JPH08146797A - Fixing device - Google Patents

Abstract

PURPOSE: To prevent the toner soiling of a pressure roller and to prevent an image supporting body rear surface staining from generating, by composing a peripheral length of the heating roll so as to become an integral multiple of a sum of the length of the image supporting body and the length of the gap between paper sheets. CONSTITUTION: Since the peripheral length of the heating roll 1 is composed corresponding to the integral multiple of the sum of the length of the image supporting body 3 and the gap length in-between the following image supporting body 10, the toner 4 being offset from the full surface of the image supporting body 3 to the heating roll 1 in a trifling amount though, is stuck on the heating roll in the extent of the length of the image supporting body 3. When the following image supporting body 10 plunges into the nip part similar to the image supporting body 3, the plunging position of the following image supporting body 10 onto the heating roll 1 becomes the same place as the plunging position of the image supporting body 3. Therefore, the toner 4 stuck on the heating roll 1 being offset from the image supporting body 3 is definitely brought into contact and stack with the following image supporting body 10. The toner 4 being offset on the heating roll 1 is not brought into contact with the pressure roller 2, hence the toner soiling on the pressure roll is not caused.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus such as a printer, a copying machine or a facsimile, and more particularly to fixing a toner image formed on the surface of an image support to the image support. Regarding the fixing device.

[0002]

2. Description of the Related Art Generally, an electrophotographic image forming apparatus is
As a method for fixing the unfixed toner image on the image support, the toner image is brought into direct contact with a heating roll made of a metal having a heat source inside and heated to a temperature sufficient to melt the toner, and at the same time applying the toner image. A heating roll fixing system is used in which fixing is performed by applying pressure with a pressure roll and passing an image support between the both rolls. The pressure contact portion between the heating roll and the pressure roll is called a nip portion.

In such a fixing device, the surface of the image support on which the unfixed toner image is adhered is brought into contact with the heating roll, but a very small amount of toner adheres to the contacting heating roll. Offset phenomenon occurs. Further, this toner comes into contact with the pressure roll when the image support is not held in the nip portion, and at that time, is transferred from the heating roll to the pressure roll. When images are continuously formed, the amount of toner transferred increases in proportion to the number of image formations, and adheres and accumulates as stains on the pressure roll.
When the temperature of the pressure roll rises and the toner melts, the dirt adheres to the contact surface of the conveyed image support with the pressure roll, causing serious misprinting, and the adhesion of the melted toner. The image support may be wound around the pressure roll due to the property, and a paper jam may occur.

For this reason, for example, as disclosed in Japanese Utility Model Publication No. 48204/1993, a cleaning means such as a heat-resistant pad, roller or blade is pressed against a heating roll to remove the adhered toner.

[0005]

The fixing device in which the cleaning means is brought into pressure contact with the above-mentioned heating roll is inevitably complicated in mechanism and structure, resulting in high cost, and further image formation. After a large number of times, when the toner accumulates in the cleaning means, the toner in contact with the heating roll is melted and retransferred to the heating roll, and finally, stains on the pressure roll or stains on the back surface occur. I found out that This is a big problem in view of the recent tendency to be maintenance-free, and a serviceman was forced to perform roll cleaning and replacement of cleaning members. In order to reduce the burden on the cleaning member, improvements have been made to the toner material, precision control of the heating roll temperature, etc., and stains on the printed image can be improved to the extent that it cannot be discerned. It is unavoidable that offset toner that cannot be confirmed by the transfer directly to the pressure roll from the heating roll or directly from the toner adhering to the back surface of the image support to the pressure roll stain that can be visually confirmed. .

It is an object of the present invention to prevent toner stains on a heating roll or a pressure roll in a fixing device comprising a heating roll and a pressure roll, and to eliminate the need for maintenance with a simple structure. (EN) Provided is a fixing device which does not cause dirt on the back surface and a paper feed jam caused by winding.

[0007]

The present invention comprises a heating roll and a pressure roll, or a heating belt and a pressure roller,
A fixing device for fixing an image by passing an image support on which an unfixed toner image is formed between both rolls, and the peripheral length of a heating roll or a heating belt is the sum of the length of the image support and the length of the paper gap. It is configured to be.

