Embossing lacquers containing aliphatic photoinitiators and bio-based microstructure systems

Abstract

Embossing lacquers for micro- or nanostructured surface layers, in particular UV-NIL embossing lacquers comprising a UV-curable compound and an aliphatic photoinitiator, articles having a micro- or nanostructured surface layer on a support, the surface layer being an embossed and UV-cured embossing lacquer, in particular a method for producing articles comprising a micro- or nanostructured surface layer from bio-based compounds, and the use of articles comprising a micro- or nanostructured surface layer as microfluidic structures or films with anti-reflection, drag-reducing or adhesive effects.

Description

[Technical Field]

[0001] The present invention relates to an embossing varnish for microstructured or nanostructured surface layers, in particular a UV-NIL embossing varnish containing a UV-curable compound and an aliphatic photoinitiator, an article having a microstructured or nanostructured surface layer on a support, the surface layer being an embossed and UV-cured embossing varnish, a method for producing an article having a microstructured or nanostructured surface layer, and the use of the article. [Background technology]

[0002] In many microfluidic-based applications, the biocompatibility or compatibility of microstructured and nanostructured substrates is a crucial factor. For example, when culturing live cells in microfluidic applications such as lab-on-a-chip or organ-on-a-chip systems, the viability of these cells on imprinted substrates is crucial. Microfluidic systems are typically fabricated by embossing nanostructures and microstructures using ultraviolet nanoimprint lithography (UV-NIL). To cure the embossed lacquer, a photoinitiator is used, which absorbs UV light and generates radicals to initiate free-radical polymerization reactions. Petrochemical-grade aromatic photoinitiators are used in all commercially available UV-NIL embossing varnishes. While UV-curable oligomers and monomers used to produce structured substrate polymers often have good cytocompatibility, these photoinitiators, used only at low concentrations, are usually cytotoxic, impairing cell growth or resulting in cell death.

[0003] Fluorescence is often used as a measurement method in microfluidic-based applications to detect selective reactions during the detection of specific biomolecules. The aromatic rings contained in all common petrochemical photoinitiators generally have a high potential for fluorescence. Even after UV curing, these aromatic rings remain in the UV-imprinted coating in the form of photoproducts or their fragments, which can lead to interference signals in fluorescence-based analytical methods due to their autofluorescence, thereby reducing the detection sensitivity.

[0004] The radical polymerization of vinyl C=C double bonds in (meth)acrylates, for example, using α-ketocarboxylic acids or their esters, pyruvic acid ethyl ester, and the aliphatic α-diketones 2,3-butanedione and 2,3-pentanedione as photoinitiators, is known in the prior art (WO 2019 / 020805; EA Lissi and MV Encina in "Polymerization Photosensitized by Carbonyl Compounds," Journal of Polymer Science: Polymer Chemistry Edition, Vol. 17, pp. 2791-2803 (1979)). This prior art only discloses the production of unstructured polymers or smooth polymer coatings, but is not related to the technical field of embossed coatings and therefore does not provide any indication of the applicability of the polymerization systems or photoinitiators mentioned therein in UV-NIL embossing processes. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2019 / 020805 [Non-patent literature]

[0006] [Non-Patent Document 1] EA Lissi and MV Encina in Polymerization Photosensitized by Carbonyl Compounds, Journal of Polymer Science: Polymer Chemistry Edition, Vol. 17, pp. 2791-2803 (1979) Summary of the Invention [Problem to be solved by the invention]

[0007] Due to the shortcomings of the prior art, there is a need for improved UV-NIL embossing coatings.

[0008] It is therefore an object of the present invention to provide an embossing lacquer with a photoinitiator that is non-toxic and therefore compatible with the skin or does not impair cell growth in microfluidic systems.

[0009] Other objects include providing an embossing varnish with a photoinitiator that does not fluoresce or fluoresces only slightly and therefore does not affect fluorescence measurements, and providing a photoinitiator that is biobased and biocompatible.

[0010] It is a further object of the present invention to provide a surface structuring system, such as a decorative surface or a microfluidic system, based on such an embossing varnish. Furthermore, it is to be possible to provide a surface layer, such as a decorative surface or a microfluidic system, that is as biobased as possible. [Means for solving the problem]

[0011] This problem has been solved by providing an embossing varnish containing an aliphatic photoinitiator, as well as articles produced using the embossing varnish having a microstructured or nanostructured surface layer.

[0012] The objects of the present invention are particularly defined in the following items [1] to

[15] and [1-1] to [11-2]:

[0013] [1] An embossing varnish for a microstructured or nanostructured surface layer, comprising a UV-curable compound having a UV-polymerizable carbon-carbon double bond (hereinafter abbreviated as a C=C double bond) and an aliphatic photoinitiator containing a moiety selected from α-diketones or α-ketocarboxylic acids or their salts, particularly metal salts such as sodium salts, or their esters. [1-1] Preferably, 90 wt % of the embossing varnish described in item [1] consists of the UV-curable compound and the photoinitiator.

[0014] [1-2] The embossing varnish according to [1] or [1-1] preferably contains 0.1 to 5 parts by mass of a photoinitiator per 100 parts by mass of the UV-curable compound. [1-3] Preferably, the embossing varnish according to any one of the preceding items contains a photoinitiator containing a group selected from α-ketocarboxylic acids or salts or esters thereof, and does not contain a coinitiator. [1-4] Preferably, in the embossing varnish according to any one of the preceding items, the molecular weight of the aliphatic photoinitiator is at most 500 g / mol, preferably at most 300 g / mol.

[0015] [2] The embossing varnish according to any one of the above items [1] to [1-4], wherein the molecular weight of the UV-curable compound is 200 to 2500 g / mol. [2-1] A combination of the features of items [1], [1-4], and [2] is preferred.

