Method for protecting a printed substrate or a to be printed substrate

Abstract

Method for protecting a printed substrate which comprises the following steps: - printing on the substrate at least two printed protective zones having a height greater than the height of said printing in the print zone, such that the printed protective zones provide protection for the print zone against contact via the face of the substrate, and - curing and / or drying the printed protective zones.

Description

[0001] The present invention is applicable to systems for digital printing and processing of substrates that need to be protected against contact with any other parts, in particular, but not only, just after they have been printed. Protection may be required on any surface of the substrate. The substrate may have any shape. In the case of flat substrates, the surface to be protected may be the top and / or bottom surface. The protection may be necessary to prevent contact between the substrate and the recently printed zone of other substrates printed using the same process, or to prevent contact with other elements on the production line. Therefore, the substrate may be, for example, a sanitary substrate for which, from a certain time in its process, avoiding direct contact with the conveyor elements on the production line would be wanted. However, the present invention is particularly applicable to the field of digital printing in which there is a subsequent step, immediately following digital printing, of stacking the substrates.

[0002] In digital printing systems which include stacking, after printing the substrate and curing and / or drying said print, the substrates are stacked one on top of the other, with the new printed substrate, which may be identical to the substrate below, being stacked on top and so on. The printed zone on the top face of a lower substrate comes into contact with the bottom surface of the upper substrate. Any type of contamination possible, owing to the contact between substrates, may pass from one face to another. For example, there may be migration of substances contained in the printed ink, even though this is completely fixed, towards the surface in contact, or simply migration of substances, particles or dirt that may be on the non-printed surface towards the printed zone.

[0003] The contamination or migration will depend on the type of ink and materials used. In the case of printed substrates that will be used as packaging for food products, the migration that may occur, during stacking, from the printed face to the non-printed face of the other substrate, may result in said compounds that migrated into the interior of the packaging subsequently migrating, during use, into the food contained inside said packaging. The list of materials containing components which must not pass into food is very long: plastic, adhesive, paper and cardboard, varnish, aluminium, coloured inks, etc. There may also be, for example, contamination from soiling as a result of contact between surfaces.

[0004] It is an aim of the present invention to disclose means for solving the problem of contamination mentioned above.

[0005] More particularly, the present invention discloses a method for protecting a printed substrate which comprises the following steps: printing at least one printed protective zone on the substrate, said printed protective zones protruding with respect to the substrate, above the print zone, such that the printed protective zone or zones provide protection for the print zone against contact via said face of the substrate, and curing and / or drying the printed protective zones.

[0006] The substrate may have a printed zone which has been printed previously, it may be printed at the same time, or the printed zone may be printed after the application of the protective zones. Therefore, as regards the steps of the method, the term "printed zone", in the present invention, should be understood to mean "(decorative) zone already printed" or "(decorative print) zone to be printed".

[0007] Preferably, at least two printed protective zones, and even more preferably, more than two printed protective zones are printed. Printing several protective zones makes it possible to generate a distribution which provides sufficient protection for the (decorative) printed zone with a minimum of material.

[0008] The printed protective zones may have, preferably, a height greater than the height of the material of the print zone. Thus, the protective zones protrude with respect to the print zone.

[0009] Preferably, the protective zones generate a distribution of raised zones which prevent contact with the printed zone of another substrate placed on top of the substrate. More preferably, the protective zones are distributed surrounding the printed zone, more preferably around the whole outer perimeter of the printed zone. In a particularly preferred embodiment, the protective zone or zones are distributed, continuously or discontinuously, surrounding the outer perimeter of the printed zone. When the protective zone or zones are located on the printed zone, it / they may be distributed along the whole printed zone, preferably in such a way as to generate a distribution of raised spots which prevent contact between another substrate and the printed zone.

[0010] In some applications, especially when the protective zones do not interfere with the printed zone, in other words are not located above it, preferably, the overall thickness of the printed protective zone is greater than the thickness of the printing material deposited in the printed zone.

[0011] The protective zone or zones may be applied to the same face as the printed zone and / or to an opposite face, printed or non-printed. In any case, the protective zone or zones is / are located in the printed zone or zone to be printed or outside of this zone, preferably surrounding this zone. When the protective zone is located on said opposite face, non-printed, this means that the protective zone is located "in the printed zone" when it coincides with the projection of the printed zone on said opposite face, "outside of this zone" and "preferably surrounding the printed zone" when it is located outside of this projection and surrounding it, respectively.

