JPS6338710B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a fixing device for an image forming apparatus that forms a powder image, such as an electrophotographic device or an electrostatic recording device, and more particularly to an improvement in a fixing device having a rotating body such as a roller. Conventionally, in a heat roller fixing device, a releasing material such as RTV silicone rubber or Teflon (product name: manufactured by DuPont, hereinafter referred to as Teflon) is provided on the surface layer of the fixing roller, and in some cases, silicone oil is further applied. Offset was prevented by applying a mold release agent like this. Fixing rollers whose surfaces are coated with RTV silicone rubber generally do not require the application of a release agent, are simple to use, and have good fixing properties due to the elasticity of the silicone rubber. The rollers changed (deteriorated) rapidly, had a very short lifespan, and had to be replaced frequently. Also, if you apply a mold release agent such as silicone oil to maintain mold release properties, the silicone rubber will swell with the silicone oil and its physical strength will decrease, resulting in the need to replace the rollers frequently. It won't happen. In addition, the surface of the fixing roller can be coated with tetrafluoroethylene-fluoroalkoxyethylene copolymer resin or polytetrafluoroethylene resin (trade name of DuPont) PFA.
Materials coated with Teflon such as or PTFE (hereinafter referred to as this product name) have higher strength than the above-mentioned silicone rubber, and have good mold releasability when coated with silicone oil. However, because it lacks elasticity, it has poor fixing performance compared to the silicone rubber roller described above, and has the disadvantage that when fixing the toner image on the toner image support material, it has a large crushing effect on the image, reducing the image quality. . Furthermore, if the roller has an object that comes into contact with it, such as a cleaning blade, and hard dirt adheres to the roller and enters between the roller and the object, there is no place for the force to escape, and the roller is likely to be damaged. The difference in fixing performance is that when using an elastic material such as silicone rubber, the shape of the fixing roller follows the unevenness of the support material and the unevenness of the toner image on the support material.
It is thought that the fixing properties are good because the entire surface is in uniform contact. On the other hand, in the case of a rigid body such as Teflon, due to the unevenness of the support material and toner image, the convex portions make strong contact with the roller, and the concave portions only make unstable contact with the roller, making it very difficult to fix the concave portions. It is thought to be sweeter. Experimental results show that silicone rubber takes 20 to 25 times longer than Teflon to completely fix the same toner image.
It is known that this process can be carried out at temperatures as low as ℃. Furthermore, Japanese Patent Application Laid-Open No. 48-85151 discloses a fixing roller made of a mixture of tetrafluoroethylene resin powder and raw silicone rubber, but in this case, silicone and Teflon are not compatible with each other and have poor dispersibility. Problems include that the strength is very weak due to poor adhesion, and when a release agent such as silicone oil is applied, the silicone rubber swells with the oil, resulting in a significant decrease in physical strength. many. On the other hand, there are also problems that need to be solved with the pressure roller provided as a back-up roller for the fixing roller that comes into contact with the unfixed toner image as described above. In other words, even if the fixing roller has good releasability,
After the unfixed toner image is fixed, a slight amount of toner offset occurs on the fixing roller. Although this offset toner can be removed from the fixing roller with a cleaning member, it cannot be completely removed. Therefore, a very small amount of offset toner remaining on the fixing roller is transferred from the fixing roller to the pressure roller between sheets, and the pressure roller is gradually contaminated. The toner deposited on the pressure roller adheres to a support material such as paper during fixing, resulting in problems such as staining of the back of the support material. Therefore, there is a need to improve the mold releasability of the surface of the pressure roller as well. Further, the pressure roller needs to have high elasticity in order to ensure an appropriate nip width for fixing. As described above, it is desired that not only the fixing roller but also the pressure roller have good mold releasability and elasticity. The present invention improves the above-mentioned conventional drawbacks. An object of the present invention is to provide a fixing device that has good release properties, fixing properties, and strength over a long period of time. An object of one embodiment of the present invention is to provide a highly efficient and energy saving fusing device. The present invention will be described below with reference to Examples. FIG. 1 shows an embodiment of the present invention. A heating roller 1 rotates in the direction of the arrow ₁₆₁ , and a pressure roller 2 slides and rotates on its outer peripheral surface in the direction of the arrow. This heating roller 1 has a mixed surface layer 4 of soft rubber and soft resin on the outer peripheral surface of a hollow metal roller core 3.
