JP2005258209A - Fixing apparatus and image forming apparatus provided with it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To carry out fixing without any oil with no occurrence of wrapping even in transfer paper with a large amount of attached toner and no margin in a leading tip part. <P>SOLUTION: In this fixing apparatus, halogen heaters 13a and 13b are each provided as heating sources to interiors of a fixing roller 10a rotated clockwise and a pressure roller 10b brought into a pressurized contact with the fixing roller 10a and rotating following it counter clockwise. The surface temperature of the rollers are controlled by thermisters 15 and 15 detecting the surface temperature. A preliminary heating means 40 consisting of a halogen heater 43 and a reflecting plate 41 is provided on a more upstream side than a nip part of the fixing roller 10a and the pressure roller 10b and the transfer material P with a toner image Pt carried on its surface is heated from the backside. Thus, the toner temperature is raised, toner temperature gradient in the nip part is made slack, toner viscosity is suppressed low and the wrapping can be prevented. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electrophotographic fixing device and an image forming apparatus including the same, and more particularly to a fixing device capable of preventing a transfer material having a color image transferred on at least one side thereof and an image forming apparatus including the fixing device.

  Conventionally, in a fixing device of this type of image forming apparatus, a predetermined pressure is applied to a fixing roller having a non-adhesive elastic body and having a heating source inside, and a pressure roller covered with the elastic body. A heat roller system is used in which a transfer material having toner transferred to the nip portion is pressed and fixed to pass through. Generally, since the toner fused to the transfer material comes into contact with the surface of the fixing roller, the fixing roller is coated with a fluorine resin having a good releasability or a PFA tube. However, even if such a fixing roller is used, the melted toner has a high viscosity, so that it easily adheres to the surface of the fixing roller and the transfer material may be wound around the fixing roller. For this reason, the fixing roller is brought into contact with the peeling claw and forcibly peeled to prevent the transfer material from being wrapped around the fixing roller, and further, the fixing roller does not leave contact marks on the surface of the fixing roller. A release agent such as silicon oil is applied to the surface.

  FIG. 10 is a configuration diagram illustrating an example of a conventional fixing device. The transfer material P having the toner Pt is conveyed leftward in the figure, and passes through a nip portion of the fixing unit 10 including a fixing roller 10a that rotates clockwise and a pressure roller 10b that is pressed against and rotates counterclockwise. pass. The fixing roller 10a and the pressure roller 10b have built-in halogen heaters 13a and 13b at their shafts, respectively, and non-contact release plates 14 and 14 for peeling the transfer material P from the fixing roller 10a and the pressure roller 10b near the surface. The thermistors 15 and 15 for detecting the surface temperature are provided to control the temperature. As a result, the toner Pt of the transfer material P that has passed through the nip portion between the fixing roller 10a and the pressure roller 10b is melted and fixed.

  FIG. 11 is a diagram showing the temperature gradient of the toner on the transfer material from the transfer material side to the fixing roller side in such a fixing device. In the conventional fixing device, the temperature gradient of the toner on the transfer material is a line (a). ) Is larger. When the temperature gradient of the toner is so large, the toner temperature Ta on the fixing roller side must be increased in order to make the toner temperature on the transfer material side equal to or higher than the fixing temperature T at which no cold offset occurs. For this reason, the toner viscosity on the fixing roller side is increased and the toner is easily wound around the fixing roller 10a. Conversely, if the toner temperature gradient can be reduced as shown in the line (b) in the figure, it can be seen that the temperature on the fixing roller 10a side becomes Tb and the toner viscosity can be lowered.

As shown in FIG. 12, the toner viscosity V increases from a low temperature to a high temperature, and decreases when a predetermined peak point is exceeded. In FIG. 12, assuming that the fixing roller surface temperature (fixing lower limit temperature) is t (° C.) and the fixing roller surface temperature is the toner temperature on the fixing means side, the set temperature on the fixing roller surface is t (° C.) or more. .
The relationship between “toner viscosity” and “separation force of the fixing roller” greatly affects the winding. Lines C and D in FIG. 12 indicate boundary lines where wrapping occurs with respect to the toner viscosity V in the small-diameter fixing roller and the large-diameter fixing roller, respectively, and the toner viscosity is higher than the line D when the fixing roller diameter is large. If it exists, winding occurs. If the diameter of the fixing roller is small, winding occurs if it is above the line C. This means that winding occurs when the toner viscosity is larger than the separation force of the fixing roller. At the same time, the small-diameter roller can separate toner with higher viscosity than the large-diameter roller due to the curvature separation effect, and the surface of the fixing roller. It shows that the temperature can be set higher than that of the large diameter roller.

