JP2015081986A - Toner fixing method and image formation apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a toner fixing method in which an image can be formed without making a paper surface dirty even when low-temperature fixing toner having a short fusion time is used.SOLUTION: There is provided a toner fixing method of fixing an unfixed toner image on a recording form by conveying the recording form having the unfixed toner image of toner to a nip part between a heated fixing member and a pressure member. The fusion time of the toner is derived by dropping toner on a heated surface of the hot plate of 230°C and photographing a state from contacting of the toner with the heated surface until fusion by a high-speed camera, toner having a fusion time of 0.035 seconds or less is used, and while the heat conductivity λ of the pressure member is set to 0.28 W/cm°C, the thermal capacity Cρ per unit volume is set to 1.3 J/°C cmor less.

Description

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

  2. Description of the Related Art Conventionally, an electrophotographic image forming apparatus such as a copying machine or a printer includes a fixing device. The fixing device includes a fixing roller that is heated by a heating unit and a pressure roller that is pressed against the fixing roller with a predetermined contact pressure. In the transfer device in the preceding stage of the fixing device, unfixed toner is placed on the surface of the fixing roller. It is known to fix unfixed toner onto a recording sheet by passing the transferred recording sheet through a fixing nip between a fixing roller and a pressure roller (see, for example, Patent Documents 1 and 2). .

In the fixing devices described in Patent Documents 1 and 2, a small part of the toner constituting the toner image or a foreign matter such as paper dust coming out of the recording paper adheres to the fixing roller during fixing. Therefore, in order to remove foreign matters such as toner and paper dust, the fixing devices described in Patent Documents 1 and 2 are provided with a cleaning mechanism and a peeling claw so as to be in contact with the surface of the fixing roller.
The cleaning mechanism has a heat-resistant cleaning web impregnated with silicone oil or the like, and is configured to remove foreign matters attached to the fixing roller by bringing the cleaning web into contact with the fixing roller.
The peeling claw is configured to scrape off foreign matter adhering to the surface of the fixing roller.

  The cleaning mechanism and the peeling claw remove and clean the foreign matter adhering to the surface of the fixing roller, but some of the foreign matter attached to the fixing roller may move to the pressure roller. Therefore, a fixing device having a peeling claw on the pressure roller side has also been proposed.

JP-A-5-53471 JP-A-5-158376

However, even in a fixing device provided with a cleaning mechanism, foreign matters such as toner and paper dust attached to the fixing roller cannot be completely removed, and fine foreign matters that cannot be seen with the naked eye pass through the cleaning web.
For this reason, when hundreds of originals with a high printing rate are continuously copied (fixed), the foreign matter that has passed through the cleaning web adheres to and accumulates on the peeling claw on the fixing roller side. Then, the foreign matter accumulated on the peeling claw by the heat of the fixing roller at the time of the next fixing (during warm-up) is melted again and retransferred (reattached) to the fixing roller.

A part of the foreign material transferred again by the fixing roller is collected by the cleaning web, but the other part moves to the pressure roller, and as a result, it is added to the back side of the next transported paper. There has been a problem that toner as a foreign matter of the pressure roller is attached and becomes dirty.
In addition, when a separation claw is provided on the pressure roller side, foreign matter adhering to the pressure roller is scraped off by the separation claw, but is deposited on the separation claw by heating the pressure roller by the heat of the fixing roller. Since the toner is melted again and re-transferred to the pressure roller, there is a problem that the back side of the next sheet to be conveyed is soiled as described above.

  Furthermore, in recent years, in order to save energy in the fixing device, development of a low-temperature fixing toner that melts and fixes at a lower temperature than before by lowering the softening point of the binder resin of the toner has been performed. When this low-temperature fixing toner is used, the melting time of the toner is shorter than before and the viscoelasticity is low. Therefore, the temperature of the pressure roller of the toner adhering to the peeling claw increases during the next fixing (when warming up). Then, it melts instantly and tends to adhere to the pressure roller in a tail shape. For this reason, the back side of the paper is soiled with a large area, and furthermore, the toner has a low melt viscosity, so that once the back side of the paper is soiled, it is difficult to remove.

SUMMARY An advantage of some aspects of the invention is that it provides a toner fixing method and an image forming apparatus capable of forming an image without soiling a paper surface even when a low-temperature fixing toner having a short melting time is used. .

Thus, according to the present invention, the recording paper having an unfixed toner image of toner is conveyed to the nip portion between the heated fixing member and the pressure member, whereby the unfixed toner image is applied to the recording paper. A toner fixing method for fixing, wherein
The toner is dropped on a heating surface of a hot plate at 230 ° C., and the melting time of the toner is derived by photographing with a high-speed camera the state from when the toner contacts the heating surface until it melts.
A toner having a melting time of 0.035 seconds or less is used, the thermal conductivity λ of the pressure member is set to 0.28 W / m ° C. or less, and the heat capacity Cρ per unit volume is 1.3 J / ° C. · cm ^3. A toner fixing method set as follows is provided.

According to another aspect of the present invention, the recording sheet having an unfixed toner image of toner is conveyed to a nip portion between a heated fixing member and a pressure member, thereby the unfixed toner image. A toner fixing method for fixing the toner on the recording paper,
The toner is dropped on a heating surface of a hot plate at 230 ° C., and the melting time of the toner is derived by photographing with a high-speed camera the state from when the toner contacts the heating surface until it melts.
A toner having a melting time of 0.035 seconds or less is used, the heat conductivity of the pressure member is λ (W / m ° C.), and the heat capacity per unit volume of the pressure member is Cρ (J / ° C. · cm ³ ), there is provided a toner fixing method in which λ · Cρ ≦ 0.364 is set.

