EP0470276B1 - Fixing roll for electrophotographic copying or printing apparatus - Google Patents

Description

The invention relates to a fixing roller for copying and printing devices according to claim 1.

Electrophotographic copying and printing devices with thermal printing fixation are generally known. When using thermal printing fixation, the record carrier, for example single sheets and continuous formats made of paper, film or cardboard, and the toner image lying on the record carrier are carried out between two rotating rollers that come into contact with pressure.

While one of the two rollers, the so-called fixing roller, is heated, the second roller, the so-called pressure roller, generates the counter pressure. In this way, the toner image is bonded to the structure of the recording medium under pressure and heat. In order for the toner image melted in a fixing nip formed by the rollers to adequately bond to the surface of the recording medium, the recording medium must be brought to a temperature above the melting point of the toner particles. The temperature at which the recording medium is heated by the fixing roller is at least 100 to 110 ° C.

Since the heat capacity of paper is relatively large and, moreover, the water present in the paper has to be heated and partially evaporated, high-power heat sources are required in the fixing roller. Especially with electrophotographic copying and printing devices in the upper speed range, specific power densities of the heat sources between 80 and 150 W / cm are required in the fusing roller. In a known manner, infrared radiators or infrared halogen radiators are used as heat sources in the fixing roller. The more famous Way along the axis of rotation, arranged in the center of the fuser heat sources have heating coils, which by a glass wall, for. B. a glass tube to be surrounded.

When the heating coil emits radiation, the concentrically emitted rays are partially absorbed by the glass wall and converted into heat. With a glass wall made of quartz glass, the absorption is approx. 4%. After the radiation has left the glass tube, it strikes an inner wall of the fixing roller. Depending on the surface quality, the radiation is absorbed, transmitted or reflected on this inner wall. Since the fixing roller is preferably made of metal, for example aluminum, the transmitted portion of the radiation is zero. The portion of the radiation reflected on the inner wall strikes the glass wall of the glass tube again, where it is divided according to the degree of transmission, reflection and absorption of the quartz glass. The parts reflected and transmitted on the glass wall then meet again on the inner wall of the fixing roller, where they are partly absorbed and reflected again. This process is repeated until the radiation energy emitted by the heating coil is completely absorbed by the inner wall of the fixing roller and the glass wall of the heat source.

If the degree of absorption of the inner wall of the fixing roller were equal to one, no radiation would be reflected back from the inner wall. As a result, the radiation would only have to pass through the glass wall of the heat source once and the loss of thermal energy due to absorption in the quartz glass when heating the fixing roller would be limited to 4%. However, since the fixing roller made of aluminum has an average degree of absorption of 0.3 and a degree of reflection of 0.7 on the inner wall, a higher heating power is required to heat the fixing roller. With a specific heating output of the heating coil of approx. 130 W / cm for electrophotographic high-performance printers, the glass wall of the Heat sources due to the absorption of 4% to over 900 ° C. At these temperatures, "devitrification" already occurs, in which the quartz glass becomes milky and the degree of absorption is increased. This then has the consequence that the heating coils in the glass tube are destroyed due to overheating of the quartz glass. At these high glass temperatures of over 900 ° C, the life of the heat source is limited to a few hours.

DE-C2-35 37 428 discloses a fixing roller device for the thermal fixing of toner images, in which a heat source of the fixing roller is protected from excessive heating by a reflection-inhibiting, heat-resistant layer arranged on the inner surface of the fixing roller. The protective layer is arranged, for example, on the inside over the entire axial length (jacket and bearing sections) of the fixing roller.

In Patent Abstracts of Japan, Vol. 9, No. 120 (P-358) (1843), May 24, 1985; JP-A-60-4970 (Konishiroku Shashin Kogyo K.K.) January 11, 1985 describes a fixing roller for copying machines in which a heating source is arranged inside. To improve the heat absorption capacity, the inner surface of the fixing roller facing the heat source is uneven, in the form of a helical recess. The heating-up time of the fixing roller is shortened by the helical turning out of the inner surface of the fixing roller. As a result, in particular the start time for the copying process can be shortened with reduced electrical power consumption.

