JPH11167311A - Image forming device, fixing device therefor, pressure roller and fixing method for image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize appropriate fixing without necessitating a transfer paper detection means and without performing complicated control. SOLUTION: This image forming device is provided with a pressure roller heating means 21 heating the pressure roller 30 of the fixing device from the outside; and the roller 30 is provided with a core roller 3, at least whose surface is partially conductive, an outside roller 4 surrounding the core roller by making at least a part of the inner peripheral surface of a hollow cylinder which can be deformed conductive, and electric insulating spacers 51 to 54 for forming a gap between the rollers 3 and 4. In such a case, gas is enclosed in the gap part and hermetically sealed with a specified pressure, and energizing to the means 21 is turned on/off in a state where the conductive part of the roller 3 and the conductive part of the inner periphery part of the roller 4 are set as the contact of a switch.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, a fixing device for the image forming apparatus, a pressure roller, and a fixing method in the image forming apparatus.

[0002]

2. Description of the Related Art An electrostatic latent image is formed on a photoconductive photoreceptor,
Image forming apparatuses that develop a toner image by developing this electrostatic latent image and transfer and fix the obtained toner image to a sheet-shaped recording medium include analog and digital copying apparatuses and laser printers. It is widely known as various types of printers. As a fixing method for fixing a toner image on a sheet-shaped recording medium, a sheet-shaped recording medium on which a toner image is formed is formed by a fixing roller having a heat source for heating therein, and a pressure roller cooperating with the fixing roller. In general, a contact fixing method of fixing a toner image to a recording medium by applying heat and pressure to the recording medium and the toner image while nipping and transporting the toner image with the fixing roller side. With such a contact fixing method, an appropriate temperature range in which a toner image can be fixed well is not so wide. If the fixing temperature is too high, a part of the toner melted by the excessive heat adheres to the fixing roller, and “hot offset” occurs in which the toner is re-adhered to another part of the recording medium. If the fixing temperature is too low, only the surface layer portion of the toner image melts, and this portion adheres to the fixing roller and causes a “cold offset” in which the toner image adheres to another portion of the recording medium. The pressing force between the fixing roller and the pressure roller is also a major factor that affects the efficiency of heat supply to the recording medium and the toner image.

In order to quickly attain an appropriate fixing temperature of a fixing device, the heat capacity of a fixing roller and a pressure roller is set to be low, and the rise of the temperature of these rollers due to heating is accelerated. In this case, at a desired fixing temperature, the absolute amount of heat stored in the fixing roller and the pressure roller is small, and when a part of the heat of the roller is taken away by the recording medium or the toner image by the fixing, the roller temperature is reduced. When the temperature drops sharply and falls below the proper fixing temperature range, and the latter half of the toner image on the same recording medium fails to fix properly or when fixing is performed continuously, fixing is performed on the second and subsequent recording media. There is a problem that failure occurs. As a method of avoiding such a problem, the surface temperature of the fixing roller is detected, and the heating value of the heating heat source is set to be larger in the latter half of the fixing operation of one transfer sheet than in the first half. A method of controlling the amount of heat generated by the heat source for use (JP-A-6-75504), and a method in which an outer peripheral surface of a heat conductive roller provided inside a fixing roller is brought into contact with an inner peripheral surface of the fixing roller, and Are relatively rotated to reduce the temperature drop at the nip between the pressure roller and the fixing roller (Japanese Patent Application Laid-Open No. H6-130843). Further, when the leading edge of the transfer paper reaches the nip, A method of detecting the temperature of the fixing roller when the trailing edge of the transfer paper has passed through the nip portion, and changing the set temperature of the fixing roller using a result obtained by adding a temperature difference before and after passing the transfer paper to a standard control temperature as a set temperature. JP-A-5-281875 publication) have been proposed. However, in the case of the method of controlling the heat generation amount, even if an attempt is made to control the heat generation amount of the heating heat source by predicting the temperature decrease amount in advance, the temperature decrease amount of the fixing roller due to the passage of the transfer paper is determined by the type of the transfer paper and Since it differs depending on the initial temperature, moisture content, and the like, it is difficult to properly predict the amount of temperature decrease, and it is difficult to properly control the amount of generated heat. Further, in the case of a method in which a heat conductive roller is provided inside the fixing roller, since heat resistance exists in heat conduction between the fixing roller and the heat conductive roller, the amount of heat supplied to the nip is limited, and the transfer paper is thick. In the case of high-speed image formation (of course, the fixing is also performed at high speed), the "effect" is questionable. Based on the temperature difference before and after the transfer paper passes through the nip,
The method of changing the set temperature of the fixing roller requires transfer paper detecting means for detecting that the leading end of the transfer paper has reached the nip portion or has passed through the nip portion, which complicates the configuration of the fixing device.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to realize a proper fixing without requiring a transfer paper detecting means and without performing complicated control.

