JPH1115314A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plurality of fixing roller devices, and to increase the fixing speed while solving the problems of the increase in the parts cost, the increase in the manufacturing cost, and the increase in size of the devices by maximizing the offset preventive capacity and/or the cleaning capacity of a heating device located on the most upstream side at least in the carrying direction of a recording medium among a plurality of heating devices. SOLUTION: A fixing roller 103 and a fixing roller 106 on the downstream side in the carrying direction of a recording medium are provided with offset preventive and cleaning means 110, 118, respectively. In comparing fixing roller devices 102, 105, the offset is easy to generate when the toner on the recording medium (p) is fixed on a nip part of the fixing roller device 102. The offset preventive and cleaning means 110 provided on the fixing roller 103 is pressed against the fixing roller 103 and rotated in the counter direction, and has higher cleaning capacity than that of the offset preventive and cleaning means 118 which is provided on the fixing roller 106 and driven thereby.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus having a fixing device.

[0002]

2. Description of the Related Art Recent OA (Office Automation)
With the progress of image formation, higher-speed image forming apparatuses such as copying machines and printers have been demanded. In such a high-speed image forming apparatus such as a copying machine or a printer, in order to ensure sufficient fixing performance, a plurality of fixing roller devices, which were conventionally one, are provided in the conveying direction of the recording medium, and a high-speed Techniques for realizing speed are known.

Further, in a color image forming apparatus such as a color copying machine or a color printer, a toner image is formed by superimposing at least three color toner images. In many cases, a large amount of toner is present on a recording medium, as compared to a monochrome image forming apparatus. Further, in order to obtain a desired color development, it is necessary to completely melt at least three color toners and to combine and mix the toners. Therefore, in the case of a fixing device using a heat roller, more heat energy is required for heating, melting and fixing the toner image than in a monochrome electrophotography in which a toner image simply needs to be fixed to a recording medium. There are many. Therefore, it is difficult to increase the fixing speed, and it has been considered that such a color image forming apparatus is provided with a plurality of fixing roller devices to realize a high fixing speed.

In a fixing device of the heat roller type, at least one of the rollers has a heat source, and the toner is conveyed between a pair of rollers that rotate while pressing against each other while enclosing and transporting a recording medium carrying an unfixed toner image. It is heated and melted to fix the toner image. The heat roller method has the advantage of high thermal efficiency because the fixing roller, which is the heating member, is in direct contact,
On the other hand, a phenomenon that a part of toner on a recording medium adheres to the fixing roller (referred to as offset) may occur. The offset toner is conversely transferred to the recording medium after one rotation of the fixing roller to stain the recording medium,
Further, the toner that has been offset for a long period of time may accumulate and adhere to the fixing roller, causing a fixing defect or causing a conveyance failure of the recording medium. For this reason, in the heat roller method, it is common to provide an offset preventing means for applying a release agent such as silicone oil or a cleaning means for cleaning the offset toner to the fixing roller so that the toner is hardly offset to the fixing roller. It is. Further, the surface roughness of the fixing roller surface is reduced by polishing or the like so that the toner is less likely to adhere and is easily cleaned, or a fluororesin such as Teflon (trademark of DuPont) having a good release property. May be used for the surface layer of the fixing roller to make it difficult to offset and to easily remove the offset toner.

That is, in many cases, the offset preventing ability and / or the cleaning ability of the fixing roller device are:
It can be said that the surface properties and material of the fixing roller, the functions of the offset preventing means such as the releasing agent applying means and the cleaning means are integrally exhibited.

[0006]

When a fixing device having a plurality of fixing roller devices as described above is used,
The following problems occurred. That is, with the use of a plurality of fixing roller devices, the above-described offset prevention means,
Cleaning means are required for the number of fixing rollers, increasing the number of parts and parts costs, increasing manufacturing and assembly costs,
Problems such as a complicated mechanism and an increase in replacement parts have occurred.

In the case where the individual fixing roller devices are independently driven, the number of driving motors required is the same as the number of the fixing rollers, which leads to an increase in the number of parts and parts costs, an increase in manufacturing and assembly costs, and a complicated mechanism. And other problems have occurred.

Further, when each of the fixing roller devices is driven by a common driving motor, an expensive and large driving motor having a large driving force is required, which causes problems such as an increase in parts cost and an increase in the size of the device. I was

[0009] The present invention has been made in view of the above problems, and increases the number of parts and the cost of parts, increases manufacturing and assembly costs,
An object of the present invention is to provide an image forming apparatus having a high fixing speed by increasing the number of fixing roller devices while suppressing problems such as a complicated mechanism, an increase in replacement parts, and an increase in size of the apparatus.

[0010]

SUMMARY OF THE INVENTION In view of the above problems, according to the present invention, there is provided a toner image forming apparatus for forming an unfixed toner image on a recording medium, and an unfixed toner image formed on the recording medium. An image forming apparatus having a fixing device for fixing, the fixing device including a plurality of heating devices having a heating member that is in direct contact with the toner image, and at least the most viewed in the transport direction of the recording medium. An image forming apparatus is provided, wherein the upstream device has the highest offset prevention capability and / or cleaning capability of the plurality of heating devices.

According to another aspect of the present invention, there is provided a toner image forming apparatus for forming an unfixed toner image on a recording medium, and a fixing device for fixing the unfixed toner image on the recording medium. Wherein the fixing device has a plurality of heating devices including an offset prevention unit and / or a cleaning unit and a heating member having a movable surface that directly contacts the toner image. The load resistance of the offset prevention means and / or the cleaning means of the heating device located at the most upstream position in the transport direction of the recording medium against the movement of the surface of the heating member of the heating device located at the most upstream position; An image forming apparatus is provided which is the largest among the plurality of heating apparatuses.

According to another aspect of the present invention, a toner image forming apparatus for forming an unfixed toner image on a recording medium, and a fixing device for fixing the unfixed toner image on the recording medium Wherein the fixing device has a plurality of heating devices each having a heating member that comes into direct contact with the toner image and a release material application unit, and the most upstream device as viewed in the transport direction of the recording medium. Wherein the amount of the release agent applied by the release agent applying means of the heating device is the largest among the plurality of heating devices.

