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. A method for removing cured ink from a plastic container, the method comprising:
(a) providing a plastic container having a curved external surface with a digital image printed directly on the curved external surface of the plastic container by a drop-on-demand ink jet printing process, the image comprising cured droplets of ink applied directly to the curved external surface of the plastic container and having an adhesion score of at least 6.0 and up through about 9.0, and the droplets of ink comprising a composition including an ink removal-promoting additive having a glass transition temperature less than about 130° C.;
(b) exposing at least a portion of the digitally printed image of the plastic container to a basic solution at an elevated temperature of at least about 70° C.; and
(c) removing at least a portion of the digitally printed image from the curved external surface on which the image was printed.
2. The method of claim 1 , wherein the container is a bottle.
3. The method of claim 1 , wherein the ink removal-promoting additive comprises a styrene maleic anhydride copolymer.
4. The method of claim 1 , wherein the ink removal-promoting additive has a glass transition temperature (Tg) in the range of from about 50° C. to about 110° C.
5. The method of claim 1 , wherein the ink removal-promoting additive has a glass transition temperature (Tg) in the range of from about 55° C. to about 85° C.
6. The method of claim 1 , wherein the ink removal-promoting additive has a glass transition temperature (Tg) in the range of from about 55° C. to about 65° C.
7. The method of claim 1 , wherein the ink removal-promoting additive has an acid number in the range of from about 150 mg KOH/gm to about 205 mg KOH/gm.
8. The method of claim 1 , wherein the ink removal-promoting additive has an acid number in the range of from about 165 mg KOH/gm to about 205 mg KOH/gm.
9. The method of claim 1 , wherein the basic solution is an aqueous solution having a pH in the range of about 12-13 and wherein the elevated temperature is in the range of from about 70° C. to about 90° C.
10. The method of claim 1 , wherein the plastic container is comprised of one or more of the following materials: polyethylene, polyethylene terephthalate, high density polyethylene, and polypropylene.
11. The method of claim 1 , wherein the step of removing includes scratching or wiping the ink from the container after exposure of the image to the basic solution.
12. The method of claim 1 , wherein the ink is mechanically removed in the form of flakes or film.