JPH0697358B2 - Electrophotographic device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electrophotographic apparatus using reversal development, in particular, a charging potential, a time from charging to development, and a potential at which a toner development density becomes half-value. The present invention relates to an electrophotographic device set to a relationship.

[Prior Art] The electrophotographic process is roughly divided into two types, that is, a normal development and a reversal development when attention is paid to a development method.

In the basic electrophotographic process of forming a latent image on the surface of a photosensitive member by primary charging of the photosensitive member, image exposure, toner development, and cleaning, positive development means that the image exposure on the photosensitive member is not applied or the amount of irradiation light is The relatively small area, in other words, the area where the absolute value of the photoreceptor surface potential is higher is developed with toner, while the reverse development is the opposite of this, where the area where the absolute value of the photoreceptor surface is lower is developed with toner. Therefore, the development is performed using a toner having the same polarity as the primary charge.

Conventionally, the method generally used as an electrophotographic apparatus is positive development, but in recent years, the reversal development method is also widely used in microfilm printers, electrophotographic printers (laser printers) that use a laser as a light source, and the like. Is becoming more common.

As electrophotographic photoreceptors, selenium, selenium-based alloys,
Cadmium sulfide resin dispersion system, amorphous silicon, organic optical semiconductor (OPC) system, etc. are used. Among them, OPC has attracted much attention recently due to its high productivity and low production cost, and it has been widely put into practical use. Is being done.

Many organic photoconductors have been developed since the discovery that certain organic compounds exhibit photoconductivity. For example, organic photoconductive polymers such as poly-N-vinylcarbazole and polyvinylanthracene, low molecular organic photoconductors such as carbazole, anthracene, pyrazolines, oxadiazoles, hydrazones, and polyarylalkanes and phthalocyanine pigments, Organic pigments and dyes such as azo pigments, cyanine dyes, polycyclic quinone pigments, perylene pigments, indigo dyes, thioindigo dyes and squaric acid methine dyes are known.

In particular, since organic pigments and dyes having photoconductivity are easier to synthesize than inorganic materials, and the variation that allows selection of compounds exhibiting photoconductivity in an appropriate wavelength range has been expanded, there are many Conductive organic pigments and dyes have been proposed.

For example, U.S. Pat.Nos. 4,123,270, 4,247,614, 4,251,413, 4,251,614, 4,256,821, 4,260,672, 426,859.
Disazo pigments exhibiting photoconductivity as a charge generating material in a photosensitive layer functionally separated into a charge generating layer and a charge transporting layer as disclosed in No. 6, No. 4278747, No. 4293628, etc. An electrophotographic photosensitive member using such an organic photoconductor is known, and an electrophotographic photosensitive member using such an organic photoconductor can be produced by coating by appropriately selecting a binder, and therefore has extremely high productivity and is inexpensive. It has the advantage that a photoconductor can be provided and that the photosensitive wavelength range can be freely controlled by selecting an organic pigment.

Laminated photoreceptors obtained by laminating a charge transport layer and a charge generation layer containing a charge generating material as a main component are more advantageous than other single-layer photoreceptors in sensitivity and increase in residual potential after durability test. Is.

In the multi-layer type photoreceptor, the charge generation layer is formed by coating a charge generation material such as a phthalocyanine pigment, a dibenzpyrene pigment, and an azo pigment and, if necessary, a charge transport material on a substrate together with an appropriate binder (without a binder). Although it can be formed by the above method, or can be obtained by forming a vapor deposition film by a vacuum vapor deposition apparatus, the coating method is currently mainly used because of the ease of formation.

However, if an organic pigment is used as the charge generating material and a charge generating layer that is dispersed and applied is used here, the dispersed particle size is not uniform, and the pigments locally aggregate on the coated surface due to aggregation of the pigments during coating. Since a large charge injection point is formed locally and a particularly large dark spot potential is locally generated, when the copy image is formed by using this as a photoconductor, the local charge injection point Appears as an image defect.