According to another aspect of the present invention, a toner image forming apparatus for forming an unfixed toner image on a recording medium, and a fixing device for fixing the unfixed toner image on the recording medium Wherein the fixing device has a plurality of heating devices having a heating member that is in direct contact with the toner image, and the heating device is located at least in the most upstream position when viewed in the recording medium conveyance direction. Provided with an offset prevention unit and / or a cleaning unit, and the heating device located at the most downstream side is not provided with the offset prevention unit and / or the cleaning unit.

According to still another aspect of the present invention, there is provided an image forming apparatus wherein the heating member is a roller member and the heating device is a fixing roller device.

Further, according to a preferred aspect of the present invention, there is provided an image forming apparatus in which the toner image forming apparatus is of a wet electrophotographic type.

As described above, the fixing of the unfixed toner image on the recording medium by the heat roller method is performed by directly contacting the fixing roller with the unfixed toner image so that the toner is heated and melted, and the toner particles are united. Then, the toner image is fixed. Here, if the adhesive force between the toner particles and the surface of the fixing roller is smaller than the adhesive force between the toner particles or between the toner particles and the recording medium and the cohesive force of the molten toner itself, no offset occurs.

According to the knowledge of the present inventor, when fixing is performed by a fixing device having a plurality of fixing roller devices, the more the toner is fixed by the fixing roller device located on the upstream side in the transport direction of the recording medium, the more the toner is fixed. In a state close to powder, the adhesion between toner particles and the adhesion between toner particles and the recording medium are small, and offset to the fixing roller is likely to occur. On the other hand, in the fixing roller device located on the downstream side, the toner image is heated and melted once or more by the fixing roller device located on the upstream side, so that the toner particles are coalesced to some extent and fixed to the recording medium. The offset is less likely to occur than when the image is fixed by the fixing roller device located on the upstream side.

In many cases, the release agent, which is often applied to the fixing roller of the fixing roller device located on the upstream side to prevent offset, adheres and remains on the toner image surface in a small amount. The present inventor has also revealed that the fixing roller device on the downstream side is less likely to cause offset.

When fixing an unfixed toner image with a fixing device having a plurality of fixing roller devices in the recording medium transport direction, the present inventor has proposed a method in which the fixing roller device is located upstream of the recording medium transport direction. It has been found that giving good anti-offset ability and / or cleaning ability for offset toner gives satisfactory results.

That is, when an unfixed toner image is fixed by a fixing device having a plurality of fixing roller devices in the recording medium conveyance direction, a high offset prevention is performed on the fixing roller device positioned upstream in the recording medium conveyance direction. With the ability and / or the cleaning ability, the offset is more likely to occur in the fixing roller device located on the upstream side, but the offset is effectively prevented, and the offset toner has a high cleaning ability. As a result, the fixing roller is effectively cleaned, and the fouling of the fixing roller by the offset toner can be prevented.

The toner image on the recording medium is further firmly fixed by a fixing roller device located downstream in the conveying direction of the recording medium, but is fixed by a fixing roller device located downstream. In many cases, the upper toner image is already fixed by the fixing roller device located upstream so as not to cause an offset in the fixing roller device located downstream, and is often fixed by the fixing roller device located upstream. In some cases, the applied release agent remains on the surface of the toner image, and the offset is less likely to occur than in the fixing roller device located upstream. For this reason, it is not necessary to provide the fixing roller device located downstream with the offset prevention ability and / or the cleaning ability of the offset toner as much as the fixing roller device located upstream, and a simple offset mechanism with a simple and small number of parts is required. Prevention means and / or cleaning means can be used. Therefore, it is possible to increase the number of parts, the cost of parts, increase manufacturing and assembly costs, complicate the mechanism, increase the number of replacement parts, and the like, to increase the number of fixing roller devices, and provide a high-speed image forming apparatus. It is possible to do.

The offset prevention ability of the fixing roller device can be evaluated and compared in the following manner.

An image in which fine dots are uniformly distributed at regular intervals is formed on the entire surface of the recording medium. The size of the fine dots is desirably the smallest size that allows the image forming apparatus to form an image. By fixing this image and counting the number of microdots per unit area that are missing or partially missing due to offset in the image after fixing, the offset prevention ability of the fixing roller device can be evaluated. The minute dots may be counted visually using a microscope. For example, if an image processing system such as Oji Scientific Instruments, or an image analyzer such as a dot analyzer (trade name) is used, missing and partially It has a function that can automatically select and count only the missing minute dots, and can measure efficiently. In this case, it goes without saying that the smaller the number of missing and partially missing minute dots per unit area, the higher the offset prevention capability of the fixing roller device.

When the temperature, specifications, cleaning means, etc. of the fixing roller of the fixing roller device to be evaluated and compared are the same and only the offset preventing means is different, a considerable number of fixings are performed using the same recording medium and toner. The amount of the offset toner that has been cleaned by the cleaning unit may be compared before and after that.

The cleaning ability of the fixing roller device can be evaluated and compared in the following manner.

The fixing roller device is placed in a state where the fixing roller device is to be normally used, and the rotation of the fixing roller is temporarily stopped. A certain amount of toner is adhered upstream of the cleaning unit as viewed in the rotation direction of the fixing roller, and after the toner is melted, the fixing roller is rotated, and the adhered toner is cleaned by the cleaning unit. The amount of toner cleaned by the cleaning means is measured. Also in this case, it can be said that the larger the amount of toner that has been cleaned, the higher the cleaning ability of the fixing roller device.

When the temperature and specifications of the fixing roller of the fixing roller device to be evaluated and compared are the same, and only the cleaning means is different but the cleaning means is different, the same number of sheets are fixed using the same recording medium and toner. Is performed continuously, and before and after that, the amount of toner cleaned by the cleaning unit may be compared.

