JP2015090383A - Fixing apparatus and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing apparatus configured to reduce warm-up time without causing image quality unevenness or fixability variation even when a thin heating roller (fixing roller) or a low-temperature fixing toner which requires short melting time is used, or to provide an image forming apparatus.SOLUTION: A fixing apparatus includes a fixing roller including a heat source arranged in a rotatable cylindrical part, and a pressure roller which comes into pressure-contact with the fixing roller. The heat source is spaced from the center of the fixing roller. The fixing roller is half-rotated only once during warm-up of the fixing roller.

Description

  The present invention relates to a fixing device that fixes a toner image on a recording material by heating and pressing, and an image forming apparatus using the same.

  2. Description of the Related Art Conventionally, an electrophotographic image forming apparatus such as an electrophotographic copying machine or a printer uniformly charges the surface of a photosensitive drum with a charging device, and then irradiates the surface of the photosensitive drum with image light to electrostatic latent images. An image is formed, and the electrostatic latent image is developed by a developing device to form a toner image. Then, after the toner image is transferred onto the recording paper, the toner image on the recording paper is fixed by heating and pressing with a fixing device, thereby forming an image.

  The fixing device includes a heating roller (fixing roller) having a built-in lamp inside a rotatable cylindrical portion, and a pressure roller that presses the sheet against the heating roller. A recording paper carrying a toner image is passed between a heating roller and a pressure roller, and the toner image is melted and fixed on the recording paper by heating and pressing.

  In recent years, there has been a demand for energy saving of the fixing device and speeding up of the image forming apparatus. For this reason, efforts are being made to reduce the warm-up time and power consumption during standby. As an example, the cylindrical cored bar of the heating roller is made as thin as possible to easily raise the surface temperature of the heating roller. In addition, the rigidity of the core metal is increased by using an iron core bar instead of an aluminum core bar.

  In the case where the heating roller is thinned in this way, if small-size recording paper is continuously passed, the surface temperature of both ends of the heating roller through which the recording paper does not pass rises, and the heating roller is damaged. In other cases, a hot offset may occur when a large-sized recording sheet is passed immediately after a small-sized recording sheet is passed continuously. For this reason, a heating roller having a plurality of heaters such as a heater for heating the central portion of the heating roller and a heater for heating the end portion is used.

  In such a fixing device provided with a heating roller, when the device is used, if energization is performed without rotating the heating roller in advance, each heater is separated from the center of the heating roller. A partial temperature difference occurs in the circumferential direction. If the paper is rotated in such a state, uneven fixing, hot offset, cold offset, etc. occur. To solve this problem, when the heating roller reaches a temperature at which fixing can be performed, pre-rotation is performed at a low speed before copying, but this is not sufficient. An apparatus for rotating a heating roller has been proposed.

  FIG. 7 is a schematic cross-sectional view of the fixing device 700 disclosed in Patent Document 1. The fixing device 700 includes a heating roller 710 having a heater therein and a pressure roller 720 that is in pressure contact with the heating roller 710. The heating roller 710 is heated by a central heater 711 that generates heat by energization and heats the central portion of the heating roller 710, and an end heater 712 that generates heat by energization and overheats the end of the heating roller 710. The roller 710 is provided apart from the center.

  In the present apparatus, when the heating roller 710 is rotated halfway every predetermined time during the warm-up, and the temperature difference between the central portion and the end portion of the heating roller 710 becomes 10 ° C. or more, the higher heater is turned off. Has been proposed. According to this, temperature unevenness in the circumferential direction of the heating roller can be reduced, and good fixing can be performed.

  Further, with regard to the toner, a toner that is melted and fixed at a lower temperature than the conventional one has been developed by lowering the softening point of the binder resin of the toner. As a result, the temperature of the heating roller required for fixing is set low, which is useful for shortening the warm-up time of the fixing device and reducing power consumption.

JP-A-9-212024

  However, in the fixing device shown in the above-mentioned patent document, since the temperature change at the time of starting up the heater and the change in the heat radiation amount with the passage of time are not taken into consideration at all, the heating roller is simply installed at every predetermined time during the warm-up. By simply rotating it counterclockwise, the temperature unevenness in the circumferential direction of the heating roller is still not solved, and there is a problem that image quality unevenness (gloss variation) and fixing property variation occur.

  In addition, as described above, when sharp-melt toner that melts at low temperature is used, the melt sensitivity to the fixing temperature is high, so even if there is a slight temperature variation, there will be noticeable image quality unevenness and fixing property variation. become.

