JPH0695411A - Electrostatic latent image forming device - Google Patents

Abstract

PURPOSE:To obtain an excellent printed image rich in gradation by using a single layer type organic photosensitive body and controlling intensity and time in the spot exposure of an exposing light source. CONSTITUTION:The single layer organic photosensitive body 1 is uniformly electrified by a photosensitive body main electrifier 2 and exposed by an optical system provided with a modulation circuit. The photosensitive body 1 has an image exposure at an exposing position A, then the development by a coloring/ electrifying grain is carried out at a developing position B, the developed powder image on the photosensitive body 1 is transferred on a transfer material 5 carried in synchronization with the rotational speed of the photosensitive body 1, by a transfer electrifier 4 and the transfer image on the transfer material 5 is fixed by a fixing means. After the transfer is performed, the surface of the photosensitive body 1 is cleaned, fully exposed by an exposing device and initialized. Then, the use of the exposing light source is regulated. In other words, the exposure is executed so that the intensity in the exposure is >=10muW/cm<2> and the exposing time is within the range of >=10ms.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic latent image forming apparatus used in an electrophotographic apparatus using a Carlson process such as charging-exposure-developing.

[0002]

2. Description of the Related Art Conventionally, as electrophotographic photosensitive materials, there are a type using an inorganic photoconductive substance such as amorphous selenium and amorphous silicon and a type using an organic photoconductive substance. Since selenium is used in an amorphous state, it has thermal stability and stress sensitivity due to the problem of phase change. Further, the spectral sensitivity is in the visible region and has no sensitivity in the infrared region. Therefore, in recent years, arsenic and tellurium are contained in order to be compatible with a laser printer having an emission wavelength in the infrared, which causes problems such as environmental safety. Although amorphous silicon has excellent characteristics such as high sensitivity and printing durability, the problems of poor charging characteristics and productivity remain unsolved.

On the other hand, the latter organic photoconductive substance (hereinafter referred to as OPC
Are more advantageous than inorganic photoconductive materials in terms of safety and economy, and improvements have been made at the same time, and sensitivity that is comparable to that of inorganic materials has been realized, and it is becoming the mainstream of electrophotographic photoreceptors in recent years.
The present invention also relates to an electrophotographic apparatus using this OPC.

OPC is usually used in a two-layer structure of a charge generation layer (CG layer) that absorbs light to generate carriers and a charge transfer layer (CT layer) that moves the generated carriers,
This is being implemented by increasing the sensitivity.

However, in such a negative charging type photoreceptor, 1) deterioration of photosensitive characteristics due to ozone generated from a negative charging charger used for charging, 2) uneven discharge state,
3) In manufacturing, there is a problem that the surface of the conductive substrate is easily affected.

In order to solve such a problem, development of an OPC which is used with a positively charged polarity is now under active development. Conventionally, to realize the positive charging method, 1) CG layer and CT
Inverted double-layer structure OPC in which the layer has the opposite structure to the case of negative charging
(OPC1), 2) A single-layer structure OPC (OPC2) in which both various CG agents and CT agents are dispersed in a binder polymer has been studied.

However, the OPC 1 has problems that the CG layer, which essentially needs to be thinned, is placed on the surface of the photoconductor to lower the printing durability, deteriorate the life characteristics, and has a double-layer structure. Due to the complexity of the manufacturing process and the problem of delamination, it has not been put to practical use. The single layer structure OPC2 is inferior to the double structure OPC in terms of sensitivity, charging characteristics (repeated deterioration) and stability of residual potential. However, in the case of a single-layer structure such as OPC2, if the dispersion is uniform, there is an advantage that even if the photoreceptor is worn, it does not immediately cause a decrease in printing durability. That is, even if the photoconductor is worn, it is considered that the photosensitivity thereof is hardly affected, and that the OPC having a single-layer structure is easier to manufacture than the OPC having a double-layer structure.

