JPH04335385A - Fixing device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device used in electrophotographic image forming apparatuses such as electrophotographic copying machines, computer printers, and facsimile machines, for fixing an unfixed developer image to a transfer material.

0002

2. Description of the Related Art Conventionally, a fixing device, as shown in FIG.
A fixing roller 1 is provided. The fixing roller 1 has a core metal 11 in the shape of a hollow pipe, and the outer peripheral surface of the core metal 11 is coated with PFA, PT.
A heat-resistant mold release layer 12 made of FE or the like is formed. Core metal 1
A heater 3 is provided inside the metal core 1.
1 is heated from its inner surface.

The surface temperature of the fixing roller 1 is measured by a temperature sensor 4.
This detection signal is input to a temperature controller (not shown). Temperature controller is temperature sensor 4
A control signal indicating an operation instruction for the heater 3 is generated based on the detection signal from the heater 3. The heater 3 is turned on and off in response to a control signal from a temperature controller, and the surface temperature of the fixing roller 1 is maintained substantially constant.

[0004] The pressure roller 2 has a core metal 21, and the core metal 2
A heat-resistant elastic layer 22 made of silicone rubber or the like is formed on the outer peripheral surface of 1. The pressure roller 2 is a pressing means made of a spring or the like, and cooperates with the fixing roller 1 to form a nip portion N. A transfer material 5 on which an unfixed developer image 6 has been formed through a well-known electrophotographic process is inserted into the nip portion N by a transfer means (not shown) in the direction indicated by the arrow. Heat and pressure are applied to the unfixed developer 6 within the nip portion N, and the unfixed developer image 6 is fixed onto the transfer material 5. The transfer material 5 discharged from the nip portion N is separated from the release layer 12 by a separation claw 7 whose tip is in contact with the release layer 12, and is separated from the release layer 12 by a guide (not shown) or a discharge roller (not shown). is discharged from the device. The surface of the fixing roller 1 is cleaned by a cleaner 8 made of felt or the like, and is used for fixing the subsequent unfixed developer image 6.

[0005]

However, in the conventional example described above, since the transfer material 5 is separated from the fixing roller 1 by the separation claw 7, the fine particles (
Hereinafter, it will be referred to as "toner". ), and as the operating time passes, toner accumulates on the tip of the separating claw 7. As a result, a separation failure may occur due to interference between the accumulated toner at the tip of the separating claw 7 and the tip of the transfer material 5, and a jam may occur. Further, the toner deposited on the separation claw 7 may adhere to the transfer material 5 in a semi-molten state, causing stains on the image.

When the surface temperature of the fixing roller 1 is maintained near the fixing temperature, the release layer 12 softens, so if the pressing force of the separating claws 7 is large, scratches caused by the separating claws 7 will easily occur. The scratches cause stains on the image on the transfer material 5. Therefore, it is necessary to reduce the pressing force of the separating claw 7 as much as possible.
When pressing the separation claw 7 with a small pressure, the tip of the separation claw 7 may touch the fixing roller 1 due to thermal deformation of the holder (not shown).
It may not come into contact with the surface and may float up. As a result, the transfer material 5 may be wrapped around the fixing roller 1 without being separated from it.

The above-mentioned problem is particularly caused by the fact that the release layer 12 of the fixing roller 1 and the transfer material 5 are in close contact with each other due to the molten unfixed developer image 6, and the rigidity of the transfer material 5 itself causes the fixing roller 1 to
This is likely to occur under conditions where separation from the molecule is not achieved. That is, the outer diameter of the fixing roller 1 is large, the rigidity of the transfer material 5 is small, the fixing temperature is high, the melt index (MI) of the toner is large, the width of the nip portion N is large, and the moving speed of the transfer material 5 is low. If the speed is high, the above-mentioned problem is likely to occur.

SUMMARY OF THE INVENTION An object of the present invention is to provide a fixing device that can reliably separate a transfer material from a rotating body forming a nip portion when the transfer material passes through the nip portion.