[0005]

According to the fixing device of the image forming apparatus of the present invention, a sheet-shaped recording medium having a toner image formed thereon is fixed to a fixing roller having a heat source for heating, and cooperates with the fixing roller. A fixing device for fixing the toner image to the recording medium by applying heat and pressure to the recording medium and the toner image while nipping and transporting the toner image with the pressing roller on the side of the fixing roller. The feature is as follows (claim 1). First, there is a "pressure roller heating means for externally heating the pressure roller". Second, the pressure roller is composed of “a core roller having at least a part of its surface being conductive;
At least a portion of the inner peripheral surface of the deformable hollow cylinder is made conductive and has an outer roller surrounding the core roller, and an electrically insulating spacer for forming a gap between the core roller and the outer roller. And a gas is sealed and sealed at a predetermined pressure in the gap, and the pressure roller is heated by using the conductive portion of the core roller and the conductive portion of the inner peripheral portion of the external roller as contact points of the switch. It is configured to turn on / off the energization of the means. The toner image to be fixed can be a “single color toner image”, a “multicolor toner image”, or a “color toner image”.

In the fixing device according to the first aspect, the fixing roller is disposed on the upper side and the pressure roller is disposed on the lower side, and "a heating lamp disposed below the pressure roller" is used as the pressure roller heating means. (Claim 2). 3. The fixing device for an image forming apparatus according to claim 1, wherein
"Fixing roller heating means" that heats the fixing roller from outside
And the conductive part of the core roller and the conductive part of the inner peripheral part of the external roller are used as the contact points of the switch to turn on and off the energization of the pressure roller heating means and the fixing roller heating means. 3). In the fixing device of the image forming apparatus according to the third aspect, the fixing roller is disposed on the upper side and the pressure roller is disposed on the lower side, and "a heating lamp disposed below the pressure roller" as pressure roller heating means. As the fixing roller heating means, the second roller provided above the fixing roller.
Heating lamp "can be used (claim 4). The fixing device according to any one of claims 1 to 4, further comprising a "pressing force increasing mechanism for additionally increasing a pressing force between the fixing roller and the pressing roller", wherein a conductive portion of the core roller and an external roller are provided. The conductive portion of the inner peripheral portion may be used as a contact point of a switch to turn on / off the energization of the press-contact force increasing mechanism.

A pressure roller according to the present invention uses a fixing roller having a heat source for heating inside a sheet-shaped recording medium having a toner image formed thereon, and a pressure roller cooperating with the fixing roller to form a toner image. A pressure roller of a fixing device for fixing the toner image to the recording medium by applying heat and pressure to the recording medium and the toner image while nipping and conveying the toner image to the fixing roller side; A core roller, a part of which is electrically conductive, an external roller surrounding at least part of the inner peripheral surface of the deformable hollow cylinder which is made conductive and surrounding the core roller, and a gap between the core roller and the external roller. And a gap is filled with gas at a predetermined pressure and hermetically sealed, and the conductive portion of the core roller and the conductive portion of the inner peripheral portion of the external roller are connected to the switch. Used as contacts "It is characterized by (claim 6).
7. The pressure roller according to claim 6, wherein the core roller is a metal roller, and the external roller is formed by forming a deformable thin metal layer on at least a part of an inner peripheral surface of a deformable hollow cylinder. (Claim 7).

An image forming apparatus according to the present invention comprises a photoconductive photoreceptor, a unit for forming an electrostatic latent image on the photoreceptor, and a developing unit for developing the formed electrostatic latent image into a toner image. When,
A transfer unit that transfers the toner image formed on the photoconductor directly to a sheet-shaped recording medium or via an intermediate transfer medium; and a fixing unit that fixes the toner image transferred to the recording medium to the recording medium. An image forming apparatus, wherein the fixing device according to any one of claims 1 to 5 is used as a fixing unit (claim 8). A fixing method in an image forming apparatus according to the present invention includes a photoconductive photoconductor, a unit for forming an electrostatic latent image on the photoconductor, and a developing unit that develops the formed electrostatic latent image into a toner image Transfer means for transferring the toner image formed on the photoreceptor directly to a sheet-like recording medium or via an intermediate transfer medium; fixing means for fixing the toner image transferred to the recording medium to the recording medium; The fixing device according to any one of claims 1 to 5, wherein the fixing is started by setting the surface temperature of the fixing roller and the pressure roller to a predetermined fixing temperature, and the surface of the pressure roller is When the temperature decreases by a predetermined temperature, the conductive portion of the core roller of the pressure roller and the conductive portion of the inner peripheral portion of the external roller come into contact with each other as a contact point of a switch, so that the amount of heat and / or pressing force for fixing can be obtained. Replenish "It is characterized by. The phrase “the hollow cylinder in the outer roller is“ deformable ”” means that the hollow cylinder is formed of an elastic material and is elastically deformed. Alternatively, a material that hardly expands and contracts but can be easily deformed may be used as the hollow cylinder, and the hollow cylinder may be elastically deformed as a cushion using a sealed gas.

