JP2006227486A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus equipped with a fixing device which can securely separate recording paper even when the recording paper to be fixed is thin or has toner over the entire surface. <P>SOLUTION: In the image forming apparatus which has a fixing device fixing a toner image on the recording paper at a nip part formed between a fixing member heated by a designated heating means and a pressurization member pressurizing the fixing member, the conveying speed of the recording paper is controlled to a speed slower than a normal speed when the tip part of the recording paper passes through the exit of the nip portion. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus provided with a fixing device that heats and pressurizes unfixed toner on a recording paper, and in particular, improves the separation performance of the recording paper after the recording paper passes through the nip portion of the fixing device. The present invention relates to an image forming apparatus.

  2. Description of the Related Art In an electrophotographic image forming apparatus such as a copying machine, a printer, a facsimile machine, and a multifunction machine having these functions, a latent image corresponding to an original is formed on a photosensitive member, and toner is applied to the latent image. Thus, the visualized toner image is transferred onto the recording paper, and then the toner image transferred onto the recording paper is fixed and discharged.

  When a color image is formed, Y, M, C, and K latent images corresponding to the original color are formed on four photosensitive drums, and the visualized four color toner images are endless. After primary transfer to an intermediate transfer member composed of a belt, secondary transfer is performed on recording paper, and the toner image transferred onto the recording paper is fixed and discharged.

  As a fixing device for fixing a toner image in this manner, a recording sheet on which a toner image is transferred is sandwiched between a nip portion formed by a heating roller incorporating a halogen heater and the like and a pressure roller that presses the heating roller. There is a fixing device of a heat roller fixing system that heats and pressurizes while conveying, and such a fixing device is widely used because of its simple configuration.

  In addition, an endless fixing belt is stretched between a heating roller incorporating a halogen heater or the like and a fixing roller, and has a pressure roller that presses the fixing roller through the fixing belt. There is a belt-fixing type fixing device that heats and pressurizes while sandwiching and transporting the recording paper onto which the toner image is transferred at the formed nip portion, and such a fixing device has a small heat capacity of the heating roller of the fixing belt. Therefore, there is an advantage that the warm-up time is shortened and energy is saved.

  However, in the fixing device, since the toner of the toner image on the recording paper is heated when passing through the nip portion, the toner acts like an adhesive, and the recording paper passing through the nip portion is applied to the surface of the fixing belt. There is a risk that jamming may occur due to winding around the fixing belt or the like without being separated. In particular, when the recording paper is a thin paper having a small basis weight and the toner is on the entire surface, the separation performance is further deteriorated.

  For this reason, a countermeasure for separating the recording paper by providing a separation claw that abuts a fixing member such as a heating roller or a fixing belt on the downstream side in the recording paper conveyance direction of the fixing device is conventionally used. There is also a measure to apply oil to the fixing member to ensure separation performance. In this case, the oil film protects the fixing member from being rubbed and wrinkled by the separation claw.

  On the other hand, in recent years, fixing devices in which oil and oil supply members are abolished to reduce the size and price are made oilless have been frequently used. In the case of forming a monochrome image, glossiness is not so required, so even if the fixing member is slightly wrinkled by the separation claw, there is no problem. However, when a color image is formed, the glossiness is increased, so that even if the fixing member is slightly wrinkled by the separation nail, the image after fixing is easily noticeable.

  Therefore, it is required to separate the recording paper without using the separation claw, and it is generally performed to increase the curvature of the fixing member at the exit of the nip portion. However, in order to increase the speed, the nip width is increased. It is necessary to increase the curvature.

In order to cope with such a problem, a technique has been disclosed in which a small-diameter pressure roller is provided near the exit of the nip portion, and the fixing roll is deformed together with the pressure belt to separate the recording paper (see Patent Document 1).
JP-A-8-166734

  However, when the recording paper to be fixed is a thin paper or recording paper on which toner is placed on the entire surface, it is difficult to reliably separate even if the technique described in Patent Document 1 is used.

  The present invention has been made in view of such a problem, and even if the recording paper to be fixed is a thin paper or a recording paper on which toner is placed on the entire surface, the recording paper can be reliably separated. An object of the present invention is to propose an image forming apparatus provided with a fixing device. It is another object of the present invention to prevent uneven glossiness even when the recording paper conveyance speed is partially different.

  The above object is achieved by the following means.

  [Claim 1] An image provided with a fixing device for fixing a toner image on a recording sheet at a nip formed between a fixing member heated by a predetermined heating means and a pressure member for pressing the fixing member. In the forming apparatus, when the leading edge of the recording paper passes through the exit of the nip portion, the conveying speed is controlled so that the conveying speed of the recording paper is lower than a normal speed. .

