Apparatus and process for pre-coating and printing on metal strip

Abstract

The invention relates to an apparatus and process for pre-coating (111) and subsequent digital sol-gel inkjet printing (122) on a metal strip, where then a protective clear coat (124) is applied over the dried ink. The core 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 layers of coating, namely a primer and a base coat, and the relative drying and cooling phases of the coatings, but by application of a single coating that combines the functions of the primer and base coat. Furthermore, the process is even further simplified by printing with a special sol-gel ink type that does not require UV treatment, only a simple drying of the ink after application.

Description

Technical Field

[0001] The present invention relates to a printing apparatus and process for digital inkjet printing, particularly for pre-coated strips, and more particularly to an arrangement of the printing process in conjunction with pre-coating to prepare the surface of the product for printing, thereby making it suitable for ink adhesion. Background Technology

[0002] Pre-coated tapes have a wide range of applications and are widely used in indoor and outdoor construction, civil and industrial building projects, and the home appliance industry. As interior design becomes increasingly complex, the demand for tapes in this industry is growing.

[0003] Common processes for producing these pre-coated tapes with complex designs involve reference to Appendix Figure 1 The following steps are explained:

[0004] The first step involves applying a first coating layer, namely primer 10, followed by drying 12 and subsequent cooling 14 of the primer; the second step involves applying a second coating layer 16, namely a base coat, that forms the background of the design to be obtained, followed by drying 18 and subsequent cooling 20. In the third step, the design or print 22 is then applied, for example, using diluted or undiluted ink with a solvent on the previously created double-coated base coat, followed by subsequent drying of the ink; and finally, in the fourth step, a clear coat 24 is applied, followed by drying 26 and subsequent cooling 28. The various steps listed above are reflected in a series of devices in the pre-coating and printing equipment, which are arranged precisely one after 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. Therefore, Figure 1 process Figure 1 One aspect represents a series of processing steps, and the other aspect represents a series of corresponding devices required to perform each individual step in the equipment or corresponding production line used for pre-coating and printing.

[0005] Over time, ink coating or printing technology has evolved in terms of processes and techniques, but the following processes are currently commonly used:

[0006] Coating can be done using printing rollers (rotary gravure printing), which typically consist of two to five rollers with negative designs printed on them; coating can also be done using printing rollers via offset printing, which typically consist of units of two to five rubber-coated rollers with embossed (positive) designs on the rubber surface; and coating can also be done using a four-color digital inkjet printer.

[0007] All technologies have their limitations. In particular, all technologies in this field share a common drawback: applying two coatings (primer + undercoat) before printing increases the operational costs and complexity of pre-coating and printing equipment setup, thus imposing the need to operate with three drying or heating ovens for three coatings (primer + undercoat + clear coat).

[0008] The disadvantages associated with roll coating are as follows: the design is limited by the circumferential development of the rolls used. Each design involves the use of a dedicated series of rolls; therefore, the investment cost is high, and the management of a large portfolio of designs to be produced is particularly complex.

[0009] Regarding the current state of the art, using digital printing for coating has other disadvantages, such as: solid solvent-free UV inks have reduced heat resistance, reduced flexibility, and reduced resistance to external environmental conditions. In the event of leakage, UV inks have a large environmental footprint and are more expensive to dispose of. Ink curing or heat drying occurs in printers that have integrated UV lamps. Documents disclosing the state of the art for ink printing on metal substrates are JP2017047370A and US2007 / 0085983A1. Summary of the Invention

[0010] The object of this invention is to overcome the aforementioned disadvantages and, taking into account the limitations of various processes and techniques for pre-coating and printing on metal strips, to propose an apparatus and process for pre-coating and printing on metal strips that is less complex, requires fewer parts, is less expensive, and preferably provides high printability with a low environmental footprint.

[0011] Further objects or advantages of the present invention will become apparent from the following description.

