JP2001134118A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device constituted so that electric charge can be stably imparted to a semiconductor transfer belt, an excellent and stable transfer action is realized and the dielectric breakdown of the semiconductor transfer belt is also prevented from occurring. SOLUTION: The electric charge can be stably imparted to the semiconductor transfer belt 11 by adopting a feeding roller 23a (23b, 23c and 23d) whose resistance value is 104 to 1010 Ω.

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 monochrome and color copying machine, a monochrome and color printer, and more particularly, to a semiconductive transfer belt for transferring a developer image developed by a dry developing method. The present invention relates to an image forming apparatus that forms an image by transferring an image to a transfer material conveyed by a conveying unit.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus using a dry developing method, transfer of a developer image from a photoreceptor or the like to a transfer material is performed by using a corona charger from a surface opposite to the image surface of the transfer material. However, this method has a problem in that the transfer voltage is extremely high at 4 to 8 kV, which is dangerous and generates ozone harmful to the human body.

As a method of forming a full-color image, a transfer device using an insulative belt and a corona charger for arranging four photoconductors horizontally and conveying a transfer material so as to be in contact with each photoconductor is practically used. Has been However, in this method, the transfer voltage is extremely high at 4 to 8 kV, which is dangerous and generates ozone harmful to the human body. In addition, there is a problem that a static eliminator is required to charge the belt itself.

Therefore, transfer can be performed with a voltage of 1 to 2 kV,
In addition, as a transfer method in which generation of ozone is small, for example, JP-B-60-10625 and JP-A-4-28053
As disclosed in Japanese Patent Publication No. 0, there has been proposed a transfer device including a conductive roller and a semiconductive belt in which conductive carbon is dispersed in an insulating resin. This semiconductive belt has an advantage that a charge eliminator is not required because charges do not continue to accumulate.

Further, as shown in, for example, JP-A-49-62135, a transfer material is conveyed by adsorbing a transfer material onto a belt by charging an electrically insulating belt at the same time as transferring a toner image. Further, for example, as shown in JP-A-49-89537, the side opposite to the photoconductor of the dielectric belt is charged at or before the transfer position, and the developed image on the photoconductor is transferred to the transfer material. One that separates the transfer material from the surface of the photoreceptor using electrostatic attraction generated between the dielectric member and the transfer material due to the charging. There are conventional methods for adsorbing a transfer material, such as those described above. However, both of these methods require a neutralization process of the belt by a static eliminator for the dielectric belt as described above.

[0006]

In the transfer apparatus using a semiconductive belt as described above, since the belt is semiconductive, there is no accumulation of electric charge, so that there is an advantage that a static eliminator is not required. However, since the belt is semi-conductive, spark discharge is easily generated locally in the conductive contact transfer charger, so that transfer charge cannot be uniformly applied, and transfer performance deteriorates. .

[0007] Similarly, with respect to a contact charger for electrostatically attracting a transfer material to a semiconductive transfer belt, a uniform charge cannot be applied to the transfer material by the conductive contact charger, and thus the attraction performance is not improved. There was a problem that was worsened.

With respect to the adsorption performance, a conductive resist roller has no problem in adsorbing the transfer material to the semiconductive belt at low humidity and normal temperature, but in a high humidity environment, the transfer material (paper) absorbs electricity due to moisture absorption. Due to the decrease in the resistance value, there is a problem in that the charge from the adsorption charger is transmitted through the transfer material (paper) and flows into the conductive resist roller, and the adsorption performance cannot be secured.

In addition, since the transfer belt is semiconductive, the charge from the transfer charger passes through the surface or inside of the transfer belt and acts on the suction portion, causing a problem that suction failure occurs.

Further, since the transfer belt is semiconductive,
Charge from the transfer charger leaks to the conductive portion in contact with the transfer belt through the surface or inside of the transfer belt,
A problem also occurred in that an effective transfer electric field could not be formed in the transfer portion, resulting in poor transfer.

The present invention has been made on the basis of the above circumstances, and has as its object to stably provide a charge to a semiconductive transfer belt, to enable good and stable transfer, and to provide a semiconductive transfer belt. An object of the present invention is to provide an image forming apparatus capable of preventing dielectric breakdown of a transfer belt.

Another object of the present invention is to enable good and stable electrostatic attraction of a transfer material to a semiconductive transfer belt and to prevent dielectric breakdown of the semiconductive transfer belt. An object of the present invention is to provide an image forming apparatus which can be used.

Another object of the present invention is to provide an image forming apparatus capable of stably adsorbing a transfer material to a semiconductive transfer belt even in a humid environment.

Another object of the present invention is to provide an image forming apparatus which can set the surface resistance of the semiconductive transfer belt to an appropriate range, can perform a stable suction operation, and does not cause transfer failure. .

Another object of the present invention is to prevent the charge applied from the transfer means to the semiconductive transfer belt from leaking to the area other than the transfer area via the semiconductive belt, and to prevent transfer failure. Accordingly, an object of the present invention is to provide an image forming apparatus capable of performing good and stable transfer.

[0016]

In order to achieve the above object, an image forming apparatus according to the present invention is provided with an image forming means for forming a developed image on an image carrier, and provided in contact with and opposed to the image carrier. Transport means for transporting the transfer material toward the image carrier, and a transfer charge disposed on the surface of the transport means opposite to the transfer material-bearing surface of the transport means so as to face the image carrier. And a transfer unit that electrostatically transfers the developed image onto the transfer material, and the transfer material is transferred to the transfer unit on the upstream side of the image carrier along a transfer direction of the transfer unit. A suction unit for electrostatically adsorbing, and a facing unit facing the suction unit via the conveyance unit for electrostatically adsorbing the transfer material to the conveyance unit by the suction unit, Contributing to transfer the developed image from the image carrier. The resistance value of the transport unit from the position where the transfer unit and the transport unit face each other to the image carrier is changed from the position where the transfer unit and the transport unit face each other to the position where the opposed unit and the transport unit face each other. The resistance value is smaller than the resistance value of the above-mentioned conveying means.

Further, according to the invention described above, the opposing means is grounded.

