JP4722758B2 - Electrophotographic photosensitive member, image forming apparatus, and process cartridge - Google Patents

Description

  The present invention relates to a single-layer type electrophotographic photoreceptor in which a photosensitive layer contains at least a specific electron transport material and a hole transport material.

  In recent years, there has been a remarkable development of information processing system machines using electrophotography. In particular, an optical printer that converts information into a digital signal and records information by light has a remarkable improvement in print quality and reliability. This digital recording technology is applied not only to printers but also to ordinary copying machines, and so-called digital copying machines have been developed. In addition, since a variety of information processing functions are added to a conventional copying machine equipped with this digital recording technology for analog copying, it is expected that its demand will increase further in the future. In addition, with the spread of personal computers and the improvement in performance, the progress of digital color printers for performing color output of images and documents is rapidly progressing.

  Electrophotographic photoreceptors used in these image forming apparatuses are roughly classified into organic photoreceptors and inorganic photoreceptors, but organic photoreceptors are easier to manufacture and less expensive than conventional inorganic photoreceptors, In recent years, it has been widely used because it has the advantages of various choices of photoconductor materials such as charge transport materials, charge generation materials, and binder resins, and a high degree of freedom in functional design.

The organic photoreceptor includes a single-layer photoreceptor in which a charge transport material (hole transport material, electron transport material) is dispersed in the same photosensitive layer together with a charge generation material, a charge generation layer containing the charge generation material, There is a laminated type photoreceptor in which a charge transport layer containing a charge transport material is laminated.
Most of the laminated photoreceptors are negatively charged, and the positively charged laminated photoreceptor has not been put into practical use. The reason is that an electron transport material having excellent electron transport ability, low toxicity, and high compatibility with the binder resin has not been put into practical use.

  On the other hand, a single-layer photoconductor including a charge generation material and a charge transport material in a single photosensitive layer can be produced by a simple manufacturing process, has improved optical characteristics due to fewer layer interfaces, and electron transport. It has been attracting attention in recent years because it has positive and negative sensitivities by including a material and a hole transport material, and is particularly advantageous in that it can cope with positive charging with low ozone generation and excellent charging uniformity.

In a single-layer photoreceptor, the charge generation material is usually contained over the entire photosensitive layer, so that the charge generation region is basically the entire layer. In general, a semiconductor laser (LD) or a light emitting diode (LED) is used as an exposure light source of a recent digital image forming apparatus, and the wavelength is mainly in the near infrared region of about 680 to 830 nm. When such a light source having a long wavelength region is used, the light penetrates to a deep region of the photosensitive layer, so that hole-electron pairs are formed over the entire layer. When hole-electron pairs are formed in all layers, movement of holes and electrons is likely to be hindered due to differences in hole and electron mobility, structural defects, recombination, and the like.
Therefore, the single-layer photoconductor is likely to cause sensitivity deterioration and a residual potential increase by repeated use, and an abnormal image called “afterimage” is likely to be generated.

  In general, an image forming apparatus using an electrophotographic method charges a photosensitive member (charging process), exposes an image to form an electrostatic latent image (exposure process), and a developing bias voltage is applied to the electrostatic latent image. In this state, the toner is developed (development process), and the formed toner image is transferred onto transfer paper (transfer process) and fixed to form an image. The residual toner on the photoconductor is cleaned by a urethane blade or the like (cleaning process), and the residual charge on the photoconductor is erased by an LED or the like (static elimination process).

Afterimage is exposed to light in the exposure process, the carrier remains in the exposure process, and the effect of exposure remains even after passing through the charge removal process. The electric potential becomes lower than that of the surroundings, and uneven density appears on the image.
Examples of single-layer photoconductors proposed so far include Patent Documents 1 to 5, etc., all of which are satisfactory in characteristics, such as significant deterioration of characteristics due to repeated use and occurrence of afterimages. It wasn't.
JP-A-8-328275 Japanese Patent Laid-Open No. 7-64301 JP-A-9-281729 JP-A-6-130688 JP-A-9-151157

  The present invention has been made in view of the above prior art, and an object of the present invention is to provide a single-layer photoconductor that does not produce an abnormal image such as an afterimage even when used repeatedly with high sensitivity.

As described above, the afterimage is considered to be caused by the carrier staying in the light-irradiated portion. Therefore, in the case of a single layer photoreceptor, it is necessary that both the electron transport material and the hole transport material have a sufficient charge transfer function.
Usually, the electron transport material is not sufficiently charged, so that carriers are likely to stay. However, the electron transport material represented by the following general formula (1) used in the present invention is an excellent electron. Since this material has a transport function, a highly sensitive single-layer photoreceptor having a sufficient electron transport function and hole transport function can be obtained by using this material.

However, it has been clarified that even a single-layer photoreceptor having such a sufficient charge transport function is liable to generate afterimages by repeated use.
As a result of studying a hole transport material to be combined in a single-layer photoreceptor using an electron transport material represented by the following general formula (1), the present inventors have found that hole transport represented by the following general formula (2) By combining with materials, it was found that no afterimage was generated even after repeated use, and the present invention was achieved.

(1) At least a photosensitive layer is provided on a conductive support, and the photosensitive layer is represented by at least a charge generation material, an electron transport material represented by the following general formula (1), and the following general formula (2). Ri Do a single layer containing a hole-transporting material, as diffraction peaks of Bragg angle 2 [Theta] (± 0.2 °) with respect to the charge generating material CuKα characteristic X-ray (wavelength 1.542 Å), at least 27.2 Has a maximum diffraction peak at °, further has major peaks at 9.4 °, 9.6 °, 24.0 °, and has a peak at 7.3 ° as the lowest diffraction peak. an electrophotographic photosensitive member, wherein titanyl phthalocyanine der Rukoto having no peak between 7.3 ° peak and 9.4 ° peak.
(In the above general formula, R1 and R2 are each independently a group selected from the group consisting of a hydrogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group, and a substituted or unsubstituted aralkyl group. R 3, R 4, R 5, R 6, R 7, R 8, R 9, R 10 are each independently a hydrogen atom, halogen atom, cyano group, nitro group, amino group, hydroxyl group, substituted or unsubstituted alkyl group, substituted or unsubstituted Represents a group selected from the group consisting of a substituted cycloalkyl group and a substituted or unsubstituted aralkyl group.
(In the above general formula, R11, R12, R13, R14, R17, R18, R19, R20 represent a hydrogen atom, a halogen atom, an alkoxy group, or an optionally substituted alkyl group or aryl group, and R15, R16 represent a hydrogen atom. Represents a halogen atom, an alkyl group, or an alkoxy group.)

