JP2007241320A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device capable of obtaining a desired glossiness by eliminating the need to switch temperature, linear velocity and, furthermore, pressure. <P>SOLUTION: The fixing device fixes an unfixed image held on a sheet S. The device includes: a pair of heat conductive belts 14, 14' disposed such that opposite extending faces move in the same direction; and nip parts N11, N2 disposed at least in two areas in the extending direction of the opposite extending faces of the heat conductive belts 14, 14' so as to press a sheet S sandwiched between the heat conductive belts 14, 14'. In the one nip N1, the heat conductive belts 14, 14' are constantly in contact with each other. In the other nip N2, the heat conductive belts 14, 14' are brought into contact with each other or separated therefrom. The length of the area where heat is transmitted to a sheet S, defined by the opposite extending faces, can be altered according to a contact/separation state. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fixing device and an image forming apparatus, and more particularly to a configuration for fixing an unfixed image on a sheet such as recording paper using a belt.

In an image forming apparatus such as a copying machine, a facsimile, a printer, or a printing machine, a copy or a recorded material can be obtained by heating and fixing an unfixed image transferred and carried on a sheet such as recording paper. it can.
The fixing device has a configuration in which an unfixed image on a sheet is heated from one roller while the sheet is nipped and conveyed by a pair of rollers.

In addition to the configuration in which the fixing is performed between the rollers, there is a configuration in which a belt having a smaller heat capacity than the rollers is used as a heating medium, and this is combined with the rollers.
In the above configuration, the belt includes a belt wound around the pair of rollers, and a pressure roller that forms a nip portion of the sheet by contacting and facing one of the rollers, and the side of the belt facing the pressure roller The extending surface is moved in the moving direction of the sheet. In this configuration, among the rollers around which the belt is wound, the belt is heated by a roller located on the upstream side in the movement direction of the expansion surface, and the sheet is guided according to the movement direction at the nip portion. An unfixed image on the sheet can be fixed.

  Since the heat capacity can be reduced by reducing the volume of the belt compared to the rollers, the temperature can be increased in a short time, and the temperature rise at the start-up is higher than when only the above-described roller pair is used. There is an advantage of being fast.

  Some image forming apparatuses have a configuration capable of forming a multicolor image including a full color. In this type of multicolor image forming apparatus (hereinafter referred to as a color image forming apparatus for a full color image), the glossiness of the obtained image may be different. For example, a photographic image and a character image often have different glossiness, which means the amount of reflected light with respect to incident light. The reason for this is that photographic images often desire better-looking saturation than character images.

  Factors affecting the glossiness include the thermal properties of the toner contained in the unfixed image, and among the thermal properties, it is influenced by the glass transition point. For this reason, conventionally, configurations have been proposed in which the temperature, the linear velocity of the sheet, and the nip pressure, which are the heating conditions for the toner in the fixing device, are made different (for example, Patent Documents 1 to 5).

  In each patent document, in a configuration in which fixing is performed using a belt, the angle of a guide member that guides the sheet with respect to the belt can be changed so that the contact area of the sheet with the belt varies, and transparent toner A configuration that improves the glossiness using a sheet, a configuration that changes any one of the linear velocity, pressure, and temperature of the sheet to be controlled, and a configuration that controls the temperature immediately after fixing, further improve the glossiness of the document. Accordingly, there are disclosed a configuration in which the coating amount of the release agent is changed and a configuration in which the linear velocity of the sheet is switched according to the selection between low glossiness and high glossiness.

Japanese Patent Laid-Open No. 11-24463 JP-A-10-123863 Japanese Patent Laid-Open No. 5-333643 JP 7-271230 A Japanese Patent Laid-Open No. 9-329928

However, the configuration disclosed in the above patent document has the following problems.
First, when the temperature is switched, it is impossible to immediately respond to the following different modes, and the time required for image formation becomes longer. In addition, depending on the switching temperature, cold offsets and color development are likely to occur at low temperatures, and hot offsets and sheet wrapping may occur at high temperatures. Is significantly narrowed. As a result, if it is attempted to switch to a temperature range that does not cause the above-described adverse effects, the desired glossiness may not be set.

  Secondly, when the linear velocity is switched, depending on the set velocity, it takes time to move, and productivity at the time of image formation decreases.

  Third, when the pressure is switched, depending on the bending rigidity of the paper, the conveyance performance is affected. In particular, when thin paper is used as a target, there is a possibility that problems such as wrinkles and clogging may occur.

  SUMMARY OF THE INVENTION An object of the present invention is to easily set a glossiness to a desired state without adversely affecting an image and without deteriorating productivity in view of the problems in the conventional fixing device and the image forming apparatus using the same. It is an object of the present invention to provide a fixing device and an image forming apparatus having a configuration capable of performing the above. In particular, it is an object of the present invention to provide a fixing device and an image forming apparatus that can obtain a desired glossiness without requiring switching of temperature, linear velocity, or pressure.

  The invention according to claim 1 is an apparatus for fixing an unfixed image carried on a sheet, and a pair of thermally conductive belts provided in a state in which opposite extending surfaces move in the same direction; A nip portion that presses the sheet sandwiched between the heat conductive belts in at least two locations in the direction of extension of the opposite facing surfaces of each of the heat conductive belts, and one of the nip portions is the heat conductive member. The length of the heat transfer region to the sheet is configured such that the conductive belts are always in contact with each other, and the other is that the heat conductive belts are in contact with and separated from each other. Can be changed.

  The invention according to claim 2 is characterized in that the position of the other nip portion is located on the upstream side in the movement direction of the sheet.

  According to a third aspect of the present invention, the heat conductive belt is wound around a pair of rollers to form a stretched surface, and a heating source is built in one of the rollers to heat the heat conductive belt. It is characterized by that.

  The invention according to claim 4 is characterized in that the heat conductive belt moves at a constant speed irrespective of the contact / separation operation of the other nip portion.

  The invention according to claim 5 is characterized in that the thermal conductive belt is maintained at a constant tension regardless of the contact and separation of the other nip portion.

  According to a sixth aspect of the present invention, the one and the other nip portions exert a pressing force at right angles to the moving direction of the heat conductive belt parallel to the sheet conveying direction, and the direction of the pressing force is Both nip portions are parallel to each other.

  The invention described in claim 7 is characterized in that, of the nip portions, the other nip portion is brought into contact with and separated from the sheet according to the selection of the heating state with respect to the sheet.

  The invention according to claim 8 is characterized in that the heating state at the other nip portion is selected on the basis of the glossiness of the unfixed image carried on the sheet.

  According to a ninth aspect of the present invention, the heat conductive belt is wound around a pair of rollers, and between the pair of rollers, the opposite stretched surfaces are brought into contact with and separated from each other, and the length of the heat transfer region of the sheet is increased. An area setting member capable of changing the height is provided.

  In the invention described in claim 10, the region setting member for setting the contact / separation relationship between the heat conductive belts is constituted by a roller, and the region setting roller has a long heat transfer region between the heat conductive belts. It is characterized by being displaceable between a position where it can be performed and a position where the length is not set.

