JP2966360B2 - Pressure roller - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure roller used for a heat fixing device, and more particularly to a low-hardness pressure roller.

[0002]

2. Description of the Related Art A heat roll fixing device has been widely put into practical use as a fixing device of a copying machine, a printer or a facsimile machine. The heat roll fixing device includes a heat roller that heats and fuses an unfixed toner image, a pressure roller that is pressed against the heat roller to form a nip, and an infrared lamp that is disposed in an internal space of the heat roller. I have. The heat roller generally has a core metal roller of an aluminum pipe, and a fluororesin layer or a silicon rubber layer is formed on an outer peripheral surface thereof. Further, the pressure roller has a dense and elastically deformable silicon rubber layer having a thickness of about 5 mm formed on the outer peripheral surface of a metal roller shaft. Pressing springs are attached to both ends of the heat roller and the pressure roller, and a nip of an appropriate uniform width is formed between the two rollers by using the elastic deformation of the pressure roller, and the recording paper passes through the nip. As a result, the unfixed toner image is heated and fused.

[0003]

On the other hand, in a heat roll fixing apparatus, it is strongly demanded that the start-up time from when a main switch is turned on to when a copying operation can be performed be as short as possible. In order to achieve this object, it is necessary to reduce the heat capacity of the heat roller by making the core of the heat roller as thin as possible. However, if the thickness of the cored bar is reduced, the heat capacity of the heat roller is reduced and the start-up time can be shortened, but the mechanical strength is reduced and the heat roller is bent. In other words, since the heat roller and the pressure roller have a strong pressing force applied by the pressing spring at both ends thereof,
As the mechanical strength of the heat roller decreases, the central portion of the heat roller in the axial direction is curved and deformed away from the pressure roller. To reduce such bending, the crimping force must be reduced.
The nip width required for fixing becomes small, and insufficient fixing occurs.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a pressure roller for a heat fixing device which can exhibit a very small amount of bending even when a thin cored roller is used, and can exhibit good fixing performance.

[0005]

A pressure roller according to the present invention comprises a metal roller shaft, an elastically deformable elastic rubber layer formed on the roller shaft, and a separation roller formed on the outer peripheral surface of the elastic rubber layer. The elastic rubber layer is made of foamed urethane having open cells, and one side of the elastic rubber layer is communicated with the other side via open cells formed inside, It is characterized in that air is circulated inside the layer.

As a result of the present inventor's experiment and analysis on the cause of the bending that occurs in the heat roller, it was found that the cause was strongly due to the hardness of the pressure roller pressed against the heat roller. In other words, since the conventional pressure roller having a dense silicon rubber layer has high hardness, it can be used in combination with a thick cored heat roll to form an appropriate nipple width with a smaller bending property. be able to. However, when used in combination with a thin-walled metal core heat roller, if the pressure force required to form a nip of the appropriate width is applied, the heat roller will be deformed before the pressure roller is sufficiently elastically deformed. Large bending occurs. Therefore, it is necessary to lower the hardness of the pressure roller for a cored heat roller having a small wall pressure. In this case, if a pressure roller made of a dense elastic rubber material is used like a conventional pressure roller, there is a limit to the amount of deformation of the rubber material itself even if the rubber hardness is reduced. is there.

Based on such recognition, the present invention uses a foamable rubber material layer as the elastic rubber layer. Urethane foam not only has a significantly low rubber hardness itself, but also has a large amount of deformable rubber material layer, so it is possible to form a sufficiently wide nip width even with a weak crimping force, thus significantly reducing the amount of bending. it can.

[0008] However, since the single-foam rubber material has low hardness but relatively low heat resistance, if the conventional foam rubber material is used as it is, the pressure roller itself will be at a high temperature, and it will take a short time. It easily deteriorated due to heat and could not be put into practical use as a specific pressure roller.

Further, since the single-cell rubber material has a much smaller heat capacity than a dense rubber material, it has a characteristic that it is easily affected by a thermal change. For example, as the copying operation is repeated, the temperature of the pressure roller rises, the outer diameter of the pressure roller increases, and the nip width greatly changes compared to the initial state. As a result, not only the fixing unevenness occurs, but also the paper passing property is adversely affected. Furthermore, since the heat capacity of the single-foam rubber material is small, the heat transmitted from the heat roll is immediately transmitted to the core roller, and the core roller heats up. As a result, the mechanical driving of the pressure roller is adversely affected. May be exerted.