  Further, since the fixing roller is rotated a plurality of times during warm-up, the amount of heat transferred to the pressure roller increases, energy loss occurs, and the temperature difference between the center and end of the heating roller is 10 ° C. In such a case, since the higher heater is turned off, shortening of the warm-up time, which is the original purpose, is hindered.

  The present invention has been made in view of the above circumstances, and its object is to achieve a low-temperature fixing with a thin heating roller (fixing roller) or a short melting time in order to save energy and increase the speed. It is an object of the present invention to provide a fixing device and an image forming apparatus that have no image quality unevenness and fixing property variation even when toner is used, and that have a short warm-up time.

  In order to solve the above problems, a fixing device according to the present invention is a fixing device that includes a fixing roller having a heat source built in a rotatable cylindrical portion, and a pressure roller in pressure contact with the fixing roller. Is provided apart from the center of the fixing roller, and the fixing roller is rotated halfway only once during the warm-up of the fixing roller.

Further, the time S from the start of the warm-up of the fixing roller to the half-rotation of the fixing roller is expressed as follows:
Sw × 0.5 <S <Sw × 0.8
It is good also as a feature.

  Further, when there is a single heat source, the heat source may be arranged in the vicinity of the fixing nip, and when there are a plurality of heat sources, the heat source having the largest output may be arranged in the vicinity of the fixing nip.

  When there is a single heat source, the heat source is arranged near the fixing nip and upstream of the fixing roller rotation direction. When there are a plurality of heat sources, the heat source with the largest output is located near the fixing nip and fixing. It may be arranged upstream with respect to the roller rotation direction.

  An image forming apparatus according to the present invention includes any one of the fixing devices described above.

  Further, the image forming apparatus may include a toner.

  The toner may have a melting time of 0.035 seconds or less.

  According to the present invention, even when a thin heating roller (fixing roller) or a low-temperature fixing toner having a short melting time is used, a fixing device and an image forming apparatus having a short warm-up time without uneven image quality and fixing property are provided. It can be realized.

1 is an internal configuration diagram illustrating a configuration of an image forming system 1 according to the present embodiment. FIG. 3 is a cross-sectional view of a fixing device 23 according to the present embodiment. FIG. 6 is a schematic diagram viewed from the axial direction of the fixing roller of the fixing device 23 according to the present embodiment. It is a figure explaining the measuring method of the melting time of the toner used in this embodiment. It is a figure explaining the position of a heater lamp. It is a figure which shows the temperature change of a fixing roller and a pressure roller. 2 is a schematic cross-sectional view of a fixing device 700 disclosed in Patent Document 1. FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, the same members are denoted by the same reference numerals. The following embodiment is an example embodying the present invention, and does not limit the technical scope of the present invention.

  FIG. 1 is an internal configuration diagram showing a configuration of an image forming system 1 according to an embodiment of the present invention. The image forming system 1 includes a scanner 3, an automatic document conveying device 4, a post-processing device 5, a recording material supply device 6, a relay conveying unit 8, and a double-sided conveying device 10, each of which is a peripheral device, with the image forming device 2 as a core. Connected and extended functionality. Among these, the image forming apparatus 2 and the post-processing apparatus 5 are placed side by side on the upper surface of the recording material supply apparatus 6, and the scanner 3 is placed above them together with the automatic document feeder 4 disposed above the system 3. It is arranged by being supported on the rack 7.

  The image forming apparatus 2 records and outputs image data from the externally connected device when an image processing device such as a personal computer is connected as an externally connected device, as well as the recording output of the image read by the scanner 3. Is.

  An electrophotographic process section (image forming section) 20 with a photoreceptor (photosensitive drum) 200 as the center is disposed on the substantially left side of the image forming apparatus 2. Around the photosensitive member 200, there are a charging roller 201 for uniformly charging the surface of the photosensitive member 200, an optical scanning unit 22 for scanning an optical image on the uniformly charged photosensitive member 200 and writing an electrostatic latent image, A developing unit 202 that reproduces the electrostatic latent image written by the scanning unit 22 with a developer, a transfer unit 203 that transfers an image reproduced on the photoconductor 200 onto a recording material, and a residual image on the photoconductor 200 after transfer. A cleaning unit 204 that enables the developed developer to be removed and a new image to be recorded on the photoconductor 200, and a static elimination lamp unit (not shown) that removes the charge on the surface of the photoconductor 200 are disposed. .

  A recording material supply unit 21 that can store a recording material is disposed below the image forming apparatus 2, that is, on the recording material supply device 6 side. The recording material supply unit 21 includes a recording material storage tray 210 that stores recording materials, and a separation supply unit 211 that separates and feeds the recording materials stored in the recording material storage tray 210 one by one. The recording materials separated and fed one by one by the separation supply unit 211 are sequentially supplied between the photosensitive member 200 and the transfer unit 203 of the electrophotographic process unit 20, and the toner recorded and reproduced on the photosensitive member 200. The image is transferred. Note that operations such as replenishing the recording material to the recording material supply unit 21 and replacing the recording material are performed by pulling out the recording material storage tray 210 to the front side of the main body of the image forming apparatus 2.

