JP2005300589A - Fixing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing apparatus capable of preventing the occurrence of image disturbance by setting and arranging constituent members of the fixing apparatus so that a prescribed relationship is fulfilled. <P>SOLUTION: The fixing apparatus includes a fixing belt 41, a fixing roller 44 and a pressurizing roller 45 forming a fixing nip part N, a heating plate 47 fixed and installed so as to come in contact with an inner periphery surface of the fixing belt 41 and a pressurizing belt 48 laid across two or more pressing rollers 56 to 58 in a tensioned condition , brought into a pressurized contact with an outer periphery surface of the fixing belt 41 and rotated following the fixing belt 41. The constituent members are set and arranged so that when the distance from a rotational center of the pressing roller 56, which is placed most downstream among the two or more pressing rollers 56 to 58, to the most upstream part of the fixing nip N is L (mm) and the temperature of the heating plate is T (°C), the relationship of L×(T-97)/S≤4.7 is fulfilled. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fixing device of a type in which a recording paper carrying a toner image to be fixed is peeled after being conveyed while being in close contact with a rotating endless fixing belt that is heated and rotated. The present invention relates to a fixing device capable of preventing image disturbance caused by water vapor generated from a recording sheet during fixing and being interposed between the recording sheet and the fixing belt.

Japanese Patent No. 2813297 JP-A-9-281822 JP 2001-166617 A Japanese Patent Laid-Open No. 6-314041 JP-A-9-160405

  In general, in a color electrophotographic image forming apparatus, it is necessary to obtain a high image gloss to improve color reproducibility. For this reason, in a fixing device in which a recording sheet having an unfixed toner image is sandwiched and heated by fixing means such as a pair of fixing rollers or a fixing roller and a fixing belt or a pair of fixing belts, the temperature of the fixing roller or fixing belt is increased. Thus, the image glossiness is increased. However, such a high fixing temperature tends to cause toner offset.

  In order to avoid such toner offset, in a fixing device having a fixing belt stretched between a heating roller and a driven roller, and a pressure roller provided opposite to the driven roller, formed by the driven roller and the pressure roller. A fixing device has been proposed in which toner and recording paper are preheated with radiant heat from the fixing belt on the upstream side where the recording paper enters the fixing nip portion, so that the set temperature of the fixing belt can be lowered (for example, Patent Document 1).

  However, in order to perform high-speed fixing using a preheating means using radiant heat, the entire apparatus becomes large. In view of this, there has been proposed a fixing device in which the recording paper is brought into contact with the fixing belt by preheating means to perform preheating using heat conduction to reduce the size of the apparatus (see, for example, Patent Documents 2 to 5). ).

  As an example of a fixing device using preheating means using such heat conduction, in Patent Document 2, an endless fixing belt stretched between a heating roller and a driven roller, and the driven roller are opposed to each other. A fixing device provided with an auxiliary roller that is in pressure contact with the fixing belt upstream of the fixing nip formed between the fixing belt supported by the driven roller and the pressure roller. Presented.

  In Patent Document 3, a belt member is provided that includes a belt member stretched between a first fixing roller and a heat generating roller, and a second fixing roller that forms a nip portion with the first fixing roller. A sheet-like heating element that heats the belt member by abutting from the inside is provided, and a transfer material is electrostatically brought into close contact with the belt member for preliminary heating, and a toner image on the recording paper is formed at the nip portion. A fixing device for fixing is presented.

  Furthermore, in Patent Document 4, a material to be heated is introduced into the pressure nip portion, and the material to be heated is nipped and conveyed to the pressure nip portion together with the heat resistant film, whereby the heat of the heating body is passed through the heat resistant film. A fixing device is proposed in which at least one of a plurality of heat generation distribution peaks of the heating body is provided on the upstream side of the heated material conveyance direction.