Further, the image forming apparatus of the present invention comprises a plurality of image forming means for forming developed images on a plurality of image carriers arranged along a predetermined direction, respectively, Transport means for sequentially transporting a transfer material toward the plurality of image carriers; and a transfer material of the transport means, disposed so as to face the plurality of image carriers via the transport means. A plurality of transfer means for supplying a transfer charge to a surface opposite to the support surface, and electrostatically transferring a developed image formed on each of the plurality of image carriers on the transfer material,
Along the transport direction of the transport unit and upstream of the plurality of image carriers, an attraction unit that electrostatically attracts the transfer material to the transport unit, and the transfer material is transported to the transport unit by the attraction unit. And an opposing unit that opposes the adsorbing unit via the conveying unit for electrostatically adsorbing the image. The most upstream image among the plurality of image carriers along the conveying direction of the conveying unit. The transfer from the position where the transfer means located at the most upstream position in the carrying direction is opposed to the transfer means to the image carrier located at the most upstream position, which contributes to transfer of the developed image from the carrier. The resistance value of the transfer means is smaller than the resistance value of the transfer means from the position where the transfer means located at the most upstream position is opposed to the transfer means to the position where the transfer means is opposed to the transfer means. .

[0019]

According to the image forming apparatus of the present invention, charge can be stably applied to the semiconductive transfer belt by employing an elastic bias applying means having a resistance of 10 ⁴ to 10 ¹⁰ Ω. In addition, good and stable transfer can be achieved, and dielectric breakdown of the semiconductive transfer belt can be prevented.

Further, according to the image forming apparatus of the present invention, the resistance of electrostatic transfer of the transfer material to the semiconductive transfer belt is 10
⁴ it is possible to good stably performed by adopting a to 10 ¹⁰ Omega elastic attraction bias applying means, it is possible also to prevent breakdown of the semiconductive transfer belt.

Further, according to the image forming apparatus of the present invention, the surface of the registration roller for feeding the transfer material in a timely manner is made insulative so that the transfer material can be stably transferred even in a humid environment to a semiconductive transfer belt. Can also be adsorbed.

Further, according to the image forming apparatus of the present invention, the resistance from the surface of the transfer material conveying member in contact with the suction means to the surface in contact with the image carrier is measured from the transfer means to the image carrier. , The suction operation is stable, and no transfer failure occurs.

Further, according to the image forming apparatus of the present invention, from the surface of the transfer material conveying member in contact with the suction means to the surface of one of the transfer material conveying member supporting / driving members in contact with the transfer material conveying member. The resistance value of the transfer material conveying member is set higher than the resistance value of the transfer material conveying member from the surface where the transfer means is in contact with the transfer material conveying member to the surface where the image carrier is in contact with the transfer material conveying member. By doing so, it is possible to prevent the electric charge applied from the transfer charge applying means to the semiconductive transfer belt from leaking out of the transfer region through the semiconductive belt, so that transfer failure does not occur, and And stable transfer becomes possible.

[0024]

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

FIG. 1 is a schematic sectional view of the image forming apparatus of the present invention. In FIG. 1, a photosensitive drum 1 as an image carrier
a is provided so as to be rotatable in the direction of the arrow shown in the figure.

The following are arranged around the photosensitive drum 1a along the rotation direction. That is, a charging roller 5a as charging means for uniformly charging the photosensitive drum 1a is provided in contact with the surface of the photosensitive drum 1a, and the charged photosensitive drum 1a is exposed downstream of the charging roller 5a. There is provided an exposure device 7a which is an electrostatic latent image forming means for forming an electrostatic latent image. Downstream of the exposure device 7a, there is provided a developing device 9a that stores black toner Ta, which is a black developer, and develops the electrostatic latent image formed by the exposure device 7a with the black toner Ta. ing. Downstream of the developing device 9a, a transporting unit 10 for transporting a transfer sheet P as a transfer material to the photosensitive drum 1a is provided. The transport means 10 will be described later.

Further, on the downstream side of the contact position of the photosensitive drum 1a with the transfer paper P, a blade type cleaning device 17a as a cleaning means and a discharging lamp 19 as a discharging means are provided.
a is provided. Blade type cleaning device 17
“a” is for removing the black toner Ta remaining on the photosensitive drum 1a by transferring the toner image Ta ′, which is a developer image, by the blade 21.

The charge removing lamp 19a removes electricity from the surface of the photosensitive drum 1a after the transfer. One cycle of image formation is completed by the neutralization by the neutralization lamp 19a, and the next time an image is formed, the uncharged photosensitive drum 1a is charged again by the charging roller 5a.

The conveying means 10 comprises an endless belt 11 as a transfer material conveying member having a width substantially equal to the drum width of the photosensitive drum 1a.

The belt 11 is stretched while being wound around a holding roller 13 provided as an opposing means provided on the upstream side of the transfer path of the transfer paper P and a holding roller 15 provided on the downstream side of the transfer path. ing. The distance from the holding roller 13 to the holding roller 15 is about 300 mm.

When the holding roller 13 and the holding roller 15 rotate in the directions indicated by arrows h and j, respectively, the belt 11 contacts the outer periphery of the holding roller 13 and the holding roller 15 in the direction indicated by the arrow e in FIG. It is designed to run. In this embodiment, the moving speed of the belt 11 is 5
0 mm / s, which is a printing speed of 8 sheets / minute on A4 paper.

The transport means 1 constructed as described above
In the vicinity of the transfer paper P, there is provided a paper feed cassette 25 for accommodating a large number of transfer papers P at a time.
Are taken out one by one.

The rotation of the pickup roller 27 causes the leading end of the transfer paper P taken out to abut a stopped registration roller pair 29 composed of a lower roller 29A and an upper roller 29B disposed on the front side of the conveying means 10. State, and
It stops continuously for a period of time until it is slightly bent. As a result, the transfer paper P is in a state where the leading end is positioned and aligned.

The registration roller pair 29 starts rotating at a timing such that the leading end of the toner image Ta 'formed on the photosensitive drum 1a comes to the leading end of the transfer sheet P, and conveys the transfer sheet P. It is sent to the means 10.

The transferred transfer paper P is conveyed to a suction roller 24 as suction means provided at a position facing the holding roller 13 with the belt 11 interposed therebetween. As the suction roller 24, a carbon dispersed urethane rubber roller having a diameter of 10 mm was used.

