JPS62116980A - Fixing device - Google Patents

Abstract

PURPOSE:To improve fixing performance by providing a parting layer which is made low in resistance as the surface layer of either of a couple of rollers constituting a heat roller fixing device. CONSTITUTION:The upper roller 1 is constituted by forming an ethylene tetrafluoride resin layer with which a low-resistance material such as carbon black is mixed on a mandrel made of SUS, Al, etc. This upper heater 1 contains a halogen heater 3, and both its end parts are supported rotatably on side plates 10 and 10' of the fixing device by ball bearings 9 and 9' through heat- resisting insulating resin members 8 and 8', so that the roller 1 is placed in an ungrounded state. The inner side (left in figure) of the roller is drawn from the side plate much more than the front side and a gear 11 made of heat resisting insulating resin is fitted loosely in the mandrel 1 of the roller. The gear 11 is coupled with a driving gear 12 to rotate the roller 1 with the driving force of a driving means. The lower roller 2, on the other hand, is held by bearings 13 and 13' and pressed against the upper roller 1 by a pressing means (not shown in figure) with proper pressure and rotates following up the upper roller 1.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a row prefixing device that fixes a toner image on a transfer material by a pair of rollers, at least one of which has a heat source.

(Prior Art) Conventionally, various types of fixing devices have been devised and implemented, but currently, from the viewpoint of thermal efficiency, the fixing device consists of a pair of rollers, at least one of which has a heat source. A so-called heat roller fixing device is the mainstream. An upper roller 1 having a heat source (in this case, a halogen lamp) 3 and a lower roller 2 having an elastic layer, the basic form of which is shown in FIG. It is rotationally driven in the direction of the arrow in the figure by the illustrated driving means. Upper roller 1 is thermistor 4
The surface temperature is detected and maintained at an appropriate surface temperature. As the transfer material passes between the pair of rollers, the heat-fusible toner on the transfer material is heated and pressurized and fixed. In this way, the toner and the upper roller with the heat source are in direct contact, so the heat transfer efficiency is extremely superior compared to other methods, but on the other hand, there are some disadvantages, and countermeasures are always taken to prevent them. The most serious problem is the phenomenon of toner transfer to the upper roller l, which is called an offset phenomenon. The offset phenomenon is usually divided into low-temperature offset that occurs due to poor fixing and high-temperature offset that occurs due to the rise in temperature of the upper roller, but the mechanism is not necessarily clear. In addition to methods for mechanically removing toner, such as cleaning with a heat-resistant pad 5 as shown in the figure and applying a release agent, countermeasures have been devised to reduce offset toner itself. In particular, lowering the surface potential of the upper roller is effective from the viewpoint that the upper roller is charged to several KV due to frictional charging between the transfer material and the lower roller, so the charged toner on the transfer material is electrostatically attracted to the upper roller. be done. To do this, we use static eliminating brushes on the rollers, apply low-resistance mold release agents, or lower the resistance of the roller surface.
In addition, measures have been taken to ground the surface layer through the core metal.

However, since the volume resistance of the material that grounds the surface potential of the roller is low, if one end of the transfer material is caught between the pair of fixing rollers while the transfer material is in the transfer area, the transfer charger will charge the surface potential of the roller. (2) Transfer defects do not occur in low humidity environments, but when the toner image approaches the first roller, the toner becomes weaker. Since the spatial electric field formed by the charge and the upper roller increases significantly and leaks, toner scatters or is abnormally drawn toward the upper roller, causing a so-called front-pulling phenomenon.

OBJECTS OF THE INVENTION It is an object of the present invention to provide a fixing device that eliminates the above-mentioned conventional drawbacks and reduces offset toner without causing disturbances in transfer and toner images.

(Summary of the Invention) The present invention provides a fixing device that fixes a toner image on a transfer material by a pair of rollers having a heat source on at least one of the rollers. It is characterized by having a release layer with low resistance, and its surface layer being in a non-grounded state.

(Example) Examples of the present invention will be described below. FIG. 1 is a sectional view showing an example of the fixing device of the present invention. The upper roller 1 has a polytetrafluoroethylene resin layer mixed with a low-resistance substance such as carbon black on a core metal (Sus, AM, etc.). The upper roller 1 includes a halogen heater 3, and both ends thereof are connected to the side plate 10 of the fixing device by means of pole bearings 9, 9' via #thermal insulating resin members 8, 8'.
, 10' are rotatably supported. The back side of the roller (the left side in FIG. 1) extends significantly from the side plate compared to the front side, and a gear 11 made of heat-resistant insulating resin is fitted into the core of the roller.

The gear 11 is connected to a drive gear 12 of a drive means (not shown), and receives a driving force to rotate the roller 1.

On the other hand, the lower roller 2 is also rotatably held by slidable bearings 13 and 13' such as bearings, and is pressed against the upper roller 1 with appropriate pressure by a pressure means (not shown). Rotates according to 1. The effect of preventing offset in the fixing device configured in this manner will be described below.

Table 1 shows the degree of offset between a conventional polytetrafluoroethylene (PTFE) resin roller and the roller according to the present invention. Compared to the one in which Becarbon [Co., Ltd.] black was mixed in to create a non-grounded state, the amount of offset was enough to clean not only in normal use mode but also during continuous paper feeding.
There was no staining of the image due to poor toner cleaning. In addition, in this experiment, negatively charged and
A conventional pure tetrafluoroethylene resin roller, which uses an OPC drum with transfer characteristics and a toner with positive charging characteristics, is shown in Table 2.
Although a roller that is mixed with black and made ungrounded tends to have a lower potential when paper is passing than when it is not passing paper.Comparing the two, a pure tetrafluoroethylene resin roller has a negative charge of up to several KV. On the other hand, a roller mixed with carbon black and made into a non-contact state exhibits -500 at most.
The minimum value is about -200v.

