JP2018097118A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device that can control glossiness of an image formed on a recording material without causing an adverse effect, and an image forming apparatus.SOLUTION: A fixing device comprises: an upper pressure roller that is opposed to an upper face of a recording material; a lower pressure roller that is opposed to the upper pressure roller to form a fixing nip and has a higher hardness than that of the upper pressure roller; a driving source that drives at least one of the upper pressure roller and lower pressure roller; and a control part that controls glossiness of a toner image formed on the recording material by controlling the rotations of the upper pressure roller and lower pressure roller so as to generate a difference in driving force between the upper pressure roller and lower pressure roller.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a fixing device and an image forming apparatus.

  2. Description of the Related Art Conventionally, in an electrophotographic image forming apparatus (a copying machine, a printer, a facsimile, or a complex machine of these) that forms a toner image on a sheet, there is a fixing device for heating and fixing the toner image formed on the sheet. Is provided. In such a fixing device, for example, the toner image formed on the paper is fixed by conveying the paper while pressing and heating the paper at a fixing nip formed by an upper fixing member such as a roller and a lower fixing member.

  As a technique for controlling the gloss of a toner image formed on a sheet by a fixing device, for example, a technique described in Patent Document 1 is known. In the technique described in Patent Document 1, the width of the fixing nip, that is, the area of the portion that presses the sheet is changed by changing the load of the fixing nip.

JP 2010-256696 A

  However, in the case of a configuration in which the load on the fixing nip is changed as in the technique described in Patent Document 1, control for increasing the load on the fixing nip is performed when the gloss of the toner image is increased. Such control is performed. There is a problem that the durability of the fixing member forming the fixing nip is lowered.

  In addition, as another configuration for controlling the gloss of the toner image formed on the paper by the fixing device, it is conceivable to increase the gloss of the toner image by controlling the paper conveyance speed. There is a problem that decreases.

  Further, as another configuration for controlling the gloss of the toner image formed on the sheet by the fixing device, it is conceivable to increase the gloss of the toner image by performing a control for raising the fixing temperature. There is a concern that this will occur.

  An object of the present invention is to provide a fixing device and an image forming apparatus capable of controlling the gloss of an image formed on a recording material without causing side effects.

The fixing device according to the present invention includes:
An upper pressure roller facing the upper surface of the recording material;
A fixing nip is formed facing the upper pressure roller, a lower pressure roller having a higher hardness than the upper pressure roller,
A drive source for driving at least one of the upper pressure roller or the lower pressure roller;
The gloss of the toner image formed on the recording material by controlling the rotation of the upper pressure roller and the lower pressure roller so that a difference occurs in the driving force between the upper pressure roller and the lower pressure roller. And a control unit for controlling.

An image forming apparatus according to the present invention includes:
An image forming unit for forming a toner image on a recording material;
A fixing device as described above;
Is provided.

  According to the present invention, it is possible to control the gloss of an image formed on a recording material without causing side effects.

1 is a diagram schematically illustrating an overall configuration of an image forming apparatus according to an exemplary embodiment. FIG. 3 is a diagram illustrating a main part of a control system of the image forming apparatus according to the present embodiment. FIG. 3 is a diagram illustrating a configuration of a fixing device. 4A and 4B are diagrams schematically illustrating a shape of a fixing nip of the fixing device, in which FIG. 4A shows a deformed state of the fixing nip in the case of lower side driving, and FIG.

  Hereinafter, the present embodiment will be described in detail with reference to the drawings. FIG. 1 is a diagram schematically showing an overall configuration of an image forming apparatus 1 according to an embodiment of the present invention. FIG. 2 shows the main part of the control system of the image forming apparatus 1 in the present embodiment. An image forming apparatus 1 shown in FIGS. 1 and 2 is an intermediate transfer type color image forming apparatus using electrophotographic process technology. That is, the image forming apparatus 1 primarily transfers the Y (yellow), M (magenta), C (cyan), and K (black) toner images formed on the photosensitive drum 413 to the intermediate transfer belt 421. After the four color toner images are superimposed on the intermediate transfer belt 421, the toner images are formed by performing secondary transfer onto the paper S.

