JPH07175233A - Single-layer electrophotographic photoreceptor - Google Patents

Abstract

PURPOSE:To provide a single-layer electrophotographic photoreceptor capable of preventing the generation of ozone as possible, excellent in electrostatic chargeability and sensitivity, excellent in the stability of the static charge characteristic even at the time of repeating copy process and suitable for LD optical writing. CONSTITUTION:In the single-layer electrophotographic photoreceptor obtained by dispersing at least a charge generating material 21, an organic positive hole moving material and an organic acceptor type compound into a binder on an electroconductive substrate directly or through an under layer, the reduction potential (Ered) of the organic acceptor compound to a saturated calomel electrode is -0.3 to -0.7V.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic electrophotographic photosensitive member, and more specifically, it is suitable for LD light writing of a single layer type (a photosensitive layer is composed of one layer) used for positive charging in an electrophotographic copying machine or printer. And an electrophotographic photosensitive member.

[0002]

2. Description of the Related Art Since the electrophotographic process uses the visualization of a latent image by electrostatic force as a principle, the electrophotographic photosensitive member used in the process has a good charging property in a dark place and a rapid irradiation by light irradiation. Attenuation of a large surface potential is required. The properties required for these processes depend on the high dark resistance, which is a physical property value, good quantum efficiency, and high charge mobility.

In order to satisfy these physical property values, a photoconductor made of an inorganic compound such as selenium, selenium-tellurium alloy and selenium arsenide has been adopted and has been used in many copying machines and printers. However, these materials have some environmental problems such as strong toxicity, are difficult to handle because they are used in an amorphous state, and are expensive because they need to be vacuum-deposited to a thickness of several + μm. However, it cannot be said that it sufficiently satisfies the necessary functions as a photoreceptor.

In order to improve these drawbacks, electrophotographic photoreceptors (OPC) using organic materials have been actively developed and put into practical use. Most of the practically used OPCs have a layer (CG) having a charge generation function.
L) and a layer having a charge transporting function (CTL), which is a laminated structure and is mainly used in a negative charging process.

The reason for this is that the photosensitive member formed by simply mixing the materials used and formed as a single layer has a drawback that the fatigue phenomenon of charging property, sensitivity and electrostatic property is lowered to a level less than practical. On the other hand, in the case of the laminated type, these defects are suppressed as much as possible, and the mechanical strength is high, and the CTL that enables thick film design is placed on the surface and is sufficient for the process. This is because it is possible to keep the photosensitive member with excellent mechanical durability. In addition, since the organic materials exhibiting a high charge mobility that does not hinder the high-speed copying process are limited to the donor compounds having only the property of hole transfer at present, the CTL formed by the donor compounds is not used. This is because the charging polarity of the photoconductor arranged on the front side is negative. However, such a function separation structure causes new problems.

The first is derived from the negative charge on the photoconductor. A highly reliable charging method in the electrophotographic process is based on corona discharge, and this method is used in most copying machines and printers. However, as is well known, the negative polarity corona discharge is unstable as compared with the positive polarity, and therefore, the charging method by the scorotron is adopted, which is one of the factors of cost increase. Also,
Because negative corona discharge accompanies more ozone generation,
Ozone filters are used in negatively-charged copying machines and printers in order to prevent discharge to the outside, which also causes an increase in the cost of the apparatus. With the positive charging method, the ozone generation amount can be suppressed to a very small amount due to the charging mechanism. Further, when the two-component type developer which is widely used in the present situation is used, a positively charged photoreceptor can produce a stable image with less environmental fluctuation, and from this viewpoint, it is desirable to adopt the positively charged photoreceptor.

The second one is derived from the laminated structure of the photosensitive layer. Although it is possible to use a solution coating method that is cheaper than the vacuum deposition method for a photoreceptor using an organic material,
In order to manufacture such a laminated type photoreceptor, at least 2
Repeated coating, usually by providing an undercoat layer immediately above the substrate (between the substrate and the photosensitive layer) to ensure the charging property of the photoreceptor 3
Needs to be applied twice. An increase in the number of solution coating steps causes an increase in the cost of the photoconductor. Furthermore, in order to maintain the balance between sensitivity and durability and obtain a good image, the thickness of CGL must be within the submicron range with considerable accuracy, which is a factor of increasing the manufacturing cost.

