JP5151086B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus.

  It is known that when the pressure roller is heated to a temperature required for fixing while the pressure roller is in pressure contact with the fixing roller, the pressure roller is heated more than necessary and a “toner blister” phenomenon occurs (for example, Patent Document 1). A toner blister is a phenomenon in which moisture in a recording medium becomes water vapor due to fixing heat, and the vapor pressure of the water vapor acts on the toner image on the recording medium, whereby the toner image on the recording medium is disturbed and gloss unevenness occurs. is there.

  In non-coated paper such as plain paper, the water vapor can be released to the outside through the inside of the recording medium, and toner blisters are not generated so much. It cannot be discharged to the outside through the inside, and water vapor accumulates between the recording medium and the toner layer, and toner blisters are easily generated.

In Patent Document 1, in order to prevent the generation of toner blisters, the pressure roller is released from pressure contact during heating, and then the temperature of the pressure roller is increased more than necessary by independently controlling the temperature of the pressure roller. I'm trying not to be.
JP 2005-215580 A

  However, even in the case of Patent Document 1, the pressure roller is pressed against the fixing roller in accordance with the printing operation. If the pressure roller is pressed too quickly, the recording medium passes through the fixing unit. If the pressure roller is heated more than necessary, toner blisters may be generated.

  On the other hand, if the pressure roller is too slow, the fixing roller stops when the pressure roller is pressed. When the pressure roller is pressed, the amount of heat in the nip portion on the fixing roller side is The recording medium reaches the recording medium before the temperature of the nip portion is sufficiently recovered by the rotation of the fixing roller, and the temperature of the nip portion is not sufficiently recovered by the subsequent rotation of the fixing roller. A corresponding belt-like portion having a low glossiness (hereinafter referred to as a nip mark) becomes conspicuous on the image. See FIG. The larger the temperature difference between the fixing roller and the pressure roller, the more easily the nip mark is generated.

  The present invention has been made in view of the above problems, and an object thereof is to provide an image forming apparatus capable of obtaining a high-quality image free from image defects.

The image forming apparatus of the present invention is a first heater that heats the heating member in an image forming apparatus that performs fixing by passing a recording medium through a nip portion of a pressure member and a heating member that can be rotationally driven and pressed against each other A second heater for heating the pressure member, a drive mechanism for rotating the heating member and the pressure member, a pressure release mechanism for pressing the heating member and the pressure member against each other, and the first heater A controller that controls the second heater, the drive mechanism, and the pressure release mechanism, and the controller controls the first heater so that the surface temperature of the heating member becomes a first temperature. And the second heater is controlled so that the surface temperature of the pressure member becomes a second temperature lower than the first temperature, and after the printing instruction, the pressure release mechanism releases the first temperature to the first temperature. Heated The heating member and the second said pressure member which is heated to a temperature of pressed each other in a stopped state, respectively, then, the recording medium is the nip portion after the heating member is rotated more than one revolution The drive mechanism and the pressure release mechanism are controlled so as to reach.

  According to the present invention, since the pressure roller is pressed at an appropriate timing, a high-quality image free from image defects can be obtained.

  Although the present invention will be described based on the illustrated embodiment, the present invention is not limited to the embodiment.

(Whole device configuration)
FIG. 1 is a configuration diagram of an image forming apparatus according to the present embodiment. The image forming apparatus 1 includes a document conveying unit 10, an image reading unit 20, an image forming unit 30, a paper feeding unit 40, a transfer unit 50, a fixing unit 60, and the like.

  The document transport unit 10 transports the placed documents D one by one toward the image reading unit 20.

  The image reading unit 20 reads an image of the document D conveyed by the document conveying unit 10 and outputs image data.

  The image forming unit 30 includes four color image forming units 30Y, 30M, 30C, and 30K, and performs full color image formation. The image forming unit 30Y includes a charger 32Y, an exposure device 33Y, a developing device 34Y, a cleaning device 35Y, and the like around the photoreceptor 31Y. The surface of the photoreceptor 31Y is charged by the charger 32Y, exposed by the exposure device 33Y based on the image data output from the image reading unit 20, and developed by the developing device 34Y, whereby a toner image is formed on the surface of the photoreceptor 31Y. Form. The toner image is transferred to a recording medium by the transfer unit 50. Residual toner on the surface of the photoreceptor 31Y after the transfer is cleaned by the cleaning device 35Y. The same applies to the image forming units 30M, 30C, and 30K.