(2) R1 and R2 of the electron transport material represented by the general formula (1) are each independently an alkyl group substituted with an alkyl group or an alkoxy group, and R3, R4, R5, R6, R7, R8 , R9, and R10 are each independently a group selected from the group consisting of a hydrogen atom, a halogen atom, and an alkyl group, and R11, R12, R13, R14, and R17 of the hole transport material represented by the general formula (2). , R18, R19, R20 are a hydrogen atom, an alkoxy group or an alkyl group, and R15, R16 are a hydrogen atom or an alkyl group.
(3) The electron transport material represented by the general formula (1) is represented by the following formulas (1-1), (1-2), (1-6), (1-7), (1-8), A hole transport material represented by the general formula (2), which is a compound selected from the group consisting of (1-9) and (1-11), is represented by the following formulas (2-1) and (2-5). , (2-6), (2-7), (2-8), (2-11), (2-13), and (2-15). The electrophotographic photosensitive member according to (1) or (2).

( 4 ) An image forming apparatus comprising the electrophotographic photosensitive member according to any one of (1) to ( 3 ).
( 5 ) The image forming apparatus includes a plurality of electrophotographic photosensitive members, and forms a color image by sequentially superimposing single color toner images developed on the respective electrophotographic photosensitive members. The image forming apparatus according to ( 4 ) above.
( 6 ) A process cartridge for an image forming apparatus that is detachable from the apparatus main body and has at least an electrophotographic photosensitive member, wherein the electrophotographic photosensitive member is any one of (1) to ( 3 ). A process cartridge comprising the electrophotographic photosensitive member according to the description.
( 7 ) An image forming apparatus comprising the process cartridge according to ( 6 ).
( 8 ) An image forming apparatus comprising a plurality of process cartridges according to ( 6 ).

The electron transport material represented by the general formula (1) used in the present invention has a very excellent electron transport function, and the hole transport material represented by the general formula (2) is an excellent hole. A photoconductor in which both are combined due to the transport function is a highly sensitive photoconductor excellent in the mobility of electrons and holes.
Even if the photoconductor using the electron transport material represented by the general formula (1) and the hole transport material represented by the general formula (2) of the present invention as a charge transport material is used repeatedly, sensitivity and residual potential are maintained. The characteristics such as chargeability are stable. In addition to the good compatibility between the electron transport material represented by the general formula (1) and the hole transport material represented by the general formula (2), the electron transport material represented by the general formula (1) is charged. It is thought that having extremely excellent resistance to the oxidizing gas generated in the process also has an influence.

  In general, the electron transport material and the hole transport material form a charge transfer complex, and the electron transport material or the hole transport material alone absorbs in a wavelength region where there is no absorption. This absorption occurs in a wavelength region of approximately 600 nm to 800 nm. That is, the transmittance of the photosensitive layer is lowered in the wavelength region (around 680 to 830 nm) of LDs and LEDs that are often used as exposure light sources in recent digital image forming apparatuses.

When the electron transport material represented by the general formula (1) of the present invention is combined with the hole transport material represented by the general formula (2), the decrease in the transmittance is specifically increased.
When the transmittance of the photosensitive layer is lowered, light does not reach the depth of the photosensitive layer, so that charge generation by exposure is limited to the vicinity of the surface of the photosensitive layer. Therefore, when forming an electrostatic latent image, the carrier travel distance from the generation of charge to the cancellation of surface charge is shortened, so that it is less susceptible to Coulomb repulsion, and it is possible to form a high-resolution latent image that is faithful to exposure. .
In the case where carriers are generated in all layers of the photosensitive layer, it is likely to cause trouble in carrier movement due to the interaction between the generated carriers, and it is easy to cause afterimages due to carrier retention and a decrease in sensitivity. When the electron transporting material represented by (1) and the hole transporting material represented by the general formula (2) are combined, charge generation is limited only to the vicinity of the surface of the photosensitive layer, and there is an extra charge inside the photosensitive layer. Since carrier generation is suppressed, it is considered that carrier movement is smooth.

  As described above, the single-layer photoreceptor using the electron transport material represented by the general formula (1) and the hole transport material represented by the general formula (2) of the present invention includes an electron transport material and a hole transport material. In addition, the charge transport function of the photosensitive layer is excellent, and the transmittance of the photosensitive layer is greatly reduced due to the formation of a charge transfer complex, and unnecessary carrier generation inside the photosensitive layer is suppressed. And the occurrence of afterimages can be suppressed.

  The characteristics of the charge generation material are improved by using a specific material. In the present invention, it is possible to use a known material as the charge generation material, but among them, those having a phthalocyanine structure are preferable in combination with the charge transport material (electron transport material, hole transport material) used in the present invention. In addition, it is possible to obtain a photoconductor having a low residual potential and little deterioration in characteristics due to repeated use of the photoconductor.

Among them, in particular, by using titanyl phthalocyanine as shown in the following structural formula (1) having titanium as a central metal, it is possible to obtain a particularly high-sensitivity photoreceptor and further increase the speed of the image forming apparatus. It becomes possible.

  References relating to the synthesis method and electrophotographic properties of titanyl phthalocyanine include, for example, JP-A-57-148745, JP-A-59-36254, JP-A-59-44054, and JP-A-59-31965. JP, 61-239248, JP, 62-67094, A, etc. are mentioned. In addition, various crystal systems are known for titanyl phthalocyanine. JP-A 59-49544, JP-A 59-166959, JP-A 61-239248, JP-A 62-67094. JP-A-63-366, JP-A-63-116158, JP-A-64-17066, JP-A-2001-19871, etc. each describe a titanyl phthalocyanine having a different crystal form. .

  Of these crystal forms, titanyl phthalocyanine having a maximum diffraction peak at 27.2 ° with a Bragg angle 2θ exhibits particularly excellent sensitivity characteristics and is used favorably. In particular, it has a maximum diffraction peak at 27.2 ° described in JP-A-2001-19871, and further has main peaks at 9.4 °, 9.6 °, and 24.0 °, In addition, by using titanyl phthalocyanine having a peak at 7.3 ° as the diffraction peak on the lowest angle side and having no peak between the 7.3 ° peak and the 9.4 ° peak, Without losing sensitivity, it is possible to obtain a stable electrophotographic photosensitive member that does not cause a decrease in chargeability even when used repeatedly.

