JP2005258263A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of preventing the generation of problems such as hot offset and separation defects which may be caused by a difference of glossiness between the first face (surface) and the 2nd face (rear face) and overheat applied to the surface because the quantity of heat fixed on the first face is larger than that of the second face even in both-side printing. <P>SOLUTION: The image forming apparatus provided with an image carrier on which a toner image is formed, a transfer means for transferring the toner image to a recording material and a plurality of fixing means for fixing the toner image transferred to the recording material comprises a means for forming images on both the faces of the recording material, a means for storing whether the face of the recording material is the first face or the second face and a means for switching the states of the plurality of fixing means. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a copying machine, a facsimile, or a printer that uses an electrophotographic system to form an image on a recording material to obtain a hard copy.

  Conventionally, the following is known as an image forming apparatus including a fixing device having a plurality of fixing units.

  (1) According to Patent Document 1, two sets of fixing rollers each including a pair of a heat roller and a pressure roller that are pressed against each other are provided, and the paper on which the toner image is transferred is pressed on the first and second levels. It is disclosed that the toner image after fixing is made glossy by passing through a portion, and it is known that a glossy image can be obtained by using two sets of fixing devices.

  (2) According to Patent Document 2, in a fixing device that passes a sheet on which an unfixed toner image is formed through a fixing device nip and fixes the unfixed toner image on the sheet, a plurality of sheets arranged in series in the sheet passing direction A fixing device is disclosed in which the gloss of a printed image can be arbitrarily adjusted by switching the number and position of nips formed in the fixing device.

  (3) Patent Document 3 discloses that the first surface of double-sided printing is preliminarily heated by re-heating the surface on the side to be re-transferred after re-feeding the image once printed on both sides of the transfer paper. It is disclosed that the gloss difference of the image on the second side is reduced.

  As described above, many examples of an image forming apparatus that outputs a high-gloss image using two fixing devices and examples of adjusting gloss are proposed.

JP-A-4-245275 JP 2000-221821 A JP-A-9-034180

  In recent years, there has been a growing demand for image forming apparatuses such as copiers and printers to fix unfixed images on recording media to recording media of various paper types from thin paper to thick paper. ing.

  Furthermore, there is an increasing demand for a fixing method capable of adjusting the gloss of the image surface depending on whether the gloss of the recording paper is high or low. In addition, while satisfying these requirements, it is also necessary to maintain high productivity without reducing the throughput for various recording media.

  However, there is a problem that cannot be solved even in the fixing device that attempts to adjust the gloss of the recording material as described above.

  That is, (1) In the case of Patent Document 1 (Japanese Patent Laid-Open No. 4-245275), there is a problem that the glossiness of the image cannot be adjusted according to the recording type.

  In (2) Patent Document 2 (Japanese Patent Laid-Open No. 2000-221821), the number of use of a plurality of fixing devices is changed by switching the position of the fixing roller. There was a problem of falling.

  Furthermore, in (3) Patent Document 3 (Japanese Patent Laid-Open No. 9-034180), it is less effective to merely preheat the surface to be retransferred at the time of duplex printing, especially when a high gloss image is formed. There was a problem that it was not effective.

  Therefore, according to the present invention, in an image forming apparatus including a plurality of fixing units, the front surface and the back surface are derived from the fact that the first surface (front surface) is fixed more than the second surface (back surface) even during duplex printing. An object of the present invention is to provide an image forming apparatus in which problems such as hot offset and poor separation due to the difference in gloss and the amount of heat received on the surface do not occur.

In order to achieve the above object, an invention according to claim 1 is directed to an image carrier on which a toner image is formed, transfer means for transferring the toner image to a recording material, and a toner image transferred onto the recording material. In an image forming apparatus provided with a plurality of fixing means for fixing,
A means for forming an image on both sides of the recording material, a means for storing whether the image is the first surface or the second surface, and depending on whether the image formation surface is the first surface or the second surface, It has a means for switching the states of a plurality of fixing means.

