JPH0830925B2 - Image forming device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a fixing device used in an image forming apparatus such as an electrophotographic copying machine, a laser beam printer, and a facsimile machine, and more particularly to a pair of fixing devices that rotate in pressure contact with each other. The present invention relates to a fixing device that fixes an unfixed image on a recording material by passing a recording material having an unfixed image between rollers.

[Prior art]

Conventionally, as the roller fixing device as described above, a heat fixing device that performs fixing by heating and pressurizing, and a pressure fixing device that performs fixing only by pressing force are known.

The roller used in the heat fixing device is formed by coating a heat resistant silicone rubber layer, a fluorine resin layer such as PTFE or PFA, or a heat resistant layer of a mixture of both on a substrate such as Al or SuS. It is common to have The above-mentioned coating layers are subjected to various improvements in order to improve the releasability of the developer (hereinafter referred to as toner) from each other so as to prevent so-called toner offset development. In order to improve the performance of this offset prevention, it is known from JP-B-58-23626 that the electric resistance value of the coating layer is reduced by mixing the above-mentioned conductive material of the coating layer. There is.

On the other hand, it is known that the roller used in the pressure fixing device also has a low electric resistance value because it is generally made of steel or the like.

[Problems that the invention is trying to solve]

However, in recent years, the image forming apparatus itself tends to be downsized, which makes the distance between the fixing unit and the transfer unit shorter than the length of the recording paper used, so that the leading end of the recording paper is located in the fixing unit. When it arrives, a state in which the rear side of the recording paper remains in the transfer portion, that is, the recording paper exists across the fixing portion and the transfer portion occurs. However, in such a state, when the electric resistance of the fixing roller is low as described above, when the electric resistance of the recording material is low, especially in a high humidity environment, the transfer charging charge leaks, resulting in a transfer failure. was there.

Therefore, increasing the resistance of the fixing roller is effective for preventing transfer omission, but increasing the resistance of the fixing roller causes the fixing roller to slide between the fixing rollers or the fixing roller and the recording paper. Due to triboelectric charging and the roller surface being charged, the performance may be inferior to the offset prevention.

[Means for solving problems]

The present invention has been made in view of the above-mentioned conventional drawbacks, and an object of the present invention is to provide a fixing device having a roller with improved offset prevention performance. In order to achieve this object, the present invention is to reduce the resistance of the surface layer of the roller and to make the roller as a whole have a predetermined resistance value or be insulated.

That is, the present invention has a transfer charging unit that transfers an unfixed image on an image carrier onto a recording material, and a fixing roller pair that sandwiches and conveys the recording material carrying the unfixed image for fixing. In an image forming apparatus in which the same recording material is nipped by the fixing roller pair during transfer to the recording material by the transfer charging means, at least one roller of the fixing roller pair is a base material,
A surface layer, an intermediate layer provided between the base material and the surface layer,
The intermediate layer has a volume resistance value of more than 10 ¹⁰ Ω · cm, and the surface layer has a volume resistance value of 10 ¹⁰ Ω · cm or less and is electrically floated.

〔Example〕

 Embodiments of the present invention will be described below with reference to the drawings.

 FIG. 1 shows an embodiment of the fixing device of the present invention.

The fixing roller 1 has a hollow cylindrical base material 13 such as SuS or Al having an intermediate layer 12 including an adhesive layer called a primer, on which a heat resistant silicone rubber, PTFE (polytetrafluoroethylene resin), PFA (par) Fluoroalkoxy resin) or the like has a surface layer 11 containing a powdery or fibrous conductive material such as carbon or metal powder in a fluorine-based resin.
A heat source 3 is provided inside the fixing roller 1.

On the other hand, the pressure roller 2 has, for example, a cored bar and a coating layer of heat-resistant silicone rubber or sponge.

The fixing roller 1 and the pressure roller 2 are pressed against each other at least at the time of fixing by pressure means (not shown).
Each of them is driven to rotate in the direction of the arrow in the figure by a driving means (not shown). Known means can be applied as the pressing means and the driving means.

In such a configuration, the recording material 4 such as paper on which the unfixed toner image T is formed passes between the fixing roller 1 and the pressure roller 2 so that the unfixed toner image is formed on the recording material 4. T is heated and fixed.

Here, the fixing roller 1 will be described in more detail. The base material 13 may be electrically grounded or may be in a floating state. The surface layer 11 has a volume resistance value of 10 ¹⁰ Ω · cm or less. The volume resistance value between the surface layer 11 and the base material 13 may be larger than 10 ¹⁰ Ωcm, and for that purpose, a material having the above volume resistance value is particularly selected as the substrate of the intermediate layer 12. Good. As a result, the surface layer 11 is electrically floated.

Next, the effect of using such a fixing roller will be described using the image forming apparatus shown in FIG. In the figure, reference numeral 5 denotes a photosensitive drum which is an image bearing member. The photosensitive drum 5 is charged by a charger 6 and imagewise exposed by an exposure optical system 7 to form a latent image. Is developed by the developing device 8. The developed toner image is transferred by the transfer charger 9 onto the recording material 4 conveyed in the direction of arrow A. The recording material 4 after the transfer is separated from the photosensitive drum 5, and then is conveyed to the fixing device F by the conveying unit 10. The recording material 4 conveyed to the fixing device F is discharged to the outside of the machine after the toner image is fixed by the pair of fixing rollers 1 and 2 as described above. On the other hand, the toner remaining on the photosensitive drum 5 after the transfer is removed and cleaned by the cleaner 14. Since the above-mentioned image forming process is well known, its detailed description is omitted.

