Methods and compositions for direct print having improved recyclability
The disclosure relates to ink compositions for digital printing on an external surface of a plastic article. The ink compositions comprise an ink removal-promoting additive. In some aspects, the ink removal-promoting additive can facilitate the separation or loosening of the image from the external surface of the article when the image is exposed to a liquid-based solution at an elevated temperature. Also disclosed are recyclable plastic articles having an external surface with an image printed thereon using the disclosed ink composition and methods for removing cured ink from a plastic container. This abstract is intended as a scanning tool for purposes of searching in the particular art and is not intended to be limiting of the present invention.
1. An ink composition for digital printing onto a plastic article, comprising:
(a) from 65 to 85 weight percent of an ultraviolet-curable (UV-curable) base ink;
(b) from 5 to 20 weight percent of an ink removal-promoting additive having one or more selected from an acid number in the range of from 100 mg KOH/gm to 250 mg KOH/gm and a glass transition temperature (Tg) of less than about 130° C., wherein the ink removal-promoting additive comprises a styrene maleic anhydride copolymer; and
(c) from 5 to 15 weight percent of a carrier capable of dissolving at least a portion of the ink removal-promoting additive, wherein the carrier is one or more aprotic solvents.
2. The ink composition of claim 1 , wherein the ink removal-promoting additive is a styrene maleic anhydride resin.
3. The ink composition of claim 1 , wherein the ink removal-promoting additive has a glass transition temperature (Tg) in the range of from 55° C. to 65° C.
4. The ink composition of claim 1 , wherein the ink removal-promoting additive has an acid number in the range of from 165 mg KOH/gm to 205 mg KOH/gm.
5. The ink composition of claim 1 , wherein the aprotic solvent is N-methyl-2-pyrrolidone (NMP), acetone, or a combination thereof.
6. The ink composition of claim 1 , wherein the UV-curable base ink is a white UV-curable base ink.
7. The ink composition of claim 6 , wherein the aprotic solvent is NMP, acetone, or a combination thereof.
8. The ink composition of claim 1 , wherein the ink composition consists essentially of:
(a) from 71 to 85 weight percent of the UV-curable base ink;
(b) from 5 to 20 weight percent of the ink removal-promoting additive-having; and
(c) from 5 to 15 weight percent of the carrier capable of dissolving at least a portion of the ink removal-promoting additive.
9. The ink composition of claim 8 , wherein the ink removal-promoting additive is a styrene maleic anhydride resin.
10. The ink composition of claim 8 , wherein the UV-curable base ink is a white UV-curable base ink.
11. The ink composition of claim 8 , wherein the aprotic solvent is N-methyl-2-pyrrolidone (NMP), acetone, or a combination thereof.
12. A recyclable plastic article comprising a curved external surface with a digitally-printed image printed directly on the curved external surface, the image comprising droplets of the ink composition of claim 1 .
13. A recyclable plastic article comprising a curved external surface with a digitally-printed image printed directly on the curved external surface, the image comprising cured droplets of ink, and the droplets of ink comprising the composition of claim 1 , wherein the digitally-printed image has an adhesion score of at least 6.0 and up through 9.0, and the removal-promoting additive is configured to cause the cured droplets of ink to separate or loosen from the curved external surface of the article when the digitally-printed image is exposed to a basic solution at an elevated temperature of at least about 70° C.
14. The plastic article of claim 13 , wherein the article comprises a plastic container.
15. The plastic article of claim 14 , wherein the plastic container is a bottle.
16. The plastic article of claim 13 , wherein the ink removal-promoting additive has a glass transition temperature (Tg) in the range of from 55° C. to 65° C.
17. The plastic article of claim 13 , wherein the ink removal-promoting additive has an acid number in the range of from 165 mg KOH/gm to 205 mg KOH/gm.
18. The plastic article of claim 13 , wherein the article is comprised of one or more of the following materials: polyethylene, polyethylene terephthalate, high density polyethylene, and polypropylene.
19. The plastic article of claim 13 , wherein the ink removal-promoting additive is configured to cause the cured droplets of ink to separate or loosen from the curved external surface of the article when the digitally-printed image is exposed to a basic solution having a pH in the range of from 12 to 13 at an elevated temperature in the range of from 70° C. to 90° C.
20. The plastic article of claim 19 , wherein after an exposure to the basic solution at the elevated temperature, at least 90 weight percent of the cured ink droplets separate from the curved external surface of the article.
21. The plastic article of claim 13 , wherein the digitally-printed image includes a base coat including a plurality of cured base coat ink droplets, and a secondary coat including a plurality of cured secondary coat ink droplets, the secondary coat being applied to at least a portion of the base coat.