EP4238768A1

EP4238768A1 - Assembly for hot rotary printing

Info

Publication number: EP4238768A1
Application number: EP23158803.9A
Authority: EP
Inventors: Mario Crocioni
Original assignee: Rotosystem Srl
Current assignee: Rotosystem Srl
Priority date: 2022-03-04
Filing date: 2023-02-27
Publication date: 2023-09-06
Also published as: IT202200004079A1

Abstract

An assembly for hot rotary printing comprising a frame (2) for the rotary support of at least two parallel cylinders (3, 4) the lateral surfaces of which face each other and are proximate at a predefined work region (5) through which it is possible to convey, mutually juxtaposed, a sheet to be printed and a laminar backing which bears a layer of pigment to be transferred onto the sheet to be printed. The first cylinder (3), which comprises shaped portions on its lateral surface which are designed to be impressed on the sheet to be printed by way of the transfer of the pigment that is present on a laminar backing, is associated with respective heating means. These heating means comprise at least one electromagnetic inductor (6) which is arranged proximate to the lateral surface of the at least one first cylinder (3). The at least one first cylinder (3) is at least partially made of ferromagnetic material.

Description

The present invention relates to an assembly for hot rotary printing.
Thermal printing is used mainly for applying metallic colors, such as for example the colors gold and silver, in the form of laminas, by transferring them from a backing sheet to the material on which to create the print.
The process can take place using flat sheets, which require the material on which the print is executed to be held in place when it is on the sheets, or with rotating apparatuses, which ensure that a predefined advancement speed of the material is maintained (optionally also according to specific laws of motion).
A rotary system for hot printing is constituted essentially by a metallic structure on which at least two cylinders are accommodated: an upper cylinder, usually made of brass, carries the printing plate, i.e. the engraving to be impressed on the target material; a lower cylinder, usually covered with a deformable material, such as an elastomer, rubber, silicone and the like, the purpose of which is to keep the material on which to create the print in contact with the sheet bearing the lamina to be transferred through the printing process onto the previously-mentioned material, during the transition in the work area.
The surface of the upper cylinder must have a certain temperature at the work region, i.e. the region where it comes into contact with the lamina to be applied to the material to be printed, in order to ensure the transfer effect.
In traditional systems, heating of the upper roller is done with electric resistance heaters or hot oil circuits, which can be arranged in the body of the upper cylinder, so as to diffuse the heat from the inside to the outside.
The limit of this implementation structure is the difficulty of controlling the temperature in the work region: this leads to the possibility that the printing processes are executed when the surface of the cylinder has not reached the ideal temperature and this can impair (or even compromise) the quality of the print.
At the same time, there is a counter-productive transfer of heat toward the region where the bearings are accommodated: this can result in problems linked to the correct maintenance of the necessary alignments and even lead to malfunctions in the bearings themselves.
The principal aim of the present invention is to solve the abovementioned drawbacks, by providing an assembly for hot rotary printing in which it is possible to precisely adjust the temperature of the work region of at least one of the cylinders present.
Within this aim, an object of the invention is to provide an assembly for hot rotary printing in which it is possible to localize the heating predominantly at the work region of the at least one cylinder.
Another object of the invention is to provide an assembly for hot rotary printing that makes it possible to preserve the bearings and the respective accommodations from excessive heating.
Another object of the invention is to provide an assembly for hot rotary printing that makes it possible to produce prints of high quality.
Another object of the invention is to provide an assembly for hot rotary printing that is simple and easy to maintain.
Another object of the present invention is to provide an assembly for hot rotary printing which is low-cost, easily and practically implemented, and safe in use.
This aim and these objects and others that will become more apparent hereinafter are achieved by an assembly for hot rotary printing of the type comprising a frame for the rotary support of at least two parallel cylinders the lateral surfaces of which face each other and are proximate at a predefined work region through which it is possible to convey, mutually juxtaposed, a sheet to be printed and a laminar backing which bears a layer of pigment to be transferred onto the sheet to be printed, and at least one first cylinder of said at least two parallel cylinders, which comprises shaped portions on its lateral surface which are designed to be impressed on the sheet to be printed by way of the transfer of said pigment that is present on a laminar backing, being associated with respective heating means, characterized in that:

said heating means comprise at least one electromagnetic inductor which is arranged proximately to the lateral surface of said at least one first cylinder;
said at least one first cylinder is at least partially made of ferromagnetic material.

