JP3148964B2 - Electrophotographic equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic apparatus, and more particularly to an electrophotographic apparatus using an a-Si drum, such as a printer, a copying machine, and a facsimile.

[0002]

2. Description of the Related Art Conventionally, respective process means of exposure, development, transfer, cleaning (removal of residual toner), charge elimination and charging are arranged on the outer peripheral surface of a photosensitive drum, and an image is formed by a predetermined electrophotographic process. Electrophotographic apparatuses based on the so-called Carlson process are well known.

In recent years, a photoconductive drum is formed by laminating a light-transmitting conductive layer and a photoconductive layer on a cylindrical light-transmitting support, and a light output corresponding to image information is formed in the drum. Exposure means (for example, an LED head) to be generated is interpolated, and the light output of the exposure means is exposed through a converging lens onto the photosensitive drum charged using a predetermined charging means at the same time as or immediately after exposure to the photosensitive drum. An electrophotographic apparatus configured to transfer (transfer) the toner image to recording paper via a transfer roller or other transfer means after forming the latent image into a toner image (development) via a developing sleeve arranged in a face-to-face manner (Japanese Patent Laid-Open No. 58
153957) are also known.

[0004]

In an electrophotographic apparatus of this type, for example, in a laser printer using a semiconductor laser as an exposure source, after the oscillation wavelength of the semiconductor laser is beam-scanned by a polygon mirror via a collimator lens, fθ Although an image is formed on a photosensitive drum via a lens, in the above-described laser printer, it is necessary to accurately form an image of a band-like light whose width is increased to around A-4 size by a polygon mirror. For this reason, the fθ lens requires a wide lens having a length corresponding to the A-4 size, and it is difficult to assemble the lens with high accuracy, and assembly, processing errors, thermal expansion, and the like are likely to occur.

For this reason, optical aberrations and image shifts occur on the photoreceptor drum due to the error and the long lens, and these aberrations occur in the conventional opc drum and a-Si type drum. Therefore, it is also difficult to increase the image contrast and the sharpness because the light amount of light is picked up.

In order to reduce the size of the laser printer, the focal length of the laser printer is shortened. However, it is necessary to accurately form an image of the band light widened to around A-4 by a polygon mirror. For this reason, the fθ lens requires a wide lens having a length corresponding to the A-4 size, and further requires various measures such as making the curved surface toric.

However, in order to form a lens having such a long width and a complicated shape, a plastic lens is preferable. However, when a lens having a low refractive index such as a plastic lens is used, an image forming portion at both ends thereof is formed. It is not necessarily a straight line that coincides with the photoconductor drum generatrix, and a design contrivance is required to form a high-quality image of equal width in the main scanning direction.

The same applies to LED printers and copiers. In general, a selfoc lens (trade name) is used to form an exposure image. When a lens having a low refractive index, such as a plastic lens, is used because it is uniform and uniform, an imaging error tends to occur due to a long focal length, and aberrations resulting from the error are picked up. As a result, the sharpness is reduced, and a high-quality and high-contrast dot image cannot be formed.

In view of the drawbacks of the prior art, the present invention provides a
-To improve image contrast and sharpness without picking up the amount of aberration on the photoconductor drum, even if imaging aberrations and focus errors occur while achieving high durability using the Si drum, Determine the degree to which the photoreceptor half-reduction sensitivity required to lower the exposure potential to half of the surface potential of the layer depends on the thickness of the photoreceptor, regulate the photoreceptor layer thickness, and reduce the photoreceptor half-reduction sensitivity. , And pick up only the center light amount without picking up the light amount for the optical aberration caused by the imaging error and others.
As a result, it is an object to provide an electrophotographic apparatus capable of forming a high-contrast high-quality image using a plastic lens .

[0010]

According to the present invention, the photoreceptor layer is formed of an a-Si layer having a thickness of 2 to 25 μm, and the thickness of the surface layer is set to 0.05 to 5 μm. The photoreceptor half-reduction sensitivity required for lowering the exposure potential to half the surface potential of the photoreceptor layer is set in the range of 8 to 1 cm ² / μJ, charged at 450 V, and using an exposure wavelength of 740 nm. A depth of focus of 300 μm or more when exposed at an energy density of 0.2 μJ / cm ² , and an optical lens for forming the exposure image is constituted by a plastic lens. . With this technology, only the center light amount is picked up without picking up the light amount corresponding to the optical aberration caused by the imaging error and the like. As a result, a high quality dot image with high image contrast and sharpness can be formed even with a plastic lens. It is.

