JPH06110343A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain an image forming device provided with a transfer device capable of performing steady transfer at constant transfer-efficiency with respect to an environmental change. CONSTITUTION:The device is provided with: a plurality of image forming means which are provided for the corresponding image-carriers 1 disposed in order, and form images on the image carriers 1; a semiconductive transfer material carrier 2; a carry means for carrying a transfer material P to the image carriers l in order; and a plurality of transfer means 3 which are provided for the corresponding image-carriers 1, and transfer the formed images on the image carriers 1 to the transfer material P, carried by the carry means, by exerting constant current control to keep a current constant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic color image forming apparatus such as a so-called full-color copying machine or a color laser printer, and more particularly to an image forming apparatus provided with a transfer apparatus capable of maintaining a constant transfer efficiency. Regarding the device.

[0002]

2. Description of the Related Art Conventionally, as a method for forming a full-color image on a transfer material such as paper, a toner image is formed on a photosensitive member which is an image carrier, and the toner image is transferred onto the transfer material. 2. Description of the Related Art A color image forming apparatus that sequentially performs color order has been put into practical use.

In a transfer device in this type of color image forming apparatus, a transfer material is carried on a transfer material carrier made of an insulating (dielectric) sheet capable of holding a charge, such as plastic formed in a drum shape or a belt shape. , A transfer unit on the same or a plurality of photoconductors, and at the transfer unit of the photoconductor, the back surface of the transfer material carrier is connected to a high-voltage power supply which is a non-contact type charger, and a high voltage of 5 to 6 kV is applied Form an electrostatic field by charging with a corona charger,
The toner image on the photoconductor charged to a predetermined polarity is transferred onto the transfer material a number of times corresponding to a predetermined color.

In the above transfer device, since an insulating sheet capable of holding a charge is used as the transfer material carrier, the surface of the transfer material carrier after separating the transfer material on which the toner image has been transferred is treated with a corona charge eliminator or the like. There is a problem in that a destaticizing means for destaticizing is required and that a corona charger is used to generate ozone harmful to the human body from the corona charger. Furthermore, in a color transfer device of a color image forming apparatus that sequentially transfers toner images on a plurality of photoconductors to a transfer material, a plurality of corona chargers corresponding to the number of photoconductors are required, and a larger amount of ozone is generated. There was a problem saying that. In recent years, people-friendly office automation equipment has been required, and eliminating ozone generation has become an urgent task.

Therefore, as a transfer device which does not generate ozone, the present inventors have previously used a semiconductive sheet as a transfer material carrier, and the transfer material of the transfer material carrier is carried at the transfer portion on the photoconductor. We proposed a transfer device that applies a bias voltage to the uncoated surface with a bias voltage application member. (Japanese Patent Application No. 3-287861) In this transfer device, since the semiconductive sheet is used as the transfer material carrier, it is possible to remove the electric charge by itself, and there is no need to remove the charge of the transfer material carrier.
No corona charger is used, so no ozone is generated.

However, in this transfer device, the temperature and
There is a problem that the characteristics of the transfer efficiency of the toner image with respect to the transfer bias voltage change due to changes in the electrical resistance of the transfer material carrier and the transfer material due to changes in the humidity environment. Therefore, there is a problem that an image having a predetermined density cannot be obtained on the transfer material.

When this transfer device is applied to a transfer device of a color image forming apparatus, the transfer efficiency of the toner image varies depending on the environment, and the transfer efficiency changes with the increase in the number of transfers in multiple transfer. However, a constant transfer efficiency cannot be obtained. That is, the transfer efficiency characteristic with respect to the transfer bias voltage changes depending on the number of times of multiple transfer. Therefore, in multiple transfer, it is necessary to sequentially increase the charging potential as the number of transfers increases. However, if the charging potential becomes high, discharge (ionization of air in the minute gap) occurs between the transfer material and the toner carrier before and after the transfer, and there is a problem that sufficient transfer efficiency cannot be obtained. Further, there is a problem that uneven transfer occurs due to partial transfer omission.

