JPH08211711A - Image forming device - Google Patents

Abstract

PURPOSE: To obtain an inexpensive and compact image forming device excellent in image quality by preventing its deterioration caused by a latent image ghost and a negative development ghost. CONSTITUTION: In the image forming device constituted in such a manner that a developing unit 2 provided with a toner carrying roll 21 is arranged to face a photoreceptor drum 1, to stick toner made a thin layer on the toner carrying roll 21 to an electrostatic latent image, formed on the drum 1 and develop the electrostatic latent image, the rotational angular velocity of the roll 21 is set to be the same as that of the drum 1 and the negative development ghost generated on the roll 21 is overlapped on the tip of the latent image ghost generated on the drum 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as an electrophotographic copying machine or a laser beam printer, and more particularly to a so-called latent image ghost and development ghost erasing technique.

[0002]

2. Description of the Related Art Recently, there has been an increasing demand for downsizing of copying machines, printers, etc. from the viewpoint of space saving. In order to meet such a demand, a charging device provided around a photosensitive drum is charged. In addition to miniaturizing each component such as the developing unit, developing unit, and cleaner, the image forming process in one rotation of the photosensitive drum is simplified as much as possible to eliminate unnecessary components, and the diameter of the photosensitive drum is minimized. It is important to design small.

For this reason, in the conventional small-sized printer, the erase lamp, that is, the lamp for erasing the potential history on the photosensitive drum at the final stage of one rotation cycle of the photosensitive drum is often omitted. In this case, there arises a problem that the influence of the potential history of the previous cycle (hereinafter referred to as a latent image ghost) appears on the image formed by the next rotation of the photosensitive drum.

The latent image ghost will be described below. FIG. 3 is a block diagram showing an apparatus for measuring the charging characteristic of the photosensitive drum. This measuring device uses a DC power supply 5
1 and a charging roll 53 connected to an AC power supply 52 are brought into contact with the photosensitive drum 54 to charge the photosensitive drum 54. The charging roll 53 has a peak-to-peak voltage of 1.5 kV and a frequency. An alternating voltage in which a DC component of -350V is superimposed on an AC component of 170Hz is applied. A surface potential sensor 55 is disposed on the downstream side of the charging roll 53 in the rotation direction of the photoconductor drum 54. Based on a detection signal of the surface potential sensor 55, a surface potential meter 56 controls the charge potential of the photoconductor drum 54. Is displayed.

[0005] Then, the charged photosensitive drum 54 by using the measuring device, was measured and the charging potential Vh, as shown in FIG. 4, the charge potential V _h at 1 rotation cycle of the photosensitive drum 54 is Despite being −340 V, the charging potential V _h in the second rotation cycle is −
It reached 360V. This is the initial state (Vh = 0)
It is shown that, when the photosensitive drum 54 in FIG. 2 is charged, a potential difference (ΔV = 20V in the example shown in FIG. 8) occurs between the charging potentials of the first rotation cycle and the second rotation cycle. When a DC component of -900V was applied to the charging roll 53, this potential difference ΔV = 30V.

As described above, the first and second rotations of the photosensitive drum
Since the charging potential is different from that at the rotation, when an electrostatic latent image is actually written on the photosensitive drum, a latent image ghost is generated as shown in FIG. First, after uniformly charging the photosensitive drum to V _h = −340 V by the charger (see FIG. 5A), the image portion is exposed by the laser beam in the first rotation cycle, and the photosensitive portion in the exposed portion is exposed. The charging potential Vi of the body drum drops to about 0 V (see FIG. 5B). When the photosensitive drum is uniformly charged again in the second rotation cycle of the photosensitive drum,
The area on the photosensitive drum corresponding to the image portion of one revolution cycle, the charged potential is maintained at V _h = -340V. However, the area on the photosensitive drum corresponding to the background portion (non-exposed portion) has already been -300V before charging.
Since the potentials are close to each other, the charging potential is close to Vh '=-360V (see FIG. 5C), as is clear from the above description. Therefore, when the area a including the image portion of the first rotation cycle is exposed in the second rotation cycle of the photosensitive drum, a potential difference ΔV is generated in the exposure portion corresponding to the image portion of the first rotation cycle (FIG. 5 ( d)
reference). Then, in the second rotation cycle of the photosensitive drum, a latent image ghost of the same image as in the first rotation cycle is generated in the electrostatic latent image.