  According to still another aspect of the present invention, the toner used in the toner fixing method has a melting time of 0.035 seconds or less, and includes core particles containing at least a binder resin and a colorant, and the core particles A capsule toner having a shell layer covering the surface is provided.

According to still another aspect of the present invention, a photosensitive member on which an electrostatic latent image is formed, a charging device that charges the surface of the photosensitive member, and an electrostatic latent image on the surface of the photosensitive member. An exposure apparatus to be formed, a toner dropped on a heating surface of a hot plate at 230 ° C., a toner having a melting time of 0.035 seconds or less from when the toner comes into contact with the heating surface, and the photosensitive A developing device for supplying the toner to the electrostatic latent image on the surface of the body to form a toner image, a transfer device for transferring the toner image on the surface of the photoreceptor to the recording paper, and an unfixed image transferred to the recording paper An image forming apparatus comprising a fixing device for fixing a toner image on a recording sheet,
The fixing device includes a fixing member to be heated and a pressure member disposed in proximity to the fixing member, and is not fixed to a nip portion formed between the fixing member and the pressure member. The recording paper having a toner image is conveyed to be fixed to the recording paper by fixing the unfixed toner image.
An image forming apparatus is provided in which the heat conductivity λ of the pressure member of the fixing device is 0.28 W / m ° C. or less and the heat capacity Cρ per unit volume is 1.3 J / ° C. · cm ³ or less.

According to still another aspect of the present invention, a photosensitive member on which an electrostatic latent image is formed, a charging device that charges the surface of the photosensitive member, and an electrostatic latent image on the surface of the photosensitive member. An exposure apparatus to be formed, a toner dropped on a heating surface of a hot plate at 230 ° C., a toner having a melting time of 0.035 seconds or less from when the toner comes into contact with the heating surface, and the photosensitive A developing device for supplying the toner to the electrostatic latent image on the surface of the body to form a toner image, a transfer device for transferring the toner image on the surface of the photoreceptor to the recording paper, and an unfixed image transferred to the recording paper An image forming apparatus comprising a fixing device for fixing a toner image on a recording sheet,
The fixing device includes a fixing member to be heated and a pressure member disposed in proximity to the fixing member, and is not fixed to a nip portion formed between the fixing member and the pressure member. The recording paper having a toner image is conveyed to be fixed to the recording paper by fixing the unfixed toner image.
When the thermal conductivity of the pressure member of the fixing device is λ (W / m ° C.) and the heat capacity per unit volume of the pressure member is Cρ (J / ° C. · cm ³ ), λ · Cρ ≦ An image forming apparatus of 0.364 is provided.

According to the present invention, even when an image is formed using a low-temperature fixing toner having a melting time of 0.035 seconds or less, the migration of the micro offset toner from the fixing member to the pressure member is suppressed, and a peeling means such as a peeling claw It is possible to prevent toner stains on the temperature detection means such as the temperature sensor and the backside of the paper due to ejection of toner stains from the peeling means and the temperature detection means.
In addition, a capsule toner having a melting time of 0.035 seconds or less is a toner that has low-temperature fixability and excellent storage stability in which toner aggregation is suppressed.

1 is an internal configuration diagram of an image forming apparatus according to Embodiment 1 of the present invention viewed from the front. FIG. FIG. 2 is a configuration diagram of the fixing device according to the first exemplary embodiment of the present invention viewed from the axial direction. FIG. 3 is a configuration diagram viewed from a direction orthogonal to the axial direction of the fixing device of FIG. 2. It is a figure explaining the measuring method of the melting time of the toner capsule which concerns on Embodiment 1 of this invention. 6 is a graph showing a temperature change of the pressure roller with respect to the fixing roller, where (A) shows a result of using the pressure roller of Example B, and (B) shows a result of using the pressure roller of Comparative Example 1. FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, after describing the overall configuration of the image forming apparatus, the fixing method that is a feature of the present invention will be described in detail.

<Embodiment 1>
(About image forming device)
FIG. 1 is an internal configuration diagram of an image forming apparatus according to Embodiment 1 of the present invention viewed from the front.
The image forming system 1 includes an image forming apparatus 2, a peripheral device such as a scanner 3, an automatic document conveying device 4, a post-processing device 5, a recording material supply device 6, a relay conveying unit 8, and a duplex conveying device 10.
The image forming apparatus 2 and the post-processing apparatus 5 are placed side by side on the upper surface of the recording material supply apparatus 6, and the scanner 3 and the automatic document feeder 4 are disposed above them, and these are supported on the system rack 7. Has been.

The image forming apparatus 2 records and outputs image data from the externally connected device when an image processing device such as a personal computer as an externally connected device is connected, as well as the recording output of the image read by the scanner 3. It is configured as follows.
An electrophotographic process section (image forming section) 20 with a photoreceptor (photosensitive drum) 200 as the center is disposed on the substantially left side of the image forming apparatus 2. Further, around the photosensitive member 200, a charging roller 201 for uniformly charging the surface of the photosensitive member 200, and an optical scanning unit 22 for scanning an optical image on the uniformly charged photosensitive member 200 and writing an electrostatic latent image. , A developing unit 202 that reproduces the electrostatic latent image written by the optical scanning unit 22 with a developer, a transfer unit 203 that transfers an image reproduced on the photosensitive member 200 onto a recording material, and a photoconductor 200 after the transfer. A cleaning unit 204 that enables the developer remaining on the surface to be removed and a new image to be recorded on the photosensitive member 200, and a static elimination lamp unit (not shown) that removes the charge on the surface of the photosensitive member 200 are disposed. Has been.

