JP2005189694A - Fixing device, fixing method and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device capable of realizing the shortening of warm-up time, being excellent in energy saving, and further restraining image deterioration caused by the shortening of operating time and the reduction of the number of operating times at the double-sided image forming time. <P>SOLUTION: The fixing device 12 is equipped with a pair of rotating bodies 13 and 14 carrying images on their surfaces, and one or a plurality of heating parts 15 heating the respective images on the rotating surfaces of a pair of rotating bodies 13 and 14, and has constitution for transferring and fixing the images on respective front and back surfaces of a recording medium P from the surfaces of a pair of rotating bodies by making the medium P pass through a nip part N between a pair of rotating bodies, and it is equipped with an intermediate transfer body 2 carrying the image on its surface, transferring the image to the surface of either 13 of a pair of rotating bodies 13 and 14, and also transferring the image to the surface 14 of the other. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a fixing device and a fixing method for fixing an unfixed image on a recording medium (hereinafter also referred to as paper or sheet), and an image forming apparatus such as a copying machine, a printer, a facsimile, and a printing machine having the fixing device. More specifically, the present invention relates to a configuration capable of forming images on both the front and back surfaces of a recording medium.

  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 heat-fixing an unfixed image that is transferred and carried on a sheet such as recording paper. it can.

  During fixing, the unfixed image is heated while nipping and transporting the sheet carrying the unfixed image, so that the developer contained in the unfixed image, in particular, the toner is melted and softened and penetrated into the sheet. Thus, the toner is fixed on the sheet.

  One of the configurations used in the fixing device is a contact between a fixing member having a built-in heat source and a pressure member, and forms a nip portion corresponding to a conveyance position and a heating position of a recording medium such as a sheet. There is a configuration. A roller or a belt is used as the fixing member, and a roller, a belt, or a fixed pad is used as the pressure member.

On the other hand, an image to be transferred includes not only a single color but also a combination of images of a plurality of colors such as full color. When fixing these images, fixing characteristics, particularly temperature characteristics, according to the image form to be transferred are important.
The temperature characteristic affects the heat transfer between the toner and the sheet, and the heat transfer varies depending on the temperature of the toner surface in contact with the fixing member and the temperature of the toner and the surface of the sheet in contact with the toner (interface temperature). Among the temperature characteristics, the surface temperature of the toner affects the glossiness required for a full-color image, and the surface temperature of the toner and the sheet in contact with the toner affects the penetration (adhesion) of the toner to the sheet.

  FIG. 5 is a diagram showing an example of a fixing structure for a full-color image. In FIG. 5, 1 has a stretched surface along the juxtaposing direction of latent image carriers A to D capable of forming images for each color. An intermediate transfer member E corresponding to the next transfer member is provided, and an image for each color is sequentially transferred to the intermediate transfer member E. The intermediate transfer member E is provided with a transfer device F as a secondary transfer member for transferring the images transferred and superimposed onto the sheet in a lump so as to face each other. It is transported toward the. The fixing device G shown in FIG. 5 employs a heat roller fixing system including a fixing roller G1 and a pressure roller G2 that can be opposed to each other to form a nip portion, and the sheet is heated by the fixing roller G1. The upper unfixed image is fixed. In recent years, the heat roller fixing method has advantages such as high heat efficiency and high speed, high heat transfer efficiency and stable fixing efficiency, and simple structure due to its use as a sheet conveyance medium. It has come to be used frequently.

  Conventionally, in a fixing device, a warm-up operation is performed until a predetermined temperature is reached. However, in the case of a full-color image, toner that is superimposed is different from the case of a single-color image such as a monochrome image. The amount of heat that is about 1.5 times greater is required due to the thick layer thickness. For this reason, the amount of heat applied to the sheet tends to increase compared to the case of a single color image, and not only the sheet is likely to fall into an overheated state, but also when a large number of full-color images are fixed at high speed, A certain power source capacity of 100 V, 15 A, etc. may cause insufficient heating power and cannot be used.

  When excessive heating occurs, the sheet itself becomes overheated, and this phenomenon does not follow the user's will when handling the sheet, but also the stacked sheets are formed when the toner causes re-softening due to overheating. Adhering to each other, the so-called stuck state is brought about, and the workability is deteriorated such that the sheet must be peeled off when the sheet is taken out.

