JPH06318006A - Roller for fixing and fixing device - Google Patents

Abstract

PURPOSE:To provide a fixing layer which is free from offsets and has low hardness by having fluororesin tubes consisting of a lower layer having an electrical conductivity and an upper layer having an insulating characteristic on an insulating elastic body and setting the length thereof longer than the length of the insulating elastic body layer to conduct a conductive core material and the tubes. CONSTITUTION:A press roller 2' has the core material 11, the insulating elastic body layer 22 formed on this core material 11 and the fluororesin tubes which are formed on this insulating elastic body layer 22 and are made of the two-layered constitution consisting of the lower layer 24 having the electrical conductivity and the upper layer 23 having the insulating characteristic. The conductive thin film layer 24 engages with a conductive sliding brush 9 at the end face of the press roller 2' and is so constituted that the charge of the polarity reverse from the polarity of toners is held in the conductive thin film layer 24 by a diode 8. The electric field to attract the toners to the press roller 2' side is generated within a nip N by the bias voltage of the same polarity as the polarity of the toners supplied from a power source 7 connected to the arbor 11 of the fixing roller 1 and the effect of the charge of the polarity reverse from the polarity of the toners induced in the conductive thin film layer 24 in such a manner, by which the electrostatic offset of the toners is prevented.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art FIG. 2 is a vertical sectional view of a conventional fixing device. The fixing roller 1 comprises a cored bar 11 on which a release layer 12 made of fluorocarbon resin such as PFA or PTFE is provided, and rotates in the direction of the arrow. The pressure roller 2 has an elastic layer 22 made of silicon rubber or the like and a release layer 23 made of fluororesin such as PFA or PTFE etc. provided on a cored bar 21, and is rotated in the direction of the arrow following the fixing roller 1. To do. A heater 3 is provided in the core metal 11 of the fixing roller 1, and the fixing roller is
Heat 1 . The surface temperature of the fixing roller 1 is the temperature sensor 4
Is input to a temperature control circuit (not shown).
The heater 3 is turned on and off by the temperature adjusting 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 means (not shown), and a fixing nip N is formed. Unfixed toner 6 electrostatically transferred onto the sheet 5 by the well-known electrophotographic process.
Is inserted into the fixing nip N through a guide means (not shown), heated and pressurized, and permanently fixed to the paper sheet 5.

A bias power supply 7 is connected to the core metal 11, a voltage having the same polarity as the intrinsic charge of the toner 6 is applied to the core metal 11, and the toner 6 is electrostatically repelled from the surface of the fixing roller 1. In this way, the toner 6 is transferred to the surface of the fixing roller 1 to prevent the offset phenomenon that stains the subsequent image. To increase the repulsive electric field in the fixing nip N,
The elastic layer 22 is preferably conductive, and as an 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 insulative and have a resistivity of 10 ¹² Ω or more to prevent current leakage of the bias power supply 7.

[0004]

However, in the above-mentioned conventional example, since the elastic layer 22 is provided with the additive such as carbon for imparting conductivity, the hardness of the pressure roller 2 becomes large and the nip N is sufficiently large. However, there is a drawback in that the fixability deteriorates.

By the way, an iron rod having a diameter of 6 mm is used as the core bar 21, an elastic layer 22 made of only silicon rubber is formed on the iron rod, and a PFA tube 23 having a thickness of 50 μm is further covered to apply a pressure of 25 mm to the outer diameter. When the roller 2 was used, a roller hardness of 35 ° (Asker C) was obtained, and the fixing roller 1 whose surface temperature was controlled to 185 ° C. was pressed with a force of 10 Newton. It becomes 0.0 mm, and sufficient fixing property is obtained with plain paper or bond paper. This pressure roller 2
In order to impart conductivity to the silicone rubber of the elastic layer 22 of
When 20 to 50 wt% of carbon is applied, the roller hardness becomes 40 ° to 45 ° (Asker C), the width of the nip N becomes 3.0 to 4.0 mm, and the fixability deteriorates in a low temperature environment. When a paper sheet 5 such as bond paper having irregularities on the surface was used, the toner sometimes peeled off when rubbed by hand. To solve these problems, (1) pressure roller 2
Or (2) increase the outer diameter of the pressure roller 2 to increase the width of the nip N, or (3)
It is possible to recover the fixing strength by raising the fixing temperature of the fixing roller 1 , but in both cases (1) ... Wrinkles are generated in the folded paper sheet 5 such as an envelope (2). Increasing the size (3) ... Accompanied by the disadvantage that a fan or the like for preventing the temperature rise in the device is required.

