JP2005189693A - Fixing method, fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device with which low temperature fixing is possible and which requires a short warm-up period, is excellent in energy saving effect, gives high image quality, and is good also in the view of durability and heat efficiency, and to provide an image forming apparatus with the fixing device. <P>SOLUTION: In a primary transfer step, an image formed by a recording material on an intermediate transfer member 2 is transferred onto a first transfer fixing member 13. In a secondary transfer step, the transferred image on the first transfer fixing member 13 is further transferred onto a second transfer fixing member 14. An image formed on the intermediate transfer member 2 is transferred again onto the first transfer fixing member 13, the image on the first transfer fixing member 13 and the image on the second transfer fixing member 14 are heated, and a recording medium P is passed through a nip part N formed by the first transfer fixing member 13 and the second transfer fixing member 14 to fix the images on both sides of the recording medium P. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a fixing method for fixing an unfixed image on a recording medium (hereinafter also referred to as paper or sheet), a fixing device, and an image forming apparatus such as a copying machine, a printer, a facsimile, and a printing machine having the fixing device.

  In an image forming apparatus such as a copying machine, a facsimile, a printer, or a printing machine, a copy or a recorded material is obtained by heating and fixing an unfixed image transferred and carried on a sheet-like medium such as recording paper. be able to.

  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.

  A known document proposes a method in which a heat source is provided inside a driving roller that stretches and drives an intermediate transfer member, and a pressure member is pressed against the intermediate transfer member to form a nip (for example, , See Patent Document 1). According to this literature technique, the toner is heated before the nip, and the heated toner is fixed to the recording medium at the nip. According to this method, the secondary transfer from the intermediate transfer member to the recording medium is performed not by electrostatic force but by fixing heat. Further, the toner heating time can be set longer.

  On the other hand, in order to prevent toner scattering and paper jamming, the first intermediate transfer member and a second intermediate transfer member onto which the toner image on the first intermediate transfer member is transferred are provided. The toner image on the intermediate transfer member and the toner image transferred to the second intermediate transfer member are heated, and the toner image on the first intermediate transfer member and the toner image on the second intermediate transfer member are recorded on the recording medium. There are those that are simultaneously transferred to each of the front and back surfaces (see, for example, Patent Document 2).

  However, in the methods described in Patent Document 1 and Patent Document 2, 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. When entering the primary transfer region, the image carrier is also heated, causing problems such as toner sticking.

  Further, as in Patent Document 2, in order to prevent the toner from adhering to the image carrier, it is necessary to provide a cooling means downstream of the transfer and fixing region, which increases the size of the apparatus. In order to obtain the temperature for fixing to the paper in such a configuration, it is necessary to heat the entire intermediate transfer member including the cooling means and the like, and since heat dissipation and heat capacity are large, energy loss is large and the start-up time is It takes.

  In addition, since the intermediate transfer member is heated, heat is applied to the photosensitive member, so that the lifetime thereof is shortened. In particular, 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.

Patent 3032414 JP 2000-250272 A

  An object of the present invention is to provide a fixing method, a fixing device, and an image forming apparatus provided with the fixing device that are capable of low-temperature fixing, have a short warm-up time, are excellent in energy saving, and are excellent in terms of high image quality, durability, and thermal efficiency. Is to provide.

  Another object of the present invention is to provide a fixing device capable of improving printing efficiency and image quality while preventing the intermediate transfer member from being heated when the intermediate transfer member is used.

  Furthermore, an object of the present invention is to provide an image forming apparatus capable of saving space, improving printing efficiency and improving image quality while preventing the intermediate transfer member from being heated when the intermediate transfer member is used. That is.

