JPH07281545A - Heat fixing device - Google Patents

Abstract

PURPOSE:To easily lower hardness even if a conductive heat resistant elastic material layer formed on the cone bar of a pressure roller is formed to have middle carrying hardness by incorporating whiskers subjected to a conducting treatment on their surfaces into this conductive heat resistant elastic material layer. CONSTITUTION:The pressure roller is constituted by successively forming the conductive heat resistant elastic material layer 1b and a heat resistant release layer 1c on the arbor 1a. The arbor 1a is used to provide the pressure roller 1 with strength, for which the arbor formed by pressurizing aluminum, stainless steel, etc., to a cylindrical shape is used. The conductive heat resistant elastic material layer 1b forms a nip part with a heating means via a fixing roller in the case of a fixing device of a heat roller system and via a fixing film in the case of a fixing device of a film system and is obtd. by incorporating fine whiskers of K2O.nTiO2 subjected to the conducting treatment into silicone rubber or fluororubber which is the heat resistant elastic material and vulcanizing and molding this rubber onto the arbor 1a. Further, fluororesins, such as PFA and PTFE, are used as the conductive heat resistant release layer 1c.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat fixing device used in an image forming apparatus such as a copying machine or a printer.

[0002]

2. Description of the Related Art Conventionally, many electrophotographic copying machines, printers, and the like employ a contact heating type heat roller fixing method or an energy-saving type film heating method, which have good thermal efficiency and safety, as a heating and fixing device. is doing.

The fixing device of the heat roller fixing type is a fixing roller having a surface of a core metal of aluminum or iron coated with a heat-resistant release layer, and a pressure roller having a heat-resistant elastic layer formed around a core metal of stainless steel or the like. It consists of and. Then, a heating means such as a heater is provided in the core metal of the fixing roller for heating, and the pressure roller is pressed against the fixing roller by a spring to form a nip, so that an unfixed toner image is formed on the fixing roller. The nip portion between the fixing roller and the pressure roller heats and pressurizes to fix onto the transfer material.

On the other hand, a film heating type fixing device is disclosed in, for example, JP-A-63-313182 and JP-A-2-1.
57878, JP-A-4-44075 to 4408.
No. 3, JP-A-4-204980 to 204984, etc., a heat-resistant film (fixing film) is brought into close contact with a heating means by a pressure roller and slidably conveyed, and the heat-resistant fixing is carried out. A transfer material carrying an unfixed toner image is introduced into the pressure contact nip portion formed by the heating means and the pressure roller with the film sandwiched between them, and the pressure contact nip portion is conveyed together with the heat resistant film to form the heat resistant film. This is a device for fixing an unfixed toner image as a permanent image on a transfer material by the heat from the heating means applied through and the pressure of the pressure contact nip portion.

As described above, in the above heat fixing device, since the pressure rotating member (pressure roller) having elasticity is used as the pressure member for forming the pressure contact nip portion, these heat fixing devices are used. When the fixing is repeated with, the surface of the pressure roller is charged up to a high voltage by frictional charging with the transfer material, the heating roller or the heat resistant film, and is charged to a high voltage. There is a problem called so-called "electrostatic offset" in which an image is disturbed due to force.

Therefore, in the conventional heat fixing device, carbon powder or the like is added to the heat-resistant elastic layer of the pressure roller as a conductivity-imparting material to form a conductive roller, which lowers the charging potential due to triboelectrification and makes it conductive. The electrostatic offset is prevented by grounding the heat-resistant elastic layer and the cored bar via a diode, or applying a bias of the opposite polarity to the toner from the cored bar to the transfer material via the conductive elastic layer. There is something.

However, according to the above-mentioned conventional example, a bias having a polarity opposite to that of the toner is applied to the conductive elastic layer, or the conductive elastic layer is grounded via a diode, and electrostatic offset is generated by the self-bias effect. In the case of preventing, if the resistance value of the conductive elastic layer is made too low, when a bias is applied, or when a transfer material holding a charge passes through the heat fixing device and a potential is induced in the diode, There has been a problem that electric charge leaks to the heating means, the frame of the heat fixing device, or the electric parts such as the excessive temperature rise prevention device and the temperature detection element to cause a failure.

Therefore, conventionally, in order to obtain a pressure roller that is effective in preventing electrostatic offset and does not cause leakage, the resistance value of the conductive elastic layer is set to a volume resistance of 1 × 10 ⁴ -1.
0 ¹⁰ Ω · cm, preferably 1 × 10 ⁶ to 10 ¹⁰ Ω · cm
It was necessary to set a medium resistance.

