JP2004021136A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device which realizes always stable and highly fine image quality and is small in size and inexpensive. <P>SOLUTION: The image forming device includes an image carrying member 1, a primary electrostatic charger 2 for uniformly electrostatically charging the member 1 by exposing the member 1, a laser exposure device 3 for forming an electrostatic latent image by exposing the member 1, and a two-component contact developing device 4 which develops the electrostatic latent image to a sensible image. An organic photoreceptor of a function separation type having a surface layer is used as the member 1 and the wavelength of a laser beam source of the laser exposure device 3 is specified to 400 nm below 500 nm. The surface layer is disposed at a film thickness of 5 μm on the surface of the image carrying member and the film thickness of a charge transfer layer on the inner peripheral side thereof is specified to 20 μm and the exposure spot area thereof to 2,000 μm<SP>2</SP>. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus, and in particular, is suitably applied to an image forming apparatus having a plurality of image carriers and forming an image by performing exposure by an exposure unit based on an image signal.
[0002]
[Prior art]
In recent years, with the progress of image forming systems, resolution has been improved, and image forming apparatuses capable of outputting extremely high-definition images have been increasing. Specifically, the resolution is 600 dpi (23.6 mm ^-1 ) And 1200 dpi (47.2 mm ^-1 ) Image forming apparatuses are becoming available on the market.
[0003]
With such an improvement in resolution, reproducibility of characters and details in an image and minute reproduction of halftones can be achieved.
[0004]
Generally, in the high definition technology, the characteristics of the image carrier, the resolution of exposure, and the spot diameter have a great influence. From such a viewpoint, various technologies have been developed for high definition technology. As an example of such a technique, for example, a technique described in JP-A-2001-194841 is known.
[0005]
On the other hand, from the viewpoint of improvement in image forming speed, full-color high-speed image forming apparatuses having a plurality of image carriers are increasing. Specifically, as seen in a small desktop color printer, four small-diameter image carriers are used, and yellow, magenta, cyan, and black developing devices are arranged in series in correspondence with each other to form a so-called tandem. A system for performing multiple transfer onto a transfer material surface or an intermediate transfer material surface is generally used.
[0006]
One of the features of a system in which a plurality of developing devices and image carriers are provided in a one-to-one relationship is the speed of productivity. Recently, an image forming apparatus having a productivity of about 30 to 40 ppm has come to be seen.
[0007]
As described above, the overall flow of technical development relating to the image forming apparatus is a situation in which higher image quality and higher speed are progressing.
[0008]
However, as described above, when the resolution of the image forming apparatus is improved, simply increasing the resolution merely increases the resolution of the image signal. That is, various characteristics of the image forming apparatus cannot follow the increase in the resolution, which may rather cause image deterioration.
[0009]
This involves all elements such as the latent image, development, and transfer of the image forming apparatus. Generally, when an image is output at a higher resolution than the potential of the image forming apparatus, an image having a completely different color may be obtained even though the image has high reproducibility in some cases. The stability is deteriorated.
[0010]
Further, the use of a plurality of image carriers to increase the image forming speed causes deterioration of image quality or enlargement of the image forming apparatus.
[0011]
In a conventional tandem-type full-color image forming apparatus, in order to achieve the same level of image quality as that of a single image forming apparatus, a high-precision developing device and a transfer device are required for each image carrier. And a control device. For this reason, there has been a problem that the size (size) of the main body of the image forming apparatus becomes very large, so that it is not possible to take a stake and very complicated control is required.
[0012]
Further, in a tandem-type image forming apparatus which is reduced in size by suppressing such an increase in size, each component such as a control system is reduced in size. For this reason, accuracy is deteriorated, and as a result, the image quality tends to be inferior.
[0013]
[Problems to be solved by the invention]
One of the causes of the image quality deterioration is the characteristic of the image carrier. That is, when a plurality of image carriers are provided, it is difficult to completely match the characteristics of the plurality of image carriers. Then, a shift in these characteristics leads to a phenomenon that image quality such as color unevenness is degraded. Note that the characteristics of the image carrier refer to the sensitivity of the image carrier, the MTF, and the like. Deterioration of image quality refers to color unevenness, tint fluctuation, density fluctuation, line width fluctuation, or the like.
[0014]
The MTF of the image carrier is greatly affected by the thickness of the image carrier. That is, it is generally known that the MTF of the image carrier decreases as the thickness of the image carrier increases. Further, as the thickness of the image carrier increases, the latent image potential for minute exposure tends to be shallower.
