JP2005181838A - Fixing device and image forming apparatus loaded to the fixing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress image deterioration by preventing toner layer turbulence due to slipping between a belt and a heating roll surface layer. <P>SOLUTION: The heating roll 1401, a pressure roll 1411 pressed to the heating roll, the belt 1431 attached wrapped to the outer periphery of the pressure roll and moved while being held between the heating roll and a belt hanging member 1421 on which the belt is hung are provided and a heating source 101 is installed to the belt hanging member. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention provides a heating roll, a pressure roll that presses against the heating roll, a belt that is attached to the outer periphery of the pressure roll and is sandwiched and moved between the heating roll, and the belt is stretched. The present invention relates to a fixing device that includes a belt stretching member and fixes an unfixed toner image formed on a sheet material, and an image forming apparatus equipped with the fixing device.

  In image forming apparatuses such as copying machines, printers, and facsimiles, as a heating roll type fixing apparatus that heats and fixes an unfixed toner image on a transfer material, the surface is covered with an elastic body and can be rotated with a built-in heating source. A heating roll, a belt stretched by a plurality of support rolls, and a belt is wound around the heating roll by a predetermined angle to form a nip region, and at the outlet of the nip region, a pressure higher than other portions is locally applied. In addition, there has been proposed a fixing device (see Patent Document 1) that is provided with a pressure unit that causes distortion on the elastic body on the surface of the heat fixing roll, and facilitates the discharge of the sheet material from the nip portion.

  In this conventional fixing device, since the surface of the heat fixing roll has distortion in advance due to the presence of pressure means, the toner is in contact with the surface of the heat fixing roll at the exit of the nip region. The surface distortion is instantaneously released. For this reason, when the sheet material is discharged from the nip portion, the adhesion force between the toner and the heat fixing roll is reduced to prevent the sheet material from being wound around the heat fixing roll. Can be easily peeled off. In this way, the above-described apparatus eliminates the peeling claw that has been conventionally required.

  However, in the fixing device structure of Patent Document 1, a movable belt stretched around a plurality of support rolls is wound around a heating roll by an angle capable of forming a nip by pressure means, and locally at the outlet of the nip region. Since it is driven by applying a large pressure, a plurality of support rolls and their rotary bearings are required. Furthermore, the perimeter of the heat-resistant belt is increased, and the fixing device is not only complicated and large, but also expensive. The complicated, large and expensive construction of the fixing device inevitably makes the image forming apparatus equipped with the fixing device complicated, large and expensive.

  In addition, the belt is heated at a nip portion with a rotatable heat fixing roll with a built-in heating source, but in a configuration in which the belt is stretched by a plurality of support rolls to increase the peripheral length, the belt moves along a predetermined path. Sometimes, heat energy is deprived by a plurality of support rolls, and natural heat dissipation increases according to the length of the circumference. For this reason, it takes a long time to reach a predetermined temperature, and a so-called warm-up time from when the power is turned on to when fixing is required is not preferable.

  Further, in the configuration in which the belt is wound around the heating roll at an angle capable of forming a nip, and a pressure greater than that of other portions is locally applied at the exit of the nip portion to form distortion in the elastic layer of the heat fixing roll, the sheet material is heated Although it is suitable for suppressing wrapping around the roll, the sheet material discharged along the strain of the elastic layer may curl following this strain or generate wrinkles due to local high pressure. Bring deformation.

  In view of this, the present applicant, in Japanese Patent Application No. 2002-158920, can simplify the structure of the heat roll type fixing device, reduce the size, reduce the cost, reduce the warm-up time, reduce the stress on the sheet material, and curl We have proposed a fixing device that can suppress the deformation of discharged sheet material, such as the occurrence of defects and wrinkles.

This will be described with reference to FIG. The heating roll 1401 is coated with an elastic layer 1402 on the outer periphery of the cored bar 1403 and has a heating source 1405 inside, and rotates in the direction A in the figure. A pressure roll 1411 and a belt 1431 supported by a belt stretching roll 1421 are pressed against the surface layer 1404 of the heating roll 1401. The pressure roll 1411 is coated with an elastic layer 1413 on the outer periphery of the core bar 1412 and rotates in the B direction in the drawing. The sheet material enters from the C direction and is discharged in the D direction. The belt tension roll 1421 is swingable in the L direction in the drawing with the pressure roll 1411 as the center.
Patent No. 3084692

  FIG. 2 is an enlarged view of the nip portion of FIG. The nip is separated from the area Nr where the pressure roll 1411 is backed up, the area Nb where there is no backup, and the heating roll 1401 and the belt stretching roll 1421 are separated from each other by a gap gs when no paper is passed. The region Ns is a nip. The gap gs is smaller than the paper thickness and is set between several μm and 100 μm. A change in temperature at a specific position on the back of the paper when the nip portion is fed is indicated by a dotted line in FIG. When the paper back specific position enters the nip region Ns, the gap gs is smaller than the paper thickness, so the belt stretching roll 1421 is pressed against the heating roll 1401 through the paper to form the nip region Ns. Then, heat flows from the high-temperature belt tension roll 1421 into the back of the room temperature, and as a result, the temperature of the back of the paper rises to Tns4. Next, when the paper back enters the nip region Nb, the paper back temperature decreases to Tnb4. This is because the belt 1431 has a small thickness and a small heat capacity, so that the temperature immediately decreases due to heat radiation to the surroundings. Finally, when the paper back enters the nip region Nr, heat flows from the high-temperature pressure roll 1411 to the paper back of Tnb4, and as a result, the temperature of the paper back rises to Tnr4.

