JP2012091337A - Recording apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the occurrence of transfer defects in a subsequent recording cycle by reducing the temperature difference generated in an intermediate transfer member after an intermediate image of a different average recording duty is heated.SOLUTION: In transfer inkjet recording, a cooling unit independently controls cooling in a first area and a second area so that a temperature difference between the first area in which the first intermediate image is formed, and the second area in which the second intermediate image following the first intermediate image is formed is reduced.

Description

  The present invention relates to a transfer type ink jet recording type recording apparatus.

  Patent Document 1 discloses a recording apparatus of a transfer type ink jet recording method in which an intermediate image (ink image) is once formed on an intermediate transfer member by an ink jet method, and the formed intermediate image is transferred to a recording medium. Since the ink viscosity of the intermediate image is important for good transfer, the ink image is evaporated by heating the intermediate image formed on the intermediate transfer member with a heater or the like to increase the viscosity. Further, in the apparatus of Patent Document 1, the surface of the intermediate transfer body is cooled by applying a cooling liquid after the transfer. A series of processes of intermediate image formation, heating, transfer, and cooling is repeated as one recording cycle, and image formation on a recording medium is repeated.

JP 2009-045885 A

  The applicant has found a phenomenon that when the intermediate transfer member forming the intermediate image is uniformly heated, the surface of the intermediate transfer member has a different temperature depending on the location. The mechanism will be described.

  When the intermediate transfer member is viewed as a whole, a plurality of intermediate images are formed side by side at a predetermined interval. Assuming that the region where the first intermediate image is formed based on the image data is the first region, and the region where the second intermediate image is formed based on the different image data is the second region, the first region and the second region And a temperature difference occurs after the heating process. The reason is as follows.

  FIG. 1A is a cross-sectional view showing a state when a high duty image (in which ink is densely applied to the surface of the intermediate transfer body) formed on the transfer body is heated. Most of the heat W (thick arrow in the figure) given from the heater from above is taken away as vaporization heat for volatilizing the ink solvent leaving the color material. For this reason, the intermediate transfer member itself is not heated so much and the temperature rise is moderate. On the other hand, as shown in FIG. 1B, when heat W is applied to a low-duty image formed on the same transfer body (the surface of the intermediate transfer body is sparsely applied with ink), the ink solvent volatilizes. Since the heat of vaporization is small, more heat is transmitted to the intermediate transfer member than in FIG. By such a mechanism, after heating, a temperature difference is generated between the surfaces of the intermediate transfer body on which the images are formed in accordance with the average recording duty of the intermediate image formed on the intermediate transfer body. The temperature difference remains maintained in the subsequent transfer process. Even if the intermediate transfer body is cooled after the transfer process as in Patent Document 1, this temperature difference is not eliminated in a short time.

  If the process proceeds to the next recording cycle without eliminating the temperature difference, there is an increased possibility of “transfer defects” due to the mechanism described below.

  The intermediate transfer surface after the transfer process having a temperature difference depending on the location is adjusted so that the intermediate transfer surface (relatively low temperature) on which the high-duty image is formed is sufficiently cooled. Suppose that it has cooled uniformly. As a result, the surface of the intermediate transfer member on which the low-duty image has been formed is not sufficiently cooled because of the higher temperature, and the temperature becomes higher than a predetermined temperature even after cooling. In the next recording cycle, the ink that has landed on the intermediate transfer member region that has reached a temperature higher than usual is volatilized by the heat of the intermediate transfer member before being heated by the heater. The ink volatilizes excessively with the subsequent heating process, and the ink may increase in viscosity beyond an acceptable range. In the transfer process, ink with excessive viscosity strongly adheres to the side of the intermediate transfer member, so that not all of the ink can be transferred to the recording medium at normal transfer pressure, resulting in “image blurring” in the transferred image. End up. One form of “transfer defect” is “image fading”.

  On the contrary, it is assumed that the transfer body is uniformly cooled with a cooling amount that sufficiently cools the surface (relatively high temperature) of the intermediate transfer body on which the low duty image was formed. As a result, the surface of the intermediate transfer member on which the high duty image was formed is excessively cooled, and the temperature becomes lower than a predetermined temperature even after cooling. In the next recording cycle, the ink that has landed on the intermediate transfer member area, which is normally at a low temperature, is deprived of heat by the low-temperature intermediate transfer member during the heating process. Therefore, the volatilization of the ink solvent becomes insufficient at a predetermined heating amount, and the ink may not reach the allowable ink viscosity. In the transfer process, the ink that does not have the required viscosity spreads greatly on the recording medium due to the transfer pressure, and an “image blur” occurs in the transferred image. Another form of “transfer failure” is “image flow”.

