Plant and method for pre-coating and printing metal strips

Abstract

The invention relates to a plant and a method in which a metal strip is pre-coated (111) and then a protective clear coat (124) is applied on the dried ink for digital sol-gel inkjet printing (122). The essence of the invention lies in the fact that the printing is of the sol-gel ink type and the pre-coating (111) is no longer performed by separate application of two coats, namely a primer and a base coat (with associated drying and cooling of the coats), but by application of a single coat combining the functions of primer and base coat. In addition, printing with special sol-gel type inks, which do not require UV treatment but only require drying of the ink after application, further simplifies the method.

Description

[Technical field]

[0001] The present invention relates to a printing plant and method, in particular for digital inkjet printing, for precoated strips, and in particular to the configuration of a printing process in series with a precoating for preparing the surface of the article to be printed and making it suitable for ink adhesion. [Background technology]

[0002] Pre-coated strips have a wide variety of applications and are widely used in the fields of indoor and outdoor architectural, civil and industrial construction as well as the home appliance industry, where there is a growing demand for strips with increasingly complex decorative designs.

[0003] A conventional technique for producing pre-coated strips having complex designs involves the following steps, which are illustrated with reference to the accompanying FIG.

[0004] The first step consists in applying a first coat, i.e. a primer (10), drying the primer (12) and then cooling (14). The second step consists in applying a second coat, i.e. a base coat, which constitutes the background of the resulting design (16), drying the coat (18) and then cooling (20). In a third step, a design or print is applied (22), for example using a solvent-thinned or unthinned ink, on top of the base coat of the previously formed double coat, then drying the ink, and finally, in a fourth step, a clear coat is applied (24), drying (26) and then cooling (28). The various steps mentioned above are reflected in a series of devices in a pre-coating and printing plant, which follow each other in exactly the following order: first coating device, first oven, first cooling device, second coating device, second oven, second cooling device, printer, third coating device, third oven and third cooling device. The flow chart of FIG. 1 therefore represents, on the one hand, the sequence of process steps and, on the other hand, the corresponding sequence of devices that are necessary to carry out each individual step in a plant or corresponding line for pre-coating and printing.

[0005] Inking or printing techniques have evolved over time, technically and artistically, but today the following techniques are commonly used: application using a printing roller, usually consisting of 2-5 rollers, on which a negative design is imprinted (rotogravure method); application using a printing roller, usually consisting of a unit of 2-5 rubber-covered rollers, on which a (positive) design is embossed in the rubber surface by flexographic printing techniques; and application using a four-color digital inkjet printer. All techniques have limitations. In particular, there are drawbacks common to all conventional techniques: the application of two coats (primer + base coat) before printing, which entails an increase in operational costs and a complexity in the configuration of the pre-coating and printing plant, and imposes the need to work with three drying or heating ovens for three coats (primer + base coat + clear coat).

[0006] The disadvantages associated with roller application are: the design is limited by the circumferential development of the rollers used, each design requires the use of its own set of rollers; therefore, capital investment costs are high and product portfolio management is particularly complex due to the large number of designs produced.

[0007] In relation to the current state of the art, application using digital printing also has other drawbacks, such as: solid, solvent-free UV inks have reduced heat resistance, reduced flexibility and reduced resistance to external environmental conditions. In case of leakage, UV inks have a larger environmental footprint and are much more expensive to address. Curing or heat drying of the ink is performed in the printing press with integrated UV lamps. Prior art documents disclosing ink printing on metal substrates are JP2017047370A and US2007 / 0085983A1. Summary of the Invention [Problem to be solved by the invention]

[0008] The object of the present invention is to overcome the aforementioned drawbacks and taking into account the limitations of the various techniques and technologies for pre-coating and printing on metal strips, to propose a plant and method for pre-coating and printing on metal strips that is relatively less complex, requires fewer components, is cheaper and preferably offers a higher print resistance with a lower environmental footprint.