[0012] In a first aspect of the invention, this objective is achieved by means of an apparatus for pre-coating and printing metal strips via digital inkjet printing, the apparatus comprising, in the following order:

[0013] (a) A first coating apparatus for applying a combined coating that serves as both a primer and a base coat;

[0014] (b) A first drying oven for drying the coating;

[0015] (c) A primary cooling system, such as an air and water cooling system;

[0016] (d) A digital sol-gel inkjet printing unit, preferably equipped with an ink drying device;

[0017] (e) A second coating apparatus, particularly a roller coater, for applying a transparent coating;

[0018] (f) A second oven for drying the coating; and

[0019] (g) Secondary cooling systems, such as air and water cooling systems.

[0020] The device specifies the application of a single coating that performs the functions of both primer and undercoat, eliminating the need for two drying ovens, two cooling units, and two coating units before printing, thus halving the number of components in the pre-coating step. This invention enables the creation of a pre-coating and printing production line that requires only two ovens to heat-dry or cure the coating. The first oven is necessary for drying and thus polymerizing the initial coating used as primer and undercoat, and the second oven, placed after the printing unit and the application of the clear coat, is necessary for drying / polymerizing the clear coat.

[0021] The apparatus according to the invention is particularly suitable for printing on continuous strips. In this regard, the apparatus advantageously includes means for conveying the strip through various components of the apparatus itself. To prevent damage to the sharpness of the printed image during its movement through the printing unit, it is recommended to center the strip to be printed and maintain a defined strip tension. In this regard, in a preferred embodiment of the invention, the printing unit comprises, in the following order:

[0022] (d-1) One or more digital sol-gel inkjet printheads;

[0023] (d-2) Ink drying oven;

[0024] (d-3) Third cooling system;

[0025] Upstream of the one or more printheads, a centering system and a first strip tension control system are provided, specifically including, in the following order:

[0026] (d-4) Coarse strip centering system;

[0027] (d-5) The first “S-shaped” tensioning system is used to control the strip tension;

[0028] (d-6) Fine strip centering system;

[0029] (d-7) Wire rolling rolls and optional deflectors;

[0030] Furthermore, downstream of the one or more printheads, a second strip tension control system is provided, specifically:

[0031] (d-8) Second “S-shaped” tensioning system.

[0032] The strip tension control system is preferably an "S-shaped" tensioning system. A possible "S-shaped" tensioning system for controlling strip tension can be installed at the inlet of the transparent coating apparatus.

[0033] These rolling rolls limit the vertical vibration of the strip.

[0034] Advantageously, the strip to be printed is guided through the centering system and the first strip tension control system, and then guided below the one or more printheads, advantageously transported by means of a conveyor belt, and then guided to the exit of the printing unit by the second strip tension control system. The conveyor may advantageously be provided with a pneumatic support surface adapted to support corresponding portions of the strip on an air cushion. The tensioning system effectively counteracts tension in the longitudinal direction of the strip. A strip leveling system placed before the one or more printheads is also conceivable. Such a strip centering and tensioning system is described, for example, in patent application IT 102018000007488.

[0035] In a preferred embodiment of the invention, the device further includes a strip position sensor in the printing unit, and the print head is mounted on a slider capable of translating orthogonally to the direction of movement of the strip, and wherein the device includes a corresponding control unit configured to manage the movement of the slider according to values ​​detected by the position sensor to compensate for lateral deviations in the position of the strip as measured by the position sensor.

[0036] To optimize the application of the transparent coating, in one embodiment of the invention, the device according to the invention further includes a strip temperature sensor, particularly a temperature transducer, downstream of the printing unit and upstream of the second coating apparatus. The strip temperature sensor is adapted to measure the temperature of the strip and send 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 to a predetermined value. Advantageously, this control unit is the same as the control unit that manages the movement of the aforementioned slider, and also the same as the control unit that controls all components of the pre-coating and printing apparatus. Different first and second control units are also conceivable for controlling the temperature of the slider capable of supporting one or more printheads and the temperature of the strip.