  Furthermore, in Patent Document 5, an endless fixing belt stretched between a first roller and a second roller provided in parallel, a third roller that contacts the outside of the fixing belt, and an inside of the fixing belt. A heating member provided at a predetermined position upstream of the nip portion with the third roller, and a pressing member provided inside the fixing belt that presses the third roller at a position where the fixing belt starts to be wound around the third roller; A fixing device is provided.

  However, in each of the above prior arts, water vapor is generated from the recording paper heated in the preheating unit, and floating occurs due to the water vapor being interposed between the recording paper and the fixing belt. The toner is transferred from the recording paper to the fixing belt. When the transferred toner is subsequently transferred again from the fixing belt to the recording paper at the fixing nip portion, the toner is displaced from the position on the recording paper that existed before the transfer, so that the image is disturbed. It was happening.

  Accordingly, the present invention has been made in view of the above-described problems of the prior art, and prevents the occurrence of image distortion by arranging and arranging the constituent members of the fixing device so as to satisfy a predetermined relationship. It is an object of the present invention to provide a fixing device capable of performing the above-described operation.

  In order to achieve the above object, a fixing device according to the present invention is arranged so as to face each other through an endless fixing belt that is stretched around a plurality of rollers and rotates in a predetermined direction. A fixing roller and a pressure roller that form a fixing nip portion in the contact area, and a fixed arrangement so as to come into contact with the inner peripheral surface of the fixing belt at the upstream side of the fixing nip portion in the rotation direction of the fixing belt. A heating plate, a plurality of pressing rollers disposed opposite to the heating plate, and stretched by the plurality of pressing rollers, and in pressure contact with the outer peripheral surface of the fixing belt, are driven by the fixing belt. An endless pressing belt that rotates in a moving manner, and a recording sheet carrying a toner image is conveyed in a predetermined direction and guided between the fixing belt and the pressing belt. Along the recording sheet conveyance direction, among the plurality of pressing rollers, the distance from the rotation center of the pressing roller disposed at the most downstream side to the most upstream portion of the fixing nip portion is L (mm), and the process speed is S ( mm / s), and the heating plate temperature is T (° C.), the fixing device is set and arranged so as to satisfy the relationship L × (T−97) /S≦4.7. To do.

  In general, in a fixing device having a heating means upstream of the fixing nip portion and preheating the fixing belt by the heating means, water vapor is generated from the recording paper heated by the fixing belt, and the water vapor is fixed. By interposing between the belt and the recording paper, the recording paper may float and image distortion such as image displacement may occur.

  The present inventors have found that the image turbulence caused by the generation of such water vapor has a correlation with the product of time (L / S) and temperature (T), and further satisfies such a predetermined relationship to satisfy the predetermined relationship. It has been found that disturbance can be prevented.

  Therefore, the fixing device according to the present invention configured as described above includes an endless fixing belt, a fixing roller and a pressure roller that are arranged so as to be pressed against each other via the fixing belt, and a fixing nip portion. Also, on the upstream side in the rotation direction of the fixing belt, a heating plate fixedly disposed so as to be in contact with the inner peripheral surface of the fixing belt, a plurality of pressing rollers disposed to face the heating plate, and the plurality of these An endless pressing belt which is stretched by a pressing roller and pressed against the outer peripheral surface of the fixing belt and rotates in accordance with the fixing belt. In the fixing device that is conveyed between the fixing belt and the pressure belt, rotation of the pressure roller disposed at the most downstream side among the plurality of pressure rollers along the recording sheet conveyance direction. L × (T−97) / S ≦ 4 where L (mm) is the distance from the center to the most upstream part of the fixing nip, S (mm / s) is the process speed, and T (° C.) is the heating plate temperature. .7 is set and arranged so as to satisfy the predetermined relationship, and by setting and arranging the constituent members of the fixing device so as to satisfy the above-described predetermined relationship, generation of excessive water vapor is suppressed and the fixing belt is also arranged. Therefore, the recording paper can enter the fixing nip portion before the recording paper floats up, and image disturbance can be prevented.

