JPH10228199A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of the blur of an image on a recording medium and its wrinkles, in a belt nipping system fixing device. SOLUTION: In the belt nipping system fixing device, one of a group of supporting rolls 3 for an endless belt 2 is disposed as a pressure roll 3a, at the exit of a nipping area formed between a heating roll 1 and the endless belt 2 and an auxiliary pressure member 4 for pressing the endless belt 2 on the side of the heating roll 1 is disposed inside the endless belt 2 corresponding to the nipping area. Then, the auxiliary pressure member 4 is provided with an element for forming a load distribution (m) for making a load exerted on a middle part in the axial direction of the heating roll 2 heavier than that exerted on both end parts in the axial direction of the heating roll 1, in the nipping area.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called heating roll type fixing device for contact-heating and fixing an unfixed image on a recording medium in an image information recording apparatus such as a copying machine, a printer, and a facsimile. The present invention relates to an improvement in a belt nip type fixing device including a belt pressing device.

[0002]

2. Description of the Related Art As a fixing device suitable for a high-speed color copying machine, an endless belt is pressed against a heating roll (a heating roll having an elastic layer) called a so-called soft roll to form a nip area. A so-called belt nip type fixing device has been proposed in which a pressure roll disposed inside an endless belt at the exit of a region is pressed against a heating roll via an endless belt (see, for example, JP-A-5-150679). . This is, for example, FIG.
As shown in FIG. 1, a heating roll 21 having a built-in halogen lamp 22 as a heating source and having an elastic layer 24,
An endless belt 32 stretched around a plurality of support rolls 34, 35, and 37 and having a nip area 43 formed between the endless belt 32 and the heating roll 21;
And a pressurizing roll 33 that is disposed inside the pressurizing roll and is pressed against the heating roll 21 by a coil spring 36.
Reference numeral 25 denotes a top coat layer covering the elastic layer 24,
26 is disposed in contact with the heating roll 21,
An oil supply device 27 for supplying a release agent to the heating roller 21 is a temperature sensor for detecting the surface temperature of the heating roll 21. This fixing device is a new belt nip type fixing device that can be applied not only to black-and-white images but also to color copiers. Can be peeled at the exit of the nip area without using any peeling device (hereinafter referred to as a self-stripping method).

If the load of the pressure roll 33 is increased in order to improve the self-stripping performance, a phenomenon (image shift) of the unfixed image T on the recording paper P occurs. This phenomenon is caused by the fact that the elastic layer 24 on the surface of the heating roll 21 is distorted by the high pressure of the pressure roll 33, and the speed of the recording paper P is increased accordingly.
In order to prevent this image shift, a large load is applied at a low pressure so as not to distort the heating roll 21 too much on the upstream side of the pressure roll 33 in the nip area 43, and the heating roll 21 in this portion is The adhesive force with the recording paper P is made larger than the adhesive force of the pressure roll 33. Thereby, the speed of the recording paper P is set to the same speed as the speed of the heating roll 21. To achieve this effect, the nip area 43
A method has been proposed in which a roll or a fixing member as an auxiliary pressing member is provided near the entrance of the heating roller and pressed against a heating roll (for example, Japanese Patent Application Nos. 6-249705 and 7-249).
No. 117402).

[0004]

However, although the problem of image misalignment can be solved by providing the auxiliary pressing member, paper wrinkles easily occur in the nip area 43 of the endless belt 32, and a good fixing result is obtained. A new technical issue has been found that can not be obtained. Accordingly, the present invention has been made to solve the above technical problem, and an object of the present invention is to provide a belt nip type fixing device that prevents image shift and wrinkling of a recording medium.

