JP2007298567A - Image forming apparatus, and method for driving heating means in the image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus of a transfer and fixing simultaneous system, where a toner image transferred to recording paper has the required density and which restrains irregularities in the toner image. <P>SOLUTION: In the image forming apparatus 10, the toner image T is transferred onto the surface of a circularly moving intermediate transfer body 61 on the upstream side, the transferred toner image T is heated and melted by a heating means 66, in contact with the surface of the intermediate transfer body 61 halfway, and the heated and melted toner image T is transferred and fixed, simultaneously on the recording paper P by a fixing means 67 on the downstream side. The heating means 66 is set so that its surface comes into contact with the surface of the intermediate transfer body 61, its surface at a contact point moves circularly, in the same direction as the moving direction of the surface of the intermediate transfer body 61 at the contact point, and so that the increase/decrease rate of the moving speed of the surface of the heating means 66 to that of the intermediate transfer body 61 is equal to or higher than +0%. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using electrophotographic processing such as a copying machine, a facsimile machine, a printer, and the like, and more particularly, transfer fixing that simultaneously transfers and fixes a toner image transferred onto an intermediate transfer member onto a recording material. The present invention relates to an image forming apparatus using a simultaneous method and a driving method of a heating unit in the image forming apparatus.

  Generally, as an image forming apparatus, conventionally, after a toner image formed on a toner image carrier is transferred onto an intermediate transfer member, the intermediate transfer member onto which the toner image has been transferred is moved to a fixing unit, and this fixing is performed. The toner image on the intermediate transfer member is transferred onto the recording paper and fixed by superimposing the recording paper as a recording material on the intermediate transfer member onto which the toner image has been transferred. The simultaneous transfer and fixing method is employed.

  However, the image forming apparatus of the simultaneous transfer and fixing method includes the following problems. That is, first, when forming a toner image by electrostatically forming a toner image on the intermediate transfer member, melting the toner image by heating, and transferring all the toner images on the intermediate transfer member to recording paper, In order to transfer the toner image to the recording paper, as shown in FIG. 7, the cohesive force F1 between the toners t, t,... In the toner layer is the adhesion force F2 of the toner t to the intermediate transfer member a. It is necessary to create a state (F1> F2 and F3> F2) in which the adhesion force F3 of the toner t to the recording paper p is greater than the adhesion force F2 of the toner t to the intermediate transfer member a.

  Therefore, when this state cannot be realized, a so-called offset phenomenon occurs in which a part of the toner layer remains on the intermediate transfer member a due to the separation of the toner layer, and normal image formation is not performed. . In FIG. 7, F is a pressure applied from the pressure roller and the intermediate transfer member a acting at a fixing nip portion between a pressure roller (not shown) and the intermediate transfer member a.

  By the way, in general, if the toner image is sufficiently melted by heating, the melted toner image is adapted to the surface of the recording paper, the intermolecular force is increased, and the throwing effect (the melted toner is caused by the capillary phenomenon or the like). The effect of being locked like a wrinkle in the fiber is also added, and a strong adhesion to the recording paper is obtained. Further, regarding the cohesive force F1 of the toner, the viscosity characteristic with respect to the temperature of the toner is taken into consideration, and the cohesive force F1 between the toners is increased by lowering the temperature of the toner melted at a high temperature to change from the softened state to the solidified state. be able to.

  On the other hand, the adhesion force F2 of the toner to the intermediate transfer member should be weak, and for this purpose, it is necessary to use a material that is difficult to adhere the toner to the surface of the intermediate transfer member. Accordingly, the temperature of the recording paper integrated with the toner and the intermediate transfer body is lowered until the cohesion force F1 between the toners becomes larger than the adhesion force F2 of the toner to the intermediate transfer body, and then the recording paper is transferred to the intermediate transfer body. By peeling from the body, it is possible to transfer all the toner images onto the recording paper without being disturbed and to fix them simultaneously.

  As described above, if the toner image is sufficiently heated and melted, the melted toner is easily adapted to the surface of the recording paper. However, in the boundary area where the toner and the recording paper are in contact, the temperature of the toner and the surface of the recording paper If the temperature is low, the toner is not sufficiently melted by heating, and the toner is difficult to wet on the surface of the recording paper, the toner and the surface of the recording paper will be difficult to adjust, and the intermolecular force between the toner and the surface of the recording paper will increase. Therefore, sufficient adhesion cannot be obtained. This is because even when only the toner is heated and the temperature rises and melts, the heat capacity of the toner is small, and when the toner comes in contact with the recording paper having a larger heat capacity and lower temperature than the toner, the heat possessed by the toner is taken away by the recording paper. This is considered to be because the toner temperature at the contact interface between the toner and the recording paper is lowered and hardly flows, and the contact becomes insufficient and a strong adhesive force cannot be obtained. In this case, the surface temperature of the recording paper hardly increases due to the amount of heat that the toner has.

  That is, in order to transfer and fix the toner image from the intermediate transfer member to the recording paper, to obtain a good fixing strength, and to obtain a high-gloss and non-uniform image and a sufficiently high-quality image of color development, the adhesion force with the toner It is necessary to employ a heating means that uses a weak intermediate transfer member and that can sufficiently melt the toner and that does not easily lower the interface temperature between the toner and the recording paper when the toner contacts the surface of the recording paper.