[0008]

As described above, in the above-mentioned transfer device, the transfer efficiency changes depending on the environment, the image density changes, and the transfer efficiency also changes depending on the number of times of transfer. However, there is a problem in that good color images cannot be formed due to poor performance.

Therefore, it is an object of the present invention to provide an image forming apparatus provided with a transfer device which can perform transfer with stable and constant transfer efficiency against environmental changes.

[0010]

An image forming apparatus according to the present invention is provided with a plurality of image carriers which are sequentially arranged and corresponding to each of the image carriers, and the image carriers are respectively provided on the image carriers. A plurality of image forming means for forming an image and a semiconductive transfer material carrier, and a transport means for sequentially transporting the transfer material to each image carrier, and a transport means provided corresponding to each image carrier. A plurality of transfer means for respectively transferring the image formed on each image carrier to the transfer material transported by the transport means by constant current control for maintaining the current constant.

Further, the image forming apparatus is provided with a plurality of image carriers that are sequentially arranged and a plurality of images that are provided corresponding to the respective image carriers and that form images on the respective image carriers. The formation means and the electric resistance per 1 m ² in the thickness direction are in the range of 10 ^{2 to} 10 ⁶ Ω, and the electrostatic capacity per 1 m ^{2 in} the thickness direction is 2 × 10 ^{−8 to} 4 × 10 ^−7.
In addition to having the transfer material carrier in the range of F, the transporting means for sequentially transporting the transfer material to each of the image carriers and the transport means provided corresponding to each image carrier are transported by the transporting means. A plurality of transfer means for respectively transferring the images formed on the respective image carriers to the transfer material.

[0012]

With the image forming apparatus of the present invention, it is possible to perform transfer with high transfer efficiency without transfer unevenness or transfer omission in the transferred image.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A transfer device according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the transfer portion of the transfer device of the first embodiment.

In this transfer section, a photosensitive drum 1 which is an image carrier having a photosensitive layer 1b on the surface of a grounded aluminum (Al) drum 1a is provided. A toner image T charged in a negative polarity is formed on the photosensitive drum 1 by a well-known image forming process, and is rotated in the direction of the arrow. A transfer material (paper) P is carried on the transfer material carrier 2 in the shape of an annular belt, a portion of which is illustrated, and is driven in the arrow direction at a speed equal to the peripheral speed of the photosensitive drum 1. It is like this. Further, a power supply roller 3 which constitutes a bias voltage applying means for applying a bias voltage to the transfer material carrier 2 is arranged on the back surface of the transfer material carrier 2.

The transfer material carrier 2 has a thickness of 140 μm,
It is made of polyvinylidene fluoride mixed with ionic conductive material, and the electric resistance per 1 m ^{2 in the} thickness direction is room temperature,
It is approximately 10 ⁵ Ω under normal humidity. This transfer material carrier 2
Are in contact with the photosensitive drum 1 with a predetermined nip width.

In this transfer device, the transfer material carrier 2
Is important, and when the electric resistance per 1 m ^{2 in the} thickness direction is 10 ¹ Ω or less, the transfer material carrier 2 imparts an electric charge to the transfer material P, and this electric charge is further imparted to the toner. Since the charging polarity of the toner is opposite, the transfer efficiency is reduced. Further, when the electric resistance per 1 m ² in the thickness direction is 10 ⁷ Ω or more, a high transfer bias voltage is required to obtain a sufficient transfer electric field, and peeling occurs when the transfer material P separates from the photosensitive drum 1 after transfer. Discharge occurs and transfer efficiency decreases.

The power feeding roller 3 has an appropriate elasticity, and the transfer material carrier 2 is arranged from the back surface of the transfer material carrier 2 so that the toner image T on the photosensitive drum 1 and the transfer material P come into contact with each other at an appropriate pressure. While rotating in contact with 1, it rotates in the direction of the arrow. The power feeding roller 3 has a structure in which an elastic image 3b made of conductive urethane foam is provided on the outer periphery of a core body 3a.
The electrical resistance per 1 m ² between a and the surface of the elastic layer 3b is 10 ¹ Ω. A bias power source 4 is connected to the core metal 3a, and the bias power source 4 is a constant current power source that maintains a constant output current.

