Colored radical curable inkjet inks

Abstract

A pigmented free radical curable inkjet ink for making decorated natural leathers, comprising a polymerizable composition satisfying the following requirements A to E, comprising a monofunctional, polyfunctional polymerizable compound: A) 65.0 to 95.0 wt% of a monofunctional polymerizable compound, where the wt% is based on the total weight of the polymerizable composition; b) the polymerizable composition comprises a monofunctional acrylate; c) from 8.0 to 25.0 wt%, based on the total weight of the UV curable inkjet ink, of an N-vinyl oxazolidinone; d) 3.0 to 30.0 wt%, based on the total weight of the UV curable inkjet ink, of a polyethylene glycol diacrylate; e) the polyethylene glycol diacrylate has a molecular weight MW of 350 to 750; and F) the polyfunctional polymerizable compound contains polyethylene glycol diacrylate in an amount of 60 to 100 wt%, based on the total weight of the polyfunctional polymerizable compound.

Description

Technical Field

[0001] The present invention relates to pigmented free radical curable inkjet inks which are particularly suitable for the production of decorated natural leather and leather products thereof. Background Art

[0002] Natural leather has traditionally been decorated by screen printing. However, screen printing is labor intensive because a separate screen is required for each color. This is expensive and time consuming, especially when personalization or customization is desired. Digital printing techniques have been disclosed for printing on natural leather using UV curable inkjet inks. UV curable inkjet inks have the advantage that they can be printed on substantially non-absorbing substrates, including natural leather that has been coated with a coloring layer after tanning and crusting.

[0003] For example, WO 2013 / 135828 (CODUS) discloses a method of printing into leather, the method comprising the steps of: a) applying an ink receptor directly to the leather surface; b) applying the ink directly to the receptor by inkjet; c) applying an additive to the ink; d) heating the surface of a barrier that is substantially impermeable to ink; and e) bringing the heated barrier into direct contact with the ink receptor, additive and ink on the leather surface to soften the additive, ink receptor and ink into the leather, allowing the ink to penetrate into the leather.

[0004] During manufacturing, the leather with the inkjet printed decorative image is stapled. It has been observed that the decorative image is often damaged during stapleing because the UV curable inkjet ink contains a very high amount of monofunctional polymerizable compounds to obtain flexibility and exhibits some stickiness to the leather deposited on the decorative image.

[0005] One option would be to increase the amount of multifunctional polymerizable compound. However, this reduces the flexibility of the printed leather, often resulting in visible cracks in the decorative image.

[0006] Another option would be not to staple the newly printed leather or not to deposit anything on the decorative image. However, this would result in a significant increase in the required storage room, which is economically disadvantageous.

[0007] Therefore, there remains a need for pigmented free radical curable inkjet inks with improved flexibility and adhesion so that printed substrates can be tacked onto limited floor space without causing visible damage to the decorative image printed on the substrate. SUMMARY OF THE INVENTION

[0009] In order to overcome the above problems, a preferred embodiment of the present invention has been achieved with a pigmented free radical curable inkjet ink as claimed in claim 1.

[0010] Surprisingly it has been found that by using a specific combination of polymerizable compounds, inkjet printed leathers can be obtained which exhibit excellent flexibility and adhesion.

[0011] These and other objects of the present invention will become apparent from the detailed description which follows. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 A traditional manufacturing process diagram of a leather product showing the different stages and locations involved.

[0014] Figure 2 Schematically showing a cross section of an animal hide comprising a grain (21) and a genuine leather (23) separated by a junction (22) of the grain and the genuine leather. Different leathers made from animal hides include full grain leather (24), top grain leather (25) and split leather (26).

[0015] Implementation Description

[0016] definition

[0017] The term "crusted leather" or "crust leather" refers to leather that has been tanned and crusted but not finished.

[0018] The term "monofunctional" as used in reference to a monofunctional polymerizable compound refers to a compound containing a single polymerizable group.

[0019] The term "polyfunctional" as used in polyfunctional polymerizable compounds refers to compounds containing two, three or more polymerizable groups.

[0020] Pigmented free radical curable inkjet inks

[0021] According to a preferred embodiment of the present invention, a free radical curable inkjet ink for making a colored decorated natural leather comprises a polymerizable composition satisfying the following requirements A to E, comprising a monofunctional, multifunctional polymerizable compound: A) 65.0 to 95.0 wt % of a monofunctional polymerizable compound, wherein the wt % is based on the total weight of the polymerizable composition; B) the polymerizable composition comprises a monofunctional acrylate; C) based on the total weight of the UV curable inkjet ink, 8.0 to 25.0 wt % of an N-vinyl oxazolidinone according to formula 1, wherein the N-vinyl oxazolidinone according to formula 1 is:

[0022]

[0023] Where R 1 To R 4 Not subject to limitations other than those imposed by use in inkjet inks, such as viscosity and ink stability. 1 To R 4 Preferred substituents include hydrogen, alkyl, cycloalkyl, aryl and combinations thereof, any of which may be interrupted by heteroatoms; D) 3.0 to 30.0 wt % of polyethylene glycol diacrylate, based on the total weight of the UV curable inkjet ink; E) the polyethylene glycol diacrylate has a molecular weight MW of 350 to 750; and F) the multifunctional polymerizable compound contains the polyethylene glycol diacrylate in an amount of 60 to 100 wt % based on the total weight of the multifunctional polymerizable compound.

[0024] In a preferred embodiment of the pigmented free radical curable inkjet ink, the N-vinyloxazolidinone according to Formula 1 is N-vinyl-5-methyl-2-oxazolidinone.

[0025] In a preferred embodiment of the pigmented free radical curable inkjet ink, the polymerizable composition has a double bond density DBD in the range of 5.12 to 5.60 mmol double bonds / g, wherein the double bond density DBD is calculated by the following formula:

[0026]

[0027] in

[0028] i represents an integer from 1 to n;

[0029] n represents the number of polymerizable compounds in the UV free radical curable inkjet ink;

[0030] F(i) represents the functionality of polymerizable compound i;

[0031] MW(i) represents the molecular weight of polymerizable compound i; and

[0032] Weight % (i) is the weight percentage of the polymerizable compound i based on the total weight of the pigmented free radical curable inkjet ink. By selecting the double bond density DBD in the above range, an ink viscosity with excellent printing reliability can be obtained.

[0033] The polyethylene glycol diacrylate has a molecular weight MW of 350 to 750. In a preferred embodiment of the pigmented free radical curable inkjet ink, the polyethylene glycol diacrylate has a molecular weight MW of 400 to 600. When the MW is below 400, the flexibility tends to be slightly deteriorated, and when the MW is above 600, the tackiness tends to be slightly deteriorated.

[0034] In a preferred embodiment of the pigmented free radical curable inkjet ink, the multifunctional polymerizable compound consists of a difunctional polymerizable compound. A functionality of the multifunctional polymerizable compound higher than 2 is beneficial for adhesiveness but rapidly reduces flexibility.

[0035] In a preferred embodiment of the pigmented free radical curable inkjet ink, the monofunctional acrylate comprises 20.0 wt% to 33.0 wt% aromatic acrylate, based on the total weight of the pigmented free radical curable inkjet ink. This has been observed to be beneficial for adhesion.

[0036] In a preferred embodiment of the pigmented free radical curable inkjet ink, the pigmented free radical curable inkjet ink contains 70.0 to 93.0 wt% of a monofunctional polymerizable compound, the wt% being based on the total weight of the polymerizable composition. It has been observed that this is beneficial for adhesion.

[0037] In a preferred embodiment of the free radical curable inkjet ink of pigmentation, the polyfunctional polymerizable compound contains polyethylene glycol diacrylate in an amount of 65 to 100 wt % based on the total weight of the polyfunctional polymerizable compound. In such a range, better results are obtained in terms of adhesion and flexibility. It is speculated that higher amounts of smaller molecular weight polyfunctional polymerizable compounds result in more crosslinking, and therefore poor flexibility. On the other hand, higher molecular weight polyfunctional polymerizable compounds result in less crosslinking, and therefore poor adhesion.

[0038] In a preferred embodiment of the pigmented free radical curable inkjet ink, the inkjet ink has a calculated glass transition temperature ink Tg of no more than 18° C., preferably no more than 13° C. The ink Tg can be calculated according to formula (I):

[0039]

[0040] wherein i and n are integers; n is the total number of polymerizable compounds in the free radical curable inkjet ink; TgPC(i) is the glass transition temperature of the polymerizable compound PC(i) in degrees Celsius; and wt%PC(i) is the weight percentage of the polymerizable compound PC(i); and wherein all weight percentages are based on the total weight of the free radical curable inkjet ink.

[0041] The glass transition temperature TgPC(i) used in the above equation is the glass transition temperature of the homopolymer of the polymerizable compound. For many compounds, TgPC(i) is found in Table 1 in paragraph 112 of WO 2020 / 030668 (AGFA). If the polymerizable compound is not listed here, the TgPC(i) of the polymerizable compound can usually be found in the manufacturer's data sheet. If not available, the TgPC(i) of a certain polymerizable compound can be determined by the DSC method as explained in ISO 11357-2:1999.

[0042] There is no limitation to the preferred embodiments of combining the above-described pigmented radical curable inkjet inks.

[0043] Free Radical Curable Inkjet Ink Kit

[0044] The pigmented free radical curable inkjet ink is preferably part of a free radical curable inkjet ink set. This allows for the printing of multi-colour images.

