JP7201112B2 - Fixing device - Google Patents

Description

The present invention relates to a fixing device for thermally fixing a toner image on a recording medium.

Conventionally, there has been known a fixing device that nips a sheet-like recording medium between a heating roller and an endless belt to thermally fix the recording medium. An elastic body is arranged inside the endless belt, and the elastic body is pressed toward the heating roller. Patent Document 1 describes a fixing device in which two elastic bodies are provided apart from each other in the conveying direction of a recording medium in order to enlarge the nip area. In this fixing device, the hardness of the elastic body on the downstream side is greater than the hardness of the elastic body on the upstream side in order to increase the nip pressure on the downstream side and reduce wrinkles on the recording medium.

Japanese Unexamined Patent Application Publication No. 2017-021068

However, if the elastic body on the upstream side is soft, when the elastic body is pressed against the heating roller, the elastic body deforms greatly following the heating roller. Therefore, since the recording medium is heated in a bent state, there is a problem that the curling (bending) of the recording medium that has passed through the nip portion becomes large.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a fixing device that suppresses curling of a recording medium.

In order to solve the above-described problems, the fixing device of the present invention is a roller having an endless belt, a first elastic body, a second elastic body harder than the first elastic body, and an elastic layer on the outer circumference, comprising: and a roller that sandwiches the endless belt between the elastic body and the second elastic body and transports the recording medium in the transport direction between the endless belt. The first elastic body is positioned upstream in the transport direction from the second elastic body. The elastic layer is softer than the first elastic body.

According to such a configuration, in the nip region between the first elastic body and the roller, the elastic layer of the roller is crushed, and the recording medium sandwiched between the roller and the first elastic body approaches a flat surface, thereby preventing curling of the recording medium. can be suppressed.

In the fixing device described above, the first elastic body may have a corner portion at the downstream end in the transport direction.

According to such a configuration, since the corner portion is provided at the downstream end of the first elastic body, the recording medium can be warped against the roller by strongly pressing the recording medium against the roller at the corner portion. Therefore, even if the recording medium is curled so as to wind around the roller in the nip region between the first elastic body and the roller, the recording medium can be warped back by pressing with the corner portion to reduce curling. .

The fixing device described above may have a configuration in which a gap is provided between the first elastic body and the second elastic body in the conveying direction.

With such a configuration, the nip area can be widened.

In the fixing device described above, the elastic layer may have a durometer hardness of less than 6, and the first elastic body may have a durometer hardness of 6-20.

In the fixing device described above, the second elastic body may have a durometer hardness of 60-90.

In the fixing device described above, the durometer hardness of the elastic layer is 5 or less, the durometer hardness of the first elastic body is 6 to 10, and the durometer hardness of the second elastic body is 70 to 90. may be configured.

According to such a configuration, it is possible to suppress the curling of the recording medium, improve the releasability of the recording medium, and suppress the driving torque of the fixing device while widening the nip width.

In the fixing device described above, the roller may have a heater.

According to the present invention, it is possible to suppress the curling of the recording medium from increasing in the fixing device.

1 is a cross-sectional view of an image forming apparatus equipped with a fixing device according to the present invention; FIG. 1 is a cross-sectional view showing a fixing device according to an exemplary embodiment; FIG. 4 is a cross-sectional view of the fixing device in an unnipped state; FIG. FIG. 5 is a diagram showing curl characteristics, peeling characteristics, and nip load when the hardness of the first elastic body and the hardness of the second elastic body are changed.

Next, embodiments of the present invention will be described in detail with reference to the drawings as appropriate. In the following description, unless otherwise specified, the vertical direction shown in FIG. 1 is up and down, the right side in FIG. indicates

As shown in FIG. 1, a laser printer 1 as an example of an image forming apparatus includes a housing 2, a supply unit 3 for supplying a recording medium S such as a recording sheet, and a toner image forming apparatus for forming a toner image on the recording medium S. It mainly includes a process section 4 and a fixing device 100 .

The supply unit 3 is provided in the lower part of the housing 2 and includes a supply tray 31 that accommodates the recording medium S and a supply mechanism 32 that conveys the recording medium S in the supply tray 31 toward the process unit 4. ing.

The process section 4 is housed inside the housing 2 and includes an exposure device 5 , a process cartridge 6 and a transfer roller 63 .

The exposure device 5 is arranged in the upper part of the housing 2, and irradiates the surface of the photosensitive drum 61, which will be described later, with a laser beam indicated by a dashed line at high speed.

The process cartridge 6 is arranged below the exposure device 5 and is detachable from the housing 2 . The process cartridge 6 includes a photosensitive drum 61 on which an electrostatic latent image is formed, a charger 62 , a toner containing portion 65 containing toner, and a supply unit for supplying the toner in the toner containing portion 65 to the photosensitive drum 61 . A roller 66 and a developer roller 64 are provided.

