JP3287195B2 - Fixing device - Google Patents

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 and a facsimile and fixes a toner image formed on a recording sheet by heating and pressing. In particular, the present invention relates to a fixing device using a belt stretched over 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 this toner image is
Transfer to PC paper or the like. Then, the recording sheet on which the toner image has been transferred is guided to a fixing device, and the toner image is fixed on the recording sheet to form a permanent image. As the fixing device, a fixing device including a heating roller that is maintained at a predetermined temperature and a pressing roller that is disposed in pressure contact with the heating roller is well known. In this fixing device, the heating roller is driven to rotate, the pressure roller is driven, and the recording sheet on which the toner image has been transferred is sandwiched and conveyed by the nip portion where the fixing roller and the pressure roller are in pressure contact. 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 the heat is pressed onto the recording sheet. At this time, the recording sheet is fed into the nip portion such that the surface on which the toner image has been transferred faces the fixing roller, and the toner image is efficiently heated and melted.

However, in recent image forming apparatuses, the colorization or the speed of the image forming process has been advanced, and in the fixing apparatus in which the heating roller and the pressure roller are pressed against each other, it may be difficult to perform sufficient fixing. Has occurred. In other words, if the speed of the fixing process is increased along with the speed of the image forming process, sufficient heating and heating can be achieved with the nip width when the two rollers are pressed against each other.
The pressurizing time cannot be secured, and poor fixing may occur. Further, in a color image, the amount of toner to be fixed is large, and the toner may not be sufficiently melted in some cases. In order to solve such a problem, there has been proposed a roller in which a belt stretched over a plurality of rollers and a roller are pressed against each other. Examples thereof include JP-B-53-17061 and JP-A-4-342275. No., JP-A-4-34
There is a fixing device disclosed in Japanese Patent No. 2276.

In the fixing devices disclosed in JP-B-53-17061, JP-A-4-342275 and JP-A-4-342276, each of the fixing devices includes a plurality of rollers including a heating roller having a built-in heating element. An endless fixing belt is stretched, and as shown in FIG.
05 is pressed by the heating roller 101 via the fixing belt (region A). The fixing belt is driven to rotate around the heating roller 101 and the pressure roller 10.
On the downstream side of the pressure contact position with No. 5, the fixing belt is pressed along the peripheral surface of the pressure roller 105 (region B). In such a fixing device, at a position where the heating roller 101 and the pressure roller 105 are pressed against each other, the recording sheet 107 carrying the unfixed toner image 108 is fixed to the fixing belt and the pressure roller 1.
05, and is heated and pressed by the pressing force of the pressing 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 pressing roller 105, the sheet is nipped between the fixing belt and the pressing roller 105, and the heating and pressing are continued. Then, the toner is sufficiently melted and fixed on the recording sheet 107.

[0005] This fixing device has the advantage that heating and pressurization can be performed while securing a sufficient nip width as described above, and a sufficient nip width can be obtained even if the diameter of the heating roller is reduced. This has the advantage that the heat capacity can be reduced, the warm-up time can be reduced, and the power consumption during standby can be reduced.

[0006]

However, the fixing device as shown in FIG. 3 has the following problems. In a 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 a portion where the fixing belt and the pressing roller are in contact with each other along the peripheral surface, 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.

For this reason, when PPC paper is used as a recording sheet, even if the toner is sufficiently heated and melted, it does not penetrate between the fibers of the PPC paper, and the adhesive force is reduced. For this reason, the toner image may not be sufficiently fixed, or a so-called offset may occur in which the toner image is transferred to the fixing belt side. Further, there is also a problem that the melted toner adheres to the fixing belt, and the recording sheet hardly peels off from the fixing belt, which causes a paper jam or the like.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to reliably fix a toner image on a recording sheet and reduce the occurrence of offset and the like. Another object of the present invention is to provide a fixing device capable of reliably separating a recording sheet from a fixing belt.