FIG. 6 shows a latent image ghost generated when an image of "G" is formed in the first rotation cycle of the photosensitive drum and visualized on a ghost check chart output from the printer. . When the electrostatic latent image formed on the photoconductor drum is developed by the developing device, in order to prevent so-called "fog" that toner adheres to the background portion, the developer carrying roll of the developing device and the photoconductor drum While the developing bias voltage Vd is applied between the developing bias voltage Vd and the image forming portion (see FIG. 5D), the amount of toner attached to the image portion is proportional to the difference between the developing bias voltage Vd and the image portion potential Vi. Therefore, for the image portion where "G" is formed in the first rotation cycle of the photosensitive drum,
When the halftone image is formed in the second rotation cycle, the potential of the area where the latent image ghost is generated is lower than the peripheral image portion by the potential difference ΔV as shown in FIG. It will be highly expressed. Therefore, the latent image ghost "G" is prominently darkened in the halftone image formed in the second rotation cycle of the photosensitive drum.

Such a phenomenon is remarkable in a grayscale image (for example, the central three types of halftone dot images in FIG. 6) in which the potential difference ΔV is easily reflected in the image density.
In the case of a completely solid black image (for example, the image at the right end in FIG. 6), the potential difference ΔV is unlikely to appear as image density unevenness, so the latent image ghost is not visualized. If the area corresponding to “G” in the first rotation cycle of the photosensitive drum becomes a white image (for example, the leftmost image in FIG. 6) in the second rotation cycle, the image portion potential is the development bias voltage. The latent image ghost is not visualized 9 unless the potential difference ΔV is very large, because it does not decrease further.

On the other hand, among developing devices for developing an electrostatic latent image formed on a photosensitive drum with toner, one suitable for downsizing a copying machine or a printer is to use a magnetic toner as a developer. A component developing device is known (Japanese Patent Laid-Open No. 54-54).
No. 51848, etc.). Unlike the two-component developing device, this one-component developing device does not need to mix and stir the toner and the carrier at a constant concentration, and has the advantage that the stirring mechanism of the developer can be simplified and downsized accordingly. Have

As shown in FIG. 7, the one-component developing device of this type includes a hopper 62 for accommodating the magnetic toner 61, a developing roll 63 which is arranged to face the photosensitive drum 60 and has a magnet roll 63a therein. One end is composed of a developer regulating member 64 that is in pressure contact with the developing roll 4,
An alternating voltage obtained by superimposing a DC voltage on an AC voltage is applied to the developing roll 63 as a developing bias voltage.
In such a configuration, the toner 61 contained in the hopper 62 is held on the peripheral surface of the developing roller 63 by the magnetic force of the magnet roller 63a, and the developing area A facing the photoconductor drum 60 as the developing roller 63 rotates. Be transported to. At this time, the toner 61 is thinned to a predetermined thickness by the developer restricting member 64, and an electric charge is applied by frictional charging with the developer restricting member 64. As a result, when the alternating voltage is applied to the developing roller 63 and an alternating electric field is formed in the developing area A where the photoconductor drum 60 and the developing roller 63 face each other, the magnetic field is held by the developing roller 63. The toner 61 receives an electrostatic attraction force corresponding to the electric charge, migrates in the developing area A, and adheres to the image portion of the electrostatic latent image formed on the photoconductor drum 60 to develop the electrostatic latent image.

