JP2009282105A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus printing an image of high image quality free from image failure due to uneven waxing, by decreasing uneven temperature of paper when it cools after passed through a fixing means. <P>SOLUTION: Recording paper ejected from the fixing means is caused to fall freely onto a guide section. Then, while stopped by a stopping means, this recording paper is cooled to harden wax. This makes it possible to print a high quality image free from uneven waxing. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to cooling of recording paper after passing through fixing.

  2. Description of the Related Art In recent years, image forming apparatuses using an electrophotographic system that copies or prints color images such as photographs on both sides of paper have been widely used. The toner used in such an image forming apparatus contains wax. This wax functions to prevent offset to the fixing roller and to improve the glossiness of the color image when passing through a fixing unit that fixes the toner on the paper by heat and pressure.

  Incidentally, since the recording paper immediately after fixing is at a high temperature, the wax component contained in the toner fixed on the recording paper is not solidified. In this situation, if the recording paper immediately after fixing is discharged or post-processed by the post-processing device, sliding marks with various guides and various rollers at the time of paper discharge or post-processing are generated, and the wax It becomes a surface state that is easily visible as unevenness.

In order to solve such image defects caused by wax unevenness, for example, Japanese Patent Application Laid-Open No. H10-260260 performs control for determining the second conveyance speed, which is the conveyance speed after fixing, according to the toner occupation area ratio, When the rate is equal to or higher than a predetermined value, the second conveyance speed is controlled to be low. By performing such control, it takes more time than usual to discharge the paper, and the temperature of the toner on the recording paper decreases and the wax component solidifies. It is described that it is possible to suppress adverse effects on images such as sliding traces at times.
JP 2005-331634 A

  However, in recent years, it has been elucidated that the main cause of the occurrence of wax unevenness is caused by the temperature unevenness of the paper when the paper after passing through the fixing means cools.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus that reduces the temperature unevenness of a sheet when the sheet is cooled after passing through a fixing unit and prints a high-quality image in order to solve an image defect due to wax unevenness. It is.

The above object can be achieved by the following configuration.
1. An image forming apparatus that forms an image by transferring a toner image formed on an image carrier in accordance with image data onto a recording sheet, the fixing unit fixing the toner image on the recording sheet, and the fixing unit A guide unit for guiding the recording paper discharged from the cooling unit; a cooling unit for cooling the recording sheet guided by the guide unit; a stop member for stopping the recording sheet at a cooling position by the cooling unit; A temperature sensor for detecting a surface temperature of the recording paper stopped at a position; a sandwiching roller pair for sandwiching the recording paper stopped at the cooling position and transporting the recording paper; and a crimping operation and a crimping of the sandwiching roller pair A roller pair driving unit that executes a releasing operation; and at least a control unit that controls the roller pair driving unit, wherein the control unit detects the surface of the recording paper detected by the temperature sensor. If the temperature is equal to or higher than a predetermined temperature, the pressure of the pair of sandwiching rollers is released, and the recording sheet stopped at the cooling position is not transported by the pair of sandwiching rollers, and the surface temperature of the recording sheet detected by the temperature sensor If the temperature is lower than a predetermined temperature, at least the roller pair driving unit is controlled so that the sandwiching roller pair is pressure-bonded and the recording paper stopped at the cooling position is conveyed by the sandwiching roller pair. Image forming apparatus.
2. 2. The image forming apparatus according to 1, wherein the recording sheet discharged from the fixing unit enters the guide unit by a conveying force from the fixing unit and free fall by its own weight.
3. 3. The image forming apparatus according to claim 1, wherein the control unit performs control so that the cooling unit is driven when the recording sheet stops at the cooling position.
4). The cooling means is for sending air to the recording paper to cool it,
The image forming apparatus according to any one of claims 1 to 3, wherein the control unit controls an amount of air blown by the cooling unit.
5. 5. The image forming apparatus according to claim 1, further comprising an assist unit that assists the leading end of the recording sheet discharged from the fixing unit to come into contact with the stop member.

  According to the present invention, the recording paper discharged from the fixing means is freely dropped onto the guide portion, and the wax is solidified by cooling in the state stopped by the stop member, so that a high-quality image free from wax unevenness can be obtained. Can be printed.

