JP4699782B2 - High frequency dielectric heating and fixing device and image forming apparatus - Google Patents

Description

  The present invention relates to a fixing device for an image forming apparatus such as a copying machine or a laser printer, and more particularly to a high frequency dielectric heating fixing device and an image forming apparatus for fixing a recording material holding a developer by a high frequency electric field.

  In general, a fixing device for an image forming apparatus such as a copying machine or a laser printer is formed by a fixing belt heated by a heating roller having a heater or a heating roller having a heater, and a pressure roller rotating in pressure contact with the fixing roller. There are known a heat fixing method in which toner as a developer is melted and fixed by a nip portion, and a pressure fixing method in which pressure is fixed only by pressure using capsule toner.

  However, each of the former methods uses a heater as a heat source, and there is a problem that the heater blinks repeatedly until power is turned on and the heater warms up and consumes power and cannot be used immediately after startup. On the other hand, since the latter does not use a heater, the former problem of power consumption and the like has been solved. However, for a recording material with a small width, an excessive pressure causes an end of the recording material to be translucent, for example. There is a problem in image quality such as deterioration in quality and high gloss, or a fixing failure due to insufficient pressure for a wide recording material.

  In view of this, a high-frequency dielectric heating and fixing apparatus has been proposed that eliminates the above-described method and realizes energy saving and adopts a high-frequency induction heating method to obtain a good image.

  For example, as shown in FIG. 14, a liquid having a large dielectric loss such as water is sprayed from a spraying device 31 onto a recording material P carrying a toner image, and parallel plate electrodes 33a and 33b connected to a high-frequency transmitter 32 are connected. There has been proposed a technique for fixing a toner image by causing a liquid to generate heat by passing a recording material P therebetween (see, for example, Patent Document 1).

  Further, as shown in FIG. 15, plate members 34 a and 34 b made of a material having a high dielectric loss are stuck inside the parallel plate electrodes 33 a and 33 b and connected to the high frequency transmitter 32. Then, a high frequency of several tens of megacycles or more is applied, and the recording material P carrying the toner image is conveyed in the high frequency electric field by the conveying roller 38 rotating in the direction of the arrow. As a result, there has been proposed a technique for fixing by causing moisture, toner t and the like contained in the recording material P to generate heat (see, for example, Patent Document 2). However, in these systems, since the electrodes are flat plates, power loss is large, and arcing between the electrodes is likely to occur, so that the system is likely to be down. Therefore, it has not yet been commercialized.

On the other hand, as shown in FIG. 16, high frequency is used for the purpose of drying the adhesive of furniture and building materials. That is, a plurality of positive electrodes 25 and negative electrodes 26 formed of conductive metal rods are arranged below the belt conveyors 35a and 35b that move in the direction of the arrow by the action of the driving roller 39 and the driven roller 37, and the belt conveyor 35a. , 35b, a device for applying a high frequency of several tens of MHz to the adhesive of the work 36 conveyed on the workpiece 36 and curing it in a short time has been put into practical use. That is, annular endless belts 24a and 24b, positive electrodes 25a and 25b, and negative electrodes 26a and 26b arranged symmetrically with respect to the workpiece 36 are provided, and between the positive electrodes 25a and 25b and the negative electrodes 26a and 26b. Apply high frequency. Then, when the work 36 is conveyed while being sandwiched between the two endless belts 24a and 24b disposed above and below, the adhesive is cured while the work 36 is conveyed. In addition, the workpiece | work 36 is the decorative sticking etc. of the door panel for a house, or a flooring (for example, refer patent document 3). In this technology, the work 36 is conveyed as close as possible to the electrode array, a substance having a high dielectric loss is mixed with the adhesive used in the work 36, and this adhesive is selectively heated to dry and cure. It is something to be made. However, if this technology is used as a fixing device for a copying machine, it cannot be put into practical use. Currently, no materials with high dielectric loss that can be mixed to maintain the performance of functional toners have been found, and since such substances are not mixed with the toner, the toner melts at the normal distance between the electrode and the recording material. The temperature does not rise to the fixing temperature. In addition, since this work is thick, the work 36 is sandwiched between two endless belts 24a and 24b and heated by positive electrodes 25a and 25b and negative electrodes 26a and 26b arranged symmetrically in the vertical direction. . In contrast, since the recording material P is generally thin, the temperature does not rise to a temperature at which the toner is melted and fixed unless the total applied voltage is theoretically increased.
Japanese Patent Publication No.43-27584 Japanese Patent Publication No.49-38171 Japanese Patent Laid-Open No. 8-96951

