JP2016177208A - Fixing device and image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate obtaining of an image of gloss targeted for an object in comparison with a case where a distortion acting on a recording material in accordance with a category of the recording material is not changed.SOLUTION: A fixing device comprises: a fixing belt 610 that is capable of a circulating movement; a rotatable fixing roll 611 that is provided inside the fixing belt 610; a rotatable pressing roll 62 that is pushed against the fixing belt 610 via the fixing belt 610 to form a roll nip part N1 for a paper P to pass through between the fixing belt 610 and the pressing roll; and a peel-off pad 64 that pushes the pressing roll via the fixing belt 610 on a movement direction side of the fixing belt 610 downstream of the fixing roll 611 and inside of the fixing belt 610, and forms a peel-off nip part N2 large in distortion acting on the paper P in comparison with the roll nip part N1 between the fixing belt 610 and the pressing roll 62, in which in accordance with a category of the paper P, a width of the peel-off nip part N2 along the movement direction of the fixing belt 610 is changeable.SELECTED DRAWING: Figure 5

Description

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

When an image is formed on a recording material using heat-meltable toner, the image is fixed by heating and pressing an unfixed toner image formed on the recording material in a fixing device.
Conventionally, in order to control the gloss (glossiness) of an image formed on a recording material, the fixing speed in the fixing device and the heating temperature in the fixing device are controlled.
For example, Patent Document 1 discloses a recording apparatus in a fixing device that has a heating rotator and a pressure rotator that form a fixing nip portion, and fixes a toner image on the recording material by passing the recording material through the fixing nip portion. A technique for controlling fixing conditions such as fixing time and fixing temperature according to the glossiness of the material surface is disclosed.

JP 2004-286992 A

In the fixing device, even when the fixing time and the fixing temperature are controlled, an image having a target gloss (glossiness) may not be obtained depending on the type of the recording material. For example, when thick paper is used as the recording material, the gloss of the image tends to be higher than when plain paper is used as the recording material.
An object of the present invention is to make it easy to obtain a target gloss image as compared with a case where the distortion acting on the recording material is not changed according to the type of the recording material.

According to a first aspect of the present invention, there is provided a belt member that can be circulated, a rotatable fixing member that is provided inside the belt member, and the belt member that is pressed against the fixing member via the belt member. A rotatable pressure member that forms a pressure part through which the recording material passes, and a belt member downstream of the fixing member in the moving direction of the belt member and inside the belt member via the belt member Pressing the pressure member, forming a strained portion between the belt member and the pressure member, the strain acting on the recording material is larger than that of the pressure member, and depending on the type of the recording material, And a pressing member capable of changing a width of the distortion portion along the moving direction of the belt member.
The invention according to claim 2 is characterized in that the pressing member has a recording medium having a basis weight larger than a predetermined value, as compared to a case where the recording material has a basis weight smaller than the predetermined value. The fixing device according to claim 1, wherein a width of the distortion portion is reduced.
According to a third aspect of the present invention, the width of the distorted portion along the moving direction of the belt member is smaller than the width of the pressurizing portion, and the pressure acting on the recording material at the distorted portion is the applied pressure. The fixing device according to claim 1, wherein the pressure is smaller than a pressure applied to the recording material at the pressure portion.
The invention according to claim 4 is characterized in that the pressing member increases the shearing force acting on the toner image formed on the recording material by increasing the width of the distorted portion. The fixing device according to claim 1.
The invention according to claim 5 is characterized in that a toner image formed using a developer having a G ′ ratio at 80 ° C. and 120 ° C. of 1.0 to 1.3 is fixed to a recording material. The fixing device according to any one of claims 1 to 4.
The invention according to claim 6 is a toner image forming unit that forms a toner image, a transfer unit that transfers a toner image formed by the toner image forming unit onto a recording material, and any one of claims 1 to 5. An image forming apparatus comprising the fixing device according to the item.

According to the first aspect of the present invention, it is easier to obtain a target gloss image as compared with the case where the distortion acting on the recording material is not changed according to the type of the recording material.
According to the second aspect of the present invention, it is possible to obtain an image with low gloss when the basis weight of the recording material is larger than a predetermined value, as compared with the case where the width of the distorted portion is not reduced.
According to the third aspect of the present invention, compared to the case where the pressure of the strained portion is larger than the pressure of the pressurizing portion, the recording material conveyance failure is suppressed.
According to the fourth aspect of the invention, the smoothness of the toner image formed on the recording material can be changed by changing the width of the distorted portion.
According to the invention which concerns on Claim 5, compared with the case where G 'ratio does not satisfy | fill this condition, it becomes easy to obtain the image of the target gloss.
According to the sixth aspect of the invention, it is easier to obtain a target gloss image as compared with the case where the distortion acting on the recording material is not changed according to the type of the recording material.

1 is a diagram illustrating a configuration example of an image forming apparatus to which a fixing unit according to an exemplary embodiment is applied. FIG. 3 is a cross-sectional configuration diagram for describing a configuration of a fixing unit of the present embodiment. FIG. 4 is an enlarged view of a nip portion in the fixing unit. FIG. 6 is a diagram illustrating a toner state in each part of the fixing unit. (A)-(b) is an enlarged view of the nip part in the fixing unit to which this Embodiment is applied. (A)-(b) is the figure which showed the surface pressure which acts with respect to the paper which passes a nip part.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
<Description of Image Forming Apparatus>
FIG. 1 is a diagram illustrating a configuration example of an image forming apparatus 1 to which a fixing unit (fixing device) 60 according to the present embodiment is applied. An image forming apparatus 1 shown in FIG. 1 is a so-called “tandem type” color printer, and controls an image forming unit 10 that forms an image based on image data, operation control of the entire image forming apparatus 1, for example, a personal computer (PC). A main control unit 50 that executes communication with the user, image processing performed on image data, and the like, and a user interface (UI) unit 95 that receives operation input from the user and displays various information to the user. .

