JP2017090621A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device that makes uniform, with a soaking roller, temperature distribution in the direction of a rotation shaft of a fixing rotor and of a pressure rotor, and reduces re-transfer of a mixture of a toner and paper powder from the soaking roller to the pressure rotor without causing an increase in size and manufacturing cost of the device, even when the pressure rotor and the soaking roller remain in contact for a long period.SOLUTION: A rectangular cross sectional and spiral groove 73 is formed in a surface of a soaking roller 7a. When the soaking roller 7a is brought into contact with a pressure roller 5, the groove 73 portion becomes a low-pressure portion at a pressure less than a predetermined pressure and the other portion becomes a high-pressure portion at a pressure equal to or higher than the predetermined pressure. At a contact part of the pressure roller 5 and soaking roller 7a, the high-pressure portion and low-pressure portion are formed alternately in the direction of a rotation shaft. The positions of the high-pressure portion and the low-pressure portion move in the axial direction in association with the rotation of the soaking roller 7a.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a fixing device, and more specifically, a transfer member having an unfixed toner image formed on one surface is passed through a nip portion formed by press-contacting a fixing rotator and a pressure rotator. The present invention relates to a fixing device that heats and presses an unfixed toner image to melt and fix it on a transfer member.

  In an electrophotographic image forming apparatus such as a copying machine, a printer, a facsimile machine, or a multifunction machine having these functions, an electrostatic latent image corresponding to an original is formed on a photosensitive drum, and the electrostatic latent image is formed on the electrostatic latent image. The toner image is made to adhere to the toner image, and the visualized toner image is transferred onto the member to be transferred. Thereafter, the toner image on the member to be transferred is fixed and discharged.

  As a device for fixing an unfixed toner image (hereinafter, also referred to as “toner image”) transferred onto a transfer member, a fixing rotator provided with heating means such as a halogen lamp and a pressure rotator are provided. A heat roller fixing type fixing device that heats and presses a transfer member on which a toner image is formed is held and conveyed at the nip portion formed by pressure contact, due to the simplicity of the device configuration. Widely used.

  In such a conventional fixing device, in a region through which the member to be transferred has passed, heat is taken away by the member to be transferred, and the temperature is lowered. For this reason, a temperature distribution is generated between a region through which the member to be transferred passes and a region through which the member to be transferred does not pass. Further, when a pressure roller having an elastic layer is used, if the temperature distribution is generated, a difference in outer diameter occurs due to thermal expansion, and the peripheral speed of the pressure roller is different in the axial direction. Therefore, for example, when a large size paper is fixed after a small size paper is continuously fixed, problems such as uneven fixing of images and hot offset may occur due to the temperature distribution generated as described above. is there. Further, when the sheet conveying speed of the fixing device is different in the axial direction, noise such as “bleeding” may occur in the image, or the sheet may be wrinkled.

  Therefore, a temperature-uniforming roller such as a heating roller or a heat pipe is brought into contact with the fixing rotator or the pressure rotator to eliminate the temperature distribution in the rotation axis direction of the fixing rotator or the pressure rotator. However, when the fixing process is performed for a long period of time, a mixture (dirt) such as toner and paper powder adheres to the fixing rotator and the pressure rotator. Since such a mixture is likely to be transferred to a lower temperature, it is transferred from the fixing rotator or the pressure rotator to the surface of the soaking roller. Then, the mixture transferred to the surface of the soaking roller may be transferred again to the fixing rotator or the pressure rotator and fixed to the surface, thereby deteriorating paper passing properties such as paper wrinkles.

  Thus, a technique has been proposed in which a cleaning member such as a brush roller or a web is brought into contact with the soaking roller to scrape off the mixture on the soaking roller surface (for example, Patent Documents 1 and 2). Patent Document 3 proposes a cleaning roller in which spiral grooves are formed on the peripheral surface as a cleaning roller for removing the mixture on the surface of the pressure rotating body.

JP 2011-22263 A JP 2014-48624 A JP 2004-191406 A

  However, in the proposed technique in which the mixture on the surface of the soaking roller is scraped off by the cleaning member, the toner and paper powder are mixed at the contact portion between the cleaning member and the soaking roller, so that the mixture is re-transferred to the pressure rotating body. It becomes easy to adhere to the surface.

  For this reason, in the proposed technique, the contact time between the pressurizing rotating body and the soaking roller is shortened, the amount of transfer of toner and paper powder to the soaking roller is reduced, and the toner on the soaking roller The amount of paper dust mixed by the cleaning member is reduced, and retransfer of the mixture to the pressure rotating body is reduced.

  However, in order to enable the pressurizing and separating roller and the soaking roller to be pressed and separated, a pressing and separating mechanism is required, resulting in an increase in the size of the apparatus and an increase in manufacturing cost. In addition, when it is necessary to press the soaking roller against the pressure rotator, that is, when there are many cases where a small-size sheet is continuously fixed, there is little time for separating the press rotator and the soaking roller. The amount of toner and paper powder transferred to the soaking roller cannot be reduced.

  The present invention has been made in view of such conventional problems, and the object thereof is not to increase the size of the apparatus or increase the manufacturing cost, and the pressure rotating body and the heat equalizing roller are in contact for a long time. In such a case, it is an object of the present invention to provide a fixing device that can reduce the retransfer of a mixture of toner, paper powder, and the like from a soaking roller to a pressure rotator.

  According to the present invention, the fixing rotator, the heating means for heating the fixing rotator, the pressure rotator that presses against the fixing rotator to form a nip portion, and the surface of the pressure rotator are contacted. And a temperature-uniforming roller that rotates around the axis in the longitudinal direction, and the temperature-uniforming roller is a high pressure whose contact pressure with respect to the pressure rotator is equal to or higher than a predetermined pressure. A fixing device is provided having a portion and a low pressure portion less than a predetermined pressure.

  The said structure WHEREIN: It is preferable that the surface where the said soaking roller contacts the said pressurization rotary body is a metal.

