Optical film with adhesive layer for reducing slope error

Abstract

An optical stack includes a polymeric optical film disposed on a curable adhesive layer. The optical film has a first major surface having a mean slope error greater than about 60 microradians. The curable adhesive layer has a tan delta of at least 1 for a frequency of 1 Hz and for at least a first temperature below, and within 35 deg. C of, a glass transition temperature of the optical film, such that when the optical stack is heated at the first temperature for at least 10 min, the mean slope error is reduced by at least 10 percent. Mean slope error is a mean of a slope magnitude error determined from a surface profile of the first major surface filtered with a bandpass Fourier filter having band edge wavelengths of W1 and W2, where 0.1 mm ≤ W1 ≤ 0.3 mm, and 2W1 ≤ W2 ≤ 10 mm.

Description

[0001] PA103012W002

[0002] OPTICAL FILM WITH ADHESIVE LAYER FOR REDUCING SLOPE ERROR

[0003] TECHNICAL FIELD

[0004] The present description relates generally to optical stacks including an adhesive layer.

[0005] BACKGROUND

[0006] An optical film may reflect light from one or more major surfaces of the optical film.

[0007] SUMMARY

[0008] In some aspects, the present description provides an optical stack including a polymeric optical film disposed on a first curable adhesive layer. The polymeric optical film has a first major surface having a mean slope error that can be greater than about 60 microradians. The first curable adhesive layer has a tan delta of at least 1 for a frequency of 1 Hz and for at least a first temperature below, and within 35 deg. C of, a glass transition temperature of the polymeric optical film, where the tan delta is a ratio of imaginary to real parts of shear modulus, such that when the optical stack is heated at the first temperature for at least 10 min, the mean slope error is reduced by at least 10 percent. Mean slope error is a mean of a slope magnitude error determined from a surface profile of the first major surface filtered with a same bandpass Fourier filter having band edge wavelengths of W1 and W2, where 0.1 mm < W1 < 0.3 mm, and 2W1 < W2 < 10 mm. W1 can be about 0.2 mm and W2 can be about 5 mm, for example.

[0009] In some aspects, the present description provides an optical assembly including first and second substrates; a polymeric multilayer optical film disposed between the first and second substrates and numbering a plurality of optical repeat units that can number at least 10 in total, where each optical repeat unit includes at least two polymeric layers, and each layer of each optical repeat unit has an average thickness less than about 500 nm; and first and second adhesive layers disposed between, and bonding together, the polymeric multilayer optical film and the respective first and second substrates. For at least one major surface of the polymeric multilayer optical film, the major surface has a mean slope error of no more than about 45 microradians, where the mean slope error is a mean of a slope magnitude error determined from a surface profile of the major surface filtered with a bandpass Fourier filter having band edge wavelengths of about 0.2 mm and about 5 mm.

[0010] In some aspects, the present description provides an optical assembly includes a first substrate; a polymeric optical film; and a first adhesive layer disposed between, and bonding together, the polymeric optical film and the first substrate. For at least one major surface of the polymeric optical film, the major surface can have a mean slope error of less than 100 microradians, where the mean slope error is a mean of a slope magnitude error determined from a surface profile of the major surface filtered with a bandpass Fourier filter having band edge wavelengths of W1 and W2, 0.1 mm < W1 < 0.3 mm, 2W1 < W2 < 10 mm. W1 can be about 0.2 mm and W2 can be about 5 mm, for example. The first adhesive layer comprises a cured product of a curable adhesive, the curable adhesive comprising: a poly(meth)acrylateor (meth)acrylate-containing polyurethane; one or more (meth)acrylate monomers, one or more (meth)acrylate-containing oligomers, or both; a free radical initiator; and polyvinylpyrrolidone or a copolymer thereof.

[0011] In some aspects, the present description provides a method of reducing a mean slope error of at least a first major surface of a polymeric optical fdm. The method includes forming an optical stack by disposing a first curable adhesive layer on the polymeric optical film and disposing a first substrate on the first curable adhesive layer opposite the polymeric optical film, where the polymeric optical fdm has a glass transition temperature Tg, and the first curable adhesive layer has a tan delta of at least 1 for a frequency of 1 Hz and for at least a first temperature Tl, where Tg - 35 deg. C < T1 < Tg, and the tan delta is a ratio of imaginary to real parts of shear modulus; and annealing the optical stack at the first temperature for at least 10 minutes. The annealing reduces the mean slope error of the first major surface of the polymeric optical film by at least 10 percent. Mean slope error is a mean of a slope magnitude error determined from a surface profde of the first major surface filtered with a same bandpass

[0012] Fourier filter having band edge wavelengths of W1 and W2, where 0.1 mm < W1 < 0.3 mm, and 2W1 < W2 < 10 mm. W1 can be about 0.2 mm and W2 can be about 5 mm, for example.

[0013] These and other aspects will be apparent from the following detailed description. In no event, however, should this brief summary be construed to limit the claimable subject matter.

[0014] BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1-2 are schematic cross-sectional views of optical stacks or assemblies, according to some embodiments.

[0015] FIG. 3 is a schematic cross-sectional view of an optical film, according to some embodiments. FIG. 4 is a schematic cross-sectional view of a major surface illustrating slope error, according to some embodiments.

[0016] FIG. 5 is a schematic plot of a bandpass Fourier filter as a function of spatial frequency, according to some embodiments.

[0017] FIG. 6 is a schematic illustration of a method of reducing a mean slope error of at least one major surface of an optical film, according to some embodiments.

[0018] FIG. 7 shows results of mean slope error (MSE) for Examples 1 and 2 before and after annealing.

