,914, and 10/900,785. 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-110-[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 polymeric charge transport material having a chemical composition represented by the following formula:
where n and m are each a distribution of integers between 1 and 50,000 with an average value of greater than one, and the n units of R1—Si—X1—Ar1 and m units of R2—Si—X2—Ar2—X3-Z form a random copolymer, an alternative copolymer, or a block copolymer comprising at least two different blocks, each of which having the same repeating silanyl units;
R1 and R2 comprise, each independently, an alkyl group, an alkoxy group, an alkenyl group, an alkynyl group, a heterocyclic group, an aromatic group, or a combination thereof;
X1, X2, and X3 comprise, each independently, a bond or a linking group, such as a —(CH2)m— group, where m 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 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, a part of a ring group, such as cycloalkyl groups, heterocyclic groups, and a benzo group, or an alkyl group where one or more of the hydrogens of the alkyl group is optionally replaced by an aromatic group, a hydroxyl group, a thiol group, a carboxyl group, an amino group, or a halogen;
A1 and A2 are each a terminal group such as a hydroxyl group, an alkoxyl group, a phenoxy group, an alkylsulfanyl group, a thiol group, and an amino group;
Ar1 and Ar2 comprise, each independently, an aromatic group; and
Z comprises a hydrazone group, an azine group, a fluorenyl group, a fluorenylidene group, an aromatic heterocyclic group, an acyl group such as formyl and acetyl, a carboxyl group, a hydroxyl group, a thiol group, an amino group such as —NH2, an N-arylamino group, an N-alkylamino group, an N,N-diarylamino group, an N-alkyl-N-arylamino group, and an N,N-dialkylamino group, a reactive ring group such as an oxiranyl group, an oxetanyl group, a thiiranyl group, and an aziridinyl group, an alkenyl group such as a vinyl group and a 2-phenylethenyl group, an acrylate group, a methacrylate group, or a combination thereof.
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 are 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 are phenyl, naphthyl, benzyl, or tolanyl group, sexiphenylene, phenanthrenyl, anthracenyl, coronenyl, and tolanylphenyl. 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, alkenyl group, alkynyl group, phenyl group, aromatic group, heterocyclic group, hydrazone group, azine group, fluorenyl group, fluorenylidene group, acyl group, amino group, oxiranyl group, oxetanyl group, thiiranyl group, aziridinyl group, acrylate group, methacrylate 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., poly(ethylene terephthalate) or poly(ethylene naphthalate)], polyimide, polysulfone, polypropylene, nylon, polyester, polycarbonate, polyvinyl resin, poly(vinyl fluoride), polystyrene and the like. Specific examples of polymers for supporting substrates included, for example, polyethersulfone (STABAR™ S-100, available from ICI), poly(vinyl fluoride) (TEDLAR®, available from E.I. DuPont de Nemours & Company), polybisphenol-A polycarbonate (MAKROFOL™, available from Mobay Chemical Company) and amorphous poly(ethylene 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. No. 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 trialkylanines 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-1164 (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(vinylchloride), 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, polyhydroxystyrene 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, polyvinyl butyral, polycarbonate, and polyester. Non-limiting examples of polyvinyl 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-polyethylene 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 form 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 material 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 material 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 protective 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, polyvinylbutyral, polyvinylpyrrolidone, 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, polyvinylbutyral, 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 polymeric charge transport material having a chemical composition represented by the following formula:
where n and m are each a distribution of integers between 1 and 50,000 with an average value of greater than one, and the n units of R1—Si—X1—Ar1 and m units of R2—Si—X2—Ar2—X3-Z form a random copolymer, an alternative copolymer, or a block copolymer comprising at least two different blocks, each of which having the same repeating silanyl units;
R1 and R2 comprise, each independently, an alkyl group, an alkoxy group, an alkenyl group, an alkynyl group, a heterocyclic group, an aromatic group, or a combination thereof; X1, X2, and X3 comprise, each independently, a bond or a linking group, such as a —(CH2)m— group, where m 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 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, a part of a ring group, such as cycloalkyl groups, heterocyclic groups, and a benzo group, or an alkyl group where one or more of the hydrogens of the alkyl group is optionally replaced by an aromatic group, a hydroxyl group, a thiol group, a carboxyl group, an amino group, or a halogen;
A1 and A2 are each a terminal group such as a hydroxyl group, an alkoxyl group, a phenoxy group, an alkylsulfanyl group, a thiol group, and an amino group;
Ar1 and Ar2 comprise, each independently, an aromatic group; and
Z comprises a hydrazone group, an azine group, a fluorenyl group, a fluorenylidene group, an aromatic heterocyclic group, an acyl group such as formyl and acetyl, a carboxyl group, a hydroxyl group, a thiol group, an amino group such as —NH2, an N-arylamino group, an N-alkylamino group, an N,N-diarylamino group, an N-alkyl-N-arylamino group, and an N,N-dialkylamino group, a reactive ring group such as an oxiranyl group, an oxetanyl group, a thiiranyl group, and an aziridinyl group, an alkenyl group such as a vinyl group and a 2-phenylethenyl group, an acrylate group, a methacrylate group, or a combination thereof.
A1 and A2 are 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 and/or the terminating step. Non-limiting examples of the terminal group include a hydroxyl group, an alkoxyl group, a phenoxy group, an alkylsulfanyl group, a thiol group, and an amino group. In general, the n and m values depend on the polymerization conditions. The presence of the polymer of Formula (I) does not preclude the presence of unreacted monomer within the organophotoreceptor. The extent of polymerization, as specified with n and m, can affect the properties of the resulting polymer. In some embodiments of interest, n and m are each a distribution of integers between 5 and 10,000. In other embodiments of interest, n and m are each a distribution of integers between 10 and 5,000. A person of ordinary skill in the art will recognize that additional ranges of average n values are contemplated and are within the present disclosure.
