JP5309933B2 - Fixing device - Google Patents

Description

  The present invention relates to a fixing device that fixes an image on a recording material in an image forming process of forming an image by an electrophotographic process.

  As a fixing device used in an electrophotographic image forming apparatus such as a copying machine or a printer, a heat roller fixing type fixing device is frequently used.

  The fixing device of the heat roller fixing system includes a pair of rollers (fixing roller and pressure roller) that are in pressure contact with each other, and the fixing roller is heated by heating means including a halogen heater or the like disposed in both or one of the roller pairs. Is heated to a predetermined temperature (fixing temperature).

  The recording material carrying the unfixed toner image passes through the nip between the pair of rollers, and the toner image is fixed by being heated and pressurized in the nip.

  By the way, in recent electrophotographic image forming apparatuses, a so-called soft roller in which an elastic layer made of silicon rubber or the like is provided on the surface of the fixing roller is often used. By making the fixing roller a soft roller, the surface of the fixing roller is elastically deformed corresponding to the unevenness of the unfixed toner image, and heats the unfixed toner image well because it contacts the surface of the toner image so as to cover it. Fixing can be performed.

  A fixing device using a soft roller is particularly effective in fixing a color toner image having a large amount of toner forming an image.

  In a fixing device using a soft roller, the surface of the fixing roller has a convex shape at the nip exit when the fixing roller is deformed at the nip. By this convex portion, the recording material is directed in a direction away from the fixing roller and passes through the nip, so that the releasability of the recording material from the fixing roller is improved. That is, an effect that it becomes unnecessary to provide separation means such as a separation claw can be obtained by the soft roller.

  In the fixing roller using the soft roller having the elastic layer as described above, the thermal conductivity of the elastic layer is very low. For this reason, when the heating means is provided inside the fixing roller, there is a problem that the heat transfer efficiency is lowered, the warm-up time is increased, and the fixing roller temperature does not follow when the process speed is increased. .

  In order to solve such a problem, there has been proposed a fixing device including an external heating unit that heats the fixing roller from the outside, that is, from the surface side (Patent Documents 1 to 3).

  In Patent Document 1, a pressing member that presses a part of a contact area of a heating belt that contacts the fixing roller and heats the fixing roller with the fixing roller is provided.

  In Patent Document 2, a heating belt stretched around a roller pair is used as an external heating means, and the distance between the roller pair is fixed. When the heating belt is not in contact with the fixing roller, no tension is applied to the heating belt, and when the heating belt is in contact with the fixing roller, tension is applied.

In Patent Document 3, even when the roller pair is separated from the fixing roller, the heating belt is brought into contact with the fixing roller, and the heating belt is moved by the rotation of the fixing roller. In Patent Document 3, the heating belt is prevented from being deteriorated in this way.
JP 2005-300800 A JP 2007-2112896 A JP 2007-248724 A

  As in Patent Documents 1 to 3, a heating belt is used as an external heating means for heating the fixing roller from the outside.

  The heating belt contacts the fixing roller over a wide area. Therefore, a large amount of heat is transferred from the heating belt to the fixing roller, and furthermore, since the heat capacity of the heating belt is small, the heating belt is quickly heated, and temperature control with high responsiveness is possible. The advantage that is obtained by the heating belt.

  However, when a heating belt is used, there are the following problems.

  When the heating belt is used as in Patent Documents 2 and 3, the heating belt is brought into contact with the fixing roller using a pair of rollers. In this configuration, the heating belt is slackened between the rollers, and the heat belt is separated from the fixing roller at the slack portion, thereby limiting the amount of heat transmitted from the heating belt to the fixing roller.

  As a result, there is a problem that the amount of heat supplied from the heating belt to the fixing roller is insufficient, and the temperature of the fixing roller is lowered during continuous image formation.

  In Patent Document 1, the heating belt contacts the fixing roller only in a part between the pair of rollers on which the heating belt is stretched. Therefore, also in Patent Document 1, the temperature of the fixing roller is lowered due to a shortage of heat supplied from the heating belt to the fixing roller.

