JP4572635B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus that forms a toner image by selectively attaching toner to a latent image due to a difference in electrostatic potential, transfers the toner image to a recording sheet, and then heats and pressurizes to form a fixed image. It is.

  High-definition images can be obtained by an image forming apparatus using powdered toner, and an image close to a photograph can be output. In such a high-definition image, the demand for gloss is also high, and a high-gloss image is often required. For this reason, a so-called coated paper having a glossy coating layer formed on the surface is used as a recording sheet. After the toner image is transferred to the recording sheet, the toner image is sufficiently heated by a fixing device to obtain a highly glossy toner image. Has been made to form.

  However, when a high-gloss image is formed in this way, a portion where the gloss is uneven, that is, uneven gloss is likely to occur, and the quality of the image may be deteriorated. A typical example of uneven gloss is a so-called roll mark. As shown in FIG. 7, the toner image on the recording sheet P heated and pressed by the fixing device 101 is sandwiched between a pair of rolls 102 for conveying the recording sheet in a state where it is not sufficiently cooled. This occurs when the peripheral surface of the roll comes into contact with the toner image. Many of the roll marks 103 thus generated reduce gloss.

Techniques for reducing such roll marks are disclosed in, for example, Patent Document 1 and Patent Document 2.
The apparatus described in Patent Document 1 blows cooling air to the recording sheet that has passed through the fixing device, and lowers the temperature of the toner image until the recording sheet comes into contact with a conveyance roll provided on the downstream side of the fixing device. It is what.

Further, in the image forming apparatus described in Patent Document 2, leveling means is provided in the area where the toner is in a soft state on the downstream side of the fixing device so that the toner image is pressed against and smoothed. Yes. As a result, even if the roll mark is formed in contact with the paper discharge roll, the surface of the toner image is smoothed and smoothed by the leveling means thereafter, and the roll mark is erased. In addition, a leveling means is provided upstream from the paper discharge roll to smooth the surface of the toner image, and contact with the paper discharge roll in a state of being cooled below the glass transition temperature of the toner, thereby generating a roll mark. It has also been proposed to prevent.
Japanese Patent Laid-Open No. 2003-21978 Japanese Patent Laid-Open No. 2003-195663

  In recent years, in order to realize a high gloss color image similar to a photograph or printing, it has been proposed to use a toner having a good melting property encapsulating wax. For example, a high gloss image can be obtained by transferring such a toner onto a coated paper and fixing it while slowing the fixing speed and sufficiently heated. Even in a state where the toner is in high temperature due to contact with the heating roll or the heating belt in the fixing device, the releasability from the heating roll or the like is ensured by the wax.

  However, when a toner containing wax is used to improve the releasability as described above, remarkable gloss unevenness that does not occur when a conventional toner is used may occur. That is, as shown in FIG. 6, when the recording sheet heated and pressed by the fixing device and having the toner image fixed thereon comes into contact with the recording sheet conveyance roll before being sufficiently cooled, the contacted portion becomes highly glossy. This causes uneven gloss. As described in Patent Document 1, this unevenness in gloss is different from a roll mark in which the gloss of an image using normal toner is lowered, and is different from a roll mark in which the gloss is lowered. It is easy to cause noticeable uneven gloss.

  It has been found that this uneven gloss does not occur if the conveyance roll or the like is not brought into contact until the toner image and the recording sheet are sufficiently cooled. When a recording sheet is used, the cooling rate is slow, and it may be difficult to sufficiently cool the sheet until it contacts the transport roll. Further, it is not clear how much the toner image and the recording sheet can be cooled to prevent the uneven gloss where the portion in contact with the roll or the like becomes extremely high gloss. For example, Patent Document 2 describes that the toner is cooled to the glass transition temperature of the toner and then brought into contact with a roll or the like. However, when toner containing wax is used, cooling is performed based on the glass transition temperature of the toner. However, the correlation with the occurrence of uneven gloss is not good.

