Process for treating a substrate with particles

Abstract

The invention relates to a process containing the steps: a) Providing a substrate b) Treating the substrate with a radiation curable adhesive composition A c) Curing composition A using electromagnetic radiation, and d) Transferring particles to the cured composition A, whereby the particles stick to the cured composition A, wherein the curable adhesive composition A comprises A1 60 to 100 pbw of one or more compounds each having one or more olefinic double bounds of the general formula [CH2=CR1-CO-], wherein R1 is H or an organic moiety, wherein A1 is not HDDA or DPDGA A2 0 to 30 pbw of HDDA A3 0 to 40 pbw of DPDGA A4 A radical photo initiator A5 Optionally fillers, pigment or other additives or solvents wherein the total amount of A1 + A2 + A3 is at least 90 wt.% of the total weight of composition A.

Description

[0001] Process for treating a substrate with particles

[0002] The present invention relates to a process, an intermediate print product and a print product.

[0003] Foil imaging is currently still one of the most practicable technologies for printing solid material on a substrate and might be used e.g. for metallization purposes. There are two different types of foil imaging, foil stamping on the one hand and foil laminating on the other hand. In a foil stamping process a metallic foil is transferred onto a surface through the transfer of heat and pressure. During the stamping process, a die is heated and applied to the foil and is then sandwiched between the die and the surface which should be stamped. The heated die pressing against the surface activates an adhesive within the foil, which fuses the foil to the substrate. Pressure and heat cause the relevant sections of the foil to become detached from the carrier material and become bonded with the printing surface. Foil laminating on the other hand differs from said foil stamping technology, as the latter requires a die to be heated. A typical foil laminating process consists of two steps: printing on the substrate and foiling itself. In the printing step a UV-curable laminating adhesive is printed onto the substrate in the areas which are to be foiled. In a second step a foil is brought into contact with the substrate as well as the uncured adhesive by a laminating roller. Subsequently the adhesive is cured through the foil using a conventional UV-lamp which bonds the foil to the substrate via the adhesive. By removing the foil reel from the substrate path the now bonded foil areas are removed from the carrier material and non-bonded foil (i.e. foil waste) is wound up on a reel.

[0004] The production of this foil waste is considered as a serious disadvantage of foil stamping or laminating process: in practice a large amount of foil and carrier material that is wasted during each stamp / laminating process, as any foil area that is not transferred to form the desired image on the substrate cannot be recovered for successive prints.

[0005] WO 2016 / 189515 proposes a printing process in which the waste and the costs for the foil is reduced. Said process is a continuous method for printing particles (e.g. metal pigment flakes) and uses a printed trigger image (receptive layer) before passing into an application unit, where a donor roll carries the particles from a reservoir to a receptive layer of the substrate to be printed. Only those particles that are in contact with the trigger image remain on the substrate, the remainder return to the reservoir for future rotations. After transferring the particles to the receptive layer the donor surface is returned to coat it again with particles in order to allow a continuous printing process. Said process is especially used as an economical metallization technology which provides attractive metallic effects. However, the receptive layer typically needs to remain sufficiently uncured so as to have enough affinity to the particles during printing. Consequently, such uncured layer material might cause several problems, e. g. said material might stick at various elements of the printing machine.

[0006] On the other hand, a receptive layer which is fully cured might not be soft enough to provide sufficient stickiness for the particles, which is a fundamental condition for a working process.

[0007] Thus, it is crucial for success to achieve a kind of “compromise” that does take these relevant different issues into consideration - especially said mechanical properties on the one hand and the stickiness on the other hand (“not too soft but soft enough”).

[0008] Especially in a (rapid) printing process it is difficult to control the relevant properties of the frequently provided receptive layer.

[0009] In this connection WO 2022 / 084027 proposes a receptive layer for the particles which consists of a coating composition comprising a multifunctional poly acrylate.

[0010] However, this document does not provide a comprehensive solution for the entire underlying problem. It was found that there are several relevant parameters which have to be controlled at the same time, such as kind of photo initiator used, the concentration of said photo initiator; relevant parameters of the printing process / printing apparatus like irradiation time (printing speed), kind of UV source (wavelength range), UV-dose, distance between the UV-source and the receptive layer, and oxygen inhibition of the polymerization initiation / reaction.

[0011] It is important that these parameters are aligned with each other - the change of one parameter might demand that other parameters have to be adapted accordingly (especially difficult if several parameters depend on each other). The change of such one parameter might be relevant in a (continuously) practiced process (e.g. caused by UV-lamp ageing). To have a working printing process is associated with considerable efforts, especially because typically the conditions vary between different printers so that a simple reproduction of an already running process is often not possible.

[0012] In order to provide an economical and more robust process, there is a need to meet these challenges accordingly.

