Decorated natural leather

Abstract

Decorated natural leather having a decorative image inkjet printed with a radiation curable inkjet ink on a half-niter leather having a colored base coat on a grain side of the half-niter leather wherein the decorative image is covered by a top coat, and wherein a barrier layer containing a thiol polymer having a molecular weight Mw of at least 500 g / mol is present on the base coat and / or in the top coat. Methods of making decorated natural leather are also disclosed.

Description

Technical Field

[0001] The present invention relates to decorated natural leather and a method for producing the same using inkjet technology. Background Art

[0002] Traditionally, natural leather has been decorated using screen printing. However, screen printing is labor-intensive, as each color requires a separate screen. This is costly and time-consuming, especially when personalization is required. Digital printing techniques using UV-curable inkjet inks have been disclosed for printing on natural leather, as described in WO 2013 / 135828 A (CODUS). The advantage of UV-curable inkjet inks is that they can also be printed on essentially non-absorbent substrates, such as natural leather that has been coated with a coloring layer after tanning and tanning.

[0003] In leather goods such as shoes and wallets, decorated natural leather must be able to withstand extensive flexing without damaging the decoration. To achieve this, flexible UV-curable inkjet inks containing high amounts of monofunctional monomers are used. For example, in EP3833720 A (AGFA), the UV-curable inkjet ink contains at least 85.0% by weight of monofunctional polymerizable compounds, based on the total weight of the polymerizable composition. Consequently, significant amounts of residual, uncured monofunctional monomers may be present in the decorated natural leather, posing a health and safety risk.

[0004] The first approach to overcome this potential drawback is to replace the UV curable inkjet ink with an aqueous inkjet ink. However, it has been observed that poor image quality is obtained, especially when aqueous inkjet inks are printed on substantially non-absorbent substrates such as semi-tan leather coated with a pigmented layer.

[0005] A second approach is to modify the polymerizable composition of UV-curable inkjet inks so that less residual uncured monomer remains in the printed image. In completely different applications, such as food packaging, this has been achieved by including significantly higher amounts of multifunctional monomers, as described in EP 2 053 101 A (AGFA). However, this can significantly reduce the flexibility of the printed leather and lead to cracking in the printed image.

[0006] Another approach is to apply a barrier layer to the printed article. EP 2326674 A (SEKISUI) discloses a barrier layer comprising a polyvinylamine-polyvinyl alcohol copolymer which is applied to a substrate as a water-soluble composition. Ultiloc 5003 is a polyvinylamine-polyvinyl alcohol copolymer commercialized under this patent. Although amines can undergo Michael addition reactions with polymerizable compounds such as acrylates, it has been observed that this technical solution does not produce good migration results in leather applications.

[0007] Therefore, there remains a need for decorated natural leather printed with UV curable inkjet inks which exhibits good flexibility and low amounts of migratable monomers and photodecomposition products of photoinitiators such as mesitaldehyde. Summary of the Invention

[0008] In order to overcome the above-mentioned problems, a preferred embodiment of the present invention has been achieved with a decorated natural leather having a decorative image inkjet printed with a radiation curable inkjet ink on a semi-tanned leather having a pigmented base coat on the grain side of the semi-tanned leather, wherein the decorative image is covered by a top coat and wherein a barrier layer comprising a thiol polymer having a molecular weight Mw of at least 500 g / mol is present on the base coat and / or in the top coat.

[0009] Surprisingly, it has been found that the use of a barrier layer comprising a thiol polymer having a molecular weight Mw of at least 500 g / mol can reduce extractables from decorated natural leather, and this applies not only to acrylate monomers and vinyl methyl It is suitable for polymerizable compounds such as oxazolidinone, but also for non-reactive compounds such as phenoxyethanol and photodegradable compounds such as methyl aldehyde.

[0010] It is also an object of the present invention to provide a method for producing decorated natural leather which has a low content of extractable compounds.

[0011] Another object of the present invention is an aqueous composition containing 2 to 50% by weight of a thiol polymer having a molecular weight Mw of at least 500 g / mol for reducing the extractability of components from decorated natural leather printed with radiation curable inks.

[0012] These and other objects of the present invention will become apparent from the detailed description below. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1The flow chart of the traditional manufacture of leather products is shown, and it can be divided into five stages generally. Preparatory stage 1 usually occurs partly in the slaughterhouse, and partly occurs in the tannery, and stage 2 to 4 occurs in the tannery, and stage 5 occurs at the leather product manufacturer. In the first stage, i.e. the preparatory stage, the skin is removed (skinned) from the animal, and pretreatment is used for the tanning in the second stage. Pretreatment may include processes such as soaking, liming, unhairing, splitting and pickling (adjusting pH to help the penetration of tanning agents). In the tanning stage, the protein of the hide or skin is converted into a stable substance that will not rot. Chromium is most commonly used as a tanning agent, and the tanned leather obtains a light blue color from it, commonly referred to as "wet blue". In the third stage, semi-tanning, the tanned leather is dried and softened. Semi-tanning usually includes processes such as stripping (stripping, removing surface-fixed tannic acid), fatliquoring (fixing fat, oil and wax to leather fibers), dyeing, whitening, physical softening and grinding (abrading the leather surface to reduce grain defects). In the fourth stage, known as the finishing stage, the leather is ready for sale to leather goods manufacturers. Finishing operations may include painting, polishing, and embossing. In the fifth stage, leather goods are manufactured, which involves a number of processes that may include cutting, perforating, stitching, leather covering, decoration, and embossing.

[0014] Figure 2 A cross section of an animal hide is schematically shown, comprising a grain (21) and dermis (23) separated by a grain-dermis junction (22). Different leathers made from animal hides include full grain leather (24), top grain leather (25), and calottes (26).

[0015] Figure 3 Layer constructions suitable for the present invention are exemplified but not limited thereto.

[0016] Figure 3 A shows a decorated natural leather comprising a semi-tanned leather having a pigmented base coat (31), an ink layer (33) sandwiched between two barrier layers (32), and an outermost top coat (34).

[0017] Figure 3 B shows a decorated natural leather comprising semi-tanned leather having a pigmented base coat (31), an ink layer (33) covered by a barrier layer (32), and an outermost top coat (34).

[0018] Figure 3 C shows a decorated natural leather comprising semi-tanned leather having a pigmented base coat (31) covered by a barrier layer (32), an ink layer (33) and an outermost top coat (34).

[0019] Figure 3D shows a decorated natural leather comprising semi-tanned leather having a pigmented base coat (31) covered by a barrier layer (32), an ink layer (33) and a second barrier layer (32) serving as a top coat.

[0020] Figure 3 E shows a decorated natural leather comprising semi-tanned leather having a pigmented base coat (31) and an ink layer (33) sandwiched between three barrier layers (32). DETAILED DESCRIPTION

[0021] definition

[0022] The term "part-tanned" or "crust leather" refers to leather that has been tanned and part-tanned but not finished.

[0023] As used in reference to monofunctional polymerizable compounds, the term "monofunctional" refers to compounds that contain a single polymerizable group.

[0024] As used in polyfunctional polymerizable compounds, the term "polyfunctional" refers to compounds containing two, three, or more polymerizable groups.

[0025] Thiol polymers

[0026] The molecular weight Mw of the thiol polymer is at least 500 g / mol, preferably at least 1000 g / mol, more preferably at least 1500 g / mol. Such a molecular weight makes the thiol polymer non-extractable.

[0027] The thiol content of the thiol polymer is preferably at least 80 or 100 g / mol, more preferably at least 300 g / mol, most preferably at least 500 g / mol.The extractability of the compound tends to decrease with increasing thiol content.

[0028] Preferred thiol polymers are selected from ethoxylated trimethylolpropane tris(3-mercaptopropionate), polycaprolactone tetrakis(3-mercaptopropionate), reaction products of alkoxysilanes including (3-isocyanatopropyl)trimethoxy groups and pentaerythritol tetrakis(3-mercaptopropionate), and alkoxysilanes whose siloxane chains are substituted with mercapto groups.

[0029] Ethoxylated trimethylolpropane tris(3-mercaptopropionate) can ETTMP1300 and ETTMP700 was commercially available from Bruno Bock Chemische Fabrik GmbH & Co. KG.

[0030] A suitable polycaprolactone tetrakis (3-mercaptopropionate) can be PCL4MP 1350 was obtained from BrunoBock Chemische Fabrik GmbH & Co. KG.

[0031] Other suitable thiol group-containing alkoxysilanes include X-12-1154 and KR-518 from Shin-Etsu Chemical Co. Ltd.

