Multi-layer optical articles and methods of preparing them

Abstract

Multi-layer optical articles include a first release liner, a first optically clear pressure sensitive adhesive layer, a microstrucured optical layer with a first major surface that is microstructured surface and a second major surface that is a nanostructured surface, where the microstructured surface of the microstructured optical layer is in contact with the first optically clear pressure sensitive adhesive and the nanostructured surface is in contact with a second optically clear pressure sensitive adhesive that is disposed on a second release liner. Upon removal of the release liners, the resultant optical article is optically clear and non-birefringent.

Description

[0001] MULTI-LAYER OPTICAL ARTICLES AND METHODS OF PREPARING THEM

[0002] Summary

[0003] Disclosed herein are multi-layer optical articles and methods of preparing them. In some embodiments, the multi-layer article comprises, in sequence, a first release liner, a first optically clear pressure sensitive adhesive layer, a microstructured optical layer with a first major surface and a second major surface, where the first major surface of the optical layer is a microstructured surface and the second major surface of the optical layer is a nanostructured surface. The first optically clear pressure sensitive adhesive layer is in contact with the first major surface of the optical layer, the microstructured surface. The second major surface of the optical layer is a nanostructured surface and the nanostructured surface is in contact with a second optically clear pressure sensitive adhesive layer. The second optically clear pressure sensitive adhesive is also in contact with a second release liner. The adhesion as measured by Peel Force for the first release liner and the first optically clear pressure sensitive adhesive is different than for the second release liner and the second optically clear pressure sensitive adhesive. Additionally, the interfacial adhesion of the first optically clear adhesive and the microstructured surface of the microstructured optical layer and the interfacial adhesion second optically clear pressure sensitive adhesive and the nanostructured surface of the microstructured optical layer is higher than the adhesion of the adhesives to either release liner such that removal of the release liners does not cause adhesive failure at either of these interfaces.

[0004] Also disclosed are multi-layer optical articles comprising the above-described articles from which the release liners are removed. The articles are optically clear and non-birefringent.

[0005] Also disclosed are methods for forming multi-layer optical articles. In some embodiments, the method comprises preparing a nanostructured film tool, providing a curable mixture of a UV-curable (meth)acrylate-based resin that upon curing forms a cured layer that has a refractive index of 1.63 at 532 nm, disposing the curable mixture on the nanostructured surface of the nanostructured film tool to form a curable layer, providing a microstructured tool with a microstructured surface, contacting the microstructured tool to the curable layer, curing the curable layer to form a cured optical layer, removing the microstructured tool from the cured optical layer such that the cured optical layer has a microstructured surface, providing a first adhesive article, disposing the first adhesive article on the microstructured surface of the cured optical layer, removing the nanostructured film tool from the nanostructured surface of the cured optical layer, providing a second adhesive article, and disposing the second adhesive article on the nanostructured surface of the cured optical layer.

[0006] Preparing the nanostructured film tool comprises providing a film, disposing a curable (meth)acrylate resin on the film, curing the curable (meth)acrylate resin to form a cured layer with a first major surface and a second major surface, where the second major surface of the cured layer is in contact with the film, providing a nanostructured tool with a nanostructured surface, contacting the nanostructured surface of the nanostructured tool to the first major surface of the cured layer to impart a nanostructured surface to the cured layer, and removing the nanostructured tool to form a nanostructured film tool.

[0007] The first and second adhesive articles independently comprise either an optically clear pressure sensitive adhesive layer disposed on a release liner or a pre-adhesive composition that can be coated and cured to form a pressure sensitive adhesive layer upon which is disposed a release liner. The method of disposing the first and second adhesive articles onto the microstructured or nanostructured surfaces depends on the nature of the adhesive article. If the adhesive article is an adhesive layer on a release liner, the adhesive article is laminated to structured surface. If the adhesive article is a pre-adhesive composition, the pre-adhesive composition is coated onto the structured surface to form a curable layer, the curable layer is cured to form the optically clear pressure sensitive adhesive layer, and a release liner is disposed on the curable layer or the cured layer.

[0008] Brief Description of the Drawings

[0009] The present application may be more completely understood in consideration of the following detailed description of various embodiments of the disclosure in connection with the accompanying drawings.

[0010] Figure 1 is a cross sectional view of an article of this disclosure.

[0011] Figure 2 is a cross sectional view of another article of this disclosure.

[0012] In the following description of the illustrated embodiments, reference is made to the accompanying drawings, in which is shown by way of illustration, various embodiments in which the disclosure may be practiced. It is to be understood that the embodiments may be utilized and structural changes may be made without departing from the scope of the present disclosure. The figures are not necessarily to scale. Like numbers used in the figures refer to like components. However, it will be understood that the use of a number to refer to a component in a given figure is not intended to limit the component in another figure labeled with the same number.

[0013] Detailed Description

[0014] As optical devices become more complex, they often include multi-layer optical articles designed to provide a variety of optical effects. These multi-layer optical articles often have layers with structured surfaces. Preparation of these multi-layer optical articles can be difficult to assemble.

[0015] Disclosed herein are multi-layer optical articles comprising a first release liner, a first optically clear pressure sensitive adhesive layer in contact with the first release liner, a microstructured optical layer with a first major surface and a second major surface, where the second major surface is a microstructured surface and is in contact with the first major surface of the first optically clear pressure sensitive adhesive layer, and the first major surface of the microstructured optical layer comprises a nanostructured surface, a second optically clear pressure sensitive adhesive layer with a first major surface and a second major surface, where the second major surface of the second optically clear pressure sensitive adhesive is in contact with the first major surface of the microstructured optical layer, the nanostructured surface, and a second release liner is disposed on the first major surface of the second optically clear pressure sensitive adhesive layer. In some embodiments, the microstructured optical layer comprises a cured layer of a UV-curable (meth)acrylate-based resin wherein the cured layer has a refractive index of 1.63 at 532 nm. The adhesion of the first release liner to the first optically clear pressure sensitive adhesive is different from the adhesion of the second release liner to the second optically clear pressure sensitive adhesive, and the interfacial adhesion of both the interface between the second major surface of the second optically clear pressure sensitive adhesive layer and the first major surface of the microstructured optical layer and the interface between the second major surface of the first optically clear pressures sensitive and the firs major surface of the microstructured optical layer are greater than the adhesion of the first and second release liners to the first and second optically clear pressure sensitive adhesives. Also disclosed herein are methods of preparing the multi-layer optical articles.