In the image forming apparatus shown in FIG. 2, the length of the recording material 4 is longer than the distance 1 between the transfer portion and the fixing nip portion. Thus, when the length of the recording material 4 is longer than the distance l, the rear portion of the recording material 4 is still at the transfer portion when the leading end of the recording material 4 is gripped by the roller pair 1 and 2 as shown in the figure. , Is being transferred. Therefore, in this case, the charge charged by the transfer charger 9 reaches the fixing portion via the recording material 4. In particular, when the recording material is paper, the surface resistance of the paper becomes 10 ⁹ to 10 ⁸ Ω when the humidity exceeds 80%, and the electric charge tries to instantly move to the fixing portion. At this time, when the fixing roller has a resistance of 10 ¹⁰ Ω or less, more notably 10 ⁸ Ω or less, the transfer charging charge leaks, the transfer charging charge of the transfer portion decreases, and transfer failure occurs. This relationship is shown in FIG. 3 at a distance of 1 ≈140 mm, a transfer charging voltage of 5.4 kV, and 80 gr paper as a recording material at 3235 ° C. and 90%.

In FIG. 3, the vertical axis represents the solid black image density indicating the transfer omission, and the image density after the distance 1 from the front end of the paper. It can be understood from the figure that when the image density when the resistance of the fixing roller is 10 ¹³ or more is 1.0, the transfer omission appears from 10 ¹⁰ Ω or less, and becomes prominent at 10 ⁸ Ω or less. This is l≈140 mm, and although the decrease of l and the transfer electric field strength are different depending on the machine, it is considered that there is substantially no adverse effect if it is approximately 10 ¹⁰ Ω or more.

Regarding the surface resistance and offset property of the fixing roller, about φ25 mm Al was used as the base material and 10 ¹³ Ω ・ cm as the intermediate layer.
Approximately 10 μm of the above primer is coated and PT is used as the surface layer.
The layer in which carbon was mixed with FE resin was used by coating it to 20 to 30 μm, the amount of carbon added was changed, and the offset property was measured visually. As the strip, the roller peripheral speed was about 52 mm / sec, the surface temperature was about 180 ° C., and both the one-component magnetic toner and the non-magnetic toner were observed as toner.

As a result, as shown in FIG. 4, the resistance value of the surface layer of the roller is
Good offset properties were obtained at 10 ¹⁰ Ω · cm or less, and more preferably at 10 ⁸ Ω · cm or less. This did not make much difference whether the Al substrate was grounded to the main body side or floated.
In the resistance value region where offset is small, even if the base layer is floated or the base layer is grounded to insulate the intermediate layer and the surface layer is charged to some extent, the surface layer is locally or partially It is considered that offset density is improved because there is no unevenness in charge density due to a general charge-dip, and therefore, the accumulated charge pattern of the toner on the recording material is not disturbed.

Next, another embodiment of the present invention will be described with reference to FIGS.
It will be described with reference to the drawings. Also in this embodiment, the effect can be obtained by satisfying the above resistance value.

In FIG. 5, the intermediate layer 12 'is composed of a heat-shrinkable tube such as PFA resin, and the surface layer 11' is covered with a tube in which a conductive material is mixed with PFA resin. According to this, while the above-mentioned embodiment coats the pliers and the surface layer,
This has an advantage that the manufacturing process can be simplified.

Further, FIG. 6 shows still another embodiment, in which the intermediate layer is not particularly coated with a coating material, Al of the base material 13 is oxidized to form the insulating coating 15 such as aluminum oxide, and then the surface layer 11 'is formed. You may coat or chew. This also simplifies the manufacturing process.

In each of the above-described embodiments, the case where the present invention is applied to the fixing roller has been shown, but the present invention is not limited to this, and may be applied to the pressure roller, or both of them may be applied if necessary. It may be applied to rollers.

Further, in the above-described embodiment, the heat fixing device is described as an example of the fixing device, but the present invention can be applied to the pressure fixing device. In this case, for example, the intermediate layer has structural strength and high resistance. The roller itself has a high resistance and the surface layer is made resistant by applying metal chrome plating to the recording material passage area of the surface layer. Even in this case, the resistance value as described above may be satisfied.

〔The invention's effect〕

As described above, according to the present invention, a fixing device with less offset can be obtained by lowering the resistance of the surface layer of the roller and electrically floating the surface layer. Furthermore, when the present invention is applied to the fixing device of the above-described downsized image forming apparatus, it is possible to prevent the transfer omission of the image.

[Brief description of drawings]

FIG. 1 is a sectional view of a pair of rollers showing an embodiment of the present invention. FIG. 2 is a schematic sectional view showing an example of an image forming apparatus using the fixing device of the present invention. FIG. 3 is a graph showing an experimental example of the image density with respect to the resistance of the fixing roller. FIG. 4 is a graph showing an experimental example of the offset amount with respect to the resistance of the surface layer of the fixing roller. 5 and 6 are sectional views of a fixing roller showing another embodiment of the present invention. 1 ... Fixing roller 2 ... Pressure roller 4 ... Recording material 11,11 '... Surface layer 12,12' ... Intermediate layer 13 '... Substrate T ... Unfixed toner image

Claims (1)

[Claims] 1. A transfer charging means for transferring an unfixed image on an image carrier onto a recording material, and a fixing roller pair for sandwiching and carrying the recording material carrying the unfixed image for fixing. In an image forming apparatus in which the same recording material is nipped by the fixing roller pair during transfer to the recording material by the transfer charging means, at least one roller of the fixing roller pair includes a base material, a surface layer, and a base material. And an intermediate layer provided between the surface layer and the surface layer, wherein the intermediate layer has a volume resistance value of more than 10 ¹⁰ Ωcm, and the surface layer has a volume resistance value of 10 ¹⁰ Ωcm or less. An image forming apparatus characterized in that the image forming apparatus is a float.