  Therefore, in the image forming apparatus of the simultaneous transfer and fixing method, a heating element is provided on a roller which is opposed to the fixing unit and is brought into contact with the surface of the intermediate transfer member opposite to the toner image transfer surface of the intermediate transfer member which contacts the fixing unit. There has been proposed an image forming apparatus employing an internal heating system that heats an intermediate transfer member that is in contact with the roller by incorporating therein. In the image forming apparatus adopting this internal heating method, when the toner image on the intermediate transfer member is transferred and fixed on the recording paper by the fixing unit, not only the fixing unit but also the intermediate transfer member is heated by the roller described above. As a result, the toner is sufficiently melted.

  However, in the image forming apparatus using this internal heating method, it is necessary to take measures such as changing the heating energy in accordance with the thickness and heat capacity of the recording paper, resulting in an increase in power consumption of the image forming apparatus.

  Therefore, in order to solve this problem, the toner image is heated to sufficiently melt the toner before the toner image and the recording paper come into contact with each other. Therefore, a heating method or means capable of raising the surface temperature of the recording paper is required.

  In order to realize such a method and means, it is essential that the toner image must be heated and melted among the three companies of the intermediate transfer member, the toner image, and the recording paper existing in the transfer fixing unit. However, in order to avoid an increase in the power consumption of the image forming apparatus, the intermediate transfer member or recording paper having a large heat capacity should not be heated to a high temperature, and the recording paper in contact with the toner image by the intermediate transfer member. It is desirable to increase the interface temperature in the boundary region.

  Therefore, a radiant heating unit that radiates and heats the intermediate transfer member in a non-contact state from the toner image transfer surface side before the intermediate transfer member and the recording paper come into contact, and a radiation absorbing layer that absorbs radiation from the radiant heating unit. Has been proposed (see, for example, Patent Document 1), which is an external non-contact heating type image forming apparatus composed of an intermediate transfer member surface or an intermediate transfer member provided near the surface.

  In the image forming apparatus described in Patent Document 1, the intermediate transfer member is heated in a non-contact manner from the toner image transfer surface side before the transfer and fixing. As the heating source, for example, a radiation wavelength of at least a wavelength of 0.75 μm or more is used. A non-contact radiant heating means is used. In addition, as described above, the image forming apparatus is provided with the radiation heating unit and a radiation absorption unit that is provided on or near the surface of the intermediate transfer body of the intermediate transfer body and absorbs radiation from the radiation heating unit. And an intermediate transfer member having a layer. The surface of the intermediate transfer body is heated by radiation from the toner image transfer surface side and a radiation absorption layer is provided on or near the surface of the intermediate transfer body, so that the surface of the intermediate transfer body becomes hot and transferred to the intermediate transfer body. The toner image is directly radiantly heated, and at the same time, is thermally conducted from the surface of the high-temperature intermediate transfer member to melt.

  However, even in this image forming apparatus, when the processing speed of the apparatus becomes high, the external non-contact heating method has poor thermal efficiency, and a toner image is necessary for fixing even if a radiation absorbing layer is provided on the intermediate transfer member. It is very difficult to raise the temperature to a high temperature (120 ° C or higher) in a short time. Therefore, in order to solve this, for example, it is necessary to reduce the processing speed or to increase the radiation width and to heat it. However, if the processing speed is reduced, high-speed processing is not possible, and the radiation width is reduced. If heating is to be performed in a large manner, it is necessary to install a plurality of radiant heating means such as halogen lamps, which causes problems such as an increase in cost due to an increase in the size of the apparatus and an increase in power consumption.

  By the way, the processing speed required for the image forming apparatus used in the current medium / high-speed color copying machine and multifunction machine is generally about 150 mm / sec to 250 mm / sec. Also, in these image forming apparatuses, a transfuse system using a transfuse belt as an intermediate transfer member is generally employed as a simultaneous transfer and fixing system.

  The transfuse belt used in this transfuse system has a multilayer structure, for example, a base material (polyimide), an intermediate layer (silicone rubber), and a release layer (PFA (tetrafluoroethylene and perfluoroalkyl vinyl ether). Copolymer) or PTFE (polytetrafluoroethylene)).

  Among these, the intermediate layer is formed of silicone rubber in order to cause the toner image to melt and transfer to the recording paper side by causing the transfuse belt to sufficiently follow the recording paper against the unevenness of the recording paper, This intermediate layer is indispensable from the viewpoint of image quality. Further, the silicone rubber forming the intermediate layer is required to have a low hardness and to have a certain thickness (300 μm or more). As described above, due to various characteristics required for the transfuse belt, the individual materials used for the transfuse belt are all poor in thermal conductivity of 1 W / mK or less, and the total belt thickness is 400 μm. This is necessary.

  For this reason, for example, when the processing speed of the image forming apparatus is 250 mm / sec, the toner image transferred to the transfuse belt is transferred to either the above-described internal heating method or the external non-contact heating method. Even if heated by this method, due to poor thermal conductivity of the belt and poor heating efficiency, the toner image is not sufficiently melted to be fixed on the recording paper, resulting in poor fixing. .

