Photoinitiators for photocurable compositions

Abstract

The present invention relates to oligomeric photoinitiating resins according to (I) wherein n1+n2+n3+n4 is from 5 to 8; and X1, X2, X3, X4 and X5 are independently selected from hydrogen, a linear C1-C6 alkyl, a branched C3-C6 alkyl, a C5-C7 cycloalkyl, an optionally substituted phenyl, a C1-C4 alkoxy, a C5-C7 cycloalkoxy or phenoxy, or X1 and X2 together may form an aromatic ring, or X2 and X3 together may form an aromatic ring.

Description

2024PF30144fcPHOTOINITIATORS FOR PHOTOCURABLE COMPOSITIONSTechnical Field

[0001] The present invention relates to photoinitiating resins that are useful as photoinitiators in free radical curable compositions, such as free radical curable coating and ink compositions. The invention further relates to free radical curable compositions comprising such a photoinitiating resin. Further, the invention relates to objects coated with such a free radical curable composition.Background

[0002] Nowadays coatings are used every day. Examples are items like coatings for transparent food packages, thin foils, paints, and car part finishes. UV curing or free radical photopolymerization is the fastest growing curing technique, with a continuously increasing number of applications. UV curing saves energy and reduces or eliminates solvent emission in comparison with solvent-based systems because most radiation-curable formulations are 100% solid formulations containing reactive oligomers and diluents. The mechanical properties of the cured formulations are generally determined by the oligomers and diluents. Photoinitiators are one of the key components for every photopolymerizable formulation as they generate upon light exposure radicals, which trigger the polymerization.

[0003] A major drawback for most photopolymerizable formulations is the amount of unreacted photoinitiator molecules remaining in the cured polymer material. The high conversion rates in a very short time imply that only a few initiator molecules are able to covalently bind to the polymer network. Ways to solve this are for example irradiating for a very long period of time or using small amounts of initiator. Both ways are not suitable for industrial scale applications as short exposure times ensure the required high throughput. A reasonable conversion is normally provided by using an increased percentage of photoinitiator leading to aforementioned increased amounts of unreacted photoinitiator in the cured formulations. Next to migrating out of the cured formulation, the remaining photoinitiators can cause yellowing, generate a variety of byproducts like for example benzaldehyde which can migrate out of the cured formulations as well. Migration is especially problematic when protective and decorative coatings are applied in the field of food packaging, health care, and other all day use items, which can come in contact with humans.

[0004] For example, benzophenone and its derivatives are more commonly used as photoinitiators in the packaging area. However, for benzophenone there is sufficient evidence in animal studies for its carcinogenicity and it is possible carcinogenic to humans (International Agency for Research on Cancer, “some chemicals present in industrial and consumer products, food and2024PF30144fc drinking water”, vol 101 p285-301). In fact one study (R. Z. Liu, S. A. Mabury,” First Detection of Photoinitiators and Metabolites in Human Sera from United States Donors” Environmental Science and Technology, vol 52(17), pl 0089- 10096 2018.) revealed that photoinitiators and co-initiators were also found in every single blood serum illustrating that photoinitiators and their photoproducts are omnipresent contaminants. This illustrates the necessity for free radical curable formulations in which alternative photoinitiators, particulary oligomeric photoinitiators, are used. By using oligomeric photoinitiators, the migratability is dramatically reduced. An example of such an oligomeric photoinitiator is given in WO2021 / 259924. However, in this application the basis for the oligomeric photoinitiator are still benzophenone derivatives.

[0005] EP-A1-6173 discloses photoinitiators according to the following formulawherein Ar is phenyl or naphthyl, R is hydrogen, alkyl with 1-4 carbon atoms, alkoxy with 1-4 carbon atoms, halogen, dialkylamino with 1-4 carbon atoms in each alkyl group, carboxyl, or alkoxy carbonyl with 1-4 carbon atoms in the alkoxy group, X is alkylene having 3 to 6 carbon atoms or alkylene having 6 to 72 carbon atoms interrupted at least once and the precursor of X being a polyol having 3 to 6 hydroxyls and having a hydroxyl number from 100 to 1850, Ri is hydrogen or methyl, n is a number with a value from about 2 to about 5, and n+m is a number with a value from about 3 to about 6. Particularly preferred compounds are disclosed to be those containing one phenylglyoxyloyloxy group and two acrylate groups and in which X denotes the trimethylolpropane group minus the hydroxyl groups or an ethoxylated trimethylolpropane (about 3 to 12 mol ethylene oxide per mole trimethylol propane) group minus the hydroxyl groups. Example 11 describes an oligomeric photoinitiator prepared by esterification of propoxylated sorbitol with phenylglyoxylic acid and acrylic acid. Testing of the photoinitiators corresponding to Examples 8 and 11 of EP-A1-6173 (see Comparative Experiments B and C herein) demonstrates that these prior art compounds exhibit low cure rates and poor stability.

