JP2003255579A - Electrophotographic photoreceptor and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrophotographic photoreceptor having good stability of electrification potential even after repeated use, free of optical memory and consequently giving high maximum image density, and free of unevenness in medium density, optical memory due to a previous exposure and a ghost phenomenon and to provide an image forming method using the same. <P>SOLUTION: In the electrophotographic photoreceptor having an intermediate layer and a photosensitive layer on an electrically conductive support, rutile type titanium dioxide is contained in the intermediate layer and a 2 to 12C alkyl diol is contained in the photosensitive layer. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic photoreceptor and an image forming method used in an image forming apparatus such as a copying machine, a printer and a facsimile.

[0002]

2. Description of the Related Art In recent years, most electrophotographic photoconductors (sometimes simply referred to as photoconductors) use organic compounds as photosensitive materials.

There are many kinds of organic compounds by nature, and taking advantage of their advantages, the charge-generating substance and the charge-transporting substance have been actively developed separately according to their functions in the development of materials.

In assembling the photoconductor, these materials can be used in combination, and therefore the combination can be appropriately selected and used depending on the use of the photoconductor to produce a product having good characteristics.

However, organic photoconductors are not completely free of problems today, and there are some characteristics which are still a problem in practical use. Among them, if the charging operation is repeated during image formation, the charging potential decreases, and when trying to form an image again on the part of the photoconductor surface where the previous image was formed, the influence of the previous image formation remains, which is the image quality. There is a phenomenon that causes deterioration (so-called optical memory phenomenon).

[0006]

Various studies have been made on the method of solving the above problems.

The photoreceptor having rutile type titanium oxide in the intermediate layer (UCL) is excellent in potential stability without lowering of charging potential even if charging operation is repeated during image formation. However, when a highly sensitive charge generation material is used for the charge generation layer (CGL), the optical memory phenomenon has become a problem.

That is, the object of the present invention is that the charge potential stability is good even if it is repeatedly used, there is no optical memory phenomenon, and therefore the maximum image density is high, there is no unevenness in intermediate density and no optical memory due to the previous exposure, and there is no ghost. An object of the present invention is to provide an electrophotographic photosensitive member that does not cause a phenomenon and an image forming method using the same.

[0009]

Means for Solving the Problems As a result of intensive studies by the present inventors, it was found that the object of the present invention can be achieved by adopting any of the following constitutions.

[1] In an electrophotographic photoreceptor having an intermediate layer and a photosensitive layer on a conductive support, the intermediate layer contains rutile titanium oxide, and the photosensitive layer contains an alkyl diol having 2 to 12 carbon atoms. An electrophotographic photosensitive member comprising:

[2] The electrophotographic photoreceptor according to [1], wherein the intermediate layer further contains polyamide.

[3] The electrophotographic photosensitive member according to [1] or [2], wherein the rutile type titanium oxide has a particle size of 0.1 μm or less.

[4] The electrophotographic photosensitive member according to [1], [2] or [3], wherein the rutile type titanium oxide is titanium oxide treated with alumina.

[5] The above-mentioned alkyl diol is contained in a layer in contact with the intermediate layer [1]
The electrophotographic photosensitive member according to any one of to [4].

[6] An electrophotographic photoreceptor having an intermediate layer and a photosensitive layer on a conductive support contains rutile type titanium oxide in the intermediate layer, and the photosensitive layer contains an alkyl diol having 2 to 12 carbon atoms. An image forming method characterized in that an image is formed by repeating at least the steps of charging, image exposure and development using the contained electrophotographic photoreceptor.

[7] The image forming method according to [6], wherein in the image forming method, the charging step is performed without the step of erasing the positional potential difference on the surface of the photoconductor.

[8] The image forming method as described in [6] or [7], wherein the charging step uses a needle electrode.

That is, the problem with the organic photoconductor so far is U
When CGL is applied onto CL, the compatibility (wetting) with the charge generating substance contained therein is not sufficient, and if the wetting is insufficient or the dispersion liquid has aggregated, a trap site is formed at the interface. It was presumed that it is likely to occur. On the other hand, it has been found that by adding a diol to CGL, the pigment and titanium oxide can be brought into sufficient contact with each other to eliminate the above problems and improve the optical memory property. We have also found that the potential characteristics can be further improved.

Further, although there was a problem of image unevenness when a band electrode having a non-uniform shape such as needle electrode charging in the drum axis direction was used, it was found that this unevenness makes it less likely to occur. It was It is presumed that the reason is to improve the blocking property of injected charges by UCL and CGL and to enhance the effect of suppressing thermally excited carriers.

