Photoinitiators for photocurable compositions

Abstract

The present invention relates to a low light concentration initiator # imgabs0 # according to formula (I) wherein m is equal to or greater than 3, R1, R2 and R3 are independently selected from H or linear or branched C1-C6 alkyl, and wherein the low light concentration initiator has a weight average molecular weight Mw, determined by GPC (THF), higher than 1000 g / mol.

Description

[0001] The present invention relates to oligomeric photoinitiators, which can be used as photoinitiators in free radical curable compositions such as free radical curable coatings and ink compositions. The present invention further relates to free radical curable compositions comprising such oligomeric photoinitiators. In addition, the present invention relates to objects coated with such free radical curable compositions.

[0002] Today, coatings are used every day. Examples of articles are coatings for transparent food packaging, thin foils, paints, and car part finishes. UV curing or free radical photopolymerization is the fastest growing curing technology with an ever-increasing number of applications. Compared with solvent-based systems, UV curing saves energy and reduces or eliminates solvent emissions because most radiation-curable formulations are 100% solid formulations containing reactive oligomers and diluents. The mechanical properties of the cured formulations are usually determined by the oligomers and diluents. Photoinitiators are one of the key components of each photopolymerizable formulation because they produce free radicals that initiate polymerization reactions when exposed to light. The main disadvantage of most photopolymerizable formulations is the amount of residual unreacted photoinitiator molecules in the cured polymer material. High conversion rates in very short times mean that only a few initiator molecules can be covalently bound to the polymer network. Solutions to this problem are, for example, irradiation for very long periods of time or the use of small amounts of initiators. But both methods are not suitable for industrial-scale applications because short exposure times achieve the required high throughput. Normally, reasonable conversions are provided by using an increased percentage of photoinitiator, but this results in the aforementioned increase in the amount of unreacted photoinitiator in the cured formulation. In addition to migrating out of the cured formulation, residual photoinitiator can cause yellowing and generate various by-products such as, for example, benzaldehyde, which can also migrate out of the cured formulation.

[0003] Migration is particularly problematic when protective and decorative coatings are applied to food packaging, healthcare and other everyday items that may come into contact with people.

[0004] Benzophenone and its derivatives are more commonly used as photoinitiators in the packaging field. However, for benzophenone, there is sufficient evidence to show that it is carcinogenic in experimental animals and may be carcinogenic to humans (International Agency for Research on Cancer, "Some Chemicals Present in Industrial and Consumer Products, Food and Drinking Water", Vol. 101, pp. 285-301).

[0005] In fact, a study (RZ Liu, SA Mabury, "First Detection of Photoinitiators and Metabolites in Human Sera from United States Donors" Environmental Science and Technology, Vol. 52(17), pp. 10089-10096 2018.) revealed that photoinitiators and co-initiators were found in every single serum, indicating that photoinitiators and their photoproducts are ubiquitous contaminants.

[0006] This illustrates the need for free radical curable formulations in which particularly alternative oligomeric photoinitiators are used. By using oligomeric photoinitiators, the mobility is significantly reduced. Examples of such oligomeric photoinitiators are given in WO2021 / 259924. However, in this application, the basis of the oligomeric photoinitiator is still benzophenone derivatives.

[0007] A very gentle (elegant) alternative to benzophenone derivatives, namely linear polymers based on α-ketoglutaric acid and hexanediol, has been described in US2020 / 0231531. However, as will be demonstrated, the reactivity of such systems is not sufficient.

[0008] Therefore, there is a need for oligomeric photoinitiators with increased reactivity.

[0009] It was an object of the present invention to provide oligomeric photoinitiators which have an increased reactivity in free-radical curing processes.

[0010] According to the present invention, there is provided an oligomeric photoinitiator according to formula (I)

[0011]

[0012] in

[0013] m is equal to or greater than 3,

[0014] R1, R2 and R3 are independently selected from H, or from linear C1-C6 alkyl, or from branched C1-C6 alkyl, and

[0015] The oligomeric photoinitiator has a weight average molecular weight M higher than 1000 g / mol as determined by GPC (THF). w , so the weight average molecular weight M w The assay was performed as described in the instructions.

[0016] It has surprisingly been found that the photoinitiators according to the invention have increased reactivity in free radical curable compositions. In particular, the photoinitiators according to the invention can be advantageously applied in free radical curable coating and ink compositions, where low mobility of chemical species is required.

[0017] For all upper and / or lower boundaries of any range given herein, unless otherwise specifically stated, the boundary values ​​are included in the given range. Thus, when it is said from x to y, it is meant to include x and y and all intermediate values.

[0018] The oligomeric photoinitiator according to formula (I) comprises m (m is equal to or greater than 3) terminal functional groups according to formula (Ia)

[0019]

[0020] Preferably, m is equal to or greater than 4, more preferably m is equal to or greater than 5, even more preferably m is equal to or greater than 6, even more preferably m is equal to or greater than 7, even more preferably m is equal to or greater than 8.

[0021] Preferably, R1, R2 and R3 are independently selected from H or CH3. More preferably, R1, R2 and R3 are H. In the case where R1, R2 and R3 are H, the terminal functional group according to formula (Ia) is derived from pyruvic acid having the formula

[0022]

[0023] The oligomeric photoinitiator can be obtained by a process comprising at least the following steps:

[0024] (1) providing a core oligomer having at least m (m≥3) terminal hydroxyl functional groups,

[0025] (2) esterifying (transesterification) the m terminal hydroxyl functional groups of the core oligomer with a compound according to formula (Ib):

[0026]

[0027] wherein R4 is H or C1-C4 alkyl, preferably C1-C3 alkyl; and R1, R2 and R3 are as described above.

[0028] The esterification (transesterification) is usually carried out using a catalyst known to those skilled in the art, for example an acid catalyst, such as methanesulfonic acid or sulfuric acid. The water formed (for R4 = H) or the small alcohol formed (for R4 = C1-C4 alkyl) (methanol, ethanol, ...) can be physically removed by means of an entrainer (such as toluene), a nitrogen stream or a vacuum. Preferably, R4 = H.

[0029] Epoxy resins, such as Epikote available from Hexion TM 828, can be used to remove acid catalysts.

[0030] In order to incorporate a large number of functional groups (including at least m terminal functional groups with formula (Ia)), the core oligomer is preferably a branched oligomer, more preferably a highly branched oligomer, and even more preferably a hyperbranched oligomer. The advantage of using branched or highly branched or hyperbranched oligomers as core oligomers is that they can have a large number of terminal groups, preferably hydroxyl terminal groups that can be easily modified, thereby producing a structure according to formula (I). In the context of the present invention, highly branched oligomers are understood to have branched structures and high density of oligomers with functional groups of formula (Ia). In the context of the present invention, hyperbranched oligomers are understood to have branched structures and higher density of oligomers with functional groups of formula (Ia).

[0031] The inventors have further found that it may be beneficial if the oligomeric photoinitiator comprises from 1 to 10 groups according to formula (II):

[0032]

[0033] wherein n is 0 to 6, preferably n is 2 or 3, and more preferably n is 2.

