JPH10186895A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To expand an allowance area of resistance value of a contact transfer member, to form an excellent image, and to reduce a cost by composing a contact transfer member by a member whose resistance value is lowered corresponding to rise of an applying voltage at least, in the range of the applying voltage. SOLUTION: As for this device, the transfer roller 5 as the contact transfer member is provided with an elastic layer 5b on a periphery a conductive core bar 5a, and the elastic layer 5b is provided with conductive property. As a method for providing the conductive property, a transferring roller 51 equipped with a electrostatic conductive type is adopted, and this transferring roller 51 supposed that inductive fillers are dispersed to the elastic layer 5b for instance, an EPDM or urethane roller dispersed with the inductive fillers such as carbon, metallic oxide can be mentioned. In the meantime, by adopting the EPDM roller whose resistance is lowered by raising the applying bias, the resistance effective range of the transferring roller 51 is widened, in the image forming device provided with plural processing speed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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 In recent years, in image forming apparatuses such as copying machines and printers, high speed and high resolution are strongly desired. For example, in an electrophotographic laser beam printer (hereinafter, appropriately referred to as "electrophotographic printer") which is said to be most suitable for high speed and high resolution, the speed and resolution limits are determined by a laser scanner. That is, in a laser beam printer of a system in which a polygon mirror is rotated and a laser beam is raster-scanned,
The limit of the rotation speed of the drive motor for rotating the polygon mirror at high speed directly determines the upper limit of the speed and resolution of the electrophotographic printer.

[0003] However, a high-speed motor capable of achieving both high speed and high resolution at a high level has the disadvantage that the cost is very high.

Therefore, as a method for achieving high resolution without excessively increasing the number of rotations of the polygon mirror, a method of reducing the image forming speed (hereinafter referred to as "process speed") of an electrophotographic printer in a high resolution mode. Has come to be taken. Specifically, the resolution is 600d
At pi, the process speed at which a throughput equivalent to 12 ppm can be achieved with an A4 size recording material is set at a resolution of 12
At 00 dpi, by switching to a process speed at which a through-top equivalent to 76 ppm can be achieved with an A4 size recording material, high-speed output is possible with a 600 dpi resolution image such as a character, and 12
A printer capable of outputting a high resolution of 00 dpi has been supplied at a low price.

In the above-described image forming apparatus in which the process speed can be changed depending on the resolution, the transfer member for transferring the toner image on the image carrier to the recording material is simplified, and the conveyance path of the recording material is simplified. Many use a contact charging member capable of stabilizing the conveyance of the recording material, that is, a charging member such as a transfer roller, which is disposed in contact with the image carrier.

[0006]

However, the image forming apparatus capable of changing the process speed depending on the resolution has the following problems.

First, in order to realize optimum image forming conditions corresponding to each process speed, a case where a contact transfer member (transfer roller) is used as a transfer member is described in JP-A-4-208971. As described above, it is known that an optimum transfer roller resistance value exists depending on the process speed. Therefore, when a plurality of process speeds are realized by one image forming apparatus, the allowable range of the transfer roller resistance value optimum for all the process speeds is very narrow, and there is a problem that the mass productivity of the transfer roller is significantly impaired. .

Second, as a means for conveying a recording material by a transfer roller, a transfer roller is brought into contact with an image carrier (hereinafter referred to as a "photosensitive drum") to constitute a transfer nip portion, and the recording material is nipped and conveyed. That is common. In this case, it is known that the recording material is conveyed faster than the peripheral speed of the photosensitive drum as a countermeasure against missing characters. However, in the above-described conventional example, a phenomenon that the output image on the recording material is elongated or chipped due to the process speed has occurred. This is because the transfer condition of the transfer roller differs depending on the process speed. That is, when the transfer roller conveys the recording material, it occurs because the dynamic frictional force between the transfer roller and the recording material is different due to the process speed, and the conveyance conditions are different. More specifically, if the transfer condition of the transfer roller is adjusted at a low speed and then the transfer speed is increased, the dynamic friction force is reduced, the transfer force is reduced, and image shrinkage occurs. Conversely, if the transfer conditions are adjusted at a high speed, the dynamic friction force increases when the speed is reduced next time, causing image chipping.

As described above, the second problem is that it is very difficult to maintain good recording material conveyance at a plurality of process speeds in one image forming apparatus.

A third problem is that a drum memory is generated at a low process speed. This is a problem that occurs in a transfer roller having a low resistance in a high-temperature, high-humidity environment, and is caused by an excessive transfer current flowing to the photosensitive drum. Generally, the transfer current is set so that a current that does not cause transfer failure through the recording material flows to the photosensitive drum. However, when the recording material absorbs moisture in a high-temperature, high-humidity environment, an excessive current flows through the photosensitive drum because the resistance of the recording material is low.

