JPH11109768A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To always obtain a stabilized transferred image having high quality by applying a current optimum for transfer regardless of transfer roller resistance, an image forming mode, a transfer material size or the like. SOLUTION: A transfer roller 9 is formed of an ionic conductive solid roller, and circumferential unevenness is set to be <=1.5, and surface roughness is set to be <=Ra=0.5, and a constant current value is changed by a transfer bias applying means 20 so as to secure a current value optimum for the transfer corresponding to a roller resistance value. Thus, an excellent image is obtained by preventing defective transfer, burst and scattering and penetration or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine and a laser beam printer.

[0002]

2. Description of the Related Art An image forming apparatus such as an electrophotographic copying machine or a laser beam printer generally includes a drum type electrophotographic photosensitive member (hereinafter, referred to as a "photosensitive drum") as an image bearing member. A transferable image (hereinafter, referred to as a “toner image”) corresponding to target image information is formed in each of the image forming processes of exposure and development, and the toner image is transferred to a transfer material such as paper by a transfer unit. The toner image is fixed by a fixing unit to obtain an image-formed product. On the other hand, the transfer residual toner remaining on the surface of the photosensitive drum after the transfer of the toner image is removed by the cleaning unit, and is used for the next image formation.

The transfer means described above has recently been of the contact type.
Rotary transfer members, which use a so-called transfer roller, are frequently used. The transfer roller is disposed in contact with the photosensitive drum and forms a transfer nip between the transfer roller and the photosensitive drum.
Further, a transfer bias is applied to the transfer roller. The transfer material is nipped and conveyed at the transfer nip, and a transfer bias is applied to the transfer roller, so that the toner image on the photosensitive drum is transferred to the surface. According to the transfer means using the transfer roller, there is an advantage that the transfer path of the transfer material is simplified, and the transfer of the transfer material is stabilized.

The above-mentioned transfer roller has a resistance value of 1 × 1.
0 is adjusted to ⁶ to 1 × 10 about ¹⁰ Omega value, but the transfer roller 16 which has been proposed in recent years, as shown in FIG. 7, an elastic layer 18 provided on the outer peripheral surface of the conductive core metal 17, The elastic layer 18 has conductivity. The transfer roller 16 is roughly classified into the following two types according to the manner of imparting the conductivity. Transfer roller having an electronic conductive system A transfer roller having an ionic conductive system is obtained by dispersing a conductive filler in an elastic layer 18. Examples of the transfer roller include an EPDM roller and a urethane in which a conductive filler such as carbon or metal oxide is dispersed. Rollers can be mentioned.

The elastic layer 18 contains an ion conductive material. Examples of the elastic layer 18 include a material made of a material such as urethane having conductivity, and a material obtained by dispersing a surfactant in the elastic layer 18. Can be

It is known that the resistance of the transfer roller 16 is apt to fluctuate in accordance with the temperature and humidity of the atmosphere environment.
There is a possibility that explosion may be scattered or paper marks may be generated.

Therefore, in order to prevent the occurrence of transfer defects and paper marks due to the fluctuation of the resistance of the transfer roller, the resistance value of the transfer roller is measured, and the transfer voltage applied to the transfer roller is changed according to the measurement result. In some cases, “applied transfer voltage control” for appropriately controlling the voltage is adopted (for example, Japanese Patent Laid-Open No.
ATVC control disclosed in JP-A-123385 (Ac
tive Transfer Voltage Control)).

The ATVC control is a means for optimizing a transfer bias applied to a transfer roller at the time of transfer, and is designed to prevent a transfer failure and the occurrence of paper marks. The transfer bias described above applies a desired constant current bias from the transfer roller to the photosensitive drum during the pre-rotation step of the image forming apparatus, detects the resistance of the transfer roller from the bias value at that time, and sets the resistance as a transfer bias during transfer. A constant voltage bias corresponding to the value is applied to the transfer roller.

