JP3053459B2 - Fixing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device for fixing an unfixed image to a latent image carrier in an electrophotographic or electrostatic recording type printer.

[0002]

2. Description of the Related Art FIG. 6 shows a heat roller fixing device used in a conventional image forming apparatus.

[0003] An apparatus shown in FIG. 6 is a fixing roller 1 in which a resin layer having heat resistance and releasability such as PFA or PTFE is provided on a core metal such as aluminum or iron, and a silicone rubber is also provided on the core metal. Roller 2 with an elastic layer of rubber or fluoro rubber
Are pressed and heated and pressed through a recording material P on which a toner image Q is placed between the pair of rollers to be fixed.

[0004] The fixing roller 1 is heated by an internal heater 3 and the surface temperature is detected by a temperature detecting element 4.
ON / OFF of energization to heater 3 based on this detection output
By doing so, the predetermined temperature is maintained.

The recording material P is guided between the pair of rollers by the entrance guide 6, is separated from the fixing roller 1 by the separation claw 5, and is sent out of the apparatus by the paper ejection guide 7.

When fixing is performed by pinching and conveying the recording material in this manner, the frictional charging between the roller and the recording material causes charges to accumulate on the surface of the fixing roller 1 to attract toner, or to prevent the pressure roller 2 from adhering. There has been a problem that charges accumulate on the surface and repel the toner to cause an electrostatic offset on the fixing roller 1. Therefore, supplying a bias voltage to the fixing roller 1 from a power supply has been proposed in Japanese Patent Application Laid-Open No. 55-96970.

In this method, the toner Q is repelled from the fixing roller 1 by applying a voltage having the same polarity as that of the toner Q to the core of the fixing roller 1.

[0008]

However, in the above-mentioned prior art, since the coating layer on the surface of the fixing roller is not a completely uniform insulator, a current flows through the recording material, causing the following problem.

[0009] Since a charge of the same polarity as that of the toner is injected into the recording material, the charge is canceled with the transfer current, and a transfer failure occurs.

In order to inject charges of the same polarity as the toner into the recording material, the toner is repelled to generate an offset.

[0011] Since an excessive current flows through the coating layer, the coating layer is broken and the releasability is impaired. As a result, the toner adheres and peels off the image or stains the white background.

As a countermeasure against the above problem, it is sufficient to improve the insulating property of the coating layer on the surface of the fixing roller, but it is difficult to form a complete insulating coating layer even by using a PFA tube having a high resin uniformity. It is. If the thickness of the PFA tube is increased, the insulation will be increased. In addition, there is a problem that heat conduction from the core metal is delayed during paper passing, the surface temperature of the fixing roller decreases, and the fixability deteriorates.

Therefore, the thickness of the PFA tube is appropriately 25 μm to 60 μm, but it is not possible to form a complete insulating coating with this thickness.

An object of the present invention is to provide a fixing device which solves the above-mentioned problems, prevents the charge from flowing into the recording material without lowering the thermal conductivity of the surface layer of the fixing roller, and does not cause an image defect. It is an object.

[0015]

SUMMARY OF THE INVENTION According to the present invention, there is provided a roller having an insulating layer on a metal core , and a core for the roller.
Power supply for applying voltage to gold, the above roller is not fixed
The unfixed image is fixed on the recording material by contacting the recording material carrying the image.
In the fixing device, the power supply and the core of the roller are
Connected through a single resistance element, and connected to the power supply and the first
Branched between the resistance elements and grounded via the second resistance element
It is achieved by that.

[0016]

According to the present invention, no current is supplied to the second resistance element.
Voltage is applied to the roller to prevent offset.
Leakage current to the recording material and the load on the power supply
Fluctuations are also small.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First to third embodiments of the present invention will be described with reference to the drawings.

<First Embodiment> First, a first embodiment of the present invention will be described with reference to FIGS.

FIG. 1 shows a first embodiment of the present invention, in which a resistor R for limiting current is connected between the fixing roller 1 and a power supply 8.

Normally, the surface layer of the fixing roller 1 has a sufficient withstand voltage, and the voltage V1 of the power supply 8 is applied as it is as a voltage necessary for preventing the offset.

In the experiment, the surface layer of the fixing roller having an outer diameter of 30 mm was covered with a PFA tube having a thickness of 50 μm, and a minus toner was used.
When the voltage was -600 V, the offset could be prevented.