That is, even if imaging aberrations occur as described above, picking up only the center wavelength results in a deeper depth of focus, and as a result, imaging aberrations occur at both ends of a long lens such as an fθ lens. Even if it occurs, a high-quality image having the same width in the main scanning direction can be formed without picking up this aberration.

In a LED printer or a copying machine, even if a focus error of about ± 300 μm is generated by using a low refractive index lens such as a plastic lens for a SELFOC lens (trade name), the error can be easily absorbed and a high error can be obtained. A high-quality and high-contrast dot image can be formed.

Therefore, according to the present invention, even when the optical lens for forming the exposure image is formed of a plastic lens having a refractive index of about 1.51, high quality image formation becomes possible. Since manufacturing errors can be tolerated, the manufacturing cost is greatly reduced.

[0014]

Next, the operation of the present invention will be described with reference to FIGS. The graph will be described in detail in Examples below. FIG. 1A is a table showing the relationship between the film thickness of the a-Si photosensitive member and the half-sensitivity of the photosensitive member, and FIG. 1B is a graph showing the relationship. It is understood that the photoreceptor half-life sensitivity decreases in proportion to the Si photoreceptor film thickness.

FIG. 2 shows the relationship between the vertical and horizontal line widths and the number of dots for each photoconductor thickness. As can be understood from FIG. 2, the photoconductor having a thickness of 25 μm has a thickness of 40 μm.
It can be understood that the line width is sharpened and the image quality is greatly improved as compared with the case of, but conversely, at 25 μm or less, the sharpness of the line width almost coincides, and no significant difference is observed between them. Was. The half sensitivity when the film thickness is 25μm and try to, 7.58cm ² / μJ at the exposure wavelength 685 nm, at the exposure wavelength 740nm at 5.85cm ² / μJ, whereas the half-sensitivity when the film thickness is 40 [mu] m, the exposure 1 at a wavelength of 685 nm
1.11cm ² / μJ, at the exposure wavelength 740nm 9.09
cm 2 ^/ according to experiments is clear in .mu.J, formation of sharpness of high dot image shown in FIG. 2 becomes possible by setting the photoreceptor half sensitivity below 8 cm 2 ^/ .mu.J.

If the half-sensitivity is too low, the line image itself will be blurred. Therefore, as is clear from the table of FIG. 1A, a half-sensitivity of 1.75 cm ² / μJ with an exposure wavelength of 740 nm and a film thickness of 7 μm is sufficient. From the fact that a certain degree of sharpness could be secured, it is understood that no problem occurs if the half sensitivity is 2 cm ² / μJ or more.

FIG. 3 shows the relationship between the depth of focus and the drum sensitivity. When the drum sensitivity is lowered, the depth of focus becomes large because aberrations around the imaging position are not picked up as described above. When the film thickness is 40 μm, the depth of focus is 15
The thickness is about 0 to 230 μm, but when the film thickness is 15 μm, the depth of focus is greatly improved to about 380 μm. Even if the film thickness is reduced to 7 μm, there is almost no change. Therefore, the increase in the depth of focus means that the processing accuracy and the assembly accuracy of the optical system for forming the exposure image on the photosensitive drum can be set roughly, and the variation in image quality is greatly reduced, as described above. Thus, the use of a plastic lens becomes possible. This is because, as shown in FIG.
The MTF value of a plastic lens or an optical glass lens hardly changes for a lens having a thickness of m or less, but the MTF value of a plastic lens using a plastic lens for a film having a thickness of 40 μm is greatly reduced. Is also understood.

[0018]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of the present invention; However, unless otherwise specified, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention, but are merely illustrative examples. Not just. FIG.
FIG. 1 shows an electrophotographic apparatus to which the present invention is applied, and an optical system including an exposure LED head 2 and a selfoc lens 3 around an a-Si photosensitive drum 1 rotating clockwise in FIG. , A two-component developing unit 4, a transfer roller 5, a cleaning blade 6, a neutralizing lamp 7, and a particle charging unit 8.

Next, each component will be described.
The photoconductor drum 1 includes a photoconductor layer 1b on a conductive support 1a,
The support 1a is generally formed of an aluminum cylindrical body, but is made of an inorganic material such as glass having a conductive film adhered to the surface, or a transparent material such as epoxy. It is formed of resin or the like, and in this embodiment, the thickness is 2
mm and the outer diameter is set to 30 mm, and 3 mm in the axial direction.
An aluminum cylinder having a length of 00 mm is used.

