A LED curable composition

Abstract

The present invention refers to a light emitting diode (LED) curable composition, wherein the composition comprises a cationic curable resin comprising a1) an epoxide, a2) an oxetane, a3) a cationic initiator, and a4) a photosensitizer, wherein the weight ratio between the epoxide a1) and the oxetane a2) is in the range of 1-5. The present invention also refers to the use of said LED curable composition for producing a coating that is cured with a LED light source at a wavelength in the range of 275-405 nm.

Description

[0001] A LED CURABLE COMPOSITION

[0002] FIELD OF THE INVENTION

[0003] The present invention refers to a light emitting diode (LED) curable composition, wherein the composition comprises a cationic curable resin comprising a1) an epoxide, a2) an oxetane, a3) a cationic initiator, and a4) a photosensitizer, wherein the weight ratio between the epoxide a1) and the oxetane a2) is in the range of 1-5. The present invention also refers to the use of said LED curable composition for producing a coating that is cured with a LED light source at a wavelength in the range of 275-405 nm.

[0004] BACKGROUND

[0005] Radiation curing is a technology used in many different industries, including coatings, varnishes, inks, electronics, adhesives and 3D printing. UV cured coatings, inks and adhesives have become very important mainly due to environmental advantages, unique physical properties and production efficiency. The most common used light source in the UV curing industry up until today has been based on mercury (Hg). Mercury is however causing a major regulatory concern and mercury lamps will indeed soon be phased out and the transition period has already started. The radiation curing industry is looking for suitable alternatives and LEDs have rapidly been considered to be the logical sustainable replacement for Hg lamps. The LED light source presents several benefits such as instantaneous on / off, fast and uniform curing, low heat emission and low power consumption in comparison to the conventional Hg light source.

[0006] The first LED systems were however not powerful enough and a lot of efforts has been required from the equipment suppliers to ensure the delivery of higher intensity / light output for these monochromatic light curing sources. In parallel, it is also necessary to work on the formulation composition in order to maximize the reactivity under these new light systems. The photoinitiator plays a crucial role to ensure efficient light absorption at a specific wavelength, but it is as important to optimize the composition by choosing the most reactive components.

[0007] There is accordingly a need in the curing industry to develop new LIV-LED curable compositions which will assure a high curing reactivity and meet the end-use application requirements.

[0008] SUMMARY OF THE INVENTION

[0009] The Applicant noted that certain cationic compositions have the ability to be efficiently cured with a LED light source. Through extensive testing, curing different compositions with a LED source emitting light at different wavelengths, the Applicant came to the conclusion that the use of oxetane chemistry is of great advantage to ensure high reactivity under these monochromatic light sources. The Applicant has been able to show how components can be selected in order to reach a highly reactive and well performant cationic system for LED curing. The Applicant has successfully designed cationic compositions that can be cured under different wavelengths which are today available in the UV- A and near visible region (365, 395 and 405 nm) but also including possible new light source emitting in the IIV-C region (275 nm). Longer wavelengths have the ability to penetrate through thick and pigmented systems producing through-cure of the material that ensures surface adhesion and the ability to cure thicker coatings. Short wavelengths (200-280 nm) is unable to penetrate very far into a material, but provides surface curing which is important for surface properties such as scratch and chemical resistance.

[0010] Cationic radiation curing, due to its photopolymerization mechanisms, offers several technical advantages such as low shrinkage, good adhesion and flexibility and the Applicant has been able to show that cationic compositions can be efficiently cured with LED if oxetanes in proper amounts are present. The cationic compositions of the present invention have shown to be even more reactive than free-radical compositions.

[0011] While free radical compositions suffer from oxygen inhibition, and this is really a drawback when curing with LED, the cationic compositions of the present invention behave excellent. The surface curing of the cationic compositions are really good and there is no big difference in the required light dose for curing with Hg or LED, whereas free radical compositions require a significantly higher light dose for LED curing compared to Hg curing. One of the main advantages of cationic compositions is clearly that they are not sensitive to oxygen and therefore can be tuned easily for efficient curing under the near monochromatic light sources of LEDs.

[0012] The present invention therefore refers, in a first aspect, to a LED curable composition, wherein the composition comprises a cationic curable resin comprising a1) an epoxide, a2) an oxetane, a3) a cationic initiator, and a4) a photosensitizer, wherein the weight ratio between the epoxide a1) and the oxetane a2) is in the range of 1-5.

[0013] In a further aspect, the present invention refers also to the use of said LED curable composition as defined in the first aspect of the invention, for producing a coating that can be cured with a LED light source at a wavelength in the range of 275-405 nm. The LED curable composition according to the present invention has turned out to be an excellent solution to reach both a sufficiently high LED curing reactivity and to result in a well performing coating.