[0032] The barrier layer may contain a single thiol polymer or a mixture thereof.

[0033] For applying the barrier layer, an aqueous composition containing 2 to 25% by weight of a thiol polymer having a molecular weight Mw of at least 500 g / mol is preferably used. Such a composition is effective in reducing the extractability of components from decorated natural leather printed with radiation curable inks, in particular selected from phenoxyethanol, methyl aldehyde, acrylate monomers and vinyl methyl Components of oxazolidinone.

[0034] Decorated natural leather

[0035] The decorated natural leather preferably has a decorative image inkjet printed with a radiation curable inkjet ink on a tan leather having a pigmented basecoat on the grain side of the tan leather, wherein the decorative image is covered by a topcoat, and wherein a barrier layer comprising a thiol polymer having a molecular weight Mw of at least 500 g / mol is present on the basecoat and / or in the topcoat.

[0036] A barrier layer on the basecoat is an effective measure to reduce extractables from shoes caused by, for example, sweaty feet or rain.

[0037] The presence of a barrier layer in the topcoat can be advantageously used, for example, in leather handbags to reduce skin sensitization caused by acrylates and other compounds upon frequent contact with the exterior of the handbag.

[0038] In a preferred embodiment of the decorated natural leather, a barrier layer comprising a thiol polymer is present on the basecoat and in the topcoat. Figure 3 A. Figure 3 D and Figure 3 Example E. By "sandwiching" a decorative image inkjet printed with a radiation curable inkjet ink between two or more barrier layers, extraction of compounds from the decorative image is reduced in both the topcoat and basecoat directions.

[0039] Natural leather is divided into different grades (see Figure 2), such as full grain (24), top grain (25) which is essentially full grain but has part of the grain layer sanded and the underlying suede layer removed, and suede (26). In the latter, the lower layer of the rawhide is removed and used to produce suede. Depending on the thickness of the lower layer, many suede splits can be produced. Suede has a rough appearance and is often used to make suede. In the present invention, it is preferred to use natural leather with a grain surface.

[0040] To prevent grain damage and weakening, the 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 to form so-called tanned leather. Tanning 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 sanding (abrasion of the leather surface to reduce grain defects). In the present invention, tanned leather is used to which a colored base coat has been applied.

[0041] Decorated natural leather can be used to make a wide range of leather products. Preferred leather products include footwear, furniture, upholstery, bags and luggage, gloves, belts, wallets, clothing, automotive leather (e.g., train, airplane, boat and car seats), interior design, books, stationery, interior decoration, packaging, equestrian products, etc.

[0042] Method for producing decorative natural leather

[0043] The method for producing decorated natural leather according to a preferred embodiment of the present invention comprises the steps of applying in sequence on a pigmented base coat present on the grain side of a semi-tanned leather: a) optionally, a barrier layer containing a thiol polymer having a molecular weight Mw of at least 500 g / mol; b) an ink layer of a radiation curable inkjet ink by inkjet printing; and c) a top coat comprising a top coat and / or, optionally, a barrier layer containing a thiol polymer having a molecular weight Mw of at least 500 g / mol; provided that at least one of the barrier layers in steps a) and c) is applied.

[0044] In a preferred embodiment of the method for producing decorated natural leather, one or more topcoat layers are present in the topcoat layer.

[0045] In a preferred embodiment of the method for producing decorated natural leather, a barrier layer containing a thiol polymer is present on the basecoat and in the topcoat. This allows for a reduction in extractables in both the basecoat and the topcoat.

[0046] inkjet printing

[0047] The inkjet printing method used in a preferred embodiment of the present invention comprises the steps of: a) jetting a pigmented free radical curable inkjet ink; and b) curing the jetted pigmented free radical curable inkjet ink by a UV LED source having a spectral emission in the range of 360-420 nm.

[0048] UV LED sources with spectral emission in the range of 360-420 nm tend to cure the interior of the ink layer much better than UV sources with spectral emission less than 360 nm. Using a UV LED source is beneficial in reducing extractables in the cured ink layer.

[0049] Basecoat

[0050] The basecoat is applied to crust leather to provide a level of image quality commensurate with the luxurious aspect of the leather, as otherwise the low viscosity of the inkjet inks would cause them to quickly penetrate the leather, resulting in reduced image quality.

[0051] The base coat preferably has a color similar to the leather and grain. Any desired color can be chosen for the leather or grain and base coat, such as red, green, brown, black, blue, ... The leather and grain are usually tanned at the semi-tanning stage (see Figure 1 The base coat is dyed with dyes during stage 3) of the base coat, while the base coat generally contains color pigments. These color pigments will reduce the fading of the leather color under prolonged UV exposure (such as from sunlight).

[0052] The primer layer can be applied as a single layer, or it can be applied as multiple layers. The multiple layers can even have different compositions to improve properties such as adhesion or flexibility.

[0053] The basecoat preferably comprises a polyurethane based polymer or copolymer as this has been found to improve the flexibility of the printed leather.

[0054] 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 INCOREZ TM CS8073 and CS065-195. The dry weight of polyurethane in the base coat or top coat is preferably 1 to 6 g / m 2 within the range.

[0055] The basecoat may comprise other types of polymers, such as polyamides or polyacrylates.

[0056] Suitable polyamides include PA emulsion types ED310 and 161148CX from MICHELMAN. The dry weight of the polyamide in the primer layer is preferably less than 7 g / m 2 , more preferably less than 5g / m 2 .

[0057] While polyurethane is preferred as the polymer for the basecoat, other polymers may be preferably used in combination with polyurethane. Such polymers preferably have an elongation at break greater than 200%, more preferably 300%. Elongation at break is measured according to ISO 527-2, for example, using an MTS Exceed 1000 from MTS Systems Corporation. TM Test equipment.

[0058] Another type of preferred polymer for use in the basecoat is polyacrylates. Polyacrylates provide good flexibility and stabilize the pigment dispersion in the basecoat.

[0059] In a preferred embodiment, the basecoat layer preferably comprises a polyurethane-based polymer or copolymer and a polyacrylate-based polymer or copolymer. Such a combination brings excellent flexibility even in the presence of pigments.

[0060] 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.

[0061] A crosslinking agent may be incorporated into the basecoat to improve strength and adhesion to crust leather. Preferred crosslinking agents include aldehyde-based crosslinkers such as formaldehyde, melamine formaldehyde derivatives, urea formaldehyde resins, glyoxal and glutaraldehyde, epoxides, Oxazoline, carbodiimide and isocyanate, isocyanate is 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 .

[0062] The basecoat is preferably applied by spraying, but may be applied by any known coating technique such as knife coating, extrusion coating, slide hopper coating, and curtain coating.

[0063] Top coating

[0064] A topcoat is often applied to enhance the scratch resistance of the decorative image.

[0065] The topcoat layer can be applied as a single layer, or it can be applied as multiple layers. The multiple layers can have different compositions to improve properties such as scratch resistance or to reduce the amount of extractables.

[0066] In a preferred embodiment, the topcoat layer comprises at least one barrier layer comprising a thiol polymer having a molecular weight Mw of at least 500 g / mol.

[0067] In the present invention, the expression "topcoat" is used for the layer other than the barrier layer, ie the layer of the topcoat which does not contain a thiol polymer having a molecular weight Mw of at least 500 g / mol.

[0068] The topcoat can have the same or similar composition as the basecoat. Typically, the topcoat is optimized to some degree based on the leather application. For example, unlike leather shoes, flexibility is less important for leather book covers. Therefore, a protective topcoat for a book cover might be optimized for scratch resistance rather than flexibility.

[0069] The topcoat layer and the barrier layer preferably comprise a polyurethane based polymer or copolymer, as this has been found to improve the flexibility of the printed leather. The topcoat layer may preferably also comprise a polyamide polymer or copolymer, as polyamides have been found to improve compatibility with crust leather and improve the scratch resistance of the topcoat layer.

[0070] 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 INCOREZ TM CS8073 and CS065-195. The dry weight of polyurethane in the top coat is preferably 1 to 6 g / m 2 within the range.

[0071] Suitable polyamides include PA emulsion types ED310 and 161148CX from MICHELMAN. The dry weight of the polyamide in the topcoat is preferably less than 7 g / m 2 , more preferably less than 5g / m 2 .

[0072] Other preferred types of polymers for use in topcoats include polyacrylates. Polyacrylates generally provide good flexibility and are preferred for use alone or in combination with polyurethanes.

[0073] A cross-linking agent may be incorporated into the topcoat to improve strength and adhesion to the ink layer. The dry weight of the cross-linking agent in the topcoat is preferably less than 1.4 g / m 2 , more preferably less than 1.0 g / m 2 .