[0019] DETAILED DESCRIPTION

[0020] In the following description, reference is made to the accompanying drawings that form a part hereof and in which various embodiments are shown by way of illustration. The drawings are not necessarily to scale. It is to be understood that other embodiments are contemplated and may be made without departing from the scope or spirit of the present description. The following detailed description, therefore, is not to be taken in a limiting sense.Optical films can have or develop a waviness, such as a texture resembling that of an orange peel, that may be quantified in terms of a slope error of major surface(s) of the optical fdm. When the optical film reflects an image light, such waviness can degrade the quality of the reflected image. It has been found, according to some embodiments, that a curable adhesive layer can be selected such that when disposed on an optical film having slope error to form an optical stack, the optical stack can be annealed (heated and allowed to relax at an elevated temperature) to reduce the slope error. The optical stack can be disposed on a desired substrate, then annealed to reduce slope error, and then the curable adhesive layer can be cured to bond the adhesive layer to the substrate and form a desired optical assembly having a low slope error. It has been found, according to some embodiments, that suitable curable adhesive layers can have a high tan delta (e.g., at least about 1) at the annealing temperature. Other properties of the curable adhesive layer that have been found to aid in reducing slope error are described elsewhere herein.

[0021] FIGS. 1-2 are schematic cross-sectional views of optical stacks or assemblies 100 and 105, respectively, according to some embodiments. Optical stack or assembly 100 includes an optical film 110 disposed on a (e.g., curable or cured) adhesive layer 120 and optionally includes a substrate 130 disposed on the (e.g., curable or cured) adhesive layer 120 opposite the optical film 110. Optical stack or assembly 105 includes an optical film 110 disposed between first and second substrates 130 and 135 and includes first and second (e.g., curable or cured) adhesive layers 120 and 125 disposed between the optical film 110 and the respective first and second substrates 130 and 135.

[0022] In some embodiments, an optical stack 100, 105 includes a polymeric optical film 110 disposed on a first curable adhesive layer 120, where the polymeric optical film 110 has a first major surface 112, 114 (or 112', 114', described elsewhere herein) having a mean slope error of greater than about 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 120, 130, 140 microradians. In some embodiments, the first major surface 112 of the polymeric optical film 110 faces the first curable adhesive layer 120. In some embodiments, the first major surface 114 of the polymeric optical film faces away from the first curable adhesive layer 120. In some embodiments, the optical stack 100, 105 further includes a substate 130 disposed on the first curable adhesive layer 120 opposite the polymeric optical film 110.

[0023] The slope error is not explicitly shown in the FIGS. 1-2 but is illustrated in FIGS. 3-4. The mean slope error is a mean of a slope magnitude error determined from a surface profile of the first major surface filtered with a bandpass Fourier filter having band edge wavelengths of W1 and W2, where 0.1 mm < W1 < 0.3 mm, and 2W1 < W2 < 10 mm. In some embodiments, W1 is about 0.2 mm and W2 is about 5 mm, for example. Mean slope error is described further elsewhere herein. The slope error can result from the manufacturing the optical film or from applying protective liners to the optical film after it has been manufactured where the protective liners have a slope error (e.g., due to a waviness of the liner) that is transferred to the optical film. For example, liners used to protect polymeric multilayer optical films can have a mean slope error of greater than about 120, 140, 150, 180, 200, or even 250 microradians.In some embodiments, the first curable adhesive layer 120 has a tan of at least 1, 1.05, 1.1, 1.15, 1.2, 1.25, or 1.3 for a frequency of 1 Hz and for at least a first temperature below, and within 35 deg. C of, a glass transition temperature of the polymeric optical film 110. The first temperature can be within 30, 25, or 20 degrees of the glass transition temperature, for example. In the case of a multilayer optical film, the glass transition temperature of the optical film can be the glass transition temperature of any layer of the optical film, such as the layer of the optical film closest to the curable adhesive layer (e.g., the layer of the optical film that physically contacts the curable adhesive layer). The tan delta, which may also be referred to as a loss tangent, is a ratio of imaginary (G") to real (G') parts of shear modulus.

[0024] In some embodiments, the optical stack 100, 105 is such that when the optical stack is heated at the first temperature for at least 10 minutes, the mean slope error is reduced by at least 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, or 60 percent. In some embodiments, this time of at least 10 minutes is at least 15, 20, or 25 minutes, for example. In some such embodiments, or in other embodiments, this time of at least 10 minutes is no more than 120, 60, 50, or 40 minutes, for example. In some such embodiments, or in other embodiments, the optical stack 105 further includes a second curable adhesive layer 125 disposed on the polymeric optical film 110 opposite the first curable adhesive layer 120. The second curable adhesive layer 125 may be as described for the first curable adhesive layer 120. In some embodiments, the first major surface 112 of the polymeric optical film 110 faces the first curable adhesive layer 120 and the polymeric optical film 110 has an opposite second major surface 114 facing the second curable adhesive layer 125. In some such embodiments, or in other embodiments, the second major surface 114 has a mean slope error of greater than about 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 120, 130, 140 microradians, such that when the optical stack is heated at the first temperature for at least 10 min (or for a time in a range described elsewhere herein), the mean slope error of the second major surface is reduced by at least 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, or 60 percent.

