JP2005099334A - Fixing device and image forming apparatus using same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the stability of conveying performance by preventing a difference between the surface temperature of a fixing roller and the surface temperature of a pressure roller from increasing by the contact of an external heat roller only with a fixing roller, thereby preventing the curling of a thin paper sheet from increasing. <P>SOLUTION: The external heat roller is brought into contact with the fixing roller only when images are formed on a thick paper sheet, thereby suppressing the curling of the thin paper sheet and enhancing an image forming productivity when using the thick paper sheet. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a fixing device used in an image forming apparatus for fixing an image formed on the surface of a recording material to the surface of the recording material. More specifically, the present invention relates to an undetermined structure formed between rollers pressed against each other. A fixing image of a heat-fixing system that fixes a non-fixed toner by heating and pressurizing through a recording material having an unfixed toner image, and an image using the heat-fixing-type fixing device The present invention relates to a forming apparatus, for example, a color image forming apparatus having a heat fixing device and a plurality of image forming means.

  As a method for forming an image by an electrophotographic method and fixing the formed unfixed image, that is, an unfixed toner image, on a surface of a recording material such as paper, a heat fixing type fixing device has been widely used. As an example of this type of image forming apparatus, FIGS. 4 and 5 show a configuration example of a color image forming apparatus that forms an image using four color toners. The configuration example shown in FIG. 4 is a configuration example of a four-drum laser beam printer in which individual light scanning units are provided for four color toners.

  In the apparatus illustrated in FIG. 4, an image forming apparatus including a developing device and a transfer device using each color toner is arranged around an electrophotographic photosensitive member (hereinafter referred to as “photosensitive drum”) as a latent image carrier. Four image forming units called “formation stations” are connected and provided. In each of the four image forming stations, the image formed on the photosensitive drum is recorded on a recording medium such as paper (hereinafter simply referred to as paper) on the conveying means that moves and passes adjacent to the photosensitive drum. In this configuration, the images are sequentially transferred. Thereafter, the toner image is conveyed to a fixing device and the unfixed toner images are fixed together.

  FIG. 5 shows the configuration of each of the four image forming station portions in more detail. Photosensitive drums 1a, 1b, 1c, and 1d are arranged on the image forming stations Pa, Pb, Pc, and Pd for forming images of magenta, cyan, yellow, and black, respectively. The drum is rotatable in the direction of the arrow. Further, around the photosensitive drums 1a, 1b, 1c, and 1d, the chargers 12a, 12b, 12c, and 12d, the developing devices 2a, 2b, 2c, and 2d for supplying the toners of the respective colors, and the cleaners 4a, 4b, and 4c. , 4d are sequentially arranged along the rotation direction of the photosensitive drum. A transfer unit 3 is disposed on the downstream side of the developing device and below each photosensitive drum. The transfer unit 3 includes a transfer belt 31 as means for conveying a recording material common to each image forming station, and transfer chargers 3a, 3b, 3c, and 3d provided at positions facing the respective photosensitive drums. doing.

  In the color printer configured as described above, the paper P supplied from the paper feed cassette 61 is supported on the transfer belt 31 and conveyed to each image forming station by means for supplying the recording material. Next, while moving together with the transfer belt 31, the toner images of the respective colors formed on the respective photosensitive drums are sequentially transferred. When this series of transfer processes is completed, the paper P having unfixed toner images of the respective colors on the surface is separated from the transfer belt 31 and is transported to the fixing device 5 by the transport belt 62 which is a recording material guide.

  FIG. 6 shows an example of the configuration of a conventionally used heat fixing apparatus in detail. The illustrated fixing device 5 of the heat fixing system is a roller composed of a fixing roller 51 that is a rotatable rotating member, and a pressure roller 52 that is a pressure rotating member that rotates while being pressed against the fixing roller 51. Have a pair. In addition, the surface of the fixing roller 51 is provided with a release agent coating device 53 that is a means for supplying and applying a release agent, and roller cleaning devices 54 and 55. The fixing roller 51 and the pressure roller 52 are respectively provided with heaters 56 and 57 such as halogen lamps. Further, the thermistors 58 and 59 are disposed so as to come into contact with the respective surfaces. By controlling the voltage supplied to the heater 56 and the heater 57 via the temperature adjustment circuit, the fixing roller 51 and the pressurization are pressed. This is a mechanism for adjusting the surface temperature of the roller 52 to a desired temperature.