  Further, on the downstream side of the fixing nip portion in the sheet conveyance direction, a peeling unit may be further provided that peels after the recording sheet is conveyed by a predetermined distance in a state of being in close contact with the outer peripheral surface of the fixing belt.

  In this case, the fixing nip portion further includes a peeling unit that transports the recording paper a predetermined distance in a state of being in close contact with the outer peripheral surface of the fixing belt, and then peels the recording paper in the downstream direction in the paper transport direction. The fixed image on the recording paper after passing through the part can be peeled off after being stabilized, thereby improving the image quality.

  Furthermore, the peeling means may include a cooling means for cooling the recording paper to a predetermined temperature.

  In this case, since the peeling means includes a cooling means for cooling the recording paper to a predetermined temperature, stable fixing of the fixed image onto the recording paper can be promoted.

  The fixing device according to the present invention is disposed so as to face an endless fixing belt that is stretched around a plurality of rollers and rotates in a predetermined direction so as to be in pressure contact with each other via the fixing belt. A fixing roller and a pressure roller that form a fixing nip portion; a heating plate fixedly arranged in contact with the inner peripheral surface of the fixing belt at an upstream side of the fixing nip portion in the rotation direction of the fixing belt; A plurality of pressing rollers disposed opposite to the plate, and stretched by the plurality of pressing rollers, and in contact with the outer peripheral surface of the fixing belt, are rotated endlessly by the fixing belt. A fixing device that includes a pressing belt, conveys a recording sheet carrying a toner image in a predetermined direction, and guides the recording sheet between the fixing belt and the pressing belt; Along the length of the fixing belt from the rotation center of the pressing roller arranged at the most downstream side to the most upstream part of the fixing nip among the plurality of pressing rollers, and the traveling speed of the fixing belt as S ( mm / s), and the fixing belt temperature is T (° C.), the fixing belt is set and arranged so as to satisfy the relationship of L × (T−97) /S≦4.7. And

  In the fixing device according to the present invention configured as described above, from the rotation center of the pressing roller arranged at the most downstream side among the plurality of pressing rollers along the traveling direction of the fixing belt to the most upstream portion of the fixing nip. When the length of the fixing belt is L (mm), the traveling speed of the fixing belt is S (mm / s), and the temperature of the fixing belt is T (° C.), the fixing belt is L × (T−97) / S. Since it is set and arranged so as to satisfy the predetermined relationship of ≦ 4.7, a fixing device capable of preventing the occurrence of image distortion by suppressing the generation of excessive water vapor by the simple setting and arrangement of the fixing belt. It can be easily realized.

  According to the present invention, the constituent members of the fixing device are set and arranged so as to satisfy a predetermined relationship, thereby suppressing the generation of excessive water vapor and fixing the recording paper before the recording paper floats from the fixing belt. And the occurrence of image disturbance can be prevented.

Embodiments of the present invention will be described below with reference to the drawings.
<Embodiment>

  First, a schematic configuration of a fixing device according to the present invention will be described with reference to FIG. FIG. 1 is a schematic configuration diagram showing an embodiment of an image forming apparatus according to the present invention.

  As shown in FIG. 1, a fixing device 10 embodying the present invention includes an endless fixing belt 41 that rotates in a predetermined direction (for example, counterclockwise), and the fixing belt 41 is a first heating roller. 42, a second heating roller 50 disposed below the first heating roller 42, a fixing roller 44 disposed substantially parallel to the second heating roller 50, and above the first heating roller 42. It is stretched by the idler roller 51 arranged. Further, a pressure roller 45 is provided to face the fixing roller 44 through the fixing belt 41, and a fixing nip portion N is configured by the contact area. In a region between the fixing roller 44 and the second heating roller 50, a heating plate 47 having a predetermined curvature comes into pressure contact with the inner peripheral surface of the fixing belt 41 suspended between these rollers 44 and 50. It is arranged like this.

