HK1146289A - Radiation curable coating compositions, related coatings and methods - Google Patents

Description

Radiation curable coating compositions, related coatings and methods

Cross Reference to Related Applications

This application claims benefit of U.S. provisional application 60/978,886 filed on 10/2007, which is incorporated herein by reference.

Technical Field

The present invention relates to radiation-curable coating compositions, radiation-cured coatings formed therefrom, related methods of coating substrates, and related coated substrates.

Background

Plastic substrates, including transparent plastic substrates, are desirable for many applications, particularly for example windshields, lenses, and consumer electronics (including, for example, mobile phones, personal digital assistants, smart phones, personal computers, digital cameras, etc.). To minimize scratches and other forms of degradation, a transparent "hard coat" is often applied to a substrate as a protective layer.

In some cases, the "hardcoat" described above is formed from the hydrolysis and condensation of one or more alkoxysilanes. The coating formed by this mechanism can be very wear resistant. However, in certain industries, they are not as easily used as coatings employing organic binder materials, e.g., organic binder materials curable by exposure to actinic radiation.

Recently, hybrid organic-inorganic coatings have been proposed. These coatings employ particles, such as silica particles, dispersed in an organic binder, such as a UV curable organic binder. They are therefore considered to be "hybrid organic-inorganic" coatings. However, the hybrid organic-inorganic coatings developed to date have not shown the following combination of properties that are desirable in certain applications, for example, certain applications involving the use of the coatings on consumer electronic devices: very high initial transparency (low haze), low color (low yellowing), good flexibility and abrasion resistance at relatively high film thicknesses (up to 2 mils).

Accordingly, it would be desirable to provide improved hybrid organic-inorganic coating compositions that exhibit the following properties that are desirable in certain demanding applications: very high initial transparency (low haze), low color (low yellowing), good flexibility and abrasion resistance at relatively high film thicknesses (up to 2 mils). Surprisingly, it has been found that the use of specific radiation curable organic film-forming binders in combination with certain nanoparticles enables the above desired combination of properties to be achieved.

Summary of The Invention

In certain aspects, the present invention relates to radiation curable coating compositions. These coating compositions comprise: (a) an organic film-forming binder comprising: (i)10 to 60 wt% of a urethane (meth) acrylate comprising the reaction product of a polyisocyanate containing two (meth) acrylate groups per molecule and a polyol, and (ii)40 to 90 wt% of a higher functional (meth) acrylate; and (b) > 10 wt% and < 40 wt% of particles having an average primary particle size of no greater than 25 nm, based on the total weight of the binder.

In other aspects, the invention relates to radiation-cured coatings. These cured coatings comprise: (a) an organic film-forming binder comprising a urethane (meth) acrylate comprising the reaction product of a polyisocyanate containing two (meth) acrylate groups per molecule and a polyol; and (b) particles having an average primary particle size of no greater than 25 nanometers dispersed in the binder. The cured coating has (1) a thickness of 3-20 microns, (2) < 1% initial haze; and (3) < 15% haze after 100 Taber cycles (Taber cycle).

In a further aspect, the invention relates to a method of coating a substrate. These methods include: (a) depositing a coating composition comprising: (1) a radiation-curable organic film-forming binder comprising a urethane (meth) acrylate comprising the reaction product of a polyisocyanate containing two (meth) acrylate groups per molecule and a polyol; and (2) particles having an average primary particle size of no greater than 25 nanometers; and (b) curing the composition by exposing the composition to actinic radiation in air, thereby producing a cured coating having (i) a thickness of 3 to 20 microns, (ii) an initial haze of < 1%, and (iii) a haze of < 15% after 100 Talbot cycles.

The invention also relates to the related coated substrate.

Detailed description of the embodiments

For the purposes of the following detailed description, it is to be understood that the invention may assume various alternative variations and step sequences, except where expressly specified to the contrary. Moreover, other than in any examples, or where otherwise indicated, all numbers expressing, for example, quantities of ingredients used in the specification and claims are to be understood as being modified in all instances by the term "about". Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements.

In addition, it should be understood that any numerical range recited herein is intended to include all sub-ranges subsumed therein. For example, a range of "1 to 10" is intended to include all sub-ranges between the recited minimum value of 1 and the recited maximum value of 10 (inclusive), i.e., all sub-ranges having a minimum value equal to or greater than 1 and a maximum value of equal to or less than 10.

As previously mentioned, certain embodiments of the present invention are directed to coating compositions comprising an organic film-forming binder. The term "film-forming binder" as used herein refers to a binder capable of forming a self-supporting continuous film on at least a horizontal surface of a substrate upon removal of any diluent or carrier present in the composition or upon curing at ambient or elevated temperature. The term "binder" as used herein refers to a continuous material in which is dispersed a particulate material, such as particles having an average primary particle size of no greater than 25 nanometers (described in more detail below). The term "organic film-forming binder" as used herein means that the film-forming binder comprises carbon-based backbone repeating units.

In certain embodiments, the coating compositions of the present invention are substantially free, or in some cases completely free, of inorganic film-forming binders, i.e., film-forming binders having a backbone repeating unit based on one or more elements other than carbon, such as silicon. Thus, in certain embodiments, the coating compositions of the present invention are substantially free, or in some cases completely free, of compounds of formula R_xM(OR′)_z-xWherein R is an organic group, M is silicon, aluminum, titanium and/or zirconium, each R' is independently a hydrocarbyl group, z is the valence of M, and x is a number less than z and may be zero, for example, as in U.S. patent application publication 2006/0247348 [0011 ]]The citation of this document is incorporated by reference herein as if fully set forth in the paragraph.