  The behavior of the toner layer at this time will be described with reference to the schematic diagrams of FIGS. 3 shows that the paper 1702 has just entered the nip area Ns, and FIG. 4 shows that the paper is passing through the nip area Ns. In FIG. 4, heat 1802 from the surface layer 1404 of the heating roll 1401 flows into the toner layer, a molten toner layer 1801 is generated on the surface of the toner layer, and the toner 1701 at the boundary between the toner layer and the paper 1702 is not melted. Indicates the state. While the paper passes through the nip area Nb, the state of FIG. 4 continues. FIG. 5 shows a state in which the paper is approaching the exit of the nip region Nr. Heat flows from the hot pressure roll 1411 to the back of the paper via the belt 1431 and the heat reaches the unfixed toner layer 1701. The entire toner layer becomes the molten toner layer 1801, indicating that the toner has been melted and fixed.

  However, when the paper 1702 is thick or there is a thick toner layer on the back of the paper in double-sided printing, the thermal resistance from the back of the paper to the boundary between the toner layer and the paper increases, and the heat inflow there decreases. As a result, the time shown in FIG. 4 becomes longer. Furthermore, in the case of the rear end of long-sized paper or continuous paper passing, the temperature of the belt 1431, the belt tension roll 1421, and the pressure roll 1411 decreases, and Tns4, Tnb4, and Tnr4 in FIG. The heat inflow to the boundary between the layer and the paper is reduced, and as a result, the time which is still in the state of FIG. 4 is lengthened.

  When the time in the state of FIG. 4 is long, when the belt 1431 and the heating roll surface layer 1404 are displaced, as shown in FIG. 6, the unfixed toner layer 1701 and the molten toner layer 1801 are displaced and the toner layer position is disturbed. End up. Therefore, in an electrophotographic system that expresses gray gradation with the arrangement interval of minute dots and fine lines, density unevenness occurs due to dot blurring and blurring, fine line distortion and blurring, and the like.

  The present invention solves the above-described conventional problems, and includes a fixing device capable of preventing toner layer disturbance due to a deviation between a belt and a heating roll surface layer and suppressing image deterioration, and an image forming apparatus equipped with the fixing device. The purpose is to provide.

Therefore, a fixing device of the present invention and an image forming apparatus equipped with the fixing device include a heating roll, a pressure roll pressed against the heating roll, and an outer periphery of the pressure roll. It is characterized by comprising a belt that is sandwiched between and moving, and a belt stretching member that stretches the belt, and a heating source is disposed on the belt stretching member.
In addition, the belt stretching member is disposed on the upstream side in the sheet material conveyance direction with respect to the pressure roll.
Further, the belt stretching member is a belt stretching roll, and a heat source is arranged in the belt stretching roll.
The belt stretching member is a belt sliding member on which a belt is slid, and a planar heating element is disposed on the belt sliding member.
Further, the belt sliding member is a half-moon shaped member.
The nip portion formed by the heating roll and the belt includes a nip region having a backup by a pressure roll, a nip region having a backup by a belt sliding member, and a nip region not having a backup, A belt temperature detection member is provided inside the belt in a region not having a backup, and the heating source is controlled based on a detection result of the belt temperature detection member.

  According to the present invention, it is possible to prevent the toner layer from being disturbed due to the deviation between the belt and the heating roll surface layer, and to suppress image deterioration.

  In addition, since the belt is wound around the heating roll by the cooperation of the pressure roll and the belt stretching member, a nip length can be easily formed, and the nip length can be easily increased, and the structure is simple, small and inexpensive. Can be. Further, when a belt sliding member is used as the belt stretching member, a bearing or the like is not necessary, and the support structure is simplified. In addition, when the belt stretching member is formed in a half-moon shape, the half-moon notch direction is arranged on the pressure roll side, and the arrangement close to the pressure roll is made possible to the limit. This also makes it possible to configure the belt with a reduced circumferential length. Therefore, the fixing device can be made simple and can be made small and inexpensive. Furthermore, since the belt moves in the minimum necessary path, the belt heated in the nip portion with the heating source built in and rotatable can minimize the heat energy lost when moving in the predetermined path. In addition to being able to be suppressed, since the perimeter is short, there is little temperature drop due to natural heat dissipation, and so-called warming time from when the power is turned on until it reaches a desired temperature and can be fixed can be shortened.

