JP2003091200A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To speed up in a fixing device of an exterior heating method. SOLUTION: In the fixing device of the exterior heating method provided with a heat roll which is brought into a pressurized contact with a fixing roll surface and rotated while heating the fixing roll by an inside heat source, a difference is held between the circumferential speed of the fixing roll and the circumferential speed of the heat roll.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device for melting and fixing a toner image on a transfer material in an image forming apparatus.

[0002]

2. Description of the Related Art An image forming apparatus using an electrophotographic system is
Usually, a toner image composed of resin, magnetic material, colorant, etc., which is electrostatically carried on a transfer material, is sandwiched and conveyed between the fixing roller and the pressure roller that are in pressure contact with each other and rotating, and heat and pressure are applied. It has a fixing device for fusing and fixing by adding.

In such a fixing device, a halogen lamp or the like is conventionally used as a heat source for heating,
A method of arranging inside the fixing roller and heating from the inside and a method of arranging outside the fixing roller and heating from the outside can be roughly classified.

In the internal heating method in which the fixing roller is heated from the inside, the heat source is operated to maintain the temperature of the roller surface which gives heat to the transfer material and the toner during the fixing operation. There is a time lag until the temperature begins to rise. Therefore, when continuous copying is performed, the temperature of the roller surface temporarily drops. Further, when the copy speed increases, the temperature drop on the roller surface becomes severe, and there is a possibility that fixing failure may occur.

On the other hand, in the external heating method for heating the fixing roller from the outside, there are various heating methods, but in consideration of safety when a paper jam occurs, a substance having a high heat conductivity with a built-in heat source is considered. The most general method is to heat the heater roller by using pressure contact with the surface of the fixing roller.

Since this external heating system has a structure in which heat is stored only in the vicinity of the surface layer of the fixing roller, the time required for the temperature of the fixing roller surface to reach an appropriate temperature for fixing when the fixing device is started is relatively short. is there.

Further, in the process of supplying the amount of heat given to the transfer material and the toner during the fixing operation from the heat source to the fixing roller, the surface temperature of the fixing roller is kept constant so that the surface of the fixing roller is brought into contact with the fixing roller. A first temperature sensor, a second temperature sensor arranged to be in contact with the surface of the heater roller, and a detection signal of the first and second temperature sensors so that the surface temperature of the fixing roller becomes a predetermined temperature. Another feature of the temperature control for controlling the energization of the heater is that the control response is better than that of the configuration in which the fixing roller is heated from the inside.

[0008]

However, the external heating method has a good thermal response from the heat source to the roller surface, and is an effective means for maintaining the temperature of the roller surface even when the copying speed is high, as compared with the internal heating method. However, since the same amount of heat that the transfer material takes away per unit time must be applied to the fixing roller side at the contact surface between the heat roller and the fixing roller, in order to further improve productivity, the heat roller and fixing roller must be fixed. The contact area with the roller must be increased or the temperature of the heat roller must be raised.
In order to achieve these in an actual system, in order to increase the contact area, it is conceivable to increase the outer shape of the heat roller or fixing roller, increase the contact pressure, or the like. Lead to On the other hand, if the temperature of the heat roller is increased, the heat deterioration of the fixing roller in contact with the peripheral members in the vicinity of the heat roller progresses.

Therefore, an object of the invention according to the present application is to improve productivity without increasing the contact area between the heat roller and the fixing roller and increasing the temperature of the heat source in the method of heating the fixing roller from the outside. It is to provide a fixing device capable of performing.

[0010]

The structure for realizing the object of the invention according to the present application is such that a fixing roller and a pressure roller which are pressed against each other at their surfaces and can rotate freely, and are pressed against the surface of the fixing roller, A fixing roller that has a heat roller that rotates while heating the fixing roller by an internal heat source, and melts and fixes the toner image formed on the transfer material by heating and nip-conveying the toner image between the fixing roller and the pressure roller. In the apparatus, the peripheral speed of the fixing roller and the peripheral speed of the heat roller are different from each other, and it is further preferable that the peripheral speed of the heat roller is variable.

Further, in more detail, the present invention can solve the above problems by the following constitution.

(1) A fixing roller and a pressure roller, which are in pressure contact with each other on the surface and can rotate freely, and a heat roller, which is in pressure contact with the surface of the fixing roller and rotates while heating the fixing roller by an internal heat source. Then, in the fixing device for fusing and fixing the toner image formed on the transfer material between the fixing roller and the pressure roller by heating and pressing, the peripheral speed of the fixing roller and the peripheral speed of the heat roller are different. A fixing device characterized by the above.