  An eleventh aspect of the invention is characterized in that the region setting roller forms a preheating region in the vicinity of a heat fixing region formed by one nip portion by bringing the heat conductive belts into contact with each other.

  The invention according to claim 12 sets the contact state between the heat conductive belts so that the region setting roller can form the preheating region continuously to the heat fixing region in the moving direction of the sheet. It is characterized by.

  The invention described in claim 13 is characterized in that the region setting member is provided with a heat source for heating the heat conductive belt.

  According to a fourteenth aspect of the present invention, there is provided an auxiliary pressure member that maintains a contact state between the heat conductive belts separately from the other nip portion between the region setting member and the one nip portion. It is characterized by being provided.

  The invention according to claim 15 is characterized in that the auxiliary pressure member is constituted by a back pressure member disposed on and in contact with the opposite surface of the heat conductive belt.

  According to a sixteenth aspect of the present invention, the auxiliary pressure member is constituted by a roller that is rotatable and can be contacted / separated on a surface opposite to the facing surface of the heat conductive belt.

  The invention described in claim 17 is characterized in that at least one of the region setting member and the auxiliary pressurizing member is constituted by a heat pipe which itself forms a heating source.

  The invention according to claim 18 is characterized in that the back pressure member forming the auxiliary pressure member has a low coefficient of friction and a low thermal conductivity.

  The invention described in claim 19 is characterized in that a heat pipe is used as the heat source for heating.

  The invention according to claim 20 is characterized in that a heat source for heating the heat conductive belt is disposed between the region setting member or the auxiliary heating member and the one nip portion in the moving direction of the heat conductive belt. It is characterized by being.

  According to a twenty-first aspect of the present invention, there is provided a fixing heating region in which the region setting member or the auxiliary pressure member in the moving direction of the heat conductive belt is formed by the one nip when the heat conductive belts are in contact with each other. It is characterized in that a preheating region located on the upstream side is formed continuously.

  According to a twenty-second aspect of the present invention, the fixing device according to the first to twenty-first aspects is used.

  The invention described in claim 23 is characterized in that the image forming apparatus has a configuration capable of forming single-color and multi-color images.

  According to the first aspect of the present invention, of the nip portions provided in at least two places in the extending direction of the heating belt that moves in the same direction, one of the nip portions is always abutted and the other is contacted and separated. With the configuration of the relationship, the length of the heat conductive region in the heat conductive belt that can directly contact the sheet can be changed. As a result, even when the glossiness is varied due to heat conduction by direct contact between the sheet and the heat conductive belt, the sheet moves substantially linearly by being sandwiched by the heating belt moving in the same direction. In addition to not degrading the sheet transportability, changing the amount of heat received on the unfixed image without changing the temperature, pressure, and linear velocity for the sheet, allows rapid switching to different modes. This makes it possible to prevent response and deterioration of productivity.

  According to the second aspect of the present invention, it is possible to change the preheating time for the sheet by positioning the other nip portion on the upstream side in the sheet moving direction.

  According to the third aspect of the invention, since the heat conductive belt is heated by one of the rollers, the fixing temperature can be set during the movement of the heat conductive belt.

  According to the fourth and fifth aspects of the present invention, the thermally conductive belts that move relative to each other have a constant speed regardless of the contact / separation operation of the nip portion. In this case, it is possible to reliably prevent image rubbing that is likely to occur in some cases and to prevent deterioration in image quality.

  According to the invention of claim 6, the nip portion provided in the extending direction of the heat conductive belt presses the sheet in a direction perpendicular to the moving direction of the belt, and the acting direction of the pressing force in each nip portion is Since they are parallel to each other, the sheet conveyance path between the nip portions is linear. Accordingly, the conveyance direction of the sheet is not changed, and the conveyance property is prevented from being deteriorated, thereby enabling high-speed conveyance.

  According to the seventh and eighth aspects of the present invention, the contact / separation relationship at the other nip portion and the overheating state due to the relationship can be changed according to the glossiness of the image. It is possible to obtain a simple configuration in which the heat receiving state on the seat side is changed while the temperature is kept constant.

  According to the ninth aspect of the present invention, the temperature, pressure and linear velocity are not changed between the rollers constituting the stretched surface of the heat conductive belt, by merely using a region setting member that brings the stretched surfaces into contact with each other. Thus, the heating area for the sheet can be changed. In other words, the desired glossiness can be obtained only by changing the heat receiving state on the sheet side. As a result, it is possible to change the glossiness without causing a change in temperature to a different mode, deterioration in transportability, and productivity.

  According to the invention described in claim 10, since the region setting member is composed of a roller which can be displaced to a position where the heat conductive region of the heat conductive belt is lengthened and a position where the length is not set, the heat conductivity is increased. When it contacts the belt, it can rotate in conjunction with this movement. Accordingly, it is possible to prevent the movement of the heat conductive belt from being hindered when the glossiness is set by changing the heat receiving state of the image without changing the temperature, pressure, and linear velocity.

  According to the eleventh and twelfth aspects of the present invention, since the region setting member can form a preheating region continuous with the heat fixing region constituted by the nip portion in the vicinity of one nip portion, the sheet has the preheating region. When passing, it is sandwiched between the belts and directly transfers heat from the belt. As a result, unlike heat transfer through space, a heat conduction relationship between the belt in direct contact with the unfixed image can be obtained, and it is possible to improve heating efficiency and set a desired gloss level. Become.

  According to the invention of claim 13, since the region setting member is provided with a heating source for the heat conductive belt, it is possible to improve the heating efficiency when the preheating region is set and to easily set the glossiness. It becomes possible to do.

  According to the fourteenth aspect of the present invention, since the auxiliary pressure member for maintaining the contact state between the heat conductive belts is provided between the nip portions separately from the other nip portion, the heat that moves in the same direction is provided. It becomes possible to improve the heat transfer efficiency in the direct heating of the sheet using the conductive belt, and to easily set the glossiness without changing the linear velocity.

  According to the fifteenth and eighteenth aspects of the present invention, since the auxiliary pressure member is composed of a back friction member with low friction and low thermal conductivity, the temperature can be switched by increasing the back pressure range to the heat conductive belt. Even if it is not performed, it is possible to improve the heat transfer property to the sheet.

  According to the sixteenth aspect of the present invention, the auxiliary pressurizing member is composed of a roller that is rotatable with respect to the heat conductive belt, so that the movement of the heat conductive belt is not hindered, in other words, the conveyance of the sheet. It becomes possible to improve the heat transfer efficiency with respect to a sheet | seat, without impairing property.

  According to the seventeenth aspect of the present invention, since the heat source is provided in at least one of the other nip portion and the auxiliary heating member, the heat receiving efficiency in the heat conduction region that is the contact range between the heat conductive belt and the sheet is improved. It becomes possible.

  According to the nineteenth aspect of the present invention, at least one of the region setting member and the auxiliary pressure member as the heating heat source is a heat pipe that itself forms a heating source, and this is used, so that it is perpendicular to the moving direction of the sheet. The above-mentioned member that contacts the entire region in the width direction corresponding to the direction can eliminate the temperature difference in the entire region in the width direction and eliminate the occurrence of deviation and hot offset related to the glossiness of the image.