  In order to solve this, in the case of the internal heating method, it is necessary to increase the heating area of the transfuse belt. For this purpose, the outer diameter of the backup roller of the belt incorporating the heater is increased. There are methods such as applying a stress to the belt and bending it to increase the amount of winding. In the case of the external non-contact heating method, there is a method of enlarging the radiation heating device. However, all of these methods bring about an increase in cost due to an increase in the size of the apparatus, an increase in power consumption, and a decrease in performance due to an increase in warm-up time.

  In order to solve this problem, in the above-described transfuse system, an external heating roller is provided as a heating unit that comes into contact with the toner transfer surface of the transfuse belt before the transfuse belt and the recording paper come into contact with each other. There has been proposed an external contact heating method in which a toner image transferred to a transfuse belt is heated by an external heating roller.

In this external contact heating method, the external heating roller contacts and heats the toner image transfer surface of the transfuse belt, so that it is not affected by the belt thickness and poor thermal conductivity, and has high thermal efficiency. The toner image can be sufficiently heated and melted even in a system subject to restrictions on the heating time. Therefore, it is possible to sufficiently cope with an increase in processing speed.
JP 2002-365934 A

  As described above, the external contact heating method described above is an extremely effective method for improving the processing speed of the image forming apparatus. Further, in this external contact heating method, a filming effect in which a powdery toner layer forming a toner image is melted and spreads thinly on the transfuse belt by contacting an external heating roller to the transfuse belt as an intermediate transfer member. It is possible to obtain

  Therefore, in order to enhance this filming effect, conventionally, the rotational speed of the external heating roller has been made slower than the moving speed of the transfuse belt. However, in this state, the density of the image transferred to the recording paper increases as compared with the above-described internal heating method or the like, but the toner image is disturbed.

  Accordingly, the present invention has been made to solve such a problem, and in the image forming apparatus using the simultaneous transfer and fixing method, the toner image transferred to the recording paper has a necessary density, and It is an object of the present invention to provide an image forming apparatus capable of suppressing the image disturbance of the toner image and a driving method of a heating unit used in such an image forming apparatus.

  First, the image forming apparatus of the present invention will be described. In the image forming apparatus of the present invention, a toner image is transferred upstream to the surface of the intermediate transfer member that circulates, and the transferred toner image is heated and melted by a heating unit that contacts the surface of the intermediate transfer member halfway. This is an image forming apparatus in which a heated and melted toner image is transferred and fixed on a recording material such as paper downstream by a fixing unit.

  In this image forming apparatus, the surface of the heating unit is in contact with the surface of the intermediate transfer member, and the surface of the heating unit at the contact point moves the surface of the intermediate transfer member at the contact point. The heating means speed increase / decrease ratio, which is the ratio of increase / decrease in the movement speed of the surface of the heating means with respect to the movement speed of the surface of the intermediate transfer member, is plus 0% or more. It is a feature.

  Specifically, in the above image forming apparatus, it is preferable that the intermediate transfer member is constituted by a belt and the heating means is constituted by a roller having a heat source.

  In the above image forming apparatus, it is preferable that the rate of increase / decrease in the heating means speed is 2% or less. That is, the moving speed of the surface of the heating means is set so that the heating means speed increase / decrease ratio in the heating means is 0% or more and 2% or less.

  By setting the moving speed of the surface of the heating means as described above, in the image forming apparatus using the simultaneous transfer and fixing method, the toner image transferred to the recording paper has a necessary density, and the image of the toner image Disturbance can be suppressed.

  Next, a driving method of the heating unit in the image forming apparatus of the present invention will be described. In the image forming apparatus of the present invention, the heating unit is driven by transferring the toner image upstream to the surface of the intermediate transfer member that circulates, and the transferred toner image contacts the surface of the intermediate transfer member halfway. The heating unit is heated and melted by the heating unit in which the surface of the heating unit is in contact with the surface of the intermediate transfer member, and the heated and melted toner image is transferred to a recording material such as paper downstream by the fixing unit. And a heating unit driving method in the image forming apparatus fixed at the same time.

  In the driving method of the heating unit in this image forming apparatus, the surface of the heating unit at the contact point in contact with the surface of the intermediate transfer member is moved in the same direction as the moving direction of the surface of the intermediate transfer member at the contact point. In addition to circulating and moving the surface of the heating unit, the rate of increase / decrease in the heating unit speed, which is the rate of increase / decrease in the moving speed of the surface of the heating unit with respect to the moving speed of the surface of the intermediate transfer member, is 0% or more, The heating means is driven.

  Specifically, in the image forming apparatus using the driving method of the heating unit in the image forming apparatus, it is preferable that the intermediate transfer member is configured by a belt and the heating unit is configured by a roller having a heat source. It is.

  In the driving method of the heating unit in the image forming apparatus, it is preferable that the heating unit speed increase / decrease rate is 2% or less.

  The driving method of the heating unit in the image forming apparatus has the same effects as those of the image forming apparatus described above.

