Method and device for offset varnishing

Abstract: The method of varnishing a printed medium is characterised in that: a laminated material (9) consisting of two connected layers is used for the production of the template (F); the upper layer (11) of said material is cut along the pattern of the template which is to be formed, while the lower layer (13) is kept whole; the areas of said upper layer corresponding to the areas not to be varnished are detached from the lower layer; and said laminated material is applied to a press means (5) capable of interacting with an opposing cylinder (7), the upper layer of said laminated material collecting the varnish from distribution means (1, 3) and applying said varnish to the medium to be varnished.

Description: The invention relates to a method for varnishing in offset printing machines, which is particularly suitable for use in the manufacture of paper and cardboard articles, and to a product for the application of said method and to a printing machine equipped to carry out said method. In the printing industry, in the manufacture of paper and cardboard articles, and in similar areas of application, it is frequently necessary to provide protective varnishing of a printed medium such as cardboard or the like. The varnishing constitutes the final stage of the printing process and consists in the application of a layer of protective varnish which covers the whole surface of the printed and varnished material on or off the production line. At the present time, indirect varnishing is carried out in the following way: a template which may be made of various types of material, such as linoleum or equivalent material, suitably coated with adhesive, is affixed to a plate designed to be applied to a rotating cylinder. The template reproduces the pattern of the areas of the medium to be varnished. For example, in the case of the production of cut-outs to form boxes, the template will have a perimeter corresponding to that of the cut-out product. The plate is then applied to the plate-cylinder. During the rotation of the plate-cylinder, the outer surface of the template is continuously in contact with the varnish. The collected varnish is transferred to the surface of a blanket cylinder. The blanket cylinder then transfers the varnish deposited on its surface directly to the medium to be processed, the transfer taking place with the aid of an opposing impression cylinder. This method has numerous disadvantages. In the first place, materials of the linoleum type are opaque, insufficiently soft, and consequently hard to cut. In offset printing machines, production line printing and varnishing systems are used, with machines printing five or more colours and a coating unit with which the complete or reserved varnish is applied. For the varnishing of areas, materials of the rubber-coated fabric type (blankets) are normally used for direct varnishing. The rubber layer is removed from the material in those areas where varnishing is not required. This system is complicated and expensive, particularly owing to the cost of the material and of the coat-removal operations. Furthermore, the rubber-coated material is opaque, and consequently the transfer of the varnish to the medium is not always optimal. From JP-A-1263049 a varnishing method and apparatus are known, wherein a template is used, which is made from a portion of laminated material consisting of two layers. The upper layer collects the varnish from distributing means and applies said varnish to the medium to be varnished, and the lower layer is attached to a plate cylinder to support said template on said plate cylinder. From JP-A-60146088 a material and a method for the production of paper stencils is known. This known material comprises an upper and a lower layer of translucent material. Said two layers are connected to one another by adhesive. The upper layer is cut along the perimeter of the stencil to be formed and is thereafter removed from the lower layer. The lower surface of the upper layer, i.e. the one which is originally connected by adhesive to the lower layer is used to pick up the ink and print the paper. The object of the invention is a method for varnishing which is simpler and more economical than the conventional methods, while maintaining a high quality of the finished product. A further object of the invention is a product which is particularly suitable for the application of this method. A further object of the invention is a varnishing assembly to carry out the method according to the invention. These objects are obtained by a method comprising the steps of claim 1. According to this method, therfore, a laminated material, from which the template to be applied to the cylinder of the varnishing assembly is formed, is used for direct varnishing, thus avoiding the operations of removing the rubber layer of the blanket. The same product may also be applied in indirect varnishing systems. In this case, the laminated material replaces the metal plate to be applied to the plate-cylinder. The varnishing assembly of the invention is characterized by the features of claim 6. The operations for the formation of the template are greatly simplified. A further simplification is achieved by specifying the use of a transparent laminated material, which enables the upper layer of the material to be cut simply by laying said material by contact on a form reproducing the pattern of the template to be formed. The laminated material, and the template obtained therefrom, according to the invention are defined in claims 2 and 7. Advantageous characteristics of the laminated material according to the invention are stated in the dependent claims. The invention will be understood more clearly by examining the description and the attached drawing, which provides a practical and non-restrictive illustration of the invention. In the drawing: Fig. 1 is a highly schematic diagram of the cylinder to which the form is applied and of the opposing element; Fig. 2 shows a roll of the laminated material according to the invention; Fig. 3 shows a portion of laminated material in which the upper layer has been cut to produce a form; and Fig. 4 shows in a highly schematic way the application of the laminated material to the press cylinder. Fig. 1 shows in a highly schematic way certain parts of a coating unit forming part of a production line with an offset printing machine, with the devices needed to varnish the medium which has been freshly printed by the up-line printing assemblies. 1 indicates a vessel containing the varnish, which may be a varnish of the water-based, UV or other type with suitably viscosity. 3 indicates a roller which distributes the varnish over a template F applied to a plate-cylinder 5 rotating in the direction f5. The cylinder 5 interacts with an opposing cylinder 7, which forms, in combination with the cylinder 5, a pair of press means for the coating of the medium S, for example cardboard or paper fed continuously from a roll, or other material. Characteristically, according to the invention, a laminated material, shown schematically in Fig. 2, is used to form the template F. The laminated material, indicated by 9, consists of two layers 11 and 13 respectively, and is preferably produced in roll form. Production in roll form enables templates of any size to be formed, with the minimum of waste and discards. The lower layer of the laminated material 9, indicated by 13, is advantageously slightly wider than the upper layer, indicated by 11. The edges 13A of the lower layer, which project beyond the upper layer, enable the portion of laminated material on which the template is formed to be easily attached to the cylinder 5. Both the lower layer 13 and the upper layer 11 may advantageously be formed from transparent or translucent plastic material. In particular, a layer of polyester whose thickness may advantageously lie in the range from 250 to 350 micrometres may be used as the lower layer. The upper layer 11 is preferably formed from polypropylene and polyethylene with a thickness from 250 to 1000 micrometres. The upper layer 11 is suitably adhesive-coated to permit the permanent connection of the two layers 11 and 13. The template F is formed by superimposing a piece of material 9 over an image, drawn on paper for example, of the pattern which the template F is to have. A calibrated blade is then used to cut the upper layer 11 of the laminated material 9 along the pattern which the template F is to have. The blade is calibrated in such a way that the depth of cut is such that it does not affect the lower layer 13, which has to remain whole. Fig. 3 illustrates an example of a template F produced by the cutting of the upper layer 11 and the detachment of the portions of the upper layer lying outside the perimeter of the template from the lower layer 13. The template F produced in this way is applied to the cylinder 5. When the template F has been mounted on the cylinder 5, as shown schematically in Fig. 4, the operation of varnishing the medium S may commence. It is to be understood that the drawing shows only an illustration provided solely as a practical demonstration of the invention, this invention being able to vary its forms and dispositions without thereby departing from the scope of the guiding concept of said invention. Any reference numbers in the attached claims has the purpose of facilitating the reading of the claims with reference to the description and drawing, and does not limit the scope of protection represented by the claims.