In particular, when such a photoreceptor is used in a copying machine that performs reversal development, the local charge injection point of the charge generation layer using the pigment described above has a lower absolute value of surface potential than other portions. Since this is a dot, this portion is subjected to toner development and becomes a black dot-like image defect.

[Problems to be Solved by the Invention] An object of the present invention is to improve the above-mentioned drawbacks and to use a laminated electrophotographic photoreceptor using a charge generation layer of an organic pigment dispersion system,
An object of the present invention is to provide an electrophotographic apparatus that supplies an image having no image defects in the electrophotographic apparatus that performs reversal development.

[Means and Actions for Solving the Problems] The present invention achieves the above object by setting the potential immediately after primary charging, the time from charging to development, and the potential at which the toner development density is half the value in a certain relation. Is what you are trying to do.

That is, the present invention is an electrophotographic apparatus that performs reversal development for developing a portion having a low absolute value of electric potential in an electrophotographic process including primary charging / image exposure, development / cleaning steps, and an organic photo-semiconductor pigment. In an electrophotographic apparatus having a laminated-type photoconductor that uses a solvent or a layer in which a solvent and a polymer binder are dispersed and applied as a charge generation layer, the potential of the photoconductor and the process conditions are under certain conditions, and the certain conditions are the primary The surface potential Vd (V) of the photoconductor immediately after being charged by the charger, the time t (sec) from primary charging to toner development, and the surface potential of the photoconductor when the toner development density becomes half the saturation density are V _H When (V) is set, Vd, t, and _VH are in the range of the following formula, which is an electrophotographic apparatus.

^│V _H │ ≦ (| Vd | ^-0.65 + 1.35 × 10 ^-2 t) ^-1.54 (Vd and V _H have the same sign) However, in the case of bias exposure (image exposure that is also performed on the white background part of the back) Is Vd, the potential immediately after image exposure, and t is the time from image exposure to toner development.

In the present invention, a layered type photoreceptor having a function separation type and a layer in which an organic pigment as a charge generating material is dispersed and coated is used as a charge generating layer, and a charge transport layer is provided thereon.

The decay of the surface potential in the dark portion of the photoconductor after being charged depends largely on the characteristics of the charge generation layer.

That is, the amount of thermal charge injected from the substrate to the charge generation layer, the amount of thermal charge in the charge generation layer, and the amount of photocharges accumulated in the charge generation layer due to light irradiation before charging are the coating state of the charge generation layer. Have a close relationship with.

Hereinafter, these relationships will be described based on experimental examples.

An experimental sample was prepared by dissolving 10 parts by weight of a copolymerized nylon resin (trade name: Toresin, manufactured by Toray Industries, Inc.) on a thin plate-like aluminum surface in a mixed solution consisting of 60 parts by weight of methanol and 40 parts by weight of butanol, and forming a conductive substrate. 2.0 μm by dip coating on top
An intermediate layer of polyamide was provided.

Next, ε-type copper phthalocyanine (trade name: Lyonol Blue
1 part by weight of ES, manufactured by Toyo Ink Co., Ltd., 1 part by weight of butyral resin (trade name: Eslec BM-2, manufactured by Sekisui Chemical Co., Ltd.), 10 parts by weight of cyclohexanone, and 50 parts of 1 mm diameter glass beads 50
Dispersion time of 0 to 20 minutes with sand mill disperser together with parts by weight.
Thirteen kinds of dispersion liquids that were changed over time were prepared.

The dispersion time of this dispersion and the average particle size of ε-type copper phthalocyanine are shown below.

Dispersion time Average particle size (min) (μm) 0 1.2 1 0.53 5 0.46 10 0.35 30 0.25 60 0.13 120 0.09 180 0.08 300 0.07 420 0.07 600 0.06 900 0.05 1200 0.05 * Sample with dispersion time 0 min is mixed with glass beads Each dispersion was applied as a coating solution on the above intermediate layer, and 100
It was dried at 0 ° C. for 5 minutes to form a 1.0 μm thick charge generation layer.

