JP2003076210A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of preventing the back surface staining of transfer material. SOLUTION: In this image forming apparatus having a fixing device thermally fixing an unfixed toner image on the transfer material while holding the transfer material between a pair of heated rotating bodies after transferring a toner image formed on an image carrier to the transfer material, the fixing device is provided with a cleaning member for a fixing roller being the rotating body on a side with which the unfixed toner image comes into contact, and the temperature of a pressure roller opposed to the fixing roller is set to be higher than that of the fixing roller and lower than that at the thermal fixing time, then the fixing roller and the pressure roller are rotated when they do not hold the transfer material.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copying machine, a printer and a fax machine which form an image on a transfer material by using electrophotographic technology.
And other image forming apparatuses.

[0002]

2. Description of the Related Art 1 of image forming means in an image forming apparatus
A type using an electrostatic transfer process is known, and in this type of image forming apparatus, a toner image electrostatically formed on a transfer material such as paper is fixed and fixed on the transfer material. A fixing device is used for. As this fixing device, a fixing roller heated by a heater and a pressure roller which is also heated and pressure-contacted with the fixing roller are provided, and a pressure-contact nip portion formed by these both rollers,
There is a type in which a toner image is passed through an electrostatically formed transfer material to fix and fix the toner image on the transfer material. This type of fixing device has high thermal efficiency and excellent safety,
It has advantages such as miniaturization and has been widely put into practical use.

However, in this type of fixing device, since the toner image on the transfer material comes into direct contact with the fixing roller, a part of the toner adheres to the fixing roller during fixing, and the adhered toner arrives next. There is a case where a so-called offset phenomenon occurs which adheres to the surface and causes deterioration of image quality.

Therefore, in order to avoid the offset phenomenon, the surface of the fixing roller is made of a material having a good releasability for the toner, and a means such as applying silicone oil is adopted.

However, since it is difficult to completely eliminate the offset phenomenon even if such means is adopted, a type of cleaning the toner adhering to the fixing roller has been proposed. As one type of this cleaning means, a cleaning web (a belt-shaped cleaning member) made of a non-woven fabric impregnated with silicon oil is always brought into contact with and pressed against a rotating fixing roller, and the web is sequentially wound. In some cases, the application of oil to the surface of the fixing roller and the cleaning of the surface of the fixing roller are simultaneously performed during the winding.

In the above-mentioned cleaning means, the fresh cleaning web surface that is successively fed is always in sliding contact with the fixing roller surface, and the offset toner wiped off when the web is wound is successively collected, so that the cleaning is performed. It has excellent functionality. Further, since the oil is applied at the same time as the cleaning, the fixing device can be made relatively simple and small and lightweight. An example of such an image forming apparatus will be described as a conventional example.

First, an outline of the entire image forming apparatus will be described with reference to FIG.

The surface of the image carrier 1 uniformly charged by the charging device 3 is irradiated with a laser or the like according to image information to form an electrostatic latent image. Then, after the electrostatic latent image is developed into a toner image by the developing device 3, the toner image on the image carrier 1 is transferred onto the transfer material by the transfer device 7. The unfixed toner image on the transfer material in this state is heated and pressed by the fixing device 9 to obtain an electrophotographic image.

Next, the outline of the fixing device 9 will be described with reference to FIG.

The fixing device 9 has a halogen heater 12 inside.
The fixing roller 10 includes a pressure roller 11, a pressure roller 11, a cleaning web 18 for cleaning the fixing roller 10, an upper fixing claw 16 and the like. The fixing roller 10 has a fluororesin formed on its surface. The pressure roller 11 has a silicon rubber layer of about 5 mm on a SUS core metal, and the top layer is covered with a fluororesin such as a PFA tube. The outer diameter of both the fixing roller 10 and the pressure roller 11 is 50 mm.