[0009]

In order to solve the above problems, the present invention provides a heating roller having a built-in heating source, at least one supporting roller disposed in parallel with the heating roller, A fixing belt stretched around a heating roller and the support roller and driven to rotate , and a pressure roller pressed against the fixing belt , wherein the fixing belt
The pressure roller has an elastic layer on a surface that is in pressure contact with the pressure roller , and the pressure roller is pressed by the heating roller via the fixing belt, and the fixing belt is located downstream of the pressing position. The fixing roller is disposed so as to contact along the peripheral surface of the pressing roller, and is urged by the pressing roller from the inside of the fixing belt to a downstream portion of a region where the fixing belt and the pressing roller contact. A press-contact member is provided ;
The member is pressed so that the elastic layer undergoes compressive deformation.
The present invention is to provide a fixing device that is used.

[Operation] Since the invention according to the present application has the above-described configuration, it operates as described below.
In this fixing device, the pressure roller is connected via a fixing belt,
The fixing belt is pressed by the heating roller, and the fixing belt is in contact with the peripheral surface of the pressing roller downstream of the pressing position, so that the contact area between the fixing belt and the pressing roller, that is, the nip area is widened. And the toner on the recording sheet can be sufficiently heated. Further, in a downstream portion of a contact area between the fixing belt and the pressure roller, a pressure contact member that presses the fixing belt toward the pressure roller is provided. Pressed strongly. And if the recording sheet is a fibrous one such as PPC paper,
The fused toner penetrates between the fibers, and a good fixing property is obtained by a so-called anchor effect.

Further, the fixing device has an elastic layer on a surface of the fixing belt that is in pressure contact with the pressure roller, and the pressing member presses the fixing belt against the pressure roller to compress the fixing belt into the elastic layer. Since the deformation has occurred, the recording sheet can be self-stripped, and it is not necessary to provide a peeling member. This is due to the following operation. When a recording sheet is fed into a nip portion between a fixing member and a pressure roller in a conventional fixing device, the toner image on the recording sheet is heated and pressed, and the fused toner adheres to the fixing member together with the recording sheet. Would. Therefore, it is necessary to provide a separate peeling member for peeling the recording sheet from the surface of the fixing member at the end of the fixing step. However , in the fixing device according to the present application, in the vicinity of the exit of the nip area,
The elastic layer undergoes compressive deformation due to the pressing force of the pressing member, and slightly slips with respect to the recording sheet when the deformed elastic layer recovers. Thereby, the recording sheet is easily peeled off from the fixing belt, so that a peeling member becomes unnecessary, and the number of components can be reduced.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram illustrating a fixing device according to an embodiment of the present invention. The fixing device includes a heating roller 21 having a built-in heating lamp 31 and two support rollers 22 arranged in parallel with the heating roller .
23 , an endless fixing belt 24 stretched around these rollers and driven to rotate, and a fixing belt 2
4 is a pressing roller pressed against the heating roller 21 via
The main part is constituted by 25 and a pressing member 26 pressed against the pressing roller via a fixing belt downstream of a position where the pressing roller 25 and the heating roller 21 are pressed against each other.

The heating roller 21 has a thickness of 0.2 to 0.1 mm.
It is constituted by a substantially cylindrical member made of a metal such as iron, stainless steel, or copper of 7 mm, and has an inner diameter of 25 mm or more so that the heating lamp 31 can be built therein. The outer diameter near the center of this cylindrical member is several hundred μm from the end.
m is larger. This is to prevent the heating roller from being bent at both ends to cause bending, and to prevent the occurrence of defects such as paper wrinkles due to the bending.
The surface of the cylindrical member is desirably covered with a heat-resistant layer such as silicone rubber or fluorine rubber having a thickness of 50 μm or less, preferably 10 to 30 μm. Thereby, appropriate friction is generated between the fixing belt and the fixing belt, so that the fixing belt can be appropriately driven. The heat capacity of the heating roller is 0.8 in terms of shortening warm-up time and strength.
It is preferably from × 10 ^{−1 to} 2.4 × 10 ⁻¹ J / ° C. · cm ² .

The heating lamp 31 uses two halogen lamps of 600 W and a temperature sensor (not shown).
ON / OFF is controlled based on the surface temperature of the heating roller 21 detected by the control. Thus, the surface temperature of the heating roller 21 is kept constant.

