JPS638470B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a fixing method for a copying machine, and more particularly to a fixing method for a copying machine in which a toner image is fixed by contact heat on the surface of a support carrying the toner image. Conventionally, a method is known in which a toner image is formed on a support by electrophotography or the like and the toner image is fixed on the surface of the support. The toner used for this is generally electrodetectable fine particles of about 0.1 to 50μ, which are a mixture of thermoplastic resin and a coloring agent such as carbon black.
Toner images are formed on the support by various development methods. This toner image is permanently fixed on the support by being melted or dissolved by heat, pressure, solvent vapor, or the like. In fixing such toner images, fixing using solvent vapor causes the solvent vapor to scatter, causing odor and hygiene problems; fixing using pressure has worse fixing properties than other fixing methods; Since there is a problem in that a complicated and expensive pressure-sensitive toner must be used, fixing by heat, so-called heat fixing, is generally widely used. That is, in the so-called heat fixing method, fixing is performed by applying a constant pressure between a pair of rolls, at least one of which is heated, and passing the toner image through a support having an unfixed toner image. FIG. 1 shows an outline of a conventional general contact heat fixing method, in which 1 is a heating roll, 4 is a pressure roll, and a toner image 16 is supported at the nip between the heating roll 1 and the pressure roll 4. By passing through the support 15, the toner is softened by heat transfer from the surface of the heating roll 2, the toners coalesce together, penetrate into the fibers of the support 15, and are then cooled to solidify. It becomes a permanently fixed image. The heating roll 1 has an Al core 3 coated with tetrafluoroethylene (trade name: Teflon) or HTV.
It is coated with a fluorine-based or silicone-based resin or rubber 2 such as silicone rubber or RTV silicone rubber, and is equipped with an infrared Kortz lamp 12 inside, a sensor 13 for temperature control, and the support 15. A peeling claw 14 for peeling off the heating roll 1 is provided. The pressure roll 4 is constructed by coating a metal core 6 with a fluorine-based or silicone-based rubber or resin 5, such as fluorine-based rubber or silicone rubber. In the above-mentioned contact heat fixing method, since the heating surface of the heating roll 1 comes into direct contact with the toner image, a phenomenon occurs in which sticky substances containing toner adhere to the heating roll surface (hereinafter referred to as offset). In order to prevent this, a release agent 10 such as silicone oil, for example dimethyl silicone oil, is applied to the surface of the heating roll 1.
Alternatively, the coating may be applied using a roll or the like, and the thickness may be regulated using a blade 8 to ensure uniform supply at all times. However, even though the mold release agent 10 such as silicone oil is supplied to the heating surface of the heating roll 1 as described above, fine particle offset occurs, although it is not obvious to the naked eye. The fine particle offset is determined by the wick 7 and the blade 8.
This gradually contaminates the oil supply means, eventually making it impossible to supply uniform oil, and as a result, the offset increases rapidly, staining the copy, or appearing as oil stains on the copy. Conventionally, attempts have been made to overcome this fine particle offset by using various cleaning members, such as the cleaning blade 9 and cleaning roll 11 shown in FIG. Although good initially, it is not stable over a long period of time, and has the disadvantage that the cleaning member must be cleaned or replaced every several thousand to tens of thousands of copies. On the other hand, the amount of offset generated in a fixing method in which toner images are fixed by contact heating varies depending on many parameters such as toner resin, roll material, roll surface temperature, pressure in the nip, oil supply amount, and nip passage time. However, according to the experiments and research conducted by the present inventors, the amount of offset is determined not only by the above-mentioned parameters but also by the charge of the toner image 16 on the pressure roll 4 and the support 15. It turned out that it was having an impact. That is, according to experiments conducted by the present inventors, when the support 15 carrying the toner image 16 is passed through the nip area between the heating roll 1 and the pressure roll 4, which are coated with Teflon or silicone rubber as described above, friction occurs. Due to the charging, negative (-) charges are generated on the surfaces of both rolls 1 and 4 coated with Teflon or silicone rubber, and positive (+) charges are generated on the support 15. In the heating roll 1, the voltage is from minus several hundred volts to minus
1000 volts, the pressure roll 4 has a voltage of several thousand volts to several tens of thousands of volts, and the voltage of the support 15 has reached several hundred volts to several thousand volts. Among these surface potentials, the pressure roll 4 has a negative several thousand volts to a negative tens of thousands of volts, and the surface potential of the heating roll 1 has a negative several hundred volts to a negative voltage.
The toner image 16 transferred to the support 15
The negative (-) charge on the pressure roll 4 is greater than the electrostatic repulsive force (repulsion) with respect to the negative (-) charge on the heating roll 1.
Because the electrostatic repulsive force (repulsion) against the electric charge is extremely large, the toner is pushed toward the heating roll 1, and as a result, toner and the like adhere to the heating roll 1, a so-called offset phenomenon. It was found that this occurs. The present invention has been devised in view of the above circumstances, and reduces the friction between the toner image 16 and the pressure roll 4 in contact with the back surface of the support 15 by lowering the surface potential of the pressure roll 4. The purpose of this invention is to reduce electrostatic repulsion caused by charging, reduce offset, and improve fixing performance. The present invention will be explained in detail below based on the embodiment shown in FIG. In this embodiment, the same reference numerals as in FIG. 1 indicate the same members. Example 1 In FIG. 2, the heating roll 1 has a diameter of 50 mm,
Al core 3 with length 380mm and wall thickness 10mm, Teflon 2
is coated with a thickness of 50μ, a tubular infrared Cortz lamp 12 with a rating of 100V and 900W is used as the heating element, and the pressure roll 4 has a diameter of 50mm and a length of
It is a 370 mm elastic roll having a steel core 6 coated with KE-550U silicone rubber (manufactured by Shin-Etsu Chemical) 5 with a thickness of 12 mm. Oil 10 for offset prevention is 100CS.
Using KE-96 silicone oil (manufactured by Shin-Etsu Chemical),
The material is sucked into the wool felt wick 7 by capillary action and is continuously supplied to the heating roll 1. Then, the surface temperature of the heating roll 1 was controlled to be 165° C., and the toner image 16 formed on the support 15 using M-2 paper (manufactured by Fuji Xerox) with 4000 toner (manufactured by Fuji Xerox) was spun at a speed of 165°C.
It was fixed by passing through the nip at 200 mm/sec. The nip width at this time was 10 mm. At this time, the surface potential of the pressure roll 4 was several thousand to tens of thousands of minus volts. In order to change the surface potential of the pressure roll 4 to positive, a high voltage of 6 KV DC was applied to the corotron 17 placed opposite the outer peripheral surface of the pressure roll 4. At this time, the surface potential of the pressure roll 4 changed from negative to positive, and was charged to a positive number of KV. In this way, the surface potential of the pressure roll 4 is lowered (discharged) by applying a positive high voltage to the corotron 17, and the surface potential of the pressure roll 4 is left as is without lowering the surface potential without applying a high voltage. In order to compare the amount of offset to the heating roll 1 with the case of , a gauze made of cotton was pressed onto the surface of the heating roll 1 immediately after the nip exit in an area of 2 cm square for 50 copies evenly with a load of 3 kg. When the degree of contamination was observed, it was found that the contamination due to offset when the surface potential of the pressure roll 4 was lowered (discharged) was about 20% of that when the surface potential was not lowered, and a remarkable effect was observed. In the above embodiment, a case was shown in which the corotron 17 was used to lower the surface potential (discharge) of the pressure roll 4, but the present invention is not limited to this, and a discharging cloth or the like may be used. Table 1 shows the experimental results when implementing the present invention.