  If the distance between the roller pairs is increased in order to increase the contact area in the heating mechanism of Patent Document 1, the space occupied by the external heating means increases, and it becomes difficult to provide the external heating means in the fixing device.

  The present invention solves the problems in the conventional fixing device having an external heating means, and uses an external heating method in which color image formation and high-speed image formation are possible without lowering the temperature of the fixing roller even during continuous image formation. It is an object of the present invention to provide a fixing device that fully utilizes the advantages.

  The object is achieved by the following invention.

1. In a fixing device having an elastic layer, comprising a fixing roller for heating and fixing a toner image on a recording material, a pressing means for bringing the recording material into contact with the fixing roller, and an external heating means for heating the fixing roller.
The external heating means includes
A first roller;
A second roller;
A non-stretchable heating belt stretched around at least the first roller and the second roller, pressed against the surface of the fixing roller by the first roller and the second roller, and rotated by being driven by the fixing roller; ,
Tension means for biasing the second roller away from the first roller and applying tension to the heating belt;
The first roller is provided on the upstream side of the second roller with respect to the moving direction of the heating belt on the surface side of the fixing roller,
The fixing device, wherein the second roller presses the heating belt against the fixing roller with a pressing force smaller than that of the first roller.

  2. 2. The fixing device according to 1, wherein a heat source for heating the heating belt is provided in the first roller or the second roller.

3 . The fixing apparatus according to 1, characterized in that a heat source for heating the heating belt in the prior SL first roller.

4). 4. The fixing device according to claim 1, further comprising a switching unit that presses the heating belt against the fixing roller and releases the pressure contact. 5.

  According to the present invention, the roller pair presses the heating belt against the fixing member with a pressing force that is not equal to each other. As a result, the heating belt contacts the fixing roller in the entire region between the roller pair.

  By increasing the contact area, the amount of heat transferred from the heating belt to the fixing roller increases.

  Therefore, satisfactory fixing is performed even in the case of an image with a large amount of toner such as a color toner image or in the case of high-speed image formation, and it is possible to sufficiently suppress the temperature drop of the fixing roller during continuous image formation.

  Hereinafter, although this invention is demonstrated based on embodiment of this invention, this invention is not limited to this embodiment.

  FIG. 1 is a diagram showing an overall configuration of a fixing device according to an embodiment of the present invention.

  The fixing device includes a fixing roller 1 as a fixing member that heats and fixes a toner image, a heating belt 2 that heats the fixing roller 1 from the outside, and a pressing belt 7 that constitutes a pressing unit that brings the recording material P into contact with the fixing roller 1. Have.

  The fixing roller 1 includes a cylindrical cored bar 1A, an elastic layer 1B made of a heat-resistant elastic material such as silicon rubber, PFA (tetrafluoroethylene perfluoroalkyl vinyl ether copolymer), PTFE (polytetrafluoroethylene), and the like. It is comprised by the mold release surface layer 1C which consists of a fluororesin.

  The endless heating belt 2 is stretched by a roller 3 as a first roller and a roller 4 as a second roller, and between a portion stretched on the roller 3 and a portion stretched by the roller 4, It contacts the fixing roller 1 as shown.

  A heater 5 as a heat source is disposed inside the roller 3, the heating belt 2 is heated by the heater 5, and the heated heating belt 2 heats the fixing roller 1.

  The heating belt 2 constitutes an external heating unit that heats the fixing roller 1 from the outside.

  Reference numeral 6 denotes a heater as an auxiliary heat source provided inside the fixing roller 1.

  A pressing belt 7 presses the recording material P against the fixing roller 1 and is stretched between three rollers 8 to 10.

  Reference numeral 11 denotes a pressing member that constitutes the pressing unit and presses the pressing belt 7 against the fixing roller 1. The pressing belt 7 is stretched around rollers 8 and 10, and a predetermined tension is applied to the pressing belt 7 by the roller 9.

