JPH0769650B2 - Fixing device - Google Patents

Description

The present invention is used in the field of fixing technology in an electrophotographic apparatus or an electrostatic recording apparatus, and particularly, an image having an unfixed toner image between a pair of rollers. The present invention relates to a fixing device that sandwiches and conveys a carrier material to perform pressure fixing.

(Prior Art and Problems) Conventionally, this type of fixing device includes a fixing roller and a pressure roller that is driven to rotate by being in pressure contact with the fixing roller.

The fixing roller has a hollow cored bar 9 made of, for example, aluminum or iron, and a layer made of a material having a good releasability such as PTFE, PFA, or silicon rubber. If necessary, a heater such as a halogen lamp is provided in the fixing roller to raise the temperature of the surface of the fixing roller to a temperature suitable for fixing. In many cases, a sensor is used to control the surface temperature of the fixing roller to a set temperature.

Further, the outer peripheral surface of the fixing roller is provided with a cleaner for removing offset toner and paper dust, and a separating claw for preventing the image bearing material from being wound around the fixing roller.

On the other hand, in the pressure roller, an elastic layer having releasability such as silicon rubber is coated on a core metal such as iron or stainless steel. The pressure roller is pressed against the fixing roller by a spring or the like.

Thus, the image bearing material having the unfixed toner image is nipped and conveyed by the fixing roller and the pressure roller under pressure, and the unfixed toner image is fixed by pressure.

However, the above-mentioned conventional device has a problem that the pressure roller is charged to, for example, 2 kV or more due to frictional charging at the time of passing the sheet, and thus the paper is wound around the pressure roller. There is also a problem that unfixed toner is scattered and the line image is blurred by the electric field of the pressure roller, or toner is attached to the surface of the fixing roller to increase offset.

As a countermeasure against the above problem, conventionally, a static elimination brush is brought into contact with a pressure roller to perform static elimination on the ground. However, even with this measure, the potential drops only to about 1 to 2 kV, and the static elimination effect is limited, so it cannot be said to be sufficient, and improvement thereof has been desired.

(Means for Solving Problems) The present invention solves the problems as described above, and suppresses the charging of the pressure roller to wind the paper of the image bearing material, the bleeding of the line image, and the offset of the toner. It is an object of the present invention to provide a fixing device that does not cause such problems.

In order to achieve the above-mentioned object, the present invention provides a fixing device which has a pair of rotating bodies which are in pressure contact with each other, and which sandwiches and conveys a recording material carrying an unfixed toner image at the pressure contact portion to perform fixing. At least one surface layer of the pair is composed of a silicon rubber layer containing a fluorine-based surfactant whose surface potential due to friction with the recording material becomes -1 kV or less.

Embodiment An embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a vertical cross-sectional view showing a schematic configuration of the fixing device of this embodiment. In the figure, 1 is a fixing roller, and the fixing roller 1 is a resin layer having heat resistance and releasability such as PFA or PTFE on the outer surface of a core metal 1A made of aluminum, iron, stainless steel or the like.
1B is formed.

A pressure roller 3 is pressed against the fixing roller 1 by a spring or the like (not shown) and is driven to rotate. In the pressure roller 3, an elastic layer 3B having heat resistance and releasability such as sirconcon rubber and fluororubber is formed on a core metal 3A made of iron, stainless steel or the like. The elastic layer 3B contains a surfactant 3B 'dispersed therein.

Around the fixing roller 1, a thermistor 4 that detects the temperature of the fixing roller 1, a separating claw 5 that separates the paper sheet 14 that is an image bearing material from the fixing roller 1, and a surface of the fixing roller 1 that contacts the fixing roller 1 to clean the surface. Cleaner 6 and paper sheet 14 to fixing roller 1
An inlet guide 11 and the like for guiding between the pressure roller 3 and the pressure roller 3 are provided. On the other hand, the core metal 3B of the pressure roller 3 is in contact with the conduction leaf spring 15 for grounding.

The apparatus of the present embodiment is configured as described above, but since the experiments were performed for each part under various conditions, the description will be given here by showing specific numerical values.

[Experimental Example 1] As the fixing roller 1, an aluminum core metal pipe having a diameter of 25 mm and a wall thickness of 0.8 mm coated with PFA at 25 μm was used.
As the pressure roller, a stainless steel cored bar shaft having a diameter of 10 mm and a silicon rubber having a thickness of 5 mm was used. The hardness of this silicone rubber was 16 ° as a result of measuring the test piece based on JIS-A standard. The fixing roller 1
The heater 2 was controlled so that the surface of the heater was about 180 ° C.

