JP2005128338A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device suppressing transfer material from wrapping to a fixing roller and suppressing failure in an image such as an image void. <P>SOLUTION: When set temperature for a first, second and third rotating pairs of fixing rollers are defined as T1, T2 and T3, the relationship becomes T3>T2>T1. Toner is fixed to a transfer material by passing the transfer material at a nip of the third rotating pair after the temperature of the toner on the transfer material side is raised by sufficiently heating the toner on the transfer material before hand by the first rotating pair and the second rotating pair. Thus, the wrapping of the transfer material to the fixing roller can be suppressed and image failure such as a void image can be also suppressed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a fixing device and an image forming apparatus.

  Conventionally, in an image forming apparatus, a latent image on an image carrier is developed with toner supplied from a developing device, and a toner image as a visible image is formed on the image carrier. The toner image on the image carrier is transferred to a transfer material by a transfer device, and fixed on the transfer material by a fixing device. As fixing means of the fixing device, for example, a fixing roller having a heater built therein and configured to be rotatable, and a pressure roller configured to be rotatable by contacting the surface of the fixing roller with a predetermined pressure It is known that the toner image on the transfer material is fixed to the transfer material by heat and pressure at the nip formed by the fixing roller and the pressure roller.

  On the other hand, in recent years, the fixing speed has been increased due to the increased printing speed. As a result of the increase in the fixing speed, the transfer material passing time of the fixing device is accelerated. For this reason, the heating time of the toner image on the transfer material is shortened, and the transfer material side of the toner is not sufficiently heated at the heating temperature of the conventional fixing roller, which may cause fixing failure. Therefore, the heating temperature of the fixing roller is set high so that the toner can be heated to the fixing temperature even by heating for a short time. However, when the toner image is heated at such a high temperature, the toner temperature on the fixing side (surface side) becomes extremely higher than the toner temperature on the transfer material side. In recent years, in order to ensure color reproducibility and gloss of an image, a toner having a low melting point that is easy to melt has been used. As described above, when a toner having a low melting point is used, the toner on the fixing side on the transfer material is liquefied due to a high temperature, and the so-called high-temperature offset that adheres to the fixing roller may occur due to a decrease in toner cohesion. there were. For this reason, if the heating temperature of the fixing roller is lowered, this time, the toner transfer material side is not sufficiently heated, causing a fixing defect.

  Therefore, Patent Document 1 and Patent Document 2 describe a fixing device in which a plurality of fixing means including a fixing roller and a pressure roller are provided, and the heating temperature of each fixing roller is different. Thus, by gradually heating the toner with a plurality of rollers, the toner can be removed without setting the heating temperature of the fixing roller to such a high temperature that the toner surface is offset at a high temperature so that the toner adheres to the transfer material. It can be adhered to a transfer material. In Patent Document 1, the heating temperature of the upstream fixing roller is set to the highest temperature, and the toner surface side is sufficiently melted by the upstream fixing roller to ensure color reproducibility and glossiness. The surface of the downstream roller is smoothed to further improve the glossiness of the image, or the surface of the downstream roller is roughened to suppress the glossiness of the image.

Japanese Patent Laid-Open No. 63-192068 JP 07-31505 A

  However, as in Patent Document 1, the heating temperature of the fixing roller on the upstream side is made the highest and the surface side of the toner image is melted to some extent. As a result, the adhesiveness of the toner increases, and the transfer material is transferred to the fixing roller on the downstream side. In some cases, winding or toner on the transfer material adheres to the fixing roller on the downstream side to form a blank image.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a fixing device capable of suppressing a transfer material from being wound around a fixing roller and suppressing an image defect such as a blank image. Is to provide.

In order to achieve the above object, a fixing device according to claim 1 includes: a fixing roller configured to be rotatable; and a pressure roller configured to be rotatable by contacting the surface of the fixing roller with a predetermined pressure. A fixing means for forming a nip portion between the fixing roller and the pressure roller, and transferring the toner image formed on the image carrier to a transfer material, and the toner image carried on the transfer material In a fixing device for fixing to a transfer material by heat and pressure at a nip portion of the fixing unit, the fixing unit includes a plurality of the fixing units, and the heating setting temperature of the fixing unit located on the most downstream side with respect to the moving direction of the transfer material is other than It is characterized by being higher than the heating set temperature of the fixing means.
The fixing device according to claim 2 is the fixing device according to claim 1, wherein at least the diameter of the fixing roller of the fixing means located on the most downstream side with respect to the moving direction of the transfer material is equal to the diameter of the fixing roller of the other fixing means. It is characterized by being smaller than.
The fixing device according to claim 3 is the fixing device according to claim 1 or 2, wherein at least the fixing roller of the fixing unit located on the most downstream side with respect to the moving direction of the transfer material has a fixing hardness of another fixing unit. It is characterized by being harder than the hardness of the roller.
According to a fourth aspect of the present invention, there is provided the fixing device according to the first, second, or third aspect, wherein at least the peripheral speed of the fixing roller of the fixing unit located on the most downstream side with respect to the moving direction of the transfer material is that of the other fixing unit. It is characterized by being faster than the peripheral speed of the fixing roller.
The fixing device according to claim 5 is characterized in that, in the fixing device according to claim 4, the pressing force of the fixing means located on the most downstream side with respect to the moving direction of the transfer material is lower than the pressing force of the other fixing means. To do.
The fixing device according to a sixth aspect is the fixing device according to the first, second, third, fourth, or fifth aspect, wherein the fixing roller and the pressure roller of the fixing unit include a metal core, It is formed of a fiber reinforced metal.
According to a seventh aspect of the present invention, in the fixing device of the first, second, third, fourth, fifth or sixth aspect, the fixing roller and the pressure roller are the same member and have the same heating set temperature. It is characterized by this.
The fixing device according to an eighth aspect is the fixing device according to the first, second, third, fourth, sixth, or seventh aspect, the most downstream side from the pressure roller located on the most upstream side with respect to the moving direction of the transfer material. A pressure belt is stretched over the pressure roller located at the position, and a nip portion is formed by the fixing roller and the pressure roller via the belt.
The fixing device according to claim 9 is the fixing device according to claim 8, wherein the transfer material is conveyed by being electrostatically attracted to the pressure belt.
The fixing device according to claim 10 is the fixing device according to claim 8 or 9, wherein the fixing roller is located on the most upstream side with respect to the moving direction of the transfer material, and the fixing device is located on the most upstream side with respect to the moving direction of the transfer material. The image forming apparatus includes a fixing belt stretched between at least one fixing roller located downstream from the roller.
The fixing device according to an eleventh aspect is the fixing device according to the first, second, third, fourth, fifth, sixth, seventh, eighth, ninth, or tenth aspect. A belt is stretched around the fixing roller.
The fixing device according to a twelfth aspect is the fixing device according to the first, second, third, fourth, fifth, sixth, seventh, eighth, ninth, tenth or eleventh fixing device, wherein the linear velocity of each fixing roller and the pressure roller is 250 mm. / Sec or more.
The image forming apparatus according to claim 13 includes fixing means for transferring the toner image formed on the image carrier to a transfer material and fixing the toner image carried on the transfer material to the transfer material. In the image forming apparatus, the fixing device according to any one of claims 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12 is used. It is.

