JP2002049272A - Fixing device and image forming apparatus having the same - Google Patents

Abstract

(57) Abstract: Provided is a belt fixing device capable of appropriately performing fixing according to various conditions, and an image forming apparatus having the same. A heating roller (3) and a fixing roller (4) wound around an endless fixing belt (2) for conveying a sheet-like medium,
A pressure roller 5 disposed opposite the fixing roller 4 via the fixing belt 2; a heating roller 3; heaters 6 and 7 provided inside the pressure roller 5; A fixing device 1 having a temperature detecting means 8 provided therein, wherein the fixing temperature and the conveying speed of the sheet-like medium by the fixing belt 2 are varied according to the type of toner and the resolution of the toner image. An image forming apparatus including the apparatus 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device, and more particularly to a so-called belt fixing device having a plurality of fixing modes and an image forming apparatus such as a copying machine, a facsimile, or a printer having the fixing device.

[0002]

2. Description of the Related Art Image forming apparatuses such as copying machines, facsimile machines, printers and printing machines generally have a fixing device for fixing a toner image on a sheet-like medium on which a toner image as an image to be fixed is formed. ing.

[0003] The fixing device includes a heating roller having a heat source therein and driven to rotate, and a pressure roller pressed against the heating roller and rotated by the heating roller, and a nip formed by both rollers. A heat roller pair-type fixing device for fixing the toner image by heating and pressing the paper by rotating the rollers and an endless fixing belt and a fixing belt for conveying a sheet-like medium on which the toner is fixed. There is known a so-called belt fixing device of a type including a heating roller and a fixing roller around which a pressure roller is wound, and a pressure roller and the like arranged as opposed to the fixing roller via a fixing belt.

There are two types of sheet-like media: plain paper generally used for copying and the like, and so-called special sheets having a larger heat capacity than paper, such as OHP sheets, cardboard, and envelopes. Japanese Patent Application Laid-Open No. 64-4457, Japanese Patent Application Laid-Open No. 4-136970, and Japanese Patent Application Laid-Open No. 4-294376.
No., proposed by US Pat.

In the fixing device described in Japanese Utility Model Laid-Open Publication No. 64-4457, a set fixing temperature or a pressure between a heating roller and a pressure roller is switched according to whether or not a sheet medium to be fixed is thick paper. And Japanese Patent Laid-Open No. 4-1
The fixing device described in JP-A-36970 can switch a nip width between a heating and a pressure roller and a fixing temperature according to a sheet-like medium on which fixing is performed.
When the sheet medium to be fixed is an OHP sheet and a color image is formed, the fixing device described in JP-294376A performs re-fixing and reduces the conveyance speed of the sheet-shaped medium at the time of re-fixing. Is what you do.

However, the configurations described in any of the above publications relate to a fixing device of a heat roller pair type.
It does not relate to the belt fixing device. In recent years, a demand for a belt fixing device having excellent thermal responsiveness has been increasing, and development of a belt fixing device capable of fixing any of the above-described sheet-like media has been desired.

Therefore, the present applicant has disclosed in Japanese Patent Laid-Open No. 11-282.
As disclosed in Japanese Patent Application Publication No. 307, the fixing mode is switched between a case where the sheet medium is plain paper and a case where the sheet medium is a special sheet such as OHP, and a belt fixing device in which the fixing temperature is different in each fixing mode. Proposed.

[0008]

However, Japanese Patent Application Laid-Open No.
The belt fixing device disclosed in Japanese Patent No. 282307 merely switches the fixing mode according to the sheet medium. In recent years, an image forming apparatus has various conditions,
For example, the image formation can be performed according to whether the image formation is performed in a single color or in multiple colors, the resolution, and the like. Therefore, also in the belt fixing device, it is necessary to perform fixing under appropriate conditions according to not only the type of the sheet-shaped medium but also the image forming conditions in the image forming apparatus.

On the other hand, in the belt fixing device, the temperature of the fixing belt, which has risen once, is deprived of heat by the rollers due to the rotation thereof.
Since there is a property that the fixing becomes unstable due to the lowering, it is necessary to propose a belt fixing device capable of performing the fixing in accordance with the various conditions as described above while avoiding this. In a fixing device, the temperature control is important. In a belt fixing device, a thermistor is conventionally provided in contact with a fixing belt or a heating roller.
Since there is a problem that the fixing belt and the heating roller are worn by the sliding contact of the thermistor, it is desired to provide a belt fixing device in which the abrasion due to the sliding contact of the thermistor is prevented. Further, in the belt fixing device, the heating roller is made of a metal such as aluminum having good heat transfer, but such a metal is relatively soft, so that the heating roller is worn by friction with the fixing belt. There was a problem.

SUMMARY OF THE INVENTION An object of the present invention is to provide a belt fixing device capable of appropriately performing fixing according to various conditions, and an image forming apparatus having the fixing device.

[0011]

According to a first aspect of the present invention, there is provided an endless fixing belt for conveying a sheet-like medium on which a toner image is fixed, and the fixing belt is wound around the endless fixing belt. A heating roller and a fixing roller, a pressure roller disposed opposite to the fixing roller via the fixing belt, and at least one of the heating roller and the pressure roller provided inside the heating roller. In a fixing device including a heater and a temperature detecting unit disposed opposite to the heating roller, fixing is performed according to a fixing mode determined by a type of a toner forming a toner image and / or a resolution of the toner image. It is characterized in that a set temperature for carrying out the process and / or a conveying speed of the sheet-like medium by the fixing belt are made variable.

According to a second aspect of the present invention, in the fixing device according to the first aspect, a set temperature for performing fixing and / or a sheet-like medium using the fixing belt according to a fixing mode determined by a type of the sheet-like medium. Is characterized in that the transfer speed is variable.