[0006] The object of the present invention is to provide oligomeric photoinitiators which combine improved reactivity with a low migration potential.2024PF30144fcBrief Summary

[0007] Described herein are several aspects and embodiments of the invention. A first aspect is an oligomeric photoinitiating resin according to formula (I)wherein nl+n2+n3+n4 is from 5 to 8; Xi, X2, X3, X4 and X5 in formula (II) are independently selected from hydrogen, a linear Ci-Ce alkyl, a branched C3-C6 alkyl, a C5-C7 cycloalkyl, an optionally substituted phenyl, a C1-C4 alkoxy, a C5-C7 cycloalkoxy or phenoxy, or Xi and X2 together may form an aromatic ring, or X2 and X3 may form an aromatic ring.

[0008] A second aspect of the current invention is a free radical curable composition comprising at least one oligomeric photoinitiating resin according to any one of the embodiments of the first aspect of the invention.

[0009] In an embodiment of the second aspect of the current invention, the free radical curable composition is a coating or ink composition.

[0010] A third aspect of the current invention is a coating or ink obtained by(1) Preparing or providing a free radical curable coating or ink composition according to one of the embodiments of the second aspect of the invention,(2) Applying the free radical curable coating or ink composition to a substrate, and(3) Free radical curing the free radical curable coating or ink composition with a light source.Detailed Description

[0011] For all upper and / or lower boundaries of any range given herein, the boundary value is included in the range given, unless specifically indicated otherwise. Thus, when saying from x to y, means including x and y and also all intermediate values.

[0012] A first aspect of the current invention is an oligomeric photoinitiating resin, wherein the oligomeric photoinitiating resin is according to formula (I)2024PF30144fcwherein nl+n2+n3+n4 is from 5 to 8; andXi, X2, X3, X4 and X5 are independently selected from hydrogen, a linear Ci-Ce alkyl, a branched C3-C6 alkyl, a C5-C7 cycloalkyl, an optionally substituted phenyl, a C1-C4 alkoxy, a C5-C7 cycloalkoxy or phenoxy, or Xi and X2 together may form an aromatic ring, or X2 and X3 together may form an aromatic ring.

[0013] It has surprisingly been found that the photoinitiators of the present invention exhibit enhanced reactivity in free radical curable compositions, in particularly when compared to their ethoxylated analogues. This enhanced reactivity results in a higher cure speed of the free radiation curable composition, generally illustrated by a higher conversion rate of the free radical curable groups. It has even more surprisingly been found that the oligomeric photoinitiating resins of the invention demonstrate not only increased reactivity in free radical curable compositions compared to their ethoxylated counterparts but also enhanced stability. Testing of the photoinitiators corresponding to Examples 8 and 11 of EP -Al -6173 (see Comparative Experiments B and C herein) demonstrates that these prior art compounds exhibit both reduced cure rates and stability compared to the oligomeric photoinitiating resins of the present invention.

[0014] The photoinitiators according to the invention can advantageously be applied in free radical curable coating and ink compositions wherein a low migration of chemical species is required.

[0015] WO-A1-9833761 discloses non-volatile phenylglyoxalic esters in which two phenylglyoxylic ester radicals are connected via a bridging group. WO-A1-2014060450 discloses hybrid photoinitiators by combining phenyl glyoxylic acid compounds with a- hydroxyketone photoinitiators. These documents does not disclose photointiators based on propoxylated pentaerythritol and comprising acrylate groups. WO-A2-2022207945 discloses (meth)acrylated modified phenylglyoxalate photoinitiators, but does not disclose photointiators based on propoxylated pentaerythritol.2024PF30144fc

[0016] Xi, X2, X3, X4 and X5 are independently selected from hydrogen, a linear Ci-Ce alkyl, a branched C3-C6 alkyl, a C5-C7 cycloalkyl, an optionally substituted phenyl, a C1-C4 alkoxy, a C5- C7 cycloalkoxy or phenoxy, or Xi and X2 together may form an aromatic ring, or X2 and X3 together may form an aromatic ring. In case Xi and X2 together form an aromatic ring, preferably the group according to formula (II) is derived from 1 -naphthalene glyoxylic acid. In case X2 and X3 together form an aromatic ring, preferably the group according to formula (II) is derived from 2-naphthalene glyoxylic acid. Preferably, Xi, X2, X3, X4 and X5 are hydrogen; or Xi, X2, X4 and X5 are hydrogen and X3 is a C1-C4 alkoxy, preferably methoxy, or optionally substituted phenyl; or X2 and X3 together form an aromatic ring. In case one or more of Xi, X2, X3, X4 and X5 is a substituted phenyl, the one or more substituents are preferably independently chosen from halogens, MeO-, Me2N-, phenyl (Ph), and (PhC(O)PhS-). More preferably, Xi, X2, X3, X4 and X5 are hydrogen.

[0017] In the oligomeric photoinitiating resin of formula (I), the total number of propoxy groups (represented by the sum nl + n2 + n3 + n4) is preferably from 5 to 7, since this advantageously balances an improved cure efficiency with reduced migration potential. More preferably, this sum is 5 or 6. Most preferably, the sum nl + n2 + n3 + n4 equals 5.

[0018] The oligomeric photoinitiating resin of formula (I) preferably has a weight-average molecular weight Mwlower than 1100 g / mol, whereby the weight-average molecular weight Mwis determined as described further herein.

