JP2006308644A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus equipped with a fixing device which heats and fixes a toner image formed on a transfer material by a heating roller and a pressurizing roller, especially a fixing device using an endless fixing belt and which forms an image of high picture quality without bringing about a difference in luster level even when the transfer material is continuously passed through the fixing device. <P>SOLUTION: The image forming apparatus has the fixing device which heats and fixes an unfixed toner image by passing a transfer material carrying the unfixed toner image at a fixation nip portion formed by a rotating heating fixing rotary body and a pressurizing rotary body rotating while being in press contact with the heating fixing rotary body. The image forming apparatus has: an external heating means which is arranged nearby the outer periphery of the heating fixing rotary body; and a control means which controls the external heating means, and the control means performs control so that the external heating means is actuated after the front end portion of the transfer material passes through the fixation nip portion and then the outer periphery of the heat fixing rotary body is heated. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fixing device for fixing an image by pressing and heating an unfixed toner image formed on a transfer material by a fixing belt or a fixing roller and a pressurizing unit, and particularly, forms a glossy image. The present invention relates to an image forming apparatus having a fixing device suitable for fixing coated paper.

  Conventionally, a fixing device used in an electrophotographic image forming apparatus such as a copying machine, a printer, a facsimile machine, and a multifunction machine having these functions has a fixing roller maintained at a predetermined temperature and an elastic layer. A heat roller fixing system that presses and heats a transfer material on which an unfixed toner image is formed is sandwiched and conveyed by a fixing nip formed by a pressure roller that is in pressure contact with the fixing roller. Widely used from monochrome machines to color machines.

  The conventional heat roller fixing type fixing device is disadvantageous in terms of power saving because it is necessary to heat the fixing roller having a large heat capacity when heating the toner on the transfer material. There is a problem that it takes time to warm up, and the time until the printing starts (warming up time) becomes long.

  In recent years, a fixing belt has been used in the fixing device, the heat capacity has been reduced by the fixing belt, and a heat-controlled heater is brought into direct pressure contact with the fixing belt to greatly improve heat conduction efficiency, requiring almost no power consumption and warm-up time. A belt-fixing type fixing device and an image forming apparatus designed for quick start are proposed and have been used recently.

  When producing a color print at a high speed, there are the following problems when a toner image layer of a plurality of colors formed on a transfer material is heated and fixed by a fixing device in an image forming unit.

  In the fixing belt type fixing device, when the transfer material is continuously passed, the fixing belt is deprived of heat by the transfer material when it passes through the fixing nip portion, and the temperature is lowered to contact with the transfer material of the fixing belt. Thus, a fixing temperature difference occurs between a region where the temperature is lowered (referred to as a transfer material contact position) and a region where the temperature of the fixing belt is not in contact with the transfer material and is not lowered (referred to as a transfer material non-contact position).

  As a result, when the rear end portion of the transfer material is continuously passed through the fixing nip portion in a state where this temperature difference occurs, a band-like image gloss unevenness (hereinafter also referred to as a gloss step) is formed on the transfer material. ) May occur. That is, since the temperature of the previous transfer material contact position is lower than the temperature of the transfer material non-contact position, the gloss is lowered. In the fixing roller type fixing device, a gloss level may be generated by the same mechanism.

In the fixing device described in Patent Document 1, in order to compensate for the amount of heat deprived by the transfer material, the amount of heat deprived by the transfer material is obtained by using an auxiliary heater at the timing when the fixing roller has completed the first rotation. This is applied directly to the surface of the fixing roller to suppress a change in fixing temperature between the first and second rounds of the fixing roller, thereby preventing the occurrence of a gloss level difference.
JP-A-9-190112

  In the fixing device of Patent Document 1, since both the transfer material contact position and the non-transfer material contact position are heated by the auxiliary heater, the occurrence of the temperature difference between the transfer material contact position and the non-transfer material contact position is not eliminated. It is impossible to prevent the occurrence of a gloss level difference due to a temperature difference.