The supply of the voltage to the suction roller 24 is performed by a power supply 4.
Perform by 1. The applied voltage was -1.5 kV. The higher the applied voltage for the adsorption, the more the charge applied to the belt 11 and the more the attraction force, but the withstand voltage of the belt 11 is limited (at most about 3 kV).

The suction roller 24 rotates following the movement of the belt 11 or the transfer paper P. At the same time as the transfer paper P is conveyed to the position where the suction roller 24 is disposed, a suction bias is applied to the suction roller 24. The transfer paper P
The surface is negatively charged, and is opposite to the belt 11 (the holding roller 1).
3) is positively charged. The transfer paper P can be attracted to the belt 11 by the electrostatic force due to the charge.

The above-mentioned photosensitive drum 1a, charging roller 5a, exposing device 7a, developing device 9a, blade cleaning device 17a, and discharging lamp 19a constitute a process unit 100a for black.

At a position corresponding to the position between the holding roller 13 and the holding roller 15 on the belt 11, in addition to the black process unit 100a, a yellow image is formed along the transfer direction of the transfer paper P. Process unit 10
0b, Process unit 100 for magenta image formation
c, and a process unit 100d for cyan image formation
Are sequentially arranged.

The yellow process unit 10
0b, the process unit 100c for magenta, and the process unit 100d for cyan have the same basic configuration as the process unit 100a for black. Therefore, the above-described code a is used, the code b is used for yellow, and the code c is used for magenta. For cyan, a detailed description is omitted by changing the sign of d.

The transfer paper P conveyed on the belt 11 sequentially contacts each of the photosensitive drums 1a, 1b, 1c and 1d. The transfer paper P and the respective photosensitive drums 1a, 1b, 1
In the vicinity of the contact positions with the rollers c and 1d, the power supply rollers 23a, 23b and 23 serving as elastic bias applying means and transfer means are provided.
c, 23d are 1 for the photosensitive drums 1a, 1b, 1c, 1d.
It is provided corresponding to one to one.

That is, the power supply rollers 23a, 23b, 2
3c and 23d are the corresponding photosensitive drums 1a, 1b, 1
In the vicinity of the contact position between the belt 11 and the belt 11, the belt 11
Is provided in contact with the rear surface of the photoconductor drum 1a, and faces the photosensitive drums 1a, 1b, 1c, 1d via the belt 11.

The power supply rollers 23a, 23b,
23c and 23d are adapted to rotate following the running of the belt 11, and to rotate along with the power feeding rollers 23a and 23d.
b, 23c and 23d are connected to bias power supplies 31a, 31b, 31c and 31d as voltage applying means.

Here, an image forming process of the image forming apparatus thus configured will be described. The above four process units 100a, 100b, 100c, 100
d, the rotating photosensitive drums 1a, 1b, 1c, 1
d is first uniformly charged to about -500 V by the charging rollers 5a, 5b, 5c, 5d.

The photosensitive drum 1a uniformly charged by the charging roller 5a is irradiated with a laser beam from the exposure device 7a to form an electrostatic latent image. This electrostatic latent image is developed with black toner Ta sufficiently charged in advance by a developing device 9a, and a black toner image Ta 'is formed on the photosensitive drum 1a.
Is formed.

The yellow process unit 10
0b, magenta process unit 100c, and cyan process unit 100d.
A yellow toner image Tb ', a magenta toner image Tc', and a cyan toner image Td 'are also formed on 1c and 1d.

On the other hand, the transfer paper P is taken out of the paper feed cassette 25 by the pickup roller 27 and sent to the registration roller pair 29. The registration roller pair 29 is the transfer paper P
The transfer paper P is fed onto the belt 11 after the rotation of the photosensitive drum 1a is synchronized with the rotation of the photosensitive drum 1a so that the tip of the toner image Ta 'comes to the tip of.

The transferred transfer paper P is applied to the suction roller 24.
Is attracted to the belt 11 and conveyed. Further, when the transfer paper P is conveyed to the transfer position, the belt 11
Are power supply rollers 23a, 23b, 23c, 23d connected to respective power supplies 31a, 31b, 31c, 31d.
Are sequentially applied. The photoconductor drums 1a, 1b, 1c, 1d
A transfer electric field is sequentially formed between the belt and the belt 11.

Accordingly, first, the black toner image Ta 'on the photosensitive drum 1a is transferred onto the transfer paper P. The transfer paper P carrying the black toner image Ta 'is conveyed and reaches the photosensitive drum 1b. The yellow toner image Tb 'formed on the photosensitive drum 1b is transferred onto the previously transferred black toner image Ta' in a superimposed manner. The transfer paper P is further conveyed and sequentially faces the photosensitive drum 1c and the photosensitive drum 1d, and the magenta toner image Tc 'and the cyan toner image Td' are similarly transferred in an overlapping manner.

The transfer paper P carrying the color toner image T 'formed by the multiple transfer as described above is applied to the holding roller 1
At a position corresponding to 5, the toner image is peeled off from the belt 11, sent to a fixing device 33 as a fixing unit, and passed between a heating roller 33 and a pressure roller 35. At this time, the color toner image T '
Is fixed on the transfer paper P in a state of contact with the heating roller 33.

Here, the belt 11 used for the conveying means 10 is used.
Will be described in detail.

The belt 11 is required to have two functions, that is, transport of a transfer sheet P as a transfer material and transfer of a toner image T 'as a developer image. explain.

The composition of the transfer belt 11 is a thermosetting polyimide 90 containing 10 parts by weight of conductive carbon particles.
This was injected into a mold in parts by weight, and a seamless transfer belt 11 was produced by an imidization reaction. The size after molding is an annular shape with a width of 270 mm and a diameter of 668 mm.
00 μm. As the base material of the belt material, besides, resins such as polycarbonate, polyethylene terephthalate, polytetrafluoroethylene (Teflon (registered trademark)), and polyfukkavinylidene (PVDF), and various synthesized polymer alloys may be used. . Further, the configuration may be not only a single layer structure but also a multilayer structure.

The electrical resistance of the polyimide film in which the conductive carbon was dispersed was measured. The measurement was made with a resistance meter made by Mitsubishi Yuka, with the product name Hiresta and the model name HR
Using an SS probe, 500 V was applied, and the resistance value after 10 seconds was determined. As the resistance value, both the volume resistance value and the surface resistance value were obtained. The measurement was performed according to the measurement manual.
The measurement environment is high temperature and humidity (30 ° C, 85% RH),
Room temperature / humidity (21 ° C, 50% RH), low temperature / low humidity (10
C., 20% RH). Table 1 shows the results.

