WO2008098872A1

WO2008098872A1 - High refractive index hard coat

Info

Publication number: WO2008098872A1
Application number: PCT/EP2008/051499
Authority: WO
Inventors: Jens Christoph Thies; Guido Jozefina Wilhelmus Meijers
Original assignee: Dsm Ip Assets B.V.
Priority date: 2007-02-12
Filing date: 2008-02-07
Publication date: 2008-08-21

Abstract

The present invention relates to a product comprising a hard coating on a plastic substrate, the substrate having an average refractive index of about 1.61 or higher, the coating having a refractive index of 1.6 or higher, a thickness of from about 1 µm to about µm and having a variation in coating thickness of about 200 nm or less.

Description

HIGH REFRACTIVE INDEX HARD COAT

The present invention relates to products comprising a substrate and a low iridescence hard coat, and to radiation-curable hard coatings with a high refractive index. Furthermore, the invention relates to films having a refractive index of 1.6 or higher, with a hard coat, showing less iridescence.

Fabricated plastic materials such as plastic optical parts, touch panels, and film-type liquid crystal elements, as well as films which are used on window panels generally benefit from a protective, hard coating to preclude wear. Hard coatings are described in for example US 6342097 and US 6521677. These coating can improve wear but often suffer from a problem of iridescence. Iridescence appears as rainbow color shades when looked on a flat surface of the plastic with the hard coating. The problem of iridescence is particularly apparent on flat surfaces, and under artificial light

It is an object of the invention to provide products comprising plastic substrates with a high refractive index having a hard coat and which exhibits low iridescence.

It is a further object of the invention to provide a hard coat which limits iridescence when coated on substrates with an average refractive index of 1.61 or higher.

It is a further object of the invention, to provide a method for lowering iridescence of a hard coat.

Other objects will be apparent from the description of the invention. The present invention provides a product comprising a hard coating on a plastic substrate, the substrate having an average refractive index of about 1.61 or higher, the coating having a refractive index of 1.6 or higher, a thickness of about 1 μm or higher, and of about 10 μm or lower and having a variance in surface thickness of about 150 nm or less if measured over an area with 3 mm diameter with a thin layer reflectometer.

The present invention provides hard coating, comprising:

(i) metal oxide particles comprising a radiation-curable group linked to a metal oxide, the metal oxide particles having a bulk refractive index of about 1.7 or higher, (ii) a multifunctional radiation curable compound having about 2 or more radiation curable groups (iii) leveling agent, wherein the refractive index of the composition is about 1.6 or higher.

In addition, the present invention provides a method for lowering iridescence in a hard coat, by providing (a) a radiation curable hard coat comprising components (i) metal oxide particles comprising a radiation-curable group linked to a metal oxide, the metal oxide particles having a bulk refractive index of about 1.7 or higher, (ii) a multifunctional radiation curable compound having about 2 or more radiation curable groups and (iii) leveling agent, (b) mixing the components in such an amount that the averaged refractive index of the substrate and hard coat is matched within 0.5 units, and (c) applying the coating to a substrate and curing the coating. Furthermore, the present invention provides articles made by curing the above compositions, including articles comprising coatings and films formed from such compositions, in particular films such as solar control films having a hard coat.

Detailed Description of the Invention The product of the present invention comprises a substrate and a hard coat. Suitable substrates include plastic sheet, and plastic film. Product are particular suitable in applications requiring transparency, and particularly as materials for optical use. Other application of the product includes cathode-ray tubes and front panels such as a flat display, laser display, photochromic display, electrochromic display, liquid crystal display, plasma display, light emitting diode display, and electroluminescent panel, as well as parts for input equipment of these front panels. Other application includes front covers such as an enclosure case, lens for optical instrument, eye glass lens, window shield, light cover, helmet shield, and the like. In addition, when a coating with a high refractive index is used as an optical material, it is desirable to provide a coating with a low refractive index to prevent reflection.

The plastic used for film or sheet preferably is a polyester, more preferable a polyester based on terephthalic acid, such as for example polyethyleneterephthalate (PET) or PBT, or from naphthalene dicarboxylic acids such as for example Polyethylene naphthalate (PEN). In a preferred embodiment, a PET film is used as substrate. The PET film may comprise a colorant or additive to control solar light. Solar light control films can be suitably used on windows of buildings, cars and the like.

PET generally has a refractive index between 1.6 and 1.7 depending on the wavelength. The average refractive index is the index obtained by dividing the combined value of the highest and lowest refractive index, measured in a spectrum of 400 to 700 nm. It is preferred to have the index of the coating matched with the average refractive index of the substrate within about 0.5 units, more preferably within 0.3 units, and more preferably within 0.1 unit.

The plastic substrate generally will be about 5 μm or thicker, preferably about 10 μm or thicker. Generally, the film will be about 1 mm or thinner, preferably about 300 μm or thinner.

The hard coat of the present invention generally will be about 1 μm or thicker, preferably about 1.5 μm or thicker. Generally, the thickness will be about 10 μm or less, preferably about 5 μm or less, more preferably 3 μm of less. Coatings with a thickness of from about 1 μm to about 10 μm seem to offer a good combination of hardness while being economical.

When the radiation-curable resin composition of the present invention is cured, the cured products preferably have a pencil hardness from 2H to 7H at 23 ⁰C. More preferably, the coating exhibits a pencil hardness of 3H or better, even more preferably 4H or 5H. The amount of shrinkage upon curing is preferably 10% or less, and more preferably 6% or less.

The resulting cured coating has a refractive index of about 1.61 or higher, preferably about 1.62 or higher, and even more preferably about 1.63 or higher, such as for example, 1.63, 1.64 1.65 or 1.66. Generally, the refractive index will be about 1.73 or lower, preferably 1.7 or lower, and more preferably 1.68 or lower.