  A recording material sent from an optional recording material supply device 6 is received on the lower surface of the main body of the image forming apparatus 2, and sequentially between the photosensitive member 200 and the transfer unit 203 of the electrophotographic process unit 20. A recording material receiving port 27 for feeding is provided.

  A fixing device 23 is disposed above the electrophotographic process unit 20 and sequentially receives recording materials onto which images have been transferred, and heat-fixes the developer transferred onto the recording material to move it out of the fixing device 23. Send out the recording material. The recording material on which the image is recorded is transferred from the paper discharge roller 28 of the image forming apparatus to the relay conveyance unit 8 on the upper surface of the main body of the image forming apparatus 2. As described above, the sheet conveyance path (recording material conveyance path) 64 of the image forming apparatus 2 is configured in a substantially vertical shape from the bottom to the top.

  The optical scanning unit 22 is disposed on the side of the electrophotographic process unit 20, that is, at a position adjacent to the electrophotographic process unit 20 in a direction substantially perpendicular to the sheet conveyance path 64. The upper and lower spaces of the optical scanning unit 22 include a device control unit 24 for accommodating a process control unit (PCU) substrate for controlling an electrophotographic process and an interface substrate for receiving image data from the outside of the device. An image control unit 25 having an image control unit (ICU) substrate for performing predetermined image processing on the received image data and causing the optical scanning unit 22 to scan and record the image on the photosensitive member 200, and these Various substrates and a power supply unit 26 for supplying power to the unit are arranged.

  The recording material supply device 6 is an optional externally attached recording material supply device and includes three recording material supply units 61, 62, and 63. In the recording material supply units 61, 62, and 63, the recording materials stored in the recording material storage trays 610, 620, and 630 are separated one by one by the separate feeding means 611, 621, and 631, respectively, The recording material is supplied toward the recording material discharge port 65 provided on the upper surface of the recording material supply device 6 and communicating with the recording material receiving port 27 of the image forming apparatus 2. At the time of operation, the recording material supply units 61, 62, and 63 that accommodate a recording material of a desired size are selectively operated. The recording material is supplied to the recording material supply units 61, 62, and 63 by pulling out the recording material storage trays 610, 620, and 630 to the front side of the unit main body.

  In addition, the recording material supply device 6 is configured to place the image forming device 2 and the post-processing device 5 on the upper portion, but can move and be fixed between the system racks 7 in this state. As described above, a moving roller 69 and a fixed portion 68 are provided at the lower portion. At the time of movement, the fixing portion 68 is rotated and raised to separate the fixing portion 68 from the floor surface. At the time of fixing, the fixing portion 68 is rotated and lowered to bring the fixing portion 68 into contact with the floor surface. The recording material supply device 6 is fixed.

  1 illustrates the case where the recording material supply device 6 includes three recording material supply units 61, 62, and 63. However, the present invention is not limited to this, and the recording material supply device 6 includes at least one recording material supply unit. What is necessary is just to have.

  The post-processing device 5 introduces a recording material on which an image discharged from the image forming device 2 and the relay conveyance unit 8 is guided by a carry-in roller 50 provided on the upper portion of the post-processing device 5, and the recording material is supplied to the recording material. And post-processing. Post-processing includes stapling, punching, sorting, and the like. The post-processing device 5 illustrated in FIG. 1 performs stapling, and the post-processing is performed on the lower output tray 59. In addition, those that are not post-processed are selectively discharged to the upper discharge tray 56 by the switching gate 52.

  The scanner 3 includes an automatic reading mode in which a sheet-like document automatically supplied by the automatic document feeder 4 is sequentially exposed and scanned one by one to read a document image, and a book-like document set by a user's manual operation. Or a manual reading mode for reading a document image of a sheet-like document that cannot be automatically supplied by the automatic document feeder 4. Then, the original image of the original set on the transparent original placing table 30 is exposed and scanned by the first scanning unit 31 and the second scanning unit 32 that move along the original placing table 30 with a predetermined speed relationship with each other. The original image is converted into an electrical signal and output by being guided by an optical component such as a mirror or an imaging lens 33 to form an image on the photoelectric conversion element 34.

