JPH04147176A - Fixation device and pressurizing roller - Google Patents

Abstract

PURPOSE:To preclude electrostatic offsetting due to the frictional electrostatic charging of the pressure roller by incorporating a low-resistance material in a fluororesin layer and a rubber layer and making the volume resistivity of the rubber layer lower than that of a fluororesin tube. CONSTITUTION:The pressure roller 12 is formed by incorporating the low- resistance material in the fluororesin layer and rubber layer and the volume resistivity of the rubber layer 13 is made lower than that of the fluororesin tube 18. Namely, electrostatic charges generated by friction are not accumulated in this tube 18 and flow to the ground through an adhesive and the rubber 13, so the surface potential of the pressure roller does not rise. Consequently, the electrostatic offsetting due to the frictional electrostatic charging of the pressure roller 2 is prevented without decreasing the peeling performance of the surface.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a fixing device used in an image forming apparatus such as a copying machine or an electrophotographic printer and fixing an unfixed image.

[Conventional technology]

Conventionally, in image forming apparatuses using an electrophotographic method or an electrostatic recording method, such as copying machines and printers, in order to fix an unfixed toner image carried on a recording material onto the transfer material, a process is performed as shown in FIG. A fixing device as shown is used.

The fixing device includes a fixing roller l and a pressure roller 2, which are fixing members, and the fixing roller 1 has a resin layer 12 with good heat resistance and mold releasability, such as PFA or PTFE, on a pipe-shaped core metal. The pressure roller 2 has an elastic layer 13 made of silicone rubber or the like having good mold releasability on a core metal 17.

A temperature detector 9 for detecting the surface temperature of the fixing roller 1 is disposed around the fixing roller l, and a heater 10 as a heating element for heating the fixing roller is located at the center of the fixing roller. is installed.

Detecting the surface temperature of the fixing roller 1 with the temperature detector 9,
Based on the results, a control circuit (not shown) controls the heater 10.
The pressure roller 2, which maintains the surface temperature of the fixing roller 1 at a predetermined constant value by intermittent control, is provided with a pressure spring 3 fitted into a pressure arm 6 on a support body 4. The fixing roller 1 is pressed against the fixing roller 1 with a predetermined pressure. Further, an entrance guide 11 for guiding the recording material to the nip portion between the fixing roller 1 and the pressure roller 2 is provided at a recording material inlet portion before the fixing roller 1 and the pressure roller 2 . Furthermore, a separating claw 7 is disposed at the recording material exit portion in contact with the fixing roller 1 .

In the fixing device as described above, when the transfer material is guided to the nip between the fixing roller 1 and the pressure roller 2 by the entrance guide, the fixing roller 1 and the pressure roller 2 record at the nip. By holding the material from above and below and rotating it while applying pressure and heat, the toner image on the recording material is continuously melted while conveying the recording material, and the toner image is fixed on the recording material.

However, when the elastic layer 13 of the pressure roller 2 is charged to the same polarity as the toner due to frictional charging, an electrostatic repulsive force acts on the toner image, and the toner is transferred to the fixing roller 2.
A so-called offset phenomenon occurs in which the material adheres to the surface of the material.

For this reason, the load on the cleaning member 9 becomes heavy (and the cleaning member has to be replaced early. Therefore, by mixing a conductive substance into the pressure roller and greatly reducing its resistance value, the pressure roller's friction Electrostatic charging can be prevented.

[Problem solved by invention]

However, if a large amount of conductive material is mixed into the elastic layer of the pressure roller, the releasability of the elastic layer 13 will be poor, and when used for a long period of time, the surface of the elastic layer 13 will gradually become stained with toner and paper. There was a problem with it getting dirty with powder. For this reason, there are problems in that the transfer material wraps around the pressure roller 2, and when double-sided printing is performed, the toner image on the side that contacts the pressure roller is peeled off.