The cured coating has good abrasion resistance, transparency, chemical resistance, and the like. The cured products preferably have a light transmittance of 80% or more at 5 μm. Preferably the cured coating, at about 3 μm thickness layer after cure, will have a light transmittance of at least 85%. The cured coating preferably exhibits a scratch resistance as measured with steel wool type 0000 over a surface area with a diameter of 2.4 mm (one inch) of C or better at 500 g pressure; more preferably B or better, and even more preferably A. In a further embodiment of the invention, the cured coating exhibits a scratch resistance as measured with steel wool of C or better at 1000 g; preferably B or better, and more preferably A.

The products of the present invention show low iridescence.

Surprisingly, this is achieved, not only by matching the refractive index to the average refractive index of the substrate, but also because the coating has an even coating thickness with a variation in the thickness of about 150 nm or less as measured with a thin layer reflectometer over a surface area of 3 mm diameter. While not wishing to be bound by theory it appears that the use of siloxane leveling agents lowers the iridescence by limiting the overall variations thickness rather than minimizing the roughness of the coating. Preferably, the variation in thickness is about 100 nm or less, and even more preferred, 70 nm or less, such as for example about 50 nm.

In another embodiment of the invention, the coating thickness of a coating of 1-10 μm varies by about 10% or less, preferably about 5% or less, and even more preferably about 3% or less.

In another embodiment of the invention the absolute and relative values as described in the above paragraphs are combined to achieve very low iridescence. In a further embodiment of the invention, the product exhibits an fringe pattern as measured with a thin layer reflectometer of about 0.6 % or less or less, preferably about 0.4 % or less. In order to determine the fringes, the substrate is coated with a hard coat. The reflection of the coating is measured with the thin film reflectomer of Filmetrics. If the the refractive index (Rl) of the hard coat does not match the refractive index of the substrate (i.e. has an Rl that differs about 0.6 or more) clear interference patterns can be seen of e.g. 1-2 % or stronger. If however the refractive index of hard coat does match the refractive index of the substrate (i.e. has a Rl that differs about 0.5 or preferably 0.3 or less) small fringes can be seen in the order of 0.6- 1 %. The smooth layer products with a variance in thickness of about 10% or less or about 100 nm or less of the present invention preferably show fringes of about 0.4% or 0.3% or even less, resulting in products that exhibit virtually no coloring even under TL light on a flat panel.

The present invention provides compositions comprising a radiation- curable metal oxide particle comprising a radiation-curable group preferably linked by a silyl group to a metal oxide, which hereinafter will also be referred to as "component

(i)". It will be appreciated by one of ordinary skill in the art that "component (i)" may refer to a single particle, multiple particles, or a mixture of particles.

The present invention provides compositions comprising these particles. Such radiation-curable compositions may be any suitable radiation-curable composition, and may further comprise a radiation curable compound such as for example a (meth)acrylic, N-vinyl, styryl or other compounds with radiation curable groups (hereinafter also referred to as "component (N)"). The composition may, independent of the presence of component (ii), also comprise further components, such as for example a radiation polymerization initiator (hereinafter also referred to as "component (Ni)").

The particles of component (i) comprise a radiation-curable group linked to a metal oxide. The metal oxide can be any suitable metal oxide, and is preferably a metal oxide from a metal selected from the metals listed in groups 2-16 from the periodic table of elements exclusive of silicon metal. Preferably the metal is selected from the metals listed in groups 3-4 and 12-15 from the periodic table of elements (exclusive of silicon metal). In particular it is preferred that the metal is selected from the group consisting of zirconium, titanium, antimony, zinc, tin, indium, cerium and aluminium, and most preferably the metal is selected from the group consisting of zirconium, antimony, zinc and cerium.

The refractive index of the neat particles generally has a bulk refractive index of about 1.7 or higher, preferably about 1.9 or higher, and even more preferably, about 2 or higher. Reference is made to the bulk refractive index as to exclude resin, air or other enclosures. Hence the refractive index of the metal oxide alone is meant. Generally, the refractive index of the metal oxide particles for zirconium, cerium, zinc or antimony is about 2 or higher, and this is preferred. The radiation curable group is suitably connected to the metal oxide particle via a silyl group, although other connection mechanisms can be used as well. It is important that the radiation curable group is covalently bound to the metal oxide particle. Hereinafter, the covalent bond will be exemplified for silyl-groups, without being limited thereto. The silyl group is preferably a substituted silyl group. The substituted silyl group may be any suitable silyl group. Preferably, the substituted silyl group comprises a urethane group, a thiourethane group and/or an alkoxy group. Preferably, the silyl group comprises at least a urethane group.

The silyl group may be derived from compounds having at least one alkoxysilyl group and mercapto group in the molecule, as noted herein below, and such compounds reacted with the isocyanates noted herein below.

In a composition that comprises components (i), (ii) and (iii), the proportion of reactive particles (component (i)) is generally about 10 wt% or more, preferably about 20 wt% or more, and particularly preferably about 30 wt% or more, relative to the total weight of the composition. The amount of reactive particles (component (i)) is generally about 98 wt% or less, preferably about 90 wt% or less, and particularly preferably about 70 wt% or less, relative to the total weight of the composition.

When component (i) is a mixture of particles, preferably at least 90 wt%, more preferably at least 95%, and most preferably at least 99 wt% of the total metal oxides (excluding the silicon in the silyl group) in component (i) is selected from zirconium, titanium, antimony, zinc, tin, indium, cerium, aluminium, or combinations thereof.

Component (i) may be a reaction product. The reaction product used as the component (i) is obtained by the reaction of an organosilicon compound having a polymerizable unsaturated group and alkoxysilyl group in the molecule and metal oxide particles, wherein the major components of metal oxide particles are oxide of metals selected from the group consisting of zirconium, titanium, antimony, zinc, tin, indium, cerium, and aluminum. The proportion of the reaction product contained in the composition of the present invention as the component (i) is preferably from 1 to 99 wt%, more preferably from 10 to 90 wt%, and particularly preferably from 30 to 70 wt%. The reaction is carried out preferably in the presence of water.

