JP2007017495A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus with a fixing device forming a high quality image without an occurrence of gloss level difference in a transfer material. <P>SOLUTION: The image forming apparatus is provided with the fixing device for heat-fixing by allowing a transfer material to pass through a fixing nip part formed from a heat fixing rotating body with a heat source and a pressurizing rotating body which is rotated in a pressurized contact with the heat fixing rotating body, in such direction that a surface carrying an unfixed toner image of the transfer material is in contact with the heat fixing rotating body. The image fixing device is provided with a pre-heating means heating the transfer material on the upstream side of the transfer material transporting direction of the heat fixing rotating body than the fixing nip part, a pressurizing rotating body temperature detection means detecting the surface temperature of the pressurizing rotating body and a control means controlling the pre-heating means. The control means controls heat supplying amount by the pre-heating means to be variable according to the surface temperature detected result of the pressurizing rotating body detected by the pressurizing rotating body temperature detection means. <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 rotate, and the transfer is transferred from the fixing nip portion of the fixing belt. A region where the temperature is lowered due to contact with the transfer material on the downstream side in the material conveyance direction (referred to as a transfer material contact portion), and a region where the temperature drop is small without contact with the transfer material when passing through the fixing nip (the transfer material non-contact portion) And a fixing temperature difference occurs.

  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 portion is lower than the temperature of the transfer material non-contact portion, the gloss becomes low. In the fixing roller type fixing device, a gloss level difference may occur due to a similar 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.

The image forming apparatus described in Patent Document 2 is provided with a preheating unit on the upstream side of the transfer unit in the transfer material conveyance direction, and the preheating unit is set with heating conditions corresponding to the type of transfer material. In other words, the transferred toner images are heated to a constant preliminary temperature with respect to various transfer materials having different materials and thicknesses.
JP-A-9-190112 JP-A-9-160408

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

  In the fixing device disclosed in Patent Document 2, the temperature of the transfer material is detected by a transfer material temperature detection unit disposed upstream of the fixing nip portion in the transfer material conveyance direction, and heated to a preliminary temperature corresponding to various transfer materials. Therefore, the occurrence of a temperature difference between the transfer material contact portion and the transfer material non-contact portion is not eliminated, and the occurrence of a gloss level difference due to the temperature difference cannot be prevented.

  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 a transfer material is not fixed to a fixing nip portion formed by a heat fixing rotator having a heating source 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 toner image carrying surface in a direction in contact with the heat-fixing rotator, the transfer material is upstream of the heat-fixing rotator in the transfer material conveyance direction. Preheating means for heating the transfer material on the side, pressure rotating body temperature detecting means for detecting the surface temperature of the pressure rotating body, and control means for controlling the preheating means, the control means Is characterized in that the amount of heat supply in the preliminary heating means is variably controlled according to the surface temperature detection result of the pressure rotating body detected by the pressure rotating body temperature detecting means.

  An image forming apparatus according to a second aspect is the image forming apparatus according to the first aspect, wherein the control unit is configured to detect a surface temperature detection result of the pressure rotator detected by the pressure rotator temperature detection unit and transfer material information. Accordingly, the heat supply amount in the preheating means is variably controlled.

  The image forming apparatus according to claim 3, wherein the heat fixing rotator includes a heating roller having a heating source therein, and a fixing roller that forms the fixing nip portion facing the pressure rotator. And an endless fixing belt.

  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 preliminary heating unit heats the back surface side of the unfixed toner image carrying surface of the transfer material.

  An image forming apparatus according to a fifth aspect is the image forming apparatus according to the first aspect, wherein the preliminary heating unit heats the unfixed toner image carrying surface of the transfer material in a non-contact manner.

  An image forming apparatus according to a sixth aspect is the image forming apparatus according to the second aspect, wherein the transfer material information is at least one of a basis weight, a type, and a size of the transfer material.

  An image forming apparatus according to a seventh aspect of the present invention is the image forming apparatus according to the first or second aspect, wherein the control unit variably controls a preheating temperature of the transfer material in accordance with a surface temperature of the pressure rotating body. To do.

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

  (1) According to the image forming apparatus of the present invention, when the transfer material passes through the fixing nip portion, the temperature of the transfer material contact portion and the transfer material non-contact portion of the transfer material is set on the heat fixing rotator and the pressure rotator. Although the difference occurs, the control means performs transfer by controlling the amount of heat supplied to the preheating means variably according to the surface temperature detection result of the pressure rotator detected by the pressure rotator temperature detection means. It is possible to reduce the temperature difference between the material contact portion and the transfer material non-contact portion, and as a result, it is possible to suppress the occurrence of a gloss level difference on the transfer material and form a high-quality image.

