JPH049888A - Fusing device - Google Patents

Abstract

PURPOSE:To prevent offset caused by an electrostatic factor by connecting a 1st rectifying element between a 1st member and a 2nd member and grounding the 1st member through a 2nd rectifying element so that it may hold the charge of the same polarity as the electrostatically charged polarity of a developer image. CONSTITUTION:The 1st rectifying element 3 is connected between the core bar of a pressure roller 2 and the hollow cylinder of a fixing roller 1 and the charge of the reverse polarity to the charged polarity of an unfixed developer image is held in the roller 2. The roller 1 is grounded in a direction where the charge of the same polarity as the charged polarity of a toner image is held in the roller 1 through the 2nd rectifying element 4. Therefore, electrostatic repulsive force is generated on a side where the unfixed developer image of a recording material P is carried, and the transfer charge is held on the back surface. When the recording material P is interposed ad carried in the fixing device, the electrostatic holding force to the develop image on the recording material 2 is maintained and the offset is prevented.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a fixing device for fixing an unfixed developer image to a recording material in a recording device such as a copying machine or printer using electrophotography. It is.

[Prior Art] Conventionally, a fixing means in an image forming apparatus using electrophotographic technology includes a fixing roller having an internal heating source such as a halogen heater, and an elastic body such as silicone rubber that rotates in pressure contact with the fixing roller. A roller fixing device that includes a pressure roller on its surface is common. This roller fixing device is superior to other fixing methods in terms of stable conveyance of the recording material and fire prevention safety in the event of heater runaway, etc., and has been widely put into practical use.

[Problem to be solved by the invention] However, in the above conventional roller fixing device,
Since the developer image on the photoreceptor is electrostatically transferred and retained on the recording material (hereinafter referred to as "unfixed toner image"), or the unfixed toner image on the recording material is in direct contact with the roller surface. There was a problem in that the particles were transferred to the surface of the roller, causing a so-called offset phenomenon.

- Offsets that occur in the above-mentioned fixing device during boat fishing can be broadly classified into those caused by temperature and those caused by static electricity. The former includes so-called low-temperature offset, which occurs when the toner temperature in the fixing device is too low and is not fixed, and conversely, high-temperature offset, which occurs when the toner temperature is too high and the toner melts into liquid. This can be prevented by determining the characteristics of the developer, the recording material conveyance speed, and the pressure applied to the roller, and then appropriately determining the temperature of the fixing roller using a temperature control means such as a thermistor.

On the other hand, regarding the latter offset due to electrostatic factors, the charged toner on the recording material is electrostatically transferred to the fixing roller, but this phenomenon largely depends on the type of recording material, environment, etc. It has been difficult to prevent the above phenomenon by controlling the electric field between the fixing roller and the pressure roller. Therefore, cleaning means such as a field pad or a blade is brought into contact with the fixing roller, and the problem caused by offset, such as staining of the recording material due to retransfer of offset toner, or wrapping of the recording material caused by offset toner staining on the roller, is avoided. It was designed to prevent jams, etc.

However, the above-mentioned cleaning means requires replacement work by a user or the like, and there are problems in terms of maintenance, cost, and miniaturization of the device.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and provide a fixing device that prevents offset caused by electrostatic factors without using cleaning means.

[Means for Solving the Problems] According to the present invention, the above object is provided with a fixing means for fixing an unfixed developer image on a recording material, and the fixing means fixes the unfixed developer image on the recording material as described in 1. A fixing device having a first member in contact with the image bearing surface, and a second member disposed in opposing pressure contact with the first member and in contact with the back surface of the unfixed developer image bearing surface, A first rectifying element is connected between the first member and the second member in a direction such that the second member retains a charge having a polarity opposite to that of the developer image; The first member is grounded via a second rectifying element so as to hold a charge having the same polarity as the charge polarity of the developer image.

This is achieved by

[Function] According to the present invention, there is a first member between the first member that contacts the surface of the recording material carrying the unfixed developer image and the second member that contacts the back surface of the recording material. A rectifying element is connected, and the direction of the rectifying element is such that charges having a polarity opposite to that of the developer image are held in the second member. Therefore, leakage of the transfer charge applied to the back surface is suppressed.

Further, the voltage held in the second member is suppressed to about the breakdown voltage of the first rectifying element to prevent charging. Further, when an electric charge having the same polarity as the charged polarity of the developer image is generated in the fixing means due to friction between the second member and the back surface of the recording material, the rectifying function of the first rectifying element causes the above-mentioned Charges of the same polarity flow into the first member. The charges of the same polarity are held in the first member without leaking due to the rectifying function of the second rectifying element connected to the first member.