[0037] A second aspect of the invention relates to a process for pre-coating and printing, particularly digital inkjet printing, of metal strips, the process comprising the following steps in the order shown:

[0038] (I) Apply a combined coating that serves as both a primer and a base coat onto the metal strip;

[0039] (II) The combined coating is heated and dried;

[0040] (III) Cool the combined coating;

[0041] (IV) Digital sol-gel inkjet printing of the pre-coated strip and drying of the ink;

[0042] (V) Apply a transparent coating to the pre-coated and printed strip;

[0043] (VI) The transparent coating is heated and dried; and

[0044] (VII) Cool the transparent coating.

[0045] In order not to compromise the clarity of the printed image, in a preferred embodiment of the invention, the strip is centered before step (IV). Advantageously, the strip is tensioned before and after step (IV), particularly using a device as defined in the second claim.

[0046] In a preferred embodiment of the process according to the invention, the composite coating is polyester-melamine based, and once dried, it enables perfect ink adhesion from digital jet printing.

[0047] The combined polyester-melamine coating is advantageously white. The coating intended for application to the strip preferably has a viscosity between 60 and 90 seconds, as measured according to DIN standard 53211. The latter standard requires a viscosity cup of 100 cm⁻¹. 2 It has a capacity and a 4mm outlet orifice. At an ambient temperature of 20°C, the test liquid was completely drained through this orifice, and the draining time was determined. The unit of measurement is the second DIN standard. Density is advantageously determined according to the method described in DIN EN ISO 2811-1-4, ranging from 1000 to 1500 kg / m³. 3 Within the range. Preferably, the composite coating is applied with a final (dry) thickness of 5 μm to 15 μm.

[0048] A combination coating is a "tackifier," more commonly referred to as an adhesive, that prepares (alters) the surface of the material to be printed, allowing the ink to adhere to the surface. It is also suitable for adhesion to various types of substrates, such as metals, plastics, glass, and other difficult-to-print substrates, without the need for pre-coating, thus acting as both a primer and a base coat. A wide range of combination coatings are available on the market, from which a person skilled in the art can choose the most suitable combination coating for the substrate and ink he / she intends to use.

[0049] Sol-gel inks avoid the use of UV lamps for drying and do not require the use of environmentally unfriendly solvents. This overcomes the limitations of currently used inks and simplifies ink drying technology. The ink appropriately developed for this application is preferably a silane-based thermally polymerized product. Advantageously, this ink uses eco-friendly solvents that reduce the environmental footprint of the ink. In a preferred variant, the ink is characterized by a dynamic viscosity of 6 to 10 cps at 25°C as determined according to ASTM D 4040 / 4207 and a density preferably between 0.9 and 1.0 g / ml as determined according to ISO 12647-3. This ink can be produced in the following printing colors: black, cyan, magenta, and yellow.

[0050] The sol-gel process is one of the methods used to create films similar to ink films applied by inkjet printers. Sol-gel inks consist of colloidal solutions (sols) that form precursors that subsequently form gels (continuous inorganic lattices containing interconnected liquid phases) through hydrolysis and condensation reactions. Thermal post-treatments such as drying and curing are typically used to remove the liquid phase from the gel, promote further condensation, and increase mechanical properties. Typical precursors for the sol-gel process are M(OR). n MX n R'-M(OR) n-1 The form appears as M, where M represents the metal center, and X and RO are common leaving groups present in metal salts or metal alkoxides, such as chloride ions in metal halides, while R' is any organic group bonded to the metal center via covalent bonds (Si-C, Sn-C) or coordination binders (M = Ti, Zr, etc.). The ink industry offers a wide selection of sol-gel inks for various media, allowing experts to easily identify the ink best suited to their needs.

[0051] To ensure the durability of the printed product, a transparent coating compatible with the printed surface is applied over the dried ink layer. Suitable coatings are commercially available and readily identifiable to those skilled in the art. In a preferred embodiment of the invention, the transparent coating is HD (high-density) polyester. HD polyester exhibits excellent resistance to external environments and chemicals. The transparent coating preferably has at least one of the following properties: viscosity (measured according to DIN 53211) between 80s and 120s, solids content >50% by weight (measured according to UNI EN ISO 3251), and a viscosity between 1000 and 1500 kg / m³. 3 The density is within the range (measured according to DIN EN ISO 2811-1 / 2 / 3 / 4). The final (dry) thickness of the coating advantageously corresponds to 10 μm to 25 μm.

