JPH08314236A - Color image recorder - Google Patents

Abstract

PURPOSE: To provide a color recorder capable of obtaining uniform electrostatic chargeability without irregularity even when electrification for the second and succeeding colors is performed on already developed toner on an image forming body, saving a space so as to be smaller than the space of a scorotron charger, and further being an energy saving type where power source voltage is low, a power source device is miniaturized and power consumption is low. CONSTITUTION: In a color image recording method where the toner images of many colors are superposed on a photoreceptor drum 10 by repeating forming and developing an electrostatic image on the drum 10; an electrifying roller 12 arranged with a minute gap of about 15 to 1000μm from the surface of the drum 10 is provided as a means for uniformly electrifying the surface layer of the drum 10. The color recorder uses the electrifying member for electrifying the drum 10 by the electrifying action of the roller 12 with an aerial discharge phenomenon by impressing electrifying voltage on the roller 12 by using a DC power source or a power source 24 where DC and AC are superposed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image recording apparatus which uses a member arranged with a minute gap from the surface layer of the photoconductor as a means for uniformly charging the image forming body having the surface layer of the photoconductive photoconductor. More particularly, the present invention relates to an improvement in obtaining a uniform chargeability even when charged from above the toner in a color image recording method in which a toner image is superimposed on an image forming body by repeatedly forming and developing an electrostatic image.

[0002]

2. Description of the Related Art For example, a corona discharge device is generally used as a means for uniformly charging an image forming body having a photoconductive photoconductor layer used in an electrophotographic device or an electrostatic recording device. For example, in the method described in Japanese Patent Laid-Open No. 60-76766, the charging device is not affected by the above-mentioned charging, especially when the charging device is charged on the surface of the already charged image forming body. It uses a scorotron type corona charger that can provide a stable charge.

A corona charger applies a high voltage (for example, about 6 KV) to a thin wire electrode to generate a corona discharge between the thin wire electrode and the shield electrode and exposes the surface of the body to be charged to the corona discharge emitted from the discharge opening. It is a non-contact type charging device. Therefore, in order to provide a mechanical feature for forming a multi-color toner layer by superposing the toner layer already developed on the image forming body, the non-contact type The use of a corona charger of 1. is preferred.

However, when this corona discharge type charger is used, an expensive and large high-voltage power supply device is required, a structure for coping with insulation against a high voltage becomes large, and power consumption is large, resulting in poor power efficiency. Corona discharge generated a relatively large amount of undesired gases such as ozone, which was inconvenient. Further, there is a disadvantage that the charging potential is lowered by the amount of the developed toner covering the surface of the body to be charged by the charging of the second and subsequent colors.

Therefore, as a charging method instead of the corona discharger, which has many disadvantages, a charging member applied with a voltage (for example, about 1 to 2 KV) lower than that of corona discharge is brought into contact with an object to be charged such as a photoconductor. The use of contact charging type charging means and devices for charging is being studied. For example, Japanese Patent Laid-Open No. 4-
In 240670 or Japanese Patent Laid-Open No. 4-240671, a roller-shaped charging member that faces the charged body via a minute interval and charges the charged body is arranged, and a specific charging member is provided between the charged body and the charging member. There has been proposed a charging device having a voltage application unit that applies an oscillating voltage or a voltage having a specific voltage value. Further, in JP-A-4-76570 and JP-A-4-116673, a spacer roller or a mesh spacer is proposed as an example of a charging member for providing the minute gaps and making them non-contact.

[0006]

However, as described above, in the color image recording method in which the electrostatic image formation and the development are repeatedly performed on the image forming body and the multicolor toner images are superposed, the above-mentioned so-called non-contact charging is applied. There has been no proposal to obtain a uniform charging property using the method.

The object of the present invention is to provide a uniform charging property without unevenness even if the second developed color toner or later is charged on the image forming body, and a space smaller than that of the scorotron charger. The purpose is to provide an energy-saving color image recording device that requires less space, requires a lower power supply voltage, and has a small power supply and low power consumption.

[0008]

A color image recording apparatus of the present invention repeats electrostatic image formation and development on an image forming body having a photoconductive photoconductor surface layer to form a toner image on the image forming body. In a superposed color image recording device, a member arranged with a minute gap from the surface layer of the photoconductor is used as a means for uniformly charging the surface layer of the photoconductor.

Further, in the above color image recording apparatus, the charging member is formed in any of a roller shape, a blade shape, and a pad shape.

Further, as the above minute gap, 15 to 10
The color image recording apparatus described above, which has a diameter of 00 μm, more preferably 25 to 250 μm.

Further, in the above color image recording apparatus, a power source for charging is a DC (direct current) or a power source in which DC and AC are superposed (DC component is superposed with AC component).