  Further, a pressing belt 48 that rotates in a direction opposite to the fixing belt 41 (for example, clockwise) is provided, and the pressing belt 48 includes pressing rollers 45 and pressing rollers 56 to 58 disposed to face the heating plate 47. And a tension roller 60, and is configured to contact the fixing belt 41 in a region extending from the heating plate 47 to the fixing nip portion N.

  The fixing belt 41 and the pressing belt 48 may be stretched so as to extend further downstream in the sheet conveyance direction of the fixing nip portion N, and the recording sheet P is closely attached to the outer peripheral surface of the fixing belt 41. You may comprise so that it peels, after conveying only a predetermined distance in the made state. Further, if necessary, a cooling device for cooling the recording paper P on which the toner image T is heated and fixed may be disposed downstream of the fixing nip portion N in the paper conveyance direction. By separating the sheet after being conveyed by a predetermined distance in this way, the fixed image on the recording paper P after passing through the fixing nip portion N is stabilized, and the image quality can be improved. Further, by providing a cooling device, it is possible to promote stable fixing of a fixed image on the recording paper P.

  Next, details of each component of the fixing device 10 according to the present invention will be described.

  First, the fixing belt 41 is made of an elastic material such as a silicone copolymer (hardness: for example, 24 °) having a thickness of about 60 μm on a belt base material having a thickness of about 50 μm made of polyimide containing carbon black. It has a structure in which layers are formed in this order.

  For example, the first heating roller 42 includes a cylindrical metal roller having an outer diameter of 80 to 100 mm and a heating source such as a halogen lamp disposed therein, and heats the fixing belt 41 from the outer peripheral surface side. . By using the heating means for heating from the outer peripheral surface side of the fixing belt 41 as described above, even if a relatively thick belt is used as the fixing belt 41, the outer peripheral surface of the fixing belt is easily heated to a desired temperature. be able to. On the other hand, the second heating roller 50 has a heating source such as a halogen lamp inside a cylindrical metal (aluminum or the like) roller having an outer diameter of 50 to 60 mm, for example. Heat from the inner surface. And each heating temperature is controlled based on the detection result of the temperature detection sensor installed in order to detect each surface temperature of the 1st and 2nd heating rollers 42 and 50. As shown in FIG.

  Further, on the outer peripheral side of the first heating roller 42, a winding web type cleaning device 60 for cleaning in contact with the roller surface is disposed. The cleaning device 60 uses a cleaning web 52 impregnated with a release agent such as silicone oil. In the process of feeding the web 52 by a predetermined amount from the feeding roller and winding it on the winding roller, The web 52 is pressed against the surface of the first heating roller 42 by a roller 53. As a result, the toner transferred and adhered from the fixing belt 41 to the first heating roller 42 is removed and cleaned, and a small amount of a release agent is applied to the surface of the first heating roller 42 so as to be applied to the outer peripheral surface of the fixing belt 41. It is designed to supply a transition.

The fixing roller 44 and the pressure roller 45 are, for example, a cylindrical metal (aluminum or the like) roller base having an outer diameter of 95 mm and a thickness of 6 mm, and a thickness made of silicone rubber (hardness: about 17 °, for example). It has a structure in which a heat-resistant elastic layer having a thickness of about 6 mm is formed. The fixing roller 44 is rotatably supported in a fixed state, and the pressure roller 45 is fixed to a predetermined pressure (for example, a nip load of about 1500 N by applying a load of about 1500 N) by a pressure mechanism (not shown). At about 0.3 N / mm ² ) and pressed against the fixing roller 44 via the fixing belt 41, and the width of the fixing nip portion N (length in the roller rotation direction) is about 20 mm. ing.

