JPS6014269A - Fixing device - Google Patents

Abstract

PURPOSE:To prevent a rear side contamination of a recording material, to extend a life of a roller, and to maintain satisfactorily a fixing performance extending over a long period of time by constituting so that a parting property of the surface of a pressure roller becomes better than a parting property of the surface of a fixing roller, with respect to a recording paper. CONSTITUTION:A comparatively thin elastic body layer 1b is provided on the outside circumferential surface of a roller core 1a of a heating roller 1 containing a heater 3, a comparatively thick elastic body layer 2b is provided on the outside circumferential surface of a pressure roller 2 containing a heater 3', and this device is constituted so that a surface parting property of the pressure roller 2 contacting to the rear side of a form P becomes better than a surface parting property of the fixing roller 1 contacting to an unfixed toner image T. A web 6a of a cleaning member 6 is impregnated with an offset preventive liquid, made to contact by pressing to the heating roller 1 by a pressing roller 6c, and the preventive liquid is applied little by little. In this way, since the parting property of the surface of the pressure roller is made better than that of the heating roller 1, a rear side contamination of a recording paper is prevented, a life of the roller is extended, and the fixing performance can be maintained satisfactorily extending over a long period of time.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fixing device for fixing an unfixed object to a support material. Preferably, the present invention relates to a fixing device having a pair of fixing rotating bodies such as a roller or a belt for fixing an unfixed toner image onto a recording material.

2. Description of the Related Art Conventionally, fixing devices have been used in image forming apparatuses such as printers, copying machines, and facsimiles, as well as in various devices for fixing objects to support materials.

Conventionally, in this fixing device, in order to prevent offset in which toner separated from the recording example adheres to the surface of the fixing roller that contacts the unfixed toner image, silicone oil is applied or the surface material of the fixing roller is made to have release properties. Efforts were being made to make it into an excellent material.

However, in order to prevent offset on the surface of the fixing roller, if toner adheres to the surface of the pressure roller, contamination of the roller surface progresses, and the toner on the surface of the pressure roller is deposited on the opposite side of the recording material from the toner image supporting surface. This will be offset again (hereinafter this will be referred to as back staining).

Conventionally, instead of solving these problems, the surface energy relationship was set to actively offset the toner on the pressure roller surface, or the cleaning roller was brought into contact with the pressure roller surface to improve the surface energy relationship. I was doing some cleaning.

However, with such a solution, the offset toner on the surface of the pressure roller causes dirt on the back of the recording material during the fixing process after the pause, making the recording material itself inferior.

In particular, if the Tx is low, at least an elastic body is used on the surface of the pressure roller,
When the above-described configuration is adopted, the fixing performance and image quality are good, but the roller is likely to be contaminated with toner due to long-term use, and once the toner adheres to the roller surface, it is difficult to remove with normal cleaning means. In addition, once the toner adheres to the surface of the pressure roller, the amount of offset toner on the surface of the pressure roller increases rapidly due to the affinity between the attached toner and the toner on the recording paper. This causes jams and various other troubles.

Furthermore, in recent years, devices that form images on both sides of a recording material have been put into practical use, and the fixing device within this device is
The pressure roller comes into contact with one side of the recording material that has been fixed once.

Once it comes into contact with one side of the recording material that has been fixed in this way,
There is a high possibility that the toner will be offset on the surface of the pressure roller, and this problem has been a major issue in practical use.

Furthermore, the above-mentioned problem is a bigger problem when heat fixing is used than when using pressure fixing as a fixing method.
There is.

A roller coated with a so-called fluorine-based resin such as PTFE (polytetrafluoroethylene) or PFA (perfluoroalkoxy) is used as the fixing roller, and a roller coated with an elastic material such as silicone rubber, fluororubber EPDM, hydrin rubber, or fluorosilicone rubber is used as the pressure roller. A system using
In addition, fixing rollers that are usually equipped with a heater inside the roller and have an elastic surface have to have a thin elastic body for heat conduction, so they are weak in strength and are used for felts, webs, blades, cleaning rollers, etc. If the cleaning member is brought into contact with strong pressure, the elastic body may be damaged or problems may occur in terms of durability.