In the above-mentioned ATVC control, a constant voltage bias is applied as a transfer bias. However, in order to realize better transfer characteristics, a constant current bias may be applied as a transfer bias.

However, in the transfer roller of the electronic conductive system, the resistance unevenness in the rotation direction of the transfer roller (hereinafter referred to as “circumferential unevenness”).
), The resistance unevenness in the longitudinal direction (hereinafter referred to as “longitudinal unevenness”) is good in measurement (circumferential unevenness 1.5 or less, longitudinal unevenness 2.
0 or less), a discharge of a transfer bias occurs in a very small area on the surface of the transfer roller at the time of transfer, and the applied constant current flows intensively, thereby causing paper marks, sand, and the like. If the flow does not flow, a transfer failure or the like occurs, so that constant current control cannot be realized.

On the other hand, an ion-conductive transfer roller has a structure in which longitudinal unevenness and circumferential unevenness are good and discharge does not occur in a small area, and constant current control of the transfer roller is possible. Hereinafter, an example in which an image is formed with an ion conductive transfer roller will be described as a conventional example. The material of the transfer roller is N
It is a solid roller made of BR rubber, in which NBR rubber has resistance. The circumferential unevenness of the transfer roller was 1.15, and the surface roughness was Ra = 3.5 (μm). The transfer roller resistance is normal temperature and normal humidity N / N (24 ° C., 65% RH)
1.0 × 10 ⁷ with 2.0 kV applied
(Ω) and 1.0 × 10 ⁸ (Ω).

[0012]

However, when an image is output using the transfer roller shown in the conventional example, the following problem has been encountered. (1) Generation of transfer failure due to image forming environment This is due to the fact that the optimum transfer current value of the transfer roller differs for each roller resistance. For example, an optimal transfer current value is determined on the high resistance side of the roller resistance using an ion conductive transfer roller, and this is set to A (μA), and this value is set as a transfer constant current bias at the time of image formation. Here, when an image was output at A (μA) using a low-resistance transfer roller, transfer failure and explosion scattering occurred. At this time, the optimum transfer current value of the low resistance roller is B (μA),
A <B, and it was found that the optimum transfer current value was higher for the low resistance roller.

Considering the reason, when compared with the transfer roller composed of an electronic conductive dispersion type sponge, the ion conductive transfer roller has better resistance unevenness and does not generate sand, paper marks, etc. Was possible. However, when the roller resistance is low, even if the longitudinal unevenness and the peripheral unevenness of the roller resistance are small with the measuring tool, there are the peripheral unevenness and the longitudinal unevenness that cannot be observed with the measuring tool or the like in the minute area of the roller surface, and the lower resistance portion. Transfer current flows in the other portions, and in other portions, the current is insufficient, resulting in poor transfer, explosion and scattering, and the like. Conversely, when the high-resistance roller is used at the optimum transfer current value B on the low-resistance side, no explosion scattering occurs, but the applied bias is increased, so that even the high-resistance roller transfers at a low-resistance portion with a small area. Discharge of current occurs, and images such as uneven discharge and sandy ground occur in the halftone image. Therefore, the optimum transfer current value is larger for the low-resistance roller and smaller for the high-resistance roller. (2) Occurrence of Transfer Failure Due to Print Mode When images were formed on both surfaces of a transfer material using the transfer roller described in the conventional example, transfer failure occurred. This is because the optimum transfer current value differs between single-sided image formation and double-sided image formation. That is, at the time of double-sided image formation, the transfer material at the time of single-sided image formation is heated once by passing through the fixing nip of the fixing device, and the resistance thereof increases.
This is because a value D (μA) (C <D) larger than the optimum transfer current C (μA) at the time of single-sided image formation is required. (3) Occurrence of transfer failure due to transfer material size difference This is because when a constant current bias is applied to the transfer roller and the toner image on the photosensitive drum is transferred to the transfer material, the transfer current is transferred through the transfer material. The transfer current for transferring the toner image via the transfer material is reduced because the transfer roller concentrates on the portion facing the photosensitive drum without the transfer material, rather than via the transfer material. Occurs in
For example, when the A4 size (296 mm × 210 mm) is vertically fed (210 mm is the leading edge), the transfer current value is the optimum value E (μA), and the B5 size (257 mm × 182 mm)
When the image was formed by feeding vertically (182 mm at the top), transfer failure occurred. At this time, the optimal transfer current value F (μA) in the B5 vertical direction was a value larger than E (F> E). The above-mentioned phenomenon is remarkable when a transfer material of a smaller size (for example, an envelope, a postcard, etc.) is used. In order to solve this, when the transfer constant current value is further increased,
Excessive current flowed through the drum abutting portion of the non-sheet passing portion, a drum memory was generated, and a paper mark image (fogged image on a white background portion) was output when an A4 vertical image was formed next. Therefore, good images could not be formed without explosion and splattering, paper marks, sandy ground, and the like occurring in all transfer material widths. (4) Generation of Transfer Material Tip, Transfer Failure, Explosion Scattering This is caused by the rise of the high-voltage power supply for applying the transfer constant current bias. In order to solve this problem with a high voltage power supply, problems such as an increase in cost of the high voltage power supply occur.