In this process cartridge 6 , the charger 62 uniformly charges the surface of the rotating photosensitive drum 61 . The exposure device 5 emits a laser beam onto the surface of the photoreceptor drum 61 to expose the surface of the photoreceptor drum 61 , thereby forming an electrostatic latent image on the surface of the photoreceptor drum 61 based on image data.

Next, a developing roller 64 that is rotationally driven supplies toner to the electrostatic latent image on the photoreceptor drum 61 to form a toner image on the surface of the photoreceptor drum 61 . After that, the toner image carried on the surface of the photoreceptor drum 61 is attracted to the transfer roller 63 when the recording medium S is conveyed between the photoreceptor drum 61 and the transfer roller 63 and is transferred onto the recording medium S. be transcribed.

The fixing device 100 is provided behind the process cartridge 6 . The toner image transferred onto the recording medium S is thermally fixed onto the recording medium S by passing through the fixing device 100 .
The recording medium S on which the toner image is thermally fixed is discharged onto the discharge tray 22 by the conveying rollers 23 and 24 .

As shown in FIG. 2, the fixing device 100 mainly includes a heating roller 110 as an example of a roller and a pressure unit 120 arranged to face the heating roller 110 .

Heating roller 110 is a cylindrical roller. The heating roller 110 has a base pipe 111 made of metal or the like, an elastic layer 112 provided on the outer periphery of the base pipe 111 , and a heater 113 provided inside the base pipe 111 . A coating having heat resistance and abrasion resistance may be provided on the outside of the elastic layer 112 . The heating roller 110 is rotatably supported by a frame (not shown) of the fixing device 100, and is rotated clockwise in FIG. to rotate.

The elastic layer 112 is made of rubber such as silicone rubber, for example. The elastic layer 112 is softer than the first elastic body 123, which will be described later. Specifically, the elastic layer 112 preferably has a durometer hardness of less than 6, more preferably 5 or less.

Here, hardness means durometer hardness defined in ISO7619-1. Durometer hardness is a value obtained from the depth of penetration of a specified indenter into a test piece under specified conditions.

The hardness of silicone rubber can be adjusted by changing the ratio of additives (silica-based filler or carbon-based filler) added during production. Specifically, increasing the ratio of the additive increases the hardness of the rubber. The hardness can also be reduced by adding silicone oil. Liquid injection molding or extrusion molding can be used as a method for producing the rubber. In general, low hardness rubber is suitable for liquid injection molding, and high hardness rubber is suitable for extrusion molding.

The heater 113 heats the elastic layer 112 of the heating roller 110 . As the heater 113, for example, a halogen lamp that emits light when energized and heats with radiant heat can be used.

The pressing unit 120 is pressed toward the heating roller 110 by a pressing mechanism (not shown) to form a nip portion N for thermally fixing the recording medium S. As shown in FIG. The nip portion N is formed of a first nip portion N1, a second nip portion N2, and a third nip portion N3.

The pressure unit 120 mainly includes an endless belt 121 , a belt guide 122 , a first elastic body 123 , a second elastic body 124 , a holder 125 , a sliding sheet 126 and a stay 127 . Belt guide 122 , first elastic body 123 , second elastic body 124 , holder 125 , sliding sheet 126 and stay 127 are positioned inside endless belt 121 when viewed from the width direction of endless belt 121 .

The endless belt 121 is sandwiched between the heating roller 110 , the first elastic body 123 and the second elastic body 124 . The endless belt 121 is an endless belt having heat resistance and flexibility. The endless belt 121 is rotatably supported at both ends thereof by side guides (not shown). The endless belt 121 is provided so as to be driven to rotate counterclockwise in FIG. 2 by the rotation of the heating roller 110 .
The recording medium S is transported in the transport direction between the heating roller 110 and the endless belt 121 . The conveying direction is the same as the direction from the entrance to the exit of the nip portion N formed between the heating roller 110 and the endless belt 121 .

The belt guide 122 is a member arranged so as to be able to come into contact with the inner peripheral surface of the endless belt 121 and guide the endless belt 121 .

The first elastic body 123 is located upstream of the second elastic body 124 in the transport direction. The first elastic body 123 sandwiches the endless belt 121 with the heating roller 110 . First elastic body 123 forms first nip portion N1 with heating roller 110 . As shown in FIG. 3, when the heating roller 110 is not in contact with the endless belt 121, the first elastic body 123 is rectangular parallelepiped and elongated in the left-right direction.

