EP0567395A2

EP0567395A2 - Electrophotographic photosensitive member, and electrophotographic apparatus and device unit employing the same

Info

Publication number: EP0567395A2
Application number: EP93401029A
Authority: EP
Inventors: Akihiro C/O Canon Kabushiki Kaisha Senoo; Toshihiro C/O Canon Kabushiki Kaisha Kikuchi; Tetsuro C/O Canon Kabushiki Kaisha Kanemaru; Takazaku Tanaka
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 1992-04-23
Filing date: 1993-04-21
Publication date: 1993-10-27
Also published as: EP0567395A3

Abstract

The present invention provides an electrophotographic photosensitive member, comprising an electroconductive support and a photosensitive layer formed thereon, the photosensitive layer containing a triphenylamine represented by the formula (1) below:

wherein R₁, R₂, and R₃ independently represent a hydrogen atom or an alkyl group of 1 to 3 carbons, and at least one of R₁, R₂, and R₃ is ethyl or propyl.

Description

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an electrophotographic photosensitive member. More particularly, the present invention relates to an electrophotographic photosensitive member comprising a photosensitive layer containing a triphenylamine of a specified structure. The present invention further relates to an electrophotographic apparatus and a device unit employing the above electrophotographic photosensitive member.

Related Background Art

Conventionally, as an electrophotographic member, photosensitive members having an inorganic photosensitive layer mainly composed of zinc oxide, cadmium etc., have been widely used. Such conventional photosensitive members satisfy the requirement for properties to some extent, but have disadvantages such as poor film-forming ability, insufficient plasticity, and high production cost. Furthermore, the inorganic photoconductive materials are generally highly toxic, restricting the production process and handling of the materials.
On the other hand, organic photosensitive members having a photosensitive layer mainly composed of an organic photoconductive compound have many advantages over the inorganic photosensitive material, and are attracting attentions in recent years. Many organic photosensitive members have been proposed, and some are practically used.
As such organic photosensitive members, there proposed those containing a photoconductive polymer such as poly-N-vinylcarbazole and a charge transfer complex formed from a Lewis acid such as 2,4,7-trinitro-9-fluorenone as main components. Compared with inorganic photoconductive polymers, such organic photoconductive polymers have advantages in lightweight and good film-forming properties but have disadvantages in lower sensitivity, durability, and stability to environmental change. Therefore, they are still unsatisfactory.
Thereafter, separate function type electrophotographic photosensitive members, in which the charge-generating function and the charge-transporting function are carried by separate substances, have brought about significant improvement in sensitivity and durability which are weak points of conventional organic photosensitive members. Such photosensitive members of the separate function type have advantages that the charge-generating substance and the charge-transporting substance may be selected from a wide variety of materials and the preparation of desired characteristics of the electrophotographic photosensitive member is not so difficult.
Known charge-generating substances include azo pigments, polycyclic quinone pigments, cyanine dyes, squaric acid dyes, and pyrylium dyes. Among them, azo pigments of various structures are disclosed because of their high light-fastness and high charge-generating ability, and relatively easy synthesis.
Known charge-transporting substances include pyrazolines disclosed in Japanese Patent Publication No. 52-4188; hydrazones disclosed in Japanese Patent Publication No. 55-42380 and Japanese Laid-Open Patent No. 55-52063; triphenylamines disclosed in Japanese Patent Publication No. 58-32372 and Japanese Laid-Open Patent No. 61-132955; stilbenes disclosed in Japanese Laid-Open Patent Nos. 54-151955 and 58-198043, and the like. The characteristics required for charge-transporting substance: (1) stability to light and heat, (2) stability to ozone, NOx, and nitric acid generated by corona discharge, (3) high charge-transporting performance, (4) high compatibility with organic solvents and binders, and (5) easy production and low cost.
According to the recent demand for high image quality and high durability of the photosensitive member, studies have been continued on charge-transporting substances to fulfil above requirements on a high level.