Incidentally, there is a pressure roller 2 disclosed in Japanese Patent Laid-Open No. 4-340579 as an improvement of the pressure roller 2 for the purpose of solving the same problem as described above. FIG. 3 shows a vertical sectional view of an example of the pressure roller 2 .
The same reference numerals as those used above indicate the same members. Reference numeral 24 denotes a PFA layer having a conductivity of about 10 ⁷ Ω / cm by adding a conductivity imparting member to PFA resin. This is because (i) the conductive PFA layer 24 prevents offset, and (ii) the insulating PFA layer 23 and the conductive PFA layer 24 have a total thickness of 50 μm or less to secure the width of the fixing nip N. It is a thing. When the pressure roller 2 was incorporated into a fixing device and tested, the following results were obtained.

(I) The effect of preventing the offset of the conductive PFA layer 24 is that the elastic layer 22 has a specific resistance of 10 ¹¹ Ω, cm or less,
It is preferable that the elastic layer 22 has a specific resistance of 10 ¹² Ω, cm, although it is sufficient if it has a conductivity of 10 ⁷ Ω, cm or less.
As described above, in particular, in the case of having an insulating property of 10 ¹⁵ Ω or more, the conductive PFA layer 24 is in an electrically floating state, and as the paper sheet 5 is inserted into the nip N, the insulating PFA layer 24 is formed. It has been found that charges are induced in the layer 23 and the conductive PFA layer 24 and the offset-preventing electric field in the nip N is diminished, causing an offset.

(Ii) In order to effectively prevent the offset, the elastic layer 22 is made conductive to have a specific resistance value of 10 ⁷ Ω / cm or less, more preferably 10 ⁵ Ω / cm to 10 ³ Ω / cm. However, for this purpose, the elastic layer 2
The conductivity-imparting member such as carbon or metal oxide powder must be dispersed and mixed in 2, and as a result, the thickness of the PFA layer should be 5
Even when the thickness is 0 μm or less, as described above, the pressure roller 2
It was found that the hardness of the nip N became high and the width of the nip N became insufficient.

[0009]

According to the present invention for solving the above problems, a conductive core material, an insulating elastic layer provided on the core material, and an insulating elastic layer provided on the insulating elastic layer are provided. The fluororesin tube has a two-layer structure in which the lower layer is conductive and the upper layer is insulative, and the length of the fluororesin tube is made longer than that of the insulating elastic layer to electrically connect the core material and the conductive tube. In a fixing device including a fixing roller, a fixing roller that contacts an unfixed image, and a pressure roller that forms a nip with the fixing roller, the pressure roller includes a core member and a core member. An electrically conductive tube comprising: an insulating elastic body layer provided on a core material; and a fluororesin tube having a two-layer structure in which the lower layer is electrically conductive and the upper layer is electrically insulating, provided on the insulating elastic body layer. And the conductive scraper placed at the end of the pressure roller. A fixing device which is characterized in that.

[0010]

1 and 4 are a longitudinal sectional view of a fixing roller and a fixing device according to a first embodiment of the present invention and a lateral sectional view of a main part taken along line XX '. The same reference numerals as those used above indicate the same members. Reference numeral 22 'is an insulating elastic layer made of silicon rubber, fluororubber or the like having a thickness of 3 to 10 mm, and 24 has a thickness of 5
Is a conductive thin film layer having a thickness of up to 50 μm, and 23 is a PFA tube or P made by a spray method or a dipping method.
The release layer is made of TFE and PFA and has a thickness of 20 to 100 μm. The conductive thin film layer 24 is formed by coating liquid rubber with carbon as a base such as Ketjen black or metal oxide such as zinc oxide as a conductivity-imparting material in an amount of 10 to 30 wt% dispersed therein, or a PFA tube. A conductive PFA tube in which carbon is dispersed in an amount of 30 to 50 wt% may be formed by adhesion firing. Alternatively, the adhesive layer between the elastic layer 22 'and the release layer 23 may be made conductive to form the conductive thin film layer 24. Furthermore, the release layer 23 is an insulating PFA tube, and the conductive thin film layer 24 is a conductive PFA tube.
These tubes may be formed in advance as a one-piece tube having a two-layer structure and bonded and fired on the insulating elastic layer 22 '.

