JP2821414B2 - 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 sheet for applying heat and pressure to an unfixed toner image, and a fixing device for performing heat and pressure fixing using the fixing sheet.

[0002]

2. Description of the Related Art Conventionally, as a fixing device for fixing an unfixed image, a heating roller maintained at a predetermined temperature and a pressure roller having an elastic layer and pressing against the heating roller are provided.
A heat roller fixing method in which a recording material on which an unfixed toner image is formed is heated while being nipped and conveyed is often used.

However, this heat roller fixing method has a problem that an offset phenomenon occurs in which toner transfers from a recording material to a heating roller.

In order to prevent this offset phenomenon, it is necessary to maintain the heating roller at an optimum temperature, and it is necessary to increase the heat capacity of the heating roller or the heating element. That is, when the heat capacity of the heating roller is small, the temperature of the heating roller tends to fluctuate greatly to the low temperature side or the high temperature side due to paper passing or other external factors depending on the amount of heat supplied by the heating element. If it fluctuates to the low temperature side,
Insufficient softening and melting of the toner causes poor fixing and low-temperature offset. If the toner fluctuates to a high temperature, the toner is completely melted and the cohesive force of the toner is reduced, resulting in high-temperature offset.

If the heat capacity of the heating roller is increased in order to avoid such a problem, the time required for heating the heating roller to a predetermined temperature becomes longer, and the standby time becomes longer when the apparatus is used. Problems arise.

As described above, in the heat roll fixing system, it is common to apply a lubricating oil to the roller surface in order to prevent offset, and to clean the offset toner.

To reduce or eliminate the problem of offset in heat fixing, US Pat.
No. 8,797, JP-B-51-29825, and JP-A-62-147884, proposed by the applicant, after heat is applied to an unfixed toner image from a heating element via a sheet to solidify the toner. It has been proposed to separate the sheet from the recording material.

[0008]

The sheet in contact with the recording material is required to have tensile strength and heat resistance.

However, even if this requirement is satisfied, the toner may be slightly offset on the sheet.

Further, there is a case where dust adheres to the sheet and the fixing property is deteriorated.

If the resistance of the sheet is reduced in order to prevent the offset and the attachment of dust, the tensile strength and durability described above are reduced.

[0012]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention relates to a heating element, wherein one surface slides on the heating element and the other surface contacts a recording material carrying an unfixed toner image. A moving resin sheet, wherein the fixing device fixes an unfixed toner image on a recording material by heat from the heating element via the resin sheet. It has a surface release layer in contact with the toner image and a resin base layer containing no low-resistance material.

[0013]

Embodiments of the present invention will be described below.

FIG. 1 is a sectional view of an electrophotographic copying apparatus to which a fixing sheet and a fixing device according to an embodiment of the present invention are applied.

In FIG. 1, reference numeral 1 denotes a document table made of a transparent material such as glass, which scans a document by reciprocating in the direction of arrow a. A short-focus small-diameter imaging element array 2 is disposed immediately below the document table, and a document image G placed on the document table 1 is disposed.
Is illuminated by an illumination lamp 7, and the reflected light image is slit-exposed on the photosensitive drum 3 by the array 2. The photosensitive drum 3 rotates in the direction of arrow b. Reference numeral 4 denotes a charger, which uniformly charges the photosensitive drum 3 covered with, for example, a zinc oxide photosensitive layer or an organic semiconductor photosensitive layer 3a. On the drum 3 uniformly charged by the charger 4, an electrostatic image subjected to image exposure by the element array 2 is formed. The electrostatic latent image is visualized by the developing device 5 using a toner made of a resin or the like which is softened and melted by heating. On the other hand, the recording material P stored in the cassette S is pressed and rotated in a vertical direction at a timing synchronized with the feed roller 6 and the image on the photosensitive drum 3 to be rotated by a pair of conveying rollers 9. It is sent onto the drum 3. Then, the toner image formed on the photosensitive drum 3 is transferred onto the recording material P by the transfer discharger 8.
After that, the recording material P separated from the drum 3 by a known separating unit is guided to the fixing device 20 by the transport guide 10, and is discharged onto the tray 11 after being subjected to the heat fixing process. After the transfer of the toner image, the residual toner on the drum 3 is removed by the cleaner 12.

