JPS58190972A - Temperature controlling metnod of heat roll of electrophotographic printer - Google Patents

Abstract

PURPOSE:To prevent a hot offset when printing is started again and at the same time to incease the service life of a fixing heat roll, by absorbing the heat from the heat roll when the printing is at pause and therefore avoiding an abnormal rise of the temperature on the surface of the heat roll after the printing is discontionued. CONSTITUTION:A fixing heat roll 1 is set oppositely to a pressure roll 6 and then controlled at a fixed temperature by a temperature controller in order to fix a toner image on paper 5. When the printing of a printer is discontinued, the roll 6 moves down. In this case, the roll 1 has a rise of its surface temperature owing to the heat capacity of the roll. Therefore, a heat absorbing roll 10 is pressed to the roll 1 to absorb the heat of the roll 1. This process prevents the rise of the surface temperature of the roll 1. A heat absorbing belt is also available in addition to the roll 10. It is also effective to use only a cooling fan to cool down the roll 1.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for preventing an abnormal rise in the surface temperature of a heat roll after stopping printing in an electrophotographic printing apparatus having a heat roll for fixing.

A conventional heat roll temperature control device will be explained with reference to FIG. In the figure, 1 is a heat roll, 2 is a temperature detection device, 3 is a heater, 4 is a heater drive device, 5 is paper, 6
is a pressure roll and a 15\'i heater control device.

The paper temperature during printing is It, the paper feed speed is v1, and the thickness is d.
If the temperature of one heat roll is T, then tαT/vd...
......(1) holds true. Therefore, since the paper temperature necessary for printing is determined, the heat roll temperature is selected according to the thickness of the paper and printing is performed. The temperature detection device 2 detects the surface temperature of the heat roll 1 and sends a signal to the heater control device 15. If the detected temperature is lower than the initially selected temperature, the heater drive device 4 turns on the heater filter, and heat is supplied from the heater filter to the heat roll 1. Further, if the temperature is higher than the selected temperature, the heater 3 is turned off and the supply of heat is stopped. In this way, the temperature of the heat roll 1 is kept constant.

The exchange of heat between the heat roll 1, heater filter, and paper 5 during printing can be expressed as follows.

Q = 'b+q2+qs・・・・・・・・・・・・
...(2) Q The amount of heat obtained by the kl heat roll from the heater, qld The amount of heat the heat roll has after inkuri, q2
h When the paper is printed, it is heated [1-Amount of heat given by the ru,
q3 is the amount of heat given by the heat roll to something other than the paper.

Here, the specific heat of the heat roll is 08%, the mass is mH1, the temperature is TR%, the specific heat of the paper is CF%, the speed of the paper is v1, the thickness of the paper is d, the width of the paper is t1, the density of the paper is ρ, and the heat roll is If the temperature of the heat roll when no other heat is taken away is T, equation (2) can be expressed as equation (3).

CHmHT= CHmHTt++Cyρvdtt+q3
- +31 Calculating the heat roll temperature TH from equation (3) results in equation (4).

Next, consider the heat roll temperature when printing is stopped. When printing is stopped, the temperature becomes v20, so it can be seen that (4) the heat roll temperature increases.

According to an example of an experiment, the paper thickness was L196JllI, the paper width was 381m, and the paper running speed was 1000 JEI/se.
When printing at c, the surface temperature of the heat roll is 16
What was 0°C rises to 200°C after printing is stopped.

The biggest problem here is hot off cents.

If printing is started again immediately after printing is stopped, hot offset occurs because the heat roll surface temperature is abnormally high. It is also known that the higher the surface temperature of the heat roll, the shorter the life of the heat roll.

Therefore, keeping the rise in surface temperature of the heat roll low when printing is stopped is one of the very important factors for printers that employ the pressurized heat roll fixing method.

An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and to prevent an abnormal rise in temperature of the heat roll after stopping printing.

