JP2016151742A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the occurrence of abnormal images due to fastening of toner according to a print condition.SOLUTION: There is provided a fixing device that brings a fixing member and a pressure member into contact to fix a toner to a print medium, the fixing device comprising: a rotational load providing member that provides a rotational load to the fixing member or the pressure member; and a mechanism part that displaces the rotational load providing member in a direction of contact of the fixing member or the pressure member to generate a difference in rotational speed between the fixing member and the pressure member, where the mechanism part changes the force of contact of the rotational load providing member with the fixing member or the pressure member according to a print condition to control fastening of the toner to the print medium.SELECTED DRAWING: Figure 1

Description

  The present invention relates to, for example, a fixing device in an electrophotographic image forming apparatus, and an image forming apparatus such as a copying machine, a printer, and a facsimile equipped with the fixing device.

  Image forming apparatuses such as copiers, printers, and facsimiles form a toner image based on image information on an image carrier, transfer the toner image onto a recording material such as paper or an OHP sheet, and carry the toner image. The recorded material is passed through a fixing device, and the toner image is fixed on the recording material by heat and pressure. The fixing method includes a “heat roller method” and a “sleeve method”.

  In the “heat roller type” fixing device, a fixing roller heated by a heating source such as a halogen heater or an induction heating coil and a pressure roller form a nip portion, and a recording material carrying an image is passed through the nip portion. The toner is melted and fixed by heat and pressure. The heat roller method is inexpensive and widely used in monochrome machines from the viewpoint of safety and compatibility with high-speed machines. However, since the core of the fixing roller is made of metal and has a large heat capacity, it takes about 10 seconds to reach a predetermined fixing temperature. For this reason, there is a problem that energy consumption is high due to standby heat that maintains the fixing roller at a certain temperature even when not in use. On the other hand, in the “sleeve type” (or film type) fixing device, there are a method in which the heat insulating roller is heated from the outside and a method in which only the image area is selectively heated based on the image information. Often used as a device.

  However, the fixing device of the above-described type has a problem that an uneven glossiness occurs due to non-uniform toner adhesion. In view of such a problem, for example, in Patent Document 1, a difference in speed is set between the rotation speeds of a plurality of pressure rollers, and these pressure rollers are rotated with the difference in speed. A technique for preventing the occurrence of irregularities in unevenness is disclosed.

  In Patent Document 1, even if the plurality of pressure rollers are rotated with a difference in speed to prevent the occurrence of the abnormality, the image area ratio on the paper and the toner used when printing the image Depending on the printing conditions on the image forming side such as the physical properties or the printing conditions on the printing medium side such as the quality of the paper, there is a problem that toner adheres to the fixing roller or the pressure roller. Specifically, the toner adhering matter is a mixture of toner and paper powder, and has high adhesive strength, so that it easily adheres to the fixing roller or pressure roller. When this toner sticking grows up to a size that can be seen on the fixing roller and is ejected onto a sheet, an abnormal image due to toner sticking called a so-called black spot may occur and a customer may receive a complaint. There was a problem.

  The present invention has been made in view of the above, and an object of the present invention is to provide a fixing device capable of suppressing the occurrence of an abnormal image due to toner fixation according to printing conditions.

  In order to solve the above-described problems, a fixing device according to the present invention is a fixing device that fixes a toner onto a printing medium by bringing a fixing member and a pressure member into contact with each other. A rotational load application member that applies a rotational load and the rotation load application member are displaced in a contact direction of the fixing member or the pressure member, so that a rotational speed difference is generated between the fixing member and the pressure member. A mechanism section for controlling the toner fixing to the print medium by changing a contact force of the rotation applying member with respect to the fixing member or the pressure member according to printing conditions. The fixing device is configured as described above.

  According to the present invention, it is possible to suppress the occurrence of abnormal images due to toner fixation according to printing conditions.