[Means to solve problems]

The present invention, which solves the above-mentioned problems, provides a pressure roller having a rubber layer provided on a conductive core bar, and a fluororesin layer as a surface release layer provided on the rubber layer.
The fluororesin layer and the rubber layer contain a low-resistance substance, and the rubber layer has a lower volume resistance than the fluororesin tube, and a moving body in contact with the unfixed image. , a pressure roller that is in pressure contact with the moving body and has a conductive core metal, a rubber layer provided on the core metal, and a surface release layer provided on the rubber layer. The fixing device is characterized in that the fluororesin layer and the rubber layer contain a low-resistance substance, and the rubber layer has a lower volume resistivity than the fluororesin layer.

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

<First Embodiment> First, a first embodiment of the present invention will be described using FIG. 1. Note that parts common to the conventional device shown in FIG. 7 are denoted by the same reference numerals, and description thereof will be omitted.

The device of this embodiment has an elastic layer made of rubber 13 made conductive with a surfactant, metal powder, carphone powder, etc., and a conductive PFA tube (for example, GF tube ST manufactured by Gunse Co., Ltd. with carbon dispersed on its surface). This device is different from the conventional device shown in FIG. 7 in that the device 18 is bonded.

As a method for bonding the conductive PFA tube 18, it is preferable to use a conductive adhesive, but a heat shrinking method may also be used.

The conductive PFA tube 18 has a volume resistance value of 107Ωc.
It is preferable to have a diameter of about m. The thickness of this tube is 30~
It is 50 μm.

Normal PFA tube has a volume resistance value of 10'4Ωcm
Because of this high frictional charge, triboelectric charges accumulate, making it impossible to prevent electrostatic offset. However, with the conductive PFA tube used in the present invention, no charge is accumulated due to friction, and the charge flows to the ground through the adhesive and rubber 13, so the surface potential of the pressure roller does not increase and no offset occurs.

The volume resistivity value of the conductive elastic layer 13 used here is 10
3 to 105 Ωcm is preferable. If this resistance value is too high, it will be difficult to reduce the charge on the surface of the pressure roller.

Furthermore, in an electrophotographic device in which an unfixed toner image on a photoreceptor is transferred onto a recording material using a transfer charger, the volume resistance of the elastic layer is 103
When it is smaller than Ωcm, the electric charge on the back side of the recording material flows to the ground, and the force that restrains the toner on the recording material decreases, causing offset. Additionally, as devices become smaller, the distance between the transfer section and the fixing section is becoming shorter than the maximum length of the recording material, but if there is a large amount of charge flowing out from the recording material, transfer defects may occur.For example, 103 ΩCm If you make and use a fixing roller with conductive rubber on its surface, the transfer current will flow out, resulting in poor transfer.

Therefore, the volume resistivity of the elastic layer is preferably 10<3 >Ωcm or more.

Further, if the volume resistivity of the fluororesin such as PFA is smaller than 1079 cm, moldability will be lowered and the mold releasability will also be lowered.

Furthermore, it is difficult to reduce the resistance of resin such as PFA to 107 Ωcm or less because it is difficult to mold it, but it is possible to thin the PFA layer with a resistance of 107 Ωcm or more and make the thick rubber layer below it even lower in resistance than the PFA layer. It has the advantage that the resistance of the pressure roller between the nip and the ground can be controlled by the thickness and composition.

In addition, if the surface resistance value is too large, it will be difficult to prevent charging, so the volume resistance of the fluororesin layer as the surface mold release layer is l
It is preferable that it is 0.011 Ωcm or less.

In fact, when forming a nip with a width of 4 mm and a length of 222 mm, the resistance value of the pressure roller between the ground and the nip should be from 103Ω to 10ILΩ, and the conductive rubber layer and conductive rubber layer should be adjusted to this value. By combining PFA layers, it is possible to create a structure in which transfer omission and offset do not occur.

Note that instead of using the conductive PFA tube 18, PFA or PTFE is used on the surface of the rubber layer 13 of the pressure roller 2.
It is also possible to adhere with a coating and mix metal powder or the like into PFA or PTFE to make it conductive.

