JP7134724B2 - image heating device - Google Patents

Description

The present invention relates to an image heating apparatus used in an image forming apparatus capable of forming an image on a recording material, such as a copying machine, a printer, or a facsimile machine employing an electrophotographic method.

In recent years, commercial printing such as catalogs, posters, pamphlets, etc., is printed according to the required number of copies, and on-demand printing, in which part of the printed contents such as various invoices and direct mails are changed for each customer and printed continuously. The market is getting bigger. Therefore, in the on-demand printing market, an electrophotographic image forming apparatus is attracting attention in place of offset printing, which requires plate making.

In such an image forming apparatus, a belt fixing device is adopted as an image heating device in order to cope with high speed operation. That is, by using a fixing belt and a pressure roller as a belt fixing device, a fixing nip portion that becomes a long heating area in the conveying direction of the recording material (recording paper) can be formed, and recording paper with a large basis weight exceeding 300 g/m ² can be formed. However, high productivity can be achieved.

In addition, in recent years, there has been a strong demand for a function to fix and convey recording sheets without waiting time even when recording sheets having different basis weights are mixed. In this case, at a fixing temperature that satisfies the fixability of recording paper exceeding 300 g/m ² , recording paper with a small basis weight such as 60 g/m ² is also fixed in the subsequent job. If the amount of heat is excessively applied to recording paper having a small basis weight, a phenomenon called blistering may occur mainly in coated paper having a small basis weight. This is a phenomenon in which the water content of the base paper in the coated paper becomes water vapor due to excessive heating, and this water vapor breaks through the weak portions of the coating layer and escapes.

Also, if the optimum fixing temperature is set for a recording paper with a small basis weight such as 60 g/m ² , there is a possibility that a recording paper with a weight exceeding 300 g/m ² will have insufficient heat and cold offset will occur.

Therefore, in order to change the amount of heat applied to each different recording sheet and to minimize the waiting time during mixed loading, it is necessary to keep the target temperature of the fixing belt as constant as possible and It is effective to control the amount of heat given to the recording paper. As such devices, a configuration for suppressing the heat source of the pressure roller (Patent Document 1) and a configuration for cooling the pressure roller (Patent Document 2) have been proposed.

JP-A-11-194647 JP-A-2003-167474

Here, the target temperature range of the pressure roller that is suitable for suppressing the occurrence of image defects due to blisters and cold offset differs depending on the basis weight of the recording paper. Therefore, when the recording paper to be fixed is changed from a small basis weight recording paper to a large basis weight recording paper, the temperature of the pressure roller will be the same as that of the small basis weight recording paper by the time the large basis weight recording paper reaches the fixing device. It is required that the temperature is changed from the temperature suitable for printing paper to the temperature suitable for large basis weight recording paper.

Therefore, when the recording paper to be fixed is changed from a small basis weight recording paper to a large basis weight recording paper, it is conceivable to change the temperature of the pressure roller after the small basis weight recording paper passes through the fixing device. .

However, in this case, until the temperature of the pressure roller, which starts to change after the small basis weight recording paper passes through the fixing device, rises to a temperature suitable for the succeeding large basis weight recording paper, the preceding small basis weight recording paper is maintained. It is necessary to leave a space between the recording paper of the following large basis weight and wait. Therefore, there was a possibility that productivity might fall.

SUMMARY OF THE INVENTION An object of the present invention is to suppress the occurrence of image defects due to cold offset and to suppress the decrease in productivity when executing a job in which a recording material having a basis weight larger than that of the preceding recording material follows. be.

In order to achieve the above object, an image heating apparatus according to the present invention is an image heating apparatus for heating an image, wherein a non-image-heated toner image on a recording material is heated at a nip portion for image-heating. a first rotating body that contacts the toner image; a second rotating body that cooperates with the first rotating body to form the nip portion; heating means that heats the nip portion; a control unit for controlling the temperature of the rotating body, the control unit controlling a preceding job to perform image heating processing on a recording material having a first basis weight and a second basis weight larger than the first basis weight; When receiving a first mixed job in which a first succeeding job to be subjected to image heating processing on a first number of sheets of recording material is received in this order, image heating is performed on the recording material of the preceding job. The temperature of the second rotating body is raised without waiting for the end of the process, and the temperature of the second rotating body at the start of the first succeeding job is controlled to be the first temperature. The control unit sends the preceding job and a second succeeding job to be subjected to image heating processing over a second number of sheets, which is smaller than the first number of sheets, to the recording material of the second basis weight in this order. When a second consolidated job is received, the temperature of the second rotating body is raised without waiting for the completion of the image heating process on the recording material of the preceding job, and the second following job is executed. is controlled so that the temperature of the second rotating body at the start of is set to a second temperature lower than the first temperature.

According to the present invention, in the case of executing a job in which a recording material having a basis weight larger than that of the preceding recording material follows, it is possible to suppress the occurrence of image defects due to cold offset and suppress the decrease in productivity. can.

Schematic diagram of an image forming apparatus equipped with a fixing device as an image heating device according to an embodiment. Short side cross-sectional view of the fixing device according to the embodiment Short side cross-sectional view of the fixing device according to the embodiment FIG. 2 is a longitudinal cross-sectional view of the fixing device according to the embodiment; FIG. 2 is a block diagram of a main body controller in an image forming apparatus equipped with the fixing device according to the embodiment; Diagram showing experimental results for blisters and cold offset FIG. 4 is a graph showing the relationship between the basis weight of recording paper and the lower limit temperature TL and upper limit temperature TU of the target temperature range of the pressure roller; Temperature transition diagram when switching from 104 gsm to 300 gsm in a conventional example as a comparative example Temperature transition diagram when switching from 104gsm to 300gsm Temperature transition diagram when switching from 104gsm to 68gsm Flowchart in the first embodiment Temperature transition diagram when switching from 68gsm to 300gsm Relationship diagram between pressure roller target temperature difference and waiting time Temperature transition diagram when switching from 300gsm paper to 68gsm paper Flowchart in the second embodiment Temperature transition diagram conceptually showing when switching from 68 gsm to 300 gsm in the third embodiment Temperature transition chart for 10 sheets of 300gsm Temperature transition chart for 20 sheets of 300gsm FIG. 10 is a diagram showing the basis weight of the succeeding recording material and the correction temperature according to the number of succeeding recording materials; Flowchart in the third embodiment

Preferred embodiments will be described below with reference to the drawings.

