JP3107664B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Conventionally, as a method of forming a full-color image on a transfer material such as paper, a method of forming a toner image on a photoreceptor as an image carrier and transferring the toner image to a transfer material by a predetermined method. 2. Description of the Related Art A color image forming apparatus that sequentially performs color image forming according to a color order has been put to practical use.

A transfer device in a color image forming apparatus of this type is configured such that 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 high-voltage power source, which is a non-contact type charger, is connected to the transfer section of the photoconductor, and a high voltage of 5 to 6 kV is applied to the transfer section of the photoconductor. Forming an electrostatic field by charging with a corona charger
The transfer of the toner image on the photoconductor charged to a predetermined polarity to a transfer material is performed a number of times corresponding to a predetermined color.

In the transfer device, since an insulating sheet capable of holding electric charges is used as the transfer material carrier, the surface of the transfer material carrier after the transfer material on which the toner image has been transferred is separated by a corona discharger or the like. There is a problem that a static elimination means for eliminating static electricity is required and ozone harmful to the human body is generated from the corona charger because the corona charger is used. Furthermore, in a color transfer apparatus of a color image forming apparatus for sequentially transferring 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. In recent years, human-friendly OA equipment has been required, and elimination of ozone generation is urgently required.

Therefore, as a transfer device that 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 section on the photoreceptor. A transfer device in which a bias voltage is applied to a non-surface by a bias voltage applying member has been proposed. (Japanese Patent Application No. 3-287861) In this transfer device, since a semiconductive sheet is used as a transfer material carrier, self-discharge can be performed, and there is no need for a means for removing the transfer material carrier.
Ozone is not generated at all because no corona charger is used.

However, in this transfer apparatus, 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 the change in the electrical resistance of the transfer material carrier and the transfer material due to the environmental change of humidity. For this reason, there is a problem that an image having a predetermined density cannot be obtained on the transfer material.

Further, when this transfer apparatus is applied to a transfer apparatus of a color image forming apparatus, the transfer efficiency of the toner image varies depending on the environment, and the transfer efficiency changes with an increase in the number of transfers in the multiple transfer. However, constant transfer efficiency cannot be obtained. That is, the characteristics of the transfer efficiency with respect to the transfer bias voltage change depending on the number of times of the multiple transfer. Therefore, in the multiple transfer, it is necessary to sequentially increase the charging potential as the number of transfers increases. However, when the charging potential becomes high, a discharge (ionization of air in a 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 due to partial transfer omission also occurs.

[0008]

As described above, in the above-described transfer device, the transfer efficiency changes depending on the environment, so that the image density changes, and further, the transfer efficiency changes depending on the number of transfers, so that the color reproduction can be performed. This is problematic in that good color images cannot be formed due to poor properties.

Accordingly, an object of the present invention is to provide an image forming apparatus provided with a transfer device capable of performing transfer at a constant transfer efficiency that is stable against environmental changes.

[0010]

An image forming apparatus according to the present invention corresponds to a plurality of image carriers which are sequentially arranged.
Provided to form an image on each of the image carriers
A plurality of image forming means and electricity per 1 m ^{2 in} the thickness direction
The resistance is in the range of 10 ^{2 to} 10 ⁶ Ω, and
Capacitance of 1 m ² per direction is 2 × ^{10 -8} to 4 × 1
0 ^-7 and has a ^F transfer material carrying member is in the range of, before
The transfer material is sequentially applied to each image carrier at 200 mm / sec.
Transport means for transporting at a speed of
Transfer material provided correspondingly and conveyed by the conveying means
The image formed on each of the image carriers is
And a plurality of transfer means for transferring.
You.

The image forming apparatus includes a plurality of image carriers which are sequentially arranged, and a plurality of images which are provided in correspondence with the respective image carriers and form images on the respective image carriers. The forming 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 capacitance per 1 m ^{2 in} the thickness direction is 2 × 10 ^{-8 to} 4 × 10 ^-7.
A transfer means having a transfer material carrier in the range of F, and transport means for sequentially transporting the transfer material to each of the image carriers, and provided corresponding to each image carrier, respectively, and transported by the transport means A plurality of transfer means for respectively transferring the images formed on the respective image carriers to the transfer material.