<Description of Image Forming Unit>
The image forming unit 10 is a functional unit that forms an image by, for example, electrophotography, and includes six image forming units 11C, 11M, 11HC, 11HM, 11Y as an example of toner image forming units arranged in parallel. 11K (hereinafter “image forming unit 11”). Each image forming unit 11 functions as a functional member, for example, a photosensitive drum 12 on which an electrostatic latent image is formed and then each color toner image is formed, and the surface of the photosensitive drum 12 is charged with a predetermined potential. A charger 13 that exposes the photosensitive drum 12 charged by the charger 13 based on image data, and development that develops the electrostatic latent image formed on the photosensitive drum 12 with toner of each color. And a cleaner 16 for cleaning the surface of the photosensitive drum 12 after transfer.
Each developing unit 15 of each image forming unit 11 is connected to toner containers 17C, 17M, 17HC, 17HM, 17Y, and 17K (hereinafter referred to as “toner containers 17”) for storing toners of respective colors by toner transport paths (not shown). ing. Each color toner is supplied from the toner container 17 to the developing device 15 by a supply screw (not shown) provided in the toner conveyance path.

  Each of the image forming units 11 is configured in substantially the same manner except for the toner accommodated in the developing device 15, and each of them is C (cyan) color, M (magenta) color, HC (high chroma cyan) color, and HM (high chroma magenta). Color, Y (yellow), and K (black) toner images are formed. The HC color here is a cyan color having a cyan hue, a hue that is brighter and higher in saturation than the C color, and the HM color has a magenta hue, and M color. It is a magenta color with a brighter color tone and a relatively high saturation.

The image forming unit 10 intermediates the intermediate transfer belt 20 to which the respective color toner images formed on the photosensitive drums 12 of the respective image forming units 11 are transferred and the respective color toner images formed by the respective image forming units 11. A primary transfer roll 21 for transferring (primary transfer) to the transfer belt 20. Furthermore, a secondary transfer roll 22 that batch-transfers (secondary transfer) each color toner image transferred onto the intermediate transfer belt 20 onto a sheet that is a recording material (recording paper), and each color toner that has been secondarily transferred. And a fixing unit 60 as an example of a fixing unit (fixing device) for fixing the image on the sheet.
In addition, the image forming unit 10 cools each color toner image fixed on the sheet by the fixing unit 60 and promotes fixing of the color toner image on the sheet, and the sheet is bent (curled). And a curl correction unit 92 for correcting the above.
In the image forming apparatus 1 of the present embodiment, the intermediate transfer belt 20, the primary transfer roll 21, and the secondary transfer roll 22 constitute a transfer unit. Further, an area where the secondary transfer roll 22 is disposed and each color toner image on the intermediate transfer belt 20 is secondarily transferred to a sheet is hereinafter referred to as a “secondary transfer area Tr”.

<Description of paper transport system>
In addition, the image forming unit 10 feeds out a plurality of (two in the present embodiment) sheet storage containers 40A and 40B that store sheets and a sheet stored in the sheet storage containers 40A and 40B as a sheet transport system. Feeding rolls 41A and 41B, a first transport path R1 for transporting paper from the paper container 40A, and a second transport path R2 for transporting paper from the paper container 40B.
For example, sheets having different sizes, thicknesses (basis weights), paper types, and the like are stored in the sheet storage containers 40A and 40B. In this example, plain paper and cardboard having different thicknesses are stored in the paper storage containers 40A and 40B, respectively.

Further, the image forming unit 10 includes a third transport path R3 that transports the paper from the paper storage container 40A and the paper storage container 40B toward the secondary transfer region Tr. In addition, the image forming unit 10 conveys the sheet on which the toner image of each color is transferred in the secondary transfer region Tr so as to pass through the fixing unit 60, the cooling unit 91, and the curl correction unit 92. And a fifth transport path R5 for transporting the paper from the curl correction unit 92 toward the paper stacking section 44 provided in the discharge section of the image forming apparatus 1.
From the first conveyance path R1 to the fifth conveyance path R5, conveyance rolls and conveyance belts are arranged along the respective conveyance paths to sequentially convey the fed sheets.

<Description of double-sided conveyance system>
In addition, the image forming unit 10 serves as a double-sided conveyance system in which an intermediate paper storage container 42 that temporarily holds the paper on which the color toner images are fixed on the first surface by the fixing unit 60, and the paper from the curl correction unit 92 as intermediate paper. A sixth transport path R6 for transporting toward the storage container 42 and a seventh transport path R7 for transporting the paper stored in the intermediate paper storage container 42 toward the third transport path R3 are provided. Further, the image forming unit 10 is disposed downstream of the curl correction unit 92 in the sheet conveyance direction, and is configured to convey a sheet toward the sheet stacking unit 44 and a sixth conveyance path R5 that conveys the sheet to the intermediate sheet storage container 42. A distribution mechanism unit 43 that selectively distributes the sheet to the path R6 and a feeding roll 45 that feeds the sheet stored in the intermediate sheet storage container 42 toward the seventh transport path R7 are provided.

<Description of image forming operation>
Next, a basic image forming operation in the image forming apparatus 1 according to the present embodiment will be described.
Each of the image forming units 11 of the image forming unit 10 forms toner images of C color, M color, HC color, HM color, Y color, and K color by an electrophotographic process using the above functional members. Each color toner image formed by each image forming unit 11 is primary-transferred sequentially on the intermediate transfer belt 20 by the primary transfer roll 21 to form a composite toner image in which the respective color toners are superimposed. The synthetic toner image on the intermediate transfer belt 20 is conveyed to the secondary transfer region Tr in which the secondary transfer roll 22 is disposed as the intermediate transfer belt 20 moves (in the direction of the arrow).