  Further, in order to stably fix an unfixed toner image formed on a sheet material, it is essential to sufficiently melt and fix the unfixed toner image, and a desired temperature and melting time are required. However, in the configuration according to the present invention, there is no need for a means to lengthen the nip length by greatly distorting the elastic body coated on the surface of the heat fixing roll in order to increase the nip length. It is configurable. In addition, it is not necessary to set the pressure contact pressure of the pressure roll to be large in order to distort the elastic body, and the sheet material carrying the unfixed toner image is applied to the sheet material that passes when passing between the heating roll and the belt. Since the stress is small, deformation of the sheet material such as wrinkles on the sheet material discharged after fixing the unfixed toner image is suppressed. Therefore, not only the mechanical rigidity of the fixing device need not be increased, but also the heating roll can be made thinner and the heating speed for heating the belt from the heating source is improved. Similarly, the pressure roll can also be made thin and thick, and the heat capacity can be made small, so that the heat energy absorption from the belt is small, so-called until the desired temperature is reached after the power is turned on and can be fixed. It is possible to shorten the warm-up time.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 7 is a cross-sectional view showing an embodiment of the fixing device of the present invention.

  In FIG. 7, the material of the core 1403 of the heating roll 1401 is an iron pipe, diameter 25 mm, thickness 0.45 mm, and the material of the elastic layer 1402 covered by the core 1403 is silicone rubber, thickness 0.5 mm, heating roll The material of the surface layer 1404 is PFA, the thickness is 30 μm, and the heat source 1405 built in the heating roll 1401 is two halogen lamps having a total of 1000 W, and is rotatable in the direction A in the figure.

  The material of the metal core 1412 of the pressure roll 1411 is an iron pipe, the diameter is 25 mm, the thickness is 0.4 mm, the material of the elastic layer 1413 covered by the metal core 1412 is silicone rubber, the thickness is 0.3 mm, and the heating roll 1401 The heating roller 1401 is pressed against the heating roll 1401 with a predetermined pressure so as to be rotatable in the direction B in the figure.

  The belt 1431 is an endless belt sandwiched between a heating roll 1401 and a pressure roll 1411 and stretched around the outer circumference of the pressure roll 1411 and the belt stretching member 1421. The material is polyimide, the diameter is 140 mm, the thickness is 90 μm and the outer surface layer is coated with PFA at a thickness of 30 μm.

  The material of the belt stretching member 1421 is an iron roll having a diameter of 20 mm and a thickness of 0.45 mm, and a heating source 101 is built therein. The belt tension roll 1421 is swingable in the L direction in the figure around the axis of the pressure roll 1411. The heating source 101 is a 100 W halogen lamp. The belt stretching member 1421 is disposed upstream of the nip portion between the heating roll 1401 and the pressure roll 1411 with respect to the paper (sheet material) conveyance directions C and D.

  The pressure roll 1411 is rotationally driven, and the belt 1431 and the heating roll 1401 are rotationally driven by a frictional force. A temperature sensor (not shown) detects the surface temperature of the heating roll 1401, controls the heating source 1405 of the heating roll 1401 on and off, and controls the temperature of the heating roll 1401 to approximately 180 ° C. Further, a temperature sensor (not shown) detects the surface temperature of the belt 1431, controls on / off of the heating source 101 of the belt stretching member 1421, and controls the surface temperature of the belt 1431 to about 120 ° C.

  In the present embodiment, in the enlarged view of the nip portion in FIG. 2, a belt stretching roll 1421 is disposed on the upstream side of the nip region Nb in the sheet material conveyance direction so as to face the heating roll 1401. Is provided with a heating source 101. As a result, the paper back temperature change at the time of paper feeding is as shown by the solid line in FIG.

  That is, the belt 1431 can be heated to a higher temperature by heating the belt 1431 with the heating source 101 of the belt tension roll 1421. Alternatively, it is possible to reduce the temperature drop of the belt 1431 at the rear end of the long paper and during continuous paper feeding. As a result, the temperatures Tns3, Tnb3, and Tnr3 higher than the temperatures Tns4, Tnb4, and Tnr4 of the conventional configuration can be obtained. The time can be shortened, and the state of FIG. 5 can be reached while passing through the nip region Ns. Therefore, the toner layer is not disturbed by the deviation between the belt 1431 and the heating roll surface layer 1404, and image deterioration can be suppressed.

  FIG. 9 shows the result of visual evaluation of the image quality by fixing the gray image by changing the paper type, paper size, and print mode level using the fixing device of FIG. As a comparative example, the result of fixing the belt stretching member 1421 with the heating source 101 turned off is also shown.

  FIG. 10 is a cross-sectional view showing another embodiment of the fixing device of the present invention. In the following description, the same components as those in the above embodiment are denoted by the same reference numerals and description thereof is omitted. In the embodiment of FIG. 7, the belt stretching member 1421 is a rotating member made of a roll. However, in this embodiment, a belt sliding member 301 on which the belt 1431 slides is disposed, and a fixing device is provided. It is possible to reduce the size.

  In addition, by using resin as the material of the belt sliding member 301, the amount of heat taken by the sliding member 301 during warm-up decreases, and the heating roll 1401, the pressure roll 1411, and the belt 1431 reach the target temperature sooner. Can be achieved. The specification of the part different from the embodiment of FIG. 7 will be described. The material of the belt sliding member 301 is polyamideimide, the half-moon shape is a half of a cylinder having a diameter of 18 mm, the sliding member heating source 302 is a panel heater, and is disposed in the nip region Ns on the outer peripheral surface of the belt sliding member 301. ing. The diameter of the belt 1431 is 120 mm.