[0016] The term “adhesive” as used herein refers to polymeric compositions useful to adhere together two adherends. Examples of adhesives are pressure sensitive adhesives.

[0017] Pressure sensitive adhesive compositions are well known to those of ordinary skill in the art to possess properties including the following: (1) aggressive and permanent tack, (2) adherence with no more than finger pressure, (3) sufficient ability to hold onto an adherend, and (4) sufficient cohesive strength to be cleanly removable from the adherend. Materials that have been found to function well as pressure sensitive adhesives are polymers designed and formulated to exhibit the requisite viscoelastic properties resulting in a desired balance of tack, peel adhesion, and shear holding power. Obtaining the proper balance of properties is not a simple process.

[0018] The term “pre-adhesive composition” as used herein refers to a curable mixture that upon curing forms an adhesive, specifically a pressure sensitive adhesive. The pre- adhesive mixtures are typically 100% solids, meaning that they are free from solvent, but may contain solvent that is removed either prior, during curing, or after curing.

[0019] The term “(meth)acrylate” refers to monomeric acrylic or methacrylic esters of alcohols. Acrylate and methacrylate monomers or oligomers are referred to collectively herein as "(meth)acrylates”. Materials referred to as “(meth)acrylate functional” are materials that contain one or more (meth)acrylate groups.

[0020] The terms “siloxane-based” as used herein refer to polymers or units of polymers that contain siloxane units. The terms silicone or siloxane are used interchangeably and refer to units with dialkyl or diaryl siloxane (-SiR.20-) repeating units.

[0021] The terms "room temperature" and "ambient temperature" are used interchangeably to mean temperatures in the range of 20°C to 25°C.

[0022] The term “adjacent” as used herein when referring to two layers means that the two layers are in proximity with one another with no intervening open space between them. They may be in direct contact with one another (e.g. laminated together) or there may be intervening layers.

[0023] The terms “polymer” and “macromolecule” are used herein consistent with their common usage in chemistry. Polymers and macromolecules are composed of many repeated subunits. As used herein, the term “macromolecule” is used to describe a group atached to a monomer that has multiple repeating units. The term “polymer” is used to describe the resultant material formed from a polymerization reaction.

[0024] The term “alkyl” refers to a monovalent group that is a radical of an alkane, which is a saturated hydrocarbon. The alkyl can be linear, branched, cyclic, or combinations thereof and typically has 1 to 20 carbon atoms. In some embodiments, the alkyl group contains 1 to 18, 1 to 12, 1 to 10, 1 to 8, 1 to 6, or 1 to 4 carbon atoms. Examples of alkyl groups include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, n-hexyl, cyclohexyl, n-heptyl, n-octyl, and ethylhexyl.

[0025] The term “aryl” refers to a monovalent group that is aromatic and carbocyclic. The aryl can have one to five rings that are connected to or fused to the aromatic ring. The other ring structures can be aromatic, non-aromatic, or combinations thereof. Examples of aryl groups include, but are not limited to, phenyl, biphenyl, terphenyl, anthryl, naphthyl, acenaphthyl, anthraquinonyl, phenanthryl, anthracenyl, pyrenyl, perylenyl, and fluorenyl.

[0026] The term “alkylene” refers to a divalent group that is a radical of an alkane. The alkylene can be straight-chained, branched, cyclic, or combinations thereof. The alkylene often has 1 to 20 carbon atoms. In some embodiments, the alkylene contains 1 to 18, 1 to 12, 1 to 10, 1 to 8, 1 to 6, or 1 to 4 carbon atoms. The radical centers of the alkylene can be on the same carbon atom (i.e., an alkylidene) or on different carbon atoms.

[0027] The term “arylene” refers to a divalent group that is carbocyclic and aromatic. The group has one to five rings that are connected, fused, or combinations thereof. The other rings can be aromatic, non-aromatic, or combinations thereof. In some embodiments, the arylene group has up to 5 rings, up to 4 rings, up to 3 rings, up to 2 rings, or one aromatic ring. For example, the arylene group can be phenylene.

[0028] The term “alkylene oxide” refers to a divalent group that includes at least two alkylene groups connected by oxy group. The alkylene groups can be linear, branched, cyclic, substituted with alkyl groups, or combinations thereof. Alkylene oides, also know as poloxyyalkylenes are of the general structure: -CFECEh OCFECFynOCFECFE-.

[0029] The terms “free radically polymerizable” and “ethylenically unsaturated” are used interchangeably and refer to a reactive group which contains a carbon-carbon double bond which is able to be polymerized via a free radical polymerization mechanism.

[0030] Unless otherwise indicated, the terms “optically transparent”, and “visible light transmissive” are used interchangeably, and refer to an article, film or adhesive that has a high light transmittance over at least a portion of the visible light spectrum (about 400 to about 700 nm). Typically, optically transparent articles have a visible light transmittance of at least 90% and a haze of less than 10%.

[0031] Unless otherwise indicated, "optically clear" refers to an adhesive or article that has a high light transmittance over at least a portion of the visible light spectrum (about 400 to about 700 nm), and that exhibits low haze, typically less than about 5%, or even less than about 2%. In some embodiments, optically clear articles exhibit a haze of less than 1% at a thickness of 50 micrometers or even 0.5% at a thickness of 50 micrometers. Typically, optically clear articles have a visible light transmittance of at least 95%, often higher such as 97%, 98% or even 99% or higher.

