JPH0153790B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fixing device for a copying machine, and more particularly to an improvement in a fixing device in which a heat insulating member is provided between both ends of a heating roller and a bearing of the roller.

In a fixing device of a copying machine, an untransferred image is passed between a heating roller and a pressure roller to be fixed. At this time, when the heating roller is heated, heat escapes from the bearings at both ends of the roller, resulting in development in which the temperature distribution along the axial direction on the surface of the heating roller becomes non-uniform. Therefore, a bush-shaped heat insulating member made of synthetic resin or the like having low thermal conductivity and heat resistance is provided between both ends of the heating roller and the bearing of the roller, and the heating roller is attached. It is thermally isolated from the housing to prevent the above phenomenon.

However, interposing such a heat insulating member between the heating roller shaft and the bearing results in electrical insulation between the heating roller and the housing of the fixing device. Therefore, when the heating roller is driven, the static charge generated by the contact between the heating roller and the pressure roller cannot escape from the heating roller, and a discharge phenomenon occurs between the heating roller and the housing. Such a discharge phenomenon becomes a noise source for the control circuit of the copying machine, and may cause malfunction.

SUMMARY OF THE INVENTION An object of the present invention is to provide a new fixing device that eliminates the above-mentioned problems in conventional fixing devices for copying machines. Therefore, the object of the present invention is to use a resin and a material with low electrical resistance contained in the resin as the material of the heat insulating member disposed between the heating roller and the bearing of the roller. This is achieved by configuring the heat insulating member to thermally isolate the heating roller and the housing of the fixing device and to electrically connect the roll and the housing. In the fixing device of the present invention in which such a heat insulating member is provided, the heating roller and the housing are maintained in an electrical connection state, so that the heating roller and the pressure roller may come into contact with each other. Since static charges are effectively dissipated through the heat insulating member, the troubles encountered in the conventional devices described above are prevented.

The type and amount of the resin and the material with low electrical resistance used in the heat insulating member that functions as a grounding device for the heating roller and the housing are not particularly limited. However, the heat insulating member should function as a heat insulating material that sufficiently blocks the heat of the heating roller, and should also be configured to have such conductivity as to effectively reduce the charging potential of the heating roller. Therefore, in general, a heat-resistant synthetic resin with low thermal conductivity is used as a base material, and a material with low electrical resistance such as carbon or metal is dispersed in the resin in the form of fibers or particles. A heat insulating member is obtained. An example of a preferable heat insulating member is a PPS resin containing approximately 30% carbon fiber.

The present invention will be further described below with reference to embodiments of the present invention shown in the drawings.

The accompanying drawings show a typical example of a copying machine to which the present invention is applied. The copy paper onto which the toner image has been transferred is passed between a heating roller 1 and a pressure roller 2 to be fixed. The heating roller 1 is generally heated by a heater 3 installed inside. The heating roller 1 is a cylinder made of a material with excellent thermal conductivity such as aluminum, and its surface is coated with a releasable material such as Teflon or silicone rubber to prevent offset. On the other hand, the pressure roller 2 is made by coating a core metal such as iron or aluminum with silicone rubber or the like.

A bushing 6 is provided between both ends of the heating roller 1 and the roller bearing 4, which acts as a heat insulating member. As mentioned above, in the conventional fixing device, this bush 6 is made only of synthetic resin, and it blocks the heat of the heating roller and causes the heat of the roller to escape from the bearing part, thereby preventing uneven temperature of the heating roller. It was merely preventing this.

When the drive gear 5 is driven and the heating roller 1 and pressure roller 2 rotate while contacting each other, static electricity is generated on the surfaces of both rollers. For example, if the surface of the heating roller is coated with Teflon coating of about 50 μm and the surface of the pressure roller is made of silicone rubber with a thickness of about 5 mm, a potential of about 500 V is applied to the surface of the heating roller under normal copying conditions. It is recognized that static electricity is generated. However, when the conventional bushing 6 made of a non-conductive synthetic resin is used, there is no current flowing between the heating roller 1 and the housing 7, so as described above, The static electricity generated is maintained at the same potential in the core of the heating roller (made of iron or aluminum) due to electrostatic induction. If the core of the heating roller is charged to a high potential and the spatial distance from the housing is approximately several mm (this varies depending on the structure of the copying machine, but generally this spatial distance cannot be increased), the distance between the two may be Discharge development occurs, and the electrical noise at this time has an adverse effect on each control circuit of the copying machine main body, causing malfunctions.

However, according to the present invention, when a bush 6 made of resin and a low electrical resistance material contained in the resin is provided between both ends of the heating roller and the bearing 4, the charged potential of the heating roller is drastically reduced. As a result, the above-mentioned discharge phenomenon is eliminated, and malfunctions associated with it are also avoided. For example, when bush 6 is made of PPS resin containing 30% carbon fiber, the charging potential of the heating roller is
It was observed that the voltage decreased to 50V or less.

As mentioned above, if the fixing device of the present invention is used,
Since the bushing used as a heat insulating member for the heating roller also functions as a grounding device, the problem of copying machine malfunctions is solved. Further, since the carbon fibers and the like contained in the heat insulating member also strengthen the member, an additional effect of increasing the strength of the bearing portion can be obtained.

[Brief explanation of drawings]

The accompanying drawing is a side sectional view schematically showing one embodiment of the fixing device of the present invention. 1...Heating roller, 2...Pressure roller, 4...Bearing,
6...Insulating member (button), 7...Housing.

Claims (1)

[Claims] 1. In a fixing device for a copying machine, in which a heat insulating member is disposed between both ends of a heating roller and a bearing of the roller, and the heat roller is attached to a housing via the bearing, the heat insulating member is made of resin. and a material with low electrical resistance contained in the resin, and the fixing device is configured to electrically connect the heating roller and the housing.