  In the above configuration, the heat equalizing roller may have a spiral groove on the surface, and the high pressure portion and the low pressure portion may be alternately positioned in the rotation axis direction. Here, the spiral groove provided on the surface of the soaking roller may be unidirectional.

  In the above configuration, the heat equalizing roller may have a plurality of circumferential grooves on the surface thereof at predetermined intervals in the rotation axis direction, and the high pressure portion and the low pressure portion may be alternately positioned in the rotation axis direction. At this time, it is preferable to further include a moving means for moving the soaking roller in the direction of the rotation axis.

  In the above configuration, the heat equalizing roller has a plurality of grooves parallel to the rotation axis at predetermined intervals in the rotation direction on the surface, and the high pressure portion and the low pressure portion are rotated with the rotation of the heat equalizing roller. It is good also as a structure which contacts a pressurization rotary body.

  In the above configuration, it is preferable that the low-pressure portion is not in contact with the pressure roller.

  In the above configuration, it is preferable that the area ratio of the high-pressure portion in the soaking roller is 65% or more and less than 100%.

  In the above configuration, it is preferable that the area ratio of the high-pressure portion in the soaking roller is 80% or more and less than 100%.

  In the above configuration, the width of the low-pressure portion is preferably 0.1 mm or greater and 5.0 mm or less.

  In the above configuration, the width of the low-pressure portion is preferably 0.1 mm or greater and 1.0 mm or less.

  Moreover, the said structure WHEREIN: It is preferable that the contact pressure of the said high voltage | pressure part is the range of 0.01 Mpa or more and 0.3 Mpa or less.

  Moreover, the said structure WHEREIN: It is preferable that the contact pressure of the said high voltage | pressure part is the range of 0.06 MPa or more and 0.17 MPa or less.

  Moreover, in the said structure, it is preferable that the edge part cross section of the said high voltage | pressure part is chamfered.

  In the above configuration, it is preferable that the pressure rotator is a pressure roller, and an outer diameter ratio of the pressure roller and the heat equalizing roller is a non-integer multiple.

  Moreover, in the said structure, it is preferable to set it as the structure further provided with the brush roller which contacts the said soaking roller and cleans the surface of the said soaking roller.

  Moreover, the said structure WHEREIN: It is good also as a structure which has the 1st spiral groove and the 2nd spiral groove of the reverse direction to a 1st spiral groove on the surface of the said soaking roller.

  In the above configuration, the first spiral groove is formed from one end in the rotation axis direction to the center in the rotation axis direction, and the second spiral groove is formed from the other end in the rotation axis direction to the center in the rotation axis direction. It is good also as composition which has.

  Moreover, the said structure WHEREIN: The 1st spiral groove and the 2nd spiral groove are good also as a structure currently formed in the rotating shaft direction whole.

  According to the invention, there is provided an image forming apparatus comprising the fixing device according to any one of the above.

  The fixing device according to the present invention does not increase the size of the device or increase the manufacturing cost, and even when the pressure rotator and the soaking roller are in contact with each other for a long time, the soaking roller applies heat. It is possible to reduce retransfer of a mixture of toner and paper powder to the pressure rotating body.

1 is a schematic diagram illustrating an example of an image forming apparatus (printer) equipped with a fixing device of the present invention. 1 is a schematic configuration diagram illustrating an example of a fixing device of the present invention. It is a schematic diagram which shows the shape and arrangement | positioning of a pressure roller, a soaking roller, and a brush roller. It is a graph which shows the relationship between the soaking | uniform-heating function and nip time when the area ratio of the high voltage | pressure part of a soaking roller is changed in steps from 40% to 100%. It is a graph which shows the trial calculation result of the soaking | uniform-heating function with respect to the area ratio of the high voltage | pressure part of a soaking roller by the trial calculation result shown in FIG. It is an expanded view of a soaking roller. It is a graph which shows the influence by the groove width of the temperature difference of the pressure roller surface after soaking and relaxation. It is sectional drawing which chamfered the edge part (end part of a high voltage | pressure part) of a groove | channel. It is a general view of the soaking roller which chamfered the edge part of the groove | channel. It is a figure explaining the rotation cycle of a soaking roller and a pressure roller. It is a figure explaining the sweeping up of the dirt on the surface of a soaking roller by a brush roller. It is a figure which shows other embodiment of the soaking roller which can be used by this invention. It is a figure which shows other embodiment of the soaking roller which can be used by this invention. It is a figure which shows other embodiment of the soaking roller which can be used by this invention. It is a figure which shows other embodiment of the soaking roller which can be used by this invention.

  Hereinafter, the fixing device according to the present invention will be described in more detail with reference to the drawings. However, the present invention is not limited to these embodiments.

  FIG. 1 is a schematic view showing an example of an image forming apparatus equipped with a fixing device according to the present invention. The image forming apparatus in FIG. 1 is a tandem digital color printer (hereinafter, simply referred to as “printer”). Of course, in addition to a printer, the present invention can also be applied to a copying machine having a scanner, a facsimile, or a multi-function machine having these functions combined. In the following, when it is necessary to clarify whether the device or member to be described is yellow (Y), magenta (M), cyan (C), or black (B), The description will be made by adding the characters “(Y)”, “(M)”, “(C)”, and “(B)” to the reference numerals, and otherwise omitting those characters.

  The printer 1 includes an intermediate transfer belt 11 at substantially the center of the inside thereof. The intermediate transfer belt 11 is stretched around the outer periphery of the roller 12, the tension roller 13, and the guide rollers 14 and 15, and is driven to rotate counterclockwise. The tension roller 13 is slidably attached to the outside and is urged by the pressing spring S from the inside to the outside of the intermediate transfer belt 11. Thus, the intermediate transfer belt 11 is always in a tensioned state.