  The invention described in claim 2 is characterized in that, in the invention described in claim 1, as means for switching the states of the plurality of fixing means, means for switching the conveyance path of the recording material between the plurality of fixing devices is provided.

  The invention described in claim 3 is characterized in that, in the invention described in claim 1, as means for switching the states of the plurality of fixing means, means for switching the number of times the recording material passes through the plurality of fixing devices is provided.

  According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, the number of times of fixing is smaller when fixing the first side when forming a double-sided image than when fixing the second side. The state is switched.

  The invention according to claim 5 is the invention according to any one of claims 1 to 3, wherein the amount of heat received by the recording material from the fixing means is greater than the amount of heat received from the front side of the recording surface from the back side. It is characterized by that.

  According to a sixth aspect of the present invention, in the invention according to any one of the first to third aspects, the fixing unit includes a heating member and a pressure member, and the temperature of the heating member is higher than the temperature of the pressure member. It is characterized by that.

  According to the present invention, an image carrier on which a toner image is formed, a transfer unit that transfers the toner image to a recording material, and a plurality of fixing units that fix the toner image transferred onto the recording material are provided. The image forming apparatus has means for forming an image on both sides of the recording material, and has means for storing whether the first side or the second side, and whether the image forming side is the first side or the second side Accordingly, since it has a means for switching the states of the plurality of fixing means, it is possible to eliminate the difference in gloss between the front surface and the back surface during double-sided printing.

  Further, as a means for switching the states of the plurality of fixing means, a means for switching the conveyance path of the recording material between the plurality of fixing devices is provided, or as a means for switching the states of the plurality of fixing means, Since the means for switching the number of times the material passes between the plurality of fixing devices is provided, the state of the fixing means is smoothly switched, and a large number of copies can be guaranteed.

  Further, the state is switched so that the number of times of fixing is smaller when fixing the first side than when fixing the second side when forming a double-sided image, or as the amount of heat that the recording material receives from the fixing unit The amount of heat received from the front side of the recording surface is greater than the amount of heat received from the back side, or the fixing means comprises a heating member and a pressure member, and the temperature of the heating member is the temperature of the pressure member. It is possible to reduce the amount of heat on the first side and solve problems such as gloss difference on both sides, hot offset and poor separation due to excessive amount of heat. .

<Embodiment 1>
Embodiment 1 of an image forming apparatus according to the present invention will be described with reference to FIG.

  In the apparatus shown in FIG. 1, first, second, third, and fourth image forming portions Pa, Pb, Pc, and Pd are arranged in parallel, and toner images of different colors are used for latent images, development, and transfer. Formed through a process.

  Each of the image forming units Pa, Pb, Pc, and Pd includes a dedicated image carrier, in this example, electrophotographic photosensitive drums 3a, 3b, 3c, and 3d, on the photosensitive drums 3a, 3b, 3c, and 3d. A toner image of each color is formed. An intermediate transfer member 130 is installed adjacent to the photosensitive drums 3a, 3b, 3c, and 3d, and the toner images of the respective colors formed on the photosensitive drums 3a, 3b, 3c, and 3d are primarily transferred onto the intermediate transfer member 130. Then, it is transferred onto the recording material P at the secondary transfer portion. Further, the recording material P to which the toner image has been transferred is fixed to the toner image by heating and pressurizing at the fixing portions 9a and 9b, and then discharged out of the apparatus as a recorded image.

  Drum chargers 2a, 2b, 2c, and 2d, developing devices 1a, 1b, 1c, and 1d, primary transfer chargers 24a, 24b, 24c, and 24d, and cleaners are disposed on the outer periphery of the photosensitive drums 3a, 3b, 3c, and 3d, respectively. 4a, 4b, 4c, and 4d are provided, and a light source device and a polygon mirror (not shown) are further provided above the apparatus.

  The laser light emitted from the light source device is scanned by rotating the polygon mirror, the light beam of the scanning light is deflected by the reflection mirror, and condensed on the buses of the photosensitive drums 3a, 3b, 3c, 3d by the fθ lens. By exposing, latent images corresponding to the image signals are formed on the photosensitive drums 3a, 3b, 3c, and 3d.