  Further, in the image forming apparatus 1, the photosensitive drums 413 corresponding to the four colors of YMCK are arranged in series in the running direction of the intermediate transfer belt 421, and the respective color toner images are sequentially transferred to the intermediate transfer belt 421 in one step. Tandem system is adopted.

  As illustrated in FIG. 2, the image forming apparatus 1 includes an image reading unit 10, an operation display unit 20, an image processing unit 30, an image forming unit 40, a paper transport unit 50, a fixing unit 60, and a control unit 100.

  The control unit 100 includes a CPU (Central Processing Unit) 101, a ROM (Read Only Memory) 102, a RAM (Random Access Memory) 103, and the like. The CPU 101 reads a program corresponding to the processing content from the ROM 102 and develops it in the RAM 103, and centrally controls the operation of each block of the image forming apparatus 1 in cooperation with the developed program. At this time, various data stored in the storage unit 72 is referred to. The storage unit 72 includes, for example, a nonvolatile semiconductor memory (so-called flash memory) or a hard disk drive.

  The control unit 100 transmits and receives various data to and from an external device (for example, a personal computer) connected to a communication network such as a LAN (Local Area Network) or a WAN (Wide Area Network) via the communication unit 71. Do. For example, the control unit 100 receives image data transmitted from an external device, and forms a toner image on the paper S based on the image data (input image data). The communication unit 71 is composed of a communication control card such as a LAN card, for example.

  The image reading unit 10 includes an automatic document feeder 11 called an ADF (Auto Document Feeder), a document image scanning device 12 (scanner), and the like.

  The automatic document feeder 11 transports the document D placed on the document tray by a transport mechanism and sends it out to the document image scanning device 12. The automatic document feeder 11 can continuously read images (including both sides) of a large number of documents D placed on a document tray all at once.

  The document image scanning device 12 optically scans a document conveyed on the contact glass from the automatic document feeder 11 or a document placed on the contact glass, and reflects light from the document to a CCD (Charge Coupled Device). ) An image is formed on the light receiving surface of the sensor 12a, and an original image is read. The image reading unit 10 generates input image data based on the reading result by the document image scanning device 12. The input image data is subjected to predetermined image processing in the image processing unit 30.

  The operation display unit 20 is configured by, for example, a liquid crystal display (LCD) with a touch panel, and functions as the display unit 21 and the operation unit 22. The display unit 21 displays various operation screens, an image status display, an operation status of each function, and the like in accordance with a display control signal input from the control unit 100. The operation unit 22 includes various operation keys such as a numeric keypad and a start key, receives various input operations by the user, and outputs an operation signal to the control unit 100.

  The image processing unit 30 includes a circuit that performs digital image processing on input image data according to initial settings or user settings. For example, the image processing unit 30 performs gradation correction based on the gradation correction data (gradation correction table) under the control of the control unit 100. Further, the image processing unit 30 performs various correction processes such as color correction and shading correction, a compression process, and the like on the input image data in addition to the gradation correction. The image forming unit 40 is controlled based on the image data subjected to these processes.

  The image forming unit 40 is based on the input image data, and image forming units 41Y, 41M, 41C, 41K, and an intermediate transfer unit 42 for forming an image using colored toners of Y component, M component, C component, and K component. Etc.

  The Y component, M component, C component, and K component image forming units 41Y, 41M, 41C, and 41K have the same configuration. For convenience of illustration and description, common components are denoted by the same reference numerals, and in order to distinguish each, Y, M, C, or K is added to the reference numerals. In FIG. 1, only the components of the Y-component image forming unit 41Y are denoted by reference numerals, and the constituent elements of the other image forming units 41M, 41C, and 41K are omitted.

  The image forming unit 41 includes an exposure device 411, a developing device 412, a photosensitive drum 413, a charging device 414, a drum cleaning device 415, and the like.