<<1st Embodiment>>
(Image forming device)
FIG. 1 is an overall schematic configuration diagram of an image forming apparatus 300 equipped with a fixing device 6 according to this embodiment. In FIG. 1, an image forming section 200 includes a drum-shaped electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) 1 as an image bearing member. The photosensitive drum 1 is made of a photosensitive material such as OPC, amorphous Se, or amorphous Si formed on a cylindrical base made of aluminum, nickel, or the like. The photosensitive drum 1 is rotationally driven in the direction of arrow c, and its surface is uniformly charged by a charging roller 2 as a charging device.

Scanning exposure is performed by a laser beam 3 that is ON/OFF controlled according to image information, and an electrostatic latent image is formed. This electrostatic latent image is developed and visualized by the developing device 4 . As a developing method, a jumping developing method, a two-component developing method, a FEED developing method, or the like is used, and image exposure and reversal development are often used in combination.

Recording materials (recording sheets) P having different basis weights are accommodated in paper feed cassettes 110a and 110b, respectively. Then, the leading edge of the fed recording material (recording paper) P is detected by a top sensor 8 installed upstream of the transfer nip portion Nt in the conveying direction of the recording material, and visualized on the photosensitive drum 1. It is conveyed to the transfer nip portion Nt in synchronism with the toner image (toner image). The toner image on the photosensitive drum 1 is transferred from the photosensitive drum 1 onto the recording material P conveyed to the transfer nip portion Nt by a transfer roller 5 as a transfer device. At this time, the recording material P is nipped and conveyed between the photosensitive drum 1 and the transfer roller 5 with a constant pressure.

Then, the recording material P onto which the toner image has been transferred is conveyed to the fixing device 6 and fixed as a fixed image. On the other hand, residual toner remaining on the photosensitive drum 1 after transfer is removed from the surface of the photosensitive drum 1 by the cleaning device 7 .

In FIG. 1, 10 is a fixing member as a first rotating body, 20 is an elastic pressing member (pressing the first rotating body) as a second rotating body, and 30 is a pressing roller. 20, which will be described in detail later.

(fixing device)
2 and 3 are schematic configuration diagrams of the fixing device 6 as an image heating device in this embodiment. In the following description, with respect to the fixing member constituting the fixing device, the longitudinal direction is the direction perpendicular to the conveying direction of the recording material and the thickness direction of the recording material, and the lateral direction is the longitudinal direction and the thickness of the recording material. It is the direction orthogonal to the direction.

As shown in FIG. 2, a fixing member 10 as a first rotating member and a pressure roller 20 as a pressure member serving as a second rotating member cooperate with each other to hold and convey a recording material at a fixing nip. A portion (hereinafter referred to as a nip portion) N having a predetermined nip width W is formed. A heater 11 is provided as a heating member for heating the nip portion. The heater 11 is held by a heater holder 12 and provided inside a fixing belt (image heating belt) 13. The heater 11 heats an unfixed toner image (unfixed image heating belt) on the recording material introduced into the nip portion N via the fixing belt 13. The toner image) is heated and melted and fixed.

The heater 11 includes a temperature control unit so that the temperature detected by the temperature sensor TH1, which is a temperature information acquiring means (temperature detecting means) such as a thermistor that contacts the inner surface of the fixing belt 13, becomes a predetermined fixing temperature. The energization is controlled by the body control unit 120 (described later with reference to FIG. 5).

Regarding the pressure roller 20 facing the fixing belt 13, the metal core 21, the elastic layer 22, and the release layer 23 are provided from the inside, and the pressure roller is cooled by the cooling device 30 provided with the fan 31 in the longitudinal direction of the pressure roller. The temperature of the central portion is detected by the temperature sensor TH2 (Fig. 4).

The fixing belt 13 is a cylindrical or endless belt-like member, or a rolled web-like member having an end. Adheres and slides on surfaces. Then, the fixing belt 13 is conveyed and moved in the direction of arrow a (FIG. 3).

The fixing belt 13 is a heat-resistant belt having a small heat capacity, and is made of a film of polyimide, polyamide-imide, PEEK, PFA, PTFE, or the like having a thickness of 100 μm or less and having heat resistance and thermoplasticity. A belt having sufficient strength and excellent durability for constructing a long-life fixing device 6 must have a thickness of 20 μm or more. Therefore, the optimum thickness of the fixing belt 13 is 20 μm or more and 100 μm or less. In this embodiment, polyimide with a thickness of 80 μm is used.

The surface layer of the fixing belt 13 is coated with a heat-resistant resin having good releasability such as PFA, PTFE, FEP, silicone resin, etc. mixed or singly in order to prevent offset and ensure separability of the recording material.

A heater holder 12 that holds the heater 11 is made of a heat insulating member to prevent heat radiation in the direction opposite to the direction approaching the nip portion N, and liquid crystal polymer, phenolic resin, PPS, PEEK, or the like is used, for example. A fixing film 13 is loosely fitted on the heater holder 12 with a margin so that the fixing film 13 can be freely rotated in the direction of arrow a (FIG. 3).
A small amount of heat-resistant grease is interposed between the heater 11 and the heater holder 12 and the fixing belt 13 . The heat-resistant grease has the effect of reducing the frictional resistance between the heating heater 11 and heater holder 12 and the fixing belt 13, thereby making the rotation of the fixing belt 13 smooth.

The temperature sensor TH1 is disposed in contact with the inner surface of the fixing belt 13 at the central portion in the longitudinal direction (width direction) of the fixing belt 13 . This temperature sensor TH1 detects the temperature of the area of the fixing belt 11 that serves as the paper passing area, and feeds back the detected temperature information to the control circuit unit (control unit, CPU) 100 included in the main body control unit 120 (FIG. 5). be done.

The control circuit unit 100 controls the electric power input to the heater 11 so that the detected temperature input from the temperature sensor TH1 is maintained at a predetermined target temperature (fixing temperature). The temperature sensors TH3 and TH4 also use thermistors like the temperature sensors TH1 and TH2. .

The pressure roller 20 has an elastic layer 22 formed by foaming heat-resistant rubber such as silicone rubber or fluororubber, or silicone rubber, on the outer side of the core metal 21. PFA, A release layer 23 such as PTFE or FEP may be formed.

The pressure roller 20 is sufficiently pressed from both ends in the longitudinal direction by a pressure mechanism (not shown) in the direction of the fixing member 10 so as to form a nip portion necessary for heat fixing. Moreover, it is rotationally driven in the direction of arrow b (FIG. 3) by a driving device (not shown) from the longitudinal end through the core metal 21 . As a result, the fixing belt 13 is driven to rotate outside the stay holder 12 in the direction of the arrow a (FIG. 3).

