Radical curable inkjet ink

Abstract

A free radical curable inkjet ink contains a color pigment, a photoinitiator, and a polymerizable composition, wherein the polymerizable composition includes greater than 88.0% of monofunctional polymerizable compounds based on the total weight of the polymerizable composition; wherein greater than 13.0 wt% of the monofunctional polymerizable compounds have a double bond density DBD greater than 7.00; wherein greater than 35.0 wt% of the multifunctional alkoxylated acrylate esters have a molecular weight MW greater than 310 based on the total weight of the multifunctional polymerizable compounds; wherein the amount of non-aromatic cyclic monofunctional acrylate esters is such that the ratio of the wt% of multifunctional alkoxylated acrylate esters having a molecular weight MW greater than 310 to the wt% of non-aromatic cyclic monofunctional acrylate esters is greater than 0.35; and wherein the double bond density DBD of the polymerizable composition is not greater than 5.55 mmol double bonds / g.

Description

Technical Field

[0001] This invention relates to free radical curable inkjet inks suitable for roll-to-roll inkjet printers, specifically for printing on flexible substrates such as backlight films. A backlight film is a material on which graphics or text are printed so that the pattern illuminates when light passes through from behind. Background Technology

[0002] Inkjet printing is a printing technology that allows for variable data printing with short run lengths or even single-shot printing without extensive pre-printing preparation. For this reason, it has become the preferred choice in so-called printing plants that provide panels and banners with advertising and other content.

[0003] Such panels and banners tend to become increasingly larger, leading to transportation problems. A shift from rigid to flexible substrates is noteworthy, as this can cause damage to corners of rigid panels, for example, during transport. Printed flexible substrates have been successfully transported in shipping tubes without damage. However, inkjet printing with widths of 5 meters or greater is not uncommon nowadays. Transporting such wide substrates in shipping tubes is not only cumbersome but also expensive when using courier services. Flexible substrates become much cheaper when folded into boxes and sent by courier services. However, it has been observed that this folding introduces new cracking problems into the printed image during transport in cold winter conditions or when unfolded.

[0004] Polymerizable compositions of UV-curable inkjet inks used in certain applications typically result in trade-offs in certain ink properties. For example, good tack and scratch resistance are achieved when the polymerizable composition contains a higher proportion of polyfunctional monomers compared to monofunctional monomers. However, monofunctional monomers generally lead to poorer flexibility, as illustrated in EP 2399965 A (AGFA). High contents of polyfunctional monomers generally also provide poor adhesion results because polyfunctional monomers exhibit a much higher polymerization shrinkage rate compared to monofunctional monomers.

[0005] One approach that combines good scratch resistance and good adhesion is to use specially designed multifunctional monomers. For example, WO 2005 / 055960 (DU PONT) discloses specific branched highly functional monomers that exhibit low polymerization shrinkage. Such compounds typically increase the viscosity of polymerizable compositions to a level still suitable for dental filling composites but not for UV-curable inkjet inks.

[0006] Another approach is to use inkjet inks that can be cured by cationic polymerization, as this polymerization exhibits low shrinkage. However, in industrial inkjet printing systems, cationic curable inkjet inks have been found to cause issues with print reliability due to UV stray light. UV curing of the ink causes reflections of UV light, including UV light striking the nozzle plate of the inkjet printhead, and nozzle malfunctions due to clogging caused by cured ink within the nozzles. Unlike free radical inks, where the free radical components have a much shorter lifespan, cationic curable inks continue to cure once the UV light in the nozzles has produced acidic substances.

[0007] There is still a need for free radical curable inkjet inks that allow the printed backlight film to fold and adhere well without cracking, while exhibiting good surface curing and high printing reliability. Summary of the Invention

[0008] To overcome the above problems, a preferred embodiment of the present invention provides a free radical curable inkjet ink as defined in claim 1.

[0009] Surprisingly, by controlling the double bond density of the polymerizable ink composition, inkjet-printed flexible substrates did not exhibit stickiness at -18°C and could be folded without damage. The polymerizable ink composition contained polyfunctional alkoxylated acrylates with a molecular weight (MW) greater than 310 and a large number of monofunctional polymerizable compounds, including specific amounts of non-aromatic cyclic monofunctional acrylates.

[0010] Other advantages and preferred embodiments of the invention will become apparent from the following description. Detailed Implementation

[0011] Free radical curable inkjet ink

[0012] The free radical curable inkjet ink according to a preferred embodiment of the present invention comprises a colored pigment, preferably an organic colored pigment, a photoinitiator, and a polymerizable composition, wherein the polymerizable composition comprises more than 88.0 wt% of a monofunctional polymerizable compound based on the total weight of the polymerizable composition; wherein more than 13.0 wt% of a monofunctional polymerizable compound having a double bond density (DBD) greater than 7.00; wherein more than 35.0 wt% of a polyfunctional alkoxylated acrylate having a molecular weight (MW) greater than 310 based on the total weight of the polyfunctional polymerizable compound; wherein the amount of non-aromatic cyclic monofunctional acrylate is such that the ratio of the wt% of the polyfunctional alkoxylated acrylate with a molecular weight (MW) greater than 310 to the wt% of the non-aromatic cyclic monofunctional acrylate is greater than 0.35; and wherein the double bond density (DBD) of the polymerizable composition is not greater than 5.55 mmol double bond / g, wherein the double bond density (DBD) is calculated by the following formula:

[0013]

[0014] in

[0015] i represents an integer from 1 to n;

[0016] n represents the number of monomers and oligomers in UV LED free radical curable inkjet ink;

[0017] F(i) represents the functionality of monomer or oligomer i;

[0018] MW(i) represents the molecular weight of monomer or oligomer i; and

[0019] wt%(i) is the weight percentage of monomers or oligomers i based on the total weight of the free radical curable inkjet ink.

[0020] In a preferred embodiment of the free radical curable inkjet ink, the content of monofunctional monomers in the free radical curable inkjet ink is greater than 88.0 wt%, preferably greater than 90.0 wt%, based on the total weight of the polymerizable composition in the free radical curable inkjet ink. At such a level, polymerization shrinkage is minimized, which is beneficial for adhesion.

[0021] In another preferred embodiment of the free radical curable inkjet ink, the polyfunctional alkoxylated acrylates with a molecular weight (MW) greater than 310 contain 80 wt% to 100 wt%, most preferably 100 wt%, of difunctional acrylates, based on the total weight of the polyfunctional alkoxylated acrylates with a molecular weight (MW) greater than 310. This allows for excellent results in folding and wrinkling tests.

[0022] In another preferred embodiment of the free radical curable inkjet ink, the polyfunctional alkoxylated acrylate with a molecular weight (MW) greater than 310 has a MW between 400 and 1000. Such a range allows for good ink viscosity and reliable inkjet printing.

[0023] In another preferred embodiment of the radical-curable inkjet ink, the radical-curable inkjet ink is a UV LED-curable radical-curable inkjet ink for use with a UV LED source whose spectral emission is in the range of 360 to 420 nm. Then, based on the total weight of the radical-curable inkjet ink, the UV radical-curable inkjet ink preferably contains one or more acylphosphine oxide photoinitiators as photoinitiators, more preferably, in a content greater than 5.0 wt%, preferably greater than 7.0 wt%. At these concentrations, curing by UV LED is possible, and good tack results are obtained.

[0024] In another preferred embodiment of the free radical curable inkjet ink, the inkjet ink contains greater than 43.0 wt% of a polyfunctional alkoxylated acrylate with a molecular weight (MW) greater than 310, based on the total weight of the polyfunctional polymerizable compound. This allows for simultaneous maximization of results in folding, wrinkling, tack, and finger tests.

[0025] In another preferred embodiment of the free radical curable inkjet ink, based on the total weight of the ink, the inkjet ink contains greater than 25 wt%, preferably greater than 30 wt%, and most preferably greater than 40 wt% of an aromatic monofunctional monomer. The aromatic monofunctional monomer preferably comprises or consists of phenoxyethyl acrylate. At such amounts, good curing speeds are obtained when combined with monofunctional polymerizable compounds with a double bond density (DBD) greater than 7.00.

[0026] In another preferred embodiment of the free radical curable inkjet ink, the inkjet ink contains 14.0 wt% to 24.0 wt% of a monofunctional polymerizable compound other than (meth)acrylate or methyl (acrylamide) with a double bond density (DBD) greater than 7.00.

[0027] Incidentally, there are no limitations on combining one or more of the above preferred embodiments.

[0028] The double bond density (DBD) of a monomer or oligomer is obtained by dividing the functionality of the monomer or oligomer by its molecular weight (MW). It is expressed as mmol double bonds / g. For illustration, Table 1 below shows the MW and DBD of some commonly used monomers in UV-curable inkjet inks.

[0029] Table 1

[0030]

[0031]

[0032] To determine the double bond density (DBD) of the polymerizable composition, the DBD of each polymerizable compound is considered and calculated according to the formula above.

[0033] Free radical curable inkjet inks are preferably free of organic solvents, but may contain organic solvents in amounts of 0 wt% to 20 wt%, preferably 0 wt% to 10 wt%, and more preferably 0 wt% to 5 wt% based on the total weight of the free radical curable inkjet ink. Sometimes, incorporating a small amount of organic solvent to improve adhesion to the substrate surface after UV curing or to promote the dissolution of a component can be advantageous.