  As the fixing roller 51 and the pressure roller 52, a roller having a plurality of elastic layers on a metal core such as aluminum or iron is widely used. As the elastic layer, silicone rubber or the like considering heat resistance and thermal conductivity is formed on the core metal, and a material such as silicone rubber or fluoro rubber considering toner separation is used for the surface layer.

  A roller cleaning device 54 attached to the fixing roller 51 has a function of cleaning toner or the like offset from the surface of the paper P onto the fixing roller 51 during fixing. With respect to the rotation direction of the fixing roller 51, a release agent coating device 53 is attached on the downstream side of the cleaning device 54. After cleaning, a release agent such as silicone oil is applied to the surface of the fixing roller 51 by the release agent application device 53. This release agent is used for the purpose of facilitating separation of the transfer paper P from the fixing roller 51 after the fixing step and preventing the toner offset described above.

  The cleaning device 54 includes a cleaning web 54a made of a belt-like heat-resistant nonwoven fabric, a pressing roller 54b that presses the cleaning web 54a against the fixing roller 51, an unwinding roller 54c that unwinds a new cleaning web 54a, toner, and the like. It is composed of a take-up roller 54d for gradually taking up the lowered cleaning web 54a. In particular, in order to prevent the offset toner from adhering to the thermistor 58 used for monitoring the surface temperature of the fixing roller 51 and causing a thermistor detection failure, the cleaning device 54 prevents the thermistor 58 from fixing the fixing roller 51. 51 is provided on the upstream side in the rotation direction.

  In the illustrated cleaning device 54, the cleaning web 54a is wound up by turning on a solenoid (not shown) and operating a one-way clutch when it is determined that a predetermined number of sheets has elapsed from the number counter of the image forming apparatus. A method of winding a predetermined amount in the direction opposite to the rotation of the fixing roller is used. By taking up in the direction opposite to the roller rotation, the cleaning web 54a is prevented from being caught on the roller side as the roller rotates.

  On the other hand, the release agent coating device 53 includes an oil tank 53a holding a release agent such as silicone oil, rollers 53b and 53c for drawing up the release agent such as silicone oil from the oil tank 53a, and pumps 53b and 53c. The application roller 53d applies a release agent such as silicone oil supplied to the fixing roller 51, and the regulating blade 53e controls the amount of release agent such as silicone oil present on the surface of the application roller 53d. . In particular, in order to ensure uniform application of a release agent such as silicone oil on the surface of the fixing roller 51, the release agent application device 53 is disposed downstream of the thermistor 58 in the rotation direction of the fixing roller 51. . That is, the above arrangement is selected in order to avoid that the release agent once applied is removed by the thermistor 58 that contacts the surface of the fixing roller 51.

  The application roller 53d has a structure in which, for example, an elastic sponge rubber surface is covered with silicone rubber, and is a roller that can rotate together with the fixing roller 51. The release agent present on the surface moves to the surface of the fixing roller 51 and is applied while the application roller 53d is rotated in contact with the fixing roller 51. The regulating blade 53e is usually an elastic blade such as fluoro rubber, and is fixed in a position where it comes into contact with the application roller 53d. When the release agent such as silicone oil supplied by the pumping rollers 53b and 53c is in an excessive amount, the release agent is removed from the surface of the application roller 53d by contacting the regulating blade 53e, and contacts the fixing roller 51. The amount of the release agent present on the surface of the application roller 53d is limited so as not to exceed a certain range.