  According to the invention of claim 20, since the heat source for heating the heat conductive belt is disposed between the region setting member or the auxiliary heating member in the moving direction of the heat conductive belt and one nip portion, It is possible to set the glossiness under a constant temperature condition by preventing the temperature decrease of the heat conductive belt heated to a predetermined temperature during the movement process of the heat conductive belt.

  According to the twenty-first aspect of the present invention, the region setting member or the auxiliary heating member constitutes the preheating region that is located upstream of the fixing heating region constituted by one of the nip portions when contacting the heat conductive belt. Therefore, when the heat conductive belts are in direct contact with the sheet, it is possible to improve the heat receiving state on the unfixed image and set the desired gloss without changing the temperature or changing the linear velocity and pressure. It becomes possible.

  According to the invention described in claims 22 and 23, when setting the glossiness corresponding to a single color or multicolor image to be formed, the sheet transportability is deteriorated, the productivity is deteriorated, and the image forming time is lengthened. It is possible to obtain a desired glossiness while preventing the above-described problem.

Embodiments of the present invention will be described below with reference to examples shown in the drawings.
FIG. 1 is a schematic diagram of an image forming apparatus to which a fixing device according to an embodiment of the present invention is applied. The image forming apparatus shown in FIG. 1 includes a photoconductor that can form an image of a color corresponding to color separation. This is a color printer that is provided with a plurality of images and can form a multicolor image by collectively transferring an image obtained by superimposing and transferring the toner image formed on each photoconductor onto an intermediate transfer body onto a sheet such as a recording sheet. In the present invention, the image forming apparatus is not limited to a color printer, but of course includes a color copying machine, a facsimile machine, and a printing machine.

In FIG. 1, in a color printer 1, an image forming unit 1A is positioned at a central portion in the vertical direction, a document feeding unit 1B is provided below the image forming unit 1A, and an original document table 1C1 is provided above the image forming unit 1A. Each of the scanning units 1C is arranged.
An intermediate transfer belt 2 having a horizontally extending surface is disposed in the image forming unit 1A, and a configuration for forming an image of a color having a complementary color relationship with the color separation color above the intermediate transfer belt 2 Is provided.

In the image forming unit 1A, photoreceptors 3Y, 3M, 3C, and 3B capable of carrying images of toners of complementary colors (yellow, magenta, cyan, and black) are juxtaposed along the extended surface of the intermediate transfer member 2. Has been.
Each of the photoconductors 3Y, 3M, 3C, and 3B is composed of a drum that can rotate in the same direction (counterclockwise in FIG. 1), and a charging device that performs image forming processing in the rotation process around the drum. 4, a writing device 5, a developing device 6, a primary transfer device 7, and a cleaning device 8 are arranged (for convenience, the reference numeral of each device is indicated by Y for the photoreceptor 3Y).

  The intermediate transfer belt 2 is configured to be wound around a plurality of rollers 2A to 2C and move in the same direction at a position facing the photoreceptor, and a roller 2C different from the rollers 2A and 2B constituting the stretched surface is The intermediate transfer belt 2 is opposed to the secondary transfer device 9. In FIG. 1, reference numeral 10 denotes a cleaning device for the intermediate transfer belt 2.

  The secondary transfer device 9 includes a transfer belt 9C that is wound around the charging drive roller 9A and the driven roller 9B and is movable in the same direction as the intermediate transfer belt 2 at the secondary transfer position where the secondary transfer device 9 is located. Thus, by charging the transfer belt 9C with the charging drive roller 9A, it is possible to transfer a multicolor image superimposed on the intermediate transfer belt 2 or a single color image carried on the sheet to the sheet.

A sheet is fed from the sheet feeding unit 1B to the secondary transfer position.
The paper feed unit 1B includes a plurality of paper feed cassettes 1B1, a plurality of transport rollers 1B2 arranged in a transport path for sheets fed from the paper feed cassette 1B1, and a registration roller 1B3 positioned in front of the secondary transfer position. ing. In this embodiment, the sheet feeding unit 1B can feed a sheet of a type not stored in the sheet feeding cassette 1B1 to the secondary transfer position in addition to the sheet conveyance path fed out from the sheet feeding tray 1B1. This configuration includes a manual feed tray 1A1 and a feeding roller 1A2 provided with a part of the wall surface of the image forming unit 1A that can be raised and lowered.
In the middle of the sheet conveyance path from the sheet feeding cassette 1B1 to the registration roller 1B3, the sheet conveyance path fed from the manual feed tray 1A1 joins, and the sheet fed from any conveyance path is registered by the registration roller 1B3. Timing is set.

  In the writing device 5, writing light is controlled by image information obtained by scanning a document on the document table 1C1 included in the document scanning unit 1C or image information output from a computer (not shown), and the photoconductors 4Y, 4M, Writing light corresponding to the image information is emitted to 4C and 4B to form an electrostatic latent image.

  The document scanning unit 1C is provided with a scanner 1C2 that exposes and scans the document on the document table 1C1, and an automatic document feeder 1C3 is disposed on the upper surface of the document table 1C1. The automatic document feeder 1C3 has a configuration capable of reversing the document fed on the document table 1C1, and can perform scanning on both sides of the document.

  The electrostatic latent image on the photoreceptor 3 formed by the writing device 5 is subjected to a visible image processing by the developing device 6 and is primarily transferred to the intermediate transfer belt 2. When the toner images for the respective colors are superimposed and transferred onto the intermediate transfer belt 2, the secondary transfer device 9 performs secondary transfer on the sheet all at once. The unfixed image carried on the surface of the secondly transferred sheet is fixed by the fixing device 11. The fixing device 11 will be described in detail later.

  The transport direction of the sheet that has passed through the fixing device 11 is switched by a transport path switching claw 12 disposed behind the fixing device 11. The transport path toward the paper discharge tray 13 and the reverse transport path The transport direction is selected for RP.

  In the color printer 1 having the above-described configuration, the uniformly charged photoconductor 3 is exposed and scanned by the document placed on the document placing table 1C1 or by image information from the computer. An electrostatic latent image is formed, and the electrostatic latent image is subjected to visible image processing by the developing device 6, and then the toner image is primarily transferred to the intermediate transfer belt 2.

  The toner image transferred to the intermediate transfer belt 2 is transferred as it is to the sheet fed from the paper feeding unit 1B in the case of a single color image, and the primary transfer is repeated in the case of a multicolor image. After being superposed, secondary transfer is performed on the sheet all at once. After the secondary transfer, the unfixed image is fixed by the fixing device 11, and then the sheet is fed to the paper discharge tray 13 or reversed and again toward the registration roller 1B3.