[0013] The solution concerning the corresponding underlying problem is a process for the manufacture of a layered structure comprising a substrate, an adhesive layer and particles, wherein the process comprises the sequential steps of: a) Providing a substrate b) Treating the substrate with a radiation curable adhesive composition A c) Curing composition A using electromagnetic radiation, and d) Transferring particles to the cured composition A, whereby the particles stick to the cured composition A, wherein the curable composition A comprises

[0014] A1 60 to 100 pbw of one or more compounds each having one or more olefinic double bounds of the general formula [CH2=CR1-CO-], wherein R1is H or an organic moiety, wherein A1 is not HDDA or DPDGA

[0015] A2 0 to 30 pbw of HDDA

[0016] A3 0 to 40 pbw of DPDGA

[0017] A4 A radical photo initiator

[0018] A5 Optionally fillers, pigment or other additives or solvents wherein the total amount of A1 + A2 + A3 is at least 90 wt.% of the total weight of composition A.

[0019] It was found that, using the curable composition A as defined above, upon (nearly) full cure of the composition, a cured adhesive layer is obtained that shows a very good and efficient transfer of particles (step d) in the above process) under various process conditions in a continuous process. It was found that in particular good results are obtained when the heat deflection temperature (HDT) of the cured adhesive composition is below 30 °C. In general, good results are obtained with HDT values below 30 °C and typically above about - 10 °C. However, it is generally possible that also lower HDT values than -10 °C provide sufficient results.

[0020] Without performing the actual measurement (as described in more detail below) it is possible to predict the HDT value of the curable composition A by using the HDT values of the homopolymers of the monomers present in the composition. If a mixture of different homopolymers is used, the HDT value of such mixture can be approximated by the weighted average of the HDT for each monomer. There is also general literature which might serve as a further support in this connection - e. g. the Polymer Handbook , Wiley; 4th Edition (March 22, 1999) of Brandrup and Immergut, section F (pages VI / 193 - VI / 268), which informs about the glass transition (TG) values, providing a helpful approximation in order to arrive at the corresponding HDT values.

[0021] In practice, the HDT or the glass transition temperature (Tg) of a homopolymer of a commercially available monomer is typically given by the supplier of said monomer. A heat deflection temperature (HDT) of below 30°C is obtained by the curing of composition A. It was found, that to obtain such HDT, at least 90% of the olefinic double bonds present in composition A should have reacted. The rate of reaction or conversion can be measured quantitatively using an infrared spectrometer, in the spectral region between 805 and 815 cm- 1. The relevant peak at about 810 cm- 1 is the CH out-of-plane bending vibration of the double bond which disappears upon polymerization of the double bond. The procedure for the measurement of the conversion is described in more detail below.

[0022] The process according to the present invention is typically a printing process, preferably a continuous printing process but might be also a different kind of process for treating a substrate with particles.

[0023] As indicated below, we have found a strong correlation between the print quality when using the process according to the present invention and the HDT-value of curable adhesive composition A. This HDT-value should be below 30°C So, it is important the know how to meet the HDT requirement:

[0024] There is a large number of different approaches as to how said HDT value of below 30 °C can be achieved. The most relevant approaches are described below - also on the basis of standard types and examples which are especially relevant for the corresponding practice. If these are not sufficient to provide guidance (for the provision of a curable adhesive composition A with a HDT value below 30 °C) in individual cases, then maximal a few simple routine tests should be sufficient to achieve the goal.

[0025] How to meet the conversion requirement:

[0026] The relevant conversion condition (on the basis that the curable adhesive composition A provided in step a) contains m mol of olefinic double bonds it is realized that in step b) at least 0.95 * m mol of all contained olefinic double bonds are converted) is defined on the background that the used quantitative infrared spectroscopy covers the conversion of all contained olefinic double bonds (also those which are not so reactive: like e. g. allyl ether moieties) and not only exclusively the conversion of the (reactive) double bonds

[0027] However, it is generally preferred that at least 70 mol %, more preferably at least 90 mol % of all olefinic double bounds that are present in the curable adhesive composition A are of the of the general formula [CH2=CR1-CO-]. The conversion condition according to the present invention refers to the amount (“m mol”) of the (reactive) double bond of the general formula [CH2=CR1-CO-] which is completely or nearly completely converted. Normally at least about 95 mol % of the double bond of the general formula [CH2=CR1-CO-] are converted. However, e. g. vinyl ether moieties or allyl ether moieties (below there are monomer species proposed containing both: such a moiety and a reactive acryloyl moiety) are generally not (radical photo polymerization) reactive enough to be completely converted in a rapid printing processes. Thus, in practice the conversion requirement according to the present invention refers only to the conversion of (reactive) double bond of the general formula [CH2=CR1-CO-].

