JP2009169156A - Fixing device, and image forming apparatus including the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device of a long life, capable of securing sufficiently an area for a nip part for a fixing belt and a pressurizing roller, and allowing pressurization in the whole area of the nip part, and an image forming apparatus including the same. <P>SOLUTION: This fixing device 7 includes: the endless fixing belt 21; a heat transfer roller 22 inscribed with the fixing belt 21, a fixing roller 23 touching internally with the fixing belt 21, and rotated along a direction same to that of the fixing belt 21, and the pressurizing roller 24 being contacted with pressure with the fixing roller 23, with the fixing belt 21 therebetween, and rotated followingly. A pressurizing member 28 constituted of a main pressurizing part 29 and a pressure distribution transfer part 30 extended over ranging from the main pressurizing part 29 to a fixing nip part N is arranged between the fixing nip part N and a guide roller 27. At least one part of the fixing roller 23 is contacted with pressure with the fixing belt 21 and the pressurizing roller 24 via the pressure distribution transfer part 30. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention uses a fixing device that inserts a sheet carrying an unfixed toner image into a nip of a heated roller pair, heats and melts the unfixed toner, and fixes the unfixed toner on the sheet, and an electrophotographic system including the same. The present invention relates to an image forming apparatus.

  In a conventional image forming apparatus using an electrophotographic system, a heat source is incorporated in at least one roller of a pair of fixing rollers forming a nip to form a heating roller, and an unfixed toner image is carried on the nip portion of the roller pair. A heat roller fixing system in which toner is fixed to a sheet by inserting the sheet is widely used.

  In such a heat roller fixing method, the efficiency of heat transfer from a heat source such as a halogen lamp built in the heat roller to the roller surface is low, and heat loss is large. Also, it takes a long time for heat to be transferred to the roller surface. As a result, there is a problem that since the heating efficiency is low, the power consumption is large and the warm-up time until the roller surface reaches a temperature at which fixing is possible becomes long.

  In order to improve this, the heating member for heating the paper is replaced with a heating roller, and a belt or film that absorbs radiation light from the heat source and generates heat, so that the heat capacity compared to the conventional heating roller. A belt fixing method has been developed to reduce the power consumption by reducing the warm-up time and reducing the power consumption.

  In a color image forming apparatus using such a belt fixing system, when toner is fixed to a recording medium, the amount of toner adhering to the recording medium is larger than that of a monochrome machine, and therefore the recording medium is in contact with the belt. It is necessary to take a long time (nip time). As a countermeasure, for example, Japanese Patent Application Laid-Open No. H10-228867 discloses a sliding pressurization in which an auxiliary nip portion is formed in advance of a fixing nip portion where a support pressure roller (fixing roller) and an external pressure roller face each other via a belt member. A method of providing a member inside the belt is disclosed.

Patent Document 2 discloses a fixing device in which a fixing member forming an auxiliary nip portion is provided in contact with a fixing roller on the upstream side of a belt member.
JP 2004-78771 A JP 2004-252354 A

  However, in the method of Patent Document 1, since there is a gap between the fixing roller and the sliding pressure member, the pressure from the external pressure roller is not applied to the recording medium between the fixing nip portion and the auxiliary nip portion. It will be in a pressure relief state. The toner layer heated in the auxiliary nip portion is in a molten state, and when a portion where the pressure is released occurs in that state, an image looks blurred due to the influence of a minute speed difference between the belt and the external pressure roller. There is a problem that a stable fixing process cannot be performed, such as uneven glossiness in the image because uniform pressure is not applied to the entire toner image.

  In the method of Patent Document 2, a low friction member is provided at the contact portion between the fixing roller and the fixing member to prevent the fixing member from being deformed or caught by the fixing roller. When worn, the fixing member may be deformed or caught and damaged. In addition, a configuration in which the contact portion is made rigid so that it does not get caught in the fixing roller is considered, but in this case, the surface of the fixing roller is worn by friction with the rigid body and cannot be used for a long time. There was a point.

  In view of the above problems, the present invention includes a long-life fixing device capable of ensuring a sufficient area of the nip portion between the fixing belt and the pressure roller and capable of uniform pressure application throughout the nip portion, and the same. An object is to provide an image forming apparatus.