  Below the lower horizontal portion of the intermediate transfer belt 11, four image forming portions 2Y, 2M, 2C, and 2B respectively corresponding to the colors of yellow (Y), magenta (M), cyan (C), and black (B). Are arranged in this order along the intermediate transfer belt 11. Each of the image forming units 2Y, 2M, 2C, and 2B includes photosensitive drums 21Y, 21M, 21C, and 21B, respectively. Around each of the photosensitive drums 21Y, 21M, 21C, and 21B, the chargers 22Y, 22M, 22C, and 22B, the print head units 23Y, 23M, 23C, and 23B, and the developing unit 24Y are sequentially arranged along the rotation direction. 24M, 24C, and 24B and cleaners 25Y, 25M, 25C, and 25B are disposed, respectively. The print head units 23Y, 23M, 23C, and 23B are configured by a large number of LEDs arranged in the main scanning direction parallel to the axial direction of the photosensitive drum.

  Primary transfer rollers 30Y, 30M, 30C, and 30B are provided at positions facing the respective photosensitive drums 21Y, 21M, 21C, and 21B with the intermediate transfer belt 11 interposed therebetween. A secondary transfer roller 16 is pressed against the portion of the intermediate transfer belt 11 supported by the roller 12. A nip portion between the secondary transfer roller 16 and the intermediate transfer belt 11 becomes a secondary transfer region 17. The toner image formed on the intermediate transfer belt 11 in the secondary transfer region 17 is transferred to the conveyed paper (transfer target member) P.

  A paper feed cassette 91 is detachably disposed at the bottom of the printer 1. The sheets P stacked and accommodated in the sheet feeding cassette 91 are pulled out one by one from the uppermost sheet by the rotation of the sheet feeding roller 92 and are sent out to the transport path 93. The conveyance path 93 extends from the paper feed cassette 91 to the paper discharge tray 98 through the nip portion of the timing roller pair 94, the secondary transfer region 17, and the fixing device T. The paper P sent out from the paper feed cassette 91 is conveyed to the timing roller pair 94 and is sent out to the secondary transfer area 17 at a predetermined timing.

  The fixing device T includes a fixing roller (fixing rotator) 4, a pressure roller (pressure rotator) 5 that is in pressure contact with the fixing roller 4, and a magnetic flux generating unit (heating) that is disposed apart from the outer periphery of the fixing roller 4. Means) 6. As the paper P passes through the nip portion between the fixing roller 4 and the pressure roller 5, the toner image secondarily transferred onto the paper P is heated and melted and fixed on the paper P. Details of the fixing device T will be described later.

  A schematic operation of the printer 1 having such a configuration will be described. First, in the full color mode for outputting a color image, when an image signal is input from an external device (for example, a personal computer) to an image signal processing unit (not shown) of the printer 1, the image signal processing unit converts the image signal to yellow, A digital image signal color-converted to cyan, magenta, and black is created, and this signal is transmitted to the LED drive circuit for the print head. This drive circuit performs exposure by causing the print head units 23Y, 23M, 23C, and 23B of the image forming units 2Y, 2M, 2C, and 2B to emit light based on the input digital signals. This exposure is performed with a time difference in the order of the print head units 23Y, 23M, 23C, and 23B. Thereby, electrostatic latent images for the respective colors are formed on the surfaces of the photosensitive drums 21Y, 21M, 21C, and 21B.

  To the electrostatic latent images formed on the photosensitive drums 21Y, 21M, 21C, and 21B, toners are attached by the developing devices 24Y, 24M, 24C, and 24B to be visualized (developed), and toners of the respective colors. Become a statue. Then, the toner images of the respective colors are sequentially primary-transferred and superimposed on the intermediate transfer belt 11 that rotates counterclockwise in the figure by the action of the primary transfer rollers 30Y, 30M, 30C, and 30B.

  The toner image formed on the intermediate transfer belt 11 in this way reaches the secondary transfer region 17 as the intermediate transfer belt 11 moves. On the other hand, the paper P sent out from the paper feed cassette 91 to the transport path 93 is transported to the secondary transfer region 17 by the timing roller pair 94 at the timing when the toner image reaches the secondary transfer region 17. A voltage having a polarity opposite to the charging polarity of the toner is applied to the secondary transfer roller 16. As a result, in the secondary transfer region 17, the superimposed color toner images are secondarily transferred collectively from the intermediate transfer belt 11 to the paper P. The toner remaining on the intermediate transfer belt 11 after the secondary transfer is collected by a belt cleaner (not shown).

  The sheet P onto which the toner image has been secondarily transferred is sent to the fixing device T through the conveyance path 93, where the toner image is fixed on the sheet P by passing through the nip portion. Then, the paper P is discharged to the paper discharge tray 98.

  FIG. 2 shows a schematic diagram of the fixing device T used in the printer 1 of FIG. In the fixing device T, the fixing roller 4 and the pressure roller 5 are pressed against each other, and a magnetic flux generator 6 is provided on the outer periphery of the fixing roller 4 at a position facing the fixing roller 4 at a distance. A soaking roller 7a is in pressure contact with the pressure roller 5, and a brush roller 8 is provided near the surface of the soaking roller 7a. Hereinafter, each member will be described in order.

  The fixing roller 4 has a five-layer structure including a hollow cylindrical cored bar 41 and a heat insulating layer 42, an electromagnetic induction heat generating layer 43, an elastic layer 44, and a release layer 45 in order from the inner peripheral side on the outer periphery of the cored bar 41. It is. The hardness of the fixing roller 4 is preferably in the range of 30 to 90 degrees in terms of Asker C hardness, for example.

  As a material of the cored bar 41, a heat resistant resin such as polyphenylene sulfide (PPS) can be used in addition to a metal material such as aluminum or iron. When electromagnetic induction heating means is used as the heating means as in the present embodiment, it is preferable to use a nonmagnetic material such as aluminum in order to prevent the cored bar 41 from being heated by electromagnetic induction.

  A silicone sponge material is preferably used as the material of the heat insulating layer 42. In the case of using a silicone sponge material, the thickness is preferably in the range of 2 mm to 10 mm, more preferably in the range of 3 mm to 7 mm. Further, the hardness of the heat insulating layer 42 is desirably in the range of 20 degrees to 60 degrees, more desirably in the range of 30 degrees to 50 degrees with an Asker C-type rubber hardness meter.

