JPH06318005A - Roller for fixing - Google Patents

Abstract

PURPOSE:To prevent an electrostatic offset by forming fluororesin layers into two-layered constitution respectively contg. low-resistance materials and setting the specific resistance of the lower layer lower than the specific resistance of the upper layer. CONSTITUTION:The high-resistance fluororesin layer 24' of 10 to 100mum thickness which is adjusted to 10<14> to 10<17>OMEGAcm specific resistance higher than the specific resistance of the fluororesin layer 23 by dispersing a conductivity imparting agent, such as carbon or tin oxide therein, is formed on the conductive fluororesin layer 23 of <=100<10>OMEGAcm specific resistance formed by a dipping method or coating method. The high-resistance resin layer 24' and the conductive resin layer 23 may be constituted as an integral two-layered tube of PFA and after elastic body 22 is formed on an arbor 21, the two-layered tube may be adhered thereto and baked. The conductive fluororesin layer 23 is electrically connected to the arbor 21 by a conductive rubber layer 25 at the end face and acts as an electrode facing the arbor within a nip N, by which an offset preventive electric field is formed.

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 on a recording material, which is used in a fixing device of an image forming apparatus such as a copying machine or a printer.

[0002]

2. Description of the Related Art FIG. 2 is a vertical sectional view of a conventional fixing device. The fixing roller 1 includes a cored bar 11 and a release layer 12 made of a fluororesin such as PFA or PTFE provided on the cored bar 11. The fixing roller 1 rotates in the arrow direction. The pressure roller 2 which was elastic layer 22 and the conductive fluorine resin layer 23 of silicone rubber or the like, an insulating fluorine resin layer 24 provided on the core metal 21, the fixing roller 1
It follows and rotates in the direction of the arrow. The metal core 1 of the fixing roller 1
A heater 3 is provided in the inside 1 to heat the fixing roller 1 from the inside. The surface temperature of the fixing roller 1 is measured by the temperature sensor 4 and input to a temperature adjusting circuit (not shown). The heater 3 is turned on and off by a temperature control circuit to control the surface temperature of the fixing roller 1 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. The paper sheet 5 on which the unfixed toner 6 that has been electrostatically transferred by the well-known electrophotographic process is placed is inserted into the fixing nip N through a guide means (not shown), heated and pressed to be permanently fixed to the paper sheet 5. To be done. A bias power supply 7 is connected to the core metal 11, and a voltage having the same polarity as the intrinsic charge of the toner 6 is applied to the core metal 11 so that the toner 6 is electrostatically repelled from the surface of the fixing roller 1. The offset phenomenon that the toner 6 is transferred to the surface of the fixing roller 1 and stains the subsequent image is prevented. In order to increase the repulsive electric field in the fixing nip N, the elastic layer 22 is generally made conductive, but as shown in FIG.
The conductive fluororesin layer 23 may be provided and used as the counter electrode of the cored bar 11.

FIG. 3 is a cross-sectional view of the pressure roller 2 taken along the line XX 'in FIG. The elastic layer 22 is made of heat resistant rubber such as solid type or sponge type silicone rubber or fluororubber. Conductive fluororesin layer 2
3 is a resin such as PFA or PTFE in which a conductivity-imparting agent made of a metal oxide such as carbon or tin oxide is dispersed, and then 10 to 100 by a dipping method or a coating method.
a PFA tube having a thickness of 10 μm to 100 μm in which a conductivity-imparting agent is dispersed,
Its volume resistivity is 10 ³ to 10 ⁷ Ω · cm. The insulating fluororesin layer 24 is a layer of only fluororesin such as PFA or PTFE, and is formed by a dipping method or a coating method.
It is made of a pure PFA tube having a thickness of 0 to 100 μm or a PFA tube having a thickness of 10 to 100 μm, which is made of PFA alone and has a volume resistivity of 10 ¹⁸ Ω · cm or more.
Conductive PFA tube 23 and insulating PFA tube 24
Is molded into a single two-layer tube in advance, and the elastic layer 2
It is also possible to fabricate the pressure roller 2 by coating it on 2 and firing it once.

On the end face of the pressure roller 2 , a conductive layer 25 having a volume resistivity of 10 ³ to 10 ⁵ Ω · cm in which a conductivity-imparting agent made of carbon or metal oxide is dispersed in silicon rubber.
Is formed, and the conductive layer 25 electrically connects the conductive fluororesin layer 23 and the core bar 21 to keep the potential of the conductive fluororesin layer 23 substantially equal to that of the core bar 21, It acts to increase the electric field strength in the nip N.