In view of the above problems, it is understood that the photoconductor is preferably a single-layer photoconductor using an organic material, particularly used in a positive charging process. Further, it is also understood that if the photoconductor can be used as it is or with a slight modification in the negative charging process, a photoconductor can be produced which has an advantage of being inexpensive and having a high degree of freedom in use environment. However, there are very few examples of photoreceptors that satisfy these conditions. As a single-layer type photoreceptor, polyvinylcarbazole and trinitrofluorenone charge transfer complex photoreceptor,
Only the eutectic complex photoconductor consisting of thiapyrylium dye and polycarbonate, the photoconductor in which the perylene pigment and the hydrazone donor are dispersed in the resin are counted. Among them, the former two examples have a problem in that they have low sensitivity and are repeatedly used, and they are used exclusively in the negative charging process, and therefore have a drawback of ozone generation. The last example has the drawback that it is not suitable for high speed copying processes due to the low sensitivity of the photoreceptor. Furthermore, a single-layer type photoconductor used in a digital copying machine or printer that uses LD light as a writing light source has not yet been put to practical use, and when the components of a put-to-use laminated type photoconductor are simply dispersed. In fact, the charging potential and the sensitivity are both low, and in particular, it is impossible to overcome the drawback that they are greatly changed in the repeated copying operation.

[0009]

SUMMARY OF THE INVENTION The object of the present invention is to prevent the generation of ozone as much as possible, to have excellent chargeability and sensitivity, and to have stable electrostatic characteristics with respect to repetition of the copying process, which is suitable for LD optical writing. The present invention provides a suitable single-layer type organic electrophotographic photoreceptor.

[0010]

According to the present invention, at least a charge-generating substance, an organic hole-transporting substance and an organic acceptor compound are dispersed in a binder directly or through an undercoat layer on a conductive substrate. In the dispersed single-layer type electrophotographic photoreceptor, the reduction potential value (Ered) of the organic acceptor compound with respect to the saturated calomel electrode is -0.3 to -0.7.
In the range of V and when the organic acceptor compound is molecularly dispersed in a polycarbonate resin in a polycarbonate resin / organic acceptor compound = 60/40 (weight composition ratio), an electric field strength of 5 × 10 ⁵ V / cm
Electron mobility is 10 in ^{- 7} cm ² / Vs which is characterized by using the above in which the organic acceptor compound single layer type electrophotographic photoreceptor is provided.

The present inventors have repeatedly studied from various angles about an organic electrophotographic photosensitive member which is a single-layer type and which is excellent in both positive and negative charging sensitivity and which is particularly suitable when LD light is used as irradiation light in positive charging. As a result, they have found that a desired photoreceptor can be obtained by using a specific organic acceptor compound as a photosensitive layer forming component, and completed the present invention.

The present invention will be described in more detail below.
In the drawings, 1 is a conductive substrate, 2 is a photosensitive layer, 21 is a charge generating substance, 22 is a layer in which an organic hole transfer substance and an organic acceptor compound are molecularly dispersed in a binder matrix. ing.

Such a photoreceptor of the present invention is excellent in chargeability and sensitivity, and is suitable for low speed to high speed copying processes.
In particular, it can be applied to a photoconductor of a digital copying machine or a page printer using LD light for optical writing. As mentioned above, what is particularly important in the present invention is that the reduction potential value (Ered) of the organic acceptor compound with respect to the saturated calomel electrode is in the range of −0.3 to −0.7 V, and the electric field strength is 5 ×. electron mobility in 10 ⁵ V / cm is, in the composition of the polycarbonate resin / organic acceptor compound = 60/40 (weight ratio), 10 ^{- 7}
It has a value of cm ² / Vs or more. By securing this characteristic value, particularly good positive chargeability and good sensitivity are realized.

