JPH03139682A - Fixing device - Google Patents

Abstract

PURPOSE:To make the distribution of the temperature of a heat roller in its axial direction uniform respective of the size of a transfer sheet fed to the fixing device by cooling an overheated part of the heat roller through the use of an air-cooled means. CONSTITUTION:An air-cooled exhaust fan 30 is provided in a device main body. Also the upper casing 23 of the fixing device 20, which is in the vicinity of the suction part of the exhaust fan 30, is provided with plural air duct windows 31,..., in the axial direction of the heat roller 21. By adjusting an amount by which the air duct windows 31 are opened, the exhaust fan 30 produces an air flow in the vicinity of a part of the heat roller 21 overheated by a heat source 21c; thus, the heat roller 21 is partially cooled. The distribution of the temperature of the heat roller in its axial direction is constantly held uniform irrespective of the size of a fed sheet, by making an air-cooled means like the fan 30, etc., generate an air flow for an overheated part of the heat roller 21, and cooling the heat roller.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a fixing device for an image forming apparatus employing an electrophotographic method, such as a copying machine or a laser printer.

(Prior Art) In a copying machine or the like, when a toner image is formed on a photosensitive drum, which is an image carrier, the toner image is transferred onto a transfer paper. Then, the transfer paper carrying the toner image is sent to a fixing device, and the toner image is firmly fixed onto the transfer paper as a permanent image by the fixing device.

In this type of fixing device, a transfer paper carrying a toner image is conveyed between a pair of fixing rollers, at least one of which is a heating roller, and the toner image on the transfer paper is heated and melted by the heating roller and transferred. A heating type fixing device that fixes the paper onto the paper is often used. A heat source such as an electric heater is installed in the heating roller of such a fixing device in the axial direction of the heating roller, and the surface temperature of the heating roller is rapidly heated as power is supplied. In addition, a temperature detection element is attached to the outer surface of the heating roller, and the temperature detection element detects the temperature of the outer surface of the heating roller, and supplies power to the heat source so that the temperature is always at a predetermined temperature suitable for fixing. quantity is controlled.

Here, when the heating roller fixes the toner image on the transfer paper, the temperature sensing element is disposed at the transfer paper passing portion of the heating roller because the heat is taken away and cooled accordingly.

(Problem to be Solved by the Invention) However, in the above-described fixing device, the size of the heating roller is determined according to the maximum size of the transfer paper, so it is difficult to continuously fix small-sized transfer paper. For example, a temperature difference occurs between a portion where heat is emitted through the transfer paper and a portion where heat is not emitted by the transfer paper. In other words, if you try to keep the temperature of the heat roller's heat emitting part (paper passing part) by the transfer paper at a constant value through the temperature detection element,
The temperature of the part of the heating roller that is not being fixed increases, which poses a safety problem, and the high heat shortens the lifespan of parts within the fixing device.

Is there any idea to attach a temperature detection element to the end of the heating roller where fixing work is rarely done? A problem arises in that the toner image is not sufficiently fixed.

The present invention has been made in view of the above problems, and an object thereof is to provide a fixing device that can always maintain a uniform temperature distribution in the axial direction of the heating roller, regardless of the paper size. .

(Means for Solving the Problems) In order to achieve the above object, the present invention includes a pair of fixing rollers, at least one of which has a heat source therein to serve as a heating roller, and a casing surrounding the fixing rollers. In the fixing device, the fixing device includes a control means for maintaining the outer surface temperature of the heating roller at a constant value, on the outside of the casing,
An air cooling means is provided to create an air flow around the heating roller.
The heating roller is characterized in that the amount of air flow by the air cooling means can be varied in the axial direction of the heating roller.

(Function) If the toner image on the transfer paper is fixed by the fixing roller,
The outer surface temperature of the heating roller decreases. For this reason, the heat source within the heating roller is controlled via a control means to maintain the outer surface temperature of the heating roller at a constant value.

However, in this case, the temperature does not drop in the portion of the heating roller that does not come into contact with the transfer paper, so the heat source inside the heating roller causes excessive heating, resulting in an excessively high temperature state.

Therefore, it was decided to cool the heating roller by generating an airflow in the excessively heated portion of the heating roller using an air cooling means such as a fan that generates an airflow around the heating roller.

