WO2019241679A1

WO2019241679A1 - Uv curable uv blocking clear coatings

Info

Publication number: WO2019241679A1
Application number: PCT/US2019/037262
Authority: WO
Inventors: Puruswottam Aryal; Glenn Allen MESA, Jr.
Original assignee: Metashield LLC
Current assignee: Metashield LLC
Priority date: 2018-06-15
Filing date: 2019-06-14
Publication date: 2019-12-19
Anticipated expiration: 2020-12-15

Abstract

The present invention relates to coatings that are UV curable and UV blocking/absorbing and to photo-initiator combinations for use in such coatings comprising a first photo- initiator compound photosensitive at UV-B and UV-C wavelengths having a ketone group and a second photo-initiator compound photosensitive at UV-A wavelengths or visible light selected from acyl phosphine oxide compounds.

Description

PATENT APPLICATION

Title

UV Curable UV Blocking Clear Coatings

Field

The present invention relates to coatings that are UV curable and UV blocking/absorbing and to photo-initiator combinations for use in such coatings.

Background

It is challenging to develop a UV curable coating that blocks UV up to 380 nm or 400 nm because the UV blocking properties of the coating itself prevent the complete curing of UV curing through the full thickness of the coating. This challenge increases when the coating needs to be optically clear with a very low yellowness index to be acceptable. Even though photo- initiators are available that absorb and block UV light in the visible wavelength range, such as diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO) and phenyl-bis(2,4,6- trimethylbenzoyl)phosphine oxide (BAPO), these photo-initiators yellow unacceptably upon UV exposure. Coatings with these photo-initiators bleach upon exposure to light and heat for a few hours after UV curing, but still look too yellow to be acceptable when a color neutral optically transparent coating is desired. Accordingly, improved photo-initiators and photo-initiator combinations are desirable to improve curing while minimizing yellowness in certain higher wavelengths above about 380 nm.

Summary

The present invention relates to UV resistant UV curable acrylate coating compositions having a photo-initiator combination comprising:

a first photo-initiator compound photosensitive at UV-B and UV-C wavelengths selected from one or more of acetophenone, benzophenone and phenyl ketone compounds, at a concentration of from about 2% to about 10% by weight of the total coating composition; and a second photo-initiator compound photosensitive at UV-A wavelengths or visible light selected from acyl phosphine oxide compounds at a concentration of from about 0.1% to about 2.0% by weight of the total coating composition;

wherein the acrylate coating after curing upon exposure to UV light emitted from a UV H bulb having a mercury spectral output has a thickness of from about 20 to about 32 pm and a Delta Yellowness Index less than or equal to about 5.3.

In some embodiments, the UV resistant UV curable acrylate coating composition, the first photo- initiator compound has a concentration of from about 2% to about 8% by weight of the total coating composition.

In some embodiments, the first photo-initiator compound has a concentration of from about 3.85% to about 7.96% by weight of the total coating composition. In one exemplary embodiment, the first photo-initiator compound has a concentration of about 3.85% by weight of the total coating composition.

In another exemplary embodiment, the first photo-initiator compound has a concentration of about 7.96% by weight of the total coating composition.

In some embodiments, the second photo-initiator compound has a concentration of from about 0.2% to about 2% by weight of the total coating composition.

In other embodiments, the second photo-initiator compound has a concentration of from about 0.2% to about 1.0% by weight of the total coating composition.

In yet other embodiments, the second photo-initiator compound has a concentration of from about 0.22% to about 0.42% by weight of the total coating composition.

In an exemplary embodiment, the second photo-initiator compound has a concentration of about 0.42% by weight of the total coating composition.

In another exemplary embodiment, the second photo-initiator compound has a concentration of about 0.22% by weight of the total coating composition.

In another embodiment, the first photo-initiator is an acetophenone has a concentration of from about 3.85% to about 7.96%, and the second photo-initiator compound has a concentration of from about 0.22% to about 0.42% by weight of the total coating composition.

In one exemplary embodiment, the first photo-initiator is 2,2- di ethoxy acetophenone and the second photo-initiator compound is diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO).

In some embodiments, the first photo-initiator compound is selected from one or more of 4'- ethoxyacetophenone, 4'-hydroxyacetophenone, 2,5-dimethylbenzophenone, 4- hydroxybenzophenone, and 1 -hydroxy cyclohexyl phenyl ketone, or combinations thereof.

In one exemplary embodiment, the first photo-initiator compound is 2,2-diethoxyacetophenone.

In other embodiments, the second photo-initiator compound is selected from one or more of diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide and bis(2,4,6-trimethylbenzoyl)- phenylphosphineoxide, or combinations thereof.

In one exemplary embodiment, the second photo-initiator compound is diphenyl(2,4,6- trimethylbenzoyl)phosphine oxide.

In another exemplary embodiment, the first photo-initiator compound is 2,2- diethoxyacetophenone and the second photo-initiator compound is diphenyl(2,4,6- trimethylbenzoyl)phosphine oxide.

In another exemplary embodiment, the concentration of the first photo-initiator compound 2,2- diethoxyacetophenone is about 3.85% by weight of the total coating composition and the concentration of the second photo-initiator compound diphenyl(2,4,6- trimethylbenzoyl)phosphine oxide is 0.22% by weight of the total coating composition. In another embodiment, the Delta Yellowness Index of the cured coating composition is less than about 3.

In another embodiment, the Delta Yellowness Index of the cured coating composition ranges from about 1 to about 3.

In another embodiment, the Delta Yellowness Index of the cured coating composition is about 1.

In another embodiment, the thickness of the cured coating composition is from about 15 pm to about 30 pm.

In another embodiment, the thickness of the cured coating composition is about 20 pm.

Drawings

Fig. 1 is a graph showing transmission spectra of the coatings MS7UV380 (dashed line) and MS7UV400 (solid line).

Fig. 2 is a graph showing Tinuvin 384-2 % as a function of total weight.

