JP2005215362A - Fixing device and image forming apparatus to which fixing device is applied - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To surely prevent the occurrence of a tailing phenomenon and an offset phenomenon in fixing processing performed to the toner image of transfer paper to which transfer processing is performed. <P>SOLUTION: In the fixing device 40 constituted by providing a heat roller 41 which performs heating processing to paper P to which the toner image of a photosensitive drum 22 is transferred and a pressure roller 42 arranged oppositely to the heat roller 41 so that circumferential surfaces are brought into contact with each other for over approximately the entire length in the longitudinal direction, the toner image is fixed to the paper P by passing the paper P between both rollers 41 and 42, the heat roller 41 is constituted by providing a cylindrical core bar 431 and a coating layer 432 formed all over the peripheral surface of the core bar 431, and the surface resistance value of the heat roller 41 varies in the longitudinal direction. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a fixing device that performs a fixing process on a toner image formed on a transfer sheet, and an image forming apparatus to which the fixing device is applied.

  Conventionally, a fixing device applied to an image forming apparatus is known. The image forming apparatus forms an image based on image information (image signal) read by the image reading apparatus or image information sent from an electronic device such as a facsimile machine, and outputs the image on a transfer sheet as a toner image. An electrostatic latent image formed by irradiating light on the peripheral surface of the photosensitive drum, which is rotated around the axis, and subjected to uniform charging processing, with light based on the image signal through an exposure unit In contrast, the toner is supplied from the developing device to form a toner image, and the toner image is transferred onto a transfer sheet.

  The fixing device performs a fixing process on the toner image formed on the transfer sheet in this way by a heat process. Such a fixing device includes a heat roller having a heat source such as a halogen lamp inside, and a pressure roller disposed so as to be opposed to the heat roller so that peripheral surfaces thereof are in contact with each other. By passing the transfer paper through, the toner image on the transfer paper is heated and melted and then solidified (that is, fixing processing).

By the way, when the toner on the transfer paper is insufficiently melted or the melted toner is not sufficiently adhered to the transfer paper, the toner image on the transfer paper moves to the peripheral surface of the heat roller, and after one round of the roller This causes not only the so-called “offset” that causes the transfer paper to become dirty, but also a problem that the image on the transfer paper is disturbed. In order to prevent the occurrence of the offset and the disturbance of the transfer image quality, in Patent Document 1, the surface roughness of the heat roller is set to 0.05 to 4.0 μm and the electric resistance (surface resistance value) of the surface is set. ) Is set to 1.0 × 10 ^{7 to} 1.0 × 10 ¹⁴ Ω. By doing so, it is stated that the increase in the charge amount of the heat roller after the fixing process can be suppressed and the image quality can be improved (paragraph [0028] of Patent Document 1).
JP 2003-76193 A

  However, Patent Document 1 does not describe “tailing”, which is another problem in the fixing process. Trailing refers to a phenomenon in which toner extends in a bowl shape from the transferred ruled line to the upstream side in the conveyance direction when a ruled line or the like extending in a direction intersecting the conveyance direction is transferred to the transfer paper. Such tailing is considered to occur by the following mechanism.

  That is, when the transfer paper is subjected to a transfer process, a transfer roller disposed opposite to the photosensitive drum via the transfer paper in order to transfer the toner image positively charged on the peripheral surface of the photosensitive drum to the transfer paper surface. The transfer sheet is conveyed to the fixing device in a state where toner is electrostatically adsorbed on the surface.

  On the other hand, the heat roller of the fixing device is at a high temperature such as 150 ° C., and the transfer sheet suddenly contacts the high-temperature heat roller. Since the transfer paper contains, for example, several percent of water, a water vapor flow is ejected from the transfer paper by heating with a heat roller, and the water vapor blows off the unfixed toner on the transfer paper to the downstream side of the transfer paper, thereby A pull-like image defect may occur.

  Since toner adheres to the transfer paper after the transfer due to electrostatic attraction force, such tailing is generally difficult to occur. However, static electricity applied to the transfer paper due to contamination of the transfer roller by toner, etc. When it decreases, the electrostatic attraction force of the toner weakens, so that tailing tends to occur.

Therefore, even if the surface resistance value of the heat roller is uniformly set to a predetermined value within a range of 1.0 × 10 ^{7 to} 1.0 × 10 ¹⁴ Ω, as disclosed in Patent Document 1. In this case, tailing cannot be prevented simultaneously with offset.

  The present invention has been made in view of the above-described situation, and in the fixing process applied to the toner image of the transfer paper subjected to the transfer process, the occurrence of the tailing phenomenon is surely generated together with the offset phenomenon. It is an object of the present invention to provide a fixing device capable of preventing the above and an image forming apparatus to which the fixing device is applied.

  The fixing device according to claim 1, wherein the heat roller that heats the transfer sheet onto which the toner image on the photosensitive drum is transferred, and the peripheral surfaces are in contact with each other over substantially the entire length in the longitudinal direction. A fixing device comprising a heat roller and a pressure roller arranged opposite to each other, and fixing the toner image onto the transfer paper by passing the transfer paper between both rollers, the heat roller having a cylindrical core The heat roller is composed of gold and a coating layer formed on the entire peripheral surface of the core metal, and the heat roller is characterized in that the surface resistance value is changed in the longitudinal direction. .

  By adopting such a configuration, by changing the surface resistance value in the longitudinal direction of the heat roller and setting the surface resistance value of the portion where tailing is likely to occur higher than the surface resistance value of the portion where tailing is difficult to occur, The insulation of the portion where tailing is likely to occur is improved as compared with the portion where tailing is unlikely to occur, whereby the charge of the charged toner transferred to the transfer paper in the portion where tailing is likely to occur is transferred to the peripheral surface of the heat roller. Therefore, the movement of the toner to the peripheral surface of the heat roller accompanying the movement of the electric charge is suppressed, and thus the occurrence of tailing is effectively prevented. Further, since the average surface resistance value of the heat roller is appropriately increased by increasing the surface resistance value of the portion where tailing is likely to occur, the toner image on the transfer sheet is transferred to the peripheral surface of the heat roller, and one rotation of the roller. Offsets that contaminate later transfer paper are less likely to occur.