Formula (I) is intended to represent the chemical composition of the polymeric charge transport material of this invention and is not intended to represent the distribution of the repeating units or the X3-Z pendant group in the polymer. The polymeric charge transport material of Formula (I) may be a homopolymer comprising n+m repeating silanyl units of the same kind (where R1 is same as R2, X1 is same as X2, and Ar1 is same as Ar2) and m X3-Z pendant groups distributed among the n+m repeating silanyl units; a random copolymer comprising two different kinds of repeating silanyl units; or a block copolymer comprising at least two different blocks, each of which having the same repeating silanyl units. In some embodiments, the polymeric charge transport material comprises a copolymer having at least two different kinds of silanyl repeating units, i.e., R1 is different from R2, X1 is different from X2, or Ar1 is different from Ar2. Similarly, the X3-Z pendant groups may distribute randomly throughout the polymeric chain, or only in some, but not all, of the blocks.
In some embodiments of interest, X1 and X2 comprise, each independently, a bond or a —(CH2)m— group, where m is an integer between 1 and 20; R1 and R2 comprise, each independently, an alkyl group, or an aromatic group; Z comprises a hydrazone group having the formula ═N—NR4R5 where R4 and R5 comprise, each independently, H, an alkyl group, an alkenyl group, an ether group, an aromatic group, a heterocyclic group, a reactive ring group, an acrylate group, a methacrylate group, or a combination thereof; and X3 comprises a ═CR3— group where R3 comprises H, an alkyl group, an alkenyl group, an aromatic group, a heterocyclic group, or a combination thereof. In further embodiments of interest, Ar1 and Ar2 comprise, each independently, a phenylene group, a triarylamino group, or a carbazolyl group. In additional embodiments of interest, R4 comprises an aromatic group and R5 comprises a Y1-Z1 group where Y1 comprises a —(CH2)k—Op— group where k is between 0 and 2, p is 0 or 1; and Z1 comprises a reactive ring group, an alkenyl group, an acrylate group, a methacrylate group, or a combination thereof.
In other embodiments of interest, X1 and X2 comprise, each independently, a bond or a —(CH2)m— group, where m is an integer between 1 and 20; R1 and R2 comprise, each independently, an alkyl group, or an aromatic group; X3 comprises a ═CR3— group where R3 comprises H, an alkyl group, an alkenyl group, an aromatic group, a heterocyclic group, or a combination thereof; and Z comprises an azine group having the formula ═N—N═X4 where X4 comprises a cyclic ring having a divalent carbon atom or a ═CR7—Ar3 group where R7 comprises H, an alkyl group, an alkenyl group, an aromatic group, a heterocyclic group, or a combination thereof; and Ar3 comprises an alkyl group, an alkenyl group, an aromatic group, a heterocyclic group, or a combination thereof. In further embodiments of interest, X4 comprises a fluorenylidenyl group or a ═CR7—Ar3 group where R7 comprises H and Ar3 comprises a triphenylamino group, or a carbazolyl group. In additional embodiments of interest, Ar1 and Ar2 comprise, each independently, a phenylene group, a triarylamino group, or a carbazolyl group.
In other embodiments of interest, X1 and X2 each comprise a bond; R1 and R2 comprise, each independently, an alkyl group, or an aromatic group; X3 comprises a —CHR3—O—(CH2)k—Op— group where k is between 0 and 2, p is 0 or 1, and R3 comprises H, an alkyl group, an alkenyl group, an aromatic group, a heterocyclic group, or a combination thereof; and Z comprises a vinyl group, a methacrylate group, an acrylate group, or a reactive ring group. In further embodiments of interest, the reactive ring group is selected from the group consisting of an epoxy group, a thiiranyl group, an aziridinyl group, and an oxetanyl group.
In some embodiments of interest, Ar1 and Ar2, each independently, 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, an ester group, an amido group, a nitro group, a cyano group, a sulfonate group, a phosphate, phosphonate, a heterocyclic group, an aromatic group, an (N,N-disubstituted)hydrazone group, an enamine group, an azine group, an epoxy group, a thiiranyl group, and an aziridinyl group.
Specific, non-limiting examples of suitable charge transport materials within Formula (I) of the present invention include the following structures:
where n and m are each a distribution of integers between 1 and 50,000 with an average value of greater than one, where the n units of CH3—Si—C6H5 and m units of CH3—Si—C6H4-Z form a random copolymer, and where A1 and A2 are, each independently, either a hydroxyl group or an ethoxy group.
Each of the above structures 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, an ester group, an amido group, a nitro group, a cyano group, a sulfonate group, a phosphate, phosphonate, a heterocyclic group, an aromatic group, an (N,N-disubstituted)hydrazone group, an enamine group, an azine group, an epoxy group, a thiiranyl group, and an aziridinyl group.
Synthesis Of Charge Transport Materials
The synthesis of the charge transport materials of this invention can be prepared by 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.
The polysilane of Formula (III) may be prepared by the alkali metal dechlorination of at least a chlorosilane monomer. The alkali metal dechlorination of chlorosilane monomers can be carried out at an elevated temperature in an aromatic solvent such as toluene or xylene with an alkali metal such as lithium, sodium, and potassium. Non-limiting examples of suitable chlorosilane monomer include dialkyldichlorosilanes such as dimethyldichlorosilane, diaryldichlorosilanes such as diphenyldichlorosilane, alkylaryldichlorosilanes such as methylphenyldichlorosilane, chlorosilanes containing an aromatic heterocyclic group such as [3-(N-carbozolyl)propylmethyl]dichlorosilane, aryltrichlorosilanes such as phenyltrichlorosilane, and alkyltrichlorosilanes such as ethyltrichlorosilane. In some embodiments, only one chlorosilane monomer, i.e., R1 is same as R2, X1 is same as X2, and Ar1 is same as Ar2, is used to prepare the polysilane of Formula (III). In other embodiments, two chlorosilane monomers, i.e., R1 is different from R2, X1 is different from X2, or Ar1 is different from Ar2, are used to prepare the polysilane of Formula (III). The values of n and m are each a distribution of integers between 1 and 50,000 with an average value of greater than one. The n units of R1—Si—X1—Ar1 and m units of R2—Si—X2—Ar2—X3-Z may form a random copolymer, an alternative copolymer, or a block copolymer comprising at least two different blocks, each of which having the same repeating silanyl units. The n/m ratio may vary from 1/100 to 100/1.
