Classifications

• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D11/00—Inks
  • C09D11/02—Printing inks
  • C09D11/10—Printing inks based on artificial resins
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
  • B41M5/00—Duplicating or marking methods; Sheet materials for use therein
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
  • B41M5/00—Duplicating or marking methods; Sheet materials for use therein
  • B41M5/0041—Digital printing on surfaces other than ordinary paper
  • B41M5/0047—Digital printing on surfaces other than ordinary paper by ink-jet printing
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
  • B41M5/00—Duplicating or marking methods; Sheet materials for use therein
  • B41M5/0082—Digital printing on bodies of particular shapes
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
  • B41M5/00—Duplicating or marking methods; Sheet materials for use therein
  • B41M5/0082—Digital printing on bodies of particular shapes
  • B41M5/0088—Digital printing on bodies of particular shapes by ink-jet printing
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
  • B41M7/00—After-treatment of prints, e.g. heating, irradiating, setting of the ink, protection of the printed stock
  • B41M7/0009—Obliterating the printed matter; Non-destructive removal of the ink pattern, e.g. for repetitive use of the support
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
  • B41M7/00—After-treatment of prints, e.g. heating, irradiating, setting of the ink, protection of the printed stock
  • B41M7/009—After-treatment of prints, e.g. heating, irradiating, setting of the ink, protection of the printed stock using thermal means, e.g. infrared radiation, heat
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D11/00—Inks
  • C09D11/02—Printing inks
  • C09D11/10—Printing inks based on artificial resins
  • C09D11/101—Inks specially adapted for printing processes involving curing by wave energy or particle radiation, e.g. with UV-curing following the printing
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D11/00—Inks
  • C09D11/02—Printing inks
  • C09D11/12—Printing inks based on waxes or bitumen
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D11/00—Inks
  • C09D11/30—Inkjet printing inks
  • C09D11/36—Inkjet printing inks based on non-aqueous solvents
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D11/00—Inks
  • C09D11/54—Inks based on two liquids, one liquid being the ink, the other liquid being a reaction solution, a fixer or a treatment solution for the ink
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
  • B41M5/00—Duplicating or marking methods; Sheet materials for use therein
  • B41M5/0041—Digital printing on surfaces other than ordinary paper
  • B41M5/0064—Digital printing on surfaces other than ordinary paper on plastics, horn, rubber, or other organic polymers

Definitions

• the present invention relates generally to ink compositions for digital printing on external surfaces of plastic articles.
• the present invention also relates to plastic articles having digital images printed thereon, including plastic containers having digital images with improved adhesion and/or recycling characteristics, as well as methods for facilitating the recycling thereof.
• an ink composition for digital printing onto a plastic article generally comprises a base ink; an ink removal- promoting additive; and a carrier capable of dissolving at least a portion of the ink removal- promoting additive.
• the removal-promoting additive is configured or selected to cause at least a portion of cured droplets of ink to separate or loosen from the external surface of a plastic article when a printed digital image is exposed to a liquid-based (e.g., water-based) solution at or about a predetermined elevated temperature.
• a liquid-based e.g., water-based
• Such predetermined elevated temperature may, without limitation, include those associated with conventional recycling processes.
• a recyclable plastic article has an external surface with a digital image printed thereon by cured droplets of ink.
• the droplets of ink comprise a composition of ink as summarized above that includes a removal-promoting additive.
• Embodiments of methods for the removal of said ink from a plastic container and methods for facilitating such recycling are also disclosed.
• FIG. 1 generally illustrates a side view of a portion of a plastic container with an embodiment of a digital image printed thereon;
• FIG. 2 is general representation of a quality review table/matrix that may be used to evaluate the acceptability of a printed image on a plastic article.
• FIG. 1 For general context, and without limitation, a portion of a surface 10 of a plastic article (e.g., a container) with an embodiment of a printed image 20 is generally illustrated in FIG. 1.
• the illustrated embodiment of the image 20 includes a base coat 30 that may be comprised of a plurality of base coat ink droplets 32, and may also include a secondary coat 40 that can be comprised of a plurality of secondary coat ink droplets 42.
• Containers which include bottles associated with the present disclosure are comprised of a plastic material or resin (e.g., acrylonitrile-butadiene-styrene (ABS), polyethylene terephthalate (PET), polystyrene (PS), polyethylene (PE)(including high-density polyethylene (HDPE)), polypropylene (PP), polyvinyl chloride (PVC), etc.).
