JPH01237587A - Electrophotographic method - Google Patents

Abstract

PURPOSE:To decrease the residual potential generated in an organic photosensitive body simply, speedily, and also without any side effects to the characteristics of electrophotography by detecting the residual potential in the photosensitive body after a destaticization stage and heating the photosensitive body responding to the potential. CONSTITUTION:After the destaticization stage the residual potential of the photosensitive body is detected, and when it has reached a highest level than the specified potential (this differs according to electrostatic charge voltage and the types of photosensitive bodies), the photosensitive body is heated to >=90 deg.C. However, with heat <90 deg.C, it is practically difficult to decrease the residual potential to a level where a correction can be carried out by a developing bias (normally around 100V). Thus the residual potential can be decreased near the low level of a primary stage, without having any side effects to the original characteristics of electrophotography, and the substantial service life of the organic photosensitive body is greatly lengthened.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in electrophotography using organic electrophotographic photoreceptors.

As is well known, the electrophotographic method typified by the conventional Carlson process is an image forming method in which the steps of charging, exposing, developing, transferring if necessary, cleaning, and removing static electricity are repeated on the same electrophotographic photoreceptor. It is. The electrophotographic photoreceptor used in this method basically has a photosensitive layer containing a photoconductive substance on a conductive support. It is broadly classified as a photoreceptor. Furthermore, inorganic photoreceptors include a selenium-based photoreceptor in which the photosensitive layer is made of a vapor-deposited layer (amorphous) of Ss or its alloy, and a selenium-based photoreceptor in which the photosensitive layer is made of a non-selenium-based inorganic photoconductive material (ZnO, TiO2, C
dS, etc.) can be classified into an inorganic photoconductive material-dispersed photoreceptor consisting of a dispersed layer dispersed in a resin binder. On the other hand, in the case of organic photoreceptors, organic photoconductive substances (e.g. phthalocyanine pigments, azo pigments, polycyclic quinone pigments, polyvinyl carbazoles, hydrazone compounds, stilbene compounds, etc.) are used.
There are two types of substances: those that mainly generate charges upon exposure to light (charge-generating substances) and those that mainly transport charges ('1
Since two types of photoreceptors (cargo transport substances) are known, the usage pattern is slightly different from that of inorganic photoreceptors, and the photosensitive layer generally has a single-layer or laminated functionally separated structure using a combination of these two types of materials. ing. That is, the single layer type consists of a dispersed layer in which a charge generating substance and a charge transporting substance are dispersed or compatible with each other in a resin binder, while the laminated type consists of a charge generating layer mainly composed of a charge generating substance and a charge transporting substance in a resin binder. It consists of two layers: a charge transport layer and a charge transport layer dispersed in the charge transport layer.

Among the electrophotographic photoreceptors mentioned above, selenium-based photoreceptors have relatively high sensitivity, and the formation of a photosensitive layer is easy because the industrial mass production technology of vacuum evaporation has been established. A crystalline Se-based vapor deposited layer has the disadvantage that it is easily crystallized by external energy such as heat and stress, and when crystallized, the electrophotographic characteristics of that portion disappear. Therefore, in the case of a selenium-based photoreceptor, the time until the amorphous layer crystallizes is essentially the lifetime. It is also well known that this crystallization is accelerated as the temperature increases. In addition, selenium-based photoreceptors have poor flexibility, so it is difficult to make them into a belt. It also has the disadvantage that it has poor abrasion resistance and is easily activated by roughening the surface after repeated use, and when condensation occurs due to changes in temperature and humidity, it adsorbs moisture and causes image blurring. be. However, in order to prevent image blur due to adsorbed moisture, the surface of the selenium-based photoreceptor must be heated to below 60°C (Japanese Patent Application Laid-open Nos. 58-72160 and 58-90650).
No. 5g-117578, No. 58-118689, No. 52-129434, No. 57-56855) are known.

