JPH0475514B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to means for preventing toner offset or paper wrapping by removing static electricity in a fixing device such as an electrophotographic device or an electrostatic recording device.

Conventionally, it has been known to eliminate electricity from the fixing roller in order to prevent copy paper from wrapping. As a method of eliminating static electricity, a conductive substance such as carbon or metal powder is mixed into the necessary rollers to lower the resistance of the rollers. A charger is placed near the roller to remove static electricity from the roller using corona. Bring the static elimination brush into contact with the roller. Further, an AC bias is applied to. This is already known.

Further, as a method of preventing toner offset to the roller, a bias having the same polarity as the toner is applied to the roller on the side that comes into contact with the toner image surface of the copy paper. It has been proposed to select a material for the roller on the side that comes into contact with the toner image surface of the copy paper from a triboelectrically charged material that is charged to the same polarity as the toner.

However, this greatly reduces the mechanical properties and mold release properties of the roller, making it impractical. In this method, the device is large and complicated, spark discharge is likely to occur near the fixing device due to the high voltage applied, and it cannot be said to be an excellent method in terms of reliability. When the static elimination brush becomes dirty, the static elimination efficiency decreases rapidly, changes over time, and is not durable. In addition to this, spark discharge is extremely likely to occur due to dirt. It is difficult to apply the bias; for example, applying it to the metal core has little effect, and applying it from the surface with a static eliminating brush or the like tends to cause spark discharge, resulting in low reliability. Similarly, there is currently no material that is effective while maintaining various physical properties.

The present invention overcomes the above-mentioned drawbacks, has a simple configuration, and
It is an object of the present invention to provide a fixing device that prevents a recording material from being wrapped around a fixing rotary member, minimizes offset toner, and has stable fixing performance over a long period of time.

The present invention provides a fixing device that fixes a recording material supporting an unfixed image by sandwiching and conveying it between a rotating body, and a separating member that comes into contact with the surface of the rotating body and separates the recording material from the rotating body, and a separating member that is integrated with the separating member. established in
A fixing device characterized in that it has a conductive member that is provided in a non-contact manner with respect to a surface of a rotating body and is grounded.

The present invention will be explained below with reference to the drawings. FIG. 1 is a side view of an embodiment of the present invention, and FIG. 2 is a perspective view of a conductive needle member and a separating claw. A heat fixing device is shown. Reference numeral 1 denotes one heating roller of a rotary body having a heating heater 3 such as a halogen heater inside, which rotates in the direction of the arrow in response to driving force from a drive motor (not shown). 2 is a heater 3a for low heating
The other pressure roller of the rotating body containing a built-in roller presses against the heating roller 1 and rotates as a result.

This heating roller 1 has a heat-resistant release resin layer such as tetrafluoroethylene resin provided on the outer peripheral surface of a hollow roller core made of metal such as aluminum, stainless steel, or copper to a thickness of 20 to 80 μm. The pressure roller 2 is rotatably supported by a bearing. This roller 2 is pressed against the heating roller 1 by a known pressure means at least during fixing, and has a relatively thick elastic material such as silicone rubber, fluorosilicone rubber, or fluorosilicone rubber on the outer peripheral surface of a metal roller core. This configuration has the purpose of securing a pressure contact area (nip portion) with the heating roller. A temperature sensing element 4 such as a thermistor or thermocouple is provided in contact with the outer circumferential surface of the heating roller 1, and the output of the heater 3 is controlled by the detection signal of the sensor, thereby controlling the temperature of the outer circumferential surface of the heating roller 1. The toner image is maintained at the melting temperature. Reference numeral 5 denotes a separating claw for reliably separating the copy paper from the heating roller 1 after fixing. Reference numeral 6 denotes a cleaning device for removing foreign matter such as offset toner and paper powder adhering to the heating roller surface from the roller surface, which uses a cleaning web 6a made of heat-resistant nonwoven fabric. The cleaning web 6a is brought into contact with the heating roller by an elastic pressing roller 6c, and moved from the supply roller 6b by a take-up roller 6d so as to change its contact position little by little, so that a new surface always comes into contact with the heating roller. Reference numeral 7 denotes a guide plate that guides a recording material such as a copy paper P carrying a toner image T toward the heating roller side. 8
is a conductive needle-like member, that is, a conductive member that prevents the pressure roller 2 from being charged in order to prevent offset and prevent the copy paper P from being wrapped. The conductive needle member 8 is spaced from the pressure roller 2. A separation claw 16 whose tip is in contact with the pressure roller 2 is provided on the conductive member. The separation claw 16 is a separation member that mechanically prevents the copy paper P from being wrapped around the pressure roller 2.

