JPH09114283A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely perform fixing of a toner image on a recording sheet, and to reduce the occurrence of offsetting, in a fixing device with a belt system. SOLUTION: The fixing device, provided with the fixing belt 4 extended on plural supporting rollers including the heat roller 1, and the pressure roller 5, is composed that the pressure roller 5 is pressed to the heating roller 1 across the fixing belt 4. On the downstream side of the pressing position, the device is arranged so that the fixing belt 4 is held in contact along with a periphery of the pressure roller 5. On the downstream side part of the contact area, the press contact member 6 is disposed so as to held in contact with the inside of the fixing belt 4, and energized corresponding to the pressure roller 5. By the described constitution, it is made possible that the nip area in-between the pressure roller 5 and the fixing belt 4 is made large, and moreover the toner image is strongly press fixed to the recording sheet in a satisfactorily heated melted state. Therefore, the excellent fixing quality and the preventive effect of offsetting can be attained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device which is used in an electrophotographic image forming apparatus such as a copying machine or a facsimile and which fixes a toner image formed on a recording sheet by heating and pressing the toner image. In particular, it relates to a fixing device using a belt stretched around a plurality of rollers including a heating roller.

[0002]

2. Description of the Related Art Generally, in an electrophotographic image forming apparatus, a toner image is formed on an image carrier, and the toner image is transferred to a P image.
Transfer to PC paper etc. Then, the recording sheet on which the toner image is transferred is guided to a fixing device, and the toner image is fixed on the recording sheet to form a permanent image. It is well known that the fixing device includes a heating roller kept at a predetermined temperature and a pressure roller arranged in pressure contact with the heating roller. In this fixing device, the heating roller is driven to rotate and the pressure roller is driven, and the recording sheet on which the toner image is transferred is nipped and conveyed in the nip portion where the fixing roller and the pressure roller are in pressure contact with each other. The recording sheet onto which the toner image has been transferred is heated and pressed while passing through the nip portion, and the toner image melted by heat is pressed onto the recording sheet. At this time, the recording sheet is fed into the nip portion so that the surface on which the toner image is transferred faces the fixing roller, and the toner image is efficiently heated and melted.

However, in recent image forming apparatuses, colorization or speeding up of the image forming process has progressed, and it may be difficult to perform sufficient fixing with the above-described fixing device that presses the heating roller and the pressure roller. Has occurred. In other words, if the fixing process is accelerated as the image forming process is accelerated, the nip width when the two rollers are pressed against each other causes sufficient heating / heating.
It may not be possible to secure the pressurizing time, which may result in defective fixing. Further, in a color image, the amount of toner to be fixed is large, and there are cases where the toner cannot be sufficiently melted. In order to solve such a problem, there has been proposed one in which a belt stretched around a plurality of rollers and a roller are brought into pressure contact with each other, and examples thereof include JP-B-53-17061 and JP-A-4-342275. Japanese Patent Laid-Open No. 4-34
There is a fixing device disclosed in Japanese Patent No. 2276.

In the fixing devices disclosed in Japanese Patent Publication No. 53-17061, Japanese Patent Application Laid-Open No. 4-342275, and Japanese Patent Application Laid-Open No. 4-342276, a plurality of rollers including a heating roller having a built-in heating element are used. An endless fixing belt is stretched around the pressure roller 1 as shown in FIG.
05 is pressed against the heating roller 101 via the fixing belt (area A). The fixing belt is orbitally driven, and includes the heating roller 101 and the pressure roller 10.
The fixing belt is pressed against the peripheral surface of the pressure roller 105 on the downstream side of the position where the fixing roller 5 is pressed (region B). In such a fixing device, at the position where the heating roller 101 and the pressure roller 105 are in pressure contact with each other, the recording sheet 107 carrying the unfixed toner image 108 is fixed to the fixing belt and the pressure roller 1.
It is sandwiched between the sheet No. 05 and the sheet No. 05 and is heated and pressurized by the pressing force of the pressure roller 105 and the heat transmitted from the fixing belt.
Further, even after passing through the pressure contact position between the heating roller 101 and the pressure roller 105, the heating roller 101 is nipped between the fixing belt and the pressure roller 105, and heating / pressurization is continued. Then, the toner is sufficiently melted and fixed on the recording sheet 107.