On the other hand, if the pressure roller is contaminated with toner, the contaminated toner will soften during standby (= the nip where the heating roller and pressure roller are in pressure contact), and as a result, the recording material after the standby pause will not be able to record. Problems such as toner stains occurring on the back side of the recording material and the recording material wrapping around the pressure roller arose.

In view of the above-mentioned points, the present invention provides a device that can solve these problems, and has a simple configuration based on a technical concept different from conventional ones, which prevents stains on the back side of the recording material and extends the life of the roller. However, it is an object of the present invention to provide a fixing device that can maintain fixing performance over a long period of time.

The present invention differs from the conventional art in that in order to fix an unfixed object to a recording material, a fixing roller that grips and conveys the recording material and comes into contact with the powder image is opposite to the recording material on the side of the fixing object. In a fixing device having a pressure roller in contact with a side surface, the surface of the fixing roller and the surface of the pressure roller have releasability with respect to the object to be fixed, and are in contact with the object to be fixed that is not yet fixed. It is characterized in that the mold releasability of the pressure roller surface is better than that of the fixing roller surface on the side where the fixing roller is applied.

Embodiments of the fixing device according to the present invention will be described below with reference to the drawings.

FIG. 1 illustrates an embodiment of a particularly effective double-sided recording apparatus among image forming apparatuses to which the present invention is applied.

In this example, in order to move the recording material in a predetermined conveyance direction,
It has means for changing the position of the transport section. The above-mentioned conveyance direction is a recording material conveyance path or a recording material holding section for selectively forming a single image or a plurality of images, and the position conversion means moves the above-mentioned direction according to a mode selection of the image. The rotating body is configured to be displaced in order to convey the recording material in a desired direction.

Further, in the embodiment, the position changing means is configured to move the recording material guiding means in response to changing the position of the rotating body.

FIG. 1 shows a copying apparatus for single-sided, double-sided, and multiple copying, which is an embodiment of the present invention. In the figure, 27 is a photosensitive drum, 3
Reference numeral 9 indicates a recording material supply table, 33 a fixing device, 34 a reversing device for reversing the recording side for double-sided image formation, and 35 a conveyance path for multiple image formation. In this copying apparatus, a recording strip sent from a supply table 39 is transferred to a photosensitive drum 27, and a toner image formed by a known cleaning means 30, a charger 29, an image exposure by an optical system 28, and a developing means 32 is transferred to a transfer means 31. After being transferred, it is sent out from the fixing device 33. In the case of single-sided copying, the recording material sent out from the fixing device is sent in the direction indicated by A in FIG. 1 and is carried out of the machine. In the case of double-sided copying, the paper is sent in the direction indicated by B in FIG. 1, fed into the reversing device 34, and then
It is reversed in direction from the reversing device 34 and sent out by the roller 36, sent again to the photosensitive drum 27, a toner image is transferred to the back surface, fixed by the fixing device 33, and then transported out of the machine. In the case of multiple copying, the recording material is sent in the direction shown by C in FIG. After that, they are sent out of the aircraft.

A is the recording material coming out of the fixing device 33 as described above.

first and second rotating bodies that sandwich and convey the recording material in order to send it in either direction B or C; recording material guiding means provided around the first and second rotating bodies; , a position converting means (not shown) for displacing at least one of the first and second rotating bodies. However, the above-mentioned conveyance direction is determined by the recording material conveyance path or the recording material holding section for selectively forming a single image or a plurality of images, that is, in the example shown in FIG. direction A, which is a recording material transport path for forming double-sided images; direction B, which is a recording material holding section for forming double-sided images; and direction C, which is a recording material transport path for forming multiple images. The position changing means is configured to displace the rotating body in accordance with the image mode selection to convey the recording material in a desired direction. In the embodiment shown in FIG. 1, these first and second rotating bodies consist of a pair of transport rollers 37 and 38, which are capable of displacing the position of one roller relative to the other roller, as indicated by a broken line.

