JP4857873B2 - Fixing apparatus, image forming apparatus using the same, and pressure pad - Google Patents

Description

  The present invention relates to a fixing device that heats and pressurizes an unfixed image formed on a recording material, and in particular, to a mode in which a fixing belt is placed in contact with a heat fixing member and pressed by a pressure pad. The present invention relates to a suitable fixing device, an image forming apparatus using the same, and a pressure pad.

2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine or a printer using an electrophotographic method, a fixing device of a heating and pressing method is used as a fixing method for making an unfixed image transferred onto a recording material a permanent image. Widely used.
The function required for this type of heat and pressure type fixing device is to transport a recording material on which an unfixed image is placed to a fixing nip area formed between the heat fixing member and the pressure fixing member, and to the recording material. Without damage, the unfixed toner is melted and fixed to the recording material by pressure, the image quality plane is flattened, the recording material is peeled off from the heat fixing member, and the fixed recording material is conveyed to the post-processing step. That is.

A fixing belt system using a so-called fixing belt has already been provided as a heat and pressure type fixing device that satisfies this type of request. In general, since this fixing belt system uses a fixing belt having a low heat capacity, the heat capacity can be reduced by the amount of heat capacity that can be reduced compared to a so-called roll pair configuration (an embodiment in which a heat fixing roll and a pressure fixing roll are arranged in pressure contact). This is preferable in that the up time can be shortened.
The basic configuration of this type of fixing belt system is a rotatable heating fixing member (for example, a heating fixing roll) whose surface is heated by a heating source, and a recording material that is placed in contact with the heating fixing member and sandwiched and conveyed. The image forming apparatus includes a fixing belt and a pressure pad that is disposed on the back side of the fixing belt and presses the fixing belt against a heat fixing member in a predetermined fixing nip region (see, for example, Patent Document 1).

Here, as the pressure pad, the fixing nip pressure peaks and valleys are provided in the process direction in the fixing nip region and in the direction of the fixing belt rotation axis so as to balance the fixing property and the posture control of the recording material and the releasability. Has been. Specifically, as the pressure pad, a fixing pad made of an elastic member is disposed in the upstream region of the fixing nip region, and a peeling pad made of an inelastic member is disposed in the downstream region of the fixing nip region. Thus, a configuration is adopted in which a desired pressure distribution is formed in the process direction in the fixing nip region and in the fixing belt rotation axis direction.
Thus, since the pressure pad is a combination of a fixing pad made of an elastic member and a peeling pad made of an inelastic member, a wide fixing nip area can be secured by the fixing pad and the peeling pad, and it is compatible with the peeling pad. Since the fixed fixing nip pressure is set higher than the fixing nip pressure corresponding to the fixing pad, it is preferable in that the fixing property and the peeling property to the recording material can be kept good.

Japanese Patent Laying-Open No. 2002-372887 (Embodiment of the Invention, FIG. 11)

However, in this type of fixing device, the fixing nip pressure corresponding to the peeling pad is set higher than the fixing nip pressure corresponding to the fixing pad, and the rotation axis direction of the fixing belt in the fixing nip region corresponding to the peeling pad ( When the pressure distribution in the axial direction (hereinafter simply referred to as necessary) is observed, the pressure tends to concentrate on the portion where the recording material is sandwiched because the recording material itself has a thickness. In particular, this tendency is remarkable when a small-sized recording material with a narrow axial dimension and a thick recording material are used.
At this time, the pressure concentration in the fixing nip region corresponding to the peeling pad causes a recording material quality problem such as the curling of the recording material, and the non-uniform pressure concentration causes peripheral members (such as a fixing belt or a fixing belt) in the fixing nip region. There is a concern that uneven wear of the heat fixing roll or the like) may be caused and the life of the members around the fixing nip region may be impaired.
In this regard, for example, if the peeling pad itself is made of an elastic member, the phenomenon of curling of the recording material and uneven wear of the peripheral members in the fixing nip area is reduced, but the performance with respect to the fixing property and peeling property to the recording material is reduced. There is concern that it will decline.
Therefore, how to suppress curling of the recording material and uneven wear of the peripheral member of the fixing nip region while maintaining good fixing property and peelability to the recording material has become a major technical problem.

  The present invention has been made to solve the above technical problems, and effectively maintains curling of the recording material and uneven wear of the peripheral member of the fixing nip region while maintaining good fixing property and peelability to the recording material. The present invention provides a fixing device, an image forming apparatus using the same, and a pressure pad.