As another sample, a dispersion liquid having a dispersion time of 1200 minutes was used as a coating liquid, and the charge generation layer film thickness was 0.1 μm, 0.2 μm, 0.4 μm, 0.7 μm, 1.0 μm, 1.5 μm, 2.0 μm, 3.0 μm, 5.0. Similarly, 9 kinds of charge generation layers having different film thicknesses were provided by coating and drying on the above intermediate layer so as to have a thickness of μm.

Then, 10 parts by weight of a hydrazone compound having the following structural formula, And 15 parts by weight of styrene-methyl methacrylate copolymer (trade name: MS200, Nippon Steel Chemical Co., Ltd.) in 90 parts of toluene
A coating solution was prepared by dissolving it in parts by weight, and was applied on the charge generation layer by dip coating. After leaving it for 10 minutes, it was heated and dried at 100 ° C. for 1 hour to form a charge transport layer having a thickness of 16 μm.

The electrophotographic photosensitive member thus produced was charged to −700 V by corona charging (negative polarity), and then the amount of attenuation of the surface potential in the dark portion for 1 second was measured, and the results shown in FIGS. 1 and 2 were obtained. .

FIG. 1 shows the relationship between the average particle size of the charge generation material and the amount of attenuation of the surface potential in the dark portion, and FIG. 2 shows the relationship between the thickness of the charge generation layer and the amount of attenuation of the surface potential in the dark portion. It is a thing.

From the results shown in FIGS. 1 and 2, the larger the average particle size of the charge generation material and the larger the thickness of the charge generation layer,
It is recognized that the surface potential is attenuated in the dark part, that is, the charge injection amount from the charge generation layer to the charge transport layer in the dark part is increased, and it tends to be saturated above a certain value.

This is an example of ε-type copper phthalocyanine, but the same tendency is observed when other organic pigment-dispersed charge generation layers are used.

As described above, the charge injection amount in the dark portion from the charge generation layer to the charge transport layer is closely related to the particle size of the organic pigment as the charge generation material and the film thickness of the charge generation layer. When dispersed as a charge generation layer, these particle diameters and film thicknesses are very uneven on the actual coated surface of the photoreceptor,
Has a wide distribution.

That is, first, as a method for dispersing the organic pigment, a roll mill, a ball mill, a vibrating ball mill, an attritor, a sand mill, a colloid mill or the like is used, but the particle diameter of the organic pigment dispersed by these methods becomes small on average. However, there are always large particles.

Further, even when these large particles are removed by filtration or the like, the average particle size tends to increase during storage of the dispersion liquid due to the cohesiveness of the pigment itself.

In addition, even during coating, the organic pigment agglomerates centering on scratches, dents, dust adhering to the substrate, dust, etc., and the coating liquid changes from the state of the coating liquid to locally reduce the particle size. The big part tends to be.

Next, with respect to the film thickness of the charge generation layer, there is always a portion where the thickness is locally increased due to the smoothness of the base and the aggregation of the organic pigment described above.

The tendency of the pigment to aggregate due to various causes during coating largely depends on the particle size distribution of the pigment in the coating liquid before coating.

As a result of studying the particle size distribution of the pigment of the coating liquid before coating and the aggregation tendency at the time of coating, it was found that the aggregation tendency rapidly increases when a relatively large amount of pigment particles is present in a certain amount or more.

Specifically, pigments having a particle size of 0.5 μm or more particularly increase the aggregation tendency.

Fig. 3 shows an example of ε-type copper phthalocyanine pigment with a particle size of 0.
The relationship between the ratio of pigments of 5 μm or more and the number of pigment agglomerated portions having a particle size (φ) of 50 μm or more per 100 cm ^{2 of} coating area is shown.

