JPH09212012A - Transfer device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of transfer defect and the lowering of recorded-image density even when environment is changed or an image forming device is used over a long period of time. SOLUTION: This device has a transfer roller disposed freely rotatably opposite an electrostatic latent image carrier 11 and made in contact with the carrier 11 via recording paper 18, and a DC power source for applying transfer voltage to the transfer roller. The transfer roller is provided with a conductive support and a semiconductive resistance layer formed on the conductive support, the resistance layer being made of a material whose resistance does not change with the applied transfer voltage. Thus, the occurrence of transfer defect such as blur and the lowering of recorded-image density are prevented even when environments such as temperature and humidity are changed or the image forming device is used over a long period of time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transfer device of an image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus using an electrophotographic recording method such as a printer, a copying machine and a FAX, an image is formed by each image forming process of charging, exposing, developing, transferring, fixing and cleaning. The surface of the electrostatic latent image carrier is uniformly and uniformly charged and exposed to form an electrostatic latent image, and then the electrostatic latent image is formed into a toner image, The toner image is transferred and fixed on the recording paper.

A transfer device is used in the transfer process, and a corona transfer device is generally used as the transfer device. However, since a high voltage power supply of 5000 to 10000 [V] is required to operate the corona transfer device, not only is it dangerous to the human body,
The cost increases. Further, the corona transfer device has low environmental stability, and in particular, is affected by humidity, and the transfer efficiency at the time of transferring the toner image formed on the electrostatic latent image carrier to the recording paper varies depending on the humidity. I will end up.

Further, since the corona transfer device utilizes the corona discharge phenomenon, ozone is generated during the operation, which not only significantly deteriorates the characteristics of the electrostatic latent image carrier but also adversely affects the human body. Will be given. Therefore, in order to prevent the human body from being affected, an ozone absorption / decomposition filter is provided in the image forming apparatus to prevent ozone from flowing out of the image forming apparatus. However, since the ozone absorption / decomposition filter has a short life in which it can absorb and decompose ozone, the ozone absorption / decomposition filter must be frequently replaced, which is troublesome.

Therefore, a semi-conductive sponge roller is used as a transfer device, the sponge roller and the electrostatic latent image carrier are brought into contact with each other via a recording sheet, and a DC voltage is applied to the sponge roller as a transfer voltage. A contact-type transfer device adapted to apply the voltage is provided (Japanese Patent Laid-Open No. 6-1927).
No. 6 publication).

[0006]

However, in the above-mentioned conventional transfer apparatus, when the environment such as temperature and humidity changes or when the image forming apparatus is used for a long period of time, transfer failure such as fading occurs. Or, the density of the recorded image, that is, the print density is reduced. The present invention solves the problems of the conventional transfer device described above, and causes a transfer failure or a decrease in print density even when the environment changes or the image forming apparatus is used for a long period of time. It is an object of the present invention to provide a transfer device that does not have such a problem.

[0007]

To this end, in the transfer device of the present invention, a transfer roller that is rotatably disposed so as to face the electrostatic latent image carrier and is in contact with the recording sheet through a recording sheet, And a DC power supply for applying a transfer voltage to the transfer roller. The transfer roller is a conductive support,
And a semiconductive resistance layer formed on the conductive support, and the resistance layer is made of a material whose resistance value does not change in response to fluctuations in the transfer voltage applied.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram of an image forming apparatus according to an embodiment of the present invention. In the figure, reference numeral 11 is an electrostatic latent image carrier (photosensitive drum) formed by disposing a photoconductive layer 11b on a conductive support drum 11a. In this embodiment, an organic photoconductor is used as the electrostatic latent image carrier 11, but any photoconductor such as a selenium photoconductor, a zinc oxide photoconductor, and an amorphous silicon photoconductor is used. You can also

Further, 12 is a charging roller disposed in contact with or in pressure contact with the surface of the electrostatic latent image carrier 11, and 13 is downstream of the charging roller 12 in the rotating direction of the electrostatic latent image carrier 11. In the exposure device, the exposure device is arranged so as to face the electrostatic latent image carrier 11. In the present embodiment, as the exposure device 13, a combination of an LED array and a SELFOC lens (trade name) is used, but a combination of a laser and an image forming optical system may be used. it can.