In view of the above, the present invention solves the above-mentioned problems in an ion-conductive solid transfer roller, and provides an optimum transfer current regardless of the transfer roller resistance, image forming mode, transfer material size, etc., so that the transfer is always stable. It is an object of the present invention to provide an image forming apparatus capable of obtaining a high quality transferred image.

[0015]

According to the first aspect of the present invention, there is provided an image carrier having a surface on which a toner image is formed, and a transfer member disposed in contact with the surface of the image carrier to form a transfer nip portion. Transfer bias applying means for applying a transfer bias to the transfer member, and applying the transfer bias to the transfer member by the transfer bias applying means while nipping and conveying the transfer material at the transfer nip portion. In the image forming apparatus for transferring the toner image on the surface of the carrier to the surface of the transfer material, the transfer member is a roller having ionic conductivity, the transfer bias applying unit is a constant current bias, and It is characterized in that a resistance value is detected and a constant current value of a constant current bias is switched according to the detected resistance value.

According to a second aspect of the present invention, the transfer roller is a solid roller, the circumferential resistance distribution on the outer peripheral surface of the transfer roller is 1.5 or less, and the surface roughness is Ra = 5. 0.0 (μm) or less.

According to a third aspect of the present invention, the transfer bias applying means switches the constant current value according to an image forming mode.

According to a fourth aspect of the present invention, the transfer bias applying means switches the constant current value according to the size of the transfer material.

According to a fifth aspect of the present invention, the transfer bias applying means is means for applying at least one of a constant current bias and a constant voltage bias, and the constant current bias depends on the size of the transfer material. At least one of a value and a constant voltage value.

According to a sixth aspect of the present invention, the transfer bias applying means corrects a constant current value before the leading end of the transfer material reaches the transfer nip portion.

[Operation] The main operation (operation corresponding to claim 1) based on the above configuration is as follows.

An optimum transfer current in accordance with the resistance value of the transfer member can be secured, and the occurrence of poor transfer, explosion and scattering, and the like can be prevented, and a good image can be output.

[0023]

