State of the art

The present industrial invention patent application refers to the computerized printing field and in particular the field of digitalized printing applied to a plasticized sheet produced via extrusion, such as, for illustrative but non-limiting purposes, PVC. Up to now, in order to print any one extrusion-produced plasticized sheet, the only option was to employ the classic silk-screen technique. For printing any one plasticized sheet, the use of the fastest and most efficient digital printing machines currently found on the market, even if hypothetically possible, was in fact prevented by the technical impossibility of correctly feeding any one digital printing machine with said extrusion-produced plasticized sheet. Said extrusion-produced plasticized sheet, wound around a common reel, tends to spontaneously create non-uniformities which induce it to be printed via digital printing. Said extrusion-produced plasticized sheet in fact tends to fold on itself near the edges, being centrally extended and unpredictably deformed in the intermediate portions. In addition, said extrusion- produced plasticized sheet structurally has a non-uniform thickness which varies between 0.18 and 0.25 hundredths of a millimeter. Industrially, said plasticized sheet is sold in common reels wound around a central cardboard core. Said reels are characterized by repeated and unpredictable thickness non-uniformities, and such non-uniformities in fact prevent the same digital printing head from correctly coloring, according to the desired scheme and design, the entire surface of the plasticized sheet. In substance, the prior art currently provides a printing medium, the plasticized sheet produced via extrusion, which is entirely unusable in digital printing since it is structurally elastic and non-uniform, i.e. the exact opposite of that required by a common digital printing machine. The substrate to be fed to said digital printing machine for obtaining a technically acceptable product must in fact be, in addition to inextensible, also perfectly flat and provided with a uniform surface. The only possible alternative to these unresolved technical problems has up to now been the use of conventional silk-screen printing. The silk-screen printing technique, when used in the process of printing plastic laminates, provides for very large and costly printing structures, along with equally expensive installation techniques every time that the printing of a new product is carried out. Moreover, by using the silk-screen printing technique, every color must be separately printed, and before applying the next color layer, it is necessary to wait until the previous one is perfectly dried. The finished product, i.e. the extrusion-produced plasticized sheet printed via silk-screen with the desired colors, therefore has a considerable ink thickness due to the repeated and successive prints. Said ink, upon a careful, close visual examination, has numerous discontinuities, since it is composed of a plurality of colored points and not by a uniform and organic distribution of the color on its surface. In order to remedy all of the above problems, the present patent application intends to describe an innovative printing technique of the extrusion-produced plasticized sheet which allows using common digital printing machines, avoiding the aforesaid problems of correct positioning and perfect stretching of the extrusion-produced plasticized sheet to be printed.

Description of the invention

The present patent application therefore intends to describe an innovative apparatus composed of a frame, which, by supporting a plurality of rolls parallel to the plane of the digital printing machine to be fed, is capable of pretensioning upon heating any one laminated plastic polymer which passes through said parallel rolls, with which it is intended to feed said digital printing machine. The present invention moreover intends to describe the method with which the optimal feeding of the digital printing machine itself is obtained. Description of the drawings

FIGURE 1 is a view of the pretensioner machine 1 according to the present invention in which the followed are observed:

- the rectangular base box section of the frame 13 provided with at least four wheels 2a, 2b, 2c, 2d;

- the vertical support box section 3a, 3b;

- the two support flanges 6a and 6b respectively anchored to the vertical uprights 3 a and 3b;

- the friction elements 7a and 7b adapted to control the rotation of the expandable tube 9 sustained by the flanges 6a and 6b;

- the attachments 14a and 14b which connect the pretensioner machine 1 to the digital printer;

- the banana-shaped curvilinear stretcher 4 of the extrusion-produced plasticized sheet to be fed to the digital printer; - the rubber-coated aluminum tube 10;

- the support bar of the lower row of heating elements 11;

- the support bar of the upper row of heating elements 12;

FIGURE 2 is a side view of the pretensioner machine 1, wherein the support 5 of the banana-shaped curvilinear stretcher 4 equipped with ball bearings 15 is observed, as is the knob 16 which is adapted to adjust the action of the friction element 7 on the free rotation of the expandable tube 9 sustained by the flange 6 installed on the vertical upright 3. The figure also shows the support bars 11 and 12 on which a plurality of heating elements 20 are installed.

FIGURE 3 is a view of the pretensioner machine according to the present invention, wherein the path which the extrusion-produced plasticized sheet follows before being fed to the digital printer is observed. Detailed description of the invention

