JPH05224546A - Fixing device of image forming device - Google Patents

Abstract

PURPOSE:To detach the unfixed developer on a recording material from a fixing roller and to prevent the offset thereof by impressing the voltage of the polarity reverse to the electrifying polarity of the developer on the mandrel of a pressurizing roller. CONSTITUTION:The fixing roller 10 constituted by forming a release layer 101 on the front layer of the mandrel 102 consisting of a good conductor metal, such as aluminum, is used. The bias voltage divided by resistors R1', R2' from the output of a high-voltage power source 14' for supplying the bias voltage to a transfer roller 8 is impressed to the mandrel 113 of the pressurizing roller 11'. Positive-polarity charges are accumulated on the elastic conductive layer 112 side in the part where the fixing roller 10 and the pressurizing roller 11, are nipped. On the other hand, negative-polarity charges are induced on the mandrel 102 side, by which the electric field for repulsing the negative-polarity toners constituting an unfixed sensible image 6' from the fixing roller 10 is formed and the generation of the offset image is suppressed. The bias voltage to be applied to the mandrel 113 is determined by the resistance values of a rubber layer 112 and the release layer 101 and is preferably in a range from +200 to +2000V.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device for an image forming apparatus such as a copying machine or a printer which utilizes electrophotography.

[0002]

2. Description of the Related Art FIG. 5 shows an example of a conventional image forming apparatus. In FIG. 5, reference numeral 1 is a photosensitive drum that is a latent image carrier. The photosensitive drum 1 has a thin layer of an organic semiconductor on the surface,
As it rotates in the direction of the arrow, it is uniformly negatively charged by the charging roller 2 as a charging means, and a desired electrostatic latent image is formed by turning on / off the laser beam 3 emitted by the exposing means (not shown). The developing device 4 stores negatively charged charged particles 5 (hereinafter referred to as toner) as a developer,
Reversal development is performed to apply the toner 5 to the portion irradiated with the laser light 3 to form a visible image 6. On the other hand, the transfer paper 7 as a recording material fed one by one from a cassette (not shown) is inserted into a nip area formed by the photosensitive drum 1 and a transfer roller 8 as a transfer means in synchronization with the visible image 6, and the power source is supplied. By a positive bias voltage applied to the transfer roller 8 from a not-shown (not shown), it is transferred onto the transfer paper 7 as a visible image 6 '. The toner remaining on the photosensitive drum 1 after transfer is cleaned by the cleaner 9, and the photosensitive drum 1 is used for the next image formation.

The transfer sheet 7 that has undergone the transfer step is guided to a fixing device composed of a fixing roller 10 and a pressure roller 11.
A heater 13 is arranged inside the fixing roller 10, and a temperature detecting element 12 is arranged in contact with the surface of the fixing roller 10. The output of the temperature detection element 12 is fed back to a controller (not shown), and the heater 13 is turned on / off to control the surface to a predetermined temperature. The pressure roller 11 is pressed against the fixing roller 10 with an appropriate pressure, and when the unfixed visible image 6 ′ on the transfer sheet 7 is inserted into the nip formed by the pressure roller 11 and the fixing roller 10, it is heated and applied. It becomes a permanent fixed image 6 ″ by being pressed. In this fixing step, a part of the unfixed visible image 6 ′ is transferred to the surface of the fixing roller 10 and again transferred to the succeeding transfer paper 7 to form a so-called offset phenomenon. In the past, it was general to arrange a cleaning unit on the surface of the fixing roller 10 to remove the toner transferred to the surface of the fixing roller 10.

However, since the toner is accumulated in the cleaning means and the cleaning capacity is eventually reached, the cleaning means has to be replaced periodically. Therefore, for example, Japanese Patent Application No. 02 was proposed.
As disclosed in Japanese Patent Application No. 013906, a bias voltage is applied to the fixing roller 10 to prevent an offset image. By this method, the cleaning means for the fixing roller 10 can be removed.

FIG. 6 shows an example of such a fixing device, and the same parts as those in FIG. 5 are designated by the same reference numerals. The fixing roller 10 is formed by forming a release layer 101 of an insulating thin film on a cylindrical core metal 102, and a negative bias voltage is applied to the core metal 102. In the image forming apparatus using the reversal development, the bias voltage applied to the charging roller 2 is negative and the charging roller 2 of the high voltage power supply 14 is charged.
The negative bias voltage divided by the resistors R1 and R2 is supplied to the core metal 102 from the output terminal for use in the. As a result, the negative-polarity toner forming the unfixed visible image 6'is electrostatically repelled from the fixing roller 10, does not transfer to the surface thereof, and the offset image does not occur even without providing cleaning means.