  A recording material supply unit 21 that can store a recording material is disposed below the image forming apparatus 2, that is, on the recording material supply device 6 side. The recording material supply unit 21 includes a recording material storage tray 210 that stores recording materials, and a separation supply unit 211 that separates and feeds the recording materials stored in the recording material storage tray 210 one by one. The recording materials separated and fed one by one by the separation supply unit 211 are sequentially supplied between the photosensitive member 200 and the transfer unit 203 of the electrophotographic process unit 20, and the toner recorded and reproduced on the photosensitive member 200. The image is transferred. Note that operations such as replenishment of the recording material to the recording material supply unit 21 and replacement of the recording material are performed by pulling out the recording material accommodation tray 210 to the front side of the image forming apparatus 2.

A recording material sent from an optional recording material supply device 6 is received on the lower surface of the image forming apparatus 2 and sequentially supplied between the photosensitive member 200 of the electrophotographic process unit 20 and the transfer unit 203. For this purpose, a recording material receiving port 27 is provided.
A fixing device 23 is disposed above the electrophotographic process unit 20. The fixing device 23 sequentially receives the recording material onto which the image has been transferred, heats and fixes the developer transferred onto the recording material, and sends the recording material to the outside of the fixing device 23. The recording material on which the image is recorded is transferred from the discharge roller 28 of the image forming apparatus to the relay conveyance unit 8 on the upper surface of the image forming apparatus 2. As described above, the sheet conveyance path (recording material conveyance path) 64 of the image forming apparatus 2 is configured in a substantially vertical shape from the bottom to the top.

  The optical scanning unit 22 is disposed on the side of the electrophotographic process unit 20, that is, at a position adjacent to the electrophotographic process unit 20 in a direction substantially orthogonal to the sheet conveyance path 64. In the upper and lower space portions of the optical scanning unit 22, a process control unit (PCU) substrate that controls the electrophotographic process and an apparatus controller 24 that accommodates an interface substrate that receives image data from outside the apparatus are received from the interface substrate. An image control unit 25 having an image control unit (ICU) substrate for performing predetermined image processing on the image data and causing the optical scanning unit 22 to scan and record an image on the photosensitive member 200, and these various substrates And a power supply unit 26 for supplying power to the unit.

  The recording material supply device 6 is an optional externally attached recording material supply device, and includes three recording material supply units 61, 62, and 63. The recording material supply units 61, 62, and 63 include recording material storage trays 610, 620, and 630, and separate feeding units 611, 621, and 631. The recording materials stored in the recording material storage trays 610, 620, and 630 are separated one by one by the separation feeding units 611, 621, and 631, provided on the upper surface of the recording material supply device 6, and recorded by the image forming apparatus 2. The recording material is supplied toward the recording material discharge port 65 communicating with the material receiving port 27. At the time of operation, the recording material supply units 61, 62, and 63 that accommodate a recording material of a desired size are selectively operated. The replenishment of the recording material to the recording material supply units 61, 62, 63 is performed by pulling out the recording material accommodation trays 610, 620, 630 to the front side of the image forming apparatus 2.

In addition, the recording material supply device 6 is configured to place the image forming device 2 and the post-processing device 5 on the upper portion, but can move and be fixed between the system racks 7 in this state. As described above, a moving roller 69 and a fixed portion 68 are provided at the lower portion. At the time of movement, the fixing portion 68 is rotated and raised to separate the fixing portion 68 from the floor surface. At the time of fixing, the fixing portion 68 is rotated and lowered to bring the fixing portion 68 into contact with the floor surface. The recording material supply device 6 is fixed.
1 illustrates the case where the recording material supply device 6 includes three recording material supply units 61, 62, and 63. However, the present invention is not limited to this, and the recording material supply device 6 includes at least one recording material supply unit. What is necessary is just to have.

The post-processing device 5 introduces a recording material on which an image discharged from the relay conveyance unit 8 of the image forming device 2 is recorded by a carry-in roller 50 provided on the upper portion of the post-processing device 5, thereby forming the recording material. On the other hand, post-processing is performed.
Post processing includes stapling processing, punching processing, sorting processing, and the like, and the post-processing device 5 illustrated in FIG. 1 performs stapling processing. The recording material is selectively discharged by the switching gate 52 to the lower discharge tray 59 when the post-processing is performed and to the upper discharge tray 56 when the post-processing is not performed.

  The scanner 3 includes an automatic reading mode in which a sheet-like document automatically supplied by the automatic document feeder 4 is sequentially exposed and scanned one by one to read a document image, and a book-like document set by a user's manual operation. Alternatively, a manual reading mode for reading a document image of a sheet-like document that cannot be automatically supplied by the automatic document feeder 4 is provided. The scanner 3 exposes a document image of a document set on a transparent document placing table 30 by a first scanning unit 31 and a second scanning unit 32 that move along the document placing table 30 with a predetermined speed relationship with each other. The document image is scanned and guided by an optical component such as a mirror or an imaging lens 33 to form an image on the photoelectric conversion element 34, thereby converting the document image into an electrical signal and outputting it.

The automatic document conveying device 4 includes a document conveying means 41 that conveys a document placed on the document setting tray 40 toward the document placing table 30 and discharges the scanned document onto a document discharge tray 42. Yes. Further, the automatic document feeder 4 rotates upward with its rear end as a fulcrum so that a sheet-like document that cannot be automatically supplied can be placed on the document table 30 and scanned. The front side is configured to open.
The relay conveyance unit 8 is mounted on an upper portion of a paper discharge tray 29 provided on the top of the image forming apparatus 2 and forms a recording material on which an image discharged from the paper discharge roller 28 of the image forming apparatus 2 is recorded. This is a transport unit for introduction toward the post-processing device 5 located on the downstream side of the device 2.