  The electromagnetic induction heat generating layer 43 is a layer that generates Joule heat by excitation by the magnetic flux generator 6. The material is preferably a magnetic metal material such as nickel, magnetic stainless steel, or iron. Moreover, you may use what mixed the magnetic metal particle in resin. The thickness of the electromagnetic induction exothermic layer 43 is preferably, for example, in the range of 10 μm to 100 μm, and more preferably in the range of 20 to 50 μm.

  The elastic layer 44 is formed from a member having heat resistance and elasticity. As such a member, for example, a silicone sponge material is suitable. When a silicone sponge material is used as the elastic layer 44, the length of the nip portion between the fixing roller 4 and the pressure roller 5 can be increased. For example, when a silicone sponge material is used for the elastic layer 44, the thickness is preferably in the range of 2 mm to 10 mm, and more preferably in the range of 3 mm to 7 mm. The hardness of the elastic layer 42 is preferably in the range of 20 degrees to 60 degrees, more preferably in the range of 20 degrees to 50 degrees with an Asker rubber hardness meter.

  The release layer 45 is a layer for enhancing the surface release property, and a material that can withstand use at the fixing temperature is used. For example, tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), polytetrafluoroethylene (PTFE), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), tetrafluoroethylene / ethylene copolymer (ETFE) And the like. The thickness of the release layer 45 is preferably in the range of 5 μm to 100 μm, for example, and more preferably in the range of 10 μm to 50 μm. In addition, you may add a electrically conductive material, an abrasion-resistant material, a good heat conductive material, etc. in the mold release layer 45 as a filler as needed. Further, in order to improve the interlayer adhesion, an adhesion treatment with a primer or the like may be performed.

  The pressure roller 5 is formed by laminating an elastic layer 52 and a release layer 53 in this order on a hollow cylindrical cored bar 51. As the metal core 51, a heat resistant resin such as PPS can be used in addition to a metal material such as aluminum or iron. As the elastic layer 52, the same material as that of the elastic layer 44 of the fixing roller 4 can be preferably used here. As the release layer 53, the same material as that of the release layer 45 of the fixing roller 4 can be preferably used here.

  The pressure roller 5 is biased toward the fixing roller 4 by a biasing member such as a spring, and forms a nip portion with the fixing roller 4. For example, the pressure roller 5 may be pressed against the fixing roller 4 with a load of 300 N to 500 N so that the length of the fixing nip portion is within a range of 5 mm to 10 mm. Note that the load may be changed according to the type of the paper P or the like. Further, here, the pressure roller 5 is rotationally driven at a predetermined speed by a drive mechanism such as a motor. On the other hand, the fixing roller 4 is rotated by the rotation of the pressure roller 5 by the pressure frictional force with the pressure roller 5. Note that these rotational driving may be performed by using the fixing roller 4 as a main drive and the pressure roller 5 as a driven rotation.

  In FIG. 2, the magnetic flux generator 6 is configured by a coil part 61 and a core part 62 covered with a coil hobbin 63. The coil unit 61 is wound around a coil hobbin 63 disposed so as to cover a part of the outer periphery of the fixing roller 4, and a litz wire bundled with thin wires is wound in the axial direction (in the direction perpendicular to the paper in FIG. 2). It is an extension. The coil hobbin 63 is made of a resin material having high heat resistance and holds the coil part 61. The core portion 62 is made of a ferromagnetic material such as ferrite (having a relative permeability of about 1000 to 3000), and forms an efficient magnetic flux toward the heat generating layer, and extends in the axial direction. It is installed so as to face the provided coil part 61.

  A high-frequency inverter (not shown) is connected to the magnetic flux generation unit 6, and an AC current of 10 kHz to 100 kHz is applied to the coil unit 61 from the high-frequency inverter, whereby the electromagnetic induction heat generating layer 43 of the fixing roller 4 generates heat. The surface temperature of the fixing roller 4 is maintained at a predetermined temperature.

It is desirable that at least the surface of the soaking roller 7a in contact with the pressure roller 5 is metal. It should be noted that the surface of the soaking roller 7a is metal in addition to the case of the metal itself, and also includes the case where a wear-resistant and stain-resistant coating layer or a resin tube is provided on the metal. The soaking roller 7 a shown in FIG. 2 includes a hollow cylindrical base 71 and a release layer 72 formed on the surface of the base 71. The base | substrate 71 consists of metal materials, such as aluminum, copper, iron, and stainless steel, and thickness is about 1 mm-5 mm. For the release layer 72, a material that can withstand use at a fixing temperature is used. For example, when the release layer 72 is a coating layer, fluororesin such as PFA, PTFE, FEP, ETFE, and a mixture thereof, Carbon, MoS ₂ or the like is preferably used. When the release layer 72 is a resin tube, a PFA tube or a PI (polyimide) tube is preferably used. Although there is no limitation in particular in the thickness of the release layer 72, Usually, the range of 20 micrometers-200 micrometers is preferable.

The heat permeation rate calculated from the following equation can be used as an index of the ability to take heat away from the pressure roller 5, and the heat soaking rate of the soaking roller 7a is 200 J / (m ² · K · s ^1/2 ) or more. It is desirable that
Thermal permeability = (thermal conductivity x specific heat x density) ^1/2
(Density and specific heat are calculated by arithmetic mean, and thermal conductivity is calculated by harmonic average)

  In addition, when the soaking roller 7a is a multilayer having a coating layer or a tube, or when an air layer is included in a sponge or brush-like configuration, the determination is made with an average value.

For example, when the soaking roller 7a is made of only aluminum, the density is 2688 kg / m ³ , the specific heat is 0.905 kJ / (kg · K), and the thermal conductivity is 237 W / (m · K), so the heat permeability is 759 J / (M ² · K · s ^1/2 ).

Also, when the temperature equalizing roller 7a is provided with a PTFE coat layer (film thickness 50 μm) on the surface of aluminum (thickness 3 mm) as a base, the density and specific heat are almost the same, and the thermal conductivity is 233 W / ( m · K) (PTFE thermal conductivity 0.24), the thermal permeability is 759 J / (m ² · K · s ^1/2 ), and the heat equalizing roller 7a is made of only aluminum. There is almost no difference in the soaking function.