  The present invention relates to a fixing device that heats and fixes a toner image formed on a transfer material by a heat fixing rotator and a pressure rotator, and more particularly, in a fixing device using an endless fixing belt. Accordingly, an object of the present invention is to provide an image forming apparatus including a fixing device that forms a high-quality image without causing a gloss difference even if it is passed through.

  The above object can be achieved by the following solutions.

  The image forming apparatus according to claim 1, wherein an unfixed toner image is carried on a fixing nip portion formed by a rotating heat fixing rotator and a pressure rotator rotating in pressure contact with the heat fixing rotator. An image forming apparatus having a fixing device that heats and fixes a material by passing therethrough, comprising: an external heating unit disposed in the vicinity of an outer periphery of the heating and fixing rotator; and a control unit that controls the external heating unit. Is characterized in that after the leading end portion of the transfer material passes through the fixing nip portion, the external heating means is activated to control to heat the outer periphery of the heating and fixing rotator.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect of the invention, the control unit detects the arrival of the transfer material at the leading end in the transfer material conveyance path for carrying the transfer material into the fixing nip portion. From the detection result of the detection means, and calculating and specifying the passage of the transfer material through the fixing nip, and starting the external heating means corresponding to the contact position with the transfer material, Control is performed to heat the outer periphery of the fixing rotator.

  According to a third aspect of the present invention, there is provided the image forming apparatus according to the first aspect, wherein the external heating unit includes a contact-type external heating unit that conducts heat by being pressed against an outer periphery of the heating and fixing rotator, and the control unit includes: Corresponding to the transfer material contact, the external heating means is pressed against and separated from the outer periphery of the heat fixing rotator by the driving means.

  According to a fourth aspect of the present invention, there is provided the image forming apparatus according to the first aspect, wherein the external heating unit includes a non-contact type external heating unit that turns on and off an external heating source disposed in the vicinity of the outer periphery of the heating and fixing rotator. The control means turns on and off the external heating source corresponding to the transfer material contact position.

  An image forming apparatus according to a fifth aspect of the present invention is the image forming apparatus according to the first aspect, wherein the heat-fixing rotator includes a heating source therein, an outer peripheral surface of a heating roller that heats the heat-fixing rotator, and the heating roller The fixing belt is an endless fixing belt that is wound around the outer peripheral surface of a fixing roller that is arranged in parallel with the rotation shaft and that rotates and rotates, and is in pressure contact with the pressure rotating body.

  An image forming apparatus according to a sixth aspect of the present invention is the image forming apparatus according to any one of the first to fifth aspects, wherein the fixing device includes a heating roller and a fixing roller that include a heating source, and outer peripheral surfaces of the heating roller and the fixing roller. A fixing belt that winds the fixing belt, an external heating unit that heats the outer peripheral surface of the fixing belt, a pressure rotator that is pressed against the fixing roller via the fixing belt, and a control unit that controls the external heating unit. It is characterized by.

  The image forming apparatus of the present invention can obtain the following effects by the configuration described above.

  According to the image forming apparatus of the first aspect of the present invention, when the transfer material passes through the fixing nip portion, a temperature difference is generated on the heating and fixing rotating body between the transfer material contact position and the transfer material non-contact position of the transfer material. However, the temperature difference is reduced by heating the transfer material contact position of the heating and fixing rotator by using an external heating unit disposed near the outer periphery of the heating and fixing rotator, thereby increasing the temperature of the temperature-lowering region. Therefore, there is no difference in gloss and a high quality image can be formed.

  In particular, in a fixing device of a color image forming apparatus that requires a high-quality image, it is effective for giving gloss to a color image when a four-color toner image is heated and fixed to form a photograph or the like.

  According to the image forming apparatus of the present invention described in claim 2, it is important to specify the contact position of the transfer material in order to achieve the above object. In order to achieve this, the transfer material contact position of the heating and fixing rotator is calculated and specified from the detection result by the detection means for detecting the transfer material transport timing on the transfer material transport path, and the transfer material contact position is determined. This is achieved by heating with an external heating means.

