JP4287707B2 - Image forming method and image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a technique relating to fixing in an electrophotographic image forming apparatus, and more particularly to a technique relating to prevention of winding for the purpose of oilless in an image forming method in a color image forming apparatus.
[0002]
[Prior art]
In an image forming apparatus using an electrophotographic image forming method, a developer image on an image carrier or an intermediate transfer member is transferred to a recording material, and the recording material onto which the developer image has been transferred is heated by a fixing device. Pressure is applied to fix the toner image on the recording material.
[0003]
For example, Patent Document 1 discloses a technique related to fixing having a fixing member containing a conductive material on a surface layer containing a curable modified silicone resin, and Patent Document 2 discloses a first technique having a heat source. A technique relating to fixing having a release sheet that is non-contact with the rotating body and prevents the recording material from being completely wound around the first rotating body is disclosed.
[0004]
[Patent Document 1]
JP 2000-112271 A
[Patent Document 2]
JP 2001-83832 A
[0005]
[Problems to be solved by the invention]
In Patent Document 1, the wear resistance is improved by devising the material of the fixing member. However, since the separation claw comes into contact, the wear cannot be completely suppressed and there is a problem in terms of durability. Further, since toner accumulates on the separation claw, scratches and toner adhesion occur on the image.
In Patent Document 2, the edge of the release sheet is not in contact with the first rotating body. However, when the amount of toner attached to the leading end of the recording material is large, the leading end of the recording material substantially sticks to the first rotating body. Since it comes out of the nip portion in a state where it is in a state, it slips through the gap between the release sheet and the first rotating body, making it difficult to peel off from the first rotating body.
SUMMARY OF THE INVENTION An object of the present invention is to solve the above-described problems and provide an image forming method having good durability and no winding of a recording material even in oilless fixing, and an image forming apparatus using the image forming method.
[0006]
[Means for Solving the Problems]
The invention of claim 1 comprises a transfer member for transferring a developer image on an image carrier or an intermediate transfer member to a recording material, and a transfer bias applying means for applying a transfer bias to the transfer member. A transfer process for transferring a developer image on an image carrier or an intermediate transfer body to a recording material by applying a predetermined transfer bias to a member from a transfer bias applying means, and carrying an unfixed developer image in the transfer process A recording material disposed on one side of the recording material, the surface layer of which forms a conductive image, and a member on the side of forming an image via a recording material carrying an unfixed developer image. A nip portion is formed with a member that does not form an image to be pressed, and at least one of a member that forms an image or a member that does not form an image is heated by a heating unit, and an unfixed developer image is supported. The recording material to be And a fixing step of fixing the unfixed developer image onto the recording material by passing the recording material, wherein the recording material that has passed through the nip portion is electrostatically attracted to a member side that does not form the image. Yes.
[0007]
In the present invention, It has a peeling member that peels off the recording material that has passed through the nip portion from a member on the image forming side, and this peeling member is not in contact with the member on the image forming side.
[0008]
In the present invention, A voltage that generates an electric field in a direction in which the recording material that has passed through the nip portion is attracted to the member that does not form an image is applied between the member that forms the image and the member that does not form the image. It is a feature.
[0009]
In the present invention, an electric field is generated in such a direction that the recording material that has passed through the nip portion is attracted to the member that does not form an image. A voltage is applied only when the leading edge of the recording material passes through the nip.
[0010]
In the present invention, The applied voltage is controlled by the relationship between the front and back image ratios at the front end of the recording material.
[0013]
In the present invention, A voltage that generates an electric field in a direction in which the recording material that has passed through the nip portion is attracted to the member that does not form an image is applied between the peeling member and the member that does not form an image.
[0014]
In the present invention, It is characterized in that the surface layer of the member on which the image is not formed is charged to a polarity opposite to the charging polarity of the recording material by a fixing charging means.
[0015]
In the present invention, The fixing charging unit is characterized in that only the surface layer portion of the member that does not form an image facing the leading end portion of the recording material at the nip portion is charged.
[0017]
In the present invention, As a developer for forming an image, a toner containing at least a binder resin, a colorant, and a wax is used.
[0018]
In the present invention, any one of the image forming methods or color image forming methods described above An image is formed by the above.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
(Technical background)
In the electrophotographic fixing, a heating roller having a non-adhesive elastic body with a heating source inside and a pressure roller covered with the elastic body are provided, and the appropriate pressure is applied between the rotating rollers. A heat roller fixing method is used in which a recording material to which toner is transferred is passed and fixed. However, in this heat roller fixing method, since the heat capacity of the heating roller is large, it takes time to heat the heating roller to a predetermined temperature necessary for fixing, and the standby time for warming up the apparatus is lengthened. Yes. Further, a large amount of power consumption is required to maintain the temperature of the heating roller, and the power consumption of the entire apparatus is greatly increased. Therefore, in order to solve these problems, a belt heating and fixing method in which the toner on the recording material is fixed on the belt surface has been developed. In the belt heating and fixing method, heat energy necessary for fixing can be obtained simply by heating a fixing belt having a relatively small heat capacity to a predetermined temperature, so that standby time can be shortened and power consumption can be reduced. .
