JPH11143264A - Heating device and image forming apparatus having the same - Google Patents

Abstract

(57) [Problem] In a fixing device of a film fixing method, there is a problem that a toner offset occurs in a pressing member, and this toner is transferred to a transfer material to generate stain on the surface of the transfer material. SOLUTION: A pressing member 28 is disposed to face a heat generating member 20, and a fixing film 25 sandwiched between the heat generating member and the pressure member so as to include the heat generating member.
And a charging member 50 disposed in contact with the pressing member.
And a voltage applying means 52 for applying a voltage to the charging member.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heating device for heating and fixing a toner image formed on a transfer material to the transfer material, and to an image forming apparatus equipped with the heating device, such as a copying machine or a laser beam printer.

[0002]

2. Description of the Related Art A conventional image forming apparatus of this type irradiates an image exposure corresponding to an original image or an image signal input from a computer onto a surface of an image carrier uniformly charged by a charging means to thereby form an electrostatic latent image. An image is formed, the electrostatic latent image is developed into a toner image by a developing unit, the toner image is transferred to a transfer material by a transfer unit, and the toner image on the transfer material is fixed on the transfer material by a fixing unit. There is an electrophotographic copying machine, a laser beam printer, and the like that output the image data.

In the fixing device, a heat-resistant fixing film is brought into sliding contact with a heat-generating member, and a pressure member is pressed into contact with the heat-generating member through the fixing film. 2. Description of the Related Art A film-fixing type heating device for applying heat energy from a heat-generating member via a fixing film to a transfer material nipped and conveyed by a pressing member to heat and fix the transfer material is used.

FIG. 5 is a sectional view showing an example of the above-mentioned film fixing type heating device. In FIG. 5, reference numeral 20 denotes a heater as a heating member supported by a stay 21 as a support, and 25 denotes a high heat resistance. The fixing film 25 is a fixing film in the form of an endless belt in which the material is coated with a material having good releasability. The fixing film 25 is suspended between a driving roller 26 and a driven roller 27 disposed substantially in parallel with the heater 20. And are arranged so as to be in sliding contact with each other.

On the lower surface of the heater 20, a pressure roller 2 as a pressure member is sandwiched so as to sandwich the fixing film 25.
8, for example, a total pressure of 5 k
The pressure roller 28 has a rubber elastic layer having good releasability such as silicon rubber and forms a fixing nip N between the pressure roller 28 and the heater 20. I have.

Next, the operation will be described.

First, when the driving roller 26 is driven to rotate in a direction indicated by an arrow by a driving motor M as a rotation driving means, the fixing film 25 given a predetermined tension by a driven roller 27 also serving as a tension roller is moved by an arrow a. The fixing film 2 rotates at a predetermined peripheral speed in the direction of
With the rotation of 5, the pressure roller 28 also rotates in the counterclockwise direction indicated by the arrow.

The transfer material P after the transfer of the toner image T is
The sheet is sequentially fed between the fixing film 25 and the pressure roller 28 by a transfer material supply unit (not shown), and the fixing nip N
, The toner image T on the transfer material P is fixed on the transfer material P while being conveyed while being pinched and conveyed with the rotation of the fixing film 25 and the pressure roller 28. .

In this type of film fixing type heat fixing apparatus, a heater 20 as a heat generating member and the heater 20
Since the heat capacity of the fixing film 25 as a member for transmitting the heat energy to the transfer material P can be reduced, there is an advantage that power saving and shortening of the wait time (quick start property) are possible.

[0010]

However, the above-mentioned conventional heating apparatus may have the following problems.

When the transfer material P having the toner image T passes through the fixing nip N, a so-called offset phenomenon that a small amount of toner is transferred from the transfer material P to the fixing film 25 occurs. A part of the transferred toner is transferred to the rear end of the transfer material P again after the fixing film 25 makes one rotation, or remains on the fixing film 25 and then transferred to the next transfer material P passing through the fixing nip N. Is done. Since the amount of the toner transferred to the transfer material P is extremely small, there is no practical problem.