In the present invention, in order to achieve the above-mentioned target, OPC having a single layer structure with various compositions has been studied. In particular, we have developed photoconductors composed of metal-free phthalocyanines having various crystal structures and polymers.

As a result, a new photoconductor and a method for producing the same have been developed in which the X-type phthalocyanine is stirred with a solvent and a polymer capable of dissolving the phthalocyanine to change the crystal system of at least a part thereof (see Japanese Patent Laid-Open No. 3-287171). ).

[0010]

As described above, despite the various advantages of the positively charged single-layer photoconductor, the actual production of an electrophotographic apparatus using the OPC is not possible. A major reason for this is that it is difficult to put it into practical use due to the low responsiveness related to the induction time, which is a feature of single-layer photoreceptors. Further, as a result of various studies on the basic characteristics of the above-mentioned photoconductor, a large change in recording density was observed due to a minute change in exposure intensity. As a result obtained by the usual measuring method as described above, low responsiveness and instability of recording density were problems.

It is an object of the present invention to solve the problems peculiar to the above-mentioned single-layer organic photoconductor and to achieve the stabilization of image quality and the improvement of image quality.

[0012]

Since the conventional single-layer photoconductor has a long induction time, it was considered impossible to put it into practical use by a usual method. However, as a result of various studies on the basic characteristics of the present photoreceptor, it was found that it can be put to practical use by defining the usage method of the exposure light source, specifically by defining the intensity and exposure time of the exposure light source. .

[0013]

With the above-described structure, the present invention makes it possible to realize an electrostatic latent image forming apparatus excellent in recording stability while making use of various characteristics of a positively charged single-layer photosensitive member.

[0014]

EXAMPLES Examples of the present invention will be described below.

FIG. 1 is a schematic view of an electrostatic latent image forming apparatus according to an embodiment of the present invention. In the figure, 1 is a single-layer organic photoreceptor. The single-layer organic photoconductor (hereinafter, simply referred to as photoconductor 1)
Is rotated in a clockwise direction at a constant speed and a constant direction by means not shown. The photoconductor 1 is uniformly charged by the photoconductor main charger 2 and exposed by an optical system having a modulation circuit shown below. In this embodiment, a laser optical system 3 having a semiconductor laser with a wavelength of 780 nm as a light source is used.

After the photosensitive member 1 is subjected to image exposure at the exposure position A, development with colored charged particles is performed at the development position B by means not shown. In the present embodiment, the time from position A to position B is the required response time. The developed powder image on the photoconductor 1 is transferred by the transfer charger 4 to the transfer material 5 that is conveyed in synchronization with the rotation speed of the photoconductor 1, and the transferred image on the transfer material 5 is a fixing unit (not shown). Fixed in. After transferring the photoconductor 1, the surface of the photoconductor 1 is cleaned by a unit (not shown).
Is exposed to light and initialized, and an image is formed by repeating this process.

Here, the photosensitive member 1 is 63.5 mm in the clockwise direction.
It rotates at a speed of / sec. Laser optics 3
Used a B4 scan width and a resolution of 400 DPI.
The required response time is 0.2 seconds in this embodiment.

Using the above-mentioned apparatus, a positively charged single-layer type photoconductor having metal-free phthalocyanine (manufactured by Dainippon Ink and Chemicals, Inc.) and Fastogen Blue as a photosensitizer was prototyped. The photosensitive member has already been disclosed in JP-A-3-287171.

The obtained photoreceptor was evaluated by a drum tester and a prototype electrophotographic apparatus manufactured by Gentec Co., Ltd. White light is not used as the exposure light source.

The exposure light source intensity is AQ manufactured by Ando Electric Co., Ltd.
-2101 (optical power meter) and T manufactured by Advantest
Q8214 (optical power meter) was used. The intensity of the light source is a value converted from the aperture area of the measuring sensor (in the case of Ando Electric Co., Ltd., the aperture diameter φ8 is used) to 1 cm ² .