The present invention has the following configuration in order to achieve the above object.
(1). The fixing device includes a pair of rotating bodies each holding an image on the surface and a heating unit that heats each image on the surface of the pair of rotating bodies, and allows the recording medium to pass through a nip portion between the pair of rotating bodies. Thus, an image is transferred and fixed on the front and back of the recording medium from the surfaces of the pair of rotating bodies.
(2). (1) In the fixing device according to (1), the pair of rotating bodies includes a first rotating body and a second rotating body, and includes an intermediate transfer body that transfers an image onto the surface of the first rotating body. The first rotating body transfers an image from the surface thereof to the surface of the second rotating body (claim 2).
(3). In the fixing device according to (1) or (2), the first rotating member is a first transfer fixing member to which an image formed on the intermediate transfer member is transferred by a recording material, and the second rotating member. The rotating body is a second transfer fixing member to which an image on the first transfer fixing member is transferred, and a first transfer means for transferring an image from the intermediate transfer body to the first transfer fixing member. A second transfer means for transferring an image from the first transfer fixing member to the second transfer fixing member, the first transfer fixing member, the second transfer fixing member, and the first transfer fixing member. The image forming apparatus includes heating means for heating the image transferred onto the transfer fixing member and the second transfer fixing member.
(4). In the image forming apparatus according to any one of (1) to (3), the circumference of the second transfer fixing member is equal to or longer than the length of the recording medium.
(5). In the image forming apparatus according to any one of (1) to (4), the second transfer fixing member is an endless belt suspended from at least the pressure member.
(6). In the image forming apparatus described in (5), the belt includes a base material, an elastic layer, and a release layer.
(7). In the fixing device according to any one of (1) to (6), the pair of rotating bodies, the first rotating body, the second rotating body, the first transfer fixing member, and the second transfer. The surface layer of the fixing member is made of a fluororesin having conductivity.
(8). In the fixing device according to any one of (3) to (7), the first transfer fixing member is an endless belt suspended on a plurality of rollers, and one of the plurality of rollers is The intermediate transfer member is opposed to the belt via the belt.
(9). In the fixing device according to any one of (1) to (8), the heating unit and the heating unit are halogen heaters provided inside the pair of rotating bodies and the transfer fixing member ( Claim 9).
(10). In the fixing device according to any one of (1) to (8), the transfer fixing member includes a base material, a heat insulating layer, a magnetic layer, an elastic layer, and a release layer, and the heating unit is electromagnetic induction heating. (Claim 10).
(11). In the fixing device according to any one of (1) to (8), the heating unit and the heating unit are halogen heaters provided outside the pair of rotating bodies and the transfer fixing member. ).
(12). (3) The fixing device according to any one of (11) to (11), further comprising temperature detection means corresponding to the first transfer fixing member and the second transfer fixing member, wherein the heating means is information on the temperature detection means. Based on the above, the first transfer fixing member and the second transfer fixing member are independently heated and controlled (claim 12).
(13). In the fixing device according to any one of (3) to (12), a pressure variable unit that varies a nip surface pressure in the nip portion formed by the first transfer fixing member and the second transfer fixing member is provided. (Claim 13).
(14). In the fixing device according to any one of (3) to (13), the recording material is a toner containing at least a binder resin, a colorant, and wax.
(15). In the fixing device described in (14), the toner has a circularity of 0.96 or more.
(16). In the fixing device described in (14) or (15), the toner has a weight average particle diameter of 2 to 6 μm.
(17). In the fixing device according to any one of (1) to (16), a cleaning member for cleaning the rotating body is provided.
(18). In the fixing device according to any one of (2) to (17), a heat shielding unit is interposed between the intermediate transfer member and the first rotating member (claim 18).
(19). An image forming apparatus including a fixing device that transfers an image formed by toner as a recording material formed on an image carrier onto a recording medium and then heat-fixes the image on the recording medium. The fixing device according to (17) is defined (claim 19).
(20). A primary transfer step of transferring an image formed of a recording material on the intermediate transfer member to a first transfer fixing member, and further transferring the transfer image on the first transfer fixing member to a second transfer fixing member A secondary transfer step, and an image formed on the intermediate transfer member is transferred again to the first transfer and fixing unit, and the image on the first transfer and fixing member and the second transfer and fixing member are transferred. A fixing method in which an image is heated and the recording medium is passed through a nip portion formed by the first transfer fixing member and the second transfer fixing member to simultaneously fix the image on both sides of the recording medium. 20).
(21). (20) In the fixing method described in (20), a heating unit that heats the first transfer fixing member and the second transfer fixing member is provided, and the second of the heating units includes the first transfer fixing member. The heating of the heating means for heating one transfer fixing member is turned off (claim 21).
(22). In the fixing method according to any one of (20) to (21), during the secondary transfer step, the temperature of the first and second transfer fixing members is set to be equal to or lower than the glass transition temperature of the recording material. .
(23). In the fixing method according to any one of (20) to (22), a nip pressure at a nip portion formed by the first transfer fixing member and the second transfer fixing member passes through the recording medium during the secondary transfer step. It is determined that the temperature is equal to or less than that during the fixing operation when paper is used (claim 23).

The invention according to claims 1 and 20 is capable of fixing at low temperature for both-side images, has a short warm-up time, is excellent in energy saving, and is excellent in terms of high image quality, durability, and thermal efficiency, fixing device, and fixing An image forming apparatus including the apparatus can be provided.
According to the second aspect of the present invention, a color image can be formed by color superposition by providing the intermediate transfer member.
According to the third aspect of the present invention, it is possible to improve the image forming efficiency for double-sided images.
According to the fourth aspect of the present invention, it is possible to form an entire image on a recording medium.
According to the fifth aspect of the present invention, it is possible to easily lengthen the image holding length by making the transfer fixing member in a belt shape as compared with the roller configuration.
According to the sixth aspect of the present invention, by providing an elastic layer on the belt, it is possible to press the toner and the unevenness of the paper so that pressurization is possible, and uneven gloss can be prevented.
According to the seventh aspect of the present invention, by providing a conductive release layer on the surface layer, by applying a bias to the surface, it becomes possible to transfer efficiently without reducing the electrostatic attraction force.
According to the eighth aspect of the present invention, the first transfer fixing member is constituted by a belt, whereby the heat capacity can be reduced and the rise time can be shortened.
According to the ninth aspect of the present invention, it is possible to provide a heating means that can be easily and easily controlled in temperature.
According to the tenth aspect of the present invention, it is possible to follow the unevenness of the recording medium by using the elastic layer and prevent uneven glossiness. Because of electromagnetic induction heating, the temperature rise time is also shortened.
According to the eleventh aspect of the invention, the temperature rise time can be shortened by direct or indirect image heating by external installation of the halogen heater.
The invention according to claim 12 can be adjusted to eliminate the difference in gloss by controlling the temperature independently on the front and back of the recording medium.
According to the thirteenth aspect of the present invention, by controlling the nip surface pressure during the secondary transfer step to be lower than that during fixing by the pressure variable means, it is possible to suppress the collapse of the toner and to suppress the image quality difference between the front and back sides.
In the invention of the fourteenth aspect, the releasability is improved by containing the wax, and the conventional release agent and the release agent coating means are not required.
According to the fifteenth aspect of the present invention, by using the toner having such a circularity, the transfer efficiency is increased, the transfer residual toner is reduced, and the paper can be prevented from being stained by the transfer residual toner.
According to the sixteenth aspect of the present invention, the temperature gradient due to heating can be reduced by reducing the toner particle diameter, and hot offset is prevented to prevent image quality deterioration. Furthermore, the area change before and after fixing can be reduced.
According to the seventeenth aspect of the present invention, it is possible to prevent the paper from being stained and improve the image quality.
The invention according to claim 18 can improve printing efficiency and image quality while preventing the intermediate transfer member from being heated. Further, the space of the image forming apparatus can be saved.