Description

The terms "and/or" or "or/and" in the present context are meant to express that not only one of the defined alternatives (substituents) may be present, but also several of the defined alternatives (substituents) together in combination, namely mixtures of different alternatives (substituents). The term "at least" is meant to define one or more than one, for example one or two or three, preferably one or two. Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise," or variations such as "comprised" or

"comprising," will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. The term "(meth)acrylate" in the context of the present application is meant to refer to the acrylate as well as to the corresponding methacrylate. The preferences indicated above for the compounds according to the present invention in the context of this invention are intended to refer to all categories of the claims, that is to the compositions, use, process claims as well.

It is to be understood that this invention is not limited to particular compounds, configurations, method steps, substrates, and materials disclosed herein as such compounds, configurations, method steps, substrates, and materials may vary somewhat. It is also to be understood that the terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting since the scope of the present invention is limited only by the appended claims and equivalents thereof.

It must be noted that, as used in this specification and the appended claims, the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. If nothing else is defined, any terms and scientific terminology used herein are intended to have the meanings commonly understood by those of skill in the art to which this invention pertains. Percentage values represent percent by weight of the total coating composition, unless expressly described otherwise (such as the percent by weight of just the photo-initiator component of the coating composition of some commercially available photo-initiators described herein). The phrase“greater than about 0%” means a value above 0%, excluding 0%.

Acrylate Coating Base

The UV photopolymerizable compositions may include free radically polymerizable monomers, oligomers, and polymers having one or more ethyl enically unsaturated acrylic groups. Suitable compounds contain at least one ethylenically unsaturated bond and are capable of undergoing addition polymerization. Examples of useful ethylenically unsaturated acrylate compounds include acrylic acid esters, methacrylic acid esters, hydroxy-functional acrylic acid esters, hydroxy-functional methacrylic acid esters, and combinations thereof.

As used in the present invention the term acrylate and acrylic refer to the same chemical functionality. The word "meth" in two brackets as "(meth)" associated to the term acrylate, specifies that relating to a molecule or to a family of molecules the acrylate function

H₂C=CHC(0)— could have a methyl group at a position of the ethylene function like

H₂C=C(CH₃)C(0)— . Thus, the term (meth)acrylate refers to both the acrylate (without the methyl group at the position of the ethylene function) and methacrylate (with the methyl group at the position of the ethylene function) variants of the monomer

The UV curable compositions may also contain monomers having hydroxyl groups and ethylenically unsaturated groups in a single molecule. Examples of such materials include hydroxyalkyl (meth)acrylates, such as 2-hydroxyethyl (meth)acrylate and 2-hydroxypropyl (meth)acrylate; glycerol mono- or di-(meth)acrylate; trimethylolpropane mono- or di- (meth)acrylate; pentaerythritol mono-, di-, and tri-(meth)acrylate; sorbitol mono-, di-, tri-, tetra-, or penta-(meth)acrylate; and 2,2-bis[4-(2-hydroxy-3-ethacryloxypropoxy)phenyl]propane (bisGMA). Suitable ethylenically unsaturated compounds are available from a wide variety of commercial sources, such as Sigma-Aldrich, St. Louis.

The (meth)acrylates described and claimed herein are multifunctional, meaning that they can be difunctional, trifunctional, tetrafunctional, pentafunctional, hexafunctional or higher functional, or combinations thereof. Typically, the higher the functionality, the greater is the crosslink density. (Meth)acrylates have slower curing than the acrylates.

The two, three, four, five or six or more (meth)acrylic functional groups may be selected from one or more of, for example, pentaerythritol triacrylate, pentaerythritol tetraacrylate,

tetraethyleneglycol diacrylate, ethyleneglycol diacrylate, diethyleneglycol diacrylate,

tri ethyleneglycol diacrylate, hexanediol diacrylate, l,6-hexanediol di(meth)acrylate, tripropylene glycol diacrylate, dipropyl eneglycol diacrylate, ethyleneglycol dimethacrylate, trimethylolethane triacrylate, trimethylolmethane triacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, l,2,4-butanetriol trimethacrylate, tri s(2-hydroxy ethyl) isocyanurate triacrylate, di-trimetholpropane tetraacrylate, ethoxylated pentaerythritol tetraacrylate, triphenylolmethane triacrylate, trisphenol triacrylate, tetraphenylol ethane triacrylate, l,2,6-hexanetriol triacrylate, glycerol triacrylate, diglycerol triacrylate, glycerol ethoxylate triacrylate, glycerine propoxylated triacrylate, ethylene glycol diacrylate, l,4-butanediol diacrylate, 1,4 butanediol dimethacrylate, neopentyl glycol diacrylate, cyclohexanedimethanol diacrylate, dipropylene glycol diacrylate, pentaerythritol tetraacrylate, polypropylene glycol diacrylate, dipentaerythritol hexaacrylate, polyester hexaacrylate, sorbitol hexaacrylate, and fatty acid-modified polyester hexaacrylate, and the like.

Free radically polymerizable compounds include di- or poly-(meth)acrylates (i.e., acrylates and methacrylates) such as glycerol tri(meth)acrylate, ethyleneglycol di(meth)acrylate,

diethyleneglycol di(meth)acrylate, triethyleneglycol di(meth)acrylate, 1, 3-propanediol di(meth)acrylate, trimethyl olpropane tri(meth)acrylate, l,2,4-butanetriol tri(meth)acrylate, 1,4- cyclohexanediol di(meth)acrylate, pentaerythritol tetra(meth)acrylate, sorbitol hex(meth)acrylate, tetrahydrofurfuryl (meth)acrylate, bis[l-(2-acryloxy)]-p-ethoxyphenyldimethylmethane, bis[l- (3-acryloxy-2-hydroxy)]p-propoxyphenyldimethylmethane, ethoxylated bisphenol A

di(meth)acrylate, and tri shy droxy ethyl -isocyanurate tri(meth)acrylate; (meth)acrylamides (i.e., acrylamides and methacrylamides) such as (meth)acrylamide, methylene bis-(meth)acrylamide, and diacetone (meth)acrylamide; urethane (meth)acrylates; the bis-(meth)acrylates of

polyethylene glycols (preferably of molecular weight 200-500); and vinyl compounds such as styrene, diallyl phthalate, divinyl succinate, divinyl adipate and divinyl phthalate. Other suitable free radically polymerizable compounds include siloxane-functional (meth)acrylates. Mixtures of two or more free radically polymerizable compounds can be used if desired.