[0045] In a preferred embodiment, the free radical curable inkjet ink set comprises at least three or four pigmented free radical curable inkjet inks as described above. This allows the formation of a CMY or CMYK ink set to obtain excellent flexibility and adhesion of multi-color images printed on flexible substrates.

[0046] In a particularly preferred embodiment, the radical curable inkjet ink set comprises a) a cyan-pigmented radical curable inkjet ink containing a β-copper phthalocyanine pigment; b) a magenta or red-pigmented radical curable inkjet ink containing a quinacridone pigment, a diketopyrrolopyrrole pigment or a mixed crystal thereof; c) a yellow-pigmented radical curable inkjet ink containing a yellow pigment 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-pigmented radical curable inkjet ink containing a carbon black pigment. By using these specific inks, excellent light stability is obtained.

[0047] In a particularly preferred embodiment of the ink set, the cyan, black, magenta or red and yellow free radical curable inkjet inks all have the ink composition as described above.

[0048] The inkjet ink set is preferably a free radical curable CMYK or CRYK inkjet ink set.Such inkjet ink sets provide a very large colour gamut.

[0049] This free radical curable inkjet ink set can also be extended with additional inks (such as red, green, blue and / or orange) to further expand the color gamut of the image.

[0050] The free radical curable inkjet ink set can also be extended by combining full density inkjet inks with light density inkjet inks.The combination of dark and light inks and / or black and grey inks improves the image quality by reducing the particle size.

[0051] The inkjet ink set may also include a colorless free radical curable inkjet ink, such as a varnish. The varnish is used to enhance the gloss of the inkjet printed color image.

[0052] The inkjet ink set may also include a white free radical curable inkjet ink. The white free radical curable inkjet ink preferably contains a titanium dioxide pigment, preferably a rutile pigment, having an average particle size greater than 180 nm, preferably 200 to 280 nm, more preferably 220 to 250 nm. This white ink layer may be placed between the substrate and the color image to make the color more vivid.

[0053] The white free radical curable inkjet ink preferably comprises a pigment having a high refractive index, preferably a refractive index greater than 1.60, preferably greater than 2.00, more preferably greater than 2.50 and most preferably greater than 2.60. Such white pigments generally have very high hiding power, i.e. a limited amount of white ink is required to hide the color of the substrate. The most preferred white pigment is titanium dioxide.

[0054] The white free radical curable inkjet ink preferably contains the white pigment in an amount of 10 to 25 wt%, more preferably 12 to 20 wt%, based on the total weight of the white inkjet ink.

[0055] The average particle diameter of the white pigment is preferably 150 to 500 nm and most preferably 180 to 300 nm. When the average particle diameter is less than 150 nm, sufficient hiding power cannot be obtained, and when the average diameter exceeds 500 nm, the storage ability and jetting suitability of the ink tend to decrease.

[0056] Polymerizable compounds

[0057] Any polymerizable compound known in the art may be used, as long as it complies with the polymerizable composition described above. The polymerizable compound may be any monomer or oligomer found in Polymer Handbook Volume 1+2, 4th Edition, edited by J. BRANDRUP et al., Wiley-Interscience, 1999. An oligomer in the present invention is understood to contain 2 or more repeating monomer units.

[0058] Combinations of monomers and oligomers may also be used. The monomers and oligomers may have varying degrees of functionality, and mixtures including combinations of monofunctional, difunctional, trifunctional and higher functionality monomers and oligomers may be used.

[0059] Monofunctional polymerizable compounds

[0060] An essential feature of the present invention is the combination of a monofunctional acrylate with a specific N-vinyl oxazolidinone according to formula 1:

[0061]

[0062] Where R 1 To R 4 Not subject to limitations other than those imposed by use in inkjet inks, such as viscosity and ink stability. 1 To R 4 Preferred substituents include hydrogen, alkyl, cycloalkyl, aryl, and combinations thereof, any of which may be interrupted by heteroatoms.

[0063] The best choice is R 1 To R4 independently selected from hydrogen or C1 to C 10 alkyl.

[0064] Preferred compounds are disclosed in WO 2015 / 022228 (BASF) and US 4831153 (DOW CHEMICAL).

[0065] In a particularly preferred embodiment, the N-vinyloxazolidinone according to formula 1 is N-vinyl-5-methyl-2-oxazolidinone.

[0066] There is no real restriction on the type of monofunctional acrylate. Combinations of monofunctional acrylates are preferably used to further optimize other properties of the pigmented free radical curable inkjet ink. However, it has been observed that if aromatic monofunctional acrylates are used within a certain range, improved results can be obtained in terms of adhesion.

[0067] In a preferred embodiment of the pigmented free radical curable inkjet ink, the monofunctional acrylate comprises 20.0 wt% to 33.0 wt% aromatic acrylate, based on the total weight of the pigmented free radical curable inkjet ink. A particularly preferred aromatic monofunctional acrylate is phenoxyethyl acrylate.

[0068] Other preferred aromatic acrylates include benzyl acrylate, 2-hydroxy-3-phenoxypropyl acrylate, phenoxy polyethylene glycol acrylate, ethoxylated (4) nonylphenol acrylate, and ethoxylated (4) phenol acrylate.

[0069] The non-aromatic cyclic monofunctional acrylates include heterocyclic monofunctional acrylates and alicyclic monofunctional acrylates.

[0070] Preferred heterocyclic acrylates contain a ring structure in which one or more heteroatoms are preferably oxygen atoms.

[0071] Preferred heterocyclic acrylates include tetrahydrofurfuryl acrylate, caprolactone-modified tetrahydrofurfuryl acrylate, cyclic trimethylolpropane formal acrylate, (2-ethyl-2-methyl-1,3-dioxolan-4-yl) methyl acrylate, (2,2-dimethyl-1,3-dioxolan-4-yl) methacrylate, cyclohexanespriro-2-(1,3-dioxolane-4-yl) methyl acrylate, and (3-ethyloxetane-3-yl) methacrylate.

[0072] Cycloaliphatic acrylates contain one or more all-carbon rings which may be saturated or unsaturated but do not have aromatic character.

[0073] Preferred alicyclic acrylates include 3,3,5-trimethylcyclohexyl acrylate, isobornyl acrylate, 4-tert-butylcyclohexyl acrylate, dicyclopentenyl acrylate; and dicyclopentenyl-oxyethyl acrylate, cyclohexyl acrylate, 1,4-cyclohexanedimethanol monoacrylate and 2-propenoic acid, (octahydro-4,7-methano-1H-inden-1-yl)methyl ester.

[0074] Other preferred monofunctional polymerizable compounds include diethylene glycol butyl ether acrylate, 2-ethylhexyl acrylate, ethoxydiethylene glycol acrylate, 2-ethylhexyl ether acrylate di(ethylene glycol), octyldecyl acrylate, n-octyl acrylate, isodecyl 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, isopentyl acrylate, methoxytriethylene glycol Acrylates, 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-diglycol acrylate, tert-butyl acrylate, carboxyethyl acrylate, 2-(butylcarbamoyl)oxy)ethyl acrylate and 2-hydroxy 3-(prop-enoyloxy)propyl 2-methyl-2-propylhexanoate.

[0075] Multifunctional polymerizable compounds

[0076] 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 a polymerizable compound may be a monomer or an oligomer.

[0077] However, it is preferred that the polyfunctional polymerizable compound contains only polymerizable compounds having two polymerizable groups (preferably two acrylate groups).

[0078] In order to achieve good adhesion and flexibility, an essential multifunctional polymerizable compound in the inkjet ink is polyethylene glycol diacrylate with a molecular weight MW of 350 to 750. This compound should be present in the pigmented free radical curable inkjet ink in an amount of 3.0 to 30.0 wt %, based on the total weight of the free radical curable inkjet ink. In addition, the multifunctional polymerizable compound should contain the polyethylene glycol diacrylate in an amount of 60 to 100 wt %, more preferably 85 to 100 wt %, and most preferably the multifunctional polymerizable compound consists of polyethylene glycol diacrylate with a molecular weight MW of 350 to 750, more preferably 400 to 600. A commercial example of such polyethylene glycol diacrylate is Sartomer from ARKEMA. TM SR344.

[0079] Photoinitiator

[0080] The pigmented free radical curable inkjet ink preferably includes one or more photoinitiators, which preferably consist of a Norrish Type I initiator or a Norrish Type II initiator. Norrish Type I initiators are initiators that cleave upon excitation, immediately generating initiating free radicals. Norrish Type II initiators are photoinitiators that are activated by actinic radiation and form free radicals by abstracting hydrogen from a second compound, which becomes the actual initiating free radical. This second compound is called a polymerization synergist or co-initiator.

[0081] Suitable photoinitiators are disclosed in CRIVELLO, JV et al., Volume III: Photoinitiators for Free Radical Cationic. 2nd edition. BRADLEY ed., G.. London, UK: John Wiley and Sons Ltd, 1998. pp. 287-294.

[0082] Norrish I type photoinitiator

[0083] The Norrish I type photoinitiator is preferably selected from benzoinethers, benzilketals, α-haloketones, α,α-dialkoxyacetophenones, α-hydroxyalkylphenones, α-halosulfones, α-aminoalkylphenones, acylphosphine oxides, acylphosphine sulfides and phenylglyoxalates.