From DE-Al-32 44 392 a fixing roller for copying machines is known which has an inner surface with a profiling to reduce the heating-up times with effective heat and as little energy input as possible. To further shorten the heating-up time, the inner surface provided with the profiling can also be blackened. Both measures have the purpose of increasing the absorptive capacity of the inner surface of the fixing roller for the heating jets emitted by a heating roller and thereby to shorten the heating-up time. This improvement in the absorption capacity is achieved by the black paint or by the increased radiation-absorbing surface due to the profiling.

The object of the invention is therefore to construct a fusing roller for copying and printing devices, in which radiation sources arranged in the fusing roller are protected against excessive heating.

The object of the invention is achieved by the features specified in claim 1.

Advantageous developments of the invention are specified in the subclaims.

• Figur 1 einen prinzipiellen Aufbau einer elektrofotografischen Druckeinrichtung,
• Figur 2 einen Aufbau einer Fixierwalze der elektrofotografischen Druckeinrichtung,
• Figur 3 einen Querschnitt durch die Fixierwalze,
• Figur 4 einen prinzipiellen Strahlungsverlauf in der Fixierwalze gemäß Figur 3,
• Figur 5 Absorptionsverläufe für verschieden beschaffene Innenflächen der Fixierwalze, bei der die Strahlungsabsorption in einer Glaswandung einer Strahlungsquelle über die Anzahl der Strahlungsdurchgänge durch die Glaswandung der Strahlungsquelle aufgetragen ist.

An embodiment of the invention is explained with reference to the drawings. Show it:

• FIG. 1 shows a basic structure of an electrophotographic printing device,
• FIG. 2 shows a structure of a fixing roller of the electrophotographic printing device,
• FIG. 3 shows a cross section through the fixing roller,
• FIG. 4 shows a basic radiation profile in the fixing roller according to FIG. 3,
• FIG. 5 absorption curves for different internal surfaces of the fixing roller, in which the radiation absorption in a glass wall of a radiation source is plotted against the number of radiation passes through the glass wall of the radiation source.

Figure 1 shows the basic structure of an electrophotographic printing device 1 for a web-shaped recording medium 2, z. B. Perforated folding paper. Characteristic of the structure of the printing device 1, which is described in detail in the European patent application 89123027.8, is a rotatably mounted photoconductor drum 10, which acts as a data intermediate carrier and which is provided by a charging corotron 11, an LED or laser beam character generator 12, a developer station 13, one Transfer station 14, an unloading station 15 and a cleaning station 16 is surrounded.

The photoconductor drum 10 rotating in the direction of the arrow is first electrically charged over the entire area via the charging corotron 11. A latent charge image is then recorded on a photosensitive layer 100 of the photoconductor drum 10 using the character generator 12. Upon further rotation of the photoconductor drum 10, the latent image in the developer station 13 is colored with a developer mixture of toner and carrier particles to form a toner image. The toner image adheres to the photoconductor drum 10 due to electrostatic forces. In the transfer printing station 14, the recording medium 2 is guided tangentially past the photoconductor drum 10 with the aid of a transport device 140. Supported by the electrostatic forces of a transfer printing corotron 141, the toner image arriving in the transfer printing area of the transfer printing station 14 is transferred to the recording medium 2. During the recording medium 2 with the still smearable toner image with the aid of the transport device 140 of a fixing station 3 is supplied, the photoconductor drum 10 is discharged via the unloading station 15 and the photosensitive layer 100 is cleaned in the cleaning station 16. The cleaned photoconductor drum 10 is then electrically charged via the charging corotron 11 in order to generate a further toner image.

The web-shaped recording medium 2, which is stacked on a storage table 4 to form a supply stack 20, is fed to the transfer station 14 via a guide device 17 which can be swiveled out and provided with guide elements. After leaving the fixing station 3, the recording medium 2 is deposited by a pulling device 18, consisting of two rollers 180, 181 rolling onto one another, on a deposit table 5 to form a stack 21. Alternatively, however, it is also possible to transport the recording medium 2 to a post-processing machine via the pulling device 18.

