PLANT AND PROCESS FOR PRE-COATING AND PRINTING ON METALLIC STRIPS

Abstract

The invention relates to a plant and a process for pre-coating and subsequent digital sol-gel inkjet printing on metallic strips, wherein on the dried ink a protective clear coat will then be applied. The core of the invention lies in the fact that printing is of the sol-gel ink type and pre-coating is no longer carried out by the separate application of two coats, a primer and a base coat, with relative drying and cooling phases of the coats, but by the application of a single coat that combines the functions of primer and base coat. In addition, printing with a special sol-gel type ink that does not require UV treatment, but only a simple drying of the ink after application, simplifies the process even further.

Claims

1. A plant for pre-coating and digital inkjet printing of a metallic strip comprising, in the following order: (a) a first coating device for applying a combined coat that serves as both a primer and a base coat; (b) a first oven for drying the coat; (c) a first cooling system, such as an air and water cooling system; (d) a digital sol-gel type inkjet printing unit, prefer-ably with an ink drying device; (e) a second coating device, in particular a roller applicator, for applying a clear coat; (f) a second oven for drying the coat; and (g) a second cooling system, such as an air and water cooling system.

2. The pre-coating and printing plant according to claim 1, wherein said printing unit comprises, in the following order: (d-1) one or more digital sol-gel type inkjet print heads; (d-2) an ink drying oven; (d-3) a third cooling system; wherein upstream of said one or more print heads, is provided a centring system and a first strip tension control system, in particular comprising, in the following order: (d-4) a rough strip centring system; (d-5) a first S-like bridle system for controlling strip tension; (d-6) a fine strip centring system; (d-7) pass-line rollers and, optionally, deflectors; wherein downstream of said one or more print heads, is provided a second strip tension control system, in particular: (d-8) a second S-like bridle system.

3. The plant according to claim 2, further comprising in the printing unit a strip position sensor, and wherein the print heads are mounted onto a slide that can translate orthogonally to the direction of the strip's motion, and wherein the plant comprises a corresponding control unit configured to manage the movement of the slide according to the values as detected by the position sensor to compensate for the lateral deviation of the strip's position as measured by the position sensor.

4. The plant according to claim 2, wherein downstream of the printing unit and upstream of the second coating device, further comprising a strip temperature sensor, in particular a temperature transducer, adapted to measure the temperature of the strip and send the measured value to a corresponding control unit configured to control automatically the speed of the strip and/or the flow rate of the third cooling system so as to bring the temperature measured by the temperature sensor back within predetermined values.

5. A process for the pre-coating and printing, in particular digital inkjet printing, of a metallic strip, comprising the following steps, in the order indicated: (I) application of a combined coat, that serves as both a primer and a base coat, onto a metallic strip; (II) heat drying of the combined coat; (III) cooling of the combined coat; (IV) digital sol-gel type inkjet printing of the pre-coated strip and preferably drying of the ink; (V) application of a clear coat onto the pre-coated and printed strip; (VI) heat drying of the clear coat; and (VII) cooling of the clear coat.

6. The process according to claim 5, wherein before step (IV), said strip is centred and wherein before and after step (IV), said strip is tensioned.

7. The process according to claim 5, wherein said combined coat is polyester-melamine based.

8. The process according to claim 5, wherein said sol-gel type ink is a silane-based thermal polymerization product.

9. The process according to claim 5, wherein before step (IV), a measurement of the position of the strip takes place and wherein, during step (IV), the position of said one or more print heads is adjusted in order to optimize the application of ink onto the strip based on the measurement of the strip's position.

10. The process according to claim 5, wherein after step (IV), the temperature of the strip is monitored and wherein if the temperature exceeds a limit value, the speed of the strip is slowed down and/or the drying of the ink is enhanced in order to regulate the drying of the ink before application of the clear coat in step (V).

11. The plant according to claim 3, wherein downstream of the printing unit and upstream of the second coating device, further comprising a strip temperature sensor, in particular a temperature transducer, adapted to measure the temperature of the strip and send the measured value to a corresponding control unit configured to control automatically the speed of the strip and/or the flow rate of the third cooling system so as to bring the temperature measured by the temperature sensor back within predetermined values.

