Patent Application
20070134031
This application claims priority under 35 USC 119 from Japanese patent document 2005-359371, the disclosure of which is incorporated by reference herein.
1. Technical Field
The present invention relates to an image forming apparatus that fixes an unfixed toner image formed on a recording material using electrophotography, electrostatic recording, or the like by heating and fusing, and a fixing device using an endless belt member at the time of fixing and an image forming apparatus using the device.
2. Related Art
Conventionally, in an image forming apparatus such as a copier and printer utilizing electrophotography or the like, as a fixing method for turning an unfixed toner image formed and carried on a recording material into a permanent image by the intermediate transfer method or direct transfer method, a fixing device of type using heat and pressure rolls has been used.
In the type using heat and pressure rolls, a heat roll (fixing roll) and a pressure roll are rotated in pressure contact with respect to each other. The recording material carrying the unfixed toner image is passed through the fixing nip region as the pressure contact part with each other of the pair of rolls. The toner image is heated, pressurized, and fixed on the recording material.
Recently, a method of outputting a digital image in the same finishing as that of a photo print in an image forming apparatus has been proposed.
On the other hand, in character output, a less glossy (low-gloss) image is preferable for better viewing of characters by human eyes. Accordingly, when not only photo printing but also conventional outputting of characters principally is performed, a technology of selectively using two fixing devices, one for fixing as a low-gloss image and another for fixing as a high-gloss image according to need, has been proposed.
As the fixing device for outputting a high-gloss print, an unfixed toner image on a recording material is brought into contact with a fixing belt surface in contact with the fixing roll side and is heated, pressurized, and fused. The fused toner image is cooled to predetermined temperature while the fixing belt is in contact with the recording material, and then, the recording material is detached from the fixing belt. Thereby, the toner image surface can be transferred to the smooth surface property of the fixing belt surface, and consequently, a high-gloss image is obtained.
According to an aspect of the invention, there is provided a fixing device for fixing an unfixed toner image by heating and pressurizing a recording material by which the unfixed toner image is carried, the fixing device including: a heating member having a heat source; a pressurizing member that faces the heating member and that forms a fixing nip region between the heating member and the pressuring member; a belt member that circulates while being tensioned around the heating member and is able to transport the recording material while in contact with a surface of the unfixed toner image of the recording material; and a belt driving device that temporarily stops or decelerates the belt member after a rear edge of the recording material passes through the fixing nip region, and that restores the belt member before a leading edge of a subsequent recording material reaches the fixing nip region.
Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein:
Hereinafter, the invention will be described in detail based on exemplary embodiments shown in the accompanying drawings.
At the beginning, a fixing device according to an aspect of the present invention is described with reference to
The image forming unit used in the exemplary embodiment adopts electrophotography, for example, and has image creating units 20 (20a to 20d) of four colors of yellow (Y-color), magenta (M-color), cyan (C-color), and black (B-color) arranged in parallel to an intermediate transfer belt 30, a so-called tandem configuration. Accordingly, the respective toner images formed in the respective image creating units 20 (20a to 20d) are sequentially transferred onto the intermediate transfer belt 30 for multiplexing, and the multiplexed toner images are transferred by one operation and fixed onto paper transported from the paper feed cassette 11. Note that the color arrangement of the four-color image creating units 20 are not limited to the above order and other orders may be adopted.
The image creating unit 20 (20a to 20d) in the exemplary embodiment has a photoconductor 21 that forms and carries each color component toner, a charger 22 that charges the photoconductor 21 such as a charging roll, an exposure unit 23 that forms a latent image on the charged photoconductor 21 such as a laser scanner, a developing unit 24 for visualizing the electrostatic latent image on the photoconductor 21, a first transfer unit 25 of a first transfer roll, for example, that transfers the toner image on the photoconductor 21 onto the intermediate transfer belt, a photoconductor cleaner 26 that cleans the residual toner left on the photoconductor 21, a static eliminator 27 that eliminates the residual charge on the photoconductor 21, etc. Note that the exposure unit 23 in the exemplary embodiment performs exposure of the entire image creating unit 20 (20a to 20d) by one exposure unit.
Further, the intermediate transfer belt 30 is tensioned around plural tension rolls, and for example, circulated and transported using a tension roll 31 as a drive roll. For example, a second transfer unit 33 of second transfer roll, is oppositely provided using a tension roll 32 as a backup roll. Further, in the position opposed to the tension roll 31 of the intermediate transfer belt 30, a belt cleaner 34 is provided that removes the residual toner on the intermediate transfer belt 30.