The present inventors have examined the cause of uneven wear of the recording material curl and the fixing nip area peripheral member, and by devising the configuration of the peeling pad, a configuration that keeps the fixing property and the peeling property to the recording material favorable. The inventors have found a mechanism in which pressure concentration does not occur in the fixing nip region corresponding to the peeling pad, and have come up with the present invention.
That is, according to the present invention, as shown in FIGS. 1A and 1B, in a fixing device that heats and presses and fixes an unfixed image on a recording material 4, the surface is heated by a heating source 2 and is rotatable. A heating and fixing member 1, a fixing belt 3 that is disposed in contact with the heating and fixing member 1 and sandwiches and conveys the recording material 4, and is disposed on the back side of the fixing belt 3 and is fixed to the heating and fixing member 1. And a pressure pad 5 that presses at a predetermined fixing nip region n. The pressure pad 5 is disposed in an upstream region in the fixing nip region n and is elastically deformable, and a fixing nip region n. A peeling pad 7 disposed in the downstream region of the inner surface and capable of being pressed at a fixing nip pressure higher than that of the fixing pad 6. The peeling pad 7 is disposed in contact with the fixing belt 3 and has a fixing nip pressure. An undeformable rigid body 7a and this rigid body 7a An elastic body 7b for supporting the recording material, and when the recording material 4 passes through the part of the peeling pad 7, the difference between the fixing nip pressure at both ends in the longitudinal direction of the recording material 4 by the peeling pad 7 and the central fixing nip pressure is recorded. The thickness Lb of the elastic body 7b is adjusted to be thicker than that of the rigid body 7a so that both end curls of the elastic body 7 can be controlled within a predetermined allowable amount or less.
1A is a schematic diagram for explaining the present invention, FIG. 1B is an enlarged view of a portion B in FIG. 1A, and the present invention is an embodiment shown in FIGS. 1A and 1B. Of course, it is not limited to.

In such technical means, the present invention assumes that the pressure pad 5 includes a fixing pad 6 having a low fixing nip pressure and a peeling pad 7 having a high fixing nip pressure.
Since the fixing pad 6 has a fixing nip pressure lower than that of the peeling pad 7, an elastic body having a hardness lower than that of the elastic body 7 b of the peeling pad 7 is usually used.
In addition, the fixing pad 6 and the elastic body 7b of the peeling pad 7 are usually configured separately, but are not limited to being separated in advance, and may be integrally joined.
Furthermore, the rigid body 7a of the peeling pad 7 only needs to have a rigidity that cannot be deformed by the fixing nip pressure, and a metal, a synthetic resin, a ceramic, or the like can be appropriately selected.
On the other hand, the elastic body 7b of the peeling pad 7 can be appropriately selected including fluoro rubber.

Furthermore, if the thickness of the elastic body 7b of the peeling pad 7 is too thin, curling at both ends of the recording material 4 cannot be suppressed, so that the curling at both ends of the recording material 4 can be suppressed. It is necessary to adjust to the range.
That is, as shown in FIGS. 2A and 2B, the pressure distribution in the fixing nip region corresponding to the peeling pad 7 when the recording material 4 passes through the part of the peeling pad 7 is the recording material 4 by the peeling pad 7. The fixing nip pressure at both ends in the longitudinal direction is the maximum pressure Pmax, and the central fixing nip pressure is the minimum pressure Pmin. In such a state, if the difference ΔP between the maximum pressure Pmax and the minimum pressure Pmin is large, curl at both ends of the recording material 4 is generated, so that curl at both ends of the recording material 4 is suppressed. It is necessary to keep it within the possible range.

In the present invention, the thickness relationship of the elastic body 7b of the peeling pad 7 includes one in which the elastic body 7b is thicker than that of the rigid body 7a. According to this aspect, it is preferable in that curl at both ends of the recording material 4 can be reliably suppressed by elastic deformation of the elastic body 7b.
Here, even if the thickness La of the rigid body 7a is equal to or greater than the thickness Lb of the elastic body 7b, curling of the recording material 4 can be suppressed if the thickness of the elastic body 7b is close to that of the rigid body 7a. On the other hand, if the elastic body 7b is too thick, the fixing property and the peelability to the recording material 4 are impaired. Therefore, it is necessary to select within a range that maintains these basic performances. .
A typical aspect of the thickness ratio between the rigid body 7a and the elastic body 7b includes a range of the thickness Lb of the elastic body 7b: the thickness La of the rigid body 7a = 6: 7 to 4: 9. When curl suppression evaluation was performed in each Example in which the hardness of the elastic body 7b was changed, a favorable result was obtained for this thickness ratio.

  Further, as a preferable aspect of the elastic body 7 b of the peeling pad 7, the recording material 4 is nipped and conveyed in the fixing nip area n between the heat fixing member 1 and the fixing belt 3 and the recording material is conveyed in the fixing nip area n. The heating and fixing member 1 and the fixing belt 3 can come into contact with each other in a fixing nip region n where the recording material 4 is not nipped under a condition where the recording material 4 has a portion where the recording material 4 is not nipped and conveyed in a direction orthogonal to the direction. And those which elastically deform the elastic body 7b. According to this aspect, as shown in FIG. 2B, the peeling pad 7 follows the sandwiching of the recording material 4 by the elastic deformation of δ of the elastic body 7b, so that the shape follows the sandwiched state. Therefore, uneven wear of the peeling pad 7 and the heat fixing member 1 can be effectively prevented.

Furthermore, as a preferable aspect of the peeling pad 7, the thing provided with the elastic body 7b whose Asuka C hardness is 30 degrees-70 degrees is mentioned.
Here, if it is less than 30 degrees, the rigidity of the peeling pad 7 is impaired, and it is difficult to obtain a fixing nip pressure necessary for peeling. On the other hand, if it exceeds 70 degrees, the elastic action of the peeling pad 7 is impaired, and it is difficult to keep the fixing nip pressure difference small.
In the present invention, the heat fixing member 1 may be appropriately selected in the form of a roll or a belt. However, from the viewpoint of ensuring the fixing nip region n more reliably, the heat fixing member 1 includes an elastic layer 1a. It is preferable to secure a desired fixing nip region n between the heat fixing member 1 and the fixing belt 3 pressed by the pressure pad 5.

