JP2006317505A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus having a fixing device that forms a high quality image without causing gloss differences despite successive passage of transfer materials. <P>SOLUTION: The image forming apparatus has the fixing device that thermally fixes an unfixed toner image by passing a transfer material with the unfixed toner image thereon through a fixing nip between a thermal fixing rotation body and a pressure rotation body disposed in pressure contact with the thermal fixing rotation body. In the image forming apparatus, the quantity Q (watt) of heat supply of a partial heating means disposed near the circumference of the thermal fixing rotation body is set to Q=K×W×M×V and 70≤K≤220, wherein K is a coefficient, W is the heating width (m) of the heat fixing rotation body, M is the basis weight (g/m<SP>2</SP>) of the transfer material, and V is the speed (m/sec) at which the transfer material is conveyed. <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.

  In the conventional heat roller fixing type fixing device, when heating the toner on the transfer material, it is necessary to heat with a fixing roller having a large heat capacity, which is disadvantageous in terms of power saving. 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 lowered by the fixing belt, and a heat-controlled heater is brought into direct contact with the fixing belt, thereby greatly improving the heat conduction efficiency and requiring little power saving and warm-up time. A belt fixing type fixing device and an image forming apparatus designed for quick start have been proposed and 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 rotate, and the transfer is transferred from the fixing nip portion of the fixing belt. An area where the temperature greatly decreases due to contact with the transfer material on the downstream side in the material conveyance direction (referred to as a transfer material contact position) and the transfer material on the upstream side in the transfer material conveyance direction from the fixing nip portion of the fixing belt when passing through the fixing nip portion. A fixing temperature difference occurs in an area where the temperature drop is small due to contact (referred to as a transfer material non-contact position).

  As a result, when this temperature difference occurs, the fixing belt rotates, and when a portion with this temperature difference comes into contact with the next transfer material, the temperature difference causes a band-like shape on the transfer material. Image gloss unevenness (hereinafter also referred to as gloss level difference) may occur. That is, since the temperature of the transfer material contact position is lower than the temperature of the transfer material non-contact position, the gloss becomes low. 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 the change in the fixing temperature between the first and second rotations of the fixing roller, thereby reducing 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 carries an unfixed toner image in a fixing nip portion 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 a fixing device that heats and fixes a transfer material by passing through, a heat supply amount Q (watt) of a local heating unit disposed in the vicinity of the outer periphery of the heating and fixing rotator is set as follows. It is what.

Q = K × W × M × V, 70 ≦ K ≦ 220
Here, K is a coefficient, W is a heating width (m) of the heating and fixing rotator, M is a basis weight (g / m ² ) of the transfer material, and V is a conveyance speed (m / sec) of the transfer material.

  According to a second aspect of the present invention, there is provided the image forming apparatus according to the first aspect, wherein the local heating unit includes a contact-type local heating unit having a local heating roller that can come in contact with and separate from an outer periphery of the heating and fixing rotator. Corresponding to the contact portion, the contact-type local heating means is pressed against and separated from the outer periphery of the heat-fixing rotator by a driving means.

  According to a third aspect of the present invention, there is provided the image forming apparatus according to the first aspect, wherein the local heating unit includes a non-contact type local heating unit having a local heating source disposed in the vicinity of the outer periphery of the heating and fixing rotator. The local heating source is turned on / off in correspondence with the contact portion.

  An image forming apparatus according to a fourth aspect of the present invention is the image forming apparatus according to the first aspect, wherein the heat fixing rotator is an endless fixing belt.

  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 a local heating means disposed near the outer periphery of the heating and fixing rotator to increase the temperature of the temperature drop region. I can do things.

  Here, when the amount of heat supplied from the local heating means is insufficient, the temperature at the transfer material contact position cannot be raised sufficiently, and the gloss level difference cannot be eliminated. In addition, when the amount of heat supplied by the local heating means is excessive, the temperature at the transfer material contact position rises excessively, and the gloss at the transfer material contact position becomes conversely high, resulting in a new gloss level difference. In order to solve this problem, it is necessary to supply an appropriate amount of heat to the transfer material non-contact position.

