JPH1048966A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the scattering of the toner of a second color when a primary transfer is carried out by overlapping the toner of a second color on the toner of the first color transferred primarily on an intermediate transfer body. SOLUTION: A toner T1 of a first color formed on a sensitive drum 3 is transferred primarily on an intermediate transfer body 2, and then, the toner T2 of a second color is formed on the sensitive drum 3, and the primary transfer is carried out by overlapping the toner T2 of the second color on the toner T1 of the first color. In this case, the toner T2 is liable to scatter by the repulsion of the toners each other. And the electrostatic capacity of the intermediate transfer body 2 is set at 13pF/cm<2> or higher. Consequently, the static power operating between the toner T1 and the intermediate transfer body 2 can be increased, and as a result, the scattering of the toner T1 can be reduced.

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 provided with an intermediate transfer member.

[0002]

2. Description of the Related Art In image forming apparatuses such as copiers and laser beam printers, the need for color is increasing. As a color image forming method, a sublimation type, a thermal transfer type, an ink jet method, an electrophotographic method, and the like are known, and the electrophotographic method is said to be the most excellent in terms of image forming speed.

[0003] In recent years, the intermediate transfer system has become the mainstream among the electrophotographic systems. This has advantages such as not selecting a transfer material and being excellent in color registration (less color shift).

In an electrophotographic apparatus of the intermediate transfer system, as shown in FIG. 1, yellow, magenta, and yellow formed on a drum type electrophotographic photosensitive member (hereinafter referred to as "photosensitive drum") 3
The primary color toner images of cyan and black are sequentially primary-transferred onto the drum-type intermediate transfer body 2 and superimposed.
The full color image with the colors superimposed on the transfer material
Next transfer.

[0005] This method does not require the transfer material to be wound around the intermediate transfer body 2, and therefore can be used for envelopes and cardboard, and is highly versatile. Also, the color registration varies depending on the thickness of the transfer material. There is an advantage that high image quality can be obtained because there is no such image.

The secondary transfer residual toner remaining on the surface of the intermediate transfer member 2 without being transferred onto the transfer material in the intermediate transfer method is
Generally, it is collected by a cleaning member such as a fur brush and prepared for the next image formation. However, when the surface of the intermediate transfer member is rubbed with a fur brush or the like, toner fusion occurs or the surface is damaged, so that there is a problem that an image is deteriorated and a device life is shortened.

In order to prevent these problems, charging means (hereinafter referred to as "ICL roller") 10 which is arranged in contact with the surface of the intermediate transfer member and charges the secondary transfer residual toner changes the tribo of the transfer residual toner. A technique of electrostatically collecting the secondary transfer residual toner on the photosensitive drum 3 simultaneously with the primary transfer of the next image has been developed (hereinafter, referred to as an “ICL method”).

More specifically, a charging roller is used as charging means for the secondary transfer residual toner, and the tribo of the transfer residual toner is charged to a polarity opposite to that of the toner tribo charged in the developing section.
At the time of the primary transfer of the toner image from the photosensitive drum 3 to the intermediate transfer body 2, the secondary transfer residual toner is simultaneously transferred from the intermediate transfer body 2 to the photosensitive drum 3 and collected.

[0009]

However, according to the above-mentioned prior art, in the intermediate transfer member system, a primary transfer step in which toner is temporarily transferred from the photosensitive drum 3 to the intermediate transfer member 2; There is a drawback that the image is liable to be degraded because it passes through two transfer steps, a secondary transfer step of transferring the upper toner image onto a transfer material.

In particular, when a full-color image is formed, the intermediate transfer member 2 comes into contact with the photosensitive drum four times and multiple layers of toner are superimposed, so that toner scattering is likely to occur.

In the case where toner is superimposed in a primary transfer portion (a portion where a toner image is transferred from the photosensitive drum 3 to the intermediate transfer member 2, the same applies hereinafter), the toner is temporarily transferred onto the intermediate transfer member 2. The toner has a negative polarity,
It is very difficult to transfer the toner of the same polarity to the same position on this, and there is a problem that scattering is intensified on the intermediate transfer body 2 when an image for secondary transfer is formed. In a system in which the secondary transfer residual toner is charged by the ICL roller 10 and collected on the photosensitive drum 3, it is desired to efficiently charge the secondary transfer residual toner. But,
Unlike a commonly used charging method for the photosensitive drum 3, such as a primary charger, the intermediate transfer member 2 is desired to have semi-conductivity close to a low resistance region, and the ICL roller 10 itself is also a medium resistance member. Actually, a so-called injection current flows due to electric contact between each other. For this reason, unlike the primary charger, which performs most charging by discharging, IC
Not all of the current flowing through the L roller 10 contributes to the charging of the secondary transfer residual toner.