  According to the present invention, in the image forming apparatus using the simultaneous transfer and fixing method, the heating unit has the surface of the heating unit in contact with the surface of the intermediate transfer member, and the surface of the heating unit at the contact point is the surface of the heating unit. It circulates and moves so as to move in the same direction as the moving direction of the surface of the intermediate transfer member at the contact point. Further, the surface of the heating unit is adjusted such that the rate of increase / decrease in the heating unit speed, which is the rate of increase / decrease in the moving rate of the heating unit surface with respect to the moving rate of the surface of the intermediate transfer member, is 0% or more and 2% or less. The moving speed is set. Therefore, the toner image transferred to the recording paper has a necessary density, and image disturbance of the toner image can be suppressed.

  Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings. In this embodiment, a case where the present invention is applied to a color laser printer will be described.

<Description of overall color laser printer configuration>
FIG. 1 is a configuration diagram showing an outline of an internal configuration of a color laser printer 10 which is an image forming apparatus according to the present embodiment using the simultaneous transfer and fixing method. The color laser printer 10 is a multicolor (full color) image or a single color (monochrome) on the recording paper P, which is a predetermined recording material, according to image data transmitted from the outside (for example, a terminal device such as a personal computer). An image is formed. As shown, the color laser printer 10 includes an exposure unit 1 (1a to 1d), a developing device 2 (2a to 2d), a photosensitive drum 3 (3a to 3d) as a toner image carrier, and a charger. 4 (4a to 4d), a cleaner unit 5 (5a to 5d), a transfuse unit 6, a recording paper conveyance path S, and the like.

  The image data handled in the color laser printer 10 corresponds to a color image using each color of black (K), cyan (C), magenta (M), and yellow (Y). Accordingly, the exposure unit 1 (1a to 1d), the developing device 2 (2a to 2d), the photosensitive drum 3 (3a to 3d), the charger 4 (4a to 4d), and the cleaner unit 5 (5a to 5d) 4 are provided so as to form four types of latent images according to the following. In FIG. 1, a is black (K), b is cyan (C), c is magenta (M), respectively. Then, d is set to yellow (Y) and constitutes four image forming stations STa to STd.

  The photosensitive drum 3 is disposed (attached) on the upper part of the color laser printer 10, and an electrostatic latent image corresponding to image data is formed by irradiation of laser light from the exposure unit 1 as described later. Yes.

  The charger 4 is a charging means for uniformly charging the surface (photoconductor layer) of the photosensitive drum 3 to a predetermined potential. In addition to a contact type roller type or brush type charger, a charger type charging unit is also used. A vessel may be used.

  The exposure unit 1 is composed of a laser scanning unit (LSU). The exposure unit 1 has a function of forming an electrostatic latent image according to image data on the surface of the photosensitive drum 3 by exposing the charged photosensitive drum 3 according to input image data. is doing.

  The developing device 2 visualizes the electrostatic latent images formed on the respective photosensitive drums 3 with toners (developers) of respective colors (K, C, M, Y). These color toners are respectively stored in developing tanks (not shown) of the developing devices 2a to 2d for the image stations STa to STd.

  The cleaner unit 5 removes and collects toner remaining on the surface of the photosensitive drum 3 after development and image transfer.

  The transfuse unit 6 is disposed above the image forming stations STa to STd, and includes a transfuse belt 61 as an intermediate transfer member, a transfuse belt driving roller 62, a transfuse belt driven roller 63, and a transfer roller 64 (64a). 64d) and a transfuse belt cleaning unit 65. Among these, the transfuse belt 61 is stretched over the transfuse belt driving roller 62, the transfer roller 64, and the transfuse belt driven roller 63, and the transfuse belt driving roller 62 is driven to rotate in the direction of the arrow Z1. Along with this, the transfuse belt 61 is driven to circulate in the direction of the arrow Z2.

  Further, on the downstream side of the first image forming station STa in the driving direction of the transfuse belt 61, an external heating roller 66 as a heating unit is disposed opposite to the transfuse belt driving roller 62 with the transfuse belt 61 interposed therebetween. ing. The external heating roller 66 is rotationally driven in the direction of the arrow Z3 and abuts from the direction of direct contact on the drive path of the transfuse belt 61 to heat and melt the toner image T on the transfuse belt 61. In addition, the transfuse belt driving roller 62 is pressed against the transfuse belt driving roller 62 with a predetermined pressure by a pressurizing means (not shown). This external heating roller 66 corresponds to the heating means described above.

  Further, on the downstream side of the external heating roller 66, a pressure roller 67 as a pressure unit is disposed opposite to the transfuse belt driving roller 62 with the transfuse belt 61 interposed therebetween. The pressure roller 67 is driven to rotate in the direction of the arrow Z4, and transfers and fixes the toner image T on the transfuse belt 61 to the recording paper P, and pressurizes the transfuse belt drive roller 62. The contact is made at a predetermined pressure by means (not shown). The pressure roller 67 corresponds to the fixing unit described above.

  Further, the transfuse belt cleaning unit 65 is disposed so as to face the transfuse belt driven roller 63 with the transfuse belt 61 interposed therebetween. A predetermined pressure unit (not shown) presses the transfuse belt driven roller 63 with a predetermined pressure. A cleaning blade 651 pressed by pressure is provided.