Therefore, the present invention is intended to increase the allowable range of the resistance value to enable mass production, to enable excellent conveyance of a recording material at a plurality of process speeds, and to prevent the occurrence of a drum memory. It is an object of the present invention to provide a contact charging member and an image forming apparatus provided with the same.

[0012]

According to the present invention, there is provided an image carrier having a movable surface, a toner image forming means for forming a toner image on the surface of the image carrier, and the image carrier. Transfer means for transferring a toner image on the surface onto a recording material, wherein the transfer means is disposed in contact with the surface of the image carrier and the image carrier is And a contact transfer member constituting a transfer nip portion between the transfer member and a transfer voltage applied to the contact transfer member, whereby a toner on the image carrier is transferred to a recording material nipped and conveyed in the transfer nip portion. A transfer power supply for electrostatically transferring an image, and control means for changing a transfer condition in accordance with the image forming speed, wherein the contact transfer member is capable of responding to an increase in an applied voltage at least within a working voltage range. And the resistance decreases Constituting the timber, characterized in that.

According to a second aspect of the present invention, in the contact transfer member, the rate of change of the resistance value with respect to the applied voltage within the operating voltage range is −3.0 × 10 ⁴ to −3.
It is within a range of 0 × 10 ⁶ (Ω / V).

According to a third aspect of the present invention, the control means performs a control operation for determining an applied voltage as the transfer condition to be applied to the contact transfer member during non-image formation, and controls the applied voltage during image formation. Is controlled at a constant voltage.

According to a fourth aspect of the present invention, the resolution is changed in accordance with the plurality of image forming speeds.

According to a fifth aspect of the present invention, the contact transfer member is a transfer roller.

According to a sixth aspect of the present invention, the condition for conveying the recording material in the transfer nip portion is changed in accordance with the plurality of image forming speeds.

According to a seventh aspect of the present invention, as the change of the recording material conveyance condition, the moving speed of the surface of the image carrier with respect to the image forming speed is changed.

The present invention according to claim 8 is characterized in that, as the change of the recording material conveyance condition, the incident speed of the recording material to the transfer nip portion is changed.

According to a ninth aspect of the present invention, the contact pressure of the transfer roller with respect to the image carrier at the transfer nip is changed as the change of the recording material conveyance condition.
It is characterized by the following.

According to a tenth aspect of the present invention, the image bearing member is a drum type electrophotographic photosensitive member.

According to an eleventh aspect of the present invention, a resistance member is interposed between the contact transfer member and the transfer power supply in series according to the plurality of image forming speeds.

[Operation] The main operation based on the above configuration is as follows.

According to the configuration of the first aspect, it is easy to secure appropriate transfer currents for different image forming speeds. Further, the allowable value of the resistance range of the contact transfer member is expanded.

According to the fourth aspect, the resolution can be switched with a simple configuration.

According to the sixth aspect of the present invention, for example, it is possible to correct the recording material conveyance force based on a change in dynamic friction force between the transfer roller and the recording material due to a change in image forming speed.

According to the tenth aspect, it is possible to prevent an excessive transfer current from flowing from the transfer power supply to the image carrier via the contact transfer member.

[0028]

Embodiments of the present invention will be described below with reference to the drawings. First Embodiment First, the resistance characteristics of a transfer roller as a contact transfer member according to the present invention will be described in detail.

In a transfer roller recently proposed, an elastic layer 5b is generally provided on an outer peripheral surface of a conductive cored bar 5a as shown in FIG. 1, and the elastic layer 5b is made conductive. Like that. The transfer roller 5 is roughly classified into the following two types depending on how to impart the conductivity. The transfer roller 51 having an electronic conductive system The transfer roller 52 having an ionic conductive system is obtained by dispersing a conductive filler in the elastic layer 5b. As an example, a conductive filler such as carbon or metal oxide is dispersed. EPDM and urethane rollers can be used.

The elastic layer 5b contains an ion conductive material. Examples of the elastic layer 5b include a material such as urethane having conductivity, a surfactant dispersed in the elastic layer 5b, and the like. Is mentioned.

The conductive characteristics of the EPDM roller (hereinafter referred to as “V
The "-R characteristic") indicates a characteristic in which the resistance decreases when the bias is increased as shown in FIG. 8, and the VR characteristic of the roller is such that even if the bias is changed as shown in FIG. It does not change.

Here, in the resistance measurement, as shown in FIG. 10, the transfer roller 5 (transfer roller 51 and transfer roller 52) is pressed against the aluminum drum 1 with a contact pressure of 1.4 kg. A bias was applied between 5a and the ground, and the resistance was calculated by measuring the current with the ammeter P. The measurement was performed after leaving the transfer roller in an environment of a temperature of 20 ° C. and a humidity of 60% for 8 hours or more, and then under the same environment. Similarly,
FIGS. 11 and 12 show the results of measuring the VR characteristics after the transfer roller 5 was installed for 8 hours or more under the environment of 15 ° C. and 10% and the environment of 35 ° C. and 80%. FIG.
1 shows the VR characteristics of the transfer roller 51 having an electronic conductive system, while FIG. 12 shows the VR characteristics of the transfer roller 52 having ionic conductivity. From these figures, it can be seen that the transfer roller 52 having an ion conductive system has a large environmental variation of resistance of about 2 orders (about 100 times), while the transfer roller 51 having an electronic conductive system has about 0.5 orders (about 3 times). Times) and it was small.