  The present invention has been made based on the recognition of the above-mentioned problems. An object of the present invention is to reduce the temperature difference that varies depending on the location of the intermediate transfer member generated by the heating process, thereby suppressing the occurrence of transfer failure in the subsequent recording cycle. The provision of equipment.

  The present invention includes an intermediate transfer member, a recording head that applies ink to the intermediate transfer member to form a plurality of intermediate images, a heating unit that heats the intermediate transfer member on which the intermediate image is formed, and the heating A recording apparatus comprising: transfer means for transferring the intermediate image formed on the intermediate transfer body heated by the means to a recording medium; and cooling means for cooling the intermediate transfer body heated by the heating means. The cooling unit is configured to reduce the temperature difference between the first region in which the first intermediate image is formed and the second region in which the second intermediate image following the first intermediate image is formed. A recording apparatus, wherein cooling of the first area and the second area by a cooling unit is individually controlled.

  According to the present invention, it is possible to suppress the occurrence of transfer defects in the subsequent recording cycles by reducing the temperature difference generated in the intermediate transfer member after the intermediate images having different average recording duties are heated.

Diagram for explaining the phenomenon in which the surface of the intermediate transfer member has different temperatures depending on the location Sectional view showing the overall configuration of the recording apparatus Block diagram of control system Top view showing an intermediate image formed on the intermediate transfer member The graph which showed transition of the surface temperature of the intermediate transfer body in Embodiment 1 Graph plotting ink solvent residual ratio against heating amount FIG. 9 is a graph showing the transition of the surface temperature of the intermediate transfer member in the second embodiment.

<Embodiment 1>
FIG. 2 is an overall configuration diagram of a transfer type ink jet recording type recording apparatus according to the first and second embodiments. The intermediate transfer member 1 includes two drum-like rotating members 12 that rotate in the direction of an arrow about a shaft 13 and an endless transfer belt 10 that rotates around the two rotating members 12. The transfer belt 10 is made of a metal material, and a surface layer 11 that receives ink is formed on the outer surface of the transfer belt 10.

  Around the intermediate transfer body 1, a group of units for repeatedly executing a series of processes of intermediate image formation, heating, transfer, and cooling as one recording cycle is arranged. These units are a recording head 14 (intermediate image forming process), a heating unit 15 (heating process), a transfer roller 17 (transfer process), and a cooling unit 19 (cooling process). The recording head 14 has a plurality of line-type ink jet heads corresponding to a plurality of colors. Ink is ejected from a number of nozzles of the inkjet head, and ink is applied onto the intermediate transfer member 1 (surface layer 11 of the transfer belt 10) to form an intermediate image (ink image). The heating unit 15 includes a heater that generates electromagnetic waves including heat rays such as infrared rays and far infrared rays, and heats the surface layer 11 by directly irradiating the surface layers 11 with heat rays or blowing them as warm air. The ink solvent of the intermediate image formed on the intermediate transfer body 1 is evaporated by heating to increase the viscosity. The transfer roller 17 transfers the image onto the recording medium 16 by pressing the ink having a high viscosity on the intermediate transfer body 1 against the recording medium 16 and applying pressure thereto. The cooling unit 19 is provided to cool the intermediate transfer member after the transfer process in a short time to return to the initial temperature in order to shorten the time of one recording cycle. As will be described later, the heating unit 15 is provided to face the moving intermediate transfer member, and has a heating element capable of controlling the heating capability. The heating unit 15 can control the heating amount of the heated region by changing the heating amount by the heating element in synchronization with the timing at which the heated region passes. Similarly, the cooling unit 19 is provided to face the moving intermediate transfer member, and has a cooling element capable of controlling the cooling capacity. The cooling unit 19 can control the cooling amount of the cooled region by changing the cooling amount by the cooling element in synchronization with the timing at which the cooled region passes.