  The pressure roller 52 is also provided with a cleaning device 55 using a mechanism similar to the cleaning device 54 for the fixing roller 1. That is, the cleaning device 55 also includes a cleaning web 55a, a pressing roller 55b, an unwinding roller 55c, and a winding roller 55d. Although the pressure roller 52 is not in direct contact with the unfixed toner image, a part of the offset toner also adheres to the pressure roller 52 via the fixing roller 51, and this adhesion is caused by the cleaning device 55. Toner etc. have been cleaned.

  In addition, the release agent applied to the surface of the fixing roller 51 is also attached to the surface of the pressure roller 52 while being in pressure contact with the fixing roller 51. For the purpose of removing excess release agent remaining on the surface of the pressure roller 52, a release agent removal blade 60 is provided in contact with the pressure roller 52. If this removal blade 60 is not provided, excess release agent that accumulates on the surface of the pressure roller 52 collects in the nip where the fixing roller 51 and the pressure roller 52 are pressed against each other, for example, adheres to the recording material. , It becomes a stain. Or, when a transparent laminated film for OHP or the like whose friction coefficient is significantly smaller than that of paper is used as a recording material, it slips and causes a failure to enter the nip formed by the roller pair. . As the material of the removal blade 60, Si rubber, fluorine rubber, or the like is used, and these resin removal blades are in contact with an appropriate amount of entry in the forward or reverse direction with respect to the rotation direction of the pressure roller 52. Has been.

  In the fixing device having this configuration, when the transfer paper P is conveyed, the fixing roller 51 and the pressure roller 52 rotate, and a release agent such as silicone oil is applied to the surface of the fixing roller 51. Further, when the transfer paper P passes between the rotating fixing roller 51 and the pressure roller 52, the transfer paper P is pressed and heated at a substantially constant pressure and temperature from both the front and back surfaces thereof, so that the unfixed on the paper surface. The toner image is melted and fixed, and a full-color image is completed on the transfer paper P. After the image has been fixed, the transfer paper P is separated from the pressure roller 52 by the lower separation claw 68 and discharged outside the apparatus.

  In addition to the heat-fixing type fixing device having the configuration described in FIG. 6, a fixing device having means for heating the surface of the fixing roller as shown in FIG. 1 from the outside of the roller is proposed in Japanese Patent Application Laid-Open No. 2001-154529. Yes. Such a fixing device has improved heat transfer efficiency as compared with a fixing device having a heating source only inside the fixing roller. In FIG. 1, 100 is an external heating roller, 101 is a heating source, 102 is a thermistor, 103 is a thermo switch, 104 is a cleaning roller, and the other members are denoted by the same reference numerals as those in FIG.

  The external heating roller 100 is a roller in which a surface of a core shaft such as Al is coated with fluorine, and the heating source 101 is a halogen heater. The external heating roller 100 is usually separated from the fixing roller 51, and temperature control is performed at a higher temperature than the fixing roller 51 by the thermistor 103. Then, when image formation is started and the recording material is conveyed, it comes into contact with the surface of the fixing roller 51. Then, heat is conducted from the surface of the external heating roller 100 to the surface of the fixing roller 51, and heat is supplied to the fixing roller 51. When the fixing of the recording material is completed, the external heating roller 100 is separated from the fixing roller 51. A cleaning roller 104 removes toner paper dust transferred from the fixing roller 51 to the external heating roller 100.

When there is a heating source only inside, the thermistor on the surface of the fixing roller 51 detects a decrease in the surface temperature of the roller, and then the heater of the heating source is turned on, and the heat is conducted through the core shaft and the elastic layer of the roller. As a result, a time lag occurs in the heat transfer. On the other hand, when there is a heating source outside the fixing roller 51, heat from this heating source can be transmitted to the surface of the fixing roller 51 without passing through the core shaft and the elastic layer, so that the heat supply time is reduced. There is an advantage that the speed can be increased and the decrease in the surface temperature of the fixing roller 51 can be reduced. Further, since heat is supplied from the outside with respect to heating only from the inner surface of the fixing roller 51, the ratio of heating from the inner surface is reduced, so that the inner surface temperature of the core metal of the fixing roller 51 can be lowered. Further, there is an advantage that the overshoot of the surface temperature after fixing can be reduced and the life of the fixing roller 51 can be extended.
JP 2001-154529 A

  However, in the fixing device having a means for heating the surface of the fixing roller 51 from the outside of the roller as shown in FIG. 1, the following problems have occurred.