  The transfer roller 64 (64a to 64d) is rotatably disposed on the inner surface side of the transfuse belt 61 facing the photosensitive drum 3 (3a to 3d) of each of the image forming stations STa to STd. A transfer bias for transferring the toner image T of the photosensitive drum 3 onto the transfuse belt 61 is applied.

<Description of transfuse unit>
Next, the transfuse unit 6 will be described in detail. In the transfuse unit 6, a transfuse belt 61 is provided so as to be in contact with each photosensitive drum 3. Then, the toner images T of the respective colors formed on the photoconductive drum 3 are sequentially transferred to the transfuse belt 61 so as to form a color toner image T (a multicolor toner composite image) on the transfuse belt 61. It has come to be.

  The transfuse belt 61 has a circumferential length of 500 mm, and as shown in FIG. 2, is made of a base material 611 made of polyimide having a thickness of 90 μm and a silicone rubber having a thickness of 1 mm covering the base material 611. The elastic layer 612 and a release layer 613 as a surface layer provided with a 10 μm thick PFA coat (surface roughness, arithmetic average roughness Ra = 0.6 μm or less) are formed into a seamless belt structure. In this case, the PFA coat constituting the release layer 613 includes a perfluoroalkoxy resin that is a copolymer of tetrafluoroethylene and perfluoroalkyl perfluorovinyl ether.

  The transfuse belt driving roller 62 includes an iron hollow core 621 having a diameter of 30 mm and a thickness of 0.5 mm, and a coating layer 622 made of fluoro rubber having a thickness of 10 μm and coated on the surface of the iron hollow core 621. Has been. The covering layer 622 is provided for the purpose of securing a driving force for the transfuse belt 61. A transfuse belt 61 is wound around the transfuse belt driving roller 62 at a winding angle of about 180 °.

  The external heating roller 66 has a halogen lamp 662 inside the hollow metal core 661, and on the upstream side in the vicinity of the fixing nip portion between the pressure roller 67 for fixing the toner image T on the recording paper P and the transfuse belt 61. It is provided in pressure contact with the fuse belt 61.

  A thermistor 69a for temperature detection is in contact with the outer peripheral portion of the external heating roller 66, and the surface temperature of the external heating roller 66 is detected to control ON / OFF of the energization to the halogen lamp 662. The surface temperature of the external heating roller 61 is maintained at a predetermined temperature (for example, 160 ° C.). Then, by adjusting the surface temperature of the external heating roller 66 to a predetermined temperature, the toner image T on the transfuse belt 61 is directly contact-heated, and the toner image T is temporarily filmed on the transfuse belt 61. Thus, it is possible to form a uniform print-like image without melting unevenness.

  In this case, the surface layer (release layer 613) of the transfuse belt 61 is formed by applying a PFA coat having a small surface energy. However, if the surface is only heated in a non-contact state as in the conventional method, the toner image T However, heat aggregation occurs on the transfuse belt 61, and there is a problem that uniform filming cannot be formed. Therefore, if the toner image T is transferred and fixed on the recording paper P in the thermally aggregated state, it causes deterioration in image quality such as white spots and image unevenness. Therefore, the toner image T is heated while being pressed by the external heating roller 66. By doing so, the toner image T after thermal aggregation can be filmed and leveled again, and the problem is solved.

  Since the external heating roller 66 contacts and heats the toner image T formed on the transfuse belt 61, it is required to coat a material that does not cause toner adhesion or offset. Since the PFA coat is used for the release layer 613 of the transfuse belt 61, basically, the release property is better than that (small surface energy), and external heating is also applied to the cohesive force of the toner. It is necessary to reduce the adhesion force to the roller 66 to prevent the adhesion transfer of the toner.

  Therefore, a rubber type silicone solution is used as the coating material 663 as the surface layer of the external heating roller 66. This is because the three-dimensional crosslinking point of the cured film is less than that of the varnish type, and the cured film becomes a rubber-like elastic body, and a flexible silicone film can be obtained. Such a coating material 663 may be directly formed on the core metal 661 of the external heating roller 66. However, in this embodiment, after forming the silicone rubber 664 as an elastic layer on the core metal 661, It is coated on top.

  In addition, as another coating material, at least a part of silicone resin (for example, any of SE5070 / SR2316 (manufactured by Toray Dow Corning Silicone Co., Ltd.), YE5505 / ME35 (manufactured by GE Toshiba Silicone Co., Ltd.)) In the case of a coating material partially containing a silicone resin, a varnish-like baking mold release silicone that is used in the form of a cured film by crosslinking and reacting the silicone by heating or the like may be used. Done with.

  This uses a hard silicone resin in which a cured film is three-dimensionally cross-linked as a constituent component. By using this, a long-term mold release effect can be obtained without applying silicone oil to the surface. When the silicone resin is coated, it is applied as it is as a stock solution or by spraying a varnish solution obtained by diluting the silicone resin with a solvent made of toluene, xylene, ethylbenzenemethylethyl ketoxime or the like onto the core metal 661 of the external heating roller 66. Thereafter, baking may be performed at a temperature of about 150 ° C. to 200 ° C. for several hours.