Further, the fixing roller 44 and the pressure roller 45 have a heating source such as a halogen lamp in their internal space, and are heated during so-called warm-up and fixing operations that raise the rollers 44 and 45 to the temperature during the fixing operation. Like to do. Each heating source of the fixing roller 44 and the pressure roller 45 performs each heating operation (power supply) based on the detection result of the temperature detection sensor installed to detect the surface temperature of each of the rollers 44 and 45. To be controlled.
The surface of the heating plate 47 in contact with the fixing belt 41 is formed in a curved mirror surface having a curvature of, for example, about R900 along the belt rotation direction (counterclockwise in the drawing in the present embodiment). The aluminum substrate having a thickness of about 3 mm and a rubber heater which is disposed on the surface not in contact with the fixing belt 41 and heats the heating plate 47 to a predetermined temperature. The heating plate 47 has a length along the fixing belt 41 of about 200 to 400 mm, and a region from a position near the downstream side of the second heating roller 50 to a position near the upstream side of the fixing nip N. In FIG. 3, the fixing belt 41 is disposed along the fixing belt 41.

  The pressing belt 48 has a structure in which an elastic layer made of silicone rubber or the like having a thickness of about 20 μm is laminated in this order on an endless belt base material made of polyimide or the like having a thickness of about 130 μm. Is approximately the same width as the fixing belt 41. The pressing belt 48 is stretched between three pressing rollers 56, 57, 58, a tension roller 60, and a pressure roller 45, and these pressing rollers 56 to 58 are interposed between the pressing rollers 56 to 58. 58 is brought into pressure contact with the outer peripheral surface of the fixing belt 41 supported by the heating plate 47, and is rotated by being driven by the fixing belt 41.

  Of the three pressing rolls 56, 57, 58, the two pressing rollers 57, 58 arranged on the upstream side are, for example, a metal roller core material having an outer diameter of 30 to 40 mm and a thickness made of silicone rubber or the like. Is formed with an elastic layer of about 4 mm, and the pressing roller 56 disposed on the most downstream side is disposed in the vicinity of the pressing roller 45. For example, a metal roller core having an outer diameter of 10 to 20 mm An elastic layer made of silicone rubber or the like and having a thickness of about 4 mm is formed on the material.

  These pressing rollers 56, 57, and 58 are connected to the heating plate 47 via the fixing belt 41 and the pressing belt 48 with a predetermined load (for example, the load is 100N to 200N) by a known pressing mechanism using a spring or the like. Are in pressure contact. The tension roller 60 is a metal roller made of stainless steel or the like. The pressure rollers 56 to 58, the tension roller 60, and the pressure roller 45 are all supported by a known displacement mechanism so as to be able to contact and separate from the fixing belt 41 supported by the heating plate 47. For example, it is displaced to a position away from the fixing belt 41 during warm-up.

In the present embodiment, the plurality of pressing rollers 56 to 58 are arranged as the introduction portion pressing roller 58, the intermediate portion pressing roller 57, and the outlet portion pressing roller 56, but the number of arrangement is limited to three. However, it may be increased or decreased as appropriate. In addition, the downstream pressure roller 56 is smaller than the other two pressure rollers, but this is due to physical restrictions in arrangement, and all of these pressure rollers are used. You may comprise by the same magnitude | size.
In the fixing device 10 configured as described above, the fixing belt 41 is heated to a predetermined temperature by the first heating roller 42 and the second heating roller 50. The recording paper P inserted from the recording paper guide 49 is sandwiched between the fixing belt 41 and the pressing belt 48 and preheated on the heating plate 47, and then the fixing nip portion N between the fixing roller 44 and the pressure roller 45. The toner image T on the recording paper P is fixed by being heated and pressurized at.

  Specifically, first, the toner image T is presupposed on the recording paper P in the preheating area A that substantially corresponds to the area where the heating plate 47 extends. In this assumption, the toner image T is sufficiently melted to be fixed to the recording paper P. Further, in the nip region C corresponding to the fixing nip portion N, the toner image T is pressurized and fixed on the recording paper P.