The a-Si photosensitive layer 1b and the surface layer 1c are formed by a glow discharge decomposition method, a sputtering method,
A film is formed by an R method, a vapor deposition method, and the like.
An element for terminating dangling bonds, for example, (H) or halogen is 5 to 40 wt. %. That is, the photoconductor layer 1b uses a photoconductor made of a-Si: H. When the developing bias is positive, the photoconductive layer 1b contains a non-doped or Va group element in order to increase the mobility of electrons. In the case of a negative value, IIIa
It is preferable to include a group element. If necessary, elements such as C, O, and N may be contained in order to obtain desired characteristics such as electric characteristics such as dark conductivity and photoconductivity, and optical band gap. The thickness of the entire photoreceptor layer 1b is 2 to 25 in order to ensure necessary charging and dielectric strength, absorb exposed light, and suppress the above-described residual potential.
It is good to be about μm.

The surface layer 1c is made of a-SiC, a-Si
A such as O, a-SiN, a-SiON, a-SiCON
-It is preferable to use an Si-based inorganic high-resistance or insulating material, an organic insulating material such as polyethylene terephthalate, parylene, polytetrafluoroethylene, polyimide, and polyfluoroethylene propylene. Particularly, when a high-resistance a-SiC layer is used. In addition, characteristics such as dielectric strength, abrasion resistance, and environmental resistance are improved. The a-Si1-xCx x value is 0.3 ≦ x <1.0, preferably by setting the 0.5 ≦ x ≦ 0.95 ¹⁰ 12 ~1
High moisture resistance can be obtained with a resistance value in the range of 0 ¹³ Ω · cm. In this case, the C amount may have a gradient in the layer. Further, by containing N, O, and Ge simultaneously with C, the moisture resistance can be further improved.

The thickness of the surface layer 1c is preferably in the range of 0.05 to 5 μm, preferably 0.1 to 3 μm, and the thickness of the surface layer 1c is set to 10 ¹² to 10 ¹³ Ω · cm.

Then, in this embodiment, a-S
The i-photoreceptor layer 1b was formed, and an a-SiC surface layer 1c was coated thereon. In this embodiment, the layer thickness of the photoconductor is changed to 7, 10, 1 by changing the film forming time.
The photosensitive drums 1 having different thicknesses were formed by forming the films to have a thickness of 5, 20, 25, and 40 μm. In this case, the thickness of the surface layer 1c is set to 3 μm or less at the maximum and to about 5% or less of the total layer thickness.

The exposure LED head 2 has an exposure wavelength of 6
A head array of 85 nm and 740 nm was used, and this was dynamically driven and 64 bits × 40 per scanning line.
It is configured to perform multiple-time division exposure.

The developing unit 4 comprises a developing container 41 in which a multi-component developer composed of a carrier and a toner is stored, and a developing roller 42 in which a fixed magnet assembly 43 is stored. The developing bias power supply 44 is connected to perform development by low electric field development.

As the carrier, a carrier is used in which conductive fine particles are fixed on the surface of carrier base particles in which a magnetic substance is uniformly dispersed in a binder resin, and the magnetic force is 5 kOe (Oersted). The maximum magnetization in a magnetic field is 55 to 80 emu / g, and the average center particle size of the carrier is 3
A developer having a particle size distribution of 5 μm, particularly containing 15 wt% or more of particles of 35 μm or less is used.

As the toner, an ordinary high-resistance or insulating toner is used. For example, a magnetic substance is added to a binder resin, a colorant, a charge control agent, an offset preventing agent, etc., and the average central particle size is 5 to 15 μm. The carrier and the toner are configured as the front and rear magnetic toners, and an appropriate mixing ratio of the carrier and the toner is set to, for example, 85 to 90:15 to 10% by weight.

The transfer roller 5 uses a conductive roller to increase the transfer efficiency, applies a transfer bias having a polarity opposite to the charging potential of the toner, and applies a transfer bias to the photosensitive drum 1.
It is configured to be uniformly pressed against the peripheral surface and to be rotatable in synchronization with the drum 1.