  In this way, transfer to the peripheral surface of the heat roller while suppressing an increase in device cost by taking a simple measure of changing the surface resistance value in the longitudinal direction according to the ease of tailing. It is possible to eliminate the tailing phenomenon and offset phenomenon that occur in the paper.

  According to a second aspect of the present invention, in the fixing device according to the first aspect, the surface resistance value of the heat roller is changed by changing the roughness in the longitudinal direction of the peripheral surface of the cored bar. It is characterized by this.

  According to this configuration, the surface resistance value of the heat roller can be easily changed by changing the roughness of the peripheral surface of the cored bar.

  According to a third aspect of the present invention, there is provided the fixing device according to the first aspect, wherein the surface resistance value of the heat roller is changed by the coating layer side.

  According to this configuration, the surface resistance value of the heat roller can be easily changed by changing the resistance value on the coating layer side.

  The fixing device according to claim 4 is the fixing device according to claim 3, wherein the coating layer uses a plurality of types of coating materials having different resistance values in a longitudinal direction of the core metal peripheral surface. The resistance value is varied.

  By adopting such a configuration, the surface resistance value of the heat roller can be easily changed by covering the peripheral surface of the heat roller with a plurality of types of coating materials.

  The fixing device according to claim 5 is the fixing device according to any one of claims 1 to 4, wherein the heat roller has a surface resistance value at both sides set higher than a surface resistance value at the center. It is a feature.

  By adopting such a configuration, the tailing phenomenon on both sides in the width direction of the transfer sheet (direction perpendicular to the sheet conveyance direction), which easily causes the tailing phenomenon, is suppressed.

The fixing device according to claim 6 is the fixing device according to claim 5, wherein the surface resistance value of the both side portions is in the range of 1.0 × 10 ^{1 to} 1.0 × 10 ³ from the surface resistance value of the central portion. It is characterized by being set higher by a value obtained by multiplying the value of.

By adopting such a configuration, the trailing phenomenon and the offset in the transfer paper are effectively prevented. Incidentally, the surface resistance value on both sides of the heat roller is set higher than the central surface resistance value by a value multiplied by a value in the range of 1.0 × 10 ^{1 to} 1.0 × 10 ³ . It was obtained as a result of the effect confirmation test.

  A fixing device according to a seventh aspect is the fixing device according to any one of the first to fifth aspects, wherein the heat roller has a surface resistance value set to the lowest in the center portion and is directed toward both sides. It is characterized by being set so as to increase stepwise.

  By adopting such a configuration, it is possible to effectively prevent the tailing phenomenon and the offset from occurring for transfer sheets of various sizes.

The fixing device according to claim 8 is the fixing device according to claim 7, wherein a surface resistance value of the both side portions is in a range of 1.0 × 10 ^{1 to} 1.0 × 10 ³ from a surface resistance value of the central portion. It is characterized in that it is set higher by a value obtained by multiplying the above value.

By adopting such a configuration, the trailing phenomenon and the offset in the transfer paper are effectively prevented. Incidentally, the set to be high by the value of both sides range surface resistivity than the surface resistance of the central portion of 1.0 × 10 ¹ ~1.0 × 10 ³ of the heat roller, the various effects confirmation test The result is obtained.

  An image forming apparatus according to a ninth aspect is characterized in that the fixing device according to any one of the first to eighth aspects is applied.

  By adopting such a configuration, the image forming apparatus includes the fixing device having the operation according to any one of claims 1 to 8.

  According to the fixing device of the first aspect of the present invention, it is generated on the transfer sheet by taking a simple measure of changing the surface resistance value in the longitudinal direction on the peripheral surface of the heat roller according to the easiness of the tailing. It becomes possible to eliminate the tailing phenomenon and the offset phenomenon, and it is possible to eliminate the inconvenience due to the tailing and offset while suppressing the increase in the apparatus cost.

  According to the fixing device of the second aspect, the surface resistance value of the heat roller can be easily changed by a simple operation of changing the roughness of the peripheral surface of the cored bar.

  According to the fixing device of the third aspect, since the surface resistance value of the heat roller is changed on the coating layer side, the surface resistance value of the heat roller is changed by changing the resistance value on the coating layer side. It can be easily changed.

  According to the fixing device of claim 4, since the coating layer has a surface resistance value changed by using a plurality of types of coating materials having different resistance values in the longitudinal direction of the core metal peripheral surface, By covering the peripheral surface of the heat roller with a plurality of types of coating materials, the surface resistance value of the heat roller can be easily changed.

  According to the fixing device of the fifth aspect, since the surface resistance value of both sides of the heat roller is set higher than the surface resistance value of the central portion, the width direction ( It is possible to effectively suppress the tailing phenomenon on both sides in the direction perpendicular to the sheet conveyance direction.

According to the fixing device of the sixth aspect, the surface resistance value of both side portions is set higher by a value in the range of 1.0 × 10 ^{1 to} 1.0 × 10 ³ than the surface resistance value of the central portion. Therefore, it is possible to effectively prevent the tailing phenomenon and the offset in the transfer paper.

  According to the fixing device of the seventh aspect, since the heat roller is set so that the surface resistance value of the central portion is the lowest and is gradually increased as it goes to both sides, For transfer sheets of various sizes, it is possible to effectively prevent the occurrence of tailing and offset.

According to the fixing device of the eighth aspect, the surface resistance value of both sides is set higher by a value within the range of 1.0 × 10 ^{1 to} 1.0 × 10 ³ than the surface resistance value of the central portion. Therefore, the trailing phenomenon and the offset in the transfer paper can be effectively prevented.

  According to the image forming apparatus of the ninth aspect, the image forming apparatus can include the fixing device having the operation according to any one of the first to eighth aspects.