[0014] The flexibility of the cured coating can be further enhanced by adding an alkoxylated polyol to the cationic resin of the LED curable composition of the present invention. As ECC regulatory classification is under revision and there is a great desire to increase the sustainable content in compositions, the inventors also found a way to lower the amount of ECC by incorporating an epoxidized vegetable oil (epoxidized linseed oil) into the cationic LED curable composition of the invention. The addition of an epoxidized vegetable oil also makes it possible to cure the coating at a broader range of LED wavelengths.

[0015] A benefit of using a 100% cationic LED curable composition is that the curing mechanism will not be suffering from any oxygen inhibition, i.e. there is therefore no need to remove oxygen from the environment, which can be both costly and complicated.

[0016] The LED curable composition of the present invention can be either a pure cationic composition, comprising only a cationic curable resin, or a hybrid composition, comprising both a cationic curable resin and a free-radical curable resin. A hybrid composition, combining the cationic polymerisation of epoxides and oxetanes with free radical polymerisation of acrylate systems build interpenetrating polymer networks (IPNs) that makes it possible to combine the high speed curing of the free-radical curing composition with all of the beneficial properties of a cationic curing composition. Indeed the LED curable composition of the present invention has the ability to fulfil the needs of the curing industry in terms of sustainability, productivity and performance.

[0017] The advantages of the these further aspects according to the present invention have been disclosed in relation to the LED curable composition according to the first aspect of the present invention and are herewith not repeated.

[0018] DETAILED DESCRIPTION OF THE INVENTION

[0019] The present invention refers to a light emitting diode (LED) curable composition, wherein the composition comprises a cationic curable resin comprising a1) an epoxide, a2) an oxetane, a3) a cationic initiator, and a4) a photosensitizer, wherein the weight ratio between the epoxide a1) and the oxetane a2) is in the range of 1-5, preferably in the range of 1-4 and most preferably in the range of 1.4-3.9.

[0020] Surprisingly, the Applicant has indeed found out that it is possible to obtain a high reactivity when curing this composition of the present invention with LED and result in a coating ensure good reactivity and final performance in end applications Within the framework of the present description and in the subsequent claims, except where otherwise indicated, all the numerical entities expressing amounts, parameters, percentages, and so forth, are to be understood as being preceded in all instances by the term "about". As used herein, the term “about” will be understood by persons of ordinary skill in the art and will vary to some extent on the context in which it is used. As used herein when referring to a measurable value such as an amount, a temporal duration, and the like, the term “about” is meant to encompass variations of ±20% or ±10%, including ±5%, ±1%, and ±0.1% from the specified value, as such variations are appropriate to perform the disclosed methods.

[0021] Also, all ranges of numerical entities include all the possible combinations of the maximum and minimum values and include all the possible intermediate ranges, in addition to those specifically indicated herein below.

[0022] Unless defined otherwise, all technical and scientific terms used herein generally have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0023] As used herein, the articles “a” and “an” refer to one or to more than one (i.e. to at least one) of the grammatical object of the article. By way of example, “an oxetane” means one oxetane or more than one oxetane.

[0024] The present invention may present in one or more of the above aspects one or more of the characteristics disclosed hereinafter. The LED curable composition comprises a cationic curable resin comprising a1) an epoxide, a2) an oxetane, a3) a cationic initiator, and a4) a photosensitizer, wherein said epoxide a1) and oxetane a2) are in a specific weight ratio.

[0025] In a preferred embodiment of the present invention said LED curable composition comprises:

[0026] A) 40-100 wt% of said cationic curable resin, wherein said cationic curable resin optionally comprises also at least one of the following compounds a5) an alkoxylated polyol, a6) an epoxidized vegetable oil,

[0027] B) 0-60 wt% of a free-radical curable resin, further comprising b1) at least one (meth)acrylate monomer or oligomer, and optionally b2) a free-radical photoinitiator, wherein the weight percent is based on the total weight of the LED curable composition.

[0028] Preferably, the cationic curable resin comprises 30-80 wt%, more preferably 50-80 wt%, of said epoxide a1), with respect to the total weight of the cationic resin composition. Preferably, said epoxide a1) in the cationic curable resin is a cycloaliphatic epoxide, preferably selected from the group consisting of at least one of: a 3,4-epoxycyclohexylmethyl-3,4-epoxy-cyclohexane carboxylate, a 3,4-epoxy-1- methyl-cyclohexyl methyl-3,4-epoxy-1 -methylcyclo-hexane carboxylate, a 6- methyl-3,4-epoxycyclohexymethyl-6-methyl-3,4-epoxy-cyclohexane carboxylate, a 3,4-epoxy-3-methylcyclohexylmethyl-3,4-epoxy-3-methylcyclohexane carboxylate, and a 3,4-epoxy-5-methylcyclohexylmethyl-3,4-epoxy-5- methylcyclohexane carboxylate.

[0029] The performance of the epoxide can really be enhanced by the presence of the oxetane a2), that has shown to successfully increase the reactivity of a pure cationic composition cured with LED at different wavelengths.