On the other hand, in the paper transport system, the feeding rolls 41A and 41B rotate in synchronization with the image formation start timing in each image forming unit 11, and the UI unit 95, for example, out of the paper storage container 40A and the paper storage container 40B. The designated sheet is fed by the feeding rolls 41A and 41B. The sheet fed by the feeding rolls 41A and 41B is transported along the first transport path R1 or the second transport path R2 and the third transport path R3, and reaches the secondary transfer region Tr.
In the secondary transfer region Tr, the composite toner image held on the intermediate transfer belt 20 is secondarily transferred collectively onto the paper by the transfer electric field formed by the secondary transfer roll 22.

Thereafter, the sheet on which the composite toner image is transferred is separated from the intermediate transfer belt 20 and conveyed to the fixing unit 60 along the fourth conveyance path R4. The synthesized toner image on the paper transported to the fixing unit 60 is fixed on the paper after being subjected to a fixing process by the fixing unit 60. The sheet on which the fixed image is formed is cooled by the cooling unit 91 and the curl correction unit 92 corrects the skew of the sheet. Thereafter, the paper that has passed through the curl correcting unit 92 is guided by the distribution mechanism unit 43 to the fifth transport path R5 during single-sided printing and transported toward the paper stacking unit 44.
The toner (primary transfer residual toner) adhering to the photosensitive drum 12 after the primary transfer and the toner (secondary transfer residual toner) adhering to the intermediate transfer belt 20 after the secondary transfer are respectively cleaner 16, And removed by the belt cleaner 26.

On the other hand, at the time of double-sided printing, the paper on which the fixed image is formed on the first surface of the paper by the above-described process passes through the curl correction unit 92 and is guided to the sixth transport path R6 by the distribution mechanism unit 43. The sixth transport path R6 is transported toward the intermediate paper storage container. Again, the feeding roll 45 rotates in accordance with the start timing of image formation on the second surface by each image forming unit 11, and the sheet is fed out from the intermediate sheet storage container 42. The sheet fed by the feed roll 45 is transported along the seventh transport path R7 and the third transport path R3 and reaches the secondary transfer region Tr.
In the secondary transfer region Tr, as in the case of the first surface, the toner images of the respective colors on the second surface held on the intermediate transfer belt 20 are collectively applied to the sheet by the transfer electric field formed by the secondary transfer roll 22. Second transfer is performed.

The paper on which the toner images are transferred on both sides is fixed by the fixing unit 60 as in the case of the first side, cooled by the cooling unit 91, and further corrected by the curl correction unit 92. Is done. Thereafter, the paper that has passed through the curl correction unit 92 is guided to the fifth transport path R5 by the distribution mechanism unit 43 and transported toward the paper stacking unit 44.
In this way, the image forming process in the image forming apparatus 1 is repeatedly executed for the number of printed sheets.

<Description of fixing unit configuration>
Next, the fixing unit 60 used in the image forming apparatus 1 of the present embodiment will be described.
FIG. 2 is a cross-sectional configuration diagram for explaining the configuration of the fixing unit 60 of the present embodiment.
The fixing unit 60 includes a fixing belt module 61 and a pressing roll 62 as an example of a pressing member configured to be movable toward and away from the fixing belt module 61.

  The fixing belt module 61 is arranged to face the pressure roll 62 with the fixing belt 610 sandwiched between the fixing belt 610 as an example of a fixing member that fixes the toner image on the paper P, and rotates while stretching the fixing belt 610. The fixing belt 610 is attached to a nip portion (fixing pressure portion) N, which is one of the tension members that operate and is a region where the fixing belt module 61 and the pressure roll 62 are in pressure contact (contact with each other while being pressed against each other). A fixing roll 611 for heating from the inside, an internal heating roll 612 for heating the fixing belt 610 while stretching the fixing belt 610 from the inside, and an external heating roll 613 for heating the fixing belt 610 while stretching the fixing belt 610 from the outside. And. The fixing belt module 61 includes a tension roll 614 that stretches the fixing belt 610 between the fixing roll 611 and the internal heating roll 612 (upstream of the nip portion N), and a downstream region of the nip portion N. And a peeling pad 64 as an example of a pressing member disposed at a position adjacent to the fixing roll 611, and a tension roll 615 for tensioning the fixing belt 610 on the downstream side of the nip portion N.

The fixing belt 610 includes, for example, a base layer formed of a polyimide resin, an elastic layer made of silicone rubber laminated on the surface side (outer peripheral surface side) of the base layer, and a PFA coated on the elastic layer. And a release layer made of (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin). Here, the elastic body layer is provided in order to improve the image quality especially for the color image. That is, the toner image held on the paper P to be fixed is formed by laminating toners of various colors that are powders. Therefore, in order to supply heat uniformly to the entire toner image at the nip portion N, it is preferable that the surface of the fixing belt 610 be deformed following the unevenness of the toner image on the paper P.
The fixing roll 611 is a cylindrical roll formed of, for example, aluminum or SUS, and receives a rotational driving force from a driving motor (not shown) and rotates in the arrow direction in the figure. Then, the fixing roll 611 is heated to a predetermined temperature (for example, 150 ° C.) by, for example, three halogen heaters 71 as heating sources disposed inside the fixing roll 611.