[0015]
Therefore, it is preferable that the film thickness of the image carrier is thin, but if the film thickness changes in accordance with the use condition, a new problem that the image quality changes accordingly occurs.
[0016]
Therefore, an object of the present invention is to provide an image carrier, uniformly charge the image carrier, emit light from a light source and perform exposure to form an electrostatic latent image, and the developing device statically forms the image. An object of the present invention is to provide a small and inexpensive image forming apparatus that can always realize stable and high-definition image quality in an image forming apparatus that visualizes an electrostatic latent image.
[0017]
[Means for Solving the Problems]
In order to solve the above problems, the present invention provides
An image carrier; a charging unit configured to uniformly charge the image carrier; an exposure unit configured to expose the image carrier to form an electrostatic latent image; and a developing unit configured to visualize the electrostatic latent image. A function-separated type organic photoconductor having a surface layer is used as an image carrier, and the wavelength of a light source of an exposure unit is set to 500 nm or less.
It is characterized by the following.
[0018]
In the present invention, typically, the image carrier is formed by laminating a charge generation layer and a charge transport layer on at least a conductive substrate, the thickness of the charge transport layer is 20 μm or less, and the film of the surface layer is formed. The thickness is 5 μm or less and the output resolution is 23 mm ^-1 (≒ 600 dpi) or more. In the present invention, preferably, the exposure spot area of the exposure means is 2000 μm ² It is as follows. The image forming apparatus to which the present invention is applied is typically a full color image forming apparatus, but can be applied to other image forming apparatuses.
[0019]
In the present invention, typically, the light source is a semiconductor laser or a light emitting diode. In the present invention, a contact developing system is typically used as a developing system.
[0020]
In the present invention, typically, there is provided a developing device which has a plurality of image carriers and develops developing materials having different spectral reflectances on each of the plurality of image carriers.
[0021]
In the present invention, preferably, the image forming apparatus is a full-color image forming apparatus. In this case, the image forming apparatus has a plurality of image carriers, and a spectral reflection is performed on each of the plurality of image carriers. It has a developing device for developing developers having different rates.
[0022]
In the present invention, typically, a contact developing system is used as a developing system.
[0023]
Further, in order to solve the problem, the image forming apparatus according to the present invention can be configured to arbitrarily and selectively combine the above-described configurations.
[0024]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings of the following embodiments, the same or corresponding parts are denoted by the same reference numerals.
[0025]
(1st Embodiment)
First, an image forming apparatus according to a first embodiment of the present invention will be described. FIG. 1 shows an image forming apparatus employing a dry electrophotographic method according to the first embodiment. First, an outline of the operation of the image forming apparatus according to the first embodiment will be described.
[0026]
That is, as shown in FIG. 1, first, an image carrier 1 including a drum-shaped functionally separated organic photoreceptor is uniformly charged by a primary charger 2 as a charging unit.
[0027]
Next, based on the image signal sent from the image data supply unit (not shown), the surface of the image carrier 1 is exposed by a laser exposure device 3 as an exposure unit. Thereby, an electrostatic latent image is formed on the surface of the image carrier 1.
[0028]
In addition, in the image forming apparatus according to the first embodiment, a case will be described where the image data is multi-level (256 levels) per pixel, but essentially any level may be employed. .
[0029]
Then, primary transfer is performed on the surface of the intermediate transfer member 5 by visualizing the electrostatic latent image formed by the two-component contact developing device 4 as a developing unit. The two-component contact developing device 4 is a device for enabling fine reproduction of development.
[0030]
The operation up to that point is repeated a total of four times in each of the two-component developing devices 4 containing the developing materials of yellow, magenta, cyan, and black, and then the image formed on the surface of the intermediate transfer member 5 is transferred. The image is secondarily transferred onto the surface of the material 6, fixed on the transfer material 6 by the fixing device 7, and discharged.
[0031]
When an image is formed through the above-described image forming process, there are various factors that determine the image quality. A general factor is that the image quality deteriorates each time the image on the image carrier 1 and the image on the intermediate transfer member 5 are sequentially processed from the level of the electrostatic latent image. Therefore, the present inventor has come to recall improving the image quality by focusing on the stage of the electrostatic latent image.