FIG. 2 shows the structure of the fixing station 3 according to FIG. 1. Since the structure and function of the fixing station 31 are already described in the European patent application 89123027.8, only the most important features of the fixing station 3 are explained below. The web-shaped recording medium 2 fed from the transfer printing station 14 to the fixing station 3 with the toner image which can still be blurred is transported into the fixing station 3 at an almost constant speed. In the fixing station 3, the recording medium 2 first arrives on a pivotably mounted saddle 30 (paper guide saddle) which is not heated and therefore has the room temperature of the fixing station 3. The recording medium 2 is brought to a fixing roller 31 via the pivoting saddle 30 and placed around the fixing roller 31 in a wrap area UB with a wrap angle α of 60 °. In the wrapping area UB, the recording medium 2 with the still smearable toner image is preheated to such an extent that the melted toner can form an adequate connection with the recording medium 2 for subsequent thermal printing fixation. Since the amount of preheating of the recording medium 2 in the loop area UB depends, inter alia, on the force with which the recording medium 2 nestles against the fixing roller 31, a vacuum suction chamber 19 is arranged in the entry area of the recording medium 2 in the fixing station 3. The vacuum medium 2 between the fixing roller 31 and the suction chamber 19 is pulled taut by the vacuum suction chamber 19.

The thermal pressure fixation takes place in a fixing nip FS, in which the fixing roller 31 contacts a pressure roller 32. The pressure roller 32 is pivotally mounted like the saddle 30. At the start of printing, the saddle 30 and the pressure roller 32 are pivoted from a standby position P1 (shown in dashed lines) into an operating position P2. The heating of the aluminum fixing roller 31 is carried out by a radiation source 310, e.g. B. an infrared halogen radiator. The radiation source 310 is arranged in a glass casing 311, for example a glass tube made of quartz glass, along the axis of rotation in the center of the fixing roller 31. The rays emitted by the radiation source 310 strike the inner wall of the fixing roller 31, where they heat the fixing roller 31 by absorption.

By heating the recording medium 2 in the wrapping area UB and fixing gap FS, heat is constantly removed from the fixing roller 31. In order to obtain a constant fixing quality, the surface temperature of the fixing roller 31 must be kept constant. For this purpose, non-contact temperature sensors 33 are provided in the fixing station 3. The temperature sensors 33 detect a decrease and increase in the surface temperature on the fixing roller 31 in a target / actual value comparison. When a lower or upper threshold value of the surface temperature is reached, the temperature sensors 33 switch the radiation source 310 on or off.

An oiling device 34 is provided so that the toner particles do not adhere to the surface of the fixing roller 31 during the thermal pressure fixing. The oiling device 34 has a felt 340 impregnated with silicone oil, which is brought into contact with the fixing roller 31. This creates a thin film acting as a repellent release agent on the surface of the fixing roller 31. Since the fixing roller 31 continuously releases silicone oil in very small quantities to the recording medium 2 during the thermal pressure fixing, the felt 340 has to be constantly fed with silicone oil. For this purpose, the oiling device 34 has a metering tube 341 with fine metering bores, from which the replacement of the used silicone oil is fed to the felt 340 from a storage area with the aid of a pump.

Since the fine pores of the felt 340 close with dust, toner and resinified silicone oil as the time progresses and thus the absorption of the new oil is no longer ensured, the felt 340 must also be renewed from time to time. For this purpose, the oiling device 34 has two felt winding elements 342, on which the used and unused felt 340 is wound up, similar to the principle of the writing tape in a typewriter. Since the recording medium 2, for example paper, fixed in the fixing station 3 has a very high dust content, a paste-like mass formed from silicone oil and dust forms on the felt 340. It must be prevented that this mass is sporadically entrained by the fixing roller 31 and transferred to the recording medium 2. A rubber lip 35 is arranged between the fixing gap FS and the oiling device 34, which floats on the surface of the fixing roller 31 and wipes off the dust that has been taken up. If the printing process is interrupted, the rubber lip 35 is pivoted away and the dirt picked up is thrown into a collecting pan 36 underneath.

Since the recording medium 2 can have a very high proportion of water, for example up to 10% by weight in the case of paper, and the recording medium 2 must be heated to over 100 ° C. in the wrapping area UB, part of this water evaporates. So that this water vapor the thermal pressure fixation and the fixing quality is not impaired, it is sucked out of the wrapping area UB with the aid of a fan 37.