The reaction product used as the component (i) in the present invention can be prepared by a method including at least an operation of mixing the organosilicon compound and metal oxide particles. The amount of residual organosilicon compounds immobilized on metal oxide particles is preferably 0.01 wt% or more, more preferably 0.1 wt% or more, and most preferably 1 wt% or more. If the amount of residual organosilicon compounds immobilized on metal oxide particles is less than 0.01 wt%, dispersibility of the reaction product containing metal oxide particles in the composition of the present invention may be insufficient, which may result in lack of transparency and abrasion resistance of the composition. The proportion of organosilicon compounds in the raw material composition to produce the component (i) is preferably 10 wt% or more, and more preferably 30 wt% or more. If proportion of organosilicon compounds is less than 10 wt%, film-forming capability of the resulting composition may be poor. The proportion of metal oxide particles in the raw material composition for the component (i) is preferably 50 wt% or less, and more preferably 20 wt% or less. Dispersibility, transparency, and abrasion resistance of the resulting composition may be insufficient, if the amount of the metal oxide particles in the raw material composition for preparing component (i) is more than 50 wt%.

Preferably the organosilicon compound possesses a polymerizable unsaturated group and alkoxysilyl group in the molecule. As preferable examples of the polymerizable unsaturated group, acrylic group, vinyl group, and styryl group can be given. As an alkoxysilyl group, the group which can be hydrolyzed in the presence of water or a hydrolysis catalyst is desirable. In addition, the organosilicon compound may contain at least one bond selected from an ester group, ether group, urethane group, sulfide group, and thiourethane group in the molecule. The organosilicon compound preferably comprises at least one polymerizable unsaturated group, urethane bond group, and alkoxysilyl group as its constituents. The alkoxysilyl group is the component which combines with adsorption water existing on the surface of metal oxide particles by a hydrolysis-condensation reaction. The polymerizable unsaturated group is the component of which the molecules chemically cross-link among themselves by an addition polymerization reaction in the presence of reactive radicals. The urethane bond group is a constitutional unit which bonds the molecules having an alkoxysilyl group and the molecules having a polymerizable unsaturated group directly or via other molecules. At the same time, the urethane bond group creates a moderate cohesive force among molecules due to hydrogen bonds, thereby providing the cured products made from the composition of the present invention with good mechanical strength, adhesion with substrates, heat resistance, and the like.

As examples of preferable organosilicon compounds, the compounds shown by the following formula (1 ) can be given.

) „ _{(1 )}

wherein R¹ is a hydrogen atom or a mono-valent organic group having from 1 to 8 carbon atoms, such as methyl, ethyl, propyl, butyl, phenyl, or octyl group; R² is a hydrogen atom or an alkyl group having from 1 to 3 carbon atoms; and m is 1 , 2 or 3. As examples of trimethoxysilyl groups represented by the formula, (RO¹)_mR²3-_mSi, triethoxysilyl group, triphenoxysilyl group, methyldimethoxysilyl group, dimethylmethoxysilyl group, and the like can be given, with preferred groups being trimethoxysilyl group and triethoxysilyl group.

A structural unit represented by the formula, -(C=O)NH-R⁴-

NH(C=O)O-X-O]_P-, is introduced to extend the molecular chain into the structure shown by the above-mentioned formula (1 ). R³ is a divalent organic group having from 1 to 3 carbon atoms. R⁴, which may be either the same with or different from R³, is a divalent organic group and selected from divalent organic groups with a molecular weight from 14 to 10,000, preferably from 78 to 1 ,000, for example, a linear polyalkylene group such as methylene, ethylene, propylene, hexamethylene, octamethylene, and dodecamethylene groups; alicyclic or polycyclic divalent organic groups such as cyclohexylene and norbornylene groups; divalent aromatic groups such as phenylene, naphthylene, biphenylene, and polyphenylene groups; and alkyl group or aryl group substitution products of these groups. These divalent organic groups may further contain atomic groups containing elements other than carbon atoms and hydrogen atoms, p and q in the above formula are 0 or 1. X is a divalent organic group, and more particularly, a divalent organic group originating from the compound having an active hydrogen atom which can react with an isocyanate group in the molecule by the addition reaction. Given as examples are divalent organic groups obtained by removing two active hydrogen atoms from the compound such as a polyalkylene glycol, polyalkylene thioglycol, polyester, polyamide, polycarbonate, polyalkylene diamine, polyalkylene dicarboxylic acid, polyalkylene diol, or polyalkylene dimercaptan. R⁵ is an organic group with a valency of (n+1 ). Such an organic group is preferably selected from linear, branched, or cyclic saturated hydrocarbon groups, unsaturated hydrocarbon groups, and alicyclic groups. Y in the above formula represents a monovalent organic group having a polymerizable unsaturated group which causes a cross- linking reaction to occur among the molecules in the presence of reactive radicals, such as, for example, acryloxy group, methacryloxy group, vinyl group, propenyl group, butadienyl group, styryl group, ethynyl group, cinnamoyl group, maleate group, acrylamide group, and the like. Among these, acryloxy group is desirable, n is a positive integer preferably from 1 to 20, and more preferably from 1 to 10, and particularly preferably from 3 to 5. The organosilicon compound used in the present invention can be prepared, for example, by (1 ) an addition reaction of an alkoxysilane having a mercapto group (i.e. a mercaptoalkoxysilane), a polyisocyanate compound, and an active hydrogen group-containing polymerizable unsaturated compound which possesses an active hydrogen which can cause an addition reaction to occur with an isocyanate group; (2) a direct reaction of an isocyanate compound having an isocyanate group and an alkoxysilyl group in the molecule with an active hydrogen-containing polymerizable unsaturated compound; or (3) an addition reaction of a compound having a polymerizable unsaturated group and an isocyanate group in the molecules and a mercaptoalkoxysilane or aminosilane compound. A more detailed description is provided in US 6521677, herewith incorporated by reference.