SUMMARY OF THE INVENTION

The present invention intends to provides an electrophotographic photosensitive member having a photosensitive layer containing a charge-transporting substance having a novel structure.
The present invention also intends to provide an electrophotographic photosensitive member having high sensitivity and stable potential characteristics even when repeatedly used.
The present invention further intends to provide an electrophotographic apparatus and an apparatus unit having the above electrophotographic photosensitive member.
The electrophotographic photosensitive member according to the present invention comprises an electroconductive support and a photosensitive layer formed thereon, the photosensitive layer containing a triphenylamine represented by the formula (1) below:

wherein R , R₂, and R₃ independently represent a hydrogen atom or an alkyl group of 1 to 3 carbons, and at least one of R₁, R₂, and R₃ is ethyl or propyl.
The electrophotographic apparatus and the device unit according to the present invention have the aforementioned electrophotographic photosensitive member.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows a schematic constitution of an electrophotographic apparatus employing an electrophotographic photosensitive member of the present invention.
Fig. 2 shows an example of a block diagram of a facsimile system employing an electrophotographic photosensitive member of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The electrophotographic photosensitive member of the present invention has a photosensitive layer containing a triphenylamine represented by the formula (1) below:

wherein R , R₂, and R₃ independently represent a hydrogen atom or an alkyl group of 1 to 3 carbons, and at least one of R₁, R₂, and R₃ is ethyl or propyl.
Preferred compound examples of the compound of formula (1) are shown belowwithout limiting the present invention thereto in any way.

[ Exemplified Compounds ]

(1) - (24)

[Exemplified compounds]

(continued)

[Exemplified Compounds]

(continued)

Synthesis examples are shown below for the compounds of the present invention.

Synthesis Example 1

(Synthesis of Exemplified Compound No. 1)

Into 200 ml three-neck flask, were placed 13.5 g of 4-propylaniline, 50 g of 4-iodotoluene, 10.0 g of anhydrous potassium carbonate, and 5.0 g of powdery copper. The mixture was stirred and heated at a temperature of from 190 to 200°C for 8 hours. After cooling, the reaction mixture was filtered and concentrated under reduced pressure. Thereto methylethyl ketone was added to collect crude crystalline matter by filtration. The crude crystalline matter was purified by column chromatography, thereby 22.5 g of p-ditolyl-4-propylaniline being obtained (81 % yield).

Synthesis Example 2

(Synthesis of Exemplified Compound No. 13)

Into 200 ml three-neck flask, were placed 12.1 g of 4-ethylaniline, 50 g of 4-iodotoluene, 10.0 g of anhydrous potassium carbonate, and 5.0 g of powdery copper. The mixture was stirred and heated at a temperature of from 190 to 200°C for 8 hours. After cooling, the reaction mixture was filtered and concentrated under reduced pressure. Thereto methyl ethyl ketone was added to collect crude crystalline matter by filtration. The crude crystalline matter was purified by column chromatography, thereby 25.6 g of p-ditolyl-4-ethylaniline being obtained (85 % yield).
The photosensitive layer of the present invention may have such construction as:

(1) (Upper layer containing a charge-transporting substance)/(Lower layer containing a charge-generating substance),
(2) (Upper layer containing a charge-generating substance)/(Lower layer containing a charge-transporting substance), and
(3) One layer containing a charge-generating substance and a charge-transporting layer.

The compound of the present invention represented by Formula (1) has high transporting ability for positive holes, and is useful as a charge-transporting substance in the photosensitive layer of the above construction. The primary charging polarity is preferably negative in the construction (1), preferably positive in the construction (2), and either positive or negative in the construction (3) of the photosensitive layer.
The electrophotographic photosensitive member of the present invention may have a protection layer on the surface of the photosensitive layer, or a subbing layer between the photosensitive layer and the electroconductive support in order to improve durability or adhesiveness, or to control charge injection. The construction of the photosensitive member is not limited to those mentioned above.
Of the aforementioned construction, the construction (1) is particularly preferred in the present invention. It is explained in more detail.
The electroconductive support in the present invention includes those shown below:

(1) Metals and alloys such as aluminum, aluminum alloys, stainless steel or copper, in a form of a plate or a drum,
(2) Non-electroconductive support such as glass, a resin and paper, or electroconductive support of (1) the surface of which is coated by vapor deposition or lamination to form a thin film of a metal or an alloy such as of aluminum, aluminum alloys palladium, rhodium, gold, and platinum formed, and
(3) Non-electroconductive support such as glass, a resin and paper, or electroconductive support of (1) having thereon a layer containing an electroconductive compound such as electroconductive polymer, tin oxide, and indium oxide, formed by vapor deposition or coating.