However, a part of the transferred toner is transferred to the pressure roller 28. Once the toner adheres to the pressure roller 28, the surface energy is significantly reduced at that portion, and the toner is more likely to adhere. As a result, a thin layer of toner is formed on the pressure roller 28 in an island shape or a planar shape. The adhesion of the thin layer of the toner to the pressure roller 28 becomes weak when the surface temperature of the pressure roller 28 is low (particularly lower than the glass transition temperature of the toner).

In the case of this type of film fixing device, when the device is in a standby state, the heater 20 is not energized. Therefore, the pressure roller 28 is also normally kept at about room temperature, at least below the glass transition temperature. When the fixing operation is started in that state, the temperature of the surface of the fixing film 25 in the fixing nip N rapidly rises.

Therefore, before the transfer material P reaches the fixing nip N, the surface of the toner layer which has adhered to the surface of the pressure roller 28 with a weak force is softened and adheres to the fixing film 25. The part of the toner is separated from the pressure roller 28 and transferred to the fixing film 25. The transferred toner is
Immediately thereafter, thermal transfer is sequentially performed on the transfer material P that arrives at and passes through the fixing nip N. As a result, spot-like stains are generated on the surface of the transfer material P.

Therefore, conventionally, in order to prevent spot-like stains on the transfer material P due to toner stains on the pressure roller 28, a cleaning member (hereinafter referred to as a scraper) is attached to the pressure roller 28 as shown in FIG. The present applicant has proposed a means for contacting the pressure roller 50 and removing the offset toner and paper dust which are stains on the pressure roller 28.

However, since the scraper 50 is in contact with the pressure roller 28, the following problems occur. 1) In addition to frictional charging caused by paper passing, a cleaning member 50
The surface of the pressure roller 28 is charged up by frictional charging due to the rubbing with the roller. 2) When the charged polarity on the surface of the pressure roller 28 is the same as that of the toner, and when the polarity is the same, an electrostatic toner offset occurs due to a component having an inverted charge in the toner. Surface dirt increases. 3) For these reasons, it becomes difficult to collect the toner using only the scraper 50, and the backing of the transfer material due to the toner passing through the scraper 50, and the pressure roller due to the excessive accumulation and fixation of the toner on the scraper 50 Stops and transfer material transfer failure occurs.

In such a case, in the case of the conventional heat roller fixing method, a voltage having a polarity opposite to that of the toner is applied to the fixing roller side in contact with the pressure roller, and the potential of the surface of the pressure roller is lowered to reduce the toner offset. Although it can be prevented, it is difficult to apply a voltage to the film in the film fixing method.

When applying a voltage to the core of the pressure roller, it is necessary to add a filler such as carbon to the elastic layer of the pressure roller to make the resistance low or medium, but the filler is uniformly dispersed. It is difficult to let.

[0019] Even if they are dispersed uniformly, the hardness of the elastic layer relatively increases, making it difficult to widen the fixing nip N. In this case, since the pressing force is lower in the film fixing method than in the conventional heat roller method, the fixing property is impaired by reducing the nip.

According to the present invention, spot-like stains on a transfer material caused by toner stains on a pressure roller caused by electrostatic offset in the conventional film fixing method described above are prevented,
It is an object of the present invention to provide a heat fixing device capable of always obtaining a good fixed image and an image forming apparatus provided with the heat fixing device.

[0021]

According to the present invention, there is provided a heating apparatus having the following constitution and an image forming apparatus provided with the same.

(1) A pressing member arranged to face the heat-generating member, a fixing film sandwiched between the heat-generating member and the pressing member so as to include the heat-generating member, The heating device includes a charging member arranged in contact with the pressure member, and voltage applying means for applying a voltage to the charging member.

(2) a pressing member arranged to face the heat generating member; a fixing film sandwiched between the heat generating member and the pressing member so as to include the heat generating member; The heating device includes a cleaning member disposed in contact with the member, and voltage applying means for applying a voltage to the cleaning member.

(3) The heating device is characterized in that the cleaning member is made of at least a metal or a resin having a body lateral resistance of 10 ⁴ Ω · cm or more and 10 ¹⁶ Ω · cm or less, and is a scraper or a blade.

