JP2002139938A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device preventing the dirt on recording medium. SOLUTION: As for this fixing device, by bias power source 122, bias voltage in a polarity opposite to the polarity of toner 42 is applied on a heat radiating roller 120.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as an electrophotographic copying machine or an electrophotographic printer for forming an image on a recording medium using a developer such as a toner. The present invention relates to a fixing device for fixing the fixing device.

[0002]

2. Description of the Related Art Conventionally, an image forming apparatus using an electrophotographic method has been widely used. This electrophotographic image forming apparatus will be described with reference to FIG.

FIG. 2 is a schematic diagram showing a schematic configuration of a conventional image forming apparatus using an electrophotographic system.

The image forming apparatus 10 includes a motor (not shown)
The photosensitive drum 12 rotates in a direction indicated by an arrow A in FIG. A primary charger 14 is arranged to face the photosensitive drum 12, and the photosensitive drum 12 is uniformly charged by corona discharge by the primary charger 14. A uniformly charged photosensitive drum 12 is irradiated with light (document reflected light) 16 carrying information of an image described on a document (not shown) to form an electrostatic latent image.

A developing device 18 for developing an electrostatic latent image is disposed downstream of the position where the document reflected light 16 irradiates the photosensitive drum 12 in the rotation direction of the photosensitive drum 12. The developing device 18 has a developing sleeve 18a that is rotated in the direction of arrow B by a motor (not shown). Toner (developer) is supplied to the photosensitive drum 12 from the developing sleeve 18a. When the electrostatic latent image formed on the photosensitive drum 12 reaches a position facing the developing sleeve 18a, toner is supplied to the electrostatic latent image from the developing sleeve 18a, and a toner image (developed image) is formed on the photosensitive drum 12. Is done.

The registration rollers 20 and 2 are synchronized at timings synchronized with the moving speed of the toner image formed on the photosensitive drum 12.
0 ′ rotates in the directions of arrows C and C ′, whereby a recording medium (not shown) such as recording paper is conveyed toward the transfer area 22. The recording medium that has passed through the registration rollers 20 and 20 ′ passes between the upper transfer guide plate 24 and the lower transfer guide plate 26 and reaches the transfer area 22. In the transfer area 22, the toner image on the photosensitive drum 12 is transferred to the recording medium by the transfer charger 28. Thereafter, the recording medium is separated from the photosensitive drum 12 by the separation charger 30.

A cleaner device 3 having a blade 32 is provided downstream of the transfer area 22 in the rotation direction of the photosensitive drum 12.
4 are arranged. The toner remaining on the photosensitive drum 12 after the transfer is scraped off by the blade 32.

An eraser 36 is disposed downstream of the cleaner device 34 in the rotation direction of the photosensitive drum 12, and the eraser 36 removes the residual potential on the photosensitive drum 12. On the other hand, the recording medium to which the toner image has been transferred is conveyed to the fixing device 40 by the conveyance unit 38 that conveys the recording medium in the direction of arrow D. The fixing device 40 fixes the toner image on the recording medium. Thereafter, the recording medium is discharged outside the apparatus, and one cycle of copying is completed.

The fixing device 40 will be described with reference to FIG.

FIG. 3 is a schematic diagram showing a schematic configuration of the fixing device 40.

The fixing device 40 is for making the toner (image) 42 into a permanent visible image on a recording medium 44. The recording medium 44 conveyed in the direction of arrow D by the conveyance unit 38 (see FIG. 2) is guided by the fixing entrance guide 46 and enters the nip 48 between the fixing roller 50 and the pressure roller 60.

The fixing roller 50 is for heating and melting the toner. Outer peripheral surface (front surface) of fixing roller 50
Is in contact with the thermistor 70.
0 is configured to measure the temperature of the outer peripheral surface of the fixing roller 50. The fixing roller 50 has a built-in heat source (heating element) such as a halogen heater 52. A controller 72 based on the outer peripheral surface temperature measured by the thermistor 70
Controls the halogen heater 52, whereby the outer peripheral surface temperature of the fixing roller 50 is maintained at a predetermined fixing temperature.

