JPH05181382A - Thermal fixing device - Google Patents

Abstract

PURPOSE:To provide a thermal fixing device capable of easily preventing a temperature rise in no-paper passing area of a fixing rotating body. CONSTITUTION:In a thermal fixing device for nipping and carrying a transfer material having an unfixed toner image by a nip part formed by a pair of rotating bodies 1, 2 at least one of which has a heating source 3, an air blowing device 4 for blowing cooling air to no-paper passing areas which are outside the passing area of a transfer material having a set width, when a determined number or more of transfer materials having the set width smaller than the axial maximum width carryable by the pair of rotating bodies 1, 2 are carried within a determined time, and guide devices 6, 9 for guiding the cooling air blown to the no-paper passing areas to the end sides of no-paper passing areas of the rotating bodies are provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat fixing device such as an electrophotographic device for fixing a transfer material carrying an unfixed developer by a pair of rotating members while pinching and conveying the transfer material.

[0002]

2. Description of the Related Art Conventionally, in the electrophotographic system, a toner image which is a developer image is formed on a transfer material such as paper by a method called the Carlson process, and then the toner image is fixed as a permanent image. It was Although various methods have been proposed as fixing methods therefor, from the viewpoint of fixability, a method of heating and fixing a toner image (heat fixing method) is generally used. A method is often used in which a toner image is directly brought into contact with the rotating body to fix the toner image. 8 and 9 show an example of a heat roller fixing method, which is a typical example of the conventional heat fixing method. The basic structure is composed of a fixing roller 1 containing a heating source 3 such as a halogen lamp, and a pressure roller 2 having an elastic layer such as silicon rubber in pressure contact with the fixing roller 1. When the transfer material P such as paper is nipped and conveyed between the rollers 1 and 2, the toner image T is melted by heat and exits the pair of rollers, and then cooled to form a fixed image as a permanent image. ..

In such a heat fixing device, it is important to make the temperature distribution on the heating rotator such as the roller including the region through which the transfer material passes in the axial direction uniform. Because there are places where the temperature is too low than the specified temperature,
This is because fixing failure occurs, and if it is too high, the rotating body and members such as separation claws that come into close contact with the peripheral surface thereof are thermally damaged.

However, in reality, it is impossible to make the temperature distribution completely uniform, and the temperature distribution may become excessively uneven. A typical example of this is what is called a non-sheet passing portion temperature rise.

Generally, when paper is passed between the pair of rollers, one side of the paper is of any size,
The roller is conveyed along a certain standard line set at a specified position in the longitudinal direction of the roller. FIG. 10 shows, as an example, a "one-sided standard" in which one side of the paper is always conveyed along a predetermined line (standard line is indicated by S). In this case, the axial length of the roller pair is somewhat longer than the maximum paper passing width (in this case, the length of the long side of the A4 paper),
The paper passing area of the widest papers A4 and A3 is L0 shown in the figure. On the other hand, narrower paper (hereinafter referred to as small size paper), for example, B5 paper, is conveyed along the reference line S, and therefore the paper passing area is L1.

At this time, L2 (= L0-L1) is called a non-sheet passing area.

Next, looking at the temperature distribution of the fixing roller 1,
Normally, when feeding the maximum size paper, a substantially uniform temperature distribution is exhibited as shown by the solid line in FIG.
Small size paper with small dimensions (eg B5, A6)
When the sheet is continuously passed, in the area where the paper does not pass (non-sheet passing area L2), the heat is partially absorbed by the roller as much as there is no heat absorbed by the paper, and the temperature of this area is indicated by the broken line in FIG. Is higher than the paper passing area. This is called the non-sheet-passing portion temperature rise, and sometimes the temperature rises by about 50 ° to 80 ° C. as compared with the sheet-passing area. Therefore, various measures have been conventionally taken. For example, increasing the thickness of the base material (core metal in the case of rollers) of the rotating body to improve heat flow in the longitudinal direction, and switching the control temperature to the low temperature side when the temperature rises Methods such as lowering or cooling the temperature rising portion have been adopted.

[0008]

However, each of these conventional methods has drawbacks and is difficult to implement.

First, when the base material is thickened, it is easy to obtain the effect of making the temperature distribution uniform, but it is inconvenient because the time until the base material is heated to a predetermined temperature, that is, the waiting time becomes long.