[0034] As measured at 45°C, the viscosity of free radical curable inkjet inks is preferably between 4 and 10 mPa·s. Within this range, high printing reliability is observed with most piezoelectric printheads.

[0035] Free radical curable inkjet inks may further contain at least one inhibitor or stabilizer to improve the thermal stability of the ink, which improves printing reliability.

[0036] Free radical curable inkjet inks may further contain at least one surfactant to achieve good spreading properties on the substrate.

[0037] The surface tension of the free radical curable inkjet ink is preferably in the range of 20 mN / m to 30 mN / m at 25°C, and more preferably in the range of about 22 mN / m to about 25 mN / m at 25°C.

[0038] Inkjet ink kit

[0039] For printing multicolor images, radical-curable inkjet inks are part of an inkjet ink kit. A radical-curable inkjet ink kit according to a preferred embodiment of the invention comprises at least three or four radical-curable inkjet inks as described above.

[0040] Multicolor images can be printed for indoor use, but when printed on backlit film, they are typically used for outdoor purposes, such as as advertising in bus shelters. In such cases, the printed backlit film is exposed to light from behind, thereby illuminating the printed image. For this type of outdoor application, organic colored pigments are selected to provide high light stability when combined with polymerizable compositions of free radical curable inkjet inks as described above.

[0041] In a particularly preferred embodiment, the free radical curable inkjet ink kit comprises at least: a) a cyan free radical curable inkjet ink containing β-copper phthalocyanine pigment; b) a magenta or red free radical curable inkjet ink containing quinacridone pigment, diketopyrrolopyrrole pigment, or mixed crystals thereof; c) a yellow free radical curable inkjet ink containing yellow pigments selected from CI Pigment Yellow 83, CI Pigment Yellow 93, CI Pigment Yellow 97, CI Pigment Yellow 110, CI Pigment Yellow 120, CI Pigment Yellow 138, CI Pigment Yellow 150, CI Pigment Yellow 151, CI Pigment Yellow 154, CI Pigment Yellow 155, CI Pigment Yellow 175, CI Pigment Yellow 180, CI Pigment Yellow 181, CI Pigment Yellow 185, CI Pigment Yellow 194, CI Pigment Yellow 213, CI Pigment Yellow 214, and mixed crystals thereof; and d) a black free radical curable inkjet ink containing carbon black pigment.

[0042] In a particularly preferred embodiment of the ink kit, the cyan, black, magenta, or red and yellow free radical curable inkjet inks all have the ink composition as described above.

[0043] The preferred inkjet ink kit is a free radical curable CMYK or CRYK inkjet ink kit. This type of inkjet ink kit offers a very wide color gamut.

[0044] This free radical curable inkjet ink kit can also be expanded with additional inks (such as red, green, blue, purple, and / or orange) to further broaden the color gamut of the image.

[0045] Free radical curable inkjet ink kits can also be expanded through combinations of full-density and low-density inkjet inks. Combinations of dark and light inks and / or black and gray inks improve image quality by reducing graininess.

[0046] Inkjet ink kits can also include colorless, free-radical-curable inkjet inks, such as varnishes. Varnishes are used to enhance the gloss of color images printed by inkjet printing.

[0047] The inkjet ink kit may also include white radical-curable inkjet ink. The white radical-curable inkjet ink preferably contains titanium dioxide pigment, preferably rutile pigment, and has an average particle size greater than 180 nm, preferably 200-280 nm, and more preferably 220-250 nm.

[0048] When no light shines through the backlight film, a white background is printed on the substrate, and a color image is printed on it. The white background improves the vividness of the color image.

[0049] White inkjet inks preferably contain pigments with a high refractive index, preferably greater than 1.60, more preferably greater than 2.00, more preferably greater than 2.50, and most preferably greater than 2.60. Such white pigments typically have very high hiding power, meaning that a limited amount of white ink is needed to cover the color of the substrate. The most preferred white pigment is titanium dioxide.

[0050] Based on the total weight of the white inkjet ink, the white inkjet ink preferably contains 8 wt% to 25 wt%, more preferably 12 wt% to 20 wt% of white pigment.

[0051] The average particle size of the white pigment is preferably between 150 nm and 500 nm, and most preferably between 180 nm and 300 nm. When the average diameter is less than 150 nm, sufficient hiding power cannot be obtained, and when the average diameter exceeds 500 nm, the ink's storage capacity and ejection adaptability tend to decrease.

[0052] polymerizable compounds

[0053] Any polymerizable compound commonly known in the art can be used, provided it conforms to the polymerizable composition described above. The polymerizable compound can be from the *Polymer Handbook*.

[0054] Any monomer or oligomer found in (Polymer Handbook) Volumes 1+2, 4th Edition, edited by J. BRANDRUP et al., Wiley-Interscience, 1999. Oligomers in this invention should be understood as containing two or more repeating monomer units.

[0055] Combinations of monomers and oligomers can also be used. Monomers and oligomers can have different functionalities, and mixtures of monomers and oligomers containing monofunctional, difunctional, trifunctional, and higher functionalities can be used.

[0056] Monofunctional monomers and oligomers

[0057] The term "monofunctional polymerizable compound" refers to a polymerizable compound having only one polymerizable group, such as an acrylate group. Such polymerizable compounds can be monomers or oligomers.

[0058] Monofunctional polymerizable compounds with a double bond density (DBD) greater than 7.00 are preferably N-vinyllactams or N-vinyloxazolidinones.

[0059] N-vinyl lactams are preferably cyclic compounds represented by formula (NV-1):

[0060]

[0061] Where n represents an integer from 2 to 6, n is preferably 3 or 5, and n is particularly preferably 5. N-vinyl lactams may have substituents such as alkyl or aryl groups on the lactam ring, and may have saturated or unsaturated ring structures bonded to the lactam ring.

[0062] N-vinyloxazolidinones are preferably compounds according to formula V-1:

[0063]

[0064] Besides the constraints imposed by its use in inkjet inks, such as viscosity and ink stability, R 1 To R 4 Unrestricted. R 1 To R 4 Preferred substituents include hydrogen, alkyl, cycloalkyl, aryl, and combinations thereof, any of which may be spaced by heteroatoms.

[0065] Most preferably, R 1To R 4 Independently selected from hydrogen or C1 to C 10 alkyl.

[0066] Preferred compounds are disclosed in WO 2015 / 022228 (BASF) and US 4831153 (DOW CHEMICAL).

[0067] In a particularly preferred embodiment, the monofunctional polymerizable compound with a double bond density (DBD) greater than 7.00 is preferably N-vinyl-5-methyl-2-oxazolidinone or N-vinylcaprolactam.

[0068] Non-aromatic cyclic monofunctional acrylates include heterocyclic monofunctional acrylates and alicyclic monofunctional acrylates.

[0069] Heterocyclic acrylates contain a ring structure in which one or more heteroatoms are oxygen atoms.

[0070] Preferred heterocyclic acrylates include tetrahydrofurfuryl acrylate, caprolactone-modified tetrahydrofurfuryl acrylate, cyclic trimethylolpropane acetal acrylate, (2-ethyl-2-methyl-1,3-dioxolane-4-yl)methyl acrylate, (2,2-dimethyl-1,3-dioxolane-4-yl)methyl acrylate, cyclohexanespiro-2-(1,3-dioxolane-4-yl))methyl acrylate, and (3-ethyloxetane-3-yl)methyl acrylate.

[0071] In a preferred embodiment of the free radical curable inkjet ink, the heterocyclic acrylate includes polymerizable compounds selected from cyclic trimethylolpropane acetal acrylate, (3-ethyloxetane-3-yl) methyl acrylate and (2,2-dimethyl-1,3-dioxolane-4-yl) methyl acrylate.

[0072] Alicyclic acrylates contain one or more fully carbon rings, which may be saturated or unsaturated, but do not have aromatic characteristics.

[0073] Preferred alicyclic acrylates include 3,3,5-trimethylcyclohexyl acrylate, isobornyl acrylate, 4-tert-butylcyclohexyl acrylate, dicyclopentenyl acrylate; and dicyclopentenoxyethyl acrylate, cyclohexyl acrylate, 1,4-cyclohexanediol monoacrylate and 2-methyl acrylate (octahydro-4,7-methylene-1H-inden-1-yl) acrylate.

[0074] In a preferred embodiment of the free radical curable inkjet ink, the alicyclic acrylate includes polymerizable compounds selected from 3,3,5-trimethylcyclohexyl acrylate, isobornyl acrylate, (octahydro-4,7-methylene-1H-indenyl) methyl acrylate and 4-tert-butylcyclohexyl acrylate.

[0075] Aromatic acrylates may include heteroaromatic acrylates, but polymerizable compounds that do not contain heteroatoms in their ring structure are preferred.

[0076] Preferred aromatic acrylates include benzyl acrylate, 2-phenoxyethyl acrylate, 2-hydroxy-3-phenoxypropyl acrylate, phenoxy polyethylene glycol acrylate, ethoxylated (4)nonylphenol acrylate, and ethoxylated (4)phenol acrylate.

