JPH0695551A - Pressure fixing device - Google Patents

Abstract

PURPOSE:To provide a pressure fixing device, wherein a soft elastic body with which a fixing roller is covered, is prevented from plastic deformation. CONSTITUTION:A pair of pressure fixing rollers are provided, and the supporting shaft of one of them is secured within a hollow roller, and a center supporting roller 5 to support the supporting shaft at the two ends and the other pressure fixing roller are formed from a simple two-end support roller 4, and an image carrier is transported while pinched by the contacting part of the roller couple where either of the rollers is covered with a soft elastic body 8, and an unfixed toner image is fixed onto the image carrier. In this pressure fixing device, a stepping 1 is furnished at the roller end outside of the region where the image carrier of either roller is transported pinchedly.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to pressure fixing used in a fixing device such as an electrophotographic or electrostatic recording apparatus in which an image support having an unfixed toner image is passed between a pair of fixing rollers to fix the toner image. Regarding the device.

[0002]

2. Description of the Related Art In a conventional pressure fixing device, the surface of a metal roller is plated with hard chrome or coated with resin and a load is applied from both ends while intersecting the axis of the roller so that the pressure required for fixing is applied in the axial direction. Are generated almost uniformly along the line (called a skew type pressure fixing device). However, since the shaft centers of both rollers are crossed, there is a problem that an axial force is generated on the rollers, while an asymmetric curl or paper wrinkle is generated on the image support.

Therefore, in order to eliminate the intersection of the roller shaft centers, one of the pair of pressure fixing rollers has a supporting shaft fixed near the central portion in the axial direction inside the hollow roller, and the supporting shaft is supported at both ends. A pressure fixing device has been proposed in which a so-called center support roller and the other roller are simple both-end supporting rollers. By adopting this fixing roller, the pressure fixing device can be made compact and lightweight, and since it is not necessary to intersect the shaft centers of both rollers, it is possible to prevent generation of axial force and curling of the asymmetric image support. Further, it is well known that the pressure can be further equalized by coating one roller with a soft elastic body.

In the pressure fixing device of the type in which a load is constantly applied, the soft elastic body is plastically deformed, and if a mechanism for releasing the load when not fixing is provided, the size and cost of the device increase. was there. In this regard, a method in which an elastic member having a hardness higher than that of the elastic roller is provided outside the region where the image support is conveyed to pass therethrough and a plastic deformation of the elastic member is prevented (Japanese Patent Laid-Open No. 58-21281).
Issue gazette).

[0005]

However, in the conventional skew type pressure fixing device, since the roller is bent by the load, it is necessary to form only the end portion of the roller as an elastic member having high hardness in the axial direction of the contact portion of the roller pair. The pressure near the center cannot be reduced. This will be explained below. Among the pair of solid rollers, in the skew type pressure fixing device in which one roller is coated with resin, the pressure distribution (when not fixing) with and without a step at one roller end is shown. Shown (see FIG. 6). As can be seen from these figures, in the skew type pressure fixing device, even if a step is provided at the roller end portion, the pressure near the center in the axial direction cannot be reduced, and plastic deformation of the soft elastic body cannot be prevented. Therefore, it is essential to dispose a pair of rollers in parallel, but with a simple solid roller supporting both ends, even if the elastic member is covered, the pressure distribution is made uniform without intersecting the axes, and paper wrinkles are not generated. It was very difficult to prevent.

Therefore, a first object of the present invention is to provide a pressure fixing device which prevents plastic deformation of the soft elastic body covering the fixing roller. A second object of the present invention is to provide a small-sized, lightweight and low-cost pressure fixing device capable of obtaining a toner image having good fixing strength.

[0007]

Among a pair of pressure fixing rollers, one has a support shaft fixed in a hollow roller, and a center support roller that supports the support shaft at both ends and the other roller are simple both-end support rollers. A pressure fixing device for conveying the image support member under pressure to the contact portion of a roller pair in which one of the rollers has an outer periphery covered with a soft elastic member, and fixing the unfixed toner image on the support member. In this case, a step is provided at the end of the roller outside the area where the image support of either one of the rollers is conveyed under pressure.

Further, the load adjusting member is provided so that the load acting between the rollers when the image support is not fixed between the rollers and not fixed is smaller than the load required for fixing.