Reference numeral 14 designates a developing device, which is in contact with the electrostatic latent image carrier 11 or at a minute position downstream of the exposure device 13 in the rotation direction of the electrostatic latent image carrier 11. The developing device 1 is arranged at a space.
A toner carrier 15 is disposed inside the toner container 4, and a toner 16 is accommodated therein. The toner carrier 15 is the toner 1
6 is adsorbed and conveyed in the direction of the arrow. As the developing device 14, any of a two-component magnetic brush developing device, a one-component magnetic brush developing device, a one-component non-magnetic developing device and the like can be used.

Further, 17 is a paper cassette, 18 is a recording paper, 19 is a paper feed roller, 20 is a paper feed roller, 21 is a conductive shaft as a conductive support, and 22 is a rubber as a semiconductive resistance layer. Resistance layer, 23 is the conductive shaft 2
1 is a sponge roller as a semi-conductive transfer roller which is composed of a rubber resistance layer 22 and a rubber resistance layer 22. The sponge roller 23 is disposed so as to face the electrostatic latent image bearing member 11 in pressure contact therewith, and is brought into contact with the recording sheet 18 through the recording paper 18.

Reference numeral 24 is a heat roller, 25 is a pressure roller, 26 is a fixing device composed of the heat roller 24 and pressure roller 25, and 27 is the sponge roller 23 in the rotational direction of the electrostatic latent image carrier 11. The cleaner is disposed on the downstream side in contact with the electrostatic latent image carrier 11.
As the fixing device 26, either an oven fixing device or a flash fixing device can be used.

Next, the operation of the image forming apparatus having the above structure will be described. First, the electrostatic latent image carrier 11 formed in a drum shape is moved in the direction of arrow a by a driving unit (not shown).
It is rotated at a peripheral speed of 0 [mm / sec]. Then, in the charging process, the electrostatic latent image carrier 11 is uniformly and uniformly charged by the charging roller 12 rotating in the direction of the arrow.

In the exposure process, the exposure device 13 emits light corresponding to the image signal to the electrostatic latent image carrier 11.
To form an electrostatic latent image on the electrostatic latent image carrier 11. Next, in the developing process, the developing device 14
Develops the electrostatic latent image formed on the electrostatic latent image carrier 11 into a toner image. By the way, in the present embodiment, since reversal development is performed in the developing device 14, a bias voltage is applied between the conductive support drum 11a of the electrostatic latent image carrier 11 and the toner carrier 15. Therefore, in the space between the toner carrier 15 and the electrostatic latent image carrier 11, lines of electric force are generated due to the electrostatic latent image formed on the electrostatic latent image carrier 11. As a result, the charged toner 16 on the toner carrier 15 adheres to the electrostatic latent image carrier 11 by electrostatic force and forms a toner image.

As the toner 16, an insulating and non-magnetic toner is used. In addition, in the present embodiment, since the electrostatic latent image carrier 11 has a negative charge polarity, the toner 16 has an average volume particle diameter of 8 to 10 filled with a negative charge type charge control agent. 12 [μm]
It is formed by a resin of styrene type or polyester type to the extent.

It is also possible to use a magnetic toner formed by adding magnetic powder such as iron or ferrite to a resin. Further, when the charge polarity of the electrostatic latent image carrier 11 is set to be positive, it is possible to use a toner filled with a positive charge type charge control agent. After that, the recording paper 18 stored in the paper cassette 17 is taken out by the paper feed roller 19 and sent to the paper feed roller 20 whose rotation is stopped, and the skew of the recording paper 18 is corrected by the paper feed roller 20. It Next, the paper feeding roller 2
When 0 is rotated, the recording paper 18 is sent to the transfer portion formed on the downstream side of the developing device 14 in the rotation direction of the electrostatic latent image carrier 11. Then, in the transfer process, the toner image is transferred to the recording paper 18 by the sponge roller 23.

Subsequently, the recording paper 18 is attached to the fixing device 2
When it is conveyed to 6, the heat of the heating roller 24 melts the toner 16 of the toner image in the fixing process, and the toner 16 permeates between the fibers of the recording paper 18 by the pressing action. In this way, the toner image is recorded on the recording paper 18.
Is established. Then, the recording paper 18 on which the toner image is fixed is discharged to the outside of the image forming apparatus.