In certain embodiments, the coating compositions of the present invention are substantially free, or in some cases completely free, of organosilanes, hydrolysis products thereof, and/or hydrolysis-condensation products thereof.

The term "substantially free" as used herein means that the material in question is present in the composition as an incidental impurity, if any. In other words, the material does not affect the properties of the composition. The term "completely free" as used herein means that the material is not present in the composition at all.

In certain embodiments, the organic film-forming binder is radiation curable, i.e., it is curable upon exposure to actinic radiation. "actinic radiation" is light having wavelengths of electromagnetic radiation ranging from gamma rays to ultraviolet ("UV") light, through the visible range, and into the infrared range. Actinic radiation that may be used to cure certain coating compositions of the present invention typically has an electromagnetic radiation wavelength of 100-. Examples of suitable ultraviolet light sources include mercury arcs, carbon arcs, low, medium or high pressure mercury lamps, swirl-flow plasma arcs, and ultraviolet light emitting diodes. The preferred ultraviolet light-emitting lamp is a medium pressure mercury vapor lamp with an output of 200- ­ 600 watts per inch (79-237 watts per centimeter) along the length of the tube. In certain embodiments, the coating compositions of the present invention may be cured in air.

Materials curable upon exposure to actinic radiation include compounds having radiation curable functional groups such as unsaturated groups including vinyl groups, vinyl ether groups, epoxy groups, maleimide groups, fumarate groups, and combinations of the foregoing. In certain embodiments, the radiation curable groups are curable upon exposure to ultraviolet radiation and may include, for example, acrylates, maleimides, fumarates, and vinyl ethers. Suitable vinyl species include those having unsaturated ester and vinyl ether groups.

In certain embodiments, the radiation curable organic film-forming binder present in the compositions of the present invention comprises a urethane (meth) acrylate. The term "(meth) acrylate" as used herein is meant to include both acrylates and methacrylates. The term "urethane (meth) acrylate" as used herein refers to a polymer having (meth) acrylate functionality and containing urethane linkages. As will be appreciated, the above-described polymers may be prepared, for example, by reacting a polyisocyanate, a polyol, and a (meth) acrylate having hydroxyl groups, such as described in U.S. Pat. No. 4 column 4 lines 4-49 of 6,899,927, the cited portion of which is incorporated herein by reference.

In certain embodiments, the radiation curable organic film-forming binder present in the compositions of the present invention comprises a urethane (meth) acrylate comprising the reaction product of a polyisocyanate having relatively few functional groups per molecule, often two (meth) acrylate functional groups per molecule, and a polyol. In some cases, the molecular weight of the above polymer is 3,000. Another example of a "urethane (meth) acrylate polymer" is described in U.S. Pat. No.6,899,927, column 4, line 50-column 5, line 3, the citation of which is incorporated herein by reference.

In certain embodiments, the urethane (meth) acrylate polymer is present in the coating composition of the present invention in an amount of at least 10 weight percent, such as at least 20 weight percent, with the weight percent being based on the total weight of the composition. In certain embodiments, the urethane (meth) acrylate polymer is present in the coating composition of the present invention in an amount of no greater than 60 weight percent, such as no greater than 40 weight percent, with the weight percent being based on the total weight of the binder. The amount of urethane (meth) acrylate polymer in the composition of the present invention can range between any combination of the recited values, inclusive.

In certain embodiments, the radiation curable coating compositions of the present invention comprise a high functional (meth) acrylate. The term "higher functional (meth) acrylate" as used herein refers to (meth) acrylates having three or more (meth) acrylate (often acrylate) functional groups per molecule, such as tri-, tetra-, penta-and/or hexa-functional (meth) acrylates.

In certain embodiments, the coating compositions of the present invention comprise a trifunctional (meth) acrylate. The term "trifunctional (meth) acrylate" as used herein is meant to include (meth) acrylate monomers and polymers containing three reactive (meth) acrylate groups per molecule. Examples of said compounds suitable for use in the present invention are propoxylated glycerol triacrylate, ethoxylated trimethylolpropane triacrylate, pentaerythritol triacrylate, propoxylated glycerol triacrylate, propoxylated trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, tris (2-hydroxyethyl) and/or isocyanurate triacrylate.

In certain embodiments, the total amount of trifunctional (meth) acrylate present in the coating composition of the present invention is at least 40 wt%, such as at least 50 wt%, with the weight percentages being based on the total weight of the binder. In certain embodiments, the total amount of trifunctional (meth) acrylate present in the coating composition of the present invention is no greater than 70 wt.%, such as no greater than 60 wt.%, with the weight percentages being based on the total weight of the binder. The total amount of trifunctional (meth) acrylate present in the coating composition of the invention may range between any combination of the recited values, inclusive.

In certain embodiments, the coating compositions of the present invention comprise tetra-and/or higher functional (meth) acrylates. The phrase "tetra-and/or higher functional (meth) acrylate" as used herein is meant to include (meth) acrylate monomers and polymers containing four or more reactive (meth) acrylate groups per molecule, such as tetra-, penta-and/or hexa-functional (meth) acrylates.