As a means for preventing the offset of the fixing roller device, a method of applying a silicone oil as a release agent to the surface of the fixing roller is usually used. The silicone oil applying means has a basic structure of applying silicone oil by bringing members such as a pad, a web, and a roller made of a porous material such as felt or sponge impregnated with silicone oil into contact with the surface of the fixing roller. Many. In the case of such a structure, a large amount of silicone oil can be supplied by increasing the contact area between the members such as the pad, the web and the roller and the fixing roller or by increasing the contact pressure. The term “contact pressure” as used herein refers to a pressing force per unit contact area, and has a unit of N / m ² .

As a cleaning means of the fixing roller device, at least a portion such as a pad, a web, and a roller made of a porous material such as felt, sponge, or nonwoven fabric is pressed against a surface of the fixing roller at least in contact with the fixing roller. A method of wiping off the offset toner by sliding or a method of scraping off the offset toner by bringing a blade member into contact with the surface of the fixing roller is often used.
In the case of such a method, a high cleaning ability can be obtained by increasing the contact pressure of members such as pads, webs and rollers, the speed difference with the surface of the fixing roller, and the pressing force of the blade member. From the above, it can be seen that if it is attempted to provide a high offset prevention capability and / or a high cleaning capability, the load resistance of the offset prevention unit and / or the cleaning unit against rotation of the fixing roller increases.

As described above, when an unfixed toner image is fixed by a fixing device having a plurality of fixing roller devices in the transport direction of the recording medium, the fixing roller device located downstream is fixed to the fixing roller device located upstream. Often it is not necessary to provide the offset prevention and / or cleaning capabilities of a roller device. Therefore, if the offset prevention unit and / or the cleaning unit of the offset prevention unit and / or the cleaning unit is provided with a simple and simple mechanism of the offset prevention unit and / or the cleaning unit, the load resistance of which is small against the rotation of the fixing roller, is used. It can reduce problems such as an increase in the number and cost of parts, an increase in manufacturing and assembly costs, a complicated mechanism, an increase in replacement parts, and the like. In addition, an inexpensive and small drive motor can be used, and the size of the apparatus can be increased. And other problems can also be reduced. This makes it possible to provide a plurality of fixing roller devices and provide an image forming apparatus having a high fixing speed.

The load resistance of the offset preventing means and / or the cleaning means against the rotation of the fixing roller means the load torque of the offset preventing means and / or the cleaning means against the rotation of the fixing roller divided by the radius of the fixing roller. It was done.

This can be easily measured as follows.

The connection between the fixing roller device and the driving motor is released. With the fixing roller heated to a predetermined temperature at which the fixing roller device is to be used, the offset prevention unit and / or the cleaning unit are removed, and the driving torque of the fixing roller pair is measured with an existing torque meter or the like. Next, the drive torque of the fixing roller pair is measured by an existing torque meter or the like with the offset prevention unit and / or the cleaning unit attached to a predetermined position. When the offset prevention unit and / or the cleaning unit is driven by a common drive motor with the fixing roller pair, another drive motor is connected only to the offset prevention unit and / or the cleaning unit, and the offset prevention unit and / or the cleaning unit is connected. There is a method of driving the cleaning unit at a predetermined driving speed, driving direction, and driving torque that should be used originally. Dividing the difference between these two measured values by the radius of the fixing roller is the load resistance to the rotation of the fixing roller by the offset prevention unit and / or the cleaning unit.

Generally, the greater the amount of silicone oil applied to the fixing roller, the higher the offset prevention ability. When fixing an unfixed toner image with a fixing device having a plurality of fixing roller devices in the conveyance direction of the recording medium, it is necessary to provide the fixing roller device located downstream with the offset prevention capability as large as the fixing roller device located upstream. In many cases, it is not necessary to apply silicone oil to a fixing roller located downstream in the conveying direction of the recording medium as compared with a fixing roller located upstream. Therefore, if a simple mechanism having a small amount of application, a simple mechanism with a small number of parts is used as an offset preventing means of the fixing roller device located downstream, an increase in the number of parts and a cost of parts, an increase in manufacturing and assembly costs, It is possible to provide an image forming apparatus with a high-speed fixing speed by reducing the number of fixing roller devices while reducing problems such as a complicated mechanism and an increase in replacement parts.

The degree of occurrence of the offset of the toner to the fixing roller and the ease of cleaning the offset toner from the fixing roller depend on the surface material, surface roughness, surface temperature, and softening of the toner. It depends on thermal properties such as temperature. Therefore, according to the surface material, surface roughness, surface temperature, thermal properties of the toner, and the like of the fixing roller, in a fixing device having a plurality of fixing roller devices in the traveling direction of the recording medium, when viewed in the transport direction of the recording medium. In some cases, offset prevention means and / or cleaning means may be provided at least at the most upstream heating device, and offset prevention means and / or cleaning means may be provided at least at the most downstream heating device.

That is, when an unfixed toner image is fixed by a fixing device having a plurality of fixing roller devices in the recording medium conveyance direction, only the fixing roller device positioned at least in the most upstream position in the recording medium conveyance direction is used. By providing the offset prevention unit and / or the cleaning unit, the offset can be prevented, and the offset toner is also cleaned by the cleaning unit, thereby preventing the fixing roller from being stained by the toner. The toner image on the recording medium is further firmly fixed by a fixing roller device located downstream as viewed in the transport direction of the recording medium.
The toner image on the recording medium is already fixed by the fixing roller device located upstream so as not to cause an offset at least in the fixing roller device located most downstream, and the fixing roller device located upstream is When the fixing is performed by the fixing roller device located at the most downstream position, the offset may not be generated because the silicone oil applied in step (1) remains on the surface of the toner image. Therefore, only the fixing roller device located upstream in the conveying direction of the recording medium has the offset preventing means and / or
Or, if the cleaning means for the offset toner is provided, the offset prevention means and the cleaning means are not required as many as the number of the fixing rollers. It is possible to provide an image forming apparatus having a high-speed fixing device without causing a problem such as an increase in the number of sheets.

