JP2007057672A - Image heating device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To shorten first print-out time without degrading image quality and increasing noise, in a heating device for partially heating a heating rotation body; and to provide an image forming apparatus that has the heating device. <P>SOLUTION: In a standby mode, the temperature of a first rotation body is controlled while the first rotation body 10 and a second rotation body 30 are separated. In a device rise mode, the first rotation body is rotated so that the rotating speed of the first rotation body when the temperature of the first rotation body shifts to a heating-fixing temperature for an unfixed image t in the standby mode is different from the rotating speed when the material P to be heated is sandwiched and conveyed by a nip part N. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image heating apparatus for heating and fixing an unfixed image formed and supported on a recording material, and particularly an image heating apparatus effective when used as a heating and fixing apparatus mounted on an image forming apparatus such as a copying machine or a printer. And an image forming apparatus provided with the image heating apparatus.

  2. Description of the Related Art Conventionally, in a heat fixing device (hereinafter referred to as a heating device) provided in an image forming apparatus employing an electrophotographic method or an electrostatic recording method, a recording material (transfer sheet / electrofax) carrying an unfixed toner image is used. Sheet, electrostatic recording paper, OHP sheet, printing paper, format paper, etc.) are passed through a nip formed by a fixing roller and a pressure roller that are pressed against each other to record an unfixed toner image 2. Description of the Related Art A so-called heat roller type heating device that fixes a permanent image on a material is widely used.

  Further, recently, a heating apparatus of a film heating system (Patent Document 1) that is advantageous in terms of energy saving, shortening of wait time, and the like has been put into practical use. In addition, a color-on-demand type heating device (Patent Document 2) has been proposed in which an elastic layer is provided on a fixing film to improve the quality of color images. Similarly, a heating device of an electromagnetic induction heating method (Patent Document 3) has also been proposed. In addition, a heating apparatus of an electromagnetic induction external heating method (Patent Document 4) in which the magnetic field generating means is arranged outside the electromagnetic induction heat generating member has been proposed. In these types of heating devices, in order to shorten the time required for the heating device to rise to a predetermined printing temperature (standby temperature), a heating roller or heating as a first rotating body in a print standby state (standby state) A method of adjusting the temperature of the film at a standby temperature at a predetermined temperature to improve the quick start property is widely used.

  In the heating device of the heat roller type, if the heating roller is not rotated and the print standby state is kept in contact with the pressure roller, the temperature of the heating roller at the pressure roller contact position (nip portion position) decreases, Temperature unevenness occurs in the circumferential direction of the heating roller. If this temperature unevenness remains at the start of printing, gloss unevenness (gloss unevenness) is generated in the toner image. In order to avoid this problem, there is a heating device that separates the heating roller and the pressure roller during printing standby. If the heating roller and the pressure roller are separated from each other and waiting for printing, the temperature unevenness of the heating roller due to the heat outflow to the pressure roller can be prevented.

  However, a heating device other than the case where the entire fixing roller is uniformly heated, such as a heating roller type heating device using a halogen heater (heating means) that has been generally used conventionally, that is, a heating (fixing) roller, A heating apparatus that locally heats a fixing member such as a heating (fixing) belt or a film has the following problems. In other words, even when the fixing member as the first rotating body and the pressure roller as the second rotating body are separated from each other during the standby temperature control, temperature unevenness due to local heating occurs in the circumferential direction of the fixing member, and printing starts. In some cases, the temperature unevenness cannot be eliminated until the output image has gloss (gross) unevenness.

  In order to avoid this, there is a heating device that controls the standby temperature while rotating the fixing member in the print standby state. There is also a heating device that rotates the fixing member and the pressure roller apart during standby temperature control in order to avoid surface layer scraping of the fixing member due to idling and reduction in durability life due to mechanical stress.

  However, it is not preferable to always rotate the fixing member in a standby state from the viewpoint of life and noise.

In order to avoid such a problem, there is a heating device that performs low-power standby temperature control by stopping rotation and rotates the fixing member by a predetermined angle (click rotation) at a constant time period (Patent Document 5). With this heating device, it is possible to improve durability life reduction due to standby temperature control of local heating of the fixing member by click rotation and temperature unevenness in the circumferential direction of the heating roller.
JP-A-63-313182 Japanese Patent Laid-Open No. 11-15303 (Patent No. 3051085) Japanese Utility Model Publication No. 51-109736 JP-A-11-135246 JP 2002-43048 A

  The present invention is a further improvement of the technique of the heating device disclosed in Patent Document 5.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a first print out time (one recording material is discharged from a print standby state) without deteriorating durability life, noise and image quality in an image heating apparatus for locally heating a heating rotator. Is to shorten the time until it is performed (FPOT).

  Another object of the present invention is to provide an image forming apparatus including the image heating device.

  A typical configuration of the image heating apparatus according to the present invention includes a heating unit, a first rotating body heated by the heating unit, and a second nip portion formed in pressure contact with the first rotating body. An image heating apparatus that heats and fixes an unfixed image on a recording material while nipping and conveying the recording material on which the unfixed image is formed and supported by the nip portion. A standby mode for controlling the temperature of the first rotating body in a state where the second rotating body is separated from the second rotating body, and the temperature of the first rotating body in the standby mode is shifted to a temperature at which the unfixed image can be heated and fixed. An apparatus start-up mode for rotating the first rotating body so that the rotating speed of the first rotating body is different from the rotating speed when the material to be heated is nipped and conveyed at the nip portion. And an image heating device.

  A typical configuration of an image forming apparatus according to the present invention includes an image forming unit that forms an unfixed image on a recording material, and an image heating that heats an unfixed image formed on the recording material by the image forming unit. An image forming apparatus comprising the above-described image heating apparatus as the image heating apparatus.

  According to the present invention, the temperature control of the first rotating body is performed in the standby mode in a state where the first rotating body and the second rotating body are separated from each other. Generation can be reduced. In the apparatus start-up mode, the temperature of the first rotating body in the standby mode shifts to the temperature at which the unfixed image can be heated and fixed, and the material to be heated is held at the nip portion. Since the first rotating body is rotated so as to be different from the rotation speed at the time of conveyance, the temperature unevenness of the first rotating body generated by the standby temperature control by local heating can be converged in a shorter time than before. . As a result, the first printout time can be shortened while suppressing the occurrence of image defects.