[0028] It is well known how to manage a complete or nearly complete conversion of the (reactive) double bond of the general formula [CH2=CR1-CO-], even in a rapid printing process: the most relevant factors are the use of corresponding sufficient reactive monomers, appropriate initiator systems with a sufficient concentration and to use a corresponding effective radiation technology (radiated layer not to thick, sufficient radiation intensity, sufficient radiation time etc.). However, in special cases some simple routine experiments might provide a helpful support to achieve said goal.

[0029] The process according to the present invention is an economical and robust process. If the curable adhesive composition is fully or nearly fully cured. In the processes disclosed in the prior art, it was necessary to find a compromise between mechanical properties and stickiness, where the curing rate of the adhesive composition was a determining factor. Undercure or overcure could have a detrimental effect on the quality of the product. Furthermore, the HDT value provides a further helpful orientation which kind of monomers or monomer mixtures should be used in the curable adhesive composition.

[0030] On this basis, the installation and operation of a working printing process is simplified (standardized) and the reproducibility of an already running process is supported. Also, the maintenance and the reliability of a corresponding printing process is improved.

[0031] Further advantages of the present invention:

[0032] The cohesion of the cured adhesive composition should be such that the adhesive layer does not deposit on a printing pressure roller and does not show mechanical brittleness (to hard). Additionally, the cured layer provides universal and efficient acceptor properties, which enable a well defined transfer of the particles from the donor roll to the adhesive / receptive layer on the substrate. According to the present invention a sufficient (particle) covering of the receptive layer is achieved: By "sufficient" covering, it is meant that the coat of particles on the relevant substrate regions will be especially devoid of defects perceptible to the naked eye so that the intended visual effect is achieved. Generally, the printed product that is obtained is optically attractive and has a good quality. The gloss of a metallized substrate might be deemed as to be a corresponding quality feature. A general quality indication is the so-called optical density (OD) which can be seen as a kind of measure of the degree of coverage of the receptor surface with the particles provided.

[0033] In one embodiment, the curable adhesive composition A provided in step a) comprises at least 5 mol / kg of compounds having only one olefinic double bond of the general formula [CH2=CR1- CO-]. . The higher the content of monofunctional monomers the higher concentration of double bonds of the of the general formula [CH2=CR1-C0-] is allowed in order to meet the relevant HDT condition. Low crosslinking density lowers the HDT which is typically achieved by the use of monofunctional monomers and / or multifunctional monomers with long chains between the double bonds of the of the general formula [CH2=CR1-C0-]. Generally, flexible chains (as side chain or as linker between two unsaturated groups) lower the HDT. In the field of inkjet inks, the main ingredients need to be low viscous compounds, thus small molecules. A corresponding preferred compound is 4-Hydroxy butyl acrylate (butandiol-1 ,4-monoacrylate). However, small bifunctional molecules automatically result in a high crosslinking density and thus hard layers with a (may be too) high HDT. The (additional) use of e. g. 2-vinyloxyethoxy ethyl acrylate (VEEA) (CAS 86273-46-3) and / or of a methyl 2-((allyloxy)methyl) acrylate (AOMA: 219828-90-7) might be an alternative. Those kind of monomers provide the basis for a sufficient low viscosity which is especially relevant in case of an ink-jetting application, where the generation of tiny (ink-jettable) ink drops is necessary: due to the relevant very low viscosity, quite high amounts of higher viscous but more flexible compounds might be added in order to maintain the needed low (overall) viscosity. Typically, in such kind of applications at least 10 wt.% of the curable adhesive composition A provided in step a) is contributed by species with a molecular weight of at least 200 g / mol having exactly one acryloyl moiety and exactly one vinyl ether moiety or one allyl ether moiety, preferably provided by VEEA and / or by a AOMA.

[0034] According to a another embodiment of the present invention at least 50 mol % (often at least 90 mol %) of the olefinic double bonds of the of the general formula [CH2=CR1-CO-] provided in step a) were contributed by acryloyl moieties. On the one hand, acryloyl moieties provide the most reactive (regarding radical polymerization) subtype of the of the general formula [CH2=CR1-CO-] and on the other hand they contribute to a relatively low HDT (only as a rough “HDT-trend” - however, there might be some exceptions: acrylate < methacrylate < acrylamide < methacrylamide). Thus, especially acrylates were very suitable in order to meet both: the conversion and the HDT requirement. Preferably, at least 50 mol.% (preferably at least 90 mol.%) of the contained acryloyl moieties (H2C=CH-C(=O)-) were provided by “the ester-type” (H2C=CH-C(=O)-O-) (containing an “acrylic acid ester function”).

