JP2018077302A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device that can reduce the occurrence of unevenness in glossiness of an image while reducing the occurrence of electrostatic offset to a heating member.SOLUTION: A fixing device comprises: a heating member that has an endless multilayer structure, and is in contact with a medium on which a toner image is formed while rotating around the axis with heat applied thereto to heat the medium; and a pressure member that rotates around the axis to apply pressure to the medium with the heating member. A material of a surface layer of the heating member contains an insulating resin and conductive particles; the content of the conductive particles is 2 wt.% or more and 5 wt.% or less; the Martens hardness of the heating member is 0.49 N/mm2 or more and 0.74 N/mm2 or less when the temperature of the surface layer is 100°C; after the lapse of a predetermined time from when the heating member is negatively charged for 0.5 seconds, the minimum surface potential of the surface layer is -0.478 kV or more and -0.041 kV or less.SELECTED DRAWING: Figure 6

Description

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

  For example, a fixing roller (heating member) made of a surface layer of a fluorine-based resin and a pressure roller (pressure member) are provided on a medium conveyed with a toner image formed thereon. A fixing device for fixing a toner image is known (see Patent Document 1). Further, it is common to use a fluorine-based resin for the fixing roller in order to provide toner releasability.

JP 2006-133624 A

  By the way, in the case of the above fixing device, since the surface layer of the fixing roller is a fluororesin, that is, the surface layer of the fixing roller has an insulating property, once the fixing roller is charged, it is difficult to remove static electricity, so-called electrostatic offset. May occur. Therefore, charging of the fixing roller can be suppressed by mixing the conductive particles with a fluororesin and using the surface layer as the surface layer of the fixing roller. However, as the mixing ratio of the conductive particles to the fluororesin increases, the surface hardness of the fixing roller increases, so that the surface layer of the fixing roller does not follow the minute irregularities of the medium such as paper, and the image Glossy spots can occur.

  SUMMARY An advantage of some aspects of the invention is that it provides a fixing device that can suppress the occurrence of image gloss while suppressing the occurrence of electrostatic offset on a heating member.

The fixing device of the present invention has an endless multi-layer structure, and is heated around the axis while being heated and contacting the medium on which the toner image is formed. A pressure member that rotates and pressurizes the medium with the heating member, and the material of the surface layer of the heating member includes an insulating resin and conductive particles, and the content of the conductive particles is 2 wt% The Martens hardness of the heating member is 0.49 N / mm ² or more and 0.74 N / mm ² or less when the temperature of the surface layer is 100 ° C., and the heating member is set to 0%. The minimum surface potential of the surface layer is negative −0.478 kV or higher and −0.041 kV or lower when a predetermined time elapses after negative charging for 5 seconds.

  An image forming apparatus of the present invention includes a toner image forming unit that forms a toner image on a medium, the fixing device, and a fixing device that fixes the toner image formed on the medium by the toner image forming unit to the medium; It has.

  The fixing device according to the present invention can suppress the occurrence of image gloss while suppressing the occurrence of electrostatic offset on the heating member.

  In the image forming apparatus of the present invention, image formation defects due to the occurrence of electrostatic offset on the heating member and the occurrence of image gloss spots are suppressed.

1 is a perspective view of an image forming apparatus according to a mode for carrying out the present invention (hereinafter referred to as the present embodiment). 1 is a schematic view of an image forming apparatus according to an embodiment as viewed from the front side. FIG. 2 is a block diagram illustrating a relationship between a control unit configuring the image forming apparatus of the present embodiment and each component configuring the fixing device. 1 is a schematic view (cross-sectional view) of a fixing device that constitutes an image forming apparatus according to an exemplary embodiment as viewed from the front side. It is a fragmentary sectional view (longitudinal sectional view) of the coating layer of the heating roller constituting the fixing device of the present embodiment. It is a table | surface which shows the conditions and result of the evaluation test about a fixing device. FIG. 6 is a schematic view (cross-sectional view) of a fixing device according to a modification as viewed from the front side.

≪Overview≫
Hereinafter, the entire configuration of the image forming apparatus 10 (see FIGS. 1 and 2) of the present embodiment, the image forming operation by the image forming apparatus 10, the configuration of the fixing device 60 (see FIG. 4) which is the main part of the present embodiment, and The effect of this embodiment will be described in the order of description.