FIG. 2 is a schematic diagram illustrating a cross section of a printing mechanism of a printer to which the fixing device and the image forming apparatus according to the invention are applied. FIG. 3 is a diagram illustrating a configuration of a fixing device adopting a heat roller method. FIG. 3 is a diagram illustrating a configuration of a fixing device adopting a sleeve method. FIG. 3 is a diagram illustrating a belt configuration example of a fixing device. FIG. 3 is a diagram illustrating an example of a rotational load applying mechanism provided in the fixing device illustrated in FIG. 2. FIG. 4 is a diagram illustrating an example of a rotational load applying mechanism provided in the fixing device illustrated in FIG. 3. FIG. 6 is a diagram illustrating an example of a rotation load applying mechanism included in the fixing device illustrated in FIG. 2 (modified example). It is a figure which shows the example of the toner omission produced by the linear velocity difference.

  Exemplary embodiments of a fixing device and an image forming apparatus according to the present invention will be described below in detail with reference to the accompanying drawings. In the following, a case where the fixing device and the image forming apparatus according to the present invention are applied to a general printer will be described. However, the present invention can be applied to an apparatus for drying and heating paper provided in an image forming apparatus such as a printer or an MFP (Multi-Function Peripheral) that forms an image by a wet process (electrophotography, ink jet, or the like).

  FIG. 1 is a schematic diagram showing a cross section of a printing mechanism of a printer 1000 to which an image forming apparatus and an image forming method according to the present invention are applied. As shown in FIG. 1, the printer 1000 includes a paper feeding unit 4, a registration roller pair 6, a photosensitive drum 8 as an image carrier, a transfer unit 10, a fixing device 12, and the like.

  The paper feeding means 4 feeds the paper Pa as recording material stored in a stacked state and the paper Pa stored in the paper feeding tray 14 one by one in order from the top. It has a roller 16 and the like. The paper Pa sent out by the paper supply roller 16 is temporarily stopped by the registration roller pair 6, and after the posture deviation is corrected, it is formed on the photosensitive drum 8 at a timing synchronized with the rotation of the photosensitive drum 8. The toner image is sent to the transfer portion N by the registration roller pair 6 at the timing when the leading edge of the toner image coincides with the predetermined position at the leading edge of the paper Pa in the transport direction.

  Around the photosensitive drum 8, in the rotation direction indicated by the arrows, a charging roller 18 as a charging unit, a mirror 20 constituting a part of an exposure unit (not shown), a developing unit 22 including a developing roller 22a, A transfer unit 10 and a cleaning unit 24 including a cleaning blade 24a are disposed. Between the charging roller 18 and the developing means 22, exposure light Lb is irradiated to the exposure unit 26 on the photosensitive drum 8 via the mirror 20 and scanned.

  The image forming operation in the printer is performed in the same manner as in the past. That is, when the photosensitive drum 8 starts to rotate, the surface of the photosensitive drum 8 is uniformly charged by the charging roller 18, and the exposure light Lb is irradiated and scanned on the exposure unit 26 based on the image information to create an image to be created. An electrostatic latent image corresponding to is formed. The electrostatic latent image is moved to the developing means 22 by the rotation of the photosensitive drum 8, where toner is supplied to be visualized to form a toner image. The toner image formed on the photosensitive drum 8 is transferred onto the paper Pa that has entered the transfer portion N at a predetermined timing by applying a transfer bias by the transfer means 10.

  The paper Pa carrying the toner image is conveyed toward the fixing device 12, fixed by the fixing device 12, and then discharged and stacked on a paper discharge tray (not shown). Residual toner remaining on the photosensitive drum 8 without being transferred at the transfer portion N reaches the cleaning means 24 as the photosensitive drum 8 rotates, and is scraped off by the cleaning blade 24 a while passing through the cleaning means 24. To be cleaned. Thereafter, the residual potential on the photosensitive drum 8 is removed by a neutralizing unit (not shown), and is prepared for the next image forming process.

(Fixing device configuration)
Here, the configuration of the fixing device 12 will be described. First, a configuration in which the heat roller method is adopted for the fixing device 12 will be described.