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

<First Embodiment> FIG. 1 is a longitudinal sectional view showing a schematic configuration of an image forming apparatus according to a first embodiment.
The image forming apparatus shown in FIG. 1 is a laser beam printer capable of performing double-sided and multiple printing by applying an electrophotographic process.
The transfer roller 9 is a roller made of an ion conductive solid rubber, has a peripheral unevenness of 1.5 or less, and has a roller surface roughness Ra.
= 5.0 (μm) or less, normal temperature and normal humidity N / N (24 ° C., 65
% RH) and the resistance value when applying 2 kV is 4 as shown in FIG.
I used a book. In the first embodiment, an image forming process of single-sided printing (image formation) will be described first. (1) Image Forming Process The image forming apparatus shown in FIG. 1 includes a drum-type electrophotographic photosensitive member (hereinafter, referred to as “photosensitive drum”) 1 as an image carrier. The photosensitive drum 1 is rotationally driven at a predetermined peripheral speed (process speed) in a direction of an arrow R1 by a driving unit (not shown). Reference numeral 2 denotes a charging member, such as a charging roller, which is arranged in contact with the surface of the photosensitive drum 1, and the surface of the photosensitive drum 1 is primarily charged to a predetermined polarity and a predetermined potential by the charging member 2. Reference numeral 3 denotes a laser beam scanner as an image exposure unit, which outputs a laser beam L on / off modulated in accordance with image information input from an external device such as an image scanner or a computer (not shown), Scanning exposure is performed on the charged surface of the surface. By this scanning exposure, an electrostatic latent image corresponding to the target image information is formed on the surface of the photosensitive drum 1.

Reference numeral 4 denotes a developing device which applies a developer (toner) to the electrostatic latent image on the surface of the photosensitive drum 1 by a developing sleeve 4a.
Is adhered, and the electrostatic latent image is developed (visualized) as a toner image.
Is done. In the case of a laser beam printer, a reversal development system is generally used in which toner is adhered to an exposed portion of an electrostatic latent image and developed.

Reference numeral 5 denotes a paper feed cassette, which is a transfer material P such as paper.
Is stored. The paper feed roller 6 is driven based on the paper feed start signal, one sheet of the transfer material P in the paper feed cassette 5 is fed, and the photosensitive drum 1 and the transfer roller 9 pass through the registration roller 7 and the paper path 8a. Is introduced into a transfer site (transfer nip portion) T, which is a contact nip portion, with a predetermined timing. That is, the transfer of the transfer material P is controlled by the registration roller 7 so that the timing at which the leading end of the toner image on the photosensitive drum 1 reaches the transfer portion T is reached.

The transfer material P introduced into the transfer portion T is conveyed while nipping the transfer portion T. At this time, a constant current bias (transfer bias) controlled in a predetermined manner from the transfer bias applying means 20 is applied to the transfer roller 9. You. The transfer roller 9 and the transfer bias control will be described in detail in the following section (2). By applying a transfer bias having a polarity opposite to that of the toner to the transfer roller 9, the toner image on the surface of the photosensitive drum 1 is electrostatically transferred to the surface of the transfer material P at the transfer portion T.

The transfer material P to which the toner image has been transferred at the transfer portion T is conveyed separately from the surface of the photosensitive drum 1 and conveyed to the fixing device 11 through the paper path 8b, where the toner image is heated and pressed. Settled on the surface.

On the other hand, after the transfer material is separated, the transfer residual toner and paper dust remaining on the surface of the photosensitive drum 1 are removed by the cleaning device 10.
And is subjected to the next image formation.

When the "single-sided printing mode" is selected, the transfer material P that has passed through the fixing device 11 is guided to the paper path 8c side by the first flapper 12 that has been switched to the first position, and is discharged. The paper is discharged from the opening 13 onto the paper discharge tray 14. (2) Transfer Roller 9 and Transfer Bias Control The transfer roller 9 as a contact-type / rotation-type transfer member is an ion-conductive solid roller, which reacts NBR rubber with a surfactant and the like, and has a circumferential unevenness of 1.5 or less. , Surface roughness Ra =
A roller made of 5.0 (μm) shown in FIG. 8 was used.
9a is a solid rubber layer, 9b is a metal core.

FIG. 2 is a schematic diagram of the above-described resistance measuring device for the transfer roller 9. That is, the transfer roller 9 is pressed against the rotatably driven aluminum drum 1A at a contact pressure of 1.5 kg and is driven to rotate, and 2.0 kV is applied between the core 9b and the ground by the bias applying power source E to The resistance was calculated by measuring the current flowing through 1A with the ammeter A.
Further, in the above measurement, a current value when the transfer roller 9 was rotated once or more was sampled, and a roller resistance was calculated from an average value of the sampled values.

