JP3345689B2 - Single-layer electrophotographic photoreceptor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic electrophotographic photoreceptor, and more particularly, to a single-layer type electrophotographic photoreceptor suitable for positively charged (single-layer photosensitive) LD light writing.

[0002]

2. Description of the Related Art Since an electrophotographic process is based on the principle of visualizing a latent image by electrostatic force, an electrophotographic photosensitive member used in the process has good charging characteristics and a rapid surface potential due to light irradiation. Attenuation is required. The properties required for these processes depend on the solid properties such as high dark resistance, good quantum efficiency, and high charge mobility. Conventionally, photoconductors composed of inorganic compounds such as selenium, selenium-tellurium alloy and selenium arsenide have been employed to satisfy these physical properties, and have been used in many copying machines. However, these materials have some environmental problems such as high toxicity, and are difficult to handle because they are used in an amorphous state. Several tens of μm
However, there is a drawback such as high cost due to the necessity of vacuum deposition to a thickness of 3 mm, and it cannot be said that the required functions of the photoreceptor are sufficiently satisfied.

In order to improve these disadvantages, an electrophotographic photosensitive member (OPC) using an organic material has been actively developed and put to practical use. Practical OP
Most of C has a laminated structure including a layer having a charge generation function (CGL) and a layer having a charge transport function (CTL), and is used exclusively in a negative charging process.

The reason is that the materials used are mixed,
In the case of a photoreceptor simply formed as a single layer, in many cases, the disadvantage that the fatigue phenomena of chargeability, sensitivity, and electrostatic properties are reduced to a level less than a practical level is exhibited, whereas the laminated type eliminates these disadvantages. By placing CTL on the surface, which is as low as possible and has high mechanical strength and can be designed with a thick film, it is possible to keep the photoconductor with sufficient mechanical durability in the state subjected to the process This is because In addition, organic materials exhibiting a high charge mobility that does not hinder even a high-speed process are currently limited to donor compounds having almost only the property of hole transfer. This is because the charging polarity of the photoreceptor disposed on the front side becomes negative. However,
Such a function separation structure has caused a new problem.

The first one is derived from negative charging. A highly reliable charging method in the electrophotographic process is based on corona discharge, and this method is adopted in most copying machines and printers. However, as is well known, the negative corona discharge is unstable compared to the positive polarity,
Therefore, a charging method using a scorotron is adopted, which is one of the causes of cost increase. In addition, since negative polarity corona discharge involves more ozone, an ozone filter is used in a negative charging type copying machine or printer to prevent external discharge, which also increases the cost of the apparatus. Has become. In the case of the positive charging system, the amount of ozone generated can be suppressed to a very low level. Further, in the case of using a two-component phenomenon agent widely used at present, when the photosensitive member is positively charged, a stable image can be obtained with less environmental fluctuation, and from this viewpoint, a photosensitive member for positive charging is also desirable.

The second one is derived from the laminated structure. In the case of a photoreceptor using an organic material, it is possible to use an inexpensive solution coating method as compared with a vacuum deposition method.
Usually, three coatings are required to provide a subbing layer immediately above the substrate (between the substrate and the photosensitive layer) in order to ensure the chargeability of the photoreceptor. These cause an increase in cost of the photoconductor. Further, in order to maintain a balance between sensitivity and durability and to obtain a good image, it is necessary to sufficiently control the thickness of the CGL in the submicron range, which raises the manufacturing cost.

In view of the above problems, it is understood that a single-layer type photoreceptor using an organic material as the photoreceptor, particularly used in a positive charging process, is desirable. It is also understood that if the photoreceptor can be used for the negative charging process as it is or with a slight change, a photoreceptor having the advantages of being inexpensive and having a high degree of freedom in the use environment can be produced.

However, there are very few examples of photoconductors that satisfy such conditions. Examples of the single-layer photoreceptor include a charge transfer complex photoreceptor of polyvinyl carbazole and trinitrofluorenone, a eutectic complex type photoreceptor comprising a thiapyrylium dye and polycarbonate, and a photoreceptor in which a perylene pigment and a hydrazone donor are dispersed in a resin. It just counts.
Among them, the former two examples have low sensitivity and have a problem in repeated use, and further have a drawback of ozone generation because they are exclusively used in a negative charging process. The last example also has disadvantages that are unsuitable for high-speed copying processes due to the low sensitivity of the photoreceptor. Furthermore, single-layer photoconductors used in digital copiers and printers using LD light as a writing light source have not been put to practical use, and when components of a laminated photoconductor that has been put into practical use are simply dispersed, The fact is that both the charging potential and the sensitivity are low, and in particular, the disadvantage that they fluctuate greatly during repeated copying operations cannot be overcome.