  The developing units 1a, 1b, 1c, and 1d are filled with a predetermined amount of cyan, magenta, yellow, and black toners as developers, respectively, by a supply device (not shown). The developing devices 1a, 1b, 1c, and 1d develop the latent images on the photosensitive drums 3a, 3b, 3c, and 3d, respectively, and visualize them as cyan toner images, magenta toner images, yellow toner images, and black toner images.

  The intermediate transfer member 130 is driven to rotate in the direction of the arrow at the same peripheral speed as that of the photosensitive drum 3.

  The yellow toner image of the first color formed and supported on the photosensitive drum 3a is subjected to a primary transfer bias applied to the intermediate transfer member 130 in the process of passing through the nip portion between the photosensitive drum 3 and the intermediate transfer member 130. The intermediate transfer is performed on the outer peripheral surface of the intermediate transfer body 130 by the formed electric field and pressure.

Reference numeral 11 denotes a secondary transfer roller, which corresponds to the intermediate transfer member 130 and is provided in parallel and in contact with the lower surface portion. A desired secondary transfer bias is applied to the secondary transfer roller 11 by a secondary transfer bias source. Transfer of the composite color toner image superimposed and transferred onto the intermediate transfer member 130 to the recording material P passes from the paper feed cassette 10 through the registration roller 12 and the pre-transfer guide, and the intermediate transfer member 130 and the secondary transfer roller 11. The recording material P is fed to the contact nip at a predetermined timing, and at the same time, a secondary transfer bias is applied from a bias power source. The composite color toner image is transferred from the intermediate transfer body 130 to the recording material P by the secondary transfer bias.
Similarly, the second color magenta toner image, the third color cyan toner image, and the fourth color black toner image are sequentially superimposed and transferred onto the intermediate transfer body 130, and a composite color toner image corresponding to the target color image is obtained. Is formed.

  After the primary transfer, the photosensitive drums 3a, 3b, 3c, and 3d are cleaned and removed of the transfer residual toner by the respective cleaners 4a, 4b, 4c, and 4d, and are subsequently prepared for forming the next latent image. The toner and other foreign matters remaining on the transfer belt 130 are wiped off by bringing a cleaning web (nonwoven fabric) 19 into contact with the surface of the transfer belt 130.

  The transfer material P that has received the transfer of the toner image is sequentially introduced into the fixing devices 9a and 9b, and is fixed by applying heat and pressure to the transfer material.

  FIG. 3 shows a basic configuration of a heat roller type fixing device as a specific example of the fixing device. This fixing device has a release property on the surface of a cylindrical metal core 71 containing a halogen lamp heater 56 as a heating body. The fixing roller 51 provided with the layer 70 and the pressure roller 52 provided with a heat-resistant rubber layer 72 around the bar-shaped cored bar 73 and further formed with a releasable layer 70 on the surface thereof. The recording material P is conveyed at the nip portion, and at the same time, the toner is fixed to the recording material P by heat and pressure. In a color fixing device, silicone oil is used instead of the release layer 70 on the surface of the fixing roller 51. Some of them use a silicone rubber layer impregnated with. In addition, a thermistor (not shown) is arranged in contact with or not in contact with the fixing roller 51, and the temperature of the surface of the fixing roller 51 is adjusted by controlling the voltage to the heater via a temperature adjustment circuit. .

  Next, the fixing units 9a and 9b studied in the present embodiment will be described in more detail with reference to FIG. The two fixing devices 9a and 9b are identically used under the same conditions.

  As the fixing roller 51, a fixing roller having an outer diameter of φ80 mm, in which 2.5 mm of silicone rubber is molded on a hollow cored bar made of Al having an outer diameter of φ75.0 mm, and a PFA tube having a thickness of 30 μm is coated on the surface thereof. . Further, a halogen heater was used inside the fixing roller 51, and the surface temperature was adjusted to 170 ° C. by a temperature sensor (not shown) and a temperature control circuit (not shown).