  Hereinafter, the present invention will be described in detail with reference to the drawings.

(1) Example of Image Forming Apparatus FIG. 14 is a schematic configuration diagram of an example of an image forming apparatus provided with the image heating apparatus according to the present invention as a heating apparatus (heat fixing apparatus). The image forming apparatus of this example is an electrophotographic color printer.

  Reference numeral 101 denotes a photosensitive drum (image carrier) made of an organic photosensitive member or an amorphous silicon photosensitive member, which is rotationally driven in a counterclockwise direction indicated by an arrow at a predetermined process speed (circumferential speed). The photosensitive drum 101 is uniformly charged with a predetermined polarity and potential by a charging device 102 such as a charging roller during its rotation.

  Next, the charged surface is subjected to a scanning exposure process of target image information by a laser beam 103 output from a laser optical box (laser scanner) 110. The laser optical box 110 outputs a laser beam 103 modulated (on / off) corresponding to a time-series electric digital pixel signal of target image information from an image signal generation device such as an image reading device (not shown) to rotate the photoconductor. An electrostatic latent image corresponding to target image information scanned and exposed on the surface of the drum 101 is formed. Reference numeral 109 denotes a mirror that deflects the output laser light from the laser optical box 110 to the exposure position of the photosensitive drum 101.

  In the case of full-color image formation, scanning exposure / latent image formation is performed on a first color separation component image of a target full-color image, for example, a yellow component image, and the latent image is subjected to yellow development in the four-color developing device 104. The yellow toner image is developed by the operation of the device 104Y. The yellow toner image is transferred to the surface of the intermediate transfer drum 105 at the primary transfer portion T1 which is a contact portion (or proximity portion) between the photosensitive drum 101 and the intermediate transfer drum 105.

  The surface of the rotating photosensitive drum 101 after the transfer of the toner image to the surface of the intermediate transfer drum 105 is cleaned by the cleaner 107 after removal of adhesion residues such as transfer residual toner.

  The process cycle of charging, scanning exposure, development, primary transfer, and cleaning as described above includes a second color separation component image (for example, a magenta component image, the magenta developer 104M is activated) of a target full color image, and a third color. An intermediate transfer body is sequentially executed for each color separation component image of the separation component image (for example, cyan component image, cyan developing device 104C is activated) and the fourth color separation component image (for example, black component image, black developing device 104BK is activated). Four color toner images of a yellow toner image, a magenta toner image, a cyan toner image, and a black toner image are sequentially superimposed and transferred onto the surface of the drum 105, and a color toner image corresponding to the target full-color image is synthesized and formed.

  The intermediate transfer drum 105 has a middle-resistance elastic layer and a high-resistance surface layer on a metal drum. The intermediate transfer drum 105 is in contact with or close to the photosensitive drum 101 at the same peripheral speed as that of the photosensitive drum 101. , And a bias potential is applied to the metal drum of the intermediate transfer drum 105 to transfer the toner image on the photosensitive drum 101 side to the surface of the intermediate transfer drum 105 by the potential difference with the photosensitive drum 101. .

  The color toner image synthesized and formed on the surface of the rotary intermediate transfer drum 105 is transferred to the secondary transfer portion T2 in the secondary transfer portion T2 which is a contact nip portion between the rotary intermediate transfer drum 105 and the transfer roller 106. Are transferred onto the surface of the recording material P fed at a predetermined timing from a paper feeding unit (not shown). The transfer roller 106 supplies a charge having a polarity opposite to that of the toner from the back surface of the recording material P, thereby sequentially transferring the combined color toner images sequentially from the surface of the intermediate transfer drum 105 to the recording material P side.

  The recording material P that has passed through the secondary transfer portion T2 is separated from the surface of the intermediate transfer drum 105 and introduced into the heat fixing device 100, and is subjected to a heat fixing process for an unfixed toner image to form a color image formed product outside the apparatus. Are discharged to a paper discharge tray (not shown). The heating device 100 will be described in detail in the next section (2).

  After the color toner image has been transferred to the recording material P, the rotating intermediate transfer drum 105 is cleaned by the cleaner 108 after removal of adhering residues such as transfer residual toner and paper dust. The cleaner 108 is always held in a non-contact state with the intermediate transfer drum 105 and is in contact with the intermediate transfer drum 105 during the secondary transfer of the color toner image from the intermediate transfer drum 105 to the recording material P. Retained.

  Also, the transfer roller 106 is always held in a non-contact state with the intermediate transfer drum 105, and the intermediate transfer drum 105 is covered with the intermediate transfer drum 105 during the secondary transfer of the color toner image from the intermediate transfer drum 105 to the recording material P. The recording material P is held in contact.

  This example apparatus can also execute a mono-color image print mode such as a monochrome image. A double-sided image print mode or a multiple image print mode can also be executed.

  In the double-sided image print mode, the recording material P on which the first-side image has been printed out of the heating device 100 is turned upside down via a recirculation conveyance mechanism (not shown) and sent again to the secondary transfer portion T2. Upon receipt of the toner image transfer to the surface, the toner image is again introduced into the heating device 100 and undergoes toner image fixing processing on the two surfaces, whereby a double-sided image print is output.

  In the multiple image print mode, the recording material P that has been printed on the first image from the heating device 100 is sent to the secondary transfer portion T2 again without being turned upside down via a recirculation conveyance mechanism (not shown). A second toner image transfer is received on the surface on which the first image has been printed, and the image is again introduced into the heating device 100 and undergoes a second toner image fixing process, whereby a multiple image print is output.

(2) Heating device 100
In this example, the heating device 100 is an electromagnetic induction heating type heating device. FIG. 1 is a cross-sectional side view of the main part of the heating apparatus 100 of this example, and FIG. 2 is a front model view of the main part.

  In the following description, the longitudinal direction refers to a direction orthogonal (crossing) to the recording material conveyance direction and parallel to the surface of the recording material.