• the containers may be mono-layer or multi-layer containers, and can be formed using various conventional forming techniques including, without limitation, injection molding, blow molding, thermoforming, etc.
• the outermost layer/surface may be comprised of a virgin plastic material.
• containers in accordance with the teachings of the disclosure may also include some percentage of recycled content, including a percentage of recycled content in the outer layer of the container.
• the article may include a first coat, or base coat (e.g. base coat 30 shown in FIG. 1).
• the base coat 30 may be comprised of a plurality of base coat ink droplets 32 that are printed (e.g., digitally printed, such as by a drop-on-demand inkjet process) on an exterior surface of the article and are subsequently cured or permitted to cure.
• the ink may be UV curable ink, which is curable by UV radiation that can be applied by various known means, including but not limited to UV or LED lamps.
• the ink droplets may be monomer-based and comprised of an ink composition that serves to improve the application of the ink droplets (e.g., provides good processing characteristics for printing) and/or provides a visual characteristic (e.g., color or texture).
• the base coat 30 may comprise white and/or colorless portions.
• curing can cause the ink droplets to polymerize. Because the inks that are employed are not solvent-based, the ink can be composed so that during recycling processes the ink does not bleed in solutions and give off volatiles, as solvents might. It is noted that the U.S.
• inks such as disclosed herein can be mechanical in nature, as the ink is in a cured polymer state and may be a physically removed (e.g., in the form of flakes or film), rather than being included as part of a chemical dissolution.
• the ink composition that makes up the ink droplets includes a removal-promoting additive.
• the "removal-promoting additive” comprises at least one hydrophilic component or acidic component.
• Hydrophilic components may comprise one or more composition elements that exhibit hydrophilic (water-loving) properties.
• Acidic components may comprise one or more composition elements that exhibit acidic properties.
• the removal-promoting additive will comprise a combination of hydrophilic and acidic components— i.e., at least two removal promoting additives.
• a "dual" composition in which the removal- promoting additive comprises both hydrophilic and acid components, a lesser percentage of weight (to total) may be used to provide comparable results to the use of composition with just a single additive.
• Such hydrophilic components may include hydrophilic monomers, hydrophilic oligomers, and water dispersible monomers that provide the desired functionality.
• Hydrophilic monomers are often characterized as having oxygen or nitrogen atoms, in addition to halogens, in their backbone structure. Such monomers are commonly prone to attack by polar solvents such as water and ketones. Hydrophilic monomers also tend to have a lesser resistance to thermal degradation. Consequently, the inclusion of one or more hydrophilic components in the associated ink droplets can, at a later point (such as the point of post-use recycling), improve the separation of the image (i.e., the cured ink droplets) from the plastic structure of the article.
• the hydrophilic portion of a polymer will typically absorb water. When this occurs, the water may act as a plasticizer, increasing the mobility of the polymer's chains.
• the increased mobility can soften the polymer, making it more susceptible to removal.
• the elevated temperature may be predetermined, and may be a temperature that is above the temperature that the article will typically encounter in normal use.
• an adhesion-separation threshold may be established such that the softening and subsequent removal substantially only occurs at elevated temperatures (e.g., during a recycling process), and is substantially prevented during normal intended use.
• aliphatic urethane acrylates are a general class of hydrophilic monomers that generally absorb water and may potentially be used as a hydrophilic component.
• hydrophilic oligomers may also be used as a hydrophilic component.
• the removal-promoting additive may include hydrophilic monomers with a percent weight as to the total weight (i.e., of the associated ink and the removal-promoting additive) within the range of near 0% to as much as 20% by weight.
• the percent weight of the removal-promoting additive will fall within the range of near 0 to 10% of the total weight.
• a hydrophilic monomer that may be employed is methoxy polyethylene glycol monoacrylate (e.g., CD 553, commercialized by Sartomer USA, LLC (Sartomer)).
• water dispersible monomers are also hydrophilic and appear to absorb water when cured.
• the water may act as a plasticizer and soften the cured ink composition (e.g., a cured ink film on the surface of a container), making it easier to remove the ink film during recycling processing.
• the inclusion of an appropriate hydrophilic component to the ink composition can add a hydrophilic quality to the ink, while maintaining the jet-ability and adhesion of the ink to the article substrate throughout the useful life of the article.