[0005]

That is, as shown in FIGS. 1A and 1B, the present invention relates to a heating roll 1 having at least an elastic layer and a plurality of support roll groups 3 (3a, 3a).
b) and a heat-resistant endless belt 2 that is placed in pressure contact with the heating roll 1 with a predetermined nip width,
In a fixing device in which a recording medium P carrying an unfixed image T is inserted into a nip area between the heating roll 1 and the endless belt 2, a nip formed between the heating roll 1 and the endless belt 2 is provided. At the exit of the area, one of the support rolls 3 is disposed as a pressure roll 3a,
Inside the endless belt 2 corresponding to the nip region, an auxiliary pressing member 4 for pressing the endless belt 2 toward the heating roll 1 is disposed.
In the nip region, there is provided a forming element of a load distribution m in which a load acting on an intermediate portion in the axial direction of the heating roll 1 is larger than a load acting on both axial end portions of the heating roll 1.

In such technical means, the auxiliary pressing member 4 is a member extending along the axial direction of the heating roll 1 and applying a predetermined pressing force to the heating roll 1 via the endless belt 2. A plate-like member having an elastic body in a base material or a roll member in which a core material is covered with an elastic layer may be appropriately selected, but from the viewpoint of reliably preventing wrinkling of the recording medium P. if,
Heating roll 1 such as a plate-like member having an elastic body
It is preferable to have a pressure contact surface opposed to substantially the entire nip area formed between the belt and the endless belt 2, and to form a desired load distribution m over substantially the entire nip area.

In this case, as the desired load distribution m, at least the load acting on the intermediate portion in the axial direction of the heating roll 1 (corresponding to the axial direction of the auxiliary pressurizing member 4) in the nip region is determined. It is necessary that the load applied to both ends in the axial direction (corresponding to the axial direction of the auxiliary pressing member 4) be larger than the load applied to both ends. Here, the maximum load and the minimum load of the load distribution m need only be basically selected within a range in which image shift is prevented, as shown in FIG.
Regarding the load distribution m pattern, regardless of whether or not it is symmetrical along the width direction of the endless belt 2,
For example, a corner registration method (a method in which the vicinity of one side edge of the endless belt 2 is used as a reference line) or a center registration method (a center line in the width direction of the endless belt 2 is used as the recording medium P).
And the size of the recording medium P to be used, as long as wrinkles do not occur. Therefore, for the load distribution m pattern, in the case of the center registration method, the maximum load position for preventing image shift of the load distribution m is set near the center line in the width direction of the endless belt 2, but in the case of the corner registration method. The maximum load position for preventing image misalignment of the load distribution m is set at an appropriate position deviated from the center line in the width direction of the endless belt 2. Also, the load at both ends of the load distribution m includes not only a mode in which both are the same with the minimum load but also a mode in which one is different from the other.

The load distribution m of the auxiliary pressurizing member 4 preferably changes continuously from the maximum load for preventing image displacement to the minimum load for preventing image displacement. It also includes aspects that change dynamically. Here, as for the forming element of the load distribution m, as the auxiliary pressing member 4, the cross-sectional shape in the width direction orthogonal to the moving direction of the endless belt 2 is such that the intermediate portion protrudes toward the heating roll 1 side with respect to both ends. Achieved by shaping. In this case, for example, in the case of the auxiliary pressing member 4 provided with an elastic body on the base material, the shape of the base material may be made convex, or the thickness of the elastic body may be variably set to be convex. It may be.

In the case of a fixing device of a roll pair configuration (a fixing device in which a pressure roll is pressed against a heating roll), as shown in FIG. 4 (a), as the load of the pressure roll increases, It is understood that the paper speed as the recording medium P increases. In the fixing device having such a roll pair configuration, from the viewpoint of preventing paper wrinkles, as shown in FIG. 4B, as a load distribution in a nip region between a heating roll and a pressing roll, Prior art has already been proposed in which the load at both ends in the axial direction is increased and the load at the intermediate portion is reduced (for example, Japanese Patent Laid-Open No. 2-2 / 1990).
77089). However, in the prior art of this type, the load distribution described above is assumed for the technical problem of preventing paper wrinkles in a fixing device having a roll pair configuration. With respect to the technical problem of preventing image misalignment and preventing paper wrinkling in a fixing device of the system, a completely different load distribution having a load distribution pattern different from that of a fixing device having a roll pair configuration is applied to the nip area. The technical problems to be solved and the means for solving them are completely different.

