JPH08328408A - Fixing device for electrophotographic device - Google Patents

Abstract

PURPOSE: To obtain both a high charge holding capacity in a nip and a high potential attenuation capacity outside the nip, to prevent the generation of offset due to separation electrification and to prevent the occurrence of offset due to a paper charge leak under a high-humidity environment by constituting the surface material of a fixing member which comes into contact with a toner image of fluororesin and ion-conductive electric resistance value control material. CONSTITUTION: The surface material of the fixing member 1 which comes into contact with the toner image in the fixing device 50 includes at least the fluororesin and the ion-conductive electric resistance value control material with a melting point > the highest using temperature of the fixing device 50. A high releasability is required for the mold-released layer of a fixing film 1 so that the layer may be proof against rubbing with the transfer material 20 and toner 21 may not stick to the layer. As the material for the layer, water- enamel is used as binder and the mixture of PTEE and PFA in the ratio of 7:3 is mixed. Resistance value control agent is mixed with the aforesaid mixture. Otherwise, instead of the agent, the ion-conductivity imparting material is mixed in the resin.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device for an electrophotographic apparatus. More specifically, the present invention relates to a fixing device for an electrophotographic device having excellent offset prevention property.

[0002]

2. Description of the Related Art Conventionally, a heat roller system has been used as a fixing device for an electrophotographic apparatus such as a printer and a copying machine.
This is because a transfer material having a toner image is passed through a fixing nip formed by a fixing roller having a heat source such as a halogen heater and a pressure roller for applying a pressure to the transfer material to heat the toner with heat. It is fixed on the transfer material by pressure. This method has been used for a long time because of its simple configuration and high speed, but it requires preheating even during standby without printing, has a large heat capacity, and takes time to wait. At the same time, it had the problem of this.

On the other hand, in recent years, an on-demand type in which a ceramic heater having a small heat capacity and a film are combined, that is, no electricity normally flows through the heater,
When necessary, for example, a fixing device in which electricity is input to a heater after paper is supplied has been put into practical use. This is to shorten the wait-up time by reducing the heat capacity of the fixing device, and to start energizing the fixing device after receiving a print signal.

[0004]

However, in both the heat roller system and the on-demand system, an electrostatic offset phenomenon may occur in which the toner on the transfer material is electrostatically transferred to the fixing roller or the fixing film. However, there is a problem that the image quality is degraded.

Explaining an on-demand type fixing device, an electric field that attracts the toner on the transfer material to the fixing film is generated by frictional charging of the transfer material and the fixing film or by transfer charge of the transfer material, and a part of the toner The toner transferred to the fixing film returns to the transfer material after the fixing film makes one round, and then becomes a ghost on the image. This is called electrostatic offset.

Electrostatic offset can be roughly divided into two ways. Here, it is classified into a total offset and a peeling offset. In the full-face offset, the transfer material and the fixing film exchange charges with each other by friction charging or the like, and an offset electric field is constantly generated, and the offset continuously appears in the entire image. On the other hand, peeling offset is that when the trailing edge of the transfer material leaves the fixing device, the trailing edge of the transfer material splashes and makes strong contact with the fixing film, leaving a potential history in a straight line along the film length.
This potential causes an offset, and is generated in a straight line in the scanning direction on the image, so that both can be distinguished.

In order to prevent these electrostatic offsets, conventionally, the potential of the fixing film is controlled to a constant value. Specifically, when a negatively chargeable toner is used, an antistatic treatment is performed to prevent the fixing film from being positively charged, and further, the fixing film is electrically conductive and connected to the ground so that the potential becomes 0V. Perform processing.

Further, in order to actively take measures against electrostatic offset, a means of connecting a diode between the fixing film and the ground to forcibly form an electric field for preventing offset is also used.

Generally, in order to prevent the surface of the fixing film from being charged, the volume resistance of the surface layer material is lowered. Specifically, carbon is added to the release layer on the surface of the fixing film.