  FIG. 1 is a perspective view showing an appearance of an embodiment of an image forming apparatus to which a fixing device according to the present invention is applied, and FIG. 2 is an explanatory diagram showing an outline of the internal structure thereof. 1 and 2, the XX direction is referred to as the width direction, and the YY direction is referred to as the front-rear direction. In particular, the -X direction is leftward, the + X direction is rightward, the -Y direction is forward, and the + Y direction is forward. It is called the back.

  First, as shown in FIG. 1, an image forming apparatus 10 according to the present invention is a so-called in-body discharge type, and includes an image forming unit 20 and a sheet storage unit 30 (FIG. 2). The device main body 11 has a rectangular parallelepiped shape, and the scanner main body 11 is disposed above the device main body 11 so as to face the device main body 11 and to which the scanner unit 50 is mounted. An in-body discharge space V for temporarily storing paper (transfer paper) P discharged from the upper front portion of the image forming unit 20 is formed between the upper surface of the apparatus main body 11 and the lower surface of the scanner unit housing 12. Has been.

  As shown in FIG. 2, a paper conveyance path 21 for conveying the paper P from the paper storage unit 30 from below to above is set at the front position in the image forming unit 20. A photosensitive drum 22 is disposed behind the center of the sheet conveyance path 21 in the vertical direction so that the axis extends in the width direction (direction perpendicular to the paper surface of FIG. 2). The cleaning device 23, the charger 24, and the developing device face the circumferential surface of the photosensitive drum 22 and from the upper side to the lower side along the rotation direction of the photosensitive drum 22 in the clockwise direction. 25, and an exposure device 26 is provided above the developing device 25. Laser light from the exposure device 26 is applied to the peripheral surface of the photosensitive drum 22 between the charger 24 and the developing device 25. Irradiated.

  In addition, a transfer roller 27 is provided in front of the photosensitive drum 22 with the paper conveyance path 21 interposed therebetween, and the paper P that has moved up the paper conveyance path 21 is pressed and nipped by the photosensitive drum 22 and the transfer roller 27. As a result, the toner image on the circumferential surface of the photosensitive drum 22 is transferred.

  Then, as the photosensitive drum 22 rotates around the axis, the peripheral surface of the photosensitive drum 22 is first cleaned by the cleaning device 23, and then the peripheral surface of the photosensitive drum 22 is uniformly charged by the charger 24. Then, an electrostatic latent image is formed by irradiating the charged same peripheral surface with a laser beam from the exposure device 26, and subsequently toner from the developing device 25 is supplied to the electrostatic latent image. A toner image is formed on the peripheral surface, and the toner image is transferred to the paper P supplied from the paper storage unit 30 to the paper transport path 21 in synchronization with the formation of the toner image.

  A fixing device 40 is provided on the downstream side of the photosensitive drum 22 in the paper conveyance path 21 (upper part of the photosensitive drum 22). The fixing device 40 includes a heat roller 41 having an energization heating element such as a halogen lamp inside, and a pressure roller 42 disposed opposite to the heat roller 41 with the paper conveyance path 21 interposed therebetween. The toner image is fixed to the paper P by heat treatment performed while the transferred paper P passes between the heat roller 41 and the pressure roller 42.

  The paper storage unit 30 is formed by detachably mounting a paper cassette 31 that stores paper P in the lower part of the apparatus main body 11 in two upper and lower stages. Each paper cassette 31 is in contact with the lift plate 32 biased upward by a biasing means (not shown), and the leading edge of the paper P biased upward by the lift plate 32 to be the uppermost position. A sheet feeding roller 33 for sequentially feeding the sheet P is provided, and each sheet P from the bundle of sheets P placed on the lift plate 32 by the driving of the sheet feeding roller 33 is fed to the sheet conveying path 21. To be sent to

  Then, the paper P fed to the paper transport path 21 by the feed roller 33 is drawn out to the paper transport path 21 by a pair of feed rollers 34 arranged to face the feed roller 33, and enters the paper transport path 21. Ascending along the direction toward the photosensitive drum 22 and the transfer roller 27.

  Further, the paper storage unit 30 is provided with a manual feed tray 35 that is formed on the front wall of the device body 11 so as to be freely opened and closed. The paper P placed on the manual feed tray 35 is supplied to the photosensitive drum 22 through the paper transport path 21 by driving a registration roller 36 provided at the upper end of the rear end.

  The scanner unit 50 (FIG. 2) includes an optical system 51 for reading a document image built in the scanner unit housing 12, and a document presser 57 connected to the upper portion of the scanner unit housing 12 so as to be openable and closable. Has been. A bottom plate 13 is provided at the bottom of the scanner unit housing 12, and the optical system 51 is partitioned from the in-body discharge space V by the bottom plate 13.

  The optical system 51 automatically reads an image of a document placed on the contact glass 52 disposed on the upper surface of the scanner unit housing 12 with the document surface facing down, or an original document mounted on the upper surface of the document retainer 57. The original image supplied from the device 58 to the automatic reading contact glass 521 is read.

  The optical system 51 includes a first mirror base 53 that emits light toward the document surface, and a second mirror base 54 that further reflects the reflected light of the light emitted from the first mirror base 53 and moves it to the rear side. And a lens unit 55 for converging the light from the second mirror base 54, and a CCD (charge coupled device) 56 for receiving the light from the lens unit 55 and converting it into an electrical signal. .

  The first mirror base 53 is configured to be movable in the front-rear direction along the lower surface of the contact glass 52. The first mirror base 53 moves light from a light source (not shown) through the contact glass 52 while moving backward from the home position H at the left end. The reflected light is reflected forward by a first mirror 531 inclined at 45 ° with respect to a horizontal line extending in the front-rear direction.

  The second mirror base 54 further reflects the reflected light from the first mirror 531 to be directed downward, and reflects the light from the second mirror 541 so as to be directed to the lens unit 55. And a third mirror 542. The second mirror table 54 is configured to move back and forth at a speed of 1/2 in synchronism with the back and forth movement of the first mirror table 53, whereby the home positions of the first mirror table 53 and the second mirror table 54 are set. Regardless of the moving distance from H, the optical path length of the reflected light reaching the lens unit 55 via the first mirror 531, the second mirror 541, and the third mirror 542 is always constant.