Next, when the control temperature is changed, the temperature of the temperature rising portion certainly lowers, but the temperature itself of the sheet passing area also lowers, so that the fixing property becomes insufficient.

As a cooling method, there is an example in which a heat pipe roller is brought into contact with a fixing roller to cool the temperature rising portion and make the temperature distribution uniform (Actual Development Sho-1 58-1).
05561), which is a complicated configuration. As another cooling method, there is also a method of blowing air to the temperature raising section to cool it (JP-A-60-136779). However, since the cooling air inevitably flows into the paper passing area, the temperature in the paper passing area will drop even if a partition plate is inserted, and fixing failure will occur especially near the boundary between the non-paper passing area and the paper passing area. There is a drawback that becomes.

The present invention does not cause the deterioration of the fixing property in the paper passing area as seen in the above-mentioned conventional method,
An object of the present invention is to provide a thermal fixing device capable of preventing a temperature rise in a non-sheet passing portion.

[0013]

According to the present invention, the above object is to provide a transfer material having an unfixed toner image at a nip portion formed by a pair of rotating bodies having a heat source in at least one of the pair of rotating bodies. In a heat fixing device that obtains a fixed image by pinching and conveying, when a transfer material having a set width smaller than the maximum width in the axial direction that a pair of rotating bodies can convey is conveyed by a predetermined number or more within a predetermined time, An air blower for sending cooling air to a non-sheet passing area outside the passing area of the transfer material having the set width on the rotating body,
This is achieved by having a guide device that guides the cooling air sent to the non-sheet passing area to the end side of the non-sheet passing area of the rotating body.

[0014]

According to the present invention having the above-described structure, it is prevented that the cooling air is blown only to the non-sheet passing area of the rotating body under a predetermined condition to raise the temperature of the non-sheet passing area to a predetermined temperature or more. At that time, since the cooling air flows toward the end portion on the non-sheet passing area side, there is no influence on the sheet passing area.

[0015]

Embodiments of the present invention will be described below with reference to FIGS. 1 to 7 of the accompanying drawings. In the figure, the same parts as those of the above-described conventional device shown in FIGS. 8 and 9 are designated by the same reference numerals, and the description thereof will be omitted.

<First Embodiment> FIG. 1 shows a first embodiment, in which a sheet passing standard line S is directed toward a fixing roller pair consisting of a fixing roller 1 and a pressure roller 2 as a rotating body. It shows the case of a system that performs one-sided standard paper passing according to.

Above the fixing roller 1, there is provided a top plate 5 which is substantially parallel to the fixing roller 1.
And a blower fan 4 as an air blower is arranged above the top plate 5. Further, the top plate 5 is provided with a window 6 as a guide device which can be opened and closed at at least one place. The window 6 is provided at a position of an area (non-sheet passing area) outside in the axial direction of the area through which the small size sheet is passed. For example, if there is one window and the small size paper to be passed is A6 size, it is located at the position in the figure on the non-passing side from the paper passing edge of the A6 paper. Further, when there are a plurality of windows, it is preferable that the windows are provided slightly outside the paper passing area depending on the size of the paper that can be passed.

The operation sequence of the apparatus of this embodiment will be described with reference to FIG. First, the user sets various copy modes such as the number of copies and the paper size to be used and the copy magnification, and presses the copy button. At this time, in the main body of the apparatus, the size of the input (designated) paper size is first judged, and if it is a large size such as A3, the copying is started as it is.
Is closed and no air is blown to the peripheral surface of the fixing roller 1, and the upper side of the top plate 5 is blown to prevent excessive temperature rise around the fixing device. Then, when copying is completed by the set number of sheets, the fan is turned off and the processing is completed. If the input paper size is a small size such as B5, a counter (count number:
C) and a timer (time: t) for counting the time from the start of copying are reset, and counting is started simultaneously with the start of copying. Further, the cooling fan 4 is turned on before and after the start of copying. Predetermined values C0 and t0 for the timer and counter
Is set, and if copying is continued even if the timer reaches t = t0 (during continuous copying), the value of the counter C is judged, and the window 6 is opened when the value is C0 or more. As a result, as shown in FIG. 1, the cooling air has its air passage changed by the window 6, flows into the non-sheet passing area of the fixing roller 1, and extends along the axial direction of the fixing roller 1 on the non-sheet passing side of the roller. It flows to the end. When the value of the counter C is less than C0 at t = t0, the window remains closed. This is in the mode where the number of small size sheets that are passed within a certain period of time is small, and if the sheet passing interval is long, the heat that is about to be accumulated in the non-sheet passing portion diffuses, This is because the temperature rise in the non-sheet passing portion is low and cooling is not required. In either case, when the initially set number of copies is completed, the cooling fan 4 is turned off and the entire sequence is completed.