The invention according to claim 19 can provide an image forming apparatus with improved fixing quality.
According to the twenty-first aspect of the present invention, it is possible to prevent the recording material (toner viscosity) from being lowered by turning off the heating means during the secondary transfer process, and to prevent image disturbance.

  According to the twenty-second aspect of the present invention, the recording material (toner temperature) can be controlled to be equal to or lower than the melting point during the secondary transfer process, and image disturbance can be prevented.

  According to the twenty-third aspect of the present invention, the nip surface pressure during the secondary transfer step is made lower than that during fixing, thereby suppressing the collapse of the recording material (toner) and suppressing the difference in image quality between the front and back sides.

[Example 1]
First, the outline of the configuration and operation of a tandem type color copier as an image forming apparatus according to the present embodiment will be described with reference to FIG. The color copying machine 1 includes an image forming unit 1A located at the center of the apparatus main body, a paper feeding unit 1B located below the image forming unit 1A, and an image reading unit (not shown) located 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, a recording material of complementary colors (yellow (Y), magenta (M), cyan (C), black (B)), for example, a photoreceptor 3Y as an image carrier capable of carrying an image of toner, 3M, 3C, and 3B are juxtaposed along the transfer surface of the intermediate transfer belt 2.

  Here, the photoreceptors 3Y, 3M, 3C, and 3B display four photoreceptors 3 having a common configuration according to the color of the toner used, 3Y for yellow, 3C for magenta, 3C for cyan, and 3B for black. ing. In the following explanation, even if the member is expressed by a number in the text, if there are numbers in the figure indicating the member with the symbols Y, M, C, B, all of these members will be shown. Suppose you are pointing.

  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 transfer device 7, and a cleaning device 8 are arranged as writing means.

  As described above, the alphabets Y, M, C, and B added to the reference numerals 4, 5, 6, 7, and 8 in the figure correspond to the toner colors as in the photosensitive member 3. . The developing devices 6Y, 6M, 6C, and 6B contain yellow, magenta, cyan, and black color toners, respectively. The intermediate transfer belt 2 has a configuration that is wound around the driving roller 9 and the driven roller 10 and can move in the same direction at a position facing the photoconductors 3Y, 3M, 3C, and 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 primarily transferred onto the intermediate transfer belt 2 by a transfer device 7Y to which a predetermined bias is applied. The

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

  A first transfer fixing roller 13 is provided with respect to the drive roller 9 via the intermediate transfer belt 2 on one end side in the extending direction of the intermediate transfer belt 2 that is stretched between the drive roller 9 and the driven roller 10. Yes.

  The first transfer fixing roller 13 is one rotating body constituting a pair of rotating bodies, and is a first rotating body (or a first transfer fixing member). The first transfer fixing roller 13 is pressed by a second transfer fixing roller 14 as a second rotating body (or a second transfer fixing member) which is the other rotating body constituting the pair of rotating bodies. Yes.

  The paper feed unit 1D includes a paper feed tray 16 that stacks and stores paper P as a recording medium, and a paper feed roller that separates and feeds the paper P in the paper feed tray 16 one by one from the topmost one. 17, a pair of conveying rollers 18 that convey the fed paper P, and the paper P are temporarily stopped and the oblique shift is corrected, and then the images on the first transfer fixing roller 13 and the second transfer fixing roller 14 are corrected. It has a registration roller pair 19 that is sent out toward the nip portion N at a timing when the front end coincides with a predetermined position in the transport direction.

  A toner image T (hereinafter also simply referred to as toner) transferred from the photoreceptors 3Y, 3M, 3C, and 3B onto the intermediate transfer belt 2 is transferred to the driving roller 9 and the first transfer and fixing by a primary bias applying unit including a power source E1. The image is primarily transferred to the first transfer fixing roller 13 by electrostatic force by a bias (including superposition of AC, pulse, etc.) applied between the rollers.

  Here, the primary bias applying means including the power source E1, the driving roller 9, and the first transfer fixing roller 13 are examples of first transfer means for transferring the image on the intermediate transfer body 2 to the second transfer fixing roller 14. The secondary bias applying means including the power source E2 and the first transfer fixing roller 13 and the second transfer fixing roller 14 are second transfer means for transferring the image on the first transfer fixing roller 13 to the second transfer fixing roller 14. It is an example.

  As shown in FIG. 2, the gap g as the distance between the intermediate transfer belt 2 and the first transfer fixing roller 13 is set to be equal to or less than the thickness of the toner layer forming the image. That is, a contact transfer system using toner T is used, and high image quality is achieved. In this case, no contact is made in the non-image portion.