  As a malfunction due to overheating, unlike a sheet of plain paper or the like to which toner is transferred, a sheet with a special coating treatment for preventing bleeding on the surface is erroneously used for image formation. The coating material is transferred to the fixing member by heat, so that a so-called offset is likely to occur, and the fixing member is likely to be contaminated or the sheet is wound. For this reason, extra work that is not originally required in the image forming apparatus, such as the removal work of the wound sheet and the cleaning work of the fixing member, is necessary, which is disadvantageous in terms of workability.

  Conventionally, in an apparatus using an electrophotographic image forming method, an image is electrostatically transferred to a sheet by applying an electrical bias from the back side of the sheet. Since the electrical characteristics of the sheet are likely to change depending on conditions such as characteristics (unevenness), it is possible to make the transfer quality constant when transferring the image on the latent image carrier directly or via the intermediate transfer unit. There was also a problem that an abnormal image was easily generated.

In order to solve such a problem, as shown in FIG. 6, a heat source 102 is provided inside the driving roller 101 of the intermediate transfer member 100, and a pressure member 103 is pressed against the intermediate transfer member 100 to form a nip. A method has been proposed (for example, Patent Document 1).
In FIG. 6, the toner is heated before the nip, and the heated toner is fixed to the recording medium 104 at the nip. Reference numeral 105 denotes an image carrier, and 106 denotes a primary transfer unit.
According to this method, since the secondary transfer from the intermediate transfer body 100 to the recording medium 104 such as a sheet is performed not by electrostatic force but by the heat of fixing, the transfer quality can be made constant. The toner heating time can be easily set long and can be sufficiently heated, and overheating of the recording medium can be prevented.

  One of the configurations used in the fixing device is a configuration in which a fixing member having a built-in heat source and a pressure member are brought into contact with each other to form a nip portion corresponding to the nipping / conveying position and the heating position of the sheet. . A roller or a belt is used as the fixing member, and a roller, a belt, or a fixed pad is used as the pressure member.

On the other hand, image formation includes image formation on both front and back surfaces of a sheet used as a recording medium.
As a configuration for executing image formation on both sides, for example, there is a configuration in which image transfer is simultaneously performed on both sides of a recording medium (for example, Patent Document 2).
The configuration disclosed in Patent Document 2 is as follows.
First and second transfer units that can be opposed to the front and back surfaces of the recording medium are provided. When forming an image on both sides, the image is transferred from the first transfer unit to the second transfer unit, and an image on one side is transferred. The first transfer unit holds the image on the other surface, and the temperature of each of the transfer units maintains the softening point of the toner in the image. The image transfer and fixing are simultaneously performed on both sides of the recording medium when the recording medium is passed between the transfer units using an adhesive different from the transfer.

JP-A-10-63121 (paragraph "0030" column) JP 2000-250272 A (paragraph “0048” column)

  However, in the configuration disclosed in Patent Document 1, since the intermediate transfer member is heated as much as the toner heating time and is heated in the entire layer thickness direction from the inner surface side, the intermediate transfer member is then moved to the primary transfer region. When entering, the image carrier is also heated, and problems such as toner sticking occur.

  Further, in this type of image forming apparatus, it is known that the transferability of the toner that affects the high image quality is related to the shape of the toner. From the viewpoint of improving the image quality, it is desired to optimize the toner shape. It is rare.

  On the other hand, in the configuration disclosed in Patent Document 2 mentioned above as the configuration for double-sided image formation, the first transfer unit that superimposes and transfers the image of each color during the formation of a full-color image is intermediate to the second transfer unit. Although it functions as a transfer member, since it is assumed that the intermediate transfer member is heated, heat transfer to the photosensitive member may occur when it is opposed to the photosensitive member, leading to toner fixation. is there. Therefore, as disclosed in Patent Document 2, it is necessary to cool the intermediate transfer member. However, when such a configuration is used, the size of the apparatus is increased. Further, when the fixing temperature is set by the intermediate transfer body to be cooled, the entire intermediate transfer body including the cooling means is heated, and the heat energy loss increases due to the increase in heat dissipation and heat capacity. For this reason, not only the start-up time to the fixing temperature is lengthened, but also the influence of the heat spread to the photoconductor causes a problem in the life of the apparatus. In particular, after many steps of image transfer to the first and second transfer means and further image transfer to the recording medium, the image deterioration may become remarkable. It is desirable to prevent

  The object of the present invention is to reduce the warm-up time and energy saving in the case of the above-described conventional fixing, particularly when the fixing is performed at the same time as the transfer. It is an object of the present invention to provide a fixing device, a fixing method, and an image forming apparatus capable of reducing image deterioration by shortening the number of operations.