[0020]
In recent years, color image forming apparatuses are required to sufficiently melt toner in order to ensure color reproducibility and glossiness of an image, and therefore, toner having a low melting point is used. The low melting point toner is likely to cause high temperature offset, and therefore a large amount of low viscosity silicone oil is applied as a release agent. When a large amount of silicon oil is used in this way, problems such as silicon oil spillage and adhesion to the recording material occur. Therefore, in order to solve such problems, a fixing device has been devised to obtain excellent color reproducibility and glossiness after fixing with little or no use of silicone oil. .
[0021]
However, in an oil-less fixing device, when the peeling member is brought into contact with the image forming member, the friction between the peeling member and the image forming member is large, and the image forming member is scratched. End up. Since the scar appears on the image, the life of the fixing device cannot be extended. Therefore, in the oilless fixing device, in order to extend the life of the fixing device, it is necessary to make the peeling member and the member on the image forming side non-contact.
[0022]
In such a background, in the present invention, a transfer member that transfers a developer image on an image carrier or an intermediate transfer member to a recording material, and a transfer bias applying unit that applies a transfer bias to the transfer member are provided. A transfer step of applying a predetermined transfer bias to the transfer member from the transfer bias applying means to transfer the developer image on the image carrier or the intermediate transfer member to a recording material, and passing through the transfer step. A fixing method for fixing an unfixed developer image on a recording material by applying heat and pressure to the recording material carrying the unfixed developer image, the image forming member, The image forming member that presses against the image forming member via the recording material carrying the developer image and the recording material that has passed through the nip portion are separated from the image forming member. A fixing step having a release member; An image forming method comprising the side member surface to form an image is electrically conductive, the recording material having passed through the nip portion, and to attract the member side on the side that does not form an electrostatically image.
[0023]
By adopting such an image forming method, the recording material that has exited the nip portion is attracted to the member on the side that does not form an image, and the gap between the recording material and the member that forms the image is increased. The recording material can be peeled off from the member on the side where the film is formed, and winding can be prevented.
[0024]
In addition, since the peeling member is in a non-contact state with the member on the image forming side, the recording material can be easily peeled off with the non-contact peeling member, and the image forming side with the peeling member can be removed. The life of the apparatus can be extended without damaging the members.
[0025]
The image forming method of the present invention will be described in the case of using a negatively charged developer. A positive bias is applied to the image bearing member or intermediate transfer member to the transfer member, and the developer image is transferred onto the recording material. At this time, the recording material is positively charged and comes out of the nip portion in a state of being charged positively.
[0026]
Hereinafter, means for attracting the recording material that has passed through the nip portion to the member side that does not electrostatically form an image will be described.
(1) A bias is applied between a member on the image forming side and a member on the non-image forming side. A positive bias is applied to the member on the image forming side, and the member on the non-image forming side is grounded. As a result, an electric field is generated from the member on the image forming side to the member on the non-image forming side.
(2) The surface layer of the member on which no image is formed is insulative, and the member on which the image is formed is grounded. If the surface layer of the member on which the image is not formed is made of a fluororesin, the member surface layer on the side where the image is not formed is charged negatively due to frictional charging with the recording material. As a result, an electric field is generated from the member on the image forming side to the member on the non-image forming side. (3) A bias is applied between the peeling member and the member on the side where no image is formed. A positive bias is applied to the peeling member, and the member on the side where no image is formed is grounded. As a result, an electric field is generated from the peeling member toward the member on which the image is not formed.
(4) A fixing charging means for charging the surface layer of the member on which no image is formed to a negative polarity is provided.
By such means, the recording material coming out of the nip portion is attracted to the member on the side not forming an image, so the gap between the member on the image forming side and the recording material is increased, and even in a non-contact peeling member The recording material can be easily peeled from the member on the image forming side.
[0027]
When the surface layer of the member on which the image is not formed is insulative, the surface layer of the member on which the image is not formed is charged by frictional charging with the recording material, and the member on which the recording material does not form an image electrostatically Therefore, the recording material can be easily peeled off by a non-contact peeling member without applying a voltage.
[0028]
When a voltage that generates an electric field in a direction in which the recording material that has passed through the nip portion is attracted to the member that does not form an image is applied between the peeling member and the member that does not form the image.
Since the recording material is attracted to the member that does not form an image, the recording material can be easily peeled off by the non-contact peeling member.
[0029]
If the surface layer of the member that does not form an image is charged to a polarity opposite to the charging polarity of the recording material, the recording material is electrostatically attracted to the member that does not form an image. The recording material can be easily peeled off.
[0030]
Here, the case where negatively charged toner is used has been described. However, in the case where positively charged toner is used, the same effect can be obtained by reversing the polarity of the applied bias or the polarity of the member on the side where no image is formed. Is obtained. However, the means (2) can be applied only when negatively charged toner is used.