  According to the present invention, there is provided a single-layer photoreceptor that does not produce an abnormal image such as an afterimage even when used repeatedly with high sensitivity. Also, by using this, an image forming apparatus capable of performing high-quality image formation over a long period of time is provided. In addition, a process cartridge with high convenience in handling is provided.

The electrophotographic photoreceptor of the present invention will be described in detail below with reference to the drawings.
FIG. 7 is a cross-sectional view schematically showing an example of an electrophotographic photosensitive member having the layer structure of the present invention, in which a photosensitive layer (22) is provided on a conductive support (21).
Examples of the conductive support (21) include those having a volume resistance of 10 ¹⁰ Ω · cm or less, such as metals such as aluminum, nickel, chromium, nichrome, copper, silver, gold, platinum, iron, tin oxide, An oxide such as indium oxide coated with film or cylindrical plastic or paper by vapor deposition or sputtering, or a plate of aluminum, aluminum alloy, nickel, stainless steel, etc., and drawing ironing method or impact ironing method It is possible to use pipes that have been surface-treated by cutting, superfinishing, polishing, etc. after being made into raw pipes by methods such as the Extruded Ironing method, Extruded Drawing method, and cutting method.

The photosensitive layer in the present invention comprises a single layer containing a charge generating material, an electron transport material of the general formula (1) and a hole transport material of the general formula (2).
First, the charge generation material in the present invention will be described.
As the charge generation material used in the present invention, a known material can be used. For example, phthalocyanine pigments such as metal phthalocyanine and metal-free phthalocyanine, azulenium salt pigments, squaric acid methine pigments, azo pigments having a carbazole skeleton, azo pigments having a triphenylamine skeleton, azo pigments having a diphenylamine skeleton, dibenzo An azo pigment having a thiophene skeleton, an azo pigment having a fluorenone skeleton, an azo pigment having an oxadiazol skeleton, an azo pigment having a bisstilbene skeleton, an azo pigment having a distyryl oxadiazol skeleton, and a distyrylcarbazole skeleton Azo pigments, perylene pigments, anthraquinone or polycyclic quinone pigments, quinoneimine pigments, diphenylmethane and triphenylmethane pigments, benzoquinone and naphthoquinone pigments, cyanine and azomethine pigments, Jigoido pigments, bisbenzimidazo - such as Le based pigments. These charge generation materials can be used alone or as a mixture of two or more.

In the present invention, phthalocyanine pigments are particularly preferable from the viewpoint of various properties necessary for the present invention.
Among them, in particular, the titanyl phthalocyanine as shown in the structural formula (1) having titanium as a central metal makes it possible to obtain a photosensitive layer having particularly high sensitivity, and the speed of the electrophotographic apparatus can be further increased. It becomes possible. Further, among various crystal forms, titanyl phthalocyanine having a maximum diffraction peak at 27.2 ° with a Bragg angle 2θ exhibits particularly excellent sensitivity characteristics and is used favorably. In particular, it has a maximum diffraction peak at 27.2 ° described in JP-A-2001-19871, and further has main peaks at 9.4 °, 9.6 °, and 24.0 °, In addition, by using titanyl phthalocyanine having a peak at 7.3 ° as the diffraction peak on the lowest angle side and having no peak between the 7.3 ° peak and the 9.4 ° peak, Without losing sensitivity, it is possible to obtain a stable electrophotographic photosensitive member that does not cause a decrease in chargeability even when used repeatedly.

Next, the charge transport material will be described.
The electron transport material represented by the general formula (1) used in the present invention has a structural skeleton shown below.
(In the above general formula, R1 and R2 are each independently a group selected from the group consisting of a hydrogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group, and a substituted or unsubstituted aralkyl group. R 3, R 4, R 5, R 6, R 7, R 8, R 9, R 10 are each independently a hydrogen atom, halogen atom, cyano group, nitro group, amino group, hydroxyl group, substituted or unsubstituted alkyl group, substituted or unsubstituted Represents a group selected from the group consisting of a substituted cycloalkyl group and a substituted or unsubstituted aralkyl group.

  The substituted or unsubstituted alkyl group is an alkyl group having 1 to 25 carbon atoms, preferably 1 to 10 carbon atoms, specifically a methyl group, an ethyl group, an n-propyl group, an n- Straight chain such as butyl group, n-pentyl group, n-hexyl group, n-peptyl group, n-octyl group, n-nonyl group, n-decyl group, i-propyl group, s-butyl group, t -Branched group such as butyl group, methylpropyl group, dimethylpropyl group, ethylpropyl group, diethylpropyl group, methylbutyl group, dimethylbutyl group, methylpentyl group, dimethylpentyl group, methylhexyl group, dimethylhexyl group, alkoxy Alkyl group, monoalkylaminoalkyl group, dialkylaminoalkyl group, halogen-substituted alkyl group, alkylcarbonylalkyl group, Kishiarukiru group, alkanoyloxy group, an aminoalkyl group, esterified optionally alkyl group substituted with a carboxyl group which have an alkyl group substituted by a cyano group are exemplified. The substitution position of these substituents is not particularly limited, and a group in which a part of carbon atoms of the substituted or unsubstituted alkyl group is substituted with a hetero atom (N, O, S, etc.) is also substituted. Included in the alkyl group.

  The substituted or unsubstituted cycloalkyl group includes a cycloalkyl ring having 3 to 25 carbon atoms, preferably 3 to 10 carbon atoms, specifically, a homocyclic ring from cyclopropane to cyclodecane, methylcyclo Those having an alkyl substituent such as pentane, dimethylcyclopentane, methylcyclohexane, dimethylcyclohexane, trimethylcyclohexane, tetramethylcyclohexane, ethylcyclohexane, diethylcyclohexane, t-butylcyclohexane, alkoxyalkyl groups, monoalkylaminoalkyl groups, dialkylamino Alkyl group, halogen-substituted alkyl group, alkoxycarbonylalkyl group, carboxyalkyl group, alkanoyloxyalkyl group, aminoalkyl group, halogen atom, amino group, esterified Which may be a carboxyl group, a cycloalkyl group substituted by a cyano group and the like. The substitution position of these substituents is not particularly limited, and a group in which a part of carbon atoms of the substituted or unsubstituted cycloalkyl group is substituted with a hetero atom (N, O, S, etc.) is also substituted. It is included in the cycloalkyl group.

