JP3251783B2 - 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 such as a printer, a copying machine, a facsimile, etc., and more particularly to an image fog using a one-component or two-component magnetic developer at a low charging potential and a low developing bias voltage. The present invention relates to an electrophotographic apparatus that forms a high-density image without images.

[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 this type of electrophotographic apparatus, a non-magnetic sleeve in which a fixed magnet assembly is inserted and a photosensitive drum face each other, and the magnetic toner conveyed to the facing position (developing gap) via the non-magnetic sleeve is removed. A developing method of selectively attaching to an exposure latent image is adopted.

In this type of developing method using a magnetic toner, only one component of the magnetic toner is used, and the toner is selectively caused to fly to the photosensitive drum side using, for example, a developing bias applied on a developing gap. A developing method using a magnetic toner and one or a plurality of carriers, carrying a magnetic toner having a charge injected in a developing container by rubbing with the carrier on a non-magnetic sleeve, and applying the magnetic toner to a photosensitive drum. And a multi-component developing method in which a toner image is formed while rubbing against the side.

[0005] Further, as in a developing method used in a copying machine or the like, a charge having a polarity opposite to the surface potential of the photosensitive drum is injected into the magnetic toner, and the image background portion of the uniformly charged photosensitive drum is exposed. A non-exposed latent image portion to which a magnetic toner having a charge of opposite polarity is attached, and a developing method used for a printer, which has a charge having a polarity opposite to the surface potential of the photosensitive drum as in a developing method used for a printer. A regular development method in which a magnetic toner is injected into a uniformly charged photoreceptor drum to expose an image background portion, and then a non-exposed latent image portion is charged with a magnetic toner of opposite polarity, and used in a printer. As in the developing method, a charge having the same polarity as the surface potential of the photosensitive drum is injected into the magnetic toner, and an image is exposed on the uniformly charged photosensitive drum to form a latent image from which the charge has been removed. The submarine In a reversal development system for attaching a magnetic toner having an electric charge of the same polarity by using the developing bias is present.

[0006] In particular, in the reversal developing method, a clear image is formed without causing toner to adhere to the latent image portion on the photoreceptor while adhering the toner to the background portion, in other words, without fogging. For this purpose, the potential difference between the surface potential of the photoconductor and the developing bias had to be 200 V or more. Also, in the charging step, the photoconductor surface potential is set to 50
0 V or more was required, and the potential difference of the electrostatic latent image after exposure was 400 V or more.

For this reason, the photoreceptor is required to have a charging ability of 500 V or more, and this charging ability depends on the film thickness.
/ Μm, to satisfy the above conditions, 34 μm
m or more, while an organic photoreceptor (OPC)
In this case, a film thickness of 20 μm or more is required.

However, increasing the charging potential and the developing bias voltage requires an increase in the withstand voltage of each electrical component, which leads to an increase in the cost of the component. On the other hand, unlike a laser printer, an LED printer in which an LED head is incorporated in the exposure means of the electrophotographic apparatus is advantageous in miniaturization.

In such a printer, the LE head is attached to the LED head.
A so-called static drive method in which the D element rows are simultaneously turned on for each pixel line, and the LED element rows are divided in chip units or n-bit units, and exposure is performed while sequentially performing time-division driving for each of the divided block units. So-called dynamic drive system (Japanese Patent Laid-Open No. 60-34877)
However, simultaneous lighting of a large number of LED elements for each pixel line requires an increase in drive current,
In addition, a number of lead wires and the like corresponding to the LED element are required, and therefore, a dynamic driving method has recently attracted attention.

In the dynamic driving, the driving time of each block is time-divided in accordance with the number of blocks within one pixel line transit time to cause the LED elements to emit light. As a result, the charge photo-excited in the photoconductor layer is further reduced, and the potential difference of the electrostatic latent image after exposure is reduced by 400
It is difficult to set V or more.