The feeding roller 3 forms a transfer electric field by applying a bias voltage to the transfer material carrier 2 while pressing the moving transfer material carrier 2 from the back surface to the photosensitive drum 1. As a result, the negatively charged toner image T on the photosensitive drum 1 is transferred and held on the transfer material P at the transfer portion.

The following experiment was conducted in the transfer device of the present invention. The experimental conditions are as follows. In the photoconductor drum 1, the photoconductor layer 1b is formed of an organic photoconductor and is rotated at a peripheral speed of 72 mm / sec. Further, the photosensitive drum 1 is negatively charged, and the electrostatic latent image formed on the photosensitive drum 1 by charging and exposure is developed by the negative polarity toner by reversal development. The width of the power feeding roller 3 in the axial direction is 22 cm. The transfer material P is A4 plain paper and is fed in the vertical direction.

Prior to this experiment, the electric resistances of the transfer material carrier 2 and the transfer material P when the environment was changed were measured. As a result, the electric resistance of the transfer material carrier 2 is (21)
10 ¹¹ Ω · cm under high temperature and humidity (30 ° C, 50% RH)
10 ⁹ Ω · cm under low temperature and low humidity (10 ° C, 84% RH)
It was 10 ¹³ Ω · cm at 20 ° C. and 20% RH. Transfer material P
Is 10 ¹⁰ Ω · cm at room temperature and humidity, and 10 at high temperature and humidity.
^{It was 7} Ω · cm and 10 ¹⁴ Ω · cm at low temperature and low humidity. That is, it is shown that the electrical resistances of both the transfer material carrier 2 and the transfer material P greatly change depending on the environment.

In the first experiment, a constant-voltage bias power supply was used, a constant voltage was supplied to the power supply roller 3, and the transfer characteristics depending on the environment were investigated. The result is shown in FIG. Figure 13
3 is a graph showing transfer characteristics in three environments when a constant-voltage bias power supply is used. The horizontal axis represents the transfer bias voltage applied to the transfer material carrier by the power feeding roller 3, and the vertical axis represents the transfer efficiency. .

As is clear from this figure, the transfer bias voltage, which is good in the case of high temperature and high humidity, shifted to the low voltage side, and to the high voltage side in the case of low temperature and low humidity. The reason for this is that the electrical resistances of the transfer material carrier 2 and the transfer material P change depending on the environment, so that when a transfer charge, that is, a transfer current is applied to the transfer material carrier 2 by the power feeding roller 3, the transfer material is transferred even with the same transfer bias voltage. The transfer charge applied to the carrier 2 changes. Therefore, when the transfer charge becomes excessive, the transfer charge is applied from the transfer material carrier 2 to the transfer material P, causing a transfer failure.

Next, a constant current bias power supply 4 was used to supply a constant current to the power feeding roller 3, and the transfer characteristics depending on the environment were examined. The result is shown in FIG. FIG. 2 is a graph showing transfer characteristics in three environments when the constant current bias power supply 4 is used. The horizontal axis represents the transfer current supplied to the power supply roller 3, and the vertical axis represents the transfer efficiency.

As is clear from this figure, by using the constant current bias power source 4, even in the three environments in which the electrical resistances of the transfer material carrier 2 and the transfer material P change.
Since the transfer charges applied to the transfer material carrier 2 can be maintained constant, almost the same transfer characteristics can be obtained.

The transfer charge amount qt (C / cm ² ) given to the transfer material carrier 2 is: transfer current It (A), axial width of the power supply roller 3 l (cm), transfer material support The moving speed of the body 2 (equal to the peripheral speed of the photosensitive drum 1) is Vt (cm / s)
ec), qt = I / l · Vt (C / cm ² ).

As the sheet-shaped transfer material carrier 2 adjusted to have an appropriate electric resistance in this embodiment, in addition to the above-mentioned polyvinylidene fluoride mixed with an ion conductive material,
Conductive particles such as carbon dispersed in a high-resistance dielectric sheet such as polycarbonate, polyethylene terephthalate, polyimide, polytetrafluoroethylene (Teflon), or high-resistivity adjusted by composition adjustment without using conductive particles. A molecular film or a rubber material such as silicon rubber or urethane rubber having a relatively low electric resistance is suitable.