  The paper feeding unit 40 feeds the recording medium P toward the transfer unit 50.

  The transfer unit 50 transfers the toner image carried on the surface of the photoreceptor 31 of the image forming unit 30 to the recording medium P fed from the paper feeding unit 40. The transfer unit 50 includes an intermediate transfer belt 51, primary transfer rollers 52Y, 52M, 52C, and 52K, a secondary transfer roller 53, a cleaning device 54, and the like. The toner images carried on the surfaces of the photoreceptors 31Y, 31M, 31C, and 31K are primarily transferred to the intermediate transfer belt 51 by the primary transfer rollers 52Y, 52M, 52C, and 52K, and then are transferred to the recording medium P by the secondary transfer roller 53. Transcribed.

  The fixing unit 60 heats and pressurizes the recording medium P on which the toner image conveyed from the transfer unit 50 is formed, and fixes the toner image on the recording medium P. The fixed recording medium P is discharged out of the apparatus.

(Configuration of the fixing unit 60)
FIG. 2 is a configuration diagram of the fixing unit 60 according to the present embodiment. The fixing unit 60 includes a fixing belt 61, a heating roller 62, a fixing roller 63, a pressure roller 64, a cam 65, a compression spring 66, one-way clutches 67, 68, 69, a fixing motor 70, and the like.

  The fixing belt 61 is wound around the heating roller 62 and the fixing roller 63 and comes into contact with the recording medium P on which the toner image is formed to fix the toner image on the recording medium P. The fixing belt 61 corresponds to the heating member of the present invention.

  The heating roller 62 has a heater H <b> 1 (corresponding to the first heater of the present invention) inside, and heats the fixing belt 61. The heater H1 is controlled so that the temperature of the fixing belt 61 is maintained at a predetermined temperature (for example, 200 ° C.).

  The fixing roller 63 urges the fixing belt 61 from the inside to bring the fixing belt 61 into contact with the recording medium P.

  The pressure roller 64 has a heater H <b> 2 (corresponding to the second heater of the present invention) inside, and is provided so as to be able to contact and separate from the fixing roller 63 via the fixing belt 61. The toner image is fixed to the recording medium P by passing the recording medium P on which the toner image is formed in a state where the pressure roller 64 is pressed against the fixing roller 63 via the fixing belt 61. The heater H <b> 2 is controlled such that the surface temperature of the pressure roller 64 is maintained at a temperature (for example, 120 ° C.) lower than the temperature of the fixing belt 61. The pressure roller 64 corresponds to the pressure member of the present invention.

  The cam 65 rotates to bring the pressure roller 64 into pressure contact with the fixing roller 63 via the fixing belt 61.

  The compression spring 66 is pressed by a predetermined load (for example, 1000 N) when the pressure roller 64 is pressed.

  The one-way clutches 67 and 68 are provided to transmit the driving of the fixing motor 70 to the fixing roller 63 and the pressure roller 64, and transmit the driving when the fixing motor 70 rotates forward. When the fixing motor 70 rotates in the reverse direction, driving is not transmitted. Further, the one-way clutch 67 is configured such that when the pressure roller 64 is in pressure contact, if the rotation speed of the pressure roller 64 is higher than the rotation speed of the fixing roller 63, the fixing roller 63 is not damaged by the gear. It is provided so that it can rotate following. The drive mechanism of the present invention is constituted by the one-way clutches 67 and 68 and a gear (not shown).

  The one-way clutch 69 is provided to transmit the driving of the fixing motor 70 to the cam 65, and transmits the driving when the fixing motor 70 rotates in the reverse direction. When the fixing motor 70 rotates forward, driving is not transmitted. That is, when the pressure roller 64 is pressed by the cam 65, the fixing roller 63 and the pressure roller 64 stop rotating. The one-way clutch 69, the cam 65, the compression spring 66, etc. constitute the pressure release mechanism of the present invention.

