|
(11) | EP 0 295 792 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
|
|
|
|
|||||||||||||||||||||||||||
| (54) | Organic photoconductor |
| (57) An organic photoconductor comprising an electrically conducting support, a charge
generation layer containing metal-free phthalocyanine in the X- or the alpha-polymorphic
form and a charge transport layer containing a compound of the formula:
wherein each of X and Z, independently, represents a phenyl or naphthyl radical and Y represents an alkyl, phenyl or naphthyl radical, each of X, Y and Z optionally carrying one or more non-ionic substituents. |
[0001] This invention relates to an organic photoconductor for use as the photosensitive element of an electrophotographic device such as a copier or printer.
[0002] Organic photoconductor (OPC) or photoreceptor devices used in electrophotographic copiers and printers generally comprise an electrically conducting support, a charge generation layer (CGL) containing a charge generation compound, which may be a dye or pigment, and a charge transport layer (CTL) containing a large transport material which may be either an n-type or a p-type semiconductor.
[0003] It has now been found that high performance OPC devices may be obtained using the combination of charge generation compounds and charge transport compounds hereinafter defined.
[0004] Thus, according to the invention, there is provided an organic photoconductor comprising an electrically conducting support, a charge generation layer containing metal-free phthalocyanine in the X- or the alpha-polymorphic form and a charge transport layer containing a compound of the formula:
wherein each of X and Z, independently, represents a phenyl or naphthyl radical and Y represents an alkyl, phenyl or naphthyl radical, each of X, Y and Z optionally carrying one or more non-ionic substituents.
[0005] In the preferred compounds of Formula I:
X is phenyl,
Y is phenyl or 1- or 2-naphthyl but may also be lower alkyl, for example methyl, and
Z is 1- or 2-naphthyl or a 4-aminophenyl radical wherein the amino group is preferably secondary or, especially, a tertiary amino group having alkyl, aralkyl or aryl substituents, the phenyl group optionally carrying one or more non-ionic substituents such as lower alkyl.
[0006] One class of compounds of Formula I has the structure:
wherein each of R¹, R², R³ and R⁴, independently, represents hydrogen, C₁₋₄-alkyl, C₁₋₄-alkoxy or halogen; R⁵ represents hydrogen, C₁₋₄-alkyl or C₁₋₄-alkoxy and each of R⁶ and R⁷, independently, represents an optionally substituted C₁₋₄-alkyl, aryl-C₁₋₄-alkyl, such as benzyl, or phenyl radical or R⁶ and R⁷ together with the attached nitrogen atom form a heterocyclic ring. Optional substituents for R⁶ and R⁷ are C₁₋₄-alkyl, C₁₋₄-alkoxy and halogen, especially chlorine. Preferred compounds are those in which R¹ to R⁵ are H and R⁶ and R⁷ are C₁₋₄-alkyl and more especially ethyl.
[0007] The X- and alpha-forms of metal-free phthalocyanine present in the CGL are known materials. The alpha form generally has poor crystallinity and the X-form moderate crystallinity (determined by X-ray diffraction). Both polymorphic forms should be substantially free of other forms such as the beta-form and gamma-forms, since these detract from their performance.
[0008] The alpha-form has high sensitivity in the green and especially red spectral regions, e.g. from 500 - 700 nm. It is therefore useful for conventional photocopiers and also for LED printers, where the typical LED output is at ca. 660 nm.
[0009] The X-form not only has high sensitivity in the green and red spectral regions, but also in the near infra-red, up to ca. 850 nm. It is particularly sensitive at 780 - 830 nm, where the solid state semiconductor lasers emit. Therefore, it is ideally suited to the new generation of laser printers based upon solid state semiconducting lasers of the gallium-aluminium-arsenide type. It is also useful for LED printers and for normal photocopying. The primary particle size of the pigment is preferably less than 1 micron, typically 0.05 - 0.2 micron or less for the X-form and 0.05 - 0.5 micron for the alpha-form.
[0010] The electrically conducting support may be a metal support preferably in the form of a drum or a composite material comprising an insulating supporting material such as a sheet of polymeric material, e.g. a polyester sheet or film, coated with a thin film of a conducting material, e.g. a metal such as aluminium, in the form of a drum or a continuous belt.
[0011] The CGL may comprise the phthalocyanine alone preferably in the form of a layer deposited on the substrate, or the phthalocyanine may be dispersed in a resin and formed into a layer on the substrate. Examples of suitable resins for use in the charge generating phase are polycarbonate, polyester, polystyrene, polyurethane, epoxy, acrylic, styrene-acrylic, melamine and silicone resins. Where the resin does not have good adhesive properties with respect to the substrate, e.g. a polycarbonate resin, adhesion between the resin and the substrate may be improved by the use of an adhesive resin. Specific examples of suitable resins for use in the charge generating phase are LEXAN 141 Natural (available from General Electric Plastics, Europe) and Styrene-Acrylate Resin E048 (available from Synres Nederland BV). A suitable adhesive resin for bonding the charge generating phase to the substrate is VMCA (available from Union Carbide).