[0019] The oligomeric photoinitiating resins of the present invention can be obtained in a process that comprises at least the following steps:(1) providing a propoxylated core having 4 terminal OH functional groups, i.e., a propoxylated pentaerythritol,(2) (trans)esterification of 2 terminal OH functional groups of the propoxylated pentaerythritol with a compound according to formula (lb) and (trans)esterification of 2 terminal OH functional groups of the propoxylated pentaerythritol with a compound according to formula (lib) :wherein R2 and Re are independently hydrogen or a C1-C4 alkyl; and Xi, X2, X3, X4 and X5 are as described above.2024PF30144fc

[0020] The (trans)esterification is usually effected with a catalyst known to the skilled in the art, for example an acid catalyst such as for example methane sulfonic acid or sulfuric acid. The formed water (for R2 = H and Re = H ) or the formed small alcohol (for R2 = C1-C4 alkyl and Re = C1-C4 alkyl) (methanol, ethanol,. . .) can be removed physically by the help of an entrainer such as toluene, a nitrogen gas stream, or vacuum. In a preferred embodiment, R2 = H and Re = a C1-C4 alkyl, preferably methyl or ethyl. In a more preferred embodiment, R2 = H and Re = H.

[0021] An epoxy resin, such as for example Epikote™ 828 obtainable from Hexion, can be used to scavenge the acid catalyst. Alternatively the resin can be washed to remove the acid catalyst.

[0022] A second aspect of the current invention is a free radical curable composition comprising at least one oligomeric photoinitiating resin as described above. The free radical curable compositions comprising the oligomeric photoinitiating resin of the present invention can be effectively cured in the presence of air.

[0023] The amount of oligomeric photoinitiating resin according to the invention in the composition can vary within wide ranges like from 0.001 wt.% up to 99 wt.%. Preferably the amount of oligomeric photoinitiating resin according to the invention is between 0.05 wt.% and 50 wt.%, relative to the entire weight of the free radical curable composition. The amount of oligomeric photoinitiating resin according to the invention is preferably higher than 0.1 wt.%, more preferably higher that 0.5 wt.% or higher than 1 wt.% or higher than 2 wt.% and preferably lower than 70 wt.% or lower than 50 wt.% or lower than 40 wt.% or lower than 35 wt.% or lower than 30 wt.%, relative to the entire weight of the free radical curable composition. Since the oligomeric photoinitiating resin according to the invention comprises 2 acrylate end groups, the oligomeric photoinitiating resin can be considered a free radical curable oligomer by itself and can be used in amounts ranging from 20 to 70 wt.%.

[0024] Although since the oligomeric photoinitiating resin comprises free radical polymerizable groups, other free radical polymerizable compounds are not required, it is preferable that the free radical curable composition 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 groups 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 (Mn) equal to or higher than 800 g / mol, more preferably equal to or higher than 1000 g / mol; and preferably lower than or equal to 15000 g / mol, more preferably lower than or equal to 5000 g / mol, whereby the number-average molecular weight Mnis determined as described herein below.

[0025] 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 preferably2024PF30144fc 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 entire weight of the free radical curable composition.

[0026] Preferably the free radical curable oligomers are selected from the group consisting of urethane (meth)acrylates, epoxy (meth)acrylates, polyester (meth)acrylates, polyether (meth)acrylates and any mixture thereof. More preferably the free radical curable oligomers are selected from the group consisting of urethane acrylates, epoxy acrylates, polyester acrylates, polyether acrylates and any mixture thereof.

[0027] The (meth)acrylate-functionalized oligomer may be selected in order to enhance the flexibility, strength and / or modulus, among other attributes, of a cured polymer prepared using the free radical curable composition of the present invention. The (meth)acrylate functionalized oligomer may have 1 to 18 (meth)acrylate groups, in particular 2 to 6 (meth)acrylate groups, more particularly 2 to 6 acrylate groups. The (meth)acrylate functionalized oligomer may have a number-average molecular weight equal of more than 800 g / mol, in particular from 800 to 15000 g / mol, more particularly from 1000 to 5000 g / mol. In particular, the (meth)acrylate-functionalized oligomers may be selected from the group consisting of (meth)acrylate-functionalized urethane oligomers (sometimes also referred to as "urethane (meth)acrylate oligomers," "polyurethane (meth)acrylate oligomers" or "carbamate (meth)acrylate oligomers"), (meth)acrylate- functionalized epoxy oligomers (sometimes also referred to as "epoxy (meth)acrylate oligomers"), (meth)acrylate-functionalized polyether oligomers (sometimes also referred to as "polyether (meth)acrylate oligomers"), (meth)acrylate-functionalized polydiene oligomers (sometimes also referred to as "polydiene (meth)acrylate oligomers"), (meth)acrylate-functionalized polycarbonate oligomers (sometimes also referred to as "polycarbonate (meth)acrylate oligomers"), and (meth)acrylate-functionalized polyester oligomers (sometimes also referred to as "polyester (meth)acrylate oligomers"), acrylic (meth)acrylate oligomers and mixtures thereof. Preferably, the (meth)acrylate-functionalized oligomer comprises a (meth)acrylate-functionalized urethane oligomer, more preferably an acrylate-functionalized urethane oligomer. Advantageously, the (meth)acrylate-functionalized oligomer comprises a (meth)acrylate-functionalized urethane oligomer having two (meth)acrylate groups, more preferably an acrylate-functionalized urethane oligomer having two acrylate groups. Exemplary polyester (meth)acrylate oligomers include the reaction products of acrylic or methacrylic acid or mixtures or synthetic equivalents thereof with hydroxyl group-terminated polyester polyols. The reaction process may be conducted such that all or essentially all of the hydroxyl groups of the polyester polyol have been (meth)acrylated, particularly in cases where the polyester polyol is difunctional. The polyester polyols can be made by polycondensation reactions of polyhydroxyl functional components (in particular, diols) and2024PF30144fc polycarboxylic acid functional compounds (in particular, dicarboxylic acids and anhydrides). The polyhydroxyl functional and polycarboxylic acid functional components can each have linear, branched, cycloaliphatic or aromatic structures and can be used individually or as mixtures. 35

