JP3005028B2 - Fixing device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device used in an image forming apparatus such as a copying machine or a printer to fix an unfixed image. The present invention relates to a roller fixing device that clamps and conveys a supporting material to be fixed.

(Prior art)

Conventionally, various types of fixing devices have been devised and implemented, but at present, a so-called heat roller fixing device, which includes a pair of rollers having a heat source on at least one side, is in the mainstream from the viewpoint of thermal efficiency.

 FIG. 2 shows an example of a conventional heat roller fixing device.

Reference numeral 1 denotes a fixing roller which is in contact with an unfixed toner image on a support member and has a halogen heater 3 as a heat source inside.

Reference numeral 2 denotes a pressure roller having an elastic layer, which is pressed against the fixing roller 1 with an appropriate nip width.

The surface temperature of the fixing roller 1 is detected by the thermistor 4 and is maintained at an appropriate surface temperature. This is a mechanism in which the heat-fusible toner on the transfer material is heated and pressed and fixed by passing the transfer material between the pair of rollers. As described above, since the toner and the fixing roller having a heat source are in direct contact with each other, the heat conduction efficiency is extremely excellent as compared with other methods.

[Problems to be solved by the invention]

However, there is a problem that an offset phenomenon in which the toner is transferred to the fixing roller occurs.

 This offset has a temperature factor and an electrostatic factor.

The temperature factor can be prevented by strictly controlling the surface temperature of the fixing roller, but it is difficult to solve the electrostatic factor.

Since the fixing roller is charged to several kV by frictional charging with the transfer material and the pressure roller, the surface potential of the fixing roller and the pressure roller is lowered from the viewpoint that charged toner on the transfer material is electrostatically attracted to the fixing roller. Things are valid. For this purpose, measures have been taken such as using a static elimination brush on the roller, applying a low-resistance release agent, or lowering the surface of the roller and grounding its surface layer via a cored bar. .

In addition, the pressure roller itself must have a surface layer that is also excellent in releasability from the toner itself. It is necessary to form an appropriate nip. For this reason,
2. Description of the Related Art A pressure roller in which silicon rubber is coated with a pure fluororesin tube is widely used.

The pressure roller, which is a rotating body that does not come into contact with the unfixed toner, may also be charged by frictional charging and cause an electrostatic offset.

For this reason, it is conceivable to dispose the static elimination brush in contact with or non-contact with the pressure roller to eliminate the charge on the surface of the pressure roller.

However, when used for a long time, paper dust, toner, etc. adhere to the neutralization brush, and the static elimination ability is rapidly reduced.

[Means to solve the problem]

The present invention which solves the above-mentioned problems has a first and a second pressure contact.
In a fixing device in which a roller supports and holds a supporting material for supporting an unfixed image, the first roller has a surface layer containing a low-resistance substance and is in contact with the unfixed image, and the second roller has a core. A low-resistance intermediate layer is provided between the insulating layer on the gold and the surface insulating layer, and the low-resistance intermediate layer is not grounded by interposing the insulating layer of the second roller between the low-resistance intermediate layer and ground. .

〔Example〕

 Hereinafter, embodiments of the present invention will be described.

 FIG. 1 is a sectional view of a fixing device according to an embodiment of the present invention.

The fixing roller 1 has a halogen heater 3 as a heat source inside.
And a thermistor for detecting the roller temperature is in contact with the surface.

A separation claw 6 is provided near the nip formed by the fixing roller 1 and the pressure roller 2 to contact the fixing roller 1 to separate the supporting material. The unfixed image is heated and fixed by nipping and conveying the recording material supporting the unfixed image with the nip.

The fixing roller 1 of this embodiment is made of a metal core 1c, which is conductive and has good thermal conductivity, such as Sus (stainless steel) or Al (aluminum).
A low-resistance substance such as carbon black (eg, carbon fibers, graphite whiskers or silicon carbide fibers, metal oxides such as silicon carbide urisca and titanium oxide, nickel, etc.) is placed on the core metal 1c. % To 40% of tetrafluoroethylene resin (PTFE) and 5 to 15% of tetrafluoroethylene-alkyl vinyl ether copolymer resin (PFA)
The mixed release layer 1a is bonded by a primer layer 1b made of a rubber-based or resin-based adhesive.

The release layer 1a has a volume resistance of 10 ¹¹ to 10
It is 10 ¹⁴ Ωcm.

The pressure roller 2 has an insulating rubber layer 2c provided on a cored bar 2d, and an insulating pure fluororesin (for example, perfluoroalkoxy, A surface release layer 2a made of PFA) is adhered by a primer layer 2b.

Silicon rubber is preferable for the rubber layer, but fluorine rubber or a mixture of fluorine rubber and silicon rubber may be used.

The primer layer 2b is formed by adding a low-resistance substance (for example, carbon fiber, graphite whisker or silicon carbide fiber, metal oxide such as silicon carbide whisker or titanium oxide, nickel, etc.) to a rubber-based or resin-based adhesive, and The resistivity is set to 10 ⁶ Ω · cm or less.

By using the low resistance intermediate layer as the primer layer between the insulating rubber layer and the surface insulating layer on the core metal, the surface potential of the pressure roller can be reduced to 100 V or less without impairing the surface releasability. did it.