  The external heating roller 66 is rotationally driven in the direction of the arrow Z3 as described above. This rotational direction is applied to the transfuse belt 61 at a contact point where the external heating roller 66 is in contact with the transfuse belt 61. The surface of the external heating roller 66 that is in contact is in a direction that moves in the same direction as the direction of movement of the transfuse belt 61 that the external heating roller 66 is in contact with. The moving speed of the contact surface of the external heating roller 66 is referred to as an external heating roller linear speed Sr, and the moving speed of the transfuse belt 61 is referred to as a transfuse belt linear speed Sb. The ratio of increase / decrease of the external heating roller linear velocity Sr to the transfuse belt linear velocity Sb is referred to as an external heating roller linear velocity ratio. This external heating roller linear speed ratio corresponds to the heating means speed increase / decrease ratio described above.

  In the present embodiment, when the external heating roller linear velocity ratio is changed, that is, when the external heating roller linear velocity Sr is changed with respect to the transfuse belt linear velocity Sr, the toner image transferred onto the recording paper. It has been found through experiments and the like that the density of the toner and the image disturbance of the toner image slightly change. The present invention has been made in view of this point, and this point will be described later.

  The pressure roller 67 is provided with an elastic layer 672 made of silicone rubber having a thickness of 0.8 mm on the surface of a stainless steel core 671 having a diameter of 11 mm, and a release layer 673 made of a PFA tube having a thickness of 30 μm is further formed thereon. It is provided and configured. The pressure roller 67 forms a fixing nip portion N by being pressed and urged by a pressure means with a pressure of 77 N across the transfuse belt 61 with respect to the transfuse belt drive roller 62. The width of the fixing nip portion N (fixing nip width) is set to 1 mm, and the surface pressure is set to 310 kPa, which is twice or more that of the conventional one (surface pressure 135 kPa). Thus, by setting the surface pressure at the fixing nip N high, the adhesion between the surface of the recording paper P and the transfuse belt 61 is improved, and the transfuseability of the molten toner image T to the recording paper P is improved. Is ensured.

  In addition, a halogen lamp 674 is provided inside the metal core 671 of the pressure roller 67, and the thermistor 69b for temperature detection is in contact with the release layer 673. Then, the surface temperature of the pressure roller 67 is detected by the thermistor 69b and ON / OFF of the energization to the halogen lamp 674 is controlled, so that the surface temperature of the pressure roller 67 is maintained at a predetermined temperature (for example, 170 ° C.). Like to do. As a result, the temperature drop due to the passing of the recording paper P at the fixing nip portion N is minimized, and a good fixed image can be obtained.

  The cleaning blade 651 of the transfuse belt cleaning unit 65 is in contact with the winding portion of the transfuse belt 61 around the transfuse belt driven roller 63, and the toner, paper dust, etc. remaining on the transfuse belt 61 are transfused. The belt 61 is collected from above.

  In the transfuse unit 6, as described above, when the external heating roller linear velocity Sr is changed with respect to the transfuse belt linear velocity Sr, that is, when the external heating roller linear velocity ratio is changed, the recording paper is changed. It has been found through experiments and the like that the density of the transferred toner image and the image disturbance of the toner image change slightly. FIG. 3 is an enlarged view of a thin line of 150 dpi in an image transferred and fixed on the recording paper P when the external heating roller linear velocity ratio is changed in this experiment, and FIG. 4 is an enlarged view of a solid image. It is. The 150 dpi thin line means each line in a state in which 150 lines are arranged in a width of 1 inch so that the line width and the distance between the lines are the same. A solid image is an image filled on one side.

  3 (a), (b), (c) and FIGS. 4 (a), (b), (c) respectively show the external heating roller linear velocity ratios of −2.5% and 0%, respectively. , And 2.5%. 3 and 4, the direction from the bottom to the top is the recording paper P discharge direction. FIG. 5 is a graph showing the density of an image transferred and fixed on the recording paper P as an ID value when the external heating roller linear velocity ratio is changed.

  In FIG. 3A, there is a whisker-like shape extending upward from the thin line, but this is a result of the toner being dragged in a solid state without being crushed. Image distortion occurs. On the other hand, in FIGS. 3B and 3C, no such whiskers exist, the toner is completely crushed, and no image distortion occurs in the fine line image. That is, when the external heating roller linear velocity ratio is −2.5%, that is, when the external heating roller linear velocity Sr is slower than the transfuse belt linear velocity Sr, image disturbance occurs in the thin line image. When the linear speed ratio is 0% and 2.5%, that is, when the external heating roller linear velocity Sr is equal to or faster than the transfuse belt linear velocity Sr, that is, the external heating roller linear velocity. When the ratio is plus 0% or more, image distortion does not occur in the fine line image.

  This is considered to be due to the following reasons. That is, in FIG. 6, when the toner layer adhering on the transfuse belt 21 is melted at the heating portion X of the external heating roller 28, the toner layer is temporarily generated at the entrance portion of the heating portion X and then the melted toner layer. Are sequentially fed to form a molten toner layer on the transfuse belt 21.

  At this time, if the external heating roller 28 is slower, the surface of the external heating roller 28 becomes a wall, so that the amount of toner accumulated at the entrance of the heating portion X increases, and this toner accumulation becomes the external heating roller 28. 3 and the transfuse belt 21, the toner layer melted while being caught by the external heating roller 28 is sent, so that it shifts in the paper discharge direction. For this reason, since the dragged toner layer adheres to the recording paper on the rear side of the toner image on the recording paper at the outlet of the heating unit X, a drag mark in the paper discharge direction is generated, resulting in image disturbance of the thin line image. .