[0077] In a preferred embodiment of the UV-curable inkjet ink, the aromatic acrylate includes a polymerizable compound selected from 2-phenoxyethyl acrylate and 2-hydroxy-3-phenoxypropyl acrylate, with 2-phenoxyethyl acrylate being the most preferred.

[0078] Other preferred monofunctional polymerizable compounds include diethylene glycol butyl ether acrylate, 2-ethylhexyl acrylate, ethoxydiethylene glycol acrylate, di(ethylene glycol) 2-ethylhexyl ether acrylate, octyl-decyl acrylate, n-octyl acrylate, isodecanyl acrylate, isononyl acrylate, methoxypolyethylene glycol (350) monoacrylate, tridecyl acrylate, 2-(2-ethoxyethoxy)ethyl acrylate, isooctyl acrylate, butyl acrylate, and polycaprolactone acrylate, methoxypolyethylene glycol (550) monoacrylate, 2-methoxyethyl acrylate, ethoxylated (4) lauryl acrylate, and isoamyl acrylate. Methoxy-triethylene glycol acrylate, ethoxylated (8)nonylphenol acrylate, 4-hydroxybutyl acrylate, lauryl acrylate, ethyl acrylate, 1H,1H,5H-octafluoropentyl acrylate, 2-hydroxypropyl acrylate, 2-propylheptyl acrylate, isostearyl acrylate, hydroxyethyl acrylate, 2,2,2-trifluoroethyl acrylate, stearyl acrylate, 2-hydroxybutyl acrylate, 2-ethylhexyl diethylene glycol acrylate, tert-butyl acrylate, carboxyethyl acrylate, 2-((butylcarbamoyl)oxy)ethyl acrylate and 2-hydroxy-3-(acryloyloxy)propyl 2-methyl-2-propylhexanoate.

[0079] Multifunctional monomers and oligomers

[0080] The term "multifunctional polymerizable compound" refers to a monomer or oligomer having two, three, or more polymerizable groups, such as two acrylate groups and one vinyl ether group. Such polymerizable compounds can be monomers or oligomers.

[0081] Based on the total weight of the multifunctional polymerizable compounds, the free radical curable inkjet ink contains more than 35.0 wt% of multifunctional alkoxylated acrylates with a molecular weight (MW) greater than 310.

[0082] Polyfunctional alkoxylated acrylates with a molecular weight (MW) greater than 310 are preferably ethoxylated or propoxylated polyacrylates with a molecular weight (MW) greater than 310, more preferably at least 450, and even more preferably at least 500.

[0083] In a preferred embodiment of the inkjet ink according to the invention, the ethoxylated and / or propoxylated polyacrylate comprises 5 to 20 ethoxy units and / or propoxy units, more preferably 6 to 15 ethoxy units and / or propoxy units.

[0084] Ethoxylated and / or propoxylated polyacrylates preferably have two acrylate groups, but may contain three, four, five or six acrylate groups.

[0085] Preferred ethoxylated and / or propoxylated polyacrylates are ethoxylated and / or propoxylated trimethylolpropane triacrylates. Commercial examples include Sartomer from ARKEMA. TM SR499, Sartomer TM SR502, Sartomer TM SR9035 and Sartomer TM SR415.

[0086] A suitable propoxylated polyacrylate is propoxylated glycerol triacrylate. A commercial example is Sartomer from SARTOMER. TM SR9021.

[0087] Ethoxylated and / or propoxylated polyacrylates having two acrylate groups include polyethylene glycol diacrylate. Commercial examples include Sartomer from ARKEMA. TM SR344.

[0088] Other multifunctional monomers and oligomers may contain 2, 3, 4 or more olefinically unsaturated polymerizable groups. However, to maximize folding properties, UV-curable inkjet inks preferably contain only other multifunctional polymerizable compounds containing 2 or 3 olefinically unsaturated polymerizable groups, and more preferably polymerizable compounds containing only 2 olefinically unsaturated polymerizable groups.

[0089] Photoinitiator

[0090] Radical-curable inkjet inks contain one or more photoinitiators, preferably Norrish Type I or Norrish Type II initiators. Norrish Type I initiators are initiators that cleave upon excitation, immediately generating initiating groups. Norrish Type II initiators are photoinitiators that are activated by photochemical radiation and form radicals by abstracting hydrogen from a second compound, which then becomes the actual initiating radical. This second compound is referred to as a polymerization synergist or co-initiator.

[0091] Suitable photoinitiators are disclosed in CRIVELLO, JV et al., Vol. III: Photoinitiators for Free Radical Cationic. 2nd ed., edited by BRADLEY, G., London, UK: John Wiley and Sons Ltd, 1998. pp. 287-294.

[0092] Norrish Type I photoinitiator

[0093] Norrish type I photoinitiators are preferably selected from benzoin ether, benzoyl ketal, α-haloketone, α,α-dialkoxyacetophenone, α-hydroxyalkylphenyl ketone, α-halosulfone, α-aminoalkylphenyl ketone, acylphosphine oxide, acylphosphine sulfide, and phenylacetalate.

[0094] To achieve high curing speed with UV LEDs, the photoinitiator preferably contains an acylphosphine oxide photoinitiator and / or an α-hydroxy ketone photoinitiator, and most preferably contains at least an acylphosphine oxide photoinitiator.

[0095] Based on the total weight of the radical-curable inkjet ink, the radical-curable inkjet ink contains an acylphosphine oxide photoinitiator, preferably in an amount of at least 5.0 wt%, more preferably in an amount of 5.5 wt% to 16.0 wt%.

[0096] Preferred examples of acylphosphine oxide photoinitiators include bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, 2,4,6-trimethylbenzoyl diphenylphosphine oxide, and ethyl(2,4,6-trimethylbenzoyl)phenyl hypophosphite, bis(2,6-dimethoxybenzoyl)2,4,4-trimethylpentylphosphine oxide. These acylphosphine oxide photoinitiators are commercially available, for example from IGM Resins under Omnirad. TM 819, Omnirad TM TPO and Omnirad TM TPO-L obtained.

[0097] Acylphosphine oxides can also be polymeric compounds, such as Omnipol derived from IGM Resins. TM TP.

[0098] Acylphosphine oxide photoinitiators may include an acyl group containing a polymerizable group or an acyl group selected from benzoyl groups substituted with urea or oxalylamide groups; 2,6-dimethylbenzoyl group substituted with urea or oxalylamide groups at the 3-position; 2,6-dimethoxybenzoyl group substituted with urea or oxalylamide groups at the 3-position; 2,4,6-trimethylbenzoyl group substituted with urea or oxalylamide groups at the 3-position; and 2,4,6-trimethoxybenzoyl group substituted with urea or oxalylamide groups at the 3-position. By using such acylphosphine oxide photoinitiators, mesitaldehyde, which causes unpleasant odors in printed materials, is not released after UV curing.

[0099] Suitable acylphosphine oxide photoinitiators having acyl groups substituted with urea or oxalylamide groups are disclosed in WO 2019 / 243039 (AGFA).

[0100] Suitable acylphosphine oxide photoinitiators containing polymerizable acyl groups are disclosed in WO 2014 / 051026 (FUJIFILM).

[0101] Combinations of different acylphosphine oxide photoinitiators can also be used. For example, combinations of monofunctional acylphosphine oxide photoinitiators such as TPO and TPO-L and polyfunctional acylphosphine oxide photoinitiators such as bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide. Preferably, such combinations contain more monofunctional acylphosphine oxide photoinitiators than polyfunctional acylphosphine oxide photoinitiators. Combinations containing at least 70 wt% monofunctional acylphosphine oxide photoinitiators, preferably TPO-L, generally exhibit higher curing efficiency.

[0102] Alternatively, acylphosphine oxide is a polymeric compound in which the acylphosphine oxide structure is bonded to the polymer chain on its acyl side. Suitable compounds are disclosed in WO 2014 / 129213 (FUJIFILM). By bonding the acyl group to the polymer chain, the odor of printed materials is also suppressed.

[0103] Suitable examples of α-hydroxy ketone photoinitiators include, but are not limited to, 1-hydroxycyclohexylphenyl ketone, 2-hydroxy-2-methyl-1-phenylprop-1-one, and 1-[4-(2-hydroxyethoxy)-phenyl]2-hydroxy-2-methyl-1-prop-1-one.

[0104] Examples of commercial α-hydroxyketone photoinitiators include, but are not limited to, Omnirad derived from IGM RESINS. M 1173, OmniradTM 184 and Omnirad TM 127 and Omnirad TM 4817.

[0105] Based on the total weight of the UV LED free radical curable inkjet ink, the content of α-hydroxy ketone is preferably 1 wt% to 10 wt%, more preferably 2 wt% to 8 wt%, and still more preferably 3 wt% to 6 wt%.

[0106] In a particularly preferred embodiment, the α-hydroxyketone photoinitiator is a polymerizable or polymerizable photoinitiator.

[0107] Examples of suitable polymerizable α-hydroxyketone photoinitiators can be found in IGM RESINS and Esacure. TM KIP150 obtained.