In a color image recording apparatus for forming a color image by repeating the steps of charging, image exposing and developing a plurality of times on an image forming body, charging for the first color charging step and the second color charging step. Both means are for charging the image forming body through the image forming body and a minute gap, and the minute gap is larger in the charging process for the second color than for the first color.

Further, in the above color image recording apparatus, the voltage applied to the charging means for forming an electric field for charging is larger in the second color charging process than in the first color charging process.

Further, the gap between the surface of the charging means and the surface of the photoconductor is set to gY, gM, gC and gK for each unit of yellow, magenta, cyan and black, and when charged in this order, gY <gM≤ The color image recording apparatus described above, wherein the relationship of gC ≦ gK holds.

In a color image recording apparatus which forms a color image by repeating the steps of charging, image exposure and development a plurality of times on an image forming body, there are a monochrome mode for forming a monochrome image and a color mode for forming a color image. A charging unit for controlling the switching is provided, and the charging unit for the charging step charges the image forming body via the image forming body and a minute gap. A color image recording apparatus having an adjusting means which sometimes becomes large.

Further, in conjunction with the adjusting operation of the adjusting means, the voltage applied to the charging means is changed to yellow, magenta,
For each cyan and black unit, VY, VM, VC,
The color image recording apparatus described above, which has a voltage control means for variably controlling VY <VM ≦ VC ≦ VK when VK.

[0017]

In addition, even if the toner is charged from above the developed toner layer, the net current amount flowing to the photoconductor is large and the charging efficiency is good, so that the uneven charging due to the presence or absence of the toner layer and the thickness is small. Even charging can be performed evenly over time.

[0018]

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows an embodiment of the color image recording apparatus of the present invention.

This figure is a cross-sectional view showing the outline of the configuration of the color image recording apparatus. In the figure, 10 is an image forming body that rotates in the direction of the arrow (clockwise) and is OP
A photosensitive drum made of C, the charging roller 12 and an image exposing unit 13 by a laser beam, etc.
Developing device 30 including a plurality of developing devices, transfer roller 17
A, a static eliminator 17B for separation, a cleaning device 31 and the like are provided.

In the basic operation of the image recording process of this embodiment, when a copy start command is sent from an operation unit (not shown) to a control unit (not shown), the photosensitive drum 10 rotates in the direction of the arrow by the control of the control unit. To start. Photoconductor drum 10
According to the rotation of, the peripheral surface thereof is uniformly charged by a charging roller 12 as a charging member described later and passes through. An image is written on the photoconductor drum 10 by an image writing device such as an image light of a laser beam on the image exposure unit 13 to form an electrostatic latent image corresponding to the image.

Yellow (Y) on the periphery of the photosensitive drum 10,
A developing device 30 for accommodating a Y unit, an M unit, a C unit, and a K unit of a developing device unit that respectively contains a developer composed of toner such as magenta (M), cyan (C), and black (K) and a carrier is provided. First, yellow (Y) development of the first color is carried out by the developing sleeve 306 which has a magnet built therein and holds the developer and rotates. The developer consists of a carrier in which ferrite is used as a core and is coated with an insulating resin around it, and a toner whose main component is polyester and pigments according to the color and charge control agents, silica, titanium oxide, etc. are added. The agent regulates the layer thickness on the developing sleeve 306 by the bristle cutting regulating plate and is conveyed to the developing area.

The gap between the developing sleeve 306 and the photosensitive drum in the developing region is larger than the thickness of the developer layer, and a bias voltage is applied between them to perform reverse development in the developing region facing the photosensitive drum 10. And
A toner image is formed.

After the image forming process for the first color, which is performed during one rotation of the photosensitive drum 10, is completed, the image forming process for magenta (M) for the second color is started, and uniform charging is performed again by the charging roller 12. A latent image based on the image data of the second color is formed by the image exposure unit 13.

Again, a latent image similar to that of the first color is formed on the portion where the first color image is not present in the portion where the static electricity is removed by the image exposure of the peripheral surface of the photosensitive drum 10 by the image exposure unit 13. However, a latent image in which a potential is slightly left is formed due to the light held by the toner of the first color and the electric charge of the toner itself in the portion where the image of the first color is developed again. Then, development is performed according to the potential difference of the bias.

An image forming process similar to that of the second color is performed for the third color of cyan (C) and the fourth color of black (K), and a total of 4 rotations are performed on the peripheral surface of the photosensitive drum 10 in four rotations.
A color image is formed.