Claims: Method of varnishing a printed medium by means of a template, comprising the step of attaching a laminated material (9), consisting of two connected layers (11,13), to a plate cylinder (5) interacting with an opposing cylinder (7), the upper layer of said laminated material collecting the varnish from distribution means (1, 3) and applying said varnish to the medium to be varnished and the lower layer (13) being attached to said plate cylinder to support said template (F) on said plate cylinder (5), characterized in that, before attaching said laminated material (9) to said plate cylinder (5), the following steps are performed: cutting a portion of said laminated material (9), which consists of two connected layers (11,13) of translucent or at least partially transparent material; superimposing said portion of laminated material (9) over an image of the pattern of the template (F) to be formed; cutting the upper layer (11) of said material along the pattern of the template which is to be formed, while the lower layer (13) is kept whole; detaching the areas of said upper layer (11), corresponding to the areas not to be varnished, from the lower layer (13), thus forming said template (F). Laminated material for the formation of templates for varnishing printed media, consisting of an upper layer (11) and a lower layer (13), both layers being translucent or at least partially transparent and connected to one another by means of adhesive, the upper layer (11) being designed to be cut along the perimeter of the template to be formed and to be removed from the lower layer (13) which remains whole and which is made of polyester, characterised in that the upper layer is a layer of polypropylene and polyethylene and that the lower layer forms the supporting layer of the template. Laminated material according to claim 2, characterised in that the lower layer has a thickness of between 250 and 350 micrometres and the upper layer has a thickness of between 250 and 1000 micrometres. Laminated material according to claim 2 or 3, characterised in that the lower layer is of a size larger than or equal to that of the upper layer, and, where it is of a larger size, projects beyond the upper layer along two edges (13A). Laminated material according to anyone of claims 2 to 4, characterised in that it is produced in roll form. Varnishing assembly, comprising a plate-cylinder (5) on which a template (F) made from a laminated material is applied to collect the varnish from distribution means (1) and transfer it to the medium (S) to be varnished, and an opposing cylinder (7), wherein said plate-cylinder (5) interacts directly with the opposing cylinder (7) to transfer the varnish directly from said template to said medium, characterised in that said template is made from a laminated material according to anyone of claims 2 to 5, the lower layer (13) being attached to the plate cylinder and supporting the template (F) formed with the upper layer (11). A template made from a portion of laminated material, said laminated material consisting of an upper layer (11) and a lower supporting layer (13) to be attached to a plate cylinder of a varnishing assembly, both layers being translucent or at least partially transparent and connected to one another by means of adhesive, the upper layer (11) being cut along the perimeter of the template, the portion of said upper layer (11) outside said perimeter being removed from the lower layer (13) and the lower layer, made of polyester remaining whole, characterized in that the upper layer is a layer of polypropylene and polyethylene and that the lower layer forms the supporting layer of the template.

Inventors: FORNER EGIDIO A, MARANGONI ROBERTO, NASSI ALDO, FORNER, EGIDIO A., MARANGONI, ROBERTO, NASSI, ALDO
Applicants: FEBA S D F DI BOLDRINI ANDREA, MOROEL DI MARANGONI ROBERTO &, SYROM 90 SPA, FEBA S.D.F. DI BOLDRINI ANDREA E FORNER EGIDIO, MOROEL DI MARANGONI ROBERTO & C., S.A.S., SYROM 90 S.P.A.
Application year: 1992
Main classification: B41F23
IPC codes: B41M7, B41F23