  At this time, a non-pressurization region B that is an intermediate region between the preheating region A and the nip region C (region corresponding to the rotation center of the pressure roller 56 disposed on the most downstream side to the most upstream portion of the fixing nip portion N). In this case, almost no force can be expected to press the recording paper P against the fixing belt 41, and the fixing belt 41 does not come into contact with a position restricting member such as the heating plate 47. . In this non-pressurized area B, if the amount of water vapor generated from the recording paper P exceeds a predetermined value, floating occurs between the fixing belt 41 and the recording paper P, resulting in image disturbance.

  This image disturbance is caused by a part of the toner image T being transferred from the recording paper P to the fixing belt 41 in the preheating process in the preheating area A, and then the recording paper P entering the fixing nip portion N, and the transferred toner image T. This occurs because when the toner image is re-transferred from the fixing belt 41 to the recording paper P, it does not return to a position that completely coincides with the position that was not fixed. At this time, the reason why the toner image T does not re-transfer to the completely coincident location is that after the fixing belt 41 and the recording paper P contact each other, they do not completely pass through the same moving path, which is the reason for the recording. It is considered that the recording paper P is lifted from the fixing belt 41 by water vapor generated from the paper P.

  In order to solve this image disturbance, first, in the preheating process, a pressing belt 48 and pressing rollers 56 to 58 are provided in a portion where the recording paper P is brought into contact with the fixing belt 41 and the recording paper P from the fixing belt 41 is provided. It is effective to prevent the floating. However, some types of recording paper (for example, coated paper) have relatively poor adhesion to the fixing belt 41, and some still cause image distortion. This is because the recording paper P floats from the fixing belt 41 in the non-pressurized area B as described above. In this non-pressurized area B, the position of the fixing belt 41 comes into contact with the back surface of the fixing belt 41. It is physically impossible to arrange a position restricting member such as a heating plate 47 that restricts the temperature, and since the straight path extends to the nip region C, the fixing belt 41 itself is wavy due to a temperature difference in the fixing belt 41. This is considered to occur because it is easy to occur and the pressing force due to the tension does not act between the fixing belt 41 and the pressing belt 48.

  Further, it is understood that the floating of the recording paper P from the fixing belt 41 in the non-pressurized area B does not occur immediately after passing through the preheating area A, but gradually occurs, so that the temperature of the fixing belt 41 or the heating plate 47 is increased. It was found that the higher the value, the faster the generation rate.

Therefore, in the fixing device 10 of the present invention, when the length of the non-pressurized region B is L (mm), the process speed is S (mm / s), and the heating plate temperature is T (° C.), the following formula ( It is configured to satisfy 1).
L × (T-97) /S≦4.7 ………………………………………… (1)

  This suppresses the generation of excessive water vapor in the non-pressurized area B and allows the recording paper P to enter the nip area C before the recording paper P floats from the fixing belt 41, which is good without image distortion. A fixed image can be obtained.

  The length of the heating plate 47 along the fixing belt 41 is a practical length of about 200 to 400 mm, and the heating plate temperature T for obtaining substantially good fixing properties is less than 110 ° C. When the temperature exceeds 130 degrees, excessive water vapor is generated. Therefore, the temperature is preferably 110 ° C. or higher and 130 ° or lower.

  Next, the grounds for deriving formula (1) will be described below as an example.

  First, it is empirically known that the image shift due to water vapor has a correlation with the product of time (L / S) and temperature (T), and the water vapor from the recording paper P is related to time (L / S). It was found that when the product with the temperature (T-97) is large, it is easy to come out.

  Therefore, in order to derive the relationship between time (L / S) and temperature (T) and image shift, the following verification experiment was performed. The configuration of the fixing device used in the verification experiment is shown in FIG.

