DESCRIPTION

The present invention relates to a method for realising on a sleeve for flexographic printing a guide for laying and cutting a cliche and/or a bi-adhesive layer interposed between the sleeve and the cliche.

These so-called "sleeves" for flexographic printing typically have a layered structure in composite material that gives appropriate characteristics of lightness but creates problems when laying the cliches on the external surface of the sleeve.

The sleeve, in fact, undergoes a finishing process that is necessary to give it the desired external diameter size with precision.

The cliches must be then positioned accurately around the sleeve.

Since for reasons of cost, the cliches are supplied thin, their precise positioning requires a certain degree of experience.

Generally, the cliche features a set of interlocking joints that can be engaged in other such joints of conjugated shape present on the surface of the sleeve and is applied to the external surface of the sleeve using a bi-adhesive layer.

At the end of the application of the cliche, the excess bi-adhesive layer around the sleeve is trimmed to match the sleeve exactly.

Trimming is performed by the operator with a cutter which, however, can cause carvings also to the external coating layer of the sleeve. This results in the need to repair the sleeve and consequently a delay in making the sleeve available for use.

Obviously, the same finishing process also exposes the cliches to possible damage from cutting.

EP0989934 proposes the use of a guide integrated in the external coating layer of the sleeve for laying and cutting the cliche and the bi-adhesive that enjoins the cliche to the sleeve.

In practice, the guide is realised as follows: first, a groove is made along the external coating layer of the sleeve, then the groove is completely filled with a reinforced epoxy glue with high hardness, then the epoxy glue is polymerised, and finally material is removed from the polymerised epoxy glue along a longitudinal track that defines the guide.

This method for realising the guide as evident requires two distinct processes of material removal, leads to a waste of the removed material in the second process of material removal, and requires significant expenditure of energy and time for the polymerisation of the epoxy glue, which must completely fill the groove along the external coating layer of the sleeve.

The technical task of the present invention, therefore, is to provide a method for realising on a sleeve for flexographic printing a guide for laying and cutting a cliche and/or a bi-adhesive layer interposed between the sleeve and the cliche and a sleeve for a flexographic printing which allow to obviate the technical drawbacks complained by the prior art.

As part of this technical task, an object of the invention is to provide a method for realising this guide in a convenient, simple, precise and safe way for the sleeve and the cliche itself.

Another object of the invention is to provide a method that is much more productive than those used to date for realising on a sleeve for flexographic printing a guide for laying and cutting a cliche and/or a bi-adhesive layer interposed between the sleeve and the cliche.

The technical task, as well as these and other objects, according to the present invention are attained by providing a method for realising on a sleeve for flexographic printing a guide for laying and cutting a cliche and/or a bi-adhesive layer interposed between the sleeve and the cliche, characterised in that it comprises the following steps:

- realising at least a longitudinal profiled element longitudinally provided with a surface guide cavity for laying and cutting the cliche and/or the bi-adhesive layer;

- making, on an external coating layer of the sleeve, a groove having a smaller depth than the thickness of the external coating layer and configured for housing said profiled element inside thereof;

- only partially filling said groove with a polymerisable glue or apply to the surface of the said groove an adhesive layer;

- positioning, on the glue or on the adhesive layer, the profiled element with the cavity facing the outside of the groove.

Advantageously this embodiment of the guide requires only one material removal process, does not involve significant material waste and allows for a significant saving of energy and time since, even if a glue is used to fasten the profiled element, it must polymerise a limited amount of glue.

In a preferred embodiment of the invention, the profiled element has a smaller height than the depth of the groove and is positioned flush in the groove.

In a preferred embodiment of the invention, the glue, when used, is applied in the form of a uniform or discontinuous layer on the whole surface of the groove.

In a preferred embodiment of the invention, the profiled element is inserted for the whole length and width thereof in contact with the glue or the adhesive layer.

In a preferred embodiment of the invention, the profiled element has a U-shaped or

V-shaped configuration in cross section.

In a preferred embodiment of the invention, the shape of the groove is congruent with the external shape of the profiled element.

In an embodiment of the invention, the profiled element is obtained by moulding. In an embodiment of the invention, the profiled element is obtained by extrusion. In an embodiment of the invention, the profiled element is obtained by 3D moulding.

In an embodiment of the invention, the profiled element is obtained by pultrusion. In an embodiment of the invention, the profiled element is made of aluminium. In a preferred embodiment of the invention, the profiled element is made of reinforced plastic.

The present invention also reveals a sleeve for flexographic printing exhibiting a guide so produced and a flexographic printing machine comprising a printing cylinder coated with such a flexographic printing sleeve. Additional characteristics and advantages of the invention will become more apparent from the description of a preferred but not exclusive embodiment of the method for realising a guide on a sleeve for flexographic printing, according to the invention, shown for illustrative and not limiting purposes in the attached drawings, in which:

figures l a, l b, lc and I d show the timeline of the processes necessary to realise the guide on the external coating layer of the sleeve;

figure 2 shows a perspective view of the sleeve;

figure 3 shows a detailed view of the cross-section of the profiled element;

figure 4 shows a variant of the sleeve with a dovetail interlocking joint of the longitudinal profiled element in the groove.

With reference to the figures mentioned above, a sleeve for flexographic printing is shown, indicated altogether with reference number 1.

Sleeve 1 has an inner side that can be applied on a printing cylinder (not shown) and an external side on which a cliche 10 can be applied using a bi-adhesive layer (not shown).