[0034] In case n is 3, the group according to formula (II) is derived from a compound having the formula:

[0035]

[0036] In case n is 2, the radical according to formula (II) is derived from 2-ketoglutaric acid having the following formula:

[0037]

[0038] Core oligomer

[0039] The core oligomer may be a polyether, polyester, polycarbonate, polyamide or polyacrylic oligomer and may optionally further comprise a urethane linkage. The preferred core oligomer is a polyether oligomer optionally further comprising a urethane linkage or a polyester oligomer optionally further comprising a urethane linkage.

[0040] The polyether core oligomer is derived, for example, from ethoxylated or propoxylated glycerol, ethoxylated or propoxylated trimethylopropane, ethoxylated or propoxylated pentaerythritol, ethoxylated or propoxylated ditrimethylolpropane and / or ethoxylated or propoxylated dipentaerythritol.

[0041] The polyester core oligomer can be derived, for example, from diacids and / or triacids or their esters together with polyols such as diols, triols, tetraols, hexols and / or octols. Examples of diacids are adipic acid, succinic acid, ketoglutaric acid and malonic acid. By using, for example, ketoglutaric acid or malonic acid, the structure according to formula (II) can be incorporated into the core oligomer. An example of a triacid is trimellitic acid (or anhydride). Suitable alcohols can be diols such as butanediol, hexanediol, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol; triols such as glycerol, such as trimethylolpropane and its alkoxylated form; tetraols such as pentaerythritol and di(trimethylolpropane) and its alkoxylated form; hexols such as dipentaerythritol and sorbitol and its alkoxylated form; octols such as sucrose and its alkoxylated form.

[0042] Obviously, hydroxy acids and / or esters can also be used to obtain the polyester core oligomers, examples being linear hydroxy acids such as lactic acid, gamma-hydroxybutyric acid, caprolactone, branched hydroxy acids such as citric acid or 2,2-dimethylolpropionic acid. The latter can be used to prepare branched core oligomers, examples of which are Boltorn TM H2004 and H311. The branched amide core is for example Hybrane TM core.

[0043] Polyester core oligomers can also be obtained via the so-called anhydride-oxetane reaction. An example of such a core oligomer can be obtained by using trimellitic anhydride in combination with trishydroxymethyloxetane.

[0044] As previously mentioned, the core oligomer can also be an acrylic oligomer with multiple hydroxyl groups. These hydroxyl-functional oligomers can be prepared, for example, from hydroxyethyl (meth)acrylate via free radical polymerization. One of ordinary skill in the art will recognize that other hydroxyl-functional unsaturated compounds can also be used. Examples are hydroxybutyl monovinyl ether, hydroxyethyl maleimide, caprolactone acrylate, ethoxylated or propoxylated acrylic acid. Hydroxy-functional unsaturated compounds can themselves be oligomerized / polymerized or copolymerized. For the copolymerization, a large amount of other unsaturated compounds are available, such as various (meth)acrylates, styrene, acrylonitrile and vinyl ether.

[0045] In view of reduced mobility, the molecular weight of the oligomeric photoinitiator according to the present invention is preferably higher than 1250 g / mol, more preferably higher than 1500 g / mol.

[0046] The oligomeric photoinitiator according to the present invention preferably comprises free radical polymerizable groups. These free radical polymerizable groups are preferably selected from methacrylate, acrylate, vinyl amide, vinyl ether, vinyl ester, fumarate, itaconate, maleate and any combination thereof. Most preferably, the free radical polymerizable groups are methacrylate and / or acrylate end groups.

[0047] The present invention further relates to a free radical curable composition comprising an oligomeric photoinitiator as described herein above.

[0048] The amount of the oligomeric photoinitiator according to the present invention in the composition can vary over a wide range, such as from 0.001 wt % to up to 99 wt %. Preferably, the amount of the oligomeric photoinitiator according to the present invention is 0.05 wt % to 30 wt % relative to the total weight of the radically curable composition. The amount of the oligomeric photoinitiator according to the present invention is preferably higher than 0.1 wt %, more preferably higher than 0.5 wt % or higher than 1 wt % or higher than 2 wt % and preferably lower than 20 wt % or lower than 15 wt % or lower than 10 wt % relative to the total weight of the radically curable composition. Depending on the amount of radically polymerizable groups in the oligomeric photoinitiator, a higher amount of oligomeric photoinitiator may also be appropriately used. For example, when the photoinitiator according to the present invention contains 2 or more acrylate end groups, the photoinitiator itself can be regarded as a radically curable oligomer and can be used in an amount of 20 to 70 wt %.

[0049] Although in the case where the oligomeric photoinitiator comprises a free radical polymerizable group, no further free radical polymerizable compound is required, the free radical curable composition preferably further comprises one or more free radical curable oligomers having one or more free radical curable ethylenically unsaturated groups, preferably having one or more (meth)acryloyl or vinyl groups. The one or more oligomers having one or more free radical curable ethylenically unsaturated groups preferably have a number average molecular weight (M) equal to or higher than 600 g / mol, particularly 800 to 15,000 g / mol, more particularly 1,000 to 5,000 g / mol. n ), so the number average molecular weight M n Determined as described below.

[0050] The one or more oligomers having one or more free radically curable ethylenically unsaturated groups are present in the free radically curable composition in an amount of preferably at least 10 wt %, or at least 15 wt %, or at least 20 wt %, and at most 80 wt %, or at most 75 wt %, or at most 70 wt %, relative to the total weight of the free radically curable composition.

[0051] Preferably, the free radical curable oligomer is selected from the group consisting of urethane (meth)acrylates, epoxy (meth)acrylates, polyester (meth)acrylates, polyether (meth)acrylates, and any mixtures thereof.