  FIG. 3 is a block diagram of the control system of the recording apparatus of the present embodiment. The controller 50 that is a controller includes a CPU, a ROM, a RAM, and a counter. The ROM stores a control program executed by the CPU. The RAM includes a working area for temporarily storing image data and the like, and a buffer area for storing various data input from the external device 57. The counter counts the number of drive pulses of the motor that moves the rotating body 12. A motor driver 52, a heating unit driver 54, a head driver 55, and a cooling unit driver 56 are connected to the control unit 50 via an interface 51. A motor 53 for rotating the rotating body 12 is driven by the motor driver 52. The heating state of the heating unit 15 is controlled via the heating unit driver 54. The ink ejection nozzles of the recording head 14 are driven by the head driver 55. The cooling unit 19 is controlled by the cooling unit driver 56. The temperature sensor 21 is provided on the downstream side of the transfer roller 17 and acquires the surface temperature of the surface layer 11. As the temperature sensor 21, a thermography that detects a two-dimensional temperature distribution, a plurality of temperature sensors that detect a spot temperature in a narrow range, and the like can be used.

  The image transfer operation in the above apparatus configuration will be described in the order of processes. While rotating the intermediate transfer member 1 in the direction of the arrow in FIG. 2, ink is ejected from the recording head 14 according to the image data to form an intermediate image on the surface layer 11 of the transfer belt 10 (intermediate image). Forming process). The image data is digital data supplied from the external device 57 and corresponding to the image to be recorded.

  In FIG. 4A, two types of dot areas show an example of an intermediate image immediately after being formed on the intermediate transfer body 1. The intermediate image 103 represents a high duty image (first intermediate image) with an average recorded duty of 90%, and the intermediate image 102 represents a low duty image (second intermediate image) with an average recorded duty of 20%. As described above, the first intermediate image and the second intermediate image mean respective ink images formed at different locations on the transfer body. Here, “printing duty” refers to the ratio of the actual number of ejections to the maximum number of ejections possible in one scan. For example, when one dot is formed by one ejection, the ratio of the number of dots actually formed to the number of pixels that can be recorded in one scanning area corresponds to the recording duty. The control unit 50 can acquire information related to the recording duty of the corresponding image by calculation from the image data. In this example, two types of recorded duty value images are included. There are two types, an image 102 with a recorded duty value of 20% and an image 103 with a recorded duty value of 90%. Here, in order to facilitate understanding, two types are used, but images having different recording duty values may be formed on the intermediate transfer member in one recording cycle.

  Before and after the first intermediate image forming process, the surface temperature of the intermediate transfer member is approximately equal to the environmental temperature (initial temperature). FIG. 5 is a graph plotting the temperatures of the intermediate transfer member surfaces forming the intermediate image 102 and the intermediate image 103 immediately after each process. In this example, the temperatures before and after the intermediate image forming process are such that the intermediate transfer member region (first region) that forms an image with a recording duty value of 90% is 25 ° C., and the intermediate temperature at which the recording duty value is 20%. The transfer body region (second region) is 25 ° C.

  The intermediate image formed on the intermediate transfer member 1 by the intermediate image forming process is heated by the heating unit 15 to evaporate the ink solvent and increase the viscosity (heating process). FIG. 4B shows a state in which the intermediate image 103 passes through the heating unit 15 and the intermediate image 102 passes through the heating unit 15 from now on.

  Next, in the transfer section, the transfer belt 10 and the recording medium 16 are sandwiched between the transfer roller 17 and the rotating body 12, and the transfer roller 17 rotates while applying an appropriate clamping pressure. As a result, the intermediate image moderately increased in viscosity by the heating process is transferred to the recording medium 16 (transfer process). FIG. 4C illustrates an area 103b (referred to as a first area) on the intermediate transfer body after the intermediate image 103 is transferred and an area 102b (second area) on the intermediate transfer body after the intermediate image 102 is transferred. Show).

  Due to the mechanism described above, the surface of the intermediate transfer member has a temperature difference according to the average recording duty of the entire image after heating and after transfer. In this example, as shown in FIG. 5, the temperature after the heating process is such that the average temperature of the first region where an image having a recording duty value of 90% is formed is 68.5 ° C., and the image having a recording duty value of 20%. The average temperature of the second region in which is formed is 86 ° C. Strictly speaking, the temperature varies depending on the location in one intermediate image, but here, the average temperature of the entire image is captured.

