PROCESS FOR PREPARING SLEEVES FOR PHOTOENGRAVING, REMOVABLE FROM GRAVURE PRINTING CYLINDERS, AND SLEEVES OBTAINED BY THIS PROCESS

Abstract: Process for preparation of a removable sleeve (30), on which a design is to be photoengraved, of the cylinder (10) of gravure printing machines, entirely of copper, by immersing, in an electro copper plating bath (25), the cylinder (10) to which a prior treatment with a solution of silver salts has been given to facilitate detachment of the sleeve (30).

Description: Process for preparing sleeves for photoengraving, removable from gravure printing cylinders, and sleeves obtained by this process The invention concerns cylinders for gravure printing. In gravure printing a cylindrical form is used to print what is desired and this is done by a photoengraving process during which tiny cells are formed that receive the ink subsequently transferred onto paper. The surface on which these cells are engraved by various methods - tra- ditional, halftone, conversion, electronic etc., - is generally of copper. Said surface is obtained by galvanic deposition on steel cylinders and, after photoengraving, is given a chromium protective process. For each fresh set of pictures the cylinders are processed by specialised engravers and are then sent to the user who mounts them onto machines for gravure printing. Bearing in mind the considerable size and weight of each cylinder as well as the great delicacy of the surfaces, already engraved or prepared for it, there are clearly problems of transport and storage with related costs and capital tied up for the purpose. To overcome these drawbacks and lower costs, metal cylindrical sleeves, usually nickel, are used, to slide on and off the cylinders. A coating of copper, like that deposited on traditional cylinders, is deposited on the surfaces of these sleeves for good engraving results. There are a various methods for assisting the work of removing sleeves from these cylinders. The best known comprises having small holes made in the surface of the cylinder to permit creation of a cushion of com¬ pressed air between the surface of the cylinder and that of the sleeve. Considering the great difference between the weight of a sleeve, 2-3 kg., and that of the cylinder, 100-200 kg., it is clearly advantageous to have a removable sleeve rather than a conventional type of cylinder. Running costs for corrections, balancing, maintenance, staff and transport are all reduced. The quality of print is higher, while adjusting movements are avoided as well as waste of costly materials. In the present situation of the market, however, requiring a greater variety of packing materials, which in turn means shorter printing runs and the ever present need to lower costs to increase competitivity, the fact that sleeves still have to be eliminated after use remains a serious loss and has a negative effect on the market. A process has therefore been devised whereby a copper film is formed on the nickel sleeve and a separator product interposed between the two so that the film can easily be slid off when a new engraving is required. A fresh film for a fresh engraving is then deposited by electroplating on the nickel sleeve. The separator product generally consists of a silver-based solution or of of passivating substances, bichromates or some others. According to a preferred method a copper film and the separator product are applied to the nickel sleeve followed by formation of the copper film to be photoengraved. To detach the copper film from the sleeve, for a fresh photoengraving process, use has to be made of mechanical means. After this a new film is deposited following application of the separator. This process offers considerable advantages compared with direct depo¬ sition on the cylinder of the film to be photoengraved . Even so, however, sleeve costs are high because of the high cost of nickel and because of the time needed to form the different layers: the copper film, the separator product and the copper film for engraving. The invention here described appreciably lowers costs of removable sleeves both as regards materials and the time needed for applying them and therefore offers considerable economic and practical advantages as will be explained below. Subject of the invention is a process for preparation of metal sleeves for photoengraving, removable from the cylinder on gravure printing machines. The removable sleeve is constructed of copper and engraving is done directly onto said sleeve. The copper sleeve is created on a cylinder by its immersion in an electro- copper plating bath. Before being put into the plating bath the cylinder is treated with a separator product to facilitate detachment of the sleeve. Once engraved the copper sleeve can be used for further engraving by mechanical removal of the engraved layer. After formation of the copper sleeve, according to one advantageous ap¬ plication of the process, the separator product is once again applied to the base formed by said sleeve and then a copper film is formed in the electroplalting bath on said base, In this way, in order to make a fresh engraving, the copper film is removed from the sleeve with or without mechanical means. By interposing a separator product, a new film can be formed and a fresh engraving