The electrophotographic method, which is one of the image forming methods using toner, includes a dry electrophotographic method in which powdery toner is used for image formation in powder form, and a liquid carrier in which powder toner is used as a liquid carrier. There is a wet electrophotographic system in which an image is formed in a state of being dispersed inside. The particle diameter of the toner particles used in the wet electrophotographic method is as small as 2 μm or less in many cases, compared with the toner particle diameter of about 7 to 10 μm in the dry electrophotographic method. For this reason, the wet electrophotographic method has an advantage that the resolution is excellent and a high quality color image can be obtained. As the liquid carrier, a hydrocarbon-based insulating solvent, for example, Isopar (registered trademark) of Exxon Inc. is often used.
In such an image forming apparatus using a wet electrophotographic method, a fixing device using a heat roller method may be used.

When the fixing device of the present invention is applied to an image forming apparatus of a wet electrophotographic system, a greater effect can be obtained.

In an image forming apparatus using a wet electrophotographic system, an unfixed toner image on a recording medium and the recording medium often hold a large amount of liquid carrier. The mass of the liquid carrier held by the unfixed toner image and the recording medium sometimes reaches twice or more the mass of the toner particles.

When fixing is performed by a fixing device having a plurality of fixing roller devices, the toner image and the recording medium hold a larger amount of liquid carrier as the fixing is performed by the fixing roller device located upstream in the transport direction of the recording medium. doing. Therefore, when the boiling point of the liquid carrier is lower than the softening temperature of the toner particles, most of the heat supplied from the fixing roller is used for vaporizing the liquid carrier, and the temperature of the toner image hardly rises, and the toner is melted by heating. Therefore, the coalescence of the toner particles and the fixation to the recording medium are hindered. Further, when the boiling point of the liquid carrier is higher than the softening temperature of the toner, the temperature of the toner image rises, and even if the toner particles are melted,
Liquid carriers exist between the individual toner particles and between the toner particles and the recording medium, which hinders the coalescence of the toner particles and the fixation to the recording medium.

As the coalescence of the individual toner particles and the sticking to the recording medium are inhibited, the toner particles are more likely to adhere to the surface of the fixing roller and offset is more likely to occur. When fixing is performed by a fixing device having the above fixing roller device, an offset is likely to occur more easily in a fixing roller device located upstream in a conveying direction of a recording medium than in a dry electrophotographic system.

On the other hand, in the fixing roller device located downstream, most of the toner image and the liquid carrier of the recording medium are already vaporized by the fixing roller device located upstream, and the occurrence of the offset is determined by the dry electrophotographic system. Namika,
Less than that. This is probably because the toner particle diameter in the wet electrophotographic method is smaller than the toner particle diameter in the dry electrophotographic method as described above, and the energy required for coalescing the toner particles is small.

As described above, when fixing is performed by a fixing device having a plurality of fixing roller devices, an offset preventing capability and / or a cleaning capability required for a fixing roller device located upstream in the transport direction of a recording medium are required. It can be seen that the difference between the offset prevention ability and / or the cleaning ability required for the fixing roller device located downstream is greater in the wet electrophotographic system than in the dry electrophotographic system.

Accordingly, when an unfixed toner image is fixed by a fixing device having a plurality of fixing roller devices in an image forming apparatus of a wet electrophotographic type, a fixing roller device located upstream in the traveling direction of the recording medium. If the fixing roller device located downstream is provided with an offset prevention capability and / or a cleaning capability higher than the offset prevention capability and / or the cleaning capability of the fixing roller device, the above-described increase in the number of parts and component costs, increase in manufacturing and assembly costs, The complexity of the mechanism,
Problems such as an increase in replacement parts and an increase in the size of the apparatus can be reduced more effectively than an image forming apparatus using a dry electrophotographic system.

In the present invention, the entire apparatus including one roller pair and the offset preventing means and the cleaning means provided on the roller pair is used as a fixing roller device, and each roller constituting the roller pair is simply fixed. Called Laura.

[0046]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A full-color wet electrophotographic printer according to one embodiment of the present invention will be described with reference to FIG. A toner image created by image data that is color-separated into four colors of cyan, magenta, yellow, and black is developed in this order in each color, and is superimposed on a recording medium 6 held on a transfer drum 3. After the black transfer, the transfer drum 3 is separated from the transfer drum 3 by the separation claw 15 and fixed by the fixing device 101.

The primary charger 7 uniformly charges the surface of the photosensitive member 2. As the surface material of the photoconductor 2, amorphous silicon, selenium, organic photoconductor (OPC: Organic Photo Cond)
uctor) and the like, but in this embodiment, OPC is used. The charged surface of the photoconductor 2 is first exposed to an optical pattern corresponding to the image data of the first toner image by a laser beam by an exposing device (not shown), and an electrostatic pattern corresponding to the image data of the first toner image is exposed. A latent image is formed. In this embodiment, a reversal developing method is used in which the absolute value of the surface potential of the latent image forming section is lower than that of the non-latent image forming section.

Next, the developing means 8 disposed on the left side of the photoreceptor 2 is horizontally moved in the direction of arrow C by a driving means (not shown), and the static electricity corresponding to the first image data formed on the photoreceptor 2 is obtained. The electrostatic latent image is developed by the first developing unit 8a in the developing means 8. At this time, the developing roller 13a contacts the photoconductor 2 to supply the developer to the surface of the photoconductor 2, and the developed toner image moves clockwise by the rotation of the photoconductor 2. Then, the squeeze roller 14a removes the excess developer on the photoconductor 2. In FIG. 1, the developing roller 13a rotates counterclockwise, and the squeeze roller 14a rotates clockwise. A certain gap is maintained. In this embodiment, the peripheral speed of each developing roller is 0.5 to 3 times the peripheral speed of the photoconductor 2 (160 m / s), and the gap between the developing roller and the photoconductor 2 is 100 to 3 times.
200 μm, 2-5 times and 50-100 μm for squeeze rollers, respectively.

On the other hand, before the development of the first toner image is started, the leading end of the recording medium 6 sent from the recording medium tray 19 by a conveying roller (not shown) is a gripper of the transfer drum 3.
The gripper 20 is held by the recording medium pressing roller 18
, The recording medium pressing roller 18 that has been separated from the transfer drum is pressed against the transfer drum 3 by a separation mechanism (not shown), and the recording medium 6 is wound around the transfer drum 3 in order from the top while pressing the recording medium 6 against the transfer drum 3. And keep it. The rear end of the recording medium 6 is a recording medium pressing roller 18.
Immediately before approaching the position, the recording medium pressing roller 18 is separated from the transfer drum 3 and the gripper 21 grips the rear end of the recording medium.