[0032]
That is, the present inventor has studied from the viewpoint of line width reproducibility in an image forming apparatus that has undergone the above-described image forming process. In the first embodiment, the resolution is set to 600 dpi (23.6 mm ^-1 ) Will be described. FIG. 2 shows a model in which a sharp (sharper) electrostatic latent image and a gentle (broad) electrostatic latent image are reproduced with the same line width.
[0033]
In order to facilitate the description in the first embodiment, the same line width is reproduced when a development threshold value indicated by a broken line in FIG. 2 is given to both electrostatic latent images. And In this state, when the sensitivity characteristic of the image carrier 1 changes, and the latent image changes with respect to the development threshold as shown in FIG. 3, the line width for each latent image differs.
[0034]
Here, it goes without saying that the smaller the change between FIGS. 2 and 3, the higher the stability of the system. From FIGS. 2 and 3, it can be seen that high system stability is provided when the electrostatic latent image is sharp.
[0035]
According to the knowledge of the inventor, the latent image factors that determine the line width of the line image formed by the image forming apparatus include the resolution of the image forming apparatus and the film from the surface of the image carrier 1 to the charge generation layer. Thickness, exposure spot area, and the like can be given. Here, a film configuration near the surface of the image carrier 1 is shown in FIG.
[0036]
That is, as shown in FIG. 4, the film configuration of the image carrier 1 includes a surface layer 1b, a charge transport layer 1c, and a charge generation layer 1d in order from the surface 1a. The charge transport layer 1c and the charge generation layer 1d are provided on a conductive substrate 1e which is a substrate of the image carrier 1.
[0037]
Here, in the first embodiment, the resolution in the image forming apparatus is, for example, 600 dpi (23.6 mm). ^-1 ), The distance from the surface 1a of the image carrier 1 to the charge generation layer 1c (hereinafter, image carrier thickness) is set to 25 μm or less. The film thickness is, for example, 5 μm or less. Specifically, the thickness of the image carrier is set to, for example, around 25 μm, and 1 / e of the peak light amount is set. ² (E is a transcendental number), that is, an exposure spot area of 2000 μm ² And
[0038]
FIG. 5 shows a latent image contrast of a cross section when a line is image-formed, that is, an exposure spot area of 2000 μm with respect to the contrast potential between the deepest part and the shallowest part of the latent image potential. ² The thickness dependence of the image carrier is shown in the case of. The drawing image used at this time is 600 dpi (23.6 mm) shown in FIG. ^-1 ) Is a one dot 1 (1 dot 1) space image.
[0039]
FIG. 7 shows the latent image contrast of the cross section (contrast potential at the deepest portion and the shallowest portion of the latent image potential) when a line is formed with the thickness of the charge transport layer 1c having the thickness of the image carrier being 20 μm. 3 shows the spot area dependence of exposure with respect to. The drawing image is the same as the one dot 1 (1 dot 1) space image shown in FIG. The spot area dependency is obtained by computer simulation.
[0040]
When it is determined that the latent image is sharp when the latent image contrast can be maintained at 150 V or more, it is determined from FIG. 7 that the image carrier film thickness is 20 μm when the exposure resolution is 600 dpi in order to draw a sharp latent image. Hereinafter, the exposure spot area is 2000 μm ² It is understood that the following is desirable.
[0041]
However, even in such a case, the latent image contrast differs by about 100 V when the thickness of the charge transport layer 1c of the image carrier 1 is 10 μm and when it is 20 μm. In the characteristics of the image forming apparatus according to the first embodiment, this potential difference is equivalent to 0.08 in the image forming apparatus when converted into the output density of an 80-level image signal.
[0042]
This difference appears as deterioration with time due to the use of the image carrier 1. Therefore, in the first embodiment, a high abrasion resistance is obtained by using an ultraviolet curable material or the like that can be cured by irradiating the image carrier 1 of the image forming apparatus with ultraviolet light such as acrylic. By providing the surface layer 1b having a thickness of about 5 μm, a change in the thickness due to the use of the image carrier 1 is minimized.
[0043]
As a result, the deterioration over time due to the use of the image carrier 1 is about 0.02 in the output density, so that it is possible to reduce the deterioration to a level that is hardly recognized as image quality deterioration.
[0044]
If the amount of wear on the surface of the image carrier 1 can be reduced without providing the surface layer 1b, the effect is the same and the original object can be achieved.
