JP2007226009A - Fixing device and image forming apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device achieving reduction of minute offset and improvement in margin of the cleaning performance, which are attained in consideration of the problem where minute offset is reduced in a tertiary transfer fixing nip part, and to provide an image forming apparatus. <P>SOLUTION: The fixing device fixes an image on a recording medium by allowing a recording medium, such as paper, to pass through the transfer fixing nip constituted by a pressuring member opposing it and made to press-contact with a transfer fixing member. The fixing device is equipped with a means for making the difference of the linear velocity between the transfer fixing member and the pressuring member. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as an electrophotographic copying machine, a printer, a facsimile, and the like, and an image fixing apparatus used for these.

  2. Description of the Related Art Conventionally, an electrophotographic fixing device heats and fixes an unfixed toner transferred onto a recording medium while nipping and conveying the toner together with the recording medium (see, for example, [Patent Document 1] and [Patent Document 2]). . The invention of [Patent Document 1] aims to provide an image recording apparatus capable of eliminating a transfer defect and suppressing the occurrence of blur at a pre-nip portion and capable of recording a high-quality image. The recording medium is passed between the nip formed by the pressure roll and the pressure roll opposed thereto, and the toner is electrostatically transferred from the image carrier at the nip portion, and at the same time, the toner is fixed to the recording medium with high pressure by the pressure roll. Is going. In the present invention, since the toner is fixed only by pressure, there remains a problem that the fixing strength obtained is significantly lower than that of fixing by heating and melting. In addition, the transfer at the nip portion uses an electrostatic force, and in order to prevent the scattering of the toner due to the action of the electric field at the pre-nip portion, a mechanism for applying a charge to the recording medium using a recording medium conveyance roller is provided. Have. [Patent Document 2] uses an intermediate transfer member for the multiple transfer fixing device.

  At the time of heat fixing, a roller / belt is well known as a heat fixing member, and a roller, a belt, and a fixed pad are known as a pressure member which is a counterpart member for holding (for example, [Patent Document 3] uses an intermediate transfer belt as an intermediate transfer member). Such a sandwiching portion of the fixing device is called a nip. In the heat transfer at the nip, the toner surface temperature in contact with the fixing member side and the toner / recording medium interface temperature in contact with the recording medium surface are important. The former is important for image quality such as gloss, and the latter is important for adhesion to the recording medium (so-called fixability).

  Conventionally, in a general color image forming apparatus, in order to obtain sufficient gloss, the fixing unit, including a recording medium, has applied heat about 1.5 times that of a black and white image forming apparatus. For this reason, the recording medium is also heated excessively, and when a large number of images are formed at high speed, there is a problem that the heating power is insufficient, and a power supply such as 100V15A that is generally widely used cannot be used. Not only that, energy savings are very important today due to the growing interest in environmental issues in recent years. In addition, not only the user does not want the recording medium that is heated excessively, but also a problem that the recording medium adheres at the exit of the image forming apparatus has occurred.

  As one of the color image forming apparatuses for solving the above-mentioned problems, the recording medium is superposed on the toner image carrier so that the toner image on the toner image carrier is sandwiched between the toner image carrier and the recording medium. There is known a system in which a toner image sandwiched between the toner images is heated and pressed to transfer and fix the toner image on the toner image carrier onto a recording medium. Such a method is known as a so-called simultaneous transfer fixing method. In the simultaneous transfer and fixing method, the toner is sufficiently heated separately from the recording medium and then transferred and fixed on the recording medium, so that the recording medium is not given excessive heat. In addition, since the toner image is uniformly heated on the toner image carrier, the image transferred and fixed on the recording medium has a smooth surface, and high gloss with a uniform feeling.

  As one of such simultaneous transfer fixing methods, [Patent Document 4] has a method in which a heat source is provided inside the driving roller of the intermediate transfer member and a pressure member is pressed against the central transfer member to form a nip. Proposed. This is because the toner image formed on the image carrier is primarily transferred to the intermediate transfer member by electrostatic adsorption, the toner on the intermediate transfer member is heated before the nip, and the heated toner is transferred to the recording medium at the nip. It is fixed at the same time as transferring. According to this method, the secondary transfer from the intermediate transfer member to the recording medium is performed not by electrostatic force but by toner aggregation due to thermal energy. In addition to the recording medium, only the toner heating time can be set long.