However, in such a one-component developing device, if the toner 61 carried into the developing area A is not sufficiently charged, the toner 61 can overcome the magnetic force and fly from the developing roller 63. However, the development density of the electrostatic latent image tends to be insufficient. Therefore, if the pressing force of the developer regulating member 64 against the developing roll 63 is unsuitable, or if the electrical insulation of the toner is insufficient, one friction of the developer regulating member is sufficient for the toner. However, there is a problem that a so-called negative development ghost is generated in which the image developed in the first rotation of the developing roll is floated thinner than the surroundings in the image developed in the second rotation.

FIG. 8 shows a state in which the negative development ghost is generated in the ghost check chart output from the printer. When the image "G" is developed by the first rotation of the developing roll, the toner corresponding to "G" is removed from the surface of the developing roll that has passed through the developing area, and the second rotation of the developing roll causes the toner to be removed. However, new toner will be replenished from the hopper. Therefore, of the toner carried out to the developing area by the second rotation of the developing roller, the toner attached to the area corresponding to the “G” of the previous rotation is rubbed against the developer regulating member for the first time, and the toner in that area is discharged. Cannot be given a sufficient charge. On the other hand, the previous rotation "G"
The toner adhering to the area other than this is rubbed against the developer regulating member again after the first rotation of the developing roll, and a sufficient charge can be given to the toner in the area. Therefore, when a halftone image or a solid black image is developed by the second rotation of the developing roll, the development density of the electrostatic latent image is reduced only in the area where the toner charge amount is insufficient, and the development image "G The negative development ghost corresponding to “” appears in the developed image.

On the other hand, in such a one-component developing device,
If the electric charge of the toner carried out to the developing area becomes excessive, a large image force for holding the toner on the surface of the developing roll acts on the toner.
1 cannot overcome the magnetic force and the image force to fly from the developing roller 63, and the developing density of the electrostatic latent image tends to be insufficient. Therefore, when the toner is repeatedly triboelectrically charged by the developer regulating member as the developing roll rotates a plurality of times, the electric charge of the toner adhering to the developing roll becomes excessive, and the toner is developed at the first rotation of the developing roll. There is a problem that a so-called positive development ghost is generated in the image developed in the second rotation, which appears more densely than the surroundings.

FIG. 9 shows how the positive development ghost occurs in the ghost check chart output from the printer. When the image of "G" is developed by the first rotation of the developing roll, as described above, the second rotation of the developing roll predominantly replenishes the area with new toner. The toner adhering to the area other than the area corresponding to “G” (that is, the background portion) is repeatedly rubbed by the developer regulating member at the first and second rotations of the developing roll, and the toner in the area is Will give an electric charge in excess of that of the toner adhering to the area corresponding to "G" in the previous rotation. Therefore,
When a halftone image or a solid black image is developed by the second rotation of the developing roll, the development density of the electrostatic latent image decreases only in the area where the toner charge amount is excessive, and it corresponds to the development image "G" of the first rotation. The positive development ghost thus created emerges in the developed image.

[0015]

As described above, when an attempt is made to reduce the size of a copying machine or printer, a latent image ghost is generated in the electrostatic latent image formed on the photosensitive drum, while the electrostatic latent image described above is generated. There is a concern that negative development ghost or positive development ghost may occur in the image developed with toner,
There is a problem that the image quality of the recorded image formed by these latent image ghost, negative development ghost and positive development ghost is impaired.

The present invention has been made in view of the above problems, and an object of the present invention is to prevent deterioration of image quality due to occurrence of latent image ghosts and negative development ghosts, and to provide excellent image quality at low cost. And to provide a small image forming apparatus.

[0017]

In order to achieve the above object, in an image forming apparatus of the present invention, a developing device equipped with a toner carrying roll is arranged so as to face a photosensitive drum, and a thin film is formed on the surface of the toner carrying roll. In an image forming apparatus for adhering layered toner to an electrostatic latent image formed on the photosensitive drum to develop the electrostatic latent image, the rotational angular velocity of the toner carrying roll is set to the photosensitive drum. And the negative development ghost generated on the toner carrying roll is superposed on the latent image ghost generated on the photosensitive drum.