The term "tetrafunctional (meth) acrylate" as used herein is meant to include (meth) acrylates containing four reactive (meth) acrylate groups per molecule. Examples of such materials suitable for use in the present invention include, but are not limited to, bis-trimethylolpropane tetraacrylate, ethoxylated 4-pentaerythritol tetraacrylate, pentaerythritol ethoxylate tetraacrylate, pentaerythritol propoxylate tetraacrylate, including mixtures thereof.

The term "pentafunctional (meth) acrylate" as used herein is meant to include (meth) acrylate monomers and polymers containing five reactive (meth) acrylate groups per molecule. Suitable examples of such materials include, but are not limited to, dipentaerythritol pentaacrylate, dipentaerythritol ethoxylate pentaacrylate, and dipentaerythritol propoxylate pentaacrylate, including mixtures thereof.

The term "hexafunctional (meth) acrylate" as used herein is meant to include (meth) acrylate monomers and polymers containing six reactive (meth) acrylate groups per molecule. Suitable examples of such materials include, but are not limited to, commercially available products such as the following and mixtures of any of them: EBECRYL^TM1290 and EBECRYL^TM8301 Hexafunctional aliphatic urethane acrylates (both from Cytec); EBECRYL^TM220 hexafunctional aromatic urethane propenesAcid esters (from Cytec); EBECRYL^TM830、EBECRYL^TM835、EBECRYL^TM870 and EBECRYL^TM2870 hexafunctional polyester acrylates (all from Cytec); EBECRYL^TM450 fatty acid modified polyester hexaacrylate (ex Cytec); DPHA^TMDipentaerythritol hexaacrylate (functionality 6; from Cytec).

In certain embodiments, the tetra-and/or higher functional (meth) acrylate is present in the coating composition of the present invention in an amount of at least 10 wt%, for example at least 15 wt%, the weight percentages being based on the total weight of the binder. In certain embodiments, the tetra-and/or higher functional (meth) acrylate is present in the coating composition of the present invention in an amount of no greater than 30 weight percent, such as no greater than 25 weight percent, with the weight percent being based on the total weight of the binder. The amount of tetra-and/or higher functional (meth) acrylate in the compositions of the present invention can range between any combination of the recited values, inclusive.

In certain embodiments, the organic film-forming binder of the coating composition of the present invention comprises (i) 20 to 40 wt%, based on the total weight of the binder, of a urethane (meth) acrylate comprising the reaction product of a polyisocyanate containing two (meth) acrylate groups per molecule and a polyol, (ii)40 to 60 wt%, based on the total weight of the binder, of a trifunctional (meth) acrylate, and 10 to 30 wt%, based on the total weight of the binder, of a tetra-and/or higher functional (meth) acrylate. In these embodiments, the amount of each (meth) acrylate in the compositions of the present invention can range between any combination of the recited values, inclusive.

In certain embodiments, the radiation curable compositions of the present invention are substantially free, or in some cases completely free, of mono (meth) acrylates and/or di (meth) acrylates. The term "mono (meth) acrylate" as used herein includes monomers and polymers containing one (meth) acrylate group per molecule. The term "di (meth) acrylate" as used herein includes monomers and polymers containing two (meth) acrylate groups per molecule.

In certain embodiments, the coating composition of the present invention comprises particles dispersed in a binder, having an average primary particle size of no greater than 25 nanometers. In certain embodiments, the particles comprise silica particles and they have an average primary particle size of about 20 nanometers.

The average particle size can be determined as follows: electron micrographs of transmission electron microscopy ("TEM") images were visually examined, the diameter of the particles in the images was determined, and the average particle size was calculated based on the magnification of the TEM images. For example, a TEM image at 105,000 magnification may be generated, with a scaling factor obtained by dividing the magnification by 1000. After visual inspection, the diameter of the particles was measured in millimeters and the measurement was converted to nanometers using a conversion factor. The diameter of a particle refers to the smallest diameter sphere that will completely encase the particle.

The shape (or morphology) of the particles may vary depending on the particular embodiment of the invention and its intended application. For example, spherical morphology (e.g., solid spheres, microbeads, or hollow spheres), as well as cubic, platy, or acicular (elongated or fibrous) particles in general may be used. In addition, the particles may have a hollow, porous or void-free internal structure, or a combination of any of the foregoing, such as a hollow core with porous or solid walls.

Mixtures of one or more particles having different compositions, average particle sizes, and/or morphologies can be incorporated into the compositions of the present invention to impart desired properties and characteristics to the compositions.

Particles suitable for use in the coating compositions of the present invention include, for example, those described in U.S. patent 7,053,149, column 19, line 5-column 23, line 39, the citation of which is incorporated herein by reference.

Prior to incorporation, one class of particles that may be used in accordance with the present invention includes sols, such as organosols, of the particles. These sols can have a multitude of small particles of colloidal silica having an average particle size such as within the ranges described above.