  FIG. 11 is a cross-sectional view of the panel heater of FIG. A resistance heating element 303 having a main component of 20 μm thick silver is provided on a crystallized glass substrate 304 with a width of 6 mm and a thickness of 3 mm, and is covered with a protective layer 305 of 10 μm thickness and material PTFE. It has become. Electrodes (not shown) are provided at both ends of the resistance heating element 303 to serve as a wiring for applying a voltage. A belt temperature sensor (not shown) detects the surface temperature of the belt 1431, controls on / off of the sliding member 301 heating source 302, and controls the belt 1431 temperature to approximately 120 ° C.

  FIG. 12 shows the result of visual evaluation of the image quality by fixing the gray image by changing the paper type, paper size, and print mode level using the fixing device of FIG. As a comparative example, the result of fixing the belt sliding member 301 with the heating source 302 turned off is also shown. In FIG. 9, the JD paper A4 horizontal single side and J paper A4 horizontal double side, which were good images, have density unevenness in FIG. This is because the belt sliding member 301 made of resin has a smaller thermal conductivity than the belt stretching member 1421 made of metal, and cools as soon as heat is taken away from the back of the paper.

  In the case where a panel heater made of a resistance heating element 303 is used as the sliding member 301 heating source 302, unlike the halogen lamp, even if stepwise power control is performed, the life is not affected. This stepwise power control is a half of applying only a half-wave component as an intermediate between an on mode (power consumption 100 W) in which a commercial AC power source is applied to the sliding member heating source 302 and a non-application mode (power consumption 0 W). A mode (power consumption 50 W) is provided. In the half mode, as shown in FIG. 13, only the shaded portion of the commercial AC power supply waveform is extracted and applied to the sliding member heating source 302. Then, as shown in FIG. 14, by performing the step control according to the belt 1431 temperature, the belt 1431 temperature fluctuation can be made smaller than the on / off control.

  FIG. 15 shows the result of performing the above-described step control using the fixing device of FIG. 10, changing the paper type, paper size, and print mode level, fixing a solid black image, and visually evaluating the image quality. . As a comparative example, a result when the heating source 302 of the belt sliding member 301 is on / off controlled is also shown. As shown in FIG. 15, in the comparative example, as the paper is thinner and the paper size is longer, slight gloss unevenness occurs, but disappears in the example.

  This is probably because the thinner the paper, the more likely it is that the temperature of the belt 1431 rises and falls due to the on / off control of the sliding member heating source 302. Further, as the paper size is longer, the sliding member heating source 302 is more likely to be turned on / off in one sheet of paper, and the influence is likely to occur. It can be presumed that the temperature fluctuation of the belt 1431 can be made smaller in the embodiment than in the comparative example, so that some gloss unevenness disappeared.

  Next, using the fixing device of FIG. 10, in the enlarged nip view of FIG. 16, a belt temperature detection member 1101 is arranged inside the belt in the nip region Nb3 without backup, and the sliding member heating source is based on the temperature detection result. 302 was controlled on and off.

  FIG. 17 is a sectional view showing the belt temperature detecting member 1101 of FIG. The temperature detecting element 1201 is disposed at the protruding end of the sponge 1203, and the surface thereof is covered with a metal foil 1205, and further, the protective film 1206 is coated thereon. The sponge 1203 is disposed on the base 1204. A signal line 1202 for transmitting a signal of the temperature detection element 1201 passes between the sponge 1203 and the protective film 1206. Then, a load is applied in the direction of the arrow K so that the tip of the belt temperature detection member 1101 contacts the inside of the belt 1431. Note that the sponge 1203 is provided so that the front end of the belt temperature detection member 1101 always contacts the inside of the belt 1431 with respect to the position change of the belt 1431. Further, by providing the metal foil 1205, the influence of the vicinity temperature on the temperature detection element 1201 is excluded, and the temperature of the belt 1431 is efficiently transmitted. The protective film 1206 is provided to reduce the frictional force between the tip of the belt temperature detecting member 1101 and the belt 1431, maintain stable contact, and prevent wear.

  When the paper passes through the nip region Nb3, the paper back temperature decreases from Tns3 to Tnb3 as shown in FIG. At this time, the toner layer is in the state shown in FIG. 5, but when Tnb3 becomes equal to or lower than the glass transition temperature Tg of the toner, fine crystals 1301 of the toner resin are deposited as shown in FIG. Since the melting point of the microcrystal 1301 is much higher than Tg, it often remains after the paper passes through the nip region Nr3 and the temperature rises to Tnr3. For example, when a full-color image is formed on OHP paper, the transmitted light is irregularly reflected by the microcrystals 1301 and the projected image is darkened. Therefore, by arranging the belt temperature detecting member 1101 in the nip region Nb3, Tnb3 can be directly detected, and the sliding member heating source 302 is controlled to be on or off so as not to drop below Tg. As a result, microcrystal precipitation in the toner layer can be prevented, and the OHP projection image can be made clear.

  FIG. 19 shows the evaluation result of the OHP projected image. A toner with Tg = 120 ° C. was used, a magenta image was formed on OHP paper, and fixing was performed by changing the environmental temperature. The OHP image was projected by an OHP projector, and the projected image was visually evaluated. As a comparative example, the case where the belt temperature detecting member 1101 is brought into contact with the point Ps in FIG. 10 is also shown.