FIG. 2 shows the fixing device 20 embodying the present invention.
FIG. In the figure, reference numeral 21 denotes a heating element, which has a width of 160 μm and a length (length in a direction perpendicular to the paper surface) on the lower surface of a heat-resistant and electrically insulating base material such as alumina or a base material made of a composite member including the same. Sa) 216 mm, for example, Ta ₂
It has a linear or belt-like heat generating surface 28 made of N or the like, and further, for example, Ta ₂ O ₅ is formed on the surface thereof as a slide protection layer. The lower surface of the heating element 21 is smooth, and the front and rear ends are rounded to enable sliding with the heat-resistant sheet 23. The heat-resistant sheet 23 is wound around a sheet feed shaft 24 so that it can be fed at the same speed as the recording material in the direction of arrow C. The heat-resistant sheet 23 comes into contact with the surface of the heating element 21 and is wound around a sheet winding shaft 27 via a separation roller 26 having a large curvature.

Next, the sheet 23 will be described.

As described above, the sheet 23 is required to have strength and heat resistance.

When a material having excellent strength and heat resistance, such as polyimide, was used, the releasability between the polyimide sheet and the toner was poor, and a slight offset was observed.

An embodiment of the sheet 23 used in the present invention will be described below.

Embodiment 1 Sheet 2 as shown in FIG.
3 includes a plurality of layers 231 and 232.

Reference numeral 231 denotes a heat-resistant layer having excellent strength, which is a base layer of the sheet 23 and is composed of a polyimide film having a thickness of 9 μm.
Contact with

A release layer 232 made of PTFE (polytetrafluoroethylene) having a thickness of 3.5 μm is provided below the heat-resistant base layer made of polyimide, and this release layer 232 comes into contact with the toner.

The sheet 23 is manufactured as follows.

The surface of the heat-resistant base layer 231 has an average particle size of about 0.1 mm.
1 μm PTFE particles and a material containing a surfactant for preventing aggregation of the PTFE particles are uniformly applied,
And then calcined at 350 ° C. for 20 minutes.

During this firing, the release layer made of PTFE thermally shrinks, and the sheet 23 curls. In order to reduce the influence of the curl, it is preferable that the thickness of the base layer 231 is larger than the thickness of the release layer 232.

The sheet 23 does not have a single-layer structure but has a multi-layer structure composed of at least a base layer having excellent strength and heat resistance and a release layer having excellent release properties. It has excellent properties and release properties.

As the release layer, those having a small surface energy can be used, but fluorine resins such as PTFE and PFA (perfluoroalkoxy) and silicone resins are particularly preferable.

The base layer 231 is made of polyether ether ketone (PEEK), polyether sulfone (PE
S), a high heat-resistant resin such as polyetherimide (PEI) can be used.

Further, the release layer may be provided by coating by electrostatic painting or the like, or may be provided by a film forming technique such as vapor deposition or CVD.

As described above, when a highly heat-resistant resin such as polyimide is used as the base layer having excellent strength and heat resistance, the sheet is charged and an unfixed toner image is disturbed by electrostatic force at the time of fixing. And the sheet may be attracted by the electrostatic force, thereby impairing the above-described high offset prevention effect.

This embodiment also prevents the sheet from being charged.

That is, the surface layer other than the base layer, in particular, at least the release layer 232 is reduced in resistance.

The release layer 232 is a PTFE layer in which carbon black is dispersed, and the volume resistivity of the PTFE layer is 10%.
Reduce the resistance to ⁸ Ωcm.