[0084] For high cure speeds with UV LEDs emitting in the range of 360-420 nm, the photoinitiator preferably comprises an acylphosphine oxide photoinitiator and / or an α-hydroxyketone photoinitiator, most preferably at least an acylphosphine oxide photoinitiator.

[0085] The pigmented free radical curable inkjet ink according to the present invention can be advantageously used in combination with UV LEDs emitting in the range of 360-420 nm to reduce tackiness. The reason is that UV LEDs emitting in the range of 360-420 nm generally cure the interior of the ink layer much better than the surface of the ink layer, causing the ink layer to become viscous.

[0086] In a preferred embodiment of the pigmented free radical curable inkjet ink, the photoinitiator comprises ethyl phenyl (2,4,6-trimethylbenzoyl) phosphinate, referred to as TPO-L. TPO-L is a liquid photoinitiator and therefore does not cause solubility problems in the pigmented free radical curable inkjet ink, in contrast to, for example, bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide.

[0087] The free radical curable inkjet ink contains the acylphosphine oxide photoinitiator preferably in an amount of at least 3.0 wt. %, more preferably in an amount of 4.0 to 16.0 wt. %, based on the total weight of the free radical curable inkjet ink.

[0088] Suitable examples of acylphosphine oxide photoinitiators include bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, and ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate, bis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide. Such acylphosphine oxide photoinitiators are commercially available, for example as Omnirad TM 819, Omnirad TM TPO and Omnirad TM TPO-L was purchased from IGM Resins.

[0089] The acylphosphine oxide may also be a polymeric compound such as Omnipol from IGM Resins TM TP.

[0090] The acylphosphine oxide photoinitiator may include an acyl group containing a polymerizable group or an acyl group selected from the following: a benzoyl group substituted by a urea group or an oxalylamide group; a 2,6-dimethylbenzoyl group substituted by a urea group or an oxalylamide group at the 3 position; a 2,6-dimethoxybenzoyl group substituted by a urea group or an oxalylamide group at the 3 position; a 2,4,6-trimethylbenzoyl group substituted by a urea group or an oxalylamide group at the 3 position; and a 2,4,6-trimethoxybenzoyl group substituted by a urea group or an oxalylamide group at the 3 position. By using such an acylphosphine oxide photoinitiator, mesitaldehyde is not released after UV curing, which causes an unpleasant odor of the printed product.

[0091] Suitable acylphosphine oxide photoinitiators having acyl groups substituted by urea groups or oxalylamide groups are disclosed in WO 2019 / 243039 (AGFA).

[0092] WO 2014 / 051026 (FUJIFILM) discloses suitable acylphosphine oxide photoinitiators comprising an acyl group containing a polymerizable group.

[0093] Combinations of different acylphosphine oxide photoinitiators can also be used. For example, a combination of a monofunctional acylphosphine oxide photoinitiator (such as TPO and TPO-L) and a polyfunctional acylphosphine oxide photoinitiator (such as bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide). Preferably, such a combination contains more monofunctional acylphosphine oxide photoinitiator than polyfunctional acylphosphine oxide photoinitiator. Combinations containing at least 70% by weight of a monofunctional acylphosphine oxide photoinitiator (preferably TPO-L) generally exhibit higher curing efficiency.

[0094] Alternatively, the acylphosphine oxide is a polymeric compound in which the acylphosphine oxide structure is bonded to a polymer chain on the acyl side thereof. Suitable compounds are disclosed in WO 2014 / 129213 (FUJIFILM). By bonding the acyl group to the polymer chain, the odor of the printed product is also suppressed.

[0095] Suitable examples of α-hydroxyketone photoinitiators include, but are not particularly limited to, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenylpropane-1-one, and 1-[4-(2-hydroxyethoxy)-phenyl]2-hydroxy-2-methyl-1-propane-1-one.

[0096] Examples of commercially available α-hydroxyketone photoinitiators include, but are not particularly limited to, Omnirad from IGM RESINS M 1173、Omnirad TM 184 and Omnirad TM 127 and OmniradTM 4817.

[0097] The content of the α-hydroxyketone is preferably 1 to 10 wt %, more preferably 2 to 8 wt %, and still more preferably 3 to 6 wt %, based on the total weight of the UV LED radical curable inkjet ink.

[0098] In a particularly preferred embodiment, the α-hydroxyketone photoinitiator is a polymeric or polymerizable photoinitiator.

[0099] An example of a suitable polymeric α-hydroxyketone photoinitiator can be found as Esacure TM KIP150 was obtained from IGMRESINS.

[0100] Suitable polymerizable α-hydroxyketone photoinitiators are disclosed in US Pat. No. 4,922,004 (MERCK), such as 4-(2-acryloyloxyethoxy)-phenyl 2-acryloyloxy-2-propyl ketone prepared in Example 3.

[0101] Norrish II photoinitiator

[0102] The UV LED free radical curable inkjet ink may contain a Norrish II type photoinitiator comprising a photoinitiating portion selected from a thioxanthone group, a carbazole group and a benzophenone group. A Norrish II type photoinitiator containing a thioxanthone group or a carbazole group is particularly preferred because it facilitates UV LED curing, especially for UV LEDs with an emission wavelength of 370 nm or greater.

[0103] Suitable examples of Norrish II type photoinitiators containing a thioxanthone group include, but are not particularly limited to, thioxanthone; diethylthioxanthone, such as 2,4-diethylthioxanthone; isopropylthioxanthone, such as 2-isopropylthioxanthone and 4-isopropylthioxanthone; and chlorothioxanthone, such as 2-chlorothioxanthone.

[0104] A specific example of a commercially available Norrish II type photoinitiator containing a thioxanthone group is Speedcure TM DETX (2,4-diethylthioxanthone) and Speedcure TM ITX (2-isopropylthioxanthone) and Kayacure from Nippon Kayaku Co. TM DETX-S (2,4-diethylthioxanthone).

[0105] EP 2509948 A (AGFA) discloses preferred carbazole photoinitiators. These carbazole photoinitiators have the advantage over thioxanthone photoinitiators of exhibiting less photoyellowing.

[0106] Suitable examples of Norrish II type photoinitiators containing a benzophenone group include, but are not particularly limited to, benzophenone; methyl benzophenone; methyl 2-benzoylbenzoate; phenyl benzophenone, such as 4-phenyl benzophenone; trimethyl benzophenone; bis(alkylamino)benzophenone; and 4-(dialkylamino)benzophenone.

[0107] A specific example of a commercially available Norrish II type photoinitiator containing a benzophenone group is Omnirad from IGMRESINS TM 4MBZ and Omnirad TM , Speedcure from LAMBSON TM PBZ and Speedcure TM 5040. The latter is a mixture of benzophenone and thioxanthone.

[0108] Preferred examples of polymerizable Norrish type II photoinitiators comprising a photoinitiating moiety selected from a thioxanthone group or a benzophenone group are disclosed in EP 2161264 A (AGFA), EP 2199273 A (AGFA) and EP 2684876 A (AGFA).

[0109] Preferred examples of polymeric Norrish type II photoinitiators comprising a photoinitiating moiety selected from a thioxanthone group or a benzophenone group are disclosed in EP 1616920 A (AGFA) and EP 1616899 A (AGFA).

[0110] Commercially available examples of polymeric thioxanthones and benzophenones include Omnipol from IGM RESINS TM BP, Omnipol TM TX and Omnipol TM 2702.

[0111] The content of the Norrish Type II photoinitiator comprising a photoinitiating moiety selected from the group consisting of thioxanthone groups, carbazole groups and benzophenone groups is preferably 0.5 to 7.5 wt%, more preferably 1 to 5 wt%, based on the total weight of the free radical curable inkjet ink. However, if the Norrish Type II photoinitiator is a polymerizable or polymeric thioxanthone or carbazole compound, the content may be higher, preferably up to 25 wt%, more preferably up to 15 wt%, based on the total weight of the free radical curable inkjet ink.

[0112] Polymerization synergist

[0113] To further increase the photosensitivity, the free radical curable inkjet ink may additionally contain one or more co-initiators, also known as polymerization synergists, typically amine synergists.

[0114] Suitable examples of amine synergists can be divided into three groups:

[0115] (1) tertiary aliphatic amines, such as methyldiethanolamine, dimethylethanolamine, triethanolamine, triethylamine and N-methylmorpholine;

[0116] (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

[0117] (3) (Meth)acrylated amines, such as dialkylaminoalkyl (meth)acrylates (eg diethylaminoethyl acrylate) or N-morpholinoalkyl-(meth)acrylates (eg N-morpholinoethyl-acrylate).

[0118] In a preferred embodiment of the free radical curable inkjet ink, the polymerisation synergist is an acrylated amine synergist.

[0119] Suitable amine synergists are available as Omnipol TM ASA, Omnipol TM 894 and Esacure TM A198 was purchased from IGM Resins.

[0120] Preferred commercially available acrylated amine synergists include Photomer TM 4068, 4250, 4771, 4775, 4780, 4967 and 5006.

[0121] Colored Pigments

[0122] Colorants in free radical curable inkjet inks are colored pigments.

[0123] The colored pigment can be black, cyan, magenta, yellow, red, orange, purple, blue, green, brown, white, mixtures thereof, etc. The colored pigment can be selected from those disclosed in HERBST, Willy et al., Industrial Organic Pigments, Production, Properties, Applications, 3rd edition, Wiley-VCH, 2004. ISBN3527305769.