[0025] In some embodiments, the optical film 110 is a polymeric multilayer optical film. As is known in the art, multilayer optical films including a plurality of optical repeat units (e.g., a plurality of alternating first and second polymeric layers) can be used to provide desired reflection and transmission in desired wavelength ranges by suitable selection of layer thicknesses and refractive index differences. Multilayer optical films and methods of making multilayer optical films are described in U.S. Pat. Nos. 5,882,774 (Jonza et al.); 6,783,349 (Neavin et al.); 6,949,212 (Merrill et al.); 6,967,778 (Wheatley et al.); 9,162,406 (Neavin et al.); and 11,493,677 (Haag et al.), for example. An optical repeat unit of a multilayer optical film is generally the smallest distinct unit of optical layers (e.g., layers that reflect or transmit light primarily by optical interference) that repeats along a thickness direction of the optical film. An optical repeat unit generally includes at least two different layers (e.g., higher index first and lower index second layers) and may optionally include additional layers as described in U.S. Pat. Nos. 5,103,337 (Schrenk et al.); 5,360,659 (Arends et al.); 5,540,978 (Schrenk); and 6,207,260 (Wheatley et al.), for example, and in U.S. Pat. Appl. Pub. No. 2024 / 0151889 (Huseby et al.), for example.FIG. 3 is a schematic cross-sectional view of an optical film 110, according to some embodiments. In some embodiments, the optical film 110 is a polymeric multilayer optical film including a plurality of optical repeat units 220 numbering at least 10, 20, 30, 50, or 100 in total, where each optical repeat unit 220 includes at least two polymeric layers 222, 224. In some such embodiments, or in other embodiments, the plurality of optical repeat units 220 number no more than 5000, 1000, 800, 600, or 500 in total. In some such embodiments, or in other embodiments, each layer of each optical repeat unit 220 has an average thickness less than about 500, 450, 400, 350, 300, or 250 nm. In some such embodiments, or in other embodiments, each layer of each optical repeat unit 220 has an average thickness greater than 40, 50, 60, or 70 nm.

[0026] In some embodiments, the plurality of optical repeat units 220 is disposed between first and second skin layers 262 and 264. The first and second skin layers 262 and 264 can be outermost layers of the optical film 110. In some embodiments, each of the first and second skin layers 262 and 264 has an average thickness greater than about 500, 750, 1000, 1250, 1500, 1750, or 2000 nm. In some such embodiments, or in other embodiments, each of the first and second skin layers 262 and 264 has an average thickness less than about 20, 15, 10, 7, 5, or 4 micrometers.

[0027] In some embodiments, the optical film 110 has outermost major surfaces 112 and 114 and the plurality of optical repeat units 220 has outermost major surfaces 112' and 114'. The major surface that has a mean slope error that is reduced upon annealing can be any one or more of major surfaces 112, 114, 112' and 114', for example. In some embodiments, each major surface (e.g., outermost major surfaces and interfaces substantially coextensive with length and width of the optical film) of the optical film 110 has a substantially same mean slope error (e.g., the film as a whole can have waviness such that each major surface has a substantially same waviness).

[0028] In some embodiments, an optical assembly 105 includes first and second substrates 130 and 135; a polymeric multilayer optical film 110 disposed between the first and second substrates 130 and 135 and including a plurality of optical repeat units 220 numbering at least 10 in total (or in a range described elsewhere herein), where each optical repeat unit includes at least two polymeric layers 222, 224, and each layer of each optical repeat unit 220 has an average thickness less than about 500 nm (or in a range described elsewhere herein); and first and second adhesive layers 120 and 125 disposed between, and bonding together, the polymeric multilayer optical film 110 and the respective first and second substrates 130 and 135. In some such embodiments, or in other embodiments, for at least one major surface (e.g., 112, 112', 114, and / or 114') of the polymeric multilayer optical film 110, the major surface has a mean slope error of no more than about 45, 42, 40, 49, 38, 37, 36, or 35 microradians. In some such embodiments, or in other embodiments, the at least one major surface of the polymeric multilayer optical film 110 includes opposing first and second major surfaces 112 and 114 of the polymeric multilayer optical film 110.

[0029] In some embodiments, the first adhesive layer 120 is substantially perminately bonded to the polymeric multilayer optical film 110 and releasably bonded to the first substrate 130. For example, thefirst substrate can be a release liner. In some embodiments, the first adhesive layer 110 is substantially perminately bonded to each of the polymeric multilayer optical film 110 and the first substrate 130 (e.g., bonded such that the optical fdm 110 and the substrate 130 cannot be separated without damage, such as cohesive failure, to at least one of the optical film 110, the substrate 130, or the adhesive 120). For example, the first substrate 130 can be a substrate onto which it is desired to bond the optical film 110. The substrate 130 can be one or more of glass or an optical lens, for example. Similarly, the second adhesive layer 125 can be substantially perminately bonded to the optical film 110 and either releasably or substantially perminately bonded to the second substrate 135. In some embodiments, each of the first and second adhesive layers 120, 125 is substantially perminately bonded to the polymeric multilayer optical film 110.

[0030] In some embodiments, the first substrate 130 is an optical lens. In some embodiments, the optical assembly 100, 105 is a component of an optical system such as an augmented / virtual reality system and / or a head-mounted display. The optical assembly 100, 105 can be used as optical components and / or in optical systems such as those described, for example, in U.S. Patent Nos. 10,678,052 (Ouderkirk et al.); 11,630,290 (Yunet al.); and 12,013,559 (Ambur etal.) and in U.S. Pat. Appl. Pub. Nos.

[0031] 2025 / 0035948 (Le et al.) and 2023 / 0314683 (Haag et al.). When the first substrate 130 is curved on a length scale large compared to a length scale on which the waviness is characterized, the xy -plane in FIGS 1 and 2, for example, can correspond to a tangent plane at a point of interest on the curved substrate.

