JP3593207B2 - Fixing device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a fixing device in an image forming apparatus.
[0002]
[Prior art]
As a conventional fixing device, a fixing device having a pair of a heating roller and a pressure roller and fixing a toner image on a sheet onto which a toner image has been transferred at a nip portion thereof is well known. However, such a fixing device has a short nip time for fixing. Therefore, when the toner is melted at a set fixing temperature with respect to a heat amount (Q) necessary for sufficiently dissolving the toner and fixing it on paper, As the temperature of the toner rises rapidly, the viscosity of a low melting point toner such as a color toner greatly decreases, and the adhesive force exceeds the cohesive force at the heating roller / toner interface. There is a problem that the offset phenomenon easily occurs.
[0003]
Therefore, in order to solve such a problem, an example disclosed in Japanese Patent Application Laid-Open No. 6-318001 has been proposed as an example. This is common to the embodiment of the invention of this application. It will be described with reference to FIG. It comprises an endless fixing belt 3 stretched between a heating roller 1 and a driven roller 2, and a pressure roller 4 provided opposite to the driven roller 2.
[0003]
Such a fixing device can preheat the toner and the paper via the fixing belt 3 heated by the heating roller 1 to raise the temperature of the toner in advance, thereby lowering the fixing temperature and setting the nip portion. By suppressing the temperature of the toner on the paper separated from the fixing belt 3 at the exit of the above, oilless or trace amount of oil can be applied, and the occurrence of the hot offset phenomenon can be prevented.
[0004]
[Problems to be solved by the invention]
However, in such a fixing device, in the preheating step of preheating the toner and the paper, the fixing belt 3 is preheated by radiant heat, so that it is necessary to bring the fixing belt 3 and the unfixed toner image sufficiently close to each other. Therefore, the unfixed toner image comes into contact with the fixing belt 3 due to the bending of the sheet, and the image is disturbed. In addition, it is necessary to increase the length of the sheet conveyance path in the preheating step in order to obtain the preheating effect. However, there is a problem that the entire device becomes large.
[0005]
Accordingly, an object of the present invention is to solve the problems of the conventional fixing device as described above, and to prevent the hot offset phenomenon from occurring. Therefore, in the preheating step of preheating the toner and the paper, the fixing belt and the unfixed belt are unfixed. It is not necessary to bring the toner image sufficiently close to the fixing belt, so that the unfixed toner image does not come into contact with the fixing belt due to the bending of the paper and the like, and the image is not disturbed. Accordingly, it is an object of the present invention to provide a fixing device that does not need to be lengthened and does not increase the size of the entire apparatus.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, the present invention comprises an endless fixing belt stretched between a heating roller and a driven roller, and a pressure roller provided opposite to the driven roller. in the fixing device, a upstream side of the inlet of the fixing nip portion an auxiliary roller which presses the fixing belt, is provided between the heating roller and the driven roller, a heating roller and a pressure low la, a heat source It is characterized by having been provided.
[0007]
According to a second aspect of the present invention, an auxiliary roller capable of coming into contact with and separating from the fixing belt is provided at the entrance side of the fixing nip portion, and when the glossy image mode is selected, the auxiliary roller is brought into contact with the fixing belt, and When the glossy image mode is selected, the auxiliary roller is separated from the fixing belt.
[0008]
According to a third aspect of the present invention, in the fixing device according to the first or second aspect, the auxiliary roller is provided near an entrance of the fixing nip portion.
[0009]
According to a fourth aspect of the invention, in the fixing device according to any one of claims 1 to 3, a detecting means for detecting the temperature of the heating roller, at a position in contact with the surface of the heat roller in the fixing belt inner It is characterized by having been provided.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described with reference to the drawings. In each of the embodiments, the same parts as those of the related art are denoted by the same reference numerals, and the description thereof will be omitted.
[0011]
In the first embodiment shown in FIG. 1, an auxiliary roller 5 that presses against the fixing belt 3 is provided upstream of the entrance of the fixing nip portion, and heating sources 6 and 7 are provided for the heating roller 1 and the pressing roller 4 respectively. Reference numeral 8 denotes an entrance guide plate, and 9 denotes a transport guide plate .