It has a thickness of 100μ and has a heater 5 such as a halogen heater inside. The above heating roller 1 is composed of a soft rubber dispersed in water, a soft resin, and a compounding agent.
A solution prepared by mixing 100 parts by weight and 7 parts by weight of a hardening agent liquid was coated on the hollow roller core 3 to a thickness of 100 μm, and then baked at 350° C. for 30 minutes and molded. The pressure roller 2 is brought into pressure contact with at least the heating roller 1 during fixing by a known pressure means, and has a relatively thick silicone rubber layer 7 provided on the outer peripheral surface of a metal roller core 6. One purpose of this configuration is to secure a pressure contact area 18 with the heating roller. A temperature sensing element 8 such as a thermistor or thermocouple is disposed on the outer peripheral surface of the heating roller 1, and its detection signal is guided to a known control means 15, and the temperature of the outer peripheral surface of the heating roller 1 is controlled by the output of the heater 5 or By controlling the applied voltage, etc., the toner image melting temperature is maintained. A paper P having an unfixed toner image T is inserted between both rollers 1 and 2 from the direction of arrow 16, and the toner image T is formed by being conveyed between the rollers and heated by the temperature.
After being fixed, it is ejected from the device. In order to reliably separate the paper P from the heating roller at this time, a plurality of separation claws 9 are provided in contact with the surface layer 4 along the roller axis direction. Reference numeral 10 denotes an applicator for applying an anti-offset liquid to the heating roller 1, and the anti-offset liquid such as silicone oil is applied to the surface of the heating roller in minute amounts through a fine continuous pore membrane 11 that is in contact with the heating roller 1. . Reference numeral 13 denotes a spill prevention member for preventing the offset prevention liquid from spilling due to vibration during transportation of the machine, and is made of urethane foam. Reference numeral 14 denotes a tube that ensures uniform contact of the porous membrane 11 with the heating roller, and is a shape-retaining member that maintains the shape of the membrane 11 and the state of pressure contact with the heating roller 1. The tube 14 has fine continuous pores made of the same material as the continuous pore membrane 11. The membrane 11 and tube 14 are porous tetrafluoroethylene thin membranes (manufactured by Sumitomo Electric, trade name: Fluoropore).
Use. (Porosity: 80%, pore size: 0.5 to 1.5μ) As an offset prevention liquid, dimethyl silicone oil with a viscosity of 10,000 cs at room temperature (Shin-Etsu Chemical's KF
-96H) is used. Note that the angle β (>0) is the angle formed by the straight line L connecting the centers of the roller pair with respect to the transport direction _L2 of the paper P, which is located in front of the roller pair and guides the paper P toward the heating roller 1 side. The angle α (>0) between the guide member 17 and the transport direction L ₂ is assumed. In this embodiment, the relationship between the illustrated angles α and β is 90°>β>α>0. In the fixing device with the above configuration, the diameter of the heating roller 1 is φ60, the paper feeding speed is 400 mm/sec, and the weight is 80 mm/sec.
When a toner image was formed on g/m ² paper and the fixing properties were examined, good fixing properties were obtained at 140° C. when the pressure area was 11 mm, and the image quality was also good. Next, when I made copies continuously at a speed of 34 sheets/A3・min, (oil application amount 2.5g/A3・min.