Since the sheet is prevented from being charged due to the lowering of the resistance, it is possible to prevent the unfixed image from being disturbed by the electrostatic force, and the sheet adsorbs dust, thereby deteriorating the releasability. Damage to the pressure roller 22 can be prevented.

In the rewinding type shown in FIG. 2 instead of the endless type, the sheet 23 is charged by contacting the surface of the non-resistance-reduced side of the sheet with the low-resistance layer due to the overlapping of the sheets. The charge dissipates.
That is, by lowering the resistance of one surface layer of the sheet 23, an antistatic effect on the toner-side surface of the sheet 23 can be obtained to some extent. However, it is needless to say that the surface layer on the toner side is preferably a low resistance layer.

Further, when the sheet and the heating element shown in FIG. 2 slide, dust is interposed between the heating element 21 fixed by the charging of the heating element side surface of the sheet, and the heating element and the sheet are damaged. Sometimes.

According to this embodiment, this problem can also be solved.

Furthermore, in order to ensure that both surfaces of the sheet are prevented from being charged, it is preferable that the surface layers on both sides of the sheet are low resistance layers. That is, a layer may be provided on the heating element side of the base layer of the sheet as in the embodiment of FIG. 6, and this layer may be a low resistance layer.

It is also conceivable to mix a low-resistance filler such as carbon black into the base layer.
Since the strength is reduced, it is preferable not to be mixed in the base layer.

Further, the low resistivity layer has a volume resistivity of 1
The antistatic effect was sufficiently achieved by controlling the resistance to 0 ¹¹ Ωcm or less. In particular, the antistatic effect was further ensured by controlling the resistance to 10 ⁹ Ωcm or less.

The low-resistance filler is not limited to carbon black, but may be titanium nitride, potassium titanate, copper, red iron or the like.

Comparative Example 1 The release layer 232 and the sliding layer 234 of the sheet were formed of a PTFE coating layer having a volume resistivity of 10 ¹⁵ Ωcm or more, which was not filled with a low-resistance substance such as carbon black.

When the fixing operation was repeated using this sheet, the sheet was charged for the following reasons, dust was attached to the sheet, and the unfixed image on the recording material was sometimes disturbed. The sheet 23 is charged by a peeling discharge when the sheet 23 is peeled off from the recording material by the separation and conveyance roller 26. When the sheet wound around the shaft 24 is pulled out, peeling discharge occurs between the sheets 23. The sheet 23 is triboelectrically charged by sliding with the heating element 21.

Example 2 Titanium oxide whiskers, which are conductive (volume resistivity 10 ⁴ Ωcm) single crystal fibers, were mixed from carbon black as a low-resistance filler.

The mixing of the conductive whiskers, in addition to the prevention of static charge, makes the whiskers excellent in hardness, so that the friction was further reduced and the durability of the sheet was further improved.

[Embodiment 3] In Embodiment 1, as shown in FIG. 8, static elimination means 50 and 51 (for example, a carbon fiber elimination brush) for static elimination of a sheet were brought into contact with each other.

The antistatic effect of the fixing film was further improved, and a high antistatic effect was obtained even when the filling amount of the low-resistance filler was reduced.

The charge eliminating means need not be provided on both sides of the sheet, but may be provided on one side.

The sheet feeding and winding shafts 24 and 2
The static elimination effect is also improved by forming 7 from a conductor such as a metal.

[Comparative Example 2] When the sheet 23 is formed only of polyimide, since the surface energy of the polyimide is large, even if the recording material is separated from the sheet after the toner is cooled, a small amount of toner is offset to the fixing film. There was something.

Comparative Example 3 The sheet 23 was made of PFA, PTF
When the sheet was formed only of a fluororesin such as E, the sheet was thermally contracted by heating by the heating element. In addition, since the sheet slides on the heating element in a heated state, the sheet is greatly worn, and durability cannot be obtained.

[Embodiment 4] When the sheet 23 is composed of a plurality of layers, if the adhesion between the layers is poor, floating or peeling may occur.