Based on the above results, the image forming speed (hereinafter referred to as “process speed”) is set to 0 to 200 mm / sec.
FIG. 13 and FIG. 14 show the results obtained by obtaining the effective range of the transfer roller resistance at each process speed by varying the range. In FIG. 13, 8 of T1 to T8 of the transfer roller 51 of the electronic conductive system.
In FIG. 14, an experiment was performed on eight of the transfer rollers 52 of T11 to T18 in FIG.
Here, the effective range of the transfer roller resistance is such that when transferring the toner image to paper as a recording material, there is no transfer failure, no paper marks are generated, and the maximum value of the transfer bias satisfies 5.0 kV. did. In addition, a PDM sponge in which carbon was dispersed was used as the transfer roller 51 of the electron conductive system, and a urethane sponge mixed with a surfactant was used as the transfer roller 52 of the ionic conductive system. In the case of an electron conductive EPDM roller, 1.0 × 10 ⁸ to 8.
The effective range was 0 × 10 ⁸ Ω, about 0.90 order (about 8 times). This applies to the transfer rollers 51 of T2 to T5. On the other hand, the urethane roller is 2.0 ×
The effective range was 10 ^{8 to} 4.0 × 10 ⁸ Ω, about 0.30 order (about 2 times). This corresponds to T1
5 to T16 transfer rollers 52.

As described above, by using the electron conductive transfer roller 51 whose resistance is reduced by increasing the applied bias, in an image forming apparatus having a plurality of process speeds, the effective resistance range of the transfer roller 51 can be increased. It turns out that you can get 0.9 order and about 1 order (about 10 times),
It is considered that mass transfer of the transfer roller 51 can be supported. In addition, the slope (change rate of the resistance value with respect to the applied voltage) in the voltage application range (operating voltage range) of the transfer roller 51 is −3.0 × 10 ⁴ to −3.0 × 10 when calculated from FIG. It turned out that it was in the range of ⁶ .

Here, the reason why the effective resistance range of the ion conductive transfer roller 52 is only 0.3 order (about twice) will be considered. As the process speed increases, the transfer current that does not cause transfer failure tends to increase. At this time, since the resistance of the transfer roller 52 does not change even when the applied bias is increased, a sufficient transfer current cannot be secured even when the applied bias is at the maximum value, and the environmental fluctuation is two orders (about 100 times). Higher, and the upper limit of resistance becomes more severe.

Next, FIG. 1 shows a schematic configuration of an image forming apparatus M to which the above-described electronic conductive transfer roller 51 is mounted as a contact transfer member according to the present invention. FIG. 2 shows a connection diagram with an external device (computer).

As shown in FIG. 2, the image forming apparatus M starts printing when the control device (control means) 17 receives a print signal from the computer 20. A drum-type electrophotographic photosensitive member (hereinafter, referred to as a “photosensitive drum”) 1 as an image carrier is rotationally driven by a driving unit (not shown), and its surface moves in the direction of arrow R1. The surface of the photosensitive drum 1 has a contact transfer member (charging roller) 2 which forms a toner image forming unit together with a scanner 3 and a developing device 4 described later.
Charged by An electrostatic latent image is formed on the surface of the charged photosensitive drum 1 by turning on a laser (not shown) in the scanner 3 based on image information sent from the computer 20 to the control device 17.

Next, the electrostatic latent image is developed as a toner image by attaching toner to the developing device 4. The transfer roller 51 described above is brought into contact with the photosensitive drum 1 with a predetermined pressing force, whereby a transfer nip portion N is formed between the photosensitive drum 1 and the transfer roller 51. The toner image on the photosensitive drum 1 is transferred to a transfer roller 5 by a transfer power supply (not shown).
1 is electrostatically transferred onto the recording material S by applying a transfer bias to the recording material S. This recording material S is fed from a paper feed cassette 7 or a paper feed tray 8 by a paper feed roller 9 or a paper feed roller 10, and a material that has been waiting by a registration roller 11 is transferred to a toner image on the photosensitive drum 1 at a timing. Are supplied while being guided by the upper guide 12 and the lower guide 13.

On the photosensitive drum 1 after the transfer of the toner image, the transfer residual toner remaining on the surface of the recording material S is removed by the cleaning device 6, and is used for the next image formation.