Furthermore, within the apparatus main body 10 above the intermediate transfer belt 30, toner boxes 35 of four colors that supply toner to corresponding developing units 24 of the respective image creating units 20 are provided, and supply the toner to the developing units 24 corresponding to the respective colors via transport paths (not shown).
Moreover, the paper transport system in the exemplary embodiment operates in the following manner. The paper fed from each paper feed cassette 11 by a pickup roll 12 is separated by the operation of a feed roll 13 and a retard roll 14, so that only one sheet of paper may be transported into the transport path at the downstream side. Further, in the transport path, a resist roll 15 that positions the paper transported from the paper feed cassette 11 before the paper enters the second transfer unit 33 is processed. A first fixing unit 40 that fixes the unfixed toner image transferred onto the paper by the second transfer unit 33 is also provided. Furthermore, a switching member 16 is provided at the downstream side of the first fixing unit 40. The paper exiting from the first fixing unit 40 may be switched between two paths toward either the post-processing device 50 side or the first eject tray 17 side which accommodates the paper directly ejected from the apparatus main body 10, by switching the switching member 16.
Although the paper feed cassettes 11 have been shown as the two paper feed cassettes 11a, 11b for accommodating paper in different sizes, three or more may be provided, or one may be provided. Further, a manual paper feed tray (not shown) may be provided for guiding the paper from the manual paper feed tray to the transport path.
The first fixing unit 40 of the exemplary embodiment has a configuration shown in
The fixing roll 41 is formed by coating the surface of a cylindrical core 41a made of metal having advantageous mechanical strength and good heat conduction such as aluminum, with an elastic layer 41b of silicone rubber or the like, and coating the surface of the elastic layer 41b with a release layer 41c of PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer) tube.
Further, a heat source 42 such as a halogen lamp or the like is provided inside of the fixing roll 41 for controlling the surface temperature of the fixing roll 41 to be a predetermined temperature.
Here, the material of the core 41a is not especially limited as long as it has mechanical strength and good heat conduction. For example, metal such as stainless, steel, and brass, or an alloy thereof may be used.
Further, the elastic layer 41b is not limited to silicone rubber, but fluorine type rubber or the like may be used as long as it has heat resistance. The method for forming the elastic layer 41b on the surface of the core 41a is not especially limited, and injection molding, coating, or the like may be adopted.
Furthermore, as long as the release layer 41c has heat resistance and adequate releasability to toner, fluorine series rubber, fluorine series resin or the like may be used.
Moreover, the shape and structure of the heat source 42 in the fixing roll 41 are not limited as long as they can be accommodated within the core 41a, and the heat source may be appropriately selected according to the purpose.
Further, in the exemplary embodiment, a temperature sensor 45 for sensing the surface temperature of the fixing roll 41 is provided around the fixing roll 41. The temperature control of the heat source 42 is performed by the temperature sensor 45 so that the surface temperature of the fixing roll 41 will be a predetermined temperature. The temperature sensor 45 is not especially limited as long as it can measure the surface temperature of the fixing roll 41, and for example, a heat-sensitive element such as a thermistor or posistor may be used.
On the other hand, a polyimide film of about 75 μm in thickness is used as a base material of the pressure belt 43, and a release layer of PFA is laminated on the surface thereof. The base material of the pressure belt 43 is not limited to polyimide, but a resin base material such as polyamide-imide or a metal base material such as stainless, nickel, and copper, for example, may be used as long as it has heat resistance. Further, the release layer is not limited to PFA as long as it has detachability of toner attached to the surface. As the material thereof, for example, a fluorine type resin such as PTFE (tetrafluoroethylene) and FEP (tetrafluoroethylene-hexafluoropropylene copolymer), fluoro-rubber, silicone rubber, or the like may be used.
As shown in
As shown in
The fixing roll 61 has a configuration in which a release layer (not shown) of PFA tube or the like is formed around a metal core 61a with high heat conduction. A heat source 65 of halogen lamp or the like is provided within the core 61a. The surface of the fixing roll 61 is heating-controlled by the heat source 65 to a predetermined temperature. Further, in the exemplary embodiment, the fixing belt 63 circulates by the rotation of the fixing roll 61.
On the other hand, in the pressure roll 62, the periphery of a metal core 62a with high heat conduction is coated with an elastic layer 62b of silicone rubber or the like. A release layer (not shown) that is the same as the release layer of the fixing roll 61 is formed on the surface of the elastic layer 62b. Further, in the exemplary embodiment, a heat source 66 of halogen lamp or the like is also provided within the core 62a of the pressure roll 62, and the surface of the pressure roll 62 is heating-controlled to a predetermined temperature. Accordingly, the paper that has been transported to the second fixing unit 60 is heated and pressurized in a fixing nip between the fixing roll 61 and the pressure roll 62 while the toner image surface is in contact with the fixing belt 63.