  The apparatus 100 includes an electromagnetic induction heat generating cylindrical fixing roller 10 as a first rotating body, a magnetic field generating unit 20 as a heating unit disposed inside the fixing roller 10, and a pressure contact with the fixing roller 10. Thus, a fixing roller driving type / electromagnetic induction heating type heating device having a basic configuration including a pressure roller 30 as a second rotating body that forms a nip portion (fixing nip portion, heating nip portion) N is provided.

  The magnetic field generation means 20 includes magnetic cores 17a, 17b, and 17c having a substantially T-shaped cross section, and an excitation coil 18 wound around a center magnetic core 17a in a ship bottom shape. The magnetic cores 17a, 17b, and 17c are members having high magnetic permeability, and are preferably made of a material used for a transformer core such as ferrite or permalloy, and more preferably ferrite having a low loss even at 100 kHz or more.

  Reference numeral 16 denotes a saddle-shaped holder having a substantially semicircular arc shape in cross section, and holds magnetic cores 17a, 17b, 17c as the magnetic field generating means 20 and the excitation coil 18 inside. A fixing roller 10, which is a cylindrical electromagnetic induction heat generating rotator, is rotatably disposed outside the holder 16 with a gap.

  Reference numeral 19 denotes an insulating member for insulating the magnetic cores 17 a, 17 b, and 17 c and the exciting coil 18 from the holding stay 22. The insulating member 19 and the holder 16 are held by a holding stay 22. Both ends of the holding stay 22 in the longitudinal direction are fixedly supported by the fixing frame 50. As the material of the holding stay 22, a metal material such as iron, aluminum, stainless steel, or nonmagnetic stainless steel can be used. Moreover, it is sufficient if the insulating member 19 and the holder 16 can be held, and a heat resistant resin can be substituted. The holder 16 may be supported by the fixing frame 50 without providing the holding stay 22.

  In the magnetic field generating means 20, the exciting coil 18 has an exciting circuit 27 connected to the power feeding portions 18a and 18b as shown in FIG. 3, so that a high frequency of 20 kHz to 500 kHz can be generated by a switching power supply. The exciting coil 18 generates an alternating magnetic flux by the alternating current (high-frequency current) supplied from the exciting circuit 27. C is an alternating magnetic flux and represents a part of the generated alternating magnetic flux. An alternating magnetic flux (hereinafter referred to as magnetic flux) C guided to the magnetic cores 17a, 17b, and 17c is generated between the magnetic core 17a and the magnetic core 17b and between the magnetic core 17a and the magnetic core 17c. An eddy current is generated in the heat generating layer 1. This eddy current causes Joule heat (eddy current loss) to be generated in the heat generating layer 1 by the specific resistance of the heat generating layer 1.

  The calorific value Q is determined by the density of the magnetic flux C passing through the heat generating layer 1, and shows a distribution as shown in the graph of FIG. The vertical axis of the graph indicates the circumferential position of the fixing roller 10 expressed by an angle θ with the center of the magnetic core 17 a being 0, and the horizontal axis indicates the heat generation amount Q in the heat generating layer 1 of the fixing roller 10. Here, the heat generation region H is defined as a region where the maximum heat generation amount is Q and the heat generation amount is Q / e or more (e is the base of the natural logarithm). This is a region where the amount of heat generated for the fixing process can be obtained.

  FIG. 4 is a model diagram of the layer structure of the fixing roller 10 in this embodiment.

  The fixing roller 10 of the present embodiment has a composite structure of a heat generating layer 1 made of an electromagnetic induction heat generating metal or the like serving as a core, an elastic layer 2 laminated on the outer surface, and a release layer 3 laminated on the outer surface. belongs to. For adhesion between the heat generating layer 1 and the elastic layer 2 and adhesion between the elastic layer 2 and the release layer 3, a primer layer (not shown) may be provided between the respective layers.

  In the fixing roller 10, the heat generating layer 1 is on the inner surface side (holder 16 side), and the release layer 3 is on the outer surface side in contact with the pressure roller 30 or the recording material P. When the above-described alternating magnetic flux acts on the heat generating layer 1, an eddy current is generated in the heat generating layer 1, and the heat generating layer 1 generates heat. This heat is transmitted to the elastic layer 2 and the release layer 3 so that the entire fixing roller 10 is heated, and the recording material P that is passed (introduced) through the fixing nip N is heated to form an unfixed toner t image. Heat fixing is performed.

  As the heat generating layer 1, magnetic and nonmagnetic metals can be used, but magnetic metals are preferably used. As such a magnetic metal, a ferromagnetic metal such as nickel, iron, ferromagnetic stainless steel, nickel-cobalt alloy or permalloy is preferably used. In order to prevent metal fatigue due to repeated bending stress received when the fixing roller 10 rotates, a member in which manganese is added to nickel may be used.

  The thickness of the heat generating layer 1 is preferably greater than the skin depth δ [m] represented by the following formula and 1 mm or less. If the thickness of the heat generating layer 1 is within this range, the heat generating layer 1 can efficiently absorb electromagnetic waves, and therefore heat can be generated efficiently.

  Here, f is the frequency [Hz] of the excitation circuit, μ is the magnetic permeability of the heat generating layer 1, and κ is the conductivity of the heat generating layer 1.

  This skin depth δ indicates the depth of absorption of electromagnetic waves used for electromagnetic induction, and the intensity of the electromagnetic waves is 1 / e or less deeper than this. Conversely, most of the energy is absorbed up to this depth (see the relationship between the heat generation layer depth and the electromagnetic wave intensity shown in FIG. 5B).

  The thickness of the heat generating layer 1 is more preferably 0.2 to 0.8 mm. When the thickness of the heat generating layer 1 is thinner than the above range, the efficiency is deteriorated because most of the electromagnetic energy cannot be absorbed. On the other hand, when the heat generating layer 1 is thicker than the above range, the heat capacity is increased and the rate of temperature increase is decreased.

  The elastic layer 2 is preferably made of a material having good heat resistance and thermal conductivity, such as silicone rubber, fluorine rubber, and fluorosilicone rubber.

