JPH0980942A - Fixing belt and heating and fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent disturbance in a toner image by preparing a belt member having permeability for water vapor so that water vapor and expanded air produced in a fixing nip part is made to escape through the fixing belt and that the amt. of air escaping to the nip entrance is decreased. SOLUTION: This fixing belt 1 is an endless belt and a belt member 2 with a recording material is passed between a heating means and a pressing means. In this belt 1, the belt member has lots of pores each formed as an almost straight line in the thickness direction. The belt member which constitutes the fixing belt 1 consists of a base layer 3 and a release layer 4 formed on the surface of the base layer 3. As for the base layer 3, a heat-resistant resin such as polyimide having about 10-70μm thickness is used. As for the release layer 4, a fluorocarbon resin such as PFA is used and a carbon powder is added to the resin to give conductivity. The diameter of lots of fine pores 2 penetrating between the top and back surfaces of the fixing belt l is controlled larger than the diameter of water vapor molecules but smaller than the toner particle size.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat fixing device used in an image forming apparatus and a fixing belt used in the heat fixing device.

[0002]

2. Description of the Related Art In recent years, as a heat fixing device, for example, a rapid heat fixing device using a fixing belt composed of a thin layer belt member has been proposed and various types have been provided. A heat-resistant resin such as PPS or polyamide or a metal belt such as Ni electroformed, Cu foil, or stainless is provided with a release layer such as fluorine resin such as PFA or PTFE or Si rubber.

[0003]

In these rapid heating and fixing, the heating nip portion is configured to heat intensively, and the fixing belt recording material is in a cold state before the heating nip. The air around the fixing belt and the recording material carried along with the rotation and the movement of the recording material also remains cool.

The fixing belt and the recording material come close to each other before the heating nip and are rapidly heated in the heating nip forming a narrow space. Therefore, the air inside the recording material and the air remaining between the fixing belt and the recording material are heated. As a result, the air blows back into the narrow space before the heating nip.

At this time, there is a possibility that the toner image on the recording material (unfixed state before heating) may be blown off to disturb the image.

In particular, when the recording material has sufficiently absorbed moisture and a large amount of water is vaporized by the heat in the heating nip, the above-mentioned image disturbance may occur.

Therefore, an object of the first invention of the present application is to provide a fixing belt which solves the above-mentioned conventional problems.

The second object of the present invention is to:
An object of the present invention is to provide a heat fixing device that solves the above-mentioned problems.

[0009]

According to a first aspect of the present invention, there is provided a fixing belt in which a belt member is passed between a heating unit and a pressure unit together with a recording material. Is a water vapor-permeable fixing belt.

The belt member of this fixing belt may have a structure in which a release layer is formed on the surface of the base layer.

Further, these belt members are provided with water vapor permeability by the innumerable holes formed in the thickness direction.

Further, these belt members are formed of a foamed member having an open-cell structure so as to obtain water vapor permeability.

On the other hand, the hole for obtaining the water vapor permeability is
The hole diameter is about 30 to 90% of the particle diameter of the toner carried on the recording material.

Further, the aperture ratio of the holes for obtaining the water vapor permeability is set to about 5 to 25%.

On the other hand, the purpose of the second invention of the present application is to
A heating and fixing device is characterized in that the fixing belt having the above-mentioned configuration is adopted.

Further, in this heating and fixing device, a space for releasing air is formed between the fixing belt and the heating means.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) FIG. 1 is a perspective view of a fixing belt showing a first embodiment of the present invention, and FIG. 2 is a partially enlarged sectional view of the fixing belt of FIG.

In FIGS. 1 and 2, reference numeral 1 denotes an endless fixing belt, in which a belt member is formed with innumerable fine holes in a substantially straight line in the thickness direction. The belt member constituting the fixing belt 1 has a release layer 4 formed on the surface of a base layer 3, and the base layer 3 includes polyimide, PET, PP.
A heat resistant resin such as S, PES, polyamide, or polyamideimide having a thickness of about 10 to 70 μm can be used. In the present embodiment, the polyimide resin is 20 μm.
A thick film is used as the base layer 3.

The release layer 4 is made of fluororesin such as PFA, PTFE, FEP, or Si rubber, and carbon powder, metal powder, or the like is mixed therein to impart conductivity. In the present embodiment, carbon is dispersed in PFA resin as the release layer 4 and the surface resistance of which is 10 ⁷ Ω per unit area is coated on the base layer 3 with a thickness of 10 μm.

The fixing belt 1 is provided with numerous minute holes 2 penetrating between the front and back. The diameter of the hole 2 is set to be larger than the water vapor molecule diameter (about 350 pm) and smaller than the toner particle diameter. The diameter of the hole 2 is preferably large in order to allow the air that is rapidly heated and expanded to escape smoothly, and the hole 2 is preferably about 30 to 90% of the toner particle size. In this embodiment, the toner particle size is 8 μm, and the diameter of the hole 2 is set to 4 μm. Forming the holes 2 larger than the toner particle size is not preferable because the toner enters the holes 2 and blocks the holes 2. The higher the density of the holes 2 on the fixing belt 1, the higher the effect. However, from the viewpoint of the strength of the fixing belt 1, the opening ratio is determined by the number of holes in a unit area × the size of the holes / the unit area × 100 (% ), It is preferable that the aperture ratio is in the range of about 5 to 25%. If it is smaller than this value, the air venting effect is small, and if it is larger than this value, the fixing belt 1 This is not preferable because the strength is impaired. In this embodiment, the aperture ratio is about 10%.