  In the present specification, the directions indicated by arrows Fr and Rr in the figure are the front and back sides of the apparatus depth direction, respectively, the directions indicated by arrows R and L are the right and left sides of the apparatus width direction, arrows U and arrows Lo, respectively. The directions shown are the upper side and the lower side of the apparatus height direction, respectively. Further, in this specification, the side of the image forming apparatus 10 viewed from the front side in the apparatus depth direction is described as the front side of the image forming apparatus 10.

<< Overall configuration of image forming apparatus >>
The overall configuration of the image forming apparatus 10 will be described with reference to FIGS. 1 and 2. The image forming apparatus 10 is an electrophotographic apparatus that includes a main body 20, a paper feed cassette 30, a conveying device 40, a toner image forming unit 50, a fixing device 60, and a control unit CU. ing.

  The main body 20 has a function of accommodating a paper feed cassette 30, a transport device 40, a toner image forming unit 50, a fixing device 60, and a control unit CU therein. The main body 20 is a box-shaped exterior. A part of the upper surface of the main body 20 is a discharge tray 22 from which the medium S on which the toner image is fixed (image is formed) is discharged. Note that a lid 24 is provided on the left end surface of the main body 20 as viewed from the front side, and a fixing device 60 described later can be attached to and detached from the main body 20 in a state where the lid 24 is tilted (see FIG. 1). ing.

  The paper feed cassette 30 is arranged on the lower side of the main body 20 and accommodates the medium S on which an image is formed in an overlapping manner. The transport device 40 has a function of transporting the medium S stored in the paper feed cassette 30 along the transport path P from the paper feed cassette 30 to the discharge tray 22. The conveying device 40 includes a plurality of driven rollers and driving rollers, and a driving source (not shown) that drives the plurality of driving rollers. Here, the direction indicated by the arrow Y in the figure is the transport direction of the medium S.

  The toner image forming unit 50 has a function of forming a toner image on the medium S conveyed by the conveying device 40. The toner image forming unit 50 is disposed in the center of the main body 20 when viewed from the front side. The toner image forming unit 50 includes a photoconductor 51, a charging device 52, an exposure device 53, a developing device 54, and a transfer roller 55.

  The toner image forming unit 50 charges the photoconductor 51 rotating around the axis by the charging device 52, exposes the photoconductor 51 by the exposure device 53 to form a latent image, and forms the latent image as a toner image by the developing device 54. The toner image is developed and the toner image is transferred to the medium S by the transfer roller 55. As described above, the toner image forming unit 50 forms a toner image on the medium S.

  The fixing device 60 has a function of fixing the toner image on the medium S (the medium on which the toner image is formed) on which the toner image is transferred by the toner image forming unit 50. The fixing device 60 is disposed on the left side in the main body 20 when viewed from the front side. Since the fixing device 60 is a main part of the present embodiment, a specific configuration of the fixing device 60 will be described later.

  The control unit CU has a function of receiving image data from an external device (not shown) and controlling each element constituting the image forming apparatus 10 based on the image data. Specific functions of the control unit CU will be described in the description of the image forming operation and the fixing operation described later.

≪Image formation operation≫
Next, an image forming operation by the image forming apparatus 10 of the present embodiment will be described with reference to FIGS.

  First, the control unit CU that has received image data from an external device (not shown) operates the toner image forming unit 50. Then, the charging device 52 charges the photoconductor 51, the exposure device 53 exposes the photoconductor 51 to form a latent image, and the developing device 54 develops the latent image as a toner image. An image is formed.

  In addition, the control unit CU operates the conveying device 40 so that the toner image formed on the photoconductor 51 is transferred around the axis of the photoconductor 51 (the portion where the photoconductor 51 and the transfer roller 55 are in contact). The medium S is sent to the transfer position in accordance with the timing of reaching the position. Then, the transfer roller 55 transfers the toner image formed on the photoconductor 51 to the medium S, and the toner image is formed on the medium S.

  Next, the control unit CU operates the fixing device 60 to fix the toner image transferred to the medium S by the transfer roller 55 on the medium S. Then, the medium S on which the toner image is fixed, that is, the medium S on which the image is formed, is further transported downstream in the transport direction by the transport device 40 and is discharged to the discharge tray 22 of the main body 20 to perform the image forming operation. finish.

≪Configuration of main part (fixing device) ≫
Next, the configuration of the fixing device 60 which is a main part of the present embodiment will be described in detail with reference to FIGS. 4 and 5 (mainly FIG. 4).