  The thickness of the elastic layer 2 is preferably 0.05 to 3 mm in order to guarantee the fixed image quality. When a color image is printed, a solid image is formed over a large area on the recording material P, particularly in a photographic image. In this case, if the heating surface (release layer 3) cannot follow the unevenness of the recording material P or the unevenness of the toner layer t, uneven heating occurs, and uneven gloss occurs in the image where the heat transfer amount is large and small. . That is, the glossiness is high in the portion where the heat transfer amount is large, and the glossiness is low in the portion where the heat transfer amount is small. When the thickness of the elastic layer 2 is smaller than the above range, the release layer 3 cannot follow the unevenness of the recording material P or the toner layer t, and image gloss unevenness occurs. On the other hand, when the elastic layer 2 is too larger than the above range, the thermal resistance of the elastic layer 2 becomes too large, making it difficult to realize a quick start. The thickness of the elastic layer 2 is more preferably 0.1 to 2 mm.

  If the elastic layer 2 is too hard, it cannot follow the unevenness of the recording material P or the toner layer t, and image gloss unevenness occurs. Therefore, the hardness of the elastic layer 2 is 60 ° (JIS-A) or less, more preferably 45 ° (JIS-A) or less.

The thermal conductivity λ of the elastic layer 2 is preferably 2.5 × 10 ^{−1 to} 8.4 × 10 ⁻¹ W / m · K. When the thermal conductivity λ is smaller than the above range, the thermal resistance is too large, and the temperature rise in the surface layer (release layer 3) of the fixing roller 10 is slow. When the thermal conductivity λ is larger than the above range, the hardness of the elastic layer 2 becomes too high or compression set tends to occur. More preferably, it is 3.3 × 10 ^{−1 to} 6.3 × 10 ⁻¹ W / m · K.

  The release layer 3 is preferably made of a material having good release properties and heat resistance such as fluororesin, silicone resin, fluorosilicone rubber, fluororubber, silicone rubber, PFA, PTFE, and FEP.

  The thickness of the release layer 3 is preferably 1 to 100 μm. If the thickness of the release layer 3 is thinner than the above range, uneven coating of the coating film occurs, causing a problem that a part having poor release property is generated or durability is insufficient. Moreover, when the thickness of the release layer 3 is thicker than the above range, the heat conduction is deteriorated. In particular, when a resin material is used for the release layer 3, the hardness of the release layer 3 becomes too high and the effect of the elastic layer 2 is lost.

  The pressure roller 30 includes a cored bar 30a and a heat-resistant / elastic material layer 30b such as silicone rubber, fluororubber, or fluororesin that is concentrically formed and coated around the cored bar in a roller shape. A release layer 30c is provided on the surface layer.

  As shown in FIG. 2, the fixing roller 10 is rotatably supported by the fixing frame 50 via a bearing 41. The pressure roller 30 is rotatably supported at both ends in the longitudinal direction of the core metal 30 a by a pressure frame 51 as a swing member via a bearing 42. The pressure frame 51 is swingably supported by a support shaft 52 fixed to the fixing frame 50, and is urged so that the pressure roller 30 is pressed against the fixing roller 10 by a pressure spring 53 as pressure means. ing.

  A gear 43 is attached to one end of the fixing roller 10 so as to rotate integrally with the fixing roller 10. The fixing roller 10 is rotationally driven in the clockwise direction indicated by an arrow when the gear 43 receives a driving force from a fixing roller rotation driving mechanism M as a first rotating body driving unit.

  Reference numeral 26 denotes a temperature sensor such as a thermistor as temperature detecting means, which detects the temperature of the fixing roller 10. The temperature sensor 26 is disposed in a non-contact manner with the fixing roller 10 within a sheet passing area (nipping and conveying area) W of the recording material P in the longitudinal direction of the fixing roller 10. In this example, the temperature sensor 26 is a non-contact type, but a contact type may be used.

  Reference numeral 44 denotes a cam as a pressure release means, which has a substantially elliptical side surface having a short diameter portion 44a and a long diameter portion 44b. The cams 44 are respectively fixed to both sides in the longitudinal direction of a cam shaft 45 that is rotatably supported by the fixing frame 50, and rotate integrally with the cam shaft 45. A gear 46 is attached to one end of the cam shaft 45 so as to rotate integrally with the cam shaft 45. The cam shaft 45 is rotationally driven when the gear 46 receives a driving force from a cam rotation driving mechanism M2 as a pressure release driving means.

  As described above, the heating device 100 of the present example fixes the pressure frame 51 by swinging the support shaft 52 around the fulcrum against the pressure force of the pressure spring 53 against the fixing frame 50 by the rotation of the cam 44. The roller 10 and the pressure roller 30 are configured to contact / separate. The contact and separation between the fixing roller 10 and the pressure roller 30 are selectively switched based on the determination of the control unit 60 as a control unit.

  The control unit 60 includes a CPU, a memory such as a ROM and a RAM, and the memory includes a contact / separation switching control, a temperature control, a fixing roller drive control, a print standby mode, a device startup mode 1, and a device startup mode 2. Various corresponding programs are stored. The CPU controls the excitation circuit 27, the fixing roller rotation driving mechanism M, and the cam rotation driving mechanism M2 in accordance with the above program.

(4) Description of Operation of Heating Device 100 At the time of image formation, the control unit 60 drives the cam rotation drive mechanism M2 to rotate the cam 44 via the cam shaft 45 and the gear 46, thereby turning the small diameter portion 44a into the pressure frame 51. The contact is made (FIG. 6A). The pressure frame 51 is pushed up to the cam 44 side by the pressure of the pressure spring 53, and the pressure roller 30 is pressed against and contacts the fixing roller 10 by the pressure of the pressure spring 53 (FIG. 1). ) Is formed.

  Next, the fixing roller rotation driving mechanism M is driven to rotate the fixing roller 10 in the counterclockwise direction indicated by the arrow (FIG. 1). As the fixing roller 10 is driven to rotate, a rotational force acts on the pressure roller 30 by a frictional force between the surface of the fixing roller 10 and the surface of the pressure roller 30 at the nip portion N. The pressure roller 30 is rotated in a clockwise direction (FIG. 1) indicated by an arrow at a peripheral speed substantially corresponding to the rotational peripheral speed of the fixing roller 10.

  Next, the excitation circuit 27 is turned on, and the excitation coil 18 is fed with a high-frequency current via the power feeding units 18a and 18b. Based on the detected temperature of the fixing roller 10 from the temperature sensor 26, the excitation circuit 27 is turned on / off (ON / OFF) to control the current supply to the exciting coil 18, and the temperature of the fixing roller 10 is set to a predetermined fixing temperature ( Adjust the temperature to maintain the target temperature.