According to a third aspect of the present invention, there is provided an endless fixing belt for conveying a sheet medium on which a toner image is fixed, a heating roller and a fixing roller around which the fixing belt is wound, and the fixing belt. A pressure roller disposed opposite to the fixing roller, a heater provided inside at least the heating roller of the heating roller and the pressure roller, and a pressure roller disposed opposite to the heating roller. Temperature for fixing in accordance with a fixing mode determined by the type of toner for forming the toner image and / or the resolution of the toner image and / or the type of sheet medium in the fixing device having the temperature detecting means. In addition, at least a set temperature for performing fixing in the conveyance speed of the sheet-like medium by the fixing belt is variable.

The invention described in claim 4 is the first to third aspects of the present invention.
In the fixing device according to any one of the above, when the fixing mode is switched from one of the fixing modes to another fixing mode, the set temperature of the other fixing mode is higher than the set temperature of the one fixing mode. When the temperature is high, the heating roller is heated by the heater, the driving of the fixing belt is started after the set temperature of the other fixing mode is detected by the temperature detecting means.

According to a fifth aspect of the present invention, in the fixing device according to the fourth aspect, after the driving of the fixing belt is started,
After the temperature detecting means detects the set temperature of the other fixing mode again, conveyance of the sheet-like medium by the fixing belt is started.

According to a sixth aspect of the present invention, in the fixing device according to the fourth aspect, after the driving of the fixing belt is started,
After a lapse of time determined according to the fixing mode before and after the switching, the conveyance of the sheet-like medium by the fixing belt is started.

[0017] The invention according to claim 7 is the invention according to claims 1 to 3.
In the fixing device according to any one of the above, when the fixing mode is switched from one of the fixing modes to another fixing mode, the set temperature of the other fixing mode is higher than the set temperature of the one fixing mode. When the temperature is low, the heating of the heating roller by the heater is stopped, and the fixing belt is driven.

According to an eighth aspect of the present invention, in the fixing device according to the seventh aspect, the heating of the heating roller by the heater is stopped to drive the fixing belt, and the temperature detecting means operates in the other fixing mode. After detecting the set temperature, conveyance of the sheet-like medium by the fixing belt is started.

According to a ninth aspect of the present invention, in the fixing device according to the seventh aspect, the heating of the heating roller by the heater is stopped, the fixing belt is driven, and the fixing mode is determined according to a fixing mode before and after switching. After a lapse of time, conveyance of the sheet-like medium by the fixing belt is started.

According to a tenth aspect of the present invention, in the fixing device according to any one of the first to ninth aspects, the heating roller has a hard protective film layer on an outer surface.

According to an eleventh aspect of the present invention, in the fixing device according to any one of the first to tenth aspects, the heating roller has a black layer on an inner surface.

According to a twelfth aspect of the present invention, in the fixing device according to any one of the first to eleventh aspects, the temperature detecting means is in contact with the heating roller.

According to a thirteenth aspect of the present invention, there is provided an image forming apparatus having the fixing device according to any one of the first to twelfth aspects.

[0024]

FIG. 1 schematically shows a fixing device to which the present invention is applied and an image forming apparatus having the fixing device. The image forming apparatus is a well-known one such as a copying machine, a facsimile, a printer and the like, and may be any type of image forming apparatus that can use a fixing device to which the present invention is applied.
The image forming apparatus of this embodiment can form a color image.

The image forming apparatus 20 includes image forming apparatuses 21C, 21Y, and 21 that form an image for each color according to a document image.
M, 21BK, image forming devices 21C, 21Y, 21M, 2
1BK, and a manual feed as sheet-like medium supply means for supplying various sheet-like media to a transfer area where the image forming apparatuses 21C, 21Y, 21M, 21BK and the transfer apparatus 22 face each other. Tray 23, paper cassettes 24, 24, manual tray 23, paper cassette 2
The image forming apparatus 2 converts the sheet-like medium conveyed from
1C, 21Y, 21M, 21BK, a registration roller 30 that supplies the sheet at the timing of image formation, and a fixing device 1 that fixes a sheet-like medium after transfer in a transfer area.
And

The image forming apparatus 20 includes plain paper (hereinafter simply referred to as plain paper) generally used for copying and the like, 90K paper such as an OHP sheet, a card, and a postcard, and a basis weight of about 10
It is possible to use as a sheet medium any of thick paper having an equivalent weight of 0 g / m ² or more, and so-called special sheets (hereinafter simply referred to as special sheets) having a larger heat capacity than paper, such as envelopes.

Each image forming device 21C, 21Y, 21M, 21
BK develops the respective colors of cyan, yellow, magenta, and black, and uses different toner colors.
The configuration of the image forming apparatus 21C, 21Y, 21M, 21B
This will be described as a representative of K. The image forming device 21C includes a photosensitive drum 25C as an electrostatic latent image carrier, and a photosensitive drum 25.
Charging devices 2 arranged in order in the rotation direction A of C
7C, a developing device 26C, a cleaning device 28C, and the like, and has a known configuration in which an exposure light 29C is received between a charging device 27C and the developing device 26C by a scanning unit having a well-known polygon mirror (not shown). The electrostatic latent image carrier may have a belt shape instead of a drum shape. However, the exposure light 29BK in the black image forming device 21BK can be two beams, and the image forming device 21BK can form images faster than the other image forming devices 21C, 21Y, and 21M. Has become.