The structure of the fixing device 11 is shown in the drawings after FIG.
The fixing device 11 in this embodiment includes a pair of thermally conductive belts 14 and 14 'whose opposing stretched surfaces move in the same direction at the same speed, and on the stretched surfaces of the thermally conductive belts 14 and 14'. Nip portions N1 and N2 (see FIG. 3) capable of sandwiching the sheet are provided in at least two places in the extending direction, and one of the nip portions (N2) is configured to be able to contact and separate. For this reason, the nip portion on the stretched surface of the heat conductive belts 14 and 14 ′ is one of the nip portions (N 1) where the fixing roller 15 and the pressure roller are opposed to each other where the nip portion is always kept in contact. The other nip portion (N2) is a position where the heating rollers 16 that come in contact with each other are opposed to each other.
Among the nip portions, the other (N2) can form one nip portion at two locations on the expansion surface together with the one when the heating rollers 16 come into contact with each other. Thus, the length of contact between the stretched surfaces of the heat conductive belts 14 and 14 'can be varied.

  In FIG. 2, the fixing device 11 includes a heat conduction that faces the image carrying surface of the sheet and the opposite side of the image carrying surface, that is, the side facing the back surface of the sheet, with the sheet conveyance path therebetween. The side heat conductive belt 14 facing the image carrying surface is a fixing side belt, and the opposite side is a pressure side belt, and both the heat conductive belts 14, 14 'are provided. No. 14 'is such that the stretched surface moves in the same direction at a constant speed.

  The fixing-side heat conductive belt 14 includes a rotatable fixing roller 15 having an elastic body layer such as silicone rubber provided on the surface of a metal core and a metal core, and includes a heat source. An endless belt that is wound around the roller 16 and includes at least a support layer and a release layer in order from the side facing the roller peripheral surface, in other words, from the back surface side.

  As the support layer, a material excellent in durability due to heat resistance, mechanical strength, etc. is used. In this embodiment, a metal film such as nickel, aluminum, copper, stainless steel, polyimide (PI), polyaramid, polyamideimide Polymer resin films such as polyester and polyetheretherketone (PEEK) are used.

  As the release layer, a material having heat resistance and low surface energy is used. In this embodiment, silicone resin such as polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) is used. ), A heat-resistant rubber such as a fluororesin including a polymer resin such as tetrafluoroethylene-hexafluoropropylene copolymer (FEP), a silicone rubber, or a fluororubber. When a resin layer is used as the release layer, it is possible to ensure shape followability by elastic deformation by providing a heat-resistant rubber layer such as silicone rubber or fluorine rubber having a function as an elastic layer as an intermediate layer. it can. This property can improve heat transfer to the sheet to be fixed.

The pressure-side heat conductive belt 14 ′ is provided with an elastic body layer such as silicone rubber on the surface of a metal core, like the fixing-side heat conductive belt 14. It is composed of an endless belt that is wound around.
The pressure roller 17 has a pressure lever 18 in contact with the rotation shaft thereof, and is directed toward the fixing roller 15 by the urging of an elastic body 19 such as a spring locked to the swing end of the pressure lever 18. It is in pressure contact.

  The heating roller 16 incorporates a halogen heater 16A as a heat source, and the surface temperature of the heat conductive belts 14 and 14 ′ is controlled by a temperature control element 20 such as a thermistor in contact with the surface of the heat conductive belts 14 and 14 ′. Although the temperature control of the halogen heater 16A, which is a heat source, is executed so that the temperature becomes a predetermined temperature, in this embodiment, the temperature is maintained at the predetermined temperature regardless of the contact and separation of the heating roller 16. In FIG. 2, reference numeral 16 </ b> B indicates a member for preventing the thermal conductive belts 14, 14 ′ from shifting.

  FIG. 3 is a schematic diagram for explaining the operation of the fixing device 11 having the above-described configuration. In FIG. 3, the heating roller 16 of the fixing device 11 constantly applies a constant tension to the heat conductive belts 14 and 14 ′. A tension urging member 21 that can be maintained is provided, and a structure that can contact and separate from each other is provided.

  An operating member 23 that can reciprocate by a driving member 22 such as a solenoid is connected to the rotating shaft of the heating roller 16. When the heating roller 16 moves in a direction approaching each other, the heat conductive belts 14, 14 ′ are connected to each other. Abut. The heating rollers 16 are usually given a movement habit in a direction away from each other by an elastic body 24 such as a spring arranged between the rotation shafts.

  The expansion surfaces of the heat conductive belts 14 and 14 ′ that come into contact with each other when the heating rollers 16 approach each other are parallel to the moving direction of the sheet by defining the approaching position between the heating rollers 16. When the moving direction of the sheet coincides with the moving direction of the stretched surfaces of the heat conductive belts 14 and 14 ', the sheet can be moved straight. As a result, when the stretched surfaces of the heat conductive belts 14 and 14 'come into contact with each other, the sheet is nipped and conveyed by this stretched surface, but the direction of the conveyance path is parallel to the movement direction so far. In addition, it does not receive bending force in the middle of the conveyance path, and can move without impairing the conveyance performance.

  When the stretched surfaces of the heat conductive belts 14 and 14 'come into contact with each other and two nip portions (N1, N2) are formed in the stretch direction of the stretch surfaces, the nip portions are perpendicular to the sheet moving direction. A pressing force is applied, and the direction of action is parallel between the nip portions. As a result, the sheet conveyance path can maintain the straight conveyance property of the sheet without making the sheet movement direction different from the conveyance direction so far.

  The nip portion is configured at two locations (N1, N2) according to the contact / separation operation of the heating roller 16, and the length of the heat transfer area for the sheet nipped and conveyed by the heat conductive belts 14, 14 ′. Can be changed.

  In this embodiment, the length of the heat transfer area is set in accordance with the glossiness required for the image. In the case of a character image, the normal glossiness can be selected when the heat transfer area is short. In the case of a multicolor image, it is possible to select a case where the heat transfer area is lengthened with high glossiness.

  In this embodiment, when the length of the heat transfer region corresponding to the state in which the heat conductive belts 14 and 14 'are in contact with each other between the two nip portions is increased, the other nip portion (N2) side is used. The temperature of the toner is set in the range of Tg to Tm in the process of moving the sheet through the range where the heat conductive belts 14 and 14 'are in contact with each other, and pressure is applied to one nip portion (N1). It has become established.

  The range where the heat conductive belts 14 and 14 ′ are in contact with each other between the nip portions is located on the upstream side in the sheet moving direction with respect to the one nip portion (N 1). A preheating region is configured with respect to the region.

  The toner on the sheet is heated in the preheating region, but unlike the nip portion, the influence of pressure is small. However, since it melts in a state where the temperature is raised and the viscosity is lowered, the fixability is obtained by receiving the action of pressure at one nip portion (N1) and the glossiness is increased by raising the temperature to the glass transition point. Will be secured. Within the above temperature range, when the upper limit temperature Tm ° is exceeded, hot offset occurs depending on the releasability of the heat conductive belts 14 and 14 ′. The length of the region is desirable.

  When the heating rollers 16 are not brought into contact with each other, the above-described preheating region is not formed, so that only the amount of heat received in the fixing heating region in one nip portion (N1) is applied to the toner.

  When changing the glossiness by changing the length of the preheating area, it is only necessary to switch the amount of heat received on the unfixed image, which is a factor in changing the glossiness of the image, by the contact / separation operation of the heat conductive belt. Therefore, it is possible to eliminate the need to change the sheet moving speed, the so-called linear speed, or the temperature switching or the pressure.