In certain embodiments, the particle prior to introduction comprises a silica organosol comprising silica nanoparticles and a polymerizable (meth) acrylate binder (bindinggent). In these embodiments, the polymerizable (meth) acrylate binder forms at least a portion of the organic film-forming binder described previously. The term "silica organosol" as used herein refers to a colloidal dispersion of finely divided silica particles, e.g., amorphous silica particles, dispersed in an organic binder, wherein the organic binder, in certain embodiments of the invention, comprises a polymerizable (meth) acrylate. The term "silica" as used herein refers to SiO₂。

Polymerizable (meth) acrylates suitable for use as binders in the silica organosols present in certain embodiments of the coating compositions of the present invention include unsaturated (meth) acrylate monomers and oligomers, such as the difunctional (meth) acrylates and higher functional (meth) acrylates previously described.

Silica organosols suitable for use in the present invention are commercially available. Examples include those from Hanse Chemie AG, geethacht, GermanyA series of products. These products are low viscosity organosols having a silica content of up to 50% by weight. Examples of such products suitable for use in the present invention areAndalso suitable are Laromer PO 9026V from BASF, nanoparticles containing polyether acrylate oligomers.

In some cases, the silica particles are dispersed in an inert organic solventIn, for exampleIt is a dispersion of silica nanoparticles in n-butyl acetate.

In certain embodiments, the above-described particles are present in the coating composition in an amount greater than 10 wt% and less than 40 wt%, such as from 20 to 30 wt%, or in some cases about 25 wt%, based on the total solids weight, i.e., non-volatile weight, of the coating composition. The amount of the above particles in the composition of the present invention may range between any combination of the recited values, inclusive.

It has been surprisingly found that the particular combination of particle size and loading of the above-mentioned particles, e.g. silica particles, in the coating composition, as with the particular composition of the organic film-forming binder, is critical to obtain a radiation-cured coating having the desired level of abrasion resistance (as described below) and flexibility together with the desired level of initial transparency (as described below) at relatively high film thicknesses (up to 2 mils) and low color (low yellowing). Indeed, it was not originally predicted that the urethane acrylates described herein are present in an amount of 10 to 60 wt%, based on the total weight of binder in the coating composition of the present invention, important to achieve the high initial clarity and low color (low yellowing) properties sought herein, which are desirable at film thicknesses up to 2 mils. The amount and size of nanoparticles that would otherwise be expected to be used in the coating compositions described herein will determine these properties. However, it was found that even with the nanoparticles used in optimal amounts and sizes, the initial transparency at 2 mil film thickness was still insufficient unless the specific binder composition of the present invention was also used.

In certain embodiments, the coating compositions of the present invention further comprise an organic solvent. The solvent may be present in an amount of from 20 to 90 percent by weight based on the total weight of the coating composition, depending on the particular composition used and the desired application technique. Suitable solvents include, but are not limited to, the following: benzene, toluene, methyl ethyl ketone, methyl isobutyl ketone, acetone,Ethanol, tetrahydrofurfuryl alcohol, propanol, butanol, propylene carbonate, N-methylpyrrolidone, N-vinylpyrrolidone, N-acetylpyrrolidone, N-hydroxymethylpyrrolidone, N-butylpyrrolidone, N-ethylpyrrolidone, N-N-octylpyrrolidone, N-dodecylpyrrolidone, 2-methoxyethyl ether, xylene, cyclohexane, 3-methylcyclohexanone, ethyl acetate, butyl acetate, tetrahydrofuran, methanol, pentyl propionate, methyl propionate, diethylene glycol monobutyl ether, dimethyl sulfoxide, dimethylformamide, ethylene glycol, the monoalkyl and dialkyl ethers of ethylene glycol and derivatives thereof (sold by Union Carbide as the CELLOSOLVE industrial solvent), propylene glycol methyl ether and propylene glycol methyl ether acetate (respectively as the Cellosolve industrial solvent), propylene glycol methyl ether and propylene glycol methyl ether acetateAnd PMA solvents sold by Dow Chemical), and mixtures of the above listed solvents.

Depending on the desired application technique, the coating composition of the present invention may be implemented as a substantially solvent-free and water-free liquid coating composition, i.e., a substantially 100% solids coating. As used herein, the term "substantially 100% solids" means that the composition is substantially free of volatile organic solvents ("VOCs"), and has substantially zero VOC emissions, and is substantially free of water. In certain embodiments, the substantially 100% solids coating of the present invention comprises less than 5% VOC and water by weight of the coating composition, in some cases less than 2% VOC and water by weight of the coating composition, in some cases less than 1% VOC and water by weight of the coating composition, and in some cases the VOC and water are not present in the coating composition at all.

In certain embodiments, the coating compositions of the present invention may also comprise additional optional ingredients, such as those well known in the art of formulating surface coatings. The optional ingredients may include, for example, surfactants, flow control agents, thixotropic agents, anti-gassing agents, antioxidants, light stabilizers, UV absorbers and other conventional adjuvants. Any of the above additives known in the art may be used.

In certain embodiments, particularly when the coating compositions of the present invention are to be cured by UV radiation, these compositions further comprise a photoinitiator. As will be appreciated by those skilled in the art, a photoinitiator absorbs radiation during the curing process and converts it into chemical energy that can be used for polymerization. Photoinitiators are classified into two broad categories based on mode of action, either or both of which may be used in the compositions of the present invention. The cleavage type photoinitiator includes acetophenones, alpha-aminoalkylphenones, benzoin ethers, benzoyl oximes, acylphosphine oxides, bisacylphosphine oxides, and mixtures thereof. The extraction type photoinitiators include benzophenone, michael ketone, thioxanthone, anthraquinone, camphorquinone, fluorone, coumarone, and mixtures thereof.