  According to the image forming apparatus of the present invention described in claim 3, when the external heating means is a contact type external heating means that can come into contact with and separate from the outer periphery of the heat fixing rotator, the contact type external heating means maintained at a predetermined temperature is provided. By contacting the transfer material contact position of the heat fixing rotator and separating from the transfer material non-contact position, only the transfer material contact position is heated and the transfer material contact position and the transfer material non-contact position are Since the temperature difference can be reduced, there is no gloss level difference and a high quality image can be formed.

  According to the image forming apparatus of the present invention described in claim 4, when the external heating unit is a non-contact type external heating unit such as a halogen lamp, the heating driving is performed with respect to the transfer material contact position of the heating and fixing rotator. By turning on and turning off the heating drive for the transfer material non-contact position, only the transfer material contact position is heated, and the temperature difference between the transfer material contact position and the transfer material non-contact position can be reduced. Therefore, a glossy step does not occur and a high-quality image can be formed.

  According to the image forming apparatus of the present invention described in claims 5 and 6, the heat-fixing rotator is wound around the outer peripheral surface of the heating roller and the outer peripheral surface of the fixing roller and is rotated to be in pressure contact with the pressure rotator. In the case of an endless fixing belt, the transfer material contact area is longer than that of the fixing roller, and the temperature drop is large. Therefore, the control means for controlling the external heating means of the present invention is effective. A fixing belt type fixing device provided with this control means is particularly effective for a color image forming apparatus that requires high-quality and high-gloss images. As a result, an image forming apparatus including a fixing device excellent in power saving by improving thermal efficiency, shortening of warm-up time, high-speed fixing, and high-quality fixing is provided.

  Embodiments of the present invention will be described below. The description in this column does not limit the technical scope of the claims or the meaning of terms.

[Image forming apparatus]
FIG. 1 is a configuration diagram of an image forming apparatus according to the present invention.

  The image forming apparatus A is called a tandem color image forming apparatus, and includes a plurality of sets of image forming units 10Y, 10M, 10C, and 10K, a transfer material feeding / conveying unit 20, and a fixing device 30.

  Above the image forming apparatus A, an image reading device SC is installed. The document placed on the document table is scanned and exposed by the optical system of the document image scanning exposure device of the image reading device SC and read by the line image sensor. The analog signal photoelectrically converted by the line image sensor is subjected to analog processing, A / D conversion, shading correction, image compression processing and the like in the image processing unit, and then input to the optical writing means 3Y, 3M, 3C, 3K. Is done.

  An image forming unit 10Y that forms a yellow (Y) image includes a charging unit 2Y, an optical writing unit 3Y, a developing device 4Y, and a cleaning unit 5Y disposed around the image carrier 1Y. An image forming unit 10M that forms a magenta (M) color image includes an image carrier 1M, a charging unit 2M, an optical writing unit 3M, a developing device 4M, and a cleaning unit 5M. An image forming unit 10C for forming a cyan (C) color image includes an image carrier 1C, a charging unit 2C, an optical writing unit 3C, a developing device 4C, and a cleaning unit 5C. An image forming unit 10K that forms a black (K) image includes an image carrier 1K, a charging unit 2K, an optical writing unit 3K, a developing device 4K, and a cleaning unit 5K.

  The charging unit 2Y and the optical writing unit 3Y, the charging unit 2M and the optical writing unit 3M, the charging unit 2C and the optical writing unit 3C, and the charging unit 2K and the optical writing unit 3K constitute a latent image forming unit.

  4Y, 4M, 4C, and 4K are developing devices that contain a two-component developer composed of a small particle size toner of yellow (Y), magenta (M), cyan (C), and black (K) and a carrier.

  The intermediate transfer body 6 is wound around a plurality of rollers and is rotatably supported.