In such a technical means, in order to generate a negative development ghost on the toner carrying roll, the charge amount of the toner carried out from the inside of the developing device to the developing area by the toner carrying roll is set to be low. It is necessary to Specifically, this can be done by adjusting the charge control agent added to the toner, or by weakening the pressure contact force of the developer regulating member that pressure-contacts the toner carrying roll to thin the toner layer. it can.

As a method for setting the rotational angular velocity of the toner carrying roll to be the same as the rotational angular velocity of the photosensitive drum, the diameter and peripheral speed of the photosensitive drum and the toner carrying roll may be appropriately combined. As the simplest method, it is preferable to make the diameters of the photosensitive drum and the toner carrying roll the same. By doing so, the photosensitive drum and the toner carrying roll can be manufactured from the same tube material, and the cost can be reduced.

[0020]

According to the above technical means, the rotational angular velocity of the toner carrying roll is set to be the same as the rotational angular velocity of the photoconductor drum, so that the negative development ghost generated on the toner carrying roll is deposited on the photoconductor drum. Since it overlaps with the latent image ghost that is occurring, the latent image ghost that is rendered darker than it should be when developed with toner, and the negative that is rendered lighter than it should be rendered. Development ghosts cancel each other out,
The latent image ghost is prevented from being visualized.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The image forming apparatus of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 shows a first embodiment of the image forming apparatus of the present invention. Reference numeral 1 in the drawing is a photosensitive drum, and an aluminum pipe having a diameter of 30 mm and a length of 253 mm is coated with a nylon resin (trade name laccamide, manufactured by Dainippon Ink and Chemicals, Inc.) to form an undercoat layer having a thickness of 1 μm A charge carrier generation layer (CGL) containing a chloroindium phthalocyanine pigment and a polyvinyl butyral resin thereon, and a charge carrier transfer layer (CTL) containing a polycarbonate Z resin and a benzidine compound.
Is a composite type organic photoconductor (OPC) drum in which the layers are sequentially laminated.

Further, reference numeral 2 is a developing device having a built-in one-component magnetic toner 20, which is a magnet roll 21a having a plurality of magnetic poles magnetized and a sleeve which rotates around the magnet roll (hereinafter referred to as a developing sleeve). 21b, a developer regulating member 22 that presses against the developing sleeve 21b and thins the toner 20 magnetically attracted to the developing sleeve 21b, and a DC superimposed AC voltage on the developing sleeve 21b. And a power supply 23 for applying The developing sleeve 21b is the photosensitive drum 1
Is formed of an aluminum pipe having the same diameter (30 mm) as the above, and its peripheral surface is ground to a predetermined surface roughness by sandblasting. Further, the developing sleeve 21b rotates in the opposite direction to the photosensitive drum 1 at the same angular velocity as the photosensitive drum 1, but in this embodiment, the photosensitive drum 1 and the developing sleeve 21b have the same diameter. The photosensitive drum 1 and the developing sleeve 21b are rotating at the same peripheral speed.

Further, a charging roll 3 connected to a DC power source is arranged upstream of the developing device 2 in the rotational direction of the photosensitive drum 1, and the charging roll 3 and the developing device 2 are arranged.
The position between and is the exposure position of the light beam by the laser beam scanner (not shown). Further, a transfer roll 4 connected to a DC power source is disposed downstream of the position where the developing device 2 is disposed in the rotational direction of the photosensitive drum 1, and the toner image formed on the photosensitive drum 1 is At the position, it is transferred to a recording sheet sent from a paper feed unit (not shown), and then inserted into the fixing device 6. Further, a cleaning blade 5 for removing the residual toner adhering to the photoconductor drum 1 is provided downstream of the position where the transfer roll 4 is provided in the rotation direction of the photoconductor drum 1. Are housed in the same unit as the charging roll 3.