[0012]

According to the image forming apparatus of the present invention, transfer with high transfer efficiency without transfer unevenness and transfer omission in a transferred image can be performed.

[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 a transfer section of the transfer apparatus 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 to a negative polarity is formed on the photosensitive drum 1 by a known image forming process, and is driven to rotate in the direction of the arrow. A transfer material (paper) P is carried on a transfer material carrier 2 in the form of an annular belt, a part of which is illustrated, and is driven in the direction of the arrow at a speed equal to the peripheral speed of the photosensitive drum 1. It has become. Further, a power supply roller 3 constituting bias voltage applying means for applying a bias voltage to the transfer material carrier 2 is disposed on the back surface of the transfer material carrier 2.

The transfer material carrier 2 has a thickness of 140 μm,
Is formed by polyvinylidene fluoride ion conductive material is mixed, electrical resistance of 1 m ² per thickness direction normal temperature,
It is approximately 10 ⁵ Ω under normal humidity. This transfer material carrier 2
Are in contact with the photosensitive drum 1 at a predetermined nip width.

In this transfer device, the transfer material carrier 2
Is important. When the electric resistance per 1 m ^{2 in the} thickness direction becomes 10 ¹ Ω or less, a charge is applied from the transfer material carrier 2 to the transfer material P, and further this charge is applied to the toner. Since the charging polarity of the toner is reversed, the transfer efficiency is reduced. If the electrical 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 the transfer material P is separated from the photosensitive drum 1 after the transfer. Discharge occurs and transfer efficiency decreases.

The power supply roller 3 has appropriate elasticity, and the transfer material carrier 2 is moved from the back surface of the photosensitive drum so that the toner image T on the photosensitive drum 1 and the transfer material P come into contact with an appropriate pressure. 1, while rotating in the direction of the arrow. The power supply roller 3 has a configuration in which an elastic image 3b made of conductive urethane is provided on the outer periphery of a core 3a.
The electric resistance per 1 m ² between a and the surface of the elastic layer 3b is 10 ¹ Ω. A bias power supply 4 is connected to the metal core 3a, and the bias power supply 4 is a constant current power supply for maintaining a constant output current.

The power supply 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 against the photosensitive drum 1 from the back surface. 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 unit.

The following experiment was conducted in the transfer apparatus of the present invention. The experimental conditions are as follows. In the photoconductor drum 1, a 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 charged to a negative polarity, and an electrostatic latent image formed on the photosensitive drum 1 by charging and exposure is developed by negative polarity toner by reversal development. The width of the power supply roller 3 in the axial direction is 22 cm. The transfer material P is supplied in the vertical direction using A4 plain paper.

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

In the first experiment, a constant voltage was used to supply a constant voltage to the power supply roller 3 using a bias power source of a constant voltage, and the transfer characteristics depending on the environment were examined. The result is shown in FIG. FIG.
In the graph showing the transfer characteristics in three environments when a constant voltage bias power source is used, the horizontal axis shows the transfer bias voltage applied to the transfer material carrier by the power supply roller 3, and the vertical axis shows the transfer efficiency. .

As can be seen from this figure, the transfer bias voltage at which the transfer was good was shifted to the lower voltage side in the case of high temperature and high humidity, and significantly shifted to the high voltage side in the case of low temperature and low humidity. The reason for this is that the electric resistance of the transfer material carrier 2 and the transfer material P changes depending on the environment. Therefore, when a transfer charge, that is, a transfer current is applied to the transfer material carrier 2 by the power supply roller 3, the transfer material The transfer charge applied to the carrier 2 changes. For this reason, if the transfer charge becomes excessive, the transfer charge is applied from the transfer material carrier 2 to the transfer material P, causing transfer failure.