  When the fixing roller 51 has an external heating roller 100 that can be brought into contact with and separated from the surface and does not have the external heating roller 100 on the pressure roller 52 side, the external heating roller 100 supplies heat to the fixing roller 51 quickly. Although there is almost no temperature drop on the crack surface, the external heating roller 100 does not come into contact with the pressure roller 52, so only heat is supplied from the inner surface of the pressure roller 52. For this reason, the temperature of the surface of the pressure roller 52 continues to decrease until the heat from the inner surface is transmitted. As a result, when the recording material is continuously conveyed, the difference in surface temperature between the fixing roller 51 and the pressure roller 52 becomes too large. As described above, when the temperature difference between the front and back sides of the recording material becomes large at the time of fixing, a difference occurs in the expansion and contraction of the fibers of the recording material between the front and back sides, resulting in a problem that the curling of the recording material increases. Especially for recording materials with a small basis weight, this effect is large and the curl amount is large. When the curl becomes large in this way, the recording material is rounded on the paper discharge tray, or a conveyance failure of the recording material occurs during double-sided image formation.

According to the first invention of the present application, the object is
A rotating rotating pair that rotates while being pressed against each other, sandwiches and conveys a recording material to fix an unfixed image, and has a heating source inside, and can rotate in contact with and away from at least one rotating body. In the fixing device having the body, the contact and separation of the heating rotator during the fixing operation is determined according to the basis weight of the recording material, and remains separated if the recording material basis weight is smaller than the preset basis weight. This is achieved by performing the fixing operation.

According to the second invention of the present application, the object is the first invention,
When the basis weight of the recording material is 105 g / m ² or less, the recording material remains separated, and when the basis weight is larger than 105 g / m ^2, it is achieved by contact.

  According to the third invention of the present application, the object is to provide a heating source so that when the heating rotator is separated from the first or second invention, the heating rotator maintains a target temperature. This is achieved by performing energization control on the.

  According to the fourth invention of the present application, the object is achieved by the fact that the basis weight threshold of the recording material for judging the contact / separation of the heating rotating body in the first invention differs depending on the type of the recording material. Is done.

  According to the fifth aspect of the present application, the above object is achieved by determining, in the fourth aspect, the type of the recording material based on whether or not the recording material is coated.

According to the first invention of the present application,
A rotating rotating pair that rotates while being pressed against each other, sandwiches and conveys a recording material to fix an unfixed image, and has a heating source inside, and can rotate in contact with and away from at least one rotating body. In the fixing device having the body, the contact and separation of the heating rotator during the fixing operation is determined according to the basis weight of the recording material, and remains separated if the recording material basis weight is smaller than the preset basis weight. By performing the fixing operation, curling can be suppressed with a recording material having a small basis weight, and productivity can be improved with a recording material having a large basis weight.

According to the second invention of the present application,
In the first invention, the basis weight of the recording material while spaced For 105 g / ^{m 2} or less, by 105 g / ^{m 2} is greater than the contacting, curling at 105 g / ^{m 2} or less of the recording medium With a recording material of greater than 105 g / m ² , productivity can be improved and merchantability is improved.

According to the third invention of the present application,
In the first and second inventions, when the heating rotator is separated, the heating rotator is energized to the heating source so as to maintain the target temperature. Since the image forming operation is not interrupted when the heating rotator is brought into contact, the user-friendliness is improved.