  Thus, the fixing roller 10 is rotated as described above, and the fixing roller 10 generates electromagnetic induction heat by supplying power from the exciting circuit 27 to the exciting coil 18, and the fixing roller 10 rises to a predetermined fixing temperature and is temperature-controlled. In the state, the recording material P on which the unfixed toner image t conveyed from the image forming unit is formed is introduced into the nip portion N with the image surface facing upward, that is, facing the fixing roller surface. The recording material P is nipped and conveyed through the nip portion N together with the fixing roller 10 with the image surface closely contacting the outer surface of the fixing roller 10 at the nip portion N. In the process in which the recording material P is nipped and conveyed, the unfixed toner image t on the recording material P receives heat and pressure and is heat-fixed as a permanently fixed image on the recording material P. When the recording material P passes through the nip portion N, it is separated from the surface of the fixing roller 10 and discharged and conveyed.

  At the time of non-image formation, the cam rotation drive mechanism M2 is driven to rotate the cam 44 by about 180 ° via the cam shaft 45 and the gear 46 so that the large-diameter portion 44b contacts the pressure frame 51 (FIG. 6B). ). The pressure frame 51 is pushed down against the pressure applied by the pressure spring 53, and the formation of the nip portion N is released by separating the pressure roller 30 and the fixing roller 10.

  Next, the operation of the heating device 100 when the image forming apparatus is turned on / off will be described.

  Normally, the pressure roller 30 and the fixing roller 10 are separated from each other when the image forming apparatus is powered off.

  When the power is turned on, heating of the fixing roller 10 is started, and warm-up is performed until the fixing is possible. Heating is performed until the fixing roller 10 reaches a predetermined temperature (fixable temperature). If the image forming apparatus receives a print command (hereinafter referred to as a print signal) from a host computer or the like, the heating apparatus 100 prints as it is. (Heat fixing) operation is performed. That is, the controller 60 drives the cam rotation driving mechanism M2 to bring the pressure roller 30 and the fixing roller 10 into contact with each other to form the nip portion N, and drives the fixing roller rotation driving mechanism M to The unfixed toner image t is heated and fixed by rotating the pressure roller 30 and nipping and conveying the recording material P at the nip portion.

  If no print signal is received, the image forming apparatus enters a print standby state. In response to this, the heating device 100 performs standby temperature adjustment to maintain the fixing roller temperature at the fixing possible temperature of the unfixed toner image t. That is, the control unit 60 executes the print standby mode to continue the separation state between the pressure roller 30 and the fixing roller 10 by the cam rotation driving mechanism M2 and to fix by exciting the current to the exciting coil 18 by the exciting circuit 27. The temperature control of the roller 10 is continued. Although the temperature control in this example is performed in a state where the fixing roller 10 is continuously stopped, the fixing roller 10 may be intermittently rotated by a predetermined angle every predetermined time.

  Here, the surface temperature of the fixing roller 10 in the print standby mode will be described. As described above, during printing standby, the fixing roller 10 and the pressure roller 30 are separated from each other to prevent compression set, and the rotation of the fixing roller 10 is stopped to prevent noise.

  FIG. 7 is a graph comparing the state of the fixing roller surface temperature when the fixing roller 10 is stopped at a temperature of 180 ° C. and when the fixing roller 10 is rotating.

  The surface temperature of the fixing roller in the stopped state increases from the center of the fixing roller to the outside, and the outermost periphery is 180 ° C. The surface temperature of the fixing roller corresponds to the arrangement of the magnetic field generating means 20 (FIG. 1).

  Here, the arrangement of the magnetic field generating means 20 in the heating apparatus according to the present invention will be described.

  When local heating is performed on the fixing roller 10, energy is concentrated on a part of the fixing roller 10, so that the temperature rise in the heat generation region is accelerated. For this reason, it was effective in shortening the warm-up time.

  However, when the nip portion N (FIG. 1) is heated, the recording material is ignited when the device stops and the heating is not stopped in a state where the recording material is present in the nip portion due to the failure of the device. It may cause smoke.

  Therefore, in this example, the heat generation area is arranged outside the nip portion. As shown in this example, a heat generation area is arranged outside the nip part, and by heating the area other than the nip part by local heating, a failure occurs in the state where the recording material stays in the nip part, and heating occurs. Even when the operation does not stop, the nip portion is not heated, so that it does not ignite or smoke.

  Furthermore, a temperature detection element (thermostat) 28 as a safety device can be disposed opposite the heat generation area as shown in FIG. 1, and the device can be safely stopped even if a failure occurs. In other words, the temperature detection element 28 is provided above the fixing roller 10 as a safety measure mechanism when the fixing roller temperature abnormally increases (during thermal runaway). The temperature detection element 28 opens the contact point when the temperature reaches a preset temperature and cuts off the energization to the exciting coil 18, thereby preventing the fixing roller 10 from being heated to a temperature higher than a predetermined temperature.

  Furthermore, when the fixing roller 10 has a rubber layer, it takes time to transfer heat from the heat generating layer 1 to the surface of the fixing roller.

  Next, the rotation speed of the fixing roller 10 in the apparatus startup mode will be described.

  When the fixing roller 10 is rotating (the rotation direction of the fixing roller is clockwise), as indicated by the solid line in FIG. 7, the heat generation area and the area that reaches the maximum temperature are different during rotation. By disposing the heating zone upstream of the nip portion N (FIG. 1), the region reaching the maximum temperature can be made the nip portion, and wasteful power consumption can be reduced. However, if the fixing roller 10 is continuously rotated during the print standby, noise due to roller rotation is generated.

  The surface temperature when the fixing roller 10 is stopped is shown by a broken line in FIG. In the stopped state, if the temperature of the heat generating area where the temperature detecting element 26 (FIG. 1) is arranged is adjusted to 180 ° C., the temperature can be maintained only at about 90 ° C. at the lowest temperature in the non-heat generating area. For this reason, it is necessary to perform the pre-rotation from the print standby state to the fixing ready state to eliminate the temperature unevenness in the circumferential direction of the fixing roller 10.