[0009]

The present invention will be described below with reference to the accompanying drawings. FIG. 1 is a left side view of a first embodiment of the present invention, and FIG. 2 is a sectional view of the first embodiment. The pressure fixing device according to the first embodiment is roughly rotatably supported by a center support roller 5 supported by a fixed housing 12 via a bearing 11, and similarly supported by a movable housing 13 via a bearing 11. It is composed of a cylindrical solid roller 4. By solidly connecting the movable housing 13 and the fixed housing 12 via the connecting shaft 14, the solid roller 4 and the center support roller 5 are arranged in parallel. Further, the movable housing 13 is provided with a pressurizing device 6 for pressing the movable housing 13 in the direction A in the figure, so that the center support roller 5 can be pressed against the solid roller 4 with an arbitrary linear pressure. Has become.

Further, the center support roller 5 is
A sleeve 51 formed in a cylindrical shape, and this sleeve 5
The support shaft 52 is press-fitted in the length direction of the first shaft and is formed so that the outer diameter of the substantially central portion is gently thicker than the outer diameter of both end portions.
It consists of and. The sleeve 51 and the support shaft 52 are made of hardened steel and have a length of 280 mm, and a step having a height of 0.6 mm is provided at both ends (each having a width of 5 mm). And
The outer peripheral surface of the sleeve 51 is covered with a soft elastic body 8 having a uniform thickness in a region (width 270 mm) in which the image support is conveyed under pressure. The outer diameter D ₁ of the portion covered with the soft elastic body 8 is φ35.02 mm
The outer diameter D ₂ of both ends 9 is φ35 mm, and the soft elastic body 8 is a hard urethane having a compression elastic modulus of 40 kg / mm ² and a thickness of 0.61 mm.

The compression elastic modulus of the soft elastic body is 20 to 100 (kg
/ Mm ² ), and the value a / t divided by the thickness t of the soft elastic body covering the compression elastic modulus a (kg / mm ² ) is 200 or less. By covering the soft elastic body 8 described above, the minute non-uniformity of the pressure distribution due to the unevenness of the arc itself can be eliminated. About 40 to 50 kg / mm ² is more preferable for practical use.

On the other hand, in the solid roller 4, the surface of the hardened steel is plated with hard chrome, and the length thereof is 280 mm and the outer diameter is φ35 mm. Also, the pressing force is a total load of 500
It was set to kgf. With such a configuration, the pressure necessary for fixing can be applied to the image support during fixing, and the plastic deformation of the soft elastic body 8 can be prevented by receiving the load at the steps 1 at both ends during non-fixing.

The width of the step 1 must be determined so that the pressure applied to the step does not exceed the compression limit pressure of the roller material. The compression limit pressure of the hardened steel of Example 1 is about 600.
Since it is 0 kg / cm ² , the width of step 1 must be set so that the pressure applied to step 1 does not exceed this value. Further, the shape of the step 1 is trapezoidal, and it is more preferable that the corners have a radius, because the strength is stronger and the local concentration of stress can be avoided.

FIG. 3 shows a second embodiment of the present invention. A step 1 having a height of 0.7 mm is provided at both ends of the solid roller 4 (width of 10 mm each), and the center support roller 5 has a uniform outer surface of the sleeve within the region (width 270 mm) in which the image support is nipped and conveyed. The soft elastic body 8 was coated with a sufficient thickness. Both rollers have a length of 290 mm, and the outer diameter of the central portion of the solid roller 4 is 35 mm.
The outer diameters of both end portions were φ35.5 mm, the outer diameter of the portion of the center support roller 5 covered with the soft elastic body 8 was φ35.02 mm, and the outer diameter of the uncoated portion was φ33.6 mm. Soft elastic body 8
Is a hard urethane having a compression modulus of 50 kg / mm ² and a thickness of 0.71 mm.

With this configuration, the same operation as that of the first embodiment can be obtained. FIG. 4 shows pressure distributions during non-fixing and fixing according to the first and second embodiments. As can be seen from these figures, the load can be received by the step portions 1 at both ends (relative to the core portion of the roller) at the time of non-fixing to prevent deformation of the soft elastic body 8, and sufficient pressure can be applied at the time of fixing. When the step 1 is not provided on both ends 9 of the roller, the soft elastic body 8 is deformed by about 20 μm under the above conditions. On the other hand, the image carrier is compressed to about 40 to 70 μm when it is conveyed while being pressed by the contact portion of the roller pair. That is, since the distance between the pair of rollers is 40 to 70 μm, the load is received by the both ends 9 of the roller at the time of non-fixing, the plastic deformation of the soft elastic body 8 is prevented, and the portion covered with the soft elastic body 8 and the solid state at the time of fixing. A pressure necessary for fixing can be applied between the roller 4 and the roller 4.