[0012] The CTL preferably comprises a layer of a resin containing the compound of Formula I and preferably has a thickness from 1.0 microns (µ) to 50µ and more preferably from 5.0µ to 30µ. Examples of suitable resins for use in the charge transport phase include one or more of polycarbonate, polyester, polystyrene, polyurethane, epoxy, acrylic, styrene-acrylic, melamine and silicone resins.
[0013] The compounds of Formula I may be included in the CTL and the OPC may be prepared using methods described in the prior art.
Example 1
[0015] Using a K-bar coater, a composite photoreceptor was prepared having a substrate of 100 microns aluminised MELINEX polyester film, an adhesive layer of VMCA (Union Carbide) 0.1 micron, a CGL comprising a mixture of X-H₂ phthalocyanine (1 part) and LEXAN 141 polycarbonate (1 part), this layer (0.6 micron) being applied from dispersion in ethylene dichloride. The CTL overcoating the CGL comprised a mixture of the compound of Formula II wherein R¹ - R⁵ = H and R⁶ = R⁷ = Et (1 part) and LEXAN 141 polycarbonate (1 part), the 14 micron layer being applied from solution in ethylene dichloride.
[0016] The photoconductive properties of this sheet were assessed using a Kawaguchi Electric Works Model SP 428 Electrostatic Paper Analyser in the dynamic mode. The following results were obtained:
Test Conditions
Test Results
[0018] Surface voltage (V₁) 790
% Dark decay (after 5 seconds) 22%
Sensitivity (lux-sec) 0.85
Residual voltage 10
[0019] These results compare extremely favourably with those for other photoreceptor devices, particularly the important parameter, sensitivity. Typical values for state of the art photoreceptor devices are 5.0 to 8.0 lux-sec (J61189, 553A; J61189, 554A).
Example 2
[0020] A composite photoreceptor was prepared as for Example 1 except the X-H₂Pc was replaced by alpha-H₂Pc. The test conditions were as for Example 1.
Test results
[0021] Surface voltage (V₁) 580
% Dark decay (after 5 seconds) 27.6%
Sensitivity (lux-sec) 5.0
Residual voltage 10
Examples 3-9
[0022] Composite photoreceptors were prepared as described in Example 1 using the X-form of metal-free phthalocyanine as the charge generation material. The charge transfer material was a compound of the formula:
the individual compounds used in each Example being identified by the substituents as follows:
| Example | Y | Z |
| 3 | 1-naphthyl | 1-naphthyl |
| 4 | 2-naphthyl | 4-diethylaminophenyl |
| 5 | phenyl | 1-naphthyl |
| 6 | phenyl | 4-diethylaminophenyl |
| 7 | methyl | 4-diethylaminophenyl |
| 8 | phenyl | 2-methyl-4-diethylaminophenyl |
| 9 | 1-naphthyl | 4-diethylaminophenyl |
Test Conditions
Test Results
1. An organic photoconductor comprising an electrically conducting support, a charge
generation layer containing metal-free phthalocyanine in the X- or the alpha-polymorphic
form and a charge transport layer containing a compound of the formula:
wherein each of X and Z, independently, represents a phenyl or naphthyl radical and Y represents an alkyl, phenyl or naphthyl radical, each of X, Y and Z optionally carrying one or more non-ionic substituents.
wherein each of X and Z, independently, represents a phenyl or naphthyl radical and Y represents an alkyl, phenyl or naphthyl radical, each of X, Y and Z optionally carrying one or more non-ionic substituents.
2. An organic photoconductor according to claim 1 wherein, in the compounds of Formula
I,
X is phenyl,
Y is phenyl or 1- or 2-naphthyl, and
Z is 1- or 2-naphthyl or a 4-aminophenyl radical wherein the amino group is a secondary or tertiary amino group having alkyl, aralkyl or aryl substituents, the phenyl group optionally carrying one or more non-ionic substituents.
X is phenyl,
Y is phenyl or 1- or 2-naphthyl, and
Z is 1- or 2-naphthyl or a 4-aminophenyl radical wherein the amino group is a secondary or tertiary amino group having alkyl, aralkyl or aryl substituents, the phenyl group optionally carrying one or more non-ionic substituents.
3. An organic photoconductor according to claim 1 wherein the compound of formula
I has the structure:
wherein each of R¹, R², R³ and R⁴, independently, represents hydrogen, C₁₋₄-alkyl, C₁₋₄-alkoxy or halogen; R⁵ represents hydrogen, C₁₋₄-alkyl or C₁₋₄-alkoxy and each of R⁶ and R⁷, independently, represents an optionally substituted C₁₋₄-alkyl, aryl-C₁₋₄-alkyl or phenyl radical or R⁶ and R⁷ together with the attached nitrogen atom form a heterocyclic ring.
wherein each of R¹, R², R³ and R⁴, independently, represents hydrogen, C₁₋₄-alkyl, C₁₋₄-alkoxy or halogen; R⁵ represents hydrogen, C₁₋₄-alkyl or C₁₋₄-alkoxy and each of R⁶ and R⁷, independently, represents an optionally substituted C₁₋₄-alkyl, aryl-C₁₋₄-alkyl or phenyl radical or R⁶ and R⁷ together with the attached nitrogen atom form a heterocyclic ring.
4. An organic photoconductor according to claim 3 wherein each of R¹ to R⁵ is hydrogen
and each of R⁶ and R⁷ is C₁₋₄-alkyl.