[0035] Preferably, at least 50 wt.% of all species of the curable adhesive composition A after its complete curing by its homo polymerisation provide a homopolymer with an HDT below 30 °C, preferably below 0 °C. This provides a helpful orientation in the light of the fact that it is possible to make a prediction concerning the HDT value (of the used curable adhesive composition A ) to a certain extent by using the HDT values of the homopolymers of the monomers used as a guide.

[0036] According to a special embodiment, at least 25 %, preferably 50 %, of all olefinic double bonds provided in step a) were contributed by 4-Hydroxy butyl acrylate (butandiol-1 ,4-monoacrylate). This compound provides a low viscosity, which is especially beneficial in connection with inkjetapplications.

[0037] In one embodiment part of the curable adhesive composition A contains ingredients having groups selected from hydroxyl moieties, carboxylic moieties, sulfonic acid moieties, thiol moieties, phosphoric acid moieties and / or phosphonic acid moieties, preferably provided by hydroxyl- and or carboxylic moieties. Using monomers which do not strongly interact on an intermolecular level generally lowers the HDT (strong interactions are often caused by H- bondings). For example, non-polar aliphatic monomers contribute to a lower HDT.

[0038] It was further found that there seems to be a trend that the use of H-donating groups contributes to a high optical density (OD) of the particle treated substrate. Although not tested in much detail, it seems that the lower the pKa value of the H-donating group, the higher the OD.

[0039] In another embodiment, at least 50 wt.% of the curable adhesive composition A provided in step a) is contributed by species having exactly one double bond of the of the general formula [CH2=CR1-CO-]. This lowers the network density and contributes to a reduced HDT value. The same effect is achieved by reducing the amount of multifunctional monomers: typically, (only) 1 - 30 wt.% of the curable adhesive composition A provided in step a) is contributed by species having more than one double bond of the of the general formula [CH2=CR1-CO-].

[0040] Multifunctional monomers of high molecular weight (especially with flexible chain segments) can also be used to obtain a composition with a moderate HDT-value: Optionally, at least 50 wt.% of the species present in curable adhesive composition A having more than one double bond of the of the general formula [CH2=CR1-CO-] were provided by compounds having at least three double bonds of the of the general formula [CH2=CR1-CO-] and a molecular weight of at least 400 g / mol. In this connection the application of corresponding ethoxylated and / or propoxylated (polyether)chains were beneficial which should be long enough in order to provide the low HDT.

[0041] Another option to have a lower HDT-value might be the provision of multifunctional monomers with flexible chains, especially provided by the contribution of ether groups, siloxane groups and / or aliphatic ester groups: Optionally, at least 50 wt.% of the species present in curable adhesive composition A having more than one double bond of the of the general formula [CH2=CR1-CO-] were provided by compounds having at least three double bonds of the of the general formula [CH2=CR1-CO-] and at least three ether moieties.

[0042] Generally, using monomers with rigid bulky groups increase the HDT (like isobornyl-, phenyl- or dicyclopentadiene-groups). However, it was found that randomization of the molecular architecture, for example by providing variation of structural units within the polymer lowers the HDT-value..

[0043] In a further embodiment, 80 - 100, preferably 95 - 100 wt.%, of the ingredients of the curable adhesive composition A provided in step a) are contributed by the curable adhesive composition A and the radical photo initiator (R). The addition of fillers, solvents and other monomer types is normally not necessary and / or beneficial.

[0044] As indicated, various type of monomers having one or more unsaturated groups can be used as an ingredient for the radiation curable adhesive composition A. The majority of these ingredients should have one or more olefinic double bounds of the general formula [CH2=CR1- CO-], wherein R1is H or an organic moiety. Examples of suitable materials include monoacrylate, di-acrylate, tri-acrylate and further acrylate compounds. Such materials are available from suppliers like Allnex, BASF, Eastman, Evonik, Miwon, Rahn, Sartomer, Solvay, and others.

[0045] According to a special embodiment, step c) is performed under an inert gas atmosphere and / or by using mechanic means which support the avoidance of oxygen inhibition. This normally serves in order to meet the conversion condition.

[0046] Generally, in step c) the electromagnetic radiation is performed by UV radiation (should fit to the used initiator system). For the UV radiation corresponding lamps using wavelengths of e.g. 200 - 400 nm might be provided. A metal-halide lamp, a 365nm or 395nm LED lamp, might be used (iron-doped mercury lamps, gallium-doped mercury lamps or non-doped mercury lamps might be used) . Typically, the substrate treated in step b) has a receptive layer at least partially covering an image-receiving surface, especially if used in a printing process.

[0047] Normally, the adhesive curable composition that is applied to the substrate in step b) of the process of the current invention has a layer thickness of 0.5 pm - 500 pm, preferably of 2 pm - 50 pm (determined via gravimetry). The layer has to be on the one hand thick enough for taking off and maintaining the particles but on the other hand not too thick because an effective (entire) curing by photo polymerization should be supported.

