Radiation curable compositions for food packaging

1. A radiation curable inkjet ink set comprising:

at least a cyan radiation curable inkjet ink, a magenta radiation curable inkjet ink, a yellow radiation curable inkjet ink, and a black radiation curable inkjet ink each having a viscosity of no more than 50 mPa·s at 25° C. and a shear rate of 90 s −1 , and each including:

at least one non-polymerizable, non-polymeric bisacylphosphine oxide present in a concentration of no more than 4.0 wt % based on a total weight of the radiation curable inkjet ink;

at least one monomer includes at least one vinyl ether group and at least one polymerizable group selected from the group consisting of an acrylate group and a methacrylate group; and

at least one polymerizable or polymeric thioxanthone, wherein if the at least one polymerizable or polymeric thioxanthone contains no tertiary amine group, then the radiation curable inkjet ink further includes at least one tertiary amine co-initiator selected from the group consisting of ethylhexyl-4-dimethylaminobenzoate, a polymerizable co-initiator containing a tertiary amine, and a polymeric co-initiator containing a tertiary amine; wherein

the at least one polymerizable or polymeric thioxanthone is a polymerizable thioxanthone according to Formula (I):

wherein

k is an integer equal to 0;

n represents an integer equal to 0 or 1, and m is equal to 1;

L represents a divalent linking group coupling A to the thioxanthone ring via an ether bond; and

A represents a structural moiety including 1 to 6 free radical polymerizable ethylenically unsaturated bonds;

or

the at least one polymerizable or polymeric thioxanthone is:

2. The radiation curable inkjet ink set according to claim 1 , wherein the at least one non-polymerizable, non-polymeric bisacylphosphine oxide is selected from the group consisting of bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide and bis(2,6-dimethoxybenzoyl)(2,4,4-trimethylpentyl)phosphine oxide.

3. The radiation curable inkjet ink set according to claim 1 , wherein the at least one non-polymerizable, non-polymeric bisacylphosphine oxide is present in an amount of 1.0 to 3.5 wt % based on a total weight of the radiation curable inkjet ink.

4. The radiation curable inkjet ink set according to claim 1 , wherein each of the radiation curable inkjet inks includes at least 10 wt % of a monomer according to Formula (III) wherein all wt % are based on the total weight of the radiation curable inkjet ink:

wherein

R 4 represents a hydrogen or a methyl group; and

L represents a divalent linking group selected from the group consisting of a substituted or unsubstituted alkylene group, a substituted or unsubstituted alkenylene group, a substituted or unsubstituted alkynylene group, a substituted or unsubstituted cycloalkylene group, and an ether containing alkylene group.

5. The radiation curable inkjet ink set according to claim 1 , wherein the black radiation curable inkjet ink includes a mixture of colour pigments.

6. The radiation curable inkjet ink set according to claim 1 , wherein the at least one polymerizable or polymeric co-initiator containing a tertiary amine includes one or more 4-dialkylaminobenzoate groups.

7. The radiation curable inkjet ink set according to claim 1 , wherein the at least one monomer is selected from the group consisting of:

8. The radiation curable inkjet ink set according to claim 7 , wherein each of the radiation curable inkjet inks includes a polymerizable composition consisting essentially of:

a) 25 to 100 wt % of 2-(2-vinyloxyethoxy)ethyl acrylate;

b) 0 to 55 wt % of one or more polymerizable compounds A selected from the group consisting of monofunctional acrylates and difunctional acrylates; and

c) 0 to 55 wt % of one or more polymerizable compounds B selected from the group consisting of trifunctional acrylates, tetrafunctional acrylates, pentafunctional acrylates and hexafunctional acrylates, wherein if a weight percentage of compounds A>24 wt %, then a weight percentage of compounds B>1 wt %; wherein

all weight percentages of A and B are based upon a total weight of the polymerizable composition.

9. A packaging comprising:

an outer surface; and

a cured layer of a radiation curable inkjet ink on the outer surface, the radiation curable inkjet ink being one of the radiation curable inkjet inks according to claim 1 .

10. A method of preparing a radiation curable inkjet ink set including at least a cyan radiation curable inkjet ink, a magenta radiation curable inkjet ink, a yellow radiation curable inkjet ink, and a black radiation curable inkjet ink, each having a viscosity of no more than 50 mPa·s at 25° C. and a shear rate of 90 s −1 , the method comprising the steps of:

for each of the radiation curable inkjet inks, mixing:

at least one non-polymerizable, non-polymeric bisacylphosphine oxide;

at least one monomer including at least one vinyl ether group and at least one polymerizable group selected from the group consisting of an acrylate group and a methacrylate group; and

at least one polymerizable or polymeric thioxanthone, wherein if the at least one polymerizable or polymeric thioxanthone contains no tertiary amine group, then the radiation curable inkjet ink further includes at least one tertiary amine co-initiator selected from the group consisting of ethylhexyl-4-dimethylaminobenzoate, a polymerizable co-initiator containing a tertiary amine, and a polymeric co-initiator containing a tertiary amine, wherein the bisacylphosphine oxide is present in each of the radiation curable inkjet inks in a concentration of no more than 4 w % based on a total weight of the radiation curable inkjet ink; wherein

the at least one polymerizable or polymeric thioxanthone is a polymerizable thioxanthone according to Formula (I):

wherein

k is an integer equal to 0;

n represents an integer equal to 0 or 1, and m is equal to 1;

L represents a divalent linking group coupling A to the thioxanthone ring via an ether bond; and

A represents a structural moiety including 1 to 6 free radical polymerizable ethylenically unsaturated bonds;

or

the at least one polymerizable or polymeric thioxanthone is:

11. A method of manufacturing a food packaging comprising the steps of:

providing a radiation curable inkjet ink set as defined by claim 1 ; and

inkjet printing an image on the food packaging with the radiation curable inkjet ink set.

12. The method according to claim 11 , wherein the food packaging includes a substrate including a surface selected from polyethylene, polypropylene, polycarbonate, polyvinyl chloride, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polylactide (PLA), and polyimide.

13. The method according to claim 11 , further comprising the step of:

at least partially curing the image with one or more UV LEDs.