[0009]

However, the above-mentioned conventional example has a problem that it is difficult to reduce the hardness of the elastic layer of the pressure roller.

The lowering of the hardness of the elastic layer of the pressure roller is
It is necessary to improve the fixability of a toner image against the reduction in the diameter of the fixing roller and the pressure roller accompanying the recent reduction in size and cost of the image forming apparatus.

In other words, other methods for increasing the fixing property include increasing the fixing temperature and increasing the pressing force. In these methods, the heat-resistant temperature of the members constituting the heat fixing device or the strength of the bearing or the like is used. Since there are many limitations such as temperature rise in the image forming apparatus and permanent deformation of the pressure roller elastic layer, there are limits to securing the fixability by these methods. Therefore, it has been desired to reduce the hardness of the pressure roller as an effective means for ensuring the fixing property.

However, when carbon or the like is mixed into the heat-resistant elastic layer of the pressure roller to prevent offset, the resistance is kept constant in order to obtain sufficient conductivity to prevent electrostatic offset. It is necessary to add carbon in an amount not less than this amount, and if the amount of this additive in the elastic layer is large, the rubber hardness will be high, making it difficult to produce a roller with low hardness.

It is also conceivable to use ZnO whiskers having a three-dimensional tetrapot structure as the conductivity-imparting material to be added to the heat-resistant elastic layer, but this method provides high conductivity with a small amount of addition. Since it is possible to reduce the hardness because it is obtained, the conductive three-dimensional tetrapot whiskers form a strong conductive structure, and the resistance decreases exponentially with respect to the added amount of whiskers. There is a problem that it is difficult to control the resistance value of the elastic layer to a desired value.

Further, the heat-resistant elastic body such as silicone rubber (sponge) and fluororubber (sponge) has a lower tensile strength as the hardness is lowered, and the rubber breaks when it is repeatedly used as a pressure roller. There was a problem.

An object of the first invention of the present application is to solve the above-mentioned problems and provide a heat fixing device capable of easily lowering the hardness even when the heat resistant elastic body layer has a medium resistance. Especially.

The second object of the present invention is to:
In addition to the above purpose, it is an object of the present invention to provide a heat fixing device in which the resistance value of the conductive elastic layer of the pressure roller can be easily controlled to a desired value.

Further, in addition to the above objects, an object of the third invention of the present application is to provide a heat fixing device which does not cause the rubber to break even when used for a long period of time.

[0018]

According to the first invention of the present application, the above object is to provide a hollow cylindrical member which is rotatably disposed and is in contact with a transfer material or an unfixed image on the transfer material. A fixing roller or an endless belt-shaped fixing film, and a heating means included in the hollow portion of the fixing roller or arranged so as to come into contact with the inner surface of the fixing film.
In a heat-fixing device comprising the fixing roller or a pressure roller arranged so as to come into pressure contact with the heating means via the fixing film, the pressure roller has a conductive heat-resistant elastic member on a core metal. This is achieved by having a body layer, and the conductive heat-resistant elastic body layer containing a whisker whose surface is treated to be electrically conductive.

According to the second invention of the present application,
For the above purpose, whiskers whose surface is made conductive are made of K ₂ O.
Achieved by being an nTiO ₂ whisker.

Further, according to the third invention of the present application, for the above-mentioned purpose, the K ₂ O.nTiO ₂ whiskers have a fine diameter of 0.2 to 0.5 μm and a fiber length of 10 to 20 μm. This is achieved by having a fiber shape.

[0021]

According to the first invention of the present application, since the electrically conductive heat-resistant elastic body layer of the pressure roller contains the whiskers whose surface is treated to be electrically conductive, even if the amount of the whiskers added is small. High conductivity is obtained, and the hardness of the elastic layer is not increased. Therefore, even if the pressure roller has a small diameter and the applied pressure is increased, good fixing property is obtained without causing permanent deformation, and electrostatic offset is ensured by the high conductivity of the conductive heat resistant elastic layer. Prevent.

According to the second invention of the present application,
As a whisker whose surface is made conductive, K ₂ O ・ nTi
Since the O ₂ whisker is used, the resistance value of the whisker itself can be easily controlled by the surface treatment, and as a result, the resistance value of the conductive heat resistant elastic body layer can be easily controlled to a desired value.

Furthermore, according to the third invention of the present application, the K ₂ O.nTiO ₂ whiskers have a fiber diameter of 0.2 to
Since it has a fine fiber shape of 0.5 μm and a fiber length of 10 to 20 μm, the fibers are entangled with each other and the strength of the elastic body is improved, so that the elastic body does not break even during long-term use.

[0024]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

(First Embodiment) First, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a schematic sectional view of a first embodiment of a pressure roller to which the present invention is applied.