The resistance of both the intermediate transfer body 2 and the ICL roller 10 varies with the environment. For example, in a high humidity environment where the resistance is low, the injection current increases to charge the secondary transfer residual toner. However, there has been a problem that is not sufficiently performed. As disclosed by the present applicant, in order to efficiently charge the secondary transfer residual toner, an AC bias is superimposed on the ICL roller 10 so that the toner is transferred between the intermediate transfer body 2 and the ICL roller 10. It is effective to break the toner layer by jumping. However, since the intermediate transfer body 2 needs to form a nip having an appropriate width at the transfer portion between the photosensitive drum 3 and the transfer material, low hardness is required and an elastic layer having a thickness of about 5 mm is provided. Is common. On the other hand, the resistance layer is often formed with a thickness of several tens of microns.

For this reason, when the resistance value of the elastic layer occupying most of the thickness of the ICL roller 10 is high, most of the AC voltage applied to the ICL roller 10 is consumed as a partial pressure in this portion, and the Intermediate transfer body 2 required for
(1) that an electric field is not formed between the ICL rollers 10. Also, when an AC bias is superimposed on the ICL roller 10 and the pre-secondary transfer charger, this causes
Current flows into the primary transfer high-voltage power supply, and fluctuates the high-voltage power supply. Specifically, an AC voltage is generated when an AC current flows through the impedance of the high-voltage power supply, and is superimposed on the primary transfer voltage, thereby adversely affecting the cleaning of the intermediate transfer body 2 or, in extreme cases, the primary transfer voltage. In the transfer section, the toner jumped and image scattering occurred.

Accordingly, the present invention has been made to solve the above-mentioned problems (1), namely, the scattering of toner on the intermediate transfer member,
It is an object of the present invention to provide an image forming apparatus which prevents the secondary transfer residual toner from being insufficiently charged and prevents toner scattering at the primary transfer portion.

[0015]

According to the first aspect of the present invention, a step of transferring a toner image formed on an image carrier onto an intermediate transfer member is performed on a plurality of color toners, and the process is performed on the intermediate transfer member. In an image forming apparatus that forms a plurality of color toner images and collectively transfers the plurality of toner images onto a transfer material, the capacitance of the intermediate transfer body is set to 13 pF / cm ² or more. And

According to a second aspect of the present invention, the intermediate transfer member has an elastic layer and a surface layer covering the outside of the elastic layer, and the elastic layer has an actual resistance of 10 ⁶ Ω or less. I do.

According to a third aspect of the present invention, the surface layer has a volume resistivity value in a range of 10 ¹² to 10 ¹⁶ mΩ · cm.

According to a fourth aspect of the present invention, the surface layer has a thickness of 30 μm or less.

According to a fifth aspect of the present invention, there is provided an image carrier having a surface on which a toner image is formed, an intermediate transfer member on which the toner image is transferred, and transferring the toner image on the intermediate transfer member to a transfer material. An image forming apparatus provided with a transfer unit that performs charging, and a toner charging unit that charges a transfer residual toner on the intermediate transfer body and electrostatically collects the toner on the image carrier, the toner charging unit, and the intermediate transfer body And a spacer that keeps a constant distance from the distance.

According to a sixth aspect of the present invention, the spacer keeps a distance between the toner charging means and the intermediate transfer member at 5 to 500 μm.

The present invention according to claim 7 is characterized in that the spacer is an abutting roller interposed between the toner charging means and the intermediate transfer member.

According to the present invention, there is provided an image carrier on which a toner image is formed, an intermediate transfer member on which the toner image is transferred, and a transfer of the toner image on the intermediate transfer member to a transfer material. An image forming apparatus provided with a transfer means for charging the toner remaining on the intermediate transfer body and electrostatically collecting the toner on the image carrier, wherein the toner charging means includes an AC component. A power supply for applying a bias, and a capacitor of 2000 pF or more disposed between the intermediate transfer body and the ground while grounding the intermediate transfer body.

According to a ninth aspect of the present invention, the capacitor is 50,000 pF or less.

According to a tenth aspect of the present invention, the intermediate transfer member is a solid drum.

[Action] The main action according to the present invention (claim 1)
Are as follows.

By setting the capacitance of the intermediate transfer member as large as 13 pF / cm ² , the electrostatic force acting between the toner and the intermediate transfer member can be increased, so that scattering of the toner can be prevented. it can.

[0027]

Embodiments of the present invention will be described below with reference to the drawings. <Embodiment 1> FIG. 1 is a longitudinal sectional view showing a schematic configuration of an image forming apparatus according to the present invention. The image forming apparatus shown in FIG. 1 uses a drum-type electrophotographic photosensitive member (hereinafter referred to as “photosensitive drum”) 3 as an image carrier, and a two-layer drum-type transfer drum 2 as an intermediate transfer member. I'm using

The image forming apparatus shown in FIG. 1 will be described more specifically. The image forming apparatus has an intermediate transfer body 2 having a diameter of 18 mm.
A 6 mm solid transfer drum is used (note that “solid” is used in the sense that the shape is constant unlike a belt or the like), the maximum paper passing size A3, the process speed is 110 mm / sec, This is a full-color electrophotographic image forming apparatus (laser beam printer) of the exposure and reversal development type.