  The invention according to claim 1 includes a pair of rotating bodies that carry images on the respective surfaces, and one or a plurality of heating units that heat the images on the rotating surfaces of the pair of rotating bodies, and the pair of rotating bodies. In a fixing device having a configuration for transferring and fixing an image from the surface of the pair of rotating bodies to the front and back surfaces of the recording medium by passing the recording medium through a nip portion between the bodies, the image can be carried on the surface. And an intermediate transfer member capable of transferring an image to one surface of the pair of rotating members and transferring an image to the other surface of the pair of rotating members.

  According to a second aspect of the present invention, in the fixing device according to the first aspect, the intermediate transfer member is configured to transfer an image to the pair of rotating members at different times in time. It is said.

  According to a third aspect of the present invention, in the fixing device according to the first or second aspect, the pair of rotating members transfers the image while facing the intermediate transfer member and heats the transferred and carried image. It is a transfer fixing means capable of transferring an image to the front and back surfaces of the recording medium introduced between the rotating members and fixing the image.

  According to a fourth aspect of the present invention, in the fixing device according to any one of the first to third aspects, the pair of rotating members are alternately opposed to an intermediate transfer member that performs image transfer to the rotating members. It is characterized in that it has a configuration and is configured to face the intermediate transfer member in a state where the relative positional relationship between the rotating members is maintained.

  According to a fifth aspect of the present invention, in the fixing device according to one of the first to fourth aspects, one of the pair of rotating bodies has a circumference set to be equal to or greater than a length of the recording medium. It is characterized by having.

  According to a sixth aspect of the present invention, in the fixing device according to any one of the first to fifth aspects, the pressure member is such that one of the pair of rotating bodies can press the recording medium against the other rotating body. And an endless belt is used as the pressure member.

  According to a seventh aspect of the present invention, in one of the first to seventh aspects, the image is transferred and fixed to the front and back surfaces of the recording medium by the fixing device.

  The invention described in claim 8 is characterized in that the fixing device according to one of claims 1 to 6 or the fixing method according to claim 7 is used in an image forming apparatus.

  According to the first to third aspects of the present invention, the intermediate transfer body capable of image transfer is provided for each of the pair of rotating bodies, and the image transfer to each rotating body is performed while being shifted in time. Unlike the case of transferring between bodies, when an image is formed on the front and back surfaces of the recording medium, images are formed on the front and back surfaces of the recording medium through transfer between the intermediate transfer body and the rotating body. Become. As a result, the number of times of transfer is reduced because the rotating bodies facing the front and back surfaces of the recording medium do not need to be transferred between the rotating bodies, and image deterioration that occurs during transfer can be prevented.

  According to the fourth aspect of the present invention, since the opposing relationship to the intermediate transfer member can be switched while the relative positional relationship between the rotating members is maintained, the state of the transfer and fixing nip constituted by both can be stabilized. Thus, it is possible to prevent the transfer failure and the fixing failure due to the change in the nip area.

  According to the fifth aspect of the present invention, since one peripheral length of the rotating body is set to be equal to or longer than the length of the recording medium, it is possible to hold an image for the sheet length used as the recording medium.

  According to the invention described in claim 6, since a belt is used as the pressure member, it is possible to prevent an increase in the size of the apparatus by obtaining a degree of freedom in the installation space unlike the case of using a roller, and unlike a roller. By making the heat capacity small, it is possible to solve the problem that a part of the image cannot be transferred corresponding to the shortening of the rise time to the fixing temperature and the length of the recording medium.

  According to the seventh and eighth aspects of the present invention, it is possible to obtain an image forming apparatus using an image transfer and fixing process that can reduce image deterioration during double-sided image formation and shorten the rise time to the fixing temperature. Become.

  The best mode for carrying out the present invention will be described below with reference to embodiments shown in the drawings.