  The photosensitive drum 413 has, for example, an undercoat layer (UCL), a charge generation layer (CGL), a charge transport layer (CGL) on the peripheral surface of an aluminum conductive cylinder (aluminum tube). It is a negatively charged organic photoreceptor (OPC: Organic Photo-conductor) in which CTL (Charge Transport Layer) is sequentially laminated. The charge generation layer is made of an organic semiconductor in which a charge generation material (for example, phthalocyanine pigment) is dispersed in a resin binder (for example, polycarbonate), and generates a pair of positive charges and negative charges by exposure by the exposure device 411. The charge transport layer consists of a material in which a hole transport material (electron donating nitrogen-containing compound) is dispersed in a resin binder (for example, polycarbonate resin), and transports positive charges generated in the charge generation layer to the surface of the charge transport layer. To do.

  The control unit 100 controls the drive current supplied to a drive motor (not shown) that rotates the photosensitive drum 413 to rotate the photosensitive drum 413 at a constant peripheral speed.

  The charging device 414 uniformly charges the surface of the photoconductive drum 413 to a negative polarity. The exposure device 411 is composed of, for example, a semiconductor laser, and irradiates the photosensitive drum 413 with laser light corresponding to the image of each color component. A positive charge is generated in the charge generation layer of the photosensitive drum 413 and is transported to the surface of the charge transport layer, whereby the surface charge (negative charge) of the photosensitive drum 413 is neutralized. An electrostatic latent image of each color component is formed on the surface of the photosensitive drum 413 due to a potential difference from the surroundings.

  The developing device 412 is, for example, a two-component developing type developing device, and forms a toner image by visualizing the electrostatic latent image by attaching toner of each color component to the surface of the photosensitive drum 413.

  The drum cleaning device 415 includes a drum cleaning blade that is slidably contacted with the surface of the photosensitive drum 413, and removes transfer residual toner remaining on the surface of the photosensitive drum 413 after primary transfer.

  The intermediate transfer unit 42 includes an intermediate transfer belt 421, a primary transfer roller 422, a plurality of support rollers 423, a secondary transfer roller 424, a belt cleaning device 426, and the like.

  The intermediate transfer belt 421 is an endless belt, and is stretched around a plurality of support rollers 423 in a loop shape. At least one of the plurality of support rollers 423 is configured by a driving roller, and the other is configured by a driven roller. For example, it is preferable that the roller 423A disposed downstream of the K component primary transfer roller 422 in the belt traveling direction is a drive roller. This makes it easy to keep the belt running speed constant in the primary transfer portion. As the driving roller 423A rotates, the intermediate transfer belt 421 travels in the direction of arrow A at a constant speed.

  The primary transfer roller 422 is disposed on the inner peripheral surface side of the intermediate transfer belt 421 so as to face the photosensitive drum 413 of each color component. The primary transfer roller 422 is pressed against the photosensitive drum 413 with the intermediate transfer belt 421 interposed therebetween, thereby forming a primary transfer nip for transferring a toner image from the photosensitive drum 413 to the intermediate transfer belt 421.

  The secondary transfer roller 424 is disposed on the outer peripheral surface side of the intermediate transfer belt 421 so as to face the backup roller 423B disposed on the downstream side in the belt traveling direction of the drive roller 423A. The secondary transfer roller 424 is pressed against the backup roller 423B with the intermediate transfer belt 421 interposed therebetween, thereby forming a secondary transfer nip for transferring the toner image from the intermediate transfer belt 421 to the paper S.

  When the intermediate transfer belt 421 passes through the primary transfer nip, the toner images on the photoconductive drum 413 are primarily transferred onto the intermediate transfer belt 421 in sequence. Specifically, a primary transfer bias is applied to the primary transfer roller 422, and an electric charge having a polarity opposite to that of the toner is applied to the back side of the intermediate transfer belt 421 (the side in contact with the primary transfer roller 422). It is electrostatically transferred to the intermediate transfer belt 421.

  Thereafter, when the sheet S passes through the secondary transfer nip, the toner image on the intermediate transfer belt 421 is secondarily transferred to the sheet S. Specifically, a toner image is applied by applying a secondary transfer bias to the secondary transfer roller 424 and applying a charge having a polarity opposite to that of the toner to the back side of the paper S (the side in contact with the secondary transfer roller 424). Is electrostatically transferred to the paper S. The sheet S to which the toner image is transferred is conveyed toward the fixing unit 60.