Further characteristics and advantages of the invention will become more apparent from the detailed description that follows of a preferred, but not exclusive, embodiment of the assembly for hot rotary printing, which is illustrated by way of non-limiting example in the accompanying drawings wherein:

Figure 1 is a schematic perspective view of a possible embodiment of an assembly for hot rotary printing according to the invention;
Figure 2 is a schematic side view of the assembly of Figure 1;
Figure 3 is a schematic view from above of the assembly of Figure 1;
Figure 4 is a cross-sectional view taken along the line IV-IV in Figure 3 of the assembly of Figure 1.

With reference to the figures, the reference numeral 1 generally designates an assembly for hot rotary printing.
The assembly 1 according to the invention comprises a frame 2 for the rotary support of at least two parallel cylinders 3, 4 the lateral surfaces of which face each other and are proximate at a predefined work region 5 through which it is possible to convey, mutually juxtaposed, a sheet to be printed and a laminar backing which bears a layer of pigment to be transferred onto the sheet to be printed.
At least one first cylinder 3 comprises shaped portions on its lateral surface which are designed to be impressed on the sheet to be printed by way of the transfer of the pigment that is present on a laminar backing. Such at least one first cylinder 3 is, for this reason, associated with respective heating means.
According to the invention such heating means can advantageously comprise at least one electromagnetic inductor 6 which is arranged proximately to the lateral surface of the at least one first cylinder 3.
The at least one first cylinder 3, according to the invention, can conveniently be at least partially made of ferromagnetic material, for the purpose of being subjected to the effects of electromagnetic induction generated by the inductor 6, with consequent circulation of induced currents which will cause a localized heating of the ferromagnetic portion of the cylinder by the Joule effect.
By virtue of the magnetic field strength it will be possible to localize the increase in temperature at the (radially) outermost lateral surface of the at least one first cylinder 3, with the advantage of containing the effects due to such heating to such portion of the at least one cylinder 3.
In particular it is necessary to highlight that an increase in temperature can determine an expansion of the material which could compromise the correct alignments (between the first cylinder 3 and the frame 2 and between the first cylinder 3 and the second cylinder 4).
Furthermore, between the first cylinder 3 and the frame respective bearings 7 can be interposed which are adapted to support and guide the first cylinder 3 in rotation, with low friction.
Overheating of the seat of the bearing could result in a displacement of said bearing which could obstruct the correct rotation of the first cylinder 3.
Furthermore, it should be noted that some bearings 7 undergo lubrication before their installation: an increase in temperature of the bearing 7 could determine a deterioration of the lubricant and, as a consequence, a worsening of the performance of the bearing 7 itself.
Therefore, confining the heating of the at least one first cylinder 3 exclusively to the portion thereof that is closest to the lateral surface makes it possible to ensure an improved overall operation, while also preserving the bearings 7 interposed between the first cylinder 3 and the frame 2.
It should furthermore be noted that the at least one first cylinder 3 can profitably comprise a through axial hole 8 for the circulation of a refrigerant fluid originating from a respective cooling circuit.
The circulation of a refrigerant fluid through the through axial hole 8 will ensure that, proximate to the walls of that hole 8, the temperature of the cylinder 3 is kept low (in any case lower than that detectable at the lateral surface of the cylinder 3 by virtue of the inductor 6), thus guarding against phenomena of thermal dilation and protecting the bearings 8 from possible overheating.
It should be noted that, between the frame 2 and the at least one second cylinder 4, respective bearings 9 can positively be interposed for supporting and guiding the second cylinder 4 in rotation.
With particular reference to a possible embodiment of undoubted practical and applicative interest, the electromagnetic inductor 6 can conveniently comprise a contoured conducting element 10 which is connected to a respective power supply (not shown in the accompanying figures) which is adapted to provide electric power and has at least one adjustable parameter chosen from power, current, frequency and waveform.
By virtue of a suitable choice of the shape of the contoured conducting element 10 of the inductor 6 and by virtue of the adjustment of the power or of the current or of the frequency provided by the power supply to the inductor 6, it will be possible to precisely adjust the temperature induced on the at least one first cylinder 3, as well as its localization (preferably by concentrating the increase in temperature at the outermost region of the cylinder 3, proximately to the lateral surface thereof).
It should be noted that the conducting element can preferably be made of a material chosen from copper, copper alloys, aluminum, aluminum alloys, metallic alloys, graphite, carbon and derivatives thereof and the like. The possibility is not ruled out of adopting other materials, however.
In a possible, extremely efficient embodiment (which can optionally be applied in an assembly 1 according to the invention), the conducting element 10 of the inductor 6 can usefully have a through internal cavity for the conveyance of a refrigerant fluid originating from a respective cooling circuit.
This embodiment will be particularly valid in those cases where it is desired to prevent the conducting element 10 from being heated by convection, given that it is very close to the surface of the at least one first cylinder 3.
In all those cases where a cooling circuit is adopted (for the refrigerant fluid circulating in the through axial hole 8 and, if such solution is adopted, for the refrigerant fluid circulating in the internal cavity of the conducting element 10), this profitably will comprise a cooling assembly for subtracting heat energy from the respective working refrigerant fluid and a pump for the forced circulation of the fluid. The possibility is not ruled out of adopting two separate cooling circuits for the refrigerant fluid circulating in the cylinder 3 and for the refrigerant fluid circulating in the internal cavity in the conducting element 10 of the inductor 6, even though the possibility is envisaged of adopting a single cooling circuit.