There were no problems even after copying 10,000 copies or 200,000 copies. In addition, assuming that dust had entered between the coating film and the roller, we rotated it with iron powder of 50μ particle size sandwiched between the rollers, but no scratches occurred at all. In the above experiment, evaluations were made by varying the coating film thickness (surface thickness) during molding of the heating roller and the firing temperature. At ℃,
Durability superior to conventional products was obtained, and good results were obtained as a heat fixing roller. Within this thickness range, especially if it is 60 μm or more, even if iron powder is sandwiched, there will be no linear scratches on the heating roller, no fixing failure will occur at that location, and a high level of fixing performance can be maintained. Moreover, the durability can be further improved. Further, when the thickness is 500 μm or more, the thermal insulation properties of the coating film (or layer) cannot be ignored, and the temperature control becomes rough, resulting in an undesirable result as a heat fixing roller. Next, when the firing temperature was lower than 250°C, toner adhered to the surface of the heating roller after 50,000 sheets passed, resulting in a jet black stain. This is because the firing temperature is low.
It is thought that the surface layer contains too much soft rubber and the properties of the soft rubber itself largely control the properties of the roller, resulting in poor mold release properties. Conversely, it has been found that the higher the firing temperature is, the more the resin content is on the surface of the molded product, and the mold releasability is improved. However, if the firing temperature exceeds 400°C, the heat resistance limit of the fluorine rubber and fluorine resin will be exceeded, making it difficult to achieve the desired properties as a heating roller. Next, as a comparative example, when using a rigid roller with internal heating means and a roller whose surface layer is coated with PFA or polytetrafluoroethylene PTFE with a thickness of 80μ, the temperature at which good fixing performance can be obtained under the same conditions as above is: The temperature was 165°C, which was significantly higher than 140°C in this example. The reason for this, as mentioned above, is
This is thought to be largely due to the difference between the elastic body and the rigid body, which explains the unique effects of this embodiment. Further, similarly to the above, when a PFA or PTFE coated heating roller was used to sandwich iron powder, the heating roller was scratched in a linear manner, resulting in poor fixing at that location. This is because, in the case of an elastic body that has both rigidity and elasticity, as in this example, even if a local force is applied, a force acts to absorb and disperse the force, but PFA and PTFE coating heating In the case of a rigid body such as a roller, it is thought that it is damaged because it is directly subjected to partial stress due to frictional force caused by the gold powder. The table below shows the results of examining the scratch resistance of this example and this coated heating roller using other methods. This is a constant load (0.15Kg) on the ballpoint pen.
The depth of the scratches was measured using a surface roughness meter (SE-3C universal surface profile measuring device manufactured by Kosaka Laboratory) after scanning the roller. The coating thickness of the surface layer was all 80μ.

[Table] That is, from the above values, the roller of this example is:
Although it fluctuates somewhat depending on the surface temperature, there is no major change. On the other hand, the above-mentioned rigid PFA rollers and PTFE rollers show extreme fluctuations in response to temperature changes, and the depth of scratches is more than 1.5 times that of this example.
In most cases, the depth is three times as deep. Therefore, the heating roller of this example exhibits durability that is several orders of magnitude better, and also has strength that is several orders of magnitude better than the conventional rollers against foreign objects such as metals. The above description has explained the features of this embodiment for a rigid roller, but next, the features of this embodiment that are superior to an elastic so-called rubber roller will be explained. As a comparative example, when using a hollow metal roller coated with a 0.5 mm thick HTV silicone rubber layer as in this example, the temperature at which good fixing performance can be obtained under the same conditions as in this example is as follows. Similarly, the temperature was 140℃. Next, when iron powder was sandwiched in the same manner as above, due to its large elastic force, there were slightly fewer scratches than in this example. However, the following drawbacks were found in terms of durability. That is, after 50,000 copies were made, the outer diameter of the heating roller became uneven and easily wrinkled, and toner offset was also likely to occur. After 70,000 to 80,000 copies were copied, the silicone rubber and the cored hollow metal roller separated and the roller was damaged. That is, the durability of this example, which allows for long-term use while maintaining fixing performance, could not be achieved with a simple rubber roller. As described above, the heat fixing roller to which the present invention is applied has good fixing properties, achieves energy saving, and has completed a long-life fixing device that maintains stable performance over a long period of time. I was able to do it. In the embodiment shown in FIG. 1 above, the present invention was applied to the heat fixing roller, but the present invention can also be applied to the pressure roller 2 that presses against the heating roller 1, or both. It can be applied to the surface of a rotating body such as a pressure fixing roller or a conveyor belt used in a fixing device. Several examples will be briefly explained below with reference to FIGS. 2 and 3. FIG. 2 is an explanatory diagram of an embodiment in which the present invention is applied to the pressure roller 2 of FIG. 1. In general, the surface layer of the pressure roller 2 rarely comes into direct contact with unfixed images, and its surface temperature is around 100°C or higher.