[0031]
If the bias is applied only when the leading edge of the recording material passes through the nip portion, the image can be peeled off without affecting the image, and a good fixed image can be obtained. In other words, by applying no voltage when the unfixed developer image passes through the nip portion, a good fixed image can be obtained without affecting the fixed image due to the voltage application.
[0032]
Further, since the adhesive force between the recording material and the image forming member changes depending on the image ratio of the image front end portion, if the applied bias is controlled by the image ratio of the image front end portion, the recording material can be peeled well. it can. Further, at the time of double-sided fixing, if the tip image ratio on the member side on which the image is not formed is high, the adhesive force to the member side on which the image of the recording material is not formed is large, and the member on the side where the recording material forms the image Can be easily peeled off, and the recording material can be prevented from being wound. In this case, if the applied bias is too large, the recording material is wound around the member that does not form an image. Therefore, if the applied bias is controlled by the tip image ratio on the member that does not form an image, the image is formed. It is possible to prevent the unwrapped member from being wound around the member side, and the recording material can be satisfactorily peeled even during double-sided fixing.
[0033]
If only the surface layer portion of the member that does not form an image facing the leading edge of the recording material is charged at the nip portion, the surface of the member that does not form an image is charged at the image fixing portion after the leading edge of the image. Therefore, a good fixed image can be obtained without affecting the fixed image. A charging means for fixing may be used for charging the surface layer of the member on which the image is not formed.
[0034]
In the transfer process, the transfer bias applied to the transfer member only at the front end portion of the recording material is increased, and the charge amount at the front end portion of the recording material is increased. As a result, the force at the leading end of the recording material is attracted to the member that does not form an image, and the gap between the leading end of the recording material and the member that forms the image is enlarged. In addition, the recording material can be easily peeled off from the member on the image forming side. In addition, since the normal transfer bias is applied to the image portion after the leading end of the recording material, the transferred image is not affected.
[0035]
When a toner containing a wax is used as a developer, peeling with a non-contact peeling member can be easily performed even in an oilless fixing process.
[0036]
【Example】
The present invention will be described in more detail with reference to the drawings. FIG. 1 shows an example of an image forming apparatus using an electrophotographic system to which the present invention is applied. This color image forming apparatus is a color image forming apparatus, in which photosensitive members 1A, 2A, 3A, and 4A on a drum as a plurality of image carriers are arranged in parallel on the same plane, and a timepiece shown in the figure by driving means (not shown). It is rotationally driven in the turning direction. Each photoconductor is composed of an organic or inorganic material having photoconductivity.
[0037]
As a color image forming apparatus, a color separation superposition transfer method is generally used. In this type of image forming apparatus, image information light obtained by separating a document into three colors of blue, red, and green is read by a document reading unit, and image calculation processing is performed based on the intensity level of each color light. On the four photoconductors 1A, 2A, 3A, and 4A based on the written image data to be developed in each color of yellow (Y), cyan (C), magenta (M), and black (BK) obtained in the above. Optical writing is performed, and the obtained electrostatic latent images are developed by developing units 1B, 2B, and 3B containing yellow, cyan, magenta, and black developers provided for the respective photoreceptors 1A, 2A, 3A, and 4A. Develop with 4B.
[0038]
In the apparatus of FIG. 1, each color separation image information is optically color-separated by a document reading unit 29 provided at the upper part of the color image forming apparatus main body 100, read by each of the three CCDs 20, and calculated based on the output signals. Optical writing is performed by the laser writing devices 1D, 2D, 3D, and 4D disposed above the photoreceptors 1A, 2A, 3A, and 4A based on the color data obtained by processing.
[0039]
The photoreceptors 1A, 2A, 3A, and 4A are charged negative (-) by the charging devices 1E, 2E, 3E, and 4E, respectively, and the portion where the optical writing has been performed developing Reversal development is performed with a negatively charged toner as an agent. For each charging device, a device that generates a charge by corona discharge, such as a corotron or a scorotron, and distributes it on the surface of each photoconductor is used. Developing devices 1B, 2B, 3B, and 4B are disposed in the vicinity of each photoconductor. These developing devices are arranged in the order of 1B, 2B, 3B, and 4B from the paper supply side 300 toward the paper discharge side 400. It is arranged. The developing devices 1B, 2B, 3B, and 4B contain yellow, cyan, magenta, and black toners, and yellow, cyan, magenta, and black developer images on the photoreceptors 1A, 2A, 3A, and 4A. As toner images. Each of the toner images is sequentially transferred onto a sheet P as a recording material conveyed from the sheet feeding side by positive corona charging from a transfer member described later in the order of yellow, cyan, magenta, and black.