[0055]

[Table 1]

From Table 1, the surface resistance is independent of the environment.
It can be seen that it is 3.0 × 10 ¹³ Ω / □. Similarly, the volume resistance value is 3 to 4 × 10 ¹³ Ω · c regardless of the environment.
m.

Next, the power supply roller 23 as a transfer unit will be described in detail.

The power supply roller 23 (23a, 23b, 2)
3c and 23d are collectively referred to simply as 23). The photosensitive drum 1 is attached to the transfer paper P being conveyed on the transfer belt 11.
(1a, 1b, 1c, and 1d are collectively referred to simply as 1). The toner image T '(Ta', Tb ', Tc', and Td 'is collectively referred to as T') is electrostatically charged. Responsible for supplying charge for transfer.

For this reason, when an experiment was initially conducted using a metal roller connected below with a bias, the discharge was unstable and spark discharge occurred, and the charge was uniformly applied to the transfer belt 11. , And many transfer defects occurred. This is considered to be because a stable nip for performing stable discharge cannot be obtained with a rigid metal roller. (A very high degree of accuracy is required mechanically.) In addition, dielectric breakdown occurred in the transfer belt due to abnormal discharge, and it became impossible to apply a voltage.

Therefore, a conductive rubber roller having resistance and elasticity than metal is used. Specifically, a urethane rubber roller in which carbon was dispersed was used.
The urethane rubber roller is formed by winding a urethane rubber having a thickness of 3 mm around a metal shaft having a diameter of 6 mm, and has a JIS-A standard rubber hardness of 60 °. This rubber hardness is 2 to form the above-mentioned stable nip.
5 ° to 65 ° is appropriate. If it is softer than this, permanent distortion occurs. The resistance value was 4 × 10 ⁴ Ω.

The method of measuring the resistance value is as shown in FIG.
500 on each side of the metal shaft of the transfer roller 23
A voltage 202 was applied to the metal shaft and the metal flat plate 200 in a state where the weight 201 was attached to the metal flat plate 200 with the weight 201 attached thereto, and the current was measured by the ammeter 203 to obtain the resistance value.

When this urethane rubber roller was used as the power supply roller in the apparatus shown in FIG. 1, a multi-transfer experiment was carried out using 64 g of ordinary PPC paper as the transfer material.

Various bias voltage values are applied to the four sets of power supply rollers 23, and the experimental environment is set to high temperature and high humidity (30 ° C.,
The evaluation of the multiple transfer characteristics was carried out at 85% RH, normal temperature and normal humidity (21 ° C., 50% RH), and low temperature and low humidity (10 ° C., 20% RH). Table 2 shows the results.

[0064]

[Table 2]

Table 2 shows that the remaining transfer image density and the transfer image density were measured by varying the voltage applied to the four kinds of power supply rollers 23 and the transfer image remaining image density was the lowest, and the transfer image density was the lowest. Is the measurement data when is high.

The transfer bias application condition at this time is that the first transfer bias value (the output voltage value of the bias power supply 31a) is 1
200V, second transfer bias value (output voltage value of bias power supply 31b) is 1250V, third transfer bias value (output voltage value of bias power supply 31c) is 1300V, fourth transfer bias value (output voltage value of bias power supply 31d) Is 14
00V. At this time, no spark discharge or the like, which is an abnormal discharge from the power supply roller 23, was recognized, and no transfer failure occurred.

Next, a power supply roller 23 having a resistance value of 10 ¹⁰ Ω by reducing the content of conductive carbon was prepared, and the same multiple transfer characteristics were evaluated. The method of measuring the resistance value is the same as the method described above. As a result, in the power supply roller 23 of 10 ¹⁰ Ω, it was necessary to apply a considerably high voltage in order to apply the charge necessary for the transfer to the transfer belt 11. Specifically, a fourth transfer bias value of about 3000 V was required. At this time, the multi-transferred image was partially defective in transfer.

This is because the electric resistance of the power supply roller 23 has become too high, and discharge has occurred only in a certain portion of the surface of the power supply roller 23 where the conditions suitable for the discharge have been satisfied. From this result, it is considered that this resistance value is the upper limit.

Next, an experiment on the optimum resistance value of the suction roller 24 was performed.

The electrostatic attraction of the transfer sheet P will be described with reference to FIG. The transfer paper P sandwiched between the transfer belt 11 and the suction roller 24 is negatively charged by the discharge of the suction roller 24 connected to the power supply 41. With this charging, a positive charge is supplied to the transfer belt 11 from the holding roller 13, so that the transfer paper P and the transfer belt 11 are electrostatically attracted.

Initially, the suction roller also used a φ10 mm metal shaft. However, when the transfer paper P was in a humid environment, the resistance value became extremely low, and the charge retention from the suction roller 24 connected to the bias power supply was performed. A phenomenon was observed in which the electrostatic attraction between the transfer belt 11 and the transfer paper P was reduced due to the reduced capacity.

In order to cope with this, the voltage applied to the attraction roller 24 was increased to compensate for the charge decay. As a result, the voltage to be applied becomes 2000 V or more, the abnormal discharge (spark discharge) of the attraction roller 24 occurs, and it becomes impossible to uniformly charge the transfer paper P. Further, as a result of the abnormal discharge, the transfer belt 11 partially caused dielectric breakdown.

It is considered that the cause is exactly the same as what occurred in the power supply roller 24. That is, it is considered that a stable nip for performing stable discharge cannot be obtained with a rigid metal roller. Therefore, very high precision is required mechanically. Therefore, the suction roller 24 is made of a resistive roller having an elastic force like the power supply roller 23, thereby achieving the stability of discharge. Disperse carbon with a thickness of 2mm on a φ6mm metal shaft to reduce the resistance to 1
0 ⁴ Omega and the results were used, without also abnormal discharge by applying a high voltage (spark discharge), a transfer material (paper) can be given a sufficient charge for adsorbing the transfer belt there were.

