JP3236091B2 - Fixing roller and fixing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art FIG. 2 is a longitudinal sectional view of a conventional fixing device. The fixing roller 1 is provided with a release layer 12 made of a fluororesin such as PFA or PTFE on a metal core 11 and rotates in the direction of the arrow. The pressure roller 2 is provided with an elastic layer 22 made of silicon rubber or the like and a release layer 23 made of a fluororesin such as PFA or PTFE on a core metal 21.
It is rotated in the direction of the arrow following 1 . The inside core metal 11 of the fixing roller 1 for heating the fixing roller 1 than the internal heater 3 is disposed. The surface temperature of the fixing roller 1 is measured by a temperature sensor 4 and input to a temperature control circuit (not shown). The heater 3 is turned on and off by a temperature control circuit, and the surface temperature of the fixing roller 1 is controlled to a substantially constant value. The pressure roller 2 is pressed against the fixing roller 1 by a biasing unit (not shown), and a fixing nip N is formed. The unfixed toner 6 electrostatically transferred onto the paper sheet 5 by a well-known electrophotographic process is inserted into the fixing nip N via guide means (not shown), and is heated and pressed to be permanently fixed to the paper sheet 5. You. A bias power source 7 is connected to the metal core 11, and a voltage having the same polarity as the intrinsic charge of the toner 6 is applied to the metal core 11 so that the toner 6 is electrostatically repelled from the surface of the fixing roller 1. This prevents an offset phenomenon in which the toner 6 is transferred to the surface of the fixing roller 1 and stains a subsequent image. In order to increase the repulsion electrolysis in the fixing nip N, the elastic layer 22 is preferably conductive. For example, the elastic layer 22 made of silicon rubber in which carbon is dispersed can be used. The release layer 12 and the release layer 23 are electrically insulating to prevent current leakage of the bias power supply 7.

[0003]

However, in the above-mentioned conventional example, when the paper sheet 5 is discharged from the fixing nip N, a separation charge is generated between the paper sheet 5 and the release layer 12 or the release layer 23, It has been found that it acts to weaken the repulsive electric field in the fixing nip N generated by the power supply 7. As a result, the offset prevention effect is reduced, and offset may occur particularly in a low-humidity environment where the sheet 5 has high resistance. Peeling charging is particularly strong when the trailing end of the sheet 5 exits the fixing nip N. Particularly strong peeling charging of the trailing end is observed when the release layer 12 and the release layer 23 are new, which corresponds to the trailing end. The surface potential of the portion locally has a polarity opposite to that of the bias power supply 7, that is, a polarity opposite to that of the toner 6, and the unfixed toner image in contact with the portion is peeled off and may be offset on a subsequent image. . FIGS. 3A and 3B show a state in which this peeling offset occurs on the succeeding paper sheet 52 due to strong peeling charging generated at the rear end of the preceding paper sheet 51. FIG. 4 shows an offset image on the paper sheet 52, and shows a state in which the toner 6 peeled off in the X portion is offset on an image behind by the circumferential length L of the fixing roller 1 . The stripping offset is most clearly generated in a halfton image as shown in FIG. 4A, and in the case of a character image as shown in FIG. Offset occurs.

In order to prevent the separation charging, the release layer 12
Alternatively, it is conceivable to make 13 electrically conductive, but the charge holding the image of the paper sheet body 5 may leak through the conductive release layer to cause an offset.

Further, a fixing roller 1 or a pressure roller 2
When a bias voltage is applied to the IGBT, the required bias voltage may not be maintained due to current leakage. This is because, when the release layer 12 is made conductive, the insulating protective sheet of the temperature sensor 4 is worn out after a long period of use, and current flows through the temperature sensor 4 or the release layer 23 becomes conductive. This is because the insulating release layer 12 that comes into contact with the temperature sensor 4 also wears out after long-term use, and current flows through the pressure roller 2 .

[0006]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention is directed to a fixing device that fixes a sheet by holding and transporting a supporting material supporting an unfixed image by a pair of fixing rollers. At least one surface is coated with a conductive layer that disappears as the number of fixings increases.

[0007]

FIG. 1 is a sectional view of a fixing device according to an embodiment of the present invention.
FIG. 5 is a cross-sectional view of a main part along α-α ′ of a pressure roller 2 which is a fixing roller used in the fixing device of FIG.

The same members as those of the apparatus shown in FIG. 2 are denoted by the same reference numerals, and description thereof will be omitted.