FIG. 2 shows one embodiment of the fixing device according to the present invention. This figure shows a device in which a toner image T formed by electrophotography is fixed onto plain paper P by a heat fixing device.

Reference numeral 1 denotes a heating roller having a heating heater 3 such as a halogen heater inside, which comes into contact with the unfixed toner image T, and rotates in the direction of the arrow in response to a driving force from a driving motor (not shown). Reference numeral 2 denotes a pressure roller having a built-in heater 3' for low heating, which is brought into pressure contact with the heating roller 1 and rotates for sliding.

The heating roller 1 is made of a material such as HTv (thermally vulcanized) silicone rubber, fluorosilicone rubber, or fluorosilicone rubber on the outer peripheral surface of a hollow roller core 1a made of metal such as aluminum, stainless steel, or copper (described later). A relatively thin elastic layer 1b (slightly inferior in releasability than the elastic layer 2b of the pressure roller 2) is provided.

The pressure roller 2 is rotatably supported by a bearing, which will be described later. This pressure roller 2 is pressed against the heating roller 1 by a known pressure means at least during fixing, and is coated with RTV (room temperature vulcanization type) silicone rubber, LTV (low temperature vulcanization type) on the outer peripheral surface of a hollow metal roller core 2a. ff from any member such as silicone rubber (elastic layer 1b of the fixing roller 1)
A relatively thick elastic layer 2b (which has better mold releasability than that of the previous example) is provided.

Among the above materials, a preferable combination (particularly effective) is HT as a fixing roller (heating roller in this example).
The best combination is to use V silicone rubber and the pressure roller to use LTV silicone rubber.The next best combination is to use a fixing roller with an HTV silicone rubber surface layer and a pressure roller with an RTV silicone rubber surface layer.

These combinations have the strength to maintain fixing performance, and have a surface that is opposite to the surface of the recording material that supports the unfixed toner image, rather than the surface releasability of the fixing roller that comes into contact with the unfixed toner image. A better combination is the surface releasability of the pressure roller in contact with the surface.

One purpose of this configuration is to secure a protrusion in the pressure contact area d with the heating roller 1. A temperature sensing element 4 such as a thermistor or thermocouple is disposed in contact with the outer peripheral surface of the heating roller 1, and its detection signal is guided to a known control means (not shown) to control the temperature of the outer peripheral surface of the heating roller 1 ( Output of heater 3,
Alternatively, the toner image is maintained at the melting temperature (by controlling the applied voltage, etc.).

Reference numeral 6 designates an anti-offset liquid coating member which also serves as a cleaning member for removing foreign matter such as offset toner and paper powder adhering to the surface of the heating roller from the roller surface. It is impregnated with an anti-offset liquid such as oil, methylphenyl silicone oil, fluorosilicone oil, amino-modified silicone oil, etc.

The cleaning web 6a is brought into contact with the heating roller by an elastic pressing roller 6c.

Further, this web 6a is moved from the supply roller 6b by a driven take-up reroller 6e (not shown) so as to slightly change its contact position, so that a new surface of the cleaning web 6a always contacts the heating roller 1. come into contact with This web 6a moves on rollers 6d interposed after the pressing roller 6c, is reversed toward the supply roller 6b, and is then turned over to the winding roller 6e.
It is wound up with the front and back sides reversed.

7 is a curved reflector having heat reflection properties, and heating roller 1
It is provided near the periphery of the heating roller 1 over the entire longitudinal direction of the heating roller 1. Further, the reflecting plate 7 has a width so as to cover the space between the position of the pressing roller 6c on the circumferential surface of the heating roller 1 and the entrance opening for the paper P.