On the other hand, when the soaking roller 7a has a brush-like shape made of aluminum, the density is 538 kg / m ³ , the specific heat is 0.987 kJ / (kg · K), and the heat conductivity is 0 if the air ratio to the volume is 80%, for example. 0.03 W / (m · K), and the heat permeability is 4.2 J / (m ² · K · s ^1/2 ), so it is not suitable as the soaking roller 7a.

  The brush roller 8 as a cleaning means is rotatably provided so as to contact the surface of the soaking roller 7a. The brush roller 8 is formed by winding a strip-shaped base fabric in which a large number of heat-resistant resin fibers 82 are planted around a metal core 81 in a spiral shape. As a material of the heat resistant resin fiber 82, for example, polyphenylene sulfide having a heat resistant temperature of 160 to 190 ° C. can be suitably used.

  The brush roller 8 is driven to rotate so that the heat drive resin fiber 82 is in contact with the surface of the soaking roller 7a by receiving rotational driving from a driving source of the pressure roller 5 via a gear (not shown). The rotation direction of the brush roller 8 may be the same direction as the heat equalizing roller 7a or the reverse direction at the contact portion. In that case, it is preferable that the peripheral speed of the front-end | tip part of the heat-resistant resin fiber 82 is the same as or faster than the peripheral speed of the surface of the soaking roller 7a. The peripheral speed of the surface of the soaking roller 7a and the peripheral speed of the tip of the brush roller 8 are usually preferably in the range of 150 to 270 mm / sec.

  The brush roller 8 and the soaking roller 7a can be contacted / separated, and the contact / separation may be performed by movement of the soaking roller 7a or by movement of the brush roller 8. As a means for moving the hammer roller 7 and the brush roller 8, a conventionally known moving means such as a solenoid can be used.

  FIG. 3 is a schematic diagram showing the shape and arrangement of the pressure roller 5, the soaking roller 7 a, and the brush roller 8. A spiral groove 73 having a rectangular cross section is formed on the surface of the soaking roller 7a. When the soaking roller 7a comes into contact with the pressure roller 5, the portion of the groove 73 becomes a low pressure portion below a predetermined pressure, and the other portion becomes a high pressure portion above the predetermined pressure. At the contact portion between the pressure roller 5 and the soaking roller 7a (hereinafter, soaking nip portion), a high pressure portion and a low pressure portion are alternately formed in the rotation axis direction. And the position of a high voltage | pressure part and a low voltage | pressure part moves to an axial direction with rotation of the soaking roller 7a. As a result, the effect of reducing dirt uniformly is exerted on the entire pressure roller 5. Here, the cross-sectional shape of the groove 73 is not particularly limited, and may be V-shaped, U-shaped, inverted trapezoidal shape, or the like.

  Note that the movement of dirt from the pressure roller 5 to the soaking roller 7a is caused by the adhesion force of dirt to the surface of the soaking roller 7a, and therefore may occur even if the contact pressure is very small. Therefore, it is desirable that the low pressure portion (groove portion) of the soaking roller 7a is not in contact with the surface of the pressurizing roller 5 from the viewpoint of suppressing contamination from the pressurizing roller 5 to the soaking roller 7a.

  Here, as the area ratio of the high pressure portion (contact portion) of the soaking roller 7a decreases, the effect of improving the dirt on the pressure roller 5 is improved. On the other hand, since the area of the high pressure portion (contact portion) is reduced, the function of soaking the pressure roller 5 is lowered. However, the decrease in the soaking function can be suppressed by increasing the circumferential width of the soaking nip. In order to increase the circumferential width of the soaking nip, for example, the outer diameters of the pressing roller 5 and the soaking roller 7a are increased, the hardness of the pressing roller 5 is lowered, and the pressing roller of the soaking roller 7a. There is a measure to increase the pressure contact force to 5.

  However, measures to increase the outer diameters of the pressure roller 5 and the soaking roller 7a may increase costs and increase the size of the apparatus. Further, there is a risk that durability may be deteriorated by a measure for reducing the hardness of the pressure roller 5 and a measure for increasing the pressure contact force of the soaking roller 7a to the pressure roller 5. For this reason, the circumferential width of the soaking nip cannot be increased indefinitely. There is a practical upper limit for the circumferential width of the soaking nip, and this determines the lower limit of the area ratio of the high pressure portion of the soaking roller 7a.

  In FIG. 4, the vertical axis is the soaking function, and the horizontal axis is the nip time that is an index of the circumferential width of the soaking nip, and the area ratio of the high pressure portion of the soaking roller 7a is stepped from 40% to 100%. The relationship between the soaking function and the nip time when changed to is shown. The data in FIG. 4 is a trial calculation result by numerical calculation. The trial calculation conditions are as follows. The higher the soaking function by the soaking roller 7a, the lower the surface temperature of the pressure roller 5 after passing through the soaking nip portion. Therefore, the conventional pressure roller having no groove on the soaking roller 7a surface (high pressure portion 100%) ), The soaking function when the conventional nip portion time is 100% is taken as 100%, and the soaking function when there is no soaking roller 7a and only a pressure roller (temperature change (only against air)) is used. Estimated as 0%.

(Numerical calculation conditions: heat conduction calculation by two-dimensional difference method)
Initial pressure roller temperature 160 ° C., pressure roller material: silicon rubber initial heat equalizing roller temperature 140 ° C., heat equalizing roller material: aluminum + 50 μPFA coating Conventional heat equalizing nip time 8 ms.
The high pressure part is in contact with the pressure roller and the soaking roller. The low pressure part is set to contact the pressure roller and air. The air temperature is 140 ° C only near the pressure roller. Otherwise, 23 ° C

  As can be seen from FIG. 4, the soaking function of each soaking roller becomes higher as the nip time becomes longer, but the soaking roller with a smaller area ratio of the high-pressure portion has a slower rise in soaking function and the desired soaking function. In order to obtain the thermal function, it is necessary to lengthen the nip time. Moreover, since the heat transfer from the pressure roller 5 to the soaking roller is due to the temperature difference between the two, the rate of increase in the soaking function decreases as the nip time increases. Therefore, the upper limit of the soaking function is 150% of the conventional one. From the viewpoint of obtaining a desired effect without causing an increase in cost or an increase in the size of the apparatus, it is desirable that the nip time is 250% or less compared with the conventional one and the heat equalizing function is 125% or less compared with the conventional.