  According to the first to twelfth aspects of the present invention, in the fixing unit on the upstream side with respect to the moving direction of the recording material, the heating temperature is kept low so that the surface of the recording material is not melted, and the temperature of the fixing unit on the most downstream side is the highest. The surface of the recording material is sufficiently melted by this fixing means at a high setting. As a result, the viscosity of the toner image is increased by the upstream fixing unit, and the recording material is wound around the downstream fixing roller, or the toner adheres to the downstream fixing roller, thereby causing image defects such as white spots. There is an effect that can be suppressed. Further, since the heating temperature of the most downstream fixing unit is set high, the surface of the toner on the recording material can be sufficiently melted to the extent that color reproducibility and gloss can be exhibited. Thereby, there is an effect that an image having good color reproducibility and gloss can be obtained.

Hereinafter, an embodiment in which the present invention is applied to a color electrophotographic copying machine (hereinafter simply referred to as “copying machine”) which is an electrophotographic image forming apparatus will be described.
First, the overall configuration of the copying machine according to the present embodiment will be described.
As shown in FIG. 1, the copying machine includes an image reading unit (hereinafter referred to as “scanner unit”) 100 and an image forming unit (hereinafter referred to as “printer unit”) 200.

  In the scanner unit 100, an image of a document placed on the contact glass 29 is imaged on the CCD 20 via an illumination lamp, a mirror group, and a lens (not shown), and color image information of the document is converted into, for example, Blue (hereinafter referred to as “Blue”). It is read as color separation light of “B”, Green (hereinafter referred to as “G”), and Red (hereinafter referred to as “R”), and converted into an electrical image signal. The B, G, and R image signals thus obtained are subjected to color conversion processing by an image processing unit (not shown) based on the intensity level. By this color conversion processing, yellow (hereinafter referred to as “Y”), cyan (hereinafter referred to as “C”), magenta (hereinafter referred to as “M”), and black (hereinafter referred to as “Bk”) color image data. Become.

In the printer unit 200, image formation is performed based on the color image data obtained by the scanner unit 100. In the present embodiment, four photosensitive drums 1A, 2A, 3A, and 4A are provided as image carriers, and each of the photosensitive drums corresponding to Y, C, M, and Bk from the paper feeding unit 10 side is substantially. They are arranged in parallel on the same plane. Each of the photosensitive drums 1A, 2A, 3A, 4A is made of an organic or inorganic material having photoconductivity. The surface of each of the photosensitive drums 1A, 2A, 3A, and 4A is uniformly charged to, for example, a negative polarity by charging devices 1E, 2E, 3E, and 4E as charging means provided for the respective photosensitive drums. As the charging devices 1E, 2E, 3E, and 4E, a system such as a corotron, a scorotron, or the like that generates a charge by corona discharge and spreads it on the surface of the image carrier.
The charged photosensitive drums 1A, 2A, 3A, and 4A are optically written by laser writing units 1D, 2D, 3D, and 4D provided for the respective photosensitive drums. Thereby, an electrostatic latent image corresponding to each image data is formed on each photoconductive drum. The electrostatic latent image is reversely developed with each color toner charged negatively by developing devices 1B, 2B, 3B, and 4B as developing means provided for the respective photosensitive drums. A toner image of each color is formed on the drum.

  Next, the transfer material P is supplied from the paper supply unit 10 to the transfer regions of the transfer material conveyance path formed between the photosensitive drums and the transfer unit 5 through the registration rollers 27. As the transfer material P, ordinary copy paper, OHP sheet, or the like can be used. The transfer unit 5 includes a transport belt 25 that is looped over a plurality of rollers, a drive roller, a driven roller, and a tension roller, and circulates in the transfer material transport direction.