• Acidic components include acidic monomers that have a measurable acidic value. It is noted that the measurable quantity may be based on pH, acid weight percentage, or titrated value of an alkaline chemical (e.g., mg KOH/g [milligrams of potassium hydroxide per gram of monomer]). Further, for example, in a cured state, the acidic portion of the polymer may be vulnerable to a caustic solution. A reaction between the acidic functionality of the polymer chain and the alkalinity of the solution can yield a decrease in adhesion to the applied substrate, promoting the separation of the polymer.
• an alkaline chemical e.g., mg KOH/g [milligrams of potassium hydroxide per gram of monomer]
• acidic monomers examples include acidic acrylate oligomer (e.g., CN 147, commercialized by Sartomer) and monofunctional acid ester (e.g., CD 9050, commercialized by Sartomer).
• acidic acrylate oligomer e.g., CN 147, commercialized by Sartomer
• monofunctional acid ester e.g., CD 9050, commercialized by Sartomer
• a wash e.g., a conventional-type caustic wash
• associated bonds may be broken, promoting an intended separation of the printed image (droplets of ink) from the plastic substrate.
• the removal-promoting additive is configured or otherwise selected according to its desired properties that can facilitate the removal of a cured ink composition from the surface of a plastic article.
• the removal-promoting additive exhibits a glass transition temperature (Tg) that is less than about 130 ° C.
• the ink removal-promoting additive has a glass transition temperature (Tg) in the range of from about 50 ° C to about 130 ° C.
• the ink removal -promoting additive has a glass transition temperature (Tg) in the range of from about 55 ° C to about 125 ° C, or from about 65 ° C to about 105 ° C, or from about 55 ° C to about 95 ° C.
• the ink removal-promoting additive can have a glass transition temperature (Tg) in any range derived from any of the above exemplary values.
• the desired level of aqueous solubility can be characterized as a function of, for example, the acid number of the removal- promoting additive.
• the acid number can be expressed in terms of a titrated value of an alkaline chemical (e.g., mg KOH/g [milligrams of potassium hydroxide per gram of removal- promoting additive]).
• the removal -promoting additive can exhibit an acid number in the range of from about 100 mg KOH/ gm to about 250 mg KOH/ gm, including values of 110 mg KOH/ gm, 120 mg KOH/ gm,130 mg KOH/ gm, 140 mg KOH/ gm, 150 mg KOH/ gm, 160 mg KOH/ gm, 170 mg KOH/ gm, 180 mg KOH/ gm, 190 mg KOH/ gm, 200 mg KOH/ gm, 210 mg KOH/ gm, 220 mg KOH/ gm, 230 mg KOH/ gm, and 240 mg KOH/ gm.
• 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, including values of 175 mg KOH/ gm, 185 mg KOH/ gm, and 195 mg KOH/ gm.
• the ink removal-promoting additive can have an acid number in any range derived from any of the above exemplary values.
• the removal-promoting additive can exhibit a glass transition temperature (Tg) that is less than about 100 ° C and an acid number in the range of from about 100 mg KOH/ gm to about 250 mg KOH/ gm.
• the ink removal-promoting additive can exhibit a glass transition temperature (Tg) in the range of from about 50 ° C to about 90 ° C and an acid number in the range of from about 150 mg KOH/ gm to about 205 mg KOH/ gm.
• the ink removal-promoting additive can have a glass transition temperature (Tg) and an acid number in any range derived from any of the above exemplary values.
• These removal-promoting additives can be present in the ink compositions in an amount from about 1 to about 20 weight percent of the ink composition. This can further include specific exemplified amounts of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 , 12, 13, 14, 15, 16, 17, 18, and 19 weight percent.
• the ink removal -promoting additive can be present in an amount any range of amounts derived from any of the above exemplary values.
• the removal-promoting additives can be present in the ink compositions in an amount from about 5 to about 20 weight percent of the ink composition.
• ink removal-promoting additives that exhibit the above combination of aqueous solubility and relatively low glass transition temperature include the styrene maleic anhydride resins.
• the styrene maleic anhydride resins can be a copolymer of styrene maleic anhydride copolymer.
• the styrene maleic anhydride is esterified styrene maleic anhydride.
• Exemplary non- limiting commercially available styrene maleic anhydride resins that are suitable for use as a removal-promoting additive are the Cray Valley SMA®3840 and SMA®1440F resins from Total.