The operation of the above technical means will be described below with reference to FIGS. Now, as shown in FIG. 2, the paper speed of the recording medium P with respect to the load of the auxiliary pressing member 4 is gradually decreased as the load of the auxiliary pressing member 4 is increased, and the image shift is performed within a predetermined load range. Is prevented.

Further, if the load of the intermediate portion (for example, the center portion is illustrated in the drawing) of the auxiliary pressing member 4 in the width direction of the endless belt 2 is increased and the load is decreased toward both ends, the recording medium P can be obtained. It is understood that the speed at the center in the width direction of the paper is slow, and the speed at both ends is fast. That is, as shown in FIG. 3, when the recording medium P having a wrinkle at the rear end in the traveling direction passes through the nip area, the speed of the recording medium P decreases at the center (Vm) and increases at both ends (Vm). Ve). At this time, due to the relative speed difference between the center and the end of the recording medium P, a rotational moment M is generated at both ends around the center. The wrinkles of the recording medium P are extended in the width direction of the endless belt 2 by the rotational force.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on an embodiment shown in the accompanying drawings. First Embodiment FIG. 5 shows a first embodiment in which the present invention is applied to a belt nip type fixing device. In FIG. 1, the fixing device according to the present embodiment employs, for example, a center registration system.
, And a belt nip device 31 that is disposed in pressure contact with the heating roll 21 on the downstream side in the rotation direction of the heating roll 21. In the drawing, reference numeral 26 denotes an oil supply device arranged in contact with the heating roll 21, and reference numeral 27 denotes a heating roll 21 of the oil supply device 26.
This is a temperature sensor that is disposed downstream of the rotation direction and detects the surface temperature of the heating roll 21.

In the present embodiment, the roll portion of the heating roll 21 includes a cylindrical core 23 covering the heating source 22 and a heat-resistant elastic body (elastic layer) 24 disposed on the outer peripheral surface of the cylindrical core 23.
And a top coat layer 25 disposed on the outer peripheral surface of the heat-resistant elastic body 24. Here, in the present embodiment, for example, the cylindrical core 23 has an outer diameter of 4 mm.
It is made of aluminum having a diameter of 7 mm and an inner diameter of 42 mm. As the heat-resistant elastic body 24, HTV silicone rubber (rubber hardness JI
S-A45 ゜) with a layer thickness of 1.5 mm. As the top coat layer 25, a silicon RTV rubber is dip-coated to a thickness of 50 μm and finished to a surface almost in a mirror-like state. is there.

As the heating source 22, for example, 85
A 0 W halogen lamp is used. As a release agent for the oil supply device 26, for example, dimethyl silicone oil having a viscosity of 3
00cSt is supplied uniformly. The driving force from the motor 51 is transmitted to the heating roll 21, and the heating roll 21 rotates at a speed of 160 mm / sec in the direction of the arrow.

Further, the belt nip device 31 is provided with an endless belt 32 which is stretched around support rolls 33, 34 and 35 and is pressed against the heating roll 21 with a predetermined nip width.

In the present embodiment, for example, the endless belt 32 is a polyimide film having a thickness of 75 μm, a width of 300 mm, and a circumference of 188 mm, and is stretched by the support rolls 33, 34, 35 under a tension of 80N. Have been.

The three support rolls 33, 34, 3
5 is made of aluminum having a drum-shaped taper, and the drum-shaped taper is attached to correct the deflection due to the tension of the endless belt 32, so that the endless belt 32 is not wavy. , With a uniform tension. In the present embodiment, the outer diameter of each of the support rolls 33 to 35 is 23 mm and 18 m, respectively.
m, 18 mm.