[0108] Suitable polymerizable α-hydroxy ketone photoinitiators are disclosed in US 4922004 (MERCK), such as 4-(2-acryloyloxyethoxy)-phenyl-2-acryloyloxy-2-propyl ketone prepared in Example 3.

[0109] Norrish type II photoinitiator

[0110] UV LED free radical curable inkjet inks may contain Norrish type II photoinitiators, which comprise photoinitiating moieties selected from thioxanthone, carbazole, and benzophenone groups. Norrish type II photoinitiators containing thioxanthone and carbazole groups are particularly preferred because they are beneficial for UV LED curing, especially for UV LEDs emitting wavelengths of 370 nm or longer.

[0111] Suitable examples of Norrish type II photoinitiators containing a thioxanthone group include, but are not specifically limited to, thioxanthone; diethylthioxanthone, such as 2,4-diethylthioxanthone; isopropylthioxanthone, such as 2-isopropylthioxanthone and 4-isopropylthioxanthone; and chlorothioxanthone, such as 2-chlorothioxanthone.

[0112] A specific example of a commercially available Norrish type II photoinitiator containing a thioxanthone group is Speedcure from Lambson. TM DETX (2,4-diethylthioxanone) and Speedcure TM ITX (2-isopropylthioxanthone), and Kayacure from Nippon Kayaku Co. TM DETX-S (2,4-Diethylthioxanone).

[0113] Preferred carbazole photoinitiators are disclosed in EP 2509948 A (AGFA), which have the advantage of exhibiting less photo-yellowing compared to thioxanthone photoinitiators.

[0114] Suitable examples of Norrish type II photoinitiators containing a benzophenone group include, but are not specifically limited to, benzophenone; methyl benzophenone; methyl 2-benzoylbenzoate; phenyl benzophenone, such as 4-phenyl benzophenone; trimethyl benzophenone; bis(alkylamino)benzophenone; and 4-(dialkylamino)benzophenone.

[0115] A specific example of a commercially available Norrish type II photoinitiator containing a benzophenone group is Omnirad from IGMRESINS. TM 4MBZ and Omnirad TM BP, derived from Lambson's Speedcure TM PBZ and Speedcure TM 5040. The latter is a mixture of benzophenone and thioxanone.

[0116] Preferred examples of polymerizable Norrish type II photoinitiators comprising a photoinitiating moiety selected from thioxanthone or benzophenone groups are disclosed in EP 2161264 A (AGFA), EP 2199273 A (AGFA) and EP 2684876 A (AGFA).

[0117] Preferred examples of Norrish type II photoinitiators for polymerization comprising a photoinitiating moiety selected from thioxanone or benzophenone groups are disclosed in EP 1616920 A (AGFA) and EP 1616899 A (AGFA).

[0118] Commercial examples of polymerized thioxanone and benzophenone include Omnipol from IGM RESINS. TM BP, Omnipol TM TX and Omnipol TM 2702.

[0119] Based on the total weight of the radical-curable inkjet ink, the content of the Norrish type II photoinitiator, comprising a photoinitiating portion selected from thioxanthone, carbazole, and benzophenone groups, is preferably from 0.5 wt% to 7.5 wt%, more preferably from 1 wt% to 5 wt%. However, if the Norrish type II photoinitiator is a polymerizable or polymerizable thioxanthone or carbazole compound, its content can be higher based on the total weight of the radical-curable inkjet ink, preferably up to 25 wt%, more preferably up to 15 wt%.

[0120] Polymerization enhancer

[0121] To further enhance photosensitivity, free radical curable inkjet inks may additionally contain one or more co-initiators, also known as polymerization synergists, for which amine synergists are typically used.

[0122] Suitable examples of amine potentiators can be divided into three categories:

[0123] (1) Aliphatic tertiary amines, such as methyldiethanolamine, dimethylethanolamine, triethanolamine, triethylamine and N-methylmorpholine;

[0124] (2) Aromatic amines, such as amyl p-dimethylaminobenzoate, 2-n-butoxyethyl-4-(dimethylamino)benzoate, 2-(dimethylamino)ethyl benzoate, ethyl-4-(dimethylamino)benzoate, and 2-ethylhexyl-4-(dimethylamino)benzoate; and

[0125] (3) (Meth)acrylate esterified amines, such as (meth)acrylate dialkylaminoalkyl esters (e.g., diethylaminoethyl acrylate) or N-morpholinoalkyl-(meth)acrylates (e.g., N-morpholinoethyl-acrylate).

[0126] In a preferred embodiment of the free radical curable inkjet ink, the polymerization synergist is an acrylated amine synergist.

[0127] Suitable amine synergists can be derived from IGM Resins and Omnipol. TM ASA, Omnipol TM 894 and Esacure TM A198 Commercial Purchase.

[0128] Preferred commercially available acrylated amine synergists include Photomer from IGM Resins. TM 4068, 4250, 4771, 4775, 4780, 4967 and 5006.

[0129] Colored pigments

[0130] Backlight film is a material with graphics or text printed on it so that the pattern lights up when light shines through from behind.

[0131] Light stability

[0132] Free radical curable inkjet inks contain colored pigments, preferably organic colored pigments. Compared to inorganic colored pigments, organic colored pigments offer a much larger color gamut, but are more prone to light fading. Color gamut refers to the number of different colors that can be produced by an ink set.

[0133] Colored pigments can be black, cyan, magenta, yellow, red, orange, purple, blue, green, brown, or mixtures thereof. Colored pigments can be selected from those disclosed in HERBST, Willy, etc., Industrial Organic Pigments, Production, Properties, Applications, 3rd Edition, Wiley-VCH, 2004. ISBN 3527305769.

[0134] The preferred pigments for cyan inkjet inks are CI Pigment Blue 60 or preferably β-copper phthalocyanine pigment, more preferably CI Pigment Blue 15:3 or CI Pigment Blue 15:4.

[0135] Magenta or red UV LED radical-curable inkjet inks preferably contain quinacridone pigments, diketopyrrolopyrrole pigments, or mixed crystals thereof. In a preferred embodiment, the magenta or red UV LED radical-curable inkjet ink preferably contains pigments selected from: CI Pigment Violet 19, CI Pigment Red 122, CI Pigment Red 144, CI Pigment Red 176, CI Pigment Red 188, CI Pigment Red 207, CI Pigment Red 242, CI Pigment Red 254, CI Pigment Red 272, and mixed crystals thereof.

[0136] Yellow free radical curable inkjet inks preferably contain yellow pigments selected from the following: CI Pigment Yellow 83, CI Pigment Yellow 93, CI Pigment Yellow 97, CI Pigment Yellow 110, CI Pigment Yellow 120, CI Pigment Yellow 138, CI Pigment Yellow 150, CI Pigment Yellow 151, CI Pigment Yellow 154, CI Pigment Yellow 155, CI Pigment Yellow 175, CI Pigment Yellow 180, CI Pigment Yellow 181, CI Pigment Yellow 185, CI Pigment Yellow 194, CI Pigment Yellow 213, CI Pigment Yellow 214, and mixed crystals thereof.

[0137] The organic colored pigments selected above for use in cyan, magenta, red, or yellow inkjet inks exhibit minimal light fading when combined with the polymerizable compositions described above.

[0138] For black inks, suitable pigments include carbon black, such as Regal from Cabot Co. TM 400R, Mogul TM L, Elftex TM 320, or Carbon Black FW18 or Special Black from DEGUSSA Co.TM 250, Special Black TM 350, Special Black TM 550, Printex TM 25. Printex TM 35. Printex TM 55. Printex TM 90. Printex TM 150T, obtained from MITSUBISHI CHEMICAL Co. MA8, as well as CI Pigment Black 7 and CI Pigment Black 11.

[0139] Mixed crystals can also be used. Mixed crystals are also known as solid solutions. For example, under certain conditions, different quinacridones are mixed together to form a solid solution, which is quite different from a physical mixture of compounds and the compounds themselves. In a solid solution, the molecules of the components enter the same crystal lattice, usually (but not always) the lattice of one of the components. The X-ray diffraction pattern of the resulting crystalline solid is unique to that solid and can be clearly distinguished from the pattern of a physical mixture of the same components in the same proportions. In such physical mixtures, the X-ray patterns of each component can be distinguished, and the disappearance of many of these lines is one of the criteria for the formation of a solid solution. A commercially available example is Cinquasia from Ciba Specialty Chemicals. TM Magenta RT-355-D.

[0140] Mixtures of pigments can also be used. For example, black inkjet ink can contain carbon black pigment and at least one pigment selected from blue, cyan, magenta, and red pigments. The discovery of such black inkjet inks allows for easier and better color management of wood.

[0141] The pigment particles in colored inkjet inks should be small enough to allow the ink to flow freely through the inkjet printing apparatus, especially at the nozzles. Small particles are also desirable for achieving maximum color intensity and reducing sedimentation.

[0142] The average particle size of the colored pigments in the inkjet ink should preferably be between 50 nm and 250 nm, more preferably between 80 nm and 200 nm. Within these ranges, the illumination of the color image on the backlight film is enhanced when light shines on the back of the backlight film.

