JPH0731464B2 - Fixing device for copier - Google Patents

Description

TECHNICAL FIELD The present invention relates to a fixing device for a copying machine, and more particularly to a heating fixing device that combines a heating roller and a pressure roller.

(Prior Art) Generally, in a copying machine, an unfixed image transferred onto a transfer material at a transfer portion is melted at a heat fixing portion and fixed on the transfer material.

Therefore, in the fixing unit, as an example, a roller heating and fixing device including a heating roller having a built-in heat source and a pressure roller that abuts on the heating roller and nips and conveys the transfer material in cooperation with the heating roller is used. ing.

By the way, in such a heat fixing device, in many cases, a coating layer for preventing offset is provided on the surfaces of the heating roller and the pressure roller, and specifically, Teflon (trade name, registered trademark). ) Or the like, or a material having a relatively high volume resistivity such as silicon rubber.

Therefore, when the roller pair having such a structure is rotated, the reason is not clear, but as a phenomenon, charging occurs on the roller surface, and in particular, uneven charging occurs where the central portion in the axial direction of the roller has a peak of charging potential. To do.

Due to such a phenomenon, after fixing, the transfer material cannot be evenly peeled from the roller in the axial direction of the roller, and it is necessary to provide a special separating mechanism for eliminating this, or In the roller axis direction, there will be some parts where dust and dirt will easily adhere to the roller surface,
This dust or dust causes problems such as damage to the roller surface or damage to the image.

(Object) In view of the problems of the conventional heat fixing device, an object of the present invention is to provide a heat fixing device that can simplify the separating mechanism in the fixing device and prevent damage to the roller surface and the image in the fixing device. To get.

(Structure) In order to achieve the above-mentioned object, the present invention is characterized by controlling a charging charge generated in an axial direction of a roller in a heat fixing device.

Hereinafter, the details of the embodiment of the present invention will be described with reference to FIGS. 1 to 7.

In FIG. 1, the heating roller 1 and the pressure roller 2 are separated,
FIG. 5 is an explanatory diagram showing changes in the surface potential of each roller when conductors such as metal are arranged with a distance 1 to the heating roller 1.

In the case of the embodiment shown in FIG. 1, a coating layer of Teflon (trade name) is formed on the surface of the heating roller, while a coating layer of silicone rubber is formed on the surface of the pressure roller 2.

Further, a conductor 3 such as a coiled metal wire whose longitudinal direction is set in the axial direction of the roller is opposed to the heating roller 1 at an interval l.

The conductor 3 is, of course, grounded, the peripheral portion of the coil is made to face the heating roller 1, and the facing distance l can be changed by a mechanism (not shown).

Now, in the conventional one in which the conductor 3 is not opposed to the heating roller 1, uneven charging occurs on the heating roller 1 in the axial direction of the roller as shown by the solid line in the figure, while the pressure roller 2 On the other hand, the charging roller is affected by the charging of the heating roller, causing uneven charging with the opposite polarity.

On the other hand, the conductor 3 is opposed to the heating roller 1 and l =
When the intervals are set to less than 5 m / m, 1 = 5 to 10 m / m, and 1 = 10 to 15 m / m, the electric charges at both ends in the axial direction of the heating roller 1 are discharged to the conductor 3. , 0 becomes saturated as the electric potential approaches 0, and the potential difference from the central portion in the axial direction becomes small. On the other hand, along with this, the pressure roller 2 side is also affected by the change in the potential level on the surface of the heating roller, and the potential difference in the axial direction is reduced, and as a result, the uneven charging in the axial direction is eliminated.

Generally, in the case of removing the charged electric charge, it is considered that the charge removing member is brought into contact with the surface of the roller that holds the electric charge. However, when the contact is made, the roller surface is rubbed by the material of the conductor. There is a risk that the surface will be damaged and the surface will be scratched. However, in the case of the present embodiment, such an adverse effect is eliminated, and uneven charging occurring in the axial direction of the roller is eliminated. In this case, the elimination of uneven charging means
It does not mean to reduce the entire charging potential in the axial direction of the roller, but to reduce the potential difference between the peak value and the minimum value of the charging potential.

Next, referring to FIG. 2, an example of reducing the potential difference between the peak value of the charging potential in the axial direction of the roller and the minimum value of the same potential by charging the roller in the opposite manner to the case of the embodiment of FIG. To do.

That is, in FIG. 2, the surface of the heating roller 1 is covered with Teflon (trade name), and the axial center portion of the roller 1 has a volume of silicon rubber or the like that provides frictional charging characteristics of the same polarity as Teflon. Friction member 4 with high resistivity
Are abutted.

Therefore, the heating roller 1 when the friction member 4 is not contacted
If the friction member 4 is brought into contact with the heating roller 1 when the charging characteristic of the heating roller 1 is in the state shown by the solid line in the figure, the same polarity as the charging polarity of the heating roller 1 is applied at the central portion in the axial direction of the heating roller 1. It

In this embodiment, the charging potential at the central portion in the axial direction of the heating roller 1 rises and approaches the peak value of the charging potential at both end portions in the axial direction, so that the potential difference in the axial direction is reduced and uneven charging occurs. Resolve.

Further, in order to eliminate such uneven charging in the axial direction of the roller, it is possible not only to take measures against the heating roller 1 but also to eliminate uneven charging in the pressure roller 2.