  That is, the temperature difference between the transfer material contact position and the transfer material non-contact position is reduced by supplying heat to the transfer material contact position under the conditions of Q = K × W × M × V and 70 ≦ K ≦ 220. As a result, the gloss level difference can be eliminated, 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 when a four-color toner image is heated and fixed so as to reduce a gloss level difference to form a photographic quality image or the like.

  According to the image forming apparatus of the present invention as set forth in claim 2, when the local heating means is a contact type local heating means capable of coming into contact with and separating from the outer periphery of the heating and fixing rotator, the contact type local heating means maintained at a predetermined temperature is provided. By contacting the transfer material contact part of the heat fixing rotator and separating from the transfer material non-contact position, only the transfer material contact part is heated so that the transfer material contact position and the transfer material do not contact each other. Since the temperature difference from the portion can be reduced, no gloss level difference occurs and a high-quality image can be formed.

  According to the image forming apparatus of the present invention as set forth in claim 3, when the local heating means is a non-contact type local heating means such as a halogen lamp or an electromagnetic induction coil, the contact portion of the transfer material of the heating and fixing rotator is contacted. The heating drive is turned on and the heating drive is turned off for the non-contact part of the transfer material, so that only the contact part of the transfer material is heated, and the temperature difference between the contact part of the transfer material and the non-contact part. Can be made small, so that 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 claim 4, the heat-fixing rotator is wound endlessly around the outer peripheral surface of the heating roller and the outer peripheral surface of the fixing roller so as to be in pressure contact with the pressure rotator. The fixing belt is particularly effective for a color image forming apparatus that requires a high-quality and high-gloss image. 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 passes through the paper feeding rollers 23, 24, 25 and the transfer material. The color image is transferred onto the transfer material P by being conveyed to the secondary transfer means 7A via the detection means 13, the registration roller (second paper feed unit) 26, the conveyance roller 27, and the like. The transfer material P onto which the color image has been transferred is sandwiched by the fixing device 30, and the toner image on the transfer material P is fixed by applying heat and pressure, and is fixed onto the transfer material P. It is sandwiched between paper rollers 28 and placed on a paper discharge tray 29 outside the apparatus.

  On the other hand, after the color image is transferred to the transfer material P by the secondary transfer means 7A, the residual toner is removed by the cleaning means 8 from the intermediate transfer body 6 from which the transfer material P is separated by curvature.

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

  The transfer material passage detection means 13 detects that the tip of the transfer material P has reached the vicinity of the registration roller 26. The control unit 12 detects the arrival of the leading end of the transfer material P by the transfer material passage detection unit 13, and then starts the transfer of the transfer material P in synchronization with the image formation timing.

  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. And a soft roller comprising a coating layer 32c having a thickness of 2.5 μm provided outside the silicone rubber layer 32b.

  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. It is configured as a roller member.

  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 heating roller 33 is detected by the non-contact temperature sensor TS1, and is maintained at a predetermined temperature by a control means (not shown).

  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 coating 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 coating 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, a contact type local heating unit or a non-contact type local heating unit is disposed, and the fixing belt 31 that rotates at a predetermined timing is heated by a control unit that will be described later.

[Contact type local heating means]
FIG. 3 is a cross-sectional view of the fixing device 30 provided with the contact-type local heating means 40.

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

  The local heating roller 41 incorporates a local heating source 43 inside the metal pipe 42, faces the heating roller 33 through the fixing belt 31, and is disposed 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 local heating source 43 is constituted by a halogen heater or the like, and is fixedly supported in the metal pipe 42.

  The contact-type local heating means 40 includes a local heating roller 41 including a metal pipe 42 and a local 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 local heating roller 41. The swinging local heating roller 41 presses the heating roller 33 via the fixing belt 31. At this time, the solenoid 46 is turned off. The local 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 local heating source 43 heats the fixing belt 31.