  According to a fourth invention of the present application, in the first invention, the threshold value of the basis weight of the recording material for determining the contact / separation of the heating rotator varies depending on the type of the recording material, thereby preventing curling. Productivity can be set more finely and productivity has been improved.

  According to the fifth invention of the present application, in the fourth invention, the type of the recording material is determined based on whether or not the recording material is coated, thereby preventing curling and improving productivity. Can be set more finely and the merchantability has been improved.

  According to the sixth aspect of the present application, there is provided an image forming apparatus in which curling can be suppressed with a recording material having a small basis weight, and productivity can be improved with a recording material having a large basis weight. be able to.

  Hereinafter, the present invention will be described more specifically with reference to examples. Although these examples are examples of the best mode of the present invention, the present invention is not limited to these examples.

  A first embodiment will be described with reference to FIGS.

  FIG. 1 is a schematic cross-sectional view of a fixing device used in this embodiment, and the same or corresponding elements as those in the conventional example are denoted by the same reference numerals and the description thereof is omitted.

  FIG. 2 is a control flowchart of the external heating roller in this embodiment.

In FIG. 2, when image formation is started, the basis weight of the recording material is determined. The basis weight is the weight of the recording material per 1 m ² expressed in grams. The basis weight of the recording material may be detected automatically (not shown) of the recording material thickness, or may be directly input by the user. Here, when the basis weight (thickness) of the recording material is 105 g / m ² or less which is a preset value, curling after fixing becomes large if external heating is used. Not performed. That is, the external heating roller 100 remains separated from the fixing roller 51. However, temperature control (temperature control) is performed on the external heating roller 100 during separation. There is a method of stopping energization of the heat source 101 of the external heating roller 100 while keeping the external heating roller 100 in contact. In this case, the surface temperature of the external heating roller 100 changes during the continuous fixing operation process. For this reason, uneven glossiness of the output image occurs, which is not preferable.

  Here, temperature control of the external heating roller 100 will be described. A thermistor 102 that is a temperature detector detects the surface temperature of the external heating roller 100. The energization amount to the heating source 101 such as a halogen heater is controlled by the energization control means so that the detected temperature becomes a preset target temperature.

  By adjusting the temperature of the external heating roller 100 at the time of separation, a job for fixing an image on a recording material having a large basis weight is completed after a fixing operation job for fixing the image on the recording material having a small basis weight is completed. Since the external heating roller 100 has already been warmed when it is input to, the wait time can be shortened and a fixing operation with a high throughput can be realized.

On the contrary, when the basis weight (thickness) of the recording material is greater than 105 g / m ^2, curling does not increase even if external heating is used and the paper is strong, so heat is supplied by external heating. That is, the external heating roller 100 contacts the fixing roller 51. Then, since the heat supply response becomes fast, the surface temperature of the fixing roller 51 hardly decreases, and the paper can be conveyed and fixed to the maximum setting, thereby improving the throughput. The timing of contact here depends on the heat capacity of the roller and the wattage of the heating source, but it is efficient to contact the recording material several seconds before entering the nip between the fixing roller 51 and the pressure roller 52. At least when the recording material passes through the fixing nip, that is, during the fixing operation, the external heating roller 100 needs to be in contact with the fixing roller 51. After the fixing is performed in this way and the final sheet passes through the fixing nip portion, the external heating roller 100 is separated from the fixing roller 51, and the fixing roller 51, the pressure roller 52, and the external heating are prepared to prepare for the next image formation. The roller 100 is on standby for temperature adjustment.

  By doing as described above, a recording material with a small basis weight does not cause curling, and a recording material with a large basis weight can maximize the throughput and improve the productivity.

In this embodiment, the contact / separation of the external heating roller 100 is determined based on the basis weight of the recording material of 105 g / m ² , but this value varies depending on the heat capacity of the roller, the wattage of the heating source, the type of the recording material, and the like. It is not necessarily limited to this value.