[0009] Further objects and advantages of the present invention will become apparent from the following description. [Means for solving the problem]

[0010] In a first aspect of the present invention, the object is to provide a method for producing a method for the production of a pharmaceutical composition comprising the steps of: (a) a first coating device for applying a composite coat which acts as both a primer and a base coat; (b) a first oven for drying the coat; (c) a primary cooling system, such as an air-cooled system and a water-cooled system; (d) a digital sol-gel type inkjet printing unit, preferably equipped with an ink drying device; (e) a second coating device, in particular a roller applicator, for applying the clear coat; (f) a second oven for drying the coat; and (g) Secondary cooling systems, such as air-cooled systems and water-cooled systems This is achieved by a plant for the pre-coating of metal strips and printing by digital inkjet, which includes

[0011] Said plant providing a single coat performing simultaneously the functions of primer and base coat eliminates the need for two drying ovens, two cooling devices and two coating devices before printing, thus halving the number of components in the pre-coating process. The invention makes it possible to create a pre-coating and printing line that requires only two ovens to heat-dry or cure the coats, i.e. a first oven required for drying and thus polymerizing the initial coats acting as primer and base coat, and a second oven required for drying / polymerizing the clear coat, located after the printing unit and application of the clear coat.

[0012] The plant of the invention is particularly suitable for printing on a continuous strip. In this respect, the plant also advantageously comprises means for conveying the strip through the various components of the plant itself. In order not to impair the sharpness of the printed image during its movement through the printing units, it is desirable to centre the printed strip and to maintain a given strip tension. In this respect, in a preferred embodiment of the invention, the printing units are arranged to carry out the following steps: (d-1) one or more digital sol-gel type inkjet printheads; (d-2) Ink drying oven; (d-3) Third cooling system upstream of said one or more printheads, a centering system and a first strip tensioning control system, in particular in the following order: (d-4) Coarse strip centering system; (d-5) A first "S-shaped" bridle system for controlling strip tension; (d-6) Fine-tuning strip centering system; (d-7) Pass line rollers and optionally deflectors and downstream of the one or more printheads, a second strip tension control system, in particular (d-8) Second "S-shaped" bridle system is provided.

[0013] The strip tension control system is preferably an "S-shaped" bridle system. A possible "S-shaped" bridle system for controlling the strip tension can be provided at the inlet of the clearcoat coating device.

[0014] The pass line rollers suppress vertical vibration of the strip.

[0015] Advantageously, the printed strip, after having been guided through said centering system and said first strip tensioning control system, is guided under said one or more printheads (here advantageously conveyed by a conveyor belt) and then guided through said second strip tensioning control system to the exit of the printing unit. The conveyor can advantageously be provided with a pneumatic support surface adapted to support the corresponding section of the strip on an air cushion. A bridle system substantially counteracts longitudinal tension of the strip. It is also conceivable that a strip levelling system is arranged in front of said one or more printheads. Such a strip centering and tensioning system is for example described in patent application IT102018000007488.

[0016] In a preferred embodiment of the invention, the plant further includes a strip position sensor in the printing unit, the print head is mounted on a slide that can translate in a direction perpendicular to the direction of movement of the strip, and the plant includes a corresponding control unit configured to manage the movement of the slide according to values ​​detected by the position sensor to correct lateral biases in the position of the strip measured by the position sensor.

[0017] To optimize the application of the clear coat, in an embodiment of the invention, the plant further comprises a strip temperature sensor, in particular a temperature transducer, downstream of the printing unit and upstream of the second coating device, adapted to measure the temperature of the strip and to transmit the measured value to a corresponding control unit, which is configured to automatically control the speed of the strip and / or the flow rate of the third cooling system to bring the temperature measured by the temperature sensor back within a predetermined value. Advantageously, such a control unit is the same control unit that manages the movement of the slide and that controls all components of the pre-coating and printing plant. Also, different first and second control units are conceivable for controlling the temperature of the slide and the strip, which may support one or more printheads.

[0018] A second aspect of the present invention relates to a process for producing a pharmaceutical composition comprising the steps of: (I) applying a composite coating layer to a metal strip, the composite coating layer acting as both a primer and a basecoat; (II) heat drying the composite coat; (III) cooling the composite coat; (IV) digital sol-gel type inkjet printing onto the pre-coated strip and drying the ink; (V) applying a clear coat to the precoated and printed strip; (VI) baking the clear coat; and (VII) Cooling the clear coat The present invention relates to a method for pre-coating and printing, in particular digital inkjet printing, of a metal strip, comprising in the stated order:

[0019] In order not to impair the sharpness of the printed image, in a preferred embodiment of the invention, the strip is centred before step (IV) and advantageously tensioned before or after step (IV), in particular using a plant as described in the second claim.