A person skill in the art may modify the procedure disclosed herein by using more than two chlorosilane monomers for the preparation of a polymeric charge transport material. The molecular weight of the polysilane of Formula (III) depends on the reaction condition, the activity of the aromatic solvent towards the the chloro groups of the chlorosilane monomer and the dichloro precursor of the polysilane of Formula (II), and the absence or presence of a chemical having at least an active hydrogen (e.g. A1—H and A2—H). Non-limiting examples of A1—H and A2—H inlcude water, alcohols, mercaptans such as n-butyl mercaptan and n-dodecyl mercaptane, phenols, and amines, that react with the the chloro groups of the chlorosilane monomer and the dichloro precursor of the polysilane of Formula (III). When water is used to terminate the polymerization, the two terminal groups A1 and A2 are hydroxyl. Similarly, when an alcohol is used to terminated the polymerization, the two terminal groups A1 and A2 are alkoxyl. Similarly, when a mercaptane is used to terminated the polymerization, the two terminal groups A1 and A2 are alkylsulfanyl. Based on the disclosure herein, a person skill in the art may change the terminal group by using any chemical having at least an active hydrogen that reacts with the chloro groups of the chlorosilane monomer and the dichloro precursor of the polysilane of Formula (III).
The alkali metal dechlorination is described in Cranstone et al., “Synthesis and characterization of polysilane precursors for silicon carbide fibers,” J. Mater. Res., Vol. 10, No. 10, p. 2659 (1996); Tabei et al., Synth. Met., Vol. 73, p. 113 (1995); Mimura et al., “Photoelectric Properties Of Organic Polysilane Containing Carbazolyl Side Groups,” Applied Physics Letters, Vol. 77, No. 14. pp. 2198-2200 (2000); Matyjaszewski et al., Macromolecules, Vol. 28, 59 (1995); and Jang et al., “Syntheses and Characterizations of Polysilanes with Bulky Substituents,” Bull. Korean. Chem. Soc., Vol. 17, pp. 443-447 (1996), all of which are incorporated herein by reference.
The polysilane of Formula (II) having an acyl group may be prepared by reacting the polysilane of Formula (III) with an acylating agent to substitute one hydrogen in the Ar2 group with an acyl group (R3CO). Depending on the acylating agent, R3 may comprise H, an alkyl group, an alkenyl group, an aromatic group, a heterocyclic group, or a combination thereof. The acylation of the polysilane of Formula (III) may be done with a mixture of a Lewis acid such as tin tetrachloride and dichloromethyl methyl ether. Alternatively, the acylation of the polysilane of Formula (III) may be done under Vilsmeier-Haack condition with a mixture of phosphorus oxychloride (POCl3) and an N,N-dialkylamide, such as N,N-dimethylformamide, N,N-dimethylacetamide, and N,N-dimethylbenzamide. Alternatively, the polysilane of Formula (III) may be acylated by a mixture of a strong base, such as butyl lithium, and an N,N-dialkylamide, or by a mixture of Lewis acid, such as stannic chloride, and an acid anhydride, such as acetic anhydride at an elevated temperature. The C-acylations of aromatic hetercycles such as thiophenes, furans, and pyrroles under Vilsmeier-Haack condition are described in Alan Katritzky, “Handbook of heterocyclic chemistry,” Pergamon Press, New York, p. 254-255 (1985), which is incorporated herein by reference. Furthermore, the Vilsmeier-Haack acylation and related reactions are described in Carey et al., “Advanced Organic Chemistry, Part B: Reactions and Synthesis,” New York, 1983, pp. 380-393, which is incorporated herein by reference.
The polymeric charge transport material of Formula (IA) is equivalent to Formula (I) where Z comprises a hydrazone group and may be prepared by reacting the polysilane of Formula (II) having an acyl group with a hydrazine, H2N—NR4R5 where R4 and R5 comprise, each independently, H, an alkyl group, an alkenyl group, an aromatic group group, a heterocyclic group, or a combination thereof. The hydrazone formation reaction may take place in a solvent, such as tetrahydrofuran and methanol. The hydrazone formation reaction may be catalyzed by an appropriate amount of acid, such as acetic acid, sulfuric acid and hydrochloric acid. The reaction mixture may be heated at an elevated temperature for a period of time, such as 2 to 14 hours. The polymeric charge transport material of Formula (IA) may be isolated and purified by conventional purification techniques, such as chromatography and recrystallization.
The charge transport material of Formula (IB) is equivalent to Formula (I) where Z comprises a hydrazone group having an N-substituted Y1-Z1 group. The charge transport material of Formula (IB) may be prepared by reacting the corresponding polymeric charge transport material of Formula (IA) where R5 is H with Z1-Y1-L1 where Z1 comprises a vinyl group, a methacrylate group, an acrylate group, or a reactive ring group; L1 comprises a leaving group, such as mesylate, tosylate, iodide, bromide, and chloride; and Y1 comprises a bond or 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 NRi group, a CRj group, a CRkRl group, a SiRmRn group, a BRo group, or a P(═O)Rp group, where Ri, Rj, Rk, Rl, Rm, Rn, Ro, and Rp are, each independently, a bond, H, a hydroxyl group, a thiol group, a carboxyl group, an amino group, a halogen, 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, a part of a ring group, such as cycloalkyl groups, heterocyclic groups, and a benzo group, or an alkyl group where one or more of the hydrogens of the alkyl group is optionally replaced by an aromatic group, a hydroxyl group, a thiol group, a carboxyl group, an amino group, or a halogen. In some embodiments, the Y1 group comprises a bond, an alkylene group, such as methylene and ethylene, or —(CH2)kO— group where k is an integer between 1 and 10.
The reaction may take place in a solvent, such as ethyl methyl ketone and tetrahydrofuran. The reaction may be catalyzed by a base, such as potassium hydroxide, potassium carbonate, and a combination thereof. The reaction mixture may be heated at an elevated temperature for a period of time, such as 2 to 48 hours. When the reaction is completed, the charge transport material of Formula (IB) may be isolated and purified by conventional purification techniques, such as chromatography and recrystallization.
Some non-limiting examples of Z1-Y1-L1 include vinyl chloroformate, isopropenyl chloroformate, vinyl chloroacetate, 2-chloroethyl vinyl ether, 6-(vinyloxy)-1-hexyl mesylate, 4-(vinyloxy)-1-butyl mesylate, 2-(vinyloxy)ethyl mesylate, 6-(vinyloxy)-1-hexyl tosylate, 4-(vinyloxy)-1-butyl tosylate, and 2-(vinyloxy)ethyl tosylate. The mesylates and tosylates can be prepared by the reaction between 6-(vinyloxy)-1-hexanol, 1,4-butanediol vinyl ether, and 2-(vinyloxy)ethanol with mesyl chloride and tosyl chloride respectively. The above-mentioned chemicals may be obtained commercially from a supplier such as Aldrich, Milwaukee, Wis.