As a result, the transfer material P fed from the paper feeding unit 10 is transported toward the left in FIG. 1 by the circular movement of the transport belt 25. At this time, the transfer material P has its print start position at the timing when the leading edge of each color toner image formed on each photoconductive drum is rotated and conveyed to each transfer area which is a point facing the conveyance belt 25. It is conveyed so as to coincide with the opposite point.
The color toner images formed on the photosensitive drums 1A, 2A, 3A, and 4A are transferred to transfer rollers 1C as transfer means disposed on the back side of the conveying belt 25 so as to face the photosensitive drums, respectively. 2C, 3C, and 4C are sequentially superimposed on the transfer material P and transferred. Specifically, the transport belt 25 is formed of a dielectric material such as a polyester film, and the transfer belt 1C, 2C, 3C, 4C causes the transport belt 25 to have a polarity opposite to the polarity of the toner (here, positive polarity). ), The negative toner on each photosensitive drum is attracted to the conveying belt 25 side by electrostatic force and transferred to the transfer material P.

The transfer material P onto which each color toner image has been transferred in this manner is separated from the conveyance belt 25 by a separation device 28 as a separation means disposed at the end on the fixing device 21 side as a fixing means. The transfer material P separated from the transport belt 25 is transported to the fixing device 21 and the toner image transferred onto the transfer material is fixed. Then, the transfer material P is discharged out of the apparatus as a color image copy.
The charges accumulated on the conveying belt 25 are neutralized and neutralized by the belt neutralizing device 26 as a neutralizing unit after the transfer material P is separated. Further, scattered toner, paper dust and the like adhering to the conveyor belt 25 in the toner image transfer process and the like are removed by a cleaning unit 22 as a cleaning unit.

  Next, the fixing device 21 in the first embodiment will be described. The fixing device 21 illustrated in FIG. 2 includes a first rotation pair A, a second rotation pair B, and a third rotation pair C from the upstream side in the traveling direction of the transfer material P. The first rotation pair A is composed of a pair of a fixing roller 6a and a pressure roller 6b, and a halogen heater 15A as a heating source is provided inside each roller. A thermistor 40, which is a temperature sensor element, is disposed near the surfaces of the fixing roller 6a and the pressure roller 6b, and detects the surface temperatures of the fixing roller 6a and the pressure roller 6b. The fixing roller 6a and the pressure roller 6b each have a control set temperature T1, and based on the temperature detection of the thermistor 40, the halogen heater 15A is turned on by a temperature control device (not shown) so as to reach the set temperature T1. Control. A non-contact release plate 14 is provided at the nip outlet to prevent the transfer material from being wound.

  Like the first rotation pair A, the second rotation pair B includes a pair of a fixing roller 7a and a pressure roller 7b, and a halogen heater 15B is built in each roller. Then, the lighting of the halogen heater 15B is controlled based on the temperature detection of the thermistor 40 as described above. Further, like the first rotation pair A, a non-contact peeling plate 14 is provided at the nip outlet. The diameter of the fixing roller 7a of the second rotating pair B is smaller than the diameter of the fixing roller 6a of the first rotating pair A. Similarly to the above, the third rotating pair C includes a fixing roller 8a in which a halogen heater 15C is built in and a pressure roller 8b, and includes a thermistor 40 serving as a temperature detecting unit and a non-contact peeling plate 14. The diameter of the fixing roller 8a of the third rotating pair C is smaller than the diameter of the fixing roller of the second rotating pair B. Further, if the fixing roller set temperatures of the first, second, and third rotation pairs are T1, T2, and T3, the relationship is T3> T2> T1. Thus, the relationship between the set temperature of the fixing roller and the fixing roller is illustrated as shown in FIG. That is, when the diameter of the fixing roller is large, the setting temperature of the fixing roller is lowered, and the setting temperature of the fixing roller is increased as the diameter of the fixing roller is reduced. This is because the larger the fixing roller diameter, the easier it is for the transfer material to be wound due to the viscosity of the toner. The larger the roller diameter, the lower the set temperature and the higher the toner viscosity. The linear speed of each fixing roller and pressure roller is 250 mm / sec or more, preferably 600 mm / sec.

  The toner on the transfer material passing through the first rotation pair A is raised to a temperature that does not cause a cold offset between the nips of the fixing roller 6a and the pressure roller 6b. Since the diameters of the fixing roller 6a and the pressure roller 6b are large, the nip width between the fixing roller 6a and the pressure roller 6b becomes long. Thereby, the toner on the transfer material is heated for a long time. Therefore, the temperature difference between the fixing side of the toner on the transfer material and the transfer material side can be almost eliminated. The set temperature T1 of the fixing roller 6a and the pressure roller 6b is set so that the viscosity of the toner is increased by heating, and the toner is attracted to the fixing roller 6a and the pressure roller 6b and the transfer material is not wound around the roller. Has been. As a result, the toner on the transfer material that has passed through the first rotation pair A is in a state of being uniformly heated in the thickness direction of the toner and heated to such an extent that it does not adhere to the fixing roller 6a and the pressure roller 6b. It is in a state.

  The toner on the transfer material that has passed through the first rotation pair A subsequently passes through the second rotation pair B. The set temperature T2 of the fixing roller 7a and the pressure roller 7b of the second rotation pair B is set higher than the set temperature T1 of the fixing roller 6a and the pressure roller 6b of the first rotation pair A. As a result, the temperature of the toner on the transfer material that has passed through the nip width formed by the fixing roller 7a and the pressure roller 7b of the second rotating pair B rises to a temperature at which the toner on the transfer material side can be fixed. . As a result, the viscosity of the toner passing through the nip width of the second rotation pair B becomes higher than the viscosity when passing through the nip width of the first rotation pair A, and the transfer material P becomes the first rotation pair. It becomes easier to wrap around the roller than when passing through A. However, the diameters of the fixing roller 7a and the pressure roller 7b of the second rotation pair B are smaller than the diameter of the first rotation pair A, and the transfer material P is less likely to be wound. Therefore, even if the toner viscosity increases as described above, the transfer material P does not wind around the roller.