  FIG. 2 is a diagram illustrating a configuration of the fixing device 12 adopting a heat roller method. As shown in FIG. 2, the fixing roller 28 of the fixing device 12 forms a nip with a pressure roller 30 on the outer periphery of a metal core such as stainless steel or aluminum, and the surface layer is made of transfer paper and toner. A release layer is provided in order to improve releasability. For the release layer, a material having heat resistance and low surface energy is used. For example, silicone resin, fluororesin, for example, polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), It is used as a heat-resistant tube made of a polymer resin such as tetrafluoroethylene-hexafluoropropylene copolymer (FEP). To the surface layer, 10% by mass of an anti-wear additive such as carbon or SiC is added in order to further secure the wear resistance. When the additive is added in an amount of 3% by mass or more, sufficient abrasion resistance can be obtained. On the other hand, when the additive is added in an amount of 20% by mass or more, the ratio of exposure to the surface of the fixing roller 28 increases, and the toner releasability deteriorates.

  Further, a heat source 33 such as a halogen heater for accelerating the temperature rise of the fixing roller 28 is disposed in the core of the fixing roller 28. The heat source 33 is not limited to a halogen heater, and induction heating or a planar heating element may be used.

  The pressure roller 30 has an appropriate thickness of an elastic layer made of a heat-resistant elastic material such as fluorine-based rubber or silicone rubber on the outer periphery of a metal core such as stainless steel or aluminum. A release layer made of fluorine resin or the like is provided. The pressure roller 30 is pressed against the fixing roller 28 by a pressure member such as a spring (not shown), and pressurizes the toner with the fixing roller 28 for a certain period of time by elastically deforming the elastic layer. -Form a nip portion N that can be heated.

  Further, a separation claw 34 for peeling the fixed transfer paper is installed in contact with the fixing roller. The separation claws 34 may be arranged in several places in the fixing roller axial direction as needed. The surface of the separation claw 34 is formed of a polymer resin such as PTFE, PFA, or FEP in order to suppress toner sticking.

  Further, in order to control the heaters such as the fixing roller 28 and the pressure roller 30, a temperature sensor 36 such as a thermistor is provided to detect the temperature of each member, and the temperature is controlled by a heating controller that is a heating control means. The The fixing set temperature in this embodiment is set to 160 ° C. from the results of the toner viscoelasticity and the fixability test. Next, a configuration in which a sleeve method (or a film method; the same applies hereinafter) is adopted for the fixing device 12 will be described.

  FIG. 3 is a diagram illustrating a configuration of the fixing device 12 employing the sleeve method. As shown in FIG. 3, the fixing device 12 has a pressure rotator (pressure roller 43 in the example shown in FIG. 3) and a fixing belt 41, and is fixed by a heat source (halogen heater 42 in the example shown in FIG. 3). The belt 41 is directly heated by radiant heat from the inner peripheral side. At this time, in the fixing belt 41 shown in FIG. 3, there is a nip forming member 46 that forms a nip portion N with a pressure roller 43 opposed via the fixing belt 41, and directly (or alternatively) to the inner surface of the fixing belt 41. It slides indirectly (through a sliding sheet not shown). In FIG. 3, the shape of the nip portion N is flat, but may be a concave shape or other shapes. The reason is that when the nip portion N has a concave shape, the discharge direction of the leading edge of the recording paper is closer to the pressure roller and the separation is improved, so that the occurrence of jam is suppressed.

  The fixing belt 41 is an endless belt (or film) using a metal belt such as nickel or SUS or a resin material such as polyimide. The surface layer of the fixing belt 41 has a release layer such as a PFA, PTFE, or FEP layer, and has release properties so that toner does not adhere. Between the base material of the fixing belt 41 and the PFA, PTFE or FEP layer, there may be an elastic layer formed of a silicone rubber layer or the like. When there is no silicone rubber layer, the heat capacity is reduced and the fixability is improved, but when the unfixed image is crushed and fixed, minute irregularities on the belt surface are transferred to the image, and the image has a crusty skin shape. There arises a problem that the gloss unevenness (zudder skin image) remains. In order to improve this, it is necessary to provide a silicone rubber layer of 100 μm or more. Due to the deformation of the silicone rubber layer, fine irregularities are absorbed and the skin image is improved.