  The recording material P enters the nip between the fixing roller 1 and the pressing belt 7 as indicated by an arrow from the roller 8 side, and is heated by the fixing roller 1 in the nip. The toner image on the recording material P is heated and melted and fixed on the recording material P.

  The roller 3 presses the heating belt 2 against the fixing roller 1 with a pressing force F1 by an urging means (not shown).

  The roller 4 presses the heating belt 2 against the fixing roller 1 with a pressing force F2 by urging means (not shown) or by its own weight.

  The pressing force F1 and the pressing force F2 are set so as to satisfy F1> F2, and the heating belt 2 is pressed against the fixing roller 1 with a pressing force that is not equal to each other.

  The roller 3 and the roller 4 press the heating belt 2 against the fixing roller 1 with an unequal pressing force, so that the heating belt 2 is fixed without being lifted between the pressing position by the roller 3 and the pressing position by the roller 4. Close contact with the roller 1.

  As a result, the fixing roller 1 is heated in contact with the heating belt 2 over a wide area. Further, the fixing roller 1 is heated uniformly.

  The smaller pressing force F2 may be zero.

  A problem in a conventional fixing device using a heating belt will be described with reference to FIG.

  When the pair of rollers press the heating belt against the fixing roller with equal pressing force, the heating belt BL is lifted from the fixing roller HR between the rollers R1 and R2, as shown in FIG. As a result, the contact area between the fixing roller HR and the heating belt BL decreases, and the amount of heat supplied from the heating belt BL to the fixing roller HR decreases.

  In the conventional heating mechanism shown in FIG. 2, the rollers R1 and R2 around which the heating belt BL is stretched are supported by one support member, and the distance between the rollers R1 and R2 is constant.

  The heating belt BL is a resin belt such as PI (polyimide) or a metal belt such as Ni, and has no stretchability.

  In order to increase the heating area of the fixing roller HR by bringing the belt portion stretched by the rollers R1 and R2 into contact with the fixing roller HR, the heating belt BL is stretched around the rollers R1 and R2 with some slack. Need to be laid.

  In this way, when the heating belt BL stretched in a slack state is pressed against the fixing roller HR with the same pressing force F3, and the surface of the fixing roller HR is deformed as shown, the heating belt BL The air floats between the roller R1 and the roller R2, and moves away from the surface of the fixing roller HR.

  As a result, the area where the fixing roller HR is heated is reduced and the amount of heat transfer is reduced.

  By pressing the heating belt 2 against the fixing roller 1 with the heating mechanism shown in FIG. 1, that is, the unequal pressing forces F 1 and F 2, the area where the fixing roller 1 is heated increases. Increases the amount of heat supplied to

  As a result, the temperature drop of the fixing roller 1 during continuous image formation is sufficiently suppressed.

  FIG. 3 shows a first example of a support mechanism for the rollers 3 and 4 that support the heating belt 2 in FIG.

  The rollers 3 and 4 are supported by a plate-like support member 20.

  The roller 3 is rotatably supported by a shaft (not shown), and the end portion of the shaft is formed as a substantially rectangular shaft end portion 3a.

  The shaft end portion 3a is fitted into a long hole 20a provided in the support member 20, and the shaft end portion 3a is movable in the horizontal direction in the figure.

  A compression spring 21 is interposed between the shaft end 3 a and the support member 20. The spring 21 is a tension unit that applies tension to the heating belt 2.

  The shaft 4 a of the roller 4 is rotatably supported by a support member 20.

  The support member 20 is connected to a lever 24 by a compression spring 22 at the position of the roller 3 and by a compression spring 23 at the position of the roller 4.

  The lever 24 is rotatable about a shaft 24a and is driven by the cam 25 to rotate.

  The state shown in the figure shows a state in which the rollers 3 and 4 press the heating belt 2 of FIG.