FIG. 3 shows a cross section through the fixing roller 31 with the radiation source 310 arranged concentrically inside the fixing roller 31 and surrounded by the glass wall 311. The roller body of the fixing roller 31 has a roughened surface 312 on its inner wall. The roughened surface 312 is preferably formed by radially symmetrically arranged teeth 313 rounded at the tips. The roughened surface 312 formed with the radially symmetrically arranged tines 313 is appropriate because the roller body of the fixing roller 31 can be produced from an extruded profile in such a structure. If production-related and cost-related reasons play no role, it is also possible to coat the inner wall of the fixing roller 31 with other surface structures, e.g. b. parabolic surface structures. It is crucial for the selection of the surface structure, however, that the light beams emitted by the radiation source 310 can be reflected several times in structural niches 314, for example the recesses formed between the teeth 313.

FIG. 4 shows the beam path of the beams emitted by the radiation source 310 in the recesses 314 of the inner wall formed by the teeth 313. The multiple reflections occurring in the recesses 314 are illustrated with the aid of two beams S1, S2, each of which strikes two different recesses 314 of the roughened surface 312 at different locations. Because the surface 312 of the inner wall has been selectively enlarged, the multiple reflections result in a greater absorption capacity of the fixing roller 31 for the rays emitted by the radiation source 310. The greater absorption capacity of the fixing roller 31 means that the heating of the glass wall 311 surrounding the radiation sources 310 is no longer as strong.

FIG. 5 shows, for different surface structures 312 of the fixing roller 31, different absorption profiles (a, b, c, d) of the percentage radiation A absorbed by the glass wall 311 over a number N of the radiation passages through the glass wall 311. A critical absorption Ac of the glass wall 311 is at an absorption Ac = 12% or a critical temperature Tc = 750 ° C. Above the critical absorption capacity Ac, the above-mentioned devitrification of the glass wall 311 made of quartz glass begins. If the absorption values or the temperature increase further, the quartz glass becomes milky and the radiation source 310 surrounded by the glass wall 311 is destroyed by overheating. The absorption curve a shows the absorption A of the radiation emitted by the radiation source 310 in the glass wall 311 when using a bare, untreated surface of the fixing roller 31. The absorption factor of the aluminum wall is 0.3, while the absorption factor of the glass wall 311 is 0.04.

A first possibility for increasing the absorption in the fixing roller 31 while simultaneously reducing the absorption A in the glass wall 311 is represented by the absorption curve b. The absorption curve b shows the absorption A of the radiation emitted by the radiation source 310 in the glass wall 311 when using a reflection-inhibiting coating applied to the surface of the fixing roller 31. The anti-reflective coating consists of a lacquer layer with embedded black particles, e.g. B. MoS2 lubricating varnish with graphite particles. The absorption factor of the surface coated with the MoS2 lubricating varnish is 0.65.

A second possibility for increasing the absorption in the fixing roller 31 while simultaneously reducing the absorption A in the glass wall 311 is represented by the absorption curve c. The absorption curve c shows the absorption A of the radiation emitted by the radiation source 310 in the glass wall 311 when using the roughened surface 312 of the fixing roller 31 shown in FIG. 3. Given the surface structure, it can be assumed that the radiation is reflected on the roughened surface 312 three times on average before a next passage through the glass wall 311 takes place. The absorption factor of the roughened surface 312 according to FIG. 3 is 0.3. The absorption curve d shows the absorption A with a combination of the absorption curves b and c.

Claims (4)

1. Fuser roller for electrophotographic copying and printing devices, having a radiation source (310), arranged inside the fuser roller (31), and having an inside wall which increases the absorption capacity of the fuser roller (31) for the beams emitted by the radiation source (310), the inside wall having a roughened surface (312) with structure niches (314) which are designed in such a way that the beams emitted by the radiation source (310) to increase the absorption capacity of the fuser roller (31) reflect many times in the structure niches (314), characterized in that the roughened surface (312) of the inside wall has a reflection-inhibiting layer of lacquer with incorporated particles which increase the absorption capacity.
2. Fuser roller according to Claim 1, characterized in that the layer of lacquer consists of MoS2 sliding lacquer.
3. Fuser roller according to Claim 1 or 2, characterized in that the roughened surface (312) is made up of jags (313) arranged radially symmetrically.
4. Fuser roller according to Claim 3, characterized in that the roughened surface (312) can be made by the extrusion method with the fuser roller (31).

Images