[0124] The colour pigments may be inorganic or organic, but for colours other than black or white they are preferably organic colour pigments. The latter provide a higher colour gamut than inorganic pigments.

[0125] Particularly preferred pigments are CI Pigment Yellow 1, 3, 10, 12, 13, 14, 17, 55, 65, 73, 74, 75, 83, 93, 97, 109, 111, 120, 128, 138, 139, 150, 151, 154, 155, 175, 180, 181, 185, 194 and 213. Most preferred pigments for yellow inkjet inks are selected from CI Pigment Yellow 120, 139, 150, 151, 155, 180, 213 and mixed crystals thereof for the sake of colour gamut and light stability. The latter provide good colour reproduction and light stability.

[0126] Particularly preferred pigments are CI Pigment Red 17, 22, 23, 41, 48:1, 48:2, 49:1, 49:2, 52:1, 57:1, 88, 112, 122, 144, 146, 149, 170, 175, 176, 184, 185, 188, 202, 206, 207, 210, 216, 221, 248, 251, 254, 255, 264, 266, 270 and 272.

[0127] Particularly preferred pigments are CI Pigment Violet 19, 23, 32 and 37.

[0128] For color gamut and light stability, the most preferred pigment for magenta or red inkjet ink is selected from CI Pigment Violet 19, CI Pigment Red 122, 176, 202 and 254, and mixed crystals containing one of the foregoing. The latter provides good color reproduction and light stability.

[0129] Particularly preferred pigments are CI Pigment Blue 15:1, 15:2, 15:3, 15:4, 15:6, 16, 56, 61 and (bridged) aluminum phthalocyanine pigments. For color gamut and light stability, CI Pigment Blue 15:3 or 15:4 is most preferably selected. The latter provides good light stability.

[0130] Particularly preferred pigments are CI Pigment Orange 5, 13, 16, 34, 40, 43, 59, 66, 67, 69, 71 and 73.

[0131] Particularly preferred pigments are CI Pigment Green 7 and 36.

[0132] Particularly preferred pigments are CI Pigment Brown 6 and 7.

[0133] Suitable pigments include mixed crystals of the above-mentioned particularly preferred pigments.Mixed crystals are also referred to as solid solutions.For example, under certain conditions, different quinacridones are mixed with each other to form solid solutions, which are quite different from the physical mixture of compounds and are different from the compounds themselves.In solid solutions, the molecules of the components enter the same lattice, usually but not always, the lattice of one of the components.The x-ray diffraction pattern of the resulting crystalline solid is a pattern that is peculiar to the solid and can be significantly different from the physical mixture of the same components in the same proportion.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 solid solution formation.A commercially available example is Cinquasia Magenta RT-355-D from BASF AG.

[0134] Carbon black is preferred as a black pigment. Suitable black pigments include carbon black, such as Pigment Black 7 (e.g. Carbon Black from MITSUBISHI CHEMICAL ), 400R, L. From CABOT Co. 320, or Carbon Black FW18, Special Black 250, Special Black 350, Special Black550 from DEGUSSA, 25. 35. 55. 90. 150T. In a preferred embodiment, the carbon black pigment used is a pigment having a toluene extractable fraction of less than 0.15% using the method described in section III, paragraph 5 of resolution AP(89)1 of the European Commission of 13 September 1989.

[0135] Mixtures of pigments can also be produced. For example, in a preferred embodiment, a neutral black inkjet ink is used. This black inkjet ink is preferably obtained by mixing a black pigment and a colored pigment having a maximum absorption of 500 to 700 nm, such as a cyan and / or magenta pigment, into the ink. The neutral black inkjet ink avoids the use of cyan or magenta inks to correct the blackness, which results in a thinner ink layer with improved flexibility.

[0136] The pigment particles in the inkjet ink should be small enough to allow the ink to flow freely through the inkjet printing device, especially at the jetting nozzle. Small particles are also desirable for maximum color intensity and to slow down sedimentation.

[0137] The numeric average pigment particle size is preferably 0.050 to 1 μm, more preferably 0.070 to 0.300 μm and particularly preferably 0.080 to 0.200 μm. Most preferably, the numeric average pigment particle size is no greater than 0.150 μm. An average particle size less than 0.050 μm is less desirable for reduced light fastness, while an average particle size greater than 0.200 μm reduces the color gamut.

[0138] The numerical average pigment particle size of the pigment particles is best determined using a Brookhaven Instruments Particle Sizer BI90plus based on the principle of dynamic light scattering. The ink is then diluted to a pigment concentration of 0.002 wt %, for example with ethyl acetate. The measurement settings of the BI90plus are: 5 runs at 23°C, angle 90°, wavelength 635 nm and pattern = correction function.

[0139] The free radical curable inkjet ink may also include a white pigment as a colorant, more preferably, the white pigment is present in the free radical curable inkjet ink in an amount of at least 17.5 wt %, preferably 18.5 to 35.0 wt %, more preferably 19.5 to 33.0 wt % and most preferably 20.5 to 25.0 wt %, based on the total weight of the free radical curable inkjet ink. Within the above range, a good opacity is obtained with a thin layer of white ink, while the viscosity does not increase too much, so that the jetting performance is not impaired. For this reason, titanium dioxide pigments (such as rutile) are particularly preferred for white pigments.

[0140] In a preferred embodiment, the polymerizable composition is 50.0 to 70.0 wt %, preferably 60.0 to 68.0 wt %, of the total weight of the free radical curable white inkjet ink.

[0141] In the case of free radical curable white inkjet inks, it is preferred to use pigments having a refractive index greater than 1.60, preferably greater than 2.00, more preferably greater than 2.50 and most preferably greater than 2.60. White pigments can be used alone or in combination. With the above refractive indices, the dry thickness of the white ink layer can be minimized, which is beneficial for flexibility.

[0142] Preferably, titanium dioxide is used for pigments with a refractive index greater than 1.60. Titanium oxide appears in the crystalline forms of anatase, rutile and brookite. Anatase has a relatively low density and is easy to grind into fine particles, while rutile has a relatively high refractive index and exhibits high hiding power. Any of these can be used in the present invention. It is preferred to utilize the characteristics to the greatest extent possible and select them according to their use. The use of anatase with low density and small particle size can achieve superior dispersion stability, ink storage stability and jetting properties. At least two different crystalline forms can be used in combination. The combined use of anatase and rutile exhibiting high tinting power can reduce the total amount of titanium oxide, resulting in improved ink storage stability and jetting performance.

[0143] For the surface treatment of titanium oxide, water treatment or gas phase treatment is applied, and an alumina-silica treatment agent is generally used. Untreated, alumina-treated or alumina-silica-treated titanium oxide can be used. Organic surface treatment can be used alone or in addition to the previous surface treatment.

[0144] The numerical average particle size of titanium oxide or other white pigment is preferably from 180 to 400 nm, more preferably from 200 to 330 nm and most preferably from 220 to 300 nm. When the average diameter is less than 180 nm, sufficient hiding power cannot be obtained, while when the average diameter exceeds 400 nm, the storage capacity and jetting suitability of the ink tend to deteriorate. The numerical average particle size is best determined by photon correlation spectroscopy on a diluted sample of the pigmented inkjet ink using a 4 mW HeNe laser at a wavelength of 633 nm. A suitable particle size analyzer used is the Malvern Spectroscopy® available from Goffin-Meyvis TM nano-S. The sample can be prepared, for example, 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 measured particle size is the average of 3 consecutive measurements consisting of 6 20-second runs.

[0145] Dispersants

[0146] Pigments are usually stabilized in the dispersion medium of the polymerizable compound by a dispersant, such as a polymeric dispersant or a surfactant. However, the surface of the pigment can be modified to obtain so-called "self-dispersible" or "self-dispersing" pigments, i.e. pigments that can be dispersed in the dispersion medium without a dispersant.

[0147] In a preferred embodiment of the pigmented free radical curable inkjet ink, the pigment is stabilized by a polymeric dispersant.

[0148] The pigment is preferably used in the concentrated pigment dispersion for preparing the inkjet ink in an amount of 10 to 40 wt %, more preferably 15 to 30 wt %, based on the total weight of the pigment dispersion.The concentrated pigment dispersion is then diluted to form a free radical curable inkjet ink.

[0149] Typical polymeric dispersants are copolymers of two monomers, but may contain three, four, five or even more monomers. The properties of polymeric dispersants depend on the properties of the monomers and their distribution in the polymer. Copolymeric dispersants preferably have the following polymer composition:

[0150] · Statistical polymerized monomers (e.g. monomers A and B polymerized to form ABBAABAB);

[0151] Alternating monomers (e.g. monomers A and B polymerized to form ABABABAB);

[0152] Gradient polymerization of monomers (e.g. monomers A and B polymerized into AAABAABBABBB);

[0153] Block copolymers (e.g. monomers A and B polymerized to AAAAABBBBBB) where the block length of each block (2, 3, 4, 5 or even more) is important to the dispersing ability of the polymeric dispersant;

[0154] Graft copolymers (graft copolymers consist of a polymeric backbone with polymeric side chains attached to the backbone); and

[0155] • Mixed forms of these polymers, such as block gradient copolymers.

[0156] The polymeric dispersant preferably has a number average molecular weight Mn of 500 to 30000, more preferably 1500 to 10000. Larger molecular weight dispersants tend to increase the viscosity of the ink too much to adequately provide good dispersion stability.

[0157] The polymeric 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.