In order to generate this effect more sufficiently,
It was also found that a polyamide resin having a polar group as the UCL binder is more preferable because of stable characteristics.

It has also been found that it is more preferred to have alumina treated titanium oxide as the titanium oxide surface will increase the interaction with the diol.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION The constitution of the photoconductor preferably used in the present invention will be described below.

Conductive Support As the conductive support used in the photoreceptor of the present invention, either a sheet or a cylinder may be used, but in order to design the image forming apparatus compactly, the conductive support is cylindrical. A support is preferred.

The cylindrical conductive support of the present invention means a cylindrical support required to be capable of forming an image endlessly by rotating, and has a straightness of 0.1 mm or less and a shake of 0.1 mm or less. Conductive supports in the range are preferred. If the straightness and the shake range are exceeded, good image formation becomes difficult.

As the conductive material, a metal drum of aluminum, nickel or the like, a plastic drum on which aluminum, tin oxide, indium oxide or the like is deposited, or a paper / plastic drum coated with a conductive substance can be used. It is preferable that the conductive support has a specific resistance of 10 ³ Ω · cm or less at room temperature.

Intermediate Layer (Undercoat Layer) The structure of the intermediate layer is not particularly limited, and those mainly composed of various resins are mainly used. Those using a polyamide resin are particularly preferable.

The rutile-type titanium oxide used in the present invention has a particle size of 0.1 μm or less, more preferably 0.01-μm.
It is preferably 0.08 μm.

Further, these rutile type titanium oxide particles are preferably treated with alumina in order to increase the interaction with the diol. A known method may be used to perform the alumina treatment. For example, Japanese Patent Application No. 2-1
As described in Japanese Patent No. 81158, it can be obtained by precipitation on the surface of titanium oxide with caustic soda.

The preferred photosensitive layer constitution of the electrophotographic photosensitive member of the present invention will be described below. Photosensitive Layer The photosensitive layer structure of the photoreceptor of the present invention may be a single-layer photosensitive layer structure in which one layer has a charge generation function and a charge transport function on the undercoat layer, but more preferably the photosensitive layer It is preferable that the function is divided into a charge generation layer (CGL) and a charge transport layer (CTL). By adopting a constitution in which the functions are separated, the increase in residual potential due to repeated use can be controlled to be small, and other electrophotographic characteristics can be easily controlled according to the purpose. In the negative charging photoreceptor, it is preferable that a charge generation layer (CGL) is formed on the undercoat layer and a charge transport layer (CTL) is formed on the charge generation layer. In the case of the photoconductor for positive charging, the order of the layers is the reverse of that of the photoconductor for negative charging. The most preferable photosensitive layer structure of the present invention is a negatively charged photosensitive member structure having the above-mentioned function separation structure.

The constitution of the photosensitive layer of the function-separated negatively charged photoreceptor will be described below. Charge Generation Layer Charge Generation Layer: The charge generation layer contains one or more charge generation materials (CGM). If necessary, a binder resin and other additives may be contained as other substances.

As the charge generating substance (CGM), a known charge generating substance (CGM) can be used. For example, a phthalocyanine pigment, an azo pigment, a perylene pigment, an azurenium pigment or the like can be used. Among these, CGM that can minimize the increase in residual potential with repeated use
Has a steric and potential structure capable of forming a stable aggregation structure among a plurality of molecules. Specific examples thereof include phthalocyanine pigments having a specific crystal structure and CGM of perylene pigments. However, there is a close relationship between the CGM and the coating property, and the fluctuation of the potential characteristics does not change depending on the presence or absence of titanium oxide, and as a particularly good example, for example, the Bragg angle 2θ with respect to Cu-Kα rays is 26.2 ° at the maximum. There are CGMs such as titanyl phthalocyanine having a peak and benzimidazole perylene having the maximum 2θ of 12.4. These hardly deteriorate with repeated use, and the increase in residual potential can be reduced.

When a binder is used as a CGM dispersion medium in the charge generation layer, a known resin can be used as the binder, but the most preferable resin is formal resin, butyral resin, silicon resin, silicon-modified butyral resin, or phenoxy resin. Resin etc. are mentioned. The ratio of the binder resin to the charge generating substance is preferably 20 to 600 parts by mass with respect to 100 parts by mass of the binder resin.
By using these resins, the increase in residual potential due to repeated use can be minimized. The thickness of the charge generation layer is preferably 0.01 μm to 2 μm.