On the other hand, in the case of an inorganic photoconductive material-dispersed photoreceptor, the photosensitive layer is formed by a coating method that includes a heating drying process, so it has much better heat resistance than a selenium-based photoreceptor, and because it contains resin, It has good abrasion resistance and flexibility, but
The basic characteristics of electrophotography, particularly sensitivity and characteristics upon repeated use (stability), are insufficient, there is no transparency, and some materials are highly toxic, so they are hardly used at present.

In contrast to the above-mentioned inorganic photoconductors, in the case of organic photoconductors, the photosensitive layer is formed by a coating method that includes a heating and drying process, similar to the inorganic photoconductor dispersion system, so it is not only heat resistant but also wear resistant. In addition to being flexible, it also has good transparency, so when a transparent support is used, it is possible to efficiently remove static electricity from the support side (by exposing the entire surface to light), and it is also suitable for industrial products. Required and generally desirable conditions.

In other words, it has the advantages of high quality, high performance, stability, safety, mass production, economic efficiency, etc., so it has attracted particular attention in recent years and has become the mainstream of electrophotographic photoreceptors. When the residual potential increases (particularly markedly under high temperature and high humidity conditions), it is extremely difficult to recover (reduce) the residual potential (at room temperature, it is reduced by half in three months), which is a drawback.

An object of the present invention is to provide an electrophotographic method that reduces the residual potential generated in an organic photoreceptor very effectively, easily, quickly, and without any side effects on the original electrophotographic properties. .

Supervisor - Ikku The electrophotographic method of the present invention involves detecting the residual potential of the photoreceptor after the static elimination process in an electrophotographic process in which at least the steps of charging, exposing, developing, and eliminating static electricity are repeatedly performed on an organic electrophotographic photoreceptor. The method is characterized in that the photoreceptor is heated to 90° C. or higher, preferably 100° C. or higher depending on this potential.

The upper limit of the heating temperature varies depending on the material constituting the photoreceptor, but is usually 150° C. or lower, which is the upper limit of the drying temperature.

As mentioned above, the residual potential generated in an organic electrophotographic photoreceptor increases over a long period of time at the normal environmental temperature in which the photoreceptor is placed (about 10 to 30 degrees Celsius at room temperature, and about 50 degrees Celsius in an electrophotographic copying machine). Conventionally, the residual potential of organic photoreceptors is thought to be caused by irreversible chemical reactions (e.g., ionic reactions within the photosensitive layer; deactivation due to decomposition of constituent components, etc.). For this reason, in the case of organic photoreceptors, emphasis has been placed on developing materials and structures that reduce the degree of residual potential. However, as a result of a detailed study by the present inventors on the residual potential in organic photoreceptors, it has been found that irreversible chemical reactions associated with photoreceptor fatigue are hardly recognized, or even if compared with other causes. It has been found that even if there is a difference, it is so slight that it can be ignored in practical terms. This means that the residual potential in the organic photoreceptor can be recovered as long as an irreversible chemical reaction is not involved. Based on these findings, the present inventors investigated this residual potential in more detail and found that in the case of the functionally separated organic photoreceptor described above, the residual potential is in the photosensitive layer in the case of a single layer type, or in the laminated layer. In the present invention, we have discovered that this is caused by extremely deep energy level traps in the charge transport layer, and that it is effective to heat the photoreceptor above a certain temperature in order to release these traps. This is based on these findings.

For the selenium-based photoreceptor described above, a method is known in which the surface of the photoreceptor is heated at a low temperature of about 60° C. or lower in order to prevent image blurring due to dew condensation. However, in the case of a selenium-based photoreceptor, crystallization is promoted even at such a low temperature, which is not preferable.

On the other hand, in the method of the present invention, in order to remove the residual potential generated in the organic photoreceptor, the photoreceptor is
It is characterized by heating to a temperature of 0°C or higher. However, even if high-temperature heating is performed in this way, in the case of organic photoreceptors, the heating temperature is usually 80 to 150°C.
Since it is manufactured using a coating method that includes (degrees of can do.

The organic photoreceptor used in the method of the present invention is preferably of the functionally separated type as described above.