[0052] In order to enhance the properties of the cured polymer prepared using the free radical curable composition of the present invention, such as flexibility, strength and / or modulus, a (meth)acrylate functionalized oligomer may be selected. The (meth)acrylate functionalized oligomer may have 1 to 18 (meth)acrylate groups, in particular 2 to 6 (meth)acrylate groups, more in particular 2 to 6 acrylate groups. The (meth)acrylate functionalized oligomer may have a number average molecular weight equal to or greater than 600 g / mol, in particular 800 to 15,000 g / mol, more in particular 1,000 to 5,000 g / mol. In particular, the (meth)acrylate functionalized oligomer may be selected from (meth)acrylate functionalized urethane oligomers (sometimes also referred to as "urethane (meth)acrylate oligomers", "polyurethane (meth)acrylate oligomers" or "carbamate (meth)acrylate oligomers"). The (meth)acrylate functional oligomers include (meth)acrylate functional epoxy oligomers (sometimes also referred to as "epoxy (meth)acrylate oligomers"), (meth)acrylate functional polyether oligomers (sometimes also referred to as "polyether (meth)acrylate oligomers"), (meth)acrylate functional polydiene oligomers (sometimes also referred to as "polydiene (meth)acrylate oligomers"), (meth)acrylate functional polycarbonate oligomers (sometimes also referred to as "polycarbonate (meth)acrylate oligomers"), and (meth)acrylate functional polyester oligomers (sometimes also referred to as "polyester (meth)acrylate oligomers"), acrylic (meth)acrylate oligomers, and mixtures thereof. Preferably, the (meth)acrylate functional oligomer comprises a (meth)acrylate functional urethane oligomer, more preferably an acrylate functional urethane oligomer. Advantageously, the (meth)acrylate functionalized oligomer comprises a (meth)acrylate functionalized carbamate oligomer having two (meth)acrylate groups, more preferably, an acrylate functionalized carbamate oligomer having two acrylate groups. Exemplary polyester (meth)acrylate oligomers include the reaction product of acrylic acid or methacrylic acid or a mixture thereof or a synthetic equivalent with a hydroxyl-terminated polyester polyol. The reaction process can be carried out so that all or substantially all of the hydroxyl groups of the polyester polyol are (meth)acrylated, particularly when the polyester polyol is difunctional. The polyester polyol can be prepared by the polycondensation reaction of a polyhydroxyl functional component (particularly a diol) with a polycarboxylic acid functional compound (particularly a dicarboxylic acid and anhydride). The polyhydroxyl functional and polycarboxylic acid functional components can each have a straight chain, a branched alicyclic or aromatic structure, and can be used alone or as a mixture.35.

[0053] Examples of suitable epoxy (meth)acrylate oligomers include reaction products of acrylic acid or methacrylic acid or mixtures thereof with epoxy resins (polyglycidyl ethers or esters). The epoxy resins may be selected in particular from bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, bisphenol 6 diglycidyl ether, brominated bisphenol A diglycidyl ether, brominated bisphenol F diglycidyl ether, epoxy novolac resins, hydrogenated bisphenol A diglycidyl ether, hydrogenated bisphenol F diglycidyl ether, hydrogenated bisphenol S diglycidyl ether, 3,4-epoxycyclohexylmethyl 3,4'-epoxycyclohexanecarboxylate, 2-(3,4-epoxycyclohexyl) ... Hexyl-5,5-spiro-3,4-epoxy)cyclohexane-1,4-dioxane, bis(3,4-epoxycyclohexylmethyl)adipate, vinylcyclohexene oxide, 4-vinylepoxycyclohexane, bis(3,4-epoxy-6-methylcyclohexylmethyl)adipate, 3,4-epoxy-6-methylcyclohexyl 1-3',4-epoxy-6-methylcyclohexanecarboxylate, methylenebis(3,4-epoxycyclohexane), bicyclo Pentadiene diepoxide, di(3,4-epoxycyclohexylmethyl) ether of ethylene glycol, ethylenebis(3,4-epoxycyclohexanecarboxylate), 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, glycerol triglycidyl ether, trimethylolpropane triglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, polyglycidyl ether of polyether polyols obtained by adding one or more alkylene oxides to aliphatic polyols such as ethylene glycol, propylene glycol and glycerol, diglycidyl esters of aliphatic long-chain dibasic acids, monoglycidyl ethers of aliphatic higher alcohols, phenol, cresol, butylphenol or monoglycidyl ethers of polyether alcohols obtained by adding alkylene oxides to these compounds, glycidyl esters of higher fatty acids, epoxidized soybean oil, epoxybutyl stearic acid, epoxyoctyl stearic acid, epoxidized linseed oil, epoxidized polybutadiene, and the like.

[0054] Suitable polyether (meth) acrylate oligomers include, but are not limited to, condensation products of acrylic acid or methacrylic acid or their synthetic equivalents or mixtures thereof with polyether alcohols, which are polyether polyols (e.g., polyethylene glycol, polypropylene glycol, or polytetramethylene glycol). Suitable polyether alcohols can be straight-chain or branched materials containing ether bonds and terminal hydroxyl groups. Polyether alcohols can be prepared by ring-opening polymerization of cyclic ethers (e.g., tetrahydrofuran) or alkylene oxides (e.g., ethylene oxide and / or propylene oxide) with starting molecules. Suitable starting molecules include water, polyhydroxy functional materials, polyester polyols, and amines.

[0055] Urethane (meth) acrylate oligomers (sometimes also referred to as "urethane (meth) acrylate oligomers") suitable for use in the curable compositions of the present invention include urethanes based on aliphatic, cycloaliphatic and / or aromatic polyester polyols and polyether polyols and aliphatic, cycloaliphatic and / or aromatic diisocyanates, and terminated with (meth) acrylate end groups. Suitable urethane (meth) acrylate oligomers include, for example, urethane di- and tetra-acrylate oligomers based on aliphatic polyesters, urethane di- and tetra-acrylate oligomers based on aliphatic polyethers, and urethane di- and tetra-acrylate oligomers based on aliphatic polyesters / polyethers. Polyurethane (meth) acrylate oligomers can be prepared by reacting aliphatic, alicyclic and / or aromatic polyisocyanates (e.g., diisocyanates, triisocyanates) with OH-group terminated polyester polyols, polyether polyols, polycarbonate polyols, polycaprolactone polyols, polyorganosiloxane polyols (e.g., polydimethylsiloxane polyols) or polydiene polyols (e.g., polybutadiene polyols) or combinations thereof to form isocyanate functional oligomers which are then reacted with hydroxyl functional (meth) acrylates (e.g., hydroxyethyl acrylate or hydroxyethyl methacrylate) to provide terminal (meth) acrylate groups. For example, polyurethane (meth) acrylate oligomers can contain two, three, four or more (meth) acrylate functional groups per molecule. Other addition sequences can also be used to prepare polyurethane (meth) acrylates, as is known in the art. For example, a hydroxyl-functional (meth)acrylate can first be reacted with a polyisocyanate to obtain an isocyanate-functional (meth)acrylate, which can then be reacted with a hydroxyl-terminated polyester polyol, a polyether polyol, a polycarbonate polyol, a polycaprolactone polyol, a polydimethylsiloxane polyol, a polybutadiene polyol, or a combination thereof. In yet another embodiment, a polyisocyanate can first be reacted with a polyol including any of the above-mentioned types of polyols to obtain an isocyanate-functional polyol, which can then be reacted with a hydroxyl-functional (meth)acrylate to prepare a polyurethane (meth)acrylate. Alternatively, all components can be combined and reacted simultaneously.