This fixing device has the advantage that a sufficient nip width can be secured and heating and pressing can be performed as described above, and a sufficient nip width can be obtained even if the diameter of the heating roller is reduced. Therefore, the heat capacity can be reduced, the warm-up time can be shortened, and the power consumption during standby can be reduced.

[0006]

However, the fixing device as shown in FIG. 5 has the following problems. At the portion where the heating roller and the pressure roller are pressed against each other via the fixing belt, the toner image on the sandwiched recording sheet can be sufficiently pressed. In the portion contacting along the peripheral surface of the toner image, the pressure contact force between the fixing belt and the pressure roller is small, and the toner image cannot be strongly pressed onto the recording sheet.

Therefore, when the PPC paper is used as the recording sheet, even if the toner is sufficiently heated and melted, the toner does not penetrate into the fibers of the PPC paper and the adhesive force becomes small. Therefore, the toner image may not be sufficiently fixed, or the toner image may be transferred to the fixing belt side, so-called offset may occur. Further, although it is not a problem peculiar to the fixing device of the type shown in FIG. 5, there is a problem that the fused toner adheres to the fixing belt and the recording sheet is hardly separated from the fixing belt, which may cause a paper jam. is there.

The present invention has been made to solve the above problems, and an object thereof is to reliably fix a toner image on a recording sheet to reduce the occurrence of offset or the like, or In addition to this, it is an object of the present invention to provide a fixing device capable of reliably peeling a recording sheet from a fixing belt.

[0009]

In order to solve the above-mentioned problems, the invention according to claim 1 provides a heating roller having a built-in heating source, and one or more supporting rollers arranged in parallel with the heating roller. A fixing belt which is stretched around the heating roller and the supporting roller and is driven to rotate, and a pressure roller which is in pressure contact with the fixing belt. While being pressed by the heating roller, the fixing belt is arranged on the downstream side of the pressing position so as to come into contact with the peripheral surface of the pressure roller, and in the area where the fixing belt and the pressure roller come into contact with each other. It is assumed that a pressure contact member that is urged by the pressure roller from the inside of the fixing belt is provided in the downstream side portion.

According to a second aspect of the present invention, in the fixing device according to the first aspect, the fixing belt has an elastic layer on a surface which is in pressure contact with a pressure roller, and the pressure contact member is It is assumed that the elastic layer is pressed so as to be compressed and deformed.

[Operation] Since the invention according to the present application has the above-mentioned structure, it operates as described below.
In the fixing device according to claim 1, the pressure roller is pressed against the heating roller via the fixing belt, and the fixing belt comes into contact along the peripheral surface of the pressure roller on the downstream side of the pressing position. Since the contact area between the fixing belt and the pressure roller, that is, the nip area can be widened, the toner on the recording sheet can be sufficiently heated. Further, in the downstream side portion of the contact area between the fixing belt and the pressure roller, a pressure contact member for pressing the fixing belt to the pressure roller side is provided, so that the toner is sufficiently melted on the recording sheet. It is strongly pressed. If the recording sheet is fibrous, such as PPC paper, the melted toner penetrates between the fibers and a good anchoring effect is obtained by the so-called anchoring effect.