Charge Transport Layer Charge Transport Layer: The charge transport layer contains a charge transport material (CTM) and a binder resin for dispersing CTM to form a film.
Other substances may optionally contain additives such as antioxidants.

As the charge transport material (CTM), a known charge transport material (CTM) can be used. For example, a triphenylamine derivative, a hydrazone compound, a styryl compound, a benzidine compound, a butadiene compound or the like can be used. These charge transport materials are usually dissolved in a suitable binder resin to form a layer. Among them, the CTM that can minimize the increase in residual potential due to repeated use has a high mobility of 10 −5 cm ² / V · sec or more, and has an ionization potential difference of 0.5 with the combined CGM. Those having a characteristic of (eV) or less are preferable, and more preferably 0.25 (eV).
V) or less.

The ionization potentials of CGM and CTM are measured by a surface analyzer AC-1 (manufactured by Riken Keiki Co., Ltd.).

Examples of the resin used for the charge transport layer (CTL) include polystyrene, acrylic resin, methacrylic resin, vinyl chloride resin, vinyl acetate resin, polyvinyl butyral resin, epoxy resin, polyurethane resin, phenol resin, polyester resin, alkyd. Resins, polycarbonate resins, silicone resins, melamine resins, and copolymer resins containing two or more of the repeating units of these resins. In addition to these insulating resins, poly-N
-Polymer organic semiconductors such as vinylcarbazole.

The most preferable binder for these CTLs is a polycarbonate resin. Polycarbonate resin is most preferable in simultaneously improving abrasion resistance, CTM dispersibility, and electrophotographic characteristics. The ratio of the binder resin to the charge transport material is the binder resin 1
10 to 200 parts by mass is preferable with respect to 00 parts by mass. or,
The thickness of the charge transport layer is preferably 10 to 40 μm.

The alkyl diol added to the photosensitive layer is
The number of carbon atoms in the molecule is not particularly limited, but is preferably 2 to 12, and more preferably 4 to 10.

Although the layer structure of the most preferred photoconductor of the present invention has been illustrated above, a photoconductor layer structure other than the above may be used in the present invention.

As the coating processing method for producing the electrophotographic photosensitive member of the present invention, coating processing methods such as dip coating, spray coating, and circular amount controlling type coating are used. The coating processing on the upper layer side of the photosensitive layer is used. Does not dissolve the lower layer as much as possible,
In order to achieve uniform coating processing, it is preferable to use a coating processing method such as spray coating or circular amount regulation type (a circular slide hopper type is a typical example) coating. The spray coating is described in detail in, for example, JP-A-3-90250 and JP-A-3-269238, and the circular amount regulating coating is described in JP-A-58-1890.
This is described in detail in Japanese Patent No. 61.

Next, FIG. 1 shows a specific example of an electrophotographic apparatus using the electrophotographic photosensitive member of the present invention. FIG. 1 is a sectional view of an image forming apparatus as an example of the image forming method of the present invention.

In this apparatus, a magnetic brush primary charging member 2, an image exposing unit 3, a developing unit 4, and a peripheral surface of an electrophotographic photosensitive member 1 are provided.
A transfer unit 6 and a fur brush auxiliary charger 8 are arranged.

In the image forming method, first, a voltage is applied to the primary charging member 2 disposed in contact with the electrophotographic photosensitive member 1, the surface of the photosensitive member 1 is charged by injecting electric charges, and the image exposing means 3 is used. An image corresponding to the original is exposed on the surface of the photoconductor 1 to form an electrostatic latent image. Next, the toner in the developing device 4 is attached to the photoconductor 1 to develop (visualize) the electrostatic latent image on the photoconductor 1. Further, the toner image formed on the photoconductor 1 is transferred onto the transfer material 7 such as paper supplied by the transfer means 6, and the residual toner remaining on the photoconductor 1 without being transferred to the transfer material is an auxiliary charger. The polarity is changed to the positive side by 8, the toner is once collected by the primary charger, discharged by the toner discharge sequence or the like, and collected by the developing device.

In this image forming apparatus, the image exposure means 3
As the light source, a halogen light, a fluorescent lamp, a laser light or the like can be used.

In the present invention, it is also possible to use a charging means (charging step) having a non-uniform shape in the direction perpendicular to the moving direction of the photosensitive member, such as a needle electrode.
Although such a method originally tends to cause unevenness on an image, such defects are rarely exposed in the present invention.