  The fixing device 60 includes a heating roller 61 (an example of a heating member), a pressure roller 62 (an example of a pressure member), a heat source 63, a temperature sensor 66, a housing HG, and a pair of side plates (not shown). It is comprised including. The heating roller 61, the pressure roller 62, and the heat source 63 are each long, and are positioned on the pair of side plates in a state where their longitudinal directions are aligned with each other (in the apparatus depth direction). The fixing device 60 is long, and is attached to the main body 20 of the image forming apparatus 10 with the longitudinal direction thereof aligned with the apparatus depth direction (see FIG. 1). Note that components other than the housing HG constituting the fixing device 60 are accommodated in the housing HG.

<Heating roller>
The heating roller 61 has a function of heating the toner image (the toner constituting the toner image) formed on the medium S by the toner image forming unit 50 and the medium S. The heating roller 61 is a roller including a long pipe 61A, an elastic layer 61B that covers the outer periphery of the pipe 61A, and a surface layer 61C that covers the outer periphery of the elastic layer 61B. That is, the heating roller 61 is endless.

  The heating roller 61 is rotated about an axis by being driven by a pressure roller 62 described later while being heated by a heat source 63 described later. Here, the symbol O in FIG. 3 indicates the axis (rotation center) of the heating roller 61, and the arrow A indicates the rotation direction of the heating roller 61. The heating roller 61 presses the medium S on which the toner image conveyed by the conveying device 40 is formed with the pressure roller 62 at a nip N described later. As a result, the heating roller 61 contacts the medium S on which the toner image is formed while rotating around the axis, heats the medium S, and pressurizes the medium S passing through the nip N with the pressure roller 62. The toner image is fixed on the medium S.

  Flange (not shown) is fitted to both ends of the heating roller 61, and the heating roller 61 is bonded and fixed to each flange. And each flange is rotatably supported by a pair of side plate via the shaft (illustration omitted) each fitted.

  Next, the configuration of the heating roller 61 will be described in detail.

  As an example, the pipe 61A is an aluminum elementary tube having an outer diameter of 35 mm and a thickness of 0.7 mm. Moreover, the elastic layer 61B is made of silicone rubber having a thickness of 100 μm as an example.

  The surface layer 61C is composed of a fluororesin (hereinafter referred to as PFA. An example of an insulating resin) and conductive carbon black (hereinafter referred to as CB. An example of conductive particles). The layer is 20 μm. Here, from another viewpoint of the surface layer 61C, it can be said that the surface layer 61C is a layer having a thickness of 20 μm in which CB is dispersed in PFA. In addition, the content rate of CB in the surface layer 61C is 2 wt% or more and 5 wt% or less as an example.

The Martens hardness of the heating roller 61 is 0.49 N / mm ² or more and 0.74 N / mm ² or less when the temperature of the surface layer 61C is 100 ° C. Here, the Martens hardness of the heating roller 61 is a maximum test load of 20 mN with respect to the heating roller 61 heated to 100 ° C. using an ultra-micro hardness meter HM2000 (manufactured by Fischer Instruments Co., Ltd.) based on ISO14577 standard. It is measured under the test conditions of a load application time of 20 seconds.

  As described above, the hardness of the heating roller 61 is specified using “Martens hardness” in the present specification, and the technical meaning thereof is as follows. That is, as described above, the surface layer 61C is a thin film having a thickness of 20 μm as an example, and therefore it is not appropriate to specify the micro Vickers hardness but to specify the Martens hardness. Further, in the micro region and nano region tests, the amount of indentation is very small, so that the surface roughness of the test piece greatly affects the measurement accuracy. Furthermore, the unevenness on the surface (outer periphery) of the surface layer 61C is related to the occurrence of image gloss spots on the medium S. For the above three reasons, in the present specification, the hardness of the heating roller 61 is specified using “Martens hardness”.

  The heating roller 61 has a minimum surface potential of −0.478 kV or more and −0.041 kV or less after a predetermined time when the corona discharge is performed for 0.5 seconds to be negatively charged. Here, the predetermined time is 30 seconds as an example. Further, the minimum surface potential means the amount of charge. In addition, the minimum surface potential is determined by installing the heating roller 61 on the ground using an electrostatic diffusion measuring device NS-D100 (manufactured by Nano Seeds Co., Ltd.) based on the JIS 61340-2-1 standard (International Organization IEC 61340-2-1). The sample was placed on a metal plate, measured under a measurement environment of 25 ° C. and a humidity of 50%, with a corona discharge time of 0.5 seconds and a charged electrode as negative polarity.

