JP2016009017A - Fixing apparatus and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing apparatus configured to prevent reduction in gloss of an image to be obtained, even when a high-speed device or low-melting point toner is employed.SOLUTION: A fixing apparatus includes a fixing rotation unit 101 having heating means 14, and a pressure rotation unit 102 arranged opposite thereto, and heats and fixes an unfixed image on a conveyed recording material P in a fixing nip part N. The fixing rotation unit 101 has a heat-resistant fixing belt 13 stretched on a plurality of fixing rotating members. The fixing rotating members include at least a fixing roller 11 for forming a fixing nip part N, and a fixing belt supporting roller 12a arranged downstream of the fixing nip part N in a conveyance direction of the recording material P. In an area between the fixing nip part N and the fixing belt supporting roller 12a, distance between a surface of the fixing belt 13 and a conveyance path TR on which the recording material P is conveyed is gradually increased toward the downstream in the conveyance direction of the recording material P.

Description

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

  In an electrophotographic image forming apparatus such as a copying machine, a facsimile machine, or a printer, reproducing an image having a high glossiness is one of the important items to be considered in order to achieve high image quality. In recent years, in the development of high-speed printing systems that can support the field of print on demand (POD) using electrophotography, high-gloss image formation is required mainly to improve the quality and quality of color images such as photographs. It has been. When the glossiness of the image is high, the image density increases, the color gamut can be widened, and a high-class feeling can be obtained.

As a fixing device used in an image forming apparatus, a belt fixing device is known (for example, see Patent Documents 1 to 4).
In a belt fixing device, a toner image is fixed on a recording material carrying an unfixed toner image in a fixing nip formed by contact between an endless fixing belt rotating in a certain direction and a pressure member. The toner image is introduced so as to be in close contact with the outer peripheral surface of the toner, and the toner image is fixed on the recording material. Since the toner image fixed on the recording material has a smooth surface following the smooth surface of the fixing belt, there is an advantage that a fixed image with particularly excellent gloss can be obtained. There has also been proposed an attempt to prevent wrapping of the recording material and paper wrinkles by using a fixing belt.

For example, Patent Document 1 discloses a fixing device in which a back surface side of an unfixed image surface of a fixing unit is a conveyance belt. According to this fixing device, the nip width can be increased as compared with the configuration in which the nip is formed by a pair of rollers, and the fixing property can be improved.
In Patent Document 2, the back side of the unfixed image surface of the fixing unit is a conveyance belt, and the recording material is electrostatically adsorbed by applying an electric charge to the conveyance belt, and the recording material is wound around the fixing roller at the nip exit. A fixing device for preventing the above is disclosed.
In Patent Document 3, the back surface side of the unfixed image surface of the fixing unit is a conveyance belt having an electrostatic adsorption mechanism, and the conveyance belt is wound around the nip surface at the nip exit portion, thereby causing paper wrinkles and trailing edge jumps of the recording material. A fixing device for preventing the occurrence is disclosed.
In Patent Document 4, in order to remove the distortion of the recording material when reading the information recorded on the recording material of continuous paper, a roller for sandwiching the recording material is disposed downstream of the fixing unit, and the recording material is pulled. A fixing device is disclosed.

  By the way, in recent image forming apparatuses, due to demands for high-speed processing and energy saving at the time of toner fixing, an oil-less fixing device and a low melting point toner containing wax and having a low melting point are used.

Low-melting toner softens at a lower temperature than conventional toners, and when the fixing temperature rises to some extent, the image surface becomes smooth and glossiness increases. However, when the temperature rises further, offset occurs and glossiness decreases. There is a problem of end up.
This phenomenon is particularly noticeable in an apparatus that performs high-speed processing, and there is a phenomenon in which the peak of the maximum glossiness decreases as the image forming speed increases (see FIG. 1A).

  In view of the above problems, an object of the present invention is to provide a fixing device capable of suppressing a decrease in glossiness of an image obtained even when the speed of the apparatus is increased or a low-melting toner is used. To do.

  In order to solve the above-described problems, a fixing device according to the present invention includes a fixing rotation unit provided with a heating unit, and a pressure rotation unit disposed at a position facing the fixing rotation unit. In the fixing device that heats and fixes an unfixed image in the fixing nip portion, the fixing rotation unit includes a heat-resistant fixing belt stretched around a plurality of fixing rotation members, and the plurality of fixing rotation members includes at least A fixing roller that forms the fixing nip portion; and a fixing belt support roller that is disposed on the downstream side of the fixing nip portion in the conveyance direction of the recording material, between the fixing nip portion and the fixing belt support roller. In the region, the distance between the surface of the fixing belt and the conveyance path through which the recording material is conveyed is configured to gradually increase toward the downstream in the conveyance direction of the recording material. A fixing device.

  According to the fixing device of the present invention, it is possible to provide a fixing device capable of suppressing a decrease in glossiness of an obtained image even when the speed of the device is increased or when a low melting point toner is used.