Therefore, in the embodiment shown in FIG. 4, a fluororesin-based adhesive layer 233 is provided between the base layer 231 and the release layer 232.

By providing the adhesive layer in this manner, the adhesion between the base layer and the release layer is improved, and the durability of the sheet is further improved.

Example 5 As described above, by providing an adhesive layer, the adhesion between the layers can be increased. However, it is preferable that the sheet 23 has good thermal responsiveness, and the heat capacity is not so large. . This is particularly necessary when the heating element disclosed in Japanese Patent Application No. 62-147883 is energized and heated in a pulsed manner.

In the embodiment shown in FIG. 5, the adhesion between the base layer 231 and the release layer 232 is improved without providing an adhesive layer.

That is, the surface of the base layer 231 is roughened, and the release layer 232 is coated on the roughened surface.

Since the heat capacity of the sheet 23 is not increased because the adhesive layer is not provided, it is particularly effective when the heating element is energized and heated in a pulse shape.

[Embodiment 6] As the release layer 52, it is also possible to provide a fluororesin film laminated on a base polyimide film. At this time, an adhesive layer 233 as shown in FIG. 5 may be provided at the interface between the polyimide film and the fluororesin film.

Since the fluororesin film is excellent in surface smoothness, the effect of preventing offset can be further enhanced, and the strength of the release layer is also increased, so that the film having a low fixing speed and a large heat generation amount of the heating element can be used. Is valid.

[Embodiment 7] In FIG. 6, a sliding layer 234 having good slip properties is provided on the base layer 231 on the side of the heating element.

With this configuration, the frictional resistance between the sheet and the heating element can be reduced, the driving force of the sheet can be reduced, and the running stability of the sheet can be realized. This is particularly effective when the heating element slides on the sheet.

[Embodiment 8] As described above, FIG. 7 shows an embodiment in which the frictional force between the sheet and the heating element is reduced without increasing the heat capacity of the sheet.

That is, the surface of the sheet that slides with the heating element is made rough, and the actual contact area between the sheet and the heating element is reduced.

[Embodiment 9] Release layer 232 and sliding layer 234
If a higher hardness is required, a high-hardness substance such as titanium oxide or titanium nitride may be mixed into this layer.

According to the embodiment described above, the strength and heat resistance of the entire sheet are ensured by the base layer 231, and the releasability from the toner is ensured by the release layer 232, so that the durability and the high offset prevention are ensured. The effect is obtained.

[0068]

As described above, according to the present invention, the sheet has excellent strength, durability and releasability, and good fixing can be obtained over a long period of time.

Further, it is possible to prevent adverse effects due to charging of the sheet.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an electrophotographic apparatus to which a fixing device embodying the present invention is applied.

FIG. 2 is a sectional view of a fixing device embodying the present invention.

FIG. 3 is a sectional view of a fixing sheet embodying the present invention.

FIG. 4 is a sectional view of a fixing sheet embodying the present invention.

FIG. 5 is a sectional view of a fixing sheet embodying the present invention.

FIG. 6 is a cross-sectional view of a fixing sheet embodying the present invention.

FIG. 7 is a sectional view of a fixing sheet embodying the present invention.

FIG. 8 is a sectional view of a fixing device according to another embodiment of the present invention.

[Explanation of symbols]

 21 Heating Element 22 Pressure Roller 23 Heat Resistant Sheet 231 Heat Resistant Base Layer 232 Release Layer

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G03G 13/20 G03G 15/20

Claims (1)

(57) [Claims] 1. A heating element comprising: a heating element; and a resin sheet having one surface sliding with the heating element and the other surface moving in contact with a recording material carrying an unfixed toner image. A fixing device for fixing an unfixed toner image on a recording material by heat from the heating element, wherein the resin sheet contains a low-resistance material, and a surface release layer in contact with the unfixed toner image; A fixing device comprising a resin base layer containing no.