  The present invention has been made to solve the above-described problems, and its purpose is to reduce gloss unevenness of a toner image using a toner containing a wax for improving releasability, It is to obtain a good image with high gloss.

  In order to solve the above-mentioned problems, the invention according to claim 1 includes an image forming unit that forms a toner image by selectively attaching powdery toner to a latent image due to a difference in electrostatic potential, and the toner. Transfer means for transferring an image directly to a recording sheet or to a recording sheet via an intermediate transfer member, and a fixing device for fixing the toner image transferred on the recording sheet by heating and pressurizing the recording sheet The toner includes a resin binder, a color material, and a wax that improves releasability, and the recording sheet discharged from the fixing device is on the downstream side. Provided is an image forming apparatus having a cooling device that cools the temperature of the toner image to a melting point or lower of a wax contained in the toner in a sheet conveyance path until entering a conveyance roll.

  It became clear in the process of completing the present invention that the wax contained in the toner is rapidly cooled from the molten state and the wax crystallizes and becomes highly glossy when the temperature falls below the melting point. The present invention has been made on the basis of this fact, and the temperature of the toner image after being fixed is cooled to a temperature equal to or lower than the melting point of the wax contained in the toner before coming into contact with the conveying roll. If this is the case, even if it comes into contact with the transport roll, the situation where only that portion becomes highly glossy is avoided. In other words, since the entire area of the toner image is uniformly cooled to the melting point or lower, gloss unevenness does not occur at this time. Thereafter, when the toner image comes into contact with the conveying roll, the temperature of the toner image is already below the melting point of the wax, so that the gloss hardly changes even if it contacts with the conveying roll, and the occurrence of uneven gloss is prevented.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the cooling device blows air onto a toner image on the recording sheet.

  In this image forming apparatus, the toner image can be quickly cooled by blowing air onto the toner image. Even if the distance from the position of the fixing device to the downstream transport roll is short, the toner image is below the melting point of the wax. It is possible to cool to a temperature of

  The invention according to claim 3 is the image forming apparatus according to claim 1, wherein the cooling device sucks air in the vicinity of the toner image.

  In this image forming apparatus, when the recording sheet is conveyed on the downstream side of the fixing device, air is sucked from the vicinity of the toner image on the recording sheet, thereby forming a gentle and uniform air flow near the toner image. . As a result, the cooling of the toner image is uniformly promoted, and the toner image can be cooled to a temperature not higher than the melting point of the wax before reaching the transport roll. Further, unlike the case where air is blown, a large wind pressure does not act on the toner image in a melted state, and it is possible to avoid the occurrence of fluctuations in gloss due to the wind pressure.

  According to a fourth aspect of the present invention, there is provided image forming means for selectively attaching powdery toner to a latent image due to a difference in electrostatic potential to form a toner image; and the toner image directly on a recording sheet or in the middle An image forming apparatus comprising: a transfer unit that transfers to a recording sheet via a transfer member; and a fixing device that heats and pressurizes the toner image transferred onto the recording sheet and fixes the toner image on the recording sheet. The toner includes a resin binder, a color material, and a wax that improves releasability, and a sheet conveyance path until the recording sheet discharged from the fixing device enters a downstream conveyance roll. In addition, the present invention provides an image forming apparatus having a heating device for heating the temperature of the toner image to a temperature higher by 10 ° or more than the melting point of the wax contained in the toner.

  In this image forming apparatus, the temperature of the recording sheet sent from the fixing device and the toner image held on the recording sheet are lowered by heat radiation, but the temperature drop is suppressed by the heating device. When the toner image is fed to the conveying roll while being maintained at a temperature higher by 10 ° C. or higher than the melting point of the wax contained in the toner, the temperature of the toner image does not fall below the melting point even if the conveying roller contacts the toner image. For this reason, only the portion of the toner image in contact with the conveyance roll does not become noticeably high gloss due to rapid cooling, and the occurrence of uneven gloss is suppressed.