Other non-limiting examples of Z1-Y1-L1 include methacryloyl chloride, acryloyl chloride, crotonoyl chloride, 3-dimethylacryloyl chloride, cinnamoyl chloride, 2,6,6-trimethyl-1-cyclohexene-1-carbonyl chloride, 2,3,3-trichloroacryloyl chloride, 3-(2-chlorophenyl)-2propenoyl chloride, 4-nitrocinnamoyl chloride, 3-(trifluoromethyl)cinnamoyl chloride, 2-[(dimethylamino)methylene]malonoyl dibromide, all of which may be obtained from commercial suppliers such as Aldrich.
Further non-limiting examples of Z1-Y1-L1 include reactive ring groups. The reactive ring group may be selected from the group consisting of heterocyclic ring groups that have a higher strain energy than their corresponding open-ring structures. The conventional definition of strain energy is that it represents the difference in energy between the actual molecule and a completely strain-free molecule of the same constitution. More information about the origin of strain energy can be found in the article by Wiberg et al., “A Theoretical Analysis of Hydrocarbon Properties: II Additivity of Group Properties and the Origin of Strain Energy,” J. Am. Chem. Soc. 109, 985 (1987), which is incorporated herein by reference. The heterocyclic ring group may have 3, 4, 5, 7, 8, 9, 10, 11, or 12 members, in further embodiments 3, 4, 5, 7, or 8 members, in some embodiments 3, 4, or 8 members, and in additional embodiments 3 or 4 members. Non-limiting examples of such heterocyclic ring are cyclic ethers (e.g., epoxides and oxetane), cyclic amines (e.g., aziridine), cyclic sulfides (e.g., thiirane), cyclic amides (e.g., 2-azetidinone, 2-pyrrolidone, 2-piperidone, caprolactam, enantholactam, and capryllactam), N-carboxy-α-amino acid anhydrides, lactones, and cyclosiloxanes. The chemistry of the above heterocyclic rings is described in George Odian, “Principle of Polymerization,” second edition, Chapter 7, p. 508-552 (1981), which is incorporated herein by reference.
In some embodiments of interest, the reactive ring group is an epoxy group. A diamino-aromatic heterocyclic compound having an epoxy group may be prepared by reacting a corresponding compound with an organic halide comprising an epoxy group. Non-limiting examples of suitable organic halide comprising an epoxy group as the reactive ring group are epihalohydrins, such as epichlorohydrin. The organic halide comprising an epoxy group can also be prepared by the epoxidation reaction of the corresponding alkene having a halide group. Such epoxidation reaction is described in Carey et al., “Advanced Organic Chemistry, Part B: Reactions and Synthesis,” New York, 1983, pp. 494-498, incorporated herein by reference. The alkene having a halide group can be prepared by the Wittig reaction between a suitable aldehyde or keto compound and a suitable Wittig reagent. The Wittig and related reactions are described in Carey et al., “Advanced Organic Chemistry, Part B: Reactions and Synthesis,” New York, 1983, pp. 69-77, which is incorporated herein by reference.
In other embodiments of interest, the reactive ring group is a thiiranyl group. A diamino-aromatic heterocyclic compound having an epoxy group, such as those described above, can be converted into the corresponding thiiranyl compound by refluxing the epoxy compound and ammonium thiocyanate in tetrahydrofuran. Alternatively, the corresponding thiiranyl compound may be obtained by passing a solution of the above-described epoxy compound through 3-(thiocyano)propyl-functionalized silica gel (commercially available form Aldrich, Milwaukee, Wis.). Alternatively, a thiiranyl compound may be obtained by the thia-Payne rearrangement of a corresponding epoxy compound. The thia-Payne rearrangement is described in Rayner, C. M. Synlett 1997, 11; Liu, Q. Y.; Marchington, A. P.; Rayner, C. M. Tetrahedron 1997, 53, 15729; Ibuka, T. Chem. Soc. Rev. 1998, 27, 145; and Rayner, C. M. Contemporary Organic Synthesis 1996, 3, 499. All the above four articles are incorporated herein by reference.
In other embodiments of interest, the reactive ring group is an aziridinyl group. An aziridine compound may be obtained by the aza-Payne rearrangement of a corresponding diamino-aromatic heterocyclic compound having an epoxy group, such as one of those epoxy compounds described above. The thia-Payne rearrangement is described in Rayner, C. M. Synlett 1997, 11; Liu, Q. Y.; Marchington, A. P.; Rayner, C. M. Tetrahedron 1997, 53, 15729; and Ibuka, T. Chem. Soc. Rev. 1998, 27, 145. All the above three articles are incorporated herein by reference. Alternatively, an aziridine compound may be prepared by the addition reaction between a suitable nitrene compound and a suitable alkene. Such addition reaction is described in Carey et al., “Advanced Organic Chemistry, Part B: Reactions and Synthesis,” New York, 1983, pp. 446-448, incorporated herein by reference.
In further embodiments of interest, the reactive ring group is an oxetanyl group. An oxetane compound may be prepared by the Paterno-Buchi reaction between a suitable carbonyl compound and a suitable alkene. The Paterno-Buchi reaction is described in Carey et al., “Advanced Organic Chemistry, Part B: Reactions and Synthesis,” New York, 1983, pp. 335-336, which is incorporated herein by reference. 3-Chloromethyl-3-alkyloxetanes may be prepared according to the procedure disclosed in Japanese Publication No. 10-212282, which is incorporated herein by reference.
In additional examples, the reactive ring may be a 5 or 7-membered ring comprising a —COO— group or a —CONR— group, such as butyrolactone, N-methylbutyrolactam, N-methylcaprolactam, and caprolactone.