Next, a suction roller 24 having a resistance value of 10 ¹⁰ Ω by reducing the content of the conductive carbon was prepared, and the suction performance was similarly evaluated. The method of measuring the resistance value is the same as the method described above. As a result, it was necessary to apply a considerably high voltage to the transfer paper P with the suction roller 24 having a resistance of 10 ¹⁴ Ω in order to apply the charge required for suction to the transfer paper P. Specifically, about 3,000 V was required. At this time, as for the suction performance, poor suction was recognized in a state where the transfer paper P was partially floated.

This is because the resistance value of the suction roller 24 was too high, and the discharge occurred only in a portion of the surface of the suction roller 24 where the conditions suitable for the discharge were satisfied. From this result, it is considered that this resistance value is the upper limit.

Next, the registration roller was studied.

This is because the operation of attracting the transfer paper P to the transfer belt 11 becomes unstable during the evaluation of the multi-transfer characteristics in a humid environment, and color shift of the multi-transfer image occurs. . The attraction force of the transfer belt 11 of the transfer paper P is
As described above, there is the holding roller 13 installed inside the transfer belt 11, and as the charge from the attraction roller 24 facing the holding roller 13 with the transfer belt 11 therebetween is applied to the transfer paper P, The electric charge of the opposite polarity to that of the attraction roller 24 is also applied to the transfer belt 11 from the installed holding roller 13. This charge causes an electrostatic force to act, and the transfer paper P is attracted to the transfer belt 11. (See FIG. 3) Here, it is considered that the decrease in the attraction force is due to leakage of the applied charges. Therefore, the evaluation of the environment (humidity) dependence of the resistance value of the transfer belt 11 and the transfer paper P was performed.

The transfer belt 11 has a volume resistance of 3 to 4 × 10 ¹³ Ω · cm and a surface resistance of 3 to 4 irrespective of the environment.
× 10 ¹³ Ω / □. (See Table 1) On the other hand, as shown in Table 3, the transfer paper P
At 3.3 ° C. and 20% RH, the volume resistivity is 3.3 × 10 ¹¹ Ω · c
m, 4.9 × 10 ¹⁰ Ω · cm at 21 ° C. and 50% RH,
At 30 ° C. and 85% RH, the resistance value changes greatly to about 6.0 × 10 ⁷ Ω · cm with respect to the environment.

[0079]

[Table 3]

Further, the surface resistance value was 10 ° C. and 20% RH.
2.2 × at 3 × 10 ¹² Ω / □, 21 ° C., 50% RH
1 × 10 ⁸ Ω at × 10 ¹⁰ Ω / □, 30 ° C., 85% RH
/ □ changes. (See Table 3) From the above, since the resistance value of the transfer paper P greatly changes due to the environment (humidity), the electric charge applied to the transfer paper P from the suction roller 24 is reduced by the resistance of the transfer paper P itself. It is probable that the fluid leaked along the registration roller pair 29, which is a conductive roller. This is shown in FIG.

Then, when this registration roller 29 was used as an insulating rubber roller and multiple transfer was performed in a humid environment, no color shift of the multiple transfer image was observed. That is, the transfer paper P was firmly attracted to the transfer belt 11.

Next, the resistance value of the transfer belt 11 was examined in detail.

The matters to be considered for the resistance value are the electrostatic attraction performance and the multiple transfer performance of the transfer paper P.
Here, the transfer performance will be discussed based on FIG. 5 in which the first transfer area is enlarged.

The transfer paper P is sandwiched between the power supply roller 23a and the photosensitive member 1a together with the transfer belt 11. In this state, a bias power supply 31a is connected to the power supply roller 23a. Electric discharge is generated from the power supply roller 24 by an electric field formed by the power supply roller 23a and the photosensitive drum 1a. The discharge voltage at this time (different from the discharge start voltage) is 120.
It was 0V.

As a result of the discharge, the discharge current i passes through the transfer belt 11 and the transfer paper P as shown in FIG.
It flows toward the photosensitive drum 1a. However, the electric charge remains on the transfer belt 11 because the resistance value of the transfer belt 11 is as high as 10 ¹³ Ω · cm. The toner image T on the photosensitive drum 1a is generated by the electric charge and the electric field formed by the photosensitive drum 1a.
a ′ is electrostatically transferred to the transfer paper P.

The transfer mechanism has been described above.
Since a semiconductive belt is used as 1, the above-described discharge charge moves along a path as shown in FIG.

That is, there are a route A1 and a route A2 in the figure. A path A1 is an electric charge that contributes to actual transfer, and leaks to the photosensitive drum 1a slightly and stays on the transfer belt 11. A path A2 is a current leaking to the grounded conductive holding roller 13 via the surface (inside) of the transfer belt 11.
Here, since A2 does not contribute to the transfer operation at all, it is an unnecessary current.

Here, the holding roller 13 needs to be conductive in order to leak the electric charge remaining on the transfer belt 11 after the transfer operation is completed. This is an indispensable component because a special static elimination step is omitted.

Therefore, in order to carry out the transfer efficiently, it is necessary to set A1> A2. In other words, it must be set so that “(volume resistance of transfer belt 11 + volume resistance of photoconductor drum 1a) <surface resistance of transfer belt 11”.

The transfer belt 11 used in the embodiment was at room temperature
At normal humidity, the volume resistance value is 3 × 10¹³Ω · cm
is there. The thickness of the transfer belt 11 is 100 μm,
The width of the roller 23a in contact with the transfer belt 11 is 200
mm, the contact nip between the power supply roller 23a and the transfer belt 11
Since the loop width is 2 mm, the volume resistance value is 7.5 × 10 ^Ten
Ω. The contact nip width of the transfer section is
The test machine is forcibly turned off and is in contact with the photosensitive drum 1a.
The width was determined by observing the appearance of the image.

Next, the volume resistance value of the photoreceptor drum 1a was measured using the above-mentioned resistance meter manufactured by Mitsubishi Yuka Co., Ltd., and the product name was Hirest.
a, using a model name HRSS probe, applying 500 V;
As a result of obtaining the resistance value after 10 seconds, it was 2 × 10 ¹⁴ Ω · cm.

Then, the resistance value was calculated in the same manner as the method for determining the actual resistance value of the transfer belt 11, and it was 1 × 10 ¹¹ Ω. (The contact nip width between the transfer belt 11 and the photosensitive drum 1a is 2 mm, and the photosensitive drum 1a
Was calculated on the assumption that the film thickness was 20 μm. Therefore, the resistance value of the transfer belt 11 and the photosensitive drum 1a in the volume direction is about 2 × 1.
0 ¹¹ Ω.