In the means for applying the bias voltage,
Appropriate means is one that can press the sheet-shaped transfer material carrier 2 and the transfer material P softly and uniformly on the photoconductor drum 1 with a lower electric resistance than that of the transfer material carrier 2. Therefore, in addition to the roller-shaped power feeding roller 3, the rotating brush 5, the fixed plate 6, and the like as shown in FIGS. 3, 4, and 5, for example.
Alternatively, the fixed brush 7 may be used. The rotating brush 5 has a core body 5a.
Has a fixed layer 5a on its surface, and the fixed layer 5a is provided with a conductive brush 5c made of a yarn such as rayon containing carbon. The fixed plate 6 is formed of a conductive rubber elastic plate member 6b fixed to a holder 6a. The fixed brush 7 is composed of a conductive brush 7b fixed to a holder 7a.

Next, FIG. 6 shows an electrophotographic color image forming apparatus to which the transfer device of the first embodiment is applied.

In the color image forming apparatus, the above-mentioned transfer device is used as the belt transfer device 17. The transfer material carrier 2 formed in the shape of an annular belt is
It is rotationally driven by a pair of drive rollers 20 and 21.
Four process units 100a, 100b, 100c, and 100d are sequentially arranged on the upper flat surface of the transfer material carrier 2, and each of the process units 100a, 100b, 100c, and 100d is black, yellow, magenta, and
A toner image of each color of cyan is formed. Each of the four process units 100a, 100b, 100c, 100d has a similar structure, and is provided with a photoconductor drum 10a, 10b, 10c, 10d that rotates in the direction of the arrow, and a stainless steel drum is provided around them. A laser beam 12 is applied to the charging rollers 11a, 11b, 11c and 11d, which are charging devices, and the photosensitive drums 10a, 10b, 10c and 10d.
Laser optical systems 16a, 16b, 16c and 16d for irradiating a, 12b, 12c and 12d, respectively, and a developing device 13.
a, 13b, 13c, 13d, cleaners 14a, 14b, 14c, 14d using blades, and static elimination lamp 1
5a, 15b, 15c and 15d are arranged respectively. The developing devices 13a, 13b, 13c and 13d contain black, yellow, magenta and cyan developers, respectively.

Inside the transfer material carrier 2, four power supply rollers 19a, 19b, 1 corresponding to each process unit are provided.
Reference numerals 9c and 19d are provided to face the four photoconductor drums 10a, 10b, 10c, and 10d via the transfer material carrier 2, and the four power supply rollers press the photoconductor drums. Power feeding rollers 19a, 19b, 19c, 19d
Applies a transfer bias voltage to the transfer material carrier 2 at the transfer portion, which is the contact portion. Each power supply roller 19a, 1
9b, 19c, and 19d include power supply rollers 19a and 19
A constant current bias power source (not shown) for supplying a constant current is connected to each of b, 19c and 19d.

Each process unit 100a, 100b,
Cassette 24 provided on the upstream side of 100c and 100d
The transfer material P is stored therein, picked up by the paper feed roller 23, and supplied onto the transfer material carrier 2 at an appropriate timing by the pair of registration rollers 22.

The four process units 100a, 100b, 100c, and 100d provided for each color perform charging, exposure, and development, respectively, and each photosensitive drum 10
A toner image is formed on a, 10b, 10c, and 10d.
The formed toner image is carried by the transfer material carrier 18.
The transfer material P that is conveyed is sequentially and multiple-transferred. The transfer material P separated from the transfer material carrier 2 is a heat roller fixing device 2
5, the toner image on the transfer material P is fixed, and the toner image is discharged to the tray 26.

In the color image forming apparatus having a plurality of transfer portions having the above-described structure, the process units 100a, 100b, 100c, and 100d provided for each color are sequentially arranged on the photosensitive drums 10a, 10b, 10c, and 10d. Since a toner image is formed and the toner images are sequentially and multiple-transferred by passing the paper once, there is an advantage that a high-speed color image can be formed.