On the other hand, on the electrostatic latent image carrier 11 after transfer,
Although a small amount of toner 16 may remain, the cleaner 27 removes the residual toner 16 during the cleaning process. In this way, the electrostatic latent image carrier 11 is repeatedly used. By the way, the electrostatic latent image carrier 11 includes a charging roller 12 and a toner carrier 1.
5, the sponge roller 23 and the like are brought into contact with each other, but the resistance value of the electrostatic latent image carrier 11 is about 3 × 10 ^7.
On the other hand, the resistance value of the charging roller 12 is about 1 × 10 ⁶ [Ω], and the resistance value of the toner carrier 15 is about 1 × 10 ⁵ [Ω]. Both are lower than the resistance value of the image carrier 11. Therefore, even if the resistance value of the charging roller 12 or the toner carrier 15 fluctuates, the influence on the image forming process is small.

However, since the resistance value of the sponge roller 23 is higher than the resistance values of the charging roller 12 and the toner carrier 15, if the resistance values fluctuate, the image forming process is greatly affected. Therefore, like a conventional sponge roller, when the resistance value shifts to a low resistance side in a high temperature or high humidity environment, or when the resistance value shifts to a high resistance side in a low temperature or low humidity environment, blurring or the like occurs. Transfer failure occurs or the print density becomes low. Further, when the image forming apparatus is used for a long period of time, the rubber material of the sponge roller deteriorates and the resistance value shifts to the high resistance side, so that transfer defects such as blurring occur and the print density becomes low. .

Therefore, in the present embodiment, the urethane rubber as the resistance component of the sponge roller 23 contains an alkali metal, so that the resistance value of the sponge roller 23 can be maintained even if the transfer voltage to be printed varies. I try to prevent it from changing. Next, the sponge roller 23 will be described.

The sponge roller 23 is constituted by forming a foam-shaped rubber resistance layer 22 on the conductive shaft 21, and is rotated in the arrow direction by a drive system (not shown). The peripheral speed of the sponge roller 23 is made substantially equal to the peripheral speed of the electrostatic latent image carrier 11. The rubber resistance layer 22 is made of urethane rubber as a resistance component containing an alkali metal and has a resistance value of 3 × 10 ^8.
It is made of urethane foam adjusted to [Ω]. The hardness of the rubber resistance layer 22 is 35 [°] (Asker C), and the pressure contact force to the electrostatic latent image carrier 11 is 200.
It is set to 0 [gf].

A DC power supply (not shown) is connected between the conductive shaft 21 of the sponge roller 23 and the conductive support drum 11a of the electrostatic latent image carrier 11, and the conductivity of the sponge roller 23 is controlled by the DC power supply. A transfer voltage of about 3000 [V] is applied to the shaft 21. The polarity of the transfer voltage applied to the sponge roller 23 of the DC power source is positive in this embodiment, but this is because the toner 16 of the negative charging type is used. When the toner 16 of the mold is used, the polarity of the transfer voltage applied to the sponge roller 23 of the DC power source is made negative. Further, although urethane rubber is used as the resistance component in the present embodiment, a rubber material such as silicone rubber may be used.

Next, the dimensions of the sponge roller 23 will be described. Diameter 8 as the conductive shaft 21
A [mm] stainless steel shaft is used, and a foam-shaped semi-conductive urethane rubber containing an alkali metal in urethane rubber is molded as the rubber resistance layer 22 on the stainless steel shaft. Therefore, the finished outer diameter of the sponge roller 23 is 18 mm, and the length of the rubber resistance layer 22 in the longitudinal direction is 220 mm.
It is. In addition, the rubber resistance layer 2 of the sponge roller 23
The length in the longitudinal direction of 2 is determined by the length in the longitudinal direction of the photoconductive layer 11b of the electrostatic latent image carrier 11.

In the electrostatic latent image carrier 11, it is difficult to form the photoconductive layer 11b on the circumference of both ends in the longitudinal direction in the manufacturing process. Therefore, the rubber resistance layer 2 of the sponge roller 23
The longitudinal dimension of the electrostatic latent image carrier 1 is set so that the direct current from the DC power source does not leak to the electrostatic latent image carrier 11.
It is made smaller than the longitudinal dimension of the first photoconductive layer 11b.
In this case, the conductive shaft 21 is made of stainless steel,
Metal shafts such as steel and aluminum are used.

As the rubber resistance layer 22, for example, rubber materials such as butyl rubber, chloroprene rubber, urethane rubber, silicone rubber, nitrile rubber, styrene rubber, butadiene rubber, fluororubber, ethylene propylene rubber, graphite, ferrite, and aluminum are used. Powder, copper powder, bronze powder, stainless powder or the like, or a material to which conductive powder such as titanium oxide or tin oxide, metal powder, metal fiber or the like is added is used and molded into a foam or solid shape. The resistance value of the rubber resistance layer 22 is preferably set within the range of 10 ⁶ to 10 ⁹ [Ω] from various experiments.