  The automatic document conveying device 4 includes a document conveying means 41 that conveys a document placed on the document setting tray 40 toward the document placing table 30 and discharges the scanned document onto a document discharge tray 42. Yes. Further, the automatic document feeder 4 rotates upward with the rear side of the apparatus as a fulcrum so that a sheet-like document that cannot be automatically supplied can be read and scanned on the document table 30, It is comprised so that the near side of may open | release.

  The relay conveyance unit 8 is mounted on an upper portion of a paper discharge tray 29 provided on the top of the image forming apparatus 2, and a recording material on which an image discharged from the paper discharge roller 28 of the image forming apparatus 2 is recorded is used as the image forming apparatus. 2 is a transport unit for introduction toward the post-processing apparatus 5 located on the downstream side. Further, in the middle of the recording material conveyance path 84 of the relay conveyance unit 8, another recording material conveyance path 83 that guides the recording material to the discharge tray 9 formed by the upper surface 82 of the unit and the upper surface 54 of the post-processing device 5. Is branched. The two discharge destinations can be changed by switching the gate 81 arranged at the branch portion of the transport path.

  The double-sided conveying device 10 is a conveying device that is attached to the side surface of the image forming apparatus 2 and reverses the recording material when forming images on both sides of the recording material. When reversing the recording material, the paper discharge roller 28 stops in a state where the recording material has been discharged halfway, and the reversing direction guides the recording material to the duplex conveying device 10 side. At this time, by switching the gate 85 provided after the fixing device 23, the recording material enters the duplex conveying device 10 without returning to the fixing device 23 side. The recording material that has passed through the double-sided conveyance device 10 enters the paper conveyance path 64 again from before the electrophotographic process unit 20 and passes through the electrophotographic process unit 20 and the like, whereby an image is formed on the back surface.

  The image forming system 1 has a structure in which the image forming apparatus 2 and the post-processing apparatus 5 are mounted side by side on the recording material supply apparatus 6. The width of the main body of the image forming apparatus 2 is L1, and the post-processing apparatus. The width L of the recording material supply device 6 is designed to be substantially equal to L1 + L2, where L2 is the width of the 5 main body.

  By configuring the system by combining peripheral devices as in the image forming system 1, an image forming system desired by the user can be easily realized. On the other hand, in such an image forming system 1, it is necessary to consider the adjustment of the temperature and humidity of the entire system. On the other hand, when a heater, a fan, or the like is provided for each peripheral device, the number of parts increases as a whole system, which causes problems such as an increase in cost of the image forming system 1. In view of this, the image forming system 1 is configured such that a heater (heating element) 300 is provided between the image forming apparatus 2 and the recording material supply apparatus 6.

  Next, the fixing device 23 will be described in detail with reference to FIGS.

  FIG. 2 is a cross-sectional view of the fixing device 23 according to the present embodiment, and FIG. 3 is a schematic view viewed from the axial direction of the fixing roller of the fixing device 23.

  The fixing device 23 includes a fixing roller 101 serving as a heating member, a pressure roller 106 serving as a pressure member, a heater lamp 105 serving as a heat source for the fixing roller, and a temperature sensor that constitutes a temperature detection unit that detects the temperature of the fixing roller 101. (Thermistors) 103a and 103b, thermostats 104a and 104b as abnormal temperature detection means, a cleaning device 110, and a control circuit (not shown) as temperature control means. The fixing roller 101 has a cylindrical shape, and bearings 102 are installed at both ends in the axial direction, and the fixing roller 101 is rotatably installed. Further, a gear (not shown) is connected to one end of the fixing roller 101 at an end in the axial direction, and a driving force from a separately installed motor is transmitted to the gear to rotationally drive the fixing roller. The pressure roller 106 is provided with a bearing (not shown) that enables the pressure roller 106 to rotate at the shaft end of the pressure roller 106, and the bearing presses the pressure roller 106 against the surface of the fixing roller 101. For this purpose, a spring 108 for supporting a load on the pressure holding unit 107 and for applying a load to the pressure holding unit 107 is provided.

  The heater lamp 105 is a halogen heater, and includes a main lamp 105a, a sub lamp 105b, and an assist lamp 105c. The heater lamp 105 is fixedly disposed inside the fixing roller 101. When the heater lamp 105 is energized from the control circuit, the heater lamp 105 emits light with a predetermined heat distribution, infrared rays are emitted, and the inner peripheral surface of the fixing roller 101 is heated. As shown in FIG. 3, the main lamp 105 a is a central heating heater in which the filament 105 af is provided at the center in the longitudinal direction of the fixing roller 101, and the rated output is 700 W. The sub lamp 105b is a heater for heating an end portion in which filaments 105bf are provided at both ends in the longitudinal direction of the fixing roller 101, and the rated output is 270W. The assist lamp 105c is a warm-up assist heater in which the filament 105cf is provided over the entire width in the longitudinal direction of the fixing roller 101. The assist lamp 105c is lit only during warm-up and has a rated output of 230W.