[0048] Typically, in step d) the particles are transferred from a donor surface, which is provided by an elastomer, preferably provided by a silicone-based material.

[0049] The particles are preferably selected to adhere to the donor surface more strongly than they do to one another. This results in the applied layer being substantially a thin layer (preferably being a monolayer) of individual particles.

[0050] The donor surface is typically made from a polymer that can be tailored with regard to its surface polarity and mechanical properties. Typically, the donor surface is made from an elastomer, for example a silicone-based material known to a skilled person. One example is made by combining three silicone-based materials: a vinyl-terminated polydimethylsiloxane in an amount of about 58% by weight of the total composition (wt.%), a vinyl functional polydimethylsiloxane containing both terminal and pendant vinyl groups, in an amount of about 11 wt.% and a branched structure vinyl functional polydimethylsiloxane in an amount of about 22.5 wt.%. To the mixture were added: a platinum catalyst in an amount of about 0.05 wt.%, an inhibitor in an amount of 2.0 wt.%, and finally a reactive cross-linker such as a methyl- hydrosiloxane-dimethylsiloxane copolymer in an amount of 6.0 wt.%. This composition can be thermally cured to produce a hydrophobic elastomeric donor surface. The process according to the present invention provides a sufficient transfer of the particles from the donor surface to the receptive layer.

[0051] According to a further embodiment of the present invention the individual particles transferred in step d) contain or consist of metal. Typically, the individual particles transferred in step d) contain or consist of flaky metallic pigments.

[0052] Such flaky metallic pigments normally have an average thickness (h50) value in the range of 20 - 200 nm (which is determined with a scanning electron microscope according to the corresponding method as described in WO 2004 / 087816). As a special type, silica encapsulated pigments as described in WO 2022 / 148658 might be used. However, also non- metallic particles might be used. Examples of such „non-metallic“ particles: glass and ceramic (metal oxides), respectively including polymeric or inorganic coating of the particles.

[0053] If the effect to be achieved is similar to foil imaging, such as used for instance for metal printing, then the particles may be grains or flakes of metals, such as aluminum, copper, iron, zinc, nickel, tin, titanium, gold or silver, or alloys, such as steel, bronze or brass, and like metallic compounds primarily including metals.

[0054] In one embodiment, the radical photoinitiator (R) is selected from the group consisting of so called Type I photoinitiators such as hydroxy acetophenones, alkylamino acetophenones, benzil ketals, dialkoxy acetophenones, benzoin ethers, phosphine oxides, acyloximino esters and / or selected from the group consisting of so called Type II photo initiators such as benzophenones, thioxanthones, anthraquinones, benzoyl formate esters, camphor quinones, keto coumarin, aromatic glyoxylates and substituted keto sulfones.

[0055] According to another embodiment, the process according to the present invention is a process for printing onto a substrate having an image-receiving surface, which comprises providing a donor surface, passing the donor surface through a coating station from which the donor surface exits coated with individual particles, and repeatedly performing the steps of:

[0056] - providing a receptive layer, at least partially covering said image-receiving surface,

[0057] - treating the receptive layer by electromagnetic radiation in order to enhance its affinity to the particles greater than the affinity of the particles to the donor surface,

[0058] - contacting the receptive layer with the donor surface to cause particles to transfer from the donor surface to the treated receptive layer, thereby exposing regions of the donor surface from which particles are transferred to the receptive layer so that generating a plurality of individual particles adhered to the receptive layer and

[0059] - returning the donor surface to the coating station to coat it again with individual particles in order to permit printing of a subsequent image on the substrate.

[0060] One possibility of applying the receptive layer is according to an analogues technology element: the receptive layer might be applied to selected regions by indirect printing which is performed by offset printing, screen printing, flexographic printing and / or gravure printing.

[0061] Alternatively, the receptive layer might be applied according to a digital technology embodiment: the receptive layer is applied to the substrate surface by direct printing, especially by direct jetting. In the latter case the coating composition should have a viscosity appropriate for the kind of printing process. The invention also concerns an intermediate print product manufactured by the process as described above.

[0062] Furthermore, the invention concerns a print product on the basis of said intermediate print product additionally comprising an overcoat layer covering the printed particles. The overcoat layer improves the stability of the print product.

[0063] A primer coating might be applied before the trigger image. Colour printing before or after the process is possible - e. g. colour printing with translucent colours on top of the metallic layer to provide metallic colours.

[0064] Below the invention is described in more detail by providing examples. In these examples various test methods are used. These test methods have been described in more detail below.