The polysilane of Formula (II) having an acyl group may be reduced by a reducing agent, such as aluminum hydride, sodium cyanoborohydride, and sodium borohydride, to the polysilane of Formula (IV) where Q is —CHR3—O (i.e., the —C(═O)R3 group is reduced to a —CHR3—OH group) where R3 may comprise H, an alkyl group, an alkenyl group, an aromatic group, a heterocyclic group, or a combination thereof. The reduction of carbonyl group is disclosed in Carey et al., “Advanced Organic Chemistry, Part B: Reactions and Synthesis,” New York, Chapter 5, pp. 193-239 (1983), which is incorporated herein by reference.
Alternatively, the polysilane of Formula (II) having an acyl group may be converted into the polysilane of Formula (IV) where Q is —CHR3—NHR6 by reductive amination where R6 may comprise H, an alkyl group, an alkenyl group, an aromatic group, a heterocyclic group, or a combination thereof. The reductive amination is the process by which ammonia or a primary amine is condensed with an aldehyde or a ketone to form the corresponding imine which is subsequently reduced to an amine. The subsequent reduction of imine to amine may be accomplished by reacting the imine with hydrogen and a suitable hydrogenation catalyst such as Raney Nickel and platinum oxide, aluminum-mercury amalgam, or a hydride such as lithium aluminum hydride, sodium cyanoborohydride, and sodium borohydride.
The reductive amination is described in U.S. Pat. No. 3,187,047; and articles by Haskelberg, “Aminative Reduction of Ketones,” J. Am. Chem. Soc., 70 (1948) 2811-2; Mastagli et al., “Study of the Aminolysis of Some Ketones and Aldehydes,” Bull. soc. chim. France (1950) 1045-8; B. J. Hazzard, Practical Handbook of Organic Chemistry, Addison-Wesley Publishing Co., Inc., pp. 458-9 and 686 (1973); and Alexander et al., “A Low Pressure Reductive Alkylation Method for the Conversion of Ketones to Primary Amines,” J. Am. Chem. Soc., 70, 1315-6 (1948). The above U.S. patent and articles are incorporated herein by reference.
The charge transport material of Formula (IC) is equivalent to Formula (I) where X3 is Q-Y2 and Z is Z2 which comprises a vinyl group, a methacrylate group, an acrylate group, or a reactive ring group. The charge transport material of Formula (IC) may be formed by reacting the polysilane of Formula (IV) with Z2-Y2-L2 where Z2 comprises a vinyl group, a methacrylate group, an acrylate group, or a reactive ring group; L2 comprises a leaving group, such as mesylate, tosylate, iodide, bromide, and chloride; and Y2 comprises a bond or 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 NRi group, a CRj group, a CRkRl group, a SiRmRn group, a BRo group, or a P(═O)Rp group, where Ri, Rj, Rk, Rl, Rm, Rn, Ro, and Rp are, each independently, a bond, H, a hydroxyl group, a thiol group, a carboxyl group, an amino group, a halogen, 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, a part of a ring group, such as cycloalkyl groups, heterocyclic groups, and a benzo group, or an alkyl group where one or more of the hydrogens of the alkyl group is optionally replaced by an aromatic group, a hydroxyl group, a thiol group, a carboxyl group, an amino group, or a halogen.
The reaction may take place in a solvent, such as ethyl methyl ketone and tetrahydrofuran. The reaction may be catalyzed by a base, such as potassium hydroxide, potassium carbonate, and a combination thereof. The reaction mixture may be heated at an elevated temperature for a period of time, such as 2 to 48 hours. When the reaction is completed, the charge transport material of Formula (IC) may be isolated and purified by conventional purification techniques, such as chromatography and recrystallization.
Some non-limiting examples of Z2-Y2-L2 include vinyl chloroformate, isopropenyl chloroformate, vinyl chloroacetate, 2-chloroethyl vinyl ether, 6-(vinyloxy)-1-hexyl mesylate, 4-(vinyloxy)-1-butyl mesylate, 2-(vinyloxy)ethyl mesylate, 6-(vinyloxy)-1-hexyl tosylate, 4-(vinyloxy)-1-butyl tosylate, and 2-(vinyloxy)ethyl tosylate. The mesylates and tosylates can be prepared by the reaction between 6-(vinyloxy)-1-hexanol, 1,4-butanediol vinyl ether, and 2-(vinyloxy)ethanol with mesyl chloride and tosyl chloride respectively. The above-mentioned chemicals may be obtained commercially from a supplier such as Aldrich, Milwaukee, Wis.
Other non-limiting examples of Z2-Y2-L2 include methacryloyl chloride, acryloyl chloride, crotonoyl chloride, 3-dimethylacryloyl chloride, cinnamoyl chloride, 2,6,6-trimethyl-1-cyclohexene-1-carbonyl chloride, 2,3,3-trichloroacryloyl chloride, 3-(2-chlorophenyl)-2-propenoyl chloride, 4-nitrocinnamoyl chloride, 3-(trifluoromethyl)cinnamoyl chloride, 2-[(dimethylamino)methylene]malonoyl dibromide, all of which may be obtained from commercial suppliers such as Aldrich.
Further non-limiting examples of Z2-Y2-L2 include reactive ring groups. The reactive ring group may be selected from the group consisting of heterocyclic ring groups that have a higher strain energy than their corresponding open-ring structures. The conventional definition of strain energy is that it represents the difference in energy between the actual molecule and a completely strain-free molecule of the same constitution. More information about the origin of strain energy can be found in the article by Wiberg et al., “A Theoretical Analysis of Hydrocarbon Properties: II Additivity of Group Properties and the Origin of Strain Energy,” J. Am. Chem. Soc. 109, 985 (1987), which is incorporated herein by reference. The heterocyclic ring group may have 3, 4, 5, 7, 8, 9, 10, 11, or 12 members, in further embodiments 3, 4, 5, 7, or 8 members, in some embodiments 3, 4, or 8 members, and in additional embodiments 3 or 4 members. Non-limiting examples of such heterocyclic ring are cyclic ethers (e.g., epoxides and oxetane), cyclic amines (e.g., aziridine), cyclic sulfides (e.g., thiirane), cyclic amides (e.g., 2-azetidinone, 2-pyrrolidone, 2-piperidone, caprolactam, enantholactam, and capryllactam), N-carboxy-α-amino acid anhydrides, lactones, and cyclosiloxanes. The chemistry of the above heterocyclic rings is described in George Odian, “Principle of Polymerization,” second edition, Chapter 7, p. 508-552 (1981), which is incorporated herein by reference.
