JPS6338711B2 - - 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 or a belt. Conventionally, in a heat roller fixing device, a release material such as RTV silicone rubber or Teflon (trade name: Dupont) is provided on the surface layer of the fixing roller, and in some cases, a release material such as silicone oil is also provided on the surface layer of the fixing roller. Offset was prevented by applying a coating agent. Fixing rollers whose surface is coated with RTV silicone rubber generally do not require the application of a release agent.
Although the device is simple and the fixing method is good due to the elasticity of silicone rubber, the releasability changes (deteriorates) over time, and the lifespan is very short.
I had to replace the rollers. Also, if you try to maintain mold release properties by applying a mold release agent such as silicone oil, the silicone rubber will swell with the silicone oil, reducing its physical strength and requiring frequent roller replacement. . In addition, the surface of the fixing roller is coated with tetrafluoroethylene-fluoroalkoxyethylene copolymer resin (hereinafter referred to as A resin) or polytetrafluoroethylene resin (hereinafter referred to as B resin).
A roller coated with Teflon (trade name: DuPont) such as resin (referred to as "resin") has higher strength than the above-mentioned silicone rubber, and has good mold releasability when coated with silicone oil. However, since the roller has no elasticity, it has poor fixing properties compared to the silicone rubber roller, and has the disadvantage that it has a large effect of crushing the image when fixing the toner image on the toner image support material, reducing the image quality. I have it. Furthermore, if the roller has an object such as a cleaning plate in contact with it, 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 scratches are likely to occur. The above difference in fixing performance is due to the fact that when using an elastic material such as silicone rubber, the shape of the fixing roller follows the irregularities of the support material and the irregularities of the toner image on the support material, resulting in uniform contact with the entire surface. It is considered that the fixing properties are good. However, in the case of a rigid body such as Teflon (trade name: DuPont), due to the unevenness of the supporting material and toner image, the convex portions make strong contact with the roller, and the concave portions only make unstable contact with the roller. , it is thought that the fixation of the concave portion becomes very difficult. Experiments have shown that the same toner image can be completely fixed using silicone rubber at a temperature 20 to 50 degrees Celsius lower than that of Teflon. Furthermore, JP-A-48-85151 discloses a fixing roller made of a mixture of tetrafluoroethylene resin powder and raw silicone rubber, but in this case, the compatibility between silicone and Teflon is poor, the dispersibility is poor, and the adhesiveness is poor. There are many problems such as the strength is very low due to the poor quality of the rubber, and when a release agent such as silicone oil is applied, the silicone rubber swells with oil, resulting in a significant decrease in physical strength. . 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 transfers from the fixing roller to the pressure roller between sheets, gradually contaminating the pressure roller. The toner deposited on this 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. 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. The heating roller 1 has a mixed surface layer 4 of 500 μm thick of a soft rubber, a soft resin, and a good thermal conductor on the outer peripheral surface of a metal hollow roller core 3, and has a heater 5 such as a halogen heater inside. The above-mentioned heating roller 1 is made of a mixture of 100 parts by weight of soft rubber and soft resin dispersed in water, a total of 25 parts by weight of nickel oxide, cobalt oxide, zinc oxide, and titanium oxide as good thermal conductors, and 6 parts by weight of a hardening agent liquid. It was formed by coating the solution on the roller core 3 to a thickness of 500 μm and then baking it at 350° C. for 40 minutes. The pressure roller 2 is brought into pressure contact with the heating roller 1 at least during fixing by a known pressure means. The configuration of the roller 2 includes a metal roller core 6
A relatively thick silicone rubber layer 7 is provided on the outer peripheral surface of. This rubber layer 7 is in pressure contact area 1 with the heating roller.
One purpose is to secure 8. A temperature sensing element 8 such as a thermistor or a 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 The toner image melting temperature is maintained by controlling the applied voltage and the like. 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 fixed by being conveyed while being pinched and heated by the temperature, and then discharged from the apparatus. be done. At this time, paper P
A plurality of separation claws 9 are provided in contact with the surface layer 4 along the axial direction of the roller in order to reliably separate it from the heating roller. 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. For the membrane 11 and tube 14, a porous tetrafluoroethylene thin film (manufactured by Sumitomo Electric Industries, Ltd., trade name: Fluoropore) with a porosity of 80% and a pore diameter of 0.5 to 1.5 μm is used. The offset prevention liquid used is dimethyl silicone oil with a viscosity of 10,000 CS at room temperature (KF manufactured by Shin-Etsu Chemical).
-96H) is used. Note that the angle β (>O) is defined by the straight line L connecting the centers of the roller pair with respect to the transport direction L ₂ of the paper P, and the guide that is located in front of the roller pair and guides the paper P toward the heating roller 1 side. The angle α (>O) between the 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>O. 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 contact area was 11 mm, and the image quality was also good. Next, I made continuous copies at a speed of 34 pages/A3/min (oil application amount: 2.5g/A3/min).
There were no problems even after copying 10,000 copies or 200,000 copies. Furthermore, in order to prevent dust from entering between the coating film and the roller, iron powder with a particle size of 50μ was sandwiched between the rollers and the rollers were rotated, but no scratches occurred. In experiments using the above configuration, evaluations were made by varying the coating film thickness (surface thickness) during molding of the heating roller and the firing temperature. 250
Good results were obtained as a heat fixing roller at temperatures between 400°C and 400°C. Outside this range of thickness, below 60 μm, when iron powder was sandwiched, the heating roller was scratched in a linear manner, resulting in poor fixing at that location. Also
If it is larger than 1500μ, the thermal insulation of the coating film (or layer) cannot be ignored, and the temperature control becomes rough.