[0028] Examples of suitable epoxy (meth)acrylate oligomers include the reaction products of acrylic or methacrylic acid or mixtures thereof with an epoxy resin (polyglycidyl ether or ester). The epoxy resin may, in particular, by selected from bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, bisphenol 6 diglycidyl ether, brominated bisphenol A diglycidyl ether, brominated bisphenol F diglycidyl ether, epoxy novolak resin, hydrogenated bisphenol A diglycidyl ether, hydrogenated bisphenol F diglycidyl ether, hydrogenated bisphenol S diglycidyl ether, 3, 4-epoxy cyclohexylmethyl 3',4’epoxycyclohexanecarboxylate, 2-(3,4- epoxycyclohexyl-5,5-spire-3,4-epoxy)cyclohexane-l,4- dioxane, bis(3,4- epoxycyclohexylmethyl)adipate, vinylcyclohexene oxide, 4-vinylepoxy cyclohexane, bis(3,4- epoxy-6-methylcyclohexylmethyl)adipate,3,4-epoxy-6-methylcyclohexy l-3',4uepoxy-6u methylcyclohexanecarboxylate, methylenebis(3,4-epoxycyclohexane), dicyclopentadiene diepoxide, di (3, 4-epoxy cyclohexylmethyl) ether of ethylene glycol, ethylenebis(3, 4- epoxy cyclohexanecarboxylate), 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 ethers of a polyether polyol obtained by the addition of one or more alkylene oxides to an aliphatic polyhydric alcohol such as ethylene glycol, propylene glycol, and glycerol, diglycidyl esters of aliphatic long-chain dibasic acids, monoglycidyl ethers of aliphatic higher alcohols, monoglycidyl ethers of phenol, cresol, butyl phenol, or polyether alcohols obtained by the addition of alkylene oxide to these compounds, glycidyl esters of higher fatty acids, epoxidized soybean oil, epoxybutylstearic acid, epoxy octyl stearic acid, epoxidized linseed oil, epoxidized polybutadiene, and the like.

[0029] Suitable polyether (meth)acrylate oligomers include, but are not limited to, the condensation reaction products of acrylic or methacrylic acid or synthetic equivalents or mixtures thereof with polyetherols which are polyether polyols (such as polyethylene glycol, polypropylene glycol or polytetramethylene glycol). Suitable polyetherols can be linear or branched substances containing ether bonds and terminal hydroxyl groups. Polyetherols can be prepared by ring opening polymerization of cyclic ethers such as tetrahydrofuran or alkylene oxides (e.g., ethylene oxide and / or propylene oxide) with a starter molecule. Suitable starter molecules include water, polyhydroxyl functional materials, polyester polyols and amines.

[0030] Polyurethane (meth)acrylate oligomers (sometimes also referred to as "urethane (meth)acrylate oligomers") suitable for use in the curable compositions of the present invention2024PF30144fc include urethanes based on aliphatic, cycloaliphatic and / or aromatic polyester polyols and polyether polyols and aliphatic, cycloaliphatic and / or aromatic diisocyanates and capped with (meth)acrylate end-groups. Suitable polyurethane (meth)acrylate oligomers include, for example, aliphatic polyester-based urethane di- and tetra-acrylate oligomers, aliphatic polyether- based urethane di- and tetra-acrylate oligomers, as well as aliphatic polyester / polyether-based urethane di- and tetraacrylate oligomers. The polyurethane (meth)acrylate oligomers may be prepared by reacting aliphatic, cycloaliphatic and / or aromatic polyisocyanates (e.g., diisocyanate, triisocyanate) with OH group terminated polyester polyols, poly ether polyols, polycarbonate polyols, polycaprolactone polyols, polyorganosiloxane polyols (e.g., polydimethylsiloxane polyols), or polydiene polyols (e.g., polybutadiene polyols), or combinations thereof to form isocyanate-functionalized oligomers which are then reacted with hydroxyl-functionalized (meth)acrylates such as hydroxyethyl acrylate or hydroxyethyl methacrylate to provide terminal (meth)acrylate groups. For example, the polyurethane (meth)acrylate oligomers may contain two, three, four or more (meth)acrylate functional groups per molecule. Other orders of addition may also be practiced to prepare the polyurethane (meth)acrylate, as is known in the art. For example, the hydroxyl-functionalized (meth)acrylate may be first reacted with a polyisocyanate to obtain an isocyanate-functionalized (meth)acrylate, which may then be reacted with an OH group terminated polyester polyol, polyether polyol, polycarbonate polyol, polycaprolactone polyol, polydimethysiloxane polyol, polybutadiene polyol, or a combination thereof. In yet another embodiment, a polyisocyanate may be first reacted with a polyol, including any of the aforementioned types of polyols, to obtain an isocyanate-functionalized polyol, which is thereafter reacted with a hydroxyl-functionalized (meth)acrylate to yield a polyurethane (meth)acrylate Alternatively, all the components may be combined and reacted at the same time.