  The fixing roller 101 is heated to a predetermined temperature (here, 180 ° C.) by the main lamp 105a, the sub lamp 105b, and the assist lamp 105c, and a recording in which an unfixed toner image T that passes through the fixing nip portion N of the fixing device is formed. This is for heating the paper P. Here, the fixing nip portion refers to a pressure contact portion between the fixing roller and the pressure roller. The fixing roller 101 includes a cored bar 101a as a main body thereof, and a release layer 101b formed on the outer peripheral surface of the cored bar 101a in order to prevent the toner T on the recording paper P from being offset.

  For the core metal 101a, for example, a metal such as iron, stainless steel, aluminum, copper, or an alloy thereof is used. In addition, as the core metal 101a of the present embodiment, an iron (STKM) core metal having a diameter of 40 mm and a wall thickness of 0.45 mm is used in order to reduce the heat capacity.

  For the release layer 101b, fluororesins such as PFA (copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether) and PTFE (polytetrafluoroethylene), silicone rubber, fluororubber, and the like are suitable. The release layer 101b of this embodiment was formed by applying and baking a blend of PFA and PTFE to a thickness of 22.5 μm through a primer layer having a thickness of 7 μm.

  The pressure roller 106 is configured to have a heat-resistant elastic material layer 106b such as silicone rubber on the outer peripheral surface of a cored bar 106a made of steel, stainless steel, aluminum or the like. On the surface of the heat-resistant elastic material layer 106 b of the pressure roller 106, a release layer 106 c made of a fluororesin similar to the case of the fixing roller 101 may be formed. In this embodiment, the pressure roller 106 includes a heat-resistant elastic body layer 106b made of silicone sponge rubber having a diameter of 40 mm and a thickness of 8 mm on a stainless steel core 106a, and a PFA tube having a thickness of 50 μm on the surface thereof. A release layer 106c is provided, and is pressed against the fixing roller 101 with a force of 22 kgf (216 N) by a spring 108 as a pressure member, so that the width between the fixing roller 101 and the fixing roller 101 is about 7.5 mm. The fixing nip portion N is formed.

  As the PFA tube used for the release layer 106c, it is more preferable to use a conductive PFA tube containing a conductive agent such as carbon. The reason for this is that when an insulating PFA tube is used, the pressure roller is charged to approximately -5 kV due to frictional charging with the recording paper and the fixing roller, and as a result, at the fixing nip portion N, the same negative polarity is obtained. An electric field that repels the toner toward the fixing roller acts and causes electrostatic offset (a phenomenon in which the toner adheres to the fixing roller electrostatically) with respect to the fixing roller. Therefore, in this embodiment, by using a conductive PFA tube, charging of the pressure roller 106 is prevented, and the occurrence of electrostatic offset is suppressed. In order to obtain this antistatic effect, a PFA tube having a volume resistance of 105 Ωcm is used in this embodiment.

  Thermistors 103 a and 103 b as temperature detecting means are disposed on the peripheral surface of the fixing roller 101 so as to detect the surface temperature of the fixing roller 101. Based on the temperature data detected by each thermistor, a temperature control means (not shown) controls energization to the main lamp 105a, the sub lamp 105b, and the assist lamp 105c so that the fixing roller temperature becomes a predetermined temperature.

  Further, a cleaning web 113 wound up from the supply roller 111 side to the take-up roller 112 side is disposed above the fixing roller 101, and the take-up roller 112 is fed at a predetermined feed amount each time the recording material is fixed. Rolled up. The cleaning web 113 is pressed against the surface of the fixing roller 101 by being pressed by a pressing roller 114 made of a heat-resistant sponge roller having a diameter of 18 mm while being wound around the winding roller 112. The release agent is applied. In this embodiment, silicone oil is used as a release agent, and the cleaning web is impregnated with an amount of 6 g / m 2.

  Then, the recording paper P on which the unfixed toner image T is formed is conveyed to the fixing nip portion N at a predetermined fixing speed (255 mm / s in this embodiment) and a copying speed (56 sheets / minute in this embodiment). Fixing is performed by heat and pressure.

  Next, experiments and experimental results regarding the relationship between the fixing temperature ripple and the image quality from when the image forming apparatus according to the present embodiment is turned on or when the image forming apparatus restarts from the preheating temperature will be described. The temperature ripple in the present invention refers to the vertical width of the temperature of the fixing roller and the pressure roller.