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to minimize the generation of ozone, to have excellent chargeability and sensitivity, to have a high stability of electrostatic characteristics with respect to repetition of a copying process, and to realize LD light writing. It is another object of the present invention to obtain a single-layer type electrophotographic photosensitive member suitable for positive charging.

[0010]

According to the present invention, there is provided an electrophotographic photosensitive member in which a single organic photosensitive layer is provided on a conductive substrate directly or via an undercoat layer, wherein the photosensitive layer is at least A single-layer electrophotographic photoreceptor characterized in that an X-type metal-free phthalocyanine, an organic acceptor compound and an organic hole transfer material represented by the following general formula (I) are dispersed in a binder. Is provided.

Embedded image (In the formula, R ₁ and R ₂ represent a hydrogen atom, an alkyl group, or an aryl group, and may form a ring between R ₁ and R _2. Ar ₁ represents a heterocyclic group. Ar ₂ and A
r ₃ represents an alkyl group or an aryl group. Or expression
, _{R 1} and _{R 2} represents an aryl group, Ar ₁ is A
Ar ₂ represents a reel group , And Ar ₃ represents an aryl group . The present invention also provides the single-layer type electrophotographic photoreceptor wherein the weight composition ratio of the organic hole transfer material to the organic acceptor compound is in the range of 1 / 2.5 to 4/1.

The present inventors have studied various aspects of an organic electrophotographic photoreceptor which is single-layered and has excellent sensitivity in both positive and negative charging, and is particularly suitable in the case of using positively charged LD light as irradiation light. As a result of the superposition, it has been found that a desired photoreceptor can be obtained by using an X-type metal-free phthalocyanine as a photosensitive layer forming component and a specific organic hole transfer material and an organic acceptor compound together with the X-type metal-free phthalocyanine, thereby completing the present invention. Reached.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings. In the figure, 1 is a conductive substrate, 2
Denotes a photosensitive layer, and 21 denotes an X-type metal-free phthalocyanine which is a charge generating substance. Reference numeral 22 denotes a layer in which an organic hole transfer material and an organic acceptor compound are dispersed in a binder matrix in a molecular state. Such a photoreceptor of the present invention is excellent in chargeability and sensitivity, suitable for low-speed to high-speed copying processes, and is particularly suitable for a photoreceptor of a digital copying machine or a page printer using LD light for optical writing. Become.

Another advantage of the photoreceptor of the present invention is that the amount of the X-type non-metallic phthalocyanine used is smaller than that of a photoreceptor in which X-type non-metallic phthalocyanine is simply dispersed in a resin. In the former photoreceptor, if the amount of the pigment used is small, the sensitivity is reduced. Therefore, it is difficult to suppress the amount of phthalocyanine to about 10 wt% or less. However, in the photoreceptor of the present invention, 1 wt. % Or less of the phthalocyanine content. For this reason, compared to the former photoreceptor, the preparation of the coating liquid becomes easier,
Storage stability increases. Further, it is considered that the yield of coating is greatly improved.

As described above, the photoreceptor of the present invention comprises at least an X-type metal-free phthalocyanine, an organic hole transfer material, and an organic acceptor compound dispersed in a binder. The compound represented by the general formula (I) is used as the organic hole transfer material. Good sensitivity is realized by this use.

According to the study of the present inventors, the mechanism for realizing good sensitivity is estimated as follows. When the photoreceptor in which the X-type metal-free phthalocyanine particles used in the photoreceptor of the present invention are dispersed in a resin is positively charged and the light attenuation characteristic is examined, a so-called induction phenomenon is observed, where the attenuation of the surface potential is low immediately after light irradiation. . This phenomenon is generally recognized in a photoconductor in which a pigment is dispersed in a resin, and it is explained that a large number of trap sites exist on the surface of the pigment. Therefore, it is considered that many trap sites also exist on the surface of the X-type metal-free phthalocyanine.

On the other hand, when the single-layer photoreceptor obtained by adding the hole transfer material according to the present invention to the dispersion film of the X-type metal-free phthalocyanine particles is positively charged, and the light decay characteristics thereof are examined, the induction phenomenon is not observed. It was found that the light decay rate in the initial stage of light irradiation increased significantly. This is probably because traps on the pigment surface were compensated by the hole transfer material.
In addition, since the hole transport material used in the present invention can be dispersed in a molecular form in a resin, a uniform matrix is formed. Therefore, the hole mobility of the photoreceptor mainly depends on the hole transport in the matrix. It is considered to be determined in degrees. In this case, since the mobility of the hole transfer material used in the present invention is high among organic substances, the holes generated in the X-type metal-free phthalocyanine and the holes injected into the hole transfer material form the matrix without being trapped. It is believed that they migrate and result in a fast drop in surface potential.