[0030] Preferably, the cationic curable resin comprises 10-50 wt%, preferably 20-40 wt%, and most preferably 20 wt% of said oxetane a2), with respect to the total weight of the cationic resin composition.

[0031] In a preferred embodiment of the present invention said oxetane a2) is a polyoxetane compound, having at least two oxetane groups.

[0032] Suitable polyoxetane compounds a2) which may be used in the composition of the present invention is preferably selected from the group consisting of at least one of: 3,7-bis(3-oxetanyl)-5-oxa-nonane, 3,3'-(1 ,3-(2-methyl-enyl)- propanediyl-bis(oxymethylene))-bis-(3-ethyloxetane), 1 ,4-bis[(3-ethyl-3-oxetanyl- methoxy)methyl]-benzene, 1 ,2-bis[(3-ethyl-3-oxetanylmethoxy)methyl]ethane, 1 ,3-bis[(3-ethyl-3-oxetanylmethoxy)methy]propane, ethylene glycol bis(3-ethyl-3- oxetanyl-methyl)ether, dicyclopentenyl bis(3-ethyl-3oxetanyl-methyl)ether, triethylene glycol bis(3-ethyl-3-oxetanylmethyl)ether, tetraethylene glycol bis(3- ethyl-3-oxetanylmethyl)ether, tricyclodecanediyldimethylene(3-ethyl-3-oxetanyl- methyl)-ether, tri methylol propane tris(3-ethyl-3-oxetanylmethyl)ether, 1 ,4-bis(3- ethyl-3-oxetanyl-methoxy)butane, 1 ,6-bis(3-ethyl-3-oxetanylmethoxy)hexane, pentaerythritol tris(3-ethyl-3-oxetanylmethyl)ether, pentaerythritol tetra kis(3-ethyl- 3-oxetanylmethyl)ether, polyethylene glycol bis(3-ethyl-3-oxetanylmethyl)ether, dipentaerythritol hexakis(3-ethyl-3-oxetanyl-methyl)ether, dipentaerythritol penta kis(3-ethyl-3-oxetanylmethyl)ether, dipentaerythritol tetra kis(3-ethyl-3- oxetanyl-methyl)ether, caprolactone-modified dipentaerythritol hexakis(3-ethyl-3- oxetanylmethyl)ether, caprolactone-modified dipentaerythritol pentakis(3-ethyl-3- oxeta nyl methyl)ether, ditri methylol propa ne tetra kis(3-ethyl-3-oxeta nyl methylether, ethylene oxide modified bisphenol-A-bis(3- ethyl-3-oxetanylmethyl)ether, propylene oxide modified bisphenol-A-bis(3-ethyl-3-oxetanylmethyl)ether, ethylene oxide modified hydrogenated bisphenol-A-bis(3-ethyl-3- oxetanylmethyl)ether, propylene oxide modified hydrogenated bisphenol-A-bis(3- ethyl-3-oxetanylmethyl)ether, ethylene oxide modified bisphenol-F-(3-ethyl-3- oxetanyl-methyl)ether, and the like. Preferably the polyoxetane compound a2) has two oxetane groups. In particularly preferred embodiments of the present invention the polyoxetane a2) is 3,3'-oxydimethylene-bis(3-ethyl)-oxetane. 3,3'-oxydimethylene-bis(3-ethyl)- oxetane, also called di-TMPO, is trademarked as Curalite™ OxPlus by Perstorp AB. When present, di-TMPO has shown to be a valuable part of the composition of the invention for assuring a well polymerized network, a good hardness and a good chemical resistance of the cured coating.

[0033] In another preferred embodiment of the present invention said oxetane a2) is a monooxetane compound, having one oxetane group.