be made in the electroplating bath. The separator product is preferably an aqueous solution of silver salts. This solution of silver salts is that given by an exhausted solution used to fix films in the engraving process on copper sleeves, loaded with silver salts which have not been darkened by photographic development and removed during the fixing process. It is an advantage if the cylinder exhibits a device able to create an air cushion to assist in sliding the sleeve off the cylinder. The invention offers evident advantages. Elimination of the nickel base and copper film, replacing said base by a copper sleeve, not only drastically reduces costs of materials but also working times and simplifies operations. Photoengraving onto an entirely copper sleeve is much quickier and easier. If, by interposition of a separator product, a copper film is formed on the copper base, a further advantage is gained as removal of the copper film for each fresh photoengraving process can be done simply and quickly. It will be seen from the foregoing that removable sleeves offer a great many advantages compared with directly photoengraved cylinders both from the point of view of cost and from that of simplifying operations. Characteristics and purposes of the invention will be made still clearer by the following examples of its execution illustrated by diagrammatically drawn figures. Fig.1 Perspective of a cylinder for creating an air cushion for formation of a copper sleeve. Fig.2 The cylinder in Fig.1 treated with a solution of separator product. Fig.3 The wet cylinder in a bath for electro copper plating. Fig.4 The cylinder with its copper sleeve after photoengraving. Fig.5 The engraved sleeve removed from the cylinder. Fig.6 Sleeve with chromium finish, ready for gravure printing. Fig.7 The cylinder after receiving a layer of electro-copper plating, given a new treatment with a separator product. Fig.8 The cylinder in Fig.7 put back into the plating bath for formation of a copper film, at the end of that process. Fig.9 The cylinder in Fig.8, taken from the bath, after photoengraving. Fig.10 The sleeve of the cylinder in Fig.9, removed and ready for gravure printing. Fig.11 The sleeve in Fig.10 having received a protective chromium coat- ing. Fig.12 The sleeve at the end of printing, when the photoengraved film is being removed to permit formation of a new copper film ready for photoengraving. In the cylinder 10 with pins 1 1 are small holes 12 on the surface 13, com- municating with the inner chamber 15 in which there is a lateral mouth 14 for passage of compressed air to create an air cushion when the copper sleeve, to be formed round said cylinder, is being taken off. The cylinder is treated with a solution 20 of separator product as seen in Fig. 2 and, after application of lateral protective strips 21 on the perfora- ted area, is immersed in the liquid 26 in the bath 25 for electro copper plating. The copper sleeve 30 having been formed, the cylinder is extracted for the photoengraving process of objects 31 as seen in Fig. 4. The engraved sleeve 30 is then removed (Fig.5), this action being assisted by presence of the separator product 20 and by the air cushion created by compressed air put into the chamber 15, after which the sleeve 30 is given a protective chromium coating 32 (Fig.6). The sleeve is then sent away for gravure printing where it will be mounted on the cylinders of the printing machine. At the end of the printing run the sleeve can be returned to its owners who do the photoengraving. According to its thickness the sleeve can be remelted or the engraved layer can be removed, the surface smoothed and the sleeve be used again for further engraving. Alternatively, the sleeve can be formed on a cylinder 40 by a layer of copper 42, with interposition of a separator product. The cylinder 40 is given a new bath of separator product 20 and once more placed in the copper plating bath 25 for formation of a copper film 44 to make a sleeve 45 (Fig.8). This film is then photoengraved with the desired design 31 (Fig.9), the sleeve is removed from the cylinder (Fig.10) and after receiving a protective chro-mium coating 46 (Fig.1 1), is sent to the printers. On completion of the printing run the sleeve 45 is returned to the engraver who can engrave a new design, detaching the film 44 using mechanical means to do so if required, as shown in Fig.12 where the edges 47, 48 of the film 44 may be seen in the process of removal. This having been done, and always with interposition of a separator pro¬ duct, a new film can be formed for a fresh engraving. Normal photoengraving work comprises preparation of the photographic material for engraving by chemical or by electromechanical methods. For fixing the photographic film, different solutions are used containing, for example, sodium hyposulphite, bisulphite, ammonium thiosulphate. These solutions remove the unoxidised silver salts from photographic development. When this solution is exhausted it will contain a high pro¬ portion of silver salts and is therefore sold to engravers who use it as a suitable separator product to interpose between the cylinder and the copper sleeve or between the copper film and the thicker layer of copper in the case of sleeves on which that layer and film are used.