[0158] The polymeric dispersant preferably has a polydispersity PD of less than 2, more preferably less than 1.75 and most preferably less than 1.5.

[0159] Commercial examples of polymeric dispersants are as follows:

[0160] DISPERBYK available from BYK CHEMIE GMBH TM Dispersants;

[0161] SOLSPERSE available from LUBRIZOL TMDispersants;

[0162] TEGO from EVONIK TM DISPERS TM Dispersants;

[0163] ·EDAPLAN from MüNZING CHEMIE TM Dispersants;

[0164] ETHACRYL FROM LYONDELL TM Dispersants;

[0165] GANEX from ISP TM Dispersants;

[0166] DISPEX from BASF TM and EFKA TM Dispersants;

[0167] DISPONER from DEUCHEM TM Dispersants

[0168] Particularly preferred polymeric dispersants include Solsperse from LUBRIZOL TM Dispersants, Efka from BASF TM Dispersants and Disperbyk from BYK CHEMIE GMBH TM Dispersant. A particularly preferred dispersant is Solsperse from LUBRIZOL. TM 32000, 35000 and 39000 dispersants.

[0169] The polymeric dispersant is preferably used in an amount of 2 to 300 wt %, more preferably 10 to 100 wt %, most preferably 50 to 90 wt %, based on the weight of the pigment. An amount of 2 to 90 wt % provides good dispersion stability combined with minimal effect on ink viscosity.

[0170] Dispersion enhancer

[0171] Dispersion synergists generally consist of an anionic part and a cationic part. The anionic part of the dispersion synergist exhibits a certain degree of molecular similarity with the color pigment, and the cationic part of the dispersion synergist consists of one or more protons and / or cations to compensate for the charge of the anionic part of the dispersion synergist.

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

[0173] Suitable commercially available dispersion enhancers include Solsperse from LUBRIZOL TM 5000 and Solsperse TM 22000.

[0174] Particularly preferred pigments for the magenta inks used are diketopyrrolopyrrole pigments or quinacridone pigments. Suitable dispersion 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 15:3, it is preferred to use a sulfonated Cu-phthalocyanine dispersion synergist, such as Solsperse from LUBRIZOL. TM 5000. Suitable dispersion synergists for yellow inkjet inks include those disclosed in EP 1790697 A (AGFA GRAPHICS).

[0176] Polymerization inhibitors

[0177] The free radical curable inkjet ink may contain a polymerization inhibitor to prevent unwanted polymerization during transportation or storage. Suitable polymerization inhibitors include phenolic antioxidants, hindered amine light stabilizers, phosphor-type antioxidants, hydroquinone monomethyl ether commonly used in (meth)acrylate monomers, and hydroquinone, tert-butylcatechol, pyrogallol may also be used.

[0178] Suitable commercial inhibitors are, for example, Sumilizer manufactured by Sumitomo Chemical Co. Ltd. TM GA-80, Sumilizer TM GM and Sumilizer TM GS; Genorad from Rahn AG TM 16. Genorad TM 18 and Genorad TM 20. Irgastab from BASF TMUV10 and Irgastab TM UV22, Tinuvin TM 460 and CGS20; Floorstab from Kromachem Ltd TM UV series (UV-1, UV-2, UV-5 and UV-8), Additol from Cytec Surface Specialties TM S Series (S100, S110, S120 and S130).

[0179] Since excessive addition of these polymerization inhibitors will reduce the ink's sensitivity to curing, it is preferred to determine the amount capable of preventing polymerization before blending. The amount of polymerization inhibitor is preferably less than 2 wt% of the total free radical curable inkjet ink.

[0180] In a preferred embodiment, the polymerization inhibitor is a polymerizable inhibitor, which preferably contains one or more acrylate groups to achieve good reactivity.

[0181] Surfactants

[0182] The free radical curable inkjet ink may contain at least one surfactant. The surfactant may be anionic, cationic, nonionic or zwitterionic and is preferably added in a total amount of less than 3 wt%, more preferably less than 2 wt% and most preferably not more than 1 wt%, based on the total weight of the free radical curable inkjet ink.

[0183] Preferably the surfactant is selected from fluorinated surfactants (such as fluorinated hydrocarbons) and organosilicon surfactants. The organosilicon surfactant is preferably a siloxane and may be alkoxylated, polyester modified, polyether modified, polyether modified hydroxyl functional, amine modified, epoxy modified and other modified or a combination thereof. Preferred siloxanes are polymeric, such as polydimethylsiloxane.

[0184] Preferred commercially available silicone surfactants include BYK TM 333 and BYK TM UV3510 and Tegoglide from EVONIK TM 410.

[0185] In a preferred embodiment, the surfactant is a polymerizable compound.

[0186] Preferred polymerizable silicone surfactants include (meth)acrylated silicone surfactants. Most preferably, the (meth)acrylated silicone surfactant is an acrylated silicone surfactant, as acrylates are more reactive than methacrylates.

[0187] In a preferred embodiment, the (meth)acrylated silicone surfactant is a polyether-modified (meth)acrylated polydimethylsiloxane or a polyester-modified (meth)acrylated polydimethylsiloxane.

[0188] Preferred commercially available (meth)acrylated silicone surfactants include: Ebecryl TM 350, silicone diacrylate from Cytec; polyether-modified acrylated polydimethylsiloxane BYK TM UV3500 and BYK TM UV3530, polyester modified acrylated polydimethylsiloxane BYK TM UV3570, all manufactured by BYK Chemie; Tego TM Rad2100, Tego TM Rad 2200N, Tego TM Rad 2250N, Tego TM Rad 2300, Tego TM Rad 2500, Tego TM Rad 2600 and Tego TM Rad 2700, Tego from EVONIK TM RC711; Silaplane TM FM7711、Silaplane TM FM7721, Silaplane TM FM7731, Silaplane TM FM0711, Silaplane TM FM0721, Silaplane TM FM0725, Silaplane TM TM0701, Silaplane TMTM0701T, 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.

[0189] Preparation of pigmented free radical curable inkjet inks

[0190] Pigment dispersions can be prepared by precipitating or grinding the pigment in a dispersion medium in the presence of a dispersant.

[0191] A method for making a free radical curable inkjet ink, the method preferably comprising the steps of: a) grinding a color pigment into a concentrated pigment dispersion in the presence of a polymeric dispersant and a polymerizable compound; and b) diluting the concentrated pigment dispersion with the polymerizable compound and other additives so that a free radical curable inkjet ink having a correct viscosity and surface tension is obtained.

[0192] Mixing equipment may include pressure kneaders, open kneaders, planetary mixers, dissolvers and Dalton universal mixers. Suitable grinding and dispersing equipment are ball mills, pearl mills, colloid mills, high-speed dispersers, double roll mills, bead mills, coating conditioners and triple roll mills. Dispersions may also be prepared using ultrasonic energy.

[0193] Many different types of materials can be used as grinding media, such as glass, ceramics, metals and plastics. In a preferred embodiment, the grinding media can comprise particles, preferably substantially spherical in shape, such as beads consisting essentially of a polymer resin or yttrium stabilized zirconium beads.

[0194] During the mixing, grinding and dispersing processes, each process is preferably carried out under cooling to prevent heat accumulation, and as far as possible under lighting conditions in which actinic radiation has been substantially excluded.

[0195] The pigment dispersion may contain more than one pigment. The pigment dispersion may be prepared using a separate dispersion of each pigment, or several pigments may be mixed and co-milled when preparing the dispersion.

[0196] The dispersion process can be carried out in a continuous, batch or semi-batch manner.

[0197] The preferred amounts and ratios of the ingredients of the grind will vary widely depending on the specific materials and intended application. The contents of the grinding mixture comprise the grind and the grinding media. The grind includes a pigment, a polymeric dispersant, and a liquid carrier.

[0198] The grinding time can vary widely and depends on the pigment, the selected machinery and dwell conditions, the initial and desired final particle size, etc. In the present invention, pigment dispersions having an average particle size of less than 100 nm can be prepared.

[0199] After grinding is complete, the grinding media is separated from the ground particulate product (dry or in liquid dispersion form) using conventional separation techniques, such as by filtration, screening through a screen, etc. The screen is usually built into the grinder, such as for a bead mill. The ground pigment concentrate is preferably separated from the grinding media by filtration.

[0200] Generally, it is desirable to prepare inkjet inks in the form of a concentrated grind, which is subsequently diluted to the appropriate concentration for the inkjet printing system. This technique allows larger quantities of colored ink to be prepared from the equipment. By dilution, the inkjet ink is adjusted to the viscosity, surface tension, color, hue, saturation density, and print area coverage required for a particular application.

[0201] natural leather

[0202] The manufacture of natural leather products is well known and can be roughly divided into five stages, such as Figure 1 As shown. Preparation stage 1 usually occurs partly in slaughterhouses and partly in tanneries, while stages 2 to 4 occur in tanneries, and stage 5 occurs at leather product manufacturers. In the first stage (preparation stage), the skin is removed (skinned) from the animal and pretreated for tanning in the second stage. Pretreatment may involve processes such as soaking, liming, dehairing, splitting and pickling (adjusting pH to help tanning agent penetration). In the tanning stage, the protein of the raw hide or skin is converted into a stable material that will not rot. Chromium is most commonly used as a tanning agent, and the tanned product thus obtains a light blue color, so it is usually called "wet blue". In the third stage of crusting, the tanned leather is dried and softened. Crusting generally includes processes such as peeling (removing surface fixed tannic acid), greasing (fixing fat, oil and wax to leather fibers), dyeing, whitening, physical softening and buffing (abrading the leather surface to reduce grain defects). In the fourth stage, called the finishing stage, the leather is ready to be sold to leather goods manufacturers. Finishing operations may include painting, polishing and embossing. In the fifth stage, leather goods are manufactured, which involves processes that may include cutting, perforating, sewing, leather wrapping, decoration and embossing.

