A device for transferring a toner image from an image-forming medium to a receiving material

Abstract: A device for transferring a toner image from an image-forming medium (1) to a receiving material comprising: an endlessly movable intermediate medium (12) provided with a top layer in contact with the image-forming medium (12) in a first transfer zone, heating means (17) for heating the toner image on the top layer of the intermediate medium (12), a biasing means (22) which in a second transfer zone can be brought into contact with the intermediate medium (12), transport means (24) for transporting the receiving material through the second transfer zone, means being provided for removing from the top layer of the intermediate medium impurities transferred thereto, by bringing said impurities into contact with a material which breaks down the impurities.

Description: The invention relates to a device for transferring a toner image from an image-forming medium to a receiving material comprising: an endlessly movable intermediate medium comprising a support provided with a top layer secured via its rear to the support, said intermediate medium being in contact with the image-forming medium in a first transfer zone, heating means for heating the toner image on the top layer of the intermediate medium, a biasing means which in a second transfer zone can be brought into contact with the intermediate medium, and transport means for transporting the receiving material through the second transfer zone. US Patent A-4 607 947 describes a contact fixing device in which a toner image is transferred from an image-forming medium to a heatable intermediate medium. The toner image is then transferred in a fixing zone, in which the intermediate medium is in contact with a biasing means, and at the same time fixed on a receiving material transported through the fixing zone. However, impurities may be transferred from the receiving material to the intermediate medium. Toner material residues may also remain as an impurity on the intermediate medium because of incomplete transfer of the toner image to the receiving material. If impurities of this kind are left on the intermediate medium, they may be transferred to the image-forming medium in the first transfer zone. This causes disturbance to the image-formation and hence, finally, image errors in the copy on the receiving material. Various cleaning means have been proposed to remove these impurities from the intermediate medium before reaching the first transfer zone. For example, US-A-4 607 947 discloses a cleaning means having a cleaning surface to which toner adheres better than to the intermediate medium. A cleaning means of this kind operates satisfactorily for removing high-melting impurities such as toner residues. This cleaning means can also be used to remove paper dust from the intermediate medium. In practice, however, it has been found that low-melting impurities from receiving materials, such as wax-like compounds, plasticisers, antifoaming agents, plastic fillers occurring in receiving papers, and dust particles from plastic receiving materials, and the like, are not removed or only partly removed from the intermediate medium with the known cleaning means. After being deposited on the intermediate medium in the second transfer zone these impurities can also be transferred in the first transfer zone to the image-forming medium, resulting in disturbed image-formation and hence, ultimately, image faults in the copy on the receiving material. This necessitates regular and premature replacement of intermediate medium and image-forming medium, involving high maintenance costs and equipment downtime. For example, it has been found that the increasingly used "alkaline" receiving papers based, inter alia, on cellulose, chalk and sizing means, such as alkyl ketene dimers, are an appreciable source of such impurities. Such receiving papers are used today because of the lower costs and better durability in comparison with the "acidic" receiving papers based, inter alia, on cellulose, clay and modified or unmodified resins. It has now been found that where such receiving papers are used reaction products of these binders are deposited from these papers in the top layer of the intermediate medium. These reaction products are then transferred to the image-forming medium with image disturbance as the result. To remove these reaction products from the top layer, EP-A-0 581 365 proposes to discharge the impurities via the rear of the top layer to a rubber intermediate or underlayer. An impurity-absorbing material, such as carbon black, is mixed in this intermediate layer. It is also proposed to bring transport rollers into contact with the intermediate or underlayer on the side thereof remote from the top layer, so that further transport