(A) is a graph showing the gloss value of an image formed by the conventional fixing device, and (B) and (C) are images formed by the fixing device of this embodiment. FIG. 10 is a schematic diagram illustrating an example of a configuration of a conventional fixing device. It is a partial enlarged view showing an example of a conventional fixing device. FIG. 6 is an explanatory diagram showing a mode of separation between a recording material and a fixing member. FIG. 2 is a schematic cross-sectional view illustrating an example of a fixing device of the present embodiment. FIG. 2 is a schematic cross-sectional view illustrating an example of a fixing device of the present embodiment. It is a cross-sectional schematic diagram which shows an example of the process cartridge of this embodiment. It is a cross-sectional schematic diagram which shows an example of the process cartridge of this embodiment. FIG. 2 is a schematic cross-sectional view illustrating an example of a fixing device of the present embodiment. FIG. 2 is a schematic cross-sectional view illustrating an example of a fixing device of the present embodiment. FIG. 2 is a schematic cross-sectional view illustrating an example of a fixing device of the present embodiment. FIG. 2 is a schematic cross-sectional view illustrating an example of a fixing device of the present embodiment. FIG. 2 is a schematic cross-sectional view illustrating an example of a fixing device of the present embodiment. FIG. 2 is a schematic cross-sectional view illustrating an example of a fixing device of the present embodiment. FIG. 2 is a schematic cross-sectional view illustrating an example of a fixing device of the present embodiment. 1 is a schematic cross-sectional view illustrating an example of a configuration of an image forming apparatus according to an exemplary embodiment. 1 is a schematic cross-sectional view illustrating an example of a configuration of an image forming apparatus according to an exemplary embodiment.

  Hereinafter, a fixing device and an image forming apparatus according to the present invention will be described with reference to the drawings. The present invention is not limited to the embodiments described below, and other embodiments, additions, modifications, deletions, and the like can be changed within a range that can be conceived by those skilled in the art, and any aspect is possible. As long as the functions and effects of the present invention are exhibited, the scope of the present invention is included.

First, the separation speed between the fixing member and the recording material in the fixing device will be described.
FIG. 2 shows an example of a conventional fixing device. The fixing device shown in FIG. 2 includes a fixing roller 61, a heating roller 62, a fixing belt 63, a halogen heater 64, and a pressure roller 66.
When fixing is performed at a high temperature in order to ensure sufficient fixability and high glossiness of the image, the adhesion between the image on the recording material P and the surface of the fixing belt 63 increases due to melting of the toner, and the fixing nip N At the outlet, the recording material P is wound around the fixing belt 63 and discharged. When winding occurs, the recording material P is forcibly separated by a separating means 60 (for example, a separation claw) as shown in FIG.

The difference in the separation mode of the recording material P is shown in FIG. FIG. 4 shows a conveyance path TR of the recording material P and a fixing roller 61 as a fixing member.
The separation angle when the fixing roller 61 is forcibly separated after the winding occurs (S2) is larger than the separation angle when the fixing roller 61 is separated in the tangential direction of the fixing roller 61 without being wound (S1). growing. That is, the distance between the recording material P and the surface of the fixing member when the forcible separation after the occurrence of winding (S2) is greater than the case where the separation is performed in the tangential direction of the fixing roller 61 without winding (S1). (Hereinafter also referred to as “separation distance”) is large, and the speed at which the separation distance increases (hereinafter also referred to as “separation speed”) becomes very large.
Even in the case of natural separation due to the curvature of the fixing roller 61 and the weight of the recording material itself, when the wrapping occurs, as in the case where the separation means 60 forcibly separates, the separation is larger than the case where the separation is performed in the tangential direction. Increases speed.

On the other hand, the glossiness of an image increases as the fixing temperature increases due to the characteristics of the toner, but decreases when the fixing temperature exceeds a certain temperature. This is because the toner surface melts due to a fixing temperature that is too high, causing an offset in which a part of the toner layer adheres to the surface of the fixing member, resulting in a rough image surface.
In the region where the glossiness with respect to temperature is saturated, the smoothing of the surface due to deformation and the occurrence of a minute offset proceed simultaneously in the image plane. At this time, when the separation speed between the image surface and the fixing member surface is low, the vicinity of the outermost surface of the toner layer having the highest temperature is offset. On the other hand, when the separation speed between the surface of the image and the surface of the fixing member is high, the toner is separated from the toner behind the surface of the toner layer due to the temperature and viscoelasticity in the toner layer, and the surface roughness is deteriorated.
Therefore, by slowing the separation speed between the image surface and the fixing member surface, an image having a high glossiness peak and having a high glossiness stably even under a high fixing temperature condition can be formed. It is thought that you can.

  Therefore, the fixing device of this embodiment reduces the separation speed between the image surface and the fixing member surface, so that the gloss of the obtained image can be obtained even when the device is speeded up or when a low melting point toner is used. It is possible to suppress the decrease in the degree.

[Fixing device]
(First embodiment)
5 and 6 show the fixing device according to the first embodiment.
The fixing device according to the present embodiment includes a fixing rotation unit 101 provided with a heating unit 14 and a pressure rotation unit 102 disposed at a position opposed to the fixing rotation unit 101. An unfixed image on the conveyed recording material P is displayed. A fixing device that heats and fixes at the fixing nip portion N, the fixing rotation unit 101 includes a heat-resistant fixing belt 13 stretched around a plurality of fixing rotation members, and the plurality of fixing rotation members includes at least It has a fixing roller 11 that forms the fixing nip N, and a fixing belt support roller 12a that is disposed downstream of the fixing nip N in the recording material conveyance direction, and between the fixing nip N and the fixing belt support roller 12a. In this area, the interval between the surface of the fixing belt 13 and the transport path TR along which the recording material P is transported is configured to gradually increase toward the downstream in the transport direction of the recording material.