[0032] As used herein, the term "microstructure" means the configuration of features wherein at least 2 dimensions of the features are microscopic. The topical and / or cross- sectional view of the features must be microscopic.

[0033] As used herein, the term "microscopic" refers to features of small enough dimension so as to require an optic aid to the naked eye when viewed from any plane of view to determine its shape. One criterion is found in Modern Optic Engineering by W. J. Smith, McGraw-Hill, 1966, pages 104-105 whereby visual acuity, ". . . is defined and measured in terms of the angular size of the smallest character that can be recognized." Normal visual acuity is considered to be when the smallest recognizable letter subtends an angular height of 5 minutes of arc on the retina. At typical working distance of 250 mm (10 inches), this yields a lateral dimension of 0.36 mm (0.0145 inch) for this object.

[0034] As used herein, the term "nanostructure" means the configuration of features wherein at least 2 dimensions of the features are on a nanometer scale, meaning that they are less than 100 nanometers.

[0035] Disclosed herein are multi-layer optical articles. In some embodiments, the multilayer optical articles comprise a first release liner, a first optically clear pressure sensitive adhesive layer in contact with the first release liner, a microstructured optical layer with a first major surface and a second major surface, where the second major surface is a microstructured surface and is in contact with the first optically clear pressure sensitive adhesive layer, and the first major surface of the microstructured optical layer is a nanostructured surface. The nanostructured surface of the optical layer is in contact with a second optically clear pressure sensitive adhesive layer. The second optically clear pressure sensitive adhesive has a first major surface and a second major surface, where the second major surface is in contact with the nanostructured first major surface of the microstructured optical layer, and a second release liner disposed on the first major surface of the second optically clear pressure sensitive adhesive layer. The microstructured optical layer comprises a cured layer of a UV-curable (meth)acrylate-based resin wherein the cured layer in some embodiments has a refractive index of 1.63 at 532 nm. The adhesion of the first release liner to the first optically clear pressure sensitive adhesive is different from the adhesion of the second release liner to the second optically clear pressure sensitive adhesive. The interfacial adhesion of the interfaces between the second optically clear pressure sensitive adhesive layer and the nanostructured surface of the microstructured optical layer and the interface between the microstructured surface of the microstructured optical layer and the first optically clear pressure sensitive adhesive are both greater than the adhesion of the first and second release liners to the first and second optically clear pressure sensitive adhesives. Thus, when the release liners are removed, the interfaces of the optically clear pressure sensitive adhesives to the structured surfaces of the microstructured optical layer do not adhesively fail.

[0036] The multi-layer optical articles comprise a first release liner. The first release liner has a first major surface and a second major surface. At least the second major surface of the release liner is a release surface. Release liners are well known in the adhesive arts. Exemplary release liners include those prepared from paper (e.g., Kraft paper) or polymeric material (e.g., polyolefins such as polyethylene or polypropylene, ethylene vinyl acetate, polyurethanes, polyesters such as polyethylene terephthalate, and the like, and combinations thereof). At least some release liners are coated with a layer of a release agent such as a silicone, a fluorosilicone-containing material or a fluorocarbon-containing material.

[0037] Typically, the first release liner is a “tight release liner”. By this it is meant that the adhesive force to remove the release liner from the adhesive layer is relatively high. Tight release is in contrast with an “easy release liner” where the adhesive force to remove the release liner from the adhesive layer is relatively low. If the first release liner is a tight release liner, the second release liner is generally an easy release liner as is described below. While in many embodiments the first release liner is a tight release liner and the second release liner is an easy release liner, the article can be configured the other way, that is to say, the first release liner could be an easy release liner and the second release liner could be a tight release liner. It is only necessary that the two liners have different release forces, the configuration is one of design choice. Release is measured by Peel Force as described in the Examples section and is well understood in the adhesive arts.

[0038] The multi-layer optical articles comprise a first optically clear pressure sensitive adhesive layer. A wide range of optically clear pressure sensitive adhesives are suitable. Examples of suitable optically clear pressure sensitive adhesives include an optically clear (meth)acrylate-based adhesive, an optically clear siloxane -based adhesive, an optically clear block copolymer adhesive, or a combination thereof.

[0039] One particularly suitable class of optically clear pressure sensitive adhesives are (meth)acrylate-based pressure sensitive adhesives and may comprise either an acidic or basic copolymer. In many embodiments the (meth)acrylate-based pressure sensitive adhesive is an acidic copolymer. Generally, as the proportion of acidic monomers used in preparing the acidic copolymer increases, cohesive strength of the resulting adhesive increases. The proportion of acidic monomers is usually adjusted depending on the proportion of acidic copolymer present in the blends of the present disclosure.

[0040] The (meth)acrylate pressure sensitive adhesives also comprise alkyl (meth)acrylate monomers. Examples of such alkyl (meth)acrylate monomers are those in which the alkyl groups comprise from about 4 carbon atoms to about 12 carbon atoms and include, but are not limited to, n-butyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, isononyl acrylate, isodecyl acrylate, and mixtures thereof. Optionally, other vinyl monomers and alkyl (meth)acrylate monomers such as methyl acrylate, methyl methacrylate, isobomyl acrylate, vinyl acetate, styrene, and the like, may also be used.

[0041] Another useful class of optically clear (meth)acrylate-based pressure sensitive adhesives are those which are (meth)acrylic block copolymers. Such copolymers may contain only (meth)acrylate monomers or may contain other co -monomers such as styrenes. Examples of such pressure sensitive adhesives are described, for example in US Patent No. 7,255,920 (Everaerts et al.).

