JPH05150674A - Belt fixing device - Google Patents

Abstract

PURPOSE:To provide the fixing device with high color reproduction even when none or a minimal quantity of releasing agent such as silicon oil is utilized, where sufficient melting of toner is secured in an image after fixing, with superior luster without causing blackening or turbidity due to air bubbles sealed in the melted toner. CONSTITUTION:This is the fixing device provided with an endless belt wound between a fixing roll and a separating roll and the fixing roll press fixed to the fixing roll through the before mentioned belt, with a heater in a core of at least one of the fixing rolls, and it is constituted by having the endless belt formed from polyimide substrate 15A and a releasing layer 15C and processed to be porous. Furthermore, it is constituted so that diameters of holes 15D and 15E which are processed to be porous are 0.1 to 1mum, and the area density of the surface hole parts is 10 to 50%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device for an electrophotographic image forming apparatus.

[0002]

2. Description of the Related Art In the fixing process of toner images for electrophotography, heat roller fixing is the most common. In recent years, in electrophotographic processes that handle color images, color reproducibility and glossiness of images after fixing are ensured, and
It is required that the toner be sufficiently melted in order to ensure the transparency when the P transfer material is used. If the melting conditions of the widely used linear polyester toner are set to the above-mentioned level, it is necessary to apply a large amount of low-viscosity silicone oil as a release agent as an essential condition from the problem of high temperature offset. Is becoming

When a large amount of silicone oil is used in this way, problems such as spillage of silicone oil and adhesion of silicone oil to a transfer material occur. In particular, when OHP is used, the transfer material is not impregnated with silicone oil, so that the user's hand is soiled with silicone oil, or the permeability of OHP itself is significantly reduced. For this problem, a general toner using polyester, that is, a wax-based toner is adopted, but it is difficult to obtain a sufficient molten state under the present circumstances. Further, as described above, the glossiness after fixing is often required for the color image. As a means in that case, in the range of the prior art, as described above, a large amount of a release agent is applied or a wax-based wax is used. When the above toner is used, the image once fixed is fixed again by the option unit.

[0004]

Since this is unsatisfactory, the applicant has not used the release agent such as silicone oil at all, or even if the release agent is used, even if the release agent is used with a small amount, the toner of the toner in the image after fixing is not formed. We proposed a belt-fixing type fixing device as a fixing device that is sufficiently melted and has excellent color reproducibility in toner melting, and can produce images with good gloss as required for color images, especially transparency when using OHP. , I tried to achieve fixing with excellent color reproducibility, but there are still insufficient aspects. Toner melts and adheres to the transfer material during thermocompression bonding, but at that time, as shown in FIG. 5, air bubbles are trapped in the toner and transparency decreases, resulting in darkening. Further, if the toner adheres with air bubbles in such a manner, the toner is likely to come off. An object of the present invention is to provide a belt fixing device that solves such a problem.

[0005]

This object is achieved by the following technical means a or b.

(A) An endless belt is stretched between an internal heating roller and a separation roller, and a pressure roller is provided in pressure contact with the internal heating roller via the endless belt. The endless belt of the belt fixing device, which heats and presses the carried transfer material from the separating roller portion and fixes the transfer material, is characterized in that the endless belt is formed of a polyimide substrate and a silicon rubber layer and is subjected to a porosification treatment. Belt fixing device.

(B) The pore diameter of the porosification treatment is 0.1 to 1 μm
And the surface area density of holes is 10 to 50%.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to a sectional view showing the structure of FIG. 1, a sectional view of an endless belt of FIG. 2, a sectional view of FIG. 3 showing a behavior when toner is melted, and a graph shown in FIG. .

As shown in FIG. 1, a cored bar 11 is provided, on which a heat-resistant synthetic rubber layer is concentrically provided as an elastic layer 12, and a heater 16 of about 650 W is provided at the center thereof, and an outer diameter of about 40 mm. Fixing roller 10 and a separating roller made of an aluminum hollow pipe provided at a specific distance to the fixing roller 10 and having an outer diameter of about 20 mm
An endless belt 15 is wound between 14 and. As shown in FIG. 2, the endless belt 15 is composed of a polyimide substrate 15A coated with a release layer 15C made of silicon rubber. The thickness of the polyimide substrate 15A is preferably 10 to 100 μm, more preferably 25 to 75 μm. The silicone rubber layer is 10 to 100 μm. The fixing roller 20 is pressure-bonded to the fixing roller 10 via the endless belt 15. The fixing roller 20 also has a heater 2 of about 300 W at the center.
3 is arranged, a core metal 21 is provided concentrically therewith, and a heat-resistant synthetic rubber layer is provided as an elastic layer 22 concentrically outside thereof.