When the resistance value of the rubber resistance layer 22 is smaller than the above range, if the photoconductive layer 11b formed on the electrostatic latent image carrier 11 has a defect such as a pinhole, the sponge roller 23 will be damaged. A direct current from the direct current power source easily leaks to the electrostatic latent image carrier 11 and a transfer failure easily occurs. Further, if the resistance value of the rubber resistance layer 22 is larger than the above range, transfer failure is likely to occur.

In order to obtain a proper contact width in the longitudinal direction of the contact surface between the sponge roller 23 and the electrostatic latent image carrier 11, in the case of the foam-shaped rubber resistance layer 22, The hardness of the rubber resistance layer 22 is preferably 20 to 60 [°] (Asker C). In the case of the solid rubber resistance layer 22, the hardness of the rubber resistance layer 22 is 30 [°].
(JIS A) is preferable.

When the pressure contact force of the sponge roller 23 to the electrostatic latent image carrier 11 is about 400 to 4000 [gf], which depends on the hardness of the rubber resistance layer 22, transfer such as hollowing at the time of transfer. It was good without any defects.
The transfer voltage applied to the conductive shaft 21 is 500 to 5000 although it depends on the resistance value of the rubber resistance layer 22.
When set to [V], transfer becomes possible.

Next, the result of comparison between the sponge roller 23 and a conventional sponge roller will be described. FIG.
FIG. 4 is a relationship diagram between a transfer voltage and a resistance value of a sponge roller. In the figure, the horizontal axis represents the transfer voltage and the vertical axis represents the resistance value of the sponge roller. In the figure, the broken line shows the resistance value of the conventional sponge roller, and the solid line shows the resistance value of the sponge roller 23 (FIG. 1) of the present invention.

In the conventional sponge roller, the resistance value is about 1 × 10 ⁹ [Ω] when the transfer voltage is 1000 [V], but as the transfer voltage is increased, the resistance value becomes smaller and the transfer voltage becomes smaller. At 4000 [V], the resistance value is about 4 x 10
It becomes ⁷ [Ω]. As described above, the resistance value of the conventional sponge roller has voltage dependency, and changes depending on the fluctuation of the transfer voltage.

On the other hand, the sponge roller 2 of the present invention
The resistance value of 3 has no voltage dependence, is always constant even when the transfer voltage changes, and is 3 × 10 ⁸ [Ω].
Next, using the conventional sponge roller and the sponge roller 23 of the present invention, the toner image on the electrostatic latent image carrier 11 is transferred to the recording paper 18 while changing the transfer voltage of the DC power supply (not shown), The OD value (print density) at that time was measured to determine the optimum range of transfer voltage.

FIG. 3 is a first diagram showing the relationship between the transfer voltage and the OD value, and FIG. 4 is a second diagram showing the relationship between the transfer voltage and the OD value. In FIG. 4, the horizontal axis represents the transfer voltage and the vertical axis represents the OD value. In the figure, L1 represents an OD value when a toner image on the electrostatic latent image carrier 11 is transferred onto the recording paper 18 while changing the transfer voltage of a DC power source (not shown) using a conventional sponge roller. Line, L2
When the toner image on the electrostatic latent image carrier 11 is transferred to the recording paper 18 while changing the transfer voltage of the DC power source using the sponge roller 23 (FIG. 1) of the present invention.
It is a line which shows D value.

By the way, when the conventional sponge roller is used, the resistance value changes when the transfer voltage fluctuates.
The transfer voltage and the transfer current are non-linear. When it is determined that the transfer efficiency is good when the OD value is 1.2 or more, the optimum transfer voltage range is 2250 to 3250 [V].
Therefore, the transfer voltage margin is narrow, about 1000 [V].

On the other hand, the sponge roller 2 of the present invention
When 3 is used, the transfer voltage and the transfer current are linear because the resistance value does not change even if the transfer voltage changes. When it is determined that the transfer efficiency is good when the OD value is 1.2 or more, the optimum transfer voltage range is 1750 to 500.
0 [V], the transfer voltage margin is wide, about 3250
[V].