  The belt cleaning device 426 includes a belt cleaning blade that is in sliding contact with the surface of the intermediate transfer belt 421 and removes transfer residual toner remaining on the surface of the intermediate transfer belt 421 after the secondary transfer. Instead of the secondary transfer roller 424, a configuration (so-called belt-type secondary transfer unit) in which a secondary transfer belt is looped around a plurality of support rollers including the secondary transfer roller is adopted. Also good.

  The fixing unit 60 includes an upper fixing unit 60A having a fixing surface side member disposed on the fixing surface (surface on which the toner image is formed) of the paper S, and the back surface (surface opposite to the fixing surface) of the paper S. A lower fixing unit 60B having a rear side support member to be disposed, a heating source 60C, and the like are provided. When the back surface side support member is pressed against the fixing surface side member, a fixing nip for nipping and transporting the paper S is formed.

  The fixing unit 60 fixes the toner image on the paper S by heating and pressurizing the paper S on which the toner image is secondarily transferred and conveyed at the fixing nip. The fixing unit 60 is disposed in the fixing device F as a unit. The fixing device F is provided with an air separation unit 60D that separates the sheet S from the fixing surface side member by blowing air.

  The paper transport unit 50 includes a paper feed unit 51, a paper discharge unit 52, a transport path unit 53, and the like. In the three paper feed tray units 51a to 51c constituting the paper feed unit 51, paper S (standard paper, special paper) identified based on basis weight, size, or the like is stored for each preset type. . The conveyance path unit 53 includes a plurality of conveyance roller pairs such as registration roller pairs 53a.

  The sheets S stored in the sheet feed tray units 51 a to 51 c are sent one by one from the top and are conveyed to the image forming unit 40 by the conveyance path unit 53. At this time, the registration roller portion provided with the registration roller pair 53a corrects the inclination of the fed paper S and adjusts the conveyance timing. In the image forming unit 40, the toner image on the intermediate transfer belt 421 is secondarily transferred onto one side of the sheet S at a time, and a fixing process is performed in the fixing unit 60. The sheet S on which the image has been formed is discharged out of the apparatus by a discharge unit 52 having a discharge roller 52a.

  Next, a configuration of the fixing unit 60 as a fixing device will be described mainly with reference to FIG.

  As shown in FIG. 3, the upper fixing unit 60A includes an endless fixing belt 61 that is a fixing surface side member, a heating roller 62, an upper pressure roller 63, and a first motor 64 as a driving source (belt heating). method). The fixing belt 61 is stretched between the heating roller 62 and the upper pressure roller 63 with a predetermined belt tension (for example, 400 N).

  The fixing belt 61 is formed by, for example, coating the outer peripheral surface of a base made of PI (polyimide) with a heat-resistant silicone rubber as an elastic layer, and further covering or coating a PFA (perfluoroalkoxy) tube, which is a heat-resistant resin, on the surface layer. Do it.

  The fixing belt 61 comes into contact with the paper S on which the toner image is formed, and heat-fixes the toner image on the paper S in a fixing allowable temperature range. Here, the fixing allowable temperature range is a temperature at which a heat amount necessary for melting the toner on the paper S can be supplied, and varies depending on the paper type of the paper S on which an image is formed.

  The heating roller 62 heats the fixing belt 61. The heating roller 62 includes a heating source 60 </ b> C that heats the fixing belt 61. The heating roller 62 is, for example, a halogen heater, and has a configuration in which an outer peripheral surface of a cylindrical metal core made of aluminum or the like is covered with a resin layer coated with PTFE.

  The temperature of the heating source 60C is controlled by the control unit 100. The heating roller 62 is heated by the heating source 60C, and as a result, the fixing belt 61 is heated.

  The upper pressure roller 63 is a solid metal core made of a metal such as iron and is covered with an elastic layer 631. As a material of the elastic layer 631, for example, heat-resistant silicon rubber can be used. Further, the elastic layer 631 can be configured such that a heat-resistant silicone rubber is coated with a resin layer coated with PTFE which is a heat-resistant resin with low friction. The upper pressure roller 63 is pressed against the lower pressure roller 65 via the fixing belt 61.