  In order to achieve the above object, the present invention provides an endless fixing belt that can be rotated at substantially the same speed as the conveyance speed of a recording medium, heating means for heating the fixing belt, and a fixing roller inscribed in the fixing belt. And a pressure roller that contacts the fixing roller with a predetermined pressure via the fixing belt, and the recording medium is inserted through a fixing nip formed by the fixing belt and the pressure roller. In a fixing device for fixing an unfixed toner image carried thereon, a main unit arranged on the upstream side of the fixing roller with respect to the rotation direction of the fixing belt and pressed against the pressure roller via the fixing belt. A pressure assisting member having a pressure part and a pressure distribution transfer part extending from the main pressure part to the fixing nip part is provided.

  According to the present invention, in the fixing device configured as described above, the pressure distribution transfer portion is formed of a flexible metal plate.

  According to the present invention, in the fixing device configured as described above, a member having a smaller friction coefficient than that of the pressure distribution transfer portion is attached to a sliding portion of the pressure distribution transfer portion with the fixing belt and the fixing roller. It is said.

  According to the present invention, in the fixing device configured as described above, a guide roller that is inscribed in the fixing belt is provided on the upstream side of the pressure assisting member with respect to the rotation direction of the fixing belt.

  The present invention is also an image forming apparatus equipped with the fixing device having the above-described configuration.

  According to the first configuration of the present invention, since the fixing belt is pressed against the pressure roller by the main pressure unit and the pressure distribution transfer unit on the upstream side of the fixing nip portion, even in color printing with a large amount of toner applied. A sufficient nip time can be ensured, and there is no possibility that a non-uniform pressure portion is generated between the pressure distribution transfer portion and the fixing roller. Furthermore, since the main pressure unit does not come into contact with the fixing roller, it is possible to prevent the main pressure unit from being damaged due to the wear of the fixing roller or being caught in the fixing roller.

  According to the second configuration of the present invention, in the fixing device of the first configuration, the pressure distribution transfer portion is formed of a flexible metal plate, so that the recording medium is applied at a constant pressure. The entire pressure distribution transfer portion can be brought into contact with the pressure roller uniformly by bending along the surface of the pressure roller while maintaining the pressureable rigidity.

  According to the third configuration of the present invention, in the fixing device having the first or second configuration, the sliding portion of the pressure distribution transfer portion with the fixing belt and the fixing roller is more rubbed than the pressure distribution transfer portion. By providing a member having a small coefficient, the friction between the pressure distribution transfer portion, the fixing belt and the fixing roller is reduced, and the fixing belt and the fixing roller rotate smoothly, and the durability of the fixing belt and the fixing roller is also improved. .

  According to the fourth configuration of the present invention, in the fixing device having any one of the first to third configurations, the fixing belt is inscribed in the upstream side of the auxiliary pressure member with respect to the rotation direction of the fixing belt. By providing the guide roller, the contact angle between the fixing belt and the pressure auxiliary member can be adjusted to reduce friction.

  Further, according to the fifth configuration of the present invention, by mounting the fixing device having any one of the first to fourth configurations, uniform and sufficient heating and heating can be performed even in color printing with a large amount of toner. An image forming apparatus capable of forming a high-quality image by pressure and having excellent durability.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing a configuration of an image forming apparatus equipped with a fixing device of the present invention. Here, a tandem color printer will be described as an example. In the main body of the image forming apparatus 100, four image forming portions Pa, Pb, Pc, and Pd are sequentially arranged from the upstream side (right side in FIG. 1) of the transport belt 8. These image forming portions Pa to Pd are provided corresponding to images of four different colors (cyan, magenta, yellow, and black), and cyan, magenta, and yellow are respectively performed by charging, exposure, development, and transfer processes. And a black image are sequentially formed.

  Photosensitive drums 1a, 1b, 1c, and 1d that carry visible images (toner images) of the respective colors are disposed in the image forming portions Pa to Pd, and are formed on the photosensitive drums 1a to 1d. The transferred toner image is transferred onto the paper P carried and transported by the transport belt 8 that moves adjacent to each image forming unit, and is further fixed on the paper P in the fixing device 7, and then from the apparatus main body. It is configured to be discharged. An image forming process for each of the photosensitive drums 1a to 1d is executed while rotating the photosensitive drums 1a to 1d clockwise in FIG.