The internal heating roll 612 is a cylindrical roll formed of, for example, aluminum or SUS. The internal heating roll 612 is heated to a predetermined temperature (for example, 190 ° C.) by, for example, four halogen heaters 72 serving as heating sources disposed inside.
The internal heating roll 612 is provided with spring members (not shown) that press the fixing belt 610 from the inside to the outside at both ends, and the tension of the entire fixing belt 610 is set to 15 kgf, for example.
Further, the internal heating roll 612 is provided with a mechanism for controlling the meandering (belt walk) of the fixing belt 610. That is, a belt edge position detection mechanism (not shown) that detects the end position (edge position) of the fixing belt 610 is disposed in the vicinity of the internal heating roll 612. The internal heating roll 612 is provided with a displacement mechanism (not shown) that displaces one end of the internal heating roll 612 in a direction perpendicular to the axial direction of the internal heating roll 612. The displacement mechanism displaces the fixing belt 610 in the axial direction of the internal heating roll 612 by displacing one end of the internal heating roll 612 according to the detection result of the belt edge position detection mechanism. Thereby, the belt walk of the fixing belt 610 is controlled.

The external heating roll 613 is a cylindrical roll formed of, for example, aluminum or SUS. Then, the external heating roll 613 is heated to a predetermined temperature (for example, 190 ° C.) by, for example, three halogen heaters 73 serving as heating sources arranged inside.
As described above, the fixing unit 60 of the present embodiment employs a configuration in which the fixing belt 610 is heated by the fixing roll 611, the internal heating roll 612, and the external heating roll 613.

The peeling pad 64 is a block member made of a metal such as SUS or a rigid body such as resin and having a substantially arc-shaped cross section. The fixing roll 611 is fixedly disposed over the entire axial direction of the fixing roll 611 at a position near the downstream side of the area where the pressure roll 62 is pressed against the fixing roll 611 via the fixing belt 610 (hereinafter referred to as “roll nip portion N1”). Has been. The peeling pad 64 has a predetermined load (for example, a nip width of 5 mm along the traveling direction of the fixing belt 610) in a predetermined width region (for example, 5 mm along the traveling direction of the fixing belt 610) via the fixing belt 610. For example, it is installed so as to press uniformly at an average of 10 kgf), and a “peeling pad nip portion N2” connected to the roll nip portion N1 is formed.
In the present embodiment, the roll nip portion N1 constitutes a pressurizing portion, and the peeling pad nip portion N2 constitutes a distorted portion.

The pressure roll 62 is a member that forms a nip portion N through which the sheet P holding an unfixed toner image passes between the pressure roller 62 and the fixing belt 610 by being pressed against the outer peripheral surface of the fixing belt 610. The pressure roll 62 is configured, for example, by using, as a base, a cylindrical roll made of aluminum or SUS, and an elastic layer made of silicone rubber and a release layer made of a PFA tube in order from the base side. The pressure roll 62 is disposed so as to be in contact with and separated from the fixing belt module 61. When the pressure roll 62 is set so as to contact (pressure contact) while pressing the fixing belt module 61, the fixing roll of the fixing belt module 61 As 611 rotates in the direction of the arrow, it follows the fixing roll 611 and rotates in the direction of the arrow.
In the present embodiment, the pressure roll 62 is heated to a predetermined temperature (for example, 90 ° C.) by, for example, three halogen heaters 74 serving as heating sources disposed inside.

<Description of the fixing operation in the fixing unit>
Next, the fixing operation in the fixing unit 60 of the present embodiment will be described.
The sheet P on which the composite toner image (unfixed toner image) is electrostatically transferred in the secondary transfer region Tr (see FIG. 1) of the image forming apparatus 1 is fixed along the fourth transport path R4 (see FIG. 1). It is conveyed toward 60. The unfixed toner image on the surface of the paper P passing through the nip N is fixed on the paper P mainly by pressure and heat acting on the roll nip N1.

  That is, in the fixing unit 60 of the present embodiment, the heat acting on the roll nip portion N1 is mainly supplied by the fixing belt 610. The fixing belt 610 is supplied with heat supplied from the halogen heater 71 arranged inside the fixing roll 611 via the fixing roll 611 and from the halogen heater 72 arranged inside the internal heating roll 612 via the internal heating roll 612. And the heat supplied from the halogen heater 73 disposed inside the external heating roll 613 through the external heating roll 613. As a result, not only the fixing roll 611 but also the internal heating roll 612 and the external heating roll 613 are replenished with heat energy, so that a sufficient amount of heat is secured at the roll nip portion N1 even if the process speed is high. .

  In the fixing unit 60 of the present embodiment, the fixing belt 610 that functions as a direct heating member can be configured to have an extremely small heat capacity. In addition, the fixing belt 610 is configured to come into contact with the fixing roll 611 that is a heat supply member, and the internal heating roll 612 and the external heating roll 613 with a wide lap area (large wrap angle). Therefore, since a sufficient amount of heat is supplied from the fixing roll 611, the internal heating roll 612, and the external heating roll 613 in a short period of one rotation of the fixing belt 610, the fixing belt 610 is returned to the necessary fixing temperature in a short time. It becomes possible. Thereby, a predetermined fixing temperature is maintained in the roll nip portion N1.

  As a result, in the fixing unit 60 of the present embodiment, the fixing temperature is maintained substantially constant even when the paper is continuously fed at a high speed. In addition, the phenomenon that the fixing temperature drops at the start of the fixing operation at high speed (so-called “temperature droop phenomenon”) is suppressed. In particular, when fixing to thick paper having a large heat capacity, the maintenance of the fixing temperature and the occurrence of the temperature droop phenomenon are suppressed, and the fixing temperature is switched in the middle according to the paper type (both the fixing temperature is increased and decreased). Even if necessary, the fixing belt 610 has a small heat capacity, so that the temperature can be easily switched by adjusting the output of the halogen heater 71, and further, the halogen heater 72 and the halogen heater 73.