Further, in the middle of the recording material conveyance path 84 of the relay conveyance unit 8, another recording material conveyance path for guiding the recording material to the discharge tray 9 formed by the upper surface 82 of the unit 8 and the upper surface 54 of the post-processing device 5. 83 is branched. The two discharge destinations can be changed by switching the gate 81 arranged at the branch portion of the transport path.
The double-sided conveying device 10 is a conveying device that is attached to the side surface of the image forming apparatus 2 and reverses the recording material when forming images on both sides of the recording material. When reversing the recording material, the paper discharge roller 28 stops in a state where the recording material has been discharged halfway, and the reversing direction guides the recording material to the duplex conveying device 10 side. At this time, by switching the gate 85 provided after the fixing device 23, the recording material enters the duplex conveying device 10 without returning to the fixing device 23 side. The recording material that has passed through the double-sided conveyance device 10 enters the paper conveyance path 64 again from before the electrophotographic process unit 20 and passes through the electrophotographic process unit 20 and the like, whereby an image is formed on the back surface.

The image forming system 1 has a structure in which the image forming apparatus 2 and the post-processing apparatus 5 are mounted side by side on the recording material supply apparatus 6. The width of the main body of the image forming apparatus 2 is L1, and the post-processing apparatus. The width L of the recording material supply device 6 is designed to be substantially equal to L1 + L2, where L2 is the width of the 5 main body.
By configuring the system by combining peripheral devices as in the image forming system 1, an image forming apparatus desired by the user can be easily realized. On the other hand, in such an image forming system 1, it is necessary to consider the adjustment of the temperature and humidity of the entire system. On the other hand, if a heater, a fan, or the like is provided for each peripheral device, the number of parts increases as a whole system, causing problems such as an increase in the cost of the image forming system 1.
In view of this, the image forming system 1 is configured such that a heater (heating element) 300 is provided between the image forming apparatus 2 and the recording material supply apparatus 6.

(Fixing device)
Next, the fixing device 23 will be described in detail with reference to FIGS.
2 is a configuration diagram viewed from the axial direction of the fixing device according to the first exemplary embodiment of the present invention, and FIG. 3 is a configuration diagram viewed from a direction orthogonal to the axial direction of the fixing device of FIG.
As shown in FIG. 2, the fixing device 23 detects the temperatures of the fixing roller 101 as a heating member, the pressure roller 106 as a pressure member, heater lamps 105 a and 105 b that are heat sources for the fixing roller, and the temperature of the fixing roller 101. Temperature sensors (thermistors) 103a and 103b constituting temperature detecting means, temperature sensors (thermistors) 103c constituting temperature detecting means for detecting the temperature of the pressure roller 106, thermostats 104a and 104b being abnormal temperature detecting means, An upper peeling claw 108 as a paper peeling means, a lower peeling claw 109, a cleaning device 110, and a control circuit (not shown) as a temperature control means are provided.

  Bearings 102 are installed at both axial ends of the fixing roller 101, and the fixing roller 101 is rotatably installed. Further, a gear (not shown) is connected to one end of the fixing roller 101 at the end in the axial direction, and a driving force from a separately installed motor is transmitted to the gear to rotate the fixing roller. The pressure roller 106 is provided with a bearing (not shown) that enables the pressure roller 106 to rotate at the shaft end of the pressure roller 106, and the bearing presses the pressure roller 106 against the surface of the fixing roller 101. A spring 108 for supporting a load on the pressure holding unit 107 and for applying a load to the pressure holding unit 10 7 is provided.

The heater lamps 105a and 105b are made of halogen heaters and are arranged inside the fixing roller 101. When the heater lamps 105a and 105b are energized from the control circuit, the heater lamps emit light with a predetermined heat distribution, and infrared rays are emitted. Then, the inner peripheral surface of the fixing roller 101 is heated.
The fixing roller 101 is heated to a predetermined temperature (170 ° C. in this embodiment) by the heater lamps 105a and 105b, and the recording paper P on which the unfixed toner image T passing through the fixing nip portion N of the fixing device is formed. It is for heating. The fixing roller 101 includes a cored bar 101a which is a main body thereof, and a coat layer 101b formed on the outer peripheral surface of the cored bar to prevent the toner T on the recording paper P from being offset.

As a material of the cored bar 101a, for example, a metal such as iron, stainless steel, aluminum, copper, or an alloy thereof is used. The cored bar 101a of this embodiment is 30 mm in diameter, and an aluminum cored bar with a thickness of 0.8 mm is used in order to reduce the heat capacity.
For the coat layer 101b, fluororesins such as PFA (copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether) and PTFE (polytetrafluoroethylene), silicone rubber, fluororubber, and the like are suitable. The coating layer 101b of this embodiment is formed by applying and baking a material obtained by blending PFA and PTFE to the outer peripheral surface of the cored bar 101a through a primer layer (thickness 7 μm) with a thickness of 22.5 μm. ing.