According to the studies by the present inventors, the mechanism of the present invention for ensuring the excellent charging property and sensitivity is presumed as follows. When the electrostatic characteristics of a single-layer photosensitive layer in which a charge-generating substance (for example, an X-type metal phthalocyanine pigment) is dispersed in a resin together with an organic hole-transporting substance are examined, the reduction potential value (Ered) of the organic acceptor compound is measured. It has been found that the chargeability, sensitivity and electrostatic properties are different in repeatability. That is, when an organic acceptor compound having a small Ered (corresponding to a small electron affinity and having a large Ered, the absolute value thereof becomes large) has low sensitivity and poor reproducibility of electrostatic characteristics. . Also, Ere
It was found that an organic acceptor compound having a large d (corresponding to a large electron affinity, and a small absolute value when Ered is negative) results in a low charging property.

Unless an organic acceptor compound is present, the electrons generated by light irradiation cause a decrease in photosensitivity accumulated in the pigment particles and a decrease in repeated use resistance. By introducing an organic acceptor compound here to enable electron injection from the pigment particles to the organic acceptor compound, the phenomenon of electron accumulation can be suppressed, leading to higher sensitivity and improved repeatability. Conceivable.

Further, since the acceptor substance having a large electron affinity has a high conductivity itself, when the amount of the acceptor substance contained in the photoconductor exceeds a certain limit, the chargeability of the photoconductor is lowered, and the actual product is deteriorated. It becomes unsuitable for the image. Therefore, E
There is an appropriate range for red. Further, since the electron mobility is high, the generated electrons can be transported quickly. That is, it is considered that the sensitivity is improved because both holes and electrons are transported.

Examples of the organic acceptor compound that can be used in the present invention include quinone compounds, π-electron compounds having a nitrile group, and π-electron compounds having a nitro group. The amount of these organic acceptor compounds in the photosensitive layer is 1 to 40% by weight, preferably 5 to 40%.
wt%.

The value of Ered is such that these compounds are dissolved in a polar solvent such as acetonitrile, tetra-n-butylammonium perchlorate is used as a supporting electrolyte, platinum is used as a working electrode and a counter electrode, and saturated as a reference electrode. It can be obtained by sweeping the potential using a calomel electrode at a speed of about 200 mV / S and measuring the cyclic poltagram. Generally, the electron mobility is determined by inserting a film in which an organic acceptor compound is dissolved in a resin between two electrode plates, at least one of which is light-transmissive, and applying a voltage between the two electrode plates, It can be obtained from the transient photocurrent waveform obtained when the pulsed light is irradiated.

The role of the organic hole-transporting substance in the present invention is to increase the speed of holes moving in the photosensitive layer and to make it an electrophotographic photosensitive member which can cope with a high speed copying process. When there is no hole transfer substance, the surface potential does not start to be attenuated unless light energy of a certain amount or more is applied. If this phenomenon occurs, the amount of exposure that gives the electrostatic contrast required for development will increase, and the surface potential will continue to drop even after the exposure is completed. There is a drawback that it does. Hole transport materials reduce these drawbacks to low levels. The organic hole transfer substance in the present invention, a compound having a triphenylamine moiety in the molecule, a hydrazone compound, a triphenylmethane compound,
Examples thereof include an oxadiazole compound, a compound containing a carbazole group, a styryl compound and a butadiene compound. The content of these components in the photoreceptor is 15% by weight or more, preferably 20 to 40% by weight.

In the present invention, it is desirable that the amount ratio of the hole transfer substance and the organic acceptor compound is 1: 2.5 to 4: 1 (weight ratio). If the amount of the hole-transporting substance is larger than this, the repetition of electrostatic characteristics is lowered, and if it is small, the sensitivity particularly at the time of positive charging is lowered.

The role of the binder in the photoconductor is not only good dispersion of the charge generating substance and molecular dispersion of the organic hole transporting substance, but also the mechanical strength of the photoconductor required in the copying process. ing. Therefore, these properties are impaired when the proportion of the binder in the photosensitive layer is low. Therefore, the blending ratio of the binder cannot be unnecessarily low.