The pressure roller 2 is formed by forming a sponge layer 24 made of insulating foamed silicon rubber on a metal core 21 and then forming a conductive elastic layer 22 made of conductive silicon rubber.
Further, the release layer 23 'of the present invention is formed as a surface layer. Here, the conductive elastic layer 22 has an adhesive property that can withstand long-term use as an adhesive layer between the sponge layer 24 and the release layer 23 '. The conductive elastic layer 22 is in contact with the electrode plate 25 at the end face, and a conductive slider 26 formed by molding a carbon chip at the tip of the electrode plate 25 comes into contact with the electrode plate 25, thereby making contact with the slider 26. The elastic layer 22 is maintained at the same potential.

The release layer 23 'is formed by dispersing conductive particles such as carbon, zinc oxide, tin oxide and titanium oxide in PFA to adjust the resistance to 10 ¹⁴ to 10 ¹⁷ Ω · cm.
A high-resistance PFA tube 23 'is placed in a mold together with a sponge layer 24 previously formed on a cored bar, and then a liquid conductive silicone rubber is injected between the tube 23' and the sponge layer 24. Pressing roller 2
Get. The end of the sponge layer 24 is chamfered so that the exposed amount of the end surface of the conductive elastic layer 22 is increased so that the contact between the electrode plate 25 and the conductive elastic layer 22 is ensured.

Next, specific experimental examples will be described.

<Experimental Example 1> The fixing roller 1 has an outer diameter of 3
PFA tube of 50μm thickness (insulating property) on aluminum core metal of 0.0mm, length 230mm, thickness 3.0mm
Resistance value is 10 ¹⁸ Ω · cm or more)
Drive at a peripheral speed of 100 mm / sec, surface temperature is 180 ° C
It was set to become.

As a pressure roller 2 , a 5.5 mm thick foamed silicone rubber layer 24 is formed on a core metal 21 having a diameter of 16.0 mm.
(Insulating property / resistance value is 10 ¹⁸ Ω · cm) · 1.5 mm thick conductive silicon rubber layer 22 (resistance value is 10 ⁰ to 10 ⁴ Ω)
· Cm) · 50 µm thick high resistance release layer 23 '(PFA
Into a tube by dispersing carbon in it, and the resistance value is 1
0 ¹⁴ to 10 ¹⁵ Ω · cm) with an outer diameter of 30.0 mm
A sheet having a length of 220 mm and a hardness of 40 ° (Asker C) was pressed against the fixing roller 1 with a total thickness of 9.0 N (Newton) to obtain a fixing nip N of 5.0 mm.

A voltage of -500 V was applied from the power supply 7 to the metal core 11, and the diode 8 was connected to the conductive elastic layer 22 via an electrode plate 25 and a slider 26.

The paper sheet 5 weighed 75 gr / m ² and 1
A history test was carried out using plain paper of ²⁰ gr / m ² or transparency (OHT) paper for OHP. The results of checking the initial performance and the performance after 100,000 sheets of 75 gr / m ² paper were paid attention to the offset were as follows.

As a comparative example, a case where only the resistance value of the release layer 23 is changed is shown. (Comparative Example 1: 10 ³ to 10 ⁵ Ωc
m, Comparative Example 2: 10 ¹⁸ Ωcm or more)

[0017]

[Table 1]

In Comparative Example 1 (conductive release layer 23), no peeling offset or other image contamination occurs at the initial stage, but after the endurance, the contact portion of the release layer 12 of the fixing roller 1 with the temperature sensor 4 is damaged. Since the bias voltage of the power supply 7 leaks and is not applied, an offset occurs in the case of thick paper or OHT. In addition, when the bias voltage leaks, the conductive release layer 23 is burned, resulting in low releasability, and the double-sided printed image is stained.

In Comparative Example 2 (insulating release layer 23), a peeling offset occurred at the initial stage as described in the conventional example.

The high-resistance release layer 23 of this embodiment showed a good image both at the initial stage and after the endurance.

The resistance value of each release layer is determined by the fixing roller.
A roller having only the aluminum core bar 11 is mounted in place of 1 and the volume is determined based on the actually measured resistance value [Ω] from the current value obtained when DC 100 V is applied between the core bar 11 and the conductive elastic layer 22. The resistivity [Ω · cm] is calculated.
For example, in the case of the release layer 23 used in this experimental example, 100 V
Since a current of 0.1 nA (nanoampere) flowed during the application, the resistance value was 1 × 10 ¹² [Ω], which was 0.5 [cm] in nip width × 22 [cm] in length × thickness. 0.005
[Cm] is a resistance value corresponding to the release layer 23, and its volume resistance is 1 × 10 ¹² × (0.5 × 22 / 0.005) =
It becomes 2 × 10 ¹⁴ [Ω · cm].