(Example) Embodiments of the present invention will be described below based on the accompanying drawings.

First, a first embodiment of the present invention will be described with reference to FIGS. 1 and 2.

FIG. 1 is a sectional view of the fixing device and the photosensitive drum surroundings of an image forming apparatus such as a laser printer. In the figure, 10 is a photosensitive drum which is an image bearing member. A charger, a developing device, a cleaning device, a scanner unit, and a transfer charger 11 are arranged, and an intermediate guide 12, a fixing device 20, a paper ejection roller 13, etc. are arranged to the left of these image forming sections. There is.

That is, a photosensitive drum l uniformly charged by a charger
When the photosensitive drum 10 is exposed to image light from the scanner unit, an electrostatic latent image is formed on the photosensitive drum 10. The electrostatic latent image is visualized by a developer and converted into a toner image, and the toner image is transferred onto the transfer paper P via the transfer charger 11. On the other hand, the transfer paper P is timed and conveyed toward the photosensitive drum 10 from a paper feed cassette (not shown), and when the transfer is completed, it is sent to the fixing device 20 via the intermediate guide 12, and the toner image is The fixation is done. When the fixing is completed, the transfer paper P is discharged from the main body of the apparatus by the paper discharge roller 13. Incidentally, the photosensitive drum 10 after the transfer is cleaned of residual toner by a cleaning device, and is prepared for the next image forming operation.

The fixing device 20 includes a pair of fixing rollers, a heating roller 21 and a pressure roller 22;
22 respectively from the top direction" 2, f casing 2
3, 24, a temperature detection means 25 for detecting the outer surface temperature of the heating roller 21, a cleaning member 26 for cleaning the outer surface of the heating roller 21, and the like.

The heating roller 21 has a heating source 21c made of a halogen catalyst or the like housed inside a hollow cylindrical roller core 21b having a resin layer 21a or coach ink coated on its outer peripheral surface, and is kept constant by a driving source (not shown). It is driven to rotate in the direction. The heating source 21c is provided along the axial direction of the roller core metal 21b, and is configured to uniformly heat the outer surface temperature of the heating roller 21 in the axial direction. still,
The roller core metal 21b is made of a material such as aluminum, stainless steel, or copper, and the resin layer 21a is made of PFA, PTFE, or the like having a thickness of 3 to 1100 IL and having heat resistance and mold releasability.

The pressure roller 22 is composed of a roller core 22b and the like having a heat-resistant elastic layer 22a attached to its outer peripheral surface, and is pressed against the heating roller 21 by a pressure means (not shown) and driven by a drive source (not shown). Rotationally driven in a fixed direction. The roller core metal 22b is made of materials such as aluminum, stainless steel, and copper like the heating roller 21, and the thermoelastic layer 22a is made of silicone rubber, fluorocarbon rubber, fluorocarbon silicone rubber, etc. with a thickness of 2 to 10 mm. The heat-resistant elastic layer 22a forms a fixing nip between the heat roller 21 and the heat-resistant elastic layer 22a. In addition, the heat-resistant elastic layer 22
PFA, PT with a thickness of 3 to 100 ILm on the outer surface of a
It is more preferable to use a heat-resistant and peelable resin layer made of FE or the like.

The temperature detection means 25 is composed of a thermistor, thermocouple, etc. disposed in contact with the heating roller 21, and the temperature detection means 25 sends a detection signal regarding the outer surface temperature of the heating roller 21 to a control means (not shown). The control means controls the heat source 21c of the heating roller 21 so that the outer surface temperature of the heating roller 21 is kept constant at the toner image fixing temperature. The temperature detection means 25 is attached to the heating roller 21 at a position where the fixing operation is always performed regardless of the size of the transfer paper P.

The cleaning member 26 is made of a heat-resistant non-woven fabric made of polyamide-imide, Boester, etc. impregnated with an anti-offset liquid such as dimethyl silicone oil, and cleans foreign matter such as offset toner and paper dust attached to the outer surface of the heating roller 21 from the roller surface. It is for removal.

The upper and lower casings 23 and 24 have a U-shaped cross section, and the upper casing 23 has a heating roller 21.
The lower casing 24 is arranged so as to enclose the pressure roller 22 and the like from below, and the transfer paper P is placed between the upper and lower casings 23 and 24. A transport path is formed. Note that the cleaning member 26 penetrates through the upper casing 23.