  Since the intermediate transfer belt 2 and the first transfer fixing roller 13 are in contact with each other only via the toner T, the intermediate transfer belt 2 can be prevented from being heated by the first transfer fixing roller 13, and the photosensitive members 3Y, 3M, 3C, The lifetime of 3B etc. can be lengthened. The gap g may be set larger than the thickness of the toner layer 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 deteriorates. For this reason, it is desirable to set an optimum value through experiments or the like. The toner T contains at least a binding member, a colorant, and wax. Further, when the circularity is 0.96 or more, preferably 0.98 or more, the variation in charging of the toner can be reduced and the transfer rate can be increased. Further, by using a small particle diameter toner having a weight average particle diameter of 2 to 6 μm, the temperature gradient during heating is reduced, and hot offset can be prevented.

  Furthermore, since the dot gain at the time of fixing becomes small, an image faithful to the latent image can be obtained and the image quality can be improved. Also, by adding wax internally, it is possible to eliminate a release agent such as silicone oil and oil application means for releasing the toner from the fixing member, and the size and cost of the apparatus can be reduced. .

  As shown in FIG. 1, as a heat shielding unit that suppresses heat radiation (heat transfer) from the first transfer fixing roller 13 to the intermediate transfer belt 2 between the intermediate transfer belt 2 and the first transfer fixing roller 13. The heat insulation plate 20 is provided.

  The heat insulating plate 20 is formed in a shape having an opening so as to suppress heat radiation to the intermediate transfer belt 2 as much as possible without obstructing the primary transfer from the intermediate transfer belt 2 to the first transfer fixing roller 13. The fixing device main body and the image forming apparatus main body (not shown) may be provided on either side.

  As the heat shielding means, a plate-like thing having a metallic luster with low emissivity is preferable, and an excellent effect can be obtained particularly when two metal sheets are arranged with a minute gap or a heat insulating material interposed therebetween. Moreover, when the thin plate which includes the micro heat pipe structure used for CPU cooling of a notebook personal computer is used, the heat shielding means can be kept at a low temperature and the heat transfer can be suppressed.

  In this example, the intermediate transfer belt 2 is located between the transfer portion of the intermediate transfer belt 2 with respect to the first transfer fixing roller 13 (the portion facing the first transfer fixing roller 13) and the transfer portion with respect to the most upstream photoconductor 3B. A cooling roller 210 is provided as a cooling member that removes the heat.

  The cooling roller 210 is made of a material having high thermal conductivity, and rotates in contact with the intermediate transfer belt 2. In this example, 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 example, the temperature of the intermediate transfer belt 2 can be reduced, and thermal deterioration on the intermediate transfer belt 2 side can be suppressed. Further, the degree of freedom in designing the transfer fixing member can be increased.

  A fixing device 12 is provided in the vicinity of the driving roller 9. The fixing device 12 includes a first transfer fixing roller 13 on which an unfixed toner image on the intermediate transfer belt 2 is primarily transferred. Cleaning around the first transfer fixing roller 13 as a cleaning member for cleaning the first transfer fixing roller 13 at a position in contact with the first transfer fixing roller 13 on the downstream side of the nip portion N in the rotational direction. A roller 69 is provided. The cleaning roller 69 has a structure in which felt is wound around the surface of the metal roller, and functions to remove the transfer residual toner that has passed through the nip portion N and to prevent the paper from being stained.

  The fixing device 12 is provided opposite to the first transfer fixing roller 13, forms a nip portion N, and further transfers and holds the toner image on the first transfer fixing roller 13. 14. The second transfer fixing roller 14 is pressed against the first transfer fixing roller 13 by a pressure spring 21.

  The first transfer fixing roller 13 and the second transfer fixing roller 14 have a common configuration. That is, a metal pipe-shaped metal core 53 such as aluminum, an elastic layer having a thickness of about 0.05 to 0.5 mm on the surface side, and a fluorine resin having a thickness of 10 to 30 μm on the surface side. This is a structure in which release layers such as PFA and PTFE, which are system materials, are coated in order. In the figure, these elastic layers and release layers are collectively indicated by hatching.

  A halogen heater is used as a heating means for heating the toner image (image) on the surface of each roller in the first transfer fixing roller 13 and the second transfer fixing roller 14, that is, in the hollow central portion of the core metal 53. 15 is provided. Thereby, temperature control is easy.

  Since it is necessary to hold an image for the length of the sheet, the circumferential length of the second transfer fixing roller 14 is equal to or longer than the length of the sheet. When the peripheral length of the second transfer fixing roller 14 is shorter than the paper length, the entire surface of the paper cannot be printed, but the peripheral length of the second transfer fixing roller 14 is equal to or longer than the paper length. By doing so, it is possible to form the entire image on the paper.

  Further, in order to measure the surface temperatures of the first transfer fixing roller 13 and the second transfer fixing roller 14, a thermistor (not shown) is provided as a temperature detecting means in the non-image region. A temperature controller (not shown) for controlling on / off of the halogen heater 15 based on the surface temperature of each of the transfer and fixing rollers is provided.

  Each halogen heater 15 can independently control each temperature of the first transfer fixing roller 13 and the second transfer fixing roller 14 based on temperature detection information from the thermistor. If the heating temperature and the heating time of the images on the front and back sides of the paper are different, a gloss difference occurs, but this does not cause a gloss difference on the front and back sides of the paper. It can be adjusted to eliminate the difference in gloss by controlling the temperature independently on the front and back of the paper. The temperature control of the heating means is the same in the following examples.