  In order to acquire temperature information, the temperature sensor 21 is used to detect the average temperature of the image forming area after the transfer process on the downstream side of the transfer roller 17. In this example, as shown in FIG. 5, the temperature after the transfer process is such that the average temperature of the first region in which an image having a recording duty value of 90% is formed is 64.5 ° C., and the image having a recording duty value of 20%. The average temperature of the second region in which is formed is 82 ° C.

  Next, the surface of the intermediate transfer body after each transfer is cooled by the cooling unit 19 so as to reach a desired temperature (cooling process). Since this cooling process is one of the points in this embodiment, it will be described in detail below.

  As shown in FIG. 4D, the cooling unit 19 is provided with a plurality of cooling elements that are divided into a plurality along a direction (Y direction) perpendicular to the belt moving direction (X direction). The arrangement of the cooling elements is not limited to one line, and may be a two-dimensional matrix arrangement. Each cooling element has a nozzle that ejects a cooling medium (gas or liquid) and sprays it onto the surface of the intermediate transfer member, and the cooling capacity is controlled by changing the flow rate and / or fluid temperature of the fluid ejected from the nozzle. it can. Alternatively, the cooling unit 19 may be a contact body that can be cooled by contacting the surface of the intermediate transfer body. In that case, a cooling mechanism such as a Peltier element for changing the temperature of the contact surface and a flow path through which the cooling medium flows is incorporated, and the cooling amount (surface temperature of the contact body) is individually controlled.

  Based on the temperature information detected by the temperature sensor 21, the control unit 50 adjusts the cooling amount to an appropriate amount in synchronism with the timing at which the transfer member surface of each passing image forming region is located immediately below the cooling unit 19. Control the capacity of the cooling element. The controller 50 controls the cooling amount of the cooling element (the amount of air blown from the nozzle and / or the cooling gas) so that the cooling amount on the surface of the intermediate transfer member having a high temperature is larger than the cooling amount on the surface of the intermediate transfer member having a low temperature. Temperature). As shown in FIG. 4D, when the low temperature first region and the high temperature second region pass through the cooling unit 19 in succession, the amount of cooling to the second region is higher than that of the first region. The cooling element is controlled so as to increase.

  Thus, cooling of the surface of each intermediate transfer member is individually controlled based on the temperature of the intermediate transfer member after being heated by the heating unit. As a result of the cooling process, the surface of the intermediate transfer member has a substantially uniform temperature distribution. The average temperature at that time is cooled so that the temperature of the intermediate transfer member itself does not promote the evaporation of the ink solvent in the next recording cycle, for example, the environmental temperature (initial temperature). In this example, as shown in FIG. 5, the temperature after the cooling process was such that the average temperature of the first region in which an image having a recording duty of 90% was formed was 25 ° C., and an image having a recording duty of 20% was formed. The average temperature in the second region is 25 ° C.

  Instead of acquiring the temperature information by the temperature sensor 21, the surface of each intermediate transfer member may be individually cooled based on the image data of the intermediate image. The control unit 50 can acquire information related to the average recording duty value of the image by calculation from the image data. A data table or a calculation formula indicating the correspondence relationship between the heating amount and the heated transfer member surface temperature is stored in advance in the memory of the control unit 50 for each recording duty. The control unit 50 analyzes the image data and obtains information related to the average recording duty of the image. Then, a cooling amount suitable for the obtained recording duty is acquired using a data table or a calculation formula. Information about the average recording duty of the entire image corresponding to the surface of the intermediate transfer body after each transfer is acquired from the image data. Control the cooling element so that the cooling amount of the intermediate transfer member surface that forms an intermediate image with a relatively low recording duty is larger than the cooling amount of the intermediate transfer member surface that forms an intermediate image with a relatively high recording duty. To do. As a result, the surface of the intermediate transfer member after transfer has a substantially uniform temperature distribution.

  As described above, a temperature difference occurs after heating in intermediate images (first area and second area) with different average recording duties. However, the temperature difference after cooling can be achieved by cooling the first area and the second area separately. Can be reduced. Therefore, it is possible to suppress the occurrence of transfer defects in the subsequent recording cycles.