On the other hand, the recording material S to which the toner image has been transferred is conveyed to the fixing device 14, where the unfixed toner image on the surface is heated and pressed to be fixed on the recording material S. Discharged above, thereby completing image formation.

In the above-described image forming operation, for example, a print signal and an image signal from the computer 20 shown in FIG.
After being transmitted to the control device 17 via the port 16, the transmission is started by being transmitted to the high voltage power supply 18.

It is assumed that the image forming apparatus M having the above configuration and operation can be switched to a plurality of process speeds. In the following, the image forming apparatus M is a computer 2
0 is not connected to an external device such as
After the image data is directly input from the O port 16, the image forming operation (printing process) is started. The switching of the process speed and the image forming operation are performed by switches (not shown).

Here, when the process speed switching is performed in two stages, the process speed on the low speed side L is A, and the process speed on the high speed side H is B. The transfer roller 51 is of an electronic conductive type having the VR characteristic shown in FIG. 13, that is, the resistance decreases when the applied bias is increased, and the slope of the resistance value change with respect to the bias is −3. 0 × 10 ⁴ to −3.0 × 10 ⁶ (Ω / V)
Was used.

According to the process speeds A and B, the ATV
An appropriate transfer bias is switched and applied by C control (constant voltage control). At this time, the resistance of the transfer roller 51 is
The process speeds A and B are adjusted so as to fall within the usable resistance range. As a result, a good image can be formed at each of the process speeds A and B, and as described above, a resistance value range of almost one order (about 10 times) can be secured. It is possible to suppress an increase in the cost when manufacturing 51. By using such a transfer roller 51, an image forming apparatus M having a plurality of process speeds A and B can be configured.

An experimental example according to the first embodiment will be described below. <Experimental Example 1> Using the image forming apparatus M shown in FIG. 1, as the switchable process speeds A and B, A: 35 mm / sec for the low speed side, 6 ppm, 600 dpi for the low speed side, and B: 70 mm / sec for the high speed side H. , 12 ppm, 600 dpi, and the transfer roller 5 described above as T1-T8 and T11-
T18 total 16 pieces (1.0 × 10 ⁸ Ω ~
2.0 × 10 ⁹ Ω: 1.5 kV applied). The maximum output value of the transfer bias was set to 5.0 kV.

In the above-mentioned setting, at the process speeds A and B, a transfer bias for preventing a transfer defect from occurring and paper marks from being generated is applied by the ATVC control as in the conventional example.

As a result, a good image could be formed in a range of 1.3 order of the common roller resistance range of the process speeds A and B.

In the image forming apparatus M described above, the switching of the process speed is not limited to the two stages of A and B, but is performed in three stages as long as a common area exists within the effective transfer roller resistance range at each process speed. It is also possible to switch and use at a plurality of process speeds described above. Further, in an image forming apparatus having a function of automatically forming images on both front and back surfaces of the recording material S, and a function of automatically multiplexing images on one surface of the recording material S automatically, etc. By changing the transfer bias under the condition that the transfer roller resistance in each image forming step is included in the effective area, the transfer roller resistance range can be secured almost one order, and good image formation can be performed. Needless to say.

The material of the transfer roller 51 used is
The present invention is not limited to the above-mentioned EPDM rubber, and even if it is other, it shows a characteristic that the resistance value is reduced by applying a bias, and the slope of the resistance value with respect to the applied bias is -3.0.
It is effective if it is × 10 ⁴ to −3.0 × 10 ⁶ (Ω / V). <Embodiment 2> In the image forming apparatus M shown in FIG.
An embodiment in which the resolution is switched will be described below. Since the configuration of this image forming apparatus is the same as that of FIG. 1, the description is omitted.

However, the resolution on the high-speed side H is Xdpi, and the process speed A on the low-speed side L is half (A = B / 2) the process speed B on the high-speed side. As a result, there is no technical or cost problem of the scanner unit as in the conventional example, and it is possible to easily configure an image forming apparatus having 2 × dpi at low speed, which is twice the resolution at high speed. That is, by inputting the image signals at the respective process speeds A and B during image formation from the I / O port 16 and switching and outputting the transfer bias according to the process speed switching as in the first embodiment. Thus, high-quality images having different resolutions can be formed. <Experimental Example 2> In the image forming apparatus used in Experimental Example 1, when the rotation speed of the scanner unit was fixed in correspondence with the process speeds A and B, the low speed side L was A: 3.
5 mm / sec, 6 ppm, 1200 dpi, and the high speed side H was B: 70 mm / sec, 12 ppm, 600 dpi.

In the above-described configuration, similarly to the first embodiment, the transfer rollers 5 in the common resistance region are used as the transfer rollers 5 in the above-described T1 to T8 and T11 to T in accordance with the process speeds A and B.
The transfer bias was switched at each of the process speeds A and B using a total of 16 prints, and a good image could be formed without replacing the transfer roller 51 in accordance with the resolution.