FIG. 1 shows an image forming apparatus using a fixing device according to an embodiment of the present invention. The image forming apparatus shown in FIG. 1 is a tandem type color copying machine. The configuration and outline will be described below.
The color copying machine 1 includes an image forming unit 1A positioned at the center of the apparatus main body, a paper feeding unit 1B positioned below the image forming unit 1A, and an image reading unit (not shown) positioned above the image forming unit 1A. Have.

  An intermediate transfer belt 2 as an intermediate transfer body having a transfer surface extending in the horizontal direction is disposed in the image forming unit 1A. The upper surface of the intermediate transfer belt 2 has a color complementary to the color separation color. A configuration for forming an image is provided. That is, the photoreceptors 3Y, 3M, 3C, and 3B as image carriers capable of carrying an image with toners (yellow, magenta, cyan, and black) used as a developer having a complementary color relationship are transferred to the intermediate transfer belt 2. It is juxtaposed along the surface.

  Each of the photoconductors 3Y, 3M, 3C, and 3B is configured by a drum that can rotate in the same direction (counterclockwise direction). A writing device 5, a developing device 6, a primary transfer device 7, and a cleaning device 8 are disposed as writing means. The alphabet added to each symbol corresponds to the color of the toner as in the photosensitive member 3. Each developing device 6 accommodates each color toner.

  The intermediate transfer belt 2 is configured to be able to move in the same direction at the facing position between the driving rollers 9, 9 'and the driven rollers 10 and the photoreceptors 3Y, 3M, 3C, 3B. A cleaning device 11 for cleaning the surface of the intermediate transfer belt 2 is provided at a position facing the driven roller 10.

The surface of the photoreceptor 3Y is uniformly charged by the charging device 4, and an electrostatic latent image is formed on the photoreceptor 3Y based on image information from the image reading unit.
The electrostatic latent image is visualized as a toner image by a developing device 6Y containing yellow toner, and the toner image is primary-transferred onto the intermediate transfer belt 2 by a primary transfer device 7Y to which a predetermined bias is applied. Transcribed. The other photoconductors 3M, 3C, and 3B also form similar images only with different toner colors, and the toner images of the respective colors are sequentially transferred onto the intermediate transfer belt 2 and superimposed.

  The toner remaining on the photosensitive member 3 after the transfer is removed by the cleaning device 8, and after the transfer, the potential of the photosensitive member 3 is initialized by a neutralizing lamp (not shown) to prepare for the next image forming process. .

  The image forming unit provided with each photoconductor is selected and used in accordance with a single-color or multiple-color image forming mode, and the image forming unit corresponding to the selected image forming mode has the above-described image forming unit. The image process is to be implemented.

In the vicinity of the drive rollers 9 and 9 ′, a fixing device 12 using a pair of rotating bodies is provided.
The fixing device 12 includes a first transfer fixing roller 13 in which a roller as a rotating body is used as a transfer fixing member to which an unfixed toner image as an image on the intermediate transfer belt 2 is transferred, and a first transfer fixing roller 13. And a second transfer fixing roller 14 using a roller that is a rotating body that forms a nip portion N by being pressed against each other by a pressing means such as a spring.

  The first and second transfer fixing rollers 13 and 14 can move along an arcuate locus that can alternately face the intermediate transfer member 2 as indicated by reference numeral L1 in FIG. FIG. 1 shows a state in which the first transfer fixing roller 13 faces the intermediate transfer belt 2, and FIG. 2 shows a state in which the second transfer fixing roller 14 faces the intermediate transfer belt 2.

  The first and second transfer and fixing rollers 13 and 14 can move in a state where the relative positional relationship is maintained when moving along the above-mentioned arcuate locus, thereby transferring and fixing composed of both. It is possible to prevent the nip portion from changing.

  The first and second transfer and fixing rollers 13 and 14 can be separated from each other as shown in FIG. 2 by a pressure release mechanism (not shown). The interval is set. This interval G is an interval at which the first transfer fixing roller 13 does not come into contact with each other when the second transfer fixing roller 14 is opposed to the intermediate transfer belt 2 and is subjected to image transfer. It corresponds to. Further, the second transfer fixing roller 14 can be reversely rotated independently of the first transfer fixing roller 13, and at the time of reverse rotation, the above-described interval G is set and separated from the first transfer fixing roller 13. ing.