[0040]
Below the photoreceptors 1A, 2A, 3A, and 4A, a transfer belt 25 as a transfer member is wound around a plurality of rollers and is disposed in close proximity to the surface of each photoreceptor. The transfer belt 25 extends from the paper supply side 300 toward the paper discharge side 400, and a driving force is transmitted to a roller from a driving source (not shown). In this embodiment, the transfer belt 25 is rotated counterclockwise in the figure. The paper P is conveyed from the paper supply side 300 to the paper discharge side 400. Reference numeral 27 in the figure denotes a registration roller.
[0041]
In the vicinity of the back side of the transfer belt 25, transfer chargers 1C, 2C, 3C, and 4C as transfer bias applying means for applying a transfer bias to the transfer belt 25 are opposed to the photoreceptors 1A, 2A, 3A, and 4A, respectively. It is arranged. The transfer belt 25 is made of a dielectric material such as a polyester film and is positively charged by the transfer chargers 1C, 2C, 3C, and 4C. In the vicinity of the transfer belt 25 on the side opposite to the arrangement side of the transfer chargers 1C, 2C, 3C, and 4C, a static eliminator 26 is provided. This neutralizing device 26 neutralizes the transfer belt 25 after the separation of the paper P. In this example, negative AC corona discharge is performed by the charger from both sides of the transfer belt 25 to neutralize the charge accumulated in the transfer belt 25 (static elimination). ) To initialize the potential of the transfer belt 25. A cleaning unit 22 for cleaning residual toner on the surface of the transfer belt 25 is disposed in the vicinity of the transfer belt 25 located on the paper feeding side 300.
[0042]
In the main body 100 located on the paper discharge side 400, the fixing device 30 is provided at a position separated from the transfer belt 25. Above the transfer belt 25 located on the fixing device 30 side, a separation device 28 is provided. Arrangement Has been. The separation device 28 performs negative AC corona discharge with a charger from the upper surface of the paper P conveyed by the transfer belt 25, neutralizes (charges out) the accumulated charge of the paper P, and separates the paper from the transfer belt 25. This prevents AC corona discharge and toner dust caused by peeling discharge. The sheet P after the image transfer is separated from the transfer belt by the curvature separation action between the charge from the separation device 28 and the curved surface of the transfer belt 25, and is conveyed to the fixing device 30, where the toner image is fixed and the color image is fixed. can get.
[0043]
The fixing device 30 in the fixing process to which the present invention is applied will be described. The fixing device 30 is an oilless fixing device that does not use so-called oil application means. As shown in FIG. 2, the fixing device 30 is an endless fixing belt as a member on the side of forming an image disposed on one side of a sheet P carrying an unfixed toner image indicated by a symbol T. 8, a fixing roller 6 as a fixing rotator around which the fixing belt 8 is wound, a heating roller 7, and a pressure roller 10 as a member on the side that does not form an image and is disposed to face the fixing belt 8. .
[0044]
The pressure roller 10 is in pressure contact with the fixing roller 6 with the fixing belt 8 interposed therebetween to form a nip portion 50. A peeling plate 14 as a peeling member for peeling the paper P from the fixing belt 8 is provided at a position facing the surface of the fixing belt 8 downstream of the nip portion 50 in the rotation direction of the fixing belt 8. The peeling plate 14 is spaced from the surface of the fixing belt 8 and is not in contact. In this example, the fixing roller 6 is rotationally driven in a clockwise direction in the figure by a driving unit (not shown). For this reason, the fixing belt 8 and the heating roller 7 rotate in the same direction, and the pressure roller 10 in pressure contact with the fixing belt 8 is driven to rotate counterclockwise in the drawing. The pressure roller 10 instead of the fixing roller 6 may be the driving side.
[0045]
The sheet P carrying the unfixed toner image T on the surface is heated and pressed by the nip portion 50 formed by the fixing roller 6 and the pressure roller 10 via the fixing belt 8 to fix the toner image. The paper P that has exited the nip 50 is peeled off from the fixing belt 8 by the peeling plate 14 and discharged from the paper discharge unit 400 in FIG. The substrate of the release plate 14 is a SUS plate having a thickness of 0.2 mm, and the surface of the substrate is covered with a fluorine resin layer having a thickness of 20 μm. Since the peeling plate 14 is not in contact with the fixing belt 8, the fixing belt 8 is not damaged, and the life of the fixing device can be extended even in an oilless fixing device.
[0046]
As the base of the fixing belt 8, an endless belt-like base made of heat-resistant resin or metal is used. As the material of the heat resistant resin, polyimide, polyamideide, polyetherketone (PEEK) or the like is used, and as the material of the belt base, nickel, aluminum, iron or the like is used. The thickness is preferably 100 μm or less. The surface of the fixing belt 8 is required to be releasable because it is in pressure contact with the paper P and the toner image, and is preferably excellent in heat resistance and durability. For this reason, the surface layer of the fixing belt 8 is configured to be coated with a conductive heat-resistant release layer (fluorine resin or the like). The fluororesin is applied to the surface of the substrate by spraying or the like, and heated and fused to form a surface release layer. As another configuration of the fixing belt 8, an elastic body layer such as a silicone rubber is provided on a base of a heat resistant resin such as polyimide, and a conductive fluororesin (PFA tube or the like) is further separated on the elastic body layer. A mold layer may be provided. The silicone rubber layer of the elastic layer is desirable as a condition for obtaining good fixability and thermal responsiveness when the rubber hardness is 25 to 65 degrees (JIS A hardness meter) and the thickness is in the range of 100 to 300 μm.