However, when coating a fluororesin layer, it is necessary to coat it in powder or liquid form, so the resin usage efficiency is poor, and if it is not fired at a high temperature, PFA, P
Since the strong adhesive strength of TFE cannot be obtained, there is a risk of deteriorating the underlying rubber layer.

For this reason, it is preferable to use a conductive PFA tube as the surface fluororesin layer.

<Second Embodiment> Next, a second embodiment of the present invention will be described using FIG. 2. Note that the same reference numerals are given to the same parts as in the first embodiment, and the explanation thereof will be omitted.

In this embodiment, the core metal 17 of the pressure roller 2 is replaced with a diode 20.
and that the power supply 1 is connected to the core metal of the fixing roller l.
The difference from the first embodiment is that 9 is connected. According to this embodiment, when using negatively charged toner T, as shown in FIG. A diode is connected in this direction. This allows the volume resistance of the conductive rubber layer 13 used in the pressure roller 2 to be less than 10<7 >Ωcm.

Furthermore, as described above, when the recording material P is applied to both the fixing nip and the transfer area as shown in Figure 8, the transfer current flows from the transfer material to the ground via the pressure roller in a high humidity environment. Although there have been cases where the transfer current has flowed out and caused a transfer defect, this problem can also be solved by inserting a diode as in this embodiment, which prevents the transfer current from flowing out and thus also prevents the transfer defect.

Further, at this time, by applying a potential of the same polarity as the toner T to the core metal of the fixing roller 1 by the power source 19, an effect of preventing offset of the negative layer can be obtained.

<Third Embodiment> Next, a third embodiment of the present invention will be described using FIG. 3. Note that the same reference numerals are given to the same parts as in the first embodiment, and the explanation thereof will be omitted.

This embodiment differs from the first embodiment in that the elastic layer is formed of a sponge layer and a rubber layer.

When the elastic layer of the pressure roller is made of a single layer of rubber, the hardness of the pressure roller tends to increase. Therefore, wrinkles are likely to occur in the transfer material, and wrinkles are particularly noticeable when passing through an envelope. Therefore, the pressure roller in this embodiment is
The elastic layer is formed of a sponge layer 15 made of silicone sponge etc. and a rubber layer 16, and a conductive PFA tube 1 is formed on the surface layer.
I rolled 8.

For comparison, a pressure roller with a single elastic layer is used, the thickness of the tube is 50 μm, and the lower elastic layer is JIS-
Outer diameter 3 using 7mm silicone rubber with A hardness of 20 degrees
A pressure roller of 0 mm was formed. As a result, the Asker-C hardness of the finished product was 64 degrees.

On the other hand, using the same conductive PFA tube as in this example, a 6 mm silicone sponge layer (Asker-C hardness of 40 degrees) and a 1 mm conductive silicone rubber layer (JIS-C hardness) were used as elastic layers. A hardness 20 degrees volume resistance value 1
03~10I'Ωcm) with an outer diameter of 30 m.
When a pressure roller of m was made, the hardness of the finished product was 40 degrees on Asker-C hardness. As a result, in order to obtain the nip width of 4 mm necessary for fixing, the former requires a total pressure of 2 mm.
It was necessary to pressurize 0Kg, but in the latter case the total pressure was 10Kg.
Fortunately, the appearance of wrinkles disappeared.

In this example as well, no offset occurs and the mold releasability is also good.

As shown in FIG. 9, the conductive silicone rubber layer 16 is
A wall 24 is formed at both ends (or one end is fine) of the pressure roller 2, and it is easy to attach contact fittings and the like for grounding.

Naturally, if the resistance of the sponge layer can be made to be 10 3 to 10 7 Ωcm, such a wall 24 is not necessary.

In this embodiment, the conductive silicone rubber layer 16 is 1 mm thick, but it goes without saying that the hardness of the pressure roller can be changed by combining it with a sponge layer, and the resistance value can also be changed by changing the thickness.

<Fourth Embodiment> Next, a fourth embodiment of the present invention will be described using FIG. 4. Note that the same reference numerals are given to the same parts as in the third embodiment, and the explanation thereof will be omitted.