The distance between the surface of the fixing belt 13 and the transport path TR along which the recording material P is transported represents the “separation distance” described above.
The fixing belt support roller 12a has an angle and a separation distance formed between the surface of the fixing belt 13 and the conveyance path TR through which the recording material P is conveyed smaller than that in the case where the fixing belt is in close contact with the fixing roller surface, and The fixing nip portion N is disposed downstream of the recording material in the conveyance direction so as to gradually increase toward the downstream in the recording material conveyance direction.

5 shows a fixing device applied to image formation on a cut sheet (for example, a sheet cut to a standard size) as the recording material P, and FIG. 6 shows a long medium (for example, the recording material P) , A fixing device applied to image formation on a roll paper or the like.
These fixing devices have a difference in the configuration of the recording material conveying means (mainly the pressure rotation unit 102) depending on the difference in the supplied paper, but the main feature is to make it possible to suppress a decrease in the glossiness of the image. The configuration (mainly, the fixing rotation unit 101) is the same.

  The fixing roller 11 is provided with an elastic layer such as silicon rubber on the surface of an iron-based core metal such as stainless steel, and has an outer diameter of 40 mm to 80 mm. The elastic layer has a thickness of 3 mm to 20 mm and an Asker C hardness of 10 to 50 degrees.

Since the surface of the fixing belt 13 is in pressure contact with the recording material P and the unfixed toner image on the recording material P, the surface of the fixing belt 13 needs to be covered with a layer having excellent releasability and heat resistance. It is preferable to cover a surface release layer made of a fluorine resin or the like.
In order to obtain the uniformity of the image to be formed, it is preferable to provide an elastic layer made of heat-resistant rubber such as 100 to 300 μm silicon rubber or fluorine rubber under the surface release layer.

As the heating roller 12c, an aluminum pipe having a thickness of 5 mm to 8 mm and an outer diameter of 80 mm is used.
Examples of the heating means 14 include a heater, a lamp, and an electromagnetic induction heating device. In this embodiment, although the heating means 14 incorporated in the heating roller 12c is shown, it is not limited to this.

First, the fixing device shown in FIG. 5 will be described.
In the fixing device of FIG. 5, the pressure rotation unit 102 includes a heat-resistant pressure belt 17 stretched around a plurality of pressure rotation members, and a charging unit 18 that charges the pressure belt 17. The plurality of pressure rotating members include at least a pressure roller 16 that forms the fixing nip portion N, and a pressure belt support roller 15a that is disposed on the downstream side of the fixing nip portion N in the conveyance direction of the recording material P.

  The surface of the pressure belt 17 defines a transport path TR for the recording material P on the surface facing the fixing rotation unit 101. That is, the recording material (cut paper) P holding a toner image (not shown) on the upper side of the figure is conveyed on the conveyance path TR from the right side to the left side of the figure.

The pressure rotating unit 102 includes a charging unit 18 for charging the pressure belt 17 on the upstream side of the fixing nip portion N in the conveyance direction of the recording material P, and a neutralizing unit 19 on the downstream side. The recording material P is electrostatically attracted to the belt 17 and conveyed.
Furthermore, a voltage control means (not shown) for controlling the value of the voltage applied to the pressure belt 17 by the charging means 18 is provided.

Examples of the pressure roller 16 include a configuration in which an elastic layer is provided on an iron-based metal core. The diameter of the pressure roller 16 is 60 mm to 100 mm.
Since the recording material P that has passed through the fixing nip N is electrostatically adsorbed to the pressure belt 17, it is possible to prevent the image surface from being wound around the fixing belt 13. Further, due to the arrangement of the fixing belt support roller 12a, the distance between the fixing belt 13 and the surface of the pressure belt 17 defining the transport path TR is gradually increased, and the image surface after passing through the fixing nip N The separation speed of the surface of the fixing belt 13 becomes slow, and the decrease in glossiness at high temperatures is reduced.

The toner remaining on the fixing belt 13 from the surface of the recording material P is removed by a fixing belt cleaning unit (not shown).
On the downstream side of the fixing nip portion N, there is provided a static elimination unit 19 that is a unit for electrostatically peeling the recording material P from the pressure belt 17. The neutralizing means 19 is a charging device using corona discharge. The recording material P is neutralized by the neutralizing means 19, and the recording material P is smoothly peeled off from the pressure belt 17 by weakening or disappearing the electrostatic adsorption force with the pressure belt 17.

The pressure belt 17 is made of a base material made of a heat resistant resin material such as polyimide, polyamideimide, polyetherketone (PEEK). The thickness of the substrate is preferably 30 to 200 μm. A heat-resistant elastic layer such as silicon rubber may be provided on the surface layer. The volume resistivity of the pressure belt 17 is preferably 10 ⁹ to 10 ¹⁶ Ωcm (ohm centimeters).

The pressure belt 17 is charged by the charging unit 18 from the surface side. The charging unit 18 is a charging roller that is in contact with the outer surface of the pressure belt 17, and has a power source that applies a voltage for applying a charge (not shown). The power source is variably controlled by a control unit (not shown). .
The voltage applied to the charging means 18 can be arbitrarily set. The ease of separation of the recording material P from the fixing belt 13 and the ease of separation of the adsorbed pressure belt 17 differ depending on the type of the recording material P (paper quality, waist strength, thickness, size, etc.) Correspondingly, it is necessary to adjust the level of the applied voltage. Moreover, it is desirable to set an optimal voltage from a viewpoint of energy saving.