The first toner image developed on the photosensitive member 2 is transferred onto the recording medium 6 on the surface of the transfer drum. here,
The recording medium 6 is held on the transfer drum 3 and
When the first development is started after the rotation, the transfer drum 3
When the transfer speed of the recording medium 6 to the recording medium 6 and the transfer process speed are different, the speed is changed after the recording medium is held on the transfer drum 3 and the photosensitive drum 2 and the transfer drum 3 that have been separated by the separating mechanism (not shown). This is preferable because it is possible to provide a time sufficient to complete the pressure contact operation.

Immediately before the transfer, the surface of the photoconductor 2 is charged to the same polarity as the charge polarity of the toner image together with the toner image developed by the pre-transfer charger 17. By this pre-transfer charging, the toner image is pressed against the photoconductor 2 by the electric field force, and the attraction between the photoconductor 2 and the toner image is increased, and the flow and thickening of the toner image in the process of transferring the toner image to the recording medium 6 are reduced. In addition, when a transfer electric field is formed from the surface of the photoconductor 2 to the surface of the transfer drum 3, a repulsive force acts between the surface of the photoconductor 2 and the toner particles. The transfer of the toner image from the photoconductor 2 to the recording medium 6 is performed by forming an electric field between the photoconductor 2 and the transfer drum 3 and moving the toner in the liquid carrier in the nip portion by the electric field force. It is more preferable to apply a bias having a polarity opposite to that of the surface of the photoconductor 2 to the transfer drum for the purpose of forming an electric field because the transfer rate increases. Further, by changing the bias value of the reverse polarity according to the recording medium, it is possible to set the optimal transfer conditions.

Although a small amount of untransferred toner remains on the photoreceptor 2, it is cleaned and removed by the cleaning roller 9 and the cleaning blade 31. Further, the remaining electrostatic latent image is also erased by the neutralizing means 16 disposed downstream of the cleaning unit 28, for example, the neutralizing lamp as in this embodiment, and the next second development is started.

When forming the second toner image, the developing means 8
Moves in the horizontal direction indicated by the arrow C by one developing unit, and the developing unit 8b for the second toner image is arranged at a position opposing the photosensitive member 2. A second toner image is developed on the photoreceptor 2 by the same process as the first toner image, is superimposed on the first toner image already existing on the recording medium, and is transferred onto the recording medium 6. You.

The above process is further repeated for the third and fourth toner images. The order in which the toner images are formed on the recording medium 6 is, for example, yellow, magenta, cyan, and black. This image forming sequence is preferable because the mixing of the other color toner into the yellow developer can be minimized.

On the other hand, it is preferable that the image forming order is black, cyan, magenta, and yellow, because a toner layer having high transparency is superposed on an upper layer on a recording medium and a color reproduction range is expanded. In addition, the order of forming images of cyan, magenta, yellow, and black is preferable because the color reproduction range of the superimposed portions of cyan, magenta, and yellow is widened in a state where the mixing of the multicolor toner into the yellow developer is reduced.

During the transfer of the last toner image, the gripper 20 on the surface of the transfer drum 3 is released immediately before the head of the recording medium 6 comes to the position of the peeling claw 15, and the peeling claw 15 is pressed against the transfer drum 3 at the same time. Thus, the recording medium 6 is moved under the head of the recording medium 6, and the recording medium 6 is separated from the transfer drum 3. here,
After the black development is completed, the recording drum 6 can be peeled off by rotating the transfer drum once. This is more preferable because mechanical vibrations and the like accompanying the separation of the recording medium do not affect the transfer of the last toner image. After the rear end of the recording medium 6 has passed the transfer position (nip portion), the recording medium 6
The rear end gripper 21 is released. After that, when the leading end of the recording medium 6 passes through the transfer drum cleaning member 10, the separated transfer drum cleaning member 10 is pressed against the transfer drum 3, and contacts the surface of the transfer drum 3 during one rotation of the transfer drum 3. At least toner particles are removed from the attached developer. While the transfer drum 3 is being cleaned, the developing means 8 returns to the original position. When the cleaning is completed, the transfer drum cleaning member 10 is separated, and the leading end of the next recording medium 6 is gripped by the gripper 20.

The recording medium 6 separated from the transfer drum 3 is conveyed to the fixing device 101 and fixed.

Next, the fixing device 101 will be described in detail with reference to FIG.

The fixing device 101 includes a fixing roller device 102 including a fixing roller 103 and a fixing roller 104;
Fixing roller device 105 including 106 and fixing roller 107
The above two fixing roller devices are provided. Each fixing roller rotates in the directions of arrows B and C, respectively.

First, the fixing roller device 102 will be described. The fixing roller 103 has a configuration in which a silicone rubber layer 103b is provided on the surface of an iron-based or aluminum-based core material 103a. A rod-shaped halogen lamp 108 is included as a heat source inside the core metal member 103a. A temperature sensor 112 is pressed against the surface of the roller while sliding lightly on the silicone rubber layer 103b to detect the temperature of the roller surface. The roller surface temperature is controlled by turning on / off the halogen lamp 108 by a temperature control unit (not shown) connected to the temperature sensor. Surface temperature is
It is controlled at 180 ° C.

The fixing roller 104 also has a structure in which a silicone rubber layer 104b is provided on the surface of an iron-based or aluminum-based metal core material 104a. A rod-shaped halogen lamp 109 is included in the core metal member 104a as a heat source. A temperature sensor 113 is pressed against the surface of the roller while sliding lightly on the silicone rubber layer 104b to detect the roller surface temperature. The roller surface temperature is controlled by turning on / off the halogen lamp 109 by a temperature control unit (not shown) connected to the temperature sensor.
The surface temperature is controlled at 160 ° C.