On the other hand, the recording paper P is fed from the paper feed cassette 16.
Are fed one by one by the first paper feed roller 15.
The fed recording paper is a pair of second paper feed rollers 18 that operate in synchronization with the toner image on the photosensitive drum 10.
Is sent onto the photosensitive drum 10. Then, the toner image on the photoconductor drum 10 is transferred onto the recording paper P by the action of the transfer roller 17A, and is separated from the photoconductor drum 10 by the separating static eliminator 17B. The recording paper P on which the toner image has been transferred is sent to the fixing device 90 via the conveying means 80, and is held by the heat fixing roller and the pressure bonding roller,
After being fused and fixed, it is discharged to the outside of the apparatus. The surface of the photosensitive drum 10 which has toner remaining without being transferred to the recording paper P and rotates, is scraped off and cleaned by a cleaning device 31 having a cleaning blade, and stands by for the next image recording.

Note that S in the drawing indicates a spacer which is provided between the charging roller 12 and the photosensitive drum 10 so as to be insertable and removable so as to maintain a predetermined minute gap described later with reference to FIG.

FIG. 2 is a diagram showing an embodiment of a charging device used in the color image recording apparatus of FIG. 2 (a),
FIG. 2B shows a cross-sectional view and a perspective view of the roller-shaped charging device 20R.

In FIG. 2, the charging roller 12, which is a charging member, includes a conductive member 42 made of a material having elasticity and conductivity such as conductive resin or conductive rubber, and a conductive core metal 4.
1. Further, it is composed of thin layer spacers 43 made of an insulating material, which are provided at both ends in the longitudinal direction outside the charging area of the conductive member 42 and are brought into pressure contact with the photosensitive drum 10 which is the member to be charged. The photosensitive drum 10 includes a conductive base material 10b and a photosensitive body layer 10a that covers the surface of the conductive base material 10b.
b is grounded. The conductive member 42 of the charging roller 12 used for the charging operation is floated from the surface of the photoconductor layer 10a with a minute gap by the spacer 43.

Reference numeral 24 denotes a bias power source for applying a bias voltage between the core metal 41 of the charging roller 12 and the conductive base material 10b of the photosensitive drum 10, and the core metal 41 is grounded via this bias power source. . Further, an oscillating electric field is formed by the bias power source 24 so that the conductive member 42 and the photoconductor layer 1 are formed.
0a and Paschen discharge (in-air discharge of a minute gap)
To form a charged area suitable for. As a result, the photosensitive layer 10a of the photosensitive drum 10 is uniformly charged while being rotated by the rotation of the photosensitive drum 10.

The bias power supply 24 is a power supply for supplying an AC bias voltage in which an AC component Va is superposed on a DC component Vd set to a value substantially equal to the voltage to be charged, and is approximately the same as the voltage to be charged, -500 to -1000V. DC component of Vd
The peak-to-peak voltage 200 to 3500 V and the frequency 0.3.
An AC bias power supply on which an AC component Va of 10 kHz is superimposed is supplied via a protective resistor.

The bias power source 24 is not limited to the AC bias voltage in which the AC component Va is superimposed on the DC component Vd as described above, but may be a power source which supplies a bias voltage of only the DC component Vd. In this case, the value obtained by adding the charging start voltage (500 to 1000 V) to the voltage to be charged is Vd.

In the above description, the embodiment in which the charging member 12 has a roller shape and is driven to rotate with respect to the photosensitive drum 10 has been described. However, the present invention is not limited to this, for example, the drive motor is provided on the roller side,
The photoconductor drum 10 may be driven to rotate. Also,
Both may have a power source and rotate at different peripheral speeds.

FIG. 3 is a diagram showing another embodiment of the charging device used in the color image recording apparatus of FIG. FIG.
(A) and (b) are blade-shaped charging devices 20B, respectively.
2 shows a cross-sectional view of FIG.

In FIG. 3, a charging blade 50, which is a charging member, has a conductive support member 51 made of metal, a conductive member 52 having elasticity and conductivity, and a blade at both ends of the blade, which is outside the maximum width of the image. And a spacer 53 made of an insulating material, and a bias power source similar to that of the embodiment of FIG. 2A is supplied to the supporting member 51 from a bias power source (not shown).
Is pressed against the rotation of the conductive member 52 and the photosensitive drum 10 at a predetermined pressure without rotating in the counter direction.
A predetermined minute gap is held between the photosensitive drum 10 and
The photoreceptor layer 10a is charged.

FIG. 4 is a sectional view showing still another embodiment of the charging device used in the color image recording apparatus of FIG. FIG. 4 shows a cross-sectional view of the pad-shaped charging device 20P.