[Table] As is clear from Table 1 above, it is clear that according to the present invention, the offset is significantly reduced. As mentioned above, according to the present invention, the pressure roll 4
By lowering the surface potential of the support 1
Charge of toner image transferred to 5 and pressure roll 4
It is possible to reduce the electrostatic repulsion force (repulsive force) with the electric charge of Reducing the electrostatic repulsion between the charge on the toner image and the charge on the pressure roll 4 results in the reduction of the electrostatic repulsion between the charge on the heating roll 1 and the charge on the toner image. This electrostatic repulsion makes it easier for the molten toner of the toner image to wet the fibers of the support 4, contributing to improved fixing properties.

[Brief explanation of the drawing]

Figure 1 is a schematic explanatory diagram of the conventional fixing method;
The figure is a schematic explanatory diagram of the fixing method according to the present invention. 1 is a heating roll, 4 is a pressure roll, 15 is a support, and 16 is a toner image.

Claims (1)

[Claims] 1. A support 15 that supports a toner image 16 to be fixed is a heating roll 1 and a pressure roll 4 coated with silicone-based or fluorine-based rubber or resin.
In a fixing method for a copying machine in which a toner image 16 is fixed on a support 15 by passing between A fixing method for a copying machine, characterized in that the surface potential of the pressure roll 4 is lowered so as to reduce the electrostatic repulsion generated.