  The driving of the fixing motor 70 is transmitted to the fixing roller 63 and the pressure roller 64 during normal rotation, and the driving is transmitted to the cam 65 during reverse rotation. The fixing motor 70 is connected to the control unit 100 and performs forward rotation, reverse rotation, and stop operations based on instructions from the control unit 100. The fixing motor 70 corresponds to the motor of the present invention.

  The control unit 100 includes a CPU that controls the fixing motor 70 and the like according to a program, a ROM that stores the program and necessary data, a RAM that is used as a work area by the CPU, and the like.

(control)
FIG. 3 is a control flow diagram of pressure roller pressure contact control according to the present embodiment. FIG. 4 is a time chart of pressure roller pressure contact control according to the present embodiment. Hereinafter, pressure roller pressure contact control will be described with reference to FIGS. 3 and 4. It is an example and the present invention is not limited to this.

  The pressure roller pressure contact control is executed by the control unit 100 based on a program stored in the ROM of the control unit 100. 3 is started by a print button (not shown) or a print start instruction such as a print instruction from a personal computer (t0 in FIG. 4). In the initial state, the pressure roller 64 is separated from the fixing roller 63, the fixing motor 70 rotates in the forward direction to drive the fixing roller 63, the pressure roller 64, and the fixing belt 61, and the heaters H1 and H2 are respectively The surface temperature of the fixing belt 61 and the surface temperature of the pressure roller 64 are controlled to be a predetermined temperature (for example, the surface temperature of the fixing belt 61: 200 ° C., the surface temperature of the pressure roller 64: 120 ° C.). And

  First, the control unit 100 determines whether or not the time T1 has elapsed. That is, it is determined whether or not the time T1 has elapsed from the print start instruction (step S1).

  If it is determined that the time T1 has elapsed (step S1; Yes), the control unit 100 reversely rotates the fixing motor 70 that has been normally rotated to drive the cam 65 (step S2) (t1 in FIG. 4). As a result, the fixing roller 63, the pressure roller 64, and the fixing belt 61 are stopped, and the pressure contact operation of the pressure roller 64 is started.

  If it is determined that the time T1 has not elapsed (step S1; No), the control unit 100 waits until the fixing belt 61 has elapsed the time T1.

  Next, the control unit 100 determines whether or not the cam 65 has rotated to a predetermined position. (Step S3).

  If it is determined that the cam 65 has rotated to a predetermined position (step S3; Yes), the control unit 100 rotates the fixing motor 70 that has been rotating in the forward direction to drive the fixing roller 63, the pressure roller 64, and the fixing belt 61. (Step S4) (t2 in FIG. 4). Thereby, the press contact operation of the pressure roller 64 is completed.

  If it is determined that the cam 65 has not rotated to the predetermined position (step S3; No), the control unit 100 waits until the cam 65 rotates to the predetermined position.

  Thereafter, at t3 in FIG. 4, the recording medium P reaches the fixing nip.

  Here, between t2 and t3, the fixing belt 61 can make at least one rotation (time for which the fixing belt 61 makes one rotation is T2: see FIG. 4). That is, t2 + T2 ≦ t3. A time T1 from the instruction to start printing to the start of the pressure contact operation of the pressure roller 64 is set so as to satisfy such conditions.

  As described above, after the pressure contact operation of the pressure roller 64 is completed, the fixing belt 61 is rotated while being heated by one or more rotations, so that the heat amount of the nip portion on the fixing roller side is deprived by the pressure roller during the pressure contact. Since the temperature of the nip portion can be recovered even when the temperature of the nip is locally reduced, the occurrence of nip marks is suppressed.

  The time T1 in step S1 is set in consideration of the generation of toner blisters. The pressure roller is controlled to a set temperature (for example, 120 ° C.), but receives heat from the fixing roller side during pressure contact, and the surface temperature rises above the set temperature. After the press contact, every time the number of rotations of the pressure roller 64 increases, the pressure roller 64 rises stepwise. Then, when the number of rotations of the pressure roller 64 exceeds the predetermined number of rotations and exceeds a predetermined temperature, toner blisters are generated. The occurrence of toner blisters varies depending on the type of recording medium, the configuration of the fixing unit, and the like. Therefore, the time T1 is appropriately set in consideration of the usage situation.