  In the fixing unit 60 of the present embodiment, the fixing roll 611 is a hard roll formed of aluminum, SUS, or the like, and the pressure roll 62 is a soft roll that covers an elastic layer. Therefore, in the roll nip portion N1, the fixing roll 611 hardly bends, and the surface of the pressure roll 62 is bent, so that a nip region having a width in the traveling direction of the fixing belt 610 is formed. As described above, in the roll nip portion N1, the fixing roll 611 on the side where the fixing belt 610 is wrapped is hardly deformed. Therefore, the fixing belt 610 passes through the roll nip portion N1 while maintaining the moving speed substantially constant. As a result, the fixing belt 610 is prevented from being wrinkled or distorted at the roll nip portion N1, so that a high-quality fixed image is stably provided.

  Subsequently, after passing through the roll nip portion N1, the paper P is conveyed to the peeling pad nip portion N2. The peeling pad nip portion N <b> 2 is configured so that the peeling pad 64 is pressed against the pressure roll 62 and the fixing belt 610 is pressed against the pressure roll 62. Accordingly, the roll nip portion N1 has a curved shape that protrudes downward due to the curvature of the fixing roll 611, while the peeling pad nip portion N2 has a contact surface shape of the peeling pad 64 processed into a substantially flat surface with the fixing belt 610. It has a shape along.

  Therefore, the paper P heated and pressed under the curvature of the fixing roll 611 in the roll nip portion N1 is changed in the traveling direction to a curvature directed in the opposite direction by the pressure roll 62 in the peeling pad nip portion N2. At that time, a minute micro slip occurs between the toner image on the paper P and the surface of the fixing belt 610. As a result, the adhesion between the toner image and the fixing belt 610 is weakened, and a state is formed in which the paper P is easily peeled off from the fixing belt 610.

  Since the fixing belt 610 is conveyed so as to be wound around the peeling pad 64 at the exit of the peeling pad nip portion N2, the conveyance direction of the fixing belt 610 changes abruptly there. That is, since the fixing belt 610 moves along the outer surface of the peeling pad 64, the bending of the fixing belt 610 becomes large. Therefore, the paper P whose adhesion with the fixing belt 610 is weakened in advance in the peeling pad nip portion N2 is separated from the fixing belt 610 by the elasticity of the paper that the paper P itself has.

  The paper P separated from the fixing belt 610 is guided in the traveling direction by the peeling guide plate 69 disposed on the downstream side of the peeling pad nip portion N2. The paper P guided by the peeling guide plate 69 is then conveyed toward the cooling unit 80 by a paper discharge guide 78 as an example of a paper discharge guide member and a paper discharge belt 79.

<Toner status during fixing operation>
Next, the state of the toner on the paper P when the fixing process is performed in the nip portion N will be described. FIG. 3 is an enlarged view of the nip portion N in the fixing unit 60, and FIGS. 4A to 4E are views showing the state of toner in each portion of the fixing unit 60. FIG. 4A to 4E show the states of the toner on the paper P in the IVA part, IVB part, IVC part, IVD part and IVE part in FIG. 3, respectively.

As described above, in the secondary transfer region Tr (see FIG. 1), the toner image T held on the intermediate transfer belt 20 (see FIG. 1) is secondarily transferred onto the paper P at once.
As a result, the paper P conveyed toward the nip portion N is in a state of being stacked such that a plurality of toner particles Tp constituting the toner image T overlap as shown in FIG. In this example, each toner particle Tp has a spherical shape. As shown in FIG. 4A, the surface of the toner image T of the paper P conveyed toward the nip portion N has an uneven shape derived from the spherical toner particles Tp.

Subsequently, as described above, heat is supplied by the fixing belt 610 to the sheet P conveyed to the roll nip portion N1 of the nip portion N.
In the roll nip portion N <b> 1, the fixing roll 611 and the pressure roll 62 are pressed against each other via the fixing belt 610. Further, in the roll nip portion N <b> 1, the pressure roll 62 rotates following the fixing roll 611. As a result, as shown in FIG. 4B, a compressive stress is generated in the direction in which the axis of the fixing roll 611 and the axis of the pressure roll 62 are connected to the sheet P conveyed to the roll nip portion N1.

  Then, as shown in FIG. 4B, in the roll nip portion N1, the toner formed on the paper P by the heat supplied by the fixing belt 610 and the compressive stress generated by the fixing roll 611 and the pressure roll 62. The toner particles Tp constituting the image T are crushed. Thereby, the surface roughness of the toner image T formed on the paper P becomes smaller than before the paper P enters the roll nip portion N1.

Next, also in the peeling pad nip portion N <b> 2 of the nip portion N, heat is supplied to the paper P by the fixing belt 610.
In the peeling pad nip portion N2, as described above, the peeling pad 64 is fixedly arranged so as to press the pressure roll 62 with a predetermined load. Thereby, the movement of the fixing belt 610 is restricted in the peeling pad nip portion N2 as compared with the roll nip portion N1. For this reason, as shown in FIG. 4C, a shearing force acting in the direction opposite to the conveyance direction of the paper P is generated on the paper P conveyed to the peeling pad nip portion N2.

  Then, as shown in FIG. 4C, the toner image T formed on the paper P is formed by the heat supplied by the fixing belt 610 and the shearing force generated by the peeling pad 64 at the peeling pad nip portion N2. The surface of the toner particle Tp is smoothed. Thereby, the surface roughness of the toner image T formed on the paper P becomes smaller than before the paper P enters the peeling pad nip portion N2.

  Subsequently, when the paper P passes through the peeling pad nip portion N2 and is peeled from the fixing belt 610, the toner image T formed on the paper P and the fixing belt 610 are separated as shown in FIG. Due to the stress with the surface, an attracting force that is pulled toward the fixing belt 610 with respect to the toner image T is generated.