As shown in FIG. 1, the pressure roller of this embodiment has a structure in which a conductive heat resistant elastic body layer 1b and a heat resistant release layer 1c are sequentially formed on a core metal 1a.

The core metal 1a is for obtaining the strength of the pressure roller 1, and is made of aluminum, stainless steel or the like processed into a cylindrical shape. The electrically conductive heat-resistant elastic layer 1b forms a nip between the fixing roller in the case of a heat roller type fixing device and the heating means via a fixing film in the case of a film type fixing device. , Solid or sponge-like silicone rubber or fluororubber in which K ₂ O · nTiO ₂ fine whiskers (trade name: Dentol, manufactured by Otsuka Chemical Co., Ltd.) whose surface has been subjected to conductivity treatment are dispersed as a conductivity-imparting material. in and, K ₂ O · nTiO ₂ in which the conductive treatment in a silicone rubber or fluorine rubber heat resistant elastic material
It is obtained by mixing fine whiskers and performing vulcanization molding on the core metal 1a. Further, as the heat-resistant release layer 1c, PFA, PT
Fluorine resin such as FE is used.

FIG. 2 is an enlarged schematic sectional view of the conductive heat resistant elastic body layer 1b. As shown in FIG. 2, K ₂ O.nTiO ₂
The fine whiskers 8a are uniformly dispersed in the elastic layer 1b,
It forms a three-dimensional network structure of fine fibers and exhibits stable conductivity.

FIG. 3 shows the relationship between the addition amount and the resistance value of the rubber in the case of adding conductive K ₂ O.nTiO ₂ fine whiskers and the case of adding carbon in the silicone rubber. In order to obtain a pressure roller that prevents electrostatic offset and does not cause leakage, the volume resistance of the pressure roller is 1 × 10 ⁴ to 10 ¹⁰ Ω · cm, preferably 1 × 1.
It is necessary to set it to 0 ⁶ to 10 ⁸ Ω · cm. Volume resistance 1 ×
The amount of addition necessary to make it 10 ⁸ Ω · cm or less is about 12 w in the conductive K ₂ O · nTiO ₂ fine whiskers.
While it is t%, in the case of carbon, it is about 33 wt%.

When about 33 wt% of carbon is added, the volume occupied by the additive in the rubber becomes large, and the original physical properties of the rubber are not exhibited, and the hardness of the conductive heat resistant elastic layer which is a composite of the rubber and carbon is increased. Becomes higher and it becomes difficult to reduce the hardness. On the other hand, conductive K ₂ O · nTiO ₂
When the fine whiskers are added, the hardness does not become hard because the addition amount is small.

FIG. 4 shows different resistance values in silicone rubber.
K₂O ・ nTiO₂Fine whisker A (specific resistance 1 × 10⁰ ~
1 x 10¹Ω ・ cm), B (specific resistance 1 × 10)¹~ 1 x 10
²Ωcm) addition amount of whisker and rubber
Shows the relationship of resistance. Whisker surface as shown
Control the resistance of the whisker itself that is used by changing the treatment
This allows the resistance value of the conductive heat resistant elastic layer to be freely controlled.
It is possible to

In Table 1, a pressure roller C having a conductive elastic layer of silicone conductive rubber having a volume resistance of 1 × 10 ⁵ Ω · cm and an Asker C hardness of 38 degrees in which carbon is mixed as a dispersant is shown.
Similarly, K ₂ O.
Volume resistance mixed with nTiO ₂ whiskers 1 × 10 ⁵ Ω ・ c
m shows the usage time and the state of rubber breakage when the pressure rollers D each having a conductive elastic layer of silicone conductive rubber having an Asker C hardness of 38 degrees are continuously used in the image forming apparatus under the same conditions.

[0033]

[Table 1]

As described above, the low hardness silicone rubber mixed with carbon causes the rubber to break in 200 hours, whereas the silicone rubber mixed with K ₂ O.nTiO ₂ whisker is double the rubber even when used for 400 hours. No breakage occurred. As shown in FIG. 2, this whisker 8a has a very fine fiber shape with a fiber diameter of 0.2 to 0.5 μm and a fiber length of 10 to 20 μm. It is considered that the strength of rubber is increased.

As described above, K ₂ O.nTiO _{2 which has been} made conductive as a material for imparting conductivity to the heat-resistant elastic layer of the pressure roller is used.
The use of the fine whiskers makes it possible to easily control the resistance and to manufacture a pressure roller having low hardness and high strength.