This was an unfavorable result for a heat fixing roller. Although the above numerical range provides better effects, it has been found that a thickness of 80 μm or more is sufficient in order to further improve fixing performance than before. With this thickness, it is thought that not only the durability of the surface of the heat fixing roller is improved, but also the surface temperature which is excellent as a heating surface can be maintained and the temperature distribution becomes stable. Next, the firing temperature will be explained. If the firing temperature of this roller was lower than 250°C, toner would adhere to the surface of the heated roller after 50,000 copies were made, resulting in black stains. This is thought to be because when the firing temperature is low, 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 releasability. On the contrary, it was found that the higher the firing temperature, the more the fluorine resin content on the surface of the molded product and the better the mold releasability. 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, and in some cases impossible, to obtain the desired properties. In addition, when the amount of the thermal conductor was 10 to 35 parts by weight per 100 parts by weight of the fluorine resin and fluorine rubber, particularly good results were obtained, such as excellent temperature control and stable fixing properties associated therewith. If the amount of the thermal conductor is less than 10 parts by weight, heat conduction will remain within a certain range, making it difficult to increase the film thickness to 500 μm or more. Therefore, it is no longer possible to further improve the elasticity effect of increasing the film thickness, that is, to suppress the occurrence of scratches and stabilize the fixing performance. or,
If the amount of the thermal conductor is greater than 35 parts by weight, problems arise in terms of mold releasability, and offset prevention means such as silicone oil are essential to improve mold releasability. The good thermal conductor is preferably carbon black or a metal oxide such as nickel oxide, titanium oxide, or cobalt oxide. Next, as a comparative example, when a rigid roller having an internal heating means and a roller whose surface layer is coated with the above-mentioned resin A or B with a thickness of 80 μm is used, the temperature at which good fixing performance can be obtained under the same conditions as above is the same as that of the present example. of
The temperature was 165°C, much higher than 140°C. The reason for this is thought to be largely due to the difference between the elastic body and the rigid body as described above, which explains the unique effects of this embodiment. Further, in the same manner as above, when iron powder was sandwiched between coated heating rollers of A and B resins, the heating rollers were 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.
In the case of a rigid body such as a heating roller coated with resin A or B, 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 applies a constant load (0.15
The depth of the scratches was measured using a surface roughness meter (used in the SE-3C universal surface profile measuring instrument manufactured by Kosaka Laboratory) after scanning the surface of the roller by applying a certain amount of weight (Kg).
The coating thickness of the surface layer is 500μ for each roller of this example.
The thickness and all others were 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 A and B resin rollers with the above-mentioned rigidity showed extreme fluctuations in response to temperature changes, and the depth of scratches was more than 1.5 times that of this example, with the most being 3.
It is twice 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 substances such as metals. In the above description, the features of this embodiment with respect to a rigid roller have been explained.Next, the features of this embodiment which are superior to an elastic so-called rubber roller will be explained. As a comparative example, hollow gold as in the above-mentioned present example was used.
When using a roller coated with a 0.5 mm thick HTV silicone rubber layer, the temperature at which good fixing performance can be obtained under the same conditions as above is 140°C, as in this example.
It was hot. Next, when iron powder was sandwiched in the same manner as above, due to its large elastic force, fewer scratches were caused than in this example. However, the following drawbacks were found in terms of durability. That is, when 50,000 copies were made, the outer diameter of the heating roller became prone to irregularities and wrinkles, and toner offset was also likely to occur. When copying was continued, the silicone rubber and the hollow metal roller, which was the core metal, separated and the roller was damaged when around 70,000 to 80,000 copies were copied. 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 heating fixing roller to which the present invention is applied has good fixing properties, thereby achieving energy savings, and completing a long-life fixing device that maintains stable performance over a long period of time. I was able to do that. In the embodiment shown in FIG. 1 above, the present invention was applied to a heat fixing roller. It can be applied to the surface of a rotating body such as a 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 around 80°C, is sufficient. Therefore, recently, the pressure roller 2 is equipped with a heating source 5.
₁ is rarely provided (heating roller 1 is not provided)
The pressure roller is required to have appropriate elasticity, heat retention on the surface, and durability. In consideration of the above points, this embodiment has a metal hollow roller 3 which has a heat source ₅₁ inside which supplies relatively low heat, and the surface of the metal hollow roller 3 is coated with fluorine resin, fluorine rubber, and a good thermal conductor to a thickness thicker than that of the heating roller 1. It has a surface layer 4 which is smoothed by mixing metal oxide. The thickness of this surface layer 4 is the same as that of the elastic roller with a rubber layer of about 0.5 mm, or is thicker than the heating roller 1, and the temperature at the time of its formation is also
The temperature may be within the range of 250°C to 400°C, but it may be 400°C or higher to improve mold release properties. 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 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. be able to. FIG. 3 shows a pressure roller ₂₁ without a heat source, which is applicable to a pressure fixing device and used as a pressure roller of a heated fixing roller. 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 2 ₁ is the first
This roller has excellent effects as a roller that comes into pressure contact with the heating roller 1 shown in the figure. In addition, the roller configured with the heat source removed from the heating roller 1 was used as the pressure roller on the side that comes into contact with the toner image, and the pressure roller ₂₁ , which is _the heat source shown in FIG. Even if the pressure fixing device is constructed, excellent fixing performance can be maintained as described above, and the device can be highly durable. In any case, the present invention is characterized by the scope of the claims, and as described above, it is possible to provide an excellent fixing device that maintains fixing performance and is durable enough to be used over a long period of time.

[Brief explanation of the drawing]

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, fluororesin, and a good thermal conductor. 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, fluororesin, and a good thermal conductor. 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, fluororesin, and a good thermal conductor 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.