[0052] To optimize the printing quality of the printed design, the measurement of the strip position is preferably performed before step (IV), and during step (IV), the printhead position is adjusted to optimize ink application onto the strip based on the measurement of the strip position.

[0053] For the purpose of perfecting the application of the transparent coating to the printed matter, advantageously, in one embodiment of the process according to the invention, the temperature of the tape is monitored after step (IV), and if the temperature exceeds a limit, the tape speed is slowed down and / or the ink drying is intensified in order to adjust the drying before applying the transparent coating in step (V).

[0054] The printing unit can be advantageously equipped with auxiliary systems for ink recirculation and cleaning or rinsing of the printhead nozzles.

[0055] The features and advantages disclosed in one aspect of the present invention may be transferred to another aspect of the present invention with necessary modifications.

[0056] The industrial practicality became apparent from the moment pre-coating and printing equipment required fewer parts, became less complex, and became cheaper and more environmentally friendly to handle.

[0057] The objects and advantages described herein will be further emphasized in the disclosure of preferred examples of embodiments of the invention given only by way of non-limiting examples.

[0058] Variations and further features of the invention are the subject of the dependent claims. The disclosure of preferred examples of embodiments of the apparatus and process for pre-coating and printing strips according to the invention, and of auxiliary systems for guiding the strip, controlling its specific tension, and centering it, is given by way of example only with reference to the accompanying drawings. In particular, unless otherwise specified, the number, shape, size, and material of the system and individual components may vary, and equivalent elements may be applied without departing from the inventive concept. Attached Figure Description

[0059] Figure 1 The state of the art in realizing printing on pre-coated tape is illustrated by block diagrams, particularly the various steps of the process and the apparatus necessary to realize each step.

[0060] Figure 2 The following block diagram illustrates embodiments of the system and method for coating and printing strips according to the present invention.

[0061] Figure 3 This is a detailed schematic diagram of the digital inkjet printing portion of the device according to the present invention. Detailed Implementation

[0062] The discussion at the outset was based on the state of the field. Figure 1 . Figure 2 A block diagram depicting an embodiment of the invention for jet printing on a strip is shown. The process begins with the application of a double coating consisting of a primer and a base coat 111 in a single step. Subsequently, the combined coating 113 is dried and then cooled 115. Printing 122 is then performed on the coating. As is the case in the art, printing 122 is followed by the application of a clear coat 124, its drying 126, and then its cooling 128. Cooling is performed using air and water. A spooling support roller system and a deflector are used to guide the strip toward the digital printing section.

[0063] Each step is connected to a corresponding device suitable for performing that step, and is performed precisely in this sequence: a first coating apparatus for applying the combined coating; a first oven for drying the coating; a first cooling device; a printer; a second coating apparatus, preferably a roller coater, for applying a clear coating; a second oven; and a second cooling device. Figure 1 Same, Figure 2 The order of steps in an embodiment of the process according to the invention and the order of apparatus in an embodiment of the device according to the invention are shown.

[0064] refer to Figure 3 The illustration shows a preferred embodiment of the inkjet printing section and related auxiliary systems of the printing unit used to perform the printing stage 122.

[0065] At the entrance of the printing unit 122 is a coarse strip centering device 130, followed by an "S-shaped" tensioning system 132 for controlling the tension of the strip 134. Downstream there is a fine strip centering device 136, followed by a wire roller 138 and a deflector (not shown) and a conveyor belt 140. Above the belt conveyor 140 are multiple digital inkjet printheads 142. Then comes an oven 144 for drying the ink. A strip cooling system 146 is required to cool the strip 134. To verify that the strip 134 has the appropriate temperature for applying a protective clear coat, a clear coat is applied... Figure 2 A probe 148 for measuring the temperature of the strip is positioned before the coating roller. The printer unit 122 terminates at the output of the printing section with an additional "S-shaped" tensioning system 150 to control the tension applied to the strip 134.