The radiation curable group of component (i) can be derived from carboxylic acid group-containing polymerizable unsaturated compounds and hydroxyl group-containing polymerizable unsaturated compounds. Specific examples of polymerizable unsaturated compound having a carboxylic acid group include unsaturated aliphatic carboxylic acid such as (meth)acrylic acid, itaconic acid, cinnamic acid, maleic acid, fumaric acid, 2-(meth)acryloxypropyl hexahydrogenphthalate, and 2- (meth)acryloxyethyl hexahydrogenphthalate; and unsaturated aromatic carboxylic acid such as 2-(meth)acryloxypropyl phthalate and 2-(meth)acryloxypropylethyl phthalate. Given as examples of hydroxyl group-containing polymerizable unsaturated compounds are hydroxyl group-containing acrylates, hydroxyl group-containing methacrylates, and hydroxyl group-containing styrenes, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 2- hydroxy-3-phenyloxypropyl (meth)acrylate, 1 ,4-butanediol mono(meth)acrylate, 2-hydroxyalkyl (meth)acryloyl phosphate, 4-hydroxycyclohexyl (meth)acrylate, neopentyl glycol mono(meth)acrylate, poly(pentamethyleneoxycarboxylate)ethoxy (meth)acrylate, hdroxy styrene, hydroxy α-methylstyrene, hydroxyethyl styrene, hydroxy-terminal polyethylene glycol styryl ether, hydroxy-terminal polypropylene glycol styryl ether, hydroxy-terminal polytetramethylene glycol styryl ether, terminal-hydroxy polyethylene glycol (meth)acrylate, terminal-hydroxy polypropylene glycol (meth)acrylate, terminal-hydroxy poly(tetraethylene glycol (meth)acrylate), trimethylolpropane di(meth)acrylate, trimethylolpropane mono(meth)acrylate, ethlenoxide(EO)-modified trimethylolpropane tri(meth)acrylate, propylene oxide (PO)- modified trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol mono(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol tetra(meth)acrylate, dipentaerythritol tri(meth)acrylate, dipentaerythritol di(meth)acrylate, and dipentaerythritol mono(meth)acrylate.

Among these, unsaturated aliphatic carboxylic acids and hydroxyl group-containing acrylate compounds are preferred, with the hydroxyl group-containing acrylate compounds, such as, for example, 2-hydroxylethyl acrylate, 2-hydroxypropyl acrylate, pentaerythritol triacylate, and dipentaerythritol pentacrylate being particularly preferred.

The metal oxide particles used for preparing the component (i) are preferably in the form of fine particles or a solvent dispersed sol. As a metal oxide, antimony oxide, zinc oxide, tin oxide, indium-tin mixed oxide, cerium oxide, aluminum oxide, titanium dioxide, and zirconium oxide can be given as examples. These may be used either individually or in combinations of two or more. In addition, from the viewpoint of ensuring mutual solubility and dispersibility with the component (ii) and mutual solubility with photo-initiators and photosensitizers, a sol in a polar solvent such as alcohol, dimethylformamide, dimethylacetamide, or cellosolve may be used rather than water sol. As particularly preferred sols, sols of antimony oxide, zinc oxide, cerium oxide, and zirconium oxide can be given. The average diameter of metal oxide particles is preferably from 0.001 to 2 μm. Such metal oxide particles are commercially available under the tradenames such as Alumina Sol-100, -200, -520 (alumina powder dispersed in water, manufactured by Nissan Chemical Industries, Ltd.), Celnax (zinc antimonate powder dispersed in water, manufactured by Nissan Chemical Industries., Ltd.), Nanotek

(alumina, titanium oxide, tin oxide, indium oxide, and zinc oxide powders dispersed in a solvent, manufactured by Cl Chemical Co., Ltd.), Titania Sol, SN-100D (a sol of antimony dope tin oxide powder dispersed in water, manufactured by lshihara Sangyo Kaisha, Ltd.), ITO powder (manufactured by Mitsubishi Material Co., Ltd.), Needral (cerium oxide powder dispersed in water, manufactured by Taki Chemical Co., Ltd.), and the like. To prepare films using the composition of the present invention, a preferable particle diameter is in the range from 0.001 to 2 μm, and more preferably from 0.001 to 0.05 μm. The form of metal oxide particles may be spherical, hollow, porous, rod-like, plate-like, fibrous, or amorphous, and is preferably spherical. The specific surface area of metal oxide particles is preferably from 10 to 3,000 m²/g, and more preferably from 20 to 1 ,500 m²/g. These metal oxide particles can be used as dry powder or as a dispersion in water or an organic solvent.

The use of a solvent dispersion sol of metal oxide is particularly preferred to give transparency. Organic solvents which can be used as a dispersion medium for metal oxide include methanol, isopropyl alcohol, 1-methoxy-2-propanol, ethylene glycol, butanol, ethylene glycol monopropyl ether, methyl ethyl ketone, methyl isobutyl ketone, toluene, xylene, dimethylformamide, and other solvents which are mutually soluble with these organic solvent, as well as mixtures of these organic solvents and water. Preferable solvents are methanol, isopropyl alcohol, methyl ethyl ketone, xylene, 1-methoxy-2-propanol, and toluene.

Component (ii) can be any suitable radiation curable compound. Preferably, component (ii) comprises at least one compound having at least two radiation curable groups, preferably 3 radiation curable groups or more in the molecule, more preferably from 3 to 10 radiation curable groups, even more preferably from 4 to 10 radiation curable groups, and most preferably from 4 to 8 radiation curable groups.

Preferably, substantially all compounds in component (ii) have 2 radiation curable groups or more.

Radiation curable groups are well known to the man skilled in the art and generally are ethylenically unsaturated groups, such as (meth)acrylate, vinyl, styryl, maleate and the like.