The present invention also includes an image forming engine (not shown) for forming an unfixed image on the recording material 4 and a fixing device for heating and pressure-fixing the unfixed image on the recording material. In this case, the fixing device of the above-described embodiment may be used as the fixing device.
Furthermore, in the present invention, as shown in FIGS. 1 (a) and 1 (b), a rotatable heat fixing member 1 whose surface is heated by a heating source 2, and the heat fixing member 1 arranged in contact with the recording are recorded. A fixing belt 3 that sandwiches and conveys the material 4, and is used in a fixing device that heats and pressurizes an unfixed image on the recording material 4. On the other hand, the pressure pad 5 that presses the fixing belt 3 in a predetermined fixing nip region n is also targeted.
That is, the pressure pad 5 according to the present invention includes an elastically displaceable fixing pad 6 disposed in an upstream region in the fixing nip region n and a downstream region in the fixing nip region n as shown in FIG. And a peeling pad 7 that can be pressed at a fixing nip pressure higher than that of the fixing pad 6 portion. The peeling pad 7 is disposed in contact with the fixing belt 3 and cannot be deformed by the fixing nip pressure. 7a and an elastic body 7b that elastically supports the rigid body 7a. When the recording material 4 passes through the part of the peeling pad 7, the fixing nip pressure at both ends in the longitudinal direction of the recording material 4 and the central fixing nip pressure by the peeling pad 7 are provided. The thickness of the elastic body 7b is adjusted to be thicker than that of the rigid body 7a so that the curl between both ends of the recording material 4 can be suppressed within a predetermined allowable amount or less. To do.

According to the fixing device of the present invention, as a pressure pad in the fixing belt system, a fixing pad having a low fixing nip pressure and a peeling pad having a high fixing nip pressure are disposed on the downstream side thereof. Since the function and the elastic function coexist, a wide fixing nip area and fixing nip pressure distribution necessary for peeling of the recording material can be easily obtained, and the fixing nip area corresponding to the peeling pad has a small size. Even when the recording material passes, pressure concentration can be effectively prevented with respect to the fixing nip pressure distribution in the fixing nip region.
For this reason, the following basic effects can be produced.
(1) It is possible to maintain good fixability and releasability with respect to a recording material, which is the basic performance of the fixing device.
(2) Since an external force exceeding the pressure necessary for fixing does not act on the recording material, it is possible to effectively prevent recording material quality problems such as curling at both ends of the recording material.
(3) Since partial pressure concentration does not occur at the part corresponding to the peeling pad in the fixing nip region, there is no possibility that the peripheral members (fixing belt and heat fixing member) in the fixing nip region will be unevenly worn. The life of peripheral members in the fixing nip region can be extended.
(4) According to the conventional fixing device, when a partial pressure concentration occurs at a portion corresponding to the peeling pad in the fixing nip region, the supporting structure of the heat fixing member must be configured to withstand the pressure concentration load. As a result, the weight and size are restricted, and there is a problem that both processing accuracy and strength must be compatible. However, in the fixing device according to the present invention, since the partial pressure concentration does not occur at the portion corresponding to the peeling pad in the fixing nip region, the support structure for the heat fixing member is provided as compared with the case where the pressure concentration occurs. Simplification and weight reduction can be achieved.

Further, in the image forming apparatus using the above-described fixing device, it is possible to effectively prevent uneven wear of the peripheral members in the both ends curl of the recording material and the fixing nip region while maintaining good fixing property and peelability to the recording material. Since the fixing device for preventing the above is used, it is possible to easily construct an image forming apparatus having good fixing performance.
Further, with the pressure pad used in the above-described fixing device, a fixing belt type fixing device with good fixing performance can be easily constructed.

Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.
Embodiment 1
-Overall configuration of image forming apparatus-
FIG. 3 shows Embodiment 1 of an image forming apparatus to which the present invention is applied.
In the figure, the image forming apparatus of the present embodiment has an image forming engine 20 capable of forming a color image in an apparatus housing 10, and an image reading unit 11 capable of reading a document on the upper portion of the apparatus housing 10. In addition, a document feeding device 12 for sending a document to the image reading unit 11 is disposed above, and a sheet as a recording material is supplied below the image forming engine 20 of the device housing 10. Possible multi-stage paper feed trays 51 to 53 are arranged. Reference numeral 57 denotes a discharge tray which is provided on the side of the apparatus housing 10 and accommodates and discharges the paper image formed by the image forming engine 20.

  The image forming engine 20 used in the present embodiment includes four image forming units 21 (21a to 21d) of yellow (Y color), magenta (M color), cyan (C color), and black (K color). The so-called tandem type arranged in parallel, each color component toner image formed by each image forming unit 21 is primarily transferred to the intermediate transfer belt 30 and supplied from the paper feed trays 51 to 53 by the secondary transfer device 35. Each color component toner image on the intermediate transfer belt 30 is secondarily transferred to a sheet and guided to the fixing device 40. The color arrangement of the four-color image forming units 21 is not limited to this order, and may be in other orders.