  Here, the pre-rotation is a process of starting up the fixing device from a standby state to a state where fixing is possible. Specifically, this is an operation of stabilizing the rotational speed until the recording material P reaches the fixing device and simultaneously setting the temperature of the fixing device to an appropriate temperature for printing.

  This pre-rotation time requires time until the temperature unevenness is eliminated, and the temperature unevenness must be converged as soon as possible in order to shorten the first printout time. In this example, the fixing roller peripheral speed at the time of pre-rotation is made faster than the peripheral speed at the time of printing, and the effect of equalizing the fixing roller surface temperature is enhanced.

  That is, the control unit 60 executes the apparatus start-up mode 1 to drive the fixing roller rotation drive mechanism M to make the fixing roller peripheral speed faster than the peripheral speed during printing, thereby equalizing the fixing roller surface temperature.

  The image forming apparatus of this example conveys the recording material at a normal speed of 144 mm / sec. In the normal paper print mode, and the pre-rotation when shifting from the print standby state to the print is 4/3 speed of the normal speed. It is performed at a certain 192 mm / sec.

  In this example, standby temperature control is performed with the fixing roller 10 and the pressure roller 30 separated from each other. However, when the image forming apparatus receives a print signal, the heating device 100 responds to this by the fixing device 10 and the pressure roller. 30 is pressed and contacted, pre-rotation is started, and the temperature is adjusted toward the printing temperature. That is, the control unit 60 executes the apparatus start-up mode 2 to drive the cam rotation driving mechanism M2 to bring the pressure roller 30 and the fixing roller 10 into contact with each other to form the nip portion N, thereby fixing the fixing roller rotation driving mechanism. M is driven to make the fixing roller peripheral speed faster than the peripheral speed at the time of printing, thereby equalizing the surface temperature of the fixing roller.

  FIG. 8 shows the fixing roller surface temperature of the present example at the time of pre-printing rotation, and the fixing roller surface temperature when the pre-rotation is performed at the same fixing roller peripheral speed as at the time of printing as Comparative Example 1.

  The surface temperature of the fixing roller indicated by the solid line in the drawing is that of the first embodiment, and that of the comparative example 1 is indicated by the broken line.

  When the pre-rotation is started, the heat flows out to the pressure roller side, so that the surface temperature of the fixing roller once falls, and the heat generation area of the fixing roller is heated by electromagnetic induction heating and starts to rise toward the printing temperature.

  In Example 1, the temperature rises along solid lines T1 and B1, and in Comparative Example 1, the temperature rises along broken lines T2 and B2.

  Here, T1 and T2 indicate changes in the upper end temperature of the fixing roller temperature ripple, and B1 and B2 indicate changes in the lower end temperature of the fixing roller temperature ripple.

  The distance between the upper end temperature transition and the lower end temperature transition gradually decreases with the passage of time, and finally the circumferential temperature unevenness due to standby temperature control is eliminated.

  Referring to FIG. 8, immediately after the start of the pre-rotation, the circumferential temperature unevenness due to the standby temperature control during the print standby remains, and a temperature ripple is generated at a cycle of one rotation of the fixing roller. However, as time elapses, the fixing roller rotates and the heat generating area generates heat, so that this temperature unevenness is leveled and the temperature ripple decreases.

  However, the temperature ripple reduction speed of Comparative Example 1 that rotates at the peripheral speed during printing is slower than that of Example 1 that rotates at the peripheral speed of 4/3 speed during printing.

  This is because the number of times that a certain portion on the circumference of the fixing roller passes through the heat generation area per unit time is smaller in Comparative Example 1 than in Example 1.

  In other words, in Example 1, the number of heat generations is increased by rotating at a high peripheral speed, temperature unevenness caused by standby temperature control can be leveled in a shorter time, and temperature ripples can be converged more quickly. it can.

  In the image forming apparatus of this example, when the temperature difference on the surface of the fixing roller is larger than 5 ° C., gloss unevenness (gloss unevenness) due to this temperature difference appears remarkably in the toner image after fixing.

  Therefore, even if the surface temperature of the fixing roller reaches the printing temperature or higher, if printing is started in a state where the temperature ripple is greater than 5 ° C., a defective image with gloss unevenness is output.

Therefore, the conditions under which printing can actually start are
1) Fixing roller temperature ≥ Print temperature
and,
2) Circumferential unevenness (ripple) of fixing roller temperature ≤ 5 °
It becomes.

  However, since the fixing roller temperature has a ripple, even if the above condition 1) is satisfied at a certain point in time, the fixing roller temperature may again fall below the printing temperature.

  In the present invention, it is not determined that printing can be started in such a case.

  That is, it is determined that the above condition 1) is satisfied only after the fixing roller temperature once rises above the print temperature and then does not drop below the print temperature again.

  Here, based on the above, FIG. 8 will be confirmed.

  First, in Comparative Example 1, the temperature of the fixing roller itself is about 5.5 sec. However, since the temperature ripple (R2 in the figure) is higher than 5 ° C., printing cannot be started at this point.

  In order to finally be able to print, it is necessary to take a time to idle and thereafter converge the temperature ripple.

  On the other hand, in Example 1, about 6.3 sec. Since the temperature has been raised to the printing temperature and the temperature ripple (R1 in the figure) has also decreased within 5 ° C., printing can be started at this point.

  Printing is possible in Example 1 at 6.3 sec. Even at this point, in Comparative Example 1, the temperature ripple (R3 in the figure) is larger than 5 ° C., so printing cannot be started and idling must be continued.

  Comparative Example 1 can finally start printing about 8.2 sec after the start of the pre-rotation. It was later.

  In this way, although the temperature rise speed tends to be faster when the peripheral speed of the fixing roller is slow, the speed of decrease of the temperature ripple is slow, so the time before the printing is actually possible is high. In Example 1, approximately 1.9 sec. It has been shortened.

  As a result, the first printout time can be shortened in the first embodiment as compared with the conventional method in which the pre-rotation speed when shifting from the print standby state to the print state is the same as the speed at the time of printing. It was.

  Further, when the method of the first embodiment is used, no noise is generated because the fixing roller idle rotation for the purpose of preventing temperature unevenness is not necessary at the time of standby temperature control of the heating device during print standby.