  An embodiment of the present invention will be described. In addition, although this invention is demonstrated based on embodiment of illustration, this invention is not restricted to this embodiment. In addition, the following assertive description in the embodiment of the present invention shows the best mode, and does not limit the meaning or technical scope of the terms of the present invention.

  FIG. 1 is a diagram showing the overall configuration of an image forming apparatus according to the present invention. The image forming apparatus includes an image forming unit GH, an image reading device YS, a fixing unit 9 and the like. The image forming unit GH is called a tandem color image forming apparatus, and includes a plurality of sets of image forming units 10Y, 10M, 10C, and 10K, an intermediate transfer member 6, a secondary transfer unit 7A, and the like.

  An image reading device YS including an automatic document feeder 501 and a document image scanning exposure device 502 is installed above the image forming unit GH. The document d placed on the document table of the automatic document feeder 501 is transported by a transport unit, and an image on one or both sides of the document is scanned and exposed by the optical system of the document image scanning exposure device 502, and the line image sensor CCD is scanned. Is read.

  The signal formed by photoelectric conversion by the line image sensor CCD is subjected to analog processing, A / D conversion, shading correction, image compression processing, and the like in the image processing unit, and then exposure means 3Y, 3M, 3C, 3K. Sent to.

  An image forming unit 10Y for forming a yellow (Y) image has a charging unit 2Y, an exposure unit 3Y, a developing device 4Y, a primary transfer unit 7Y, and a cleaning unit 8Y around a photosensitive drum 1Y as an image carrier. . The image forming unit 10M that forms a magenta (M) color image includes a charging unit 2M, an exposure unit 3M, a developing device 4M, a primary transfer unit 7M, and a cleaning unit 8M around the photosensitive drum 1M. An image forming unit 10C for forming a cyan (C) color image includes a charging unit 2C, an exposure unit 3C, a developing device 4C, a primary transfer unit 7C, and a cleaning unit 8C around the photosensitive drum 1C. The image forming unit 10K that forms a black (Bk) image includes a charging unit 2K, an exposure unit 3K, a developing device 4K, a primary transfer unit 7K, and a cleaning unit 8K around the photosensitive drum 1K. The charging unit 2Y and the exposure unit 3Y, the charging unit 2M and the exposure unit 3M, the charging unit 2C and the exposure unit 3C, and the charging unit 2K and the exposure unit 3K constitute a latent image forming unit.

  The developing devices 4Y, 4M, 4C, and 4K contain a two-component developer composed of a toner having a small particle size of yellow (Y), magenta (M), cyan (C), and black (K) and a carrier.

  The intermediate transfer body 6 is wound around a plurality of rollers and is rotatably supported. The fixing unit 9 includes a fixing roller 93 and a pressure roller 94, and fixes the toner image on the recording paper P by heating and pressing at a nip portion formed between the fixing roller 93 and the pressure roller 94. .

  Each color image formed by the image forming units 10Y, 10M, 10C, and 10K is sequentially transferred onto the rotating intermediate transfer body 6 by the primary transfer means 7Y, 7M, 7C, and 7K, and the color image is combined. An image is formed.

  The recording paper P stored in the paper supply tray 21 serving as the recording paper storage means is separated and fed by the paper supply roller 22 of the paper supply means 20, and is in a stopped state via the paper supply roller 23. The paper is fed to the registration roller 24. Therefore, once stopped, the registration roller 24 starts rotating at the timing when the positional relationship between the leading edge and the toner image on the intermediate transfer body 6 exactly coincides, and is fed to the secondary transfer means 7A. A color image is transferred onto the recording paper P (secondary transfer). The recording paper P to which the color image has been transferred is heated and pressurized by the fixing means 9 and the color toner image on the recording paper P is fixed.

  On the other hand, after the color image is transferred to the recording paper P by the secondary transfer means 7A, the residual toner is removed by the intermediate transfer body cleaning means 8A from the intermediate transfer body 6 from which the recording paper P is separated by curvature.

  Although the above is an image forming apparatus that forms a color image, an image forming apparatus that forms a monochrome image may be used.