  According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect, the heating device blows heated air onto a toner image on the recording sheet.

  In this image forming apparatus, hot air is blown from the heating device onto the recording sheet sent out from the fixing device, and the temperature of the toner image can be maintained at a temperature higher than the melting point of the wax by 10 ° C. or more and sent to the conveying roll. . As a result, it is possible to suppress the occurrence of uneven glossiness in which the portion in contact with the transport roll is highly glossy.

  According to a sixth aspect of the present invention, in the image forming apparatus according to the fifth aspect, the heated air sprayed on the toner image is heated by a heating source of the fixing device.

  In this image forming apparatus, the heating source of the fixing device can be used for heating the toner image and the recording sheet, and there is no need to provide a separate heating source. For this reason, the structure of the apparatus is simplified, and it is possible to reduce the size and the manufacturing cost.

  According to a seventh aspect of the present invention, in the image forming apparatus according to the fourth aspect, the heating device maintains a guide member in contact with the recording sheet in a high temperature state.

  In this image forming apparatus, the guide member that guides the recording sheet is heated at a high temperature on the downstream side of the fixing device, and heat radiation from the guided recording sheet and the toner image is suppressed and the guide member is heated. The Thus, the temperature of the toner image can be maintained at a temperature that is 10 ° C. or higher higher than the melting point of the wax contained in the toner when the toner image is fed to the transport roll. Therefore, the toner image is not rapidly cooled to below the melting point of the wax even when it comes into contact with the transport roll, and the contact portion is prevented from being extremely glossy and uneven gloss.

  The invention according to claim 8 is the image forming apparatus according to any one of claims 1 to 5, further comprising a temperature sensor that detects the temperature of the toner image on the recording sheet immediately before the conveyance roll. The driving of the cooling device or the heating device is controlled based on the output of the temperature sensor.

  In this image forming apparatus, since the temperature of the toner image is detected by the temperature sensor, the toner image can be reliably detected even when the temperature in the apparatus fluctuates due to changes in the external environment such as the air temperature or the duration of use of the apparatus. The temperature can be maintained at a temperature not higher than the melting point of the wax or higher than the melting point of the wax by 10 ° C. or more and fed to the transport roll.

  As described above, in the image forming apparatus according to the first, second, or third aspect of the present invention, the toner image after passing through the fixing device is uniformly cooled, and the melting point of the wax contained in the toner It comes into contact with the transport roll after becoming below. As a result, the contact portion with the transport roll is prevented from becoming highly glossy by the rapid cooling of the wax from the melting point to the melting point, and the gloss of only the contact portion does not fluctuate significantly. Therefore, the occurrence of uneven gloss is effectively prevented.

Further, in the image forming apparatus according to the fourth, fifth, sixth or seventh aspect of the invention, when the recording sheet sent from the fixing device is sent to the transport roll, the temperature of the toner image is the wax level. Since the temperature is higher by 10 ° C. or more than the melting point, it is possible to avoid being rapidly cooled below the melting point of the wax when passing through the transport roll. As a result, the occurrence of gloss unevenness in which the contact portion with the transport roll becomes significantly high gloss is prevented.
In addition, by detecting the temperature of the toner image immediately before being sent to the transport roll, the state of cooling or heating of the toner image or the recording sheet can be adjusted, and the temperature is always appropriately adjusted and sent to the transport roll. Is possible.

Hereinafter, embodiments of the invention according to the present application will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram showing an image forming apparatus which is an embodiment of the invention according to claim 1, claim 2 or claim 8.
The image forming apparatus includes a cylindrical photosensitive drum 1 on which a latent image is formed on the surface by irradiation with image light after uniform charging, and around the photosensitive drum 1. A charging device 2 for uniformly charging the surface of the photosensitive drum 1, an exposure device 3 for irradiating the photosensitive drum 1 with image light to form a latent image on the surface, and a toner on the latent image on the photosensitive drum. Is transferred to the developing unit 4 to form a toner image, the endless belt-shaped intermediate transfer member 5 that is opposed to the photosensitive drum 1 and is supported so as to be able to circulate on the peripheral surface, and after the toner image is transferred. A cleaning device 6 that removes toner remaining on the photosensitive drum 1 and a static elimination exposure device 7 that neutralizes the surface of the photosensitive drum 1 are provided.