Further, the support roll 33 is
And a pressure roller disposed at the exit of the nip area 43 between the endless belt 32 and the endless belt 32. The pressure roller is urged toward the center of the heating roller 21 by a compression coil spring 36 as a pressing means. It is pressed against the heating roll 21. In the present embodiment, the winding angle of the endless belt 32 around the heating roll 21 (the nip area 43
Is about 45 °, and the nip width at this time is about 20 mm. A support roll (pressure roll) 33 is pressed against the outlet of the nip area 43 with a load of about 360 N via the endless belt 32, thereby enabling self-stripping.
In this embodiment, the support roll 35 functions as a steering roll for preventing the endless belt 32 from walking.

Further, the belt nip device 31 includes an auxiliary pressing member 41 which is disposed under pressure by a coil spring 42 inside the endless belt 32 in the nip area 43. In the present embodiment, the auxiliary pressing member 41 is
As shown in the figure, the elastic body 41 is placed on the plate-shaped base material 412.
For example, the base member 412 is made of stainless steel, and the elastic body 411 is made of silicon rubber having a thickness of 3 mm (rubber hardness: JIS A: 20 °). Further, a Teflon-impregnated glass fiber sheet (not shown) is coated on the silicon rubber, so that sliding resistance with the inner surface of the endless belt 32 is reduced.
In particular, in the present embodiment, the base member 412 has a constant thickness, and the elastic body 411 has a thickness of about 0.5 m at the central portion rather than at both ends.
m is formed to have a convex section.

At this time, the load distribution in the axial direction of the auxiliary pressing member 41 (corresponding to the width direction of the endless belt 32) is shown in FIG.
As shown in (1), the maximum load for preventing image misalignment is at the center, and the minimum load for preventing image misalignment is shown at a portion corresponding to the end in the width direction of the recording paper P. On the other hand, when the load on both ends of the recording paper P is larger than the central portion and higher than the maximum load for preventing image shift (in FIG. 7), both image shift and paper wrinkling occur.
When the load at both ends of the recording paper P is smaller than the minimum load for preventing image shift (FIG. 7), wrinkles can be prevented, but image shift cannot be prevented.

As shown in FIG. 8A, the load distribution in the axial direction of the auxiliary pressing member 41 may be such that the peak of the load slightly deviates from the central portion (deviation: δ). As shown in FIG. 8B, the load on the portion corresponding to the end of the sheet only needs to be within the load range for preventing image shift, and the respective portions may have different loads.

Next, the operation of the present embodiment will be described with reference to FIGS. The endless belt 32 is driven by the rotation of the heating roll 21, and the endless belt 3
The recording paper P on 2 passes through the nip area 43. At this time, if the speed difference between the recording paper P and the heating roll 21 is adjusted to be almost zero by the pressing force of the auxiliary pressing member 41, the unfixed image on the recording paper P does not shift. Also, since the traveling speed of each part in the width direction of the recording paper P becomes slower at the center and becomes faster at both ends, the traveling speed difference between the central part and the both ends of the recording paper P indicates that the center of the recording paper P is centered. Is applied to the end of each sheet, and the wrinkles of the recording sheet P are extended in the sheet width direction. As described above, according to the present embodiment, image shift is prevented and paper wrinkles are also prevented.

Table 1 shows that the present embodiment has
This is the result of examining the paper wrinkle prevention performance by examining the number of paper wrinkles generated when making 00 continuous copies. At this time, three types of paper, J-paper, S-paper, and R-paper, manufactured by Fuji Xerox Co., Ltd. were used. However, these papers are apt to wrinkle in the order of J-paper, S-paper, and R-paper. However, water-containing paper tends to wrinkle more easily than open paper. As a result, in this embodiment, it was confirmed that paper wrinkling did not occur for any type of paper. On the other hand, according to the comparative embodiment having the flat auxiliary pressing member, it was confirmed that the number of paper wrinkles increased as the paper quality was reduced.

[0024]

[Table 1]

Second Embodiment FIG. 9 shows the structure of an auxiliary pressing member according to a second embodiment. In this case, the shape of the base member 412 of the auxiliary pressing member 41 is convex in cross section, and the central part is higher by 0.5 mm than both ends. An elastic body 411 made of silicon rubber having a uniform thickness is fixed thereon. Also in the present embodiment, in the nip area 43 formed between the heating roll 21 and the endless belt 32,
A load distribution similar to that of the first embodiment is obtained in the axial direction of the auxiliary pressing member 41, and image shift and paper wrinkling are prevented.

