JP4863726B2 - Fixing device, image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, a printer, and a printing machine, and more specifically, energy saving and prevention of uneven gloss of an image in an image forming fixing apparatus using electrophotography used in these apparatuses. It relates to technology.

  Conventionally, demands for resource saving and energy saving have been increasing in order to preserve the global environment. In electrophotography, there is an active movement to suppress power consumption for energy saving, and research is being conducted on fixing at low temperature, particularly in the field of fixing where power consumption is intense. At present, a fixing temperature of about 200 ° C. to 150 ° C. is generally used, and it takes about 1 to 5 minutes to start up the fixing device from room temperature. It is desired that this can be fixed at 150 ° C. or less, preferably around 100 ° C., for energy saving and fixing start-up time reduction.

  In order to realize fixing at such a temperature, naturally, the softening point or melting point of the toner must be lowered to 100 ° C. or lower, but generally, the same kind of organic polymer substance has a decrease in melt viscosity when the melting point is lowered. Inevitable. This is because the melting point of the resin depends on the molecular weight. Naturally, if the molecular weight is low, the entanglement of the molecular chains is loosened, and the melt viscosity is lowered by weakening the interaction. Accordingly, when fixing is performed using an ultra-low melting point toner, the viscosity is rapidly lowered after the melting point. For this reason, the effective rubber width is narrow, and it is difficult to prevent the toner on the paper from being offset to the fixing heating member side.

  In order to solve such a problem, it is conceivable to prevent the offset of the toner image by using a fixing belt, and heat-dissipating the solidified toner while solidifying it to solidify it, and then separating it from the belt.

  When the toner image is brought into close contact with the fixing belt in this way to perform overheating and heat dissipation, if the contact state becomes uneven due to the waviness of the belt during conveyance, variations in the contact heat retention time will appear as uneven gloss of the image. There is a problem.

  In Patent Document 1, a cooling fan connected to a duct for supplying fresh air is provided on the surface of an endless belt hung on a fixing roller, and toner in a molten state is condensed on transfer paper to prevent offset. .

  In Patent Document 2, a fixing belt hung on a plurality of rollers, a heating unit, and leading and trailing ends of a recording paper conveyance path are provided with guide rollers between them, and the image surface is used as a fixing belt by pressing the paper. They are transported in close contact. In this case, there is a problem of paper floating or image blurring at a portion where the guide roller does not contact.

In Patent Document 3, an endless fixing belt that is bridged between a heating roller and a fixing roller, and a pressure roller that is pressed from below are provided. The fixing roller and the heating roller are in contact with the pressure roller, and between the corresponding contact portions. The nip is formed with In this case, there is a problem of image blur due to conveyance of the recording paper with a high curvature in the fixing nip.
Japanese Patent Laid-Open No. 5-019466 Japanese Patent Laid-Open No. 10-221982 JP 2000-89593 A

  The present invention relates to a fixing device and an image forming apparatus using an electrophotographic image forming method such as a copying machine, which saves energy and prevents uneven gloss of an image, and saves energy by heating-contact conveyance using a toner having a low melting point. An object of the present invention is to provide a fixing system which can detect a waviness of a fixing belt and stably carry out close contact conveyance to prevent gloss unevenness and obtain a good color print.

Fixing device according to claim 1 of the present invention, a recording medium by a pair of endless belts are nipped, the image plane in one with the fixing belt is of the pair of belts recording medium by pinching by the tension of the pair of belt when it is intended to be carried in close contact state, the fixing device comprising means for performing an operation of the detection to swell removing waviness of the fixing belt surface,
The waviness is detected by a light reflection type sensor. The light reflection type sensor irradiates light at a predetermined angle with respect to the fixing belt surface, and detects the incident amount of the reflected light, thereby detecting the waviness of the fixing belt surface. Is to detect,
Each of the pair of endless belts is stretched around a tensioning member, and the tension applied to each endless belt by changing the position of the tensioning member according to the information on the undulation of the belt surface by the light reflection sensor. By adjusting this, the undulation of the fixing belt surface is removed .

  According to the present invention, in an energy-saving fixing system using heat-contact conveyance using a toner having a low melting point, belt undulation is detected by detecting the undulation, and the correction operation is performed. Can prevent gloss unevenness and obtain a good color print.