  Further, inside the intermediate transfer member 5, a transfer charger 8 for primarily transferring the toner image formed on the photosensitive drum to the intermediate transfer member 5, two support rolls 9a and 9b, and secondary transfer are performed. A transfer counter roll 10 for carrying out is disposed, and the intermediate transfer body 5 is stretched around these rolls so as to be able to go around. A transfer roll 11 for transferring the toner image on the intermediate transfer member to the recording sheet is disposed at a position facing the transfer opposing roll 10 via the intermediate transfer member 5. The recording sheet P is fed from a paper tray (not shown) to the pressure contact portion. A fixing device 12 that heats and melts the toner image on the recording sheet and press-bonds it to the recording sheet P is provided on the downstream side of the press contact portion, and the recording sheet that has passed through the fixing device 12 is provided on the downstream side. A transport roll 14 that transports and discharges to the paper discharge tray 13 is disposed. A cooling device 20 that blows air on the toner image on the recording sheet to cool the toner image on the recording sheet is provided on the conveyance path from the fixing device 12 to the conveyance roll 14, and a temperature sensor 15 that detects the temperature of the toner image on the downstream side. Is arranged.

  The photosensitive drum 1 has a metal drum surface with various inorganic photosensitive materials such as Se, a-Si, a-SiC, and Cds, organic photosensitive materials, amorphous selenium photosensitive materials, amorphous silicon photosensitive materials, and the like. What formed the layer can be used.

  The charging device 2 is obtained by coating a metal roll having conductivity such as stainless steel or aluminum with a coating of a high resistance material. The charging device 2 is in contact with the photosensitive drum 1 and is driven to rotate. When a predetermined voltage is applied, a continuous discharge is generated in a minute gap in the vicinity of the contact portion between the roll and the photosensitive drum 1, and the surface of the photosensitive drum 1 is charged almost uniformly. It is.

  The exposure device 3 generates blinking laser light based on the image signal, and scans this in the main scanning direction of the photosensitive drum 1 by a polygon mirror. As a result, an electrostatic latent image is formed on the surface of the photosensitive drum 1.

In the developing unit 4, four developing devices 4 a, 4 b, 4 c, and 4 d containing yellow, magenta, cyan, and black toners are rotatably supported, and each developing device sequentially approaches the photosensitive drum 1. Opposite, toner is transferred to a latent image corresponding to each color to form a visible image.
The toner used in this developing device is charged negatively by friction with a magnetic carrier, and contains a color material, a binder resin, and paraffin wax. The melting point of the binder resin is about 250 ° C., the glass transition temperature is about 100 ° C., and the melting point of the paraffin wax is about 90 ° C.

  The belt-like intermediate transfer member 5 has a two-layer structure of a base layer and a surface layer, and the base layer includes polyimide, polyamide, polyamideimide, etc. in consideration of heat resistance, strength, and surface smoothness. The heat resistant resin, metal such as aluminum and stainless steel is used, and the surface layer is made of silicone rubber, fluorine rubber or the like having high heat resistance and high releasability from the toner.

  The transfer charger 8 applies a voltage to the back surface of the intermediate transfer member 5 by applying a voltage so that the toner image on the photosensitive drum 1 is efficiently transferred to the intermediate transfer member 5. The transfer roll 11 is made of a conductive or semiconductive roll-shaped member, and a toner image on the intermediate transfer member 5 is collectively applied to the recording sheet P by applying a voltage between the transfer opposing roll 10. Transcript.