According to a second aspect of the present invention, the fixing device has an elastic layer on the surface of the fixing belt which is in pressure contact with the pressure roller, and the pressure contact member presses the fixing belt against the pressure roller to form an elastic body. Since the layers are compressed and deformed, the recording sheet can be self-striped, and it is not necessary to provide a peeling member. This is due to the following actions. When a recording sheet is fed to the nip portion between the fixing member and the pressure roller in the conventional fixing device, the toner image on the recording sheet is heated and pressed, and the melted toner adheres to the fixing member together with the recording sheet. Will end up. Therefore, it is necessary to separately provide a peeling member for peeling the recording sheet from the surface of the fixing member at the end of the fixing process. However, in the fixing device according to the second aspect, when the elastic layer is compressed and deformed by the pressing force of the pressure contact member near the exit of the nip region and the deformed elastic layer is restored, Slip slightly. As a result, the recording sheet is easily peeled off from the fixing belt, so that a peeling member is unnecessary and the number of parts can be reduced.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram showing a fixing device according to an embodiment of the present invention. This fixing device includes a heating roller 1 having a heating lamp 11 therein,
Two supporting rollers 2 and 3 arranged in parallel with the heating roller, an endless fixing belt 4 stretched around these rollers and driven to rotate, and the fixing belt 4
The pressure roller 5 pressed against the heating roller 1 via the
The pressure contact member 6 that is pressed against the pressure roller via the fixing belt on the downstream side of the position where the pressure roller 5 and the heating roller 1 are in pressure contact constitutes the main part.

The heating roller 1 has a thickness of 0.2 to 0.7.
It is composed of a substantially cylindrical member made of metal such as iron, stainless steel, and copper, and has an inner diameter of 25 mm or more so that the heating lamp 11 can be built therein. The outer diameter near the center of this cylindrical member is several hundred μm from the end.
It is getting bigger. This is to prevent the heating roller from being bent by being pivotally supported at both ends, and to prevent defects such as paper wrinkles due to the bending. The surface of the cylindrical member is preferably covered with a heat-resistant layer such as silicone rubber or fluororubber having a thickness of 50 μm or less, preferably 10 to 30 μm. As a result, appropriate friction is generated between the fixing belt and the fixing belt, and the fixing belt can be appropriately driven. The heat capacity of the heating roller is
0.8 × 1 in terms of shortening warm-up time and strength
0 ^{−1 to} 2.4 × 10 ⁻¹ J / ° C. · cm ² is preferable.

The heating lamp 11 uses two 600 W halogen lamps, and a temperature sensor (not shown).
Based on the surface temperature of the heating roller 1 detected by
ON / OFF is controlled. As a result, the heating roller 1
The surface temperature of is kept constant.

The supporting rollers 2 and 3 are preferably rollers having a high heat insulating property so as not to remove heat from the fixing belt 4. For example, the surface of a cylindrical metal roller having an inner diameter of 20 mm or less and a thickness of 0.5 to 3 mm, Sponge hardness (Asker C) 20-6
Those covered with a heat resistant layer such as silicone rubber or fluororubber at 0 °, preferably 30 to 50 ° can be used. Instead of the heat-resistant layer, a heat-resistant ring made of silicone rubber, viton rubber, etc. is used as shown in FIG.
The contact area between the support roller and the fixing belt may be reduced by setting the interval of 10 mm to reduce the amount of heat transferred from the fixing belt to the support roller.

The fixing belt 4 is composed of a metal belt made of stainless steel or nickel steel having a thickness of 15 to 100 μm, or a heat resistant resin film such as polyimide. Further, in order to prevent the toner on the recording sheet from being transferred onto this surface, a release layer made of silicone rubber, fluororubber or fluororesin such as polytetrafluoroethylene (PTFE) or perchloroalkoxy (PFA). Are stacked. The thickness of the release layer can be set to about 5 to 500 μm, and 10 to 100 μm is preferable in terms of releasability and heat capacity. The heat capacity of the fixing belt is 0.9 × 10 ^{-2 to} 2.7 × in terms of warm-up time and strength.
10 ⁻² J / ° C. · cm ² is preferable.

Since the fixing belt 4 is heated by the heating roller 1 and then directly contacts the recording sheet 7 for fixing, the fixing belt 4 is sufficiently heated before reaching the nip portion with the pressure roller 5. Need to be. Therefore, it is stretched so that the contact area with the heating roller 1 is as large as possible. Further, by reducing the diameter of the support roller 3 and setting the winding angle to an acute angle, the recording sheet can be easily separated from the fixing roller.