In FIG. 4, a charging pad 60 as a charging member is composed of a conductive support member 61 made of metal, a conductive member 62 having a rectangular cross section and having elasticity and conductivity, and an insulating material. It is composed of spacers 63 located at both ends of the pad and outside the maximum image width, and a bias power supply similar to that of the embodiment of FIG. 2A is supplied to the support member 61 from a bias power supply not shown. The surface of the charging pad 60 facing the photoconductor drum 10 is curved in a shape forming a part of a cylinder, and abuts against the photoconductor drum 10 at a predetermined pressure with a non-rotational force by an urging means (not shown). A predetermined minute gap suitable for Paschen discharge is held between the elastic member 62 and the photoconductor drum 10, and the photoconductor layer 10a of the photoconductor drum 10 is uniformly charged.

In each of the charging blade and the charging pad described above, the area where the surface of the charging blade and the charging pad is gradually separated from the photosensitive drum is
If it is secured at least on one of the upstream side and the downstream side of the nip, it can be used. In the case of one, the downstream side is preferable from the viewpoint of charging stability.

FIG. 5 shows the charging roller 12 and the photosensitive drum 1.
FIG. 6 is an enlarged cross-sectional view in the vicinity of the nip position of 0, and FIG. 6 is a diagram showing Paschen air discharge generation conditions.

In FIG. 5, the distance between the charging roller surface 42 and the photosensitive drum 10 is maintained at a distance suitable for air discharge. In the image forming process, the charging roller 12 rotates around with the rotation of the photoconductor 10, but the photoconductor drum 1
Attention is paid to the specific portion x on 0. As the photosensitive drum 10 rotates, the specific portion x enters from the left side of the drawing, passes through the nip with the charging roller 12, and moves to the right side. Here, as a region corresponding to a gap suitable for air discharge such as Paschen discharge, there is a width W in the rotation direction. It is generally known that the value (V) of the discharge start voltage of Paschen discharge in a minute interval (d) can be calculated from the “Paschen curve”. When the air gap is 10 μm or more in the atmosphere, V = 312 + 6.2d Can be approximated (from "Basics and Applications of Electrophotographic Technology" edited by the Institute of Electrophotography).

Referring again to FIG. 5, the core metal 41 of the charging roller 12 is connected to the bias power source 24, and has a width W between a little before and a little after passing through the nip as the photosensitive drum 10 rotates. Charging is performed by Paschen discharge. Paschen discharge starts when each part on the photoconductor drum approaches the distance shown by the above formula according to the voltage applied to the charging roller.

That is, the air discharge from the charging roller to the photosensitive drum occurs in the region where the electric field strength applied to the gap (Z) is equal to or exceeds the "Paschen curve" as shown in FIG. To do. However, the width W corresponding to the gap (Z) in which the air discharge is performed differs depending on the presence or absence and the thickness of the toner layer on the surface of the photoconductor. As shown in FIG. 5, when only the photosensitive member (without the toner layer), the air discharge occurs in the corresponding region W1 where the gap is Z0 or less. Further, when the toner layer is charged from above, the region having a gap suitable for the air discharge expands by the thickness of the toner layer, and the air discharge occurs in the corresponding region width W2 where the gap becomes Z0 or less. in this way,
It is considered that when the toner layer is present, the electric field strength is the same as when there is no toner layer when the discharge is stopped by going out of the area as the photosensitive drum rotates. The surface potential obtained as a result also has a very small fluctuation due to the presence or absence of the toner layer.

In any of the above charging roller, charging blade and charging pad, the value of the gap Z0 suitable for air discharge preferably satisfies the following two conditions.

(1) 1 of developed toner layer on photoreceptor
The thickness of the color component is about 5 μm for fine toner. To this, add the above-mentioned lower limit value of Paschen's formula of 10 μm,
15 μm in total.

(2) The distance is suitable for Paschen discharge. That is, it is 10 μm or more and 1000 μm or less.

Here, 10 μm is the lower limit of the above formula.

When 1000 μm is substituted into the Paschen's formula, the applied voltage becomes 6512V. This is a high voltage of the same level as the conventional charging method using corona discharge, and the merit of introducing this method is diminished.

Therefore, the value of the gap Z0 suitable for the air discharge satisfying these two conditions is 15 μm to 1000 μm.

Further, in order to obtain more stable and uniform charging, the thickness is preferably 25 μm to 250 μm.

The reason for this 25 μm is that the thickness of the developed toner layer at the charging process portion becomes maximum when the fourth color is charged, that is, when three solid colors overlap each other. This is for fine toner (5 μm × 3 =
15 μm). A total of 25 μm is obtained by adding 10 μm, which is the lower limit value of the above formula, to this. (For a conventional toner having a large particle diameter, since it is about 11 μm per layer, the gap corresponding to the above is 43 μm.) The reason for the above 250 μm is 1862 when 250 μm is substituted into the Paschen's formula.
It becomes V. When AC (alternating current component) is superposed on this, the peak-to-peak voltage of AC to be applied is 1120 V when the charging start voltage of the photoconductor is 560 V (see JP-A-63-
No. 149668), the voltage on one side (negative side for OPC) is as high as 2982 V (about 3000 V), and the merit of introducing this method is diminished.