[0056] Suitable acrylic (meth) acrylate oligomers (sometimes also referred to in the art as "acrylic oligomers") include oligomers that can be described as materials having an oligomeric acrylic backbone that is functionalized with one or more (meth) acrylate groups (which can be located at the end of the oligomer or on the side chains of the acrylic backbone). The acrylic backbone can be a homopolymer, a random copolymer, or a block copolymer comprising repeating units of acrylic monomers. The acrylic monomers can be (meth) acrylates of any monomer, such as C1-C6 alkyl (meth) acrylates, and functionalized (meth) acrylates, such as (meth) acrylates with hydroxyl, carboxylic acid and / or epoxy groups. Acrylic (meth)acrylate oligomers can be prepared using any method known in the art, for example by oligomerizing monomers at least a portion of which are functionalized with hydroxyl, carboxylic acid and / or epoxy groups (e.g., hydroxyalkyl (meth)acrylates, (meth)acrylic acid, glycidyl (meth)acrylate) to obtain a functionalized oligomer intermediate, which is then reacted with one or more (meth)acrylate-containing reactants to introduce the desired (meth)acrylate functionality.

[0057] The curable composition of the present invention may comprise 10 to 80 wt %, in particular 15 to 75 wt %, more particularly 20 to 70 wt % of the (meth)acrylate functional oligomer, relative to the total weight of the free-radically curable composition.

[0058] For viscosity considerations, the use of reactive diluents can be beneficial. Reactive diluents refer to compounds that can reduce the viscosity of the formulation while being capable of free radical copolymerization. Therefore, the present invention also relates to free radical curable compositions comprising reactive diluents. One or more diluents having one or more free radical curable ethylenically unsaturated groups are present in the free radical curable composition in an amount of at least 1 wt %, or at least 5 wt %, or at least 10 wt %, and at most 85 wt %, or at most 80 wt %, or at most 75 wt %, or at most 70 wt % relative to the total weight of the free radical curable composition.

[0059] As reactive diluents, various acrylic, methacrylic or vinyl functional monomers can be used. Suitable examples are, for example, diacrylates or dimethacrylates of diols or polyether diols, such as propoxylated neopentyl glycol diacrylate, 1,6-hexanediol diacrylate, dipropylene glycol diacrylate (DPGDA), tripropylene glycol diacrylate (TPGDA), diethylene glycol diacrylate, triethylene glycol diacrylate, triethylene glycol dimethacrylate, neopentyl glycol diacrylate, 1,4-butanediol diacrylate (e.g. SR213), alkoxylated aliphatic diacrylates (e.g. SR9209A), alkoxylated hexanediol diacrylates (e.g. SR561, SR562, SR563, SR564 from Sartomer Co., Inc.), polyethylene glycol (200) diacrylate (SR259), polyether glycol-200-diacrylate, PEG300-diacrylate. Acrylates, polypropylene glycol diacrylate, ethoxylated (3) bisphenol A diacrylate, BDDA butanediol diacrylate, BDDMA butanediol dimethacrylate or higher functional acrylates, such as trimethylolpropane triacrylate (TMPTA), ethoxylated trimethylolpropane triacrylate, TMP3EOTA ethoxylated (3) trimethylolpropane triacrylate, TMP6EOTA ethoxylated (6) trimethylolpropane triacrylate, propoxylated trimethylolpropane triacrylate, pentaerythritol triacrylate, pentaerythritol (4)-propoxylated triacrylate, pentaerythritol tetraacrylate, ethoxylated or propoxylated neopentyl glycol, propoxylated (4) glycerol triacrylate, trifunctional monomers, such as the Laromer types from BASF or the Ebecryl from Allnex 2047 or Ebecryl 12, di-trimethylolpropane tetraacrylate, dipentaerythritol pentaacrylate (Di-PEPA), dipentaerythritol hexaacrylate (DPHA). Examples of vinyl compounds are compounds such as butanediol divinyl ether, or N-vinyl caprolactam as a monofunctional compound. Although monofunctional (meth)acrylates such as lauryl (meth)acrylate, phenoxyethyl (meth)acrylate, etc. can also be used, for low mobility, reactive diluents with at least two free radical-curable ethylenically unsaturated groups are preferably used. Of course, mixtures can also be used.

[0060] In a preferred embodiment of the present invention, the oligomeric photoinitiator further comprises one or more free radical curable ethylenically unsaturated groups, preferably one or more (meth)acryloyl or vinyl groups, more preferably at least two (meth)acryloyl groups; and

[0061] The free radical curable composition optionally further comprises one or more oligomers having one or more free radical curable ethylenically unsaturated groups, preferably having one or more (meth)acryloyl or vinyl groups; and

[0062] The free radical curable composition further comprises one or more diluents having one or more free radical curable ethylenically unsaturated groups, preferably, the one or more diluents have at least two free radical curable ethylenically unsaturated groups; and

[0063] The free radical curable composition comprises

[0064] (i) an oligomeric photoinitiator in an amount of 20 to 70% by weight,

[0065] (ii) oligomers in an amount of 0 to 40% by weight,

[0066] (iii) a diluent in an amount of 10 to 60% by weight,

[0067] The amounts are given therein relative to the total weight of (i) to (iii).

[0068] According to another aspect, the present invention relates to a free radical curable ink composition or a free radical curable coating composition comprising: a) at least one binder, b) at least one ethylenically unsaturated compound selected from monomers and / or oligomers, and one or more oligomeric photoinitiators of the present invention.

[0069] If the radically curable composition is a radically curable ink composition, it contains at least one pigment. Preferably, the amount of the pigment is preferably between 0.5 and 50% by weight, and more preferably between 3 and 20% by weight, based on the total amount of the radically curable ink composition (i.e., the composition before curing). The curable ink composition preferably contains 0.5 to 50% by weight, and more preferably 3 to 20% by weight of the pigment.

[0070] In addition to the oligomeric photoinitiators according to the present invention, other initiators and various other additives may also be used. Examples of these additives include, but are not limited to, those selected from the group consisting of rheological additives, adhesion promoters, defoamers, slip agents, wetting agents, leveling agents, brighteners, waxes, wetting agents, curing agents, chelating agents, additional photoinitiators, amine synergists, inhibitors, desiccants, stabilizers, emulsifiers, wear resistant additives, plasticizers, antistatic additives, matting agents, and any combination of two or more of the above additives.

[0071] The free radical curable ink composition or the free radical curable coating composition can be formulated to be suitable for any known printing technology, such as offset printing, lithography, intaglio printing, flexographic printing, gravure printing, screen printing, digital printing, inkjet printing, pad printing, transfer printing, letter printing, etc.

[0072] The present invention further relates to a method for free radical curing a free radical curable composition, the method comprising the steps of:

[0073] (1) preparing or providing a free radical curable composition as described herein, and

[0074] (2) Radically curing the radically curable composition using a light source.

[0075] The light source is preferably a UV light source that emits UV light in at least one of the UVA, UVB and UVC ranges, or an LED light source that emits light in the range of 350 to 450 nm.

[0076] The method preferably includes the step of applying the free radical curable composition to a substrate prior to free radical curing thereof.

[0077] The present invention further relates to a coating or ink obtained by the following steps:

[0078] (1) preparing or providing a free radical curable coating or ink composition as described herein above,

[0079] (2) applying a free radical curable coating or ink composition to a substrate, and

[0080] (3) Using a light source to free radical cure a radical-curable coating or ink composition.

[0081] The invention will now be illustrated by reference to the following examples. Unless otherwise indicated, all parts, percentages and ratios are by weight.