As shown in FIG. 2, the fixing device 1 includes an endless fixing belt 2 for conveying a sheet-like medium on which toner is fixed, a heating roller 3 around which the fixing belt 2 is wound, and a fixing roller 4. A pressure roller 5 disposed opposite to the fixing roller 4 via the fixing belt 2, a heating roller 3, and heaters 6 and 7 provided inside the pressure roller 5.
Thermistor 8 disposed as opposed to and in contact with heating roller 3 as temperature detecting means for detecting the temperature of heating roller 3
A thermistor 18 as a temperature detecting means for detecting the temperature of the pressure roller 5, which is disposed to face and contact the pressure roller 5, and a cleaning roller disposed to face the fixing roller 4 via the fixing belt 2. 31, a coating roller 32 as a releasing agent supply means, a casing 33, and a guide 12 fixed to the casing 33.

In order to apply an appropriate predetermined tension to the fixing belt 2, the heating roller 3 and the fixing roller 4 are urged away from each other by an elastic body (not shown) such as a spring. The fixing roller 4 includes a metal core 9 and a heat-resistant porous elastic layer 10 covering the metal core 9, and the metal core 9 is rotationally driven by a shaft 11 by driving means (not shown). Then, the fixing roller 4 is driven to rotate, and the fixing belt 2 is driven by the driven rotation of the heating roller 3.

The pressure roller 5 and the fixing roller 4 are pressed against each other because a support (not shown) for separately supporting them is urged toward each other by an elastic body (not shown) such as a spring. 84N
The size is biased. The pressure roller 5 has two apexes with the axis of the fixing roller 4 as the apex, and two straight lines connecting the axis of the fixing roller 4 and the axis of the heating roller 3 and the axis of the heating roller 3 and the axis of the pressure roller 5, respectively. Is in contact with the fixing roller 4 so that the corner sandwiched by the fixing roller 4 forms an acute angle.
A first fixing unit 15 that serves as a fixing area where the toner is fixed on the sheet-shaped medium and is in contact with only the fixing belt 2 at a position where the pressure roller 5 does not face the fixing roller 4;
And a second fixing portion 16 which contacts the fixing roller via the fixing belt 2 is formed.

The casing 33 is provided at a position facing the transfer device 22, and sandwiches the opening 34 for receiving the sheet-like medium conveyed by the transfer device 22, the first fixing unit 15 and the second fixing unit 16. An opening 35 provided on the opposite side of the opening 34 for discharging the fixed sheet medium.
And The guide 12 has a base fixed to the outer surface of the casing 33 below the opening 34, and a tip extending into the inside of the casing 33 from the opening 34 and extending toward the first fixing portion 15.

The fixing belt 2 is made of nickel and has a thickness of 100 mm.
A release layer made of silicon rubber of 200 μm is formed on a substrate of μm, which has a small heat capacity and good thermal responsiveness. The length of the fixing belt 2 is such that the diameter of the fixing belt 2 becomes 60 mm when the belt 2 has a circular shape. The substrate may be made of SUS or polyimide. The thickness may be about 30 to 150 μm in consideration of flexibility.
The release layer has a thickness of 50 to 30 when silicon rubber is used.
0 is desirable, and when a fluororesin is used, the thickness is 1
About 0 to 50 μm is desirable. Further, the release layer may have a configuration in which a fluororesin is laminated on silicon rubber. It is desired that the fixing belt 2 is heated instantaneously and the surface of the belt is self-cooled in the fixing area to the extent that hot offset does not occur. On the other hand, in the fixing area, the toner is sufficiently melted and fixed. Must have the necessary heat capacity for The above-mentioned material and thickness of the fixing belt 2 satisfy this condition. Self-cooling refers to a phenomenon in which the belt cools in the fixing process due to the absence of a heating source on the unfixed image side of the sheet medium in the fixing area.

The fixing belt 2 is given a tension of 3 kgf / one side because the heating roller 3 and the fixing roller 4 are urged so as to be separated from each other. This tension can be set by adjusting the urging force of the elastic body (not shown), from 1 kgf (9.8 N) to 3 kgf (29.
4N) is preferable for good fixing.

Each of the heating roller 3 and the pressure roller 5 is made of a thin cylindrical cored bar to reduce the heat capacity. The diameter of the core of the heating roller 3 is 20 mm or more and 30 mm or less, the thickness of the concentric metal is 0.3 mm or more and 2.0 mm or less, and the diameter of the core of the pressure roller 5 is 30 mm or more and 50 m.
m or less, and the thickness of the concentric metal is 0.3 mm or more and 1.5 mm
It is as follows. Thereby, the heat capacity of the heating roller 3 becomes 26
cal / ° C. or less, heat capacity of the pressure roller 5 is 36 cal
/ ° C or less.

In the present embodiment, the core metal of the heating roller 3 is made of aluminum and has a diameter of 30 mm and a thickness of 0.1 mm.
7 mm. It is preferable that the material has a low specific heat and a high thermal conductivity, and other metals such as iron, copper, and stainless steel can be used. In addition, when the roller diameter is 30 mm made of aluminum, the thickness is 0.6 mm or more.
When the roller diameter is 20 mm, the wall thickness is 0.7 mm to 1.4 mm when the roller diameter is 1.4 mm, and the wall thickness is 0.3 mm to 0.9 mm when the roller diameter is 30 mm. Can be set. The reason why the wall thickness is reduced as the diameter increases is in consideration of the axial bending of the roller.

The lower limit of the thickness is an allowable value in consideration of the deformation of the heating roller 3 due to the tension of the fixing belt 2, and the upper limit is an allowable value for obtaining a desired rise time. I have. The reason why the roller diameter is set to 20 mm or more is to secure the belt tension so that the roller does not bend in the axial direction. Roller diameter is 20mm
The reason for setting the sheet-like medium conveyance speed to 200 mm
mm / s or less, the fixing belt 2 even during continuous paper passing
26ca to keep the temperature of the toner at a constant temperature required for fixing.
This is for obtaining a heat capacity of about 1 / ° C.