Furthermore, in the fixing belt 63, a highly smooth covering layer of fluoro-rubber, silicone rubber, or the like is formed on the surface of an endless film made of thermosetting polyimide resin, for example. The belt is tensioned around the fixing roll 61, a detaching roll 67, and a steering roll 68 so as to be circulated by the rotation of the fixing roller 61. The detaching roll 67 follows the movement of the fixing belt 63 and rotates. When the detaching roll 67 tensions the fixing belt 63 around itself, the movement direction of the fixing belt 63 is drastically changed. The paper on the fixing belt 63 is naturally detached from the fixing belt 63 because of the rigidity of the paper itself at the location of the detaching roll 67. Further, the steering roll 68 is to constantly tension the fixing belt 63 itself, and is provided for maintaining the tension by pressing the fixing belt 63 outwards and correcting the bias (the phenomenon that the fixing belt 63 moves toward one of the ends of the steering roll 68) that occurs when the fixing belt 63 circulates.
As the base material and covering layer of the fixing belt 63, the covering layer of about 35 μm is formed on the base material of about 75 μm in order to maintain the mechanical strength and effectively utilize the heat energy.
Furthermore, the cooler 64 within the second fixing unit 60 in the exemplary embodiment is provided between the fixing roll 61 and the detaching roll 67. The cooler is in contact with the fixing belt 63 rear surface, and cools the fixing belt 63 by absorbing heat of the fixing belt 63. Accordingly, the paper transported in close contact with the fixing belt 63 is cooled. The cooler 64 in the exemplary embodiment has a cylindrical shape including a fin member 64a with many heat release fins extending nearly perpendicularly from the surface along the fixing belt 63, and a cover 64b provided so as to cover the fin member. The heat of the fin member 64a is forcibly released by flowing air inside using a blower (not shown) In the drawing, the sign 51 denotes a sensor that senses the passing timing of the paper, and the signs 52, 53 denote paper guides provided in the paper transport path of the second fixing unit 60, and the sign 54 denotes a transport roll.
In the exemplary embodiment, a drive motor 691 that drives the fixing roll 61 is controlled by a control device 69 to turn ON/OFF the rotation of the fixing roll 61. Further, the control device 69 sequence-controls the rotation of the fixing roll 61 according to the passing timing of the paper obtained from the sensor 51. In the exemplary embodiment, the fixing roll 61 stops at the position where the rear edge of the paper exits the fixing nip and then advances by a predetermined distance. The paper stops while attached to the fixing belt 63. The control device 69 turns back the rotation of the fixing roll 61 before the subsequent paper reaches the second fixing unit 60.
Further, the sheet cutting device 70 shown in
On the other hand,
Here, as the circular cutter 72, for example, a roller cutter may be provided along the axial direction for cutting the paper while transporting it.
In the exemplary embodiment as shown in
Further, not only can the sheet cutting device 70 cut the paper into four pieces as shown in the drawing, but it is also capable of turning one sheet of L-size image printed in a postcard-size (100×150 mm) sheet, for example, into a borderless print. Furthermore, by combining the printing of four images on an A4-size sheet and the printing of images one by one in an arbitrary number of postcard-size sheets, an arbitrary number of L-size digital photos can be obtained. Moreover, by varying the width direction position of the blade of the slitter 71, the sheet can be cut into various sizes such as a quarter, a sixth, or an eighth.
Next, an operation in the image forming apparatus will be described.
As shown in
In the exemplary embodiment, switching between paper transport directions by the switching member 16 is performed in the following manner. That is, in the plain paper printing mode of forming normal images (low-gloss printing), after fixing in the first fixing unit 40, the paper is ejected to the first eject tray 17 by the switching member 16. On the other hand, in the photo printing mode of forming high-gloss images like photographic images (high-gloss printing), after fixing in the first fixing unit 40, the paper is ejected to the second fixing unit 60 side by the switching member 16 and fixing by the second fixing unit 60 is further performed. Then, the paper is ejected to the second eject tray 18 via the sheet cutting device 70. Specifically, the sheet cutting device 70 may be used when a borderless print like a photographic image is preferable, and the paper may be ejected to the second eject tray 18 without cutting when there is no need for cutting.