A relatively low temperature such as about 80°C is sufficient. Therefore, recently, the pressure roller 2 is equipped with a heating source 5.
₁ is rarely provided, and what is required of the pressure roller is appropriate elasticity, heat retention on the surface, and durability. In consideration of the above points, this embodiment has a surface made of fluorocarbon resin and fluorocarbon rubber, which is coated thicker than the heating roller 1 on the surface of the metal hollow roller 3, which has a heat source ₅₁ inside that supplies relatively low heat. It has layer 4. The thickness of this surface area 4 is
Similar to an elastic roller with a rubber layer of about 0.5mm, or
It is thicker than the heating roller 1, and the temperature at the time of molding may be within the range of 250°C to 400°C, but it may be set to 400°C or higher to improve mold releasability. In this way, by adopting a surface layer containing a mixture of fluorocarbon resin and fluorocarbon rubber as the surface layer of the pressure roller, the fluorocarbon resin present in the surface portion of the surface layer makes the pressure roller The mold release property is good, and since the fluororesin layer on this surface part is very thin, sufficient rubber elasticity can be utilized in the surface layer, and therefore the elasticity of the pressure roller is also good. can do. FIG. 3 shows a roller that can be applied to a pressure fixing device and used as a pressure roller of a heat fixing roller.
A pressure roller 2 ₁ without a heat source is shown.
This roller 2 ₁ is constructed by providing a relatively thick elastic rubber layer 7 ₁ on the peripheral surface of a metallic roller core 6, and fitting a polytetrafluoroethylene tube around the rubber layer 7 1 . This roller ₂₁ has an excellent effect as a roller that comes into pressure contact with the heating roller 1 shown in FIG. Excellent fixing performance can be maintained even if a pressure fixing device is configured in which a roller configured without the heat source of the heating roller 1 is used as a pressure roller on the side in contact with the toner image, and a pressure roller ₂₁ is brought into pressure contact with the pressure roller. It becomes highly durable. As described above, the present invention can provide an excellent fixing device that is durable and can be used for a long period of time while maintaining fixing performance.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of an embodiment of the present invention, FIG.
FIG. 3 is an explanatory diagram for explaining other embodiments of the present invention. 1 is a heating roller, 2, 2 ₁ is a pressure roller, 3 is a hollow roller core, 4 is a surface layer, 5, 5 ₁ is a heater,
6 is a metal roller core, 7 is a silicone rubber layer, 8 is a temperature sensing element, and 15 is a control means.

Claims (1)

[Scope of Claims] 1. In a fixing device that fixes an unfixed image on a support material by sandwiching and conveying the support material supporting the unfixed image between a first and second rotating body, the first rotation The body is a rotating body on the side that contacts the unfixed image, and the second rotating body on the opposite side from the first rotating body has a surface layer containing a mixture of fluororubber and fluororesin. A fixing device characterized by: 2. The fixing device according to claim 1, wherein the surface layer of the second rotating body has a large amount of fluororesin in its surface portion. 3. The fixing device according to claim 2, wherein the surface layer of the second rotating body is formed by heating and baking a mixture of fluororubber and fluororesin. 4. The fixing device according to claim 3, wherein the surface layer of the second rotating body is formed by heating and baking a mixture of fluororubber and fluororesin dispersed in water or a solvent. 5. The method according to claim 1, 2, 3, or 4, wherein at least the first rotating body of the first and second rotating bodies is heated by a heating means. Fusing device.