Thus, when the transfer paper P is carried into the fixing device 20 with toner images formed in two directions in FIG. 1, the transfer paper P
The toner image on the transfer paper P is heated and conveyed while being sandwiched between the nip portion of the pressure rollers 21 and 22, or the toner image on the transfer paper P is heated and melted by the heating roller 21 and fixed onto the transfer paper P. Here, the temperature of the portion of the heating roller 21 that pinches the transfer paper P decreases due to the fixing operation, and the temperature drop is detected by the temperature detection means 25, and the heating source 21c is controlled via the control means. He will be immediately recovered.

Now, the temperature drop due to the fixing of the heating roller 21 is detected via the temperature detection means 25, and is recovered by heating up the heat source 21c, or in this case, the temperature drop due to the fixing of the heating roller 21 is detected by the portion of the heating roller 21 that is not involved in fixing, that is, the transfer paper P. Since the fixing operation is not performed on the portions where the light does not pass, the temperature of the heating roller 21 does not decrease and is excessively heated to a predetermined fixing temperature or higher due to heating up of the heat source 21c.

Therefore, in this embodiment, a heat exhaust fan 30 for air cooling is provided in the main body of the image forming apparatus, and the shaft of the heating roller 21 is attached to the upper casing 23 of the fixing device 20 near the suction section of the heat exhaust fan 30. A plurality of air passage windows 31. ...and...
The air passage window 31. By adjusting the opening degree of..., an air flow is generated by the heat exhaust fan 30 near the portion that is overheated by the heat source 21c of the heating roller 21,
The heating roller 21 is partially cooled.

That is, as shown in FIG. 1, a heat exhaust fan 30 is provided between the outer wall l of the main body of the apparatus above the paper ejection roller 13 and the upper casing 23 of the fixing device 20, and a looper 2 capable of discharging air is provided on the outer wall 1. In addition, a plurality of air passage windows 31. are provided in the upper casing 23 along the axial direction of the heating roller 21. ... has been established. An air passage adjustment plate 32 is disposed inside the upper casing 23 of the air passage window 31 to cover the air passage window 31 and block the flow of suction air by the heat exhaust fan 30. As shown in FIG. 2(a), the bimetal 33
so that it is supported by the upper casing 23.

As a result of the fixing work, if an excessively high temperature area is generated in a part of the heating roller 21 in the 1st axis direction, the air temperature etc. around the excessively high temperature area will rise, so it is necessary to adjust the air passage in the vicinity. The temperature of the bimetal 33 supporting the plate 32 also rises. Therefore, when the temperature of the bimetal 33 rises above a certain level, the bimetal 33 tilts, and as shown in FIG. . Therefore, an airflow is generated around the heating roller 21 by the heat exhaust fan 30 through the opening of the air passage window 31, and the excessively high temperature portion of the heating roller 21 is cooled by the airflow. Further, when the excessively high temperature part of the heating roller 21 is cooled down to a predetermined temperature by the air flow of the heat exhaust fan 30, the temperature of the bimetal 33 also decreases, the bimetal 33 returns to its original position, and the air path The window 31 will be covered with an air path adjustment plate 32.

As described above, even if an excessively high temperature area occurs in the axial direction of the heating roller 21 where heat is not absorbed by fixing, the heat exhaust fan 30 generates an air flow around the excessively high temperature area to cool the excessively high temperature area. Therefore, the axial temperature distribution of the heating roller 21 can always be kept uniform.

Next, a second embodiment of the present invention will be described with reference to FIGS. 3 and 4. Components having the same functions as those in the first embodiment are designated by the same reference numerals, and their explanations will be omitted.

In this embodiment, a part of the upper casing 23 is attached to the heating roller 21.
The upper and lower ends 23b and 23c of the arcuate casing 23a are extended to the looper 2 of the side wall l of the device main body to form an exhaust passage 40. In addition, a heat exhaust fan 30 is provided immediately before the looper 2, and a plurality of slits 41. ... has been established. Also, the arc-shaped casing 23a
slit 41. ... A temperature sensor 42 is attached close to the outer surface of the nearby heating roller 12, and if the temperature sensor 42 detects an excessively high temperature, the heat exhaust fan 30 is activated.