Specific non-limiting examples of photoinitiators that may be used in certain embodiments of the coating compositions of the present invention include benzil, benzoin methyl ether, benzoin isobutyl ether phenol (benzophenon), acetophenone, benzophenone, 4, 4 ' -dichlorobenzophenone, 4, 4 ' -bis (N, N ' -dimethylamino) benzophenone, diethoxyacetophenone, fluoroketones, such as the H-Nu series of initiators available from Spectra Group Ltd., 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-hydroxycyclohexylphenyl ketone, 2-isopropylthioxanthone, alpha-aminoalkylphenyl ketones, such as 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -1-butanone, acylphosphine oxides, such as 2, 6-dimethylbenzoyldiphenylphosphine oxide, 2, 4, 6-trimethylbenzoyldiphenylphosphine oxide, bis (2, 4, 6-trimethylbenzoyl) phenylphosphine oxide, 2, 6-dichlorobenzoyldiphenylphosphine oxide and 2, 6-dimethoxybenzoyldiphenylphosphine oxide, bisacylphosphine oxides, such as bis (2, 6-dimethoxybenzoyl) -2, 4, 4-trimethylpentylphosphine oxide, bis (2, 6-dimethylbenzoyl) -2, 4, 4-trimethylpentylphosphine oxide, bis (2, 4, 6-trimethylbenzoyl) -2, 4, 4-trimethylpentylphosphine oxide and bis (2, 6-dichlorobenzoyl) -2, 4, 4-trimethylpentylphosphine oxide, and mixtures thereof.

In certain embodiments, the coating compositions of the present invention comprise from 0.01 to 15 wt% photoinitiator, or in some embodiments from 0.01 to 10 wt%, or in other embodiments from 0.01 to 5 wt% photoinitiator, based on the total weight of the coating composition. The amount of photoinitiator present in the coating composition can range between any combination of these values, inclusive.

In certain embodiments, the coating compositions of the present invention further comprise a colorant. The term "colorant" as used herein refers to any substance that imparts color and/or other opacity and/or other visual effect to the composition. The colorant may be added to the coating in any suitable form, such as discrete particles, dispersions, solutions, and/or flakes. A single colorant or a mixture of two or more colorants can be used in the coating of the present invention.

Examples of colorants include pigments, dyes, and tints, such as those used in the coatings industry and/or listed in the Dry Color Manufacturers Association (DCMA), as well as special effect compositions. The colorant may comprise, for example, a finely divided solid powder that is insoluble but wettable under the conditions of use. The colorant may be organic or inorganic and may be aggregated or non-aggregated. The colorants can be incorporated into the coating by use of a grind vehicle, such as an acrylic grind vehicle, the use of which is well known to those skilled in the art.

Examples of pigments and/or pigment compositions include, but are not limited to, carbazole dioxazine crude pigments, azo, monoazo, disazo, naphthol AS, salts (lakes), benzimidazolone, condensates, metal complexes, isoindolinone, isoindoline and polycyclic phthalocyanine, quinacridone, perylene, perinone, diketopyrrolopyrrole, thioindigo, anthraquinone, indanthrone, anthrapyrimidine, flavanthrone, pyranthrone, anthanthrone, dioxazine, triarylcarbonium, quinophthalone pigments, diketopyrrolopyrrole red ("DPPBO red"), titanium dioxide, carbon black, and mixtures thereof. The terms "pigment" and "colored filler" are used interchangeably.

Examples of dyes include, but are not limited to, those that are solvent and/or aqueous based such as phthalocyangreen or phthalocyanblue, iron oxide, bismuth vanadate, anthraquinone, perylene, aluminum, and quinacridone.

Examples of tints include, but are not limited to, pigments dispersed in an aqueous-based or water-miscible vehicle such as AQUA-CHEM 896 commercially available from Degussa, inc. and CHARISMA COLORANTS and maxi minor COLORANTS commercially available from Accurate Dispersions of Eastman Chemical, inc.

As noted above, the colorant can be in the form of a dispersion, including but not limited to in the form of a nanoparticle dispersion. Nanoparticle dispersions can include one or more highly dispersed nanoparticle colorants and/or colorant particles that produce a desired visible color and/or opacity and/or visual effect. The nanoparticle dispersion may include a colorant, such as a pigment or dye, having a particle size of less than 150nm, such as less than 70nm or less than 30 nm. Nanoparticles can be produced by milling raw organic or inorganic pigments with grinding media having a particle size of less than 0.5 mm. Examples of nanoparticle dispersions and their methods of manufacture are described in U.S. Pat. No.6,875,800B 2, incorporated herein by reference. Nanoparticle dispersions can also be produced by crystallization, precipitation, gas phase condensation, and chemical attrition (i.e., partial dissolution). To minimize re-aggregation of the nanoparticles in the coating, a dispersion of resin-coated nanoparticles may be used. As used herein, a "dispersion of resin-coated nanoparticles" refers to a continuous phase in which are dispersed discrete "composite particles" comprising nanoparticles and a resin coating on the nanoparticles. Examples of dispersions of resin-coated nanoparticles and methods for their manufacture are described in U.S. patent application publication 2005-0287348a1, filed 24.6.2004, and U.S. provisional application No. 60/482,167, filed 24.6.24.2003, and U.S. patent application No. 11/337,062, filed 20.1.2006, which are also incorporated herein by reference.