[0016] [3] The embossing varnish according to any one of the preceding items, wherein the UV-curable compound is an alcohol esterified with one or more, preferably two, (meth)acrylate groups. [3-1] A combination of the features of [1], [2-1], and [3] is preferred. [3-2] The embossing varnish according to [3], wherein the alcohol has a molecular weight of 100 to 5,000 g / mol, more preferably 100 to 2,000 g / mol, and is selected from the group consisting of hydroxyl-containing biomolecules, hydroxylated derivatives of biomolecules, hydroxyl-containing or hydroxylated degradation products of biomolecules, and esters or ethers of hydroxyl-containing or hydroxylated degradation products of biomolecules. [3-3] A combination of the features of [3-1] and [3-2] is preferred.

[0017] [4] The UV-curable compound is an aliphatic hydroxy group-containing compound esterified with two or more (meth)acrylate groups, and the aliphatic hydroxy group-containing compound is a C6-C 24 Alcohols, oligoethers or polyethers containing C2-C6 alkoxy groups, oligoesters or polyesters containing hydroxylated C2-C6 monocarboxylic or dicarboxylic acids, oligoesters or polyesters containing C2-C6 alkoxy groups and C2-C6 dicarboxylic acids, hydroxyl group-containing polyurethanes, in particular non-isocyanate polyurethanes (non-isocyanate PU = NIPU), glycerol oligomers or polymers, C6-C 24 Epoxidized triglycerides of fatty acids, or epoxidized C6-C 24 The embossing varnish according to any one of the preceding items, wherein the compound is selected from the group consisting of fatty acids. Each of these compounds contains at least one hydroxyl group and is therefore also called an alcohol. At least one hydroxyl group can be esterified with a carboxylic acid. A combination of the features of items [4-1], [2-1] and [4] is preferred.

[0018] [5] The embossing varnish according to any one of the preceding items, containing a UV-curable compound and a surface-active non-stick additive that does not fall under the definition of an aliphatic photoinitiator. [5-1] The embossing varnish according to [5] preferably contains 90 to 99 parts by mass of the UV-curable compound, 0.1 to 5 parts by mass of the photoinitiator, and 0.1 to 5 parts by mass of the surface-active non-stick additive, the total parts by mass being 100. [5-2] The embossing varnish according to [5] or [5-1] is preferred, in which the surface-active non-stick additive contains an optionally branched alkyl group having at least 10 carbon atoms in its main chain, or a sugar surfactant consisting of a carbohydrate and a fatty alcohol or fatty acid.

[0019] [6] The embossing varnish according to any one of the preceding items, wherein the UV-curable compound and the photoinitiator are selected so that the absorption coefficient of the photoinitiator in the embossing varnish comprising the UV-curable compound and 1 wt% of the photoinitiator at room temperature and a wavelength of 365 nm is at least twice as high as the absorption coefficient of the photoinitiator in a composition comprising water and 1 wt% of the photoinitiator or in a composition comprising hexane and 1 wt% of the photoinitiator. [6-1] A combination of the features of [1], [3], and [6] is preferred. [6-2] A combination of the features of [1], [3-1], and [6] is more preferred. [6-3] A combination of the features of [1], [4-1], and [6] is even more preferred.

[0020] [7] The embossing varnish according to any one of the preceding items, wherein the UV-curable compound and the photoinitiator are selected such that when a 400 μm-thick layer of each embossing varnish is cured by exposure to an LED lamp having a wavelength of 365 nm and an intensity of 100 mW at room temperature for 60 seconds, curing the embossing varnish comprising the UV-curable compound and 1 wt% of the photoinitiator results in at least 90% of the double bond conversion that occurs when curing an embossing varnish comprising the UV-curable compound and 1 wt% of α-hydroxy-4-(2-hydroxyethoxy)-α-methylpropiophenone. Therefore, the curing of the embossing varnishes is compared under the same conditions, i.e., the aforementioned conditions. [7-1] A combination of the features of [1], [3], and [7] is preferred. [7-2] A combination of the features of [1], [3-1], and [7] is even more preferred. [7-3] A combination of the features of [1], [4-1], and [7] is even more preferred.

[0021] [8] An article having a microstructured or nanostructured surface layer on a support, the surface layer being an embossed and UV-cured embossing varnish according to any one of items [1] to [7-3]. [8-1] Preferred is the article according to item [8], which is suitable, in particular in the form of a film, as a microfluidic structure for culturing living cells, as a structure having a functional microstructured or nanostructured surface, as a structure having an antibacterial, antiviral or antifungal surface, or as a structure having an antireflection, flow friction reduction or adhesive effect.

[0022] [9] A method for producing an article having a microstructured or nanostructured surface layer, preferably as described in [8] or [8-1], comprising applying an embossing varnish according to any one of items [1] to [7-3] to a substrate, and embossing and UV-curing the embossing varnish on the substrate.

[0023]

[10] The method according to item [9], wherein the substrate is a film and the method includes roll-to-roll embossing.

[0024]

[11] A method for producing an article, comprising the following steps (i) to (vi): (i) providing a starting compound having a molecular weight of 100 to 5000 g / mol, preferably 100 to 2000 g / mol, wherein the starting compound is a biomolecule or a derivative thereof, and is preferably selected from the group consisting of a hydroxyl group-containing biomolecule, a hydroxylated derivative of a biomolecule, a hydroxyl group-containing or hydroxylated degradation product of a biomolecule, and an ester or ether of a hydroxyl group-containing or hydroxylated degradation product of a biomolecule; (ii) functionalizing a starting compound with a radically polymerizable group having a C=C double bond, preferably a (meth)acrylate group, to form a UV-curable compound having a molecular weight of 200 to 5500, preferably 200 to 2500 g / mol; (iv) providing an aliphatic photoinitiator having a moiety selected from an α-diketone or an α-ketocarboxylic acid, or a salt or ester thereof; (v) preparing a composition containing the functionalized biomolecule and the aliphatic photoinitiator; and (vi) curing the composition with UV light. [11-1] Preferably, the method according to claim

[11] is a method for producing the article according to item [8] or [8-1]. [11-2] Preferably, the method according to item

[11] or [11-1] is a method in which the composition obtained in step (v) is the embossing varnish according to any one of items [1] to [7-3].