In the fixing device for an image forming apparatus according to any one of the first to fifth aspects described above, the gas that is sealed and sealed in the gap between the core roller and the external roller in the pressure roller is “improper”. Activated gas "(Claim 1
0). Therefore, in the pressure roller according to the sixth or seventh aspect, the "gas sealed and sealed in the gap between the core roller and the external roller" can be an inert gas (claim 11). And a photoconductive photoconductor, a unit for forming an electrostatic latent image on the photoconductor, a developing unit for developing the formed electrostatic latent image into a toner image, and a developing unit formed on the photoconductor. A fixing unit for transferring the toner image to a sheet-shaped recording medium directly or via an intermediate transfer medium, and a fixing unit for fixing the toner image transferred to the recording medium to the recording medium; In this image forming apparatus, the fixing is started by setting the surface temperatures of the fixing roller and the pressure roller to a predetermined fixing temperature. When the surface temperature of
Implementing a fixing method in which the conductive portion of the core roller in the pressure roller and the conductive portion of the inner peripheral portion of the external roller come into contact as a contact of a switch, thereby replenishing the amount of heat and / or pressing force for fixing. (Claim 1
3). Examples of the “inert gas” include an argon gas and a helium gas. Of course, the invention is not limited thereto, and a known appropriate inert gas can be used. When the filling gas is an inert gas, the metal constituting the conductive portion of the core roller or the external roller does not chemically change even when the temperature rises.

[0010]

FIG. 1 is a view for explaining an embodiment of a fixing device according to the present invention. In FIG. 1A, reference numeral 10 denotes a fixing roller, reference numeral 30 denotes a pressure roller,
Reference numeral 21 indicates a heating lamp. Fixing roller 10
Is configured to have a heating heat source 1 inside a hollow roller 2. The hollow roller 2 is provided on the outer peripheral surface of a hollow metal roller.
In order to prevent toner adhesion, a thin layer of a material having good releasability such as Teflon (registered trademark, DuPont) is formed. The metal roller is made of a material having a high thermal conductivity so as to have “stiffness so as not to be deformed by pressing the pressure roller 30”. That is, the metal roller is preferably as thin as possible (about 1 to 1.5 mm) so that a uniform fixing temperature is quickly achieved by the heat source 1 for heating. Rigidity that does not cause “dents” or “axial deflection” is required, and aluminum, stainless steel, or the like is preferable as a material. The heating heat source 1 is for giving a fixing temperature to the hollow roller 2, and various heaters such as a resistance heating wire, an infrared lamp, and the like can be used, and a halogen lamp can be suitably used. The heating heat source 1 has substantially the same length as the hollow roller 2 so that the hollow roller 2 can be uniformly heated in the longitudinal direction (the direction perpendicular to the drawing), and the heating region extends over the entire longitudinal direction of the hollow roller 2. Will be deployed as In addition, in order to prevent a temperature decrease at the both ends of the hollow roller 2 due to heat radiation at both ends in the longitudinal direction, the heating value of the heating light emitting source 1 is:
It is set larger than the central part on both sides in the longitudinal direction. The surface temperature of the fixing roller 10 is detected by a temperature detector (not shown) (such as a thermistor), and the heat generation of the heating heat source 1 is controlled based on the detected temperature.