The present invention focuses on the fact that the reason why the temperature of the heat roll abnormally rises immediately after stopping printing is that the paper stops absorbing heat from the heat roll. This device is designed to prevent an abnormal rise in the temperature of the heat roll by providing the heat roll with something that removes heat from the heat roll.

FIG. 2 shows a specific example of the present invention. In the figure, 1 is a heat roll, 5 is paper, 6 is a pressure roll, 7 is an air volume control device for controlling the air volume of a Vi fan, and 8 is a fan for sending air to the heat roll.

When a signal to stop printing is input to the air volume control device, the fan 8 rotates and sends air to the heat roll 1 to remove heat. The air volume of F/8 is controlled by air volume control device #7 and changes depending on the thickness of the paper. Next, when printing is started in response to a print start signal, the fan 8 stops blowing air.

A modification of the invention is shown in Figure 3.4.5.6.7. Third
The diagram shows the direction of the fan in the specific example diagram reversed.
The mechanism is exactly the same as the specific example. The difference is that the heat from the heat roll is exhausted by a fan. Figures 4 and 5 show a case in which a medium other than air is used as the medium for removing heat from the heat roll. The medium is an endothermic roll in FIG. 4 and an endothermic belt in FIG. Both of these are made of materials with good thermal conductivity and rotate at the same peripheral speed as the heat roll. Next, Figures 4 and 5
The mechanism of the modified example shown in the figure will be explained. After the printing is stopped, the pressure roller 6 is lowered, and the heat absorption roll 10 and the heat absorption bell (1!) connected thereto are lowered. 1 is pressed against the heat roll. The heat absorption roll 10 and the heat absorption belt 15 are
Because it absorbs more heat than the heat roll, it also accumulates heat. Therefore, the accumulated heat is removed by cooling fans 9 and 12. The force with which the heat absorbing roll 10 and the heat absorbing belt 13 are pressed against the heat roll can be adjusted by a tension variable device. The amount of heat absorbed from the heat roll is changed depending on the strength of this pressing force.

A feature of the heat absorbing roll and heat absorbing belt system is that it is easy to remove heat evenly from the heat roll surface.

The modified example shown in FIGS. 6 and 7 has a shutter 14 added to the specific example (FIG. 2) and modified example (FIG. 5).

It is something that

This shutter is provided for the purpose of improving the response speed of the fan and making it easier to adjust the airflow.

According to the present invention, after printing is stopped, air from a fan, an endothermic roll, an endothermic belt, etc. are brought into contact with the heat roll to remove heat from the heat roll and prevent a sudden reduction in the thermal load on the heat roll. , it is possible to eliminate abnormal rise in heat roll temperature after printing is stopped. As a result, it is possible to prevent hot offset when printing is restarted and to extend the life of the heat roll.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the components of the prior art. In the figure, 1 is a heat roll, 2 is a temperature detection device, 3ii heater, 4 is a heater drive device, 5 is paper, 6 is a pressure roll,
15 is a heater control device. FIG. 2 is a schematic diagram showing a specific example of the present invention. In the figure, 7 is an air volume control device, and 8 is a fan. FIGS. 5, 4, 5, 6, and 7 are schematic diagrams showing modifications of the present invention. In the figure, 9 is an endothermic roll cooling fan, 10 is an endothermic roll, 11 is a tension variable device, 12
13 is an endothermic belt cooling fan, 13 is an endothermic belt, and 14 is a shutter. Name of patent applicant Hitachi Koki Co., Ltd.

Claims (1)

[Claims] A heat roll, a heater for heating the heat roll, an electric circuit for turning on/off electricity to the heater, a control circuit for controlling the electric circuit, and a heater for heating the heat roll, a control circuit for controlling the electric circuit, and a heater for heating the heat roll. In an electrophotographic printing apparatus in which the control circuit is controlled by a temperature detecting device and a change in a signal from the temperature detecting device, by applying a heat load to the heat roll in place of the paper when printing is stopped. A heat roll temperature control method for an electrophotographic printing apparatus, characterized by preventing an abnormal rise in heat roll temperature after printing is stopped.