  As shown in FIG. 2, this fixing device has the same basic configuration as the fixing device according to the embodiment, but in order to clarify the influence of image shift in the non-pressurized region B, the nip region A cooling plate 70 as a cooling device is further provided on the downstream side of C, and accordingly, the fixing belt 41 and the pressing belt 48 are both extended and stretched to the downstream side of the fixing nip portion N. is there. Others are the same as in the embodiment, and the description thereof is omitted. Note that the length of the cooling plate 70 is set such that the temperature at the most downstream portion is 90 degrees or less, and the toner image T heated and pressed at the fixing nip portion N is sufficiently cooled. Then, the recording paper P itself is configured to be naturally separated from the fixing belt 41 due to the rigidity of the recording paper P itself.

  The general specifications of the fixing device used in the examples are shown below.

  As the pressing belt, a belt in which an elastic coating layer made of silicone rubber and having a thickness of 20 μm was laminated on a belt base material made of polyimide and having a thickness of 130 μm was used.

  As the pressure rollers, five similar sized rollers were arranged at intervals of 55 mm. Each roller had a diameter of 20 mm (surface rubber layer 5 mm), a roller length of 340 mm, and a pressing load of 150 N was applied.

  The fixing roller 44 and the pressure roller 45 had a diameter of 95 mm (surface rubber layer 6 mm), a roller length of 400 mm, a contact load of 2000 N, and a fixing nip width of 18 mm. The length of the heating plate 47 along the fixing belt 41 was 240 mm.

  As a sampling chart, a pattern as shown in FIG. 3 was used, a transfer image was formed on the recording paper P, and image fixing was performed.

  In FIG. 3, the patterns used are K (black) from the left, process black PB (black formed by Y, M, C), B (blue formed by M, C), G (Y, C (green formed by C), R (red formed by Y, M), Y (yellow), M (magenta), and S (cyan). Is a pattern image in which the area ratios are varied in stages in the vertical direction.

  As recording paper P, OK Top Coat N 127.9 gsm manufactured by Oji Paper Co., Ltd. was used, and the presence or absence of image shift was visually observed.

Using such a verification fixing device, the length L of the non-pressurized area B, the temperature T of the heating plate 47 / fixing roller 44, and the process speed S were changed to verify the occurrence of image shift. The verification result is shown in Table 1, and the calculation result based on the expression (1) corresponding to the verification result is shown in Table 2.

  As can be seen from Tables 1 and 2, it can be seen that image displacement occurs as the calculation result of Expression (1) increases. It is also understood that the maximum value of the calculation result of Expression (1) within a range where no image shift occurs is 4.7.

  Therefore, by setting and arranging the length L of the non-pressurized region B, the process speed S, and the temperature T of the heating plate 47 so that the calculation result of the expression (1) becomes 4.7 or less, the image shift is reduced. It can be seen that the occurrence can be prevented.

  When it can be considered that the temperatures of the heating plate 47 and the fixing roller 44 and the fixing belt 41 are equal, the equation (1) can be read as an equation representing the characteristics of the fixing belt 41.

That is, the length of the fixing belt 41 corresponding to the non-pressure area B is L (mm), the traveling speed of the fixing belt 41 is S (mm / s), and the temperature of the fixing belt 41 in the non-pressure area B is T ( ° C), the fixing belt 41 is
L × (T-97) /S≦4.7
It suffices if they are arranged so as to satisfy the above.

  Even under such conditions, the simple setting and arrangement of the fixing belt can suppress the generation of excessive water vapor as in the case described above, and can easily obtain a good fixed image without image distortion. It becomes possible.

  As described above, in the fixing device according to the present invention, the constituent members are set and arranged so as to satisfy the predetermined relationship, thereby suppressing the generation of excessive water vapor and before the recording sheet floats from the fixing belt. In addition, it was verified that the recording paper can enter the fixing nip portion and prevent the occurrence of image disturbance.