[0006]

However, in the conventional example shown in FIG. 6, it has been found that the following problems occur because the negative bias voltage is applied to the core metal 102. (1) When the transfer paper 7 absorbs moisture in a high humidity environment, the resistance of the transfer paper 7 is reduced, and when the transfer paper 7 is sandwiched between the transfer roller 8 and the fixing roller 10 and is sandwiched by both rollers, the transfer paper 7
In some cases, the positive bias voltage for transfer and the negative bias for fixing are short-circuited via the transfer bias voltage, and the transfer bias voltage drops, resulting in a transfer failure phenomenon in which the transfer efficiency of the visible image 6 is greatly reduced. (2) Due to long-term use, the insulating layer 101 on the surface layer of the fixing roller 10 is worn at the contact portion of the temperature detecting element 12, and the core metal 1
02 and the temperature sensing element 12 come into direct contact with each other, the bias voltage supplied to the core metal 102 is applied to the temperature sensing element 12 itself, and the temperature sensing element 12
The circuit of itself or a temperature controller (not shown) may be damaged.

The present invention solves the above problems and provides a fixing device for an image forming apparatus which can prevent offset without causing transfer failure in a high humidity environment and damage to the temperature detecting element during long-term use. The purpose is to

[0008]

According to the present invention, the above object is to provide a latent image carrier whose surface is endlessly movable, charging means for uniformly charging the surface, and exposing the charged surface. And an exposing unit for forming an electrostatic latent image, a developing device for developing the electrostatic latent image to form an unfixed developer image, and a transfer unit for transferring the unfixed developer image to the surface of the recording material. In a fixing device of an image forming apparatus having a fixing device having an elastic layer formed on a core metal and a pressure roller for fixing and conveying the recording material by pinching, the back surface of the recording material is contacted. It is achieved by applying a voltage having a polarity opposite to the charging polarity of the developer from the power source of the charging unit or the transfer unit to the core metal of the pressure roller.

[0009]

According to the present invention, when a voltage having a polarity opposite to the charge polarity of the developer is applied to the core metal of the pressure roller, the charge of the polarity is stored in the elastic layer of the pressure roller.

On the other hand, since the core metal of the fixing roller is grounded, a charge having the same polarity as the charge polarity of the developer is induced in the elastic layer of the fixing roller by the above charge. As a result, an electric field is generated in the direction in which the unfixed developer image on the recording material is separated from the fixing roller and attracted to the recording material, so that offset is prevented. Further, even if the recording material whose resistance has been reduced in a high humidity environment straddles the transfer unit and the fixing device, a voltage having a polarity opposite to the charge polarity of the developer is applied to the pressure roller from the transfer unit or the charging unit, Since the transfer means and the pressure roller have the same potential, the transfer voltage is not lowered via the recording material. Further, even if the surface of the fixing roller is worn due to long-term use and the temperature detecting element and the cored bar come into contact with each other, the cored bar is grounded so that the temperature detecting element is not damaged.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First to third embodiments of the present invention will be described with reference to the drawings.

<First Embodiment> First, a first embodiment of the present invention will be described with reference to FIG. The parts common to those of the conventional apparatus of FIGS. 5 and 6 are designated by the same reference numerals, and the description thereof will be omitted.

[0013] PTFE of the fixing roller 10 surface layer 30~100μm thick electrical resistance 10 ¹³ ~10 ¹⁵ Ω · cm of the core metal 102 made of a good heat conductor metal such as aluminum, PF
By using a release layer 101 such as A formed by winding an element such as a thermistor with an insulating coating tape such as polyimide having a thickness of 30 to 50 μm, the temperature detecting element 12 is pressed into contact with the release layer 101 to form a core. Gold 102 is grounded. Pressure roller 1
1'is an electric resistance of 10 ² to 1 obtained by dispersing carbon in liquid silicone rubber (LSR) as an elastic layer on the core metal 113.
A conductive rubber layer 112 having a thickness of 0 ⁶ Ω · cm is formed, and a release layer 111 having a high resistance is provided as a surface layer around which a carbon-dispersed PFA tube having an electric resistance of 10 ⁷ to 10 ¹⁰ Ω · cm is wound. Then, the core metal 113 is connected to the resistors R1 'and R1 from the output of the high voltage power source 14' which supplies the bias voltage to the transfer roller 8.
Bias voltage divided by 2'is applied. In the nip portion between the fixing roller 10 and the pressure roller 11 ′, the positive charge is stored on the conductive rubber layer 112 side, while the core metal 10
A negative charge is induced on the second side, an electric field that repels the negative toner that forms the unfixed visible image 6 ′ from the fixing roller 10 is formed, and the occurrence of an offset image is suppressed. Core 1
The magnitude of the bias voltage to be applied to the rubber layer 13 is
2. It may be determined by the resistance values of the release layer 111 and the release layer 101, but experiments have revealed that the offset image can be effectively prevented in the range of + 200v to + 2000v.