As described above, in the resolution switching, when the rotation speed of the polygon mirror is fixed, the process speed on the highest speed side is B ₀ , and the resolution at that time is X.
Assuming that the resolution is ₀ dpi, the process speed at the time of switching is Y, and the resolution at that time is Z, the relationship of Z = X ₀ × (B ₀ / Y) holds. Therefore, by switching the process speed not only in two steps but also appropriately, it is possible to switch to an arbitrary resolution satisfying the above equation. <Embodiment 3> An embodiment in which a change in the recording material conveyance force in the transfer nip N is corrected at the time of switching the process speed will be described below.

The configuration of the printer is the same as that of FIG. 1, but when the transport speed of the recording material S at the transfer nip N is set to be the same as the process speed, that is, when the transport speed with respect to the process speed is set to 100%, the process speed is reduced. The photosensitive drum peripheral speed (drum peripheral speed) at the time of switching was set as shown in FIG. The image writing speed of the photosensitive drum 1 is the same as the process speed.

In FIG. 15, the peripheral speed of the drum, which is faster when the process speed is switched, is set lower. In addition to these settings, the transfer roller diameter, the transfer roller pressing spring, and the like were adjusted so that the transfer speed of the recording material at the transfer nip N was 100%. As described above, in the setting of the process speed B on the high-speed side H where the dynamic friction force is small, by increasing the drum peripheral speed β, it is possible to prevent image shrinkage due to a decrease in the transfer force in the transfer nip N, and In the setting of the process speed A on the side L, image loss due to an increase in the conveying force is prevented by reducing the drum peripheral speed α. In addition, it is needless to say that the recording material S is conveyed faster than the peripheral speed of the drum, so that the hollowing out can be prevented.

In addition to the above description, even when the process speed of the image forming apparatus M is switched to a plurality of processes, the drum peripheral speed is minimized when the process speed is minimum, and the drum peripheral speed is sequentially increased according to the process speed. The drum peripheral speed must be lower than the recording material transport speed, and the recording material transport speed must be equal to the process speed.

By satisfying the above three points, it is possible to prevent image shrinkage, chipping, omission, and the like, and to perform image formation with a stable sub-scanning magnification during image formation. <Experimental Example 3> In the image forming apparatus used in Experimental Example 2, the peripheral speed of the drum and the transfer roller 51 were set as shown in FIG.

When an image was output based on the conditions shown in FIG. 16, at each process speed, a good image was obtained without any image shrinkage or chipping and without any voids.

Here, when the sub-scanning magnification was measured, both became 100%, and it was confirmed that the conveyance of the recording material was stable. <Embodiment 4> In Embodiment 3 described above, the drum peripheral speed is changed according to the process speed, and the recording material conveyance speed in the transfer nip N is corrected to stabilize the recording material conveyance. . However, when the process speed switching speed difference is large and the process speed on the low-speed side L is extremely small, simply reducing the drum peripheral speed does not sufficiently stabilize the conveyance of the recording material and may cause image chipping. .

FIG. 3 shows a recording material conveying means according to the fourth embodiment. This recording material conveying means is provided with a paper feed cassette 7 (FIG. 1).
The recording material S fed from the registration roller 1
1, the sheet is fed between the upper guide 12 and the lower guide 13 at a predetermined speed, moves substantially along the lower guide 13 in the direction of the arrow K1, and hits the surface of the photosensitive drum 1 before the leading end enters the transfer nip N. Then, the transfer is performed. Here, the upper guide 12 and the lower guide 13 regulate the direction in which the recording material S enters the photosensitive drum 1. If the recording material S hits the transfer roller 5 before the photosensitive drum 1 before the leading end of the recording material S enters the transfer nip portion N, the recording material S receives a transfer electric field, and scatters around characters. . The upper guide 12 and the lower guide 13
When the recording material S exits, the rear end of the recording material S jumps, and an image blur occurs due to a shock caused by the jump. In particular, it has been found that when the process speed is high and the conveying speed of the recording material S is high, the shock of the guide dropout is large, and image blur is likely to occur.

Therefore, the upper guide 12 and the lower guide 13
Are arranged such that the leading end of the recording material S first strikes the photosensitive drum 1 and the rear end of the recording material S is arranged at a position where no shock occurs due to the guide missing.

Embodiment 4 will be described based on the above description.

FIG. 3 is a block diagram showing the vicinity of the transfer roller 51 in the image forming apparatus capable of changing the set position of the lower guide 13 based on the information input to the I / O port 16. In this image forming apparatus, the process speed can be switched similarly to the third embodiment.