Reference numeral 8 denotes a thick cover for preventing heat radiation, which is provided in close contact with the entire convex surface of the reflecting plate 7 to prevent wasteful radiation of heat from the reflecting plate 7. Reference numeral 16 denotes a casing member on the upper side of the fixing device, which surrounds the cleaning member 6, the reflection plate 7, the cover 8, and the temperature sensing element 4. The temperature sensing portion of the temperature sensing element 4 is located closer to the roller 1 than the reflecting plate 7 is.

On the other hand, a reflecting plate 9 similar to the reflecting plate 7 is also provided on the pressure roller 2 side.
A cover 10 similar to the cover 8 is provided to cover most of the circumferential surface of the pressure roller 2.

By providing these reflective plates 7, 9 and covers 8, 10, it is possible to reduce wasted heat from the surfaces of the heating roller and pressure roller, and to stabilize the temperature measurement performance of the temperature sensing element 4. can be converted into

Furthermore, temperature control for the set temperature of the heating roller 1 can be stabilized and power consumption can be reduced.

22 is a guide plate that guides the paper P toward the heating roller 1 side, and a reflection plate 7
The heating roller 1 is provided close to the heating roller 1 so as to be located between one end of the reflecting plate 9 and the reflecting plate 9.

Reference numeral 24 denotes a support plate that supports the pressure roller, and the pressure roller is pressed against the heating roller 1 by the spring 23 .

Now, the plain paper P having the unfixed toner image T is heated and conveyed while being sandwiched between the circumferential surfaces of one heating roller, and the toner image T is fixed by the heat applied by the surface temperature of the rollers 1 and 2, and then the paper ejection roller 20 , 21 and is ejected from the device. Plain paper P is placed on the ejection port side of this heating roller.
A plurality of separation claws 5a are provided in contact with the roller surface along the roller axis direction in order to reliably separate the heat roller from the heating roller.

Also, a separating claw 5b is provided on the discharge port side of the pressure roller 2.
is placed in contact with the surface of the

The separation claw 5a is held by a support plate 18a separated from the casing member 16, and the separation claw 5b is also held by a support plate 181) separated from the casing member 17 on the lower side of the fixing device. The casing member 17 is the reflection plate 9 of the pressure roller 2,
It is provided so as to be spaced apart from the cover 10 and cover them.

The reflective plates 7 and 9 are preferably made of a metal with a glossy surface, such as an aluminum plate with a polished surface, a copper plate, or an iron plate with a surface treatment such as Cr plating. Further, the shape of the reflecting plates 7 and 9 is preferably one having a curvature/curvature concentric with the circumferential surface of the roller, and the thickness thereof is preferably relatively thin.

The cover 8.10 is preferably made of any one of glass wool, rock wool, ceramic fiber, or foam such as phenol foam or epoxy foam, or is made of a composite material.

Next, the configuration of the end portion of the heating roller 1 will be described in detail with reference to FIG. 2, which is an explanatory diagram of the fixing device taken along the line x-x' in FIG. 1.

11a and 11b are rotating shafts 1c at both ends of the heating roller 1, respectively.
.

The heat-resistant sleeves 1d are respectively fitted to the bearings 12a and +2b, which are respectively attached to the frames 13a and 13b of the fixing device. Heat-resistant gears 14a and 14b are fitted onto the rotating shafts 1c and ld of the heating roller 1, respectively, and receive the driving force from the driving source M.

This heat-resistant 'gear 14b meshes with another drive transmission gear 25, and rotates together with the heating roller 1 in response to the driving force. A gear 26a of a manual knob 26 is engaged with the heat-resistant gear 14 to transmit manual driving force.

Since the heat-resistant gears 14a and 14b are made of a heat-insulating material, the gears 14a and 14b are connected to the heating roller 1.
Heat is not dissipated to other drive transmission members such as gears via 14b. This gear improves the heat retention of the heating roller 1.