The pressure roller 30 has a core roller 3, an external roller 4, and spacers 51 to 54. Core roller 3
Must be "at least part of the surface is conductive", but in this embodiment, the above-mentioned "conductive condition" is satisfied by using a metal roller.
As another example, a metal layer may be formed on (at least part of) the peripheral surface of a roller made of a hard plastic or the like by vapor deposition or the like to make “at least a part of the surface conductive”. Core roller 3
The outer roller 4 surrounding the outer cylinder must have "at least a part of the inner peripheral surface of the deformable hollow cylinder made conductive". In this embodiment, the outer roller 4 is made of an elastic material having a thickness of about 3 mm. By forming the metal layer 41 on the inner peripheral surface of the cylinder, the above-mentioned “at least a part of the inner peripheral surface is made conductive”.
The conditions are met. Various rubber materials can be used as the elastic material constituting the external roller 4, but in this embodiment, silicone rubber is used as a suitable elastic material. Further, the metal layer 41 is formed on the external roller 4.
Is formed in a thin layer (about 1 to 2 μm) by sputtering or the like so as not to hinder the deformation of. As another method for making at least a part of the inner peripheral surface of the outer roller conductive, a method of dispersing and containing carbon particles or the like in a desired portion of the inner peripheral surface of the outer roller can be considered. Spacers 51-5
Numeral 4 is for maintaining a gap 42 of a predetermined size (about 1 to 2 mm) between the core roller 3 and the external roller 4, and has a columnar shape having the same diameter as the gap 42. It is. In this embodiment, the number of spacers is four. However, five or more spacers may be used, or only three spacers may be used. Further, in this embodiment, the spacers 51 to 54 are made of “soft and elastic sponge”, but are not limited thereto and may be made of hard plastic or the like. Core roller 3 and external roller 4 maintained by spacers 51 to 54
Is sealed at a “predetermined pressure”. The "gas" to be enclosed and sealed may be air,
Other gas such as helium gas can be appropriately sealed and sealed. As described above, an inert gas such as helium gas or argon gas is suitable as a sealing gas because it does not chemically change the metal parts of the core roller and the external roller. The heating lamp 21 is a “pressure roller heating means” for heating the pressure roller 30 from the outside, and is configured to be energized and heated by the heating lamp power supply circuit 50. One of a pair of lead wires from the heating lamp power supply circuit 50 is connected to the core roller 3, and the other is connected to the metal layer 41.
1 constitutes a “contact switch” that is turned on and off by contact and separation. A sheet-shaped recording medium (normal transfer paper or an OHP sheet for an overhead projector) 12 on which the toner image TI is formed is guided by a guide 11 to a nip portion between a fixing roller 10 and a pressure roller 30, and is fixed to the fixing roller 10. Heat and pressure are applied while the toner image TI is fixed while being conveyed by the pressure roller 30 and the pressure roller 30 to fix the toner image TI.

That is, the fixing device shown in FIG. 1 is a sheet-like recording medium 1 on which a toner image TI is formed.
A fixing roller 10 having a heating heat source 1 therein;
The toner image TI is applied by applying heat and pressure to the recording medium 12 and the toner image TI while the toner image TI is pinched and conveyed toward the fixing roller 10 by the pressure roller 30 cooperating with the fixing roller 10. Is a fixing device for fixing the pressure roller 30 to the recording medium 12, comprising a pressure roller heating means 21 for externally heating the pressure roller 30, wherein the pressure roller 30 is a core roller having at least a part of its surface being conductive. 3, an outer roller 4 having at least a portion of the inner peripheral surface of the deformable hollow cylinder made conductive and surrounding the core roller, and forming a gap between the core roller 3 and the external roller 4. It has electrically insulating spacers 51 to 54, and gas is sealed and sealed at a predetermined pressure in the gap, and the conductive portion of the core roller 3 and the conductive portion 41 of the inner peripheral portion of the external roller 4 are connected to a switch contact. As a pressure roller Energizing means 21 is configured fixing device to turn on and off (claim 1). In this embodiment, the fixing roller 10 is provided on the upper side, the pressure roller 30 is provided on the lower side, and the pressure roller heating means 21 is a “heating lamp provided below the pressure roller 30” ( Claim 2). Further, the pressing roller 30 of the embodiment shown in FIG. 1 is configured to transfer the sheet-shaped recording medium 12 on which the toner image TI is formed to a fixing roller 10 having a heat source 1 for heating therein.
And the pressure roller 30 cooperating with the fixing roller 10, while pressing and conveying the toner image TI toward the fixing roller 10, applying heat and pressure to the recording medium 12 and the toner image TI to apply toner. A pressure roller of a fixing device for fixing the image TI to the recording medium 12, wherein at least a part of the surface is a conductive core roller 3 and at least a part of the inner peripheral surface of the deformable hollow cylinder is a conductive roller External roller 4 surrounding core roller 3 and an electrically insulating spacer 51 for forming a gap between core roller 3 and external roller 4.
The gap is filled with gas at a predetermined pressure and hermetically sealed, and the conductive portion of the core roller 3 and the conductive portion 41 of the inner peripheral portion of the external roller are used as contact points of a switch. The core roller 3 is a metal roller, and the outer roller 4 is formed by forming a deformable thin metal layer 41 on at least a part of an inner peripheral surface of a hollow cylinder made of an elastic material. 7).