The surface resistance will be described with reference to FIG.

The surface resistance of the transfer belt 11 is about 3 × 10 ¹³
Ω / □, and the holding roller 13 is in contact with the transfer belt 11 of the power supply roller 23a.
The distance (L1) until it comes into contact with is 52 mm. The width of the power supply roller 23 in contact with the transfer belt 11 is 200 mm.
Therefore, the resistance value between the feeding roller 23a and the holding roller 13 is 3 × 10 ¹³ (Ω / □) / 200 × 52 = 7.
It becomes 8 × 10 ¹² Ω.

Therefore, the volume resistance of the transfer belt 11 + the volume resistance of the photosensitive drum 1a (2 × 10 ¹¹ Ω) is smaller than the surface resistance of the transfer belt 11 (7.8 × 10 ¹² Ω). Therefore, the discharge charge effectively forms a transfer electric field. The actual image was also a good image with no transfer failure.

Now, returning to FIG. 6, it is necessary to consider the influence of the suction roller 24.

The suction roller 24 also applies a bias voltage to apply electric charge to the transfer paper P, and the transfer belt 1
1 has a role of being adsorbed.

The charges at this time are A4 flowing along the transfer paper P and A3 leaking to the holding roller 13. Considering the resistance component of A4, the surface resistance of the transfer paper P is 2.2 × 10 ¹⁰ Ω / □ at normal temperature and normal humidity according to Table 3, and the distance between the suction roller 24 and the first transfer unit (FIG. 7). L1) is 52m
m. Since the width of the suction roller 24 is 200 mm, the surface resistance value of the transfer paper P is 5.5 × 10 ⁸ Ω.

Further, since the resistance value of the photosensitive drum 1a is 1 × 10 ¹¹ Ω from the above calculation result, the resistance value of the path through which the current of A4 flows is approximately 1 × 10 ¹¹ Ω. .

Further, when the same examination is performed for A3, the volume resistance value of the transfer paper is 4.9 × 10 ¹⁰ Ω · cm.
The nip width of the suction roller 24 with respect to the transfer paper P is 2 mm
Since the width of the suction roller 24 is 200 mm and the thickness of the transfer paper P is 0.1 mm, the volume resistance of the transfer paper P is
1.2 × 10 ⁸ Ω. Further, since the volume resistance of the transfer belt 11 is 7.5 × 10 ¹⁰ Ω as described above,
The resistance value of the path through which the current of A3 flows is approximately 7.5 × 10
¹⁰ Ω.

Here, in order that the adsorption process does not affect the transfer process, A1 and A4 involved in each process are so small that the charges of A2 and A4 do not affect each other.
And A3 are not affected. Considering this, as described above, the resistance value related to A2 (7.8 × 1
0 ¹² Ω) is larger than the resistance value related to A1 (2 × 10 ¹¹ Ω), indicating that the transfer process does not adversely affect the adsorption process. Further, the resistance value related to A4 (1 × 10 ¹¹ Ω) is changed to the resistance value related to A3 (7.
It can be seen that the adsorption process does not adversely affect the transfer process because it is larger than 5 × 10 ¹⁰ Ω).

Next, the transfer belt 11 manufactured by dispersing carbon in polycarbonate resin was evaluated. First, the results obtained by measuring the volume resistance value and the surface resistance value of the transfer belt 11 with the above-described measuring device and measuring method are shown in Table 4.

[0103]

[Table 4]

Table 4 shows measurement data of the resistance value of the carbon-dispersed polycarbonate transfer belt under each environment. Discussion is made on the resistance value under the normal temperature and normal humidity environment. (The results are basically the same under other environments.) From Table 4, the volume resistivity is 4 × 10 ⁷ Ω · cm.

The thickness of the transfer belt 11 was set to 100 μm as in the case of the carbon-dispersed polyimide transfer belt. Further, the width of the power supply roller 23a in contact with the transfer belt 11 was 200 mm, and the contact nip width of the power supply roller 23a with the transfer belt 11 was 2 mm as in the case of the carbon-dispersed polyimide transfer belt. It becomes 10 ⁵ Ω.

Since the same photosensitive drum 1a was used, the photosensitive drum 1a had a volume resistance of 1 × 10 ¹¹ Ω. Therefore, the resistance value in the volume direction between the transfer belt 11 and the photosensitive drum 1a is about 1 × 10 ¹¹ Ω. That is, it can be seen that the resistance value of the carbon-dispersed polycarbonate transfer belt 11 is extremely smaller than the resistance value of the photosensitive drum 1a.

The surface resistance will be described with reference to Table 4. The surface resistance of the transfer belt 11 is 8 × 10
⁸ Ω / □, and the holding roller 13 is in contact with the transfer belt 11 of the power supply roller 23a.
The distance (L1) until it comes into contact with 1 is 52 mm. The width of the power supply roller 23a in contact with the transfer belt 11 is 200
mm, the resistance value between the feeding roller 23a and the holding roller 13 is 8 × 10 ⁸ (Ω / □) / 200 × 52 =
It becomes 2 × 10 ⁸ Ω.

Therefore, the volume resistance of the transfer belt 11 + the volume resistance of the photosensitive drum 1a (1 × 10 ¹¹ Ω) is larger than the surface resistance of the transfer belt 11 (2 × 10 ⁸ Ω). In other words, the discharged charges flow to the conductive holding roller 13 without effectively forming the transfer electric field. This is also reflected in the actual image, and a transfer failure has occurred. Further, since a large amount of charges flowed into the holding roller 13, the suction operation became unstable.

A similar phenomenon also occurred at the fourth transfer station. This will be described with reference to FIG.

The transfer paper P is sandwiched between the power supply roller 23d and the photosensitive drum 1d together with the transfer belt 11. In this state, a bias power supply 31d is connected to the power supply roller 23d. Electric discharge is generated from the power supply roller 23d by an electric field formed by the power supply roller 23d and the photosensitive drum 1d. Discharge voltage at this time (different from discharge start voltage)
Was 1400V.