  The toner on the transfer material that has passed through the second rotation pair B subsequently passes through the third rotation pair C. When fixing the toner on the transfer material with one conventional rotating pair, the set temperature of the fixing roller and pressure roller should be high so that the toner is sufficiently melted to ensure the color reproducibility and glossiness of the image. Must be set. However, when the toner is melted, the viscosity of the toner becomes high and winding becomes easy. If the roller diameter is reduced to prevent this winding, a sufficient nip width for heating the toner will not be obtained, and the toner will not melt sufficiently, resulting in color reproducibility and glossiness. The transfer material side toner may not reach the fixing temperature T, and the toner may not be sufficiently fixed on the transfer material. Therefore, if the fixing roller (fixing member) is set to a very high temperature Ta in order to fix the toner to the transfer material, the transfer material on the transfer material at the nip of the rotating pair is shown as a solid line (a) in FIG. The temperature gradient between the toner transfer material side and the fixing member side (surface side) becomes large. As a result, high temperature offset may occur where the toner on the fixing member side liquefies and adheres to the fixing roller. However, in this embodiment, since the toner on the transfer material is sufficiently heated in advance by the first rotation pair A and the second rotation pair B, the roller diameter is reduced and the nip width is narrowed. Even if the temperature T3 is set lower than that in the prior art, the toner can be heated to a fixable temperature at which the toner is fixed to the transfer material, as indicated by a dotted line (b) in FIG. Further, as indicated by a dotted line (b) in FIG. 4, the temperature gradient between the transfer material side of the toner on the transfer material and the fixing member side (surface side) at the nip of the rotating pair can be reduced. Therefore, the high temperature offset in which the toner on the fixing member side is liquefied and adheres to the fixing roller does not occur. Further, since the roller diameter is small, the transfer material is not wound.

  Further, the peripheral speeds of the fixing roller 8a and the pressure roller 8b of the third rotation pair C are higher than the peripheral speeds of the fixing roller 7a and the pressure roller 7b of the second rotation pair B. The distance from the nip of the second rotating pair B to the nip of the third rotating pair C is sufficiently shorter than the length of the transfer material. For this reason, when the leading edge of the transfer material passes through the nip width of the third rotation pair C, the vicinity of the center of the transfer material is sandwiched between the second rotation pair B. Further, a linear pressure of about 107 N / m is applied to the transfer material from both the fixing roller 7a and the pressure roller 7b of the second rotating pair B. On the other hand, a linear pressure of about 35 N / m is applied to the transfer material from the fixing roller 8a and the pressure roller 8b of the third rotating pair C, respectively, and the pressing force is weaker than that of the second rotating pair B. Yes. As a result, when the leading edge of the transfer material passes through the nip of the third rotation pair C, the transfer material P does not move at the same speed as the peripheral speed of the third rotation pair C, and the circumference of the second rotation pair B It moves at a constant speed. For this reason, a displacement force acts between the transfer material P and the third rotation pair C, so that the separation between the fixing roller 8a and the pressure roller 8b can be improved. Moreover, it is preferable that the circumferential speed difference between the third rotation pair C and the second rotation pair is within 3%. If the peripheral speed difference is made larger than this, there is a risk of image misalignment in the fixed image. In this embodiment, the peripheral speed difference and the applied pressure between the third rotation pair C and the second rotation pair B are changed, but the present invention is not limited to this. For example, when the distance from the nip of the first rotation pair A to the nip of the third rotation pair C is sufficiently shorter than the length of the transfer material, the peripheral speed of the first rotation pair A is set to the other rotation pairs B and C. And the pressure applied to the transfer material from the first rotation pair A is greater than the pressure applied to the other rotation pairs B and C, so that the moving speed of the transfer material P is increased. It may be made slower than the peripheral speeds of the other rotational pairs B and C by moving at the same speed as the peripheral speed of the rotational pair A. In this way, when the leading edge of the transfer material passes through the nip of the second rotation pair B, the transfer material P and the transfer material P are separated by the difference between the moving speed of the transfer material P and the peripheral speed of the second rotation pair B. A displacement force is generated between the second rotation pair B and the transfer material P is less likely to adhere to the second rotation pair. Similarly, when the leading edge of the transfer material P passes through the nip of the third rotation pair C, the transfer material P and the second rotation material C are also different depending on the difference between the moving speed of the transfer material P and the peripheral speed of the third rotation pair C. A displacement force is generated between the third rotation pair C and the transfer material P is less likely to adhere to the third rotation pair, thereby preventing winding.

  In this embodiment, the fixing roller 6a and pressure roller 6b of the first rotation pair A, the fixing roller 7a and pressure roller 7b of the second rotation pair B, and the fixing roller 8a of the third rotation pair C are added. Each of the pressure rollers 8b has the same shape. Further, the set temperatures T1, T2, and T3 of the fixing rollers of the respective rotation pairs and the pressure rollers that are paired with the set temperatures T1, T2, and T3 are made the same. Thereby, the fixing condition on the fixing roller side and the fixing condition on the pressure roller side can be made the same. As a result, winding can be prevented even in simultaneous double-sided fixing, and a fixed image with the same image quality can be obtained. When printing a single-sided image, only the fixing roller side needs to be heated to a set temperature.

  Each fixing roller 6a, 7a, 8a and each pressure roller 6b, 7b, 8b have a cored bar made of iron fiber reinforced metal, and the fiber arrangement direction is the axial direction. Although the fiber reinforced metal differs depending on the fiber content, the Young's modulus can be set to 170 to 520 GPa. The Young's modulus of iron is 200 GPa, and the Young's modulus of aluminum is 70 GPa. By using fiber reinforced metal, the Young's modulus can be about 2.5 times that of iron and 7.5 times that of aluminum. . Thus, by using the core metal as a fiber reinforced metal, the Young's modulus of the core metal can be increased, and deflection can be prevented. In particular, in the case of a small-diameter roller, the strength of the cored bar cannot be maintained, and the cored bar is easy to bend. Silicone rubber is formed on the outer peripheral surface of the fiber reinforced metal core, and a PFA tube is coated thereon to form fixing rollers 6a, 7a, 8a and pressure rollers 6b, 7b, 8b.