• the ink composition that makes up the ink droplets also comprises a carrier capable of solubilizing and dissolving at least a portion of the ink removal-promoting additive.
• the carrier can be monomer based or solvent based.
• Exemplary monomers that can be used as a carrier include the class of acrylic monomers.
• suitable acrylic monomers can include 1 ,3-butylene glycol diacrylate, 1 ,6-hexanediol diacrylate, 1,3-butylene glycol dimethacrylate, isobornyl acrylate, or isodecyl methacrylate, or a combination thereof.
• the acrylic monomer is selected from 1,3-butylene glycol diacrylate, 1,6-hexanediol diacrylate, and 1,3-butylene glycol dimethacrylate.
• the carrier capable of solubilizing the removal- promoting additive can be solvent based.
• Suitable solvents can, in some aspects, be aprotic solvents or aqueous based solvents.
• suitable solvent carriers include N-methyl-2-pyrrolidone (NMP) and acetone.
• the carrier component can be present in the ink compositions in an amount from about 1 to about 20 weight percent of the ink composition. This can further include specific exemplified amounts of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 , 12, 13, 14, 15, 16, 17, 18, and 19 weight percent. In a further aspect, the carrier can be present in an amount any range of amounts derived from any of the above exemplary values. For example, the carrier can be present in the ink compositions in an amount from about 5 to about 15 weight percent of the ink composition.
• the base ink portion of the ink composition can be any conventionally known curable ink, such as conventional UV curable ink.
• the base ink can be present in the ink composition in an amount in the range of about 50 to about 85 weight percent of the ink composition, including exemplary weight percent values of 51 , 52, 53, 54, 55, 56, 57, 58, 59, 60, 61 , 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, and 84 weight percent.
• the base ink can be present in any range of amounts that is derived from any of the above exemplary values.
• base ink can be present in the ink compositions in an amount from about 65 to about 85 weight percent of the ink composition.
• a ink composition comprising:
• the base ink can be a base UV white ink
• the ink removal promoting additive can be styrene maleic anhydride resin
• the carrier can be solvent based and can comprise N-methyl-2-pyrrolidone (NMP), or acetone, or other acceptable solvent.
• an exemplary recyclable plastic article comprises 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 a composition including an ink removal- promoting additive having a glass transition temperature less than about 100 ° C.
• the digitally -printed image has an adhesion score of at least 6.0 and up through 9.0
• 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 the basic solution at an elevated temperature of at least about 70° C.
• the article comprises a plastic container.
• the plastic container is a bottle.
• the plastic container is comprised of one or more of the following materials: polyethylene, polyethylene
• the removal-promoting additive present in the ink composition 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 an a liquid based solution, such as an aqueous or water based solution, at a predetermined elevated temperature.
• an a liquid based solution such as an aqueous or water based solution
• the cured droplets of ink can 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 of at least about 10, 1 1, 12, or 13 and an elevated temperature in the range of from about 70 to 90° C.
• the basic solution has a pH in the range of from about 12-13.
• 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.
• PET polyethylene terephthalate
• the blended removal -promoting additive of the tested containers included acidic monomers of the type noted above, i.e., acidic acrylate oligomer and/or monofunctional acid ester.
• the containers may be subj ected to a bath solution comprising a pH level of at least 9.0, which can assist label removal as generally known in the art of plastic container recycling, with the solution being heated to approximately 85° C.
• Various samples were exposed to such conditions for 12 minutes, and were evaluated on a scale of 0 to 5 as follows:
• the testing was intended to, among other things, identify solutions that provided a removal performance level of 4 or 5. However, a level of at least 4 is not necessarily a requirement, and for some applications a lower removal level may also be acceptable.
• the results of the testing indicated that the inclusion of the removal-promoting (acidic) additives blended into the ink composition provided a significant improvement in the removal of the cured ink from the plastic (PET) material. While both forms of acidic additives exhibited an improvement promoting ink removal, with the instant test
• the ink composition may optionally include a hydrophobic component. That is, the ink composition may, for example, include hydrophilic and hydrophobic components. Hydrophobic components may include hydrophobic (water-hating) monomers. The hydrophobic properties generally relate to polarity. A number of hydrophobic monomers are characterized as having an organic backbone structure composed primarily of hydrogen and carbon; and thus, such monomers tend to be non-polar and offer resistance to polar solvents (such as water and alcohols), as well as to acids and bases.