  As described above, in order to transfer the image on the first transfer fixing roller 13 to the second transfer fixing roller 14, the secondary bias applying means including the power source E2 is provided. The secondary bias applying means applies a bias to each core metal 53 of the first transfer fixing roller 13 and the second transfer fixing roller 14 (including superposition of AC, pulse, etc.), and applies electrostatic force to the second transfer fixing roller 14. Transcription with. In addition, the release layer of the first transfer fixing rollers 13 and 14 is made of a conductive fluorine-based resin material in which a conductive substance such as carbon is dispersed and connected to a cored bar, thereby transferring the transfer bias between the release layers. Can be applied, the transfer bias can be lowered, and scattering during transfer can be suppressed.

Next, the operation will be described.
The toner image T formed on the intermediate transfer belt 2 is negatively charged, the power supply E1 so that the driving roller 9 side is -0.5 KV to 2 KV, and the core metal 53 of the first transfer fixing roller 13 is 0 V. Is applied to the first transfer fixing roller 13 by applying a bias voltage by a primary bias applying means including

  At this time, the surface temperature of the first transfer fixing roller 13 is heated to a predetermined temperature by the halogen heater 15. In the case of single-sided printing, the transferred toner image T is fixed on the sheet P conveyed at the nip portion 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. At the time of double-sided printing, the toner image T1 on the first side is transferred from the intermediate transfer belt 2 to the first transfer fixing roller 13 as in the case of single-sided printing. The toner image T1 (image) on the first transfer / fixing roller 13 is 0V to the first transfer / fixing roller 13 and +0 to the core metal 53 of the second transfer / fixing roller 14 by the secondary bias applying means including the power source E2 at the nip N. The toner image T1 on the surface of the first transfer fixing roller 13 is transferred to the second transfer fixing roller 14 by applying a bias of .5 KV to +2 KV.

  Subsequently, the toner image T2 is transferred to the first transfer fixing roller 14 at a timing when the predetermined position coincides with the toner image T2 on the second transfer fixing roller 14, and the paper P is passed through the nip portion N. The toner images T1 and T2 are simultaneously fixed on both sides of the paper P, respectively. Here, the toner images T <b> 1 and T <b> 2 can be formed as color images by color superposition formed on the intermediate transfer belt 2.

  In addition, 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 heated at the same time. 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, the conventional color image forming apparatus gives a heat amount of about 1.5 times that of the black and white image forming apparatus in consideration of the temperature drop due to the paper in order to obtain sufficient gloss. 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 example, since the temperature for obtaining sufficient gloss can be set independently without considering the paper P, the temperature of the first transfer fixing roller 13 (fixing set temperature) can be lowered. Further, since the paper P is heated only at the nip portion N, it is not heated excessively, and the adhesion between the toner T and the paper is not increased more than necessary.

  Further, when fixing is performed with the rotating body having both the fixing function and the transfer function, the nip portion N is heated by temporarily holding either the front or back image on the second transfer fixing roller 14. When the paper P passes only once, printing on both sides of the paper P becomes possible, and image forming efficiency and printing efficiency can be improved.

  Conventionally, when performing double-sided printing, firstly fixing one side and then fixing the opposite side requires a mechanism for switching the paper passing path, which is expensive and time consuming. It was getting bigger.

  As in this example, when fixing, either the front or back image is temporarily held on the second transfer fixing member, so that the fixing device can pass both sides of the paper only once. Thus, printing (fixing) can be performed, so that the printing efficiency can be improved and the printing efficiency in double-sided printing can be improved.

[Example 2]
This example has substantially the same configuration as that of Example 1 (FIG. 1), and is different from the first example shown in FIG. 3 in the second configuration facing the first transfer fixing roller 13 in the configuration shown in FIG. Instead of the transfer fixing roller 14, an endless transfer fixing belt 55 is provided as a second rotating body, that is, a second transfer fixing member.

  The circumferential length of the transfer fixing belt 55 is set to be equal to or longer than the sheet length. When configured with a roller, the diameter of the device increases, and the rise time increases due to an increase in heat capacity. By using a belt, the length of the image can be easily held longer than the roller configuration. can do.

  The transfer fixing belt 55 is stretched around a pressure roller 56 and a heating roller 57. The pressure roller 56 forms a nip portion N via the transfer fixing belt 55. The heating roller 57 has a function of heating the transfer fixing belt 55.

  The pressure roller 56 has a rubber layer 54b in which a conductor such as carbon is dispersed on the surface of a metal roller such as aluminum or a metal roller 54a.

  The transfer and fixing belt 55 has a three-layer structure. From the inside, a polyimide film serving as a base material is 70 μm, silicon rubber as an elastic layer is 200 μm, and the surface (surface layer) is coated with 20 μm of PFA which is a fluororesin. . By making the release layer conductive PFA, a bias voltage is applied to the release layer by means of a brush or the like, thereby suppressing the scattering of the transfer without reducing the electrostatic adsorption force, thereby enabling efficient transfer. .

  When transfer is performed with a bias applied to the base material or the cored bar, an elastic layer is interposed, so that the electrostatic adsorption force is weak and the transfer efficiency is poor. However, this point is improved and the transfer efficiency is improved. In addition, by providing an elastic layer, when fixing at the nip N, the heating surface easily follows the unevenness of the toner T and the paper and pressurizes, preventing uneven glossiness of the image, and improving the image quality by preventing skin fading. it can.

  The heating roller 57 is formed of an aluminum cylinder and rotates following the transfer and fixing belt 55. Further, inside the heating roller 57, a halogen heater 15 as a heating unit for heating the transfer and fixing belt 55 and an image on the belt is provided.