The image forming unit 21 (21a to 21d) in the present embodiment adopts, for example, an electrophotographic system, and charges the photosensitive drum 22 that forms and supports each color component toner image. A charging device 23 such as a charging roll, a laser exposure device 24 that forms a latent image on the charged photosensitive drum 22, a developing device 25 that visualizes the electrostatic latent image on the photosensitive drum 22, and the photosensitive drum 22 The toner image is primarily transferred onto the intermediate transfer belt 30 by a primary transfer device 26 including a primary transfer roll, and a cleaning device 27 that cleans residual toner remaining on the photosensitive drum 22. In the present embodiment, the laser exposure device 24 exposes the entire four-color image forming unit 21 with one laser exposure device 24.
Further, the intermediate transfer belt 30 is stretched around a plurality of stretching rolls 31 to 33, and is circulated and conveyed using, for example, the stretching roll 31 as a driving roll. For example, a secondary transfer device 35 including a secondary transfer roll. However, the tension roll 33 is disposed opposite to the backup roll. Further, a belt cleaning device 36 for removing residual toner on the intermediate transfer belt 30 is disposed at a position facing the tension roll 32 of the intermediate transfer belt 30.

Further, the sheet conveyance system in the present embodiment includes a vertical conveyance path 61 extending substantially vertically upward from each of the paper feed cassettes 51 to 53, and extending substantially horizontally on the downstream side of the vertical conveyance path 61 and an image forming engine. Main transfer path 62 toward the discharge tray 57 through the secondary transfer portion 20 and the fixing device 40, and extends downward in a substantially Y shape near the most downstream of the main transfer path 62, and reverses the front and back of the sheet for conveyance A reversing conveyance path 63 that communicates with a part of the reversing conveyance path 63, and a return conveyance path 64 that returns the sheet with the front and back reversed to the vertical conveyance path 61 in front of the image forming engine 20 again.
A registration roll 54 that transports the paper after positioning the paper is positioned upstream of the secondary transfer portion of the main transport path 62, and a transport belt 55 that transports to the fixing device 40 is further downstream of the secondary transfer portion. At the outlet of the main conveyance path 62, a discharge roll 56 that discharges paper to a discharge tray 57 is provided. Furthermore, a reversing mechanism 65 that reverses and conveys the front and back of the sheet is disposed in the reversing conveyance path 63. In these conveyance paths 61 to 64, conveyance members such as a conveyance roll 66 and a conveyance guide (not shown) that ensure the conveyance of the paper are appropriately disposed.

-Fixing device-
In the present embodiment, as shown in FIG. 4, the fixing device 40 includes a heat fixing roll 41 having a heating source 42 such as a halogen lamp inside, and a fixing that rolls with the heat fixing roll 41 and holds and conveys the paper. A belt 43 and a pressure pad 46 that is disposed in contact with the back side of the fixing belt 43 and forms a fixing nip region n between the heat fixing roll 41 and the fixing belt 43 are provided.
A support base 44 having a recess 44 a (see FIG. 5) is provided in the fixing belt 43, and the pressure pad 46 is fitted and held in the recess 44 a of the support base 44. The heat fixing roll 41 is pressed in the fixing nip area n.
Further, a belt travel guide 45 made of, for example, a rigid and low thermal conductive resin is provided below the support base 44 in order to smoothly rotate the fixing belt 43.
Further, a temperature sensor 49 for measuring the surface temperature of the heat fixing roll 41 is disposed around the heat fixing roll 41, and the surface temperature of the heat fixing roll 41 is set to a predetermined temperature by the temperature sensor 49. The temperature control of the heating source 42 is performed. The temperature sensor 49 is not particularly limited as long as it can measure the surface temperature of the heat-fixing roll 41. For example, a temperature sensitive element such as a thermistor or a posistor can be used.
Further, at a position facing the heat fixing roll 41 on the downstream side of the fixing nip area n, a peeling auxiliary plate 48 that prevents the paper discharged from the fixing nip area n from adhering to the heat fixing roll 41 comes close to or contacts. Is provided.

The heat-fixing roll 41 used in this embodiment includes a cylindrical core 41a made of metal such as aluminum having excellent mechanical strength and good thermal conductivity, silicone rubber formed on the surface of the core 41a, and the like. The elastic layer 41b and a release layer 41c that covers the surface of the elastic layer 41b and is provided to prevent the offset of the unfixed toner image on the paper.
Here, the material of the core 41a is not particularly limited as long as it has mechanical strength and good thermal conductivity, and may be a metal or an alloy such as stainless steel, steel, or brass.
Further, the elastic layer 41b is not limited to silicone rubber, and may be, for example, fluorine rubber as long as it has heat resistance. The method of forming the elastic layer 41b on the surface of the core 41a is not particularly limited, An injection molding method or a coating method can be employed.
Further, the release layer 41c may be any material that has heat resistance and appropriate release properties for the toner. For example, fluorine rubber or fluorine resin is used.
Furthermore, the heating source 42 in the heat fixing roll 41 is not particularly limited as long as it has a shape and structure that can be accommodated in the core 41a, and may be appropriately selected according to the purpose. The heating source 42 may be one that heats the heat fixing roll 41 from the outside, or one that heats both from the inside and outside of the heat fixing roll 41.

On the other hand, the fixing belt 43 may have a single-layer structure, but in the present embodiment, a belt having a laminated structure in which a release layer is provided on the surface of the substrate is used.
As the base material of the fixing belt 43, if it has heat resistance, for example, a resin base material such as thermosetting polyimide, thermoplastic polyimide, polyamide, polyamideimide, or a metal base material such as stainless steel, nickel, copper alloy, or the like. Used. Further, the release layer preferably has good releasability of the toner adhering to the surface, and examples of the material include PTFE (polytetrafluoroethylene) and PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer). ) And FEP (tetrafluoroethylene-hexafluoropropylene copolymer).