[0012] Said protective zones may be printed using various types of printing technology, such as, for example: rotogravure, spray printing, or inkjet printing and the like. In a preferred embodiment, it is printed by means of inkjet printing.

[0013] The decorative print (printed zone) may be printed using various types of printing technology, such as, for example: rotogravure, spray printing or inkjet printing and the like. In a preferred embodiment, it is printed by means of inkjet printing.

[0014] Preferably, both the protective zones and the decorative print may use the same printing technology.

[0015] Also preferably, the protective zones and the decorative print may use a different printing technology.

[0016] In a particularly preferred embodiment, both the protective zone and the printed zone (decorative print) are printed by means of inkjet printing.

[0017] The present invention, to solve the above problem, proposes printing, and curing or drying, a material at strategic points of the substrate, forming a protective pattern. The printed protective zones, since they protrude with respect to the printed zone, act as spacers which prevent contamination or migration from or to the printed zone. The spacers may be applied in liquid form, by means of printing, and subsequently solidified by means of curing and / or drying. The spacers may be applied during the same printing process, or before or after printing of the print zone.

[0018] Preferably, the zones in which the material is printed must not affect subsequent functionality thereof but must make it possible to prevent undesired contamination. The printed protective zones may form a "mask" which may be "touchable". The series of printed protective zones form a series of raised zones which prevent undesired contact. Taking, as a particular example, the printing of sheets of corrugated cardboard for packaging in the food industry, usually several repeated designs are printed on the same sheet. In this case, it is possible to print, between these designs, printed protective zones using a material which creates a certain height with respect to the substrate so that subsequently, when they are stacked, the upper substrate is not in contact with the printed zones, but is in contact with the protective zones. The type of material used to print the protective zones which generate a spacing between substrates does not have to be specifically a 'low migration' material. In the case where the selected zones in which the printed protective zones are printed are zones which will subsequently be thrown away, it does not matter whether the material is high migration or low migration. Likewise, if the pattern of printed protective zones is distributed in such a way that any resulting migration is below admissible limits, it also would not be necessary to use low migration products. It is also advantageous if the material of the protective zone or zones is stronger, and / or has a higher coefficient of friction than the material of the printed zone.

[0019] For example, in the case where both the printed zone and the protective zone(s) are printed by means of inkjet printing, the material with which the protective zone(s) are printed, preferably, has a higher viscosity than the ink or inks used to print the printed zone. A higher viscosity makes it easier - possibly with adjustments to the printing parameters - for the printer to generate droplets of greater volume which ultimately protrude above the print zone. For example, the material used for the protective zone could be a finishing varnish which has a higher viscosity than a decorative ink, and which also has properties which make it stronger, either owing to the type of polymers or because it contains specific solids, etc.

[0020] Preferably, the printed protective zones all have the same height, which promotes the creation of said protective pattern.

[0021] When used as protection against the contamination which may occur upon stacking, preferably, the printed protective zones generate a network of protruding spots which prevent another substrate, having the same characteristics, stacked above, from coming into contact with the print zone, inter alia.

[0022] One advantage associated with the distribution or network of protruding spots is that it may be easier, since the substrates are in not contact over their entire surface, to subsequently remove said substrates at the time of unstacking, as no "vacuum" force, or electrostatic charge force, or any other type of force is generated between the surfaces of the substrates when an attempt is made to move them.

[0023] Another advantage of the distribution or network of spots or protective zones, especially when the protection material is stronger and / or has a higher coefficient of friction than the ink of the print zone, is that said zones make it more difficult that a substrate will slide on another substrate when the substrates are being stacked or when substrates are being removed from the stack. To sum up, the present invention not only protects against contamination but also counteracts slipperiness between substrates when they are being stacked. This problem of slipperiness arises owing to the low coefficient of friction that some inks may have when cured.