In order to form a full-color image, yellow (Y), magenta (M), cyan (C), and black (B) are formed on the photosensitive drum 3 which is driven to rotate in the direction of arrow R3.
The toner images of k) are sequentially formed, and the toner images of the respective colors are sequentially transferred to the surface of the intermediate transfer body 2 so that toner images of four colors are superimposed on the surface of the intermediate transfer body 2. This transfer is performed via a primary transfer nip N1 formed between the photosensitive drum 3 and the intermediate transfer body 2. The transfer of the toner image from the photosensitive drum 3 to the intermediate transfer member 2 is called primary transfer, and the toner image for four colors is superimposed on the surface of the intermediate transfer member 2 by rotating the intermediate transfer member 4 four times. Is primarily transferred.

Next, toner images of four colors on the intermediate transfer body 2 are collectively transferred onto a transfer material P such as paper. This transfer is performed by the transfer between the intermediate transfer body 2 and a transfer unit 1 described later.
This is a transfer performed through the next transfer nip portion N2, and is called a secondary transfer.

As the transfer unit 1 as a transfer means, a unit in which a transfer belt 13 is stretched over two rollers 11 and 12 is used, and the transfer belt 13 is moved by the transfer roller 11 on the upstream side in the conveying direction of the transfer material P. To the intermediate transfer member 2
Are brought into contact with each other to perform secondary transfer of the toner, and at the same time, the transfer material P is attracted to the transfer belt 13 to separate the transfer material P from the intermediate transfer body 2. The other roller is a drive roller 12, which drives the unit such that the peripheral speed of the intermediate transfer body 2 and the peripheral speed of the transfer belt 13 in the secondary transfer nip portion N2 are equal. Further, the transfer unit 1 has an arrow R on the transfer roller 11 side with the drive roller 12 side as a center.
The transfer belt 13 is swingably supported in one direction so that the transfer belt 13 can be moved toward and away from the intermediate transfer body 2.

The toner image secondarily transferred onto the transfer material P is
The transfer material P is fixed on the surface of the transfer material P by a heat fixing roller unit (not shown) as a fixing device disposed downstream of the secondary transfer nip portion N2 in the transport direction of the transfer material P. The transfer material P after the fixing of the toner image is transferred to an image forming apparatus main body (not shown).
Is discharged.

Next, each member and each unit will be described in detail.

The photosensitive drum 3 is a negatively chargeable OPC (organic optical semiconductor) drum having a diameter of 64 mm, and its surface is first uniformly charged by a charging roller 4 as a primary charger.
The bias applied to the charging roller 4 includes a DC component and an AC component.
Component is a superimposed bias, and the DC component is −60.
0 V, and the AC component is 2000 V _pp , 1000 Hz, and a sine wave. Thus, the surface of the photosensitive drum 3 is charged to about -600 V regardless of the surrounding environment.

Next, the surface of the photosensitive drum 3 is exposed by a laser exposure device. In the present embodiment, image exposure is performed by combining an infrared laser diode 5 having a wavelength of 760 nm and a polygon scanner 6 and using an exposure apparatus having a lens and a mirror (both not shown).

Next, the electrostatic latent image formed by the laser exposure is developed with toner by a developing device. In the image forming apparatus of this embodiment, four color toners of Y, M, C, and Bk are used. Specifically, a fixed black developing device 7 and a rotary color developing device as shown in FIG. Unit 8 is used.

The black developing device 7 employs a jumping developing method using a magnetic one-component toner. A toner having a particle diameter of 6 μm is applied to a conductive non-magnetic developing sleeve 72 having a diameter of 16 mm including a fixed magnet roll 71 by using an elastic blade 7.
3 and DC applied to the developing sleeve 72
Component -350V, AC component 1600V _pp , frequency 200
The photosensitive drum 3 is jumped by a rectangular wave of 0 Hz to perform reversal development.

The color developing unit 8 comprises three yellow
The developing units 81, 82, and 83 for each of the colors magenta and cyan are incorporated in the rotary rotary 8a, and the developing unit for the toner of the color to be used for development is moved to the developing position facing the photosensitive drum 3 by rotating the rotary rotary 8. Place and develop. The developing units 81, 82, and 83 of each color perform development by a jumping development method using a non-magnetic one-component toner. The toner has a particle diameter of a core / shell structure containing a wax therein.
μm polymerized toner, which is coated on a developing sleeve (not shown) by an application roller (not shown), and is sent to a developing position with a layer thickness regulated by an elastic blade (not shown). Development is performed under the same bias conditions.

The primary transfer is performed by applying a voltage to the intermediate transfer member 2, and the primary transfer residual toner on the photosensitive drum 3 is scraped off by a cleaning unit 9 having a urethane cleaning blade 91. In the printer of the present embodiment, the secondary transfer residual toner on the intermediate transfer body 2 is transferred to an ICL roller (toner charging unit) serving as a charging roller.
Since the process of recharging at 10 and transferring (collecting) to the photosensitive drum 3 is adopted, the secondary transfer residual toner collected on the photosensitive drum 3 is similarly scraped off by the cleaning blade 91.

The ICL roller 10 has a single-layer structure composed of an elastic layer, and is a solid roller having a diameter of 20 mm in which the resistance value is adjusted by dispersing carbon in EPDM rubber.