The fixing roller 104 is supported by a pressing arm 121 rotatably supported by a shaft 120 via a bearing (not shown), and is urged toward the fixing roller 103 by a pressing spring 122. ing. Therefore, a pressing force is applied to the fixing roller 104, and the fixing roller 104 is pressed against the fixing roller 103 to form a nip portion with the fixing roller 103. In order to form this nip part widely, the fixing roller 10
The fourth silicone rubber layer 104b is set to be thicker than the silicone rubber layer 103b of the fixing roller 103. Specifically, the thickness of the silicone rubber layer 103b is 2 mm, and the thickness of the silicone rubber layer 104b is
Has a thickness of 5 mm.

The fixing roller 103 is provided with an offset prevention / cleaning means 110. The offset prevention and cleaning means 110 is a hollow metal core part 110a made of metal.
And a felt portion 11 attached to the outside of the cored bar portion 110a.
0b, is pressed against the fixing roller pair 103, and is indicated by an arrow D in the figure.
It is rotated in the direction by driving means (not shown). By being pressed against the fixing roller 103 and driven to rotate in the counter direction, the offset toner is wiped off to remove and clean. Also, the core metal part
Silicone oil having a viscosity of 10 Pa · s is sealed in the inside of 110 a. The silicone oil exudes from a number of small holes (not shown) opened in the cored bar 110 a, and the felt 11
Ob has a structure in which a fixed amount is applied to the fixing roller 103. In this way, the structure is such that the silicone oil is applied to the fixing roller and the offset toner is cleaned at the same time. Silicone oil is thinly applied to the fixing roller 103 to prevent the toner from offsetting at the nip portion.

The fixing roller 104 is also provided with an offset prevention and cleaning means 111. this is,
This is for double-sided printing, and is for preventing the front side toner image already fixed at the time of back side printing from being offset to the fixing roller 104. Here, the front surface means the surface on which printing is first performed on the recording medium p, and the back surface is 2
The surface on which printing is performed the second time. The offset prevention and cleaning means 111 has the same structure as the offset prevention and cleaning means 110 of the fixing roller 103, but is pressed against the fixing roller 104 and is driven to rotate in the direction of arrow E. When the fixing roller 104 is pressed and rotated in the direction of arrow E, the offset toner on the surface of the fixing roller pair 104 is removed.
Cleaning is performed by absorbing the felt 111b. Silicone oil having a viscosity of 10 Pa · s is sealed inside the cored bar 111a, and the silicone oil seeps out from a number of small holes (not shown) opened in the cored bar 111a, and 111b allows a certain amount of fixing roller 104
The cleaning of the offset toner and the application of the silicone oil to the fixing roller 104 are performed simultaneously. In this way,
Silicone oil is thinly applied to the fixing roller 104,
This prevents the toner from being offset at the nip.

A fixing roller device 105 is disposed on the left side of the fixing roller device 102, that is, on the downstream side in the transport direction of the recording medium.

The fixing roller 106 also has a structure in which a silicone rubber layer 106b is provided on the surface of an iron-based or aluminum-based core material 106a. A rod-shaped halogen lamp 114 is included as a heat source inside the metal core material 106a. A temperature sensor 116 is pressed against the roller surface in such a manner as to slide lightly on the silicone rubber layer 106b to detect the roller surface temperature. The roller surface temperature is controlled by turning on / off the halogen lamp 114 by a temperature control unit (not shown) connected to the temperature sensor.
The surface temperature is controlled at 180 ° C.

The fixing roller 106 is provided with an offset prevention / cleaning means 118. The offset prevention and cleaning means 118 has the same structure as the offset prevention and cleaning means 110 provided on the fixing roller 103, and is attached to the outside of the metal hollow core part 118a and the metal core part 118a. Unlike the offset prevention and cleaning means 110 provided on the fixing roller 103, the fixing roller 103 is pressed against the fixing roller 106 and is driven to rotate in a direction indicated by an arrow F. Press against the fixing roller 106 and press the arrow
By rotating in the F direction, the offset toner on the surface of the fixing roller 106 is absorbed by the felt 118b to clean the toner. In addition, silicone oil having a viscosity of 10 Pas is sealed inside the cored bar portion 18a,
The silicone oil exudes from a number of small holes (not shown) formed in the cored bar 118a, and a fixed amount is applied to the fixing roller 106 by the felt 118b. The cleaning of the offset toner and the application of the silicone oil to the fixing roller 106 are performed simultaneously. Silicone oil is thinly applied to the fixing roller 106 to prevent the toner from being offset at the nip portion.

The fixing roller 107 has the same configuration as the fixing roller 104, and is made of an iron or aluminum core metal 107a.
Is provided with a silicone rubber layer 107b on the surface thereof. A rod-shaped halogen lamp 11 is provided inside the metal core 107a.
5 is included as a heat source. A temperature sensor 117 is pressed against the roller surface in such a manner as to slide lightly on the silicone rubber layer 7b to monitor the roller surface temperature, and a temperature control unit (not shown) controls the halogen lamp 115.
Is turned on and off to control the roller surface temperature. The surface temperature is controlled at 160 ° C. The fixing roller 107 is supported by a pressing arm 123 rotatably supported by a rotating shaft 120 via a bearing (not shown), and is urged toward the fixing roller 106 by a pressing spring 124. . Therefore, a pressing force is applied to the fixing roller 107, and the fixing roller 107 is pressed against the fixing roller 106 to form a nip portion with the fixing roller 106.
In order to form the nip portion widely, the silicone rubber layer 107b of the fixing roller 107 is set to be thicker than the silicone rubber layer 106b of the fixing roller pair. Specifically, the thickness of the silicone rubber layer 106b is 2 mm, and the thickness of the silicone rubber layer 107b is 5 mm. When the toner image passes through the nip portion, the toner image is further heated, and the fixing is completely completed.

The fixing roller 107 is also provided with an offset prevention and cleaning means 119. this is,
This is for double-sided printing, and is for the offset to the fixing roller 107 of the front side toner image already fixed at the time of back side printing. The offset prevention and cleaning means 119 is the same as the offset prevention and cleaning means 118 of the fixing roller 105.