  A thermistor (not shown) provided in a non-image area for measuring the surface temperatures of the first transfer fixing roller 13 and the transfer fixing belt 55 and a temperature (not shown) for controlling on / off of the halogen heater 15 based on the respective surface temperatures. A controller is provided to control the temperature independently.

  The operation is almost the same as in Example 1, and the toner image T1 on the first surface side is transferred from the intermediate transfer belt 2 to the first transfer fixing roller 13 during duplex printing. The toner image T1 on the first transfer and fixing roller 13 is 0V at the nip portion N by the secondary transfer bias applying means including the power source E2, and the pressure roller 56 on which the transfer and fixing belt 55 is stretched. When a bias of +0.5 KV to +3 KV is applied to the toner image T1, the toner image T1 on the first transfer fixing roller 13 is transferred to the transfer fixing belt 55.

  Subsequently, the toner image T2 is transferred to the first transfer and fixing roller 13 at a timing when the predetermined position coincides with the toner image Y2 on the second transfer and fixing roller 14, and the paper P is passed through the nip portion N. The toner images T1 and T2 are fixed on both sides of the paper P, respectively.

  By thus forming the first transfer and fixing member in a belt shape, the heat capacity can be reduced and the rise time can be further shortened as compared with the configuration of Example 1. Next, the example shown in FIG. 4 is obtained by adding a heat insulating roller 67 in addition to the overheating roller 57 as a roller for supporting the transfer fixing belt 55 in the example shown in FIG. In this way, by stretching the inside of the transfer fixing belt 55 with a plurality of rollers, the degree of freedom in layout can be increased.

[Example 3]
This will be described with reference to FIG. The example of FIG. 5 has a configuration in which the first transfer fixing roller 13 in the example of FIG. 4 is replaced with a first fixing member as a rotating body composed of an endless belt, specifically, the first transfer fixing belt 62. It is a thing. The first transfer fixing belt 62 is stretched around the first transfer roller 59, the first heating roller 60, and the transfer roller 61.

  The first transfer roller 59 is provided at a position facing the driving roller 9 via the transfer fixing belt 62, and the heating roller 60, downstream of the facing position in the rotation direction of the first transfer fixing belt 62. Further, a transfer roller 61 is provided on the downstream side.

  The transfer roller 61 is provided opposite to the pressure roller 56. The pressure roller 56, the heating roller 57, and the heat insulating roller 67 stretch a transfer fixing belt 55 as an endless second transfer fixing belt, and this configuration conforms to the configuration shown in FIG. The transfer roller 61 and the pressure roller 56 form a nip N via the transfer fixing belt 61 and the transfer fixing belt 55. The heating roller 57 heats the transfer fixing belt 55. Similarly, the heating roller 60 heats the transfer fixing belt 62.

  The transfer roller 61 and the pressure roller 56 have a metal roller such as aluminum or a rubber layer 54b in which a conductor such as carbon is dispersed on the surface of the metal roller 54a.

  The transfer fixing belt 62 and the transfer fixing belt 55 have a three-layer structure, and have the same configuration in which a polyimide film as a base material is 70 μm from the inside, silicon rubber of an elastic layer is 200 μm, and PFA is coated on the surface by 20 μm. is there.

  By making the release layer conductive PFA, scattering of transfer can be suppressed. In addition, by providing an elastic layer, when fixing at the nip portion N, the heating surface can easily follow the unevenness of the toner T and the paper, thereby preventing uneven glossiness of the image and improving the image quality.

  In order to transfer the image on the transfer and fixing belt 62 to the transfer and fixing belt 55, a secondary transfer bias applying means including a power source E2 is provided, and the surface layer of the transfer and fixing belt 62 and the transfer and fixing belt 55 is biased by means such as a brush. A voltage is applied.

  The first heating roller 60 is configured as an aluminum cylinder and rotates following the transfer and fixing belt 62. The heating roller 57 is similarly formed in an aluminum cylinder, and rotates following the transfer fixing belt 55.

  Inside the first heating roller 60 and the heating roller 57, a halogen heater 15 is provided as a heating means for heating the transfer and fixing belts 62 and 55, respectively. A thermistor (not shown) for measuring the surface temperature of the transfer fixing belt 62 and the transfer fixing belt 55 is 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. It is provided so that the temperature can be controlled independently.

  The toner image T1 on the intermediate transfer belt 2 is electrostatically transferred from the intermediate transfer body 2 to the transfer fixing belt 62 by a bias voltage by the primary transfer bias applying means including the power source E1.

  The toner image T1 transferred to the transfer fixing belt 62 is transferred from the transfer fixing belt 62 to the transfer fixing belt 55 by the bias voltage of the secondary transfer bias applying means including the power source E2 at the nip portion N.

  By transferring the toner image T2 to the transfer and fixing belt 62 at a predetermined timing and passing the paper P through the nip portion N, the toner images T1 and T2 are fixed on both sides of the paper P, respectively.

  In this way, the heat capacity is reduced by using a pair of rotating members facing each other, that is, the transfer and fixing belt 62 and the transfer and fixing belt 55 as a belt having a three-layer structure, and the rise time is shortened compared to the first and second examples. it can.

[Example 4]
In this example, as shown in FIG. 6, instead of the transfer fixing belt 62 in the structure shown in FIG. 5, the first transfer fixing belt 50 is wound around the first transfer roller 59 and the transfer roller 61. Instead of 55, the second transfer fixing belt 51 was wound around the pressure roller 56 and the heat insulating roller 67. Further, the first heating roller 60 is removed from the heating unit 15 and the heating roller 57 as a stretching roller. Instead, the first transfer fixing belt 50 and the second transfer fixing belt 51 are provided outside the respective belts as a heating unit. An induction coil 65 for performing electromagnetic induction heating was disposed.