As described above, by constructing the pressure roller 2 ', since the elastic layer 22' does not need to add carbon or the like, it is possible to exhibit the original elasticity of the rubber and the conductive thin film layer 24.
While having a sufficient thickness as the electrode for preventing offset, since the fastened to a thickness that does not cause adverse effect to increase the hardness of the pressure roller 2, realized the pressure roller 2 'of low hardness I can. As an example, the insulating pressure roller described above in the conventional example showed 35 ° (Asker C), but instead of the insulating PFA tube (50 μm thick) of the release layer 23, the insulating PFA tube (25 μm) was used. Insulating PF
The pressure roller 2 ′ of this example using a two-layer PFA tube (total thickness 50 μm) in which A tubes (25 μm) were stacked showed 36 ° (Asker C). As described above, the pressure roller 2 ′ having sufficiently low hardness and conductivity can be realized as compared with the case where the elastic layer 22 is made conductive.

The conductive thin film layer 24 engages with the conductive sliding brush 9 at the end face of the pressure roller 2 ', and the diode 8 holds a charge having a polarity opposite to that of the toner 6 in the conductive thin film layer 24. Is configured to. In this way, the nip N
In the inside, the toner 6 is caused by the action of the bias voltage having the same polarity as the toner 6 supplied from the power source 7 connected to the core metal 11 of the fixing roller 1 and the charge having the opposite polarity to the toner 6 induced in the conductive thin film layer 24. An electric field that attracts the toner to the pressure roller 2 ′ side is generated, and electrostatic offset of the toner 6 to the fixing roller 1 can be prevented. In the case of the conventional conductive elastic layer 22, charge traps occur in the elastic layer to form a space charge layer,
Although the electric field inside the nip N may be weakened, the conductive layer of the present invention has a sufficiently small thickness and provides a good offset prevention electrode.

[0013] Figure 5 shows an essential part cross-sectional view of a modification of this embodiment, unlike the above embodiment, a two-layer PFA tube only tubes extend to the end surface of the pressure roller 2 'cylinder The parts 23 'and 24' are formed. The conductive slider 9 is arranged so as to come into contact with the extension portion 24 'of the conductive PFA tube, and has the advantage that the contact area can be made wider and the resistance at the contact portion can be made smaller than in the example of FIG.

[0014] <Second Embodiment> FIG. 6 shows a cross sectional view of the pressure roller 2 'of the second embodiment of the present invention, the same reference numerals O to supra shows the same member. Reference numerals 23 and 24 denote the two-layer PFA tubes similar to those described in FIG. 5 as a modified example of the above-described first embodiment. The two-layer tubes are extended from the end surface of the elastic layer 22 'and the extended cylindrical portion 23' is formed. , 24 'are narrowed down by a fixing means 26 such as an annular spring and fixed to the cored bar 21. A groove is provided in the cored bar 21 in accordance with the fixing means 26 so that the fixing means 26 does not move in the axial direction.

[0015] Figure 7 is the pressure roller 2 of a modification of the present embodiment '
FIG. 2 is a cross-sectional view of a main part of a two-layer tube with an electrode plate 27 fixed on a cored bar 21 and made of a thin metal plate.
Conductive PFA tube 2 with 3'and 24 'narrowed down
4'is arranged so as to contact the electrode plate 27. Two
Reference numeral 8 is a leaf spring which is attached to the cored bar 21 as one body and presses the two-layer tubes 23 'and 24' against the electrode plate 27 to ensure contact between the conductive PFA tube 24 'and the electrode plate 27. Is.

In this way, the conductive thin film layer 24 can be supplied with power from the cored bar 21, and the degree of freedom in designing the arrangement of the slider 9 is increased.

