JPH04322270A - Electrophotographic copying device - Google Patents

Abstract

PURPOSE:To enable the desired density of a picture element to be selected and to obtain a high-quality image by providing a picture element density change means and an exposure intensity change means in an exposure means and supplying toner having fixed average grain size to a developing means. CONSTITUTION:A cleaning means 3, an erase means 4, an electrostatic charge means 5, the exposure means 6, the developing means 7, a transfer means 8 and a destaticization means 9 are arranged around a photosensitive body 1. Then, the picture element density change means 13 and the exposure intensity change means 12 are provided in the exposure means 6. Besides, the toner whose average grain size is <=8.0mum is supplied to the developing means 7 from a toner supply means 11. In such a case, any means can be used as the picture element density change means 13 if it can change the density of the picture element and any means can be used as the exposure intensity change means 12 if it can change the intensity of exposure. Besides, any toner can be used regardless of magnetic or non-magnetic and it is good to add an additive such as a charge controlling material to it.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention generally relates to an electrophotographic device that forms an electrostatic latent image on an electrophotographic photoreceptor and uses a developer to turn the latent image into a visible image (toner image). In particular, high-quality images with excellent resolution and image density are produced by changing the exposure intensity according to the pixel density and converting the latent image into a toner image using a developer containing toner with an average particle size of 8.0 μm or less. The present invention relates to an electrophotographic apparatus that can provide the following.

0002

2. Description of the Related Art In recent years, image output devices using electrophotography, such as copying machines, laser beam printers, and LED printers, that is, electrophotographic devices, have been widely used. In particular, with the recent spread of personal computers, there is a strong demand for inexpensive and compact electrophotographic devices as page printers for personal use, and several companies have already released products for this purpose.

However, with this type of electrophotographic apparatus currently available on the market, it cannot be said that the image quality is sufficiently satisfactory.
In particular, when using the image as an output for computer graphics or when using the output as a base paper for DTP, higher image quality has been desired.

0004

[Problems to be Solved by the Invention] As one of the means to meet such demands, an electrostatic latent image retained on an electrophotographic photoreceptor by reducing the particle size of toner particles forming a developer is proposed. A method has been devised to more faithfully reproduce the

On the other hand, in order to cope with the diversification of printing, there is an increasing demand for a device that can switch the pixel density in a single printer in order to obtain an optimal image depending on the printing purpose. However, in such an apparatus, the exposure light amount (or exposure intensity) is fixed, and it is difficult to handle images of all pixel densities with the fixed exposure light amount.

That is, if the amount of exposure light is set relatively small in order to obtain high resolution at a high pixel density, the solid density of an image with a low pixel density will be low. On the other hand, if the amount of exposure light is increased in order to obtain a sufficient solid density, images with high pixel density will become blurred. This tendency was particularly remarkable when a developer having toner particles with a small particle size as described above was used.

The present inventors have found that when a high pixel density is selected, by lowering the exposure intensity, the bright area potential increases and high resolution is obtained, and when a low pixel density is selected, the exposure By increasing the intensity, the bright area potential decreases,
It has been found that sufficient solid density can be obtained. The present invention has been made based on this new knowledge.

Therefore, an object of the present invention is to be able to select an image with a desired pixel density using one device, and to produce a high-quality image that is sufficiently satisfactory in both resolution and solid density at the selected pixel density. An object of the present invention is to provide an electrophotographic device that can be obtained.

[0009]

Means for Solving the Problems The above objects are achieved by an electrophotographic apparatus according to the present invention. In summary, the present invention:
In an electrophotographic apparatus that forms an electrostatic latent image on an electrophotographic photoreceptor and makes the electrostatic latent image a visible image using a developer containing a toner having an average particle size of 8.0 μm or less, the electrostatic latent image The electrophotographic apparatus is characterized in that the exposure means for forming the pixel density has a pixel density changing means and an exposure intensity changing means, and changes the exposure intensity in accordance with the pixel density. Preferably,
When the pixel density is xdpi, the bright area potential VL of the electrophotographic photoreceptor is Vr +20×(x/100)≦VL≦Vr +10
The exposure intensity is changed so that x(x/100) (where Vr is the residual potential of the electrophotographic photoreceptor).