[0025]

[12] The method according to any one of items

[11] to [11-2], wherein the starting compound is an aliphatic alcohol and the UV-curable compound is an ester of an aliphatic alcohol and one or more (meth)acrylate groups.

[0026]

[13] The method according to any one of items

[11] to

[12] , wherein the method comprises applying the composition obtained in step (v) to a substrate and embossing the composition applied to the substrate before or simultaneously with step (vi), thereby obtaining an article having a microstructured or nanostructured surface layer.

[0027]

[14] An article obtained by the method described in any one of items [9] to

[13] .

[0028]

[15] Use of an article having a microstructured or nanostructured surface layer according to item [8] or an article obtained by the method according to item

[13] , in particular as a microfluidic structure for culturing living cells, as a structure having a functional microstructured or nanostructured surface, as a structure having an antibacterial, antiviral or antifungal surface, or as a structure having an anti-reflection, flow friction reduction or adhesive effect, wherein any of the structures may be present on the surface of the film or in the film itself. [Effects of the Invention]

[0029] The use of biomaterials in the embossing varnish of the present invention allows fossil raw materials to be replaced with biobased, sustainable, and renewable raw materials, enabling the embossing varnish to be produced entirely from renewable raw materials. In particular, the present invention makes it possible for the first time to formulate UV-NIL embossing varnishes based entirely on renewable raw materials. Compared to conventional aromatic photoinitiators, the photoinitiators of the present invention exhibit little or no fluorescence because they lack an aromatic ring. Photoinitiators can be advantageously used in microfluidic systems for culturing live cells, since they are generated during cellular metabolism and may even be partially utilized by cells. Pyruvate ethyl ester even has a cytoprotective effect. Photoinitiators can replace conventional petrochemical photoinitiators in both conventional and primarily biobased embossing varnishes. By using the appropriate combination of biobased UV-curable materials and photoinitiators, the use of co-initiators can be eliminated. The use of bio-based and biocompatible materials opens up new application possibilities in the microfluidic sector, for example as lab-on-foil or lab-on-chip. [Brief explanation of the drawings]

[0030] [Figure 1] 1 is a graph showing the extinction coefficients of solutions of BTS, EP, KGS, and DMKG (1 wt %) in water at a layer thickness of 1 cm. [Figure 2] 1 is a graph showing the absorption spectrum of an acrylate monomer with a layer thickness of 1 cm in a quartz cuvette, measured against an empty, i.e., air-filled, quartz cuvette. [Figure 3] 1 is a graph showing the extinction coefficients of solutions of pyruvic acid (1 wt %) in water, M2010, M3150, TGDA, and M286 / H2O=1 / 1. [Figure 4] 1 is a graph showing the extinction coefficients of solutions of pyruvate ethyl ester (1 wt %) in water, M2010, M3150, TGDA, and M286 / H2O=1 / 1. [Figure 5] 1 is a graph showing the extinction coefficients of solutions of α-ketoglutaric acid (1 wt %) in water, M2010, M3150, TGDA, and M286 / H2O=1 / 1. [Figure 6] 1 is a graph showing the extinction coefficients of solutions of dimethyl-α-ketoglutarate (1 wt %) in water, M2010, M3150, TGDA, and M286 / H2O=1 / 1. [Figure 7] 1 is a graph showing the extinction coefficients of solutions of 4,4-dimethyldihydrofuran-2,3-dione (1 wt %) in water, M2010, M3150, TGDA, and M286 / H2O=1 / 1. [Figure 8] 1 is a graph showing the extinction coefficients of α-ketocarboxylic acids and their esters in acrylate monomer M2010. [Figure 9] 1 shows the extinction coefficients of α-ketocarboxylic acids and their esters in the acrylate monomer M3150. [Figure 10] 1 shows the extinction coefficients of α-ketocarboxylic acids and their esters in the acrylate monomer TGDA. [Figure 11] 1 is a graph showing the photoconversion (DBC: double bond conversion) of the acrylate monomer M2010 as a function of exposure to UV light of wavelength 365 nm, as determined by ATR-FT-IR spectroscopy. [Figure 12] 1 is a graph showing the photoconversion (DBC: double bond conversion) of the acrylate monomer M3150 as a function of exposure to UV light of wavelength 365 nm, as determined by ATR-FT-IR spectroscopy. [Figure 13] 1 is a graph showing the photoconversion (double bond conversion or DBC for short) of the acrylate monomer TGDA as a function of exposure dose with UV light of wavelength 365 nm as determined by ATR-FT-IR spectroscopy.

[0031] FIG. 1 is a graph showing the photoconversion (DBC: double bond conversion) of the acrylate monomer M2010 as a function of exposure to UV light of wavelength 365 nm, as determined by ATR-FT-IR spectroscopy.

[0032] FIG. 2 is a graph showing the photoconversion (DBC: double bond conversion) of the acrylate monomer M3150 as a function of exposure to UV light of wavelength 365 nm, as determined by ATR-FT-IR spectroscopy.

[0033] FIG. 3 is a graph showing the photoconversion (double bond conversion or DBC for short) of the acrylate monomer TGDA as a function of exposure to UV light of wavelength 365 nm, as determined by ATR-FT-IR spectroscopy. DETAILED DESCRIPTION OF THE INVENTION

[0034] The following abbreviations or names are used in this invention: BTS: Pyruvate EP: Pyruvate ethyl ester KGS: α-ketoglutaric acid DMKG: α-ketoglutarate dimethyl ester DDFD: 4,4-dimethyldihydrofuran-2,3-dione EMOB: Ethyl-3-methyl-2-oxobutanoate A2KGS: Di-L-arginine α-ketoglutarate OKGS: L-ornithine-α-ketoglutarate M2010: 1,10-decanediol diacrylate TGDA: Triglycerol diacrylate M3150: Triacrylate of ethoxylated trimethylolpropane M286: Polyethylene glycol diacrylate Sarbio 7101: Acrylated Epoxidized Soybean Oil Rob72: Itaconate-containing UV-curable polyester with over 90% biorenewable carbon content (BRC) TPO-L: Ethyl (2,4,6-trimethylbenzoyl)phenylphosphinate Irgacure 2959: α-hydroxy-4-(2-hydroxyethoxy)-α-methylpropiophenone EDMAB: Ethyl dimethylaminobenzoate