Next, after the paper P passes through the nip portion N and is separated from the fixing belt 610, the stress on the paper P via the fixing belt 610 is released. As a result, as shown in FIG. 4 (e), a force that restores the toner particles Tp to the original spherical shape is generated by the residual stress of the toner particles Tp themselves crushed at the roll nip portion N1 and the peeling pad nip portion N2. As the toner particles Tp are restored to the original spherical shape, the smoothness of the surface of the toner image T decreases.
In addition, since the heat supply from the fixing belt 610 to the paper P is released after the paper P is separated from the fixing belt 610, the paper P heated at the nip portion N dissipates heat, and the paper P and The toner image T formed on the paper P is gradually cooled and solidified.

By the way, in the fixing unit 60, the gloss (gloss) of the image formed on the paper P may differ depending on the type of the paper P, the type of the image formed on the paper P, and the like. For example, when thick paper is used as the paper P, the gloss of the image formed on the paper P tends to be higher than when plain paper or thin paper is used as the paper P. That is, the toner heated on the thick paper has a faster cooling rate after being peeled off from the fixing belt 610 than the toner heated on the plain paper, so that the toner image T is solidified before the toner particles Tp are restored. Easy to be. For this reason, when thick paper is used as the paper P, the surface of the toner image T is more easily pasted and the gloss of the image is likely to be higher than when plain paper or thin paper is used as the paper P.
In the fixing unit 60, when using thick paper as the paper P, if the fixing operation is performed under the same conditions as when using plain paper or thin paper as the paper P, there is a possibility that an appropriate gloss image cannot be obtained. is there.

On the other hand, in the fixing unit 60 of the present embodiment, the position of the peeling pad 64 is switched according to the thickness (basis weight) of the paper P, whereby the paper P is conveyed in the nip portion N2 at the nip portion N2. The width along is changed.
5A and 5B are enlarged views of the nip portion N in the fixing unit 60 to which the exemplary embodiment is applied. FIG. 5A shows a state in which the peeling pad 64 is disposed at the first position, and FIG. 5B shows that the peeling pad 64 is located at the peeling pad nip portion N2 as compared with the first position. The state arrange | positioned in the 2nd position with a long width | variety is shown.
FIGS. 6A to 6B are diagrams showing the surface pressure that acts on the paper P passing through the nip portion N. FIG. FIG. 6A shows the surface pressure when the peeling pad 64 is arranged at the first position, and FIG. 6B shows the surface when the peeling pad 64 is arranged at the second position. Pressure.

  When the main control unit 50 receives a print instruction, the image forming unit 10 acquires information on the thickness (basis weight) of the paper P on which an image is to be formed. Then, the main control unit 50 determines whether or not the thickness of the paper P is larger than a predetermined thickness based on the acquired information. In other words, the main control unit 50 determines whether or not the paper P corresponds to a thick paper based on the acquired information.

Then, when the thickness of the paper P is thicker than a predetermined thickness, the main control unit 50 switches the position of the peeling pad 64 to the first position. Here, when the peeling pad 64 is moved to the first position, as shown in FIGS. 5A and 6A, the width of the peeling pad nip portion N2 along the moving direction of the fixing belt 610 is as follows. The predetermined first width D1 is set.
On the other hand, when the thickness of the paper P is equal to or less than a predetermined thickness, the main control unit 50 switches the position of the peeling pad 64 to the second position. Here, when the peeling pad 64 is moved to the second position, as shown in FIGS. 5B and 6B, the width of the peeling pad nip portion N2 along the moving direction of the fixing belt 610 is as follows. The second width D2 is set wider than the first width D1 (see FIG. 5A).

  As described above, the shearing force acts on the toner image T formed on the paper P at the peeling pad nip portion N2. As the width of the peeling pad nip portion N2 is increased, the shearing force acting on the toner image T is increased, and the surface of the toner image T is easily smoothed. In this case, the gloss of the image formed on the paper P tends to be high. Conversely, the shorter the width of the peeling pad nip portion N2, the smaller the shearing force acting on the toner image T, and the unevenness derived from the toner particles Tp tends to remain on the surface of the toner image T. In this case, the gloss of the image formed on the paper P tends to be low.

  Therefore, in the fixing unit 60 of the present embodiment, when the paper P is thick paper that tends to have high image gloss, the peeling pad 64 is moved to the first position and the paper P is plain paper or thin paper. By reducing the width of the peeling pad nip portion N2 as compared with the case of using the plain paper or the thin paper as the paper P, it is possible to form an image with low gloss.

  In the present embodiment, as shown in FIGS. 6A to 6B, in the state where the peeling pad 64 is arranged at both the first position and the second position, the sheet is formed at the peeling pad nip portion N2. The surface pressure acting on P is smaller than the surface pressure acting on the paper P in the roll nip portion N1. As described above, in the peeling pad nip portion N2, a force acting on the paper P in the direction opposite to the conveyance direction of the paper P is applied. Therefore, by reducing the surface pressure at the peeling pad nip portion N2 as compared with the surface pressure at the roll nip portion N1, the surface pressure at the peeling pad nip portion N2 is larger than the surface pressure at the roll nip portion N1. Further, the conveyance of the paper P is prevented from being hindered. Further, the occurrence of defects such as rubbing of the toner image T formed on the paper P at the peeling pad nip portion N2 is suppressed.

In this example, the position of the peeling pad 64 is switched based on information on the thickness (basis weight) of the paper P as information on the image forming conditions, but this affects the gloss of the image formed on the paper. The position of the peeling pad 64 may be switched based on other conditions to be obtained. Specifically, examples of the information on the paper type include information on the paper model number, information on the heat capacity of the paper, information on the surface gloss of the paper, and the like. Examples of the information related to the image formed on the paper P include whether or not the image is a color image, the density of the image, and the type of image (photograph, document image, etc.).
Further, the information regarding the image forming conditions may be automatically detected by the image forming apparatus 1, for example, and the user operating the image forming apparatus 1 via the UI unit 95, a PC (not shown), or the like. May be input.