[0143] Based on the total weight of the free radical inkjet ink, pigment is typically used in the inkjet ink at an amount of 0.1 wt% to 15 wt%, preferably 1 wt% to 10 wt%, and most preferably 2 wt% to 6 wt%. A pigment concentration of at least 2 wt% is preferred to reduce the amount of inkjet ink required to produce a colored pattern, while a pigment concentration higher than 5 wt% reduces the color gamut and increases the graininess for printing colored patterns. The ink kit may also contain low-density inkjet ink. In such cases, the low-density inkjet ink contains pigment, the amount of which is preferably 0.1 wt% to 1.0 wt%, more preferably 0.5 wt% to 0.8 wt%, based on the total weight of the free radical inkjet ink.

[0144] The average particle size was best determined by photon correlation spectroscopy at a wavelength of 633 nm using a 4 mW HeNe laser on diluted samples of colored inkjet ink. A suitable particle size analyzer was the Malvern from Goffin-Meyvis. TM nano-S. For example, a sample can be prepared by adding a drop of ink to a cuvette containing 1.5 mL of ethyl acetate and mixing until a homogeneous sample is obtained. The particle size measured is the average of three consecutive measurements, which consist of six 20-second runs.

[0145] dispersant

[0146] Coloring free radical curable inkjet inks contain dispersants to further improve pigment dispersion characteristics. For high printing reliability, polymeric dispersants are preferred. The lower settling velocity of such dispersants, especially when they contain secondary or tertiary amine groups, improves the reliability of inkjet printing methods.

[0147] Typical polymer dispersants are copolymers of two monomers, but they can contain three, four, five, or even more monomers. The properties of a polymer dispersant depend on both the nature of the monomers and their distribution within the polymer. Copolymer dispersants preferably have the following polymer composition:

[0148] • Statistically aggregated monomers (e.g., monomers A and B aggregate to form ABBAABAB);

[0149] • Alternating polymerization of monomers (e.g., monomers A and B polymerize to form ABABABAB);

[0150] • Monomers that undergo gradient polymerization (e.g., monomers A and B polymerize into AAABAABBABBBB);

[0151] • Block copolymers (e.g., monomers A and B polymerized into AAAAABBBBBB), where the block length of each block (2, 3, 4, 5 or more) is important for the dispersing ability of the polymer dispersant;

[0152] • Graft copolymers (graft copolymers consist of a polymer backbone and polymer side chains attached to the backbone); and

[0153] • Mixed forms of these polymers, such as block gradient copolymers.

[0154] The polymer dispersant preferably has a number average molecular weight Mn between 500 and 30,000, more preferably between 1,500 and 10,000.

[0155] The polymer dispersant preferably has a weight-average molecular weight Mw of less than 100,000, more preferably less than 50,000, and most preferably less than 30,000.

[0156] The polymer dispersant preferably has a polymerization dispersibility PD of less than 2, more preferably less than 1.75, and most preferably less than 1.5.

[0157] Commercial examples of polymer dispersants are as follows:

[0158] ·DISPERBYK TM Dispersant, obtained from BYK CHEMIE GMBH;

[0159] SOLSPERSE TM Dispersant, obtained from LUBRIZOL;

[0160] ·TEGO TM DISPERS TM Dispersant, obtained from EVONIK;

[0161] ·EDAPLAN TM Dispersant, derived from CHEMIE;

[0162] ·ETHACRYL TM Dispersant, obtained from LYONDELL;

[0163] ·GANEX TM Dispersant, obtained from ISP;

[0164] DISPEX TM and EFKA TM Dispersant, obtained from BASF;

[0165] ·DISPONER TM Dispersant, derived from DEUCHEM.

[0166] Particularly preferred polymer dispersants include Solsperse from LUBRIZOL. TM Dispersant, Efka from BASF TM Dispersant, Disperbyk, obtained from BYK CHEMIE GMBH TM Dispersant and Ajisper from AJINOMOTO FINE-TECHNOCo TM Dispersant. A particularly preferred dispersant is Solsperse from LUBRIZOL. TM Dispersants 32000, 35000 and 39000, and Disperbyk from BYK CHEMIE GMBH. TM 162.

[0167] The dispersant can be used alone or in combination of two or more of them.

[0168] Based on the weight of the pigment, the polymer dispersant is preferably used in an amount of 2 wt% to 600 wt%, more preferably 5 wt% to 200 wt%, and most preferably 50 wt% to 90 wt%.

[0169] Dispersing synergists

[0170] Free radical curable inkjet inks can contain dispersions to further improve dispersion stability via polymer dispersants, and thus also improve printing reliability, as less pigment will deposit in the nozzles of the printhead when the inkjet unit is idle.

[0171] Dispersing synergies typically consist of anionic and cationic moieties. The anionic moieties of dispersing synergies exhibit a certain molecular similarity to colored pigments, while the cationic moieties consist of one or more protons and / or cations to compensate for the charge of the anionic moieties.

[0172] The dispersant synergist is preferably added in a smaller amount than the polymeric dispersant. The ratio of polymeric dispersant to dispersant synergist depends on the pigment and should be determined experimentally. Typically, the ratio of wt% polymeric dispersant to wt% dispersant synergist is selected between 2:1 and 100:1, preferably between 2:1 and 20:1.

[0173] Commercially available suitable dispersants include Solsperse from LUBRIZOL. TM 5000 and Solsperse TM 22000.

[0174] For the magenta ink used, particularly preferred pigments are diketopyrrolopyrrole pigments or quinacridone pigments. Suitable dispersing synergists include those disclosed in EP 1790698 A (AGFA GRAPHICS), EP 1790696 A (AGFA GRAPHICS), WO 2007 / 060255 (AGFA GRAPHICS) and EP 1790695 A (AGFA GRAPHICS).

[0175] When dispersing CI pigment blue at a ratio of 15:3, it is preferable to use a copper phthalocyanine sulfonate dispersing synergist, such as Solsperse from LUBRIZOL. TM 5000. Dispersing synergists suitable for yellow inkjet inks include those disclosed in EP 1790697 A (AGFAGRAPHICS).

[0176] Polymer inhibitors

[0177] Radical-curable inkjet inks can also contain polymerization inhibitors. Because of the presence of polymerization inhibitors, polymerization reactions that may occur before curing, such as during storage or transportation, are prevented. Furthermore, because the UV LEDs in the printhead of the inkjet printer maintain the radical-curable ink at relatively high temperatures, such as 45°C to 55°C, printing reliability is also improved.

[0178] Suitable polymerization inhibitors include phenolic antioxidants, hindered amine light stabilizers, phosphorescent antioxidants, benzoquinone, hydroquinone and its derivatives, such as hydroquinone monomethyl ether, which is commonly used in (meth)acrylate monomers.

[0179] Examples of phenol polymerization inhibitors include, but are not limited to, the following substances: p-methoxyphenol, cresol, tert-butylcatechol, di-tert-butyl-p-cresol, hydroquinone monomethyl ether, α-naphthol, 3,5-di-tert-butyl-4-hydroxytoluene, 2,6-di-tert-butyl-4-methylphenol, 2,2'-methylene-bis(4-methyl-6-tert-butylphenol), 2,2'-methylene-bis(4-ethyl-6-butylphenol), and 4,4'-thio-bis(3-methyl-6-tert-butylphenol) and pyrogallol.

[0180] Suitable commercially available inhibitors include, for example, Sumilizer. TM GA-80, Sumilizer TM GM and Sumilizer TM GS, manufactured by Sumitomo Chemical Co., Ltd.; Genorad TM 16. Genorad TM 18 and GenoradTM 20, derived from Rahn AG; Irgastab TM UV10 and Irgastab TM UV22, Tinuvin TM 460 and CGS20, obtained from Ciba Specialty Chemicals; Floorstab TM The UV series (UV-1, UV-2, UV-5, and UV-8) is derived from KromachemLtd; Additol TM The S series (S100, S110, S120 and S130) are from Cytec Surface Specialties.

[0181] The preferred polymerization inhibitor is Irgastab, obtained from BASF. TM UV10. Other examples of polymerization inhibitors include TEMPO, TEMPOL, and the Al copper-iron reagent.

[0182] Polymerization inhibitors can be used alone or in combination of two or more of them.

[0183] In a preferred embodiment, the polymerization inhibitor is a mixture of different types of polymerization inhibitors. Preferred polymerization inhibitors are mixtures of oxy radical-based polymerization inhibitors, phenol-based polymerization inhibitors, and amine-based polymerization inhibitors. Suitable examples are given in EP 2851402A (FUJIFILM).

[0184] Based on the total weight of the free radical curable inkjet ink, the polymerization inhibitor is preferably present in an amount of 0.1 wt% to 5 wt%. Below 0.1 wt%, undesirable polymerization is not adequately inhibited, while above 5 wt%, the curing rate is severely reduced.

[0185] surfactants

[0186] Radical-curable inkjet inks may contain surfactants. These surfactants can be anionic, cationic, nonionic, or amphoteric. Based on the total weight of the radical-curable inkjet ink, the surfactant is preferably present in an amount of 0.1 wt% to 3 wt%. At concentrations above 3 wt%, adhesion may deteriorate rapidly, while at concentrations below 0.1 wt%, insufficient ink spreading is typically observed.

