JPH07114239A - Fixing device - Google Patents

Abstract

PURPOSE:To eliminate an image quality difference between the front and back of a recording material by preventing the heating means of a pressure rotor from being operated when an image is formed on the back of the recording material, thereby reducing the gloss of the surface of the recording material which is subjected to fixing twice. CONSTITUTION:In the case of the formation of full color images on both sides of the recording material, the recording material with an unfixed image held on its front is first held and carried between the fixing roller 31 and pressure roller 32, and fixing on the front of the recording material is carried out by applying the unfixed image the pressure of both rollers 31 and 32 and the heat of only the heater 31a of the fixing roller 31. Subsequently, an unfixed image is formed on the back of the recording material, and fixing on the back of the recording material is carried out by inverting the recording material, back to front, and again applying the unfixed image the pressure of both rollers 31 and 32 and the heat of only the heating means 31a of the fixing roller 31. Thus, because the heating means 32a of the pressure roller 32 stops at the time of fixing on both the front and back surface, the pressure roller 32 is held to a low temperature, the image on the front of the recording material which comes into contact with the pressure roller 32 does not receive excess heat, and is prevented from being fixed excessively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat roller type fixing device in an image forming apparatus such as a copying machine or a laser beam printer, and more particularly to a fixing device in an image forming apparatus capable of forming a full color image.

[0002]

2. Description of the Related Art A conventional electrophotographic apparatus for forming a color image forming apparatus is shown in FIG.

The color electrophotographic apparatus shown in FIG. 7 includes a recording material conveying system I provided from the right side of the apparatus main body 1 to a substantially central portion of the apparatus main body, and a recording material conveying system I at a substantially central portion of the apparatus main body 1.
A latent image forming section II provided in the vicinity of the transfer drum 15 constituting the recording material conveying system I, and the latent image forming section
II is roughly divided into a developing means arranged in the vicinity, that is, a rotary developing device III.

The recording material conveying system I has the following structure. First, an opening is formed in the right wall of the apparatus main body 1, and removable recording material supply trays 2 and 3 are disposed in the opening so as to partially project outside the machine. Paper feed rollers 4 and 5 are arranged substantially directly above the trays 2 and 3, and arrow A is arranged on the left side of the paper feed rollers 4 and 5.
A paper feed roller 6 and paper feed guides 7 and 8 are provided so as to communicate with a transfer drum 15, which is a transfer means rotatable in any direction. In the vicinity of the outer peripheral surface of the transfer drum 15, a contact roller 9, a gripper 10, a recording material separating charger 11 and a separating claw 12 are sequentially arranged from the upstream side to the downstream side in the rotation direction. A transfer charger 13 and a recording material separating charger 14 are provided on the inner peripheral side of the transfer drum 15. The separation claw 1 is provided on the upper right side of the transfer drum 15.
2 in the vicinity of the conveying belt means 16, and the fixing device 3 at the end (right) end of the conveying belt means 16 in the recording material conveying direction.
0 is set. A discharge tray 17 that extends to the outside of the apparatus main body 1 and is detachable from the apparatus main body 1 is disposed downstream of the fixing device 30 in the transport direction.

Next, the structure of the latent image forming section II will be described. First, a photosensitive drum 19, which is a latent image carrier that is rotatable in the direction of arrow B in FIG. 7, is arranged with its outer peripheral surface in contact with the outer peripheral surface of the transfer drum 15. Above the photosensitive drum 19 and in the vicinity of the outer peripheral surface thereof, a discharging charger 20, a cleaning means 21, and a primary charger 23 are sequentially arranged from the upstream side to the downstream side in the rotation direction of the photosensitive drum 19, and further. An image exposure unit 24 such as a laser beam scanner for forming an electrostatic latent image on the outer peripheral surface of the photosensitive drum 19,
And an image exposure reflection means 25 are provided.

Finally, the structure of the rotary developing device III is as follows. A rotatable housing (hereinafter referred to as "rotating body") at a position facing the outer peripheral surface of the photosensitive drum 19
26 is provided, and four types of developing devices are mounted in the rotating body 26 at four positions in the circumferential direction to visualize (that is, develop) the electrostatic latent image formed on the outer peripheral surface of the photosensitive drum 19. ). The above four types of developing devices
Yellow developing device 27Y and magenta developing device 2 respectively
7M, cyan developing device 27C and black developing device 27
It is BK.