[0020] In a preferred embodiment of the method of the present invention, the composite coat is a polyester / melamine resin system, which, once dry, makes it possible to obtain perfect ink adhesion from digital inkjet printing.

[0021] The composite polyester / melamine resin coat is advantageously white in colour. The coat intended for application to the strip preferably has a viscosity of 60 to 90 seconds, measured according to DIN standard 53211. The latter standard is based on a viscosity of 100 cm 2 A flow cup with a volume of 1000 g / cm and an outlet hole of 4 mm is required. At an ambient temperature of 20°C, the test liquid is forced through the hole to drain completely and the drainage time is measured. The unit of measurement is seconds DIN standard. The density is advantageously between 1000 and 1500 kg / m, measured according to the method given in DIN EN ISO 2811-1-4. 3 Preferably, the composite coat is applied to a final (dry) thickness of 5 to 15 μm.

[0022] A composite coat is a type of "adhesion promoter" (more commonly known as adhesive) that is adapted to prepare (modify) the surface of the material to be printed so that the ink adheres to it and at the same time adheres without pre-coating to substrates that can be of various kinds, such as metal, plastic, glass and other difficult-to-print substrates, thereby acting simultaneously as a primer and a base coat. The market offers a wide range of composite coats, from which the skilled person can select the one that best suits the substrate and ink with which it is intended to be used.

[0023] Sol-gel type inks avoid the use of UV lamps for drying and do not require the use of environmentally unfriendly solvents. This is an ink technology that overcomes the limitations of currently used inks and simplifies ink drying. The inks preferably developed for this application are preferably silane-based thermal polymerization products. Advantageously, the inks use environmentally friendly solvents that reduce the environmental footprint of the ink. In its preferred variant, the ink is characterized by a kinematic viscosity of 6-10 cps measured at 25° C. according to ASTM D4040 / 4207 and a density of 0.9-1.0 g / ml, preferably measured according to ISO 12647-3. The inks can be made in the following colors for printing: black, cyan, magenta and yellow.

[0024] Sol-gel processing is one of the methods used to create coatings such as ink coatings applied by inkjet printers. Sol-gel type inks contain a colloidal solution (sol) that constitutes a precursor for the subsequent formation of a gel (a continuous inorganic lattice containing interconnected liquid phases) by hydrolysis and condensation reactions. Generally, thermal post-treatments of drying and solidification are used to remove the liquid phase from the gel, promote further condensation, and enhance mechanical properties. Common precursors for sol-gel processing are M(OR) n , M.X. n , R′-M(OR) n-1where M represents the metal center, X and RO are alternatively common leaving groups present in metal salts or metal alkoxides, e.g. chloride anion in metal halides, and R′ is any organic group bonded to the metal center via a covalent bond (Si—C, Sn—C) or a coordinating agent (M=Ti, Zr...). The ink industry offers a wide selection of sol-gel type inks for various media, from which a person skilled in the art can easily identify the one that best suits his needs.

[0025] To ensure durability of the printed product, a clear coat compatible with the printed surface is applied over the dried ink layer. Suitable coatings are commercially available and easily identifiable by the skilled artisan. In a preferred embodiment of the invention, the clear coat is HD (High Density) polyester. HD polyester has excellent resistance to external environments and chemicals. The clear coat layer preferably has the following properties: viscosity of 80-120s (measured according to DIN 53211), solids content of >50% (measured according to UNI EN ISO 3251) and viscosity of 1000-1500 kg / m 3 The final (dry) thickness applied is advantageously equal to 10 to 25 μm.

[0026] In order to optimise the quality of the printing and the printed design, preferably prior to step (IV) a measurement of the position of the strip is performed and during step (IV) the position of the print head is adjusted based on the measurement of the strip position in order to optimise the application of ink to the strip.