The achievement of the present invention is now described in detail, specifying that this is an illustrative description, in no way limiting that claimed in the present patent application. The pretensioner machine 1 is essentially composed of a base frame 13, mounted on at least four rotatable wheels 2a, 2b, 2c, 2d, each provided with brake, capable of sustaining the weight of the entire pretensioner machine 1 equipped with a common reel of extrusion-produced plasticized sheet. Said rotatable wheels 2a, 2b, 2c, 2d serve to make the entire pretensioner machine 1 easily removable and movable by one or more operators inside the operating structure, rendering it capable of being easily and quickly brought close to any one digital printing machine. Said approaching the digital printing machine is constrained by the presence of at least two adjustable attachments 14a and 14b, which, by being abutted against and/or coupling by means of common coupling means to the base of the digital printing machine, adjust and maintain constant the distance between the pretensioner machine 1, object of the present invention, and the digital printing machine, when said machines operate in sequence. Said adjustable attachments, 14a and 14b, are installed on the front portion 17 of the base frame 13. At the upper ends of the portion 17 of the base frame 13, two supports 5a and 5b are present, respectively adapted to support the two ball bearings 15a and 15b which sustain the banana-shaped curvilinear stretcher 4 so as to also allow it to freely rotate around its own axis. On the rear portion 18 of the base frame 13, two vertical uprights 3a and 3b are installed, made in a manner so as to respectively support, starting from the bottom and moving upward, the support flanges 6a and 6b, the support bar 11 of the lower row of the heating lamps, the support bar 12 of the upper row of the heat lamps, and finally, near the upper end of the two vertical uprights 3a and 3b, respectively the supports 19a and 19b of the bearings 10a and 10b which allow the rubber-coated aluminum roll 10 to freely rotate around its own axis. On the support flanges 6a and 6b, respectively anchored to the support uprights 3a and 3b, the ends of the expandable roll 9 are fixed. Said expandable roll 9 is a common roll capable of being expanded - hydraulically, mechanically, or due to a mechanism which allows the increase of the internal air pressure - after said expandable roll 9 has been inserted in the central cavity of the cardboard roll around which the plasticized sheet reel to be printed is wound. The expandable roll 9 is equipped with two friction systems, 7a and 7b, placed on the respective external faces of the flanges 6a and 6b. The two friction systems 7a and 7b, by acting directly on the free rotation of the expandable roll 9, are capable of progressively slowing the rotation of the expandable roll 9, consequently increasing the tension to be applied to the extrusion-produced plasticized sheet in order to cause the unwinding of the reel on which it was previously wound. Said unwinding tension is mechanically regulated by operating the knobs 16a and 16b respectively acting on the two friction elements 7a and 7b. The two support bars 11 and 12, sustained by the two vertical uprights 3a and 3b, are arranged parallel to each other and in a manner such that the lower support bar 11 is at the same height as the reel of extrusion- produced plasticized sheet installed on the expandable roll 10. The second bar, 12, is instead positioned about thirty centimeters above the bar 11. A plurality of heating elements 20 are attached to said support bars 11 and 12, normally four heating elements 20 for every single bar, in a manner such that said heating elements 20 are offset from each other. This technical expedient allows the extrusion-produced plasticized sheet to be uniformly heated over its entire width by said heating elements 20. Due to this distribution of the heating elements 20, the heating occurs both while said extrusion-produced plasticized sheet is still wound around the expandable roll 9 and along the path which leads it to feed the digital printing machine. Said feed path to the digital printing machine provides for the following steps: 1) positioning and locking of the cardboard roll, around which the extrusion-produced plasticized sheet reel is wound, on the expandable roll 9; 2) initial heating of the plasticized sheet reel to be printed due to the action of the heating elements placed on the support bar 11; 3) passage of the extrusion-produced plasticized sheet on the rear portion of the rubber-coated aluminum roll 10, so that it is heated, in its ascending phase, by the heating elements placed on the second support bar 12;

4) passage and stretching of the extrusion-produced plasticized sheet below, at the banana-shaped curvilinear stretcher 4;

5) insertion of the extrusion-produced plasticized sheet in the digital printing machine placed at a distance which is approximately double the distance existing between the roll 10 and the curvilinear stretcher 4.

Due to the presence of the friction element placed on the expandable roll 9, it is thus possible to brake the unwinding of the extrusion-produced plasticized sheet from the reel on which it is wound. Said slowing down of the unwinding causes the substantial increase of the traction exerted on the same plasticized sheet, so that such sheet completes the entire path described above under the constant action of said increased tractive force. Along with the increased tractive force, the pretensioner machine 1 according to the present patent application produces, due to the combined action of the two rows of offset heating elements 20, the uniform heating of the extrusion- produced plasticized sheet to be printed. This double action ensures that said plasticized sheet is uniformly heated, stretched and pretensioned when it enters into the digital printing machine. The amount of traction and heating of the extrusion- produced plasticized sheet are directly proportional to the thickness of the material to be printed and are in any case such to not cause liquefaction and/or excessive stretching of the plasticized sheet itself.

The innovative technique introduced with the present invention allows obtaining an extrusion-produced plasticized sheet that is perfectly pretensioned, heated and uniformly extended so as to be easily subjected to the printing process by means of any one digital printing machine. Once printed, the single sheets of extrusion- produced plasticized sheet can be handled with extreme ease, since they are perfectly foldable, unaffected by any bending and weatherproof. These characteristics allow said processed films to be ideal for being employed in signage of various type, in advertising and in any other field requiring quick use, ease in unfolding and optimal packing quality. The extreme ductility of the plastic film digitally printed with the technique described in the present patent application allows applying the product thus obtained on backlit boards, even if said printed plasticized sheet was repeatedly folded on itself during packing. In addition, since it is resistant and moderately elastic, the extrusion-produced plasticized sheet printed according to the technique described in the present invention is unfolded and fixed on the frames of advertising posters or on any other support in a very quick manner, since said printed plasticized sheet is about 50% lighter than any plastic substrate used up to now. All of the above occurs while maintaining a final appearance that is unchanged over time, greatly superior to that produced by any conventional silk-screen printer. A further advantage of the technique introduced with the present patent application consists of the quick processing typical of digital printing together with the fact that a costly installation does not have to be prepared. The latter passage is indispensable, on the other hand, in the classic silk-screen technique. The present patent application thus intends to describe a new pretensioner apparatus 1 and its innovative use technique, so as to be capable of economically, quickly and industrially printing any one extrusion- produced plasticized sheet, using only the digital printing technique.