[0074] Suitable polyacrylates and crosslinkers for the topcoat are given in the section on the basecoat.

[0075] The topcoat is preferably applied by spraying, but may be applied by any known coating technique such as knife coating, extrusion coating, slide hopper coating, and curtain coating.

[0076] The topcoat is most preferably a transparent topcoat, but can be a translucent topcoat. By having a transparent topcoat, the decorative image will be clearly visible through the topcoat. By using a translucent topcoat, a special aesthetic effect is produced.

[0077] 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 commercially available example of a silica dispersion is Euderm® from LANXESS. TM SN2.

[0078] inkjet inks

[0079] Inkjet inks for printing on leather typically contain a colorant. The colorant can be a dye, but pigments are preferred because decorative images made with colored pigments are less susceptible to light fading.

[0080] Pigmented inkjet inks preferably contain organic color pigments because they allow a high color gamut to be achieved on natural leather. The color gamut refers to the number of different colors that an ink set can produce. Carbon black and titanium dioxide are inorganic pigments that can be advantageously used to form black and white pigmented inkjet inks, respectively.

[0081] Inkjet inks are radiation-curable inks that can be cured by UV radiation if a photoinitiator system is present. Alternatively, inkjet inks can be cured by electron beam curing. In the latter case, a photoinitiator is not required in the ink, which is generally beneficial in reducing odor and migratable photodecomposition products.

[0082] To achieve good flexibility, the polymerizable composition of the inkjet ink preferably contains at least 60 wt% of monofunctional polymerizable compounds. More preferably, between 85 and 95 wt% of monofunctional monomers and oligomers are used in the inkjet ink.

[0083] Color pigments

[0084] Pigmented inkjet inks preferably contain organic color pigments, as they allow a high color gamut to be obtained on natural leather.Carbon black and titanium dioxide are inorganic pigments that can be advantageously used in the present invention to constitute black and white pigmented inkjet inks, respectively.

[0085] The organic color pigments may be selected from those disclosed in HERBST, Willy et al., Industrial Organic Pigments, Production, Properties, Applications. 3rd edition. Wiley-VCH, 2004. ISBN 3527305769.

[0086] 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 preferably, for the sake of color gamut and light stability, the pigment used for the yellow inkjet ink is selected from CI Pigment Yellow 120, 139, 150, 151, 155, 180, 213 and mixed crystals thereof.

[0087] 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.

[0088] Particularly preferred pigments are CI Pigment Violet 19, 23, 32 and 37.

[0089] Most preferably, the pigment for the 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 provide good color reproducibility and light stability.

[0090] 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. Most preferably, CI Pigment Blue 15:3 or 15:4 is selected for color gamut and light stability.

[0091] Other particularly preferred pigments are CI Pigment Orange 5, 13, 16, 34, 40, 43, 59, 66, 67, 69, 71 and 73; CI Pigment Green 7 and 36; and CI Pigment Brown 6 and 7. These pigments can be used to expand the color gamut by adding orange, green or brown inks to the inkjet ink set.

[0092] 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 mix with each other to form solid solutions, which are very different from physical mixtures of compounds and the compounds themselves. In a solid solution, the molecules of each component enter the same crystal lattice, usually but not always the crystal lattice of one of the components. The x-ray diffraction pattern of the resulting crystalline solid is a characteristic of the solid and can be clearly distinguished from the pattern of physical mixtures of the same components in the same proportions. In such physical mixtures, the x-ray pattern of each component can be identified, and the disappearance of many of these lines is one of the criteria for forming a solid solution. A commercially available example is Cinquasia Magenta RT-355-D from BASF AG.

[0093] Carbon black is preferred as the black pigment. Suitable black pigments include carbon black such as Pigment Black 7 (e.g., Carbon Black from MITSUBISHI CHEMICAL ); from CABOTCo. 400R, L. 320; or Carbon Black FW18, Special Black 250, Special Black 350, Special Black550 from DEGUSSA, 25. 35. 55. 90. In a preferred embodiment, the carbon black pigment used is one having a toluene extractable fraction of less than 0.15% using the method described in section III, paragraph 5, of European Council resolution AP(89)1 of 13 September 1989.

[0094] Mixtures of pigments can also be prepared. For example, in a preferred embodiment, a neutral black inkjet ink is used. Such a black inkjet ink is preferably obtained by mixing a black pigment with a color pigment having a maximum absorption between 500 and 700 nm (such as a cyan and / or magenta pigment) into the ink. A neutral black inkjet ink avoids the need to apply cyan or magenta ink to correct the blackness, which results in a thinner ink layer with improved flexibility.

[0095] The pigment particles in inkjet inks should be small enough to allow the ink to flow freely through the inkjet printing device, especially at the jetting nozzles. It is also desirable to use small particles to obtain maximum color intensity and slow down sedimentation.

[0096] The number average pigment particle size is preferably between 0.050 and 0.500 μm. For organic color pigments and inorganic black pigments, the average pigment particle size is particularly preferably between 0.070 and 0.200 μm, and most preferably between 0.100 and 0.150 μm. Average particle sizes less than 0.050 μm are less desirable due to reduced lightfastness, while average particle sizes greater than 0.200 μm reduce the color gamut.

[0097] The number-average pigment size of the pigment particles is best determined using a Brookhaven Instruments Particle Sizer BI90plus based on dynamic light scattering. The ink is then diluted, for example, with ethyl acetate, to a pigment concentration of 0.002% by weight. The BI90plus measurement settings are: 5 runs at 23°C, an angle of 90°, a wavelength of 635 nm, and the Graph = calibration function.

[0098] The inkjet ink may further comprise 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 15.0 wt. %, preferably 17.0 to 35.0 wt. %, and more preferably 18.0 to 25.0 wt. %, based on the total weight of the free radical curable inkjet ink. Within the above range, a thin layer of the white ink will achieve good opacity without increasing the viscosity too much to impair jetting performance.

[0099] White pigments can be used alone or in combination in white inkjet inks. Pigments used in white inkjet inks preferably have a refractive index greater than 1.60, preferably greater than 2.00, and most preferably greater than 2.60. Having such a refractive index minimizes the dry thickness of the white ink layer, which improves flexibility.

[0100] For pigments with a refractive index greater than 1.60, titanium dioxide is preferably used. Titanium dioxide exists in the crystal forms of anatase, rutile and brookite. The anatase type has a relatively low density and is easy to grind into fine particles, while the rutile type 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 as much as possible and select according to its use. The use of anatase type with low density and small particle size can obtain excellent dispersion stability, ink storage stability and jettability. At least two different crystal forms can be used in combination. The combined use of anatase type and rutile type exhibiting high tinting power can reduce the total amount of titanium dioxide, thereby improving the storage stability and jetting performance of the ink.

[0101] Titanium dioxide surface treatments are typically performed using aqueous or vapor-phase treatments, typically with an alumina-silica treatment agent. Untreated, alumina-treated, silica-treated, or alumina-silica-treated titanium dioxide can be used. Organic surface treatments can be used alone or in addition to the aforementioned surface treatments.

[0102] The number average particle diameter of the titanium dioxide 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 shielding power will not be obtained, while when the upper size limit is exceeded, the storage capacity and jetting suitability of the ink tend to be reduced. The number average particle diameter is preferably determined by photon correlation spectroscopy using a 4 mW He-Ne laser at a wavelength of 633 nm on a diluted sample of the pigmented inkjet ink. A suitable particle size analyzer for use is the Malvern Spectroscopy Spectrometer available from Goffin-Meyvis. TM nano-S. Samples can be prepared by adding one 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 three consecutive measurements consisting of six 20-second runs.

[0103] dispersants

[0104] Pigments are typically stabilized in a dispersion medium of polymerizable compounds by a dispersant, such as a polymeric dispersant or surfactant. Alternatively, 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 a dispersion medium without the need for a dispersant.

[0105] In a preferred embodiment of the pigmented free radical curable inkjet ink, the pigment is stabilized by a polymeric dispersant.

[0106] The pigment is preferably used in the concentrated pigment dispersion used to prepare 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 into the inkjet ink.

[0107] Typical polymeric dispersants are copolymers of two monomers, but they can contain three, four, five or even more monomers. The properties of polymeric dispersants depend on both the properties of the monomers and their distribution in the polymer. Copolymer dispersants preferably have the following polymer composition:

[0108] Statistical polymerization of monomers (e.g., monomers A and B polymerize to form ABBAABAB);

[0109] Alternating monomers (e.g., monomers A and B polymerize to form ABABABAB);

[0110] Gradient (tapered) polymerization of monomers (e.g., monomers A and B polymerize to AAABAABBABBB);

[0111] 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 for the dispersing ability of the polymeric dispersant;

[0112] Graft copolymers (graft copolymers consist of a polymer backbone with polymer side chains attached to the backbone); and

[0113] • Mixed forms of these polymers, such as block gradient copolymers.