<Pressure roller>
The pressure roller 62 has a function of pressing the toner image (the toner constituting the toner image) formed on the medium S by the toner image forming unit 50 and the medium S together with the heating roller 61. The pressure roller 62 is a roller including a long shaft and a coating layer (made of silicon rubber as an example) that covers the outer periphery of the shaft. The pressure roller 62 is disposed on the lower side of the heating roller 61 when viewed from the apparatus depth direction. Further, the lower part of the heating roller 61 in a state of being recessed along the outer periphery of the pressure roller 62 is in contact with the upper part of the pressure roller 62. The above-described nip N means a contact portion between the pressure roller 62 and the heating roller 61 formed by the pressure roller 62 and the heating roller 61.

  A driving source (not shown) is connected to one end of the shaft of the pressure roller 62. The pressure roller 62 is driven by a drive source, rotates around the axis, and rotates the heating roller 61. Here, an arrow B in FIG. 3 indicates the rotation direction of the pressure roller 62.

<Heat source>
The heat source 63 has a function of applying heat to the heating roller 61 so that the heating roller 61 heats the medium S. As an example, the heat source 63 is a rod-shaped halogen lamp. The heat source 63 is disposed in the heating roller 61 and faces the inner periphery of the heating roller 61 with its own axis overlapped with the axis O. The heat source 63 emits light and applies heat to the heating roller 61 when a voltage is applied from a power source (not shown).

<Temperature sensor>
The temperature sensor 66 has a function of detecting the temperature of the heating roller 61. For example, the temperature sensor 66 is disposed so as to face the outer periphery of the heating roller 61. In addition, the temperature (data regarding temperature) detected by the temperature sensor 66 is transmitted to the control unit CU at a predetermined cycle.

≪Effect≫
Next, the effect of this embodiment will be described with reference to the table of FIG. The effect of the present embodiment is obtained from comprehensive evaluation derived from two evaluation experiments described later.

<Description of each sample>
As shown in the table of FIG. 6, heating rollers of Samples 1 to 8 were prepared as samples, and Martens hardness and minimum surface potential were measured for each sample. These measuring methods are as described above. Each sample has a different CB content in the surface layer 61C. As a result, the measurement results of Martens hardness and minimum surface potential are different.

<Description of evaluation method>
As an evaluation experiment for each sample, an evaluation experiment for image gloss spots and an evaluation experiment for electrostatic offset were performed.

  In an evaluation experiment for image gloss spots, a fixing device 60 having a heating roller for each sample is mounted on a printer FS-4300DN (manufactured by Kyocera Document Solutions Co., Ltd.), and an image is formed on the medium S (on the medium S). An image sample was printed) and the tester evaluated the presence or absence of image gloss spots. As a result, the case where no image gloss spots were generated was evaluated as “good”, the case where it was generated was evaluated as “occurrence”, and the case where it was generated was determined as “slightly generated”. In the evaluation experiment on the glossy image, if it was “good”, it was accepted.

  In an evaluation experiment for electrostatic offset, a fixing device 60 having a heating roller for each sample was mounted on a printer FS-4300DN (manufactured by Kyocera Document Solutions Co., Ltd.), and 500 sheets of medium S were passed. Thereafter, an image sample was printed on the medium S. And it was confirmed by the tester whether the electrostatic offset has generate | occur | produced in the heating roller of each sample. The confirmation was made based on whether or not the toner adhered to the heating roller of each sample. As a result, the case where electrostatic offset did not occur was evaluated as “good”, the case where it occurred was evaluated as “occurrence”, and the case where it occurred slightly was determined as “somewhat occurred”. And in the evaluation experiment about electrostatic offset, if it was "good", it was set as the pass.

  In this evaluation experiment, in both the evaluation experiment for image gloss spots and the evaluation experiment for electrostatic offset, the case of “good” was set to “pass”.

<Results of evaluation test on glossy image>
As shown in the table of FIG. 8, Samples 1 to 5 were “good”. In sample 6, it was “slightly occurring”. In samples 7 and 8, it was “occurrence”. That is, when the CB content is 5 wt% or less, when the Martens hardness of the heating roller is 0.74 N / mm ² or less, and when the minimum surface potential is −0.041 kV or less, “Good” "Met.