The pressure roller 20 has an elastic layer 22 of 5.0 mm formed of silicon rubber on the outer side of a metal core 21, and PFA formed thereon as a release layer 23. The diameter of the pressure roller 20 is 50 mm.

The temperature sensor TH2 that acquires the temperature information of the pressure roller is a temperature sensor (temperature detection element) such as a non-contact thermopile. are placed in In this embodiment, the pressure roller 20 does not have a heat source inside, but may have a heat source inside.

The recording material P is conveyed at a speed of 321 mm/sec, the pressure applied to the pressure roller 20 is 50 kgf, the nip width W of the nip portion N is 15 mm, and the test environment is set at room temperature of 23° C. and humidity of 50%.

(Cooling means for pressure roller)
Fan 31, which is an air-cooling type cooling device, will be described as cooling device 30 for pressure roller 20 with reference to FIG. 4 shows a configuration in which four fans 31(a), 31(b), 31(c), and 31(d) are provided in the longitudinal direction of the pressure roller 2. As shown in FIG. For A4 paper, fans 31(b) and (c) are provided corresponding to the paper passing areas, and (a) and (d) are provided corresponding to the paper non-passing areas.

The fan 31 is a device that blows air toward the pressure roller 20 to cool the pressure roller 20 . A sirocco fan, a cross-flow fan, an axial fan, or the like is used as the fan 31 . As the fan 31, an axial fan was used, and the number of revolutions used was 3000 rpm at maximum. The maximum number of rotations of the fan 31 may be larger or smaller than this, and the voltage may be adjusted to make the number of rotations variable.

A temperature sensor TH2 detects the temperature of the pressure roller, and the detected temperature information is fed back to the control circuit section 100. FIG. The control circuit unit 100 controls the electric power input to the fan 31 so that the detected temperature input from the temperature sensor TH2 is maintained at a predetermined target temperature.

(Processing part of job information)
FIG. 5 is a block diagram of the main control unit 120 in the image forming apparatus. The body control portion 120 has a control circuit portion (control portion) 100 , an operation portion 101 , an image processing portion 102 , an image formation control portion 103 , an image reading control portion 104 and a storage portion 105 . Further, it has a page information acquisition unit 107 that acquires at least basis weight (basis weight only, or basis weight and continuous number of sheets) as a recording material information acquisition unit, and a recording paper conveyance interval changing unit 108 .

A control circuit unit (control means) 100 mainly executes a program. The operation unit 101 is electrically connected to the control circuit unit 100 and receives input from the user. When accepting an input of a print job, the operation unit 101 accepts instructions such as information on the number of prints, setting of double-sided/single-sided printing, type of recording paper, etc., in addition to image information to be printed. Here, the information about the type of recording paper refers to the size, basis weight, material, and the like. Information such as the size, basis weight, and material of the recording paper contained in the paper feed tray is registered in association with the paper feed tray. may be configured to be specified by the user.

The image processing unit 102 is electrically connected to the control circuit unit 100 and processes image information from the image reading unit 1 or image information of a PDL image. The image forming control section 103 is electrically connected to the control circuit section 100 and controls the image forming section of the image forming apparatus. The image reading control unit 104 is electrically connected to the control circuit unit 100 and controls the image reading unit. The storage unit 105 is electrically connected to the control circuit unit 100 and constitutes temporary storage means for arithmetic processing.

The page information acquisition unit 107 also acquires setting information such as the number of prints of a job, a so-called "mixed basis weight job" for printing by continuously switching the basis weight of recording paper, etc. based on the information of the print job input by the user. to get That is, the grammage of recording paper to be used in a print job, the number of continuous sheets of recording paper with that grammage, the order for each grammage, and information are acquired. The page information acquisition means 107 transmits the information acquired by the page information acquisition means 107 to the control circuit section 100 .

A print job input to the control circuit unit 100 is notified to the storage unit 105, and basis weight information of recording paper to be printed from now on is stored. Thereby, the control circuit unit 100 can determine how many sheets of recording paper on which an image is formed by the image forming unit 200 and which is fixed by the fixing device 6 to which basis weight the recording paper will be changed to, It is possible to acquire information indicating how many sheets of recording paper continue. More specifically, it is possible to acquire information that the currently printed page has a basis weight of 300 g/m 2 and that recording paper with a basis weight of 60 g/m 2 will be conveyed to the fixing device after 30 pages.

In the first embodiment, for the sake of simplification, a case where a mixed basis weight job is input as one print job will be described as an example, but the following cases may also occur. When print job A, which prints only on recording paper with a first basis weight, and print job B, which prints only on recording paper with a second basis weight different from print job A, are input in succession. This is a case where two print jobs are continuously output like one mixed basis weight job.

Even in such a case, the page information acquisition unit 107 transmits information to the control circuit unit 100 based on the information of the print jobs A and B input by the user. The control circuit unit 100 determines after how many sheets of recording paper on which an image is formed by the image forming unit 200 and fixed by the fixing device 6, the basis weight of the recording paper is changed, and after that, recording with the same basis weight is performed. Information indicating how many sheets of paper continue can be obtained.

Note that the page information acquisition unit 107 may acquire information on the material of the recording paper in addition to the basis weight. The information on the material of the recording paper is, for example, information indicating that it is plain paper, coated paper, OHP, or label. Examples of the information of each page acquired by the page information acquiring unit 107 include the toner printing rate on the recording paper, the toner printing locations within the surface of the recording paper, and the like.

Copiers and the like used for on-demand printing have a productivity-prioritizing mode that emphasizes productivity, and for example, perform fixing operations at the same temperature control temperature even if plain paper and coated paper have different basis weights. In this embodiment, the fixing temperature of the fixing belt 13 is controlled to be 180° C. in surface temperature.

Also, the recording paper conveyance interval changing unit 108 controls the interval between each recording paper (paper interval) based on the paper feeding timing information received from the control circuit unit 100 .

(Conditions for occurrence of blister and cold offset)
FIG. 6 shows the results of confirming the conditions under which blisters and cold offset occur when the temperature of the fixing belt 13 is fixed at 180° C. and the surface temperature of the pressure roller 20 is changed. The checked recording papers are 68 g/m ² basis weight recording paper (Canon CS680 A4; hereinafter abbreviated as 68 gsm) and 104 g/m ² basis weight recording paper (Canon GFC104 A4; hereinafter abbreviated as 104 gsm). Further, the recording paper has a basis weight of 300 g/m ² (Canon GFC300 A4, hereinafter abbreviated as 300 gsm).