  However, in the method described in [Patent Document 4], the intermediate transfer member is also heated as much as the toner heating time. Therefore, when the intermediate transfer member next enters the primary transfer region, the image carrier is also heated, Problems such as sticking and melting, and performance deterioration of the image carrier will occur.

  In view of the above problems, [Patent Document 5] proposes a tertiary transfer fixing technique. In other words, the toner image is formed on the intermediate transfer member by primary transfer in the same manner as before, but after the toner image is secondarily transferred from the intermediate transfer member onto the transfer fixing member, it is heated to the recording medium. It contacts and is fixed at the same time as the tertiary transfer. According to this method, it is possible to provide a high-quality image forming apparatus capable of lowering the temperature of the transfer and fixing member, speeding up quickly, and saving energy, and at the same time, raising the temperature of the image carrier as compared with the secondary transfer fixing method. Less overheating can be prevented.

JP-A-6-175513 Japanese Patent No. 3095480 JP 2005-189612 A JP-A-10-063121 JP 2004-145260 A

  However, in the above-described tertiary transfer fixing technology, a slight amount of toner offset in the tertiary transfer fixing unit is a problem. In the tertiary transfer fixing technology, in a process in which a toner image is heated on a transfer fixing member, the toner image aggregates while melting and forms a cluster for each block of images such as dots. Further, it becomes easy to transfer an image onto a recording medium at the time of tertiary transfer fixing. On the other hand, isolated toner (a small amount of toner) that is not clustered (aggregated), such as that found in dust or image edge portions, tends to be easily left on a transfer fixing member without being transferred to a recording medium. This tendency is particularly great when paper having a rough surface with low surface smoothness is passed. This is because the isolated toner is easily affected by the surface irregularities caused by the fibers of the recording medium and hardly contacts the concave portions of the fibers, so that it is left on the transfer and fixing member. In addition, in a halftone or isolated dot image, there is a large tendency to generate toner that does not cluster. The molten toner remaining on the transfer and fixing member in this way is offset to the rear end of the recording medium after one rotation unless it is collected by the cleaning means, and adversely affects the next formed image. This phenomenon is hereinafter referred to as a minute offset.

  As a means for solving this micro-offset problem, a cleaning means can be provided. If an offset occurs, the transfer fixing member surface layer is wiped once, that is, once in one rotation (one rotation) in order to eliminate the influence on the image. Further, it is necessary to have a performance capable of completely removing the molten toner, and depending on the paper type and image pattern of the paper passing, there is a possibility that a large load is applied to the cleaning means. For example, when outputting a large amount of an image pattern with a large amount of offset, a large load is applied to the cleaning member.

  Accordingly, the present invention has been made in view of the problem of reducing the fine offset in the tertiary transfer fixing nip portion as described above, and the fixing device and the image forming which realize the reduction of the fine offset and the improvement in the margin of the cleaning performance. An object is to provide an apparatus.

  The inventors have found that it is effective to generate a linear velocity difference between the transfer fixing member and the recording medium in the tertiary transfer fixing nip portion as a means for reducing a minute offset in the tertiary transfer fixing nip portion. By such means, it is possible to reduce the fine offset and improve the margin of cleaning performance.

  That is, the present invention forms an unfixed image on an image carrier, subsequently transfers the unfixed image to an intermediate transfer member, and then at least releases the unfixed image transferred to the intermediate transfer member. After transferring to a transfer fixing member having a layer, an unfixed image is further heated on the transfer fixing member by an external heating unit, and the transfer fixing member and a pressure member pressed against the transfer fixing member are configured. In a fixing device for fixing an image on a recording medium by passing the recording medium through a transfer fixing nip, the image forming apparatus includes means for generating a linear velocity difference between the transfer fixing member and the pressure member. And Thus, by providing a linear velocity difference between the transfer fixing member and the pressure member, a linear velocity difference is generated between the transfer fixing member and the recording medium when the recording medium enters the nip. Therefore, the chance of contact between the isolated toner and the concavo-convex portion of the fiber of the recording medium is increased, thereby reducing the offset.