  Next, the image forming units Pa to Pd will be described. Around and around the photosensitive drums 1a to 1d rotatably arranged, image information is supplied to the chargers 2a, 2b, 2c and 2d for charging the photosensitive drums 1a to 1d and the photosensitive drums 1a to 1d. LED heads 4a, 4b, 4c and 4d to be exposed, developing devices 3a, 3b, 3c and 3d for forming toner images on the photosensitive drums 1a to 1d, and a developer remaining on the photosensitive drums 1a to 1d ( Cleaning portions 5a, 5b, 5c and 5d for removing toner are provided.

  First, the surfaces of the photosensitive drums 1a to 1d are uniformly charged by the chargers 2a to 2d, and then light is irradiated by the LED heads 4a to 4d, and electrostatic charges corresponding to the image signals are applied to the photosensitive drums 1a to 1d. A latent image is formed. Each of the developing devices 3a to 3d is filled with a predetermined amount of cyan, magenta, yellow, and black toner by a replenishing device (not shown). The toner is supplied onto the photosensitive drums 1a to 1d by the developing units 3a to 3d and electrostatically attached to the toner in accordance with the electrostatic latent images formed by exposure from the LED heads 4a to 4d. An image is formed.

  The paper P onto which the toner image is transferred is housed in a paper cassette 16 at the lower part of the apparatus, and is supplied onto the conveying belt 8 via the paper supply roller 12a and the registration roller 12b, and is supplied to each of the photosensitive drums 1a to 1d. Transported to position. A sheet made of dielectric resin is used for the conveyor belt 8, and a belt in which both ends thereof are overlapped and joined to form an endless shape or a seamless belt is used.

  The conveyor belt 8 is stretched between an upstream conveyor roller 10 and a downstream drive roller 11. When the conveyor belt 8 starts to rotate counterclockwise, the sheet P is transferred from the registration rollers 12b to the conveyor belt. It is conveyed onto the conveyor belt 8 via a suction roller (not shown) provided on the most upstream side. A predetermined voltage is applied to the suction roller, and the paper P is held on the transport belt 8 by an electrostatic suction force. At this time, the image writing signal is turned ON, and an image is formed on the uppermost photosensitive drum 1a at a predetermined timing. A cyan toner image on the photosensitive drum 1a is transferred onto the paper P by applying an electric field to the lower portion of the photosensitive drum 1a with a transfer roller 6a to which a predetermined transfer voltage is applied. Thereafter, the sheet P is conveyed to the next image forming portion Pb, and a magenta toner image is transferred by the photosensitive drum 1b and the transfer roller 6b in the same manner as described above.

  Thereafter, yellow and black toner images are transferred by the photosensitive drums 1c and 1d and the transfer rollers 6c and 6d, respectively, by the same method as described above. These four color images are formed with a predetermined positional relationship with respect to the paper P in order to form a predetermined full color image. The paper P on which the four color toner images are transferred is separated from the transport belt 8 and transported to the fixing device 7. In addition, the photosensitive drums 1a to 1d after the toner images are transferred are prepared by the cleaning units 5a to 5d in preparation for new electrostatic latent images to be subsequently formed.

  The paper P transported from the transport belt 8 to the fixing device 7 is heated and pressurized to fix the toner image on the surface of the paper P, thereby forming a predetermined full-color image. The paper P on which the full-color image is formed is discharged to the discharge tray 15 on the upper surface of the apparatus main body by the discharge roller 13.

  FIG. 2 is a side sectional view of the fixing device according to the first embodiment of the present invention. As shown in FIG. 2, the fixing device 7 includes an endless fixing belt 21 that rotates clockwise in the drawing, a hollow cylindrical heat transfer roller 22 inscribed in the fixing belt 21, and an inscribed in the fixing belt 21. The fixing roller 23 rotates in the same direction as the fixing belt 21, and the pressure roller 24 presses against the fixing roller 23 with the fixing belt 21 interposed therebetween and rotates counterclockwise in the drawing.