Next, as described with reference to FIG. 5, the gap (Z) in which the air discharge is performed differs depending on the presence or absence of the toner layer on the surface of the photosensitive member and the thickness of the toner layer. It is better to control the applied voltage to
The influence of the thickness of the toner layer on the surface potential of the resulting photoreceptor can be suppressed to a smaller value.

The merits and reasons for variably controlling the voltage applied to the charging means (for example, the charging roller) in relation to the size of the minute gap (Z) are as follows.

When the toner layer is covered on the photoconductor, if the charging process is performed at the same voltage as when the toner layer is not present, the surface potential of the photoconductor becomes low but the image density becomes insufficient, or the image density becomes insufficient. Alternatively, on the contrary, the surface potential is too high and the toner tends to be repelled due to an excessive surface potential during development, resulting in uneven repellency of the image.

Therefore, the voltage applied to the charging member is very small so that the surface potential when the surface of the photoconductor comes out of the discharge region due to the rotation is less uneven due to the presence or absence of the toner layer and the thickness. The fine adjustment is performed by increasing or decreasing in relation to the size of the gap (Z). That is, the voltage applied to the charging roller is controlled so as to increase from the second color onward.

In the color image recording apparatus of this embodiment, an electrostatic image is formed on the photosensitive drum by the number of developing colors by one charging roller and one image exposure source, and the development is repeated to form an electrostatic image on the photosensitive drum. The toner images (for four colors) are superposed. Here, the minute gap is configured such that the gap (d2) in the second (second color) charging process is larger than the gap (d1) in the first (first color) charging process. Furthermore, the voltage applied to the charging roller that forms the electric field for charging is large (V1 <V
2) If the image forming method is also adopted, the effect of uniformization becomes greater.

Specific numerical examples of the gaps (d1, d2) and applied voltages (V1, V2) in the above-mentioned first (first color) and second (second color) charging process are shown below. Show. Note that this is the case of a toner having a particle diameter such that the solid layer thickness is 11 μm.

The DC components are respectively d1 = 35 μm, Vdc1 = -650v, Vac1 = 1.
250v, d2 = 45 μm, Vdc2 = −670v, V
ac2 = 1310 v, AC frequency and current value were 1000 Hz and 700 μA for both the first and second times.

When a large number of types of images having a high area coverage of solid toner are handled, it is necessary to deal with a thicker toner layer. Therefore, the third time should not be the same as the second time. After increasing the gap and the voltage, d3 = 50 μm, Vdc3 = −685v, Vac3 = 1
Adjust to 340v. As a result, the uneven charging due to the presence or absence of the toner layer is further reduced.

In this way, the gap in the charging step is gradually increased after one rotation of the photosensitive drum for each color, as shown in FIG. 7, by sequentially inserting the spacer S having a predetermined thickness. FIG. 7A is a diagram showing the state of the charging process of the first color in the monochrome mode or in the spacer S.
Is not inserted. FIG. 7B is a diagram showing a state of the charging process in the color mode or the second and subsequent colors, and the spacer S is inserted.

The voltage applied to the charging roller is controlled so as to gradually increase from the second color onward.

That is, in order to form a gap (d1 = 35 μm) in the first charging process (first color), ten ultrathin PET sheets made of an insulating material and having a thickness of 3.5 μm are stacked to make a total thickness of 35 μm. Outside the charging area of the charging roller, they are adhered to the surfaces of both ends in the longitudinal direction to form the space collar 43 (see FIG. 2B).

Next, in order to form the minute gaps (d2, d3, d4) after the second time (second color), the above-mentioned thickness of 3.5 is used.
Predetermined number of μm ultra-thin PET sheets are laminated and bonded,
The spacers S having thicknesses corresponding to the minute gaps (d2, d3, d4) are prepared in advance, and the second time (2
The minute gaps (d2, d3, d4) are secured by sequentially inserting the space color 43 and the photosensitive drum 10 in conjunction with the subsequent charging process.

The ultra-thin PET sheet is used as a means for accurately obtaining the above-mentioned minute gap. The inventors
A PET sheet used as a support for an ink ribbon for word processing was used. As a result, an extremely thin gap of 3.5 μm can be accurately obtained. As a specific material example, “Lumirror” manufactured by Toray Industries, Inc., 4AF53N type (thickness: 3.
5 μm) or K-200-6E manufactured by Dia foil Co., Ltd.
Type, (thickness 3.5 μm), etc.