In the conventional example, with the silicon rubber as it is, the surface potential of the pressure roller becomes −2 kV or more due to the friction with the paper, as shown by the broken line in FIG. Therefore, in this experiment, when a fluorinated alkyl ester, which is a fluorine-based surfactant, was dispersed in the silicone rubber in an amount of 0.001 wt% to 0.3 wt%, as shown by the solid line in FIG. Inside pressure roller 3
It was confirmed that the surface potential of sucrose decreased to less than -1 kV.

The solid line and the broken line shown in FIG. 2 are shown with the passage of time while comparing changes in the surface potential of the pressure roller when one sheet is printed by the product of the present invention and the conventional product. As is clear from the figure, the effect of putting a fluorine-based surfactant in the silicone rubber is that the charging of the pressure roller can be suppressed by the friction between the paper and the pressure roller.
Next, it is to accelerate the decay of the surface potential of the pressure roller.

As a result, the wrapping of the sheet around the pressure roller does not occur, and the amount of toner accumulated in the cleaner 6 in contact with the fixing roller 1 is less than 1/10 of the conventional case, and the offset is reduced. It was confirmed that it did. In addition, blurring of the line image no longer occurs on the image.

In the present invention, preferred surfactants include fluorine-based surfactants. The reason is that it is more heat resistant than other surfactants. The surface temperature of the rubber layer of the pressure roller becomes 110 ° C. or higher and the normal surfactant is divided, but if it is a fluorine-based surfactant, the effect can be maintained without being decomposed.

[Experimental Example 2] In the above-mentioned [Experimental Example 1], a fluorinated alkyl ester was used as the fluorine-based surfactant, but perfluoroalkylpolyoxyethylene ethanol, perfluoroalkylcarboxylic acid salt, and perfluoroalkylammonium salt were also used. , Perfluoroalkyl betaine, perfluoroalkyl amine oxide, perfluoroalkyl ethylene oxide adduct, perfluoroalkyl phosphate ester, non-dissociative perfluoroalkyl compound and EFTOP-EF122B (trade name) manufactured by Mitsubishi Metals Co., Ltd. There is.

Also, the dispersion ratio of the fluorine-based surfactant to the silicone rubber was 0.001 wt% in the above-mentioned [Experimental Example 1], but the dispersion ratio between 0.003 wt% and 0.3 wt% is good, and more preferably 0.01 wt% to 0.1 wt% is good.

The lower limit here was determined from the effect of reducing the surface tension, which is the main effect of the surfactant. The reason is that the effect of lowering the surface potential and the effect of accelerating the decay of the surface potential, which are the effects aimed at in the present invention, become more remarkable as the surface energy is lowered. The surface energy is correlated with the surface tension. Therefore, the concentration for obtaining the target effect of the present invention is determined based on FIG. 3 showing the change in surface tension.

For example, it can be said that there was a sufficient static elimination effect even with the effect of 1/2 or more of the saturation level, but for that purpose, it is understood that the concentration of the surfactant of at least about 0.003 wt% or more is sufficient.
Also, if 0.01 wt% or more is mixed, the surface tension can be reduced to almost the limit, and thereby the static elimination effect also reaches the limit. Therefore, it is preferable to add the surfactant at a concentration of 0.003 wt% or more, more preferably 0.01 wt% or more.

On the contrary, if the surface-active agent is added too much, the curing of the rubber will be hindered, so the upper limit of the amount added will be determined from this. From this, it was found that the amount of the surfactant added is preferably 0.3 wt% or less, more preferably 0.1 wt% or less.

In the present experimental example, the earth of the pressure roller is made by contacting the core spring with the leaf spring, but the same brush neutralization as in the conventional case may be performed. Further, a bias voltage having a polarity opposite to that of the triboelectrification potential of the pressure roller may be applied to the brush or the leaf spring to enhance the static elimination effect.

[Experimental Example 3] In the experimental example described above, a fluorine-based surfactant was added to the rubber of the pressure roller, but the surfactant may come off from the rubber after long-term use. For example, the above-mentioned [Experimental Example 1]
When 100,000 or more sheets of A4 size paper were printed, the surfactant tended to escape from the rubber, reducing the offset prevention effect and winding prevention effect.