In order to provide a hard coat, the hardness is preferably about 2H or higher. The hardness will be dependent on the crosslink density and the chemical composition of the constituents. It is preferred to have a high cross-link density. This can be achieved with particles that have a relatively high concentration of radiation curable groups, particularly when combined with di-functional radiation curable compounds. In case the amount of radiation curable groups on the surface of the particles is relatively low, it is preferred to use higher functional radiation curable compounds. It may furthermore be preferred to have highly functionalized particles combined with higher functional radiation curable compounds to achieve optimum hardness. It is further preferred to use radiation curable compounds that influence the Tg by the existence of rigid cyclic structures, such as iso-bornyl, phenyl, admantanyl, cyclohexyl or the like.

Preferred radiation curable groups are (meth)acrylate or vinyl groups., in particular (meth)acrylate. Acrylate groups are more preferred.

Examples of difunctional-functional radiation curable compounds include (meth)acryloyl group-containing compounds such as ethylene glycol di(meth)acrylate, dicyclopentenyl di(meth)acrylate, triethylene glycol diacrylate, tetraethylene glycol di(meth)acrylate, tricyclodecanediyldimethylene di(meth)acrylate, tripropylene diacrylate, neopentyl glycol di(meth)acrylate, both terminal (meth)acrylate of ethylene oxide addition bisphenol A, both terminal (meth)acrylate of propylene oxide addition bisphenol A, both terminal (meth)acrylate of ethylene oxide addition tetrabromobisphenol A, both terminal (meth)acrylate of propylene oxide addition tetrabromobisphenol A, bisphenol A diglycidyl ether, both terminal (meth)acrylate of tetrabromobisphenol A diglycidyl ether, 1 ,4-butanediol di(meth)acrylate, 1 ,6-hexanediol di(meth)acrylate, polyester di(meth)acrylate, and polyethylene glycol di(meth)acrylate. Of these, both terminal (meth)acrylate of ethylene oxide addition bisphenol A, both terminal (meth)acrylate of propylene oxide addition bisphenol A, tricyclodecanediyldimethylene di(meth)acrylate, tetraethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, and polyethylene glycol di(meth)acrylate are preferred. As commercially available products of poly-functional monomers,

Yupimer UV, SA1002 (manufactured by Mitsubishi Chemical Corp.), Viscoat 700 (manufactured by Osaka Organic Chemical Industry Co., Ltd.), Kayarad R-604 (manufactured by Nippon Kayaku Co., Ltd.), Aronix M-210 (manufactured by Toagosei Co., Ltd.), and the like can be used. Examples of a radiation curable compounds with three or more radiation curable groups include are trimethylolpropane tri(meth)acrylate, trimethylolpropane trioxyethyl (meth)acrylate, tris(2-hydroxyethyl)isocyanurate tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and the like.

As examples of commercially available products of the (meth)acrylic compound having at least three (meth)acryloyl groups in the molecule, Kayarad DPHA, DPCA-20, DPCA-30, DPCA-60, DPCA-1 20, D-310, D-330, PET-30, GPO-303, TMPTA, THE-330, TPA-330 (manufactured by Nippon Kayaku Co., Ltd.), Aronix M-315, M-325 (manufactured by Toagosei Co., Ltd.), and the like can be given.

The amount of the radiation curable compound having at least two radiation curable groups in the molecule used as the component (ii) in the composition of the present invention is preferably about 1 wt% or higher, more preferably about 10 wt% or higher, and even more preferably about 30 wt% or higher. The amount of the radiation curable compound having at least two radiation curable groups in the molecule used as the component (ii) in the composition of the present invention is preferably about 99 wt% or lower, more preferably about 90 wt% or lower, and even more preferably about 70 wt% or lower. The number of (meth)acryloyl groups in the molecule is preferably from 4 to 10, and more preferably from 4 to 8.

In one embodiment of the invention, the component (ii) comprises two or more (meth)acryloyl compounds with different refractive index. By adjusting the relative amounts of the different (meth)acryloyl compounds, it is possible to fine-tune the refractive index of the total composition. An example of a (meth)acryloyl compound with relatively high refractive index is tris-hydroxyethyl-isocyanurate-triacrylate, and for compound with relatively low refractive index an aliphatic multi-functional acrylate.

Preferably, acrylate functional compounds are used, as these exhibit high cure speed.

The coating preferably comprises a leveling agent. Suitable leveling agents comprise compounds that give both lower surface tension, and surface slip characteristics. Preferably the amount of leveling again is such that the coating has a thickness variation of about 200nm or less over a 3 mm diameter surface-area as measured with thin layer reflectometry. More preferably the thickness variation is about

150nm or less, even more preferably 100nm or less, even more preferably still 70nm, or less over a 3mm diameter surface area.

A preferred category of leveling agents include siloxane gents such as siloxane oligomers or polymers. Siloxane oligomers generally have a molecular weight of 300 or more and preferably about 500 or more. Generally, the siloxanes polymers have a molecular weight of 100,000 or less, preferably about 10,000 or less, and most preferably about 4000 or less. Suitable siloxane oligomers or polymers comprise linear and branched molecules. Preferably, organic modified poly- dimethylsiloxanes are used. Preferably, the siloxane oligomer or polymer comprise other organic groups having ether, carboxy, amine, hydroxy, (meth)acrylate or other functionality. In order to increase compatibility of the siloxane compound with the rest of the coating composition, preferably polyether chains are attached to the siloxane. Preferred polyethers include polyethyleneglycol and polypropyleneglycol. The polyether chains can for example be present as branches or as block-copolymer.

Siloxanes preferably are used in such an amount that a smooth layer is obtained, preferably with a thickness variation of about 150 nm or less over a 3 mm diameter surface-area as measured with thin layer reflectometry. More preferably the thickness variation is about 100nm, even more preferably 70nm, or less over a 3mm diameter surface area. Generally, the amount of leveling and slip agent is about 0.1 wt% or more, preferably about 0.2 wt% or more, and most preferably about 0.5 wt% or more. Generally, the amount of leveling agent will be about 5 wt% or less, preferably about 3 wt% or less. In addition to the smoothness of the layer, which appeared to be important to lower an iridescent effect, the siloxane leveling agent aided in achieving high scratch resistance.