  When the fixing roller temperatures Ta and Tb in FIG. 11 are plotted in FIG. 12, Ta becomes point A and Tb becomes point B. Winding occurs because point A exceeds the line C even in the case of a small-diameter roller, whereas winding does not occur because point B does not exceed the line D even in the case of a large-diameter roller. As described above, even when the toner temperature on the transfer material side is the same, winding is less likely to occur when the temperature gradient is smaller. Also, if the nip time is short, the heat on the fixing roller side is not easily transferred to the toner on the transfer material side, so the temperature gradient of the toner image becomes large. If the nip time is long, the heat on the fixing roller side is transferred to the toner on the transfer material side. As a result, the temperature gradient of the toner image becomes small.

  On the other hand, in recent years, in a color image forming apparatus, in order to ensure color reproducibility and glossiness of an image, it is required to sufficiently melt the toner, and a toner having a low melting point is used. Such a toner having a low melting point is liable to cause a high temperature offset, so that it is necessary to apply a large amount of low viscosity silicone oil as a release agent. The high temperature offset is a phenomenon in which the temperature of the toner rises too much so that the toner liquefies, the cohesive force of the toner is reduced, and a part of the toner adheres to the fixing roller at the time of fixing. In addition, when a large amount of silicon oil is used, problems such as oil contamination in the apparatus due to silicon oil spillage and deterioration of writing performance due to oil adhesion to the transfer material occur.

In order to solve such problems, several fixing devices have been proposed in order to obtain excellent color reproducibility and gloss after fixing by using little or no silicone oil.
That is, a fixing method in which a fixing roller and a pressure roller are paired and an unfixed image is allowed to pass through the nip portion continuously at least twice, and the surface roughness of the pressure roller is expressed by a ten-point average roughness Rz. The surface temperature of a plurality of heating and pressure rollers is set to T1>T2> T3... Tn> Ts (Tn: surface temperature of the roller disposed last, Ts: glass transition temperature) ) Has been proposed (see, for example, Patent Document 1).

In addition, a nip portion is formed by including a fixing roller or a fixing film and a pressure roller, and the pressure roller or the pressure roller is newly provided downstream of the nip portion in the transfer material traveling direction. There has also been proposed a fixing device in which a fixing roller is provided so as to be in pressure contact with the pressure roller, and the surface of the fixing roller has a 10-point average roughness Rz of 1 to 50 μm (see, for example, Patent Document 2).
Further, the first and second fixing units are arranged along the moving direction of the transfer material, and the second fixing unit is arranged at a position where the temperature of the toner does not fall below the glass transition point, and the toner is changed according to the glossiness. A fixing device has also been proposed in which the surface smoothness can be changed by re-pressurization of the second fixing means (see, for example, Patent Document 3).

Japanese Patent Laid-Open No. 63-192068 JP-A-7-31505 JP 2002-304072 A

  Each of these conventional techniques aims to improve the color reproducibility and glossiness of the image after fixing by passing the transfer paper on which the image has been formed twice or more through the nip portion of the fixing device. However, the following problems occur when silicone oil is not used at all. That is, since the friction coefficient of the fixing roller is high, the contact trace of the peeling plate is attached to the fixing roller, and the scar appears on the fixed image. Further, when a contact-type release plate is not used, an image having a large amount of adhesion and a strong winding force is wound around the fixing roller.

  The present invention has been made in view of the above points. In particular, even when the toner adhesion amount is large and the wrapping force is strong, oilless color fixing is possible, and furthermore, transfer of an entire image without a margin at the tip. It is an object of the present invention to provide a fixing device in which no wrapping occurs even with a material and an image forming apparatus including the same.

  In order to achieve the above-mentioned object, the present invention comprises a fixing means comprising a rotatable fixing roller and a pressure roller capable of being driven to rotate while being pressed against the fixing roller and forming a nip portion with the fixing roller. In the fixing device that heats and presses the toner image carried on the transfer material at the nip portion and fixes the toner image on the transfer material, the transfer material is preheated upstream of the fixing unit in the moving direction of the transfer material. The present invention provides a fixing device in which preheating means is provided and the heating set temperature of the fixing roller and the pressure roller is made different.