[0009]

[Means for Solving the Problems] According to the present invention, the above object is achieved by providing a first rotating body and a transfer material on the surface of which an unfixed developer image is formed in cooperation with the first rotating body. In the fixing device including a second rotating body forming a nip portion for conveying the transfer material under pressure, an elastic layer having conductivity is provided at least near the circumferential surface of the second rotating body that contacts the back surface of the transfer material. This is achieved by applying a bias voltage to the elastic layer.

0010

In the fixing device of the present invention, the elastic layer is provided on the second rotating body, and a bias voltage is applied to the elastic layer. When the transfer material is conveyed through the nip portion under pressure, an attractive electric field is formed in the nip portion by applying a bias voltage to the elastic layer of the second rotating body, and the transfer material is conveyed under the attracted electric field. is electrostatically attracted to the second rotating body.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the fixing device of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the fixing device of the present invention.

The fixing device includes a fixing roller 1 and a pressure roller 2, as shown in FIG. The fixing roller 1 has a hollow pipe-shaped iron core 11, and a heat-resistant release layer 12 of PFA is formed on the outer peripheral surface of the core 11. Core metal 11
The thickness of the release layer 12 is 30 μm, and the outer diameter of the fixing roller 1 is 20 mm.
It is. A heater 3 is provided inside the metal core 11, and the heater 3 heats the metal core 11 from its inner surface. The surface temperature of the fixing roller 1 is detected by a temperature sensor 4, and the detection signal is input to a temperature controller (not shown). The temperature controller generates a control signal indicating an operation instruction for the heater 3 based on the detection signal from the temperature sensor 4. The heater 3 is turned on and off in response to a control signal from the temperature controller, and the surface temperature of the fixing roller 1 is maintained substantially constant. In this embodiment, the surface temperature of the fixing roller 1 is maintained at 170°C.

The surface of the fixing roller 1 is cleaned by a cleaner 8. The cleaner 8 is made of heat-resistant felt such as Nomex (trade name, DuPont), and the heat-resistant felt is pressed against the fixing roller 1.

The pressure roller 2 has an iron core 21 with a diameter of 10 mm, and on the outer peripheral surface of the core 21 is a 4 mm thick layer of conductive silicone rubber in which carbon is dispersed.
A heat-resistant elastic layer 30 is formed. It is preferable that the heat-resistant elastic layer 30 has a volume resistivity of 10 2 to 10 11 Ω·cm, and in this embodiment, the volume resistivity is 10 3 Ω·cm.
It is. The resistance value between the nip part N and the core metal 21 is 101
It is preferable that it is 0Ω or less. It is preferable that the hardness of the heat-resistant elastic layer 30 is 30 to 50 degrees (Asker C),
In this example, the hardness is 50 degrees. The pressure roller 2 has an outer diameter of 18 mm.

The pressure roller 2 is pressed against the fixing roller 1 by a pressing means (not shown), and the pressure roller 2 and the fixing roller 1 cooperate with each other to form a nip portion N. Pressure roller 2
The pressing force against the fixing roller 1 is 8 kg·w, and a nip portion N with a width of 2.0 mm is formed.

A separation claw 32 is brought into contact with the outer peripheral surface of the pressure roller 2. The separation claw 32 has a base material made of polyimide, and a layer made of PFA with a thickness of 10 μm is formed on the base material. The separation claw 32 is arranged at a position 5 mm downstream of the nip portion N so that its tip is in contact with the pressure roller 2.

A bias voltage from a bias power source 9 is applied to the elastic layer 30 of the pressure roller 2 . In this embodiment, the transfer material 5 on which the developer image (hereinafter referred to as "toner image") 6 is formed is positively charged in a previous process, and the bias power source 9 is connected to the nip portion of the pressure roller 2. A negative bias voltage is applied to the elastic layer 30 so that negative charges are induced in N. The bias voltage applied to the core metal 21 from the power source 9 is -500V, and the core metal 11 is grounded. Note that since the charging polarity of the transfer material 5 depends on its image forming process, the polarity of the bias voltage is determined according to the charging polarity due to the image forming process. Furthermore, an alternating current voltage on which a direct current voltage is superimposed can also be used as the bias voltage.