Table 1 shows specific examples of the hole transfer material used in the present invention.

[0018]

[Table 1- (1)]

[0019]

[Table 1- (2)]

[0020]

[Table 1- (3)]

The amount of the X-type metal-free phthalocyanine used in the present invention in the whole photosensitive layer is 0.1 to 40 wt%,
Preferably, 0.3 to 25 wt% is appropriate. The role of the organic acceptor compound in the single-layer type photoreceptor of the present invention is to reduce the residual potential and extend the life of the electrostatic characteristics of the photoreceptor. Although the cause of these improvements is not clear, one of them is to prevent the reduction of the internal electric field of the charge generation material and to reduce the electric resistance by extracting electrons out of the holes and electrons generated by the charge generation material by light irradiation. It is conceivable to prevent the drop.

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

In the present invention, it is preferable that the amount ratio of the hole transfer material to the organic acceptor compound is between 1 / 2.5 and 4/1 (weight ratio). When the amount of the hole transporting substance is larger than this, the repetition of the electrostatic characteristics is reduced, and when the amount is smaller, the sensitivity particularly at the time of positive charging is reduced.

The role of the binder in the photoreceptor plays a role not only in the good dispersion of the charge generating substance and the molecular dispersion of the charge transfer substance, but also in the mechanical strength of the photoreceptor required in the copying process. . Therefore, when the composition at the time of binding is low, these properties are impaired. Therefore, the composition of the binder cannot be unnecessarily reduced. The proportion of these binders in the entire photosensitive layer is 30 to 90% by weight, preferably 40 to 70% by weight.

Examples of the binder that can be used in the present invention include polyethylene, polypropylene, acrylic resin, methacrylic resin, vinyl chloride resin, vinyl acetate resin, epoxy resin, polyurethane resin, phenol resin, polyester resin, alkyd resin, and polycarbonate. resin,
Silicone resin, addition polymerization type resin such as melamine resin, polyaddition type resin, polycondensation type resin and copolymer resin containing two or more of these repeating units, for example, vinyl chloride-
Examples thereof include a vinyl acetate copolymer and a vinyl chloride-vinyl acetate-maleic anhydride copolymer resin.

The thickness of the photosensitive layer is preferably from 5 to 100 μm. If the thickness is smaller than this, the chargeability is reduced, and if the thickness is larger, the sensitivity is reduced. As the conductive substrate that can be used in the present invention, aluminum, nickel, copper, a metal plate such as stainless steel, a metal drum or metal foil, aluminum, tin oxide,
Examples include a plastic film coated with a thin film of copper iodide, or glass.

In the photoreceptor of the present invention, an undercoat layer can be provided between the photosensitive layer and the conductive substrate for the purpose of improving the chargeability. As these materials, in addition to the binder material,
Polyamide resin, polyvinyl alcohol, casein, polyvinylpyrrolidone and the like can be used.

To prepare the photoreceptor of the present invention, the photosensitive layer forming liquid prepared by dissolving the above-mentioned materials in an organic solvent or dispersing the same by a ball mill, ultrasonic wave or the like is applied by dipping or blade coating.
What is necessary is just to apply | coat on a base | substrate by spray application etc. and to form a photosensitive layer.

[0029]

The present invention will be described below with reference to examples. Example1-2, Reference Examples 1-6  1 g of X-type metal-free phthalocyanine pigment in polycarbonate
10 g of Z (PC-Z) solution (1 in tetrahydrofuran
0 wt%), 9 g of tetrahydrofuran and
After both are ball milled, pigment 2wt%, PC-Z
Is 50 wt%, and the catalyst represented by the following formula (II) (Formula 2)
18 wt% of the septum compound, the hole transfer material shown in Table 2
15 wt% PC-Z solution so that the quality is 30 wt%,
Add the acceptor compound and the hole transport material, and apply the photoreceptor
A liquid was prepared. This solution is applied on an aluminum substrate and added.
Heat drying was performed to produce a single-layer photoreceptor of about 20 μm.

Embedded image

Comparative Example 1 The same procedures as in Example 1 were carried out except that the hole transporting substance was replaced with PC.
A single-layer type photoreceptor was produced in the same manner as in Example 1 except that -Z was used.