In this way, an electrostatic repulsive force is generated on the side of the recording material that supports the unfixed developer image, and since the transferred charge is retained on the back side, electrostatic offset is prevented.

[Embodiments] Hereinafter, first to fourth embodiments of the present invention will be described in detail using FIGS. 1 to 6 of the accompanying drawings.

<First Embodiment> First, a first embodiment of the present invention will be described using FIGS. 1 to 3.

In Fig. wJ1, the fixing roller 1, which is the first member of the fixing means, has P'r on the outer peripheral surface of a hollow cylinder such as aluminum or iron.
It is coated with coach ink or Tutu material with good mold releasability such as FE, PFA or silicone rubber, and has a heating source such as a Herokane heater inside, and its surface is heated by a temperature control means (not shown). Controlled at a constant temperature.

The pressure roller 2, which is the second member of the front means arranged to rotate under pressure from the fixing roller l, is formed of a layer of silicone rubber or fluorine rubber on a core metal such as iron or stainless steel. It is something.

A first rectifying element 3 (for example, tie auto) is connected between the core bar of the pressure roller 2 and the hollow cylinder of the fixing roller 1, and the unfixed developer image (hereinafter, unfixed toner image) The pressure roller 2 holds an electric charge having a polarity opposite to that of the image. In addition, the fixing roller l
, the second rectifying element 4 is grounded in such a direction as to hold the charge having the same polarity as the charge polarity of the toner image on the fixing roller l. Since the apparatus of this embodiment uses negatively charged toner, the pressure roller holds a positive charge, and the fixing roller holds a negative charge. Further, the recording material P sandwiched and conveyed by the fixing roller 1 and the pressure roller 2 carries a toner image formed on the surface of a photosensitive drum 5, which is a latent image carrier, by a known electrophotographic process. The image is transferred by transfer means 6
As a result, a charge having a polarity opposite to the toner charging polarity (a positive charge in this embodiment) is applied to the back surface of the recording material P, and the toner is electrostatically transferred and retained on the recording material. The recording material is guided to an abutting nip formed by a fixing roller 1 and a pressure roller 2, and is heated and fixed.

According to experiments, the above-mentioned fixing offset due to electrostatic factors is caused by the transfer charge having the opposite polarity to the toner charge polarity given to the back side of the recording material P to electrostatically hold the developer on the recording material P, It was found that the main cause was leakage through the pressure roller 2 that came into contact with the back surface of the recording material P within the apparatus F.

In particular, the occurrence of the electrostatic offset and soto mentioned above is less
As shown in the figure, this is noticeable in the OF(P transparent film), which has a sandwich structure in which both sides of an insulating Mylar sheet, which is widely used these days, is coated with a medium-resistance material having a surface resistance of about 109 to 1012 Ω.

In such a leaf P film, during the separation process from the photosensitive drum, the reverse charge -Qo that depends on the transfer charge amount +Q applied in the transfer process is 0) + 11 due to peeling discharge on the recording surface of the film (the side with the toner image) granted to. As a result of experiments, Qo was about 50 to 90% of the transferred charge Q. Therefore, if there is a leakage of the back transfer charge through the pressure roller, the peeling charge on the recording surface will remain on the IP film, so the holding force of the toner image due to electrostatic force will rapidly decrease, resulting in an offset. It is thought that this will be more likely to occur.

Table 1 shows how 0f(P sheet) is applied to pressure rollers of various resistances using 3M's 0)IP film (surface resistance: 1012Ω) in a conventional heat roller fixing device in which the pressure roller core metal is grounded. It shows the work current during paper passing and the offset evaluation at that time.

Regarding the pressure roller resistance, press it against an uncoated stainless steel roller so as to form a nip of about 2 to 3 layers.
The resistance between the pressure roller core metal and the stainless steel roller was measured using a high resistance needle.

(Leaving space below) Table 1 , an offset also occurs. On the contrary, 1
Even if the resistance is 0.013Ω or more, there is no transfer charge leakage or an offset occurs. Even when the pressure roller resistance was 1012Ω or less, no offset occurred when the pressure roller was floated. However, using a low-resistance pressure roller to float the core metal is effective for preventing electrostatic offset, but when printing continuously or in a low-humidity environment, There is a possibility of leakage to surrounding conductors due to charge-up of the pressure roller, and there is a risk that the leakage noise may cause mechanical or electrical malfunction.