  When the cam 25 rotates 180 ° from the position shown in the drawing, the lever 24 rotates clockwise and the pressing is released.

  In the state of FIG. 3, the spring 22 presses the roller 3 against the fixing roller 1 with a pressing force F1, and the spring 23 presses the roller 4 against the fixing roller 1 with a pressing force F2 smaller than the pressing force F1.

  The spring 21 urges the roller 4 in a direction away from the roller 3. Thereby, a predetermined tension is applied to the heating belt 2.

  By making the pressing force F2 of the roller 4 smaller than the pressing force F1 of the roller 3, the heating belt 2 is in close contact with the surface of the roller 1, and the fixing roller 1 is heated with high efficiency.

  FIG. 4 shows a second example of a support mechanism for the rollers 3 and 4 that support the heating belt 2 in FIG.

  In FIG. 4, the support member 20 has support arms 20b and 20c extending from the support member main body.

  A support member 26 that supports the roller 4 is fitted into a space formed between the support arm 20b and the support arm 20c. The roller 3 is rotatably supported by a support member 26 on its shaft 3b.

  As shown in FIG. 4B, after the unit composed of the roller 4 and the support member 26 is inserted between the support arms 20b and 20c as indicated by the arrows, the heating belt 2 is stretched between the roller 3 and the roller 4. Thus, the heating belt 2 and the rollers 3 and 4 are attached to the support member 20 as shown in FIG.

  FIG. 5 shows the operation of the belt support mechanism shown in FIGS.

  As the cam 25 rotates, the lever 24 rotates about the shaft 24a. The roller 3 is supported by the support member 20 at a position closer to the shaft 24 a than the roller 4.

  In a state where the cam 25 is not pressed, the heating belt 2, the rollers 3 and 4, the support member 20, and the lever 24 are placed on the fixing roller 1 by the weight of the unit composed of these members.

  That is, the roller 3 is placed on the fixing roller 1.

  On the other hand, since the tension is applied to the heating belt 2 by the spring 21, the roller 4 is separated from the fixing roller 1 by this tension as shown in FIG.

  The cam 25 rotates, the lever 24 rotates counterclockwise, the spring 22 presses the roller 3 and the spring 23 presses the roller 24, whereby the heating belt 2 is fixed to the fixing roller as shown in FIG. 1 is pressed.

  In the process of operation from FIG. 5A to FIG. 5B, the roller 3 contacts the fixing roller 1 first, and the roller 4 contacts later.

  As described above, when the roller 3 and the roller 4 come into contact with the fixing roller 1 at different timings, the heating belt 2 is brought into close contact with the surface of the fixing roller 1 without causing slack between the rollers 3 and 4. A large contact area between 1 and the heating belt 2 is ensured.

  In the embodiment described above, the distance between the roller 3 and the roller 4 on which the heating belt 2 is stretched is variable, and a tension is applied to the heating belt 2 by applying a spring in a direction in which both rollers are separated. Yes. However, the roller 3 and the roller 4 that stretch the heating belt 2 can be supported by a fixed shaft, and the interval between the rollers can be fixed.

  Even in such a configuration, the pressing force for pressing the heating belt against the fixing roller is made different between the two rollers, and the timing at which the two rollers press the heating belt against the fixing roller is shifted, so that the heating belt between the two rollers is shifted. The slack can be eliminated.

  In this case, it is preferable that the roller to be pressed with a large pressing force is first brought into contact with the fixing roller.

  Further, as shown in FIG. 5, the pressing force F1 of the upstream roller 3 with respect to the moving direction W of the fixing roller 1 at the contact portion between the fixing roller 1 and the heating belt 2 is greater than the pressing force F2 of the downstream roller 4. It is preferable to enlarge it.

  The heat source may be provided either inside the roller 3 or inside the roller 4.