[0035] The embossing varnish according to the present invention is suitable for microstructured or nanostructured surface layers. In other words, it is suitable as a starting material for such layers. The production of such layers involves embossing and curing the embossing varnish according to the present invention as a starting material. For this purpose, the embossing varnish is applied to a support layer as a surface layer. Therefore, the viscosity of the embossing varnish needs to be adjusted so that it can be easily applied. Since the embossing varnish is not cured, i.e., not polymerized, it has the desired viscosity so that it can be applied, for example, by brushing or pouring. After application, the embossing varnish is embossed using an embossing tool. Therefore, in order to be suitable for the production of microstructured or nanostructured surface layers, the embossing varnish according to the present invention needs to have a viscosity within a certain range. A further requirement is that the embossing varnish according to the present invention does not adhere to the embossing tool during embossing, and can form a stable microstructured or nanostructured layer after curing.

[0036] The term "microstructured or nanostructured" means that depressions in the micrometer or nanometer range, i.e., 1 nm to 999 μm, are embossed on the surface of the layer of embossing varnish. Preferably, the microstructured or nanostructured surface layer has depressions of 10 nm to 500 μm. The surface layer preferably has a thickness of 10 nm to 1000 μm, more preferably 50 nm to 500 μm, i.e., in the range perpendicular to the contact surface with the support, and the embossing depth is preferably less than 50% to 100% of the thickness of the surface layer. The term "microfluidic" as used herein includes embossing depths in the above-mentioned micrometer to nanometer range.

[0037] The embossing varnish contains at least two components: a UV-curable compound and an aliphatic photoinitiator. The two components are structurally different from each other. They are not chemically bonded and therefore exist as separate substances in the embossing varnish. The photoinitiator preferably does not fall within the definition of a UV-curable compound, and in this case does not contain a UV-polymerizable C=C double bond, so the two components differ in this respect. However, the photoinitiator may also fall within the definition of a UV-curable compound and have a polymerizable C=C double bond. In this case, the two components differ from each other in that the UV-curable compound does not fall within the definition of a photoinitiator, that is, it does not contain a moiety selected from α-diketones or α-ketocarboxylic acids or their salts or esters.

[0038] In the present invention, the verb "comprise" or its derivatives means that the composition comprises the component, preferably in an amount of 1 to 100 wt %. This therefore includes the meaning that the composition consists of the component. Preferably, this component is the main component and is therefore contained in an amount of more than 50 wt %. The embossing varnish may contain water. It may be an aqueous dispersion.

[0039] For the sake of brevity, the present invention uses the singular to designate components, groups, etc. However, this does not exclude the presence of more than one component, group, etc., unless specifically indicated. For example, an embossing varnish includes a UV-curable compound and an aliphatic photoinitiator. This formulation includes embodiments in which multiple UV-curable compounds and / or multiple aliphatic photoinitiators are included. A UV-curable compound "having a UV-polymerizable C=C double bond" may contain several UV-polymerizable C=C double bonds.

[0040] In the context of the present invention, the term "oligomer" is used for two to five consecutive related structural units, and molecular structures with six or more such structural units are called "polymers."

[0041] UV curable compound The UV-curable compound used in the embossing varnish according to the present invention contains a UV-polymerizable C=C double bond. This compound is UV-curable, i.e., it can be cured with UV light. Curing by other means, such as light of other wavelengths or electron beams, is not excluded. The UV-curable compound is not polymerized or not fully polymerized, but is converted into a hardened coating by radical polymerization, preferably photopolymerization using UV light. The UV-curable compound is a monomer or oligomer.

[0042] The radical polymerizable group is a non-aromatic C=C double bond, such as a vinyl, allyl, or norbornenyl group. Examples are vinyl ether, allyl ether, propenyl ether, alkene, diene, unsaturated ester, allyl triazine, allyl isocyanate, and N-vinyl amide. Preferred UV-curable compounds are (meth)acrylates and their derivatives. The term "(meth)acrylate" means "acrylate and / or methacrylate" unless otherwise specified. The same applies to the expressions "(meth)acrylic acid" and "(meth)acrylate ester." Examples of (meth)acrylates are 1,4-butanediol dimethacrylate (BDDMA), hexanediol dimethacrylate (HDDMA), 1,3-butylene glycol dimethacrylate (1,3-BGDMA), ethylene glycol dimethacrylate (EGDMA), dodecanediol dimethacrylate (DDDMA), trimethylolpropane trimethacrylate (TMPTMA), trimethacrylate esters (TMA esters), and these monomers can be used individually or in combination of two or more.

[0043] In addition to the UV-curable compound having a C=C double bond, the embossing varnish may also contain a monomer having two thiol groups, such as glycol di(3-mercaptopropionate) (GDMP). The reaction of a thiol group with a carbon-carbon double bond is a thiol-ene reaction. Further examples of monomer building blocks having at least two thiol groups are 3-mercaptopropionate, 3-mercaptoacetate, thioglycolate, and alkylthiol. The embossing varnish according to the invention may contain, for example, a monomer having at least two thiol groups in an amount of 1 wt% to 50 wt%, in particular 5 wt% to 10 wt%, and a monomer or oligomer having at least one polymerizable double bond in an amount of 1 wt% to 90 wt%, in particular 10 wt% to 50 wt%.

[0044] The UV-curable compound preferably contains at least one ester of an alcohol and an acid having a C=C double bond. More preferably, the UV-curable compound is an alcohol esterified with one or more, preferably two, (meth)acrylate groups. Alternatively, the (meth)acrylate groups can be coupled via NH or SH to form an amide or thioester bond. To bind at least two (meth)acrylic acid molecules, the biomolecule preferably has at least two such groups.

[0045] In the present invention, bio-based UV curable compounds are preferred.