The sampling current value and the maximum value are represented by I
_{If MAX} and the minimum value are I _MIN , as in the conventional example, I _MAX
The transfer roller 9 _satisfies / I _MIN ≦ 1.5, that is, the transfer roller 9 whose resistance unevenness (circumferential unevenness) in the rotation direction is 1.5 or less. In addition, the surface roughness of the transfer roller 9 is Ra = 5.0 (μm) or less. FIG. 3 shows a VR curve (voltage-resistance curve) of the transfer roller 9 measured by the measuring device of FIG.

The transfer bias control will be described below.

In the transfer step, a constant current bias is applied to the transfer roller 9 as a transfer bias. Here, FIG.
The constant current value of the constant current bias is switched according to the resistance value of the transfer roller 9 as shown in FIG. The transfer current value differs depending on the transfer roller resistance, and the optimum transfer current value is small at high resistance and large at low resistance. FIG. 4 shows the relationship between the transfer roller resistance and the optimum transfer current value I shown in FIG. The reason that the optimum transfer current value does not change linearly with the change in resistance is that the higher the resistance becomes, the higher the voltage value for applying the current becomes, and the toner image on the surface of the photosensitive drum 1 is transferred even by the action of this high electric field. Since the current is transferred to the material P, the current becomes small.

As described in the problem (1), the transfer roller 9 has a low resistance in order to prevent poor transfer and explosion due to uneven resistance in a small area which cannot be measured by the measuring device shown in FIG. In this case, the optimum transfer current value becomes large, and when the resistance is high, it becomes small. The transfer roller resistance range and the optimum transfer current value vary depending on the process speed, the photosensitive drum length, the transfer material width, and the like. In the first embodiment, the process speed is 50 mm / sec, the photosensitive drum length is 260 mm, and the transfer material width is A4 length 210 mm. explained.

Next, means for detecting the transfer roller resistance and determining the constant current value of the transfer constant current bias at that time will be described. As in the ATVC control, the resistance detection and the determination of the constant current value are performed during the pre-rotation process of the image forming apparatus. In this method, a constant voltage bias is applied to the transfer roller 9, a current value flowing through the photosensitive drum 1 at that time is detected, and a resistance value is detected from an IR curve (current-resistance curve) as shown in FIG. And determine the constant current value. A constant current bias is applied to the transfer roller 9, and a voltage flowing through the photosensitive drum 1 at that time is detected.
-A constant current value is determined by detecting a resistance value from the R curve. Is mentioned.

In these methods, by applying a bias to the transfer roller 9 with an external bias to the image forming apparatus main body and knowing the VI and VR curves of the actual machine, an accurate control formula (constant current value) is obtained. Is determined.

As described above, with the ion-conductive solid transfer roller 9, the peripheral unevenness is 1.5 or less, and the surface roughness Ra is
= 0.5 or less, and in the image forming apparatus in which a constant current is applied with a transfer bias, by changing the constant current value so as to secure an optimum transfer current value corresponding to each roller resistance value, transfer failure and explosion scattering occur. , Penetration and the like can be prevented, and a good image can be obtained.

<Second Embodiment> In the above-described first embodiment, in an image forming apparatus that performs single-sided printing, the transfer bias constant current value is switched according to the transfer roller resistance value to secure the optimum transfer current. A good image could be output.
However, when double-sided, multiple printing was performed, transfer failure and explosion scattering occurred on the second side image.

Therefore, a second embodiment will be described below.

FIG. 6 is a longitudinal sectional view showing a schematic configuration of an image forming apparatus according to the second embodiment. The configuration for printing on one side of the transfer material P is the same as that of the image forming apparatus shown in FIG. 1 described above, and a duplicate description thereof will be omitted.