  Generally, since the toner of the developer is mainly composed of polyester or polyol, the toner itself is not selectively heated by the high frequency dielectric heating and fixing device, and the toner does not melt.

  Therefore, the present invention solves the problems of the conventional ones as described above, and raises the temperature of the recording material using a high-frequency electric field to increase the temperature of the toner mainly composed of polyester and polyol, which are currently mainstream. It is an object of the present invention to provide a high-frequency dielectric heating fixing device and an image forming apparatus that can fuse and fix toner and realize energy saving together with a good fixed image.

In order to solve the above-mentioned problems, the invention according to claim 1 is provided with a high-frequency dielectric heating fixing comprising a recording material conveying means and fixing a toner image carried on the recording material by a high-frequency electric field generated by a plurality of electrode groups. In the apparatus, the plurality of electrode groups are unified so that the electrode group on one side has a different polarity from the electrode group on the other side across the recording material placement surface of the transport unit, and the transport of the recording material The electrodes are arranged so that the polarities of the electrodes adjacent to each other in the direction are staggered, and the spacing between the electrodes of different polarities adjacent to each other in the direction orthogonal to the surface of the recording material is the entrance side and the discharge side of the recording material. It is characterized by being gradually wider than the middle part.

According to a second aspect of the present invention, there is provided a high frequency dielectric heating and fixing apparatus comprising a recording material conveying means and fixing a toner image carried on the recording material by a high frequency electric field generated by the plurality of electrode groups. The electrode group on one side across the mounting surface of the recording material of the transport means is unified with a different polarity from the electrode group on the other side, and the electrodes adjacent to each other along the transport direction of the recording material The electrodes are arranged so that the polarities are staggered, and the distance between adjacent electrodes of different polarities along the recording material conveyance direction is gradually wider than the intermediate portion on the recording material entry side and discharge side. It is characterized by.

The invention according to claim 3 is the invention according to claim 1 or 2 , wherein the plurality of electrode groups are placed on the recording material of the conveying means when entering the recording material in a direction crossing the conveying direction of the recording material. It approaches the surface, and when discharging the recording material, it can be contacted and separated so as to be separated from the recording material mounting surface of the conveying means.

According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, the recording material heated by the electrode group is added downstream of the plurality of electrode groups in the conveyance direction of the recording material. A pressing member for pressing is provided.

According to a fifth aspect of the present invention, there is provided an image forming apparatus equipped with the high-frequency dielectric heating and fixing device according to any one of the first to fourth aspects.

The present invention is as described above, and the plurality of electrode groups are unified so that the electrode group on one side is different in polarity from the electrode group on the other side across the recording material placing surface of the transporting means. and with which, along the conveying direction of the recording material are arranged so that polarities of adjacent electrodes is staggered, the distance between the electrodes of different polarities adjacent to each other in a direction to further perpendicular to the surface of the recording material, the recording Since the material gradually becomes wider than the intermediate portion on the material entry side and the material discharge side, a good fixed image can be obtained by high frequency heating, and energy can be saved because the heater is not used as a heat source.

  The best mode for carrying out the present invention will be described with reference to the embodiments shown in the accompanying drawings.

  FIG. 1 is a front view showing a schematic overall configuration of an image forming apparatus (full-color copying machine) including a high-frequency dielectric heating and fixing device as a first embodiment.