In some embodiments disclosed herein, the coating compositions comprise one or more photocurable acrylate or methacrylate monomers or copolymers, which react to form a polymeric matrix having high surface hardness and high crosslinking density of coatings. In some embodiments, the curable acrylate may comprise a first multifunctional acrylate monomer or oligomer with three or more functional polymer bonding groups. In other embodiments, the curable acrylate may also comprise aliphatic urethane acrylates.

For example, the acrylate polymer may be obtained using multifunctional acrylate monomers such as trimethylolpropane triacrylate (TMPTA) and dipentaerythritol penta-hexa acrylate.

Multifunctional aliphatic urethane acrylates include, for example, EBECRYL® 1290 (a hexafunctional aliphatic urethane acrylate oligomer) and EBECRYL® 225 (an aliphatic urethane -deca-acrylate monomer), commercially available from Allnex (Luxembourg, Belgium).

In some embodiments, the multifunctional acrylate may be preloaded with nanoparticles. Such nanoparticles may be metal oxide nanoparticles, such as silica nanoparticles. For example, one suitable multifunctional acrylate is TMPTA, which is commercially available as NANOCRYL^®

C 150 (Evonik Resource Efficiency GmbB, BL Coating Additives) with 50% silica nanoparticles by weight of the TMPTA/nanoparticle composition.

The acrylate monomer may be present in a concentration range of from about 10% to about 50%. The acrylate monomer may be present in a concentration range of from about 10% to about 46%. The acrylate monomer may be present in a concentration range of from about 35% to about 50%. The acrylate monomer may also be present in a concentration range of about 40% to about 41% by weight of the total composition.

The acrylate portion of the composition may also include two or more of the acrylate monomer compounds described above. The acrylate portion of the composition may also include a second multifunctional acrylate monomer or oligomer having two or more functional polymer bonding groups. The second acrylate monomer or copolymer may include any of the multifunctional acrylate monomers or oligomers described above for the first acrylate monomer or oligomer that have two or more functional polymer bonding groups. For example, the second acrylate monomer may be dipentaerythritol penta-hexa acrylate.

The second acrylate monomer or oligomer having two or more functional polymer bonding groups may be present in a concentration of from about 5% to about 40% by weight of the total composition. The second acrylate monomer having two or more functional polymer bonding groups may be present in a concentration range of from about 5% to about 15% by weight of the total composition. The second acrylate monomer having two or more functional polymer bonding groups may be present in a concentration range of from about 7% to about 38% by weight of the total composition. The second acrylate monomer having two or more functional polymer bonding groups may be present in a concentration range of from about 7% to about 12% by weight of the total composition. The second multifunctional acrylate monomer may be present in a concentration of about 8% by weight of the total composition.

In other embodiments, the curable acrylate compound may include a third polyfunctional acrylate monomer or oligomer having one or more bonding functional groups. Such acrylate monomers or oligomers may be, for example, l,6-hexanediol diacrylate.

The multifunctional acrylate may be present in a concentration of from about 5% to about 30% by weight of the total composition. The third multifunctional acrylate may be present in a concentration range of from about 6% to about 20% by weight of the total composition. The third multifunctional acrylate may be present in a concentration range of from about 9% to about 12% by weight of the total composition. The third acrylate may be present in a concentration of about 12% by weight of the total composition.

Photo-Initiators

The acrylate monomers described above may also be combined with a plurality of free-radical photo-initiators to initiate polymerization of the acrylate monomers.

The UV resistant UV curable acrylate monomers or copolymers are curable using first photo- initiator that is primarily photoactivated by UA-B and UV-C light. Such photo-initiators may include compounds having a reactive phenome or phenyl ketone group having a carbon-oxygen double bond, such as compounds having a ketone group having the structure RC(=0)R’ where R is an aromatic group, such as a phenyl group. Suitable phenyl ketone-based photo-initiators may include one or more phenyl ketone, such as acetophenone and/or benzophenone, and/or other phenyl ketone-based compound. For example, the phenyl ketone photo-initiator compound may be just one of an acetophenone, benzophenone, and/or other phenyl ketone-based compound or a mixture of two or more of these compounds.

The UV resistant UV curable acrylate monomers or copolymers are curable using a second photo-initiator that is primarily photoactivated by UV-A light. Such photo-initiators may include compounds having a reactive phosphoryl group having a phosphorous-oxygen double bond. Suitable compounds having a reactive phosphoryl group include phosphine oxides, which are phosphorus compounds having the formula OPX3, where X may be an organic alkyl or aryl group or an inorganic group, such as a halogen group. Such phosphine oxide compounds may be used alone or in a mixture of two or more of these compounds.

A photo-initiator is typically added to the mixture of polymerizable ingredients. The photo- initiator is sufficiently miscible with the resin system to permit ready dissolution in (and discourage separation from) the polymerizable composition. Typically, the photo-initiator is present in the composition in effective amounts, such as from about 0.1% weight percent to about 5.0% by weight percent of the total weight of the composition.

The mixture of monomers is photopolymerizable and the composition contains a photo-initiator (i.e., a photo-initiator system) that upon irradiation with actinic radiation initiates the

polymerization (or hardening) of the composition. Such photopolymerizable compositions can be free radically polymerizable. The photo-initiator system typically has a functional wavelength range from about 200 nm to about 400 nm. The photo-initiator system may also have a functional wavelength range from about 200 nm to about 410 nm. The photo-initiator system may also have a functional wavelength range from about 200 nm to about 420 nm.