The binder which can be used in the present invention includes styrene, polyethylene, polypropylene, acrylic resin, methacrylic resin, vinyl chloride resin, vinyl acetate resin, epoxy resin, polyurethane resin, phenol resin, polyester resin, alkyd resin. , Addition resins such as polycarbonate resins, silicone resins, and melamine resins, polyaddition resins, polycondensation resins, and copolymer resins containing two or more of these repeating units, such as vinyl chloride-vinyl acetate copolymers. Polymer resin, vinyl chloride-
Vinyl acetate-maleic anhydride copolymer resin, styrene-
A butadiene copolymer etc. can be mentioned. The amount of these binders in the entire photosensitive layer is 30 to 90% by weight,
It is preferably 40 to 70% by weight, more preferably about 50% by weight. Examples of the charge generating substance used in the present invention include monoazo pigments, bisazo pigments, trisazo pigments, phthalocyanine pigments, perylene pigments, quinone pigments, indigo pigments, and quinacridone pigments. The composition of these is 0.1 to 40 wt%, preferably 0.3 to
20 wt% is suitable.

The thickness of the photosensitive layer of the present invention is preferably 5 to 100 μm. If it is thinner than this, the charging property is lowered, and if it is thicker, the sensitivity is lowered.

The conductive substrate that can be used in the present invention is a metal plate of aluminum, nickel, copper, stainless steel or the like, a metal drum or metal foil, a plastic on which a thin film of aluminum, tin oxide or copper iodide is vapor-deposited or applied. Examples thereof include film and glass.

In the photoreceptor of the present invention, an undercoat layer may be provided between the photosensitive layer and the conductive substrate for the purpose of improving the charging property. As the material for the undercoat layer, polyamide resin, polyvinyl alcohol, casein, polyvinylpyrrolidone, or the like can be used in addition to the binder material.

In order to prepare the photoreceptor of the present invention, a photosensitive layer forming solution prepared by dissolving or dispersing the above-mentioned materials in an organic solvent by a ball mill, ultrasonic waves or the like is applied by a dipping method or a blade coating method,
The photosensitive layer may be formed by coating the substrate with a spray coating method or the like.

[0027]

EXAMPLES The present invention will be specifically described with reference to Examples.
This does not limit the embodiments of the present invention.

Examples 1 to 5, Comparative Examples 1 to 2 1 g of X-type metal-free phthalocyanine pigment was added with 10 g of a polycarbonate Z (PC-Z) solution (1 in tetrahydrofuran).
(Dissolved in 0 wt%), ball milled with 9 g of tetrahydrofuran, then pigment composition 2 wt%, PC
-Z composition is 50 wt%, the acceptor compound shown in Table 1 below is 18 wt%, and the hole transfer substance shown in the following chemical formula 1 is added to the PC-Z solution, the acceptor compound, and the hole transfer substance so that the photosensitivity is increased. A body coating solution was prepared.
This solution is applied on an aluminum substrate and dried by heating to about 2
A 0 μm single-layer type photoreceptor was prepared.

[Chemical 1] Separately, a solution prepared by dissolving 0.4 g of the acceptor compound of Table 1 in 6 g of the PC-Z solution was applied onto an aluminum mylar and dried to give PC-Z / organic acceptor compound = 6.
A 10 μm film having a 0/40 weight composition ratio was provided, and gold was further vapor-deposited on the film to prepare a cell having a sandwich structure for measuring mobility. In addition, 10 mg of each of the organic acceptor compounds shown in Table 1 was dissolved in acetonitrile to obtain 0.1 m of tetra-n-butylammonium perchlorate.
It was dissolved in 25 g of ol / 1 and used as a sample for measuring the reduction potential value of the acceptor compound.

The reduction potential value (Ered) of the acceptor compound of Examples 1 to 5 and Comparative Examples 1 and 2 with respect to the saturated calomel electrode, and the sample in which the acceptor compound was molecularly dispersed in PC-Z were used to generate an electric field. Strength is 5 × 10 ⁵
The results of measuring the electron mobility (μ) at V / cm are shown in Table 1.