(1) Embodiment Using the fixing device shown in FIG. 1, the recording material was continuously passed through the fixing device under the conditions shown in Table 1 and the following conditions, and the changes in the heating belt temperature, the fixing roller temperature, and the pressing belt temperature. I investigated.
・ Conveying speed of recording material in fixing device: 400 mm / sec
・ Control target value Fixing roller temperature: 185 ℃
Pressure belt temperature: 95 ° C
Heating belt temperature: 195 ° C

  FIG. 6 shows the temperature change during continuous paper feeding.

As shown in FIG. 6, the lowest point temperature of the surface temperature of the fixing roller was about 160.degree.
(2) Comparative Example 1
A continuous paper passing test was performed under the same conditions as in Example 1 except that the pressing force F1 = F2 = 80 N and the interval between the rollers 3 and 4 was constant.

  FIG. 7 shows the temperature change during continuous paper feeding.

  As shown in FIG. 7, the lowest point temperature of the fixing roller was 148 ° C.

As both rollers strongly press the heating belt, the heating belt moves away from the fixing roller between the two rollers, resulting in a decrease in heating efficiency. As a result, the temperature of the heating belt does not decrease and the amount of heat transferred from the heating belt to the fixing roller. The decrease in the fixing roller temperature was large due to the small amount.
(3) Comparative Example 2
The fixing device shown in FIG. 8 was used.

  In this fixing device, the roller 3 presses the heating belt 2 against the fixing roller 1, but the roller 4 is floating, and the heating belt 2 is separated from the fixing roller 1 at the roller 4 portion.

  The embodiment was continuously fed under the same conditions except that the pressing force F1 = 80 N and F2 = x.

  F2 = x indicates that the roller 4 is floating.

  As shown in FIG. 9, the lowest point temperature of the fixing roller was 158 ° C.

  Although the lowest point temperature was higher than that of Comparative Example 1, there was a large temperature drop of the fixing roller.

1 is a diagram illustrating an overall configuration of a fixing device according to an embodiment of the present invention. It is a figure which shows the heating mechanism of the conventional fixing roller. It is a figure which shows the 1st example of the support mechanism of the rollers 3 and 4 which support the heating belt 2 in FIG. It is a figure which shows the 2nd example of the support mechanism of the rollers 3 and 4 which support the heating belt 2 in FIG. It is a figure which shows operation | movement of the belt support mechanism shown to FIG. It is a figure which shows the change of the temperature of the fixing roller at the time of continuous paper passing in an Example. 6 is a diagram illustrating a change in temperature of a fixing roller during continuous paper feeding in Comparative Example 1. FIG. FIG. 6 is a view showing a fixing device used in Comparative Example 2. 10 is a diagram illustrating a change in temperature of a fixing roller during continuous paper feeding in Comparative Example 2. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fixing roller 2 Heating belt 3, 4 Roller 5, 6 Heater 7 Pressing belt 11 Pressing member F1, F2, F3 Pressing force

Claims (4)

In a fixing device having an elastic layer, comprising a fixing roller for heating and fixing a toner image on a recording material, a pressing means for bringing the recording material into contact with the fixing roller, and an external heating means for heating the fixing roller.
The external heating means includes
A first roller;
A second roller;
A non-stretchable heating belt stretched around at least the first roller and the second roller, pressed against the surface of the fixing roller by the first roller and the second roller, and rotated by being driven by the fixing roller; ,
Tension means for biasing the second roller away from the first roller and applying tension to the heating belt;
The first roller is provided on the upstream side of the second roller with respect to the moving direction of the heating belt on the surface side of the fixing roller,
The fixing device, wherein the second roller presses the heating belt against the fixing roller with a pressing force smaller than that of the first roller.   The fixing device according to claim 1, wherein a heat source for heating the heating belt is provided in the first roller or the second roller. The fixing device according to claim 1, characterized in that a heat source for heating the heating belt in the prior SL first roller.   4. The fixing device according to claim 1, further comprising a switching unit that presses the heating belt against the fixing roller and releases the pressure contact. 5.

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