However, according to the conventional apparatus, when the above-described bias is applied, a current flows to the recording material at a portion of the fixing roller having poor insulation (hereinafter referred to as a pinhole), and the coating of the fixing roller is broken. I have. When the coating is broken in this way, the toner is fixed and the image is stained.

In view of the above, a second method for limiting the current as in the present invention is described .
When a resistor R as a one-resistance element was connected, it was found that the current flowing through the pinhole was reduced, and the coating was not broken. When the resistance R was actually changed, it was found that when R ≧ 120 MΩ, the current flowing through the pinhole was 5 μA or less, thereby preventing the coating from being broken.

Furthermore, as a second resistive element as shown in FIG. 2
It is also conceivable to apply the offset prevention voltage while flowing a current toward the resistor R ′. In this case, it is assumed that R′≪R, and if the power supply 8 is a constant current power supply, the current flowing from the fixing roller through the pinhole will be the current i of the power supply 8

[0025]

(Equation 1) Becomes This is a value that can be sufficiently reduced to 5 μA or less. For example, if R '= 60 MΩ and the output of the constant current power supply 8 is 10 μA, if R = 400 MΩ, the pinhole is 1.3.
μA flows. With such a current, the coating is not broken at the pinhole portion.

Further, there is an advantage that a load variation applied to the power supply 8 can be stabilized. In particular, in recent years, a plurality of loads are often connected to the power supply in order to reduce the size and cost of the power supply. However, this method can stabilize the power supply and reduce the influence on other output sides.

<Second Embodiment> Next, a second embodiment of the present invention will be described with reference to FIG. The same parts as those in the first embodiment are denoted by the same reference numerals, and the description is omitted.

FIG. 3 shows a second embodiment of the present invention in which the bias voltage is obtained by dividing the output of the power supply 8 by R1 as the third resistance element and R2 as the second resistance element . In the present embodiment , R1 as the third resistance element and the first resistance element
It is possible to reduce the load variation occurring when a pinhole is there than the first embodiment idea to increase the R3 as.

In the apparatus of this embodiment shown in FIG. 3, the voltage V applied to the fixing roller 1 is equal to the power supply voltage V1 and the resistance R.
1, for R2

[0030]

(Equation 2) Is obtained. This is when the surface of the fixing roller 1 has a good insulating property and is in contact with the recording material. At this time, no current flows through R3.

On the other hand, when the pinhole on the surface of the fixing roller 1 comes into contact with the recording material, a current tends to flow through R3. At this time, the current that is going to flow is the combined resistance R of R2 and R3.

[0032]

(Equation 3) Therefore, the current i flowing out of the power supply 8 is

[0033]

(Equation 4) Becomes

From this, the current i flowing through R3 is

[0035]

(Equation 5) It is.

If this leak current is limited to a certain value or less,
Destruction of the coating layer of the fixing roller 1 can be prevented.

The resistors R1 and R2 are determined so as to obtain a voltage required for preventing offset. From equations (1) and (2), R1
When you erase

[0038]

(Equation 6) Becomes

When i3 ≧ 4 μA or more, the coating layer is destroyed.

[0040]

(Equation 7) V1, R1, R2, and R3 may be selected so that Especially for R3,

[0041]

(Equation 8) Is obtained.

(Experimental Example) The fixing roller 1 has an outer diameter of 30 mm.
The pressure roller 2 was coated with a conductive silicone rubber so as to be able to serve as a counter electrode for the bias voltage of the fixing roller 1, and the core was grounded. The temperature of the fixing roller 1 was 190 ° C., and the peripheral speed was 90 mm.

The toner used was charged to -5 to -15 .mu.c / g. Under these conditions, the voltage to be applied to the fixing roller core metal to prevent offset is at least-
It was 600V.

Table 1 shows the results of observing the presence or absence of toner sticking due to the leak current while changing the values of the power supply voltage V1 and R1, R2, and R3.

[0045]

[Table 1]

As described above, even if a pinhole is present in the surface coating of the fixing roller, by adding the resistor R3 for limiting the current flowing to the recording material, it is possible to prevent the toner from sticking and to prevent the image from being stained. .

Since the resistance Rp exists in the actual recording material, R3 can be reduced accordingly, but in this embodiment, Rp is excluded from the calculation as a margin. Strictly, R3 may be replaced with R3 + Rp.