  When the fixing device is performing single-side fixing, the preheating unit heats the back side of the transfer material, and the heating set temperature of the pressure roller is set higher than the heating set temperature of the fixing roller. In the case of double-sided fixing or simultaneous double-sided fixing, the preset heating temperature of the preliminary heating means, the fixing roller, and the pressure roller according to the image ratio between the front and back surfaces of the front end of the transfer material. It is even better to control each of these. Further, at the time of double-sided fixing or simultaneous double-sided fixing, the heating setting temperature of the fixing roller or the pressure roller on the side in contact with the surface with the high image ratio of the front and back surfaces at the leading edge of the transfer material is set to the other heating setting. The temperature is preferably lower than the temperature.

  Further, the toner carried on the transfer material is provided with a fixing means comprising a rotatable fixing roller and a pressure roller that is in contact with the fixing roller and can be driven to rotate to form a nip portion with the fixing roller. In the fixing device for fixing an image to the transfer material by heating and pressing at the nip portion, the fixing device includes a plurality of fixing devices, and at least a fixing roller of the fixing device disposed on the most downstream side in the moving direction of the transfer material. The diameter of the fixing roller is smaller than the diameter of the fixing roller of the other fixing means, and the heating set temperature of the fixing roller of the fixing means arranged on the most upstream side is different from the heating set temperature of the pressure roller. An apparatus is also provided.

  Then, at the time of single-side fixing of the fixing device, the heating set temperature of the pressure roller of the fixing means arranged on the most upstream side in the moving direction of the transfer material is set higher than the heating set temperature of the fixing roller. It is also possible to control the heat setting temperature of the fixing roller and the pressure roller of the fixing means arranged on the most upstream side in the traveling direction of the transfer material according to the type of the transfer material. It is further preferable to provide a preheating means for preheating the transfer material on the further upstream side of the fixing means arranged on the most upstream side in the traveling direction of the transfer material.

Further, at the time of double-sided fixing or simultaneous double-sided fixing of the fixing device, the fixing disposed on the most upstream side in the advancing direction of the transfer material according to the image ratio between the front surface and the back surface at the front end portion of the transfer material It is also possible to control the heat setting temperature of the fixing roller and the pressure roller of the fixing unit, the fixing unit disposed on the most upstream side in the traveling direction of the transfer material, and the downstream of the fixing unit Glossiness detection means for detecting the glossiness on the front surface side and the back surface side of the transfer material is provided between the fixing device and the transfer material, and in accordance with the detected glossiness, It is also possible to control the heat setting temperature of the fixing roller and the pressure roller of the fixing unit disposed on the most downstream side. In these fixing devices, the linear speed of the fixing roller and the pressure roller is 250 mm / sec or more.
An image forming apparatus including any of the above is also provided.

  Since the fixing device according to the present invention is configured as described above, the temperature gradient in the vertical direction of the toner image carried on the transfer material can be reduced, so that the heat setting temperature of the fixing roller and the pressure roller can be lowered. And it becomes possible to prevent winding. In addition, when a plurality of fixing units are provided, the temperature gradient of the toner image from the transfer material side to the fixing member side can be almost eliminated, and the heating temperature of the fixing roller surface in each fixing unit can be set low. Thus, the effect of preventing wrapping can be further improved, and the separation roller is further improved by reducing the diameter of the fixing roller on the downstream side in the traveling direction, so that the effect of preventing wrapping of the transfer material to the fixing roller is further improved. According to the image forming apparatus provided with the fixing device according to the present invention, it is possible to effectively prevent winding of any kind of transfer material.

Hereinafter, the best method for carrying out the present invention will be described with reference to the drawings.
FIG. 9 is a configuration diagram of an image forming unit of a color image forming apparatus capable of simultaneous double-sided fixing to which the fixing device according to the present invention is applied. In this configuration diagram, a pair of image forming portions are provided symmetrically with respect to the transfer path of the transfer material P. Therefore, in order to simplify the drawing, a part of the lower portion is omitted, and only the upper portion is mainly described. To do.

  In an electrophotographic full-color image forming apparatus, a color separation / superposition transfer method is generally used. Yellow (Y), cyan (obtained by reading image information light obtained by separating a document (not shown) into three colors of blue, red, and green by the document reading unit and performing image calculation processing on the intensity level of each color light. C), magenta (M), black (B) based on the writing image data to be developed, laser writing devices 3Y, 3C, 3M, 3B are arranged vertically on the same plane, and charging device Optical writing is performed on the four photoconductors 1Y, 1C, 1M, and 1B negatively charged by 4Y, 4C, 4M, and 4B. Each of the photoconductors 1Y, 1C, 1M, and 1B is made of a photoconductive organic or inorganic material, and rotates in the direction indicated by the arrow. The electrostatic latent images obtained by optical writing are developed by developing units 2Y, 2C, 2M, and 2B containing yellow, cyan, magenta, and black developers, respectively. Reversal developed.