The sequence of the entire image forming apparatus having the above-described structure will be briefly described first by taking the case of the full color mode as an example. When the above-described photosensitive drum 19 rotates in the direction of arrow B in FIG. 7, the photosensitive member on the photosensitive drum 19 is uniformly charged by the primary charger 23. When the photoconductor is uniformly charged by the primary charger 23, image exposure is performed by the laser light E modulated by the yellow image signal of the document 28, and an electrostatic latent image is formed on the photoconductor drum 19. The electrostatic latent image is developed by the yellow developing device 27Y which is fixed at the developing position in advance by the rotation of the rotating body 26.

On the other hand, the recording material conveyed through the paper feed guide 7, the paper feed roller 6, and the paper feed guide 8 is held by the gripper 10 at a predetermined timing and brought into contact with the contact roller 9 in a corresponding manner. It is electrostatically wound around the transfer drum 15 by the use roller 9 and the opposing electrode. The transfer drum 15 rotates in the direction of arrow A in FIG. 7 in synchronism with the photosensitive drum 19, and the visible image developed by the yellow developing device 27Y is transferred to the outer peripheral surface of the photosensitive drum 19 and the transfer drum 1.
5 is transferred by the transfer charger 13 at a portion in contact with the outer peripheral surface of 5. The transfer drum 15 continues to rotate and is ready for transfer of the next color (magenta in FIG. 7).

On the other hand, the photosensitive drum 19 is destaticized by the decharging charger 20, is cleaned by the cleaning means 21 by the conventionally known blade method, is charged again by the primary charger 23, and is recharged by the next magenta image signal. Receive image exposure like. The rotary developing device rotates while an electrostatic latent image is formed on the photosensitive drum 19 by the image exposure by the magenta image signal,
The magenta developing device 27M is fixed at the above-mentioned predetermined developing position to perform predetermined magenta development. Subsequently, the above-described process is performed for cyan color and black color respectively, and when the transfer of four colors is completed, the four-color developed image formed on the recording material is discharged by the chargers 20 and 14. Then, the gripping of the recording material by the gripper 10 is released, the recording material is separated from the transfer drum 15 by the separating claw 12, and the fixing device 30 is fixed by the conveying belt 16.
And is fixed by heat and pressure to complete a series of full-color print sequences, and a desired full-color print image is formed.

Next, the fixing device in the above-described full-color image formation will be described in detail with reference to FIG. In FIG. 8, a fixing roller 31 is rotatably arranged. The fixing roller 31 has a structure in which the surface of a metal cored bar is covered with silicone rubber and fluororubber to a predetermined thickness. Etc., including a heater 31a, etc., and rotatably supported in the direction of the arrow.

A pressure roller 32 is disposed below the fixing roller 31 so as to come into pressure contact therewith, and the fixing roller 3 is provided.
1 is pivotally supported so as to rotate. The pressure roller 32 has a structure in which the surface of a metal cored bar is covered with silicone rubber and fluororubber to a predetermined thickness. Inside the pressure roller 32, like the fixing roller 31, a heater 32 such as a halogen lamp is provided.
a is provided.

Further, the fixing roller 31 and the pressure roller 32
Is arranged so that the thermistor 36 is in contact therewith,
The temperature of the surface of the fixing roller 31 and the pressure roller 32 is adjusted by controlling the voltage to the heater 31a and the heater 32a via the temperature adjusting circuit.

The release agent applying device 33, which is disposed so as to come in contact with and separate from the fixing roller 31, has a release agent tank 33a which is a release agent container containing silicone oil as a release agent.
A scooping roller 33b that scoops the release agent from the release agent tank 33a, an application roller 33c that is a coating rotary member that applies the release agent to the fixing roller 31, and an amount of the release agent applied. The blade 33d is a regulating member. The coating roller 33c rotatably supported has a sponge rubber surface coated with silicone rubber,
It is removably arranged on the fixing roller 31 to apply a release agent. The blade 33d is fixed to the sheet metal at a constant angle with respect to the coating roller 33c, and is pressed against the coating roller 33c with a constant pressure. Therefore, the coating amount of the release agent pumped up by the scooping roller 33b is
The recording material P is constantly adjusted by the blade 33d and applied from the front end to the rear end of the recording material P.