FIG. 3 is a schematic sectional view of a heat fixing device using the fixing belt 1 of the present embodiment. In FIG. 3, 1
Is a fixing belt of the present embodiment, 31 is a heating element, 32 is a heating element, 36 is a support, 33 is a pressure roller, 34 is a driving roller for the fixing belt 1, and 35 is a tension roller for applying tension to the fixing belt 1. Is.

The fixing belt 1 is in the shape of an endless belt, and includes a driving roller 34, a tension roller 35, and a heating element 3.
It is suspended between 1 and 2.

The fixing belt 1 has a surface coated with a rubber layer such as silicon rubber to rotate in the direction of arrow a of the driving roller 34 whose friction coefficient has been increased, and therefore wrinkles and meander at a predetermined peripheral speed in the direction of arrow a. , It is driven to rotate without speed delay.

Reference numeral 33 denotes PFA as a pressurizing means for applying a pressure between the heating body 31, the fixing belt 1 and the recording material P,
It is a pressure roller having a surface layer having good releasability such as PTFE, FEP, and silicone rubber, and an elastic layer. The fixing belt 1 of the present embodiment is sandwiched between the heating body 31 and the heating body 31.
For example, an axial length of 1
The contact pressure is applied with a contact pressure of 50 N to 200 N per m, and the recording material P rotates in the C direction in the drawing, which is the forward direction in the conveyance direction b.

The heating element 31 comprises a heating element 32 having a low heat capacity and a heating element support 36.

The heating element 32 having a low heat capacity has, for example, a thickness of 1.
A resistive material such as silver palladium ruthenium oxide having a thickness of 10 μm and a width of 2.0 mm is applied to an alumina substrate having a good thermal conductivity of 0 mm, a width of 8.0 mm and a longitudinal length of 250.0 mm to form a heat generating layer. A glass protective layer having a thickness of 20 μm is formed on the upper portion of the glass protective layer, and the glass protective layer is attached to and fixedly supported by the heating element support 36.

The heating element support 36 has a heat insulating property, a high heat resistance, and rigidity for adiabatically supporting the heating element 32 and the fixing device and the image forming apparatus. For example, PPS (polyphenylene sulfide) or PEEK (polyether). Ether ketone), a liquid crystal polymer or other high heat resistant resin, or a composite material of these resins and ceramics, metal or the like.

The heating layer 3 of the heating element is energized from both ends in the longitudinal direction. The energization is 100V AC, and the temperature is detected by a temperature detection element such as an NTC thermistor that is adhered or pressure-bonded or integrally formed on the back surface of the substrate with a heat-conductive silicon adhesive, etc. Computer mp
The energization is controlled by U.

Next, the fixing operation of this embodiment will be described.

The fixing operation start signal starts rotation of the fixing belt 1 and energization of the heating element 32.

A transfer material sheet P having an unfixed toner image T, which is a recording material, carried on its upper surface is conveyed to a fixing device in the direction of arrow b. The transfer material sheet P enters in close contact with the fixing belt 1 with the unfixed toner on the heating body 31 side at the pressure contact portion between the heating element 32 that has rapidly raised to a predetermined temperature and the pressure roller 33.

The sheet P passes through the fixing nip portion between the heating body 31 and the pressure roller 33 while receiving a pressing force in an overlapping state with the fixing belt 1 which is movable without causing surface deviation or wrinkling. .

The heat of the heating element 31 in the fixing nip portion vaporizes the moisture in the sheet P to form water vapor.
Although the air expands and the air pressure increases, the air travels through the holes 2 provided in the fixing belt 1 and escapes. Therefore, the toner image on the sheet P is not disturbed and is in a good state. The toner image melts at a high temperature and softens and adheres to the surface of the sheet P. At this time, since the holes 2 provided on the fixing belt 1 are smaller than the toner particle size and the fluidity of the toner melted at a high temperature is low, the toner does not enter, and the initial performance is maintained even after repeated use. You can

In the case of the apparatus of this example, a sheet P which is a recording material
The fixing belt 1 is separated from the fixing belt 1 when the sheet P passes through the fixing nip portion and exits. At the time of this separation, the temperature of the molten toner is still higher than the glass transition point of the toner. Since the toner at a temperature higher than the glass transition point at this separation point has an appropriate rubber elasticity, the toner image surface at the time of separation has an appropriate uneven surface property without following the fixing film surface. Since the surface property is maintained and it is cooled and solidified, the toner image surface after fixing does not generate an excessive image gloss and a high quality image is obtained.