  In the present embodiment, the upper pressure roller 63 is connected to a first motor 64 as a drive source. Specifically, as shown in FIG. 3, the gear 632 provided on the rotation shaft of the upper pressure roller 63 meshes with the intermediate gear 642, and the intermediate gear 642 meshes with the gear 641 of the first motor 64. The driving force of the first motor 64 is transmitted to the upper pressure roller 63.

  The lower fixing unit 60B includes a lower pressure roller 65 that is a back surface side support member (roller pressure method). The lower pressure roller 65 is obtained by coating an outer peripheral surface of a base material layer made of PI (polyimide) with an elastic layer 651. As a material of the elastic layer 651, for example, heat-resistant silicon rubber can be used. Further, the elastic layer 651 can be configured by covering a heat-resistant silicone rubber with a resin layer of a PFA tube as a surface release layer.

  The lower pressure roller 65 incorporates a heating source 65A such as a halogen heater. When the heating source 65A generates heat, the lower pressure roller 65 is heated. The control unit 100 controls the power supplied to the heating source 65A and controls the lower pressure roller 65 to a predetermined temperature.

  The lower pressure roller 65 is pressed against the upper pressure roller 63 with a predetermined fixing load via the fixing belt 61. In this way, a fixing nip NP for nipping and transporting the paper S is formed between the upper pressure roller 63 and the fixing belt 61 and the lower pressure roller 65.

  In the present embodiment, the lower pressure roller 65 is connected to a second motor 66 as a drive source. Specifically, as shown in FIG. 3, the gear 652 provided on the rotation shaft of the lower pressure roller 65 meshes with the intermediate gear 662, and the intermediate gear 662 meshes with the gear 661 of the second motor 66. The driving force of the second motor 66 is transmitted to the lower pressure roller 65.

  The control unit 100 performs drive control of the first motor 64 and the second motor 66 as drive sources (for example, control of rotation on / off, peripheral speed, etc.). This control content will be described later.

  In the fixing unit 60, the upper fixing unit 60 </ b> A, the lower fixing unit 60 </ b> B, and the heating source 60 </ b> C fix the unfixed toner image on the sheet S by conveying the sheet S while heating and pressing at the fixing nip NP. . The air separation unit 60D (see FIG. 1) separates the paper S from the fixing belt 61 by blowing air to the leading edge of the paper S that has passed through the fixing nip NP. Accordingly, it is possible to prevent the sheet S that has passed through the fixing nip NP from being wound around the surface of the fixing belt 61 and being separated and causing a winding jam or the like.

  When the gloss control of the toner image formed on the paper S by the image forming unit 40 is performed by the fixing unit 60, (1) the load of the fixing nip NP is controlled, and (2) the paper S is conveyed at the fixing nip NP. It is conceivable to control the speed or (3) to control the fixing temperature at the fixing nip NP.

  However, in the control (1), when the load at the fixing nip NP is increased to increase the gloss of the toner image, the fixing members that form the fixing nip NP, that is, the lower pressure roller 65, the upper pressure roller 63, and the fixing are formed. There is a problem that the durability performance of the belt 61 and the like deteriorates.

  Further, in the control (2), there is a problem that if the paper transport speed at the fixing nip NP is lowered in order to increase the gloss of the toner image, the productivity is lowered.

  Further, in the control (3), when the fixing temperature at the fixing nip NP is increased to increase the gloss of the toner image, image noise occurs due to the toner on the paper S being offset to the fixing belt 61 and the like. There is an easy problem.

  In view of such a situation, in the present embodiment, as the configuration of the fixing unit 60, a difference in hardness between the elastic layers 631 and 651 is provided between the upper and lower pressure rollers 63 and 65. In the present embodiment, the toner on the sheet S is changed by changing the nip width of the fixing nip NP by switching the driving source of the roller pair 63 and 65 between the upper roller driving and the lower roller driving. Control the gloss of the image.

