JPS61255371A - Fixing device for heat roller - Google Patents

Abstract

PURPOSE:To charge electrostatically the coating layer of a heat-roller fixing device to positive polarity which is the same as that of a positively charged toner so as to prevent electrostatic offsets stably and inexpensively, by using tetrafluoroethylene containing chromic acid for forming the coating layer. CONSTITUTION:A heat roller 1 contains a heater 3 at the inside of its body and is provided with a coating layer 5 on its core 4. A supporting body 8 holding positively charged toner 6 is passed through the space between the heat roller 1 and a press roller 2 and a toner image 7 is thermally fixed on the supporting body 8. Since the coating layer 5 of the heat roller 1 is usually provided on a fluorocarbon resin, the coating layer 5 is negatively charged as the fixing device is actually used. However, since the coating layer 5 of this inventions is formed of tetrafluoroethylene containing chromic acid as an additive, this coating layer 5 is charged to positive polarity which is the same as that of the toner 6 and electrostatic offsets can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD The present invention relates to a hot roller fixing device that can prevent electrostatic offset.

PRIOR ART In general, in copiers, facsimile machines, printers, etc., the heat roller of a heat roller fixing device that develops a toner image on a support using an electrostatic process and heats and fixes the image has a surface made of silicone rubber or fluorine rubber. It is usually coated with a resin such as Teflon (PFA, PTFE), etc. The present invention relates to an improvement in a heated roller fixing device that includes a heated roller coated with a fluororesin.

In a fixing device equipped with a heat roll coated with such a fluororesin, the fluororesin coating layer is negatively charged as the device is operated, while the toner is positively charged.
This method had the problem of electrostatic offset. Although this offset can be reduced to some extent by applying an anti-offset agent, it cannot be completely prevented.

In the past, various proposals have been made to prevent this off-cella trap.For example, q# 1985-55374 discloses a method of preventing a charger from being attached to the fixing roller, and 1971 I$-96970 discloses a method of preventing a charger from being attached to a fixing roller. It has been proposed to apply a full potential of the same polarity as the toner to the fixing roller, but these methods have problems in terms of cost and safety. Furthermore, Japanese Patent Application Laid-open No. 57-1150869 proposes mixing carbon into Teflon as a fluororesin, but the effect of carbon mixing in preventing offset was not sufficiently satisfactory.

OBJECTS It is an object of the present invention to provide a heat roller fixing device which eliminates the above-mentioned problem of offset occurrence in a heat roller whose coating layer is a fluororesin having excellent release properties and heat resistance.

Structure The present invention has a heating roller coated with a fluororesin layer and an elastic pressure roller that is in pressure contact with the heating roller, and a support holding a positively charged toner 1 is passed between these rollers, A heat roller fixing device for thermally fixing a toner image on the entire support body is characterized in that the fluororesin which is the coating layer of the heat roller is tetrafluoroethylene containing chromium #lt- as an additive.

As a result of various studies on the above-mentioned electrostatic offset phenomenon in a heat roller fixing device, the present inventor confirmed that this electrostatic offset phenomenon is caused by electrostatic adsorption of toner, and also It has been found that by using tetrafluoroethylene with chromic acid as an additive as the fluororesin, the hot roll is positively charged with the same polarity as the toner, and electrostatic offset is prevented. The present invention is based on these findings.

In the present invention, the amount of chromic acid added to tetrafluoroethylene may be within the range generally included in what is known as tetrafluoroethylene used as a chromic acid t-S additive. More specifically, Depon's Tpgssx- which uses chromic acid as an additive.
224 (trade name) can be used very preferably.

The attached drawing is a schematic explanatory diagram of a heat roller fixing device of the present invention, and in the figure, 1 is a heat roller and 2 is a pressure roller. The heat roller 1 includes a heater 3 therein, and a coating layer 5 is provided on a core metal 4. Support body 8f holding positively charged toner 6 between heat roller 1 and pressure roller 2:
The toner image 7 is thermally fixed onto the support 8 by passing the toner image 7 therethrough. Since the coating layer 5 of this heat roller l is normally provided with a fluororesin, the coating layer 5 becomes negatively charged with the actual operation of the device, but the coating layer 5 according to the present invention is made of chromium #l.
Since the coating layer 5 is made of tetrafluoroethylene as an additive, the coating layer 5 is positively charged with the same polarity as the toner 6, and electrostatic offset can be prevented. In the present invention, it has not been theoretically elucidated that the coating layer 6 is positively charged by using tetrafluoroethylene with chromic acid as an additive as the coating layer. There is no doubt that this contributes to positively charging the coating layer 6.

In the above description, the coating layer 5 of the heat roller 1 is made of chromic acid-added tetrafluoroethylene, but this coating layer may also be provided on the pressure roller 2. That is, the pressure roller 2 usually has HT on its surface.
Although VSI rubber or the like is coated, a chromic acid-added tetrafluoroethylene layer of 30 μm or less may be further provided on this TVSl rubber layer.

Examples are shown below.

Conventional Example A thermal roller was prepared by applying three pieces of PFA Teflon manufactured by Fluorochemical Co., Ltd. to a thickness of 20 μm after polishing on an AA core metal. HTV81 rubber was used as the pressure roller. This device is identical to the Ricoh copier FT-5050. When this device was tested by installing it in a copying machine using all positively charged toner, the PFA Teflon gold-coated heat roller was charged to -150V, and offset occurred. Also, attach a charger to this heat rollerff, +x
When I set it to sov, the offset completely disappeared. This also confirms that the cause of the offset is electrostatic adsorption.

Embodiment The device is similar to the conventional example, but the layer t-P of the heat roller is
When FA Teflon was replaced with DuPont's TFK851-224 with chromic acid as an additive, the heat roller became +150V and the offset completely disappeared. Further, although Daikin TFE ES-5183GB t-, which does not contain chromic acid as an additive, was used as a coating layer, there was no offset prevention effect.

Effects According to the present invention as described above, by using tetrafluoroethylene containing chromic acid as the coating layer of the heat roller fixing device, the coating 1 is charged to the same polarity as the positively charged toner, and the static electricity is reduced. Electrical offset can be prevented safely and at low cost.

[Brief explanation of drawings]

The drawing is a schematic explanatory diagram of main parts of a heat roller fixing device according to the present invention.

Claims (1)

[Claims] 1. It has a heating roller coated with a fluororesin layer and an elastic pressure roller that comes into pressure contact with the heating roller, and a support holding positively charged toner is passed between these rollers,
A heat roller fixing device for thermally fixing a toner image onto a support, wherein a fluororesin forming a coating layer of the heat roller is tetrafluoroethylene containing chromic acid as an additive.