JPH01315769A - Method and device for fixing image - Google Patents

Abstract

PURPOSE:To restrain adverse effects by triboelectrification and change in the surface potential of a fixing roll, and to prevent the scatter and disturbance of toner by fixing an image while a DC bias of prescribed polarity is applied to a member brought into contact with a supporting material in the fixed position. CONSTITUTION:One-component toner which is negatively electrified by the triboelectrification of a developing device 3 is made to stick to a latent image part without potential on the surface of a drum 1, and a transfer charger 4 injects positive electric charges by discharging high voltage of polarity opposite from the charged toner in order to transfer and electrostatically maintain the toner. The fixing roll 8 covers an Al roll 8b incorporating a heater 8a with a tetrafluoroethylene resin film 8c, a pressure roll 9 has an Si rubber layer 9b around an Al roll 9a. A bias is applied to the roll 8a through a lead wire 14 from a DC power supply 10. A DC bias (-200V) of negative polarity opposite from a toner image supporting material is applied to the roll 8. Here, the surface potential of a fixing roll 8 is maintained at -100V at all times both before and after the supporting body is inserted, so that the scatter and disturbance of the toner does not occur without being affected by the electric charges of the supporting material and unfixed toner.

Description

Detailed Description of the Invention: 1. Field of Industrial Application The present invention relates to a method for fixing an unfixed toner image carried on a paper material or other support material, and particularly relates to a method for fixing an unfixed toner image carried on a paper material or other supporting material, and in particular, a heat roller or other fixing means is The present invention relates to a fixing method and apparatus for fixing an image while bringing it into contact with a toner image.

``Prior art'' Conventionally, transfer chargers and other transfer means have been used to
A laser printer or other printer in which an unfixed toner image transferred from a toner carrier side to a support material side is guided into a fixing means through a conveyance path, the image is fixed by the fixing means, and then the paper is discharged to the outside. Electrophotographic apparatuses are well known, and the fixing means used in this type of apparatus includes a non-contact type fixing means that thermally fixes an unfixed toner image while applying radiant heat from above the toner image in a non-contact manner. A fixing device and a roller pair consisting of a combination of a fixing roller and a pressure roller, for example, are configured to be rotatable in synchronization, and the unfixed toner image on the fixing roller side is pressurized while a support material is inserted between the pair of rollers. It is broadly classified into contact-type fixing devices that fix images while heating, but in recent years contact-type fixing devices have been used because the latter are more advantageous in terms of fixing reliability, high speed, and safety. is often used.

There are two types of contact type fixing devices: one has a built-in heater in the fixing roller and uses heat/pressure to perform thermal fixing, and the other uses the pressure of the fixing roller itself to perform pressure fixing, but in both cases the toner In order to fix the image by applying appropriate pressure to the image, a pressure roller that applies pressure from the back side of the fixing roller and the support material is coated with a fluorine-based or/and silicone-based material on the surface of the aluminum or other metal cylinder. The fixing roller is coated with resin, rubber, etc., and one surface of the fixing roller is coated with silicone oil to prevent toner from fusing.

On the other hand, the support material inserted through the pair of fixing rollers is unfixed toner image support material due to the charge injected into the toner itself as well as the charge having the opposite polarity to the toner applied to the support material via the transfer charger during toner image transfer. It is guided to the opposite side of the fixing roller via the conveyance path with the space between them being held electrostatically.As mentioned above, the pair of fixing rollers is insulating and does not meet the supporting material or toner material. Since they are made of materials with different frictional charging series, the amount of charging of the roller pair changes due to the frictional charging that occurs when the roller pair is inserted into the roller pair, and the toner image and the supporting material are each charged due to the electric field fluctuation. Disturbances occur in the electric charges that are present, and toner scattering and tailing phenomena (a phenomenon in which a toner image is partially disturbed in one direction, such as a tail fin) may occur.