In the sequence of the apparatus of this embodiment having the above-mentioned structure, when C ≧ C0 at t = t0, that is,
When small-sized paper is successively passed in a short time, cooling air is introduced from the window 6 to cool the non-sheet-passing portion of the fixing roller 1, so that the broken line in the graph of FIG. The temperature rise in the non-sheet passing portion is 20 to 30 ° C., which is suppressed within the allowable range. Further, at that time, the blown cooling air flows over the fixing roller 1 in the axial direction toward the non-sheet passing side end of the roller, so that there is almost no cooling air blown into the sheet passing area. This is because the temperature distribution (the temperature drop at the end of the paper passing area) as shown by the one-dot chain line in the graph of FIG. This means that no bad effects such as defects will occur.

<Second Embodiment> Next, a second embodiment for improving the cooling of the previous embodiment by further utilizing the cooling air to the non-sheet passing area will be described.

FIGS. 4 and 5 show this embodiment. Above the fixing roller 1, a top plate 5 is provided above the fixing roller 1.
There is a blower / cooling fan 4 through the, and there is a window 6 that opens when the temperature of the non-sheet-passing portion rises to introduce cool air to the non-sheet-passing area. In the present embodiment, the duct 7 that takes in the cooling air (heated in the non-sheet passing area) that is introduced and flows to the end of the fixing roller has its opening at the end of the fixing roller as shown in the figure. is set up. Further, the duct 7 is connected to a duct 9 formed on the back surface of an entrance guide 8 which is one of the transport members located upstream of the fixing roller pair in the paper transport direction. In such a configuration, when a predetermined number or more of small-sized sheets are passed within a predetermined time in the same sequence as in the previous embodiment, the non-sheet passing area gradually rises in temperature, so that the window 6 is illustrated. Thus, the opening cooling air is introduced into the non-sheet passing area of the fixing roller. The introduced cooling air is warmed when cooling the non-sheet passing area of the fixing roller 1. This warm air flows to the end portion of the fixing roller 1 as it is and flows into the duct 7. Warm air
After that, it flows as shown by the arrow in the figure, and is discharged through the duct 9 under the inlet guide. When the warm air passes through the duct 9, the inlet guide 8 is warmed and further the small-sized paper passing on the inlet guide 8 is warmed. If the paper is warmed before it reaches the pair of fixing rollers, the fixing property will be good and
Since the amount of heat given from the fixing roller is small, the heating time of the heater 3 is reduced to that much, and the heat which is unnecessarily given and accumulated in the non-sheet passing area is correspondingly reduced. Therefore, the temperature rise in the non-sheet passing portion is also small.

As described above, after the cooling air is used to cool the non-sheet passing area, the paper is preheated by the warmed air, so that the temperature rise of the non-sheet passing portion can be suppressed more efficiently. Becomes

<Third Embodiment> In the above-mentioned embodiments, the fixing by the heat roller pair has been described, but the present invention can be implemented in other heat fixing systems. An example thereof is shown in FIGS. 6 and 7 as a third embodiment. The feature here is that a thin belt-shaped rotating body is used in place of the pressure roller of the previous embodiment. A pair of rollers 11 and 11 ′ rotatable with respect to the heat roller 1 including the heater 3 and a belt 10 stretched over the roller pair are provided. The belt 10 is pressed against the heat roller 1 to form a nip portion. is doing. In the fixing device as in this embodiment, it is easier to secure a wide nip portion with light pressure as compared with the pressure roller of the previous embodiment, and the belt is made of a heat-resistant resin film (eg, polyimide) or thin rubber ( (Example: silicone rubber) and the small heat capacity,
The heat is not unnecessarily taken by the belt and it is easy to secure the fixing property. On the other hand, however, in the small size sheet passing, since the belt is thin, the heat flow rate in the axial direction is small and the heat capacity is small, so not only the temperature rise in the non-sheet passing area of the heat roller 1 but also the belt 10 However, the temperature rises violently in the non-paper passing area. Therefore, in the present invention, the blower pipe 12 is provided across the inside of the belt 10 instead of the heat roller 1 side. There is an air blower fan at a position from one end of the air blower pipe 12 so that air can be blown from the paper passing standard side to the other direction side. Further, the blower pipe 12 has one valve 13 for forming an opening. Alternatively, a plurality of them are provided (in the figure, the case of one is shown as a typical example).