The pressure of the gas sealed in the gap between the core roller 3 of the pressure roller 30 and the external roller 4 varies depending on the temperature of the gas. Since the external roller 4 of the pressure roller 30 is deformable, when the pressure roller 30 is pressed against the fixing roller 10, the external roller 4 is pressed at the pressure contact portion (in the embodiment described, the elastic material is elastic). The gas is deformed to form a “nip portion”, but the gas sealed in the gap acts as a cushion against the pressure contact force, and the pressure of the gas causes the pressure contact portion between the fixing roller 10 and the pressure roller 30. The “width of the nip portion” formed in the first portion changes. That is, if the pressure of the atmospheric pressure is higher, the width of the nip portion becomes smaller, and the width of the nip portion becomes larger as the pressure decreases. When the surface temperature of the fixing roller 10 and the pressure roller 30 is set to an appropriate fixing temperature and the toner image TI is fixed,
The heat of the fixing roller 10 and the pressure roller 30 is taken by the recording medium 12 and the toner image TI, and the surface temperature of each roller decreases. The decrease in the surface temperature of the fixing roller 10 is detected by the above-mentioned "temperature detecting means not shown", and the heat generation of the heating heat source 1 is controlled so as to compensate for the temperature decrease.
On the other hand, a decrease in the temperature of the pressure roller 30 causes a decrease in the temperature of the gas sealed between the core roller 3 and the external roller 4. As the temperature decreases, the pressure of the gas decreases, the "cushion effect" decreases, the amount of deformation of the external roller 4 of the pressure roller 30 increases, and the nip width between the pressure roller 30 and the fixing roller 10 increases. And the pressure at the nip, ie, the "nip pressure", also decreases. When the amount of deformation reaches a certain level, the metal layer 41 formed on the inner peripheral surface of the outer roller 4 comes into contact with the core roller 3 due to deformation, as shown in FIG. Then, the heating lamp power supply circuit 50 is turned on, the energization of the heating lamp 21 is started, the heating lamp 21 generates heat, and the pressure roller 30 is turned on.
Is heated. As the surface temperature of the pressure roller 30 recovers due to this heating, the temperature and pressure of the gas sealed in the gap also increase, and when the gas pressure recovers sufficiently, the metal layer 41 and the core roller 3 become " Contactless "
The heating lamp power supply circuit 50 is turned off again, and the power supply to the heating lamp 21 is stopped. Thus, a change in the temperature of the gas causes a change in the pressure in the gas, and this pressure change turns on and off the “contact switch” formed by the core roller 3 and the metal layer 41 to turn on the energization of the heating lamp 21.・ Turn off.

In consideration of the heating effect of the pressure roller 30 due to the heat generated by the heating lamp 21, when the temperature becomes slightly higher than the lower limit of the "surface temperature range of the pressure roller 30" at which proper fixing is performed. If the contact switch is turned on, and if the "nip pressure is adjusted" so that an appropriate nip width, in other words, a nip pressure is realized in the surface temperature range, the pressure roller 30 The surface temperature can always be maintained in an appropriate temperature range, and the nip pressure can be maintained at an appropriate level. By doing so, the fixing roller 1
0 is not cooled by the pressure roller 30, and the fixing roller 10 is warmed by the contact with the heated pressure roller 30 or the air flow heated by the pressure roller 30, so that the cold offset is reduced. It can be effectively prevented. The gas pressure adjusted as described above is the “predetermined pressure”. FIG. 2 is a flowchart showing the above fixing process. In FIG. 2, the “contact switch” is, of course, a contact switch formed by the core roller 3 and the metal layer 41. In the above-described embodiment, as described above, the spacers 51 to 54 are made of “a soft and elastic sponge”.
For this reason, the spacer is deformed so as to be crushed with the deformation of the external roller 4, so that the metal layer 41 and the core roller 3 can be continuously contacted before and after the spacer, and the pressure of the sealed gas is maintained. Is lower, the contact switch is continuously turned on regardless of the presence of the spacer. However, when a spacer made of hard plastic or the like is used, the "on state" of the contact switch may be turned off at the spacer portion. In such a case, the heating lamp power supply circuit 50 is provided with a "circuit for holding this state for a longer time than the actual ON state when the contact switch is turned on", Irrespective of the off state of the contact switch in the above, the continuous on state may be maintained.