  FIG. 20 is a schematic cross-sectional view of the overall configuration showing an embodiment of an image forming apparatus according to the present invention. In the figure, 10 is an image forming apparatus, 10a is a housing, 10b is a door, 11 is a paper transport unit, 15 is a cleaning means, 17 is an image carrier, 18 is an image transfer transport means, 20 is a developing means, and 21 is a scanner. Means, 30 is a paper feeding unit, 40 is fixing means, W is an exposure unit, and D is an image forming unit.

  The image forming apparatus 10 of the present embodiment includes a housing 10a, a paper discharge tray 10c formed on the top of the housing 10a, and a door body 10b that is attached to the front surface of the housing 10a so as to be openable and closable. 1 includes an exposure unit (exposure means) W, an image forming unit D, a transfer belt unit 29 having an image transfer and conveyance means 18, and a paper feed unit 30, and a paper conveyance unit 11 is arranged in the door body 10b. ing. Each unit has a configuration that can be attached to and detached from the main body, and can be removed and repaired or replaced integrally during maintenance or the like.

  The image forming unit D includes image forming stations Y (for yellow), M (for magenta), C (for cyan), and K (for black) that form a plurality (four in this embodiment) of different color images. I have. In each of the image forming stations Y, M, C, and K, an image carrier 17 that is a photosensitive drum, a charging unit 19 that is a corona charging unit and a developing unit that are disposed around the image carrier 17 are provided. Means 20 are included. These image forming stations Y, M, C, and K are arranged in parallel on the lower side of the transfer belt unit 29 so that the image carrier 17 faces upward along an oblique arched line. The order of arrangement of the image forming stations Y, M, C, and K is arbitrary.

  The transfer belt unit 29 is disposed below the housing 10a and is driven to rotate by a drive source (not shown), a driven roll 13 disposed obliquely above the drive roll 12, a tension roll 14, An image transfer conveying means 18 composed of an intermediate transfer belt that is stretched between these three and at least two rolls and driven to circulate in the direction of the arrow in the figure, and a cleaning means 15 that contacts the surface of the image transfer conveying means 18. I have. The driven roll 13, the tension roll 14, and the image transfer / conveying means 18 are arranged in a direction inclined to the left in the drawing with respect to the drive roll 12, and thereby the belt conveying direction when driving the image transfer / conveying means 18 is downward. The belt surface 18a is positioned below, and the belt surface 18b whose transport direction is upward is positioned above.

  Accordingly, the image forming stations Y, M, C, and K are also arranged in a direction inclined to the left in the drawing with respect to the drive roll 12. Then, the image carrier 17 is brought into contact with the belt surface 18a facing downward in the transport direction of the image transfer transport unit 18 along the arched line, and is rotationally driven in the transport direction of the image transfer transport unit 18 as indicated by the arrows in the drawing. The The flexible endless sleeve-shaped image transfer / conveyance means 18 is brought into contact with the image carrier 17 from substantially the same wrapping angle so as to be covered from above, so that the image carrier 17 and the image transfer / conveyance means 18 are in contact with each other. The contact pressure and the nip width between them can be adjusted by controlling the tension applied to the image transfer / conveying means 18 by the tension roll 14, the arrangement interval of the image carrier 17, the winding angle (arch curvature), and the like. .

The drive roll 12 also serves as a backup roll for the secondary transfer roll 39. A rubber layer having a thickness of, for example, about 3 mm and a volume resistivity of 10 ⁵ Ω · cm or less is formed on the peripheral surface of the drive roll 12, and the secondary transfer roll is grounded through a metal shaft. This is a conductive path for the secondary transfer bias supplied via the line 39. Thus, by providing the drive roll 12 with a rubber layer having high friction and shock absorption, it is difficult for the impact when the sheet material enters the secondary transfer portion to be transmitted to the image transfer conveying means 18, and the image quality is deteriorated. Can be prevented. Further, by making the diameter of the driving roll 12 smaller than the diameter of the driven roll 13 and the backup roll 14, the sheet material after the secondary transfer can be easily peeled off by the elastic force of the sheet material itself. Further, the driven roll 13 is also used as a backup roll for the cleaning means 15 described later.

  The image transfer / conveying means 18 is arranged in a direction inclined to the right in the drawing with respect to the drive roll 12, and correspondingly, each of the image forming stations Y, M, C, K is also illustrated with respect to the drive roll 12. Then, it may be arranged along the oblique arch shape in the direction inclined to the right side, that is, on the left and right objects in FIG.

  Suitable materials for the image transfer / conveyance means include PC resin, PET resin, polyimide resin, urethane resin, silicon resin, polyether resin, polyester resin, etc. Of course, conductivity, rigidity, etc. For the purpose of setting the degree, friction coefficient and the like to desired characteristics, a corresponding additive or the like may be added, and the rigidity can be set to a desired rigidity by setting the thickness.

  In this embodiment, the image transfer / conveying means is formed of urethane resin and polyether resin which are relatively small in rigidity and have permanent distortion and no creep, and the tension is 40 N by the urging force of the roll, and the winding angle of the image carrier is 4 °. The contact pressure acting on the nip portion was set to about 2.8 N (= 40 N × sin 4 °), and stable transfer conditions were set. However, in consideration of the above-mentioned materials, the desired transfer conditions can be set by setting a combination of a tension of 10N to 100N and a winding angle of the image carrier of 0.5 ° to 15 ° by the urging force of the roll. It was confirmed that it was possible.