  On the other hand, when the external heating roller 28 is faster, the surface of the external heating roller 28 sequentially stirs the toner layer into the heating part X, so that the amount of toner remaining at the entrance of the heating part X is reduced, and the molten toner The layers are sent without shifting in the paper discharge direction. For this reason, at the outlet of the heating unit X, the toner layer adheres to the original position, so that there is no dragging trace in the paper discharge direction, and image distortion of the fine line image does not occur. Although not shown, the same phenomenon occurs in the edge portion of the solid image.

  Further, regarding the density of the image transferred and fixed on the recording paper P, in FIG. 4 (a), there are fewer white portions than in FIGS. 4 (b) and 4 (c). It can be seen that the density of the solid image is higher than the density of the solid images in FIGS. That is, when the external heating roller linear velocity Sr is slower than the transfuse belt linear velocity Sr, the external heating roller linear velocity Sr is solid compared to the case where the external heating roller linear velocity Sr is equal to or faster than the transfuse belt linear velocity Sr. The image density increases. In this regard, from the graph showing the density of the image transferred and fixed on the recording paper P in FIG. 5, as a general tendency, when the linear speed ratio of the external heating roller increases, the image is transferred and fixed on the recording paper P. The image density becomes lower.

  Table 1 shows the results obtained based on experimentally measured values and the like. In Table 1, “◯” indicates good, “Δ” indicates slightly poor, and “×” indicates slightly poor. From Table 1, if the external heating roller linear velocity ratio is plus 0% or more, image disturbance does not occur in the fine line image. Further, as the external heating roller linear velocity ratio increases, the density of the image transferred and fixed on the recording paper P decreases. Therefore, if the ID value is required to be 1.3 or more from the practical viewpoint according to the density of the image transferred and fixed on the recording paper P, the external heating roller linear velocity ratio is 2% or less from FIG. I just need it. Therefore, the image transferred and fixed on the recording paper P is not disturbed and the required density is obtained when the external heating roller linear velocity ratio is in the range of 0% to 2%.

<Description of image forming operation by color laser printer>
Next, an image forming operation by the color laser printer 10 will be described. First, in a warm-up state in which the transfuse belt 61 is stopped, the halogen lamp 662 in the external heating roller 66 and the halogen lamp 674 in the pressure roller 67 are turned on, and the surfaces of the external heating roller 66 and the pressure roller 67 are turned on. Is raised to a predetermined temperature.

  In this case, the reason why the transfuse belt 61 is stopped in the warm-up state is to prevent the rise of the external heating roller 66 and the pressure roller 67 from being delayed due to the heat deprived by the transfuse belt 61. This is also for the two purposes of preventing the temperature of the photosensitive drum 3 from being raised by the heated transfuse belt 61. Further, as a temperature necessary for fixing the toner image T on the recording paper P, the interface temperature between the recording paper P and the toner image T immediately after the entrance of the fixing nip N is raised to 120 ° C. or more. It is necessary to keep.

  Then, after the warming up of the external heating roller 66 is completed, the external heating roller 66 and the pressure roller 67 are rotated to rotate the transfuse belt 61 and at the same time, the first to fourth image forming stations STa, STb, STc. , STd, the respective color toner images T are sequentially transferred onto the transfuse belt 61. At this time, the external heating roller 66 is driven and controlled so that the external heating roller linear velocity ratio in the external heating roller 66 is in the range of 0% to 2%.

  The toner image T transferred onto the transfuse belt 61 is heated and melted by heat from the external heating roller 66 maintained at 125 ° C. The melted toner image T is conveyed to a position facing the pressure roller 67 (fixing nip portion N) by the movement of the transfuse belt 61, and the transfuse belt 61 and the pressure roller 67 are synchronized with the conveyance timing. The recording paper P is fed into the fixing nip N between the two. Then, when the recording paper P is pressed by the pressure roller 67, the molten toner image T is transfused onto the recording paper P.

  At this time, even if the toner is offset to the surface of the transfuse belt 61 due to the occurrence of a jam or the like, the transfuse belt cleaning unit 65 that is in contact with the outer peripheral surface of the transfuse belt 61 on the downstream side of the fixing nip portion N. The cleaning blade 651 cleans offset toner, paper dust, and the like attached to the surface of the transfuse belt 61.

  Further, the transfuse belt 61 has a low thermal conductivity and a large heat capacity, and when heated, the pressure roller 67 and the recording paper P are deprived of heat at the fixing nip portion N, and further in a long conveying section downstream thereof. Since heat is deprived in the heat radiation to the atmosphere and also in the contact portion with the transfuse belt driven roller 63, it is sufficiently cooled before returning to the contact portion with the fourth image forming station STd, and the photosensitive drum 3 does not affect the photosensitive characteristics.