Next, another embodiment relating to a configuration for changing the length of the heat transfer region in the heat conductive belts 14 and 14 'will be described with reference to FIG.
In the embodiment shown in FIG. 4, one nip portion (N 1) that is a position facing the fixing roller and the pressure roller on the stretched surface of the heat conductive belts 14 and 14 ′, and the other where the heating rollers are in contact with each other. In addition to the nip portion, a nip portion (for convenience, a nip portion indicated by N2 'in FIG. 5) is provided, and the length of the heat transfer region can be changed according to the contact / separation operation at the nip portion. It is.
In FIG. 4, between the nip portions of the heat conductive belt 14 on the fixing side and between the nip portions of the heat conductive belt 14 'on the pressure side corresponding to the fixing side, the heat conductive belts 14 and 14' are connected to each other. There are provided region setting members for contacting and separating the stretched surfaces (for convenience, members positioned on the fixing side are indicated by reference numeral 25 and members positioned on the pressing side are indicated by reference numeral 25 '). The region setting members 25 and 25 ′ can change the length of the heat transfer region on the stretched surface of the heat conductive belts 14 and 14 ′ by moving in the direction of contacting and separating from each other.

The region setting members 25 and 25 ′ are configured by rollers which are provided in contact with the back surfaces of the heat conductive belts 14 and 14 ′ and can rotate in conjunction with each other, and the heat transfer regions between the heat conductive belts 14 and 14 ′. It is a member that can reciprocate between a pressing position to be lengthened and a non-pressing position in which the length is not set. Hereinafter, a configuration related to the contact / separation operation of the region setting members 25 and 25 ′ will be described.
In FIG. 4, reference numeral 26 denotes a habit of increasing the distance between the fixing roller 15 and the pressure roller 17 with respect to the heating roller 16 while supporting the rotating shaft of the heating roller 16 by an elastic body 27 such as a spring. The shaft support member is provided so as to keep the tension of the heat conductive belts 14 and 14 'constant irrespective of the contact and separation operation of the region setting members 25 and 25'. The operation is as follows.

  When the heat conductive belts 14 and 14 'come into contact with each other due to the proximity of the region setting members 25 and 25', the opposite stretched surfaces of the heat conductive belts 14 and 14 'are changed from the straight line shown in FIG. It bulges toward the extended surface of the heat conductive belt on the other side. For this reason, the heating roller 16 receives a load in a direction in which the stretched surfaces of the heat conductive belts 14 and 14 ′ are in contact with each other. If the heating roller 16 is restricted from moving the heat conductive belts 14 and 14 'in the bulging direction, the tension of the heat conductive belts 14 and 14' changes.

  In this embodiment, as a configuration for maintaining a constant tension regardless of the contact / separation operation of the heat conductive belts 14 and 14 ', an elastic body 28 such as a spring hooked on the heating roller 16 in FIG. 4 is used. Thus, the heating roller 16 is always pulled to the opposite side to the bulging direction of the heat conductive belts 14 and 14 '. As a result, when the heat conductive belts 14 and 14 ′ are brought into contact with each other, if part of the stretched surface bulges in a direction in which they are in contact with each other, a load in the bulging direction acts on the heating roller 16. The heating roller 16 can move against the urging of the elastic body 28 to prevent an increase in tension.

  The region setting members 25 and 25 ′ are positioned on the stretched surface side of the heat conductive belts 14 and 14 ′ that are in contact with each other with respect to the heating roller 16 when the heat conductive belts 14 and 14 ′ are brought into contact with each other. It has become. Thereby, on the sheet introduction side on the extended surface, the extended surfaces protruding from the heating roller 16 constitute a wedge-shaped space.

  In the present embodiment, the position of the heating roller 16 and the approaching state so that the opening angle in the wedge-shaped space, in other words, the space where the front side of the sheet moving direction is tapered, can be set to 10 ° or more, preferably 10 to 30 °. The positions of the area setting members 25 and 25 ′ are defined. Accordingly, it is possible to prevent sheet flapping that tends to occur when the opening angle of both the heat conductive belts 14 and 14 ′ is small, and to prevent the image before fixing from being rubbed.

Since the present embodiment is configured as described above, when high glossiness is selected, the heating rollers 16 are brought close to each other so that the heat conductive belts 14 and 14 'are in contact with each other.
When the heat conductive belts 14 and 14 'come into contact with each other, as shown in FIG. 6, the preheating region L2 for the unfixed image on the sheet between the nip portions (N1, N2) and the fixing at one nip portion (N1). A heating region L1 is configured. As a result, the temperature of the toner in the unfixed image is set to Tg to Tm, and the toner layer can be sufficiently melted in the preheating region L2 to reduce the viscosity of the toner. In this state, one nip portion (N1) The glossiness of the image can be increased by applying a pressure at.

Since the length of the preheating region L2 and the length of the fixing heating region L1 are not the same, and the amount of heat received by the sheet is different due to the different mechanical conditions in each region, in order to balance the amount of received heat, It is desirable to set the length relationship between regions.
In the present embodiment, the preheating region where only the heat conductive belts 14 and 14 are in pressure contact with each other has a smaller amount of heat reception than the fixing heating region where the effects of pressure and heat are applied to each other. For this reason, the length of the heat transfer area in the preheating area is set to be 1.5 to 2.0 times the length of the heat transfer area in the fixing heating area. If the length is reduced, the arrangement positions of the region setting members 25 and 25 ′ are defined.

Next, a modified example of the configuration related to the contact / separation mechanism of the region setting members 25 and 25 ′ will be described.
In FIG. 7, one of the swinging ends of the swinging levers 29 and 29 ′ with the rotating shaft of the heating roller 16 as a fulcrum is engaged with the rotating shafts of the region setting members 25 and 25 ′.
The other of the swinging ends of the swing levers 29 and 29 ′ is connected to an actuator for the region solenoids 30 and 30 ′ serving as a region setting drive source.
The other end of the swing end is hooked with one end of a spring 31 on the side opposite to the side to which the actuator is connected. When the area solenoids 30 and 30 'are not excited, the swing lever 29 on the fixing side is shown in FIG. In FIG. 2, a habit is given to swing the pressure-side swing lever 29 'counterclockwise.

  Due to the habits of the swing levers 29 and 29 ′, the region setting members 25 and 25 ′ are arranged so that the heat conductive belts 14 and 14 ′ are in an initial state when the region solenoids 30 and 30 ′ are not excited. When the region solenoids 30 and 30 ′ are excited at positions away from each other, the heat conductive belts 14 and 14 ′ are positioned to contact each other against the habit of the spring 31.

  In the configuration shown in FIG. 7, when the region setting members 25 and 25 ′ bring the heat conductive belts 14 and 14 ′ into contact with each other, the axial center position of the heating roller 16 by the overhang of the heat conductive belts 14 and 14 ′ is automatically set. Therefore, even when the heat conductive belts 14 and 14 'are in contact with each other, the same tension as that in the non-contact state can be maintained.

  In FIG. 7, the shaft support member 26 provided on the rotating shaft of the heating roller 16 can be interlocked with an anchor member 32 having a leftward T-shape via an elastic body 27. A tension spring 33 that urges the heating roller 16 in a direction to separate the heating roller 16 from the fixing roller 15 and the pressure roller 17 is hooked between the fixed portion and the non-moving portion.