Further, the fixing roller after the durability used in Comparative Example 1
With 1, by changing the resistance value of the release layer 23 processing the bias voltage of the power supply 7 was determined resistance limit of leaking, 10 ¹³ Omega ·
It was found that current leakage started at less than 1 cm, and the bias voltage was lowered. If it was 10 ¹⁴ Ω · cm or more, no leakage occurred.

The amount of carbon dispersed in PFA is 1
By setting the content to ８8% by weight, a tube of 10 ¹⁴ 〜１０10 ¹⁷ Ωcm can be obtained. Comparative Example 1 was a tube containing 10% by weight of carbon, and Comparative Example 2 was a pure PF.
A tube.

As described above, the high-resistance release layer 23 has an effect of preventing offset, but when the PFA tube is placed in the mold at the time of molding the pressure roller 2 , it contains more carbon than the pure PFA tube. The high-resistance PFA tube has high rigidity, so the tube adheres well to the mold,
Another advantage is that the conductive silicone rubber can be easily injected at the time of molding and the yield of the shape at the time of molding is better than that of a pure PFA tube.

FIG. 6 is a longitudinal sectional view of a fixing device according to another embodiment of the present invention.

The feature of this embodiment is that the rotating body that comes into contact with the toner 6 is a thin fixing belt 1 ', and the plate heater 3' having a small heat capacity is turned on and off based on the output of the temperature sensor.
This is an energy-saving type fixing device which can instantaneously realize a fixing-possible state by being turned off. The fixing belt 1 'is based on a resin film 10 of polyimide or the like having a thickness of 30 to 100 [mu] m, on which a conductive layer 11' also serving as an adhesive layer having a thickness of 5 to 10 [mu] m and a thickness of 30 to 100 [mu] m.
Has an insulating release layer 13 made of a fluororesin such as PTFE or PFA, and is rotated by drive rollers 9 and 9 '. The conductive layer 11 'is grounded via a diode 8' and cooperates with the diode 8 connected to the metal core 21 of the pressure roller 2 'to electrostatically release the release layer 1 in the fixing nip N.
An electric field repelling the toner 6 from 3 is formed to prevent offset.

The pressure roller 2 has a conductive sponge layer 22 provided on a metal core 21 and a high-resistance PFA tube 23 'similar to that disclosed in the first embodiment is formed on the surface thereof. The conductive sponge layer 22 is formed by foaming silicon rubber in which carbon is dispersed on the metal core 21, cutting and polishing the resulting shape, and then bonding the high-resistance PFA tube 23 ′.

Also in this embodiment, it was found that the occurrence of offset can be prevented at the initial stage and after the endurance.

In the case of an energy-saving type fixing device as in this embodiment, it is preferable that the pressure roller 2 is a sponge roller having good heat insulating properties.

FIG. 7 shows still another embodiment of the present invention.

In this embodiment, a high-resistance release layer 12 'is provided on the surface of the fixing roller 1. In the above embodiment, the example in which the release layer 23 'is formed in the form of a high-resistance PFA tube is shown.
A solution obtained by dispersing a fine powder of tin oxide in E is applied by a spray method or a dipping method and then baked.

The pressure roller 2 has a volume resistance value of 1
0 on the formation of the ^{2 ~10 3 Ω} · cm solid shaped conductive silicone rubber 22 is obtained by coating the insulating PFA tube 23.

As the resistance value of the high-resistance release layer 12 ′, a conductive roller in which the insulating PFA tube 23 is peeled off from the pressure roller 2 as a roller facing the fixing roller 1 is arranged. And a voltage was applied to the conductive elastic layer 22. As a result, there was no peeling offset or offset due to transfer charge leakage in the range of 10 ¹⁴ to 10 ¹⁷ Ω · cm, which was the same measured value as described in Example 1. A fixing device was realized.

Next, still another embodiment of the present invention will be described.

As can be seen from Comparative Example 2 in Table 1, even if a release layer having a volume resistance value of 10 ¹⁸ Ωcm or more is used, no peeling offset occurs after durability.