Here, the responsiveness (charge half time) means that the potential charged on the surface of the photosensitive drum by passing through the charger is eliminated by the exposure light source. At this time, it means the time from the start of static elimination until the surface potential is attenuated by half. For example, when the surface of the photosensitive drum charged to 800V is exposed, it is the time from the start of exposure until the charged potential is reduced to 400V.

Next, the prescribed exposure time shown in the claims will be described. Various studies have been made so far on the positively charged single-layer photoconductors described in the above claims. As a result, with regard to the exposure intensity and exposure time, if the exposure light source intensity is fixed to a certain constant value and the exposure time is shortened in this state, the half-time of the charge potential will increase from a substantially constant time to a sudden increase. The time immediately before this abrupt change is defined as the specified exposure time at this exposure intensity. Figure 2 schematically shows this state. Further, the specified time Tn shown in the drawing is 65% or less as a proportion of the charge potential half time Tt as shown in the claims.

Example 1 In this example, the exposure intensity and exposure time were examined. The sample was produced by a usual method (JP-A-3-287171). For the measurement, the drum measurement evaluation device was used. As for the exposure light source, 567, 660 is 100 μw / cm ² or less,
The measurement was carried out at 780 nm, but there was no difference in evaluation evaluation between the three types of light sources.

The results are as shown in (Table 1). In the table, the horizontal axis shows the exposure intensity and the vertical axis shows the exposure time. The lower side of the diagonal line in the table is based on the drum test apparatus, and especially the residual potential is evaluated. The cause of the defect of the exposure time of 30 ms in the table is due to the instability of the charged position.

[0025]

[Table 1]

From the above results, the exposure intensity is 10 μw / c
If it is larger than m ² and the exposure time is within the range of 10 ms or more, good conditions can be obtained although not all, but if it is out of this range, a good recording state cannot be obtained even if the conditions are changed. .

The above results are subtly different depending on the difference of drum samples (trial manufacturing process, material lot difference, etc.), but since they are within the above range, they are not described here.

(Embodiment 2) In this embodiment, the relationship between the exposure intensity shown in the above-mentioned Embodiment 1 and the exposure time, in particular, the specified exposure time and the half-time of the charge potential was examined. The purpose is to further clarify the range in the first embodiment. A prototype evaluation device was used for evaluation, and an LED array (665n
m) was also used with a surface electrometer to measure the half-life of the charge potential. The measurement conditions were the same as in Example 1 and evaluated. The measurement drum sample is the same as that used in Example 1.

As described above, the specified exposure time is
When the exposure intensity is specified, when the exposure time is changed under the condition of that constant intensity, the half-time of the charge position is almost constant, and when the exposure time is further shortened, the half-time sharply increases. This is the time before this increase (Fig. 2). In the figure, Vo represents the surface potential charged on the surface of the photoconductor, St represents the exposure start point, and Vo / 2 represents the charging potential half point.

When the specified time is compared with the charge position half time, the ratio of the specified exposure time to the charge position half time is important. In the actual evaluation judgment, the recording state of the recording test result by the prototype evaluation device was visually observed to evaluate the density stability, and the ratio with the appropriate exposure time was determined from the result.

The results are (Table 2). The recording failure in the lower left corner of the diagonal line in the table indicates that the specified exposure time is 65% of the charge position half time.
Accounted for more than that. The mark * in the table is good in Example 1. From the above results, the optimum range in Example 1 is
Further, it is narrowed in the second embodiment. In addition, on the upper right of the diagonal *
The cause of the defect is unknown.

[0032]

[Table 2]

The above results are the same samples as in Example 1, but Table 3 shows that the results are slightly different in different lots. # In the table is different from the above (Table 2). The lower left defect seen in the results is the same as above in that the ratio of the specified exposure time is 65% or more, and these results satisfy the range of Example 1 as in the above example.