By setting the heat roller 3 to have a low heat capacity in this manner, even if the fixing belt 2 rotates, heat is less likely to be taken out, and adverse effects on fixing and prolonged rise time are prevented. . Further, even if the temperature is lowered due to continuous fixing or the like, the time until recovery is shortened. The heater 6 heats the fixing belt 2 via the heating roller 3 and the heating roller 3. The temperature of the heater 6 is input to a control unit (not shown) as a detection signal by the thermistor 8 and is compared with a target fixing temperature. When the detected temperature is lower than the fixing temperature, the power supply to the heater 6 is performed. When the detected temperature is higher than the fixing temperature, the power supply to the heater 6 is stopped. The fixing temperature is controlled by feeding back the detection signal of the thermistor 8 in this manner. Note that the thermistor 8 is in contact with the heating roller 3 at an obtuse angle with respect to the rotation direction of the heating roller 3 so as to reduce mutual wear caused by the rotation of the heating roller 3.

The heating roller 3 has an alumite layer as a hard protective film on the outer surface. This alumite layer was formed by anodic electric field treatment, and had a Vickers hardness H
V200 or higher. When the heating roller 3 does not have an alumite layer, the heating roller 3 wears due to friction with the fixing belt 2. However, the formation of the alumite layer prevents such abrasion. In the experiment, it was confirmed that aluminum powder was not generated due to abrasion even after passing 60,000 sheets. Further, a black alumite layer can be formed by performing an alumite treatment on the inner surface of the heating roller 3, thereby preventing heat reflection by the heater 6 on the inner surface of the heating roller 3 and increasing the heat absorption rate of the heating roller 3. As a result, the thermal efficiency can be increased, and breakage of the heater 6 due to excessive temperature rise can be prevented. The black alumite treatment inside the heating roller 3 can be performed simultaneously with the outer surface.

The elastic layer 10 of the fixing roller 4 has an outer diameter of 3
It is set to 0 mm, and the Asker C has a relatively low roller rubber hardness of 33 °, which can be set in the range of 10 ° to 50 °. If the angle is less than 10 °, the nip pressure in the second fixing portion B is insufficient, so that the fixing of the toner becomes insufficient, and the fixing lower limit temperature must be increased. Beyond 50 °
This is because wrinkles occur in the sheet medium. In consideration of the nip pressure and prevention of wrinkling of the sheet-like medium, it is desirable to set the angle to 33 ° as in this embodiment. The material is a heat-resistant porous elastic body with low heat conductivity and heat insulation, so it reduces the belt heat loss, reduces the temperature drop after rising, and increases the pre-rotation time for temperature recovery. Shortened. Further, since the elastic layer 10 has a relatively low hardness, a sufficient nip width can be obtained even when the pressing force of the pressure roller 5 is small, and good fixing performance can be obtained even under a relatively low temperature and low pressure condition. Obtainable.

The core of the pressure roller 5 is made of iron and has a diameter of 40 mm and a thickness of 1.0 mm. It is preferable that the material has a low specific heat and a high thermal conductivity, and other metals such as aluminum, copper, and stainless steel can be used. In addition, when the roller diameter is 30 mm made of iron, the thickness is in the range of 0.4 mm to 1.0 mm. When the roller diameter is 50 mm, the thickness is 0.3 mm to 0.8 mm in the case of iron. When the roller diameter is 30 mm, the thickness is in the range of 1.3 mm to 1.5 mm. When the roller diameter is 50 mm and made of aluminum, the thickness is 0.6 mm to 1.2 m.
m can be set. The reason why the wall thickness is reduced as the diameter increases is in consideration of the axial bending of the roller.

The lower limit of the thickness is an allowable value in consideration of the deformation of the pressure roller 5 due to the surface pressure of 0.6 kg / cm ² corresponding to the lower limit of the fixing pressure, and the upper limit is a desired value. An allowable value for obtaining a rise time is shown. The reason why the roller diameter is set to 30 mm or more is to secure the fixing pressure so that the roller is not bent in the axial direction. The reason why the roller diameter is set to 30 mm to 50 mm is that the fixing belt 2 keeps a constant temperature necessary for fixing even during continuous paper feeding when the sheet-like medium conveying speed is 200 mm / s or less. / ° C.

By setting the pressure roller 5 to have a low heat capacity in this way, even if the fixing belt 2 rotates, heat is hardly taken away. In particular, in the present embodiment, since the pressure roller 5 has the heater 7, This prevents the temperature of the fixing belt 2 from being lowered to adversely affect the fixing, and prevents the rise time from being prolonged. Further, even if the temperature is lowered due to continuous fixing or the like, the time until recovery is shortened. The heater 7 raises the temperature of the pressure roller 5, shortens the rise time, and also supplies heat from the back surface of the sheet-shaped medium at the time of fixing to obtain more stable fixing performance. The pressure roller 5 can form a release layer of 10 μm to 300 μm on a cored bar. The heater 7 heats the pressure roller 5, and the temperature of the heater 7 is input to a control unit (not shown) as a detection signal by the thermistor 18, the energization is controlled in the same manner as the heater 6, and the fixing temperature is controlled. You. The thermistor 18 is in contact with the heating roller 3 at an obtuse angle with respect to the rotation direction of the pressure roller 5 so as to reduce mutual wear caused by the rotation of the pressure roller 5.