The surface layer of the fixing film is required to have heat resistance and high releasability. In order to satisfy this, conventionally used fixing films include a water-soluble binder, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), and polytetrafluoroethylene (PTF).
A dispersion such as E) and carbon are further mixed to form a film. When the surface potential of the fixing film prepared by using such a means is measured by a surface potential meter during paper passing, it is almost charged to tens of volts even during paper passing, and the antistatic effect is confirmed.

However, electrostatic offset may occur in spite of the film having such a surface potential, and if the structural conditions of the fixing film fluctuate for some reason, the surface potential of the fixing film is sufficiently low. There was a case where a strong electrostatic offset occurred.

Further, in order to control the electric field for generating the offset, it is preferable that the resistance value of the fixing film is low, but if it is too low, the problem of leakage of transfer charge occurs. This is a phenomenon in which the transfer charge held by the transfer material escapes, which weakens the force for attracting the toner to the transfer material, resulting in an electrostatic offset.

In order to prevent this, the surface resistance of the fixing film must be 1 × 10 ⁶ Ωcm □ or more. In order to realize this resistance value, conventionally, it is general to optimize the amount of carbon as a conductive material added to the surface layer of the fixing film. For example, by adding 0.7% by weight of a slurry in which Ketjen black (a kind of carbon black) is dispersed in water to the binder, the surface resistance of the film can be about 1 × 10 ¹⁰ Ω □. it can.

However, the viscosity and pH of the coating solution during manufacture
The resistance value drastically changes depending on the value, the dispersion state of carbon, the change over time, etc., and it has been difficult to control the resistance value of the film to a constant value. Therefore, conventionally, in the fixing film manufacturing method and structure, the range in which the entire surface offset and the electrostatic charge can be prevented is narrow, and it has been difficult to achieve both.

In order to solve the above-mentioned conventional problems, the present invention aims to provide a fixing device of an electrophotographic apparatus which prevents the occurrence of electrostatic offset and reduces the fluctuation of the resistance value in the production of a fixing film. And

[0016]

In order to achieve the above object, a fixing device for an electrophotographic apparatus of the present invention is a fixing device for heating and melting a toner image to fix it on a transfer material. The surface material is made of at least a fluororesin and an ionic conductive electric resistance value control material.

In the above structure, the fixing device is composed of a seamless film and a heating device composed of a heater and a pressure roller having elasticity, and the surface of the seamless film contains a fluororesin and an ion conductive electric resistance control material. It is preferable.

Further, in the above structure, the fixing roller is composed of a heating device including a heater and a pressure roller having elasticity, and the surface of the fixing roller contains a fluororesin and an ion conductive electric resistance control material. preferable.

Further, it is preferable that the ion conductive electric resistance control material has a melting point higher than the maximum operating temperature of the fixing device.

Further, in the above-mentioned constitution, it is preferable that the ionic conductive electric resistance value controlling substance is an organic phosphorus salt. More specifically, the organic phosphorus salts include diphenyl phosphite, triethyl phosphite, triphenyl phosphite, decyl diphenyl phosphite, (nonylphenyl and dinonylphenyl mixture) triphosphite, triphenyl phosphate, triethyl phosphite. At least one substance selected from fate, tri (butoxyethyl) phosphate, hexamethylphosphonamide, dimethylphosphonate, phosphine oxide, alkylphosphine oxide, alkylphosphine sulfide, and phosphonium salt is preferable. More preferably, in addition to the organic phosphorus salt, antimony pentoxide, K ₄ T
iF ₆ is preferable, and a mixture of these may be added. It is preferable that the above-mentioned ionic conductive electric resistance control substance has a melting point not lower than the maximum operating temperature of the fixing device. That is, the general operating temperature of the fixing device is usually 120.
It is in the range of up to 200 ° C., and is at least 20 higher than the operating temperature.
It is preferable to have a melting point higher by ° C.

In the above constitution, it is preferable that the organic phosphorus salt is present in a state of being dispersed in an amount of 0.1 to 20% by weight with respect to the fluororesin.

In the above structure, the surface electric resistance of the fluororesin is 1 × 10 ⁶ Ω · cm □ to 1 × 10 ¹⁴ Ω · cm.
It is in the range of □, and preferably has an antistatic function. In this structure, it is preferable that the fluororesin is laminated in a film form on the surface layer of the polyimide seamless base material film or the fixing roller, for example.