[0031] Suitable acrylic (meth)acrylate oligomers (sometimes also referred to in the art as "acrylic oligomers") include oligomers which may be described as substances having an oligomeric acrylic backbone which is functionalized with one or (meth)acrylate groups (which may be at a terminus of the oligomer or pendant to the acrylic backbone). The acrylic backbone may be a homopolymer, random copolymer or block copolymer comprised of repeating units of acrylic monomers. The acrylic monomers may be any monomeric (meth)acrylate such as Ci-Ce alkyl (meth)acrylates as well as functionalized (meth)acrylates such as (meth)acrylates bearing hydroxyl, carboxylic acid and / or epoxy groups. Acrylic (meth)acrylate oligomers may be prepared using any procedures known in the art, such as by oligomerizing monomers, at least a portion of which are functionalized with hydroxyl, carboxylic acid and / or epoxy groups (e.g.,2024PF30144fc 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 functional groups.

[0032] The curable composition of the invention may comprise from 10 to 80 wt.%, in particular from 15 to 75 wt.%, more particularly from 20 to 70 wt.% (meth)acrylate- functionalized oligomer, relative to the entire weight of the free radical curable composition.

[0033] For viscosity reasons it might be beneficial that reactive diluents are used. With reactive diluent is meant a compound being able to reduce the viscosity of the formulation while being able to free radically copolymerize. The invention therefore also relates to free radical curable compositions which comprise a reactive diluent. The one or more diluents having one or more, preferably two or more, free radical curable ethylenically unsaturated groups may be 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 in an amount of at most 85 wt.%, or at most 80 wt.%, or at most 75 wt.%, or at most 70 wt.%, relative to the entire weight of the free radical curable composition.

[0034] As reactive diluent various acrylic, methacrylic or vinyl functional monomers can be used. Suitable examples are for instance diacrylates or dimethacrylates of diols or of poly etherdiols, such as propoxylated neopentyl glycol diacrylate, 1,6- hexanediol diacrylate, dipropylene glycol diacrylate (DPGDA), tripropylene glycol diacrylate (TPGDA), diethylene glycol diacrylate, triethylene glycol diacrylate, triethylenglycol dimethacrylate, neopentylglycol diacrylate, 1,4-butanediol diacrylate (e.g, SR213), alkoxylated aliphatic diacrylate (e.g. SR9209A), alkoxylated hexanediol diacrylate (e.g, SR561, SR562, SR563, SR564 from Sartomer Co., Inc), polyethylene glycol (200) diacrylate (SR259), polyether glycol-200- diacrylate, PEG300-diacrylate, polypropyleneglycol diacrylate, ethoxylated (3) bisphenol-A- diacrylate, BDDA butanediol diacrylate, BDDMA butane diol 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 neopentylglycol, propoxylate (4) glycerol triacrylate, tri -functional monomers, such as Laromer types from BASF or Ebecryl 2047 or Ebecryl 12 from Allnex, di-trimethylolpropane tetraacrylate, dipentaerythritol-pentaacrylate (Di-PEPA), dipentaerythritol hexaacrylate (DPHA). Examples of vinyl compounds are compounds like butanediol divinyl ether or as mono functional compound N-vinyl caprolactam. Although mono functional (meth)acrylates like for example lauryl (meth)acrylate, phenoxyethyl (meth)acrylate2024PF30144fc can be used as well, it is preferred for low migratability to employ reactive diluents with at least two free radical curable ethylenically unsaturated groups. Obviously mixtures can be used as well.

[0035] In a preferred embodiment of the invention, the free radical curable composition comprising at least one oligomeric photoinitiating resin according to the invention optionally further comprises one or more oligomers having one or more free radical curable ethylenically unsaturated groups, preferably having one or more (meth)acryloyl groups 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 the one or more diluents having at least least two free radical curable ethylenically unsaturated groups; and the free radical curable composition comprises the oligomeric photoinitiating resin in an amount of from 3 to 70 wt.%, the oligomer in an amount of from 0 to 80 wt.%, the diluent in an amount of from 10 to 70 wt.%, whereby the amounts are given relative to the entire weight of (i) to (iii).

[0036] In accordance with a further aspect, the present invention refers to a free radical curable ink composition or 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 c) one or more oligomeric photoinitiating resin of the present invention.

[0037] If the free radical curable composition is a free radical curable ink composition, it contains at least one pigment. Preferably, the amount of pigment based on the total amount of the free radical curable ink composition, i.e., the composition before curing, is preferably between 0.5 and 50% by weight and more preferably from 3 to 20% by weight. The cured ink composition preferably contains from 0.5 to 50% by weight and more preferably from 3 to 20% by weight of pigment.