Examples of the substituted or unsubstituted aralkyl group include groups in which an aromatic ring is substituted on the above-described substituted or unsubstituted alkyl group, and an aralkyl group having 6 to 14 carbon atoms is preferable. More specifically, benzyl group, perfluorophenylethyl group, 1-phenylethyl group, 2-phenylethyl group, terphenylethyl group, dimethylphenylethyl group, diethylphenylethyl group, t-butylphenylethyl group, 3- Examples thereof include a phenylpropyl group, a 4-phenylbutyl group, a 5-phenylpentyl group, a 6-phenylhexyl group, a benzhydryl group, and a trityl group.
Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.

Examples of the method for producing the electron transport material represented by the general formula (1) include the following methods. Naphthalenecarboxylic acid is synthesized from the following reaction formula according to a known synthesis method (for example, US Pat. No. 6,794,102, Industrial Organic Pigments 2nd edition, VCH, 485 (1997)).
In the formula, Rn represents R3, R4, R7, R8, and Rm represents R5, R6, R9, R10.

  The electron transport material represented by the general formula (1) used in the present invention is a method of reacting the above naphthalenecarboxylic acid or its anhydride with amines to monoimidize, or using a buffer solution for naphthalenecarboxylic acid or its anhydride. It is obtained by a method of adjusting pH and reacting with diamines. Monoimidization is carried out without solvent or in the presence of a solvent. The solvent is not particularly limited, but it does not react with raw materials or products such as benzene, toluene, xylene, chloronaphthalene, acetic acid, pyridine, methylpyridine, dimethylformamide, dimethylacetamide, dimethylethyleneurea, dimethylsulfoxide, and the like. It is good to use what can be made to react at the temperature of -250 degreeC. For pH adjustment, a buffer solution prepared by mixing a basic aqueous solution such as lithium hydroxide or potassium hydroxide with an acid such as phosphoric acid is used. Carboxylic acid derivative dehydration reaction obtained by reacting carboxylic acid with amines or diamines is carried out in the absence of a solvent or in the presence of a solvent. Although there is no restriction | limiting in particular as a solvent, It is good to use what reacts at the temperature of 50 to 250 degreeC, without reacting with raw materials and products, such as benzene, toluene, chloronaphthalene, bromonaphthalene, and acetic anhydride. Any reaction may be carried out without a catalyst or in the presence of a catalyst, and is not particularly limited. For example, molecular sieves, benzenesulfonic acid, p-toluenesulfonic acid and the like can be used as a dehydrating agent.

The hole transport material represented by the general formula (2) used in the present invention has a structural skeleton shown below.
In the formula, R11, R12, R13, R14, R17, R18, R19, R20 each represents a hydrogen atom, a halogen atom, an alkoxy group, or an optionally substituted alkyl group or aryl group, and R15, R16 each represents a hydrogen atom, a halogen atom, Represents an alkyl group or an alkoxy group;

Examples of the alkyl group include chain alkyl groups such as a methyl group, an ethyl group, and a propyl group, and cyclic alkyl groups such as a cyclohexyl group and a cycloheptyl group.
Examples of the aryl group include a phenyl group, a naphthyl group, and an anthryl group.
Examples of the halogen atom include a fluorine atom, a chlorine atom, and a bromine atom.
Examples of the alkoxy group include a methoxy group, an ethoxy group, and a propoxy group.
Examples of the substituent that each of the above groups may have include alkyl groups such as a methyl group, an ethyl group, a propyl group, a cyclohexyl group, and a cycloheptyl group, a nitro group, and a halogen atom such as a fluorine atom, a chlorine atom, and a bromine atom. Atoms, halogenated alkyl groups such as perfluoroalkyl groups, aryl groups such as phenyl groups, naphthyl groups, anthryl groups, aralkyl groups such as benzyl groups and phenethyl groups, methoxy groups, ethoxy groups, propoxy groups, etc. An alkoxy group etc. are mentioned.

Preferred examples of the electron transport material represented by the general formula (1) and the hole transport material represented by the general formula (2) are given below.
However, the present invention is not limited to these compounds.

In the present invention, it is essential to include the electron transport material of the general formula (1) and the hole transport material of the general formula (2). In addition to this, a known charge transport material, that is, an electron transport material, A hole transport material can also be used in combination.
Examples of the electron transport material include chloroanil, bromoanil, 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-4H-indeno [1,2-b] thiophen-4-one, 1,3,7-tri Examples thereof include electron accepting substances such as nitrodibenzothiophene-5,5-dioxide.
These electron transport materials may be used alone or as a mixture of two or more.

As the hole transport material, an electron donating substance is preferably used.
Examples thereof include oxazole derivatives, oxadiazole derivatives, imidazole derivatives, triphenylamine derivatives, 9- (p-diethylaminostyrylanthracene), 1,1-bis- (4-dibenzylaminophenyl) propane, styrylanthracene, Examples include styrylpyrazolines, phenylhydrazones, α-phenylstilbene derivatives, thiazole derivatives, triazole derivatives, phenazine derivatives, acridine derivatives, benzofuran derivatives, benzimidazole derivatives, and thiophene derivatives.
These hole transport materials may be used alone or as a mixture of two or more.

Known polymer compounds can be used as the polymer compound that can be used as the binder component of the photosensitive layer. For example, polystyrene, styrene / acrylonitrile copolymer, styrene / butadiene copolymer, styrene / maleic anhydride copolymer, polyester, polyvinyl chloride, vinyl chloride / vinyl acetate copolymer, polyvinyl acetate, polyvinylidene chloride, Thermoplastic such as polyarylate resin, polycarbonate, cellulose acetate resin, ethyl cellulose resin, polyvinyl butyral, polyvinyl formal, polyvinyl toluene, acrylic resin, silicone resin, fluorine resin, epoxy resin, melamine resin, urethane resin, phenol resin, alkyd resin Although thermosetting resin is mentioned, it is not limited to these.
Among these polymer compounds, polycarbonate resin is particularly preferable from the viewpoint of film quality.