  The pressure roller 106 is a porous body layer made of a closed-cell silicone elastomer prepared from a low-hardness or high-hardness silicone sponge rubber or emulsion composition on the outer peripheral surface of a core metal 106a such as steel, stainless steel, or aluminum. It is formed by covering with a heat-resistant elastic material layer 106b such as a low heat capacity type non-foamed (solid) rubber elastic layer mixed with a low density / low specific heat filler. On the surface of the heat-resistant elastic material layer 106b of the pressure roller 106, a coating layer 106c made of the same fluororesin as that of the fixing roller may be formed. In this embodiment, the pressure roller 106 is formed by forming a heat-resistant elastic body layer 106b made of silicone sponge rubber having a thickness of 5.5 mm on a stainless steel core 106a having a diameter of 23 mm, and further having a thickness of 50 μm on the surface thereof. A coat layer 106c made of a PFA tube is formed. The pressure roller 106 is pressed against the fixing roller 101 with a force of 11 kgf (108 N) by a pressure member 108 made of a spring, thereby forming a fixing nip portion N having a width of about 4 mm between the pressure roller 106 and the fixing roller 101. ing.

As the PFA tube used for the coat layer 106c, it is more preferable to use a conductive PFA tube containing a conductive agent such as carbon. The reason for this is that when an insulating PFA tube is used, the pressure roller is charged to about −5 kV due to frictional charging with the recording paper and the fixing roller, and as a result, the fixing nip portion N has the same negative polarity. An electric field that repels the toner toward the fixing roller acts and causes electrostatic offset (a phenomenon in which the toner adheres to the fixing roller electrostatically) with respect to the fixing roller. Therefore, in this embodiment, by using a conductive PFA tube, charging of the pressure roller is prevented and generation of electrostatic offset is suppressed. In order to obtain this antistatic effect, a PFA tube having a volume resistance of 10 ⁵ Ωcm is used in this embodiment.

  For measurement of the thermal conductivity of the pressure roller, a rapid thermal conductivity meter QTM-500 manufactured by Kyoto Electronics Industry Co., Ltd. was used.

Regarding the heat capacity Cρ (J / ° C · cm ³ ) of the pressure roller, the specific heat of the silicone rubber material used is C (J / g · ° C), the specific gravity is ρ (g / cm ³ ), and the foaming rate is η (%), The following formula Cρ = η × C × ρ / 100
I asked more.

  Further, the hardness of the pressure roller was measured using a constant pressure loader for a rubber hardness meter manufactured by Kobunshi Keiki Co., Ltd. under a load condition of 9.8 N.

Thermistors 103a and 103b as temperature detecting means are disposed on the peripheral surface of the fixing roller 101 so as to detect the surface temperature of the fixing roller 101. Based on the temperature data detected by each thermistor, a temperature control means (not shown) controls energization to the heater lamps 105a and 105b so that the fixing roller temperature becomes a predetermined temperature.
A cleaning web 113 wound from the supply roller 111 side to the take-up roller 112 side is disposed above the fixing roller 101. The take-up roller 112 is fed at a predetermined feed amount each time the recording material is fixed. Rolled up. The cleaning web 113 is pressed against the surface of the fixing roller 101 by being pressed by a pressure roller made of a heat-resistant sponge roller having a diameter of 18 mm while being wound around the winding roller 112, so that the surface of the fixing roller 101 is cleaned and separated. The mold is being applied. In this embodiment, silicone oil is used as a release agent, and the cleaning web is impregnated with an amount of 6 g / m ² .

  Further, an upper peeling claw 108 and a lower peeling claw 109 are installed as a sheet peeling means on the downstream side in the rotation direction of the fixing roller 101 and the pressure roller 106 in the fixing nip N, and the tips of these claws are fixed. It is in contact with the roller 101 and the pressure roller 106. Thus, even when a document with a high printing rate is fixed, the paper is prevented from being wound around the fixing roller 101 and the pressure roller 106, and the paper is reliably peeled off from the fixing roller and the pressure roller. Yes. The lower peeling claw 109 is configured such that the tip of the claw portion 109a can be rotated (moved) in the direction of the arrow with the rotation shaft 109b as a fulcrum, and is driven by a drive device including a solenoid (not shown) and a control circuit for controlling the drive device. In addition, the pressure roller 106 is configured to perform the contact / separation operation at a predetermined timing.

  In the fixing device 23 configured as described above, an unfixed toner image T is transferred to the fixing nip portion N at a predetermined fixing speed (225 mm / s in this embodiment) and a copying speed (46 sheets / minute in this embodiment). The formed recording paper P is conveyed and fixed by heat and pressure.

(About toner)
Next, one embodiment of the toner used in the fixing method of the present invention will be described.
The toner used in this example is a capsule toner having core particles including a binder resin, a colorant, and a release material, and a shell layer covering the core particles, and is melted as compared with a toner having no conventional shell layer. It is characterized by a short time.

  In this capsule toner, for example, in order to shorten the melting time of the toner in order to correspond to the nip passage time, a resin component having a characteristic (sharp melt characteristic) that instantaneously melts and spreads is used for the core particle, and as a shell layer. Can use a resin component that can prevent aggregation of toner particles even when stress is applied by stirring in the developing container. By using the capsule toner having such a core-shell structure, it is possible to prevent changes in the properties of the toner due to long-term use while maintaining sharp melt characteristics.

  As a method for producing a capsule toner, for example, first, core particles are produced by the same pulverization method as that of conventional toner, and coating of resin fine particles on the core particles is performed using a surface modifying apparatus. Next, capsule toner is manufactured by attaching and fusing resin fine particles as a shell to the core particles.

The toner production method is not limited to the above-described method, and the toner is prepared from a wet material as represented by suspension polymerization method, emulsion aggregation method (Emulsion-Aggregation method), and dissolution suspension method. A method (chemical method) in which toner particles are prepared by wet or wet preparation using direct or submicron sized component fine particles may be used. The toner used in the present invention is not limited to the core-shell capsule toner as long as the melting time is 0.035 seconds or less.