(Second Embodiment) Next, a second embodiment of the present invention will be described with reference to FIG. The same parts as those of the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

FIG. 5 shows a schematic sectional view of a pressure roller according to the second embodiment of the present invention. A thin conductive sponge layer 5b and a heat-resistant release layer 5c are sequentially formed on the cored bar 5a. The core metal 5a is for obtaining the strength of the pressure roller, and is made of aluminum, stainless steel, or the like processed into a cylindrical shape.

The thin conductive sponge 5b forms a nip with the fixing roller or with the heating means via the fixing film and has a thickness of 1.5 to. A layer of about 3 mm, as the conductivity imparting agent to the sponge-like silicone rubber or fluorine rubber, surface conductive treatment was K ₂ O · nTiO ₂ fine whiskers (manufactured by Otsuka Chemical Co., Ltd., trademark: DENTALL) volume is dispersed resistance is the ^{1 × 10 6 ~10 8 Ω ·} cm and the Asker C hardness 35 degrees heat resistant thin conductive elastic layer of, K ₂ O · nTiO that the electroconductive treatment on a silicone rubber or fluorine rubber heat resistant elastic material ₂ Fine whiskers are mixed and foamed, wrapped around the core metal 5a, and the heat-resistant release layer 5
It is obtained by coating c and then vulcanizing it. As the heat-resistant release layer 5c, a fluororesin such as PFA or PTFE is used.

The thin conductive sponge layer 5b is grounded via a cored bar 5a and a diode (not shown). As shown in the above examples, by using K ₂ O · nTiO ₂ fine whiskers whose surface is made conductive as a conductivity-imparting material for the thin-walled sponge layer 5 c, the sponge layer has a medium resistance, a low hardness, and Strength can be increased.

In this embodiment, K ₂ O having its surface treated for conductivity is used.
-The thickness of the conductive heat-resistant elastic body layer is reduced by using an elastic body whose hardness is reduced by using nTiO ₂ fine whiskers. By reducing the thickness of the conductive sponge layer,
The thermal expansion of this conductive sponge layer can be reduced,
For example, in a film heating type fixing device, when the transfer material and the fixing film are conveyed by using the pressure roller as a driving roller, the change in the outer diameter of the pressure roller is reduced, so that the conveyance speed is more stable. In addition, when small-size paper is continuously fed, the difference in thermal expansion between the paper-passing part and the non-paper-passing part causes the shape of the pressure roller to change. Etc. can be prevented.

Further, the K ₂ O.nTiO ₂ whiskers have a very fine fiber shape with a fiber diameter of 0.2 to 0.5 μm and a fiber length of 10 to 20 μm, as shown in the above examples. Has the effect of penetrating into the partition walls that divide the fine foam cells in the sponge to be dispersed and exhibiting uniform conductivity, and reinforcing the thin and fragile partition walls to prevent the bubbles from breaking due to long-term use.

(Third Embodiment) Next, a third embodiment of the present invention will be described with reference to FIGS. 6 and 7. The same parts as those of the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

FIG. 6 is a schematic sectional view of a pressure roller according to the third embodiment of the present invention. As shown in FIG. 6, the pressure roller of the present embodiment has a high hardness first elastic layer 6 on a core metal 6a.
b, the second elastic layer 6c having a low hardness is sequentially formed. The core metal 6a is for obtaining the strength of the pressure roller,
A cylindrical product made of aluminum or stainless steel is used.

The first elastic layer 6b is a conductive heat-resistant elastic layer mainly for imparting conductivity to the pressure roller. Solid silicone rubber or fluororubber is provided with a conductivity-imparting material and carbon powder is added thereto. Asker C hardness of 50 degrees or higher,
A low resistance elastic layer having a volume resistance of 1 × 10 ⁵ Ω · cm or less.

The second elastic layer 6c forms a nip with the fixing roller or with the heating means via the fixing film, and is made of solid or sponge-like silicone rubber or fluororubber. As a conductivity-imparting material,
Asker C hardness in which K ₂ O · nTiO ₂ fine whiskers (Otsuka Chemical Co., Ltd., trademark: Dentol) having a surface made conductive are dispersed, low hardness of 40 degrees or less, volume resistance 1 × 1.
It is a heat resistant thin conductive elastic body layer with a medium resistance of 0 ⁶ to 1 × 10 ⁸ Ω · cm, and is made by mixing conductive rubber-treated K ₂ O · nTiO ₂ fine whiskers with a heat resistant elastic material such as silicone rubber or fluororubber. It is obtained by vulcanizing after coating on the first elastic layer.

The cored bar 6a is grounded via a diode to prevent electrostatic offset, or a bias of the opposite polarity to the toner is applied to the pressure roller via the cored bar 6a to prevent electrostatic offset. Is also good.

