JPH06266255A - Fixing device - Google Patents

Abstract

PURPOSE:To prevent an offset and implement good thermal fixing by keeping a conducting elastic layer at the prescribed potential with a slider rubbing the end section of a fixing roller formed with the conducting elastic layer on an insulating elastic layer. CONSTITUTION:A paper sheet carrying an unfixed toner image is inserted between a fixing roller 1 and a pressure roller 2' to be fixed in a fixing device, and the pressure roller 2' is constituted of a core metal 21, an insulating elastic layer 22 formed on the core metal 21, and a conducting elastic layer 23 formed on the elastic layer 22. A slider 27 having a brush made by bundling stainless steel fibers buried in a metal carrier rubs the exposed portion of the end face of the conducting elastic layer 23 of the pressure roller 2' at an optional position other than the vicinity of a nip (n) in no possibility of interfering with the fixing roller 1 on the end face of the pressure roller 2'. The electric continuity paths A, A' are formed from the portion of the conducting elastic layer 23 kept in contact with the slider 27 on the portion of the conducting elastic layer 23 facing the nip (n), and it is kept at the desired bias potential.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art FIG. 2 shows an end view of an example of a conventional fixing device. The fixing roller 1 is formed by forming a release layer 12 such as PFA or PTFE on a cored bar 11 made of a pipe such as aluminum or iron, and is heated by a heater 3 arranged in the cored bar 11. The surface temperature of the fixing roller 1 is detected by the temperature sensor 4, the output thereof is input to a temperature controller (not shown), the heater 3 is controlled to be turned on and off, and is maintained at a predetermined temperature.

The pressure roller 2 is an elastic roller having a release layer 24 of PFA / PTFE or the like on its surface, and a cross-sectional view taken along the line XX 'is shown in FIG. An insulating elastic layer 22, such as foamed silicone rubber, foamed fluororubber, etc., a conductive silicone rubber 23, and a release layer 24 are formed in this order on a pipe 21 made of aluminum, iron or the like. Is rotatably mounted on the shaft 20. A pressing force is applied to the shaft 20 toward the fixing roller 1 by a spring (not shown), and a nip n is formed. The fixing roller 1 rotates in the direction of the arrow, and the pressure roller 2
Rotates following it. The paper sheet 5 on which the unfixed toner 6 is placed is inserted into the nip n by a guide unit (not shown), and is heated and pressed to permanently fix the toner 6 on the paper sheet 5.

A bias voltage having the same polarity as that of the toner 6 is supplied to the core metal 11 from the power source 7, and in combination with the electric charge of the opposite polarity to the toner induced in the conductive elastic layer 23, the toner 6 is stored in the nip n. To form an electric field that attracts to the pressure roller 2 side,
The toner 6 is prevented from electrostatically adhering to the fixing roller 1 so as to prevent an offset phenomenon in which a subsequent image is contaminated by the toner 6 transferred to the fixing roller 1 without any special cleaning means.

The pressure roller 2 has an Asker-C hardness 35 mainly composed of a sponge-like elastic layer 22 such as foamed silicon rubber.
It is a roller with low hardness of ° ~ 45 ° and its outer diameter is 20 ~.
Even with a small size of 40 mmφ, the total pressing force can be set to a relatively large value of 4 to 7 mm at a low pressure of 5 to 15 N (Newton), so the peripheral speed is 100 to 200 mm / s.
It is used in a relatively high speed device of ec, and is suitable for fixing a paper sheet 5 folded like an envelope.

The sponge elastic layer 22 is an essential element for realizing the low-hardness pressure roller 2 as described above.
This layer 22 itself is insulative, and a conductive elastic layer 23 is formed on the sponge elastic layer 22 to form the electric field in the nip n described above. This is sponge layer 2
Since the hardness of 2 itself becomes high when it is made conductive, a conductive elastic layer is provided by separating the functions. The conductive elastic layer 23 is t = 1 so as not to impair the low hardness of the sponge layer 22.
A thin layer of ˜2 mm is formed, the end face of the sponge layer 22 is covered 23 ′, and the electrode plate 28 is pressed against the electrode plate 28 so that the sliding electrode 25 having a carbon chip is in contact with the electrode plate 28. There is. That is, the electrode plate 28 rotates together with the conductive elastic layers 23 and 23 ′ to rotate, and the sliding electrode 25
Is fixed to the main body of the fixing device. In this way, the conductive elastic layer 23 includes the end face coating 23 ′, the electrode plate 28, and the sliding electrode 2.
It is connected to the diode 8 via 5. Conductive elastic layer 2
3 is a path for applying a bias voltage to the electrode plate 28.
It is also possible to connect the slider 25 to the shaft 20 through the end face coating 23 ', the pipe 21, the bearing 26, and the shaft 20 without using the above. It is unsuitable because it oxidizes and becomes insulating, resulting in poor conduction. On the other hand, by using the electrode plate 28, a bias voltage supply path having excellent durability and heat resistance is formed, and a fixing device without offset is realized.