  Each color image formed by the image forming units 10Y, 10M, 10C, and 10K is sequentially transferred onto the rotating intermediate transfer body 6 by the primary transfer units 7Y, 7M, 7C, and 7K, and a combined color image is formed. It is formed.

  The transfer material P accommodated in the paper feeding cassette 21 of the transfer material paper feeding / conveying means 20 is fed by a paper feeding means (first paper feeding unit) 22, and is fed with paper feeding rollers 23, 24, 25, registration rollers ( The transfer material P, which is conveyed to the secondary transfer means 7A through the second paper feed unit) 26, the conveyance roller 27, etc., and the color image is transferred onto the transfer material P, is transferred to the fixing device. At 30, the transfer material P is sandwiched, and the toner image on the transfer material P is fixed by applying heat and pressure, and is fixed on the transfer material P, and is sandwiched between the discharge rollers 28 and discharged outside the machine. 29.

  On the other hand, after the color image is transferred to the transfer material P by the secondary transfer unit 9, the residual toner is removed by the cleaning unit 8 from the intermediate transfer body 6 from which the transfer material P is separated by curvature.

  In the description of the image forming apparatus A, the color image formation has been described. However, the present invention includes a case of forming a monochrome image.

[Fixing device]
FIG. 2 is a cross-sectional view of the fixing device 30 according to the present invention.

  The fixing device 30 according to the present invention includes a fixing roller 32 disposed inside a heat fixing member (hereinafter referred to as a fixing belt) 31, a heat fixing rotating body (hereinafter referred to as a heating roller) 33, a heating source 34, a fixing device. It is composed of a pressure rotator (hereinafter referred to as a pressure roller) 35 disposed outside the belt 31.

  The fixing belt 31 is composed of an endless belt member, and is wound around the outer periphery of the fixing roller 32 and the heating roller 33.

  The fixing roller 32 faces the pressure roller 35 and supports the fixing belt 31 on one of the inner peripheral surfaces of the fixing belt 31. The heating roller 33 incorporates a heating source 34 and supports the fixing belt 31 on the other inner peripheral surface of the fixing belt 31.

  The pressure roller 35 has a built-in heating source 36 and presses the fixing roller 32 with the fixing belt 31 and the transfer material P carrying the toner image interposed therebetween.

As the heating sources 34 and 36, a radiation heating source such as a halogen lamp, a carbon heater, or a xenon lamp can be applied. However, if an appropriate roller core is selected, heating by electromagnetic induction or the like is also possible. Moreover, it is also possible to incorporate a plurality of heaters in each roller as required.

  A fixing nip N is formed between the fixing roller 32 and the pressure roller 35 with the fixing belt 31 heated by the heating roller 33 interposed therebetween.

  The fixing device 30 fixes the single color toner image or the multicolor toner image on the transfer material P through the fixing nip portion N by heating and pressing. In addition, a guide member (not shown) for stretching the fixing belt 31 is provided inside the fixing belt 31.

  The fixing belt 31 uses a heat-resistant resin belt such as polyimide as a base, and the outer (outer peripheral surface) of the base is covered with a 200 μm-thick silicone rubber as a rubber layer, and a silicone rubber as a release layer. A layer whose surface is coated with 30 μm thick PFA (perfluoroalkoxy) or a layer coated with a PFA tube is used.

  The fixing roller 32 includes a cylindrical metal pipe 32a having a thickness of 2 to 5 mm made of STKM (carbon steel pipe for mechanical structure) and the like, and a silicone rubber layer 32b having a thickness of 4.5 mm provided on the outer peripheral surface of the metal pipe 32a. The coating layer 32c having a thickness of 50 μm provided outside the silicone rubber layer 32b is configured as a soft roller having an outer diameter of 20 to 50 mm.