Examples of special effect compositions that may be used in the compositions of the present invention include pigments and/or compositions that produce one or more appearance effects such as reflectance, pearlescence, metallic sheen, phosphorescence, fluorescence, photochromism, photosensitivity, thermochromism, goniochromism (goniochromism), and/or color change. Additional special effect compositions may provide other perceptible properties such as opacity or texture. In certain embodiments, the special effect composition may produce a color shift such that the color of the coating changes when the coating is viewed at different angles. Examples of color effect compositions are described in U.S. Pat. No.6,894,086, which is incorporated herein by reference. Additional color effect compositions can include transparent coated mica and/or synthetic mica, coated silica, coated alumina, transparent liquid crystal pigments, liquid crystal coatings, and/or any composition in which interference is caused by refractive index differences within the material and not due to refractive index differences between the surface of the material and the air.

In general, the colorant can be present in any amount sufficient to impart the desired visual and/or color effect. The colorant may comprise 0.1 to 65 weight percent, such as 0.1 to 10 weight percent or 0.5 to 5 weight percent of the composition of the present invention, wherein weight percent is based on the total weight of the composition of the present invention.

The coating compositions of the present invention may be prepared by any suitable technique, including those described in the examples herein. The coating components can be mixed using, for example, a stirred tank, dissolver (including in-line dissolvers), ball mill, agitator mill, static mixer, and the like. If appropriate, mixing is carried out with the exclusion of actinic radiation in order to prevent damage to the coating according to the invention which is curable with actinic radiation. During the preparation, the individual constituents of the mixture according to the invention can be introduced separately. Alternatively, the mixture of the present invention may be prepared separately and mixed with the other components.

The coating composition of the present invention can be applied to any suitable substrate, however, in many cases the substrate is a plastic substrate, such as a thermoplastic substrate including, but not limited to, polycarbonate, acrylonitrile butadiene styrene, blends of polyphenylene ether and polystyrene, polyetherimide, polyester, polysulfone, acrylic, and copolymers and/or blends thereof.

The substrate surface may be treated by cleaning prior to applying the coating composition to the substrate. Effective treatment techniques for plastics include ultrasonic cleaning; washing with an aqueous mixture of organic solvents, such as a 50: 50 mixture of isopropanol: water or ethanol: water; UV treatment; activated gas treatment, such as with low temperature plasma or corona discharge treatment, and chemical treatment, such as hydroxylation, i.e., etching the surface with an aqueous solution of a base, such as sodium or potassium hydroxide, which may also contain a fluorosurfactant. See column 3, lines 13-25 of U.S. patent 3,971,872, column 6, lines 10-48 of U.S. patent 4,904,525, and column 13, lines 10-59 of U.S. patent 5,104,692, which describe surface treatment of polymeric organic materials.

The coating composition of the present invention can be applied to a substrate using, for example, any conventional coating technique, including flow coating, dip coating, spin coating, roll coating, curtain coating, and spray coating. If desired, application of the coating composition to the substrate can be accomplished in an environment substantially free of dust or contaminants, such as a clean room. The coating produced by the process of the present invention may have a thickness of 0.1 to 50 micrometers (μm). However, it has been found that a coating thickness of 3-20 μm may be critical to achieve the transparency and abrasion resistance described below.

After application of the coating composition of the present invention to a substrate, the coating is cured, for example, by exposing the coated substrate to actinic radiation as described previously in air. The terms "cured" and "curing" as used herein refer to at least partial crosslinking of components of a coating that are intended to be cured, i.e., crosslinked. In certain embodiments, the crosslink density, i.e., the degree of crosslinking, is from 35 to 100% of full crosslinking. The presence and extent of crosslinking, i.e., crosslink density, can be determined by a variety of methods, such as by Dynamic Mechanical Thermal Analysis (DMTA) using a Polymer Laboratories MK III DMTA analyzer, as described in U.S. Pat. No.6,803,408, column 7, line 66-column 8, line 18, the contents of which are incorporated herein by reference.

In certain embodiments, coatings formed from the coating compositions of the present invention are resistant to abrasion and exhibit excellent initial clarity at film thicknesses up to 2 mils. For the purposes of the present invention, the term "initial clarity" means that the cured coating has an initial haze% of less than 1% before any taber abrasion. For the purposes of the present invention, the term "abrasion resistance" means that the cured coating has a haze% of less than 15%, and in some cases less than 10%, when determined after 100 taber abrasion cycles according to the standard taber abrasion test (ASTM D1044-49 modified by using the conditions described in the examples). In certain embodiments, the cured coatings of the present invention also have a haze% of less than 25%, and in some cases less than 15%, when determined after 300 taber abrasion cycles according to the standard taber abrasion test (ASTM D1044-49 modified by using the conditions described in example NSI/SAE 26.1-1996). Additionally, the coating compositions of the present invention exhibit low color, meaning that the coating has a yellowness index of less than 1.3 when measured according to ASTM D1925 using a Hunter laboratory spectrophotometer.

The following examples illustrate the invention, however, the examples should not be construed as limiting the invention to the details thereof. All parts and percentages in the following examples, as well as throughout the specification, are by weight unless otherwise specified.