  When the local 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 in the figure, so that the swing plate 44 is centered on the support shaft 44A via the link 45. The local heating roller 41 is swung in the direction of the white arrow shown in the figure.

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

[Non-contact type local heating means]
FIG. 4 is a cross-sectional view of the fixing device 30 provided with the non-contact type local heating means 50.

  The non-contact type local heating means 50 includes a local heating source 51 fixedly disposed in the vicinity of the outer periphery of the heating roller 33 and a reflection plate 52. The local 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 local heating source 51 and heats the local part of the fixing belt 31 around which the heating roller 33 is wound. The local heating source 51 is turned on and off by the control means 12 described later.

  FIG. 5 is a cross-sectional view of the fixing device 30 including the electromagnetic induction heating unit 60 which is another embodiment of the non-contact type local heating unit 50.

  The fixing belt 31 includes a release layer, an elastic layer, a heat generation layer, and a support layer. The heating roller 33 is composed of a magnetic heat generating layer, an elastic heat insulating layer, and a heat conductive substrate.

  The electromagnetic induction heating means 60 includes a guide plate 61, an excitation heating coil 62, a magnetic core 63, a support member 64, and the like. The excitation heating coil 62 is connected to a drive power supply 65 and an AC power supply 66 whose oscillation circuit has a variable frequency, and is supplied with a high-frequency alternating current, thereby generating an alternating magnetic field around the excitation heating coil 62.

  This alternating magnetic field acts on the heat generating layer of the heating roller 33 and the heat generating layer of the fixing belt 31, and an eddy current flows in these directions in a direction that prevents the magnetic field from being changed by the alternating magnetic field. Due to this eddy current and the electrical resistance of these heat generating layers, Joule heat is generated, and the heating roller 33 and the fixing belt 31 generate heat by electromagnetic induction heating.

[Fixing set temperature switching control]
FIG. 6 is a block diagram of a control unit that controls the local heating unit 70 of the fixing device 30.

  In the operation display unit 11, the size (A4 size, A3 size, etc.) of the transfer material P is set by the transfer material size setting means, the number of prints of the transfer material P is set by the transfer material number setting means, and the transfer material paper type is set. The paper type of the transfer material P (plain paper, coated paper, special paper, thick paper, thin paper, etc.) is set by the means.

  The transfer material passage detection means 13 disposed in the vicinity of the registration roller 26 detects the passage of the transfer material P conveyed from the transfer material feed / conveyance means 20. The transfer of the transfer material P is stopped by the detection signal of the transfer material passage detection means 13. The front end portion of the transfer material P comes into contact with the registration roller 26 and waits, and then the conveyance by the registration roller 26 is resumed in synchronization with the image formation timing.

  From the detection result of the transfer material P by the transfer material passage detection means 13, the control means 12 calculates and specifies the time when the transfer material P passes through the fixing nip N, and makes contact type local heating means 40 or non-contact type local heating. The means 50 is activated to control the outer periphery of the fixing belt 31 to be heated.

  The contact position between the fixing belt 31 and the transfer material P can be specified from the distance from the transfer material passage detection means 13 to the fixing nip N, the transfer material conveyance speed, the rotation speed of the fixing belt 31, and the like.

  Hereinafter, the contact type local heating unit 40 or the non-contact type local heating unit 50 and the electromagnetic induction heating unit 60 will be collectively referred to as the local heating unit 70.

  The control unit 12 controls the driving of the local heating unit 70 in accordance with the timing at which the transfer material P reaches the fixing nip N, the size of the transfer material P, the number of transfer materials P, and the paper type of the transfer material P. That is, the driving of the contact type local heating means 40 shown in FIG. 3, the non-contact type local heating means 50 shown in FIG. 4, and the non-contact type local heating means 60 shown in FIG. 5 is controlled.

  FIG. 7 and FIG. 8 are explanatory views showing the conveyance state of the three transfer materials P1, P2, and P3 in the fixing device of the present invention.