Normally, to obtain a high-gloss image as a photographic image, specialized paper as shown in
The moisture-proof layer L2 is formed by a resin with no air permeability such as polyethylene, and the thickness on the order of several micrometers makes the base material layer L1 moisture-proof. Further, the image receiving layer L3 consists primarily of a thermoplastic resin such as polyester with a melting temperature at about 130° C., for example, and formed with a thickness of 5 to 20 μm. On the other hand, although the base material layer L1 has a composition consisting primarily of cellulose, which is the same composition as plain paper, exclusive base material layer L1 having a different composition can be used.
Therefore, like photographic paper used for silver halide photography, air permeability can be removed by providing the moisture-proof layers L2 on both sides of base material layer L1, and further providing the image receiving layer L3 similar to the toner material. Defects that the base material layer L1 absorbs moisture and expands under the high humidity environment, and curls thereby occur or the toner image is extended and cracked, etc. can be prevented. Smooth print surfaces can be obtained since the toner image is fused together with the receiving layer L3 by the receiving layer L3, and the toner image is embedded in the receiving layer L3 by applying pressure,.
When fixing is performed using the specialized paper by the second fixing unit 60 at the time of photo print mode, the toner image is embedded in the receiving layer L3 as in
In the exemplary embodiment, since the paper is stopped at the position where the paper exits the fixing nip between the fixing roll 61 and the pressure roll 62 and then advanced by a predetermined distance, the paper temperature stops at a relatively high temperature. At this time, although the cooling action on the paper by the cooler 64 is interrupted and the cooling action itself becomes insufficient, there is no problem as long as the position is where no image defect occurs.
Generally, when coated paper having coated layers on both sides like double-sided coated paper or the like is used, the water contained in the base material layer L1 becomes water vapor and expands during heating, and the expanded air bubbles (blisters) cause holes to form in the paper surface.
Therefore, in the exemplary embodiment, it is necessary that the position is set to the shortest stop position where the temperature of the rear edge of the paper becomes 100° C. or less so as to avoid occurrence of blisters. Note that the blisters notably occur even when the heating time is about one second if the temperature is more than 100° C. (one atmospheric pressure environment).
Further, the position where the rear edge of the paper is stopped relates to the viscosity of toner and the viscosity of the image receiving layer L3 of paper. It is provided in a position where the toner viscosity is equal to or more than 105 Pa·s and the viscosity of the image receiving layer L3 is equal to or more than 105 Pa·s. When the toner viscosity and the viscosity of the image receiving layer L3 are less than this, the image attached to the fixing belt 63 is insufficiently solidified and rubbed against the fixing belt 63 during subsequent detachment of paper, and uniform gloss is damaged or image distortion is caused.
As described above, in the exemplary embodiment, since paper is once stopped at predetermined distance from the fixing nip during passing through the second fixing unit 60, the temperature reduction of the fixing belt 63 performed by the cooler 64 is interrupted. The reduction speed in the surface temperature of the fixing roll 61 and the pressure roll 62 can be slowed down and the power applied to the heat sources 65, 66 can thus be reduced. Further, since no image defect occurs in the image at this time, the high-quality and low-power-consumption image forming apparatus is possible.
Although the stop position of paper is performed by the sensor 51 at the upstream side of the fixing nip in the exemplary embodiment, for example, the fixing belt 63 may be stopped by providing a sensor at the downstream side of the fixing nip for directly sensing the rear edge of the paper after passing through the fixing nip.
Further, the timing of stopping the paper may be linked with the power to the heat sources 65, 66 of the fixing roll 61 and the pressure roll 62 being reduced or shut down. Further, for example, air blasting to the cooler 64 may be stopped. The power reduction to the heat sources 65, 66 is performed in a range in which the fixing operation of the subsequent paper is not hindered.
Furthermore, although the post-processing device 50 is used as an optional device in the exemplary embodiment, it may be provided integrally in the apparatus main body, or only the second fixing unit 60 may be provided as the post-processing device 50. It is possible that the first fixing unit 40 is deleted, but, in this case, when the paper is transported to the second fixing unit 60, it is necessary to make sure that image distortion not occur from scraping of the unfixed toner image.
Further, although the fixing belt 63 is stopped at the predetermined distance after the paper exits the fixing nip in the exemplary embodiment, for example, the high-quality and low-power-consumption image forming apparatus can be realized not by stopping the fixing belt 63 but decelerating it instead.
Furthermore, when the rear edge of the paper is cut off by the sheet cutting device 70, because the final image is not hindered even if blisters occur in the cut off part, the stop position of the paper may be brought closer to the fixing nip side by a distance corresponding to the cut off part.