By applying the transfer device of the present invention to such a color image forming apparatus, transfer can be realized with high transfer efficiency without transfer unevenness or transfer omission in the transfer image of each color.

Using the above-described color image forming apparatus, four colors were multi-transferred in the order of black, yellow, magenta and cyan. The specifications of each device are as follows.

The transfer material carrier 2 is made of polyvinylidene fluoride mixed with an ionic conductive material and has a thickness of 14
The electrical resistance per 0 μm and 1 m ² in the thickness direction is about 10 ⁵ Ω at room temperature and normal humidity (21 ° C., 50% RH).
Also, four power supply rollers 19a, 19b, 19c, 19
d has conductive urethane foam on the outer periphery of the core, and has an electrical resistance of about 10 ¹ Ω per 1 m ² between the core and the surface.

The transfer efficiency with respect to the transfer current, that is, the transfer characteristic in this transfer device is shown in FIG.

As shown in FIG. 7, it can be seen that by increasing the transfer current sequentially according to the number of times of transfer, extremely high transfer efficiency can be obtained for each color in a wide transfer current range. This indicates that in the case of multiple transfer, the amount of toner transferred to the transfer material P increases each time the transfer is repeated, and accordingly, it is more efficient to increase the transfer current accordingly. Further, for each color, for the reasons described above, there is no partial transfer failure or transfer omission, and good constant transfer characteristics with respect to environmental changes can be obtained.

A transfer device according to the second embodiment of the present invention will be described below.

In the second embodiment, the structure of the transfer device is basically the same as that of the first embodiment, and the difference from the first embodiment is the method of applying the transfer bias of the transfer device. And specifications such as materials for each device. Therefore, the first
The description of the configuration similar to that of the embodiment is omitted.

The structure of the second embodiment is shown in FIG. 1 as in the first embodiment. In the second embodiment, unlike the first embodiment, the transfer material carrier 2 is formed of a 1 mm thick urethane elastomer in which carbon is dispersed,
The electric resistance per 1 m ^{2 in the} thickness direction is 10 ⁵ Ω, and the capacitance per 1 m ^{2 in the} thickness direction is 5 × 10 ^-8.
It is F.

Further, the bias power source 4 connected to the power feeding roller 3 is a bias power source which is charged to an ordinary negative polarity, unlike the constant current power source which maintains a constant output current in the first embodiment.

FIG. 8 is a graph showing the transfer characteristics when the electric resistance per 1 m ^{2 in} the thickness direction of the transfer material carrier 2 according to the second embodiment is variously changed, and the horizontal axis represents the transfer bias voltage and the vertical axis represents the transfer bias voltage. The axis shows the transfer efficiency. Transfer material carrier 2
The electric resistance of is adjusted by the amount of carbon dispersed in urethane rubber, and the electric resistance value is 10 ¹ , 10 ² , 10 ⁴ , 10
Experiments were performed for ⁶ and 10 ⁷ Ωm ² .

As is clear from this figure, when the electric resistance of the transfer material carrier 2 is as low as 10 ¹ Ωm, an electric charge is applied from the transfer material carrier 2 to the transfer material P, and this charge is further applied to the toner. Therefore, high transfer efficiency cannot be obtained because the charging polarity of the toner is reversed to the opposite polarity. Further, when the electric resistance of the transfer material carrier 2 is as high as 10 ⁷ Ωm, a high bias voltage is required to obtain a sufficient transfer electric field, and discharge easily occurs. Therefore, 1 m ^{2 in} the thickness direction of the transfer material carrier ²
The electric resistance of is preferably in the range of 10 ² to 10 ⁶ Ω.
The electric resistance in the thickness direction of the transfer material carrier 2 has the above-mentioned value depending on the change in the thickness of the transfer material carrier 2, the volume resistivity of the transfer material carrier 2, or both.