  In this embodiment, the elastic layer 631 that forms the roller surface of the upper pressure roller 63 is more elastic than the elastic layer 651 that forms the roller surface of the lower pressure roller 65 in order to realize a hardness difference between the rollers 63 and 65. It is also thick. That is, the elastic layer 651 of the lower pressure roller 65 is coated thinner than the elastic layer 631 of the upper pressure roller 63 (see FIG. 3).

  Hereinafter, the principle of controlling the gloss by changing the nip width of the fixing nip NP will be described with reference to FIG. 4A shows the deformation state of the fixing nip when the lower roller is driven, and FIG. 4B shows the deformation state of the fixing nip when the upper roller is driven.

In the case of lower roller driving in which the second motor 66 drives the lower pressure roller 65, the elastic layer 631 of the upper pressure roller 63, which is a soft roller, is transported in the transport direction by the rotation of the lower pressure roller 65 in the pressure contact state. Stress is generated so as to be pulled downstream (exit side of the fixing nip NP). Due to such stress, the elastic layer 631 (rubber layer) of the upper pressure roller 63 on the outlet side of the fixing nip NP is deformed so as to be pulled by the lower pressure roller 65, and as shown in FIG. The nip width changes from the width W ₁ when the rollers 63 and 65 are stopped to the width (W ₁ + W ₂ ). In other words, the nip width of the fixing nip NP is the amount corresponding _{W 2} increases. Therefore, when the lower roller is driven, the gloss of the toner image on the paper S that has passed through the fixing nip NP is relatively high.

On the other hand, in the case of upper roller driving in which the upper pressure roller 63 is driven by the first motor 64, the lower pressure roller 65 is a hard roller. As shown in FIG. 4, the elastic layer 651 (rubber layer) of the lower pressure roller 65 hardly deforms. Further, since the lower pressure roller 65 is merely driven by the upper pressure roller 63, no force is generated to pull the upper pressure roller 63 toward the lower pressure roller 65. For this reason, in the case of driving the upper roller, the nip width of the fixing nip NP hardly changes from the width W ₁ when the rollers 63 and 65 are stopped. Therefore, when the upper roller is driven, the gloss of the toner image on the paper S that has passed through the fixing nip NP is lower than that of the lower roller.

  Therefore, in the present embodiment, in the low gloss mode in which the gloss of the toner image on the paper S is lowered, the control unit 100 drives the upper pressure roller 63 by turning on the first motor 64 in the fixing process. The upper roller driving is performed, and the upper pressure roller 63 is rotated clockwise in the figure. When the upper pressure roller 63 is driven to rotate in the clockwise direction in the figure, the fixing belt 61 and the heating roller 62 are driven to rotate in the clockwise direction in the figure, and the lower pressure roller 65 is driven to rotate in the counterclockwise direction in the figure. (See FIG. 4B).

On the other hand, in the high gloss mode in which the gloss of the toner image on the paper S is increased, the control unit 100 performs lower roller driving for driving the lower pressure roller 65 by turning on the rotation of the second motor 66 in the fixing process. The lower pressure roller 65 is rotated counterclockwise in the figure. When the lower pressure roller 65 is driven to rotate counterclockwise in the figure, the fixing belt 61, the upper pressure roller 63, and the heating roller 62 are driven to rotate clockwise in the figure. In the case of such lower roller driving, as described above with reference to FIG. 4A, the nip width of the fixing nip NP increases by W ₂ , so that the gloss of the toner image on the paper S that has passed through the fixing nip NP can be increased. .

  To select the level of gloss, that is, switching between the high gloss mode and the low gloss mode, the control unit 100 displays the gloss level of the toner image in a selectable manner on the operation display unit 20 or a display of an external device. As a result, the drive target by the drive source can be switched. For example, the control unit 100 displays a gloss control mode screen in which the glossiness of the toner image can be adjusted according to the user's preference on the display unit 21 or the like, and selects one of the two buttons for the high gloss mode and the low gloss mode. 22 so that it can be selected. In the fixing process, the control unit 100 sets the drive source of the fixing unit 60 to drive the lower roller when the high gloss mode is selected and to drive the upper roller when the low gloss mode is selected. Drive control. In the image forming apparatus 1, by performing such control, it is possible to easily obtain an image having gloss that matches the user's preference.