In the case of single-color printing, after the primary transfer is performed, the toner image is directly transported on the intermediate transfer member 2 to the secondary transfer nip portion N2, and undergoes the secondary transfer.

In the case of full-color printing, the intermediate transfer member 2 is rotated four times so that each toner of YMCK
Next transfer.

In the case of monochromatic printing, the primary transfer bias is set to + 100V. In the case of performing full-color printing, as shown in FIG. 2, if primary transfer is performed by further superimposing the second color toner T2 on the intermediate transfer body 2 where the first color toner T1 already exists, Since the transfer contrast substantially decreases, it is necessary to increase the transfer bias to compensate for this. On the other hand, if the primary transfer bias is too high, a discharge occurs between the photosensitive drum 3 and the intermediate transfer body 2, and image deterioration and toner tribo on the intermediate transfer body 2 change. Can not. Further, in the image forming apparatus of the present embodiment, 1
Since the intermediate transfer body 2 is also cleaned at the same time as the next transfer, multi-color image formation (hereinafter referred to as “multi-color print”)
The fourth rotation at the time is the first rotation of the next image, and must have the same bias value.

In view of these circumstances, the primary transfer bias during multicolor printing is set to 100 V, 500 V, 500 V, and 100 V for each rotation of Y, M, C, and Bk.

In the present embodiment, in order to improve the secondary transfer efficiency, the pre-secondary-transfer corona charger disposed to the right of the intermediate transfer member 2 in FIG. 15 performs corona charging. The corona charger 15 shown in FIG.
A current of −100 μA is passed as a DC component to 5a, and 7 kV _pp , 500H is applied to prevent contamination of the corona wire 15a.
The sine wave of z is superimposed. The shield potential is grounded. Due to the corona charging, the tribo of the toner on the intermediate transfer body 2 is a black toner, and the negative charge of the toner increases from -10 μC / g to about −20 μC / g.

At the time of the secondary transfer, the transfer material P is supplied from a paper feeding unit (not shown), and the transfer belt 13 which can be separated and brought into contact with the intermediate transfer body 2. The secondary transfer bias performs a constant current control of +20 μA, and a charge is supplied to the transfer material P from the transfer belt 13 so that the toner image on the intermediate transfer body 2 is transferred to the transfer material P.
Is secondarily transferred.

The transfer unit 1 is composed of a transfer roller 11, a drive roller 12, and a transfer belt 13. Each of the transfer roller and the drive roller has a conductive rubber layer having a volume resistance of 10 ⁵ Ω · cm on a core metal having a diameter of 14 mm. 20m in diameter
m. The transfer roller 11 has a core connected to a high-voltage power supply via a power supply spring.
It follows and rotates. The driving roller 12 has a gear attached to the end of the cored bar, and is driven by meshing with a gear train of the image forming apparatus main body.

The transfer belt 13 is a seamless two-layer rubber belt, and the base layer 13a is urethane rubber having a thickness of 300 μm and a volume resistance value adjusted to 10 ⁷ Ω · cm by dispersing carbon. The surface layer 13b needs to adsorb the transfer material P, and has a high resistance in order to prevent the transfer current from excessively flowing into the non-sheet-passing portion when the small-size transfer material P is passed. In addition, it is necessary to select a material that does not easily stain with toner.

In this embodiment, a fluorine-based resin paint is used as the material of the surface layer 13b in order to satisfy such characteristics. Specifically, PVDF, or PVDF or PTFE
A resin obtained by coating a resin obtained by copolymerizing a resin with another olefin-based resin on the base layer 13a was used.

More specifically, the surface layer 13 b is
After molding and cross-linking, the transfer belt 13 was formed by molding the urethane conductive base layer 13a to a thickness of 300 μm.

The transfer belt 1 used in this embodiment is
Reference numeral 3 denotes a seamless belt having an inner diameter of 65 mm, which is stretched by 5% and stretched between the rollers 11 and 12.

Next, the intermediate transfer member 2 will be described. First, an elastic layer (conductive rubber layer) 22 having a thickness of 5 mm is formed on a base (aluminum drum) 21 as an intermediate transfer member 2 to have a real resistance value of 5 × 10 ⁶ Ω · cm and a single-layer intermediate transfer member. 2
Was used for image evaluation.

The resistance value of the intermediate transfer member 2 is determined by contacting a metal roller to the intermediate transfer member 2 to form a contact nip having a size of 30 cm × 5 mm and rotating at a peripheral speed of 110 mm / sec. Is used as the actual resistance value, converted from the value of the current flowing when is applied.

As an evaluation image, a blue fir image obtained by superimposing a magenta toner and a cyan toner was output.

First, magenta toner has a primary transfer voltage of +5.
The toner image is primarily transferred from the photosensitive drum 3 onto the intermediate transfer member 2 at 00 V, and then cyan toner is applied on this toner image by the same +50.
Primary transfer is performed at a voltage of 0V. At this point, the operation of the image forming apparatus was stopped, and the toner image formed on the intermediate transfer member 2 was observed. As a result, it was confirmed that severe scattering of the second color cyan toner had occurred. On the other hand, scattering does not occur in the first color magenta toner.