  The full-color copying machine 1 includes a sheet feeding unit 3 having box-shaped sheet feeding cassettes 2a to 2d loaded with recording materials P arranged in parallel in the vertical direction, and photoconductors 5Y, 5M, and 5C charged by an exposure device 4. An image forming unit 6 that forms an electrostatic latent image on 5K by optical writing and visualizes it with toner, and a high-frequency dielectric heating and fixing device that fixes the toner image visualized by the image forming unit 6 to the recording material P 7. A document conveying unit 8 that conveys a sheet-like document to the document reading unit, and a document reading unit 9 that reflects the light and reads the document.

  The image forming unit 6 includes an image forming unit 11 that forms a color toner image. The image forming unit 11 includes photoreceptors 5Y, 5M, 5C, and 5K corresponding to yellow, magenta, cyan, and black colors. The image forming unit 11 is different only in the color of the toner and the other parts are the same. Around the photoconductors 5Y, 5M, 5C, and 5K, a developing device 12, a laser irradiator 13, a mirror 14, and the like that visualize the electrostatic latent image formed on the photoconductor with toner as a developer are provided. An exposure device 4; a charging roller 15 that uniformly charges the surface of the photoconductor by generating corona discharge with the photoconductor; and a static eliminator (not shown) that applies a predetermined voltage to bring the surface of the photoconductor to an initial state. The cleaning device 16 removes the toner that cannot be transferred onto the recording material P and remains on the surface of the photosensitive member, and the intermediate transfer belt 17 is sandwiched between the photosensitive member and a toner image is formed on the intermediate transfer belt 17. A primary transfer roller 21 for transferring is disposed.

  The user places a document on the document transport unit 8 and presses a copy switch (not shown). Then, the original is conveyed to the original reading unit 9 and the recording material P is conveyed from the paper feed cassette 2 to the image forming unit 6. Then, the recording material P on which the image is formed by the image forming unit 6 is discharged to the discharge tray 10 through a process of transfer and fixing. When the copying is completed, the document is discharged to the document reading unit 9 by the document transport unit 8.

  FIG. 2 is a perspective view showing the appearance of the high-frequency dielectric heating and fixing device 7 according to the first embodiment, and FIG. 3 is a schematic side view of the high-frequency dielectric heating and fixing device 7 shown in FIG. The high-frequency dielectric heating and fixing device 7 includes a driving roller 22 and a driven roller 23 disposed at a predetermined distance from the driving roller, and an endless belt 24 is suspended between the driving roller 22 and the driven roller 23. Has been. The endless belt 24 is made of a material with little dielectric loss, such as polypropylene or Teflon (registered trademark). A positive electrode 25 in which a conductive metal rod is formed in a U-shape is disposed so as to straddle the width direction of the endless belt 24 so as to straddle the photosensitive member side and the upper side of the mounting surface 24c of the recording material P. The A negative electrode 26 in which a conductive metal bar is formed in a U-shape straddles the width direction of the endless belt 24 on the downstream side in the transport direction of the positive electrode 25 and below the placement surface 24 c of the endless belt 24. It is arranged as follows. Similarly, on the downstream side of the negative electrode 26 in the transport direction, a positive electrode 25 and a negative electrode 26 are sequentially arranged. Therefore, the recording material P on which the toner image is carried by the image forming unit 6 is placed on the placement surface 24 c of the recording material P of the endless belt 24. That is, in the plurality of electrode groups 25 and 26, the electrode on one side has the same polarity and the electrode on the other side has the same polarity as the electrode on one side across the recording material placement surface of the endless belt 24. They are polar and arranged so that the polarities are staggered in the conveyance direction of the recording material P.

  When the recording material P on which the image is formed by the image forming unit 6 is conveyed in the direction of the arrow and is detected by a sensor (not shown), the endless belt 24 which has been stopped until then starts to be driven. At the same time, a high frequency voltage of several tens of MHz is applied to the negative electrode 26 and the positive electrode 25 from a high frequency generation means (not shown). When a high-frequency voltage is applied, an electric field is generated between the adjacent positive electrode 25 and negative electrode 26 as shown by a broken line in the figure, as shown in FIG. Since the recording material P carrying toner passes through a high-frequency electric field generated between the negative electrode 26 and the positive electrode 25, the recording material P breaks through a portion connecting the strongest electric field strength, that is, the center of the heteropolar electrode. As a result, a strong electric field is applied to the recording material P carrying the toner image. As described above, since the toner has a low dielectric loss, it is not selectively heated. However, the paper that is the recording material P is heated because the dielectric loss is relatively high near this frequency, and the toner that forms the image is It is melted and fixed by the heat transmitted from the recording material P.