(4) An image forming means for forming a document image or a toner image corresponding to an input image signal on an image carrier, and transferring the toner image on the image carrier to a recording material, and the image forming means An image forming apparatus comprising: the heating device according to claim 1, wherein the toner image formed on the recording material is heat-fixed to the transfer material.

[0026]

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

Embodiment 1 FIG. 1 is a schematic configuration diagram showing an image forming apparatus according to Embodiment 1 of the present invention.
In the figure, reference numeral 10 denotes a drum-type electrophotographic photosensitive member (hereinafter, referred to as a photosensitive drum) as an image carrier, and the photosensitive drum 10 is, for example, an OPC photosensitive drum.

Above the photosensitive drum 10, a primary charging device 11 as charging means is provided. The primary charging device 11 uniformly charges the surface of the photosensitive drum 10 during image formation. On the charged surface of the photosensitive drum 10, an image exposure light 12 corresponding to an image signal such as a document image is formed. Irradiation via the mirrors 15 to 17 forms an electrostatic latent image. Then, the developing device 13 develops the electrostatic latent image on the photosensitive drum 10 to form a toner image.

The toner used in the first embodiment is a one-component negative toner having a volume average particle diameter of about 7 μm, and the binder resin is mainly polyester. The glass transition temperature (Tg) of this toner is about 60 ° C., and the softening temperature or fixable temperature (Tm) is about 130 ° C.

A transfer charging device 14 serving as a transfer unit is provided with a transfer paper 18 for transferring the toner image on the photosensitive drum 10 as a transfer material.
The transfer paper 18 on which the toner image on the photosensitive drum is transferred is conveyed to a fixing device 19 by a transfer material conveying device 32, where the toner image is fixed by the heat fixing device 19 and output. The image is formed and discharged. The photosensitive drum 10 and the primary charging device 1
1. The image forming means 18 comprises the developing device 13 and the transfer charging device 14.

The fixing device 19 is a film fixing type fixing device as shown in FIG. 2, and an endless belt-shaped fixing film 25 made of a material having high heat resistance is used as a fixing device.
The roller 20 is suspended between a driving roller 26 and a driven roller 27 disposed substantially in parallel with the heater 20 so as to be in sliding contact with the heater 20 which is a heat generating member supported by the support 21.

On the lower surface of the heater 20, a pressing roller 2 serving as a pressing member is provided with a fixing film 25 interposed therebetween.
8, for example, a total pressure of 5 k
They are opposed to each other with a contact pressure of about g weight. The pressure roller 28 is made of a rubber elastic layer having good releasability such as silicone rubber,
Further, on the surface thereof, there is provided a fluororesin layer such as PFA, PTFE, FEP, etc., which has better releasability than silicone rubber, and presses against the heater 20 to form the fixing nip N. The outer diameter of the pressure roller 28 is 20 mm
Or 30 mm.

When the drive roller 26 is driven to rotate clockwise by a drive motor M as a rotation drive means,
The fixing film 25 given a predetermined tension by a driven roller 27 also serving as a tension roller rotates at a predetermined peripheral speed in a clockwise direction, and as the fixing film 25 circulates, the pressing roller 28 also moves in a counterclockwise direction. As a result, the transfer material P is conveyed while being sandwiched between the fixing film 25 and the pressure roller 28. The drive motor M can rotate at a predetermined timing according to a detection signal selected by a pressure roller cleaning mode selection switch 31 described later.

The fixing film 25 circulated in this way
Is a film excellent in heat resistance, release property and abrasion resistance and generally has a total thickness of 100 μm or less, preferably 4
Use a thin material of 0 μm or less. For example, polyimide, polyetherimide, a single layer of heat-resistant resin such as PES,
Alternatively, the surface of these heat-resistant resins is made of PFA, PTF
It is preferable to use a film covered with a fluorine resin layer consolidation layer such as E or FEP. The circumference is 30 to 60 mm.

The heater 20 has a thickness of 1.0 mm, a cap of 10.0 mm, and a length of 350 mm, and is formed on a substrate made of a good heat conductor, for example, alumina, aluminum nitride, or the like, with an electric resistance material of 2.5 mm in width and 300 mm in length. Coated on the
Heat energy is generated by energizing the electric resistance material.