Suitable siloxane based leveling agents comprise amino-functional siloxanes, hydroxy functional siloxanes, acrylate functional siloxanes, non-functional siloxanes and the like. Examples of siloxane based leveling agents include those available by Byk, DowCorning and Degussa (TegoRad).

Examples of other suitable compounds that may be present are one or more radiation polymerization initiator (or photoinitators), silane coupling agents, stabilizers, and the like.

Any compounds which decompose upon irradiation of radioactive rays and initiate the polymerization can be used as the radiation polymerization initiator. A photosensitizer may be added as required. The words "radiation" as used in the present invention include infrared rays, visible rays, ultraviolet rays, deep ultraviolet rays, X-rays, electron beams, γ-rays, and the like. When using for example EB or v- rays, it may not be necessary to use a photoinitiator.

Given as specific examples of the above-mentioned radiation polymerization initiators are acetophenone, acetophenone benzyl ketal, anthraquinone, 1-hydroxycyclohexylphenyl ketone, 2,2-dimethoxy-2-phenylacetophenone, xanthone compounds, triphenylamine, carbazole, 3-methylacetophenone, 4- chlorobenzophenone, 4,4'-dimethoxybenzophenone, 4,4'-diaminobenzophenone, 2- hydroxy-2-methyl-1-phenylpropan-1-one, 1-(4-isopropylphenyl)-2-hydroxy-2- methylpropan-1-one, xanthone, 1 ,1-dimethoxydeoxybenzoin, 3,3'-dimethyl-4- methoxybenzophenone, thioxanethone compounds, diethylthioxanthone, 2- isopropylthioxanthone, 2-chlorothioxanthone, 1 -(4-dodecylphenyl)-2-hydroxy-2- methylpropan-1-one, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-propan-1-one, triphenylamine, 2,4,6-trimethylbenzoyldiphenylphosphineoxide, bis-(2,6- dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide, bisacylphosphineoxide, benzyl dimethyl ketal, fluorenone, fluorene, benzaldehyde, benzoin ethyl ether, benzoin propyl ether, benzophenone, Michler's ketone, 2-benzyl-2-dimethylamino-1-(4- morpholinophenyl)-butan-1-one, 3-methylacetophenone, and 3,3',4,4'-tetra(t- butylperoxycarbonyl)benzophenone (BTTB). Combinations of BTTB and a coloring matter photosensitizer such as xanthene, thioxanthene, cumarin, or ketocumarin can also be given as specific examples of the initiator. Of these, benzyl dimethyl ketal, 1- hydroxycyclohexyl phenyl ketone, 2,4,6-trimethylbenzoyl diphenylphosphine oxide, bis- (2,6-dimethoxybenzoyl)-2,4,4-trimethylpentyl phosphine oxide, 2-benzyl-2- dimethylamino-1-(4-morpholinophenyl)-butan-1-one, and the like are particularly preferred.

As examples of commercially available products of photoinitiators, lrgacure 184, 651 , 500, 907, 369, 784, 2959, Darocur 1 116, 1173 (manufactured by Ciba Specialty Chemicals Co., Ltd.), Lucirine TPO (manufactured by BASF), Ubecryl P36 (manufactured by UCB), and Escacure KIP150, KIP100F (manufactured by Lamberti) can be given.

As examples of photosensitizers, triethylamine, diethylamine, N- methyldiethanolamine, ethanolamine, 4-dimethylaminobenzoic acid, methyl A- dimethylaminobenzoate, ethyl 4-dimethylaminobenzoate, and isoamyl 4- dimethylaminobenzoate, as well as commercially available products such as Ubecryl P102, 103, 104, 105 (manufactured by UCB), and the like can be given.

The proportion of the photoinitiators if used in the composition of the present invention is generally about 0.2 wt% or more, more preferably about 0.5 wt% or more, and particularly preferably about 1 wt% or more. Generally, the amount of photoinitiator will be about 10 wt% or less, preferably about 5 wt% or less. If more than 10 wt%, storage stability of the composition and properties of the cured products may be adversely affected. If less than 0.2 part by weight, on the other hand, a cure speed may be retarded. Polymerizable compounds having one radiation curable group like vinyl or (meth)acryloyl or other radiation curable group, other than the above- mentioned component (ii) can be used in the present invention as optional components.

Examples of mono-functional radiation curable compounds incude N- vinyl caprolactam, N-vinyl pyrrolidone, N-vinylcarbazole, and vinylpyridine; styrene, methylstyrene, hydroxystyrene, acrylamide, acryloyl morpholine, 7-amino-3,7- dimethyloctyl (meth)acrylate, isobutoxymethyl (meth)acrylamide, isobornyloxyethyl (meth)acrylate, isobornyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, ethyldiethylene glycol (meth)acrylate, t-octyl (meth)acrylamide, diacetone (meth)acrylamide, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, lauryl (meth)acrylate, dicyclopentadiene (meth)acrylate, dicyclopentenyloxyethyl

(meth)acrylate, dicyclopentenyl (meth)acrylate, N₁N- dimethyl(meth)acrylamide, tetrachlorophenyl(meth)acrylate, 2-tetrachlorophenoxyethyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, tetrabromophenyl (meth)acrylate, 2- tetrabromophenoxyethyl (meth)acrylate, 2-trichlorophenoxyethyl (meth)acrylate, tribromophenyl (meth)acrylate, 2-tribromophenoxyethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, phenoxyethyl (meth)acrylate, butoxyethyl (meth)acrylate, pentachlorophenyl (meth)acrylate, pentabromophenyl (meth)acrylate, polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, bornyl (meth)acrylate, and methyltriethylene diglycol (meth)acrylate.

Of these, N-vinyl caprolactam, N-vinyl pyrrolidone, acryloyl morpholine, N-vinylcarbazole, isobornyl (meth)acrylate, phenoxyethyl (meth)acrylate, and the like are preferred, with N-vinyl caprolactam, N-vinyl pyrrolidone, and acryloyl morpholine being particularly preferred. The most preferred monofunctional polymerizable monomer is acryloyl morpholine.