<Embodiment 2>
In the fixing device described in the first exemplary embodiment, a cleaning web for cleaning the fixing roller may be provided.

  Table 1 shows the specifications of the toners used in the present examples and comparative examples.

  An experimental result (experiment 1) of measuring the melting time of the toner will be described with reference to Table 1.

<Example 1>
In Example 1, core particles were prepared using a binder resin having a glass transition temperature of 45 ° C. and a softening temperature of 120 ° C. (in this example, styrene-acrylic resin), and the glass transition point was formed on the entire surface of the core particles. A capsule toner was obtained by coating resin fine particles (styrene-acrylic resin in this example) having a temperature of 60 ° C. and a softening temperature of 130 ° C. to form a shell layer.

<Example 2>
In Example 2, a capsule toner was obtained in the same manner as in Example 1 except that the glass transition temperature of the styrene-acrylic resin as the core binder resin was 50 ° C. and the softening temperature was 130 ° C.

<Comparative Example 1>
On the other hand, as a comparative example 1, a conventional toner having no shell layer was also produced. The manufacturing method consists of only the method for producing the core particles of Example 1. However, the toner (core particles) of Comparative Example 1 needs to be composed of a resin component that can prevent aggregation of toner particles even when stress due to stirring in the developing container is applied. Therefore, as the styrene-acrylic resin used for the toner of Comparative Example 1, those having the same glass transition temperature and softening point temperature as those of the shell layers of Examples 1 and 2 of 60 ° C. and 130 ° C. were used. The other compositions in the toner of Comparative Example 1 are the same as those in Examples 1 and 2.

Next, a method for measuring the melting time of the toner used in this embodiment will be described with reference to FIG.
As shown in FIG. 4, the melting time of the toner T was measured using a hot plate H, a high-speed camera V, and a spoid S filled with the toner T. The hot plate H was heated to an arbitrary temperature, and a small amount of toner T was dropped on the heated surface of the hot plate H using the dropoid S. By observing the melted state after the toner T dropped on the heating surface of the hot plate H with a high-speed camera V, the melting time of the toner T was measured.
The high-speed camera V can shoot every 1 msec (0.001 sec), and from the moment the toner T falls on the heating surface of the hot plate H, the toner T becomes elliptical on the hot plate H and begins to spread. The time until this was taken as the melting time of the toner T. The melting time was measured in the same manner for the toner of Comparative Example 1 that does not have a core-shell structure.

First, the temperature of the hot plate was set to 230 ° C. The reason will be described below.
The fixing control temperature (fixing roller surface temperature) of the fixing device used in this embodiment is 170 ° C. as described above, and the pressure roller surface temperature (≈average paper temperature) is the heat from the fixing roller. And stable at 80 ° C or higher. That is, the toner passing through the fixing nip N receives an average temperature of 125 ° C. (= (170 + 80) / 2) from the top and bottom.

On the other hand, since the toner dropped on the hot plate is heated only from the lower side, the ambient temperature is 20 ° C. in order to obtain the same average temperature as the fixing nip portion N. From the following formula, 125 × 2-20 = 230
The hot plate temperature was set to 230 ° C.
As a result of measuring the melting time of each toner under these conditions, as shown in Table 1, the melting time of the toner of Example 1 is 0.015 seconds, and the melting time of the toner of Example 2 is 0.035 seconds. all right. On the other hand, the melting time of the toner of Comparative Example 1 was found to be 0.055 seconds.

  Next, using the toners of Examples 1 and 2 and Comparative Example 1 and the six types of pressure rollers of Examples A to D and Comparative Examples A and B described below, the lower nail dirt level, that is, the lower peeling nail An experiment was conducted on the toner ejection level (re-transfer level) from (No. 2).

  Table 2 shows the specifications of the pressure roller used in Experiment 2.

  The pressure roller of Example A in which the thermal conductivity λ, the heat capacity Cρ, and λ · Cρ are within the scope of the present invention has a hardness of 40 degrees in Asker C and a thickness of 5 on a stainless steel core having a diameter of 23 mm. A heat-resistant elastic body layer made of .5 mm silicone sponge rubber is formed, and a coat layer made of a PFA tube having a thickness of 50 μm is further formed on the surface.

  The pressure roller of Example B in which the thermal conductivity λ, the heat capacity Cρ and λ · Cρ are within the scope of the present invention is the same as that of Example A except that the hardness is 60 degrees in Asker C. The same configuration was used.

  The pressure roller of Example C in which the thermal conductivity λ, the heat capacity Cρ, and λ · Cρ are within the scope of the present invention has a hardness of 50 degrees in Asker C and a thickness of 5 mm on a stainless steel core having a diameter of 23 mm. A porous body layer made of .5 mm silicone elastomer is formed as a heat-resistant elastic body layer, and a coat layer made of a PFA tube having a thickness of 50 μm is further formed on the surface.

  The pressure roller of Example D in which the thermal conductivity λ, the heat capacity Cρ, and λ · Cρ are within the scope of the present invention has a hardness of 50 degrees according to JIS-A and is formed on a stainless steel core having a diameter of 23 mm. A low heat capacity type non-foamed (solid) rubber elastic layer mixed with 5.5 mm low density and low specific heat filler is formed as a heat resistant elastic layer, and a coating layer made of a PFA tube having a thickness of 50 μm is formed on the surface. Formed and configured.

  The pressure roller of Comparative Example A, whose thermal conductivity λ, heat capacity Cρ and λ · Cρ are outside the scope of the present invention, has a hardness of 40 degrees according to JIS-A, and a silicone elastomer on a stainless steel core having a diameter of 23 mm. A low-hardness solid layer having a thickness of 5.5 mm is formed as a heat-resistant elastic layer, and a coating layer made of a PFA tube having a thickness of 50 μm is formed on the surface thereof.