  The primary transfer member 16 is disposed at a position in contact with the inner side of the image transfer conveying means as a transfer bias applying means for forming an image by sequentially superimposing and transferring the toner images, but applying the contact pressure as described above. Therefore, it is not necessary to apply a pressing force for forming the transfer nip. Simply contact with the image transfer / conveying means as a means capable of ensuring energization, for example, a conductive roll or rigid contactor rotating in contact with the image transfer / conveying means, or a conductive elastic member such as a leaf spring, resin A conductive brush formed by a group of fibers such as can also be configured. Accordingly, the sliding resistance with the image transfer / conveying means is small, and not only can the lifetime of each other be improved, but also it can be constructed at low cost.

  As described above, in the image forming apparatus according to the present embodiment, a plurality of image carriers 17 are arranged in parallel, and the endless sleeve-like shape is flexible with a posture having substantially the same winding angle with respect to each image carrier 17. The image transfer / conveying means 18 is placed in contact and stretched around at least two rolls 12 and 13 and rotated. The image transfer / conveying means 18 is applied with tension by any of the rolls 12 and 13 to carry an image. The toner image on the body 17 is configured to be transferred in a superimposed manner. In this way, substantially the same nip is easily formed at the contact portion between the image carrier 17 and the image transfer conveying means 18 according to substantially the same winding angle, and the contact pressure at the contact portion is also substantially the same. Composed.

  On the other hand, in the image transfer member 17 and the image transfer / conveying means 18 driven in contact therewith, it is preferable that the moving peripheral speeds of the contact portions coincide with each other. It is not realistic to set the speed completely at a constant speed due to variations in the outer diameter of 17 or the eccentricity or the eccentricity of the driving means, the diameter of the driving roll 12 of the image transfer conveying means 18, or the driving means.

  Therefore, when these variations are taken into consideration, the moving speed of the image transfer / conveying means 18 becomes relatively fast or slow with respect to the moving speed of the image carrier 17, and the transfer conditions are set. This is not preferable. Rather, it is preferable to provide a relative speed difference that is shifted to one of the image carrier 17 and the relative speed. However, if an extreme speed difference is provided, the toner image transported by the image carrier 17 is transferred to the image transfer transport means 18, and the position of the toner image is shifted to cause image disturbance. It is preferable to provide a speed difference.

  When the speed difference caused by the above contents is set to a relative speed difference shifted to one of the plurality of image carriers 17, the speed difference is calculated in consideration of the ability from mass production and the limit of image disturbance. The speed of the image transfer / conveying means 18 with respect to the moving speed of the image carrier 17 is preferably about ± (direction) 3 ± (variation) 2%.

  Further, when the moving speed of the image carrier 17 and the moving speed of the image transfer / conveying means 18 are constant, the toner image is transferred by the electric energy action of the transfer bias, but when the above speed difference is provided. Since the mechanical scraping action is added in addition to the electric energy action to improve the transfer efficiency, the process of cleaning the transfer residual toner on the image carrier 17 can be eliminated or simplified.

  Further, if a relative speed difference is provided between the moving speed of the image carrier 17 and the moving speed of the image transfer / conveyance means 18, the flexible image transfer / conveyance means 18 is placed between the drive rollers 12 or to the image carrier 17. It is not preferable because slack occurs between the contact nips. Therefore, when the speed of the image transfer / conveyance means 18 is shifted in the fast direction with respect to the image carrier 17, the drive roll 12 of the image transfer / conveyance means 18 is disposed on the downstream side, and When shifting the speed of the transfer / conveyance means 18 in the slow direction, if the drive roll 12 of the image transfer / conveyance means 18 is arranged on the upstream side, the occurrence of the slack can be prevented, and a preferable transfer condition can be set.

  The cleaning unit 15 is provided on the side of the belt surface 18a facing downward in the transport direction, and a cleaning blade 15a that removes toner remaining on the surface of the image transfer transport unit 18 after the secondary transfer, and a toner transport that transports the collected toner A member 15b is provided. The cleaning blade 15 a is in contact with the image transfer / conveyance means 18 at a portion where the image transfer / conveyance means 18 is wound around the driven roll 13. Further, a primary transfer member 16 is brought into contact with the back surface of the image transfer conveying unit 18 so as to face an image carrier 17 of each of the image forming stations Y, M, C, and K described later. A transfer bias is applied.

  The exposure means W is disposed in a space formed obliquely below the image forming unit D disposed in the oblique direction. A paper feeding unit 30 is disposed below the exposure unit W and at the bottom of the housing 10a. The exposure means W is entirely housed in a case, and the case is disposed in a space formed obliquely below the belt surface facing downward in the transport direction. A single scanner means 21 comprising a polygon mirror motor 21a and a polygon mirror (rotating polygon mirror) 21b is horizontally disposed at the bottom of the case, and a plurality of laser light sources 23 modulated by image signals of respective colors. In the optical system B that reflects and scans the laser beam by the polygon mirror 21b and deflects and scans the image carrier, the single f-θ lens 22 and the scanning light path of each color are not parallel to the image carrier 17 respectively. A plurality of reflecting mirrors 24 are arranged so as to be folded.