[0034]

[Table 3]

Example 3 In this example, the optimum range for a wider exposure intensity was examined. The equipment used is
In the prototype evaluation system, the LED and 780 were used as the exposure light source.
nm laser diode is used. The laser output is rated at 15 mw / dot, and the maximum on the surface of the photoconductor is 3
Since it was used at mw / dot and 12 dot / mm, the maximum strength of 1 cm ² was 3 × 12 × 12 × 100 = 43.
w / cm ² .

Table 4 shows the results. From the above results, it is found that a suitable range is obtained from the product of the exposure intensity and the specified exposure time. It is within the range of 3 × 10 ^-5 to 10 ^-7. Is possible. The subtle differences in the photoconductors do not exceed the evaluation range, as shown in Example 2.

[0037]

[Table 4]

As described above, in the electrophotographic apparatus using the positively charged single-layer organic photoreceptor, the exposure light source and the exposure time should be within the optimum range, and the optimum ratio range between the specified exposure time and the half-time of the charge position should be specified. This enabled a stable recording device.

Further, in the following embodiments, the characteristics in consideration of reproducibility will be shown. In order to transfer the colored particles from the developing device to the photoconductor with good reproducibility, the potentials of the image-exposed portion and the unexposed portion of the photoconductor must be controlled. Therefore, it is necessary to control the behavior of the potential decay of the photoconductor with the required response time. In particular, in recent years, the demand for improving the image quality of optical printers has increased, and the development of electrophotographic devices with rich gradation is desired. From the above viewpoints, we conducted the following studies in order to provide an electrophotographic apparatus with excellent gradation reproducibility.

Here, the required response time is defined as the time from the exposure position to the development position. First, after passing through the charger to give a specified charge to the surface of the photoreceptor to charge it to a predetermined potential,
Image exposure is performed on the photoconductor with light emitted from the exposure light source.

(Embodiment 4) FIG. 3 is a block diagram showing the concept of an electrostatic latent image forming apparatus in another embodiment of the present invention. First, the image reading unit 11 encodes the image signal with a binary signal, and the halftone generating processor 12 transfers the data output signal to the exposure light source drive circuit 13. The exposure light source drive circuit 13 is provided with an exposure power modulation circuit 15 which modulates the exposure light source supply current according to the output data of the halftone generation processor 12. Here, the power modulation circuit can set the minimum exposure intensity I _min of spot exposure corresponding to the minimum image density, the maximum intensity I _{max of} spot exposure corresponding to the maximum density, and the number N of divisions of power modulation as initial values. The exposure light thus power-modulated is exposed to the single-layer organic photoconductor provided in the print output unit 14 shown in FIG.

In this embodiment, the spot exposure condition I of the photoconductor is used.
_{The min} and I _max and the gradation reproducibility of the output image were examined. Number of divisions N
Is 8 steps for all exposure conditions. The reproduction result of the output image of this embodiment is shown in (Table 5). The symbol A in the table indicates that the gradation is poor and the image density is extremely insufficient. The symbol B in the table is poor in gradation, and the reproducibility of highlight as image density is insufficient, so that all output densities are covered by shadow portions.

[0043]

[Table 5]

The results inferred from Table 5 are that the exposure intensity is 0.05 to 0.6 mW as the range of modulation, and if desired, multistep exposure modulation is performed in the range of 0.2 mW to 0.6 mW. Suitable gradation reproduction can be obtained.

When a halftone image was output in this way, a beautiful image rich in gradation reproduction was obtained. Also, when a similar experiment was conducted using a system having a linear velocity of the photoconductor of 300 mm / sec and a resolution of 400 DPI, the preferable range of the modulated exposure intensity range was examined according to the preferable range of (Table 5). It was found to change in proportion to the product of the speed and the scanning width of the laser. Therefore, the upper limit of the laser intensity on the surface of the photoconductor is 2 mW, which corresponds to the practically used maximum output paper size of A3 plate and the copying speed of 70 sheets per minute (A4 plate). There is. Further, the value of 0.1 mW which is the lower limit exposure condition described in claim 5 corresponds to the lower limit value of the specifications that should be practically satisfied as a low speed output printer.