[0034] Suitable monooxetane compounds a2) which may be used in the composition of the present invention is preferably selected from the group consisting of at least one of: 3-ethyl-3-hydroxymethyloxetane, 3-(meth)allyl-oxymethyl-3-ethyl- oxetane, (3-ethyl-3-oxetanyl-methoxy)-methyl benzene, 4-fluoro-[1-(3-ethyl-3- oxetanyl-methoxy)methyl]benzene, 4-methoxy-[1-(3-ethyl-3-oxetanylmethoxy)- methyl]-benzene, [1 -(3-ethyl-3-oxeta nyl methoxy)-ethyl] phenyl ether, isobutoxymethyl(3-ethyl-3-oxetanylmethyl)-ether, isobomyloxyethyl(3-ethyl-3- oxeta nyl methyl)- ether, isobomyl(3-ethyl-3-oxetanyl-methyl)ether, 2-ethylhexyl(3- ethyl-3-oxetanylmethyl)ether, ethyldiethylene glycol-(3-ethyl-3-oxetanylmethyl)- ether, dicyclopentadiene(3-ethyl-3-oxetanyl-methyl)ether, dicyclopentenyl- oxyethyl(3-ethyl-3-oxetanylmethyl)ether, dicyclopentenyl(3-ethyl-3-oxetanyl- methyl)ether, tetrahydrofurfuryl-(3-ethyl-3-oxetanylmethyl)ether, tetrabromo- phenyl(3-ethyl-3-oxetanyl-methyl)ether, 2-tetrabromophenoxyethyl(3-ethyl-3- oxetanylmethyl)ether, tribromo-phenyl(3-ethyl-3-oxetanylmethyl)ether, 2- tribromophenoxyethyl(3-ethyl-3-oxetanylmethyl)-ether, 2-hydroxyethyl(3-ethyl-3- oxetanylmethyl)ether, 2-hydroxypropyl(3-ethyl-3-oxetanylmethyl)-ether, butoxy- ethyl(3-ethyl-3-oxetanylmethyl)ether, pentachlorophenyl(3-ethyl-3-oxetanyl- methyl)ether, penta bromophenyl(3-ethyl-3-oxetanylmethyl)ether, bornyl(3-ethyl-3- oxetanyl-methyl)ether, and the like. Other examples of oxetane compounds suitable for use include trimethylene oxide, 3,3-dimethyloxetane, 3,3- dichloromethyloxetane, 3, 3-[1 ,4- phenylene-bis(methylene-oxymethylene)]-bis(3- ethyloxetane), 3-ethyl-3-hydroxymethyl-oxetane, and bis-[(1 -ethyl(3- oxetanyl)methyl)]ether.

[0035] In particularly preferred embodiments of the present invention the monooxetane a2) is 3-ethyl-3-hydroxymethyl-oxetane. 3-ethyl-3-hydroxymethyl-oxetane, also called TMPO, is trademarked as Curalite™ Ox by Perstorp AB. When present, TMPO has shown to be a valuable part of the composition of the invention for assuring a well polymerized network, a good flexibility of the cured coating and also improved adhesion.

[0036] In yet another preferred embodiment of the present invention said oxetane a2) is a mixture of a polyoxetane and a monooxetane, preferably a mixture of 3,3'- oxydimethylene-bis(3-ethyl)-oxetane and 3-ethyl-3-hydroxymethyl-oxetane, and preferably said polyoxetane and monooxetane are present in equal amounts. Preferably each of the polyoxetane and the monooxetane is present in an amount of 5-20 wt%, more preferably 5-15 wt%, and most preferably 5-10 wt%, with respect to the total weight of the cationic resin composition.

[0037] Preferably, the cationic curable resin comprises 1-5 wt%, more preferably 2-4 wt%, of said cationic initiator a3), with respect to the total weight of the cationic resin composition.

[0038] The cationic initiator a3) in the LED curable composition of the present invention is preferably an onium salt, more preferably an iodonium salt, such as iodonium hexafluorophosphate or iodonium hexafluoroantimonate. Most preferably the cationic initiator a3) is a blend of iodonium hexafluorophosphate salt and propylene carbonate, like for instance 4-lsobutylphenyl-4'-methylphenyliodonium hexafluorophosphate, trademarked as Omnicat 250 by IGM resins.

[0039] Preferably, the cationic curable resin comprises 0.5-3 wt%, preferably 1-2 wt%, of said photosensitizer a4), with respect to the total weight of the cationic resin composition.

[0040] The photosensitizer a4) in the LED curable composition of the present invention is preferably a thioxanthone, more preferably a chloro-propoxythioxanthone. Most preferably the photosensitizer a4) is 1-chloro-4-propoxythioxanthone, trademarked as CPTX by Arkema. The presence of an alkoxylated polyol in the LED curable composition of the invention has shown to bring flexibility to the coating system.

[0041] When present in the cationic resin composition according to the invention, said alkoxylated polyol a5) is comprised in a quantity of 0-20 wt%, more preferably 0-10 wt%, with respect to the total weight of the cationic resin composition.

[0042] A suitable alkoxylated polyol a5) is either hexafunctional, tetrafunctional, trifunctional or difunctional, and either ethoxylated, propoxylated, and / or butoxylated. Preferably said alkoxylated polyol a5) is an ethoxylated and / or propoxylated polyol selected from the group consisting of: tri methylol propane, ditrimethylolpropane, pentaerythritol, dipentaerythritol, tripentaerythritol, and neopentyl glycol.

[0043] The epoxide content of the LED curable composition of the invention might be lowered by the addition of an epoxidized vegetable oil a6). When present in the cationic resin composition according to the invention, said epoxidized vegetable oil a6) is comprised in a quantity of 0-20 wt%, preferably 0-10 wt%, with respect to the total weight of the cationic resin composition.

[0044] A suitable epoxidized vegetable oil a6) which may be used in the composition of the present invention is preferably selected from the group consisting of: epoxidized linseed oil, epoxidized soyabean oil, and epoxidized sunflower oil, more preferably epoxidized linseed oil.