As a result of the discharge, a discharge current A5 flows to the photosensitive drum 1d through the transfer belt 11 and the transfer paper P as shown. However, transfer belt 1
Since the resistance value of 1 is as high as 10 ¹³ Ω · cm, the charge remains on the transfer belt 11. The toner image Td 'on the photosensitive drum 1d is electrostatically transferred to the transfer paper P by the electric charge and the electric field formed by the photosensitive drum 1d.

The transfer mechanism has been described above.
Since a semiconductive belt is used as 1, some of the above-described discharge charges follow the path indicated by A6 in the drawing.

The path A5 is an electric charge that contributes to the actual transfer, and leaks slightly to the photosensitive drum 1d side and stays on the transfer belt 11. A6 is a current leaking to the grounded conductive holding roller 15 via the surface (inside) of the transfer belt 11. Here, A6
Is an unnecessary current because it does not contribute to the transfer operation at all.

Here, the holding roller 15 needs to be conductive in order to leak the charge remaining on the transfer belt 11 after the transfer operation is completed. This is an indispensable component because a special static elimination step is omitted. Therefore, in order to perform transfer efficiently, it is necessary to set A5> A6. In other words, it is necessary to set “(the volume resistance value of the transfer belt 11 + the volume resistance value of the photosensitive drum 1d) <the surface resistance value of the transfer belt 11”.

The transfer belt 11 used in the embodiment was used at room temperature
At normal humidity, from Table 1, the volume resistivity is 3 × 10 ¹³ Ω · cm.
It is. The thickness of the transfer belt 11 is 100 μm, and the width of the power supply roller 23d in contact with the transfer belt 11 is 20 μm.
0 mm, and the contact nip width of the power supply roller 23d to the transfer belt 11 is 2 mm, so that the volume resistance value is 7.5 × 10
¹⁰ Ω. The contact nip width of the transfer portion was determined by observing the state of the image by observing the state of the image while forcibly turning off the experimental machine during the transfer operation.

Next, the volume resistance value of the photosensitive drum 1d was measured using the above-described resistance measuring device manufactured by Mitsubishi Yuka, and its product name was Hirest.
a, using a model name HRSS probe, applying 500 V;
As a result of obtaining the resistance value after 10 seconds, it was 2 × 10 ¹⁴ Ω · cm. Then, the resistance value was calculated in the same manner as the method of calculating the actual resistance value of the transfer belt 11, and
× 10 ¹⁰ Ω. (Calculated assuming that the contact nip width between the transfer belt 11 and the photosensitive drum 1d is 2 mm.)
The resistance value in the volume direction between the transfer belt 11 and the photosensitive drum 1d is about 2 × 10 ¹¹ Ω.

The surface resistance will be described with reference to FIG. The surface resistance of the transfer belt 11 is about 3 ×
10 ¹³ Ω / □, transfer belt 1 of power supply roller 23d
The distance (L2) from the contact with the transfer roller 11 to the contact of the holding roller 15 with the transfer belt 11 is 40 mm.
The width of the feeding roller 23d in contact with the transfer belt 11 is 2
00 mm, the feeding roller 23d and the holding roller 1
The resistance value between 5 is 3 × 10 ¹³ (Ω / □) / 200 × 4
0 = 6 × 10 ¹² Ω.

Therefore, the volume resistance of the transfer belt 11 + the volume resistance of the photosensitive drum 1d (1 × 10 ¹¹ Ω) is smaller than the surface resistance of the transfer belt 11 (6 × 10 ¹² Ω). As a result, the discharge charges effectively form a transfer electric field. In the actual fourth transfer image, a good image was obtained without transfer failure.

Next, the transfer belt 11 manufactured by dispersing carbon in polycarbonate resin was evaluated. First, the results of measuring the volume resistance value and the surface resistance value of the transfer belt 11 with the above-described measuring device and measuring method are shown in Table 5.

[0120]

[Table 5]

Table 5 shows the measured data of the resistance value of the carbon-dispersed polycarbonate transfer belt under each environment. Discussion will be made on the resistance value under the normal temperature and normal humidity environment. (Basically the same result in other environments.)
From Table 5, the volume resistance value is 4 × 10 ⁷ Ω · cm.

The thickness of the transfer belt 11 was set to 100 μm as in the case of the carbon-dispersed polyimide transfer belt. Further, the width of the power supply roller 23d in contact with the transfer belt 11 was 200 mm, and the contact nip width of the power supply roller 23d to the transfer belt 11 was 2 mm as in the case of the carbon-dispersed polyimide transfer belt. It becomes 10 ⁵ Ω.

Since the same photosensitive drum 1d was used, the volume resistivity of the photosensitive drum 1d was 1 × 10 10 Ω. Therefore, the resistance value in the volume direction between the transfer belt 11 and the photosensitive drum 1d is about 1 × 10 ¹⁰ Ω. That is, it is understood that the resistance value of the carbon-dispersed polycarbonate transfer belt 11 is extremely smaller than the resistance value of the photosensitive drum 1d.

The surface resistance will be described with reference to Table 5.

The surface resistance of the transfer belt 11 is 8 × 10 ⁸ Ω
/ □, the distance (L1) from the contact of the power supply roller 23d with the transfer belt 11 to the contact of the holding roller 15 with the transfer belt 11 is 40 mm. The width of the power supply roller 23d in contact with the transfer belt 11 is 200 mm.
Therefore, the resistance value between the feeding roller 23d and the holding roller 15 is 8 × 10 ⁸ (Ω / □) / 200 × 40 = 6 ×
10 ⁸ Ω.

Therefore, the volume resistance of the transfer belt 11 + the volume resistance of the photosensitive drum 1d (1 × 10 ¹⁰ Ω) is larger than the surface resistance of the transfer belt 11 (1.6 × 10 ⁸ Ω). As a result, the discharged charges flow to the conductive holding roller 15 without effectively forming a transfer electric field. This was reflected in the actual image.

That is, since the transfer efficiency is poor, even if the bias application condition of the carbon-dispersed polyimide / transfer belt 11 having a volume resistivity of 3.2 × 10 ¹³ Ω · cm at normal temperature and normal humidity is changed, Transfer efficiency was not improved, and transfer failure occurred. Further, the function of the bias power supply 31d has been stopped by itself due to the flow of excess current.