A thermistor 13 for detecting the temperature of the rollers is in contact with the transfer material sheet passing area on the surfaces of the fixing roller 10 and the pressure roller 11, and the thermistor 13 is provided.
The output of the fixing heater 12 is controlled based on the temperature detected in. The maximum output of the fixing heater 12 during image formation is 500 W, and 60 A4 size transfer materials can be passed per minute. The fixing roller 10 is controlled by the control device so as to be maintained at 200 ° C.

The cleaning web 18 is a nonwoven fabric such as polyamide impregnated with silicon oil, and is pressed against the fixing roller 10 by the web pressure roller 19 and wound in a direction counter to the rotation of the fixing roller 10. In order to reduce the frequency of replacement of the cleaning web 18 (reduction of running cost), the winding speed of the web 18 is extremely slowed down to about 0.05 mm per one transfer material, but it is sufficient for normal copying. A cleaning effect can be exhibited.

The silicone oil supplied from the cleaning web 18 forms a film on the fixing roller 10,
Since part of the oil is absorbed by the transfer material, the fixing roller 1
The oil above 0 is kept at a substantially constant amount. The web pressure roller 19 is a single foam roller having an outer diameter of 24 mm and having a single foam sponge layer formed by foaming a silicon rubber material having a thickness of 8 mm on a solid core metal made of stainless steel having a diameter of 8 mm, and is perpendicular to the transfer material conveying direction. At both ends in the longitudinal direction, the web 18 is pressed against the fixing roller 10 by a pressure mechanism (not shown). The contact Nip between the cleaning web 18 and the fixing roller 10 is about 6 mm.

A fixing upper separation claw 16 is provided on the downstream side of the fixing roller 10 and the pressure roller 11 at the Nip portion.
Is abutted against the roller with a pressing force of about 20 gf. The top fixing separation claw 16 has a width of 2.
With a width of 5 mm, the entire width is in stable contact with the fixing roller 10. In the transfer material that has passed through the fixing Nip, the melted toner plays the role of an adhesive agent and easily winds around the fixing roller 10, so the transfer material is separated by the fixing upper separation claw 16. In addition, the curl of the transfer material itself also causes the winding around the fixing roller 10 depending on its direction.

The fixing upper separating claws 16 are symmetrically arranged in the longitudinal direction at positions of about 40 mm and 120 mm from the center, and the front and rear 1 respectively.
A total of four are installed, one by one. The minimum width in the longitudinal direction of the transfer material on which the image forming apparatus can form an image is 100 mm,
The maximum length is 296 mm, and the paper is fed through the center. The two center separation claws 16 are used to separate all paper sizes,
The two end portions do not contribute to separation because the contact position with the roller is outside the sheet passing area when an image is formed on a transfer material having a narrow width in the longitudinal direction of about 235 mm or less.

[0016]

However, in the image forming apparatus as in the conventional example, there is a problem of back stain on the transfer material.

The phenomenon of backside smearing of the transfer material is caused by the fact that a small amount of toner on the fixing roller 10 which has not been completely cleaned by the cleaning web 18 once moves to the pressure roller 11,
Further, it is a phenomenon that the transfer material is transferred to the back side of the transfer material when passing through the transfer material. This phenomenon is more frequently generated because a small amount of toner is accumulated on the pressure roller 11 for a long period of time.

This phenomenon disturbs the image in the mutual fixing process when the image is formed on both sides of the transfer material.
There is a particular need for improvements in today's imaging systems that form double-sided images.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus capable of preventing back stain on a transfer material.

[0020]

In order to achieve the above object, the present invention transfers a toner image formed on an image carrier onto a transfer material, and then sandwiches the transfer material between a pair of heated rotating bodies. In an image forming apparatus having a fixing device that heats and fixes an unfixed toner image on a transfer material, a cleaning member is provided on the fixing roller, which is a rotating body on the side of the fixing device that comes into contact with the unfixed toner image, and the fixing roller is attached to the fixing roller. The temperature of the facing pressure roller is higher than that of the fixing roller and lower than the temperature of the fixing roller, and the fixing roller and the pressure roller are rotated when the transfer material is not sandwiched.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings.