[0082] Determination of viscosity

[0083] Viscosity was measured on an Anton Paar Physica MCR301 rheometer equipped with 2.5 cm diameter / 1° cone / plate geometry at 25°C and a shear rate of 100 s-1.

[0084] Molecular weight determination by GPC

[0085] The number average molecular weight (Mn) and weight average molecular weight (Mw) were determined by SEC at 40 °C with a flow rate of 1 mL / min using a set of molecular weights ranging from 500 to up to 7 × 10 6 g / mol polystyrene standards were used for calibration and stabilized tetrahydrofuran [THF, containing 0.007-0.015% w / w butylhydroxytoluene (BHT)] modified with 0.8% acetic acid was used as the eluent. More specifically, 50 mg of a polyester resin solid sample was dissolved in 5 mL of the eluent at room temperature without shaking for 16 hours. 10 μL of the thus prepared solution was injected into the system for measurement. SEC measurements were performed on a Waters APC TM The system consisted of the following components: i) a Waters UPLC RI refractive index detector, ii) Waters APC TM Column Manager–S, equipped with three different APC TM Chromatographic column( and aperture), I / d = 150 / 4.6 mm, and filled with 2.5 ( and Column) or 1.7μm( Chromatographic column)(1μm=1×10 -6 m) of particle size, (supplied by Waters Corporation), iii) APC TM Sample Manager–pFTN injection system, and iv) APC TM p-Isocratic Solvent Manager isotonic pump. Mn and Mw were determined by using Empower 3 software from Waters.

[0086] Photo reactivity was determined using the Photo DSC standard procedure

[0087] These analyses were performed in a nitrogen atmosphere using approximately 30 mg of the formulation using a microscope equipped with an Excelitas Omnicure LX 500 385 nm LED source (1.7 W / cm 2 ) was performed using a Mettler Toledo DSC3+ Photo DSC fixture.

[0088] The following protocol was used: After calibrating the sample under nitrogen for 150 seconds, the sample was irradiated for 150 seconds. This was followed by a 50 second dark period and then a second irradiation for 50 seconds. The second irradiation was performed to verify that complete conversion had been achieved during the first irradiation. Reactivity was expressed as the time to maximum heat flow (seconds) and the maximum double bond conversion rate (in mmol s - 1 l -1 The units are calculated from the maximum heat flow (W / g) using 78.5 kJ / mol as the reaction enthalpy of acrylate and assuming a density of 1 kg / l).

[0089] Reactivity was measured using a UV device (Rig)

[0090] 100 μm thick films were prepared from the formulations on glass plates and cured on a Fusion UV unit equipped with a high power water-cooled 395 nm LED (16 W / cm 2 ), using 0.8 J / cm 2 total dose, or with a Fusion F600 D bulb (6W / cm 2 ), using 1 J / cm 2 The total dose is 200 mg / ml, which is determined using an EIT power puck II unless otherwise stated. After curing, the conversion of the acrylate was determined using IR spectroscopy. The error in the conversion measurement is estimated to be about + 5%.

[0091] Reactivity determination using RT-DMA: Maximum modulus (G') and T30%, modulus maximum

[0092] The value of the maximum modulus (G') was determined according to the following procedure described herein. The hardware / equipment used in this procedure is as follows:

[0093] Rheometer + Accessories

[0094] ARESG2-Rheometer (Manufacturer: TA Instruments)

[0095] APS temperature control device (Advanced Peltier System)

[0096] APS standard plate (lower geometry)

[0097] ARESG2 UV curing accessories (upper plate fixture, UV hood back plate & access door, collimating optical lens)

[0098] Φ20mm acrylic plate, upper plate fixture with UV curing option (upper geometry)

[0099] Silverline UV radiometer, UV light sensor (non-calibrated), UV sensor geometry and disposable plate holder

[0100] UV light source & others

[0101] Omnicure LX500 with attached 385nm LED and 8mm lens

[0102] Moeller Easy 412-DC-TC control relay (trigger box)

[0103] UV PowerPuckII (Electronic Instrumentation & Technology, calibrated)

[0104] Subsequently, the above hardware was set up and arranged according to the following steps. First, UV curing measurements were performed on an ARES G2 rheometer (TAInstruments). The rheometer was equipped with an APS temperature control device, an APS standard flat plate as the lower geometry, and an ARES G2 UV curing option. The upper geometry used was the upper plate fixture in the ARES G2 UV curing option, which was combined with a 20 mm diameter acrylic plate. As a UV light source, an Omnicure LX500 spot curing system was used in combination with a 385 nm LED (8 mm lens). The 385 nm LED was then inserted into the collimating optical lens of the ARES G2 UV curing accessory. The collimating lens was secured to the light shield and aligned with the upper UV geometry mirror, and then the alignment screws were tightened. In order to accommodate the 385 nm UV-LED, the diameter of the original 5 mm light guide bracket component of the collimating lens was increased to 12 mm.

[0105] The Omnicure LX500 spot curing system was then connected to the digital I / O connector on the ARESG2 via a Moeller Easy412-DC-TC control relay. This control relay acts as a trigger box for the UV light source. The delay time of the trigger was set to 1.5 seconds, which means that after the data collection of the modulus measurement started on the ARESG2, the 385nm UV-LED was automatically turned on with a delay of 1.5 seconds. The light intensity was set to 95%, and the duration of the UV light was fixed to 128 seconds.

[0106] Alignment of UV light: Alignment was performed before installing the APS temperature control unit. The UV sensor geometry was attached to a disposable plate holder and mounted as the lower geometry. The UV light sensor connected to the Silverline UV radiometer was positioned in the outer hole of the UV sensor geometry. The upper geometry was positioned on top of the UV light sensor by applying an axial force of about 100 grams. The light intensity was then measured at four positions by rotating the lower geometry by about 90° between each consecutive measurement. In order to make the light distribution at each point as equal as possible, the alignment of the collimating lens was subsequently adjusted using the alignment screws on the light shield. The difference in light intensity at the four different positions was kept below 10%.

[0107] Determination of light intensity: Prior to the RT-DMA measurement, the UV intensity was measured with the aid of a calibrated UV Power Puck II. To achieve this, the sensor of the UV Power Puck II was positioned directly below the surface of a 20 mm acrylic plate in the upper plate fixture (distance <0.5 mm), with the surface of the acrylic plate completely covering the sensor surface. Next, the Omnicure LX500 UV source (intensity value set to 95%) was manually turned on for 10 seconds. During this 10 second interval, the UVA2 intensity (i.e., radiation between 380-410 nm wavelengths) was measured using the UVPowerPuckII instrument. The measured UVA2 intensity was determined to be 60-70 mW / cm 2 The actual recorded value is 67mW / cm 2 .

[0108] Determination of the actual delay time: When starting measurement, there is a delay between the start of data sampling and the start of UV irradiation. In the settings of the Moeller Easy412-DC-TC control relay, the delay is set to 1.5 seconds, which means that UV irradiation starts 1.5 seconds after the start of data sampling.

