Classifications

• • 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
  • B41M5/50—Recording sheets characterised by the coating used to improve ink, dye or pigment receptivity, e.g. for ink-jet or thermal dye transfer recording
  • B41M5/52—Macromolecular coatings
  • B41M5/5227—Macromolecular coatings characterised by organic non-macromolecular additives, e.g. UV-absorbers, plasticisers, surfactants

Definitions

• the present invention is directed generally to improving lightfastness of ink for inkjet printing, and, more particularly, to coated print media including at least an ink-receptive layer containing a photoinitiator to improve the lightfastness of the ink.
• Inkjet dyes can degrade by many mechanisms once dried in an inkjet receptive coating.
• UV radiation may enter the coating, strike a dye molecule and cleave a bond in the chromophore, thus changing/eliminating its color characteristics.
• Free radical formation has proven to be another enemy of dyes.
• Any quasi-stable mobile formation has proven to be another enemy of dyes.
• Any quasi-stable mobile electrons in a coating could attack the chromophore and result in its demise. Thermal and chemical degradation could also reduce the dye's ability to absorb and reflect at the desired wavelength.
• oxygen may diffuse freely into our coatings, be struck by UV radiation, and form singlet oxygen. This singlet oxygen acts much like a free radical in that it catalyzes the degradation of dyes.
• the most probable mechanism for the photoinitiator LF improvement stems from the reduction in singlet oxygen formation.
• the UV radiation that would normally form singlet oxygen is preferentially absorbed by the initiator that then crosslinks the polymers used in the media coating, e.g., polyethylene oxide.
• a small amount of photoinitiator in a coating on glossy print media tends to improve lightfastness by about 5 to 20%.
• the photoinitiator is included in the coating in the range of about 0.001 to 0.01 wt%, resulting in a concentration after drying the coating of about 0.008 to 0.08 wt%, based on a total solids content of 12 wt% in the coating composition prior to applying and drying it on the print media.
• a print medium having at least one coating thereon, including an inkjet receptive coating. At least the inkjet receptive coating contains the photoinitiator.
• a method for improving lightfastness in coated print media provided with the inkjet receptive coating comprises:
• the magnitude of the lightfastness improvement has varied by formulation, but there is always some improvement over the same system without the photoinitiator.
• the coating comprises (a) a binder comprising (1) an organic polymer which is substantially free of onium groups and (2) an onium addition polymer consisting essentially of onium-containing mer units derived from addition monomer and onium-free mer units derived from addition monomer of which from 20 to 100 wt% is hydrophobic addition monomer, wherein the binder constitutes from 20 to 90 wt% of the coating; and (b) finely divided substantially water-insoluble pseudoboehmite particles which have a maximum dimension of less than 500 nm, are distributed throughout the binder, and constitute from 10 to 80 wt% of the coating.
• the coating also referred to as an inkjet receptive coating herein, is formed on a backing substrate, which can comprise a porous or non-porous substrate, which is transparent or opaque or intermediate therebetween.
• a suitable substrate is of a photobase construction, comprising a paper base with a polyethylene film molten-extruded thereon.
• the '196 patent is one example of a coating composition for inkjet printing media. Another example is disclosed and claimed in application Serial No. 09/491,642. filed January 27, 2000.
• a process is provided that allows the production of multi-layer coatings in which one or more topcoats can be applied to a porous basecoat to produce a uniform and defect-free coating layer.
• a process is provided in which a liquid (called a "re-wetting" liquid) is applied to the basecoat prior to topcoating such that the air in the basecoat is removed prior to topcoating. This process can occur in-line with a simple apparatus as described therein.
• the wetting liquid may contain, but is not limited to, surfactants, pH modifiers, polymers, crosslinkers, pigments, and/or dye stabilizers.
• Advantages over what has been done before include the use of re-wetting process that allows a topcoat to be applied to a porous basecoat that is coated on a non-porous substrate such that bubbles are not formed in the topcoat.
• the process is simple to implement and is compatible with many general coating methods, such as slot-die coating, rod coating, blade coating, gravure coating, knife-over-roll coating, or the like.