As shown in FIG. 2, the pressure contact member 6 contacts the inside of the fixing belt on the downstream side of the position where the heating roller 1 and the pressure roller 5 are in pressure contact with each other. It has a urging base 34 and an elastic body 35 supported by the urging base 34, and the surface thereof is covered with a surface layer 36 for imparting lubricity and heat insulation. The base 34 directly bears a load for pressing the pressing member 6 against the pressure roller at a pressure of 1 to 7 N / cm ² , and therefore can withstand this. As the surface layer 36, a film member made of a fluororesin layer such as PTFE or PFA, a woven fabric made of fluororesin fibers, or the like can be used.

The pressure roller 5 is formed by coating the surface of a cylindrical metal core 9 with a heat resistant sponge 10. The heat-resistant sponge is made of, for example, fluororubber or silicone rubber and has a thickness of 0.5 to 3 mm and a hardness (Asker C) of 2.
Those having a temperature of 0 to 60 °, preferably 30 to 50 ° can be used. A fluororesin layer such as PFTE or PFA may be formed on the surface. The pressure roller 5
Is rotatably supported by the frame of the fixing device main body, and is rotated by the fixing belt 4. The pressing force of the pressure roller 5 against the heating roller is 0.5 to 4 N / cm.
^{Assume 2} .

In such a fixing device, when the power source of the image forming device is turned on, the two heating lamps 11 are turned on, and the surface temperature of the heating roller 1 reaches the set temperature of 150 ° C. It is heated rapidly until. At the same time, the heating roller 1 and the support rollers 2 and 3 rotate to heat the fixing belt 4 while moving it around. When the surface temperature of the heating roller 1 detected by the temperature sensor reaches 150 ° C., image formation is started and the toner image 8 formed on the image carrier is transferred onto the recording sheet 7 and sent to the fixing step. Come on. After the surface temperature of the heating roller 1 reaches 150 ° C., the heating lamp 11 is temporarily turned off by the controller, but thereafter, it is appropriately blinked so as to keep the surface temperature of the heating roller 1 at 150 ° C.

In the fixing step, the recording sheet 7 is fed between the fixing belt 4 and the pressure roller 5, and first passes through the pressure contact portion between the heating roller 1 and the pressure roller 5, and then the recording sheet 7 and the toner image 8 are formed. Is heated and pressurized. Thereafter, the recording sheet 7 passes through the portion where the fixing belt 4 is pressed against the pressure roller 5, and the heating is continued. The recording sheet 7 reaches the pressure contact portion between the pressure contact member 6 and the pressure roller 5 in a state where the toner is sufficiently melted, and the toner is pressed against the recording sheet by a large pressing force. After that, the fixing belt 4 and the pressure roller 5 are released from the nip region, and the fixing process is completed.

In the fixing device as described above, the contact area between the fixing belt and the pressure belt, that is, the nip area is wide, and the toner image can be sufficiently heated and pressed.
Further, the recording paper is strongly pressed twice on the upstream side and the downstream side of the nip area. When the first strong pressing is performed, the fixing belt and the toner are brought into close contact with each other to promote the melting, and the toner is sufficiently melted. In this state, the toner can be firmly pressed again to enhance the fixing property of the toner. As a result, a good fixed image can be obtained even when fixing is performed at high speed.

FIG. 4 is a schematic configuration diagram (a) showing an example of a fixing device according to the second aspect of the invention and an enlarged view (b) of a main part.
It is. The fixing belt 24 used in this fixing device has an elastic layer 33 on the side that is in pressure contact with the pressure roller.
Further, as the pressure roller 25, a cylindrical metal core 29 coated with a surface layer 30 such as a fluororesin is used. The configuration other than the above, that is, the heating roller 21, the support rollers 22 and 23, the pressure contact member 26 and the like are the same as those of the fixing device shown in FIG.

