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US-12617223-B2 - Plant and process for pre-coating and printing on metallic strips

US12617223B2US 12617223 B2US12617223 B2US 12617223B2US-12617223-B2

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.

Inventors

  • Luciano Vignolo
  • Michele CHIAPPA

Assignees

  • DANIELI & C. OFFICINE MECCANICHE S.P.A.

Dates

Publication Date
20260505
Application Date
20220331
Priority Date
20210401

Claims (12)

  1. 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, with an ink drying device; (e) a second coating device, in particular a roller applicator, for applying a clear coat; (g) a second cooling system, such as an air and water cooling system.
  2. 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. 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. 4 . 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.
  5. 5 . 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.
  6. 6 . 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.
  7. 7 . The process according to claim 6 , wherein before step (IV), said strip is centred and wherein before and after step (IV), said strip is tensioned.
  8. 8 . The process according to claim 6 , wherein said combined coat is polyester-melamine based.
  9. 9 . The process according to claim 6 , wherein said sol-gel type ink is a silane-based thermal polymerization product.
  10. 10 . The process according to claim 6 , 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.
  11. 11 . The process according to claim 6 , 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).
  12. 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; (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

TECHNICAL FIELD The present invention relates to a printing plant and process, in particular for digital inkjet printing, for pre-coated strips, and in particular to the arrangement of a printing process in-line with pre-coating to prepare the surface of the product for printing, making it suitable for ink adhesion. BACKGROUND ART Pre-coated strips have a variety of applications and are widely used in the field of indoor and outdoor architecture, in civil and industrial construction and in the household appliance industry. There is a rising demand in this sector for strips with increasingly complex decorative designs. The usual technique for producing these pre-coated strips with complex designs involves the following steps, illustrated with reference to the attached FIG. 1: The first step sees the application of a first coat, the primer 10, followed by the drying 12 and subsequent cooling 14 of said primer; the second step involves the application of a second coat 16, that is, the base coat, which constitutes the background of the design to be obtained, followed by drying 18 and subsequent cooling 20 of the coats. In a third step, there follows the application of the design or the print 22, for example using thinned or unthinned inks with a solvent on the base coat of the previously created double coat, with the subsequent drying of the ink, and finally, in a fourth step, the application of a clear coat 24 also followed by drying 26 and subsequent cooling 28. The various steps listed above are reflected in a succession of devices in the pre-coating and printing plant, which precisely follow one another in this order: a first coating device, a first oven, a first cooling device, a second coating device, a second oven, a second cooling device, a printer, a third coating device, a third oven and a third cooling device. The flowchart of FIG. 1 therefore represents, on the one hand, the succession of the processing steps and, on the other, the succession of the corresponding devices required to carry out each individual step in a plant or corresponding line for pre-coating and printing. Ink application or printing technologies have evolved technically and technologically over time, but the following techniques are generally used today: Application with printing rollers (rotogravure), usually consisting of two to five rollers, with a negative design imprinted on the roller; application with printing rollers by flexographic technique, usually consisting of a unit of two to five rubber-coated rollers with an embossed (positive) design on the rubber surface; and application with a four-colour digital inkjet printer. All technologies have their limits. In particular, there is a common disadvantage to all state-of-the-art technologies: The application of two coats (primer+base coat) before printing entails an increase in operating costs and a complexity in the arrangement of the pre-coating and printing plant, imposing the need to operate by using three drying or heating ovens for the three coats (primer+base coat+clear coat). The disadvantages associated with the roller application are as follows: The design is constrained by the circumferential development of the roller used. Each design involves the use of a dedicated series of rollers; therefore, the cost of investment is high and the management of a product portfolio with numerous designs to be produced is particularly complex. In relation to the current state of the art, application using digital printing has other drawbacks such as: Solid-state, solvent-free UV inks have reduced heat resistance, reduced flexibility and reduced resistance to external environmental conditions. In the event of leakage, UV ink has a greater environmental footprint and is much more expensive to handle. Curing or heat drying of the ink takes place in the printing machine which has integrated UV lamps. State-of-the-art documents disclosing ink printing on metal substrates are JP 2017 047370 A and US 2007/0085983 A1. SUMMARY OF THE INVENTION The object of the invention is to overcome the aforementioned drawbacks and to propose, in view of the limitations of the various techniques and technologies for pre-coating and printing on metallic strips, a plant and process for pre-coating and printing on metallic strips, which is less complex, requires fewer components, is cheaper, and preferably provides higher print resistance with a lower environmental footprint. Further objects or advantages of the invention will become apparent from the following description. In a first aspect of the invention, the object is achieved by means of a plant for pre-coating and printing, by digital inkjet, 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 uni