[0109] [The actual delay time was measured to be 1.519 seconds using a light dependent resistor (LDR) and an oscilloscope (PicoScope 3424). The delay time of 1.519 seconds is the measured average of 10 individual measurements with a standard deviation of 0.004 seconds.]

[0110] [RT-DMA Measurements: RT-DMA UV cure measurements were then performed using an ARESG2 rheometer paired with an Advanced Peltier System (APS) as a temperature control device, an APS plate, and an ARESG2 UV cure accessory configuration. A 385nm LED with an 8mm lens connected to an Omnicure LX500 was used as the UV light source.

[0111] [Sample loading: Before loading each corresponding sample, the temperature of the bottom plate is set to 50°C. When the temperature reaches 50°C, the upper parallel plate is balanced to the set temperature of 50°C by applying an axial force between 200-400 grams to make the surface of the upper plate (which is an acrylic plate with a thickness of 20mm) contact the lower plate (i.e., there is a gap of 0mm with the lower plate). After the initial contact, the system is allowed to further balance its temperature for at least 5 minutes. Next, a zero fixture procedure is performed according to a known method to determine the position of gap = 0. After determining the position of gap = 0, the upper plate is moved to a position 10mm away. Then, a portion of each corresponding sample is transferred to the center of the lower plate with the tip of a small scraper, and then the upper geometry is lowered to the position of gap = 0.120mm. The amount of sample must be sufficient to ensure that after the upper geometry is lowered to the reduced gap, the excess sample will be pushed out of the gap, thereby covering the entire periphery of the upper parallel plate. Next, the excess sample that had shifted out of the gap was removed and the upper geometry was further lowered to the measurement position (gap = 0.100 mm). After loading into the measurement position, the sample temperature was allowed to equilibrate to 50°C. Finally, when the sample temperature was measured to be stable between 49.90 and 50.10°C, the measurement process was started by activating the trigger box (MoellerEasy412-DC-TC) and using the interface and interconnections provided by the TRIOS software package.

[0112] [Measurement: The actual UV-curing RT-DMA measurement is a so-called "fast sampling" measurement performed at 50°C. That is, it is an oscillating fast sampling at 50°C for 128 seconds duration, with a strain of 1%, a rotation speed of 52.36 rad / s, and a measurement frequency of 50 points per second (i.e., 0.020 seconds between each consecutive measurement point).

[0113] The measurement was then started via the Start button in the TRIOS software. After data sampling began, the rheometer sent a signal to the control relay, which in turn activated the Omnicure LX500 UV light source to irradiate the corresponding sample after the aforementioned 1.519 second delay after data sampling began. As described above, during the 128 second fast sampling data collection period, the sample was irradiated with 385 nm UV light (intensity 70 mW / cm 2 ) irradiation. After the measurement is completed, the TRIOS data file is exported to Microsoft Excel. Then, the sample is removed and the plate is subsequently cleaned thoroughly with ethanol before loading the next sample.

[0114] Data Analysis: As previously described, TRIOS data was exported to Microsoft Excel. Excel was used to plot graphs and calculate various parameters to characterize the cure speed performance of the tested formulations, as described below. The graphs include those corresponding to the storage modulus (G') as a function of UV time (UV time was calculated by subtracting the delay time (1.519 seconds) from the actual time for each individual data point), and the relative storage modulus (rel G') as a function of UV time (rel G' was calculated by the quotient of the G' value measured at a specific UV time and the maximum G' value obtained during the cure measurement). The maximum value observed in the graph in the G' graph was determined by taking the average of the G' values ​​between 110 seconds and 120 seconds and reported in the column headed "Maximum G'" in Table 6 below.

[0115] Also, characteristic parameters include: (1) time to achieve 30% increase in total storage modulus (G'), and (2) average G' 110-120 seconds (average storage modulus values ​​of 6 data points near the end of the cure measurement). The results of (1) for each formulation are reported in Table 6 below in the column headed T30%, Modulus Max. Example

[0116] These examples illustrate embodiments of the present invention. Table 1 describes the various components used to prepare the photoinitiators and free radical curable compositions used in this example. Table 2 describes the relative amounts of the reagents described in Table 1 used to synthesize the photoinitiators used in this example. Tables 3 to 6 report the photoreactivity of the photoinitiators.

[0117] Table 1: Components for preparing photoinitiators and free radical curable compositions

[0118]

[0119]

[0120] Synthesis of Oligomeric Photoinitiators OPI 1-8 (Table 2) - Typical Procedure

[0121] OPI 1:

[0122] Step 1) 16.7 g of adipic acid (AdA), 102.9 g of propoxylated glycerol (POG), 240 g of toluene and 0.74 g of methanesulfonic acid MSA were charged into a 500 ml reactor equipped with a stirrer, a nitrogen inlet and a Dean-Stark configuration. The reaction was heated to reflux under a gentle nitrogen stream and maintained at this temperature until no more reaction water was formed (4 hours).

[0123] Next (step 2), 40.2 g of pyruvic acid were added and the reaction mixture was heated to reflux under a gentle nitrogen stream and maintained at this temperature until no more water of reaction was formed (4 hours). Next, all toluene was removed by distillation under reduced pressure at a temperature of 95°C. Next, 2.7 g of Epikote TM 828, and the reaction was stirred for another 30 minutes, and after cooling, OPI 1 was obtained, which was -1 The viscosity is 4Pa . s.

[0124] The synthesis of oligomeric photoinitiators OPI 2-8 was performed similarly to OPI1, except for the amounts of components reported in Table 2.

[0125] For example, the structural formula of OPI5 with the ideal structure (KGA)1(POG)2(PA)4 is:

[0126]

[0127] Among them, a+b+c=5.

[0128] Synthesis of Acrylate-functional Oligomeric Photoinitiators OPI9 and OPI 10

[0129] OPI9: The synthesis was carried out similarly to OPI 7, except that in step 2, 24.9 g of pyruvic acid, 4.1 g of acrylic acid and 0.07 g of methoxyphenol were added instead of 29.9 g of pyruvic acid.

[0130] OPI 10: Similar to OPI 9, using the amounts reported in Table 2, with 0.07 g of methoxyphenol.

[0131] Synthesis of Urethane Acrylate Functional Oligomer Photoinitiator OPI11

[0132] A 100 ml reactor equipped with a mechanical stirrer and a dry air inlet was charged with 20 g of OPI 7 and 0.05 g of DBTDL. Next, 1.1 g of KAoi was added under vigorous stirring and a gentle dry air flow. The reaction mixture was heated to 60°C with stirring and maintained at this temperature until the isocyanate was completely reacted (about 30 minutes, no NCO was visible in IR), thereby obtaining the urethane acrylate functional oligomer photoinitiator OPI 11. The ideal structure is

[0133] (KGA) (3-x) (POG)4(PA) (6-y) KAoi (x+y＝1) , because both α-ketoglutarate and pyruvate can be enolized.