Furthermore, the heat-resistant sleeves lla and llb are also heat-blocking insulators, and are designed to extend from the end of the heating roller 1 to the bearing 1.
This prevents heat loss due to heat transfer to 2a, 12b and frames 13a, 13b. Therefore, the heat loss from the end of the heating roller 1 can be reduced by the heat-resistant gears 14a, 14b, and the heat-resistant sleeves 11a, ll
By adding b, it was possible to further reduce it significantly or to almost eliminate it.

Generally, the heat-resistant gears 14a and 14b are often provided with a number of other drive transmission members in conjunction with each other. Therefore, conventional heat losses are predominant in such drive systems. On the other hand, in the second embodiment, heat loss to the drive system can be reduced or eliminated, so thermal efficiency can be greatly improved and power consumption can be reduced. Furthermore, in the above embodiment, heat-resistant sleeves 11a and llb are used in addition to heat-resistant gears 14a and 14b, so that heat loss from the roller ends to frames 13a and 13b can be prevented and thermal efficiency can be further improved. In the above example, the heating roller 1 is provided at both ends, but it is effective if a heat insulating portion is provided at least between the roller 1 and the side receiving the driving force of the member that transmits the driving force to the roller 1. The above heat resistant sleeve 12
As a and 12b, polyimide, polyamideimide,
Polyamide, pps (polyphenylene thilphide)
, PBT (polybutylene terephthalate) resin, phenol resin, etc., or a material made of a heat-insulating material made of a mixed material of this type is preferable. The gears 14a and 14b are preferably made of a heat-resistant material with good heat insulation properties, such as polyimide, polyamide-imide, pps 1 modified phenol, and tetrafluoroethylene with reinforcing optical fibers added. .

As mentioned above, the heating roller 1 includes the heat-resistant sleeve 11a,
1 lb and heat-resistant gears 14a and 14b, the machine is thermally isolated from the machine body and frames 13a and 13b, and heat loss transmitted through these is extremely small.

With the above configuration, the thermal efficiency is very high, and uniform and good fixing performance can be obtained in non-continuous copying, but when continuous copying is performed, the fixing performance in the center of the copy paper is lower than that in the periphery of the copy paper. The fixability of the toner becomes weaker, and this becomes more noticeable as the number of sheets that are continuously passed increases.

The following two points are cited as the reasons for the above. The first reason is that the temperature at the center of both the heating roller 1 and the pressure roller 2 decreases as heat is taken away by the copy paper. On the other hand, at the ends of both rollers, less heat is transferred to the copy paper than at the center, so the temperature drop at the ends of both rollers is less than that at the center. This is because the roller surface temperature is higher at the ends of both rollers.The second reason is that from the first reason above, the amount of heat that the pressure roller 2 receives from the heating roller 1 is higher at the ends than at the center. Therefore, the temperature of the pressure roller 2 is higher at the end than at the center.Therefore, the pressure roller 2 thermally expands in an inverted crown shape, and the pressing force between both rollers is also higher at the end. This is because it becomes expensive.

Therefore, it is preferable to use a heater 3 in the heating roller 1 that generates a larger amount of heat at the center than at the ends. Further, it is preferable that the heat generation length of the heater 3 is equal to or shorter than the width of the maximum sheet passing size. For example, if the heater shown in FIG. 3 is used, uniform and good fixing performance can always be obtained in both non-continuous copying and continuous copying.

Further, good results were obtained even when a uniformly wound heater was used and a heater whose heat generation length was about 10 to 60 steps shorter than the maximum sheet passing size 1].