  As a method for forming the photosensitive layer, a casting method from a solution dispersion system is preferable. In order to provide a photosensitive layer by the casting method, a coating solution prepared by dispersing or dissolving a charge generating material, a charge transporting material, a binder resin, and, if necessary, other components in an appropriate solvent is adjusted to an appropriate concentration. Adjust and apply.

In order to uniformly disperse the charge generation material in the photosensitive layer (in the coating solution), the charge generation material is previously ball milled with a binder resin, if necessary, using a solvent such as tetrahydrofuran, cyclohexanone, dioxane, dichloroethane, butanone, It is preferable to prepare a dispersion liquid dispersed by an attritor, a sand mill or the like.
Application can be performed by dip coating, spray coating, bead coating, or the like.

  Examples of the dispersion solvent that can be used in preparing the photosensitive layer coating solution provided as described above include ketones such as methyl ethyl ketone, acetone, methyl isobutyl ketone, and cyclohexanone, and ethers such as dioxane, tetrahydrofuran, and ethyl cellosolve. And aromatics such as toluene and xylene, halogens such as chlorobenzene and dichloromethane, and esters such as ethyl acetate and butyl acetate. These solvents can be used alone or in combination.

  In the photosensitive layer, the charge generating material is 0.1 to 30% by weight, preferably 0.5 to 10% by weight, based on the entire photosensitive layer. The electron transport material is suitably 5 to 300 parts by weight, preferably 10 to 150 parts by weight, based on 100 parts by weight of the binder resin component. However, the electron transport material represented by the general formula (1) is preferably 50 to 100% by weight with respect to the entire electron transport material. The hole transport material is suitably 5 to 300 parts by weight, preferably 20 to 150 parts by weight with respect to 100 parts by weight of the binder resin component. However, the hole transport material represented by the general formula (2) is preferably 50 to 100% by weight with respect to the whole hole transport material. The total amount of the electron transport material and the hole transport material is 20 to 300 parts by weight, preferably 30 to 200 parts by weight, based on 100 parts by weight of the binder resin component.

Further, if necessary, low-molecular compounds such as antioxidants, plasticizers, lubricants and ultraviolet absorbers and leveling agents can be added to the photosensitive layer. These compounds can be used alone or as a mixture of two or more. The amount of the low molecular compound used is 0.1 to 50 parts by weight, preferably 0.1 to 20 parts by weight, based on 100 parts by weight of the binder resin, and the amount of leveling agent used is 100 parts by weight of the binder resin. About 0.001 to 5 parts by weight is appropriate.
The film thickness of the photosensitive layer is suitably about 5 to 40 μm, preferably about 15 to 35 μm.

As shown in FIG. 8, the electrophotographic photosensitive member used in the present invention may be provided with an undercoat layer (23) between the conductive support (21) and the photosensitive layer (22). The undercoat layer is provided for the purpose of improving adhesiveness, improving the coatability of the upper layer, reducing the residual potential, and preventing charge injection from the conductive support.
In general, the undercoat layer is mainly composed of a resin. However, considering that the photosensitive layer is applied on the resin using a solvent, the resin is a resin having high resistance to general organic solvents. Examples of such resins include water-soluble resins such as polyvinyl alcohol, casein, and sodium polyacrylate, alcohol-soluble resins such as copolymer nylon and methoxymethylated nylon, polyurethane, melamine resin, alkyd-melamine resin, and epoxy. Examples thereof include a curable resin that forms a three-dimensional network structure such as a resin.

  In addition, a fine powder such as a metal oxide such as titanium oxide, silica, alumina, zirconium oxide, tin oxide, or indium oxide, or a metal sulfide or metal nitride may be added to the undercoat layer. These undercoat layers can be formed using an appropriate solvent and coating method, as in the case of the above-described photosensitive layer.

Further, as the undercoat layer, a metal oxide layer formed by using, for example, a sol-gel method using a silane coupling agent, a titanium coupling agent, a chromium coupling agent, or the like is also useful. In addition to this, alumina is provided by anodic oxidation, organic materials such as polyparaxylylene (parylene), and inorganic materials such as silicon oxide, tin oxide, titanium oxide, ITO, ceria are provided by the vacuum thin film manufacturing method. It can be used well as an undercoat layer.
The thickness of the undercoat layer is suitably from 0.1 to 10 μm, more preferably from 1 to 5 μm.
In the present invention, an antioxidant, a plasticizer, an ultraviolet absorber, and a leveling agent can be added to the photosensitive layer in order to improve gas barrier properties and environmental resistance.

Next, the image forming apparatus of the present invention will be described.
FIG. 1 is a schematic view for explaining an image forming apparatus of the present invention, and modifications as described later also belong to the category of the present invention.
In FIG. 1, a photoreceptor (11) is a photoreceptor that satisfies the requirements of the present invention. Although the photoconductor (11) has a drum shape, it may have a sheet shape or an endless belt shape.
As the charging means (12), known means such as a corotron, a scorotron, a solid state charger (solid state charger), and a charging roller are used. The charging means (12) is preferably used in contact with or in close proximity to the photoreceptor from the viewpoint of reducing power consumption. In particular, in order to prevent contamination of the charging means (12), a charging mechanism disposed in the vicinity of the photoreceptor having an appropriate gap between the photoreceptor and the surface of the charging means is desirable.
In the present invention, either positive or negative can be used as the polarity of the charge. However, the positive charge is more preferable than the negative charge because the chargeability is stable and the amount of ozone generated is small.

As the transfer means (16), the above charger can be generally used, but a combination of a transfer charger and a separation charger is effective.
The light source used for the exposure means (13), the charge removal means (1A), etc. includes fluorescent lamps, tungsten lamps, halogen lamps, mercury lamps, sodium lamps, light emitting diodes (LEDs), semiconductor lasers (LDs), electroluminescence ( EL) in general. Various types of filters such as a sharp cut filter, a band pass filter, a near infrared cut filter, a dichroic filter, an interference filter, and a color temperature conversion filter can be used to irradiate only light in a desired wavelength range.

  The toner (15) developed on the photoreceptor by the developing means (14) is transferred to the image receiving medium (18), but not all is transferred, and toner remaining on the photoreceptor is also generated. Such toner is removed from the photoreceptor by the cleaning means (17). As the cleaning means, a rubber cleaning blade, a brush such as a fur brush, a mag fur brush, or the like can be used.