Suitable photo-initiators (i.e., photo-initiator systems that include one or more compounds) for polymerizing free radically photopolymerizable compositions include binary and tertiary systems. Typical tertiary photo-initiators include an iodonium salt, a photosensitizer, and an electron donor compound as described in U.S. Pat. No. 5,545,676 (Palazzotto et ah). Iodonium salts include diaryl iodonium salts, e.g., diphenyliodonium chloride, diphenyliodonium hexafluorophosphate, and diphenyliodonium tetrafluoroboarate. Some photosensitizers may include monoketones and diketones (e.g. alpha diketones) that absorb some light within a range of about 300 nm to about 800 nm (or about 400 nm to about 500 nm) such as camphorquinone, benzil, furil, 3,3,6,6-tetramethylcyclohexanedione, phenanthraquinone and other cyclic alpha diketones. Of these camphorquinone is typical. Electron donor compounds include substituted amines, e.g., ethyl 4-(N,N-dimethylamino)benzoate.

Acetophenone and acetophenone derivative photo-initiators can include a-hydroxy-cycloalkyl phenyl ketones or a-hydroxyalkyl phenyl ketones. Particular examples include acetophenone, p- tert-butyl trichloroacetophenone, chloroacetophenone, 2,2-diethoxy acetophenone, hydroxy acetophenone, 2,2-dimethoxy-2'-phenyl acetophenone, 2-aminoacetophenone, and dialkyl aminoacetophenone, 2-hydroxy-2-methyl propiophenone, 2-hydroxy-4'-(2- hydroxyethoxy)-2- methyl propiophenone, 2-hydroxy-2,2-dimethylacetophenone, acetonaphthoquinone, valerophenone, hexanophenone, a-phenylbutyrophenone, dibenzosuberone, p-diacetylbenzene, 4'-methoxyacetophenone, a-tetralon, 9-acetylphenanthrene, 2-acetylphenanthrene, 3- acetylphenanthrene, 3-acetylindole, 9-fluorenone, l-indanone, l,3,4-triacetylbenzene, 1- acetonaphthone, 2-acetonaphthone, 2,2-dimethoxy-2-phenylacetophenone, 2,2-diethoxy-2- phenyl acetophenone, l,l-dichloroacetophenone, 1 -hydroxyacetophenone, 2,2- diethoxyacetophenone, 2,2-dimethoxy-l,2-diphenylethan-2-one, 1 -(4-dodecylbenzoyl)-l- hydroxy- 1 -methyl -ethane, 1 -( 4-i sopropylbenzo-yl)- 1 -hydroxy- 1 -methyl-ethane, 2-hydroxy- 1 - {4-[4-(2-hydroxy-2-methyl-propion-yl)-phenoxy]-phenyl } -2-methyl-propan- 1 -one, 4'- ethoxyacetophenone, 4'-hydroxyacetophenone, benzyl dimethyl ketal, 4-isopropyl-2-hydroxy-2- methylpropiophenone, 1 -hydroxyacetophenone, l-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2- m ethyl- 1 -propan- 1 -one, dialkoxyacetophenones a-hydroxy- or a-am-inoacetophenones such as diethoxyacetophenone and a-a-dimethoxy a-phenyl acetophenone, and

benzylideneacetophenone; (4-(2 -hydroxy ethyl)aminobenzoyl)- 1 -benzyl- 1 - dimethylaminopropane), (3 ,4-dimethoxybenzoyl)- 1 -benzyl- 1 -dimethylaminopropane; 4-aroyl- 1 ,

3-dioxolanes, benzoin alkyl ethers and benzil ketals, e.g. dimethyl benzil ketal, phenylglyoxalic esters and derivatives thereof, e.g. methyl a-oxo benzeneacetate, oxo-phenyl-acetic acid 2-(2- hydroxy-ethoxy)-ethyl ester, dimeric phenylglyoxalic esters, e.g. 9H-thioxanthene-2- carboxaldehyde 9-oxo-2-(0-acetyloxime), per- esters, e,g. benzophenone tetracarboxylic peresters as described for example in EP 126541.

Free radical acetophenone photo-initiators are available commercially as (l-[4-(2- hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-l-propan-l-one) (IRGACURE ® 2959 from CIBA), 2,2-di-sec-butoxyacetophenone, 2,2-diethoxy-2-phenyl-acetophenone, 1 -hydroxy- cyclohexyl -phenyl-ketone (IRGACURE ® 184 from CIBA) and 2-hydroxy-2-methyl-l- phenylpropan-l-one (such as DAROCUR® 1173 sold by CIBA); alpha amino ketones, particularly those containing a benzoyl moiety, otherwise called alpha-amino acetophenones, such as 2-hydroxy-l-{4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]-phenyl}- 2-methyl-propan-

1-one (IRGACURE® 127), oxo-phenyl-acetic acid l-methyl-2-[2-(2-oxo-2-phenyl-acetoxy)- propoxy] -ethyl ester (IRGACURE® 754); ketosulfones, e.g. ESACURE KIP 1001 M®; oxime- esters, such as l,2-octanedione l-[4-(phenylthio)phenyl]-2-(0-benzoyl oxime) (IRGACURE® OXEOl ), and ethanone l-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]-l-(0-acetyloxime) (IRGACURE® OXE02).