FIG. 2 is a diagram showing an example of the structure of a needle-shaped electrode charging device. This charging device includes an electrode plate 11 on which needle electrodes 10 are formed at predetermined intervals in the longitudinal direction of the photoconductor 1, a stabilizing plate 12 for stabilizing discharge from the needle electrodes 10, and a needle electrode 1.
0 and the grit electrode 13 provided between the photoconductor 1. The grid electrode 13 is electrically connected to the substrate of the photoconductor 1 via the power source GV. Electrode plate 1
1 is a metal plate cut into a sawtooth shape,
The sawtooth has a shape in which the tips of the teeth serve as a plurality of needle-shaped electrodes 10. FIG. 3 shows a part of the acicular electrode charging device as the photosensitive member 1.
It is a block diagram seen from the advancing direction. Although the needle electrodes 10 are arranged at a predetermined interval and face the photoconductor 1, the needle electrodes 10
Since there is a space between them, the charging potential of the photoconductor tends to have a waveform as shown by the broken line in the figure.

Further, in the present invention, the charging of the surface of the photoconductor is started without passing through the processing steps such as pre-charging exposure before the series of steps of image formation is completed and the image formation is started again (that is, In FIG. 1, it is preferable in the case where a process such as image formation using an apparatus not particularly provided with the auxiliary charger 8), an image memory, or the like does not occur and a process without a charge eliminating step is taken.

[0048]

The preferred structure of the present invention and its effects will be described below.
Although the description will be given based on a specific embodiment, it goes without saying that the configuration of the present invention is not limited to this.

In the text, "part" means "part by mass". Example 1 Polyamide resin CM8000 (manufactured by Toray) 1 part, rutile type titanium oxide SMT500SAS (first: silica / alumina treatment, second: methylhydrogenpolysiloxane treatment: Teika) 3 parts, methanol 10 parts The mixture was added to the container and dispersed using a 1/4 gallon (1 gallon is about 3.8 liter) sand grinder to prepare an intermediate layer coating liquid 1.

The coating solution for intermediate layer 1 was provided on an amylnium cylinder having a diameter of 30 mm and a length of 260.5 mm so that the dry film thickness was 1.3 μm.

Further, 2 parts of a titanyl phthalocyanine compound having an X-ray diffraction spectrum (Bragg angle 2θ ± 0.2 °) of Cu-Kα ray having a maximum diffraction peak at 26.3 °,
Butyral resin (S-REC BMS manufactured by Sekisui Chemical Co., Ltd.) 1
Part, 1,4-butanediol 0.1 part, t-butyl acetate 70 parts, 4-methoxy-4-methyl-2-pentanone 3
A liquid in which 0 part was dispersed using a sand mill was applied by dip coating to form a charge generation layer having a dry film thickness of about 0.3 μm.

Next, a charge transport material (compound A below);
0.75 parts, polycarbonate resin "Iupilon-Z3"
00 "(manufactured by Mitsubishi Gas Chemical Co., Inc.) with 1 part of methylene chloride 7.5
The solution dissolved in the solution is applied onto the charge generation layer by dip coating.
After drying at 60 ° C. for 60 minutes, a charge transport layer having a thickness of about 24 μm was formed.

[0053]

[Chemical 1]

Example 2 A photoconductor of Example 2 was prepared in the same manner as in Example 1 except that 1,4-butanediol was replaced with 1,5-pentanediol.

Example 3 Example 1 was repeated except that rutile type titanium oxide was changed to TTO55N (Ishihara Sangyo), polyamide resin was changed to X-1874M (manufactured by Daicel Hüls), and diol compound was changed to 1,3-octanediol. Similarly, a photoconductor of Example 3 was prepared.

Example 4 TTO55N (Ishihara Sangyo) was used as the rutile type titanium oxide and Erbax 426 was used as the polyamide resin for the polyamide resin.
A photoreceptor of Example 4 was prepared in the same manner as in Example 1 except that 1,5-pentanediol was used as the diol compound and methyl ethyl ketone was used as the solvent for the charge generation layer.

Example 5 Rutile type titanium oxide TA-300 of untreated titanium oxide
A photoconductor of Example 5 was prepared in the same manner as in Example 1 except that the diol compound was changed to 1,3-butanediol (manufactured by Fuji Titanium Co., Ltd.).

Comparative Example 1 A photoconductor of Comparative Example 1 was prepared in the same manner as in Example 1 except that the diol compound was changed to 1,5-pentanediol without adding rutile type titanium oxide.

Comparative Example 2 A photoconductor of Comparative Example 2 was prepared in the same manner as in Example 1 except that the diol compound was not added.

