JPH036506B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a fixing device in a copying machine, printer, etc. that uses an electrophotographic process, and particularly relates to an improvement of a fixing device that uses a so-called hot roll method.

[Conventional technology]

Generally, copying machines, printers, etc. that use an electrophotographic process are equipped with a fixing device that fixes unfixed toner images on paper, and a so-called heat roll type fixing device is widely used as an example of this fixing device. ing.

Conventionally, this type of fixing device has a heating roll 1 heated by a heat source, for example, as shown in FIG.
and a pressure roll 5 that is in pressure contact with the heating roll 1 and rolls together with the heating roll 1. The heating roll 1 has, for example, a metal cylindrical core 2 with shafts integrally formed at both ends, and a heater 3 as a heat source is disposed inside the cylindrical core 2. The surface of the cylindrical core 2 is coated with a heat-resistant mold release layer 4, and the pressure roll 5 has a cylindrical roll 7 made of a heat-resistant elastic material fitted onto a metal shaft 6. in,
When it comes into contact with the heating roll 1, a predetermined fixing nip is formed.

In this type, the heating roll 1
When the paper 8 carrying the unfixed toner image passes between the heating roll 1 and the pressure roll 5, the heat from the heating roll 1 and the pressure from the pressure roll 5 act on the toner and the paper 8, The unfixed toner image will be fixed on the surface of the toner image. In addition, in Figure 4,
10 is a peeling claw that peels off the paper 8 wrapped around the heating roll 1, 11 is a blade that cleans dirt on the surface of the heating roll 1, 12 is a temperature sensor that detects the surface temperature of the heating roll 1, and 13 is a part after passing through the fixing device. A discharge roll 14 is a guide for guiding the paper 8 after passing through the fixing device to the discharge roll 13, which discharges the paper 8 to a storage tray (not shown).

[Problem to be solved by the invention]

Incidentally, in such a conventional fixing device, a predetermined warm-up time is required until the thermal energy from the heater 3 is transmitted to the surface of the heating roll 1. In this case, in order to shorten the warming-up time, conventionally, the heat capacity of the heating roll 1 is usually set to be small so that the surface temperature of the heating roll 1 rises quickly. However, as the heat capacity of the heating roll 1 is small, the surface temperature of the heating roll 1 locally increases too much, especially when a small-sized paper 8 passes between the pair of rolls 1 and 5. A situation arises. That is,
When the large-sized paper 8 passes between the pair of rolls 1 and 5, substantially the entire surface of the heating roll 1 in the axial direction comes into contact with the paper 8, so thermal energy is released from the entire surface of the heating roll 1 in the axial direction. Since the heat is emitted onto the paper 8, the surface temperature of the heating roll 1 does not locally rise to an extreme extent.
On the other hand, when a small size paper 8 passes between the pair of rolls 1 and 5, since the width of the normal paper 8 is shorter than the axial dimension of the heating roll 1, A part of the surface of the heating roll 1, for example, near both ends of the heating roll 1 in the axial direction becomes a part through which the paper 8 does not pass. At this time, thermal energy is not released from the vicinity of both axial ends of the surface of the heating roll 1 to the paper 8, so the surface temperature of the heating roll 1 near both axial ends is as shown by the dashed line in FIG. In addition, there is a possibility that the temperature rises extremely compared to other parts within the width dimension l of the paper 8 and exceeds the allowable temperature (To) of the surface of the heating roll 1. In this case, not only the heating roll 1 itself deteriorates due to heat, but also the peeling claws 10 and blades 11 installed around the heating roll 1
Also, a situation occurs in which the temperature sensor 12 and the like become easily burnt out.

As a conventional means for solving this situation, for example, as shown in FIGS. 5a and 5b, there is a method in which a heat pipe 15 is embedded inside the heating roll 1. The heat pipe 15 is a closed tube filled with a liquid (such as water) having high thermal conductivity, and is arranged along the axial direction of the heating roll 1. According to this type, the paper 8 of small size (width dimension l) is transferred to the pair of rolls 1 and 5.
If the surface temperature of the heating roll 1 corresponding to the area where the paper 8 does not pass increases when the sheet 8 passes through the gap, the thermal energy of the area will be increased as indicated by the arrow A in FIG. 5b.
As shown in FIG. 3, since the heat is transmitted to other parts through the heat pipe 15, the surface temperature of the above part does not rise excessively, and the surface temperature distribution of the heating roll 1 is as indicated by the two-dot chain line in FIG. As shown, it is applied almost uniformly. However,
In this type, manufacturing the heating roll 1 built into the heat pipe 15 is relatively time-consuming, which increases the manufacturing cost of the heating roll 1 and makes the fixing device itself expensive. The technical problem of getting used to it arises.