  The heating roller 33 has a 2 mm thick metal pipe 33 a made of a heat conductive material such as an aluminum alloy material as a base, and a coating layer 33 b made of PFA having a thickness of 10 to 30 μm on the outer peripheral surface of the metal pipe 33 a. The roller member has an outer diameter of 30 to 60 mm.

  Inside the heating roller 33, a heating source 34 is provided as a heating element for heating the heating roller 33. The surface temperature of the fixing belt 31 is detected by the non-contact temperature sensor TS1, and the heating roller 33 is heated by control means (not shown), and is maintained at a predetermined temperature by heat conduction from the heating roller 33.

  The pressure roller 35 is configured as a soft roller having an outer diameter of 50 mm, which includes a metal pipe 35a, a silicone rubber layer 35b, and a release layer 35c. The metal pipe 35a has a cylindrical shape with a thickness of 2 to 5 mm made of a heat conductive material such as a steel material such as STKM or an aluminum alloy material. The silicone rubber layer 35b is a silicone rubber layer having a thickness of about 3 to 8 mm provided on the outer peripheral surface of the metal pipe 35a. The release layer 35c is a PFA tube having a thickness of 20 to 50 μm provided outside the silicone rubber layer 35b.

  Further, a heating source 36 as a heating element for heating the pressure roller 35 is provided inside the pressure roller 35. The surface temperature of the pressure roller 35 is detected by the non-contact temperature sensor TS2, and is maintained at a predetermined temperature by a control means (not shown).

  The fixing roller 32 is rotationally driven by a driving unit (not shown), and the fixing belt 31 is driven to rotate. Alternatively, the pressure roller 35 may be rotationally driven by a driving unit, the fixing belt 31 may be conveyed by the pressure roller 35, and the fixing belt 31 may be driven to rotate. Further, driving may be input to both the fixing roller 32 and the pressure roller 35.

  The fixing nip portion N formed between the fixing roller 32 and the pressure roller 35 pressurizes and heats the single color toner image or the multicolor toner image on the transfer material P entering the fixing region, and then on the transfer material P. To settle.

  In the vicinity of the outer periphery of the heating roller 33, contact-type external heating means or non-contact-type external heating means is arranged, and the fixing belt 31 that rotates at a predetermined timing is heated by a control means described later.

[Contact external heating means]
FIG. 3 is a cross-sectional view of the fixing device 30 including the contact-type external heating unit 40.

  The external heating roller 41 of the contact-type external heating unit 40 is disposed to face the outer peripheral surface of the heating roller 33 with the fixing belt 31 interposed therebetween.

  The external heating roller 41 incorporates an external heating source 43 inside the metal pipe 42, faces the heating roller 33 through the fixing belt 31, and is arranged so as to be able to contact and separate from the fixing belt 31. The metal pipe 42 is formed of a heat conductive material and is rotatably supported. The external heating source 43 is constituted by a halogen heater or the like, and is fixedly supported in the metal pipe 42.

  The contact type external heating means 40 includes an external heating roller 41 including a metal pipe 42 and an external heating source 43, a link 45, a solenoid 46, a cleaning roller 47, and the like.

  A rotating shaft 48 that supports both ends of the metal pipe 42 is rotatably supported by the swing plate 44. The lower end portion of the swing plate 44 is supported so as to be swingable about the support shaft 44A. The upper end of the swing plate 44 is rotatably supported at one end of the link 45. The other end of the link 45 is connected to the plunger 46A of the solenoid 46.

  The swing plate 44 is urged by a spring 49 and swings while supporting the external heating roller 41. The swinging external heating roller 41 presses the heating roller 33 through the fixing belt 31. At this time, the solenoid 46 is turned off. The external heating roller 41 is driven to rotate while being pressed against the rotating fixing belt 31, and the metal pipe 42 heated by the built-in external heating source 43 heats the fixing belt 31.

  When the external heating roller 41 is separated from the fixing belt 31, an ON signal is given to the solenoid 46, and the plunger 46A is pulled in the direction of the arrow shown in the figure, so that the swing plate 44 is centered on the support shaft 44A via the link 45. Thus, the external heating roller 41 is swung in the direction of the outlined arrow.