  Incidentally, when the document is supplied from the automatic document reading device 58, the first mirror table 53 and the second mirror table 54 are contact glass for automatic reading of the image of the document that moves while stopped at the home position H. 521 is read through.

  The document image information converted into an electrical signal by the CCD 56 is temporarily stored in a storage device (not shown), and is output to the exposure device 26 in synchronization with the paper P sent from the paper storage unit 30. The toner image formed on the photosensitive drum 22 is transferred to the paper P.

  FIG. 3 is a perspective view showing an embodiment of the transfer / fixing unit 60. As shown in this figure, the transfer / fixing unit 60 is disposed opposite to the photosensitive drum 22, the heat roller 41, and the pressure roller 42 mounted in the apparatus main body 11 to form a part of the paper transport path 21. The transfer roller 27 is provided. 3 shows a state in which the photosensitive drum 22, the heat roller 41, and the pressure roller 42 face the transfer / fixing unit 60.

  The transfer / fixing unit 60 includes a unit main body 61 having a gentle mountain shape whose top is formed to the right (in the direction of the photosensitive drum 22) in FIG. 3 in a side view, and from both sides of the lower end of the unit main body 61. A pair of width direction brackets 62 projecting downward is provided.

  A circular arc recess 621 having a central angle slightly larger than 180 ° and an opening facing downward is provided at the lower end of each bracket 62, and these arc recesses 621 pass through the opening in the device main body 11 (FIG. 2). An external fitting press fit can be performed on a predetermined support shaft 14. The transfer / fixing unit 60 is supported by the respective circular arc recesses 621 that are externally fitted to the support shaft 14, so that the transfer / fixing unit 60 can be rotated forward and backward around the support shaft 14, thereby standing upright on the shaft. The posture can be changed between (the posture shown in FIG. 3) and the inspection posture rotated approximately 90 ° counterclockwise from the standing posture.

  The unit main body 61 is mounted with the transfer roller 27 in a state where the peripheral surface of the unit main body 61 is set so as to face the peripheral surface of the photosensitive drum 22 over the entire length in the longitudinal direction. In addition, a guide roller 63 for guiding the paper P between the photosensitive drum 22 and the transfer roller 27 is provided slightly below the transfer roller 27. Then, with the transfer / fixing unit 60 set to the upright posture, the guide roller 63 is opposed to a roller (not shown) in the apparatus main body 11, and the paper P is sandwiched between the opposite roller and the guide roller 63. In this state, the toner is fed between the photosensitive drum 22 and the transfer roller 27.

  The unit main body 61 has a plurality of guide ribs 64 extending in the sheet conveyance direction arranged in parallel in the width direction on the inner surface side (photosensitive drum 22 side) and on the downstream side (upper side) of the transfer roller 27. The sheet P sent from between the photosensitive drum 22 and the transfer roller 27 is directed upward while being guided by these guide ribs 64.

  In addition, a guide plate 65 for directing the paper P toward the fixing device 40 is provided at the bottom of the upper portion of the unit main body 61 having a mountain shape. The guide plate 65 faces the contact position between the pressure roller 42 and the heat roller 41 mounted in the apparatus main body 11 with the transfer / fixing unit 60 set in the standing posture. The dimensions are set as follows.

  The transfer roller 27 is supplied with a voltage from a power source (not shown) and is applied with a negative charge. This is because the negatively charged toner image formed on the peripheral surface of the photosensitive drum 22 is attracted and separated by the positive charge on the surface side of the paper P, and is effectively transferred to the paper P. Because.

  According to the transfer / fixing unit 60 configured as described above, the sheet P fed from the sheet storage unit 30 (FIG. 1) in the state where the transfer / fixing unit 60 is set in the standing posture is guided by the guide. It is supplied between the photosensitive drum 22 rotating in the clockwise direction and the transfer roller 27 rotating in the counterclockwise direction via the roller 63, and when passing between these rollers 22, 27, the photosensitive drum The toner image formed on the peripheral surface 22 is transferred onto the paper P.

  At the time of this transfer, the transfer roller 27 is negatively charged. Therefore, the paper P that is in contact with the transfer roller 27 is positively charged on the contact surface, while the opposite surface (that is, the surface on which the toner image is transferred). ) Will generate a negative charge. Therefore, the positively charged toner image on the circumferential surface of the photosensitive drum 22 is attracted to the negative charge on the surface of the paper P, and the toner image peeled off from the photosensitive drum 22 is thereby reliably transferred to the paper P. Will be.

  Next, the sheet P on which the toner image on the photosensitive drum 22 is transferred is guided by the guide rib 64 and the guide plate 65 and reaches the fixing device 40. Then, the paper P that has reached the fixing device 40 is introduced between the heat roller 41 and the pressure roller 42, where heat from the heat roller 41 is obtained and fixing processing is performed by heating, and then the in-body paper discharge space The paper is discharged to V.

  4A and 4B are diagrams showing an embodiment of the heat roller 41, where FIG. 4A is a partially cutaway perspective view, and FIG. 4B is a cross-sectional view taken along line AA in FIG. FIG. 5 is a plan view of the heat roller 41 shown in FIG. As shown in these drawings, the heat roller 41 includes a cylindrical heat roller body 43, a pair of sockets 44 that are concentrically mounted on both ends of the heat roller body 43, and a pair of the sockets 44. And a pair of halogen lamps 45 as heat sources interposed between the sockets 44.

  The heat roller main body 43 includes a cylindrical cored bar 431 and a coating layer 432 formed by being uniformly laminated on the peripheral surface of the cylindrical cored bar 431. A cylindrical base 433 concentrically and integrally fixed is provided at both ends of the heat roller main body 43, and the base 433 is fitted into the socket 44 in a sliding contact state. The socket 44 is rotatable relative to the socket 44.

  In the present embodiment, the cylindrical cored bar 431 is formed of an aluminum alloy. However, the cylindrical cored bar 431 is not limited to an aluminum alloy, and may be iron, stainless steel, copper, brass, or the like. Various metals can be used. In the present embodiment, the coating layer 432 is made of a fluororesin such as PTFE (polytetrafluoroethylene). However, the coating layer 432 is not limited to being made of a fluororesin. Various synthetic resins such as these synthetic resins can be used.