The conductive needle member 8 is provided on a support base 9, which is rotatably supported around a pivot point 11 and biased in the direction of arrow A by a spring (not shown). The separating claw 16 functions to always maintain the distance between the conductive needle member 8 and the pressure roller 2 at a constant value d. The conductive needle member 8 is made of a thin metal plate with a sharp tip or a conductive substance such as a large number of metal fibers or carbon fibers each having a cotton diameter of about 100 μm or less, and is grounded.

The effects of the embodiment of the present invention and the conventional example will be shown below through experiments.

(1) Experimental conditions Heating roller...3μm on a 7mm thick aluminum core
Thick PFA coated roller.

Pressure roller: 5mm thick HTV silicone rubber coating on stainless steel hollow core.

Pressure pressure…Total pressure 60Kg Copy…A3 size 23 sheets per minute (roller speed 270mm/sec) Original…
Image area: 28% (toner consumption is relatively high) Environment: Humidity: 60% Temperature: 23°C Measurement of amount of static electricity removed: Coulomb meter (product name - 616 electrometer (2)) The results are shown in Figure 3. Figure 3 shows the durability. FIG. 3 is a diagram in which the number of copies is plotted on the horizontal axis and the amount of static electricity removed is plotted in μc on the vertical axis.

Curve a shows the case where the tip of the conductive needle electrode is brought into contact with the pressure roller 2 in the conventional manner. When the number of sheets is around 3,000, the amount of charge removal begins to decrease rapidly, and at 6,000 sheets, the toner offset increases and the cleaning web 6a
At the feed speed of 0.5 mm/min, the cleaning could not be completed, and the toner accumulated on the web 6a and fell off. Furthermore, the toner that passed through the web 6a adhered to the copy paper, significantly deteriorating the copy quality.

Curve b indicates that the tip of the conductive needle-like member is separated from the roller by 3
This is the case when they are placed at a distance of mm, and the static elimination effect is small from the beginning, and when the web 6a is fed at a speed of 0.5 mm/min, toner adheres to the copy paper due to poor cleaning, resulting in a significant drop in copy quality.
However, electrostatic winding of the paper around the pressure roller 2 could be prevented.

Curve c shows the conductive needle member 8 disposed near the nip portion on the paper discharge side with distance d=0.4 mm.

Although 100,000 copies were made, the amount of toner offset on the heating roller 1 was small, cleaning was sufficient even with the web 6a feeding speed of 0.5 mm/min, and the paper did not get wrapped around the pressure roller 2. The results were obtained.

Curve d is a dotted line representing static elimination of -2.14 .mu.c, which indicates the limit line of the safe area for toner offset. (The amount of static electricity removed from -3800v to -500v) Curve e represents static electricity removal of -1.2μc as a dotted line.
This shows the limit line of the safe area against wrapping around the pressure roller 2. (-3800v to -2000v
Note that it is also effective to prevent offset when the conductive needle member 8 is disposed within a distance d = 0.6 mm from the surface of the pressure roller 2. A conductive needle-like member 8 is placed near the paper ejection side of the nip.
The static elimination efficiency was better when the

As mentioned above, the conventional static elimination method in which the conductive needle member 8 is brought into contact with the pressure roller as shown in Figure 3a has a good initial static elimination effect, but as the number of copies increases, If the tip of the conductive needle-like member becomes contaminated with toner, paper dust, and other foreign matter, the static elimination ability decreases rapidly, and copying cannot continue unless it is replaced once every 5,000 sheets. According to the present invention, by disposing a conductive needle-like member in the vicinity of the paper ejection side of the nip portion of the pressure roller in a non-contact manner, static electricity is removed and there is no change over time due to long-term use, and the pressure It always follows changes in the outer diameter of the roller due to long-term use of the roller, and even after long-term use, good offset prevention (including paper wrapping prevention) can be achieved by eliminating static electricity in the same way as in the initial stage. Efficient static elimination can be achieved even with the conductive needle member 8 if they are placed close to each other, but if only the tip of the static eliminating member close to the roller surface is made conductive, electric field concentration will also occur at the tip of the static eliminating member, further improving static elimination efficiency. be done.

Further, the present invention is effective not only for a pressure roller but also for a heating roller, and is also effective for a pressure fixing device using an insulating roller.

[Brief explanation of drawings]

FIG. 1 is a side view showing an embodiment of the present invention, FIG. 2 is a perspective view of essential parts of the embodiment of the present invention, and FIG. 3 is a diagram showing the relationship between the number of copies and the amount of charge removal. 1... Heating roller, 2... Pressure roller, 8...
Conductive needle-like member, 16...separation claw.

Claims (1)

[Scope of Claims] 1. A fixing device that fixes a recording material supporting an unfixed image by conveying it between rotating bodies, comprising: a separating member that comes into contact with the surface of the rotating body and separates the recording material from the rotating body; A fixing device comprising: a conductive member that is provided integrally with the separation member, is provided in a non-contact manner with respect to the surface of the rotating body, and is grounded.