In other words, this type of organic photoreceptor is one in which a single-layer photosensitive layer containing a charge generating substance, a charge transporting substance and a resin binder as main components is provided on a conductive support, and one in which a charge generating substance is provided on a conductive support. It is provided with a charge generation layer whose main components are a charge generation layer and a charge transport layer whose main components are a charge transport substance and a resin binder.

As the conductive support, a material having an electrical resistance of 10" Ωl or less, such as a drum or plate of metal or alloy such as AQ, Ni, Cr, NiCr, stainless steel; AQ, Ni, Cr, Ni
Cr.

Metals or alloys such as Cu, Ag, Au, Pt, carbon,
Conductive substances made of metal oxides such as tin oxide and indium oxide are coated on the surface of plastic films such as polyester, polyimide, polycarbonate, paper, processed paper, etc. by vacuum deposition, sputtering, coating, etc. (the shape is sheet-like or belt-like).

Examples of the charge generating substance include CI Pigment Blue 25 [Color Index (CI) 211803,
Benzine derivative disazo pigments such as C.I. Pigment Red 41 (CI21200); xanthine dyes such as C.I. Acid Red 52 (CI 45100) and C.I. Basic Red 3 (CI 45210); phthalocyanine pigments having a porphyrin skeleton; azulenium salt pigments; Squaric Salt raw materials: disazo pigments having a carbazole skeleton (described in JP-A No. 53-95033), disazo pigments having a styrylstilbene skeleton (described in JP-A-53-138229), trisazo pigments having a triphenylamine skeleton (Unexamined Japanese Patent Publication No. 53-
132547), disazo pigments having a dibenzothiophene skeleton (described in JP-A-54-21728), disazo pigments having an oxadiazole skeleton (described in JP-A-54-12742), fluorenone skeleton disazo pigment having (JP-A-54-22834
Disazo pigments having a bisstilbene skeleton (described in JP-A-54-17733), disazo pigments having a distyryloxadiazole skeleton (described in JP-A-54-2129), Disazo pigment with styrylcarbazole skeleton (Japanese Patent Application Laid-Open No. 54-1773
4), trisazo pigments having a carbazole skeleton (JP-A-57-195767, JP-A-57-1)
Azo pigments such as CI Pigment Blue 16 (CI 74100); CI Bat Brown 5 (CI 734);
10) Indigo pigments such as CI Bat Dye (CI 73030); organic pigments such as perylene pigments such as Argol Scarlet B and Indus Thread Scarlet R (/(manufactured by Inil)).

Among these charge-generating substances, azo pigments are particularly preferred, and among the azo pigments, disazo pigments and trisazo pigments as shown below are most preferred.

(1) Disazo pigments with a fluorenone skeleton A (2) 141 sets of trisazo pigments with a triphenylamine skeleton (blank below) (3) Disazo pigments with a styrylstilbene skeleton (
A−N=N+■c=HCeor=co×N=NA) Next, as charge transport substances, poly-N-vinylcarbazole and its derivatives, poly-carbazolylethyl glutamate and its derivatives, pyrene- Formaldehyde condensates and their derivatives, polyvinylpyrene, polyvinylphenanthrene, oxazole derivatives, oxadiazole derivatives, imidazole derivatives, triphenylamine derivatives, 9-(P-diethylaminostyryl)anthracene, 1,1-bis-(4-dibenzyl) Examples include electron-donating substances such as aminophenyl)propane, styryl anthracene, styryl pyrazoline, phenylhydrazones, and α-phenylstilbene derivatives.

Examples of the resin binder include polystyrene, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-maleic anhydride copolymer, and polyester. Polyvinyl chloride, vinyl chloride-vinyl acetate copolymer,
Polyvinyl acetate, polyvinylidene chloride, acrylic resin,
Phenoxy resin, polycarbonate, cellulose acetate resin, ethyl cellulose resin, polyvinyl butyral, polyvinyl formal, polyvinyltoluene, poly-N-
Examples include thermoplastic or thermosetting resins such as vinyl carbazole acrylic resin, silicone resin, epoxy resin, melamine resin, urethane resin, phenol resin, and alkyd resin.

