JPH03284781A - Fixing device - Google Patents

Abstract

PURPOSE:To obtain a carrier which maintains high abrasion resistance and has a surface where electrified charge is not retained by allowing the carrier to have a surface layer consisting of fluororesin film containing low resistance material. CONSTITUTION:The surface of a roll 7 is constituted of the fluororesin film or tube 1 in which the low resistance material or whiskers 14 made of conductive material are added, and a core bar 3 being a layer under the fluororesin tube 1 is electrically grounded. By adding the low resistance material or the whiskers 14 made of conductive material also in this intermediate layer, the electrification or charge-up by the contact or friction with an image carrier is not caused in course of operation and electrostatic attracting force between positive toner 9 and a recording material 8 is not impaired, so that the offset of the toner is surely prevented without impairing the characteristic of the fluororesin tube 1. This effect makes the state of a device uniform and stable because of no pinhole.

Description

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

[Prior Art] Various fixing methods have been used in conventional image forming apparatuses such as electrophotographic copying machines, but currently the thermal fixing method is the mainstream. Among these, a heat roll fixing method using a pair of rollers is widely used because of its high thermal efficiency.

An example of this heat roll fixing device is shown in FIG. 7 is a fixing roller, which has a heat generation source such as a halogen heater 4 inside, and is paired with a pressure roller 6 whose surface layer is made of an elastic material 5 such as rubber, with an appropriate nip; The receiver is rotated by driving from the main body by a driving means (not shown).

The unfixed image is fixed onto the recording paper by heat and pressure when the recording paper passes between the pair of rollers. During operation, the surface of the roller 7 is maintained at a substantially constant temperature by a thermistor 13.

Generally, a heat fixing roller is coated with a resin having good mold releasability, such as a fluororesin, in order to prevent toner from adhering to the roller.

Conventionally, such rollers have been manufactured by using a fluororesin powder coating or a dispersion coating and firing the coating.

However, such a manufacturing method tends to have low coating efficiency and high costs for boat fishing.

Further, when applying and firing fluororesin particles in this manner, many pinholes are generated.

For this reason, when applying a mold release liquid such as silicone oil, the silicone oil enters the pinhole, and the intruding oil expands due to the fixing heat (150-200°C), causing problems such as blistering of the film. be.

As a method to solve the above-mentioned problems, for example, a method was devised in which a heat-shrinkable fluororesin tube is heat-fused to a cylindrical core made of metal, as described in Japanese Patent Application Laid-open No. 198118/1983. has been done.

[Problems to be Solved by the Invention] However, when a fluororesin film is used as the release layer, the surface is triboelectrically charged, and this charged potential sometimes causes electrostatic offset.

[Means for Solving the Problems] The present invention, which solves the above-mentioned problems, provides a fixing device having a conveying body that nip-conveys and fixes a support material supporting an unfixed image, wherein the conveying body contains a low-resistance material. It is characterized by having a surface layer made of a fluororesin film.

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

FIG. 1 is a sectional view of a fixing device embodying the present invention. In the figure, an unfixed image formed by a powder magnetic toner 9 is conveyed while being sandwiched between a fixing roller having a heat generating source 4 such as a halogen heater inside and a pressure roller 6 in contact with the fixing roller with an appropriate niP. It is fixed on the recording material 8 when it is printed.

The fixing roller 7 has an electrically grounded core metal 3 covered with a PFA tube to which conductive titanium oxide whiskers are added as a surface layer via an epoxy adhesive layer 2 in which carbon powder is dispersed.

Next, regarding the case where the fixing device fixes an unfixed image formed with the above-mentioned positively charged toner (hereinafter referred to as positive toner), a pseudo-enlarged view of the nip section (Fig. 4) and a conventional example nip section are shown. This will be explained with reference to a pseudo-enlarged diagram (FIG. 6).