  The socket 44 is provided with a predetermined number of connection terminals 46, and electric power is supplied to the halogen lamp 45 through these connection terminals 46, and voltage is supplied to the cylindrical cored bar 431, thereby heating. A negative charge is charged on the surface of the roller 41.

And in this invention, the electrical surface resistance value of the both-sides peripheral surface of the heat roller 41 (heat roller main body 43) is set larger than the electrical surface resistance value of the center part peripheral surface. Usually, the surface resistance value of the heat roller 41 is in the range of 1.0 × 10 ⁶ Ω to 1.0 × 10 ¹² Ω, and is an optimum value according to various local conditions (this value was found as a result of a field test). Is adopted. In the present invention, the surface resistance value of both side portions 435 of the heat roller body 43 is set to be larger than the surface resistance value of the central portion 434 by a predetermined value. The predetermined value is preferably 1.0 × 10 ¹ Ω to 1.0 × 10 ³ Ω. Therefore, for example, when the surface resistance value of the center portion of the heat roller body 43 is set to 1.0 × 10 ⁹ Ω, the surface resistance value of both side portions is “1.0 × 10 ⁹ Ω × (1 0.0 × 10 ¹ Ω to 1.0 × 10 ³ Ω) = 1.0 × 10 ^{10 to} 1.0 × 10 ¹² Ω ”.

  In the heat roller main body 43, the difference in surface resistance value is provided between the central portion and both side portions for the following reason.

  That is, as shown in FIG. 5, the heat roller body 43 normally has an A3 size fed from the paper storage unit 30 (FIG. 2) in the so-called longitudinal direction so that the long side is parallel to the paper transport direction. The length dimension is set slightly longer than 297 mm so as to correspond to the paper (long dimension 420 mm × short dimension (L1) 297 mm).

  In the image forming apparatus 10 to which the heat roller main body 43 having such a length dimension is mounted, the most frequently used sheet P is A4 size (longitudinal dimension 297 mm × short dimension (L2) 210 mm). Therefore, when the A4 size paper P is fed in the longitudinal direction, as shown in FIG. 5, the heat roller main body 43 has only the short dimension (L2) of the A4 size paper P at the central portion 434 thereof. Do not participate in the fixing process. Therefore, since both side portions 435 of the heat roller main body 43 are not wiped with the paper P, dirt due to adhesion of toner scattered in the apparatus main body 11 is not wiped with the paper P, and accumulated dirt. The surface state is different from that of the central portion 434, for example, the surface resistance value becomes small.

  Moreover, the heat roller main body 43 is heated to a high temperature such as 150 ° C., and the paper P that normally contains several percent of moisture is suddenly brought into contact with the high temperature heat roller main body 43 and heated. The water vapor is ejected from the water, and the water vapor blows off the unfixed toner on the paper P to the downstream side, and the blown toner may adhere to the peripheral surface of the heat roller main body 43. That is, the moisture content of the paper P greatly affects the tailing.

  In addition, the bundle of sheets P stacked and stored in the sheet storage unit 30 has more moisture than the center part because both sides absorb moisture in the air. Therefore, both sides of the paper P have a greater amount of water evaporation than the center, and this causes the both sides of the paper P to be more easily tailed than the center.

  For these reasons, that is, the heat roller main body 43 has different surface states at the central portion 434 and both side portions 435, and the moisture content of both side portions 435 of the paper P is larger than the moisture content of the central portion 434. Therefore, the side portions 435 are more likely to be tailed than the center portion 434. In order to cope with this, in the present invention, the surface resistance between the center portion 434 and the side portions 435 of the heat roller body 43 is reduced. There is a difference in value.

  Conventionally, there has been no difference in the surface resistance value between the central portion 434 and both side portions 435 of the heat roller main body 43, but the sheet P on which the toner image is formed, the photosensitive drum 22 and the transfer drum. In general, each device is electrically adjusted so as to realize an electrostatic equilibrium state in which tailing or offset hardly occurs between the roller 27 and the heat roller body 43.

Then, as one of measures for preventing tailing and offset for each device, the surface resistance value of the heat roller body 43 may be set within a range of “1.0 × 10 ⁶ Ω to 1.0 × 10 ¹² Ω”. Can be mentioned. It has been empirically known from many operational results that tailing phenomenon and electrostatic offset are less likely to occur due to such setting.

However, even if the surface resistance value of the heat roller main body 43 is set uniformly within the range of “1.0 × 10 ⁶ Ω to 1.0 × 10 ¹² Ω”, the A4 size paper P in the heat roller main body 43 For the portion corresponding to the short dimension (L2) (FIG. 5) (the center portion 434), there is no particular problem, but when the A3 size paper P is fed in the longitudinal direction with low frequency. As described above, when the A4 size paper P is fed in the short direction, the tailing phenomenon is likely to occur in the outer portion (both side portions 435) of the central portion 434 of the heat roller main body 43. It is.

Therefore, in the present invention, the surface resistance value of the central portion 434 corresponding to the short dimension (L2) of the heat roller main body 43 follows the current state, and the surface resistance values of the both side portions 435 are the same as those of the central portion 434. It is set higher by 1.0 × 10 ¹ Ω to 1.0 × 10 ³ Ω than that. With this setting, even if both side portions 435 of the heat roller body 43 are contaminated with toner or the like, or the electrostatic equilibrium state is out of order, the tailing phenomenon and the offset phenomenon do not occur. The reason for this will be described in the “Example” section below.

  Next, setting of the surface resistance value of the heat roller body 43 will be described. In the present embodiment, the surface resistance value of the heat roller main body 43 is adjusted by adjusting the roughness of the surface of the cylindrical cored bar 431. FIG. 6 is a partial enlarged cross-sectional view of the heat roller body 43 in the longitudinal direction. As shown in this figure, the cylindrical cored bar 431 at the central portion 434 of the heat roller main body 43 is set so that the surface roughness is rougher than the surface roughness of the side portion 435.