  The anchor member 32 is connected to an actuator of a tension adjusting solenoid 34 on the shaft support member side.

  The tension adjusting solenoid 34 is a drive source for reciprocating the anchor member 32 in accordance with the contact and separation of the heating roller 16, and the excitation state is set in conjunction with the operation of the area solenoids 30 and 30 '. Is done. The tension adjusting solenoid 34 is normally maintained in the non-excited state in synchronization with the non-excited timing of the region solenoids 30 and 30 '.

The tension of the heat conductive belts 14 and 14 'by the tension adjusting solenoid 34 is made constant based on the following principle.
The elastic body 27 and the tension spring 33 have an urging force in the same direction, and the urging force, that is, the elastic restoring force (P1, P2) is P1 <P2. Accordingly, when the tension adjusting solenoid 34 is not excited, the difference between the elastic force of the elastic body 27 and the tension spring 33 acts on the shaft support member 26, thereby separating the heating roller 16 from the fixing roller 15 and the pressure roller 17. Can be pulled in the direction. At this time, since the region solenoids 30 and 30 ′ are in a non-excited state, the region setting members 25 and 25 ′ are pulled away from each other by the spring 31, so that the heat conductive belts 14 and 14 ′ are loosened. A constant tension is applied without causing

  When the tension adjusting solenoid 34 is excited, a force (F) for pulling the actuator in the tension adjusting solenoid 34 is generated more than the elastic force of the elastic body 27 and the tension spring 33, so that the anchor member 32 is used for tension adjustment. Due to the difference between the attractive force (F) of the solenoid 34 and the difference in force between the elastic body 27 and the tension spring 33, the anchor member 32 moves in the direction in which the tension adjusting solenoid 34 generates the attractive force. As a result, the heating roller 16 can approach the fixing roller 15 and the pressure roller 17 side, and the heat conductive belts 14 and 14 'are slackened. , 30 'is excited so that the region setting members 25, 25' bulge in a direction in which the opposing stretched surfaces of the heat conductive belts 14, 14 'are brought into contact with each other. The tension 14 'is maintained at substantially the same tension as when the region setting members 25 and 25' do not approach each other.

  When the area solenoids 30 and 30 'and the tension adjusting solenoid 34 are excited, the area setting members 25 and 25' come close to each other, so that the heat is moved forward in the moving direction of the sheet S continuously to one nip portion N1. A preheating region is formed by contact between the conductive belts 14 and 14 '.

The region solenoids 30 and 30 'and the tension adjusting solenoid 34 are driven by the control unit shown in FIG.
In FIG. 8, the control unit 35 is constituted by a microcomputer that controls image forming processing in the image forming unit, and members related to the present embodiment are provided on the input side via an I / O interface (not shown). The thermistor 20 for detecting the temperature of the heat conductive belts 14 and 14 ', the operation panel 36, and sensors for detecting the passage of the sheet (in FIG. 5, for convenience, indicated as a sheet detection sensor) are connected to the output side. Are connected to a driving unit (collectively indicated as a driving unit in FIG. 5), region solenoids 30 and 30 ′, and tension adjusting solenoid 34 which are subjected to processing in the image forming unit.
The operation panel 36 is provided with a mode selection switch, and the mode selection switch is provided for the user to select the glossiness of the image.

The glossiness of the image is set to low glossiness (low gloss mode) as an initial characteristic, and the user can select a glossiness higher than this glossiness (high gloss mode).
The glossiness can be selected for both character images and photographic images. In particular, in the case of photographic images that often require color images, the reflectance is 20 to 30% in the low gloss mode. In the high gloss mode, a reflectance of 50 to 60% can be set.
The control unit 35 sets the nip formation state for the sheet according to the glossiness selection for each job performed on the operation panel 36, and sets the length of the heat transfer area by the heat conductive belts 14 and 14 '. It has become.

Since the present embodiment is configured as described above, the operation will be described as follows based on the flowchart of FIG. 9 showing the operation of the control unit 35.
In FIG. 9, it is determined whether or not the user has selected the high gloss mode (ST1).
When the high gloss mode is selected in step ST1, both the area solenoids 30, 30 'and the tension adjusting solenoid 34 are excited (ON) (ST2).

  When the area solenoids 30 and 30 'and the tension adjusting solenoid 34 are respectively excited, the area setting members 25 and 25' move in a direction approaching each other as shown in FIG. 14 'are brought into contact with each other. Accordingly, the shaft support member 26 of the heating roller 16 is thermally conductive so as to allow the region setting members 25, 25 ′ to bulge out the heat conductive belts 14, 14 ′ according to the displacement of the anchor member 32. The belts 14 and 14 'can be slackened, and the tension of the heat conductive belts 14 and 14' when the region setting members 25 and 25 'come close to each other can reduce the preheating region by the heat conductive belts 14 and 14'. Maintain a tension similar to that of the unconfigured initial state.

  When excitation of each solenoid is completed, in addition to one nip portion N1, a preheating region continuous to the other nip portion (indicated for convenience by N2 'in FIG. 7) is heated by the region setting members 25 and 25'. It is comprised in the contact range of conductive belts 14 and 14 ', and also the expansion surface of the side in which the sheet | seat is introduce | transduced in heat conductive belts 14 and 14' tapers toward the back from the front along the moving direction of a sheet | seat. It is considered as a conical space. As a result, the heat from the heating roller 16 reaches the preheating region, the sheet is preheated in the preheating region, and the toner temperature is brought close to the upper limit temperature T1 / 2f °.

  Along with the excitation of each solenoid, the sheet feeding is started (ST3), the image forming process is executed, and the toner image is transferred to the sheet (ST4). After the image forming process, the introduction detection sensor detects that the sheet is introduced toward the fixing device 11 (ST5). This detection is for releasing the heat conductive belts 14 and 14 'maintained in contact with each other when a sheet conveyance failure occurs in the conveyance process. Such a process is not necessarily required as long as the temperature control of the thermistor at the heating roller 16 is strict and the heat conductive belts 14 and 14 'do not overheat.

  When it is detected by the sheet detection sensor that the sheet is discharged from the fixing device 11 (ST6), the set number of sheets per job is determined (ST7), and until the set number of sheets is reached. When the contact state of the heat conductive belts 14 and 14 'is maintained and the set number of sheets is reached, the excitation states of the area solenoids 30 and 30' and the tension adjusting solenoid 34 are released to return to the initial state (ST8). The region setting members 25 and 25 'are separated from each other, and the heat conductive belts 14 and 14' are separated from each other.

  According to the embodiment as described above, when the heat conductive belts 14 and 14 'are in contact with each other to form the preheating region, the belts move in the same direction at the same speed. There is no relative speed difference, and this prevents the unfixed image from being rubbed and disturbed during fixing.

Next, another example according to the embodiment of the present invention will be described.
FIG. 10 is a schematic view of a fixing device according to another embodiment. In the embodiment shown in FIG. 10, the contact state between the belts is maintained between the nips of the heat conductive belts 14 and 14 ′. The auxiliary pressure member is provided on the back side of each belt.

