JPH06324588A - Fixing device - Google Patents

Abstract

(57) [Summary] [Purpose] To prevent the wrinkling of the recording material after fixing and the poor stackability due to curling. A fixing roller and a pressure roller that forms a nip with the fixing roller and has a hardness lower than that of the fixing roller are provided.
In a fixing device for fixing by conveying a recording material supporting an unfixed image at a nip, the fixing roller has a maximum diameter portion between a central portion and an end portion and within a maximum recording material passage area. The diameter gradually decreases from the maximum diameter portion toward the inside and the outside.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device provided in an image forming apparatus adopting an electrophotographic system, an electrostatic recording system or the like, and more specifically, a fixing member and a pressure member arranged in pressure contact with each other. And a heat fixing device composed of

[0002]

2. Description of the Related Art Conventionally, in a fixing device provided in an image forming apparatus which employs an electrophotographic system, an electrostatic recording system, etc., a transfer roller carrying an unfixed toner image is pressed against each other to rotate a fixing roller. A so-called heat fixing device is widely used which fixes a permanent image on a transfer material by passing through a nip portion formed by a pressure roller and a pressure roller. In such a heat fixing device, in order to prevent wrinkles of the transfer material caused by passing through the nip portion, at least one of the fixing roller and the pressure roller has a maximum outer diameter at both longitudinal ends. Generally, it is configured in a so-called inverted crown shape so that the outer diameter of the central portion is minimized. However, in such a configuration, the transfer material is forcibly stretched in the longitudinal direction of the fixing roller and the like, and its distortion extends to both ends of the transfer material with weak stiffness, and as a result, both ends of the transfer material undulate. In some cases, so-called “waviness” occurs, and the image quality is impaired. Therefore, in order to prevent this, the maximum outer diameter portion of the pressure roller configured in an inverted crown shape,
There is an improvement proposal in which both ends of the transfer material are made to have rigidity by being positioned inside both ends thereof and forming a slight streak in the transfer material corresponding thereto.
No. 4 publication.

[0003]

However, the inventors of the present invention have earnestly studied and found that, even with the above-mentioned improvement plan, when the downsizing of the fixing device is realized along with the personal use of the image forming apparatus. In, it was found that the following problems occur.

That is, in the case where the diameter of the fixing roller is reduced in order to realize the downsizing of the image forming apparatus, the mechanical strength of the fixing roller decreases, and when the fixing roller is brought into pressure contact with the pressure roller. It bends in an arc shape, which causes more pressure and heat to reach both ends of the transfer material, the fibers of the transfer material are greatly stretched, and the output transfer material is curved along the non-printing surface, So-called reverse curl is likely to occur. This reverse curl cannot be completely removed even by the reverse curl correcting means in the image forming apparatus in which face-down paper ejection is frequently used such as a printer for a personal computer, and it can be said that the stacking property is good. In addition, in the face-up paper ejection, the ejected transfer material is curled up and the image quality is remarkably deteriorated.

Further, like the fixing roller, when the diameter of the pressure roller is reduced, in order to secure a sufficient nip width for fixing the unfixed toner image on the transfer material, It is necessary to reduce the hardness, but in this case, even if the end shape of the pressure roller is changed as shown in the above improvement proposal, the effect is diminished and "waviness" occurs. It tends to occur.

Further, as shown in the above improvement proposal, the shape of both ends of the pressure roller made of an elastic body is finely adjusted,
Molding was a very difficult task in terms of accuracy and was inferior in productivity.

[0007]

According to the present invention for solving the above-mentioned problems,
A fixing rotator and a pressing rotator that forms a nip with the stopper rotator and has a hardness lower than that of the fixing rotator, and nips and conveys a recording material supporting an unfixed image at the nip to perform fixing. In the fixing device, the fixing rotator has a maximum diameter portion between the central portion and the end portion and within the maximum recording material passage area, and has a shape in which the diameter gradually decreases from the maximum diameter portion toward the inside and the outside. It is what

[0008]

EXAMPLES Examples of the present invention will be described below.

FIG. 1 is a configuration diagram of a main part of an image forming apparatus using a fixing device according to an embodiment of the present invention.