  (2) According to the image forming apparatus of the present invention, the amount of heat supplied to the preheating means according to the surface temperature detection result of the pressure rotating body detected by the pressure rotating body temperature detecting means and the transfer material information. By variably controlling the temperature, the temperature difference between the transfer material contact portion and the transfer material non-contact portion can be reduced, and as a result, the occurrence of a gloss level difference on the transfer material can be suppressed.

  (3) According to the image forming apparatus of the present invention, the heat fixing rotator is an endless fixing belt, which is effective for shortening the warm-up time and improving the fixing efficiency by increasing the fixing nip portion.

  (4) According to the image forming apparatus of the present invention, the preheating means contacts and heats the back surface of the unfixed toner image carrying surface of the transfer material, thereby efficiently transferring the transfer material by heat conduction from the preheating means. Can be preheated.

  (5) According to the image forming apparatus of the present invention, the preheating unit heats the unfixed toner image carrying surface side of the transfer material in a non-contact manner, so that the unfixed toner image side is radiated from the preheating unit. Preheating can be performed efficiently.

  (6) According to the image forming apparatus of the present invention, the heating and fixing rotation is performed by variably controlling the preheating temperature of the transfer material in accordance with the transfer material type information such as the basis weight, material, and size of the transfer material. The amount of heat taken by the transfer material by the transfer material is replenished and maintained at a constant temperature, so that the occurrence of a gloss level difference on the transfer material can be suppressed, and a high-quality image can be formed.

  (7) According to the image forming apparatus of the present invention, the preheating temperature of the transfer material is changed according to the surface temperature of the pressure rotator. For example, when the temperature of the pressure rotator is low, the transfer material is preheated. When the temperature is set relatively low and the temperature of the pressure rotator becomes high, the preheating temperature of the transfer material is also set relatively high. As a result, the amount of heat taken from the pressure rotator and the fixing belt of the transfer material becomes substantially equal, and the temperature of the transfer material contact portion on the pressure rotator and the transfer material non-contact portion corresponding between the transfer materials is almost equal. As a result, it is possible to suppress the gloss difference on the transfer material.

  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 sheet is conveyed to the secondary transfer unit 7A through the second sheet feeding unit 26, the conveyance roller 27, and the like, and the color image is transferred onto the transfer material P. 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 sectional view of the fixing device 30 and the preheating means 40 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 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 covering 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 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.

  A contact-type preheating unit 40 or a non-contact type preheating unit 50 is disposed upstream of the fixing nip N of the fixing device 30 in the transfer material conveyance direction, and is conveyed at a predetermined timing by a control unit described later. The transfer material P is preheated.

[Contact type preheating means 40]
The fixing device 30 shown in FIG. 2 includes contact-type preheating means 40.

  The preheating means 40 includes a planar heater 41 provided as a heating member, a temperature sensor TS3 installed in the heater 41, and an endless conveying belt 42 that is circulated around the heater 41 and conveyed. Has been. The conveying belt 42 is stretched between the driving roller 43 and the driven roller 44, and rotates counterclockwise in the drawing at a speed equal to the peripheral speed of the fixing belt 31 by the driving force of the driving roller 43.

  The rotating conveyor belt 42 is configured to place the transfer material P on which the unfixed toner image has been transferred by the secondary transfer unit 7 </ b> A and convey it toward the fixing nip N of the fixing device 30. Is preliminarily heated to a predetermined temperature by the amount of electric heat of the heater 41 that is in contact with the inner peripheral surface side.

For example, a conductive layer is provided on the inner peripheral surface of the transport belt 42 as a material having a small heat capacity and good heat resistance and thermal conductivity, and a Teflon (registered trademark) coat is provided on the outer peripheral surface. A polyimide film having a thickness of 30 μm to 200 μm adjusted to 10 ⁸ to ¹¹ Ω · cm by mixing a conductive filler is used. The conductive layer is grounded.