[0203] There are different grades of natural leather (see Figure 2), such as full grain (24), top grain (25), which is essentially full grain but has a portion of the grain layer sanded and the bottom split layer removed, and split leather (26). For the latter, the bottom layer of the cowhide is removed and used to make split leather. Depending on the thickness of the bottom layer, many splits may be produced. Split leather has a rough appearance and is typically used to make suede leather.

[0204] To prevent grain damage and weakness, hides or skins are preferably chrome tanned, but other tanning methods such as vegetable tanning may also be used. After tanning, the leather is dried and softened into so-called crusted leather. Crusting may include processes such as stripping (removal of surface-fixed tannic acid), fatliquoring (fixation of fats, oils and waxes to the leather fibers), dyeing, whitening, physical softening and buffing (abrasion of the leather surface to reduce grain defects).

[0205] In the present invention, the decorated leather is obtained by the above-mentioned manufacturing method. The decorated natural leather can be used to manufacture a wide range of leather products. Preferred leather products include footwear, furniture, upholstery, bags, gloves, belts, wallets, clothing, automotive leather (such as train, airplane, boat and car seats), interiors, books, stationary, interior decoration, packaging, equestrian supplies, etc.

[0206] Other substrates

[0207] There is no restriction on the nature of the substrate onto which the pigmented free radical curable inkjet ink may be printed. However, the pigmented free radical curable inkjet ink may be printed advantageously for use on flexible substrates.

[0208] Another example of a flexible substrate that requires good flexibility and adhesiveness is a so-called backlight film. A backlight film is a material on which graphics or text are printed so that when light shines from behind, the design lights up.

[0209] In a preferred embodiment, the substrate is a backlight film comprising a material selected from the group consisting of polyvinyl chloride, polyethylene terephthalate (PET), polyethylene, polypropylene, polycarbonate, polyacrylate, polystyrene, nylon, and polyvinyl acetate.

[0210] The pigmented free radical curable inkjet inks according to the present invention can also be used advantageously on tarpaulins.

[0211] A tarp or tarpaulin is a large flexible sheet of waterproof material. In Australia, a tarp may be called a "hootch". Tarps usually have reinforced grommets at the corners and along the sides to form attachment points for ropes, allowing them to be tied or hung. The latter are advantageously used for truck curtains in so-called tautliners.

[0212] Preferred tarps are selected from the group consisting of woven polyethylene, canvas, polyester coated with polyurethane, vinyl tarps, and silnylon.

[0213] A particularly preferred tarpaulin is a vinyl tarpaulin carrying a cured layer of the pigmented free radical curable inkjet ink according to the present invention.

[0214] In a preferred embodiment, the tarpaulin has a thickness of at least 130 μm, preferably at least 180 μm, more preferably 230 μm to 600 μm. A thickness of 230 μm allows for heavy duty flexin.

[0215] Inkjet printing method

[0216] The inkjet printing method according to a preferred embodiment of the present invention comprises the following steps:

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

[0218] b) Curing the jetted pigmented free radical curable inkjet ink by a UV LED light source having a spectral emission in the range of 360-420 nm.

[0219] The pigmented free radical curable inkjet inks of the present invention are advantageously used for UV curing by UV LED light sources having a spectral emission in the range of 360-420 nm. These UV LED light sources tend to cure the interior of the ink layer much better than the surface of the ink layer, resulting in a tacky surface that is easily damaged.

[0220] Manufacturing method for decorative natural leather

[0221] According to a preferred embodiment of the present invention, a manufacturing method for decorating natural leather comprises an inkjet printing method as described above, wherein a pigmented free radical curable inkjet ink, optionally in combination with other pigmented free radical curable inkjet inks, is sprayed onto a base coat present on a crusted leather surface to form a decorative image.

[0222] In a preferred embodiment of the manufacturing process for decorating natural leather, a protective topcoat is applied over the decorative image after curing the pigmented free radical curable inkjet ink.

[0223] Primer and topcoat

[0224] The primer is applied to crust leather to provide a level of image quality commensurate with the luxurious aspect of the leather, otherwise the low viscosity of the inkjet ink would cause it to quickly penetrate into the leather, resulting in reduced image quality.

[0225] The base coat preferably has a similar color to the leather and grain. Any desired color may be selected for the leather or grain and base coat, such as red, green, brown, black, blue, etc. The leather and grain are usually in the crusting stage (see Figure 1 The paint is dyed with dyes during stage 3) in the primer, whereas the colored pigments are usually contained in the primer.

[0226] The primer can be applied as a single layer, or can be applied as multiple layers. The multiple layers can even have different compositions to improve properties like adhesion or flexibility.

[0227] A topcoat may be applied over the decorative image and primer to improve the scratch resistance of the decorative image.

[0228] The topcoat can be applied as a single layer, or can be applied as multiple layers. The multiple layers can even have different compositions to improve properties like scratch resistance.

[0229] The protective topcoat may have the same or similar composition as the basecoat. Typically, the protective topcoat is slightly optimized depending on the leather application. For example, in contrast to leather shoes, the flexibility of a leather book cover does not play an important role. Therefore, the protective topcoat of a book cover may be optimized for scratch resistance.

[0230] The primer and / or topcoat preferably comprises a polyurethane based polymer or copolymer, as this has been found to improve the flexibility of the printed leather. The primer and / or topcoat preferably further comprises a polyamide polymer or copolymer, as polyamides have been found to improve compatibility with crust leather and improve the strength of the primer.

[0231] Suitable polyurethanes include Urepal from CHEMIPAL SpA TM PU147 and PU181; Melio from STAHL TM Promul 61; Astacin from BASF TM Finish PS; Ecrothan from MICHELMAN TM 4075, 4078 and 4084; Incorez from INCOREZTM CS8073 and CS065-195. The dry weight of polyurethane in the primer or topcoat is preferably 1 to 6 g / m 2 range.

[0232] Suitable polyamides include PA emulsion types ED310 and 161148CX from MICHELMAN. The dry weight of polyamide in the primer or topcoat is preferably less than 7 g / m 2 , more preferably less than 5g / m 2 .

[0233] Although polyurethane and / or polyamide are preferred as polymers for the primer, other polymers may also be used preferably in combination with polyurethane and / or polyamide. Such polymers preferably have an elongation at break of greater than 200%, more preferably 300%. The elongation at break is measured according to ISO 527-2, for example using MTS Exceed from MTS Systems Corporation. TM Test device to measure.

[0234] Another type of preferred polymer for use in primers or topcoats is polyacrylates. Polyacrylates provide good flexibility in primers and stabilize pigment dispersions.

[0235] In a preferred embodiment, the primer and / or topcoat preferably comprises a polyurethane-based polymer or copolymer and a polyacrylate-based polymer or copolymer. This combination brings about excellent flexibility even in the presence of pigments.

[0236] Preferred polyacrylates are Roda TM Base 5514 and Primal from LANXESS TM HPB980. A suitable polymerized acrylate emulsion is Bioflex from LMF Biokimica TM KGA.

[0237] A crosslinking agent may be incorporated into the primer and / or topcoat to improve strength and adhesion to crust leather. Preferred crosslinking agents include aldehyde-based crosslinking agents such as formaldehyde, melamine formaldehyde derivatives, urea-formaldehyde resins, glyoxal and glutaraldehyde, epoxides, oxazolines, carbodiimides and isocyanates, with isocyanates being particularly preferred. The dry weight of the crosslinking agent in the primer and / or topcoat is preferably less than 1.4 g / m 2 , more preferably less than 1.0 g / m 2 .

[0238] The primer and / or topcoat are preferably applied by spraying, but may also be applied by any known coating technique, such as knife coating, extrusion coating, slide hopper coating and curtain coating.

[0239] The topcoat is most preferably a transparent topcoat, but may also be a translucent topcoat. By having a transparent topcoat, the inkjet printed image is clearly visible through the topcoat. By using a translucent topcoat, a special aesthetic effect is created.

[0240] If a matte top surface is desired for the inkjet printed leather, a matting agent may be included. Any suitable matting agent may be used. Preferred matting agents include silica. A preferred commercial example of a silica dispersion is Euderm® from LANXESS. TM SN2.

[0241] Inkjet printing device

[0242] Pigmented free radical curable inkjet inks may be jetted by one or more printheads that eject small droplets of ink in a controlled manner through nozzles onto an ink receiver surface that is in motion relative to the printheads.

[0243] The preferred printhead for the inkjet printing system in the present invention is a piezoelectric head. Piezoelectric inkjet printing is based on the movement of a piezoelectric ceramic transducer when a voltage is applied thereto. The application of voltage changes the shape of the piezoelectric ceramic transducer in the printhead to create a void, which is then filled with ink. When the voltage is removed again, the ceramic expands to its original shape to eject ink droplets from the printhead. However, the inkjet printing method in the present invention is not limited to piezoelectric inkjet printing. Other inkjet printheads can be used, and inkjet printheads include various types, such as continuous types as well as thermal, electrostatic and acoustic drop on demand types.

