JPH08220922A - Fixing device - Google Patents

Abstract

PURPOSE: To provide a fixing device capable of preventing the accumulation of a foreign matter such as toner stuck to a heating roller and the occurrence of black spots due to the transfer of the accumulated foreign matter to a recording paper by surely preventing the soiling of the heating roller. CONSTITUTION: This fixing device is provided with the heating roller 1 and a pressure roller 2 which are rotated in press contact with each other through the outer peripheral surfaces, an oil applying roller 5 for applying the oil to the roller surface in contact with at least one outer peripheral surface of either the heating roller 1, or the pressure roller 2 and a cleaning means which comes in contact with the surface of the pressure roller 2. In the device, the release property to the toner on the surface of the pressure roller 2 is set lower than the release property to the surface of the heating roller 1, and on the surface of the pressure roller 2, and a part with the low release property where the release property to the toner is set lower than the release property to the heating roller 1 is all of, or a part of the surface of the heating roller 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a fixing device used in an image forming apparatus having an electrophotographic image forming section such as a copying machine, a printer, a facsimile machine, etc. In a fixing device for heat melting and fixing, the foreign matter such as toner adhering to the heating roller forming the fixing device is positively transferred to the pressure roller side, so that the heating roller becomes dirty and the image quality The present invention relates to a fixing device that can prevent deterioration.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine, a printer, a facsimile machine, etc., which is equipped with an electrophotographic image forming section, optical image information such as reflected light from a document is preliminarily uniformly charged on a photoreceptor. The electrostatic latent image obtained by irradiation,
Toner is supplied from a developing device to form a visible image, the toner image is transferred onto a recording paper, and then the paper is passed through a fixing device for thermal fixing. This fixing device has a heating roller having a heater inside and a pressure roller that is in pressure contact with the outer peripheral surface of the heating roller, and heats the transferred recording paper passing between both rollers while applying pressure, The toner image is being fixed. In the above-mentioned conventional fixing device, in order to prevent the adhesion of toner to the heating roller and the occurrence of offset (decrease in fixing ability) due to the adhesion, an oil in which high-viscosity silicone oil is impregnated on the outer peripheral surface of the heating roller is used. An oil film is formed by press-contacting the application means or the oil application means for applying a small amount of oil that oozes out from an oil tank provided in the roller through a felt. Since it is in constant contact with the heating roller, foreign matter such as toner and paper dust that adheres to the peripheral surface of the heating roller is transferred to the oil application means side, which not only reduces the ability to apply oil uniformly, but also reduces the oil The foreign matter gradually accumulated on the coating means side flows backward to the heating roller side,
Finally, there is a problem that it adheres to the recording paper and causes deterioration of image quality (Japanese Patent Laid-Open No. 61-109084, 62-5).
284, 1-120171, 3-114064).

That is, FIG. 5 is an explanatory view of the configuration of a conventional fixing device, in which a recording paper P having unfixed toner T is conveyed from an image forming section located on the right side of the drawing, and the heating roller 1 is fed.
01 and the pressure roller 102 enter the nip portion, the toner T on the recording paper P is fixed on the paper and discharged to a paper discharge unit (not shown) located on the left side of the fixing device. Normal,
The recording paper P holding the toner T is melted by the heat of the fixing roller 101 and fused to the recording paper. However, when the releasability of the surface of the heating roller 101 is poor, a part of the toner adheres to the surface of the heating roller 101, causing a slight offset. As a countermeasure for this, it is possible to prevent the offset by pressing the oil applying roller 105 filled with silicone oil into the heating roller 101 to constantly supply the silicone oil to the heating roller 101 to enhance the mold release property. It is being appreciated. Reference numeral 103 is a heater, 104 is a thermistor for temperature detection, 108 is a separation pawl, 109 and 110 are paper ejection guides, 111 is a separation pawl spring, 112 is a paper ejection roller, 1
Reference numeral 13 is an inlet guide, and 114 is an oil supply unit.

However, as described above, the oil applying roller 10
It is difficult to completely prevent the offset even by using No. 5, and there is a problem that a slight amount of offset remains on the heating roller 101. That is, the roller 105 also serves as a cleaning roller. As the roller 105 is used, the oil application roller 105 becomes dirty, the amount of oil applied is reduced, and the toner adhering to the cleaning roller 106 is retransferred to the heating roller 101. Occurs and stains the image. In particular, the toner adhering to the cleaning roller 106 is mixed with the components in the recording paper and accumulated to form a lump, and when this lump falls from the cleaning roller 106, black large-grained stains (hereinafter referred to as “black spots”) on the recording paper. It is necessary to improve this point.