  As described above, in the first embodiment, it is not necessary to perform a special operation during print standby, and it is possible to shorten the first printout time while performing standby temperature control in a very simple sequence that does not generate noise. did it.

  FIG. 9 is a cross-sectional side view of the main part of the heating apparatus 100 of the present embodiment.

  The heating device 100 of this example also has a heat source 31 on the pressure roller 30 side, and performs standby temperature adjustment of the pressure roller 30 based on the print standby mode during print standby.

  Other configurations and sequences are the same as those in the first embodiment, and the description thereof will be omitted.

  A halogen heater 31 is included in a core metal 30 a as a heat source for the pressure roller 30. The halogen heater 31 is adjusted to a fixing temperature by controlling the energization of the halogen heater 31 by the controller 60 driving a heater drive circuit (not shown) based on the temperature detected by the temperature sensor 32 as pressure roller surface temperature detecting means. Temperature control is performed.

  In this example, the halogen heater 31 on the pressure roller side is used only during standby temperature adjustment during printing standby, and is turned off simultaneously with the start of rotation before printing.

  The standby temperature adjustment temperature of the pressure roller 30 is 160 ° C., and the standby temperature adjustment temperature of the fixing roller 10 is 180 ° C. (= printing temperature) as in the first embodiment.

  FIG. 10 shows the surface temperature of the fixing roller of this example during rotation before printing, and the surface temperature of the fixing roller of Example 1 as Comparative Example 2.

  In Example 2, the temperature rises along solid lines T3 and B3, and in Comparative Example 2 (Example 1), the temperature rises along broken lines T1 and B1.

  Here, T1 and T3 indicate the transition of the upper end temperature of the fixing roller temperature ripple, and B1 and B3 indicate the transition of the lower end temperature of the fixing roller temperature ripple.

  In the second embodiment, the pressure roller 30 is heated during printing standby, so that the temperature drop of the fixing roller after the start of the pre-rotation is smaller than that in the second comparative example (first embodiment).

  Accordingly, the temperature raising rate is the same as that in Comparative Example 2, but the time required to reach the printing temperature is shortened.

  From FIG. 10, in Example 2, about 4.9 sec. At this time, the print temperature is reached, and the temperature ripple (R4 in the figure) is within 5 ° C.

  Therefore, fixing can be started at this point, and the 6.3 sec. The first printout time can be further shortened because the temperature rise time can be made shorter.

  In the heating device 100 in this example, when a print signal is received in a print standby state, the fixing roller 10 and the pressure roller 30 are not brought into contact with each other, and first, the pre-rotation is started in a separated state.

  When the temperature of the fixing roller 10 reaches a predetermined temperature, the fixing roller 10 and the pressure roller 30 are brought into contact with each other to adjust the temperature of the fixing roller 10 to the printing temperature.

  The other operations are the same as those in the first embodiment, and the description thereof will be omitted.

  FIG. 11 shows an operation timing chart comparing the above operation with the first and second embodiments.

  The drawing shows the operating state (standby / printing) of the image forming apparatus, the rotating state of the fixing motor included in the fixing roller rotation drive mechanism M, and the contact state between the fixing roller 10 and the pressure roller 30.

  In the first and second embodiments, as soon as the print signal flag is turned ON (t = t0), the fixing roller 10 and the pressure roller 30 are brought into contact with each other, and the rotation of the fixing motor is started.

  On the other hand, in the third embodiment, the contact between the fixing roller 10 and the pressure roller 30 is not performed at the time t = t0, and only the rotation of the fixing motor is started.

  Thereafter, the fixing roller 10 and the pressure roller 30 are brought into contact with each other only when t = t1.

  Here, t1 is a time for the fixing roller temperature to reach a target temperature 1 described later.

  FIG. 12 shows the surface temperature of the fixing roller of this example during rotation before printing, and the surface temperature of the fixing roller of Example 2 as Comparative Example 3.

  In Example 3, the temperature rises along solid lines T4 and B4, and in Comparative Example 3 (Example 2), the temperature rises along broken lines T3 and B3.

  Here, T3 and T4 indicate the transition of the upper end temperature of the fixing roller temperature ripple, and B3 and B4 indicate the transition of the lower end temperature of the fixing roller temperature ripple.

  In Example 3, only the fixing roller 10 is heated at first. Therefore, the temperature rise rate is faster than that of Comparative Example 3 (Example 2), and about 2.3 sec after the start of the pre-rotation. The target temperature 1 is reached.

  The target temperature 1 is set to 187 ° C. which is the printing temperature + 7 ° C.

  When the fixing roller temperature reaches the target temperature 1, the pressure roller 30 is brought into contact with it to continue the pre-rotation.

  At this time, the fixing roller temperature is once lowered, and then the temperature is increased along the solid lines T4 'and B4'.

  Here, as before, T4 'represents the transition of the upper end temperature of the fixing roller temperature ripple, and B4' represents the transition of the lower end temperature of the fixing roller temperature ripple.

  Although the temperature increase rate at this time is almost the same as that of Comparative Example 3 (Example 2), the ripple is leveled to some extent only with the fixing roller 10, so the temperature ripple after contacting the pressure roller 30 Becomes smaller than Comparative Example 3.

  Therefore, about 3.6 sec. When the fixing roller temperature reaches the printing temperature, the temperature ripple (R5 in the figure) is already within 5 ° C., and printing is possible.

  In this way, by contacting the fixing roller 10 and the pressure roller 30 during the pre-rotation, the 4.9 sec. As a result, the heating time can be further shortened and the first printout time can be shortened.

[Other]
1) In each embodiment, the heating device of the electromagnetic induction heating method having the magnetic field generating means inside the fixing roller 10 is exemplified, but the image heating device of the present invention is not limited to the electromagnetic induction heating method. For example, an electromagnetic induction external heating method in which a magnetic field generating means is provided outside a fixing roller or a fixing film (belt), a film heating method using a ceramic heater, or a color on demand type in which an elastic layer is provided on a film heating method fixing film If it is a system which performs standby temperature control by local heating, such as a heating device, the same effect as described above can be obtained.