[0244] A preferred piezo printhead is a so-called push mode piezo printhead having a relatively large piezo element capable of ejecting more viscous inkjet ink drops. Such a printhead is available from RICOH as a GEN5s printhead.

[0245] Another preferred piezoelectric printhead is a so-called through-flow piezoelectric drop-on-demand inkjet printhead. Such printheads are available from TOSHIBA TEC as CF100 printheads. Through-flow printheads are preferred because they enhance the reliability of inkjet printing due to the continuous flow of ink through the printhead.

[0246] The inkjet printhead typically scans back and forth across the moving ink-receiving surface in the transverse direction. Sometimes the inkjet printhead does not print on the return pass, but bidirectional printing is preferred for obtaining high area throughput.

[0247] Another preferred inkjet device uses a "single pass printing process" which can be performed by using a page-wide inkjet printhead or multiple staggered inkjet printheads covering the entire width of the substrate surface. In a single pass printing process, the inkjet printhead generally remains stationary while the substrate surface is transported beneath the inkjet printhead.

[0248] Curing device

[0249] The pigmented free radical curable inkjet ink of the present invention is cured by exposing it to actinic radiation, preferably to ultraviolet radiation. The actinic radiation may also originate from an electron beam curing device.

[0250] The pigmented free radical curable inkjet inks of the present invention can also be advantageously used for electron beam curing, since the latter also cures the interior of the layer of polymerizable composition better than its surface. In addition, electron beam curing eliminates the need for photoinitiators, which is an economic benefit.

[0251] In inkjet printing, the curing device may be arranged in combination with the print head of the inkjet printer, traveling therewith, so that the curable composition is exposed to curing radiation soon after being jetted, which is beneficial to image quality.

[0252] In such an arrangement, it may be difficult to provide a sufficiently small radiation source connected to and travelling with the print head. Therefore, a static fixed radiation source may be employed, such as a curing UV light source, connected to the radiation source by means of a flexible radiation conducting means such as an optical fibre bundle or an internally reflecting flexible tube.

[0253] Alternatively, the actinic radiation may be supplied to the radiation head from a fixed source by an arrangement of mirrors including a mirror on the radiation head.

[0254] The radiation source arranged not to move with the printhead may also be an elongated radiation source extending laterally across the ink receptor surface to be cured and adjacent to the lateral path of the printhead so that subsequent rows of images formed by the printhead pass gradually or continuously underneath the radiation source.

[0255] Any UV light source, as long as a portion of the emitted light can be absorbed by the photoinitiator or photoinitiator system, can be used as a radiation source, such as high-pressure or low-pressure mercury lamps, cold cathode tubes, black lights, UV LEDs, UV lasers and flashes. Among them, preferred sources are those that exhibit a relatively long wavelength UV contribution with a dominant wavelength of 300-400 nm. In particular, UV-A light sources are preferred due to their reduced light scattering leading to more efficient internal curing.

[0256] UV radiation is usually classified as UV-A, UV-B and UV-C as follows:

[0257] UV-A: 400nm to 320nm

[0258] UV-B: 320nm to 290nm

[0259] UV-C: 290nm to 100nm.

[0260] Two light sources of different wavelengths or illumination can be used sequentially or simultaneously to cure the image. For example, a first UV source rich in UV-C can be selected, particularly in the range of 260nm-200nm. Then, the second UV source can be rich in UV-A, such as a gallium-doped lamp, or a different lamp high in both UV-A and UV-B. It has been found that using two UV sources has advantages, such as fast curing speed and high degree of cure.

[0261] In a preferred embodiment of the inkjet printing method according to the invention, the inkjet printing device comprises a UV LED with a wavelength greater than 360 nm, preferably a UV LED with a wavelength greater than 380 nm and most preferably a UV LED with a wavelength of about 395 nm.

[0262] To promote curing, inkjet printers typically include one or more oxygen depletion units. The oxygen depletion unit places a blanket of nitrogen or other relatively inert gas (e.g., CO2) with an adjustable position and adjustable inert gas concentration to reduce the oxygen concentration in the curing environment. Residual oxygen levels are typically kept as low as 200 ppm, but are typically 200 ppm to 1200 ppm. Example

[0263] Material

[0264] Unless otherwise stated, 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 was demineralized water.

[0265] PR122 is a quinacridone pigment available as Pigment Red 122TCR 12203IJ from TRUST CHEM EUROPE BV.

[0266] SYN is a dispersion synergist according to formula (A):

[0267]

[0268] and was synthesized in the same manner as described in Example 1 of WO 2007 / 060254 (AGFA GRAPHICS) for the synergist QAD-3.

[0269] DB162 is a polymeric dispersant for Disperbyk available from BYK CHEMIE GMBH. TM 162 from which the solvent mixture of 2-methoxy-1-methylethyl acetate, xylene and n-butyl acetate has been removed.

[0270] PEA is available as a Sartomer TM SR339C 2-phenoxyethyl acrylate available from ARKEMA.

[0271] NVC is N-vinylcaprolactam available from BASF BELGIUM, NV.

[0272] V-MOX is available as VMOX TM Vinylmethyloxazolidinone (CAS No.: 3395-98-0) available from BASF.

[0273] TBCH is 4-tert-butylcyclohexyl acrylate available from ARKEMA under the trade name Sartomer CD217.

[0274] IDA is available as a Sartomer TM SR395 isodecyl acrylate available from ARKEMA.

[0275] G1122 is a monofunctional urethane acrylate with a Tg of -3°C and can be used as a genomer TM 1122 was obtained from RAHN and has formula (B):

[0276]

[0277] IBOA is available as a Sartomer TM SR506D is isobornyl acrylate (MW = 208) obtained from ARKEMA.

[0278] PDA is available as a Sartomer TM SR344 is polyethylene glycol 400 diacrylate available from ARKEMA.

[0279] DPGDA is available as a Sartomer TM SR508 dipropylene glycol diacrylate available from ARKEMA.

[0280] HDDA is available as SR238 1,6-hexanediol diacrylate available from ARKEMA.

[0281] VEEA is 2-(2-vinyloxyethoxy)ethyl acrylate, a difunctional monomer available from Nippon Shokubai, Japan.

[0282] OLIGO is a urethane acrylate oligomer (MW=1900) with two acrylate groups, which can be used as a sartomer TM CN963B80 was obtained from ARKEMA.

[0283] INHIB is a mixture of polymer-forming inhibitors having a composition according to Table 1.

[0284] Table 1

[0285] Components weight% DPGDA 82.4 p-Methoxyphenol 4.0 BHT 10.0 <![CDATA[Cupferron TM AL]]> 3.6

[0286] Cupferron TM AL is aluminum N-nitrosophenylhydroxylamine from WAKO CHEMICALS LTD.

[0287] UV10 is available as Irgastab TM UV 10 was obtained from BASF as 4-hydroxy-2,2,6,6-tetramethylpiperidinyloxysebacate.

[0288] TPL is available as SpeedCure TM TPO-L Ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate was obtained from ARKEMA.

[0289] OTP is available as Omnipol TM TP was obtained from polymerized acylphosphine oxides from IGM Resins.

[0290] ITX is Darocur TM ITX, which is an isomeric mixture of 2- and 4-isopropylthioxanthone from BASF.

[0291] T410 is available as TegoglideTM 410 Silicone surfactant available from EVONIK.

[0292] Measurement method

[0293] 1. Average particle size

[0294] The particle size of the pigment particles in the pigment dispersion was determined by photon correlation spectroscopy on a diluted sample of the pigment dispersion using a 4 mW HeNe laser at a wavelength of 633 nm. The particle size analyzer used was a Malvern TM nano-S.

[0295] The sample can be prepared, for example, by adding a drop of the pigment dispersion to a cuvette containing 1.5 ml of ethyl acetate and mixing until a homogeneous sample is obtained. The measured particle size is the average of 3 consecutive measurements consisting of 6 runs of 20 seconds.

[0296] 2. Adhesiveness

[0297] The adhesion of pigmented free radical curable inkjet inks was investigated in “quality mode” using Anapurna from AGFA. TM The 2050i LED was tested on a substrate printing a 13 cm x 19 cm square at 720 x 720 dpi resolution with 100% ink coverage. The samples were printed on black coated leather from NUTI IVO SpA as substrate and run in two different UV curing modes (4 passes at 40% UV lamp power and 4 passes at 80% UV lamp power).

[0298] The printed samples were compared with the unprinted MultiArt from PAPYRUS TM The glossy substrates were pinned and kept in an oven for 24 hours at A°C and B% relative humidity under a 4.85 kg weight steel plate. The ink transfer to the unprinted MultiArt TM The amount of gloss on the back of the substrate is measured and scored according to Table 2.

[0299] Table 2

[0300]

[0301]

[0302] Add the tack scores obtained in Table 3 under the following temperature and relative humidity % conditions:

[0303] Table 3

[0304]

[0305] For the sum of the tackiness scores obtained above, the desired score is less than 4.0, preferably less than 3.0 and most preferably 0.0.

[0306] 3. Flexing

[0307] The deflection of each pigmented free radical curable inkjet ink was measured in “quality mode” using Anapurna from AGFA. TM 2050i LED measured at 720x1440 dpi printing on red crusted leather from NUTI IVO SpA with a CB03 Primer. Four different samples of each inkjet ink were obtained by printing samples at two different ink coverages (70% and 160%) and at two different UV curing modes (8 passes at 20% UV lamp power and 8 passes at 80% UV lamp power).