<Toner>
First, the toner used in this experiment will be described. The toner according to the exemplary embodiment is a toner having a core particle including a binder resin, a colorant, and a release material, and a shell layer that covers the core particle. The toner has a shorter melting time than a toner having no conventional shell layer. It is. Since this toner has a shell layer formed on the surface of the core particles, for example, in order to shorten the melting time of the toner so as to correspond to the passing time of the nip portion, the core is instantaneously melted and stretched. While containing a component having a spreading characteristic (sharp melt characteristic), the shell agent is composed of a component that can prevent aggregation of toner particles even when stress due to stirring in the developing container is applied. By using such a core-shell capsule toner, it is possible to prevent changes in toner properties due to long-term use while maintaining sharp melt characteristics.

  As a method for producing the toner, for example, it is produced by attaching and fusing resin fine particles as a shell to the core particles. The core particles are produced by the same pulverization method as in conventional toners, and the coating of resin fine particles on the core particles is performed using a surface modification device.

  The method for producing the toner is not limited to the above-described method, and it is wet and the material is used as represented by the suspension polymerization method, the emulsion-aggregation method, and the dissolution suspension method. A method (chemical method) in which toner particles are prepared by wet or wet preparation using direct or submicron sized component fine particles may be used. Furthermore, the toner is not limited to the core-shell structured capsule toner as long as the toner has a melting time of 0.035 seconds or less. The shorter the melting time, the lower the temperature of the fixing roller required for fixing, which helps shorten the warm-up time of the fixing device.

  For toner A, core particles are prepared using a binder resin (styrene-acrylic resin in this embodiment) having a glass transition temperature of 45 ° C. and a softening temperature of 120 ° C., and a glass transition temperature of 60 is formed on the entire surface of the core particles. A capsule toner was obtained by coating resin fine particles (styrene-acrylic resin in this embodiment) having a softening temperature of 130 ° C. to form a shell layer.

  A toner B was obtained in the same manner as in the toner A, except that the glass transition temperature of the styrene-acrylic resin as the core binder resin was 50 ° C. and the softening temperature was 130 ° C.

  Further, a toner C having a structure without a conventional shell layer was also produced as a comparative example. The production method is only the step of producing the core particles of the toners A and B. Therefore, since the toner C needs to be composed of a component capable of preventing aggregation of the toner particles even when stress due to agitation in the developing container is applied during the core particle preparation process, A toner having the same glass transition temperature as that of the shell layers of the toners A and B of 60 ° C. and a softening temperature of 130 ° C. was prepared for the acrylic resin, and the other compositions were the same as those of the toners A and B.

  Next, a method for measuring the melting time of the toner used in this embodiment will be described with reference to FIG. As shown in FIG. 4, the melting time of the toner T is measured using a hot plate H, a high-speed camera V, and a spoid P filled with the toner T. The hot plate H is heated to an arbitrary temperature, and a small amount of toner T is dropped on the heated surface of the hot plate H using the drop P. By observing the melted state after the toner T has dropped on the heating surface of the hot plate H with the high-speed camera V, the melting time of the toner T can be measured.

  The high-speed camera V can shoot every 1 msec (0.001 second). From the moment when the toner T falls on the heating surface of the hot plate H, the toner T becomes elliptical on the hot plate H and spreads. The time until the start was defined as the melting time of the toner T. As a comparative example, the melting time of a conventional toner C that does not have a core-shell structure was also measured this time.

The temperature of the hot plate H was set to 230 ° C. The reason will be described below. As described above, the fixing control temperature (fixing roller surface temperature) of the fixing device of the present embodiment is 180 ° C., and the surface temperature of the pressure roller (≈average paper temperature) receives heat from the fixing roller. Stable at about 70 ° C. In other words, the toner passing through the fixing nip N receives an average temperature of 125 ° C. (= (180 + 70) / 2) from above and below. On the other hand, since the toner dropped on the hot plate is heated only from the lower side, the ambient temperature is 20 ° C. in order to obtain the same average temperature as that of the fixing nip portion. The temperature was set to 230 ° C. and the melting time of the toner was measured.
125 × 2−20 = 230 Formula (1)
Table 1 shows the measurement results of the characteristics and melting time of each toner.

As shown in Table 1, the toner A could be melted in 0.015 seconds. Similarly, toner B could be melted in 0.035 seconds. On the other hand, the toner C used in the comparative example was found to be 0.055 seconds.

<Heater lamp position>
Next, the heater lamp position will be described with reference to FIG.

  In FIG. 5A, the assist lamp 105c is arranged in the vicinity of the fixing nip portion N. In FIG. 2B, the main lamp 105a is arranged in the vicinity of the fixing nip N. FIG. 5C shows an arrangement in which the main lamp 105a is shifted from the arrangement of FIG. 5B by an angle of 5 degrees (θ = 5 °) upstream in the fixing roller rotation direction (paper input side).