Conventionally, as shown in FIG. 6, the surface layer of a heat fixing roller, etc. tends to be negatively charged due to the characteristics of its material (fluororesin such as PFA and PTFE), and when trying to fix the positive toner 9, the surface layer tends to be negatively charged. An electrostatic attraction force greater than the attraction force between the recording material 8 and the positive toner 9 acts between the charged resin layer 12 and the positive toner 9, resulting in offset development in which the toner on the recording material is transferred to the fixing roller side. This is a particularly serious problem when using positive toner, which often appears significantly. In recent years, research and development has been actively conducted to reduce the volume resistivity of the surface layer in painting/baking type surface layer formation in order to weaken the attractive force between the resin layer and toner. The offset prevention effect is insufficient.

As shown in FIG. 4, in the present invention, the surface layer is composed of a fluororesin film or tube 1 to which whiskers of a low-resistance material or a conductive material are added, and the core bar, which is the lower layer, is electrically connected. By grounding the intermediate layer and adding a low-resistance material to these intermediate layers, there will be no charge-up due to contact or friction with the image carrier during operation, and the positive toner 9
Since the electrostatic attraction between the recording material 8 and the recording material 8 is not impaired, it is possible to reliably prevent toner offset without damaging the characteristics of the fluororesin tube (film). Furthermore, since there is no pinhole, this effect can be obtained evenly and stably.

According to experiments by the present inventors, when titanium oxide whiskers are used, whiskers of about 10μ to 30μ can be reduced to 0.5μ to 30μ.
When dispersed at about 15wt%, the volume resistance becomes 1o1.
It decreases to about 0 [Ω·cm]. At this time, mold releasability and durability were not impaired at all.

Note that in this embodiment, conductive whiskers are used as the low resistance material.

This is because conductive whiskers can reduce the volume resistance of the tube by adding a small amount, whereas when carbon powder is used, it is necessary to add a powder of about 10 to 20 μ to make the volume resistance about 10 [Ω・cm]. must be dispersed by about 30 to 40%, resulting in a decrease in surface releasability.

Moreover, wear resistance will also be impaired.

(See FIGS. 2 and 3) [Example 2] Next, an example in which toner having a negative charge (hereinafter referred to as negative toner) is fixed will be described with reference to FIGS. 5 and 7.

Conventionally, when fixing negative toner with a fixing roller using a fluororesin tube, as shown in FIG.
2 is negatively charged, and an electrostatic repulsive force is generated between the toner 2 and the negative toner 9. However, the resin layer made of a fluororesin tube is extremely likely to be negatively charged, and the full force of the reaction e between the resin layer 12 and the negative toner 9 (0 in FIG. 7) is due to various attractive forces between the negative toner 9 and the recording material 8. This overcomes the adsorption force, and as a result, the unfixed toner image on the recording material is blown away by electrostatic repulsion, causing large disturbances on the image.

In this example, as shown in Fig. 5, a PFA tube with titanium oxide whiskers added and dispersed therein is similarly coated on an electrically grounded core bar via an epoxy primer containing carbon. There is no charging or charge-up due to contact friction with the image bearing member or pressure roller inside, and there is almost no electrostatic repulsion between it and the negative toner 9, so there is no disturbance in the image.
Offset can be reliably prevented electrostatically, and of course the advantageous characteristics of the fluororesin tube are not impaired.

[Example 3] FIG. 8 is a cross-sectional view of another example of the fixing roller according to the present invention.

This fixing roller is made of an elastic layer 11 in which alumina (aluminum oxide) is added and dispersed, and a titanium oxide whisker according to the present invention, which is placed on an electrically grounded core metal 3 via a carbon-dispersed epoxy-based brusher 2. Additive PFA
It is composed of a tube 1. At first glance, it looks similar to a so-called rubber roller, but thanks to the present invention, low-resistance and conductive materials are added to all materials, from the electrically grounded core metal to the fluororesin on the surface, making it easy to operate. There is no charge-up due to contact with the image carrier or pressure roller inside, and the rubber roller retains its properties as it is, and a fluororesin tube with excellent mold releasability is used on the surface. Furthermore, electrostatic offset can be reliably prevented without affecting the electrostatic attraction between the developer 9 and the transfer material 8.