In the above structure, the thickness of the fluororesin is preferably in the range of 1 to 50 μm. As a fluororesin, polytetrafluoroethylene (PTF
E), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP)
It is preferably composed of at least one fluororesin selected from at least one compound selected from

[0024]

According to the above-described structure of the present invention, the surface material of the fixing member in contact with the toner image of the fixing device that heats and melts the toner image and fixes it on the transfer material is at least the fluororesin and the maximum operating temperature of the fixing device or more. By including an ionic conductive electric resistance control material having a melting point, it is possible to realize a fixing device for an electrophotographic apparatus in which the occurrence of electrostatic offset is prevented and the fluctuation of the resistance value in manufacturing the fixing film is reduced. . That is, by containing the ion conductive electric resistance control material, it is uniformly mixed with the fixing film, the binder forming the surface layer of the fixing roller, and the fluororesin, and the surface of the surface is neutralized by the movement of ions. And give an appropriate resistance value. Therefore, the ionic conductive resistance control agent can be diffused uniformly over the entire surface without localization of the resistance control agent, so that a very uniform surface resistance value can be obtained. In this way, by eliminating fillers such as carbon and metal oxides, dispersion unevenness and nonuniformity of surface resistance, which are inherent in the resistance control agent of the electron conduction system, which lowers the resistance value by dispersing, electrostatic offset is eliminated. Can be prevented. Further, generally, the ionic conductive resistance control agent has a problem that the resistance value greatly changes depending on the temperature and humidity of the material surface, but when used for a fixing film or a fixing roller as in the present invention, Since these surfaces are constantly controlled to the fixing temperature during printing, they can be used without being affected by temperature and humidity.

In the above, the fixing device is composed of a heating device composed of a seamless film and a heater, and a pressure roller having elasticity, and the surface of the seamless film has at least a fluorine resin and a melting point higher than the maximum operating temperature of the fixing device. According to a preferable example of containing an ion conductive electric resistance control material, a substantially anti-electric resin seamless film such as a polyimide film and a fluororesin layer are provided with a preferable antistatic action / function. However, even if it contacts the passing printing paper, the electrostatic charge can be prevented, and the occurrence of electrostatic offset can be effectively prevented.

Further, in the above description, the fixing device is a heat roller fixing device, and the surface of the heat roller contains at least a fluororesin and an ion conductive electric resistance control material having a melting point higher than the maximum operating temperature of the fixing device. According to a preferred example, for example, a heat roller having a silicon rubber layer on the surface of a metal roll and a fluororesin layer on the surface thereof is provided with a preferable antistatic action / function and is brought into contact with a passing printing paper. It is possible to prevent electrification and effectively prevent the occurrence of electrostatic offset.

Further, in the above, when the ion conductive material is an organic phosphorus salt, antimony pentoxide, or K ₄ TiF ₆ , a particularly preferable antistatic function can be imparted.

Further, in the above, it is preferable that the organic phosphorus salt is present in a state of being dispersed in an amount of 0.1 to 20% by weight with respect to the fluororesin, because electrostatic offset can be effectively prevented from occurring. .

In the above description, the surface electric resistance of the fluororesin is 1 × 10 ⁶ Ω · cm □ to 1 × 10 ¹⁴ Ω · cm □.
It is preferable for it to be in the range of 1 to effectively exhibit the antistatic function.

Further, in the above, when the fluororesin is laminated in a film shape on the surface layer of the polyimide seamless base material film, when performing the on-demand fixing,
The occurrence of electrostatic offset can be effectively prevented, which is particularly preferable.

In the above, the thickness of the fluororesin is
When the thickness is in the range of 1 to 50 μm, the peelability of the paper is good, and the occurrence of electrostatic offset can be effectively prevented, which is preferable.

[0032]

EXAMPLES The present invention will be further described below with reference to examples.