The charge transport material of Formula (ID) is equivalent to Formula (I) where Z comprises an azine group, ═N—N═X4 where X4 may be a cyclic ring having a divalent carbon atom such as a fluorenylidenyl group or X4 may be a ═CR7—Ar3 group where R7 comprises H, an alkyl group, an alkenyl group, an aromatic group, a heterocyclic group, or a combination thereof, and Ar3 comprises an alkyl group, an alkenyl group, an aromatic group, a heterocyclic group, or a combination thereof. The charge transport material of Formula (ID) may be formed by reacting the polysilane of Formula (V) having a hydrazone group with O═X4 which may be an aldehyde such as Ar3—CHO, acyclic ketone such as Ar3—COR7, or cyclic ketone such as 9-fluorenone. The polysilane of Formula (V) may be prepared by reacting the polysilane of Formula (II) having an acyl group with hydrazine, H2N—NH2.
The hydrazone formation reaction and the azine formation reaction may take place in a solvent, such as tetrahydrofuran and methanol. The hydrazone formation reaction and the azine formation reaction may be catalyzed by an appropriate amount of acid, such as acetic acid, sulfuric acid and hydrochloric acid. The reaction mixture may be heated at an elevated temperature for a period of time, such as 2 to 14 hours. The polymeric charge transport material of Formula (ID) may be isolated and purified by conventional purification techniques, such as chromatography and recrystallization.
The desired product may be isolated and purified by the conventional purification techniques such as column chromatography and recrystallization.
The invention will now be described further by way of the following examples.
This example describes the synthesis and characterization of Polymers (1)-(14) in which the numbers refer to formula numbers above. The characterization involves chemical characterization of the compositions. The electrostatic characterization, such as mobility and ionization potential, of the materials formed with the compositions is presented in a subsequent example.
Synthesis of Poly(methylphenylsilane) of Formula (III) where R1=R2=methyl, X1=X2=a Bond, and Ar1=Ar2=1,4 Phenylene
A mixture of sodium metal (11 g, 0.48 mol) and 140 ml dry toluene was added under dry nitrogen atmosphere to a 500 ml four-neck round-bottom flask equipped with a dry nitrogen supply inlet, a reflux condenser, a pressure equalizing addition funnel and a motor-driven steel wire stirrer. The mixture was refluxed and stirred vigorously to form a dispersion of sodium in toluene. The stirred sodium dispersion was heated to a gentle reflux and a solution of dichloro(methyl)phenylsilane (obtained from Aldrich, 34 ml, 0.21 mol) in 35 ml dry toluene was added quickly enough to maintain the reflux. The reaction mixture was refluxed for 3 hours, then cooled to the room temperature, and quenched with ethanol (50 ml) and then water (250 ml). The toluene layer was separated and washed with water twice (2×250 ml) and the solvent was evaporated. The greasy residue was dissolved in tetrahydrofuran (50 ml, THF) and the THF solution obtained was dropped into 1000 ml of isopropanol to precipitate out the product. The precipitated white powder was filtered off and dried under a vacuum generated by an oil pump at room temperature. The yield of the product was 14.8 g (58.9%). The 1H-NMR spectrum (100 MHz) of the product in C6D6 was characterized by the following chemical shifts (δ, ppm): 0.5-0.75 (broad peak, 3H, CH3), 6.75-7.75 (broad peak, 5H, C6H5). The infrared absorption spectrum of the product was characterized by the following absorption wave numbers (KBr window, cm−1): 3067; 3048, 3012 (C6H5, C—H), 2956, 2894 (CH3, C—H), 1948, 1888, 1814 (C6H5, comb.) 1484 (C6H5, C═C), 1427, 1098 (Si—C6H5), 1246 (Si—CH3), 781, 752, 729 (C6H5, C—H out of plane), 696, 668 (Si—C), 462 (Si—Si).
Synthesis of a Formyl Derivative of Poly(methylphenylsilane) of Formula (II) where R1=R2=Methyl, X1=X2=a Bond, Ar1=Ar2=1,4 Phenylene, and R3=H
Poly(methylphenylsilane) (1.5 g, prepared previously) was dissolved in 35 ml of dichloromethane under dry nitrogen atmosphere and with the exclusion of light. After the solution was cooled to −7° C., tin(IV) chloride (obtained from Aldrich, SnCl4, 6.5 g, 0.023 mol) and α,α-dichloromethyl methyl ether (obtained from Aldrich, 2.26 ml, 0.023 mol) were added. The mixture was stirred at −7° C. for 3 hours and then poured onto 50 g of crushed ice. The organic layer was separated and washed with water twice (2×50 ml). The solvent was evaporated and the residue was dissolved in 25 ml of tetrahydrofuran (THF). The THF solution was added to methanol (500 ml) to precipitate out the product. The white polymer product that was precipitated out was filtered off and dried under a vacuum generated by an oil pump at room temperature. The yield of the product was 0.9 g (48.65%). The 1H-NMR spectrum (100 MHz) of the product in C6D6 was characterized by the following chemical shifts (δ, ppm): 0.5-0.75 (broad peak, 3H, CH3), 6.75-7.75 (broad peak, C6H5), 9.6-9.9 (s, CHO). The infrared absorption spectrum of the product was characterized by the following absorption wave numbers (KBr window, cm−1): 3067; 3048, 3023 (C6H5, C—H), 2994 (CHO, C—H), 2955, 2895 (CH3, C—H), 1951, 1889, 1818 (C6H5, comb.), 1702 (CHO, C═O), 1485 (C6H5, C═C), 1427, 1099 (Si—C6H5), 1247 (Si—CH3), 781, 753, 732 (C6H5, C—H out of plane), 697, 669 (Si—C), 464 (Si—Si). The ratio of n to m in Formula (II) was found to be 6:1.