When the transfer material 5 is in an uncharged state, the transfer material 5 itself has an insulating property, and under a strong electric field, the transfer material 5 undergoes induced polarization and is attracted to the side where the electric field is concentrated.
Therefore, in the case of the transfer material 5 in an uncharged state, a higher bias voltage is required than in the case of the transfer material 5 in a charged state, but a bias voltage of either positive or negative polarity can be applied. Alternatively, alternating current voltage can also be used.

Next, the operation of the fixing device will be explained. The transfer material 5 is provided with a positive corona charger (not shown).
After the toner image 6 made of negative polarity toner is transferred, the charge is removed by a charge removal needle (not shown), and the charged polarity of the transfer material 5 exhibits weak positive polarity.

After neutralization, the transfer material 5 is conveyed toward the nip portion N. When the leading edge of the transfer material 5 reaches the nip portion N,
The transfer material 5 is inserted into the nip portion N by the rotating fixing roller 1 and pressure roller 2. Heat and pressure are applied to the toner image 6 within the nip portion N, and the toner image 6 is fixed on the transfer material 5. Further, an attractive electric field is formed in the nip portion N, and the transfer material 5 is electrostatically attracted to the pressure roller 2. Therefore, the transfer material 5 is easily separated from the fixing roller 1, and there is no need to provide a separating claw on the fixing roller 1 side.

The transfer material 5 attracted to the pressure roller 2 may be naturally separated from the pressure roller 2, or the transfer material 5 may be separated from the pressure roller 2 naturally.
may be separated from the pressure roller 2 by the separation claw 32. However, when the transfer material 5 contacts the separation pawl 32, the tip of the separation pawl 32 contacts the back surface of the transfer material 5, so toner does not adhere to the tip of the separation pawl 32, and the transfer material 5 is stained with toner. There is no risk of it happening.

Next, a paper passing test for verifying the effects of the fixing device of the present invention will be described.

The circumferential speed of the fixing roller 1 is 30 mm/sec.
is set to . The transfer material 5 has a basis weight of 50 to 135.
Plain paper of gr/m2 and A4 size is used. The toner used has a volume average particle diameter of 12 μm, a charge amount of -10 μc/gr, and an MI value of 3 to 4. Furthermore, a margin of 2 mm from the leading edge of the transfer material 5 is provided so that the leading edge of the transfer material 5 can be easily separated from the fixing roller 1. The environmental conditions are low temperature and low humidity (1
Three conditions were set: 0°C, 20%), high temperature and high humidity (30°C, 60%), and normal temperature and humidity (23°C, 30%).

A paper feeding test was carried out on 10,000 sheets using a printing pattern with an image ratio of 3 to 10% for each basis weight of the transfer material 5 under various environmental conditions.
gr/m2, 64gr/m2, 75gr/m2, 90g
r/m2, 135gr/m2. As a result, it was confirmed that no stains or jams occurred on the image.

[0026] Also, the transfer material 5 has a weight of 50g/m2 to 64g.
It is a thin paper of r/m2, and the paper making direction is transfer material 5.
If the transfer material 5 absorbs moisture in a high-temperature, high-humidity environment and the stiffness of the transfer material 5 decreases,
Under any of the following operating conditions, the image ratio is 4% or less and the adsorption force to the fixing roller 1 is relatively low, the transfer material 5 is transferred to the pressure roller 2 by the separating claw 32.
It is confirmed that the separation claws 32 are separated from each other, and there is no need to provide the separation claw 32 in a usage environment that does not meet the above-mentioned usage conditions.

Next, a paper passing test for verifying the effects of other fixing devices will be described. The circumferential speed of the fixing roller 1 is set to 50 mm/sec. The toner had a volume average particle diameter of 7 μm, a charge amount of −12 μc/gr,
A toner having an MI value of 2 to 3 is used.

Under each of the three environmental conditions mentioned above, a 10,000-sheet feeding test was conducted using a printing pattern with an image ratio of 3 to 10% for each basis weight of the transfer material 5, and as a result, it was found that the transfer material 5 was separated from the fixing roller 1 or the pressure roller 2, and it was confirmed that no stains or jams would occur on the image due to poor separation.