Therefore, when a fluorine-based surfactant is added to the silicone oil impregnated in the cleaning felt of the cleaner 6 shown in FIG. 1 and supplied to the surface of the pressure roller through the fixing roller, the above tendency is observed. Good results were obtained.

Specifically, a cleaner felt having a density of 0.15 g / cm ³ woven from aromatic polyamideimide fibers has a thickness of 6 mm and a width of
I used it as 10mm and 220mm in total length. In addition, dimethyl silicone oil (KF-96,1 manufactured by Shin-Etsu Silicone Co., Ltd.)
0,000 cs) and 0.0 g in this silicone oil.
A4 size paper 1 by adding 6g of fluorinated alkyl ester
About 0.5 mg per sheet was applied to the fixing roller, and the felt was replaced after 4,000 sheets.

As a result, the surface potential of the pressure roller can be maintained below -1 kV over 200,000 sheets, and the offset prevention effect and paper wrapping prevention effect can be maintained.

In this case, the fluorinated alkyl ester was used as the surfactant, but it may be selected from the various fluorinated surfactants listed in [Experimental Example 2].

Further, the fluorine-based surfactant added to the silicone rubber of the pressure roller and the fluorine-based surfactant added to the silicone oil may be a different combination.

The lower limit of the fluorine-based surfactant added to the silicone oil is preferably 0.003 wt% or more, more preferably 0.01 wt% or more, for the same reason as in the above-mentioned experimental example. Further, the upper limit is determined depending on the type of fluorine-based surfactant, which causes gelation depending on the amount added to the silicone oil. If it was less than 3 wt%, most of the fluorine-based surfactants did not gel the silicone oil. Further, since the fluorine-based surfactant is expensive, it is better to use less. From the viewpoint of the effect, a sufficient effect can be obtained even at 1 wt%, so that for practical use, it is preferably 0.003 wt% to 3 wt%, more preferably 0.01 wt% to 1 wt%.

Alternatively, a felt impregnated with silicon oil containing a fluorine-based surfactant may be directly brought into contact with the surface of the pressure roller 3. This allows the fluorine-based surfactant to be efficiently supplied to the surface of the pressure roller.

In the case of the above including this experimental example, when the pressure roller has a multi-layered rubber layer, a fluorine-based surfactant may be added only to the outermost rubber layer. As a result, the fluorine-based surfactant can be used in a small amount, and the desired performance can be obtained at low cost.

[Experimental Example 4] In the above experimental example, since the temperature of the fixing roller 1 was as high as about 180 ° C., a fluorine-based surfactant was used. However, by lowering the melting point of the toner itself,
Since the fixing can be performed at about 140 ° C., the surface temperature of the pressure roller 3 is only about 90 ° C. in this case. Therefore, the decomposition temperature of the surfactant added to the pressure roller may be 100 ° C. or higher, and a surfactant having low heat resistance other than fluorine can be used.

(Advantages of the Invention) As described above, the present invention provides a fixing device that has a pair of rotating bodies that are in pressure contact with each other, and that sandwiches and conveys a recording material carrying an unfixed toner image at the pressure contact portion to perform fixing. Since at least one surface layer of the body pair is a silicone rubber layer containing a fluorine-based surfactant whose surface potential due to friction with the recording material becomes -1 kV or less, heat resistance is improved by the fluorine-based surfactant. In addition to ensuring the elasticity, the elasticity is not impaired by the silicone rubber layer, and as a result, the surface potential of the pressure roller is lowered, and the potential decay is accelerated so that paper wrapping around the pressure roller, offset, and line image The effect of preventing the phenomenon of bleeding can be obtained.
Get the effect.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing an apparatus according to an embodiment of the present invention, FIG. 2 is a view showing changes in surface potential of a pressure roller in an embodiment according to FIG. 1, and FIG. 3 is a surfactant. It is a figure which shows the fall of the surface tension by putting in. 1,3 ... Roller (1 ... Fixing roller, 3 ... Pressure roller) 2 ... Heating means (heater) 8 ... Surface layer (elastic body) 3B '... Surfactant

Claims (1)

[Claims] 1. A fixing device comprising a pair of rotating bodies which are in pressure contact with each other, and at which the recording material carrying an unfixed toner image is sandwiched and conveyed at the pressure contact portion to perform fixing, at least one surface layer of the rotating body pair. Is a silicone rubber layer containing a fluorine-based surfactant whose surface potential due to friction with a recording material is -1 kV or less.