  In this embodiment, the peeling pad 64 is switched to the first position or the second position according to the image forming conditions, and the width of the peeling pad nip portion N2 is set to 2 of the first width D1 or the second width D2. Switch to one width. However, the width of the peeling pad nip portion N2 may be switched in multiple steps to a plurality of widths of 3 or more according to the image forming conditions, or the width of the peeling pad nip portion N2 may be linearly changed according to the image forming conditions. It is good.

  Next, the present invention will be specifically described based on examples. The present invention is not limited to the following examples. The inventor formed an image in the image forming apparatus 1 using the following developer, and measured and evaluated the gloss of the image formed on the paper.

<Measuring method of various characteristics>
First, a method for measuring physical properties of the toner and the like in the developer used in the examples will be described.
[Measurement method of toner particle size and particle size distribution]
The particle size and particle size distribution of the toner are measured as follows using a Coulter Counter TA-II type (manufactured by Beckman-Coulter) as a measuring device and ISOTON-II (manufactured by Beckman-Coulter) as an electrolytic solution. It was.
First, 0.5 mg to 50 mg of a measurement sample was added to 2 ml of a 5% aqueous solution of a surfactant, preferably sodium alkylbenzenesulfonate as a dispersant, and this was added to 100 ml to 150 ml of the electrolytic solution. Subsequently, the electrolytic solution in which the measurement sample is suspended is dispersed for about 1 minute with an ultrasonic disperser, and the particle size distribution in the range of 2 μm to 60 μm using the Coulter counter TA-II type with an aperture having an aperture diameter of 100 μm. Was measured. Thus, the volume average particle size, the volume average particle size distribution index (GSDv), and the number average particle size distribution index (GSDp) of the toner particles were obtained.
In the particle size distribution, a cumulative distribution is drawn from the smaller diameter side to the divided particle size range (channel), and the particle size that becomes 16% cumulative is defined as the volume average particle size D16v and the number average particle size D16p. In addition, the particle size that is 84% cumulative is defined as the volume average particle size D84v and the number average particle size D84p, and using these, the volume average particle size distribution index GSDv is obtained from D84v / D16v. / D16p.

[Measurement method of resin molecular weight and molecular weight distribution]
The weight average molecular weight Mw and the molecular weight distribution (weight average molecular weight Mw / number average molecular weight Mn) of the resin were measured under the following conditions. First, HLC-8120GPC and SC-8020 (manufactured by Tosoh Corporation) are used as the GPC apparatus, TSKgel and SuperHM-H (6 mmID × 15 cm) (manufactured by Tosoh Corporation) are used as the column, and tetrahydrofuran is used as the eluent. (THF) was used.
The measurement conditions were a sample concentration of 0.5%, a flow rate of 0.6 ml / min, a sample injection amount of 10 μl, a measurement temperature of 40 ° C., and detection was performed using an IR detector. Moreover, polystyrene is used as the standard sample, specifically, polystyrene standard samples TSK standard: A-500, F-1, F-10, F-80, F-380, A-2500 manufactured by Tosoh Corporation. , F-4, F-40, F-128, and F-700 were used to create a calibration curve.

[Method for measuring volume average particle diameter of resin fine particles, colorant particles, etc.]
Volume average particle diameters of resin fine particles, colorant particles, and the like were measured using a laser diffraction particle size distribution measuring apparatus (LA-700, manufactured by Horiba, Ltd.).

[Measuring method of resin, toner melting point, resin glass transition temperature]
The resin, the melting point of the toner, and the glass transition temperature of the resin were measured by the methods specified in ASTM D3418-8.

<Create developer>
[Preparation of resin fine particle dispersion (1)]
-25 parts by weight of bisphenol A ethylene oxide 2 mol adduct-25 parts by weight of bisphenol A propylene oxide 2 mol adduct-30 parts by weight of terephthalic acid-5 parts by weight of succinic acid-15 parts by weight or more of trimellitic anhydride, It put into the round bottom flask provided with the gas introduction pipe | tube, the temperature sensor, and the rectification tower, and it heated up to the predetermined temperature using the mantle heater. Next, nitrogen gas was introduced through a gas introduction tube, and the raw material was stirred with a stirrer while keeping the inside of the round bottom flask in an inert gas atmosphere. Thereafter, 0.05 part by weight of dibutyltin oxide was added to 100 parts by weight of the raw material mixture, and the resin (1) was obtained by reacting for 4 hours while keeping the temperature of the reaction product at 200 ° C.

Next, the obtained resin (1) was transferred to an emulsifier (Cavitron CD1010, manufactured by Eurotech) at a rate of 100 g / min in a molten state.
In addition, 0.40% diluted ammonia water obtained by diluting reagent ammonia water with ion-exchanged water is placed in a separately prepared aqueous medium tank, and heated to 120 ° C. with a heat exchanger, 0.1 liter per minute At the same time, the resin (1) in the molten state was transferred to the emulsifier at the same time.
In this state, the emulsifier is operated under the conditions of a rotor rotation speed of 60 Hz and a pressure of 0.49 MPa (5 kg / cm ² ) to disperse resin (1) particles (resin fine particles). (1) was obtained.

[Adjustment of release agent dispersion]
・ 50 parts by weight of polyethylene wax (Toyo Petrolite, Polywax 725, melting temperature 102 ° C.) 5 parts by weight of anionic surfactant (Daiichi Kogyo Seiyaku Co., Ltd., Neogen RK) 200 parts by weight or more of ion-exchanged water The components were mixed, heated and melted to 110 ° C., and dispersed using a homogenizer (manufactured by IKA, Ultra Turrax T50). Subsequently, a release agent dispersion (1) was prepared by dispersing with a Menton Gorin high-pressure homogenizer (manufactured by Gorin) to disperse a release agent having a volume average particle size of 220 nm. The mold release agent concentration in the obtained mold release agent dispersion (1) was 20%.