The reason why the heat roller 3 and the pressure roller 5 can be made thinner to reduce the heat capacity is that the fixing device 1 is a so-called belt fixing device using the fixing belt 2.
That is, since the fixing is performed by relatively long portions such as the fixing units 15 and 16, the fixing pressure can be reduced, and the strength of the pressure roller 5 can be reduced.
Further, since the heating roller 3 is not pressed against the pressure roller, the thickness of the heating roller 3 can be reduced. Performing the fixing at a relatively long distance portion enables fixing at a relatively low temperature, which also contributes to shortening the rise time. Further, when the fixing belt 2 is used, there is an advantage that the fixing belt 2 heated by the heater is cooled to a temperature suitable for fixing in a process of being conveyed, thereby preventing an offset. Heaters 6, 7
Is 700W considering the inrush current when the power switch is turned on and the flickering phenomenon of the fluorescent lamp when the heater is turned on and off.
It is as follows.

Cleaning roller 31 and coating roller 32
The cleaning roller 31 is located upstream of the application roller 32 in the moving direction of the fixing belt 2. Both the cleaning roller 31 and the application roller 32 are always fixed to the fixing belt 2.
Is in contact with The cleaning roller 31 has a diameter of 20 m
The driving unit (not shown) is driven to move in a direction opposite to the moving direction of the fixing belt 2 at a portion facing the fixing belt 2. Thus, the toner transferred to the fixing belt 2 from the sheet medium is scraped. The toner scraped off from the fixing belt 2 by the cleaning roller 31 is wiped off from the cleaning roller 31 by a cleaning means (not shown) so that the cleaning roller 31 can always perform good cleaning. The application roller 32 applies a release agent containing silicone oil as a main component to the fixing belt 2, has a diameter of 16 mm, and is driven to rotate by the fixing belt 2. A release agent supply member (not shown) and a blade are in contact with the application roller 32, and the thickness of the release agent supplied to the application roller 32 by the release agent sharing means is made uniform by the blade. Thus, an appropriate amount of the release agent is always applied to the fixing belt 2.

As shown in FIG. 3, in the fixing device 1, the type of toner forming the toner image formed on the sheet medium in the main body of the image forming apparatus 20, the resolution of the toner image, and the toner image are formed. No. which is determined according to the type of sheet-like medium There are fixing modes represented by 1 to 8. In the present embodiment, the type of toner refers to the type of toner used in the main body of the image forming apparatus 20.
The black toner used in the image forming device 21BK, that is, the black toner, or each of the image forming devices 21C, 21Y,
1M, cyan, yellow used in 21BK,
This means that the toner is magenta or black toner. That is, the type of the toner that forms the toner image means whether the toner image is a black image or a full-color image. Further, the resolution of the toner image is any of 600 dpi and 1200 dpi, and the type of the sheet medium is any of the above-described plain paper and special sheet. The fixing device 1 determines the NO. It has a fixing mode represented by 1 to 8.

As shown in the figure, a set temperature for performing fixing, that is, a target fixing temperature and a conveying speed in the above-mentioned control means, that is, a conveying speed of the sheet-like medium by the fixing belt 2 in other words, according to each fixing mode. And the moving speed of the fixing belt 2 are determined. Fixing temperature is 1
60 ° C., 150 ° C., or 130 ° C., and the transport speed is 185 mm / s, 125 mm / s, 62.5 mm / s
s. The transport speed is made variable by adjusting the rotation speed of the fixing roller 4.

Exposure, that is, writing by two beams in the image forming apparatus 21BK is performed only in the fixing mode 1. The conveyance speed is 185 mm / s only in the fixing mode 1, but this can be achieved by performing writing with two beams. 185
The transport speed of mm / s is a limit speed determined by the maximum number of rotations of the polygon mirror provided in the image forming apparatus 21BK. Since an image forming apparatus that performs writing using two beams is expensive, the most frequently used black image forming apparatus 21 is used.
Only the BK can perform writing by two beams.

When a full-color toner image is formed, the other image forming devices 21C and 21C are used in the image forming device BK.
Since one-beam writing is performed in the same manner as Y and 21M, 6
When a 00 dpi toner image is formed (fixing mode 5,
In 6), the conveying speed is 185 mm in the fixing mode 1.
/ S lower than 125 mm / s and 1200 d
In the case of forming a pi toner image (fixing modes 7 and 8), the conveyance speed is 62.5 mm / s, which is half that of the pi. The fixing temperature is set to be the highest temperature in a range where hot offset does not occur at each transport speed. This is desirable when a full-color image is formed, in which the glossiness of the image is preferably high, and it is also effective to apply a large amount of heat to increase the glossiness. Since the heat capacity of the special sheet is larger than that of the plain paper, the amount of heat supplied is increased by lowering the conveying speed or increasing the fixing temperature. Also, especially when the special sheet is thick paper, the conveyance speed is always 62.5
mm / s. The fixing temperature in mode 1 can be set in the range of 160 to 170 ° C.

In this embodiment, the control means automatically switches the fixing modes for the type of toner for forming the toner image in accordance with the document information of the toner image to be formed. The operator selects either a black image or a full-color image by pressing a key on an operation panel (not shown) provided on the main body of the image forming apparatus 20. It may be performed. The switching of each fixing mode relating to the resolution of the toner image may be automatically performed by the control unit in accordance with the document information of the toner image to be formed, similarly to the switching relating to the type of the toner, or the operator may be set to 600 dpi. Or an image of 1200 dpi may be formed by selecting by pressing a key.

In this embodiment, the switching of each fixing mode relating to the type of the sheet medium is performed by a well-known means until the sheet medium reaches the fixing device 1 by a known means. Is determined automatically by determining whether the sheet is a special sheet. Alternatively, the special sheet may be determined when the manual feed tray 23 is used. An operator can select a desired mode by pressing a key on an operation panel (not shown) provided on the main body side, and the operator can use any of the sheet cassettes 24 in a similar operation. The control means (not shown) automatically determines whether the sheet medium stored in the sheet cassette 24 is a plain sheet or a special sheet by designating whether the sheet medium is to be processed. Mode Te can be so switched.