<First Embodiment> When the main body of the image forming apparatus is operated (hereinafter referred to as "morning one"), the temperature control of the fixing roller is delayed. As a result, a temperature difference is formed between the fixing roller and the pressure roller, and the toner that has adhered to the pressure roller from the pressure roller to the fixing roller during the previous rotation in the morning is moved to the fixing roller, and finally the toner on the fixing roller is removed. An example of wiping with a cleaning web will be described. Since the outline of the entire image forming apparatus is almost the same as that of the conventional example, a description thereof will be omitted. Also, the fixing device has the same hardware configuration as that of the conventional example, which will be described with reference to FIG.

The fixing device 9 has a halogen heater 12 inside.
The fixing roller 10 includes a fixing roller 10, a pressure roller 11, a cleaning web 18 for cleaning the fixing roller 10, a fixing upper separation claw 16 and the like.
About 12 mm S as an intermediate layer on a 2 mm Al cored bar
An i rubber layer is provided, and a fluorine resin such as PTFE is coated on the Si rubber layer to a thickness of about 20 μm to form a surface layer. The pressure roller 11 has a thickness of 25 μm on a 12 mm thick Al cored bar.
With a silicone rubber layer of about 50 μm
It covers the FA tube. The outer diameter of both the fixing roller 10 and the pressure roller 11 is 50 mm.

The cleaning web 18 is made of a non-woven fabric such as polyamide having a thickness of 50 μm, is impregnated with silicone oil having a viscosity of 10,000 cs, is pressed against the fixing roller 10, and is wound in a direction against the rotation of the fixing roller 10. . The winding speed is 0.05 per image.
mm (when continuous paper is fed, 0.05 m per second
m). Regarding the feeding of the web 18, the rotation of the winding roller is supported by a one-way clutch, an arm is provided for the clutch, and one end of the arm is operated by a solenoid magnet, so that a small amount of stable web feeding operation is performed. Has been achieved.

The maximum output of the fixing heater 12 during image formation is 1000 W in total, and 60 A4 size transfer materials can be passed per minute. The rotation speed of the fixing roller 10 is controlled to 300 mm / s. The fixing roller 10 and the pressure roller 11 are controlled by the control device so as to be maintained at 200 ° C. during the image forming process.

A fixing upper separation claw 16 is provided on the downstream side of the fixing roller 10 and the pressure roller 11 at the Nip portion.
Is abutted against the roller with a pressing force of about 20 gf. The top fixing separation claw 16 has a width of 2.
With a width of 5 mm, the entire width of the tip portion is in stable contact with the fixing roller 10. The fixing upper separation claws 16 are arranged symmetrically in the longitudinal direction at the positions of about 40 mm and 120 mm from the center, respectively.
A total of four are installed, one by one.

Next, temperature adjustment and rotation timing of the fixing roller 10 and the pressure roller 11 will be described.

Regarding the temperature adjustment of the fixing roller 10 and the pressure roller 11, first, until the temperature detected by the thermistor 13a in contact with the surface of the fixing roller 10 rises to 100 ° C. Until the temperature detected by the thermistor 13b rises to 150 ° C, the halogen heater 12a
And turn on 12b. When both the rollers 10 and 11 reach the temperature, the fixing roller 10 and the pressure roller 11 are rotated. In addition to the cleaning web 18
Is started 10 seconds after the rotation of the fixing roller 10 is started, and is carried out 25 seconds after the rotation of the fixing roller 10 is started (the 0.75 mm cleaning web 18 is fed over 15 seconds). The cleaning web 18
Is carried out in synchronization with the rotation of the fixing roller 10.

