JP2001183919A - Roll transfer device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a roll transfer device which allows enhancing an efficiency in the case of bringing a transfer roll into contact with the surface of an image carrier and transferring a toner image from the surface of the image carrier to a recording medium and suppressing the scattering of toner. SOLUTION: An electrification member 5, an exposing member 6, a developing device 7, the roll transfer device 1 and a cleaning member 9 are disposed along the outer peripheral surface of a cylindrical photoreceptor 4. An electrostatic latent image 15 formed by the exposing member 6 is developed by the toner 14 supplied from the developing device 7. A toner image 16 is transferred onto the surface of a recording medium 3 by the roll transfer device 1. A transfer bias voltage is applied onto the transfer roll 10 from a power source 11. When resistance value of an electrical conductive elastic layer 10b is made to be 107-108 Ωcm, the transfer bias voltage V1 allowing the maximum transfer efficiency becomes equal approximately to the transfer bias voltage V2 allowing the minimum scattering of the toner 14 and, thus, an excellent picture can be obtained while enhancing the transfer efficiency.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a roller transfer device provided in an electrophotographic image forming apparatus or the like.

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic image forming apparatus, an electrostatic latent image is formed on a photoreceptor, developed with a toner, which is a charged developer, to form a toner image, and transferred to paper or the like. The image is transferred onto a transfer material to form an image on the transfer material. The transfer of the toner image from the surface of the image carrier such as the photoconductor to the transfer material is performed by a transfer device. As a transfer device, a corona discharger is arranged at an interval from the surface of the image carrier, and the toner is electrostatically applied to the back side of the transfer material while the surface of the transfer material is brought into close contact with the surface of the image carrier. Conventionally, a method of forming an electric field to be attracted by a corona discharger and transferring a toner image electrostatically attached to the surface of an image carrier to a transfer material surface to transfer the toner image has been known.

As a transfer device, a transfer roller made of a conductive elastic material is pressed against an image carrier, a transfer material is passed between the two, and a transfer voltage is applied to the transfer roller by applying a bias voltage having a polarity opposite to that of toner. Is also known. A transfer device using a transfer roller requires a much lower transfer bias voltage than a transfer device that uses a corona discharger, eliminates the generation of harmful corona products such as ozone and nitride, and stabilizes the transfer material. It has the advantage that it can be transported. On the other hand, in a transfer device using a transfer roller, a problem of toner scattering may occur due to the physical properties of the roller.

In a transfer device using a transfer roller, the transfer roller is pressed against the image carrier to form a portion called a transfer nip. When the transfer material passes through the nip portion, a charge is applied to the back surface of the transfer material by a bias voltage applied to the transfer roller, and transfer is performed by sucking toner from the image carrier. The potential of the surface of the image carrier is
There is a great difference between an image area where an image is formed by toner and a non-image area where no image is formed. For this reason, according to the bias applied to the transfer roller, the amount of electric charge applied to the back surface of the transfer material is significantly different between a portion corresponding to the image portion on the surface of the image carrier and a portion corresponding to the non-image portion. It is known. This is because the potential contrast between the transfer bias applied to the transfer roller and the surface potential of the image carrier is larger in the non-image portion than in the image portion, and the amount of charge applied to the back surface of the transfer material Also, the non-image portion is larger than the image portion. As a result, an electric field is formed on the transfer material passing through the transfer nip so that the toner moves from a portion corresponding to the image portion of the image carrier to a portion corresponding to the non-image portion of the image carrier, and an image is formed. The toner to be transferred to the portion corresponding to the image portion of the carrier scatters on the portion of the base, which is the portion corresponding to the non-image portion, causing bleeding in the image, reducing the reproducibility of fine lines, There is a problem that toner is scattered, which causes stains and significantly lowers the quality of the transferred image.