  The auxiliary pressurizing members 37 and 37 ′ shown in FIG. 10 are arranged so that one nip portion N1 and the region setting members 25 and 25 ′ on the stretched surface of the heat conductive belts 14 and 14 ′ come close to each other to hold the belts 14 and 14 ′. The back pressure member 37 is composed of a back pressure member (hereinafter referred to as an auxiliary pressure member shown in FIG. 10) disposed between the other nip portion N2 ′ obtained by pressing. , 37 'are made of a material having a low coefficient of friction and low thermal conductivity, and can be brought into surface contact with substantially the entire preheating region on the back surface of the thermal conductive belts 14, 14'.

  According to the present embodiment, when heat transfer to the sheet is performed only by contact between the heat conductive belts 14 and 14 ', the heat transfer efficiency is improved by improving the adhesion between the heat conductive belts 14 and 14' and the sheet. Can be improved. In particular, the back pressure member 37 can prevent the heat conductive belts 14 and 14 'from being lifted in the preheating region and can convey and hold the sheet. It can be maintained well.

FIG. 11 is a view showing a modification of the configuration of the auxiliary pressure member, and the auxiliary pressure members 38 and 38 ′ shown in FIG. 11 are constituted by rollers. Auxiliary pressure members 38 and 38 'formed of rollers are provided in a single or plural juxtaposition in the preheating region, and nipping and conveying sheets while rotating in conjunction with the movement of the heat conductive belts 14 and 14'. Is possible.
According to the configuration shown in FIG. 11, when the auxiliary pressurizing members 38 and 38 ′ are in contact with each other, they rotate without hindering the movement of the heat conductive belts 14 and 14 ′, so that there is no difference in speed between the belts. In addition, it is possible to transmit heat in the preheating region while preventing the occurrence of the toner rubbing phenomenon.

Next, another embodiment for the preheating region will be described.
The embodiment shown in FIG. 12 is characterized in that the preheating region located between the nips of the heat conductive belts 14, 14 'is heated.

  In FIG. 12, the region setting member 25 on the side facing the unfixed image surface of the sheet S in the region setting members 25, 25 'constituting the preheating region includes a heat source 25A. Accordingly, it is possible to suppress a temperature drop that occurs when the sheet S is introduced into the heat conductive belts 14 and 14 ′ that are heated by the heating roller 16 and maintained at a temperature. That is, when the sheet is introduced into the preheating region, the temperature of the heat conductive belt that has been maintained at the temperature required for preheating until then decreases, and the heat capacity of the heat conductive belts 14 and 14 is insufficient. In particular, the heat conductive belts 14 and 14 'have a small heat capacity unlike the case where the sheets are heated by metal rollers, and therefore, when the belts come into contact with the sheets, a sudden temperature drop occurs. Therefore, in the embodiment shown in FIG. 12, the region setting member 25 is provided with a heat source 25A to prevent a temperature drop in the preheating region.

  According to this embodiment, since the region setting member 25, which is a member that can increase the length of the heat transfer region, can be used as a heating source in the preheating region, the region setting member 25 that exhibits the most significant temperature drop. , 25 ′ can prevent a shortage of heat to the unfixed image due to a decrease in temperature at the opposing contact position, thereby reducing the difference from the set temperature in the fixing heating region and increasing the glossiness. In particular, when continuous paper feeding is performed, if a plurality of sheets are fed, the temperature drop in the preheating region tends to become noticeable. However, in this embodiment, since the temperature drop is suppressed, continuous paper feeding is performed. In this case, the heat receiving state for obtaining a stable glossiness can be maintained.

  The heating structure in the preheating region is not limited to providing the heat source 25A only in one of the region setting members shown in FIG. 12 (region setting member indicated by reference numeral 25 in FIG. 12). As shown in FIG. 14, it is also possible to provide a heat source for the auxiliary pressurizing members 37 and 38 disposed in the preheating region. In this case, the heat source 37A or 38A may be incorporated in the auxiliary pressure member 37 or 38 located on the back surface of the thermal conductive belt 14 on the side actually in contact with the unfixed image. Furthermore, it is also possible to provide a heating source for the region setting member and / or the auxiliary pressure member.

Next, another example according to the embodiment of the present invention will be described.
The embodiment shown in FIG. 15 has a configuration for heating the heat conductive belt 14 in the preheating region separately from the region setting members 25 and 25 ′ or the auxiliary pressure members 37 and 38 located in the preheating region. It is characterized by.
In FIG. 15, at a position facing the image surface of the sheet in the preheating region, in the vicinity of one nip portion (N1), a position corresponding to the front of the nip portion (N1) forming the fixing heating region in the sheet moving direction. A heater 39 for radiatively heating the belt 14 from the back side of the heat conductive belt 14 facing the image surface is provided.

  In this embodiment, since the heat conductive belt 14 that has fallen due to the introduction of the sheet is heated in front of the fixing heating region, the upper limit temperature is reached immediately before reaching one nip portion (N1) that is the fixing heating region. It is possible to increase the glossiness by reducing the difference between the two and shortening the time to reach the upper limit temperature in the fixing heating region.

Next, a modification of the heating structure in the preheating region in the above embodiment will be described.
The configuration shown in FIG. 16 is that the area setting member 25 facing the unfixed image is equipped with the heat pipe 40 among the area setting members located in the other nip portion (N2) constituting the preheating area. It is a feature.
The region setting member 25 is required to have a uniform temperature distribution in the width direction corresponding to the direction perpendicular to the sheet moving direction. In particular, when feeding a small-sized sheet having a narrower width than the width of the heat conductive belts 14 and 14 ', the temperature may rise to about 230 ° C. at the end in the width direction. In such a case, there are problems such as thermal degradation of the region setting member 25, occurrence of glossiness deviation due to temperature deviation in the width direction in a large size, and further occurrence of hot offset.

  In the configuration shown in FIG. 16, the region setting member 25 that is in direct contact with the heat conductive belt 14 is configured by a heat pipe (indicated by reference numeral 40 for convenience). According to such a configuration, the temperature gradient in the width direction can be made uniform, and even when a temperature difference occurs due to a temperature drop that occurs particularly when sheets are fed continuously, the temperature gradient is uniformed. Thus, the temperature difference in the width direction can be eliminated. Further, as a modified example, although not shown, not only the region setting member 25 but also the auxiliary pressurizing member 30 can be configured similarly.

With respect to the above embodiment, the control unit 35 shown in FIG. 8 is not limited to the contact / separation control of the region setting member in the configuration shown in FIG. 7, but is not shown in FIG. It is also possible to use for the contact / separation control for the region setting member shown. Further, in each embodiment, the description is given for fixing an unfixed image carried on one side of the sheet. However, in the present invention, the case where an unfixed image exists on both sides of the sheet is also targeted. Of course it is possible.
In this case, when the fixing roller and the pressure roller have the same configuration as described in the embodiment of the present invention, the nip form is horizontal, the thin paper is transportable, and wrinkles are generated. Although not seen, it may be wound around the pressure roller side depending on the paper type during double-sided fixing. Therefore, in such a case, the rubber hardness on the fixing roller side is lowered to make it softer, or the fixing roller side is made slightly thicker so that the nip form at one nip portion is slightly pressurized in the sheet discharge direction. It is also possible to obtain the necessary heat receiving state and transportability by making it face the roller side so that the above-described winding or the like is less likely to occur.