  FIG. 9 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 at a position upstream and near the fixing nip N of the fixing belt (hereinafter referred to as the X position).

  The fixing device of the present invention will be described with reference to FIG. 7 and FIG. 8 illustrating the transfer material conveyance state and the timing chart showing the temperature course of the fixing belt 31 in FIG.

  An example of the fixing belt 31, the transfer material P, and the transfer material conveyance interval G is shown below.

  The fixing belt 31 has an outer peripheral diameter of 80 mm, an outer peripheral length L1 = 251.3 mm, a thickness of 70 μm, the transfer material P is A4 size, the length L2 in the transport direction is 210 mm, and the interval between the plain paper or coated paper and the transfer material P When G is about 80 mm, the distance G (G = L1-L2) between the two transfer materials P1 and P2 when continuously feeding is 41.3 mm or more, and the transfer material P is other than A4 size. In the case of different papers, the interval G between the transfer materials 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 operation display unit 11, and the interval between the transfer materials P. A case where G is changed will be described.

  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. After a predetermined time has elapsed since the transfer material P detection signal generation (time t0 in FIG. 9) of the transfer material P by the transfer material passage detection means 13 disposed in the vicinity of the registration roller 26, the front edge of the first transfer material P1 is detected. It reaches the fixing nip N.

  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. 7A and 7B). 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. 9 is T1.

  When the tip of the temperature-decreasing portion of the fixing belt 31 exits the fixing nip N and reaches the position facing the local heating means 70, the local heating means 70 is turned on.

  When the rear end portion of the temperature-decreasing portion passes the position facing the local heating means 70, the local heating means 70 is turned off. By heating the portion whose temperature has decreased due to contact with the transfer material P1 by the local heating means 70, the temperature is recovered from the broken line to the solid line in FIG. 9 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 local heating means 70 is set by calculating from the passing timing of the transfer material P1, the distance from the fixing nip N to the local heating means 70, 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. 7 (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. 9 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 tip of the temperature-decreasing portion of the fixing belt 31 exits the fixing nip portion N and reaches the position facing the local heating means 70, the local heating means 70 is turned on.

  When the rear end portion of the temperature-decreasing portion reaches the position facing the local heating means 70, the local heating means 70 is turned off.

  By heating the portion whose temperature has been lowered by the contact with the transfer material P2 with the local heating means 70, the temperature of T3 and T4 is recovered from the broken line to the solid line in FIG. 9, 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. 8 (h) to (k)).

  In the fixing device having the above-described local heating means of the present invention, the temperature of the fixing belt 31 changes from the highest set temperature T0 to the lowest temperature T3. That is, in the fixing device of the present invention having the local heating means 70 as compared with the temperature of the conventional fixing device, the upper limit temperature and the lower limit temperature are compressed and concentrated in the vicinity of the set temperature T0 as shown by the outlined arrows in the figure. 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.

[Image formation conditions]
Image forming apparatus: full color, A4 size paper, 51 sheets per minute output, tandem full color copier (Konica Minolta 8050 (registered trademark) remodeling machine, see Fig. 1)
Fixing device: fixing belt type fixing device, with local heating means, see FIGS. 1 to 4 Transfer material: plain paper PA 80 g / m ² , coated paper PB 80 g / m ² , coated paper PC 128 g / m ²
[Developer]
Two-component developer Average particle size of carrier: 20-60 μm, Average particle size of polymerized toner: 3-7 μm
Softening point of polymerized toner TA: 100 ° C. Softening point of polymerized toner TB: 120 ° C.
[Examination of gloss difference]
The energy given to the transfer material P by the fixing device 30 is determined by the temperature rise amount of the transfer material P and the heat capacity of the transfer material P. The amount of temperature rise of the transfer material P is determined by the fixing state of the toner. The heat capacity of the transfer material P is determined by the specific heat of the transfer material P and the paper type (basis weight).