  Opposite to the photoreceptors 1Y, 1C, 1M, and 1B, an intermediate transfer belt 20 as an intermediate transfer body having a transfer surface is provided. The intermediate transfer belt 20 is looped over the drive roller 21, the secondary transfer roller 22, the driven roller 23, and the tension roller 24, and circulates in the direction indicated by the arrow. The toner images on the respective photoreceptors 1Y, 1C, 1M, and 1B are sequentially primary-transferred and superimposed on the intermediate transfer belt 20 by primary transfer rollers 5Y, 5C, 5M, and 5B to which a predetermined bias is applied. . A cleaning device 25 for cleaning the surface of the intermediate transfer belt 20 is provided at a position facing the driven roller 23. As described above, the intermediate transfer belt 20 having the secondary transfer roller 22 on the back surface side of the transfer material P is also provided symmetrically at the lower portion so as to face the secondary transfer roller 22. A charger 26 is provided to charge the toner on the intermediate transfer belt 20. The discharge by the charger 26 gives a charge having a polarity opposite to that of the toner on the intermediate transfer belt 20 on the surface side of the transfer material P.

  The transfer material P fed from the paper feeding unit 30 is conveyed toward the secondary transfer rollers 22, 22 disposed facing each other via the registration roller 31. At this time, the transfer material P is sent out by the registration roller 31 at a timing at which the leading edge of the image formed on the intermediate transfer belt 20 coincides with a predetermined position in the transfer material conveyance direction. The secondary transfer roller 22 on the front side of the transfer material P is biased by secondary transfer bias applying means (not shown), and the toner images on the front and back intermediate transfer belts 20 are transferred to the front and back sides of the transfer material P. Transfer to both sides. The secondary transfer roller 22 on the back side of the transfer material P is grounded. The transfer material P that has passed through the secondary transfer portion is sent to a fixing device provided near the secondary transfer outlet, where the toner image is fixed and a color image is obtained. Hereinafter, a specific configuration of the fixing device will be described for each embodiment.

[Example 1]
FIG. 1 is a block diagram of Embodiment 1 of the fixing device according to the present invention. The fixing unit 10 includes a fixing roller 10a that rotates in the clockwise direction, and a pressure roller 10b that is driven to rotate counterclockwise while being in pressure contact with the fixing roller 10a. The fixing roller 10a is provided with an elastic layer having a thickness of 4 mm on the surface of a metal core such as aluminum, stainless steel, or carbon steel, and a PFA tube having a thickness of 50 μm is coated thereon, and a halogen heater 13a is provided as a heat source therein. ing. In the first embodiment, the pressure roller 10b is a roller having the same configuration as the fixing roller 10a, and has a halogen heater 13b as a heat source. Near the surfaces of the fixing roller 10a and the pressure roller 10b, a thermistor 15 for detecting the respective surface temperatures is arranged, and each halogen is controlled by a temperature control device (not shown) so as to reach a predetermined heating set temperature. Energization to the heaters 13a and 13b is controlled. In the first embodiment, the heating setting temperature of the pressure roller 10b is set higher than the heating setting temperature of the fixing roller 10a.

  Further, a preheating means 40 for heating the transfer material P from the back surface side of the transfer material P is provided upstream of the nip portion between the fixing roller 10a and the pressure roller 10b in the transport direction of the transfer material P. The preheating means 40 includes a halogen heater 43 and a reflection plate 41 thereof. The thermistor 45 is attached to the reflection plate 41 to detect the temperature of the reflection plate 41 and thereby control the energization to the halogen heater 43. Yes. On the downstream side of the nip portion, release plates 14 and 14 for separating the transfer material P that has passed through the nip portion from the fixing roller 10a and the pressure roller 10b are arranged in a non-contact state.

  In this way, by preheating the transfer material from the back side on the upstream side of the nip portion, the toner temperature on the transfer material side is increased, and the toner temperature gradient in the nip portion is as shown by the line (b) in FIG. Therefore, the set temperature of the fixing roller 10a can be set lower than the conventional line (a). As a result, the viscosity of the toner can be kept low, and the wrapping can be prevented even in the oilless color fixing in which the toner adhesion amount is easy to be wound and the fixing of the entire image having no leading edge margin.