As shown in FIG. 2, since the magenta toner T1 previously transferred onto the intermediate transfer member 2 has a tribo, the cyan toner T2 is scattered by the potential generated by this. When the toner potential of the magenta toner T1 on the intermediate transfer body 2 was measured, it was -10
A potential of about 0 V was observed. In the primary transfer nip N1, the photosensitive drum 3 and the intermediate transfer body 2 are in contact with each other under pressure, so that no scattering occurs. T2
Scatters on the intermediate transfer member due to repulsion between the toners T2.

In order to prevent the scattering, it is effective to increase the electrostatic force acting between the toner and the intermediate transfer member 2 by using the intermediate transfer member 2 having a multilayer structure and a high capacitance. A repulsive force acting between the toner on the surface layer and the toner on the lower layer, a capacitance between the intermediate transfer body 2 and a Coulomb force (attraction) acting on the charge of the toner itself act on the toner on the intermediate transfer body. Can be suppressed by increasing the capacitance of the scatter.

In this embodiment, in order to increase the capacitance, the intermediate transfer member 2 has a two-layer structure, a low elastic layer resistance, and a thin surface layer made of a high-resistance material.

As a comparative example, the intermediate transfer member 2 was experimentally manufactured by changing the actual resistance of the elastic layer resistance by two levels, and changing the volume resistance and the film thickness of the material forming the surface layer, and evaluated the image.

The results are shown in the following table. The 〇 × evaluation relates to scattering.

Elastic layer actual resistance 10 ⁶ Ω Elastic layer actual resistance 5 × 10 ⁶ Ω 10 ¹⁰ , 15 μm 150 pF × 100 pF × 10 ¹⁰ , 30 μm 130 pF × 90 pF × 10 ¹⁰ , 45 μm 100 pF × 80 pF × 10 ¹² , 15 μm 300 pF〇180 pF × 10 ¹² , 30 μm 200 pF △ 130 pF × 10 ¹² , 45 μm 130 pF × 90 pF × 10 ¹⁴ , 15 μm 500 pF ２００200 pF △ 10 ¹⁴ , 30 μm 250 pF １８０ 180 pF × The electrostatic capacity of the intermediate transfer body 2 is the same as that of the intermediate transfer body 2 and metal. The nip of 30 cm x 5 mm was formed by contacting the plates, and the value measured with an LCR meter in a stationary state was used. The LCR meter measures at 1 V at 1000 Hz.

In the present embodiment, in order to evaluate the degree of improvement of scattering, the indices of △, △, and × are used as indices. However, in practice, scattering of about △ level does not matter.

From the above results, in order to improve scattering, it is desirable that the capacitance of the intermediate transfer member 2 is 200 pF or more, which is 13 pF / cm ² or more in terms of capacitance per unit area. Will be.

As a means for realizing this value, when the actual resistance of the elastic layer 22 of the intermediate transfer member 2 is 10 ⁶ Ω or less, and the intermediate transfer member 2 has a surface layer covering the outside of the elastic layer 22, the volume specific to the material of the surface layer It has been found that it is desirable that the resistance be 10 ¹² Ω · cm or more and the film thickness be 30 μm or less.

By using the intermediate transfer member 2 as described above, it is possible to prevent the toner of the second and subsequent colors from being scattered at the primary transfer nip N1. <Embodiment 2> In Embodiment 2, the ICL roller 1
An object of the present invention is to improve the cleaning performance of the intermediate transfer body 2 by limiting the DC current flowing directly from 0 to the intermediate transfer body 2.

As described in the first embodiment, in the present invention, the secondary transfer residual toner on the intermediate transfer member 2 is transferred to the ICL roller 1.
In this method, the toner image is positively charged at 0, and is collected on the photosensitive drum 3 simultaneously with the primary transfer of the toner image of the next color.

The mechanism of charging the secondary transfer residual toner on the intermediate transfer member 2 by the ICL roller 10 is based on discharge. In the discharge (small) gap between the ICL roller 10 and the intermediate transfer body 2 to which the voltage is applied, discharge is excited according to Paschen's law. Generally, a charging roller of the photosensitive drum 3 is well known as a charging means based on such discharge. In this case, all the DC current supplied from the charging roller becomes the charging current of the photosensitive drum 3.

However, in the above-described method, the intermediate transfer member 2
Since both ICL rollers 10 are medium resistance members,
Not all of the DC current supplied to the roller 10 contributes to charging, and most is an injection current that flows directly ohmic.

For this reason, if the ICL current is controlled at a constant current, the ratio of the direct injection current to the current contributing to toner charging changes when the resistance value of the member fluctuates due to environmental fluctuations or manufacturing fluctuations. There is a problem that the toner tribo after passing is not stabilized.

In order to solve such a problem, in the second embodiment, the ICL roller 10 which directly contributes to the injection current is used.
The purpose is to secure the chargeability of the toner by limiting the contact nip N3 between the toner and the intermediate transfer member 2 and desirably maintaining a discharge gap of 5 to 500 μm.