[0012]
In the first embodiment, when performing the fixing operation, the rollers 1, 2, 4 and 5 are rotated to move the fixing belt 3 in the direction of the arrow, and the heating sources 6 and 7 are turned on. In the first embodiment in such a state, an unfixed toner image is transferred through a charging device, an exposure device, a developing device, and a transferring process in a transfer device (not shown). 5, a fixing nip portion formed between the driven roller 2 and the pressure roller 4 along the conveyance guide plate 9 and between the fixing inlet and the fixing outlet of the fixing belt 3. The toner image is fixed on paper by heating and pressing.
[0013]
At this time, the fixing belt 3 is heated by the heating roller 1 and preheats the toner to raise the temperature. Therefore, the amount of heat necessary to sufficiently melt the unfixed toner in the fixing nip portion and fix the toner on the paper. In contrast to (Q), the fixing temperature can be set lower. Therefore, at the fixing outlet of the fixing belt 3, the interface temperature between the fixing belt and the toner is sufficiently low. Further, at the time of fixing, the toner image is heated from both the front and back sides by the fixing belt 3 and the pressure roller 4, so that the temperature difference in the thickness direction of the toner is eliminated and the excessive melting of the toner is prevented. Furthermore, since no heating source is provided inside the driven roller 2 located on the fixing surface side, the self-cooling action of the fixing belt 3 at the fixing nip reduces the fixing belt / toner interface temperature. These prevent the occurrence of hot offset.
[0014]
In the second embodiment shown in FIG. 2, the auxiliary roller 5 is provided so as to be able to contact and separate from the fixing belt 3, and the auxiliary roller 5 is moved upward to contact the fixing belt 3 shown in the drawing, The second embodiment is different from the first embodiment in that a moving unit 10 for moving between the positions is provided.
[0015]
In the second embodiment, the fixing operation is performed in the same manner as in the first embodiment. However, when the glossy image mode is selected, the moving unit 10 is turned off, and the auxiliary roller 5 is pushed up by the spring 11. When the non-glossy image mode is selected by bringing the auxiliary roller 5 into contact with the fixing belt 3, the moving unit 10 is turned off to separate the auxiliary roller 5 from the fixing belt.
[0016]
When the glossy image mode is selected and the auxiliary roller 5 is brought into contact with the fixing belt 3 as described above, the unfixed toner having the uneven surface receives sufficient heat and is fused and fixed. Sufficient smoothness is formed in the fixing nip portion by the surface accuracy of the fixing belt 3, and the glossiness of the image is increased to obtain a glossy glossy image. Next, when the non-glossy image mode is selected and the auxiliary roller 5 is separated from the fixing belt 3, the unfixed toner having the uneven surface receives less heat than in the gloss image mode, and the toner surface is fixed. Since the toner is not sufficiently melted in the nip portion and is fixed on the paper and peeled off from the fixing belt 3, sufficient smoothness cannot be formed, and the glossiness of the image is low and the glossy non-glossy image is low. Can be obtained.
[0017]
The third and fourth embodiments shown in FIGS. 3 and 4 are different from the first and second embodiments in that the auxiliary roller 5 is provided near the entrance of the fixing nip portion, and are otherwise the same. .
[0018]
In the third and fourth embodiments, the fixing operation is performed in the same manner as in the first and second embodiments. However, since the auxiliary roller 5 is provided near the entrance of the fixing nip portion, After passing through the auxiliary roller 5, due to its rigidity, it is inserted into the entrance of the fixing nip portion in close contact with the fixing belt 3, so that uneven gloss of the image does not occur.
[0019]
In the fifth embodiment shown in FIG. 5, in each of the above embodiments, a detecting means 12 for detecting the temperature of the heating roller 1, for example, a thermistor, is provided inside the fixing belt at a position in contact with the surface of the heating roller 1. In this regard, the present embodiment differs from the embodiments in that the other embodiments are the same.
[0020]
In the fifth embodiment, the temperature of the heating roller 1 is detected in the same manner as in the related art, and when the temperature exceeds a set value, the temperature of the heating roller 1 is adjusted to keep the fixing belt 3 at an appropriate temperature. It will be. At this time, the fixing belt 3 does not come into contact with the detecting means 12, so that it does not wear due to this contact.