  A support member 47 (stay) for supporting the nip portion N is provided inside the fixing belt 41 to prevent the nip forming member 46 that receives pressure from the pressure roller 43 from bending and to have a uniform nip width in the axial direction. I try to get it. By supporting the pressure by the support member 47, a surface pressure value at the fixing nip necessary for fusing and fixing the toner can be obtained. However, the support member 47 is formed by bending iron or stainless steel and has a large heat capacity because it uses an iron plate or SUS plate having a thickness of about 5 mm.

  Further, the support member 47 is held and fixed to the holding member 48 (flange) at both ends, and is positioned. In addition, a reflection member 49 is provided between the heat source 42 and the support member 47, and wasteful energy consumption due to the support member 47 being heated by radiation heat from the heat source 42 or the like is suppressed. Here, instead of providing the reflecting member 49, the same effect can be obtained even if the surface of the supporting member 47 is heat-insulated or mirror-finished.

  The pressure roller 43 has an elastic rubber layer 44 on a metal core 45, and a release layer (PFA or PTFE layer) is provided on the surface in order to obtain releasability. The pressure roller 43 is rotated by a driving force transmitted from a driving source such as a motor provided in the image forming apparatus via a gear. The pressure roller 43 is pressed against the fixing belt 41 by a spring or the like, and has a predetermined nip width when the elastic rubber layer 44 is crushed and deformed. The pressure roller 43 may be a hollow roller, and the pressure roller 43 may have a heating source such as a halogen heater. The elastic rubber layer 44 may be solid rubber, but if there is no heater inside the pressure roller 43, sponge rubber may be used. Sponge rubber is more desirable because it increases heat insulation and makes it difficult for the fixing belt to lose heat.

  The fixing belt 41 is rotated by the pressure roller 43. In the case shown in FIG. 3, the pressure roller 43 is rotated by a driving source (not shown), and the driving force is transmitted to the belt at the nip portion N, whereby the fixing belt 41 is rotated. The fixing belt 41 is sandwiched and rotated at the nip portion N, and travels while being guided by the holding member 48 (flange) at both ends except the nip portion. With the above-described configuration, it is possible to realize a fixing device 12 that is inexpensive and has a fast warm-up.

  FIG. 4 is a diagram illustrating a belt configuration example of the fixing device 12. As shown in FIG. 4, the belt configuration of the fixing device 12 has a soaking layer made of Cu in the belt and diffuses a local high temperature. For example, the Cu layer is formed with a thickness of 15 μm or more. On the other hand, the Cu layer is desirably bendable from the viewpoint of nip formation by a pad, and is preferably 30 μm or less. When a metal layer such as SUS304 is used for the base material layer, it is desirable to adjust the thickness so that it can be bent. In addition to SUS, PI (polyimide), Ni or the like is used for the base material layer. Conventionally, the structure of the heat generating layer in the sleeve for induction heating has been disclosed. For example, as disclosed in Japanese Patent No. 3901414, the thickness of the Cu layer is optimized at about 5 to 15 μm in consideration of the heat generation efficiency. It is known. On the soaking layer, for example, an antioxidant layer made of Ni, an elastic layer made of silicone rubber, and a release layer made of PFA are sequentially formed.

(Toner fixing)
As shown in FIGS. 2 and 3, in the fixing device 12 to which the present invention is applied, the toner on the recording paper receives heat and pressure in the fixing roller in the fixing device 12 or the nip between the fixing belt and the pressure roller. . At this time, the toner is melted by heat, and the elasticity is lowered. At the same time, when the pressure is applied, the sheet spreads on the recording paper and enters into the fibers of the recording paper. Next, the recording paper comes out of the nip, and in the case of the heat roller system, the recording paper is peeled off and separated from both rollers by the separation claw 34.

  The toner is melted by heat and can penetrate between the fibers of the recording paper. At the same time, it easily adheres to the fixing roller. Further, when the toner melts and becomes viscous, and the adhesion force to the fixing roller or the fixing belt becomes larger than the adhesive force to the paper, the molten toner moves from the recording paper to the fixing roller or the fixing belt and becomes an offset. . In the case of the heat roller system, the transferred offset toner is accumulated on the temperature sensor 36 such as the separation claw 34 or the thermistor, and the fixing roller or the fixing belt repeatedly stops rotating, so that the accumulated toner becomes the fixing roller or the fixing belt. May fall on the recording paper and re-attach to the recording paper, so-called black spots may be generated and the image may be soiled.