[0114] The polymeric dispersant preferably has a number average molecular weight Mn between 500 and 30000, more preferably between 1500 and 10000. Dispersants with a larger molecular weight tend to increase the viscosity of the ink too much and fail to provide adequate dispersion stability.

[0115] 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.

[0116] The polymeric dispersant preferably has a polydispersity PD of less than 2, more preferably less than 1.75, most preferably less than 1.5.

[0117] Commercially available examples of polymeric dispersants are as follows:

[0118] DISPERBYK available from BYK CHEMIE GMBH TM dispersants;

[0119] SOLSPERSE available from LUBRIZOL TM dispersants;

[0120] TEGO from EVONIK TM DISPERS TM dispersants;

[0121] From CHEMIE's EDAPLAN TM dispersants;

[0122] ETHACRYL from LYONDELL TM dispersants;

[0123] GANEX from ISPTM dispersants;

[0124] DISPEX from BASF TM and EFKA TM dispersants;

[0125] DISPONER from DEUCHEM TM Dispersant.

[0126] Particularly preferred polymeric dispersants include Solsperse from LUBRIZOL TM Dispersant, Efka from BASF TM Dispersants and Disperbyk from BYK CHEMIE GMBH TM Dispersants. Particularly preferred dispersants are Solsperse from LUBRIZOL TM 32000, 35000 and 39000 dispersants.

[0127] The polymeric dispersant is preferably used in an amount of 2 to 200 wt %, more preferably 10 to 100 wt %, and most preferably 50 to 90 wt %, based on the weight of the pigment. An amount between 2 and 90 wt % will provide good dispersion stability combined with minimal effect on ink viscosity.

[0128] Dispersion synergist

[0129] Dispersion synergists generally consist of an anionic part and a cationic part. The anionic part of the dispersion synergist shows a certain 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.

[0130] The amount of dispersion synergist added is preferably less than the amount of polymeric dispersant added. The ratio of polymeric dispersant to dispersion synergist depends on the pigment and should be determined experimentally. Typically, the ratio of polymeric dispersant (wt%) to dispersion synergist (wt%) is selected between 2:1 and 100:1, preferably between 2:1 and 20:1.

[0131] Suitable commercially available dispersion synergists include Solsperse from LUBRIZOL TM 5000 and Solsperse TM 22000.

[0132] Particularly preferred 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).

[0133] When dispersing CI Pigment Blue 15:3, it is preferred to use a sulfonated Cu-phthalocyanine dispersion synergist, for example Solsperse from LUBRIZOL. TM 5000. Suitable dispersion synergists for yellow inkjet inks include those disclosed in EP 1790697A (AGFA GRAPHICS).

[0134] polymerizable compounds

[0135] Any polymerizable compound commonly known in the art can be used. The polymerizable compound can be any monomer or oligomer described in Polymer Handbook, Volumes 1+2, 4th Edition, edited by J. BRANDRUP et al., Wiley-Interscience, 1999. In the present invention, an oligomer is understood to contain two or more repeating monomer units.

[0136] Combinations of monomers and oligomers may also be used.The monomers and oligomers may have different functionalities, and mixtures including combinations of mono-, di-, tri- and higher functionality monomers and oligomers may be used.

[0137] In a preferred embodiment, the pigmented free radical curable inkjet ink used in the present invention comprises a polymerizable composition of monofunctional and multifunctional polymerizable compounds meeting the following requirements A to E: A) 65.0 to 95.0 wt% of the 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 acrylate according to Formula 1, based on the total weight of the UV curable inkjet ink. Oxazolidinone, wherein the N-vinyl Oxazolidinone is:

[0138]

[0139] where R 1 to R 4 Unrestricted, except for limitations imposed by use in inkjet inks such as viscosity and ink stability. 1 to R 4Preferred 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) between 350 and 750; and F) the multifunctional polymerizable compound contains 60 to 100 wt. % of polyethylene glycol diacrylate, based on the total weight of the multifunctional polymerizable compound.

[0140] In a more preferred embodiment of the pigmented free radical curable inkjet ink, the N-vinyl Oxazolidinone is N-vinyl-5-methyl-2- Oxazolidinone.

[0141] 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:

[0142]

[0143] in

[0144] i represents an integer from 1 to n;

[0145] n represents the number of polymerizable compounds in the UV radical curable inkjet ink;

[0146] F(i) represents the functionality of polymerizable compound i;

[0147] MW(i) represents the molecular weight of polymerizable compound i; and

[0148] Wt% (i) is the weight percentage of polymerizable compound i based on the total weight of the pigmented free radical curable inkjet ink. By selecting the double bond density DBD within the above range, an ink viscosity with excellent printing reliability can be obtained.

[0149] In a more preferred embodiment of the pigmented free radical curable inkjet ink, the molecular weight MW of the polyethylene glycol diacrylate is between 400 and 600. Below MW 400, flexibility tends to be reduced, while above MW 600, viscosity tends to be reduced.

[0150] In a more 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 will be beneficial for adhesion but will quickly reduce flexibility.

[0151] Photoinitiator system

[0152] UV curable inkjet inks comprise a photoinitiating system containing one or more photoinitiators and optionally a co-initiator.

[0153] The photoinitiator is preferably a Norrish Type I initiator and / 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 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 referred to as a polymerization synergist or coinitiator.

[0154] Suitable photoinitiators are disclosed in CRIVELLO, JV et al., Volume III: Photoinitiators for Free Radical Cationic. 2nd edition. BRADLEY, G. ed. London, England: John Wiley and Sons Ltd, 1998. p. 287-294.

[0155] Norrish Type I photoinitiator

[0156] The Norrish type I photoinitiator is preferably selected from benzoin ethers, benzil ketals, α-haloketones, α,α-dialkoxyacetophenones, α-hydroxyalkanoylphenones, α-halosulfones, α-aminoalkanoylphenones, acylphosphine oxides, acylphosphine sulfides and phenylglyoxylates.

[0157] For high curing 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.

[0158] 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 present solubility issues in the pigmented free radical curable inkjet ink, as opposed to, for example, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide.

[0159] The free radical curable inkjet ink contains an acylphosphine oxide photoinitiator, which is preferably present 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.

[0160] Suitable examples of acylphosphine oxide photoinitiators include bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, 2,4,6-trimethylbenzoyldiphenylphosphine oxide and ethyl (2,4,6-trimethylbenzoyl)phenylphosphinate, 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 commercially available from IGM Resins.

[0161] Acylphosphine oxides can also be polymeric compounds such as Omnipol from IGM Resins TM TP.

[0162] In a particularly preferred embodiment, the acylphosphine oxide photoinitiator may comprise an acyl group containing a polymerizable group or an acyl group selected from the group consisting of: a benzoyl group substituted with a urea group or an oxalylamide group; a 2,6-dimethylbenzoyl group substituted with a urea group or an oxalylamide group at the 3-position; a 2,6-dimethoxybenzoyl group substituted with a urea group or an oxalylamide group at the 3-position; a 2,4,6-trimethylbenzoyl group substituted with a urea group or an oxalylamide group at the 3-position; and a 2,4,6-trimethoxybenzoyl group substituted with a urea group or an oxalylamide group at the 3-position. By using such an acylphosphine oxide photoinitiator, no aldehyde is released after UV curing, which can cause an unpleasant odor to printed products.

[0163] Suitable acylphosphine oxide photoinitiators having an acyl group substituted by a urea group or an oxalylamide group are disclosed in WO 2019 / 243039 (AGFA).

[0164] Suitable acylphosphine oxide photoinitiators comprising an acyl group containing a polymerizable group are disclosed in WO 2014 / 051026 (FUJIFILM).

[0165] Combinations of different acylphosphine oxide photoinitiators can also be used. For example, a combination of a monofunctional acylphosphine oxide photoinitiator such as TPO or TPO-L with 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 efficiencies.

[0166] Alternatively, the acylphosphine oxide is a polymeric compound in which the acylphosphine oxide structure is bonded to a polymer chain on the side of its acyl group. Suitable compounds are disclosed in WO 2014 / 129213 (FUJIFILM). By having an acyl group bonded to the polymer chain, the odor of the printed article is also suppressed.

