JPH03139684A - Fixing device - Google Patents

Abstract

PURPOSE:To shorten the rising time and to improve heat efficiency by constituting the heat roller of the fixing device with a heat pipe. CONSTITUTION:The heat roller 20 is such that a resin coat 21 composed of fluorocarbon resin, etc., is provided on the outside of the heat pipe 22, by taking wear resistance, high temperature stability, durability, and chemical resistance into account. The heat pipe 22 itself is composed of a hermetically sealed container 22a, a mesh part 22b, which is inside the container, and an internal, depressurized hollow 22c. Generally the heat pipe 22 transfers heat at the high speed, and its heat capacity is small; therefore, heating of the heat roller 20 to a prescribed temperature suitable for fixing can be performed in a short time and also heat efficiency can be improved by composing the heat roller 20 of the fixing device with the heat pipe 20.

Description

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

(Prior Art) In copying machines and the like, it is necessary to fix a toner image on a photosensitive drum, which is an image carrier, as a permanent image using a fixing device.

A fixing device generally consists of a pair of upper and lower fixing rollers, one of which is a heating roller, and by passing transfer paper between the fixing rollers, the toner image on the transfer paper is heated and melted and fixed onto the transfer paper. It is something. An electric heater or the like is generally provided inside the heating roller.

(Problems to be Solved by the Invention) However, in the conventional type of fixing device as described above, since a small heat source with high temperature is used, it is necessary to set the heat capacity of the heating roller to be large. For this reason, it is necessary to wait a considerable amount of time for the surface temperature of the heating roller to reach a temperature suitable for fixing after the heating roller's heater starts operating. Time was the dominant factor.

Also, because the heating roller has a large heat capacity, it is necessary to supply extra heat until the heating roller reaches the fixing temperature.
The thermal efficiency of the heating roller was also not good.

The present invention has been made in view of the above problems, and it is an object of the present invention to provide a fixing device that takes a short time from the start of heating until reaching the fixing temperature and has high thermal efficiency.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a fixing device that fixes an image on a transfer material, in which one of a pair of fixing rollers is a heating roller, and the heating roller is placed on one end side. It is characterized by being configured with a heat pipe that provides a heat source.

(Function) Since a heat pipe generally has a high heat transport speed and a small heat capacity, if this heat pipe is used as the heating roller of the fixing device, heating the heating roller to a predetermined temperature suitable for fixing can be shortened. It is possible to save time and increase thermal efficiency.

In particular, since the temperature of the heat pipe itself is set close to a predetermined temperature suitable for fixing the heating roller, no extra heat insulating material is required, and in this sense as well, the heat capacity of the heating roller can be reduced.

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

First, an overview of image forming work using a laser printer or the like will be explained with reference to FIG. 6. In the figure, 1 is a photosensitive drum which is an image bearing member, and around the photosensitive drum there are a primary charger 2, a developer 3, A transfer charger 4 and a cleaning device 5 are provided, and when the photosensitive 1ζ ram 1 uniformly charged by the negative charger 2 is exposed to only image light from a scanner unit (not shown), the photosensitive tram 1 is exposed to image light. An electrostatic latent image is formed.

As the photosensitive drum 1 rotates, the electrostatic latent image is sent to a developing device 3, which supplies developer (toner) and converts it into a toner image. The toner image is transferred to a transfer material (transfer paper) PL via a transfer charger 4, and the photosensitive tram 1 after the transfer is cleaned by a cleaning device 5 to collect residual toner.

On the other hand, the transfer paper P is supplied from a paper feed system (not shown) to the photosensitive tram 1 at the same timing, and when the toner image on the photosensitive tram 1 is transferred, it is sent to the fixing device 6 and the toner image is transferred to the photosensitive tram 1. or fixed as a permanent image. The fixing device 6 is composed of a pair of upper and lower fixing rollers 20 and 30. For example, the upper fixing roller 20 is a heating roller, and the transfer paper P carrying a toner image is sandwiched between the pair of fixing rollers 20 and 30. While conveying the toner image, the toner image is fixed on the transfer paper P while being heated and melted by the heating roller 20 on the negative edge side.