[0065] Measurement methods

[0066] Optical density (OD) measurement:

[0067] The optical density (OD, expressed in %) provides an indication of the amount of transferred metallic pigments. To determine the optical density a black / white transmission densitometer (device: 341C manufactured by X-Rite Inc., Grand Rapids Ml 49512, USA) was used. To calibrate the pure substrate was first measured and the value set to zero. For each sample three measurements in different areas were performed and the values were arithmetically averaged.

[0068] HDT measurement:

[0069] The heat deflection temperature was determined in a three-point-bending test under a stress of 0,45 MPa that was performed on a HDT-measuring device Compact 3 from Coesfeld on specimens with dimensions of 80 x 10 x 4 mm according to DIN EN ISO 75. The heat rate was set to 2 K / min in a range from -30 °C until reaching the HDT-value. The temperature at which the specimen deflects by a predetermined amount of 0.25 mm is recorded as the HDT.

[0070] Sample preparation: the formulations (with 1 wt% TPO-L) are put in a translucent silicon mold with the above dimensions. The molded specimens are cured for 30 s from each side in translucent silicon molds from the bottom at a distance of 15 cm by irradiation with UV-light (LED 395 nm, 16 W / cm2).

[0071] Conversion measurement: Conversion measurement was performed as follows:

[0072] The measurement is performed on an IR spectrophotometer, for example an ALPHA II spectrometer from Bruker. For this measurement, the signal in the spectral region between 805 and 815 cm-1 is integrated. The peak at 810 cm-1 is the CH out-of-plane bending vibration of the vinyl group (acrylate) and disappears upon polymerization. The integration is measured for a liquid uncured sample (Io) and of a sample after curing (lc) and the conversion is calculated as follow: conversion (%) = (lo-lc) / lo*100. Please note that the C=O stretch vibration at around 1700 cm-1 can be used as internal calibration method to compare the liquid uncured and solid cured samples. Only if the intensity of the C=O stretch vibration is both samples is (nearly) equal, the above conversion calculation can be made, the error seems to be very small, probably due to a robust ATR optical path and method and an efficient pressing of the soldi samples against the ATR crystal.

[0073] Curing coatings:

[0074] The formulations (with 5 wt% TPO-L) are coated between 2 polypropylene foils (to avoid oxygen inhibition), cured with a 200 W / cm from 1ST at 55% power and 13 m / min. The toppolypropylene foil was removed after curing.

[0075] Flake transfer:

[0076] First a water-based mixture bearing flaky (hydrophobized) metallic pigments is applied and manually wiped on a silicon-based donor roll (see later) using a sponge. After vigorous wiping, the excess of flaky metallic pigments is rinsed extensively with DI water. The excess rinsing water is removed by a compressed air blower. By this process, a thin and dry layer of flaky metallic pigments is present on the silicon-based donor roll surface.

[0077] In a second step, the metallized donor roll is manually pressed against a cured UV layer (as described above) resulting in the dry transfer of flaky metallic pigments from the donor roll to the cured UV layer.

[0078] In contrast to the proposal according to WO 2022 / 084027 all (OD, HDT and conversion) experiments were performed with coatings protected with a foil (avoid oxygen inhibition - details as described above) which provides much higher conversion degrees (such conversion degrees were not intended according to the teaching of the WO) - which is one decisive difference in comparison to the experiments provided in WO 2022 / 084027.

[0079] Inventive and comparative examples:

[0080] All inventive and comparative examples (CE) were performed under identical conditions. The experiments were performed in order to screen different photo polymerization reactive compounds containing olefinic double bonds of the general formula [CH2=CR1-CO-]. In order to have comparable results, the radical photo initiator was kept identical (TPO-L, CAS nr. 84434-11-7) for all experiments and the photopolymerization experiments were performed in the absence of oxygen to avoid oxygen inhibition. For the comparative experiments taken from WO 2022 / 084027, the exact coating compositions were taken with the exception that the photoinitiators as described in WO 2022 / 084027 were replaced by TPO-L as for all the other experiments.

[0081] The tables hereunder describing the ingredients of the inventive and comparative examples contain all coating ingredients except the photoinitiators. For the samples to measure the HDT- values, 99% of the composition described in the tables 1-2 was taken and combined with 1% of TPO-L. For the coatings used in the measurement of the optical density, 95% of the composition described in the tables 1-2 was taken and combined with 5% of TPO-L.

[0082] Details concerning the print trials for the comparative examples (referring to WO 2022 / 084027):

[0083] After application of the pigments the metallized samples were characterized by optical density measurement.