  The fixing device 12 includes a heating roll 12a with a built-in heating source and a pressure roll 12b pressed against the heating roll 12a, and these are arranged in parallel to form a nip portion that is pressed against each other. ing. The recording sheet P to which the toner image has been transferred is fed into the nip portion, and is heated and pressed between the heated roll 12a and the pressure roll 12b that are rotationally driven. It is to be crimped.

  The heating roll 12a is formed by forming an elastic body layer such as heat-resistant rubber on the peripheral surface of a metal core, and forming a release layer on the surface thereof. A halogen heater is incorporated as a heating source. ing. The pressure roll 12b is formed by laminating and covering an elastic body layer and a surface release layer on a metal core as in the case of the heating roll 12a.

  The transport rolls 14 are provided so that a pair of rolls are opposed to the recording sheet transport path on the downstream side of the fixing device 12, and each of the transport rolls is supported by a metal shaft so as to be rotatable about a central axis. Has been. Each roll has a plurality of cylindrical members made of synthetic resin having a small width in the width direction of the conveyance path, and the circumferential surfaces of these cylindrical members are pressed against each other, and one of them is By being driven to rotate, the recording sheet is sandwiched and conveyed.

  The temperature sensor 15 detects the temperature of the toner image on the recording sheet being conveyed immediately before the conveyance roll 14, and preferably detects the temperature in a non-contact manner, such as an infrared sensor. Data detected by the temperature sensor is input to the control device 24, and the drive of the fan 22 of the cooling device 20 is controlled based on these detected values.

  The cooling device 20 includes a duct 21 that guides air to be blown to the recording sheet, a fan 22 that sends air to the duct, and a motor 23 that rotationally drives the fan 22. The air that is sent to the duct 21 is an image. It is desirable to introduce from outside the housing of the forming apparatus. The driving of the motor 23 is controlled by a control device 24 and adjusts the rotational speed of the fan 22 based on the detection value of the temperature sensor 15.

In such an image forming apparatus, the toner image is formed by the following process.
First, the surface of the photosensitive drum 1 is charged almost uniformly by the charging device 2, and subsequently, image light is irradiated from the exposure device 3 to form a latent image on the surface of the photosensitive member 1 due to the difference in electrostatic potential. . Then, the rotation of the photosensitive drum 1 moves to a position facing one developing device 4a of the developing unit 4, and the toner of the first color is transferred from the developing device 4a to form a toner image. This toner image is conveyed to a position facing the intermediate transfer member 5 by the circumferential movement of the photosensitive drum 1 and is electrostatically primary-transferred onto the intermediate transfer member. On the other hand, the toner remaining on the photosensitive drum 1 after the transfer of the toner image is removed by the cleaning device 6, and the surface of the photosensitive drum 1 is potentialally initialized by the static elimination exposure device 7 and again opposed to the charging device 2. Move to position.

  Thereafter, the three developing devices 4b, 4c, and 4d of the developing unit 4 sequentially move to positions facing the photosensitive drum 1, and similarly, second, third, and fourth color toner images are sequentially formed, and intermediate transfer is performed. It is transferred onto the body 5 in a superimposed manner. At this time, the transfer roll 11 for secondary transfer is retracted to a position where it does not come into contact with the intermediate transfer member 5.

  The toner images superimposed on the intermediate transfer member 5 are conveyed to a position where the transfer roller 11 and the transfer counter roller 10 face each other by the circumferential movement of the intermediate transfer member 5, and come into contact with the recording sheet P fed from the paper tray. Is done. A transfer bias voltage is applied between the transfer roll 11 and the transfer facing roll 10, and the toner image is electrostatically secondarily transferred onto the recording sheet. Then, the recording sheet P to which the toner image is transferred is conveyed to the fixing device 12.

  The fixing device 12 is in a standby state in which the image forming apparatus is turned on and preheated, and the heating roll 12a is heated to a predetermined temperature, and is further heated with the start of the image forming operation. When the recording sheet is conveyed, the temperature is sufficient for fixing the toner image. Then, the recording sheet led to the nip portion with the pressure roll 12b is heated and pressurized, and the molten toner is pressed onto the recording sheet to form a fixed image.