In order to eliminate the inconvenience caused by using the foamable rubber material described above, in the present invention, the elastic rubber layer is formed of a foamed rubber material having open cells. In the case of a single-bubble rubber layer, heat transmitted from the heat roller accumulates inside the elastic rubber layer, and the temperature of the foam rubber layer rises to a high temperature.
On the other hand, in the case of open-cell elastic rubber, since the air flow passes through the inside of the elastic rubber layer through the open cells, the heat conducted from the heat roller is removed to the outside through the open cells, The temperature of the foamed rubber layer is always kept at a certain temperature or lower, and there is no thermal deterioration. Moreover, the heat is not transmitted to the inner core roller, and the temperature rise of the core roller can be effectively prevented. That is, the foamed rubber layer having open cells exerts a kind of heat-insulating action against heat conducted from the heat roller. In addition, since the air flow that has been heated through the continuous air bubbles is discharged to the outside of the device by the fan provided in the device, the temperature rise of the entire device can be effectively prevented.
As a result, a release material layer is formed on the outer peripheral surface, and a pressure roller having extremely low hardness can be realized.

[0011]

FIG. 1 is a diagrammatic sectional view showing the structure of an example of a pressure roller for a heat roll mounting apparatus according to the present invention. The pressure roller has a roller shaft 1 made of metal,
An elastic rubber layer 2 that is elastically deformable is provided on the outer peripheral surface of the roller shaft. This elastic rubber layer is made of, for example, urethane foam. This foamed rubber material is a continuous foamed rubber material having open cells. The release material layer 3 is provided on the elastic rubber layer 2. In this example, the release material layer 3 is made of an RTV that can be vulcanized at room temperature.
Composed of silicone rubber. Therefore, a high release material layer is formed in which the silicon rubber of the RTV has entered from the outer peripheral surface of the foamed rubber layer 2 to a shallow depth.

In this pressure roller, the elastic force is given by the elastic rubber layer 3, and the releasing performance is given by the releasing material layer 2 formed on the roller surface. That is, since the performance of providing elasticity and the release performance are separately borne by the two individual layers, a pressure roller having a desired hardness can be realized, for example, when the Asker hardness is about 10 ° to 15 °. A pressure roller having extremely low hardness can be realized.

What is important here is that the elastic rubber layer 2 is made open-celled. A large amount of heat flows into the pressure roller by heat conduction from a high-temperature heat roller in contact with and disposed through the release material layer 3. In this case, if the elastic rubber layer is formed of a single-foam rubber material, the heat that has flowed in accumulates inside the elastic rubber layer, and the temperature of the elastic rubber layer rises to a high temperature, resulting in thermal degradation. . In contrast, in the present invention,
Since the elastic rubber layer 2 has open cells, the side surface 1 of the roller
The inside of the elastic rubber layer 3 communicates with the outside via a and 1b, and air always flows through the inside of the elastic rubber layer. As a result, the heat that has flowed in through the release material layer 3 is quickly discharged to the outside through the open cells inside the elastic rubber layer and the side surfaces 1a and 1b, and the temperature rise of the elastic rubber layer is prevented.

FIG. 2 is a schematic sectional view showing a modification of the pressure roller according to the present invention. Note that the same members as those used in FIG. In this example, the release material layer 3 provided on the outer peripheral surface of the elastic rubber layer 2 is formed of a tube of a fluororesin. Since the fluororesin has heat shrinkability, an adhesive layer is formed on the surface of the elastic rubber layer 2 and a fluororesin tube is put on the adhesive layer, so that a fluororesin roller with lower hardness can be realized.

The present invention is not limited to the above-described embodiment, and various modifications and changes are possible. For example, in the above-described embodiment, a heat roll fixing device has been described as an example. However, the present invention can also be applied to various types of fixing devices in which heat flows from a release material layer. The present invention can also be applied to a fixing device that heats through a conductive film. Further, as the release material layer, a material obtained by covering a dense silicon rubber layer with a fluororesin tube may be used.

[0016]

As described above, according to the present invention, a release material layer is formed on an elastically deformable elastic rubber layer, and the elastic rubber layer is formed of a foamed rubber material having open cells. The inside of the elastic rubber layer is communicated with the outside of the roller, so that an air flow always flows through the inside of the elastic rubber layer, and as a result, a desired low hardness pressure roller which is not affected by the heat flowing through the release material layer. Can be realized.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing a configuration of an example of a pressure roller according to the present invention.

FIG. 2 is a schematic sectional view showing a modified example of the pressure roller according to the present invention.

[Explanation of symbols]

 1 roller shaft 2 elastic rubber layer 3 release material layer

Claims (3)

(57) [Claims] A metal roller shaft, an elastically deformable elastic rubber layer formed on the roller shaft, and a release material layer formed on an outer peripheral surface of the elastic rubber layer. The elastic rubber layer was made of urethane foam having open cells, and one side of the elastic rubber layer was connected to the other side through the open cells formed therein, so that air flowed through the elastic rubber layer. A pressure roller characterized by the above-mentioned. 2. The method according to claim 1, wherein the release material layer is formed of a dense silicon rubber layer or a fluororesin layer.
2. The pressure roller according to 1. 3. The pressure roller according to claim 2, wherein the release material layer has a dense silicone rubber layer and a fluororesin layer formed thereon.