[0038] In addition to the oligomeric photoinitiating resin according to the invention, other initiators can be employed as well next to various other additives. Examples for such additives are those selected from the group consisting of rheological additives, adhesion promoters, defoamers, slip additives, wetting agents, levelling agents, gloss additives, waxes, wetting agents, curing agents, chelating agents, additional photoinitiators, amine synergists, inhibitors, desiccants, stabilizers, emulsifiers, abrasion resistance additives, plasticizers, antistatic additives, matting agents and arbitrary combinations of two or more of the aforementioned additives.

[0039] The free radical curable ink composition or free radical curable coating composition may be formulated so as to be suitable for any known printing technique, such as offset, lithography,2024PF30144fc intaglio printing, flexographic printing, gravure printing, screen printing, digital printing, inkjet printing, pad printing, transfer printing, letter printing and the like.

[0040] Another aspect of the present invention is a process for free radical curing the free radical curable composition of the current invention, which comprises the following steps:(1) Preparing or providing a free radical curable composition as described herein above, and(2) Free radical curing the free radical curable composition with a light source.

[0041] Said light source is preferably a UV light source emitting UV light in at least one of the UVA, UVB and UVC ranges or a LED source emitting light in the range from 350 to 450 nm.

[0042] The process preferably comprises the step of applying the free radical curable composition to a substrate prior to free radical curing it.

[0043] Another aspect of the present invention is a coating or ink obtained by(1) Preparing or providing a free radical curable coating or ink composition as described herein above,(2) Applying the free radical curable coating or ink composition to a substrate, and(3) Free radical curing the free radical curable coating or ink composition with a light source.

[0044] The following examples further illustrate the invention but, of course, should not be construed as in any way limiting its scope.Examples

[0045] These examples illustrate embodiments of the instant invention. Table 1 describes the various components used to prepare the oligomeric photoinitiating resins and the free radical curable compositions used in the present examples. Table 2 reports the photoreactivity of the oligomeric photoinitiating resins. Table 3 reports the viscosity stability of the oligomeric photoinitiating resins. Unless otherwise specified, all parts, percentages and ratios are on a weight basis.2024PF30144fcTable 1 - Formulation Components2024PF30144fcPreparation of formulations

[0046] Unless otherwise specified, each of the formulations described were prepared by conventional methods by using a 50 ml mixing cup suitable for use with a Speedmixer™. The components, adding up to around 10 g in total, were added in the mixing cup. The cup was then closed and vigorously mixed in a Speedmixer™ DAC150FVZ for 5 minutes, stopped, and mixed again for 5 additional minutes via the same method.Determination of viscosity

[0047] Viscosities were determined on a BROOKFIELD DVNXB5CBG rheometer equipped with 2.5cm diameter / l° cone / plate geometry at 25°C at a shear rate of 100s'1. CPA-40Z spindle (2.4 cm diameter / 0.8° cone / plate geometry) was equipped for sample with viscosity between 0.65 and 25 Pa.s; CPA-52Z (1.2 cm diameter / 3° cone / plate geometry) was equipped for sample with viscosity from 25- 800 Pa.s.Determination of molecular weight by GPC

[0048] The number-average molecular weight (Mn) and the weight-average molecular weight (Mw) were measured via SEC calibrated with a set of polystyrene standards with a molecular weight range of from 500 up to 7 xlO6g / mol and using as an eluent stabilized tetrahydrofuran [THF with 0.007- 0.015% w / w butyl-hydroxytoluene (BHT)] modified with 0.8 % acetic acid, at a flow rate of 1 mL / min at 40 °C.More specifically, 50 mg of an oligomeric photoinitiating resin was dissolved in 5 mL eluent for 16 hours at room temperature without shaking. 10 pL of the solution thus prepared were injected into the system for the measurement.The SEC measurements were carried out on a Waters GPC system which consisted of: i) a Waters 2414 refractive index detector at 40°C, ii) a Waters Shodex packed Column at 40°C - with four different Shodex packed columns (5000A, 500 A, 150A and 50A pore size) with I / d = 300 / 8 mm and are filled with particles having a particle size of 10 (the 5000A) or 6 pm (the 500A , 150A and 150A column) (1 pm= 1x10-6 m), (supplied by Waters), iii) a Waters 2707 Autosampler - injection system and iv) a Waters 1515 -Isocratic HPLC pump. The n and Mwwere determined by the use of Empower 3 software from Waters.2024PF30144fcDetermination of reactivity using a UV Rig

[0049] A 12 micron thick film was prepared from the formulations on a glass plate and cured on a Fusion UV Rig equipped with a Fusion F600 H bulb (IW / cm2) using a total dose of 0.8 J / cm2as determined with an EIT power puck II. After cure the acrylate conversion was determined using IR spectroscopy. The error in the conversion measurement is estimated to be around ±5%.Determination of reactivity using RT-DMA : Maximum Modulus (G ) and T30%, modulus max values