[0011]

SUMMARY OF THE INVENTION In view of the drawbacks of the prior art, the present invention is directed to a reversal developing method, in which a low surface charging potential, a low developing bias voltage, and a small potential difference of an electrostatic latent image after exposure are reduced. An object of the present invention is to provide an image forming method in an electrophotographic apparatus capable of forming a clear image without causing image fogging or insufficient density. It is another object of the present invention to provide an image forming method in an electrophotographic apparatus which is suitably applied to a printer using a dynamically driven LED head as the exposure means.

[0012]

According to the present invention, there is provided an a-Si photosensitive member as shown in FIG.
Photoconductor drum with a fixed magnet assembly
The magnetic sleeve faces each other, and a layer is formed on the surface of the non-magnetic sleeve.
Two-component magnet whose thickness is regulated at a predetermined layer thickness by thickness regulating means
The developer is led to the developing gap formed between the two.
A toner image on the exposed part of the photoreceptor
In the electrophotographic apparatus, the a-Si photoreceptor is
When the layer thickness is 2 to 25 μm,
And the developing bias voltage is 50 to 450 V.
Set V, the sets the development gap width B to larger than regulating layer thickness A by the layer thickness regulating means, nip amount C of the two-component magnetic developer located in the development gap
Configure (puddle developer), the more development gap width B
The was that the first feature.

In order to obtain the developer pool, the rotation direction of the non-magnetic sleeve on the developing gap is set to the forward feed rotation in the forward direction with respect to the rotation direction of the photosensitive drum, and the peripheral speed is set to the photosensitive member. It is set to 2.5 to 5.0 times the peripheral speed of the drum, and the nip amount C
Is preferably set to 3 to 5 mm. However, by setting the peripheral speed to be 2.5 times or more the peripheral speed of the photosensitive drum, the amount of toner supplied to the developing gap is increased, in other words, the toner density is increased, resulting in a short time. Development efficiency can be increased. In this case, if the peripheral speed difference is 10 times or more, contamination in the machine due to an increase in the relative rubbing speed, a reduction in the life of the developer, and the like are likely to occur. Therefore, the second aspect of the present invention
The feature is that the rotation direction of the non-magnetic sleeve is
Forward on the developing gap with respect to the rotation direction of
Feed rotation, and set the peripheral speed to
2.5 to 5 times the peripheral speed of the
C is set to 3 to 5 mm.

When the non-magnetic sleeve is rotated by counter feed, the developer pool can be obtained without restricting the peripheral speed, but it is necessary to take measures to prevent contamination inside the machine. is there. The layer thickness of the photoreceptor is set to 2 to 25 μm in the case of a-Si, and the layer thickness of the photoreceptor is set to 20 μm or less in the case of an OPC photoreceptor so that sufficient development is possible by the developer pool. Good to do. By setting in this manner, the image resolution and the sharpness of the line drawing are also reduced to a thickness of 25 μm as shown in FIG.
In the following cases, it can be understood that the film thickness is greatly improved as compared with the case where the film thickness is 40 μm, and no afterimage occurs.

Further, as shown in FIG. 5, when exposure is performed with the film thickness reduced to 25 μm or less, the conventional a-S
Compared with the case of performing exposure using an i-drum, the half reduction sensitivity is greatly reduced to about 1/2 to 1/3. As a result, the exposure resolution can be improved and the depth of focus from the viewpoint of image quality can be deepened. It becomes possible. Therefore, when the photoreceptor is formed of an a-Si-based material, a predetermined potential degree can be obtained with a small light output by reducing the film thickness.
It is preferably set to μm.

Accordingly, in the present invention, since the photosensitive member for receiving the light output from the exposure means is formed in a thin film of a-Si, it is possible to use a dynamically driven LED head for the exposure means. Thus, according to the present invention, when a dynamic drive LED head is used as the exposure means, the light emission time is 1 / m (m: number of LED blocks) as compared with the static drive, so that a clear image is formed. As described above, a substantially small exposure energy can be effectively captured on the light receiving side as described above, and a latent image generated by capturing the exposure energy can be solved. A visible image can be efficiently formed without lowering the potential or causing a background fog. In particular, the a-Si based photoconductor layer is made of other SeAs, SeTe, CdS, OP
Compared to C and other photoreceptor materials, it has higher light absorbing ability and photo carrier generating ability and higher mobility of generated carriers, enabling efficient photoelectric conversion even with very short optical output by dynamic driving. Become.