In FIG. 3, when the process speed B is on the high speed side H, the leading end of the lower guide 13 is at the position g3, and the recording material S is conveyed along the lower guide 13 as described above. However, it does not get squeezed by the lower guide 13 and enters the transfer nip N while maintaining the speed at the time of entering the guide. When the process speed A is switched to the low speed side L, the lower guide 13 is driven and controlled to the position g1 by the control signal from the control device 17. At this time, the recording material S that has entered the lower guide 13 is sufficiently squeezed by the lower guide 13 because the position of the lower guide 13 has been raised. Therefore, the recording material S enters the transfer nip portion N at a reduced speed when the lower guide enters, and the recording material conveyance speed in the transfer nip portion N is smaller than that in the third embodiment. Become slow. Therefore, at the process speed A on the low speed side L, the recording material S
Can be set to 100%, which is the same as the image information.

The control means of the lower guide 13 includes a shaft attached to the gear 13a by the rotation of the drive unit (motor) 21 and the gear trains 22, 23, 24, 25, 13a according to a signal from the control device 17. 13b and rotates together.

The angle of the lower guide 13 changes, and the incident point of the recording material S on the photosensitive drum 1 and the transfer roller 51 is controlled. Here, the tip of the lower guide 13 is located at g3 or g4 when the process speed is high, and is located at g1 or g2 when the process speed is low.

As described above, the difference in transport speed due to the difference in the dynamic friction force between the transfer roller 51 and the recording material S at a low speed is determined by changing the peripheral speed of the drum and the lower guide. By correcting the two points, that is, changing the height of the leading end of the recording medium 13, it is possible to prevent image deficiency in the transfer nip N and to stabilize the conveyance of the recording material.

It is preferable that the conveying speed of the recording material is changed depending on the type, thickness, environment, etc., and accordingly, the position of the tip of the lower guide 13 is appropriately changed to g1 to g4 in FIG. By doing so, it is possible to realize a more optimal conveyance speed of the recording material S.

Incidentally, as the control of the speed of the recording material entering the transfer nip N, the recording material conveyance speed may be changed by changing the rotation speed of the registration roller 11. Alternatively, at low speed, the paper feed cassette 7
The back tension of the recording material S at the time of paper feeding is increased by increasing the pressure of the paper feeding rollers 9 and 10 (see FIG. 1), the double feeding prevention pad (not shown) provided on the paper feeding tray 8, and the paper feeding rollers 9, 10. It is also possible to reduce the recording material transport speed. <Embodiment 5> With reference to FIG. 4, a configuration in which the transfer roller 5 corrects the recording material conveyance speed in the transfer nip N will be described. FIG. 2 is a unit configuration diagram of the transfer roller 5.

The transfer roller 5 includes a conductive roller core 35.
The roller core metal 35a is rotatably supported at both ends in the axial direction by bearings 36. The outer peripheral surface of the roller core a is surrounded by a conductive elastic body 35b. The distal end of the power supply compression spring 34 is connected to the bearing 36, and the base end of the compression spring 34 is attached to the insulator 33. The transfer roller 5 is brought into contact with the surface of the photosensitive drum 1 with a predetermined pressure by a compression spring 34 and a bearing 36, and a transfer bias is applied by a power supply (transfer power supply) 34 a connected to the compression spring 34. . The above-described insulator 33 is swingably supported about a shaft 33 a, and is swung by the cam 30. The cam 30 has driving gears 31 and 32 for driving the cam 30.
The D drive gear 32 is driven by a motor M1 whose rotation is controlled by a control signal from the control device 17.

The motor M2 is rotated by a predetermined angle according to a control signal from the control device 17, and the drive gears 32, 3
1. The insulator 33 swings via the cam 30 and the compression spring 3
4, the pressing force of the transfer roller 5 on the photosensitive drum 1 is changed.

When the process speed is switched, in the case of the high-speed side, the insulator 33 is installed at a position where the transfer roller 5 shows a normal pressing force from the position of the compression spring 34 at its natural length. On the other hand, in the case of the low speed side, the insulator 33 moves in a direction to compress the compression spring 34, and the transfer roller 5 with respect to the photosensitive drum 1 is moved.
To increase the pressure. Thereby, the transfer nip portion N
In this case, the slip between the transfer roller 5 and the recording material S is reduced, and the conveying speed of the recording material S is increased as compared with the case where the pressing force is not increased. That is, on both the high-speed side and the low-speed side, the conveyance speed of the recording material S can be appropriately corrected, and the prevention of image chipping and the stabilization of the conveyance of the recording material can be achieved.

The above-mentioned pressing force of the transfer roller 5 against the photosensitive drum 1 is a total pressure of 40 at high speed (normal time).
From 0 to 1000 g, and at low speeds, from 1000 to 2000 g, it is desirable from the viewpoint of good transport of the recording material S, transfer characteristics such as prevention of dropout, and the like. <Embodiment 6> Next, an arrangement for preventing a drum memory of the photosensitive drum 1 will be described.

