JPH04274471A - Fixing device - Google Patents

Abstract

PURPOSE:To prevent the leak of a voltage from a roller core metal and an electrostatic offset, stably by providing specific insulating parts coming into contact with a core material on both the driving part and the supporting part of the core material, respectively. CONSTITUTION:A brush made of resin, for insulation in inserted between the core metal 18A of a fixing roller and a bearing 8 composed of a conductive metallic ball bearing. The bush 10 is formed by using Polyphenylesulfide so as to have >=10<14>OMEGAcm volume resistivity, and has a constitution so that a sufficient distance is taken between the roller core metal 18A and the bearing 8. On the other hand, a driving gear 7 is provided on the core metal 18A and made of heat resistance and insulation resin having >=10<14>OMEGAcm volume resistivity, such as polyamide. Therefore, the applying of the voltage to the others except the core metal 18A can be prevented, and simultaneously, the leak of a charge to the conductor frame 9, shafts 14 and 15, etc., of a circumference can be prevented, as well.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device used in image forming apparatuses such as electrophotographic devices and electrostatic recording devices, for fixing toner images on a support material.

0002

2. Description of the Related Art A heat roller fixing method is widely used as a fixing method for fixing a toner image on a recording material.

An example of this heat roller fixing device is shown in FIG.

1 is a fixing roller, 2 is a pressure roller, 3 is a temperature detection element, 4 is an entrance guide, 5 is a separation claw, and 17 is a cleaner for cleaning offset toner. P is a paper sheet, and T is a toner image.

[0005] The fixing roller 1 has a core metal 1A coated with a release layer 1B made of fluororesin, and has a hollow interior in which a heater 6 is inserted. The heater 6 is caused to blink by a control circuit (not shown) in accordance with the temperature of the fixing roller detected by the temperature detection element 4. The paper sheet P is guided to the entrance guide 4 and carried between the fixing roller and the pressure roller, which are maintained at a predetermined temperature in this manner. The paper sheet P that has passed through the roller pair is transferred to the fixing roller 1 by the separating claw 5.
more peeled off.

[0006] When a pair of rollers nip and convey a sheet of paper supporting a toner image to fix the image, toner offset occurs.

Factors contributing to this offset include temperature factors and electrostatic factors. Offset due to temperature fluctuations can be prevented by accurately maintaining the surface temperature of the fusing roller, but
Electrostatic offset is affected by the environment, pure species, etc., so it is difficult to completely prevent it.

Therefore, Japanese Patent Laid-Open No. 55-96970 discloses a technique for preventing offset by applying a voltage of the same polarity as the toner to the fixing roller to cause electrical repulsion.

[0009]

However, when voltage is applied to the fixing roller, the voltage may be applied to unnecessary parts, resulting in wasted power consumption or leakage to surrounding conductors.

0010

[Means for Solving the Problems] The present invention, which solves the above-mentioned problems, consists of a conductive core material that rotates under the driving force from a driving source and is used to sandwich and convey a supporting material that supports a toner image. and a voltage applying means for applying a voltage of the same polarity or opposite polarity to the toner to the core material of the roller, the driving part and the supporting part of the core material are in contact with the core material, respectively. It is characterized by being provided with an insulating member having a volume resistance of 1014 Ωcm or more.

[0011]

[Embodiments] Hereinafter, embodiments of the present invention will be explained based on the drawings.

The same members as in the example in FIG. 6 are denoted by the same numbers, and their explanations are omitted. (Embodiment 1) FIGS. 1 and 2 show a first embodiment of the present invention. The fixing roller 18 is a conductive A highly insulating pure PFA tube is coated on a core metal 18A made of a metal such as aluminum or stainless steel.

The pressure roller 19 is coated with a PFA tube made of silicone rubber 19A with carbon black dispersed therein to provide low resistance.

Further, a bias voltage of 1 to 4 KV having the same polarity as that of the toner T is applied to the core bar 18A of the fixing roller by the power supply 16, and electrostatic offset is prevented by the electrostatic repulsive force between the fixing roller and the toner. be done.

The fixing roller 18 rotates by receiving a driving force from a driving source (not shown).

In this embodiment, an offset toner cleaner is not required by applying a bias voltage.

FIG. 2 shows a cross-sectional view of the driving section side of the fixing roller.

The end of the fixing roller 19 is narrowed to a small diameter, and this narrowed journal portion is supported by a bearing, and a driving gear is fitted therein.

By narrowing the ends of the rollers in this manner, the bearing 8 and gear 7 can be made smaller. A resin bush 10 for insulation and heat insulation is inserted between the core metal 18A of the fixing roller and the bearing 8 made of a conductive metal ball bearing. This bush is formed of polyphenyl sulfide to have a volume resistance of 1014 Ωcm or more, and is configured to provide a sufficient insulation distance between the roller core metal 18A and the bearing 8. 9 is a side plate, and 11 is a stopper for regulating the position of the fixing roller in the thrust direction.

[0020] Reference numeral 7 denotes a driving gear between the core bar 18A.

The gear 7 is made of a resin having heat resistance and insulation properties such as polyamideimide having a volume resistance of 1014 Ωcm or more.

[0022] This insulating gear ensures a sufficient insulation distance between the core bar 18A and the valley of the gear.