It is a schematic diagram for explaining an example of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a schematic diagram for explaining an overall configuration of a fixing device used in the image forming apparatus illustrated in FIG. 1. FIG. 3 is a schematic diagram for explaining the operation of the fixing device shown in FIG. 2. It is a schematic diagram showing a fixing device according to another example according to the embodiment of the present invention. FIG. 5 is a schematic diagram for explaining the operation of the fixing device shown in FIG. 4. It is a schematic diagram for demonstrating the heating area | region in the operation | movement process shown in FIG. FIG. 3 is a schematic diagram for explaining a contact / separation mechanism of a region setting member used in the fixing device of the embodiment shown in FIG. 2. FIG. 3 is a block diagram illustrating a configuration of a control unit used in the fixing device according to the embodiment of the present invention. It is a flowchart for demonstrating the effect | action of the control part shown in FIG. It is a schematic diagram showing an example of an auxiliary pressure member used in the fixing device according to the embodiment of the present invention. It is a schematic diagram which shows the modification of the auxiliary | assistant pressurization member shown in FIG. FIG. 5 is a schematic diagram for explaining a heating structure in a preheating region in the fixing device shown in FIG. 4. It is a schematic diagram which shows the modification of the heating structure shown in FIG. It is a schematic diagram which shows another example of the heating structure shown in FIG. It is a schematic diagram which shows the further another example of the heating structure shown in FIG. FIG. 9 is a schematic diagram for explaining still another example of the fixing device according to the embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Color printer which is an example of image forming apparatus 2 Intermediate transfer belt 3 Photoconductor 4 Charging device 5 Writing device 6 Developing device 7 Transfer device for primary transfer 9 Transfer device for secondary transfer 11 Fixing device 14, 14 ′ Thermal conductivity Belt 15 Fixing roller 16 Heating roller 17 Pressure roller 25 Area setting member 30, 30 ′ Solenoid 37, 37 ′, 38, 38 ′ as contact / separation drive source of area setting member Auxiliary pressure member N1 Fixing roller and pressure One nip portion where the roller is always in contact N2 The other nip portion where the heating rollers come in contact with and away from each other N2 'The other nip portion where the region setting members come in contact with and away from each other L1 Fixing heating region L2 Preheating region S Sheet

Claims (23)

An apparatus for fixing an unfixed image carried on a sheet,
A pair of thermally conductive belts provided in a state in which opposing stretched surfaces move in the same direction;
A nip portion that presses a sheet sandwiched between the thermal conductive belts in at least two locations in the extending direction of the opposing extending surfaces in each of the thermal conductive belts,
One of the nip portions is always in contact with the heat conductive belts, and the other is in contact with and away from each other, and the stretched surfaces face each other according to the contact and separation state. The fixing device is characterized in that the length of the heat transfer area to the sheet to be applied can be changed. The fixing device according to claim 1.
The fixing device according to claim 1, wherein the position of the other nip portion is located upstream of the sheet in the moving direction. The fixing device according to claim 1 or 2,
A fixing device, wherein the heat conductive belt is wound around a pair of rollers to form a stretched surface, and one of the rollers has a built-in heating source to heat the heat conductive belt. The fixing device according to any one of claims 1 to 3,
The fixing device according to claim 1, wherein the heat conductive belt moves at a constant speed regardless of the contact / separation operation of the other nip portion. The fixing device according to any one of claims 1 to 3,
The fixing device according to claim 1, wherein the heat conductive belt is maintained at a constant tension regardless of the contact and separation of the other nip portion. The fixing device according to any one of claims 1 to 5,
The one nip portion and the other nip portion exert a pressing force at right angles to the moving direction of the heat conductive belt parallel to the sheet conveying direction, and the acting direction of the pressing force is parallel between both nip portions. A fixing device. The fixing device according to any one of claims 1 to 6, wherein:
Among the nip portions, the other nip portion is in contact with and separated from the sheet according to the selection of the heating state for the sheet. The fixing device according to claim 7.
The fixing device is characterized in that the heating state at the other nip portion is selected on the basis of the glossiness of an unfixed image carried on the sheet. The fixing device according to any one of claims 1 to 8,
The heat conductive belt is wound around a pair of rollers, and an area setting member capable of changing the length of the heat transfer area of the sheet by contacting and separating the facing extending surfaces between the pair of rollers. And a fixing device. The fixing device according to any one of claims 1 to 9,
The region setting member for setting the contact / separation relationship between the heat conductive belts is constituted by a roller, and the region setting roller sets a position where the heat transfer region between the heat conductive belts can be lengthened and its length. A fixing device characterized in that it can be displaced to a position where it does not. The fixing device according to claim 10.
The region setting roller forms a preheating region in the vicinity of a heat fixing region formed by one nip portion by bringing the heat conductive belts into contact with each other. The fixing device according to claim 11.
The fixing device according to claim 1, wherein the region setting roller sets a contact state between the heat conductive belts so that the preheating region can be configured continuously to the heat fixing region in the moving direction of the sheet. The fixing device according to any one of claims 8 to 12,
The fixing device, wherein the region setting member is provided with a heat source for heating the heat conductive belt. The fixing device according to any one of claims 8 to 13, wherein
An auxiliary pressurizing member is provided between the region setting member and the one nip portion to maintain the contact state between the heat conductive belts separately from the other nip portion. Fixing device to do. The fixing device according to claim 14.
The fixing device according to claim 1, wherein the auxiliary pressure member is a back pressure member disposed on and in contact with the opposite surface of the heat conductive belt. The fixing device according to claim 14.
The fixing device according to claim 1, wherein the auxiliary pressure member is constituted by a roller that is rotatable and can be contacted / separated on a surface opposite to a surface facing the heat conductive belt. The fixing device according to claim 14.
At least one of the region setting member and the auxiliary pressure member is provided with a heat source for heating the heat conductive belt. The fixing device according to claim 15.
The fixing device according to claim 1, wherein the back pressure member forming the auxiliary pressure member has a low coefficient of friction and a low thermal conductivity. The fixing device according to claim 17.
At least one of the region setting member and the auxiliary pressure member is constituted by a heat pipe that serves as a heating source itself. The fixing device according to any one of claims 9, 14 to 19,
A heat source for heating the heat conductive belt is disposed between the region setting member or the auxiliary heating member and the one nip portion in the moving direction of the heat conductive belt. Fixing device. The fixing device according to claim 20, wherein
The region setting member or the auxiliary pressure member in the moving direction of the heat conductive belt is continuously upstream of the fixing heating region formed by the one nip when the heat conductive belts are in contact with each other. A fixing device comprising a preheating region positioned.   An image forming apparatus using the fixing device according to claim 1.   23. The image forming apparatus according to claim 22, comprising a configuration capable of forming single-color and multicolor images.

Images