In FIG. 1, 1 is a photosensitive drum,
A photosensitive material such as OPC, amorphous Se, or amorphous Si is formed on a cylindrical base such as aluminum or nickel. The photosensitive drum 1 is rotationally driven in the direction of the arrow, and its surface is first uniformly charged by a charging roller 2 as a charging device. Next, scanning exposure is performed by the laser beam 3 whose ON / OFF is controlled according to the image information, and an electrostatic latent image is formed. This electrostatic latent image is developed and visualized by the developing device 4. As a developing method,
A jumping developing method, a two-component developing method, an FEED developing method, or the like is used, and image exposure and reversal developing are often used in combination.

The visualized toner image is transferred onto a transfer material P conveyed at a predetermined timing by a transfer roller 5 as a transfer device. The transfer material P on which the toner image has been transferred is conveyed to the fixing device 6 and fixed as a permanent image, and is then discharged face-down onto the discharge tray 7. On the other hand, transfer residual toner remaining on the photosensitive drum 1 is removed from the surface of the photosensitive drum 1 by the cleaning device 8.

FIG. 2 shows the structure of the heat fixing device 6 according to the present invention. In FIG. 2, 9 is a fixing roller, and 10 is a pressure roller, each rotating in the direction of the arrow. In the fixing roller 9, the surface layer of the hollow cored bar 11 made of aluminum having a thickness of 2 mm and an inner diameter of 26 mm and having excellent heat resistance is coated with PFA 12 which is a fluororesin having excellent releasability in a thickness of 30 μm. Further, a halogen heater 13 for heating the fixing roller 9 is provided inside the hollow cored bar 11. On the other hand, in the pressure roller 10, a silicone rubber 15 having a thickness of 10 mm and excellent in releasability is formed on the outer peripheral portion of a core metal 14 made of iron having an outer diameter of 10 mm, and positioned at both ends in the longitudinal direction. The outer diameter difference between the largest outer diameter portion and the smallest outer diameter portion located in the central portion is 0.2 mm, which is a so-called inverted crown shape. The pressure roller 10 has a hardness of 50 ° (under a load of ASKER C500g). The fixing roller 9 and the pressure roller 10 are
At both ends of each longitudinal direction, by springs (not shown),
Pressed against each other. A thermistor 16 for detecting the surface temperature of the fixing roller 9 is in contact with the fixing roller 9, and the surface temperature information of the fixing roller 9 detected by the thermistor 16 is A / D converter ( It is sent to the CPU (not shown) via the
(Not shown) controls the surface temperature of the fixing roller 9 to a predetermined value by controlling ON / OFF of the halogen heater 13 via an AC driver (not shown).

Further, the shape of the fixing roller provided in the heat fixing device according to the present invention will be described in detail with reference to FIG.

The fixing roller 9 has an inverted crown shape such that the outer diameter of the central portion in the longitudinal direction is smaller than the maximum outer diameter portion in order to prevent the transfer material P from wrinkling. The maximum outer diameter portion is arranged outside the central portion and inside the both longitudinal end portions. Specifically, the outer diameter D ₁ of the smallest outer diameter portion = 30 mm, the outer diameters D ₂ , D _{3 of} the largest outer diameter portion a = 30.25 mm, and the outer diameters D ₄ , D ₅ = 29.4 mm of both end portions b. And maximum outer diameter part a
Is inside the position c where both ends of the transfer material P having the maximum width pass, and the distance L between a and c is 4 mm. Further, the position c where both ends of the transfer material P having the maximum width pass is inside the both ends b of the fixing roller 9, and the distance L ′ between b and c is 3 m.
m.

In order to have such an outer diameter, the core metal 11 is processed into a small shape having a diameter of 30 × 2 = 60 μm in the longitudinal direction, and a releasable resin layer having a substantially uniform thickness is provided on the core metal. The above-mentioned outer shape which is in the shape of a core metal is obtained.

Now, the effects of the present invention will be described while showing the results of a comparative experiment conducted by the present inventors with a conventional heat fixing device. In the conventional heat fixing device used for comparison, as shown in FIG. 4, the outer diameter of the central portion in the longitudinal direction is minimum (D ₆ = 30 mm) and the outer diameter of both end portions is maximum (D ₇ ,
D ₈ = 30.3 mm) and the reverse crown-shaped fixing roller and the maximum outer diameter portion configured in the reverse crown shape as shown in FIG. D ₉ = 30 mm, D ₁₀ , D ₁₁ = 30.25
mm, D ₁₂ , and D ₁₃ = 29.4 mm and a pressure roller having a diameter of 29.4 mm are pressed against each other.