The prior art for solving such a problem of toner scattering is disclosed in, for example, JP-A-2-226283 and JP-A-3-21974.
Japanese Patent Laid-Open No. 226283/1990 discloses that the potential contrast between the transfer bias applied to the transfer member and the surface potential of the image portion of the image carrier is represented by A (V), and the transfer bias and the surface potential of the non-image portion of the image carrier. It is described that A: B is set to 1: 1.4 or less when a potential contrast with B is V (V). JP-A-3-21974 describes that the amount of charge applied to an image portion of a transfer material such as paper is represented by A (C / c
m ² ), and A ≧ B / 2 when the charge amount applied to the non-image portion is B (C / cm ² ).

In the transfer device, it is also important that the toner image formed on the image carrier is transferred as completely as possible onto the transfer material. The ratio of the toner image migrating from the surface of the image carrier to the surface of the transfer material is called transfer efficiency. If the transfer efficiency is low, the transfer of a sufficient image onto the transfer material is not performed, and the toner remains on the image carrier. However, if the state where the remaining toner adheres to the surface of the image carrier is continued, the toner is transferred onto the transfer material at an undesired timing, and the image is stained, thereby deteriorating the image quality. In order to avoid a decrease in image quality, it is necessary to sufficiently clean the surface of the image carrier. Therefore, it is also very important to improve the transfer efficiency, Japanese example No. Hei 5-107794, 10 ⁸ to 10
It is described that a transfer roller having a multilayer structure having a surface area of a volume resistivity of ¹² Ωcm can increase transfer efficiency. According to this publication, although the transfer efficiency can be increased by increasing the voltage applied to the transfer roller,
It is described that a discharge is caused when the applied voltage is too high. It is known that increasing the transfer efficiency can also improve the gradation of a solid portion in an image to be transferred.

[0007]

SUMMARY OF THE INVENTION The above-mentioned Japanese Patent Laid-Open No. 2-22
JP-A-6283 and JP-A-3-21974 disclose the potential contrast between the transfer bias and the surface potential between the image portion and the non-image portion, and the transfer material, for the purpose of suppressing toner scattering. Although the amount of charge applied to the back surface is specified, there is no description about transfer efficiency. Therefore, even if the image quality does not decrease due to the scattering of the toner, the image quality may decrease due to the decrease in the transfer efficiency, for example, the gradation of the solid portion may decrease.

Japanese Patent Application Laid-Open No. 5-107794 describes a resistance value of a transfer roller capable of increasing transfer efficiency.
Further, although it is described that a discharge occurs when the voltage applied to the transfer roller is excessively increased, it does not describe how much voltage is applied to cause the discharge and a relationship between the discharge and the resistance value. Therefore, although the transfer efficiency can be increased, there is a possibility that the image quality may be deteriorated due to the scattering of the toner.

An object of the present invention is to provide a roller transfer device capable of performing highly efficient transfer while suppressing toner scattering.

[0010]

According to the present invention, a transfer roller made of a conductive elastic member is partially pressed against an image carrier which electrostatically carries an image formed by a charged developer, and is formed by pressure contact. In a roller transfer device that transfers a sheet-like transfer material through a nip portion and applies a transfer bias voltage to a transfer roller to transfer an image formed by a developer from an image carrier to the transfer material, the transfer roller has a transfer efficiency of V1 ≧ V2, where V1 is the transfer bias voltage at the maximum and V2 is the transfer bias voltage at the time when the scattering area ratio is minimum in the applied voltage region higher than the maximum point of the scattering area ratio of the developer.
Is a transfer device having electrical characteristics satisfying the following relationship.