[0046] Acrylic acid can be produced from renewable raw materials, for example, the synthesis of acrylic acid from lactic acid is known.

[0047] Alcohols esterified with acids, such as (meth)acrylic acid, are compounds having at least one hydroxyl group, including mono- and polyols. Polyols are compounds having at least two hydroxyl groups. Alcohols that serve as starting compounds for UV-curable compounds are selected from the group consisting of hydroxyl-containing biomolecules, hydroxylated derivatives of biomolecules, hydroxyl-containing or hydroxylated degradation products of biomolecules, and esters or ethers of hydroxyl-containing or hydroxylated degradation products of biomolecules. Such alcohols are referred to herein as bio-based alcohols. They preferably have a molecular weight of 100 to 2000 g / mol. C6 to C6 24 Alcohols, C2-C6 alkoxy group-containing oligoethers or polyethers, hydroxylated C2-C6 monocarboxylic or dicarboxylic acid-containing oligoesters or polyesters, oligoesters or polyesters containing C2-C6 alkoxy groups and C2-C6 dicarboxylic acids, NIPU, glycerol oligomers or polymers, C6-C 24 Epoxidized triglycerides of fatty acids, or epoxidized C6-C 24 Fatty acid fatty alcohols, preferably bio-based fatty alcohols, are more preferred. The aforementioned alcohols can serve as starting compounds for UV-curable compounds.

[0048] The UV-curable compounds used in the present invention can be prepared by providing a starting compound and functionalizing the starting compound with a group that contains a free-radically polymerizable C=C double bond.

[0049] The group having a polymerizable C=C double bond that can be polymerized by free radicals is preferably a (meth)acrylate group, but may also be, for example, an itaconate group. Since the starting compound may contain an amine or thio group, coupling occurs via an amide bond or a thioester bond. However, since a hydroxy group is preferred, the starting compound is coupled via an ester group.

[0050] Starting compounds with a molecular weight of 100 to 2000 g / mol are preferred, which are preferably (a) a biomolecule containing a hydroxyl group; (b) hydroxylated derivatives of biomolecules; (c) hydroxy-containing or hydroxylated degradation products of biomolecules, and (d) Esters or ethers of hydroxy-containing or hydroxylated degradation products of biomolecules is selected from the group consisting of:

[0051] (a) Suitable hydroxy group-containing starting compounds include C6-C8 hydroxy groups such as amino acids, peptides, mononucleotides, oligonucleotides, monosaccharides, disaccharides, oligosaccharides, or mono-, di-, or polyols. 24 The biomolecule is selected from alcohols and has a molecular weight of 100 to 2000 g / mol.

[0052] (b) The biomolecules referred to in (a) or other biomolecules may be provided with one or more hydroxyl groups. For example, triglycerides may be epoxidized or acids may be reduced. C6-C 24 The fatty acids can be reduced and optionally epoxidized. The hydroxylated biomolecules have molecular weights between 100 and 2000 g / mol.

[0053] (c) Biomolecules whose degradation products may contain hydroxyl groups or may be hydroxylated include peptides, proteins, oligonucleotides, polynucleotides, disaccharides, oligosaccharides, polysaccharides, triglycerides, or fatty acids. Such degradation products may be produced from animal or vegetable oils or fats, i.e., triglycerides from glycerol and fatty acids. The fatty acids are preferably saturated or unsaturated C8-C6 fatty acids. 24 These are fatty acids which, optionally after epoxidation, can be converted into alcohols, preferably polyols. After optional hydroxylation, these degradation products have molecular weights of 100 to 2000 g / mol.

[0054] (d) The starting compounds can also be esters or ethers with molecular weights of 100 to 2000 g / mol derived from hydroxyl-containing or hydroxylated degradation products of biomolecules, where the degradation products involving the ester bond additionally contain one or more carboxyl groups.

[0055] The following degradation products can be produced from biomolecules such as polysaccharides, especially cellulose or starch: - Diols: ethylene glycol, 1,3-propanediol, 2,3-butanediol, 1,4-butanediol - Polyols: glycerol, pentaerythritol, mesoerythritol, diglycerol - Dicarboxylic and tricarboxylic acids: citric acid, succinic acid, methylsuccinic acid, itaconic acid, fumaric acid, maleic acid, citraconic acid, itaconic anhydride - Hydroxyalkanoic acids: lactic acid, hydroxybutanoic acid - Furan: Furandicarboxylic acid

[0056] Hydroxy-containing degradation products, i.e., diols, polyols, and hydroxyalkanoic acids, can be used as starting compounds as they are or in the form of their ethers. The aforementioned hydroxy-containing degradation products can be used as esters with the aforementioned acids as starting compounds. Further esters or ethers according to (d) can be prepared from the aforementioned triglycerides. Glycerol can be used as polyglycerol. Fatty acids can be esterified with diols, if necessary, after additional epoxidation. The esters or ethers according to (d) are, in particular, oligoesters and polyesters, as well as oligoethers and polyethers.

[0057] Particularly preferred starter compounds with a molecular weight of 100 to 2000 g / mol are C6-C6 monopolyols, dipolyols or polyols.24 Alkyl alcohols, polyethers such as polyethers containing ethoxy groups, glycerol oligomers such as triglycerol, fatty derivatives such as epoxidized unsaturated triglycerides, or optionally epoxidized C-C 24 It is a fatty acid.

[0058] The following are examples of UV-curable compounds that can be produced entirely biobased: 1,10-Decanediol diacrylate (e.g., M2010) (non-polar, derived from castor oil)

[0059] [ka]

[0060] Triglycerol diacrylate (polar, protic)

[0061] [ka]

[0062] Ethoxylated trimethylolpropane triacrylate (polar, aprotic)

[0063] [ka]

[0064] PEG diacrylate (polar, protic)

[0065] [ka]

[0066] Acrylated epoxidized soybean oil (e.g., Sarbio 7101) (non-polar)

[0067] [ka]

[0068] Polyitaconate ester (semi-polar)

[0069] [ka]

[0070] Photoinitiator Photoinitiators do not fall within the definition of UV curable compounds.