Still another embodiment will be described below with reference to FIGS. 1 and 8 and 9.

The apparatus shown in FIG. 1 has an image of any one of yellow (Y), magenta (M), cyan (C), and black (K) in addition to the color mode having the above-described color image forming function. A monochrome mode having a forming function is also provided. For example, when the black (K) image formation monochrome mode is selected, the charging roller 12 and the exposure optical system 1 are selected.
Only the latent image formation by 3 and the black development process by the black developing device K are performed.

As shown in FIG. 8, the apparatus of this embodiment is provided with a color mode designation button and a monochrome mode designation button on the main body operation section, and controls switching between the color mode and the monochrome mode according to the selection operation of the designation buttons. It has a main body control section. The main body control unit inserts a charging unit spacer, which is an adjusting unit, so that the minute gap between the charging roller 12 and the photoconductor drum 10 required for the above-described air discharge becomes larger in the color mode than in the monochrome mode. The spacer S, which is the same as that used in the above-described embodiment, is used to control the insertion / removal of the spacer S via a solenoid for removal SD (not shown). Further, a voltage control means for variably controlling the voltage applied to the charging roller is provided in the main body control section in association with the adjusting operation of the adjusting means, and corresponds to each color (Y, M, C, K). The applied voltage is controlled.

FIG. 9 is a flowchart showing the control of the insertion / removal of the spacer S and the control of the charging applied voltage in accordance with the switching between the color mode and the monochrome mode.

First, when the display "Ready to copy" appears on the operation unit, the operator presses the color mode or monochrome mode specification button to specify either copy mode. If a color mode is specified,
The minute gap corresponding to the color mode sequence and the charging applied voltage are set. Then, the charging section spacer insertion / removal solenoid is turned on to adjust the charging applied voltage. At this point, a state of waiting for the copy start button being pressed is entered. When the button is pressed, the copy operation is started and each color is sequentially copied. When the copy operation in the last color mode ends, the copy operation ends, and the initial state is restored. If the copy operation of the last color mode has not finished,
Return to the next step of setting the color mode sequence.
On the other hand, if monochrome mode is specified, pressing the copy start button will perform the specified monochrome copy,
When the copy operation ends, the initial state is restored.

Next, prior to description of another embodiment of the present invention, another configuration of the color image recording apparatus will be described with reference to FIG.

Reference numeral 10 denotes a belt-shaped image forming body, a so-called photosensitive belt, which is formed by applying an organic photosensitive body (OPC) to the peripheral surface of a flexible endless substrate, and which is horizontal between the rotating rollers 9A and 9B. In the state of being stretched in the direction, it is circulated in the clockwise direction by the rotation roller 9A being driven and conveyed.

The peripheral surface of the photosensitive belt 10 is rubbed against the guide member 11 by the bias of the tension roller 9C to form an image forming surface.

Twelve (Y, M, C, K) are provided in the units corresponding to yellow (Y), magenta (M), cyan (C), and black (K), respectively, and the configuration described in FIG. The charging roller 12 has a
It rotates in the same direction as the photoconductor belt 10 while maintaining a predetermined minute gap so that the air discharge from (Y, M, C, K) to the photoconductor belt 10 is performed. Furthermore, each charging roller 1
2 (Y, M, C, K), DC and A described in FIG.
A charging power source 24 superimposing C or a charging power source 24 for applying only DC is connected to each other, and a uniform surface is formed on the photosensitive belt 10 by the charging action accompanied by the air discharge phenomenon of each charging roller. Apply an electric potential.

Although the charging roller is used as the charging means in this embodiment, the charging blade or the charging pad described in FIGS. 3 and 4 may be used instead.

13 (Y, M, C, K) is the photosensitive belt 1.
Light emitting elements arranged in a line in the depth direction of 0 in an array F
L, EL, PL, LED, or LISA, PLZT, LCS in which a light source section and an element having an optical shutter function are arranged in parallel, and a SELFOC lens as an equal-magnification imaging element, or each color using a laser as a light source In the exposure optical system provided in the unit corresponding to, the image signals of the respective colors read by another image reading device are sequentially taken out from the memory and input to the respective exposure optical systems as electric signals.

14 (Y, M, C, K) are provided in the units corresponding to the respective colors of yellow (Y), magenta (M), cyan (C), and black (K), and each developer is A developing sleeve 1 which is housed in the developing device and rotates in the same direction with respect to the photoconductor belt 10 with a predetermined gap.
40 is provided.

Each of the developing devices 14 (Y, M, C, K) is
The electrostatic latent image formed on the photoconductor belt 10 by the charging by the charging rollers 12 (Y, M, C, K) and the image exposure by the exposure optical systems 13 (Y, M, C, K) is described. Reverse development is performed in a non-contact state by applying a development bias voltage.