As shown in FIG. 4, when the fixing mode is switched and the fixing temperature (T ₂ ) after the switching is higher than the fixing temperature (T ₁ ) before the switching, the heater 6 is energized. Then, after the thermistor 8 detects T ₂ , the fixing belt 2 starts to be driven to perform pre-rotation, and after the thermistor 8 detects T ₂ again, the conveyance of the sheet-like medium by the fixing belt 2 can be started. It is supposed to. By performing this pre-rotation, the entire fixing belt 2 can be efficiently heated. Although not shown, when the fixing mode is switched and the fixing temperature (T ₂ ) after the switching is lower than the fixing temperature (T ₁ ) before the switching, the power supply to the heater 6 is stopped and the fixing is performed. The belt 2 is started to be driven to perform pre-rotation, and the thermistor 8 is again driven to T ₂
Is detected, the conveyance of the sheet-like medium by the fixing belt 2 can be started. By performing this pre-rotation, the heat radiation of the fixing belt 2 is promoted, and the temperature of the fixing belt 2 can be efficiently reduced. The moving speed of the fixing belt 2 during the pre-rotation is 125 m
m / s, which is common to that at the time of fixing.

Here, the pre-rotation time required when switching from one fixing mode to another fixing mode is T ₁ and T ₂
It is known from the relationship with that that it is substantially constant. Therefore, as shown in FIG. 5, the pre-rotation is performed for a time determined according to the fixing mode before and after the switching, that is, for a time determined from the relationship between T ₁ and T _2, and after the elapse of this time, the fixing is performed. The conveyance of the sheet-like medium by the belt 2 can be started. The fixing temperature is 150 ° C.
When switching between and fixing temperature of 160 ° C.,
Since these temperature differences are relatively small, no pre-rotation is performed. The heat dissipation is less efficient than the heating by the heater 6, T _1> it is pre-rotation time when a T ₁ <T ₂ than when it is T ₂ are the shorter.

Controlling the fixing temperature at any of the three temperatures, controlling the transport speed at any of the three speeds,
Controlling the pre-rotation time by any of the four times
This is for simplifying the control, and the control may be performed according to different fixing temperatures, transport speeds, and pre-rotation times according to the respective fixing modes. Further, the fixing mode does not need to be determined according to all of the type of toner, the resolution of the toner image, and the type of sheet medium, and may be determined by a combination of some of these parameters. Of the set temperature and the conveying speed of the sheet-shaped medium, only one of them may be controlled.

In the present embodiment, when the power of the image forming apparatus 20 is turned on, the power supply to the heater 6 and the pre-rotation (T ₁ in FIG. 4 is the ambient temperature) are performed based on the temperature detection of the thermistor 8. By doing so, a state in which good fixing can be performed is completed, and the start-up is completed, and a state in which image formation and fixing can be performed. When the fixing mode is switched, the power supply to the heater 6 is switched, a predetermined pre-rotation is performed, the start-up is completed, and a state in which image formation and fixing can be performed. When the operator performs a well-known operation of starting image formation, the photosensitive drum 25C is charged by the charging device 27C with the rotation of the photosensitive member 25C in the direction A, and the photosensitive drum 25C is charged by the exposure light 29C according to the original image. A latent image is formed, this electrostatic latent image is developed by a developing device 26C, and the toner image formed on the photoconductor 25C is transferred onto a sheet-like medium conveyed in the direction of arrow B on a known transfer device 22. Then, the toner remaining on the photoconductor 25C after the transfer is scraped off by the cleaning device 28C to clean the photoconductor 25, and is used for the next charging.

The sheet-like medium to which the cyan toner has been transferred is conveyed in the direction of arrow B by the transfer device 22 and performs the same image forming process as the above-described image forming process in the image forming device 21C. 21M and 21BK sequentially transfer yellow, magenta, and black toners as appropriate, transfer all the toner necessary for image formation, and then transfer the toner to the guide 12 from the transfer device 22, and guide the toner to the fixing area by the guide 12. Is done.

The sheet-like medium is conveyed by the movement of the fixing belt 2 whose moving speed is controlled in the fixing mode. In the first fixing unit 15 and the second fixing unit 16 continuous with the first fixing unit 15, the sheet-like medium is conveyed. At a temperature controlled by the fixing mode, the toner is heated and pressed to be fused and fixed. Specifically, when the sheet-shaped medium passes through the first fixing unit 15, the toner to which heat is applied from the fixing belt 2 gradually melts and is temporarily attached to the surface of the sheet-shaped medium, and the second fixing is performed. In the unit 16, the toner is completely fixed on the sheet-like medium by the pressing force between the fixing roller 3 and the pressure roller 5. Even when continuous fixing is performed, the heater 7
In this heating, heat is supplied to such an extent that hot offset does not occur and good fixing is performed, and there is no need to interrupt fixing and perform reheating. Since the set temperature at the time of fixing and the conveyance speed of the sheet medium are controlled in accordance with each mode, good fixing is performed, and the sheet medium after fixing is discharged out of the image forming apparatus.

In the fixing device of the heat roller pair type, there is a limit to the nip width formed by the roller pair, and since the nip width is small, the region having a temperature suitable for fixing, that is, the width of the fixing region is narrow, and fixing is performed. In order to apply a sufficient amount of heat, it is necessary to increase the fixing temperature. In this case, heat is rapidly applied to the plain paper or the special sheet and the toner, which generally causes a problem that a hot offset occurs. According to the belt fixing device of the present embodiment, since the length of the fixing area is sufficiently long, good fixing is performed. According to the belt fixing device, particularly when fixing an OHP sheet, it is possible to supply a sufficiently large amount of fixing heat within a range that does not cause deterioration of fixing quality such as hot offset as described above. It becomes smooth and irregular reflection is suppressed, and the gloss, that is, the HEIZ degree is improved. Also, absorption and scattering of transmitted light are suppressed inside the toner, so that a good image can be formed.