[0047]
The heating roller 7 is disposed above the fixing roller 6. The heating roller 7 is a thin metal roller made of iron or aluminum having an outer diameter φ20 to φ30 and having a thickness of 0.3 to 1 mm, and includes a halogen heater 16 as a heating means. The halogen heater 16 is controlled to have a constant temperature by a known temperature control element such as a thermistor and control means, and has a function of heating the fixing belt 8 to a necessary temperature. The heating roller 7 also functions as a tension roller, and a fixing belt 8 is stretched in the direction of arrow A in the drawing by a tension spring 9.
[0048]
The fixing roller 6 has an outer diameter φ40 larger than that of the pressure roller 7, and an elastic layer made of a heat-resistant elastic body such as foamed silicone rubber or liquid silicone rubber in order to obtain a nip width on the outer periphery of the iron cored bar. I have. The thickness of the elastic layer is about 3 to 6 mm, and the surface hardness of the fixing roller 6 is about Asker C 30 to 70 Hs.
[0049]
The pressure roller 10 has a heat-resistant elastic layer such as fluorine-based rubber or silicone rubber and a surface release layer made of fluorine-based resin formed on the outer periphery of an iron or aluminum core. The thickness of the elastic layer of the pressure roller 10 is about 0.5 to 2 mm, and its surface hardness is Asker C 70 to 90 Hs. In the pressure roller 10, a halogen heater 15 as a heating unit may be provided in order to accelerate the temperature rise of the pressure roller 10.
[0050]
When a toner containing a binder resin, a colorant, and wax is used as the toner, a color fixed image can be obtained satisfactorily even in an oilless fixing device. In this example, the heating means is provided inside the heating roller 7 and the pressure roller 10, but it is provided outside the roller instead of inside the roller to heat the fixing belt 8, the pressure roller 7 or the pressure roller. You may make it do. As the heating means, induction heating or the like may be used instead of the halogen heater. Further, an image forming apparatus to which the image forming method of the present invention is applied can perform image formation at a linear speed of 200 mm / s.
Example 1
FIG. 3 is a block diagram for explaining the concept of an image forming method having a transfer process and a fixing process to which the present invention is applied.
Transcription process
A toner image is formed on the photoconductor 31 by a charging, exposure, and developing device (not shown). In the present embodiment, a negative toner is used, and a transfer device having a transfer roller 32 facing the photoconductor 31 and a transfer bias power source 17 for applying a positive transfer bias to the transfer roller 32 is provided. The toner carried on the photoreceptor 31 is transferred to the paper P by a transfer device. In this transfer process, since a positive transfer bias is applied to the transfer roller 32, the paper P is charged to a positive polarity. Further, when the front end P1 of the paper P passes through the nip portion between the photosensitive member 31 and the transfer roller 32, a transfer bias larger than the transfer bias of the image portion may be applied to increase the charge amount of the front end P1 of the paper.
Fixing process
The sheet P that has passed through the transfer process and is positively charged is conveyed to the fixing device 30 having the basic configuration described above. Here, the surface 8a of the fixing belt 8 has conductivity. 3 further includes a power supply brush 19 that contacts the surface 8a of the fixing belt 8, a belt bias power source 18 that applies a positive bias to the power supply brush 19, and a surface 10a of the pressure roller 10. The neutralizing brush 33 is provided. The surface layer 10a of the pressure roller 10 is covered with a conductive PFA tube. The base material and the elastic layer of the fixing belt 8 may also be conductive, and the power supply brush 19 may be brought into contact with the inner surface of the fixing belt 8.
[0051]
FIG. 4 shows the charged state of the paper P and the electric field on the outlet 51 side of the nip 50. The neutralizing brush 33 in contact with the surface 10a of the pressure roller 10 is grounded, and the surface potential of the pressure roller 10 is set to 0V. The belt bias power source 18 applies a positive bias to the power supply brush 19 and charges the surface 8a of the fixing belt 8 to a positive polarity. As a result, an electric field is generated in the direction from the fixing belt 8 to the pressure roller 10 indicated by an arrow curve on the exit 51 side of the nip portion. Since the sheet P is positively charged, the sheet 51 is electrostatically attracted to the pressure roller 10 side on the exit 51 side, and the gap between the sheet leading end P1 and the fixing belt 8 is increased. As a result, the paper can be easily peeled from the fixing belt 8 even with the non-contact peeling plate 14.