  Specifically, only the peripheral surface of the side portion 435 of the cylindrical cored bar 431 is subjected to surface finishing by cutting or the like, while the peripheral surface of the central portion 434 is subjected to the surface finishing as described above. For example, the surface roughness is increased by so-called blasting, in which fine sand or glass ball particles are sprayed together with air at high pressure.

  Due to the reaction caused by the formation of the concave portion by the blasting process, the peripheral portion of the concave portion is swelled. As a result, as shown in FIG. 6, the top of the large unevenness in the central portion 434 of the heat roller main body 43 and the surface of the coating layer 432 Is smaller than the distance D1 between the top of the small irregularities of the cylindrical metal core 431 on the same side portion 435 and the surface of the coating layer 432, and thus the electrical distance of the coating layer 432 in the central portion 434 Therefore, the surface resistance value of the central portion 434 of the heat roller main body 43 is smaller than that of the side portion 435 (that is, the surface resistance value of the side portion 435 is smaller than that of the central portion). Larger than that of 434).

In the present embodiment, the surface roughness of the central portion 434 of the cylindrical cored bar 431 is set to 5.0 to 8.0 μm, and the surface roughness of the same side portion 435 is 1.0 to 2. .0 μm. The surface roughness is set in this way when the surface roughness of the central portion 434 is less than 5.0 μm or exceeds 8.0 μm, the surface resistance of the central portion 434 of the heat roller main body 43. This is because the value does not fall within the range of 1.0 × 10 ⁹ Ω to 1.0 × 10 ¹¹ Ω, which tends to cause an offset, and the surface roughness of the side portion 435 is less than 1.0 μm. If it exceeds 2.0 μm, the surface resistance value of the side portion 435 of the heat roller main body 43 does not fall within the range of 1.0 × 10 ¹² Ω to 1.0 × 10 ¹³ Ω. This is because the tailing phenomenon easily occurs in the portion 435.

  As described above in detail, the fixing unit 40 according to the present invention includes the heat roller 41 that heats the sheet P on which the toner image of the photosensitive drum 22 is transferred, and the substantially entire length of the circumferential surfaces in the longitudinal direction. A heat roller 41 and a pressure roller 42 disposed so as to face each other, and the toner image is fixed on the paper P by passing the paper P between the rollers 41 and 42. The heat roller 41 includes a cylindrical cylindrical cored bar 431 and a coating layer 432 formed on the entire peripheral surface of the cylindrical cored bar 431. The heat roller 41 has a long surface resistance value. Since the surface resistance value in the longitudinal direction of the heat roller 41 is changed, the surface resistance value of the portion where tailing is likely to occur is higher than the surface resistance value of the portion where tailing is difficult to occur. With this setting, the insulation of the portion where tailing is likely to occur is improved as compared with the portion where tailing is unlikely to occur, whereby the charge of the charged toner transferred to the paper P in the portion where tailing is likely to occur is improved. A short circuit to the circumferential surface of the heat roller 41 can be suppressed.

  Therefore, the movement of the toner to the peripheral surface of the heat roller 41 due to the movement of the electric charge is suppressed, and this can effectively prevent the occurrence of tailing. Further, since the average surface resistance value of the heat roller 41 is appropriately increased by increasing the surface resistance value of the portion where tailing is likely to occur, the toner image on the paper P moves to the peripheral surface of the heat roller 41 (attachment). Yes) offset can be effectively prevented.

  As described above, the tailing phenomenon and the offset phenomenon that occur in the paper P by taking a simple measure of changing the surface resistance value in the longitudinal direction on the peripheral surface of the heat roller 41 according to the easiness of the tailing. It is possible to eliminate the inconvenience due to tailing and offset while suppressing an increase in apparatus cost.

  And since the change of the surface resistance value of the heat roller 41 is performed on the cylindrical cored bar 431 side, by changing the surface resistance value of the heat roller 41 on the cylindrical cored bar 431 side, The surface resistance value can be easily changed. The surface resistance value is changed by changing the roughness of the circumferential surface of the cylindrical cored bar 431 in the longitudinal direction, so that the roughness of the circumferential surface of the cylindrical cored bar 431 is easily changed. By the simple operation, the surface resistance value can be easily changed, and the manufacturing cost can be reduced.

  In the present embodiment, the heat roller 41 is set such that the surface resistance value of both side portions 435 of the heat roller main body 43 is higher than the surface resistance value of the central portion 434, and thus the tailing phenomenon is likely to occur. When the size paper P is fed in the longitudinal direction, it is possible to effectively suppress the tailing phenomenon that is likely to occur at both side portions 435 in the width direction of the paper P (the direction orthogonal to the paper transport direction).

Since the surface resistance value of both side portions 435 of the heat roller main body 43 is set higher than the surface resistance value of the central portion 434 by a value in the range of 1.0 × 10 ^{1 to} 1.0 × 10 ³ , the sheet P Can effectively prevent the tailing phenomenon and offset.

  By applying the fixing device 40 configured in this way to the image forming apparatus 10, the image forming apparatus 10 has the effect of the fixing device 40, that is, a tailing phenomenon caused by the heat roller 41. Thus, the offset phenomenon in which the toner image on the paper P moves to the peripheral surface of the heat roller 41 is less likely to occur.

  The present invention is not limited to the above embodiment, and includes the following contents.

  (1) In the above embodiment, the surface resistance value of the heat roller main body 43 is changed by changing the roughness of the surface of the cylindrical cored bar 431. Instead of this, the coating layer 432 The surface resistance value of the heat roller main body 43 may be changed by changing the material. By doing so, the surface resistance value of the heat roller body 43 can be easily changed without subjecting the surface of the cylindrical cored bar 431 to blasting. In this case, the coating layer 432 may use a plurality of types of coating materials having different resistance values in the longitudinal direction of the circumferential surface of the cylindrical metal core 431. That is, the surface resistance value of the heat roller 41 can be easily changed by covering the peripheral surface of the heat roller 41 with a plurality of types of coating materials.

