DESCRIPTION

The invention relates to a rubber blanket for offset printing.

As is well known, at present rubber-coated fabrics for offset printing are made up of a plurality of layers normally composed of elastomers and fabric reinforcements.

Moreover, rubber blankets are subject to yielding and must undergo very careful monitoring of the laser engraving print technique.

In particular, in the case of rubber-coated fabrics or blankets for offset printing, for example of metal containers such as beverage cans, the printing speed is very high and if the engraving on the rubber blanket is not perfect, this can originate printing defects, with very serious consequences for the production costs.

What has been mentioned above implies that for every rubber blanket on which laser engraving is performed, it is indispensable to conduct an in-depth analysis of the quality of the engraving using adequate instruments.

This fact implies a considerable expenditure of time and an increase in printing costs together with the fact that, at times, whoever is monitoring, in order to save time, relies solely on his visual perception, with the possibility that some imperfection might escape his notice, with all the problems that could derive therefrom.

The task that the present invention sets itself is that of eliminating the aforementioned drawbacks of the prior art.

Within the scope of this task, it is an object of the invention to devise a rubber blanket for offset printing that enables an immediate optical detection of any engraving defects.

It is another object of the invention to devise a rubber blanket for offset printing that enables the possibility of monitoring engraving defects without the use of specific instruments dedicated to this purpose.

It is a further object of the invention to devise a rubber blanket for offset printing which makes it possible to speed up the process of inspecting the engravings made with the laser technique on rubber blankets.

The invention further relates to a rubber blanket for offset printing which, though offering the possibility of a simplified and rapid inspection of the engraving made on it, equally ensures valid resistance over time both to wear and yielding.

It is a further object of the invention to devise a rubber blanket for offset printing which enables the grinding of a layer thereof to permit adjustment of its thickness. This task and these and other objects are achieved by a rubber blanket for offset printing having a plurality of layers, of which the inner layer is wrapped over the rubber blanket cylinder and the outer layer comes into contact with the object to be printed, whereupon the print engraving present on said outer layer is reproduced, characterized in that said outer layer has a main printing layer which comes into contact with said object to be printed and at least one underlay er in contact with said main printing layer, said underlayer being formed with the same material, but with a different colouring from said main printing layer.

Additional features of the invention are better specified in the dependent claims.

In particular, the rubber blanket for offset printing has at least a first part of the print engraving of substantially the same height as said main layer and the walls thereof are of the same colouring as the main printing layer, whereas the bottom is of the same colouring as the underlayer.

Moreover, the rubber blanket for offset printing comprises at least a second part of the engraving having a lower height than the main printing layer, with walls and a bottom of the same colouring and the colouring of the underlayer comprised in the visible spectrum of white light, and situated between yellow and green relative to the colouring of the main printing layer, which is in the visible spectrum of white light at the two red and violet extremities so that the underlayer stands out more than the main printing layer.

It should also be pointed out that the rubber blanket for offset printing has a main layer of a lower height than the underlayer and both the main layer and the underlayer are elastomers of a thermoplastic nature.

Additional features and advantages of the invention will become more apparent from the description of a preferred but non-exclusive embodiment of a rubber blanket for offset printing, illustrated by way of non-limiting example in the appended drawings, in which:

fig.1 is a plan view of the rubber blanket according to the invention;

fig. 2 is an enlarged view of the engraving of the rubber blanket according to the invention; and

fig. 3 is a view along the section line III-III of fig. 1 according to the invention.

With particular reference to the above-described figures, the rubber-coated fabric or blanket for offset printing according to the invention is generically indicated by 1. An offset printing machine (not shown), as known, has a plate cylinder touched by dampening rollers and ink rollers, and a blanket cylinder 1 interposed between the plate cylinder and a counter-pressure cylinder. The image is transferred from the plate to the blanket and from this to the medium which passes between the blanket cylinder and the counter-pressure cylinder. The rubber blanket 1 or blanket has a plurality of layers and in particular, as represented in fig. 3, for the sake of simplicity, only three layers have been represented, of which the inner layer 2 is wrapped over the blanket cylinder, not represented, and the outer layer, denoted in its entirety by 3, comes into contact with the object to be printed.

The object to be printed can be, for example, a metal body, such as a beverage can, not represented, whereupon the print engraving present on the outer layer 3 is reproduced.

Advantageously, the outer layer 3 has a main printing layer 5 which comes into contact with the object to be printed and at least one underlay er 6 of the same material but a different colouring from that of the main printing layer 5.

Conveniently, a first part of the print engraving 7 has substantially the same height as the main layer 5.

Obviously, according to requirements, the first part of the engraving 7 can be defined by the entire engraving present on the rubber blanket, or else define only a part, whilst the remaining second part 4, as represented in fig. 1, can be produced according to known engraving procedures.

The first part of the engraving 7 has walls 8 of the same colouring as the main printing layer 5 and a bottom 9 of the same colouring as the underlay er 6.

The second part 4 of the engraving has a lower height than the main printing layer 5 with walls and a bottom of the same colouring as the latter, since it never reaches the underlayer 6 of a different colouring. In particular, the colouring of the underlayer 6 belongs to the visible spectrum of white light and is situated between yellow and green relative to the colouring of the main printing layer 5, which is in the visible spectrum of white light at the two red and violet extremities.

In this manner, the under layer 6 stands out more than the main printing layer 5 and makes it possible to detect, in an extremely simple and rapid manner, without the use of specific equipment dedicated to this purpose, the presence of any defects in the first part of the engraving 7, which would prove practically impossible in the case, for example, of the second part of the engraving 4.

It should also be pointed out that the main layer 5 has a lower height than the underlayer 6 and that both the outer layer 3 and the lower layer 2 can preferably be elastomers of a thermoplastic nature.

By way of example, the layers of the rubber blanket in accordance with the invention can be formulations of elastomers or polymers of the TPU type in combination with other polymers, dynamically vulcanized elastomers of the type based on PP, PAN and PVC, elastomers of the styrene family, formulations of elastomers of the olefin family, copolymers of olefins and functionalized olefins, elastomers of the acrylonitrile family, EPDM or MSC, or else ACM or AEM and combinations of modified or unmodified elastomers, aramid-type fibre or yarn reinforcements, polyethylene- or polypropylene-type fibre or yarn reinforcements, polyester-type fibre or yarn reinforcements or mixtures of such fibres or yams.

Last but not least, advantageously, it should be highlighted that the lower layer 2 can be made of a polymer material that can be ground in such a way that the thickness of the rubber blanket can be rendered uniform by grinding the lower layer 2 while maintaining or even improving the printing quality of the rubber blanket.

Alternatively, the inner layer 2 can be a fabric such as cotton, polyester or a blend thereof. A controlled thickness improves the print quality and longevity of rubber blankets and moreover extends their useful life, enabling a reduced height of the covering, limiting the mechanical stresses on the rubber blanket and thus delaying the possible appearance of dents on the print. It is possible to maintain the excellent print quality both in the presence only of a first engraving part 7 or with the addition also of a second engraving part 4 and to generate what is called "high-fidelity" printing.

The rubber blanket for offset printing thus conceived is susceptible of numerous modifications and variants, all falling within the scope of the inventive concept; moreover, all of the details can be replaced with technically elements.

The materials used, as well as the dimensions, may in practice be of any type, according to needs and the state of the art.

In particular the rubber blanket of the present invention can also be employed as a coating of the printing cylinder of a flexographic printing machine.