This fixing device 20 allows the small-sized transfer paper P to be
When the fixing operation is performed continuously, the transfer paper P passes through the approximate center of the heating roller 21, so that the temperature at both ends of the heating roller 21 gradually becomes higher. Therefore, the temperature detector 42 detects the ambient temperature at both ends of the heating roller 21, and when this temperature exceeds a predetermined value, the heat exhaust fan 30 is activated. Due to the operation of the heat exhaust fan 30, slits 41° are formed at both ends of the heating roller 21.
An air flow is generated through the heating roller 21, and both ends of the heating roller 21 are cooled. When the ambient temperature at both ends of the heating roller 21 falls below a predetermined value, the operation of the heat exhaust fan 30 is stopped via the temperature detector 42.

Thus, in this embodiment as well, the axial temperature distribution of the heating roller 21 can be maintained uniformly as in the first embodiment.

Next, a third embodiment of the present invention will be described with reference to FIG. still,
Components having the same functions as those in the first embodiment are given the same reference numerals, and their explanations will be omitted.

In this embodiment, a part 1a of the side wall 1 of the apparatus main body below the paper ejection roller 13 is extended to the paper feed side of the paper ejection roller 13, and one end 1b thereof is used as a transfer paper guide for the paper ejection roller 13. A part 24a of the lower casing 24 of the fixing device 20 was heated and extended to the paper discharge section side of the pressure rollers 21 and 22, and an air passage 50 was formed between the side wall l of the device main body and the lower casing 24. A cooling fan 51 is installed in the air passage 50, and the airflow caused by the cooling fan 51 is connected to the heating roller 2.
A part of the upper casing 23 was cut so that it could be moved sufficiently toward the upper casing 23.

Therefore, if the transfer paper P is sandwiched between the heating and pressure rollers 21 and 22, the airflow by the cooling fan 51 that has passed through the air passage 50 will avoid the transfer paper P and will cause the transfer paper P to reach both ends of the transfer paper P. It moves from the side toward the louver 2 through the heating roller 21.

Therefore, both ends of the heating roller 21 , which are becoming hotter due to the passage of the transfer paper P, are sufficiently cooled by the air flow generated by the cooling fan 51 , and are cooled in the axial direction of the heating roller 21 .
5. The temperature will always be maintained uniformly.

In this embodiment, no matter what size the transfer paper P is, the air flow is directed to the heating roller 21 according to the size of the transfer paper P.
Since the necessary portions of the heating roller 21 can be cooled more completely than in other embodiments, the temperature distribution in the axial direction of the heating roller 21 can be made more uniform. Note that when the fixing device 20 is not performing fixing work, the cooling fan 51 may be stopped.

(Effects of the Invention) As is clear from the above description, according to the present invention, since the overheated portion of the heating roller can be cooled by air cooling means, the axial direction of the heating roller can be cooled regardless of the size of the transfer paper to the fixing device. Temperature distribution can be made uniform.

Therefore, there will be no abnormally high temperature parts on the heating roller.
There are no problems in terms of safety or component life.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view around the fixing device according to the first embodiment. FIG. 6 and FIG.
(b) shows the state before operation of the air passage adjustment plate, (b) shows the state after operation), FIG. 3 is a cross-sectional view of the fixing device and its surroundings according to the second embodiment, and FIG. FIG. 5 is a cross-sectional view taken along the line IV-IV, and is a cross-sectional view around the fixing device according to the third embodiment. 20...Fixing device, 21...Heating roller, 21c.
...Heat source (heat source), 22...Pressure roller, 23.2
4...-Thing, 25... Temperature detection means (control means), 30... Exhaust heat fan (air cooling means), 51... Cooling fan (air cooling means).

Claims (1)

[Claims] a pair of fixing rollers, at least one of which has a heat source therein and serves as a heating roller; a casing that covers the fixing roller; and a control means for maintaining an outer surface temperature of the heating roller at a constant value. In the fixing device, an air cooling means for generating an air flow around the heating roller is provided on the outside of the casing, and the amount of air flow by the air cooling means can be varied in the axial direction of the heating roller. fixing device.