Insulating fluororesin layer 24 and release layer 12
In each case, the characteristics of the fluororesin, which has a high insulation property of 10 ¹⁸ Ω · cm or more together with the releasability, are used to prevent current leakage of the bias power source 7, and transfer charges of the paper sheet 5 are leaked. The toner 6 is not disturbed.

Although it is possible to disperse the above-mentioned conductivity imparting agent in the elastic layer 22, the conductive fluororesin layer 2
3, the counter electrode effect in the nip N can be obtained, so that the elastic layer 22 does not have conductivity but has a low hardness to reduce the hardness of the nip N.
It has been attempted to secure a sufficient size and obtain sufficient fixing property even at high speed. Further, from the viewpoint of energy saving, it is desirable to use a sponge having excellent heat insulating properties as the elastic layer 22.

[0007]

However, in the above-mentioned conventional example, peeling electrification occurs between the paper sheet 5 and the release layer 12 or the release layer 24 when the paper sheet 5 is discharged from the fixing nip N. It was found that it acts to weaken the repulsive electric field in the fixing nip generated by the power supply 7. As a result, the offset prevention effect is diminished, and offset may occur especially in a low humidity environment in which the paper sheet 5 has a high resistance. The peeling charge occurs particularly strongly when the rear end of the paper sheet 5 leaves the fixing nip N, and when the release layer 12 and the release layer 24 are new, particularly strong peeling charge at the rear end is observed. The surface potential of the corresponding portion has a polarity locally opposite to that of the bias power source 7,
That is, the polarity of the toner 6 is opposite to that of the toner 6, and the unfixed toner image that is in contact with that portion may be peeled off and offset on the subsequent image. FIGS. 4A and 4B show how the peeling offset occurs on the succeeding paper sheet 52 due to the strong peeling charge generated at the trailing end of the preceding paper sheet 51. In FIG. 5, the offset on the paper sheet 52 shows an image, and the toner 6 peeled off at the X portion is the fixing roller 1.
It shows a state of being offset on the image behind by the perimeter L of. The stripping offset occurs most clearly in the halftone image as shown in FIG. 5A, and in the case of the character image as shown in FIG. 4B, character loss due to stripping does not occur, but the subsequent portion Offset to.

In order to prevent this peeling electrification, the release layer 12
Alternatively, it is conceivable that the release layer 24 is made conductive, but the electric charge holding the image on the paper sheet 5 may leak through the conductive release layer to cause offset on the contrary.

Further, the fixing roller 1 or the pressure roller 2
When a bias voltage is applied to the device, current leakage may occur and the required bias voltage may not be maintained. This is because when the release layer 12 is made conductive, the insulating protective sheet of the temperature sensor 4 is worn after a long period of use, current flows through the temperature sensor 4 portion, and the release layer 24 is made conductive. This is because the insulating release layer 12 that comes into contact with the temperature sensor 4 is worn out after a long period of use, and an electric current may flow through the pressure roller 2 if it is used.

[0010]

The present invention for solving the above-mentioned problems has a core material, an elastic layer provided on the core material, and a fluororesin layer provided on the elastic body. In the fixing roller, each of the fluororesin layers has a two-layer structure containing a low resistance substance, and the lower layer has a lower specific resistance than the upper layer.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a fixing roller 2 according to a first embodiment of the present invention.
The same reference numerals as those used above indicate the same members. 24 'of the high-resistance dispersion and the specific resistance conductive agent such as carbon or tin oxide than the fluororesin layer 23 10 ¹⁴
It is a high resistance fluororesin layer having a thickness of 10 to 100 μm adjusted to 10 ¹⁷ Ω · cm, and can be formed by a similar method on the conductive fluororesin layer 23 formed by a dipping method or a coating method. I can. Also, the high resistance resin layer 24 '
Alternatively, the conductive resin layer 23 may be configured as one PFA two-layer tube, the elastic body 22 may be molded on the cored bar 21, and then the two-layer tube may be bonded and fired. Similar to the conventional example, the conductive fluororesin layer 23 is electrically connected to the cored bar 21 by the conductive rubber layer 25 on the end face, acts as an electrode facing the cored bar 11 in the nip N, and forms an offset prevention electric field. . The high-resistivity fluororesin layer 24 'prevents leakage of electric charge of the paper sheet 5 and current leakage of the bias power source 7 due to damage to the contact portion of the temperature sensor 4 of the release layer 12 after long-term use. By relaxing the insulating property, it acts so as not to cause peeling offset.

Experimental Example 1 The fixing roller 1 has an outer diameter of 3
50 mm PFA tube 12 on an aluminum core 11 of 0.0 mm, length 230 mm, wall thickness 3.0 mm
(Insulating property / specific resistance of 10 ¹⁸ Ω · cm or more) was used, and the surface temperature was set to 180 ° C. by driving at a peripheral speed of 100 mm / sec.