  The pressure roller 52 is provided with a 2.0 mm elastic layer 72 made of silicone rubber around a hollow core metal 73 made of Al having an outer diameter of φ76 mm, and further coated with a 30 μm-thick PFA tube on the surface thereof to have an outer diameter of φ80 mm. The fixing roller 51 was pressurized with a total pressure of 70 kgf and rotated. Further, a halogen heater was used inside the pressure roller 52, and the surface temperature was adjusted to 140 ° C. by a temperature sensor (not shown) and a temperature control circuit (not shown).

  Next, a fixing condition switching method in the present embodiment will be described.

  First, the case of single-sided printing will be described.

  After the recording material that has passed through the secondary transfer portion is fixed for the first time by the first fixing device 9a, if the recording material is glossy, such as coated paper, the second fixing device 9b is used as it is. After the second fixing, the paper is discharged to a paper discharge tray 63 outside the main body.

  If the image does not require gloss, it passes through the first fixing device 9a and then does not pass through the second fixing device 9b, but passes through the second fixing avoidance path as shown in the figure, and the paper discharge tray 63. The paper is discharged.

  Next, the case of duplex printing will be described.

  First, at the time of printing on the first surface (hereinafter referred to as the front surface), the recording material after the first fixing by the first fixing device 9a does not pass through the second fixing device 9b but passes through the avoidance path. Thereafter, after the front and back sides of the recording material are reversed through a reversal pass, an image is formed on the second surface (hereinafter referred to as the back surface).

  When printing on the back side, the recording material that has passed through the secondary transfer section needs to have a glossy image like the coated paper after the first fixing by the first fixing device 9a, as in the case of single-sided printing. In this case, the sheet passes through the second fixing device 9b as it is, and after the second fixing is performed, the sheet is discharged to a discharge tray 63 outside the main body.

Fixing when the fixing roller side is in contact with the image surface (front surface fixing) is called front fixing, and fixing when the pressure roller side is in contact (back surface fixing) is called back fixing. The number of times of fixing of the front surface is: front fixing once + back fixing twice; back surface: front fixing twice. Actually, the back side is fixed once, but at that time, the image is still only on the front side and the back side is in a blank state, so the influence on the gloss of the image is small.

  On the other hand, the pressure roller is in contact with the image surface at the time of backside fixing. However, since the temperature control of the pressure roller is kept lower than that of the fixing roller, the amount of heat received during backside fixing is smaller than the amount of heat received during frontside fixing. . As a result, the amount of heat received by the front and back image planes can be made substantially the same.

  As described above, by changing the usage state of the first fixing device and the second fixing device at the time of front side printing and back side printing at the time of double-sided printing, it becomes possible to reduce the heat amount difference between the front side and the back side as much as possible. Even when a high image is formed on both sides, it is possible to eliminate the difference in gloss between the front surface and the back surface.

  In addition, problems such as hot offset and poor separation due to excessive heat received on the surface during duplex printing can be avoided.

<Embodiment 2>
Second Embodiment of the Present Invention will be described with reference to FIG. 3. In the configuration of FIG. 3, the basic configuration of the image forming unit is the same as that of the first embodiment. After passing through the first fixing device 9a, an image that does not require gloss or an avoidance path that avoids the second fixing device 9b during duplex printing passes under the second constant tea device 9b.

  Thus, also in this embodiment, the same effect as in the first embodiment was confirmed.

<Embodiment 3>
Embodiment 3 of an image forming apparatus according to the present invention will be described with reference to FIG. In addition, the same code | symbol is attached | subjected to the member same as the above-mentioned member.

  In the first embodiment, the fixing unit is a pair of a heating roller and a pressure roller. However, in this example, a fixing belt stretched by a plurality of rollers is brought into contact with the heating roller, and a pressure member is formed from the fixing belt. Thus, the heating roller is pressurized. The two fixing devices 9a and 9b are identically used under the same conditions.

  As shown in detail in FIG. 5, the fixing device 9 includes a fixing roller 51 that is rotatably arranged, and an endless belt 52 that is stretched between a plurality of rollers 55, 56, and 57 and rotates while being pressed against the fixing roller 51. And a pressure pad 70 for pressing the endless belt to the fixing roller 51 and a pressure pad support 71.

