JPH0623907B2 - Fixing roller - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a fixing roller that fixes unfixed images and that is pressed against each other and is rotationally driven.

<Prior Art> An electrophotographic copying machine generally forms a toner image on the surface of a photoreceptor by charging, exposing and developing the photoreceptor, which is an image forming member, and the toner image is appropriately conveyed. After the transfer is performed on the copy paper, the paper holding the toner image is passed through the fixing unit to perform copying. As the fixing means, there are one that uses heat to perform heat fixing and one that uses pressure to fix the pressure roller. As using heat,
With the method in which radiant heat is applied to the conveyed sheet, the toner on the sheet does not come into contact with the sheet, and there is no problem such as offset development. However, in the case of using a roller, the toner on the paper and the roller come into contact with each other, and offset development occurs. Therefore, various preventive measures have been taken. For example, the roller surface is coated with PTFE (polytetrafluoroethylene), or an offset prevention liquid (silicon or the like) is applied to the roller surface and a cleaning member is brought into contact with the roller.

Here, as the fixing roller, there are a fixing roller which fixes by pressure itself and a roller which heats and fixes the roller itself, and a specific example thereof is generally that shown in FIG. In the figure, 1 is a roller having a heater therein, 2
Is a roller pressed against the roller 1. Upper roller 1 above
Is PTFE, which is a heat-resistant material having a good releasability for toner around the core metal 3 made of cylindrical Al or stainless steel.
Etc. is coated with layer 4. The lower roller 2 covers the core metal 5 with a silicon rubber 6 having a considerable thickness in order to bring the sheet into contact with the upper roller 1 in contact with the toner image with a certain width (nip width).

In such fixing rollers 1 and 2, in order to prevent toner from adhering to the surface of the roller 1, a silicone liquid applying means 7 is provided facing the roller 1. In addition to this, a cleaning member 9 including a blade 8 for uniformizing the application amount of the offset prevention liquid applied to the roller 1 and removing the adhered toner, and a felt for cleaning the surface of the roller 1 faces the roller 1. It is provided. Reference numeral 10 is a cleaning roller for cleaning the lower roller 2. Further, A is a copy sheet holding the toner image B.

As described above, according to the conventional fixing roller, it is necessary to provide a large number of means for preventing the offset.

<Object of the Invention> It is an object of the present invention to provide a fixing roller that does not require a means for applying an offset prevention liquid for preventing offset in the fixing roller.

<Example> According to an electrophotographic copying machine, a photoreceptor is charged with, for example,-(negative), image exposure is performed, and then development is performed using toner charged with + (positive). In addition, when the photoconductor is positively (positively) charged, development is performed by using toner that is negatively (negatively) charged. The toner image developed in this manner is transferred to a copy sheet, guided to a fixing roller unit, and fixed there on the sheet. When the copying operation is started, the fixing roller is rotationally driven before the paper reaches the fixing roller.

The present inventor has found that when the fixing roller rotates, it is charged by frictional charging of the roller itself with a cleaning device provided for the roller, and in view of this, the frictional charging is used to transfer to the roller. It was proposed to prevent the toner adhesion of the above. That is, conventionally, the roller 1 whose surface is in contact with the toner is coated with PTFE as shown in FIG. In this case, with such a roller structure, the upper roller 1 is negatively charged by the rotation of the roller. Therefore, if the toner is developed with the toner that is positively (positively) charged, it is considered that the toner is electrostatically attracted to the upper roller 1 to cause the offset.

Therefore, according to the present invention, particularly in the case of developing using toner charged to + (positive), the roller on the side in contact with the toner image is charged to + (positive) to prevent offset. There is. The fixing roller of the present invention is the second
As shown in the figure, the upper roller 1 in contact with the toner 12 on the paper 11
3, a cylindrical cored bar 14 made of Al, stainless steel or the like is directly coated with silicone rubber 15, and a lower roller 16 pressed against the upper roller 13 is attached to the cored bar 17 by a PTF.
A rubber 18 such as silicon whose surface is coated with E is directly coated. The following table shows the experimental results of stains on the upper roller in contact with the toner when the toner image charged with + (positive) is developed in the developing unit in the fixing roller having such a configuration and the developed toner image is fixed. Are shown in comparison with those of other materials.

