JPS6221370A - Electrophotographic method - Google Patents

Abstract

PURPOSE:To improve the reproducibility of minute lines in the sub scanning direction while suppressing strip fog running in the main scanning direction by approximating the light discharge curve of a photosensitive body by two straight lines and using an exposure energy corresponding to a cross point of the straight lines as a reference exposure energy. CONSTITUTION:An electrostatic latent image is formed to the photosensitive body charged uniformly by using a light beam in response to a picture signal so as to expose a background part. In expressing the light discharge characteristic of the photosensitive body whose potential is lowered as the energy exposing the photosensitive body is increased as opproximate lines whose gradient is decreased at a point, the exposure energy corresponding to the point is used as the reference exposure energy and the background part is irradiated by using the light beam having the exposure energy being 1.1-1.4 time of that of the reference exposure energy. The edge density of a minute line is lowered at a portion where exposure energy I > 1.4 X (reference exposure energy) exists and the adhesion of a thin toner layer known as the scattered toner takes place in the vicinity of the edge.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electrophotographic method that suppresses band-like fog in the main scanning direction and improves the reproducibility of fine lines such as one-dot lines in the sub-scanning direction.

[Conventional technology]

An example of an electrophotographic apparatus using a light beam (a type that exposes a background area; the same applies hereinafter) is shown in FIG. 4. This electrophotographic apparatus modulates a light beam 2 of a laser beam 1 with a modulator 3 according to an image signal, deflects the modulated light beam 4 in the main scanning direction with a rotating polygon mirror 5, and rotates it through a lens diameter 6. This is for exposing the photoreceptor 7.

This exposure forms an electrostatic latent image on the photoreceptor 7, which is transferred to the recording paper 8 after development.

FIG. 5 shows the energy density ratio of the light beams exposing the photoreceptor 7, which has a maximum value on each scanning line S I + S z, S 3, and on each scanning line S1 . It has a Gaussian distribution shape with a maximum value of 1/e'' at the midpoint position G + and G t of St, S. The diameter d of the light beam is such that the light intensity is 1/e'' from the center of the light beam. Since it is defined as being determined by points with values, each scan-line S, , S,
, S, and the diameter of the light beam are k=d/P=1 in the case of FIG.

In the figure, 81 indicates the energy density ratio of a single light beam,
B2 indicates the synthesized energy density ratio.

When the photoreceptor 7 is exposed to the light beam 4 modulated according to the image signal, the area corresponding to the background is exposed to the light beam having an energy pattern of curve B2, which runs in the main scanning direction. Causes a band-like fog.

For example, the scanning line interval P is 64μ for a laser printer with a resolution of 4,003PI, and 3μ for a laser printer with a resolution of 800SPI.
It becomes 2μ. Therefore, in the electric field directly applied to the development, the exposure unevenness is accentuated at ε.

In order to suppress this band-like fog, it is possible to raise the developing bias voltage, but if the bias voltage is increased to the extent that the band-like fog disappears, the potential contrast in the image area may be insufficient, and even the carriers in the developer may be damaged by the photoreceptor. Inconveniences such as adhesion may occur.

An electrophotographic method disclosed in Japanese Patent Application Laid-open No. 152269/1983 has been proposed as a method for suppressing band-like fog without causing such inconveniences. According to this electrophotographic method,
It is stated that the band-like fog mentioned above can be suppressed by setting the diameter d of the light beam and the scanning line interval P so that the above-mentioned ratio is 1.3≦=d/P≦1.9.

[Problem that the invention seeks to solve]

However, according to conventional electrophotography, the band-like fog is suppressed by optimizing the beam diameter. reproducibility may be reduced.

[Means and effects for solving the problem] The present invention has been made in view of the above-mentioned problems, and in order to improve the reproducibility of thin lines in the sub-scanning direction while suppressing band-like fog running in the main-scanning direction, Approximate the optical static elimination curve of with two straight lines,
When the exposure energy corresponding to the intersection of these straight lines is taken as the standard exposure energy, 1.1 of this standard exposure energy
The present invention provides an electrophotographic method in which a background portion is irradiated with a light beam having an energy in a range of 1.4 times from .