FIG. 3 shows another embodiment of the fixing device of the present invention. To avoid complication, the same parts as those in the embodiment of FIG. 1 are denoted by the same reference numerals as in FIG.
A detailed description of these parts will be omitted. The difference from the embodiment described with reference to FIG.
The second heating lamp 22 is provided on the upper part of the heater, and is energized by the heating lamp power supply circuit 50. That is, FIG.
In the embodiment shown in FIG. 1, a toner image is formed on a sheet-shaped recording medium 12 on which a toner image TI is formed by a fixing roller 10 having a heat source for heating and a pressure roller 30 cooperating with the fixing roller. A fixing device for fixing a toner image to a recording medium by applying heat and pressure to the recording medium and the toner image while nipping and conveying the toner image on the side of the fixing roller 10,
The pressure roller 30 includes a pressure roller heating unit 21 that heats the pressure roller 30 from the outside. The pressure roller 30 includes a core roller 3 having at least a part of the surface of which is electrically conductive, and an inner peripheral surface of a deformable hollow cylinder. An outer roller that is at least partially conductive and surrounds the core roller; and electrically insulating spacers 51 to 5 for forming a gap between the core roller and the external roller.
And pressurizing roller heating means 2 using the conductive portion of the core roller and the conductive portion of the inner peripheral portion of the external roller as contact points of a switch.
And a fixing roller heating means 22 for heating the fixing roller 10 from the outside. The conductive portion of the core roller 3 and the external roller 4 are electrically connected to each other.
The conductive part of the inner peripheral portion of the roller is used as a contact point of a switch to turn on / off the energization of the pressure roller heating means 21 and the fixing roller heating means 22 (Claim 3). , A pressure roller 30 is disposed on the lower side, the pressure roller heating means is a heating lamp 21 provided below the pressure roller 30, and the fixing roller heating means is a second lamp provided above the fixing roller 10. (Claim 4). When the temperature of the pressure roller 30 decreases with the fixing operation, the pressure of the gas sealed in the pressure roller decreases, and the “contact switch” comes into contact to be turned “on”. The energization of the heating lamp 21 from the lamp power supply means 50 and the heating of the outer peripheral surface of the pressure roller 30 are performed exactly as in the embodiment described with reference to FIG. On one hand, the fixing roller 10
As described above, as described above, the surface temperature is detected by a temperature detecting means such as a thermistor, and the heat generation of the heating heat source inside the fixing roller is controlled based on the result, but the heating by the heating heat source is performed from the inside. It takes some time for the result to be reflected on the surface temperature of the fixing roller 10.
Further, since the heat from the externally heated pressure roller 30 is not efficiently transmitted to the fixing roller 10 when the recording medium 12 is interposed in the nip portion, in the embodiment of FIG. If the recovery of the lowered fixing roller surface temperature is delayed, it cannot be said that there is no possibility of the occurrence of cold offset. Therefore, in the embodiment of FIG. 3, when the contact switch is turned on, not only the pressure roller 30 is externally heated, but also
The peripheral surface of the fixing roller 10 is also externally heated by the second heating lamp 22. According to such external heating, the surface temperature of the fixing roller 10 can be immediately recovered, so that the above-described cold offset is favorably avoided. The “flow” in this case refers to the heating lamp when the heating lamp is turned on / off in the flowchart of FIG.
This is replaced by turning on / off the heating lamp 21 and the second heating lamp 22. In FIGS. 1 and 3, the position where the heating lamp 21 is provided does not necessarily need to be directly below the pressure roller 30, and the side surface of the pressure roller is not limited as long as the conveyance of the recording medium on which the toner image is fixed is not hindered. The position of the second heating lamp 22 in FIG. 3 is not limited to the position directly above the fixing roller 10 but may be the side portion of the fixing roller as long as the conveyance of the recording medium is not hindered. May be arranged so as to be opposed.

FIG. 4 shows only a portion necessary for explaining one embodiment of the fixing device according to the fifth aspect of the present invention. In FIG. 4, reference numeral 31 denotes “elastic spring means for realizing a pressing force between the fixing roller 10 and the pressing roller 30”, and reference numeral 3 denotes
Reference numeral 2 denotes a "contact pressure increasing mechanism for additionally increasing the contact pressure". The pressing force increasing mechanism 32 is turned on / off by the contact switch (with the conductive portion of the core roller and the conductive portion of the inner peripheral portion of the outer roller as contacts). As described above, the fixing of the toner image to the recording medium depends on the temperature at the nip between the fixing roller 10 and the pressure roller 30 as well as the nip pressure. In the state where the contact switch is turned on, as described above, the width of the nip portion increases, and the area of the nip portion increases, so that the nip pressure is maintained even when the pressing force between the fixing roller 10 and the pressing roller 30 is the same. Become smaller. Then, the contact switch in the pressure roller 30 is turned off by the heating of the heating lamp, and it takes some time for the nip pressure to recover. If fixing is performed in a state where the nip pressure is insufficient, the efficiency of heat transfer to the toner image and the recording medium is low, and there is a possibility that cold offset may occur. Therefore, in the invention according to claim 5, when the contact switch is turned on, the contact pressure increasing mechanism 32 is used to recover the reduced nip pressure, and when the contact switch is turned on, This is to increase the pressing pressure in a load manner and measure the recovery of the nip pressure. Pressing force increasing mechanism 32 in the embodiment shown in FIG.
Is a "solenoid" which operates when the contact switch is turned on, pulls the elastic spring means 31, increases the pressure contact force between the fixing roller 10 and the pressure roller 30, and recovers the nip pressure. The “recovery of the nip pressure by the pressing force increasing mechanism” described with reference to FIG. 4 may be performed in combination with the embodiment described with reference to FIG. 1 or may be performed with reference to the embodiment described with reference to FIG. It may be performed in combination with the form.

In each of the embodiments described above, the gas sealed and sealed in the gap between the core roller and the external roller in the pressure roller is an inert gas. The pressure roller in this fixing device is next to the pressure roller according to the eleventh embodiment.

