Process for preparing a surface for printing and product obtained thereby

Abstract: The invention relates to a process for preparing a surface (1) on which a print is to be made, in particular a surface (1) of a sheet of paper or card which is to be subjected to offset lithographic printing perhaps after having been aluminized or metallized, wherein before a printing phase a partial metallizing or aluminizing of the surface to be printed upon is effected only in some predetermined zones (2) of the surface. The invention also relates to a sheet of paper or card, in particular of the type destined to be folded and glued to make up a box wrapper, comprising, on a printed side thereof, a partial aluminization or metallization in accordance with the above-described process.

Description: The invention relates to a process for preparing a surface on which printing will take place, and a product obtained thereby. The invention relates in particular to the preparation of sheets of paper or card on which offset lithographical printing is to take place after said sheets have been metallized or alluminized. The product obtained by means of the process is a sheet of paper or card, in particular of the type destined to be folded and glued to make up a box wrapper. A first process of known type involves heat-impression of aluminate on paper or card as a final operation performed on pre-printed and painted sheets, where the paint serves to protect the printed zones. The aluminate is monochromatic and covers the underlying tones, and can be said to have a graphic function without substituting the characteristics of an aluminate base, and is used prevalently for texts, friezes and line graphics. A second process involves the laying of a coat of aluminated polyester on a sheet of paper or card, and thereafter printing a white background on the zones of the paper or card where the metallized effect is not desired; these white zones will usually have photographs, pictures and in some cases texts printed on them. On sheet prepared as above, once the white paint has dried, lithographical printing can begin, using UV drying paints or other rapid-drying colours. In any case the print quality of the photographic images obtained by the above method is lower than that obtained by printing on a laminated sheet of paper or card, or without any further aluminization or metallization. A further drawback is the fact that the sheets of paper or card will usually be folded and glued in some well-defined zones, as they generally are used to make up boxes for containing products of various kinds. In such cases, the zones destined to be glued, being covered with polyester aluminate film, require the use of special glues exhibiting considerable limitations, particularly in the case of boxes destined for storage in deeply refrigerated environments. The special glues referred to above tend to lose their adhesive properties vis-à-vis the coats of aluminate. A further drawback inherent in printing on previously-aluminated material consists in the considerable final product cost, both with regard to the cost of the aluminate itself and the aluminizing of the whole surface of the paper of card sheet, and to to need to print zones in white paint in the areas destined to receive a four colour process. The four-colour process is a photomechanical technique for obtaining printed reproductions in the original shades by superposing black and the three primary colours, yellow, magenta and cyan. A further drawback of printing on sheets which are completely covered with polyester aluminate is the difficulty of recycling the sheets, an ecologically important factor. JP-A-5-77859 discloses a process for printing on wrapping paper or economy gift-wrap paper by means of the application of a transferable sheet which contains the decorations to be applied on the wrapping paper. This is useful in particular in the case of embossed paper or paper with a wavy surface which gives rise to considerable printing difficulties, which are overcome by the Japanese document by means of the application of the transferable sheet, allowing the application of ornamental motives which have a perfectly smooth and hence printable surface. The Japanese document therefore teaches the application of decorations or metallized decorations so as to be able to then write or print over them. However it does not provide any teaching as to the possiblity of printing on nondecorated zones. The principal aim of the present invention is to obviate the abovementioned drawbacks by providing a process of preparation of a surface to be printed on, which permits of effecting on said surface a high-quality print at a considerably lower price with respect to that which could be obtained using similar-quality traditional processes. A further aim is to render the product obtained using the process almost entirely recyclable and usable in deeply refrigerated environments without a loss in glue effectiveness. The set aims are fully attained by the process, object of the present invention, for preparing a surface for printing, in particular for sheets of paper or card which are to be printed on by offset lithographical printing after having been previously aluminized or metallized, which is characterized as set out in the following claims and especially in that before a printing phase begins the surface of the paper or card to be printed on is metallized or aluminized only in specific zones of said surface. A further aim of the present invention is a sheet of paper or card, in particular of the type destined to be folded and glued to constitute a box, characterized in that on the printed side said sheet is partially aluminized or metallized. Further characteristics and advantages of the present invention will better emerge from the detailed description that follows, of an embodiment of the invention, illustrated in the form of a non-limiting example in the accompanying drawings, in which: figures 1 and 2 show respectively in an enlarged perspective view and in an enlarged vertical section according to line A-A of figure 1, a detail of the layers realized on the sheet using the preparation process; figure 3 is a block diagram of the process. With reference to the figures, 1 denotes a sheet of paper or card of the type destined to be printed on at least one of two sides of said sheet, constituting surface destined for printing. Said sheet can be used for realizing, for example, a poster, or can be a sheet destined to be folded and glued to form a box for containing various articles. The preparation process of the surface to be printed on initially involves using a heated metal plate to impress a film of polyester aluminate in such a way that the aluminization or metallization occurs only in the zones of the sheet built up on the plate. The unused polyester aluminate film is eliminated, and on the surface of the sheet a layer of a few microns of aluminate remains only in predetermined zones 2, defined by the plate. The zones 2 do not comprise the areas destined for gluing, nor the areas destined to receive photographic or graphic images, in other words the zones where a print quality is required which is as good as like printing on non-aluminized paper or card (with respect to inking, print contrast, increase in screen fineness). It is particularly important that the zones destined for gluing are not aluminized so that normal paper glues can be used, and not special ones. Subsequently the surface is overprinted by lithographical offset, denoted by 4, both in the non-aluminized zone (paper-laminated paper) and in the aluminized zone. With the process of the present invention the areas 3 which are not aluminized can be printed on to a level of quality which is qualitatively equal to printing on other, equally untreated paper or card surfaces, while in the aluminized zones 2 the printing bears all the characteristics of a metallic effect performed on paper or card surfaces which are entirely aluminized. After lithographical offset printing, a final protective varnishing phase is carried out in the printed zones. Thus the present process affords a considerable saving, since a box wrapper obtained through it can be only partially aluminized and thus costs between 15-50% less that a similar box aluminized over all of its surface. Further, a relatively better photographic image print is obtained using like means for reproducing same. A further advantage is given by the fact that the partially aluminized sheet is recyclable almost in the same way as a normal sheet of paper or card. This is because the film of polyester and the aluminized zone is smaller than it would be in a completely aluminized sheet.