Table 1 Table 2 From these results, when using a fluororesin-based roller that is inherently prone to negative frictional charging, the roller surface is strongly negatively charged, while the transfer material that is rubbed against the roller The toner is
On the other hand, since it is positively charged, the electrostatic adhesion of the toner to the roller becomes strong, and even if it is completely melted by heat, it is thought to peel off from the transfer material and transfer to the roller as offset toner. Therefore, it is natural that this tendency becomes stronger when a toner with positive charging characteristics is used. However, when a low-resistance substance such as carbon black is mixed, this frictional charging property is reduced, or the capacitance becomes smaller, resulting in a lower potential, and the charging of the transfer material and toner. Since the amount is small, the electrostatic adsorption force that acts between the toner and the roller is weakened, and the ratio of toners being bonded together and the toner and transfer material being bonded together by heat due to thermal melting is increased, which is thought to reduce the amount of offset. . This is supported by the fact that the amount of charge on the ejected transfer material is significantly smaller with a roller mixed with carbon than with a pure polytetrafluoroethylene resin roller, and the amount of offset is also smaller. Therefore, it can be said that the fixing performance is significantly improved with the roller containing carbon black.

Furthermore, unlike conventional methods, the core metal etc. are not grounded, so
The surface layer of the roller is not grounded, and (1) even under high humidity, the flow of corona current into the roller by the transfer charger is small;
Transfer charge is retained on the transfer material, so no transfer defects occur, and (2) the roller is stably maintained at a low potential even under low humidity, so there is no risk of toner image scattering due to leakage with toner charge, etc. No pulling phenomenon occurs.

Therefore, while reducing the amount of offset and improving fixing performance, uniform and high quality images were obtained under each environment.

Further, in the above embodiment, an example was described in which a mold release layer was provided directly on the core metal, but similar effects can be obtained with rollers having an elastic layer, which have been increasingly adopted in recent years. FIG. 2 is a cross-sectional view of the upper roller l', which has a heat-resistant elastic layer 14 made of silicone, fluororubber, etc. on the core bar 6, and further has the low-resistance mold release layer 7 as a surface layer thereon. has been established. In this case, if an elastic body having a volume resistance of 1012 Ωφcm or more is normally used, the release layer 7 will be in a non-grounded state even if it is grounded to the core metal, so the gear fitted to the core metal as in the above example will be It does not matter if it is an inexpensive metal body. It will be easily understood that the same effects as in the above embodiments were obtained in this example as well.

Further, in the above embodiment, the upper roller has been described, but the offset reduction effect can also be obtained when the lower roller is subjected to the above-described processing. Usually, the lower roller uses a heat-resistant elastic material such as silicon to form the nip width, but these elastic materials originally have strong negative charging characteristics of 1 (some even reach several KV). Therefore, especially when negatively charged toner is used, the electrostatic attraction between the upper roller and the upper roller is weak, but the electrostatic repulsion from the lower roller is strong, so the toner is pushed toward the upper roller. Therefore, the toner tends to become an offset toner. On the other hand, by providing a low-resistance release layer on the elastic layer as the lower roller, similar to the one shown in FIG. 2, the surface potential of the lower roller is lowered, reducing offset toner as in the previous embodiment. In addition, it was also found that since it has a release layer, staining of the lower roller due to toner is reduced.

In the above example, carbon black was used as the low-resistance material, but other materials such as titanium oxide, metal oxides such as nickel, carbon fiber, etc. may also be used. Also, by mixing a low resistance substance, the volume resistivity of the roller surface layer is 101
It is desirable that the resistance is 2Ω・0m or less.

(Effects of the Invention) As explained above, in a heat roller fixing device consisting of a pair of rollers, by providing a release layer with low resistance as the surface layer of at least one of the rollers, electrostatic offset can be prevented. In addition to improving the fixing performance by reducing the humidity, by making this surface layer non-contacting, it was possible to obtain uniform, high-quality images regardless of whether the humidity is high or low.

[Brief explanation of drawings]

FIG. 1 is a schematic sectional view of a fixing device showing an embodiment of the present invention;
FIG. 2 is a sectional view showing another example of the configuration of the roller, and FIG. 3 is a side sectional view of a general fixing device. 1, l' --- Upper roller 2 --- Lower roller 3 --- One heat source 6 --- One core metal

Claims (4)

[Claims] (1) In a fixing device that fixes a toner image on a transfer material by a pair of rollers, at least one of which has a heat source, at least one of the pair of rollers has a relatively low-resistance release layer as a surface layer of the roller. What is claimed is: 1. A fixing device having a surface layer that is not in contact with the ground. (2) The fixing device according to claim 1, wherein the surface layer of the roller is formed of a fluororesin containing a low resistance substance. (3) The fixing device according to claim 1 or 2, wherein the roller has an insulating elastic layer below the surface layer of the roller. (4) The volume resistivity of the surface layer of the roller is 10^1^2
Claim 1 characterized in that it is Ω・cm or less
The fixing device according to items 1 to 3.