[0084] List of chemicals used:

[0085] Name Description

[0086] 4-HBA 4-Hydroxybutyl Acrylate, CAS nr. 2478-10-6 BYK-1790 silicone free defoamer commercially available from BYK-Chemie BYK-378 silicone based surface additive commercially available from BYK-Chemie CA caprolactone Acrylate, CAS nr. 110489-05-9 CEA carboxyethyl acrylate CAS nr. 9003-01-4 difunctional acrylate oligomer which contains 14 “moiety-heteroatoms”

[0087] DFAO14 stemming from urethane and ester moieties difunctional acrylate oligomer which contains around 42 “moiety-

[0088] DFAO42 heteroatoms” stemming from urethane and ether moieties

[0089] DPGDA dipropylene Glycol Diacrylate, CAS nr. 57472-68-1 EOEOA ethoxy ethoxy ethyl acrylate, CAS nr. 7328-17-8 EO-HDDA ethoxylated hexanediol diacrylate EO-TMPTA ethoxylated TMPTA HDDA 1 ,6-Hexanediol diacrylate, CAS nr. 13048-33-4 a hexafunctional acrylate oligomer which contains 6 “moiety-heteroatoms”

[0090] HFAO stemming from urethane moieties

[0091] LA lauryl acrylate CAS nr. 2156-97-0 MAES mono(2-acryloyloxyethyl) Succinate CAS nr. 50940-49-3 MEHR methyl ester of hydrogenated rosin MFAOXA monofunctional oxyethylated aromatic acrylate monomer PE-APGMA phosphate esters of acrylic polypropylene glycol monomethacrylate PEGDA poly(ethylene glycol) (300) diacrylate PEGMA poly(ethylene glycol) methyl ether acrylate TCA 3,3,5 Trimethyl Cyclohexanol Acrylate, CAS nr. 86178-38-3 .[-F Q tetrafunctional acrylate oligomer which contains 10 “moiety-heteroatoms” stemming from ester and ether moieties

[0092] Comparative Examples 1 , 2 and 3 which relate to the technology of WO 2022 / 084027 were presented for a comparison with the technology according to the present invention.

[0093] Table 1: Ingredients (without photo initiator) of inventive examples 1-6

[0094] Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6

[0095] EO-HDDA 100 89 100 75

[0096] PEGDA 100

[0097] EO-TMPTA 100

[0098] HDDA 11

[0099] DPGDA 25

[0100] Table 2: Ingredients (without photo initiator) of comparative examples 1-6

[0101] CE 1 CE 2 CE 3 CE4 CE5 CE6

[0102] DFAO14 29,51 TFAO 29,51 24,21 DFAO42 39,13 HFAO 15,22 HDDA 30,05 31,91 EO-HDDA 25 50

[0103] DPGDA 44,89 0,3 75 50 100 EO-TMPTA 11 TCA 31,91 MEHRF 10,93 BYK-1790 0,76 0,33

[0104] BYK-378 0,33

[0105] Table 3: Test results of the examples and the comparative examples (CE)

[0106] HDT OD Conversion acrylates

[0107] (°C) (%) (%)

[0108] Example 1 <30 83 98,3

[0109] Example 2 <30 71 97,6

[0110] Example 3 <30 73 97,1

[0111] Example 4 <30 64 99

[0112] Example 5 <30 98,5

[0113] Example 6 <30 73 98,5 CE 1 <30 31 85,7

[0114] CE 2 72,9 15 91 ,8

[0115] CE 3 62.2 5 92,3

[0116] CE 4 50.2 31 96,4

[0117] CE 5 34,4 55 96,5

[0118] CE 6 78.2 9 92,3

[0119] A sufficient OD should provide at least a value of 60.

[0120] As can be seen in the tables above, only the examples according to the present invention result in high OD values (above 60) and this is obtained for coatings with a conversion above 95% and a HDT below 30°C.

[0121] In a reference formulation containing 5% DPGDA as crosslinker, 1% TPO-L as photoinitiator and 94% of a monofunctional monomer, coatings were prepared and cured in the absence of oxygen as described here above. The following monofunctional monomers were tested: LA, 4- HBA, CEA, MAES, PE-APGMA, PEGMA, SR4955, EOEOA and MFAOXA. It was found that the coatings containing monomers bearing a hydroxyl moiety (4-HBA and CA), a carboxylic acid moiety (CEA and MAES) or a phosphoric acid moiety (PE-APGMA) resulted in a higher OD compared to the coatings containing monomers without one of these moieties. Without being bonded to any theory, it is believed that these functional moieties increase the adhesion between the cured coating and the metallic flakes.

Claims

CLAIMS1. A process for the manufacture of a layered structure comprising a substrate, an adhesive layer and particles, wherein the process comprises the sequential steps of: a) Providing a substrate b) Treating the substrate with a radiation curable adhesive composition A c) Curing composition A using electromagnetic radiation, and d) Transferring particles to the cured composition A, whereby the particles stick to the cured composition A, wherein the curable adhesive composition A comprisesA1 60 to 100 pbw of one or more compounds each having one or more olefinic double bounds of the general formula [CH2=CR1-CO-], wherein R1is H or an organic moiety, wherein A1 is not HDDA or DPDGAA2 0 to 30 pbw of HDDAA3 0 to 40 pbw of DPDGAA4 A radical photo initiatorA5 Optionally fillers, pigment or other additives or solvents wherein the total amount of A1 + A2 + A3 is at least 90 wt.% of the total weight of composition A.