In addition, in a print pattern with an image ratio of 3 to 10%, the tip of the separating claw 32 and the tip of the transfer material 5 do not come into contact with each other, and the separation of the transfer material 5, which has a margin at the tip, is difficult. It has been confirmed that the function of the separation claw 7 is not necessary, and the separation claw 7 prevents the transfer material 5 on which a solid black image is formed, for example, with no margin, from wrapping around the fixing roller 1.

Next, another fixing device will be explained. FIG. 2 is a configuration diagram showing another embodiment of the fixing device of the present invention. Note that the same members as those in FIG. 1 are given the same reference numerals.

Another fixing device is used in an image forming apparatus compatible with high-speed processing that performs transfer by bringing contact charging means such as a transfer roller (not shown) into contact with the back surface of the transfer material 5.

The fixing roller 1 has a stainless steel core 11 with a thickness of 3 mm, and a release layer 12 made of a PFA tube with a thickness of 50 μm is provided on the outer peripheral surface of the core 11.
is formed. The outer diameter of the fixing roller 1 is 25 mm.
It is. The surface temperature of the fixing roller 1 is maintained at 180°C.

On the other hand, the pressure roller 2 has an outer diameter of 2
A core metal 21 made of a 0 mm stainless steel hollow pipe,
It has an elastic layer 30 formed on the outer peripheral surface of the core bar 21 and made of conductive silicone rubber in which carbon is dispersed. A release layer 23 is provided on the outer peripheral surface of the elastic layer 30. Like the release layer 12, the release layer 23 has a volume resistivity of 10<14 >Ω·cm or more and is an electrical insulator. The thickness of the release layer 23 is 30 to 100 μm so that an electric field attracting the transfer material 5 to the pressure roller 2 within the nip portion N is formed.
Let it be m. In this example, the release layer 23 is made of PFA material and has a thickness of 50 μm.

The outer diameter of the pressure roller 2 is 36 mm, and the pressing force of the pressure roller 2 against the fixing roller 1 is 10 k.
g and w, and a nip portion N with a width of 4.5 mm is formed.

The bias voltage applied from the power source 9 to the metal core 21 is +1000V, and the metal core 11 is grounded. Note that when a metal roller having the same outer diameter was attached instead of the fixing roller 1 and the value of the current flowing through the nip portion N was measured, a measured value of 2 μA was obtained.

The separating claw 32 is arranged at a position 7 mm downstream of the nip portion N so that its tip comes into contact with the fixing roller 1.

Next, the operation of other fixing devices will be explained. The transfer material 5 has a transfer roller (not shown) on its back surface.
After a positive charge is applied at , a toner image 6 made of negative toner is transferred. Next, the transfer material 5 is neutralized with a charge eliminating needle (not shown), and the charged polarity of the transfer material 5 is neutralized.

After neutralization, the transfer material 5 is conveyed toward the nip portion N. The transfer material 5 is inserted into the nip portion N, and the toner image 6 is fixed on the transfer material 5. Since an attractive electric field is formed in the nip portion N, the transfer material 5 is attracted toward the pressure roller 2, so the transfer material 5 is attracted to the fixing roller 1.
easily separated from In addition, a release layer 2 is provided on the pressure roller 2.
2, the toner that has adhered to the back surface of the transfer material 5 via the transfer roller is not accumulated on the release layer 22, so that the surface of the transfer material 5 is not smudged by toner when passing through the nip portion N. This can be prevented from occurring.

Next, still another fixing device will be explained. FIG. 3 is a block diagram showing still another embodiment of the fixing device of the present invention, and FIG. 4 is a longitudinal sectional view of a pressure roller used in the fixing device of FIG. 3. Note that the same members as those in FIG. 1 are given the same reference numerals.

The fixing roller 1 has a core metal 11 made of a hollow iron pipe with a thickness of 3 mm, and a release layer 12 made of a PFA tube with a thickness of 50 μm on the outer peripheral surface of the core metal 11. is formed. The outer diameter of the fixing roller 1 is 30 mm. The surface temperature of fixing roller 1 is 19
It is kept at 0°C.