When no blistering or cold offset occurred, it was classified as ◯, when it occurred, it was classified as x, and when blistering was slightly generated, it was classified as Δ according to the visual rank. From this, it was found that 68 gsm causes blistering when the pressure roller temperature exceeds 100°C, and cold offset does not occur in the range of 70 to 120°C.

On the other hand, with 300 gsm, cold offset occurred when the pressure roller temperature was 100°C or less, and blistering did not occur in the range of 70 to 120°C. It was found that 104 gsm, which is between the two, causes blisters when the pressure roller temperature is 120° C. or higher, and cold offset when it is 80° C. or lower.

FIG. 7 shows the target temperature of the pressure roller for each recording sheet when the fixing belt temperature is 180.degree. TU is the upper limit temperature (upper target temperature) of the target temperature range, and TL is the lower limit temperature (lower target temperature) of the target temperature range, which is determined according to the basis weight of the recording material. By controlling the pressure roller temperature Tp so as to satisfy TL≦Tp≦TU, it is possible to prevent (suppress) both blistering and cold offset.

(Control when recording paper is mixed)
Temperature control of the pressure roller in a mixed job in which recording sheets of different basis weights are connected will be described below. In the fixing device 6 of the present embodiment, when the recording paper to be subjected to fixing processing (image heating processing) is changed from a recording paper having a small basis weight to a recording paper having a large basis weight, the fixing device 6 of the large basis weight is used at the start of the fixing processing for the recording paper having a large basis weight. Set the temperature of the pressure roller suitable for the recording paper. This is achieved by starting to raise the temperature of the pressure roller without waiting for the completion of the fixing process for the recording paper having a small basis weight.

Here, the recording paper with a small basis weight that is previously fixed is called a preceding job, and the recording paper with a large basis weight that is subsequently fixed is called a succeeding job. These jobs may be a part of one grammage mixed job, or may be considered as the first and second jobs when different jobs are continuously input in a short period of time. .

Here, a job is taken as an example in which continuous printing at 104 gsm is switched to continuous printing at 300 gsm midway through.

FIG. 8 shows the temperature transition of a conventional example as a comparative example. As for the fixing belt, the target temperature is fixed at 180° C. and controlled. Tb is the target temperature of the pressure roller when the 104 gsm preceding sheet is passed, and Ta is the target temperature of the pressure roller when the 300 gsm succeeding sheet is passed. In this example, Tb is 100.degree. C. and Ta is 120.degree.

In FIG. 8, regarding the temperature of the pressure roller, the dotted line indicates the time change of the actual temperature of the pressure roller, and the solid line indicates the time change of the target temperature of the pressure roller.

In such a conventional example, if the succeeding paper of 300 gsm is passed without providing a waiting time when switching the recording paper, the temperature of the pressure roller is low and cold offset may occur. Therefore, it is necessary to provide a waiting time until the temperature rises to Ta suitable for the pressure roller temperature of 300 gsm. In this case, the decrease in productivity when recording sheets are mixed becomes large.

On the other hand, FIG. 9 shows the temperature transition of the pressure roller of the first embodiment. In FIG. 9, regarding the temperature of the pressure roller, the dotted line indicates the time change of the actual temperature of the pressure roller, and the solid line indicates the time change of the target temperature of the pressure roller.

In the first embodiment, an upper limit temperature TU and a lower limit temperature TL are set as the target temperature range of the pressure roller 20 for each basis weight of the recording paper, and the target temperature is set within the target temperature range from the upper limit temperature TU to the lower limit temperature TL. change. In FIG. 9, the upper limit temperature TU104 and the lower limit temperature TL104 of the pressure roller 20 are set when the preceding sheet of 104 gsm is passed. TU104 is 110°C and TL104 is 90°C. In the case of the preceding paper of 104 gsm, the target temperature Tb of the pressure roller is set to 100° C. regardless of whether recording paper is mixed.

Here, when the information of 300 gsm is acquired in advance as the page information of the succeeding paper while the 104 gsm paper is being passed, the target temperature of the pressure roller 20 is changed as shown in FIG. Specifically, the pressure roller target temperature Ta of 300 gsm is compared with TU104 and TL104, and the temperature closer to Ta is set to TU104 (Tb').

Here, the change from Tb to Tb' is performed after the page information of the succeeding sheet whose basis weight is changed is acquired, without waiting for the completion of the fixing process of the preceding sheet before the change. Specifically, the temperature of the pressure roller is increased by weakening the output of the cooling fan 31 of the cooling device 30 or turning it off. Conversely, by increasing the output of the cooling fan 31, the temperature of the pressure roller is lowered.

Here, Tb' is the target temperature of the pressure roller when the leading edge of the recording paper of the first page of the succeeding paper whose grammage is changed reaches the nip portion N. temperature. That is, the control circuit unit 100 adjusts the temperature of the pressure roller so that the target temperature of the pressure roller at the start of the succeeding job becomes Tb' without waiting for the completion of the fixing process of the preceding sheet before switching. start to rise. In the first embodiment, the control circuit unit 100 starts exposing the image formed on the first page of the succeeding sheet in response to the target temperature of the pressure roller reaching Tb'.

Therefore, in the first embodiment, the subsequent job starts when the exposure of the image formed on the first page of the succeeding sheet is started. , may be set as the start time of the succeeding job.

In this embodiment, the pressure roller does not have a heat source, but if the pressure roller has a heat source, the output of the heat source may be increased.

Further, in the present embodiment, the case where Tb is changed to Tb' at the point in time when the page information of the succeeding sheet whose basis weight is changed is acquired as an example, but the following may be done. That is, after printing 30 sheets of 104 gsm, if information indicating that the 31st sheet of 300 gsm is obtained, wait until the predetermined number of sheets from the end of 104 gsm (for example, print 10 sheets of 104 gsm). ), the target temperature may be switched. Also, the number of sheets to wait may be determined based on the output of the detection unit that detects the temperature of the pressure roller at the time when the page information of the succeeding paper whose basis weight is changed is acquired. It should be noted that the control is performed within a range in which defects such as blisters do not occur on recording paper with a small basis weight before the basis weight is switched.

As a result, compared to the case where the target temperature of the pressure roller is changed after waiting for the completion of the fixing process on the preceding paper before switching, the temperature of the pressure roller is immediately changed to that required for the subsequent paper when the recording paper is switched. can.

After that, when 300 gsm is passed, the target temperature of the pressure roller is changed to Ta. Ta is 120°C.