[0134] Synthesis of Oligomeric Photoinitiator OPI12

[0135] Step 1) 249.7 g of hexahydrophthalic acid (HHPZA), 250.1 g of trimethylolpropane oxetane (TMPO) and 0.250 g of sodium acetate (500 ppm) were charged into a 1-liter reactor equipped with a stirrer, a nitrogen inlet and a cooler. The reaction was heated to 170° C. under a gentle nitrogen stream and maintained at this temperature for 17 hours. When the acid value was less than 20, the resin was discharged.

[0136] Step 2) A 500 ml reactor equipped with a stirrer, nitrogen inlet and Dean Stark configuration was charged with 92.1 g of the hydroxy-functional resin from step 1, 52.6 g of pyruvic acid, 0.69 g of MSA and 221.8 g of toluene. The reaction was heated to reflux under a gentle nitrogen stream and maintained at this temperature until no more reaction water was formed (6 hours).

[0137] Next, all toluene was removed by vacuum distillation at 95°C. Next, 2.5 g of Epikote TM 828, and the reaction was stirred for another 30 minutes, and OPI12 was obtained as a solid after cooling.

[0138] Synthesis of Oligomeric Photoinitiator OPI13

[0139] To a 500 ml reactor equipped with a stirrer, nitrogen inlet and Dean-Stark formulation was added 123.7 g of high Mw propoxylated glycerol (Voranol CP1055, PO17), 32.7 g of pyruvic acid, 240 g of toluene and 0.77 g of MSA. The reaction was heated to reflux under a gentle nitrogen stream and maintained at that temperature until no more reaction water was formed (4 hours). Next, all toluene was removed by vacuum distillation at a temperature of 95°C. Then 2.7 g of Epikote TM 828, and the reaction was stirred for another 30 minutes, and after cooling, OPI 13 was obtained, which was -1 The viscosity is 0.33 Pa·s.

[0140] Synthesis of comparative linear oligomer example (Liska) Comp L1

[0141] The synthesis was carried out similarly to (R. Taschner, P. Gauss, P. Knaack, R. Liska, "Biocompatible Photoinitiators Based on Poly-α-ketoesters", Journal of Polymer Science, Vol. 58, pp. 242-253, (2020), except on a similar scale to OPI 1-9) using 100.6 g of α-ketoglutaric acid, 89.5 g of hexanediol (1.1 molar equivalents), 270 g of toluene and 0.7 g of MSA. The resulting solid comparative initiator L1 had an M of 2.6 kg / mol. n and 9.2 kg / mol M w . Tm is 46-54℃ (1.1 equivalent)

[0142] Synthesis of comparative linear oligomer example (Liska) Comp L2

[0143] The procedure of L1 was repeated using 98.9 g of α-ketoglutaric acid, 80.70 g of hexanediol (1.01 molar equivalent, similar to US2020 / 0231531), 220 g of toluene and 0.26 g of MSA. After precipitation and evaporation of the residual solvent, L2 was obtained in the form of a white powder. The resulting comparative initiator L2 had an M of 5.1 kg / mol. n and 17.2 kg / mol M w . Tm is 40-51°C (1.01 equivalent)

[0144] Synthesis of comparative linear oligomer example (Liska) Comp L3

[0145] The procedure of L1 was repeated using 100.6 g of α-ketoglutaric acid, 78.6 g of hexanediol (0.96 molar equivalents), 270 g of toluene, and 0.7 g of MSA. Using this equivalent relationship, an acid-functional linear polyester was prepared. The resulting solid comparative example L3 had an M of 3.4 kg / mol. n and 12.1 kg / mol M w . Tm is 52-59°C (0.96 equivalent)

[0146]

[0147]

[0148] Synthesis of carbamate oligomer 1

[0149] First, the reactor is purged with dry lean air. Then, 2.19 parts of BHT are added to the reactor (equipped with an agitator, air inlet, dropping funnel and condenser), followed by 52.76 parts of TDI and then 0.02 parts of acrylic acid. After loading, the reactor is heated to 45°C. Then, half of the specified amount of catalyst (e.g. 0.06g of bismuth neodecanoate) and then 35.43 parts of HEA are charged into the reactor while stirring. After waiting for one (1) hour for the reaction to start, the temperature is then raised to 60°C. At 60°C, 700 parts of PPG4000 and a second part of catalyst (e.g. 0.07g) are added, after which the reaction temperature is raised to 85°C and then further maintained for an additional two (2) hours.

[0150] After this additional two (2) hours of reaction time, the amount of isocyanate (NCO) content is measured by potentiometric titrator to ensure that it is less than 0.1% relative to the total weight of the composition. If the isocyanate content is not less than this value, the mixture is returned to the reaction chamber, and this step is repeated with additional increments of 15 minutes (also at 85°C) and checked again until the isocyanate content falls within the desired range. Finally, the resulting synthetic oligomer is slowly cooled and discharged for use. The resulting oligomer 1 has the desired structure HEA-TDI-PPG4000-TDI-HEA.

[0151] Preparation of formulations

[0152] Each of the formulations described in Tables 3-6 below was prepared by using a Speedmixer TM A 50 ml mixing cup was prepared by conventional methods. A total of 10 g of the components were added to the mixing cup. The mixing cup was then closed and placed in a Speedmixer. TM The DAC150FVZ was mixed vigorously for 5 minutes, stopped, and mixed again by the same method for an additional 5 minutes.

[0153] Examples 1-2 and Comparative Experiment A

[0154] In a speed mixer, the formulations were prepared using 99.5 parts of Neorad U25-20D and 0.5 parts of various initiators. Curing was carried out on a UV device. The results are shown in Table 3 below.

[0155] Table 3 :UV device curing

[0156]

[0157]

[0158] These examples clearly show that the structures according to the invention enable a more efficient curing process compared to the linear polymer L1. This high efficiency is particularly surprising when comparing the amount of active chromophores present in the formulation. Even with less active chromophores, curing with the OPI according to the invention proceeds much more efficiently.

[0159] This efficient cure was further demonstrated by using 0.5 parts of benzophenone (27.4 mmol chromophore / kg) and 0.2 parts of ethyl 4-N,N-dimethylaminobenzoate (amine synergist) as a well-known Type II initiation system. After curing with a D-bulb, a conversion of 82% was observed.

[0160] Examples 3-15 and Comparative Experiments BD

[0161] Formulations were prepared in a speed mixer using 70 parts of urethane oligomer 1, 30 parts of phenoxyethyl acrylate and 0.5 parts of various initiators. Curing was performed using photo-DSC using a 385 nm LED. The results are shown in Table 4.

[0162] Table 4 :Photo-DSC curing

[0163]

[0164]

[0165] This again shows the surprisingly high efficiency of the oligomeric photoinitiators according to the invention compared to L1-L3.

[0166] Examples 16-26 and Comparative Experiments EG

[0167] In a speed mixer, the formulations were prepared using 70 parts of urethane oligomer 1, 30 parts of phenoxyethyl acrylate and 5 parts of various initiators. Curing was done on a UV unit using a 395 nm LED with only 0.4 J / cm 2 This low dose is used to ensure that complete conversion is not achieved.