[Example 2]
FIG. 2 is a configuration diagram of the second embodiment in which the first embodiment is adapted to double-sided fixing or simultaneous double-sided fixing. In the second embodiment, preheating means 40 and 40 for heating the transfer material P from both the front and back sides from the nip portion between the fixing roller 10a and the pressure roller 10b in the conveying direction of the transfer material P Provided above and below. The halogen heaters 13a and 13b of the fixing roller 10a, the pressure roller 10b, and the halogen heaters 43 and 43 of the preheating means 40 are connected to the temperature control device 102, respectively, and are based on the front and back image information 101 carried by the transfer material P. The preset heating temperature of the preheating means 40, the fixing roller 10a, and the pressure roller 10b is controlled.

  That is, the control unit 100 captures the image information 101 to detect the front and back leading edge image ratios, sets the heating setting temperatures of the preheating means 40, the fixing roller 10a, and the pressure roller 10b, and the temperature controller 102 uses the halogen heater 13a. , 13b and 43 are controlled. The temperature control device 102 is fed back to the temperature detected by the thermistors 15 and 45. Other configurations are the same as those of the first embodiment shown in FIG.

  At the time of double-sided fixing or simultaneous double-sided fixing, the surface with a high image ratio at the leading edge of the transfer material has a large amount of toner adhesion, and when the toner viscosity increases, the winding force becomes stronger than the surface with a low front-end image ratio. . For this reason, in the second embodiment, the heating set temperature of the fixing roller or pressure roller on the side in contact with the surface having the high tip image ratio between the front surface and the back surface of the transfer material is set higher than the heating setting temperature of the other pressure roller or fixing roller. It is low. In this way, the wrapping force on the front surface and the back surface can be made equal, and each wrapping force can be canceled to prevent wrapping even during double-sided fixing or simultaneous double-sided fixing. Here, the area where the leading edge image ratio is detected is the distance from the position where the leading edge of the transfer material P exits the nip portion to the peeling plate 14, and the detecting method is that the control unit 100 captures the image information 101 and the leading edge on the front and back sides. A method of detecting the image ratio is adopted.

Example 3
FIG. 3 is a block diagram of Embodiment 3 of the fixing device according to the present invention. The third embodiment includes two or more stages of fixing means, but here, a description will be given in the form of two fixing means. In the figure, the first fixing means 11 on the upstream side of the transfer material P is the same as in the first embodiment. Similar to the first fixing unit 11, the second fixing unit 12 disposed on the downstream side thereof includes a fixing roller 12a and a pressure roller 12b, and a thermistor 15 is disposed in the vicinity of each surface to fix the fixing roller 12a. The surface temperature of the pressure roller 12b is detected. The fixing roller 12a and the pressure roller 12b are set to heating set temperatures, respectively. Based on the temperature detection of each thermistor 15, the fixing roller 12a and the pressure roller 12a are pressed by a temperature control device (not shown) so as to reach the respective set temperatures. Energization to the halogen heaters 13c and 13d built in the roller 12b is controlled.

  The downstream fixing roller 12a and the pressure roller 12b are smaller in diameter than the upstream fixing roller 11a and the pressure roller 11b, respectively. In Example 3, the elastic layers of the fixing roller 11a and the pressure roller 12b were 2 mm. Further, on the downstream side in the rotational direction from the nip portion of both the fixing and pressure rollers 12a and 12b, a release plate 14 for separating the transfer material P that has passed through the nip portion from the fixing roller 12a and the pressure roller 12b is provided in a non-contact manner.

  In the one-side fixing with the above configuration, the heating set temperature of the pressure roller 11b of the first fixing unit 11 is set higher than the heating set temperature of the fixing roller 11a. The heating setting temperature of the fixing roller 11a is set to a low temperature such that the toner image Pt on the transfer material P is not cold offset to the fixing roller 11a. In this way, no wrapping occurs in the first fixing unit 11 on the upstream side, and the temperature of the toner image Pt of the transfer material P that has passed through the first fixing unit 11 can be increased.

  Accordingly, when the transfer material P enters the second fixing unit 12 on the downstream side in such a state, even if the heating setting temperature of the fixing roller 12a is set lower than the conventional temperature, the inside of the nip portion of the second fixing unit 12 is set. The toner temperature gradient at can be made as shown by a line (b) in FIG. As a result, the heating set temperature of the fixing roller 12a can be set lower than before, the viscosity of the toner can be suppressed low, the amount of toner adhesion increases, and oilless color fixing that is easy to wind, and there is no margin at the tip portion. Winding can also be prevented in fixing the entire image.