  When the transfer material P is thicker than plain paper, the paper absorbs heat from the roller, and the toner is not sufficiently heated, which may cause cold offset or the like. On the other hand, when the transfer material P is thinner than plain paper, the toner is excessively heated, which may cause high temperature offset or winding around the roller. Furthermore, an image having no margin at the leading edge of the image is easier to wrap around each roller than when there is a margin at the leading edge. For this reason, the set temperatures T1, T2, and T3 of the rotation pairs A, B, and C are changed depending on the thickness of the transfer material P, the presence / absence of a leading edge margin, and the like. As shown in FIG. 5, the thickness of the transfer material P is determined by the user's operation or paper determination means 302 such as a transmission sensor, and the data is sent to the control unit 301. Further, the presence / absence of an image leading edge margin is detected from the image reading information 303 from the scanner unit 100, and the data is sent to the control unit 301. Based on these data, the set temperatures T1, T2, and T3 of the fixing roller and pressure roller of each rotation pair A, B, and C are controlled. In this way, the set temperature of the rollers of each rotating pair is changed according to the paper quality and image conditions, so that fixing failure due to the paper quality and image conditions does not occur.

  Next, a fixing device according to the second embodiment will be described. FIG. 6 is a schematic configuration diagram of the fixing device according to the second embodiment. The fixing device includes a first rotation pair D and a second rotation pair E. The first rotation pair D includes a fixing roller 16a and a pressure roller 16b. The second rotation pair E includes a fixing roller 16a and a pressure roller 17b having a smaller diameter than the fixing roller 16a and the pressure roller 16b of the first rotation pair D. A heating roller 18 is in contact with the fixing roller 16a and the pressure roller 16b of the first rotation pair D, and the fixing roller 16a and the pressure roller 16b are heated by the heating roller 18. Inside the heating roller 18, a halogen heater 19A is provided. The temperature of the fixing roller 16a and the pressure roller 16b is detected by the thermistor 40, and lighting of the halogen heater 19A is controlled based on the detection result. Thereby, the temperature of the fixing roller 16a and the pressure roller 16b can be controlled to a constant temperature T4. A halogen heater 19B is built in the fixing roller 17a and the pressure roller 17b of the second rotating pair E. Similar to the first rotation pair D, the fixing roller 17a and the pressure roller 17b are each provided with a thermistor 40. Based on the temperature detection of the thermistor 40, lighting control of the halogen heater 19B is performed to fix the fixing roller 19a. The pressure roller 19b is controlled to a constant temperature T5. Similarly to the first rotating pair D, the fixing roller 19a and the pressure roller 19b are provided with non-contact release plates 14, respectively. Each roller of the second rotating pair E is formed by forming a silicone rubber on the outer peripheral surface of a cored bar made of iron fiber reinforced metal and coating a PFA tube thereon.

  Further, the fixing roller 16a and the pressure roller 16b of the first rotating pair D are formed by forming foamed silicone rubber on the outer peripheral surface of a cored bar made of iron fiber reinforced metal and covering the PFA tube thereon. As a result, the fixing roller 16a and the pressure roller 16b have a low hardness of about JIS A10Hs. As described above, when the fixing roller and the pressure roller 16b have low hardness, the nip width can be increased. As a result, the toner on the transfer material can be heated for a long time, and the toner on the transfer material that has passed through the first rotation pair D can reduce the temperature gradient between the transfer material side and the surface side. The installation temperature T4 of the first rotating pair D is such that when the toner of the transfer material passes through the nip of the first rotating pair D, at least a cold offset does not occur and the viscosity of the toner increases due to heating, so that the transfer material P The temperature is set such that the toner is heated to such an extent that the toner is not attracted to the roller.

  The toner on the transfer material that has passed through the first rotation pair D subsequently passes through the second rotation pair E. Since the toner is uniformly heated in advance by the first rotation pair D, the toner is sufficiently melted even if the nip width of the second rotation pair E is narrow and the set temperature T5 of each roller is not so high. Thus, the color reproducibility and glossiness of the image can be ensured, and the toner can be fixed to the transfer material. For this reason, the diameter of the second rotating pair can be reduced, and the transfer material is less likely to be wound around the roller.

  Also in the second embodiment, as in the first embodiment, the peripheral speed of each roller of the first rotation pair D is made slower than the peripheral speed of each roller of the second rotation pair E, and the first Even if the pressing force applied to the transfer material P at the nip of the rotating pair D is made larger than the pressing force of the second rotating pair E, a difference occurs between the peripheral speed of the second rotating pair E and the moving speed of the transfer material. Good. Accordingly, as in the first embodiment, a displacement force is generated between each roller of the second rotation pair E and the transfer material, and the transfer material is less likely to be wound around the roller of the second rotation pair E. In addition, the pressure roller and the fixing roller of each rotation pair D and E have the same shape, and the set temperature of the fixing roller of each rotation pair is the same as that of the pressure roller paired therewith. As a result, winding can be prevented even in simultaneous double-sided fixing, and a fixed image with the same image quality can be obtained. When printing a single-sided image, the power consumption of the apparatus can be suppressed by heating only the fixing roller side to the set temperature.

  In the second embodiment, the fixing roller 16a and the pressure roller 16b of the first rotational pair D are made of foamed silicone rubber in order to have a low hardness of about JIS A10Hs. However, the present invention is not limited to this, and JIS A10Hs is not limited thereto. It may be formed of silicone rubber having a low hardness.