〔Example〕

Hereinafter, the electrophotographic method according to the present invention will be explained in detail.

(A) Prevention of band-like fogging (1) Quantum efficiency of carrier light generation of photoreceptor ηη=η
. X (E/E6) '−・・・−・・・−・(1)
Here, η. : Quantum efficiency E in a certain electric field E0 : Internal electric field of the photoreceptor n : A constant representing the electric field dependence of quantum efficiency. For example, n = % for S, - organic composite sensitive material, n = 0 for α - S, sensitive material (2) Optical static elimination characteristics of photoreceptor When the relationship of equation (1) is satisfied, the optical static elimination characteristic of the photoreceptor is expressed as follows.

y (+-111= y. (1-R) -SX 1 song (2) where, vo: Initial potential of photoreceptor S: Sensitivity constant of photoreceptor ■: Exposure energy (3) Photoreceptor's photostatic charge removal characteristic CharacteristicsAs a photoreceptor,
S, - When an organic composite sensitive material is used, equation (2) becomes n''%
Then, ET= , f'i −s X I −−−−−−−
--------(3). Here, the exposure energy I was varied to measure the potential (2) based on the optical static elimination characteristics of the photoreceptor. The measurement results are shown in Figure 1. The horizontal axis represents the exposure energy at the intersection X of two straight lines, Lx, which will be described later, as the reference light! The real axis shows the ratio of exposure energy when (1, 0), and the vertical axis shows the potential ■ converted to the A power (the vertical axis is the (1-n) power axis). Yes, n==%
, it becomes the % power axis).

As is clear from FIG. 1, if the horizontal axis shows the exposure energy I as a real axis, and the vertical axis shows the photoreceptor potential ■ as the (1-n) power axis, the photostatic charge removal characteristic can be expressed by two straight lines Lt, It has been found that a characteristic feature is approximately expressed by Lt. The straight line L2 is a straight line, has a smaller slope, and corresponds to the residual potential portion.

(4) Modeling of photostatic charge removal characteristics of photoconductor Considering the residual potential mentioned above, equation (3) can be modeled as follows.

(4,1) Area a (area below the reference light amount) V =
(yo(+-nl (Vo(+-11> 9p+1
-n))
−−−−−−−(4,1)(4,2) b area (area with reference light amount or more) y = (VR(+-1'l
l (ER(yo o-n) VR(1-
11))XI) In the model formula of 7, if n”%, then V=
1)) ”−−−−−−−(4,2) Here, V: Photoreceptor potential after exposure energy ■CER: Ratio of slopes of two straight lines L + and L t ■R
: Potential at intersection X (generally called residual potential) (5) Potential unevenness in sub-scanning direction Δ■ Δv=vI11. ．． −v,,,I−=−−−−−−−
--- (5) Here, V 1llaX 'minimum value of exposure energy ■ 11!
Maximum value of photoreceptor potential V when given 7 @in: Maximum value of exposure energy ■1. ,,,
Minimum value of photoreceptor potential ■ when given (6) Light amount unevenness Δ■ in the sub-scanning direction The potential unevenness Δ■ in (5) described above is caused by the following light amount unevenness Δ■.

I +++mx Here, k p ” d p / P, dp: light beam diameter in sub-scanning direction P: scanning line interval According to the measurement results shown in FIG. 1, V o ” 800
(V), VR-200(V), and CER=0.3 were obtained.

Now, let kp = d p / P = 1.6, and (
4,1), (4,2), (5), and (6), exposure energy 1 = (Ismx ”
I +++i. )/2 and the potential unevenness ΔV is determined. The calculation results are shown in Figure 2.

Here, as a concept for suppressing the band-like fog running in the main scanning direction, ``Even if there is exposure unevenness ΔI, potential unevenness ΔI
We decided to make it difficult to output V, and the conditions for this were: ``Normal bias voltage setting value Vm (Vs = background background value potential + 1
00V)''), the potential unevenness Δ■ must be less than ±15 (V) (contrast 30 (V)). It was set as 1.

From FIG. 2, in order to satisfy this condition, the exposure energy (2) must be 1.1 times or more the reference exposure energy.