[0021]
【The invention's effect】
The invention has been described above, the invention described in 請 Motomeko 1, and endless fixing belt that is stretched between the heating roller and the driven roller, pressure provided opposite the driven roller in the fixing device with a pressure roller, a upstream side of the inlet of the fixing nip portion an auxiliary roller which presses the fixing belt, it is provided between the heating roller and the driven roller, the heating roller and the pressure low La Since the heating source is provided, the hot offset phenomenon does not occur. Therefore, in the preheating step of preheating the toner and the paper, it is not necessary to bring the fixing belt and the unfixed toner image sufficiently close to each other. There is no need for an unfixed toner image to come into contact with the fixing belt due to paper deflection or the like, causing image disturbance, and it is not necessary to increase the length of the paper transport path in the preheating step. Body there is an effect that there is no such thing as that becomes large.
[0022]
According to the invention described in claim 2, an auxiliary roller that can be separated from and separated from the fixing belt is provided at the entrance side of the fixing nip portion, and when the glossy image mode is selected, the auxiliary roller comes into contact with the fixing belt, When the non-glossy image mode is selected, the auxiliary roller is separated from the fixing belt.Therefore, when the auxiliary roller is brought into contact with the fixing belt, the unfixed toner receives sufficient heat and is fused and fixed. In the fixing nip part, sufficient smoothness is formed by the surface accuracy of the fixing belt, the glossiness of the image is increased and a glossy glossy image is obtained, and when the auxiliary roller is separated from the fixing belt, the unfixed toner becomes glossy Receives less heat than in the image mode, and the toner surface is fixed to the paper and released from the fixing belt without being sufficiently melted in the fixing nip, so that sufficient smoothness is obtained. Can not be formed, the glossiness of an image is kept low there is the effect that non-glossy image without gloss will be obtained.
[0023]
According to a third aspect of the present invention, the auxiliary roller is provided in the vicinity of the entrance of the fixing nip, and the rigidity of the sheet after passing through the auxiliary roller causes the paper to come into close contact with the fixing belt and to enter the entrance of the fixing nip. Since the image is inserted, there is an effect that uneven gloss of an image does not occur.
[0024]
According to the fourth aspect of the present invention, since the detecting means for detecting the temperature of the heating roller is provided at a position in contact with the surface of the heating roller inside the fixing belt, the temperature of the heating roller is detected and the temperature is set. If it exceeds the value, the temperature of the heating roller is adjusted to keep the fixing belt at an appropriate temperature. At this time, however, the fixing belt does not come into contact with the detecting means, so that there is an effect that the fixing belt does not wear.
[Brief description of the drawings]
FIG. 1 is a schematic front view of a first embodiment of the present invention.
FIG. 2 is a schematic front view of a second embodiment of the present invention.
FIG. 3 is a schematic front view of a third embodiment of the present invention.
FIG. 4 is a schematic front view of a fourth embodiment of the present invention.
FIG. 5 is a schematic front view of a main part according to a fifth embodiment of the present invention.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 heating roller 2 driven roller 3 fixing belt 4 pressure roller 5 auxiliary roller 6 heating source 7 heating source 8 entrance guide plate 9 transport guide plate 10 moving means 11 spring 12 detection means

Claims (4)

In a fixing device having an endless fixing belt stretched between a heating roller and a driven roller, and a pressing roller provided opposite to the driven roller, an auxiliary roller pressed against the fixing belt is fixed. a upstream of the inlet of the nip portion, is provided between the heating roller and the driven roller, a heating roller and a pressure low la, a fixing device, characterized in that a heat source. In a fixing device having an endless fixing belt stretched between a heating roller and a driven roller, and a pressure roller provided opposite to the driven roller, an auxiliary device capable of coming into contact with and separating from the fixing belt. A roller should be provided on the entrance side of the fixing nip, and when the glossy image mode is selected, the auxiliary roller should be in contact with the fixing belt, and when the non-glossy image mode is selected, the auxiliary roller should be separated from the fixing belt. A fixing device. The fixing device according to claim 1, wherein the auxiliary roller is provided near an entrance of the fixing nip portion. Wherein the detecting means for detecting the temperature of the heat roller fixing device according to any one of claims 1 to 3, characterized in that provided at a position in contact with the surface of the heat roller in the fixing belt inner side.

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