[0071] The following α-ketocarboxylic acids and their salts, e.g., sodium salts or esters, initiate free radical polymerization without the addition of a coinitiator: Pyruvate (BTS)

[0072] [ka]

[0073] Pyruvate ethyl ester (EP)

[0074] [ka]

[0075] α-Ketoglutaric acid (KGS)

[0076] [ka]

[0077] α-Ketoglutaric acid dimethyl ester (DMKG)

[0078] [ka]

[0079] 4,4-Dimethyldihydrofuran-2,3-dione (DDFD)

[0080] [ka]

[0081] Ethyl-3-methyl-2-oxobutanoate (EMOB)

[0082] [ka]

[0083] Oxaloacetate

[0084] [ka]

[0085] Oxaloacetic acid diethyl ester

[0086] [ka]

[0087] Diethyl methyloxaloacetate

[0088] [ka]

[0089] Di-L-arginine-α-ketoglutarate (A2KGS)

[0090] [ka]

[0091] L-Ornithine-α-Ketoglutarate (OKGS)

[0092] [ka]

[0093] UV curing of biobased and conventional embossing varnishes can be initiated with a series of simple aliphatic α-diones. Examples of such aliphatic α-diones are 2,3-pentanedione, 2,3-hexanedione, 3,4-hexanedione, and α-furil. Such α-diketones do not initiate free radical polymerization very effectively by themselves. As Norrish Type II photoinitiators, they require a co-initiator. The mode of action of Norrish Type II photoinitiators is based on the abstraction and intermolecular transfer of a hydrogen atom from a co-initiator, such as a tertiary amine, to the initiator molecule. Therefore, for the purposes of this invention, a co-initiator is defined by the fact that it can abstract a hydrogen atom from the co-initiator and transfer it to the initiator molecule. An example of a co-initiator is ethyl dimethylaminobenzoate (EDMAB). Furthermore, for the purposes of this invention, a co-initiator is defined as something that does not fall within the definitions of UV-curable compounds, photoinitiators, and surface-active non-stick additives. In embodiments of the present invention, the addition of a coinitiator can be omitted as the UV curable compound or surface active anti-stick additive can take over its function.

[0094] Since the photoinitiators used in the present invention are also present in living cells and are in part intermediate products of or can be utilized by cellular metabolism, photoinitiators that are not converted during the curing of the embossed coating do not pose a toxicity risk in applications involving living cells, such as cell cultures. Indeed, some of these photoinitiators even function as nutrients for cells.

[0095] support The embossing varnish is applied to a substrate. There are no particular restrictions on the material of the substrate. The substrate can be a polymer substrate, such as a film. The substrate can be bio-based. Films based on cellulose and polylactate are commercially available.

[0096] Surface Active Non-Stick Additives To reduce or completely prevent adhesion of the embossing varnish to the embossing tool, the embossing varnish according to the present invention may contain a surface-active anti-stick additive. Surface-active anti-stick additives do not fall under the definition of UV-curable compounds and aliphatic photoinitiators. They may contain silicon or fluorine. In particular, the additive is at least one member selected from the group containing silicon- or fluorine-containing additives. Specific examples are nonionic surfactants such as polyether siloxanes, fatty alcohol ethoxylates such as polyoxyethylene (9) lauryl ether, monofunctional polydimethylsiloxane polyethoxy (meth)acrylates, alkyl (meth)acrylates, perfluoroalkyl (meth)acrylates, and perfluoropolyether (meth)acrylates. Amphiphilic alkyl-, silicon-, or fluorine-containing additives contribute to reducing adhesion and detaching the embossing lacquer from the embossing tool, while perfluorinated additives have proven particularly advantageous, allowing for reliable multiple imprinting of the pattern. At least one additive may be contained in the starting varnish in an amount of 0.1 to 3 wt %. By modifying the surface of the embossing tool, in particular the embossing die, with respect to its hydrophobicity, adhesion of the embossing varnish to the embossing tool can also be prevented.

[0097] method The embossing varnish is applied to a support layer, such as a polymer substrate. Preferably, the embossing varnish has the desired viscosity so that it can be applied, for example, by brushing or molding. In a roll-to-roll process, the embossing varnish is applied to the substrate, for example, by using a slot die or by gravure printing with an engraved roller. A microstructured or nanostructured stamp bearing the inverse profile of the desired microstructured or nanostructured surface is used as a negative mold and pressed against the embossing lacquer, and the desired structure is then embossed as a positive mold. The embossing die can be made of metal, such as nickel, or a polymeric material, which may have a lower surface energy than nickel, thereby reducing paint adhesion during the embossing process. When exposed to UV light, the embossing varnish polymerizes and becomes solid. After separating the stamp from the embossed pattern, the stamp profile is replicated in reverse. When using a continuous roll-to-roll process, a cylindrical stamp is part of the roll. This makes it possible to structure very large areas in a short time. [Example]

[0098] A variety of bio-based UV-curable compounds and photoinitiators were investigated. Below, the invention is explained in more detail based on the test results shown in the figures.

[0099] Figure 1 shows that the extinction coefficients of various α-ketocarboxylic acids and their esters in water are similar. α-Ketocarboxylic acids and their esters absorb in the UV-A spectral range (λ = 380-315 nm), which is beneficial for UV curing. The extinction coefficients are not high, typically in the single order of magnitude between λ = 380-315 nm. This absorption in UV-A is due to the n-π * In the UV-C range, λ<280 nm, these molecules undergo a π-π transition. *However, this spectral range is not very beneficial for UV curing, since the (meth)acrylates themselves already absorb there.

[0100] Figure 2 shows that M2010, M3150, and M286 exhibit very sharp absorption edges around λ = 310 nm, while TGDA exhibits a sharp absorption edge at λ = 320 nm. The absorption is very strong in the wavelength range below 310 nm and below 320 nm. The UV absorption spectra and extinction coefficients for the photoinitiators in these acrylate monomers are shown below only in the wavelength range from 450 to 300 nm, because the photoinitiator absorption at shorter wavelengths is completely hidden by the strong absorption of the monomer.