  As described above, according to the present embodiment, it is possible to obtain a high-quality image without image defects by setting the time T1 in step S1 so that nip marks and toner blisters are not generated.

  As in the present embodiment, in the full-color image forming apparatus, the amount of toner adhering to the recording medium is large and toner blisters are likely to occur. Therefore, the control of the present embodiment is particularly effective.

  In this embodiment, a belt is used as the heating member. However, a heat roller may be used, and a pressure roller may be pressed against the heat roller.

(Configuration of fixing unit)
A test was conducted using the fixing unit shown in FIG. The configuration of the fixing belt 61, the heating roller 62, the fixing roller 63, and the pressure roller 64 will be described below.

  The fixing belt 61 has a diameter of 80 mm and has a layer structure of PFA tube (0.2 mm) / silicon rubber (0.2 mm) / polyimide substrate (0.11 mm).

  The heating roller 62 is φ52 mm and has a layer structure of PFA coating (0.3 mm) / aluminum cored bar.

  The fixing roller 63 has a diameter of 40 mm and a layer structure of silicon rubber (7.5 mm) / aluminum cored bar.

  The pressure roller 64 has a diameter of 50 mm and has a layer structure of PFA coating (0.3 mm) / silicon rubber (2.0 mm) / aluminum cored bar.

  The total load at the time of press contact with the pressure roller 64 was 1000 N, and the nip width with the fixing roller 63 at this time was about 12 mm.

  The process speed of the image forming apparatus 1 is about 300 mm / sec.

(Test conditions)
The surface temperature of the fixing belt 61 is set to 200 ° C., and the surface temperature of the pressure roller 64 is set to 120 ° C., and the recording medium P is coated paper manufactured by Oji Paper Co., Ltd. OK Kanto (amount of 104.7 g / kg). The following tests were conducted using m ² ).

  A color photographic image is formed on the recording medium P by changing the time from pressing the copy button of the image forming apparatus 1 to starting the pressing of the pressure roller 64 (pressing start timing). Based on the color photographic image on which the image was formed, the state of occurrence of toner blisters and nip marks was visually evaluated. At each pressing start timing, the number of rotations of the fixing belt 61 after pressing (the number of rotations rotating between t2 and t3 in FIG. 4) and the number of rotations of the pressure roller 64 after pressing (from t2 to t3 in FIG. 4). The number of rotations until the time is also shown.

  The surface temperature of the pressure roller 64 immediately before the recording medium reached the fixing nip was also measured.

  The measurement results are shown in Table 1. In the toner blister and the nip mark, ◯ indicates a good case, a slight defect is observed, but an acceptable level is indicated by Δ, and an NG level is indicated by ×.

  In the toner blister, the pressure contact start timing was “◯” when 2.6 sec or more, “Δ” when 1.5 to 2.5 sec, and “X” when 1.0 sec or less. In terms of the number of rotations of the fixing belt 61 after pressure contact, it was evaluated as “◯” when 2.6 times or less, “△” when 2.7 to 3.9 times, and “x” when 4.5 times or more. In terms of the number of rotations of the pressure roller 64 after the press contact, it was ○ at 4.2 times or less, Δ at 4.4 to 6.3 times, and × at 7.3 times or more. In terms of the temperature of the pressure roller 64, it was ◯ at 131 ° C or lower, Δ at 131-135 ° C, and x at 139 ° C or higher.

  The nip mark was evaluated as ○ when the pressure contact start timing was 3.2 sec or less, Δ when 3.3 to 3.9 sec, and x when 4.0 sec or more. In terms of the number of rotations of the fixing belt 61 after pressure contact, it was ◯ at 1.9 times or more, Δ at 1.1 to 1.8 times, and × at 1.0 times or less. In terms of the number of rotations of the pressure roller 64 after the pressure contact, it was evaluated as ◯ at 3.1 times or more, Δ at 1.7 to 2.9 times, and × at 1.5 times or less. In terms of the temperature of the pressure roller 64, it was ○ at 128 ° C or higher, Δ at 124 to 127 ° C, and x at 123 ° C or lower.