Thus, the sponge roller 23 of the present invention
In, the voltage dependency of the resistance value is low, it does not change even if the transfer voltage fluctuates, and the transfer voltage margin becomes wide. Therefore, even if the resistance value characteristic shifts to the high resistance side or the low resistance side due to changes in the environment such as temperature and humidity or when the image forming apparatus is used for a long period of time, the transfer voltage margin is wide, which is optimal. The transfer voltage can be maintained. As a result, transfer defects such as blurring do not occur and the density of the recorded image does not decrease.

In the present embodiment, the sponge roller 23 in which the resistance value does not change even if the transfer voltage changes and the transfer voltage and the transfer current are completely linear has been described. It is also possible to use a sponge roller having a voltage dependency. In this case, for example, 1000
Sponge roller 23 when a transfer voltage of [V] is applied
When the resistance value of R1 is R1 [Ω], the transfer voltage is increased to obtain a transfer voltage V1 [V] at which the resistance value of the sponge roller 23 becomes 0.1 × R1 [Ω].

At this time, the potential difference V2 [V] is V2 = V1-1000. Further, for example, when the conventional sponge roller is described with reference to FIG. 2, the resistance value of the conventional sponge roller when a transfer voltage of 1000 [V] is applied is about 1.
Although it is × 10 ⁹ [Ω], the transfer voltage is about 3000 [V] when the resistance value becomes 1/10, that is, when it becomes about 1 × 10 ⁸ [Ω]. Therefore, the potential difference V
2 becomes about 2000 [V].

The higher the potential difference V2, the lower the voltage dependence of the resistance value. When a sponge roller having a potential difference V2 of 4000 [V] or more is used, the transfer voltage margin is about the same as when the conventional sponge roller is used. It turned out to be more than twice as wide. In the present embodiment, when applying the transfer voltage to the sponge roller 23,
Although constant voltage control is performed, for example, constant current control can also be performed. In this case, the voltage is determined by performing the constant current control, and the constant voltage control is performed using the voltage as the transfer voltage.

As the sponge roller 23, a two-layer structure in which a conductive shaft 21 and a rubber resistance layer 22 are molded is used. The resistance layer, the intermediate layer, the elastic layer, the surface layer, etc. are made conductive. It is also possible to use a semi-conductive rubber roller having a three-layer structure or a four-layer structure formed on the shaft 21 or a sponge roller. It should be noted that the present invention is not limited to the above-described embodiment, but can be variously modified based on the gist of the present invention, and these are not excluded from the scope of the present invention.

[0040]

As described above in detail, according to the present invention, in the transfer device, the transfer is arranged so as to face the electrostatic latent image carrier so as to be rotatable and contacted through the recording paper. It has a roller and a DC power supply for applying a transfer voltage to the transfer roller. The transfer roller includes a conductive support and a semiconductive resistance layer formed on the conductive support, and the resistance layer has a resistance value with respect to a change in an applied transfer voltage. Consists of a material that does not change.

In this case, when a transfer voltage is applied to the transfer roller by the DC power source, the toner image on the electrostatic latent image carrier is transferred to the recording paper. Since the semiconductive resistance layer is made of a material whose resistance value does not change in response to fluctuations in the applied transfer voltage, the resistance value of the transfer roller has a low voltage dependence, and the transfer voltage fluctuates. Does not change.

Therefore, even if the environment such as temperature and humidity is changed, or the image forming apparatus is used for a long period of time, a transfer defect such as blurring does not occur and the print density does not decrease. .

[Brief description of drawings]

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

FIG. 2 is a relationship diagram between a transfer voltage and a resistance value of a sponge roller.

FIG. 3 is a first diagram showing a relationship between a transfer voltage and an OD value.

FIG. 4 is a second diagram showing the relationship between transfer voltage and OD value.

[Explanation of symbols]

 11 Electrostatic Latent Image Carrier 18 Recording Paper 21 Conductive Shaft 22 Rubber Resistance Layer 23 Sponge Roller

Claims (2)

[Claims] 1. A transfer roller, which is rotatably disposed so as to face an electrostatic latent image carrier and is in contact with a recording sheet, and (b) a direct current (DC) for applying a transfer voltage to the transfer roller. And (c) the transfer roller has a power source,
A conductive support and a semiconductive resistance layer formed on the conductive support, wherein the resistance layer is made of a material whose resistance value does not change in response to fluctuations of an applied transfer voltage. Transfer device characterized by. 2. The transfer device according to claim 1, wherein the resistance layer is made of a material having a resistance component containing an alkali metal.