Benzophenones and related aromatic ketones may include, for example, benzophenone, benzophenone derivatives, such as xanthones, thioxanthones such as 2-chlorothioxanthone, 2- methylthioxanthone, 2-isopropylthioxanthone, camphor quinone, methyl benzophenones, such as

2-methylbenzophenone, 3-methylbenzophenone, 4-methylbenzophenone, 1 -hydroxy cyclohexyl phenyl ketone, benzoyl benzoic acid, benzoyl benzoic acid methyl, methyl-o-benzoyl benzoate,

4-phenyl benzophenone, hydroxy benzophenone, hydroxy propyl benzophenone, acryl benzophenone, and 4,4'-bis(dimethyl amino)benzophenone, 4,4'~bis(chloromeihy{)~

benzophenone 2,5-dimethylbenzophenone, 4-hydroxybenzophenone, 4-aminobenzophenone, 4- chlorobenzophenone, Michler's ketone, o-methoxybenzophenone, 2,4,6-trimethylbenzophenone, 2,4,6-trimethyl-4'-phenylbenzophenone 4-methylbenzophenone, 2,4-dimethylbenzophenone, 4- isopropylbenzophenone, 2-chlorobenzophenone, 2,2'-dichlorobenzophenone, 4- methoxybenzophenone, 3,3^!-dimethyl-4-methoxy-benzophenone 4-propoxybenzophenone or 4- butoxybenzophenone, 2-methoxycarbonylbenzophenone, 4-phenylbenzophenone, [4-(4- methylphenylthio)phenyi]-phenylmethanone, 3-m ethyl -4'-phenylbenzophenone, 4,4'- bis(dimethylamino)benzophenone, 4,4'~bis(diethyiamino)benzophenone, 2,2-dimethoxy-l,2- diphenylethane-l-one, a-hydroxy-alkyl-aryl ketones, such as l-benzoylcyclohexan-l-ol (1- hydroxy-cyclohexyl-phenyl ketone), 1 -hydroxy cyclohexyl phenyl ketone, (2-hydroxy-2-m ethyl - 1 -phenyl-propan- 1 -one), dicyclopentadiethyltitanium-di(pentafluorophenyl), haloalkylated aromatic ketones such as chloromethylbenzophenones; some benzoin ethers such as benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutylether ether, benzoin, benzyl, benzyl disulfide, methyl orthobenzoyl benzoate, methyl-2-benzoyi- benzoate, or polymer that contains 2-hydroxy-2-methyl-l-(4-isopropen-2-yl-phenyl)propan-l-one incorporated by polymerization.

Photo-initiators based on acyl phosphine oxides are photosensitive at longer wavelengths (UV-A or visible light). The UV photo-initiators used for polymerizing free radically

photopolymerizable compositions may include the class of phosphine oxides that typically initiate polymerization at a functional wavelength range of about 380 nm to about 1200 nm.

Some phosphine oxide free radical initiators, such as acyl and bisacyl phosphine oxides, initiate polymerization at a functional wavelength range of about 380 nm to about 450 nm.

Examples of acylphosphine oxide compounds are monoacyl and bisacyl phosphine oxides and sulphides; monoacyl phosphine oxides, e.g. (2,4,6-trimethylbenzoyl)diphenylphosphine oxide, ethyl (2,4,6 trimethylbenzoyl phenyl) phosphinic acid ester; bisacyl-phosphine oxides, e.g.

bis(2,6-dimethoxy-benzoyl)-(2, 4, 4-trimethyl -pentyl)phosphine oxide, bis(2,4,6-trimethyl- benzoyl)-2,4-dipentoxyphenylphosphine oxide, trisacylphosphine

oxidestriacyl phosphine oxides, methyl isobutyryl-methylphosphinate, methyl isobutyryl- phenylphosphinate, methyl pivaloylphenylphosphinate, methyl 2-ethylhexanoyl- phenyl phosphinate, isopropyl pivaloyl -phenyl phosphinate, methyl p-toluyl phenyl phosphinate, methyl o-toluyl-phenylphosphinate, methyl 2,4-dimethylbenzoyl-phenylphosphinate, isopropyl p-tert-butyl-phenylphosphinate, methyl pivaloyl-(4-methylphenyl)phosphinate, vinyl pivaloyl- phenylphosphinate, methyl acryloyl-phenylphosphinate, isobutyryl-diphenylphosphine oxide, pivaloyl-diphenylphosphine oxide, 1 -methyl- 1 -cyclohexanoyl-diphenylphosphine oxide, 2- ethylhexanoyl-diphenylphosphine oxide, p-toluyl-diphenylphosphine oxide, o- toluyldiphenylphosphine oxide, p-tert-butyldiphenylphosphine oxide, 3 -pyridyl carbonyl - diphenylphosphine oxide, acryloyldiphenylphosphine oxide, benzoyl-diphenylenephosphine oxide, 2,2-dimethyl-heptanoyl-diphenylphosphine oxide, terephthaloyl-bis-diphenylphosphine oxide and adipoyl-bis-diphenylphosphine oxide_, 2_,4_,6-trimethylbenzoyldiphenylphosphine oxide, ethyl-2, 4, 6-trimethylbenzoylphenylphosphinate, 2,4,6,

trimethylbenzoylethoxydiphenyl phosphine oxide, bisacylphosphine oxides (BAPO) or bis(2,6- dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide; benzyltrimethylbenzoyl diphenyl phosphinoxide; and mixtures thereof.

Acyl phosphine oxide photo-initiators are available commercially as bis(2,4,6- trimethylbenzoyl)phenyl phosphine oxide (IRGACURE® 819, Ciba Specialty Chemicals, Tarrytown, N.Y.), bis(2,6-dimethoxybenzoyl)-(2,4,4-trimethylpentyl) phosphine oxide (CGI® 403, Ciba Specialty Chemicals), a 25:75 mixture, by weight, of bis(2,6-dimethoxybenzoyl)- 2,4,4-trimethylpentyl phosphine oxide and 2-hydroxy-2-methyl-l-phenylpropan-l-one

(IRGACURE® 1700, Ciba Specialty Chemicals), a 1 : 1 mixture, by weight, ofbis(2,4,6- trimethylbenzoyl)phenyl phosphine oxide and 2-hydroxy-2-methyl-l-phenylpropane-l-one (DAROCUR® 4265, Ciba Specialty Chemicals), and ethyl 2,4,6-trimethylbenzylphenyl phosphinate (LUCIRIN® LR8893X, BASF Corp., Charlotte, N.C.). Phosphine oxide photo- initiators may include acyl phosphine oxide photo-initiators, for example, diphenyl(2,4,6- trimethylbenzoyl)phosphine oxide, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide;