<Experiment method>
As an experimental method, the fixing roller 101 is warmed up from a normal temperature state to a fixing temperature (180 ° C.), and after the warm-up is completed, immediately after copying 8 sheets of a solid black image, gloss unevenness occurs. I confirmed.

The gloss unevenness was evaluated by visual sensory evaluation based on the following criteria.
X: Gloss unevenness can be clearly confirmed visually, and there is a problem in image quality Δ: Gloss unevenness can be confirmed visually, and image quality is case-by-case ○: Gloss unevenness can be slightly confirmed visually No problem in image quality A: Uneven gloss cannot be confirmed at all <Experimental results>
The results of experiments conducted by the above method will be described with reference to FIGS. FIG. 6 is a diagram illustrating temperature changes of the fixing roller and the pressure roller. Table 2 shows the toner used in Examples 1 to 7 and Comparative Examples 1 to 3, the main lamp position, the time s (seconds) from the start of warm-up to the half rotation, and s (seconds) for the entire time required for warm-up. ), The temperature ripple of the fixing roller and the pressure roller, and the determination results of these gloss unevenness.

Here, Comparative Example 1 in Table 2 is an experiment using toner A at the main lamp position shown in FIG. 5A without performing half rotation control of the fixing roller 101 during warm-up. is there. FIG. 6A shows the temperature change at this time. From Table 2 and FIG. 6A, under the conditions of Comparative Example 1, the temperature ripple of the fixing roller 101 immediately after the completion of warm-up is 30 deg and the temperature ripple of the pressure roller 106 is as large as 55 deg. As a result, clear gloss unevenness due to this temperature ripple occurred.

  The same experiment as described above was performed using toner B and toner C in Comparative Example 2 and Comparative Example 3 in Table 2. From this, it was found that the gloss unevenness is worsened in the toner B having a melting time of 0.035 seconds and the toner A having a melting time of 0.015 seconds compared to the toner C having a long melting time of 0.055 seconds. The reason for this is that toner A and toner B are sharp melt toners that are fixed at a low temperature and have a short melting time. Therefore, the melting sensitivity is high with respect to the fixing temperature, and even if there is a slight temperature variation, image quality unevenness (glossy) This is because it appears as variation.

  From the above examination results, the toner A to be used was further experimented with the toner A that is most likely to have uneven gloss. Examples 1 to 5 in Table 2 show the experimental results when the toner A is used and the half-rotation control of the fixing roller 101 is performed once at the main lamp position in FIG. Show. From the comparison between Comparative Example 1 and Examples 1 to 5, the temperature ripple of the fixing roller and the pressure roller is reduced by inserting the half rotation control once during the warm-up, and as a result, the gloss unevenness is also improved. I understand. The reason for this is that, even if the main lamp as a heat source is offset as shown in FIG. 5A, the heat energy transmitted from the main lamp to the fixing roller is caused by rotating the fixing roller halfway during warm-up. This is because the temperature unevenness in the circumferential direction of the fixing roller is improved by averaging in the circumferential direction, and as a result, the gloss unevenness in the sheet conveying direction due to the temperature unevenness in the circumferential direction is improved. Further, since the fixing roller is rotated only once, it is possible to reduce the amount of heat transfer to the pressure roller and the loss of energy.

  In addition, from the comparison of Examples 1 to 5, when the half-rotation control is performed, when the time required for warm-up is 1, the range of 0.5 to 0.8 (Examples 2 to 4) is the temperature. It can be seen that the ripple becomes smaller and gloss unevenness is improved. In other words, a preferable time S from the start of warming up of the fixing roller 101 to the half rotation of the fixing roller 101 is expressed by the following formula (2), where the warmup time is Sw.

Sw × 0.5 <S <Sw × 0.8 Formula (2)
The reason for this is that the amount of heat released from the fixing roller 101 increases as the temperature of the fixing roller 101 increases. Therefore, the higher the temperature of the fixing roller 101 in the second half of the warm-up, the higher the total amount than the lower side. This is because the amount of heat radiation increases and the temperature in the circumferential direction of the fixing roller does not become uniform when viewed strictly. For this reason, the temperature ripple can be made smaller by performing half rotation in the latter half portion than in the middle point (0.5) of warm-up.

  Next, the experimental results of Example 6 will be described with reference to FIGS. In Example 6, as shown in FIG. 5B, the result when the main lamp 105 a (700 W) having the largest output among the three heater lamps is arranged in the vicinity of the fixing nip portion N is shown. It is. The half-rotation control is performed at a timing of 10 seconds (0.671) after the start of warm-up.