In the fixing device of the present embodiment, the recording medium is conveyed while being sandwiched between an endless fixing belt and a pressure belt, the toner image on the surface of the recording medium is brought into close contact with the fixing belt, heated, and radiated from the fixing belt. Separate the toner surface. When such a configuration is used, the toner image is solidified at the time of separation from the fixing belt. Therefore, even when a toner that melts at about 100 ° C. is used, the low-viscosity toner is prevented from being offset to the fixing belt side. Fixing is easy. Therefore, a good energy saving fixing system can be obtained. In such a system, it is necessary to apply a certain tension to the pair of belts suspended, as described above, to hold the recording medium between the pair of belts so as to maintain a close contact state. It is not preferable because the belt tends to be stretched or broken when the tension is too strong. A preferable tension is 0.01 to 5 N / mm, more preferably 0.05 to 4 N / mm, and still more preferably 0.1 to 2 N / mm. Each of the pair of belts has a tension roller adjusted by a tension roller, and the tension is adjusted by information on the undulation of the belt surface by the light reflection type sensor. The tension of the pair of belts is adjusted by a tension roller, and the tension is adjusted by the undulation information of the belt surface of the light reflection type sensor. This pair of belt tensions is adjusted to a predetermined tension. However, if the belt tension is insufficient due to the extension of the belt circumference due to heating or the extension over time, the belt surface will be wavy and wrinkled. Is detected by an optical sensor. Then, the tension roller moves in the direction of increasing the tension to remove wrinkles and maintain close contact conveyance. For example, when the light reflection sensor detects the undulation on one side of the belt, the tension on one side of the tension roller is increased. In this way, it is possible to provide a good energy-saving fixing device that eliminates the occurrence of uneven glossiness of the image over time.
In the embodiment of the present invention, the recording medium sandwiched between the pair of belts after the nip between the heating roller and the pressure roller keeps the toner in a close contact state for 50 to 1000 milliseconds so that the heat is sufficiently transmitted to the toner. To. If this clamping time is short, the toner does not receive the necessary heat and the fixing performance is lowered. Also, if the holding time is too long, the entire belt surface area increases, and heat dissipation increases, which is not preferable. A preferable holding time is 60 to 800 milliseconds, more preferably 80 to 700 milliseconds, still more preferably 100 to 500 milliseconds, and still more preferably 200 to 400 milliseconds.
In addition, the state of waviness of a pair of close-conveyance belts is detected, and when waviness is removed, the belt waviness is detected to constantly monitor whether close-conveyance is being carried out well and maintain a good conveyance state. Make it possible. In other words, it is an energy-saving fixing system using heat-contact transportation using low melting point toner, and the undulation detection sensor detects the undulation of the fixing belt and performs the correction operation. Get a good color print.
In an embodiment of the present invention, the waviness is detected by a light reflection sensor, and the light reflection sensor irradiates light at a predetermined angle with respect to the fixing belt surface to detect the incident amount of the reflected light. Thus, the undulation of the fixing belt surface is detected. A light reflection type sensor can be used as the sensor for detecting the swell. Waviness of the belt surface is detected by applying light to the belt surface at a predetermined angle and detecting the amount of incident reflected light. When the belt surface is stretched, the reflected light is detected as almost 100% incident light. However, if waviness occurs on the belt surface due to belt circumference extension due to heating, shrinkage due to cooling, elongation over time, dimensional error, etc., incident light is not detected and it is determined that the belt is wavy. In this way, it is possible to always monitor whether the close contact conveyance is performed well and maintain a good transfer state.
Moreover, in embodiment of this invention, the light reflection type sensor which detects the said waviness is provided in the contact | adherence conveyance part back surface of a pair of said unsupported belt. In this way, it is possible to always monitor whether or not the image surface is closely transported and maintain a good transport state.
In an embodiment of the present invention, the light reflection sensor for detecting the swell is provided on each of the fixing belt surface and the pressure belt surface which is the other of the pair of belts. The sensor for detecting the undulation detects the fixing belt surface and the pressure belt surface. In this way, a plurality of light reflecting sensors for detecting the waviness are arranged in the belt width direction so that it is possible to always monitor whether the close contact conveyance is performed well from the front and back sides of the conveyance paper and to maintain a good conveyance state. May be. Then, the amount of waviness at the end and center of the belt can be detected, and the waviness can be monitored over the entire width direction to maintain a good conveyance state.
In the embodiment of the present invention, when the sensor for detecting undulation detects the undulation on one side, only the one-side tension for detecting the undulation is increased. If one sensor detects the undulation and the other sensor does not detect it, only one side of the tension roller moves and the one-side tension increases. In this way, it is possible to provide a favorable energy-saving fixing device in which belt wrinkles are removed and the close contact conveyance is always maintained, and the occurrence of uneven glossiness of the image is removed.
In the embodiment of the present invention, the belt has a thickness in the range of 50 μm to 500 μm. This is because when the belt thickness is 50 μm or less, the strength is reduced and the risk of breaking when the belt tension is increased by increasing the tension is increased. When the belt thickness is 500 μm or more, the heat capacity of the belt increases and the belt is heated to a predetermined temperature. This is because it is necessary for a long time. For this reason, when the belt thickness is in the range of 50 μm to 500 μm, it is possible to provide a favorable energy-saving fixing device that always maintains close contact conveyance while controlling waviness removal and eliminates occurrence of uneven glossiness of the image. Furthermore, when the belt has a high release resin layer formed as a surface layer on a polyimide substrate, belt durability is obtained by the polyimide resin belt, and when waviness occurs and belt tension is increased, Even when the belt adhesion of the paper is increased, the paper can be stably separated by the release resin layer on the surface. In this way, it is possible to provide a good energy-saving fixing device that eliminates the occurrence of uneven glossiness of the image. When an elastic layer is formed between the belt base and the surface layer, even when undulation occurs on one side and the tension on one side is increased, the elastic layer applies a close contact pressure in the width direction and the applied pressure becomes uneven. It is prevented.
The best mode for carrying out the present invention will be described below with reference to the embodiments shown in the drawings.