  [Claim 2] According to the first aspect of the present invention, when the leading edge of the recording paper passes through the outlet of the nip portion, the nip width is controlled to be narrower than a normal width corresponding to the control. The image forming apparatus described.

  [Claim 3] When the leading edge of the recording paper passes through the exit of the nip portion, the pressure applied by the pressure member is controlled to be lower than the normal pressure corresponding to the control. The image forming apparatus according to claim 1.

  [Claim 4] The conveying speed when the leading edge of the recording paper passes through the exit of the nip portion is controlled in accordance with the thickness of the recording paper. The image forming apparatus described in the item.

  [Claim 5] The conveying speed when the leading edge of the recording paper passes through the outlet of the nip portion is controlled in accordance with the environmental humidity. Image forming apparatus.

  According to the image forming apparatus of the first aspect, since the conveyance speed is lowered only when the leading end of the recording paper passes through the exit of the nip portion, the recording paper to be fixed is thin paper or the toner is on the entire surface. Even if the recording paper is placed on the recording paper, the recording paper can be reliably separated and the number of output sheets after fixing is not greatly affected.

  According to the image forming apparatus of the second and third aspects, even if the conveyance speed of the recording paper is partially different, gloss unevenness does not occur.

  According to the image forming apparatus of the fourth aspect, since the control according to the first to third aspects is performed corresponding to the paper thickness of the recording paper, the recording paper can be further reliably separated.

  According to the image forming apparatus of the fifth aspect, since the control according to the first to fourth aspects is performed corresponding to the environmental humidity, the recording paper can be more reliably separated.

  Embodiments of the image forming apparatus according to the present invention will be described below with reference to the drawings.

  First, an example of an image forming apparatus will be described based on the configuration diagram of FIG.

  The image forming apparatus includes an image forming apparatus main body GH and an image reading apparatus YS.

  The image forming apparatus main body GH is called a tandem type color image forming apparatus, and a plurality of sets of image forming units 10Y, 10M, 10C, and 10K, a belt-like intermediate transfer member 6, a sheet feeding and conveying unit, a fixing device 9, and the like. Consists of.

  An image reading device YS including an automatic document feeder 201 and a document image scanning exposure device 202 is installed on the upper part of the image forming apparatus main body GH. The document d placed on the document table of the automatic document feeder 201 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 202, and the line image sensor CCD is scanned. Is read.

  A 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 an image processing unit, and then exposure means 3Y, 3M, 3C, 3K. Sent to.

  In the image forming unit 10Y that forms a yellow (Y) image, a charging unit 2Y, an exposure unit 3Y, a developing device 4Y, and a cleaning unit 8Y are arranged around the photosensitive drum 1Y. In the image forming unit 10M that forms a magenta (M) color image, a charging unit 2M, an exposure unit 3M, a developing device 4M, and a cleaning unit 8M are arranged around the photosensitive drum 1M. In the image forming unit 10C that forms a cyan (C) color image, a charging unit 2C, an exposure unit 3C, a developing device 4C, and a cleaning unit 8C are arranged around the photosensitive drum 1C. In the image forming unit 10K that forms a black (K) image, a charging unit 2K, an exposure unit 3K, a developing device 4K, and a cleaning unit 8K are arranged 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 device 3C, and the charging unit 2K and the exposure device 3K constitute a latent image forming unit.

  The developing devices 4Y, 4M, 4C, and 4K include a two-component developer including yellow (Y), magenta (M), cyan (C), and black (K) toner having a small particle diameter and a carrier.

  The intermediate transfer body 6 is wound around a plurality of rollers and is rotatably supported.

  The fixing device 9 includes a pressure roller 94 that stretches an endless fixing belt 91 between a heating roller 92 and a fixing roller 93 and presses the fixing roller 93 via the fixing belt 91. The toner image on the recording paper (transfer material) P is heated and pressed at a nip formed between the pressure roller 94 and fixed.

  Thus, 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 transfer means 7Y, 7M, 7C, and 7K (primary transfer). A toner image synthesized with a color image is formed. The recording paper P stored in the paper feeding cassette 20 is fed by the paper feeding means 21 and is conveyed to the transfer means 7A via the paper feeding rollers 22A, 22B, 22C, 22D, the registration rollers 23, etc. A color image is transferred onto P (secondary transfer). The recording paper P to which the color image has been transferred is heated and pressurized by the fixing device 9 and the color toner image on the recording paper P is fixed. Thereafter, the sheet is sandwiched between the sheet discharge rollers 24 and placed on the sheet discharge tray 25 outside the apparatus.