  Further, the heating set temperature of the pressure roller 12b is set higher than the heating set temperature of the fixing roller 12a, and the temperature of the toner image Pt on the transfer material P side is raised to the lower limit fixing temperature. Since the fixing roller 12a has a smaller diameter than the fixing roller 11a, the second fixing unit can obtain higher separation than the first fixing unit. FIG. 4 is a diagram showing the relationship between the heat setting temperature t ° C. of the fixing roller and the fixing roller diameter φmm. When the fixing roller diameter is large, the heat setting temperature of the fixing roller is set low and the fixing roller diameter becomes small. It can be seen that the heating set temperature of the fixing roller can be increased. The reason for this is that, as the diameter of the fixing roller is reduced, the separability due to the curvature separation increases, so that the separation becomes possible even when the toner viscosity increases compared to the case of a large diameter. Therefore, according to the configuration of the third embodiment, even when the toner viscosity of the second fixing unit 12 is higher than the toner viscosity of the first fixing unit 11, the wrapping can be prevented.

  Further, by controlling the heat setting temperature of the fixing roller 11a and the heat setting temperature of the pressure roller 11b of the first fixing unit 11 according to the type of the transfer material P, the toner can be used regardless of the type of the transfer material P. As shown in the line (b) of FIG. 11, the temperature gradient can be made flat, so that any transfer material can be prevented from being wound. Similarly, controlling the heating set temperatures of the fixing roller 12a and the pressure roller 12b of the second fixing unit 12 according to the type of the transfer material P is more effective in preventing winding. At this time, as the transfer material P becomes thicker, the heating set temperature of the pressure rollers 11b and 12b is preferably increased.

Example 4
FIG. 5 is a configuration diagram of the fourth embodiment in which the third embodiment is adapted to double-sided fixing or simultaneous double-sided fixing. At the time of double-sided fixing or simultaneous double-sided fixing, a surface having a large image ratio at the front end portion of the transfer material is likely to be wound. Therefore, in the fourth embodiment, the heating set temperatures of the fixing roller 11a and the pressure roller 11b are controlled based on the image information 101. That is, the control unit 100 sets the heating set temperatures of the fixing roller 11a and the pressure roller 11b based on the image information 101, and controls the energization of the halogen heaters 13a and 13b by the temperature control device 102. At this time, a temperature detected by each thermistor 15 is fed back to the temperature control device 102. Other configurations are the same as those of the third embodiment shown in FIG.

  Hereinafter, the heating set temperatures of the fixing roller 11a and the pressure roller 11b will be described as T1 and T2, and the heating set temperatures of the fixing roller 12a and the pressure roller 12b will be described as T3 and T4. When the image ratio of the front end portion of the transfer material P is higher on the front surface than on the back surface, T2> T1 is set in the first fixing unit 11 on the upstream side. At this time, the heating set temperature T1 of the fixing roller 11a is set to a temperature that does not cause a cold offset. Further, in the second fixing unit 12 on the downstream side, if T is T4> T3> T as the fixing possible temperature shown in FIG. 11, the winding can be more effectively prevented.

On the contrary, when the image ratio of the back surface is higher than the front surface of the transfer material front end portion, in the first fixing unit 11, T2 is set to T1> T2 as a temperature that does not cause cold offset to the pressure roller 11b, and the second fixing is performed. If T3>T4> T in the means 12, the winding can be more effectively prevented. Also in this case, T3> T1, T4> T2.
Further, when the transfer material information 103 is transferred to the control unit 100 and the heating set temperatures T1 to T4 are controlled in consideration of the type of the transfer material, any transfer material can be prevented from being wound. As the transfer material becomes thicker, the roller heating set temperature on the side in contact with the surface where the image ratio of the tip portion is small is preferably increased.

Example 5
FIG. 6 is a configuration diagram of Example 5 in which Example 4 is made compatible with double-sided fixing or simultaneous double-sided fixing. In the fifth embodiment, in addition to the configuration of FIG. 5, preheating means 40 and 40 for preheating both the front and back surfaces of the transfer material P are provided upstream of the first fixing means 11, and the image ratio at the leading edge of the transfer material is provided. Accordingly, the temperature control of each preheating means 40 is performed. Thereby, it becomes possible to set the heating set temperature of the fixing roller 11a and the pressure roller 11b of the first fixing unit 11 to be lower. Note that the temperature control method and the leading edge image detection method of the preheating means 40 at the time of double-sided fixing or simultaneous double-sided fixing are the same as those in the second embodiment shown in FIG.