The halogen heaters 12a and 12b are turned on again when both the fixing roller 10 and the pressure roller 11 start to rotate, and the fixing roller 10
Both the pressure roller 11 and the pressure roller 11 have a target temperature of 200.degree. C. and the halogen heater 1 according to the temperature detection of the thermistors 13a and 13b.
The temperature is adjusted depending on whether or not 2a and 12b are turned on, and when both rollers 10 and 11 reach the target temperature, the rollers enter a standby state and accept an image forming command. The fixing device according to the present embodiment has a configuration including both rollers 10, 1
Due to the relationship between the heat capacity of 1 and the output wattage of the halogen heater 12, the standby state is not entered by the time the feeding of the cleaning web 18 by 0.75 mm is completed.

In the present embodiment, 5,000 sheets of image were formed per day, and the back surface of the transfer material was checked during the durability of 500,000 sheets. As a result, the transfer of toner to the back surface of the transfer material was confirmed. The frequency of occurrence decreased to 1/10. Further, it was confirmed that the amount of toner adhered to the surface of the pressure roller 11 after the endurance of 500,000 sheets was reduced to 1/4 per area by measuring the reflection density of the surface of the pressure roller 11.

Once the toner adheres to the pressure roller 11, the toner further promotes the adhesion of the toner. Therefore, cleaning at regular intervals is very effective for the adhesion. The endurance life setting of the roller 11 is extended, and the life setting of the fixing roller 10 that is in contact with the pressure roller 11 via Nip is also extended.

<Second Embodiment> Next, assuming that the temperature of the fixing roller 10 and the pressure roller 11 is not adjusted independently at the time of start-up in the morning, the start-up in the morning can be achieved in a minimum time. A configuration in which the same effect as that of the first embodiment is obtained is shown.

In the present embodiment, the fixing roller 10
A hollow roller having a thickness of 4 mm and an Si rubber layer of 1.0 mm as an intermediate layer on a core metal of Al is used, and a so-called thin roller structure is selected. In such a configuration, in the present embodiment, after the standby state after image formation, the temperature detected by the thermistor 13a contacting the surface of the fixing roller 10 reaches 120 ° C. The pressure roller 11 is rotated (the temperature controlled temperature in the standby state is 100 ° C.). The rotation time is 30 seconds, and in addition, the feeding of the cleaning web 18 is started 15 seconds after the rotation of the fixing roller 10 is started and 15 seconds after the rotation of the fixing roller 10 is started (0. 75
mm cleaning web 18).

In the present embodiment, the pressure roller 11
The heat capacity of the fixing roller 10 is smaller than that of the fixing roller 10, and even when the surface temperature of the fixing roller 10 is lowered to 120 ° C., the surface temperature of the pressure roller 11 is maintained at around 170 ° C. Temperature is pressure roller 11
The temperature is lower than the surface temperature of. The surface temperatures of the fixing roller 10 and the pressure roller 11 during image formation are adjusted to 200 ° C.

The roller rotation during standby in this embodiment is performed when the cumulative number of image formations from the previous standby reaches 1000 or more, so that the feeding amount of the cleaning web 18 is suppressed to a small amount. It was confirmed that the same effect as in the first embodiment can be obtained.

<Third Embodiment> In the present embodiment, in order to improve the degree of freedom in selecting the thickness of the fixing roller 10, the temperature difference between the fixing roller 10 and the pressure roller 11 is achieved at a controlled temperature. The case will be described.

The temperature of the pressure roller 11 is 2 during standby.
With a temperature of the stages, the first temperature is 150 ° C., the second
The temperature is 100 ° C. As shown in the second embodiment, at the standby time when the cumulative number of image formations exceeds 1000, the standby temperature of the surface of the standby fixing roller 10 is set to 100 ° C. as in the second embodiment, and the temperature is increased. The standby temperature of the surface of the pressure roller 11 is the first temperature.

When both the thermistors 13a and 13b can detect that the temperature has reached the predetermined temperature, the fixing roller 10 and the pressure roller 11 are rotated at that time (the temperature control temperature in the standby state is 100). ° C). The rotation time is 30 seconds. In addition, the feeding of the cleaning web 18 is started 15 seconds after the rotation of the fixing roller 10 and the pressure roller 11 is started, and is performed until 15 seconds after the start of rolling of the fixing roller 10 ( 0.75 over 15 seconds
mm cleaning web 18).