  Further, a corona charger 45 and a corona neutralizer 46 are installed at the entrance portion and the carry-out portion of the transfer material P, respectively, and the transfer material P separated from the secondary transfer means 7A is charged by the corona charger 45 and electrostatically. After passing through the heater 41 in close contact with the conveyor belt 42 and preheated, it is neutralized by the corona neutralizer 46, separated from the conveyor belt 42, and conveyed to the fixing nip N of the fixing device 30.

  The conveyor belt 42 of the preheating means 40 starts to rotate when the transfer of the toner image to the transfer material P is started or when the transfer of the transfer material P is detected.

  When the heater 41 is turned on, the conveyor belt 42 is heated to at least 100 ° C., preferably 100 ° C. to 160 ° C., at a peripheral surface portion that faces the heater 41 within a short time due to heat generated from the heater 41, and the peripheral surface temperature is the toner. Before reaching the softening point, control is performed to turn off the heater 41 by the detection signal of the temperature sensor TS3, and a constant peripheral surface temperature within the range of 100 ° C. or more and below the softening point is maintained.

  It is desirable that the electric power of the heater 41 or the set temperature of the heater 41 is variable, and the basis weight, material, and heat supply amount to the transfer material P can be changed. In the case of the heater 41 whose power is not variable, there is a method of changing the effective power by changing the on / off ratio.

  Further, an infrared temperature sensor that can measure the temperature of the transfer material P in a non-contact manner is provided, and the power of the heater 41 is changed according to the detection result of the temperature sensor, so that the preheating temperature of the transfer material P can be more accurately determined. It becomes possible to control.

  In FIG. 2, when the transfer material P that has received the transfer of the toner image is carried into the fixing nip portion N of the fixing device 20, the corona charger 45 provided at the entry portion of the preheating means 40 starts discharging. The transfer material P is charged to the same polarity as that of the toner, whereby the transport belt 42 transports the transfer material P in an electrostatic close contact. Thereby, the heat conduction to the transfer material P is kept good.

  The transfer material P is discharged by the AC discharge of the corona discharger 46 at the carry-out portion after the moisture in the transfer material P is evaporated by absorbing heat of vaporization due to heat transfer by the heater 41 while being transferred by the transfer belt 42. Then, it is separated from the conveying belt 42 and conveyed to the fixing nip N of the fixing device 30.

  When the transfer material P is conveyed to the fixing device 30, it is nipped and conveyed by the fixing belt 31 and the pressure roller 35. At the same time, the toner is melted and fixed by the amount of heat of the fixing belt 31, and then discharged.

  Immediately before the transfer material P is heated by the fixing belt 31, most of the water in the transfer material P evaporates in the preheating means 40, and the toner is preheated to 100 ° C. to 160 ° C. near the softening point in advance. Therefore, the amount of heat required for fixing may be small, the time required for the fixing belt 31 to reach a predetermined melting temperature (190 ° C. to 200 ° C.) required for melting the toner and the duration of the predetermined melting temperature may be short. Even if the heat capacity of the fixing belt 31 is small, it is possible to stably fix the transfer material P conveyed at high speed without causing a temperature drop, and it is possible to use the fixing device 30 having a short time required for warming up. Further, by reducing the heat capacity of the roller portion of the fixing device 30, the mass can be reduced and a small fixing device can be realized, and since the amount of heat taken away by the passage of the transfer material P is small, local high temperature can be avoided and fixing can be performed. The life of the belt 31 is increased.

[Non-contact type preheating means 50]
FIG. 3 is a cross-sectional view of the fixing device 30 including the non-contact type preheating stage 50. In addition, about the code | symbol used in this drawing, the same code | symbol is attached | subjected to the part which has the same function as FIG. Moreover, a different point from the said preheating means 40 is demonstrated.

  The preheating means 50 includes an external heating source 51 fixedly disposed above the conveyor belt 42 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 local heating source 51 to heat the local portion of the conveyor belt 42. The external heating source 51 is turned on and off by the control means 12 described later.

[Preheating temperature switching control]
FIG. 4 is a block diagram of a control unit that controls the preheating unit 40 (or the preheating unit 50) 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 11A, and the basis weight (plain paper, thick letter) of the transfer material P is set by the transfer material basis weight setting means 11B. , Thin letter, etc.) and the paper type of the transfer material P (plain paper, coated paper, special paper, cardboard, thin paper, OHP film, etc.) is set by the transfer material paper type setting means 11C.