Third Embodiment FIG. 10 shows a fixing device according to a third embodiment. The fixing device according to the present embodiment has substantially the same configuration as that of the first embodiment as shown in FIG. 10A, but an auxiliary pressing member 41 is provided on a plate-shaped base member 412 in a rectangular parallelepiped shape. It is characterized in that an elastic body 427 having a low elastic modulus is arranged at the center of the elastic bodies 421 to 427 of the shape, and elastic bodies 426 to 421 are arranged so that the elastic modulus increases in order toward both ends. According to the present embodiment, as shown in FIG. 10B, a load distribution is obtained in which the load decreases stepwise from the center of the auxiliary pressurizing member 41 toward both ends, resulting in image shift and paper wrinkling. Both are prevented.

[0027]

According to the present invention, a predetermined load distribution is provided in the width direction of the endless belt of the auxiliary pressing member so that the traveling speed of both ends of the recording medium is made faster than that of the central portion. Paper wrinkles can be reliably prevented while preventing image shift.

[Brief description of the drawings]

FIG. 1A is an explanatory view showing an outline of a fixing device according to the present invention, and FIG. 1B is a graph showing a load distribution in a nip region between a heating roll and an endless belt according to the present invention.

FIG. 2 is an explanatory diagram showing a relationship between a load of an auxiliary pressing member and a paper speed / heating roll speed.

FIG. 3 is a schematic explanatory view showing the operation of the present invention.

4A is an explanatory diagram showing a relationship between a pressure roll load and a paper speed / heating roll speed of a fixing device having a roll pair configuration, and FIG. 4B is a load distribution in a pressure roll axial direction in a nip region. FIG.

FIG. 5 is a first embodiment of a fixing device to which the present invention is applied.
FIG.

FIG. 6 is an explanatory view showing an enlargement of an auxiliary pressing member according to FIG. 5;

FIG. 7 is an explanatory diagram showing a load distribution in a nip region according to FIG. 5;

8 (a) and 8 (b) are explanatory diagrams showing a modified example of the load distribution according to FIG. 7;

FIG. 9 is an explanatory diagram illustrating a fixing device according to a second embodiment.

10A is an explanatory diagram illustrating a fixing device according to a third embodiment, and FIG. 10B is an explanatory diagram illustrating a load distribution in a nip region at that time.

FIG. 11 is an explanatory diagram illustrating an example of a conventional fixing device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Heating roll, 2 ... Endless belt, 3 ... Support roll, 3a ... Pressing roll, 4 ... Auxiliary pressing member, 21 ... Heating roll, 32 ... Endless belt, 33 ... Supporting roll (pressing roll), 34, 35: support roll, 41: auxiliary pressing member

Claims (2)

[Claims] 1. A heating roll (1) having at least an elastic layer and a plurality of support roll groups (3: 3a, 3b). The heating roll (1) is placed in pressure contact with the heating roll (1) with a predetermined nip width. A heat-resistant endless belt (2),
A recording medium (P) having an unfixed image (T) carried in a nip area between the heating roll (1) and the endless belt (2)
In the fixing device, one of the support rolls (3) is connected to a pressure roll at an outlet of a nip area formed between the heating roll (1) and the endless belt (2). (3a), an auxiliary pressing member (4) for pressing the endless belt (2) toward the heating roll (1) is provided inside the endless belt (2) corresponding to the nip area. In the auxiliary pressing member (4), a load acting on the axially intermediate portion of the heating roll (1) in the nip region is larger than a load acting on both axial end portions of the heating roll (1). Load distribution (m)
A fixing device characterized by comprising a forming element of (1). 2. The fixing device according to claim 1, wherein the auxiliary pressing member has a cross-sectional shape in a width direction orthogonal to a moving direction of the endless belt, the intermediate portion being a heating roll with respect to both ends. (1) A fixing device having a convex shape protruding to the side.