<Results of evaluation test for electrostatic offset>
As shown in the table of FIG. 8, Samples 3 to 8 were “good”. In sample 2, it was “slightly occurring”. In sample 1, it was “occurrence”. That is, when the CB content is 2 wt% or more, when the Martens hardness of the heating roller is 0.49 N / mm ² or more, and when the minimum surface potential is −0.478 kV or more, the electrostatic offset is “good” "Met.

<Result of comprehensive evaluation>
Since it is as above-mentioned, only the samples 3-5 were "pass" by comprehensive evaluation.

<Discussion>
The higher the CB content, the greater the Martens hardness value of the heating roller. Then, when the value of the Martens hardness of the heating roller is about 0.8 N / mm ² , image gloss spots start to occur. This is thought to be because the surface layer of the heating roller cannot follow the minute irregularities of the medium S due to the increased hardness of the surface of the heating roller. However, even when the Martens hardness value of the heating roller exceeds 0.8 N / mm ² , no electrostatic offset is generated. This is considered because the static electricity of the heating roller is likely to leak due to the high CB content.

  The heating rollers of samples 3 to 5 are superior to the heating rollers of samples 1 and 2 in terms of generation of electrostatic offset. In addition, the heating rollers of Samples 3 to 5 are superior to the heating rollers of Samples 6 to 9 in terms of occurrence of image gloss spots. From the above, the heating rollers of Samples 3 to 5 are superior to the heating rollers of Samples 1, 2, and 6 to 8 in terms of generation of electrostatic offset and image gloss. In addition, the heating roller of samples 3-5 is a form included in the technical scope of the present invention, and the heating roller of samples 1, 2, 6-8 is a form not included in the technical scope of the present invention.

  According to the above comprehensive evaluation, when the heating roller 61 of the present embodiment is used in the fixing device 60, it is possible to suppress the occurrence of image gloss while suppressing the occurrence of electrostatic offset. Accordingly, the fixing device 60 of the present embodiment can suppress the occurrence of image gloss while suppressing the occurrence of electrostatic offset to the heating roller 61. Further, in the image forming apparatus 10 of the present embodiment, image formation defects due to the occurrence of electrostatic offset on the heating roller 61 and the occurrence of image gloss spots are suppressed.

  As described above, the present embodiment has been described by taking the present embodiment as an example, but the technical scope of the present invention is not limited to the present embodiment. For example, the following forms are also included in the technical scope of the present invention.

  For example, in the description of the present embodiment, an example of the insulating resin constituting the surface layer 61C has been described as PFA, but the insulating resin may not be PFA. For example, silicone resin, polyamide resin, or other insulating resin may be used.

  In the description of the present embodiment, an example of the conductive particles constituting the surface layer 61C has been described as CB, but the conductive particles may not be CB. For example, iron particles, aluminum particles, or other conductive particles may be used.

  In the fixing device 60 of the present embodiment, an example of the heating member has been described as the heating roller 61. However, the heating member may not be in the form of a roller. For example, like the fixing device 60D of the modification of FIG. 7, the heating member may be a heating belt 61D.

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 50 Toner image forming part 60 Fixing apparatus 61 Heating roller (an example of a heating member)
61C surface layer 62 pressure roller (an example of a pressure member)
S Medium

Claims (2)

A heating member that has an endless multi-layer structure, contacts the medium on which the toner image is formed while rotating about an axis while being heated, and heats the medium;
A pressure member that rotates about an axis and pressurizes the medium with the heating member;
With
The material of the surface layer of the heating member includes an insulating resin and conductive particles, and the content of the conductive particles is 2 wt% or more and 5 wt% or less,
The Martens hardness of the heating member is 0.49 N / mm ² or more and 0.74 N / mm ² or less when the temperature of the surface layer is 100 ° C.,
When the heating member is negatively charged for 0.5 seconds and a predetermined time has elapsed, the minimum surface potential of the surface layer is −0.478 kV or more and −0.041 kV or less,
Fixing device. A toner image forming unit for forming a toner image on a medium;
The fixing device according to claim 1, wherein the toner image formed on the medium by the toner image forming unit is fixed on the medium.
An image forming apparatus.

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