[0045] In a preferred embodiment of the present invention, the cationic curable resin comprises 30-80 wt% of said epoxide a1), 10-50 wt% of said oxetane a2), 1- 5 wt% of said cationic initiator a3), 0.5-3 wt% of said photosensitizer a4), 0- 20 wt% of said alkoxylated polyol a5), and 0-20 wt% of said epoxidized vegetable oil a6).

[0046] In another preferred embodiment of the present invention, the cationic curable resin comprises 50-80 wt% of said epoxide a1), 20-40 wt% of said oxetane a2), 2-4 wt% of said cationic initiator a3), 1-2 wt% of said photosensitizer a4), 0-10 wt% of said alkoxylated polyol a5), and 0-10 wt% of said epoxidized vegetable oil a6).

[0047] In yet a further preferred embodiment of the present invention, the cationic curable resin comprises 70-75 wt% of said epoxide a1), 20-25 wt% of said oxetane a2), 2-4 wt% of said cationic initiator a3), and 1 -2 wt% of said photosensitizer a4).

[0048] In another preferred embodiment of the present invention, the cationic curable resin comprises 60-65 wt% of said epoxide a1), 20-25 wt% of said oxetane a2), 2-4 wt% of said cationic initiator a3), 1-2 wt% of said photosensitizer a4), and 5-15 wt% of said alkoxylated polyol a5).

[0049] In yet another preferred embodiment of the present invention, the cationic curable resin comprises 60-65 wt% of said epoxide a1), 20-25 wt% of said oxetane a2), 2-4 wt% of said cationic initiator a3), 1 -2 wt% of said photosensitizer a4), and 5-15 wt% of said epoxidized vegetable oil a6).

[0050] The LED curable composition of the present invention might advantageously also comprise other polyols, like Pentaspiroglycol (PSG) to increase the overall hardness and resistance of a cured cationic coating, or a polyol according to Structure 1 , to improve scratch resistance and maintain good gloss level of the cured coating.

[0051] Structure 1

[0052] The LED curable composition of the present invention may be a 100% cationic curable composition with the benefit of eliminating concern for oxygen inhibition. Cationic curable systems are normally not affected by air, but humidity may decrease the effect of the acidic initiator. In case of very humid air conditions, the LED curing is preferably conducted under dry atmosphere, like for example a nitrogen blanket.

[0053] In a preferred embodiment of the present invention, the cationic curable resin

[0054] A) of the present invention is used together with a free-radical curable resin

[0055] B) in a hybrid LED curable composition. A hybrid curable coating combines both cationic and free-radical curing mechanisms to achieve the best of both worlds. This type of coating can balance the advantages and disadvantages of each mechanism, and provide reduced shrinkage, increased adhesion, improved flexibility, enhanced toughness, and increased cure speed.

[0056] Acrylates polymerize radically, while epoxides polymerize cationically and in the presence of each other during the curing process, an interpenetrating polymer network (IPN) of the two polymers is formed, a polymer blend rather than a copolymer. Although the acrylate and epoxide react independently they affect each other physically during the curing process. As a result, the acrylate polymerizes more extensively in the presence of epoxy and the acrylate is less sensitive to oxygen. The acrylate / epoxide hybrid system requires a shorter exposure time to be cured than either of the two taken separately. The acrylate and the epoxide benefit from each other by a synergistic effect. Increasing the acrylate content increases the cure speed but decreases the adhesion and the flexibility characteristics and increases the brittleness, while increasing the epoxy content reduces the shrinkage of curing, allows significant dark curing and improves the adhesion, but decreases the cure speed. With a LED curable composition according to the present invention it is possible to combine high speed curing with all of the beneficial properties of a cationic radiation curing composition.

[0057] The (meth)acrylate monomer b1) in the free-radical curable resin B) of the present invention is preferably selected from the group consisting of: hexanediol di(meth)acrylate, dipropylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaeryhtritol tri(meth)-acrylate, pentaeryhtritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, alkylene oxide modified glycerol tri(meth)acrylate, alkylene oxide modified neopentyl glycol di(meth)acrylate, alkylene oxide modified trimethylolpropane tri(meth)acrylate, alkylene oxide modified pentaeryhtritol tetra(meth)acrylate, and ditrimethylolpropane tetra(meth)acrylate. More preferably said (meth)acrylate monomer b1) is selected from the group consisting of: propoxylated glycerol triacrylate, ethoxylated tri methylol propane triacrylate, pentaerythritol tetraacrylate, and dipentaerythritol hexaacrylate.

[0058] The (meth)acrylate oligomer b1) in the free-radical curable resin B) of the present invention is preferably selected from the group consisting of: an epoxy (meth)acrylate, a polyester (meth)acrylate, a polyether (meth)acrylate, a melamine (meth)acrylate, a polycarbonate (meth)acrylate, a dendritic (meth)acrylate, and an unsaturated polyester.