[0167] Suitable examples of α-hydroxyketone photoinitiators include, but are not particularly limited to, 1-hydroxycyclohexylphenylketone, 2-hydroxy-2-methyl-1-phenylpropane-1-one, and 1-[4-(2-hydroxyethoxy)-phenyl]2-hydroxy-2-methyl-1-propane-1-one.

[0168] 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 Omnirad TM 4817.

[0169] The content of the α-hydroxyketone is preferably 1 to 10 wt%, more preferably 2 to 8 wt%, still more preferably 3 to 6 wt%, based on the total weight of the UV LED free radical curable inkjet ink.

[0170] In a particularly preferred embodiment, the α-hydroxyketone photoinitiator is a polymeric or polymerizable photoinitiator.

[0171] An example of a suitable polymeric α-hydroxyketone photoinitiator can be Esacure TM KIP150 was obtained from IGMRESINS.

[0172] 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.

[0173] Norrish II photoinitiator

[0174] The free radical curable inkjet ink may contain a Norrish Type II photoinitiator comprising a photoinitiating moiety selected from a thioxanthone group, a carbazole group, and a benzophenone group. Norrish Type II photoinitiators containing a thioxanthone group or a carbazole group are particularly preferred because they facilitate UV LED curing, especially for UV LEDs emitting at a wavelength of 370 nm or longer.

[0175] Suitable examples of Norrish Type II 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.

[0176] Specific examples of commercially available Norrish II type photoinitiators containing thioxanthone groups are Speedcure from LAMBSON TM DETX (2,4-diethylthioxanthone) and Speedcure TM ITX (2-isopropylthioxanthone) and Kayacure from Nippon Kayaku Co. TM DETX-S (2,4-diethylthioxanthone).

[0177] Preferred carbazole photoinitiators are disclosed in EP 2509948 A (AGFA). These carbazole photoinitiators have the advantage over thioxanthone photoinitiators of exhibiting less photoyellowing.

[0178] Suitable examples of Norrish Type II photoinitiators containing a benzophenone group include, but are not particularly limited to, benzophenone; methylbenzophenone; methyl 2-benzoylbenzoate, phenylbenzophenone, such as 4-phenylbenzophenone; trimethylbenzophenone; bis(alkylamino)benzophenone; and 4-(dialkylamino)benzophenone.

[0179] Specific examples of commercially available Norrish type II photoinitiators containing benzophenone groups are Omnirad from IGM RESINS. TM 4MBZ and Omnirad TM BP, Speedcure from Lambson TM PBZ and Speedcure TM 5040. The latter is a mixture of benzophenone and thioxanthone.

[0180] Preferred examples of polymerisable 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).

[0181] 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).

[0182] Commercially available examples of polymeric thioxanthones and benzophenones include Omnipol from IGM RESINS. TM BP, Omnipol TM TX and Omnipol TM 2702.

[0183] The amount of the Norrish Type II photoinitiator comprising a photoinitiating moiety selected from the group consisting of thioxanthone, carbazole and benzophenone groups is preferably from 0.5 to 7.5 wt%, more preferably from 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 amount 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.

[0184] Polymerization synergist

[0185] To further increase the photosensitivity, the free radical curable inkjet ink may additionally contain one or more co-initiators, also known as polymerization synergists, which are typically amine synergists.

[0186] Suitable examples of amine synergists can be divided into three categories: 1) tertiary aliphatic amines, such as methyldiethanolamine, dimethylethanolamine, triethanolamine, triethylamine and N-methylmorpholine; (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 (3) (meth)acrylated amines, such as dialkylaminoalkyl (meth)acrylates (e.g., diethylaminoethyl acrylate) or N-morpholinoalkyl (meth)acrylates (e.g., N-morpholinoethyl acrylate).

[0187] In a preferred embodiment of the free radical curable inkjet ink, the polymeric synergist is an acrylated amine synergist.

[0188] Suitable amine synergists can be Omnipol TM ASA, Omnipol TM 894 and Esacure TM A198 was purchased commercially from IGM Resins.

[0189] Preferred commercially available acrylated amine synergists include Photomer from IGM Resins TM 4068, 4250, 4771, 4775, 4780, 4967 and 5006.

[0190] Polymerization inhibitors

[0191] The free radical curable inkjet ink may contain a polymerization inhibitor to prevent undesired polymerization during transportation or storage. Suitable polymerization inhibitors include phenolic antioxidants, hindered amine light stabilizers, phosphorus antioxidants, hydroquinone monomethyl ether commonly used in (meth)acrylate monomers, and hydroquinone, tert-butylcatechol, and pyrogallol may also be used.

[0192] Suitable commercially available 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 TM UV10 and Irgastab TM UV22, Tinuvin TM 460 and CGS20; Floorstab from Kromachem Ltd TM UV range (UV-1, UV-2, UV-5 and UV-8); Additol from Cytec Surface Specialties TM S range (S100, S110, S120 and S130).

[0193] Since excessive addition of these polymerization inhibitors will reduce the ink's sensitivity to curing, it is preferred to determine the amount that can prevent polymerization before blending. The amount of polymerization inhibitor is preferably less than 2% by weight of the total free radical curable inkjet ink.

[0194] In a preferred embodiment, the polymerization inhibitor is a polymerizable inhibitor, which preferably contains one or more acrylate groups to obtain good reactivity.

[0195] surfactants

[0196] 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.

[0197] Preferred surfactants are selected from fluorosurfactants (such as fluorinated hydrocarbons) and silicone surfactants. The silicone surfactant is preferably a siloxane and can be alkoxylated, polyester-modified, polyether-modified, polyether-modified hydroxy-functional, amine-modified, epoxy-modified, and other modifications or combinations thereof. Preferred siloxanes are polymeric, such as polydimethylsiloxane.

[0198] Preferred commercially available silicone surfactants include BYK TM 333 and BYK TM UV3510 and Tegoglide from EVONIK TM 410.

[0199] In a preferred embodiment, the surfactant is a polymerizable compound.

[0200] 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.

[0201] In a preferred embodiment, the (meth)acrylated silicone surfactant is a polyether-modified (meth)acrylated polydimethylsiloxane or a polyester-modified (meth)acrylated polydimethylsiloxane.

[0202] Preferred commercially available (meth)acrylated silicone surfactants include: Ebecryl TM 350, a silicone diacrylate from Cytec; polyether-modified acrylated polydimethylsiloxane BYK TM UV3500 and BYK TM UV3530, polyester modified acrylated polydimethylsiloxane BYK TM UV3570, both manufactured by BYK Chemie; Tego from EVONIK TM Rad 2100, Tego TM Rad 2200N, Tego TM Rad2250N, Tego TM Rad 2300, Tego TM Rad 2500, Tego TM Rad 2600 and Tego TM Rad 2700, Tego TM RC711; Silaplane TMFM7711, 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; 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.

[0203] Preparation of pigmented free radical curable inkjet inks

[0204] Pigment dispersions can be prepared by precipitating or grinding the pigment in a dispersion medium in the presence of a dispersant.

[0205] The method of making a free radical curable inkjet ink preferably comprises 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 to obtain a free radical curable inkjet ink having the correct viscosity and surface tension.

[0206] 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, two-roll mills, bead mills, paint conditioners, and three-roll mills. Dispersions may also be prepared using ultrasonic energy.

[0207] Many different types of materials can be used as grinding media, such as glass, ceramic, metal, and plastic. In a preferred embodiment, the grinding media can comprise particles, preferably generally spherical in shape, such as beads consisting essentially of a polymer resin or yttrium stabilized zirconium beads.

[0208] During the mixing, grinding and dispersing processes, each process is preferably carried out under cooling to prevent heat buildup and, whenever possible, under lighting conditions in which actinic radiation has been substantially excluded.

[0209] The pigment dispersion may contain more than one pigment.Such pigment dispersions may be prepared using separate dispersions of each pigment, or alternatively several pigments may be mixed and co-milled when preparing the dispersion.

[0210] The dispersion process can be performed in continuous, batch or semi-batch mode.

[0211] The preferred amounts and ratios of the components of the mill grind will vary widely depending on the specific materials and intended application. The contents of the grinding mixture comprise the mill grind and the grinding media. The mill grind comprises pigment, polymeric dispersant, and liquid carrier.

[0212] Milling times can vary widely and depend 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.

[0213] After grinding is complete, the grinding media is separated from the ground particulate product (in dry or liquid dispersion form) using conventional separation techniques such as filtration, screening through a mesh screen, etc. The screen is usually built into the mill, for example, for a bead mill. The ground pigment concentrate is preferably separated from the grinding media by filtration.