In this embodiment having such a structure, all the valves 13 are closed when the full-size sheet is passed, but in the small-size sheet, the non-sheet-passing is performed as in the case of the previous embodiment. A valve corresponding to the area is opened, cooling air is blown as shown in the figure, and a part thereof flows between the belt 13 and the fixing roller 1 and flows through the non-sheet passing area toward its end. .. At that time, the belt in the non-sheet passing area is cooled, and since the belt is thin, the heat roller 1 is also cooled via the belt. That is, since the belt having a large temperature rise in the non-sheet passing portion is first cooled and then the heat roller 1 is indirectly cooled, the room temperature of the non-sheet passing portion can be suppressed as a whole.

In the embodiment of the present invention, the one-sided standard paper-passing system has been described as an example. However, in the present invention, the central-standard paper-passage which always conveys the paper in alignment with the axial center line of the rotating body. It can also be applied to systems. In addition to the examples described above, application to existing heat fixing devices using a pair of rotating bodies is possible.

[0026]

As described above, in a thermal fixing device using a pair of rotating members, when a small number of small-sized sheets are pinched and conveyed by a predetermined number or more within a predetermined time, the rotating members are not fixed. Cooling air is blown to the paper passing area and is guided to the end on the non-paper passing area side, so it is possible to circulate the cooling air to the paper passing area while preventing temperature rise in the non-paper passing area. It is possible to avoid the fixing failure due to.

If the warmed air is guided to the paper conveying path by cooling the non-paper passing area, it is possible to preheat the paper, thereby effectively fixing the paper while securing the fixing property. It is possible to suppress the temperature rise in the paper section.

[Brief description of drawings]

FIG. 1 is a partially cutaway front view showing the configuration of a first embodiment device of the present invention.

FIG. 2 is a temperature distribution diagram of the apparatus shown in FIG.

FIG. 3 is a diagram showing an operation sequence of the apparatus in FIG.

FIG. 4 is a partially cutaway front view showing the configuration of the second embodiment device.

5 is a side view of the FIG. 4 device.

FIG. 6 is a partially cutaway front view showing the configuration of the third embodiment device.

FIG. 7 is a side view of the FIG. 6 device.

FIG. 8 is a front view showing a configuration of a conventional device.

9 is a side view of the FIG. 8 device.

10 is a temperature distribution diagram of the apparatus of FIG.

[Explanation of symbols]

 1 Rotating Body (Fixing Roller) 2 Rotating Body (Pressure Roller) 3 Heat Source (Heater) 4 Blower (Blower Fan) 6 Guide Device (Window) 9 Guide Device (Duct)

Claims (2)

[Claims] 1. A thermal fixing device for obtaining a fixed image by nipping and conveying a transfer material having an unfixed toner image at a nip portion formed by the pair of rotating bodies having a heat source in at least one of the pair of rotating bodies. When a transfer material having a preset width smaller than the maximum width in the axial direction that can be conveyed by a pair of rotary members is conveyed by a predetermined number or more within a predetermined time, a passage area of the transfer material having the preset width on the rotary member In the outer non-sheet passing area, there is provided a blowing device for sending cooling air, and a guide device for guiding the cooling air sent to the non-sheet passing area to the end side of the non-sheet passing area of the rotating body. A heat fixing device characterized by. 2. The guide device is formed so as to guide the cooling air to the conveying path for guiding the transfer material to the pair of rotating bodies after guiding the cooling air to the non-sheet passing area side end of the rotating body. The heat fixing device according to claim 1.