  The fixing belt 21 has a plurality of layers including a base layer (base material) provided on the innermost side in contact with the heat transfer roller 22 and the fixing roller 23 and a release layer provided on the outermost side in contact with the pressure roller 24. It is an endless belt formed by lamination. The fixing belt 21 is wound around a heat transfer roller 22, a fixing roller 23, and a guide roller 27, and given a predetermined tension.

  As the base layer, a metal layer obtained by plating or rolling a metal such as nickel, or a synthetic resin layer such as a polyimide film is used. The release layer is made of a fluorine resin such as PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), and is formed by applying a paint or covering the tube. The release layer has a thickness of about 10 to 50 μm for a PFA tube and about 10 to 30 μm for a fluororesin paint.

  Further, a silicon rubber layer having a thickness of about 100 to 1000 μm may be provided as an elastic member layer between the base layer and the release layer. According to this configuration, the elastic member layer wraps the unfixed toner image on the paper and can be fixed softly. As a result, the image quality can be improved, and a high-performance fixing device can be obtained.

  Further, it is possible to provide a heat storage layer between the base layer and the release layer so as not to let the heat obtained from the heat transfer roller 22 escape and to keep the surface temperature of the fixing belt 21 uniform. As a result, higher heating efficiency can be obtained, and the effects of shortening the warm-up time and reducing power consumption can be enhanced.

  The heat storage layer is composed of silicon rubber having a high thermal conductivity, such as silica, alumina, magnesium oxide powder or the like, and a metal having a high thermal conductivity, such as aluminum, copper, nickel, etc. These are formed by covering or plating a tube-shaped product. The heat storage layer may be made of an elastic material such as silicon rubber. However, when it is made of metal, if the wall thickness is made too thick, the belt hardness increases, and the nip amount necessary to melt the toner is obtained. It will not be possible. Therefore, the thickness of the heat storage layer is 10 to 1000 μm, desirably 50 to 500 μm.

  A thermistor (not shown) is provided so as to contact the surface of the fixing belt 21. The temperature of the fixing belt 21 is detected by this thermistor, and the fixing temperature is controlled by controlling ON / OFF of the light source 25.

  The width of the fixing belt 21 is set to be narrower than the width of the light source 25 and wider than the maximum sheet width that passes through the fixing nip portion N. As a result, the light source 25 uniformly heats the entire fixing belt 21 to prevent the occurrence of uneven fixing, and the fixing belt 21 can cover the entire surface of the sheet regardless of the sheet size. Adhering toner can be prevented.

  The heat transfer roller 22 heats the fixing belt 21, and a light source 25 is provided in the inside thereof over almost the entire area in the longitudinal direction (paper surface direction in the drawing). As the light source 25, a halogen lamp, a xenon lamp, or the like that radiates infrared rays efficiently is used, and a halogen lamp that has high-speed startup characteristics and responsiveness when the power is turned on is preferable. As the material of the heat transfer roller 22, a metal such as stainless steel or aluminum having good thermal conductivity is used.

  The fixing roller 23 is in contact with the pressure roller 24 via the fixing belt 21 to form a fixing nip portion N through which a sheet is inserted, and is rotated clockwise in the drawing by a driving source (not shown) such as a motor. It rotates to apply a driving force to the fixing belt 21. As the configuration of the fixing roller 23, for example, a configuration in which a silicon rubber layer 23b constituting an elastic layer is provided around an iron core 23a is used.

  The pressure roller 24 is provided with, for example, a silicon rubber layer 24b constituting an elastic layer on the outside of an aluminum cored bar 24a, and the surface is covered with a PFA tube. A pressure adjusting mechanism (not shown) for adjusting the pressure of the pressure roller 24 is disposed on the cored bar 24a.

  The separation plate 26 is peeled off when the paper that has passed through the fixing nip N adheres to the fixing belt 21, and in the rotational direction of the fixing roller 23 on the surface of the fixing belt 21 downstream from the fixing nip N. It is pressed against the counter.

  Between the fixing nip portion N and the guide roller 27, a pressure auxiliary member 28 is disposed over the entire width direction (paper surface direction) of the fixing belt 21, and fixing is performed on the upstream side of the fixing nip portion N. The belt 21 is pressed against the pressure roller 24. The guide roller 27 adjusts the contact angle between the fixing belt 21 and the pressure auxiliary member 28 by changing the angle of the fixing belt 21 on the upstream side of the pressure auxiliary member 28.