According to the structure of the present embodiment, the polarity of the bias voltage applied to the fixing device is positive and the same as that of the transfer, so that the transfer paper 7 that has absorbed moisture in a high humidity environment as in the conventional example is used. There is no short circuit between the positive high voltage for transfer and the negative high voltage for fixing, and good transfer performance can be secured even in a high humidity environment. Further, even if the temperature detecting element 12 wears the surface layer 101 due to long-term use and the core metal 102 comes into contact with the temperature detecting element 12 itself, the core metal 1
Since 02 is the ground potential, the temperature detecting element 12 and the temperature control circuit (not shown) are not damaged.

Further, in this embodiment, the bias voltage divided from the transfer bias by the resistors R1 'and R2' is applied to the pressure roller 1.
Since it is supplied to 1 ', the power source dedicated to the pressure roller 11' can be omitted. Further, when a power supply having a constant current characteristic is used, the transfer roller 8 itself has a high resistance in a low humidity environment, so the transfer bias voltage becomes high in a low humidity environment, and only in a low humidity environment in which an offset image is likely to occur. The bias voltage of the pressure roller 11 ′ can also be made high, and a measure against leakage around the bias wiring, which tends to occur especially in a high humidity environment, can be easily performed because the bias voltage becomes low in a high humidity environment. is there.

Incidentally, the electrically conductive rubber layer 112 having a lower electrical resistance is more effective in preventing offset of the bias voltage applied to the core metal 113, but the hardness of the rubber layer 112 is increased as the resistance is lowered. Since the paper 7 is wrinkled or the nip width is reduced to cause improper fixing, the resistance value of the conductive rubber layer 112 is selected according to the conditions such as the process speed, the diameter of the fixing roller 10 and the diameter of the pressure roller 11 '. I have to do it.

Further, as the surface release layer 111, an insulating material such as a PFA tube containing no carbon may be used, but especially when the process speed is about 100 mm / sec or more, the friction between the transfer paper 7 and the surface layer 111 occurs. Since an offset image may be generated due to charging, carbon or the like may be dispersed in the surface layer 111 at such a relatively high speed,
It is preferable to reduce frictional electrification with the transfer paper 7. In addition, a material having a good releasability is indispensable as the surface layer 111. Without this, the surface is contaminated with the toner 5 and the like due to the durability, and the transfer paper 7 is wound around. Regarding the electric resistance value of the surface layer 111, if the resistance value is too low, the bias voltage of the pressure roller 11 ′ is short-circuited via the fixing roller 10, so that the resistance value is preferably high.

<Second Embodiment> Next, a second embodiment of the present invention will be described with reference to FIGS. The same parts as those of the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

In the first embodiment described above, the pressure roller 11 'is a two-layer roller in which the conductive rubber layer 112 and the surface layer 111 are provided on the core metal 113, but in this structure, the roller is integrated as a roller. The hardness is 50 to 70 degrees (Asker C), and there is a problem that wrinkles are generated especially when a folded bag-like object such as an envelope is used as the transfer paper 7. This embodiment provides a fixing device that can deal with transfer paper 7 such as an envelope and can effectively prevent an offset image, and has the same configuration as the first embodiment except for the pressure roller 11 ″. Descriptions other than the pressure roller 11 ″ will be omitted.

2 shows a vertical cross section of the pressure roller 11 "of this embodiment. A sponge layer 114, which is electrically insulative, is provided on the core metal 113, and a conductive rubber is sequentially formed on the sponge layer 114. A layer 112 and a surface release layer 111 are formed.
2 shows a portion of a cross section of the device shown in FIG. 2 taken along the line AA ′.
This shows a state in which the end face of 1 "is covered and is electrically coupled to the core metal 113. With such a three-layer structure, the electrical conductivity is a relatively thin conductive rubber layer. It is possible to prevent envelope wrinkles and offset images by securing the elasticity with an insulating thick sponge layer, so that the surface PFA layer is 50 μm thick and the conductive rubber layer 112 is 1 mm thick. Thickness and sponge layer 114 is 5 mm
When the thickness was set, the hardness was 40 degrees (Asker C), and the fixability was good under the condition that envelope wrinkling did not occur.