[0042] Silicone pressure sensitive adhesives typically comprise two major components, a polymer or gum, and a tackifying resin. The polymer is typically a high molecular weight polydimethylsiloxane or polydimethyldiphenylsiloxane, that contains residual silanol functionality (SiOH) on the ends of the polymer chain, or a block copolymer comprising polydiorganosiloxane soft segments and urea or oxamide terminated hard segments. The tackifying resin is generally a three-dimensional silicate structure that is endcapped with trimethylsiloxy groups (OSiMe3) and also contains some residual silanol functionality. Examples of tackifying resins include SR 545, from General Electric Co., Silicone Resins Division, Waterford, N.Y., and MQD-32-2 from Shin-Etsu Silicones of America, Inc., Torrance, Calif. Manufacture of typical silicone pressure sensitive adhesives is described in U.S. Pat. No. 2,736,721 (Dexter). Manufacture of silicone urea block copolymer pressure sensitive adhesive is described in U.S. Pat. No. 5,214,119 (Leir, et al). Other materials can be added for special purposes, including pigments, plasticizers, and fillers. Fillers are typically used in amounts from 0 parts to 10 parts per 100 parts of silicone pressure sensitive adhesive. Examples of fillers that can be used include zinc oxide, silica, carbon black, pigments, metal powders and calcium carbonate. One particularly suitable class or siloxane -containing pressure sensitive adhesives are those with oxamide terminated hard segments such as those described in US Patent No. 7,981,995 (Hays) and US Patent No. 7,371,464 (Sherman).

[0043] Block copolymer pressure sensitive adhesives generally comprise elastomers of the A-B or A-B-A type, where A represents a thermoplastic block, typically polystyrene, and B represents a rubbery block of polyisoprene, polybutadiene, or poly(ethylene / butylene), and resins. Examples of the various block copolymers useful in block copolymer pressure sensitive adhesives include linear, radial, star and tapered styrene-isoprene block copolymers such as “KRATON D1107P”, available from Shell Chemical Co., and “EUROPRENE SOL TE 9110”, available from EniChem Elastomers Americas, Inc.; linear styrene-(ethylene-butylene) block copolymers such as “KRATON G1657”, available from Shell Chemical Co.; linear styrene-(ethylene-propylene) block copolymers such as “KRATON G1750X”, available from Shell Chemical Co.; and linear, radial, and star styrene-butadiene block copolymers such as “KRATON D1118X”, available from Shell Chemical Co., and “EUROPRENE SOL TE 6205”, available from EniChem Elastomers Americas, Inc. The polystyrene blocks tend to form domains in the shape of spheroids, cylinders, or plates that causes the block copolymer pressure sensitive adhesives to have two-phase structures.

[0044] The first optically clear pressure sensitive adhesive may be an adhesive layer disposed on the first release liner or it may be a curable pre-adhesive composition. In instances when the adhesive layer is disposed on a release liner, the adhesive layer is contacted to surfaces by lamination. In instances when the adhesive layer is a curable preadhesive composition, the pre-adhesive composition is coated onto a surface and then cured. The first release liner may be disposed on the coated layer of adhesive either before or after the pre-adhesive composition of the coated layer is cured. In some embodiments, for convenience, the first release liner is disposed on the coated layer prior to curing.

[0045] In some embodiments, the use of a coating of a pre-adhesive may be desirable, as the first optically clear pressure sensitive adhesive is disposed on a structured surface, and the uncured composition is able to flow into the structures to give strong interfacial bonding.

[0046] The first optically clear adhesive may have a wide range of thicknesses. In some embodiments, the first optically clear adhesive has a thickness from 20-60 micrometers.

[0047] The multi-layer optical article also comprises a microstructured optical layer. The microstructured optical layer has a first major surface and a second major surface, where the second major surface is a microstructured surface and is in contact with the first major surface of the first optically clear pressure sensitive adhesive layer described above. The first major surface of the microstructured optical layer is a nanostructured surface as is described below.

[0048] The microstructured optical layer comprises a cured layer of a UV-curable (meth)acrylate-based resin. In some embodiments, the cured layer has a refractive index of 1.63 at 532 nm. Examples of such layers are described in US Patent No. 9,360,591. The microstructured surface comprises the reaction product of a polymerizable composition comprising at least 20 wt-% of inorganic nanoparticles and a non-aromatic multi-(meth) acrylate monomer comprising at least three contiguous alkylene oxide repeat units. The multi-(meth)acrylate monomer typically comprises two or three (meth)acrylate groups.

[0049] Typically, the microstructured surface of the microstructured optical layer is formed by disposing the UV-curable (meth)acrylate-based resin on a surface to form a layer, contacting the exposed surface of the layer with a microstructuring tool, curing the UV-curable (meth)acrylate -based resin, and removing the microstructuring tool. This process provides for a microstructured surface in the microstructured optical layer. Typically, this method forms a microstructured surface comprising protrusions. Typically, the microstructured optical layer has a thickness of from 0.7 - 550 micrometers. In some embodiments, the microstructured optical layer comprises a microstructured surface containing a plurality of protrusions with a height of from 0.2 -500 micrometers.

[0050] The second major surface of the microstructured optical layer comprises a nanostructured layer. This nanostructured layer is typically built into the microstructured optical layer at the same time as the first major surface is microstructured and the layer is cured. In some embodiments, the nanostructured surface contains nanostructures no greater than 60 nanometers in height.

[0051] In some embodiments, a nanostructured film tool is used to impart a nanostructured surface to the second major surface of the microstructured optical layer. In these embodiments, the nanostructured film tool is formed by disposing a layer of curable resin onto a film to form a layer, contacting the uncured resin layer with a nanostructuring tool, curing the resin layer, and removing the nanostructuring tool. This generates a nanostructured film tool.

[0052] The UV-curable (meth)acrylate-based resin that forms the microstructured optical layer is disposed on the nanostructured surface of the nanostructured film tool to form a layer. This layer is then contacted to the microstructuring tool and the layer is cured to generate an optical layer with a microstructured first major surface and a nanostructured second major surface.