[0007]

However, in the above-mentioned conventional example, when the pressure roller 2 is heated, the end face coating 2 is formed.
Since the amount of thermal expansion of the 3'portion differs from that of the central portion, the overall shape of the pressure roller 2 has a larger outer diameter at the central portion than at the end portions, and becomes a so-called crown shape. A large amount or large area has a drawback that wrinkles occur under high humidity. In addition, there is a problem that the sliding noise becomes loud due to the relative rotational movement between the electrode plate 28 and the sliding electrode 25 after long-term use or when rotating at a particularly high speed.

Further, when the end face coating 23 'of the pressure roller 2 is molded, the cylindrical shape of the pressure roller 2 as a whole may be distorted. This is adjusted by the rubber injection amount of the conductive elastic layer 23. However, there is a problem in that the productivity is unstable because the injection amount must be adjusted according to the hardness of the sponge layer 22.

The present invention is intended to solve the above problems.

[0010]

According to the present invention, the end face coating 23 'is eliminated to keep the pressure roller 2 in a stable shape and prevent the paper sheet 5 from wrinkling. In addition, by providing a conductive brush that rubs the end face portion of the thin conductive elastic layer 23, the conductive elastic layer 23 is maintained at a predetermined potential, offset is prevented, and good thermal fixing is performed.

[0011]

【Example】

<First Embodiment> FIGS. 1 and 4 are an end view of a fixing device according to a first embodiment of the present invention and a cross-sectional view of a main portion taken along line YY 'in FIG. The same reference numerals as those used above indicate the same members. Reference numeral 27 is a slider or a scraper in which stainless fibers or carbon fibers are bundled to form a brush 271 and embedded in a metal support 272. The scraper 27 is a pressure roller 2 '.
The end surface of the conductive elastic layer 23 is rubbed at a position other than the vicinity of the nip n at any position where there is no risk of interfering with the fixing roller 1.

With this structure, the portion 23 '' of the conductive elastic layer facing the nip n is electrically connected to the electric conduction path A from the portion 23 '''of the conductive elastic layer which is in contact with the sliding contact 27.・
A'is formed, the portion 23 '' is kept at a desired bias potential, and an offset preventing electric field can be created in the nip n portion.

The conductive elastic layer 23 must be sufficiently conductive in order to form the electrical conduction paths A and A '. With respect to the degree of conductivity, the magnitude of the electric field to be formed in the nip n is determined by the moving speed of the paper sheet 5, the amount of electric charge of the toner 6 and the like from the viewpoint of preventing offset, and the elastic layer corresponding thereto is obtained. Since the conductivity of 23 is required, the optimum value can be obtained by each device.

Incidentally, when the paper sheet 5 is conveyed at 100 mm / sec and the specific charge amount of the toner 6 is -20 to -5 μc / gr, the core metal 11 of the fixing roller 1 is supplied with -500 from the power supply 7.
When V was applied to prevent the offset, the conductive elastic layer 23 was made to have a thickness of 1.5 mm and its specific resistance was set to 1
Good results were obtained by setting the resistance to 0 ⁶ Ω · cm or less.

When the specific resistance is 10 ⁷ Ω · cm or more, an offset may occur, which is large between the portion 23 ″ ′ in contact with the slider 27 and the portion 23 ″ just below the nip n. Due to the potential difference, the potential of the portion 23 ″ becomes a value deviated to a negative value from the ground potential, and it is sufficient that the electric field in the nip n electrostatically attracts the toner 6 to the pressure roller 2 side. It is thought that it is because it does not become big.

In this embodiment, the releasing layer 12 of the fixing roller 1 is a PFA tube having a thickness of 30 μm, and the releasing layer 24 of the pressure roller 2'is a PFA tube having a thickness of 50 μm.
The thing with a micrometer was used. Further, when the resistance value of the conductive elastic layer 23 is measured, a metal pipe having only the cored bar 11 is used instead of the fixing roller 1, and the release layer 24 of the pressure roller 2'is peeled off so that the conductive elastic layer 23 has a conductive elasticity. The resistance value was obtained from the value of the current flowing when -500 V was applied to the core metal 11 so that the layer 23 was in direct contact with the core metal 11 and the slider 27 was grounded. Further, the specific resistance was obtained by converting the resistance value from the area and thickness of the conductive elastic layer 23 corresponding to the nip n.