Next, the structure and operation of this fixing device 6 will be explained with reference to FIGS. 1 to 4.

In the present invention, the heating roller 20 of the pair of fixing rollers 20 and 30 is configured as a heat pipe. First, the overall configuration of the fixing device 6 will be explained with reference to FIG.
The fixing section 10 is located in the center, and the heating section 1 is located on the left side of the fixing section 10.
1, a rotation drive unit 12 on the right side, and a fixing unit lO
The heating roller 20 on the upper side and the fixing roller 30 on the lower side come into contact with each other, making it possible to fix the toner image on the transfer paper P. The heating section 11 is disposed so as to wrap around a heat input section at one end of the heating roller 20 with a support member 31 made of steel or the like having high thermal conductivity. It is rotatably supported via a sliding member 32 consisting of a plurality of balls.

An electric heater 33 for heating the support member 31 is attached to the lower side of the support member 31 below the heat input portion of the heating roller 20, and power is supplied to the electric heater 33 via a heater drive circuit 34. . The temperature of the support member 31 is controlled by detecting the temperature of the support member 3 with a temperature detection element 35 that is pressed against the support member 31, and based on the detection signal, the amount of electricity sent to the electric heater 33 is controlled by the heater drive circuit. This is done by adjusting according to 34.

The rotation drive unit 12 is for rotating the heating roller 20 and the fixing roller 30 , and a drive gear 37 is attached to one end of the heating roller 20 via a heat insulating member 36 . Drive gear 38 also at one end
These drive gears 37 and 38 are rotationally driven via a drive force transmission mechanism 39.

As shown in FIG. 2, the heating roller 20 has a heat pipe 22 coated with a resin coat 21 made of fluororesin or the like in consideration of wear resistance, high temperature stability, durability, and chemical resistance. The heat pipe 22 itself is composed of a closed container part 22a, a mesh part 22b inside the closed container part 22a, and a vacuum hollow part 22c inside. Since the temperature set on the outer surface of the heating roller 20 is generally around 180°C, the closed container portion 22a and the mesh portion 22b are made of copper, and the working fluid inside is water.

That is, when power is input to the heater drive circuit 34 of the fixing device 5, the support member 31 is heated via the electric heater 33, and the support member 31 is kept at a constant temperature by controlling the heater drive circuit 34 by the temperature detection element 35. It will be heated up. Therefore, heat is input into the heat pipe 22 (heat input part) in the heating part 11 of the heating roller 20, vaporizes the working fluid (water) in the heat pipe 22, and fixes the vapor in the heat pipe 22. The vapor is propagated toward the fixing section 10 side at a speed equal to the difference in sound speed, and the fixing section 10 side of the heat pipe is heated by this steam. The heat of evaporation of this working fluid is released by fixing the toner image on the transfer paper P in the fixing section 10, and the condensed working fluid is transferred to the mesh section 22.
In b, the heat is refluxed toward the heating section 11 side by the same effect as the osmotic pressure in the capillary, a circulation cycle is formed, and the same heat exchange is repeated thereafter. That is, heat is exchanged based on the operating principle of the heat pipe 22 based on the phase transition of the working fluid in the heat pipe 22.

Therefore, as shown in FIG. 3, from the start of power input to the electric heater 22, the outer surface temperature of the heating roller 20 is set at a temperature T suitable for fixing. Compared to the conventional fixing device (kerf A) in which an electric heater is disposed inside the heating roller, the time it takes to reach the fixing device (kerf B) according to the present invention in which the heating roller 20 is configured with a heat pipe 22, etc. is longer. This method is much shorter (a fraction of the time compared to the conventional method) and can significantly shorten the start-up time of the device.

This is because the main part of the heating roller 20 is only composed of the heat pipe 22 and the resin coat 21 around the heat pipe 22, so its heat capacity is small and the temperature rises easily, and the heat pipe 22 is heat conductive. This is because it has a heat transfer effect hundreds of times faster than copper, silver, etc., which have a lower temperature, and the heat transfer rate is faster. The heat capacity of the heating roller 20 can be kept small because the heat pipe 22 itself has a larger diameter than an electric heater, etc., and the internal temperature can be brought closer to the fixing temperature, so no extra heat insulating material is required. This is for a reason. Also, for the same reason, after the first fixing is completed, the time until the next fixing is possible is short, and the device itself performs a series of process operations such as charging, exposure, development, transfer, and separation without waiting time. I can do things.