When the ICL roller 10 and the intermediate transfer member 2 are not in contact with each other, the substantial discharge nip increases as shown in FIG. This is based on the fact that it is difficult for a discharge gap to be generated in a discharge gap of 5 μm or less according to Paschen's law. When the two are in contact, no discharge occurs in the contact nip N3, and the toner is charged only in a narrow area at both ends of the contact nip. Is not performed. When the two are in contact with each other, as shown in the left diagram of FIG. 3, the substantial discharge region is narrow when the nip width is large, and when the nip width is small, the discharge region is small as shown in the center diagram of FIG. growing. Further, when the two are not in contact with each other, as shown in the right figure, the substantial discharge region is enlarged as described above. When a practical bias is applied to the ICL roller 10, the discharge gap at which the toner can be charged is considered to be 500 μm or less, and it is desirable to maintain the discharge gap in this range.

In the present embodiment, as shown in the right diagram of FIG. 3, a gap roller (abutting roller) 16 is provided as a spacer at the end of the ICL roller 10, and the gap roller 16 is applied to the surface of the intermediate transfer member 2D. 200 μm by contact
Is maintained.

An experiment was conducted using the ICL roller 10 having such a configuration and a conventional contact type ICL roller.
The bias applied to the ICL roller 10 was subjected to constant current control as a DC component, and a rectangular wave of 2 kHz and 3 kV _pp was superimposed on the AC component. The following shows the constant current control value and the change amount of the toner tribo before and after passing through the ICL roller 10 (unit is μC
/ G).

10 μA 20 μA 30 μA 40 μA 50 μA With discharge gap 5 15 25 35 45 Contact 1 3 8 15 25 As described above, when the discharge gap is provided, the amount of change in toner tribo is large even at the same constant current value, and good charging can be achieved. I understand.

This phenomenon occurs particularly when the ICL roller 10
This becomes significant when a bias is superimposed.

Although the discharge occurs only in one direction and the charge amount is small due to only the DC bias, when AC is superimposed, the toner is discharged from both the intermediate transfer member 2 and the ICL roller 10 so that the discharge gap is increased. By doing so, the chargeability is further improved.

By comparing the left figure of FIG. 3 with the center figure, it is clear that the discharge area is expanded by restricting the contact nip (reducing the nip width) with a roller or the like, even if it is not in non-contact. In this embodiment, the IC
The main purpose is to keep the distance between the L roller 10 and the intermediate transfer body 2 at a target value for securing a discharge gap.

As described above, in the present embodiment, the IC
By limiting the contact nip between the L roller 10 and the intermediate transfer body 2, the injection current is suppressed, and by further increasing the substantial discharge gap, good charging of the transfer residual toner can be performed. <Embodiment 3> In Embodiment 3, the actual resistance of the surface layer 22 occupying a large part of the thickness of the intermediate transfer body 2 is 10 ⁶ Ω ·
cm or less, the AC applied to the ICL roller 10
It is intended to effectively apply a voltage to the toner.

The intermediate transfer body 2 may be in the form of a solid drum-shaped intermediate transfer drum, a belt-shaped intermediate transfer belt, or the like. In order to form a nip with the photosensitive drum 3 and the transfer material P, these may be elastic. Is required. In the case of the intermediate transfer drum, an elastic layer (conductive rubber layer) 2 having a thickness of about 5 mm is formed on a base (aluminum cylinder) 21 as described in the first embodiment.
2 and a surface layer (resistance layer) of about 15 μm is coated thereon.

In addition, the intermediate transfer belt needs to have strength so that the belt is not stretched in order to match the color registration, and also needs a certain thickness to prevent meandering, buckling and deviation of the belt. .

In such a drum or belt, the base layer or the elastic layer occupies most of the thickness, and plays a dominant role with respect to the resistance value.

However, when the ICL method is used, I
It has been found that applying an AC voltage to the CL roller 10 is effective for cleaning the intermediate transfer member 2. A
The C voltage is applied with respect to the core metal of the ICL roller 10 and the reference potential of the intermediate transfer body 2, but the actual formation of the AC electric field is at the discharge gap between the ICL roller 10 and the surface of the intermediate transfer body 2. is there.

In this embodiment, in order to minimize the AC bias applied to the intermediate transfer member 2, the resistance of the elastic layer 22 of the intermediate transfer member 2 and the resistance of the ICL roller 10 are set to 10 ⁶ Ω or less. It is intended to be.

The intermediate transfer member 2 and the IC
An example in which an experiment was performed using the L roller 10 is shown below.

As the intermediate transfer member 2, a prototype produced in the first embodiment with the resistance of the elastic layer 22 set to two levels of 10 ⁶ Ω and 10 ⁷ Ω was used. Further, as an ICL roller 10, an elastic layer having an actual resistance of 10 ⁶ Ω and 10 ⁷ Ω and a urethane resin having a volume resistance value of 10 ¹⁴ Ω · cm coated with a thickness of 70 μm was experimentally manufactured.