This is because the peeling charge that causes the peeling offset is applied to the release layer 12 or the release layer 2 with the insertion of the paper sheet 5.
3, the history of peeling charge overlaps with the increase in the number of paper sheets 5 to be inserted, and there is no portion where the surface potential on the release layer 12 or the release layer 23 changes rapidly. Can be

Therefore, in this embodiment, the peeling charge at the initial stage is prevented.

FIG. 8 is a perspective view of a main part of this embodiment.

The fixing roller 1 has a pure PF
The pressure roller 2 has an elastic layer 22 made of conductive silicon rubber or the like on a metal core 21.
And a release layer 23 formed of a pure PFA tube on the uppermost layer. The shaded area A on the surface of the fixing roller 1
Is coated with a thin layer of conductive oil in which a surfactant is dispersed and mixed in dimethyl silicone oil. As dimethyl silicone oil, a mixture of 5 to 30 wt% of a fluorine-based surfactant EF-122B (trademark: manufactured by Mitsubishi Materials Corporation) mixed with a viscosity of 10,000 to 50,000 CPS at 20 ° C. is used for a felt cloth or the like. Fixing roller 1 after infiltration
And the fixing roller 1 is rotated to rotate the fixing roller 1 at 2 to 8 μg / cm.
² was applied to the shaded area A. The width l ₁ of the hatched area A is selected to be smaller by Δl at the end than the width l ₂ of the release layer 12 of the fixing roller 1 and to be wider than the width l _{0 of the} paper sheet 5.
(L ₀ <l ₁ <l ₂ ) Further, the width l ₃ of the release layer 23 of the pressure roller 2 is set to l ₁ <l ₃ .

By forming the conductive thin layer in the shaded area A as described above, the rear end of the sheet 5 is discharged from the fixing nip N even when the fixing roller 1 and the pressure roller 2 are new. In this case, local strong peeling charging can be prevented, and peeling offset does not occur. In addition, as the number of sheets passed through the sheet 5 increases, the conductive area A gradually disappears due to the transfer of the silicone oil to the sheet 5, but in the course of the disappearance, the release layer 12 has a strong local charge. The release layer 12 is entirely charged when a large number of sheets 5 have passed through so that the conductive area A disappears, and strong peeling charging is observed locally. Not done. Here, a large number is 100 to 1
The number of sheets passed is about 000 sheets.

Since the conductive region A is applied only in the above-described range, the conductive thin layer formed thereon has a function as a float electrode. When the conductive area 24 is expanded to the width l ₂ of the fixing roller 1, the point of preventing peeling charging is as described above. However, the conductive thin layer is in contact with the core 11, or the conductive elastic layer 22 is not in contact with the conductive elastic layer 22. The transfer charge to be held by the sheet body 5 leaks to the ground due to the contact, so that the holding force of the toner 6 is reduced, and the fixing is particularly performed on the sheet body 5 such as an OHP film in which an insulating film is subjected to a conductive treatment. Since there is a problem of offset to the roller 1 , it is desirable to provide the non-application region Δl of the conductive oil.

As described above, according to the present embodiment, 10 ¹⁸ Ωcm
The release layer described above can be used.

The purpose of the present embodiment is to provide a conductive thin layer that exists only for a necessary period for the purpose of preventing a peeling offset that is temporarily generated in a new state. At the time of disappearance, the conductive thin layer also has the characteristic of disappearing.

[0044] Conventionally, which presses the impregnated pad or the like the oil to the fixing roller 1 is known to be continuously supplied releasability oil to the fixing roller 1, which is periodically pad exchange The user feels inconvenience, such as the need. The fixing device of the present embodiment prevents image contamination due to offset or the like without using such a pad or other cleaning means, and provides a fixing device that does not require replacement by a user and requires no maintenance.

FIG. 9 shows still another embodiment of the present invention.

This embodiment includes a thin fixing belt 1 and a plate heater 3 'having a low heat capacity, as in the embodiment shown in FIG.

The fixing belt 1 'is based on a resin film 11' of polyimide or the like having a thickness of 30 to 100 .mu.m, on which a conductive layer 12 'serving as an adhesive layer having a thickness of 5 to 10 .mu.m and PTFE having a thickness of 30 to 100 .mu.m. Alternatively, it has a release layer 13 made of a fluororesin such as PFA, and is rotated by the drive rollers 9 and 9 '. The conductive layer 12 'is grounded via the diode 8', and the core 21 of the pressure roller 2 'is grounded.
Cooperates with the diode 8 connected to the fixing member N to form an electric field that electrostatically repels the toner 6 from the release layer 13 in the fixing nip N to prevent offset. Reference numeral 25 denotes a conductive thin layer formed on the surface of the pressure roller 2 , which is coated with conductive silicon oil and acts as a float electrode in the same manner as in the above-described embodiment.