Polymer (1)
A solution of 0.02 g N-methyl-N-phenylhydrazine (obtained from Aldrich) in 10 ml of tetrahydrofuran was added dropwise to a solution of 0.2 g of the previously prepared formyl derivative of poly(methylphenylsilane) in 10 ml of tetrahydrofuran at 70° C. over a period of 10 minutes. After the addition was completed, 3 drops of acetic acid was added to the reaction mixture. The reaction mixture was maintained at 70-90° C. for 4 hours. Then the reaction mixture was cooled down to room temperature, concentrated to 5 ml volume, and added to 400 ml of methanol to precipitate out the product. The precipitated product was filtered off and dried under a vacuum generated by an oil pump at room temperature. The yield of the product was 0.19 g. The 1H-NMR spectrum (100 MHz) of the product in C6D6 was characterized by the following chemical shifts (δ, ppm): 0.5-0.75 (broad peak, 3H, CH3), 2.5-3.0 (CH3—N), 6.75-7.75 (broad peak, C6H5+CH═N—). From the 1H NMR spectrum, the content of hydrazone groups was determined to be 19.3% by mole. The infrared absorption spectrum of the product was characterized by the following absorption wave numbers (KBr window, cm−1): 3067; 3048, 3012 (C6H5, C—H), 2954, 2895 (CH3, C—H), 1950, 1887, 1816 (C6H5, comb.), 1599, 1586, 1575 (CH═N—, C═N), 1498 (C6H5, C═C), 1427, 1099 (Si—C6H5), 1322, 1305 (N—C6H5, N—C), 1247 (Si—CH3), 1191, 1177 (N—CH3, N—C) 780, 752, 732 (C6H5, C—H out of plane), 697, 668 (Si—C), 464 (Si—Si).
Polymer (2)
Polymer (2) may be prepared by the procedure for Polymer (1) except that N-methyl-N-phenylhydrazine is replaced with N,N-diphenylhydrazine.
Polymer (3)
Polysilane of Formula (IV) where R1=R2=methyl, X1=X2=a bond, Ar1=Ar2=phenylene, and Q=—CH2O— may be prepared by reducing the formyl groups in the previously prepared formyl derivative of poly(methylphenylsilane) to methylol groups. The reduction can be carried out by a reducing agent such as lithium aluminum hydride and sodium borohydride. The reduction of a carbonyl group to a hydroxyl group is described in Carey et al., “Advanced Organic Chemistry, Part B: Reactions and Synthesis,” New York, Chapter 5, pp. 199-213 (1983), which is incorporated herein by reference.
Polymer (3) may be prepared by the reaction between 2-chloroethyl vinyl ether (available from Aldrich) and the polysilane of Formula (IV) where R1=R2=methyl, X1=X2=a bond, Ar1=Ar2=phenylene, and Q=CH2O in a solvent. The reaction is catalyzed by a base, such as potassium hydroxide and potassium carbonate. The reaction mixture is heated at an elevated temperature for a period of time, such as 2 to 48 hours. When the reaction is completed, Polymer (3) is isolated and purified by conventional purification techniques, such as chromatography and recrystallization.
Polymer (4)
Polysilane of Formula (IV) where R1=R2=methyl, X1=X2=a bond, Ar1=Ar2=1, 4-phenylene, and Q=CH2O may be prepared by reducing the formyl groups in the previously prepared formyl derivative of poly(methylphenylsilane) to methylol groups. The reduction can be carried out by a reducing agent such as lithium aluminum hydride and sodium borohydride.
Polymer (4) may be prepared by the reaction between methacryloyl chloride (available from Aldrich) and the polysilane of Formula (IV) where R1=R2=methyl, X1=X2=a bond, Ar1=Ar2=phenylene, and Q=CH2O in a solvent. When the reaction is completed, Polymer (4) is isolated and purified by conventional purification techniques, such as chromatography and recrystallization.
Polymer (5)
Polysilane of Formula (IV) where R1=R2=methyl, X1=X2=a bond, Ar1=Ar2=1,4-phenylene, and Q=CH2O may be prepared by reducing the formyl groups in the previously prepared formyl derivative of poly(methylphenylsilane) to methylol groups. The reduction can be carried out by a reducing agent such as lithium aluminum hydride and sodium borohydride.
Polymer (5) may be prepared by the reaction between epichlorohydrine (available from Aldrich) and the polysilane of Formula (IV) where R1=R2=methyl, X1=X2=a bond, Ar1=Ar2=phenylene, and Q=CH2O in a solvent. The reaction is catalyzed by a base, such as triethylamine. The reaction mixture is heated at an elevated temperature for a period of time, such as 2 to 48 hours. When the reaction is completed, Polymer (5) is isolated and purified by conventional purification techniques, such as chromatography and recrystallization.
Polymer (6)
Polysilane of Formula (IA) where R1=R2=methyl, X1=X2=a bond, Ar1=Ar2=1,4-phenylene, X3=CH, R4=phenyl, and R5=H may be prepared by the procedure for Polymer (1) except that N-methyl-N-phenylhydrazine is replaced with N-phenylhydrazine.
Polymer (6) may be prepared by the reaction between 2-chloroethyl vinyl ether (available from Aldrich) and the polysilane of Formula (IA) where R1=R2=methyl, X1=X2=a bond, Ar1=Ar2=1,4-phenylene, X3=CH, R4=phenyl, and R5=H in a solvent. The reaction is catalyzed by a base, such as potassium hydroxide and potassium carbonate. The reaction mixture is heated at an elevated temperature for a period of time, such as 2 to 48 hours. When the reaction is completed, Polymer (6) is isolated and purified by conventional purification techniques, such as chromatography and recrystallization.
Polymer (7)
Polysilane of Formula (IA) where R1=R2=methyl, X1=X2=a bond, Ar1=Ar2=1,4-phenylene, X3=CH, R4=phenyl, and R5=H may be prepared by the procedure for Polymer (1) except that N-methyl-N-phenylhydrazine is replaced with N-phenylhydrazine.
Polymer (7) may be prepared by the reaction between methacryloyl chloride (available from Aldrich) and the polysilane of Formula (IA) where R1=R2=methyl, X1=X2=a bond, Ar1=Ar2=1,4-phenylene, X3=CH, R4=phenyl, and R5=H in a solvent. When the reaction is completed, Polymer (7) is isolated and purified by conventional purification techniques, such as chromatography and recrystallization.
Polymer (8)
Polysilane of Formula (IA) where R1=R2=methyl, X1=X2=a bond, Ar1=Ar2=1,4-phenylene, X3=CH, R4=phenyl, and R5=H may be prepared by the procedure for Polymer (1) except that N-methyl-N-phenylhydrazine is replaced with N-phenylhydrazine.