[0027] To complete the application of the clear coat to the print, advantageously the method of the invention provides in its embodiments to monitor the temperature of the strip after step (IV) and, if the temperature exceeds a limit value, to slow down the speed of the strip and / or enhance the drying of the ink in order to regulate said drying prior to the application of the clear coat in step (V).

[0028] The printing unit may advantageously be equipped with auxiliary systems for circulating the ink and for cleaning or washing the nozzles of the printhead.

[0029] Features and advantages disclosed in relation to one embodiment of the invention may be transferred, mutatis mutandis, to other embodiments of the invention. [Industrial Applicability]

[0030] The industrial applicability is evident from the moment pre-coating and printing plants require fewer components, become simpler, and processing becomes cheaper and more environmentally friendly.

[0031] The above objects and advantages will be further emphasized in the following disclosure of preferred embodiments of the invention, given by way of non-limiting example only.

[0032] Variations and further features of the invention are the object of the dependent claims. The disclosure of preferred embodiments of the inventive plant and method for pre-coating and printing a strip, as well as the auxiliary systems for guiding the strip, controlling its inherent tension and centering it, is given by way of example only with reference to the accompanying drawings, in which: In particular, unless otherwise specified, the number, shape, size and material of the system and the individual components may vary and equivalent elements may be applied without departing from the concept of the invention. [Brief description of the drawings]

[0033] [Figure 1] 1 shows a block diagram of a prior art technique for achieving printing on a pre-coated strip, in particular the various steps of the method and the devices required to achieve each step; [Diagram 2] 1 illustrates a block diagram of an embodiment of a system and method for coating and printing a strip in accordance with the present invention. [Diagram 3]FIG. 2 is a detailed view of the digital inkjet printing section of the plant of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] Description of the Preferred Embodiment Figure 1 was described at the outset with reference to the state of the art. Figure 2 shows a block diagram of an embodiment of the invention for jet printing a strip. The start of the method sees the application 111 of a double coat consisting of a primer and a base coat in a single step. The composite coat is then dried (113) and then cooled (115). The coat is then printed (122). As in the prior art, printing 122 is followed by the application 124 of a clear coat, its drying 126 and then its cooling 128. The cooling is by air and water cooling. An idle support roller system and a deflector guide the strip to the digital printing section.

[0035] Each step is connected to a corresponding device adapted to perform it, exactly in the following order: a first coating device for applying the composite coat; a first oven for drying the coat; a first cooling device; a printer; a second coating device, preferably a roller applicator, for applying the clear coat; a second oven; and a second cooling device. Figure 2, like Figure 1, represents both the sequence of steps of an embodiment of the method of the invention and the sequence of the devices in an embodiment of the plant of the invention.

[0036] Referring to FIG. 3, there is shown a preferred embodiment of an inkjet printing section representing a printing unit 122 and associated auxiliary systems for performing the printing steps.

[0037] At the entrance of the printing unit 122 there is a coarse strip centering device 130 followed by an "S-shaped" bridle system 132 for controlling the tension of the strip 134. Downstream of this there is a fine strip centering device 136, then a pass line roller 138, a deflector (not shown) and a conveyor belt 140. Above the belt conveyor 140 there are a number of digital inkjet printheads 142. Then there is an oven 144 for drying the ink. To cool the strip 134 a strip cooling system 146 is needed. To make sure that the strip 134 has a suitable temperature for applying a protective clear coat, a probe 148 is foreseen to measure the temperature of the strip before the coating roller that applies the clear coat (FIG. 2). The printing unit 122 ends with a further "S-shaped" bridle system 150 at the output of the printing section for controlling the tension applied to the strip 134.

[0038] A possible variant could consider the addition of a strip position sensor 152 placed after the digital inkjet printhead 142. Said sensor measures the possible deviation of the strip 134 relative to the center of the line. In a further embodiment, the deviation measurement is sent to a control unit 154 which controls the lateral movement 156 of a slide (not shown) on which the printhead 142 is mounted in order to correct the lateral displacement.

[0039] In a further embodiment, the temperature of the strip measured by the temperature transducer 148 is transmitted to a line controller 154 which, if the temperature of the strip 134 exceeds a temperature considered to be a limit, intervenes by modifying the process speed and the capacity of the cooling system 146 to bring the temperature of the strip 134 back within limits deemed acceptable. The control unit 154 manages the entire printing unit 122 and in this regard can be connected to the individual elements by cables or can communicate telematically.