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an electrophotographic apparatus according to the present invention will be explained in more detail with reference to the drawings.

Referring to FIG. 1, the electrophotographic apparatus in this embodiment has a drum-shaped electrophotographic photoreceptor 1 that rotates in the direction of the arrow. A cleaning means 3 is provided around the photoreceptor 1.
, erasing means 4, charging means 5, exposing means 6, developing means 7, transfer means 8, and charge eliminating means 9 are arranged. The recording paper 2 is fed so as to travel in the tangential direction of the photoreceptor 1 so as to come into contact with the circumferential surface of the photoreceptor 1 at a transfer portion where the transfer means 8 is disposed.

With this configuration, the photoreceptor 1 is uniformly charged by the charging means 5, and an electrostatic latent image is formed by irradiating a light image from the exposing means 6. This latent image is made into a toner image by the developing means 7, and is transferred onto the recording paper 2 at the position of the transfer means 8. The recording paper 2 is separated from the photoreceptor 1, the charge is removed by the charge removing means 9, and then the toner image is thermally fixed on the recording paper 2 by the fixing means 10.

On the other hand, after the transfer of the toner image onto the recording paper 2 is completed, the photoreceptor 1 is subjected to the removal of residual toner by the cleaning means 3 and the erasing process by the erasing means 4, and then is subjected to an erasing process by the charging means 5. It is charged and used for the next image formation. Toner is supplied to the developing means 7 from a toner supply means 11 .

The above structure and operation are well known to those skilled in the art, and further detailed explanation will be omitted. Next, the characteristic portions of the present invention will be explained.

A feature of the present invention is that in the electrophotographic apparatus as described above, the exposure means 6 is provided with a pixel density changing means 13 and an exposure intensity changing means 12, and the developing means 7 is provided with an average Toner with a particle size of 8.0 μm or less is supplied.

As mentioned above, the toner constituting the developer used in the present invention is not particularly limited as long as the average particle size is 8.0 μm or less, but it can be easily manufactured by a pulverization method or the like. Considering this point, the thickness is preferably about 4.0 μm to 8.0 μm. Further, the properties of the toner may be magnetic or non-magnetic, and a charge control material and various other additives may be added, and any developing method may be used.

As the light source of the exposure means 6 used in the present invention, various known means such as a laser and an LED can be used. When using a laser, a semiconductor laser is generally the easiest to use in terms of cost, but dye lasers and gas lasers can also be used depending on the combination with the photoreceptor 1.

The pixel density changing means 13 of the present invention is not particularly limited as long as it is capable of changing the pixel density. When the exposure means 6 adopts a method in which the polygon mirror is rotated to scan the laser beam, the pixel density is generally changed by changing the rotation speed of the polygon mirror. Further, if the light source of the exposure means 6 is an LED array or the like, the pixel density changing means 13 may be a means of switching LED chips prepared in advance for each pixel density.

As a procedure for changing the pixel density, a switch or the like may be provided in the main body of the electrophotographic apparatus, but for ease of operation and prevention of mistakes, it is preferable to change the pixel density using a software command from a host computer.

The exposure intensity changing means 12 in the present invention is basically not limited as long as it is a means for changing the exposure intensity.

When the light source is a laser, specific methods include a method of changing the forward current applied during laser lighting, a method of changing the lighting pulse width of the laser, and a method of using an ND between the laser light source and the photoreceptor 1. A method of inserting a filter or the like, or a method of changing the exposure intensity by changing the emission wavelength if the wavelength of the laser used is variable such as a dye laser can also be used.

These exposure intensity changing means 12 work in conjunction with the pixel density changing means 13, and when each pixel density is selected, the exposure intensity is changed to a preset value corresponding to each pixel density. This is desirable.

Embodiment 1 A semiconductor laser is used as the light source, a method of rotating a polygon mirror is adopted as the scanning device of the exposure means 6, and the rotation speed of the polygon mirror is changed as the pixel density changing means 13 to achieve 240 dpi, 300 dpi, and 400 dpi.
Adjustments were made to obtain pixel densities of 480 dpi, 480 dpi, and 600 dpi. Further, as the exposure intensity changing means 12, a method of changing the laser drive current is adopted, and the exposure intensity on the surface of the photoreceptor 1 is 2.8 μJ/c at 240 dpi.
m2, 2.1μJ/cm2 at 300dpi, 40
1.7μJ/cm2 at 0dpi, 1.5μJ/cm2 at 480dpi, 1.3μJ/cm2 at 600dpi
cm2. In this example, the exposure intensity is "laser light amount", which means the amount of laser irradiation per unit time on the surface of the photoreceptor.