As the pressure roller 2 , a 7.0 mm thick foamed silicone rubber layer (insulating property / specific resistance of 10 ¹⁸ Ω · cm or more) is formed on a core metal 21 having a diameter of 16.0 mm, and the thickness is increased. 25 μm thick conductive PFA tube 23 (specific resistance 10 ⁰ to 10 ⁴ Ω · cm) and high resistance PFA 25 μm thick
Tube 24 '(specific resistance 10 ¹⁴ to 10 ¹⁵ Ω · cm) 2
The layer tube is bonded and fired to give an outer diameter of 30.05
mm, length 220 mm, hardness 40 ° (Asker C), fixing roller 1 at total pressure 9.0 N (Newton)
And a nip N having a width of 5.0 mm was obtained.

A power source 7 applies -500 V to the core metal 11, and the conductive PFA tube layer 23 is an end surface conductive rubber layer 25.
Via a diode (not shown) so that the potential thereof is non-negative.

Paper sheets weighed 75 gr / m ² and 12
A paper passing test was carried out using 0 gr / m ² of plain paper or OHP transparency (OHT) paper. The initial performance and the performance after 100,000 sheets of 75 gr / m ² paper were checked by focusing on the offset, and the results were as follows. As a comparative example, a PFA tube 24 'in which only the resistance value is changed is shown.

[0016]

[Table 1]

Comparative Example 1 (conductive PFA tube 24 ')
In the initial stage, peeling offset and other image stains do not occur, but after endurance, the temperature sensor contact portion of the release layer 12 of the fixing roller 1 is damaged and the bias voltage of the power supply 7 leaks,
Offset is generated in the case of thick paper or OHT because it is no longer applied. Further, when the bias voltage leaks, the conductive PFA tube 24 'is burned and the releasability is deteriorated, and the double-sided print image is contaminated. In Comparative Example 2 (insulating PFA tube 24 '), peeling offset was initially generated as described in the conventional example. In the case of the high resistance PF tube 24 'of this embodiment, a good image was shown both at the initial stage and after the durability test. Regarding the specific resistance of each fluororesin layer 24 ', instead of the fixing roller 1 , a roller having only an aluminum core metal 11 is mounted, and the core metal 11 and the conductive PFA tube 23 (specific resistance 10 ⁰ to 10 ⁴ Ω). -Cm) based on the measured resistance value [Ω] from the current value obtained when DC 100 V is applied,
It is calculated as a specific resistance [Ω · cm]. For example, in the case of the PFA tube 24 'used in this experiment, 10
When 0 V was applied, a current of 0.1 nA (nanoampere) flowed, so the resistance value was 1 × 10 ¹² [Ω], which was nip width 0.5 [cm] × length 22 [cm] × Thickness 0.0
This is a resistance value corresponding to the 025 PFA tube 24 ′, and this specific resistance is 1 × 10 ¹² × (0.5 × 22 / 0.0
025) = 4 × 10 ¹⁵ [Ω · cm].

Further, the fixing roller after endurance 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 value drops, 10 ¹³ Omega ·
It was found that the current leakage becomes large and the bias voltage drops when the pressure is less than 10 cm. When it was 10 ¹⁴ Ω · cm or more, the voltage drop was negligible.

The amount of the conductivity-imparting agent with respect to PFA is
In this example, a tube of 10 ¹⁴ to 10 ⁷ Ω · cm could be obtained by setting the amount of carbon dispersed to 1 to 8% by weight. Comparative Example 1 is a tube containing 10% by weight or more of carbon, and Comparative Example 2 is a pure PFA tube.

FIG. 6 shows a pressure roller which is a modified example of this embodiment.
2 shows a cross-sectional view of the main part of FIG. In this modification, the conductive fluororesin layer 23 is formed by a dipping method, and the end surface of the elastic layer 22 is formed so that the angle θ is an acute angle with respect to the core metal 21, so that the conductive fluororesin layer is formed. When forming 23 by dipping, the end face coating portion 25 ′ can also be in contact with the cored bar 21 in a shape in which the conductive fluororesin layer 23 is extended. By making the angle θ acute, the end face can be uniformly coated with the coating liquid by the action of gravity, and the peripheral surface portion 23 and the end face portion 25 'can be formed by one coating step, and the conductive rubber layer 25 is formed on the end face later. You can save the trouble of applying. The high resistance fluororesin layer 24 'can be formed by dipping coating, tube coating or the like after that.