As examples of commercially available products of these mono- functional radiation curable compounds, Aronix M-1 11 , M-113, M-1 17 (manufactured by Toagosei Co., Ltd.), Kayarad TC1 10S, R-629, R-644 (manufactured by Nippon Kayaku Co., Ltd.), Viscoat 3700 (manufactured by Osaka Organic Chemical Industry Co., Ltd.), and the like can be given.

In addition to the above-described components, various additives can be optionally added to the composition of the present invention. Given as examples of such additives are antioxidants, UV absorbers, light stabilizers, silane coupling agents, antioxidants, thermal polymerization inhibitors, coloring agents, surfactants, preservatives, plasticizers, lubricants, solvents, inorganic fillers, organic fillers, wettability improvers, coating surface improvers, and the like. As commercially available products of antioxidants Irganox 1010, 1035, 1076, 1222 (manufactured by Ciba Specialty Chemicals Co.), and the like can be given. As commercially available products of UV absorbers, Tinuvin P, 234, 320, 326, 327, 328, 213, 400 (manufactured by Ciba Specialty Chemicals Co.), Sumisorb 1 10, 130, 140, 220, 250, 300, 320, 340, 350, 400 (manufactured by Sumitomo Chemical Industries Co., Ltd.), and the like are given. As commercially available products of light stabilizers, Tinuvin 292, 144, 622LD (manufactured by Ciba Specialty Chemicals Co.), Sanol LS-770, 765, 292, 2626, 11 14, 744 (manufactured by Sankyo Chemical Co.), and the like can be given. As silane coupling agents, γ-aminopropyl triethoxysilane, v- mercaptopropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, and commercially available products such as SH6062, SZ6030 (manufactured by Dow Corning Toray Silicone Co., Ltd.), KBE903, KBM803 (manufactured by Shin-Etsu Silicone Co., Ltd.), and the like can be given. As commercially available products of aging preventives, Antigene W, S, P, 3C, 6C, RD-G, FR, AW (manufactured by Sumitomo Chemical Industries Co., Ltd.), and the like can be given.

Polymers or oligomers such as epoxy resins, polymerizable compounds (such as urethane (meth)acrylate, vinyl ether, propenyl ether, maleic acid derivatives), polyamide, polyimide, polyamideimide, polyurethane, polybutadiene, chloroprene, polyether, polyester, pentadiene derivatives, styrene/butadiene/styrene block copolymer, styrene/ethylene/butene/styrene block copolymer, styrene/isoprene/styrene block copolymer, petroleum resin, xylene resin, ketone resin, fluorine-containing oligomers, polysulfide-type oligomers can also be incorporated in the composition of the present invention as other additives.

The coating composition generally comprises a non-reactive solvent, such as for example methyl-ethyl-ketone, isopropanol, 1-methoxy-2-propanol, ethyl- acetate and the like. The solvent is used to lower the viscosity to such a value, that good flow is obtained, and that thin coatings can be applied. Generally, the solid content is about 10 wt% or higher, preferably about 20 wt% or higher. The composition may be used as 100% solids, but generally it will be preferred to use the composition at 80% solids or lower.

It is preferred, to match the refractive index of the coating with that of the substrate. In order to achieve this, it is effective to measure the refractive index of the particles (component (i)), the refractive index of the remainder of the composition, and combine the two parts in such an amount that - on average - the required refractive index is obtained. In case a relatively high refractive index is required, it is preferred to use high-refractive index particles, as to allow sufficient multi-functional acrylate compounds to achieve a strong coating.

After application of the coating composition, the coating is dried in an oven or with IR radiation, and thereafter actinic radiation is applied to initiate the photopolymerisation. Preferably UV or UV-Vis light is used. Suitable amounts of energy applied are about 0.1 J/m² or higher, preferably about 0.2 J/m² or higher. Generally, the amount will be about 5 J/m² or lower. It is also well possible to use electron beam curing, without the need for a photoinitiator.

The radiation curable resin composition of the present invention can produce cured products with excellent characteristics such as a high refractive index, superior abrasion resistance, transparency, chemical resistance, and the like. The composition is thus suitable for use as a hard coat for plastic optical parts, touch panels, and film-type liquid crystal elements, and fabricated plastic materials, and also as a stain-proof or mar-proof coating material for floors and walls inside buildings. In addition, because the composition does not produce interference fringes when applied to a substrate with a similar refractive index due to its high refractive index, the composition can be used suitably in optical applications.

Examples

The present invention will now be described in more detail by way of examples which should not be construed as limiting the present invention. In the following examples, unless otherwise indicated, "parts" and "%" means respectively

"parts by weight" and "wt%".

Test Examples

Test specimens were prepared using the resin compositions prepared in the above Examples and Comparative Examples to evaluate pencil hardness, mar resistance, abrasion resistance, adhesion to substrates, transmittance, and refractive index of the cured films according to the following methods. The results are shown in Table 2.

Preparation of test specimens:

The resin compositions prepared in the below Examples and

Comparative Examples were applied on a commercially available PET film (thickness: 25 μm) using a gravure roll-to-roll coater to a thickness of about 3 μm. The coatings were allowed to dry in an infrared dryer oven at 40 ⁰C, followed by irradiation with ultraviolet rays at a dose of 0.22 or 1.0 J/cm² in air to obtain cured coating films. The lower amount of energy was used with colored PET films. Appearance and iridescence:

The appearance and in particular iridescence was evaluated by naked eye observation under a TL lamp. Furthermore, the fringes were measured with a thin film reflectometer of Filmetrics over a minimum of 1 mm² surface.

Light transmittance:

Light transmittance at a wavelength of 500 nm was measured using a spectrophotometer and corrected for reflectance and transmittance of the substrates.

Refractive index:

The refractive index was measured with an elipsometer.