[0214] Typically, it is desirable to prepare inkjet inks as concentrated mill grinds, which are then diluted to the appropriate concentration for use in an inkjet printing system. This technique allows for the production of larger quantities of pigmented ink from the equipment. By dilution, the inkjet ink is adjusted to the desired viscosity, surface tension, color, hue, saturation density, and print area coverage.

[0215] Inkjet printing device

[0216] Free radically curable inkjet inks may be jetted by one or more printheads that eject small droplets of ink through nozzles in a controlled manner onto an ink-receiver surface that moves relative to the printheads.

[0217] The preferred print head for the inkjet printing system of 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 to the piezoelectric ceramic transducer. The application of voltage changes the shape of the piezoelectric ceramic transducer in the print head, creating a gap that is then filled with ink. When the voltage is removed again, the ceramic expands to its original shape, ejecting ink droplets from the print head. However, the inkjet printing method used in the present invention is not limited to piezoelectric inkjet printing. Other inkjet print heads can be used, and include various types, such as continuous types as well as thermal, electrostatic and acoustic drop-on-demand ink types.

[0218] A preferred piezoelectric print head is a so-called push mode type piezoelectric print head which has a relatively large piezoelectric element and is also capable of ejecting more viscous inkjet ink drops. Such a print head is available from RICOH as a GEN5s print head.

[0219] Another preferred piezoelectric print head is a so-called through-flow piezoelectric drop-on-demand print head. Such a print head can be obtained from TOSHIBA TEC as a CF100 print head. Through-flow print heads are preferred because they enhance the reliability of inkjet printing due to the continuous flow of ink through the print head.

[0220] The inkjet print head typically scans back and forth in the transverse direction across the moving ink-receiver surface. Sometimes the inkjet print head does not print on the return pass, however, in order to obtain high areal throughput, bidirectional printing is preferred.

[0221] Another preferred inkjet device uses a "single pass printing process", which can be performed by using a page-wide inkjet print head or multiple staggered inkjet print heads covering the entire width of the substrate surface. In a single pass printing process, the inkjet print head generally remains stationary while the substrate is transported below the inkjet print head.

[0222] Curing device

[0223] The free radical curable inkjet inks used in the present invention are cured by exposure to actinic radiation, preferably ultraviolet radiation. The actinic radiation may also originate from an electron beam curing device.

[0224] The pigmented free radical curable inkjet inks of the present invention can also be advantageously used for electron beam curing, because the latter also cures the interior of the layer of polymerizable composition better than its surface. In addition, electron beam curing does not require a photoinitiator, which has economic benefits.

[0225] In inkjet printing, the curing device may be arranged in combination with the print head of the inkjet printer, traveling with the print head so that the curable composition is exposed to curing radiation soon after jetting, which is beneficial for image quality.

[0226] In such an arrangement, it may be difficult to provide a sufficiently small radiation source that is connected to and travels 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 a fiber optic bundle or an internally reflecting flexible tube.

[0227] Alternatively, actinic radiation may be supplied to the radiation head from a fixed source by a mirror arrangement comprising a mirror on the radiation head.

[0228] The radiation source arranged not to move with the print head may also be an elongated radiation source extending laterally across the ink-receiver surface to be cured and adjacent to the lateral path of the print head so that image lines subsequently formed by the print head pass stepwise or continuously underneath the radiation source.

[0229] Any UV light source, such as a high-pressure or low-pressure mercury lamp, a cold cathode tube, a black light, a UV LED, a UV laser, and a flash lamp, can be used as the radiation source, as long as a portion of the emitted light can be absorbed by the photoinitiator or photoinitiator system. Preferred sources are those that exhibit a relatively long-wavelength UV contribution with a dominant wavelength of 300-400 nm. Specifically, a UV-A light source is preferred because the reduced light scattering with this light source results in more efficient internal curing.

[0230] UV radiation is generally classified as UV-A, UV-B, and UV-C as follows:

[0231] UV-A: 400nm to 320nm

[0232] UV-B: 320nm to 290nm

[0233] UV-C: 290nm to 100nm.

[0234] Two light sources with different wavelengths or illumination levels can be used sequentially or simultaneously to cure the image. For example, the first UV source can be selected to be rich in UV-C, particularly in the 260nm-200nm range. The second UV source can then be rich in UV-A, such as a gallium-doped lamp, or a different lamp high in both UV-A and UV-B. Using two UV sources has been found to offer advantages such as faster curing speed and higher degree of cure.

[0235] In a preferred embodiment of the inkjet printing method used in the present invention, the inkjet printing device contains a UV LED with a wavelength greater than 360 nm, preferably a UV LED with a wavelength greater than 380 nm, most preferably a UV LED with a wavelength of about 395 nm.

[0236] To promote curing, inkjet printers typically include one or more oxygen depletion units. These units place a blanket of nitrogen or other relatively inert gas (e.g., CO2) with adjustable position and concentration to reduce the oxygen concentration in the curing environment. Residual oxygen levels are typically maintained as low as 200 ppm, but are typically within the range of 200 ppm to 1200 ppm.

[0237] Example

[0238] Measurement method

[0239] 1. GPC method

[0240] The molecular weight (Mw) of the polymer was determined by gel permeation chromatography. Sample preparation was performed by dissolving 25 mg of polymer in 10 mL of THF (tetrahydrofuran). Chromatographic conditions used were: 100 μL of sample was injected onto a 3x Mixed B column set, eluent: THF + 5% HoAC, and detection was performed using a refractive index detector. Polystyrene standards were used for the calibration curve.

[0241] 2. Migration testing

[0242] Migratable species were determined by UPLC using an Acquity UPLC BEH C18 1 / 7 μm 100 x 2.1 mm column at 40°C.

[0243] The sample was prepared by placing a 17 mm diameter punch (ink layer facing the water) into the cap of a GC headspace vial and extracting it with 2 ml of H2O for 1 hour at room temperature using a mixing console. Extraction area = 1.131 cm 2 (Inner diameter of GC headspace vial opening = 12 mm).

[0244] After extraction, 1 mL of CHCN was added to the GC headspace vial. The sample was mixed and filtered through a MN chromafil 0.2 μm filter. A 7.5 μL sample was then injected and quantified using a DAD with external calibration points for each compound. The UPLC settings (Table 1) were used: water for solvent A, acetonitrile for solvent B, a flow rate of 0.35 mL / min, and a maximum pressure limit of 1000 bar. Each sample was measured in duplicate, and the average value for each mobile component is presented.

[0245] Table 1

[0246] Time (min) A(％) B(％) 0.00 80 20 1.00 80 20 9.00 100 15.00 100 15.10 80 20 18.00 80 20

[0247] 3. Average particle size

[0248] The particle size of the pigment particles in the concentrated pigment dispersion was determined by photon correlation spectroscopy using a 4 mW HeNe laser at a wavelength of 633 nm on a diluted sample of the pigment dispersion. The particle size analyzer used was a Malvern Spectroscopy instrument available from Goffin-Meyvis. TM nano-S.

[0249] The samples were prepared by adding one drop of the pigment dispersion to a cuvette filled with 1.5 mL of ethyl acetate and mixing until a homogeneous sample was obtained. The measured particle size was the average of three consecutive measurements consisting of six 20 second runs.

[0250] Material

[0251] 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.

[0252] ETTMP is an ethoxylated trimethylolpropane tris(3-mercaptopropionate) ETTMP1300 (CAS No. 345352-19-4) was obtained from Bruno Bock Chemische Fabrik GmbH & Co. KG and, according to the supplier's technical data sheet, had an SH content of 7.1% by weight. The molecular weight Mw determined by the above-mentioned GPC method was 1744 g / mol (pd=1.08).

[0253] X12 is a reaction product of an alkoxysilane containing a (3-isocyanatopropyl)trimethoxy group and pentaerythritol tetrakis(3-mercaptopropionate) and is available from Shin-Etsu Chemical Co. Ltd. as X-12-1154 (CAS No. 1639946-87-4). According to the supplier's technical data sheet, it has an SH content of 240 g / mol. The molecular weight Mw, measured by the above-mentioned GPC method, is 1449 g / mol (pd=1.33).

[0254] KR518 is an alkoxysilane in which the siloxane chain is substituted with mercapto groups and is available as KR-518 from Shin-Etsu Chemical Co. Ltd., having an SH content of 800 g / mol according to the supplier's technical data sheet. The molecular weight Mw measured by the above-mentioned GPC method is 3071 g / mol.

[0255] SELVOL is a polyvinyl alcohol / vinylamine copolymer that Ultiloc 5003 was obtained from Sekisui Specialty Chemicals Europe SL.