  According to the color laser printer 10 using the simultaneous transfer and fixing method in the present embodiment, the external heating roller (heating means) 66 has a surface of the external heating roller 66 of the transfuse belt (intermediate transfer member) 61. The surface of the external heating roller 66 at the contact point circulates and moves so as to move in the same direction as the direction of movement of the surface of the transfuse belt 61 at the contact point. Further, the heating means speed increase / decrease ratio, that is, the ratio of increase / decrease in the movement speed of the surface of the external heating roller 66 with respect to the movement speed of the surface of the transfuse belt 61, that is, the external heating roller linear speed ratio is plus 0% or more, and The moving speed of the surface of the external heating roller 66 is set so as to be 2% or less. Therefore, the toner image transferred to the recording paper P has a necessary density, and image disturbance of the toner image can be suppressed.

  In addition, this invention is not limited to this Embodiment, The other various modifications are included. For example, in the present embodiment, the case where the image forming apparatus of the present invention is applied to a color laser printer has been described. However, the present invention is not limited to this, and a monochrome image forming apparatus such as a monochrome laser printer or a color copying machine. The present invention can also be applied to an image forming apparatus configured as a multi-function peripheral having a plurality of functions.

  In this embodiment, the case where a transfuse belt is used as the intermediate transfer member has been described. However, the present invention is not limited to the belt shape, and for example, a drum shape may be applied.

1 is a configuration diagram illustrating a configuration of a color laser printer according to an embodiment of the present invention. It is a detailed enlarged view near the transfuse belt drive roller. (a), (b), (c) are enlarged views of a 150 dpi fine line transferred and fixed on a recording sheet when the external heating roller linear velocity ratio is changed. (a), (b), and (c) are enlarged views of a solid image transferred and fixed on a recording sheet when the external heating roller linear velocity ratio is changed. 6 is a graph showing the density of an image transferred and fixed on a recording sheet when the external heating roller linear velocity ratio is changed. It is an enlarged view near the external heating roller for explaining the operation related to the external heating roller. FIG. 4 is an explanatory diagram conceptually showing a force acting on toner in a transfuse image forming method.

Explanation of symbols

1 (1a to 1d) Exposure unit 2 (2a to 2d) Developing device 3 (3a to 3d) Photosensitive drum (toner image carrier)
4 (4a to 4d) Charger 5 (5a to 5d) Cleaner unit 6 Transfuse unit 61 Transfuse belt (intermediate transfer member)
611 Base material 612 Elastic layer 613 Release layer (surface layer)
62 Transfuse belt driving roller 63 Transfuse belt driven roller 64 (64a to 64d) Transfer roller 65 Transfuse belt cleaning unit 66 External heating roller (heating means)
661 Hollow cored bar 662 Halogen lamp 663 Coating material (release layer, surface layer)
664 Silicone rubber (elastic layer)
67 Pressure roller (Pressure means)
671 Core metal 672 Elastic layer 673 Release layer 674 Halogen lamp 69a Thermistor 69b Thermistor 10 Color laser printer (image forming apparatus)
N Fixing nip P Recording paper (recording material)
S Recording paper transport path STa to STd Image forming station T Toner image Z1 arrow Z2 arrow Z3 arrow Z4 arrow

Claims (6)

A toner image is transferred upstream to the surface of the intermediate transfer body that circulates, and the transferred toner image is heated and melted by a heating means that comes in contact with the surface of the intermediate transfer body in the middle, and the heated and melted toner An image forming apparatus in which an image is transferred to a recording material such as paper downstream by a fixing unit and fixed at the same time,
In the heating unit, the surface of the heating unit is in contact with the surface of the intermediate transfer member, and the surface of the heating unit at the contact point is the same as the moving direction of the surface of the intermediate transfer member at the contact point. The heating means speed increase / decrease ratio, which is the ratio of increase / decrease in the movement speed of the surface of the heating means to the movement speed of the surface of the intermediate transfer member, is plus 0% or more. An image forming apparatus.   The image forming apparatus according to claim 1, wherein the intermediate transfer member is configured by a belt, and the heating unit is configured by a roller having a heat source.   The image forming apparatus according to claim 1, wherein the heating unit speed increase / decrease ratio is 2% or less. A toner image is transferred upstream to the surface of the intermediate transfer member that circulates, and the transferred toner image is a heating unit that contacts the surface of the intermediate transfer member halfway. In the image forming apparatus in which the toner image heated and melted by the heating means in contact with the surface of the intermediate transfer member is transferred to a recording material such as paper downstream by the fixing means and fixed at the same time. A method for driving the heating means,
Circulating movement of the surface of the heating means so that the surface of the heating means at the contact point in contact with the surface of the intermediate transfer member moves in the same direction as the movement direction of the surface of the intermediate transfer member at the contact point. At the same time, the heating means is driven such that the heating means speed increase / decrease ratio, which is the ratio of increase / decrease in the movement speed of the surface of the heating means with respect to the movement speed of the surface of the intermediate transfer member, is 0% or more. A driving method of a heating unit in an image forming apparatus.   5. The method for driving a heating unit in an image forming apparatus according to claim 4, wherein the intermediate transfer member is configured by a belt, and the heating unit is configured by a roller having a heat source.   6. The method for driving a heating unit in an image forming apparatus according to claim 4, wherein the rate of increase / decrease in the heating unit speed is 2% or less.

Images