Further, cleaning devices 34 and 35 are in contact with the fixing roller 31 and the pressure roller 32, a nickel web 34a is in contact with the fixing roller 31 and a Nomex felt 35a is in contact with the pressure roller 32. Then the rollers are being cleaned.

When the recording material P is conveyed to the fixing device as described above, the fixing roller 31 and the pressure roller 32 rotate at a constant speed, and the recording material P is fixed to the fixing roller 31 and the pressure roller 3.
When passing between the two, the unfixed toner carried on the surface by being pressed and heated at a substantially constant pressure and temperature from both the front and back sides was melted and good fixing was performed.

[0016]

However, in a color image forming apparatus such as the above-mentioned conventional example, when performing double-sided copying, the image quality of the recording material surface (hereinafter referred to as the first surface) after fixing is deteriorated. There was a problem.

First, an apparatus for forming and fixing an image on both the front and back surfaces of a color copying machine will be described. The apparatus shown in FIG. 9 is a color image like the apparatus shown in FIG. 7, but is different from the above apparatus in that an image can be formed on both sides of the recording material. The mechanism for double-sided image formation will be described below, but the same parts as those of the above-mentioned apparatus will be designated by the same reference numerals and the description thereof will be omitted.

This apparatus is provided with a re-feeding roller 40 and a conveyance path 41 which are conveyance mechanisms for double-sided image formation. The sheet re-feeding roller 40 is disposed below the sheet ejection roller 42, and re-feeds the recording material once placed on the sheet ejection tray 17 to the latent image forming section II. A transport path 41 for transporting the recording material is disposed behind the.

Next, the operation of the above-described apparatus for double-sided copying of a color image will be described.

The recording material, which has been developed in the developing device III and has an unfixed toner image on its surface, is transported by the transport belt means 16 and fixed by the fixing roller 31 and the pressure roller 32 (hereinafter, this fixing will be referred to as "first fixing"). Then, the sheet is fed to the sheet discharge tray 17 by the sheet discharge roller 42.
After that, the sheet is re-fed by the re-feed roller 40, passes through the conveyance path 41, and is conveyed again to the latent image forming unit II to form a color image on the back surface in the same manner as the front surface. In this way, the recording material having the color image already fixed on the front surface and carrying the unfixed color toner image transferred on the back surface is conveyed to the fixing roller 31 and the pressure roller 32 by the conveying belt means 16 and fixed. (Hereinafter, this fixing is referred to as second fixing.) Finally, it is carried to the paper discharge tray 17 and the double-sided color copy is completed.

Here, the image formed on the surface of the recording material (hereinafter referred to as the first surface) is fixed by the first fixing, after which the recording material is turned upside down, and subsequently the back surface of the recording material (hereinafter referred to as the second surface). An image is formed on the surface) and is fixed by the second fixing. Therefore, since the image on the first surface of the recording material is supplied with heat from the fixing roller side by the first fixing and further from the pressure side by the second fixing, the fixing is performed twice, resulting in excessive fixing. Was there. As a result, the image on the first surface after fixing has a high glossiness, and a difference occurs from the image on the second surface of the recording material that has been fixed only once by the second fixing.

It is an object of the present invention to solve the above problems and to provide a fixing device which does not cause a difference in glossiness between the front and back surfaces of a recording material even when a color image is formed on both surfaces of the recording material. I am trying.

[0023]

According to the present invention, the above object is to provide a fixing rotator and a pressure rotator which are rotatably arranged while being in pressure contact with each other, and the fixing rotator and the pressure transfer. A recording material having a plurality of color unfixed images carried thereon, the recording material being sandwiched and conveyed such that the surface on the unfixed image side and the fixing rotator are in contact with each other, and In a fixing device of a multicolor image forming apparatus that heats and fixes an image, a multicolor image that reverses the front and back of the recording material and fixes the multicolor image on the other surface after fixing the multicolor image on one surface This is achieved by that the heating means for heating the pressurizing rotary member at the time of double-sided fixing is set so as not to perform the heating operation at the time of fixing on both the front and back surfaces of the recording material.