Further, a temperature sensor 29 as temperature detecting means is mounted on the back surface of the substrate of the heater 20, and the temperature sensor 29 is provided with a predetermined substrate during the image forming operation. Set temperature (control temperature)
Is connected to an energization control unit 30 that is an energization control unit that controls electric power supplied to the heater 20 according to the temperature detected by the temperature sensor. Further, the power supply control unit 30 controls electric power supplied to the heater 20.

Below the pressure roller 28, a scraper 51 as a charging member is provided in a forward direction with respect to the rotation direction of the pressure roller 28. Scraper 51 shown in FIG.
Is formed of stainless steel having a thickness of 20 to 500 μm, but may be formed of iron, aluminum, or the like.
The scraper 51 has a power supply 5 as a voltage applying means.
2 are connected, and a DC voltage V is applied.

Table 1 shows a DC voltage V, a spot-like stain, and a scraper 51 when an image forming apparatus using the fixing device 19 shown in FIG.
The relationship of the degree of occurrence of the stoppage of the pressure roller 28 due to the melt-fixed toner accumulated above is shown.

[0039]

[Table 1] From the above results, in the case of the negative toner as in the first embodiment, most of the toner on the transfer material is inverted to the positive polarity by the positive transfer bias, and PFA, whose surface material is easily charged to the negative polarity, This is probably because the negative potential on the surface of the pressure roller 28 is reduced by applying a positive voltage of 400 V or more because it easily adheres to the surface of the pressure roller 28 formed of PTFE or the like.

Even when the surface of the pressure roller 28 is the same and a positive toner is used, a non-inverted component is contained in the toner on the transfer material.
In this case as well, spot-like dirt can be prevented by applying an appropriate voltage of positive polarity in this case as well.

In the experiments conducted by the applicants, the polarity of the surface material of the pressure roller 28 is determined when paper is passed. Generally, by applying a voltage having a polarity opposite to the charging polarity, spot-like stains are prevented. The effect to be obtained is obtained.

As described above, according to the first embodiment, by applying a voltage to the metal scraper 51 in contact with the pressure roller 28, spot-like stains can be prevented.

Embodiment 2 FIG. 3 is a cross-sectional view showing a film fixing type fixing device according to a second embodiment of the present invention. The same parts as those in the first embodiment shown in FIG. The scraper 100 shown in FIG. 3 uses a heat-resistant polyimide resin having a thickness of 20 to 500 μm as a base material 101. As the base material 101, in addition to the polyimide resin, a heat-resistant resin such as phenol resin, polyetherimide, PES, or PPS, a liquid crystal polymer, or a material obtained by mixing these resins with glass or carbon fiber to increase the strength. Can be used.

On the surface of the scraper 100, a primer layer 102 having a surface resistance of 107 Ω / port or less and a thickness of 3 to 8 μm is provided. This primer layer 102 has a volume resistance of 10 11 Ω · cm or more, which is excellent in insulation and release properties,
A release layer 103 made of a fluororesin such as PFA or PTFE or a silicone resin having a thickness of 5 to 20 μm is adhered.

In the second embodiment, the volume resistance 10 14
A primer 102 having a surface resistance of 5 × 10 4 Ω / port and a thickness of 6 μm is formed on the surface of a polyimide substrate 101 having a thickness of 100 μm and a thickness of 100 μm.
/ 25 was spray-coated with a fluororesin having a thickness of 10 μm. The volume resistance of this fluororesin layer is 10 12 Ω · cm.

As described above, according to the second embodiment, by making the scraper 100 have a medium resistance, the environmental stability of the scraper increases, and the humidity and temperature are detected and the scraper 100 becomes stable without control. Performance is obtained.

Embodiment 3 FIG. 4 is a sectional view showing a heating device used as a film fixing type fixing device according to a third embodiment of the present invention. In FIG. 4, the same parts as those in the first embodiment shown in FIG. Description is omitted. In the third embodiment, as shown in FIG. 4, a DC power supply 53 and an AC power supply 54 as voltage applying means are connected to a scraper 51 so that a superimposed voltage can be applied. 200 V, Vpp = 1.4 kV and Vf (frequency) = 2 kHz are applied as AC components.