As is known from FIG. 3, it is known that when the proportion of pigments having a particle size of 0.5 μm or more is 5 wt% or more, the number of agglomerated portions tends to rapidly increase.
When using a photoconductor prepared by applying a coating liquid containing wt% or more, it is necessary to take measures against image defects due to this aggregation.

As described above, due to the dispersion of the organic pigment and the coating problem, there are locally a large pigment particle size portion and a thick film thickness portion on the coating surface of the charge generation layer. As shown in FIGS. 2 and 3, the injection of charges from the charge generation layer to the charge transport layer is larger than that in other portions.

Therefore, when it is used as a photoconductor for electrophotography, there is a portion where the absolute value of the surface potential is lower than that of other portions even in a dark portion. In the portion used as the photoconductor, the portion where the absolute value of the electric potential is locally low is toner-developed, resulting in an image defect.

The present invention, in order to prevent the defects of the copy image caused by the nonuniformity of the charge generation layer as described above, as a result of studying the charge injection property in the dark portion from the charge generation layer to the charge transport layer, The attenuation of the surface potential at the dark part in the part where the charge injection property is maximum due to the charge generation layer was obtained as an approximate expression, and the process conditions of the electrophotographic apparatus without image defects were found based on the expression.

That is, in an electrophotographic apparatus that repeats the basic processes of primary charging, image exposure, development, and cleaning, the surface potential of the photoconductor immediately after being charged by the primary charger is Vd.
(V), time t (se from primary charging to toner development)
c) and when the surface potential of the photoconductor at which the toner development density becomes half the saturation density is V _H (V), these are | V _H | ≤ (| Vd | ^-0.65 + 1.35 × 10 ^-2 t) It has become possible to provide an electrophotographic apparatus having no image defect in the process design under the condition that the relationship of ^-1.54 (Vd and _VH are the same sign) is satisfied.

The formula will be specifically described below.

This formula was considered based on the experimental data shown in FIG.

FIG. 4 shows the electrophotographic photosensitive member having the average particle diameter of the charge generating material of 1.2 μm shown in FIG. 1 for simulating the decay curve of the agglomerates of the charge generating layer. , -500V, and then the time dependence of the surface potential decay in the dark part was measured.

Since this surface potential decay curve is generally considered to be a space charge limited current, the injected current J is J = KV ^a (K, a
Can be expressed as a constant, and V can be expressed as a voltage applied to the photoconductor).

And Solve the differential equation as Is derived.

Substituting the measurement results of the surface potential decay curve shown in FIG. 4 into the above equation, the equation (1) has the highest correlation coefficient when K = 1.35 × 10 ² and a = 2.54.

Note that V _H is the value of the photosensitive member surface potential when the image density becomes a half value of D _sat (saturated image density) (D _H ) as shown in FIG.

Further, FIG. 6 shows a model of the decay curve of the surface potential at the pigment aggregation portion in the charge generation layer.

That is, during the time t (sec) from the primary charging to the toner development when the surface potential of the pigment agglomeration portion is V _H or more, the pigment agglomeration portion is so small that toner development is not performed.
Even if it is done, it cannot be confirmed with the naked eye, and there is no problem on the image.

In the present invention, for measuring the particle size, an ultracentrifugal automatic particle size distribution measuring device (CAPA-700 type) manufactured by Horiba Ltd.
Was used.

As the particle size, the weight average particle size was used as the value of the particle size.

As the charge generating material, a phthalocyanine pigment, anthanthrone pigment, dibenzpyrene pigment, pyranthrone pigment, azo pigment, indigo pigment, quinacridone pigment, pyrylium dye, thiapyrylium dye, xanthene dye, quinoneimine dye, triphenylmethane dye. , Styryl dyes and the like.

The charge generating material is not limited to those described here, and when used, one kind or a mixture of two or more kinds of charge generating materials can be used.

The charge transport layer can be formed by coating the above-mentioned charge generating material and, if necessary, the charge transport material with a suitable binder (without a binder) on a substrate.