[0045]
However, according to experiments and studies by the inventor, in this case, another problem that the life of the image carrier is shortened occurs separately. If the service life is shortened, the running cost increases, and the unit price per image becomes high.
[0046]
Therefore, in order to avoid these problems, it is desirable to form the surface layer 1b having high hardness and being hard to wear. As a result, a high-definition image can be stably output at low cost.
[0047]
Since the resistance value of the surface layer 1c is an important factor in image quality, in the image forming apparatus according to the first embodiment, the viewpoint of preventing the horizontal movement of the charges in the surface layer 1b, that is, the so-called image deletion. From a normal temperature and normal humidity environment of a temperature of 23 ° C. and a humidity of 60%, the volume resistance value is 1.0 × 10 ¹³ Set to about.
[0048]
The three factors of the above-described exposure resolution, image carrier film thickness, and exposure spot area independently contribute to the electrostatic latent image. However, when these three factors of the exposure resolution, the thickness of the image carrier, and the area of the exposure spot are all attained to this value, further higher image quality can be achieved. It should be noted that these conditions are conditions that should be satisfied at a minimum, and therefore it is desirable that as the resolution increases, the exposure spot area should be reduced while reducing the thickness of the image carrier.
[0049]
Further, the exposure spot area is greatly related to the wavelength in the exposure apparatus. In the first embodiment, the light emitted from the exposure apparatus is a laser light, and the wavelength is 500 nm or less, for example, 400 nm. On the other hand, the spot diameter Φ and the wavelength λ of the laser exposure are
Spot diameter Φ = kF · λ (k: proportional constant, F: F number of optical system)
Has the relationship
[0050]
Incidentally, as a conventional exposure light source, an infrared laser light having a wavelength of about 780 nm or a red laser light having a wavelength of about 680 nm is generally used. Considering the relational expression of the spot diameter Φ, by using an optical element that emits light with a wavelength of 500 nm or less, for example, about 400 nm, compared to a laser beam having these wavelengths, it is almost the same as the conventional one. The spot diameter can be reduced while using the optical system.
[0051]
Specifically, the spot diameter can be reduced to 0.51 times by using laser light having a wavelength of 400 nm with respect to laser light having a wavelength of 780 nm. Further, by increasing the spot diameter by a factor of 0.51, the spot area can be reduced to ((0.51) ² Ii) 0.25 times, that is, about 1/4 times.
[0052]
In general, the depth of focus d of the spot depends on the square (square) of the F-number and the wavelength,
Depth of focus d = l '・ FＦF ・ λ (l': proportional constant)
Satisfy the relationship.
[0053]
Therefore, when the incident diameter is increased by using a laser beam having a large wavelength and the F-number is reduced to align the spots, the depth of focus d becomes smaller and shallower than when the wavelength is shortened and the same spot diameter is obtained. Problem arises. On the other hand, if the spot diameter is reduced by using a laser beam having a short wavelength, there is a margin for the depth of focus, and the accuracy can be reduced by the margin. This makes it possible to reduce costs.
[0054]
Therefore, when the spot area is reduced, it is possible to manufacture the exposure apparatus at low cost without adding components constituting the optical system or manufacturing the optical system specially.
[0055]
Here, FIG. 2 and FIG. 3 described above show that the exposure spot area is 2000 μm when the image carrier thickness is 20 μm. ² And an exposure spot area of 3600 μm with an image carrier thickness of 30 μm ² And a system with a resolution of 600 dpi (23.6 mm ^-1 ) Is a comparison of a latent image when forming a line having a width of one pixel. Note that in FIGS. 2 and 3, the integrated light amount per pixel is standardized so as to be the same integrated light amount.
[0056]
2 and 3, the exposure spot area was 2000 μm with the thickness of the image carrier being 20 μm. ² It can be seen that the system described in (1) can form a sharper latent image. In other words, it can be seen that the system is resistant to fluctuations in the characteristics of the image carrier 1 and changes in the threshold as development characteristics.
[0057]
As described above, according to the first embodiment, it is possible to form an electrostatic latent image that is strong against image quality deterioration factors such as a change in the characteristics of the image carrier, thereby achieving stable image quality. It is possible to do. Further, it is possible to use almost the same optical system as conventional long-wavelength exposure without specially tailoring the optical system, and it is possible to provide stable image quality in an inexpensive and small-sized image forming apparatus, Since the surface layer 1b is provided on the outermost layer of the image carrier 1, shaving of the image carrier 1 can be suppressed to a minimum, and a change in the thickness of the image carrier caused by use of the image forming apparatus can be suppressed. Therefore, the characteristic fluctuation itself can be minimized.
