JPH0455330Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Field of Application] This invention relates to a fixing device for an electrophotographic copying machine that mainly performs copying using color toner.

[Prior Art] Some conventional electrophotographic copying machines use a heated roll fixing device.

As shown in FIG. 5, the heat roll fixing device consists of a heat roll b equipped with a heat source a and a pressure roll c, and the sheet e onto which the toner image d has been transferred is pressed onto the heat roll b by the pressure roll c. The toner is melted and fixed onto the sheet e by the heat of the heating roll b, and the surface roughness of the heating roll b is usually about 0.25 μm Ra.

[Problems to be solved by the invention] In the above fixing device, the black toner image d
There is no problem when fixing the image on a sheet e, but when copying using color toner on a transparent sheet for an overhead projector (OHP), the following problem occurs.

In other words, when a color toner image d is fixed on a transparent sheet e using a conventional heating roll b with a surface roughness of about 0.25 μm Ra, the surface of the toner image d after fixing is covered with a heating roll as shown in FIG. Unevenness occurs depending on the surface roughness of b.

When this transparent sheet e is projected by an OHP, light refraction occurs due to the unevenness of the surface, and there is a problem in that the image quality is deteriorated, especially when the concave portions appear as black dots or streaks on the projected image.

Furthermore, the release agent applied to the heating roll b to prevent the toner image d from being offset to the heating roll b becomes uneven due to surface roughness, resulting in poor mold releasability. There were also problems such as the paper getting wrapped around the paper, causing paper jams, and offset.

This invention was made for the purpose of improving the above-mentioned problems.

[Means and effects for solving the problem] The toner image transferred onto the transparent sheet for overhead project through the transfer process is transferred to the transparent sheet for overhead project using a fixing device consisting of a heating roll and a pressure roll. For fixing products, by setting the surface roughness of the heating roll to 0.1μmRa or less, the surface of the fixed toner image is smoothed and black dots and streaks do not occur even when projected on OHP. .

[Example] An example of this invention will be described in detail with reference to the drawings. FIG. 3 shows the schematic configuration of an electrophotographic copying machine that employs the fixing device of this invention. Reference numeral 1 denotes a drum-shaped photoreceptor, and a charger 2 around the drum-shaped photoreceptor 2 uniformly charges the surface of the photoreceptor 1. an exposure lamp 4 that illuminates the original 3 to be copied; a light focusing optical system 5 that focuses reflected light from the original 3 onto the photoreceptor 1; and an electrostatic charge formed on the surface of the photoreceptor 1 during the exposure process. A developing device 6 for developing a latent image into a toner image, and a transparent sheet 8 for overhead project fed from a paper feeding device 7.
(Hereinafter, in this embodiment, a transparent sheet for overhead project will be simply referred to as a sheet.) A transfer device 9 transfers the above toner image onto a sheet, and a sheet 8 that is in close contact with the surface of the photoreceptor 1 during the transfer process is peeled off. A peeling corotron 10 , a static eliminator 11 that removes static electricity from untransferred toner remaining on the surface of the photoreceptor 1 after the transfer process, and a cleaning device 12 that removes the neutralized untransferred toner from the surface of the photoreceptor 1 are arranged in the direction of rotation of the photoreceptor 1 . They are installed in the above order along (arrow A).
In the copying machine configured as described above, the surface of the photoreceptor 1 is first uniformly charged by the charger 2 as the photoreceptor 1 rotates, and then an original image is formed on the surface of the photoreceptor 1 in the exposure process and becomes static. A latent image is formed. This electrostatic latent image is developed into a toner image by a developing device 6, and then transferred by a transfer device 9 onto a sheet 8 fed from a paper feeding device 7 in a transfer step.

The sheet 8 on which the toner image has been transferred is peeled off from the photoreceptor 1 by a peeling corotron 10, and then conveyed to a fixing device 15, which will be described later.
The untransferred toner remaining on the surface of the photoreceptor 1 is removed from the surface of the photoreceptor 1 by the cleaning blade 12a of the cleaning device 12 after being neutralized by the static eliminator 11.

On the other hand, as shown in FIGS. 1 and 2, a fixing device 15 that fixes the sheet 8 to which the toner image has been transferred is
A heating roll 17 equipped with a heat source 16, and a pressure roll 18 that presses the sheet 8 onto the heating roll 17.
It becomes more.

The heating roll 17 is made of a metal core 17a made of aluminum or the like, and the outer periphery thereof is made of tetrafluoride resin (registered trademark Teflon).
The metal core 17a has a thickness of, for example, 3 mm, and the thickness of the mold release layer 17b has a thickness of, for example, 25 μm.

The surface roughness of the release layer 17b is 0.1 μm.
Formed below Ra. The above surface roughness can be easily obtained by conventional techniques by polishing the surface of the release layer 17b.

The pressure roll 18 that presses the sheet 8 to be fixed onto the heating roll 17 is made of a metal core 18a made of iron or the like that has a heat source 19 therein, and the outer periphery of the metal core 18a is covered with an elastic layer 18b made of rubber. The thickness is, for example, 3 mm, and the thickness of the elastic layer 18b is, for example, 8 mm.
mm.

Heating roll 17 of fixing device 15 configured as above
The surface temperature of the heating roll 17 and the pressure roll 18 are heated to, for example, 150°C, and the surface temperature of the pressure roll 18 is heated to, for example, 130°C to fix the toner image transferred onto the sheet 8. The sheet 8 that has passed through the gap and has been fixed is transferred to the paper output tray 20.
is discharged to. Furthermore, the surface of the toner image 21 fixed by the heating roll 17, which has an extremely fine surface roughness of 0.1 μm Ra, becomes a smooth surface with no irregularities as shown in FIG. There are also no black spots or streaks on the projected image.

[Effects of the invention] As detailed above, this invention reduces the surface roughness of the heating roll that fixes the toner image transferred onto the transparent sheet for overhead projects to 0.1 μm.
Since it is less than Ra, the surface of the fixed toner image will be a smooth surface with no irregularities, even if it is copied onto a transparent sheet for overhead project using color toner and projected using OHP. A clear image without black dots or streaks can be obtained on the projected image.

[Brief explanation of the drawing]

The drawings show one embodiment of this invention, and FIG. 1 is a cross-sectional view of the fixing device, FIG. 2 is a cross-sectional view taken along the line of FIG. 1, FIG. 3 is a schematic configuration diagram of the copying machine, and FIG. The action explanatory diagrams, FIGS. 5 and 6, are conventional explanatory diagrams. 8 is a sheet, 15 is a fixing device, 17 is a heating roll, and 18 is a pressure roll.

Claims (1)

[Scope of utility model registration request] The toner image transferred onto the overhead projector transparent sheet 8 in the transfer process is transferred to a fixing device 15 consisting of a heating roll 17 and a pressure roll 18.
A fixing device for an electrophotographic copying machine that fixes images on a transparent sheet 8 for an overhead projector, characterized in that the heating roll 17 has a surface roughness of 0.1 μmRa or less.