First, the image forming process in the duplex printing mode will be described. In FIG. 6, when the “double-sided printing mode” is selected, the transfer material P having been printed on one side after passing through the fixing device 11 is transferred to the paper path 8 d by the first flapper 12 switched to the second position. Path 8g (switchback section) by the switchback roller pair 8f which is guided to the paper path 8e side by the second flapper 15 which is further switched to the first posture and is forwardly driven. It is carried into. After the rear end of the conveyed transfer material P has passed through the second flapper 15, the switchback roller pair 8
f before the switchback roller pair 8f
Is switched to the reverse rotation drive, the second flapper 15 is switched to the second position, the transfer material P in the paper path 8g is drawn out and conveyed, and is introduced from the paper path 8h to the paper path 8i in a reversed state. Then, the second side of the transfer material P is re-input into the transfer portion T in the path of the paper path 8k, the registration roller 7, and the paper path 8a, and the toner image is transferred to the second side of the transfer material P. Is re-introduced into the first position, the fixing process is performed on the second side, and the first position is switched to the first position.
The paper is guided by the flapper 12 toward the paper path 8c, and is discharged from the paper discharge port 13 onto the paper discharge tray 14 as a double-sided printed product (both sides printed).

When the "multiple printing" mode is selected, the transfer material P having been printed on one side after passing through the fixing device 11 is moved toward the paper path 8d by the first flapper 12 switched to the second position. The path is guided to the paper path 8j by the second flapper 15, which is further guided to the third position, and is introduced into the paper path 8i without being reversed. Then, the paper path 8k, the registration roller 7, and the paper path 8a are re-introduced to the transfer portion T along the path, and are superimposed on the one-sided printing for 2 hours.
Upon receiving the re-transfer of the toner image on the surface, a multiple print image is discharged in the same manner as in the above-described steps.

The transfer roller 9 is an ion conductive solid rubber roller having the same structure as that of the first embodiment. The transfer roller 9 has a peripheral unevenness of 1.5 or less, a surface roughness Ra of 5.0 (μm) or less, and a resistance of The one shown in FIG. 8 was used.

The transfer roller control switches the constant current value of the transfer bias according to the transfer roller resistance as shown in FIG.
Further, it is set to be larger than during single-sided printing (see FIG. 8). The transfer roller resistance value detection and the optimum transfer current value are determined by the same means as in the first embodiment.

With this, when performing double-sided and multiple printing, once,
Even if the resistance rises due to the transfer material P passing through the fixing device 11, a transfer current enough to compensate for the increase during re-transfer can be secured, so that a good image can be output without occurrence of transfer failure, explosion scattering, etc. .

As described above, with the ion-conductive solid transfer roller 9, the peripheral unevenness is 1.5 or less, and the surface roughness Ra is
= 5.0 (μm) and the transfer bias is a constant current, so that an appropriate transfer current can be secured more stably than an electronic conductive roller for constant voltage printing, and high quality can be achieved regardless of the roller resistance. Can provide a perfect image.

<Third Embodiment> With the image forming apparatus capable of performing double-sided printing and multiple printing described in FIG. 6 of the second embodiment, a good image can be output in A4 portrait printing. However, when the B5 size was printed by vertical feeding (182 mm width), poor transfer and explosion scattering occurred.

Therefore, a third embodiment will be described below.

The configuration of the image forming apparatus is the same as that of the second embodiment shown in FIG. As shown in FIG. 10, in the transfer bias control, the transfer bias constant current value is set to be larger than the A4 size when the B5 size paper is passed. A4 from this
In a B5 vertical size having a transfer material width shorter than the vertical size by 28 mm, even when a current flows directly into the photosensitive drum 1 when a constant current bias is applied, a sufficient transfer current can be secured via the transfer material P, resulting in poor transfer, explosion scattering, etc. The occurrence can be prevented and a good image can be output. The constant current value of the small-size transfer material according to the third embodiment is obtained by detecting the transfer roller resistance in the pre-rotation step, and then determining the constant current value according to the used transfer material size, print mode, and roller resistance value, as in the second embodiment. Can be determined.