FIG. 4 shows a third embodiment of the present invention. In this embodiment, a capacitor C is connected in parallel with the resistor R3 as the first resistance element of the second embodiment. In this case, when the pinhole in the fixing roller 1 does not come in contact with the recording material P, the voltage at the point A is an offset prevention voltage since no current flows.

FIG. 4 shows a third embodiment of the present invention. In this embodiment, a capacitor C is connected in parallel with the resistor R3 of the second embodiment. In this case, when the pinhole in the fixing roller 1 does not come in contact with the recording material P, the voltage at the point A is an offset prevention voltage since no current flows.

[0050]

(Equation 9) Is applied.

When the pinhole comes into contact with the recording material P, a current flows through the point A and a voltage drop starts.

The voltage V 'at point A is

[0053]

(Equation 10) To time constant

[0054]

[Equation 11] so

[0055]

(Equation 12) Decay to That is,

[0056]

(Equation 13) Becomes

FIG. 5B shows a change in voltage at point A.
In the second embodiment, as shown in FIG. 5A, the voltage immediately drops when the pinhole comes into contact with the recording material. When the resistance Rp of the recording material is low, the voltage becomes

[0058]

[Equation 14] And the offset cannot be prevented. On the other hand, when the voltage V is increased, the voltage at the point A can be increased up to the offset prevention voltage. To this end, the power supply voltage V1 must be increased and the voltage when there is no pinhole.

[0059]

(Equation 15) The problem is that the discharge rate becomes higher and further measures against discharge are required.

On the other hand, when a capacitor is connected as in the present embodiment, the voltage V 'at the point A can be maintained at a voltage V0 or more that can prevent the offset during the time of passing through the nip even if a current flows through a pinhole. It is possible. The width of the nip that determines V ′, the peripheral speed of the roller, the resistance of the recording material, the bias power supply voltage, the division resistance, and the capacitor are appropriately selected.

(Experimental example 2) R1 = 400 MΩ, R2 = 1
10 MΩ, R3 = 500 MΩ, Rp = 50 MΩ, C = 1
If μF, τ = 107 sec, and the nip is 4.5
mm, the time for the pinhole to pass through the nip is 0.
It is 05 sec. Assuming that V1 = −2.8 KV, the point A
Is calculated as V ′ = − 582V. The voltage drop due to the leak from the pinhole is 18 V, and if it is about this level, no offset occurs.

On the other hand, when the bias decreases stepwise in the second embodiment, the voltage at the point A decreases to V '=-26 V, and the offset could not be prevented at this time.

As described above, in the second embodiment, when the resistance of the recording material is lowered, the presence of the pinhole causes an offset, but this embodiment can solve the problem.

In the above embodiment, the bias is applied to the fixing roller. However, it goes without saying that the present invention can be applied to a configuration in which a bias is applied to the pressure roller.

[0065]

As described above, according to the present invention,
The power supply and the core of the roller are connected via a first resistance element.
Connected between the power supply and the first resistance element.
Was grounded via the second resistance block
To apply voltage to the roller while passing current to the second resistance element.
Can be added to the recording material while preventing offset.
Leakage current can be suppressed and load fluctuation on the power supply
Can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of an apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a schematic configuration of a first embodiment device in which another resistor is added to the device of FIG. 1;

FIG. 3 is a diagram showing a schematic configuration of an apparatus according to a second embodiment of the present invention.

FIG. 4 is a diagram showing a schematic configuration of an apparatus according to a third embodiment of the present invention.

5A is a diagram showing a change in a voltage of a cored bar in the apparatus shown in FIG. 3, and FIG. 5B is a view showing a change in a voltage of a cored bar in the device shown in FIG.

FIG. 6 is a diagram showing a schematic configuration of a conventional apparatus.

[Explanation of symbols]

 1 fixing roller 3 pressure roller 8 power supply R resistance

Claims (3)

(57) [Claims] A roller provided with an insulating layer on a metal core;
And a power source for applying a voltage to the core of the roller.
Is in contact with the recording material carrying the unfixed image and the unfixed image is
In the fixing device, the power supply and the roller are fixed.
The core is connected through the first resistance element, and is connected to the power supply.
The first resistive element is branched and passes through the second resistive element.
A fixing device, which is grounded . 2. A third resistor between a power supply and a branched portion.
The fixing device according to claim 1, further comprising an element . 3. The first resistance element is connected in parallel with a capacitor.
The fixing device according to claim 1, wherein the fixing device is used.