According to the present invention, the roller transfer device transfers an image with a charged developer from an image carrier to a transfer material. The image carrier electrostatically carries an image formed by a charged developer. The roller transfer device partially presses a transfer roller made of a conductive elastic member to an image carrier, passes a sheet-like transfer material through a nip portion formed by the pressure contact, and forms an image with a developer on the transfer material. Is transferred. A transfer bias voltage is applied to the transfer roller. The transfer efficiency changes depending on the transfer bias voltage, and the transfer bias voltage when the transfer efficiency is maximized is V1. The scattered area ratio of the developer corresponding to the scattered developer also changes more rapidly than the change in the transfer efficiency due to the transfer bias voltage. , It tends to increase gradually as the applied voltage increases. The transfer bias voltage at the smallest peak after the scattering area ratio reaches the largest peak is defined as V2. Since the transfer roller has electrical characteristics satisfying the relationship of V1 ≧ V2, the developer can be transferred in a state where the transfer efficiency is high and the scattering area ratio is small. When V1 <V2, the transfer bias voltage V1 when the transfer efficiency is maximized shifts to the side where the scattering area ratio sharply increases compared to the transfer bias voltage V2 when the scattering area ratio is minimized, and toner scattering occurs. This makes it impossible to increase the transfer efficiency while suppressing the transfer.

In the present invention, the transfer roller has a resistivity of 10 ⁷ Ωcm or more and 10 ¹⁰ Ωcm or less.

According to the present invention, the transfer bias voltage V1 at which the transfer efficiency is maximized is set substantially equal to the transfer bias voltage at which the scattering of the developer is minimized, or the transfer bias at which the scattering is sharply increased. Since the degree of scattering can be set to a side where the degree of scattering gradually increases instead of the direction of decreasing, the transfer efficiency of 85% or more can be ensured and the scattering of toner can be suppressed. By setting the upper limit of the resistivity, the occurrence of a discharge can be avoided.

In the present invention, the transfer roller has a resistivity of 10 ⁷ Ωcm or more and 10 ⁸ Ωcm or less.

According to the present invention, the resistivity of the transfer roller is
Transfer bias voltage V1 at which developer transfer efficiency is maximized
And the transfer bias voltage V at which the scattering rate of the developer is minimized.
2, the transfer efficiency can be maintained at 85% or more, and the scattering of the developer can be suppressed. In addition, the applied transfer bias voltage can be kept low, so that the roller transfer device can be formed in the most suitable state.

In the invention, it is preferable that a transfer nip passing time of the transfer material passing through the nip portion is 4 msec or more.

According to the present invention, since the transfer nip passage time of the transfer material passing through the nip portion where the image carrier and the transfer roller are pressed against each other is set to 4 msec or more, the developer from the image carrier to the transfer material is Can be sufficiently transferred, and a decrease in transfer efficiency can be avoided.

[0018]

FIG. 1 shows a schematic configuration of a roller transfer device 1 according to an embodiment of the present invention. The roller transfer device 1 functions as a part of an image forming device 2 that forms an image by an electrophotographic method. The image forming apparatus 2 forms an image on the surface of a sheet-like transfer material, for example, a recording medium such as recording paper. In the electrophotographic image forming apparatus 2, a cylindrical photoconductor 4 having an axis perpendicular to the paper surface of FIG. 1 and rotating in the direction of arrow A is provided.

The cylindrical photoconductor 4 rotates around an axis perpendicular to the plane of the drawing. Around the photoconductor 4, a charging member 5 for uniformly charging the surface of the photoconductor 4 along an arrow A direction, and an exposure member 6 for forming an electrostatic latent image on the surface of the photoconductor 4. A developing device 7 for visualizing the electrostatic latent image on the surface of the photoreceptor 4 with toner as a developer is disposed, and reaches the roller transfer device 1. In the image forming apparatus 2, after the toner image as the developer is transferred onto the recording medium 3 by the roller transfer device 1, the recording medium 3 is transported to the fixing member 8 to fix the toner image. The toner remaining on the surface of the photoconductor 4 without being transferred from the surface of the photoconductor 4 to the surface of the recording medium 3 by the roller transfer device 1 is located downstream of the roller transfer device 1 in the rotation direction of the photoconductor 4. Cleaning member 9 to be arranged
Removed by