FIG. 5 conceptually shows an embodiment of the image forming apparatus according to the present invention. This image forming apparatus is a “color image forming apparatus”. The photoconductive photoreceptor 100 rotates in the direction of the arrow and is uniformly charged by the charging means 101, and Y (yellow), M
A Y latent image, an M latent image, a C latent image, and a K latent image to be visualized with (magenta), C (cyan), and K (black) toners are sequentially written. The image exposure unit is a known optical scanning device.
The written and formed Y latent image is visualized with the Y toner in the developing means 105, and the obtained Y visible image is
6 is transferred. Similarly, the M latent image is visualized with the M toner, the C latent image is visualized with the C toner, and the K latent image is visualized with the K toner.
Both the C visible image and the K visible image are sequentially transferred to the intermediate transfer medium 106. In this way, the four types of visible images are superimposed on the intermediate transfer medium 106 to form a “color visible image”. This color visible image is transferred by the transfer roller 107.
The image is secondarily transferred onto a sheet-shaped recording medium 12. The recording medium 12 has the color toner image fixed in the fixing device 110 and is discharged out of the device. That is, the embodiment shown in FIG. 5 is described as “photoconductive photoconductor 100, means 101 and 103 for forming an electrostatic latent image on the photoconductor, and a toner image formed by developing the formed electrostatic latent image. Developing means 105, transfer means 106 and 107 for transferring the toner image formed on the photoconductor 100 to the sheet-like recording medium 12 via the intermediate transfer medium 106, and the toner image transferred to the recording medium 12. And an image forming apparatus having a fixing unit 110 for fixing the fixing unit 100 to a recording medium, wherein the fixing unit 100 is “any of the fixing devices described in the above embodiments”. Therefore, in the image forming apparatus of FIG. 5, "fixing is started by setting the surface temperatures of the fixing roller and the pressure roller to a predetermined fixing temperature, and when the surface temperature of the pressure roller decreases by a predetermined temperature,
A fixing method of replenishing the amount of heat and / or the pressing force for fixing by the contact between the conductive portion of the core roller and the conductive portion of the inner peripheral portion of the outer roller as the contact point of the switch in the pressure roller is implemented. (Claim 9). in this case,
If an inactive gas is sealed and sealed in the gap between the pressure rollers in the fixing device, the image forming apparatus is an embodiment of the image forming apparatus according to the twelfth aspect. Will be carried out.

[0019]

As described above, according to the present invention, it is possible to realize a novel image forming apparatus, a fixing device and a pressure roller of the image forming apparatus, and a fixing method in the image forming apparatus. Since the pressure roller of the present invention functions as a contact switch utilizing a pressure change due to a temperature change of the sealed gas, the temperature change of the pressure roller can be detected without using any special means. The fixing unit of the present invention uses the pressure roller, and does not use the transfer paper detecting unit.
Further, without performing complicated temperature control, the surface temperature of the pressure roller, the surface temperature of the fixing roller, or the nip pressure of the both can always be kept in an appropriate range, and proper fixing can be realized. According to the image forming apparatus and the fixing method of the present invention, by using the fixing device, good fixing can be realized and good image formation can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram for describing one embodiment of a fixing device of the present invention.

FIG. 2 is a flowchart showing heating of a pressure roller in the embodiment of FIG.

FIG. 3 is a view for explaining another embodiment of the fixing device of the present invention.

FIG. 4 is a view showing only a portion necessary for explanation of one embodiment of the fixing device according to claim 5;

FIG. 5 is a diagram conceptually showing an embodiment of the image forming apparatus of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Fixing roller 12 Recording medium 30 Pressure roller 3 Core roller 4 External roller 51 Spacer

Claims (13)