  The solenoid 46 is turned on and off by the control means 12 described later.

  At the end of the swing, the outer peripheral surface of the external heating roller 41 and the fixing belt 31 are separated by a distance d. After the end of the swinging, the external heating roller 41 comes into contact with the cleaning roller 47. The cleaning roller 47 is rotated by a driving unit (not shown) to remove paper dust, scattered toner, and the like attached to the external heating roller 41.

[Non-contact external heating means]
FIG. 4 is a cross-sectional view of the fixing device 30 including the non-contact type external heating unit 50.

  The non-contact type external heating means 50 includes an external heating source 51 fixedly disposed in the vicinity of the outer periphery of the heating roller 33 and a reflection plate 52. The external heating source 51 is constituted by a halogen heater or the like. The reflection plate 52 reflects and focuses the heat rays emitted from the external heating source 51 and heats the local portion of the fixing belt 31 around which the heating roller 33 is wound. The external heating source 51 is turned on and off by the control means 12 described later.

[Fixing set temperature switching control]
FIG. 5 is a block diagram of control means for controlling the external heating means of the fixing device 30.

  The operation display unit 11 installed in the upper part of the main body of the image forming apparatus A in FIG. 1 has a transfer material selection setting unit, and sets various transfer materials P such as plain paper and coated paper. Further, the thickness of the transfer material P, the size of the transfer material P, and the like are set.

  The control means 12 is connected to a transfer material conveyance path for carrying the transfer material P into the fixing nip N, and a transfer material detection means 13 for detecting the conveyance timing of the transfer material P is connected to the transfer material P by the transfer material detection means 13. From the detection result, the time when the transfer material P passes through the fixing nip N is calculated and specified, and the contact type external heating unit 40 or the non-contact type external heating unit 50 is activated to heat the outer periphery of the fixing belt 31. Control to do. The transfer material detection unit 13 is disposed in the vicinity of the registration roller 26, and detects the arrival of the transfer material P fed by the paper supply unit 22 (see FIG. 1).

  From the transfer material conveyance timing detection result by the transfer material detection means 13, the distance from the transfer material detection means 13 to the fixing nip N, the transfer material conveyance speed, the rotation speed of the fixing belt 31, and the like, the fixing belt 31 and the transfer material P It is possible to specify the contact position.

  FIGS. 6 and 7 are explanatory views showing the conveyance process of the transfer materials P1, P2, and P3 in the fixing device of the present invention. Hereinafter, the contact-type external heating means 40 or the non-contact-type external heating means 50 will be collectively referred to as the external heating means 60.

  FIG. 8 is a timing chart showing the temperature course of the fixing belt 31. The horizontal axis represents the elapsed time, and the vertical axis represents the temperature in the vicinity of the entrance (position X) of the fixing nip N of the fixing belt.

Fixing belt 31: inner diameter 80 mm, inner peripheral length L1 = 251.3 mm, thickness 70 μm
Transfer material P: A4 size, conveyance direction length L2 = 210 mm, plain paper or coated paper L3 of transfer material P: about 80 mm
The distance L3 (L3 = L1−L2) between the two transfer materials P1 and P2 when continuously feeding requires 41.3 mm or more. When the transfer material P is a different paper other than the A4 size, the interval of the transfer material P is changed corresponding to the transfer material size. Specifically, the control unit 12 controls the rotation start timing of the registration roller 26 shown in FIG. 1 according to the size of the transfer material P input by the user on the scanning display unit 11, and the interval of the transfer material P is set. Change.

  Hereinafter, the fixing device of the present invention will be described with reference to FIGS. 6 and 7 illustrating the transfer material conveyance process and the timing chart illustrating the temperature of the fixing belt 31 illustrated in FIG.