[0032] FIG. 4 is a schematic cross-sectional view of a major surface 113 illustrating slope error, according to some embodiments. The major surface 113 extends primarily in the x'- and y'-directions and has a displacement in the z-direction. The x'- and y'- directions in FIG. 4 may correspond to the x- and y-directions in FIGS. 1-3 or to the x- and y-directions rotated about the z-axis (e.g., by 90 degrees or such that the tangent plane to the curve at the point indicated for the angle Al is parallel to the x' -direction) so that Al depicted in FIG. 4 may correspond to the slope measured along the x-direction or measured along the y-direction, or so that Al depicted in FIG. 4 corresponds to the angle between the tangent plane at the indicated point and the xy -plane, for example. The major surface 113 may be represented by a displacement h of the surface as a function of x- and y-coordinates. Near a point xO, yO, the displacement may be written as h ~ h(x0,y0) + a(x-x0) + b(y-yO) where a and b are constants corresponding to cli / cx and cli / cy. respectively, evaluated at the point xO, yO. Rotating about a z-axis through the point xO, yO to define x", y" coordinates (corresponding to x', y' coordinates in FIG. 4 but shifted to the point of interest) where x" is tangent to the surface at xO, yO, the displacement near the point xO, yO may be written h ~ h(x0,y0) ± (a2+b2)1 / 2y" where the ± depends on the signs of a and b. A slope (corresponding to ± (a2+b2)1 / 2) may be defined at each point of the major surface as the slope of a tangent plane at the point which can be expressed as the tangent of an angle Al between the tangent plane at the point and the xy-plane. The magnitude of the slope (corresponding to (a2+b2)1 / 2) may be calculated as a square root of the sum of a square of the slope (e.g., ch / cx) of the major surface along a first in-plane direction (e.g., x-direction) and a square of the slope (e.g., cli / cy ) of the major surface along an orthogonal second in-plane direction (e.g., y-direction). The angle Al between the major surface 113 and the xy -plane is typically less than a milliradian so that the angle and the tangent of the angle are typically the same to a very good approximation. Slope error can be characterized as described in U.S. Pat. Appl. Pub. No. 2024 / 0012179 (Haag et al.), for example. A bandpass Fourier filter may be used to pass slope error corresponding to waviness or orange peel, while blocking high spatial frequencies correspond to surface roughness (e.g., Ra surface roughness) and blocking low spatial frequencies corresponding to overall surface shape (e.g., surface curvature), for example.

[0033] FIG. 5 is a schematic plot of a bandpass Fourier filter 250 as a function of spatial frequency, according to some embodiments. The bandpass Fourier filter 250 typically includes a pass band 251 between spatial frequencies Fl and F2. Alternatively, or in addition, the bandpass Fourier filter can be characterized in terms of band edge wavelengths W 1 and W2, where F 1 is 1 / W2, and F2 is 1 / W1. The Fourier filter 250 can be substantially unity between the spatial frequencies F 1 and F2 except possibly for spatial frequencies close to Fl and F2. In some embodiments, mean slope error is a mean of a slope magnitude error (e.g., corresponding to Al) determined from a surface profile of a major surface filtered with a same bandpass Fourier filter 250 having band edge wavelengths of W1 and W2, where 0.1 mm < W1 < 0.3 mm, and 2W1 < W2 < 10 mm. The band edge wavelengths W1 and W2 may be described as wavelengths of opposing band edges (e.g., wavelengths where the bandpass Fourier filter is about 0.5) of the pass band 251. In some embodiments, W1 is about 0.2 mm and W2 is about 5 mm, for example.

[0034] Mean slope error can be measured by determining a surface profile (height or displacement as a function of in-plane x- and y-coordinates), then filtering the surface profile with the bandpass Fourier filter, then determining the slope (e.g., corresponding to the angle Al, or the tangent of the angle Al, which can be expressed in radians or microradians) of the fdtered surface profile as a function of the inplane coordinates (x-, and y-coordinates), and then averaging the magnitude of the slope over the in-plane coordinates. The surface profile can be determined using a surface profilometer (e.g., an optical profdometer or a stylus profilometer) when the surface is an exposed outermost major surface or can be determined by interferometry (e.g., for reflective optical films). For example, for a multilayer optical film with layers that reflect in red at a first major surface, the surface profile of the first major surface can be determined using interferometry with a red laser. Typically, waviness of a major surface results from an overall waviness of the optical film (see, e.g., FIG. 3), so that each major surface has a very similar mean slope error. The surface profile of the first major surface of an optical film in an optical stack or assembly may be determined via interferometry measuring from the side of the optical stack or assembly closest to the first major surface, for example.

[0035] FIG. 6 is a schematic illustration of a method 300 of reducing a mean slope error of at least one major surface of an optical film, according to some embodiments. In some embodiments, a method 300 of reducing a mean slope error of at least a first major surface (e.g., at least one of 112, 112', 114, 114') of a polymeric optical film 110 includes forming an optical stack (step 301) by disposing a first curableadhesive layer 120 on the polymeric optical film 110 and disposing a first substrate 130 on the first curable adhesive layer opposite the polymeric optical film 100, where the polymeric optical film 110 has a glass transition temperature Tg, and the first curable adhesive layer 120 has a tan delta (a ratio of imaginary to real parts of shear modulus) of at least 1 for a frequency of 1 Hz and for at least a first temperature T1 where Tg - 35 deg. C < T1 < Tg; and annealing the optical stack (step 302) at the first temperature for at least 10 minutes. In some embodiments, the annealing reduces the mean slope error of the first major surface of the polymeric optical film by at least 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, or 60 percent. In some embodiments, the method 300 further includes, after annealing the optical stack, curing (step 303) the curable adhesive layer 120. In some embodiments, the polymeric optical film 110 incudes a plurality of optical repeat units 220 numbering at least 10 in total (or in a range described elsewhere herein), where each optical repeat unit comprising at least two polymeric layers 222, 224, and where each layer of each optical repeat 220 unit has an average thickness less than about 500 nm (or in a range described elsewhere herein). In some embodiments, the first major surface is an outermost major surface (e.g., 112' or 114') of the plurality of optical repeat units 220.