Examples

Example 1

Coating compositions were prepared from the ingredients listed in table 1. Charge I was added to a suitable flask and stirred. Charge II was then added to the flask and the mixture of charge I and charge II was stirred until the solids had dissolved. Feed III was then added with continued agitation. The premixed combination of feeds I, II and III was then added to the flask containing feed IV under agitation. The resulting combination was filtered twice with a 0.45 μm filter.

TABLE 1

¹A 73% solids solution in an organic solvent of a urethane acrylate resin having a molecular weight of about 3,000, the resin comprising the reaction product of a polyisocyanate having two acrylate groups per molecule and a polyol.

²Dipentaerythritol pentaacrylate, available from Sartomer Company, inc.

³Ethoxylated trimethylolpropane triacrylate, available from Sartomer Company, inc., Exton, PA.

⁴Photoinitiators, available from CIBA Specialty Chemicals.

⁵Photoinitiators, available from CIBA Specialty Chemicals.

⁶A photoinitiator, available from Rahn, inc.

⁷Polyether modified acryl functional polydimethylsiloxane, commercially available from Byk-Chemie.

⁸Flow modifiers, commercially available from Cytec Surface Specialties.

⁹Flow modifier, commercially available from Tego Chemie，Essen，Germany。

¹⁰A silica organosol, available from Hanse Chemie AG, geethacht, which is an 50/50 weight percent dispersion of amorphous silica particles having an average primary particle size of about 20 nanometers in trimethylolpropane triacrylate.

To coat the test specimens with the aforementioned composition, the specimens are wiped with 2-propanolTransparent polycarbonate plate (Bayer AG). The coating solution was spin-coated onto an unprimed substrate and the UVA dose was 1J/cm²And an intensity of 0.6W/cm²The H lamp (H bulb) of (1) was cured in air. Samples with different final dry film thicknesses of 3-18 μm were prepared. The coated samples were evaluated for adhesion, optical clarity and taber abrasion resistance.

As shown in Table 2, the polycarbonate coupons coated with the inventive coatings were very clear with low initial haze at different film thicknesses. The coatings also provide good adhesion and abrasion resistance.

TABLE 2

¹Adhesion force: cross-hatch method, Nichibon LP-24 tape. Rating 0-5 (no adhesion after pulling off tape-100% adhesion).

²Haze% was measured with a Hunter laboratory spectrophotometer.

³And (3) wear test: taber 5150 Mill, CS-10 grinding wheel, S-11 dressing disk (refacing disk), weighs 500 g. Haze% was determined after 300 taber cycles. Haze < 25% after 300 Taber cycles% is acceptable.

Comparative examples 2, 3,4

The radiation curable coating compositions of examples 2, 3,4 were prepared from the ingredients listed in table 3. Charge III was added to the flask followed by charge I and charge II with agitation. The mixture was stirred for an appropriate time to form a clear solution.

TABLE 3

¹Hexafunctional aliphatic urethane acrylates, available from Cytec Industries.

²Polyfunctional polyester acrylates, commercially available from Cytec Industries.

³Difunctional monomers, commercially available from Cray Valley.

⁴Photoinitiators, available from CIBA Specialty Chemicals.

⁵Photoinitiators, available from CIBA Specialty Chemicals.

⁶30% colloidal silica in isopropanol, available from Clariant.

⁷30% colloidal silica in 1, 6-hexanediol diacrylate, available from Clariant.

⁸30% colloidal silica in diacrylate, available from Clariant.

⁹Silica organosol, available from Nanoresins AG, Geesthacht, which is an amorphous silica having an average primary particle size of about 20 nanometers50/50 weight percent dispersion of silicon particles in 1, 6-hexanediol diacrylate.

To coat the test specimens with the aforementioned composition, the specimens are wiped with 2-propanolTransparent polycarbonate plate (Bayer AG). The coating solution was spin-coated onto an unprimed substrate and the UVA dose was 1J/cm²And an intensity of 0.6W/cm²The H lamp (H bulb) of (1) was cured in air. Samples with a final dry film thickness of about 15.0 μm were prepared. The coated samples were evaluated for optical clarity and yellowness.

As shown in table 4, polycarbonate coupons coated with different acrylate coating systems based on nanosilica dispersions exhibited different levels of initial haze and yellowness.

TABLE 4

¹Haze% was measured with a Hunter laboratory spectrophotometer.

²The color based on the yellow index was determined with a Hunter laboratory spectrophotometer.

Examples 5, 6 and 7

The radiation curable coating compositions of examples 5, 6, 7 were prepared from the ingredients listed in table 5. Charge IV was added to the flask followed by charge I and charge II with agitation. Feed III was then added in order with agitation. The mixture was stirred for an appropriate time to form a clear solution.

TABLE 5

¹A 73% solids solution in an organic solvent of a urethane acrylate resin having a molecular weight of about 3,000, the resin comprising the reaction product of a polyisocyanate containing two acrylate groups and a polyol.

²Dipentaerythritol pentaacrylate, available from Sartomer Company, inc.

³Ethoxylated trimethylolpropane triacrylate, available from Sartomer Company, inc., Exton, PA.

⁴Photoinitiators, available from CIBA Specialty Chemicals.

⁵Photoinitiators, available from CIBA Specialty Chemicals.