Comparative Example 2 A single-layer type photoreceptor was prepared in the same manner as in Example 1, except that the hole transfer material was replaced with the acceptor compound represented by Chemical formula 2.

The photoreceptors of the above Examples , Reference Examples and Comparative Examples were charged with a charge potential Vo (charged for 20 seconds and surface potential value after dark decay for 20 seconds) using an electrostatic copying paper tester (SP-428) manufactured by Kawaguchi Electric Co., Ltd. ) And the exposure amount (E1 / 2) required for the surface potential to attenuate to 後 after light irradiation, and the results in Table 2 were obtained.

[0033]

[Table 2] As is evident from Table 2, the sensitivity of the example was very excellent.

[0034]Reference Examples 7 to 11 Reference example Hole transfer material used in 4 and organic acceptor compound
And the composition ratio (hole transfer material / organic acceptor)
Example 3 except that the weight ratio of the active compound was changed as shown in Table 3.
A photosensitive layer was prepared in the same manner as in Example 1, and the electrostatic characteristics were measured.
In addition, this photoconductor is used as a digital copier (IMA
GIO420, but change the charging polarity to positive)
Charge, light quenching, and charging potential (Vd) and light
The potential (Vr) after quenching was measured. The results are shown in Table 3.
You.

[0035]

[Table 3] From Table 3, the charging characteristics and sensitivity vary depending on the weight ratio of the hole transfer material to the organic acceptor compound. In particular, when the weight ratio of the hole transfer material is more than 4/1, the repetition of the electrostatic characteristics is reduced, It can be seen that when the ratio is less than 1 / 2.5, the sensitivity decreases.

[0036]

The single-layer type electrophotographic photoreceptor of the present invention can minimize the generation of ozone, and has excellent chargeability and sensitivity.
It is highly stable in electrostatic characteristics against repetition of the copying process, and is therefore suitable for LD optical writing.
Further, by setting the weight ratio of the organic hole transfer material to the acceptor compound in the range of 1 / 2.5 to 4/1, sensitivity and repetition characteristics are further improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a single-layer type electrophotographic photoreceptor of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Conductive substrate, 2 ... Photosensitive layer, 21 ... Charge generating substance, 2
2 ... A layer in which an organic hole transport material and an acceptor compound are dispersed in a molecular form in a binder matrix.

──────────────────────────────────────────────────続 き Continued on the front page (72) Kaoru Teramura, Inventor Kaoru 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company, Ltd. (72) Emi Kawahara 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (72) Inventor Masayuki Koyano 1-3-6 Nakamagome, Ota-ku, Tokyo Co., Ltd. Inside Ricoh Co., Ltd. (72) Hisao Kurosu 1-3-6 Nakamagome, Ota-ku, Tokyo Co., Ltd. Inside Ricoh Company (72) Ikuko Yamada 1-3-6 Nakamagome, Ota-ku, Tokyo Co., Ltd. Inside Ricoh Company (72) Inventor Yumi Ichikawa 1-3-6 Nakamagome, Ota-ku, Tokyo Ricoh Company, Ltd. (56) References JP-A-62-103651 (JP, A) JP-A-62-24265 (JP, A) JP-A-6-130694 (JP, A) JP-A-6-130691 (JP, A) JP-A-6-13068 6 (JP, A) JP-A-5-45915 (JP, A) JP-A-5-45908 (JP, A) JP-A 4-295853 (JP, A) JP-A-3-256050 (JP, A) JP-A-1-319752 (JP, A) JP-A-1-24255 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 5/06

Claims (2)

(57) [Claims] 1. An electrophotographic photoreceptor having a single organic photosensitive layer provided directly or via an undercoat layer on a conductive substrate, wherein the photosensitive layer is at least an X-type metal-free phthalocyanine, an organic acceptor compound. And a single-layer type electrophotographic photoreceptor, wherein an organic hole transfer material represented by the following general formula (I) is dispersed in a binder. Embedded image (In the formula, R ₁ and R ₂ represent a hydrogen atom, an alkyl group, or an aryl group, and may form a ring between R ₁ and R _2. Ar ₁ represents a heterocyclic group. Ar ₂ and A
r ₃ represents an alkyl group or an aryl group. Or expression
, _{R 1} and _{R 2} represents an aryl group, Ar ₁ is A
Ar ₂ represents a reel group , And Ar ₃ represents an aryl group . ) 2. A single-layer type electrophotographic photoreceptor in which the weight composition ratio of an organic hole transfer material to an organic acceptor compound is in the range of 1 / 2.5 to 4/1.