If the refrigerant fluid is water, the possibility is likewise envisaged of connecting a first end of the hole 8 to a delivery conduit for the water that arrives directly from the water mains, and connecting a second end of the hole 8 to an outflow (or to an accumulation tank in which the water that has absorbed heat from the cylinder 3 can subsequently be used for other purposes).
With reference to a particularly versatile embodiment, the at least one first cylinder 3 could advantageously comprise a rigid outer covering jacket, which is provided with the necessary shaped portions on its outer surface.
This embodiment makes it possible to modify the subject matter to be printed on the respective sheet simply by substituting the outer jacket of the at least one first cylinder 3: the advantages of this contrivance are evident since it is not necessary to have a plurality of first cylinders 3; instead it will be sufficient to have just one cylinder on which to install (and substitute as needed) all the jackets one desires.
It should be noted however that the at least one second cylinder 4 can profitably comprise a respective deformable outer covering jacket which is made of a material of a type chosen from silicone and derivatives thereof, elastomers and derivatives thereof, rubber and derivatives thereof, polymers and derivatives thereof.
The deformability of the deformable outer jacket of the at least one second cylinder 4 is extremely useful because it makes it possible to compress the laminar backing loaded with the pigment onto the sheet to be printed, and to bring them both together on the surface of the at least one first cylinder 3.
The protection offered by the present invention also extends to a method of hot printing that entails the execution of a series of consecutive steps.
First it is necessary to perform the juxtaposition of a sheet to be printed against a laminar backing which is provided with a pigment on the surface thereof that is directed toward the sheet.
Subsequently a first cylinder 3 is subjected to heating by way of an inductor 6 connected to a respective power supply which delivers electric power and has at least one adjustable parameter (chosen from power, current, frequency and the like), until a predefined temperature is reached on its lateral surface.
The first cylinder 3 will be part of a printing assembly 1 and will be provided with specific shaped portions on its lateral surface (shaped portions that will correspond to the subject to be impressed on the sheet to be printed through the transfer of the pigment present on the laminar backing).
It will then be necessary to conduct the juxtaposed sheet and laminar backing between the first cylinder 3 and a second cylinder 4 which faces and is proximate to the first cylinder 3.
The juxtaposed sheet and laminar backing will then be pressed onto each other (between the lateral surfaces of the two cylinders), and the shaped portions present on the lateral surface of the first cylinder 3 will determine localized pressures on the laminar backing that are such as to support the detachment of the pigment and transfer it onto the sheet to be printed (by virtue of the high temperature to which the first cylinder 3 is heated).
The working temperatures to which the lateral surface of the first cylinder 3 will need to be brought are generally higher than 50° C (generally such temperature is chosen in a range comprised between 90° C and 600° C, with the preferred value in the neighborhood of 400° C, although particular cases are not ruled out in which higher temperatures can be adopted).
It should be noted that the method according to the invention can furthermore conveniently comprise a step of limiting the temperature of the first cylinder 3 which consists in conveying a refrigerant fluid along a through axial hole 8 thereof: in such case the through axial hole 8 positively will be connected to a respective cooling circuit.
Advantageously the present invention solves the abovementioned problems, by providing an assembly 1 for hot rotary printing in which it is possible to precisely adjust the temperature of the work region 5 of at least one of the cylinders 3, 4 present (in particular, adjustment of the temperature of the cylinder 3 will be possible and precise by virtue of the adoption of a system of induction heating thereof).
Conveniently the assembly 1 according to the invention makes it possible to localize the heating predominantly at the work region 5 of the at least one cylinder 3, 4 (in particular by way of the induction heating of the cylinder 3).
Profitably the assembly 1 according to the invention makes it possible to preserve the bearings 7 and the respective accommodations from excessive heating (given that, using induction heating, it is possible to limit the extent of the portions of the cylinder 3 that are subjected to heating and also by virtue of the presence of the through axial hole 8 inside which a refrigerant fluid can flow that makes it possible to maintain the part of the cylinder 3 closest to the axis of symmetry at a much lower temperature than the lateral surface which bears the shaped portions).
Usefully the assembly 1 according to the invention makes it possible to produce printed designs of high quality, since it is possible to control the temperature of the lateral surface of the cylinder 3 with extreme precision, and the localization of the heated regions makes it possible to guard against misalignments owing to thermal dilations.
Advantageously the assembly 1 according to the invention is of the simple type and is easy to maintain.
The assembly 1 according to the invention is easily and practically implemented and is low-cost: such characteristics make the assembly 1 according to the invention an innovation that is safe in use.
The invention, thus conceived, is susceptible of numerous modifications and variations, all of which are within the scope of the appended claims. Moreover, all the details may be substituted by other, technically equivalent elements.
In the embodiments illustrated, individual characteristics shown in relation to specific examples may in reality be interchanged with other, different characteristics, existing in other embodiments.
In practice, the materials employed, as well as the dimensions, may be any according to requirements and to the state of the art.
The disclosures in Italian Patent Application No. 102022000004079 from which this application claims priority are incorporated herein by reference.
Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly, such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.