In this embodiment, a static elimination brush 21 is provided in the apparatus of the third embodiment.

The reason why the wall 24 was provided on the end face of the pressure roller 2 in the third embodiment is that it was difficult to make the sponge layer conductive.

However, providing walls 24 at the ends often results in incorrect dimensions and shapes.

Therefore, the static electricity may be removed directly from the surface by the static elimination blade 21 without using the end wall 24. In this case, a conductive P is generated as shown by the arrow from the nip portion where the surface of the pressure roller is charged.
Charge flows out through the path of FA tube → conductive rubber layer → conductive PFA tube → static elimination blank 21 → ground.

Current flows easily through the low-resistance conductive rubber layer, which increases the antistatic effect and prevents offset.

Fifth Embodiment> Next, a fifth embodiment of the present invention will be described using FIG. 5. Note that the same reference numerals are given to the same parts as in the third embodiment, and the explanation thereof will be omitted.

This embodiment differs from the third embodiment in that a power supply 19 and a diode 20 are provided. As shown in FIG. 5, when using negatively charged toner, a power source 19 is connected to the core metal 17 of the fixing roller 1 so that the potential is the same as that of the toner. Further, a diode 20 is connected to the core metal 17 of the pressure roller 2 to provide a potential of a different polarity from that of the toner. As a result, the toner is pressed against the transfer material by electrostatic action, and offset can be prevented from occurring.

According to this embodiment, offset can be more reliably prevented.

<Sixth Embodiment> Next, a sixth embodiment of the present invention will be described using FIG. 6. Note that the same reference numerals are given to the same parts as in the fifth embodiment, and the explanation thereof will be omitted.

The device of this embodiment differs from the fifth embodiment in that the static elimination brush and the metal core are grounded via a diode as shown in FIG. Even in the configuration of this embodiment, offset can be reliably prevented.

In addition, among the embodiments described above, in the case where a diode is provided and a positively charged toner is used,
It goes without saying that the diode and power supply are oriented in opposite directions. In addition, in the third to sixth embodiments, the reason why the rubber layer 16 is inserted between the sponge layer 15 and the tube layer 18 is to achieve dimensional accuracy and improve adhesiveness, and if these can be solved, it will be omitted. It is possible.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to prevent electrostatic offset due to frictional charging of the pressure roller without reducing the surface releasability.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view of a fixing device according to an embodiment of the present invention, FIGS. 2 to 6 are vertical cross-sectional views of a fixing device according to another embodiment of the present invention, and FIG. 7 is a vertical cross-sectional view of a conventional fixing device. Figure 8 is a diagram showing the flow of transfer current between transfer and fixing, Figure 9 is a diagram showing the flow of transfer current between transfer and fixing.
The figure is a sectional view of the end of the pressure roller. l... Fixing roller 2... Pressure roller 13.16... Conductive rubber layer 17... Core bar 18... Conductive PFA layer 20... Diode

Claims (4)

[Claims] (1) A rubber layer provided on a conductive core metal, a fluororesin layer as a surface release layer provided on this rubber layer,
A pressure roller having a pressure roller, wherein the fluororesin layer and the rubber layer contain a low-resistance substance, and the rubber layer has a volume resistance lower than that of the fluororesin tube. (2) The volume resistance of the above fluororesin layer is 10^7 to 10^
At 1^1Ωcm, the volume resistivity of the above rubber layer is 10^3 to 10
A pressure roller characterized by a resistance of ＾5Ωcm. (3) A moving body in contact with the unfixed image, a conductive metal core in pressure contact with the moving body, a rubber layer provided on the core metal, and a surface release layer provided on the rubber layer. a pressure roller having a fluororesin layer; the fluororesin layer and the rubber layer contain a low-resistance substance, and the rubber layer has a volume resistivity lower than that of the fluororesin. A fixing device characterized by: (4) The volume resistance of the above fluororesin layer is 10^7 to 10^
At 1^1Ωcm, the volume resistivity of the rubber layer is 10^3~1
The fixing device according to claim 3, characterized in that the resistance is 0^5 Ωcm.