As described above, the feeding roller 23a (23d) as the transfer means is moved from the surface in contact with the transfer belt 11 as the transfer material transporting member to the holding roller as one of the transfer material transporting member supporting and driving members. The resistance value of the transfer belt 11 from the surface where the power supply roller 23a (23d) is in contact with the transfer belt 11 to the surface where the transfer belt 11 is in contact with the transfer belt 11 is the photosensitive drum 1a as the image carrier.
It can be seen that the resistance must be higher than (1d).

The present invention is not limited to the above-described embodiment. For example, as the transporting means 10, the belt 11 as the transfer material transporting member and the holding rollers 13, 15 as the transfer material transporting member supporting / driving member may be used. In the above description, the flat member is stretched, but the drum member may be stretched.

Of course, various modifications can be made without departing from the scope of the present invention.

[0131]

As described above, the present invention has the following effects.

That is, according to the image forming apparatus of the present invention, the electric charge is applied to the semiconductive transfer belt with a resistance value of 10 ^4.
By adopting the elastic bias applying means of 10 to 10 ¹⁰ Ω, the transfer can be stably performed, so that good and stable transfer can be performed, and the dielectric breakdown of the semiconductive transfer belt can be prevented.

Further, according to the image forming apparatus of the present invention, the resistance of the electrostatic attraction of the transfer material to the semiconductive transfer belt is 10
By employing an elastic adsorption bias applying means of ⁴ to 10 ¹⁰ Ω, it is possible to carry out the operation in a good and stable manner, and it is possible to prevent the dielectric breakdown of the semiconductive transfer belt.

Further, according to the image forming apparatus of the present invention, by making the surface of the registration roller that feeds the transfer material in a timely manner insulative, the transfer material can be transferred to a semiconductive transfer belt that is stable even in a humid environment. Can also be adsorbed.

Further, according to the image forming apparatus of the present invention, the resistance from the surface of the transfer material transporting member in contact with the suction means to the surface in contact with the image bearing member varies from the transfer device to the image bearing member. , The suction operation is stable, and no transfer failure occurs.

Further, according to the image forming apparatus of the present invention, from the surface of the transfer material conveying member in contact with the suction means to the surface of one of the transfer material conveying member supporting / driving members in contact with the transfer material conveying member. The resistance value of the transfer material conveying member is set higher than the resistance value of the transfer material conveying member from the surface where the transfer means is in contact with the transfer material conveying member to the surface where the image carrier is in contact with the transfer material conveying member. By doing so, it is possible to prevent the electric charge applied from the transfer charge applying means to the semiconductive transfer belt from leaking out of the transfer region through the semiconductive belt, so that transfer failure does not occur, and And stable transfer is possible.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an embodiment of an image forming apparatus according to the present invention.

FIG. 2 is an explanatory diagram of resistance measurement of a roller.

FIG. 3 is an explanatory diagram of a suction operation of a transfer sheet.

FIG. 4 is a diagram showing a flow of charges during an adsorption operation.

FIG. 5 is an explanatory diagram of a transfer operation.

FIG. 6 is a diagram illustrating a flow of charges during a first transfer.

FIG. 7 is a diagram illustrating an arrangement of a first transfer unit and a suction unit.

FIG. 8 is a diagram showing a flow of charges in a final transfer section.

FIG. 9 is a diagram illustrating a positional relationship between a final transfer unit and a holding roller of a transfer belt.

[Explanation of symbols]

1 (1a, 1b, 1c, 1d): Photosensitive drum (image carrier), 10: Conveying means, 11: Transfer belt (conveying means), 13: Holding roller (opposing means), 15: Holding roller, 23 ( 23a, 23b, 23c, 23d): power supply roller (transfer means), 24: suction roller (suction means), 29: pair of registration rollers, 31a, 31b, 31c, 31d: bias power supply, P: transfer paper (transfer material) , T ′ (Ta ′, Tb ′, Tc ′, Td ′)... Toner image (developed image).

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masashi Takahashi 70, Yanagicho, Kochi-ku, Kawasaki City, Kanagawa Prefecture Inside the Toshiba Yanagimachi Plant Co., Ltd. Inside

Claims (3)

[Claims] An image forming unit configured to form a developed image on an image carrier; a conveying unit provided in contact with the image carrier to convey a transfer material toward the image carrier; A transfer charge is supplied to a surface of the conveying unit opposite to the transfer material carrying surface, and the developed image is electrostatically transferred onto the transfer material. A transfer unit, an adsorption unit that electrostatically adsorbs the transfer material to the conveyance unit on the upstream side of the image carrier along a conveyance direction of the conveyance unit, and An opposing unit that opposes the adsorbing unit via the conveying unit in order to electrostatically adsorb the conveying unit, and contributes to transferring the developed image from the image carrier.
The resistance value of the transfer unit from the position where the transfer unit and the transfer unit oppose each other to the image carrier is from the position where the transfer unit and the transfer unit oppose each other to the position where the counter unit and the transfer unit oppose each other. An image forming apparatus which is smaller than a resistance value of the conveying means. 2. The image forming apparatus according to claim 1, wherein said facing means is grounded. 3. A plurality of image forming means for forming a developed image on each of a plurality of image carriers arranged along a predetermined direction; and a transfer material provided in contact with and facing the plurality of image carriers. Conveying means for sequentially conveying the plurality of image carriers, and disposed so as to face the plurality of image carriers via the conveying means, and a surface opposite to the transfer material carrying surface of the conveying means A plurality of transfer means for supplying a transfer charge and electrostatically transferring a developed image formed on each of the plurality of image carriers on the transfer material; and the plurality of transfer means along a transport direction of the transport means. Upstream of the image bearing member, an attraction unit for electrostatically adsorbing the transfer material to the transport unit; and the transport unit for electrostatically attracting the transfer material to the transport unit by the attraction unit. Opposing means opposing the suction means via And a transfer located at the most upstream position in the transport direction, which contributes to transfer of a developed image from the most upstream image carrier among the plurality of image carriers along the transport direction of the transport unit. The resistance value of the conveying means from the position where the means is opposed to the conveying means to the most upstream image carrier is
The image forming apparatus according to claim 1, wherein a resistance value of the conveyance unit from a position where the transfer unit located at the most upstream position and the conveyance unit is opposed to a position where the conveyance unit is opposed to the opposition unit is smaller.