  In the present invention, the friction coefficient of the pressure member surface may be higher than that of the transfer fixing member surface. As a result, the rotation of the recording medium to the pressure member side can be made more reliable, the occurrence of a difference in linear velocity between the transfer fixing member and the recording medium can be made more reliable, and the offset can be made more suitable. Reduce. Further, the pressure member surface may be provided with means for applying static electricity, and by utilizing the electrostatic attraction force to the pressure member surface, the recording medium is pressed toward the pressure member side. The accompanying rotation can be made more reliable, the difference in linear velocity between the transfer fixing member and the recording medium can be made more reliable, and the offset can be reduced more suitably. The image forming apparatus according to the present invention is characterized by using any of the fixing devices as described above, and offset in the fixing device section is reduced.

  According to the present invention, by providing a linear velocity difference between the transfer fixing member and the pressure member, it is possible to reduce a minute offset in the fixing device section.

[First Embodiment]
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows an entire image forming apparatus according to a first embodiment of the present invention. This image forming apparatus includes a transfer fixing device (209) of the present invention. An outline of the configuration and operation of a tandem type color copier as an image forming apparatus in the present embodiment will be described with reference to FIG. The color copying machine 201 is positioned below the image forming unit 201A located in the center of the apparatus main body, the transfer fixing device 209 installed at a position where the image forming unit 201A can be contacted and separated, and the image forming unit 201A A sheet feeding unit 201B and an image reading unit (not shown) are provided above the image forming unit 201A.

  An intermediate transfer belt 202 as an intermediate transfer body having a transfer surface extending in the horizontal direction is disposed in the image forming unit 201A, and the upper surface of the intermediate transfer belt 202 has a color complementary to the color separation color. A configuration for forming an image is provided. That is, the photosensitive members 204Y, 204M, 204C, and 204B as image bearing members capable of carrying an image of toners of complementary colors (yellow, magenta, cyan, and black) are juxtaposed along the transfer surface of the intermediate transfer belt 202. Has been.

  Each of the photosensitive members 204Y, 204M, 204C, and 204B is configured by a drum that can rotate in the same direction (counterclockwise direction). A writing device 206, a developing device 205, a primary transfer device 207, and a cleaning device 8 are arranged as writing means. The alphabet added to each symbol corresponds to the color of the toner as in the photoconductor. Each developing device 205 accommodates each color toner. The intermediate transfer belt 202 is configured so as to be wound around the driving roller 9 and the driven roller 10 and move in the same direction at the position facing the photoconductors 204Y, 204M, 204C, and 204B. A cleaning device 11 that cleans the surface of the intermediate transfer belt 202 is provided at a position facing the driven roller 10.

  The surface of the photoreceptor 204Y is uniformly charged by the charging device 208, and an electrostatic latent image is formed on the photoreceptor 204Y based on the image information from the image reading unit. The electrostatic latent image is visualized as a toner image by powder or liquid charged by a developing device 205Y containing yellow toner, and the toner image is a primary transfer device 207Y to which a predetermined bias is applied. As a result, primary transfer is performed on the intermediate transfer belt 202. The other photoconductors 204M, 204C, and 204B 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 202 and superimposed. The toner remaining on the photoconductor 204 after the transfer is removed by the cleaning device 8, and the electric potential of the photoconductor 204 is initialized by a neutralizing lamp (not shown) after the transfer to prepare for the next image forming process.

  A paper feed unit 201B stacks and stores paper P as a recording medium, and a paper feed roller 17 that feeds paper P in the paper feed tray 16 one by one in order from the top. And a pair of transport rollers 18 for transporting the fed paper P, and after the paper P is temporarily stopped and the oblique displacement is corrected, the leading edge of the image on the transfer fixing roller 1 and the pressure roller 2 and the transport direction A registration roller pair 19 is sent out toward the nip N at a timing when the predetermined position coincides.

