Flexible packaging substrates compromising thermally-stable prints

Abstract

The present invention is related to a flexible packaging substrate comprising one or more crosslinked ink layers and to a method for the production of said printed substrate.

Claims

1. A flexible packaging substrate comprising one or more digitally-printed electron-beam crosslinked ink layers, wherein the concentration of ethylenically unsaturated groups and alicyclic epoxides in said ink layers is less than 0.05 meq/g, preferably less than 0.03 meq/g, more preferably less than 0.01 meq/g, most preferably less than 0.005 meq/g, the crosslinked ink layers being the top surface of the flexible packaging substrate.

2. The flexible packaging substrate of claim 1, being free of an additional layer, protecting said one or more crosslinked ink layers.

3. The flexible packaging substrate of claim 1, comprising a primer layer sandwiched between the crosslinked ink layers and the substrate.

4. The flexible packaging substrate of claim 1, wherein the total layer thickness of primer and ink layer(s) is comprised between 0.4 and 4 , preferably between 0.6 and 3.5 , more preferably between 0.8 and 3 .

5. The flexible packaging substrate of claim 1, wherein the layer thickness of the primer is comprised between 0.01 and 0.5 , preferably between 0.05 and 0.4 and most preferably between 0.1 and 0.3 .

6. A method for forming a printed flexible packaging substrate according to claim 1 comprising the steps of: a. providing a flexible packaging substrate; b. applying at least one digital print by a digital printing process of at least one ink composition, said ink composition having a concentration of ethylenically unsaturated groups, preferably (meth)acrylic double bonds and a concentration of alicyclic epoxides of less than 0.2 meq/g, preferably less than 0.1 meq/g, more preferably less than 0.05 meq/g, most preferably less than 0.01 meq/g; c. subjecting the digital print to an electron beam irradiation.

7. The method according to claim 6, wherein the at least one ink composition is substantially free of components comprising molecular structures with dangling and/or end-standing ethylenically unsaturated double bonds.

8. The method according to claim 6, wherein the flexible packaging substrate is plasma treated, preferably corona plasma treated.

9. The method according to claim 6, comprising the additional step of applying a primer composition before initiating step b).

10. The method according to claim 6, wherein the digital printing process of step b) is liquid electrographic printing.

11. The method according to claim 6, wherein the electron beam irradiation dose in step c) is at least 15 kGy, preferably at least 18 kGy, more preferably at least 20 kGy.

12. The method according to claim 6, wherein the electron beam irradiation dose in step c) is comprised between 20 and 100 kGy, preferably between 25 and 80 kGy, more preferably between 30 and 60 kGy.

13. The method according to claim 6, wherein the electron beam irradiation in step c) is performed at an oxygen concentration of less than 300 ppm, preferably less than 250 ppm, more preferably less than 200 ppm, most preferably less than 150 ppm.

14. The method according to claim 6, wherein the flexible packaging substrate of step a) comprises polyethylene terephthalate, high density polyethylene, oriented polypropylene, oriented polyamide, polystyrene or paper.

15. The method according to claim 6, wherein the primer composition comprises one or more polyacrylamide(s).

16. The method according to claim 6, wherein the ink formulation comprises one or more (meth)acrylic (co)polymer(s) resin(s).

17. The method according to claim 6, wherein the ink formulation comprises: from 20 to 95% by weight of hydrocarbon carrier liquid, from 5 to 80% by weight of one or more (meth)acrylic (co)polymer(s) resin(s), from 10 to 50% by weight of one or more carboxyl-functional ethylene comprising copolymer(s) co-resin(s) and from 0.1 to 80% by weight of one or more colorants.

18. The method according to claim 6, comprising the additional lamination step of the flexible packaging substrate to a seal layer.

19. The method according to claim 6, comprising the step of heat sealing the printed flexible substrate or the laminate in a heat sealing assembly at a temperature comprised between 100 and 250 C., preferably between 110 and 230 C., more preferably between 120 and 220 C.

20. Flow pack comprising the flexible packaging substrate according to claim 1.

Description

EXAMPLES

(1) The following illustrative examples are merely meant to exemplify the present invention but is not destined to limit or otherwise define the scope of the present invention.

Example 1

(2) A polyethylene terephthalate (PET) 12 film was treated by Corona (400 W) and subsequently introduced into the HP 20000 Indigo digital printing system where it was provided with a colorless digital primer Digiprime 050 from Michelman at a layer thickness of about 0.2 and a cyan ink layer, at a layer thickness of about 1 , was printed thereon.

(3) The digitally-printed PET film was then transferred to a vacuum electron beam processing device.

(4) The electron beam gun has a deflection system which is computer-controlled and has been programmed in a manner that the gun, was radiating onto the drum, normally used as a coating drum. The printed film, passing over this coating drum, was irradiated by the electron beam gun. The deflection system was programmed to allow the electron beam scanning over an area of 200 mm (winding direction)400 mm (cross direction) and therefore radiating this area. By passing the web with a speed of 15 m/min through this zone, the ink was irradiated for 0.6 seconds. The electron beam gun was operated at an acceleration voltage of 35 kV, resulting in electrons with an energy of 35 keV. The emission current was 0.42 A, resulting in a total radiation power of 15 kW is scanning over an area.

(5) The electron beam irradiated digitally-printed PET samples were laminated. The lamination was carried out with the use of an aromatic adhesive UK2640/H6800 against a cast-polypropylene 80 m thick film as the sealant layer.

(6) The PET/PP laminates were sealed, outside to outside, at temperatures of 150 C., 180 C., 200 C., 210 and 220 C., respectively at a pressure of 3.5 bar for 0,6 s with two heated jaws.

(7) At an irradiation dose of 10 kGy, the digital print showed defects, such as ink removal, ink shrinkage and gloss change, at sealing temperatures from 150 to 220 C. Said defects completely disappeared for an irradiation dose of 18 kGy and higher.

Example 2

(8) Example 1 was repeated, wherein the cyan ink was substituted by respectively black ink, magenta ink, orange ink, violet ink, white ink and yellow ink.

(9) At an irradiation dose of 10 kGy the digital prints of the respective colors showed similar defects as in example 1. Said defects disappeared once an irradiation dose of 18 kGy or higher was applied.

Example 3 (Comparative Example)

(10) Example 2 was repeated, yet omitting electron beam irradiation. For all colors, severe print defects were observed for sealing temperatures of 150 C. and higher.

Example 4 (Comparative Example)

(11) Example 2 was repeated wherein the respective digital prints were subjected to electron beam irradiation and wherein the irradiation dose was limited to 15 kGy. For all colors, severe print defects were observed for sealing temperatures of 200 C. and higher.

Example 5

(12) Example 1 was repeated wherein the PET film was replaced by a 30 -thick polymer coated paper. Similar results as for Example 1 were observed.