[0036] Properties (e.g., tan delta, shear modulus) of a curable adhesive layer can be adjusted by suitable selection of monomers, oligomers, and / or polymers used in the adhesive formulation, as would be appreciated by those of ordinary skill in the art. For example, utilizing polymers with long flexible chains and / or including long side groups can result in a high tan delta and low modulus of the curable adhesive.

[0037] In some embodiments, it is desired that when the curable adhesive is cured to form a cured adhesive, the cured adhesive have a high modulus. It has been found, according to some embodiments, that providing an increased modulus upon curing can result in reduced creep which can substantially reduce or prevent waviness increasing over time. For conventional adhesives, including pressure sensitive adhesives, an increase in modulus generally correlates with certain desirable effects, such as an increase in the mechanical strength of the bond, along with an improvement in peel and tensile adhesion. Further technical benefits associated with increased modulus include improved die-cut stability for converting and storage, improving impact resistance and waviness control, and enhanced outgassing resistance of bubbles at elevated humidity and temperature.

[0038] Modifications to increase adhesive modulus without sacrificing other performance parameters such as adhesion have been explored, but many have not been successful. For example, the adhesive could be processed prior to curing as a pressure sensitive adhesive for good lamination and process control, and then modulus increased by adding reactive high glass transition temperature (high-Tg) oligomers or monomers to form a semi-tacky or non-tacky adhesive film. Yet, this approach can often degrade initial adhesion strength, create undesirable “sharkskin” peel from release liners, and require additional lamination steps to achieve adequate wetting of the adhesive to the adherend. Such steps can include, for example, the application of heat to close the bond. Matching these adhesives with release liners that securely couple to the adhesives while providing a clean release therefrom can also be a significant technical challenge.It has been found, according to some embodiments, that these problems can be overcome using a curable adhesive based on a (meth)acrylate-containing polyurethane, one or more (meth)acrylate monomers and / or (meth)acrylate-containing oligomers, a free radical initiator, and polyvinylpyrrolidone (PVP) or a copolymer thereof. Optionally, the curable adhesive can further include a silane adhesion promoter, such as 3-glycidyloxypropyl trimethoxy silane. Without PVP, the modulus of the adhesive typically increases and the mechanical performance (the peeling adhesion) typically decreases with increasing the concentration of reactive high-Tgmonomers and / or oligomers. By incorporating PVP and moderating the amount of reactive monomers / oligomers, both high post-curing modulus and excellent adhesive performance can be achieved simultaneously. As an added benefit, optical films coupled to the adhesive can resist undesirable changes in flatness during assembly by virtue of this decoupling between modulus and adhesive performance. Once film processing is complete, the provided adhesives can be cured to obtain high post-curing modulus while retaining the flatness of bonded optical films.

[0039] In some embodiments, a curable adhesive includes: a poly(meth)acrylate or (methjacrylate-containing polyurethane; one or more (meth)acrylate monomers and / or (meth)acry late -containing oligomers; a free radical initiator; and polyvinylpyrrolidone or copolymer thereof.

[0040] In some embodiments, a method of making a curable adhesive includes: providing a poly(meth)acrylate, or alternatively reacting an aliphatic polyisocyanate with an aromatic polyester polyol to obtain a (meth)acry late-containing polyurethane; and mixing the poly(meth)acrylate or (meth)acrylate-containing polyurethane with one or more (meth)acrylate monomers and / or (meth)acrylate-containing oligomers, a free radical initiator, optionally an adhesion promoter comprised of a silane adhesion promoter, and polyvinylpyrrolidone or copolymer thereof to obtain the curable adhesive.

[0041] In some embodiments, a method of making a bonded assembly includes: disposing the curable adhesive between opposing major surfaces of first and second adherends, wherein the free radical initiator comprises a photoinitiator; and exposing the curable adhesive to actinic radiation to obtain a cured adhesive, where the cured adhesive has a tan delta of from 0.2 to 1 when tested at 70°C and a frequency of 1 Hz and a storage modulus of at least 500 kPa under ambient conditions.

[0042] As used herein:

[0043] “alkyl” refers to a monovalent group that is a radical of an alkane and includes straight-chain, branched, cyclic, and bicyclic alkyl groups, and combinations thereof, including both unsubstituted and substituted alkyl groups. Unless otherwise indicated, the alkyl groups typically contain from 1 to 30 carbon atoms. In some embodiments, the alkyl groups contain 1 to 20 carbon atoms, 1 to 10 carbon atoms, 1 to 6 carbon atoms, 1 to 4 carbon atoms, or 1 to 3 carbon atoms. Cyclic groups can be monocyclic or polycyclic and typically have from 3 to 10 ring carbon atoms. Examples of “alkyl” groups include methyl, ethyl, n-propyl, n-butyl, n-pentyl, isobutyl, t-butyl, isopropyl, n-octyl, n-heptyl, ethylhexyl, cyclopentyl, cyclohexyl, cycloheptyl, adamantyl, and norbomyl.

[0044] “allyl” refers a functional group having the formula CH2=CH-CH2-.“ambient conditions” means at 21°C and 101.3 kilopascals.

[0045] “ambient temperature” means 21 °C.

[0046] “curable adhesive” refers to an adhesive that can be cured.

[0047] “cure” refers to the joining of polymer chains together by covalent chemical bonds, usually via crosslinking molecules or groups, to form a network polymer. Therefore, in this disclosure the terms “cured” and “crosslinked” may be used interchangeably. A cured or crosslinked polymer is generally characterized by insolubility but may be swellable in the presence of an appropriate solvent.

[0048] “halogen” refers to a halogen atom or one or more halogen atoms, including chlorine, bromine, iodine, and fluorine atoms or fluoro, chloro, bromo, or iodo substituents.