In the image forming apparatus of this embodiment having the above-mentioned structure, the image formation on the recording sheet is performed as follows. That is, -1 is applied to the charging roll 2.
After applying a DC voltage of kV to uniformly charge the photoconductor drum 1, the photoconductor drum 1 is exposed by a laser beam scanner to form an electrostatic latent image according to image information. The image is developed by the developing device 2 to form a toner image on the photosensitive drum 1. At this time, a DC superimposed AC voltage in which a DC component of -270 V was superimposed on the AC component of the sin wave having a peak-to-peak voltage of 1.9 kV and a frequency of 2.4 kHz was applied to the developing sleeve 21b. Then, the toner image thus formed on the photosensitive drum is transferred onto a recording sheet by the transfer roll 4 to which a DC voltage of 800 V is applied, and the recording sheet is inserted into the fixing device 6 so that the toner image is transferred onto the recording sheet. A recorded image corresponding to the image information is formed on.

At this time, when the area corresponding to the background portion is recharged at the second rotation of the photosensitive drum 1 at the second rotation of the photosensitive drum 1, the charging potential V _h2 is changed to the charging potential V _h at the first rotation.
_It becomes higher than _h1 (25 V in this embodiment), and a latent image ghost occurs in the electrostatic latent image formed in the second rotation.

However, in the image forming apparatus of this embodiment, since the angular velocity of the photoconductor drum 1 and the angular velocity of the developing sleeve 21b are set to be the same, the second rotation of the photoconductor drum 1 in the above-mentioned image forming operation. Even if a latent image ghost occurs, the latent image ghost and the negative development ghost overlap each other to cancel each other when the negative development ghost occurs in the recorded image due to the setting of the developing device 2. The quality of the formed recorded image is not impaired.

The inventors of the present application use a plurality of developing devices A to D in which the particle size distribution of the toner 20 and the linear pressure of the developer regulating member 22 with respect to the developing sleeve 21b are changed, and the ghost described above for each developing device. A check chart was formed to compare the erasing ability of latent image ghosts. Table 1 below shows specific settings of each developing device. The prepared developing devices A to D are set so as to generate a development ghost (negative development ghost or positive development ghost) by changing the particle size distribution of the toner 20 and the linear pressure of the developer regulating member 22. ΔD indicates the density fluctuation of the recorded image caused by the development ghost when the latent image ghost does not occur. A positive development ghost occurs when ΔD increases, and a negative development ghost occurs when ΔD decreases.
Further, ΔV _c in the table indicates a potential difference V _h1 -V _h2 (V _d in FIG. 5D) of the latent image ghost corresponding to the density variation ΔD. The particle size distribution of the toner is represented by the content of the small particle size toner. This is because if the content of the small particle size toner is large, the charge amount of the toner is large, whereas if the content of the small particle size toner is small, the charge amount of the toner is small.

[0028]

[Table 1]

As is apparent from this table, the latent image ghost can be eliminated and the potential difference V _{h1 of the} latent image ghost can be eliminated by using the developing device which causes the negative development ghost.
When −V _h2 was equal to ΔVc, the latent image ghost and the negative development ghost were completely canceled each other, and a good recorded image without any latent image ghost and negative development ghost could be formed. Therefore, in order to completely cancel the latent image ghost and the negative development ghost, it is important to make the value of ΔVc equal to V _h1 −V _h2 .

In order to match the angular velocity of the photosensitive drum 1 with that of the developing sleeve 21b, in this embodiment, the photosensitive drum 1 and the developing sleeve 21b have the same diameter, and the peripheral velocities thereof are the same. I did it. In such a case, since the aluminum drum as the base material of the photosensitive drum 1 and the developing sleeve 21b can be made common, a pair of aluminum pipes are formed by extrusion molding in this embodiment, and one of them is subjected to sandblasting treatment to develop. The sleeve 21b was produced, and the other side was subjected to honing treatment, and then a photosensitive layer was formed to produce the photosensitive drum 1.
This makes it possible to reduce the manufacturing costs of the photosensitive drum 1 and the developing sleeve 21b.