⁶A photoinitiator, available from Rahn, inc.

⁷Polyether modified acryl functional polydimethylsiloxane, commercially available from Byk-Chemie.

⁸Flow modifiers, commercially available from Cytec Surface Specialties.

⁹Flow modifiers, commercially available from Tego Chemie, Essen, Germany.

¹⁰Silica organosol, available from Nanoresins AG, geethacht, is an 50/50 weight percent dispersion of amorphous silica particles having an average primary particle size of about 20 nanometers in trimethylolpropane triacrylate.

To coat the sample with the aforementioned composition, it was wiped with 2-propanolTransparent polycarbonate plate (Bayer AG). The coating solution was spin-coated onto an unprimed substrate and the UVA dose was 1J/cm²And an intensity of 0.6W/cm²The H lamp (H bulb) of (1) was cured in air. The coated specimens were evaluated for abrasion resistance, optical clarity and yellowness.

As shown in Table 6, polycarbonate specimens coated with a coating having more than 60% urethane acrylate in the binder (i.e., example 5) exhibited low abrasion resistance, high yellowness, and reduced transparency at about 2 mils thickness. The samples coated with the coating without urethane acrylate (i.e., example 6) showed low flexibility.

TABLE 6

¹Haze% was measured with a Hunter laboratory spectrophotometer.

²And (3) wear test: taber 5150 grinder, CS-10 grinding wheel, S-11 dressing disk, weight 500 g. The% haze was determined after 100 and 300 taber cycles. Haze% of < 25% after 300 taber cycles was acceptable.

³The color based on the yellow index was determined with a Hunter laboratory spectrophotometer.

It will be readily appreciated by those skilled in the art that changes could be made to the invention without departing from the concepts disclosed in the foregoing description. Such variations are to be considered as included in the following claims unless these claims by their language expressly state otherwise. Accordingly, the particular embodiments described in detail herein are illustrative only and are not limiting to the scope of the invention, which is to be given the full breadth of the appended claims and any and all equivalents thereof.

Claims (17)

1. A radiation curable coating composition comprising:

(a) an organic film-forming binder comprising:

(i)10 to 60 weight percent, based on the total weight of the binder, of a urethane (meth) acrylate comprising the reaction product of a polyisocyanate containing two (meth) acrylate groups per molecule and a polyol; and

(ii)40 to 90 wt%, based on the total weight of the binder, of a high functional (meth) acrylate; and

(b) (ii) greater than 10 wt% and less than 40 wt% of particles having an average primary particle size of no greater than 25 nanometers, based on the total solids weight of the composition.

2. The composition of claim 1, wherein the cured coating is substantially free of inorganic film-forming binders.

3. The composition of claim 1, wherein the organic film-forming binder comprises:

(i) 20 to 40 wt%, based on the total weight of the binder, of the urethane (meth) acrylate,

(ii)40 to 60 wt%, based on the total weight of the binder, of a trifunctional (meth) acrylate, and

(iii) 10-30 wt% of a tetra-and/or higher functional (meth) acrylate, based on the total weight of the binder.

4. The composition of claim 1, wherein the particles comprise silica particles.

5. The composition of claim 4, wherein the silica particles comprise amorphous silica particles.

6. The composition of claim 4, wherein the silica particles have an average primary particle size of about 20 nanometers.

7. A radiation-cured coating comprising:

(a) an organic film-forming binder comprising the reaction product of a polyisocyanate containing two (meth) acrylate groups per molecule and a polyol; and

(b) particles having an average primary particle size of no greater than 25 nanometers dispersed in the binder, wherein

The cured coating has:

(1) a thickness of 3-20 microns and,

(2) initial haze < 1%; and

(3) haze after 100 Talbot cycles of < 15%.

8. The cured coating of claim 7, wherein said particles comprise silica particles.

9. The cured coating of claim 7, wherein the particles are present in the coating composition in an amount of > 10 wt% and < 40 wt%, based on the total weight of the cured coating.

10. The cured coating of claim 7, wherein the cured coating is deposited on a plastic substrate.

11. The cured coating of claim 7, wherein the cured coating has a% haze of less than 10% when determined after 100 taber abrasion cycles as per ANSI/SAE 26.1-1996 and a% haze of less than 15% when determined after 300 taber abrasion cycles as per ANSI/SAE 26.1-1996.

12. The cured coating of claim 7, wherein the cured coating is substantially free of inorganic film-forming binders.

13. A method of coating a substrate comprising:

(a) depositing a coating composition comprising:

(1) a radiation-curable organic film-forming binder comprising a urethane (meth) acrylate comprising the reaction product of a polyisocyanate containing two (meth) acrylate groups per molecule and a polyol; and

(2) particles having an average primary particle size of no greater than 25 nanometers; and

(b) curing the composition by exposing the composition to actinic radiation in air to produce a cured coating comprising

(1) A thickness of 3-20 microns and,

(2) an initial haze of < 1%, and

(3) haze after 100 Talbot cycles of < 15%.

14. The method of claim 13, wherein the particles comprise silica particles.

15. The method of claim 13, wherein the particles are present in the coating composition in an amount > 10 wt% and < 40 wt% based on the total weight of the cured coating.

16. The method of claim 13, wherein the substrate is a plastic substrate.

17. The method of claim 13, wherein the cured coating is substantially free of inorganic film-forming binders.