[0058]
(Second embodiment)
Next, an image forming apparatus according to a second embodiment of the present invention will be described. FIG. 8 shows an image forming apparatus according to the second embodiment.
[0059]
As shown in FIG. 8, the image forming apparatus according to the second embodiment is an image forming apparatus having four tandem-type image carriers unlike the first embodiment.
[0060]
That is, as shown in FIG. 8, in the image forming apparatus according to this embodiment, the image forming units 13, 14, 15, 16 are sequentially arranged above the endless transfer belt 11 extending in the left-right direction. Are arranged in a row. The image forming units 13, 14, 15, and 16 have the same configuration.
[0061]
An image carrier 17 is provided in each of the image forming units 13, 14, 15, and 16. Image forming members such as a primary charger 20, a neutralization lamp (not shown), a cleaner 21, and a developing unit 22 are arranged around the image carrier 17. Further, an image reading unit 25 having an optical scanning unit 25a is provided on the upper part.
[0062]
Further, each of the developing devices 22 stores yellow, magenta, cyan, and black toners, respectively.
[0063]
Further, transfer chargers 18 are disposed inside the endless belt of the transfer belt 11 and on the opposite sides of the positions corresponding to the respective image carriers 17.
[0064]
Further, above the image forming units 13, 14, 15, 16 are provided optical scanning devices (not shown) corresponding to the image forming units 13 to 16, respectively. Then, by these optical scanning devices, image signals corresponding to a plurality of component colors in the document are irradiated on the image carrier 17. Thereby, an electrostatic latent image corresponding to each component color is formed on each image carrier 17.
[0065]
In the image forming section 13, when the latent image arrives at a development position facing the developing device 22 due to the rotational movement of the image carrier 17, yellow toner is supplied from the developing device 22, and the image carrier 17 17, a yellow toner image is formed.
[0066]
Then, when the yellow toner image reaches a transfer portion that is disposed opposite to the transfer charger 18, the transfer bias of the transfer charger 18 transfers the yellow toner image to the transfer belt 11.
[0067]
Thereafter, when the transfer belt 11 advances to reach the image forming unit 14, the magenta toner image is formed by superimposition on the yellow toner image already transferred to the transfer belt 11 by the image forming unit 14 in the same manner as described above. You.
[0068]
Thereafter, in the image forming units 15 and 16, similarly, a cyan toner image and a black toner image are sequentially superimposed on the transfer belt 11. Subsequently, the four color toner images formed on the transfer belt 11 are separated from the transfer belt at the transfer section 23 and transferred to the transfer material 12. Thereafter, the transfer material 12 reaches the fixing device 24, and the respective color toner images are dissolved and mixed to form a color image. Thereafter, the color image is fixed to the transfer material 12 and fixed, and then discharged out of the apparatus.
[0069]
The residual toner remaining on each image carrier 17 without being transferred is removed by the cleaner 21. Then, as the toner is cleaned by the cleaner 21, each image carrier 17 is in a ready state in which the subsequent image forming operation can be executed.
[0070]
That is, the image forming apparatus according to the second embodiment has a transfer belt 11 stretched over four rollers, a toner image is formed on the transfer belt 11 in a superimposed manner, and a transfer material filled in a paper feed cassette is provided. The image data is transferred to a paper cassette 12 and discharged from a paper discharge cassette (not shown).
[0071]
Next, in the above-described image forming apparatus, during the image forming process, when the image carrier 1 as shown in FIG. 1 is a single image forming apparatus, and when the image carrier 17 is plural as shown in FIG. Is compared with the case of the image forming apparatus in the case of (1).
[0072]
That is, as in the image forming apparatus according to the first embodiment shown in FIG. 1, when the image carrier 1 is single, the image forming apparatus performs charging, exposure, development, and primary transfer four times in total for each color. The operation of repeatedly performing the secondary transfer once is performed.
[0073]
On the other hand, in the image forming apparatus according to the second embodiment shown in FIG. 8, images of the respective colors are formed almost simultaneously by different image carriers 17 and serially formed on a transfer belt 11 as an intermediate transfer body. Is that the operation of primary transfer is performed.