  The pressure roller of Comparative Example B, whose thermal conductivity λ, heat capacity Cρ and λ · Cρ are outside the scope of the present invention, is that of Comparative Example A, except that the hardness is 60 degrees in JIS-A. What was comprised similarly to was used.

  In Experiment 2 to check the level of the lower nail stain, after copying (fixing) 250 original documents with a printing rate of 20%, the fixing operation was completed and left for about 3 minutes. The five sheets were fixed, and it was checked whether or not the five sheets were stained by the ejection of toner from the lower peeling claw. In addition, the lower peeling claw is always brought into contact with the pressure roller (claw fixing), and is brought into contact with the pressure roller only when the leading edge of the paper comes, and separated at other times. Comparison was made for two cases of (nail separation). The results are shown in Table 2.

Here, regarding the level of toner contamination on the back of the recording paper due to the ejection of toner from the lower peeling claw,
1: No toner contamination 2: Slight toner contamination, but no problem in image quality 3: Toner contamination length of less than 10 mm 4: Toner contamination length of 10 mm or more and less than 30 mm 5: Toner contamination length Was evaluated in five stages of 30 mm or more.

  From the results shown in Table 2, the pressure roller of Comparative Example A or B in which the thermal conductivity λ, the heat capacity Cρ and λ · Cρ are outside the scope of the present invention was used, and the toner of Examples 1, 2 or Comparative Example 1 was used. Comparing the lower nail stain level when used, the sharp peeling low-temperature fixing toner having a short melting time as in Examples 1 and 2 uses lower peeling than the case of using the toner of Comparative Example 1. It can be seen that the toner stains on the back side of the recording paper easily occur due to the nail. The reason for this is as described for the problem of the present invention.

  In addition, the pressure roller of Example A, B, C or D having thermal conductivity λ, heat capacity Cρ and λ · Cρ within the scope of the present invention is used, and the toner of Example 1, 2 or Comparative Example 1 is used. Comparing the lower nail stain level when used, it can be seen that the smaller the thermal conductivity λ, the heat capacity Cρ, and λ · Cρ, the better the level of toner stain on the back surface of the recording paper due to the ejection of toner from the lower peeling nail. Recognize. The reason for this will be described with reference to FIG.

FIG. 5 is a graph showing the temperature change of the pressure roller with respect to the fixing roller. FIG. 5A shows the result of using the pressure roller of Example B, and FIG. 5B shows the result of using the pressure roller of Comparative Example A.
As shown in FIG. 5A, the temperature of the pressure roller of Example B is maintained at about 90 ° C. from the beginning of paper feeding. On the other hand, as shown in FIG. 5B, the temperature of the pressure roller of Comparative Example A is about 73 ° C. at the initial stage of sheet passing and gradually increases from there, and is about 150 seconds (the number of sheets 115). ) And reached 88 ° C.

  The toner adhering to the fixing roller and melted is transferred to the pressure roller at the fixing nip portion N. When the temperature of the fixing roller is the same, the lower the pressure roller temperature, the easier it is to move to the pressure roller side. In Comparative Example A, it is considered that the toner stain on the lower peeling claw becomes more remarkable than that in Example B, and the paper back surface stain is deteriorated. Here, the reason why the pressure roller of Example B can maintain the temperature higher than that of the pressure roller of Comparative Example A is that the thermal conductivity λ and the heat capacity Cρ are small.

  Furthermore, from the results shown in Table 2, the lower peeling claw is more likely to be in contact with the pressure roller (claw separation / contact) than to be in constant contact with the pressure roller (claw fixing). It can be seen that the level of dirt is improved. The reason for this is considered that when the lower peeling claw is separated, the contact time with the pressure roller is shortened, so that the amount of toner transferred to the pressure roller adheres to the lower peeling claw decreases. .

From the results in Table 2, when the nail is separated, the thermal conductivity λ of the pressure roller is 0.28 W / m ° C. or less, the heat capacity per unit volume (cm ³ ) Cρ is 1.3 J / ° C. · cm ³ or less, If the product λ · Cρ of the thermal conductivity λ and the heat capacity Cρ is set to 0.368 or less, the lower peeling nail can be obtained even when the sharp melt low temperature fixing toner having a short melting time as in the first and second embodiments is used. It can be seen that toner contamination on the back side of the recording paper due to can be reliably prevented.

  In the above embodiment, an example of a monochrome multifunction device has been described. Needless to say, the present invention is not limited to a monochrome multifunction device, and can also be applied to a color multifunction device.

(Summary)
In the toner fixing method of the present invention, a recording paper having an unfixed toner image of toner is conveyed to a nip portion between a heated fixing member and a pressure member, whereby the unfixed toner image is applied to the recording paper. A toner fixing method for fixing, wherein
The toner is dropped on the heating surface of a hot plate at 230 ° C., and the time from when the toner contacts the heating surface until it melts is photographed with a high-speed camera to derive the melting time of the toner. A toner having a time of 0.035 seconds or less is used.
Further, the thermal conductivity λ of the pressure member is set to 0.28 W / m ° C. or less and the heat capacity Cρ per unit volume is set to 1.3 J / ° C. · cm ³ or less, or the heat of the pressure member When the conductivity is λ (W / m ° C.) and the heat capacity per unit volume of the pressure member is Cρ (J / ° C. · cm ³ ), λ · Cρ ≦ 0.364 is set.
The toner fixing method of the present invention may be as follows.