An embodiment of this case is shown in FIGS. 3 and 4.

That is, in the embodiment shown in FIG. 3, the sheet metal member 5 having a comb-teeth-shaped tip portion is closely opposed to the axial center portion of the pressure roller 2 made of silicon rubber.

In this embodiment, the pressure roller 2 is similar to the case where the conductor 3 is closely opposed to the heating roller 1 shown in FIG.
A discharge is generated between the central portion in the axial direction and the tip of the sheet metal member 5, the potential at the central portion is lowered, and the potential difference between the both end portions in the axial direction is reduced to eliminate uneven charging.

Therefore, when the uneven charging in the axial direction of the pressure roller 2 is eliminated in this way, the uneven charging on the surface of the heating roller in contact with the roller 2 is also affected as described with reference to FIG. As a result, uneven charging on the heating roller is also eliminated.

In the embodiment shown in FIG. 4, a conductive curved plate 6 having a curvature is made to face the central portion of the pressure roller 2 in the axial direction so that a portion having a small area approaches.

Even in the case of this embodiment, as in the case shown in FIG. 3, the charging unevenness in the axial direction of the pressure roller 2 is eliminated, and in the axial direction of the heating roller 1 as well, the conventional structure shown by the solid line in the figure. Compared to, uneven charging is eliminated.

All of the above-mentioned examples are specific examples in which measures are taken to eliminate uneven charging on the heating roller or the pressure roller, but in the present invention, one of these rollers is used. However, it is not limited to taking measures to eliminate uneven charging only.

That is, FIG. 5 and FIG. 6 show examples in which measures for eliminating uneven charging are taken for both the heating roller and the pressing roller.

In the embodiment shown in FIG. 5, the electrically conductive static-eliminating brush 7 is made to face the area of the heating roller 1 excluding the central portion in the axial direction, while the central portion of the pressure roller 2 in the axial direction is also electrically conductive. The static elimination brush 8 is opposed.

The static elimination brush 7 on the heating roller 1 side is set so that the interval l ₁ between the axial end of the roller 1 and the peripheral surface of the heating roller 1 is narrower than the interval l ₂ on the axial center side of the roller 1, and In the static elimination brush 8 on the pressure roller 2 side, the distance l ₃ between the axial center portion of the roller 2 and the peripheral surface of the pressure roller 2 is the distance l between both sides of the central portion and the peripheral surface of the roller 2. It is set narrower than ₄ .

Therefore, in this embodiment, the same effect as the embodiment shown in FIG. 4 is obtained on the pressure roller 2 side, and the same operation as the embodiment shown in FIG. 1 is obtained on the heating roller 1 side. As a result, in comparison with the conventional one shown by the solid line in the figure, charging unevenness is eliminated on the pressure roller 2 side.

In addition, with the arrangement configuration of the static elimination brush, the same state as that in which the static elimination is performed uniformly over the entire axial direction of the roller can be obtained, so that the level of the charging potential can be reduced over the entire axial direction. Becomes

Further, as shown in FIG. 5, instead of changing the distance between the static eliminating brush and the peripheral surface of each roller in the axial direction,
As shown in FIG. 6, it is possible to set sparseness and denseness between the brushes of the static eliminating brushes 9 and 10 in the axial direction, and even in this case, similarly to the embodiment shown in FIG. It is possible to reduce the charging level in the axial direction of the roller and eliminate uneven charging.

On the other hand, it is also possible to apply the charge eliminating brush of the embodiment shown in FIG. 6 to a heating roller having improved charging characteristics.

That is, the heating roller in this case is configured, for example, by dispersing carbon in a coating layer of Teflon (trade name). According to the structure of this heating roller, as compared with the charging characteristics of the heating roller composed of the coating layer of only Teflon shown by the solid line in FIG. 7, some charging unevenness is eliminated as shown by the broken line. When the charge eliminating brush shown in FIG. 6 is applied to such a heating roller, uneven charging in the axial direction of the roller is eliminated and the charging potential is The result reached almost 0V.

(Effect) As is apparent from the above description, according to the present invention, the static elimination member or the charging member is opposed to the central portion or both ends in the axial direction of at least one of the heating roller and the pressure roller. Since the charging potential of the roller in the axial direction is controlled and uneven charging in the axial direction can be eliminated, the transfer material can be uniformly peeled from the roller. Therefore, it is possible to eliminate the need for a special transfer material separating mechanism, and it is also possible to eliminate the generation of dust or a portion where dust is likely to adhere on the roller.

[Brief description of drawings]

FIG. 1 is an explanatory view showing the structure of a roller according to an embodiment of the present invention and its action, and FIGS. 2 to 6 are explanatory views showing the structure of a roller according to another embodiment of the present invention and its action, respectively. FIG. 7 is a diagram showing the operation according to another embodiment of the present invention. 1 ... Heating roller, 2 ... Pressure roller, 3 ... Conductor,
4 ... Friction member, 5 ... Sheet metal member, 6 ... Curved plate, 7-10
…… A static elimination brush.

Claims (1)

[Claims] 1. A fixing device comprising a heating roller and a pressure roller which are in contact with each other and have a coating layer having a high volume resistivity such as fluorinated resin or silicon rubber and which can rotate in a relative direction. A fixing device for a copying machine, wherein a discharging member or a charging member is opposed to a central portion or both end portions of at least one axial direction of each roller to control a charging potential in the axial direction of the roller.