(Example 1) In the fixing device having the above configuration, the heating roller 1 has an aluminum core with a wall thickness of 6.5 Wn as the hollow roller core 1a, and a H'rV with a thickness of 0.5 Wn as the elastic layer 1b. (Heat vulcanization type) Silicone rubber i-covered (manufactured by Toshiba Silicone: Product code T)
SE 220-6U) with an inverted crown shape with an outer diameter of 60mm (the diameter of the center part is 150mm compared to the end part)
μ small roller) is used as the pressure roller 2.
As the metal roller core 2a, the entire iron core with an outer diameter of 50mm is coated with LTV (low temperature vulcanization type) silicone rubber with a wall thickness of 5mm as the elastic layer 2b (made by Shin-Etsu Kagaku Steel): product code,
A roller made of E-1202 (E-1202 modified to facilitate injection molding) and having an outer diameter of 60 mm was used. The heating roller 1 was manufactured by press molding, and the pressure roller 2 was manufactured by LIM (liquid injection molding).

A 650W halogen heater is used as the heater 3 in the heating roller 1, and a thermistor is used as the temperature sensing element 4 to detect the roller surface temperature.The heater is turned on and off by a control circuit (not shown) to adjust the surface temperature of the heating roller 1. is maintained at 170°C.

The copy paper processing speed of the fixing device is 40 tran/s.
EE is 60 A4 size sheets/minute. The web 6a of the cleaning section 6 is impregnated with dimethyl silicone oil (manufactured by Shin-Etsu Chemical, product code: KF 96 H, 25°C (viscosity 10,000 CPS at 20°C), and the web 6a is gradually moved during copying. Then, 1X10-'9 of silicone oil was applied to the surface of the heating roller 1 per A4 size sheet, and the sheet was passed through the sheet.

Place the toner image on the 15th section of the entire area of A4 size paper, and
I passed 1,000,000 sheets in a row and there were no jams.

Furthermore, the very small amount of offset toner that is applied to the heating roller 1 is transferred to the web 6a and the next sheet of paper.
The heating roller 19-1 after passing 100,000 sheets was very clean. On the other hand, since the pressure roller 2 is made of a material that has better releasability than the heating roller 11, there was no dirt at all.

(Example 2) The conditions were the same as in Example 1 except that HTV silicone rubber (manufactured by Shin-Etsu Chemical Co., Ltd., product code: KE 1406) was used as the heating roller 1. Same as Example 1 (110
Even after passing 10,000 sheets of paper, both rollers remain completely stained.
It was also possible to pass paper.

(Comparative Example 1) HTV silicone rubber (manufactured by Toshiba Silicone Company, product code: ISE 220-6 U) was used as the heating roller, and HTV silicone rubber (manufactured by Shin-Etsu Chemical Company, product code, KE7424) was used as the pressure roller. is Example 1
The same conditions were used. After approximately 30,000 sheets had been passed, the entire pressure roller began to become contaminated with toner, and after 100,000 sheets had been passed, the pressure roller became completely black with toner.

When copying was made after leaving the printer on standby for 10 minutes in this state, stains appeared on the back of the copy paper due to the roller cycle.

It was found that during standby, the toner 20-1 in the nip portion softened and melted, and it adhered to the back side of the copy paper in the form of a black band. Depending on the timing, the softened toner could cause the copy paper to stick to the pressure roller, resulting in a jam. Therefore, it became necessary to clean the pressure rope once every 30,000 sheets. Note that the stain on the pressure roller was extremely difficult to remove.

(Comparative Example 2) Both the heating roller and the pressure roller were made of LTV silicone rubber (
The conditions were the same as in Example 1, except that Shin-Etsu Chemical Co., Ltd. (product code: KE-1202) was used.

After passing approximately 20,000 sheets, the heating roller was damaged by the separation claw that was in contact with the heating roller.

I tried to reduce the contact pressure of the separation claw and feed the paper again, but with a light pressure that did not damage the roller, the paper could not be separated completely from the heating roller, and jams often occurred. Ta. Damage to the roller also occurred when the heating roller was formed from RTV silicone rubber.