Although the fixing device to which the present invention is applied and the image forming apparatus provided with the fixing device have been described, the heater may be provided only in the heating roller of the heating roller and the pressing roller. The thermistor is not limited to a position in contact with the heating roller, but may be any position in the driving direction of the fixing belt from a position facing the heating roller via the fixing belt to a position before reaching a fixing region where the toner is fixed on the sheet-shaped medium. It can also be placed at that position. The thickness and material of the fixing belt, the diameter, the thickness, and the material of the heating roller and the pressure roller can be appropriately combined. If the heating roller and the pressure roller have a low heat capacity and can perform satisfactory fixing, the fixing unit is configured to include only a portion where the fixing roller and the pressure roller are pressed against each other via the fixing belt. It can also be. Although the image forming apparatus of the present embodiment can form a color image and can form a single-color image, the image forming apparatus may form only a single-color image.

[0059]

According to the first aspect of the present invention, there is provided an endless fixing belt for conveying a sheet-like medium on which a toner image is fixed, a heating roller and a fixing roller around which the fixing belt is wound. A pressure roller disposed to face the fixing roller via the fixing belt, the heating roller, a heater provided at least inside the heating roller among the pressure rollers, and a heater facing the heating roller. A fixing temperature determined by the type of toner for forming the toner image and / or the fixing mode determined by the resolution of the toner image. Since the conveyance speed of the sheet-like medium by the fixing belt is variable, it is possible to appropriately perform fixing according to the type of toner forming the toner image and / or the resolution of the toner image. It is possible to provide a fixing device capable.

According to the second aspect of the present invention, in the fixing device according to the first aspect, a set temperature for performing fixing and / or a sheet by the fixing belt are set according to a fixing mode determined by a type of the sheet medium. Since the transport speed of the sheet-like medium is variable, it is possible to provide a fixing device that can appropriately perform fixing on the sheet-like medium according to the type.

According to the third aspect of the invention, an endless fixing belt for conveying a sheet-like medium on which a toner image is fixed, a heating roller and a fixing roller around which the fixing belt is wound, A pressure roller disposed to face the fixing roller via a belt; a heater provided at least inside the heating roller among the heating roller and the pressure roller; and a heater facing the heating roller. A fixing device provided with a temperature detecting means provided for fixing in accordance with a fixing mode determined by the type of toner for forming the toner image and / or the resolution of the toner image and / or the type of sheet medium. Since the set temperature and the set temperature for performing fixing at least among the conveyance speed of the sheet-like medium by the fixing belt are variable, the toner for forming the toner image is changed. It is possible to provide a fixing device which can appropriately perform fixing in accordance with the type of the type and / or the toner image resolution and / or the sheet-like medium.

According to the fourth aspect of the present invention, in the fixing device according to any one of the first to third aspects, when one of the fixing modes is switched to another fixing mode, When the set temperature of the other fixing mode is higher than the set temperature of the one fixing mode, the heater is heated by the heater, and the set temperature of the other fixing mode is detected by the temperature detecting means. Since the driving of the fixing belt is started, it is possible to provide a fixing device in which the temperature can be quickly increased by the heater with relatively simple control.

According to a fifth aspect of the present invention, in the fixing device according to the fourth aspect, after the driving of the fixing belt is started, the temperature detecting means detects the set temperature of the other fixing mode again. Since the conveyance of the sheet-like medium by the fixing belt is started, the fixing can be performed relatively quickly by a relatively simple control, and the fixing belt has a uniform temperature, so that stable fixing can be performed. A fixing device capable of performing the fixing can be provided.

According to a sixth aspect of the present invention, in the fixing device according to the fourth aspect, after the driving of the fixing belt is started, and after a lapse of a time determined according to the fixing mode before and after the switching, Provided is a fixing device that can simplify the control until the start of fixing because the conveyance of the sheet-shaped medium by the fixing belt is started, and can perform stable fixing because the temperature of the fixing belt is uniform. be able to.

According to the seventh aspect of the present invention, in the fixing device according to any one of the first to third aspects, when one of the fixing modes is switched to another fixing mode, When the set temperature of the other fixing mode is lower than the set temperature of the one fixing mode, the heating of the heating roller by the heater is stopped, and the fixing belt is driven. A fixing device capable of reaching a temperature can be provided.

According to an eighth aspect of the present invention, in the fixing device according to the seventh aspect, the heating of the heating roller by the heater is stopped to drive the fixing belt, and the temperature detecting means causes the other fixing to be performed. After the set temperature of the mode is detected, the conveyance of the sheet-like medium by the fixing belt is started, so that the control until the start of fixing can be relatively easily performed, and the temperature of the fixing belt is uniform, so that the fixing belt is stable. It is possible to provide a fixing device capable of performing fixed fixing.

According to the ninth aspect of the present invention, in the fixing device according to the seventh aspect, the heating of the heating roller by the heater is stopped to drive the fixing belt, and the fixing belt is determined according to the fixing mode before and after the switching. Since the conveyance of the sheet-like medium by the fixing belt is started after the lapse of the given time, the control until the start of fixing can be simplified,
Since the temperature of the fixing belt is made uniform, a fixing device capable of performing stable fixing can be provided.

According to the invention of claim 10, according to claim 1,
In the fixing device according to any one of Items 1 to 9, since the heating roller has a hard protective film layer on an outer surface,
Even when the base of the heating roller is made of a relatively soft material, it is possible to provide a long-life fixing device in which abrasion of the heating roller due to contact with the fixing belt is prevented.