As described above, according to this embodiment, the end face coating 23 'shown in the conventional example is not provided, and the conductive elastic layer 2 is provided on the end face.
Even if there is only a slight exposure amount of 3, the bias voltage supply path for preventing the offset can be secured. That is, the conductive elastic layer 23 has a substantially uniform thickness over the entire area of the pressure roller 2, and the amount of expansion of the central portion is the same as the amount of expansion at the end even when heated, and does not become a crown shape. Does not occur. Also, since the end face coating 23 'is not required,
The defective shape during molding does not occur, and the productivity of the pressure roller 2'is improved.

The pressure roller 2'of this embodiment has an insulating release layer 24 on the entire surface and covers the slider 2 '.
7 has a structure in which the end face is in contact with the conductive elastic layer 23. However, when the release layer 24 is composed of a conductive member such as a PFA tube in which carbon is dispersed, a slider 27 is used.
Can be arranged in the non-paper passing area or the non-image area at the surface end of the pressure roller 2 ′.

That is, the slider 27 is composed of the conductive elastic layer 2
By engaging with part 1 of 3, the potential of the portion 23 ″ immediately below the nip n can be guaranteed. When the surface of the pressure roller 2'is conductive, the slider 27 may be placed in the center from the viewpoint of supplying the bias voltage, but if the slider 27 is placed in the image area, it will be used after a long period of use. However, there is a disadvantage that the paper dust of the paper sheet 5 and a small amount of the offset amount of the toner 6 are accumulated on the fiber 271 and the electrical continuity cannot be finally obtained.

FIG. 5 shows a modification of this embodiment in which only the end of the insulating release layer 24 is peeled off and the slider 27 is brought into contact therewith. By arranging the slider 27 in this way, offset can be effectively prevented.

FIG. 5 shows an example in which the insulating elastic layer 22, the conductive elastic layer 23, and the release layer 24 are formed on the solid cored bar 21 'instead of the hollow pipe cored bar 21. However, it goes without saying that the shaft 20 may be used as shown in FIG.

<Second Embodiment> FIG. 6 is an end view of a fixing device according to a second embodiment of the present invention. The same reference numerals as those used above indicate the same members. The pressure roller 2 ′ is eccentrically arranged at a position biased to the downstream side of the fixing roller 1 when viewed in the conveyance direction of the paper sheet 5.
Sliding elements or sliding elements 27 and 27 'are arranged at positions which are substantially horizontally opposed to each other with the cored bar 21' interposed therebetween so as to come into contact with the exposed end surface of the conductive elastic layer 23.

A bias voltage having a polarity opposite to that of the intrinsic charge of the toner 6 is applied from a power source 7'to the sliding scraper 27 'arranged upstream of the sheet body 5 in the conveying direction and arranged downstream thereof. A bias voltage having the same polarity as that of the toner 6 is applied from the power source 7 to the sliding scraper 27.

Therefore, charges having a polarity opposite to that of the toner 6 are induced in the portion of the conductive elastic layer 23 facing the nip n, and this is combined with the effect of biasing the core 8 of the fixing roller 1 by the diode 8. , An electrostatic force that attracts the toner 6 to the pressure roller 2 ′ side is generated, and the offset is prevented.

Since the electric charge having the same polarity as that of the toner 6 is induced in the conductive elastic layer 23 in the downstream region from the outlet of the nip n of the pressure roller 2 ', the charge polarity of the paper sheet 5 is the polarity of the toner 6. In general, the paper sheet 5 discharged from the nip n is electrostatically attracted to the pressure roller 2 due to the opposite polarity, and separation of the paper sheet 5 from the fixing roller 1 is promoted. There is an advantage that good transportation can be performed.

Regarding the absolute value of the applied voltage of the power source 7 and the power source 7 ', depending on the positional relationship between the fixing roller 1 and the pressure roller 2, what kind of potential gradient is applied to the transport path in the conductive elastic layer 23. You can decide the appropriate value after seeing whether it is good to create along.

In the present embodiment, the power source 7 and the power source 7'are different power sources, but when the bias absolute values of both are the same, for example, the same AC power source is used and positive and negative power sources are used. The components are rectified and smoothed, and the respective sliders 27, 2 are
It is also possible to apply to 7 '.

<Third Embodiment> FIGS. 7 and 8 are an end view and a transverse sectional view of a main part of a fixing device according to a third embodiment of the present invention, in which the same reference numerals as those used in the preceding description denote the same members. The feature of this embodiment is that the roller of the present invention is used as the fixing roller 1 '.
An insulating sponge layer 13, a conductive elastic layer 14, and a release layer 12 are formed in this order on a hollow cored bar 11. The surface temperature of the fixing roller 1'is detected by the temperature sensor 4, and the heater 3 is turned on / off based on the output of the temperature sensor 4 so that the surface temperature is controlled to be constant.