In addition, in roller fixing devices for boat fishing, the pressure roller or fixing roller is pressed against the pressure roller or the fixing roller with a force of several kilograms to several tens of kilograms. They may be charged with the same polarity, which is also a factor in electrostatic offset. Therefore, in order to prevent electrostatic offset, the following requirements are required for the device configuration.

(1) To prevent leakage of transferred charges through the pressure roller.

(2) Prevent charge-up of the pressure roller.

(3) Erasing charges of opposite polarity to the transfer charges generated by friction between the pressure roller and the fixing roller and the recording material.

In the present invention, as shown in FIG. 1, a rectifying element such as a diode is connected to the pressure roller 2 in a direction that holds a charge (positive charge) opposite in polarity to the toner image charging polarity (negative charge). , 1 (],), it is possible to prevent leakage of transferred charges (positive charges) to GND (ground terminal) by the rectifying function of the tie auto. Furthermore, when positive charges flow into the pressure roller under the influence of the fixing roller, the electric field that holds the toner image on the recording material 1 is strengthened, further increasing the offset prevention effect.

FIG. 3 shows the voltage and current characteristic curves of the diode 3, which is the first rectifying element.

As is clear from FIG. 3, the voltage of the tie auto 3 does not increase in the forward connection area A no matter how much current flows. However, in region B where the connection is in the reverse direction, the voltage rises to the breakdown voltage point C just by passing a small amount of current, and even if further current flows, the voltage does not rise much. The breakdown voltage point of a normal diode is a few kV or less, so malfunction of the device does not occur due to discharge accompanying charge-up of the pressure roller regarding the above requirement (2).

Regarding the requirement (3) above, as shown in Figure 1, if a negative charge of opposite polarity to the transferred charge is generated on the pressure roller due to friction with the recording material, the negative charge will function as the diode 3 which is the first rectifying element. is applied to the fixing roller l by. Therefore, it is possible to prevent a decrease in the holding force of the developer to the recording material at the contact portion of the fixing roller 1 due to the frictional charge. Furthermore, the positive charge generated by frictional charging between the fixing roller l and the recording material passes through the tie auto 4, which is a second rectifying element, to the GN.
Since the opposite negative charge escapes to D and is blocked by the diode 4, it is possible to prevent the retention force of the developer image on the recording material P from decreasing.

Furthermore, in recent years, recycled paper is sometimes used to reuse resources, but when recycled paper is used, a positive charge may be formed on the fixing roller l, or a strong negative charge may be generated on the pressure roller. However, if the present invention is used, offset can be reliably prevented as in the case of the above OHP film.

Table 2 shows the surface potential, leakage current, and offset evaluation of the fixing roller and the pressure roller when tie autos with a breakdown voltage value of +1 kV are connected to the fixing roller and the pressure roller, respectively, based on the present invention. .

The fixing roller has a volume resistivity of 10I4 with a thickness of 30JL11.
Ω・C layer ~ 1016Ω・CIl PFA tube
Using a reminium cylinder coated with a diameter of 20 mm,
The pressure roller used had a diameter of 16 m1i and had various resistances depending on the amount of the resistance control material. Approximately 7 times the pressure roller
The evaluation was conducted by applying a transfer current of 1.5 pA to an OHP sheet that was pressed under a total pressure of 1.5 kg and conveyed at a speed of 241 cm/sec.

Table 2 (blank space below) ○...No offset occurs △...Offset occurs or is tolerable for practical use As shown in Table 2, for pressure rollers of 10'2 Ω or less The surface potential of the OHP sheet was maintained at +800 V, which was slightly lower than the tie-off voltage value, and no electrostatic offset of the OHP sheet occurred.

On the other hand, in a system using a pressure roller with a resistance of 10'3 Ω or more, there is no leakage current through the tie auto, and the potential of the pressure roller becomes several kV or more, or the surface of the fixing roller is controlled by a second rectifying element. The potential was increased in the negative direction, and the occurrence of offset was small enough to withstand practical use.

<Second Embodiment> Next, a second 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 first embodiment, and the explanation thereof will be omitted.

This embodiment differs from the first embodiment in that a positively charged developer is used. Therefore, in this embodiment, the polarity of the transfer charge applied to the recording material is negative, and in order to prevent this negative charge from leaking through the pressure roller, the first rectifying element and the second rectifying element are used. The orientation is opposite to that of the configuration described in the first embodiment. Even in this case, the negative transfer charge leakage through the diode was at a level of about several nA, and no offset of the OHP film or recycled paper occurred.