[0066] One possible variation could specify a strip position sensor 152 added after the digital inkjet printhead 142. This sensor measures possible deviations of the strip 134 relative to the center of the production line. In another embodiment, the deviation measurement is sent to a control unit 154, which controls a lateral movement 156 of a slider (not shown, on which the printhead 142 is mounted) to compensate for any lateral displacement.

[0067] In another embodiment, the temperature of the strip, measured by the temperature transducer 148, is sent to the production line controller 154. If the temperature of the strip 134 exceeds a temperature considered to be a limit, the production line controller 154 intervenes by modifying the processing speed and capacity of the cooling system 146 to bring the temperature of the strip 134 within a considered acceptable limit. The control unit 154 manages the entire printing unit 122 and, for this purpose, can be connected to individual components via cables or communicate remotely.

[0068] One possible variation could specify the measurement of product / process quality parameters for both the top and bottom surfaces of strip 134.

[0069] Suitable, the composite coating may be based on a polyester coating compatible with subsequent ink application. In an exemplary embodiment, layers may be created on the strip in the following order: a first layer based on a composite polyester-based coating with a thickness of about 5 μm to 10 μm; an ink layer with a thickness of about 0.5 μm to 3 μm; and finally a clear coating with a thickness of about 10 μm to 20 μm.

Claims

1. An apparatus for continuous pre-coating and digital inkjet printing of a continuous metal strip (134), said apparatus comprising, in the following order: (a) A first coating apparatus (111) for applying a composite coating that serves as both a primer and a base coat, and the composite coating is polyester-melamine based; (b) A first oven (113) for drying the coating; (c) First cooling system (115); (d) Digital sol-gel inkjet printing unit (122); (e) A second coating device (124) for applying a transparent coating; (f) A second oven (126) for drying the coating; and (g) Second cooling system (128); Furthermore, the device includes means for conveying the metal strip through various components of the device itself.

2. The apparatus for continuous pre-coating and digital inkjet printing of continuous metal strip (134) according to claim 1, characterized in that... The printing unit (122) comprises, in the following order: (d-1) One or more digital sol-gel inkjet printheads (142); (d-2) Ink drying oven (144); (d-3) Third cooling system (146); Furthermore, upstream of the one or more digital sol-gel inkjet printheads (142), a centering system (130, 136, 138) and a first strip tension control system (132) are provided; Furthermore, a second strip tension control system (150) is provided downstream of the one or more digital sol-gel inkjet printheads (142).

3. The apparatus for continuous pre-coating and digital inkjet printing of continuous metal strip (134) according to claim 2, characterized in that... The device further includes a strip position sensor (152) in the printing unit, wherein the print head (142) is mounted on a slider capable of translating orthogonally to the direction of movement of the strip, and wherein the device includes a corresponding control unit (154) configured to manage the movement of the slider based on values ​​detected by the position sensor (152) to compensate for lateral deviations in the position of the strip (134) measured by the position sensor (152).

4. The apparatus for continuous pre-coating and digital inkjet printing of continuous metal strip (134) according to claim 2 or 3, characterized in that, Downstream of the printing unit (122) and upstream of the second coating apparatus (124), the device further includes a strip temperature sensor (148) adapted to measure the temperature of the strip (134) and send the measured value to a corresponding control unit (154), the control unit (154) 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 to a predetermined value.

5. The apparatus for continuous pre-coating and digital inkjet printing of continuous metal strip (134) according to any one of claims 1 to 3, characterized in that, The first cooling system (115) is an air and water cooling system.

6. The apparatus for continuous pre-coating and digital inkjet printing of continuous metal strip (134) according to any one of claims 1 to 3, characterized in that, The digital sol-gel inkjet printing unit (122) has an ink drying device (146).

7. The apparatus for continuous pre-coating and digital inkjet printing of continuous metal strip (134) according to any one of claims 1 to 3, characterized in that, The second coating device (124) is a roller coater.

8. The apparatus for continuous pre-coating and digital inkjet printing of continuous metal strip (134) according to any one of claims 1 to 3, characterized in that, The second cooling system (128) is an air and water cooling system.