  In the exposure means W configured as described above, an image signal corresponding to each color is emitted from the polygon mirror 21b with a laser beam modulated and formed based on a common data clock frequency, and the f-θ lens 22 and the reflection mirror 24 are passed through. After that, the image carrier 17 of each image forming station Y, M, C, K is irradiated to form a latent image. By providing the reflection mirror 24, the scanning optical path can be bent, the height of the case can be lowered, and the optical system can be made compact. In addition, the reflection mirror 24 is arranged so that the scanning optical path lengths to the image carrier 17 of the image forming stations Y, M, C, and K are the same. In this way, the length of the optical path from the polygon mirror 21b of the exposure means W to the image carrier 17 to the image carrier 17 (optical path length) for each image forming unit D is configured to be substantially the same, thereby scanning in each optical path. The scanning widths of the emitted light beams are also substantially the same, and no special configuration is required for image signal formation. Therefore, the laser light source can be modulated and formed based on a common data clock frequency even though it is modulated corresponding to images of different colors by different image signals, and uses a common reflecting surface. Color misregistration caused by a relative difference in the sub-scanning direction can be prevented, and a simple and inexpensive color image forming apparatus can be configured.

  Further, in this embodiment, by arranging the scanning optical system below the apparatus, the vibration of the scanning optical system due to the vibration that the drive system of the image forming means gives to the frame that supports the apparatus can be minimized. Degradation of image quality can be prevented. In particular, by arranging the scanner means 21 at the bottom of the case, the vibration that the polygon motor 21a itself gives to the entire case can be minimized, and deterioration of the image quality can be prevented. Further, by making the number of polygon motors 21a, which are vibration sources, one, vibration applied to the entire case can be minimized.

  The sheet feeding unit 30 includes a sheet feeding cassette 35 in which sheet materials are stacked and held, and a pickup roll 36 that feeds sheet materials from the sheet feeding cassette 35 one by one. The paper transport unit 11 includes a pair of gate rolls 37 (one roll is provided on the housing 10a side) that regulates the timing of feeding the sheet material to the secondary transfer unit, the drive roll 12 and the image transfer transport means 18. A secondary transfer roll 39 serving as a secondary transfer unit pressed against the main recording medium, a main recording medium conveyance path 38, a fixing unit 40, a discharge roll pair 41, and a duplex printing conveyance path 42.

  The secondary image (unfixed toner image) secondarily transferred to the sheet material is fixed at a predetermined temperature at the nip portion formed by the fixing unit 40. In the present embodiment, the fixing unit 40 is disposed in a space formed obliquely above the belt surface 18b facing upward in the transfer belt conveyance direction, in other words, in a space opposite to the image forming station with respect to the transfer belt. Therefore, heat transfer to the exposure unit W, the image transfer conveyance unit 18, and the image formation unit can be reduced, and the frequency of performing the color misregistration correction operation for each color can be reduced. In particular, the exposure means W is located farthest from the fixing means 40, and the displacement of the scanning optical system components due to heat can be minimized, thereby preventing color misregistration. In addition, 1 is a heating roll, 2 is a pressure roll, 3 is a belt, 4 is a belt sliding member.

  In the present embodiment, the image transfer / conveyance means 18 is arranged in a direction inclined with respect to the drive roll 12, so that a wide space is created in the right side space in the drawing, and the fixing means 40 can be arranged in that space. In addition, downsizing can be realized, and heat generated by the fixing unit 40 is transmitted to the exposure unit W, the image transfer conveyance unit 18 and the image forming stations Y, M, C, and K located on the left side. Can be prevented. Further, since the exposure unit W can be arranged in the space on the lower left side of the image forming unit D, the vibration of the scanning optical system of the exposure unit W due to the vibration applied to the housing 10a by the drive system of the image forming means is minimized. The image quality can be suppressed and deterioration of the image quality can be prevented.

  In this embodiment, the use of the spherical toner increases the primary transfer efficiency (approximately 100%), and each image carrier 17 is provided with a cleaning means for collecting the primary transfer residual toner. Not done. Thereby, it becomes possible to arrange each image carrier 17 composed of a photosensitive drum having a diameter of 30 mm or less close to each other, and the apparatus can be miniaturized.

  Further, the corona charging means 19 is adopted as the charging means in accordance with the absence of the cleaning means. When the charging unit is a roll, a small amount of primary transfer residual toner that is present on the image carrier 17 accumulates on the roll to cause a charging failure, but the corona charging unit 19 that is a non-contact charging unit. Can prevent toner from adhering and can prevent charging failure.

  In the above-described embodiment, the intermediate transfer belt is configured to come into contact with the image carrier 17 as the image transfer conveyance unit 18. However, the sheet material is adsorbed and conveyed to the surface, and a toner image is formed on the surface of the sheet material. A sheet material conveyance belt that forms and conveys an image by sequentially superimposing and transferring the image may be configured to contact the image carrier 17 as the image transfer conveyance means 18. In this case, the difference from each of the above embodiments is that the belt conveyance direction of the sheet material conveyance belt which is the image transfer conveyance means 18 is upward in the opposite direction on the lower surface in contact with the image carrier 17.