[0074]
In the image forming apparatuses according to the first and second embodiments configured as described above, the inventor of the present invention has described the effects of the single image forming apparatus 1 and the plural apparatuses on the image quality of each other. An experiment was performed. In this experiment, the thickness of the image carrier was set to 30 μm, and the exposure spot area was set to 3600 μm. ² Use a system with
[0075]
First, it is assumed that, when the image carrier 1 is single, the characteristics of the image carrier 1 deviate from the ideal characteristics and have a sensitivity gradient in the thrust direction as shown in FIG. The horizontal axis indicates the thrust position, and the vertical axis indicates the circumferential average potential distribution on the surface of the image carrier when the image signal 80 level is input with respect to the thrust position.
[0076]
Here, it is assumed that the characteristics of the developing devices for the four colors of yellow, magenta, cyan and black are exactly the same, and gray is output when an image signal of an amount equal to yellow, magenta and cyan is input. In this state, assuming that a uniform image signal 80 level is input to the entire surface of yellow, magenta, and cyan, the density distribution of each color in the thrust direction is as shown in FIG.
[0077]
This image is an image in which the density remains gray and has a distribution in the thrust direction. In FIG. 10, the mechanism of the change in density with respect to the change in sensitivity is the same as in the first embodiment.
[0078]
On the other hand, as shown in FIG. 8, when there are a plurality of image carriers, the image carriers of the yellow and magenta stations have an ideal surface potential distribution without unevenness in the thrust direction, whereas the cyan and Consider a case where only the image carrier has a distribution in the thrust direction as shown in FIG.
[0079]
In this state, a uniform image signal 80 level is input to the entire surface of yellow, magenta, and cyan. In this case, the density distribution of each color in the thrust direction is as shown in FIG. At this time, in the above-described image, the front side is gray, but the back side is reddish gray.
[0080]
When the user observes such a color with the naked eye, the change in color is generally more noticeable than the slight change in density. In such a case, an image forming apparatus having a plurality of image carriers is displayed as color unevenness even if only one of the image carriers has different characteristics. Therefore, it can be seen that image deterioration is more likely to occur as compared with a single image carrier image forming apparatus.
[0081]
That is, as a result of the study by the present inventors as described above, as compared with a single image forming apparatus having the image carrier shown in FIG. 1, the image forming apparatus having a plurality of image carriers shown in FIG. He recalled that it was necessary to sharply draw an electrostatic latent image.
[0082]
In view of this, the present inventor has proposed a method of forming an image by arranging a plurality of image carriers in tandem, and setting the thickness of the charge transport layer 1c of the image carrier 17 to 20 μm or less, preferably around 20 μm, A surface layer 1b, which is made of an ultraviolet curable material that is cured by irradiating an ultraviolet ray onto acrylic, is provided so as to be hardly abraded by use so as to have a thickness of 5 μm. We devised to keep it to a minimum.
[0083]
Further, the present inventor has set the wavelength of light used for exposure to 500 nm or less, preferably about 400 nm, so that the spot area (1 / e of peak light quantity) ² 2000 μm ² Therefore, the present inventors have devised that the present invention is desirably applied to a tandem-type image forming apparatus.
[0084]
According to the image forming apparatus of the second embodiment, as in the first embodiment, it is possible to form a latent image on each image carrier sharply, Characteristic fluctuations can also be reduced. Therefore, in the image forming apparatus according to the second embodiment having a plurality of image carriers 17, the characteristics of each image carrier 17 are unlikely to change, and even if the characteristics are changed, the image quality is displayed as uneven color. It is possible to provide a high image quality with high productivity by minimizing the output.
[0085]
In addition, it is possible to use almost the same optical system in conventional exposure using long-wavelength light without separately manufacturing each optical system. Therefore, it is possible to provide stable image quality in an inexpensive and small-sized image forming apparatus.
[0086]
Although the embodiments of the present invention have been specifically described above, the present invention is not limited to the above embodiments, and various types of modifications based on the technical idea of the present invention are possible.
[0087]
For example, the numerical values given in the above embodiment are merely examples, and different numerical values may be used as needed.
[0088]
Further, for example, in the above-described embodiment, a full-color image forming apparatus is described as an example of the configuration of the image forming apparatus. The present invention can be applied to an image forming apparatus using a light source such as a copying machine.