Note that resin binders such as those mentioned above are usually used in combination with the charge generation layer. Furthermore, additives such as plasticizers and leveling agents may be added to the single-layer type photosensitive layer and the laminated type photosensitive layer, especially the charge transport layer, if necessary.

Generally, both the single-layer type photosensitive layer and the laminated type photosensitive layer (charge generation layer and charge transport layer) are formed by a coating method.

The charge generation layer can be formed by vapor deposition when a resin binder is not used.

The amount of the charge generating substance and the charge transporting substance in the single-layer photosensitive layer is 1.5 to 25 parts by weight, respectively, per 100 parts by weight of the resin binder.
0 parts by weight, and about 25 to 200 parts by weight. In addition, the amount of charge transport material in the charge transport layer is 100% of the resin binder.
Approximately 25 to 300 parts by weight is the weight part. On the other hand, the appropriate thickness of the single-layer type photosensitive layer is about 5 to 1004 m, and the thickness of the laminated type photosensitive layer is 0.0 m for the charge generation layer.
01-5μm, about 5-100μm for charge transport layer
A seaweed level is appropriate.

In the present invention, in addition to the functionally separated photoconductor described above, a type of photoconductor that does not have any functional separation can also be used. Such a non-functionally separated type photoreceptor is one in which a photosensitive layer containing the above-mentioned charge transporting substance (electron donating substance) and a resin binder as main components is provided on a conductive support. The formation method, thickness, additives, etc. of such a photosensitive layer may be substantially the same as those for a single-layer sensitized photosensitive layer of a functionally separated photoreceptor.

Note that in the organic photoreceptor as described above, a resin subbing layer can be provided between the conductive support and the photosensitive layer. Examples of the resin for the undercoat layer include polyvinyl alcohol, polyvinyl butyral, methyl cellulose, polyamide, casein, phenol resin, and epoxy resin. Further, conductive powders such as tin oxide and antimony oxide; white pigments such as zinc oxide, zinc sulfide, and titanium oxide; and light-absorbing pigments such as carbon, various metal powders, and organic pigments may be added to the undercoat layer. Can be done. Note that these powders and pigments may be added to the plastic support as described above.

Next, the heating means used in the method of the present invention include an electric heater using a resistor such as a nichrome wire or ceramic as a heat source;
Examples include infrared lamps and hot air devices. These may be provided on the front side (photosensitive layer side) or the back side (support side) of the photoreceptor. In the case of electric heaters, a resistor may be provided within the support. Furthermore, when plastic is used as the support for the photoreceptor, a suitable resistive substance may be added to the plastic to generate heat when energized.

The steps of charging, exposing, developing, and eliminating static electricity in the present invention may be exactly the same as those in the conventional method. That is, V is between -4 and -10 for an organic photoreceptor.
After applying electrical charge and exposing the image. The image is developed with a dry developer, and if necessary, the resulting image is transferred and fixed onto a transfer paper, and/or after the photoreceptor is cleaned, the entire surface of the photoreceptor is exposed to light to eliminate static electricity.In the present invention, after the static elimination step, the photoreceptor is The residual potential of the body is detected, and when it reaches a predetermined potential or higher (varies depending on charging pressure and type of photoreceptor), the photoreceptor is heated to 90° C. or higher as described above. As is clear from the examples, it is practically difficult to reduce the residual potential to a level (usually around 100 V) that can be corrected by a developing bias when heating at a temperature lower than 90°C.

The present invention will be explained in more detail below with reference to Examples. Note that all parts are parts by weight.

Example A Ni-based heat-resistant alloy [Ni,
56%, Cr16.5%, Fe5%, 14.2%, M
nO, 6%.