The roller transfer device 1 is a semiconductive elastic transfer member, and has a transfer roller 10 arranged so as to be pressed against a part of the surface of the photoreceptor 4. The surface of the transfer roller 10 is compressed at a portion where the transfer roller 10 is pressed against the surface of the photoconductor 4, and a nip portion is formed along the outer periphery of the photoconductor 4 as a transfer portion where the photoconductor 4 and the transfer roller 10 contact. It is formed. With the rotation of the photoconductor 4, the recording medium 3 is transported in the direction of arrow B to pass through the nip portion at the timing when the toner image formed on the surface reaches the nip portion. The transfer roller 10 is operated by the power supply 11.
When a transfer bias voltage is applied to the toner, the toner on the surface of the photoconductor 4 is transferred to the surface of the recording medium 3. After the transfer, the recording medium 3 on which the toner image has been transferred is further transported in the direction of arrow B and reaches the fixing member 8. The photoconductor 4 is an OPC photoconductor in which a photoconductive layer 13 having a thickness of, for example, 20 μm is formed on an outer peripheral surface of a base material 12 made of a cylindrical metal, for example, aluminum, and has a dielectric constant εs of the photoconductive layer 13. Is 3
It is. The photoconductor 4 has a CGL layer and a CT on the aluminum tube 12.
A photosensitive layer 13 made of opc having an L layer laminated thereon is arranged, and has a cylindrical shape with an outer diameter of 35 mm. The CTL layer contains a phthalocyanine compound as a main component, and a CGL layer is formed by dispersing a hydrazone compound in polycarbonate.

The charging member 5 is constituted by a corona charger, which supplies a uniform charge to the surface of the photoreceptor and reduces the surface potential of the charging member to -60
A charging potential is supplied from a charging power supply (not shown) so as to be charged to 0V. The developing device 7 encapsulates a magnetic one-component toner 14 in which a magnetic powder is mixed into a vinyl resin. Inside the developing device 7, a sleeve 7a having a magnetic pole is disposed at a position opposing the photoconductor 4, and a toner layer is formed on the surface. The toner layer is formed by bringing a doctor blade 7b made of urethane into contact with the sleeve 7a to form a uniform layer, and applying a toner of -7 to -10 .mu.c to the toner 14.
/ G.

The transfer roller 10 is composed of an EPD as a conductive elastic layer 10b around, for example, a core 10a having a diameter of 8 mm.
The solid rubber of M is coated so as to have an outer diameter of 20 mm, and further covered with a coating layer 10c. As the conductive elastic layer 10b, conductivity is imparted by adding carbon black as an electronic conductive agent to EPDM solid rubber. By changing the addition amount of carbon black, 10
^One having six kinds of resistance values of ⁶ , 10 ⁷ , 10 ⁸ , 10 ⁹ , 10 ¹⁰ and 10 ¹¹ can be prepared. As the conductive elastic layer 10b, sponge rubber formed by foaming inside can be used instead of solid rubber of EPDM. The coating layer 10c is, for example, 50 to 80 μm
Use a thick fluororesin tube. An olefin tube may be used instead of the fluororesin tube.

The photoconductive layer 13 of the photoreceptor 4 is uniformly charged by the charging member 5 and then irradiated with an image-modulated laser beam by an exposing member 6 such as a laser scanner to form an electrostatic latent image 15. It is formed. Since the photoconductive layer 13 irradiated with the laser beam has a partially increased conductivity and loses the charged electric charge, the laser beam is image-modulated, so that the photoconductive layer 1 is modulated according to the density of the image.
The state of disappearance of the charge on the surface of No. 3 changes, and an electrostatic latent image 15 is formed. The toner 14 is formed by covering the surface of fine particles made of, for example, a phthalocyanine pigment with a thermoplastic resin, is stored inside the developing device 7, and is in a state of being charged with a certain polarity. When the charged toner 14 is brought into contact with the electrostatic latent image 15, the toner 14 adheres to the surface of the photoconductive layer 13 according to the charging pattern of the electrostatic latent image, and a toner image 16 is formed on the surface of the photoconductor 4. And the electrostatic latent image 1
5 is visualized. The toner image 16 is transferred onto the recording medium 3 passing through a nip portion 17 formed at a pressure contact portion between the photoconductor 4 and the transfer roller 10.