In this embodiment, as the pressure roller 2 ', an insulating sponge layer 22, a conductive elastic layer 23, and
The release layer 24 is formed in this order using the same rollers as in the above-described embodiment, and the fixing roller 1'and the pressure roller 2'are used.
In the nip portion n, the slider 27 is arranged so as to contact the conductive elastic layers 14 and 23, respectively.

Therefore, the conductive elastic layer 1 of the fixing roller 1 '
4 and the conductive elastic layer 23 of the pressure roller 2 ′ are kept at the same potential, an electric field is not formed in the nip n, an electrostatic force that attracts the toner 6 to the fixing roller 1 ′ is not generated, and the offset is generated. Does not occur.

As described above, the offset can be prevented by positively setting the potential difference between the fixing roller 1'and the pressure roller 2'to zero because the sheet body 5 is charged to a polarity different from that of the toner 6. And the paper sheet 5 and the release layer 1
Nip n generated by frictional charging of 2 and 24 or peeling charging
This is the case when the electric field inside is small.

This corresponds to the case where printing is performed on one side of the ordinary paper sheet 5, but in the case of double-sided printing in which the back surface of the paper sheet 5 once having a permanently fixed image on one side is further printed, Since the paper sheet 5 is once dehumidified by the fixing device and has a high resistance, the frictional charge and the peeling charge between the paper sheet 5 and the release layers 12 and 24 are increased, so that the toner 6 is removed in the nip n. The electric field in the direction of drawing toward the fixing roller 1 ′ may have a size that cannot be ignored.

This may occur not only in double-sided printing but also in single-sided printing when the sheet material 5 having extremely high resistance (for example, one exposed to low humidity for a long time) is used. In such a case, the conductive elastic layer 14 and the conductive elastic layer 2 are applied so that different electric potentials are applied to the fixing roller 1'and the pressure roller 2'to create an electric field for offset prevention.
It is needless to say that a slider that comes into contact with each of the parts 3 other than the nip part n may be arranged.

Further, in each embodiment, the insulating elastic layer 2
Although the sponge-shaped one is shown as 2, the sponge is not essential, and needless to say, solid rubber may be used.

[0035]

As described above, according to the present invention,
With the slider 27 that rubs the end of the conductive elastic layer 23,
Keeping the conductive elastic layer 23 at a predetermined potential has the effect of preventing offset. Further, since the conductive elastic layer 23 and the slider are brought into conduction with each other, there is an advantage that abnormal noise due to sliding does not occur even after long-term use or during high speed rotation.

Further, since the end surface coating 23 'of the pressure roller 2 can be eliminated, the deformation of the pressure roller 2'at the time of heating can be prevented, and the wrinkles of the paper sheet can be eliminated, and the pressure is applied. The productivity of the roller 2'is also improved.

[Brief description of drawings]

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

FIG. 2 is an end view of a conventional fixing device.

FIG. 3 is a cross-sectional view of a main part of a conventional fixing device.

FIG. 4 is a lateral cross-sectional view of the essential parts of the first embodiment of the present invention.

FIG. 5 is a lateral cross-sectional view of a main part of a modified example of the first embodiment of the present invention.

FIG. 6 is an end view of the second embodiment of the present invention.

FIG. 7 is an end view of the third embodiment of the present invention.

FIG. 8 is a lateral cross-sectional view of the essential parts of a third embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Fixing roller 11, 21 ... Mandrel 12, 24 ... Release layer 13 ... Insulation sponge layer 14 ... Conductive elastic layer 2 ... Pressure roller 22 ... Insulating elastic layer 23 ... Conductive elastic layer 24 ... Release layer 25, 27 ... Slider 26 ... Bearing 271 ... Conductive brush 272 ... Support 28 ... Electrode plate 3 ... Heater 4 ... Temperature sensor 5 ... Paper sheet 6 ... Toner 7 ... Power supply 8 ... Diode

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

Claims (1)

[Claims] 1. A fixing device for permanently fixing a paper sheet carrying an unfixed toner image between a pair of rotating bodies, wherein at least one rotating body has an insulating elastic layer on a core metal. And a conductive roller having a conductive elastic layer having a substantially uniform thickness formed on the insulative elastic layer, the conductive sliding engaging at the end of the conductive elastic layer. A fixing device comprising a child, and the conductive elastic layer is kept at a predetermined potential through the conductive slider.