  FIG. 5 shows a trial calculation result of the soaking function with respect to the area ratio of the high-pressure portion of the soaking roller and the effect of reducing the dirt on the pressure roller based on the trial calculation result shown in FIG. Note that the effect of reducing the dirt on the pressure roller was the reciprocal of the area ratio of the high-pressure portion of the soaking roller. For example, if the area ratio of the high pressure portion of the soaking roller is 80%, the amount of dirt transferred from the pressure roller 5 to the soaking roller is 80% of the conventional ratio. 80 = 125%.

  In FIG. 5, when both the soaking function and the dirt reducing effect are compared, the soaking function is lowered as the area ratio of the high pressure portion of the soaking roller is reduced if the soaking nip time is the same. On the other hand, the soaking function improves as the nip time increases. Therefore, the decrease in the soaking function due to the decrease in the area ratio of the high pressure portion of the soaking roller can be compensated by the increase in the nip time, and the soaking function equivalent to the conventional example can be maintained. A preferable range of the area ratio of the high pressure portion of the soaking roller is 65% or more and less than 100%, and a more preferable range is 80% or more and less than 100%. On the other hand, as described above, the effect of reducing dirt is the reciprocal of the area ratio of the high-pressure portion of the soaking roller. Therefore, it is desirable that the ratio of the high-pressure portion of the soaking roller be a smaller area ratio within the above preferred range.

  Next, the width | variety of the groove | channel 73 as a low voltage | pressure part formed in the soaking roller 7a is demonstrated. FIG. 6 shows a development view of the soaking roller 7a. In the heat equalizing roller 7a shown in FIG. 6, since the high pressure portion and the low pressure portion are alternately arranged in the rotation axis direction, the width of the groove 73 refers to the length in the rotation axis direction, as shown in FIG. In the case of the groove 75 parallel to the rotation axis, the width of the groove 75 is the length in the rotation direction.

  If the width of the groove 73 is too wide, the difference in the compression state between the high pressure portion and the low pressure portion in the soaking nip portion becomes too large, and the deformation of the soaking roller 7a on the surface of the pressure roller 5 becomes large and the durability deteriorates. . Moreover, since the pressure of the whole soaking nip part changes according to the rotation, the soaking roller 7a may be non-uniformly rotated. For this reason, the upper limit of the width of the groove 73 is preferably set within a range that is generally smaller than the soaking nip width, and the upper limit is preferably, for example, 5.0 mm or less.

  Further, heat is transferred from the pressure roller 5 to the heat equalizing roller 7a in the high pressure portion of the heat equalizing roller 7a, whereas heat is not transferred so much from the pressure roller 5 to the heat equalizing roller 7a in the low pressure portion. A temperature difference occurs on the surface of the pressure roller 5 after passing. This temperature difference is alleviated and reduced by the ambient air and heat conduction from the inside of the pressure roller while the pressure roller 5 rotates from the soaking nip portion to the sheet passing portion (hereinafter, fixing nip portion). . As the groove 73 has a narrower width, the heat capacity of the portion with the temperature difference becomes smaller, so that the temperature difference is easily relaxed. On the other hand, when the width of the groove 73 is large and the temperature difference on the surface of the pressure roller is large, a temperature difference occurs in the paper and the toner image with which the pressure roller 5 contacts during the image fixing process in the fixing nip portion. Image problems such as uneven fixing strength and uneven gloss will occur. Therefore, the upper limit value of the width of the groove 73 is more preferably a value that does not cause an image problem.

  FIG. 7 shows changes in the surface temperature difference of the pressure roller before and after relaxation with respect to the groove width, where the vertical axis is the surface temperature difference of the pressure roller 5 and the horizontal axis is the groove width. “After soaking” means immediately after passing through the soaking nip, and “after relaxation” means after the corresponding part has moved from the soaking nip to the fixing nip. The data in FIG. 7 is a trial calculation result by numerical calculation. The trial calculation conditions are as follows. The numerical calculation condition is a heat conduction calculation by a two-dimensional difference method.

(Calculation conditions)
Temperature difference between pressure roller and soaking roller: 20 ° C
Initial pressure roller temperature: 160 ° C., pressure roller material: silicon rubber, initial soaking roller temperature: 140 ° C., soaking roller material: aluminum + 50 μPFA-coated soaking nip time: 8 ms.
In the soaking nip, the high pressure part of the soaking roller contacts the pressure roller. The low pressure part is not in contact with the pressure roller, and the pressure roller is in contact with air. The air temperature is 140 ° C only near the pressure roller. Otherwise, 23 ° C
The entire pressure roller is in contact with air between the soaking nip and the fixing nip. The temperature is 140 ° C only in the vicinity, 23 ° C otherwise.
Relaxation time (from soaking nip to fixing nip): 250 ms

  As shown in FIG. 7, the pressure roller surface temperature difference after soaking does not change greatly depending on the groove width formed on the surface of the soaking roller, but the pressure roller surface temperature difference after relaxation has a narrow groove width. It gets smaller. When the pressure roller surface temperature difference after relaxation is 10 ° C. or less, the temperature difference on the paper surface (= toner surface) is within 2 ° C. when using a paper with a fixing nip width of 10 ms and a thickness of 100 μm. Hardly occurs. Then, when the temperature difference between the initial pressure roller and the soaking roller is 20 ° C. at the maximum, in order to make the pressure roller surface temperature difference after relaxation 10 ° C. or less, the groove width is 1 mm or less. Is desirable.

  On the other hand, if the groove width is narrow, it may be difficult to obtain the effect of cleaning the soaking roller 7a by the brush roller 8 shown in an embodiment described later. Therefore, the groove width needs to be a width that allows the brush fibers of the brush roller 8 to enter, and is preferably 0.1 mm or more.