[0049] “(methjacrylate group” refers to a functional group that is either an acrylate group of the formula CH2=CH-C(O)O- or a methacrylate group of the formula CH2=C(CH3)-C(O)O-.

[0050] “molecular weight” refers to weight average molecular weight, unless otherwise indicated. “oligomer” refers to a molecule that comprises at least two repeat units and that has a molecular weight less than its entanglement molecular weight; such a molecule, unlike a polymer, exhibits a significant change in properties upon the removal or addition of a single repeat unit.

[0051] “weight average molecular weight” is a parameter reflecting the weight fraction of individual polymer chains in a polymer sample and measured using known gel permeation chromatography (GPC) techniques.

[0052] In various embodiments, the provided adhesive compositions include a poly(meth)acrylate or (methjacrylate-containing polymethane; one or more (methjacrylate monomers or (methjacrylate-containing oligomers; a free radical initiator; polyvinylpyrrolidone or a copolymer thereof, and optionally, a silane adhesion promoter.

[0053] Poly(meth)acrylates are inclusive of acrylic polymers in general and need not be particularly limited. Useful poly(meth)acrylates can be homopolymers or copolymers polymerized alkyl (methjacrylate monomers, such as an alkyl (methjacrylate containing an alkyl group including from 4 to 18 carbon atoms.

[0054] To provide strong adhesion and / or flexibility to the fully cured adhesive and obtain good wettability to an adherend, it can be beneficial for the poly(meth)acrylate to contain polymerized units of one or more alkyl (methjacrylate monomers whose respective homopolymers have a glass transition temperature of 25°C or lower. Suitable alkyl (methjacrylates can include, for example, n-butyl acrylate, isobutyl acrylate, isoamyl acrylate, hexyl acrylate, cyclohexyl acrylate, 2-ethylhexyl (methjacrylate, isooctyl (methjacrylate, isononyl (methjacrylate, n-decyl (methjacrylate, isodecyl (methjacrylate, lauryl (methjacrylate, isomyristyl (methjacrylate, isocetyl (methjacrylate or isostearyl (methjacrylate.

[0055] In combination with any of the monomers above, an alkyl (methjacrylate monomer having an alkyl group of 4 to 18 carbon atoms whose homopolymer has a glass transition temperature of 25°C or higher can also be used. Examples of the alkyl (methjacrylate having an alkyl group of 4 to 18 carbon atoms whose homopolymer has a glass transition temperature (Tg) of 25°C or higher include linear orbranched alkyl (meth)acrylates such as t-butyl (meth)acrylate, n-butyl methacrylate and isobutyl methacrylate; and alicyclic alkyl (meth)acrylates such as cyclohexyl methacrylate, 4-t-butylcyclohexyl (meth)acrylate and isobomyl (meth)acrylate. Having polymerized units of alkyl (meth)acrylate monomers associated with higher Tgas noted above can be beneficial because these monomers can impart enhanced mechanical behavior in the cured adhesive to impart greater resistance to debonding.

[0056] Other alkyl (meth)acrylates that can be included in the poly(methacrylate) copolymer are classified as high-Tgmonomers based on the glass transition temperature of the corresponding homopolymers. The high-Tgmonomers often have a Tg greater than 30°C, greater than 40°C, or greater than 50°C when homopolymerized (i.e., a homopolymer formed from the monomer has a Tg greater than 30°C, greater than 40°C, or greater than 50°C). Some suitable high-Tgalkyl (meth)acrylate monomers include, for example, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, sec -butyl methacrylate, tert-butyl (meth)acrylate, cyclohexyl methacrylate, isobomyl (meth)acrylate, stearyl (meth)acrylate, and 3,3,5-trimethylcyclohexyl (meth)acrylate.

[0057] In some embodiments, it can be further advantageous for the poly(meth)acrylates to include polymerized units of one or more hydrophilic monomers whose homopolymer has a Tgof 10°C or lower. These monomers may enable greater association with substrates of interest, improved electrical properties and moisture management, or improved cohesive strength within the adhesive. Examples of the hydrophilic monomer whose homopolymer has a Tgof 10°C or lower.

[0058] Useful monomers include hydroxyalkyl acrylates having an alkyl group of 4 or fewer carbon atoms, and a (meth)acrylic compound having an oxyethylene group or an oxypropylene group, or a polyoxyethylene group or a polyoxypropylene group. Particular examples include, but are not limited to, 2 -hydroxyethyl acrylate and hydroxypropyl acrylate. Among these, in view of imparting flexibility to the adhesive layer, the hydrophilic monomer is preferably a hydrophilic monomer whose homopolymer has a Tgof 0°C or lower, and more preferably a hydrophilic monomer whose homopolymer has a glass transition temperature of -5°C or lower, such as 2-hydroxyethyl acrylate or 2-hydroxypropyl acrylate.

[0059] In some embodiments, the (meth)acrylate polymer may include a non-hydroxy functional polar copolymerizable monomer. Examples of suitable non-hydroxy functional polar copolymerizable monomers include, but are not limited to: acrylic acid, methacrylic acid, itaconic acid, fumaric acid, ether functional monomers such as 2 -ethoxy ethyl (meth)acrylate, 2-ethoxyethoxyethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, nitrogen containing monomers such as acrylamide, methacrylamide, N-alkyl substituted and N,N-dialkyl substituted acrylamides or methacrylamides where the alkyl group has up to 3 carbons, and N-vinyl lactams. Examples of suitable substituted amide monomers include, but are not limited to: N,N-dimethylacrylamide, N,N-diethyl acrylamide, N-morpholino (meth)acrylate, N-vinyl pyrolidone and N-vinyl caprolactam. In some embodiments, the (meth)acrylate polymer can include between 0 and 25 parts by weight of the polar copolymerizable monomer, particularly between 1 and 20 parts, and more particularly between 1 and 15 parts.In some embodiments, the (meth)acrylate polymer may include a vinyl ester, and particularly a Cl to CIO vinyl ester. An example of commercially available suitable vinyl esters include, but are not limited to, vinyl acetate and VEOVA 9 or VEOVA 10 (available from Momentive Specialty Chemicals, New Smyrna Beach, Florida).