  The difference between the toner re-adhering toner generation and the fixing property to the fixing roller and the fixing belt due to the difference in the physical properties of the toner is large, and the influence of the filler contained in the paper is large. In particular, when a paper containing heavy calcium carbonate (hereinafter referred to as “heavy carbonate”) prepared by a pulverization method is used as a filler, the fixing or fixing of the toner and the fixed matter formed by the heavy carbonate of paper is used. Adhesion to the pressure roller is high, and it tends to occur as an abnormal image including the black spots. Further, as the toner, the deterioration is remarkable in the toner having poor offset property.

  As a printed image, a white background toner is poor in both offset and fixing properties. On the other hand, the pre-stage fixed toner generated on the fixing roller is discharged onto the paper together with the unfixed toner by a self-cleaning effect. The effect is greater as the image area ratio is higher, and toner sticking is less likely to occur. The precursor stage is a stage where the toner is not larger than a size that can be visually confirmed, and is a stage where, for example, toner of about 1 mm or less is fixed.

  As described above, the factors that cause the toner to re-adhere to the fixing roller and the fixing belt to generate an abnormal image including black spots are the image area ratio indicating the ratio of the area occupied by the image to the paper, and the print image is printed in monochrome. It can be said that the frequency of occurrence depends on the printing conditions such as the monochrome printing rate indicating the ratio being printed and the amount of heavy coal cal of the sheet indicating the ratio including the filler that determines the quality of the sheet. The monochrome printing rate can be considered as an index indicating the influence of the toner physical properties of black (K) on the paper. That is, the abnormal image including the black spots depends on the printing condition on the image forming side such as the image area ratio on the paper and the physical properties of the toner used when printing the image, or the printing condition on the printing medium side such as the quality of the paper. It can be said that the occurrence of is affected.

(Rotation load applying mechanism)
In the fixing device 12 (fixing device 1 in Table 3 to be described later) adopting the heat roller method, for example, a rotational load is applied to the fixing roller 28 by a rotational load applying mechanism shown in FIG. The pressure roller 30 included in the fixing device 12 usually rotates by obtaining a driving force M from the image forming apparatus main body outside the fixing device 12. In the example shown in FIG. 5, the fixing roller 28 that is in pressure contact with the pressure roller 30 to which the driving force is transmitted is driven to rotate. Conventionally, the fixing roller 28 rotates at the same rotational speed as the pressure roller 30 by a frictional force generated between the fixing roller 28 and the pressure roller 30. On the other hand, a switching mechanism X for changing the load (torque) with respect to the driven rotation by increasing or decreasing it is disposed at the end of the fixing roller 28 shown in the present embodiment.

  The switching mechanism X increases or decreases the frictional force by increasing or decreasing the contact force of the fixing roller 28 with respect to the core metal (or the non-image forming portion of the fixing roller 28 where no image is formed). The pressurization level indicating the degree of rotational load on is changed. Specifically, the core of the fixing roller 28 or the non-image forming unit is displaced by a displacement mechanism M for displacing the position of the rotation load applying member Y applied to the rotation roller shaft of the switching mechanism X in the contact direction. And the contact force between the rotational load applying member Y is increased or decreased. In this way, there is no risk of scratches or the like occurring on the image by applying a load to the non-image forming portion or the cored bar.

  The displacement mechanism M is composed of, for example, a well-known cam mechanism. In the example shown in FIG. 5, the switching mechanism X indicates that the pressurization level can be adjusted in multiple stages (pressurization level 1: weak load or no load, pressurization level 2: strong load or load), In particular, the load is changed when a sheet is passed. By applying the load only when the paper is passed, the durability of the application member can be improved.