1 is a diagram illustrating a schematic configuration of a fixing device according to the present invention. FIG. 3 is a diagram illustrating a configuration of a fixing device used for verification performed to derive a relational expression according to the present invention. It is a figure which shows the image formation pattern used for verification.

Explanation of symbols

  10: fixing device, 41: fixing belt, 42: first heating roller, 44: fixing roller, 45: pressure roller, 47: heating plate, 48: pressing belt, 49: recording paper guide, 50: second heating roller , 51: idler roller, 52: cleaning web, 55: cleaning device, 56, 57, 58: pressure roller, 60: tension roller, 70: cooling plate, A: preheating area, B: non-pressurizing area, C: Nip area, N: fixing nip, P: recording paper

Claims (6)

An endless fixing belt that is stretched around a plurality of rollers and rotates in a predetermined direction, and a fixing roller that forms a fixing nip portion in the contact region, and a fixing roller that are disposed so as to be in pressure contact with each other via the fixing belt. A pressure roller, a heating plate fixedly arranged in contact with the inner peripheral surface of the fixing belt, upstream of the fixing nip portion in the rotation direction of the fixing belt, and a plurality of plates arranged facing the heating plate And an endless pressure belt which is stretched by the plurality of pressure rollers and is pressed against the outer peripheral surface of the fixing belt and rotates by being driven by the fixing belt. In a fixing device that conveys the recording sheet thus formed in a predetermined direction and guides the recording paper between the fixing belt and the pressing belt,
Along the recording sheet conveyance direction, the distance from the rotation center of the pressure roller arranged at the most downstream of the plurality of pressure rollers to the most upstream portion of the fixing nip portion is L (mm), and the process speed is S. (Mm / s), when the heating plate temperature is T (° C.),
The fixing device includes:
L × (T-97) /S≦4.7
A fixing device characterized by being set and arranged so as to satisfy the above relationship.   2. The image forming apparatus according to claim 1, further comprising a separating unit that conveys the recording sheet by a predetermined distance in a state in which the recording sheet is in close contact with the outer peripheral surface of the fixing belt at a downstream side of the fixing nip portion in the sheet conveying direction. The fixing device according to 1.   The fixing device according to claim 2, wherein the peeling unit includes a cooling unit that cools the recording sheet to a predetermined temperature. An endless fixing belt that is stretched around a plurality of rollers and rotates in a predetermined direction, and a fixing roller that forms a fixing nip portion in the contact region, and a fixing roller that are disposed so as to be in pressure contact with each other via the fixing belt. A pressure roller, a heating plate fixedly arranged in contact with the inner peripheral surface of the fixing belt, upstream of the fixing nip portion in the rotation direction of the fixing belt, and a plurality of plates arranged facing the heating plate And an endless pressure belt which is stretched by the plurality of pressure rollers and is pressed against the outer peripheral surface of the fixing belt and rotates by being driven by the fixing belt. In a fixing device that conveys the recording sheet thus formed in a predetermined direction and guides the recording paper between the fixing belt and the pressing belt,
Along the traveling direction of the fixing belt, the length of the fixing belt from the rotation center of the pressing roller disposed at the most downstream side to the most upstream portion of the fixing nip among the plurality of pressing rollers is L (mm), fixing. When the belt traveling speed is S (mm / s) and the fixing belt temperature is T (° C.),
The fixing belt is
L × (T-97) /S≦4.7
A fixing device characterized by being set and arranged so as to satisfy the above relationship.   2. The image forming apparatus according to claim 1, further comprising a separating unit that conveys the recording sheet by a predetermined distance in a state in which the recording sheet is in close contact with the outer peripheral surface of the fixing belt at a downstream side of the fixing nip portion in the sheet conveying direction. 5. The fixing device according to 4.   The fixing device according to claim 5, wherein the peeling unit includes a cooling unit that cools the recording sheet to a predetermined temperature.

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