As the fixing roller 50, a roller in which an outer peripheral surface of a core metal 54 made of, for example, a pipe member made of iron or aluminum is coated with a fluororesin layer 56 having good releasability is generally used. The fixing roller 50 is rotated in the direction of arrow E by a driving source (not shown).

The pressure roller 60 is for pressing the recording medium 44 against the fixing roller 50 at a predetermined pressure. As the pressure roller 60, for example, an elastic layer 6 made of, for example, silicon rubber or fluorine rubber is provided on the outer peripheral surface of a metal core 62.
4 coated with a predetermined thickness is generally used. The elastic layer 64 has a release layer 6 made of fluororesin.
6 are coated. While pressing the pressure roller 60 against the fixing roller 50 with a predetermined pressure and rotating in the direction of arrow F, a load for fixing the toner 42 to the recording medium 44 is applied.

When the recording medium 44 enters the nip portion 48, the toner 42 on the recording medium 44 is melted at the above fixing temperature, and the melted toner 42 is pressed against the recording medium 44 by the above load. The image is fixed on the recording medium 44. The recording medium 44 to which the toner 42 has been fixed is
The paper reaches a paper discharge roller (not shown), and is discharged out of the apparatus by the paper discharge roller.

In order to completely fix the toner 42 on the recording medium 44 in the fixing device 40 as described above, it is important to raise the temperature of the fixing roller 50 to a predetermined fixing temperature and maintain the fixing temperature. is there. Halogen heater 5
The time required to raise the temperature of the fixing roller 50 to the fixing temperature after turning on the power to the fixing roller 2 is “wait time”.
Called. This "wait time" for the user
Is preferably shorter. Therefore, the core metal 5 of the fixing roller 50
A technique has been proposed in which the "weight time" is reduced by reducing the thickness (wall thickness) of No.4.

In this technique, since the core metal 54 of the fixing roller 50 is thinned, its heat capacity is reduced, and the fixing roller 50 rapidly rises to the fixing temperature even with a small amount of heat. Further, since the heat capacity of the fixing roller 50 is small, the amount of heat required to maintain the fixing roller 50 at the fixing temperature can be reduced, thereby saving energy.

Here, the core metal 5 of the fixing roller 50 described above is used.
Consider the problem of the technology for thinning 4. When the core metal 54 is made thinner, its heat capacity becomes smaller, and accordingly, the heat capacity of the fixing roller 50 also becomes smaller. Also, the thin metal core 54
Has insufficient heat conduction. For this reason, when the heat of a region of the outer peripheral surface of the fixing roller 50 that is in contact with the passing recording medium 44 (hereinafter, referred to as a “paper passing region”) is taken away, the temperature is greatly reduced in this paper passing region. In the area other than the paper passing area (non-paper passing area), the temperature hardly decreases, and the temperature distribution in the surface layer of the fixing roller 50 becomes non-uniform.

Therefore, the fixing roller 50 and the pressure roller 60
When a large number of recording media 44 continuously pass through the nip portion 48 during the image forming operation (the image forming operation is performed), the temperature difference between the paper passing area and the non-paper passing area becomes even larger, and the above temperature distribution becomes extremely large. Becomes uneven.

Incidentally, in the fixing device 40 described above, the thermistor 70 is generally disposed in the paper passing area.
When the thermistor 70 is arranged in the paper passing area as described above,
Toner and paper dust accumulate in a portion where the thermistor 70 is in contact with the fixing roller 50, and this portion is soiled. The stain becomes more intense as the fixing device 40 is used for a longer time, and such toner and paper dust damage the outer peripheral surface of the fixing roller 50 and stain an image on a recording medium.

As a technique for preventing such contamination, a technique for cleaning the fixing roller 50 with a web or a roller has been proposed. Further, a technique has been proposed in which silicone oil is applied to the outer peripheral surface (front surface) of the fixing roller 50 so that dirt such as toner is easily removed from the fixing roller 50. However, these techniques have problems that the cost of the fixing device 40 increases and that regular maintenance is required. Therefore, a technique has been proposed in which the thermistor 70 is disposed in a non-sheet passing area other than the sheet passing area on the outer peripheral surface of the fixing roller 50.