A comparison between the fixing roller device 102 and the fixing roller device 105 indicates that the recording medium p
The offset is more likely to occur when the upper toner is fixed. Therefore, the offset prevention and cleaning means 110 provided on the fixing roller 103 is rotated by pressing against the fixing roller 103 in the counter direction, and is smaller than the driven and rotated offset prevention and cleaning means 118 provided on the fixing roller 106. Has a high cleaning ability. Since the fixing roller 106 does not require as much cleaning performance as the fixing roller 103, the fixing roller 106 is a simple driven and rotated offset prevention and cleaning means that does not require a driving source or a driving mechanism. Further, the load resistance of the offset prevention and cleaning means 110 that is being pressed against the fixing roller 103 in the counter direction against the rotation of the fixing roller 103 is the offset prevention and cleaning means that is pressed and driven against the fixing roller 106. In FIG. 118, the load resistance is larger than the load resistance to the rotation of the fixing roller 105.

The fixing of the toner image by the fixing device 101 is performed as follows. A recording medium p carrying an unfixed toner image t is conveyed from the right direction of the fixing device 101 with the toner image t having the fixing roller 103 side. The recording medium p is guided to the nip portion of the fixing roller device 102 by the fixing device 101 guide plates 125 and 126, and the toner image is heated while passing through the nip portion so that the toner is melted and fixed.

The recording medium p that has passed through the nip portion of the fixing roller device 102 is guided to the nip portion of the fixing roller device 105 by guides 127 and 128, and the toner image t is heated while passing through the nip portion. The toner melts and the fixing is completely completed. Thereafter, the recording medium p is guided by the guide plates 129 and 131.
Is discharged out of the fixing device.

In the above embodiment, the fixing roller device 10
Although the amount of silicone oil applied to the offset prevention / cleaning means 110 and the offset prevention / cleaning means 118 of the fixing roller device 105 is set to be the same, the amount of silicone oil applied is, for example, the core of the offset prevention / cleaning means. By adjusting the number and size of the small holes formed in the fixing roller 106, or by changing the viscosity of the silicone oil, and further by changing the contact pressure with the fixing roller, the silicone oil flows to the fixing roller 106 located downstream. Next, a fixing device 201 according to a second embodiment of the present invention will be described with reference to FIG. 3, the same members as those of the fixing roller device 101 are denoted by the same reference numerals as in FIG. Further, the structure of the fixing roller, the pressing mechanism, the transporting mode of the recording medium p, and the like are the same as those in the first embodiment, and thus detailed description is omitted. In the second embodiment, an offset prevention unit and a cleaning unit of a fixing roller are different from those of the first embodiment. Fixing roller 10
The cleaning means 231 is provided downstream of the nip portion in the rotation direction 3. The cleaning means 231 is a felt pad impregnated with a certain amount of silicone oil, and is pressed against the fixing roller 103 with a contact pressure p1 by a pressing mechanism (not shown). An offset prevention unit 232 is provided downstream of the rotation direction cleaning unit 231 of the fixing roller 103. The offset prevention means 232 is composed of a hollow metal core 232a made of metal and a felt part 232b attached to the outside of the metal core 232a. As described above, in the second embodiment, the cleaning unit and the offset prevention unit are separated from each other.
35 and offset prevention means 232 are provided. The cleaning unit 235 is a cleaning unit for the fixing roller device 102.
The felt pad 231 has the same structure as that of the cleaning unit 231 and is in pressure contact with the fixing roller 105 with the same contact pressure p1, but has a smaller contact width in the rotation direction of the fixing roller 105 than the cleaning unit 231. Therefore, comparing the cleaning unit 231 with the cleaning unit 235, the cleaning unit 231 that is in pressure contact with the fixing roller 103 with a larger area has a larger cleaning ability. Cleaning means233
Downstream of the fixing roller 102, the same offset prevention means 232 as that provided for the fixing roller 102 is provided.

The fixing rollers 104 and 107 are provided with anti-offset and cleaning hands 111 and 119 for double-sided printing. However, since they are the same as those in the first embodiment, description thereof will be omitted.

In the second embodiment, the cleaning ability is reduced in the conveying direction of the recording medium p by changing the contact area with the same contact pressure. On the contrary, the contact pressure can be reduced with the same contact area. However, a reduction in the cleaning capacity is possible.

In the first embodiment, a felt roller also serving as an offset preventing means is used as the cleaning means, and in the second embodiment, a felt pad is used. In addition, a suede-like synthetic leather roller, A winding type nonwoven web, rubber blade, or the like can also be used, and the cleaning ability can be adjusted by changing the contact area, contact pressure, and relative speed with the fixing roller.

As the offset preventing means, a felt roller in which silicone oil is sealed is used in both the first embodiment and the second embodiment.
A system using a felt pad or a felt roller impregnated with silicone oil, or a system in which silicone oil is directly dropped and supplied to the fixing roller by an appropriate pump mechanism can be used. With a felt pad or felt roller impregnated with silicone oil, it is possible to adjust the silicone oil supply amount, that is, the offset prevention ability, by the contact pressure and the contact area. When a pump mechanism is used, the supply amount of the silicone oil, that is, the offset prevention ability can be adjusted by the drop amount.

Next, a third embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG.

FIG. 4 is a sectional view of a fixing device 301 having two fixing roller devices as in the first and second embodiments. As described above, in a fixing device having a plurality of fixing roller devices, the offset of the toner on the recording medium is more likely to occur as the fixing roller is positioned more upstream in the conveyance direction of the recording medium. Further, since the degree of toner offset and the ease of cleaning the offset toner depend on the surface material, surface roughness, surface temperature, and thermal properties such as toner softening temperature of the fixing roller,
It may be considered that the fixing roller device located on the downstream side may not be provided with the offset prevention unit and / or the cleaning unit. Such an example is shown in FIG.

In FIG. 4 as well, the recording medium is conveyed in the same manner, and the configuration and material of the fixing roller used are the same. In the figures, the same numbers are used for common members.