[0050] For RT-DMA, formulations were prepared using 70 parts urethane oligomer 1 (prepared as described below), 30 parts 2-phenoxy ethyl acrylate and 5 parts of the oligomeric photoinitiating resin (prepared as described below). These formulations were analyzed on a TA instruments Rheometer (HR20) equipped with UV curing accessories (320-500 nm, OmniCure® Series 2000). The UV output intensities were calibrated at the sample position using an external radiometer. For the light guide accessory, the intensity (25_mW / cm2) was applied and recorded as total intensity without any filter. Thickness of the sample was 0.25 mm and a single frequency oscillatory measurement was carried out under a control strain of 1% at 5 Hz. Dynamic time sweep experiments were used to monitor the curing process.Illumination started after 60 sec of measuring. Reported herein are the maximum modulus and the time to reach 30% of the maximum modulus after start of illumination as measure of cure speed.Synthesis of oligomeric photoinitiating resin OPI 1

[0051] Step 1) A 500 ml reactor equipped with a stirrer, nitrogen inlet, and Dean-Stark set-up was charged with 85.2 g pentaerythritol propoxylate (PP), 60.0 g phenylglyoxylic acid (PhG), 28.8g acrylic acid (Ac), 240 g toluene and 0.74 g methane sulphonic acid MSA. The reaction was heated to reflux under a gentle stream of nitrogen and kept at this temperature until reaction water was no longer formed (4hr).After washing the reaction mixture 3 times with water and overnight drying over sodium sulphate the toluene was removed by distillation under reduced pressure at a temperature of 95°C after which a resin was obtained with having a viscosity of 1.7 Pa.s. and an Mwof 930 g / mol.2024PF30144fcSynthesis of oligomeric photoinitiating resin OPIA

[0052] The synthesis of OPI A was prepared similar to OPI 1 , except using pentaerythritol ethoxylate (PE) instead of pentaerythritol propoxylate (PP).Synthesis of oligomeric photoinitiating resin OPIB

[0053] OPI B was prepared analogously to the procedure described in Example 8 of EP-A1-6173.Synthesis of oligomeric photoinitiating resin OPI C

[0054] OPI C was prepared analogously to the procedure described in Example 11 of EP-A1-6173.Synthesis of urethane oligomer 1

[0055] First, a 1 L reactor (equipped with a stirrer, air inlet, dropping funnel, and condenser) was purged with dry lean air. Then 2.19 parts of BHT was charged into the reactor, followed by 52.76 parts of TDI, followed by 0.02 parts of acrylic acid. After charging, the reactor was heated to 45 °C. Then half of the specified amount catalyst (i.e., 0.06 g bismuth neodecanoate) followed by 35.43 parts HEA were charged into the reactor whilst stirring. After waiting one (1) hour for the reaction to commence, the temperature was then raised to 60°C. At 60 °C, 700 parts PPG4000 and the second part of the catalyst (i.e., 0.07 g) were added after which the reaction temperature was raised to 85°C which was further maintained for two (2) additional hours.After this, two (2) additional hours of reaction time, the quantity of isocyanate (NCO) content was measured by a potentiometric titrator to ensure it was lower than 0.1% relative to the entire weight of the composition. If the isocyanate content was not lower than this value, the mixture was placed back in the reaction chamber in 15-minute additional increments (again at 85 °C) and checked again, with this step repeated until the isocyanate content fell to within the desired range. Finally, the resulting synthesized oligomer 1 with the idealized structure HEA-TDI-PPG4000-TDI-HEA was cooled slowly and discharged for use.2024PF30144fcExample 1 and Comparative Experiments A-C

[0056] Formulations for RT-DMA analysis were prepared using 70 parts of urethane oligomer 1, 30 parts of 2-phenoxy ethyl acrylate and 5 parts of oligomeric photoinitiating resin, the cure results using RT-DMA are shown in table 2.

[0057] Formulations for a clear varnish OPV were prepared using 40 parts of Neorad™ U25-20D, 50 parts of Agisyn™ 2844 and 10 parts of oligomeric photoinitiating resins. These formulations were cured on the UV Rig in air (H-bulb) and the conversions were determined with IR. The cure results are also shown in table 2.Table 2

[0058] The viscosity stability over 7 days in an oven at 75°C was tested for the oligomeric photoinitiating resins OPI I, OPI A, OPI B and OPI C as indicated in Table 3.Table 3

[0059] These experiments show that the oligomeric photoinitiating resins according to the invention surprisingly possess enhanced reactivity in combination with improved stability, which is even more surprising since an increased reactivity usually correlates with decreased stability.

[0060] Comparison of Comparative Experiment B with Comparative Experiment C in Table 2 shows that for oligomeric photoinitiating resins having one phenylglyoxyloyloxy group and two acrylate2024PF30144fc groups, different combinations of polyvalent alcohol (trimethylolpropane versus sorbitol) and alkoxylation method (ethoxylation versus propoxylation) have minimal effect on the reactivity of the oligomeric photoinitiating resins, since the oligomeric photoinitiating resins used in Comparative Experiments B and C have approximately the same molar amounts of chromophores present. This is demonstrated by both similar times to reach 30% of the maximum modulus with RT-DMA and similar conversions when cured in air using an OPV formulation with the UV rig.