In addition, as other prior art, for example, JP-A-59
As shown in Publication No. 84272, only when passing small size paper, a heat dissipation roll with high thermal conductivity is placed in contact with the area of the circumferential surface of the heating roll or pressure roll where the paper does not pass. A mechanism to prevent temperature rise has also been proposed, but for this type, a mechanism for moving the heat dissipation roll back and forth between the contact position and the non-contact position is essential. Since the advancing and retracting mechanisms must be driven and controlled, the technical problem of complicating the device configuration is unavoidable.

The present invention has been made to solve the above technical problems, and has a simple configuration while minimizing deterioration of fixing performance and wasteful discharge.
The present invention provides a fixing device that can effectively prevent heat-induced deterioration of the heating roll itself and burnout of parts around the heating roll.

[Problem to be solved by the invention]

That is, the present invention includes a heating roll that is heated by a heat source, and a pressure roll that is in pressure contact with the heating roll and rolls together with the heating roll,
The fixing device is designed to fix the unfixed toner image onto the sheet by passing the sheet holding the unfixed toner image between both rolls, and heat is applied along the axial direction of the pressure roll. A feature is that highly conductive heat dissipating members are arranged in parallel, and that contact portions are provided on both sides of the heat dissipating member in the axial direction to contact portions of the circumferential surface of the pressure roll located on both sides of the small-sized sheet passage area. That is.

In such technical means, the design of the heating roll and pressure roll may be changed as appropriate within a range that maintains fixing properties.

In addition, the heat dissipation member can be selected as appropriate as long as it can maintain contact with the pressure roll, but from the viewpoint of not unnecessarily increasing the driving force of the pressure roll, it is important to reduce the contact resistance. Preferably, the number of rolls is small.

Furthermore, regarding the placement location of the above-mentioned heat dissipation member, the small size sheet passing portion (the central part in the axial direction of the heating roll or the part offset toward one end in the axial direction of the heating roll)
It can be selected as appropriate.

[Effect]

According to the above-mentioned technical means, when a small-sized sheet passes between a heating roll and a pressure roll, the thermal energy of the part of the heating roll that contacts the sheet is released to the sheet, while the thermal energy of the part of the heating roll that is in contact with the sheet is released to the sheet, while Thermal energy of the heating roll portion is conducted to the heat radiating member via the pressure roll and is emitted to the outside.

At this time, since the heat dissipation member is in contact with the pressure roll on both sides of the area where the small size sheet passes, the heat dissipation member forms a kind of heat circulation path for the pressure roll, and the pressure roll equalizes the thermal energy distribution within.

Further, when a large-sized sheet passes between a heating roll and a pressure roll, all of the thermal energy of the heating roll portion is released to the sheet.

At this time, since almost no thermal energy is transferred to the heat radiating member through the pressure roll, no thermal energy is released from the heat radiating member.

〔Example〕

Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.

In the first embodiment shown in FIGS. 1 and 2,
The fixing device includes a heating roll 1 and a pressure roll 5 similar to the conventional example shown in FIG. It is located along the
The heat dissipation roll 20 is made of copper, aluminum, etc. with high thermal conductivity, and the pressure roll 5
It has an axial dimension that is approximately equal to the axial dimension of. The axial center portion of the heat dissipation roll 20 is formed as a small diameter portion 20a with an axial dimension range approximately equal to the width l of the small-sized paper 8, and the vicinity of both axial ends of the heat dissipation roll 20 have a large diameter. The heat dissipation roll 20 is rotatably supported by a shaft 21, and the circumferential surface of the large diameter section 20b of the heat dissipation roll 20 is placed in contact with the circumferential surface of the pressure roll 5 near both ends in the axial direction. has been done. It should be noted that components of the fixing device and its peripheral parts that are the same as those in the prior art are given the same reference numerals as in the prior art, and detailed explanation thereof will be omitted here.

Therefore, according to the fixing device according to this embodiment,
Now, if we assume that when the small size paper 8 passes between the heating roll 1 and the pressure roll 5, the paper 8 comes into contact with the axial center of the heating roll 1, then near both axial ends of the heating roll 1. The surface of the above paper 8
Since the heating roll 1 is in a non-contact state, the thermal energy in the area is not released to the paper 8, and the surface temperature near both ends of the heating roll 1 in the axial direction begins to rise compared to other areas. However, in this embodiment, the thermal energy in the high temperature part of the heating roll 1 is directly conducted to the large diameter part 20b of the heat dissipation roll 20 via the surface of the pressure roll 5. will be emitted to the outside through the heat dissipation roll 20. Therefore, the surface temperature near both ends of the heating roll 1 in the axial direction does not rise significantly compared to other parts, and the surface temperature distribution of the heating roll 1 is approximately as shown by the solid line in FIG. given as uniform. Therefore, the heating roll 1 itself may deteriorate due to heat, or the peeling claw 1 installed around the heating roll 1 may
0, the situation where the blade 11, temperature sensor 12, etc. are burnt out can be effectively avoided.