The supporting rollers 22 and 23 are preferably rollers having a high heat insulating property so as not to deprive the fixing belt 24 of heat. For example, the surface of a cylindrical metal roller having an inner diameter of 20 mm or less may be used.
0.5 to 3 mm thick, sponge hardness (Asker C) 2
Those covered with a heat-resistant layer of 0 to 60 °, preferably 30 to 50 °, such as silicone rubber or fluorine rubber, can be employed. As shown in FIG. 2 , a heat-resistant ring made of silicone rubber, viton rubber, or the like is used in place of the heat-resistant layer at intervals of 1 to 10 mm to reduce the contact area between the support roller and the fixing belt, and transmit the fixing roller to the support roller. The amount of heat performed may be reduced.

The fixing belt 24 has a thickness of 15 to 100 μm.
It consists of a heat-resistant resin film such as a metal belt or a polyimide consisting of stainless steel and nickel steel, the pressure roller
The elastic layer 33 is provided on the side pressed against the elastic layer. Above elasticity
The body layer 33 is made of silicone rubber or fluorine rubber or the like.
And a thickness of 1 μm to 200 μm, preferably 10 μm to 1 μm.
As shown in FIG.
So that the pressing portion between the pressing member 26 and the pressing roller 25 is
Therefore, compression deformation mainly occurs in the elastic layer 33.
ing.

After the fixing belt 24 is heated by the heating roller 21 , the fixing belt 24 is directly contacted with the recording sheet 27 to perform fixing, so that the fixing belt 24 is sufficiently heated before reaching the nip portion with the pressure roller 25. Need to be. For this reason, it is stretched so that the contact area with the heating roller 21 is as large as possible. Also, by reducing the diameter of the support roller 23 and setting the winding angle to an acute angle, the recording sheet can be easily separated from the fixing roller.

As shown in FIG. 1B, the pressing member 26 is
The heating roller 21 and the pressure roller 25 are in contact with the inside of the fixing belt 24 downstream of the position where the pressure roller 25 is pressed, and the base 34 is urged toward the pressure roller 25 and is supported by the base 34. It has an elastic body 35, and its surface is covered with a surface layer 36 to impart lubricity and heat insulation. The base 34 moves the pressing member 26 to the pressing roller 25 by 1 to
Since a load for press-contacting at a pressure of 7 N / cm ² is directly received, it should be able to withstand this. The surface layer 36 is made of PTF
A film-like member made of a fluororesin layer such as E or PFA or a woven fabric made of a fluororesin fiber can be used.

The pressing roller 25 has a cylindrical metal core 29.
What is covered with a surface layer 30 such as fluororesin is used.
ing. The pressure roller 25 is rotatably supported by a frame of the fixing device main body, and rotates following the fixing belt 24 . The pressing force of the pressing roller 25 against the heating roller is set to 0.5 to ⁴ N / cm ² .

In such a fixing device, when the power supply of the image forming apparatus is turned on, the two heating lamps 31 are turned on, and the surface temperature of the heating roller 21 reaches the set temperature of 150 ° C. Heated rapidly until: At the same time, the heating roller 21 and the supporting rollers 22 and 23 rotate to heat the fixing belt 24 while moving it around. The surface temperature of the heating roller 21 detected by the temperature sensor is 150
Upon reaching ° C., the image formation is started, the toner image 28 formed on the image bearing member is transferred onto the recording sheet 2 7,
It is sent to the fixing process. After the surface temperature of the heating roller 21 reaches 150 ° C., the heating lamp 31 is once turned off by the controller, but thereafter, is appropriately flashed so as to maintain the surface temperature of the heating roller 21 at 150 ° C.