• ink-receptive coatings applied to print media, and are suitably modified by the teachings herein to provide inkjet printed ink with improved lightfastness.
• Other ink-receptive coatings may be similarly modified according to the teachings herein to provide inkjet printed ink with improved lightfastness.
• the coating composition is modified to include a photoinitiator in the amount of 0.001 to 0.01 wt% in the formulation used to apply the coating.
• the coating composition that is so modified is the final coating, e.g., topcoat or ink-receptive layer, that is formed on the print medium.
• the topcoat is, in fact, the ink-receptive layer.
• the photoinitiator is preferably included in that lower coating.
• the printed ink is often distributed to some extent over other layers in addition to that layer which is designated the ink-receptive layer.
• the photoinitiator it may simply be expedient to include the photoinitiator in all such coatings.
• a basecoat is first applied onto the print medium, e.g., paper, followed by application of a topcoat.
• the basecoat and the topcoat each comprise one or more pigments and one or more binders, which are polymeric compounds soluble or dispersible in the solvent in which the basecoat and topcoat are applied to the substrate.
• pigments include silica and alumina and its various hydrates, titania, carbonates (e.g., calcium carbonate, magnesium carbonate), glass beads, and organic pigments (e.g., plastic or polymer pigments such as crosslinked SBR latexes, micronized polyethylene or polypropylene wax, acrylic beads, and methacrylic beads).
• the pigment may be the same in both the basecoat and topcoat or different.
• the binder is a polymeric matrix which serves, among other things, to hold the pigment(s) in place.
• the binder can be water-soluble or water-dispersible.
• water-soluble binders include polyvinyl alcohol and its derivatives, polyvinyl pyrrolidone/polyvinyl acetate copolymer, cellulose derivatives, polyamides, and polyethylene oxide.
• water-dispersed binders include styrene-butadiene latexes, polyacrylics, polyurethanes, and the like.
• the binder may be the same in both the basecoat and topcoat or different.
• the basecoat and topcoat are separately applied in solution to the substrate and allowed to dry.
• the substrate comprises non-permeable (non-air permeable) material.
• non-permeable (non-air permeable) material such as a film-based material, e.g., Mylar, or a resin-coated papers (e.g., photobase paper).
• pores in the basecoat are saturated, or nearly saturated, with a liquid, also called a re-wetting solution therein, before the topcoat solution is applied.
• a liquid also called a re-wetting solution therein
• the pores in the basecoat are saturated with liquid before the topcoat solution is applied.
• a solvent that is compatible with the solvent in the topcoating is believed to give the best adhesion between coating layers.
• the liquid may comprise one or more solvents.
• the liquid may be heated or chemically modified to increase the penetration rate in the precoat.
• the liquid is heated to any temperature below its boiling point (or the minimum boiling point if two or more solvents are used).
• chemically modified is meant the addition of one or more surfactants, adhesion promoters, pH modifiers, polymers, crosslinkers, pigments, and/or dye stabilizers to the liquid.
• the chemically modified re-wet solution thus serves to modify the properties of the basecoat, topcoat, the coating process, or the performance of the coatings as it relates to its use as a printing media.
• Any of the usual surfactants, pH modifiers, and/or crosslinkers may be used in the practice of the present invention.
• a suitable crosslinker added to the liquid is a borate or glyoxyl. This process is especially useful for chemistries that are not compatible with the coating fluids or process.
• excess fluid on the surface of the basecoat be removed before topcoating. This can be accomplished by a nip, doctoring blade, or the like. Alternatively, the re-wet solution can be metered by a pump directly onto the basecoat, thus eliminating the need for doctoring.
• topcoat is then applied to the re-wet basecoat.
• the topcoat is considered to be the ink-receptive layer, as discussed above.
• the solids content is on the order of 12 wt%, although this may be varied, depending on the particular application of the coated print medium.
• a small amount of a photoinitiator is included in the composition of at least the ink-receptive coating, as discussed above.
• topcoat refers to the final coating formed on the print medium, and could comprise a single coating, the upper coating of a dual coating system, as described above, or other combinations of coatings.