2. A process according to claim 1 , where at least a part of the curable adhesive composition A contains groups selected from hydroxyl moieties, carboxylic moieties, sulfonic acid moieties, thiol moieties, phosphoric acid moieties and / or phosphonic acid moieties, preferably provided by hydroxyl- and or carboxylic moieties.

3. A process according to one of the claims 1 - 2, where at least 25 %, of all olefinic double bonds in the curable adhesive composition A are contributed by 4-Hydroxy butyl acrylate (butandiol-1 ,4-monoacrylate).

4. A process according to one of the claims 1 - 3, where at least 50 wt.% of the curable adhesive composition A provided in step a) is contributed by species having exactly one double bond.

5. A process according to one of the claims 1 - 4, where at least 10 wt.% of the curable adhesive composition A provided in step a) is contributed by species with a molecular weight of at least 200 g / mol having exactly one acryloyl moiety and exactly one vinyl ether moiety or one allyl ether moiety.

6. A process according to one of the claims 1 - 5, where 1 - 30 wt.% of the curable adhesive composition A provided in step a) is contributed by species having more than one double bond.

7. A process according to the claim 6, where at least 50 wt.% of the curable adhesive composition A having more than one double bond of the of the general formula [CH2=CR1-CO-] were provided by compounds having at least three double bonds of the of the general formula [CH2=CR1-CO-] and a molecular weight of at least 400 g / mol.

8. A process according to claim 6 or 7, where at least 50 wt.% of the curable adhesive composition A having more than one double bond of the of the general formula [CH2=CR1-CO-] were provided by compounds having at least three double bonds of the of the general formula [CH2=CR1-CO-] and at least three ether moieties.

9. A process according to one of the claims 1 - 8, where 80 - 100 wt.%, of the ingredients of the curable adhesive composition A provided in step a) are contributed by the curable adhesive composition A and the radical photo initiator (R).

10. A process according to one of the claims 1 - 9, where step c) is performed under an inert gas atmosphere and / or by using mechanic means which support the avoidance of oxygen inhibition.

11. A process according to one of the claims 1 - 13, where in step c) the electromagnetic radiation is performed by UV radiation, preferably by using a metal-halide lamp.

12. A process according to one of the claims 1 - 14, where the substrate treated in step b) has a receptive layer at least partially covering an image-receiving surface.

13. A process according to claim 12, where the receptive layer in step b) has a thickness of 0.5 pm - 500 pm, preferably of 2 pm - 50 pm (determined via gravimetry).

14. A process according to one of the claims 1 - 13, where in step d) the particles are transferred from a donor surface, which is provided by an elastomer, preferably provided by a silicone-based material.

15. A process according to one of the claims 1 - 14, where the individual particles transferred in step c) contain or consist of metal16. A process according to one of the claims 1 - 15, where the individual particles transferred in step c) contain or consist of metallic pigments, preferably in the form of flakes17. A process according to one of the claims 1 - 16, where the radical photoinitiator (R) is selected from the group consisting of so called Type I photoinitiators such as hydroxy acetophenones, alkylamino acetophenones, benzil ketals, dialkoxy acetophenones, benzoin ethers, phosphine oxides, acyloximino esters and / or selected from the group consisting of so called Type II photo initiators such as benzophenones, thioxanthones, anthraquinones, benzoyl formates esters, camphor quinones, keto coumarin, aromatic glyoxylates and substituted keto sulfones.

18. A process according to one of the claims 1 - 17, which is a process for printing onto a substrate having an image-receiving surface, which comprises providing a donor surface, passing the donor surface through a coating station from which the donor surface exits coated with individual particles, and repeatedly performing the steps of:- providing a receptive layer, at least partially covering said image-receiving surface,- treating the receptive layer by electromagnetic radiation in order to enhance its affinity to the particles greater than the affinity of the particles to the donor surface,- contacting the receptive layer with the donor surface to cause particles to transfer from the donor surface to the treated receptive layer,- thereby exposing regions of the donor surface from which particles are transferred to the receptive layer so that generating a plurality of individual particles adhered to the receptive layer and- returning the donor surface to the coating station to coat it again with individual particles in order to permit printing of a subsequent image on the substrate.

19. An intermediate print product manufactured by a printing process according to of one of the claims 1 - 18.

20. A print product on the basis of an intermediate print product according to claim 19 further comprising an overcoat layer covering the printed particles.

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