As an experimental method, each fixing roller was combined with a pressure roller having a different hardness, and at that time, the degree of "waviness" generated at both ends of the transfer material and the stackability during face-down sheet discharge were evaluated. . Table 1 shows the experimental results when the conventional fixing device is used. In the table, ◯ means good, Δ means no problem in practical use, and × means poor.

[0018]

[Table 1]

According to this, when the hardness of the pressure roller is low, the effect of improving the shape of the end portion of the pressure roller is diminished, and "waviness" becomes prominent, and when the hardness is high. As a result, a large amount of pressure and heat are applied to both ends of the transfer material, the fibers of the transfer material are greatly stretched, and reverse curl occurs in the transfer material, which tends to deteriorate the stackability. It can be seen that it is difficult to achieve both “waviness” and stackability when using the fixing device.

On the other hand, Table 2 shows the experimental results when the heat fixing device according to the present invention was used.

[0021]

[Table 2]

According to this, even when the hardness of the pressure roller is low, by giving the transfer material an appropriate rigidity, it is possible to obtain an effect of preventing "waviness" from occurring at both ends of the transfer material. In addition, even if the pressure roller has a high hardness, a large amount of pressure and heat do not reach both ends of the transfer material, and the stackability can be improved. However, when the pressure roller hardness is high as described above, streaks due to the end shape of the fixing roller appear prominently in the vicinity of both ends of the transfer material, and the image quality is impaired. I understood. Therefore, in order to achieve both "waviness" and loadability and to prevent the occurrence of streaks,
The end portion shape of the fixing roller is improved as in the present invention, and the hardness of the pressure roller is 70 ° or less, preferably 60 °.
The following is effective.

Now, in this embodiment, the pressure roller 1
The shape of 0 is an inverted crown shape in which the outer diameter of the central portion in the longitudinal direction is the smallest and the outer diameter of both end portions is the largest, but conversely, the outer diameter of both longitudinal end portions is the smallest. When the crown shape is such that the outer diameter of the central portion is maximized, when the transfer material passes through the nip portion formed by the fixing roller and the pressure roller, the transfer material is fixed by the fixing roller or the like. As a result, the reverse curl becomes large and the stackability is extremely deteriorated. Furthermore, a large force is exerted on the transfer material toward the central portion in the longitudinal direction, which makes the transfer material less elastic, such as thin paper or paper that has been absorbed in a high humidity environment. In the above, wrinkles are likely to occur near the center of the transfer material in the longitudinal direction. In order to prevent these, it is preferable that the pressure roller has a straight shape or an inverted crown shape.
In the case of using the fixing roller having the end shape as shown in this embodiment, the action of stretching the fibers on the non-printing surface side of both ends of the transfer material contributes to the prevention of reverse curl. Further, by using the pressure roller having the straight shape or the inverted crown shape as described above, the both ends of the transfer material can be effectively provided with stiffness, and thus the effect of preventing wrinkles can be obtained. Therefore, the range of the applicable end shape of the fixing roller can be widened.

In the above description, the shape of the pressure roller is preferably a straight shape or an inverted crown shape, but in order to obtain this effect, as shown in FIG. It is necessary to have a substantially inverted crown shape. For example, in the pressure roller shown in this embodiment, both ends of the pressure roller are bent by about 0.2 mm in a pressure state. As a result, it was found that the above effect can be sufficiently obtained if the difference ΔR between the outer diameter of the central portion in the longitudinal direction of the pressure roller and the outer diameter of both end portions is 0.2 mm or less. Generally speaking, it is necessary that the difference ΔR between the outer diameter of the central portion of the pressure roller in the longitudinal direction and the outer diameter of both end portions thereof satisfies the following equation.

[0025]

[Outer 1] Where w is the load per unit length, l is the length of the core bar,
E is the Young's modulus and d is the outer diameter of the cored bar.

As described above, by constructing the heating and fixing device as shown in this embodiment, it is possible to prevent the defects such as "waviness", streaks, reverse curls, and wrinkles, which may occur in the transfer material, all at once. It is possible to significantly improve the image quality without causing improvement, cost increase, productivity deterioration, and the like.