[0024] It must be borne in mind, in such cases, that the upper substrate will rest on the network of protruding spots which generate the printed protective zones. When designing the distribution and height of the printed protective zones, account must be taken of the fact that the upper substrate may bend between protective zones. The network of protruding spots or printed protective zones, according to the present invention, may have some patterns which are more intense than others, in other words with a higher density of spots and / or greater extent of spots, depending on the weight of the stack that each specific substrate has to support.

[0025] In some embodiments, it will be possible for all of the protective zones to be outside the print zone. In the case where they are moreover located in zones that will be thrown away in later stages when it comes to stacking and transport, these zones of material do not need to be made of low migration material, and may be made of high migration materials.

[0026] It is also possible for at least one printed protective zone to be printed in or on the print zone. In such cases, it is strongly recommended that the material of the printed protective zone be transparent, or have a colour integrated in the colour of the printed zone at the spots at which the printed protective zone is printed. For example, the printed protective zone may have the same colour as the printed zone at said spots. It is also strongly recommended that said printed protective zone be produced using a low migration material. The material of the protective zone, therefore, and for certain applications, could be a transparent material and / or a material without pigments. In general, the desired materials for the protective zone will be materials which do not exhibit migration of undesired substances from the protective zone to another substrate, preferably stacked. Whether or not a substance is considered to be undesirable will depend on the particular application (for example, food, cosmetics or pharmaceutical industry).

[0027] However, it is also possible for the printed protective zones within the print zone not to be made of a material different to the material used for printing, even if said material is not a low migration material. For example, there may be zones of greater height which form said protective pattern or part thereof. In such cases, migration or contamination will be controlled in defined zones by the printed protective zones. This may be useful in applications in which a certain degree of contamination / migration is acceptable.

[0028] As stated above, preferably, the method according to the present invention may comprise subsequently placing an element on the printed substrate, such that said element rests on top of the printed protective zones. Said element may be another printed substrate, for example a substrate identical to the substrate with the protective zones.

[0029] The substrate may undergo shaping and / or filling processes to create packaging, preferably food packaging.

[0030] More preferably, these shaping and / or filling processes are carried out after stacking.

[0031] Preferably, the present invention carries out the process of printing of the protective zones and / or said decoration by digital inkjet printing.

[0032] In one especially advantageous embodiment, the present invention preferably uses inkjet printing technology in the decorative print and in the protective zones. The use of inkjet technology both in the process of printing of the decoration and in the process of printing of the protective zones advantageously allows a saving on resources and time, thanks to the uniformity of the process. For example, the printed zone (decorative print) and the protective zone may be printed in the same printer, using different heads for the printed zones and the protective zones.

[0033] The present invention is preferably applicable when the substrate is a food packaging material, as well as in other fields in which protection is necessary against possible contamination and / or migration during manufacturing processes.

[0034] To sum up, the present invention discloses the use of a method according to the invention (in any variant thereof) for producing food packaging. Preferably, the substrate forms food packaging. Also preferably, the substrate is printed only on one face. In this application, it is additionally advantageous to eliminate any possible migration of undesired substances from faces printed with the decorative print to faces which will be in contact with food.

[0035] For a better understanding of the present invention, drawings of possible embodiments of the subject matter thereof are attached by way of explanatory but non-limiting example. Figure 1 schematically shows, in plan view, a substrate on which print zones and printed protective zones have been marked. Figure 2 is an elevation of Figure 1 showing the different heights of the print zones and the printed protective zones. Figure 3 shows two substrates, produced after cutting of the substrate of Figures 1 and 2, and stacked one on top of the other. Figure 4 schematically shows, in plan view, a substrate on which print zones and printed protective zones have been marked, with the protective zones on the opposite face to the print zone. Figure 5 is an elevation of Figure 4 showing the different heights of the print zones and the printed protective zones. Figure 6 shows two substrates, produced after cutting of the substrate of Figures 4 and 5, and stacked one on top of the other.

[0036] Figure 1 shows a substrate 1, for example a corrugated cardboard substrate taken from a reel, on which a repetitive pattern is printed in the print zone 2. The substrate 1 is then cut along the dotted line and the cut portions of substrate will be stacked, with a view to being conveyed for the purpose of subsequent operations such as cutting, folding, etc. This means that, in the stacking, the underside of each cut portion of substrate comes into contact with the printed zone of the cut portion below. To prevent contamination, a series of printed protective zones 3 are also printed, having a height greater than the height of the printed zone 2. When the elements are stacked one on top of the other, as shown in Figure 3, the printed protective zones of greater height prevent the underside of the cut portion above 1' from coming into contact with the printed zone 2 of the cut portion of substrate 1 positioned below it.