  When the soaking roller 7a is a metal roller and the pressure roller 5 is an elastic body such as sponge or rubber, the pressure contact force of the soaking roller 7a with respect to the pressing roller 5 is to some extent to ensure the soaking nip width. It needs to be set higher. Further, it is desirable that there is no speed difference between the soaking roller 7 a and the pressure roller 5, and it is desirable that the soaking roller 7 a is driven to rotate by the rotation of the pressure roller 5. In that case, the surface of the soaking roller may have a low friction coefficient depending on the coating film, and if the pressure contact force is low, a problem that the soaking roller 7a does not rotate properly occurs. Therefore, the pressure contact force of the high pressure portion of the soaking roller 7a is usually preferably in the range of 0.01 MPa to 0.3 MPa, more preferably in the range of 0.06 MPa to 0.17 MPa.

  Since the groove 73 formed on the surface of the soaking roller 7a is pressed against the pressure roller 5 at the soaking nip portion, when the edge portion (the end portion of the high pressure portion) is vertical, the pressure is concentrated there and applied. There is a risk of damaging the surface of the pressure roller 5. Therefore, as shown in FIG. 8, it is desirable that the edge of the groove 73 be chamfered on the C surface (FIG. 8A), the R surface (FIGS. 8B and 8C), or the like. The size of the chamfer is preferably larger than the amount of biting between the soaking roller 7a and the pressure roller 5 in the soaking nip portion. For example, when the soaking roller 7a has a diameter of 21 mm and a soaking nip width of 2 mm, the chamfering amount of the edge of the groove 73 is desirably about 50 μm.

  FIG. 9 shows a soaking roller 7a in which the edge portion (end portion of the high pressure portion) of the spiral groove 73 having a V-shaped cross section is chamfered on the R surface, and the bottom surface of the groove 73 is also chamfered on the R surface. In the heat equalizing roller 7a of this figure, as a result of all the corners of the groove 73 being R surfaces, the surface shape of the vertical cross section passing through the rotation axis of the heat equalizing roller 7a becomes a corrugated uneven shape, and damage to the surface of the pressure roller 5 Is significantly reduced.

  FIG. 10 is a development view of the soaking roller 7a. As shown in this figure, when the groove 73 formed on the surface of the soaking roller 7a is spiral, the high pressure portion and the low pressure portion of the soaking roller 7a are alternately in contact with the surface of the pressure roller 5 with a time lag. However, when the outer diameter of the soaking roller 7a and the pressure roller 5 is an integral multiple (FIG. 10 (a)), the rotation period of the two regularly coincides, so the high pressure portion and the low pressure of the soaking roller 7a. The portion repeatedly hits the same location on the surface of the pressure roller 5, and the dirt on the pressure roller 5 is concentrated on a specific location on the soaking roller 7a. In order to prevent such a problem, it is desirable that the outer diameter ratio between the soaking roller 7a and the pressure roller 5 is a non-integer multiple (FIG. 10B).

  When the brush roller 8 that cleans and collects dirt on the surface of the soaking roller 7a is provided in contact with the soaking roller 7a as in the embodiment of FIGS. ), The dirt on the surface of the soaking roller 7 a is swept up in the groove 73 by the brush 82 of the brush roller 8. Further, the dirt taken into the brush 82 is also discharged into the groove 73 when the brush 82 is struck against the side wall of the groove 73. And as shown in FIG.11 (c), the dirt collected in the groove | channel 73 is discharged | emitted below by gravity, when the groove | channel 73 turns downward with rotation of the soaking roller 7a. Further, the dirt remaining in the groove 73 accumulates in the groove 73, but moves in the direction of the rotation axis due to the inclination of the inner surface of the spiral groove 73 along the rotation axis direction with the rotation of the soaking roller 7a. Thus, the heat is discharged from one end surface of the heat equalizing roller 7a in the rotation axis direction. As a result, the dirt on the soaking roller 7a is prevented from moving to the pressure roller 5.

  FIG. 12 shows another embodiment of the soaking roller that can be used in the present invention. The soaking roller 7b shown in this figure has a plurality of circumferential grooves 74 at predetermined intervals in the rotation axis direction. When the soaking roller 7b comes into contact with the pressure roller 5, the circumferential groove 74 becomes a low pressure portion less than a predetermined pressure, and the other portions become high pressure portions higher than the predetermined pressure. However, in the soaking roller 7b having such a shape, the contact area of the high pressure portion and the low pressure portion with the pressure roller 5 is fixed, so that the soaking roller 7b is reciprocated in the direction of the rotation axis to apply pressure. It is desirable that the high pressure portion and the low pressure portion of the soaking roller 7 are alternately contacted at any position of the roller 5. As a result, the effect of reducing dirt uniformly is exerted on the entire pressure roller 5. For the movement of the soaking roller 7b in the direction of the rotation axis, a conventionally known moving means such as a solenoid can be used.

  FIG. 13 shows another embodiment of the soaking roller that can be used in the present invention. The soaking roller 7c shown in this figure has a plurality of grooves 75 parallel to the rotation axis at equal intervals in the rotation direction. When the soaking roller 7c comes into contact with the pressure roller 5, the portion of the groove 75 becomes a low pressure portion below a predetermined pressure, and the other portion becomes a high pressure portion above the predetermined pressure. By the rotation of the soaking roller 7c, the high pressure portion and the low pressure portion of the soaking roller 7c are alternately brought into contact with the pressure roller 5, and the entire pressure roller 5 is uniformly reduced. In order to prevent the high pressure portion and the low pressure portion of the soaking roller 7c from repeatedly hitting the same part of the surface of the pressure roller 5, the outer diameter ratio between the soaking roller 7c and the pressure roller 5 is a non-integer multiple. Is desirable