As described above, switching from a paper with a small basis weight to a paper with a large basis weight has been described, but switching from a paper with a large basis weight to a paper with a small basis weight also has the effect of improving productivity. FIG. 10 shows temperature transition when switching from continuous printing at 104 gsm to continuous printing at 68 gsm midway. When the preceding sheet of 104 gsm is passed, the upper limit temperature TU104 and the lower limit temperature TL104 of the target temperature range of the pressure roller are set. TU104 is 110°C and TL104 is 90°C. In the case of the preceding paper of 104 gsm, the target temperature Tb of the pressure roller is set to 100.degree.

Here, when 68 gsm information is acquired in advance as the page information of the succeeding paper while 104 gsm paper is being passed, the pressure roller target temperature is changed as shown in FIG. Specifically, the pressure roller target temperature Ta of 68 gsm is compared with TU104 and TL104, and the temperature closer to Ta is set to TL104 (Tb').

Here, the change from Tb to Tb' is performed when the page information of the succeeding paper is obtained prior to the switching of the recording paper. As a result, compared to the case where the target temperature of the pressure roller is changed at the time when the recording paper is switched, the temperature of the pressure roller can be immediately changed to the required pressure roller temperature when the recording paper is switched. After that, when 68 gsm is passed, the target temperature of the pressure roller is changed to Ta. Ta is 80°C.

(control flow)
FIG. 11 shows a control flowchart of the first embodiment.
(S001)
When the body control section 120 (FIG. 5) receives the print job signal, the page information acquisition means 107 (FIG. 5) acquires the page information of the recording paper, and the control circuit section 100 (FIG. 5) determines the target temperature of the fixing belt. set. Specifically, referring to FIG. 7, control circuit unit 100 (FIG. 5) sets upper limit temperature TU and lower limit temperature TL of the target temperature range of the pressure roller.
(S002)
The control circuit unit 100 (FIG. 5) refers to the upper limit temperature TU and the lower limit temperature TL, sets the target temperature Tb, and starts cooling control of the pressure roller.
(S003)
If there is preceding page information of the succeeding sheet, the process proceeds to S004. If not, proceed to S008.
(S004)
During printing, the page information acquisition means 107 (FIG. 5) preliminarily acquires subsequent recording paper page information.
(S005)
If the preceding page information includes information on a basis weight different from that of the recording paper currently being printed, the process proceeds to S006. If not included, proceed to S003.
(S006)
The control circuit unit 100 (FIG. 5) changes the target temperature of the pressure roller to Tb' and changes the pressure roller cooling control. In the present embodiment, by changing the target temperature of the pressure roller to Tb', the preceding sheet can be set without widening the sheet interval between the preceding sheet and the succeeding sheet (that is, the same sheet interval as during the fixing process of the preceding sheet). During the fixing process or between sheets immediately after, the temperature of the pressure roller reaches the lower limit temperature suitable for the basis weight of the succeeding sheet. Therefore, it is possible to continuously start feeding subsequent sheets.
(S007)
The control circuit unit 100 (FIG. 5) changes the target temperature of the pressure roller to Ta and changes the cooling control of the pressure roller at the timing when the type of recording paper passing through the fixing device is switched.
(S008)
After printing all recording sheets, the process ends.

As described above, the upper and lower limits are set for the target temperature range of the pressure roller, and when different recording papers are mixed, the information of the succeeding paper is acquired in advance, and the target temperature of the pressure roller is set before the recording paper is switched. The first embodiment for changing the has been described. As a result, it is possible to both improve productivity and suppress (prevent) image defects when different recording sheets are mixed.

<<Second embodiment>>
A second embodiment different from the above-described first embodiment will be described below as an embodiment of the present invention. In addition, about the structure similar to the above-mentioned embodiment, description is abbreviate|omitted by assign|providing the same code|symbol.

As described in the first embodiment, before recording paper with a different basis weight is conveyed as a subsequent job, the recording paper information (basis weight) for the subsequent job is acquired in advance, and the fixed image is affected. It is preferable to change the target temperature of the pressure roller in advance within a range that does not cause . In the case where the difference in basis weights of mixed recording papers is large and even the temperature change in advance is not enough, it is preferable to shorten the time for temporarily stopping the transportation of subsequent recording papers as much as possible so as not to lower the productivity as much as possible. .

That is, in the first embodiment, a case in which no waiting time occurs when changing the basis weight has been described as an example. A case where it is difficult to change the target temperature of the pressure roller and switch the recording paper will be described. Also in this embodiment, if the basis weight difference is small and possible, it is preferable to switch the recording paper without waiting time as in the first embodiment.

In the second embodiment, the recording paper conveying interval changing unit 108 (FIG. 5) predicts the waiting time necessary for switching the recording paper when the preceding page information is acquired. That is, FIG. 12 shows temperature transition when switching from continuous printing at 68 gsm to continuous printing at 300 gsm midway. When the preceding sheet of 68 gsm is passed, the upper limit temperature TU68 and the lower limit temperature TL68 in the target temperature range of the pressure roller are set. TU68 is 90°C and TL68 is 70°C. In the case of 68 gsm, the target temperature Tb of the pressure roller is set to 80° C. regardless of whether recording sheets are mixed.

Here, when the information of 300 gsm is acquired as the page information of the subsequent paper in advance while the 68 gsm paper is being passed, the target temperature of the pressure roller is changed from Tb to Tb'. Specifically, as the target temperature Tb' of the pressure roller, TU68, TL68, and the target temperature Ta of the pressure roller of 300 gsm are compared, and TU68, which is closer to Ta, is set. Here, the target temperature of the pressure roller is changed from Tb to Tb' when the page information of the succeeding job is acquired before switching the recording paper.

As a result, compared to the case where the target temperature of the pressure roller is changed at the time when the recording paper is switched, the temperature of the pressure roller can be immediately changed to the required pressure roller temperature when the recording paper is switched.

Here, the target temperature of the pressure roller at the end of 68 gsm printing is 90° C. (Tb′). When the succeeding paper of 300 gsm is passed, cold offset may occur during continuous printing of 300 gsm unless at least the lower limit temperature TL300 (110° C.) of the target temperature of the pressure roller is exceeded. Therefore, until the temperature of the pressure roller rises from 90.degree. C. (Tb') to 110.degree.

At this time, the target temperature difference (90° C.-110° C.) of the pressure roller and the time required for temperature rise can be determined at the time when the page information for the subsequent job is preliminarily acquired. FIG. 13 shows the relationship between the target temperature (Tb′) of the pressure roller before switching the recording paper and the target temperature (TU300 or TL300) of the pressure roller after switching and the wait time. When the target temperature (Tb') of the pressure roller before switching is 90° C. and the upper limit temperature TU300 or the lower limit temperature TL300 as the target temperature range of the pressure roller after switching is 110° C., the waiting time is 10 seconds.