• the photoinitiator is included in at least the ink-receptive layer formed on the print medium.
• the photoinitiator may comprise any of the commonly-known photoinitiators, including ⁇ -hydroxy-ketones, ⁇ -amino-ketones, and benzophenones. Included within the generic class of ⁇ -hydroxy-ketones are acetophenones.
• An example of a photoinitiator suitably employed in the practice of the present invention is ⁇ , ⁇ -dimethyl- ⁇ -hydroxy acetophenone (2-hydroxy-2-methyl-1-phenyl-propan-1-one), which is available from Ciba Co. under the trade mark Darocur® 1173.
• the concentration of the photoinitiator in the coating applied to the base substrate, or print medium is in the range of about 0.001 to 0.01 wt%, preferably about 0.005 wt%, based on the total coating composition. In general, a higher concentration does not provide any improvement, and, in fact, results in lightfastness that is only marginally improved over an absence of the photoinitiator. On the other hand, at least some photoinitiator is required in order to realize the benefits of the present invention.
• the final composition of photoinitiator in the coating after drying is in the range of about 0.008 to 0.08 wt%, and preferably about 0.042 wt%.
• a change in the solids content would, of course, result in a corresponding change in the final composition of photoinitiator in the coating after drying.
• photoinitiator in accordance with the teachings of the present invention improves the lightfastness to the printed ink that is on the order of 5 to 20% better than inks printed on coated print media that do not include the photoinitiator.
• magenta is usually the worst dye for lightfastness considerations, and thus in any ink set, efforts are made to improve the lightfastness of the ink containing that dye.
• Cyan dyes generally exhibit improved lightfastness properties over magenta, followed by yellow dyes; often, yellow produces such low contrast that the change is not noticed by the human eye. It should be noted, however, that illuminant, environmental conditions, and airborne pollutants, among other factors, can affect this order.
• optical density In the lightfastness test, a measurement is made of the optical density (OD) prior to the test and subsequent to the test.
• the severity in the decrease in optical density is a measure of lightfastness; a larger decrease in OD is indicative of poorer lightfastness.
• Glossy print media were coated with ink-receptive coatings, such as taught in above-referenced U.S. Patent 5,880,196, with and without the presence of a photoinitiator.
• the photoinitiator was Darocur® 1173.
• the coated glossy print media were printed with a set of inkjet inks (cyan, yellow, and magenta).
• Each ink comprised colorant (or colorant mixture) and a vehicle comprising a surfactant (or surfactant mixture), at least one water-miscible organic co-solvent, and water.
• the inks in the ink set had a composition similar to that commercially available with Hewlett-Packard's DeskJet 970C series.
• Accelerated lightfastness was conducted with a fadeometer, using high intensity cool-white fluorescent light bulbs, to simulate office conditions. An exposure of about 4 to 5 days in the fadeometer has been determined to be substantially equivalent to an exposure of 5 years under ordinary office lighting conditions. The test is carried out in two separate time periods in order to obtain three optical density points for interpolation/extrapolation.
• the Table below provides the results in hue shift/color for three separate series of compositions, one containing 0.005 wt% of photoinitiator (PI) in the coating as applied, one containing 0.01 wt% of the photoinitiator in the coating, and one containing no photoinitiator.
• the photoinitiator was ⁇ , ⁇ -dimethyl- ⁇ -hydroxy acetophenone, from Ciba Co. under the trade mark Darocur® 1173.
• the % loss is based on the optical density loss starting at an OD of 0.5.
• the "Acceptable?" is based on the perception for each color, given above.
• photoinitiators in coated papers is expected to find use in providing improved lightfastness of printed inkjet inks.

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• Ink Jet (AREA)
• Ink Jet Recording Methods And Recording Media Thereof (AREA)
• Application Of Or Painting With Fluid Materials (AREA)

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• 2001
  • 2001-08-27 JP JP2001256134A patent/JP4739604B2/ja not_active Expired - Fee Related
  • 2001-09-20 DE DE2001615179 patent/DE60115179T2/de not_active Expired - Lifetime
  • 2001-09-20 EP EP20010308011 patent/EP1193079B1/de not_active Expired - Lifetime

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