<Embodiment 2>
A second embodiment of the present invention will be described. The difference from the first embodiment is a heating unit 15, and the other entire configuration of the recording apparatus is the same as that in FIG. 2. In the second embodiment, in the heating process, the plurality of intermediate images are not uniformly heated as in the first embodiment, but the heating amount is controlled to be different based on the average recording duty of each intermediate image. It is.

  Strictly speaking, the amount of heating required to obtain an “appropriate ink viscosity” after the heating process varies depending on the average recording duty of the intermediate image formed on the intermediate transfer member. “Moderate ink viscosity” refers to the ink viscosity before the transfer process in order to prevent “transfer defects” such as “image blurring” and “image blurring” from occurring in the image transferred to the recording medium, as described above. means.

The graph shown in FIG. 6 is a plot of the residual ratio (%) of the ink solvent with respect to the heating amount of the intermediate image, with the amount of solvent contained during ink adjustment as a reference (100%). In this example, the 90% recording duty area (A) and the 20% recording duty area (C) are respectively graphed. The ink solvent gradually evaporates during the heating process. When the remaining ratio (%) finally falls within a predetermined range, “appropriate ink viscosity” is reached. In this example, “appropriate ink viscosity” is in the range of 16% to 8% of the remaining amount of ink solvent. As can be seen from the graph, the heating amount required to obtain “appropriate ink viscosity” differs between (A) and (C). That is, in (C), “appropriate ink viscosity” is obtained within the range of the heating amounts E _{1 to} E ₂ , whereas in (A), “appropriate ink viscosity” is obtained within the range of E _{3 to} E _4. Become. As described above, the heating amount for achieving an “appropriate ink viscosity” varies depending on the recording duty.

  As in the first embodiment, when the heating unit uniformly heats the inside of the image, a heating amount is set so that both the minimum recorded duty image and the maximum recorded duty image have “appropriate ink viscosity”.

In the example of FIG. 6A, by providing a heating amount E between the heating amounts E _{3 to} E ₂ , all intermediate images having different recording duties have “appropriate ink viscosity”. However, although the maximum recording duty image and the minimum recording duty image are within the allowable range of “appropriate ink viscosity”, the ink viscosity is different. That is, the maximum recorded duty image has an ink viscosity (point i) that is close to the upper transfer failure area (ink viscosity that does not have sufficient viscosity), and conversely, the minimum recorded duty image has a lower transfer failure area (excessive viscosity). Ink viscosity (point ii). Therefore, when recording an image having a high gradation such as a photographic image, there is a possibility that the improvement of the recording quality may be hindered.

On the other hand, in the second embodiment, as shown in FIG. 6B, the ink viscosity (the remaining ratio (%) of the ink solvent after heating) that enables the transfer with the highest quality within the allowable range of “appropriate ink viscosity”. ) (Z%)). Then, instead of heating all the intermediate images uniformly, in each of the intermediate images formed on the intermediate transfer body, the residual ink solvent after heating is in the vicinity of Z% so that each of the intermediate images Control the amount of heating. In the example of FIG. 6B, (A) and (C) where the remaining ratio of the ink solvent is Z% are the heating amounts E _i and E _ii , respectively.

  The heating unit 15 gives different heating amounts according to the recording duty obtained in this way. Specifically, a data table or a calculation formula indicating the correspondence between the recorded duty and the necessary heating amount is stored in advance in the memory of the control unit 50. The control unit 50 analyzes the image data and obtains an average recording duty of each intermediate image. Then, a heating amount suitable for the obtained average recording duty is acquired using a data table or a calculation formula. If the heating unit 15 is controlled so as to obtain the acquired heating amount, all intermediate images have a distribution that is almost uniform with the most preferable ink viscosity among the “appropriate ink viscosities”. In addition, the surface temperature distribution of the intermediate transfer member after heating is different from that of the first embodiment, but it is also a non-uniform distribution having different temperatures depending on the location.

  As in the cooling unit 19, the heating unit 15 has heating elements arranged in a line along the Y direction as shown in FIG. 5 or is provided in a two-dimensional matrix. Each heating element has a built-in heater and can individually control the amount of heat generated. The control unit 50 drives the heating element to change the amount of heating by the heating unit 15 in synchronization with the movement of the intermediate image in the belt movement direction (X direction) when the intermediate image passes directly below the heating unit 15. Thus, an appropriate amount of heating is applied to each intermediate image.