In order to efficiently perform photoelectric conversion even with light output for a shorter time, it is necessary to increase the electric field strength by reducing the thickness of the photoreceptor layer. In the case of an LED array conventionally used as an exposure means, When the photoconductor layer is made thinner, the light absorption efficiency of the photoconductor layer decreases, and it becomes difficult to obtain a preferable exposure charge. Therefore, when an LED is used as the exposure means, for example, in consideration of the fact that the film thickness until 90% of the incident light of the a-Si: H material is absorbed is about 2.2 μm,
The lower limit is set to 2 μm.

In this case, when the photoconductor layer is thinned,
If the charging potential applied to the photoconductor layer is too high, the resulting film may be electrically destroyed. Therefore, the present invention provides a surface potential of the photoconductor layer of 500 V or less, preferably 4 V or less.
50 V or less, and a developing bias voltage of 50 to 450 V,
Preferably, it was set to 100 to 300V. As a result, the withstand voltage can be set low for each electrical component for charging or developing bias, and this leads to a reduction in component cost and prevention of deterioration or fatigue of the photosensitive drum.

[0019]

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 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 a dangling bond, 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 film thickness of the entire photosensitive layer 1b is:
The thickness is preferably about 2 to 25 μm in order to ensure necessary charging and insulation withstand voltage, absorb exposed light, and suppress the residual potential as described above.

The surface layer 1c is made of α-SiC, α-Si
A such as O, α-SiN, α-SiON, α-SiCON
-It is preferable to use an organic insulating material such as an inorganic high-resistance or insulating material of a Si type, such as polyethylene terephthalate, parylene, polytetrafluoroethylene, polyimide, or polyfluoroethylene propylene. In addition, characteristics such as dielectric strength, abrasion resistance, and environmental resistance are improved. The x value of this a-Si _1-x C _x is set to 0.3 ≦ x <1.0, preferably 0.5 ≦ x ≦ 0.95, whereby 10 ¹² to 10
High moisture resistance can be obtained with a resistance value in the range of ¹³ Ω · cm, and 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.

In this embodiment, the a-Si photoconductor layers 1b and a
-SiC surface layer 1c is sequentially laminated, and as described later,
The layer thickness of the photoreceptor is 7, 10, 15, 20, 25, 40, respectively.
A photosensitive drum 1 having a film layer having a thickness of μm was produced. 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.

In this case, the circularity of the aluminum cylinder having a thickness of 2 mm is not obtained in the case of a film having a thickness of 40 μm.
For this reason, film formation was performed again, but the result was not good. Therefore, in the present embodiment, when the film was formed again using an aluminum pipe having a thickness of 4 mm, roundness could be obtained. Therefore, reducing the film thickness also makes it possible to reduce the thickness of the base, that is, the aluminum cylinder, thereby achieving weight reduction.

A 740 nm head array is used as the exposure LED head 2, and the head array is divided into 64 bits × 40 times for each scanning line by dynamic driving, and the light input intensity from each LED element is set to 0. The exposure pulse time is set to 1 μJ / cm ² or more and the exposure pulse time is set to 5 to 100 μs, preferably 10 to 30 μs. You.

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 non-magnetic developing sleeve 42 in which a fixed magnet assembly 43 is stored. A DC developing bias power supply 44 variable to 450 V is connected to perform development. The configuration of the developing unit 4 will be described in more detail with reference to FIG. 1. The developing unit 4 is provided with a toner container 45 via a supply roller 44 at a position above the developing container 41.
The magnetic toner can be supplied into the developing container 41 at appropriate intervals based on a signal from a detection sensor 46 for detecting the T / C concentration in the inside.