Similar studies were attempted using other photosensitive materials, such as α-S, but similar results were obtained.

[B] Regarding the reproducibility of thin lines such as one-dot lines, in order to understand the relationship between the reproducibility of one-dot lines and the beam diameter, the inventors first performed simulation calculations using development electric field analysis.

The values used in the calculation (sensitivity material, exposure energy) are as described above (
The value is the same as A). As a result, the range of exposure energy in which a good one-dot line can be reproduced is: ■≦1.4 X (standard exposure energy) The line width W that is reproduced is W/ p = o, ss ~ for the scanning hit p. 0
．． It was stable at 88, and the value itself was not a problem. vice versa,! >1.4X (standard exposure energy), it was found that the density at the edge of the thin line decreased and a thin layer of toner, generally called scattered toner, was deposited near the edge. Figure 3 (a) and (U) show this when , and in (b) it is 1.6. In (b), scattered toner t can be seen.

Based on the above analysis results, the inventor determined that the optimum light amount range was ■ I got it.

[C] Experimental Verification Results The above analysis results were verified by the inventors through experiments. The experimental machine used was equipped with beam expanders in both the main and sub-directions, and the beam diameter in both directions could be changed independently.
It is also a laser printer with a laser scanning optical diameter that can change the writing resolution from 400 to 14003 PI. The experiment was conducted at 800 SPI. First, d/p
= 1.6, the occurrence of band-like fog in the background area was investigated.

As a result, it was confirmed that when the developing bias was set to -background potential +100 (V), band-like fog did not occur in case (2).

Next, we investigated the reproduction of one-dot lines, and found that stable and good fine line reproducibility was obtained for one-dot lines in either the main scanning direction or the sub-scanning direction with w/p":o of 94 to 0.98. The reason why the W/P was larger than the analysis result was because the line width became thicker due to fixing, and this was actually a favorable result.

In this case, although the line width was the same for both the main and sub-scanning one-dot lines, the edges of the thin lines were particularly poorly reproduced in the lines running in the sub-scanning direction.

The quality of the reproduction lines between the two became clearer when comparing samples made by using a print sample as the original and copying it with a normal copying machine.

〔Effect of the invention〕

As explained above, according to the electrophotographic method of the present invention, when the optical static elimination curve of the photoreceptor is approximated by two straight lines and the exposure energy corresponding to the intersection of these straight lines is set as the reference exposure energy, this reference exposure By irradiating the background area with a light beam with energy in the range of 1.1 to 1.4 times the energy, the reproducibility of fine lines in the sub-scanning direction is improved while suppressing band-like fog running in the main scanning direction. can be improved.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the optical static elimination characteristics of a photoreceptor. FIG. 2 is an explanatory diagram showing potential unevenness on a photoreceptor. Figure 3 ((), (
tl) shows the reproducibility of thin lines in the sub-scanning direction, (A) is an explanatory diagram showing what is according to the present invention, and (0) is what is out of the scope of the present invention. FIG. 4 is an explanatory diagram showing a conventional laser printer. FIG. 5 is an explanatory diagram showing the exposure energy of a Gaussian distributed light beam. Explanation of symbols V-・-・Photoconductor potential■ −・・・・Exposure energy ΔV-Photoconductor potential unevenness Patent Applicant Agent: Fuji Xerox Co., Ltd.
Patent Attorney Shin Matsubara 2 Same as Seiji Muraki Same Same as Tadao Hirata Same Same as Jun Ueshima - Figure 1 111 Figure 3 c (D) Figure 4 Figure 5

Claims (1)

[Claims] In an electrophotographic method in which an electrostatic latent image is formed by exposing a uniformly charged photoreceptor to a background part with a light beam according to an image signal, an electrophotographic method is used to increase the amount of energy used to expose the photoreceptor. When the optical static elimination characteristic of a photoreceptor whose potential decreases in response to a change in potential is expressed by an approximate straight line whose slope decreases at one point, the exposure energy corresponding to the one point is set as the reference exposure energy, and 1 of the reference exposure energy.
．． An electrophotographic method characterized in that the background portion is irradiated with a light beam having an exposure energy of 1 to 1.4 times.