Polymer (8) may be prepared by the reaction between epichlorohydrine (available from Aldrich) and the polysilane of Formula (IA) where R1=R2=methyl, X1=X2=a bond, Ar1=Ar2=1,4-phenylene, X3=CH, R4=phenyl, and R5=H in a solvent. The reaction is catalyzed by a base, such as triethylamine. The reaction mixture is heated at an elevated temperature for a period of time, such as 2 to 48 hours. When the reaction is completed, Polymer (5) is isolated and purified by conventional purification techniques, such as chromatography and recrystallization.
Polymer (9)
Polysilane of Formula (III) where R1=R2=methyl, X1=a bond, X2=propylene, Ar1=1,4-phenylene, and Ar2=carbazolyl may be prepared by the condensation of [3-(N-carbozolyl)propylmethyl]dichlorosilane and phenylmethyldichlorosilane with sodium in xylene, as disclosed in Mimura et al., “Photoelectric Properties Of Organic Polysilane Containing Carbazolyl Side Groups,” Applied Physics Letters, Vol. 77, No. 14. pp. 2198-2200 (2000), which is incorporated herein by reference.
Polysilane of Formula (III) where R1=R2=methyl, X1=a bond, X2=propylene, Ar1=1,4-phenylene, and Ar2=carbazolyl may be formylated with dichloromethyl methyl ether by a procedure similar to that for the formyl derivative of poly(methylphenylsilane) of Formula (II) where R1=R2=methyl, X1=X2=a bond, Ar1=Ar2=1,4-phenylene, and R3=H. The product is a polysilane of Formula (II) where R1=R2=methyl, X1=a bond, X2=propylene, Ar1=1,4-phenylene, Ar2=carbazolyl, and R3=H.
Polymer (9) may be prepared by the procedure for Polymer (1) except that the formyl derivative of poly(methylphenylsilane) of Formula (II) where R1=R2=methyl, X1=X2=a bond, Ar1=Ar2=1,4-phenylene, and R3=H is replaced with the polysilane of Formula (II) where R1=R2=methyl, X1=a bond, X2=propylene, Ar1=phenylene, Ar2=carbazolyl, and R3=H.
Polymer (10)
Polymer (10) may be prepared by the procedure for Polymer (2) except that the formyl derivative of poly(methylphenylsilane) of Formula (II) where R1=R2=methyl, X1=X2=a bond, Ar1=Ar2=1,4-phenylene, and R3=H is replaced with the polysilane of Formula (II) where R1=R2=methyl, X1=a bond, X2=propylene, Ar1=phenylene, Ar2=carbazolyl, and R3=H.
Polymer (11)
Polymer (11) may be prepared by the procedure for Polymer (1) except that N-methyl-N-phenylhydrazine is replaced with 4-(diphenylamino)benzaldehyde hydrazone. 4-(Diphenylamino)benzaldehyde hydrazone may be prepared by the following procedure. A mixture of hydrazine (0.1 mole, available from Aldrich, Milwaukee, Wis.) and 4-(diphenylamino)benzaldehyde (0.1 mole, available from Fluka, Buchs SG, Switzerland) is dissolved in 100 ml of isopropanol in a 250 ml 3-neck round bottom flask equipped with a reflux condenser and a mechanical stirrer. After the solution is refluxed for 2 hours, the mixture is cooled to room temperature. The product, 4-(diphenylamino)benzaldehyde hydrazone, is isolated and purified by conventional techniques such as recrystallization and column chromatography.
Polymer (12)
Polymer (12) may be prepared by the procedure for Polymer (1) except that N-methyl-N-phenylhydrazine is replaced with 9-fluorenone hydrazone. 9-Fluorenone hydrazone may be prepared by the following procedure. 9-Fluorenone (0.05 mol, available from Aldrich, Milwaukee, Wis.) is dissolved in 300 ml of methanol under mild heating. Then, a solution of hydrazine (0.05 mol, available from Aldrich) in methanol was added. The reaction mixture is refluxed for 2 hours. After the solution is refluxed for 2 hours, the mixture is cooled to room temperature. The product, 9-fluorenone hydrazone, is isolated and purified by conventional techniques such as recrystallization and column chromatography.
Polymer (13)
Polymer (13) may be prepared by the procedure for Polymer (1) except that N-methyl-N-phenylhydrazine is replaced with 9-ethyl-3-carbazolecarboxaldehyde hydrazone. 9-Ethyl-3-carbazolecarboxaldehyde hydrazone may be prepared by the following procedure. 9-Ethylcarbazole-3-carbaldehyde (0.05 mol, available from Aldrich, Milwaukee, Wis.) is dissolved in 300 ml of methanol under mild heating. Then, a solution of hydrazine (0.05 mol, available from Aldrich) in methanol was added. The reaction mixture is refluxed for 2 hours. After the solution is refluxed for 2 hours, the mixture is cooled to room temperature. The product, 9-ethyl-3-carbazolecarboxaldehyde hydrazone, is isolated and dried at 40° C. vacuum oven for 4 hours then used immediately in the next reaction.
Polymer (14)
Polymer (14) may be prepared by the procedure for Polymer (9) except that N-methyl-N-phenylhydrazine is replaced with 4-(diphenylamino)benzaldehyde hydrazone. 4-(Diphenylamino)benzaldehyde hydrazone may be prepared by the following procedure. A mixture of hydrazine (0.1 mole, available from Aldrich, Milwaukee, Wis.) and 4-(diphenylamino)benzaldehyde (0.1 mole, available from Fluka, Buchs SG, Switzerland) is dissolved in 100 ml of isopropanol in a 250 ml 3-neck round bottom flask equipped with a reflux condenser and a mechanical stirrer. After the solution is refluxed for 2 hours, the mixture is cooled to room temperature. The product, 4-(diphenylamino)benzaldehyde hydrazone, is isolated and purified by conventional techniques such as recrystallization and column chromatography.
This example describes the measurement of charge mobility and ionization potential for charge transport materials, specifically Polymer (1).
Sample 1
0.1 g of the Polymer (1) was dissolved in 2 ml of tetrahydrofuran (THF). 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
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.
This example describes the measurement of the ionization potential for the charge transport materials described in Example 1.
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.