In the present embodiment, optimum relationship data between the type and voltage of the recording material P is obtained in advance by experiments or the like (including computer simulation), and this relationship data table is stored in a ROM or the like of voltage control means (not shown).
The voltage control means recognizes the type of the recording material P based on input information from an operation panel (not shown), detection information from a sensor (not shown), reception information from an external connection device (for example, a host PC), and the like. The optimum voltage is selected from the relational data table based on the type of the recording material P thus applied, and the applied voltage is controlled.
By controlling the voltage control means, it is possible to prevent troubles caused by different types of the recording material P, improve the separation of the recording material P, and improve energy saving.

In the present embodiment, in order to prevent the toner from scattering due to an electric field, a charge having a polarity opposite to that of the toner may be applied to the pressure belt 17 from the surface side.
The recording material P that reaches the front of the fixing nip N is electrostatically attracted to the pressure belt 17 by being polarized in contact with the charged pressure belt 17. Therefore, the leading edge margin where no toner is present is attracted by the electrostatic force due to the charging of the pressure belt 17 and advances into the nip without fluttering. In this way, charges are applied so that an electrostatic force is generated from the vicinity of the upstream entrance of the fixing nip N.
The charging method may be an AC voltage application method or a DC voltage application method. Further, the charging means may be a corona charging method.

Next, the fixing device shown in FIG. 6 will be described.
In the fixing device of FIG. 6, the pressure rotation unit 102 supports the pressure roller 16 that forms the fixing nip portion N and the long recording material P that has passed through the fixing nip portion N on the downstream side in the transport direction. A straight line connecting the fixing nip portion N and the contact portion of the stretching roller 15d with the recording material P is recorded on the surface facing the fixing rotation unit 101. A transport path TR of the material P is defined.

In the fixing device of FIG. 6, a recording material (roll paper) P holding a toner image (not shown) on the upper side of the drawing is stretched in a region between the fixing nip portion N and a stretching roller (stretching roller pair) 15d. It will be in a suspended state.
Since the recording material P is not stretched until the leading end passes through the fixing nip portion N and reaches the stretching roller 15d in the conveyance of the recording material P, the winding around the fixing belt 13 cannot be prevented. Similarly, since the rear end of the recording material P is not stretched after passing through the fixing nip portion N, it is not possible to prevent the recording material P from being wound around the fixing belt 13. Therefore, it is preferable that the recording material P that has passed between the fixing nip portion N and the stretching roller 15d in a state where it is not stretched is not used for image formation.

  Note that a support member (not shown) that guides the leading end of the recording material P so that the leading end of the recording material P reaches the stretching roller 15d after the passage of the fixing nip portion N, and specifically, is sandwiched between the pair of rollers. It may be arranged.

Examples of the pressure roller 16 include a configuration in which an elastic layer is provided on an iron-based metal core. The diameter of the pressure roller 16 is 60 mm to 100 mm.
Since the recording material P that has passed through the fixing nip N is in a state of being pulled by the stretching roller 15d, the image surface can be prevented from being wound around the fixing belt 13. Further, due to the arrangement of the fixing belt support roller 12a, the distance between the fixing belt 13 and the surface of the stretched recording material P itself constituting the transport path TR is gradually increased, and after passing through the fixing nip portion N. The separation speed between the image surface and the surface of the fixing belt 13 becomes slow, and the reduction in glossiness at high temperatures is reduced.

  The toner remaining on the fixing belt 13 from the surface of the recording material P is removed by a fixing belt cleaning unit (not shown).

(Second embodiment)
A fixing device according to the second embodiment is shown in FIGS. 9, 10, 11 and 12.
In the fixing device of this embodiment, the fixing rotation unit 101 includes a pressing member 51 that can press the fixing belt 13 against the recording material P conveyed between the fixing roller 11 and the fixing belt support roller 12a. In the region between the fixing roller 11 and the pressing members 51 and 52, the recording material P adheres to the fixing belt 13 and is conveyed.

9 and 11 show a modification of the first embodiment (a fixing device to which cut paper is applied) shown in FIG. 5 described above, and the first embodiment except that the pressing member 51 or the pressing member 52 is provided. It is the same composition as.
10 and 12 show a modification of the first embodiment (a fixing device to which roll paper is applied) shown in FIG. 6 described above. The first embodiment except that the pressing member 51 or the pressing member 52 is provided. It is the same composition as.

The pressing member may be a roller-shaped member or a pad-shaped member.
For example, in the example shown in FIGS. 9 and 10, the pressing member 51 is a roller-like member, and in the examples shown in FIGS. 11 and 12, the pressing member 52 is a pad-like member.
The pressing members 51 and 52 are arranged so that the fixing belt 13 is pressed against the surface on which the image of the recording material P is formed during fixing, and a nip is formed between the fixing roller 11 and the pressing members 51 and 52. .

A roller or a pad for applying pressure may be disposed at a position where the pressing members 51 and 52 of the pressure rotating unit 102 face each other.
The distance between the surface of the fixing belt 13 and the conveyance path TR through which the recording material P is conveyed downstream from the pressing members 51 and 52 in the conveyance direction of the recording material P gradually increases toward the downstream in the conveyance direction of the recording material P. It is configured as follows.

  By adopting such a configuration, it is possible to provide a nip portion wider than the fixing nip portion N, it is possible to ensure good fixability even in a high-speed apparatus, and to form an image to be formed. A reduction in glossiness can be suppressed.