of the impurities from the top layer can take place. EP-A-0 581 355 proposes using a cleaning means which between the second transfer zone and the first transfer zone can be brought into contact with the top layer of the intermediate medium, the outside of the cleaning means being provided with an impurity-absorbing material. In the devices described in the above patent applications, the amount of impurities in the top layer is reduced, but a problem which still remains is that after some time the intermediate layer or underlayer is saturated with impurity-absorbing material and the cleaning means is saturated with the impurities originating from the receiving materials, thus necessitating premature replacement of intermediate medium and/or cleaning means. The object of the invention is to reduce the above problem. To this end, according to the invention, in a device according to the preamble of claim 1, means are provided for breaking down impurities transferred by receiving materials to the top layer of the intermediate medium. As a result, the amount of impurities in the top layer is reduced for a long period, so that the life of the intermediate medium and the image-forming medium, i.e. the time during which said medium can be used without image faults occurring, is greatly increased. Preferably, the means comprise a material which breaks down impurities and which can be brought into contact with the impurities, the said material which breaks off the impurities containing a transition metal compound. Transition metals are defined here as metals of group IIIB to group VIIIB, including the "inner transition metals", such as the lanthanides, according to the periodic table given in Inorganic Chemistry, J.E. Huheey, Harper & Row, Publishers, New York, 1978. Transition metal compounds can be used in the form of salts, such as chlorides, as oxides, as co-ordination complexes, such as carboxylates and beta-diketonates, as organometal complexes and the like. Preferably, carboxylates are used. The transition metal compounds can react with the low-melting impurities from the alkaline papers, so that the impurities are broken down. One class of compounds representative of these low-melting compounds is the dialkyl ketones. One example of a dialkyl ketone is distearyl ketone. Although the breakdown mechanism of such dialkyl ketones under the influence of transition metal compounds is not completely clear, we assume, on the basis of experiments, that oxidation may play a part in the breakdown. For the breakdown of such dialkyl ketones it has in practice been found favourable to use a transition metal compound in which the transition metal has a reduction potential of more than 0.7. Reduction potentials of this kind are given, inter alia, in the "Handbook of Chemistry and Physics", 57th Edition, 1976, published by the CRC Press, Cleveland, Ohio, page D141 et seq. Suitable transition metal compounds are the transition metal compounds in which the transition metal is selected from group VIIB or group VIIIB, such as Mn, Co, Fe, Pt. The breakdown of the low-melting compounds with these compounds is reasonable to good. Manganese compounds have preference, because of their high activity even mixed in a rubber matrix. Examples of manganese compounds with very good breakdown properties are manganese octoate, manganese cyclohexylbutyrate, manganese stearate and manganese acetylacetonate. The materials which break down impurities can be used in various ways. In a first embodiment, the transition metal compound is mixed in the top layer of the intermediate medium. As a result, it is possible locally to break down the impurities deposited in the top layer. In a second embodiment, the transition metal compound is mixed in an intermediate layer disposed beneath the top layer. An advantage of this is that the top layer properties necessary for the toner transfer do not need to be affected by the admixture of a breakdown material in the top layer. A rubber material is advantageously selected for the intermediate layer. A silicone rubber layer has proved particularly suitable. In this way, it is possible during stand-by and run periods continuously to discharge impurities from the top layer to the intermediate layer so that the useful life of the intermediate medium and the period of use of the image-forming medium are greatly increased. A third embodiment is characterised in that the transition metal compound is preferably mixed in a rubber material for application to a cleaning means which can be brought into contact with the top layer of the intermediate medium between the second and first transfer zones. RTV or HTV silicone rubbers, inter alia, are used as top layer for intermediate media. They are obtained by curing to an elastomeric composition polyorganosiloxane mixtures bearing reactive