In addition to the above, as a conventional example for preventing toner stains on the surface of the heating roller, Japanese Patent Laid-Open No. 3-28873 discloses a fixing unit in which a cleaning felt is brought into contact with the surface of the heating roller, and a rotary member is provided near the felt. A technique has been disclosed in which a cleaner is provided to remove stains on the surface of a heating roller due to toner or the like, and to prevent stains on the front and back surfaces of a copy at the time of fixing. Generally, recording paper has fillers such as calcium carbonate attached to paper fibers, but when there are many components with large particle diameters such as calcium carbonate like European paper, the adhesiveness between the filler and the fibers may be weak. Relatedly, the filler is easily offset together with the toner on the surface of the heating roller during fixing, and the cleaning means of the heating roller is easily soiled. Therefore, in order to maintain the performance of the cleaning means, it is necessary to perform maintenance at short intervals, and it becomes impossible to guarantee the performance of the cleaning member at the inspection intervals of normal regular inspection.

Further, in Japanese Patent Application Laid-Open No. 4-107489, the outer peripheral felt portion of the offset preventing agent application roller is integrally formed of a felt member and a reinforcing member, and the outer peripheral felt portion is attachable to and detachable from the supporting portion. By configuring
A configuration in which the offset prevention agent supply means is simplified and the cost is reduced is disclosed. In this conventional example, as in the case of the above-mentioned Japanese Patent Laid-Open No. 3-28873, an offset frequently occurs when a European paper containing a large amount of calcium carbonate as a filler is passed, and a cleaning felt is used as a regular one-time cleaning. It is necessary to replace it several times during the inspection, which is not desirable for service.

Japanese Patent Laid-Open No. 5-53468 discloses a pair of rotating bodies for nip-conveying a transfer material on which an unfixed developer is formed in cooperation with each other, and at least one of the rotating bodies. And a cleaning means having a pressure contact roller for pressing one surface and the other surface of the web-shaped cleaning member against the rotating body, the surface layer of the pressure contact roller is formed of a layer containing a fluororesin. As a result, a technique is disclosed in which the occurrence of image stains due to foreign substances such as developer and paper dust remaining on the heating roller is prevented. However, this device has a large cleaning mechanism, which causes drawbacks such as increase in space and cost.

Japanese Patent Laid-Open No. 5-119656 discloses a release agent applying means for applying a release agent to the surface of a heating roller, and a contact / separation control means for allowing the release agent applying means to contact / separate from the heating roller. There is disclosed a technology in which the toner and the paper powder are prevented from adhering to the heating roller by the release agent applying means and the offset is prevented from occurring on the image fixed on the recording paper by including the above. However, this technique requires a contacting / separating means and its control, so that the cost is high. Further, there is a drawback that the life improving effect is small in spite of increasing the cost by adopting a complicated mechanism and control for separating the release agent applying means from the heating roller.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above, and is provided on at least one of a heating roller and a pressure roller, which rotate while being pressed against each other on the outer peripheral surface, and an outer peripheral surface of at least one of the heating roller and the pressure roller. A fixing device comprising: an oil application roller that comes into contact with the roller to apply oil to the roller surface; and a cleaning unit that contacts the pressure roller surface.
By reliably preventing the heating roller from becoming dirty, a fixing device that can prevent the accumulation of foreign matter such as toner adhering to the heating roller and the occurrence of "black spots" due to the transfer of the accumulated foreign matter onto the recording paper. It is intended to be provided.

[0010]

In order to achieve the above object, the invention according to claim 1 comprises a heating roller and a pressure roller which rotate while being in pressure contact with each other on the outer peripheral surface, and at least one of the heating roller and the pressure roller. In a fixing device provided with an oil application roller that comes into contact with the outer peripheral surface and applies oil to the roller surface, and a cleaning unit that contacts the pressure roller surface, the releasability of the pressure roller surface from toner is determined. The releasing property is set lower than the releasing property of the heating roller surface, and the low releasing property portion of the pressing roller surface whose releasing property to toner is set lower than the releasing property of the heating roller is the heating roller surface. Is a whole or a part thereof.