[0168] For the comparative examples, the formulation had to be heated to 50° C. before mixing in the speed mixer. Otherwise, a clear formulation could not be obtained.

[0169] Table 5 : Reactivity on UV device using 395nm LED

[0170]

[0171]

[0172] Examples 27-38 and Comparative HK Reactivity RT-DMA

[0173] In a speed mixer, the formulations were prepared using 70 parts of urethane oligomer 1, 30 parts of phenoxyethyl acrylate and 5 parts of various initiators. An intensity of 70 mW / cm was used in RT-DMA. 2 For the comparative examples, the formulation had to be heated to 50°C before mixing in the speed mixer. Otherwise, a clear formulation could not be obtained.

[0174] In the case of amines, formulations were prepared using 70 parts of urethane oligomer 1, 30 parts of phenoxyethyl acrylate and 5 parts of various initiators and 5 parts of ethyl 4-N,N-dimethylaminobenzoate.

[0175] Table 6

[0176]

[0177]

[0178] *Not reaching plateau value, incomplete cure modulus to low. **@Values ​​based on modulus at 120 seconds.

Claims

1. Oligomeric photoinitiators according to formula (I) in m is equal to or greater than 3, R1, R2 and R3 are independently selected from H or linear or branched C 1- C6 alkyl, and The oligomeric photoinitiator has a weight average molecular weight M higher than 1000 g / mol as determined by GPC (THF). w , wherein the weight average molecular weight M w The assay was performed as described in the instructions.

2. The oligomeric photoinitiator according to claim 1, wherein the oligomeric photoinitiator has a weight average molecular weight M greater than 1250 g / mol, more preferably greater than 1500 g / mol. w .

3. The oligomeric photoinitiator according to any one of the preceding claims, wherein R1, R2 and R3 are independently selected from H or CH3, more preferably R1, R2 and R3 are H.

4. The oligomeric photoinitiator according to any one of the preceding claims, wherein m is equal to or greater than 5, more preferably m is equal to or greater than 8.

5. The oligomeric photoinitiator according to any one of the preceding claims, wherein the oligomeric photoinitiator comprises 1 to 10 groups according to formula (II) wherein n is 0 to 6, preferably n is 2 or 3, and more preferably n is 2.

6. The oligomeric photoinitiator according to any one of the preceding claims, wherein the oligomeric photoinitiator is obtained by a process comprising at least the following steps: (1) providing a core oligomer having at least m (m≥3) terminal OH functional groups, (2) esterifying (transesterifying) the m terminal OH functional groups of the core oligomer with a compound according to formula (Ib): Wherein R4 is H or C1-C4 alkyl, preferably R4 is H; and R1, R2 and R3 are as described in claim 1 or 3.

7. The oligomeric photoinitiator according to any one of the preceding claims, wherein the oligomeric photoinitiator comprises free radical polymerizable groups.

8. The oligomeric photoinitiator according to any one of the preceding claims, wherein the free radical polymerizable group is selected from methacrylate, acrylate, vinyl amide, vinyl ether, vinyl ester, fumarate, itaconate, maleate and any combination thereof, more preferably the free radical polymerizable group is methacrylate and / or acrylate.

9. The oligomeric photoinitiator according to any one of the preceding claims, wherein the oligomer is highly branched, more preferably hyperbranched.

10. A free-radically curable composition comprising at least one oligomeric photoinitiator according to any one of claims 1 to 9.

11. The free radical curable composition according to claim 10, wherein the oligomeric photoinitiator is present in an amount of 0.05 to 30 wt%, preferably 0.1 to 20 wt%, more preferably 0.1 to 15 wt%, relative to the total weight of the free radical curable composition.

12. The free radical curable composition according to claim 10 or 11, wherein the free radical curable composition further comprises one or more oligomers having one or more free radical curable ethylenically unsaturated groups, preferably having one or more (meth)acryloyl or vinyl groups.

13. The free radical curable composition according to claim 12, wherein the one or more oligomers having one or more free radical curable ethylenically unsaturated groups are independently selected from urethane (meth) acrylate oligomers, epoxy (meth) acrylate oligomers, polyether (meth) acrylate oligomers and polyester (meth) acrylate oligomers, more preferably the one or more oligomers having one or more free radical curable ethylenically unsaturated groups are urethane (meth) acrylate oligomers.

14. The free radical curable composition according to claim 12 or 13, wherein the one or more oligomers having one or more free radical curable ethylenically unsaturated groups have a number average molecular weight (M) equal to or higher than 600 g / mol, in particular from 800 to 15,000 g / mol, more in particular from 1,000 to 5,000 g / mol. n ), wherein the number average molecular weight M n The assay was performed as described in the instructions.

15. The free radical curable composition according to any one of claims 12 to 14, wherein the one or more oligomers having one or more free radical curable ethylenically unsaturated groups are present in the free radical curable composition in an amount of at least 10 wt%, or at least 15 wt%, or at least 20 wt%, and at most 80 wt%, or at most 75 wt%, or at most 70 wt%, relative to the weight of the entire free radical curable composition.

16. The free radical curable composition according to any one of claims 10 to 15, wherein the free radical curable composition further comprises one or more diluents having one or more free radical curable ethylenically unsaturated groups, preferably at least two free radical curable ethylenically unsaturated groups.

17. The free radical curable composition of claim 16, wherein the one or more diluents having one or more free radical curable ethylenically unsaturated groups are present in the free radical curable composition in an amount of at least 1 wt%, or at least 5 wt%, or at least 10 wt%, and at most 85 wt%, or at most 80 wt%, or at most 70 wt%, relative to the total weight of the free radical curable composition.

18. The free radical curable composition of claim 10, wherein The oligomeric photoinitiator further comprises one or more free radical curable ethylenically unsaturated groups, preferably one or more (meth)acryloyl or vinyl groups, more preferably at least two (meth)acryloyl groups; The free radical curable composition optionally further comprises one or more oligomers having one or more free radical curable ethylenically unsaturated groups, preferably having one or more (meth)acryloyl or vinyl groups; and The free radical curable composition further comprises one or more diluents having one or more free radical curable ethylenically unsaturated groups, preferably having at least two free radical curable ethylenically unsaturated groups; and wherein The free radical curable composition comprises (i) an oligomeric photoinitiator in an amount of 20 to 70% by weight, (ii) oligomers in an amount of 0 to 40% by weight, (iii) a diluent in an amount of 10 to 60% by weight, The amounts are given therein relative to the total weight of (i) to (iii).

19. The free radical curable composition according to any one of claims 10 to 18, wherein the free radical curable composition is a coating or ink composition.

20. A coating or ink obtained by the following steps: (1) preparing or providing a radically curable coating or ink composition according to claim 19, (2) applying the radically curable coating or ink composition to a substrate, and (3) Radically curing the radically curable coating or ink composition by means of a light source.

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