[Adjustment of colorant dispersion]
・ 1000 parts by weight of cyan pigment (Pigment Blue 15: 3 (copper phthalocyanine) manufactured by Dainichi Seika Co., Ltd.) 150 parts by weight of anionic surfactant (Neogen RK, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) 9000 A colorant (cyan pigment) having a volume average particle size of 0.15 μm is mixed and melted in an amount of at least parts by weight and dispersed for about 1 hour using a high-pressure impact disperser ultimateizer (manufactured by Sugino Machine Co., Ltd., HJP30006). A colorant dispersion (1) was prepared. The colorant particle concentration in the obtained colorant dispersion (1) was 23%.

[Production of toner particles]
-Resin fine particle dispersion (1) 400 parts by weight-Release agent dispersion (1) 50 parts by weight-Colorant dispersion (1) After adding 22 parts by weight or more to the round stainless steel flask, 1.5 parts by weight of a 10% polyaluminum chloride aqueous solution (manufactured by Asada Chemical Co., Ltd.) was added, and the pH in the system was adjusted to 2.5 with a 0.1N nitric acid aqueous solution. Then, it stirred for 30 minutes at room temperature. Next, it was mixed and dispersed with a homogenizer (manufactured by IKA, Ultra Turrax T50), heated to 45 ° C. while being stirred in a heating oil bath, and held for 30 minutes. Next, 50 parts by weight of the resin fine particle dispersion was additionally added, the temperature was raised to 50 ° C., and the mixture was further maintained for 1 hour.

When the obtained contents were observed with an optical microscope, it was confirmed that aggregated particles having a particle diameter of around 7.5 μm were formed. Subsequently, the pH was adjusted to 7.5 with an aqueous sodium hydroxide solution, and then the temperature was raised to 80 ° C. with a heating oil bath and held there for 2 hours.
Subsequently, the obtained content was cooled to room temperature, filtered, washed with ion-exchanged water, and then dried using a vacuum dryer to obtain toner particles.

[Preparation of toner for developing electrostatic image]
To 100 parts by weight of the obtained toner particles, 1 part by weight of colloidal silica (manufactured by Nippon Aerosil Co., Ltd., R972) is added, and externally added and mixed with a Henschel mixer to develop an electrostatic charge image developing toner (hereinafter simply referred to as toner and toner). Sometimes obtained).

[Preparation of electrostatic charge image developer]
Trifunctional isocyanate 80% ethyl acetate solution (Takeda) was added to carbon dispersion obtained by mixing 0.12 part by weight of carbon black (VXC-72, manufactured by Cabot Corporation) with 1.25 parts by weight of toluene and stirring and dispersing in a sand mill for 20 minutes. 1.25 parts by weight of Yakuhin Kogyo Co., Ltd., Takenate D110N) was mixed and stirred to obtain a coating agent resin solution. Next, the obtained coating agent resin solution and Mn—Mg—Sr ferrite particles (volume average particle size: 35 μm) were put into a kneader, mixed and stirred at room temperature for 5 minutes, and then increased to 150 ° C. at normal pressure. Warm and distill off the solvent. Further, after mixing and stirring for 30 minutes, the heater was turned off and the temperature was lowered to 50 ° C. The obtained coated carrier was sieved with a 75 μm mesh to obtain a carrier.
95 parts by weight of the obtained carrier and 5 parts by weight of the electrostatic charge image developing toner prepared above were mixed in a V blender to obtain an electrostatic charge image developer (hereinafter sometimes simply referred to as a developer). It was.

<Evaluation>
In adjusting the resin fine particle dispersion (1), the temperature and reaction time of the reaction product are varied to change the weight average molecular weight Mw and molecular weight distribution (Mw / Mn) of the resin, and the storage elastic modulus G ′ of the toner at 80 ° C. A plurality of developers having different ratios (G ′ ratios) of (Pa) and storage elastic modulus G ′ (Pa) at 120 ° C. were obtained.
An image is formed with the image forming apparatus 1 of the present embodiment using these developers, and the gloss of the obtained image is measured. As a result, the G ′ ratio of the toner to 80 ° C. and 120 ° C. is 1. A preferable result was obtained when it was 0 or more and 1.3 or less.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 50 ... Main control part, 60 ... Fixing unit, 61 ... Fixing belt module, 62 ... Pressure roll, 64 ... Release pad, 610 ... Fixing belt

Claims (6)

A belt member provided so as to be capable of circulating movement;
A rotatable fixing member provided inside the belt member;
A rotatable pressure member that is pressed against the fixing member via the belt member and forms a pressure member through which the recording material passes.
The pressure member is pressed via the belt member on the downstream side of the fixing member in the moving direction of the belt member and inside the belt member, and the pressure is applied between the belt member and the pressure member. And a pressing member capable of changing a width of the distorted portion along the moving direction of the belt member according to the type of the recording material. apparatus.   The pressing member reduces the width of the distortion portion when the basis weight of the recording material is larger than a predetermined value, as compared with a case where the basis weight of the recording material is smaller than the predetermined value. The fixing device according to claim 1.   The width of the strained part along the moving direction of the belt member is smaller than the width of the pressurizing part, and the pressure acting on the recording material at the strained part acts on the recording material at the pressurizing part. The fixing device according to claim 1, wherein the fixing device is smaller than the pressure.   4. The fixing according to claim 1, wherein the pressing member increases a shearing force applied to a toner image formed on a recording material by increasing a width of the distortion portion. 5. apparatus.   5. The toner image formed using a developer having a G ′ ratio of 1.0 to 1.3 in 80 ° C. and 120 ° C. of the toner is fixed on the recording material. The fixing device according to claim 1. Toner image forming means for forming a toner image;
Transfer means for transferring the toner image formed by the toner image forming means onto a recording material;
An image forming apparatus comprising: the fixing device according to claim 1.

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