  On the other hand, after the color image is transferred to the recording paper P by the transfer means 7A, the residual toner is removed by the 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, the fixing device according to the present invention will be described with reference to the sectional view of FIG.

  The fixing belt 91 (fixing member) is formed in an endless shape. For example, a heat-resistant resin belt made of PI (polyimide) or the like having a thickness of 70 μm is used as the base, and the outer peripheral surface of the base is heat-resistant to 200 μm in thickness. It is covered with silicon rubber, and is further covered with a 30 μm thick PFA (perfluoroalkoxy) tube as a release layer.

  The heating roller 92 incorporates a halogen lamp 92A as a heating means for heating the fixing belt 91. For example, the outer peripheral surface of a cylindrical hollow rotating body 92B having a thickness of 2 mm formed of aluminum or the like is formed on a heat-resistant PFA. It is covered with a tube 92C and configured as a hard roller.

  The fixing roller 93 is formed by, for example, covering a solid core metal 93A formed of a metal such as iron with a heat-resistant silicon rubber 93B having a thickness of 4.5 mm, and further using a sponge 93C having a thickness of 2.5 mm. Covered and configured as a soft roller.

  The pressure roller 94 (pressure member) incorporates a halogen lamp 94A as a heating means for heating the fixing belt 91. For example, the outer peripheral surface of a cylindrical hollow rotating body 94B having a thickness of 3 mm formed of aluminum or the like. Is covered with a heat-resistant silicone rubber 94C having a thickness of 3 mm, and further covered with a PFA (perfluoroalkoxy) tube 94D having a thickness of 30 μm as a release layer to constitute a soft roller.

  Note that any heating means may be used as a heating means for heating the fixing belt 91, for example, an induction heating heating element using an excitation coil may be used. Further, the heating means is not necessarily arranged in the heating roller 92 or the like, and may be arranged anywhere.

  Further, a position sensor S for detecting the position of the leading end of the recording paper is disposed on the upstream side in the conveyance direction of the recording paper P with respect to the fixing device.

  In the above configuration, when the fixing roller 93 is rotated in the clockwise direction by a driving unit (not shown), the fixing belt 91 stretched on the fixing roller 93 and the heating roller 92 that stretches the fixing belt 91 are also rotated in the clockwise direction. The pressure roller 94 rotates counterclockwise. Further, the fixing belt 91 in contact with the heating roller 92 is heated by the halogen lamp 92A, and the pressure roller 94 is also heated by the halogen lamp 94A. Since the pressure roller 94 presses the fixing roller 93 by a pressing means (not shown), a nip portion N1 formed between the fixing belt 91 wound around the fixing roller 93 and the pressure roller 94 is formed. Thus, the fed recording paper P is heated and pressurized, and the toner image on the recording paper P is fixed.

  Here, when the recording paper is a thin paper and the toner image is placed on the entire surface of the recording paper P, the recording paper P adheres to the surface of the fixing belt 91 even after passing through the nip portion N1. Therefore, it tends to be difficult to separate from the fixing belt 91.

  Therefore, if the rotation speed of the fixing roller 93 or the like is decreased and the conveyance speed of the recording paper P is decreased, the time that the toner adhering to the fixing belt 91 is peeled off due to viscosity becomes long, and the toner peels even with a weak peeling force. Even with thin paper, the separation performance is improved.

  Table 1 shows an example of separation performance when the conveyance speed of the recording paper P is lowered in this way.

  The test conditions in Table 1 are as follows.

Recording paper: J paper, manufactured by Konica Minolta, basis weight 64 g / m ²
Toner adhesion amount: 10 g / m ²
Number of test sheets: 20 sheets fixed at each conveyance speed Fixing belt temperature: 180 ° C.

  Thus, when the recording paper conveyance speed is reduced, the separation performance is improved even for thin paper.

  However, if the recording paper transport speed is simply reduced, the number of output sheets of the recording paper on which the image is formed is reduced, and the productivity of the image forming apparatus is reduced.

  Therefore, as shown in the graph of FIG. 3, the conveyance speed of the recording paper is reduced only when the leading edge of the recording paper passes through the exit of the nip portion of the fixing device. Then, after the leading end of the recording paper is reliably separated from the fixing belt or the like, the conveyance speed is returned to the normal speed. By controlling in this way, the number of output sheets of recording paper P does not decrease so much, and the productivity of the image forming apparatus is not affected.