groups, under the influence of a suitable catalyst and at room temperature or at elevated temperature. The top layer can also contain additives to improve its properties, such as mechanical strength, thermal conductivity and antistatic behaviour. Typical rubber compositions for forming a top layer for intermediate media usable as a temporary support for a powder image are described in UK patent No. 1 279 687 and Example 1 of European patent application number 146 980. The intermediate medium can be constructed as a cylindrical metal roller provided with an elastic rubber intermediate layer to which a top layer is applied. Another embodiment is characterised in that the intermediate medium is constructed as an endless belt which is trained around two or more shafts, the support being in the form of a layer of material which breaks down impurities. A possibly fibre-reinforced belt of this kind can also be brought into contact adjacent its inside with a cleaning means, such as, for example, a rubber-covered roller provided with a material which breaks down impurities. The shafts can also be covered with a rubber material of this kind. An intermediate medium belt of this kind is simple and economic to manufacture and easily replaced at the end of its life. Another embodiment is characterised in that the support is constructed as a fabric belt, the fabric belt being provided with a layer of material which breaks down impurities, to which a top layer is applied. Silicone rubber, for example, is suitable for the rubber material in the intermediate layer. The invention will now be explained with reference to the accompanying drawings and examples. Fig. 1 is a diagrammatic cross-section of one embodiment of the device according to the invention. Fig. 2 is a diagrammatic cross-section of another embodiment of the device according to the invention. The image-forming device shown in Fig. 1 is provided with an endless photoconductive belt 1 which is advanced at a uniform speed by means of drive and guide rollers 2,3 and 4 respectively. The image of an original on a window 5 is projected on to the belt 1 by means of flashlights 6 and 7, a lens 8 and a mirror 9, after the belt has been electrostatically charged by a corona device 10. The latent charge image formed on the belt 1 after the flash exposure is developed with toner powder by a magnetic brush device 11 to give a toner image which is then brought into contact under pressure with an endless intermediate medium belt 12 in a first transfer zone, the belt 12 being provided with a top layer of soft elastic and heat-resistant material, e.g. silicone rubber. The toner image in this case is transferred to the belt 12 from the belt 1 by adhesion forces. After this image transfer, any remaining image residues are removed from belt 1 by means of a cleaning device 13, whereafter the photoconductive belt 1 is ready for fresh use. The intermediate medium belt 12 is trained over drive and guide rollers 14, 15, and is heated to a temperature above the toner powder softening temperature, e.g. by an infrared heater 17 disposed inside roller 14. While belt 12 with the toner image thereon is advanced, the toner image becomes tacky as a result of the heating. In a second transfer zone the tacky toner image is then transferred, under the influence of pressure in a second transfer zone, by means of a pressure member in the form of a belt 22 trained over rollers 23 and 24, and is at the same time fixed on a sheet of receiving material supplied from reservoir 18 via rollers 19, 20. Finally, the copy obtained in this way is deposited in collecting tray 25 by belt 22, which is trained over rollers 23 and 24. The intermediate medium belt 12 shown in Fig. 2 is constructed as a polyester fabric belt 40 provided with a 2 mm thick layer of peroxide-hardened silicone rubber 41, in which 1% by weight of manganese octoate has been mixed. A 60 µm thick top layer 42 is applied to this layer as stated in Example 1 of European patent application EP-A-0 146 980. A cleaning means 30 is also provided for toner residues in accordance with US-A-4 607 947, and its surface 31 can be brought into contact with the intermediate medium. In another embodiment the top layer can be provided with 1% by weight of manganese octoate. In one embodiment in which the top layer is provided with a transition metal compound, the above-described intermediate layer provided with a transition metal compound may be provided. A third embodiment of the device according to the invention is shown in Fig. 2. Like references refer to the same parts as in Fig. 1. In order to remove impurities from the intermediate medium belt 12, the device is provided with a cleaning means 35, e.g. in the form of a freely rotatable roller 36 provided with a layer of peroxide-hardened silicone rubber, in