In order to reliably fix the toner 42 on the recording medium 44 (maintain the fixability) in the fixing device 40, it is necessary to keep the surface temperature of the fixing roller 50 in the sheet passing area at a predetermined fixing temperature. is there. However, as described above, the core metal 54 of the fixing roller 50 is made thinner, and the thermistor 70 is arranged in the paper passing area, so that the thermistor 70 is continuously connected to the recording medium 44 having a short width (length in the longitudinal direction of the fixing roller 50). When an image is formed, the non-sheet passing area is heated but hardly loses heat. Therefore, the non-sheet passing area becomes too high and the temperature of each member of the fixing device 40 exceeds its heat-resistant temperature or the durability performance is deteriorated. Or decrease. Such a problem is that even if the thermistor 70 is arranged in the non-sheet passing area, the recording medium 4 having a short width (the length of the fixing roller 50 in the longitudinal direction) is short.
This occurs when an image is formed continuously from step 4.

In order to solve the above problem, when continuously forming images on the recording medium 44 having a short width, the number of output sheets (the number of images to be formed) per unit time is reduced so that the paper passing area and the non-printing area are not changed. A technique for preventing the temperature difference in the paper passing area from increasing is considered. However, this technique is inconvenient for the user because the number of output sheets per fixed time is reduced.

When the core metal 54 of the fixing roller 50 is made thinner and the thermistor 70 is arranged in the non-sheet passing area,
The halogen heater 52 is controlled to adjust the temperature of the sheet passing area while predicting the temperature of the sheet passing area so that the temperature of the sheet passing area becomes the fixing temperature. Therefore, the size of the recording medium 44,
Considering factors such as the thickness, the material, and the environmental conditions in which the image forming apparatus 10 (see FIG. 1) is installed, the halogen heater 52 is used.
May need to be controlled. In order to perform such control, a device for inputting control factors such as the size of the recording medium 44 is required, and a user must operate the device.

As described above, various techniques have been proposed for maintaining the fixing property in the fixing device 40, but various problems have been encountered. Therefore, a technique has been proposed in which a heat dissipating roller 80 is used, which rotates in the direction of arrow G while contacting the outer peripheral surface of the pressure roller 60 and removes heat from the pressure roller 60. The heat dissipating roller 80 has substantially the same length as the pressure roller 60, and contacts both the sheet passing area and the non-sheet passing area. Further, the heat radiating roller 80 is made of, for example, aluminum having excellent thermal conductivity, and also has excellent thermal conductivity in the longitudinal direction (rotation axis direction).

Therefore, even when images are continuously formed on the recording medium 44 having a short width, the heat radiating roller 80 can remove heat from the entire area in the longitudinal direction of the pressure roller 60, so that a large amount of heat is radiated from the high temperature area. Thus, the temperature difference between the sheet passing area and the non-sheet passing area is reduced. Further, the heat radiating roller 80 is
Since the toner is rotated in contact with the outer peripheral surface of the pressure roller 60, the toner attached to the outer peripheral surface of the pressure roller 60 is transferred to the heat radiation roller 80. Therefore, the heat dissipation roller 80 also has a cleaning function of removing toner from the pressure roller 60.

[0027]

However, the heat radiating roller 80 exerts a cleaning function only when both the pressure roller 60 and the heat radiating roller 80 are sufficiently warm. Therefore, when both the pressure roller 60 and the heat radiating roller 80 are at a low temperature, the heat radiating roller 80 does not perform the cleaning function. For example, when the surface of the fixing roller 50 is at the fixing temperature just after the power is turned on to the image forming apparatus 10 (see FIG. 2), but the surface temperatures of the pressing roller 60 and the heat radiating roller 80 are low. In other words, the heat dissipation roller 80 does not exhibit a cleaning function. Further, for example, the image forming apparatus 10
When a long time has passed since the power supply was turned on, but the rollers 50, 60, and 80 were stopped without forming an image, only the portion near the nip portion 48 reached the fixing temperature, and Since the temperature of the portion is low, the heat radiating roller 80 does not exhibit the cleaning function.