[0256] Fix SFD is a 26% waterborne polyurethane dispersion from TFL LEDERTECHNIK GMBH.

[0257] Car Dull 92 / N is a 24% waterborne polyurethane dispersion from TFL LEDERTECHNIK GMBH.

[0258] Feel S 5796 is a 17% aqueous silicone emulsion from TFL LEDERTECHNIK GMBH.

[0259] Link C 70 is a 55% aqueous crosslinker emulsion from TFL LEDERTECHNIK GMBH.

[0260] TiO2 is titanium dioxide pigment, which can be Tronox TM CR834 was obtained from TRONOX PIGMENTS BV.

[0261] PB15:4 is for Sunfast TM Abbreviation for Blue 15:4, a CI Pigment Blue 15:4 pigment from SUN CHEMICAL CORPORATION.

[0262] PB7 is for Special Black TM Abbreviation for 550, which is a carbon black available from EVONIK.

[0263] PY155 is for Inkjet Yellow TM 4GC is the abbreviation of CI Pigment Yellow 155 pigment from CLARIANT.

[0264] PR122 is an abbreviation of CI Pigment Red 122, and Pigment Red 122 TCR12203IJ from TRUST CHEM EUROPE BV was used.

[0265] SYN is a dispersion synergist according to formula (A):

[0266]

[0267] and synthesized in the same manner as described for the synergist QAD-3 in Example 1 of WO 2007 / 060254 (AGFA GRAPHICS).

[0268] 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 is removed.

[0269] PEA is 2-phenoxyethyl acrylate, which can be Sartomer TM SR339C was obtained from ARKEMA.

[0270] V-MOX is vinyl methyl Oxazolidinone (CAS No.: 3395-98-0), can be VMOX TM Available from BASF.

[0271] TBCH is 4-tert-butylcyclohexyl acrylate, available from ARKEMA under the trade name Sartomer CD217.

[0272] IDA is isodecyl acrylate, which can be Sartomer TM SR395 was obtained from ARKEMA.

[0273] G1122 is a monofunctional urethane acrylate, g -3℃ and can be Genomer TM 1122 was obtained from RAHN and has the formula (B):

[0274]

[0275] PDA is polyethylene glycol 400 diacrylate, which can be Sartomer TM SR344 was obtained from ARKEMA.

[0276] DPGDA is dipropylene glycol diacrylate, which can be Sartomer TM SR508 was obtained from ARKEMA.

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

[0278] INHIB is a mixture of polymerization inhibitors having Table 2 composition.

[0279] Table 2

[0280] Components weight% DPGDA 82.4 p-Methoxyphenol 4.0 BHT 10.0 <![CDATA[Cupferron TM AL]]> 3.6

[0281] Cupferron TM AL is aluminum N-nitrosophenylhydroxylamine from WAKO CHEMICALS LTD.

[0282] BHT is butylated hydroxytoluene.

[0283] UV10 is 4-hydroxy-2,2,6,6-tetramethylpiperidinyloxy sebacate, which can be TM UV 10 was obtained from BASF.

[0284] TPL is ethyl phenyl (2,4,6-trimethylbenzoyl) phosphinate, which can be SpeedCure TM TPO-L was obtained from ARKEMA.

[0285] ITX for Darocur TM ITX is a mixture of isomers of 2- and 4-isopropylthioxanthone available from BASF.

[0286] T410 is a silicone surfactant that can Tegoglide TM 410 was obtained from EVONIK.

[0287] RL is a red dyed cowhide with a red pigmented base coat available from TFL LEDERTECHNIK GMBH as TFL Crust-MicrotecRed.

[0288] WL is a white cowhide with a white pigmented base coat available from TFL LEDERTECHNIK GMBH as TFL Crust-Microtec White.

[0289] PVA1 is a polyvinyl alcohol with a degree of hydrolysis of 98 mol%, which can 4-98 was obtained from KURARAY.

[0290] PVA2-sol is a 20 wt% polyvinyl alcohol with a degree of hydrolysis of 88% (can be 4-88 obtained from KURARAY) and a 0.2 wt% aqueous solution of a biocide.

[0291] SURF is a fluorinated surfactant that can FS-3100 was obtained from DUPONT.

[0292] The biocide was a 5% aqueous solution of Proxel K (CASRN 127553-58-6), available from ARCH UK BIOCIDES.

[0293] Example 1

[0294] This example illustrates the effect of an additional barrier layer containing a polymer thiol on migratable species from a UV curable inkjet ink layer.

[0295] Preparation of concentrated pigment dispersion CPK

[0296] By using DISPERLUX from DISPERLUX SARL, Luxembourg TM Disperser Table 3The components were mixed for 30 minutes to prepare a concentrated pigment dispersion CPK. The dispersion was then ground using a Bachofen DYNOMILL ECM Poly mill filled with 0.4 mm yttrium-stabilized zirconia beads from TOSOH. The mixture was circulated through the mill for 3 hours and 15 minutes. After grinding, the concentrated pigment dispersion was discharged through a 1 μm filter into a container. The average particle size of the concentrated pigment dispersion CPK was 109 nm.

[0297] Table 3

[0298] Weight % of components: CPK PB7 13.32 PB15:4 4.77 PR122 3.33 SYN 0.13 DB162 9.13 INHIB 2.04 DPGDA 1.85 PEA 65.43

[0299] Preparation of concentrated pigment dispersion CPC

[0300] By using DISPERLUX from DISPERLUX SARL, Luxembourg TM Disperser Table 4 The components were mixed for 30 minutes to prepare a concentrated pigment dispersion (CPC). The dispersion was then ground using a Bachofen DYNOMILL ECM Poly mill filled with 0.4 mm yttrium-stabilized zirconia beads from TOSOH. The mixture was circulated through the mill for 4 hours and 45 minutes. After grinding, the concentrated pigment dispersion was discharged through a 1 μm filter into a container. The average particle size of the concentrated pigment dispersion (CPC) was 96 nm.

[0301] Table 4

[0302] Weight % of components: CPC PB15:4 25.00 DB162 10.00 INHIB 1.00 PEA 64.00

[0303] Preparation of concentrated pigment dispersion CPM

[0304] By using DISPERLUX from DISPERLUX SARL, Luxembourg TM Disperser Table 5 The components were mixed for 30 minutes to prepare a concentrated pigment dispersion (CPM). The dispersion was then ground using a Bachofen DYNOMILL ECM Poly mill filled with 0.4 mm yttrium-stabilized zirconia beads from TOSOH. The mixture was circulated through the mill for 6 hours and 11 minutes. After grinding, the concentrated pigment dispersion was discharged through a 1 μm filter into a container. The average particle size of the concentrated pigment dispersion (CPM) was 116 nm.

[0305] Table 5

[0306] Weight % of components: CPM PR122 20.00 SYN 1.00 DB162 10.00 INHIB 1.00 PEA 68.00

[0307] Preparation of concentrated pigment dispersion CPY

[0308] By using DISPERLUX from DISPERLUX SARL, Luxembourg TM Disperser Table 6 The components were mixed for 30 minutes to prepare a concentrated pigment dispersion (CPY). The dispersion was then milled using a Bachofen DYNOMILL ECM Poly mill filled with 0.4 mm yttrium-stabilized zirconia beads from TOSOH. The mixture was circulated through the mill for 2 hours and 20 minutes. After milling, the concentrated pigment dispersion was discharged through a 1 μm filter into a container. The average particle size of the concentrated pigment dispersion (CPY) was 151 nm.

[0309] Table 6

[0310] Weight % of components: CPY PY155 21.43 DB162 6.86 INHIB 1.00 PEA 70.71

[0311] Preparation of concentrated pigment dispersion CPW

[0312] By using DISPERLUX from DISPERLUX SARL, Luxembourg TM Disperser Table 7 The components were mixed for 70 minutes to prepare a concentrated pigment dispersion (CPW). The dispersion was then milled using a Bachofen DYNOMILL ECM Poly mill filled with 0.4 mm yttrium-stabilized zirconia beads from TOSOH. The mixture was circulated through the mill for 2 hours and 33 minutes. After milling, the concentrated pigment dispersion was discharged through a 1 μm filter into a container. The average particle size of the concentrated pigment dispersion (CPW) was 200 nm.

[0313] Table 7

[0314] Weight % of components: CPW TiO2 50.0 DB162 4.0 INHIB 3.0 PEA 43.0

[0315] Preparation of UV curable inkjet ink

[0316] The concentrated pigment dispersion prepared above was used to Table 8 Free radical curable inkjet inks Ink-K, Ink-C, Ink-M, Ink-Y and Ink-W were prepared.