  From the above, in this embodiment, the pressure contact start timing is 1.5 to 3.9 seconds, the number of rotations of the fixing belt 61 after pressure contact is 1.1 to 3.9 times, and the number of rotations of the pressure roller 64 after pressure contact. Is set to 1.7 to 6.3 times, or the temperature of the pressure roller 64 is set to 124 to 135 ° C., an acceptable image of toner blisters and nip marks can be obtained.

  More preferably, the pressure contact start timing is 2.6 to 3.2 seconds, the number of rotations of the fixing belt 61 after pressure contact is 1.9 to 2.6 times, and the number of rotations of the pressure roller 64 after pressure contact is 3.1 to 3.1. 4. When the temperature of the pressure roller 64 is set to 128 to 131 ° C. twice, a good image without toner blisters and nip marks can be obtained.

In this embodiment, the test was performed using Oji Paper's OK Kanfuji (basis weight 104.7 g / m ² ) as the recording medium P, and the surface temperature of the pressure roller 64 at which the toner blister was NG was 139 ° C. However, Table 2 shows the surface temperature of the pressure roller 64 at which the toner blister becomes NG when using another recording medium, together with the amount of the recording medium. Both recording media are coated paper manufactured by Oji Paper Co., Ltd. Other test conditions other than the recording medium are the same as those in the above example.

  The surface temperature of the pressure roller 64 at which the toner blister becomes NG is lower as the amount of wrinkle of the recording medium is smaller. This is because the thinner the recording medium, the smaller the heat capacity, and the easier the temperature of the recording medium rises, so that the water in the recording medium is likely to evaporate.

1 is a configuration diagram of an image forming apparatus according to an exemplary embodiment. 2 is a configuration diagram of a fixing unit 60 according to the present embodiment. FIG. It is a control flow figure of pressure roller press-contact control concerning this embodiment. It is a time chart of pressure roller press-contact control concerning this embodiment. It is explanatory drawing of a nip mark.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 60 Fixing part 61 Fixing belt 62 Heating roller 63 Fixing roller 64 Pressure roller 65 Cam 66 Compression spring 67,68,69 One-way clutch 70 Fixing motor 100 Control part P Recording medium H1, H2 Heater

Claims (5)

In an image forming apparatus that performs fixing by passing a recording medium through a nip portion between a rotationally driven heating member and a pressure member that are pressed against each other,
A first heater for heating the heating member;
A second heater for heating the pressure member;
A drive mechanism for rotationally driving the heating member and the pressure member;
A pressure release mechanism for releasing the pressure of the heating member and the pressure member;
A control unit that controls the first heater, the second heater, the drive mechanism, and the pressure release mechanism;
The control unit controls the first heater so that the surface temperature of the heating member becomes a first temperature, and the surface temperature of the pressure member becomes a second temperature lower than the first temperature. The second heater is controlled as described above, and after the print instruction, the heating member heated to the first temperature by the pressure release mechanism and the pressurizing member heated to the second temperature are stopped. The image forming apparatus is configured to control the driving mechanism and the pressure releasing mechanism so that the recording medium reaches the nip portion after the heating member is driven to rotate more than one rotation. apparatus.   The image forming apparatus according to claim 1, wherein the heating member is a belt.   The control unit presses the heating member and the pressure member against each other by the pressure release mechanism and before the surface temperature of the pressure member reaches a temperature at which unacceptable toner blisters are generated, The image forming apparatus according to claim 1, wherein the image forming apparatus is controlled to reach the nip portion.   The control unit presses the heating member and the pressure member against each other by the pressure release mechanism, and then reaches the temperature at which a toner blister whose surface temperature of the pressure member is unacceptable is generated. The image forming apparatus according to claim 1, wherein the number of rotations is controlled so that the recording medium reaches the nip portion before.   5. The image forming apparatus according to claim 3, wherein the temperature at which the unacceptable toner blister is generated is a temperature set based on a haze amount of the recording medium.

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