  The fixing roller 51 has a structure in which a core bar made of Al, Fe or the like is covered with an elastic body layer such as silicone rubber or fluorine rubber. The endless belt 52 has a configuration in which an elastic body layer such as silicone rubber or fluorine rubber is coated on the surface of a base material made of a resin such as polyimide or a metal such as nickel.

  Inside the fixing roller 51, heaters such as halogen lamps are disposed. In addition, a thermistor (not shown) is arranged in contact with or not in contact with the fixing roller 51, and the temperature of the surface of the fixing roller 51 is adjusted by controlling the voltage to the heater via a temperature adjustment circuit. .

  The roller 56 is a separation roller made of metal and presses the endless belt 52 so as to bite into the fixing roller 51, thereby deforming the elastic body of the fixing roller 51 and separating the transfer paper P from the surface of the fixing roller 51.

  As described above, when the fixing nip is formed by the fixing roller 51, the endless belt 52, and the pressure pad 70, it is possible to form a wide nip so as to wrap around the outer periphery of the fixing roller 51, which is advantageous for speeding up. Become. Further, in the case of a fixing device using a conventional roller pair, when the nip width is wide, the elastic layer has to be thick, which is disadvantageous for energy saving. Such a belt is used. In the fixing device, it is possible to form a wide nip without increasing the thickness of the elastic layer of the fixing roller 51. Therefore, loss of heat transfer due to the elastic layer can be prevented, which is effective for energy saving.

  According to the configuration of the present embodiment, an experiment similar to that of the first embodiment was performed under the same conditions except for 100 sheets per minute at a process speed of 500 mm / sec. did it.

  As described above, it has been confirmed that the same effect can be obtained even in a high-productivity image forming apparatus by widening the fixing nip with the fixing roller and the fixing belt and sufficiently heating the recording material.

  The present invention can be applied to an image forming apparatus such as a copying machine, a facsimile, or a printer that forms an image on a recording material to obtain a hard copy.

1 is a cross-sectional view of an image forming apparatus according to Embodiment 1 of the present invention. 1 is a cross-sectional view of a fixing device of an image forming apparatus according to Embodiment 1 of the present invention. It is sectional drawing of the image forming apparatus which concerns on Embodiment 2 of this invention. It is sectional drawing of the image forming apparatus which concerns on Embodiment 3 of this invention. FIG. 6 is a cross-sectional view of a fixing device of an image forming apparatus according to Embodiment 3 of the present invention.

Explanation of symbols

3 Photosensitive drum (image carrier)
DESCRIPTION OF SYMBOLS 9 Fixing device 51 Fixing roller 52 Pressure roller or fixing belt 70 Pressure pad 130 Intermediate transfer body

Claims (6)

An image forming apparatus provided with an image carrier on which a toner image is formed, a transfer unit that transfers the toner image to a recording material, and a plurality of fixing units that fix the toner image transferred onto the recording material.
A means for forming an image on both sides of the recording material, a means for storing whether the image is the first surface or the second surface, and depending on whether the image formation surface is the first surface or the second surface, An image forming apparatus comprising means for switching states of a plurality of fixing means.   2. The image forming apparatus according to claim 1, further comprising means for switching a conveying path of the recording material between the plurality of fixing devices as means for switching the states of the plurality of fixing means.   2. The image forming apparatus according to claim 1, further comprising means for switching the number of times the recording material passes through the plurality of fixing devices as means for switching the states of the plurality of fixing means.   The image forming apparatus according to claim 1, wherein the state is switched so that the number of times of fixing is smaller when fixing the first side than when fixing the second side when forming a double-sided image. .   The image forming apparatus according to claim 1, wherein the amount of heat received by the recording material from the fixing unit is greater than the amount of heat received from the front side of the recording surface than from the back side.   The image forming apparatus according to claim 1, wherein the fixing unit includes a heating member and a pressure member, and the temperature of the heating member is higher than the temperature of the pressure member.

Images