Example 6
FIG. 7 is a configuration diagram of Embodiment 6 of the fixing device according to the present invention. The glossiness of the transfer material P after fixing becomes higher as the fixing temperature is higher. When the glossiness is higher, the transfer material P is easily wound. In other words, the high glossiness of the transfer material P after fixing indicates that the fixing temperature is high, and the toner temperature immediately after the nip portion is high. In this case, the toner temperature at which the fixing temperature of the second fixing unit 12 on the downstream side is high also increases, and the second fixing unit 12 is likely to be wound.

Accordingly, when the glossiness of the transfer sheet P after passing through the nip portion of the first fixing unit 11 is high, the winding can be prevented by lowering the fixing temperature of the second fixing unit 12.
In the sixth embodiment, between the first fixing unit 11 and the second fixing unit 12, glossiness detection units 44 and 44 that can detect the glossiness of the front and back surfaces of the transfer material P are provided above and below the transfer material conveyance path. The glossiness of the front end portion on both surfaces of the transfer material P after passing through the nip portion of the first fixing unit 11 is detected. Other configurations are the same as those of the third embodiment shown in FIG.

  That is, the control unit 100 sets the heating set temperatures of the fixing roller 12a and the pressure roller 12b of the second fixing unit 12 based on the glossiness of the front and back surfaces of the transfer material P detected by the glossiness detection units 44 and 44. The temperature controller 102 controls the energization of the halogen heaters 13c and 13d. It should be noted that the temperature detected by each thermistor 15 is fed back to the temperature control device 102.

  Here, the heating setting temperature of the fixing roller 12a of the second fixing unit 12 is T5, the heating setting temperature of the pressure roller 12b is T6, and these heating setting temperatures T5 and T6 are two stages of high temperature H and low temperature L, respectively. And is usually set to a high temperature H. If the gloss level of the transfer material P immediately after the nip portion of the first fixing unit 11 is set, and the gloss level of the transfer sheet P detected by the gloss level detection units 44 and 44 is higher than the set value, The roller heating set temperature on the side in contact with the surface is switched to a low temperature L. As a result, an increase in toner temperature in the second fixing unit 12 can be suppressed, and it is possible to prevent the transfer paper from being wrapped around the second fixing unit 12 during double-sided fixing or simultaneous double-sided fixing. A fixed image with a small difference in gloss between the front and back sides can be obtained.

Example 7
FIG. 8 is a block diagram of Embodiment 7 of the present invention in which the second fixing means 12 on the downstream side of FIG. 7 is a belt system having a small heat capacity to improve the thermal response and prevent the winding more reliably. The other configuration is the same as that of the sixth embodiment shown in FIG. 7, and the control system for the heating set temperature is not shown. Further, since the seventh embodiment also corresponds to double-sided fixing or simultaneous double-sided fixing, and the second fixing unit is also vertically symmetrical, only one of them will be described in order to simplify the description.

  The fixing belt 16 is obtained by providing an elastic body layer of silicon rubber on a polyimide base, and further coating a PFA tube thereon. The fixing roller 17 has an aluminum core, and is provided with foamed silicon rubber on the surface thereof. The heating roller 18 is a hollow cylindrical thin roller made of aluminum, and includes a halogen heater 13e as a heat source therein. The front side and the back side have the same configuration, and the temperature is detected by the thermistor 15.

According to such a configuration, since the fixing roller 17 is formed of foamed silicon rubber, the nip time of the transfer material P can be lengthened, and a transfer speed of the transfer material P of, for example, 250 mm / s or more is sufficient. Fixing is possible.
In each of the above embodiments, the halogen heater is provided inside the roller as a heat source. However, this may be provided outside the roller. It is also possible to provide an exciting coil around the roller and use heating by induction heat generation. Since these external heating or induction heat generation has good thermal responsiveness on the roller surface, it is possible to quickly control the temperature of the roller and is effective in preventing winding.

1 is a configuration diagram of a fixing device according to the present invention. FIG. (Example 1) 1 is a configuration diagram of a fixing device according to the present invention. FIG. (Example 2) 1 is a configuration diagram of a fixing device according to the present invention. FIG. Example 3 FIG. 5 is a diagram showing a relationship between a heating set temperature of a fixing roller and a fixing roller diameter according to the present invention. 1 is a configuration diagram of a fixing device according to the present invention. FIG. (Example 4) 1 is a configuration diagram of a fixing device according to the present invention. FIG. (Example 5)

1 is a configuration diagram of a fixing device according to the present invention. FIG. (Example 6) 1 is a configuration diagram of a fixing device according to the present invention. FIG. (Example 7) 1 is a schematic configuration diagram of an image forming apparatus embodying the present invention. It is a block diagram showing an example of a conventional fixing device. It is explanatory drawing which shows the toner temperature gradient on a transfer material. FIG. 6 is an explanatory diagram showing whether or not there is winding based on toner viscosity and fixing roller diameter.