Claims: Process for printing on a surface, in particular for sheets of paper or card which are to be printed on by an offset lithographic printing technique after having been previously aluminized or metallized, characterized in that before the printing phase begins the surface (1) of the paper or card is metallized or aluminized only in specific zones (2) of said surface (1) in such a way as to leave not metallized or aluminized areas (3) which are subsequently printed on by an offset lithographic printing technique. A process as in claim 1, wherein aluminization or metallization is realized in zones (2) which are not destined subsequently to receive glue nor destined to be overprinted with photographic or pictorial images, whereby said glue or said images are subsequently printed directly on areas (3) not metallized or aluminized. A process as in claim 1, characterized in that the process of a partial aluminization or metallization consists in a laying of a polyester aluminate film on said sheets of paper or card wherein the polyester aluminate spread on the printing plate which is not used is eliminated and therefore does not transfer on to the surface to be printed on. A process as in claim 1, wherein following aluminization or metallization of a part of the sheet of paper or card, subsequently there is a phase of lithographic overprinting (4) of the surface (1), which occurs both in the aluminized or metallized zone (2) and in areas (3) which are not aluminized or metallized. A process as in claim 4, wherein following lithographic overprinting a protective finishing of varnish is applied to the printed zones. A sheet of paper or card, defining a surface, characterized in that it comprises a partial aluminization or metallization of the surface (1) of the sheet of paper or card, which partial aluminization extends only over some predetermined zones (2) of said surface (1), and in particular does not extend over areas (3) which are subsequently printed on or which are subsequently folded and glued to obtain a box wrapping, said areas (3) being left without aluminization or metallization. A sheet as in claim 6, characterized in that it exhibits printed images on the metallized or aluminized zones (2). A process as in claim 1, wherein the zones (2) do not comprise the areas designed to receive photographic or graphic images where a print quality is required as good as like printing on not-aluminized paper or card. A sheet as in claim 6, wherein the zones (2) do not comprise the areas designed to receive photographic or graphic images where a print quality is required as good as like printing on not-aluminized paper or card.

Inventors: PAPOTTI GIUSEPPE, PAPOTTI, GIUSEPPE
Applicants: PAPOTTI GIUSEPPE, PAPOTTI, GIUSEPPE
Application year: 1995
Main classification: B44C1
IPC codes: B44C1, D21H19, B41M1