[0008]

The toner offset on the heating roll (heating belt) is transferred only to the image support at the nip portion and does not contact the pressure roll, so that the toner stain on the pressure roll does not occur.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to FIG. FIG. 1 is a cross-sectional side view of a fixing device according to an embodiment of the present invention and a diagram showing a relationship between an image support and a heating roll circumference. 1 is a heating roll, 2 is a pressure roll, 3 is an image support, 4 is toner, 5 is a toner image, 6 is a heater lamp, 1
0 is the latter image support. The heating roll 1 is heated,
The heating roll 1 and the pressure roll 2 are pressed against each other and rotated. The pressure contact portion of both rolls is called a nip portion. By inserting the image support 3 into the contact surface, the toner image 5 arranged as an image on one surface of the image support 3 is melted, pressed and fixed.

The fixing device includes a heating roll 1 having a release layer on a metallic cored bar having a heater lamp 6 as a heat source in the central portion, and an elastic body such as silicon rubber on the metal cored bar. The pressure roll 2 is arranged. The heating roll 1 is fixed at a fixed position by a driving device (not shown) of the image forming apparatus main body, and is driven and rotated in the direction of arrow A in the figure. The pressure roll 2 faces the heating roll 1 and is pressed against it by a pressure device (not shown) to be driven and rotated in the direction of arrow B in the drawing. The image support 3 on which the toner image 5 is formed is conveyed from the direction of arrow C in the figure toward the nip portion of the heating roll 1 and the pressure roll 2. Image support 3
Are nipped and conveyed at the nip portion. At this time, the toner image 5 on the image support 3 is melted and deformed by applying heat energy and pressure energy at the nip portion between the heating roll 1 and the pressure roll 2. Most of the toner image 5 in this state penetrates into the image support 3 and is fixed, but only a small part thereof adheres to the surface of the heating roll 1. This phenomenon is called offset. The offset toner 4 reaches the nip portion again when the heating roll 1 makes one rotation.

In the present embodiment, the circumference of the heating roll 1 corresponds to the sum of the length of the image support 3 and the gap length between the image support 10 and the image support 10 which will be provided later. The toner 4 offset to the heating roll 1 by a slight amount adheres to the heating roll 1 by the length of the image support 3. Then, when the image support 3 passes, there is a gap until the subsequent image support 10 penetrates into the nip portion, and the heating roll 1 and the pressure roll 2 are in direct contact with each other in this gap. Similar to the image support 3, the rear image support 10 plunges into the nip portion. At this time, the plunge position of the rear image support 10 on the heating roll 1 is the same as the plunge position of the image support 3. Become. Therefore, the image support 3 attached to the heating roll 1
The toner 4 offset from is always in contact with and adheres to the image support 10 later. By repeating this operation continuously, the offset toner 4 from the image support 3 always contacts and adheres to the subsequent image support 10 during the image forming operation. The portion of the heating roll 1 corresponding to the gap between the image support 3 and the subsequent image support 10 does not come into contact with the image support 3 holding the toner 4, and the pressure roll 2 is always provided.
Contact only with. Therefore, in this region, there is no toner 4 that adheres to the pressure roll 2 as dirt. With the above configuration, the pressure roll 2 is not soiled. The amount of the toner 4 that comes into contact with the image support 3 and adheres to the heating roll is such that when the toner 4 normally adheres to the image support 10 after that,
If the toner 4 is in an amount that cannot be visually confirmed, erroneous printing does not occur. Therefore, the fixing condition may be set so that the offset amount of the toner 4 falls within the above amount.

For example, an A4 sheet (short side length 210 mm) has a gap length of 50 between the image support 3 and the subsequent image support 10.
When the image forming operation is performed in mm, it was confirmed that when the diameter of the heating roll 1 was set to 82.76 mm, stains due to the offset toner on the pressure roll did not occur as shown in this embodiment.

Further, the circumference of the heating roll 1 is set to the image support 3
Also, when the sum of the length of the image support 3 and the gap length between the image support 3 and the subsequent image support 10 is set to an integer multiple, the offset toner 4 is not attached to the pressure roll 2 as in the above-described embodiment. .

According to the present invention, the toner 4 offset from the image support 3 to the heating roll 1 can be always adhered to and removed from the subsequent image support 10 according to the present invention by the above-described structure and operation. The adhered offset toner 4 does not transfer to the pressure roll 2 and the pressure roller is not contaminated by the offset toner 4.
It is possible to provide a fixing device that does not cause erroneous printing or winding of the image support 3 around the pressure roll 2.

Another embodiment of the present invention will be described below with reference to FIG. FIG. 2 is a cross-sectional side view of a fixing device showing one embodiment of the present system and a diagram showing the relationship between the image support and the fixing belt circumference. Reference numeral 2 is a pressure roll, 3 is an image support, 14 is unfixed toner, 5 is a toner image, 7 is a fixing belt, 8 is a heater, 9 is a drive roll, and 10 is a subsequent image support.
The present embodiment is a fixing method using the fixing belt 7. The fixing belt 7 is pressure-contacted by the pressure roll 2, and this pressure-contact portion is called a nip portion.