<Third Embodiment> Next, a third embodiment of the present invention will be described with reference to FIG. The same parts as those of the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

FIG. 4 shows a third embodiment of the present invention. In this embodiment, a corona charger 2'is used as the primary charging means, and its charging polarity is positive polarity which is opposite to that of the toner 5. That is, unlike the first and second embodiments, the laser light 3 is used in this embodiment.
The offset image is prevented in the image forming apparatus using the regular development in which the toner 5 is adhered to the portion not irradiated by the light. The output of the high voltage power supply 14 "supplying the positive bias voltage to the primary charger 2'is connected to the resistor R1 '. A positive bias voltage divided by R2 'is applied to the pressure roller 11'.Depending on the type of the organic semiconductor of the photosensitive drum 1, it may be easily affected by the transfer charging history, and the transfer is performed depending on the presence or absence of the transfer paper 7. There is a case where the value and polarity of the bias voltage applied to the roller 8 must be switched, and when a bias is supplied from the transfer bias to the pressure roller 11 ′, the bias voltage of the pressure roller 11 ′ also changes in conjunction. The effect of preventing the generation of offset images may be diminished, whereas in comparison with primary charging, stable positive bias voltage is applied at least during a series of image forming periods. Since maintaining a positive bias voltage is also stabilized the pressure roller 11 'is applied, occurrence of the offset image can be effectively prevented.

The core metal 1 of the fixing roller 10 of this embodiment is
02 is grounded via the diode 15, and the potential of the cored bar 102 is maintained at zero or negative. This utilizes self-charging due to frictional charging of the transfer paper 7 and the fixing roller 10,
This reinforces the repulsive electric field of the toner 5 constituting the unfixed visible image 6'in the nip portion, and cooperates with the positive bias voltage of the pressure roller 11 'to more effectively prevent the offset image. In this embodiment, the cored bar 102 has only a small amount of electric charge that is self-charged, which causes transfer failure (short-circuit with the transfer bias) and damage to the temperature detection element 12 in a high humidity environment. There is no such thing.

[0024]

As described above, according to the present invention,
Since a voltage having a polarity opposite to the charge polarity of the developer is applied to the core metal of the pressure roller, the unfixed developer image on the recording material can be separated from the fixing roller to prevent offset. Further, since the voltage applied to the pressure roller is supplied from the charging unit or the transfer unit and has a polarity opposite to the charge polarity of the developer, the transfer unit is used when the recording material has a low resistance in a high humidity environment. Even when it straddles the fixing roller, the transfer voltage is not lowered and the transfer failure does not occur. Further, even if the temperature detecting element wears the elastic layer of the fixing roller due to long-term use and the temperature detecting element and the core metal of the fixing roller come into contact with each other, since the core metal is grounded, the temperature detecting element is Do not damage.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a schematic configuration of a device according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a schematic configuration of a second embodiment device of the present invention.

FIG. 3 is a sectional view taken along the line A-A ′ of the apparatus shown in FIG.

FIG. 4 is a sectional view showing a schematic configuration of a device of a fourth embodiment of the present invention.

FIG. 5 is a sectional view showing a schematic configuration of a conventional device.

FIG. 6 is a cross-sectional view showing a schematic configuration of another conventional device.

[Explanation of symbols]

 1 latent image carrier (photosensitive drum) 2 charging means (primary charger) 4 developing device 6'unfixed developer image 7 recording material (transfer paper) 8 transfer means (transfer roller) 10 fixing roller 11 'pressure roller 101 elastic layer (release layer) 102 core metal 111, 112 elastic layer (release layer, rubber layer) 113 core metal

Front page continuation (72) Inventor Yasumasa Otsuka 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (2)

[Claims] 1. A latent image carrier having an endlessly movable surface, a charging unit for uniformly charging the surface, an exposing unit for exposing the charged surface to form an electrostatic latent image, A developing device that develops an electrostatic latent image to form an unfixed developer image, a transfer unit that transfers the unfixed developer image to a recording material surface, a fixing roller having an elastic layer formed on a core metal, and In a fixing device of an image forming apparatus including a fixing device that conveys and fixes the recording material by a pressure roller while sandwiching the recording material, a core metal of the pressure roller that contacts the back surface of the recording material,
A fixing device for an image forming apparatus, wherein a voltage having a polarity opposite to a charging polarity of a developer is applied from a power source of the charging unit or the transfer unit. 2. The fixing device of the image forming apparatus according to claim 1, wherein the elastic layer of the pressure roller has a surface layer in which a thin high resistance release layer is formed on the low resistance elastic layer.