In this way, in the second embodiment, the required waiting time can be grasped in advance as the shortened waiting time, and reduction in productivity can be suppressed.

The target temperature (Ta') of the pressure roller during this waiting time is the upper limit temperature TU300 and the lower limit temperature TL300 as the target temperature range of the pressure roller set when 300 gsm is passed, and the pressure roller of 300 gsm. It is set by comparing the target temperature Ta. Specifically, the TL 300 closer to Ta is set.

After that, when 300 gsm is passed, the target temperature of the pressure roller is changed to Ta. Ta is 120°C.

As described above, switching from paper with a small basis weight to paper with a large basis weight has been described as the second embodiment. It is effective and will be explained below.

FIG. 14 shows temperature transition when switching from continuous printing at 300 gsm to continuous printing at 68 gsm midway. When 300 gsm is being passed, an upper limit temperature TU300 and a lower limit temperature TL300 are set as the target temperature range of the pressure roller. TU300 is 130°C and TL300 is 110°C. In the case of the preceding paper of 300 gsm, the target temperature Tb of the pressure roller is set to 120° C. regardless of whether recording paper is mixed.

Here, when the information of 68 gsm is acquired as the page information of the subsequent paper in advance while the paper of 300 gsm is being passed, the target temperature of the pressure roller is changed from Tb to Tb'. Specifically, the pressure roller target temperatures Ta of TU300, TL300, and 68 gsm are compared, and the temperature closer to Ta is set to TL300 (Tb').

The target temperature of the pressure roller is changed from Tb to Tb' when page information is acquired before switching the recording paper. As a result, compared to the case where the target temperature of the pressure roller is changed at the time when the recording paper is switched, the temperature of the pressure roller can be immediately changed to the required pressure roller temperature when the recording paper is switched.

Here, the target temperature of the pressure roller at the end of printing of 300 gsm is 110° C. (Tb′), but when the succeeding paper of 68 gsm is passed, the target temperature of the pressure roller is at least 68 gsm. The upper temperature limit of the range TU68 (90°C) must be exceeded. That is, if the upper limit temperature TU68 (90° C.) is not exceeded, blistering may occur during continuous printing at 68 gsm.

Therefore, until the pressure roller temperature drops from 110° C. (Tb′) to 90° C. (TU68), the 300 gsm sheet feeding is temporarily stopped to provide a waiting time. Here, the target temperature difference (110° C.-90° C.) of the pressure roller and the time required for the temperature drop can be determined at the time when the preceding page information is acquired.

FIG. 13 shows the relationship between the target temperature (Tb') of the pressure roller before switching the recording paper and the target temperature (TU68 or TL68) of the pressure roller after switching and the wait time. If the target temperature (Tb') of the pressure roller before switching is 110° C. and the upper limit temperature TU68 or lower limit temperature TL68 as the target temperature range of the pressure roller after switching is 90° C., the waiting time is 10 seconds.

After that, when 68 gsm is passed, the target temperature of the pressure roller is changed to Ta. Ta is 80°C.

As described above, in the second embodiment, the required waiting time can be grasped in advance, and reduction in productivity can be suppressed.

(control flow)
FIG. 15 shows a control flowchart of the second embodiment.
(S001)
When the body control section 120 (FIG. 5) receives the print job signal, the page information acquisition means 107 (FIG. 5) acquires the page information of the recording paper, and the control circuit section 100 (FIG. 5) determines the target temperature of the fixing belt. set. Specifically, referring to FIG. 7, control circuit unit 100 (FIG. 5) sets upper limit temperature TU and lower limit temperature TL of the target temperature range of the pressure roller.
(S002)
The control circuit unit 100 (FIG. 5) refers to the upper limit temperature TU and the lower limit temperature TL, sets the target temperature Tb, and starts cooling control of the pressure roller.
(S003)
If there is preceding page information of the succeeding sheet, the process proceeds to S004. If not, proceed to S018.
(S004)
During printing, the page information acquisition means 107 (FIG. 5) preliminarily acquires subsequent recording paper page information.
(S005)
If the preceding page information includes information on a basis weight different from that of the recording paper currently being printed, the process proceeds to S006. If not included, proceed to S003.
(S006)
The control circuit unit 100 (FIG. 5) changes the target temperature of the pressure roller to Tb' and changes the pressure roller cooling control.
(S007)
If Tb' is included between the upper limit temperature TU and the lower limit temperature TL of the target temperature range of the pressure roller for the succeeding sheet, the process proceeds to S008; otherwise, the process proceeds to S012.
(S008)
The recording paper conveyance interval changing unit 108 (FIG. 5) determines the waiting time (Tw) at the time of recording paper switching with reference to FIG.
(S009)
The recording paper conveyance interval changing unit 108 (FIG. 5) starts waiting for the waiting time (Tw) at the time when printing of the preceding recording paper ends.
(S010)
After the waiting time Tw has elapsed, the process proceeds to S011.
(S011)
Starting to feed the succeeding sheet, the control circuit unit 100 (FIG. 5) changes the target temperature of the pressure roller to Ta, changes the cooling control of the pressure roller, and proceeds to S013.
(S012)
It is assumed that Tb' is not included in the target temperature range of the pressure roller for the succeeding sheet from the upper limit temperature TU to the lower limit temperature TL. In this case, the control circuit unit 100 (FIG. 5) changes the pressure roller target temperature to Ta and changes the cooling control of the pressure roller in accordance with the timing when the type of recording paper passing through the fixing device is switched.
(S013)
After printing all recording sheets, the process ends.

As described above, the upper and lower limits are set for the target temperature of the pressure roller, and when different recording papers are mixed, the information of the succeeding paper is acquired in advance, and the target temperature of the pressure roller is changed before the recording paper is switched. , the second embodiment for determining the waiting time at the time of recording material switching has been described.

In the second embodiment, based on at least the grammage as the recording material information in the subsequent job in which the recording material type is switched, if the grammage increases in the subsequent job before the recording material type is switched, Increase the target temperature of the pressure roller. In addition, the target temperature of the pressure roller is lowered when the grammage is reduced in subsequent jobs.

Then, the control unit further sets the target temperature of the pressure roller before the type of recording material is switched as the first target temperature, and sets the temperature to be changed from the first target temperature before the type of recording material is switched. When the pressure roller target temperature is set to the second target temperature, the control section performs the following control. That is, based on the first target temperature and the second target temperature, the recording material conveyance interval in the subsequent job is controlled (the waiting time is controlled).

As a result, in the second embodiment, the waiting time at the time of recording material switching is shortened, and it is possible to both improve productivity and suppress (prevent) image defects when different recording sheets are mixed.