FIG. 2 shows another example of an electrophotographic process according to the present invention. In FIG. 2, the photoconductor (11) satisfies the requirements of the present invention and has an endless belt shape.
Driven by drive means (1C), charged by charging means (12), image exposure by exposure means (13), development (not shown), transfer by transfer means (16), cleaning by pre-cleaning exposure means (1B). Pre-exposure, cleaning by the cleaning means (17), and static elimination by the static elimination means (1A) are repeated. In FIG. 2, light irradiation for pre-cleaning exposure is performed from the support side of the photoreceptor (in this case, the support is translucent).

  The above electrophotographic process exemplifies an embodiment of the present invention, and other embodiments are of course possible. For example, in FIG. 2, the pre-cleaning exposure is performed from the support side, but this may be performed from the photosensitive layer side, or image exposure and neutralization light irradiation may be performed from the support side. On the other hand, the light irradiation process is illustrated as image exposure, pre-cleaning exposure, and static elimination exposure. In addition, a pre-transfer exposure, a pre-exposure of image exposure, and other known light irradiation processes are provided to light the photosensitive member. Irradiation can also be performed.

  Further, the image forming means as described above may be fixedly incorporated in a copying machine, a facsimile, or a printer, but may be incorporated in these apparatuses in the form of a process cartridge. A process cartridge is a single device (part) that contains a photosensitive member and includes a charging unit, an exposure unit, a developing unit, a transfer unit, a cleaning unit, and a charge eliminating unit. There are many shapes and the like of the process cartridge, but a general example is shown in FIG. Also in this case, the photoreceptor (11) is a photoreceptor that satisfies the requirements of the present invention. Although the photoconductor (11) has a drum shape, it may have a sheet shape or an endless belt shape.

  FIG. 4 shows an example of a full-color image forming apparatus according to the present invention. In this electrophotographic apparatus, charging means (charging device) (12), exposure means (13), black (Bk), cyan (C), magenta (M), and yellow (Y) are disposed around the photoreceptor (11). Developing means (14Bk, 14C, 14M, 14Y) for each color toner, an intermediate transfer belt (1F) as an intermediate transfer member, and a cleaning means (17) are arranged in this order. Here, the subscripts Bk, C, M, and Y shown in the figure correspond to the color of the toner, and are added or omitted as appropriate.

  The photoreceptor (11) is an electrophotographic photoreceptor that satisfies the requirements of the present invention. Each color developing means (14Bk, 14C, 14M, 14Y) can be controlled independently, and only the color developing means for image formation is driven. The toner image formed on the photoreceptor (11) is transferred onto the intermediate transfer belt (1F) by the first transfer means (1D) disposed inside the intermediate transfer belt (1F). The first transfer means (1D) is arranged so as to be able to come into contact with and separate from the photoreceptor (11), and the intermediate transfer belt (1F) is brought into contact with the photoreceptor (11) only during the transfer operation. The respective color images are sequentially formed, and the toner images superimposed on the intermediate transfer belt (1F) are collectively transferred to the image receiving medium (18) by the second transfer means (1E) and then fixed by the fixing means (19). The image is formed by fixing. The second transfer means (1E) is also arranged so as to be able to contact and separate from the intermediate transfer belt (1F), and abuts on the intermediate transfer belt (1F) only during the transfer operation.

  In the transfer drum type electrophotographic apparatus, since the toner images of the respective colors are sequentially transferred onto the transfer material electrostatically attracted to the transfer drum, there is a limitation on the transfer material that cannot be printed on cardboard, as shown in FIG. Such an intermediate transfer type electrophotographic apparatus has an advantage that the toner images of the respective colors are superimposed on the intermediate transfer body (1F), and thus are not limited by the transfer material. Such an intermediate transfer method is not limited to the apparatus shown in FIG. 4, but can be applied to the electrophotographic apparatus shown in FIGS. 1, 2, and 3 and FIG. 5 (a specific example is shown in FIG. 6) described later. it can.

  FIG. 5 shows another example of a full-color image forming apparatus according to the present invention. This image forming apparatus is of a type using four colors of yellow (Y), magenta (M), cyan (C), and black (Bk) as toner, and an image forming unit is provided for each color. In addition, photoconductors (11Y, 11M, 11C, 11Bk) for each color are provided. The photoreceptor used in this electrophotographic apparatus is a photoreceptor that satisfies the requirements of the present invention. Around each photoconductor (11Y, 11M, 11C, 11Bk), charging means (12Y, 12M, 12C, 12Bk), exposure means (13Y, 13M, 13C, 13Bk), developing means (14Y, 14M, 14C, 14Bk), cleaning means (17Y, 17M, 17C, 17Bk) and the like are provided. Further, a transfer transfer belt (1G) as a transfer material carrier that comes in contact with and separates from each transfer position of each photoconductor (11Y, 11M, 11C, 11Bk) arranged on a straight line is hung by a driving means (1C). Has been passed. Transfer means (16Y, 16M, 16C, 16Bk) are disposed at transfer positions facing the respective photoconductors (11Y, 11M, 11C, 11Bk) with the conveyance transfer belt (1G) interposed therebetween.

  The image forming means as described above may be fixedly incorporated in a copying apparatus, a facsimile, or a printer, but may be incorporated in these apparatuses in the form of a process cartridge. A process cartridge is a single device (part) that contains a photoconductor and further includes a charging unit, an exposure unit, a developing unit, a transfer unit, a cleaning unit, a neutralizing unit, and the like.

  Hereinafter, the present invention will be described by way of examples. Note that this does not limit the scope of the present invention. All parts are parts by weight.