According to the eleventh aspect, according to the first aspect,
11. The fixing device according to any one of Items 10 to 10, wherein the heating roller has a black layer on an inner surface thereof, so that the heat absorption efficiency of the heating roller is increased to increase the thermal efficiency and to prevent damage due to excessive heating of the heater. It is possible to provide a fixing device capable of preventing the fixing.

According to the twelfth aspect of the present invention, the first aspect is provided.
In the fixing device according to any one of the first to eleventh aspects, since the temperature detecting unit contacts the heating roller, the fixing belt can prevent deterioration of the fixing belt due to the temperature detecting unit contacting the fixing belt. An apparatus can be provided.

According to the thirteenth aspect of the present invention, it is possible to provide an image forming apparatus provided with a fixing device having the above-described effects.

[Brief description of the drawings]

FIG. 1 is a side view schematically illustrating a fixing device to which the present invention is applied and an image forming apparatus including the fixing device.

FIG. 2 is a side sectional view of the fixing device shown in FIG.

FIG. 3 is a diagram illustrating a fixing temperature and a conveyance speed in each fixing mode determined by a type of a toner, a resolution of a toner image, and a type of a sheet medium.

FIG. 4 is a correlation diagram showing a relationship between a change in the temperature of the fixing belt and a pre-rotation time when switching from a low-temperature fixing mode to a high-temperature fixing mode in the fixing device shown in FIG. 1;

FIG. 5 is a diagram illustrating a pre-rotation time determined according to a fixing mode before and after switching.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fixing apparatus 2 Fixing belt 3 Heating roller 4 Fixing roller 5 Pressure roller 6 Heater provided in heating roller 7 Heater provided in pressure roller 8 Temperature detecting means provided opposite heating roller 20 Image formation apparatus

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hideo Furukawa 1-3-6 Nakamagome, Ota-ku, Tokyo, Ricoh Co., Ltd. (72) Inventor Hiroshi Ogawa 1-3-6 Nakamagome, Ota-ku, Tokyo・ F-term in Ricoh Co., Ltd. (reference) 2H033 AA47 BA11 BA12 BA25 BA32 BA58 BB04 BB13 BB14 BB37 CA01 CA07 CA16 CA17 CA30 CA36 CA37 CA40 CA48 3K058 AA02 AA34 AA45 AA65 AA86 AA87 BA18 CA22 CA45 CA61 DA02 DA26 GA06

Claims (13)

[Claims] An endless fixing belt for conveying a sheet-like medium on which a toner image is fixed; a heating roller and a fixing roller around which the fixing belt is wound; and a fixing roller via the fixing belt. A pressure roller disposed opposite to the heating roller, a heater provided at least inside the heating roller of the pressure roller, and a temperature detection unit disposed opposite to the heating roller. In the fixing device provided, a set temperature for fixing and / or a conveying speed of the sheet-like medium by the fixing belt are set according to a fixing mode determined by a type of toner for forming a toner image and / or a resolution of the toner image. A fixing device characterized by being variable. 2. The fixing device according to claim 1, wherein a set temperature for fixing and / or a conveying speed of the sheet-like medium by the fixing belt are variable according to a fixing mode determined by a type of the sheet-like medium. A fixing device. 3. An endless fixing belt for conveying a sheet-like medium on which a toner image is fixed, a heating roller and a fixing roller around which the fixing belt is wound, and a fixing roller via the fixing belt. A pressure roller disposed opposite to the heating roller, a heater provided at least inside the heating roller of the pressure roller, and a temperature detection unit disposed opposite to the heating roller. A fixing device provided with: a set temperature for performing fixing in accordance with a fixing mode determined by a type of toner for forming a toner image and / or a resolution of the toner image and / or a type of sheet-shaped medium; A fixing device characterized in that at least a set temperature for performing fixing among the transport speeds of the medium is variable. 4. The fixing device according to claim 1, wherein when one of the fixing modes is switched to another fixing mode, the set temperature of the one fixing mode is set. When the set temperature of the other fixing mode is higher, the heating roller is heated by the heater, and the driving of the fixing belt is started after the set temperature of the other fixing mode is detected by the temperature detecting means. A fixing device. 5. The fixing device according to claim 4, wherein after the driving of the fixing belt is started, the temperature detecting means detects the set temperature of the other fixing mode again, and thereafter, the sheet-like medium by the fixing belt is used. A fixing device for starting the conveyance of the fixing device. 6. The fixing device according to claim 4, wherein after the driving of the fixing belt is started, a time determined according to a fixing mode before and after the switching elapses, and then the sheet-like medium is conveyed by the fixing belt. The fixing device. 7. The fixing device according to claim 1, wherein, when one of the fixing modes is switched to another fixing mode, the set temperature of the one fixing mode is set. When the set temperature of the other fixing mode is lower, the heating of the heating roller by the heater is stopped, and the fixing belt is driven. 8. The fixing device according to claim 7, wherein the heating of the heating roller by the heater is stopped to drive the fixing belt, and after the temperature detecting means detects the set temperature of the other fixing mode. A fixing device for starting the conveyance of the sheet-like medium by the fixing belt. 9. The fixing device according to claim 7, wherein the heating of the heating roller by the heater is stopped, the fixing belt is driven, and after a time determined according to the fixing mode before and after the switching is elapsed, A fixing device, wherein conveyance of a sheet medium by the fixing belt is started. 10. The fixing device according to claim 1, wherein the heating roller has a hard protective film layer on an outer surface. 11. The fixing device according to claim 1, wherein the heating roller has a black layer on an inner surface. 12. The fixing device according to claim 1, wherein said temperature detecting means is in contact with said heating roller. 13. An image forming apparatus having the fixing device according to claim 1.