IRGACURE® 1800 (manufactured by Ciba Specialty Chemicals Corporation) which is a 75%/25% mixture of 1 -hydroxy cyclohexyl phenyl ketone (IRGACURE 184®, Ciba Specialty Chemicals Corporation) and bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentyl phosphine oxide (Ciba Specialty Chemicals Corporation); IRGACURE® 1850 (Ciba Specialty Chemicals Corporation) which is a 50%/50% mixture of the preceding compounds; bis(2,4,6- trimethylbenzoyl)phenyl phosphine oxide (IRGACURE® 819, Ciba Specialty Chemicals Corporation); 2,4,6-trimethylbenzoyl diphenyl phosphine oxide (LUCIRIN® TPO, BASF AG); DAROCUR® 4265 which is a 50%/50% mixture of 2-hydroxy-2-methyl-l-phenylpropane-l-one and diphenyl (2,4,6-trimethylbenzoyl)-phosphine oxide, 2-hydroxy-2-methyl-l -phenyl- 1- propanone (DAROCUR® 1173, Ciba Specialty Chemicals Corporation) and 2,4,6- trimethylbenzoyldiphenyl phosphine oxide (LUCIRIN® TPO, BASF AG), monoacyl phosphine oxides, e.g. (2,4,6-trimethylbenzoyl)diphenylphosphine oxide (DAROCUR® TPO).

Some particular photo-initiators may be 2,2-diethoxyacetophenone, diphenyl(2,4,6- trimethylbenzoyl)phosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide, dimethoxyphenyl acetophenone, and 2,5-dimethylbenzophenone

One particular combination of photo-initiators is 2,2-diethoxyacetophenone, diphenyl(2,4,6- trimethylbenzoyl)phosphine oxide.

Another particular combination of photo-initiators is 2,2-diethoxyacetophenone and bis(2,4,6- trimethylbenzoyl)-phenylphosphineoxide.

Another particular combination of photo-initiators is dimethoxyphenyl acetophenone and diphenyl (2,4, 6-trimethylb enzoyl)phosphine oxi de .

Another particular combination of photo-initiators is 2,5-dimethylbenzophenone and

diphenyl (2,4, 6-trimethylb enzoyl)phosphine oxi de .

Another particular combination of photo-initiators is 2,5-dimethylbenzophenone and bis(2,4,6- trimethylbenzoyl)-phenylphosphineoxide.

In some embodiments, the acetophenones, benzophenones, and related phenyl ketones (or total combination of these compounds) may be present in a concentration of from about 2% to about 10% by weight of the total coating composition. The acetophenones, benzophenones, and related phenyl ketones (or total combination of these compounds) may be present in a concentration of about 3.88% by weight of the total coating composition.

In some embodiments, the acyl phosphine oxide photo-initiator may be present in a

concentration ranging from about 0.1% to about 2% by weight of the total coating composition. The acyl phosphine oxide photo-initiator may also be present in a concentration range of from about 0.11% to about 0.42% by weight of the total coating composition. The acyl phosphine oxide photo-initiator may also be present in a concentration of about 0.22 % by weight of the total coating composition.

These above radical polymerization photo-initiators may be used singly or in combination of two or more.

UV Blocking/Absorbing

The coating compositions may also include one or more UV blocking/absorbing compound, such as a tetratriazole type UV blocker.

Examples of tetratriazole UV blockers include, for example, hydroxyphenyl-triazine or hydroxyphenylbenzotriazole class UV blocking compounds, which are commercially available as TINUVIN^® 400, TINUVIN^® 384-2, and TINUVIN^® 328 (BASF Corporation).

In some embodiments, the UV blocking compound may be TINUVIN® 384-2, which can be present in a concentration ranging from about 1% to about 15% by weight of the total composition. In other embodiments, the UV blocking compound may be TINUVIN 384-2 present in a concentration ranging from about 1.5 to about 2.4 grams. In some particular embodiments, the TINUVIN® 384-2 compound may be present in a concentration of about 9.93% by weight. However, TINUVIN® 384-2 does not block completely up to 400 nm. Thus, in some embodiments, the UV blocking/absorbing compound may be mixed with a second UV blocking/absorbing compound that blocks UV up to 400 nm, such as TINUVIN® 400.

The concentration of the UV blocking/absorbing compound depends on the wavelengths that need to be completely blocked and the thickness of the coating, which is a function of the particular application of the coating. The concentration of the UV blocking/absorbing compound may be from about 1% to about 15% by weight of the total composition. The concentration of the UV blocking/absorbing compound may be from about 6% to about 15% by weight of the total composition. The concentration of the UV blocking/ab sorbing compound may be about 10% by weight of the total composition.

Optical Brightener

The coating composition may also include an optical brightener. Optical brighteners generally decrease the yellowness of the coating. Optical brighteners such as UVITEX^® OB (2,5-Bis(5- tert-butyl-2-benzoxazolyl)thiophene), MPI^® BRIGHT FP 127 (4,4'-bis(2-methoxystyryl)-l,T- biphenyl), MPI BRIGHT^® ER-3 (4,4'-(p-phenylenediethene-2,l-diyl)bisbenzonitrile). UVITEX OB is available commercially from BASF Corporation. MPI BRIGHT^® is available

commercially from MPI Chemie B.V. (The Netherlands). The optical brightener may be 2,5- Bis(5-tert-butyl-2-benzoxazolyl)thiophene).

The concentration of the optical brightener may depend on the wavelengths that need to completely blocked and the thickness of the coating. The concentration of the optical brightener may be from about greater than 0% to about 1.5% by weight of the total coating composition.

Solvents

The solvents used in the compositions disclosed herein may be organic solvents, such as acetone, ethanol, isopropyl alcohol, dichloromethane, toluene, benzene, hexane, n-butyl acetate, 1- methoxy-2-proponol (such as Dowanol PM glycol ether), propylene glycol monomethyl ether acetate (PGMEA),etc. or a combination of two or more of these solvents.

The solvent may be in a concentration of from about greater than 0 to about 50% by weight of the total coating composition.