[0101] Figure 3 shows that the absorption of pyruvic acid (BTS) in the UV-A range is significantly stronger in all three acrylate monomers than in water. * The absorption maximum of this transition is clearly bathochromically shifted (red-shifted) in both the nonpolar M2010 with its aliphatic decane backbone and the polar M3150 with its polyether backbone. The absorption maximum of this excitation in water occurs at 322 nm, while the maximum in M2010 and M3150 is at 340 nm. This is highly favorable for UV curing of embossing varnishes. In the aqueous polyethylene glycol diacrylate M286 / H2O = 1 / 1, the absorption is stronger than in water and slightly bathochromically shifted, thus approximately averaging between water and M286, which is chemically similar to M3150. BTS absorbs most strongly in triglycerol diacrylate. In this polar and protic medium, the absorption maximum is similar to the absorption maximum in water at approximately 320 nm. The n-π of BTS * The ability of the medium to donate a proton appears to play a larger role in the transition than pure polarity.

[0102] Figure 4 shows that pyruvate ethyl ester (EP) absorbs much more strongly in all three acrylate monomers analyzed than in water. The extinction coefficients of EP in M2010 and M3150 are almost identical to that of BTS. The polarity of the medium also does not play a significant role here. The n-π of EP * The absorption maxima of the band are barely shifted for TGDA. Therefore, the ability of TGDA to protonate is comparable to the n-π of EP. * It does not appear to significantly affect the absorption. In aqueous polyethylene glycol diacrylate M286 / H2O=1 / 1, the absorption is not much stronger than in water and is slightly bathochromically shifted.

[0103] By investigation, n-π * In the case of the favorable bathochromic shift of the transition, the proton donating ability of the medium is shown to play a larger role than pure polarity.

[0104] Figure 5 shows the n-π α-ketoglutaric acid (KGS) solution at M2010 and M3150. * The band intensity is also slightly higher than in water and is bathochromically shifted by approximately 20 nm. In the protic medium TGDA, the absorption intensity is significantly higher, and the absorption maximum is at approximately the same wavelength as in water. In all media analyzed, the extinction coefficient of KGS is very similar to that of pyruvic acid, except for the slightly stronger absorption in water. In the aqueous polyethylene glycol diacrylate M286 / H2O = 1 / 1, the absorption intensity of KGS is similar to that of M3150, which is chemically similar to M286. The position of the absorption maximum is almost exactly centered between water and M3150, which also has a PEG backbone.

[0105] Figure 6 shows that the spectra of dimethyl-α-ketoglutarate (DMKG) at non-polar M2010 and polar M3150 are identical. In both cases, the n-π *The absorption of the transition is more than twice as strong as in water and in each case is bathochromically shifted by about 20 nm. Therefore, the spectra of these two esters DMKG and EP are very similar. The absorption intensity in the M286 / H2O = 1 / 1 system is similar to that in water. The absorption maximum is bathochromically shifted by about 6 nm.

[0106] Figure 7 shows the n-π structure of dimethyldihydrofuran-2,3-dione (DDFD). * The absorption maxima of the transition show a clear bathochromic shift to about 375 nm for all acrylate monomers, which is due to the coplanar fixation of the carbonyl oxygen atoms in the cyclic DDFD and the resulting increased conjugation of the n-π orbitals. * The intensities of the transitions are significantly higher for the two aprotic monomers M2010 and M3150 than for the protic TGDA. The extinction coefficient of DDFD in water and M286 / H2O = 1 / 1 are unusual. DDFD may undergo saponification in water, which would explain the low long-wavelength band at 380 nm and the absorption at 320 nm.

[0107] Table 1 summarizes the results shown in Figures 1-7. Table 1 shows the wavelength of absorption maximum, maximum extinction coefficient, and extinction coefficient at 365 nm for solutions of the investigated α-ketocarboxylic acids and their esters in the acrylate monomers M2010, M3150, and TGDA, and as extreme references, i.e., polar / protic and nonpolar / aprotic water and n-hexane. Furthermore, solutions of the listed α-ketocarboxylic acids and their esters, as well as two amino acid α-ketoglutarate conjugates, di-L-arginine α-ketoglutarate (A2KGS) and L-ornithine α-ketoglutarate (OKGS), were also analyzed in mixtures of polyethylene glycol diacrylate (PEGDA) (Miramer M268, M = 600 g / mol) and water (with a mass ratio of M286 / HO = 1 / 1). Stable hydrogels were formed from aqueous PEGDA solutions of the aforementioned α-ketocarboxylic acids and their derivatives by UV irradiation. The investigated α-ketocarboxylic acids and their esters, as well as two highly water-soluble amino acid complexes, also initiated radical polymerization very effectively in aqueous media.

[0108] [Table 1]

[0109] Figures 8 and 9 show that, with the exception of DDFD in the acrylate monomers M2010 and M3150, the spectra of the analyzed α-ketocarboxylic acids and their esters are very similar in both absorption position and intensity. The strong bathochromic shift of DDFD is due to the coplanar anchoring of the carbonyl oxygen atom as described above. DMKG exhibits a small hypsochromic (blue-shift) of approximately 10 nm compared to BTS, EP, and KGS.

[0110] Figure 10 shows that the absorption intensity of TGDA is significantly lower compared to BTS, EP, and KGS. The hypsochromic shift of DMKG observed here also means that the absorption maximum is already within the strong absorption of the medium TGDA and therefore can no longer be resolved.

[0111] ATR-FT-IR study of photoinitiator efficiency An embossed varnish containing acrylate monomers and 1 wt% of photoinitiator was exposed between two glass plates with a layer thickness of 400 μm (using a 400 μm thick spacer) under an LED lamp with UV-A light of wavelength 365 nm and an intensity of 100 mW.

[0112] These results are shown in Figures 11 to 13.