Further, as shown in FIGS. 5A and 5B, the pressure pad 46 in the present embodiment includes an elastically deformable fixing pad 71 disposed in an upstream region within the fixing nip region n, and fixing. Divided into a separation pad 72 that is disposed in a downstream region in the nip region n and can be pressed with a fixing nip pressure Ps higher than the fixing pad 71 site (fixing nip pressure Pf at the fixing pad 71 site: Pf <Ps). In the state where both are arranged adjacent to each other, they are fitted and arranged in the recess 44a of the support base 44. The width dimension of the pressure pad 46 in the fixing nip area n in the process direction (corresponding to the sheet conveying direction) is substantially the same from the longitudinal center to both ends of the pressure pad 46. .
Here, the fixing pad 71 is formed of an elastic material such as silicone rubber, and forms a pre-nip region of the fixing nip region n between the heat-fixing roll 41 and the fixing belt 43 to stabilize the unfixed toner image on the paper. And become established. In order to keep the frictional resistance with the fixing belt 43 small and make the fixing belt 43 rotate more smoothly on the surface of the fixing pad 71, for example, a low friction sheet made of a fluorine resin sheet is provided by adhesion or the like. But it doesn't matter. Examples of the low friction sheet include fluorine resin sheets such as PTFE and PFA from the viewpoint of workability and low friction. Further, a glass fiber as a substrate and impregnated with fluorine resin or bonded with a fluorine resin sheet may be used.

Further, the peeling pad 72 forms a post nip area (peeling nip area) in the fixing nip area n, and a pressure distribution higher than that in the pre-nip area is provided.
In particular, in the present embodiment, the peeling pad 72 is disposed in contact with the back surface of the fixing belt 43 and has a highly rigid pad rigid body 72a that cannot be deformed by the fixing nip pressure, and a pad elasticity that elastically supports the pad rigid body 72a. The body 72b is integrally joined.
Here, as the pad rigid body 72a, for example, a highly rigid material made of a metal, an alloy such as aluminum, stainless steel, steel, copper, brass or the like and a resin material is mainly used. Preferable representative materials include a composite material (for example, Xenite 3226L manufactured by DuPont manufactured by DuPont) and a heat-resistant polyethersulfone (PES) such as BEAN manufactured by NTN. ES: trade name), for example, formed by injection molding.

The shape of the pad rigid body 72a is a substantially rectangular parallelepiped shape in the present embodiment, but is not limited to this, for example, from the viewpoint of maintaining a good paper transport posture, the pad rigidity A part of the top surface of the pad rigid body 72a is placed on the heat fixing roll 41 side from the viewpoint of providing a predetermined inclined surface or a curvature surface in the process direction on the top surface of the body 72a, or securing the sheet peeling performance, for example. The design may be changed as appropriate, such as to make it bulge.
Accordingly, the shape of the nip area corresponding to the peeling pad 72 in the fixing nip area n is usually surface contact, but the shape of the pad rigid body 72a (for example, the surface of the peeling pad 72 on the heating and fixing roll 41 side has a large inclination). Depending on the shape etc. given, there is also an aspect in which line contact occurs.
In addition, the pad rigid body 72a may be a long object that extends integrally in the longitudinal direction, but is configured as a plurality of divided bodies along the longitudinal direction, and the plurality of divided bodies are made of flexible rubber or string. You may make it make it a continuous body using a raw material.

The pad elastic body 72b is made of an elastic material such as fluorine rubber. And as a preferable hardness of this pad elastic body 72b, an Asuka C hardness of 30 degrees to 70 degrees is used. Furthermore, the shape of the pad elastic body 72b is usually a substantially rectangular parallelepiped shape, but is not limited to this, and the shape of the bonding surface is inclined, for example, in the process direction according to the bonding surface with the pad rigid body 72a. It may be selected as appropriate.
As for the thickness ratio between the pad rigid body 72a and the pad elastic body 72b, the thickness of the pad rigid body 72a is La and the thickness of the pad elastic body 72b is Lb, as shown in FIG. For example, the pad thickness ratio is preferably selected in the range of La: Lb = 6: 7 to 4: 9.
At this time, if the pad rigid body 72a is thicker than the pad thickness ratio (La: Lb) of 6: 7, the elastic action of the pad elastic body 72b is too weak, and the fixing nip region n corresponding to the peeling pad 72 The pressure concentration is not sufficiently suppressed. On the other hand, if the pad elastic body 72b is thicker than the pad thickness ratio of 4: 9, the rigid action by the pad rigid body 72a is too weak, and there is a possibility that the paper peeling action by the peeling pad 72 is impaired.

  Here, La and Lb mean the thickness if the pad rigid body 72a and the pad elastic body 72b have a constant thickness, but if the thickness is not constant, the peeling pad 72 is used. The thickness of the portion including the portion having the highest fixing nip pressure in the process direction in the fixing nip region n corresponding to the above may be set as the representative thickness.