  FIG. 7 is a graph showing the transition of the surface temperature of the intermediate transfer member immediately after each process, plotted for each average recording duty of each intermediate image. The temperature before and after the intermediate image forming process is uniformly 25 ° C. regardless of the recording duty, as in the first embodiment. The temperature before and after the intermediate image forming process is uniformly 25 ° C. regardless of the recording duty, as in the first embodiment. On the other hand, after the heating process, the average temperature of the area (first area) in which an image having an average recording duty of 90% is formed is 69 ° C., and the area in which an image having a recording duty of 20% is formed (second area). The average temperature of the region is 42 ° C.

  As described above, the second embodiment controls the heating amount of the region where the intermediate image is formed based on the image data. In the subsequent cooling process, the cooling of each region is individually controlled so as to reduce the temperature difference that varies depending on the location of the intermediate transfer member generated in the heating process. Thereby, in addition to the effects of the first embodiment, the following effects can be obtained. That is, by controlling the heating amount of each region where the intermediate image is formed, the residual amount of ink solvent after heating of all the different average recorded duty images is uniformly around Z% as shown in FIG. 6B. It becomes. That is, since it is uniformized with the most preferable ink viscosity among “appropriate ink viscosity”, the recording quality of an image having high gradation such as a photographic image is further improved as compared with the first embodiment. In addition, from the viewpoint of energy consumption, since the overall energy is reduced by the amount of heating for the low duty image, there is an advantage that the energy consumption is lower than that in the first embodiment.

DESCRIPTION OF SYMBOLS 1 Intermediate transfer body 12 Rotating body 14 Recording head 15 Heating part (corresponding to heating means)
16 Recording medium 17 Transfer roller (corresponding to transfer means)
19 Cooling unit (corresponding to cooling means)
100 Control unit

Claims (9)

An intermediate transfer member;
A recording head that forms a plurality of intermediate images by applying ink to the intermediate transfer member;
Heating means for heating the intermediate transfer body on which the intermediate image is formed;
Transfer means for transferring the intermediate image formed on the intermediate transfer body heated by the heating means to a recording medium;
A cooling means for cooling the intermediate transfer member heated by the heating means;
A recording device comprising:
The cooling unit is configured to reduce a temperature difference between the first region where the first intermediate image is formed and the second region where the second intermediate image following the first intermediate image is formed. According to the recording apparatus, the cooling of the first area and the second area is individually controlled.   The recording apparatus according to claim 1, wherein the cooling unit controls cooling based on temperature or image data of the intermediate transfer body after being heated by the heating unit.   The cooling means acquires information relating to an average recording duty of the first intermediate image and the second intermediate image, and a cooling amount of an area where an intermediate image having a relatively low average recording duty is formed is the average The recording apparatus according to claim 2, wherein the cooling is performed so as to be larger than a cooling amount of an area where an intermediate image having a relatively high recording duty is formed.   Based on the temperature of the first area and the second area after being heated by the heating means, the cooling means has a higher cooling amount in the high temperature area than in the low temperature area. The recording apparatus according to claim 2, wherein the recording apparatus is cooled as described above.   The cooling means sets the cooling amount for each average recording duty of the intermediate image by using a data table or a calculation formula showing a correspondence relationship between the heating amount and the surface temperature of the transfer body after heating. Item 5. The recording device according to any one of Items 1 to 4.   The cooling means has a plurality of cooling elements capable of controlling the amount of cooling, and each cooling element sprays a fluid from the nozzle onto the surface of the intermediate transfer member, or a contact member on the surface of the intermediate transfer member. The recording apparatus according to claim 1, wherein the recording apparatus is brought into contact with the recording apparatus.   The heating means controls the heating amount of the first region based on the first image data for forming the first intermediate image, and converts the second image data for forming the second intermediate image. The recording apparatus according to claim 1, wherein a heating amount of the second area is controlled based on the recording area.   The heating means acquires information relating to an average recording duty for each of the first image data and the second image data, and a heating amount in a region where an intermediate image having a relatively high average recording duty is formed is the average The recording apparatus according to claim 7, wherein heating is performed so as to be larger than a heating amount of an area where an intermediate image having a relatively low recording duty is formed.   The recording apparatus according to claim 7, wherein the heating unit includes a plurality of heating elements capable of controlling a heating amount.

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