[0017] <Third Embodiment> FIG. 8 shows a main portion cross-sectional view of the pressure roller 2 'of the third embodiment of the present invention, the same reference numerals O to supra shows the same member. 22 "is an elastic layer made of insulative foamed silicone rubber, and the conductive thin film layer 2 is provided on the end face portion thereof.
A conductive coating film 25 in contact with No. 4 is formed so as not to cover the insulating elastic layer 22 ″ entirely but to expose a part thereof.
The conductive sliding brush 9 engages the conductive coating 25 to keep the conductive thin film layer 24 at ground or at a predetermined bias voltage. When the foamed silicone rubber 22 ″ is heated, the internal air pressure rises, the shape of the pressure roller 2 ′ expands into a balloon shape, and the outer diameter of the central portion becomes larger than the end portions, forming a crown shape. Although there is a problem that the body 5 is wrinkled, by forming the exposed portion of the foamed silicone rubber layer 22 ″ on the end face as in the present embodiment, it is possible to degas the inside air, so that there is little change in shape. Is obtained.

[0018] Figure 9 is the pressure roller 2 of a modification of the present embodiment '
FIG. The same reference numerals as those used above indicate the same members.
In this modified example, the feeding method at the end surface of the pressure roller 2 ′ is different from the above example, and the electrode plate 2 fixed on the cored bar 21 is different.
7'engages the conductive coating film 25, and the conductive slider 9'having a carbon tip at its tip engages the electrode plate 27 '.
The power supply method, since as compared to the brush type slider 9 described above can press the 'slider 9 on the end face' pressure roller 2 at a greater pressure, especially at high temperature reliable fixing device life Suitable for

In all of the above-mentioned embodiments, the present invention is applied to the pressure roller 2 ', but a hollow pipe is used as the cored bar 21 instead of the rod-shaped core, and the present invention is applied to the fixing roller 1. It is clear that can be applied.

[0020]

According to the present invention, there is an effect that it is possible to obtain a fixing roller having no offset and low hardness.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a fixing device according to a first embodiment of the invention.

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

FIG. 3 is a vertical sectional view of a conventional pressure roller.

FIG. 4 is a lateral cross-sectional view of a main part of the fixing device according to the first embodiment of the present invention.

FIG. 5 is a lateral cross-sectional view of a main part of a fixing device according to a modification of the first embodiment of the present invention.

FIG. 6 is a lateral cross-sectional view of a main part of a pressure roller according to a second embodiment of the present invention.

FIG. 7 is a lateral cross-sectional view of a main part of a pressure roller according to a modified example of the second embodiment of the present invention.

FIG. 8 is a cross-sectional view of a main part of a fixing device according to a third embodiment of the invention.

FIG. 9 is a lateral cross-sectional view of a main part of a fixing device according to a modification of the third embodiment of the present invention.

[Explanation of symbols]

1 fixing roller 2, 2 'pressure roller 3 heater 4 Temperature sensor 5 Kamihatai 6 Toner 7 power supply 8 diodes 9, 9' slider 11 metal core 12 releasing layer 21 metal core 22 conductive elastic layer 23 insulating Thin film layer 24 conductive thin film layer 25 conductive coating film 26 annular spring 27, 27 'electrode plate

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takayasu Yuminochi 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Toru Saito 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Within the corporation

Claims (2)

[Claims] 1. A two-layer structure in which a conductive core material, an insulating elastic layer provided on the core material, a lower layer provided on the insulating elastic layer are conductive, and an upper layer is insulating. A fixing roller, comprising: a fluororesin tube, wherein the length of the fluororesin tube is longer than that of the insulating elastic layer to electrically connect the core material and the conductive tube. 2. A fixing device having a fixing roller in contact with an unfixed image and a pressure roller forming a nip with the fixing roller, wherein the pressure roller is provided on a core material and on the core material. And an insulating elastic layer, and a fluororesin tube having a two-layer structure in which the lower layer is conductive and the upper layer is insulative, the fluororesin tube being provided on the insulating elastic layer and being electrically connected to the conductive tube, and applying pressure. A fixing device comprising a conductive scraper disposed at an end of the roller.