(Third embodiment)
A fixing device according to a third embodiment is shown in FIGS.
In the fixing device of this embodiment, the pressure rotation unit 102 conveys the pressure roller 16 that forms the fixing nip portion N and the fixing roller 11 to the downstream side of the fixing nip portion N in the conveyance direction of the recording material P. In the area between the pressure roller 16 and the pressing member 53, the recording material P adheres to the fixing roller 11 and is conveyed.

FIG. 13 is a modification of the first embodiment (a fixing device to which cut paper is applied) shown in FIG. 5 described above, and has the same configuration as that of the first embodiment except that a pressing member 53 is provided.
FIG. 14 is a modification of the first embodiment (a fixing device to which roll paper is applied) shown in FIG. 6 described above, and has the same configuration as that of the first embodiment except that a pressing member 53 is provided.

The pressing member 53 is, for example, a roller-shaped member.
The pressing member 53 is disposed so as to be pressed against the fixing roller 11, and an area where the fixing belt 13 and the recording material P are wound around the fixing roller 11 is formed.
The distance between the surface of the fixing belt 13 and the conveyance path TR in which the recording material P is conveyed downstream from the pressing member 53 in the conveyance direction of the recording material P gradually increases toward the downstream in the conveyance direction of the recording material P. It is configured.

With such a configuration, a nip portion wider than the fixing nip portion N can be provided along the fixing roller 11, and a plurality of pressure peaks can be provided in the nip portion region.
By providing a plurality of pressure peaks, good fixability can be ensured even in a high-speed apparatus, and a reduction in glossiness of the formed image can be suppressed, and in addition, the gloss of the image The degree of image deterioration such as blistering caused by water evaporation in the recording material P can be reduced.

(Fourth embodiment)
FIG. 15 shows a fixing device according to the fourth embodiment.
FIG. 15 is a modification of the above-described first embodiment (fixing device to which roll paper is applied) shown in FIG. 6, and includes a collection roller PR that winds and collects the recording material P, and includes a stretching roller 15d. The configuration is the same as that of the first embodiment except that is a member that supports the recording material P.
The recording material P is supported and stretched by the stretching roller 15d by the pulling force of the collection roller PR while winding the recording material P.

  With such a configuration, the distance between the fixing belt 13 and the surface of the stretched recording material P itself constituting the transport path TR is gradually increased, and the image surface after passing through the fixing nip portion N and the fixing are fixed. The separation speed of the surface of the belt 13 is slowed, and a decrease in glossiness at high temperatures is reduced.

(Process cartridge)
Examples of the process cartridge of this embodiment are shown in FIGS.
FIG. 7 shows an example of a process cartridge provided with the fixing device shown in FIG. 5 in the casing, and FIG. 8 shows an example of a process cartridge provided with the fixing device shown in FIG. 6 in the casing.
By making the process cartridge detachable from the image forming apparatus described later, the fixing device can be easily replaced.

(Image forming device)
The image forming apparatus according to the present embodiment includes at least an electrostatic latent image holding body that holds an electrostatic latent image, a developing unit that forms an electrostatic toner image on the electrostatic latent image, and the electrostatic latent image holding A transfer device for transferring the electrostatic toner image carried on the surface of the image carrier, which is a body or an intermediate transfer body, to a recording material, and a fixing device of the present invention for fixing the electrostatic toner image on the recording material. Prepare.

The image forming apparatus of this embodiment is shown in FIGS.
FIG. 16 is an example of an image forming apparatus to which cut paper is applied, and FIG. 17 is an example of an image forming apparatus to which roll paper is applied, and each includes the above-described fixing device of the present embodiment.
The configuration is the same in FIGS. 16 and 17 except that a fixing device corresponding to the type of the recording material P is provided and a paper feeding and conveying mechanism corresponding to the type of the recording material P is provided.

The image forming apparatus according to the present embodiment includes a unit for outputting four colors of yellow (Y), magenta (M), cyan (C), and black (K). The number of colors is not limited to four, and an apparatus having units of five or more colors may be employed. In particular, when a colorless and transparent clear toner is used, it is often used for the fifth and subsequent colors in addition to the four colors that are mainly used. In this case, an image is formed with the above four colors, and a clear toner layer is formed so as to cover from above, or a clear toner layer is formed so as to fill the image step, thereby obtaining a high gloss image. Can do. In addition, there is a utilization method such as forming a clear toner layer only for a part of an image or printing as a hidden character.
Since the image forming method for five or more colors is basically the same as the image forming method for four colors shown in FIGS. 16 and 17, a four-color image forming apparatus will be described here.

The mechanism of the image forming unit 20 will be described using the yellow unit 20Y.
The image forming unit 20 includes an image carrier 22, a charging device 21, a developing device 23, a drum cleaning device 24, a static elimination device (not shown), and the like. The surface of the image carrier 22 is charged by the charging device 21, a latent image is formed by the exposure device (optical writing unit) 110, and a toner image is formed by the developing device 23. These devices are each held by a common holding body and are integrally attached to and detached from the device main body so that they can be exchanged simultaneously.