  FIG. 1 is a schematic configuration diagram of an image forming apparatus including a fixing device according to an embodiment of the present invention. In the case of operating as a copier, the reading unit 1 reads an original and then converts it into a writing signal as digital data. When operating as a printer, the image signal from the computer is converted into a write signal. The writing signal is obtained by adding black to three primary colors of yellow, magenta, and cyan, and optical writing is performed from the polygon mirror 3 to the photosensitive units 4 to 7 of the respective colors. In each color photoconductor unit, a toner image is formed on the photoconductor by a process of charging, writing, and developing in accordance with each color, and the toner image is superimposed on the intermediate transfer belt 8 and recorded by the secondary transfer roller 11. It is transferred onto the paper at once. The recording paper on which the toner image is placed is conveyed to the fixing device 13 by the conveying belt 12, and after the toner is heated and fixed, it is discharged to the paper discharge unit 17.

  FIG. 2 is a schematic view of the fixing device 13. An endless fixing belt 23 is hung between the heating roller 21 and the overstretching roller 22, and is tensioned on the upper side by a tension roller 29. A heater 24 is contained in the heating roller 21 and heats the fixing belt 23 to a predetermined temperature. The pressure belt 25 is hung between the pressure roller 26 and the lower tension roller 27, is tensioned downward by a tension roller 30, and is driven while being in contact with the fixing belt 23.

  The heating roller 21 and the pressure roller 26 are pressurized by a spring on one side 50N, and the conveyed recording paper 28 receives heat while being pressurized at the paper entrance. Then, the toner image is melted and the sheet is conveyed while being in close contact with the fixing belt. In the close-contact conveyance unit, the sheet is conveyed by applying a tension of 1 N / mm to the upper and lower belts, and the toner image is radiated and solidified. Since the control temperature of the heating roller 21 of this fixing device is 130 ° C., the paper feed speed is 300 mm / second, and the nip width of the upper and lower belts is 90 mm, the recording medium is sandwiched for 300 milliseconds.

  As shown in FIG. 3, the undulation of the belt is monitored from the back surface of the sheet contact conveyance unit of the fixing device by a light reflection type sensor (hereinafter simply referred to as a sensor). The sensor 31 emits light from the semiconductor laser 32, and the light detection unit 33 detects reflected light. Then, as shown in FIG. 3B, if the incident of reflected light is not detected, the belt 23 is swelled, and it is determined that the image is not closely conveyed. The image below the wavy portion 34 of the belt 23 is in a frosted state, and gloss unevenness occurs with other image portions. Therefore, when the undulation is detected, the end fulcrum of the tension roller 30 in FIG. 2 is pulled upward by a solenoid mechanism (not shown), the belt is stretched, and the undulation is removed.

  As a result of such a configuration, even when A3 size paper having a full-surface image was continuously passed, gloss unevenness due to waviness was prevented, and a high-quality color print was obtained over the entire width.