  In the operation display unit 11, the size and number of transfer materials P are set. The length of the conveyance path from the registration roller 26 to the fixing nip N and the conveyance speed of the transfer material P are determined by the model of the image forming apparatus. The leading end of the first transfer material P1 reaches the fixing nip N after a predetermined time has elapsed since the detection signal is generated by the transfer material detection means 13 disposed in the vicinity of the registration roller 26.

  When the transfer material P1 passes through the fixing nip portion N (time t1, t2), the fixing belt 31 is deprived of heat by contact with the transfer material P1, so that the portion of the fixing belt 31 that has been in contact with the transfer material P1 The temperature decreases (see FIGS. 6A and 6B). The timing at which the temperature drop due to the transfer material P1 is detected at the position X is a region where the temperature of the fixing belt 31 shown in FIG. 8 is T1.

  When the leading end of the temperature-decreasing portion of the fixing belt 31 exits the fixing nip N and reaches the position facing the external heating means 60, the external heating means 60 is turned on.

  When the rear end portion of the temperature-decreasing portion passes the position facing the external heating means 60, the external heating means 60 is turned off. By heating the portion whose temperature has been lowered by the contact with the transfer material P1 by the external heating means 60, the temperature is recovered from the broken line 8 to the solid line up to the temperature T1, and the temperature difference from the portion where the transfer material P1 is not in contact ( T0-T1) can be reduced. The on / off timing of the external heating unit 60 is set by calculating from the passing timing of the transfer material P1, the distance from the fixing nip N to the external heating unit 60, and the rotation speed of the fixing belt 31. Do.

  When the transfer material P2 passes through the fixing nip portion N (time t4 to t6), the temperature of the fixing belt 31 is the temperature T0 at the front end portion of the transfer material P2, and the temperature T1 at the rear end portion. The gloss of the toner image varies depending on the temperature of the fixing belt 31, but since this temperature difference (T0-T1) is small, there is no gloss level difference that can be visually judged, and a substantially uniform gloss toner image is obtained (FIG. 6 (d) to (f)).

  As the transfer material P2 passes through the fixing nip portion N, the fixing belt 31 is deprived of heat by contact with the transfer material P2 as in the case of the transfer material P1, and thus contacts the transfer material P2 of the fixing belt 31. The temperature of the part that had been reduced falls. The timing at which the temperature drop due to the transfer material P2 is detected at the position X is the region where the temperature of the fixing belt 31 in FIG. 8 is T3 and T4. The region where the temperature is T2 is a portion where the influence of the transfer material P1 remains.

  When the leading end of the temperature-decreasing portion of the fixing belt 31 exits the fixing nip N and reaches the position facing the external heating means 60, the external heating means 60 is turned on.

  When the rear end portion of the temperature-decreasing portion reaches the position facing the external heating means 60, the external heating means 60 is turned off.

  By heating the portion whose temperature has decreased due to the contact with the transfer material P2 with the external heating means 60, the temperature of T3 and T4 is recovered from the broken line to the solid line in FIG. 8, and the transfer material P2 is not in contact with the transfer material P2. The temperature differences (T0 to T3) and (T0 to T4) can be reduced.

  The temperature of the fixing belt 31 when the transfer material P3 passes through the fixing nip portion N (time t8 to t11) is the temperature T3 at the front end portion of the transfer material P3 and becomes a temperature T4 on the way, and the rear end portion of the transfer material P3. Becomes the temperature T0. The gloss of the toner image varies depending on the temperature of the fixing belt 31, but since the temperature differences (T0 to T3) and (T0 to T4) are small, there is no gloss level difference that can be visually judged, and the toner has a substantially uniform gloss. An image is obtained (see FIGS. 7 (h) to (k)).

  In the above-described fixing device having the external heating means of the present invention, the temperature of the fixing belt 31 changes from the highest set temperature T0 to the lowest temperature T4. That is, as compared with the temperature of the conventional fixing device, in the fixing device of the present invention having the external heating means 60, the upper limit temperature and the lower limit temperature are compressed and concentrated in the vicinity of the set temperature T0 as indicated by the outlined arrows. As a result, the temperature change of the fixing belt when the transfer material P passes through the fixing nip N is reduced, and the occurrence of a gloss level difference on the transfer material P is remarkably reduced.