The charge-generating substance which may be used in the present invention includes substances shown below. Such charge-generating substances may be used singly or in combination of two or more thereof.

(1) Azo pigments, including monoazo, bisazo, trisazo, etc.
(2) Phthalocyanine pigments including metal phthalocyanines and nonmetal phthalocyanines, etc.,
(3) Indigo pigments including indigo, thioindigo, etc.,
(4) Perylene pigments including perylenic anhydride, perylenimide, etc.,
(5) Polycyclic quinone pigments including anthraquinone, pyrenequinone, etc.,
(6) Squarilium dyes,
(7) Pyrylium salts and thiopyrylium salts,
(8) Triphenylmethane dyes, and
(9) Inorganic substances including selenium, amorphous silicon, etc.

The layer containing a charge-generating substance, namely a charge-generating layer is formed by dispersing a charge-generating substance as above in a suitable binder and applying the resulting dispersion on an electroconductive support, or otherwise by forming a thin film of a charge-generating substance on an electroconductive support by a dry process such as vapor deposition, sputtering, or CVD.
The aforementioned binder may be selected from a variety of binding resins such as polycarbonate resins, polyester resins, polyarylate resins, butyral resins, polystyrene resins, polyvinylacetal resins, diallyl phthalate resins, acrylic resins, methacrylic resins, vinyl acetate resins, phenol resins, silicone resins, polysulfone resins, styrene-butadiene copolymer resins, alkid resins, epoxy resins, urea resins, and vinyl chloride-vinyl acetate copolymer resins, but is not limited thereto. The above resins may be used singly or in combination of two or more thereof.
The binder resin in the charge-generating layer is in an amount of preferably not more than 80 %, more preferably not more than 40 % by weight based on the total weight of the charge-generating layer. The thickness of the charge-generating layer is preferably not more than 5 f..lm, more preferably from 0.01 f..lm to 2 µm.
A sensitizing agent may be added to the charge-generating layer.
The layer containing a charge-transporting substance, namely a charge-transporting layer, may be formed from combination of at least one triphenylamine represented by Formula (1) and a suitable binder resin. The binder resin employed for the charge-transporting layer includes those mentioned above for the charge-generating layer and additionally photoconductive polymers such as polyvinylcarbazoles and polyvinylanthra- cenes.
The binder resin and the triphenylamine of the present invention are blended in a ratio of from 10 to 500 parts by weight to 100 parts by weight of the binder resin.
The charge-transporting layer is connected electrically to the charge-generating layer, and has function of receiving the charge carriers generated in the charge-generating layer and transporting the charge carriers to the surface of the photosensitive member. Since the ability of the charge-transporting layer in transporting the charge carriers has limitation, the layer should not be unnecessarily thick, and is preferably in the range of from 5 µm to 40 µm, more preferably from 10 µm to 30 µm.
The charge-transporting layer may further contain an antioxidant, a UV-absorber, a plasticizer, or a known charge-transporting substance.
The above-described layers may be formed by a coating process such as dip coating, spray coating, spinner coating, roller coating, Meyer bar coating or blade coating using a suitable organic solvent.
The electrophotographic photosensitive member of the present invention is useful not only for electrophotographic copying machines, but also for a variety of electrophotography application fields, such as laser beam printers, CRT printers, LED printers, facsimile machines, and electrophotographic engraving systems.
Fig. 1 illustrates schematically an example of the constitution of a transfer type electrophotographic apparatus employing an electrophotographic photosensitive member of the present invention.
In Fig. 1, a drum type photosensitive member 1 as an image holding member is driven to rotate around the axis 1a in the arrow direction at a prescribed peripheral speed. The photosensitive member 1 is uniformly charged positively or negatively at the peripheral face by an electrostatic charging means 2 during rotation, and then exposed to image-exposure light L (e.g., slit exposure, laser beam-scanning exposure, etc.) at the exposure part 3 with an image-exposure means (not shown in the drawing), whereby an electrostatic latent image is sequentially formed on the peripheral surface in accordance with the exposed image.
The electrostatic latent image is developed with a toner by a developing means 4. The developed toner image is successively transferred by a transfer means 5 onto a surface of a transfer-receiving material P which is fed from a transfer-receiving material feeder not shown in the drawing, between the photosensitive member 1 and the transfer means 5 synchronistically with the rotation of the photosensitive member 1.
The transfer-receiving material P which has received the transferred image is separated from the photosensitive member surface, and introduced to an image fixing means 8 for fixation of the image and sent out from the copying machine as a duplicate copy.
The surface of the photosensitive member 1, after the image transfer, is cleaned with a cleaning means 6 to remove any remaining un-transferred toner, and is treated for charge elimination with a pre-exposure means 7 for repeated use for image formation.
The generally employed charging means 2 for uniformly charging the photosensitive member 1 is a corona charging apparatus. The generally employed transfer means 5 is also a corona charging means. In the electrophotographic apparatus, two or more of the constitutional elements, the above described photosensitive member, the developing means, the cleaning means, etc. may be integrated into one device unit, which may be made removable from the main body of the apparatus. For example, at least one of the charging means, the developing means, and the cleaning means is combined with the photosensitive member 1 into one device unit which is removable from the main body of the apparatus by aid of a guiding means such as rails of the main body of the apparatus.
When the electrophotographic apparatus is used as a copying machine or a printer, the image exposure light L projected onto the photosensitive member may be reflected light or transmitted light from an original copy, or otherwise the information is read out by a sensor from an original and signalized, and the exposure light is projected onto a photosensitive member, by scanning with a laser beam, driving an LED array, or driving a liquid crystal shutter array according to the signal.
When the electrophotographic apparatus is used as a printer of a facsimile machine, the optical image exposure light L is employed for printing the received data. Fig. 2 is a block diagram of an example of this case.
A controller 11 controls the image-reading part 10 and a printer 19. The entire of the controller 11 is controlled by a CPU 17. Readout data from the image reading part 10 are transmitted through a transmitting circuit 13 to the other communication station. Data received from the other communication station are transmitted through a receiving circuit 12 to a printer 19. The image data are stored in an image memory 16. A printer controller 18 controls a printer 19. The numeral 14 denotes a telephone set.
The image received through a circuit 15, namely image information from a remote terminal connected through the circuit, is demodulated by the receiving circuit 12, decoded in CPU 17, and successively stored in the image memory 16. When at least one page of image information has been stored in the image memory 16, the images are recorded in such a manner that the CPU 17 reads out one page of the image information, and sends out the one page of the decoded information to the printer controller 18, which controls the printer 19 on receiving the one page of the information from CPU 17 to record the image information.
During recording by the printer 19, the CPU 17 receives the subsequent page of information.
Images are received and recorded in the manner as described above.
The present invention is described in more detail by reference to examples.