(Embodiment 5) FIG. 4 shows an example of a block diagram showing the concept of an electrostatic latent image forming apparatus in still another embodiment of the present invention. First, the image reading unit 21 encodes the image signal with a binary signal, and the halftone generating processor 22 transfers the data output signal to the exposure light source drive circuit 23. The exposure light source drive circuit 23 includes a halftone generation processor 22.
A spot exposure lighting time modulation circuit 25 is provided for modulating the exposure spot lighting time according to the output data of. The exposure light whose lighting time is modulated in this way is exposed to the single-layer organic photoconductor provided in the print output unit 24 shown in FIG.

In this example, the spot exposure of the photoconductor was fixed to 0.5 mW on the photoconductor surface. We produced a prototype laser drive circuit that can switch the pulse of the laser spot in eight steps from 70 × ^10-9 to 140 × ^10-9 seconds. In this example, the isolated dot diameter was measured when switching was performed in eight steps within this modulation range. The isolated dot diameter represents the average of 10 points measured by microscopic observation. In addition, the results of measuring the maximum density in the dots with a microdensitometer are also shown. The results are shown in (Table 6).

[0048]

[Table 6]

From Table 6, in addition to the dot shape, the density of the output dot also maintained a smooth gradation according to the modulation time.

In actual use, it is necessary to satisfy the specification of about 10 times the copying speed of this embodiment. Therefore, there is a possibility that the lighting time of the isolated dot may be reduced to about 10 × 10 ⁻⁹ . When the laser exposure intensity for this minimum lighting time was investigated, a laser exposure amount of 4 mW was required. Further, the lower limit of the copying speed in actual use is about one fifth of that of this embodiment. The above is the reason for defining the numerical values in the claims.

(Embodiment 6) FIG. 5 shows an example of a block diagram showing the concept of an electrostatic latent image forming apparatus in another embodiment of the present invention. First, the image reading unit 31 encodes the image signal with a binary signal, and the halftone generating processor 32 transfers the data output signal to the exposure light source drive circuit 33. The exposure light source drive circuit 33 is provided with an exposure light source modulation circuit 35 for simultaneously modulating the spot exposure lighting time and the exposure output according to the output data of the halftone generation processor 32.
The exposure light whose lighting time and output is modulated is
The single layer organic photoconductor provided in the print output unit 34 shown in FIG. 5 is exposed.

In this embodiment, the spot exposure of the photoconductor is ImW on the surface of the photoconductor, and the laser exposure energy E per spot, which is the product of I and T, is 0 J / 1 dot-100 when the pulse of the laser spot is T seconds. × ^10-12 J /
We made a prototype of a laser drive circuit that can be switched in 8 steps up to 1 dot. Image exposure of the thus-obtained solid halftone image was performed, and the surface potential of the photoconductor at the developing position was measured.
The results are shown in (Table 7).

[0053]

[Table 7]

The exposure levels (1) to (8) are 100 × 10.
^{Over 12} J / 1dot be divided into eight, exposure energy enough to go up chestnut numbers is meant to be a powerful. From Table 7, the exposure range shows suitable potential responsiveness in the exposure levels (3) to (6), and the level corresponding to this range reduces the surface potential of the photoreceptor to 1/10. This is the exposure energy required for.

[0055]

INDUSTRIAL APPLICABILITY As described above, the present invention uses a single-layer type organic photoconductor, particularly a photoconductor containing X-type phthalocyanine and a binder resin as main components, and uses spot exposure intensity, spot exposure time, and spot exposure energy of an exposure light source. A beautiful print image with rich gradation can be obtained by controlling.

[Brief description of drawings]

FIG. 1 is a schematic view of an electrostatic latent image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing an optical attenuation curve in this example.

FIG. 3 is a block diagram showing the concept of an electrostatic latent image forming apparatus according to another embodiment of the present invention.