  The recording sheet sent out from the fixing device 12 is guided by the guide member 16, and an air flow from the cooling device 20 is blown on the guide member. As a result, the toner image is cooled to a temperature not higher than the melting point of the wax contained in the toner. At this time, the temperature of the toner image is detected by the temperature sensor 15, and this detected value is input to the control device 24. When the detected temperature of the toner image is higher than a control temperature set in advance below the melting point, the rotational speed of the fan 22 is increased, and a strong air flow is blown onto the toner image. This ensures that the toner image is cooled below the melting point of the wax contained in the toner before the temperature of the toner image reaches the transport roll 14. Further, when the temperature of the toner image is detected low by the temperature sensor 15, the rotational speed of the fan 22 is reduced to save power.

  As described above, the toner image is uniformly cooled by the time it comes into contact with the conveyance roll 14 and is below the melting point of the wax contained in the toner, so that the portion in contact with the conveyance roll 14 is rapidly cooled from the melting point to the melting point. In other words, it is possible to prevent the occurrence of uneven glossiness due to remarkably high gloss.

In the image forming apparatus, the cooling device 20 blows airflow onto the recording sheet to cool the toner image. However, the fan 22 is driven to rotate in reverse to suck air around the recording sheet. The air flow along the surface of the recording sheet is generated by suction, and the heat radiation from the recording sheet or the toner image is promoted to cool the toner image.
An image forming apparatus including this cooling device is an embodiment of the invention according to claim 3 of the present application.

FIG. 2 is a schematic configuration diagram showing an image forming apparatus which is an embodiment of the invention according to claim 4 or claim 5. FIG. 3 is a schematic configuration diagram of a heating device used in the image forming apparatus.
In this image forming apparatus, a heating device 30 is provided instead of the cooling device 20 of the image forming apparatus shown in FIG. 1, and hot air is blown onto the recording sheet sent out from the fixing device 12 to adjust the temperature of the toner image. The temperature is maintained at 10 ° C. or higher than the melting point of the wax.
Other configurations are the same as those of the image forming apparatus shown in FIG.

  The heating device 30 includes a duct 31 that guides heated air to the recording sheet that has passed through the fixing device, a fan 32 that generates an air flow in the duct, and a heater 33 that heats the air in the duct 31. ing. A temperature sensor 15 for detecting the temperature of the toner image is provided immediately before the recording sheet is fed to the transport roll 14, and this detected value is input to the control device 36. The drive of the fan 32 and the heater 33 is controlled by the control device 36.

  The fan 32 is rotationally driven by a motor 34 to generate an air flow that passes through the duct and reaches the surface on which the toner image of the recording sheet is fixed. Electric power is supplied to the heater 33 from the power source 35 to generate heat and heat the air moving in the duct 31. The heated air is blown onto the surface of the recording sheet to suppress heat dissipation from the toner image or to be heated with warm air blown onto the toner image. The energization of the heater 33 and the motor 34 is controlled by the control device 36, and based on the detection value of the temperature sensor 15, the temperature of the toner on the recording sheet is 10 from the melting point of the wax immediately before the transport roll 14. The temperature is controlled so as to be higher than ℃.

  In this image forming apparatus, the temperature of the toner image on the recording sheet is 10 degrees or more higher than the melting point of the wax immediately before being sent to the transport roll 14. For this reason, even if the recording sheet is sandwiched between the two rolls of the transport roll 14 and the toner image comes into contact with the peripheral surface of the roll, the temperature of the toner image is the melting point of the wax until it passes through the pressure contact portion of the transport roll 14. It will not be below. Therefore, high glossiness due to the rapid cooling of the contact portion with the transport roll 14 from the melting point of the wax to the melting point or less is avoided, and the occurrence of uneven gloss is suppressed. Thereafter, the recording sheet transported by the transport roll 14 is discharged to the paper discharge tray 13 and is uniformly and slowly cooled in the paper discharge tray, so that the toner image becomes a good fixed image without causing uneven gloss.