Example 1

A coating liquid for a charge-generating layer was prepared by dispersing 1.0 g of the azo pigment represented by the formula below in a solution of 0.5 g of a butyral resin (butyralation degree of 80 mol%) in 60 ml of tetrahydrofuran by means of a sand mill for 48 hours.
This coating liquid was applied on an aluminum sheet with a Meyer bar to obtain a charge-generating layer of 0.2 µm in dry thickness.
Separately, 1.0 g of Exemplified Compound No. 1, as a charge-transporting substance, and 1.0 g of a polycarbonate resin (weight-average molecular weight of 20,000) were dissolved in 7.0 g of monochlorobenzene. The resulting solution was applied on the aforementioned charge-generating layer with a Meyer bar and was dried to form a charge-transporting layer of 23 µm in dry thickness.
The resulting electrophotographic photosensitive member was tested for charging characteristics by subjecting it to static corona charging with an electrostatic copying paper tester (Model-SP-428 made by Kawagichi Denki K.K.) at -5 KV, keeping it in the dark for one second, and exposing it to the light of 20 lux.
The measured charging characteristics were the surface potential (V_o) immediately after the charging, the surface potential (V_i) after the one-second dark decay, and the E_1/5 exposure light which decreases the surface potential from V₁ to (1/5)V , corresponding to sensitivity.
Additionally, the changes of the light area potential and the dark area potential during repeated use were evaluated by attaching the photosensitive member prepared in this Example to a photosensitive drum cylinder of a copying machine (NP-3825 made by Canon K.K.), practicing 5000 sheets of copying, and measuring the light-area potentials (V_L) and the dark-area potentials (V_D) at the beginning of the copying test and just after 5000th sheet copying. The potentials ofVo and V_L at the beginning were adjusted respectively to be at about -700 V and -200 V. The results are shown in Table 1.