  The first transfer fixing roller 13 and the second transfer fixing roller 14 are made of a metal pipe 53 such as aluminum, an elastic layer having a thickness of about 0.05 to 0.5 mm provided on the surface thereof, A release layer such as PFA (perfluoroalkoxy / fluorine resin) or PTFE (polytetrafluoroethylene), which is a fluorine-based resin material having a thickness of 10 to 30 μm, is provided on the surface layer.

  The release layers of the first and second transfer and fixing rollers 13 and 14 are made of a conductive fluororesin material in which a conductive material such as carbon is dispersed, and are electrically connected to a metal pipe 53 that is a core metal. This makes it possible to apply a transfer bias between the release layers, lowering the transfer bias, and lowering the charging effect on the toner by lowering the voltage prevents the toner from repelling and scattering from the roller surface. can do. Inside the first and second transfer and fixing rollers 13 and 14, a halogen heater 15 is provided as a heating source for heating the toner image held on the roller surface layer.

The second transfer fixing roller 14 is a pressure member that can form a transfer / fixing nip portion N by being pressed against the first transfer fixing roller 13, and is pressed when an image is formed on the direction of the recording medium. It functions as a member, and functions as a member for holding a toner image when images are formed on both sides of a recording medium.
Since the second transfer fixing roller 14 functions as an image transfer member when forming an image on both sides of the recording medium, the peripheral length thereof is set to be equal to or longer than the length of the recording medium. Thereby, a part of the image transferred to the recording medium is not lost.

  Since the first transfer and fixing roller 13 is disposed on the surface side with a recording medium path fed out from a sheet feeding device to be described later, the first transfer and fixing roller 13 can receive continuous image transfer from the intermediate transfer unit belt 2. On the other hand, the second transfer fixing roller 14 is provided at a position where the image transfer cannot be received after the image transfer is once received. Therefore, unlike the first transfer / fixing roller 13, while the recording medium passes through the transfer / fixing nip N, only image transfer to the recording medium is possible, and no new image transfer is received. Therefore, image transfer over the entire back surface of the recording medium can be performed by receiving image transfer for a peripheral length range equal to or greater than the length of the recording medium in advance.

  The surface temperatures of the first and second transfer and fixing rollers 13 and 14 are monitored by temperature detection means such as a thermistor (not shown), and the halogen heater 15 is independently turned on and off via a temperature controller (not shown). The surface temperature is maintained at a predetermined temperature independently for each roller.

  On the other hand, the sheet feeding unit 1B separates and feeds the sheet P in the sheet feeding tray 16 one by one in order from the uppermost one, and the sheet feeding tray 16 in which sheets P such as sheets as recording media are stacked and stored. A feeding roller 17 that carries the fed sheet P, and a pair of conveying rollers 18 that feed the fed sheet P. After the sheet P is temporarily stopped and the skew is corrected, the leading edge of the image on the transfer fixing roller 13 and a predetermined conveying direction are set. A registration roller pair 19 is sent out toward the nip N at the timing when the position coincides.

  A toner image T (hereinafter also simply referred to as toner) that has been primarily transferred from the photoreceptors 3Y, 3M, 3C, and 3B onto the intermediate transfer belt 2 is biased (AC) by a bias applying unit (not shown). , Including superimposition of pulses and the like) and electrostatically secondary transfer to the transfer fixing roller 13.

  Although not shown, a gap which is set to be equal to or less than the thickness of the toner T is provided between the intermediate transfer belt 2 and the transfer fixing roller 13, and the intermediate transfer belt 2 and the transfer fixing roller 13 are interposed with the toner T interposed therebetween. The contact transfer method. Accordingly, the non-image portion is maintained in a non-contact state.

Since the intermediate transfer belt 2 contacts the transfer fixing roller 13 only at a portion through the toner T, the intermediate transfer belt 2 is transferred unlike the case where the intermediate transfer belt 2 is always in contact with the transfer fixing roller 13. Since direct heat from the fixing roller 13 is reduced, heat transfer from the heated intermediate transfer belt 2 to the photoreceptors 3Y, 3M, 3C, and 3B is performed as in the case where the intermediate transfer belt 2 is heated. As a result, the life of the photoreceptor can be extended.
The gap described above may be set larger than the thickness of the toner T. In this case, the heating of the intermediate transfer belt 2 can be further suppressed, and the life of the photoreceptors 3Y, 3M, 3C, 3B, etc. can be further extended. Further, energy is saved because the intermediate transfer belt 2 is not deprived of heat. However, although it is thermally stable, there is a concern that the transfer distance of the toner T becomes long and the image quality is deteriorated. Therefore, it is desirable to set an optimum value by an experiment or the like.