  In the embodiment of the present invention, the belt fixing type fixing device has been described as an example, but the present invention is also effective in a roller fixing type fixing device.

1 is a configuration diagram of an image forming apparatus including a fixing device according to the present invention. 1 is a cross-sectional view of a fixing device according to the present invention. Sectional drawing of the fixing device which has a drive mechanism of a contact-type external heating means. FIG. 3 is a cross-sectional view of a fixing device including a non-contact type external heating unit. The block diagram of the control means which controls the external heating means of a fixing device. FIG. 6 is an explanatory diagram illustrating a transfer process of a transfer material in the fixing device of the present invention. FIG. 6 is an explanatory diagram illustrating a transfer process of a transfer material in the fixing device of the present invention. 6 is a timing chart showing the temperature course of the fixing belt.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Operation display part 12 Control means 13 Transfer material detection means 26 Registration roller (2nd paper feed part)
30 Fixing Device 31 Fixing Belt 32 Fixing Roller 33 Heating Fixing Rotator (Heating Roller)
34, 36 Heating source 35 Pressure rotating body (pressure roller)
40 Contact type external heating means 41 External heating roller 42 Metal pipe 43 External heating source 44 Oscillating plate 45 Link 46 Solenoid 46A Plunger 48 Rotating shaft 50 Non-contact type external heating means 51 External heating source 52 Reflecting plate 60 External heating means A Image Forming device P, P1, P2, P3 Transfer material

Claims (6)

A fixing device that heats and fixes a transfer material carrying an unfixed toner image through a fixing nip formed by a rotating heat fixing rotator and a pressure rotator rotating in pressure contact with the heat fixing rotator. In an image forming apparatus having
An external heating means disposed in the vicinity of the outer periphery of the heat fixing rotator;
Control means for controlling the external heating means,
The control means controls the external heating means to be activated after the leading end of the transfer material has passed through the fixing nip portion to heat the outer periphery of the heating and fixing rotator. apparatus. The control means arranges a detection means for detecting arrival of the transfer material at a transfer material conveyance path for carrying the transfer material into the fixing nip portion, and based on a detection result by the detection means, And calculating and specifying the passage through the fixing nip, and starting the external heating unit corresponding to the contact position with the transfer material to control the outer periphery of the heating and fixing rotator to be heated. The image forming apparatus according to claim 1. The external heating means has contact-type external heating means that conducts heat by being pressed against the outer periphery of the heating and fixing rotator, and the control means controls the external heating means by a driving means in response to contact with a transfer material. The image forming apparatus according to claim 1, wherein the image forming apparatus is pressed against and separated from an outer periphery of the heat fixing rotator. The external heating means has a non-contact type external heating means for driving on and off an external heating source disposed in the vicinity of the outer periphery of the heating and fixing rotator, and the control means corresponds to a transfer material contact position, The image forming apparatus according to claim 1, wherein the external heating source is turned on and off. The heat-fixing rotator has a heating source therein, an outer peripheral surface of a heating roller that heats the heat-fixing rotator, and an outer peripheral surface of a fixing roller that is arranged in parallel with the rotation axis of the heating roller and rotates. The image forming apparatus according to claim 1, wherein the image forming apparatus is an endless fixing belt that is wound and rotated to be in pressure contact with the pressure rotating body. The fixing device includes a heating roller and a fixing roller having a heating source therein, a fixing belt that winds each outer peripheral surface of the heating roller and the fixing roller, an external heating unit that heats the outer peripheral surface of the fixing belt, and the fixing roller 6. The image forming apparatus according to claim 1, further comprising: a pressure rotator that is in pressure contact with the fixing belt, and a control unit that controls the external heating unit.

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