Examples 2 - 20

Electrophotographic photosensitive members were prepared and evaluated in the same manner as in Example 1 except that Exemplified Compound No. 1 as the charge-transporting substance was replaced respectively with Exemplified Compounds Nos. 2, 3, 4, 5, 7, 9, 10, 11, 12, 13, 14, 15, 16, 18, 19, 20, 22, 23, and 24. The results are shown in Table 2.

Comparative Examples 1 - 4

Electrophotographic photosensitive members were prepared and evaluated in the same manner as in Example 1 except that Exemplified Compound No. 1 as the charge-transporting substance was replaced respectively with Comparative Compounds Nos. 1 to 4. The results are shown in Table 3.

[ Comparative Compounds ]

(1) - (4)

It is clear that the electrophotographic photosensitive members of the present invention are superior to those using the Comparative Compound in the sensitivity and the potential stability on repeated use.

Example 21

1.0 Gram of oxytitanium phthalocyanine was dispersed in a solution of 0.4 g of a phenoxy resin in 100 g of cyclohexanone by means of a ball mill for 40 hours. The resulting dispersion was applied on an aluminum sheet with a Meyer bar and was dried at 80°C for 0.5 hour to obtain a charge-generating layer of 0.15 µm thick.
Separately, 1.0 g of Exemplified Compound No. 1, and 1.0 g of a bisphenol Z type polycarbonate resin (weight-average molecular weight of 20,000) were dissolved in 7.0 g of monochlorobenzene. The resulting solution was applied on the aforementioned charge-generating layer with a Meyer bar and was dried at 120°C for 1.0 hour to form a charge-transporting layer of 21 µm thick.
The obtained electrophotographic photosensitive member was subjected to corona discharge of -5 KV. The measured charging characteristics were the surface potential (V_o) immediately after the charging, the surface potential (V_i) after the dark decay for one second, and the E_1/6 exposure light, namely the sensitivity, which decreases the surface potential from V₁ to (1/6)V . In the measurement, the light source was a gallium/alumi- num/arsine ternary semiconductor laser (power: 5 mW, wavelength: 780 nm). The results are as shown below. V₀: -710 (V), V₁: -705 (V) E_1/6: 0.25 (µJ/cm2)
Actual image formation test was conducted with the above photosensitive member installed on a laser beam printer (LBP-CX, made by Canon K.K.) which is an electrophotographic printer of a reversal development type equipped with a semiconductor laser similar to the one above. The test was conducted under the conditions of surface potential after primary charging: -700 V, surface potential after imagewise exposure: -150 V, image transfer potential: +700 V, development polarity: negative, processing speed: 50 mm/sec, developing bias: -450 V, system of scanning after image exposure: image scanning, and pre-exposure before primary charging: red-color light exposure of 22.0 luxsec. Continuous printing of image of 3000 sheets was conducted. Satisfactory images were printed stably from the beginning of the printing test to the printing of 3000th sheet.