Next, the operation of the image forming apparatus according to the present embodiment will be described focusing on the fixing device.
Now, the image forming engine 20 shown in FIG. 3 creates each color component toner image in each image forming unit 21, sequentially transfers the toner image to the intermediate transfer belt 30, and then the toner images that are multiple transferred onto the intermediate transfer belt 30. Are collectively transferred onto a sheet by the secondary transfer device 35.
Thereafter, the unfixed image on the batch-transferred paper is fixed by heating and pressure in the fixing nip area n of the fixing device 40, and then the fixed paper is peeled off from the fixing device 40 and discharged.
Now, as shown in FIGS. 5A and 6A, a large-size (S1) sheet (for example, a thick sheet) 80 holding an unfixed toner image has entered the fixing nip region n of the fixing device 40. Assuming that the unfixed toner image on the paper 80 is sufficiently heated and pressed by the fixing pad 71 of the pressure pad 46, the paper 80 passes through the peeling pad 72 and is peeled off.
At this time, since the fixing nip pressure Ps in the process direction of the fixing nip area n corresponding to the peeling pad 72 is larger than the fixing nip pressure Pf of the part corresponding to the fixing pad 71, the leading end portion of the sheet 80 is in the fixing nip area n. Head in the direction of peeling from the exit.
In particular, in the present embodiment, the peeling pad 72 is a combined configuration of the pad rigid body 72a and the pad elastic body 72b. Therefore, while maintaining the fixing nip pressure Ps at a pressure necessary for the peeling operation, the pad elastic body 72b An increase in the fixing nip pressure distribution in the longitudinal direction of the fixing nip region corresponding to the peeling pad 72 is suppressed by an elastic action.
For this reason, the difference between the fixing nip pressure at both ends in the longitudinal direction and the fixing nip pressure at the center of a large size sheet is not so large, and the thickness Lb of the pad elastic body 72b is appropriately adjusted. Is suppressed to such an extent that curl at both ends of the paper 80 does not occur, and thereby curl at both ends of the paper 80 is effectively suppressed.

Further, as shown in FIGS. 5A and 6B, a small size (S2) paper (for example, thick paper) 80 on which an unfixed toner image is held enters the fixing nip area n of the fixing device 40. Assuming that the unfixed toner image on the paper 80 is sufficiently heated and pressed by the fixing pad 71 of the pressure pad 46, the paper 80 passes through the peeling pad 72 and is peeled off.
At this time, due to the fixing nip pressure distribution in the process direction of the fixing nip area n corresponding to the fixing pad 71 and the peeling pad 72, the leading end portion of the sheet 80 moves in the direction of peeling from the exit of the fixing nip area n.
In this embodiment, the peeling pad 72 (pad rigid body 72a + pad elastic body 72b) is applied to the peeling pad 72 by the elastic action of the pad elastic body 72b while maintaining the fixing nip pressure Ps at a pressure necessary for the peeling operation. In addition to suppressing an increase in the fixing nip pressure distribution in the longitudinal direction of the corresponding fixing nip area, in the fixing nip area n corresponding to the peeling pad 72, in the area where the sheet 80 is not interposed, the pad elasticity of the peeling pad 72 Since the body 72b presses the pad rigid body 72a only on the fixing belt 40 side δ, the fixing belt 43 and the heat fixing roll 41 are arranged in contact with each other. That is, in this embodiment, the rigidity in the direction facing the heat-fixing roll 41 is maintained by the presence of the pad rigid body 72a, and the longitudinal bending of the peeling pad 72 is performed by the presence of the pad elastic body 72b. The rigidity can be reduced.
For this reason, the difference between the fixing nip pressure at both ends in the longitudinal direction and the fixing nip pressure at the center of a small size sheet is not so large, and the thickness Lb of the pad elastic body 72b is appropriately adjusted. Is suppressed to such an extent that curl at both ends of the paper 80 does not occur, and thereby curl at both ends of the paper 80 is effectively suppressed. In addition, since the shape of the peeling pad 72 follows the nipping of the paper 80 due to elastic deformation of the pad elastic body 72b, partial pressure concentration in the fixing nip region n is less likely to occur. Further, uneven wear of the heat fixing roll 41 is effectively prevented.

In the present embodiment, the fixing pad 71 and the peeling pad 72 are supported by the single support base 44. However, for example, as shown in FIG. The fixing pad 71 may be supported by an elastic support base 47 having a biasing spring 47a between the fixing pad 71 and the support base 44. In this embodiment, the fixing pad 71 itself is supported so as to be elastically displaceable without using an elastic material.
Here, for example, as shown in FIG. 7B, when the thicknesses of the pad rigid body 72a and the pad elastic body 72b of the peeling pad 72 are not uniform, the fixing nip pressure in the fixing nip region becomes high. What is necessary is just to select thickness La and Lb in a part.

Now, with respect to the fixing device (FIG. 4) according to the embodiment, the configuration of the peeling pad 72 of the pressure pad 46 is changed as appropriate, and as shown in FIGS. Examples 1 and 2 were made.
In the same figure, the comparative example 1 is the aspect which used peeling pad 72 '(total thickness: 6.5 mm) which consists only of pad rigid body 72a' (for example, liquid crystal polymer resin DuPont Zenite) on the support stand 44, In Comparative Example 2, the pad rigid body 72a ′ (thickness 5) is formed on the support 44 via a thin pad elastic body 72b ′ (fluorine rubber (or silicone rubber) having a thickness t1 = 1.5 mm, Asuka C hardness 30 degrees). A mode in which 0.0 mm of, for example, a liquid crystal polymer resin (DuPont Xenite) is combined, Example 1 is a thick pad elastic body 72b (thickness t2 = 3.0 mm fluororubber (or silicone rubber), Asuka C on the support base 44. Embodiment in which the pad rigid body 72a (for example, a liquid crystal polymer resin xenite manufactured by DuPont Co., Ltd. having a thickness of 3.5 mm) is combined via the hardness of 70 degrees), Example 2 is thicker on the support base 44. Pad rigid body 72a (2.0 mm thick, for example, Zenitite manufactured by DuPont, a liquid crystal polymer resin) through a pad elastic body 72b (fluorine rubber (or silicone rubber) having a thickness t3 = 4.5 mm, Asuka C hardness 70 degrees) ).