The fixing device includes a fixing belt 7 in which a release layer is formed on a metallic belt made of a nickel alloy having a heater 8 as a heat source therein, and an elastic body such as silicon rubber on a metal cored bar. The pressure roll 2 is arranged. The fixing belt 7 is fixed at a fixed position by a driving device (not shown) of the image forming apparatus main body, and power is transmitted by a driving roll 9 to drive and rotate in the direction of arrow A in the figure. Fixing belt 7
The pressure roller 2 is opposed to the pressure roller 2 by a pressure device (not shown) and is driven and rotated in the direction of arrow B in the figure. The image support 3 on which the toner image 5 is formed is conveyed in the direction of arrow C in the figure to the nip portion between the fixing belt 7 and the pressure roll 2. Then, the image support 3 is nipped and conveyed at the nip portion. At this time, the unfixed toner 14 on the image support 3 is melted by applying heat energy and pressure energy at the nip portion between the fixing belt 7 and the pressure roll 2. Most of the unfixed toner 14 in this state is the image support 3
A toner image 5 that penetrates into and is fixed is formed, but a small part thereof is transferred to the surface of the fixing belt 7. The transferred offset toner 4 reaches the nip portion again after the fixing belt makes one round.

In the case of this embodiment, the circumference of the fixing belt 7 corresponds to the sum of the length of the image support 3 and the gap length of the image support 3. In this case, the subsequent image support 10 is the image support 3
Similarly, the plunge into the nip portion occurs, but the plunging position of the image support 10 after the fixing belt 7 is the same as the plunging position of the image support 3. Therefore, the toner 4 offset from the image support 3 attached to the fixing belt 7 contacts and attaches to the image support 10 after being conveyed. By repeating this operation continuously, the offset toner 4 from the image support 3 comes into contact with only the subsequent image support 10 and is transferred. Further, the area of the fixing belt 7 where the offset toner 4 is not adhered is the image support 3 and the image support 1 later.
Since the portion corresponding to the gap of 0 is always in contact with only the pressure roll 2, the toner 4 is not attached to the pressure roll 2 as dirt. Therefore, the pressure roll 2 is not soiled. Further, if the amount of the toner 4 to be transferred to the image support 10 after contacting the image support 3 is such that the toner 4 cannot be visually confirmed when it is attached to the image support 3, erroneous printing is not performed. Set the fixing conditions so that the amount cannot be confirmed with.

Further, although the pressure roll 2 is used in this embodiment, not only the pressure roll 2 but also any component can be used as long as it can form a pressure contact portion.

According to the present invention, the toner 4 offset from the image support 3 to the fixing belt 7 can be always adhered to the subsequent image support 10 according to the present invention with the above-described structure and operation. Therefore, it is possible to provide a fixing device which is free from erroneous printing and winding of the image support 3 around the pressure roll 2.

[0020]

As described above in detail, according to the present invention, the dirt toner adhering to the heating roll is adhered only to the image support to be conveyed and is not adhered to the pressure roll. There is an effect that erroneous printing due to stains on the sheet and winding of the image support on the fixing device do not occur.

[Brief description of drawings]

FIG. 1 is a side cross-sectional view of a fixing device according to an exemplary embodiment of the present invention and shows a relationship between an image support and a heating roll circumference.

FIG. 2 is a side sectional view of a fixing device according to an exemplary embodiment of the present invention and shows a relationship between an image support and a fixing belt circumference.

[Explanation of symbols]

1 ... Heating roll, 2 ... Pressure roll, 3 ... Image support, 4
... offset toner, 7 ... fixing belt, 14 ... unfixed toner.

Claims (2)

[Claims] 1. A fixing device comprising a heating roll and a pressure roll, wherein an image support is sandwiched and conveyed at a pressure contact portion between the heating roll and the pressure roll, and the toner on the image support is fused to the image support. The fixing device is characterized in that the peripheral length of is a multiple of the sum of the length of the image support to be fixed on the first sheet and the length of the gap between the image support to be fixed next. 2. A fixing belt having a heating element inside is used,
In a fixing device having a pressure roller facing the fixing belt, the length of the image support to which the unfixed toner for fixing is fixed and the length of the gap between the image support and the unfixed toner to be fixed next. A fixing device characterized in that the perimeter of the fixing belt is set to an integer multiple of the sum of the above and the above.