The composition may further comprise a solvent having a Hildebrand solubility parameter d value of less than about 7.2 cal ^1/2 cm ^3/2 and a hydrogen bonding index of less than about 13.6 kJ/mol.

Substrate Wetting and Flow Additive

The compositions disclosed herein may include a flow additive for wetting the substrate and promoting even flow of the coating over the substrate. The substrate wetting or flow additive may be a silicone or polyacrylate based wetting, flowing and leveling additive, such as TEGO^® Rad 2100, BYK^® 306, BYK^® 361 N, BYK^® 378, TEGO^® Twin 4000, TEGO^® Twin 4100, TEGO^® Twin 4200, TEGO^® Flow 300, TEGO^® Flow 460 N, TEGO^® Flow ATF 2, and similar wetting, flowing and leveling additives.

The substrate wetting and flow additive may be in a concentration of greater than about 0% to about 3% by weight of the total coating composition

Blue Dye

The coating compositions of the present invention may also include a blue dye for the purposes of diminishing the yellowness of the coating. For example, a suitable blue dye may be l-[(4- methylphenyl)amino]-4-hydroxy-9,l0-anthracenedione.

The blue day may be present in a concentration of greater than about 0% to about 3% by weight of the total coating composition.

Experimental Results

The compositions MS7ETV380 and MS7ETV400 were made as described below by mixing the ingredients (in any order) and stirring for 2 hours.

MS7UV380

MS7UV400

Chemicals Used

1. NANOCRYL C 150 is trimethylpropane triacrylate with 50% silica by weight.

2. Dipentaerythritol penta-hexa acrylate is an acrylate used to improve the hardness of the

coating though increased cross-linking

3. l,6-Hexanediol diacrylate is a difunctional acrylate used to lower the viscosity of the solution for spraying

4. 2,2-Diethoxyacetophenone is a free radical photo-initiator that has high absorption

coefficient in the UV-C part of the electromagnetic spectrum. In a coating with UV blocking compounds, this photo-initiator provides good surface cure, but not depth cure due to low penetration depth

5. Diphenyl (2, 4, 6-trimethylbenzoyl)phosphine oxide is a free radical photo-initiator used for good depth of cure

6. TINUVIN 384-2 is a UV blocking compound (alternatives such as TINUVIN 400 can be used too)

7. 2,5-Bis(5-tert-butyl-2-benzoxazolyl)thiophene is an optical brightener. Its function is to absorb UV and reemit blue light

8. Toluene or dichloromethane are used as a solvent for 2,5-Bis(5-tert-butyl-2- benzoxazolyl)thiophene as well as for lowering the viscosity of the final solution 9. TEGO Rad 2100 and TEGO Flow 460 N are used as surface wetting and flow additives

UV curing

The MS7UV380 and MS7UV400 coatings can be cured with an H type UV bulb, having a mercury spectral output, which is a surprising result. Without diphenyl (2,4,6- trimethylbenzoyl)phosphine oxide (DPTBP), surface cure occurs with the H bulb which leads to the formation of a skin on top of liquid coating underneath. With the addition of diphenyl (2,4,6- trimethylbenzoyl)phosphine oxide, one would expect that the coating would cure better with either a D type UV bulb or a V type UV bulb due to a greater penetration depth into the coating. However, the coating does not cure with a D or V bulb, unless the amount of diphenyl (2,4,6- trimethylbenzoyl)phosphine oxide is increased significantly, which leads to unacceptable yellowing of the coating. However, surprisingly, the coating cures well with the combination of an acetophenone photo-initiator at a concentration ranging from about 2% to about 10%, in combination with an acylphosphine oxide photo-initiator at a concentration ranging from about 0.1 to about 2%, with an H bulb. The concentration of the acetophenone photo-initiator may be about 3.88%. The concentration of the acylphosphine oxide photo-initiator may be about 0.22%. Furthermore, it was observed that reducing the amount of the acylphosphine oxide to less than about 0.1% by weight fails to cure the coating or cures the coating with unacceptable surface quality, while increasing the concentration to greater than about 2% by weight results in unacceptable yellowness.

UV absorption, visible transmission, and color indices

The transmission spectra of the coatings MS7UV380 (dashed line) and MS7UV400 (solid line) are shown in FIG. 1. MS7UV380 and MS7UV400 block up to about 380 nm and about 400 nm, respectively. Due to a sharp absorption onset of the coatings, and hence minimum light absorption above 400 nm, the coatings are almost color neutral.

Additional Experimental Results

Additional coatings were prepared as described below in Table A, using a similar process as described above for MS7UV380 and MS7UV400, resulting the properties shown below in Table B, with values shown in wt.% of the total composition.

The graph shown in FIG. 2 shows various percentages of liquid UV absorber of the

hydroxyphenylbenzotriazole class were used starting at 8.90% and up to 14.66%. All were low haze, low Yellowness index, and high transmission about 90%). Multiple runs were averaged. So each line represents an average of multiple samples with the same percentage and approximately the same thickness. All testing was done with a UV-VIS on transmission mode and a crossover of 420nm. Table A - Examples of Coatings

(All values above are in weight percentage based on the total composition) Table B: Coating properties

Delta Yellowness Index

The Delta Yellowness Index was evaluated using the D65 source spectrum with 2° observer and CIE 1931 color matching functions to calculate the xyz color coordinates from the transmittance data obtained from a spectrophotometer. ASTM E313 was then used to calculate the Delta Yellowness Index from the color coordinates.

Example 13

Claims

1. A UV resistant UV curable acrylate coating composition having a photo-initiator combination comprising:

a first photo-initiator compound photosensitive at UV-B and UV-C wavelengths selected from one or more of acetophenone, benzophenone and phenyl ketone compounds, at a concentration of from about 2% to about 8% by weight of the total coating composition; and a second photo-initiator compound photosensitive at UV-A wavelengths or visible light selected from acyl phosphine oxide compounds at a concentration of from about 0.1% to about 2% by weight of the total coating composition;

wherein the acrylate coating after curing upon exposure to UV light emitted from a UVH bulb having a mercury spectral output has a thickness of from about 20 to about 32 pm and a Delta Yellowness Index less than or equal to about 5.3.