Pencil hardness: The pencil hardness was measured according to JIS K5400 using a pencil scratch tester with pencils up to a hardness of 6H and a loading up to 750 g.

Scratch resistance: Steel wool abrasion test

Steel wool scratch resistance was measured as follows: a flat circular steel surface (diameter = 2.4cm (1 inch)) was covered evenly with steel wool (grade:

0000) with a normal weight of 25Og, 50Og or 1000g. The steel wool was then moved back and forth over the surface 5 times making for a total of 10 rubs over a distance of ca 5 to 10cm. At this point the surface of the coating is visually inspected and rated according to the table 1 below.

Table 1 : Rating of abrasion resistance according to number of observable scratches after steel wool testing.

Substrate adhesion (cross hatch resistance): JIS K5400 was followed. 100 squares (1 mm x 1 mm) were produced on the surface of the cured test specimen by 1 1 x 11 cross-cut lines. A commercially available cellophane tape was adhered and rapidly peeled off. The substrate adhesion was indicated by X/100, wherein X is the number of squares left on the substrate without being detached.

Examples 1-3 and comparative experiments A-D

Formulations were based either on functionalized zirconium-oxides (ZrOx), or cerium- oxides (CeOx). Mixtures were made from ZrOx and a mixture of polyacrylates (dipentaerytritol pentaacrylate and tris (2-hydroxy ethyl) isocyanurate triacrylate) with lrgacure 184 (2 wt% on solids) as photoinitiator. By choosing certain amounts of particles and resin, the average refractive index of the substrate could be matched. Further, as leveling agent BykUV3500 was added in 0.5 wt% (relative to solids) in example 1 , and 2 wt% in examples 2 and 3. Further, in examples 2 and 3 acryloyl propyl trimethoxysilane was added as further surface modifying agent in respectively 1 and 2.5 wt% on solids. The coating compositions were applied as about 40 wt% solids in MEK. The comparative experiments did not contain leveling agent.

The formulation of example 1 : Acrylated PIS-ZrO₂: 28.7 ( 90 wt % ZrOx)

SR 399 11.6 p-Methoxyphenol 0.01

MEK 58.2

BYK UV 3500 0.5 The acrylated part of the zirconia particles was made from IPDI, 3- mercaptopropyltrimethoxysilane and pentaerythritol tri/tetraacrylate in 5% MEK as discribed in US 6521677.

Table 2

In the cross-hatch of the coating of example 1 , 100% remained attached to the substrate.

As appears from these results, it is possible to match the refractive index of a substrate by using a suitable amount of resin and high refractive index particles. However, in order to achieve a colorless coating (with no iridescent colors under TL light), it is necessary to have a slip agent present. The slip agent also improves the scratch resistance and pencil hardness.

The radiation curable resin composition of the present invention can produce cured products with excellent characteristics such as a high refractive index, superior abrasion resistance, transparency, chemical resistance, and the like. The composition is thus suitable for use as a hard coat for plastic optical parts, touch panels, and film-type liquid crystal elements, and fabricated plastic materials, and also as a stain-proof or mar-proof coating material for floors and walls inside buildings. In addition, because the composition does not produce reflection interference stripes when applied to a substrate with a similar refractive index due to its high refractive index, the composition can be used suitably in optical applications.

Claims

1. Article comprising a hard coating on a plastic substrate, the substrate having an average refractive index of about 1.61 or higher, the coating having a refractive index of 1.6 or higher, a thickness of from about 1 μm to about 10 μm and having a variation in coating thickness of about 200nm or less when measured over a surface area of 3 mm diameter with a thin layer reflectometer.

2. Article comprising a hard coating on a plastic substrate, the substrate having an average refractive index of about 1.61 or higher, the coating having a refractive index of 1.6 or higher, a thickness of from about 1 μm to about 10 μm and having a fringe pattern of about 0.4% or less when measured with a thin layer reflectometer over a wavelength of 400 to 700 nm.

3. An article according to any preceding claim wherein the coating has a pencil hardness of 2H or better.

4. An article according to any preceding claim wherein the coating has a steel wool resistance of C or better with 500 g pressure.

5. An article according to any preceding claim wherein the coating has a variance in coating thickness of about 100 nm or less.

6. An article according to any preceding claim wherein the substrate comprises a film of polyethyleneteraphthalate.

7. An article according to the preceding claim wherein the coating comprises a leveling agent.

8. An article according to any preceding claim wherein the coating has a refractive index which is within 0.3 units of the average refractive index of the substrate as measured between 400 and 700 nm.

9. A hard coating composition comprising i. metal oxide particles comprising a radiation-curable group linked to a metal oxide, the metal oxide particles having a bulk refractive index of about 1.7 or higher, ii. a multifunctional radiation curable compound having about 2 or more radiation curable groups, iii. silicon leveling agent, wherein the refractive index of the composition is about 1.6 or higher.

10. Coating according to claim 9, wherein the metal oxide is selected from zirconium, titanium, antimony, zinc, tin, indium, cerium, and aluminium oxides or combinations thereof.

11. Coating according to claims 9-10, wherein the metal oxide particles have a refractive index of about 1.9 or higher.

12. Coating according to any one of claims 9-11 , wherein the particles comprise metal oxide reacted with an organosilicon compound.

13. A cured coating, obtained from curing the coating composition of claims 9-12

14. Method for reducing iridescence in a hard coat, by providing (a) a radiation curable hard coat comprising (i) metal oxide particles comprising a radiation-curable group linked to a metal oxide, the metal oxide particles having a bulk refractive index of about 1.7 or higher, and (ii) a multifunctional radiation curable compound having about 2 or more radiation curable groups, (b) mixing the components in such an amount that the averaged refractive index of the substrate and hard coat is matched with 0.5 units, (c) applying the coating to a substrate and curing the coating.

15. Use of a coating according to any one of claims 9-13 for solar control films.

16. Use of a leveling agent to reduce the iridescence of a coating.