The average particle size of the charge generation material when dispersed is preferably 3 μm.
It is preferably 1 μm or less, more preferably 1 μm or less.

The coating can be carried out using a coating method such as a dip coating method, a spray coating method, a spinner coating method, a bead coating method, a Meyer bar coating method, a blade coating method, a roller coating method or a curtain coating method.

The charge transport layer is electrically connected to the charge generation layer described above, and has a function of receiving charge carriers injected from the charge generation layer in the presence of an electric field and capable of transporting these charge carriers.

At this time, the charge transport layer is laminated on the charge generation layer.

As the charge transport layer, an organic charge transport material such as a hydrazone-based compound, a pyrazoline-based compound, a stilbene-based compound, an oxazole-based compound, a thiazole-based compound, or a triarylmethane-based compound should be formed by coating together with a binder resin as necessary. Obtained by

In addition, dye-sensitized inorganic semiconductor powder such as zinc oxide, selenium, and amorphous silicon can be used, and further, these materials can be formed by vapor deposition.

[Examples] Example 1 A bottomed cylindrical substrate was prepared as an aluminum substrate. Cylinder average diameter 60 mm, average wall thickness 0.5 mm, length 260
It was mm.

On this aluminum cylinder, τ-type phthalocyanine (Toyo Ink Co., Ltd.) having different dispersed particle diameters is used as a charge generating material.
5 types of photoconductors are manufactured, and as an electrophotographic apparatus, a reversal development type laser beam printer (LBP-CX, manufactured by Canon Inc.) having primary charging, image exposure, development, transfer, and cleaning steps. ) Was modified so that the process speed and charging potential setting could be changed, and the image after each potential and process setting of each photoreceptor was evaluated.

The coating of the photoreceptor on the aluminum cylinder was performed as follows.

10 parts by weight of titanium oxide powder (manufactured by Titanium Industry Co., Ltd.) and 10 parts by weight of titanium oxide powder (manufactured by Sakai Chemical Industry Co., Ltd.) surface-coated with conductive tin oxide were used as a phenol resin (trade name Praiofen J325, Dainippon Daini). 17 parts by weight of Ink Co., Ltd., 3 parts by weight of tamenol and 10 parts by weight of 2-methoxyethanol were mixed and then dispersed by a ball mill. This conductive coating material was applied onto each substrate by dip coating and heat-cured at 140 ° C. for 20 minutes to form a conductive layer having a thickness of 20 μm. This conductive layer is provided to conceal microscopic scratches of about μm on the substrate.

Next, copolymer nylon (product name CM8000, manufactured by Toray Industries, Inc.)
4 parts by weight and 8 nylon (trade name: lucamide 5003,
4 parts by weight of Dainippon Ink Co., Ltd. was dissolved in 50 parts by weight of methanol and 50 parts of n-butanol, and was applied onto the conductive layer by dip coating to form a 0.6 μm thick polyamide resin layer as an undercoat layer. .

Next, 1 part by weight of τ-type phthalocyanine, 1 part by weight of butyral resin (trade name S-REC BM-2, manufactured by Sekisui Chemical Co., Ltd.), 10 parts by weight of cyclohexanone, and 1 part of glass beads having a diameter of 1 mm 50
Disperse with a sand mill disperser together with parts by weight, and prepare dispersions having an average particle size after dispersion of 0.10 μm, 0.15 μm, 0.25 μm, 0.50 μm, and 1.10 μm, respectively, and dip-coat on the undercoat layer, 1.5μ after drying by heating at 100 ℃ for 10 minutes
A charge generation layer having a coating thickness of m was provided.

Then, 10 parts of a hydrazone compound having the following structural formula, And 15 parts by weight of styrene-methyl methacrylate copolymer (trade name: MS200, Nippon Steel Chemical Co., Ltd.) in 90 parts of toluene
A coating solution was prepared by dissolving it in parts by weight, and was applied on the charge generation layer by dip coating. After leaving it for 10 minutes, it was heated and dried at 100 ° C. for 1 hour to form a charge transport layer having a thickness of 16 μm.