[0061] In contrast, comparison of Example 1 with Comparative Experiment A in Table 2 shows that for oligomeric photoinitiating resins having two phenylglyoxyloyloxy groups and two acrylate groups, significantly higher cure efficiency can be obtained when applying the propoxylated oligomeric photoinitiating resin compared to the ethoxylated oligomeric photoinitiating resin. This is demonstrated by both a shorter time to reach 30% of the maximum modulus with RT-DMA and higher conversions when cured in air using an OPV formulation with the UV rig. This enhanced performance is even more surprising since, due to the lower molecular weight of the oligomeric photoinitiating resin of Comparative Experiment A (i.e., higher molar amounts of chromophores present), the opposite would have been expected. This indicates an unexpected synergistic effect on reactivity between propoxylation and the presence of at least two chromophores. Comparison of OPI 1 with OPI A demonstrates that the oligomeric photoinitiating resin according to the invention surprisingly also possesses an increased stability compared to the ethoxylated oligomeric photoinitiating resin. This is especially surprising since Table 2 shows that the propoxylated oligomeric photoinitiating resin has an increased reactivity compared to the ethoxylated oligomeric photoinitiating resin.

[0062] Comparison of OPI B with OPI C in Table 3 shows that for oligomeric photoinitiating resins having one phenylglyoxyloyloxy group and two acrylate groups, propoxylation also surprisingly results in increased stability compared to ethoxylation. Furthermore, comparison of OPI A with OPI B, both being ethoxylated, and OPI 1 with OPI C, both being propoxylated, in Table 3 demonstrates that the use of pentaerythritol compared to trimethylolpropane and sorbitol, respectively, surprisingly results in further enhanced stability.

Claims

2024PF30144fcWhat is claimed is:

1. An oligomeric photoinitiating resin of formula (I)wherein nl+n2+n3+n4 is from 5 to 8; andXi, X2, X3, X4 and X5 are independently selected from hydrogen, a linear Ci-Ce alkyl, a branched C3-C6 alkyl, a C5-C7 cycloalkyl, an optionally substituted phenyl, a C1-C4 alkoxy, a C5-C7 cycloalkoxy or phenoxy, or Xi and X2 together may form an aromatic ring, or X2 and X3 together may form an aromatic ring.

2. The photoinitiating resin according to claim 1, wherein Xi, X2, X3, X and X5 are hydrogen, or Xi, X2, X and X5 are hydrogen and X3 is a C1-C4 alkoxy or substituted phenyl, or X2 and X3 together form an aromatic ring.

3. The photoinitiating resin according to claim 1, wherein Xi, X2, X3, X and X5 are hydrogen.

4. The photoinitiating resin according to any one of the preceding claims, wherein nl+n2+n3+n4 is from 5 to 7, more preferably nl+n2+n3+n4 is 5 or 6, most preferably nl+n2+n3+n4 is 5.

5. The photo initiating resin according to any one of the preceding claims, wherein the photoinitiating resin has a weight-average molecular weight Mwlower than 1100 g / mol, whereby the weight-average molecular weight Mwis determined as described in the description.

6. A free radical curable composition comprising at least one oligomeric photoinitiating resin according to any of claims 1 to 5.

7. The free radical curable composition according to claim 6, wherein the oligomeric photoinitiating resin is present in an amount of from 0.05 to 50 wt.%, preferably from 0.1 to2024PF30144fc40 wt.%, more preferably from 0.1 to 30 wt.%, even more preferably from 2 to 30 wt.%, relative to the entire weight of the free radical curable composition.

8. The free radical curable composition according to claim 6 or 7, 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 groups or vinyl groups.

9. The free radical curable composition according to claim 8, 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, poly ether (meth)acrylate oligomers, polyester (meth)acrylate oligomers and any mixture thereof, more preferably the one or more oligomers having one or more free radical curable ethylenically unsaturated groups are urethane (meth)acrylate oligomers, even more preferably the one or more oligomers having one or more free radical curable ethylenically unsaturated groups are urethane acrylate oligomers.

10. The free radical curable composition according to claim 8 or 9, wherein the one or more oligomers having one or more free radical curable ethylenically unsaturated groups have a number-average molecular weight (Mn) from 800 to 15000 g / mol, preferably from 1000 to 5000 g / mol, whereby the number-average molecular weight Mnis determined as described in the description.

11. The free radical curable composition according to any one of claims 8 to 10, 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.

12. The free radical curable composition according to any of claims 6 to 11, 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 least two free radical curable ethylenically unsaturated groups.

13. The free radical curable composition according to claim 12, 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.%, or2024PF30144fc at least 10 wt.%, and in an amount of at most 85 wt.%, or at most 80 wt.%, or at most 70 wt.%, relative to the entire weight of the free radical curable composition.

14. The free radical curable composition according to claim 6, wherein 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 groups 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) the oligomeric photoinitiating resin in an amount of from 3 to 70 wt.%,(ii) the oligomer in an amount of from 0 to 80 wt.%,(iii) the diluent in an amount of from 10 to 70 wt.%, whereby the amounts are given relative to the entire weight of (i) to (iii).

15. The free radical curable composition according to any of claims 6 to 14, wherein the free radical curable composition is a coating or ink composition.

16. A coating or ink obtained by(1) Preparing or providing a free radical curable coating or ink composition according to claim 15,(2) Applying the free radical curable coating or ink composition to a substrate, and(3) Free radical curing the free radical curable coating or ink composition with a light source.

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