  Here, since the time from when the leading edge of the conveyed recording paper P passes through the position sensor S to the outlet of the nip portion N1 is known in advance, the position sensor S detects the leading edge of the recording paper P. After the detection, when the time slightly shorter than the above time, that is, the time when the leading edge of the recording paper P is transported to just before the exit of the nip portion N1, has passed, the transport speed of the recording paper P is lowered. Further, after the time when it is considered that the recording paper P passes through the exit of the nip portion N1 and is reliably separated, the transport speed that has been reduced may be returned to the original normal transport speed.

  Note that the low speed at which the recording paper is reliably separated is affected by many parameters such as the normal transport speed, paper thickness, curvature of the exit of the nip, and environmental humidity. Absent. Therefore, it is desirable to conduct an experiment with a predetermined image forming apparatus to obtain a transport speed at which the recording paper is reliably separated and as fast as possible.

  However, if only the leading edge of the recording paper passes through the nip at a low speed and the other part of the recording paper passes through the nip at a normal speed, the heating and pressing time is partially different and glossy. A difference occurs in the degree, resulting in so-called gloss unevenness. Note that although there is a difference in the degree of gloss unevenness depending on the characteristics of the toner used, it is difficult to ignore the gloss unevenness.

  For this purpose, the nip width may be reduced corresponding to the reduction in the conveying speed. For example, if the conveyance speed is reduced to 70% of the normal speed, the nip width may be reduced to 70%. In this way, even if the conveyance speed is changed, the fixing conditions are not changed, and the uneven gloss is eliminated.

  In the fixing device shown in FIG. 2, the heating roller 92 is rotated counterclockwise about the axis of the fixing roller 93 in response to the lowering of the speed of the fixing roller 93, and is at a position indicated by a two-dot chain line. If moved, the nip width can be reduced from N1 to N2.

  There is also a belt fixing device configured as shown in FIG.

  Reference numeral 193 denotes a fixing roller (fixing member) which incorporates a halogen lamp 193A as a heating means and covers the outer peripheral surface of a cylindrical hollow rotating body 193B made of aluminum or the like with a heat-resistant silicone rubber 193C. ing.

  Reference numeral 191 denotes a pressure belt (pressure member), which is stretched between support rollers 195 and 196 and a pressure roller 197, and a pressure auxiliary roller 198 is disposed between the support roller 195 and the pressure roller 197. . The pressure roller 197 and the pressure auxiliary roller 198 press the fixing roller 193 via the pressure belt 191 to form a nip portion N1.

  The position sensor S performs the same operation as the position sensor S shown in FIG.

  As described above, in order to reduce the nip width corresponding to the decrease in the conveyance speed of the recording paper P, the pressure assist roller 198 may be moved to the left. If the pressure auxiliary roller 198 is moved to the position of the two-dot chain line, for example, the nip width can be reduced from N1 to N2.

  FIG. 5 is a diagram of a known heat roller fixing device.

In this fixing device, a nip portion N is formed between a heating roller 292 (fixing member) incorporating a halogen lamp 292A as a heating unit and a pressure roller 294 (pressure member) that presses the heating roller 292. Yes. Further, the arm 295 that can rotate around the support shaft 295A is engaged with the shaft 294A of the pressure roller 294, and the arm 295 is provided by a compression spring 297 provided between the end 295B and the support plate 296. The pressure roller 294 is urged in the direction of the heating roller 292. The position sensor S performs the same operation as the position sensor S shown in FIG.

  In the heat roller fixing device having such a configuration, it is difficult to change the nip width as in the belt fixing device described above, and therefore, the pressure applied by the pressure roller 294 in response to the decrease in the conveyance speed of the recording paper P. To change.

  The relationship between the applied pressure and the glossiness in this case will be described based on the graphs of FIGS.

  FIG. 6 is a graph showing the relationship between the nip time (ms) for the recording paper to pass through the nip portion and the glossiness when the temperature of the fixing roller is 180 ° C. and the pressing force of the pressure roller, that is, the surface pressure is 0.23 MPa. .

  FIG. 7 is a graph showing the relationship between the surface pressure and the glossiness when the temperature of the fixing roller is 180 ° C. and the nip time is 60 ms.

  In FIG. 6, when the conveyance speed is decreased by, for example, 30%, the nip time is increased from 50 ms to 71 ms, and the glossiness is increased by 7 degrees. Therefore, in FIG. 7, in order to reduce the glossiness by 7 degrees, for example, the surface pressure may be decreased from 0.2 MPa to 0.17 MPa.