[0053] The nanostructured second major surface of the microstructured optical layer is in contact with a second optically clear pressure sensitive adhesive. The second optically clear pressure sensitive adhesive has a first major surface and a second major surface. The first major surface of the second optically clear pressure sensitive adhesive is in contact with the nanostructured surface of the microstructured optical layer. The second major surface of the second optically clear pressure sensitive adhesive is in contact with the release surface of a second release liner. The second release liner has been referred to above, and typically is an easy release liner when the first release liner is a tight release liner.

[0054] The second optically clear pressure sensitive adhesive can be the same as the first optically clear pressure sensitive adhesive or it may be different. Regardless of whether the pressure sensitive adhesives are the same or different, the second optically clear pressure sensitive adhesive is selected from the optically clear adhesives described above. The second optically clear adhesive may have a wide range of thicknesses. In some embodiments, the first optically clear adhesive has a thickness from 20-60 micrometers.

[0055] Release liners are described above. As was mentioned previously, often the second release liner is an easy release liner, meaning that the release force necessary to remove the second release liner from the second optically clear pressure sensitive adhesive is relatively low.

[0056] The difference in the release force between the first optically clear pressure sensitive adhesive / first release liner and the second optically clear pressure sensitive adhesive / second release liner can be described in a variety of ways. Peel Force is a particularly suitable method for describing the adhesion. In general, the adhesion as measured by Peel Force of the first release liner to the first optically clear pressure sensitive adhesive layer is greater than the adhesion as measured by Peel Force of the second release liner to the second optically clear pressure sensitive adhesive layer.

[0057] The above-described articles contain two release liners to protect and cover the two optically clear adhesive layers of the articles. The presence of the release liners facilitates the shipping and handling of the multi-layer articles, but in use the release liners are removed to reveal an article that is optically clear and non-birefringent. These articles are described in greater detail below. The release liners may be removed sequentially, i.e. first one liner is removed and the exposed adhesive surface is contacted to a surface and then the other release liner is removed and the exposed adhesive surface is contacted to a different surface.

[0058] Also disclosed herein are multi-layer optical articles comprising a first optically clear pressure sensitive adhesive layer with a first major surface and a second major surface, a microstructured optical layer with a first major surface and a second major surface, where the first major surface is a microstructured surface and is in contact with the second major surface of the first optically clear pressure sensitive adhesive layer, and the second major surface of the microstructured optical layer is a nanostructured surface, and this nanostructured second major surface is in contact with a second optically clear pressure sensitive adhesive layer with a first major surface and a second major surface, where in the first major surface is in contact with the nanostructured surface of the microstructured optical layer. The multi-layer article is optically clear and non- birefringent.

[0059] The elements of these articles: the first optically clear pressure sensitive adhesive; the microstructure optical layer; and the second optically clear pressure sensitive adhesive are described in detail above.

[0060] Also disclosed herein are methods for forming multi-layered optical articles. In some embodiments, the method comprises preparing a nanostructured film tool, providing a curable mixture of a UV-curable (meth)acrylate-based resin that upon curing the cured layer in some embodiments has a refractive index of 1.63 at 532 nm, disposing the curable mixture on the nanostructured surface of the nanostructured film tool to form a curable layer with a first major surface and a second major surface, where the second major surface is disposed on the nanostructured surface of the nanostructured film tool, providing a microstructured tool with a microstructured surface comprising a plurality of microstructured features, contacting the microstructured tool to the first major surface of curable layer, curing the curable layer to form a cured optical layer with a first major surface and a second major surface, removing the microstructured tool from the cured optical layer such that the first major surface of the cured optical layer is a microstructured surface, providing a first adhesive article, disposing the first adhesive article on the microstructured surface of the cured optical layer, removing the nanostructured film tool from the nanostructured surface of the cured optical layer, providing a second adhesive article, and disposing the second adhesive article on the nanostructured surface of the cured optical layer. The Peel Forces and interfacial adhesion characteristics of the formed articles are described above.

[0061] In this method, forming a nanostructured film tool comprises providing a film such as a PET (polyethylene terephthalate) film, disposing a curable resin, typically a curable (meth)acrylate resin, on the film, curing the curable (meth)acrylate resin to form a cured layer with a first major surface and a second major surface, where the second major surface of the cured layer is in contact with the film. A nanostructured tool with a nanostructured surface is provided, and the nanostructured surface of this tool is contacted to the first major surface of the cured layer to impart a nanostructured surface to the cured layer. The nanostructured tool is then removed to form a nanostructured film tool. In the above method, the first adhesive article may have several different configurations. In some embodiments the first adhesive article comprises a first release liner with a first major surface and a second major surface, where the second major surface is a release surface and a first optically clear pressure sensitive adhesive layer with a first major surface and a second major surface, where the first major surface of the first optically clear pressure sensitive adhesive layer is in contact with the second major surface of the first release liner. In other embodiments, the first adhesive article comprises a preadhesive composition that can be coated and cured to form an optically clear pressure sensitive adhesive layer. A release liner is disposed on the optically clear pressure sensitive adhesive layer, either prior to curing or after curing, typically prior to curing.

[0062] The same criteria apply to the second adhesive article. The article may be an adhesive / liner article, or it may be a curable pre-adhesive composition to which a liner is attached.

[0063] In the above method, the method for disposing the first adhesive article on the microstructured surface of the cured optical layer depends on the configuration of the first adhesive article. In the adhesive article is an adhesive / liner article, disposing comprises laminating the optically clear pressure sensitive adhesive layer to the microstructured surface. If the adhesive article is a curable pre-adhesive composition to which a liner is attached disposing comprises coating the pre-adhesive composition on the microstructured surface of the cured optical layer to form a curable layer, disposing the first release liner on the curable layer, and curing to form the first adhesive article.

[0064] The same criteria apply to disposing the second adhesive article on the nanostructured surface of the microstructured optical layer. Like the first adhesive article, the second adhesive article is laminated to the nanostructured surface if the second adhesive article is an adhesive / liner article, or it coated and cured if the second adhesive article is a curable pre-adhesive composition to which a liner is attached.

[0065] As mentioned above, the curable layer to form a cured microstructured optical layer is a UV-curable material. Curing of this layer comprises exposing the curable layer to UV radiation. A wide variety of UV sources are suitable.

[0066] Each of the materials and components of the multi-layer article are described in detail above. The materials and components include the first and second release liners. The articles of this disclosure have 4 adhesive-substrate interfaces. Besides the two release liner / adhesive interfaces described above, there is an adhesive / microstructured optical layer interface, and an adhesive / nanostructured surface interface. The adhesive / microstructured optical layer interface, and the adhesive / nanostructured surface interface must have higher adhesion than the adhesion of the adhesive layers to the release liners, otherwise when the release liners are removed, there can be adhesive failure at these interfaces.

[0067] The optically clear pressure sensitive adhesives, the microstructured optical layer, and nanostructured layer present between the microstructured optical layer and the second optically clear pressure sensitive adhesive layer are all described in detail above.

[0068] The disclosure may be more fully understood by the drawings. Figure 1 shows article 100. Article 100 has first release liner 110, first optically clear pressure sensitive adhesive 120, microstructured optical layer 130 with microstructures 135 and nanostructured surface 145, second optically clear pressure sensitive adhesive 140 adhered to nanostructured surface 145, and second release liner 150.

[0069] Figure 2 shows article 200. Article 200 has first optically clear pressure sensitive adhesive 220, microstructured optical layer 230 with microstructures 235, and nanostructured surface 245, second optically clear pressure sensitive adhesive 240 adhered to nanostructured surface 245.

[0070] Examples

[0071] These examples are merely for illustrative purposes only and are not meant to be limiting on the scope of the appended claims. The following abbreviations are used: cm = centimeters; mm = millimeters; in = inch; min = minutes; sec = seconds; N = Newtons. All parts, percentages, ratios, etc. in the examples and the rest of the specification are by weight, unless noted otherwise.

[0072] Table of Abbreviations

[0073] Test Methods

[0074] 180° Peel Testing

[0075] Peel tests were conducted on the air side of boro-float glass. Prior to testing, the glass surface was cleaned with an isopropanol-moistened wipe, then a dry wipe. One release liner was removed from the OCA sample which was then manually laminated to a 2 -mil (51 micrometer) thick primed PET backing film (Skyrol SH81, SKC, South Korea), with the primer facing the OCA. Then the release liner on the opposite side of the adhesive was removed, and the OCA sample laid on the glass slide with light tension. The OCA was manually laminated to the glass with a roller and cut to strips either 1 cm or 1 in (2.5 cm) wide, extending longer than the glass substrate. The free end of the sample was attached to the clamp of a peel arm for an IMASS-SP2100 Peel Tester. Then the peel arm was carefully set in place on the IMASS load cell. The test was commenced with the IMASS platen moving at 12 in / min (305 cm / sec) and the arm peeling back the OCA at an angle close to 180 degrees. When recording the peel force data from the IMASS, the first two seconds of each peel were excluded as the transient initiation force. Following that, the subsequent 10 seconds of each peel were averaged to provide the values in the table. Results are presented in Newtons / centimeter (N / cm).

[0076] Optical Tests

[0077] In one of the embodiments of this disclosure, the optical films may be used to reduce the sparkle in displays such as in liquid crystal displays (LCDs) or in Organic Light Emitting Diode displays (OLEDs). The sparkle performance of the optical films were evaluated using a custom built test system. The optical film under test was placed in between a photolithographically patterned chromium mask (with 75.6 micrometers x 23.5 micrometers pixels that are separated by 72.5 micrometers in one direction and 20.2 micrometers in orthogonal direction mimicking a typical LCD pixel layout) and -1100 micrometers thick matte cover glass (EagleEtch XS AG 70 Gloss glass, Coming INC NY). The whole stack was then illuminated by a Lambertian white light source (Part # 83873 Metaphase Technologies, Bristol, PA). For sparkle measurements, the pixels on the mask were then imaged using a complementary metal oxide semiconductor (CMOS) camera (Blackfly, Teledyne FLIR LLC, Wilsonville, OR) equipped with a 50 mm lens with f / 8 aperture (C203218, Tamron Co. Ltd. Japan). The sparkle values were then calculated as the variance of local intensity after removing the low frequency modulations from the pixels. Detailed descriptions of calculations of sparkle are described in US Patent No. 10,353,214 (Sitter et al.), or in the product literature of a sparkle measurement system SMS- 1000 (Display-Messtechnik & Systeme, Rottenburg am Neckar, Germany), for example. The same images captured by the camera were used to calculate the Distinctness of Image (DOI) by measuring the intensity modulation (peak-to-valley amplitude) with the mask only and then with the test film and cover glass on top of the mask. DOI was calculated as: DOI = (Modulation with test film and cover glass / modulation with mask only) * 100 %. For the relative luminance measurements, the CCD camera was replaced with a spectrophotometer (PR650, Photo Research Inc, North Syracus, NY) and the luminance of first measured with mask only on the light box and then it was measured again with the optical film between the mask and the cover glass. The relative luminosity was calculated as: Relative Luminosity = (luminosity with test film / luminosity with mask only) * 100 %.

[0078] Examples

[0079] Synthesis Example S 1 : Preparation of OCA pre-adhesive composition

[0080] List of components used in preparing the OCA pre-adhesive composition:

[0081] Preparation of Pre-adhesive Coating Solutions

[0082] Pre-adhesive coating compositions were prepared according to the following procedure with the amounts indicated in Table A below. The components listed in the premix section of Table A were first charged to a clear jar and allowed to mix for 30 minutes. The solution was then exposed to approximately 350 nm UV irradiation until a viscous solution was obtained. Additional components as listed in the compounding section of Table A were then added to the jar and allowed to mix on a jar roller for greater than 4 hours. Table A

[0083] Preparation of Article

[0084] Step 1: Preparation of Nanostructured layer

[0085] A film tool was prepared by contacting Tool-1 to a film article with a cured layer of CM on a layer of polyester film. Tool-1 was removed from the surface of the film article to form a nanostructured film tool.