[0040] A possible variation may allow for measurement of product / process quality parameters on both the top and bottom surfaces of the strip 134 .

[0041] Suitably, the composite coat may be based on a polyester coating that is compatible with subsequent ink application. In an exemplary embodiment, the following sequence of layers may be formed on the strip: a first layer based on a composite polyester-based coat, approximately 5-10 μm thick; an ink layer, approximately 0.5-3 μm thick; and finally a clear coat, approximately 10-20 μm thick.

Claims

1. A plant for pre-coating and digital inkjet printing of metal strips (134), comprising, in the following order: (a) a first coating device (111) for applying a composite coat which acts as both a primer and a base coat; (b) a first oven (113) for drying the coat; (c) a first cooling system (115); (d) a digital sol-gel type inkjet printing unit (122); (e) a second coating device (124), in particular a roller applicator, for applying a clear coat; (f) a second oven (126) for drying the coat; and (g) a second cooling system (128) Including, plant.

2. The digital sol-gel type inkjet printing unit (122) prints a liquid containing a plurality of ink droplets in the following order: (d-1) one or more digital sol-gel type inkjet printheads (142); (d-2) Ink Drying Oven (144): (d-3) Third cooling system (144) upstream of said one or more printheads (142), a centering system (130, 136, 138) and a first strip tensioning control system (132), in particular in the following order: (d-4) coarse strip centering system (130); (d-5) a first "S-shaped" bridle system (132) for controlling strip tension; (d-6) fine adjustment strip centering system (136); (d-7) Pass line rollers (138) and optionally deflectors and downstream of said one or more printheads (142) a second strip tension control system (150), in particular (d-8) Second "S-shaped" bridle system (150) 2. The plant for pre-coating and printing according to claim 1, further comprising:

3. The plant of claim 2, further comprising a strip position sensor (152) in the digital sol-gel type inkjet printing unit, the print head (142) being mounted on a slide capable of translation in a direction perpendicular to the direction of movement of the strip, and the plant including a corresponding control unit (154) configured to manage the movement of the slide in accordance with values ​​detected by the position sensor (152) to correct lateral bias in the position of the strip (134) measured by the position sensor (152).

4. A plant as described in claim 2 or 3, further comprising a strip temperature sensor (148), in particular a temperature transducer, downstream of the digital sol-gel type inkjet printing unit (122) and upstream of the second coating device (124), the strip temperature sensor adapted to measure the temperature of the strip (134) and send the measured value to a corresponding control unit (154), the control unit being configured to automatically control the speed of the strip (134) and / or the flow rate of the third cooling system (146) to bring the temperature measured by the temperature sensor (148) back within a predetermined value.

5. A method for pre-coating and printing, in particular digital inkjet printing, of a metal strip (134), comprising the following steps: (I) applying a composite coat (111) that acts as both a primer and a base coat to a metal strip (134); (II) baking the composite coat (113); (III) cooling the composite coat (115); (IV) digital sol-gel type inkjet printing (122) onto the pre-coated strip; (V) applying a clear coat to the pre-coated, printed strip (124); (VI) baking the clearcoat (126); and (VII) Cooling the clear coat (128) in the order listed.

6. The method of claim 5, further comprising centering the metal strip (134) prior to step (IV).

7. The method of claim 5 or 6, wherein the composite coat is a polyester / melamine resin system.

8. The method according to any one of claims 5 to 7, wherein a silane-based thermal polymerization product is applied as an ink for said digital sol-gel type ink jet printing.

9. 9. The method according to claim 5, further comprising, before step (IV), performing a measurement of the position of the strip (134), and adjusting the position of one or more printheads (142) applied to the digital sol-gel type ink jet printer in step (IV) based on the measurement of the position of the strip in order to optimize the application of ink to the strip (134) during step (IV).

10. 10. The method according to claim 5, further comprising monitoring the temperature of the strip (134) after step (IV) and, if the temperature exceeds a limit value, slowing down the speed of the strip (134) and / or enhancing the drying of the ink in order to control the drying of the ink before the application of the clear coat (124) in step (V).

Images