FIG. 2 shows the transfer bias voltage applied from the power source 11 to the transfer roller 10 when three resistance values of the conductive elastic layer 10b are used as the transfer roller 10, namely, 10 ⁶ , 10 ⁷ and 10 ^8. An example of test data obtained on the relationship between the transfer efficiency and the flying area ratio is shown. Photoconductor 4
The peripheral speed in the direction A, that is, the process speed as the conveying speed of the recording medium 3 in the direction B is 125 mm / sec, and 64 g paper is used as the recording medium 3 and the transfer nip passing time passing through the nip portion 17 is 6 mm. .5 msec. In FIG. 2, the solid line is the resistivity of 10 ⁶ Ωcm, and the broken line is 10 ⁷ Ωcm.
Ωcm and a conductive elastic layer 10b having a dotted line of 10 ⁸ Ωcm
The test results when using are shown below.

The upper curve in FIG. 2 shows the change in the transfer efficiency with respect to the transfer bias voltage, and the lower curve in FIG. 2 shows the change in the flying area ratio with the transfer bias voltage. Transfer bias voltages V1a, V1b, V1 at which the transfer efficiency is maximized are applied to the transfer roller 10 formed with each resistance value.
c exists. The change in the transfer efficiency changes relatively smoothly with respect to the change in the applied transfer bias voltage. The voltages V1a, V1b, and V1c at which the transfer efficiency is maximized inevitably increase as the resistance value of the conductive elastic layer 10b of the transfer roller 10 increases, and V1a <V1b <V1c. The transfer efficiency indicates the ratio of the amount of the toner 14 transferred from the surface of the photoconductor 4 to the surface of the recording medium 3 in the toner image 16 formed on the surface of the photoconductor 4.

FIG. 3 shows a method of calculating the scattering area ratio shown in FIG. As shown in FIG. 3A, a character "i" is formed as an image, and a square area 20 of, for example, 1 mm square is set next to the vertical bar portion of the character as shown in FIG. 3B. Then, it is calculated as the ratio of the area occupied by the toner scattered in the area 20. That is, the scatter area ratio is a value calculated by the following first equation.

[0027]

(Equation 1)

The scattering area ratio is 1 mm × 1 mm area 20
It is also possible to count the number of toners 14 inside and use that numerical value. This is because the partial area formed by the adhesion of each toner 14 is considered to be proportional to the number thereof. It is preferable that the scattering area ratio of the toner 14 is small.
As shown in FIG. 2, the scattering area ratio has a maximum value at a certain transfer bias voltage, and sharply decreases before and after the transfer bias voltage to a minimum value.

FIG. 3 shows the scattering area ratio. FIG.
The scattering area ratio is around the linear portion of the i character (1 square m
m) shows the ratio of the total area of the scattered toner aggregate existing in the area m). In the present embodiment, the scattering is measured using a nine-point i-character in the Mincho style as shown in FIG. 3, but the font and the number of points are not particularly limited. The value of the scattering area ratio varies depending on the font and size used for the measurement, or depending on the development conditions, etc. If the development conditions, etc. are within a common sense range, the characteristics shown in FIG. The relative relationship between the graph showing the scattering and the graph showing the scattering, in particular, its peak does not change. Furthermore, the so-called fog toner may be measured together with the scattered toner at the time of measurement, but this is usually not very small compared to the scattered toner, and the fog toner is usually constant regardless of the transfer potential, As long as the transfer does not affect the surface potential of the photoconductor or the charge of the toner in the developing device, it is constant,
The relative position of the graph showing the scattering in FIG. 2 with respect to the graph of the transfer efficiency does not change.

Therefore, from FIG. 2, the conductive elastic layer 10
The applied voltage V1a at which the transfer efficiency becomes maximum when the transfer roller 10 having a resistance value of b of 10 ⁶ Ωcm is used is 1.0
It can be seen that the applied voltage V2a at the right peak where the scattering area ratio is minimum is about 1.12 kV. As described above, when V1 is smaller than V2, the scattering area ratio is high when the transfer bias voltage that maximizes the transfer efficiency is applied, and when the transfer efficiency is increased, the image quality is deteriorated due to the scattering of toner. I will.

