JPH04305679A - Fixing device - Google Patents

Abstract

PURPOSE:To prevent rising of temperature of a heat roll in a non paper passing part and to provide a heat roll with a temperature control function. CONSTITUTION:A heating element 27 is installed freely rotatable or fixed against a backup roll installed freely rotatable. And, the heating element 27 is formed by connecting in parallel a multiple number of resistors. The element is constituted by resistors provided with the characteristic of increasing resistance as the temperature rises and the direction of imparting voltage to each resistor is matched with the paper feeding direction. When the paper is passed, the temperature in a paper passing part is lowered because the heat is imparted to the paper, but since no paper passes through the non paper passing part, the temperature tend to rise. At this time, the resistance values of the resistors positioned in the non paper passing part is increased, the rising of temperature is controlled by reducing the energized current. There-fore, even when the paper of a narrow paper width is passed, a constant temperature can be obtained in the direction of the paper width, as well.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device for an electrophotographic apparatus.

0002

2. Description of the Related Art Conventionally, when forming images in printers, copying machines, etc., an electrophotographic recording method based on the Carlson method has generally been used. According to this method, a charged photoreceptor drum is exposed to light by an exposure device, and an image on a document read by an optical means is formed as an electrostatic latent image on the photoreceptor drum. This electrostatic latent image is developed by a developing device, transferred onto a recording medium by a transfer device, and fixed by a fixing device to form an image. Since the photosensitive drum is used repeatedly, residual toner after transfer is cleaned by a cleaning device.

[0003] The above fixing device is usually composed of a heat roller fixing device consisting of a heat roller and a backup roller, and the heat roller is heated by various methods (Japanese Patent Laid-Open Nos. 56-162772 and 60-260077).
(see Japanese Utility Model Application Publication No. 57-22763). FIG. 2 is a schematic diagram of a conventional fixing device.

In the figure, 1 is a heat roller, and 2 is a backup roller disposed opposite to the heat roller 1. The heat roller 1 is rotated via a gear 3 by a drive section (not shown). Above heat roller 1
When paper carrying unfixed toner is passed between the back-up roller 2 and the back-up roller 2, the toner is heated by the heat roller 1 and thermally fixed. The heat roller 1 is formed by covering the periphery of a metal pipe 4 with an electrical insulating layer 5, further providing a heating element 7 around it, and covering the outermost part with a mold release layer 8 made of a fluororesin film. . Ring-shaped electrodes 6A and 6B are provided at both ends of the heating element 7, are in contact with the power supply section 9, and are supplied with power from an AC power source 10. The heating element 7 is heated and controlled to a fixing temperature by detecting the temperature with a thermistor (not shown) or the like.

FIG. 3 is a diagram showing a circuit model of a heating element in a conventional fixing device. In the figure, 7 is a heating element, 1
5 to 20 are a plurality of resistors constituting the heating element 7. The resistors 15 to 20 are connected and arranged in series in the paper width direction. A power supply section 9 is provided at both ends in the paper width direction, and the power supply section 9
It is connected to the power supply 21 via. Further, A is a paper passing section where paper that does not have a width that spans the entire area of the heat roller 1 is passed, and B is a non-paper passing section. Above paper passing section A
resistors 17 to 20, and resistors 15 and 16 to non-paper passing section B.
Each of them generates heat.

[0006]

[Problems to be Solved by the Invention] However, in the fixing device configured as described above, if narrow paper is used continuously and the paper passes only a part of the heat roller 1, the heat roller 1 may not pass. The temperature of the paper portion B becomes higher than the fixing temperature. In other words, when the heat roller 1 is controlled to the fixing temperature using a thermistor or the like, heat is absorbed by the paper in the paper passing section A, but heat is not absorbed by the paper in the non-paper passing section B. and,
If a wide sheet of paper is passed in this state, the temperature of the non-sheet passing portion B will become higher than the fixing temperature, resulting in excessive fixing, and the toner that was once transferred to the paper will adhere to the heat roller 1 again.

The present invention solves the problems of the conventional fixing device described above, prevents the temperature of the heat roller in the non-sheet passing area from rising, and provides a heat roller having a temperature control function. purpose.

[0008]

[Means for Solving the Problems] To this end, the fixing device of the present invention includes a backup roller that is rotatably disposed, and a heating element that is rotatably or fixedly disposed opposite to the backup roller. be done. The heating element is formed by connecting a plurality of resistors in parallel, a power source is connected to each resistor, and a voltage is applied by the power source. Each of the resistors has a characteristic that the resistance increases as the temperature rises, and the direction in which voltage is applied to each resistor is made to coincide with the paper feeding direction.

[0009]

According to the present invention, a backup roller is rotatably disposed as described above, and a heating element is rotatably or fixedly disposed opposite the backup roller. Then, paper with unfixed toner attached is sent between the backup roller and the heating element, and is heated by the heating element to perform fixing.

The heating element is formed by connecting a plurality of resistors in parallel, a power source is connected to each resistor, and a voltage is applied by the power source. Each of the resistors has a characteristic that the resistance increases as the temperature rises, and the direction in which voltage is applied to each resistor is made to coincide with the paper feeding direction. When paper is passed between the backup roller and the heating element, the paper passing section applies heat to the paper, causing the temperature to drop, but the paper does not pass through the non-paper passing section, so the temperature tends to rise. . At this time, the resistance value of the resistor located in the paper non-passing portion increases to reduce the flowing current and suppress the rise in temperature.