[0113] Figure 11 shows the results of curing M2010 with various photoinitiators. The conventional aromatic photoinitiators TPO-L and Irgacure 2959 were used as references. TPO-L, known for its high efficiency, showed the highest efficiency, followed by pyruvic acid (BTS) and Irgacure 2959. Pyruvate ethyl ester (EP) also initiated polymerization faster than Irgacure 2959, but the final double bond conversion was slightly lower than that of Irgacure 2959. KGS and its ester DMKG showed similar efficiencies to Irgacure 2959, with only the cyclic ester DDFD initiating photopolymerization of M2010 slightly slower. The maximum double bond conversion was 90% for all photoinitiators.

[0114] Figure 12 shows that photopolymerization with all photoinitiators tested is significantly faster in M3150 than in M2010, with nearly complete conversion of the acrylate double bonds. Here, Irgacure 2959 initiates the fastest, but pyruvic acid and α-ketoglutaric acid are nearly as fast. The corresponding esters EP and DMKG, as well as the cyclic ester DDFD, initiate photopolymerization of M3150 somewhat more slowly.

[0115] Figure 13 shows that pyruvic acid is the most effective initiator for photopolymerization of TGDA, even before the reference Irgacure 2959. The cyclic ester DDFD is more effective than the esters EP and DMKG. KGS is the least effective for TGDA. The maximum achievable double bond conversions for TGDA with BTS and Irgacure 2959 are 84% and 83%, respectively. With other initiators, 75-80% conversions are achieved.

[0116] The difference in maximum double bond conversion may be due to the different glass transition temperatures of the acrylate monomers. M3150 has a very low glass transition temperature of -31°C. Because solidification does not occur during photopolymerization at room temperature, reactive groups and monomers do not freeze, and therefore high polymerization conversion is achieved. M2010 has a glass transition temperature of 36°C, which limits group mobility during polymerization, resulting in a slight decrease in the final double bond conversion. The high number of hydrogen bonds in triglycerol diacrylate may increase the glass transition temperature, which may explain the decrease in maximum double bond conversion.

[0117] The UV curing of different monomers was tested using various photoinitiators. In each case, a solution containing 1 wt% of the photoinitiator was placed between two glass plates in a layer thickness of 400 μm (using a 400 μm thick spacer) and exposed for different times under an LED lamp with UV-A light of wavelengths 365 nm or 395 nm and an intensity of 100 mW. The consistency of the UV-polymerized films was then qualitatively evaluated. The results are summarized in Tables 2 and 3.

[0118] [Table 2A]

[0119] [Table 2B]

[0120] Table 2C

[0121] Table 3

Claims

1. An article having a microstructured or nanostructured surface layer on a support, the surface layer being obtained by embossing and UV-curing an embossing varnish, the embossing varnish containing a UV-curable compound having a UV-polymerizable C=C double bond and an aliphatic photoinitiator comprising a moiety selected from an α-ketocarboxylic acid or a salt or ester thereof.

2. 10. The article of claim 1, wherein the molecular weight of the UV-curable compound in the embossing varnish is between 200 and 2500 g / mol.

3. 3. An article according to claim 1 or 2, wherein the UV-curable compound in the embossing varnish is an alcohol esterified with one or more (meth)acrylate groups.

4. The UV-curable compound in the embossing varnish is an aliphatic hydroxy group-containing compound esterified with two or more (meth)acrylate groups, and the aliphatic hydroxy group-containing compound is C 6 ~C 24 Alcohol, C 2 ~C 6 Oligo- or polyethers containing alkoxy groups, hydroxylated C 2 ~C 6 Oligoesters or polyesters containing monocarboxylic or dicarboxylic acids, C 2 ~C 6 Alkoxy group and C 2 ~C 6 Oligoesters or polyesters containing dicarboxylic acids, non-isocyanate-based polyurethanes, glycerol oligomers or polymers, C 6 ~C 24 Epoxidized triglycerides of fatty acids, or epoxidized C 6 ~C 24 4. The article of any one of claims 1 to 3, which is a fatty acid.

5. 5. The article of claim 1, wherein the embossing varnish contains at least one additive selected from the group consisting of nonionic surfactants, fatty alcohol ethoxylates, monofunctional polydimethylsiloxane polyethoxy (meth)acrylates, alkyl (meth)acrylates, perfluoroalkyl (meth)acrylates, and perfluoropolyether (meth)acrylates.

6. 6. A method for producing an article according to any one of claims 1 to 5, comprising applying an embossing varnish as defined in any one of claims 1 to 5 to a substrate, and embossing and UV-curing the embossing varnish on the substrate.

7. The method of claim 6, wherein the substrate is a film and the method comprises roll-to-roll embossing.

8. 1. A method of manufacturing an article, comprising the steps of: (i) providing a starting compound having a molecular weight of 100 to 2000 g / mol, wherein the starting compound is a biomolecule or a derivative thereof; (ii) functionalizing the starting compound with a radically polymerizable group having a C=C double bond to form a UV-curable compound having a molecular weight of 200 to 2500 g / mol; (iv) providing an aliphatic photoinitiator having a moiety selected from an α-ketocarboxylic acid or a salt or ester thereof; (v) preparing a composition comprising a functionalized biomolecule and an aliphatic photoinitiator; (vi) curing the composition with UV light; Including, applying the composition obtained in step (v) to a substrate and, prior to or simultaneously with step (vi), embossing the composition applied to the substrate, thereby obtaining an article having a microstructured or nanostructured surface layer. method.

9. 9. The method of claim 8, wherein the starting compound is an aliphatic alcohol and the UV-curable compound is an ester of an aliphatic alcohol with one or more (meth)acrylate groups.

10. 10. Use of an article having a microstructured or nanostructured surface layer according to any one of claims 1 to 5 or an article obtainable by the method according to claim 8 or 9 as a microfluidic structure, in particular as a microfluidic structure for culturing living cells, as a structure having a functional microstructured or nanostructured surface, as a structure having an antibacterial, antiviral or antifungal surface, or as a structure having an antireflection, flow friction reduction or adhesive effect.

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