On the other hand, when the transfer roller 10 in which the resistance value of the conductive elastic layer 10b is 10 ⁷ Ωcm is used, the applied voltage V1b at which the transfer efficiency is maximized is about 1.4 kV, and the scattering area ratio is reduced. The applied voltage V2b at the minimum right peak is also about 1.4 kV. Such V1 and V2
In this relation, the scattering area ratio at the applied voltage at which the transfer efficiency is maximized is low, and transfer can be performed with high transfer efficiency while suppressing toner scattering.

The conductive elastic layer 10 having a resistance value of 10 ⁸ Ωcm
In the case of using the transfer roller 10 having b, the applied voltage V1c that maximizes the transfer efficiency is about 1.83 kV,
Applied voltage V2c at right peak when scattering area ratio is minimized
Is about 1.72 kV. Even in such a relationship between V1 and V2, the scattering area ratio at the applied voltage at which the transfer efficiency is maximized is in a low state, and transfer can be performed with high transfer efficiency while suppressing toner scattering. When the transfer roller 10 having a resistance value of the conductive elastic layer 10b of 10 ⁹ Ωcm or 10 ¹⁰ Ωcm is used, the applied voltage V1 at which the transfer efficiency is maximized is about 2.1 kV and 2.4 kV, and the scattering area The results show that the applied voltage V2 at the right peak when the rate is minimum is about 1.9 kV and 2.1 kV. That is, the resistance value of the conductive elastic layer 10b is 10 ⁷ Ω.
applied voltage V corresponding to the transfer roller 10 larger than
1 and the applied voltage V2 are as shown in Table 1 below.

[0033]

[Table 1]

Table 1 shows that the relationship between V1 and V2 tends to become larger than V2 as the resistance value of the conductive elastic layer 10b of the transfer roller 10 increases. Conversely, the resistance value of the conductive elastic layer 10b shown in FIG.
When V1 is larger than V2, as in the case of 0 ⁶ Ωcm, if the transfer bias voltage is set to V1 in order to increase the transfer efficiency, the scattering area ratio sharply increases and the scattering of toner cannot be suppressed. . On the other hand, if the transfer bias voltage is applied so as to suppress the toner scattering, the transfer efficiency cannot be maximized, and the transfer efficiency decreases. Accordingly, if the applied voltage at which the transfer efficiency is maximum is V1 and the applied voltage at which the scatter area ratio is minimum in the region of the applied voltage higher than the maximum point of the scatter area ratio is V2, V1 ≧ V2 is set. By doing so, it is possible to perform transfer with high efficiency and suppressed scattering, and it is possible to improve image quality.

As a result of the experiment, when the resistance value of the conductive elastic layer 10b of the transfer roller 10 exceeds 10 ¹¹ Ωcm, the applied voltage becomes high, so that abnormal discharge occurs and the transfer current becomes insufficient. In either case, the image quality is reduced. For this reason, as long as the conditional expression V1 ≧ V2 is satisfied and the image quality is not deteriorated due to abnormal discharge or the like, the resistance value of the transfer roller 10 is set to 10 ⁷ Ωcm to
It turns out that it is good to be 10 ¹⁰ Ωcm. Also, in this case, considering that the transfer bias voltage applied from the power supply 11 to the transfer roller 10 can be kept low, it is found that the transfer bias voltage is more preferably in the range of 10 ⁷ Ωcm to 10 ⁸ Ωcm.

FIG. 4 shows that the recording medium 3 is the nip portion 1 of FIG.
7 shows an example of data obtained on the relationship between the nip passage time passing through the transfer roller 7 and the transfer efficiency. The transfer roller 10 has a resistance value of 10 ⁷ Ωcm of the conductive elastic layer 10b, and the transit time of the nip portion 17 is 3 msec.
The results obtained by examining the relationship with the transfer efficiency while changing the values to 4.3 msec, 5.3 msec, and 6.5 msec are shown. FIG.
As can be seen from the figure, the longer the time passed through the nip portion 17, the higher the transfer efficiency. In a normal judgment, it is known that it is sufficient to secure the transfer efficiency of 85% or more, so that it is sufficient to set the nip passage time to 4 msec or more.