Further, in this embodiment, the electrostatic capacity of the transfer material carrier 2 is adjusted by changing the thickness of the polyurethane elastomer so as to be changed in the range of 7 × 10 ^-7 to 10 ^-8 F / m ² . As a result, the state of discharge in the minute air gap (the air layer formed by the transfer material carried on the transfer material carrier 2 and the toner carrier near the transfer portion) was examined. First, the possibility of discharge was examined by theoretical calculation, and then it was determined by experiment whether or not discharge was generated from the transferred image. In this case, the electric resistance value of the transfer material carrier 2 was 10 ⁵ Ωm ² , the relative dielectric constant was 5, and the transfer voltage was changed from 700 v to 2500 v.

9 and 10 show the results of theoretical calculation by solving the differential equation. 9 shows the case where the electrostatic capacity of the transfer material carrier 2 is large, and FIG. 10 shows the case where the electrostatic capacity is small. The horizontal axis represents the size (G1) of the air gap between the surface of the transfer material P and the surface of the photosensitive drum 1 in the transfer portion, and at this time, the transfer material P is the transfer material carrier 2
The toner image T is carried on the photosensitive drum 1 and is moved at the same speed as the photosensitive drum 1 carrying the toner image T. The size (G1) of this air gap is expressed in units of microns. The vertical axis represents the potential difference (V) between the surface of the transfer material P and the surface of the photosensitive drum 1.

Curve A in the figure represents a Paschen discharge curve in air at room temperature and pressure. Curves B1 and B in FIG.
2 (these curves are referred to as potential drop curves) show changes in the magnitude of the potential difference due to the air gap G1.
In the case of FIG. 9, the curves B1 and B2 contact the curve A at the gap G1 = about 100 microns and predict the possibility of discharge. B1 is the case where a high resistance transfer material having a specific resistance of 10 ¹⁵ Ωcm is used, and B2 is the case where a low resistance transfer material having a specific resistance of 10 ⁸ Ωcm is used. The former corresponds to the state of OHP paper, and the latter corresponds to the state of paper in a humid environment. Further, according to the experiment, when this transfer material carrier 2 was used, avatars (uneven density) after discharge were observed in the whole solid image (toner is uniformly spread on the entire surface of the transfer material). . In FIG. 10, the curves B1 ′ and B2 ′ are the same as the results of theoretical calculation, and the curves B1 ′ and B2 ′ are not in contact with the Paschen curve A and have lower potentials than the Paschen curve. Curve B1 ',
B2 'corresponds to the above-mentioned high resistance transfer material and low resistance transfer material, respectively. In the case of the curves B1 'and B2' in FIG. 10, it is theoretically predicted that no discharge will occur,
Even in the experiment, no density unevenness due to discharge was observed.

The experimental conditions are shown below.

Condition A Condition B Thickness of transfer material carrier 2: 100 μm 1 mm Electric resistance value of transfer material carrier 2: 10 ⁵ Ωm ² 10 ⁵ Ωm ² Capacitance of transfer material carrier 2: 7x10 ^{− 7} F / m ² 2x10 ^-8 F / m ² Process speed: 200 mm / sec 200 mm / sec Transfer voltage: 1200 v 1500 v Capacitance is greatly different between the above two conditions.
In this case, the slope of the potential drop curve is large under the condition that the capacitance is small. The reason for this is described below. Since the transfer material P is carried on the transfer material carrier 2 and is moved at the same speed as the photosensitive drum 1, the potential drop curve shows the relationship between the air gap and its potential difference, and the time from the front of the transfer portion. It is also the relationship between the course of and the potential difference. With the lapse of this time, charges are accumulated near the transfer portion on the surface of the moving transfer material carrier 2 and the potential at each time is determined.

FIG. 11 shows a model of this transcription. Vt is a transfer voltage, V1 is a potential difference of the transfer material carrier 2,
V2 is the potential difference of the transfer material, V3 is the potential difference of the air gap, V4 is the potential difference of the toner layer, and V5 is the potential difference of the photoconductor layer. This air gap is changed with time, and the larger the electrostatic capacity of the transfer material carrier 2 is, the smaller the rate of change of V1 with time. Therefore, the rate at which the potential difference in the air gap changes also decreases. As a result, the slope of the potential drop curve becomes smaller.