In FIG. 1, between the intermediate transfer belt 2 and the first and second transfer fixing rollers 13 and 14, a heat shielding member for suppressing heat radiation (heat transfer) from the transfer fixing roller 13 to the intermediate transfer belt 2 or A heat insulating plate 20 is provided as a heat transfer inhibiting member.
The heat insulating plate 20 is formed so as to suppress heat radiation to the intermediate transfer belt 2 as much as possible without inhibiting secondary transfer from the intermediate transfer belt 2 to the transfer fixing roller 13. It may be provided on either side of the apparatus main body. The heat shielding member or heat transfer restraining member in which the aggregate plate 20 is used is preferably a plate-shaped member using a material having a metallic luster with low emissivity. If it is arranged with a pinch in between, it exhibits an excellent effect in heat shielding or heat transfer inhibition. In addition, as a configuration for suppressing heat transfer, for example, a thin plate including a micro heat pipe structure known for CPU cooling such as a notebook personal computer can be used. In this case, the heat transfer suppressing member is set to a low temperature. Heat transfer can be suppressed.

  In this embodiment, as a configuration for preventing the thermal deterioration of the intermediate transfer belt 2, a position where the first transfer fixing roller 13 faces the intermediate transfer belt 2 in the circumferential direction of the intermediate transfer belt 2, and an intermediate A cooling roller 210 serving as a cooling member that can contact the intermediate transfer belt 2 and remove heat from the belt between the transfer position from the photosensitive body 3B located on the most upstream side in the moving direction of the transfer belt 2 is provided. Has been placed.

  The cooling roller 210 is made of a material having high thermal conductivity, and rotates in contact with the intermediate transfer belt 2. In the present embodiment, the heat insulating plate 20 and the cooling roller 210 are provided at the same time, but either one may be provided. According to this embodiment, the temperature of the intermediate transfer member can be reduced, and thermal deterioration on the intermediate transfer member side can be suppressed. Further, the degree of freedom in designing the transfer fixing member can be increased.

Since the present embodiment is configured as described above, the operation thereof will be described as follows.
FIG. 2 shows a case where image formation is performed on both sides of a sheet P used as a recording medium.

  In the case of duplex printing on the paper P in FIG. 2, first, an image to be transferred to the back surface of the paper P is formed. In this case, the first transfer fixing roller 13 and the second transfer fixing roller 14 move to the positions shown in FIG. That is, the first transfer fixing roller 13 is separated from the intermediate transfer belt 2 along the arcuate locus L1 (corresponding to one of the directions indicated by the arrow S in FIG. 2), and the second transfer fixing roller 14 is moved to the intermediate transfer belt 2. The intermediate transfer belt 2 is almost in contact with the intermediate transfer belt 2.

  At this time, the first transfer fixing roller 13 and the second transfer fixing roller 14 are separated by the gap G by the pressure release mechanism, and both the rollers are not rotated together.

  The toner image T formed on the intermediate transfer belt 2 is negatively charged, and a bias is applied so that the drive roller 9 side is −0.5 kV to 2 kV and the core of the second transfer fixing roller 13 is 0 V. As a result, the images are sequentially transferred to the second transfer fixing roller 13. At this time, the surface temperature of the second transfer fixing roller 13 is heated to a predetermined temperature by the halogen heater 15. The toner image T2 transferred at this time is formed so that the front and rear thereof are reversed with respect to the conveyance direction of the image finally formed on the recording medium.