In the present embodiment, the rotary member including the halogen heater is used as the heating member, but the fixing member 18 including the heating member 17 is heated as shown in the schematic view of FIG. The heat-resistant film 19 is used as a member, and the heat-resistant film 19 is conveyed between the fixing member 18 and the pressure member 10, and the heat of the heating body 17 is applied to the transfer material P via the heat-resistant film 19 and applied to the heat fixing device. Needless to say, it is okay.

(Embodiment 2) Another embodiment according to the present invention will be described below. FIG. 7 shows the heat fixing device 6 used in this embodiment.
However, the same members as those shown in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted. In this embodiment, the fixing roller 9 according to the present invention is made of silicone rubber 15
The PFA 20 is combined with the pressure roller 10 whose surface layer is covered with 30 μm. By providing a release layer such as PFA on the surface of the pressure roller in this way, it is possible to prevent toner, paper dust, etc. from adhering to the surface of the pressure roller and accumulate as dirt, and to apply pressure without a cleaning member. It is extremely important in terms of extending the life of the roller.

Now, the effects of the present invention will be shown while showing the results of a comparative experiment conducted by the present inventors with a conventional heat fixing device. The structure, experimental method, and evaluation standard of the conventional heat fixing device used for comparison are the same as those in the first embodiment.

First, Table 3 shows the experimental results when the conventional heat fixing device was combined with a pressure roller having no release layer and a pressure roller having a release layer.

[0031]

[Table 3]

According to this, when the pressure roller has a release layer on its surface, "waviness" occurs at both ends of the transfer material regardless of the hardness of the pressure roller. It was This is because both the fixing roller and the pressure roller have a release layer with good slipperiness on the surface layer thereof, so that the transfer material existing between them slips and gives both ends of the transfer material a stiffness. It is considered that the effect is diminished.

Therefore, Table 4 shows the experimental results when the heat fixing device equipped with the fixing roller according to the present invention was combined with the pressure roller having no release layer and the pressure roller having the release layer. Shown in.

[0034]

[Table 4]

According to this, the release layer is provided on the surface of the pressure roller to extend the life thereof, and the transfer material has an appropriate rigidity, so that "waviness" occurs at both ends of the transfer material. In order to prevent the above, and not to apply a great amount of pressure and heat to both ends of the transfer material and to improve the stacking property, the end shape of the fixing roller is improved as in the present invention. It is effective to set the hardness of the pressure roller to 30 ° or more, preferably 40 ° or more. Further, as shown in Example 1, in order to prevent the occurrence of streaks due to the end shape of the fixing roller near the both ends of the transfer material, the pressure roller has a hardness of 70 ° or less, Preferably 6
It is effective to set it to 0 ° or less.

In this embodiment, the rotating member including the halogen heater is used as the heating member, but the fixing member 18 including the heating member 17 is heated as shown in the schematic view of FIG. The heat-resistant film 19 is used as a member, and the heat-resistant film 19 is conveyed between the fixing member 18 and the pressure member 10, and the heat of the heating body 17 is applied to the transfer material P via the heat-resistant film 19 and applied to the heat fixing device. Needless to say, it is okay.

(Embodiment 3) Still another embodiment of the present invention will be described below. In this embodiment, the first embodiment will be described.
A fixing roller having a diameter smaller than that of the fixing roller used in 1 above is used. Specifically, the outer diameter D ₁ of the smallest outer diameter portion = 20 mm, and the outer diameters D ₂ , D _{3 of} the largest outer diameter portion a = 2
0.25 mm, outer diameters D ₄ and D _{5 of} both ends b = 19.4 m
m, and the positional relationship among the maximum outer diameter portion a, both end portions b, and the position c at which both end portions of the transfer material P pass is the same as in the first embodiment.

Now, the effects of the present invention will be described by showing the results of a comparative experiment conducted by the present inventors with a conventional heat fixing device. For the configuration of the conventional heat fixing device used for comparison, the experimental method, and the evaluation criteria,
This is the same as the first embodiment.

First, the conventional fixing rollers having different outer diameters are
Table 5 shows the experimental results of the heat fixing device combined with the pressure roller having the release layer on the surface layer portion.