The relationship between the roller outer diameters D ₁ and D ₂ may be D ₁ > D ₂ as long as the contact pressure between the roller pair during non-fixing can be limited to the extent that the soft elastic body 8 does not undergo plastic deformation, and is also required during fixing. D ₁ <D ₂ may be used as long as it can apply a sufficient pressure. That is, the height of the step 1 is h, the thickness of the soft elastic body 8 is tc, the thickness of the image support is tp, and the thickness of the image support is between the soft elastic body 8 and the image support while the image support is being conveyed under pressure. The strain amounts are Δtc and Δtp, and the elastic limit strains of the soft elastic body 8 are Δtc.
_{When max} / tc, tc-Δtc _max ≤h <tc + tp
The step 1 satisfying -Δtc -Δtp may be provided.

FIG. 5 (a) shows tp, tc, h under no load, and (b) shows tp-.DELTA.tp, tc-.DELTA.tc under load. In the first and second embodiments, the roll is provided with a step, but an example in which a step is provided by providing a protrusion on a frame that supports the roll will be described below. Figure 7
Is a left side view of the third embodiment of the present invention, and FIG. 8 is a sectional view thereof. The same components as those in FIGS. 1 and 2 are designated by the same reference numerals, and the same description will not be repeated.

In the pressure fixing device of the third embodiment, the sleeve 51 and the support shaft 52 are made of hardened steel, and have a length of 270 μm and an outer diameter D ₄ of 35 mm.
The soft elastic body 28 covering the sleeve 51 is made of hard urethane having a compression elastic modulus of 50 kg / mm ² and a thickness of 1.0 mm.
On the other hand, in the solid roller 4, the surface of the hardened steel is hard chrome plated, the length is 270 mm, and the outer diameter D ₃ is φ3.
It is set to 5 mm. The pressing force was set to a total load of 500 kgf. Then, a gap of about 10 μm is provided between the pair of rollers by the stopper 29 at the time of non-fixing. When the stopper is not provided, the soft elasticity 28 deforms by about 20 μm. On the other hand, when the image carrier is conveyed while being nipped by the contact portion of the roller pair,
It is compressed to about 40 to 70 μm. That is, since the distance between the pair of rollers is 40 to 70 μm, the stopper 29 provides a gap between the pair of rollers at about 10 μm during non-fixing to prevent the soft elastic body 8 from being plastically deformed during non-fixing. A sufficient load can be applied during fixing.

As the stopper 29, it is sufficient to limit the contact pressure between the roller pair during non-fixing to the extent that the soft elastic body 28 does not undergo plastic deformation, and it is not always necessary to provide a gap between the roller pair. That is, the distance between the centers of the upper and lower rollers is h, and the thicknesses of the soft elastic body and the image support are tc, tp, and
When the compression deformation amounts of the soft elastic body and the image support while the image support is being conveyed under pressure are Δtc and Δtp, and the elastic limit strain of the soft elastic body is Δtc _max / tc, (D ₃ + D A stopper 29 satisfying ₄ ) / 2-Δtc _max ≦ h <(D ₃ + D ₄ ) / 2 + tp-Δtc-Δtp may be provided. However, the above conditions are satisfied when the load change between fixing and non-fixing is small. When the change in load between fixing and non-fixing is large and the change Δtc (during fixing) -Δtp (during non-fixing) of the soft elastic body is larger than the thickness tp-Δtp of the image support during fixing. Does not satisfy the above conditions.

The stopper 29 has a substantially trapezoidal shape and has a radius at each corner. The size of the stopper 29 is preferably as large as possible in consideration of the compression limit pressure of the material. In the third embodiment, a stopper 29 made of hardened steel is attached to the fixed housing 12, and the contact area with the movable housing 13 is 1.5 mm × 1.0 mm.
So that The mounting position was 70 mm from the connecting shaft. The attachment position is preferably far from the connecting shaft.