In the inside of the developing container 41, a non-magnetic doctor blade 48 is disposed above the developing gap so as to face the stirring roller 47 for stirring the carrier and the toner and the non-magnetic sleeve 42. Further, the layer thickness regulation interval by the doctor blade 48 is smaller than the development gap interval B, specifically, the development gap interval B is set to 2 mm, the layer thickness regulation interval A is set to 1 mm, and the photosensitive drum 1 is turned clockwise. Magnetic sleeve 4
2 rotates counterclockwise, and both rotate forward feed on the developing gap. The peripheral speed of the non-magnetic sleeve 42 can be variously changed with respect to the peripheral speed of the photosensitive drum 1 as described later.

The fixed magnet assembly 43 has a main pole N ₁ at a position corresponding to the developing gap, S ₂ and N ₃ across a doctor blade , and further has a shield pole S ₁ and a transport pole N _2.
Having.

The carrier contained in the developing container includes a magnetic powder carrier made of a ferrite carrier, iron powder, magnetite, and the like, and a magnetic resin carrier made of a magnetic substance uniformly dispersed in a binder resin. Using a mixed carrier, the magnetic force is preferably such that the maximum magnetization in a magnetic field of 5 kOe (Oersted) is 55 emu / g or more,
More preferably, it is 55 to 80 emu / g. Also, 1
The maximum magnetization in a kOe magnetic field is preferably 45 emu / g or more, more preferably 45 to 60 emu / g. If the magnetic force of the carrier 14 becomes too small, the transportability of the developer deteriorates, and the carrier is developed together with the toner.

As the toner, a normal 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 anti-offset agent and the like, 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 the appropriate mixing ratio of the carrier and the toner is set to, for example, 85 to 95:15 to 5% by weight. Transfer roller 5
Reference numeral 4 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 uniformly presses against the peripheral surface of the photosensitive drum 1 to synchronize with the drum 1 It is configured to be rotatable.

The charging unit 8 was uniformly charged on the photoreceptor by a known corotron type charger.
In the figure, 81 is a corona discharge line, 82 is a control grid, 83 is a discharge bias, and 84 is a charge control bias. In this embodiment, the surface of the photosensitive drum 1 is charged to a predetermined surface potential of 500 V or less by applying a high-voltage discharge bias in a state where the charging control bias is variably set from about 150 V to about 500 V. . Next, the following experiment was performed using such an apparatus.

First, the photosensitive drum 1 having a thickness of 25 μm is used, the charging control bias and the like are adjusted so that the surface potential of the photosensitive drum 1 becomes 300 V, and the developing bias voltage is set to 210 V. The energy level to be imaged on the body drum 1 is 1.0 μJ / cm ² ,
After adjusting the output of the exposure head 2, the relative peripheral speed of the non-magnetic sleeve with respect to the photosensitive drum is increased by 1.5 times and 2.5 times.
, 2.9 times, and 5 times, respectively, and the nip amount C of the magnetic developer located on the developing gap is 2 mm, 3 mm, 5 mm.
mm and 5 mm, and the fog and image density at each nip amount C were examined. The results were as shown in Table 1.

[0035]

[Table 1]

[0036] Note that the saturation point of the nip width, the maximum value of the nip amount C which is held on the developing gap by magnetic holding force of the main arranged on the back development gap pole N ₁ of the non-magnetic sleeve 42, Therefore, in the case of the present embodiment, the nip amount C is set to a value which does not increase any more at the developing gap position even when the peripheral speed of the sleeve is increased 2.9 times or more, specifically 4 to 5 mm. Point.

As can be understood from the table, when the peripheral speed of the non-magnetic sleeve relative to the photosensitive drum is 2.9 times or more, the nip amount C does not change to 5 mm and reaches the saturation point. It is understood that, in the saturation region, even when the surface potential of the photosensitive drum 1 is as low as 300 V and the developing bias voltage is as low as 210 V, a favorable image was obtained without occurrence of image density and fogging.

Next, with the relative peripheral speed of the non-magnetic sleeve to the photosensitive drum set to 2.9 times, the surface potential 2
FIG. 3 shows the relationship between the drum film thickness and the line width when an image is formed at 00 V and a developing bias voltage of 150 V. FIG. 3A is a graph showing line drawings in the horizontal direction and FIG. As can be understood from this figure, the line width when the photoconductor thickness is 40 mm or less in both the horizontal line and the vertical line is 25 mm.
It is understood that the line width is thicker than that in the case of μm or less, and the sharpness and the resolution are reduced by that amount. In the case of 25 μm or less, the sharpness and the resolution are almost the same, and there is no significant difference.