[0052]
As an example of bias application, the belt bias may be applied only when the paper leading edge P1 passes through the outlet 51. Also in this case, since the paper leading edge P1 is attracted to the pressure roller 10, the gap between the paper leading edge P1 and the fixing belt 8 can be increased in the same manner as described above. As a result, the recording material can be easily peeled from the fixing belt 8 even with the non-contact peeling plate 14. Since no belt bias is applied to the image portion after the paper leading end portion P1, a good fixed image T1 can be obtained without affecting the fixed image. Further, as described in the above description of the transfer process, if the charge amount of the paper front end portion P1 is increased, the paper front end portion P1 receives a large force from the electric field toward the pressure roller 10 side. The gap of the belt 8 becomes larger, and the paper P can be more easily peeled from the fixing belt 8 even with the non-contact peeling plate 14.
[0053]
Next, the case where the control part 34 which controls the applied voltage of the belt bias power supply 18 is provided is demonstrated. The control unit 34 receives the front and back image data recorded on the paper P, and calculates the front and back image ratio. When the image ratio on the front surface is high, the adhesive force between the paper P and the fixing belt 8 is large, so the applied voltage of the belt bias power supply 18 is increased, and the paper P is attracted to the pressure roller 10 to increase the force. When the image ratio on the front side is low or the image ratio on the back side is high, the paper P is easily peeled off from the fixing belt 8, so the applied voltage of the belt bias power source 18 may be lowered or the application may be stopped. On the other hand, when the image ratio on the back surface is high and the paper can be easily wound around the pressure roller 10, the paper P can be prevented from being wound around the pressure roller 10 by applying a negative bias to the fixing belt 8.
[0054]
In this embodiment, since the paper P is electrostatically attracted to the pressure roller 10 side, a good fixed image can be obtained by the non-contact release plate 14 even in a color image having a large toner adhesion amount. Further, when a toner containing a binder resin, a colorant, and wax is used as the toner, a good color fixed image can be obtained even in an oilless fixing device.
(Example 2)
Next, another example of an image forming method having a transfer process and a fixing process to which the present invention is applied will be described. Since the transfer process is the same as in Example 1, the fixing process will be described. FIG. 5 is a schematic configuration diagram of a fixing device for carrying out the second embodiment. The sheet P that has passed through the transfer process and is positively charged is conveyed to the fixing device 30 having the basic configuration described above. In the second embodiment, the nip portion 50 is formed using a pressure roller 35 instead of the pressure roller 10. The pressure roller 35 is covered with an insulating PFA tube, and the surface layer 35a of the pressure roller 35 is made insulating. The fixing belt 8 is covered with a conductive PFA tube, and a neutralizing brush 33 is brought into contact with the surface 8 a of the fixing belt 8. The neutralizing brush 33 is grounded, and the surface potential of the fixing belt 8 is set to 0V. The insulating PFA tube on the surface layer 35a of the pressure roller 35 is frictionally charged with the paper when the paper P is passed, and is negatively charged.
[0055]
With such a configuration, an electric field is generated in the direction from the fixing belt 8 to the pressure roller 35 on the outlet 51 side of the nip portion 51. Since the sheet P is positively charged, the sheet P is electrostatically attracted to the pressure roller 35 side on the exit 51 side, and the gap between the sheet leading end portion P1 and the fixing belt 8 is increased. As a result, the paper P can be easily peeled from the fixing belt 8 even with the non-contact peeling plate 14.
[0056]
In FIG. 5, the surface layer of the pressure roller 35 is formed of PFA, and the PFA charging series is negative with respect to the paper P. Further, by using such an insulating PFA for the surface layer, electric charges are likely to accumulate on the surface layer of the pressure roller 35. That is, in the case of frictional charging, it is known that the charging polarity changes depending on the order of the charging series of the two materials to be rubbed. However, in the case of friction between the paper P and the PFA as in this example, the PFA Since the charging series is on the negative side, the paper P is charged positively (+) and the PFA is negatively charged (-).
(Example 3)
Next, a third embodiment of the image forming method having the transfer process and the fixing process to which the present invention is applied will be described. Since the transfer process is the same as in Example 1, the fixing process will be described. FIG. 6 is a schematic configuration diagram of a fixing device for carrying out the third embodiment.
Fixing process
FIG. 6 is a schematic configuration diagram of the fixing device according to the third embodiment. The sheet P that has passed through the transfer process and is positively charged is conveyed to the fixing device 30 having the basic configuration described above. The configuration of the pressure roller 10 is the same as that of the first embodiment. The neutralizing brush 33 is brought into contact with the surface 10a of the pressure roller 10, the neutralizing brush 33 is grounded, and the surface potential of the pressure roller 10 is set to 0V. The surface 8a of the fixing belt 8 is covered with a PFA tube.