(2) A fixing roller and a pressure roller which are in pressure contact with each other on their surfaces and can rotate freely, and a heat roller which is in pressure contact with the surface of the fixing roller and rotates while heating the fixing roller by an internal heat source. Then, in a fixing device for fusing and fixing the toner image formed on the transfer material between the fixing roller and the pressure roller by heating and pinching, the difference between the peripheral speed of the fixing roller and the peripheral speed of the heat roller. A fixing device, which is provided with a peripheral speed changing mechanism that can be controlled by changing the.

(3) The peripheral speed changing mechanism has a temperature detecting device which is arranged so as to come into contact with at least one surface of the fixing roller and the heat roller or each surface, and is capable of detecting the surface temperature of the roller. The fixing device according to (2), which can be controlled so that the peripheral speed of the heat roller can be changed with respect to the peripheral speed of the fixing roller according to the output value.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) FIG. 1 is a schematic sectional view of a fixing device showing a first embodiment of the present invention. In the image forming apparatus to which the fixing device according to the present embodiment is attached, the toner image on the photosensitive drum, which is an image carrier (not shown), is transferred to the recording material, and the recording material is passed through the nip portion of the fixing device. The toner image is fixed by the action of heat and pressure.

In the fixing device constitution used in this embodiment, the fixing roller 1 has a thickness of 6 [m] in a core metal cylinder made of iron having a thickness of 3 [mm].
m] is coated with HTV silicone rubber having a JIS-A hardness of 30 to 60 degrees and an outer diameter of 50 [mm]. Further, in order to improve the releasability of the surface, for example, PTFE 20 to 70 [μm]
Alternatively, a layer of PFA 50-100 [μm] may be provided.

The pressure roller 2 has an outer diameter of 38 [mm] and a thickness of 2
An aluminum cylinder of [mm] having a surface layer coated with a fluororesin in order to enhance releasability is used.

The heat roller 3 is an aluminum cylinder having an outer diameter of 28 [mm] and a thickness of 2 to 4 [mm], and a fluorine resin is provided on the surface layer in order to enhance releasability. The inner surface of the cylinder is painted black (also known as the brand name).

The heater 4 is a halogen lamp arranged in the center of the heat roller 3 along the direction of the rotation axis, and has a uniform calorific value distribution over the entire area of the heater as shown in FIG.

A first temperature sensor 5 is arranged in the central portion of the fixing roller 1 along the rotation axis direction so as to contact the surface of the fixing roller, and the heat roller 3 has a central portion in the roller rotation axis direction. The second temperature sensor 6 is disposed so as to come into contact with the surface of the heat roller 3, and the detection information of each of these sensors is input to a temperature control device (not shown).
Maximum power supplied to the heater is 800-2000 in total
[W], the power supply is automatically controlled based on the detection signals of the first temperature sensor 5 and the second temperature sensor 6 so that the surface of the fixing roller 1 has a predetermined constant temperature. It The first temperature sensor 5 and the second temperature sensor 6
As the element, an element such as a thermistor or a thermocouple can be used.

The transport guide 10 is provided with an unfixed toner image 1
The transfer material 12 conveyed while carrying 1 is a fixing roller 1
It is arranged at a position where it is guided to a pressure contact portion (nip portion) between the pressure roller 2 and the pressure roller 2. The separation claw 13 is arranged in contact with or close to the surface of the pressure roller 2.

Next, a method of rotating and driving each roller will be described.

Each of the rollers is rotatably supported and configured to drive the fixing roller 1. Pressure roller 2
Is arranged so as to be in pressure contact with the surface of the fixing roller 1 and to be driven to rotate by the frictional force at the pressure contact portion (nip portion). On the other hand, the heat roller 3 has a gear set so as to have a desired rotation speed, and a driving force is obtained from a driving unit of the fixing roller.

The pressure roller 2 and the heat roller 3 are pressed in the rotation axis direction of the fixing roller 1 by a mechanism (not shown) such as a spring. The pressure roller is about 140 [kg weight]
In this case, the width of the press contact portion (nip width) is about 7.5 [mm]. However, the nip width may be changed by changing the load depending on circumstances.

The pressure applied to the heat roller 3 is about 20 to 70 [kg weight] in this embodiment. In this case, the width of the pressure contact portion (nip width) is about 2 to 7 [m].
m]. It goes without saying that this value changes depending on the thickness and hardness of the rubber of the fixing roller.

With the above configuration, a large number of transfer materials 12 are continuously formed.
When the toner image 11 formed on the toner image 11 is heated and nipped and conveyed between the fixing roller 1 and the pressure roller 2 to be fused and fixed, the nip portion is formed at a portion (sheet passing portion) of the fixing roller 1 that contacts the transfer material 12. In order to supply heat to the transfer material 12 and toner, the temperature decreases after passing through the nip portion, and when the continuous passing speed is high,
The target temperature cannot be maintained by the heat supply at the contact portion between the heat roller and the fixing roller.