Explanation of symbols

1Y, 1C, 1M, 1B: photoconductors 2Y, 2C, 2M, 2B: developing unit 10: fixing unit 11: first fixing unit 12: second fixing unit 10a, 11a, 12a, 17: fixing roller 10b, 11b, 12b: Pressure roller 13a, 13b, 13c, 13d, 13e: Halogen heater 14: Peeling plate 15, 45: Thermistor 16: Fixing belt 20: Intermediate transfer belt 30: Paper feed unit 40: Preheating means P: Transfer Material Pt: Toner image

Claims (12)

Fixing means comprising a rotatable fixing roller and a pressure roller that is in contact with the fixing roller and can be driven to rotate and forms a nip portion between the fixing roller, and a toner image carried on a transfer material is In the fixing device for fixing to the transfer material by heating and pressing at the nip portion,
Preliminary heating means for preheating the transfer material is provided upstream of the fixing means in the moving direction of the transfer material, and the heating set temperatures of the fixing roller and the pressure roller are made different. Fixing device.   2. The one-side fixing, wherein the preheating means heats the back side of the transfer material, and the heating set temperature of the pressure roller is higher than the heating set temperature of the fixing roller. The fixing device described.   At the time of double-sided fixing or simultaneous double-sided fixing, the preset heating temperature of the preliminary heating means, the fixing roller, and the pressure roller are controlled according to the image ratio of the front and back surfaces at the leading edge of the transfer material. 2. The fixing device according to claim 1, wherein the fixing device is configured as described above.   At the time of double-sided fixing or simultaneous double-sided fixing, the heating setting temperature of the fixing roller or the pressure roller on the side in contact with the surface with the high image ratio of the front and back surfaces at the leading edge of the transfer material is set to the other heating setting temperature. The fixing device according to claim 1, wherein the fixing device is lower. The toner image carried on the transfer material is provided with a fixing means comprising a rotatable fixing roller and a pressure roller that presses against the fixing roller and can be driven to rotate and forms a nip portion with the fixing roller. In the fixing device for fixing to the transfer material by heating and pressurizing at the nip portion,
The fixing unit is provided with a plurality of stages, and the diameter of at least the fixing roller of the fixing unit disposed on the most downstream side in the advancing direction of the transfer material is smaller than the diameter of the fixing roller of the other fixing unit and the most upstream side. The fixing device is characterized in that the heating set temperature of the fixing roller of the fixing means arranged in is different from the heating set temperature of the pressure roller.   6. The heating setting temperature of the pressure roller of the fixing means arranged on the most upstream side in the traveling direction of the transfer material is set higher than the heating setting temperature of the fixing roller during single-side fixing. The fixing device described.   The heating set temperature of the fixing roller and the pressure roller of the fixing unit disposed on the most upstream side in the traveling direction of the transfer material is controlled according to the type of the transfer material. Item 7. The fixing device according to Item 5 or 6.   6. The fixing device according to claim 5, further comprising a preheating unit that preheats the transfer material upstream of the fixing unit disposed on the most upstream side in the moving direction of the transfer material.   At the time of double-sided fixing or simultaneous double-sided fixing, the fixing roller of the fixing unit disposed on the most upstream side in the moving direction of the transfer material according to the image ratio of the front surface and the back surface at the front end portion of the transfer material and the fixing roller 6. The fixing device according to claim 5, wherein a heating set temperature with the pressure roller is controlled.   Between the fixing unit disposed on the most upstream side in the advancing direction of the transfer material and the fixing unit disposed on the downstream side of the fixing unit, the glossiness on the front surface side and the glossiness on the back surface side of the transfer material Glossiness detection means for detecting the temperature of the fixing roller and the pressure setting temperature of the pressure roller of the fixing means arranged on the most downstream side in the moving direction of the transfer material according to the detected glossiness The fixing device according to claim 5, wherein the fixing device is controlled.   The fixing device according to any one of claims 1 to 10, wherein a linear velocity of the fixing roller and the pressure roller is 250 mm / sec or more. An image forming apparatus comprising the fixing device according to claim 1.

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