[0057]
In this example, a peeling plate bias power source 36 for applying a bias to the peeling plate 14 is provided. The peeling plate bias power source 36 applies a positive bias to the peeling plate 14. As a result, an electric field is generated from the peeling plate 14 toward the pressure roller 10 on the outlet 51 side of the nip portion 50. Since the paper P is positively charged, the paper P is electrostatically attracted to the pressure roller 10 side on the outlet 51 side, so that the gap between the paper leading edge P1 and the fixing belt 8 is increased. As a result, the paper P1 can be easily peeled from the fixing belt 8 even with the non-contact peeling plate 14. As shown in FIG. 6, since the peeling member 14 is not in contact with the fixing roller 6, the fixing roller 6 is not charged to +. For this reason, the unfixed toner image T transferred to the paper P is not disturbed.
[0058]
Next, the case where the control part 34 which controls the applied voltage of the peeling plate bias power supply 36 is provided is demonstrated. As in the first embodiment, the front and back image data recorded on the sheet is input to the control unit 34, and the front and back image ratios are calculated. When the image ratio on the front surface is high, the adhesive force between the paper P and the fixing belt 8 is large. Therefore, the applied voltage of the peeling plate bias power source 36 is increased, and the paper P is electrostatically attracted to the pressure roller 10 to increase the force. Increase When the image ratio on the front side is low or the image ratio on the back side is high, the paper P is easily peeled off from the fixing belt 8, so the applied voltage of the peeling plate bias power source 36 may be lowered or the application may be stopped. On the other hand, when the image ratio on the back surface is high and it is easy to wind around the pressure roller 10, conversely, when a negative bias is applied to the release plate 14, the recording material can be prevented from being wound around the pressure roller 10.
(Example 4)
Next, a fourth embodiment of the image forming method having the transfer process and the fixing process to which the present invention is applied will be described. Since the transfer process is the same as in Example 1, the fixing process will be described. 7 and 8 are schematic configuration diagrams of a fixing device for carrying out the fourth embodiment.
Fixing process
The sheet P that has passed through the transfer process and is positively charged is conveyed to the fixing device 30 having the basic configuration described above. Similar to the second embodiment, the pressure roller 35 is covered with an insulating PFA tube, and the surface layer 35a of the pressure roller 35 is made insulating. The fixing belt 8 is covered with a conductive PFA tube, and the neutralizing brush 33 is brought into contact with the surface 8 a of the fixing belt 8. The neutralizing brush 33 is grounded, and the surface potential of the fixing belt 8 is set to 0V.
[0059]
In this example, a pressure roller charging roller 37 is provided as a fixing charging means for charging the surface 35 a of the pressure roller 35 to a negative polarity by contacting the surface 35 a of the pressure roller 35. The pressure roller charging roller 37 is made of foamed silicone and charges the surface 35a of the pressure roller 35 by frictional charging. As another configuration of the pressure roller charging roller 37, the pressure roller charging roller 37 is formed of a solid rubber roller, a negative bias is applied to the pressure roller charging roller 37, and the surface of the pressure roller 35. 35a may be negatively charged.
[0060]
With such a configuration, the insulating PFA tube of the surface layer 35a of the pressure roller 35 is negatively charged. Therefore, on the outlet 51 side of the nip portion 50, an electric field extends from the fixing belt 8 to the pressure roller 35. Occurs. Since the sheet P is positively charged, the sheet P is electrostatically attracted to the pressure roller 35 side on the exit 51 side, so that the gap between the sheet leading end portion P1 and the fixing belt 8 is increased. As a result, the paper can be easily peeled from the fixing belt 8 even with the non-contact peeling plate 14.
[0061]
In FIG. 7, the −potential is also charged upstream of the nip portion 50 of the pressure roller 35. However, since the paper P is not in contact with the pressure roller 35 before entering the nip portion 50, the positive potential on the back side of the paper P is lost and the toner holding power does not disappear. Some positive potential of the paper P is lost when it passes through the nip 50. However, in this example, the transfer bias at the leading end portion P1 of the paper P is increased to increase the negative charge amount of the paper P so that electrostatic force acts on the paper P also at the outlet 50B of the nip portion 50. For this reason, before entering the nip portion 50, the sheet P is not in contact with the pressure roller 35. Therefore, the positive potential on the back side of the sheet P is not lost, and the unfixed toner image is not disturbed.
[0062]
Further, the pressure roller charging roller 37 may charge only the pressure roller 35 portion facing the paper front end portion P1. In this case, the pressure roller charging roller 37 is brought into contact with the pressure roller 35 only when the surface portion of the pressure roller 35 facing the front end P1 of the sheet passes the position facing the pressure roller charging roller 37. It is done. Specifically, a pressure roller charging roller 37 is rotatably attached to one end of an arm 41 having a fulcrum 42, and a movable piece 38 a of an electromagnetic solenoid 38 is pin-coupled to the other end of the arm 41. Further, the charging roller 37 for the pressure roller is urged in a direction away from the pressure roller 35 by the tension spring 40 hooked on the arm 41, and is normally not in contact with the pressure roller 35. The electromagnetic solenoid 38 is connected to the control unit 39, and when receiving a signal from the control unit 39, as shown in FIG. 8, the electromagnetic solenoid 38 operates in the direction of pulling the movable piece 38a and pulls the other end of the arm 41, In the illustrated example, the arm 41 is rotated in the clockwise direction. That is, the arm 41 is operated in a direction in which the pressure roller charging roller 37 is brought into contact with the pressure roller 35. By operation of this electromagnetic solenoid 38. The pressure roller charging roller 37 is brought into contact with the surface 35a of the pressure roller 35 to be frictionally charged. The control unit 39 generates a signal when the surface portion of the pressure roller 35 facing the paper front end portion P1 passes through a position facing the pressure roller charging roller 37. In this example, the arm 41, the electromagnetic solenoid 38, and the control unit 39 constitute a contact / separation mechanism 60 for the pressure roller charging roller 37.