FIG. 4 shows that the energy density of the LED head is 0.2 μJ / c after charging at a surface potential of 450 V.
pulled m ^2, other shows the relationship between focal depth and drum sensitivity when exposed under the same conditions, as compared with the case of the film thickness 40 [mu] m, 7 [mu] m, the depth of focus as the 15 [mu] m 3
With a depth of focus of 70 μm, the depth of focus is improved by a factor of less than two, and a large depth of focus means that the processing accuracy and assembly accuracy of the optical system for forming an exposure image on the photosensitive drum are roughly set. In addition to this, variations in image quality are greatly reduced.

In order to confirm the effect of the present invention also on the OPC photosensitive drum, an OPC photosensitive drum having a thickness of 15 μm was used, and the surface potential of the photosensitive drum 1 was 300 V.
The charging control bias, etc. adjusted to, also after setting the developing bias voltage to 210 V, the energy level to be imaged on the photosensitive drum 1 is such that the 1.0μJ / cm ^2, the exposure head 2 After adjusting the output, the relative peripheral speed of the non-magnetic sleeve with respect to the photosensitive drum is set to 2.9.
When the image density and the fogging state were examined by doubling the density, good results were obtained as shown in Table 1.

[0041]

As described above, according to the present invention, image fogging and insufficient density do not occur even when the potential difference between a low surface charge potential, a low developing bias voltage, and an electrostatic latent image after exposure is reduced. And a clear image can be formed. Further, according to the present invention, afterimages do not occur even in an electrophotographic apparatus using a thin-film a-Si drum, and high image quality and sharpness can be obtained even in a printer using a dynamically driven LED head as the exposure unit. Image can be easily formed, and a high-quality image can be easily formed even if an assembly and processing error of the exposure unit occurs. And so on.

[Brief description of the drawings]

FIG. 1 is an enlarged view of a main part of FIG. 2, showing a relationship between a photosensitive drum and a non-magnetic sleeve.

FIG. 2 is a schematic view showing an electrophotographic apparatus to which the present invention is applied.

FIG. 3 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. 4 is a graph showing a relationship between a drum sensitivity and a depth of focus for each drum film thickness.

FIG. 5 is a graph showing a relationship between a drum film thickness and half sensitivity.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Exposure head 3 Optical system 4 Two-component developing unit 8 Charging device 42 Non-magnetic sleeve 43 Fixed magnet assembly

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-6-124027 (JP, A) JP-A-1-13086 (JP, A) JP-A-4-212181 (JP, A) JP-A-2- 73383 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G03G 15/08-15/095

Claims (2)

(57) [Claims] 1. A photoconductor drum having an a-Si photoconductor and a non-magnetic sleeve containing a fixed magnet assembly are opposed to each other. An electrophotographic apparatus in which a toner image is attached to an exposed portion of a photoconductor by reversal development while guiding the two-component magnetic developer thus obtained to a developing gap formed between the two, the layer thickness of the a-Si photoconductor. Is set to 2 to 25 μm, the surface charging potential of the photosensitive drum is set to 500 V or less, the developing bias voltage is set to 50 to 450 V, and the developing gap width B is set to be larger than the regulation layer thickness A by the layer thickness regulation means. In addition, the nip amount C of the two-component magnetic developer located in the developing gap is set to be equal to or greater than the developing gap width B, and the non-magnetic sleeve rotation direction is the rotation direction of the photosensitive drum. Against, 3-5 set to the forward feed rotation on the developing gap, as well as the peripheral speed 2.5 to 5 times the peripheral speed of the photosensitive drum, the nip amount C
An electrophotographic apparatus characterized in that the distance is set to mm. 2. An electrophotographic apparatus according to claim 1, wherein said exposure means for exposing said photoreceptor comprises a dynamic drive type LED head.