[0011]

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 4 is a diagram showing changes in resistance value due to temperature rise of the heating element. As shown by the straight line α in the figure, the resistance value of each of the resistors 15 to 20 of the heating element 7 increases as the temperature rises. Therefore, in the conventional fixing device, the resistance value of the resistances 15 and 16 in the non-paper passing section B is the same as the resistance value of the resistance 17 in the paper passing section A.
Since the resistance value increases from 20 to 20, the resistance value of the entire heating element 7 becomes small and the amount of heat generated decreases. Therefore, if control is performed to maintain the paper passing section A at the fixing temperature, the temperature of the non-paper passing section B will be fed back in an upward direction.

FIG. 1 is a sectional view of the heat roller in the fixing device of the present invention, and FIG. 5 is a sectional view of the main part of the heat roller in the fixing device of the present invention. In the figure, 4 is a metal pipe, and the metal pipe 4 is coated with an electrically insulating layer 5. The electrode 26A includes a ring-shaped portion 26A1 and a thin strip-shaped portion 2 formed in the axial direction of the metal pipe 4, that is, in the paper width direction.
Consists of 6A2. Similarly, the electrode 26B also has a ring-shaped portion 26.
B1 and a thin band-shaped portion 26B2 formed in the axial direction of the metal pipe 4. Band-shaped portion 26B of the electrode 26B
2 is formed on the opposite side of the metal pipe 4 to the strip portion 26A2 of the electrode 26A, and is arranged in parallel so that the distance between the two in the circumferential direction is equal. A heating element 2 is further placed on the electrodes 26A and 26B having such a configuration.
7. A release layer 8 made of fluororesin is sequentially coated. In the embodiment, a voltage is applied to the heating element 27 in the circumferential direction, that is, in the paper width direction.

FIG. 6 is a diagram showing a circuit model of the heating element in the fixing device of the present invention. In the figure, 27 is a heating element, and 31 to 37 are a plurality of resistors constituting the heating element 27. The resistors 31 to 37 are connected and arranged in parallel in the paper width direction, and are connected to the power source 21 via electrodes 26A and 26B. Further, A is a paper passing section where paper that does not have a width that spans the entire area of the heat roller 1 is passed, and B is a non-paper passing section. Resistors 33 to 37 are provided in the paper passing section A.
There are resistors 31 and 32 in the paper non-passing section B, each of which generates heat.

In this case, as the temperature of the non-sheet passing portion B increases, the resistance values of the resistors 31 and 32 increase, so that heat generation in this portion is suppressed. On the other hand, the current flowing through the resistors 33 to 37 in the sheet passing section A does not change even if the resistance values of the resistors 31 and 32 increase, and the amount of heat generated does not change. Therefore, even if the paper passing section A is controlled to maintain the fixing temperature, the temperature of the non-paper passing section B will not rise.

FIG. 7 is a diagram showing the variation in resistance value due to temperature rise of the heating element in the fixing device of the present invention. By using the resistors 31 to 37 that exhibit temperature dependence as shown by the curve β in the figure, it is possible not only to maintain the temperature at a constant temperature T, but also to suppress the occurrence of temperature unevenness in the paper width direction.

Further, the electrodes 26A and 26B may be installed outside the heating element 27, or may be configured as a plurality of pairs. In this way, a voltage is applied between the electrodes 26A and 26B to heat up to the fixing temperature, and thereafter the fixing temperature is controlled by a thermistor (not shown) or the like to maintain the fixing temperature. If a ceramic material mainly composed of barium titanate is used as the heating element 27, a thermistor or the like can be made unnecessary due to its self-temperature control function.

Furthermore, even in a fixing device in which the heating element is fixed rather than disposed on a rotating heat roller, a voltage can be similarly applied to the heating element in the paper feeding direction. Note that the present invention is not limited to the above-mentioned embodiments, and various modifications can be made based on the spirit of the present invention, and these are not excluded from the scope of the present invention.

[0018]

As described in detail above, according to the present invention, the heating element disposed opposite the backup roller is formed by connecting a plurality of resistors in parallel, each resistor having
The resistor is constructed of a resistor whose resistance increases as the temperature rises, and a voltage is applied to each resistor in the same direction as the paper feeding direction.

[0019] Therefore, even if paper having a narrow width is passed through, a uniform temperature can be obtained in the width direction of the paper.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a heat roller in a fixing device of the present invention.

FIG. 2 is a schematic diagram of a conventional fixing device.

FIG. 3 is a diagram showing a circuit model of a heating element in a conventional fixing device.

FIG. 4 is a diagram showing a change in resistance value due to a rise in temperature of a heating element.

FIG. 5 is a sectional view of a main part of a heat roller in the fixing device of the present invention.

FIG. 6 is a diagram showing a circuit model of a heating element in the fixing device of the present invention.

FIG. 7 is a diagram showing a change in resistance value due to a rise in temperature of a heating element in the fixing device of the present invention.

[Explanation of symbols]

1 Heat roller 2 Backup roller 4 Metal pipe 5 Electrical insulation layer 8 Release layer 26A, 26B Electrode 26A1, 26B1 Ring-shaped portion 26A2, 2
6B2 Band-shaped portion 27 Heating elements 31 to 37 Resistance

Claims (1)

[Claims] Claim 1: (a) a backup roller disposed rotatably; (b) a heating element disposed opposite the backup roller and comprising a plurality of resistors connected in parallel; c) a power supply that applies a voltage to each resistor of the heating element; (d) each of the resistors has a property that the resistance increases as the temperature rises; (e) each of the resistors has a A fixing device characterized in that a direction in which voltage is applied is made to match a paper feeding direction.