  Further, in the fixing device 12 (fixing device 2 in Table 3 to be described later) adopting the sleeve method, for example, a rotational load application as a sliding member is applied to the sleeve inner surface by a contact / separation mechanism Z included in the rotational load mechanism shown in FIG. The member Y ′ is arranged so as to be able to contact and separate. It is desirable that the rotational load applying member Y 'is covered with a slidable fluororesin sheet or the like so that the frictional resistance becomes extremely high and the rotation of the sleeve does not stop. Since the rotation load applying member Y ′ is a sliding member, a load can be easily applied. Further, since the sliding member is provided on the inner surface side of the sleeve, the image surface is not deteriorated even if it slides. The contact / separation mechanism Z has a well-known cam mechanism N, and the cam mechanism N and the rotational load applying member Y ′ are connected by an expansion / contraction member A composed of an expandable / contractible arm or the like, and the rotation The position of the load applying member Y ′ is displaced in the contact direction of the sleeve inner surface.

  The left side of FIG. 6 shows that the rotational load applying member Y ′ is separated from the inner surface of the sleeve and is in an unloaded state. On the right side of FIG. 6, the rotational load applying member Y ′ is in contact with the inner surface of the sleeve. It is shown that the load is applied. Further, as with the switching mechanism X provided in the fixing device 12 employing the heat roller method, the pressure level is multi-stage (pressure level 0: no load, pressure level 1: weak). Load, pressurization level 2: strong load).

  Further, as a modification of the fixing device 12 employing the heat roller method (fixing device 3 in Table 3 described later), as shown in FIG. 7, the rotational load applying mechanism includes an electromagnetic clutch connected to the load. Also good. The electromagnetic clutch functions as a rotational load applying member Y ″ of the switching mechanism X ′, and a rotational load is applied by the electromagnetic clutch. With such a configuration, the responsiveness is higher than that of the mechanical mechanism of the electromagnetic clutch. There is an advantage of being fast, and a load having a large weight is arranged at the connection destination of the electromagnetic clutch, so that the rotational load can be increased.

  As the rotational load, for example, in the fixing device 12 adopting a heat roller system that normally conveys A4Y width paper at a linear speed of 150 mm / sec, a dynamic torque of about 0.2 N · m or less is applied. When a rotational load is applied, it is desirable to increase the torque to about 180% or less of the dynamic torque. However, the setting is appropriately adjusted depending on the configuration of the roller, nip width, bearing type, and the like. Further, if the torque is increased too much due to the increase in the rotational load, a minute linear velocity difference of about 1% or less does not occur between the fixing roller 28 and the pressure roller 30, and slipping may cause a sheet conveyance failure. I know. For this reason, it is desirable to experimentally adjust the torque increase.

  On the other hand, in the fixing device 12 adopting the sleeve method for conveying A4Y width paper at a linear speed of 250 mm / sec, a dynamic torque of about 0.5 N · m is applied. In order to obtain a minute linear velocity difference between the two, it is desirable to increase the torque even when the dynamic torque is 150% or less. The reason is to prevent the occurrence of paper conveyance failure due to the slip.

(Operation example)
When the rotational load is increased by switching the rotational load applying member as described above, for example, when the rotational torque of the fixing roller or the fixing belt increases, the fixing roller slightly slips against the rotational speed of the pressure roller. The rotation speed is delayed. In order to cause such a delay, when the fixing roller side obtains a driving force and the pressure roller is driven, a rotation load applying member may be provided on the pressure roller side.

  When the paper is passed in this state, a frictional force is generated between the fixing roller and the surface of the paper, so that the fine fixed matter such as the fixing toner on the fixing roller is peeled off, and the fine fixed matter is visible. It was confirmed by a paper passing test that it did not grow to a certain extent. Further, as shown in FIG. 8, when such a linear velocity difference becomes 2% or more, a remarkable toner loss occurs, so that the linear velocity difference is preferably within 1%. FIG. 8 illustrates the case where the linear velocity difference is 2.4% and 7.2%, but it can be seen that remarkable toner omission occurs in both cases.