[0063]
In this way, if only the pressure roller 35 portion facing the paper front end portion P1 is charged, the paper P is charged positively, so that the paper front end portion P1 is electrostatically charged on the outlet 51 side of the nip portion 50. As a result, the gap between the leading end P1 of the sheet and the fixing belt 8 is increased, and the sheet P can be easily peeled from the fixing belt 8 even with the non-contact peeling plate 14. In the image fixing section after the leading edge of the image, since the surface 35a of the pressure roller 35 is not charged, a good fixed image can be obtained without affecting the fixed image.
[0064]
In the above four embodiments, the toner image on each photoconductor is transferred to the paper P. However, the same effect can be obtained by transferring the toner image on the intermediate transfer body to the paper P. In the above four embodiments, the fixing belt is used as the image forming member, but the same effect can be obtained by using a roller member having a heating means as the image forming member. it can.
[0065]
【The invention's effect】
According to the present invention, the surface layer of the image forming member has conductivity, and the recording material is electrostatically attracted to the non-image forming member side. It is possible to provide an image forming apparatus according to an image forming method that can peel the material and prevent the recording material from being wound around the image forming member. In addition, when the peeling member is not in contact with a member on the image forming side, the peeling member does not damage the member on the image forming side, and an image forming apparatus using a long-life image forming method is provided. it can.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram showing an example of a color image forming apparatus using an image forming method of the present invention.
FIG. 2 is a configuration diagram of a fixing device to which the present invention is applied.
FIG. 3 is a diagram illustrating a configuration example of an apparatus using the image forming method according to the first exemplary embodiment.
4 is an enlarged view showing another configuration example of an apparatus using the image forming method of Embodiment 1. FIG.
FIG. 5 is a diagram illustrating a configuration example of an apparatus using the image forming method according to the second embodiment.
FIG. 6 is a diagram illustrating a configuration example of an apparatus using an image forming method according to a third embodiment.
7 is a diagram illustrating a configuration example of an apparatus using an image forming method according to a fourth embodiment. FIG.
FIG. 8 is a diagram showing an operating state of the contacting / separating means.
[Explanation of symbols]
1A, 2A, 3A, 4A Image carrier
1C, 2C, 3C, 4C transfer charger (transfer bias applying means)
8 Member on the image forming side
10, 35 Non-image forming member
10a, 35a Surface layer of the member on which no image is formed
14 Peeling member
15, 16 Heating means
17 Transfer bias power supply (transfer bias applying means)
25 Transfer belt (transfer member)
32 Transfer roller (transfer bias applying means)
37 Charging means for fixing
50 Nip part
51 Nip exit
P1 Recording material tip
P Recording material

Claims (4)

A transfer member that transfers the developer image on the image carrier or the intermediate transfer member to a recording material; and a transfer bias applying unit that applies a transfer bias to the transfer member. The transfer bias is applied to the transfer member. A transfer step of applying a predetermined transfer bias from the means to transfer the developer image on the image carrier or intermediate transfer member to a recording material;
A member on the surface side of the recording material carrying the unfixed developer image in the transfer step, the surface layer forming a conductive image, and the unfixed developer image. A nip portion is formed with a member that does not form an image that is in pressure contact with a member that forms an image through a recording material to be formed, and at least a member that forms an image or a member that does not form an image A fixing step of fixing one of the unfixed developer image to the recording material by passing one of the recording material carrying the unfixed developer image through the nip portion while heating one by a heating unit;
A peeling member for peeling the recording material that has passed through the nip portion from a member on the image forming side is not in contact with a member on the image forming side, and
Between the member that forms the image and the member that does not form the image, a voltage that generates an electric field in a direction in which the recording material that has passed through the nip portion is attracted to the member that does not form the image. When the relationship between the front and back image ratios at the front end of the recording material using the control unit is high, the applied voltage is increased when the front image ratio is high, and the front image ratio is low or the back image ratio. An image forming method, wherein the applied voltage is lowered or the application is stopped when the voltage is high . The image forming method according to claim 1.
An image forming method, wherein a toner containing at least a binder resin, a colorant, and a wax is used as the developer . An image forming apparatus for forming an image by the image forming method according to claim 1. An image forming apparatus for forming a color image by the image forming method according to claim 1 .

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