Example 22

An electrophotographic photosensitive member was prepared and evaluated in the same manner as in Example 21 except that Exemplified Compound No. 13 was used as the charge-transporting substance in place of the Exemplified Compound No. 1. The charging characteristics were excellent as below, and the printed images of excellent quality were obtained from the beginning of the test to 3000th sheet of printing. V_o: -720 (V), V₁: -715 (V) E_1/6: 0. 25 (µJ/cm²)

Example 23

A 2% solution of alcohol-soluble nylon (6-66-610-12 quaternary nylon copolymer) in methanol was applied on an aluminum sheet to form a subbing layer of 0.5 µm in dry thickness.
Separately, 0.5 g of the azo pigment represented by the formula below was dispersed in 10 ml of tetrahydrofuran by means of a sand mill.
To the dispersion, was added a solution of 10g g of the Exemplified Compound No. 1 and 10 g of a bisphenol A type polycarbonate resin (weight-average molecular weight of 30,000) in 70 g of a mixed solution of monochlorobenzene (80 weight parts) and dichloromethane (20 parts by weight), and the mixture was dispersed for 2 hours by the sand mill.
The resulting dispersion was applied on the subbing layer prepared above with a Meyer bar so as to obtain a dry thickness of 18 µm.
The electrophotographic characteristics of the obtained electrophotographic photosensitive member was evaluated in the same manner as in Example 21. The results were as below. V_o: -710 (V), V₁: -700 (V) E_1/6 : 0.67 (µJ/cm²)

Example 24

An electrophotographic photosensitive member was prepared and evaluated in the same manner as in Example 23 except that Exemplified Compound No. 13 was used as the charge-transporting substance in place of the Exemplified Compound No. 1. The results were as below. V₀: -700 (V), V₁: -690 (V) E_1/6 : 0.64 (µJ/cm²)
As explained above, the electrophotographic photosensitive member having a photosensitive layer containing the triphenylamine of the present invention has high sensitivity, causing less change of light-area potential and dark-area potential in continuous image formation, and having excellent durability.

Claims

1. An electrophotographic photosensitive member, comprising an electroconductive support and a photosensitive layer formed thereon, the photosensitive layer containing a triphenylamine represented by the formula (1) below:

wherein R_1' R₂, and R₃ independently represent a hydrogen atom or an alkyl group of 1 to 3 carbons, and at least one of R_1' R₂, and R₃ is ethyl or propyl.

2. An electrophotographic photosensitive member according to claim 1, wherein at least one of R₁, R₂, and R₃ is ethyl.

3. An electrophotographic photosensitive member according to claim 1, wherein at least one of R₁, R₂, and R₃ is propyl.

4. An electrophotographic photosensitive member according to claim 1, wherein the photosensitive layer contains the triphenylamine represented by the formula (1) as a charge-transporting substance.

5. An electrophotographic photosensitive member according to claim 1, wherein the photosensitive layer comprises a charge-generating layer and a charge-transporting layer.

6. An electrophotographic photosensitive member according to claim 5, wherein the photosensitive layer comprises the charge-generating layer formed on the electroconductive support, and the charge-transporting layer formed on the charge-generating layer.

7. An electrophotographic photosensitive member according to claim 1, wherein the electrophotographic photosensitive member has a subbing layer between the electroconductive support and the photosensitive layer.

8. An electrophotographic photosensitive member according to claim 1, wherein a protection layer is provided on the photosensitive layer.

9. An electrophotographic apparatus, comprising an electrophotographic photosensitive member, an image- forming means for forming an electrostatic latent image, a developing means for developing the formed latent image, and a transferring means for transferring the developed image to an image-receiving material;
said electrophotographic photosensitive member comprising an electroconductive support and a photosensitive layer formed thereon, the photosensitive layer containing a triphenylamine represented by the formula (1) below:

wherein R₁, R₂, and R₃ represent independently a hydrogen atom or an alkyl group of 1 to 3 carbons, and at least one of R₁, R₂, and R₃ is ethyl or propyl.

10. A device unit, comprising an electrophotographic photosensitive member, and at least one means selected from the group of a charging means, a developing means, and a cleaning means; said electrophotographic photosensitive member comprising an electroconductive support and a photosensitive layer formed thereon, the photosensitive layer containing a triphenylamine represented by the formula (1) below:

wherein R₁, R₂, and R₃ represent independently a hydrogen atom or an alkyl group of 1 to 3 carbons, and at least one of R₁, R₂, and R₃ is ethyl or propyl; and said unit holding integrally the electrophotographic photosensitive member and at least one of the charging means, a developing means, and the cleaning means, and being removable from the main body of an electrophotographic apparatus.