which 0.5% of a transition metal compound, such as manganese stearate, has been mixed. other impurity-absorbing rubbers may be used as stated in EP-A-0 581 355, in combination with a transition metal compound. Furthermore, an impurity-absorbing material such as carbon black may be admixed. The cleaning means may be used on its own but can also be used in combination with an intermediate medium, in which an impurity-breakdown material is mixed in the intermediate layer and/or the top layer. Examples of transition metal compounds are given in Table 1 together with the reduction potential of the transition metal. The percentage breakdown is also indicated, determined by bringing 0.02 g of a suitable model compound (distearyl ketone) into contact with 0.05 g of transition metal compound for 24 hours at 100°C and then measuring the amount of residual distearyl ketone. Transition metal compound Reduction potential % breakdown Cobalt octoate 1.842 Co 3+ → Co 2+ 55 Cerium octoate 1.61 Ce 4+ → Ce 3+ 96 Manganese stearate 1.51 Mn 2+ → Mn + 96 Manganese acetate 1.51 Mn 2+ → Mn + 73 Manganese acetylacetonate 1.51 Mn 2+ → Mn + 28 Manganese octoate 1.51 Mn 2+ → Mn + 100 Manganese maleinate 1.51 Mn 2+ → Mn + 91 Manganese(IV) dioxide 1.51 Mn 2+ → Mn + 63 Manganese chloride 1.51 Mn 2+ → Mn + 96 Pt on activated carbon 1.2 Pt 2+ → Pt 79 Iron (III) stearate 0.77 Fe 3+ → Fe 2+ 30 Copper phthalocyanine 0.16 Cu 2+ → Cu + 0 Chromium acetylacetonate -0.41 Cr 3+ → Cr 2+ 0

Claims: A device for transferring a toner image from an image-forming medium (1) to a receiving material comprising: an endlessly movable intermediate medium (12) comprising a support (40) provided with a top layer (42) secured via its rear to the support (40), said intermediate medium (12) being in contact with the image-forming medium (12) in a first transfer zone, heating means (17) for heating the toner image on the top layer (12) of the intermediate medium, a biasing means (22) which in a second transfer zone can be brought into contact with the intermediate medium (12), and transport means (24) for transporting the receiving material through the second transfer zone, characterised in that means are provided for breaking down impurities transferred by receiving materials to the top layer (42) of the intermediate medium. A device according to claim 1, characterised in that the means for breaking down the impurities comprise a material which breaks down impurities and which can be brought into contact with the impurities, the said material which breaks down the impurities containing a transition metal compound. A device according to claim 2, characterised in that the transition metal of the transition metal compound has a reduction potential greater than 0.5. A device according to claim 2 or 3, characterised in that the transition metal compound contains a transition metal from group VIIB or group VIIIB. A device according to claim 4, characterised in that the transition metal compound contains manganese. A device according to claim 5, characterised in that the transition metal compound is selected from the series: manganese octoate, manganese cyclohexylbutyrate, manganese stearate, manganese acetylacetonate. A device according to any one of claims 2 to 6, characterised in that the transition metal compound contains one or more carboxylate ligands. A device according to any one of claims 2 to 7, characterised in that the transition metal compound is mixed in the top layer. A device according to claim 8, characterised in that at least 0.5% by weight of transition metal compound is mixed in the top layer. A device according to any one of claims 2 to 7, characterised in that the transition metal compound is mixed in an intermediate layer disposed beneath the top layer. A device according to claim 10, characterised in that the intermediate layer comprises a rubber material. A device according to claim 11, characterised in that the rubber material comprises silicone rubber. A device according to claim 10 or 11, characterised in that that at least 0.5% by weight of transition metal compound is mixed in the rubber material. A device according to any one of claims 2 to 7, characterised in that the transition metal compound is disposed on a cleaning means (35) which can be brought into contact with the top layer of the intermediate medium between the second and first transfer zones. A device according to claim 14, characterised in that the transition metal compound is mixed in a rubber material. A device according to claim 15, characterised in that at least 0.5% by weight of transition metal compound is mixed in the rubber material.

Inventors: MARKIES PETER RICHARD, MIEDEMA MARK, MARKIES, PETER RICHARD, MIEDEMA, MARK
Applicants: OCE TECH BV, OCE-TECHNOLOGIES B.V.
Application year: 1995
Main classification: G03G15
IPC codes: G03G15