• the ink composition should strike a balance between the hydrophilic and hydrophobic components (e.g., hydrophilic monomers and hydrophobic monomers).
• the hydrophobic monomers may help keep the ink drops adhered to the article substrate, and the hydrophilic monomers may help soften (and even separate) when the image is exposed to a recycling process/bath (e.g., agitated water at an elevated temperature).
• a first base coat 30 (which may include a hydrophilic component) may be applied to a surface of a container at a first time ti and at a first temperature Ti.
• the temperature Ti will be in the range of temperatures that are appropriate for application of the associated base coat.
• the base coat 30 may be curable (e.g., ultraviolet (UV) curable), and further may be cured prior to an application of a secondary coat.
• a secondary coat 40 may be comprised of a plurality of secondary coat ink droplets 42 that are distributed on at least a portion of the base coat 30. Further, if desired, additional layers of "secondary" coats (e.g., a tertiary layer, etc.) may also be applied on the secondary coat 40. With embodiments of the disclosure, the secondary coat ink droplets 42 may also be comprised of an ink composition including a hydrophilic component.
• a plurality of secondary coat ink droplets 42 may collectively form a part of an application partem which, in turn, may form all or a portion of an image. Furthermore, as generally illustrated in FIG. 1, portions of one or more adjacent secondary coat ink droplets 42 may overlap or intermix with each other.
• the secondary coat 40, and the constituent secondary coat ink droplets 42 may comprise various known colors, including without limitation, primary printing colors such as cyan, magenta, and yellow. Further, controlling the overlapping of or combinations of certain colors in certain areas can provide additional "process" colors. Additionally, the secondary coat ink droplets 42 may be curable. For example, UV curable secondary coat ink droplets may comprise all or a portion of the intended image.
• the ink composition may include a photo initiator. It is additionally noted that cured ink on a container surface may be primarily held by two bonds— i.e., a polar bond between the ink polymer and the plastic, and a mechanical bond due to the plastic surface having an uneven surface at a microscopic level (e.g., microstructures). For a number of embodiments of the present disclosure, it is best to attack both bonds. For some applications, a hydrophilic component may work better on mechanical bonds, while an acidic component may work better on polar bonds.
• the secondary coat ink droplets can vary in diameter, which can range, for instance, from about 10 microns to about 200 microns.
• the secondary coat 40 may be applied to a surface 10 of a container at a second time t2 and at a second temperature T 2 , wherein the second temperature T 2 at which the secondary coat 40 is applied is typically less than the first temperature Ti at which the base coat 30 is applied.
• the time between application of a base coat and the application of a secondary coat may be reduced— for example, to as little as ten seconds or less.
• the application time differential will be within two to six seconds.
• the application temperature differential between the temperature at which the base coat 30 is applied and the temperature at which a secondary coat 40 is applied to a portion of the base coat 30, i.e., Ti minus T 2 may be controlled to be equal to or less than about 10° F.
• the application temperature differential will be within about 5° F. to about 10° F.
• This can be accomplished, for instance, by (a) lowering/decreasing T 1; (b) raising/increasing T 2 , or (c) a combination of (a) and (b).
• Such aforementioned time and/or temperature control with respect to the base coat and secondary coat can provide for better adhesion of the resulting printed image with respect to the article.
• irradiance is a factor that can also affect the effective cure rate for a printed image.
• Irradiance i.e., si and 82.
• a base coat may be cured at irradiance ⁇ 1; and an associated secondary coat may be cured at irradiance 82.
• the effective cure rate— which may be based on a combination of time, temperature, and irradiance— the irradiance may generally be provided by the following equation:
• embodiments will be between about 0.1 watts/cm 2 and about 10.0 watts/cm 2 .
• the relevant coat or ink may be cured after each respective print station.
• a process may, at least in part, comprise: application of base coat; cure step; application of secondary coat; and cure step.
• the process may, at least in part, comprise: application of base coat; cure step; application of base coat; cure step; application of secondary coat, and cure step.
• the quality of printed images may be, at least in part, controlled and/or improved through one or more of the following techniques:
• the selection and/or calibration of the inks comprising the base and secondary coats can be selected to provide desired time and/or temperature characteristics, including relative to one another in combination. For example, selection of certain inks having given viscosities can exhibit or provide certain desired temperature related effects.
• the temperature of a relevant portion of a sidewall can be treated or controlled to some measure.
• a given portion of the container can be pre-treated.