Using Goo, 5%, SiO, 2% (all percentages are VTG) targets, a semi-transparent conductive layer of about 200 layers was formed by sputtering so that the average transmittance in the visible range was 35%. 6wt% of polyamide resin (CM-8000 manufactured by Toshisha Co., Ltd.) was applied to the surface of this conductive layer, which was used as a conductive support.
Solution [Solvent is methyl alcohol 10 to polystyrene sulfone fiNa (Chemistat C6120 manufactured by Sanyo Chemical Co., Ltd.)
Water content (content is 6wt% based on polyamide resin) 2~
Butyl alcohol 1 (weight ratio) mixture was coated with a roll coater and dried at 115°C for 10 minutes to form a 1μI thick subbing layer.2.5 parts of 6th pigment & 1 disazo pigment, polyvinyl Butyral resin (1 part of XYI (L) manufactured by Union Carbide, 39 parts of tetrahydrofuran, and 58 parts of ethyl cellosolve) was ball-milled for 72 hours, and this liquid was applied to the surface of the undercoat layer so that the light transmittance at a wavelength of 580 nm was 0.7. % with a roll coater, 110%
It was dried for 10 minutes at .degree. C. to provide a charge generation layer with a thickness of about 0.5 .mu.I. Further, on this charge generation layer, 9 parts of polycarbonate (C-1400 manufactured by Yojin Kasei Co., Ltd.) was added as a charge transport material.
A solution consisting of 10 parts and 0.002 parts of silicone oil (KF-50, manufactured by Shin-Etsu Chemical Co., Ltd.) as a leveling agent was applied with a blade and dried at 120°C for 15 minutes to form a charge transport layer with a thickness of 28 μm. I made a photoreceptor.

■A photogenic and natural conductive layer was formed by vacuum evaporation of AQ to about 600 ml, and an organic electron layer was formed using the same method as in the case of photoreceptor A, except that no subbing layer was provided and a charge transporting material was used. Photographic photoreceptor B was made.

Organic electrophotographic photoreceptor C was prepared in the same manner as photoreceptor A except that C6120 was removed from the Naoko Hondachi underlayer forming solution.

Organic electronics were prepared in the same manner as in the case of photoreceptor B, except that the thickness of the AJII conductive layer was set to approximately 200 mm so that the average transmittance in the visible range was 30%. I made a photoreceptor. Next, each of the photoreceptors described above is processed into an endless belt shape, and this is used in an electrophotographic copying machine for plain paper as shown in Fig. 1 (in the figure, 1 is a photoreceptor belt, 2 is a flash lamp, 3 is a mirror, and 4 is a lens). .

5 is a charging charger, 6 is a developing device, 7a is a transfer charger, 7b is a separation charger, 8a is a static elimination lamp, 8b is a light guide, 9 is a cleaning device, 10 is a fixing device, 11 is a paper discharge tray, 12 is a cassette for storing transfer paper, 13 is a registration roller, 14 is an electric heater, 15 is a potential sensor, 16 is a timing sensor, ] 7 is a static elimination lamp), and heated at 30°C at 90°C.
%RH atmosphere, the steps of charging, exposure, development (however, no developer was supplied), transfer (however, the transfer paper was not passed), cleaning, and static elimination were repeated 5000 times. The reason for operating under high temperature and high humidity was to increase the residual potential in a short time. The operating conditions at this time are charger discharge voltage -8KV (
Charge to photoreceptor 4-1300V).

Photoreceptor linear speed 37ax/sec, exposure amount 1 nux-sa
c. Transfer charger discharge voltage -8KV (-230μA
), and the static elimination lamp exposure amount was 3.5 Qux-sec. Incidentally, each of the irradiation lights for charge removal, exposure, and erasing is filtered by a Y48 filter to remove wavelength components of 480 nm or less.

After that, the temperature was returned to normal temperature (20°C) and normal humidity (65% R1 ()), the residual potential vR was measured, and the residual potential was measured again after being left overnight.
(consisting of a reflecting mirror) was heated for the temperature and time shown in Tables 1 to 4, and then returned to room temperature and the residual potential was measured. The reason why the photoreceptor after fatigue was left for a day and night was to show how slow the recovery speed of the residual potential is, and also to show that it is unrelated to mere temporary adsorption of moisture.