<Experimental example>
Used toner: cyclized isoprene 30 wt%
Polyester 60wt%
Carnauba wax 10wt%
Carbon black 10 parts by weight Negatively chargeable charge control agent 1 part by weight This toner has a softening point of 80 ° C and a minimum fixing temperature of 85 ° C.
Belt configuration: polyimide substrate 70 μm
Silicon rubber elastic layer 150μm
Surface PFA tube layer 30μm

  A device similar to that of the first embodiment is used, but sensors are provided at three positions, that is, at both ends in the width direction of the fixing belt 23 and at the center as shown in FIG. When only the front sensor 41 detects the undulation, the front fulcrum A of the tension roller 29 is lifted upward by a solenoid mechanism (not shown) to increase the tension only on the front side and remove the undulation. If only the back sensor 43 detects the undulation, the tension is raised only on the back side. If the undulation on the near side is detected in a state where the fulcrums A and B are pulled up, the tension on the near side is relatively increased by lowering the fulcrum B on the back side, thereby removing the undulation.

  As a result of such control, even when A3 size paper of the entire surface image was continuously fed, gloss unevenness due to waviness was prevented, and high-quality color prints were always obtained over the full width.

1 is a schematic configuration diagram of an image forming apparatus including a fixing device according to an embodiment of the present invention. Schematic of the fixing device of Example 1 Schematic diagram of light reflection sensor used for undulation detection (A) and schematic diagram of swell detection state (B) Schematic of the fixing device of Example 2

Explanation of symbols

1: Reading unit
3: polygon-mirror
4-7: photoconductor unit
8: The intermediate transfer belts
11: secondary transfer roller over
12: transport belts
13: The fixing equipment
17: Paper discharge unit
21: heating roller over
22: overlayer rack roller over
23: The fixing belts
24: Heater
25: Pressure belt
26: Pressure roller
27: Underlay roller
28: Recording paper
29: tension roller over
30: tension roller over
31: Light reflection type sensor (sensor )
32: semiconductor laser over
33: light detection unit
34: belt swell part worth of
41 to 43: sensor

Claims (12)

Recording medium by a pair of endless belts are nipped, when one in which the image plane to one in the fixing belt is of the pair of belts recording medium by pinching by the tension of the pair of belts are conveyed in close contact, In the fixing device having means for detecting the undulation of the fixing belt surface and performing the undulation removal operation ,
The waviness is detected by a light reflection type sensor. The light reflection type sensor irradiates light at a predetermined angle with respect to the fixing belt surface, and detects the incident amount of the reflected light, thereby detecting the waviness of the fixing belt surface. Is to detect,
Each of the pair of endless belts is stretched around a tensioning member, and the tension applied to each endless belt by changing the position of the tensioning member according to the information on the undulation of the belt surface by the light reflection sensor. The fixing device is characterized by removing waviness of the surface of the fixing belt by adjusting the width of the fixing belt . The fixing device according to claim 1, a fixing device according to claim Rukoto includes a pre Symbol light reflection sensor adhesion conveying portion rear surface of the pair of endless belts. Te fixing device smell of claim 2, before Symbol light reflection sensor the fixing belt surface, the fixing device characterized in that it comprises in each other pressing belt surface which is of the pair of belts. It claims 1 to Te fixing device odor according to any one of 3, before Symbol light reflection sensor of the fixing device to a plurality arranged to said tare Rukoto in a width direction of the endless belt. The fixing device according to any one of claims 1 to 4, when the optical reflection type sensor detects the belt sac kneading, a fixing device, characterized in that to strengthen Tension member subjecting the tension. 6. The fixing device according to claim 1 , wherein the belt has a high release resin layer formed as a surface layer on a polyimide substrate . The fixing device according to claim 6 Symbol mounting, a fixing device which is characterized that you have an elastic layer is formed between the belt substrate and the surface layer. The fixing device according to claim 1 , wherein the belt has a thickness in a range of 50 μm to 500 μm. The fixing device according to any one of claims 1 to 8, a fixing apparatus wherein a recording medium is characterized Rukoto is sandwiched belt tension 0.001~5.4N / mm. The fixing device according to any one of claims 1 to 9, the fixing device the time the recording medium is held by the belt is characterized 50-1000 milliseconds der Rukoto. The fixing device according to claim 1 1 0, members applying the tension, the fixing device which is a tension roller.
An image forming apparatus comprising the fixing device according to claim 1.