<Third Embodiment> Next, a third 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 first embodiment, and the explanation thereof will be omitted.

This embodiment differs from the first embodiment in that a fixing film is used instead of the fixing roller. In FIG. 5, 7 is a low heat capacity linear heating element fixedly supported on the device. The heating body 7 has a thickness of 1.0 mm, a width of 10 mm, and a longitudinal diameter of 24 mm.
0m5 alumina substrate 8 with resistance material 9 width 1.0sm+
The 12 currents applied from both ends in the longitudinal direction are given in a DClooV pulse-like waveform with a period of 20m5ec, and the pulse width is adjusted according to the desired temperature and energy release amount controlled by the thermometer IO. change. The approximate pulse width is 0.5m5ec to 5sec.

The fixing film II, which is the fixing means, comes into contact with the heating body 7 whose energy and temperature are controlled as described above, and moves in the direction of arrow G in FIG. The fixing film has a thickness of 20
It is an endless heat-resistant film with a base layer of polyimide, polyetherimide, PES, PFA, etc., and at least the image contact side coated with a release layer of 10 pm of a conductive material added to a fluororesin such as PTFE, PFA. It's a film. The total thickness of the above-mentioned fixing film (1) may be thinner than 100μ, preferably less than 40ILs. The film is driven by a drive roller 12 and a driven roller I3, and moves in the direction of arrow G without being bent.

A pressure roller 14 is a fixing means having a rubber elastic layer made of silicone rubber or the like having good release properties, and presses the heating body 7 through the fixing film 11 with a total pressure of 4 to 7 kg, and rotates in pressure contact with the fixing film.

The unfixed toner T, which is larger than the recording material, is guided to the fixing section by the entrance guide 5, and a fixed image is obtained by the above-mentioned heating.

In this embodiment, the unfixed toner T has a negative charge, and by connecting the polarities of the rectifying elements 3.4 in the same direction as in the first embodiment, the same effect as in the first embodiment can be obtained. In this embodiment, by disposing the electrode 16 on the inflow side of the recording material P close to the heating body 7, the rectifying element 3
are connected/connected.

<Fourth Example> Next, a fourth embodiment will be described using FIG. 6.

This embodiment differs from the third embodiment in that the fixing film 11 is formed as an edged film.

Note that the present invention is applicable to all fixing devices of devices that form images using toner, such as copying machines, printers, and facsimiles.

[Effects of the Invention] As explained above, according to the present invention, the first member in contact with the unfixed developer image bearing surface of the recording material and the second member in contact with the back surface of the supporting surface are connected to each other. In preparation for the fixing means, a first rectifying element is connected between the first member and the second member in such a direction that a charge having a polarity opposite to that of the developer image is retained. ing. Further, the first member is grounded via a second rectifying element so as to hold a charge having the same polarity as the charged polarity.

Therefore, when the recording material is being nipped and conveyed within the fixing device, it is possible to maintain the electrostatic holding force of the recording material to the developer image and prevent offset. Moreover, since the first member and the second member are grounded via the rectifying element, an increase in the amount of charge due to causes other than frictional charging is prevented, and there is no generation of electrical noise and malfunction of the device.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view showing the schematic configuration of the device according to the first embodiment of the present invention, Fig. 2 is a partially cutaway cross-sectional view of an OHP film used in the device shown in Fig. 1, and Fig. 3 is a cross-sectional view showing the schematic structure of the device shown in Fig. 1. FIG. 4 is a sectional view showing a schematic configuration of a device according to a second embodiment of the present invention, and FIG. 5 is a diagram showing a schematic configuration of a device according to a third embodiment of the present invention. FIG. 6 is a sectional view showing a schematic configuration of a device according to a fourth embodiment of the present invention. 1... Fixing roller 2... Pressure roller 3... Diode 4... Diode

Claims (1)

[Scope of Claims] A fixing means for fixing an unfixed developer image onto a recording material, the fixing means comprising: a first member in contact with the unfixed developer image bearing surface of the recording material; In the fixing device, the fixing device includes a second member disposed in opposing pressure contact with the first member and in contact with the back surface of the unfixed developer image bearing surface, wherein between the first member and the second member, , a first rectifying element is connected to the second member in a direction in which a charge having a polarity opposite to that of the developer image is retained, and the first member has a polarity equal to that of the developer image. A fixing device characterized in that the fixing device is grounded via a second rectifying element so as to hold an electric charge of the fixing device.