FIG. 4 is a block diagram showing the concept of an electrostatic latent image forming apparatus according to another embodiment of the present invention.

FIG. 5 is a block diagram showing the concept of an electrostatic latent image forming apparatus according to another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 photoconductor 2 main photoconductor charger 3 laser optical system 4 transfer charger 5 transfer material 6 exposure device 11 image reading unit 12 halftone generation processor 13 exposure light source drive circuit 14 print output unit 15 exposure power modulation circuit 21 image reading unit 22 Halftone Generating Processor 23 Exposure Light Source Driving Circuit 24 Print Output Section 25 Spot Exposure Lighting Time Modulating Circuit 31 Image Reading Section 32 Halftone Generating Processor 33 Exposure Light Source Driving Circuit 34 Print Output Section 35 Spot Exposure Lighting Time & Exposure Output Modulating Circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Souji Tsuchiya 3-10-1 Higashisanda, Tama-ku, Kawasaki City, Kanagawa Prefecture Matsushita Giken Co., Ltd.

Claims (8)

[Claims] 1. An electrostatic latent image forming apparatus using a single-layer type organic photoconductor, wherein the intensity of an exposure light source is at least 10 μw / cm ² or more and the exposure time is 10 ms or less. 2. The response of the photosensitive member according to claim 1 (half-time of charging position) includes a specified exposure irradiation time, and the specified exposure irradiation time is the entire response of the photosensitive member (half charging position). The electrostatic latent image forming device is used in a state of occupying at least 65% or less of the time). 3. A single-layer type organic photoconductor characterized by using a metal-free phthalocyanine as a part of the photosensitive material used in the photoconductor according to claim 1 and having a positively charged single-layer structure. An electrostatic latent image forming device characterized in that 4. The product of the intensity of the exposure light source and the prescribed exposure irradiation time in claim 1 is 3 × 10 ⁻⁵ −10 ⁻⁷ (sec ·
W / cm ² ) The electrostatic latent image forming device. 5. An organic photoconductor is used, wherein the photoconductor is a single layer in which at least a part of a photosensitive material used is X-type metal-free phthalocyanine, and the photoconductor is uniformly charged to a positive polarity. After that, means for forming an electrostatic latent image by performing spot exposure is provided, and the exposure time T of the spot exposure is a fixed value defined by the system conditions, and the minimum value I ₀ of the center intensity of the spot exposure on the photoconductor surface is 0. The light intensity amount I in the range of 1 mW to 2 mW divided by the photoconductor 1/10 attenuated exposure amount E _1/10 by the spot exposure time T is divided into N to obtain the minimum value I ₀ . An electrostatic latent image forming device characterized by superposed exposure. 6. The photosensitive member according to claim 5, further comprising means for uniformly charging the single-layer organic photosensitive member to a positive polarity and then performing spot exposure to form an electrostatic latent image. The central intensity I of exposure is a fixed value of 0.1 mW or more and 4 mW or less, and the spot image exposure time T ₀ is 10 × 10 ^−9.
Second or more, and 1/10 attenuated exposure amount E _{1/10 of the} photoconductor
Is divided by the spot intensity I to perform N-divided exposure time modulation on the T _{0 so as} to be superimposed on the T ₀ . 7. The photoreceptor according to claim 5, further comprising means for forming an electrostatic latent image by performing spot exposure after uniformly charging the single-layer organic photoreceptor to a positive polarity. Has a minimum central intensity I ₀ of 0.1 mW or more,
The minimum value T ₀ of the spot exposure time is 10 × 10 ⁻⁹ seconds or more, and the 1/10 attenuated exposure amount E _1/10 of the photoconductor is N
An electrostatic latent image forming apparatus characterized by superposing a divided exposure time T and an exposure intensity I on spot exposure. 8. An electrostatic latent image formation, characterized in that the image exposure means according to any one of claims 5 to 7 uses a semiconductor laser or a high density LED coupling device in the wavelength range of 500 to 800 nm. apparatus.