As described above, when the heat radiating roller 80 does not perform the cleaning function, the pressure roller 60 remains dirty. For this reason, the contamination of the pressure roller 60
4 can get dirty.

The present invention has been made in view of the above circumstances, and has as its object to provide a fixing device that prevents a recording medium from being stained.

[0030]

According to a first aspect of the present invention, there is provided a fixing device including a fixing roller having a built-in heat source, a pressing roller pressed against the fixing roller, and an outer peripheral surface of the pressing roller. A fixing roller for fixing toner to the recording medium while nipping and transporting the recording medium between the fixing roller and the pressure roller, the heat releasing roller being configured to rotate while contacting the recording medium to remove heat from the pressure roller. And (1) an application means for applying a bias voltage having a polarity opposite to a polarity of a toner transferred to a recording medium sandwiched between the fixing roller and the pressure roller to the heat radiating roller. Is what you do.

Here, the applying means is (2) 200 V
A bias voltage within a range of not less than 1000 V and not more than 1000 V may be applied to the heat radiating roller.

The fixing device may further include (3) a cleaning member for removing the toner attached to the heat radiating roller.

Further, the fixing roller is (4) 1 mm
It may have a metal core having the following thickness.

[0034]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a fixing device according to the present invention will be described below.

An embodiment of the fixing device of the present invention will be described with reference to FIG.

FIG. 1 is a schematic diagram showing an embodiment of a fixing device. In this figure, the same components as those shown in FIG. 2 are denoted by the same reference numerals.

The fixing device 90 includes a fixing roller 100 and a pressure roller 110 for fixing the toner (image) 42 to the recording medium 44 while nipping and transporting the recording medium 44.

The fixing roller 100 has a core bar 102 made of an aluminum pipe having a thickness of 0.8 mm. The outer peripheral surface of the cored bar 102 is covered with a resin layer (surface release layer) 104 such as PTFE or PFA having excellent releasability and heat resistance via a primer or the like. Fixing roller 1
00 is rotated in the direction of arrow E by a drive source (not shown).

One halogen heater 52 is incorporated in the cored bar 102 described above. The thermistor 70 is in contact with a non-sheet passing area of the outer peripheral surface (front surface) of the fixing roller 100, and the thermistor 70 measures the temperature of the outer peripheral surface of the fixing roller 100. The controller 72 controls the halogen heater 52 based on the outer peripheral surface temperature measured by the thermistor 70, whereby the outer peripheral surface temperature of the fixing roller 100 is maintained at a predetermined fixing temperature (about 160 ° C. to 210 ° C.). Note that the thermistor 70 is a fixing roller 10
0 from the longitudinal center line to the longitudinal end
mm.

In the pressure roller 110, the metal core 11
2 is covered with a porous elastic layer (foamed layer) 114 of silicon sponge rubber. This elastic layer 114
Is covered with a PFA tube 116 having a thickness of 50 μm, which is a surface release layer. The elastic layer 114 has a plurality of through-holes 114 a extending in the longitudinal direction (rotational axis direction) of the pressure roller 110 and penetrating the elastic layer 114.

The pressure roller 110 is pressed against the fixing roller 100 at a predetermined pressure, and thereby the nip 48
Are formed. When the fixing roller 100 rotates in the direction of the arrow E, the pressure roller 110 rotates in the direction of the arrow F.

When the fixing device 90 is turned on, the halogen heater 52 is energized to heat the fixing roller 100. In this case, the core metal 102 is thin and the fixing roller 100
Has a small heat capacity, so the wait time is short. In addition,
As described above, since the thermistor 70 is in contact with the non-sheet passing area, no dirt due to the thermistor 70 is generated, and a member for cleaning the dirt is unnecessary.

The fixing device 90 includes a pressure roller 110
A heat dissipating roller 120 that rotates in the direction of arrow G while taking contact with the outer peripheral surface of the roller and removes heat from the pressure roller 110 is provided. The heat radiating roller 120 has substantially the same length as the pressure roller 110 and contacts both the paper passing area and the non-paper passing area. Further, the heat radiating roller 120 is made of, for example, aluminum having excellent thermal conductivity, and has a longitudinal direction (a rotation axis direction).
Also has excellent thermal conductivity. Therefore, even when images are continuously formed on the recording medium 44 having a short width, the heat radiating roller 120 can remove heat from the entire area in the longitudinal direction of the pressure roller 110, so that a large amount of heat is released from the high temperature area. Thus, the temperature difference between the paper passing area and the non-paper passing area is reduced.