  On the other hand, when a linear velocity difference is applied in a state where the paper is not passed, a fixed peeling or stretching effect is recognized with respect to the fixed toner, but the fixed toner is not discharged to the paper, and thus the fixing property is not improved. Is allowed. Therefore, when the fixing device 12 is started up, between papers, or idling, the rotation load application member, the cam mechanism, and the like can be prevented from being deteriorated by not applying the rotation load. Therefore, it is desirable from the viewpoint of durability that the frequency with which the rotation addition imparting member imparts a load is minimized.

  Regarding the timing for applying the rotational load, the fixing device 12 detects the occurrence of toner sticking by a sensor or the like, the detection information is received by the image forming apparatus main body, and the fact is displayed on an operation unit such as an operation panel. The operation unit may accept the setting from a user who is an administrator or a serviceman who is a maintenance person and switch the setting. Alternatively, the position of the rotational load applying member may be manually changed mechanically. It has been found that the minute fixed matter can be removed from the fixing roller or the pressure roller by printing several sheets of white paper.

  In addition, toner sticking is likely to occur when the image area ratio is low and there is a lot of background stains, or when blank pages are continuously output in the paper surface. Therefore, more preferably, it is effective to suppress the toner fixing by continuously passing the paper in a state where the rotational load is applied and discharging the sticking toner in the sign stage to the paper. By adjusting the rotational load according to the printing conditions such as the image area ratio, monochrome printing ratio, and heavy coal cal volume of paper, abnormal images including so-called black spots are not generated, and the fixing life is also long. There is no loss.

  The switching of the pressurization level is set according to the conditions shown in Tables 1 and 2 below, for example.

  Table 1 is a table showing an example of the pressurization level set according to the operation state of the image forming apparatus. As shown in Table 1, in this table, the operation mode indicating the operation state and the pressure level in the operation mode are stored in association with each other. Table 1 shows that when the operation mode is “warming up” or “standby”, since there is no cleaning effect, the pressure level is set to “0” and no rotation load is applied. ing. Further, when the operation mode is “in-job”, it indicates that the following Table 2 is followed.

  Table 2 is a table showing an example of the pressurization level when the operation mode is a job. As shown in Table 2, when the operation mode is “during job”, the pressurization level is switched according to the printing conditions such as the image area ratio, the monochrome printing ratio, and the heavy coal cal volume of the paper.

  For example, when the image area ratio is 5% or more, the image is cleaned when the image and the fixed object come into contact with each other, and image blurring is also noticeable. Is set to “0” and no rotational load is applied. When the image area ratio is 2% or more and less than 5%, the pressure level is set to “1” only when the amount of heavy carbonic acid on the paper is 20% by mass or more. Further, when the image area ratio is less than 2%, the monochrome printing ratio is 80% or more, and the heavy carbonate carbon amount of the paper is 20 mass% or more, the pressure level is “2”, and the heavy carbonate carbonate amount of the paper. Is 10 mass% or more and less than 20 mass%, the pressure level is set to “1” and a rotational load is applied. The amount of heavy carbonic acid on the paper is obtained in advance by obtaining information such as the results of component analysis of the paper and observation results with an electron microscope, and the above users and service personnel operate the operation unit such as the operation panel for use. It can be set according to the paper.

(Details of verification experiment)
Using Ricoh Co., Ltd. imageio NEO451 as a fixing roller, A4Y was set with commercially available PPC (Plain Paper Copier) paper containing 25%, 15%, and 5% by weight of heavy carbonate. A copy copy test was conducted. The verification results are shown in Table 3. As printing conditions, the settings of the image area ratio, monochrome printing ratio, and paper heavy coal cal volume were set to the values shown in Table 3. As shown in Table 3, the copy image used was a character image randomly formed so that the image area ratio was 1%, 3%, and 8% on a white paper, and the monochrome printing rate was 70 for 100K sheets. % And 90%. Concerning toner adhesion, intermittent printing of scummed toner on white paper is in acceleration mode, so the above image is copied and printed intermittently for 20 seconds for each 100K sheets, confirming that the toner stuck to the white paper is dropped And △△ × was judged. Here, “◯” indicates a case where “no sticking occurs”, “Δ” indicates a case where “sticking occurs when the cumulative value is 1% or less”, and “×” indicates that “a fixed image is generated when the cumulative value is 1% or more. Is the case.