  (2) In the above embodiment, a copying machine is adopted as the image forming apparatus 10 to which the fixing device 40 is applied. However, the present invention is limited to the image forming apparatus 10 being a copying machine. Rather, the present invention can be applied to any apparatus provided with the fixing device 40 in the apparatus body, such as a facsimile machine or a printer attached to a computer.

  (3) In the above-described embodiment, the surface resistance value of the peripheral surface of the heat roller main body 43 is different between the central portion 434 and the both side portions 435. The surface resistance value may be changed in a plurality of steps over the portion 435. By doing so, it is possible to contribute to the suppression of the tailing phenomenon and the offset phenomenon not only for the paper P of size A but also for the paper P of size B.

  (4) In the above-described embodiment, an in-cylinder discharge type is used as the image forming apparatus 10 to which the fixing device 40 is applied. It is not limited to this, and a paper discharge tray may be provided protruding from the side wall of the apparatus main body 11.

  (5) In the above embodiment, the surface roughness of the cylindrical cored bar 431 in the central portion 434 is set so that the surface resistance value of the central portion 434 of the heat roller main body 43 is lower than the surface resistance value of the both side portions 435. Although the surface roughness of the cylindrical cored bar 431 at the gripping part 435 is rougher, instead of this, the overall diameter of the peripheral surface of the cylindrical cored bar 431 at the central part 434 is changed to the cylinders at both side parts 435. The diameter may be set slightly larger than the diameter of the cored bar 431 on the order of several to several tens of μm, or a thin wire made of metal may be wound around the cylindrical cored bar 431.

  In order to find out how the surface resistance value of the heat roller body 43 according to the present invention can be set to prevent the tailing phenomenon and the offset phenomenon caused by the heat roller 41, a confirmation test was performed.

  First, as a preparatory work, a large number of heat roller bodies 43 having a total length slightly longer than 270 mm, which is the short dimension of A3 paper, were manufactured. In this production, first, many samples having different surface roughness are produced by cutting or blasting the surface of the cylindrical cored bar 431 of each sample, and each cylindrical shape. The surface roughness of the core metal 431 was measured.

  Incidentally, the surface roughness of the cylindrical cored bar 431 is measured using a surface roughness meter SE3500 manufactured by Kosaka Laboratory in a measurement environment of normal temperature and normal humidity (23.5 ° C., relative humidity 60%). It was.

  Subsequently, a coating layer 432 made of a fluororesin was laminated on the peripheral surface of each cylindrical cored bar 431 after measuring the surface roughness by a predetermined method. The surface resistance value was measured for each sample of the heat roller main body 43 thus obtained. The surface resistance value is measured by using a Hiresta IP, which is a measuring instrument manufactured by Mitsubishi Yuka Co., Ltd., and a voltage of 10 to 500 V is applied with the probe (electrode) pressed against the surface of the heat roller body 43. This was performed by applying to the surface of the heat roller body 43 via a probe.

Based on the measurement result of the surface resistance value, the heat roller main body 43 was grouped for each surface resistance value. As a group, the surface resistance value R is “1.0 × 10 ⁵ Ω ≦ R <1.0 × 10 ⁶ Ω”, “1.0 × 10 ⁶ Ω ≦ R <1.0 × 10 ⁸ Ω”, “ 1.0 × 10 ⁸ Ω ≦ R <1.0 × 10 ⁹ Ω ”,“ 1.0 × 10 ⁹ Ω ≦ R <1.0 × 10 ¹⁰ Ω ”,“ 1.0 × 10 ¹⁰ ≦ R ≦ 1 0.0 group with 10 × 10 ¹² Ω ”and“ 1.0 × 10 ¹² Ω ≦ R <1.0 × 10 ¹³ Ω ”. This grouping of the surface resistance values corresponds to the measurement result of the surface roughness (that is, the surface resistance value becomes smaller as the surface roughness becomes larger).

  Next, a base 433, a socket 44, and the like are attached to each heat roller main body 43 subjected to such grouping to form a heat roller 41, and each heat roller 41 is provided in the apparatus main body 11 of the image forming apparatus 10. A practical test was performed in which the toner image was transferred to the paper P by being mounted at a predetermined position and the image forming apparatus 10 was operated, and the fixing device 40 fixed the toner image.

  In this practical test, the copying state of the paper P on which the copying process was completed was visually confirmed, whether or not a tailing phenomenon occurred and whether or not an electrostatic offset occurred was also confirmed. The test results are shown in Table 1.

  In Table 1, the double circle indicates “very good” (in the case of “tailing”, “no tailing occurs”), and in the case of “offset”, “no offset occurs”. The single circle indicates “good” (in the case of “tailing”, “the tailing that is not noticed by normal visual recognition has occurred”), and in the case of “offset”, “offset does not occur” ), The triangle indicates “slightly good” (in the case of “tailing”, “notice the tailing when viewed carefully”), and in the case of “offset”, the “offset is likely to occur” X indicates “bad” (in the case of “tailing” indicates “tailing occurs” and “offset” indicates “offset occurs”), respectively. Yes.

As can be seen from Table 1, when the surface resistance value R of the heat roller body 43 is “1.0 × 10 ⁵ Ω ≦ R <1.0 × 10 ⁶ Ω”, both “tailing” and “offset” are Therefore, the heat roller body 43 having the surface resistance value R in this range cannot be used.

Next, when the surface resistance value R of the heat roller body 43 is “1.0 × 10 ⁶ Ω ≦ R <1.0 × 10 ⁸ Ω”, “tailing” is “bad” but “offset”. Is “good”, the heat roller main body 43 having a surface resistance value R in this range can be employed if the occurrence of tailing is tolerated.

Further, the surface resistance value R of the heat roller body 43 is “1.0 × 10 ⁸ Ω ≦ R <1.0 × 10 ⁹ Ω” and “1.0 × 10 ⁹ Ω ≦ R <1.0 × 10 ¹⁰ Ω”. ”,“ Tailing ”is“ slightly good ”, and“ offset ”is“ very good ”. Therefore, if the heat roller body 43 has a surface resistance value R within this range, the heat roller The roller main body 43 can be preferably used as a tailing and offset prevention.