Next, a constant current was supplied to the power supply roller 3 using a bias power supply 4 having a constant current, 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 a constant-current bias power supply 4 is used. The horizontal axis shows the transfer current supplied to the power supply roller 3, and the vertical axis shows the transfer efficiency.

As is apparent from this figure, the use of the constant-current bias power supply 4 allows the transfer material carrier 2 and the transfer material P to be changed in three environments in which the electric resistance changes.
Since the transfer charge applied to the transfer material carrier 2 can be kept 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 such that the transfer current is It (A), the width of the power supply roller 3 in the axial direction is 1 (cm), The moving speed of the body 2 (equal to the peripheral speed of the photosensitive drum 1) is Vt (cm / s).
ec), qt = I / I · Vt (C / cm ² ).

In the present embodiment, the sheet-like transfer material carrier 2 adjusted to have an appropriate electric resistance is, in addition to the above-mentioned polyvinylidene fluoride mixed with the ionic conductive substance,
Conductive particles such as carbon dispersed in a high-resistance dielectric sheet such as polycarbonate, polyethylene terephthalate, polyimide, and polytetrafluoroethylene (Teflon), or a high-resistance material whose electric resistance is adjusted by adjusting the composition 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 a bias voltage,
It is appropriate that the sheet-like transfer material carrier 2 and the transfer material P can be softly and uniformly pressed against the photosensitive drum 1 with lower electric resistance than the transfer material carrier 2. Therefore, in addition to the roller-shaped power supply roller 3, for example, the rotating brush 5, the fixed plate 6, and the like as shown in FIGS.
Alternatively, the fixed brush 7 may be used. The rotating brush 5 has a core 5a.
Has a fixed layer 5a on the surface thereof, and a conductive brush 5c made of a thread such as rayon containing carbon is provided on the fixed layer 5a. The fixing plate 6 is formed of a conductive rubber elastic plate material 6b fixed to the holder 6a. The fixed brush 7 includes a conductive brush 7b fixed to a holder 7a.

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

In this color image forming apparatus, the above-described transfer device is used as the belt transfer device 17. The transfer material carrier 2 formed in an annular belt shape
It is rotationally driven by a pair of drive rollers 20 and 21.
On the upper flat surface of the transfer material carrier 2, four process units 100a, 100b, 100c, and 100d are sequentially arranged, and black, yellow, magenta, and
A toner image of each color of cyan is formed. Each of the four process units 100a, 100b, 100c, and 100d has the same configuration, and includes photoconductor drums 10a, 10b, 10c, and 10d that rotate in the directions of arrows, respectively. A charging roller 11a, 11b, 11c, 11d, which is a charger, and a laser beam 12 on the photosensitive drums 10a, 10b, 10c, 10d.
laser optical systems 16a, 16b, 16c, and 16d for irradiating the laser beams a, 12b, 12c, and 12d, respectively;
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 so as to face the four photosensitive drums 10a, 10b, 10c and 10d with the transfer material carrier 2 interposed therebetween, and the four power supply rollers press the photosensitive drums. Each power supply roller 19a, 19b, 19c, 19d
Applies a transfer bias voltage to the transfer material carrier 2 in a transfer portion that is a contact portion. Each feeding roller 19a, 1
9b, 19c, and 19d include power supply rollers 19a, 19
A constant current bias power supply (not shown) for supplying a constant current to each of b, 19c and 19d is connected.

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

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

In the color image forming apparatus having a plurality of transfer sections having the above-described configuration, the process units 100a, 100b, 100c, and 100d provided for each color are sequentially placed on the photosensitive drums 10a, 10b, 10c, and 10d. Since a toner image is formed and the toner image is sequentially multiplex-transferred with one pass of a paper, 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 a transfer image of each color.

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

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

FIG. 7 shows the transfer efficiency with respect to the transfer current in this transfer apparatus, that is, the transfer characteristics.