In order to eliminate this drawback, conventional methods have been used to remove static from the fixing roller by bringing a static eliminating brush, metal plate, or other static eliminating member into contact with the surface of the fixing roller, and by placing a charger using high-pressure discharge facing the surface of the fixing roller. However, a method has been adopted in which the fixing roller is neutralized by corona discharge generated from the charger. (Unexamined Japanese Patent Publication No. 58-503 [No. 11 et al.]) [Problems to be Solved by the Invention] However, on the circumferential surface of the fixing roller, there are minute particles attached to the circumferential surface of the peeling side L roller that peels off the support material after fixing. Because a cleaning member for removing toner, a temperature sensor, etc. are attached, it is difficult to install the static eliminator and charger through the installation gap, especially with the miniaturization that has occurred in recent years. As the demands become stronger, the difficulty becomes even more obvious.

However, the frictional electrification of the fixing roller occurs not only between the support material and the toner image, but also between various members that come into contact with the roller circumferential surface, and the effects of these frictional electrifications can be completely eliminated. It is quite difficult to find a position where static electricity can be removed.

In addition, in the configuration using the static eliminating member, since the static eliminating member is brought into contact with the roller circumferential surface to eliminate static, the silicone oil coating applied to the roller circumferential surface is partially scraped off.
This has the disadvantage of causing minute particles of toner to adhere to the circumferential surface of the roller.

On the other hand, the configuration using a charger uses a high voltage, which is not desirable from a safety standpoint, and requires the provision of a special member to remove ozone generated by the high voltage, resulting in an increase in the number of parts and a reduction in size. This would go against the request.

The first problem to be solved by the present invention is to smoothly and reliably prevent miniaturization, safety, layout, and other various obstacles caused by using the above-mentioned static eliminating member and high-pressure discharge means. The object of the present invention is to provide a method and apparatus for fixing unfixed toner images.

A second problem to be solved by the present invention is to provide a method and apparatus for fixing an unfixed toner image that can reliably prevent the disturbance of the toner image that cannot be solved by the static eliminating means.

That is, a static eliminating member or a charger is arranged immediately before the pressure contact position of the pair of fixing rollers, and the support material carrying the unfixed toner image is inserted into the pressure contact position with the surface potential of the fixing roller completely removed yE. Even in this case, since the supporting material itself has a charge of opposite polarity to that of the toner, the surface potential of the fixing roller changes greatly to ee due to the influence of the charge, and as a result, the gap between the toner and the fixing roller A repulsive force or an attractive force is generated instantaneously, which causes toner scattering and trailing.

Therefore, such toner disturbance cannot be solved by the static eliminating means.

"Means for Solving the Problems" In order to achieve the first and second technical problems, in the first invention described in claims 1) to 3), a static eliminating means as described above is provided. Rather, the image fixing method is simply to perform image fixing while applying a DC bias of a predetermined polarity to a member that contacts the support material at least at the fixing position, preferably a fixing roller.

In this case, the polarity of the DC bias is preferably a voltage with a polarity opposite to that of the charge injected into the support material during transfer.

The second invention described in claim 4) relates to an apparatus embodying the invention, in which the fixing roller located on the side facing the unfixed toner image is surrounded by an insulating thin film around a metal cylinder. Formed by a roller body with layers formed,
A DC bias power source having a polarity opposite to that of the charge injected into the support material during transfer is connected to the metal cylinder.

"Operation" According to this technical means, the surface potential of a predetermined polarity corresponding to the DC bias is applied to the entire circumferential surface of the fixing roller, so that the influence of frictional charging can be eliminated by the pressure roller. The present invention is not limited to only the press-contact position, but it is also possible to eliminate the effects of various types of frictional electrification that occur between the roller circumferential surface and various members that come into contact with it.

In addition, since the DC bias has the opposite polarity to the charge held by the support material, when the support material is inserted, it acts in the direction of canceling the charge held by the support material itself, and is influenced by the charge. It can prevent the surface potential of the fixing roller from fluctuating,
Since a constant surface potential can be obtained, the possibility of instantaneous repulsion or attraction between the toner carried on the support material and the fixing roller is eliminated, and toner scattering, trailing, etc. This prevents toner from being disturbed.