  FIG. 14 shows still another embodiment of the soaking roller that can be used in the present invention. The soaking roller 7d shown in this figure is formed from a first spiral groove 76a formed from one end in the rotation axis direction to the center in the rotation axis direction, and from the other end in the rotation axis direction to the center in the rotation axis direction. The first spiral groove 76a has a second spiral groove 76b opposite to the first spiral groove 76a. The directions of the spiral grooves 76a and 76b are directions from the center in the rotation axis direction toward the respective ends when the soaking roller 7d rotates. Similar to the above-described embodiment, when the soaking roller 7d contacts the pressure roller 5, the portions of the spiral grooves 76a and 76b become low pressure portions below a predetermined pressure, and the other portions are high pressure portions above the predetermined pressure. It becomes. By the rotation of the soaking roller 7d, the high pressure portion and the low pressure portion of the soaking roller 7c are alternately brought into contact with the pressure roller 5, and the entire pressure roller 5 is uniformly reduced. In addition, in the soaking roller 7d of the present embodiment, dirt is discharged from both ends of the soaking roller 7d as compared with the soaking roller 7a in which one spiral groove 73 shown in FIG. 3 is formed. Therefore, the effect of reducing dirt is further improved.

  The soaking roller 7e shown in FIG. 15 has the first spiral groove 77a and the second spiral groove 76b in the direction opposite to the first spiral groove 77a, so that the soaking roller shown in FIG. Although it is the same as the roller 7d, it differs from the spiral grooves 77a and 77b in that it is formed in the entire axial direction of the soaking roller 7e. Even with such a configuration, as with the heat equalizing roller 7d shown in FIG. 14, the entire pressure roller 5 has a uniform dirt reducing effect, and the dirt can be discharged from both ends of the heat equalizing roller 7e. Therefore, the dirt reducing effect is further improved.

  As described above, in the embodiment described above, the electromagnetic induction heating method is used as the heating means. However, the heating means of the present invention is not limited to this, and conventionally known heating means such as infrared irradiation heating with a halogen lamp is used. Can be used. When a heating means other than the electromagnetic induction heating method is used, the electromagnetic induction heat generating layer 43 made of a magnetic metal material is not necessary as a configuration of the fixing roller 4 as a matter of course.

  The fixing device according to the present invention does not increase the size of the device or increase the manufacturing cost, and even when the pressure roller and the heat equalizing roller are in contact with each other for a long time, the pressure is applied from the heat equalizing roller. This is useful because it can reduce the retransfer of the mixture of toner and paper powder to the roller.

1 Printer (image forming device)
4 Fixing roller (fixing rotor)
5 Pressure roller (Pressure rotating body)
6 Magnetic flux generator (heating means)
7a, 7b, 7c, 7d, 7d, 7e Soaking roller 8 Brush roller P Paper (member to be transferred)
T fixing device 73 groove 74 circumferential groove 75 groove 76a first spiral groove 76b second spiral groove 77a first spiral groove 77b second spiral groove

Claims (21)

A fixing rotator, a heating unit that heats the fixing rotator, a pressure rotator that presses against the fixing rotator to form a nip portion, and a surface of the pressure rotator that contacts the surface of the pressure rotator. A temperature equalizing roller, and a soaking roller that rotates about the longitudinal axis of the temperature distribution roller,
The fixing device, wherein the heat equalizing roller has a high pressure portion whose contact pressure with respect to the pressure rotator is a predetermined pressure or higher and a low pressure portion whose pressure is lower than the predetermined pressure.   The fixing device according to claim 1, wherein a surface of the soaking roller that contacts the pressure rotator is metal.   The fixing device according to claim 1, wherein the heat equalizing roller has a spiral groove on a surface thereof, and the high-pressure portion and the low-pressure portion are alternately positioned in a rotation axis direction.   The fixing device according to claim 3, wherein the spiral groove provided on the surface of the heat equalizing roller is in one direction.   The fixing device according to claim 1, wherein the heat equalizing roller has a plurality of circumferential grooves on a surface thereof at predetermined intervals in a rotation axis direction, and the high pressure portion and the low pressure portion are alternately positioned in the rotation axis direction.   The fixing device according to claim 5, further comprising a moving unit that moves the soaking roller in a rotation axis direction.   The heat equalizing roller has a plurality of grooves parallel to the rotation axis at predetermined intervals in the rotation direction on the surface, and the high pressure portion and the low pressure portion are turned into the pressure rotating body as the heat equalizing roller rotates. The fixing device according to claim 1, which contacts the fixing device.   The fixing device according to claim 1, wherein the low-pressure portion is not in contact with the pressure rotating body.   The fixing device according to claim 1, wherein an area ratio of the high-pressure portion in the heat equalizing roller is 65% or more and less than 100%.   The fixing device according to claim 9, wherein an area ratio of the high-pressure portion in the heat equalizing roller is 80% or more and less than 100%.   The fixing device according to claim 1, wherein the low-pressure portion has a width of 0.1 mm to 5.0 mm.   The fixing device according to claim 11, wherein a width of the low-pressure portion is 0.1 mm or greater and 1.0 mm or less.   The fixing device according to claim 1, wherein a contact pressure of the high-pressure portion is in a range of 0.01 MPa to 0.3 MPa.   The fixing device according to claim 1, wherein a contact pressure of the high-pressure portion is in a range of 0.06 MPa to 0.17 MPa.   The fixing device according to claim 1, wherein an end cross section of the high pressure portion is chamfered.   The fixing according to claim 1, wherein the pressure rotating body is a pressure roller, and an outer diameter ratio between the pressure roller and the heat equalizing roller is a non-integer multiple. apparatus.   The fixing device according to claim 1, further comprising a brush roller that contacts the heat equalizing roller and cleans a surface of the heat equalizing roller.   The fixing device according to claim 17, further comprising a first spiral groove and a second spiral groove in a direction opposite to the first spiral groove on a surface of the heat equalizing roller.   The first spiral groove is formed from one end in the rotation axis direction to the center in the rotation axis direction, and the second spiral groove is formed from the other end in the rotation axis direction to the center in the rotation axis direction. The fixing device described.   The fixing device according to claim 18, wherein the first spiral groove and the second spiral groove are formed in the entire rotation axis direction.   An image forming apparatus comprising the fixing device according to claim 1.