<<Third embodiment>>
A third embodiment will be described below. In addition, about the structure similar to the above-mentioned embodiment, description is abbreviate|omitted by assign|providing the same code|symbol.

As described in the first embodiment, before recording paper with a different basis weight is conveyed as a subsequent job, the recording paper information for the subsequent job is acquired in advance, and the fixed image is not affected. It is preferable to change the target temperature of the pressure roller in advance. In the case where the difference in basis weights of mixed recording papers is large and even the temperature change in advance is not enough, it is preferable to shorten the time for temporarily stopping the transportation of subsequent recording papers as much as possible so as not to lower the productivity as much as possible. . Then, it is preferable to change the target temperature of the pressure roller to a necessary and sufficient target temperature according to the number of sheets of subsequent recording paper to be continuously printed so as not to lower the productivity as much as possible.

That is, in the present embodiment, the target temperature of the pressure roller is determined according to the number of sheets of mixed recording paper that are continuously printed.

In this embodiment, the recording paper conveyance interval changing unit 108 (FIG. 5) predicts the waiting time required for switching the recording paper when the preceding page information is acquired. That is, FIG. 16 shows temperature transition when switching from continuous printing at 68 gsm to continuous printing at 300 gsm midway. When the preceding sheet of 68 gsm is passed, the upper limit temperature TU68 and the lower limit temperature TL68 in the target temperature range of the pressure roller are set. TU68 is 90°C and TL68 is 70°C. In the case of 68 gsm, the target temperature Tb of the pressure roller is set to 80°C.

Here, when the information of 300 gsm is acquired as the page information of the subsequent paper in advance while the 68 gsm paper is being passed, the target temperature of the pressure roller is changed from Tb to Tb'. Specifically, as the target temperature Tb' of the pressure roller, TU68, TL68, and the target temperature Ta of the pressure roller of 300 gsm are compared, and TU68, which is closer to Ta, is set. Here, the target temperature of the pressure roller is changed from Tb to Tb' when the page information of the succeeding job is acquired before switching the recording paper.

As a result, compared to the case where the target temperature of the pressure roller is changed at the time when the recording paper is switched, the temperature of the pressure roller can be immediately changed to the required pressure roller temperature when the recording paper is switched.

Here, the lower limit temperature of the target temperature of the pressure roller when passing the succeeding paper of 300 gsm changes depending on the number of successively printed succeeding papers. In other words, when the number of consecutive sheets is large, the amount of heat required is large, but when the number of consecutive sheets is small, the amount of heat required is small, so the lower limit temperature can be set low.

Here, the lower limit temperature of the pressure roller determined from information on the number of subsequent sheets is defined as correction lower limit temperature TL′=reference lower limit temperature TL−correction temperature p. In this example, the reference lower limit temperature TL is set to TL300 (110° C.), which is the lower limit temperature of the target temperature of the pressure roller when a large amount of 300 gsm paper is fed (20 sheets or more in the example of FIG. 17). FIG. 16C is a diagram showing an example of change in the target temperature of the pressure roller at this time. FIG. 16B is a diagram showing an example of changes in the target temperature of the pressure roller when the reference lower limit temperature TL is used to pass a moderate amount of paper of 300 gsm (6 to 10 sheets in the example of FIG. 17).

FIG. 17 shows the relationship between the corrected temperature p and the number of successive sheets of succeeding paper. Here, if the number of consecutive 300 gsm subsequent sheets is not 20 but is, for example, 3, the correction lower limit temperature TL'300 is TL'300 from the relationship between the lower limit temperature TL (110° C.) and the correction temperature p (10° C.). = 100°C.

Here, the target temperature of the pressure roller at the end of 68 gsm printing is 90° C. (Tb′). When the succeeding paper of 300 gsm is passed, if it does not exceed at least the correction lower limit temperature TL'300 (100° C.) of the target temperature of the pressure roller, cold offset may occur during continuous printing of 300 gsm. There is Therefore, until the temperature of the pressure roller rises from 90.degree. C. (Tb') to 100.degree. At this time, the target temperature of the pressure roller is Ta'.

At this time, the target temperature difference (90° C.-110° C.) of the pressure roller and the time required for temperature rise can be determined at the time when the page information for the subsequent job is preliminarily acquired. From the relationship in FIG. 13, when the target temperature (Tb') of the pressure roller before switching is 90° C. and the target temperature of the pressure roller after switching is 100° C., the waiting time is 5 seconds.

As described above, in this embodiment, the required waiting time can be shortened by using the information on the number of sheets to be continuously printed on subsequent sheets, and reduction in productivity can be suppressed.

Note that FIGS. 16B and 16C illustrate examples in which the target temperature Tb' of the pressure roller during fixing at 68 gsm is not changed, but Ta' is changed according to the number of subsequent sheets. However, if the temperature can be controlled within the range of TL68 or more and TU68 or less, Tb' may be set to a higher temperature than when the number of consecutive prints of succeeding paper is small when the number of consecutive prints of succeeding paper is large.

(control flow)
FIG. 18 shows a control flowchart of this embodiment.
(S001)
When the body control section 120 (FIG. 5) receives the print job signal, the page information acquisition means 107 (FIG. 5) acquires the page information of the recording paper, and the control circuit section 100 (FIG. 5) determines the target temperature of the fixing belt. set. Specifically, referring to FIG. 7, control circuit unit 100 (FIG. 5) sets upper limit temperature TU and lower limit temperature TL of the target temperature range of the pressure roller.
(S002)
The control circuit unit 100 (FIG. 5) refers to the upper limit temperature TU and the lower limit temperature TL, sets the target temperature Tb, and starts cooling control of the pressure roller.
(S003)
If there is preceding page information of the succeeding sheet, the process proceeds to S004. If not, proceed to S018.
(S004)
During printing, the page information acquisition means 107 (FIG. 5) preliminarily acquires subsequent recording paper page information.
(S005)
If the preceding page information includes information on a basis weight different from that of the recording paper currently being printed, the process proceeds to S006. If not included, proceed to S003.
(S006)
The control circuit unit 100 (FIG. 5) changes the target temperature of the pressure roller to Tb' and changes the pressure roller cooling control. By controlling the operation of the cooling fan and weakening the output of the cooling fan or turning it off as described above, the temperature of the pressure roller can be increased. The temperature of the pressure roller can be lowered by increasing the output of the cooling fan.
(S007)
The control circuit unit 100 (FIG. 5) calculates the correction lower limit temperature TL' from the consecutive number of sheets previously acquired by the page information acquisition means 107 (FIG. 5).
(S008)
If Tb' is included between the upper limit temperature TU and the lower limit temperature TL' of the target temperature range of the pressure roller for the succeeding sheet, the process proceeds to S013; otherwise, the process proceeds to S009.
(S009)
The recording paper conveyance interval changing unit 108 (FIG. 5) determines the waiting time (Tw) at the time of recording paper switching with reference to FIG.
(S010)
The recording paper conveyance interval changing unit 108 (FIG. 5) starts waiting for the waiting time (Tw) at the time when printing of the preceding recording paper ends.
(S011)
After the waiting time Tw has elapsed, the process proceeds to S012.
(S012)
Starting to feed the succeeding sheet, the control circuit unit 100 (FIG. 5) changes the target temperature of the pressure roller to Ta, changes the cooling control of the pressure roller, and proceeds to S014.
(S013)
It is assumed that Tb' is not included in the target temperature range of the pressure roller for the succeeding sheet from the upper limit temperature TU to the lower limit temperature TL. In this case, the control circuit unit 100 (FIG. 5) changes the pressure roller target temperature to Ta and changes the cooling control of the pressure roller in accordance with the timing when the type of recording paper passing through the fixing device is switched.
(S014)
After printing all recording sheets, the process ends.