Then, the developed unfixed image in which the toner 52 is adhered onto the transfer material 51 is conveyed onto the entrance guide 17,
While being pressed by the fixing rollers 10 and 20 and the endless belt 15, it is sent in the direction of the arrow, passes through the guide 33, completes the fixing to the outside of the separation roller 14, and is discharged and collected via the conveying roller pair 65. ..

Silicon rubber is coated on the outer side of the endless belt 15 as the release layer 15C, and also serves as an elastic body.

Further, a sensor 13 as a temperature detecting means is provided in contact with a position where the endless belt 15 is not in contact with the outer peripheral surface of the fixing roller 10, and another fixing roller is provided.
A sensor 24 as a temperature detecting means is provided in contact with the outer peripheral surface of 20.

As shown in FIG. 3, the endless belt 15 has its substrate 15A and coating layer 15C subjected to a porosification treatment for removing bubbles. The pore diameter is 0.3 to 0.5 μm, and the area occupancy ratio of the pores to the surface, that is, the perforation density is about 10 to 40%.

An endless belt is provided above the fixing roller 10.
A cleaning roller 63 having an outer diameter of about 20 mm, which is composed of a foam roller having a surface containing silicon or a roller having a non-woven fabric containing silicon on the surface is provided via 15, and the tension of the endless belt 15 is adjusted. Also, it can move up and down for both skew control and has an outer diameter of 10 mm with a tension release mechanism.
A skew control roller 64 is provided.

A cooling fan 32 is provided below the endless belt 15 between the fixing rollers 10 and 20 and the conveying rollers.
The toner 52 heated and melted on the transfer material 51 is solidified to perform stable fixing so that the melted toner is not offset on the endless belt 15.

Next, the operation of the fixing device 1 thus constructed will be described.

First, the viscosity-temperature characteristic curves of the linear polyester toner and the general polyester toner shown in the graph of FIG. 4 will be described.

In this graph, the vertical axis represents the viscosity in common logarithmic values in Poise units, and the horizontal axis represents the temperature. The linear polyester toner is shown by a solid line, and the general polyester toner is shown by a chain line. Both toners have a high viscosity of about 100,000 poise around 100 ° C, that is, a glass transition state, and both toners are in a molten state when the temperature exceeds 100 ° C. The optimum molten state has a viscosity of 5000
It's about Poise. As for the viscous state, the heating temperature of a general polyester toner reaches 150 ° C., but that of a linear polyester toner is 120 ° C., which is a much lower temperature.

Further, in the apparatus used in the present invention, the endless belt 15 is interposed, as compared with the conventional fixing apparatus in which the heat fixing is performed by the nip of only the pair of rollers formed by the two fixing rollers. Since the cooling time until peeling can be secured, the melting temperature can be expanded to a higher temperature than before, and the heating region can be made much wider. In this heating region, the unfixed image is sufficiently melted by a toner such as a linear polyester resin which is melted at a low temperature. And the endless belt according to the present invention
No. 15 is toner because it has been subjected to porosity treatment as described above.
The bubbles generated when 52 is melted are not trapped in the melted toner and escape through the perforated holes 15D and 15E of the endless belt 15. Therefore, the air bubbles are confined in the toner to become dark and opaque, and the toner does not easily peel off. In particular, when a transparent sheet used for OHP is used as a transfer material, the air bubbles trapped in the toner become black spots, so that the transparency is poor and the image has a noticeable dustiness, but such a bad phenomenon is completely eliminated. Image quality can be obtained. Due to the adhesive force between the toner 52 and the transfer material 51 in the molten state and natural cooling, or the airflow from the cooling fan 32 applied from the back surface of the transfer material as shown in FIG.
The toner 52 is conveyed while being attached to the endless belt 15 to lower the temperature.