[Claims] An image forming apparatus according to claim 1, wherein a toner image is formed on the sheet-shaped recording medium by a fixing roller having a heat source for heating and a pressure roller cooperating with the fixing roller. A fixing device that applies heat and pressure to the recording medium and the toner image to fix the toner image on the recording medium while nipping and conveying the recording medium and the toner image. Means, wherein the pressure roller surrounds the core roller, at least a part of the surface of which is conductive, and at least a part of the inner peripheral surface of the deformable hollow cylinder which is conductive. An external roller, an electrically insulating spacer for forming a gap between the core roller and the external roller, and a gas filled and sealed in the gap at a predetermined pressure; Part and external roller A conductive portion of the inner peripheral portion as a contact of a switch, a fixing device of an image forming apparatus characterized by being configured to turn on or off the energization of the pressure roller heating means. 2. A fixing device for an image forming apparatus according to claim 1, wherein a fixing roller is disposed on an upper side and a pressure roller is disposed on a lower side, and a pressure roller heating means is provided below said pressure roller. A fixing device for the image forming apparatus, wherein the fixing device is a heating lamp. 3. A fixing device for an image forming apparatus according to claim 1, further comprising a fixing roller heating means for externally heating the fixing roller, wherein a conductive part of the core roller and a conductive part of an inner peripheral part of the external roller are provided. A fixing device for an image forming apparatus, wherein a part of the fixing device is used as a contact point of a switch so as to turn on and off energization of a pressure roller heating unit and a fixing roller heating unit. 4. A fixing device for an image forming apparatus according to claim 3, wherein a fixing roller is disposed on an upper side and a pressure roller is disposed on a lower side, and a pressure roller heating means is provided below said pressure roller. The fixing roller heating means is a second heating lamp provided above the fixing roller. 5. A fixing device for an image forming apparatus according to claim 1, further comprising: a press-contact force increasing mechanism for additionally increasing a press-contact force between the fixing roller and the pressure roller; A fixing device for an image forming apparatus, characterized in that the conductive portion of the external roller and the conductive portion of the inner peripheral portion of the external roller are used as contact points of a switch to turn on / off the energization of a pressing force increasing mechanism. 6. A sheet-shaped recording medium having a toner image formed thereon is fixed to a fixing roller by a fixing roller having a heat source for heating and a pressure roller cooperating with the fixing roller. A pressure roller of a fixing device for fixing the toner image to the recording medium by applying heat and pressure to the recording medium and the toner image while nipping and transporting the recording medium and the toner image. A core roller, an external roller surrounding at least a portion of the inner peripheral surface of the deformable hollow cylinder which is made conductive and surrounding the core roller, and forming a gap between the core roller and the external roller. It has an electrically insulating spacer, and gas is sealed and sealed at a predetermined pressure in the gap, and the conductive part of the core roller and the conductive part of the inner peripheral part of the external roller are used as contact points of a switch. It is characterized by Pressure roller. 7. The pressure roller according to claim 6, wherein the core roller is a metal roller, and the outer roller has a deformable thin metal layer formed on at least a part of the inner peripheral surface of the deformable hollow cylinder. A pressure roller, characterized in that: 8. A photoconductive photoreceptor, means for forming an electrostatic latent image on the photoreceptor, developing means for developing the formed electrostatic latent image into a toner image, Image forming apparatus comprising: a transfer unit for transferring a toner image formed on a recording medium directly or via an intermediate transfer medium; and a fixing unit for fixing the toner image transferred to the recording medium to the recording medium. An image forming apparatus, wherein the fixing device according to any one of claims 1 to 5 is used as a fixing unit. 9. A photoconductive photoreceptor, means for forming an electrostatic latent image on the photoreceptor, developing means for developing the formed electrostatic latent image into a toner image, Image forming apparatus comprising: a transfer unit for transferring a toner image formed on a recording medium directly or via an intermediate transfer medium; and a fixing unit for fixing the toner image transferred to the recording medium to the recording medium. The fixing device according to claim 1, wherein the fixing device starts fixing the surface temperature of the fixing roller and the pressure roller to a predetermined fixing temperature, and the surface temperature of the pressure roller is a predetermined temperature. When the temperature drops, the conductive portion of the core roller in the pressure roller and the conductive portion of the inner peripheral portion of the external roller come into contact as a switch contact, thereby replenishing the amount of heat and / or pressure for fixing. Fixing method of the image forming apparatus according to claim. 10. The fixing device for an image forming apparatus according to claim 1, wherein the gas sealed in a gap between the core roller and the external roller in the pressure roller is an inert gas. A fixing device for an image forming apparatus. 11. The pressure roller according to claim 6, wherein the gas sealed in the gap between the core roller and the external roller is an inert gas. 12. A photoconductive photoreceptor, means for forming an electrostatic latent image on the photoreceptor, developing means for developing the formed electrostatic latent image into a toner image, Image forming apparatus comprising: a transfer unit for transferring a toner image formed on a recording medium directly or via an intermediate transfer medium; and a fixing unit for fixing the toner image transferred to the recording medium to the recording medium. An image forming apparatus, wherein the fixing device according to claim 10 is used as a fixing unit. 13. A photoconductive photoreceptor, means for forming an electrostatic latent image on the photoreceptor, developing means for developing the formed electrostatic latent image into a toner image, Image forming apparatus comprising: a transfer unit for transferring a toner image formed on a recording medium directly or via an intermediate transfer medium; and a fixing unit for fixing the toner image transferred to the recording medium to the recording medium. The fixing device according to claim 10, wherein the fixing is started by setting the surface temperatures of the fixing roller and the pressure roller to a predetermined fixing temperature, and when the surface temperature of the pressure roller decreases by a predetermined temperature, the pressing roller Wherein the conductive portion of the core roller and the conductive portion of the inner peripheral portion of the outer roller contact each other as a contact point of a switch to replenish the amount of heat and / or pressure for fixing. Set Method.