On the other hand, the pressure roller 2 has an outer diameter of 12 m.
It has a core metal 21 made of a hollow iron pipe of m. Core metal 2
1 has an electrically insulating sponge layer 24 on its outer peripheral surface.
is formed. The thickness dimension of the sponge layer 24 is 2.9
It is 5mm. An elastic layer 30 made of conductive silicone rubber (volume resistivity: 2.5×10 3 Ω·cm) is formed on the outer peripheral surface of the sponge layer 24 . The thickness of the elastic layer 30 is 1 mm. On the surface of the elastic layer 30, a release layer 23 having a thickness of 50 μm and made of a PFA tube in which carbon is dispersed is formed. The elastic layer 30 and the core bar 21 are electrically connected.

The pressure roller 2 has an outer diameter of 30 mm and an Asker C hardness of 40 degrees. The pressing force of the pressure roller 2 against the fixing roller 1 is 9.5 kg・w, and the width is 5.
．． A nip portion of 0 mm is formed.

The bias voltage applied to the core metal 21 from the power source 9 is +600V, and the measured current value at the nip portion N obtained by installing a metal roller having the same outer diameter instead of the fixing roller 1 is 60 μA. It is.

In this embodiment, the charge polarity of the transfer material 5 before being inserted into the nip portion N exhibits a weak negative polarity.

Next, a 10,000-sheet feeding test was conducted under each of the three environments described above using a printing pattern with an image ratio of 3 to 10% for each basis weight of the transfer material 5.
As a result, the transfer material 5 is transferred to the fixing roller 1 or the pressure roller 2.
It was confirmed that there were no stains or jams on the image due to poor separation.

[0046] Furthermore, by reducing the hardness with the sponge layer 24 and realizing conductivity with the elastic layer 30, the pressure roller 2
The hardness of the transfer material 5 is reduced, and the transfer material 5 can be attracted to the pressure roller 2 side by an attractive electric field without causing wrinkles on the transfer material 5, which is folded double or triple folded like an envelope. .

Although the above embodiment shows an example in which the core bar 11 of the fixing roller 1 is grounded, a diode or a resistor may be used as long as the adsorption of the transfer material 5 to the pressure roller 2 is not inhibited. It can also be grounded via a voltage generating element such as, or it can be floated. In addition, the pressure roller 2
It is also possible to supply power to the core metal 21 not directly from the power supply 9 but via a voltage generating element such as a resistor, and to limit the current in the event of leakage as an unexpected situation.

[0048]

As described above, according to the fixing device of the present invention, an attractive electric field is formed in the nip portion by applying a bias voltage to the elastic layer of the second rotating body. Since the transfer material is electrostatically attracted to the second rotating body by the attraction electric field, the transfer material can be reliably separated from the first rotating body, and the image is not smudged by the separation claw. It is possible to prevent jamming caused by the wrapping of the transfer material around the first rotating body.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a fixing device of the present invention.

FIG. 2 is a configuration diagram showing another embodiment of the fixing device of the present invention.

FIG. 3 is a configuration diagram showing still another embodiment of the fixing device of the present invention.

FIG. 4 is a longitudinal sectional view of a pressure roller of the fixing device in FIG. 3;

FIG. 5 is a configuration diagram showing a conventional fixing device.

[Explanation of symbols]

1 Fixing roller 2 Pressure roller 5 Transfer material 6 Toner image 9 Bias power supply 11, 21 Core metal 12, 23 Release layer 22, 30 Elastic layer 24 Sponge layer

Claims (1)

[Claims] 1. A first rotating body and a second rotating body that cooperates with the first rotating body to form a nip portion for conveying a transfer material with an unfixed developer image on its surface under pressure. In the fixing device including a rotating body, an electrically conductive elastic layer is provided at least near the circumferential surface of the second rotating body that contacts the back surface of the transfer material, and a bias voltage is applied to the elastic layer. A fixing device characterized by: