Classifications

• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D4/00—Coating compositions, e.g. paints, varnishes or lacquers, based on organic non-macromolecular compounds having at least one polymerisable carbon-to-carbon unsaturated bond ; Coating compositions, based on monomers of macromolecular compounds of groups C09D183/00 - C09D183/16
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C17/00—Surface treatment of glass, not in the form of fibres or filaments, by coating
  • C03C17/006—Surface treatment of glass, not in the form of fibres or filaments, by coating with materials of composite character
  • C03C17/007—Surface treatment of glass, not in the form of fibres or filaments, by coating with materials of composite character containing a dispersed phase, e.g. particles, fibres or flakes, in a continuous phase
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82B—NANOSTRUCTURES FORMED BY MANIPULATION OF INDIVIDUAL ATOMS, MOLECULES, OR LIMITED COLLECTIONS OF ATOMS OR MOLECULES AS DISCRETE UNITS; MANUFACTURE OR TREATMENT THEREOF
  • B82B3/00—Manufacture or treatment of nanostructures by manipulation of individual atoms or molecules, or limited collections of atoms or molecules as discrete units
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
  • C04B41/009—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone characterised by the material treated
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
  • C04B41/45—Coating or impregnating, e.g. injection in masonry, partial coating of green or fired ceramics, organic coating compositions for adhering together two concrete elements
  • C04B41/4584—Coating or impregnating of particulate or fibrous ceramic material
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
  • C04B41/80—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone of only ceramics
  • C04B41/81—Coating or impregnation
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D7/00—Features of coating compositions, not provided for in group C09D5/00; Processes for incorporating ingredients in coating compositions
  • C09D7/40—Additives
  • C09D7/60—Additives non-macromolecular
  • C09D7/61—Additives non-macromolecular inorganic
  • C09D7/62—Additives non-macromolecular inorganic modified by treatment with other compounds
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B1/00—Optical elements characterised by the material of which they are made; Optical coatings for optical elements
  • G02B1/10—Optical coatings produced by application to, or surface treatment of, optical elements
  • G02B1/11—Anti-reflection coatings
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C2217/00—Coatings on glass
  • C03C2217/40—Coatings comprising at least one inhomogeneous layer
  • C03C2217/425—Coatings comprising at least one inhomogeneous layer consisting of a porous layer
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K3/00—Use of inorganic substances as compounding ingredients
  • C08K3/18—Oxygen-containing compounds, e.g. metal carbonyls
  • C08K3/20—Oxides; Hydroxides
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K3/00—Use of inorganic substances as compounding ingredients
  • C08K3/34—Silicon-containing compounds
  • C08K3/36—Silica
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K9/00—Use of pretreated ingredients
  • C08K9/08—Ingredients agglomerated by treatment with a binding agent
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/249921—Web or sheet containing structurally defined element or component
  • Y10T428/249953—Composite having voids in a component [e.g., porous, cellular, etc.]
  • Y10T428/249967—Inorganic matrix in void-containing component
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/249921—Web or sheet containing structurally defined element or component
  • Y10T428/249953—Composite having voids in a component [e.g., porous, cellular, etc.]
  • Y10T428/249978—Voids specified as micro
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/249921—Web or sheet containing structurally defined element or component
  • Y10T428/249953—Composite having voids in a component [e.g., porous, cellular, etc.]
  • Y10T428/249978—Voids specified as micro
  • Y10T428/249979—Specified thickness of void-containing component [absolute or relative] or numerical cell dimension
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/31504—Composite [nonstructural laminate]
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/31504—Composite [nonstructural laminate]
  • Y10T428/31855—Of addition polymer from unsaturated monomers
  • Y10T428/31909—Next to second addition polymer from unsaturated monomers
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/31504—Composite [nonstructural laminate]
  • Y10T428/31855—Of addition polymer from unsaturated monomers
  • Y10T428/31935—Ester, halide or nitrile of addition polymer

Definitions

• the invention relates to a new process for the preparation of nano-structured and/or nano-porous surfaces, coatings having a nano-structured and/or nano-porous surface and articles comprising said coatings.
• the invention also relates to the use of said coatings, in particular as anti-reflective coatings.
• the first class is know as the top down approach and is primarily concerned with the manufacture of progressively smaller and smaller feature sizes in photolithographic processes. Top down lithographic techniques are especially applied where regular and straight features are required as is the case for photo-resists in the microprocessor field. Manufacture of random, irregular structures and structuring via these techniques over large surface areas (dm 2 to m 2 ) is extremely difficult, time consuming and therefore expensive.
• the second class of nano-structuring techniques can be regarded as so-called bottom up techniques and are usually based on phase separation, which can be achieved in two ways. Firstly, by phase separation of two incompatible polymers (e.g. Polymethylmethacrylate and Polystyrene,Steiner et al., Science, Vol 283, pg 520-522, 1999), during the evaporation of a solvent. After that the nano-structure is formed by removal of one of the polymers by a selective solvent, that dissolves only one of the polymers.
• two incompatible polymers e.g. Polymethylmethacrylate and Polystyrene,Steiner et al., Science, Vol 283, pg 520-522, 1999
• the nano-structure is formed by removal of one of the polymers by a selective solvent, that dissolves only one of the polymers.
• phase separation can be induced by crosslinking a mixture of components where at least one component is capable of crosslinking and at least one other is not(Ibn-Elhaj and Schadt, Nature, Vol 410, pg 796-799, 2001).
• the mixture is homogeneous prior to crosslinking and the phase separation occurs during the formation of the crosslinked network.
• the nano-structure is formed by removal of the non-crosslinkable component.
• phase separation is a dynamic process, the size and distribution of the features formed under both of the above techniques is strongly dependent on the rate or kinetics of the phase separation. Parameters such as temperature and in the case of photo-induced crosslinking the photo-initiator concentration and/or radiation intensity all will affect the feature size of the nano-structured coatings.
• the process according to the invention which is a process for the preparation of nano-structured and/or nano-porous coatings, comprises the steps of
• a coating or a film is obtained with the propcess of the present invention having a nano-structured surface. Furthermore the coating or film has favourable mechanical properties and adheres well on several substrates.
• the coating or film has a variety of applications, amoung which are films or coatings having super hydrophobic properties and especially coatings having anti-reflective properties.
• step b Since the reactive nano-particles in step a) always have more than one reactive group on their surface, the polymerisation in step b results in the formation of a crosslinked phase, comprising the nanoparticles interconnected. Therefore, in this text, the terms polymerise or polymerisation is used interchangeably with cross-linking or cross-linked and polymerisable group is used interchangeably with cross-linking group.
• surface nano-structured coatings refers to coatings having a surface roughness, and in which surface the dimensions of the features on the surface are larger than or equal to the smallest cross-sectional dimension of an individual nano-particle.
• the dimensions of the fatures are smaller than 1200 nm, more preferably smaller than 800 nm, still more preferably smaller than 400 nm, most preferably smaller than 300 nm.
• nano-particles is defined as particles of which the majority has a diameter of less than a micrometer. Within the framework of the invention a nano-particle is elongated when the aspect ratio, defined as the length divided by the diameter is greater than unity.
• the preparation of reactive nano-particles as such is known in the art, and has been described in e.g. US06025455. In a preferred embodiment of the process according to the invention, all nano-particles are reactive.
• the compound having at least one polymerisable group is in this text also referred to as both diluent or reactive diluent.
• the term hard coat refers to a coating comprising nano-particular species, optionally reactive nano-particular species, in a crosslinked polymeric network, wherein the volume fraction of reactive diluent is such that there are no or at least hardly no void spaces and/or surface nano-structures present in the coating.
• the nano-structured surface it is important that no or a relatively small amount of the reactive diluent and optional further components is present in the coating obtained with the process according to the invention. If a too high amount of reactive diluent and optional further components is used, the nano particles will be embedded and a coating having a smooth surface and not having any pores will be obtained. Normally the amount of reactive diluent and eventually further components in the final coating (after evaporation of the solvent) as expressed in volume fraction may not exceed 1-(the random close packing volume fraction of the reactive nanoparticles).
• the skilled person can easily determine the amount of diluent and eventually further additives by varying the amount and measuring the surface roughness or a parameter as for instance the transmission or the reflection of the coating as a function of this amount. Above a certain concentration of reactive diluent (or optionally further additives) the surface roughness of the coating has vanished and no special anti-reflective properties are detected any more.
• the invention also relates to the mixture for the preparation of nano-structured and/or nano-porous coatings, the coatings or films obtained from the process according to the invention, articles comprising said coatings and the use of said coatings.
• the majority of the nano-particles in the mixture according to the invention have a diameter of less than 400 nm, more preferably the majority of particles have a diameter of less than 50 nm. Most preferably all particles have a diameter of less than 50 nm. In a preferred embodiment, the majority of the nano-particles have a length in the range of 40 to 300 nm. Preferably, the particles used have such a dimensions that they do not (or not significantly) influence the transparency of the eventual coating. Most preferably the increase in haze of a transparent substrate comprising the coating in a thickness of 0.1 micrometer, compared to the substrate not yet comprsising the coating is less than 2%, preferably less than 1%, most preferably less than 0.5%.
• the random packing density of the nano-particlar species is detemined by the shape and the relative size and size distribution of the nano-particles.
• the reactive nano-particles have an aspect ratio greater than 1, more preferably, they have an aspect ratio (length/diameter) greater than 3, still more preferably greater than 5, and most preferably, they have an aspect ratio of greater than 10. If elongated reactive nano-particles are used it is possible to obtain a coating having even further improved anti-reflective properties or to use a higher concentration of reactive diluent, which gives better mechanical properties to the coating. More preferably the nanoparticles are wormlike. Of a wormlike nano particle the primary axis is curved.
• Methods for determining the particle dimension include optical or scanning electron microscopy, or atomic force microscopy (AFM) imaging.
• the particles are in a very dilute mixture applied on a surface in a thin layer, so that at a SEM photographic image of the layer, the single nano-particles are observable. Than from 100 nanoparticles, ad random selected, the dimensions are determined and the average value is taken. In case of particles having an aspect ratio above 1, like worm-shaped nano-particles, the total length is determined, from one end to the other end, by following the primary axis as projected in the plane of the photo. For the diameter the longest straight line that can be drawn from one side of the particle to the other side, perpendicular to the primary axis is taken.
• the coating may comprise either organic or inorganic nano-particles.
• organic nano-particles are carbon nano-tubes or nano-spheres.
• the nano-particles are inorganic nano-particles.
• Suitable inorganic particles are for example oxide particles.
• Preferred oxide particles are particles of an oxide selected from the group of aluminium oxide, silicium oxide, zirconium oxide, titanium oxide, antimony oxide, zinc oxide, tin oxide, indium oxide, and cerium oxide. It is also possible to use a mixture of particles from different oxides or to use particles of mixed oxides.
• the nano-particles are particles of aluminium oxide, zirconium oxide or silicium oxide.
• the refractive index of the coating and effective refractive index of the coating/air interface can in part be tuned by the choice of oxide used.
• the nano-particles have reactive organic groups on their surface. Such reactive nano-particles may or may not comprise additional, non-reactive organic groups. Additional non-polymerisable groups may be used to tune the overall polarity and thus the hydrophobicity or hydrophilicity of the particle and the resultant coating. In a preferred embodiment of the process according to the invention, all nano-particles are reactive nanoparticles.
• the reactive groups of the nano-partciles, and if present, the polymerisable groups of the diluent may polymerise in a homopolymerisation reaction or a copolymerisation reaction. In such a case the reactive groups are polymerisable groups.
• a copolymerisation reaction is possible when in the mixture different groups are present that can polymerise, for example if the groups of the particles and of the reactive diluent are different, or if mixtures of reactive diluent and reactive/or particles are used that comprise such different groups. It is also possible that the reactive groups of the nanoparticles react with a polymer network that is formed by the polymerisation of one or more reactive diluents. Important however, is that the nanoparticles are chemically interconnected in a cross-linked phase.
• the reactive groups of the reactive nano-particles are polymerisable groups.
• substrates may be used as a substrate in the process according to the invention.
• Suitable substrates are for example flat or curved, rigid or flexible substrates including films of for example polycarbonate, polyester, polyvinyl acetate, polyvinyl pyrollidone, polyvinyl chloride, polyimide, polyethylene naphthalate, polytetrafluoro ethylene, nylon, polynorbornene or amorphous solids, for example glass or crystalline materials, such as for example silicon or gallium arsenide.
• Metallic substrates may also be used.
• Preferred substrates for use in display applications are for example glass, polynorbornene, polyethersulfone, polyethyleneterphtalate, polyimide, cellulose triacetate, polycarbonate and polyethylenenaphtalate.
• a free-standing single layer anti-reflective film obtainable by a process according to the invention may be obtained by preparing a film or coating on a substrate and subsequently removing the film or coating from the substrate after crosslinking. The removal of the film or coating from the substrate should always take place after the crosslinking.
• the mixture may be applied onto the substrate by any process known in the art of wet coating deposition.
• suitable processes are spin coating, dip coating, spray coating, flow coating, meniscus coating, capillary coating and roll coating.
• he mixture according to the invention is applied in a single layer.
• the mixture is applied on a further coating, as long as this is not a coating according to the invention.
• the reactive nano-particles are mixed with at least one solvent and, optionally crosslinking initiator and optionally a reactive diluent, to prepare a mixture that is suitable for application to the substrate using the chosen method of application.
• the solvent preferably has the ability to form stable suspensions of the reactive nano-particles in order to facilitate a random close packing arrangement of the reactive nano-particles upon application, i.e. after evaporation of the solvent.
• Nano-particles typically are added to the mixture in the form of a suspension.
• the same solvent as used in the suspension may be used to adjust the mixture so that it has the desired properties. However, other solvents may also be used.
• the solvent used evaporates after applying the mixture onto the substrate.
• the mixture may after application to the substrate be heated or treated in vacuum to aid evaporation of the solvent.
• solvent examples include 1,4-dioxane, acetone, acetonitrile, chloroform, chlorophenol, cyclohexane, cyclohexanone, cyclopentanone, dichloromethane, diethyl acetate, diethyl ketone, dimethyl carbonate, dimethylformamide, dimethylsulphoxide, ethanol, ethyl acetate, m-cresol, mono- and di-alkyl substituted glycols, N,N-dimethylacetamide, p-chlorophenol, 1,2-propanediol, 1-pentanol, 1-propanol, 2-hexanone, 2-methoxyethanol, 2-methyl-2-propanol, 2-octanone, 2-propanol, 3-pentanone, 4-methyl-2-pentanone, hexafluoroisopropanol, methanol, methyl acetate, methyl acetoacetate, methyl
• Alcohols, ketones and esters based solvents may also be used, although the solubility of acrylates may become an issue with high molecular weight alcohols.
• Halogenated solvents such as dichloromethane and chloroform
• hydrocarbons such as hexanes and cyclohexanes
• methanol, methyl ethyl keton or isopropanol are used.
• a way of determining of a coating has a surface nano-structure and/or nano-pores is to apply the coating to a transparent substrate, crosslinking, and subsequently measuring the transmission.
• the amount of reactive diluent and optional further components in the mixture is that low, that if applied as a coating at one side of a transparent substrate, in a thickness between 100-200nm, there is an increase in transmission of light at at least one wave length between 400 and 800 nm of at least 0.5% relative to the same substrate without the coating.
• the increase in transmission is at least 0.75%, more preferably at least 1%, still more preferably at least 1.5%, still more preferably at least 2%, still more preferably at least 2.5%, most preferaby at least 3%.
• the exact amount of reactive diluent depends on the particle size, shape, and size distribution, and can thus not be given exactly.
• the amount of diluent may be less than 40 wt %, relative to the total weight of the mixture as applied in step a) of the process according to the invention, however without taking the solvent into account (total weight of solid).
• the amount of diluent is less than 20 wt %.
• the mechanical properties of the coating will generally be better when at least some diluent is present, e.g., at least 1 wt %, more preferably at least 2 wt. %, still more preferably at least 5 wt. %, most preferably at least 10 wt. %.
• the reactive diluent for example monomers or oligomers having crosslinking groups.
• Monomers or oligomers having only one crosslinking group per molecule may be used, but preferably in combination with other crosslinking components that do have at least two crosslinking groups.
• Preferably monomers or oligomers having at least two or more crosslinking groups per molecule are used.
• the reactive diluent comprises a mixture of compounds that after the induction of crosslinking in step b, together form a crosslinked phase.
• the mixture may comprise compounds that are by itself crosslinking, such as for example different acrylates or it may comprise compounds that will riot crosslink by itself but which form a crosslinked phase in combination with another compound after initiation of the crosslinking reaction, for example copolymerising systems comprising electron rich and electron poor double bonds such as for example maleate/vinyl ether copolymerising systems.
• Examples of monomers suitable for use as a reactive diluent and having at least two crosslinking groups per molecule include monomers containing (meth)acryloyl groups such as trimethylolpropane tri(meth)acrylate, pentaerythritol (meth)acrylate, ethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, polybutanediol di(meth)acrylate, tripropyleneglycol di(meth)acrylate, glycerol tri(meth)acrylate, phosphoric acid mono- and di(meth)acrylates, C7-C20 alkyl di(meth)acrylates, trimethylolpropanetrioxyeth
• Suitable monomers having only one crosslinking group per molecule include monomers containing a vinyl group, such as N-vinyl pyrrolidone, N-vinyl caprolactam, vinyl imidazole, vinyl pyridine; isobornyl (meth)acrylate, bornyl (meth)acrylate, tricyclodecanyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate, 4-butylcyclohexyl (meth)acrylate, acryloyl morpholine, (meth)acrylic acid, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl
• Oligomers suitable for use as the reactive diluent are for example aromatic or aliphatic urethane acrylates or oligomers based on phenolic resins (ex. bisphenol epoxy diacrylates), and any of the above oligomers chain extended with ethoxylates.
• Urethane oligomers may for example be based on a polyol backbone, for example polyether polyols, polyester polyols, polycarbonate polyols, polycaprolactone polyols, acrylic polyols, and the like. These polyols may be used either individually or in combinations of two or more. There are no specific limitations to the manner of polymerization of the structural units in these polyols.
• Any of random polymerization, block polymerization, or graft polymerization is acceptable.
• suitable polyols, polyisocyanates and hydroxylgroup-containing (meth)acrylates for the formation of urethane oligomers are disclosed in WO 00/18696, which is incorporated herein by reference.
• Combinations of compounds that together may result in the formation of a crosslinked phase and thus that in combination are suitable to be used as the reactive diluent are for example carboxylic acids and/or carboxylic anhydrides combined with epoxies, acids combined with hydroxy compounds, especially 2-hydroxyalkylamides, amines combined with isocyanates, for example blocked isocyanate, uretdion or carbodiimide, epoxies combined with amines or with dicyandiamides, hydrazinamides combined with isocyanates, hydroxy compounds combined with isocyanates, for example blocked isocyanate, uretdion or carbodiimide, hydroxy compounds combined with anhydrides, hydroxy compounds combined with (etherified) methylolamide (“amino-resins”), thiols combined with isocyanates, thiols combined with acrylates or other vinylic species (optionally radical initiated), acetoacetate combined with acrylates, and when cati
• Further possible compounds that may be used as the reactive diluent are moisture curable isocyanates, alkoxy titanates, alkoxy zirconates, or urea-, urea/melamine-, melamine- formaldehyde or phenol-formaldehyde (resol, novolac types), or radical curable (peroxide- or photo-initiated) ethylenically unsaturated mono- and polyfunctional monomers and polymers, e.g. acrylates, methacrylates, maleate/vinyl ether), or radical curable (peroxide- or photo-initiated) unsaturated e.g. maleic or fumaric, polyesters in styrene and/or in methacrylates.
• moisture curable isocyanates alkoxy titanates, alkoxy zirconates, or urea-, urea/melamine-, melamine- formaldehyde or phenol-formaldehyde (resol, novolac
• cross-linking method that may cause the mixture to crosslink so that a coating is formed is suitable to be used in the process according to the invention.
• Suitable ways to initiate crosslinking are for example electron beam radiation, electromagnetic radiation (UV, Visible and Near IR), thermally and by adding moisture, in case moisture curable compounds are used.
• crosslinking is achieved by UV-radiation.
• the UV-crosslinking may take place through a free radical mechanism or by a cationic mechanism, or a combination thereof.
• the crosslinking is achieved thermally.
• An initiator may be present in the mixture to initiate the crosslinking reaction.
• the amount of initiator may vary between wide ranges.
• a suitable amount of initiator is for example between above 0 and 5 wt % with respect to total weight of the compounds that take part in the crosslinking reaction.
• the mixture preferably comprises a UV-photo-initiator.
• a photo-initiator is capable of initiating a crosslinking reaction upon absorption of light, thus, UV-photo-initiators absorb light in the Ultra-Violet region of the spectrum. Any known UV-photo-initiators may be used in the process according to the invention.
• the coating according to the invention can be prepared in any desired thickness.
• the coatings according to the invention typically have a thickness ranging between 50 nm to several micrometer. In case of application as an anti-reflective coating the thickness is preferably between 50 and 200 nm, more preferably between 100 and 150 nm.
• the nano-structured and/or nano-porous films or coatings according to the invention increases the optical transmission of a substrate on which they are present for at least a range of visible wavelengths of the electromagnetic spectrum. Therefore the coating shows a reflection of light, at at least one wavelenth in the area between 400-800 nm, measured under normal incidence of less than 3%, preferably less than 2%, more preferably less than 1.5%, most preferably less than 1%, per coated side of the substrate in a coating layer thickness between 100-200 nm.
• the combination of good mechanical properties as well as anti-reflective performance will allow for the use of these single layer anti-reflective hard-coats in applications were mechanical durability and anti-reflective performance on flat or on non-flat substrates are advantageous.
• These applications include anti-reflective coatings for automobile and airplane wind screens, displays in general, television tubes, flexible displays and lenses, for example in spectacles.
• the anti-reflective coating is applied to the substrate as a single coating. It is also possible that before the application of the anti-reflection coating, the substrate is coated with a further coating, for example to improve the adhesion between the anti-reflective coating and the substrate.
• At least an advantage of the anti-reflective coating of the present invention is, that the coating, bringing the anti-reflective properties only needs to be applied in a single layer,
• the surface nano-structured and/nano-porous coating according to the invention can be used to affect the wetting properties of the coating.
• a hydrophobic material or coating is characterised by a static contact angle of water of 90° or above.
• Hydrophobic polymeric materials such as poly(tetrafluorethene) (PTFE) or polypropylene (PP) have been available for decades. These materials suffer from a limited hydrophobicity, as well as inferior mechanical properties as compared to engineering materials or highly crosslinked coatings. For instance, PP has a static contact angle of water of roughly 100° whereas PTFE, which is amongst the most hydrophobic polymeric material known, has a static contact angle of water of roughly 112°.
• PTFE poly(tetrafluorethene)
• PP polypropylene
• Superhydrophobic coatings are being referred to in the art as superhydrophobic coatings.
• Superhydrophobic coatings are generally defined by a static water contact angle above 140° (Nun, Oles & Schleich, Macromol. Symp. 187 (2002) 677-682).
• a combination of surface roughness, due to surface nano-structures and/or nano-pores, together with polar surface chemistry achieves static water contact angles below 60°, preferably below 40°.
• the coating may also be affected so that the static water contact angle is above 90° and preferably 120° if the surface chemistry of the nano-structured and/nano-porous coating is apolar, for example via the presence of apolar surface modifying groups on the nano-particles.
• the surface nano-structured and/or nano-porous films or coatings according to the invention increases the optical transmission of a substrate on which they are present to visible wavelengths of the electromagnetic spectrum while simultaneously exhibiting a static water contact angle of above 90°, preferably 120° and most preferably 140°.
• the surface nano-structures and/or nano pores other properties such as low refractive index, low optical dissipation (low optical loss), low dielectric constant, high relative surface area, low contact area, low adhesion and coating porosity are envisaged.
• Applications derived from the above properties include the following: anti-reflective coatings for all kinds of display applications, for biological devices and coatings with improved wetting characteristics; easy to clean and self-cleaning coatings; easy to clean and self-cleaning anti-reflective coatings; non-stick coatings, low dielectric coatings for semi-conductors, low dissipation (low optical loss) coatings for optical wave guides; controlled release coatings, hard membranes, biologically active surfaces, anti-fouling and anti-bacterial coatings.
• patterned coatings for example, alternating hydrophobic and hydrophilic regions
• this can also be achieved by the process according to the invention, by using photolithographic processes.
• applications where patterning of nano-structured and/or nano-porous coatings is desired may also result. This could lead to coatings and articles where the optical or wetting properties are patterned as desired.
• the mixture according to the invention comprises an adhesion promoter.
• An adhesion promoter enhances the adhesion between the coating of the present invention and its substrate. In this way the scratch resistance of the coating is also improved.
• adhesion promoters are compounds having at least one reactive group capable of reacting with the groups at the surface of the reactive nano particles and/or with the reactive diluent and further have at least one reactive group capable of reacting or physically interacting, e.g. H bonding with the substrate.
• adhesion promoters can include but are not limited to acrylate, methacrylate or thiol functional trialkoxy silanes, where the trialkoxy groups of the silane can be propoxy or butoxy but is preferably ethoxy or methoxy.
• silane adhesion promoters include: ⁇ -mercaptopropylmethylmonomethoxysilane, ⁇ -mercaptopropylmethyldimethoxysilane, ⁇ -mercaptopropyltrimethoxysilane, ⁇ -mercaptopropylmonoethoxysilane, ⁇ -mercaptopropyldiethoxysilane, ⁇ -mercaptopropyltriethoxysilane, ⁇ -mercaptoethylmonoethoxysilane, ⁇ -mercaptoethyltriethoxysilane, ⁇ -mercaptoethyltriethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyidimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, ⁇ -aminopropyltriethoxysilane, ⁇ -glycidoxy
• Examples of commercially available products of these compounds include SILAACE S310, S311, S320, S321, S330, S510, S520, S530, S610, S620, S710, S810 (manufactured by Chisso Corp.), Silquest A-174NT (manufactured by OSI Specialties—Crompton Corp.).
• acidic adhesion promoters such as acrylic acid may be used.
• Phosphate esters such as Eb168 or Eb170 from UCB are feasible adhesion promoters.
• adhesion to polymeric substrates such as, for example polyethylene terephthalate (PET) and or cellulose triacetate(TAC) the above adhesion promoters may be feasible but also good results are obtained with epoxy functional acrylate or methacrylate compounds.
• PET polyethylene terephthalate
• TAC cellulose triacetate
• thiol compounds are very suitable as adhesion promoters.
• Such thiol compounds may be mono-functional, di-functional, preferably tri-functional and most preferably tetra-functional with respect to the number of thiol groups per molecular species.
• the thiol compounds may comprise next to the thiol group a further reactive group. In case the thiol compound comprises only one thiol group, it must comprise at least one further reactive group. Examples of thiol compounds may be any of those known in the art.
• thiol compounds such as the aliphatic monomeric polythiols e.g.ethane dithiol, hexamethylene dithiol, decamethylene dithiol, tolylene-2,4-dithiol, and the like, and some polymeric polythiols such as a thiol-terminated ethylcyclohexyl dimercaptan polymer, and the like, and similar polythiols which are conveniently and ordinarily synthesized on a commercial basis are suitable.
• polythiols such as the aliphatic monomeric polythiols e.g.ethane dithiol, hexamethylene dithiol, decamethylene dithiol, tolylene-2,4-dithiol, and the like, and some polymeric polythiols such as a thiol-terminated ethylcyclohexyl dimercaptan polymer, and the like, and similar polythiols
• polythiol compounds preferred because of relatively low odor level include but are not limited to esters of thioglycolic acid (HS—CH 2 COOH), ⁇ -mercaptopropionic acid (HS—CH(CH 3 )—COOH and ⁇ -mercaptopropionic acid (HS—CH 2 CH 2 COOH) with polyhydroxy compounds such as glycols, triols, tetraols, pentaols, hexaols, and the like.
• polythiols include but are not limited to ethylene glycol bis(thioglycolate), ethylene glycol bis ( ⁇ -mercaptopropionate), trimethylolpropane tris(thioglycolate), trimethylolpropane tris ( ⁇ -mercaptopropionate), pentaerythritol tetrakis ( ⁇ -mercaptopropionate), all of which are commercially available.
• a specific example of a preferred polymeric polythiol is polypropylene ether glycol bis( ⁇ -mercaptopropionate) which is prepared from polypropylene-ether glycol (e.g.
• Pluracol P201, Wyandotte Chemical Corp. and ⁇ -mercaptopropionic acid by esterfication.
• Poly- ⁇ -mercaptoacetate or poly- ⁇ -mercaptopropionate esters, particularly the trimethylopropane triesters or pentaerythritol tetra esters are preferred.
• Other polythiols which can be suitably employed include alkyl thiol functional compounds such as 1,2-dimercapthoethane, 1,6-dimercaptohexane and the like.
• Thiol terminated polysulfide resins may also be employed.
• Suitable examples of aliphatic dithiols include 1,2-ethanedithiol, butanedithiol, 1,3-propanedithiol, 1,5-pentanedithiol, 2,3-dimercapto-1-propanol, dithioerythritol, 3,6-dioxa-1,8-octanedithiol, 1,8-octanedithiol hexanedithiol, dithiodiglycol, pentanedithiol,decanedithiol, 2-methyl 1,4 butanedithiol, bis-mercaptoethylphenyl methane, 1,9-nonanedithiol(1,9-dimercaptononane), glycol dimercaptoacetate.
• aromatic dithiols include 1,2-benzenedithiol, 1,3-benzenedithiol, 1,4-benzenedithiol, 2,4,6-trimethyl-1,3-benzenedimethanethiol, durene- ⁇ 1, ⁇ 2-dithiol, 3,4-dimercaptotoluene, 4-methyl-1,2-benzenedithiol, 2,5-dimercapto-1,3,4-thiadiazole, 4,4′-thiobisbezenedithiol, bis(4-mercaptophenyl)-2,2′-propane(bisphenoldithiol) (made according to the method of Meng Y. Z., Hay. A. S., J. of App. Polym. Sci., V74, 3069-3077(1999).
• oligomeric dithiols include difunctional mercapto functional urethane oligomers derived from end capping moieties of hydroxyethyl mercaptan, hydroxypropyl mercaptan, dimercaptopropane, dimercapto ethane as described in patent by Shustack U.S. Pat. No. 5,744,514.
• trithiol functional compounds examples include, trimethylolethane tris-mercaptopropionate, trimethylolpropane tris-mercaptopropionate (TMPTSH), trimethylolethane tris-mercaptoacetate, and trimethylolpropane tris-mercaptoaacetate glycerol tri(11-mercaptoundecanoate), trimethylol propane tri(11-mercaptoundecate).
• TMPTSH trimethylolethane tris-mercaptopropionate
• TMPTSH trimethylolethane tris-mercaptopropionate
• glycerol tri(11-mercaptoundecanoate) trimethylol propane tri(11-mercaptoundecate
• a preferred trithiol is trimethylolpropane tris(2-mercapto-propionate) TMPTSH.
• tetrafunctional thiols examples include pentaerythritol tetramercapto propionate, pentaerythritol tetramercapto acetate, and pentathritoltetra(11-mercaptoundecate)
• Examples of multifunctional thiols having functionality greater than 4, include polythiols as described on page 7 of WO 88/02902.
• Multi functional thiols can be obtained by reacting thioalkyl carboxylic acids e.g. thioglycolic acid, mercapto propionic acid with high functional alcohols, amines and thiols. Furthermore, multifunctional thiols can be obtained by reacting mercapto alkyl trialkoxy silanes with silanols that may be polymeric or silica based silanols.
• thiol carboxylic acids HS—R—COOH
• R alkyl
• aryl groups eg thioundecanoic acid of which the COOH groups are reacted with reactive enes, alcohols, thiols or amines that are multifunctional.
• the adhesion promoters may be used in an amount of 0.1-10 wt-% of the total solids in the mixture, after evaporation of the solvent. Preferably the adhesion promoter is used in an amount of 5-10 wt-%.
• the mixture according to the invention comprises a compound having a surface energy of less than 25 milli Joules per square meter (mJ/m 2 ).
• the surface energy is preferably measured of the pure compound according to ASTM D2578, preferably using a ACCU DYNE TESTTM marker pen.
• An example of such compounds are reactive polydimetylsiloxane compounds.
• Preferred are reactive fluoro compounds. Reactive fluoro compounds are for example described in U.S. Pat. No. 6,391,459. The fluoro compounds further have the advantage that they don't disturb the anti-reflective properties very much.
• the substrate is in a first step coated with a first coating, preferably a highly crosslinked coating or a hard coat, and in a second step the mixture according to the present invention is applied on top of the first coating.
• the first coating acts as the substrate for the mixture of the present invention.
• the first coating preferably comprises vinyllic unsaturations and thiol compounds are preferably used as adhesion promotors. In this way a still better scratch resistance of the coating of the present invention is obtained.
• Suitable examples for the first coating are the coatings described in EP-A-1276810.
• the first coating is partly cured at least at the surface.
• a radical curing resin system like for example an acrylate based resin system
• partly surface curing is preferably obtained by curing in the presence of oxygen, for example curing in an air atmosphere.
• the scratch resistance can be still further improved by thermally treating the first coating and the coating according to the invention, by for example Infra red lamps or thermal ovens.
• good results are obtained if the coating according to the invention and preferably also the first coating comprise a thermal initiator for subsequent cross-linking during thermal post-treatment, especially if the cure of hard coat and nano-structured coatings has been induced photo-chemically.
• the skilled artisan knows how to select such a thermal initiator.
• the coating according to the invention in a process of reverse sorption of at least one non-cross-linkable species.
• Nano-silicate particles MT-ST (spherical particles) and IPA-ST-UP (elongated particles) were obtained from Nissan Chemical American Corporation. These particles were used in illustration of the invention. Their properties and properties of their supensions are listed in table 1 below. TABLE 1 Types and properties of nano-silica particles.
• Reactive organic groups were grafted onto the silica nano-oxide particles by adding a trimethoxy-silane compound comprising an acrylate group (e.g., a compound according to formula II) together with p-methoxy-phenol, a compound that inhibits polymerization of the acrylate groups, to a suspension of the oxide particles in methyl ethyl ketone.
• a trimethoxy-silane compound comprising an acrylate group (e.g., a compound according to formula II) together with p-methoxy-phenol, a compound that inhibits polymerization of the acrylate groups, to a suspension of the oxide particles in methyl ethyl ketone.
• Table 2 shows the exact amounts of chemicals used. After stirring, a catalytic amount of water was added to the mixture and the mixture was refluxed at 80° C. for at least 3 hours. Subsequently as a dehydrating agent trimethyl orthoformate was added to remove any traces of water, and
• Another method for preparing the grafted particles was to add a methoxy-silane compound comprising an acrylate group together with p-methoxy-phenol, to a suspension of the oxide particles in methanol. After stirring, the mixture was refluxed at 60° C. for at least 1.5 hours for MT-ST nano-silicates particles or at least 3 hours for IPA-ST-UP nano-silicate particles, and subsequently a trialkoxy silane compound, was added. As subsequent trialkoxy silane methyl trimethoxy silane, or in case hydrophobic apolar surface characteristics are required a perfluoroalkyl trialkoxy silane was used. After refluxing for at least one more hour at 60° C., a dehydrating agent was added and the resultant mixture was stirred at 60° C. for at least one hour.
• a drop of a mixture (see table 3 and 4 for the mixtures) was applied to the substrate by spin-coating at a rate of 4800 r.p.m.
• Thin films (100-200 nm) were spin coated from mixtures containing less than 10 wt-% solids while thicker (1-5 ⁇ m) coatings were spin coated from formulations with ca 35-50 wt-% solids, see table 3, 4 and 5.
• the resultant wet film was crosslinked with UV radiation using a D-bulb under nitrogen at a dose of 1.7 J/cm2.
• the thickness of the crosslinked transparent coating was measured with a multi-spectral reflectometer (F20, AG Electro Optics). Samples for contact angle determination were post baked (i.e heated) for 1 hour at 70° C., prior to contact angle determination.
• Nano-structured and/or nano-porous films or coatings were prepared as described under “B. Preparation of a coating on a substrate”, on one side or both sides of either glass microscope slides or polyethyleneteraphthalate (PET) films from various formulations as listed in Table 3, 4 and 5. Spectral transmission in the visible region of the spectrum was measured with a Perkin-Elmer Lambda-20 UV-Vis spectrometer.
• Static contact angles were measured using a FTA (First Ten Angstroms) 200 apparatus. This piece of equipment consisted of a motorised syringe pump, a sample stage and a video camera. The software used with the system was FTA Video drop shape analysis version 1.98 Build B.
• the surface tension of the water in the syringe was measured. This was done by dispensing a droplet from the syringe, and then recording an image whilst the droplet was still attached to the syringe. The droplet was lit from behind, so it appeared black on a white background. The software measured the dimensions of the droplet and used them to calculate the surface tension.
• examples 7-11 show the effect of increasing amount (wt-%) of reactive diluent (Dipentaerythritol pentaacrylate) on the anti-reflective properties of surface nano-structured and nano-porous coating comprising elongated acrylated nano-particles (modified particle B (Acry-IPA-ST-UP)). It can be seen that increasing the relative weight percentage of reactive diluent with respect to nano-particles reduces the anti-reflective performance of the coatings as the maximum percentage of transmission decreases.
• reactive diluent Dipentaerythritol pentaacrylate
• the static water contact angle of Example 1 as shown in Table 6 is typical that of a polar acrylate hard coating. If the surface is surface nano-structured and/or nano-porous, the static water contact angle drops significantly. This is the case for Example 2 (Acry-MT-ST) where the value of the contact angle was 50.3° and for Example 5 (Acry-lPA-ST-UP) where the value is 28.2°. Similary, the static water contact angle of Example 6, a coating of a formulation comprising hydrophobically modified reactive nano-particles (Acry-F-MT-ST) with hydrophobic reactive diluents (Fluorodiacrylate), was 108.5° and its roughness was relatively low, 27 nm.
• Example 4 In the case of Example 4 (Acry-F-MT-ST) (thickness 1-5 ⁇ m) and 3 (Acry-F-MT-ST) (thickness 100-200 nm) the value of the roughness increased and therefore the static contact angle increased respectively as well.
• FIG. 1 depicts the three dimensional (3D) topography of the coatings obtained in various examples and the comparative experimentas acquired by atomic force microscopy (AFM).
• the maximum height of the features (Rmax) in these images is given as the maximum height difference over the whole area of the image.
• FIG. 1 a shows the surface roughness ofthe coating according to the comparative experiment, the conventional hard coat sample, the components of which can be found in table 3, example 1.
• the surface roughness of the coating is very small and only in the range of ca 6 nm, which is well below the smallest dimension of the nanoparticles used in the coating. Therefore this is a not a nano-structured and/or nano-porous coating as described within the framework of the invention.
• FIG. 1 b and FIG. 1 c show the surface topography of coatings of fluorinated acrylated spherical nano-silicates (modified nano-particle C) (Table 3, Example 3) and a coating of acrylated spherical nano-silicates (modified nano-particle A) (Table 3, Example 2), respectively.
• FIG. 1 d shows a coating with a surface roughness of ca 140 nm, which is formed by the crosslinking of elongated acrylated nano-silicate particle (modified nano-particle B) (table 4, example7) without any reactive diluent.
• modified nano-particle B modified nano-particle B
• FIG. 2 shows the cross-sectional topography as acquired by Atomic force microscopy.
• the Rmax given in FIG. 2 is the maximum height difference across the cross-section.
• FIG. 2 a shows the cross-sectional topography of a coating of acrylated spherical nano-silicates (modified nano-particle A) (Table 3, Example 2).
• a surface nano-structure roughness on the surface
• nano-pores deeper features
• FIG. 2 b shows the cross-sectional topography of a coating of elongated acrylated nano-silicates (modified nano-particle B) (Table 4, Example 7).
• the roughness on the surface is the surface nano-structure while the deepest features can be regarded as nano-pores. It is also expected that small voids of air Will exist in the bulk of the coating between individual nano-particles or clusters thereof however, these nano-pores cannot be visualised by AFM.
• FIG. 3 shows the visible transmission spectra of a number of example and comparative coatings on one side of a glass microscope slide substrate.
• Spectrum 5 is of an uncoated glass microscope slide.
• Spectrum 1 is of unmodified MT-ST nano-particles, which were spin-coated at 4800 rpm from a suspension of 3wt-% solids, giving a coating thickness in the range of 100-200 nm.
• This spectrum shows that unmodified MT-ST nano-silicates display anti-reflective properties as the maximum transmission increases to ca 96.8% with respect to the maximum that of the uncoated glass microscope slides (94.8%).
• FIG. 4 shows the visible transmission spectra of of the coatings of example 7 (spherical particles, spectrum 2) and example 7(elongated particles, spectrum 1) Spectrum 3 is the uncoated glass microscope slide. It is clearly shown that the coating compriseng elongated particles shows even furher improved anti-reflctive properties compared to the coating comprising the spherical particles.
• FIGS. 5 and 6 show the effect of coating both sides of reflective substrate, glass microscope slides in the case of FIG. 5 and PET films in case of FIG. 6, with a coating of crosslinked acrylated elongated nano-particles (Acry-IPA-ST-UP, modified particle B).
• Acry-IPA-ST-UP crosslinked acrylated elongated nano-particles
• both the top and bottom surface of the untreated substrates cause reflection transmission greater than 98% are usually only possible if both sides of the substrate have been coated.
• the coating on both sides of the substrates results in objects, which are almost invisible to the naked eye and where surface reflections are only observable, by direct reflection of bright light sources.
• FIG. 7 shows that in case of elongated particles there is only a small decrease in anti-reflective properties if a reactive diluent is used.
• a hard coat according to comparative experiment 1 is applied to the substrate to a thickness of ca 3-5 ⁇ l and cured in Air at a total UV dose of 0.75 Jcm 2 .
• the surface of the resulting hard coat was parially cured.
• a coating according to the invention is applied on top of the Hard coat to a thickness of 100-200 nm by spin coating as described previously.
• the said coating according to the invention consists of the following components; 0.376 g (dry weight) reactive nano-partilce (modified Particle B. Table 2), 0.061 g of Dipentaerythritol penta-acrylate (reactive diluent), 0.013 g tri-methylolpropane tri-(3-mercaptopropionate) (reactive diluent and adhesion promoter), 0.8 mg of propyl gallate (polymerisation inhibitor), 5.1 mg of Irgacure 907 (photo-initiator), 12.902 g of methyl ethyl ketone (solvent) and 1.642 g of isopropanol (solvent).
• the said coating according to the invention is then fully cured with a total of 2 ⁇ 1Jcm ⁇ 2 and subsequently heated to 120° for ca 1 minute using an infra red lamp.
• the resultant nano-structured coating has a pencil hardness of 2-3H according to ASTM D3363-00, while retaining anti-reflective properties.

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