Claims

An assembly for hot rotary printing of the type comprising a frame (2) for the rotary support of at least two parallel cylinders (3, 4) the lateral surfaces of which face each other and are proximate at a predefined work region (5) through which it is possible to convey, mutually juxtaposed, a sheet to be printed and a laminar backing which bears a layer of pigment to be transferred onto the sheet to be printed, and at least one first cylinder (3) of said at least wo parallel cylinders (3, 4), which comprises shaped portions on its lateral surface which are designed to be impressed on the sheet to be printed by way of the transfer of said pigment that is present on a laminar backing, being associated with respective heating means, characterized in that:
- said heating means comprise at least one electromagnetic inductor (6) which is arranged proximate to the lateral surface of said at least one first cylinder (3);

- said at least one first cylinder (3) is at least partially made of ferromagnetic material.
The assembly according to claim 1, characterized in that said at least one first cylinder (3) comprises a through axial hole (8) for the circulation of a refrigerant fluid originating from a respective cooling circuit.
The assembly according to one or more of the preceding claims, characterized in that said electromagnetic inductor (6) comprises a contoured conducting element (10) which is connected to a respective power supply which is adapted to provide electric power and has at least one adjustable parameter chosen from power, current, frequency and waveform.
The assembly according to the preceding claim, characterized in that said conducting element (10) is preferably made of a material chosen from copper, copper alloys, aluminum, aluminum alloys, metallic alloys, graphite, carbon and derivatives thereof and the like.
The assembly according to one or more of claims 3 and 4, characterized in that said conducting element (10) has a through internal cavity for the conveyance of a refrigerant fluid originating from a respective cooling circuit.
The assembly according to one or more of the preceding claims, characterized in that said at least one cooling circuit comprises a cooling assembly for absorbing thermal energy from a working refrigerant fluid and a pump for the forced circulation of said fluid.
The assembly according to one or more of the preceding claims, characterized in that said at least one first cylinder (3) comprises a rigid outer covering jacket which is provided with said shaped portions on its outer surface, said shaped portions being designed to be imprinted on the sheet to be printed by way of the transfer of said pigment.
The assembly according to one or more of the preceding claims, characterized in that at least one second cylinder (4) of said at least two parallel cylinders comprises a deformable outer covering jacket which is made of a material of a type chosen from silicone and derivatives thereof, elastomers and derivatives thereof, rubber and derivatives thereof, polymers and derivatives thereof.
A method of hot printing which consists in:
- juxtaposing a sheet to be printed against a laminar backing which is provided with a pigment on the surface thereof that is directed toward said sheet;

- subjecting to heating at least one cylinder (3) of a first printing assembly (1), which is provided with specific shaped portions on its lateral surface, by way of an inductor (6) connected to a respective power supply which delivers electric power and has at least one adjustable parameter, until a predefined temperature is reached on its lateral surface;

- guiding said sheet and said laminar backing, juxtaposed between said at least one first cylinder (3) and at least one second cylinder (4) which faces and is proximate to said at least one first cylinder (3).
The method of hot printing according to claim 9, characterized in that it comprises a step of limiting the temperature of said at least one first cylinder (3) which consists in conveying a refrigerant fluid along a through axial hole (8) thereof which is connected to a respective cooling circuit.