The first elastic body 123 is made of rubber such as silicone rubber, for example. The first elastic body 123 is harder than the elastic layer 112 of the heating roller 110 and softer than the second elastic body 124 . Specifically, the first elastic body 123 has a durometer hardness of 6-80, preferably 6-20, more preferably 6-10.

The first elastic body 123 has a corner portion 123A at the downstream end in the transport direction. More specifically, the portion where the surface of the first elastic body 123 in contact with the inner peripheral surface of the endless belt 121 and the side surface of the first elastic body 123 facing the second elastic body 124 are connected has a substantially right angle. It has a portion 123A.

The second elastic body 124 is arranged downstream of the first elastic body 123 in the transport direction at a predetermined distance. A gap 128 is provided between the first elastic body 123 and the second elastic body 124 by a predetermined distance. The second elastic body 124 sandwiches the endless belt 121 with the heating roller 110 . Second elastic body 124 forms second nip portion N2 with heating roller 110 . Further, the endless belt 121 forms a third nip portion N3 at a position corresponding to the gap 128 in the conveying direction. The second elastic body 124 is rectangular parallelepiped in a state where the heating roller 110 is not in contact with the endless belt 121, and is formed in an elongated shape elongated in the left-right direction. The dimension of the second elastic body 124 is smaller than the dimension of the first elastic body 123 in the direction in which the heating roller 110 and the pressure unit 120 are arranged, which is the vertical direction in this embodiment.

The second elastic body 124 is made of rubber such as silicone rubber, for example. The second elastic body 124 is harder than the first elastic body 123 . Specifically, the second elastic body 124 has a durometer hardness of 10-90, preferably 60-90, more preferably 70-90.

The holder 125 is a member that holds the first elastic body 123 and the second elastic body 124 . The sliding sheet 126 is sandwiched between the inner peripheral surface of the endless belt 121 and the first elastic body 123 and the second elastic body 124 . The stay 127 is arranged between the belt guide 122 and the holder 125 and supports the belt guide 122 and the holder 125 .

According to the fixing device of this embodiment described above, the following functions and effects can be obtained.

When the recording medium S is conveyed to the fixing device 100, the recording medium S is first nipped at the first nip portion N1. Since the elastic layer 112 of the heating roller 110 is softer than the first elastic body 123, the elastic layer 112 of the heating roller 110 is crushed at the first nip portion N1, and the recording medium is sandwiched between the heating roller 110 and the first elastic body 123. The S is thermally fixed while maintaining a nearly planar shape. As a result, curling of the recording medium S can be suppressed.

In the first nip portion N1, the recording medium S may curl so as to wind around the heating roller 110. FIG. However, since the first elastic body 123 has a corner portion 123 A at the downstream end, the corner portion 123 A strongly presses the recording medium S against the heating roller 110 , thereby warping the recording medium S against the heating roller 110 . . Therefore, even if the recording medium S is curled at the first nip portion N1, the recording medium S can be returned in the opposite direction. Therefore, it is possible to suppress the curl of the recording medium S from increasing.

After passing through the first nip portion N1, the recording medium S is nipped at the third nip portion N3. Since the recording medium S can also be nipped in the third nip portion N3 positioned corresponding to the gap 128, the nip area can be widened.

After passing through the third nip portion N3, the recording medium S is nipped at the second nip portion N2. At the second nip portion N2, the second elastic body 124 is considerably harder than the elastic layer 112, so the second elastic body 124 hardly deforms. As a result, at the second nip portion N2, the nip pressure can be increased and the peelability of the recording medium S is improved as compared with the first nip portion N1 and the third nip portion N3.

In addition, since the second elastic body 124 has a smaller vertical dimension than the first elastic body 123, the second elastic body 124 is very difficult to elastically deform.

FIG. 4 shows the results of measuring curl characteristics, peeling characteristics, and nip loads when the hardnesses of the first elastic body 123 and the second elastic body 124 in this embodiment described above are changed, and will be described below. .

Plain paper was used as the recording medium, and the durometer hardness of each member was set as follows.
Elastic layer of fixing roller 5
First elastic body 4, 6, 7, 8, 9, 10, 15, 20
Second elastic body 40, 50, 60, 70, 80, 90

For the curl characteristics, the degree of curvature (curling) of the recording medium after the recording medium is heat-fixed by the fixing device is visually determined. B,""C," and "D."
As for the peeling property, the peeling property from the fixing device was visually evaluated. "A" indicates the best peelability, and "B", "C", and "D" indicate the worse peelability.
The nip load is the nip load for keeping the nip width of the nip portion constant in the conveying direction, that is, the load that presses the pressure unit against the heating roller. and "B", "C", and "D" as the nip load increases. If the nip load becomes large, it is necessary to increase the torque of the motor for rotationally driving the heating roller 110, so the smaller the nip load, the better.