The constant current value according to the transfer material size is A
It can be set arbitrarily according to the size of the transfer material such as a series, a B series, and overseas paper (letter size, legal size, etc.).

As described above, it is possible to obtain a good image regardless of the transfer material size, the printing mode, and the roller resistance by controlling the transfer bias by using the solid transfer roller 9 of the ion conductive type at a constant current.

<Embodiment 4> An image forming apparatus for switching the transfer bias constant current value for each transfer material size described in Embodiment 3 prints a postcard and an envelope, and then prints A4 paper.
When I printed it vertically, a paper mark image was output.

This phenomenon is remarkable when a large constant current value that does not cause transfer failure or explosion scattering due to postcard size or the like with a low resistance roller is guaranteed. That is, at this time, an excessive current flows to the photosensitive drum 1 and serves as a drum memory.

Therefore, a fourth embodiment will be described below.

The structure of the image forming apparatus is the same as that of the third embodiment shown in FIG. As shown in FIG. 11, in the transfer bias control, a constant voltage bias calculated from the ATVC control is applied as described in the conventional example at the time of printing an envelope, a postcard size, or the like. In the determination of the transfer bias, the transfer roller resistance is detected in a pre-rotation step, and a constant voltage bias that can secure a desired current is determined from the value of the transfer roller resistance. envelope,
The optimum transfer current is ensured by switching the constant current value for each transfer roller resistance at the transfer material size described in the third embodiment except for the transfer material of extremely small size such as a postcard. With the above configuration, when a transfer material having a very small size is transferred with a constant voltage bias, an excessive transfer current can be prevented from flowing to the photosensitive drum 1, so that no drum memory is generated and paper marks are generated at the next printing. And a good image can always be obtained.

<Fifth Embodiment> When an image is formed by the image forming apparatus described in the first embodiment, explosion and scattering may occur at the leading end image (about 0 to 20 mm) of the transfer material P, and transfer failure may occur. there were. The above phenomenon occurs when a high-voltage power supply that outputs a transfer constant current bias rises. Also,
When a constant current bias is applied, the voltage value changes due to the impedance change between the transfer material and the transfer roller and the photosensitive drum at the time of transfer, but the transfer material exists and becomes larger at the time of transfer, and the high voltage power supply rises at this time (Response), however, leading edge transfer failure occurs. To solve this problem with a high-voltage power supply, problems such as an increase in the cost of the high-voltage power supply occur.

The fifth embodiment will be described below.

The configuration of the image forming apparatus is the same as that of the first embodiment shown in FIG. As the transfer bias control, in addition to the configuration of the first embodiment, correction is performed so that a constant current value higher than the optimum constant current value determined in the previous multiple rotations is output at the leading end of the transfer material. That is, the time required for the transfer material P to pass through the registration roller 7 and enter the transfer nip portion T is determined in the sequence, and it is possible to control so that the corrected constant current value is output at the leading end of the transfer material. is there. By applying a constant current bias in consideration of the rise of the high voltage power supply, it is possible to prevent poor transfer at the leading end of the transfer material and explosion scattering caused by insufficient transfer current. Further, when the transfer material P starts passing through the transfer nip portion T and the power supply high voltage has sufficiently risen, the constant current value is returned to the initially determined value. The rise of the power supply high voltage varies depending on the capacity of the power supply, but is generally about 50 to 200 mm / sec. With the above configuration, it is possible to output a good image without transfer failure, explosion splattering, punch-through, paper marks, etc. over the entire printed image.

The above-described Embodiments 2 to 4 are also applicable to the configuration of Embodiment 5 described above. In the image forming apparatus using Ra = 5.0 (μm) and switching the transfer bias between a constant current value and a constant voltage value in accordance with the transfer roller resistance, the print mode, and the transfer material size, the transfer material tip due to the high voltage rise Transfer failure, explosion scattering and the like can be prevented, and a good image can always be obtained.