The actual resistance of the elastic layer of the ICL roller 10 is the same as the measurement of the resistance value of the intermediate transfer member 2, and the total pressure of the metal roller is 1 k.
g, the ICL roller 10 is brought into contact, a voltage of 1 kV is applied, and the roller is rotated at a peripheral speed of 100 mm / sec.

The ICL roller 10 has a DC component of +1
A rectangular wave of 2 kHz and 3 kV _pp as 000 V and AC components was superimposed and applied to the core of the ICL roller 10. A character image was printed under these conditions, the image forming apparatus was stopped during printing, and the tribo change of the untransferred toner before and after passing through the ICL roller 10 was measured. At the same time, the appearance of the untransferred toner was observed. ICL roller elastic layer resistance 10 ⁶ Ω 10 ⁷ Ω Intermediate transfer member elastic layer resistance 10 ⁶ Ω 30 μC / g 18 μC / g 10 ⁷ Ω 18 μC / g 5 μC / g The amount of change in tribo before and after passing through the ICL roller 10 is as described above. It can be seen that the charging ability of the ICL roller 10 is higher when an AC electric field is applied with a lower resistance of the elastic layer.

FIGS. 4 (a) and 4 (b) are conceptual diagrams showing the appearance of toner before and after passing through the ICL roller 10. FIG.
Shown in

Intermediate transfer member 2 having an elastic layer resistance of 10 ⁶ Ω, IC
In the case where the L roller 10 is used, as shown in FIG. 4A, the character image can be read as it is from the untransferred toner which has not been secondary-transferred before passing through the ICL roller 10, but after passing through the ICL roller 10, the AC electric field causes The toner was disturbed, and the transfer residual toner on the intermediate transfer member 2 was observed as a uniform fog.

[0090] On the other hand, the elastic layer resistance in FIG. 4 (b) 10 ⁷ Omega
In this case, it was found that the toner image after passing through the ICL roller 10 did not scatter so much, and that no AC electric field was formed in the discharge gap.

As described above, in the present embodiment, the elastic layer 22 of the intermediate transfer body 2 and the I
By setting the actual resistance of the elastic layer of the CL roller 10 to 10 ⁶ Ω or less, the toner is charged while disturbing the toner, thereby enabling more effective simultaneous transfer cleaning. <Embodiment 4> In the present embodiment, in an electrophotographic apparatus using an ICL system having a member on which an AC bias is superimposed around the intermediate transfer member 2 and It is characterized by providing a capacitor between them.

In the image forming apparatus of the intermediate transfer system used in the first embodiment, the photosensitive drum 3, the corona charger 15 before the secondary transfer, the transfer belt (the secondary transfer Member) 13, the ICL roller 10, and the like.

All of the current flowing from such a member into the intermediate transfer member 2 flows into a power supply that applies a voltage to the intermediate transfer member 2. The intermediate transfer member 2 bias is a voltage applied for performing the primary transfer, and changes when the voltage changes.
Next transfer efficiency may be reduced. However, in the case of a general high-voltage power supply, the bias is rarely changed by the flow of the secondary transfer current and the ICL current of about several tens of μA.

However, the situation is different when an ICL system is used in which an AC current is applied to these members and cleaning is performed simultaneously with transfer.

As described in the third embodiment, the elastic layer resistance of the intermediate transfer member 2 and the ICL roller 10 can be reduced,
In order to improve the scattering of the second color, the intermediate transfer member 2
, The AC current flowing through the ICL roller 10 becomes a very large value. As described in the second embodiment, providing a discharge gap between the intermediate transfer member 2 and the ICL roller 10
This is effective for suppressing the direct injection current of the DC component flowing into the capacitor, but is not so effective for the AC current flowing through the capacitance.

As an example, in the image forming apparatus used in the first embodiment, the AC current flowing into the intermediate transfer member 2 from the ICL roller 10 reaches 1500 μA. In addition, when an AC voltage for preventing wire contamination is applied to the corona charger 15 charged before the secondary transfer, the AC current caused by the voltage also flows into the intermediate transfer body 2.

These currents escape to the ground via the high voltage power source of the primary transfer bias applied to the intermediate transfer member 2. Since there is a transformer and a resistor inside the high voltage power supply, AC
When current passes through these impedance components,
A voltage is generated, so that the AC voltage is superimposed on the voltage applied to the intermediate transfer body 2.

A general high-voltage DC power supply has one between the output terminals.
A capacitor of about 000 pF is provided (inserted in parallel with the high voltage power supply), and a certain amount of AC current can be released. However, when such a general power supply is used,
In the configuration of the present embodiment, the amplitude of the AC voltage superimposed on the primary transfer bias reaches as much as 500 V. When printing was performed in this state, cleaning failure of the intermediate transfer member 2 occurred. This is because the peak of the superimposed AC bias has exceeded the range of the primary transfer bias in which the intermediate transfer member 2 can be cleaned.

In order to prevent such a situation, in the present embodiment, at least two lines are provided between the intermediate transfer member 2 and the ground.
Capacitor 2 with a value between 000 pF and 50,000 pF
0 is provided.