On the other hand, the photosensitive drum 1 and the developing sleeve 21
In order to make the angular velocity b the same, the diameter and peripheral speed of the photosensitive drum 1 and the diameter and peripheral speed of the developing sleeve 21b may be adjusted. As shown in FIG. 2, when the diameter of the photosensitive drum 1 is R ₁ , the peripheral speed is V ₁ , the diameter of the developing sleeve 21b is R ₂ , and the peripheral speed is V ₂ , the photosensitive drum 1 and the developing roll 4 are In order to match the angular velocities, it is necessary to satisfy the following formula, R ₁ / R ₂ = V ₂ / V ₁ . Table 2 shows specific combinations of R ₁ , V ₁ , R ₂ and V ₂ .

[0032]

[Table 2]

As described above, there are many combinations in which the angular velocity of the photosensitive drum 1 and that of the developing sleeve 21b are matched with each other, but if the developing sleeve 21b is too large for the photosensitive drum 1, the apparatus becomes large in size. If it is too small, the peripheral speed must be reduced correspondingly, and the amount of toner conveyed to the developing area is reduced, resulting in a decrease in development density. Therefore, R ₁ and R ₂ are 10 to 30 mm, V ₂ / V ₁
Is preferably in the range of 0.5 to 1.5.

[0034]

As described above, according to the image forming apparatus of the present invention, the negative development ghost generated on the toner carrying roll overlaps with the latent image ghost generated on the photoconductor drum to form a latent image. Since the image ghost and the negative development ghost cancel each other out to prevent the latent image ghost from becoming visible, a recorded image with excellent image quality can be formed even if the erase lamp is omitted when downsizing the image forming apparatus. It becomes possible to do.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a first embodiment of an image forming apparatus of the present invention.

FIG. 2 is an explanatory diagram showing diameters and peripheral velocities of a photosensitive drum and a developing sleeve.

FIG. 3 is a schematic configuration diagram of an apparatus that measures a charging characteristic of a photosensitive drum.

FIG. 4 is a graph showing charging characteristics when a photosensitive drum is repeatedly charged.

FIG. 5 is a diagram illustrating a potential history of a photosensitive drum when a latent image ghost is formed.

FIG. 6 is a diagram showing a ghost check chart in which a latent image ghost is visualized.

FIG. 7 is a configuration diagram of a one-component developing device using magnetic toner.

FIG. 8 is a diagram showing a ghost check chart in which a negative development ghost occurs.

FIG. 9 is a diagram showing a ghost check chart in which a positive development ghost occurs.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Photosensitive drum, 2 ... Developing device, 21 ... Developing roll (toner carrying roll), 21a ... Magnet roll, 21b
... developing sleeve, 22 ... developer regulating member

Continuation of front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical display location G03G 21/14 (72) Inventor Yuki Nagamori 2274 Hongo, Ebina City, Kanagawa Prefecture, inside Fuji Xerox Co., Ltd.

Claims (2)

[Claims] 1. A developing device provided with a toner carrying roll is arranged to face a photoconductor drum, and toner thinned on the surface of the toner carrying roll is used as an electrostatic latent image formed on the photoconductor drum. In an image forming apparatus that adheres and develops this electrostatic latent image, the rotational angular velocity of the toner carrying roll is set to be the same as the rotational angular velocity of the photosensitive drum, and the latent image ghost generated on the photosensitive drum is set. An image forming apparatus is characterized in that a negative development ghost generated on the toner carrying roll is superposed. 2. The image forming apparatus according to claim 1, wherein the photosensitive drum and the toner carrying roll have the same diameter.