The recording medium conveyed from the right in the figure.
p is first fixed by the fixing roller device 302. Fixing roller
A cleaning unit 231 is provided downstream of the rotation direction nip portion of the 103, and cleans the offset toner. An offset prevention unit 232 is provided downstream of the cleaning unit 231, and applies silicone oil to the fixing roller 103 to prevent offset. The toner image on the recording medium is further fixed by the fixing roller device 305 located downstream, but at this time, the toner image on the recording medium is already fixed to some extent by the fixing roller device 302, and is fixed. No offset occurs in the roller 305. Therefore, it is not necessary to provide the fixing roller 305 with an offset prevention unit and a cleaning unit.

In the embodiment shown in FIG. 3, neither the offset prevention means nor the cleaning means is provided on the fixing roller 106 located on the downstream side. The ease with which the toner is cleaned depends on the surface material, surface roughness, thermal properties such as the surface temperature and the softening temperature of the toner of the fixing roller. It is also conceivable to provide only one.

The above three embodiments are all directed to a fixing device having two fixing roller devices, but the present invention can also be applied to a case where three or more fixing roller devices are provided.
In this case, for example, the fixing roller devices counting from the upstream in the conveying direction of the recording medium have the same offset prevention capability and / or cleaning capability, and the remaining fixing roller devices have lower offset prevention capability and / or cleaning capability. Is also conceivable.

The offset resistance means and / or the cleaning means have the same load resistance to the rotation of the fixing roller from the upstream in the conveying direction of the recording medium to the counted fixing roller apparatus. A configuration is also conceivable in which the load resistance of the offset prevention unit and / or the cleaning unit with respect to the rotation of the fixing roller is smaller than these.

Further, the fixing roller device is provided with an offset preventing device and / or a cleaning device from the upstream in the conveying direction of the recording medium to the counted fixing roller device, and the remaining fixing roller device is provided with the offset preventing device and / or the cleaning device. The form which does not do is also considered.

As an embodiment of the present invention, an example of a heat roller type fixing device in which the heating member is a roller member and the heating device is a fixing roller device has been described. However, the present invention is limited to the heat roller type. Instead, the present invention can be applied to a fixing device provided with a heating device having a heating member such as a metal or resin belt or a film material.

[0087]

As is apparent from the above description, according to the present invention, even when a plurality of fixing devices in the transport direction of a recording medium are provided, the number of parts and the cost of parts, the cost of manufacturing and assembly are increased, and the mechanism is complicated. Therefore, it is possible to provide an image forming apparatus having a high fixing speed without causing problems such as increase in number of replacement parts, increase in size of the apparatus, and the like.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an electrophotographic apparatus using a fixing device according to an embodiment of the present invention.

FIG. 2 is a sectional view of the fixing device according to the first embodiment of the present invention.

FIG. 3 is a sectional view of a fixing device according to a second embodiment of the present invention.

FIG. 4 is a sectional view of a fixing device according to a third embodiment of the present invention.

[Explanation of symbols]

 1: full-color wet electrophotographic printer 2: photoreceptor 3: transfer drum 6: recording medium 7: primary charger 8: developing means 8a: first developing unit 8b: second developing unit 8c: third developing unit 8d: fourth Developing unit 9: Cleaning roller 10: Transfer drum cleaning member 13a, 13b, 13c, 13d: Developing roller 14a, 14b, 14c, 14d: Squeeze roller 15: Peeling claw 16: Static eliminator 17: Charger before transfer 18: Recording medium Pressing roller 19: Recording medium tray 20, 21: Gripper 25a, 25b, 25c, 25d: Developer tank 28: Cleaning unit 101, 201, 301: Fixing device 102, 105, 202, 205, 302, 305: Fixing roller device 103, 104, 106, 107: Fixing roller 108, 109, 114, 115: Halogen lamp 110, 111, 118, 119: Offset prevention and cleaning means 112, 113, 116, 117: Temperature sensor 120: Rotating shaft 121, 123: Press arm 122, 124: Press spring 125, 126, 127, 128, 129, 130 : Guide plate 231,235: Cleaning means 232: Offset prevention means

Claims (6)

[Claims] An image forming apparatus comprising: a toner image forming apparatus for forming an unfixed toner image on a recording medium; and a fixing device for fixing the unfixed toner image to the recording medium. Wherein the fixing device has a plurality of heating devices having a heating member that is in direct contact with the toner image, and the offset prevention capability and / or cleaning capability of the heating device that is located at least in the most upstream position in the transport direction of the recording medium. Is the highest among the plurality of heating devices. 2. An image forming apparatus comprising: a toner image forming apparatus for forming an unfixed toner image on a recording medium; and a fixing device for fixing the unfixed toner image to the recording medium. The fixing device includes a plurality of heating devices each including an offset prevention unit and / or a cleaning unit, and a heating member having a movable surface that comes into direct contact with the toner image. The load resistance of the offset prevention means and / or the cleaning means of the upstream heating device to the movement of the surface of the heating member of the most upstream heating device is the most resistant among the plurality of heating devices. An image forming apparatus characterized by being large. 3. An image forming apparatus comprising: a toner image forming apparatus for forming an unfixed toner image on a recording medium; and a fixing device for fixing the unfixed toner image on the recording medium. The fixing device includes a plurality of heating devices each having a heating member that comes into direct contact with the toner image and a release material applying unit, and the release device of the heating device that is located at the most upstream position in the conveyance direction of the recording medium. An image forming apparatus wherein the amount of the release agent applied by the agent applying means is the largest among the plurality of heating devices. 4. An image forming apparatus comprising: a toner image forming apparatus for forming an unfixed toner image on a recording medium; and a fixing device for fixing the unfixed toner image to the recording medium. The fixing device has a plurality of heating devices having a heating member that is in direct contact with the toner image, and the heating device located at least in the most upstream position in the recording medium conveyance direction is provided with an offset prevention unit and / or a cleaning unit. An image forming apparatus, wherein the heating device located at the most downstream position is not provided with an offset prevention unit and / or a cleaning unit. 5. An image forming apparatus according to claim 1, wherein said heating member is a roller member, and said heating device is a fixing roller device. 6. An image forming apparatus according to claim 1, wherein said toner image forming apparatus is of a wet electrophotographic type.