  Next, experiments conducted by the inventors will be described.

  According to the experiments by the present inventors, in FIG. 4, the distance between the positive electrode 25 and the negative electrode 26 in the direction intersecting the transport direction is 2 mm, and the distance between the adjacent negative electrode 26 and the positive electrode 25 in the transport direction is When 10 mm, the number of rod-shaped electrodes is 19, applied power is 2 kw, frequency is 40 MHz, and the recording material conveyance speed is 50 mm / s, either polyester toner or polyol toner carried on the recording material P is used. Even when it was used, it was melted by the heat transmitted from the recording material P and sufficient fixing strength was obtained. The applied voltage at the time of fixing is 2 kw, which is 30 to 40% higher than that of the conventional heat fixing method using a halogen heater, but it is not necessary to energize the high frequency dielectric heating fixing device during standby. In other words, unlike the conventional fixing device, it is not necessary to heat the heater immediately after the power is turned on, so that energy saving can be achieved.

  On the other hand, as shown in FIG. 5, the positive electrode 25 and the negative electrode 26 are juxtaposed only on one side with the recording surface P of the recording material P of the endless belt 24 in between, and are close to the positive electrode 25 and the negative electrode 26. The recording material P carrying the toner t was allowed to pass therethrough and an attempt was made to melt and fix it. In this case, the negative electrode 26 and the positive electrode 25 are disposed at an equal distance from the surface of the endless belt 24. This distance has a great influence on the electric field strength. According to the experiments by the present inventors, the recording material P carrying the toner did not rise to a temperature at which the toner was melted and fixed at about 2 mm considered to be necessary in practice. If the toner is mixed with a substance having a high dielectric loss, the result will be different. However, a material having a high dielectric loss that can be mixed while maintaining the performance of the functional toner has not been found.

  Further, as shown in FIG. 6, the positive electrode 25 and the negative electrode 26 are arranged to face each other across the mounting surface 24c of the recording material P of the endless belt 24, and a plurality of recording materials P carrying unfixed toner are provided. It was conveyed between the positive electrode 25 and the negative electrode 26. In this case, since the recording material P passes through the portion where the electric field strength is strong, the power loss is small. More specifically, as shown in FIG. 7, when a high frequency electric field is generated between the electrodes, the portion sandwiched between the positive electrode 25 and the negative electrode 26 of the recording material P is heated as shown in FIG. Therefore, assuming that the recording material P is stopped, the heated portion 27 has a number of striped patterns equal to the number of electrodes. That is, when the endless belt 24 conveys the heated portion 27 continuously, the entire recording material P is fixed.

FIG. 8 is a graph based on the simulation result of the ratio of the electric field strength in each method shown in FIG. 8 corresponds to (1) in FIG. 9, (2) in FIG. 8 corresponds to (2) in FIG. 9, and (3) in FIG. 8 corresponds to (3) in FIG. (1) in FIG. 9 shows that l ₁ = l ₂ = 2 mm when the distance l ₁ between adjacent electrodes in the transport direction and the distance l ₂ between adjacent electrodes in the direction intersecting with the distance l ₁ are shown in FIG. and (3), when the distance _{l 2} between the direction of the electrode crossing distances _{l 1} and that of between electrodes adjacent in the conveying _direction, l ₁ = 2 mm, an _{l 1/2 = l 2 =} 1mm. Referring to FIG. 8, when the distance between the electrode centers is assumed to be an arbitrary value, it can be seen that the electric field strength has a difference of about 30% between the maximum value of (1) and the highest value. In this case, a slight striped pattern tends to remain in the image after actual fixing. On the other hand, in FIG. 8 (2) of the present invention, the MAX value (assumed to be 100%) is about 11% lower than (1) (89%), but the intensity difference is small and only about 6%, so the fixed image. It is hard to show a striped pattern. Further, it can be seen that the configuration of (3) can obtain only an electric field strength of 50% or less as compared with the MAX value of (1). From the above, it can be seen that the configuration of the present invention shown in FIG.