  As described above, when the conveyance speed of the recording paper P is decreased, the pressing force of the pressure roller, that is, the surface pressure may be decreased so that the glossiness does not increase.

  In the heat roller fixing device shown in FIG. 5, in order to change the pressing force of the pressure roller 294, the cam 298 engaged with the support plate 296 may be rotated around the support shaft 298A.

  Here, the control related to the change in the conveying speed and the nip width described above will be described based on the block diagram of FIG.

  The recording paper leading edge detection means 501 corresponds to the position sensor S shown in FIGS. 2, 4, and 5, and detects the leading edge of the recording paper. Based on this detection result, the control means 500 comprising a CPU, after the time stored in advance, which is the time during which the leading edge of the recording paper is transported to just before the exit of the nip portion of the fixing device, The fixing member driving unit 502 is driven, and in the example of FIG. 2, the rotation speed of the fixing roller 93 is reduced, and the conveyance speed of the recording paper is lowered. At the same time, the control means 500 drives the nip width changing means 503, and in the case of FIG. 2, the heating roller 92 is rotated to reduce the nip width. In the example of FIG. 5, the control unit 500 drives the pressure member driving unit 504 to rotate the cam 298 to reduce the applied pressure.

  Further, the recording paper separation performance also affects the paper pressure, that is, the basis weight.

An example of this is shown in the graph of FIG. FIG. 9 is a graph showing the relationship between the basis weight of the recording paper and the conveyance speed at which the recording paper can be separated when the temperature of the fixing roller is 180 ° C. and the toner adhesion amount is 10 g / m ² . Therefore, when a recording paper with a predetermined basis weight is used, if the normal conveyance speed is on the upper side of the graph, the conveyance speed of the recording paper is only shown when the leading edge of the recording paper passes through the exit of the fixing device. It needs to be lowered so that it is on the lower side.

  Therefore, in FIG. 8, based on the information of the recording paper detection means 505 that detects the paper thickness of the recording paper set by the user on the operation board, or automatically detects the paper thickness of the recording paper using the sensor. The control unit 500 changes the driving amount of the fixing member driving unit 502 and the like.

  Further, when the environmental humidity is high, the separation performance of the recording paper is deteriorated. Therefore, when the amount of decrease in the conveyance speed is determined in advance, it is necessary to consider the humidity.

  Therefore, in FIG. 8, the control unit 500 changes the driving amount of the fixing member driving unit 502 and the like based on the information of the humidity detecting unit 506 that detects humidity.

1 is a configuration diagram of an image forming apparatus. It is sectional drawing of a belt fixing apparatus. It is a graph which shows the change of the conveyance speed of a recording paper. It is sectional drawing of another belt fixing device. It is sectional drawing of a heat roller fixing device. It is a graph which shows the relationship between nip time and glossiness. It is a graph which shows the relationship between surface pressure and glossiness. It is a block diagram regarding control of conveyance speed, nip width, and the like. It is a graph which shows the relationship between the basic weight of a recording paper, and the conveyance speed which can separate a recording paper.

Explanation of symbols

P Recording paper S Position sensor N1, N2 Nip part 91 Fixing belt 92, 292 Heating roller 93, 193 Fixing roller 94, 294 Pressure roller 191 Pressure belt 500 Control means

Claims (5)

In an image forming apparatus including a fixing device that fixes a toner image on a recording sheet at a nip formed between a fixing member heated by a predetermined heating unit and a pressure member that presses the fixing member.
An image forming apparatus, wherein when the leading edge of a recording sheet passes through the exit of the nip portion, the conveying speed is controlled so that the conveying speed of the recording sheet is lower than a normal speed. 2. The image forming apparatus according to claim 1, wherein when the leading end portion of the recording paper passes through the exit of the nip portion, the nip width is controlled to be narrower than a normal width corresponding to the control. . 2. The control unit according to claim 1, wherein when the leading end portion of the recording paper passes through the outlet of the nip portion, the pressing force by the pressing member is controlled to be lower than a normal pressing force corresponding to the control. The image forming apparatus described in 1. The image according to any one of claims 1 to 3, wherein a conveyance speed when the leading end portion of the recording paper passes through the exit of the nip portion is controlled in accordance with a thickness of the recording paper. Forming equipment. 5. The image forming apparatus according to claim 1, wherein the conveyance speed when the leading end portion of the recording paper passes through the exit of the nip portion is controlled according to environmental humidity.

Images