In this region, the toner 52 and the transfer material 51, which have been sufficiently cooled and have a high viscosity to be in a glass transition state, are
The endless belt 15 supported by the separation roller 14 is separated from the endless belt 15. At this time, since the toner 52 is almost in the solidified glass transition state, the surface property of the belt 15 is maintained as it is, and a glossy surface close to a mirror surface is obtained. In this way, the toner 52 is solidified after it has been sufficiently melted, so that color reproducibility by melting and mixing a plurality of color toners can be secured, and the transparency when fixed on OHP or the like can also be stably secured. As described above, since the surface material constituting the endless belt is a material such as silicone rubber which is a release agent, the release layer itself has elasticity as well as releasability. In addition to the effect of a damper between the toner 52 and the endless belt 15, the offset state does not occur even if a toner such as a linear polyester toner that easily melts at a relatively low temperature is used. However, even if it occurs, it is very small and can be kept at a level that can be cleaned.

At this time, since the elastic layer is provided on both of the pair of rollers, the buffering effect of the elastic layer acts on the melted toner coming out from the nip portion and the transfer material supporting it. This prevents the occurrence of an offset state due to cohesive failure inside the molten toner layer. With respect to the thickness of the elastic layer of the roller, when the thickness t ₁ on the roller side around which the belt is hung is made larger than the thickness t _{2 of the} other side, the effect of preventing offset with respect to the toner layer is further increased. In addition, the rubber hardness of the former roller and that of the latter roller are set to h ₁ and h _{2 respectively.}
In that case, h ₁ <h ₂ is more preferable because the effect of preventing offset is further increased.

Further, in the case of the fixing device using the endless belt 15, the reading value of the sensor 24 as the temperature detecting means attached to the fixing roller 20 to be pressure-bonded and the reading value of the temperature sensor 19 attached in the vicinity of the separating roller are described above. By controlling the heating of the heater in accordance with the reading value of the sensor 13, it becomes possible to maintain the temperature of the fixing portion within a stable range.

By doing so, the heater 16 may be removed from the fixing roller 10, and the roller 10 may be composed of the core metal 11A at the central portion and the elastic layer 12A at the peripheral portion.

That is, even in such a state, by controlling the heating state of the heater 23 by the temperature sensors 13, 19, 24, the temperature of the fixing portion can be maintained within a stable range. Since the elastic layer is provided on both of the pair of rollers, cohesive failure does not easily occur inside the molten toner layer, and offset onto the endless belt 15 is prevented.

Even when the cooling fan 32 is not provided, the transfer material 51 and the toner 52 are carried in the state of being in close contact with the surface of the endless belt 15 by the heating control of the heaters by the above-mentioned temperature sensors 13, 19, 24. It is possible to allow the separation roller portion at the end portion to peel off and collect very naturally without offsetting on the surface of 15.

[0026]

EFFECTS OF THE INVENTION According to the present invention, a low temperature melting type toner does not cause the problem of transfer (offset) of the oil even if a releasing agent such as silicone oil is not used at all or even if it is used very little. By using, it was possible to sufficiently dissolve the toner and obtain a fixed image excellent in transparency and color reproducibility. In particular, even when a transparent sheet for OHP is used as a transfer material, a sharp and high-quality color image can be stably obtained due to the improved transparency.

Further, since the transfer material at this time uses a very small amount of silicon oil, the image is not contaminated. Further, a gloss image required for a color image can be obtained at a sufficient level.

[Brief description of drawings]

FIG. 1 is a sectional view showing the configuration of an embodiment of the present invention.

FIG. 2 is a sectional view of an endless belt used in the present invention.

FIG. 3 is a cross-sectional view showing the behavior when the toner is melted in the belt fixing of the present invention.

FIG. 4 is a toner viscosity-temperature characteristic curve.

FIG. 5 is a cross-sectional view showing the behavior when toner is melted in conventional belt fixing.

[Explanation of symbols]

 10,20 Fixing roller 11,21 Core metal 12,22 Elastic layer 13,19,24 Temperature sensor 14 Separation roller 15 Endless belt 17 Inlet guide 15A Polyimide substrate 15C Release layer 15D, 15E Porous hole 32 Cooling fan 33 Guide 51 Transfer material 52 Toner

Claims (2)

[Claims] 1. An endless belt is stretched between an internal heating roller and a separation roller, and a pressure roller is provided in pressure contact with the internal heating roller via the endless belt, and carries a toner image carried in from the pressing portion. A belt characterized in that the endless belt of the belt fixing device, which heats and presses the transferred transfer material from the separating roller portion to fix the transfer material, is formed of a polyimide substrate and a silicone rubber layer and is subjected to a porosification treatment. Fixing device. 2. The belt fixing device according to claim 1, wherein the pore diameter of the pore-forming treatment is 0.1 to 1 μm, and the surface area density of pores is 10 to 50%.