The particle charging unit 8 has a charging gap (0.5 mm) with respect to the photosensitive drum 1 rotating rightward in FIG.
The non-magnetic sleeve 8 is rotatable in the rotational direction of the photosensitive drum 1 and the opposite direction (left direction in the figure) through the
1 and a fixed magnet body 82A fixedly disposed on the downstream side of the charging area on the back side of the non-magnetic sleeve 81, and on the upstream side of the charging area of the fixed magnet body 82A, in other words, on the downstream side in the sleeve rotation direction, A repulsion magnet body 82B having the same polarity as the fixed magnet body 82A, and a magnet body 82C having a polarity opposite to that of the fixed magnet body 82A are arranged on the upstream side in the sleeve rotation direction. Reference numeral 86 denotes a bias power supply for applying a charging bias to the conductive magnetic particle group 84 via the non-magnetic sleeve 81.

The conductive magnetic particles interposed on the charged area are not particularly limited as long as they are conductive. However, the conductive magnetic particles in which the surface of a magnetic core such as ferrite, iron powder or magnetite is coated with a conductive resin are used. Or a mixed particle group of conductive particles and magnetic particles.
For example, a mixture of a magnetic particle base material having an average particle size of about 30 μm and a conductive particle material having an average particle size of about 15 μm may be used. In this example, ferrite core particles having an average particle diameter of 20 to 35 μm and a resistivity of 10 ⁵ to 10 ⁶ Ω · cm were used, and the magnetic characteristics were 60 to 70 emu / cm 2.
g (1 k Oe) is used.

On the other hand, on the back side of the photosensitive drum 1, a first magnet body 85A substantially facing the fixed magnet body 82A located downstream of the charging area, and a first magnet body 85A
A second magnet body 85B is arranged adjacent to the charging area upstream side adjacent to the first magnet body 85A, and the first magnet body 85A is set to an S pole having a polarity opposite to that of the fixed magnet body 82A.
B is set to an N pole having a polarity opposite to that of the first magnet body 85A, and forms a horizontal magnetic field on the photosensitive drum 1 between the two magnet bodies 85A and 85B.

In this embodiment, after the surface of the photosensitive drum 1 is smoothly charged while the magnetic particles 84B are brought into close contact with each other on a horizontal magnetic field between the two magnets 85A and 85B on the photosensitive drum 1, After exposing a predetermined latent image by the exposure head 2 and attaching a toner image to the latent image by the developing unit 4, the latent image can be transferred to a recording medium (not shown) using the transfer roller 5.

Next, the following experiment was carried out using such a device and using the photosensitive drums 1 having different film thicknesses.

The surface potential of the photosensitive drum 1 is 200 V
After adjusting the particle charging bias so as to obtain the half-sensitivity (exposure energy required to reduce the exposure potential to half the surface potential) in each photosensitive drum having a different film thickness while adjusting the output of the exposure head 2. Looking at the density)
The half sensitivity decreases in proportion to the film thickness, and the exposure wavelength 68
It can be understood that 740 nm is lower than 5 nm.

FIG. 2 shows a surface potential of 200 V and an exposure wavelength of 74.
The relationship between the drum film thickness and the line width when exposed at 0 nm is shown. As can be understood from this drawing, the line width when the photoconductor film thickness is 40 μm or less in both horizontal and vertical lines is It is understood that the line width is thicker than that in the case of 25 μm or less, and the sharpness and the resolution are reduced correspondingly. 25
In the case of μm or less, the sharpness and the resolution are almost the same, and there is no significant difference. As shown in FIG. 1, the half-reduction sensitivity when the film thickness is 25 μm is 7.58 cm ² / μJ at an exposure wavelength of 685 nm and 5.85 cm ² / μJ at an exposure wavelength of 740 nm.
In cm ² / ^μJ, whereas thickness half sensitivity in the case of 40μm is, 11.11cm ² / ^μJ at the exposure wavelength 685 nm, as it is clear from such experiments with 9.09cm ² / μJ at the exposure wavelength 740 nm, the photosensitive member 8 cm ² / μJ half sensitivity
By setting as follows, it is possible to form a dot image with high sharpness shown in FIG. If the half sensitivity is too low, the line image itself will be blurred.
As is clear from the table, the film thickness is 7 μm at the exposure wavelength of 740 nm.
Since sufficient Naru sharpness even exposure wavelength 1.75 cm ² / .mu.J of m could be secured, the half sensitivity 2 cm ² / .mu.J
It is understood that the above does not cause a problem.