Next, the color image forming process in the apparatus of this embodiment will be described.

The image read by the image pickup device or the image edited by the computer in the image reading device different from this device is yellow (Y), magenta (M), cyan (C), and black (K). It is once stored and stored in the memory as another image signal.

When the image recording is started, the rotating roller 9A
The drive motor is started to convey the photoconductor belt 10 in the clockwise direction, and at the same time, application of electric potential to the photoconductor belt 10 is started by the charging action of the charging roller 12 (Y).

After the photoconductor belt 10 is applied with an electric potential, the exposure optical system 13 (Y) starts exposure by an electric signal corresponding to the first color signal, that is, the image signal of yellow (Y), and the belt An electrostatic latent image corresponding to the yellow (Y) image of the original image is formed on the photosensitive layer on the peripheral surface by the conveyance scanning of.

The latent image is reversely developed by the developing device 14 (Y) with the developer on the developing sleeve 140 in a non-contact state, and a yellow (Y) toner image is formed in accordance with the conveyance of the photosensitive belt 10. It

Then, the photosensitive belt 10 is further given a potential on the yellow (Y) toner image by the charging action of the charging roller 12 (M), and the exposure optical system 13 (M) is applied.
Exposure with an electric signal corresponding to the second color signal, that is, the image signal of magenta (M), is carried out, and non-contact reversal development by the developing device 14 (M) causes magenta to be formed on the yellow (Y) toner image. The toner images of (M) are formed in an overlapping manner.

By the same process, the charging roller 12
(C), exposure optical system 13 (C), and developing device 14 (C)
Further, a cyan (C) toner image corresponding to the third color signal is generated by the charging roller 12 (K), the exposure optical system 1
3 (K) and the developing device 14 (K) sequentially form a black (K) toner image corresponding to the fourth color signal, and the color image is formed on the peripheral surface of the photoconductor belt 10 within one revolution. Toner image is formed.

In addition, in parallel with the formation of the color toner image described above, in the paper feeding portion, the operation of feeding the transfer paper P from the paper feeding cassette 16 by the drive of the first paper feeding roller 15 is started,
The color toner image is transferred onto the transfer paper P that is synchronously fed by the second paper feed roller 18 in the transfer area formed by the transfer roller 17A.

The transfer paper P on which the toner image has been transferred is removed from the charge by the static eliminator 17B and separated from the peripheral surface of the belt. It is discharged onto the tray.

On the other hand, the photoreceptor belt 1 from which the transfer paper P is separated
In the cleaning device 31, the blade 31 </ b> A removes and cleans the residual toner in the cleaning device 31 to continue the formation of the original image, or the operation is temporarily stopped to form a new toner image of the original image.

In the apparatus of this embodiment constructed as described above, the minute gaps between the surface of the charging roller and the photosensitive belt are yellow (Y), magenta (M), cyan (C) and black (K). GY, gM, gC, gK for each unit,
When charged in this order, the second stage is larger than the first stage and is equal to or larger than the first stage. GY <gM ≦ gC ≦ g
The relationship K is established. Of course, gM =
It may be gC = gK or gM <gC <gK.

Further, the voltage applied to the charging roller is
If VY, VM, VC, and VK are set for each of the yellow (Y), magenta (M), cyan (C), and black (K) charging rollers, the second stage becomes larger than the first stage, that is, VY. <VM
It is preferable that the relationship of ≦ VC ≦ VK is satisfied.

The method of adjusting each minute gap is performed by inserting and removing the spacer S described above with reference to FIG. 8 (not shown), and the variable control of each applied voltage is performed by the method described in FIG. (Not shown).

In addition, the apparatus of this embodiment has any one of yellow (Y), magenta (M), cyan (C), and black (K) in addition to the color mode having the color image forming function described in FIG. The charging roller 12 is also provided with a monochrome mode having a function of forming an image of one color. For example, when the black (K) image forming monochrome mode is selected.
(K), exposure optical system 13 (K), and developing device 14 (K)
Only the process of forming a black image is performed. In this case, insertion / removal of the spacer S and variable control of each applied voltage are
It is not performed as described in the monochrome mode of FIG.

[0092]

Since the present invention is constructed as in the above embodiment, the following effects will appear.

(1) Regarding the process of charging the toner layer over the developed toner layer on the photoconductor, non-contact charging in which the charging member is slightly floated from the photoconductor instead of the conventional corona discharge type charger. By adopting the method,
Uniform and efficient charging property, space saving, and low power consumption can be achieved.