For Examples 1 and 2 and Comparative Example 2, the average curl amount (curl amount ave.) Was measured under the following conditions using the fixing device testing machine according to the embodiment shown in FIG. As shown in FIG. 9, it was found that Examples 1 and 2 had a lower curl amount than Comparative Example 2.
・ Environment: 22 ℃, 55% RH
・ Fixing nip width corresponding to the fixing pad: set to be 4.8 mm ・ Fixing nip pressure corresponding to the fixing pad: set to be a surface pressure of 2.1 kg / cm ²・ Fixing nip width corresponding to the peeling pad : Set to 2.1 mm ・ Fixing nip pressure corresponding to peeling pad: Set to surface pressure 4.2 kg / cm ²・ Fixing speed: 280 mm / sec
・ A4 size P paper (manufactured by Fuji Xerox Office Supply Co., Ltd.) was run with the short side first, and after fixing, it was placed on a flat surface, and the curl heights at the four corners were measured. Turned into.
In particular, among Examples 1 and 2, it is understood that Example 2 in which the pad elastic body 72b is thicker is more effective in curling suppression than Example 1.

In Comparative Example 2, when the hardness of the pad elastic body 72b ′ of the peeling pad 72 ′ was changed to 30, 40, 56, and 70 degrees, as shown in FIG. The lower the hardness, the higher the desired SN ratio using the quality engineering technique in the longitudinal direction. The desired S / N ratio here indicates that the higher the value, the less the variation, indicating that the fixing nip pressure is stable at a desired value.
This tendency is the same in the first and second embodiments.
In general, since there are minute irregularities and undulations with a period of 20 to 30 mm that cannot be removed in the frame of the support base 44, for example, in the comparative example 1 shown in FIG. It becomes very small, and influences such as minute irregularities appear on the fixing nip forming surface. On the other hand, as shown in Comparative Example 2 and Examples 1 and 2, if the pad elastic bodies 72b ′ and 72b are used for the peeling pads 72 ′ and 72, the influence of minute irregularities on the fixing nip forming surface can be absorbed. It is understood that there is.

Further, in Example 2 and Comparative Example 2, in the fixing nip region longitudinal direction (axial direction) corresponding to the peeling pad when A4SEF (A4 size paper Short Edge Feed) and A4LEF (A4 size paper Long Edge Feed) are performed. When the fixing nip pressure distribution was examined, the results shown in FIGS. 11 and 12 were obtained.
11 and 12, the M density indicates the pressure sensitive paper reflection density, and the darker the color, the higher the surface pressure.
According to FIGS. 11 and 12, in Example 2, the differential pressure between the fixing nip pressure at both ends of the sheet and the fixing nip pressure at the center of the sheet is larger in the fixing nip region of the sheet than in Comparative Example 2. It is understood that there is a reduction.
The result is shown in FIG.
That is, in Example 2, the fixing nip pressure difference is sufficiently small, and accordingly, curling at both ends of the sheet can be effectively suppressed.
In Example 2 and Comparative Example 2, when the hardness of the pad elastic body was changed, the same tendency as in FIGS. 11 and 12 was confirmed when the Asuka C hardness was in the range of 30 to 70 degrees.
Further, Comparative Example 2 and Examples 1 and 2 were evaluated for the non-sheet-passing pressure distribution, the fixing temperature latitude, and the curl amount at both ends of the paper, and the results shown in FIG. 13 were obtained. According to this, it was confirmed that Examples 1 and 2 can sufficiently exhibit the curl suppressing function in addition to the fixing performance of Comparative Example 2.

(A) is explanatory drawing which shows the outline | summary of the fixing device based on this invention, (b) is explanatory drawing which shows the outline | summary of the press pad used for the identification attaching apparatus equivalent to the B section in (a). (A) is explanatory drawing which shows the state at the time of recording material passing the fixing device based on this invention, (b) is sectional explanatory drawing equivalent to the BB line in (a). 1 is an explanatory diagram illustrating a first embodiment of an image forming apparatus to which the present invention is applied. FIG. 2 is an explanatory diagram showing an outline of a fixing device used in the first embodiment. (A) is explanatory drawing which shows the detail of the press pad of the fixing device used in Embodiment 1, (b) is explanatory drawing which shows typically the pressure distribution of the fixing nip area corresponding to the press pad. . FIGS. 5A and 5B are explanatory views (corresponding to a cross section taken along line VI-VI in FIG. 5A) schematically showing a state of the fixing device when passing through recording materials of different sizes. (A) is explanatory drawing which shows the deformation | transformation form of the fixing device used in Embodiment 1, (b) is explanatory drawing which shows the detail of the peeling pad. (A)-(d) is explanatory drawing which shows the outline | summary of the peeling pad which concerns on Comparative Examples 1 and 2 and Example 1,2. FIG. 10 is an explanatory diagram illustrating curl performance evaluation of fixing devices according to Examples 1 and 2 and Comparative Example 2. 10 is an explanatory diagram showing a relationship between an elastic body hardness of a peeling pad and a desired SN ratio (an index indicating stability of a fixing nip) viewed from the longitudinal direction in Comparative Example 2. FIG. FIG. 9 is an explanatory diagram illustrating a pressure distribution when a recording material passes through a fixing device according to a second embodiment. FIG. 10 is an explanatory diagram illustrating a pressure distribution when a recording material passes through a fixing device according to Comparative Example 2. 6 is an explanatory diagram showing various performance evaluations of fixing devices according to Examples 1 and 2 and Comparative Example 2. FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Heat fixing member, 1a ... Elastic layer, 2 ... Heat source, 3 ... Fixing belt, 4 ... Recording material, 5 ... Pressure pad, 6 ... Fixing pad, 7 ... Release pad, 7a ... Rigid body, 7b ... Elasticity Body, La ... thickness of rigid body, Lb ... thickness of elastic body