[0059] The free-radical curable resin B) of the present invention may also comprise a free-radical photoinitiator b2). The free radical photoinitiator invention is preferably selected from the group consisting of: benzoin or a benzoin derivative, acetophenone, benzil or a benzil ketal, an anthraquinone, a triphenylphosphine oxide, a benzoylphosphine oxide, bisacylphosphine oxide, a benzophenone, a thioxanthone, a xanthone, an acridine derivative, aphenazene derivative, a quinoxaline derivative, 1-phenyl-1 ,2- propanedione 2-O-benzoyl oxime, 4-(2-hydroxyethoxy)phenyl-(2-propyl)ketone, 1 -aminophenyl ketone, and 1 -hydroxy phenyl ketone.

[0060] Additionally, the LED curable composition of the present invention may include other components, for example, matting agents, flow / levelling agents, rheology modifying agents, dyes, pigments, stabilizers, modifiers, tougheners, antifoaming agents, thickening agents, flame retardants, antioxidants and / or fillers.

[0061] The present invention also refers to the use of the LED curable composition of the present invention for producing a coating that is cured with a LED light at a wavelength in the range of 275-405 nm. To increase the hardness or the chemical resistance of the coating even further, either the composition could be altered, e.g. by increasing the content of dioxetane of the cationic curable resin, or the process could be altered, e.g. by having a post curing step for example with IIV-C, to combine a good through-cure of the material, ensuring good surface adhesion, with a good surface cure, ensuring good hardness and good chemical resistance. A combination of LED curing at different wavelengths, like curing with LED 365 nm followed by curing with LED 280 nm, can be used to mimic the light from a mercury lamp and enhance the properties of the coating.

[0062] The present invention is further explained with reference to enclosed embodiment Examples, which are to be construed as illustrative and not limiting in any way.

[0063] EXAMPLES

[0064] Example 1 is a comparative example and Example 2-7 illustrate embodiments of the present invention. Example 1 demonstrates a LED-UV cationic curable composition only comprising a cycloaliphatic epoxide, a cationic photoinitiator and a sensitizer. Example 2 demonstrates a LED-UV curable composition additionally comprising a dioxetane (Curalite™OxPlus) as reactive diluent. Example 3 demonstrates a LED-UV curable composition comprising a monooxetane (Curalite™Ox) instead of the dioxetane as reactive diluent. Examples 4 demonstrates a LED-UV curable composition like the one in Example 3, comprising a monooxetane (Curalite™Ox), but with a lower amount of photoinitiator and sensitizer. Examples 5-7 demonstrate LED-LIV curable compositions comprising dioxetane and different combinations of monooxetane, alkoxylated polyol, epoxidized vegetable oil and sensitizer. Table 1 describes the components of the LED curable compositions demonstrated in Table 2. Figure 1 shows the curing reactivity of the compositions and Table 2 shows the flexibility of the cured coatings.

[0065] Table 1

[0066] The cationic curable compositions of Example 1-7 in Table 2 were prepared. The cationic curable components were blended and the photoinitiator was mixed into the composition with a wooden stick and heated to 60-80°. Storing of the components were made in dark bottles to avoid activation of the photoinitiator.

[0067] Table 2 The compositions of Example 1-7 were then applied with a thickness of 12 pm on aluminium plates using a K-bar. After they had been applied to the substrates, the coatings were cured by passing on an conveyor equipped with LEDs (from Efsen) emitting light at different wavelengths: 275, 365, 395 and 405 nm. After irradiation, the coating surface was checked by gently drawing a cotton stick over the film and verifying there is no mark meaning that that the sample is not tacky.

[0068] A reactivity test was performed by measuring the lowest UV dose required to get a tack free surface. The coatings were stored at 23°C and 50% relative humidity before the mechanical properties were tested, the reactivity results are disclosed in Figure 1.

[0069] From the reactivity results presented in Figure 1 , it can be seen that cationic compositions benefit from the oxetane chemistry. Compared to the composition of Example 1 (only based on ECC), it is possible to cure the other compositions with lower UV doses. Oxetanes are proven to be efficient reactive diluents and contribute significantly to good reactivity results under LED curing. It seems like the oxetanes are needed to compensate for the lower efficiency of LED curing photoinitiators compared to the more efficient UV curing photoinitiators.

[0070] The composition of Example 2 containing 20 wt% Di-TMPO was tack free with a UV dose of 109 mJ / cm2under Hg light, but when cured under LED 365 and 405 nm, a UV dose of 45 respectively 84 mJ / cm2was sufficient. Similar trend can be observed for the composition of Example 3 containing 20 wt% TMPO: it required 199 mJ / cm2under Hg light, while the lower values of 45 and 140 mJ / cm2was sufficient when cured under LED 365 and 405 nm, respectively.