After this step is completed, the standby temperature of the pressure roller 11 is the second temperature of 100.
℃. As a result, the pressure roller 11 can be cleaned after the formation of a certain number of images, and the standby temperature when the pressure roller 11 is not cleaned is maintained at 100 ° C., and the power consumption is suppressed to the minimum necessary. .

The present embodiment is different from the second embodiment only in the method of forming the temperature difference between the fixing roller 10 and the pressure roller 11, and the effect is not much different.

[0041]

As is apparent from the above description, according to the present invention, after transferring the toner image formed on the image carrier to the transfer material, the transfer material is sandwiched between a pair of heated rotating bodies. In an image forming apparatus having a fixing device that heats and fixes an unfixed toner image on a transfer material, a cleaning member is provided on the fixing roller, which is a rotating body on the side of the fixing device that comes into contact with the unfixed toner image, and the fixing roller is attached to the fixing roller. The temperature of the opposing pressure roller is higher than that of the fixing roller and lower than that of the heat fixing, and the fixing roller and the pressure roller are rotated when the transfer material is not sandwiched. The effect of being able to prevent the dirt on the back side is obtained.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of an entire image forming apparatus.

FIG. 2 is a schematic sectional view of a fixing device of the image forming apparatus.

[Explanation of symbols]

1 Image carrier 2 Pre-exposure device 3 charging device 4 Developing device 7 Transfer device 8 cleaning device 9 Fixing device 10 heating roller 11 Pressure roller 12 Fixing heater 13a Temperature detection device (thermistor) 13b Temperature detection device (thermistor) 14 Control device 15 Fixing entrance guide 16 Separation nail on fixing 17 Separation under fixing nail 18 cleaning web

Claims (7)

[Claims] 1. A fixing device for transferring a toner image formed on an image carrier to a transfer material, and then sandwiching the transfer material between a pair of heated rotating bodies to heat and fix an unfixed toner image on the transfer material. In the image forming apparatus, a cleaning member is provided on the fixing roller, which is the rotating body on the side of the fixing apparatus that comes into contact with the unfixed toner image, and the temperature of the pressure roller facing the fixing roller is set higher than that of the fixing roller. Further, the image forming apparatus is characterized in that the fixing roller and the pressure roller are rotated when the transfer material is not sandwiched after the temperature is lower than that at the time of heat fixing. 2. The image forming apparatus according to claim 1, wherein the cleaning member is caused to function when the fixing roller and the pressure roller rotate. 3. A process of rotating the fixing roller and the pressure roller when the transfer material is not sandwiched after the temperature of the pressure roller is higher than that of the fixing roller and lower than that at the time of heat fixing. 3. The image forming apparatus according to claim 1, wherein the power is turned on once in the morning and before the image is formed. 4. A step of rotating the fixing roller and the pressure roller when the transfer material is not sandwiched after the temperature of the pressure roller is higher than that of the fixing roller and lower than that at the time of heat fixing. The image forming apparatus according to claim 1, wherein the image forming apparatus is performed during standby. 5. A process of rotating the fixing roller and the pressure roller when the transfer material is not sandwiched after the temperature of the pressure roller is higher than that of the fixing roller and lower than that at the time of heat fixing. When performing during standby,
The image forming apparatus according to any one of claims 1 to 4, wherein the interval between the steps is limited depending on the number of image formed sheets. 6. The surface temperature of the fixing roller decreases faster than the surface temperature of the pressure roller as a result of interrupting the heating of the fixing roller and the pressure roller after the heating and fixing process of the fixing device is completed. The image forming apparatus according to any one of claims 1 to 5. 7. The image forming apparatus according to claim 6, wherein the heat capacity of the fixing roller is smaller than that of the pressure roller.