  Next, a fixing device according to the third embodiment will be described. FIG. 7 is a schematic configuration diagram of the fixing device according to the third embodiment. The fixing device includes a first rotation pair F, a second rotation pair G, and a third rotation pair H. The fixing rollers 30a, 31a, and 32a provided in each of the rotation pairs F, G, and H have the same configuration as that of the first embodiment. The diameters of the pressure rollers 30b, 31b, and 32b of each rotation pair F, G, and H are the same as the diameters of the paired fixing rollers 30a, 31a, and 32a. The thermistor 40 is provided on the outer periphery of the pressure roller. A pressure belt 33 is bridged between the pressure rollers 30b, 31b, and 32b. The pressure belt 33 is formed by forming a 200 μm-thick silicone rubber intermediate layer on a 90 μm-thick polyimide substrate, and covering the intermediate layer with a 30 μm-thick PFA tube. Further, a bias having the same polarity as the toner is applied from the power source 41 to the pressure roller 30b. Thereby, the conveyed transfer material P is electrostatically adsorbed to the pressure belt 33 and conveyed. As a result, it becomes difficult to wind around the fixing rollers 30a and 31a, and the transfer material P can be stably conveyed. Further, a neutralizing brush 39 is provided between the pressure roller 31 b of the second rotation pair G and the pressure roller 32 b of the third rotation pair H, and is provided on the inner peripheral surface of the pressure belt 33. In contact. The static elimination brush 39 neutralizes the pressure belt. As a result, the transfer material that has passed through the third rotation pair H does not wrap around the pressure belt 33.

  In the third embodiment, as in the first embodiment described above, the diameter of the rotating pair decreases from the upstream side to the downstream side with respect to the moving direction of the transfer material. The size of the transfer material is increased from the upstream side to the downstream side with respect to the moving direction of the transfer material. This makes it difficult for the toner to be wound around the fixing roller of each rotating pair. Further, since the toner on the transfer material is uniformly heated before passing through the third rotation pair H, the third rotation pair H can sufficiently supply the toner even if the heating is not so high with a short heating time. It can be melted to ensure the color reproducibility and glossiness of the image and can be fixed to the transfer material. In this embodiment, since the transfer material P is transported by the pressure belt 33, the transfer material P can be transported stably. Further, since the transfer material P is electrostatically adsorbed by the pressure belt 33, it is difficult to wind it around the fixing rollers 30a and 31b of the first and second rotating pairs F and G. As described above, since the transfer material P can be stably conveyed, the fixing speed can be increased as compared with the first and second embodiments.

  Next, a fixing device according to the fourth embodiment will be described. FIG. 8 is a schematic configuration diagram of a fixing device according to the fourth embodiment. The first rotation pair I and the second rotation pair J of this embodiment have the same configuration as that of the first embodiment. A fixing side heating roller 35a is provided above the fixing roller 36a of the third rotation pair F in the figure, and the fixing side heating belt 34a is stretched between the fixing roller 36a and the fixing side heating roller 35a. Similarly, the pressure roller 36b is provided with a pressure side heating roller 35b at the lower portion in the drawing, and the pressure side heating belt 34b is stretched between the pressure roller 36b and the pressure side heating roller 35b. The heating rollers 35a and 35b include a halogen heater 37 therein. The thermistor 40 is provided at a position facing each of the heating rollers 35a and 35b. Based on the temperature detection of the thermistor 40, the halogen heater 37 is controlled to be turned on by a temperature control device (not shown), so that each heating The belts 34a and 34b are controlled to a constant temperature. The fixing roller 36a and the pressure roller 36b are formed by forming silicone rubber on the outer peripheral surface of a cored bar made of iron fiber reinforced metal and coating it with a fluororesin.

  The diameter of the third rotation pair K is reduced so that the transfer material does not wind around the roller. Therefore, the circumference is short, the roller is easily soiled, the surface layer is quickly deteriorated, and the durability may be inferior. However, as described above, by stretching the heating belts 34a and 34b around the fixing roller 36a and the pressure roller 36b, the circumferential length can be increased and the durability can be improved. In addition, when the diameter is small, it is difficult to manufacture a halogen heater, but in this embodiment, a heating means can be provided separately, and manufacturing can be facilitated. In this embodiment, the third rotation pair K has a shape in which a heating belt is stretched. However, the present invention is not limited to this, and the first and second rotation pairs I and J are the same as the third rotation pair K. It is good also as a shape.

Next, a fixing device according to a fifth embodiment will be described. FIG. 9 is a schematic configuration diagram of a fixing device according to a fifth embodiment. This embodiment is substantially the same as the third embodiment, except that the fixing roller 30a of the first rotation pair F and the fixing roller 31a of the second rotation pair G are stretched by the fixing belt 38. By the way. Thus, the nip width can be increased by stretching the fixing roller 30a of the first rotation pair F and the fixing roller 31a of the second rotation pair G by the fixing belt 38. Thereby, the toner on the transfer material can be heated for a long time, and the temperature difference between the fixing side of the toner on the transfer material and the transfer material side can be almost eliminated. As a result, the toner can be fixed to the transfer material P even when the set temperature of the third rotation pair H is low, the nip width is narrow, and the toner heating time is short. When only the fixing roller 30a of the first rotating pair F and the fixing roller 31a of the second rotating pair G are stretched, the peripheral speed of the third fixing roller is made faster than the peripheral speed of the fixing belt, and The pressurizing force of the two rotation pairs is set larger than the pressurizing force of the third rotation pair. The transfer material is moved at the same speed as that of the second fixing belt, and the circumferential speed is different from that of the third rotation pair. A displacement force is generated to prevent winding around the fixing roller.
In this embodiment, the fixing belt 38 is stretched between the fixing roller 30a of the first rotation pair F and the fixing roller 31a of the second rotation pair G. However, the first to third rotation pairs F, G H fixing rollers may be stretched by a fixing belt. In this way, by making the fixing roller side and the pressure roller side have the same shape, it is possible to prevent winding even in simultaneous double-sided fixing, and to obtain a fixed image with the same image quality on both sides.