[0187] Based on the total weight of the ink, the total amount of surfactant is preferably less than 3 wt%, and more preferably less than 1.5 wt% based on the total weight of the free radical curable inkjet ink, to prevent the ink from foaming in its container. Such foaming has a negative impact on printing reliability.

[0188] Preferred surfactants are selected from fluorinated surfactants (such as fluorinated hydrocarbons) and silicone surfactants. The silicone surfactant is preferably a siloxane and may be alkoxylated, polyester-modified, polyether-modified, polyether-modified hydroxyl-functionalized, amine-modified, epoxy-modified, or other modified or combinations thereof. Preferred siloxanes are polymers, such as polydimethylsiloxane.

[0189] Preferred commercially available silicone surfactants include BYK from BYK Chemie. TM 333 and BYK TM UV3510 and Tegoglide obtained from EVONIK TM 410.

[0190] In a preferred embodiment, the surfactant is a polymerizable compound.

[0191] Preferred polymerizable silicone surfactants include (meth)acrylated silicone surfactants. Most preferably, (meth)acrylated silicone surfactants are acrylated silicone surfactants because acrylates are more reactive than methacrylates.

[0192] In a preferred embodiment, the (meth)acrylated silicone surfactant is a polyether-modified (meth)acrylated polydimethylsiloxane or a polyester-modified (meth)acrylated polydimethylsiloxane.

[0193] Preferred commercially available (meth)acrylated silicone surfactants include: silicone diacrylate Ebecryl TM 350, obtained from Cytec; polyether-modified acrylated polydimethylsiloxane BYK TM UV3500, BYK TM UV3510 and BYK TM UV3530; Polyester-modified acrylated polydimethylsiloxane BYK TM UV3570, entirely manufactured by BYK Chemie; Tego TM Rad 2100, Tego TM Rad 2200N, Tego TM Rad 2250N, Tego TM Rad 2300, Tego TM Rad2500, Tego TM Rad 2600, Tego TM Rad 2700 and Tego TMRC711, entirely manufactured by EVONIK. Another preferred silicone is Silwet from OSI SPECIALITIES BENELUX NV. TM L7500; Silaplane TM FM7711, Silaplane TM FM7721, Silaplane TM FM7731, Silaplane TM FM0711, Silaplane TM FM0721, Silaplane TM FM0725, Silaplane TM TM0701, Silaplane TM TM0701T, all manufactured by CHISSO Corporation; and DMS-R05, DMS-R11, DMS-R18, DMS-R22, DMS-R31, DMS-U21, DBE-U22, SIB1400, RMS-044, RMS-033, RMS-083, UMS-182, UMS-992, UCS-052, RTT-1011 and UTT-1012, all manufactured by GELEST Inc.

[0194] The preferred surfactant for free radical inkjet inks is derived from SILTECH CORPORATION. Surfactants, such as ACR Di-1508.

[0195] Preparation of free radical curable inkjet inks

[0196] The preparation of UV-curable inkjet inks is generally well known to those skilled in the art.

[0197] The average particle size and distribution of colored pigments are important characteristics of inkjet inks. Inkjet inks can be prepared by precipitating or grinding pigments in a dispersion medium in the presence of a dispersant.

[0198] Mixing equipment can include pressure kneaders, open kneaders, planetary mixers, dissolvers, and Dalton general-purpose mixers. Suitable grinding and dispersing equipment includes ball mills, pearl mills, colloid mills, high-speed dispersers, two-roll mills, bead mills, paint conditioners, and three-roll mills. Dispersions can also be prepared using ultrasonic energy.

[0199] Different types of materials can be used as abrasive media, such as glass, ceramics, metals, and plastics. In a preferred embodiment, the abrasive media may comprise particles, preferably substantially spherical in shape, such as beads composed substantially of polymer resin or yttrium-stabilized zirconia beads.

[0200] During the mixing, grinding, and dispersing processes, each process is carried out under cooling to prevent heat accumulation and, as far as possible, under light conditions that largely exclude photochemical radiation.

[0201] Inkjet inks can contain more than one pigment and can be prepared using separate dispersions for each pigment, or alternatively, multiple pigments can be mixed and co-ground during the preparation of the dispersion.

[0202] The dispersion process can be carried out in continuous, intermittent, or semi-intermittent modes.

[0203] The preferred amounts and ratios of the abrasive components will vary depending on the specific material and intended application. The contents of the abrasive mixture include abrasive particles and abrasive media. The abrasive particles contain pigments, polymeric dispersants, and liquid carriers. For inkjet inks, pigments are typically present in the abrasive particles at 5 wt% to 50 wt%, in addition to the abrasive media. The weight ratio of pigment to polymeric dispersant is preferably 20:1 to 1:2, more preferably 2:1 to 1:1.

[0204] The optimal grinding time can vary and depends on the selected pigment, mechanical means and residence conditions, initial and desired final particle size, etc. In this invention, pigment dispersions with an average particle size of less than 100 nm can be prepared.

[0205] After grinding, conventional separation techniques, such as filtration and sieving, are used to separate the grinding media from the ground particulate product (in dry or liquid dispersion form). Typically, the sieve is integrated into the grinding mill, such as a bead mill. The ground pigment concentrate is preferably separated from the grinding media by filtration.

[0206] Typically, it is desirable to prepare inkjet inks in the form of concentrated pigment dispersions, which are then diluted to the appropriate concentration for use in inkjet printing systems. This technology allows for the self-preparation of larger quantities of colored inks. Through dilution, the inkjet ink is adjusted to the desired viscosity, surface tension, color, hue, saturation density, and print coverage for a specific application.

[0207] inkjet device

[0208] The inkjet device according to the present invention preferably includes the above-described inkjet ink kit and a UV LED source with spectral emission in the range of 360-420 nm.

[0209] Radical-curable inkjet ink is ejected from a printhead that propels small droplets through nozzles onto a substrate moving relative to one or more printheads in a controlled manner. A preferred printhead for inkjet printing systems is a piezoelectric printhead. Piezoelectric inkjet printing is based on the movement of a piezoelectric ceramic transducer when a voltage is applied to it. The applied voltage alters the shape of the piezoelectric ceramic transducer in the printhead, creating voids that are then filled with inkjet ink or liquid. When the voltage is removed again, the ceramic expands back to its initial shape, ejecting ink droplets from the printhead. Piezoelectric printheads have proven to be the most reliable printheads in industrial printing.

[0210] The preferred piezoelectric printhead is the so-called push-mode piezoelectric printhead, which has a relatively large piezoelectric element that is also capable of ejecting more viscous ink droplets. Such a printhead is available from RICOH with the GEN5s printhead.

[0211] Another preferred piezoelectric printhead is the so-called through-flow piezoelectric on-demand inkjet printhead. Such printheads are available from TOSHIBA TEC as CF1ou printheads. Through-flow printheads are preferred because they enhance the reliability of inkjet printing due to the continuous flow of ink through the printhead.

[0212] Inkjet printheads typically scan laterally back and forth across a moving, ink-receiving surface. Sometimes the printhead does not print on the return path; however, bidirectional printing is preferred for high area throughput.

[0213] Another preferred inkjet device uses a "single-pass printing method," which can be performed using a page-width inkjet printhead covering the entire width of the substrate surface or multiple staggered inkjet printheads. In the single-pass printing method, the inkjet printhead is typically stationary, and the substrate is fed beneath the printhead.

[0214] To facilitate curing, inkjet printers may include one or more oxygen-deficient devices. To reduce the oxygen concentration in the curing environment, the oxygen-deficient devices are arranged with a coating of nitrogen or other relatively inert gases (e.g., CO2) in an adjustable position and with an adjustable inert gas concentration. Residual oxygen levels are typically maintained as low as 200 ppm, but generally range from 200 ppm to 1200 ppm.

[0215] Inkjet printing method

[0216] The inkjet printing method according to the present invention preferably includes the following steps:

[0217] a) Spraying the free radical curable inkjet ink as described above onto the substrate; and

[0218] b) Free radical curable inkjet inks are cured by a UV LED source that emits light in the 360-420 nm range.

[0219] In a preferred embodiment of the inkjet printing method, the substrate is a backlight film comprising a material selected from polyethylene terephthalate (PET), polyethylene, polypropylene, polycarbonate, polyacrylate, polystyrene, nylon, and polyvinyl acetate.

[0220] Any inkjet device as described above can be used in inkjet printing methods. The UV LED has an emission wavelength greater than 360 nm, preferably greater than 370 nm.

[0221] In a particularly preferred embodiment, inkjet printing of UV-curable inkjet inks is performed in a multi-pass printing mode. Multi-pass printing is a technique used to reduce banding in inkjet printing. When ink droplets are still in liquid form, they tend to move together due to surface tension. This is called coalescence. For printing high-quality images, it is important to print individual dots. However, to achieve fully saturated colors, the dots must overlap to completely cover the substrate. Coalescence can be largely avoided by printing only a portion of the image data to avoid printing adjacent dots simultaneously in each printing cycle. In addition, by avoiding all horizontally adjacent portions, the lateral speed of the printing mechanism can be increased to twice the rated printing speed of the print head. In a preferred embodiment, the number of passes used is 2 to 6, more preferably no more than 4. Multi-pass printing offers higher printing reliability than single-pass inkjet printing.