FIG. 4 is a schematic diagram showing an image forming apparatus according to an embodiment of the invention. FIG. 5 is a schematic configuration diagram of a fixing device used in the image forming apparatus and a heating device provided on the downstream side thereof.
In this image forming apparatus, as in the apparatus shown in FIGS. 2 and 3, the heating device 40 blows heated air onto the recording sheet. The air to be blown is heated by the heating source of the fixing device 12. Things are to be used. Other configurations are the same as those of the image forming apparatus shown in FIG.

  In this image forming apparatus, a cover member 42 for preventing the diffusion of heat is provided around a heating roll 12 a provided in the fixing device 12. The air in the cover member is heated by the heating roll 12a, and the air is guided through the duct 41 to the surface of the recording sheet conveyed on the downstream side of the fixing device.

  A fan 43 that generates an air flow is provided in the duct 41 and is driven to rotate by a motor 44. As a result, air heated around the heating roll 12 a is blown onto the surface of the recording sheet via the duct 41. The driving of the motor 44 is controlled by a control device 45, and the amount of air blown onto the surface of the recording sheet is adjusted based on the detection value of the temperature sensor 15. When the temperature of the toner image is higher than the control reference value set at a temperature higher than the melting point of the wax by 10 ° C. or more, the amount of air sprayed on the recording sheet is decreased. . As a result, the temperature of the toner image when it is fed into the transport roll 14 is adjusted to be 10 ° C. or more higher than the melting point of the wax, and the toner image is brought into contact with the transport roll from the melting point of the wax to the melting point or less. It suppresses occurrence of uneven gloss due to rapid cooling.

  In such a device, the heat of the fixing device 12 can be used to maintain the temperature of the toner image at a temperature higher than the melting point of the wax by 10 ° C. or more. Therefore, a good image can be formed efficiently using energy without providing a separate heating source.

FIG. 6 is a schematic configuration diagram showing an image forming apparatus which is an embodiment of the invention according to claim 7.
The image forming apparatus includes a heating device that maintains a guide member that guides the recording sheet at a high temperature, instead of the heating device in the devices illustrated in FIGS. 2 and 3.
Other configurations are the same as those of the image forming apparatus shown in FIG.

  The heating device 50 is provided on the downstream side of the fixing device 12 and is provided on the back side of the guide member 51 for contacting and guiding the recording sheet being conveyed, and heats the guide member 51. And a heater 52. A temperature sensor 15 is provided immediately before the transport roll, and this detected value is input to the control device 53. The control device 53 controls the power value supplied from the power source 54 to the heater 52 or ON / OFF of power supply based on the detection value of the temperature sensor 15.

The guide member 51 is a plate-like member made of metal or heat-resistant resin, and supports the recording sheet from the lower side and guides it to the transport roll 14. The upper surface of the guide member is flat and is in close contact with the recording sheet so that heat easily moves to the recording sheet when the guide member 51 is at a high temperature.
As the heater 52, various types of heating sources such as a ceramic heater, a resistance wire heater, and a halogen lamp can be used.

  In an image forming apparatus provided with such a heating device, when the recording sheet that has passed through the fixing device 12 is conveyed along the upper surface of the guide member 51, the recording sheet and the recording sheet are caused by heat conduction or radiant heat from the guide member 51. Heat is supplied to the upper toner image. Although heat is radiated from the toner image, when the heat is supplied from the guide member 51 as described above and the temperature of the toner image after fixing enters the transporting roll 14, it is 10 ° C. or higher than the melting point of the wax contained in the toner. It is maintained at a high temperature. As a result, even if the toner image is sandwiched between the conveying rolls 14, the toner image is not rapidly cooled below the melting point of the wax, and the occurrence of significant gloss unevenness is prevented.