The primary high-voltage power supply originally provided 1
With a capacitor of 000 pF, A superimposed on the bias
The amplitude of the C voltage was 500 V.
The amplitude could be reduced to 200 V by setting to F, and to almost negligible by setting to 5000 pF. On the other hand, when a capacitor of 50,000 pF was used, the rise of the primary transfer bias was delayed by about 1 second, and if the value was longer than this, transfer failure at the leading end of the image occurred, which was not preferable.

The gist of the present embodiment is that the ICL roller 10
And to prevent the voltage of the intermediate transfer body 2 from fluctuating due to an AC current flowing from the corona charger. Base (drum cylinder) 2
It is also possible to use a method in which a terminal is brought into direct contact with the first or elastic layer 22 and this is grounded via a capacitor.

As described above, in this embodiment, in the apparatus having the ICL roller 10 and the corona charger 15 to which the AC bias is applied around the intermediate transfer member 2, the intermediate transfer member 2 is connected via the capacitor 20. Grounding can prevent primary transfer failure and cleaning failure of the intermediate transfer body 2.

[0103]

As described above, according to the present invention,
By setting the capacitance of the intermediate transfer member to 13 pF / cm ² or more, an electrostatic force acting between the toner and the intermediate transfer member can be ensured, so that toner scattering can be prevented.

Further, since the distance between the intermediate transfer member and the toner charging means can be kept constant without contact by the spacer, the direct injection from the toner charging means to the intermediate transfer member can be restricted. The toner can be charged efficiently.

Further, the actual resistance of the elastic layer of the intermediate transfer member is set to 1
With less 0 ⁶ Omega, it is possible to minimize the partial pressure of the AC voltage applied to the elastic layer, so as to be able to effectively disturb the toner between the toner charging means and the intermediate transfer member became.

Furthermore, in parallel with a high voltage power supply,
By inserting a capacitor of F or more, an AC current flowing through a process member disposed around the intermediate transfer body flows into the primary transfer high-voltage power supply, and the primary transfer bias fluctuates.
It is possible to prevent poor cleaning of the intermediate transfer member and image deterioration.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of an image forming apparatus according to the present invention.

FIG. 2 is a conceptual diagram showing how a second color toner scatters when a second color toner is superimposed on a first color toner on an intermediate transfer member.

FIG. 3 is a conceptual diagram showing a discharge area between an ICL roller 10 and an intermediate transfer member 2.

FIGS. 4A and 4B are conceptual diagrams illustrating images of secondary transfer residual toner before and after an ICL roller.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transfer unit 2 Intermediate transfer body (transfer drum) 3 Image carrier (photosensitive drum) 4 Charging roller 7 Black developing device 8 Color developing unit 9 Cleaning unit 10 Toner charging means (ICL roller) 13 Transfer means 15 Corona before secondary transfer Charger 16 Spacer (abutting roller) 20 Capacitor 21 Base 22 Elastic layer

Claims (10)

[Claims] A step of transferring a toner image formed on an image carrier onto an intermediate transfer member for a plurality of color toners to form a plurality of color toner images on the intermediate transfer member; An image forming apparatus for transferring images collectively on a transfer material, wherein the capacitance of the intermediate transfer body is set to 13 pF / cm ² or more. 2. The image according to claim 1, wherein the intermediate transfer body has an elastic layer and a surface layer covering the elastic layer, and the elastic layer has an actual resistance of 10 ⁶ Ω or less. Forming equipment. 3. The surface layer has a volume resistivity value of 10 ^{12 or} less.
The image forming apparatus according to claim 1, wherein the value is in a range of 10 ¹⁶ mΩ · cm. 4. The image forming apparatus according to claim 3, wherein the surface layer has a thickness of 30 μm or less. 5. An image carrier having a surface on which a toner image is formed, an intermediate transfer member on which the toner image is transferred, and a transfer unit for transferring the toner image on the intermediate transfer member to a transfer material. In the image forming apparatus, a toner charging unit that charges the transfer residual toner on the intermediate transfer body and electrostatically collects the toner on the image carrier, and keeps a distance between the toner charging unit and the intermediate transfer body constant. An image forming apparatus, comprising: 6. The image forming apparatus according to claim 5, wherein the spacer maintains a distance between the toner charging unit and the intermediate transfer member at 5 to 500 μm. 7. The image forming apparatus according to claim 5, wherein the spacer is an abutting roller interposed between the toner charging unit and the intermediate transfer member. 8. An image carrier having a surface on which a toner image is formed, an intermediate transfer body on which the toner image is transferred, and a transfer unit for transferring the toner image on the intermediate transfer body to a transfer material. In the image forming apparatus, a toner charging unit that charges the transfer residual toner on the intermediate transfer body and electrostatically collects the toner on the image carrier, a power supply that applies a bias including an AC component to the toner charging unit, An image forming apparatus comprising: a grounding means for grounding the intermediate transfer body; and a capacitor of 2000 pF or more disposed between the intermediate transfer body and grounding. 9. The image forming apparatus according to claim 8, wherein the capacitor has a capacity of 50,000 pF or less. 10. The image forming apparatus according to claim 1, wherein the intermediate transfer member is a solid drum.
An image forming apparatus according to any one of the preceding claims.