In the above-mentioned examples, PFA was cited as the fluororesin, but it may also be PTFE, FEP, etc., and the low-resistance material and conductive material were mainly explained using titanium oxide whiskers, or the low-resistance conductive material Whiskers made of fluorine-containing materials have a similar effect, and the amount of whiskers added can be adjusted to avoid any problems that may occur during molding, without impairing the beneficial properties of fluororesin, such as mold releasability, abrasion resistance, and durability. Unless otherwise specified, there is no particular limitation. Further, the shape of the surface layer fluororesin is not limited to a tube shape, but may be a film shape as shown in FIGS. 10 and 11.

Further, in the embodiments, the fluororesin layer and the like were provided via a brimer, but the inner surface of the fluororesin may be etched and provided directly on the core bar.

Regarding the amount added, whether it is powder or whiskers, the limit is approximately 40 to 50%, and if this is exceeded, the advantages of the fluororesin itself, such as its shape, will be lost. Therefore, compared to powder, fewer whiskers are added! In addition to being able to lower the resistance, it is also possible to achieve a lower resistance that cannot be achieved with powder.

Further, in this embodiment, a whisker which is a single crystal of titanium oxide whisker was explained as an example, but in the present invention, a non-crystalline acicular fiber such as a glass-like fiber may be used.

[Effects of the Invention] As explained above, according to the present invention, while maintaining high abrasion resistance and durability, electrostatic charges are not retained on the surface. Since no special means is required, the device can be simplified. And it is stable and preventable under actual operating conditions. In addition, unlike the case where chemicals are added to the mold release agent, it is extremely safe, and no matter what operating conditions (i.e., the operating condition of the main unit, such as at the beginning of operation or after 100,000 sheets have been used), its effect is completely absent. Yes, it will be damaged. Furthermore, unlike the painted type, there are no pinholes, so the effect can be made uniform and stable.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a fixing device according to the present invention, FIG. 2 is a pseudo-enlarged view of a fluororesin layer to which whiskers of low resistance and conductive materials are added according to the present invention, and FIG. 3 is a conventional Figs. 4 and 5 are pseudo-enlarged views of fluororesin to which powders of low-resistance materials and conductive materials have been added. Figs. Fig. 7 is a close-up enlarged view of the nip section in the conventional case, Fig. 8 is a cross-sectional view of a rubber roller type fixing roller in which the present invention is implemented, and Fig. 9 is a cross-sectional view showing the basic configuration of a conventional heat roll fixing roller. 10 and N11 are sectional views of a fixing device according to another embodiment of the present invention. 1...Fluororesin tube/film added with whiskers of conductive material 2...Brimer layer (adhesive layer) added with conductive material 3...Core 4...Heating source <halogen heater) 5 ...Elastic body 6...Pressure roller 7...Fixing roller 8...Transfer material 9...Developer 10...Heating element 11...Alumina-added/dispersed elastic layer 12...・Conventional resin layer 13 ・Thermistor 14 ・Whiskers 15 made of low resistance material/conductive material
・・Low resistance material/conductive material powder Figure 5＼2 Measure 1 step

Claims (4)

[Claims] (1) A fixing device having a conveying body that pinches and conveys a support material supporting an unfixed image for fixing, wherein the conveying body has a surface layer made of a fluororesin film containing a low resistance material. Device. (2) The fixing device according to claim 1, wherein the low-resistance material is a conductive acicular fiber. (3) The fixing device according to claim 1 or 2, wherein the conveying body is electrically grounded. (4) The conveying body has an electrically grounded core bar and an intermediate layer provided between the core bar and the film and containing a low resistance material.
The fixing device according to items 1 to 3.