2. The composition of claim 1, further comprising a solvent having a Hildebrand solubility parameter d value of less than about 7.2 cal ^1/2 cm ^3/2 and a hydrogen bonding index of less than about 13.6 kJ/mol.

3. The UV resistant UV curable acrylate coating composition of claim 1, wherein the first photo-initiator compound has a concentration of from about 6% to about 7% by weight of the total coating composition.

4. The composition of claim 1, wherein the second photo-initiator compound has a concentration of from about 0.1% to about 0.4% by weight of the total coating composition.

5. The UV resistant UV curable acrylate coating composition of claim 1, wherein the second photo-initiator compound has a concentration of about 0.3% by weight of the total coating composition.

6. The composition of claim 1, wherein the first photo-initiator compound is selected from one or more of 4'-ethoxyacetophenone, 4'-hydroxyacetophenone, 2,5-dimethylbenzophenone, 4- hydroxybenzophenone, and 1 -hydroxy cyclohexyl phenyl ketone, or combinations thereof.

7. The composition claim 1, wherein the second photo-initiator compound is selected from one or more of diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide and bis(2,4,6- trimethylbenzoyl)-phenylphosphineoxide, or combinations thereof.

8. The composition of claim 1, wherein the first photo-initiator compound is 2,2- diethoxyacetophenone and the second photo-initiator compound is diphenyl(2,4,6- trimethylbenzoyl)phosphine oxide.

9. The composition of claim 1, wherein the Delta Yellowness Index of the cured coating composition ranges from about 1 to about 3.

10. A UV resistant UV curable acrylate coating composition, comprising:

two or more acrylates, wherein each of the two or more acrylates is independently selected from a mono- or multi-functional acrylate;

a first photo-initiator compound photosensitive at UV-B and UV-C wavelengths selected from one or more of acetophenone, benzophenone and phenyl ketone compounds, at a concentration of from about 2% to about 8% by weight of the total coating composition; and a second photo-initiator compound photosensitive at UV-A wavelengths or visible light selected from acyl phosphine oxide compounds at a concentration of from about 0.1% to about 1% by weight of the total coating composition; and

one or more tetratriazole UV blocking compound;

an optical brightener;

a compatible solvent; and

a flow additive;

11. The composition according to claim 10, wherein the solvent has a Hildebrand solubility parameter d value of greater than about 7.2 cal ^1/2 cm ^3/2 and a hydrogen bonding index of greater than about 13.6 kJ/mol.

12. The composition according to claim 10, wherein tetratriazole UV blocking compound is selected from one or more of a hydroxyphenyl-triazine and hydroxyphenylbenzotriazole type UV blocking compounds or combinations thereof.

13. The composition according to claim 10, wherein the tetratriazole UV blocking compound is present in a concentration ranging from about 6% to about 15% by weight of the total coating composition.

14. The composition according to claim 10, wherein the optical brightener is selected from one or more of 2,5-Bis(5-tert-butyl-2-benzoxazolyl)thiophene, 4,4'-bis(2-methoxystyryl)-l,T- biphenyl, 4,4'-(p-phenylenediethene-2, l-diyl)bisbenzonitrile.

15. The composition according to claim 10, wherein the concentration of the optical brightener is from about 0.23% to about 0.81% by weight of the total coating composition.

16. The composition according to claim 10, wherein the solvent is selected from acetone, ethanol, isopropyl alcohol, dichloromethane, toluene, benzene, hexane, n-butyl acetate, propylene glycol monomethyl ether acetate (PGMEA), or a combination of two or more thereof.

17. The composition according to claim 10, wherein the solvent is in a concentration of from aboutabput 12% to about 30% by weight of the total coating composition.

15. The composition according to claim 7, wherein flow additive is in a concentration of greater than about 0% to about 3% by weight of the total coating composition.

18. The composition of claim 10, wherein the first photo-initiator compound has a concentration of from about 2% to about 8% by weight of the total coating composition.

19. The composition of claim 10, wherein the second photo-initiator compound has a concentration of from about 0.1% to about 1.0% by weight of the total coating composition.

20. The composition of claim 10, wherein the second photo-initiator compound has a concentration of from about 0.22% to about 0.42% by weight of the total coating composition.

21. The composition of claim 10, wherein the first photo-initiator is 2,2- diethoxyacetophenone and the second photo-initiator compound is diphenyl(2,4,6- trimethylbenzoyl)phosphine oxide (TPO).

22. The composition of claim 10, wherein the first photo-initiator compound is selected from one or more of 4'-ethoxyacetophenone, 4'-hydroxyacetophenone, 2,5-dimethylbenzophenone, 4- hydroxybenzophenone, and 1 -hydroxy cyclohexyl phenyl ketone, or combinations thereof.

23. The composition of claim 10, wherein the first photo-initiator compound is 2,2- di ethoxy acetophenone .

24. The composition claim 10, wherein the second photo-initiator compound is selected from one or more of diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide and bis(2,4,6- trimethylbenzoyl)-phenylphosphineoxide, or combinations thereof.

25. The composition of claim 10, wherein the second photo-initiator compound is diphenyl (2,4, 6-trimethylb enzoyl)phosphine oxi de .

26. The composition of claim 10, wherein the first photo-initiator compound is 2,2- diethoxyacetophenone and the second photo-initiator compound is diphenyl(2,4,6- trimethylbenzoyl)phosphine oxide.

27. The composition of claim 10, wherein the concentration of the first photo-initiator compound 2,2-diethoxyacetophenone is about 3.85% by weight of the total coating composition and the concentration of the second photo-initiator compound diphenyl(2,4,6- trimethylbenzoyl)phosphine oxide is 0.22% by weight of the total coating composition.

28. The composition of claim 10, wherein the Delta Yellowness Index of the cured coating composition ranges from about 1 to about 3.

29. The composition of claim 10, wherein the thickness of the cured coating composition is from about 15 pm to about 30 pm.