[0308] At SATRA TM The flexibility of the printed samples was measured on a STM 701 Bally flexometer, where the printed samples had to withstand the following number of dry flexion cycles: 500; 1000; 2500; 5000; 7500; and 20000 cycles. Photos were taken after each of the above number of dry flexion cycles and then the printed samples were scanned using a flexometer from Media Cybernetics. The cracks in the photos were analyzed using the analysis software. According to the criteria shown in Table 4, the scores were given by judging the cracks in the photos.

[0309] Table 4

[0310]

[0311]

[0312] The average score for each inkjet ink was calculated from the results of each of the dry flex cycles under four different UV curing conditions (20% UV / 70% ink coverage; 20% UV / 160% ink coverage; 80% UV / 70% ink coverage; 80% UV-160% ink coverage). For good flex results, the average score should be 4.0 or higher.

[0313] 4. Viscosity

[0314] Using Rotovisco from HAAKE TM RV1 viscometer at 45°C and 1000s -1The viscosity of the pigmented free radical curable inkjet ink was measured at a shear rate of 1.5 Å.

[0315] For reliable spraying, the viscosity should be 5.0 to 12.0 mPa.s, preferably 6.0 to 10.0 mPa.s.

[0316] 5. Static surface tension

[0317] The static surface tension of the pigmented free radical curable inkjet inks was measured after 60 seconds at 25°C using a KRüSS Tensiometer K9 from KRüSS GmbH, Germany.

[0318] Example 1

[0319] This example illustrates the improved adhesion and flex obtained on natural leather using a pigmented free radical curable inkjet ink according to the present invention while being cured by a UV LED source emitting in the spectral range of 360-420 nm.

[0320] Preparation of Magenta Pigment Dispersion CPM

[0321] Concentrated pigment dispersions CPM were prepared by using DISPERLUX from DISPERLUX SARL, Luxembourg TM The disperser was prepared by mixing its components according to Table 5 for 30 minutes. The dispersion was then ground using a Bachofen DYNOMILL ECM mill filled with 0.4 mm yttrium-stabilized zirconium oxide beads from TOSOH. The mixture was circulated on 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 CPM had an average particle size of 127 nm.

[0322] Table 5

[0323]

[0324]

[0325] Preparation of Magenta Inkjet Ink

[0326] The concentrated pigment dispersion CPM prepared above was used to prepare comparative radical curable inkjet inks COMP-1 to COMP-13 according to Tables 6 and 7 and inventive radical curable inks INV-1 to INV-7 according to Table 8.

[0327] Table 6

[0328]

[0329]

[0330] Table 7

[0331]

[0332]

[0333] Table 8

[0334]

[0335]

[0336] Results and Evaluation

[0337] The tack, deflection and viscosity of each pigmented free radical curable inkjet ink were determined according to the above measurement methods. The results are shown in Table 9. The headings in this table have the following meanings:

[0338] · wt% VMOX = wt% of N-vinylmethyloxazolidinone based on the total weight of UV curable inkjet ink;

[0339] · wt% PDA = wt% of polyethylene glycol diacrylate based on the total weight of UV curable inkjet ink

[0340] · Monofunctional (Mono) % on ink = weight % of monofunctional polymerizable compound based on the total weight of the polymerizable composition;

[0341] %PDA = weight % of polyethylene glycol diacrylate based on the total weight of the multifunctional polymerizable compound;

[0342] DBD = double bond density DBD of the polymerizable composition. In units of mmol double bonds / g; and

[0343] • Ink Tg = de-glass transition temperature of the free radical curable inkjet ink calculated according to formula (I).

[0344] The surface tension is not shown in Table 9, but all inkjet inks were found to have a static surface tension of 20 to 23 mN / m at 25°C.

[0345] Table 9

[0346]

[0347]

[0348] From the results in Table 9 it is clear that only the inventive pigmented free radical curable inkjet inks INV-1 to INV-7 are able to achieve the desired adhesion and flexural properties.

[0349] Reference Mark List

[0350] Figure 2 The reference symbols used in are shown in Table 10.

[0351] Table 10

[0352]

[0353]

Claims

1. A free radical curable inkjet ink for making a pigmented natural leather, comprising a polymerizable composition meeting the following requirements A to E, comprising a monofunctional, multifunctional polymerizable compound: A) 65.0 to 95.0 wt % of a monofunctional polymerizable compound, wherein the wt % is based on the total weight of the polymerizable composition; B) the polymerizable composition comprises a monofunctional acrylate; C) 8.0 to 25.0 wt % of an N-vinyl oxazolidinone according to Formula 1, based on the total weight of the UV curable inkjet ink, wherein the N-vinyl oxazolidinone according to Formula 1 is: Where R 1 To R 4 Not subject to limitations other than those imposed by use in inkjet inks such as viscosity and ink stability. 1 To R 4 Preferred substituents include hydrogen, alkyl, cycloalkyl, aryl, and combinations thereof, any of which may be interrupted by heteroatoms; D) 3.0 to 30.0 wt. % of polyethylene glycol diacrylate, based on the total weight of the UV curable inkjet ink; E) the polyethylene glycol diacrylate has a molecular weight MW of 350 to 750; and F) The multifunctional polymerizable compound contains polyethylene glycol diacrylate in an amount of 60 to 100 wt % based on the total weight of the multifunctional polymerizable compound.

2. The pigmented free radical curable inkjet ink as claimed in claim 1, wherein the polymerizable composition has a double bond density DBD in the range of 5.12 to 5.60 mmol double bonds / g, wherein the double bond density DBD is calculated by the following formula: in i represents an integer from 1 to n; n represents the number of polymerizable compounds in the UV free radical curable inkjet ink; F(i) represents the functionality of polymerizable compound i; MW(i) represents the molecular weight of polymerizable compound i; and Weight % (i) is the weight percent of polymerizable compound i based on the total weight of the pigmented free radical curable inkjet ink.

3. A pigmented free radical curable inkjet ink as claimed in claim 1 or 2, wherein the polyethylene glycol diacrylate has a molecular weight MW of 400 to 600 and / or the N-vinyl oxazolidinone according to formula 1 is N-vinyl-5-methyl-2-oxazolidinone.

4. A pigmented free radical curable inkjet ink as claimed in any one of claims 1 to 3 containing an acylphosphine oxide photoinitiator.

5. A pigmented free radical curable inkjet ink as claimed in claim 4, wherein the photoinitiator comprises ethyl phenyl (2,4,6-trimethylbenzoyl) phosphinate.

6. A pigmented free radical curable inkjet ink as claimed in any one of claims 1 to 5, wherein the ink Tg is calculated to be less than 18°C, wherein the ink Tg is calculated according to formula (I): wherein i and n are integers; n is the total number of polymerizable compounds in the free radical curable inkjet ink; TgPC(i) is the glass transition temperature of the polymerizable compound PC(i) in degrees Celsius; and wt%PC(i) is the weight percentage of the polymerizable compound PC(i); and wherein all weight percentages are based on the total weight of the free radical curable inkjet ink.

7. A pigmented free radical curable inkjet ink as claimed in any one of claims 1 to 6, wherein the monofunctional acrylate comprises 20.0 wt% to 33.0 wt% of phenoxyethyl acrylate, based on the total weight of the pigmented free radical curable inkjet ink.

8. A pigmented free radical curable inkjet ink as claimed in any one of claims 1 to 7, containing from 70.0 to 93.0 wt% of the monofunctional polymerisable compound, wherein the wt% is based on the total weight of the polymerisable composition.

9. A pigmented free radical curable inkjet ink as claimed in any one of claims 1 to 8, wherein the multifunctional polymerizable compound contains polyethylene glycol diacrylate in an amount of 65 to 100 wt%, based on the total weight of the multifunctional polymerizable compound.

10. A free radical curable inkjet ink set comprising at least three pigmented free radical curable inkjet inks as claimed in any one of claims 1 to 9.

11. A free radical curable inkjet ink set as claimed in claim 10, comprising: a) a cyan pigmented free radical curable inkjet ink containing β-copper phthalocyanine pigment; b) a magenta or red pigmented free radical curable inkjet ink containing a quinacridone pigment, a diketopyrrolopyrrole pigment or a mixed crystal thereof; c) a yellow pigmented free radical curable inkjet ink containing a yellow pigment 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) Black pigmented free radical curable inkjet ink containing carbon black pigment.

12. An inkjet printing method comprising the following steps: a) jetting a pigmented free radical curable inkjet ink as claimed in any one of claims 1 to 9 onto a substrate; and b) Curing the jetted pigmented free radical curable inkjet ink by a UV LED light source having a spectral emission in the range of 360-420 nm.

13. An inkjet printing method as claimed in claim 12, wherein the substrate is a backlight film comprising a material selected from the group consisting of polyvinyl chloride, polyethylene terephthalate (PET), polyethylene, polypropylene, polycarbonate, polyacrylate, polystyrene, nylon and polyvinyl acetate.

14. An inkjet printing method as claimed in claim 12, wherein the substrate is a tarpaulin, preferably a vinyl tarpaulin.

15. A manufacturing process for decorating natural leather comprising an inkjet printing process as claimed in claim 12, wherein the pigmented free radical curable inkjet ink, optionally in combination with other pigmented free radical curable inkjet inks, is jetted onto a primer present on a crusted leather surface to form a decorative image.

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