  By the way, in all of the systems using the plurality of positive electrodes 25 and negative electrodes 26 shown in FIG. 9, the phenomenon that the electric field is applied more strongly than the predetermined value on the entry side and the discharge side of the recording material P occurs. . That is, as compared with a state in which all of the recording material P has entered the high-frequency dielectric heating and fixing device 7, the temperature of the recording material P immediately before entering or discharging immediately before the recording material P partially enters the high-frequency dielectric heating and fixing device 7. It goes up suddenly. This phenomenon is because electric power concentrates on the entering part, and is not a preferable phenomenon from the viewpoint of uniform fixing.

  10 to 12 are intended to solve this phenomenon.

In the second embodiment shown in FIG. 10, a plurality of electrode groups 25 and 26, the distance between the electrodes 25 and 26 adjacent to each other in a direction perpendicular to the surface of the recording material P, an intermediate in the entry side and the discharge side of the recording material It is gradually wider than the department. With this configuration, when the recording material P enters the high-frequency dielectric heating and fixing device 7, the applied voltage is low because the distance between the electrodes is wide, and a predetermined voltage is applied in the central portion. In addition, the entire surface of the recording material P is heated at a uniform temperature.

In the third embodiment shown in FIG. 11, the plurality of electrode groups 25, 26 are intermediate between the adjacent electrodes 25, 26 in the recording material P conveyance direction on the recording material P entry side and discharge side. The effect is the same as that in FIG. 10.

  In the fourth embodiment shown in FIG. 12, the plurality of electrode groups 25 and 26 are arranged on the endless belt 24 by an electrode group contacting / separating means (not shown) when the recording material P enters in the direction crossing the conveying direction of the recording material P. The recording material P approaches the placement surface, and when the recording material P is discharged, the recording material P can be moved away from the placement surface of the recording material P of the conveying means. FIG. 12A is a diagram illustrating a state in which the recording material P to be conveyed reaches the positive electrode 25 and the negative electrode 26. The electrodes 25 and 26 and the endless belt 24 are separated from each other by a predetermined distance. Yes. In this state, although the electric field concentration described above occurs, the recording material P is not heated more than necessary because the distance between the electrodes 25 and 26 is large. FIG. 12B is a diagram illustrating a state in which the entire recording material P has entered the electrodes 25 and 26. The electrodes 25 and 26 are close to a predetermined distance set in advance. In this state, a predetermined electric field is applied. In FIG. 12 (3), as in FIG. 12 (1), even if electric field concentration occurs, the electrodes 25 and 26 are separated from each other, so that overheating due to electric field concentration does not occur. In any of the configurations shown in FIGS. 10 to 13, it was confirmed that the recording material P was uniformly fixed.

  Further, the fifth embodiment shown in FIG. 13 is a pressure member that pressurizes the recording material heated by the electrode groups 25 and 26 on the downstream side in the transport direction of the recording material P with respect to the electrode groups 25 and 26. A metal roller 28 is provided. That is, a predetermined pressure f is applied to the transfer material P that has passed through the metal roller 28 in the direction of the arrow, and pressure is applied to the high-frequency dielectric heat-fixed toner image. As a result, the high-frequency dielectric heat-fixed toner t is turned into a film, and a glossy image can be obtained.