  FIG. 3 is an enlarged view around the fixing nip portion N in FIG. The configuration of the auxiliary pressure member 28 will be described with reference to FIG. The pressure assisting member 28 includes a main pressure unit 29 and a pressure distribution transfer unit 30 extending from the main pressure unit 29 to the fixing nip N, and on the upstream side of the main pressure unit 29. Is formed with a curved surface 29 a for reducing friction with the fixing belt 21. Further, the front end portion 30 a of the pressure distribution transfer unit 30 enters between the fixing belt 21 and the fixing roller 23, and at least a part of the fixing roller 23 is connected to the fixing belt 21 and the pressurizing belt 30 via the pressure distribution transfer unit 30. It is in pressure contact with the pressure roller 24.

  The material of the pressure assisting member 28 is not particularly limited, but the main pressure unit 29 has a certain degree of rigidity in order to uniformly press the paper that has entered between the fixing belt 21 and the pressure roller 24. There is a need. Further, the pressure distribution delivery unit 30 needs to have flexibility that can be curved along the surface of the pressure roller 24 and a repulsive force for uniformly pressing the paper. Therefore, for example, the main pressurizing portion 29 is formed of a metal member such as aluminum, and a pressure distribution delivery portion 30 is formed by attaching a stainless steel (SUS) thin plate having a thickness of about 0.1 mm to the outside of the main pressurizing portion 29. It is preferable.

  According to the above-described configuration, the fixing belt 21 is pressed against the pressure roller 24 by the main pressure unit 29 and the pressure distribution transfer unit 30 on the upstream side of the fixing nip N. Therefore, in color printing with a large amount of applied toner. Sufficient nip time can be secured. Further, since the tip end portion 30a of the pressure distribution transfer portion 30 is nipped by the fixing roller 23 and the pressure roller 24, no gap is generated between the pressure distribution transfer portion 30 and the fixing roller 23, and the pressure is not uniform. This eliminates the possibility of generating parts. Further, since the main pressure unit 29 does not come into contact with the fixing roller 23, it is possible to prevent the main pressure unit 29 from being damaged due to wear of the fixing roller 23 or being caught in the fixing roller 23.

  In the configuration of FIG. 3, the tip end portion 30 a of the pressure distribution transfer portion 30 is sandwiched between the fixing nip portion N, but the pressure distribution transfer portion 30 so that the tip end portion 30 a is located on the downstream side of the fixing nip portion N. May be further extended along the outer peripheral surface of the fixing roller 23.

  FIG. 4 is an enlarged view around the fixing nip N in the fixing device according to the second embodiment of the present invention. In the present embodiment, a low friction member 31 (a member having a smaller frictional resistance than that of the pressure distribution transfer portion 30, indicated by a dotted line in the figure) at the sliding portion of the pressure distribution transfer portion 30 with the fixing belt 21 and the fixing roller 23. Are stacked. Since the configuration of the other parts is the same as that of the first embodiment, description thereof is omitted.

  According to this configuration, since the friction between the pressure distribution transfer section 30 and the fixing belt 21 and the fixing roller 23 is reduced, the fixing belt 21 rotates smoothly and the durability of the fixing belt 21 and the fixing roller 23 is improved. Further improve. As the low friction member 31, for example, a fluororesin-based sheet such as PFA or a fluororesin paint can be used.

  In addition, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the meaning of this invention. For example, in the above-described embodiment, the fixing belt 21 and the pressure roller 24 are driven to rotate at a predetermined speed by connecting a motor to the fixing roller 23 and rotationally driving. However, for example, the heat transfer roller 22 or the pressure roller 24 It is good also as a structure which connects with a motor and rotationally drives. In addition, the guide roller 27 is not an essential component, and the fixing belt 21 may be directly wound around the auxiliary pressure member 28 from the heat transfer roller 22.