  In this apparatus, the image carrier 22 is a photoconductor. The image carrier 22 has a drum shape in which an organic photosensitive layer is formed on the surface of a drum base, and is rotated by a driving unit (not shown). The charging device 21 is a roller, and generates an electric discharge between the charging device 21 and the image carrier 22 while bringing the charging device 21 to which a charging bias is applied into contact with or close to the image carrier 22 to thereby carry the image carrier. The surface of the body 22 is uniformly charged. In this embodiment, the toner is uniformly charged to the same negative polarity as the normal charging polarity of the toner. As the charging bias, one in which an AC voltage is superimposed on a DC voltage is employed. The charging device 21 is obtained by coating a metal cored bar with a conductive elastic layer made of a conductive elastic material. Instead of a method of bringing a charging member such as a charging roller into contact with or close to the image carrier 22, a method using a charging charger may be adopted.

The uniformly charged surface of the image carrier 22 is optically scanned by a laser beam emitted from the optical writing unit 110 to carry an electrostatic latent image. An optical writing unit 110 serving as a latent image writing unit is disposed above the image forming unit 20 and optically scans the image carrier 22 with laser light emitted from a laser diode based on image information. By this optical scanning, an electrostatic latent image is formed on the image carrier 22.
Specifically, in the entire region of the uniformly charged surface of the image carrier 22, the portion irradiated with the laser light attenuates the potential. Thereby, an electrostatic latent image is obtained in which the potential of the laser irradiation portion is smaller than the potential of the other portion (background portion).

  The optical writing unit 110 irradiates the photosensitive member through a plurality of optical lenses and mirrors while polarizing the laser light emitted from the light source in the main scanning direction with a polygon mirror rotated by a polygon motor (not shown). Is. You may employ | adopt what performs optical writing by the LED light emitted from several LED of the LED array. The electrostatic latent image formed on the surface of the image carrier 22 in this manner is visualized by attaching a charged toner by the developing device 23.

  The developing device 23 includes a developing unit that encloses a developing roll and a developer transport unit that stirs and transports the developer. The developer transport section includes a screw member having a rotary shaft member whose both ends in the axial direction are rotatably supported by bearings, and a spiral blade projecting spirally on the peripheral surface thereof. When the screw member rotates, the developer is stirred and conveyed to the developing roll.

  In the developer conveying portion, a toner concentration sensor (not shown) is provided on the lower wall of the casing, and detects the toner concentration of the developer in the developer conveying portion. As the toner concentration sensor, a sensor comprising a magnetic permeability sensor is used. Since the magnetic permeability of the developer containing the toner and the magnetic carrier has a correlation with the toner concentration, the magnetic permeability sensor detects the toner concentration.

  The image forming apparatus is provided with a toner replenishing unit (not shown) for replenishing toner to the developer transport section of the developing device. The control unit of the image forming apparatus stores Vtref, which is a target value of the output voltage value from the toner density detection sensor, in the RAM. When the difference between the output voltage value from the toner density detection sensor and Vtref exceeds a predetermined value, the toner replenishing means is driven for a time corresponding to the difference. As a result, the toner is supplied to the developer transport section in the developing device 23.

  The developing roll accommodated in the developing unit faces the screw member and also faces the image carrier 22 through an opening provided in the casing. Further, the developing roll includes a cylindrical developing sleeve made of a nonmagnetic pipe that is driven to rotate, and a magnet roller fixed inside the developing sleeve so as not to rotate with the sleeve. Then, while the developer supplied from the screw member is carried on the sleeve surface by the magnetic force generated by the magnet roller, the developer is transported to the developing area facing the image carrier 22 as the sleeve rotates.

  A developing bias having the same polarity as the toner and larger than the electrostatic latent image of the image carrier 22 and smaller than the uniform charging potential of the image carrier 22 is applied to the developing sleeve. As a result, a developing potential for electrostatically moving the toner on the developing sleeve toward the electrostatic latent image acts between the developing sleeve and the electrostatic latent image on the image carrier 22. Further, a non-developing potential that moves the toner on the developing sleeve toward the sleeve surface acts between the developing sleeve and the background portion of the image carrier 22. By the action of the development potential and the non-development potential, the toner on the development sleeve is selectively transferred to the electrostatic latent image on the image carrier 22, and the electrostatic latent image is developed into a toner image.

The image forming apparatus according to the present embodiment uses a development system that uses a two-component developer having toner and carrier. Of these, a development system that uses a one-component developer having only toner may be used. it can. In this way, the toner image is developed on the image carrier 22 and then sequentially transferred onto the intermediate transfer belt 30.
As the toner, a low melting point toner can be used.
The transfer residual toner remaining on the surface of the image carrier 22 after the toner image is transferred to the intermediate transfer belt 30 is removed by the cleaning device 24 for the photosensitive member, and the photosensitive member surface is cleaned. The surface potential is initialized by a static eliminator (not shown), for example, a static elimination lamp. As the cleaning device 24, a cleaning blade, a cleaning roller, a cleaning brush, or the like can be used, and these may be used in combination. Further, the cleaning efficiency can be increased by applying a voltage having a polarity opposite to that of the toner to these cleaning members.

  The image forming apparatus according to this embodiment is an intermediate transfer type image forming apparatus that once transfers a toner image formed on a photosensitive member to an intermediate transfer medium, and then transfers the toner image from the intermediate transfer medium to a transfer material. . Although an example of the intermediate transfer belt 30 is shown as an intermediate transfer medium, the intermediate transfer medium may be a drum shape.

  Below the image forming unit 20, an endless intermediate transfer belt 30 is stretched. In addition to the intermediate transfer belt 30 as an image carrier, a driving roller 32 and a driven roller (cleaning backup roller) 31, a secondary The transfer back roller 33 includes four primary transfer rollers 25, a secondary transfer roller 43, a belt cleaning device 130, a potential sensor 140, and the like.