According to a second aspect of the present invention, the heating roller and the pressure roller which rotate while being in pressure contact with each other on the outer peripheral surface, and the outer surface of at least one of the heating roller and the pressure roller are in contact with the roller surface. In a fixing device provided with an oil applying roller for applying oil and a cleaning means in contact with the surface of the oil applying roller, at least intermittently, at least intermittently, each of the roller groups provided in the fixing device is awaited during a copy operation standby. It is characterized in that it is configured to rotate.

According to a third aspect of the present invention, the heating roller and the pressure roller that rotate while being in pressure contact with each other on the outer peripheral surface, and the roller surface by contacting the outer peripheral surface of at least one of the heating roller and the pressure roller. In a fixing device provided with an oil application roller for applying oil and a cleaning means in contact with the surface of the oil application roller, the surface of the cleaning roller is made of a substance having a high thermal conductivity, and the inside of the roller is thermally conductive. It is characterized by being composed of a substance having a low rate.

[0013]

As described above, the releasability of the pressure roller surface with respect to the toner is set lower than the releasability of the heating roller surface, and the releasability of the pressure roller surface with respect to the toner is equal to that of the heating roller. Since the low releasability portion set lower than the releasability is configured to be the whole or a part of the heating roller surface, the dirt on the heating roller surface is surely transferred to the pressure roller side, It is possible to easily prevent the heating roller from being soiled, and also to prevent "black spots" from being generated due to a lump of foreign matter such as toner falling on the heating roller in terms of copy quality.

Further, since the respective roller groups provided in the fixing device are made to idle at least intermittently during the copy operation standby, the cleaning rollers such as the oil application roller cleaning roller are always kept at a predetermined temperature or higher. Therefore, it is possible to prevent the occurrence of "black spots" stain due to the fall of a lump of foreign matter such as toner that is likely to occur when the temperature of a cleaning roller such as a cleaning roller for an oil application roller decreases.

The surface of the cleaning roller is made of a substance having a high thermal conductivity, and the inside is made of a substance having a low thermal conductivity. In other words, the heat capacity of the cleaning roller for the oil application roller is reduced, and the surface area of the cleaning roller is increased for the small heat capacity to shorten the temperature rise of the cleaning roller, thus stabilizing the performance of the cleaning roller. Further, it is possible to prevent the occurrence of the above-mentioned "black spot" image.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1A is a structural explanatory view of an embodiment of a fixing device of the present invention, and FIG. 1B is an enlarged view of a main part of a pressure roller. This fixing device includes a heating roller 1 having a heater 3 therein, a pressure roller 2 in pressure contact with the heating roller 1, and a thermistor 4 for detecting the surface temperature of the heating roller 1.
An oil application roller 5 that is pressed against the surface of the heating roller 1 and is rotated by frictional force; a cleaning roller 6 for the application roller that is pressed against the surface of the oil application roller 5 and is rotated; The pressure roller cleaning roller 8 is in contact with the surface of the pressure roller 2.

The heating roller 1 is, for example, an aluminum journal portion whose surface is treated with a fluororesin as a release layer, and PFA, PTFA or the like is used as the fluororesin. As the oil application roller 5, one having a surface made of PTFA resin or the like, an oil tank provided inside, and a minute oil bleeding hole on the surface is used.
The cleaning roller 6 is, for example, a roller formed by coating the surface of a metal roller with fluororubber in an amount of 10 to 100 μm. The pressure roller cleaning roller 8 is made of metal or the like, and is made of a material having a lower releasability than the surface material of the pressure roller.

Next, the pressure roller 2 of this embodiment is constructed so that the surface layer is elastically deformed, and the outermost layer surface is made of a material having a toner releasability worse than that of the heating roller 1. Has been. For example, a material in which carbon graphite or particles of SiC (silicon carbide) are dispersed in a surface layer of a member made of an elastic material is used. As shown in FIG. 1B, in the pressure roller 2 of this example, an elastic layer 11 made of heat-resistant silicon rubber or the like is laminated on the outer periphery of a cored bar 10, and the releasability is further provided on the outer periphery of the elastic layer 11. The low releasability layer 12 having a low dielectric constant is laminated. The low releasability layer 12 has a lower releasability than the surface of the heating roller 1 by mixing particles such as carbon graphite in the surface portion of the elastic layer 11, and is lower than the surface of the cleaning roller 6. Good releasability.