  The number of endless belts and electrodes, which are the components of the high-frequency dielectric heating and fixing device shown in each of the above embodiments, is merely a preferred example, and in the implementation, these components are described in the claims. It goes without saying that changes, corrections, etc. can be made as appropriate within the range, and the present invention can also be applied to, for example, a drying device of an ink jet printer.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front view showing a schematic overall configuration of an image forming apparatus including a high-frequency dielectric heating and fixing device according to the present invention. It is a perspective view which shows the external appearance of the high frequency dielectric heating fixing apparatus which concerns on this invention. It is a side view showing the outline of the high frequency dielectric heating fixing device concerning a 1st embodiment. It is a side view showing the outline of the high frequency dielectric heating fixing device concerning a 1st embodiment. It is a side view which shows the outline of the aspect of the experiment which inventors conducted. It is a side view which shows the outline of the aspect of the experiment which inventors conducted. It is a figure which shows the fixed image obtained by experiment which the inventors conducted. It is a graph based on the calculation result of the ratio of the electric field strength simulated using various methods. It is a side view which shows the outline of the high frequency dielectric heating fixing apparatus using various systems. It is a side view which shows the outline of the high frequency dielectric heating fixing apparatus which concerns on 2nd Embodiment. It is a side view which shows the outline of the high frequency dielectric heating fixing apparatus which concerns on 3rd Embodiment. It is a side view which shows the outline of the high frequency dielectric heating fixing apparatus which concerns on 4th Embodiment. It is a side view which shows the outline of the high frequency dielectric heating fixing apparatus which concerns on 5th Embodiment. It is a side view which shows the outline of the conventional high frequency dielectric heating fixing apparatus. It is a side view which shows the outline of the conventional high frequency dielectric heating fixing apparatus. It is a side view which shows the outline of the conventional high frequency dielectric heating fixing apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Full-color copier 2 Paper feed cassette 3 Paper feed part 4 Exposure apparatus 5 Photoconductor 6 Image formation part 7 High frequency induction heating fixing apparatus 8 Document conveyance part 9 Document reading part 10 Paper discharge tray 11 Image formation unit 12 Developing apparatus 13 Laser irradiation Device 14 Mirror 15 Charging roller 16 Cleaning device 17 Intermediate transfer belt 21 Primary transfer roller 22 Drive roller 23 Driven rollers 24a, 24b Endless belt (conveying means) 24c Mounting surface 25, 25a, 25b Positive electrode 26, 26a, 26b Negative Electrode 27 Heated portion 28 Metal roller P Recording material t Toner

Claims (5)

In a high frequency dielectric heating and fixing device comprising a recording material conveying means and fixing a toner image carried on the recording material by a high frequency electric field generated by a plurality of electrode groups,
Wherein the plurality of electrode groups, with one electrode group side across the mounting surface of the recording material of the conveying means is unified to a polarity different from that of the electrode groups on the other side, along the conveying direction of the recording material Are arranged so that the polarities of adjacent electrodes are staggered,
Further, the high frequency dielectric heating and fixing apparatus is characterized in that the gap between the electrodes of different polarities adjacent in the direction orthogonal to the surface of the recording material is gradually wider than the intermediate portion on the recording material entrance side and discharge side. In a high frequency dielectric heating and fixing device comprising a recording material conveying means and fixing a toner image carried on the recording material by a high frequency electric field generated by a plurality of electrode groups,
In the plurality of electrode groups, the electrode group on one side is unified with a polarity different from that of the electrode group on the other side across the recording material placement surface of the conveying means, and the recording material is conveyed in the conveying direction. Are arranged so that the polarities of adjacent electrodes are staggered,
Further , the high frequency dielectric heating and fixing apparatus is characterized in that the gap between adjacent electrodes of different polarities along the recording material conveyance direction is gradually wider than the intermediate portion on the recording material entrance side and discharge side.   In the direction intersecting with the recording material conveyance direction, the plurality of electrode groups approach the recording material placement surface of the conveyance means when the recording material enters, and the recording material placement surface of the conveyance means when the recording material is discharged. The high-frequency dielectric heating and fixing device according to claim 1, wherein the high-frequency dielectric heating and fixing device can be contacted and separated so as to be separated from the high-frequency dielectric.   The high-frequency dielectric heating fixing according to any one of claims 1 to 3, further comprising a pressing member that pressurizes the recording material heated by the electrode group downstream of the plurality of electrode groups in the recording material conveyance direction. apparatus.   An image forming apparatus comprising the high-frequency dielectric heating and fixing device according to claim 1.

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