(Examples 1-20, Comparative Examples 1-8)
In Examples 1 to 20, even in the case of a sheet with a low image area ratio, a high monochrome printing ratio, and a heavy carbonic acid cal content, the sticking occurrence level is “◯” for up to 100K copies of a sheet set with A4Y. It was confirmed that. Further, in the case of a color image and a high image area ratio, it was confirmed that no image blurring occurred because the pressure level was lowered. On the other hand, in Comparative Examples 1 to 6, since the rotational load is insufficient, the sticking occurrence level is “×” to “Δ”. In Comparative Examples 7 and 8, the pressurization level is increased more than necessary, so the image blur is “ X ”was confirmed. It was also confirmed that the durability after 100K sheets was sufficient.

  As described above, the fixing device included in the printer according to the present embodiment controls the toner fixing to the paper by changing the contact force of the rotation applying member to the fixing roller or the pressure roller according to the printing condition. ing. Therefore, for example, depending on the printing conditions on the image forming side such as the image area ratio on the paper and the physical properties of the toner used when printing the image, or the printing conditions on the printing medium side such as the quality of the paper, the toner is fixed. The occurrence of abnormal images can be suppressed.

  Further, as shown in the verification experiment result, since the rotational load is applied only when the image area ratio is equal to or lower than the predetermined value, the durability of the rotational load applying member is not deteriorated. Further, image blurring in a high image area is not caused. Furthermore, since the rotation load is applied only when the monochrome printing rate is equal to or higher than a predetermined value, the durability of the rotation load application member is not deteriorated. This is because in the case of a high image area, the self-cleaning is performed as described above, so that a rotational load is unnecessary. In addition, no color image is produced. This is because, in the case of a color image, the probability of self-cleaning is high as described above, and therefore a rotational load is unnecessary. Furthermore, since the rotational load is applied according to the quality of the used paper, the durability of the applying member is not deteriorated. This is because a sheet with a small amount of heavy calcium carbonate is less likely to be fixed as described above, and therefore a rotational load is not necessary.

1000 Printer 4 Paper feed means 6 Registration roller pair 8 Photosensitive drum 10 Transfer means 12 Fixing device 28 Fixing roller 30 Pressure roller 33 Heat source 34 Separation claw 36 Temperature sensor 41 Fixing belt 42 Halogen heater 43 Pressure roller 44 Elastic layer 45 Core Gold 46 Nip forming member 47 Support member 48 Holding member 49 Reflecting member A Telescopic member M Displacement mechanism N Cam mechanism X Switching mechanism Y Rotating load applying member Z Contact / separation mechanism

Japanese Unexamined Patent Publication No. 2014-081610

Claims (7)

A fixing device that fixes a toner to a print medium by bringing a fixing member and a pressure member into contact with each other,
A rotation load applying member that applies a rotation load to the fixing member or the pressure member; and the rotation load applying member is displaced in a contact direction of the fixing member or the pressure member, and the fixing member and the pressure member. A mechanism that produces a rotational speed difference between
The mechanism unit controls toner adhesion to the print medium by changing a contact force of the rotation applying member with respect to the fixing member or the pressure member according to printing conditions.
A fixing device. The mechanism section is defined by combining an image forming side print condition including an image area ratio or / and toner physical properties with respect to the print medium and a print medium side print condition including the quality of the print medium. The contact force is changed according to printing conditions.
The fixing device according to claim 1. The fixing device is a sleeve-type or film-type fixing device, and the mechanism section changes the abutting force of the rotational load applying member formed by a sliding member.
The fixing device according to claim 1, wherein The mechanism section changes the contact force of the rotational load applying member installed on the inner surface of the fixing rotator.
The fixing device according to claim 3. The fixing device is a heat roller type fixing device, and the mechanism unit contacts the non-image portion or a cored bar of the fixing rotating body to change the contact force by causing the rotational load applying member to contact the fixing load member.
The fixing device according to claim 1, wherein The mechanism portion causes the rotational load applying member to abut against the fixing member or the pressure member when passing paper.
The fixing device according to claim 1, wherein An image forming apparatus comprising the fixing device according to claim 1.