 The reason is considered as follows.

Since the surface layer of the fixing roller is semiconductive, it functions as an electrode together with the core metal of the pressure roller, and the conventional pressure roller can be represented by a capacitor model shown in FIG. 3 (a).

In contrast, in the present embodiment, as is apparent from FIG. 3 (b), since the low-resistance intermediate layer is not grounded by interposing the insulating layer of the pressure roller between the low-resistance intermediate layer and ground, The resistance intermediate layer also serves as an electrode, and is shown by the capacitor model in FIG. 3 (b).

That is, in the present embodiment shown in FIG. 3 (b) as compared with FIG. 3 (a), since the low resistance material is dispersed in the primer layer, the thickness of the capacitor becomes relatively small, and the capacitance of the capacitor is reduced. C is , It becomes larger.

For this reason, even if the same amount of triboelectric charge is generated, the generated voltage V is Smaller. That is, the model (b) has a lower surface potential and does not cause a charge gap.

 Next, a second embodiment of the present invention will be described.

 The same fixing roller as that in the above-described embodiment was used.

The pressure roller uses a low-resistance substance in the elastic layer 2c on the core bar.
Conductive silicon rubber with a volume resistance of 10 ⁶ Ω · cm or less was used by mixing 50%, and a pure PFA tube was used for the surface release layer.

As the primer layer, the core metal / elastic layer, elastic layer /
An insulating material was used for both the surface release layers.

Also in this example, the surface of the pressure roller was not extremely charged and no electrostatic offset was generated.

 Next, a third embodiment of the present invention will be described.

In this embodiment, the fixing roller is supported via an insulating heat-insulating bush, a bias voltage having the same polarity as that of the toner is applied to the fixing roller, and the pressure roller is insulated from the insulating surface release layer. A low-resistance substance is added to the primer layer between the elastic layers, so that the volume resistance of the primer layer is 10 Ω · cm or less.

Applying a bias voltage having the same polarity as that of the toner to the fixing roller is effective in preventing electrostatic offset, but in this embodiment, the effect of preventing electrostatic offset is very small because the pressure roller surface that is in pressure contact with the fixing roller has a small gap. Big.

In addition, since the surface of the pressure roller is an insulating layer and there is no movement of electric charge, the bias applied to the fixing roller is not affected at all, and very stable performance can be maintained.

Table 1 below shows the offset test results for the conventional example and Examples 1 to 3 of the present invention, and the surface potential measurement results for the roller pair at that time. The original is an ordinary character original, and the toner is of positive polarity. The test was conducted by passing 100 sheets continuously. In the table, “upper” indicates a fixing roller and “lower” indicates a pressure roller.

From the above table, the offset prevention effect of this embodiment is remarkably good as compared with the prior art, and the surface potential of each roller is low and stable, and the surface potential of each roller is low. The use of a semiconductive release layer made of a fluororesin containing, the surface potential of the roller is very low, electrostatic offset can be prevented, and especially when a positively charged toner is used, It is effective for

〔The invention's effect〕

As described above, according to the present invention, it is possible to keep the charge gap between both roller surfaces extremely low without deteriorating the releasability of the pressure roller surface, and to apply the pressure roller between the low resistance intermediate layer and the ground. Since the low-resistance intermediate layer is not grounded through the insulating layer, it is possible to reliably prevent the charge of the recording material from leaking to the pressure roller while suppressing an increase in the potential of the entire pressure roller, thereby preventing electrostatic offset. it can.

[Brief description of the drawings]

1 is a cross-sectional view of a fixing device according to an embodiment of the present invention, FIG. 2 is a cross-sectional view of a conventional fixing device, and FIGS. 3 (a) and 3 (b) are a conventional example and an embodiment of the present invention, respectively. It is explanatory drawing of an example. DESCRIPTION OF SYMBOLS 1 ... Fixing roller 2 ... Pressure roller 3 ... Halogen heater 4 ... Thermistor 6 ... Separating claw

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-61-250668 (JP, A) JP-A-55-164858 (JP, A) JP-A-1-227179 (JP, A) JP-A 64-64 59278 (JP, A) JP 58-23626 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 15/20

Claims (7)

(57) [Claims] An image fixing apparatus comprising: a first roller having a surface layer containing a low-resistance substance; and a first roller having a surface layer containing a low-resistance substance. The second roller has a low-resistance intermediate layer between the insulating layer on the metal core and the surface insulating layer, and the low-resistance intermediate layer is interposed between the second roller and the ground through an insulating layer of the second roller. The fixing device is not grounded. 2. The fixing device according to claim 1, wherein the low-resistance surface layer of the first roller is a fluororesin layer containing a low-resistance substance. 3. The fixing device according to claim 2, wherein the low-resistance surface layer of the first roller is PTFE mixed with PFA. 4. The fixing device according to claim 1, wherein said low-resistance intermediate layer is an elastic layer. 5. The fixing device according to claim 1, wherein said surface insulating layer is a fluororesin tube. 6. The fixing device according to claim 1, wherein the insulating layer on the metal core of the second roller is an elastic layer. 7. The fixing device according to claim 1, wherein the low-resistance surface layer of the first roller is substantially grounded.