FIG. 3 shows the particle charging device 8 shown in FIG.
Shows the relationship between the depth of focus and the drum potential when exposed at a wavelength of 740 nm and an energy density of 0.2 μJ / cm ² after charging at a surface potential of 450 V using a corona discharger instead of When the film thickness is 40 μm, the depth of focus is about 150 to 230 μm. However, when the film thickness is 15 μm, the depth of focus is greatly improved to about 380 μm. no change. Therefore, when the drum sensitivity decreases, as a result, as described above, in order to not pick up the aberration around the imaging position,
Although the depth of focus becomes large, in this figure, it is estimated that a depth of focus of 300 μm or more can be obtained even if the thickness is 25 μm or less in consideration of FIG. In addition, 8 in FIG.
1 is a corona discharge line, 82 is a control grid, 83 is a discharge bias, and 84 'is a charging control bias.

Next, as a selfoc lens for forming an exposure image on the photosensitive drum, a selfoc lens SLA-20 (refractive index: approximately 1.63) manufactured by Nippon Sheet Glass and RA57S-S21 (refractive index) manufactured by Mitsubishi Rayon Co., Ltd. : About 1.50
The relationship of 8) was set by using the apparatus of FIG.
V (surface potential: 300 V) for examination. First, the focal length between the photosensitive drum and the SELFOC lens is 15 m.
m, the exposure energy was 2 at a speed of 10 sheets / min by longitudinally feeding A-4 size paper while maintaining the exposure wavelength at 685 nm.
0.5 to 0.6 for a photosensitive drum having a thickness of 5 μm.
μJ / cm ² , and 0.7 μm for a film thickness of 10 μm.
~0.9μJ / cm ^2, where the film thickness is about what the 40μm is was subjected to exposure at an exposure energy of 0.3~0.4μJ / cm ^2, as shown in FIG. 4, the film thickness is 10μm and 25μm For plastic lenses,
The MTF value of the optical glass lens hardly changes and can be maintained at 65 or more. However, it is understood that the MTF value of the plastic lens having a film thickness of 40 μm is greatly reduced. .

[0038]

As described above, according to the present invention, the exposure potential is reduced to 1/2 of the thickness of the surface layer of the photoreceptor, the thickness of the photoreceptor layer, the exposure wavelength, and the surface potential of the photoreceptor layer. 2. The photoreceptor half-reduction sensitivity required for the exposure, the energy density for exposure using the exposure wavelength, the charging potential at the time of exposure, and the depth of focus.
By setting as described in the above, the optical lens for forming the exposure image, it is possible to configure and arrange a plastic lens, optical aberration due to imaging errors and other due to such technology Only the central light quantity is picked up without picking up the minute light quantity. As a result, an electrophotographic apparatus capable of forming a high-quality dot image with high image contrast and sharpness even when using a plastic lens can be provided. In particular, by using a plastic lens as the exposure means, a lens having a free length and a curved surface can be formed, and the manufacturing cost can be reduced. And so on.

[Brief description of the drawings]

FIG. 1 shows the relationship between photoreceptor half-life sensitivity and film thickness,
(A) is a table, (B) is a graph.

FIG. 2 shows a relationship between a drum film thickness and a line width, wherein (A) shows a horizontal line and (B) shows a vertical line.

FIG. 3 is a graph showing a relationship between a drum sensitivity and a half sensitivity.

FIG. 4 is a graph showing a relationship between a film thickness and a lens type.

FIG. 5 is a schematic view showing an electrophotographic apparatus to which the present invention is applied.

FIG. 6 is a schematic view showing an electrophotographic apparatus to which the present invention is applied.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Exposure head 3 Optical system 4 Two-component developing unit 8, 8 'Charging device

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-21858 (JP, A) JP-A-5-249723 (JP, A) JP-A-5-72782 (JP, A) JP-A-60-1985 249170 (JP, A) JP-A-4-32464 (JP, A) JP-A-5-27464 (JP, A) JP-A-58-2802 (JP, A) JP-A-4-255818 (JP, A) 60-90467 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 5/00-5/16 G03G 15/00

Claims (1)

(57) [Claims] An exposed image is formed on a photoreceptor layer supported on a substrate.
An electrophotographic apparatus for forming an image while writing, wherein the photosensitive layer is an a-Si layer having a thickness of 2 to 25 μm.
And the thickness of the surface layer is reduced to 0.05 to 5 μm.
Setting, the exposure potential is reduced to half of the surface potential of the photoconductor layer.
8 to 1 cm²/ ΜJ range
, And charged at 450 V, using an exposure wavelength of 740 nm.
Energy density 0.2μJ / cm²Exposure atIffocus
Constructed to have a depth of 300μm or moreAnd  The optical lens for forming the exposure image is made of plastic.
An electrophotographic apparatus characterized in that it is constructed and arranged with cleanse.
Place.