[0061]

As described above, according to the present invention,
An image forming apparatus using a transfer roller having a peripheral unevenness of 1.5 or less and a surface roughness Ra of 5.0 (μm) or less using an ion conductive solid roller. By switching the constant current value, an optimal transfer current can be secured, and a good image can be obtained without transfer failure, explosion and scattering, and the like.

Further, regardless of the printing mode and the size of the transfer material, an optimum transfer current can be secured, and a good image free from poor transfer, explosion and scattering can be obtained.

Further, by correcting the constant current value or the constant voltage value of the transfer bias, it is possible to prevent poor transfer at the tip and the occurrence of explosion and scattering, and to always obtain good high-quality images.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view illustrating a schematic configuration of an image forming apparatus according to a first embodiment and a fifth embodiment.

FIG. 2 is a perspective view showing a transfer roller resistance measuring device.

FIG. 3 is a diagram illustrating a VR curve of the transfer roller according to the first embodiment.

FIG. 4 is a diagram illustrating a relationship between a transfer roller resistance and an optimum transfer current value according to the first embodiment.

FIG. 5 is a diagram showing an IR curve of the transfer roller according to the first embodiment.

FIG. 6 is a longitudinal sectional view illustrating a schematic configuration of an image forming apparatus according to Embodiments 2 to 4.

FIG. 7 is a perspective view illustrating a configuration of a transfer roller.

FIG. 8 is a diagram illustrating a relationship between a resistance of a transfer roller and a constant current value.

FIG. 9 is a diagram illustrating a relationship between a resistance of a transfer roller and a constant current value at the time of printing on a second surface of a transfer material.

FIG. 10 is a diagram showing the relationship between the resistance of a transfer roller and the constant current value during single-sided and double-sided printing in B5 lengthwise.

FIG. 11 is a diagram illustrating transfer bias control for postcards and envelopes.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image carrier (photosensitive drum) 2 Charging member (charging roller) 3 Exposure means (scanner) 4 Developing device 9 Transfer member (transfer roller) 9a Solid rubber layer 9b Core metal 20 Transfer bias applying means N Transfer nip portion (transfer site) ) P transfer material

Claims (6)

[Claims] An image bearing member having a surface on which a toner image is formed; a transfer member disposed in contact with the surface of the image carrier to form a transfer nip portion; and a transfer bias applying a transfer bias to the transfer member. Means for transferring a toner image on the surface of the image carrier to the transfer material surface by applying a transfer bias to the transfer member by the transfer bias applying means while nipping and transferring the transfer material at the transfer nip portion. In the image forming apparatus, the transfer member is a roller having ion conductivity, and the transfer bias applying unit is a constant current bias and detects a resistance value of the transfer member, and responds to the detected resistance value. An image forming apparatus, wherein the constant current value of the constant current bias is switched by a switch. 2. The transfer roller is a solid roller, the peripheral surface of the transfer roller has a resistance distribution in the circumferential direction of 1.5 or less, and has a surface roughness Ra = 5.0 (μ).
The image forming apparatus according to claim 1, wherein m) is the following. 3. The image forming apparatus according to claim 1, wherein the transfer bias applying unit switches the constant current value according to an image forming mode. 4. The transfer bias applying unit according to claim 1, wherein the constant current value is switched according to the size of the transfer material.
An image forming apparatus according to any one of the preceding claims. 5. The transfer bias applying means is means for applying at least one of a constant current bias and a constant voltage bias, wherein a constant current value and a constant voltage value are set according to the size of the transfer material. The image forming apparatus according to claim 4, wherein at least one of them is switched. 6. The image forming apparatus according to claim 1, wherein the transfer bias applying unit corrects a constant current value before the leading end of the transfer material reaches the transfer nip.