12. A plant for pre-coating and digital inkjet printing of a metallic strip comprising, in the following order: (a) a first coating device for applying a combined coat that serves as both a primer and a base coat; (b) a first oven for drying the coat; (c) a first cooling system, such as an air and water cooling system; (d) a digital sol-gel type inkjet printing unit, preferably with an ink drying device; (e) a second coating device, in particular a roller applicator, for applying a clear coat; (f) a second oven for drying the coat; and (g) a second cooling system, such as an air and water cooling system, wherein said combined coat is polyester-melamine based, and wherein said sol-gel type ink is a silane-based thermal polymerization product.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0056] FIG. 1 represents in a block diagram the state of the art for the realization of a print on a pre-coated strip, in particular the various steps of the process and the devices necessary to realize each of them.

[0057] FIG. 2 represents in a block diagram an embodiment of the system and method for coating and printing a strip according to the invention.

[0058] FIG. 3 is a detailed schematic view of the section of a digital inkjet print of the plant according to the invention.

DETAILED DESCRIPTION

[0059] FIG. 1 was discussed at the outset with reference to the state of the art. FIG. 2 depicts a block diagram of one embodiment of the invention for making a jet print on a strip. The beginning of the process sees the application of a double coat consisting of a primer and a base coat 111 in a single step. Subsequently, the combined coat 113 is dried and then cooled 115. Printing 122 is then executed on the coat. As in the state of the art, printing 122 is followed by the application of a clear coat 124, its drying 126 and then its cooling 128. Cooling is by air and water. Idle support roller systems and deflectors can guide the strip towards the digital printing section.

[0060] Each step is connected to a corresponding device adapted to perform that step, and precisely in this order: a first coating device for applying the combined coat; a first oven for drying the coat; a first cooling device; the printer; the second coating device for applying a clear coat, preferably with a roller applicator; a second oven; and a second cooling device. FIG. 2, as FIG. 1, represents both the sequence of steps of an embodiment example of the process according to the invention and the order of the devices in an embodiment example of the plant according to the invention.

[0061] With reference to FIG. 3, a preferred embodiment of an inkjet printing section and related auxiliary systems representing the printing unit for performing the printing phase 122 is illustrated.

[0062] At the inlet of the printing unit 122 is a rough strip centring device 130 followed by an S-like bridle system 132 for controlling tension of the strip 134. Downstream there follows a fine strip centring device 136 and subsequently pass-line rollers 138 and deflectors (not shown) and a conveyor belt 140. Above the belt conveyor 140 is a plurality of digital inkjet print heads 142. An oven 144 for drying the ink then follows. For cooling of the strip 134 a strip cooling system 146 is needed. To verify that the strip 134 has a suitable temperature to apply the protective clear coat, a probe 148 to measure the temperature of the strip is foreseen before the coating rollers that apply the clear coat (FIG. 2). The printer unit 122 ends with an additional S-like bridle system 150 at the output of the printing section to control the tension applied to the strip 134.

[0063] A possible variant may provide for the addition of a strip position sensor 152 placed after the digital inkjet print heads 142. Said sensor measures the possible deviation of the strip 134 with respect to the centre of the line. In a further embodiment, the deviation measurement is sent to a control unit 154 that controls the transverse movement 156 of a slide (not shown) onto which the print heads 142 are mounted so as to compensate for any lateral displacement.

[0064] In a further embodiment, the temperature of the strip measured by a temperature transducer 148 is sent to the line controller 154 which, in the event that the strip's 134 temperature exceeds what is considered to be the limit, intervenes by modifying the process speed and the capacity of the cooling system 146 so as to bring the strip's temperature 134 within the limits deemed acceptable. The control unit 154 manages the entire printing unit 122 and can, in this regard, be connected by cable to the individual elements, or else communicate telematically.

[0065] A possible variant may provide for the measurement of the product/process quality parameters for both the top and bottom surfaces of the strip 134.

[0066] Appropriately, the combined coat can be based on a polyester coating compatible with the subsequent application of the ink. In an exemplary embodiment, the following sequence of layers may be created on the strip: a first layer based on a combined polyester-based coat with a thickness of about 5-10 m; an ink layer with a thickness of about 0.5-3 m; and, finally, a clear coat with a thickness of about 10-20 m.