As described above, the upper and lower limits are set for the pressure roller target temperature, and when different recording papers are mixed, the information of the succeeding paper is obtained in advance, and the target temperature of the pressure roller is changed before the recording paper is switched. Along with this, the present embodiment has been described in which the target temperature of the pressure roller is corrected in accordance with the number of sheets of succeeding paper to be continuously printed, and the waiting time at the time of recording material switching is determined.

As a result, in the present embodiment, the waiting time at the time of recording material switching is greatly shortened, and it is possible to both improve productivity and suppress (prevent) image defects when different recording sheets are mixed.

Also in this embodiment, if the basis weight difference is small and possible, it is preferable to switch the recording paper without waiting time as in the first embodiment.

(Modification)
Although preferred embodiments of the present invention have been described in the above-described embodiments, the present invention is not limited thereto, and various modifications are possible within the scope of the present invention.

(Modification 1)
In the above-described embodiment, the target temperature of the pressurizing rotor is changed based on the recording material information for the post-switching job (subsequent job) while the last sheet of the recording material is being passed in the current job. . However, the present invention is not limited to this, and based on the recording material information in the post-switching job (subsequent job), while passing the nth sheet (n≧2) from the end of the recording material in the current job, The target temperature of the pressurizing rotor may be changed. In other words, for the last nth sheet to the last sheet of the recording material in the current job, the weight is different from the last to the (n+1)th sheet of the recording material in the current job within a range that does not affect fixability. It may be the target temperature of the pressure rotor.

(Modification 2)
In the above-described embodiment, a pressure roller is shown as a pressure rotary body, but a rotatable pressure belt that is intermittently suspended over a plurality of pulleys as described in Patent Document 1 may be used.

Moreover, in the embodiment described above, the heater 11 is provided as a heating member for heating the nip portion, but the present invention is not limited to this. For example, the rotatable fixing belt 13 may generate heat by electromagnetic induction using an exciting coil or by energization.

(Modification 3)
In the above-described embodiments, recording paper is used as the recording material, but the recording material in the present invention is not limited to paper. In general, a recording material is a sheet-like member on which a toner image is formed by an image forming apparatus. Includes glossy paper. In the above-described embodiment, for the sake of convenience, the handling of the recording material (sheet) P is described using terms such as paper feeding, but this does not limit the recording material in the present invention to paper.

(Modification 4)
In the above-described embodiments, an apparatus that fixes an unfixed toner image on a sheet is described as an example, but the present invention is not limited to this. The present invention is also applicable to a device that heats and presses a toner image preliminarily adhered to a sheet in order to improve the glossiness of the image.

10 Fixing member 11 Heater 20 Pressure roller 30 Cooling device 100 Control circuit unit (control unit) Control circuit unit (control unit)

Claims (7)

An image heating device for heating an image,
a first rotating body that contacts the unheated toner image at a nip portion that heats the unheated toner image on the recording material;
a second rotating body that cooperates with the first rotating body to form the nip portion; a heating means that heats the nip portion;
a control unit that controls the temperature of the second rotating body,
The control unit performs image heating processing for a preceding job to perform image heating processing on recording materials having a first basis weight, and image heating processing for a first number of sheets of recording materials having a second basis weight larger than the first basis weight. When the first mixed job sent in this order with the first succeeding job to be executed is received, the temperature of the second rotating body is changed without waiting for the completion of the image heating process on the recording material of the preceding job. and controlling the temperature of the second rotating body at the start of the first subsequent job to be the first temperature;
The control unit sends the preceding job and a second succeeding job to be subjected to image heating processing over a second number of sheets, which is smaller than the first number of sheets, to the recording material of the second basis weight in this order. When the incoming second consolidated job is received, the temperature of the second rotating body is raised without waiting for the completion of the image heating process on the recording material of the preceding job, and the second following job is executed. An image heating apparatus, wherein the temperature of the second rotating body at the start is controlled to be a second temperature lower than the first temperature. Having a cooling fan for cooling the second rotating body,
2. The image heating apparatus according to claim 1, wherein said control section controls operation of said cooling fan in order to control the temperature of said second rotor. The target temperature of the second rotating body before the type of the recording material is switched is set as a first target temperature, and the second target temperature changed from the first target temperature before the type of the recording material is switched. When the target temperature of the rotating body of is set as a second target temperature, and the target temperature of the second rotating body after the type of recording material is switched is set as a third target temperature,
the third target temperature is a temperature within a target temperature range having an upper limit temperature and a lower limit temperature determined according to the basis weight of the recording material;
correcting the lower limit temperature according to the first number or the second number;
2. If the second target temperature is not between the upper limit temperature and the corrected lower limit temperature, a waiting time is set before the type of recording material is switched. 2. The image heating device according to 2 above. When the target temperature of the second rotor during the waiting time is set as a fourth target temperature,
4. An image heating apparatus according to claim 3, wherein said fourth target temperature is said lower limit temperature. When the second target temperature is between the upper limit temperature and the corrected lower limit temperature, the control unit sets the third target temperature without setting the waiting time. 5. The image heating device according to claim 3 or 4. 6. The image according to any one of claims 1 to 5, wherein temperature detecting means for detecting the temperature of said second rotating body is provided at a central portion in the longitudinal direction of said second rotating body. heating device. 7. The image heating apparatus according to claim 1, wherein said first rotating member is an image heating belt, and said second rotating member is a pressure roller.

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