The outline of the operation of the entire image forming apparatus as described above is as follows.
(1) When a print command signal (image forming signal) from a host computer or the like (not shown) is input to the control unit of the image forming apparatus 10, the image of each image forming station Y, M, C, K is displayed. The carrier 17, each roll of the developing unit 20, and the image transfer / conveying unit 18 are driven to rotate.
(2) The outer peripheral surface of the image carrier 17 is uniformly charged by the charging means 19.
(3) The exposure unit W selectively exposes the outer peripheral surface of the image carrier 17 that is uniformly charged in each image forming station Y, M, C, K according to the image information of each color. An electrostatic latent image is formed.
(4) The toner image is developed by the developing means 20 from the electrostatic latent image formed on each image carrier 17.
(5) The primary transfer member 16 of the image transfer conveying means 18 is applied with a primary transfer voltage having a polarity opposite to the charged polarity of the toner, so that the toner image formed on the image carrier 17 is transferred to the primary transfer portion. As the conveying means 18 moves, the images are sequentially transferred onto the image transfer conveying means 18.
(6) In synchronism with the movement of the image transfer conveying means 18 that primarily transferred the primary image, the sheet material stored in the paper feed cassette 35 is fed to the secondary transfer roll 39 through the resist roll pair 37. Is done.
(7) The primary transfer image is a secondary transfer roll 39 that is synchronously joined with the sheet material at the secondary transfer portion and pressed toward the drive roll 12 of the image transfer conveyance unit 18 by a pressing mechanism (not shown). A bias having a polarity opposite to that of the next transfer image is applied, and the primary transfer image formed on the image transfer conveyance unit 18 is secondarily transferred to the sheet material fed in synchronization.
(8) The transfer residual toner in the secondary transfer is conveyed in the direction of the driven roll 13 and scraped off by the cleaning means 15 disposed opposite to the roll 13, and the image transfer conveyance means 18 is It is refreshed and the cycle can be repeated again.
(9) When the sheet material passes through the fixing unit 40, the toner image on the sheet material is fixed, and then the sheet material is directed to a predetermined position (if it is not double-sided printing, the double-sided printing is directed to the discharge tray 10c). In this case, it is conveyed toward the conveyance path 42 for double-sided printing).

  Although the embodiment of the present invention has been described above, the present invention is not limited to this, and a conventionally known or well-known technique can be replaced or added as necessary.

It is sectional drawing which shows the fixing device of Japanese Patent Application No. 2002-158920 (prior application). It is an enlarged view of the nip part of FIG. FIG. 3 is a schematic diagram for explaining the behavior of a toner layer in FIG. 2. FIG. 3 is a schematic diagram for explaining the behavior of a toner layer in FIG. 2. FIG. 3 is a schematic diagram for explaining the behavior of a toner layer in FIG. 2. It is a figure for demonstrating the subject of this invention, and is a schematic diagram for demonstrating the behavior of a toner layer. 1 is a cross-sectional view showing an embodiment of a fixing device of the present invention. It is a figure which shows the temperature change of the specific position of the paper back at the time of nip part paper feeding of FIG. It is a figure for demonstrating the result of the visual evaluation of the image using the fixing device of FIG. It is sectional drawing which shows other embodiment of the fixing device of this invention. It is sectional drawing which shows the heating source of FIG. It is a figure for demonstrating the result of the visual evaluation of the image using the fixing device of FIG. It is a figure for demonstrating the step control of FIG. It is a figure for demonstrating the step control of FIG. It is a figure for demonstrating the result of the visual image evaluation at the time of carrying out step control using the fixing device of FIG. It is an enlarged view of the nip part of FIG. It is sectional drawing which shows the belt temperature detection member of FIG. It is a schematic diagram of a toner layer. It is a figure for demonstrating the result of the visual evaluation of the image using the fixing device of FIG. 10, and the belt temperature detection member of FIG. 1 is a configuration diagram showing an embodiment of an image forming apparatus of the present invention.

Explanation of symbols

101, 302 ... heating source, 301 ... belt sliding member, 1101 ... belt temperature detecting member
1401 ... Heating roll, 1411 ... Pressure roll, 1421 ... Belt tension member, 1431 ... Belt

Claims (7)

A heating roll; a pressure roll pressed against the heating roll; a belt that is attached to the outer periphery of the pressure roll and sandwiched between the heating rolls; and a belt stretcher that stretches the belt And a heating source disposed on the belt stretching member. The fixing device according to claim 1, wherein the belt stretching member is disposed on the upstream side in the sheet material conveyance direction with respect to the pressure roll. The fixing device according to claim 2, wherein the belt stretching member is a belt stretching roll, and a heat source is disposed in the belt stretching roll. The fixing device according to claim 2, wherein the belt stretching member is a belt sliding member on which a belt is slid, and a planar heating element is disposed on the belt sliding member. The fixing device according to claim 4, wherein the belt sliding member is a half-moon shaped member. The nip formed by the heating roll and the belt includes a nip area having a backup by a pressure roll, a nip area having a backup by a belt sliding member, and a nip area having no backup, and the backup is performed. The fixing device according to claim 4, further comprising a belt temperature detection member inside the belt in a region not having the belt, and controlling the heating source based on a detection result of the belt temperature detection member. An image forming apparatus comprising the fixing device according to claim 1.

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