Furthermore, when the large-sized paper 8 passes between the pair of rolls 1 and 5, the entire surface of the heating roll 1 in the axial direction contacts the paper 8, so all the thermal energy from the surface of the heating roll 1 is absorbed. The heat is released onto the paper 8, and the surface temperature of the heating roll 1 does not locally increase accordingly. At this time, the heat radiation roll 20 is in contact with the pressure roll 5, but since the thermal energy on the surface of the heating roll 1 is not conducted to the heat radiation roll 20 when the paper 8 passes, the heat of the heating roll 1 is There is no risk that energy will be unnecessarily consumed due to the presence of the heat dissipation roll 20.

Furthermore, in this embodiment, the small size paper 8
During the passage, thermal energy from the high temperature portion of the heating roll 1 is conducted to the surface near both axial ends of the pressure roll 5, so there is a risk that the temperature distribution of the pressure roll 5 may become uneven. . However, since the heat radiation roll 20 forms a kind of heat circulation path for the pressure roll 5, a part of the thermal energy conducted to the heat radiation roll 20 is transferred to the pressure roll 5 via the heat circulation path. As a result, the temperature distribution of the pressure roll 5 is kept substantially uniform. Therefore, the coefficient of thermal expansion of each part of the pressure roll 5 is kept approximately constant, so that the degree of pressure of the pressure roll 5 against the heating roll 1 does not become uneven, and the toner image is fixed. properties are maintained well.

Furthermore, in this embodiment, the heat dissipation roll 20 is in contact with the pressure roll 5, but since the contact area between the two is in line contact, the contact resistance is extremely small. Therefore, a situation in which the driving force of the pressure roll 5 needs to be increased unnecessarily can be avoided.

[Structure of the invention]

As described above, the fixing device according to the present invention provides the following effects.

When the small size sheet passes through, the heat energy of the part of the heating roll that does not pass through the small size sheet is released to the heat radiating member via the pressure roll, which prevents thermal deterioration of the heating roll and burnout of parts around the heating roll. It can be effectively prevented.

When the large size sheet passes through, all of the heat energy of the heating roll is released to the sheet, so there is no risk that the heat energy of the heating roll will be unnecessarily consumed by the heat radiating member via the pressure roll.

When a small size sheet passes through, the heat dissipation member functions as a kind of heat circulation path for the pressure roll,
Since the temperature distribution of the pressure roll can be made uniform, it is possible to keep the coefficient of thermal expansion of the pressure roll approximately constant in the axial direction, and the pressure level of the pressure roll can be made uniform. Therefore, it is possible to maintain good fixing properties of the toner image.

Since the heat dissipation member can be simply fixedly arranged with respect to the pressure roll, there is no need to drive and control the advance/retreat mechanism of the heat dissipation member or the advance/retreat mechanism according to the sheet size, and the device configuration can be simplified accordingly. can.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional explanatory diagram showing one embodiment of the fixing device according to the present invention, FIG. 2 is a view taken from the direction of the arrow in FIG. 1, and FIG. 3 is an axis of the heating roll when passing small-sized paper. FIG. 4 is an explanatory cross-sectional view showing an example of a conventional fixing device; FIG. Figure b is the fifth
It is a sectional view taken along the line in Figure a. [Explanation of symbols] 1... Heating roll, 3... Heater (heat source), 5... Pressure roll, 8... Paper,
20... Heat radiation roll (heat radiation member).

Claims (1)

[Claims] 1. A heating roll heated by a heat source, and a pressure roll that is in pressure contact with the heating roll and rolls together with the heating roll, and an unfixed toner image is held between the two rolls. In the fixing device, an unfixed toner image is fixed on the sheet by passing the sheet through the pressure roll, and a heat radiation member having high thermal conductivity is arranged in parallel along the axial direction of the pressure roll, and the heat radiation member is arranged in parallel along the axial direction of the pressure roll. A fixing device characterized in that contact portions are provided on both sides of the member in the axial direction to contact portions of the circumferential surface of the pressure roll located on both sides of a small-sized sheet passing portion.