[0222] The advantage of using multi-pass printing is that UV-curable inkjet inks cure in a continuous pass, rather than in a single pass, which requires a curing unit with high UV output. For multi-pass printing, the printhead life is also longer. While in single-pass printing, one side emitter is sufficient to replace the entire printhead, in multi-pass printing, many side emitters can be accommodated, and even failures can be tolerated. Furthermore, multi-pass printing presses are generally much less expensive, especially for wide-format substrates.

[0223] substrate

[0224] There are no practical limitations on the type of substrate on which the UV-curable inkjet ink of the present invention is applied for inkjet printing. The substrate can be rigid, but the inkjet ink of the present invention can be advantageously used on flexible substrates. The substrate can also be primed or pretreated, for example, by corona, plasma, or flame treatment.

[0225] A particularly preferred substrate is that used in so-called backlit display systems. Backlit display systems enhance graphics by illuminating the image from behind, thus displaying the image more clearly. Such systems are commonly seen in airports, shopping malls, restaurants, and the like.

[0226] Backlight films are readily available commercially (e.g., from GRIMCO). A semi-transparent PVC film, and typically contains materials selected from polyvinyl chloride, polyethylene terephthalate (PET), polyethylene, polypropylene, polycarbonate, polyacrylate, polystyrene, nylon, and polyvinyl acetate.

[0227] The backlight film is semi-transparent, allowing light to pass through from the back. Backlight films are typically reinforced by incorporating fabric. For example, DERFLEX... TM PVC backlit banners consist of a semi-transparent PVC layer, polyester fabric, and a semi-transparent PVC backing. The backlight film can be glossy or matte.

[0228] The preferred backlight film is a PVC backlight film with a thickness of less than 300μm.

[0229] Example

[0230] Measurement methods

[0231] 1. Average particle size

[0232] The average particle size of pigment particles in diluted samples of colored inkjet inks was determined by photon correlation spectroscopy at a wavelength of 633 nm using a 4 mW HeNe laser. The particle size analyzer used was a Malvern from Goffin-Meyvis. TM nano-S.

[0233] The sample was prepared by adding one drop of ink to a cuvette containing 1.5 mL of ethyl acetate and mixing until a homogeneous sample was obtained. The particle size was measured as the average of three consecutive measurements, which consisted of six 20-second runs.

[0234] 2. Folding test

[0235] After inkjet printing, the A5-sized printed sample is folded twice, with the printed images touching each other. The sample is then placed between two steel plates weighed down with 30 kg each and stored in a refrigerator at -18°C for 24 hours. Afterward, the sample is unfolded, and the images are examined and scored according to Table 2, where a score of C or D is unacceptable.

[0236] Table 2

[0237] score observe A No visible cracks B Some small cracks are visible. C Small and larger cracks are clearly visible. D The ink layer is partially removed from the substrate.

[0238] 3. Wrinkle test

[0239] After inkjet printing, the A5-sized printed sample is layered belly-against back. The printed sample is placed between two steel plates weighed down by 3.6 kg each (plates + weight = 4.8 kg) and stored in a refrigerator at -18°C for 24 hours. Immediately afterwards, the printed sample is wrinkled in all directions at -18°C.

[0240] Examine the printed image and give a score according to Table 3, where a score of C or D is unacceptable.

[0241] Table 3

[0242] score observe A No visible defects B A small portion (<5%) of the ink detached from the substrate. C A significant portion (5% to 25%) of the ink detaches from the substrate. D More than 25% of the ink detached from the substrate.

[0243] 4. Finger test

[0244] Press your thumbnail against the substrate on the opposite side of the printed image. Examine the image of the printed sample and give a score according to Table 4, where a score of B or C is unacceptable.

[0245] Table 4

[0246] score observe A No visible cracks in the ink layer B Cracks are visible in the ink layer. C Part of the ink layer detached from the substrate.

[0247] 5. Adhesion

[0248] The viscosity of free radical curable inkjet inks was improved by applying Anapurna inks from AGFA to a 230μm PVC backlight film. TM The 2050i LED was measured in "Quality Mode" with 100% ink coverage and a 720x720dpi resolution printed in a 13cm x 19cm square.

[0249] After inkjet printing, the printed sample was directly covered with an unprinted substrate on the printed surface and placed between two steel plates. It was then kept in an oven at 25°C and 95% relative humidity under a weight of 4.85 kg for 24 hours. The amount of ink transferred to the back of the unprinted substrate was then checked, and a score was given according to Table 5.

[0250] Table 5

[0251]

[0252] 6. Viscosity

[0253] Uses Rotovisco obtained from HAAKE TM RV1 viscometer, at 45°C and 1,000 s -1 The viscosity of UV-curable inkjet inks was measured at shear rates.

[0254] Material

[0255] Unless otherwise specified, all materials used in the following examples are readily available from standard sources such as Aldrich Chemical Co. (Belgium) and Acros (Belgium). Any water used is demineralized water.

[0256] PB15:4 is used for Heliogen TM Blue D 7110F is an abbreviation for Blue D, which is a 15:4 pigment derived from BASF's CI pigment blue.

[0257] PY155 is CI Pigment Yellow 155 pigment, which uses Inkjet from CLARIANT. TM Yellow 4GC.

[0258] PB15:4 is used for Sunfast TM The abbreviation for Blue 15:4 is derived from the C1 pigment Blue 15:4 of Sun Chemical Corporation.

[0259] PB7 is for Special Black TM 550 is an abbreviation for carbon black derived from EVONIK.

[0260] PR122 is an abbreviation for CI Pigment Red 122, which is derived from TRUST CHEM EUROPE BV's PIGMENT RED 122TCR12203IJ.

[0261] SYN is a dispersant according to formula (A):

[0262]

[0263] It was synthesized in the same manner as described in Example 1 of WO 2007 / 060254 (AGFA GRAPHICS) regarding synergist QAD-3.

[0264] DB162 is used in the polymer dispersant Disperbyk. TM The abbreviation 162 is available from BYK CHEMIE GMBH, which removes the solvent mixture of 2-methoxy-1-methylethyl acetate, xylene, and n-butyl acetate. The polymer dispersant is a polyester-polyurethane dispersant based on caprolactone and toluene diisocyanate, with an amine value of 13 mg KOH / g, Mn of approximately 4,425, and Mw of approximately 6,270.

[0265] PEA is 2-phenoxyethyl acrylate (MW = 192), available from ARKEMA via Sartomer. TM SR339C obtained.

[0266] NVC is N-vinylcaprolactam (MW = 139), which is available from BASF BELGIUM, NV.

[0267] TBCH is 4-tert-butylcyclohexyl acrylate (MW = 210), available from ARKEMA under the trade name Sartomer CD217.

[0268] IBOA is isobornyl acrylate (MW = 208), available from ARKEMA as Sartomer. TM SR506D obtained.

[0269] 4-HBA is 4-hydroxybutyl acrylate (MW=144) derived from BASF.

[0270] IDA is isodecyl acrylate (MW = 212), available from ARKEMA via Sartomer. TM Obtained from SR395.

[0271] CTFA is a cyclic trimethylolpropane-formaldehyde acrylate (MW = 200), available from ARKEMA via Sartomer. TM SR531 obtained.

[0272] DPGDA is dipropylene glycol diacrylate (MW = 252), available from ARKEMA as Sartomer. TM SR508 obtained.

[0273] 15EO-TMPTA is an ethoxylated (15)trimethylolpropane triacrylate (MW = 956) containing fifteen ethoxy units, available from ARKEMA via Sartomer. TM SR9035 obtained.

[0274] PEG400DA is polyethylene glycol diacrylate (MW=508), available from ARKEMA as Sartomer. TM SR344 obtained.

[0275] PEG200DA is polyethylene glycol diacrylate (MW=302), available from ARKEMA as Sartomer. TM SR259 obtained.

[0276] M202 is hexanediol ethoxylated (3) diacrylate (MW = 314), available from Miwon Specialty Chemical Co., Ltd. via Miramer. TM M202 obtained.

[0277] CN963B80 is a urethane acrylate oligomer (MW = 1900) with two acrylate groups, available from ARKEMA as Sartomer. TM CN963B80 was obtained.

[0278] CN704 is an acrylated polyester oligomer (MW = 5000) with two acrylate groups, available from ARKEMA as Sartomer. TM CN704 was obtained.

[0279] TPO is developed by IGM RESINS under Omnirad. TM TPO supplies trimethylbenzoyl diphenylphosphine oxide.

[0280] T410 is a silicone surfactant available from EVONIK as Tegoglide. TM 410 was obtained.

[0281] B3510 is a polyether-modified polydimethylsiloxane wetting agent available from BYK CHEMIE GMBH. TM UV3510.

[0282] UV10 is 4-hydroxy-2,2,6,6-tetramethylpiperidinoxy sebacate, available from Shanghai FINC Chemical Technology Co., Ltd.

[0283] INHIB is a mixture of polymerization inhibitors that form a composition according to Table 6.