FIG. 9 is a diagram showing a fourth embodiment of the present invention. The bolt 9A is used as a stopper.
The use of the bolt 9A has a feature that the adjustment becomes easy. FIG. 10 is a diagram showing a fifth embodiment of the present invention. A spacer 9B is used on the shaft of the pressure device 6 as a stopper. The spacer 9B is not necessarily fixed.

FIG. 11 is a diagram showing a sixth embodiment of the present invention. The spring 9C is used as a stopper. The spring 9C is installed between the fixed housing 12 and the movable housing 13 so as to apply a load in the opposite direction to the pressurizing device 6, and is preferably installed outside the pressurizing device (farther from the connecting shaft).

[0023]

With the pressure fixing device of the present invention, curling of the image support can be suppressed and paper wrinkles can be prevented. Further, the pressure fixing device which is small in size and low in cost makes it possible to make the pressure distribution uniform.

[Brief description of drawings]

FIG. 1 is a left side view of a first embodiment of the present invention.

FIG. 2 is a sectional view of the first embodiment of the present invention.

FIG. 3 is a diagram showing a second embodiment of the present invention.

FIG. 4 is a diagram showing a pressure distribution during non-fixing and during fixing according to the first embodiment of the present invention.

FIG. 5 is a diagram showing the thickness of the soft elastic body when no load is applied and the amount of strain of the soft elastic body when a load is applied.

FIG. 6 shows a pressure distribution in the case where there is a step in the pressure fixing device of the related art.

FIG. 7 is a left side view of the third embodiment of the present invention.

FIG. 8 is a sectional view of a third embodiment of the present invention.

FIG. 9 is a diagram showing a fourth embodiment of the present invention.

FIG. 10 is a diagram showing a fifth embodiment of the present invention.

FIG. 11 is a diagram showing a sixth embodiment of the present invention.

[Explanation of symbols]

 1 step 4 solid roller 5 center support roller 8 soft elastic body 11 bearing 12 fixed housing 13 movable housing 51 sleeve

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kaoru Yoshida 2274 Hongo, Ebina City, Kanagawa Prefecture Fuji Xerox Co., Ltd.

Claims (4)

[Claims] 1. A pair of pressure fixing rollers, one of which has a support shaft fixed in a hollow roller, and a center support roller which supports the support shaft at both ends, and the other roller which is a simple both end support roller, In a pressure fixing device that conveys an image support under pressure to the contact portion of a roller pair in which either one of the rollers has a soft elastic body coated on the outer periphery, and fixes an unfixed toner image on the support. A pressure fixing device characterized in that a step is provided at an end portion of a roller outside a region where one of the rollers carries the image support with pressure. 2. The height of the step is h, the thickness of the soft elastic member is tc, the thickness of the image supporting member is tp, and the soft elastic member and the image supporting member when the image supporting member is being conveyed under pressure. The compression deformation amount of
2. The pressure fixing device according to claim 1, wherein tc, .DELTA.tp and the elastic limit strain of the soft elastic body are .DELTA.tc _max / tc, tc-.DELTA.tc _max .ltoreq.h <tc + tp-.DELTA.tc-.DELTA.tp. 3. A pair of pressure fixing rollers, one of which has a support shaft fixed in a hollow roller, and a center support roller which supports the support shaft at both ends, and the other roller which is a simple both-end support roller, In the pressure fixing device for fixing the unfixed toner image to the support by conveying the image support under pressure to the contact portion of the roller pair in which one of the rollers has a soft elastic body coated on the outer periphery thereof, A pressure fixing device characterized in that a load adjusting member is provided so that a load acting between the rollers when the support is not interposed between the rollers and unfixed is smaller than a load required for fixing. 4. The outer diameters of the upper and lower rollers under no load are D ₃ , D ₄ , the center distance is h, the thicknesses of the soft elastic body and the image support are tc, tp, and the image support is pinched, respectively. Let Δtc be the compression deformation amount of the soft elastic body and the image support while being conveyed.
, Δtp, the elastic limit strain of the soft elastic body is Δtc _max / tc
And a load adjusting member satisfying (D ₃ + D ₄ ) / 2-Δtc _max ≦ h <(D ₃ + D ₄ ) / 2 + tp-Δtc-Δtp is provided. 3. The pressure fixing device according to item 3.