Further, FIG. 4 shows the temperature distribution in the longitudinal direction in the fixing section 1O of the heating roller 20, where P is the heating section 11 side of the fixing section 10, Q is the center part of the fixing section 10, and R is the temperature distribution on the fixing section 10. P and Q respectively indicate the positions on the rotation drive unit 12 side.

There is almost no temperature difference at point R, and the temperature of the heating roller 20 is almost uniform throughout the fixing section IO.

When the main power of the image forming apparatus is turned on, power is supplied to the heater drive circuit 34 of the fixing device 5, and
The heating roller 20 and the fixing roller 30 start rotating via the rotational drive transmission mechanism 39. Since the heating roller 20 reaches the fixing temperature in a short time via the electric heater 33 and the support member 31, this image forming apparatus can immediately form an image. Furthermore, the time required to start the next fixing operation after the -th fixing operation is also shortened.

The drive gear 37 of the heating roller 20 is connected to the heat insulating member 36.
Since it is attached to this heating roller 20 via
Heat is not transferred to this drive gear 37 unnecessarily.

Further, the electric heater 33 is connected to the support member 31 and the heating roller 20.
Since it is only necessary to heat a part of the electric heater 33, the retained heat of these elements is small, and the thermal efficiency of the electric heater 33 is improved. Furthermore, since the heating roller 20 is constructed of a hollow and lightweight heat pipe 22, etc., the weight of the apparatus can be reduced, and the capacity of the rotational drive source for the heating roller 20 can also be reduced.

Further, in FIG. 5, the thickness of the closed container part 22a of the heat pipe 22 of the heating roller 20 is gradually increased from the heating part 11 side toward the fixing part 20, and the internal mesh part 22b is eliminated. The heating roller 20 can cause the condensed working fluid in the fixing section 10 of the heat pipe 22 to flow back toward the heating section 11 by the centrifugal force caused by the rotation of the heating roller 20. Therefore, this type of heating roller 2
0 is suitable for a high-speed rotation type fixing device.

1 (Effects of the Invention) As is clear from the above description, according to the present invention, since the heating roller of the fixing device is constructed with a heat pipe, the heating roller can be heated to a predetermined temperature in a short time due to the properties of the heat pipe, and the image The start-up time of the forming apparatus can be shortened and the thermal efficiency can be improved. Similarly, the time from the first fixing operation until the next fixing operation becomes possible can be shortened.

[Brief Description of the Drawings] Fig. 1 is a conceptual diagram showing the overall structure of the fixing device, Fig. 2 is a partial sectional view of the heating roller, and Fig. 3 is the setting of the fixing device according to the present invention and the conventional fixing device. FIG. 4 is a diagram showing the temperature distribution in the longitudinal direction of the fixing part of the heating roller; FIG. 5 is a partial cross-sectional view of the heating roller according to a modified example; FIG. 6 is a diagram for explaining the outline of image forming work using a laser printer or the like. 5... Fixing device, 20... Heating roller, 22...
Heat pipe, 30... Fixing roller, P... Transfer paper 2 (transfer material).

Claims (4)

[Claims] (1) A fixing device that fixes an image on a transfer material by using one of a pair of fixing rollers as a heating roller, characterized in that the heating roller is constituted by a heat pipe to which a heat source is applied to one end side. . (2) The fixing device according to claim 1, wherein an outer peripheral portion of the heat pipe is coated with fluorine resin. (3) Claim 1 characterized in that the heating roller and the rotational force transmitting portion of the heating roller are coupled via a heat insulating member.
Or the fixing device according to 2. (4) The fixing device according to claim 1, 2 or 3, wherein the wall thickness of the airtight container of the heat pipe is gradually increased from the heat source side at one end to the other end side.