A bias voltage having a polarity opposite to the polarity of the toner 42 is applied to the heat radiating roller 120 by a bias power supply 122 (an example of an application unit according to the present invention). When negative toner (which is negatively charged) is used as the toner 42, the bias voltage is +2.
00V to + 1000V. Conversely, when the positive toner is used, the bias voltage is -200 V
To -1000V.

By applying the bias voltage to the heat radiating roller 120 as described above, the toner adhering to the pressure roller 110 moves (transfers) to the heat radiating roller 120. Therefore, even if the toner 42 of the recording medium 44 adheres to the fixing roller 100 at the nip portion 48 and the adhered toner adheres to the pressure roller 110 from the fixing roller 100, the toner adhered to the pressure roller 110 remains It moves to the heat radiation roller 120. Therefore, the toner is substantially removed from the pressure roller 110, and the recording medium is not stained by the toner. In addition, since the toner hardly moves from the pressure roller 110 to the fixing roller 100, the toner attached to the fixing roller 100 also prevents the recording medium 44 from being stained.

A cleaning blade 124 made of stainless steel (an example of a cleaning member according to the present invention) is in contact with the surface of the heat radiating roller 120. Therefore, the toner attached to the heat radiating roller 120 is scraped off by the cleaning blade 124.

When a bias voltage of about 200 V or more is applied to the heat radiating roller 120, the toner of the pressure roller 110 starts to move to the heat radiating roller 120. Bias voltage is 2
As the voltage becomes higher than 00V, the toner of the pressure roller 110 is efficiently transferred to the heat radiating roller 120 in a large amount. When the bias voltage is 700 V or higher, a large amount of toner on the pressure roller 110 is transferred to the heat radiation roller 120 most efficiently. However,
When the bias voltage exceeds 1000 V, the size of the bias power supply 122 increases, which leads to an increase in cost, and the applied bias voltage leaks to a member around the heat radiating roller 120. For this reason, the bias voltage should not exceed 1000V.

Table 1 shows the relationship between the bias voltage and the degree (level) of stain on the recording medium after fixing the toner on 1000 recording media. In the table, x indicates that there is much dirt, Δ indicates that there is little dirt, and o indicates that there is no dirt. Note that the degree of dirt was visually confirmed.

[0049]

[Table 1] As is clear from Table 1, when the bias voltage becomes 700 V or more, the recording medium is not stained.

The time required for the fixing device 90 to rise from a room temperature to a temperature at which good fixing can be performed (weight time) is 25 seconds, which is a sufficiently short wait time. In the fixing device 90, the recording medium 44 is
The toner image is conveyed at a speed of 00 mm / sec and can be fixed on a recording medium having a maximum width of 300 mm. Further, in the fixing device 90,
An A4 size (210 mm × 297 mm) recording medium can be fixed at an output number of 12 / min while transporting the recording medium such that the short side of the recording medium is parallel to the longitudinal direction of the fixing roller 100. In addition, A4 size (210mm x 297m
When the recording medium is conveyed such that the long side of the recording medium of m) is parallel to the longitudinal direction of the fixing roller 100, 1
Fixing can be performed with an output number of 6 sheets / min. The recording medium 44
The recording medium 44 is conveyed so that the center line in the width direction of the fixing roller 100 substantially coincides with the center line in the longitudinal direction of the fixing roller 100 (on the basis of the center).

When the recording medium 44 is conveyed such that the short side of the recording medium 44 coincides with the longitudinal direction of the fixing roller 100 and is continuously fixed at a fixing temperature of 210.degree. The surface temperature of the fixing roller 100 became 170 ° C. However, even in this case, the fixing property was not impaired in the paper passing area. In the non-sheet passing area, no damage was given to peripheral components.