(2) It is possible to eliminate the disadvantage that the charging potential becomes low at the portion already covered with the toner due to the charging of the second and subsequent colors, which is seen in the conventional corona system.

(3) Since the value of the electric current discharged by the air discharge in the non-contact minute gap is smaller than that in the corona discharge, the ozone generation can be greatly reduced (2 to 3 digits).

(4) Since the charging efficiency is high and the net amount of current used for charging the photoconductor is large, it can be easily applied to a high speed machine.

[Brief description of drawings]

FIG. 1 shows an embodiment of a color image recording apparatus of the present invention.

FIG. 2 is a sectional view (a) and a perspective view thereof (b) showing an embodiment of a charging roller of a charging device used in a color image recording apparatus.

3A and 3B are sectional views showing an embodiment of a charging blade of a charging device used in a color image recording apparatus.
FIG. 3B is a bottom view of FIG.

FIG. 4 is a sectional view showing an embodiment of a charging pad of a charging device used in a color image recording device.

FIG. 5 is an enlarged sectional view of the vicinity of a nip position between a charging roller and a photosensitive drum.

FIG. 6 is a view showing conditions for generating Paschen's air discharge.

FIG. 7 shows a spacer S between the charging roller and the photosensitive drum.
FIG. 7A shows a state before the spacer S is inserted, and FIG. 7B shows a state after the spacer S is inserted.

FIG. 8 shows a charging unit spacer insertion / removal control method.

FIG. 9 shows a method of controlling a charging applied voltage.

FIG. 10 shows another embodiment of the color image recording apparatus of the present invention.

[Explanation of symbols]

 9A, 9B Rotating roller 10 Image forming body (photosensitive drum, photosensitive belt) 11 Guide member 12 Charging roller 13 LED array 14 Developing device 15 First paper feeding roller 16 Paper feeding cassette 17A Transfer roller 17B Separating charge eliminator 18 Second feeding roller 19 Fixing device 20B Blade-shaped charging device 20P Pad-shaped charging device 20R Roller-shaped charging device 30 Developing device 31 Cleaning device 41, 51, 61 Core bar 42, 52, 62 Conductive member 43, 53, 63 Spacer 50 Charging blade 60 Charging pad Va AC voltage component Vd DC voltage component Z, Z0 Minute gap

Claims (11)

[Claims] 1. A color image recording apparatus in which an electrostatic image is formed and developed repeatedly on an image forming body having a photoconductive photoreceptor surface layer to superimpose a toner image on the image forming body. A color image recording apparatus using a member arranged with a minute gap from the surface layer of the photoconductor as a means for charging likewise. 2. The color image recording apparatus according to claim 1, wherein the charging member is formed in any of a roller shape, a blade shape, and a pad shape. 3. The above minute gap has a size of 15 to 1000 μm.
The color image recording apparatus according to claim 1, further comprising: 4. The color image recording apparatus according to claim 1, wherein the charging power source is a direct current or a power source in which an alternating current component is superimposed on a direct current. 5. A color image recording apparatus for forming a color image by repeating the steps of charging, image exposing and developing a plurality of times on an image forming body, for the first color charging step and the second color charging step. Both of the charging means charge the image forming body through the image carrier and a minute gap, and the minute gap is larger in the second color charging process than in the first color charging process. 6. The color image recording apparatus according to claim 5, wherein the voltage applied to the charging means for forming an electric field for charging is higher in the second color charging process than in the first color charging process. 7. The gaps of the first, second, third, and fourth colors between the surface of the charging means and the surface of the photoconductor are respectively g.
1, g2, g3, g4, and when charging in this order,
The color image recording apparatus according to claim 5, wherein a relationship of g1 <g2 ≦ g3 ≦ g4 is established. 8. The color image recording apparatus according to claim 7, wherein the gaps g1, g2, g3 and g4 are yellow, magenta, cyan and black, respectively. 9. A color image recording apparatus for forming a color image by repeating the steps of charging, image exposure and development a plurality of times on an image forming body, and a monochrome mode for forming a monochrome image and a color for forming a color image. The charging means for switching the modes is provided, and the charging means for the charging step charges the image forming body via the image forming body and the minute gap, and the minute gap is larger than that in the monochrome mode. A color image recording apparatus having an adjusting unit that becomes larger in a color mode. 10. The voltage applied to the charging means is set to V1 and V, respectively, in conjunction with the adjusting operation of the adjusting means.
10. The color image recording apparatus according to claim 9, further comprising a voltage control unit that variably controls so that V1 <V2 ≦ V3 ≦ V4 when V2, V3, and V4. 11. The color image recording apparatus according to claim 10, wherein the voltages V1, V2, V3 and V4 are voltages corresponding to yellow, magenta, cyan and black units, respectively.