The elastic layer 33 is made of silicone rubber or fluororubber, and has a thickness of 1 μm to 200 μm, preferably 10 μm to 100 μm and a hardness of about 20 ° to 60 °, as shown in FIG. 4B. At the pressure contact portion between the pressure contact member 26 and the pressure roller 25, the elastic layer 33 is mainly compressed and deformed.

In such a fixing device, the recording sheet 27 on which the toner image 26 is transferred is sandwiched between the fixing belt 24 and the pressure roller 25, and heated and pressed. Then, the toner reaches a position where the pressure contact member 26 is pressed in a state where the toner is sufficiently melted, and the melted toner is transferred to the recording sheet 27.
Is crimped. At this time, the elastic layer 33 formed on the surface of the fixing belt 24 is compressed and deformed, and circumferential distortion is generated on the surface. The strain passes through the pressing position of the pressure contact member 26 and is canceled by the deformation of the elastic body layer 33 being restored.
A slight slip occurs between the and.

As a result, the adhesion between the toner and the fixing belt is weakened, and the recording sheet 27 is easily separated from the fixing belt 24. As described above, the present fixing device has the same effect as that of the fixing device shown in FIG.
7 self-stripping is possible.

[0028]

In the fixing device according to the first aspect of the present invention, the pressure roller is pressed against the heating roller via the fixing belt, and the fixing belt extends along the peripheral surface of the pressure roller downstream of the pressing position. Since they are in contact with each other, the nip area is wide and sufficient heating can be performed. Further, since a pressure contact member for pressing the fixing belt to the pressure roller side is provided on the downstream side of the contact area between the fixing belt and the pressure roller, the sufficiently melted toner can be pressure-bonded to the recording sheet. it can. Therefore, excellent fixability can be obtained, and a good image can be obtained even when fixing is performed at high speed.

Further, the fixing device according to the second aspect has an elastic layer on the side of the fixing belt which is in pressure contact with the pressure roller,
Since the elastic layer is compressed and deformed at the position where the pressure contact member is provided, when the recording sheet passes through this portion, a slight slip occurs with the fixing belt. As a result, the recording sheet that is in close contact with the fixing belt can be self-striped. Therefore, stable high-speed fixing can be performed, and the number of parts can be reduced without specially providing a peeling member.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an example of a fixing device according to a first aspect of the invention.

FIG. 2 is an enlarged view of a main part of the fixing device shown in FIG.

FIG. 3 is a schematic perspective view illustrating an example of a support roller that stretches a fixing belt.

FIG. 4 is a schematic configuration diagram and an enlarged view of a main part showing an example of a fixing device according to a second aspect of the invention.

FIG. 5 is a schematic configuration diagram showing a conventional fixing device.

[Explanation of symbols]

 1, 21 heating roller 2, 22 support roller 3, 23 support roller 4, 24 fixing belt 5, 25 pressure roller 6, 26 pressure contact member 7, 27 recording sheet 8, 28 toner image 9, 29 pressure roller core 10 Elastic layer of pressure roller 11,31 Heating lamp 30 Surface layer of pressure roller 32 Base layer of fixing belt 33 Elastic layer of fixing belt 34 Base of pressure contact member 35 Elastic body 36 Surface layer of pressure contact member

Claims (2)

[Claims] 1. A heating roller having a built-in heating source, one or more supporting rollers arranged in parallel with the heating roller, and a fixing belt which is stretched around the heating roller and the supporting roller and is driven to rotate. A pressure roller that is in pressure contact with the fixing belt, wherein the pressure roller is pressed by the heating roller via the fixing belt, and the fixing belt is applied downstream of the pressing position. A pressure contact member that is arranged so as to contact along the peripheral surface of the pressure roller and is urged by the pressure roller from the inside of the fixing belt at the downstream side portion of the region where the fixing belt and the pressure roller contact. The fixing device is provided with. 2. The fixing device according to claim 1, wherein the fixing belt has an elastic layer on a surface thereof that is in pressure contact with a pressure roller, and the pressure contact member has a compression deformation in the elastic layer. A fixing device characterized by being pressed so as to occur.