When the toner image T2 transferred to the second transfer fixing roller 14 is completely held on the second transfer fixing roller 14 in a state where the second transfer fixing roller 14 is softened by the heating by the halogen heater 15, the sheet is then transferred to the sheet. An image to be transferred to the surface of P is formed.
In this case, as shown in FIG. 3, the first transfer fixing roller 13 is moved to a position facing the intermediate transfer belt 2 which is the original position, and the second transfer fixing roller 14 is also moved to the first transfer fixing roller. 13, the transfer / fixing nip portion N is formed by the second transfer fixing roller 14 once stopping rotation. Thereafter, the toner image T1 transferred to the front side of the paper P is transferred from the intermediate transfer belt 2 to the first transfer fixing roller 13 in the same manner as the case where the second transfer fixing roller 14 is targeted.

  At this time, the transfer timing of the toner image T1 to the first transfer fixing roller 13 is synchronized and pressure is applied between both rollers so that the predetermined position with the toner image T2 on the second transfer fixing roller 14 coincides. When the paper P is introduced into the nip N formed in step S1, the toner images T1 and T2 are simultaneously fixed on both sides of the paper P, respectively.

  On the other hand, when image transfer onto the surface of the paper P is performed, the fixing device 12 maintains the state shown in FIG. 3, that is, the state where the first transfer fixing roller 13 faces the intermediate transfer belt 2. The toner image is only the surface image, and the transfer is performed only to the first transfer fixing roller 13. That is, the transferred toner image T1 is fixed on the sheet P conveyed at the nip N while being heated alone on the first transfer fixing roller 13 and discharged. In this case, only the halogen heater 15 in the first transfer roller 13 is driven.

  As described above, since the process of heating only the toner image T in advance is sufficiently obtained, the heating temperature can be lowered as compared with the conventional method in which the toner T and the paper P are simultaneously heated. As a result of the experiment, it was confirmed that sufficient image quality can be obtained even when the temperature of the first transfer fixing roller 13 and the second transfer fixing roller 14 is as low as 110 to 120 ° C.

  As described above, in the conventional color image forming apparatus, in order to obtain sufficient gloss, a heat amount about 1.5 times that of the black-and-white image forming apparatus is given in consideration of the temperature drop due to the paper. For this reason, the paper is heated more than necessary, and the adhesion between the toner and the paper is increased more than necessary.

  In this embodiment, the temperature for obtaining sufficient gloss without considering the paper P can be set independently, so that the temperature (fixing set temperature) of the first transfer fixing roller 13 can be lowered. Further, not only the adhesion between the toner T and the paper is not increased more than necessary, but also the paper P is heated only by the nip N and is not excessively heated, which contributes to energy saving.

  Furthermore, when fixing is performed, either the front or back image is temporarily held on the second transfer fixing roller 14 and heated, so that the paper P passes only once through the nip N, and the both sides of the paper P are transferred. Printing is possible, and the number of times of transfer can be reduced to improve printing efficiency.

Next, another embodiment of the present invention will be described.
This embodiment is characterized in that a belt is used in place of the second transfer fixing roller 14 that can function as a pressure member for the first transfer fixing roller 13.

In FIG. 4, an endless transfer fixing belt 55 is disposed at a position facing the first transfer fixing roller 13.
The transfer fixing belt 55 is wound around the transfer roller 56 and the heating roller 57, and the transfer roller 56 is pressed against the first transfer fixing roller 13 by the pressure biasing means 21 such as a spring to form a nip N. Yes.

  The transfer roller 56 is configured by providing a metal roller such as aluminum or a rubber layer in which a conductor such as carbon is dispersed on the surface of the metal roller, and is connected to a bias applying unit (not shown).

  The transfer and fixing belt 55 has a three-layer structure. From the inside, a polyimide film as a base material is 70 μm, an elastic layer of silicon rubber is 200 μm, and the surface is coated with PFA of 20 μm. By using a conductive PFA as the release layer, similar to the configuration shown in FIG. 1, the toner is repelled from the transfer and fixing belt 55 by suppressing an inadvertent charging action on the toner, thereby causing scattering of the transfer. Can be suppressed. Further, by providing the elastic layer, the heating surface can easily follow the unevenness of the toner T and the paper when fixing at the nip N, and uneven glossiness of the image can be prevented and the image quality can be improved.

  The heating roller 57 is formed in an aluminum cylinder and can rotate following the transfer and fixing belt 55. A halogen heater 15 for heating the transfer and fixing belt 55 is provided inside the heating roller 57.