In the fixing step, the recording sheet 27 is fed between the fixing belt 24 and the pressure roller 25, and first passes through the pressure contact portion between the heating roller 21 and the pressure roller 25 .
The recording sheet 27 and the toner image 28 are heated and pressed.
After that, the recording sheet 27 is fixed to the pressure roller 2 by the fixing belt 24.
Heating is continued by passing the portion pressed along 5 . Then, with the toner sufficiently melted, the recording sheet
Reference numeral 27 denotes a pressing portion between the pressing member 26 and the pressing roller 25, and the toner is pressed against the recording sheet by a large pressing force. At this time, the elastic body formed on the surface of the fixing belt 24
The layer 33 undergoes compressive deformation, and its surface has circumferential strain.
Only occurs. This distortion causes the pressing position of the pressure contact member 26 to move.
Pass, and the deformation of the elastic layer 33 is restored.
Between the surface of the elastic layer 33 and the recording sheet 27.
Small slip occurs. This allows toner and fixing
Adhesion with the belt is weakened, and the recording sheet 27 is fixed.
It is easily peeled from the belt 24. Thereafter, the fixing belt 24 and the pressure roller 25 escape from the nip region, and the fixing process is completed.

In the above-described fixing device, 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 recording paper is first strongly pressed, the fixing belt and the toner are brought into close contact with each other to promote melting, and the toner is sufficiently melted. In this state, the toner can be strongly pressed again to improve the fixing property of the toner. As a result, a good fixed image can be obtained even when fixing is performed at high speed. Also record
The sheet 27 is easily peeled from the fixing belt 24,
The self-stripping of the loose recording sheet 27 becomes possible.
You.

[0023]

As described above, in the fixing device according to the present invention , the pressing roller is pressed by the heating roller via the fixing belt, and the fixing belt is rotated downstream of the pressing position by the peripheral portion of the pressing roller. Since the contact is made along the surface, the nip area is wide, and sufficient heating can be performed. Further, since a pressure contact member for pressing the fixing belt toward the pressure roller is provided downstream of the contact area between the fixing belt and the pressure roller, it is possible to press the sufficiently melted toner onto the recording sheet. it can. For this reason, excellent fixability is obtained,
A good image can be obtained even when fixing is performed at high speed.

Further, since the fixing belt has an elastic layer on the side to be pressed against the pressure roller, the elastic layer undergoes compression deformation at the position where the pressing member is provided. When passing through the fixing belt, a slight slip occurs between the fixing belt and the fixing belt. As a result, the recording sheet that is in close contact with the fixing belt can be self-stripped. Accordingly, stable high-speed fixing can be performed, and the number of components 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 the present invention and an enlarged view of a main part.

FIG. 2 is a schematic perspective view illustrating an example of a support roller that stretches a fixing belt.

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

[Explanation of symbols]

 REFERENCE SIGNS LIST 21 heating roller 22 support roller 23 support roller 24 fixing belt 25 pressure roller 26 pressure contact member 27 recording sheet 28 toner image 29 core of pressure roller 30 surface layer of pressure roller 31 heating lamp 32 base layer of fixing belt 33 of fixing belt Elastic layer 34 Base of press-contact member 35 Elastic body 36 Surface layer of press-contact member

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mitsuhiro Matsumoto 430 Nakai-cho, Nakai-machi, Ashigara-gun, Kanagawa Prefecture Green Tech Nakai Fuji Xerox Co., Ltd. (56) References JP-A 7-210020 (JP, A) JP-A 5- 165350 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 15/08 G03G 15/09 G03G 15/20 G03G 21/00

Claims (1)

(57) [Claims] A heating roller having a built-in heating source; at least one supporting roller disposed in parallel with the heating roller; a fixing belt stretched around the heating roller and the supporting roller and driven to rotate; A pressure roller that is in pressure contact with the fixing belt , and the fixing belt has an elastic surface on a side that is in pressure contact with the pressure roller.
Having a body layer , the pressing roller is pressed by the heating roller via the fixing belt, and the fixing belt contacts the peripheral surface of the pressing roller downstream of the pressing position. A pressure contact member urged from the inside of the fixing belt to the pressure roller is provided at a downstream portion of a region where the fixing belt and the pressure roller are in contact with each other, and the pressure contact member is Compression deformation occurs in the elastic layer
A fixing device that is pressed against the fixing device.