FIG. 5 is a schematic configuration diagram of a power supply unit for supplying power to the transfer roller 6 in the sixth embodiment.
In the figure, 5 is a transfer roller, 37 is a resistor (resistance member, 1 × 10 ⁸ Ω in this embodiment), and 18 is a high voltage power supply.
4, the transfer bias is applied to the transfer roller 5 through the resistor 37, unlike the case of FIG. The other configuration is the same as that of the first embodiment, and the description thereof is omitted. For example, the low-speed side throughput is 6 ppm.

In the above-described configuration, the transfer roller (see FIGS. 10, 11 and 12) in which a drum memory is generated under a high-temperature and high-humidity environment (temperature of 35 ° C., humidity of 80%) is similarly used for VI. The properties were measured. The measurement is performed under normal environment (25
C., 40%). FIG. 6 shows the result. In the figure, I ₁ is the time when the recording material S is out of paper and the photosensitive drum 1
Is charged to a predetermined potential (−700 V in this embodiment), the current flowing through the photosensitive drum 1, I ₂ is the current flowing through the photosensitive drum 1 during printing, and I ₃ is The current flowing through the photosensitive drum 1 when paper is not passing, I ₄
Is a current flowing through the photosensitive drum 1 via the resistor 37 during printing.

As shown in FIG.
The slope of the −I curve becomes gentler, and the change of the current with respect to the change of the voltage is smaller than when the resistor 37 is not provided.

Next, FIG. 7 shows the result of performing the same measurement under the above-mentioned environment where the drum memory is generated. In the figure, a broken line D indicates a conventional current line generated by the drum memory without the resistor 37, and at 6 ppm, the drum memory generates 8 μA. Plot in the figure shows the same parameters as FIG. 5, also, A ₁ is 5μ
Shows A, A ₂ is 10μA, respectively. In FIG. 6, a current of 5 μA at which no transfer failure occurs through the resistor 37
The current is 8 even when paper is not passed or paper is passed.
μA and no drum memory occurred. The reason will be discussed below.

By providing a resistor between the transfer roller 5 and the high voltage power supply 18, the gradient of the VI curve becomes gentle. For this reason, due to variations and tolerances of the high voltage power supply 18,
Since the variation of the current flowing through the transfer roller 5 is also reduced, it is possible to prevent an excessive current from flowing through the photosensitive drum 1 in a high-temperature and high-humidity environment. This is because the recording material S is paper or the like,
It is considered that this is effective even when moisture is absorbed. Therefore, generation of a drum memory can be prevented.

If the resistance value of the resistor 37 is too high,
A voltage drop occurs due to the current flowing during transfer, and the voltage actually applied to the transfer roller 5 decreases. For this reason, for example, when the high voltage power supply 18 that generates a transfer voltage of 5 kV is used, the transfer voltage is actually applied only to 4.5 kV on the transfer roller 5, and a transfer failure may occur. For this reason, the upper limit of the transfer roller resistance becomes low. On the other hand, if the resistance value of the resistor 37 is too low, the above-described current suppressing effect cannot be obtained. Hereinafter, as a result of the examination, the range of the resistance value is from 2.0 × 10 ⁷ Ω to 1.5 × 1 Ω.
0 ⁸ Ω was found that may be in the between.

Since the generation of the drum memory is likely to occur on the low speed side of the process speed and on the low resistance side of the transfer roller 5, the configuration of FIG. Effective for prevention.

As described above, the drum memory prevention has been described for the printer speed at which the process speed can be switched and the low speed side. With the above-described configuration, the VI characteristics of the transfer rollers T1 to T8 in FIG. 13 were measured in the same manner as in FIG. In this case, since the gradient of the VI curve becomes gentler, the transfer roller T1 cannot be used because the output bias at which the current of 5 μA flows becomes larger than the high voltage maximum output value of 5.0 kV. Conversely, the transfer roller T8 showed good transfer characteristics without any paper marks or drum memory. Therefore, the transfer roller resistance use range at the low-speed side L: 6 ppm is 6.0 × 10 ⁷ Ω like the high-speed side H: 12 ppm.
２．０2.0 × 10 ⁹ Ω. Thus, in the image forming apparatus capable of switching the process speed, by setting the transfer roller resistance range to be the same regardless of the speed, the cost can be reduced because the roller selection at the time of manufacturing the transfer roller is not required. Note that, even when the variable value of the process speed is different from the embodiment, by adjusting the value of the resistor 37,
Needless to say, a similar effect can be expected.

[0081]

As described above, according to the present invention,
Since the allowable range of the resistance value of the contact transfer member is widened, a good image can be formed and the cost can be reduced.

Further, the resolution can be switched with a simple configuration, and a high-quality image can be provided.

Further, by changing the conveyance condition of the recording material in accordance with a plurality of image forming speeds, it is possible to prevent the dropout, image missing, shrinkage and the like, and to realize the stable conveyance of the recording material.