The image forming apparatus used for the evaluation of characteristics was basically the one having the structure shown in FIG. 1 (having charging, image exposure, development, transfer / separation, steps, and no static elimination step). .

30 ° C., 80% RH environment and 10 ° C., 20%
It was evaluated in the RH environment and 50,000 prints of the live-action run were taken. For each image, a 30 × 30 mm patch image (maximum density image) was printed every 10,000 prints, then a halftone image with a density of 0.3 was printed, and the following evaluations were performed.

Evaluation reference potential characteristics unexposed portion potential, intermediate potential 0.3 image potential (light amount when the initial image has a density of 0.3), exposed portion potential (exposed portion potential when the laser max light amount is turned on) ) Was measured.

Black solid image density (measured using RD-918 manufactured by Macbeth Co., relative reflection density with paper reflection density set to "0") ⊚: Black solid image is 1.2 or more ○: Black solid image is less than 1.2 to 1.0 ×: Black solid image is less than 1.0 Memory (Initial and halftone images are judged from every 10,000 copies to 50,000 copies) ○: Density of memory part The difference is less than 0.05, and the memory is almost invisible.

Δ: The density difference of the memory portion is 0.05 to 0.15, which can be visually confirmed with caution. ×: The density difference of the memory portion is greater than 0.15, which can be clearly confirmed visually. A potential sensor was installed, and the unexposed portion potential of the first and second charging of the photoconductor was measured from the uncharged state, and the absolute value of the difference was set to ΔV12. Actually, ΔV12 was evaluated at the start and after copying 50,000 sheets, with a one-hour pause.

The results are shown in Tables 1 and 2.

[0066]

[Table 1]

[0067]

[Table 2]

It is understood that Examples 1 to 5 in the present invention have good characteristics, but Comparative Examples 1 and 2 have a problem in at least one of the characteristics.

[0069]

According to the present invention, the charge potential stability is good even if it is repeatedly used, there is no optical memory, therefore the maximum image density is high, there is no unevenness in intermediate density and no optical memory due to the previous exposure, and the ghost phenomenon etc. It is possible to provide an electrophotographic photosensitive member that does not occur and an image forming method using the same.

[Brief description of drawings]

FIG. 1 is a sectional view of an image forming apparatus.

FIG. 2 is a diagram showing a configuration example of a needle-shaped electrode charging device.

FIG. 3 is a configuration diagram in which a part of a needle-shaped electrode charging device is viewed from a traveling direction of a photoconductor.

[Explanation of symbols]

1 Electrophotographic photoreceptor (photoreceptor) 2 Magnetic brush primary charging member 3 Image exposure means 4 developing device 6 Transfer means 7 Transfer material 8 Fur brush auxiliary charger 10 Needle electrode 11 electrode plate 13 Grit electrode

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 2H068 AA14 AA21 AA34 AA43 AA44                       BA03 BB28 CA29 CA33 FA12                       FA18 FC02                 2H200 FA02 FA03 GA23 GA31 GA41                       HA02 HA28 HB06 HB08 HB22

Claims (8)

[Claims] 1. An electrophotographic photoreceptor having an intermediate layer and a photosensitive layer on a conductive support, wherein the intermediate layer contains rutile-type titanium oxide, and the photosensitive layer contains an alkyl diol having 2 to 12 carbon atoms. An electrophotographic photosensitive member characterized by containing. 2. The electrophotographic photosensitive member according to claim 1, wherein the intermediate layer further contains polyamide. 3. The rutile type titanium oxide has a particle size of 0.1.
The electrophotographic photosensitive member according to claim 1 or 2, wherein the electrophotographic photosensitive member has a thickness of not more than μm. 4. The rutile type titanium oxide is an alumina-treated titanium oxide.
Or the electrophotographic photosensitive member according to item 3. 5. The layer according to claim 1, wherein the alkyl diol is contained in a layer in contact with the intermediate layer.
The electrophotographic photosensitive member according to any one of 1. 6. An electrophotographic photoreceptor having an intermediate layer and a photosensitive layer on a conductive support contains rutile type titanium oxide in the intermediate layer, and the photosensitive layer contains an alkyl diol having 2 to 12 carbon atoms. An image forming method characterized in that an image is formed by repeating at least the steps of charging, image exposure and development using the electrophotographic photosensitive member. 7. The image forming method according to claim 6, wherein in the image forming method, the charging step is performed without passing through the step of eliminating the positional potential difference on the surface of the photoconductor. 8. The image forming method according to claim 6, wherein the charging step uses a needle-shaped electrode.