[0037] The printed protective zones 3 of the example shown are outside the print zone 2. In the case where, in subsequent operations, the substrate is to be cut again along the borders of the print zone 2, the printed protective zones 3 will not form part of the final packaging, and therefore said printed protective zones 3 may be made from any material, including materials which may contaminate the cut portion of substrate 1' immediately above, since the contaminated zone of the substrate above 1' will also be cut and thrown away. However, during stacking, the printed protective zones 3, by virtue of their greater height, prevent the printed zone 2 of the substrate 1 below from coming into contact with the rear zone of the substrate 1' immediately above.

[0038] In the case where the printed protective zones 3 will not be left out of the final packaging, they may be made of low migration materials, meaning that the material / ink of the print zones 2 does not have to be low migration. It is also possible for all or some of the printed protective zones 3 to be inside the print zone. In this case, moreover, it may be preferable for the material to be transparent, or have a colour integrated in the colour of the design printed on the substrate.

[0039] Figure 4 shows another possible embodiment in which a substrate 1 is printed with a repetitive pattern inside the print zone 2. The substrate 1 is then cut along the intermediate dotted line and the cut portions of substrate will be stacked, with a view to being conveyed for the purpose of further operations such as cutting, folding, etc. This means that, in the stacking, the underside of each cut portion of substrate comes into contact with the printed zone of the cut portion below, giving rise to contamination through contact. To prevent this happening, a pattern of printed protective zones 3, having a height greater than the height of the printed zone 2, is printed on the opposite face to the print zone. When the elements are stacked one on top of the other, as shown in Figure 6, the printed protective zones 3' of greater height prevent the underside of the cut portion above 1 from coming into contact with the printed zone 2 of the cut portion of substrate 1 positioned below it.

[0040] Although the invention has been presented and described with reference to embodiments thereof, it will be appreciated that these are non-limiting embodiments of the invention and therefore several different structural or other details could become obvious to a person skilled in the art after interpreting the subject matter disclosed in the present description, claims and drawings. Consequently, the present invention encompasses all variants and equivalents if they can be considered to fall within the broadest scope of the claims which follow.

Claims

1. Method for protecting a printed substrate or substrate to be printed, characterized in that it comprises the following steps: - printing at least one printed protective zone on the substrate, said printed protective zones protruding with respect to the substrate, above the print zone, such that the printed protective zone or zones provide protection for the print zone against contact via the face of the substrate, and - curing and / or drying the printed protective zones.

2. Method, according to the preceding claim, characterized in that at least two printed protective zones are printed on the substrate.

3. Method, according to the preceding claim, characterized in that the printed protective zones all protrude equally with respect to the substrate.

4. Method, according to Claim 2 or 3, characterized in that the printed protective zones generate a network of protruding protective zones which prevent another substrate, having the same characteristics, stacked above, from coming into contact with the print zone.

5. Method, according to any one of the preceding claims, characterized in that all of the printed protective zone or zones are located outside of the print zone.

6. Method, according to any one of the preceding claims, characterized in that at least one printed protective zone is printed in the print zone.

7. Method, according to any one of the preceding claims, characterized in that said printed protective zone is made of a transparent material or a material having the same colour as the printed zone.

8. Method, according to either of Claims 6 and 7, characterized in that said printed protective zone is made of a low migration material.

9. Method, according to any one of the preceding claims, characterized in that it comprises subsequently placing an element on the printed substrate, such that said element rests on top of the printed protective zone or zones.

10. Method, according to the preceding claim, characterized in that said element is another printed substrate.

11. Method, according to the preceding claim, characterized in that said printed substrate that rests on top of the printed protective zones rests on said printed protective zones in a non-printed zone.

12. Method, according to any one of the preceding claims, characterized in that the substrate is a food packaging material.

13. Method, according to any one of the preceding claims, characterized in that the printing of the protective zones and / or said decoration are carried out by digital inkjet printing.

14. Use of a method according to any one of the preceding claims in the process for producing food packaging.

Images