  The intermediate transfer belt 30 is stretched by a driving roller 32, a secondary transfer back roller 33, a driven roller (cleaning backup roller) 31, and four primary transfer rollers 25 disposed inside the loop. Then, it is moved endlessly in the same direction by the rotational force of the drive roller 32 that is rotationally driven by a drive means (not shown).

The volume resistivity of the intermediate transfer belt 50 is about 1e ⁶ [Ωcm] to 1e ¹² [Ωcm], and preferably about 1e ⁹ [Ωcm] (Mitsubishi Chemical Hiresta UP MCP HT45 under the condition of an applied voltage of 100V. Measurement).

The four primary transfer rollers 25 sandwich the intermediate transfer belt 30 that is moved endlessly between the image carriers 22. As a result, primary transfer nips for Y, C, M, and Bk where the outer surface of the intermediate transfer belt 30 and the image carrier 22 abut are formed.
A primary transfer bias is applied to the primary transfer roller 25 by a transfer bias power source (not shown). As a result, a transfer electric field is formed between the Y, C, M, and Bk toner images on the image carrier 22 and the primary transfer roller 25.

The primary transfer rollers 25 can be separated from each other. When only Bk is transferred, the units of other colors are separated from each other. The primary transfer roller 25 is composed of an elastic roller including a metal cored bar and a conductive sponge layer fixed on the surface thereof. A primary transfer bias controlled by a constant voltage or a constant current is applied to such a primary transfer roller 25.
In place of the primary transfer roller 25, a transfer charger, a transfer brush, or the like may be employed.

  First, the intermediate transfer belt 30 enters the primary transfer nip for Y toner as the image carrier 22 rotates, and the Y toner image is transferred to the intermediate transfer belt 30 by the action of the transfer electric field and nip pressure. Is done. Thereafter, the intermediate transfer belt 30 sequentially passes through the primary transfer nips for C, M, and Bk. The C, M, and Bk toner images on the image carrier 22 are sequentially superimposed on the intermediate transfer belt 30 and primarily transferred.

  Next, the toner image on the intermediate transfer belt 30 is transferred from the intermediate transfer belt 30 to the recording material P in the secondary transfer portion. In the secondary transfer portion, a nip is formed by sandwiching the intermediate transfer belt 30 and the secondary transfer roller 43 between the secondary transfer back roller 33 and the secondary transfer roller 43 disposed inside the loop of the intermediate transfer belt 30. ing. The recording material P enters this nip.

While the secondary transfer roller 43 is grounded, a secondary transfer bias is applied to the secondary transfer back roller 33 by a secondary transfer bias power source 34. As a result, a secondary transfer electric field that electrostatically moves negative polarity toner from the secondary transfer back roller 33 side to the secondary transfer roller 43 side between the secondary transfer roller 43 and the secondary transfer back roller 33. Is formed.
The secondary transfer bias power source 34 has a DC power source, and a constant voltage or a constant current controlled voltage having the same polarity as the normal charging polarity of the toner is applied.
The secondary transfer bias power supply may be a power supply that can be applied by superimposing an alternating current on a direct current. In this case, good transferability can be obtained even for paper with large irregularities.

A sheet feeding unit of the image forming apparatus in FIG. 16 will be described.
As shown in FIG. 16, below the image forming apparatus, a paper feed cassette 40 that stores a plurality of recording materials P, which are cut sheets, in a stack of paper sheets is disposed. In the paper feed cassette 40, a paper feed roller 40a is brought into contact with the top recording material P of the paper bundle, and the recording material P is fed to the paper feed path by being rotated at a predetermined timing. Send it out.

A registration roller pair 41 is disposed near the end of the paper feed path. The registration roller pair 41 stops the rotation of both rollers as soon as the recording material P fed from the paper feed cassette 40 is sandwiched between the rollers.
Then, rotation driving is restarted at a timing at which the sandwiched recording material P can be synchronized with the toner image on the intermediate transfer belt 30 in the secondary transfer nip, and the recording material P is sent out toward the secondary transfer nip.

  The four-color superimposed toner image on the intermediate transfer belt 30 brought into intimate contact with the recording material P at the secondary transfer nip is collectively transferred onto the recording material P by the action of the secondary transfer electric field and nip pressure, and is a full color toner. Become a statue.

The toner image on the recording material P is heated and fixed by the fixing device 100 of this embodiment, and then the recording material P is discharged out of the apparatus.
Here, the fixing device 100 is the fixing device shown in FIG. The fixing device 100 is provided as a detachable process cartridge housed in a housing.

Next, a sheet feeding unit of the image forming apparatus in FIG. 17 will be described.
As shown in FIG. 17, a recording material P, which is a long roll paper (continuous paper), is fed by a paper feed roller 40c, and is rotated at a predetermined timing. Send it out toward the paper feed path.

  The four-color superimposed toner image on the intermediate transfer belt 30 brought into intimate contact with the recording material P at the secondary transfer nip is collectively transferred onto the recording material P by the action of the secondary transfer electric field and nip pressure, and is a full color toner. Become a statue.

The toner image on the recording material P is heated and fixed by the fixing device 100, and then the recording material P is discharged out of the apparatus.
Here, the fixing device 100 is the fixing device shown in FIG. The fixing device 100 is provided as a detachable process cartridge housed in a housing.
The discharged recording material P may be collected in a roll shape by a collecting means as shown in FIG. 15, or may be subjected to processing such as cutting.