As shown in FIG. 7, it can be seen that by sequentially increasing the transfer current according to the number of transfers, extremely high transfer efficiency can be obtained for each color in a wide range of transfer current. 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, the transfer is more efficiently performed if the transfer current is increased accordingly. Further, for each color, there is no partial transfer failure or transfer omission for the above-mentioned reason, and good and constant transfer characteristics with respect to environmental changes can be obtained.

A transfer device according to a 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. The difference from the first embodiment lies in the method of applying a transfer bias of the transfer device. And specifications such as the material of each device. Therefore, the first
The description of the same configuration as 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 urethane elastomer having a thickness of 1 mm 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.

The bias power supply 4 connected to the power supply roller 3 is a bias power supply for charging to a normal negative polarity, unlike the constant current power supply for maintaining the output current constant in the first embodiment.

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

As is apparent from this figure, when the electric resistance of the transfer material carrier 2 is as low as 10 ¹ Ωm, a charge is applied from the transfer material carrier 2 to the transfer material P, and this charge is further transferred to the toner. And the charge polarity of the toner is reversed, so that high transfer efficiency cannot be obtained. 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 is likely to occur. Accordingly, 1 m ^{2 in} the thickness direction of the transfer material carrier ²
Is preferably in the range of 10 ² to 10 ⁶ Ω.
The electrical resistance in the thickness direction of the transfer material carrier 2 can be obtained by changing the thickness of the transfer material carrier 2, the volume resistivity of the transfer material carrier 2, or both.

In this embodiment, the capacitance of the transfer material carrier 2 is adjusted by changing the thickness of the polyurethane elastomer, and is changed in the range of 7 × 10 ⁻⁷ to 10 ⁻⁸ F / m ² . Thus, the state of discharge in a minute air gap (an air layer formed by the transfer material carried on the transfer material carrier 2 and the toner carrier near the transfer section) was examined. First, the possibility of discharge was examined by theoretical calculation, and then, it was determined by experiment whether or not discharge occurred 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.

FIGS. 9 and 10 show the results of theoretical calculations for solving differential equations. FIG. 9 shows a case where the capacitance of the transfer material carrier 2 is large, and FIG. 10 shows a case where the capacitance 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 section.
And is moving at the same speed as the photosensitive drum 1 carrying the toner image T. The size (G1) of this air gap is expressed in 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.

The curve A in the figure represents a Paschen discharge curve in air at normal temperature and normal pressure. Curves B1, B in FIG.
Reference numeral 2 (these curves are called potential drop curves) indicates a change in the magnitude of the potential difference due to the air gap G1.
In the case of FIG. 9, the curves B1 and B2 are in contact with the curve A where the gap G1 = about 100 microns, and predict the possibility of discharge. B1 is a case where a high-resistance transfer material having a specific resistance of 10 ¹⁵ Ωcm is used, and B2 is a 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. According to an experiment, when this transfer material carrier 2 was used, an avatar (density unevenness) after discharge was observed in all solid images (the toner was uniformly applied on the entire surface of the transfer material). . In FIG. 10, curves B1 'and B2' are the results of the theoretical calculation, and the curves B1 'and B2' do not touch the Paschen curve A and have a lower potential than the Paschen curve. Curve B1 ',
B2 'corresponds to the high-resistance transfer material and the low-resistance transfer material described above, respectively. In the case of the curves B1 'and B2' in FIG. 10, it is theoretically predicted that no discharge occurs,
No density unevenness due to discharge was observed in the experiment.

The experimental conditions are described 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: 7 × 10 ^{− 7} F / m ^{2 2} × 10 ⁻⁸ F / m ² Process speed: 200 mm / sec 200 mm / sec Transfer voltage: 1200 v 1500 v The difference between the above two conditions is the capacitance.
In this case, under the condition that the capacitance is small, the slope of the potential drop curve is large. The reason is described below. Since the transfer material P is carried on the transfer material carrier 2 and is being moved at the same speed as the photosensitive drum 1, the potential drop curve shows the relationship between the air gap and the potential difference and the time before the transfer section. And the potential difference. As this time elapses, charges are accumulated on the surface of the moving transfer material carrier 2 near the transfer portion, and the potential at each time is determined.