  Heretofore, a halogen heater built in the roller has been used as a heat source for the pressure roller and the fixing roller. However, the present invention is not limited to this, and the heat source may be provided outside the roller. Further, an exciting coil may be provided around the pressure roller or the fixing roller, and heating by induction heat generation may be used.

As described above, according to the fixing device of the present embodiment, assuming that the fixing roller set temperatures of the first, second, and third rotation pairs are T1, T2, and T3, the relationship is T3>T2> T1. As described above, the toner on the transfer material is sufficiently heated in advance by the first rotation pair and the second rotation pair to raise the temperature of the toner on the transfer material side, and then the nip of the third rotation pair. The transfer material is passed to fix the toner to the transfer material. As a result, the toner can be fixed to the transfer material even if the set temperature is lower than the set temperature when the toner is fixed to the transfer material P with a single rotating pair. Conventionally, in order to fix the toner on the transfer material side, the setting temperature of the fixing roller is set to a high temperature, so that the toner surface melts and causes problems such as hot offset that adheres to the fixing roller. However, in this embodiment, since the toner can be fixed to the transfer material even if the set temperature of the fixing roller is lowered, problems such as hot offset do not occur. Further, in the fixing unit on the upstream side with respect to the moving direction of the transfer material, the heating temperature is kept low so that the surface of the transfer material is not melted, and the temperature of the fixing unit on the most downstream side is set to be the highest. The surface of the recording material is melted. As a result, the viscosity of the toner image does not increase, and the transfer material is not wound around the downstream fixing roller, and the toner does not adhere to the downstream fixing roller and cause image defects such as white spots. In addition, since the surface of the transfer material is melted by the most downstream fixing means, an image having good color reproducibility and gloss can be obtained.
Further, according to the fixing device of the present embodiment, the diameter of the rotating pair decreases as the diameter of the fixing roller of the rotating pair moves from the upstream side to the downstream side with respect to the moving direction of the transfer material. As the toner moves from the upstream side to the downstream side, the toner is heated and the viscosity increases. As a result, the transfer material is easily wound around the roller, but as described above, the diameter of the rotation pair is reduced from the upstream side to the downstream side to increase the separation property from the transfer material. Therefore, the transfer material is not wound. Also, if the set temperature of the upstream rotating pair is set to a low setting that does not cause a cold offset of the toner, the viscosity of the toner can be kept low, so that the diameter of the rotating pair can be increased accordingly. Thereby, the nip width can be increased and the toner can be heated for a long time. As a result, the toner is uniformly heated, and the temperature gradient of the toner between the transfer material side and the fixing side can be almost eliminated. Therefore, the nip width of the rotating pair for fixing the most downstream toner to the transfer material is narrow, and the toner can be fixed to the transfer material even by heating for a short time. As a result, even if the most downstream rotating pair is heated to sufficiently melt the toner surface to improve the color reproducibility and glossiness of the image, the rotating pair has a small diameter, so that the winding is not wound. Therefore, it is not necessary to force the peeling claw 14 to contact the roller to forcibly peel off the transfer material. As a result, it is not necessary to apply silicon oil to the roller surface, and the inside of the apparatus is not contaminated or attached to the transfer material, and the writing property is not deteriorated. Further, since the toner is uniformly heated by the upstream rotating pair, the toner can be fixed to the transfer material even in a short heating time. As a result, it is possible to obtain a high-quality image that is difficult to wind around the fixing roller, has good color reproducibility, and good gloss.
Further, according to the fixing device of the present embodiment, the peripheral speed of the roller of the most downstream rotating pair is made faster than the peripheral speed of the roller of the upstream rotating pair, and the transfer material is transferred to the transfer material at the nip of the most downstream rotating pair. This applied pressure is made smaller than the applied pressure of the upstream rotating pair, and a difference is caused between the peripheral speed of the most downstream rotating pair and the moving speed of the transfer material. As a result, a displacement force is generated between each roller of the most downstream rotating pair and the transfer material, and the transfer material can be made difficult to wind around the roller of the most downstream rotating pair.
In the fixing device of this embodiment, the fixing roller and the pressure roller of each rotation pair have the same shape. In addition, the set temperature of the fixing roller of each rotating pair and the set temperature of the pressure roller paired therewith are the same. Thereby, the fixing condition on the fixing roller side and the fixing condition on the pressure roller side can be made the same. As a result, winding can be prevented even in simultaneous double-sided fixing, and a fixed image with the same image quality can be obtained.
In the fixing device of this embodiment, each fixing roller or each pressure roller has a cored bar made of iron fiber-reinforced metal, and the fiber arrangement direction is an axial direction. Thereby, the Young's modulus of the cored bar can be increased and the deflection can be prevented. As a result, the pressure applied to the transfer material of the roller is not uniform in the axial direction due to the deflection, and it is possible to prevent paper wrinkles that occur when the conveying force is not constant in the axial direction.
In the fixing device according to the third embodiment, the pressure belt 33 is stretched around the pressure rollers 30b, 31b, and 32b of each rotation pair. Thereby, since the transfer material P is conveyed by the pressure belt 33, the transfer material P can be conveyed stably. As a result, the fixing speed can be increased compared to the first and second embodiments.
In the fixing device of the third embodiment, a bias having the same polarity as the toner is applied from the power source 41 to the pressure roller 30b. Thereby, the conveyed transfer material P is electrostatically adsorbed to the pressure belt 33 and conveyed. As a result, it becomes difficult to wind around the fixing rollers 30a and 31a, and the transfer material P can be stably conveyed.
In the fixing device of the fourth embodiment, the fixing side heating belt 34a is stretched around the fixing roller 36a of the third rotation pair F, and the fixing side heating belt 34a and the fixing side heating roller 35a are fixed. It is stretched by a roller 36a. Further, the pressure roller 36b of the third rotation pair F also has a pressure side heating belt 34b stretched between the pressure side heating roller 35b and the pressure roller 36b, similarly to the fixing roller. Thereby, the perimeter of the 3rd rotation pair can be lengthened, and progress of surface layer degradation of a rotation pair can be delayed. Thereby, the durability of the third rotation pair F can be improved. Further, the heating means can be provided separately from the fixing roller and the pressure roller by stretching the belt, and the manufacturing can be facilitated.
In the fixing device of the fifth embodiment, the fixing roller 30a of the first rotation pair F and the fixing roller 31a of the second rotation pair G are stretched by the fixing belt 38. Thereby, the nip width can be increased. Therefore, since the toner on the transfer material can be heated for a long time, the temperature difference between the fixing side of the toner on the transfer material and the transfer material side can be almost eliminated. As a result, the toner can be fixed to the transfer material P even when the set temperature of the third rotation pair H is low, the nip width is narrow, and the heating time is short. Even if the fixing speed is increased, the nip width is large, so that the toner can be heated uniformly.
In the fixing device of this embodiment, the linear speed of each fixing roller and the pressure roller is 250 mm / sec or more. Thereby, the fixing speed is increased and the printing speed can be increased.