(Glossiness evaluation)
FIG. 1B and FIG. 1C show the results of measuring the glossiness of an image formed using the fixing device and the image forming apparatus of this embodiment.
1B is obtained by the image forming apparatus provided with the fixing device of the present embodiment shown in FIG. 5, and FIG. 1C is obtained by the image forming apparatus provided with the fixing device of the present embodiment shown in FIG. It is a measurement result of an image.
FIG. 1A shows the result of using the conventional fixing device shown in FIG.

The glossiness was measured at 60 ° C. using a gloss meter GM-26D manufactured by Murakami Color Research Laboratory.
Although the gloss level varies depending on the surface shape of the recording material, a sufficiently smooth recording material is applied when high gloss is required. Therefore, “POD gloss coat A4 (128 g / m ² )” paper was used as the recording material.

  The fixing belt temperature on the horizontal axis of the graph is the temperature of the surface of the fixing rotating belt before the entrance of the fixing nip portion obtained from a temperature sensor (not shown) in the apparatus, and “♦” is a value at which the linear velocity of the fixing belt is 100 mm / s. , “□” is a value at which the linear velocity of the fixing belt is 200 mm / s, and “Δ” is a value at which the linear velocity of the fixing belt is 400 mm / s.

As is apparent from the results of FIGS. 1B and 1C, in the image forming apparatus using the fixing device of the present embodiment, the peak value of the glossiness is greatly reduced even when the linear velocity is increased. You can see that they are not.
Comparing the results of FIG. 1A with the results of FIG. 1B and FIG. 1C, even if the speed of the apparatus is increased by using the fixing device of the present embodiment, the obtained image is obtained. It can be seen that a decrease in glossiness of the film can be suppressed.

DESCRIPTION OF SYMBOLS 11 Fixing roller 12 Fixing belt support roller 13 Fixing belt 14 Heating means 15a, 15b, 15c Pressure belt support roller 15d Stretching roller 16 Pressure roller 17 Pressure belt 18 Charging means 19 Static elimination means 51, 52, 53 Pressing member 100 Fixing apparatus 101 Fixing rotation unit 102 Pressure rotation unit TR Conveying path P Recording material N Fixing nip portion

JP 61-132972 A JP 2004-133377 A JP 2005-55786 A JP 2005-153313 A

Claims (9)

In a fixing device having a fixing rotation unit provided with a heating means and a pressure rotation unit disposed at an opposing position thereof, and heating and fixing an unfixed image on a conveyed recording material in a fixing nip portion,
The fixing rotation unit has a heat-resistant fixing belt stretched around a plurality of fixing rotation members,
The plurality of fixing rotation members include at least a fixing roller that forms the fixing nip portion, and a fixing belt support roller that is disposed downstream of the fixing nip portion in the conveyance direction of the recording material,
In the region between the fixing nip portion and the fixing belt support roller, the interval between the surface of the fixing belt and the conveyance path for conveying the recording material gradually increases toward the downstream in the conveyance direction of the recording material. The fixing device is configured as described above. The fixing rotation unit has a pressing member capable of pressing the fixing belt against the conveyed recording material between the fixing roller and the fixing belt support roller;
The fixing device according to claim 1, wherein the recording material is attached to the fixing belt and conveyed in a region between the fixing roller and the pressing member. The pressure rotation unit can press the recording material conveyed to the fixing roller downstream of the pressure roller forming the fixing nip portion and the fixing nip portion in the conveyance direction of the recording material. Having a pressing member,
The fixing device according to claim 1, wherein the recording material adheres to the fixing roller and is conveyed in a region between the pressure roller and the pressing member. The pressure rotation unit has a heat-resistant pressure belt stretched around a plurality of pressure rotation members, and charging means for charging the pressure belt;
The plurality of pressure rotation members include at least a pressure roller that forms the fixing nip portion, and a pressure belt support roller that is disposed on the downstream side of the fixing nip portion in the conveyance direction of the recording material,
4. The fixing device according to claim 1, wherein a surface of the pressure belt defines a conveyance path for the recording material on a surface facing the fixing rotation unit. 5.   The pressure rotating unit includes charging means for charging the pressure belt on the upstream side of the fixing nip portion in the conveyance direction of the recording material, and charge eliminating means on the downstream side. The fixing device according to claim 4, wherein the recording material is conveyed while being electrostatically attracted.   The fixing device according to claim 5, further comprising a voltage control unit that controls a value of a voltage applied to the pressure belt by the charging unit. A tensioning unit in which the pressure rotating unit supports or sandwiches the pressure roller that forms the fixing nip portion and the long recording material that has passed through the fixing nip portion on the downstream side in the conveyance direction. And having a roller
The straight line connecting the fixing nip portion and a contact portion of the stretching roller with the recording material defines a conveyance path for the recording material on a surface facing the fixing rotation unit. The fixing device according to any one of 1 to 3. An electrostatic latent image holding body for holding at least an electrostatic latent image;
Developing means for forming an electrostatic toner image on the electrostatic latent image;
A transfer device for transferring the electrostatic toner image carried on the surface of the image carrier, which is the electrostatic latent image carrier or the intermediate transfer member, to a recording material;
An image forming apparatus comprising: a fixing device that fixes an electrostatic toner image on the recording material, wherein the fixing device is the fixing device according to claim 1. .   A process cartridge comprising the fixing device according to claim 1 in a housing and detachable from an image forming apparatus.

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