As described above, the slope of the potential drop curve of the air gap is a factor that determines whether or not discharge occurs near the transfer portion together with the magnitude of the transfer voltage. The capacitance of the transfer material carrier 2 is a major factor in determining the capacitance. As a result of examining the condition that the slope of the potential drop curve is larger than the slope of the Paschen's discharge curve when the electrostatic capacity of the transfer material carrier 2 is changed, 4 ×
It was shown by theoretical calculation that it is sufficient if it is 10 ⁻⁷ F / m ² or less, and it was also confirmed by experiments. If the electrostatic capacity of the transfer material carrier 2 is too small, the transfer voltage must be raised, and in order to maintain the transfer voltage of 2 kV or less, the electrostatic capacity is 2 × 10 ⁻⁸ F / m ² or more. It was confirmed by experiments that sufficient transfer can be carried out.

In the second embodiment, as the material used as the transfer material carrier 2 in which the electric resistance value and the electrostatic capacitance value are appropriately adjusted, in addition to the above-mentioned polyurethane elastomer in which carbon is dispersed, carbon or the like is used. Highly conductive dielectric sheet such as polycarbonate, polyimide, polytetrafluoroethylene (Teflon), etc., in which conductive particles are dispersed,
Alternatively, it may be a polymer film whose electric resistance value is adjusted by adjusting the composition without using conductive particles.

The bias applying means such as the power feeding roller 3 has a lower electric resistance value than the transfer material carrier 2 and has a sheet-like transfer material carrier 2 and the transfer material P, as in the first embodiment. Any means may be used as long as it can softly and uniformly press the photosensitive drum 1. Therefore, for example, the rotating brush 5, the fixed plate 6, and the fixed brush 7 as shown in FIGS. 3, 4, and 5 may be used.

Next, an electrophotographic color image forming apparatus to which the transfer device of the second embodiment is applied will be described.

The structure of the color image forming apparatus of the second embodiment is basically the same as that of the color image forming apparatus of the first embodiment, and the difference from the first embodiment is the transfer of the transfer device. It is a method of applying a bias power source, specifications of materials of each device, and a charger for charging the photosensitive drum. Therefore, the description of the same components as in the first embodiment will be omitted. Further, since the difference of the transfer device of the second embodiment provided in this color image forming apparatus has been described above, the description thereof will be omitted.

The structure of the color image forming apparatus of the second embodiment is shown in FIG. 6 as in the first embodiment. In this color image forming apparatus, the configuration other than the transfer device is different from that of the first embodiment in that corona chargers 11a and 11b are used instead of the charging rollers 11a, 11b, 11c and 11d which are chargers for charging the photosensitive drums. , 11c, 11d are arranged. This is because the charging state of the corona charger is less affected by environmental changes than the charging roller.

In the color image forming apparatus to which the transfer device of the second embodiment is applied, in each transfer image for each color,
It is possible to realize transfer with high transfer efficiency without uneven transfer or missing transfer. The transfer material carrier of this color image forming apparatus is a 1 mm thick polyurethane elastomer in which carbon is dispersed, and has an electric resistance of 10 ⁵ Ωm ² and a capacitance of 2 in the thickness direction.
× 10 ⁻⁸ F / m ² . Further, the four power supply rollers are provided with conductive urethane foam on the outer periphery of the core, and the electric resistance between the core and the surface is 10 ⁴ Ω. This second
The transfer efficiency with respect to the transfer bias voltage of the example is shown in FIG.

As shown in FIG. 12, by increasing the transfer bias voltage little by little according to the number of times of transfer, extremely high transfer efficiency can be obtained for each color in a wide transfer bias range. This indicates that, in the case of multiple transfer, the amount of toner transferred to the transfer material P increases as the transfer is repeated, and therefore it is more efficient to increase the transfer bias voltage accordingly. Further, for each color, for the reasons described above, there is no partial transfer failure or transfer omission, and good constant transfer characteristics with respect to environmental changes can be obtained.

