JPH0697368B2 - Heating roll type fixing device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device using a heating roll, and more particularly to a fixing device that prevents a copy image on a sheet from being offset to the heating roll.

2. Description of the Related Art In a copying machine, a developing image corresponding to an electrostatic latent image on a photosensitive drum is transferred onto a sheet of paper, and the transferred image (unfixed copy image) is transferred to a sheet of paper by, for example, a heating roll type fixing device. Fix on top.

In the fixing device using the heating roll, as shown in FIG. 4, the heating roll 1 and the pressure roll 2 are provided so as to face each other. In the heating roll 1 of these, a surface layer 4 made of, for example, parafluoroalkoxylene (PFA) is formed on the outer peripheral surface of the cylindrical core 3, and on the central axis of the cylindrical core 3, a colts lamp 5 as a heat source is formed. Is provided. Pressure roll 2
Has a cylindrical rubber portion 7 formed on the outer periphery of the shaft 6.

Paper conveyed from the inlet chute 8 to the fixing device 9
When 10 is inserted between the heating roll 1 and the pressure roll 2,
The copy image represented by the toner 11 is fixed by the heat and pressure between both rolls.

If the toner 11 is positively charged and the heating roll 1 is negatively charged, the toner 11 and the heating roll 1 are
Part of the toner 11 is heated by the electric attraction between the heating rolls 1.
May be attached to the surface layer 4 of the above, and an offset may occur. The higher the density of the copy image, the more the offset occurs.

Problems to be Solved by the Invention According to the conventional fixing device, for example, the positive charge amount of the toner 11 forming the unfixed copy image on the sheet 10 is different from the negative charge amount of the surface layer 4 of the heating roll 1. If it is large, there is a problem that the toner 11 is likely to adhere to the surface layer 4 of the heating roll 1 due to the electric attraction force, and an offset is likely to occur.

The present invention has been made to solve such a problem, and its object is to control the charge amount of the heating roll surface layer according to the image density of the unfixed toner on the paper,
It is to prevent the offset reliably.

Means for Solving the Problems In order to achieve the above object, the heating roll type fixing device of the present invention is arranged such that the heating roll and the pressure roll are opposed to each other,
An image density detecting means for detecting the image density of the unfixed copy image on the paper is provided by pressing the heating roll and the pressure roll to fix the copy image on the paper. A charge eliminating brush for changing the charge amount is provided, and a control unit for controlling the voltage applied to the charge eliminating brush according to the image density detected by the image density detecting unit is provided.

Effect According to the present invention, the image density of the unfixed copy image on the paper is detected by the image density detecting means, and the voltage applied to the charge eliminating brush by the control means is controlled according to the image density. The charge amount of the layer is set to a value according to the image density of the unfixed toner, and the offset of the unfixed toner is surely prevented.

Embodiment An embodiment of the present invention will be described with reference to the drawings.

FIG. 3 shows an embodiment in which the present invention is applied to a fixing unit of an electrophotographic copying machine.

The surface of the photosensitive drum 13 is uniformly charged by the charging corotron 12, and when the photosensitive drum 13 is irradiated with light corresponding to the original, an electrostatic latent image corresponding to the original is formed on the peripheral surface of the photosensitive drum 13. To be done. The electrostatic latent image formed on the photosensitive drum 13 is visualized by the adhesion of the toner supplied from the developing device 14, and a copy image as this visible image is formed on the paper supplied from the direction of arrow A. Transferred by transfer corotron 15,
The sheet is peeled from the photosensitive drum 13 by the peeling corotron 16 and sent to the fixing device 20 via the conveying belt 18. The toner remaining on the photosensitive drum 13 is cleaned by a cleaning blade.
The peripheral surface of the photosensitive drum 13 is cleaned by being scraped off by 17, and thus one copy cycle is completed.

In the fixing device 20, as shown in FIG. 1, a heating roll 1 and a pressure roll 2 are arranged to face each other. Heating roll 1
A surface layer 4 made of, for example, parafluoroalkoxylene (PFA) is formed on the outer peripheral surface of the cylindrical core 3, and a Colts lamp 5 as a heat source is provided on the central axis of the cylindrical core 3. The pressure roll 2 pressed against the surface layer 4 of the heating roll 1 has a cylindrical rubber portion 7 fixed to the outer periphery of a shaft 6.