  From the comparison with Example 3, it can be seen that by disposing the main lamp 105a in the vicinity of the fixing nip portion N, the temperature ripples of the fixing roller 101 and the pressure roller 106 are further reduced, and gloss unevenness is improved. The reason for this is that the temperature of the fixing roller area closest to the main lamp 105a with the highest output is the highest in temperature, but the area where the temperature rises most is located near the fixing nip portion N. Thus, since the heat of the fixing roller 101 is taken away by the pressure roller 106, temperature unevenness in the circumferential direction of the fixing roller is improved as a result. FIG. 6B is a graph showing the temperature data at this time. From Table 2 and FIG. 6B, under the conditions of Example 6, the temperature ripple of the fixing roller immediately after completion of warm-up is as small as 10 deg and the temperature ripple of the pressure roller is as small as 30 deg. Did not occur.

  Next, the experimental result of Example 7 is demonstrated using FIG. In the seventh embodiment, as shown in FIG. 5C, the main lamp 105a further has an angle of 5 degrees (θ = 5 °) on the upstream side (paper input side) in the fixing roller rotation direction from the lamp arrangement of FIG. ) Only shifted. The half-rotation control is performed at a timing of 10 seconds (0.671) after the start of warm-up.

  Comparison with Example 6 shows that the temperature ripples of the fixing roller and the pressure roller are further reduced by disposing the main lamp 105a slightly upstream of the fixing nip (paper entering side). The reason will be described below. In general, the fixing unit has a larger opening area and a larger amount of heat radiation on the paper input side than on the paper discharge side. Therefore, placing the main lamp with the largest output near the fixing nip and upstream (paper input side) improves the heat balance in the circumferential direction of the fixing roller 101 and further improves temperature unevenness in the circumferential direction of the fixing roller. This is because it can be done.

  In the present embodiment, the heater lamp 105 has been described with a plurality of examples. However, the same can be said for a case where the heater lamp is singular and is provided apart from the center of the fixing roller. . That is, the heater lamp is desirably disposed in the vicinity of the fixing nip portion N, and more desirably disposed in the vicinity of the fixing nip portion and on the upstream side (paper input side).

  As described above, according to the present invention, even when a thin heating roller (fixing roller) or a low-temperature fixing toner with a short melting time is used, there is no unevenness in image quality or fixing property, and the fixing device has a short warm-up time. And an image forming apparatus can be realized.

  In the above embodiment, an example of a monochrome multifunction peripheral has been described. However, it goes without saying that the present invention is not limited to a monochrome multifunction peripheral and can also be applied to a color multifunction peripheral.

  The fixing device and the image forming apparatus according to the present invention can be suitably used for an image forming apparatus such as a copying machine, a printer, a facsimile, or a composite machine using an electrophotographic system.

DESCRIPTION OF SYMBOLS 1 Image forming system 2 Image forming apparatus 3 Scanner 4 Automatic document conveying apparatus 5 Post-processing apparatus 6 Recording material supply apparatus 8 Relay conveying unit 10 Double-sided conveying apparatus 23 Fixing apparatus 101 Fixing roller 101a, 106a Core metal 101b, 106c Release layer 103a , 103b Thermistor 104a, 104b Thermostat 105 Heater lamp 105a Main lamp 105b Sub lamp 105c Assist lamp 106 Pressure roller 107 Pressure holding part 108 Spring 111 Supply roller 112 Winding roller

Claims (7)

A fixing roller having a heat source built in a rotatable cylindrical portion;
A fixing device including a pressure roller that is in pressure contact with the fixing roller,
The heat source is provided apart from the center of the fixing roller;
A fixing device characterized in that the fixing roller is rotated halfway only once during the warm-up of the fixing roller. The time S from the start of warming up of the fixing roller to the half rotation of the fixing roller is as follows:
Sw × 0.5 <S <Sw × 0.8
The fixing device according to claim 1, wherein: When the heat source is single, the heat source is disposed in the vicinity of the fixing nip,
3. The fixing device according to claim 1, wherein when there are a plurality of heat sources, the heat source having the largest output is disposed in the vicinity of the fixing nip portion. When the heat source is singular, the heat source is disposed in the vicinity of the fixing nip and upstream of the fixing roller rotation direction,
4. The fixing device according to claim 3, wherein when there are a plurality of heat sources, the heat source having the largest output is disposed in the vicinity of the fixing nip and upstream with respect to the rotation direction of the fixing roller.   An image forming apparatus comprising the fixing device according to claim 1.   The image forming apparatus according to claim 5, further comprising a toner. The image forming apparatus according to claim 6, wherein the toner has a melting time of 0.035 seconds or less.