Claims (7)

In a fixing device that heats and pressurizes an unfixed image on a recording material,
A rotatable heat fixing member whose surface is heated by a heating source;
A fixing belt disposed in contact with the heat fixing member and sandwiching and conveying the recording material;
A pressure pad disposed on the back side of the fixing belt and pressing the fixing belt against the heat fixing member in a predetermined fixing nip region;
The pressure pad is elastically displaceable fixing pad disposed in the upstream region in the fixing nip region, and is disposed in the downstream region in the fixing nip region and can be pressed at a fixing nip pressure higher than the fixing pad portion. A peeling pad,
The release pad includes a rigid body that is in contact with the fixing belt and cannot be deformed by the fixing nip pressure, and an elastic body that elastically supports the rigid body, and when the recording material passes through the release pad portion, the release pad is provided. The thickness of the elastic body is rigid so that the difference between the fixing nip pressure at both ends in the longitudinal direction of the recording material and the central fixing nip pressure can be kept within a range where the curling at both ends of the recording material can be suppressed to a predetermined allowable amount or less. A fixing device characterized by being adjusted to be thicker than that of the body . The fixing device according to claim 1 .
In the fixing device, the ratio of the thickness of the rigid body to the thickness of the elastic body is in the range of 6: 7 to 4: 9. The fixing device according to claim 1.
The peeling pad is a portion where the recording material is nipped and conveyed in the fixing nip area between the heat fixing member and the fixing belt and the recording material is not conveyed in the nip direction in the direction perpendicular to the recording material conveying direction of the fixing nip area. And a fixing device that elastically deforms the elastic body so that the fixing heating member and the fixing belt can come into contact with each other in a fixing nip region where the recording material is not nipped. The fixing device according to claim 1.
The fixing device, wherein the peeling pad includes an elastic body having an Asuka C hardness of 30 degrees to 70 degrees. The fixing device according to claim 1.
The fixing device according to claim 1, wherein the heat fixing member has an elastic layer. An imaging engine that forms an unfixed image on the recording material;
A fixing device that heats and presses and fixes an unfixed image on the recording material,
The fixing device includes a rotatable heat fixing member whose surface is heated by a heating source;
A fixing belt disposed in contact with the heat fixing member and sandwiching and conveying the recording material;
A pressure pad disposed on the back side of the fixing belt and pressing the fixing belt against the heat fixing member in a predetermined fixing nip region;
The pressure pad is elastically displaceable fixing pad disposed in the upstream region in the fixing nip region, and is disposed in the downstream region in the fixing nip region and can be pressed at a fixing nip pressure higher than the fixing pad portion. A peeling pad,
The release pad includes a rigid body that is in contact with the fixing belt and cannot be deformed by the fixing nip pressure, and an elastic body that elastically supports the rigid body, and when the recording material passes through the release pad portion, the release pad is provided. The thickness of the elastic body is rigid so that the difference between the fixing nip pressure at both ends in the longitudinal direction of the recording material and the central fixing nip pressure can be kept within a range where the curling at both ends of the recording material can be suppressed to a predetermined allowable amount or less. An image forming apparatus characterized by being adjusted to be thicker than that of a body . A rotatable heat fixing member whose surface is heated by a heating source, and a fixing belt which is disposed in contact with the heat fixing member and sandwiches and conveys the recording material, and heats and pressurizes an unfixed image on the recording material. A pressure pad that is used in a fixing device for fixing, is disposed on the back side of the fixing belt, and presses the fixing belt against a heat fixing member in a predetermined fixing nip region;
An elastically displaceable fixing pad disposed in an upstream region in the fixing nip region, and a peeling pad disposed in a downstream region in the fixing nip region and capable of being pressed with a fixing nip pressure higher than the fixing pad portion. ,
The release pad includes a rigid body that is in contact with the fixing belt and cannot be deformed by the fixing nip pressure, and an elastic body that elastically supports the rigid body, and when the recording material passes through the release pad portion, the release pad is provided. The thickness of the elastic body is rigid so that the difference between the fixing nip pressure at both ends in the longitudinal direction of the recording material and the central fixing nip pressure can be kept within a range where the curling at both ends of the recording material can be suppressed to a predetermined allowable amount or less. A pressure pad adjusted to be thicker than that of the body .

Images