When the recording paper carrying the unfixed toner is fixed by the fixing device as described above, no matter how good the releasability of the surface of the heating roller 1, the amount of toner or the like on the surface of the heating roller is small, even if the amount is very small. When foreign matter adheres and accumulates, it becomes a lump and causes various problems. Therefore, in this embodiment, the releasability of the pressure roller surface is intentionally lowered so that a slight amount of offset toner does not accumulate on the heating roller 1, the oil applying roller 5, and the applying roller cleaning roller 6. In this way, a small amount of the offset toner is positively transferred to the surface of the pressure roller, and further, the toner is more releasable from the pressure roller 2 and is transferred to the cleaning roller 6 having a relatively high offset toner carrying ability. . The low releasability portion of the surface of the pressure roller 2 where the releasability to toner is set lower than the releasability of the heating roller may be the entire surface of the heating roller or a part thereof. When a part of the part has a low mold release property, the shape can be variously set such as an island shape, a dot shape, and a band shape.

FIG. 2 is a timing chart showing a control method according to another embodiment of the present invention, in which the respective roller groups provided in the fixing device are idled continuously or intermittently while waiting for a copying operation. The feature is that it is configured. That is,
After the power supply of the image forming apparatus is turned on, the surface temperature of the heating roller 1 is detected by the thermistor 4 even when the fixing device is in the non-sheet passing state, so that the heater 3 is ON-OFF controlled to be within a predetermined temperature range. The surface temperature is maintained. However, the temperature of the cleaning roller 6 for the coating roller is not controlled even for heating, so that the temperature of the heating roller rapidly decreases when the heating roller is stopped. As a result, the offset toner adhering to the surface of the cleaning roller 6 and the desorbed components of the recording paper are easily aggregated and solidified. This coagulum is brittle,
It is easily peeled off and dropped by an external force, which adheres to the recording paper and causes "black spots". Therefore, in the present invention, the cleaning roller 6 and the heating roller 1 are intermittently rotated during standby lighting. That is, the cleaning roller 6 and the heating roller 6 have a duty ratio higher than a predetermined value.
By rotating, the extreme decrease in temperature of the cleaning roller 6 can be prevented, and the occurrence of the "black spot" phenomenon can be prevented.

In FIG. 2, the heating roller 1 and the cleaning roller 6 are caused to idle by turning on the driving of the heating roller at a predetermined interval even when the fixing nip portion is not passing the sheet (when the sheet is not passing). The temperature of the cleaning roller 6 is prevented from lowering. It is sufficient to perform this idle rotation intermittently.

Next, the offset toner and the detached components of the recording paper accumulated on the surface of the oil applying roller cleaning roller 6 become brittle and easily fall when cooled, but in the third embodiment of the present invention, the cleaning roller is used. Since the surface of 6 is made of a substance having a high thermal conductivity and the inside thereof is filled with a substance having a low thermal conductivity, such a problem can be solved. That is, as shown in FIGS. 3 and 4, in this embodiment, the surface layer 8a is made of a material having a good thermal conductivity, such as a metal, but has a very small heat capacity.
b having a low thermal conductivity (for example, a hollow pipe having a thickness of 1 mm or less, a roller having a resin surface coated with metal, etc.)
The temperature of the accumulated material on the surface of the cleaning roller 6 can be immediately increased after the driving of the heating roller 1 and the cleaning roller 8 is started, and as a result, the embrittlement of the accumulated material is prevented and the accumulation roller is prevented from falling. It is possible to prevent "black spots" -like copy stains as a result. Examples of the internal substance 8b having a low thermal conductivity include air, vacuum, resin, foamed resin and the like.

In the above embodiment, the oil applying roller cleaning roller 6 is described as an example, but this embodiment may be applied to the pressure roller cleaning roller 8 shown in FIG. That is, when the toner is positively transferred to the pressure roller side as in the first embodiment, the cleaning roller 8 removes the toner on the pressure roller. If the roller structure as shown in FIGS. 3 and 4 is adopted in order to prevent the situation where the above toner becomes a lump and is reversely transferred to the pressure roller and adheres to the recording paper, the toner lump becomes brittle due to cooling. Can be prevented.

As described above, according to this embodiment, the heat capacity of the cleaning roller 6 (8) for the oil applying roller is reduced, and the surface area of the cleaning roller is widened for the small heat capacity, so that the temperature of the cleaning roller rises. Since the length of the cleaning roller is shortened, the performance of the cleaning roller can be stabilized and the occurrence of the above-mentioned "black spot" image can be prevented.