The image forming apparatus in the exemplary embodiment is detachably provided with the post-processing device 50 as an optional device at the side of the apparatus main body 10. Further, no fixing unit is provided within the apparatus main body 10, and fixing is performed by the fixing unit (the second fixing unit) 60 of the post-processing device 50.
The image creating unit 20 provided within the apparatus main body 10 includes the photoconductor 21 and the charger 22, the exposure unit 23, the developing unit 24, the first transfer unit 25, the photoconductor cleaner 26, the intermediate transfer belt 30, etc. provided around the photoconductor 21.
Especially, in the exemplary embodiment, the developing unit 24 is a rotary developing unit, and development is performed on each color latent image formed on the photoconductor 21 with each toner, and the development color is switched with respect to each rotation of the photoconductor 21. Then, the toner is replenished from each color toner box 35 to each corresponding position within the developing unit 24.
Further, in the exemplary embodiment, only one paper feed cassette 11 is provided below the image creating unit 20 of the apparatus main body 10, and a paper feed unit 80 is mounted in the lower part of the apparatus main body 10 and two paper feed cassettes 81, 82 are provided within the unit.
Furthermore, in the apparatus main body 10, the paper onto which unfixed toner images have been transferred by one operation by the second transfer unit 33 is transported by a transport belt 91, and transported to the post-processing device 50 side via an eject roll 92. On the side of the apparatus main body 10 at the upstream side of the resist roll 15, a manual paper feed tray 93 for manually feeding paper is provided.
Moreover, in the exemplary embodiment, the sensor 51 that senses the passing timing of the paper in the fixing unit 60 is provided at the apparatus main body 10 side.
Further, the fixing unit 60 within the post-processing device 50 has the same configuration as that of the second fixing unit 60 of the first exemplary embodiment (see
The example is that, when a high-gloss print is formed on paper of L-size (89×127 mm) with margins and then four sides thereof are cut and a borderless print is output by the image forming apparatus of the first exemplary embodiment, an evaluation test is performed at the time of detachment on occurrence of blisters of paper on the fixing belt and image defects.
The test conditions are as follows.
(1) Condition of Fixing Unit Settings
The blister evaluation is performed by observing what the distance at which the rear edge of paper departs from the fixing nip is good. As shown in
On the other hand, regarding image defects, the relationship between temperature and glossiness at the time of detachment from the fixing belt is checked by changing air blasting conditions to the cooler, and the result as in
Further, focusing attention on toner viscosity, when it exceeds 105 Pa·s, it is found that the gloss never changes depending on the detachment speed or temperature at the time of detachment, and uniform and good-quality gloss can be obtained.
Furthermore, when the gloss irregularities are visually recognized in images when the detachment temperature is changed, the result as in
The measurement of glossiness is performed using gloss measurement equipment (manufactured by BYK-Gardner) with high sensitivity in specular gloss, incident angle of 20°, and reflection angle of 20°.
Next, a comparison test with respect to average power consumption in the fixing unit when the drive control method of the fixing belt is changed is performed in the above described conditions.
The three kinds of drive conditions of the fixing unit are as follows.
The evaluation is performed by measuring average power consumption after the continuous printing has been maintained for five minutes in the above drive conditions.
The result is as shown in
Further,
When the fixing belt is stopped at timing with no paper in the fixing nip as with the intermittent drive in the example, sometimes the fixing belt thermally deforms into a shape that wraps around the fixing roll depending on the material of the fixing belt and the temperature of the fixing roll. In this case, the power reduction can be realized without causing thermal deformation of the fixing belt by not stopping the fixing belt but decelerating the driving speed.
The example is that, when A4-size printing with four sheets of L-size (89×127 mm) paper is continuously performed by the image forming apparatus of Embodiment 2, an evaluation test is performed on occurrence of blisters of paper on the fixing belt and image defects at the time of detachment.
The test conditions are as follows.
(1) Condition of Fixing Unit Settings
As the blister evaluation, the same evaluation as that in Example 1 is performed. As shown in
On the other hand, regarding image defects, after temperature and glossiness irregularities at the time of detachment from the fixing belt are checked, the result as in
Next, a comparison test with respect to average power consumption in the fixing unit when the drive control method of the fixing belt is changed is performed in the above described conditions.
The three kinds of drive conditions of the fixing unit are as follows as with the Example 1.
The evaluation is performed by measuring average power consumption after the continuous printing has been maintained for five minutes in the above drive conditions.
The result is as shown in
Further,
The foregoing description of the embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| P2005-359371 | Dec 2005 | JP | national |