When the surface resistance value R of the heat roller body 43 is “1.0 × 10 ¹⁰ Ω ≦ R ≦ 1.0 × 10 ¹² Ω”, “tailing” is “good” but “offset”. Is “slightly good”.

Furthermore, when the surface resistance value R of the heat roller main body 43 is “1.0 × 10 ¹² Ω ≦ R <1.0 × 10 ¹³ Ω”, “tailing” is “very good”, and the tailing phenomenon. It can be said that there is no possibility of occurrence of “offset”, but “offset” is “bad”.

From the above test results, the “tailing” is less likely to occur as the surface resistance value R is higher, while the “offset” has a surface resistance value R within a predetermined range (1.0 × 10 ⁶ Ω). ~1.0 × 10 ¹² Ω) in the not occur if, but when it exceeds a case and this range of less than this range, it was possible to obtain a knowledge that offset occurs. That is, when the value of the surface resistance value R is increased in order to eliminate “tailing”, if it exceeds a certain value (1.0 × 10 ¹² Ω in this test result) as a boundary, “offset” Will occur.

  In the present invention, as described above, the tailing phenomenon is likely to occur on both side portions 435 (FIG. 5) of the heat roller main body 43, and the offset is the heat roller in which the paper P of all sizes always contacts. Focusing on the points that are likely to occur in the central portion 434 of the main body 43, the surface resistance value R is set to a value higher than that of the central portion 434 for both side portions 435 of the heat roller main body 43.

In the present embodiment, the surface resistance value R of the central portion 434 of the heat roller body 43 is set within the range of “1.0 × 10 ⁹ Ω ≦ R <1.0 × 10 ¹⁰ Ω” in Table 1, The surface resistance value R of both side portions 435 is set to “1.0 × 10 ¹⁰ Ω ≦ R ≦ 1.0 × 10 ¹² Ω”. That is, the surface resistance value R of the both side portions 435 of the heat roller main body 43 is a value obtained by multiplying the surface resistance value R of the central portion 434 by a value within the range of 1.0 × 10 ^{1 to} 1.0 × 10 ^3. It is only set high. By providing such a difference, it is possible to prevent the occurrence of “offset” as much as possible and to prevent occurrence of “tailing” at the same time.

1 is a perspective view showing an external appearance of an embodiment of an image forming apparatus to which a fixing device according to the present invention is applied. FIG. 2 is an explanatory diagram illustrating an outline of an internal structure of the image forming apparatus illustrated in FIG. 1. FIG. 4 is a perspective view showing an embodiment of a transfer / fixing unit. It is a figure which shows one Embodiment of a heat roller, (A) is a partially notched perspective view, (B) is the sectional view on the AA line of (A). It is a top view of the heat roller shown to (a) of FIG. It is a partial expanded sectional view of the longitudinal direction of a heat roller main body.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 11 Apparatus main body 12 Scanner part housing | casing 13 Bottom plate 14 Support shaft 20 Image forming part 21 Paper conveyance path 22 Photoconductor drum 23 Cleaning device 24 Charger 25 Developing device 26 Exposure apparatus 27 Transfer roller 30 Paper storage part 31 Paper Cassette 32 Lift plate 33 Feed roller 34 Feed roller pair 35 Manual feed tray 36 Registration roller 40 Fixing device 42 Heat roller 43 Heat roller main body 431 Cylindrical cored bar 432 Coating layer 433 Base 434 Central part 435 Side part 44 Socket 45 Halogen lamp 46 Connection Terminal 50 Scanner Unit 51 Optical System 52 Contact Glass 53 First Mirror Stand 531 First Mirror 54 Second Mirror Stand 541 Second Mirror 542 Third Mirror 55 Lens Unit 56 CCD 57 Document Press 58 Original Document Reader 60 Transfer / Fixing Unit 61 Unit Body 62 Bracket 621 Arc Concave 63 Guide Roller 64 Guide Rib 65 Guide Plate V In-Cylinder Discharge Space L1 A3 Size Paper Short Size L2 A4 Size Paper Short Size P Paper (Transfer Paper) )
D1 Distance between the top of the irregularities of the cylindrical cored bar and the surface of the coating layer D2 Distance between the top of the irregularities of the central part of the cylindrical cored bar and the surface of the coating layer

Claims (9)

A heat roller that heats the transfer sheet onto which the toner image on the photosensitive drum is transferred, and a pressure that is disposed opposite the heat roller so that the peripheral surfaces abut each other over substantially the entire length in the longitudinal direction. A fixing device for fixing a toner image to the transfer paper by passing the transfer paper between both rollers,
The heat roller includes a cylindrical cored bar and a coating layer formed on the entire peripheral surface of the cored bar,
The fixing device according to claim 1, wherein a surface resistance value of the heat roller is changed in a longitudinal direction.   The fixing device according to claim 1, wherein the surface resistance value of the heat roller is changed by changing a roughness in a longitudinal direction of a peripheral surface of the cored bar.   The fixing device according to claim 1, wherein the surface resistance value of the heat roller is changed by the coating layer side.   The surface resistance value of the coating layer is changed by using a plurality of types of coating materials having different resistance values in the longitudinal direction of the core metal peripheral surface. Fixing device.   5. The fixing device according to claim 1, wherein the heat roller has a surface resistance value at both sides set higher than a surface resistance value at a center portion. 6. The surface resistance value of the both side portions is set higher by a value obtained by multiplying the surface resistance value of the central portion by a value in the range of 1.0 × 10 ^{1 to} 1.0 × 10 ^3. Item 6. The fixing device according to Item 5.   5. The heat roller is set such that the surface resistance value at the center portion is set to be the lowest and is set to increase stepwise as it goes to both sides. A fixing device according to claim 1. The surface resistance values of the both side portions are set higher than the surface resistance value of the central portion by a value multiplied by a value within a range of 1.0 × 10 ^{1 to} 1.0 × 10 ^3. The fixing device according to claim 7.   An image forming apparatus to which the fixing device according to claim 1 is applied.

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