  Further, since the external heating roller 100 is not used when an image of a recording material having a small basis weight is formed, heating is not necessarily required in a separated state, and extra energy can be reduced if heating is not performed. However, when heating is not performed, the external heating roller 100 must be heated after determining the basis weight, and the image forming operation must be interrupted, which is not convenient. Accordingly, it is desirable that the external heating roller 100 is heated even in the separated state, but switching control of whether or not the external heating roller 100 in the separated state is heated may be performed according to a user's request, or the external heating roller 100 may be controlled. It is also possible to wait at a target temperature lower than the target temperature during use.

In the present embodiment, the same control as in the first embodiment is further subdivided according to the type of recording material, and will be described in detail with reference to FIG. FIG. 3 is a control flowchart of the external heating roller in this embodiment. In this embodiment, the basis weight threshold value for judging contact / separation of the external heating roller 100 is changed between a recording material (hereinafter, coated paper) whose surface is coated and a recording material (hereinafter, plain paper) which is not coated. It is. In general, coated paper has a smooth surface, and even with the same basis weight, the thickness is thin and there is no stiffness, so the curl tends to be larger than plain paper. Therefore, if the contact of the heating roller is determined with the same basis weight as that of the plain paper, even if the curl amount of the plain paper is small, there is a basis weight that becomes large in the coated paper, which may cause a problem. Specifically, the basis weight between 100 and 200 g / m ² tends to show a difference in the curl amount, and varies depending on the type of coated paper, the amount of coating, and the type.

In the present embodiment, the threshold value of the contact / separation condition of the external heating roller 100 is set to 150 g / m ^{2 in} the case of a coat, and 105 g / m ^{2 in} the case of plain paper. By doing so, the external heating roller 100 does not come into contact with the coated paper near 105 to 150 g / m ^2, so that the curl amount can be reduced. Moreover, since the external heating roller 100 abuts on coated paper of 150 g / m ² or more, the productivity can be improved.

  Note that the threshold value of the basis weight of the recording material used in this embodiment differs depending on the type of the recording material and is not necessarily limited to this value.

FIG. 2 is a cross-sectional view of a fixing device used in this embodiment. It is a control flowchart of the 1st example of the present invention. It is a control flowchart of the 2nd example of the present invention. It is sectional drawing which shows typically an example of the whole structure of the conventional image forming apparatus. In the conventional image forming apparatus, it is sectional drawing which shows the structure of the image forming means part which comprises it in detail. FIG. 10 is a cross-sectional view schematically illustrating an example of a device configuration of a fixing device used in a conventional image forming apparatus.

Explanation of symbols

5 Fixing Device 51 Fixing Roller 52 Pressure Roller 56, 57 Heater 58, 59 Thermistor 100 External Heating Roller 101 Heating Source 102 Thermistor 103 Thermo Switch 104 Cleaning Roller

Claims (6)

  A rotating rotating pair that rotates while being pressed against each other, sandwiches and conveys a recording material to fix an unfixed image, and has a heating source inside, and can rotate in contact with and away from at least one rotating body. In the fixing device having the body, the contact and separation of the heating rotator during the fixing operation is determined according to the basis weight of the recording material, and remains separated when the basis weight of the recording material is smaller than a preset basis weight. In the fixing device, a fixing operation is performed. ^2. The fixing device according to claim 1, wherein when the basis weight of the recording material is 105 g / m ² or less, the recording material is separated, and when the recording material is larger than 105 g / m ^2, contact is made.   3. The energization control is performed on the heating source so that the heating rotator is maintained at a target temperature when the heating rotators are separated from each other. 4. Fixing device.   2. The fixing device according to claim 1, and an image forming apparatus using the fixing device, wherein a threshold value of a basis weight of the recording material for determining contact / separation of the heating rotator varies depending on a type of the recording material.   5. The fixing device according to claim 4, and an image forming apparatus using the same, wherein the type of the recording material is determined based on whether or not the recording material is coated.   An image forming apparatus having an unfixed image forming means for forming an unfixed image, comprising the fixing device according to any one of claims 1 to 5.

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