As shown in the above table, when developing with positively charged toner, by selecting a material in which the upper roller 13 is strongly positively charged with respect to the lower roller, the roller surface is contaminated by the toner due to the offset. Can be prevented. In particular, it is desirable that the difference in charging potential between the upper and lower rollers is large and the upper roller is positively charged. In the above table, if the charging potential of the lower roller is sufficiently larger (absolute value) than the charging potential of the upper roller +20, such as −700, the attracting force of the positively charged toner to the lower roller is sufficient. In great condition,
The toner is held and fixed on the transfer paper 11. At this time, although the toner is repelled by the upper roller, the attraction force of the lower roller is sufficiently large, so that the toner image 12 can be effectively fixed without the possibility of being disturbed. Moreover, since the upper roller has a repulsive action with respect to the toner, there is no transfer of the toner and no offset occurs. Therefore, in order to regulate the charge amount of the upper and lower rollers as in the example of the uppermost portion specified in the above table, the upper roller 13 should be + (positive) as much as possible.
Suitable for silicone rubber materials that are electrically charged to the lower roller 16
On the contrary, it is sufficiently larger than the charge amount of the upper roller −
The surface shown in the uppermost row in the table so that it is charged negatively (P)
It is optimal to use TFE coated rubber (silicone rubber). Incidentally, as the silicone rubber of the upper roller 13, one containing silicone oil can be used in the same manner.

As an example, as shown in FIG.
TV silicone rubber (impregnated with silicone oil)
The core metal 14 is directly coated with 15 and the above-mentioned HTV silicone rubber whose surface is coated with PTFE is directly coated with the core metal 17 as the lower roller 16 to form a fixing roller, and the fixing roller is charged to +. The developed product using the prepared toner was fixed. Further, a heater 17 is provided inside the upper roller 13. In this case, a normal copy without any offset could be obtained without using any cleaning system. Further, the surface of the upper roller 13 was not soiled at all.

Further, as a second example, the same fixing roller as that described above is used, and as shown in FIG. 3, a paper roll 2 for the purpose of supplying silicon oil to the lower roller and cleaning at the same time.
In the case where 0 was provided, fixing was similarly performed. The paper roll 20 is impregnated with silicon oil in advance. In this case, the charging of the upper and lower rollers 13 and 16 is completely the same as that in FIG. 2, and the cleaning of the lower roller 16 and the upper roller 13 are performed.
It was possible to prevent the silicone oil from leaking out of the silicone rubber. There was no difference in copy quality from that shown in FIG.

<Advantages of the Invention> According to the fixing roller of the present invention, since the upper roller is positively charged, the positively charged toner image is repelled, and the toner does not transfer to the upper roller, and the offset phenomenon occurs. Can be prevented.

Moreover, even if the toner image is repelled by the upper roller, the attraction force of the toner image positively charged by the lower roller that is sufficiently larger negatively charged is larger, so that the disturbance of the toner image is prevented, In addition to preventing the above-mentioned offset phenomenon, fixing can be effectively performed in a stable state where the toner image is sucked onto the copy sheet.

[Brief description of drawings]

FIG. 1 is a sectional view showing the structure of a conventional fixing roller, FIG. 2 is a sectional view showing one specific example of the fixing roller of the present invention, and FIG. 3 is a sectional view showing another specific example of the fixing roller of the present invention. It is a figure. 11: copy paper, 12: toner image, 13: upper roller, 1
5: Silicone rubber, 16: Lower roller, 18: PTFE coating layer, 20: Paper roll (silicone oil impregnation)

Continuation of the front page (56) References JP-A-56-149076 (JP, A) JP-A-57-172372 (JP, A) JP-A-58-144866 (JP, A) JP-A-52-29228 (JP , A) JP 52-72238 (JP, A) JP 58-79272 (JP, A) JP 50-99156 (JP, A) JP 58-38974 (JP, A) JP 59-126579 (JP, A) JP-A-58-134673 (JP, A)

Claims (1)

[Claims] 1. An electrostatic latent image formed on a recording medium is developed with positively charged toner, the developed toner image is transferred to a copy sheet, and then the pair of upper and lower rollers is provided. The core metal is directly impregnated with silicone oil so that the roller surface on the side facing the positively charged toner image is positively charged. The upper roller covered with HTV rubber and the roller surface on the side facing the opposite side of the toner image transfer surface of the copy paper on which the toner image is transferred are sufficiently larger than the charge amount of the upper roller. A fixing roller comprising: a lower roller having a core metal whose surface is directly covered with HTV rubber coated with polytetrafluoroethylene (PTFE) so as to be negatively charged.