[0284] Table 6

[0285] Components wt% DPGDA 82.4 p-Methoxyphenol 4.0 Butylated hydroxytoluene (BHT) 10.0 <![CDATA[Cupferron TM AL]]> 3.6

[0286] BHT is an abbreviation for 2,6-di-tert-butyl-4-methylphenol (CASRN128-37-0), derived from ALDRICH CHEMICAL CO.

[0287] Cupferron TM AL is N-nitrosophenylhydroxylamine aluminum obtained from WAKO CHEMICALS LTD.

[0288] Example 1

[0289] This embodiment illustrates the improved adhesion and scratch resistance obtained using the UV LED radical curable inkjet ink according to the present invention, while achieving good surface curing (low viscosity) through UV LED curing.

[0290] Preparation of concentrated pigment dispersions

[0291] The preparation of concentrated pigment dispersions is illustrated using a concentrated cyan pigment dispersion (CPC) as an example. Other concentrated pigment dispersions can be prepared in the same manner, except for those using the components listed in Table 7.

[0292] Used from DISPERLUX SARL, Luxembourg TM A concentrated cyan pigment dispersion (CPC) was prepared by mixing the components according to Table 7 for 30 minutes in a disperser. The dispersion was then ground using a Bachofen DYNOMILL ECM mill filled with 0.4 mm yttrium-stabilized zirconia beads (from TOSOH). The mixture was circulated in the mill for 2 hours. After grinding, the concentrated pigment dispersion was discharged into a container through a 1 μm filter. The concentrated pigment dispersion (CPC) had an average particle size of 90 nm.

[0293] Table 7

[0294] The following wt%: CPC CPY CPK PB15:4 25.00 4.77 PY155 25.00 PB7 13.32 PR122 3.33 SYN 0.13 DB162 10.00 8.00 9.13 INHIB 1.00 1.00 2.04 PEA 64.00 68.00 67.28 Total = 100.00 100.00 100.00 Average particle size 99nm 163nm 123nm

[0295] Preparation of inkjet ink

[0296] The concentrated dispersions prepared above were used to prepare free radical curable inkjet inks COMP-1 to COMP-10 and INV-1 to INV-12 according to Tables 8 to 11.

[0297] Table 8

[0298]

[0299]

[0300] Table 9

[0301]

[0302]

[0303] Table 10

[0304]

[0305] Table 11

[0306]

[0307]

[0308] Evaluation and Results

[0309] The viscosity of each free radical curable inkjet ink was measured, and it was found that the viscosity was in the range of 6 to 8 mPa·s at 45°C.

[0310] Anapurna, obtained from AGFA TM For the 2050i LED, each free radical-cured inkjet is printed in "quality mode" with 100% ink coverage and a resolution of 720x720dpi on an A4-sized 230μm thick PVC backlight film as a rectangle, leaving a 1cm unprinted border on the substrate.

[0311] The inkjet inks were then subjected to folding, wrinkling, tack, and finger tests. The results are shown in Table 12. In the table, the headings have the following meanings:

[0312] •DBD7 = wt% of monofunctional polymerizable compounds with a double bond density DBD greater than 7.00;

[0313] •% Mono = wt% of the monofunctional polymerizable compound based on the total weight of the polymerizable composition;

[0314] PAA = wt% of polyfunctional alkoxylated acrylates with a total weight molecular weight (MW) greater than 310 based on the total weight of the polyfunctional polymerizable compound;

[0315] • Ratio = The ratio of wt% of polyfunctional alkoxylated acrylates with a molecular weight (MW) greater than 310 to wt% of non-aromatic cyclic monofunctional acrylates; and

[0316] •DBD = Double bond density of a polymerizable composition in mmol / g.

[0317] Table 12

[0318]

[0319]

[0320] The results in Table 12 clearly show that only free radical curable inkjet inks INV-1 to INV-12 can achieve the desired properties for folding, wrinkling, tack, and finger testing. It can also be seen that this was achieved for different types of colored pigments.

Claims

1. A free radical curable inkjet ink comprising a colored pigment, a photoinitiator, and a polymerizable composition, wherein the polymerizable composition comprises a monofunctional polymerizable compound and a polyfunctional polymerizable compound; The monofunctional polymerizable compound may be a monomer or an oligomer; The multifunctional polymerizable compound is a monomer or oligomer having two, three or more polymerizable groups; The polymerizable composition comprises more than 90.0 wt% of monofunctional monomers based on the total weight of the polymerizable composition; Of which more than 13.0 wt% of the monofunctional polymerizable compound has a double bond density DBD of more than 7.00 mmol / g, and the wt% is based on the total weight of the radical curable inkjet ink; Based on the total weight of the multifunctional polymerizable compounds, there are more than 35.0 wt% of multifunctional alkoxylated acrylates with a molecular weight (MW) greater than 310; The presence of non-aromatic cyclic monofunctional acrylates results in a ratio of wt% of polyfunctional alkoxylated acrylates with a molecular weight (MW) greater than 310 to wt% of non-aromatic cyclic monofunctional acrylates greater than 0.35; and the double bond density (DBD) of the polymerizable composition is not greater than 5.55 mmol / g. The double bond density (DBD) of the polymerizable composition is calculated using the following formula: ， in i represents an integer from 1 to n; n represents the number of monomers and oligomers in UV LED free radical curable inkjet ink; F(i) represents the functionality of monomer or oligomer i; MW(i) represents the molecular weight of monomer or oligomer i; and wt%(i) is the weight percentage of monomers or oligomers i in the total weight of the free radical curable inkjet ink.

2. The free radical curable inkjet ink of claim 1, wherein, based on the total weight of the polyfunctional alkoxylated acrylates with a molecular weight (MW) greater than 310, the polyfunctional alkoxylated acrylates with a molecular weight (MW) greater than 310 comprise 80 wt% to 100 wt% of difunctional acrylates.

3. The free radical curable inkjet ink according to claim 1, wherein the polyfunctional alkoxylated acrylate with a molecular weight MW greater than 310 has a molecular weight MW between 400 and 1000.

4. The free radical curable inkjet ink according to claim 1, wherein the free radical curable inkjet ink is a UV LED curable free radical curable inkjet ink for UV LED sources with spectral emission in the range of 360 to 420 nm.

5. The free radical curable inkjet ink of claim 4, wherein, based on the total weight of the free radical curable inkjet ink, the photoinitiator comprises an amount of greater than 5.0 wt% of an acylphosphine oxide photoinitiator.

6. The free radical curable inkjet ink according to claim 1, wherein, based on the total weight of the multifunctional polymerizable compound, the free radical curable inkjet ink contains more than 43.0 wt% of multifunctional alkoxylated acrylates with a molecular weight (MW) greater than 310.

7. The free radical curable inkjet ink according to claim 1, wherein, based on the total weight of the free radical curable inkjet ink, the free radical curable inkjet ink contains more than 40 wt% of aromatic monofunctional monomers.

8. The free radical curable inkjet ink according to claim 7, wherein the aromatic monofunctional monomer comprises phenoxyethyl acrylate.

9. The free radical curable inkjet ink according to claim 1, wherein the free radical curable inkjet ink contains 14.0 wt% to 24.0 wt% of a monofunctional polymerizable compound with a double bond density (DBD) greater than 7.

00.

10. The free radical curable inkjet ink according to claim 1, wherein the monofunctional polymerizable compound with a double bond density (DBD) greater than 7.00 is N-vinylmethyloxazolidinone or N-vinylcaprolactam.

11. A free radical curable inkjet ink kit comprising at least three free radical curable inkjet inks according to any one of claims 1 to 10.

12. The free radical curable inkjet ink kit according to claim 11, comprising: a) Cyan free radical curable inkjet inks containing β-copper phthalocyanine pigment; b) Magenta or red free radical curable inkjet inks containing quinacridone pigments, diketopyrrolopyrrole pigments or mixed crystals thereof; c) Yellow free radical curable inkjet inks containing yellow pigments selected from the following: CI Pigment Yellow 83, CI Pigment Yellow 93, CI Pigment Yellow 97, CI Pigment Yellow 110, CI Pigment Yellow 120, CI Pigment Yellow 138, CI Pigment Yellow 150, CI Pigment Yellow 151, CI Pigment Yellow 154, CI Pigment Yellow 155, CI Pigment Yellow 175, CI Pigment Yellow 180, CI Pigment Yellow 181, CI Pigment Yellow 185, CI Pigment Yellow 194, CI Pigment Yellow 213, CI Pigment Yellow 214, and mixed crystals thereof; and d) Black free radical curable inkjet inks containing carbon black pigments.

13. An inkjet apparatus comprising an inkjet ink kit as claimed in claim 11 or 12 and a UV LED source with spectral emission in the range of 360-420 nm.

14. An inkjet printing method comprising the following steps: a) Spraying the free radical curable inkjet ink according to any one of claims 1 to 10 onto a substrate; and b) The sprayed free radical curable inkjet ink is cured by a UV LED source with spectral emission in the 360-420 nm range.

15. The inkjet printing method according to claim 14, wherein the substrate is a backlight film, the backlight film comprising a material selected from polyvinyl chloride, polyethylene terephthalate (PET), polyethylene, polypropylene, polycarbonate, polyacrylate, polystyrene, nylon, and polyvinyl acetate.

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