Gears 12 and 13 are connected to the drive gear 7 and transmit driving force, and are made of a heat insulating resin.

[0024] The support part that supports the core metal 18A in this way,
and insulating members 7 and 10 that come into contact with the core metal to drive the drive.
By providing this, it is possible to prevent voltage from being applied to other than the core metal, and also to prevent electric charge from leaking to the surrounding conductor frame 9, shafts 14, 15, etc.

Furthermore, since the gear 7 and the bush 10 are made of a heat insulating resin, heat radiation from the ends of the fixing roller can be prevented, and the temperature distribution in the axial direction of the roller can be made uniform. This prevents fixing failure at the end, particularly on the gear side.

FIG. 3 shows how the gears 7, 12, and 13 mesh.

[0027] When securing the insulation distance with the drive gear,
As shown in the cross-sectional view of the hub of gear 7 in Figure 4, the creepage distance is increased by cutting out the thickness, and by making the hub thinner, the transfer of heat from the fixing roller to gears 12 and 13 is reduced, making it easier to use. The amount of resin used can also be reduced.

(Embodiment 2) Gear 7 was made of polyamideimide, gears 12 and 13 were made of cast iron, and the bearing portion was made of copper-based sintered alloy.

In this manner, by forming only the gear 7 from an insulating resin and forming the gears 12 and 13 by casting or cutting metal, it is possible to prevent the gears from skipping or chipping.

If the gear 7 is made of resin and the gears 12 and 13 are made of metal, lubricity is provided by the powder generated when the gear 7 wears a little, so that the wear does not progress any further. In particular, gears have become smaller in recent years due to the miniaturization of devices, but in the case of this embodiment, the gear 7 that wears out is large.
Since the metal gears 12 and 13 are smaller, a protective film of abrasion powder is quickly formed on the surface of the metal gears, and a sufficient life can be maintained. Also, since there is less wear on the gears, pitch unevenness is less likely to occur.

In this example, 200,000 copies were printed, but there was no wear or damage to the gear.

(Embodiment 3) FIG. 5 shows a sectional view of a third embodiment. Descriptions of components similar to those in the first embodiment will be omitted. Reference numeral 7 denotes a gear made by transplant molding, and a portion 7a that contacts the core metal is made of an insulating and heat-resistant resin. The tooth portion 7b of the gear is made of metal.

[0033] This makes it possible to obtain not only the insulation properties of the gear but also the strength of the gear teeth at high temperatures. With this configuration, even heat-resistant resin that does not have the strength of a normal gear can be used, expanding the range of options. For example, polyphenylene sulfide, polyamideimide, polyimide, polyethylene terephthalate, etc. can also be used.

(Comparative Example) Gear 7 was made of conductive material such as metal, and gears 12 and 13 were made of insulating resin. Unless reliable continuity was established between the fixing roller 1 and the gear 7, a potential difference would occur between the two, resulting in noise. In particular, this problem became noticeable when the durability progressed and an oxide film formed between the roller core metal and the gear 7.

In Examples 1, 2, and 3, a bush and a ball bearing were used to support the fixing roller, but it is also possible to use an insulating sliding bearing.

Furthermore, although the case has been described in which a voltage is applied to the fixing roller in contact with an unfixed toner image, the present invention can also be applied to a case in which a voltage of opposite polarity to that of the toner is applied to the pressure roller.

Furthermore, in addition to the power supply, the means for applying the bias is
A diode or a varistor can also be used.

[0038]

According to the present invention, leakage of voltage from the roller core metal can be prevented, and electrostatic offset can be stably prevented.

[Brief explanation of the drawing]

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

FIG. 2 is an axial cross-sectional view of a drive unit of a fixing roller according to an embodiment of the present invention.

FIG. 3 is a diagram showing a gear arrangement of the embodiment shown in FIG. 2;

FIG. 4 is a cross-sectional view of the hub of the drive gear.

FIG. 5 is an axial cross-sectional view of a drive unit of a fixing roller according to another embodiment of the present invention.

FIG. 6 is a sectional view of a conventional fixing device.

[Explanation of symbols]

1,18 Fixing roller 2,19 Pressure roller 3 Temperature sensing element 4 Entrance guide 5 Separation claw 6 Heater 7 Insulating gear 8 Bearing 9 Side plate 10 Insulating bushing 12,13 Metal gear P Paper leaf T Toner image

Claims (6)

[Claims] Claim 1: Rotates in response to driving force from a driving source,
a roller having a conductive core material for pinching and conveying a supporting material that supports a toner image; a voltage applying means for applying a voltage of the same polarity or opposite polarity to the toner to the core material of the roller;
In the fixing device, the driving part and the supporting part of the core material are each provided with an insulating member having a volume resistance of 1014 Ωcm or more and in contact with the core material. 2. The fixing device according to claim 1, wherein the insulating member of the driving section is a driving gear fitted to the core material. 3. The fixing device according to claim 1, wherein the insulating member of the support portion is a bush provided between the core material and the bearing. 4. The fixing device according to claim 1, wherein the roller has a heating source therein, and the insulating member is made of a heat insulating material. 5. The fixing device according to claim 1, wherein the voltage applying means has a bias power source. 6. The fixing device according to claim 1, wherein the roller is provided on a side in contact with unfixed toner, and a voltage having the same polarity as the toner is applied to the core material.