As a result of passing sheets in various combinations, we found that HT, which has excellent strength, was used as the elastic layer 1b of the relatively thin coating layer of the heating roller 1.
V-silicon rubber (organic peroxide vulcanization), fluorosilicone rubber, and fluorosilicone rubber are suitable, and as the elastic layer 2a of the relatively thick coating layer of the pressure roller 2, LTV, which has excellent mold release properties, is suitable. Very good results were obtained when silicone rubber (condensation reaction type) and RTV silicone rubber (condensation polymerization type) were suitable, and when the anti-offset liquid was applied from the heating roller 1 side.

Below-1-1: In a preferred embodiment of the present invention for IH, in a fixing device that uses a heat roller for fixing, the surface layer of the heat roller is made larger than the surface layer of the elastic body of the pressure roller.
By applying offset prevention 1 and 2 liquids to the heating roller, excessive 1L
T1: Copying with good fixing properties and image properties is possible because there is no offset of the toner onto the paper roller.
It's H. Furthermore, since the rollers are not stained with toner, maintenance of the fixing device itself has become easier.

The above embodiment is an example of a heat fixing device, in which the present invention is extremely effective and highly effective, but the present invention is also applicable to a pressure fixing device.

Further, in the above embodiment, the heating roller such as the fixing roller has a thin elastic layer such as rubber 1 on the surface layer, and the effect of the present invention can be exhibited very well. It is not necessary that the rollers have elastic surfaces. The present invention provides particularly excellent anti-offset properties and durability when the oil field roller has an elastic surface layer.

Further, in the above embodiment, the anti-offset liquid is applied to the surface of the heating roller serving as the fixing roller, but as a result of this, the anti-offset liquid is supplied to the surface of the fixing roller as much as the surface of the pressure roller. Coupled with the balance between the release properties of the fixing roller and the pressure roller, it prevents offset to the surface of the pressure roller as well as the fixing roller. Since it is supported by the surface of the record while it is impossible to visually confirm its existence, as a result, almost no offset phenomenon occurs.

Applying Offcera I/prevention liquid to the surface of the fixing roller in this manner produces effects different from those of the conventional method.

In the above embodiment, a member (including felt, etc.) that performs both cleaning and anti-offset liquid is provided on the surface of the fixing roller, but these functions may be divided into separate parts.

As described in detail below, the present invention improves the releasability of the pressure roller surface than that of the fixing roller surface that comes into contact with objects to be fixed such as toner images. It is possible to prevent back dirt, which is a big problem when it occurs, and to maintain the surface of the pressure roller in a clean state for a long period of time.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram of an example of a double-sided image forming apparatus in which the present invention can be particularly effectively implemented; Figure 2 is an explanatory diagram of an embodiment of a fixing device according to the present invention; FIG. 4, a partial cross-sectional view taken along the -x' line, is an explanatory diagram showing the heat generation distribution of the heater. 1... Heating roller 1a... Metal hollow roller core 11]... Elastic body layer 2... Pressure roller 2a... Metal roller core 2b... Elastic body layer 3.3... Heater 4... Temperature sensing element 5a, 5b... Separation claw 6
...Cleaning Department 11a, 1 lb...Heat-resistant sleeve patent applicant Gyanon Co., Ltd.

Claims (4)

[Claims] (1) A fixing roller that is in contact with the powder image, which grips and conveys the unfixed object to fix the unfixed object onto the recording material, and a surface of the recording material opposite to the object to be fixed. In a fixing device having a pressure roller that is in contact with the fixing roller, the surface of the fixing roller and the surface of the pressure roller have releasability with respect to the object to be fixed, and the fixing roller on the side that contacts the object to be fixed is A fixing device characterized in that the mold releasability of the pressure roller surface is better than that of the roller surface. (2) The fixing device according to claim 1, wherein the surface of the pressure roller is a releasable elastic layer. (3) The fixing device according to claim 2, wherein the surface of the fixing roller is a releasable elastic layer. (4) The fixing device according to claim 3, wherein the fixing roller has a built-in heating means.