In addition, by interposing a resistance member between the contact transfer member and the transfer power supply, an excessive transfer current flows from the transfer power supply to the electrophotographic photosensitive member via the contact transfer member. To prevent the occurrence of a drum memory in the electrophotographic photosensitive member.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a schematic configuration of an image forming apparatus according to a first embodiment.

FIG. 2 illustrates a connection between the image forming apparatus according to the first embodiment and an external device.

FIG. 3 is a diagram illustrating a configuration of a recording material conveying unit according to a fourth embodiment.

FIG. 4 is a diagram illustrating a configuration for correcting a recording material conveyance speed by a transfer roller according to a fifth embodiment.

FIG. 5 is a diagram illustrating a configuration of a power supply unit that supplies power to a transfer roller according to a sixth embodiment.

FIG. 6 is a diagram showing VI characteristics according to the sixth embodiment.

FIG. 7 is a diagram showing VI characteristics when a resistor is interposed in the sixth embodiment.

FIG. 8 is a diagram illustrating the conductive characteristics (VR characteristics) of an electronic conductive (EPDM) transfer roller.

FIG. 9 is a diagram illustrating the conductive characteristics of a transfer roller of an ion conductive transfer roller.

FIG. 10 is a perspective view showing a method for measuring the resistance of the transfer roller.

FIG. 11 is a diagram illustrating a difference in conductive characteristics of an electronic conductive transfer roller due to a difference in environment.

FIG. 12 is a diagram showing a difference in conductive characteristics of an ion conductive transfer roller due to a difference in environment.

FIG. 13 is a diagram illustrating an effective range of resistance of an electronic conductive transfer roller.

FIG. 14 is a diagram illustrating an effective range of resistance of an ion conductive transfer roller.

FIG. 15 is a diagram showing a drum peripheral speed when a process speed is switched.

FIG. 16 is a diagram showing a drum peripheral speed setting in Experimental Example 3.

[Explanation of symbols]

Reference Signs List 1 image carrier (photosensitive drum) 2 toner image forming means (charging member, charging roller) 3 toner image forming means (scanner) 4 toner image forming means (developing device) 5, 51 contact transfer member (transfer roller) 6 cleaning device Reference Signs List 14 fixing device 16 I / O port 17 control means (control device) 18 high-voltage power supply 34a transfer power supply M image forming apparatus N transfer nip

Claims (11)

[Claims] 1. An image carrier having a movable surface, a toner image forming means for forming a toner image on the surface of the image carrier, and a transfer means for transferring the toner image on the surface of the image carrier onto a recording material An image forming apparatus capable of selecting a plurality of image forming speeds, wherein the transfer unit is disposed in contact with the surface of the image carrier and forms a transfer nip between the image carrier and the contact transfer member A transfer power supply for electrostatically transferring a toner image on the image carrier to a recording material nipped and conveyed at the transfer nip portion by applying a transfer voltage to the contact transfer member; Control means for changing a transfer condition in accordance with an image forming speed, wherein the contact transfer member is constituted by a member whose resistance value decreases in accordance with an increase in applied voltage at least within a use voltage range. Characterized by Image forming apparatus. 2. The contact transfer member according to claim 1, wherein a rate of change of the resistance value with respect to the applied voltage within the working voltage range is -3.0 × 10 ⁴ to −3.0 × 10 ⁶ (Ω / V). The image forming apparatus according to claim 1, wherein: 3. The control unit performs a control operation for determining an applied voltage as the transfer condition applied to the contact transfer member during non-image formation, and performs constant voltage control of the applied voltage during image formation. The image forming apparatus according to claim 1, wherein: 4. A method according to claim 1, wherein said plurality of image forming speeds are different from each other.
4. The method according to claim 1, wherein the resolution is changed.
An image forming apparatus according to any one of the preceding claims. 5. The method according to claim 1, wherein the contact transfer member is a transfer roller.
4. The method according to claim 1, wherein
An image forming apparatus according to any one of the preceding claims. 6. A method according to claim 1, wherein said plurality of image forming speeds are
The image forming apparatus according to claim 5, wherein a condition for conveying the recording material in the transfer nip portion is changed. 7. The image forming apparatus according to claim 6, wherein, as the change of the recording material conveyance condition, a moving speed of the surface of the image carrier with respect to the image forming speed is changed. 8. The image forming apparatus according to claim 6, wherein, as the change of the recording material conveyance condition, an incident speed of the recording material with respect to the transfer nip portion is changed. 9. The image forming apparatus according to claim 6, wherein the contact pressure of the transfer roller with respect to the image carrier at the transfer nip portion is changed as the change in the conveyance condition of the recording material. 10. The image bearing member according to claim 1, wherein the image bearing member is a drum-type electrophotographic photosensitive member.
An image forming apparatus according to any one of the preceding claims. 11. The image forming apparatus according to claim 10, wherein a resistive member is interposed between the contact transfer member and the transfer power supply in accordance with the plurality of image forming speeds.