  Further, as another method of selecting the level of gloss (switching between the high gloss mode and the low gloss mode), a control method for automatically switching the drive target by the drive source according to the paper type of the paper S may be used. For example, uncoated paper is generally preferred for low gloss and coated paper is often preferred for high gloss. For this reason, when executing a print job, the control unit 100 performs upper roller driving when uncoated paper is selected as the paper S to be used, and lower roller driving when coated paper is selected. The drive source of the fixing unit 60 is automatically selected or switched to control the drive. The image forming apparatus 1 can obtain an image having a desired gloss for each paper type by performing such control.

  In the above-described embodiment, the motor (64, 66) is provided in each of the upper pressure roller 63 and the lower pressure roller 65 as a drive source. As another configuration, by using one motor and switching the gear connection state by the control unit 100, the drive target driven by such a single motor is either the upper pressure roller 63 or the lower pressure roller 65. It is good also as a structure switched to.

  In the above-described embodiment, only one of the upper pressure roller 63 and the lower pressure roller 65 is driven by the drive source. As another configuration, the driving target by the driving source is both the upper pressure roller 63 or the lower pressure roller 65, and a difference occurs in the driving force of the upper pressure roller 63 and the lower pressure roller 65 in the high gloss mode. The drive control may be performed as described above. Specifically, the control unit 100 performs drive control so that the rotation speeds (linear speeds) of the upper pressure roller 63 and the lower pressure roller 65 are equal in the low gloss mode, and in the high gloss mode. Controls driving so that the linear velocity of the lower pressure roller 65 is higher than that of the upper pressure roller 63. Also in this case, the nip width of the fixing nip NP increases in the high gloss mode, and the gloss of the toner image on the paper S can be increased.

  Thus, according to the present embodiment, there are provided a fixing device and an image forming apparatus capable of easily controlling the gloss of an image formed on a recording material without causing side effects such as a decrease in durability performance. be able to.

  Hereinafter, the results of experiments conducted by the present inventors will be described as more specific examples.

Example 1
In Example 1, the image forming apparatus having the above-described configuration (upper belt fixing method) in FIG. 3 and the like was used, and the glossiness was measured by passing the sheet S through the fixing nip NP.

The common conditions in Example 1 are shown below.
Upper pressure roller: outer diameter φ90, rubber thickness 20mm (Asker C hardness 30 °)
Lower pressure roller: outer diameter φ90, rubber thickness 1mm (Asker C hardness 70 °)
Heating roller: outer diameter φ90, PTFE coating Fixing belt: outer diameter φ168, base PI, surface layer PFA tube Fixing belt tension: 100N
Linear speed setting of each pressure roller: 450mm / s
Paper type of recording material (paper) used: POD gloss coat 158 g / m ²

  The present inventors use the above-described image forming apparatus to form a toner image (Blue image) on a sheet, and transport the sheet to a fixing nip where the upper pressure roller or the lower pressure roller is driven to rotate. After fixing the toner image, the glossiness of the toner image was measured.

  The glossiness of the toner image on the paper was measured according to JIS Z 8741 using a 75 ° gloss meter “Micro Gloss 75 °” (manufactured by BYK Gardner).

When the drive source was the first motor (upper roller drive), the lower pressure roller was driven, and when the drive source was the second motor (lower roller drive), the upper pressure roller was driven. Table 1 shows the results of measuring the glossiness of the toner image twice under each of these conditions.

  As shown in Table 1, the first measurement result of the glossiness of the toner image on the paper is 71 ° for the upper roller drive (upper drive) and 80 ° for the lower roller drive (lower drive). Higher gloss was obtained with the lower drive. In the second measurement result, the upper drive was 68 ° and the lower drive was 81 °, and the lower drive also showed higher glossiness. The average of these two measurement results is 70 ° for the upper drive and 81 ° for the lower drive. Thus, it can be seen that the effect of changing the glossiness of the toner image on the paper by about 10 ° was obtained by switching the drive source between the first motor (upper drive) and the second motor (lower drive). .