The means for applying the DC bias as described above may be simply connected to the DC bias power source via a lead wire or the like to the cylindrical metal tube located at the innermost layer of the fixing roller, for example, as described in claim 0, In addition, since the metal tube is conductive, its connection position can be arbitrary, so there is no need to secure installation space on the circumferential surface of the fixing roller unlike the above-mentioned static eliminator and charger, which results in miniaturization. There are no equivalent restrictions on the requirements, and there is no fear of partially scraping off the silicone oil film applied to the circumferential surface of the roller, and offset phenomena such as minute toner adhesion can be completely prevented.

Also, the DC bias is 200 to 500V as described later.
Since it can sufficiently perform the above action with a relatively low voltage, it is safer than a charger, and there is no need to provide special components to remove ozone generated by high voltage, so it is a component This meets the requirements of reducing the number of points and downsizing.

``Example'' A preferred embodiment of the present invention will be described in detail below by way of example with reference to one drawing. However, unless otherwise specified, the dimensions, materials, shapes, and relative arrangements of the components described in this example are not intended to limit the scope of this invention, but are merely illustrative examples. It's nothing more than that.

FIG. 1 shows the configuration of main parts of an image forming apparatus that employs a so-called reversal development system according to an embodiment of the present invention, in which 1 is a photoreceptor drum, and the surface of the drum 1 is uniformly charged by a charger 2 as is known in the art. After the upper surface is exposed by the optical system 15 to form a potential-free latent image, a toner image is attached to the latent image portion by the developing device 3.

A transfer charger 4 is disposed on the peripheral surface of the drum 1 on the downstream side of the developing device 3, and discharges high voltage from the back side of the support material (paper) guided to the transfer position by the registration rollers 5 at a predetermined timing. , the toner image is transferred to the support material side and held electrostatically, and in this state is led to the fixing rotor pair 7 through the conveyance path 6 . By passing the supporting material through the pair of fixing rollers 7, the unfixed toner image carried on the supporting material is fixed.

Next, the structure of the main parts of the device will be explained in detail. First, the developer contained in the developing device 3 is
A one-component toner that can be negatively charged by frictional charging inside is used, and after being charged, it is attached to a potential-free latent image portion formed on the surface of the drum 1.

The transfer charger 4 is configured to perform high voltage discharge with a polarity opposite to that of the charged toner, inject positive charge into the support material, and transfer and electrostatically hold the charged toner.

The fixing roller pair 7 includes a tetrafluoroethylene resin film 8 on the outer peripheral surface of an aluminum roll 8b containing a heater 8a, as is well known.
A fixing roller 8 on which C is formed, and a pressure roller 3 on which a silicone rubber layer 9b is formed on the outer circumferential surface of an aluminum roll 9a. a peeling claw 11 for peeling off the supporting material after fixing; a silicone oil applying means 12 also serving as a cleaning member for applying silicone oil to the circumferential surface of the roller and removing fine toner adhering to the circumferential surface; A temperature sensor 13 is attached. Further, a DC bias power source IO is connected to the aluminum roll forming the fixing roller 8 via a lead wire 14. Note that FIG. 1 shows a measuring device 15 for measuring the surface potential of the fixing roller 8, which is used when conducting a confirmation experiment to be described later.

Next, a comparative experiment between the conventional example and the present invention will be conducted using such an apparatus.

First, we used plain paper just after opening as the support material, and after the surface of the fixing roller 8 was grounded to eliminate static electricity, we measured the change in the surface at about 7fi when fixing was performed without applying a DC bias. As shown in Figure (a), immediately after the starting end of the support material is inserted, the surface potential of the fixing roller 8 greatly swings toward the positive side due to the influence of the charge injected into the support material, and then the unfixed toner The shadow of the charge! It was confirmed that after the end of the support material was discharged, it changed to the negative electrode side due to frictional charging with the pressure roller 8.