  Next, cooling of the recording paper P after passing through the fixing unit 9 according to the present invention will be described. The recording paper P discharged from the fixing unit 9 enters the guide unit 11 as it is due to the conveying force of the fixing unit 9. The guide unit 11 performs a cooling fan 110 as a cooling unit that sends air to the recording paper P to cool it, a sandwiching roller pair 111 for transporting the recording paper P, and a crimping operation and a crimping releasing operation of the sandwiching roller pair. It has a roller pair drive section. Further, a stop member 112 for stopping the recording paper P at the cooling position of the cooling fan 110, a switching claw portion 113 for transporting the recording paper P in the direction of the reversing portion RT, and a paper discharge for transporting in the direction of the paper discharge tray 26. And a switching claw portion 114. Further, in order to measure the surface temperature of the recording paper P, temperature sensors S1 are provided at positions corresponding to the leading edge and the trailing edge of the recording paper P. A plurality of temperature sensors S1 are provided in order to cope with recording paper of a small size such as a postcard size to a large size such as A3 size. The pair of nipping rollers 111 stands by in a state where the pressure bonding of the rollers is released when the recording paper P enters the guide unit 11.

  The recording paper P that has entered the guide unit 11 falls freely by its own weight and stops at the stop member 112. S <b> 2 is a sensor that detects that the leading edge of the recording paper P has come into contact with the stop member 112. If the surface temperature of the recording paper P detected by the temperature sensor S1 is equal to or higher than the predetermined temperature, the control means included in the main body device releases the pressure-bonding of the pair of nipping rollers 111 and stops the recording paper P stopped at the cooling position. No conveyance is performed by the pair of nipping rollers 111. If the surface temperature of the recording paper P detected by the temperature sensor S1 is less than a predetermined temperature, the sandwiching roller pair 111 is pressure-bonded, and the recording paper P stopped at the cooling position is moved to the guide portion 11 by the sandwiching roller pair 111. Transport in the direction opposite to the direction of entry. The predetermined value is determined by the size, basis weight, etc. of the recording paper P, and an optimum value is obtained in advance by experiments and stored in a memory of the control means as a table. After the user inputs the size of the recording paper P or the like from an operation unit (not shown) and the control means receives the input signal, the sandwiching roller pair 111 is driven on the basis of the table stored in the memory to load the recording paper P. Transport. Specifically, the nipping roller pair 111 is driven when the surface temperature of the recording paper P becomes 60 ° C. or lower.

  The toner on the recording paper P immediately after being discharged from the fixing unit 9 and the wax contained therein are in a semi-fixed state by heat. As the recording paper P cools, the toner is fixed on the recording paper P. At this time, a high-definition image such as a photographic image transferred to the recording paper P has a temperature rapidly when passing through a conveyance roller or the like. When it falls, the glossiness of the wax changes and appears as wax unevenness. In the image forming apparatus of the present invention, the wax unevenness is avoided by preventing the recording paper P immediately after being discharged from the fixing means 9 from undergoing a rapid temperature change.

  FIG. 2 shows a second embodiment in which the cooling fan 110 is used at the bottom of the image forming apparatus. In FIG. 2, portions common to FIG. 1 are omitted. Also, parts having common functions are given the same reference numerals, and descriptions thereof are omitted.

  In the structure in which the cooling fan 110 is arranged at the bottom of the image forming apparatus, the guide unit 11 is provided with a corner unit 120 for changing the direction of the recording paper P from the vertical position to the horizontal position. Reference numeral 115 denotes assist means for pushing the trailing edge of the recording paper P so that the recording paper P passes through the corner portion and causing the leading edge of the recording paper P to contact the stop member 112. The assist means 115 is stretched around a driving roller 116 and a driven roller 117 that are rotationally driven from a driving unit (not shown), and pushes the trailing end of the paper against an endless belt 118 that rotates in the direction of arrow X and a part of the belt 118. A pushing claw 119 made of an elastic body is provided.

  Further, the guide unit 11 includes a stop member 112 that stops conveyance of the recording paper P at a predetermined position, a sensor S2 that detects that the leading edge of the recording paper P has come into contact with the stop member 112, and the recording paper that is stopped. A plurality of nipping roller pairs 111 for nipping and conveying P and a plurality of temperature sensors S1 for measuring the surface temperature of the recording paper P are provided.

  The assisting means 115 pushes the rear end of the recording paper P with the pressing claw 119 so that the recording paper P reaches the stop member 112 from the corner portion 120. When the sensor S2 detects the recording paper P, the driving of the assist means 115 is stopped.