Further, the electrophotographic characteristics of the single layer type photoreceptors of Examples 1 to 5 and Comparative Examples 1 and 2 were positively charged at an applied voltage of about +6 kV and the electrophotographic characteristics were measured under the following conditions. Table 1 shows the obtained results. Electrophotographic characteristic condition: Irradiation light wavelength: 780 nm Exposure intensity: 1 μW / cm ^{2 In} Table 1, E1 / 2 (μJ / cm ² ) is the exposure amount required to attenuate the surface potential from 800V to 400V.

[0031]

[Table 1] In addition, A ₁ , A ₂ , A ₃ , A ₄ , A ₅ , A ₆ and A ₇ in Table 1 mean the compounds shown in Table 2, respectively.

[0032]

[Table 2]

The photoconductors obtained in Examples 1 to 5 and Comparative Examples 1 and 2 were used as digital copying machines (IMAGIO420 manufactured by Ricoh,
However, charging and photoquenching were repeated in the charging polarity changed to plus), and the charging potential (Vd) and the potential after photoquenching (Vr) were measured. The results are shown in Table 3.

[0034]

[Table 3]

Examples 6 to 8 and Comparative Examples 3 to 4 The hole transfer substance and the organic acceptor compound used in Example 2 were used, and the composition thereof (composition ratio = hole transfer substance / organic acceptor compound weight ratio). Example 2 except that
A photoconductor was prepared in the same manner as in. This photoconductor is +6 KV using an electrostatic copying tester (SP-428) manufactured by Kawaguchi Electric Co., Ltd.
Surface potential Vo (V) after 20 seconds of corona discharge for charging and dark decay for 20 seconds, and the exposure amount E1 / 2 required to decay to 1/2 of the surface potential Vo after white light exposure.
(Lux · sec) was measured, and charging and photoquenching were repeated to measure the charging potential (Vd) and the potential after photoquenching (Vr). The results are shown in Table 4.

[Table 4] *: Polycarbonate resin / organic acceptor compound (weight ratio)

[0036]

INDUSTRIAL APPLICABILITY The photoconductor of the present invention has an organic acceptor compound as a reducing potential value (E) with respect to a saturated calomel electrode.
red) is in the range of -0.3 to -0.7V, and
The electron mobility at an electric field strength of 5 × 10 ⁵ V / cm is polycarbonate resin / organic acceptor compound = 60 /
In the composition of 40 (by weight), 10 ^- from ⁷ cm ² / Vs for the use of more organic acceptor compound, it is possible to prevent the occurrence of ozone, also is excellent in chargeability and sensitivity. Further, when the weight composition ratio of the organic hole transfer substance and the organic acceptor compound is between 1 / 2.5 and 4/1, a single layer type electrophotographic photoreceptor having excellent sensitivity and good repeatability can be obtained. To be

[Brief description of drawings]

FIG. 1 is a schematic view of a typical single-layer type electrophotographic photosensitive member according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Conductive substrate 2 Photosensitive layer 21 Charge generating substance 22 Binder layer A layer in which an organic hole transfer substance and an organic acceptor compound are molecularly dispersed

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akio Kojima 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd.

Claims (3)

[Claims] 1. A single-layer type electrophotographic photoreceptor in which at least a charge-generating substance, an organic hole-transporting substance and an organic acceptor compound are dispersed in a binder, either directly or through an undercoat layer on a conductive substrate. In, the reduction potential value (Ered) of the organic acceptor compound with respect to a saturated calomel electrode
Is in the range of -0.3 to -0.7 V, and a single-layer type electrophotographic photosensitive member. 2. An electric field strength of 5 × 10 ⁵ V / cm when the organic acceptor compound is molecularly dispersed in a polycarbonate resin in a polycarbonate resin / organic acceptor compound = 60/40 (weight composition ratio). electron mobility is 10 in ^{- 7} cm ² / single-layer type electrophotosensitive material of claim 1, wherein Vs be used more than is organic acceptor compound characterized. 3. The single-layer type electrophotographic photosensitive member according to claim 1, wherein the weight composition ratio of the organic hole transfer material to the organic acceptor compound is 1: 2.5 to 4: 1.