[0060] In some embodiments, the (meth)acrylate polymer may include a polar (meth)acrylate monomer. Examples of suitable polar (meth)acrylate monomers include, but are not limited to, hydroxy ethyl acrylate, hydroxypropyl acrylate, hydroxylbutyl acrylate, tetrahydrofuryl acrylate, acrylamide, N,N-dimethyl acrylamide, N-vinyl pyrrolidone, and acrylic acid.

[0061] In some embodiments, the (meth)acrylate polymer may include a monofunctional non-(meth)acrylate vinyl monomer. Examples of suitable monofunctional non-(meth)acrylate vinyl monomers include but are not limited to: N-vinyl pyrrolidone, N-vinyl carbazole, vinyl acetate, and vinyl ether.

[0062] The poly(meth)acrylate may be a copolymer that also comprises pendant vinyl groups, such as pendent acrylate groups, that can undergo further free radical addition. In one embodiment, the functionalized copolymer may be formed by firstly polymerizing a mixture of monomers comprising at least one (Cl -Cl 8) alkyl (meth)acrylate monomer and a hydroxy containing (meth)acrylate monomer. After polymerization, a portion of pendant hydroxyl groups may be further converted to pendant unsaturated (meth)acrylate groups.

[0063] In one embodiment, unsaturated pendent groups may grafted through the reaction of isocyananatoethyl (meth)acrylate with the hydroxy groups of the copolymer. The IEM creates the pendant unsaturated groups on the copolymer after thermal processing. An example of a commercially suitable isocyananatoethyl (meth)acrylate includes 2-isocyanatoethyl acrylate and 2-isocyanatoethyl methacrylates sold under the trade designations KARENZAOI and KARENZMOI from Showa Denko, Toyko, Japan.

[0064] (Meth)acry late-containing polyurethanes can have a polyurethane backbone. Polyurethanes are generally made by reacting a polyisocyanate component with a polyol component.

[0065] The polyol component comprises an aromatic and / or aliphatic polyester or polycaprolactone polyol that comprises at least two hydroxyl terminal groups. When the polyol averages two or three hydroxyl groups, it may be characterized as a diol or triol, respectively. In yet other embodiments, the polyol may include a mixture of one or more diols and one or more triols, wherein the number of hydroxyl groups averages greater than 2, yet less than 3. Other polyols can have 4, 5 or 6 hydroxyl terminal groups.

[0066] Polyester polyols can be obtained by, for example, an esterification reaction between a polyol component and an acid component. Examples of acid components include succinic acid, methylsuccinic acid, adipic acid, pimelic acid, azelaic acid, sebacic acid, 1,12-dodecanedioic acid, 1,14-tetradecanedioic acid, dimer acid, 2-methyl-l,4-cyclohexanedicarboxylic acid, 2-ethyl-l,4-cyclohexanedicarboxylic acid, terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 4,4'-biphenyldicarboxylic acid, and acid anhydrides thereof.The polyol component can be, in some embodiments, an aromatic polyester polyol. An aromatic polyester polyol can be produced by polymerizing an aromatic dicarboxylic acid with an aliphatic diol, as known in the art. In some embodiments, the aromatic dicarboxylic acid includes isophthalic acid or phthalic acid. The polyester polyol may optionally be produced from some amount of other aromatic dicarboxylic acid such as terephthalic acid. Optionally, the polyester polyol can be produced from cycloaliphatic dicarboxylic acids such as 1,3 -cyclopentanedicarboxy lie acid; 1,2-cyclohexanedicarboxylic acid; 1,4-cyclohexanedicarboxylic acid; or 2,5-norbomanedicarboxylic acid. These dicarboxylic acids are commonly provided in the form of acid anhydrides.

[0067] The aliphatic diol used to produce the aromatic or aliphatic (e.g., polyester or polycarbonate) polyol can include a straight-chain or branched alkylene group such as ethylene glycol, diethylene glycol, propylene glycol, 1,3 -propanediol, 1,3 -butanediol, 1,4 -butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 2,4-dimethyl-2-ethylhexane-l,3-diol, 2,2-dimethy 1-1, 3 -propanediol (neopentyl glycol), 2-ethyl-2-butyl-l,3-propanediol, 2-ethy 1-2 -isobutyl- 1,3-propanediol, 3 -methyl- 1,5 -pentanediol, 2, 2, 4-trimethyl- 1,6-hexanediol, octadecanediol, and the like. At least one of the aliphatic diols can include a straight-chain or branched alkylene group comprising from 4 to 36 carbon atoms, or in some embodiments, less than, equal to, or greater than 4, 5, 6, 8, 10, 12, 15, 17, 20, 22, 24, 26, 28, 30, 32, or 36 carbon atoms.

[0068] In some embodiments, the polyol can comprise a polycaprolactone polyol. The polycaprolactone polyol can be obtained by subjecting a cyclic ester monomer such as epsilon-caprolactone or sigma-valerolactone to ring-opening polymerization. Polycaprolactone polyols comprise an alkylene group having 5 carbon atoms.