[0024]

According to the present invention, when a multicolor image is formed on both sides of a recording material, first, a recording material having an unfixed image on its surface is nipped and conveyed by a fixing rotary member and a pressure rotary member. Then, the surface of the recording material is fixed by applying pressure contact force from both rotating bodies and heat from only the heating means on the side of the fixing rotation body to the unfixed image. Next, an unfixed image is formed on the back surface of the recording material, the front and back of the recording material are reversed, and the recording material is nipped and conveyed again by the pressure contact portions of both rotating bodies. The back surface of the recording material is fixed by applying heat only by the heating means on the rotating body side. In this way, since the heating means on the side of the pressure-applying rotor is stopped at any time of fixing on both the front and back sides, the temperature of the body for pressurizing is kept low, and the image on the surface side of the recording material which is in contact with the body for pressurizing is pressed. Does not receive excess heat and is not over-fixed.

[0025]

Embodiments of the present invention will be described with reference to the accompanying drawings. In addition, the same parts as those of the conventional apparatus shown in FIGS.

<First Embodiment> First, a first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a flowchart showing the control in the first embodiment of the present invention. First, as shown in FIG. 1, the main power switch is turned off in the image forming apparatus.
Then, the fixing roller side heater 31a (hereinafter referred to as an upper heater) and the pressure roller side 32a (hereinafter referred to as a lower heater) are turned on. When the roller surface reaches the controlled temperature, both the upper and lower heaters are turned off, and then the upper and lower heaters are repeatedly turned on and off during standby to control the temperature. When the copy mode is selected, the heater lighting control is performed according to each mode.

First, when the normal copying mode is selected, if the temperature of the roller surface is lowered due to the passage of paper during fixing, both the upper and lower heaters are turned on, and when the temperature is restored after the copying is completed, it is turned on and off again. Repeat the temperature control.

Next, the case where the double-sided copy mode is selected will be described. First, when a recording material carrying an unfixed image on the first surface is conveyed, the first fixing is performed, but the roller surface and the pressure roller whose temperature is controlled to a constant temperature during standby are the recording material. Heat is taken away by the heat and the surface temperature drops.

When this is detected by the thermistor 36, only the upper heater 31a is turned on so as to recover the surface temperature of the fixing roller 31. At this time, in this embodiment, the lower heater 32a remains unlit. As a result, heat is supplied to the fixing roller 31 from the upper heater 31a, and the temperature of the fixing roller surface is recovered. However, since the lower heater 32a remains unlit, heat is not supplied, and the surface temperature of the pressure roller 32 is the fixing roller 3a.
It is kept lower than the surface temperature of 1. In this state, the recording material on which the first fixing has been completed is turned upside down, the unfixed image is again carried on the second surface, and the fixing is carried out again. At this time,
The first surface once fixed is facing the pressure roller 32 side, and the surface temperature of the pressure roller 32 is the fixing roller 31.
The image on the first surface at the end of the second fixing has a lower gloss than before and the image quality is improved.

Since the recording material is heated and warmed during the first fixing, the upper heater 31 is heated during the second fixing.
A full-color image can be fixed by heating only a.

By controlling in this way, the gloss of the first surface can be suppressed to a low level, and the difference in image quality between the first surface and the second surface can be reduced.

<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 FIG. 2, reference numeral 38 denotes a cooling fan, which can blow air to the pressure roller 32. In this embodiment, the pressure roller 32 is forcibly cooled by using the cooling fan 38 at the time of double-sided copying, and a flow chart of the control is shown in FIG.