Here, for comparison, the heat releasing roller 120 was removed, and fixing was performed in the same manner as described above. In this case, the surface temperature of the fixing roller 100 decreased to 155 ° C. at the center of the paper passing area. As a result, the fixing property was insufficient in the paper passing area.

Further, the durability test of the fixing operation was performed using the heat radiating roller 120 but without using the bias power supply 122. In this durability test, since the bias power supply 122 is not used, a bias voltage having a polarity opposite to the polarity of the toner is not applied to the heat radiating roller 120.

In the durability test, after a power supply was turned on and a wait time had elapsed, images were continuously formed on ten recording media, and the power was turned off. The apparatus was paused for 1 hour with the power turned off. Thereafter, the power was turned on again, images were continuously formed on the ten recording media, and the power was turned off. This operation was repeated. As a result, when an image is formed on 10,000 sheets of recording media, the toner stains accumulated on the pressure roller 110 appear on the rear surface of the recording medium (surface opposite to the printing surface) as stains. .

On the other hand, as described above, in an experiment in which a bias voltage (700 V) having a polarity opposite to the polarity of the toner was applied to the heat radiating roller 120 using the bias power supply 122, 150,000 sheets were recorded. Even after the image was formed on the medium, the back surface of the recording medium and the image were not stained.

[0056]

As described above, according to the fixing device of the present invention, a bias voltage having a polarity opposite to the polarity of the toner of the recording medium sandwiched between the fixing roller and the pressure roller is applied to the heat radiating roller by the applying means. Has been applied. For this reason, even if the toner on the recording medium adheres to the pressure roller, the toner adhered to the pressure roller moves to the heat radiating roller. Therefore,
The toner hardly adheres to the pressure roller, and the toner does not stain the recording medium. Further, since the toner hardly moves from the pressure roller to the fixing roller, it is possible to suppress the toner attached to the fixing roller from staining the recording medium.

Here, the applying means is 200 V or more and 1
When a bias voltage within the range of 000 V or less is applied to the heat radiating roller, the bias voltage is 200 V
As described above, the toner adhering to the pressure roller easily moves to the heat radiation roller. When the bias voltage is 10
Since the voltage is 00 V or less, the increase in the cost of the application unit can be suppressed, and the applied bias voltage does not easily leak to a conductive component or the like close to the heat radiating roller.

When a cleaning member is provided for removing the toner adhered to the heat radiating roller, the cleaning member removes the toner from the heat radiating roller. Go to

Further, when the fixing roller has a core metal having a thickness of 1 mm or less, since the core metal of the fixing roller is thin, the temperature distribution tends to be uneven in the axial direction of the fixing roller. Since the roller removes heat from the pressure roller, the heat of the fixing roller is easily conducted to the pressure roller, and uneven temperature distribution of the fixing roller is suppressed.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating an embodiment of a fixing device.

FIG. 2 is a schematic diagram illustrating a schematic configuration of a conventional image forming apparatus using an electrophotographic method.

FIG. 3 is a schematic diagram illustrating a schematic configuration of a fixing device.

[Explanation of symbols]

 42 Toner 44 Recording Medium 52 Halogen Heater 90 Fixing Device 100 Fixing Roller 110 Pressure Roller 120 Heat Release Roller 122 Bias Power Supply 124 Cleaning Blade

Claims (4)

[Claims] 1. A fixing roller having a built-in heat source, a pressure roller pressed against the fixing roller, and a radiating roller rotating while contacting an outer peripheral surface of the pressure roller to take heat from the pressure roller. A fixing device for fixing a toner to the recording medium while nipping and conveying the recording medium between the fixing roller and the pressure roller, wherein the image is transferred to the recording medium nipped by the fixing roller and the pressure roller. A fixing device for applying a bias voltage having a polarity opposite to the polarity of the applied toner to the heat radiating roller. 2. The fixing device according to claim 1, wherein the applying unit applies a bias voltage within a range of 200 V or more and 1000 V or less to the heat radiating roller. 3. The fixing device according to claim 1, further comprising a cleaning member that removes toner attached to the heat radiating roller. 4. The fixing device according to claim 1, wherein the fixing roller has a metal core having a thickness of 1 mm or less.