Therefore, in this embodiment, since the rotation speed of the heat roller is faster than the rotation speed of the fixing roller,
The feature is that the rotation speed of the heat roller is set so as to satisfy the heat supply amount to the fixing roller.

With such a structure, when the fixing operation is continuously performed at a high speed in the related art, the temperature of the fixing roller is lowered as shown in FIG. 3, whereas the surface temperature of the fixing roller is changed as shown in FIG. It becomes possible to keep up.

In the present embodiment, the peripheral speed of the heat roller is set to be higher than that of the fixing roller, so that the apparatus is not upsized and the temperature of the heat roller is not set higher than before. It is possible to achieve the purpose of improving the stability of fixability during high-speed copying.

(Second Embodiment) The second embodiment of the present invention is characterized in that the speed of the heat roller of the first embodiment can be changed by the output of the temperature sensor.

In the first embodiment, the peripheral speed of the heat roller is set to a fixed speed with respect to the peripheral speed of the fixing roller. However, even when the roller is rotated in a state where the fixing operation is not performed, such as during standby, the roller also rotates with a difference in peripheral speed. Therefore, when the fixing roller and the heat roller rotate, they rub against each other at the contact portion to promote deterioration of the surface of each roller such as scratches. Therefore, in the case other than the fixing operation, it is preferable that the fixing roller and the heat roller rotate at the same speed when the roller rotates.

Similarly to the above, when the fixing property is not impaired, the peripheral speed difference between the heat roller and the fixing roller is as small as possible, and only when the fixing property is impaired, that is, when the temperature of the fixing roller drops. By controlling so that the peripheral speed difference becomes large, it becomes possible to improve the durability of each roller as described above.

As described above, each roller is rotatably supported and drives each of the fixing roller 1 and the heat roller 3. Similarly to the above, the pressure roller 2 is in pressure contact with the surface of the fixing roller 1, and is arranged so as to be driven to rotate by the frictional force at the pressure contact portion (nip portion).

In this embodiment, by setting the peripheral speed of the heat roller to be variable with respect to the peripheral speed of the fixing roller, the temperature of the heat roller can be kept higher than before without increasing the size of the apparatus. It is possible to achieve the purpose of improving the stability of the fixing property at the time of high-speed copying without setting it to a high value, and at the same time, improving the durability of the fixing roller and the heat roller.

[0035]

As described above, according to the present invention,
In a fixing device configured to heat the fixing roller from the outside by a heat source located outside the fixing roller, by providing a peripheral speed difference between the fixing roller and the heat roller, a fixing device compatible with high-speed copying can be realized without increasing the size of the device. .

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a fixing device showing a first embodiment of the present invention.

FIG. 2 is a diagram showing changes in surface temperature of a fixing roller and a heat roller during continuous copying when the fixing device of the present invention is used.

FIG. 3 is a diagram showing changes in surface temperatures of a fixing roller and a heat roller during continuous copying when a conventional fixing device is used.

[Explanation of symbols]

1 fixing roller 2 pressure roller 3 heat roller 4 heater 5 First temperature sensor 6 Second temperature sensor 10 Transport guide 11 Toner image 12 Transfer material 13 Separated nail

Claims (3)

[Claims] 1. A fixing roller and a pressure roller, which are in pressure contact with each other on their surfaces and can rotate freely, and a heat roller, which is in pressure contact with the surface of the fixing roller and rotates while heating the fixing roller by an internal heat source. In a fixing device for fusing and fixing a toner image formed on a transfer material by heating and sandwiching the toner image between the fixing roller and the pressure roller,
The peripheral speed of the fixing roller and the peripheral speed of the heat roller are different from each other. 2. A fixing roller and a pressure roller which are in pressure contact with each other on their surfaces and can rotate freely, and a heat roller which is in pressure contact with the surface of the fixing roller and rotates while heating the fixing roller by an internal heat source. In a fixing device for fusing and fixing a toner image formed on a transfer material by heating and sandwiching the toner image between the fixing roller and the pressure roller,
A fixing device comprising a peripheral speed changing mechanism that can be controlled by changing a difference between the peripheral speed of the fixing roller and the peripheral speed of the heat roller. 3. The peripheral speed changing mechanism has a temperature detecting device which is arranged so as to come into contact with at least one surface of a fixing roller and a heat roller or which can detect the surface temperature of the roller, and the output of the temperature detecting means. The fixing device according to claim 2, wherein the fixing device can be controlled so that the peripheral speed of the heat roller can be changed with respect to the peripheral speed of the fixing roller by a value.