Embodiment 1 In this embodiment, an on-demand type fixing device is used as the fixing device. The outline is shown in FIG. The fixing device 50 includes a heating unit and a pressure roller, and the heating unit includes a fixing film 1, a ceramic heater 3, and a film guide 2. The fixing device is driven by the pressure roller 4,
The transfer material (paper) 20 and the film 1 are driven by the pressure roller 4. The heater 3 is formed by printing a heating paste on a ceramic substrate, and heat is generated by passing an AC current whose power is controlled. Glass is coated on the heat generation pattern for protection and insulation. A chip thermistor 5 is adhered to the back of the ceramic substrate, and the energization of the heater 3 is controlled based on the temperature detected by this. The film guide 2 is made of thermosetting plastic, and a heater is attached to the lower surface of the film guide 2. The fixing film 1 moves along the film guide 2. The transfer material (paper) 20 is supplied from the right side with toner adhered to the surface,
It is heated at the nip point N between the heater 3 and the pressure roller 4, and the fixed image 22 is discharged to the right. Heater 3
Is controlled between 135 ° C. and 170 ° C., and the fixing film 1 is also heated to almost the same temperature.

Next, the fixing film 1 will be described. The fixing film 1 has a three-layer structure, and the base layer has a thickness of 50.
It is a cylindrical polyimide film having a μm and an outer diameter of 24 mm. Since the base layer slides on the heater and is required to have abrasion resistance and strength, polyimide is used as the material. A conductive primer layer is provided on this. This is because by energizing the heater pattern, a potential that induces an offset is prevented from reaching the film surface due to an AC electric field generated and frictional electrification between the heater and the film inner surface, and further adhesion between the polyimide and the surface layer is prevented. It is for securing. By exposing the conductive layer at the edge of the film and connecting it to the ground, the potential of the conductive layer is set to 0 V and the potential of the film is stabilized.

A release layer is provided on this. The release layer is required to have a high release property so as to withstand rubbing against the transfer material and prevent toner from adhering thereto. Aqueous enamel (aqueous dispersion) is used as a material, and a mixture of PTFE and PFA in a ratio of 7: 3 is mixed. In this example, 10% by weight of a product name “Hishicolin PX-2B” manufactured by Nippon Kagaku Kogyo Co., Ltd. was mixed as a resistance adjusting agent. This is an organic phosphorus compound (phosphonium salt) represented by (C ₂ H ₅ ) ₄ P · Br, and imparts conductivity mainly by the movement of positive phosphorus ions. It also dissolves well in water. Or Hishicolin PX-2B
(Melting point: 333 ° C), antimony pentaoxide, K ₄
An ionic conductivity imparting substance such as TiF ₆ is mixed into the resin.

FIG. 2 shows two consecutive 2 in the embodiment of the present invention.
FIG. 6 is a cross-sectional view showing a pattern in which a sheet of paper is being conveyed. The paper is being fed at the transport speed V. Further, when the outer diameter of the fixing film is D, the offset due to the peeling charge on the fixing film generated at the rear end of the paper should occur at a position of πD-L from the front end of the second paper. . Here, L is a sheet interval. However, in the present invention, since the peeling charge is sufficiently attenuated while the fixing film makes one round,
No offset occurs. The fixing film in this case is 1
The time required to make a round is obtained in πD / V. If the electric charge generated by peeling electrification is sufficiently attenuated within this time, the electric field from the film does not affect the toner on the next paper, so more accurately when the nip width is set to w. It is preferable to attenuate within the time given by (πD-w) / V. Thus no offset occurs.

In the present invention, the fixing film is made to have such an attenuation characteristic. That is, an organic phosphorus salt, antimony pentoxide, K ₄ Ti is contained in the fluorine resin coat.
The coating layer is fired in a state in which a material such as F ₆ which imparts ionic conductivity is dissolved to obtain a fixing film.
FIG. 3 shows the measurement of the potential decay after corona charging is applied to the surface of the film having the fluororesin release layer in which such an organic phosphorus salt is dissolved. The conditions were set so that the fluororesin release layer without addition was charged with 800V. On the other hand, it can be seen that the carbon black described above lowers the initial potential, but the attenuation is not great.

On the other hand, it was found that the one to which the organic phosphorus salt was added had a high initial potential but a large attenuation.