Claims: Claims 1. Process for preparation of removable metal sleeves (30, 45) on which the design (31) is photoengraved on the cylinder (10, 40) for gravure printing machines, characterized in that the removable sleeve (30, 45) is constructed of copper, the design (31) being photoengraved directly on said sleeve (30, 45). 2. Process as in claim 1 , characterized in that the sleeve (30) is obtained by forming a copper layer on a cylinder (10) by immersing it in an electro-copper plating bath (25), 3. Process as in claim 2, characterized in that before its immersion in the copper plating bath (25) the cylinder (10) is treated with a separator product (20) to assist de¬ tachment from the sleeve (30) 4. Process as in claim 1 , characterized in that the photoengraved copper sleeve (30) is used for a new photoengraved design (31), removing the engraved layer from said sleeve (30) by mechanical means. 5. Process as in claim 2, characterized in that the sleeve (45) is obtained by applying a separator product (20) to the layer (42) of copper formed on the cylinder (40) and then forming, in the copper plating bath (25), a copper film (44) upon said layer (42). 6. Process as in claim 5, characterized in that, to make a new engraving, the copper film (44) is taken off the sleeve (45), removing it with or without mechanical means, after which a new copper film (44) is formed in the copper plating bath (25), with interposition of a separator product (20). 7. Process as in claims 3 and 5, characterized in that the separator product is a solution (20) of silver salts. 8. Process as in claim 7, characterized in that the aqueous solution of silver salts (20) is what remains of the exhausted solution, used as a fixer of the photographic film in the photoengraving process on the copper sleeve (30, 45), charged with unoxidised silver salts from photographic developing processes and removed during the fixing operation. 9. Process as in claim 1 , characterized in that the cylinder (10, 40) exhibits a device (12, 14, 15) able to create a cushion of air to assist the sleeve (30, 40) to slide off when it is being detached from the cylinder (10, 40). 10. Metal sleeve (30, 45) for photoengraving removable from the cylinder (10, 40) of machines for gravure printing, characterized in that it is constructed in copper, the design (31) being photoengraved directly on said sleeve (30,45). 11. Copper sleeve (30, 45) as in claim 10, characterized in that it is obtained by forming a layer of copper on a cylin¬ der (10, 40) during its immersion in an electro copper plating bath (25). 12. Copper sleeve (30, 45) as in claim 11 , characterized in that before immersion in the copper plating bath (25) the cylinder (10, 40) is treated with a separator product (20) to facilitate de¬ tachment of said sleeve (30, 45). 13. Copper sleeve (30) as in claim 10, characterized in that it is used for a new photoengraved design (31) me¬ chanically removing the engraved layer from it. 14. Copper sleeve (45) as in claim 11 , characterized in that it is obtained by applying a separator product (20) to the copper layer (42) on the cylinder (40) and then forming a copper film (44) upon said layer in the copper plating bath (25). 15. Copper sleeve (45) as in claim 1 , characterized in that, to make a new photoengraving, the copper film (44) is removed, with or without mechanical means, then in the copper plating bath (25) a new copper film (44) is deposited with interposition of a separator product (20).

Inventors: VENTURATI LAURA TERESA, VENTURATI, LAURA, TERESA
Applicants: ROTOINCISA SRL, VENTURATI LAURA TERESA, ROTOINCISA S.R.L., VENTURATI, LAURA, TERESA
Application year: 1996
Main classification: B41N1
IPC codes: B41C1, B41N1