  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. After the leading end of the transfer material P abuts on the registration roller 26 and waits, 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 of passage of the transfer material P through the preheating means 40 (or the preheating means 50), which is shown in FIG. The heating unit 40 or the preheating unit 50 shown in FIG. 3 may be activated to control the conveyance belt 42 to be heated. Alternatively, in the case of the preheating means 40, the heater 41 may be controlled on and off so as to maintain a predetermined temperature using the detection result of the temperature sensor TS3 regardless of the transfer material conveyance timing.

  Hereinafter, the preheating means 40 will be described as a representative.

  The control means 12 controls the drive of the preheating means 40 corresponding to the size of the transfer material P, the basis weight of the transfer material P, and the paper type of the transfer material P. That is, the drive of the preheating means 40 shown in FIG. 2 is controlled.

  When the transfer material P passes through the fixing nip N, a temperature difference is generated in the fixing belt 31 between the contact portion of the transfer material P and the transfer material non-contact portion between the transfer materials P. This is because the amount of heat taken from the fixing belt 31 differs between the transfer material P and the pressure roller 35.

  The amount of heat that the pressure roller 35 takes away from the fixing belt 31 depends on the temperature of the pressure roller 35. Further, the amount of heat taken by the transfer material P from the fixing belt 31 depends on the temperature of the transfer material P. Therefore, the temperature of the transfer material P is changed according to the temperature of the pressure roller 35 so that the amount of heat taken from the fixing belt 31 by the temperature of the pressure roller 35 and the temperature of the transfer material P becomes substantially equal. The temperature of the transfer material contact portion on the belt 31 and the temperature of the transfer material non-contact portion corresponding to the transfer material P can be made substantially equal. As a result, the toner image formed on the transfer material P It is possible to reduce the gloss difference.

  The amount of heat taken by the transfer material P from the fixing belt 31 varies depending on transfer material conditions such as the paper type of the transfer material P (plain paper, coated paper, basis weight, etc.). Therefore, the temperature difference can be reduced by changing the amount of heat supplied to the transfer material P by the preheating means 40 and changing the temperature of the transfer material P according to the transfer material conditions.

  Therefore, it is desirable that the preheating means 40 is controlled so that the heating power is variably controlled or the control temperature is variable according to the transfer material conditions. Examples of the heating source with variable heating power include the heater 41 of the contact-type preheating means 40 and the external heating source 51 of the non-contact type preheating means 50.

  FIG. 5 is a flowchart of a process for controlling the preheating means 40 of the fixing device 30.

  Step 1: The surface temperature Tp of the pressure roller 35 is detected by the temperature sensor TS2.

  Step 2: The control means 12 acquires transfer material information such as basis weight and material of the transfer material P.

  Step 3: The control unit 12 refers to the stored data in the storage unit 15 and acquires preheating temperature information (set temperature Ty) corresponding to the transfer material information.

  Step 4: The control means 12 sets the set temperature Ty of the preheating means 40.

  The control unit 12 changes the preheating temperature of the transfer material P according to the surface temperature Tp of the pressure roller 35. For example, when the temperature of the pressure roller 35 is low, the preheating temperature of the transfer material P is relatively set. If the temperature of the pressure roller 35 is increased, the preheating temperature of the transfer material P is set relatively higher. As a result, the amount of heat taken from the pressure roller 35 and the fixing belt 31 of the transfer material P becomes substantially equal, and the temperatures of the transfer material contact portion and the transfer material non-contact portion on the pressure roller 35 become substantially equal. As a result, it is possible to suppress the gloss difference on the transfer material P.

  Hereinafter, the fixing device of the present invention will be described with reference to FIGS. 6 and 7 and a timing chart of FIG.

  FIG. 6 and FIG. 7 are explanatory diagrams showing the conveyance process of the three transfer materials P1, P2, and P3 in the fixing device of the present invention. FIG. 8 is a timing chart showing the temperature change of the fixing belt 31. In FIG. 8, 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 position X).

  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, and a thickness of 70 μm. The transfer material P is A4 size, the transfer material conveyance direction length L2 = 210 mm, and between the plain paper or coated paper and the transfer material P When the gap G is about 80 mm, the gap 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 A4 size. In the case of different papers other than the above, the interval G of the transfer material P is changed in accordance with 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. The leading end of the first transfer material P1 reaches the fixing nip portion N after a predetermined time has elapsed since the detection signal is generated by the transfer material passage 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 on the fixing belt 31 in the vicinity of the fixing nip N is a region where the temperature of the fixing belt 31 shown in FIG. 8 is T1.