  An induction coil 65 is provided at each upstream position of the nip portion N between the first transfer fixing belt 50 and the second transfer fixing belt 51. The first transfer and fixing belt 50 and the second transfer and fixing belt 51 have a four-layer structure. A polyimide film as a base material is 70 μm from the inside, a metal layer of Ag, SUS, nickel, or the like as a magnetic layer is 10 μm, elastic. The layer is coated with 200 μm of silicone rubber and 20 μm of PFA on the surface.

The magnetic layers of the first transfer fixing belt 50 and the second transfer fixing belt 51 are induction-heated by the induction coil 65, the toner image T is melted, and is fixed to the paper P at the nip portion N. In this example, since only the belt portion is heated by induction heating compared to the cases of Examples 1 to 3, there is no risk of paper ignition at the time of jam as in the case of using a halogen heater, and the heat capacity is small and the rise time is short. Can be done quickly.
[Example 5]
As shown in FIG. 7, instead of the induction coil 65 in Example 4, the position of the halogen heater 15 in Example 1 was provided so as to be radiantly heated from the outside to the upstream side of the nip portion N from the inside of the roller. In this way, the toner image T can be directly heated and the start-up time can be made almost zero, and fixing can be performed with less energy.

  This example can be applied in place of the example in which the halogen heater is provided inside the roller in each of the above examples.

[Example 6]
Each of the examples 1 to 5 described so far includes a primary transfer step of transferring an image formed of a recording material on an intermediate transfer member to a first transfer fixing member, and the first transfer. A secondary transfer step of transferring the transfer image on the fixing member to a second transfer fixing member; and an image formed on the intermediate transfer member is transferred again to the first transfer fixing portion and the first transfer fixing portion is transferred. The recording medium is heated by heating the image on the transfer fixing member and the image on the second transfer fixing member and passing the recording medium through a nip portion formed by the first transfer fixing member and the second transfer fixing member. A fixing device and an image forming apparatus execute a fixing method for simultaneously fixing images on the front and back of a medium.

  In this fixing method, in this example, in the case of Examples 1 to 5, the toner image T2 is transferred from the intermediate transfer belt 2 to the first transfer fixing roller 13 or the transfer fixing belt 62 (first transfer fixing belt 50) during duplex printing. Further, until the transfer to the second transfer fixing roller 14 or the transfer fixing belt 55 (second transfer fixing belt 51) is completed, the first transfer fixing roller 13 or the transfer fixing belt 62 (first transfer fixing belt 50) side is complete. The driving (heating) of the halogen heater 15 or the induction coil 65 is turned off, and the temperature is lower than the glass transition temperature of the toner T (claims 21 and 22).

  By doing so, secondary transfer can be performed in a state where the toner image T1 is not melted at the nip portion N, and the toner image T1 is not crushed. Therefore, image disturbance can be prevented. After the toner image T1 is secondarily transferred, both the halogen heater 15 or the induction coil 65 are driven to a predetermined temperature, thereby reducing the heating time difference between the toner image T1 and the toner image T2 and reducing the difference in gloss between the front and back sides. it can. In particular, in the configurations of Example 4 and Example 5, the heating times of the toner images T1 and T2 can be made equal to prevent the difference in gloss between the front and back sides.

[Example 7]
In this example, as shown in FIG. 8, in the configuration shown in FIG. 7, the shaft of the pressure roller 56 is installed so as to be movable by a cam 70 as a pressure variable means. The pressurizing force (nip surface pressure) is made variable.

  The above examples in FIGS. 1 to 6 are also performed in accordance with this. In other words, the cam 70 is acted on the shaft of the second transfer fixing roller 14 or the pressure roller 56 so that the pressing force (nip surface pressure) of the nip portion N is variable. The cam 70 can be arbitrarily driven by a drive source (not shown).

During secondary transfer, the cam 70 is driven to rotate, and the pressure at the nip portion N is passed through to fix the paper on both sides to a pressure of 1 to 3 kg / cm ² to 0.05 to 0.5 kgf / cm ^2. Change to low pressure. By doing this, even when the toner image T1 is always heated, even when the toner image T1 is in a semi-molten state at the time of secondary transfer, the pressure is low so that it is not crushed more than necessary, and image deterioration due to dot gain can be prevented.

  If the surface pressure at the transfer nip is high, the toner is crushed twice during the secondary transfer process and during fixing, and gloss and dot thickness are different on the front and back sides. As in this example, the crushing of the toner is suppressed by making the nip pressure variable, such as by using a cam 70 or the like to make the surface pressure during the secondary transfer process lower than that during fixing, thereby reducing the image quality difference between the front and back sides. It can be suppressed and image quality deterioration can be prevented.

  In the explanation so far, in addition to using a brush as a bias voltage applying means, a portion of the core bar is exposed and a conductive roller is contacted and rotated there, and the bearing portion of the conductive roller is constituted by a conductive member. Then, a configuration is adopted in which the fixed side of the bearing is connected to a power source.

1 is a diagram illustrating a configuration of a main part of a color image forming apparatus. It is an enlarged view of the nip part between rollers. FIG. 3 is a diagram illustrating a main configuration of a fixing device. FIG. 3 is a diagram illustrating a main configuration of a fixing device. FIG. 3 is a diagram illustrating a main configuration of a fixing device. FIG. 3 is a diagram illustrating a main configuration of a fixing device. FIG. 3 is a diagram illustrating a main configuration of a fixing device. FIG. 3 is a diagram illustrating a main configuration of a fixing device.