(Example 2)
In Example 1, it was an experiment when the hardness difference between the upper pressure roller and the lower pressure roller was 40 ° in Asker C hardness. On the other hand, in Example 2, the gloss difference of the toner image on the paper was measured in the same manner as described above by changing the hardness difference between the upper pressure roller and the lower pressure roller. The measurement results of Example 2 are shown in Table 2.

  In Table 2, “x” indicates that the difference in glossiness between the upper drive and the lower drive is 5 ° or less, and “◯” indicates that the difference in glossiness between the upper drive and the lower drive is 10 ° or more. Indicates that there is.

  As shown in Table 2, when the hardness difference between the upper pressure roller and the lower pressure roller is changed to 20 °, 40 °, and 60 ° in Asker C hardness, the toner due to the upper drive and the lower drive at a hardness difference of 20 °. The difference in the glossiness of the image was hardly obtained, and the effect of gloss control was insufficient. On the other hand, when the hardness difference was 40 ° and 60 °, the difference in glossiness of the toner image between the upper drive and the lower drive was 10 ° or more, and a clear effect was obtained. Therefore, the difference in hardness between the upper pressure roller and the lower pressure roller is preferably 40 ° or more in Asker C hardness.

  However, if the hardness difference between the upper pressure roller and the lower pressure roller is greater than 80 °, the durability performance of the fixing members (such as the lower pressure roller, the upper pressure roller, and the fixing belt) that form the fixing nip deteriorates. It becomes easy. In addition, when the hardness difference is greater than 80 °, there is a high possibility that quality defects such as paper curl and separation failure and toner image fixing failure will occur. Therefore, the hardness difference between the upper pressure roller and the lower pressure roller is preferably 80 ° or less, more preferably 60 ° or less in Asker C hardness.

  The above-described embodiments and examples are merely examples of the implementation of the present invention, and the technical scope of the present invention should not be construed in a limited manner. is there. That is, the present invention can be implemented in various forms without departing from the gist or the main features thereof.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10 Image reading part 20 Operation display part 30 Image processing part 40 Image forming part 50 Paper conveyance part 60 Fixing part (fixing apparatus)
60A Upper fixing unit 60B Lower fixing unit 60C, 65A Heating source 60D Air separation unit 61 Fixing belt 62 Heating roller 63 Upper pressure roller 64 First motor (drive source)
65 Lower pressure roller 66 Second motor (drive source)
100 Control Unit 631 Elastic Layer 651 Elastic Layer NP Fixing Nip S Paper (Recording Material)

Claims (9)

An upper pressure roller facing the upper surface of the recording material;
A fixing nip is formed facing the upper pressure roller, a lower pressure roller having a higher hardness than the upper pressure roller,
A drive source for driving at least one of the upper pressure roller or the lower pressure roller;
The gloss of the toner image formed on the recording material by controlling the rotation of the upper pressure roller and the lower pressure roller so that a difference occurs in the driving force between the upper pressure roller and the lower pressure roller. A control unit for controlling
Fixing device. The control unit controls the gloss of the toner image formed on the recording material by switching a driving target by the driving source to either the upper pressure roller or the lower pressure roller.
The fixing device according to claim 1. The controller is
The drive source is switched so that the lower pressure roller is driven when the gloss of the toner image is increased, and the upper pressure roller is driven when the gloss of the toner image is decreased. ,
The fixing device according to claim 2. The control unit displays the toner image so that the level of glossiness can be selected, and switches the drive target by the drive source according to the selection result.
The fixing device according to claim 2. The control unit switches a drive target by the drive source according to the type of the recording material.
The fixing device according to claim 2. A heating roller having a heating source, and a fixing belt stretched between the heating roller and the upper pressure roller,
The fixing device according to claim 1. The upper pressure roller and the lower pressure roller each have an elastic layer, and the elastic layer of the lower pressure roller is thinner than the elastic layer of the upper pressure roller,
The fixing device according to claim 1. The hardness difference between the upper pressure roller and the lower pressure roller is 40 ° to 80 ° in Asker C hardness.
The fixing device according to claim 1. An image forming unit for forming a toner image on a recording material;
A fixing device according to any one of claims 1 to 8,
An image forming apparatus.