The five types of electrophotographic photosensitive members produced in this way were sampled in the order of decreasing average particle size after dispersion of the charge generating material.
Let C, D, E.

Using the photosensitive drums of Samples A to E, image evaluation was performed with the above-mentioned modified laser beam printer (LBP-CX).

First, by setting Vd = -700V and _VH = -350V and changing the process speed, the number of black dot image defects in 100 cm ² of the white background image when t was changed was measured. The results are shown.

In this setting, the time t that satisfies the condition of | V _H | ≦ (| Vd | ^−0.65 + 1.35 × 10 ⁻² t) ^−1.54 (Vd and V _H have the same sign) is t ≦ 0.60. .

As shown in the above results, under the condition that the above formula is satisfied, no black spot image defect occurs at all in any sample, but when t> 0.87 other than that, the black spot image defect increases as t increases. is doing.

Therefore, under the condition that the above formula is satisfied, it is possible to obtain a good image without any image defect in any of the samples.

Next, the results of similarly measuring the number of black dot image defects when _VH was changed by setting Vd = -800V and t = 0.8 sec, changing the developing DC bias applied to the developing device, and showing VH are shown.

Here, the condition of V _H satisfying the condition of the above equation is | V _H | ≦ 316.8 and V _H <0.

As shown by these results, here as well, at V _H satisfying the above formula, no image defect was generated in any of the samples, and a good image can be obtained.

Further, the results of similarly measuring the number of black-spot image defects when V d is changed by setting V _H = −450 V and t = 0.5 sec are shown.

Here, the condition of Vd satisfying the condition of the above equation is | Vd | ≧ 881.4 and Vd <0.

Here again, under the condition of Vd satisfying the above equation, no black spot image defect has occurred in any of the samples, and a good image can be obtained.

Example 2 An aluminum cylindrical substrate was prepared in the same manner as in Example 1, and the same conductive layer and undercoat layer were formed thereon.

Further, 1 part by weight of each of the pigments of the pigment examples (1) to (6) having the following structural formulas, 1 part by weight of polycarbonate (trade name: Panlite L-1250) and 10 parts by weight of cyclohexane are added to 1 m.
Dispersion was carried out with a sand mill disperser together with 50 parts by weight of m-diameter glass beads, the dispersion time was adjusted so that the average particle size after dispersion was 0.3 μm, and dispersion liquids of 6 types of charge generating materials were prepared.

This dispersion is dip-coated on the undercoat layer at 100 ° C., 10
After heat-drying for 1 minute, a charge generation layer having a coating thickness of 0.7 μm was provided.

Next, a charge transport layer was formed in the same manner as in Example 1 to prepare 6 types of electrophotographic photosensitive members.

Sample F corresponding to the charge generating material of pigments (1) to (6),
G, H, I, J, K.

Charge generation material Pigment (1) Pigment (2) AlCl Phthalocyanine Pigment (3) Pigment (4) Pigments (5) Pigment (6) For the sample F～K, by a laser beam printer used in Example 1 (LBP-CX modified machine), Vd = -700V, V _H
= -250 V, t (sec) was changed to 0.5, 0.7, 0.9, 1.2, 1.4, and the number of black dot image defects at that time was measured. The results are shown.

As shown here, in any of the photoconductors of Samples F to K, | V _H | ≦ (| Vd | ^−0.65 + 1.35 × 10 ⁻² t) ^−1.54 (Vd and V _H have the same sign) The time t that satisfies the condition is t ≦ 1.01, and it can be seen that a black dot image defect does not occur at all within this range and a good image can be obtained.

Example 3 An aluminum cylindrical base body having an average diameter of 80 mmφ was prepared by a drawing method, and the surface thereof was mirror-finished by cutting, and then an undercoat layer was formed by the same method as that of the example.