[0071] For the compositions of Example 3 and 4, both containing 20 wt% TMPO, the effect of lowering the photoinitiator package concentration, from 6 to 3 wt%, was investigated and there was a positive effect on the reactivity at 275 and 405 nm.

[0072] The compositions of Example 6, containing a blend of Di-TMPO and TMPO as well as epoxidized linseed oil, seems to be one of the best composition options to guarantee a good surface cure when switching from one wavelength to another, even including the IIV-C LED. The addition of an epoxidized vegetable oil makes it possible to cure the coating at a broader range of LED wavelengths. The fact that the composition of Example 6 is efficiently cured also at 275 nm makes it suitable for applications like top coatings.

[0073] For coating evaluation of flexibility, the cationic compositions were applied with a thickness of 40 pm on aluminum plates and cured with a belt speed of 30 m / min and a LED intensity of 60%. 30 m / min is a relatively high speed to ensure efficient productivity in industry and an intensity of 60% allows to reduce energy consumption and ensure good time life of the LED unit. The dose obtained during these conditions was 280 mJ / cm2at 405 nm. The flexibility, i.e. the ability of the coated metal plates to undergo plastic deformation in stretch forming, was measured by the Erichsen ductility test according to ISO 1520-1999. The result from the coating evaluation flexibility test is presented in Figure 2.

[0074] The addition of alkoxylated polyol lead to increased flexibility as can been seen when comparing the composition of Example 2 with the composition of Example 7. The presence of TMPO also increase the flexibility to a certain extent, as can be seen for the composition of Example 3.

Claims

CLAIMS1. A light emitting diode (LED) curable composition, wherein the composition comprises a cationic curable resin comprising a1) an epoxide, a2) an oxetane, a3) a cationic initiator, and a4) a photosensitizer, wherein the weight ratio between the epoxide a1) and the oxetane a2) is in the range of 1-5.

2. The LED curable composition according to claim 1 , wherein the weight ratio between said epoxide a1) and said oxetane a2) is in the range of 1-4 and preferably in the range of 1.4-3.9.

3. The LED curable composition according to claim 1 or 2, wherein the composition comprises:A) 40-100 wt% of said cationic curable resin, wherein said cationic curable resin optionally comprises also at least one of the following compounds a5) an alkoxylated polyol, a6) an epoxidized vegetable oil,B) 0-60 wt% of a free-radical curable resin, further comprisingb1) at least one (meth)acrylate monomer or oligomer, and optionally b2) a free-radical photoinitiator, wherein the weight percent is based on the total weight of the LED curable composition.

4. The LED curable composition according to any of the claims 1-3, wherein said cationic curable resin comprises 30-80 wt%, preferably 50-80 wt%, of said epoxide a1).

5. The LED curable composition according to any of the claims 1-4, wherein said cationic curable resin comprises 10-50 wt%, preferably 20-40 wt%, and most preferably 20 wt% of said oxetane a2).

6. The LED curable composition according to any of the claims 1-5, wherein said cationic curable resin comprises 1-5 wt%, preferably 2-4 wt%, of said cationic initiator a3).

7. The LED curable composition according to any of the claims 1-6, wherein said cationic curable resin comprises 0.5-3 wt%, preferably 1-2 wt%, of said photosensitizer a4).

8. The LED curable composition according to any of the claims 3-7, wherein said cationic curable resin comprises 0-20 wt%, preferably 0-10 wt%, of said alkoxylated polyol a5).

9. The LED curable composition according to any of the claims 3-8, wherein said cationic curable resin comprises 0-20 wt%, preferably 0-10 wt%, of said epoxidized vegetable oil a6).

10. The LED curable composition according to any of the claims 3-9, wherein said cationic curable resin comprises 30-80 wt% of said epoxide a1), 10-50 wt% of said oxetane a2), 1-5 wt% of said cationic initiator a3), 0.5-3 wt% of said photosensitizer a4), 0-20 wt% of said alkoxylated polyol a5), and 0-20 wt% of said epoxidized vegetable oil a6).

11. The LED curable composition according to any of the claims 3-10, wherein said cationic curable resin comprises 50-80 wt% of said epoxide a1), 20-40 wt% of said oxetane a2), 2-4 wt% of said cationic initiator a3), 1-2 wt% of said photosensitizer a4), 0-10 wt% of said alkoxylated polyol a5), and 0-10 wt% of said epoxidized vegetable oil a6).

12. The LED curable composition according to any of the claims 1-11 , wherein said cationic curable resin comprises 70-75 wt% of said epoxidea1), 20-25 wt% of said oxetane a2), 2-4 wt% of said cationic initiator a3), and 1-2 wt% of said photosensitizer a4).

13. The LED curable composition according to any of the claims 3-11 , wherein said cationic curable resin comprises 60-65 wt% of said epoxide a1), 20-25 wt% of said oxetane a2), 2-4 wt% of said cationic initiator a3), 1-2 wt% of said photosensitizer a4), and 5-15 wt% of said alkoxylated polyol a5).