<Second Embodiment> FIG. 7 is a cross-sectional view of a main part of a pressure roller 2 according to a second embodiment of the present invention, in which the same symbols as those used in the preceding description represent the same members. Both the conductive fluororesin layer 23 and the high resistance fluororesin layer 24 'are made of PFA tubes in which a conductivity-imparting agent such as carbon is dispersed, and each tube has a predetermined amount by controlling the dispersion amount of the conductivity-imparting agent. The conductive PFA tube 23 and the high-resistance PFA tube 24 'are formed as a single two-layer tube so as to obtain a specific resistance, and are bonded and fired on the elastic layer 22. At the end face of the pressure roller 2 , the two-layer tube 2
The length of the tube 3/24 'is set so as to project beyond the end position of the elastic layer 22, and the conductive sliding brush is designed to engage with the conductive PFA tube 23 at the projecting portion. 8 is provided, which controls the potential of the conductive PFA tube 23 to strengthen the electric field in the nip N and prevent offset. High resistance PFA tube 2
No. 4'has the same effect as shown in Example 1, and a good image having no offset can be obtained both at the initial stage and after the endurance.

<Third Embodiment> FIG. 8 shows a fixing roller according to a third embodiment of the present invention, which is applied to the fixing roller 1 unlike the above-mentioned example. In the above, the same reference numerals indicate the same members. Silicon rubber with a thickness of 2-5 mm on the core 11
Insulating heat-resistant solid rubber layer 15 made of fluororubber, etc.
Is formed, and the conductive fluororesin layer 13 and the high-resistivity fluororesin layer 14 are sequentially formed thereon. The fluororesin layers 13 and 14 may be sequentially formed by the dipping method / coating method as in the above-described embodiment, or may be formed by bonding and firing a single molded two-layer tube. A conductive roller 9 that engages with the conductive fluororesin layer 13 is arranged at the end of the fixing roller 1, and the conductive fluororesin layer 13 and the power source 7 are electrically coupled to prevent offset. . Further, the high-resistivity fluororesin layer 14 prevents the peeling offset and the bias potential drop during the initial stage and after the endurance as in the previous example.
The high-resistivity fluororesin layer 14 is also a layer in contact with the toner 6, and thus requires high releasability. When a large amount of a conductivity-imparting agent such as carbon is dispersed, the original releasability of the fluororesin tends to be impaired, but the high resistance (specific resistance 10
^{When the} amount of dispersion was controlled in the range of ¹⁴ to 10 ¹⁷ Ω · cm, no adverse effect such as offset due to the reduction of releasability was observed.

In the fixing roller 1 of this embodiment, since the solid rubber layer 15 does not contain foreign matter such as a conductivity-imparting agent dispersed therein, the elasticity of the rubber layer is sufficiently exerted, and the conductive fluororesin layer 13 and the high resistance are provided. The fluororesin layer 14 does not cause an offset from the initial stage to the end stage, and is suitable especially when the width of the nappe N needs to be increased in a high speed process.

[0024]

The present invention can prevent electrostatic offset,
Moreover, it is possible to provide a fixing roller having a low hardness.

[Brief description of drawings]

FIG. 1 is a lateral cross-sectional view of a main part of a pressure roller 2 according to a first embodiment of the present invention,

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

FIG. 3 is a cross-sectional view of a main part of a conventional pressure roller 2 ,

FIG. 4 is a diagram for explaining the occurrence of peeling offset,

FIG. 5 is a diagram illustrating a peeling offset image,

FIG. 6 is a cross-sectional view of a main part of a pressure roller 2 according to a modified example of the first embodiment of the present invention,

FIG. 7 is a cross-sectional view of a main part of a pressure roller 2 according to a second embodiment of the present invention,

FIG. 8 is a lateral cross-sectional view of a main part of a pressure roller 1 according to a third embodiment of the present invention.

[Explanation of symbols] 1 fixing roller 11 core metal 12 release layer 2 pressure roller 21 core metal 22 elastic layer 24 insulating fluororesin layer 13/23 conductive fluororesin layer 14/24 ′ high resistance fluororesin layer 25 conductive Rubber layer 3 Heater 4 Temperature sensor 5 Paper sheet 6 Toner 7 Power supply 8 Conductive sliding brush 9 Conductive roller

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

Claims (3)

[Claims] 1. A fixing roller having a core material, an elastic layer provided on the core material, and a fluororesin layer provided on the elastic body, wherein each of the fluororesin layers has a low resistance. A fixing roller having a two-layer structure containing a substance, wherein the lower layer has a lower specific resistance than the upper layer. 2. The specific resistance of the upper fluororesin layer is from 10 ¹⁴ to
10 ¹⁷ Ωcm, the specific resistance of the lower fluororesin layer is 10 ¹⁰ Ω
The fixing roller according to claim 1, wherein the fixing roller has a diameter of not more than cm. 3. The fixing roller according to claim 1, wherein the fluororesin layer is a two-layer tube.