Further, a charge generation layer similar to Sample F in Example 2 was formed on the undercoat layer by the same method, and further, Example 1
A charge transport layer was formed in the same manner as in.

The electrophotographic photosensitive member manufactured in this way is used as a copying machine (trade name: NP-3
525, modified for reversal development by Canon Co., Ltd.), using a modified the machine to be freely replaced with further process _{speed, Vd = -900V, V H =} -450V, t a (sec) 0.3 , 0.5, 0.7,
The number of black-spot image defects when changed to 0.9 and 1.2 was measured in the same manner, and the following results were obtained. Here, t that satisfies the condition is
t ≦ 0.51.

As described above, at t satisfying the conditions of the present invention, even in the experiment using the modified NP-3525, no black dot image defect occurred, and a good image was obtained.

In addition, this photoconductor is a copy machine (NP-3525 modified machine) described above.
_{At, Vd = -700V, V H =} -450V, under the conditions of t = 0.7sec A4
A high-quality image with no image defects was obtained even after repeatedly printing 10,000 sheets of paper.

From the above results, it is excellent that an excellent image free from black spot image defects can be obtained when image formation is performed under the conditions of the present invention regardless of the difference in the outer diameter of the photoconductor cylinder and the form of the copying machine. Acknowledged.

[Effects of the Invention] As described above, the electrophotographic apparatus of the present invention, when the specific conditions are set, causes a black dot image defect which appears due to the non-uniformity of the coating surface of the organic pigment dispersion type charge generation layer. A remarkable effect is obtained that a good image in which the occurrence of the image does not occur can be obtained.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the average particle size of the charge generation material and the amount of attenuation of the surface potential in the dark part, and FIG. 2 is the graph of the thickness of the charge generation layer and the amount of attenuation of the surface potential in the dark part. Fig. 3 is a graph showing the relationship between the ε-type copper phthalocyanine pigment and the ratio of the pigment having a particle diameter of 0.5 μm or more in the coating liquid and the coating area of 100 cm ^{2 in} the case of dip coating on an aluminum substrate. A graph showing the relationship between the number of pigment agglomerates having a particle diameter (φ) of 50 μm or more, FIG. 4 is a graph showing the relationship between surface potential decay and time dependence in the dark area, and FIG. 5 is image density versus contrast. FIG. 6 is a model diagram showing a decay curve of the surface potential at the pigment aggregation portion in the charge generation layer, and FIG. 6 is a graph showing the potential relationship.

Claims (3)

[Claims] 1. An electrophotographic apparatus for performing reversal development for developing a portion having a low absolute value of electric potential in an electrophotographic process including primary charging, image exposure, development and cleaning steps, and an organic photo-semiconductor pigment as a solvent. Alternatively, in an electrophotographic apparatus having a laminated-type photoreceptor that uses a layer dispersed and coated in a solvent and a polymer binder as a charge generation layer, the potential of the photoreceptor and the process conditions are constant conditions, and the constant conditions are primary charging. The surface potential Vd (V) of the photoconductor immediately after being charged by the container, the time t (sec) from the primary charging to the toner development, and the surface potential of the photoconductor when the toner development density becomes half the saturation density are V _H ( V), then V
An electrophotographic apparatus characterized in that d, t, and _VH are in the range of the following formula. ^│V _H │ ≦ (| Vd | ^-0.65 + 1.35 × 10 ^-2 t) ^-1.54 (Vd and V _H have the same sign) However, in the case of bias exposure (image exposure that is also performed on the white background part of the back) Is Vd, the potential immediately after image exposure, and t is the time from image exposure to toner development. 2. An organic photo-semiconductor pigment dispersion used in a charge generation layer of a photoconductor comprises 5% of a pigment having a particle size of 0.5 μm or more.
The electrophotographic apparatus according to claim 1, wherein the photoconductor containing the above is used. 3. The electrophotographic apparatus according to claim 1, wherein 500 ≦ | Vd | ≦ 1000.