In the color image forming apparatus of the second embodiment, the corona charger is used as the charger for charging the photosensitive drum, but it is obvious that a charging roller may be used instead of the corona charger as in the first embodiment. Is.

[0061]

According to the image forming apparatus of the present invention, since the transfer efficiency of the transfer device is stable even when the environment changes, a constant transfer efficiency can be obtained.

[Brief description of drawings]

FIG. 1 is a plan view showing a part of a transfer device according to an embodiment of the present invention.

FIG. 2 is a graph showing a relationship graph of transfer current and transfer efficiency in the transfer device according to the first embodiment of the present invention.

FIG. 3 is a plan view showing a first modification of the transfer device according to the present invention.

FIG. 4 is a plan view showing a second modification of the transfer device according to the present invention.

FIG. 5 is a plan view showing a third modification of the transfer device according to the present invention.

FIG. 6 is a plan view schematically showing a color image forming apparatus to which the transfer device of the present invention is applied.

FIG. 7 is a diagram showing a relationship graph of transfer current and transfer efficiency of the transfer device of the color image forming apparatus according to the first embodiment of the present invention.

FIG. 8 is a diagram showing a relationship graph of transfer bias voltage and transfer efficiency of the transfer device according to the second embodiment of the present invention.

FIG. 9 is a graph showing a relationship (by theoretical calculation) between a potential drop curve of an air layer and a Paschen discharge curve under conditions where a transfer failure image due to discharge is likely to appear.

FIG. 10 is a diagram showing a graph of a relationship (by theoretical calculation) between a potential drop curve of an air layer and a Paschen discharge curve under the condition that no discharge occurs.

FIG. 11 is a diagram showing a transcription model used for theoretical calculation.

FIG. 12 is a graph showing a relationship between transfer bias voltage and transfer efficiency of the color image forming apparatus according to the second embodiment.

FIG. 13 is a graph showing a relationship graph of transfer bias voltage and transfer efficiency of a transfer device of a comparative example in an experiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Photosensitive drum (image carrier) 2, ... Transfer material carrier, 3
... power supply roller, 4 ... bias power supply, 10a, 10b, 1
0c, 10d ... Photosensitive drums, 11a, 11b, 11
c, 11d ... Charging rollers, 13a, 13b, 13c, 1
3d ... Developer, 14a, 14b, 14c, 14d ... Cleaner, 15a, 15b, 15c, 15d ... Static elimination lamp,
16c, 16d, 16a, 16b ... Laser optical system, 17
... Belt transfer device, 19a, 19b, 19c, 19d ...
Power feeding roller, 20, 21 ... Driving roller, 22 ... Registration roller, 23 ... Paper feeding roller, 24 ... Cassette, 25 ... Heat roller fixing device, 26 ... Tray, 100a, 100
b, 100c, 100d ... Process unit, P ... Transfer material.

Claims (2)

[Claims] 1. A plurality of image forming means, which are respectively provided corresponding to a plurality of image carriers that are sequentially arranged and each form an image on each of the image carriers, and a semiconductive transfer material carrier. In addition, the transfer means that sequentially transfers the transfer material to each of the image carriers, and the constant current control that is provided corresponding to each of the image carriers and keeps the current constant, perform the transfer by the transfer means. And a plurality of transfer means for transferring the images formed on the respective image carriers to the transfer material to be transferred. 2. A plurality of image forming means, which are respectively provided corresponding to a plurality of image carriers that are sequentially arranged and each form an image on each image carrier, and electricity per 1 m ^{2 in} the thickness direction. Resistance is 10 ^{2 to} 10 ⁶
In addition to having a transfer material carrier having a capacitance of 2 × 10 ^{−8 to} 4 × 10 ⁻⁷ F per 1 m ² in the thickness direction with respect to each of the image carriers, Conveying means for sequentially conveying the transfer material, and the image forming means, which are provided corresponding to the respective image carriers, respectively, transfer the images formed on the respective image carriers to the transfer material conveyed by the conveying means. An image forming apparatus comprising: a plurality of transfer means.