Explanation of symbols

13 First transfer fixing roller 14 Second transfer fixing roller 15 Halogen heater 65 Induction coil N Nip portion

Claims (23)

  A pair of rotating bodies each holding an image on the surface, and heating means for heating each image on the surface of the pair of rotating bodies, and by passing a recording medium through a nip portion between the pair of rotating bodies, A fixing device that transfers and fixes an image on the front and back of the recording medium from a pair of rotating body surfaces. The fixing device according to claim 1.
The pair of rotating bodies includes a first rotating body and a second rotating body, and includes an intermediate transfer body that transfers an image onto the surface of the first rotating body, and the first rotating body extends from the surface. A fixing device for transferring an image to a surface of the second rotating body. The fixing device according to claim 1 or 2,
The first rotator is a first transfer and fixing member to which an image formed on the intermediate transfer member is transferred by a recording material, and the second rotator is on the first transfer and fixing member. A second transfer-fixing member to which the image is transferred,
First transfer means for transferring an image from the intermediate transfer member to the first transfer fixing member;
A second transfer means for transferring an image from the first transfer fixing member to the second transfer fixing member;
The image forming apparatus includes a first transfer fixing member, a second transfer fixing member, and a heating unit that heats the images transferred onto the first transfer fixing member and the second transfer fixing member. A fixing device. The image forming apparatus according to any one of claims 1 to 3,
A fixing device, wherein a circumference of the second transfer and fixing member is equal to or longer than a length of the recording medium. The image forming apparatus according to claim 1,
The fixing device, wherein the second transfer fixing member is an endless belt suspended from at least the pressure member. The image forming apparatus according to claim 5.
The fixing device according to claim 1, wherein the belt includes a base material, an elastic layer, and a release layer. The fixing device according to claim 1,
The surface layers of the pair of rotating bodies, the first rotating body, the second rotating body, the first transfer fixing member, and the second transfer fixing member are conductive fluororesins. A fixing device. In the fixing device according to any one of claims 3 to 7,
The first transfer fixing member is an endless belt suspended on a plurality of rollers, and one of the plurality of rollers faces the intermediate transfer member via the belt. A fixing device. The fixing device according to any one of claims 1 to 8,
The fixing device, wherein the heating unit and the heating unit are halogen heaters provided inside the pair of rotating bodies and the transfer fixing member. The fixing device according to any one of claims 1 to 8,
The transfer fixing member includes a base material, a heat insulating layer, a magnetic layer, an elastic layer, and a release layer, and the heating unit is electromagnetic induction heating. The fixing device according to any one of claims 1 to 8,
The fixing device according to claim 1, wherein the heating unit and the heating unit are a halogen heater provided outside the pair of rotating bodies and the transfer fixing member. The fixing device according to any one of claims 3 to 11,
Temperature detecting means corresponding to the first transfer fixing member and the second transfer fixing member is provided, and the heating means is the first transfer fixing member and the second transfer fixing member based on information of the temperature detection means. The fixing device is characterized in that the heating is controlled independently of each other. The fixing device according to any one of claims 3 to 12,
A fixing device comprising: a variable pressure means for varying a nip surface pressure in the nip portion formed by the first transfer fixing member and the second transfer fixing member. The fixing device according to claim 3,
The fixing device, wherein the recording material is a toner containing at least a binder resin, a colorant, and wax. The fixing device according to claim 14.
The fixing device according to claim 1, wherein the toner has a circularity of 0.96 or more. The fixing device according to claim 14 or 15,
The fixing device according to claim 1, wherein the toner has a weight average particle diameter of 2 to 6 μm. The fixing device according to claim 1,
A fixing device comprising a cleaning member for cleaning the rotating body. The fixing device according to claim 2,
A fixing device, wherein a heat shielding means is interposed between the intermediate transfer member and the first rotating member. In an image forming apparatus comprising a fixing device that heats and fixes the image on the recording medium after transferring an image formed by toner as a recording material formed on the image carrier to the recording medium.
An image forming apparatus, wherein the fixing device is the fixing device according to claim 1.   A primary transfer step of transferring an image formed of a recording material on the intermediate transfer member to a first transfer fixing member, and further transferring the transfer image on the first transfer fixing member to a second transfer fixing member A secondary transfer step, and an image formed on the intermediate transfer member is transferred again to the first transfer and fixing unit, and the image on the first transfer and fixing member and the second transfer and fixing member are transferred. A fixing method comprising fixing an image simultaneously on the front and back of the recording medium by heating the image and passing the recording medium through a nip portion formed by the first transfer fixing member and the second transfer fixing member. . The fixing method according to claim 20, wherein
A heating unit for heating the first transfer fixing member and the second transfer fixing member is provided, and a heating unit for heating the first transfer fixing member among the heating units in the secondary transfer step. The fixing method is characterized by turning off the heating. The fixing method according to claim 20 to 21, wherein
In the secondary transfer step, the temperature of the first and second transfer fixing members is equal to or lower than the glass transition temperature of the recording material. The fixing method according to any one of claims 20 to 22.
A nip pressure of a nip portion formed by the first transfer fixing member and the second transfer fixing member is equal to or lower than that during a fixing operation when the recording medium is passed in the secondary transfer step. Fixing method to do.

Images