( Reference Example 1)
Metal-free phthalocyanine was dispersed under the following composition and conditions to prepare a pigment dispersion.
Metal-free phthalocyanine pigment (Dainippon Ink Industries, Ltd .: Fastogen Blue 8120B): 3 parts Cyclohexanone: 97 parts These were placed in a glass pot with a diameter of 9 cm and dispersed for 5 hours at a rotation speed of 100 rpm using PSZ balls with a diameter of 0.5 mm. To obtain a pigment dispersion.
A photoreceptor coating solution having the following composition was prepared using the pigment dispersion.
Pigment dispersion: 60 parts Electron transport material of Exemplified compound 1-1: 25 parts Hole transport material of Exemplified compound 2-1: 25 parts Z-type polycarbonate resin (manufactured by Teijin Chemicals Ltd .: Panlite TS-2050): 50 parts Silicone oil (manufactured by Shin-Etsu Chemical Co., Ltd .: KF50): 0.01 part Tetrahydrofuran: 350 parts The coating solution for photosensitive layer thus obtained was applied on an aluminum drum having a diameter of 30 mm and a length of 340 mm by a dip coating method at 120 ° C. And dried for 20 minutes to form a photosensitive layer having a thickness of 25 μm, thereby preparing a photosensitive member (referred to as photosensitive member 1).

(Example 2)
A photoconductor was prepared in the same manner as in Reference Example 1 except that titanyl phthalocyanine prepared according to the following synthesis example was used instead of the metal-free phthalocyanine pigment (Fastogen Blue 8120B) used in Reference Example 1 (Photoconductor 2). And).
(Titanyl phthalocyanine used in Example 2)
A pigment was prepared according to Japanese Patent Application Laid-Open No. 2001-19871. That is, 29.2 g of 1,3-diiminoisoindoline and 200 ml of sulfolane are mixed, and 20.4 g of titanium tetrabutoxide is added dropwise under a nitrogen stream. After completion of the dropwise addition, the temperature was gradually raised to 180 ° C., and the reaction was carried out by stirring for 5 hours while maintaining the reaction temperature between 170 ° C. and 180 ° C. After completion of the reaction, the mixture was allowed to cool and then the precipitate was filtered, washed with chloroform until the powder turned blue, then washed several times with methanol, further washed several times with hot water at 80 ° C. and dried, Crude titanyl phthalocyanine was obtained. Dissolve the crude titanyl phthalocyanine in 20 times the amount of concentrated sulfuric acid, add dropwise to 100 times the amount of ice water with stirring, filter the precipitated crystals, and then repeat washing with water until the washing solution becomes neutral (ion-exchanged water after washing). PH value was 6.8), and a titanyl phthalocyanine pigment wet cake (water paste) was obtained. 40 g of the obtained wet cake (water paste) was put into 200 g of tetrahydrofuran, stirred for 4 hours, filtered and dried to obtain titanyl phthalocyanine powder.
The solid content concentration of the wet cake was 15 wt%. The weight ratio of the crystal conversion solvent to the wet cake is 33 times.

The obtained titanyl phthalocyanine powder was subjected to X-ray diffraction spectrum measurement under the following conditions. As a diffraction peak (± 0.2 °) with a Bragg angle 2θ with respect to the characteristic X-ray of Cu-Kα (wavelength 1.542 mm), at least It has a maximum diffraction peak at 27.2 °, and further main peaks at 9.4 °, 9.6 °, and 24.0 °, and a peak at 7.3 ° as the lowest diffraction peak. And titanyl phthalocyanine powder having no peak between the peak at 7.3 ° and the peak at 9.4 °.
An X-ray diffraction spectrum is shown in FIG.
(X-ray diffraction spectrum measurement conditions)
X-ray tube: Cu
Voltage: 50kV
Current: 30mA
Scanning speed: 2 ° / min Scanning range: 3 ° to 40 °
Time constant: 2 seconds

(Examples 3 to 15)
Photoconductors were prepared in the same manner as in Example 2 except that the electron transport materials and hole transport materials used in Example 2 were changed to those shown in Table 3 (referred to as photoconductors 3 to 15).

(Comparative Example 1)
A photoconductor was prepared in the same manner as in Example 2 except that the hole transport material used in Example 2 was changed to a hole transport material (HTM1) having the following structure (referred to as photoconductor 16).

(Comparative Example 2)
A photoconductor was prepared in the same manner as in Example 2 except that the hole transport material used in Example 2 was changed to a hole transport material (HTM2) having the following structure (referred to as Photoconductor 17).

(Comparative Example 3)
A photoconductor was prepared in the same manner as in Example 2 except that the hole transport material used in Example 2 was changed to a hole transport material (HTM3) having the following structure (referred to as photoconductor 18).

(Comparative Example 4)
A photoconductor was prepared in the same manner as in Example 2 except that the electron transport material used in Example 2 was changed to an electron transport material (ETM1) having the following structure (hereinafter referred to as photoconductor 19).

(Comparative Example 5)
A photoconductor was prepared in the same manner as in Example 2 except that the electron transport material used in Example 2 was changed to an electron transport material (ETM2) having the following structure (referred to as photoconductor 20).

(Photoreceptor Evaluation Example 1)
After the photoreceptors 1 to 20 are mounted for mounting as described above, they are mounted on an electrophotographic apparatus (Ricoh's imgio Neo 270 remodeled machine, a power pack is replaced to be positively charged), and the writing rate is 5%. A printing durability test was performed on a total of 50,000 sheets printed using a chart (characters equivalent to 5% as an image area are written on the entire A4 surface).
The toner and developer used were exchanged for toner and developer having polarity reversed from those dedicated to imgio Neo 270.
In addition, the charging means of the electrophotographic apparatus uses an external power source, and the bias voltage applied to the charging roller is set so that the charging potential of the photosensitive member at the start of the test is +600 V. The test is performed under this charging condition until the end of the test. Went. The developing bias was + 450V. The test environment is 23 ° C. and 55% RH.

Image evaluation (afterimage and resolution evaluation) and bright portion potential were evaluated before and after the printing durability test.
Image evaluation: An evaluation image having a black solid portion and a halftone portion as shown in FIG. 10 was output, and an afterimage was evaluated. In addition, the dot formation state (dot scattering state and dot reproducibility) was observed for the halftone portion, and the resolution was evaluated.
Rank evaluation was performed for both afterimage and resolution. The evaluation rank is as follows.
<Afterimage rank>
◎: No afterimage occurs ○: It looks faint △: Afterimage occurs ×: Very bad <Resolution rank>
◎: Very good ○: Good (slightly scattered dots)
Δ: Dot scattering and dot spread are observed. ×: Very bad light area potential: After primary charging, image exposure (entire exposure) was performed, and the photoreceptor surface potential when moving to the development position was measured. .
The above evaluation results are shown in Table 3.