• Such pre-treatment can be facilitated using various known techniques that may include, without limitation, flame, corona, and plasma treatment.
• the invention is not limited to those specific pre-treatment techniques.
• the time associate with the movement of containers for instance through a production machine, as well as the timing of the applications of the base coat and/or secondary coat, can be controlled. It can be desirable for the production/subsequent handling rate of containers/bottles to match or substantially match the flow/processing rates of the associated printing machine(s).
• the present disclosure may also include a system for assessing or evaluating the "acceptability,” such as the commercial acceptability, of a container having a printed image—such as a digitally printed label. That is, for embodiments of the invention, the system for assessing or evaluating can provide an "adhesion score.”
• FIG. 2 generally represents a quality review table/matrix that can be used to assess or evaluate the
• the Y-axis may involve numbers associated with an overall pass-or-fail score.
• numbers 1 through 5 indicate that the containers are not acceptable, while numbers 6 through 9 indicate that the associated containers are acceptable.
• a plurality of tests which may include various standard tests, including those previously noted— are represented in the columns provided on the X-axis.
• Test 1 may include a "Sutherland Rub Test”
• Test 2 may comprise a “3M #610 Tape Test”
• Test 3 may include a “Simulated Ship Test”
• Test 4 may comprise a "3M #810 Tape Test.”
• various pass-or-fail designations may be represented on the table in connection with each noted Test.
• the tests may be modified as appropriate for use in connection with a printed image as opposed to a traditionally applied label.
• the tests associated with the table/matrix may or may not involve the cutting of the image portion with a cutting tool prior to applying a pressure sensitive tape. That is, in an embodiment, "Test 2" may involve a "modified” 3M #610 Tape Test in so far as the portion of the image portion of a container that is subjected to testing may not be cross-cut or otherwise separated from the container.
• an indication of a "pass,” with respect to tape tests directly practicing the modified ASTM standard i.e., the test does not involve cross-cutting/separation
• an indication of "pass” would generally be a classification "4B” or "5B” (under the ASTM FIG. 1 Classification of Adhesion Test Results), or would involve less than 5% of the printed area removed.
• a digital image that is printed on a container is considered to be “recyclable” if it would achieve less than a "4B" classification (i.e., 5% of more of the area is removed) employing an ASTM D 3359 standard #810 tape test.
• Such a container with a printed image having an adhesion score of 6.0 or 7.0 is commercially suitable for shipment (i.e., passing a Simulated Ship Test) while providing an adhesion associated with the printed image that is sufficient for normal/intended use but is favorably separable for subsequent recycling.
• the adhesion associated with the configured digital image is sufficiently strong for intended use but does not impede separation during recycling.
• each test may be conducted on an adequate (e.g., statistically significant or representative) sampling of containers. After all tests are completed, results may be tabulated and entered into the table/matrix, to provide an "adhesion" score. The associated score outcomes can then be correlated.
• containers with digitally printed images (which may be formed by cured UV or radiation curable ink) that are comprised, at least in part, of an ink composition including a hydrophilic and/or an acidic component can be conveniently removed in connection with conventional plastic recycling processes.
• Industry standard recycling process of plastic containers conventionally include grinding containers into granulated plastic flakes, subjecting these flakes to a high-heat caustic wash process, drying the cleaned flakes, sorting, and extruding into resin pellets for resale.
• digital image on the container may remain with the resin flakes after the grinding process, the digital image will be substantially separated from the resin flakes during the high-heat caustic wash process, which may be agitated, and thereby not contaminating the clean resin flakes to be formed into resin pellets.
• the techniques include those using: (1) water or liquid-based solutions (e.g., for additives with hydrophilic components or having the desired Tg and acid numbers as described herein); (2) caustic components (e.g., for additives with acidic components or the desired combination of Tg and acid number as described herein)— i.e., chemical reactions may be used to release polar bonds; (3) heat or temperature; and/or (4) mechanical force (e.g., high pressure spray (psi)).; or any combinations thereof.
• the disclosure envisions a number of recycling processes that may be used to remove the ink from the article.
• one embodiment of a method for recycling plastic containers comprises: providing a plastic container having a digital image, the ink composition including a removal-promoting additive (e.g., a hydrophilic or acidic component); and exposing the digital image to a liquid-based solution— e.g., water with or without a caustic component)— at an elevated temperature; optionally agitating the solution.