14. The LED curable composition according to any of the claims 3-11 , wherein said cationic curable resin comprises 60-65 wt% of said epoxide a1), 20-25 wt% of said oxetane a2), 2-4 wt% of said cationic initiator a3), 1-2 wt% of said photosensitizer a4), and 5-15 wt% of said epoxidized vegetable oil a5).

15. The LED curable composition according to any of the claims 1-14, wherein said epoxide a1) is a cycloaliphatic epoxide.

16. The LED curable composition according to claim 15, wherein said cycloaliphatic epoxide a1) is selected from the group consisting of: a 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate, a 3,4- epoxy-1-methyl-cyclohexyl methyl-3,4-epoxy-1 -methylcyclo-hexane carboxylate, a 6-methyl-3,4-epoxycyclohexymethyl-6-methyl-3,4-epoxy-cyclohexane carboxylate, a 3,4-epoxy-3-methylcyclohexylnnethyl-3,4- epoxy-3-methylcyclohexane carboxylate, and a 3,4-epoxy-5- methylcyclohexylnnethyl-3,4-epoxy-5-nnethylcyclohexane carboxylate.

17. The LED curable composition according to any of the claims 1-16, wherein said oxetane is a polyoxetane compound, having at least two oxetane groups.

18. The LED curable composition according to claim 17, wherein said polyoxetane a2) is 3,3'-oxydimethylene-bis(3-ethyl)-oxetane.

19. The LED curable composition according to any of the claims 1-16, wherein said oxetane is a monoxetane compound, having one oxetane group.

20. The LED curable composition according to claim 19, wherein said monooxetane a2) is 3-ethyl-3-hydroxymethyl-oxetane.

21. The LED curable composition according to any of the claims 1-16, wherein said oxetane is a mixture of a polyoxetane and a monoxetane, preferably a mixture of 3,3'-oxydimethylene-bis(3-ethyl)-oxetane and 3- ethyl-3-hydroxymethyl-oxetane.

22. The LED curable composition according to claim 21, wherein said polyoxetane and monooxetane are present in equal amounts.

23. The LED curable composition according to claim 22, wherein each of the polyoxetane and the monooxetane is present in an amount of 5-20 wt%, more preferably 5-15 wt%, and most preferably 5-10 wt%, with respect to the total weight of the cationic resin composition.

24. The LED curable composition according to any of the claims 1-23, wherein said cationic initiator a3) is an onium salt, preferably an iodonium salt, more preferably an iodonium hexafluorophosphate.

25. The LED curable composition according to any of the claims 1-24, wherein said photosensitizer a4) is a thioxanthone, preferably a chloropropoxythioxanthone.

26. The LED curable composition according to any of the claims 3-25, wherein said alkoxylated polyol a5) is an ethoxylated or propoxylated polyol selected from the group consisting of trimethylolpropane, ditrimethylolpropane, pentaerythritol, dipentaerythritol, tripentaerythritol and neopentyl glycol.

27. The LED curable composition according to any of the claims 3-26, wherein said epoxidized vegetable oil a6) is selected from the group consisting of: epoxidized linseed oil, epoxidized soyabean oil, and epoxidized sunflower oil, preferably epoxidized linseed oil.

28. The LED curable composition according to any of the claims 3-27, wherein said (meth)acrylate monomer b1) is selected from the group consisting of: hexanediol di(meth)acrylate, dipropylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaeryhtritol tri(meth)-acrylate, pentaeryhtritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, alkylene oxide modified glycerol tri(meth)acrylate, alkylene oxide modified neopentyl glycol di(meth)acrylate, alkylene oxide modified trimethylolpropane tri(meth)acrylate, alkylene oxide modified pentaeryhtritol tetra(meth)acrylate, and ditrimethylol-propane tetra(meth)acrylate.

29. The LED curable composition according to any of the claims 3-27, wherein said (meth)acrylate monomer b1) is selected from the group consisting of: propoxylated glycerol triacrylate, ethoxylated trimethylolpropane triacrylate, pentaerythritol tetraacrylate, and dipentaerythritol hexaacrylate.

30. The LED curable composition according to any of the claims 3-27, wherein said (meth)acrylate oligomer b1) is selected from the group consisting of: an epoxy (meth)acrylate, a polyester (meth)acrylate, a polyether (meth)acrylate, a melamine (meth)acrylate, a polycarbonate (meth)acrylate, a dendritic (meth)acrylate, and an unsaturated polyester.

31. The LED curable composition according to any of the claims 1-30, wherein said composition additionally comprises a matting agent, a flow / levelling agent, a rheology modifying agent, a dye, and / or a pigment.

32. Use of the LED curable composition according to any of the claims 1 - 31 , for producing a coating that is cured with a LED light at a wavelength in the range of 275-405 nm.

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