As described above, according to the third embodiment, by applying an AC voltage, the cleaning ability was improved, and spot-like stains did not occur even after 100K of paper was passed. As a result, the stability in the long-term durability test was further improved.

Embodiment 4 In the fourth embodiment, humidity information is obtained from a humidity sensor (not shown), and the voltage applied to the scraper 51 is controlled based on this information. That is, in a low humidity environment where toner offset is likely to occur, the voltage is increased to prevent contamination. Thus, in order to control to an appropriate voltage, there is little change in the resistance value of the scraper,
Stable performance can be obtained over a long period.

[0050]

As described above, according to the present invention, the charging member is provided in contact with the pressing member arranged opposite to the heating member, and the voltage is applied to the charging member. Therefore, there is an effect that it is possible to prevent charge-up that causes contamination of the pressing member.

Further, according to the present invention, the cleaning member is provided in contact with the pressing member disposed opposite to the heat generating member, and a voltage is applied to the cleaning member. There is an effect that contamination of the pressing member due to the offset can be prevented.

Further, according to the present invention, the cleaning member is formed of a scraper or a blade made of metal or a resin having a volume resistance of 10 ⁴ Ω · cm or more and 10 ¹⁶ Ω · cm or less. The above effects can be obtained effectively.

Further, according to the present invention, the charging member is provided in contact with the pressing member arranged opposite to the heating member, and the heating device for applying a voltage to the charging member or the heating member arranged opposite to the heating member is provided. A cleaning member is provided in contact with the pressing member to be applied, and a heating device for applying a voltage to the cleaning member is configured to be used as a fixing device of the image forming apparatus. Thus, it is possible to provide an image forming apparatus capable of preventing spot-like stains on a transfer material caused by stains caused by the image forming apparatus and obtaining a good fixed image. In addition, by controlling the voltage, it is possible to provide an image forming apparatus having high environmental stability and high durability.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a film fixing type fixing device using the heating device of the present invention applied to the image forming apparatus.

FIG. 3 is a cross-sectional view showing a film fixing type fixing device using a heating device according to a second embodiment of the present invention.

FIG. 4 is a cross-sectional view showing a film fixing type fixing device using a heating device according to Embodiment 3 of the present invention.

FIG. 5 is a cross-sectional view showing a film fixing type fixing device to which a conventional heating device is applied.

FIG. 6 is a cross-sectional view showing another conventional film fixing type heat fixing device.

[Explanation of symbols]

 10: Image carrier (photosensitive drum) 11: Primary charging device (image forming device) 12: Image exposure (image forming device) 13: Developing device (image forming device) 14: Transfer charging device (image forming device) 18: Transfer Material 19: Fixing device 20: Heater (heating member) 25: Fixing film 28: Pressure roller (Pressing member) 50, 100: Scraper (Charging member) 52: Power supply (Voltage applying means) 53: DC power supply (Voltage application) Means) 54: AC power supply (voltage applying means)

Claims (4)

[Claims] A pressure member disposed to face the heat generating member; a fixing film sandwiched between the heat generating member and the pressure member so as to include the heat generating member; A charging member disposed in contact with the charging member; and a voltage applying means for applying a voltage to the charging member. 2. A pressing member disposed to face a heat generating member, a fixing film sandwiched between the heat generating member and the pressure member so as to include the heat generating member, and the pressing member. And a voltage applying means for applying a voltage to the cleaning member. 3. The heating apparatus according to claim 2, wherein the cleaning member is made of at least a metal or a resin having a volume resistance of 10 ⁴ Ω · cm or more and 10 ¹⁶ Ω · cm or less, and is a scraper or a blade. . 4. An image forming means for forming a document image or a toner image corresponding to an input image signal on an image carrier, and transferring the toner image on the image carrier onto a recording material, and the image forming means. 4. The toner image formed on the recording material is heat-fixed to the transfer material.
An image forming apparatus, comprising: the heating device according to any one of the above.