(1) The pressure member may be a pressure roller having a heat resistant elastic material layer.
In this way, the thermal conductivity λ of the pressure member is easily 0.28 W / m ° C. or less, the heat capacity Cρ per unit volume is 1.3 J / ° C. · cm ³ or less, and λ · Cρ ≦ 0.364. can do.

(2) A peeling part that can be separated from or attached to the pressure member may be provided, or a temperature detection part that can be separated from or attached to the pressure member may be provided.
In this case, the toner contamination of the peeling means and the temperature detection means can be suppressed as much as possible by separating the peeling means and the temperature detection means from the pressing member.

DESCRIPTION OF SYMBOLS 1 Image forming system 2 Image forming apparatus 22 Optical scanning unit (exposure apparatus)
23 Fixing device 101 Fixing roller (fixing member)
103c Temperature sensor (temperature detector)
106 Pressure roller (Pressure member)
106b Heat-resistant elastic material layer 109 Lower peeling claw (peeling part)
200 Photoconductor (Photoconductor drum)
201 Charging roller (charging device)
202 Developing unit (developing device)
203 Transfer unit (transfer device)
H Hot plate N Nip part P Recording paper T Toner V High speed camera

Claims (11)

A toner fixing method for fixing an unfixed toner image on a recording sheet by conveying a recording sheet having an unfixed toner image of toner to a nip portion between a heated fixing member and a pressure member. ,
The toner is dropped on a heating surface of a hot plate at 230 ° C., and the melting time of the toner is derived by photographing with a high-speed camera the state from when the toner contacts the heating surface until it melts.
A toner having a melting time of 0.035 seconds or less is used, the thermal conductivity λ of the pressure member is set to 0.28 W / m ° C. or less, and the heat capacity Cρ per unit volume is 1.3 J / ° C. · cm ^3. A toner fixing method comprising the following settings. A toner fixing method for fixing an unfixed toner image on a recording sheet by conveying a recording sheet having an unfixed toner image of toner to a nip portion between a heated fixing member and a pressure member. ,
The toner is dropped on a heating surface of a hot plate at 230 ° C., and the melting time of the toner is derived by photographing with a high-speed camera the state from when the toner contacts the heating surface until it melts.
A toner having a melting time of 0.035 seconds or less is used, the heat conductivity of the pressure member is λ (W / m ° C.), and the heat capacity per unit volume of the pressure member is Cρ (J / ° C. · cm ³ ), a toner fixing method, wherein λ · Cρ ≦ 0.364 is set.   The toner fixing method according to claim 1, wherein the pressure member is a pressure roller having a heat-resistant elastic material layer.   The toner fixing method according to claim 1, wherein a separation portion that can be separated from and brought into contact with the pressure member is provided.   The toner fixing method according to claim 1, further comprising a temperature detection unit that can be separated from and brought into contact with the pressure member.   A toner having a melting time of 0.035 seconds or less used in the toner fixing method according to claim 1, wherein the core particles include at least a binder resin and a colorant, A capsule toner having a shell layer to be coated. A photosensitive member on which an electrostatic latent image is formed, a charging device for charging the surface of the photosensitive member, an exposure device for forming an electrostatic latent image on the surface of the photosensitive member, and heating of a hot plate at 230 ° C. The toner is dropped on the surface, and the toner is supplied to the electrostatic latent image on the surface of the photosensitive member and the toner having a melting time of 0.035 seconds or less from when the toner comes into contact with the heating surface. A developing device for forming a toner image, a transfer device for transferring the toner image on the surface of the photosensitive member to the recording paper, and a fixing device for fixing the unfixed toner image transferred to the recording paper to the recording paper. An image forming apparatus,
The fixing device includes a fixing member to be heated and a pressure member disposed in proximity to the fixing member, and is not fixed to a nip portion formed between the fixing member and the pressure member. The recording paper having a toner image is conveyed to be fixed to the recording paper by fixing the unfixed toner image.
The image forming apparatus, wherein the pressure member of the fixing device has a thermal conductivity λ of 0.28 W / m ° C. or less and a heat capacity Cρ per unit volume of 1.3 J / ° C. · cm ³ or less. A photosensitive member on which an electrostatic latent image is formed, a charging device for charging the surface of the photosensitive member, an exposure device for forming an electrostatic latent image on the surface of the photosensitive member, and heating of a hot plate at 230 ° C. The toner is dropped on the surface, and the toner is supplied to the electrostatic latent image on the surface of the photosensitive member and the toner having a melting time of 0.035 seconds or less from when the toner comes into contact with the heating surface. A developing device for forming a toner image, a transfer device for transferring the toner image on the surface of the photosensitive member to the recording paper, and a fixing device for fixing the unfixed toner image transferred to the recording paper to the recording paper. An image forming apparatus,
The fixing device includes a fixing member to be heated and a pressure member disposed in proximity to the fixing member, and is not fixed to a nip portion formed between the fixing member and the pressure member. The recording paper having a toner image is conveyed to be fixed to the recording paper by fixing the unfixed toner image.
When the thermal conductivity of the pressure member of the fixing device is λ (W / m ° C.) and the heat capacity per unit volume of the pressure member is Cρ (J / ° C. · cm ³ ), λ · Cρ ≦ An image forming apparatus having a value of 0.364.   The image forming apparatus according to claim 7, wherein the pressure member is a pressure roller having a heat-resistant elastic material layer.   The image forming apparatus according to claim 7, wherein a peeling portion that can be separated from and brought into contact with the pressure member is provided.   The image forming apparatus according to claim 7, wherein the toner is a capsule toner having core particles containing at least a binder resin and a colorant, and a shell layer covering the core particles.