[0086] Step 2: Preparation of Microstructured layer

[0087] CM was disposed on the nanostructured surface of the fdm tool to form a curable layer, and Tool-2 was contacted to the surface of the curable layer. The curable layer was cured with UV light and Tool-2 was removed to form a microstructured surface on the cured layer of CM.

[0088] Step 3: Formation of an Intermediate Adhesive Article

[0089] A curable layer of uncured OCA was disposed onto the microstructured surface of the cured layer of CM. Release Liner- 1 was disposed on the curable layer and the OCA was cured by exposure to UV light through the release liner.

[0090] Step 4: Removal of Film Tool

[0091] The fdm tool was removed from the Intermediate Adhesive Article to expose a nanostructured surface.

[0092] Step 5: Preparation of Final Adhesive Article

[0093] A curable layer of uncured OCA was disposed onto the nanostructured surface of the Intermediate Adhesive Article. Release Liner-2 was disposed on the curable layer and the OCA was cured by exposure to UV light through the release liner.

[0094] Testing of Article

[0095] The Final Adhesive Article was tested for 180° Peel at various temperatures according to the Test Method Described above. The results are presented in Table 1 below.

[0096] Table 1: 180° Peel

[0097] To test the performance of the article for sparkle reduction, both the liners from the Final Adhesive Article were removed and replaced with 1.14 mil (29 micrometer) thick primed PET (polyethylene terephthalate) resulting an approximately 150 micrometer thick laminate that was used as the test film under test between cover glass and the pixel mask. In order to avoid any unwanted wet-out between the PET surface and the surfaces of the cover glass and pixel mask, the primer on PET surfaces in contact with the cover glass and pixel mask with 2 micrometer beads. A Comparative Example (CE) was prepared by laminating 3M Anti-Sparkle Film

[0098] (available from 3M Company, St Paul, MN) between two 1.1 4mil (29 micrometer) PET substrates as described above using a 38-micrometer thick OCA on the top and a 10- micrometer thick OCA on the bottom side. The Results are presented in Table 2 below. Table 2: Optical Test

Claims

What is claimed is:

1. A multi-layer optical article comprising: a first release liner with a first major surface and a second major surface, wherein the second major surface comprises a release surface; a first optically clear pressure sensitive adhesive layer with a first major surface and a second major surface, wherein the first major surface of the first optically clear pressure sensitive adhesive layer is in contact with the second major surface of the first release liner; a microstructured optical layer with a first major surface and a second major surface, wherein the first major surface is a microstructured surface and is in contact with the second major surface of the first optically clear pressure sensitive adhesive layer, and the second major surface of the microstructured optical layer is a nanostructured surface, and wherein the microstructured optical layer comprises a cured layer of a UV-curable (meth)acrylate-based resin; a second optically clear pressure sensitive adhesive layer with a first major surface and a second major surface, where in the first major surface is in contact with the nanostructured surface of the microstructured optical layer; and a second release liner with a first major surface and a second major surface, wherein the first major surface comprises a release surface and is disposed on the second major surface of the second optically clear pressure sensitive adhesive layer, wherein the adhesion as measured by Peel Force of the first release liner to the first optically clear pressure sensitive adhesive is different from the adhesion as measured by Peel Force of the second release liner to the second optically clear pressure sensitive adhesive, and wherein the interfacial adhesion of the interfaces between the first optically clear pressure sensitive adhesive and the microstructured surface of the microstructured optical layer and the second optically clear pressure sensitive adhesive and the nanostructured surface of the microstructured optical layer is greater than the adhesion of the first release liner to the first optically clear pressure sensitive adhesive layer and the second release liner to the second optically clear pressure sensitive adhesive layer such that peeling of the first release liner from the first optically clear adhesive layer or peeling the second release liner from the second optically clear adhesive layer does not cause adhesive failure at the interface between the first optically clear pressure sensitive adhesive and themicrostructured surface of the microstructured optical layer or the second optically clear pressure sensitive adhesive and the nanostructured surface of the microstructured optical layer.

2. The multi-layer optical article of claim 1, wherein upon the removal of the first and second release liners, the resultant article is optically clear and non-birefringent.

3. The multi-layer optical article of claim 1, wherein the first and second optically clear pressure sensitive adhesives comprise an optically clear (meth)acrylate-based adhesive, an optically clear siloxane -based adhesive, an optically clear block copolymer adhesive, or a combination thereof.

4. The multi-layer optical article of claim 1, wherein the first and second optically clear pressure sensitive adhesives are the same.

5. The multi-layer article of claim 1, wherein the adhesion as measured by Peel Force of the first release liner to the first optically clear pressure sensitive adhesive layer is greater than the adhesion as measured by Peel Force of the second release liner to the second optically clear pressure sensitive adhesive layer.

6. The multi-layer article of claim 1, wherein the adhesion as measured by Peel Force of the first release liner to the first optically clear pressure sensitive adhesive layer is less than the adhesion as measured by Peel Force of the second release liner to the second optically clear pressure sensitive adhesive layer.

7. The multi-layer article of claim 1, wherein the microstructured optical layer comprises a microstructured surface containing a plurality of protrusions with a height of from 0.2 - 500 micrometers.

8. The multi-layer article of claim 1, wherein the nanostructured surface on the second major surface of the microstructured optical layer is imparted to surface through contact with a nanostructured film tool.

9. The multi-layer article of claim 1, wherein the nanostructured surface on the second major surface of the second optically clear pressure sensitive adhesive contains nanostructures no greater than 60 nanometers in height.