FIG. 3 is an explanatory diagram of a main part of the image forming apparatus according to the embodiment. FIG. 3 is an explanatory diagram of a main part of the fixing device according to the first embodiment. FIG. 6 is an explanatory diagram for explaining a relationship between a fixing roller diameter and a fixing roller set temperature depending on the position of the rotation pair. FIG. 6 is an explanatory diagram of a toner temperature gradient on a transfer material. FIG. 3 is a block diagram for explaining temperature control of a fixing roller set temperature. FIG. 6 is an explanatory view of a main part of a fixing device according to a second embodiment. FIG. 10 is an explanatory diagram of a main part of a fixing device according to a third embodiment. Explanatory drawing of the principal part of the fixing device which concerns on 4th Embodiment. FIG. 7 is a main part explanatory diagram of a fixing device according to a fifth embodiment.

Explanation of symbols

1A, 2A, 3A, 4A Photosensitive drum 1B, 2B, 3B, 4B Developing device 1E, 2E, 3E, 4E Charging device 5 Transfer unit 10 Feeding unit 14 Peeling claw 25 Conveying belt 28 Separating device 33 Pressure belt 38 Fixing Belt 39 Static elimination brush 40 Thermistor 41 Power supply

Claims (13)

  A toner carried on a recording material, comprising a fixing roller configured to be rotatable and a pressure roller configured to be rotatable, and having fixing means for forming a nip portion between the fixing roller and the pressure roller. In a fixing device for fixing an image to a recording material by heat and pressure at a nip portion of the fixing unit, the fixing unit includes a plurality of the fixing units, and the heating setting temperature of the fixing unit located on the most downstream side with respect to the moving direction of the recording material is A fixing device having a temperature higher than a preset heating temperature of another fixing unit.   2. The fixing device according to claim 1, wherein the diameter of at least the fixing roller of the fixing unit located on the most downstream side with respect to the moving direction of the recording material is smaller than the diameter of the fixing roller of the other fixing unit. .   3. The fixing device according to claim 1, wherein at least the fixing roller of the fixing unit located on the most downstream side with respect to the moving direction of the recording material is harder than the fixing roller of the other fixing unit. apparatus.   4. The fixing device according to claim 1, wherein at least the peripheral speed of the fixing roller of the fixing means located on the most downstream side with respect to the moving direction of the recording material is faster than the peripheral speed of the fixing roller of the other fixing means. A fixing device characterized.   5. The fixing device according to claim 4, wherein the pressing force of the fixing unit located on the most downstream side with respect to the moving direction of the recording material is lower than the pressing force of the other fixing units.   6. The fixing device according to claim 1, wherein the fixing roller and the pressure roller of the fixing unit include a cored bar, and the cored bar is formed of a fiber reinforced metal. A fixing device characterized.   7. The fixing device according to claim 1, wherein the fixing roller and the pressure roller have the same material and the same shape, and have the same heating set temperature. .   8. The fixing device according to claim 1, wherein the pressure belt extends from a pressure roller located on the most upstream side to a pressure roller located on the most downstream side with respect to the moving direction of the transfer material. And a nip portion is formed by the fixing roller and the pressure roller via the belt.   9. The fixing device according to claim 8, wherein the recording material is conveyed by being electrostatically attracted to the pressure belt.   10. The fixing device according to claim 8, wherein the fixing roller is located on the most upstream side with respect to the moving direction of the recording material, and the fixing roller is located on the downstream side with respect to the fixing roller located on the most upstream side with respect to the moving direction of the recording material. A fixing device comprising a fixing belt stretched between rollers.   11. The fixing device according to claim 1, wherein a belt is stretched over at least the fixing roller located on the most downstream side with respect to the moving direction of the recording material. A fixing device.   5. The fixing device according to claim 1, wherein a linear velocity of each fixing roller and pressure roller is 250 mm / sec or more. Fixing device.   An image forming apparatus comprising: a fixing unit that transfers a toner image formed on an image carrier to a recording material and fixes the toner image carried on the recording material to the recording material. Item 15. An image forming apparatus using the fixing device according to any one of Items 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12.

Images