  By changing the preheating condition of the transfer material P in accordance with the temperature of the heating roller 33, the temperature is recovered from the broken line to the solid line in FIG. 8 to the temperature T1, and the set temperature of the portion where the transfer material P1 is not in contact with The temperature difference (T0−T1) can be reduced.

  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 set 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 fell is lowered. 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. The region where the temperature is T2 is a portion where the influence of the transfer material P1 remains.

  By heating the temperature-decreasing portion due to the contact with the transfer material P2 with the preheating means 40, the temperature of T3 and T4 is recovered from the broken line to the solid line in FIG. 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 fixing device 30 having the preheating means 40 of the present invention described above, 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 30 of the present invention having the preheating means 40 as compared with the temperature of the conventional fixing device, the upper limit temperature and the lower limit temperature are compressed and are close to the set temperature T0 as indicated by the outlined arrows in the figure. As a result, the temperature change of the fixing belt 31 when the transfer material P passes through the fixing nip portion N is reduced, and the occurrence of a gloss level difference on the transfer material P is significantly reduced.

  As described above, in the fixing device 30 including the preheating unit 40, the gloss level difference between the various transfer materials P is detected by the detection signal of the transfer material temperature detection unit 14 and the paper type of the transfer material P. 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. Further, a contact type preheating temperature 40 and a non-contact type preheating means 50 may be provided.

1 is a configuration diagram of an image forming apparatus including a fixing device according to the present invention. FIG. 3 is a cross-sectional view of a fixing device and preheating means according to the present invention. FIG. 3 is a cross-sectional view of a fixing device including a non-contact type preheating stage. FIG. 3 is a block diagram of a control unit that controls a preheating unit of the fixing device. 6 is a flowchart of a process for controlling preheating means of the fixing device. FIG. 4 is an explanatory diagram showing a conveyance process of three transfer materials in the fixing device of the present invention. FIG. 4 is an explanatory diagram showing a conveyance process of three transfer materials in the fixing device of the present invention. 6 is a timing chart showing a temperature change of the fixing belt.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Operation display part 11A Transfer material size setting means 11B Transfer material basis weight setting means 11C Transfer material paper type setting means 12 Control means 13 Transfer material passage detection means 14 Transfer material temperature detection means 30 Fixing device 31 Heating fixing member (fixing belt)
32 Fixing roller 33 Heat fixing rotator (heating roller)
34 Heating source 35 Pressure rotating body (Pressure roller)
36 Heating source 40 Preheating means 41 Heater 42 Conveying belt 45 Corona charger 46 Corona static eliminator 50 Preheating means 51 External heating source 52 Reflector A Image forming apparatus N Fixing nip P, P1, P2, P3 Transfer material

Claims (7)

An unfixed toner image carrying surface of a transfer material is attached to the heat fixing rotator formed in a fixing nip formed by a heat fixing rotator having a heating source 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 the transfer material in a contacting direction,
Preheating means for heating the transfer material upstream of the fixing nip portion in the transfer material conveyance direction of the heating and fixing rotator;
A pressure rotator temperature detecting means for detecting a surface temperature of the pressure rotator;
Control means for controlling the preheating means,
The image forming apparatus is characterized in that the control unit variably controls a heat supply amount in the preliminary heating unit in accordance with a surface temperature detection result of the pressure rotating body detected by the pressure rotating body temperature detecting unit. apparatus. The control means variably controls the heat supply amount in the preliminary heating means according to the surface temperature detection result of the pressure rotary body detected by the pressure rotary body temperature detection means and the transfer material information. The image forming apparatus according to claim 1. The heating and fixing rotator is an endless fixing belt that winds a heating roller having a heating source therein and a fixing roller that forms the fixing nip portion so as to face the pressure rotator. The image forming apparatus according to claim 1. The image forming apparatus according to claim 1, wherein the preheating unit heats a back side of an unfixed toner image carrying surface of the transfer material. The image forming apparatus according to claim 1, wherein the preheating unit heats an unfixed toner image carrying surface of the transfer material in a non-contact manner. The image forming apparatus according to claim 2, wherein the transfer material information is at least one of a basis weight, a type, and a size of the transfer material. The image forming apparatus according to claim 1, wherein the control unit variably controls a preheating temperature of the transfer material in accordance with a surface temperature of the pressure rotator.

Images