[0089]
【The invention's effect】
As described above, according to the image forming apparatus of the present invention, a function-separated organic photoconductor having a surface layer is used as the image carrier, and the wavelength of the light source of the exposure unit is set to 500 nm or less. As a result, it is possible to form an electrostatic latent image that is strong against image quality deterioration factors such as changes in the characteristics of the image carrier, thereby achieving stable image quality and running costs due to the provision of a surface layer. Therefore, stable and high-definition image quality can always be realized, and a compact and inexpensive image forming apparatus can be provided.
[0090]
Another advantage of the present invention is that it is possible to use an optical system that is almost the same as conventional long-wavelength exposure without specially manufacturing an optical system. And an image forming apparatus capable of performing the above.
[0091]
Further, a further advantage of the present invention is that in an image forming apparatus having a plurality of image carriers, it is possible to minimize the difference in the characteristics of each image carrier from appearing in the image quality as uneven color, thereby improving productivity. It is possible to provide an image forming apparatus capable of forming a high quality image while maintaining a high level.
[Brief description of the drawings]
FIG. 1 is a sectional view of an image forming apparatus according to a first embodiment of the present invention.
FIG. 2 is a conceptual diagram showing a model for reproducing the same line width between a sharp electrostatic latent image and a gentle electrostatic latent image according to the first embodiment of the present invention.
FIG. 3 is a conceptual diagram showing a model in which the photosensitive characteristics of an image carrier change from the state shown in FIG. 2 and are reproduced with different line widths.
FIG. 4 is a sectional view showing a film configuration of the image carrier according to the first embodiment of the present invention.
FIG. 5 shows a spot area of 2000 μm according to the first embodiment of the present invention. ² 9 is a graph showing the relationship between the thickness of the image carrier and the contrast of the latent image in the case where.
FIG. 6 is a diagram showing a drawn image according to the first embodiment of the present invention.
FIG. 7 is a graph showing the relationship between the exposure spot area and the latent image contrast when the thickness of the charge transport layer of the image carrier according to the first embodiment of the present invention is 20 μm.
FIG. 8 is a sectional view showing an image forming apparatus according to a second embodiment of the present invention.
FIG. 9 is a graph showing a potential distribution along the thrust direction of the image carrier when the image carrier according to the second embodiment of the present invention has a sensitivity gradient in the thrust direction.
FIG. 10 is a graph showing respective output density distributions in the thrust direction of yellow, magenta, and cyan when an image is formed using the image carrier according to the second embodiment of the present invention.
11 is a graph showing the distribution of output densities of yellow, magenta, and cyan along the thrust direction when the potential distribution shown in FIG. 10 exists only in the image carrier of the cyan station.
[Explanation of symbols]
1,17 Image carrier
1a Surface
1b Surface layer
1c Charge transport layer
1d charge generation layer
1e Conductive substrate
2 Primary charger
3 Laser exposure equipment
4-component contact developing device
5 Intermediate transfer member
6,12 Transfer material
7 Fixing device
11 Transfer belt
13, 14, 15, 16 Image forming unit
18 transfer charger
20 Primary charger
21 Cleaner
22 Developing device
23 Transfer part
24 Fixing device
25 Image reading unit
25a Optical scanning unit

Claims (7)

An image carrier;
Charging means for uniformly charging the image carrier,
Exposure means for exposing the image carrier to form an electrostatic latent image,
Developing means for visualizing the electrostatic latent image,
An image forming apparatus, wherein a function-separated organic photoreceptor having a surface layer is used as the image carrier, and a wavelength of a light source of the exposure unit is 500 nm or less. The image carrier is configured by laminating a charge generation layer and a charge transport layer on at least a conductive substrate,
The charge transport layer has a thickness of 20 μm or less, and the surface layer has a thickness of 5 μm or less;
2. The image forming apparatus according to claim 1, wherein the output resolution is 23 mm ^-1 or more. 3. The image forming apparatus according to claim 2, wherein an exposure spot area of the exposure unit is 2000 μm ² or less. The image forming apparatus according to claim 3, wherein the light source is a semiconductor laser or a light emitting diode. The image forming apparatus according to claim 3, wherein the image forming apparatus is a full-color image forming apparatus. 2. The image forming apparatus according to claim 1, wherein a contact developing method is used as a developing method. 2. The image according to claim 1, further comprising a plurality of image carriers, and a developing device for developing a developer having a different spectral reflectance to each of the plurality of image carriers. Forming equipment.

Images