10. The multi-layer article of claim 1, wherein the first optically clear pressure sensitive adhesive layer and the second optically clear pressure sensitive adhesive layer have a thickness of from 20-60 micrometers.

11. The multi-layer article of claim 1, wherein the microstructured optical layer has a thickness of from 0.7 - 550 micrometers, and a refractive index of 1.63 at 532 nm.

12. A multi-layer optical article comprising: a first optically clear pressure sensitive adhesive layer with a first major surface and a second major surface; a microstructured optical layer with a first major surface and a second major surface, wherein the first major surface is a microstructured surface and is in contact with the second major surface of the first optically clear pressure sensitive adhesive layer, the second major surface of the microstructured optical layer is a nanostructured surface, and wherein the microstructured optical layer comprises a cured layer of a UV-curable (meth)acrylate-based resin; and a second optically clear pressure sensitive adhesive layer with a first major surface and a second major surface, where in the first major surface is in contact with the nanostructured surface of the microstructured optical layer; and wherein the article is optically clear and non-birefringent.

13. A method for forming a multi-layered optical article comprising: preparing a nanostructured film tool, comprising: providing a film; disposing a curable (meth)acrylate resin on the film; curing the curable (meth)acrylate resin to form a cured layer with a first major surfaceand a second major surface, wherein the second major surface of the cured layer is in contact with the film; providing a nanostructured tool with a nanostructured surface; contacting the nanostructured surface of the nanostructured tool to the first major surface of the cured layer to impart a nanostructured surface to the cured layer; and removing the nanostructured tool to form a nanostructured film tool; providing a curable mixture of a UV-curable (meth)acrylate-based resin; disposing the curable mixture on the nanostructured surface of the nanostructured film tool to form a curable layer with a first major surface and a second major surface, wherein the second major surface is disposed on the nanostructured surface of the nanostructured film tool; providing a microstructured tool with a microstructured surface comprising a plurality of microstructured features; contacting the microstructured tool to the first major surface of curable layer; curing the curable layer to form a cured optical layer with a first major surface and a second major surface; removing the microstructured tool from the cured optical layer such that the first major surface of the cured optical layer is a microstructured surface; providing a first adhesive article, wherein the first adhesive article comprises: either a first release liner with a first major surface and a second major surface, wherein the second major surface is a release surface; and a first optically clear pressure sensitive adhesive layer with a first major surface and a second major surface, wherein the first major surface of the first optically clear pressure sensitive adhesive layer is in contact with the second major surface of the first release liner; or a pre-adhesive composition that can be coated and cured to form an optically clear pressure sensitive adhesive layer, upon which is disposed a first release liner prior to or after curing;disposing the first adhesive article on the microstructured surface of the cured optical layer, wherein disposing comprises either laminating the optically clear pressure sensitive adhesive layer to the microstructured surface or coating the pre-adhesive composition on the microstructured surface of the cured optical layer to form a curable layer, disposing the first release liner on the curable layer, and curing to form the first adhesive article; removing the nanostructured film tool from the nanostructured surface of the cured optical layer; providing a second adhesive article, wherein the second adhesive article comprises: either a second release liner with a first major surface and a second major surface, wherein the first major surface is a release surface; and a second optically clear pressure sensitive adhesive layer with a first major surface and a second major surface, wherein the second major surface of the second optically clear pressure sensitive adhesive layer is in contact with the first major surface of the second release liner; or a pre-adhesive composition that can be coated and cured to form an optically clear pressure sensitive adhesive layer, upon which is disposed a second release liner prior to or after curing; disposing the second adhesive article on the nanostructured surface of the cured optical layer, wherein disposing comprises either laminating the optically clear pressure sensitive adhesive layer to the nanostructured surface or coating the pre-adhesive composition on the nanostructured surface of the cured optical layer to form a curable layer, disposing the second release liner on the curable layer, and curing to form the second adhesive article; wherein the adhesion as measured by Peel Force of the first release liner to the first optically clear pressure sensitive adhesive is different from the adhesion as measured by Peel Force of the second release liner to the second optically clear pressure sensitive adhesive, and wherein the interfacial adhesions of an interface between the first major surface of the second optically clear pressure sensitive adhesive layer and the nanostructured surface of the microstructured optical layer and an interface between thesecond major surface of the first optically clear adhesive and the first major surface of the microstructured optical layer are greater than the adhesion of the first release liner to the first optically clear pressure sensitive adhesive layer and the second release liner to the second optically clear pressure sensitive adhesive layer such that peeling of the first release liner from the first optically clear adhesive layer or peeling the second release liner from the second optically clear adhesive layer does not cause adhesive failure at the interface between the first major surface of the second optically clear pressure sensitive adhesive layer and the nanostructured surface of the microstructured optical layer or the interface between the second major surface of the first optically clear pressure sensitive adhesive and the first major surface of the microstructured optical layer.

14. The method of claim 13, wherein curing the curable layer to form a cured microstructured optical layer comprises exposing the curable layer to UV radiation.

15. The method of claim 13, wherein the first and second optically clear pressure sensitive adhesives comprise an optically clear (meth)acrylate-based adhesive, an optically clear siloxane-based adhesive, an optically clear block copolymer adhesive, or a combination thereof.

16. The method of claim 13, wherein the first and second optically clear pressure sensitive adhesives are the same.

17. The method of claim 13, wherein the first adhesive article comprises a curable preadhesive composition on which is disposed the first release liner prior to curing and the second adhesive article comprises a curable pre-adhesive composition on which is disposed the second release liner prior to curing.

18. The method of claim 13, wherein the microstructured surface of the cured microstructured optical layer comprises a plurality of protrusions with a height of 0.7 - 500 micrometers.

19. The method of claim 13, wherein the nanostructured surface on the second major surface of the second optically clear pressure sensitive adhesive contains nanostructures no greater than 30 nanometers in height.

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