  A transfer fixing device 209 is provided in the vicinity of the driving roller 9. The transfer fixing device 209 is provided with a transfer fixing roller 1 as a transfer fixing member and a pressure roller 2 as a pressure member. The transfer fixing roller 1 and the pressure roller 2 are provided opposite to each other, and the nip N Is forming. The transfer fixing roller 1 and the pressure roller 2 are pressed against each other by a pressing means (not shown) such as a spring. Further, the cleaning member 21 is pressed against the surface of the transfer fixing roller 1 with a constant pressure. The surface of the cleaning member 21 is made of resin or metal.

  The transfer fixing roller 1 includes a metal base 1a made of iron, aluminum, etc., a hard heat insulating layer 1b made of porous ceramic, glass, etc., an elastic layer 1c made of silicone rubber, etc., and a release layer 1d made of fluorine-based resin. It is formed. The metal substrate 1a preferably has a thickness of 1 mm or less in order to increase the warm-up speed. In order for the heat insulating layer 1b to have both high heat insulating performance and compressive strength that can withstand the load applied to the nip, it is desirable that the thermal conductivity is 0.1 W / mK or less and the compressive strength is 3 MPa or more. In the elastic layer 1c, the lower limit of the thickness is desirably 0.1 mm or more in order to ensure a certain surface universal hardness, and the upper limit of the thickness is desirably 0.5 mm or less in order to increase the speed of warm-up. The release layer 1d desirably has a thickness of 30 μm or less in order to ensure a constant surface layer universal hardness.

  The pressure roller 2 is formed of a metal base 2a made of iron or the like, a hard heat insulating layer 2b made of porous ceramic or glass, an elastic layer 2c made of silicone rubber or the like, and a release layer 2d made of fluorine-based resin or the like. The The metal substrate 2a preferably has a thickness of 1 mm or less in order to increase the warm-up speed. In order for the heat insulating layer 2b to have both high heat insulating performance and compressive strength that can withstand the load applied to the nip, it is desirable that the thermal conductivity is 0.1 W / mK or less and the compressive strength is 3 MPa or more. For the elastic layer 2c, the lower limit of the thickness is desirably 0.1 mm or more in order to ensure a certain surface universal hardness, and the upper limit of the thickness is desirably 0.5 mm or less for speeding up the warm-up. The release layer 2d desirably has a thickness of 30 μm or less in order to ensure a constant surface layer universal hardness.

  A drive unit that generates a linear velocity difference is provided between the transfer fixing roller 1 and the pressure roller 2 of the transfer fixing device 209. As this driving means, it is also possible to use a follower with a gear whose number of teeth has been changed, a means by a separate independent drive, or the like. FIG. 2 shows a specific example of the driving means as a schematic diagram. The drive source is a pressure roller drive motor 44a, which is transmitted to the pressure roller 2 via the pressure roller drive gear 43a and the pressure roller gear 42a. The rotation of the pressure roller 2 is transmitted to the transfer fixing roller gear 41a of the transfer fixing roller 1 through the pressure roller driving gear 42a. The pressure roller gear 42a and the transfer fixing roller gear 41a are rotated with each other, but the number of teeth is different, which can cause a difference in linear velocity between the transfer fixing roller 1 and the pressure roller 2. . Furthermore, another specific example of the driving means is shown in the schematic diagram of FIG. In FIG. 3, the transfer fixing roller 1 and the pressure roller 2 are not driven together but are driven independently. The transfer fixing roller 1 is driven from a transfer fixing roller driving motor 46 as a driving source via a transfer fixing roller gear 45, and the pressure roller 2 is driven from a pressing roller driving motor 44b as a driving source via a pressure roller gear 43b. Is done. That is, the speed of the transfer fixing roller 1 and the pressure roller 2 are controlled by different drive sources and gear pairs. In this way, the transfer fixing roller 1 and the pressure roller 2 can be rotated at different linear speeds. Further, the friction coefficient of the surface of the pressure roller 2 is higher than the friction coefficient of the surface of the transfer fixing roller 1, and when the recording medium is inserted into the nip, the recording medium is conveyed integrally with the surface of the pressure roller 2, and the recording medium A linear velocity difference is generated between the toner and the transfer fixing roller 1.