Although the toner cleaning structure by the pressure roller in the first embodiment can be established as a single embodiment, it can be used in the second embodiment, the third embodiment, or a combination of both. Can be established. Further, the idle rotation during the standby for the copying operation in the second embodiment can be established as a single embodiment, but can also be established in combination with the first and third embodiments. Further, the structure of the cleaning roller of the third embodiment can be established as a single embodiment, but can also be established by combining it with the first and second embodiments.

[0026]

As described above, in the fixing device of the present invention, the heating roller 1 which rotates while being in pressure contact with each other on the outer peripheral surface thereof.
And a pressure roller 2, an oil application roller 5 that contacts the outer peripheral surface of at least one of the heating roller and the pressure roller to apply oil to the roller surface, and a cleaning unit 6 that contacts the pressure roller surface. In the fixing device, the releasing property of the pressure roller surface to the toner is set lower than the releasing property of the heating roller surface, and the releasing property of the pressure roller surface to the toner is heated. The low releasability part, which is set lower than the releasability of the roller,
It was configured to be all or a portion of the heating roller surface.
Therefore, the dirt on the surface of the heating roller is surely transferred to the pressure roller side, and the dirt on the heating roller can be easily prevented, and the lump of foreign matters such as toner on the heating roller can drop in terms of copy quality. It is possible to prevent the occurrence of "black spots" stains due to.

Further, since the respective roller groups provided in the fixing device are made to idle at least intermittently during the copying operation standby, the cleaning rollers such as the oil application roller cleaning roller are always kept at a predetermined temperature or higher. Therefore, it is possible to prevent the occurrence of "black spots" stain due to the fall of a lump of foreign matter such as toner that is likely to occur when the temperature of a cleaning roller such as a cleaning roller for an oil application roller decreases.

The surface of the cleaning roller is made of a substance having a low thermal conductivity, and the inside is made of a substance having a low thermal conductivity. In other words, the heat capacity of the cleaning roller for the oil application roller is reduced, and the surface area of the cleaning roller is increased for the small heat capacity to shorten the temperature rise of the cleaning roller, thus stabilizing the performance of the cleaning roller. Further, it is possible to prevent the occurrence of the above-mentioned "black spot" image.

[Brief description of drawings]

FIG. 1A and FIG. 1B are a configuration explanatory view and a principal configuration explanatory view of a fixing device according to an embodiment of the present invention.

FIG. 2 is a timing chart for explaining a second embodiment of the present invention.

FIG. 3 is an explanatory diagram of a third embodiment of the present invention.

FIG. 4 is an explanatory diagram of a third embodiment of the present invention.

FIG. 5 is an explanatory diagram of a conventional example.

[Explanation of symbols]

1 heating roller, 2 pressure roller, 3 heater, 4 thermistor, 5 oil application roller, 6 cleaning roller, 7 separation claw, 8 cleaning roller,

Claims (3)

[Claims] 1. A heating roller and a pressure roller that rotate while being in pressure contact with each other on the outer peripheral surface, and an oil application that contacts the outer peripheral surface of at least one of the heating roller and the pressure roller to apply oil to the roller surface. In a fixing device provided with a roller and a cleaning unit in contact with the surface of the pressure roller, the releasability of the pressure roller surface from the toner is set lower than the releasability of the heating roller surface, A fixing device characterized in that a low releasable portion of the surface of the pressure roller whose releasability to toner is set lower than that of the heating roller is the whole or a part of the surface of the heating roller. 2. A heating roller and a pressure roller that rotate while being in pressure contact with each other on the outer peripheral surface, and an oil application for contacting the outer peripheral surface of at least one of the heating roller and the pressure roller to apply oil to the roller surface. In a fixing device including a roller and a cleaning unit that comes into contact with the surface of the oil application roller, each roller group included in the fixing device is idled at least intermittently during a copy operation standby. A fixing device characterized by the above. 3. A heating roller and a pressure roller that rotate while being in pressure contact with each other on the outer peripheral surface, and an oil application for contacting the outer peripheral surface of at least one of the heating roller and the pressure roller to apply oil to the roller surface. In a fixing device including a roller and a cleaning unit that contacts the surface of the oil application roller, the surface of the cleaning roller is made of a substance having high thermal conductivity, and the inside is made of a substance having low thermal conductivity. The fixing device characterized in that