(Second Embodiment) The fixing belt 1 of the first embodiment uses a heat-resistant resin provided with holes, but in the present embodiment, a heat-resistant foam member having open-celled bubbles is used. Is used. FIG. 4 is a sectional view of such a fixing belt. 2 are designated by the same reference numerals, and detailed description thereof will be omitted.

In FIG. 4, the base layer 3 is an open-celled silicone rubber. In the present embodiment, a silicone rubber layer having a thickness of about 50 μm is used as the base layer 3, PFA resin is mixed with PTFE particles as the release layer 4, and carbon is dispersed to obtain a surface resistance of 10 per unit area. ⁹ Ω is coated to a thickness of 5 μm. The release layer 4 is provided with fine holes 2 in some places, and is configured so that air can escape between the front and back sides through the silicone sponge layer of the base layer 3.

By using the foamed member having the open-celled foam as the base layer 3, the air can be released not only in the front and back directions of the fixing belt 1, but also in the lateral direction through the open-air bubbles, so that the air can be more effectively discharged. It is possible to escape.

(Third Embodiment) In the present embodiment,
In order to effectively release steam and expanding air due to heat, the heating element 32 immediately before the sheet P, which is a recording material, and the fixing belt 1 are conveyed in the fixing nip together as an overlap.
A space is provided between the fixing belt 1 and the fixing belt 1.

The heating nip portion of such a fixing device is shown in FIG.
This will be described with reference to FIG. The pressure roller 33, which is a support member for the heating element 31, is configured to surround the heating element 32 together with the fixing belt 1, and the fixing belt intrusion guide portion 51 is provided on the upstream side with respect to the traveling direction a of the fixing belt 1. There is.

The fixing belt intrusion guide portion 51 is located in a direction in which the fixing belt 1 and the heating element 32 are separated from each other, so that the fixing belt 1 comes into contact with the heating element 32 only at the portion where the fixing belt 1 is pressed by the pressure roller 33. It is configured. At the portion where the fixing belt 1, the sheet P, and the pressure roller 33 first overlap (the portion D in the figure), the space 5 for venting air is created between the fixing belt 1 and the heating element 32 by the action of the intrusion guide portion 51.
2 is formed, and the air that has escaped to the back side can be exhausted, so that the air that has been heated by the fixing belt 1 and the pressure roller 33 and expanded can be smoothly released from between the fixing belt 1 and the transfer material sheet P. Is more preferable.

[0041]

According to the first, second and third aspects of the present invention,
For example, water vapor and expanded air generated by heating in the fixing nip portion can escape through the fixing belt, so that the amount of air escaping to the nip entrance side can be reduced and the disturbance of the toner image on the recording material can be prevented. it can.

According to the fourth aspect of the invention, the water vapor can be released not only in the thickness direction but also in the lateral direction, so that the disturbance of the toner image on the recording material during fixing can be further prevented.

According to the fifth aspect of the present invention, only the air can be removed efficiently without the toner blocking the fine holes.

According to the invention of claim 6, it is possible to obtain the above effect without impairing the strength of the fixing belt.

According to the seventh aspect of the present invention, it is possible to prevent the generation of excessive image gloss on the toner image surface after fixing, and it is possible to obtain a high quality image.

According to the eighth aspect of the invention, the expanded air that has come out, for example, to the back surface side of the fixing belt can be released from between the fixing belt and the transfer material, and the air can be smoothly exhausted.

[Brief description of drawings]

FIG. 1 is a perspective view of a fixing belt showing a first embodiment of the invention according to the present application.

FIG. 2 is an enlarged sectional view of FIG.

FIG. 3 is a schematic cross-sectional view of a heating and fixing device showing a first embodiment of the invention according to the present application.

FIG. 4 is a cross-sectional view of a fixing belt showing a second embodiment of the invention according to the present application.

FIG. 5 is a schematic cross-sectional view of a heating nip portion of a heating and fixing device showing a third embodiment of the invention according to the present application.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Fixing film 2 ... Hole part 3 ... Base layer 4 ... Release layer

Claims (8)

[Claims] 1. A fixing belt in which a belt member is passed between a heating unit and a pressure unit together with a recording material, wherein the belt member is formed to be permeable to water vapor. 2. The fixing belt according to claim 1, wherein the belt member has a release layer formed on the surface of the base layer. 3. The fixing belt according to claim 1, wherein the belt member is provided with water vapor permeability by the innumerable holes formed in the thickness direction. 4. The fixing belt according to claim 1 or 2, wherein the belt member is formed of a foamed member having continuous air bubbles to obtain water vapor permeability. 5. The method according to claim 1, wherein
The fixing belt is characterized in that the pores for obtaining the water vapor permeability have a pore diameter of about 30 to 90% of the particle diameter of the toner carried on the recording material. 6. The fixing belt according to claim 1, wherein the opening ratio of the holes for obtaining the water vapor permeability is about 5 to 25%. 7. A heat fixing device comprising the fixing belt according to any one of claims 1 to 6. 8. The heat fixing device according to claim 7, wherein a space for air escape is formed between the fixing belt and the heating means.