  The nipping roller pair 111 releases the nip when the recording paper P enters. When the leading edge of the recording paper P is detected by the sensor S2, the control means included in the image forming apparatus presses the clamping roller pair 111 when the surface temperature of the recording paper P detected by the temperature sensor S1 is equal to or higher than a predetermined temperature. The recording paper P stopped at the cooling position is not conveyed by the pair of nipping rollers 111. If the surface temperature of the recording paper P detected by the temperature sensor S1 is less than a predetermined temperature, the pair of nipping rollers 111 are pressure-bonded, and the recording paper P stopped at the cooling position is moved to the guide portion 11 by the nipping roller pair 111. Transport in the direction opposite to the direction of entry.

  Next, the control performed by the control means according to the present invention will be described using the flowchart of FIG. In FIG. 3, the sensor S2 detects that the recording paper P has stopped at the stop member 112 (step S1), and the cooling fan 110 is driven to rotate (step S2). The surface temperature of the recording paper P is measured by the sensor S1 (step S3), and it is determined whether the temperature is equal to or lower than a predetermined temperature (step S4). When step S4 is Yes, the rotation of the cooling fan 110 is stopped (step S5), and the pair of nipping rollers 111 is pressed and rotated to convey the recording paper P in the direction opposite to the direction of entering the guide member 11 (step S6). ). When step S4 is No, the cooling fan 110 is rotated until it reaches a predetermined temperature.

  After step S6, steps such as whether the recording paper P is conveyed in the direction of the reversing part RT or in the direction of the paper discharge tray 26 are performed, but the description thereof is omitted.

  As described above, in the image forming apparatus of the present invention, in order to solve the image defect due to the wax unevenness of the recording sheet P immediately after fixing, the recording sheet P discharged from the fixing unit is freely dropped on the guide portion 11 and used as a stop member. When the wax is solidified by cooling in the stopped state, a high-quality image free from wax unevenness can be printed.

1 is a diagram illustrating an overall configuration of an image forming apparatus according to the present invention. This is a second embodiment in which a cooling fan is used at the bottom of the image forming apparatus. It is a flowchart about the control which a control means performs.

Explanation of symbols

DESCRIPTION OF SYMBOLS 9 Fixing means 11 Guide part 110 Cooling fan 111 Clamping roller pair 112 Stop member 115 Assist means S1 Temperature sensor P Recording paper

Claims (5)

An image forming apparatus that forms an image by transferring a toner image formed on an image carrier in accordance with image data onto a recording paper,
Fixing means for fixing a toner image on the recording paper;
A guide unit for guiding the recording paper discharged from the fixing unit;
A cooling means for cooling the recording paper guided by the guide portion;
A stop member for stopping the recording paper at a cooling position by the cooling means;
A temperature sensor for detecting a surface temperature of the recording paper stopped at the cooling position;
A pair of nipping rollers for nipping the recording sheet stopped at the cooling position and conveying the recording sheet;
A roller pair driving unit that performs a crimping operation and a crimping releasing operation of the pair of clamping rollers;
And at least control means for controlling the roller pair drive unit,
If the surface temperature of the recording paper detected by the temperature sensor is equal to or higher than a predetermined temperature, the control means releases the pressure-bonding of the sandwiching roller pair and causes the recording paper stopped at the cooling position to be removed by the sandwiching roller pair. If the surface temperature of the recording paper detected by the temperature sensor is less than a predetermined temperature without being transported, the sandwiching roller pair is pressed and the recording paper stopped at the cooling position is transported by the sandwiching roller pair. In addition, the image forming apparatus controls at least the roller pair driving unit. 2. The image forming apparatus according to claim 1, wherein the recording sheet discharged from the fixing unit enters the guide unit by a conveying force from the fixing unit and a free fall due to its own weight. The image forming apparatus according to claim 1, wherein the control unit performs control so that the cooling unit is driven when the recording sheet stops at the cooling position. The cooling means is for sending air to the recording paper to cool it,
The image forming apparatus according to claim 1, wherein the control unit controls an amount of air blown by the cooling unit. 5. The image forming apparatus according to claim 1, further comprising an assist unit configured to assist the leading end of the recording sheet discharged from the fixing unit so as to contact the stop member.

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