[0040]

[Table 5]

According to this, as the outer diameter of the fixing roller becomes smaller, the mechanical strength of the fixing roller decreases, and when the fixing roller is brought into pressure contact with the pressure roller, the mechanical strength of the fixing roller is bent into an arc shape. It can be seen that a greater amount of pressure and heat are applied to both ends of the sheet, the fibers of the transfer material are greatly stretched, and reverse curl occurs in the transfer material, which tends to deteriorate the stackability.

Table 6 shows the experimental results when the fixing rollers according to the present invention having different outer diameters were combined with a pressure roller having a release layer on the surface layer portion thereof.

[0043]

[Table 6]

According to this, when the diameter of the fixing roller is reduced, the wall thickness of the fixing roller is increased in order to obtain mechanical strength, so that the power consumption is not increased. Even if the outer diameter is small, it is possible to improve the stacking property without applying a large amount of pressure and heat to both ends of the transfer material. In an image forming apparatus such as a personal computer printer which is becoming more and more used for personal use, it is important to keep power consumption as low as possible, and 600 W is generally set as an upper limit. In such a situation, it is preferable to set the outer diameter of the fixing roller to 30 mm or less in order to reduce the wait-up time so that the user does not feel any trouble. In this case, "waviness" and loadability In order to achieve both of these, it is effective to improve the end shape of the fixing roller as in the present invention.

[0045]

As described above, according to the present invention, both end portions of the recording material are provided with a stiffness to prevent "waviness" from occurring in this portion and to prevent reverse curling of the recording material. It is possible to prevent the load and improve the loadability.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an image forming apparatus according to the present invention.

FIG. 2 is a configuration diagram of a heat fixing device according to the present invention.

FIG. 3 is a diagram showing a shape of a fixing roller according to the present invention.

FIG. 4 is a diagram showing a shape of a fixing roller included in a heat fixing device as a comparative example.

FIG. 5 is a diagram showing a shape of a pressure roller included in a heat fixing device as a comparative example.

FIG. 6 is a configuration diagram of a heat fixing device in another embodiment according to the invention.

FIG. 7 is a configuration diagram of a heat fixing device in still another embodiment according to the present invention.

FIG. 8 is a diagram showing a pressure state of a fixing roller and a pressure roller according to the present invention.

[Explanation of symbols]

 9 Fixing roller 10 Pressure roller 13 Halogen heater 16 Thermistor

Front Page Continuation (72) Inventor Koichi Tanigawa 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Hiromichi Tsujii 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (4)

[Claims] 1. A fixing rotating body having a core material and a releasable resin layer provided on the core material, and a pressure rotating body having a rubber layer forming a nip with the fixing rotation body. In a fixing device having a recording material supporting an unfixed image in a nip and fixing the recording material, the core material of the fixing rotating body has a maximum diameter portion between the central portion and the end portion and within the maximum recording material passage area. The fixing device has a shape in which the diameter gradually decreases from the maximum diameter portion toward the inside and the outside, and the outer shape also follows this core material shape. 2. A recording in which an unfixed image is supported by the nip, which has a fixing rotator in contact with the unfixed image and a pressure rotator which forms a nip with the fixing rotator and has a hardness lower than that of the fixing rotator. In the fixing device for sandwiching and conveying a material for fixing, the fixing rotator has a maximum diameter portion between the central portion and the end portion and within the maximum recording material passage area. A fixing device having a shape in which a facing diameter is gradually reduced, and the pressing rotary body is substantially straight or an inverted crown shape. 3. A recording material which has an unfixed image in contact with the unfixed image and a pressure rotator which forms a nip with the fixing rotator and has a hardness lower than that of the fixing rotator. In the fixing device for sandwiching and carrying the sheet for fixing, the fixing rotator has a maximum diameter portion between the central portion and the end portion and within the maximum recording material passage area, and the hardness of the pressing rotator is 30.
A fixing device characterized in that the angle is not less than 70 ° and not more than 70 °. 4. A recording method comprising: a fixing rotator in contact with an unfixed image; and a pressure rotator that forms a nip with the fixing rotator and has a hardness lower than that of the fixing rotator, and supports the unfixed image in the nip. In a fixing device for nipping and conveying a material for fixing, the fixing rotator has a diameter of 30 mm or less, and has a maximum diameter portion between a central portion and an end portion and within a maximum recording material passage area. A fixing device having a shape in which the diameter gradually decreases from the diameter portion toward the inside and the outside.