When the leading end 10a of the paper 10 guided by the inlet chute 8 is inserted between the heating roll 1 and the pressure roll 2, the paper 10 is conveyed in the direction of the arrow by the rotation of both rolls 1 and 2 and the rolls 1 The copy image represented by the toner 11 is fixed by the heat and pressure of Nos. 2 and, and is conveyed to the discharged toner (not shown).

An image density sensor 21 for detecting the density of the toner 11 forming a copy image on the paper 10 is provided on the upstream side of the inlet chute 8. The image density sensor 21 is attached to the bottom surface of a cleaner box (not shown), and for example, a reflection type optical sensor is used.

The image density signal detected by the image density sensor 21, is input to the control means 22, this control means 22 compares the preset image density signal value with the preset value, based on these comparison values, A predetermined voltage is applied to the static elimination brush 24 by the DC power source 23. Brush part 24a of the static elimination brush 24
Has a distance l (eg,
2 mm) apart from each other, and controls the potential of the surface layer 4 without contacting the surface layer 4.

In the case of this embodiment, the photosensitive material of the photosensitive drum 13 is negatively charged, and the toner is positively charged magnetic one-component toner.
The toner after the transfer onto the sheet 10 is positively charged as shown in FIG. On the other hand, heating roll 1 and pressure roll 2
Are both negatively charged. Therefore, the electric charge of the toner 11 on the paper 10 and the electric charge of the surface layer 4 of the heating roll 1 are attracted to each other by the electrostatic attraction force, and the positively charged toner 1 is easily offset. However, according to this embodiment, the static elimination brush
Since the surface layer 4 of the heating roll 1 is positively charged by 24 and the amount of this charge is controlled by the voltage applied to the static elimination brush 24 according to the image density of the toner on the paper 10, Prevents toner offset. To control the voltage applied to the static elimination brush 24 to an appropriate predetermined value,
This is because if the toner 11 is positively charged, offset tends to occur if the absolute value of the negatively charged electric charge of the surface layer 4 is too large.

In the case of this embodiment, when the distance l between the brush portion 24a of the static elimination brush 24 and the surface layer 4 of the heating roll 21 is l = 2 mm, the second
As is apparent from the graph shown in the figure, the DC voltage applied to the static elimination brush 24 is set to + 1000V, which is the voltage value with the lowest offset generation level. In this embodiment, the DC power source 23 is provided as the power source of the DC voltage applied to the static elimination brush 24, but instead of this, the developing bias power source applied to the developing sleeve of the developing device 14 is rectified and used. It is also possible. Further, the image density sensor 21 may be provided in a part of the conveyance path of the paper 10, or may be provided along the direction orthogonal to the conveyance path so as to correspond to the maximum paper width.

As described above, according to the present invention, the charge amount of the heating roll surface layer of the fixing device is controlled according to the image density of the unfixed copy image on the paper. It is possible to reliably prevent toner offset.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of a fixing device to which the present invention is applied, FIG. 2 is a graph showing a relationship between a DC applied voltage to the charge eliminating brush and an offset generation level, and FIG. 3 is shown in FIG. FIG. 4 is a schematic configuration diagram showing an example of a copying machine to which the fixing device shown in FIG. 4 is applied, and FIG. 4 is a schematic configuration diagram showing a conventional fixing device. DESCRIPTION OF SYMBOLS 1 ... Heating roll, 2 ... Pressure roll 3, Cylindrical core, 4 ... Surface layer, 5 ... Colts lamp, 6 ... Shaft, 7 ... Cylindrical rubber part, 8 ... Inlet chute, 10 ... Paper, 11 ... Toner, 21 ... Image density sensor, 22 ... Control means, 23 ... DC power supply, 24 ... Static elimination brush.

Claims (1)

[Claims] 1. A non-fixed copy image on a sheet in a fixing device in which a heating roll and a pressure roll are arranged to face each other and a copy image on the sheet is fixed by being pressed by the heating roll and the pressure roll. While providing the image density detecting means for detecting the image density of the, the static eliminating brush for changing the charge amount of the heating roll surface layer is provided, the voltage to be applied to the static eliminating brush according to the image density detected by the image density detecting means. A heating roll type fixing device comprising control means for controlling.