  The surface temperatures of the first transfer fixing roller 13 and the transfer fixing belt 55 are controlled by a thermistor (not shown) provided in the non-image area and a temperature controller (not shown) that controls on / off of the halogen heater 15 based on the respective surface temperatures. Each can be controlled independently. Note that the circumferential length of the transfer and fixing belt 55 is set to be equal to or longer than the length of the paper P as in the case of the second transfer and fixing roller 14 shown in FIG.

  Since the present embodiment is configured as described above, at the time of image formation on both sides of the paper P, transfer is performed from the intermediate transfer belt 2 to the first transfer fixing roller 13 as in the configuration illustrated in FIG. The transferred toner image is transferred to the transfer and fixing belt 55, and then intermediated with respect to the first transfer and fixing roller 13 at the timing when the predetermined position with respect to the toner image T2 on the transfer and fixing belt 55 coincides with the conveyance timing of the paper P. An image for the front surface of the paper P is transferred from the transfer belt 2, and when the paper P is introduced into the nip portion N, the toner images T 1 and T 2 are simultaneously transferred and fixed to the front and back surfaces of the paper P.

  Although details are not described when an image is formed on one side of the paper P, the transfer and fixing belt 55 can be separated from the first transfer and fixing roller 13.

  In the present embodiment, unlike a roller, the use of a belt having a small heat capacity makes it possible to further shorten the temperature rise time compared to the case where a roller is used. Further, since the belt can take a form corresponding to the occupied space unlike the case of the roller, the degree of freedom of layout including the space necessary for installation can be increased as compared with the case of using the roller.

  In the embodiment as described above, when the paper P is introduced, the image can be transferred and fixed on both the front and back surfaces simultaneously. Therefore, the paper is not circulated again after the surface transfer, and the first transfer fixing is performed. Since the number of times of image transfer from the member to the second transfer fixing member is only one, deterioration does not increase according to the number of transfers, and deterioration of image quality can be prevented.

1 is a schematic diagram for explaining a configuration of an image forming apparatus using a fixing device according to an embodiment of the present invention. FIG. 2 is a schematic diagram illustrating an aspect of a fixing device in the image forming apparatus illustrated in FIG. 1. FIG. 6 is a schematic diagram for explaining another aspect of the fixing device in the image forming apparatus shown in FIG. 1. FIG. 6 is a schematic diagram for explaining a main configuration of a fixing device according to another embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Color copier 2 Intermediate transfer belt 3 Photoconductor 13 1st transfer fixing roller 14 2nd transfer fixing roller 15 Halogen heater 55 Transfer fixing belt

Claims (8)

A pair of rotating bodies that carry images on the respective surfaces, and one or a plurality of heating sections that heat each image on the rotating surfaces of the pair of rotating bodies, and a recording medium in a nip portion between the pair of rotating bodies In a fixing device having a configuration in which an image is transferred and fixed on the front and back surfaces of the recording medium from the surface of the pair of rotating bodies by passing the
An intermediate transfer member capable of carrying an image on the surface and transferring an image to one surface of the pair of rotating members and transferring the image to the other surface of the pair of rotating members. A fixing device characterized by the above. The fixing device according to claim 1.
The fixing device according to claim 1, wherein the intermediate transfer member is configured to transfer an image to the pair of rotating members at different times. The fixing device according to claim 1 or 2,
The pair of rotators is a transfer fixing unit that can transfer an image facing the intermediate transfer member and heat the transferred and carried image, and a recording medium introduced between the rotators. A fixing device characterized in that image transfer and image fixing can be performed on both front and back surfaces. The fixing device according to any one of claims 1 to 3,
The pair of rotators is configured to alternately oppose an intermediate transfer body that performs image transfer to the rotators, and faces the intermediate transfer body in a state where the relative positional relationship between the rotators is maintained. A fixing device having a configuration. The fixing device according to any one of claims 1 to 4, wherein:
One of the pair of rotating bodies has a circumferential length set to be equal to or longer than the length of the recording medium. The fixing device according to any one of claims 1 to 5,
One of the pair of rotating bodies is used as a pressing member capable of pressing the recording medium against the other rotating body, and an endless belt is used as the pressing member.   8. The fixing method according to claim 1, wherein the fixing device performs image transfer and fixing to the front and back surfaces of the recording medium by a fixing device. An image forming apparatus using the fixing device according to claim 1 or the fixing method according to claim 7.

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