(Photoreceptor Evaluation Example 2)
After the produced photoreceptors 1 to 20 are mounted, a full color electrophotographic apparatus having a tandem mechanism (Ricoh's IPSiO Color 8100 remodeling machine, a power pack is replaced to be positively charged, and the wavelength of the LD used for writing is further changed. Is printed on a 780 nm device), and a total of 10,000 sheets are printed using a 5% writing rate chart (characters equivalent to 5% are written as an image area on the entire A4 surface). A printing durability test was conducted.
The toner and developer used were changed from a dedicated one for IPSiO Color 8100 to a toner and developer having opposite polarity.
The charging means of the electrophotographic apparatus used an external power source, and the voltage applied to the charging roller was selected as an AC component with a peak-to-peak voltage of 1.9 kV and a frequency of 1.35 kHz. For the DC component, a bias was set so that the charged potential of the photosensitive member at the start of the test was +600 V, and the test was performed under this charging condition until the end of the test. The developing bias was + 450V. The test environment is 23 ° C. and 55% RH.
After the printing durability test, afterimage evaluation and color reproducibility were evaluated.
Afterimage evaluation: An evaluation image having a solid black portion and a halftone portion as shown in FIG. 10 was output, and the afterimage was evaluated.
The evaluation rank is as follows.
<Afterimage rank>
A: No afterimage is generated. O: Appears faint. Δ: Afterimage is generated. X: Very poor Color reproducibility: An ISO / JIS-SCID image N1 (portrait) is output and the color reproducibility is evaluated.
In either case, the evaluation rank is as follows: ◎: Very good ○: Good △: Slightly inferior ×: Very bad Table 4 shows the above evaluation results.

1 is a schematic cross-sectional view illustrating an example of an image forming apparatus according to the present invention. It is a schematic cross section which shows another example of the image forming apparatus which concerns on this invention. It is a schematic cross section showing an example of a process cartridge according to the present invention. It is a schematic cross section which shows another example of the image forming apparatus which concerns on this invention. FIG. 6 is a schematic cross-sectional view showing still another example of the image forming apparatus according to the present invention. FIG. 6 is a schematic cross-sectional view showing still another example of the image forming apparatus according to the present invention. It is sectional drawing which shows the example of the layer structure of the electrophotographic photoreceptor which concerns on this invention. It is sectional drawing which shows the example of another layer structure of the electrophotographic photoreceptor which concerns on this invention. It is a X-ray-diffraction spectrum figure of the titanyl phthalocyanine synthesize | combined in the Example. It is a figure which shows the image for evaluation used in the photoreceptor evaluation example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Electrophotographic photoreceptor 12 ... Charging means 13 ... Exposure means 14 ... Developing means 15 ... Toner 16 ... Transfer means 17 ... Cleaning means 18 ... Image receiving medium 19 ... Fixing means 1A ... Charging means 1B ... Pre-cleaning exposure means 1C ... Drive means 1D ... First transfer means 1E ... Second transfer means 1F ... Intermediate transfer member 1G ... Conveyance transfer belt 21 ... Conductive support 22 ... Photosensitive layer 23 ... Undercoat layer

Claims (8)

At least a photosensitive layer is provided on a conductive support, and the photosensitive layer comprises at least a charge generation material, an electron transport material represented by the following general formula (1), and a hole transport represented by the following general formula (2). Ri Do a single layer containing a material, as diffraction peaks of Bragg angle 2θ with respect to the charge generating material CuKα characteristic X-ray (wavelength 1.542 Å) (± 0.2 °), the maximum of at least 27.2 6. It has a diffraction peak, further has main peaks at 9.4 °, 9.6 °, and 24.0 °, and has a peak at 7.3 ° as the lowest diffraction peak. an electrophotographic photosensitive member, wherein titanyl phthalocyanine der Rukoto having no peak between 3 ° peak and 9.4 ° peak.
(In the above general formula, R1 and R2 are each independently a group selected from the group consisting of a hydrogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group, and a substituted or unsubstituted aralkyl group. R 3, R 4, R 5, R 6, R 7, R 8, R 9, R 10 are each independently a hydrogen atom, halogen atom, cyano group, nitro group, amino group, hydroxyl group, substituted or unsubstituted alkyl group, substituted or unsubstituted Represents a group selected from the group consisting of a substituted cycloalkyl group and a substituted or unsubstituted aralkyl group.
(In the above general formula, R11, R12, R13, R14, R17, R18, R19, R20 represent a hydrogen atom, a halogen atom, an alkoxy group, or an optionally substituted alkyl group or aryl group, and R15, R16 represent a hydrogen atom. Represents a halogen atom, an alkyl group, or an alkoxy group.) R1 and R2 of the electron transport material represented by the general formula (1) are each independently an alkyl group substituted with an alkyl group or an alkoxy group, and R3, R4, R5, R6, R7, R8, R9, R10 is a group independently selected from the group consisting of a hydrogen atom, a halogen atom and an alkyl group, and R11, R12, R13, R14, R17, R18 of the hole transport material represented by the general formula (2), 2. The electrophotographic photoreceptor according to claim 1, wherein R19 and R20 are a hydrogen atom, an alkoxy group or an alkyl group, and R15 and R16 are a hydrogen atom or an alkyl group.   The electron transport material represented by the general formula (1) is represented by the following formulas (1-1), (1-2), (1-6), (1-7), (1-8), (1- 9), a compound selected from the group consisting of (1-11), and the hole transport material represented by the general formula (2) is represented by the following formulas (2-1), (2-5), (2 The compound is selected from the group consisting of -6), (2-7), (2-8), (2-11), (2-13), and (2-15). Or the electrophotographic photosensitive member according to 2.
Image forming apparatus characterized by an electrophotographic photosensitive member according is mounted to any one of claims 1 to 3. Claim 4, wherein the image forming apparatus is comprises a plurality of electrophotographic photosensitive member, successively superimposed toner images of a single color that developed on each of the electrophotographic photosensitive member onto and forming a color image The image forming apparatus described in 1. A process cartridge for an image forming apparatus, which is detachable from an apparatus main body and has at least an electrophotographic photosensitive member, and the electrophotographic photosensitive member according to any one of claims 1 to 3. Process cartridge characterized by being. An image forming apparatus comprising the process cartridge according to claim 6 . An image forming apparatus comprising a plurality of process cartridges according to claim 6 .