FIG. 9 is a schematic configuration diagram illustrating an image forming apparatus that is an embodiment of the invention according to claim 1, claim 2, or claim 8. It is a schematic configuration diagram showing an image forming apparatus which is an embodiment of the invention according to claim 4, claim 5 or claim 8. FIG. 3 is a schematic configuration diagram illustrating a fixing device of the image forming apparatus illustrated in FIG. 2 and a heating device provided on the downstream side thereof. FIG. 9 is a schematic configuration diagram illustrating an image forming apparatus that is an embodiment of the invention according to claim 6 or claim 8. FIG. 5 is a schematic configuration diagram illustrating a fixing device of the image forming apparatus illustrated in FIG. 4 and a heating device provided on the downstream side thereof. FIG. 10 is a schematic configuration diagram showing an image forming apparatus which is an embodiment of the invention according to claim 7 or claim 8. FIG. 10 is a schematic perspective view for explaining a problem in a conventional image forming apparatus, and shows a fixing device, a transport roll provided on the downstream side thereof, and a roll mark generated on a recording sheet.

Explanation of symbols

1: photosensitive drum, 2: charging device, 3: exposure device, 4: developing unit, 5: intermediate transfer member, 6: cleaning device, 7: static elimination exposure device, 8: transfer charger, 9: support roll, 10 : Transfer opposing roll, 11: Transfer roll, 12: Fixing device, 13: Paper discharge tray, 14: Transport roll, 15: Temperature sensor, 16: Guide member,
20: Cooling device, 21: Duct, 22: Fan, 23: Motor, 24: Control device,
30: Heating device, 31: Duct, 32: Fan, 33: Heater, 34: Motor, 35: Power supply, 36: Control device,
40: heating device, 41: duct, 42: cover member, 43: fan, 44: motor, 45: control device,
50: Heating device, 51: Guide member, 52: Heater, 53: Control device, 54: Power supply

Claims (8)

Image forming means for selectively attaching powdery toner to a latent image due to a difference in electrostatic potential to form a toner image;
Transfer means for transferring the toner image directly to the recording sheet or to the recording sheet via an intermediate transfer member;
An image forming apparatus comprising: a fixing device that heats and pressurizes the toner image transferred onto the recording sheet and fixes the toner image on the recording sheet;
The toner includes a resin binder, a coloring material, and a wax that improves releasability,
A cooling device that cools the temperature of the toner image below the melting point of the wax contained in the toner in a sheet conveyance path until the recording sheet discharged from the fixing device enters a downstream conveyance roll; An image forming apparatus.   The image forming apparatus according to claim 1, wherein the cooling device blows air onto a toner image on the recording sheet.   The image forming apparatus according to claim 1, wherein the cooling device sucks air near the toner image. Image forming means for selectively attaching powdery toner to a latent image due to a difference in electrostatic potential to form a toner image;
Transfer means for transferring the toner image directly to the recording sheet or to the recording sheet via an intermediate transfer member;
An image forming apparatus comprising: a fixing device that heats and pressurizes the toner image transferred onto the recording sheet and fixes the toner image on the recording sheet;
The toner includes a resin binder, a coloring material, and a wax that improves releasability,
Heating that heats the temperature of the toner image to at least 10 ° higher than the melting point of the wax contained in the toner in the sheet conveyance path until the recording sheet discharged from the fixing device enters the downstream conveyance roll. An image forming apparatus having the apparatus.   The image forming apparatus according to claim 4, wherein the heating device blows heated air onto a toner image on the recording sheet.   The image forming apparatus according to claim 5, wherein the heated air sprayed on the toner image is heated by a heating source of the fixing device.   The image forming apparatus according to claim 4, wherein the heating device maintains a guide member in contact with the recording sheet in a high temperature state. A temperature sensor that detects a temperature of a toner image on the recording sheet immediately before the conveyance roll, and controls driving of the cooling device or the heating device based on an output of the temperature sensor. The image forming apparatus according to claim 1.

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