In this configuration, when the rear end of the sheet 5 is discharged from the fixing nip N, the conductive thin layer 25 is separated from the release layer 13.
By contacting with, the peeling charge of the rear end portion is prevented, and no peeling offset occurs. Further, the conductive thin layer 24 disappears with an increase in the number of sheets passed, but by then the charging of the release layer 13 is averaged due to the effect of the conductive oil transferred from the pressure roller 2. Therefore, even after the disappearance of the conductive thin layer 25, strong local electrification does not occur, and no peeling offset occurs.

FIGS. 10 and 11 show still another embodiment of the present invention.

The fixing roller 1 is placed on the cored bar 11 by 30 to 100.
After coating the micron insulating PFA tube 12,
Aluminum is formed by vacuum evaporation to form a thin conductive layer 26 having a thickness of 0.1 to 0.5 μm. Masking is performed at the time of vapor deposition.
2 are exposed over the length of Δl so that the conductive thin film 24 ′ is kept electrically floating without conducting to the metal core 11.

The conductive thin film 26 is formed to be extremely thin. When the conductive area 26 of the fixing roller 1 is observed microscopically, discrete aluminum electrodes are formed on the PFA tube 12. In other words, if an excessively thick aluminum layer is formed as the conductive layer 26, the PFA surface will be covered and the releasability will be remarkably reduced, causing an offset. The releasability of the tube was not significantly reduced, and no offset image was generated. The conductive thin layer 26 is a microscopically discrete aluminum electrode,
It was confirmed that there was a sufficient effect to prevent the trailing end peeling electrification of the paper sheet 5, and no peeling offset occurred.

Also in this embodiment, several thousand paper sheets 5 are used.
The conductive thin layer 26 disappears by passing the sheet, but at that time, the local peeling charge has become inconspicuous, and it has been confirmed that the peeling offset does not occur.

[0053]

As described above, according to the present invention, it is possible to prevent offset generated due to peeling charging without losing the charge supporting the unfixed image of the support material.

[Brief description of the drawings]

FIG. 1 is a sectional view of a fixing device according to an embodiment of the present invention.

FIG. 2 is a sectional view of a conventional fixing device.

FIG. 3 is a diagram illustrating occurrence of an offset.

FIG. 4 is a diagram illustrating occurrence of an offset.

FIG. 5 is a sectional view of a pressure roller.

FIG. 6 is a sectional view of a fixing device according to another embodiment of the present invention.

FIG. 7 is a sectional view of a fixing device according to still another embodiment of the present invention.

FIG. 8 is a perspective view of a main part of a fixing device according to still another embodiment of the present invention.

FIG. 9 is a sectional view of a fixing device according to still another embodiment of the present invention.

FIG. 10 is a partial perspective view of a fixing roller according to still another embodiment of the present invention.

FIG. 11 is a sectional view of a fixing device according to still another embodiment of the present invention.

[Description of Signs] 1 Fixing roller 2 Pressure roller 3 ・ 3 ′ Heater 4 Temperature sensor 5 Paper leaf 6 Toner 7 Power supply 8.8 ′ Diode 9 Driving roller 11.21 Core 12 ・ 23 Insulating tube 23 ′ High Resistance tube 24 Sponge layer 25/26 Conductive layer

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroaki Sakai 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor 7 ▲ Taki ▼ Hideo 3-30-2 Shimomaruko, Ota-ku, Tokyo (56) References JP-A-4-274472 (JP, A) JP-A-1-161278 (JP, A) JP-A-4-93875 (JP, A) JP-A-4-340579 (JP, A) JP-A-62-291685 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 15/20

Claims (2)

(57) [Claims] An image forming apparatus comprising: a fixing roller for nipping and transporting a supporting material supporting an unfixed image by a fixing roller pair to perform fixing, wherein only a surface of at least one of the roller pair disappears as the number of times of fixing progresses only at an initial stage. A fixing device characterized by being coated with a layer. 2. The fixing device according to claim 1, wherein the conductive layer is in a floating state.