  The external heating means 14 for heating the surface layer of the transfer fixing roller 1 is composed of the heater 3 and the reflection plate 4. A heater 3 composed of a halogen heater or the like is provided in the vicinity of the outside of the fixing roller 1 and immediately before the nip. A reflection plate 4 that reflects the radiation energy from the heater 3 is provided so as to cover the heater 3, and by directing the opening toward the surface layer of the fixing roller 1, the heat energy is concentrated on the surface layer of the fixing roller 1. Only the surface layer can be efficiently heated. Further, a thermistor (not shown) provided in a non-image area for measuring the surface temperature of the transfer fixing roller 1 and a temperature controller (not shown) for controlling on / off of the heater 3 based on each surface temperature are provided. The temperature can be controlled.

  The toner 6a primarily transferred from the photoconductors 104Y, 104M, 104C, and 104B onto the intermediate transfer belt 202 is secondarily transferred onto the transfer fixing roller 1 as illustrated. The driving force of this transfer is mainly due to toner aggregation due to thermal energy received from the transfer fixing roller 1, but bias (AC, pulse, etc.) applied to the driving roller 9 by a secondary bias applying means (not shown). By applying electrostatic force to the toner, it is possible to ensure better secondary transfer properties.

  As shown in FIG. 1, the transfer fixing device 209 is covered with a heat shielding member 20 so that the image forming unit 201A is not affected by heat as much as possible. The heat shielding member 20 is made of a highly heat insulating material such as foamable resin, and has a role as a heat transfer inhibiting member that suppresses heat radiation (heat transfer) from the transfer fixing roller 1 to the intermediate transfer belt 202. Yes. The heat shielding member 20 has a shape having an opening in the secondary transfer nip so as to suppress heat radiation to the intermediate transfer belt 202 as much as possible without inhibiting secondary transfer from the intermediate transfer belt 202 to the transfer fixing roller 1. Is formed. An entrance guide plate 12 is provided at the entrance where the recording medium passes, and an exit guide plate 23 and an exit transport roller 22 are provided at the exit.

  Next, a specific operation will be described. The toner 6 a formed on the intermediate transfer belt 202 is negatively charged, and a bias is applied so that the driving roller 9 side is −0.5 kV to −2 kV, and the core metal substrate 1 a of the transfer fixing roller 1 is 0 V. And the heat received from the transfer and fixing roller 1 are sequentially transferred to the transfer and fixing roller 1. At this time, the toner 6 b on the transfer fixing roller 1 is heated to a predetermined temperature by the heater 3.

  In the process in which the recording medium P is conveyed along the entrance guide plate 12 into the transfer fixing device 209, the recording medium P is preliminarily heated by heat received from the entrance guide plate 12. The transfer fixing roller 1 and the pressure roller 2 are rotationally driven by a driving mechanism (not shown), and the recording medium P is conveyed to a nip N formed by both, and the toner image 6b heated and melted there is transferred by heat and pressure. The image is fixed and an image is formed on the recording medium.

  Further, the release layer of the transfer fixing roller 1 and the pressure roller 2 is made of a conductive fluorine resin material in which a conductive material such as carbon is dispersed or an extremely thin insulating fluorine resin material such as 10 μm, By connecting, a transfer bias can be applied between the release layers, the transfer bias can be lowered, and scattering during transfer can be suppressed.

  As described above, a process of heating only the toner 6 in advance can be sufficiently obtained, and a high surface pressure can be applied in the nip N. Therefore, the heating temperature is higher than that in the conventional method in which the toner 6 and the recording medium P are heated simultaneously. Can be lowered. In addition, by causing a linear velocity difference between the transfer fixing roller 1 and the recording medium P in the nip N, it is possible to significantly reduce the fine offset.