Concrete Example The paper conveyance speed is 50 mm / sec, the paper interval is 50 mm,
As the fixing film, one having an outer diameter of 24 mm was used, a conductive primer layer of about 4 μm was attached on a polyimide base layer of 40 μm, and PFA and PTFE were used as a fluororesin layer in a ratio of 3: 7. Mix and mix 5
An antimony oxide having a solid content ratio of 15 wt% melted was used as a coating. The nip width w should be 4 mm so that the silicone rubber thickness is 3 mm and the rubber hardness is JIS A.
A pressure roller having 50 °, an outer diameter of 20 mm, and a rubber surface length of 220 mm was loaded under a total pressure of 7.5 kg. In this configuration, (π
Since Dw) /V=71.4/50=1.428,
It is sufficient that the peeling charge is sufficiently attenuated within 1.4 seconds. It has been experimentally known that the offset does not occur if the peeling charge potential is lower than 400 V. In this case, 5
It was confirmed that the fixing film having the top coat in which antimony oxide was melted had a sufficient peeling charge, which prevented the offset.

Comparative Example 1 When 0.7% by weight of carbon black was added to the top coat, peeling charge remained and offset occurred.

Comparative Example 2 When 2.0 wt% of carbon black was added to the top coat, peeling charge was reduced, but charge leaked from the paper and offset occurred in a high humidity environment.

Potential measurement and image evaluation were performed using these samples. The apparatus used for image evaluation is an electrophotographic printer as shown in FIG. The photosensitive member 6 is a negatively charged OPC photosensitive member having a diameter of 24 mm, which is first uniformly charged to 650 V by the charging roller 7 and then the laser exposure device 8.
Then, the image area is imagewise exposed and the area is neutralized.
In the developing device 9, the negatively charged one-component magnetic toner undergoes a reversal phenomenon. The developing device 9 uses a non-contact jumping developing method. The developing sleeve has a DC voltage of 500 V, 1600 Vpp, 1800 Hz, and a rectangular AC.
A voltage and voltage are applied. The toner image thus developed is transferred onto the transfer material 20 by the transfer roller 10 to which +2 kV is applied, and is conveyed to the fixing device 50. After the transfer, the cleaning device 11 removes the toner after the transfer and the toner is ready for the next image formation.

Example 2 In this example, a heat roller type fixing device is used. The structure of the electrophotographic printer used in this embodiment is the same as that of the first embodiment, and only the fixing device is different. An outline of the heat roller type fixing device used is shown in FIG. Since the pressure roller 4 is the same as that used in the first embodiment, its explanation is omitted. The base material 12 of the fixing roller is an aluminum cylinder having an outer diameter of 30 mm, a wall thickness of 2 mm, and a length of 240 mm, and has a halogen heater 14 of 500 W inside. A contact type thermistor 5 is arranged in the base material 12 of the fixing roller on the side opposite to the nip with the pressure roller, that is, in the hollow inside of the base material 12 of the fixing roller. It detects and controls the energization of the halogen heater. This keeps the surface of the fixing roller at 190 ° C. The surface release layer 13 of PFA / PTFE is formed on the surface of the base material of the fixing roller. Since the base material 12 of the fixing roller is a rigid aluminum cylinder, it is not necessary to use a binder to give flexibility to the coating film during coating as in the case of a film, and the dispersion of PFA / PTFE can be achieved. A release layer can be formed by mixing a resistance control agent with and baking.

Conventionally, in order to prevent transfer charge from leaking from the fixing roller, the surface resistance value of the fixing roller is 1 ×.
It was necessary to be 10 ⁶ Ω · cm □ or more, and 0.7% by weight of carbon was dispersed to adjust to a desired resistance value.

However, even if the same amount of carbon is added, the resistance value after forming a coating film may change greatly depending on the temperature during coating, the dispersion state, the standing state of the coating liquid, the humidity during drying, etc. . For this reason, there is a problem in that stability during manufacture is poor and resistance value adjustment is difficult. This is because the dispersed state of carbon in the coating liquid changes due to various factors, and once the carbon has aggregated, it will not be dispersed again into primary particles. Therefore, the present embodiment is characterized in that the manufacturing stability is ensured by using an ionic conductive resistance control agent such as a filler such as carbon which does not change its resistance due to dispersibility.