The latent image thus formed was developed using a magnetic toner having an average particle size of 6.0 μm, transferred onto recording paper 2, and then thermally fixed as an image for image evaluation. In this image evaluation, the DC bias voltage applied to the developing means 7 when developing the latent image on the photoreceptor is set to the center value, the center value + 100
It was performed at three points: V and the center value -100V. The results are shown in Table 1-
Shown in 1.

Example 2 Image evaluation was carried out in the same manner as in Example 1, except that the exposure intensity changing means 12 changed the pulse width of the laser. The results are shown in Table 1-2.

Example 3 Image evaluation was carried out in the same manner as in Example 1, except that an ND filter was inserted between the laser light source and the photosensitive drum as the exposure intensity changing means 12. Table 1 shows the results.
-3.

Example 4 Image evaluation was carried out in the same manner as in Example 1, except that a developer toner having an average particle size of 4.0 μm was used. The results are shown in Table 2-1.

Comparative Example 1 Image evaluation was carried out in the same manner as in Example 1 except that the exposure intensity was fixed at 2.1 μJ/cm 2 . The results are shown in Table 2-2.

Comparative Example 2 Image evaluation was carried out in the same manner as in Example 1 except that the exposure intensity was fixed at 1.5 μJ/cm 2 . The results are shown in Table 2-3.

The criteria for image evaluation regarding resolution and solid density shown in each of the above tables are as follows.・Resolution ○: Even complex characters are fully resolved. △: Characters are slightly blurred. ×: Characters are blurred. - Solid density ○: There is sufficient solid density. Δ: Slightly uneven density. ×: It can be seen that the density is clearly uneven. Or the concentration is insufficient.

In each of the above Examples and Comparative Examples, the electrophotographic photoreceptor 1 was an organic photoreceptor using an azo pigment. The residual potential of this organic photoreceptor and the bright area potential at each exposure intensity were as shown in Table 3.

From Table 1 (Table 1-1 to Table 1-3) and Table 2 (Table 2-1 to Table 2-3), according to the present invention, both resolution and solid density are achieved at a desired pixel density. It can be seen that a sufficiently satisfactory image can be obtained.

According to the present invention, from Table 3, if the pixel density is xdpi, the bright area potential of the photoreceptor at this time is VL, and the residual potential of the photoreceptor is Vr, then Vr +20×(x/100) ≦VL ≦Vr +10
It was found that the relationship consisting of x(x/100) holds true.

[0034]

[Table 1]

[0035]

[Table 2]

[0036]

[Table 3]

[0037]

Effects of the Invention The electrophotographic apparatus according to the present invention configured as described above can select an image with a desired pixel density with one apparatus, and can achieve both resolution and solid density at the selected pixel density. You can obtain high-quality images that are completely satisfactory.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing an embodiment of an electrophotographic apparatus according to the present invention.

[Explanation of symbols]

1 Electrophotographic photoreceptor 2
Recording paper 5 Charging means 6 Exposure means 7 Developing means 8 Transfer means

Claims (2)

[Claims] Claim 1: forming an electrostatic latent image on an electrophotographic photoreceptor;
In an electrophotographic apparatus in which the electrostatic latent image is made into a visible image using a developer containing toner having an average particle size of 8.0 μm or less, the exposure means for forming the electrostatic latent image includes a pixel density changing means. 1. An electrophotographic apparatus, comprising: and an exposure intensity changing means, which changes the exposure intensity in accordance with pixel density. [Claim 2] When the pixel density is xdpi, the bright area potential VL of the electrophotographic photoreceptor is Vr +20×(x/100)≦VL≦Vr +10
2. The electrophotographic apparatus according to claim 1, wherein the exposure intensity is changed so that x(x/100) (where Vr is a residual potential of the electrophotographic photoreceptor).