When the image (characters) fixed in this manner was enlarged, it was confirmed that the toner was scattered all around the characters.

Next, when a similar experiment was conducted using humidified paper exposed to high temperature and high humidity of 85% at 35° C., as shown in FIG. 2(b), the surface potential of the fixing roller 8 was Immediately after the starting end is inserted, it swings significantly toward the positive electrode side due to the influence of the charge injected into the support material, but since the support material is humidified and has low insulation, the surface potential decreases thereafter. ,o
After varying around Q toov, it was confirmed that after the support material was discharged, it changed to the negative polarity side due to frictional charging with the pressure roller 9, as described above.

When the image fixed in this manner was enlarged, it was confirmed that a trailing phenomenon had occurred in some of the characters.

On the other hand, when a similar experiment was conducted using the humidifying paper and applying a DC bias (-200V) with a negative polarity opposite to that of the support material, as shown in FIG. 2(C),
The surface potential of the fixing roller 8 is always maintained at -100V regardless of whether it is before or after inserting the support material, and is not affected by the charge injected into the support material or the unfixed toner. It was confirmed that the material was not affected by frictional electrification.

Even when the image fixed in this manner was enlarged, it was confirmed that there was no trailing or toner scattering in some of the characters.

In addition, when a similar experiment was conducted using plain paper immediately after opening under the same conditions as above, the same results as above were obtained.

Next, in order to investigate the effects of changes in DC bias and image characteristics, we used humidified paper to change the DC bias to -250V and -500V.
When a similar experiment was conducted with the voltage lowered to V, the same results as above were obtained; however, when a similar experiment was conducted with the DC bias raised to -5'OV and +200V, , the same tailing phenomenon as when no bias was applied occurred. This is because even if the voltage is low, the effect of the present invention cannot be achieved even if the voltage is a DC/Haas with the opposite polarity to the charge injected into the support material, and similarly, the effect of the present invention cannot be achieved with a voltage of the same polarity. I can understand things.

Note that in this example, the experiment was conducted using the l-component toner.
It is easy to understand that similar effects can be obtained when using a two-component toner.

"Effects of the Invention" As described above, according to the inventions described in claims 1) to 3), the fixing roller is not affected by frictional charging during conventional fixing, but also by the electric charge held in the support material itself, etc. It is possible to completely suppress changes in the surface potential of the toner, and prevent toner scattering, trailing, and other toner disturbances.

Further, according to the invention described in claim 3), in addition to the above-mentioned effects, various obstacles such as miniaturization, safety, layout, etc. caused by using the above-mentioned static eliminating member and high-pressure discharge means are eliminated. At the same time, it is possible to smoothly and reliably prevent toner disturbance.

It has various effects such as

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the main part configuration of an image forming apparatus that adopts a so-called reversal development method according to an embodiment of the present invention, and FIG.
The figures show graphs showing changes in the surface potential of the fixing roller performed using the device. (a) (b) shows a state in which no direct current bias is applied, and (C) shows a state in which a direct current bias is applied. .

Claims (1)

[Claims] 1) Applying pressure or/to the unfixed toner image carried on the support material
and a fixing method in which an image is fixed while a heating member is in contact with the supporting member, the image fixing method being characterized in that image fixing is carried out while applying a direct current bias of a predetermined polarity to the member that contacts the support material at least at the fixing position 2) 3) The image fixing method according to claim 1, wherein the DC bias is a voltage having a polarity opposite to that of the charge injected into the support material during transfer. 4) An image fixing device comprising a pair of fixing rollers through which a support material carrying an unfixed toner image is inserted. The fixing roller located on the side facing the unfixed toner image is formed of a roller body having an insulating thin layer formed around a metal cylinder, and the supporting material is applied to the metal cylinder during transfer. An image fixing device characterized by connecting a DC bias power source with a polarity opposite to that of the charge injected into the image fixing device.