In the above description, the photosensitive member 4 as an image bearing member
Indicates a cylindrical shape, but the present invention can be similarly applied to other shapes such as an endless belt shape. The photoconductive layer 13 on the surface of the photoconductor 4
Material, toner 14 material, or transfer roller 10
The material of the conductive elastic layer 10b and the coating layer 10c is not limited to the described material, and the same kind of material can be used.

[0038]

As described above, according to the present invention, the transfer efficiency is close to the maximum by the transfer bias voltage applied to the transfer roller for transferring the developer from the image carrier to the transfer material, and the developer is scattered. The transfer can be performed in a state close to the minimum, and a high-quality developer image can be obtained on the transfer material.

Further, according to the present invention, it is possible to secure a transfer efficiency of 85% or more, suppress the scattering of the developer, and avoid a situation where a higher transfer bias voltage is applied to cause a discharge.

Further, according to the present invention, the voltage applied as the transfer bias voltage can be further reduced while the transfer efficiency is high and the scattering of the developer is suppressed.

Further, according to the present invention, a sufficient transfer of the developer from the image carrier to the transfer material can be performed while allowing sufficient time for the transfer material to pass through the transfer nip portion.

[Brief description of the drawings]

FIG. 1 is a simplified cross-sectional view showing a schematic configuration of an embodiment of the present invention.

FIG. 2 shows an example of a result obtained by measuring a relationship between a transfer bias voltage applied to a transfer roller 10 and a transfer efficiency and a toner scattering area ratio by changing the resistivity of the transfer roller 10 in the roller transfer device 1 of FIG. It is a graph shown.

FIG. 3 is a diagram showing a method of calculating a scattering area ratio shown in FIG.

FIG. 4 is a graph showing an example of an experimental result showing a relationship between a time required to pass through a nip portion and a transfer efficiency in the roller transfer device 1 of FIG.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 roller transfer device 2 image forming device 3 recording medium 4 photoreceptor 5 charging member 6 exposure member 7 developing device 8 fixing member 9 cleaning member 10 transfer roller 10b conductive elastic layer 11 power supply 13 photoconductive layer 14 toner 15 electrostatic latent image 16 toner image 17 nip

 ──────────────────────────────────────────────────の Continuing from the front page (72) Inventor Kokazu Kamei 22-22, Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (72) Inventor Hideki Onishi 22-22, Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Within Sharp Co., Ltd. (72) Inventor Hiroshi Doshoda 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka F-term within Sharp Co., Ltd. (reference) 2H032 AA05 CA02

Claims (4)

[Claims] 1. A transfer roller made of a conductive elastic member is partially pressed against an image carrier that electrostatically carries an image formed by a charged developer, and a sheet-like transfer is performed on a nip formed by the pressure contact. In a roller transfer device that passes a material and applies a transfer bias voltage to a transfer roller to transfer an image formed by a developer from an image carrier to a transfer material, the transfer roller uses a transfer bias voltage when the transfer efficiency is maximized. V1 and the transfer bias voltage when the scattering area ratio is minimized in the applied voltage region higher than the maximum point of the scattering area ratio of the developer is V2, and the electrical characteristics satisfying the relationship of V1 ≧ V2 are obtained. A transfer device, comprising: 2. The transfer roller has a resistivity of 10 ⁷ Ωc.
2. The roller transfer device according to claim 1, wherein the transfer resistance is not less than m and not more than 10 ¹⁰ Ωcm. 3. The transfer roller has a resistivity of 10 ⁷ Ωc.
2. The roller transfer apparatus according to claim 1, wherein the transfer resistance is not less than m and not more than 10 ⁸ Ωcm. 4. The roller transfer device according to claim 1, wherein a transfer nip passage time for the transfer material to pass through the nip portion is 4 msec or more.