From the experimental results shown in FIG. 4, it can be seen that when the durometer hardness of the first elastic body 123 is 4, the curl characteristic is not good. Moreover, when the durometer hardness of the second elastic body 124 is 40 or 50, the peeling characteristics are poor and the nip load is large.
In summary, when the durometer hardness of the first elastic body 123 is 6 to 20 and the durometer hardness of the second elastic body 124 is 60 to 90, the nip width is widened and the recording medium S is curled. is suppressed.
Further, when the durometer hardness of the first elastic body 123 is 6 to 10, the nip load is small, so the driving torque of the fixing device 100 can be suppressed. If the durometer hardness of the second elastic body 124 is 70 to 90, the curling property can be improved.

The present invention is not limited to the above-described embodiments, and can be used in various forms as exemplified below. In the following description, members having substantially the same structure as those of the above-described embodiment are denoted by the same reference numerals, and descriptions thereof are omitted.

In the above embodiment, a monochrome laser printer is exemplified as an example of the image forming apparatus, but the image forming apparatus may be a color image forming apparatus, a copier, or a multifunction machine. Also, the recording medium is not limited to paper, and may be an OHP sheet or the like.

In the above embodiment, the roller is a heating roller having a heater, but the roller may not have a heater. In this case, a heater may be arranged inside the endless belt to heat the endless belt. Alternatively, a heater may be arranged outside the roller to heat the roller surface.

In the above-described embodiment, there is a gap between the first elastic body and the second elastic body, but the gap may be eliminated.

In the above embodiment, the first elastic body and the second elastic body are rectangular parallelepipeds, but the elastic bodies are not limited to rectangular parallelepipeds, and may have other shapes.

In the above embodiment, the dimension of the second elastic body is configured to be smaller than the dimension of the first elastic body in the vertical direction, but the dimension of the second elastic body may be equal to or larger than the dimension of the first elastic body.

In the above embodiment, the halogen lamp was exemplified as the heater, but the heater may be, for example, a carbon heater. Further, the heat source may be an induction heating type heater.

It should be noted that the elements described in the above embodiments may be combined arbitrarily.

REFERENCE SIGNS LIST 100 fixing device 110 heating roller 112 elastic layer 113 heater 121 endless belt 123 first elastic body 123A corner 124 second elastic body 128 gap S recording medium

Claims (8)

endless belt and
a first elastic body;
a second elastic body harder than the first elastic body;
A roller having an elastic layer softer than the second elastic body on the outer periphery, sandwiching the endless belt between the first elastic body and the second elastic body, and conveying a recording medium between the endless belt and the endless belt. a roller for conveying in the direction of
The first elastic body is positioned upstream in the conveying direction from the second elastic body,
having a gap between the first elastic body and the second elastic body in the conveying direction;
The first elastic body forms a first nip portion that nips the recording medium with the roller,
the second elastic body forms a second nip portion that nips the recording medium with the roller;
the endless belt forms a third nip portion that nips the recording medium at a position corresponding to the gap;
The first elastic body is a rectangular parallelepiped, and has an upstream end corner located at the upstream end in the transport direction and a downstream end corner located at the downstream end in the transport direction at the end near the roller. and a corner portion of the downstream end having a deformation amount larger than that of the corner portion of the upstream end,
The second elastic body is a rectangular parallelepiped, and has an upstream end corner located at the upstream end in the transport direction and a downstream end corner located at the downstream end in the transport direction at the end near the roller. and a downstream corner that does not form the second nip,
The fixing device, wherein the dimension of the third nip portion is larger than the dimension of the second nip portion in the conveying direction. 2. The fixing device according to claim 1, wherein the second nip portion has a higher nip pressure than the first nip portion. 3. The fixing device according to claim 1, wherein the dimension of the second elastic body is smaller than the dimension of the first elastic body in the direction in which the roller and the endless belt are aligned. a holder that holds the first elastic body and the second elastic body in the direction in which the roller and the endless belt are arranged;
A surface of the holder for holding the first elastic body and a surface for holding the second elastic body are positioned at different positions in a direction in which the roller and the endless belt are arranged. 4. The fixing device according to any one of 3. a holder that holds the first elastic body and the second elastic body in the direction in which the roller and the endless belt are arranged;
5. The fixing device according to claim 1, wherein a surface of the holder that holds the first elastic body and a surface of the holder that holds the second elastic body are parallel to each other. . The surface of the first elastic body facing the roller and the surface of the second elastic body facing the roller are parallel to each other, according to any one of claims 1 to 5. fuser. 7. The fixing device according to claim 1, further comprising a sliding sheet interposed between the first elastic body and the second elastic body and the endless belt. 8. The fixing device according to claim 1, wherein the roller has a heater.

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