Sleeve 1 has in succession from the inner to the external side, an inner layer 3 in composite material made from fibres embedded in a resin matrix, a thickness compensation layer 4 made of cellular material, a high rigidity layer 5 and an external coating layer 6 made of resin or otherwise devoid of fibres to be suitable for a surface machining to adjust the thickness.

Layer 6 can be made of epoxy resin or even polyurethane resin for example, with a hardness in the order of Shore D. The method for realising on sleeve 1 a guide 2 for laying and cutting the cliche 10 and/or the bi-adhesive layer interposed between the sleeve 1 and the cliche 10 is characterized by the following steps.

A longitudinal profiled element 7 longitudinally provided with a surface cavity 8 acting as a guide 2 for laying and cutting the cliche 10 and/or the bi-adhesive layer is realised.

A groove 9 having a smaller depth than the thickness of the external coating layer 6 and configured for housing the profiled element 7 inside thereof is formed on the external coating layer 6.

The profiled element 7 is supplied with a smaller height than the thickness of the coating layer 6.

The profiled element 7 can be obtained by hot or cold moulding or by extrusion, and is made of aluminium or reinforced plastic.

In the case illustrated wherein guide 2, and consequently groove 9, extend along an axial generatrix of sleeve 1, the longitudinal profiled element 7 consists of a bar with a straight longitudinal axis.

Instead, in the case not illustrated wherein guide 2, and consequently groove 9, extend along a circumferential generatrix of sleeve 1, the longitudinal profiled element 7 consists of a bar with a curved longitudinal axis, curved according to a curvature radius congruent to that of groove 9.

The profiled element 7 has more precisely a height and width smaller than the depth and width of groove 9, respectively.

The profiled element 7 has a length less than or equal to the length of groove 9. The profiled element 7 has constant shape and size along its longitudinal axis.

The profiled element 7 has, in particular, a generically U-shaped cross section, but could also have a generically V-shaped cross section.

The concave surface T of the profiled element 7 delimits the cavity 8, while the convex surface 7" of the profiled element 7, when this is housed in the groove 9, faces onto the surface of groove 9.

Groove 9 in turn has constant shape and size along its longitudinal axis.

The shape of groove 9 is congruent with the external shape of the profiled element

7.

After having realised the groove 9, it is filled only partially with a thermosetting glue 1 1.

The glue 1 1 is applied preferably in the form of a uniform layer on the whole surface of groove 9.

It must be remarked that glue 1 1 occupies a much lower volume than the overall volume delimited by groove 9, as it is applied in the form of a layer having a uniform thickness far lower than the width and depth of groove 9.

At this point, the profiled element 7 with the cavity 8 facing the outside of groove 9 is positioned on the glue 11 in groove 9.

The profiled element 7 is positioned across its height and width in contact with the glue 11.

After having completed positioning it, the profiled element 7 is placed with its longitudinal axis parallel to the longitudinal axis of groove 9 and is flush with groove 9, namely the external end of the profiled element 7 is placed on the external cylindrical surface extension of the external coating layer 6.

The profiled element 7 is fixed in this position, supplying to the glue 11 the thermal energy necessary for its polymerisation.

It is possible to alternatively provide for the fixing of the profiled element 7 a non- thermosetting glue, such as a glue polymerisable at room temperature or polymerisable with moisture or UV light.

In place of the glue, a layer of adhesive can also be used, such as a phenolic adhesive.

The glue or adhesive can be applied in the form of a uniform or even discontinuous layer.

Of course, on sleeve 1 even two or more guides 2 can be included with axial and/or circumferential extension to delimit a special area of positioning a cliche 10.

With reference to figure 4, the profiled element 7 and groove 9 are shaped for coupling with a dovetail interlocking joint. The bottom of groove 9 can also include a slight concavity to encourage the accumulation of glue 1 1.

Advantageously a tapering of groove 9 from the bottom towards the top configures groove 9 for mechanical interlocking with the profiled element 7, if the latter presents a shape conjugated to it, otherwise it creates glue reserves useful to strengthen the connection of the profiled element 7 in groove 9.

If there is an interlocking conformation between the profiled element 7 and groove 9, the profiled element 7 is slid in the longitudinal direction of sleeve 1 in groove 9, where the glue has been applied previously, if, instead, there is no interlocking conformation between the profiled element 7 and groove 9, the profiled element 7 can be inserted into groove 9 in the same way or even in the diametrical direction of sleeve 1.

The introduction of the profiled element in the diametrical direction of sleeve 1 allows a more uniform wetting of the profiled element 7 with the glue, while the introduction in the longitudinal direction of the sleeve allows a highly accurate positioning of the profiled element 7 when an interlocking conformation is envisioned between the profiled element 7 and groove 9.

The glue that is used in a preferred embodiment in which the external layer 6 of sleeve 1 is in epoxy resin and the profiled element 7 is made of aluminium or an alloy thereof, is a structural, epoxy-based adhesive with amine accelerators, for example but not necessarily DP410™ manufactured by 3M™. In this case, the glue has a dual function, namely a filling function of the gap between the profiled element 7 and groove 9 and a function of adhesion to the interface with the profiled element 7 and the wall of groove 9.

The method for making a sleeve for flexographic printing thus conceived is susceptible to numerous modifications and variants, all falling within the scope of the inventive concept; furthermore, all the details can be replaced by technically equivalent elements.

In practice, the materials used and the size can be any, depending on the needs and the state of the art.