  FIG. 13 shows an example of a heater heating type heating device using a ceramic heater 25 inside the fixing roller 10 as a heating means (heating body). The ceramic heater 25 includes an elongated ceramic substrate 25a, an electrode portion (not shown) disposed on the surface of the substrate 25a, and a resistance heating layer 25b as a resistance heating element connected to the electrode portion. The ceramic heater 25 is held by the holder 26 at the nip portion N and is in contact with the inner surface of the fixing roller 10. Then, the control unit 62 drives the heater drive circuit 62 based on the temperature detected by the temperature sensor 29 disposed on the back surface of the substrate 25a, and energizes the resistance heat generation layer 25b from the heater drive circuit through the electrode unit. Is heated to control the temperature of the fixing roller 10 to the fixing temperature. Reference numeral 27 denotes a holding stay for holding the holder 26.

  2) In each embodiment, the standby temperature is set equal to the print temperature (fixing temperature). However, when the standby temperature is set lower than the print temperature for the purpose of reducing power consumption or reducing the temperature rise in the image forming apparatus, Alternatively, the same effect can be obtained when the standby temperature is set higher than the printing temperature for the purpose of further reducing the first printout time.

  3) In addition, when the temperature rise time of the fixing device can be increased to some extent, such as when returning from the image forming apparatus sleep mode, the roller peripheral speed during the previous rotation is made slower than the peripheral speed used in this example, and the rotation speed It is also possible to improve the durability life of the fixing roller and the pressure roller by reducing the amount of toner. Here, the image forming apparatus sleep mode refers to a state of waiting at a lower temperature and lower power than standby. Therefore, the rise time until printing is possible is longer than that in the standby state.

  4) Further, the first printout time can be further shortened if the temperature unevenness of the fixing roller is reduced to some extent by changing the heating position of the fixing roller at predetermined time intervals during standby temperature control.

  5) The image heating apparatus of the present invention is not limited to the heating apparatus of the embodiment, and is an assumption fixing apparatus that presupposes an unfixed image on a recording material, and an image such as a gloss by reheating a recording material carrying a fixed image. It is also effective as an image heating apparatus such as a surface modification apparatus for modifying the surface property.

Cross-sectional side view of the main part of the heating apparatus according to Example 1 Similarly, front view of the main part Perspective model view of right holder with magnetic field generating means installed and supported inside Model diagram of layer structure of electromagnetic induction heat-generating fixing roller (A) The figure which showed the heat_generation | fever distribution of a heating apparatus, (B) is the graph which showed the relationship between the heat generating layer depth and electromagnetic wave intensity FIG. 1 shows a heating device in the section aa ′ in FIG. 1, (A) is a schematic diagram of a main part showing a contact state between a fixing roller and a pressure roller, and (B) shows a separated state between the fixing roller and the pressure roller. Model diagram of the main part shown Graph showing the temperature distribution in the circumferential direction of the fixing roller The graph which showed the fixing roller temperature transition of Example 1. Cross-sectional side view of the main part of the heating apparatus according to Example 2 The graph which showed the fixing roller temperature transition of Example 2. Operation timing chart in the heating apparatus according to Examples 1, 2, and 3. The graph which showed the fixing roller temperature transition of Example 3 Cross-sectional side view of the main part of the heating device of the heater heating system to which the present invention is applied Schematic configuration model diagram of an image forming apparatus

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Heat generation layer 2 ... Elastic layer 3 ... Release layer 4 ... Heat insulation layer 10 ... Fixing roller (1st rotary body)
16 ... holders 17a, 17b, 17c ... magnetic core 20 ... magnetic field generating means (heating means)
26 Temperature detecting element 28 Temperature detecting element 30 as safety element Pressure roller (second rotating body)
60 ... Control unit 100 ... Heat fixing device (heating device)
N: Fixing nip (nip area)
P ... Recording material

Claims (11)

A heating unit; a first rotating body heated by the heating unit; and a second rotating body that presses against the first rotating body to form a nip portion, and forms an unfixed image. In an image heating apparatus that heats and fixes an unfixed image on a recording material while nipping and conveying the recorded recording material at the nip portion,
A standby mode for controlling the temperature of the first rotating body in a state in which the first rotating body and the second rotating body are separated from each other;
The rotational speed of the first rotating body when the temperature of the first rotating body in the standby mode shifts to a temperature at which the unfixed image can be heated and fixed is determined when the material to be heated is nipped and conveyed at the nip portion. An image heating apparatus comprising: an apparatus start-up mode for rotating the first rotating body so as to be different from a rotation speed.   2. The image heating apparatus according to claim 1, further comprising a second heating unit configured to heat the second rotating body, wherein temperature control of the second rotating body is performed in the standby mode.   The rotation speed of the first rotating body in the apparatus start-up mode is faster than the rotation speed when the recording material is nipped and conveyed by the nip portion. Image heating device.   In the apparatus startup mode, after the first rotating body is driven to rotate while the first rotating body and the second rotating body are separated from each other, and the temperature of the first rotating body reaches a predetermined temperature, The image heating apparatus according to claim 1, wherein the first rotating body and the second rotating body are brought into contact with each other.   The image heating apparatus according to claim 1, wherein in the standby mode, the temperature of the first rotating body is controlled in a continuous rotation stopped state.   The image heating apparatus according to claim 1, wherein the first rotating body has a standby state in which the first rotating body rotates by a predetermined angle at a predetermined time period.   2. The image heating apparatus according to claim 1, wherein the heating unit locally heats or heats a part of the circumference of the first rotating body other than the fixing nip. 3.   The image heating apparatus according to claim 1, wherein the heating unit heats the first rotating body by electromagnetic induction by the action of a magnetic field of a magnetic field generation unit.   The image heating apparatus according to claim 8, wherein the magnetic field generation unit is provided outside the first rotating body.   The heating means is a heating body having a substrate and a resistance heating element disposed on the substrate, and contacts the first rotating body from the inside at the nip portion to heat the first rotating body. The image heating apparatus according to claim 1, wherein: An image forming apparatus comprising: an image forming unit that forms an unfixed image on a recording material; and an image heating device that heats an unfixed image formed on the recording material by the image forming unit.
An image forming apparatus comprising the image heating apparatus according to claim 1 as the image heating apparatus.