9. The apparatus for continuous pre-coating and digital inkjet printing of continuous metal strip (134) according to claim 2 or 3, characterized in that, The centering system (130, 136, 138) and the first strip tension control system (132) are included in the following order: (d-4) Coarse strip centering system (130); (d-5) First "S-shaped" tensioning system (132) for controlling strip tension; (d-6) Fine strip centering system (136); (d-7) Wire roll (138).

10. The apparatus for continuous pre-coating and digital inkjet printing of continuous metal strip (134) according to claim 2 or 3, characterized in that, The centering system (130, 136, 138) and the first strip tension control system (132) are included in the following order: (d-4) Coarse strip centering system (130); (d-5) First "S-shaped" tensioning system (132) for controlling strip tension; (d-6) Fine strip centering system (136); (d-7) Wire roll (138) and deflector.

11. The apparatus for continuous pre-coating and digital inkjet printing of continuous metal strip (134) according to claim 2 or 3, characterized in that, The second strip tension control system (150) is the second "S-shaped" tensioning system (150).

12. The apparatus for continuous pre-coating and digital inkjet printing of continuous metal strip (134) according to claim 4, characterized in that, The strip temperature sensor (148) is a temperature transducer.

13. A process for continuous pre-coating and digital inkjet printing of a continuous metal strip (134), said process comprising the following steps in the order shown: (I) Apply (111) a combined coating that serves as both a primer and a base coat onto the metal strip (134); (II) The combined coating is heated and dried (113); (III) Cooling (115) the combined coating; (IV) Digital sol-gel inkjet printing (122) of the pre-coated tape; (V) Apply (124) a transparent coating onto the pre-coated and printed strip; (VI) The transparent coating is heated and dried (126); and (VII) Cool the transparent coating (128); The composite coating is polyester-melamine based.

14. The process for continuous pre-coating and digital inkjet printing of a continuous metal strip (134) according to claim 13, characterized in that, Prior to step (IV), the strip (134) is centered.

15. The process for continuous pre-coating and digital inkjet printing of a continuous metal strip (134) according to claim 13 or 14, characterized in that... The ink used for the digital sol-gel inkjet printing is a silane-based thermally polymerized product.

16. The process for continuous pre-coating and digital inkjet printing of a continuous metal strip (134) according to claim 13 or 14, characterized in that, Prior to step (IV), the position of the tape (134) is measured, and during step (IV), the position of one or more printheads (142) is adjusted to optimize ink application onto the tape (134) based on the measurement of the position of the tape.

17. The process for continuous pre-coating and digital inkjet printing of a continuous metal strip (134) according to claim 13 or 14, characterized in that, After step (IV), the temperature of the tape (134) is monitored, and if the temperature exceeds a limit, the speed of the tape (134) is slowed down and / or the drying of the ink is enhanced in order to adjust the drying of the ink before the application (124) of the transparent coating in step (V).

18. The process for continuous pre-coating and digital inkjet printing of a continuous metal strip (134) according to claim 13 or 14, characterized in that, In step (IV), the ink is dried after the tape has been pre-coated by digital sol-gel inkjet printing (122).

19. The process for continuous pre-coating and digital inkjet printing of a continuous metal strip (134) according to claim 13 or 14, characterized in that, The strip (134) is tensioned before and after step (IV).

20. A process for continuous pre-coating and digital inkjet printing of a continuous metal strip (134), the process comprising the following steps in the order shown: (I) Apply (111) a combined coating that serves as both a primer and a base coat onto the metal strip (134); (II) The combined coating is heated and dried (113); (III) Cooling (115) the combined coating; (IV) Digital sol-gel inkjet printing (122) of the pre-coated tape; (V) Apply (124) a transparent coating onto the pre-coated and printed strip; (VI) The transparent coating is heated and dried (126); and (VII) Cool the transparent coating (128), The composite coating is polyester-melamine based; The feature is that, prior to step (IV), the strip (134) is centered, and wherein, before and after step (IV), the strip (134) is tensioned using the continuous pre-coating and digital inkjet printing apparatus for continuous metal strip (134) according to claim 2.

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