• a removal-promoting additive e.g., a hydrophilic or acidic component
• a liquid-based solution e.g., water with or without a caustic component
• the container may be subject to a grinding operation. Similar embodiments may be said to be along the lines of including dry grind, elutriate, wash, dry, and elutriate.
• Another process which may be more similar to conventional industrial recycling and is commercially available (for example, from SOREMA (Italy)), may be said to involve a single wash, wet grinding, centrifuge, sorting, and float tank/separation.
• a "single wash” may, for instance, be employed by having bottles conveyed (e.g. by a set screw or multi-screw system) through a high-pressure wash (e.g., a high-temperature caustic wash). This can add a mechanical force component to assist with label removal.
• the bottles are whole— that is, not ground prior to such a wash. Materials, including polymerized inks, may be washed away and fall into a collection or grating system below the conveying mechanism.
• the present disclosure provides 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 100 ° 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.
• the plastic container is a bottle.
• the plastic container is comprised
• the ink removal-promoting additive comprises a styrene maleic anhydride copolymer.
• the ink removal-promoting additive has a glass transition temperature (Tg) in the range of from about 50 ° C to about 130 ° C.
• the ink removal-promoting additive has a glass transition temperature (Tg) in the range of from about 65 ° C to about 110 ° C.
• the ink removal- promoting additive has a glass transition temperature (Tg) in the range of from about 55 ° C to about 65 ° C.
• 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. In a still further aspect, 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.
• 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 to 90° C.
• the step of removing includes scratching or wiping the ink from the container after exposure of the image to the basic solution.
• the ink is mechanically removed in the form of flakes or film.
• various ink compositions according to the present disclosure were prepared and tested for use in direct printing on an external surface of a plastic article.
• the ink compositions can be prepared by first dissolving the ink removal-promoting additive in the carrier, and then adding the carrier solution to a base ink.
• the prepared ink composition can then be used in direct printing on the external surface of the plastic article.
• the ink compositions including UV-curable ink having a removal-promoting additive and a carrier, were direct printed on the surface of a polyethylene terephthalate (PET), polyethylene (PE), and/or high density polyethylene (HDPE) samples and cured.
• PET polyethylene terephthalate
• PE polyethylene
• HDPE high density polyethylene
• the cured ink of the sample was then subjected to ink-removal testing, which can include testing of one or more of: adhesion, scratch resistance and solvent resistance properties.
• the samples can be subjected to various bath solutions which can assist label removal as generally known in the art of plastic container recycling, for example, a bath solution comprising a pH level of at least 9.0 and with the solution being heated to approximately 75°C or 85°C.
• the testing was performed at time periods including immediately after treatment (imm) and at 1 hour (lhr) after treatment.
• the removal-promoting additives of the tested samples were waxes and resins.
• the carrier was acetone or N-methyl-2-pyrrolidone (NMP) (commercially available from Sigma Aldrich).
• NMP N-methyl-2-pyrrolidone
• Tables 2-5 The inventive ink formulations and performance data are provided in Tables 2-5 below. For the following data, "pass” indicates that no ink removal was observed, and “fail” indicates that significant and/or complete ink removal was observed. Any % value listed corresponds to the observed % ink removal.
• Formulation scratch scratch 610 tape scratch scratch 610 tape imm 1 hr 1 hr imm 1 hr imm
• the SMA3840 and SMA1440F ink formulation samples exhibited improved performance.
• the SMA3840 ink formulation showed some signal of improvement, which indicates an improvement in ink removal when compared to control.
• the SMA1440F ink formulation demonstrated no significant signal during normal use ("in use") tests, but strong removal during caustic wash testing. Testing was repeated several times on PET, EPET, and PE, all showing good removal in the caustic test. 2 EXAMPLE 2.
• ink compositions including white UV-curable ink having a removal-promoting additive and a carrier, were direct printed on the surface of a polyethylene terephthalate (PET) and high density polyethylene (HDPE) samples and cured.
• the removal- promoting additive of the tested samples was styrene maleic anhydride copolymer
• inventive ink compositions As the data show, near 100% removal of the inventive ink compositions were observed compared with only 50-60% removal of the standard ink controls. On HDPE samples, the inventive ink compositions exhibited greater than 50% ink removal compared to only approximately 10% ink removal for the standard ink controls. The inventive ink compositions results satisfy the current recycle guidelines published by The Association of Postconsumer Plastic Recyclers.

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