[0317] Table 8

[0318] Weight % of components: Ink-K Ink-C Ink-M Ink-Y Ink-W CPK 12.70 CPC 10.00 CPM 17.50 CPY 14.00 CPW 32.00 PEA 32.41 31.95 28.02 30.49 21.36 V-MOX 8.50 10.00 10.00 9.00 8.00 PDA 6.00 6.00 6.00 6.00 IDA 7.50 8.00 10.00 7.50 8.00 G1122 13.50 15.00 8.00 13.50 13.00 TBCH 8.00 8.00 10.00 8.00 4.00 OLIGO 2.00 2.00 1.50 2.00 6.00 T410 0.30 0.30 0.30 0.30 0.60 INHIB 0.74 0.90 0.83 0.86 0.04 UV10 0.35 0.35 0.35 0.35 TPL 7.00 7.00 7.00 7.00 7.00 ITX 1.00 0.50 0.50 1.00

[0319] Preparation of barrier and topcoat coating compositions

[0320] By mixing Table 9 Barrier layer compositions S-1, S-2 and S-3 were prepared using the following components:

[0321] Table 9

[0322] Weight % of components: S-1 S-2 S-3 PVA1 2.00 SELVOL 2.00 ETTMP 10.00 SURF 0.50 0.50 0.50 biocides 0.40 0.40 0.40 water 97.10 97.10 89.10

[0323] By mixing Table 10 Three thiol polymer emulsions, E-1, E-2, and E-3, were prepared using the following components. Pot A and Pot B were prepared in separate vessels. Pot B was added to Pot A under high shear using a T25 Digital Ultra-Turrax (available from IKA) with an 18N rotor at 1600 rpm for 3 to 5 minutes. Pot A was kept in an ice bath during this operation.

[0324] Table 10

[0325] Weight % of components: E-1 E-2 E-3 Pot ingredients X12 10.00 20.00 B KR518 20.00 B PVA2-sol 10.00 20.00 20.00 B SURF 0.50 0.50 0.50 B biocides 0.40 0.40 0.40 B water 79.10 59.10 59.10 A

[0326] By first applying the binder Fix SFD and Mix Car Dull 92 / N into water and then add silicone Feel S 5796 and crosslinker Link C 70, prepare top coating composition TC-1. The obtained composition is composed of Table 11 Shown.

[0327] Table 11

[0328]

[0329] By following Table 12 The top coating composition TC-1 of Example 1 was mixed with the thiol polymer emulsions E-2 and E-3 to prepare barrier layer compositions TC-2 and TC-3.

[0330] Table 12

[0331] Weight % of components: TC-2 TC-3 E-2 50.0 E-3 50.0 TC-1 50.0 50.0

[0332] Preparation of inkjet printed leather

[0333] Using the Red leather RL and white leather WL were inkjet printed with Ink-W and then with Ink-Combination-K (a homogeneous mixture of Ink-C, Ink-M, Ink-Y, and Ink-K) using an eTU 25LED in high-quality mode at 100% ink coverage and a resolution of 1016 x 1200 dpi. The samples were cured with six passes at 80% UV lamp power.

[0334] according to Table 13 The following samples were prepared using barrier layers S-1, S-2, S-3, and E-1 and topcoat coating compositions TC-1, TC-2, and TC-3.

[0335] Table 13

[0336]

[0337] Each barrier layer S-1, S-2, S-3, and E-1 was sprayed onto the inkjet-printed leather using a PRO-TEK 2600 spray gun with a nozzle diameter of 1.4 mm at a pressure of approximately 4 bar to a wet thickness of approximately 1.0 g / A5. The coated leather was dried in an oven at an average temperature of 85°C for 20 minutes. Thereafter, two topcoats of composition TC-1 were applied to the barrier layers of COMP-1, COMP-2, INV-1, and INV-2 using a PRO-TEK 2600 spray gun with a nozzle diameter of 1.4 mm at a pressure of approximately 6 bar to a wet thickness of approximately 1.2 g / A5. The coated leather was dried in an oven at an average temperature of 85°C for 5 minutes.

[0338] For samples INV-3 and INV-4, barrier layers TC-2 and TC-3 were sprayed onto inkjet-printed leather using a PRO-TEK 2600 spray gun with a nozzle diameter of 1.4 mm at a pressure of approximately 4 bar to a wet thickness of approximately 1.0 g / A5. The coated leather was dried in an oven at an average temperature of 85° C. for a period of 20 minutes.

[0339] Results and Evaluation

[0340] Each sample was then tested for migratory substances using the above migration test. The extraction results for the non-reactive components phenoxyethanol and methyl aldehyde (photodecomposition products of TPL) and the reactive components V-MOX, G1122 and PEA were Table 14 Shown in.

[0341] Table 14

[0342]

[0343] Table 14 The results in clearly show that the inclusion of the thiol polymer not only reduces the amount of reactive monomers (V-MOX, G1122 and PEA), but also reduces the amount of non-reactive components (such as phenoxyethanol and maltaldehyde), which are often the culprits of bad odor.

Claims

1. A decorated natural leather having a decorative image inkjet printed with a radiation curable inkjet ink on a tan leather having a pigmented basecoat on the grain side of the tan leather, wherein the decorative image is covered by a topcoat, and wherein a barrier layer comprising a thiol polymer having a molecular weight Mw of at least 500 g / mol is present on the basecoat and / or in the topcoat. 2 . The decorated natural leather according to claim 1 , wherein the thiol polymer has a thiol content of at least 100 g / mol. 3 . The decorated natural leather according to claim 1 , wherein the barrier layer containing the thiol polymer is present on the base coat and in the top coat.

4. The decorated natural leather according to any one of claims 1 to 3, wherein the thiol polymer is selected from ethoxylated trimethylolpropane tris(3-mercaptopropionate), polycaprolactone tetrakis(3-mercaptopropionate), the reaction product of an alkoxysilane comprising a (3-isocyanatopropyl)trimethoxy group and pentaerythritol tetrakis(3-mercaptopropionate), and an alkoxysilane whose siloxane chain is substituted by a mercapto group.

5. The decorated natural leather according to any one of claims 1 to 4, wherein at least one of the radiation curable inkjet inks contains a vinyl methyl Oxazolidinone.

6. The decorated natural leather according to any one of claims 1 to 5, wherein at least one of the radiation curable inkjet inks contains an acylphosphine oxide photoinitiator.

7. A method for producing decorated natural leather, said method comprising the steps of applying in sequence on a pigmented base coat present on the grain side of a semi-tanned leather: a) optionally a barrier layer comprising a thiol polymer having a molecular weight Mw of at least 500 g / mol; b) an ink layer of a radiation curable inkjet ink by inkjet printing; and c) a topcoat layer comprising a topcoat layer and / or optionally a barrier layer comprising a thiol polymer having a molecular weight Mw of at least 500 g / mol; provided that at least one of said barrier layers in steps a) and c) is applied.

8. The method for producing decorated natural leather according to claim 7, wherein one or more top coating layers are present in the top coating layer.

9. The method for producing decorated natural leather according to claim 7 or 8, wherein the thiol content of the thiol polymer is at least 100 g / mol.

10. The method for producing decorated natural leather according to any one of claims 7 to 9, wherein the barrier layer containing the thiol polymer is present on the base coat and in the top coat.

11. The method for producing decorated natural leather according to any one of claims 7 to 10, wherein the thiol polymer is selected from ethoxylated trimethylolpropane tris(3-mercaptopropionate), polycaprolactone tetrakis(3-mercaptopropionate), the reaction product of an alkoxysilane comprising a (3-isocyanatopropyl)trimethoxy group and pentaerythritol tetrakis(3-mercaptopropionate), and an alkoxysilane whose siloxane chain is substituted by a mercapto group.

12. The method for producing a decorated natural leather according to any one of claims 7 to 11, wherein at least one of the radiation curable inkjet inks contains a vinyl methyl Oxazolidinone and / or acylphosphine oxide photoinitiators.

13. A method for producing decorated natural leather according to any one of claims 7 to 12, wherein at least one of the radiation curable inkjet inks contains an acylphosphine oxide photoinitiator.

14. Use of an aqueous composition comprising 2 to 25% by weight of a thiol polymer having a molecular weight Mw of at least 500 g / mol for reducing the extractability of components from decorated natural leather printed with radiation curable inks.

15. The method according to claim 14, wherein the component is selected from phenoxyethanol, methyl aldehyde, acrylate monomer and vinyl methyl Oxazolidinone.

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