The heat supply amount Q (watt) of either the contact-type local heating means 40 or the non-contact-type local heating means 50, 60 disposed near the outer periphery of the fixing belt 31 is the maximum heating width W (m) of the fixing belt 31. It is related to the basis weight M (g / m ² ) of the transfer material P and the conveyance speed V (m / sec) of the transfer material P passing through the fixing device 30.

  Therefore, the heat supply amount Q (watt) of the contact type local heating means 40 or the non-contact type local heating means 50, 60 is set as follows.

Q = K × W × M × V
Here, W and V are values determined by the image forming apparatus A, and M is determined by the paper type of the transfer material P. The coefficient K is determined in a range that does not cause a gloss level difference.

  Table 1 shows the examination results of experiments on the gloss level difference and the coefficient K using two types of polymerization toners TA and TB and three types of transfer materials PA, PB, and PC.

Polymerized toner: toner TA having a softening point of 100 ° C., toner TB having a softening point of 120 ° C.
Heating width of the fixing belt 31: 0.34 (m)
The transfer material P: basis weight 80 g / m ² plain paper PA, coated paper PB having a basis weight of 80 g / m ^2, a basis weight 128 g / m ² of coated paper PC
Transfer speed P of transfer material P: 0.1, 0.2, 0.3 m / sec
Original image: Solid image Gloss level judgment: Visual judgment, in the table, ○ indicates no gloss level difference, × indicates gloss level difference Judgment result: Good coefficient level without gloss level difference (◯) within a range of K ≦ 70 ≦ K ≦ 220 Results were obtained. When the coefficient K was in the range of 60 or less and the coefficient K was in the range of 230 or more, there was a gloss level difference (x).

  As described above, in the fixing device 30 provided with the local heating means, the gloss level difference with respect to the various transfer materials P is selected by selecting the heat supply amount Q with the coefficient K in the range of 70 ≦ K ≦ 220. An image that does not occur is obtained.

  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 local heating means. FIG. 3 is a cross-sectional view of a fixing device including a non-contact type local heating unit. Sectional drawing of the fixing apparatus provided with the electromagnetic induction heating means which is other embodiment of a non-contact-type local heating means. The block diagram of the control means which controls the local heating means of a fixing device. FIG. 4 is an explanatory diagram illustrating a transfer material conveyance state in the fixing device of the present invention. FIG. 4 is an explanatory diagram illustrating a transfer material conveyance state 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 passage | pass 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)
DESCRIPTION OF SYMBOLS 40 Contact-type local heating means 41 Local heating roller 42 Metal pipe 43 Local heating source 44 Oscillating plate 45 Link 46 Solenoid 46A Plunger 48 Rotating shaft 50 Non-contact type local heating means 51 Local heating source 52 Reflector plate 60 Electromagnetic induction heating means ( Non-contact type local heating means)
70 Local heating means A Image forming apparatus P, P1, P2, P3 Transfer material

Claims (4)

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 that rotates in pressure contact with the heat fixing rotator. In an image forming apparatus having
An image forming apparatus characterized in that a heat supply amount Q (watt) of a local heating unit disposed in the vicinity of the outer periphery of the heat fixing rotator is set as follows.
Q = K × W × M × V, 70 ≦ K ≦ 220
Here, K is a coefficient, W is a heating width (m) of the heating and fixing rotator, M is a basis weight (g / m ² ) of the transfer material, and V is a conveyance speed (m / sec) of the transfer material. The local heating means is constituted by a contact type local heating means having a local heating roller that can be brought into contact with and separated from the outer periphery of the heating and fixing rotating body, and the contact type local heating means by a driving means corresponding to a contact portion of the 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 local heating means is constituted by a non-contact type local heating means having a local heating source arranged in the vicinity of the outer periphery of the heating and fixing rotator, and turns on and off the local heating source corresponding to the contact portion of the transfer material. The image forming apparatus according to claim 1. The image forming apparatus according to claim 1, wherein the heat fixing rotator is an endless fixing belt.

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