[Experimental example]
An experiment in the case of using black toner using the image forming apparatus corresponding to the configuration of the first embodiment was performed, and the ID of the generated offset was measured (Table 1 below; Experiments No1 to No6). The offset improvement rate with respect to the obtained linear velocity ratio is shown in the graph of FIG. As a result of the experiment, it was confirmed that the offset ID value was reduced by about 90% at maximum by causing a linear speed difference of 2%.

[Second Embodiment]
FIG. 5 shows the entire image forming apparatus according to the second embodiment of the present invention. In the second embodiment, the configuration of the transfer fixing device 209 is substantially the same as that of the first embodiment, but an electrical bias is provided between the core metal of the transfer fixing roller 1 and the core metal of the pressure roller 2. The main difference is that. By applying a high voltage of about ± 1 to 10 kV, the recording medium inserted in the nip is attracted to the pressure roller 2 side, thereby generating a linear velocity difference with the transfer fixing roller 1. it can.

  The external heating means 14 uses an induction heating type consisting of a coil 26 and a core 27 as a heating source. Correspondingly, the transfer fixing roller 1 is provided with an extremely thin heat generating layer 1e between the elastic layer 1c and the heat insulating layer 1b (boundary portion). The heat generating layer 1 e is made of a thin metal layer such as a ferromagnetic material, and generates heat due to an eddy current induced inside by a magnetic field generated from the core 17. The thickness is preferably about 200 um to 1 mm in view of the balance between the heat generation amount and the heat capacity. Accordingly, the transfer fixing member can be heated more efficiently, and the heating unit can be downsized. The external heating means 14 is not limited to this, and an electrical bias is applied between the core metal of the transfer fixing roller 1 and the core metal of the pressure roller 2, and the external heating means is of a radiant heating type. Of course, a configuration using the above may be used.

1 is a schematic diagram illustrating an image forming apparatus according to a first embodiment of the present invention. It is the schematic which shows the specific example of the drive means in this invention. It is the schematic which shows another specific example of a drive means. It is a graph which shows the experimental result using the image forming apparatus of 1st Embodiment. It is a schematic diagram which shows the image forming apparatus in the 2nd Embodiment of this invention.

Explanation of symbols

1. Transfer fixing roller (transfer fixing member)
1e ... heating layer 2 ... pressure roller (pressure member)
DESCRIPTION OF SYMBOLS 3 ... Heater 4 ... Reflective member 5 ... Shielding plate 6 ... Toner 7 ... Entrance guide 8 ... Recording medium 9 ... Intermediate transfer body support member 10 ... Support member 11 ... Cleaning member 12 ... Entrance guide plate 14 ... External heating means 16 ... Supply Paper tray 17 ... feed roller 18 ... conveying roller 19 ... registration roller 20 ... heat shielding member 21 ... cleaning member 22 ... exit conveying roller 23 ... exit guide plate 26 ... coil 27 ... core 41a ... transfer fixing roller gear 42a ... pressure roller gear 43a ... Pressure roller driving gear 43b ... Pressure roller gear 44a ... Pressure roller driving motor 44b ... Pressure roller driving motor 45 ... Transfer fixing roller gear 46 ... Transfer fixing roller driving motor 201 ... Color copier 202 ... Intermediate transfer belt (intermediate transfer belt) Transcript)
204 ... Photoconductor 209 ... Transfer fixing device N ... Nip

Claims (4)

Transfer fixing member having an unfixed image formed on an image carrier, subsequently transferring the unfixed image to an intermediate transfer member, and then transferring the unfixed image transferred to the intermediate transfer member to at least a release layer After the image is transferred to the transfer fixing member, an unfixed image is further heated by an external heating unit on the transfer fixing member, and the transfer fixing nip constituted by the transfer fixing member and a pressure member pressed against the transfer fixing member. In a fixing device for fixing an image on a recording medium by passing the recording medium,
A fixing device comprising means for generating a linear velocity difference between the transfer fixing member and the pressure member.   2. The fixing device according to claim 1, wherein a friction coefficient of the surface of the pressure member is higher than that of the surface of the transfer fixing member.   3. The fixing device according to claim 1, further comprising means for applying static electricity to the surface of the pressure member. An image forming apparatus using the fixing device according to claim 1.

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