  Further, the configuration of the fixing belt 21, the heat transfer roller 22, the fixing roller 23, and the pressure roller 24 shown in the above embodiment is a preferable example, and other configurations capable of achieving the object of the present invention may be adopted. it can. Moreover, it is good also as a structure which replaces with the light source 25, arrange | positions the heating excitation coil in the heat transfer roller 22, and heats the heat transfer roller 22 by sending a high frequency current to the heating excitation coil. Further, other heating means may be provided in place of the heat transfer roller 22.

  The fixing device of the present invention is not limited to the tandem type color printer shown in FIG. 1, but uses an electrophotographic process such as a digital multifunction machine, a color copying machine, an analog type monochrome copying machine, a monochrome printer or a facsimile. The present invention can be applied to various image forming apparatuses.

  The present invention relates to an endless fixing belt that can be rotated at a substantially equal speed to the recording medium conveyance speed, a heating means for heating the fixing belt, a fixing roller inscribed in the fixing belt, and a fixing belt on the fixing roller. A pressure roller that abuts at a predetermined pressure via the fixing roller, and fixes the unfixed toner image carried on the recording medium by inserting the recording medium through a fixing nip formed by the fixing roller and the pressure roller. In the fixing device, a main pressure unit disposed upstream of the fixing roller with respect to the rotation direction of the fixing belt and pressed against the pressure roller via the fixing belt, and extends from the main pressure unit to the fixing nip unit. A pressure assisting member having a pressure distribution delivery portion is provided.

  As a result, when a sufficient nip time is secured using the pressure assisting member, a non-uniform portion of pressure does not occur, and it is possible to prevent damage to the pressure assisting member due to wear of the fixing roller or entanglement with the fixing roller. Therefore, it is possible to provide a belt-fixing type fixing device that can be suitably used particularly for a color image forming apparatus in which the amount of applied toner increases. The pressure distribution transfer portion can be formed of a flexible metal plate such as a stainless steel thin plate.

  Further, by providing a low friction member such as a fluororesin-based sheet on the sliding portion of the pressure distribution transfer portion with the fixing belt and the fixing roller, the fixing belt rotates more smoothly, and the fixing belt and the fixing roller The fixing device is further improved in durability. Further, if a guide roller is disposed on the upstream side of the pressure assisting member, the contact angle between the fixing belt and the pressure assisting member can be adjusted to reduce friction.

1 is a schematic cross-sectional view of an image forming apparatus equipped with a fixing device of the present invention. FIG. 3 is a side sectional view of the fixing device according to the first embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view showing the vicinity of a fixing nip portion in the fixing device of the first embodiment. These are the expanded sectional views which show the fixing nip part vicinity in the fixing device of 2nd Embodiment of this invention.

Explanation of symbols

7 Fixing device 8 Conveying belt 21 Fixing belt 22 Heat transfer roller (heating means)
DESCRIPTION OF SYMBOLS 23 Fixing roller 24 Pressure roller 25 Light source 26 Separator plate 27 Guide roller 28 Pressure auxiliary member 29 Main pressure part 30 Pressure distribution delivery part 31 Low friction member 100 Image forming apparatus N Fixing nip part P Paper (recording medium)

Claims (5)

An endless fixing belt that can be rotated at substantially the same speed as the conveyance speed of the recording medium;
Heating means for heating the fixing belt;
A fixing roller inscribed in the fixing belt;
A pressure roller that contacts the fixing roller with a predetermined pressure via the fixing belt,
In a fixing device for fixing an unfixed toner image carried on a recording medium by inserting a recording medium through a fixing nip formed by the fixing belt and the pressure roller,
A main pressure portion disposed upstream of the fixing roller with respect to the rotation direction of the fixing belt and pressed against the pressure roller via the fixing belt, and extends from the main pressure portion to the fixing nip portion. A fixing device comprising a pressure assisting member having a pressure distribution transfer portion provided.   The fixing device according to claim 1, wherein the pressure distribution transfer unit is formed of a flexible metal plate.   3. The member according to claim 1, wherein a member having a smaller friction coefficient than that of the pressure distribution transfer portion is attached to a sliding portion between the pressure distribution transfer portion and the fixing belt and the fixing roller. Fixing device.   4. The fixing device according to claim 1, further comprising a guide roller inscribed in the fixing belt on an upstream side of the pressure assisting member with respect to a rotation direction of the fixing belt.   An image forming apparatus comprising the fixing device according to claim 1.

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