On the other hand, a part of each photoreceptor was cut out at each step of measuring the residual potential as described above, and other electrophotographic characteristics were measured using a paper analyzer (manufactured by Kawaguchi Electric Co., Ltd., 5P-428).

The results are also shown in Tables 1 to 4 below. The measurement conditions were dynamic mode, and the discharge flow was -2, 47! A, light amount 4,
5Qux, charging time 30 seconds, dark decay time 20 seconds, and exposure time 30 seconds.

Also, v2 after 1112 seconds, V+wax after 30 seconds,
The dark decay for 20 seconds from Vmax was defined as DD. In addition, the initial potential is -aoov, and the new potential is 1/2.1
The exposure amount (corresponding to sensitivity) required to attenuate to El/2.15 and El/10, respectively. E115. El/10 (Q
ux-sec).

Regarding photoreceptors A and C, in order to show the effect of C6120 as reference data in Tables 4 and 5, low temperature and low humidity (10℃,
The steps of charging, exposure, etc. are carried out in an atmosphere of 15% R1.
The data obtained when the test was repeated 000 times are shown together with the data on the reduction in residual potential due to heating.

(Margin below) Table-1 Opaque body A) *After 5000 repetitions at 30°C, 90ZRI+).

*Repeatedly at 30°C twice) From these tables, it is difficult to recognize that the residual potential of the organic photoreceptor has recovered to 1 level in practice when heated to less than 90°C, let alone at room temperature. It can be seen that when heated to 90° C. or higher as in this example, the residual potential can be rapidly reduced to a low level that does not pose a problem in practice. At the same time, organic photoreceptors show almost no fatigue other than residual potential (and therefore sensitivity of El/2. It will be understood that there is no.

As can be seen from the above table, the effect of reducing residual potential in a functionally separated organic photoreceptor depends on the type of conductive layer, the type of charge generating agent and charge transport material, and the type of undercoat layer (added with ionic substance C6120). The presence or absence of (and non-added) is irrelevant. Incidentally, if the level of the residual potential and the film thickness of the charge generation layer are taken into consideration, it can be inferred that the extent to which the residual potential is related to the charge generation layer in a stacked functionally separated organic photoreceptor is extremely small.

Furthermore, the above experimental results suggest that the residual potential of an organic photoreceptor is caused by charge traps at an extremely deep energy level in the charge transport layer in the case of a laminated type photoreceptor.

When the photoreceptor was similarly tested using 5,000 charge-exposure repetitions as one unit, a residual potential that did not recover even with heating appeared after the 5th time, and it stopped showing light attenuation halfway through the 15th time (Table 1). 4).

This is because the thin layer of AQ becomes insulated during anodization, and the effect of the present invention cannot be maintained semi-permanently on organic photoreceptors having such a conductive layer. The method of the present invention is particularly effective for organic photoreceptors having a conductive layer.

According to the method of the present invention, by heating an organic photoreceptor that has generated a residual potential to 90°C or higher, the residual potential can be almost completely eliminated without any side effects on the original electrophotographic characteristics. Since the heat treatment can be reduced to an initial low level, the practical life of the organic photoreceptor can be dramatically increased, and it is therefore clear that the heat treatment of the present invention has great significance.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of an electrophotographic copying machine used in Examples. 1...Organic photoreceptor belt 2...Flash lamp 3...Mirror 4...Lens 5...Charging charger 6...Developing device W 7a...Transfer charger 7b... Separation charger 88... Static elimination lamp 8b... Light guide 9.
...Residual toner collection device 10...Fixing device 11...Output tray 12...
Transfer paper storage cassette 13... Registration roller 14... Heater 15... Potential sensor 16
... Timing sensor 17 ... Static elimination lamp Patent applicant Rico Co., Ltd. -

Claims (1)

[Claims] 1. In an electrophotographic method in which an organic electrophotographic photoreceptor is repeatedly subjected to at least the steps of charging, exposure, development, and charge removal, the residual potential of the photoreceptor is detected after the charge removal step, and the photoreceptor is heated to 90% according to this potential. An electrophotographic method characterized by heating above ℃.