The ionic conductive material does not disperse in the coating liquid but is dissolved ionicly, so that it is not localized and stable in a low entropy state without using a special mixing means. Therefore, even if the liquid is newly re-prepared, the concentration unevenness does not occur. However, since they are formed into a fixing film and do not deteriorate or volatilize even after durable paper passing, in the present embodiment, an ion conductive material whose melting point is higher than the maximum operating temperature of the fixing device is used. Is used.

Examples of such a material include antimony pentoxide and K ₄ TiF ₆ in addition to the above-mentioned organic phosphorus salt, hishicolin, as described in the first embodiment.

With such a structure, the nip width is 4 mm,
When the paper transport speed is 60 mm / sec and the paper interval is 50 mm, (πD−w) /V=1.50.
Offset can be prevented if the stripping potential falls below 400 V (which can vary from system to system) within 1.5 seconds.
This was achievable by mixing the above-mentioned antimony pentaoxide, K ₄ TiF ₆ and organic phosphorus salt into the fluororesin.

Needless to say, the aluminum core of the fixing roller is grounded.

Example 3 In the previous example, the paper interval was not related, but if the paper interval L is longer than D × π, the above equation becomes different.

In the case of D × π <L <2D × π, it suffices that the peeling charge potential is attenuated during (2D × π-W) / V. In general, if the paper interval L is lengthened, the decay time can be taken, so N × D × π <L
<(N + 1) D × π, (N × D × π−W) /
It suffices that the peeling charging potential be attenuated during V. In this way, it is possible to adjust the sheet interval as appropriate and to adapt it to the charge attenuation capability of the surface of the fixing film.

[0052]

As described above, the present invention differs from the conventional method of imparting conductivity by dispersing conductive particles, and by melting an ion conductive material in a fluororesin, the resistance value can be increased. Is to control both the high electric charge holding ability inside the nip and the high electric potential damping ability outside the nip. This makes it possible to prevent both offset due to peeling charging, which cannot be achieved with conventional carbon, and offset due to leakage of paper charge in a high humidity environment.

[Brief description of drawings]

FIG. 1 is an example of a sectional view of a film type fixing device using the present invention.

FIG. 2 is a diagram illustrating a dimensional relationship in a fixing device.

FIG. 3 is a diagram showing potential decay when carbon or an ion conductive material is added to a fluororesin.

FIG. 4 is a sectional view of an electronic processing apparatus of the present invention.

FIG. 5 is a sectional view of a heat roller type fixing device using the present invention.

[Explanation of symbols]

 1 Fixing Film 2 Film Guide 3 Ceramic Heater 4 Pressure Roller 5 Thermistor 6 Photoreceptor 7 Charging Roller 8 Laser Exposure Device 9 Developing Device 10 Transfer Roller 11 Cleaning Device 12 Base Material 13 Surface Release Layer 14 Halogen Heater 20 Transfer Material 21 Toner 22 fixing image 41 pressure roller core metal 50 fixing device

Claims (5)

[Claims] 1. A fixing device for heating and melting a toner image to fix it on a transfer material, wherein the surface material of the fixing member in contact with the toner image is at least a fluororesin and an ionic conductive electric resistance control substance. Fixing device for photographic equipment. 2. The fixing device is composed of a heating device including a seamless film and a heater and a pressure roller having elasticity, and the surface of the seamless film is made of a fluororesin and an ionic conductive electric resistance control substance. The fixing device for an electrophotographic apparatus according to claim 1. 3. The fixing device is constituted by a heating device including a fixing roller and a heater and a pressure roller having elasticity, and the surface of the fixing roller is made of a fluororesin and an ionic conductive electric resistance control substance. The fixing device for an electrophotographic apparatus according to claim 1. 4. The electrophotography according to claim 1, wherein the ionic conductive electric resistance control substance is any one of organic phosphoric acid, antimony pentoxide, and K ₄ TiF _6. Fixing device of the device. 5. The fixing device for an electrophotographic apparatus according to claim 1, wherein the ionic conductive electric resistance value controlling substance has a melting point higher than the maximum operating temperature of the fixing device.