FIG. 3 is similar to that described with reference to FIG.
When the double-sided copy mode is selected, the lower heater 32a is turned on after the first fixing is finished, the second image formation and the second fixing are performed, and at that time, the cooling fan 38 is turned on and the pressure roller 32 is blown. It is designed to be cooled by.
By controlling in this manner, the surface temperature of the pressure roller 32 at the time of the second fixing can be suppressed to be lower,
The gloss of the image on the first surface at the end of the second fixing was suppressed to be lower than that in Example 1, and the image quality was further improved.

<Third Embodiment> Next, a third 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 FIG. 4, 39 is a heat pipe which can be brought into contact with and separated from the pressure roller. FIG. 5 shows a schematic view of the heat pipe. The heat pipe 39 is the pressure roller 32.
And a portion 39b extending outside the fixing area of the recording material by the roller pair.
A plurality of fins 39c are attached. Part 39d
Blows the fan 39c to the heat pipe 3
9 is cooling. As a result, the heat pipe 39 is vaporized by the working fluid contained therein so that the pressure roller 3
Can efficiently transfer heat to the fins 39c,
Since it is cooled and liquefied by the fan 39d, the heat dissipation efficiency is very good. In this embodiment, the pressure roller 32 is forcibly cooled by bringing the heat pipe 39 into contact with the pressure roller 32 during double-sided copying.
Shows the flow chart of the control. In the case where the double-sided copy mode is selected in the same manner as described with reference to FIG. 1, the lower heater 32a is turned off after the completion of the first fixing, and the second image formation and the second fixing are performed. The heat pipe 39 is brought into contact with the pressure roller 32. As a result, the surface temperature of the pressure roller 32 can be made lower than that in the second embodiment, the gloss of the image on the first surface at the end of the second fixing can be suppressed to be lower than that in the first embodiment, and the image quality can be further improved. Improved.

[0037]

As described above, according to the present invention,
In a fixing device of an image forming apparatus capable of forming a multicolor image on both front and back surfaces of a recording material, when an image is formed on the back surface of the recording material, the heating means on the side of the pressing rotary member is not operated, or at the same time, the rotation for pressing is performed. By cooling the body with the cooling means, it is possible to lower the gloss of the surface of the recording material that is to be fixed twice than before, and as a result, it is possible to eliminate the difference in image quality between the front and back of the recording material. It was

[Brief description of drawings]

FIG. 1 is a flowchart showing control in a first embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating a schematic configuration of a fixing device according to a second exemplary embodiment of the present invention.

FIG. 3 is a flowchart showing control in Embodiment 2 of the present invention.

FIG. 4 is a sectional view showing a schematic configuration of a fixing device according to a third embodiment of the invention.

5 is a perspective view showing a schematic configuration of a heat pipe of the apparatus shown in FIG.

FIG. 6 is a flowchart showing control in Embodiment 3 of the present invention.

FIG. 7 is a sectional view showing a schematic configuration of a conventional color image forming apparatus.

8 is a cross-sectional view showing a schematic configuration of a fixing device used in the device of FIG.

FIG. 9 is a cross-sectional view showing a schematic configuration of a color image forming apparatus capable of double-sided copying.

[Explanation of symbols]

 31 fixing roller (fixing rotator) 31a, 32a heater (heating means) 32 pressure roller (pressurizing rotator) 38 cooling fan (cooling means) 39 heat pipe (cooling means)

Claims (2)

[Claims] 1. A fixing rotator and a pressure rotator, which are rotatably arranged while being in pressure contact with each other, and heating means for heating the fixing rotator and the pressure transfer body, respectively.
A recording material carrying an unfixed image of a plurality of colors is nipped and conveyed such that the surface on the unfixed image side and the fixing rotator are in contact with each other,
In a fixing device of a multicolor image forming apparatus that heat-fixes the unfixed image, after the fixing of the multicolor image on one surface is completed, the front and back of the recording material are reversed to fix the multicolor image on the other surface. Multi-color image fixing, characterized in that the heating means for heating the pressing rotary member at the time of double-sided fixing of a color image is set so as not to perform a heating operation at the time of fixing either the front surface or the back surface of the recording material. apparatus. 2. The cooling device according to claim 1, further comprising a cooling unit for cooling only the pressurizing rotary member, wherein the cooling unit is set to perform a cooling operation during double-sided fixing of a multicolor image. Fixing device.