FIG. 7 is an enlarged schematic sectional view of the nip portion when a bias is applied from the pressure roller side to the heat roller fixing device using the pressure roller of this embodiment, and Table 2 contains carbon as a dispersant. Single-layer pressure roller E using a conductive elastic layer made of silicone conductive rubber having a volume resistance of 1 × 10 ⁵ Ω · cm
And the relationship between the applied bias and the offset level when the bias is applied to both of the two-layer pressure roller F having the configuration of this embodiment.

[0048]

[Table 2]

The two-layer pressure roller of the present embodiment is improved in electrostatic offset level by applying a lower bias than the single-layer roller.

The electrostatic offset occurs when there is an electric field that repels the toner from the transfer material to the heating roller side immediately before the nip portion N and the nip portion N. Therefore, when a bias having a polarity opposite to that of the toner is applied to the transfer material from the pressure roller side, the toner holding ability of the transfer material is enhanced and electrostatic offset is prevented. When the roller having the structure shown in this embodiment is used as the pressure roller, the second elastic layer 6c, which is the outermost surface layer, is compressed and deformed as shown in FIG. 7, and the density of the conductive whiskers near the nip portion N is increased. , The volume resistance of the nip portion N becomes relatively lower than that of the other portion of the second elastic layer. In this state, if a bias is applied from a power source (not shown) through the core metal, the bias is concentrated on the nip portion N where the resistance is partially low. It is possible to effectively prevent electrostatic offset with a lower bias than when using a single-layer pressure roller having only a body layer.

[0051]

As described above, the first aspect of the present application
According to the invention, since the whiskers whose surface is made conductive are added to the heat-resistant elastic layer of the pressure roller, even if the resistance is made medium, the hardness of the elastic layer can be easily reduced. Even when the diameter of the pressure roller is reduced, permanent deformation does not occur, and electrostatic offset does not occur, so that good fixability can be obtained.

According to the second invention of the present application,
As a whisker whose surface is made conductive, K ₂ O ・ nTi
Since O ₂ whiskers are used, in addition to the same effect as the first aspect of the invention, the resistance value of the conductive heat-resistant elastic body layer can be easily controlled to a desired value without causing leakage. It is possible to reliably prevent electrostatic offset.

Furthermore, according to the third invention of the present application, the K ₂ O.nTiO ₂ whiskers have a fiber diameter of 0.2 to
Since it has a fine fiber shape of 0.5 μm and a fiber length of 10 to 20 μm, it exhibits the same effects as those of the first and second inventions, and also causes breakage of the elastic body even during long-term use. It is possible to maintain a good fixing property for a long period of time without causing it.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a pressure roller according to a first embodiment of the present invention.

FIG. 2 is an enlarged schematic view of a conductive elastic layer in the pressure roller of FIG.

FIG. 3 is a graph showing the relationship between the added amount of the conductivity-imparting material and the resistance value.

FIG. 4 is a graph showing the relationship between the added amount of the conductivity-imparting material and the resistance value.

FIG. 5 is a schematic cross-sectional view of a pressure roller according to a second embodiment of the present invention.

FIG. 6 is a schematic sectional view of a pressure roller according to a third embodiment of the present invention.

FIG. 7 is a schematic cross-sectional view of a nip portion of a heat fixing device according to a third embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Pressure roller 1a, 5a, 6a Core metal 1b Conductive heat resistant elastic body layer 5b Thin conductive sponge layer (conductive heat resistant elastic body layer) 6c Second elastic body layer (conductive heat resistant elastic body layer) 8a K ₂ O nTiO ₂ Fine whisker P Transfer material T Toner (unfixed image)

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Satoru Izawa 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (3)

[Claims] 1. A hollow cylindrical fixing roller or an endless belt-shaped fixing film, which is rotatably disposed and is in contact with a transfer material or an unfixed image on the transfer material, and is enclosed in a hollow portion of the fixing roller. Or a heating means arranged so as to come into contact with the inner surface of the fixing film and a pressure roller arranged so as to come into pressure contact with the fixing roller or the heating means via the fixing film. In the heating and fixing device including, the pressure roller has a conductive heat-resistant elastic body layer on a core metal, and the conductive heat-resistant elastic body layer contains whiskers whose surface is made conductive. The heat fixing device is characterized by being provided. 2. The whiskers whose surface is made conductive are made of K ₂
The heat fixing device according to claim 1, wherein the heat fixing device is an O.nTiO ₂ whisker. 3. The K ₂ O.nTiO ₂ whiskers have a fine fiber shape with a fiber diameter of 0.2 to 0.5 μm and a fiber length of 10 to 20 μm. Heat fixing device.