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

As described above, the slope of the potential drop curve of the air gap, together with the magnitude of the transfer voltage, is a factor in determining whether or not discharge occurs near the transfer portion. A major factor to determine is the capacitance of the transfer material carrier 2. As a result of examining the condition that the slope of the potential drop curve becomes larger than the slope of the Paschen's discharge curve when the capacitance of the transfer material carrier 2 is changed, 4 ×
The theoretical calculation shows that it should be less than 10 ^-7 F / m ² , 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 increased. To maintain the transfer voltage at 2 kV or less, the electrostatic capacity should be 2 × 10 ⁻⁸ F / m ² or more. It was confirmed by experiments that sufficient transfer could be performed if there was.

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

As in the first embodiment, the bias applying means such as the power supply roller 3 has a lower electric resistance value than the transfer material carrier 2 and has a sheet-like transfer material carrier 2 and a transfer material P. Any means can be used as long as it can press the photosensitive drum 1 softly and uniformly. 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. It is a method of applying a bias power supply, specifications of materials of each device, and a charger for charging the photosensitive drum. Therefore, description of the same components as in the first embodiment will be omitted. Further, the difference of the transfer device of the second embodiment provided in the color image forming apparatus is also described above, and thus the description is omitted.

The configuration of the color image forming apparatus according to 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 apparatus differs from the first embodiment in that corona chargers 11a, 11b are used instead of charging rollers 11a, 11b, 11c, 11d which are chargers for charging a photosensitive drum. , 11c and 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,
Transfer with high transfer efficiency without transfer unevenness and transfer omission can be realized. The transfer material carrier of this color image forming apparatus is a polyurethane elastomer having a thickness of 1 mm in which carbon is dispersed, and has an electrical resistance in the thickness direction of 10 ⁵ Ωm ² and a capacitance of 2 mm.
× 10 ⁻⁸ F / m ² . 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
FIG. 12 shows the transfer efficiency with respect to the transfer bias voltage in the embodiment.

As shown in FIG. 12, by gradually increasing the transfer bias voltage gradually according to the number of transfers, 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 when the transfer is repeated, so that the transfer is more efficiently performed by increasing the transfer bias voltage accordingly. Further, for each color, there is no partial transfer failure or transfer omission for the above-mentioned reason, and good and constant transfer characteristics with respect to environmental changes can be obtained.

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

[0061]

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

[Brief description of the 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 diagram showing a relationship graph between a transfer current and a 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 of the present invention.

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

FIG. 5 is a plan view showing a third modification of the transfer device of 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 between a transfer current and a 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 between a transfer bias voltage and a transfer efficiency of a transfer device according to a 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 a condition where a transfer failure image due to discharge easily appears.

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

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

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

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

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Photoreceptor 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 roller, 13a, 13b, 13c, 1
3d: developing device, 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 rollers, 20, 21 drive roller, 22 registration roller, 23 paper feed roller, 24 cassette, 25 heat roller fixing device, 26 tray, 100a, 100
b, 100c, 100d: process unit, P: transfer material.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-228179 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 15/16 G03G 15/01 114

Claims (1)

(57) [Claims] 1. A method according to claim 1 , wherein each of the plurality of image carriers is sequentially arranged.
The image is provided on each of the image carriers.
A plurality of image forming units to be formed, and an electric resistance per 1 m ^{2 in} a thickness direction is 10 ^{2 to} 10 ⁶
As well as a range of Omega, capacitively 1 m ² per thickness direction
Rolls having a capacity in the range of 2 × 10 ^{−8 to} 4 × 10 ⁻⁷ F
Having a copying material carrier, and
A transporter that transports the next transfer material at a speed of 200 mm / sec.
A step, and a corresponding one of the image carriers.
The transfer material conveyed by means is formed on each of the image carriers.
An image forming apparatus , comprising: a plurality of transfer units for respectively transferring formed images.