[0069] In some embodiments, the polyol component can comprise a polycarbonate polyol such as obtained from the reaction of aliphatic diols such as butanediol-(l,4) and / or hexanediol-(l,6) with phosgene, diaryl-carbonates such as diphenylcarbonate or with cyclic carbonates such as ethylene or propylene carbonate. Also suitable are polyester carbonates obtained from the above-mentioned polyesters or polylactones with phosgene, diaryl carbonates or cyclic carbonates. The preparation of the polyester or polycarbonate polyol generally includes utilizing at last one aliphatic diol as previously described. The alkylene group of the aliphatic diol and polyester or polycarbonate polyol may comprise hydrophobic substituents such halogen substituents. One illustrative polycarbonate polyol is sold from Covestro AG under the trade designation DESMOPHEN C2200.

[0070] In some embodiments, a single aliphatic diol is used to prepare the polyol. In this embodiment, the aliphatic diol comprises an alkylene group comprising at least 4, 5, or 6 carbon atoms as previously described. Alternatively, two or more aliphatic diol may be used in the preparation of the polyol wherein at least one of such diols comprises an alkylene group comprising at least 4, at least 5, or least 6 carbon atoms. When a mixture of aliphatic diols are used, at least 50, 60, 70, 80, 90 or 95 wt-% of the total amount of diol are alkylene groups comprising at least 4, 5, or 6 carbon atoms as previously described.The polyol is typically a polymer. The polyol can have an equivalent weight (molecular weight per hydroxyl group) ranging from about 250 g / mol to about 30,000 g / mol. In some embodiments, the equivalent weight of the polyol is from 500 g / mol to 30,000 g / mol, from 2000 g / mol to 20,000 g / mol, from 2000 g / mol to 10,000 g / mol, from 2000 g / mol to 4000 g / mol, or in some embodiments, less than, equal to, or greater than 250 g / mol; 500; 1000; 2000; 3000; 3500; 4000; 5000; 6000; 7000; 8000; 10,000; 20,000; or 30,000 g / mol. For diols and triols, typical molecular weights for the polyol can be two or three times of the equivalent weight ranges above, respectively. In some embodiments, the polymeric polyol has a molecular weight of less than 4000, 3500, or 3000 g / mole.

[0071] In some embodiments, the aliphatic polyester polyol includes repeat units comprised of an alkylene group and a terminal ester group or more than one alkylene group bonded by means of an ester linkage and a terminal ester group.

[0072] In other embodiments, the aliphatic polycarbonate polyol can include repeat units comprising an alkylene group and a terminal carbonate group or more than one alkylene group bonded by means of a carbonate linkage and a terminal carbonate group.

[0073] In still other embodiments, the aromatic polyester polyol may include polymerized units comprised of an aromatic group of the dicarboxylic acid bonded to the alkylene group of the aliphatic diol by ester linkages. In this embodiment, the molar ratio of six-member rings to alkylene groups having at least 4, 5, or 6 carbon atoms can be approximately 1:1 and can range from about 1.5:1 to 1:1.5.

[0074] In a preferred embodiment, an aromatic polyester polyol is used that can be obtained by reacting an aromatic ortho- or meta-dicarboxylic acid anhydride component and an aliphatic diol component. Thus, the polyol component comprises polymerized units of an ortho- or meta-phthalate and comprises polymerized units of an alkylene group comprising at least 4 carbon atoms.

[0075] In some embodiments, the polyester polyol is prepared from isophthalic acid or phthalic acid, and represented by structure I below:

[0076]

[0077] where R1 is independently an alkylene group comprising at least 4 carbon atoms, n is at least 2, 3, 4 or 5, and the ester group substituents are bonded to the ring at an ortho- or meta-position.

[0078] In some embodiments, n is no greater than 25, 20, 15, or 10. When the aromatic polyester polyol includes ortho- or meta-ester moieties, the polyester polyol tends to have a relatively low glass transition temperature, such as less than 0°C, less than 5°C, or less than 10°C. Further, such aromatic polyesterpolyols tend to be amorphous viscous liquids at 25°C. In some embodiments, the aromatic polyester polyols have a viscosity of less than 10,000 cP, or even less than 5,000 cP at 80°C.

[0079] Aromatic polyester polyols derived from orthophthalic acid are commercially sold from Stepan Co. under the trade designation STEPANPOL. These can be represented, for example, by structure II below:

[0080]

[0081] where R1 and n have any of the values set out above.

[0082] When the aromatic polyester polyol is derived from isoterephthalic acid, the polyester polyol can be represented by structure III below:

[0083]

[0084] where R1 and n have any of the values set out above.

[0085] The poly isocyanate component can be any of various polyfunctional isocyanate compounds. Examples of such polyfunctional isocyanate compounds include polyfunctional aliphatic isocyanate compounds, polyfunctional aliphatic cyclic isocyanate compounds, and a polyfunctional aromatic isocyanate compounds. Examples of the polyfunctional aliphatic isocyanate compounds include trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, 1,2-propylene diisocyanate, 1,3 -butylene diisocyanate, dodecamethylene diisocyanate, and 2,4,4 -trimethylhexamethylene diisocyanate .

[0086] Examples of polyfunctional aliphatic cyclic isocyanate compounds include 1,3 -cyclopentene diisocyanate, 1,3 -cyclohexane diisocyanate, 1,4-cyclohexane diisocyanate, isophorone diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated xylylene diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated tetramethylxylene diisocyanate, partially bio-based aliphatic isocyanate polymer sold under the trade designation TOLONATE X FLO 100 from Vencorex US, Inc., Freeport, TX, and bio-based polyfunctional aliphatic cyclic isocyanates, such as 2-heptyl-3,4-bis(9-isocyanatononyl)-l-pentylcyclohexane sold by BASF Corporation under the trade designation DDI 1410.

[0087] Examples of polyfunctional aromatic isocyanate compounds include phenylene diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 2,2'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, 4,4'-toluidine diisocyanate, 4,4'-diphenyl ether diisocyanate, 4,4'-diphenyl diisocyanate, 1,5 -naphthalene diisocyanate, and xylylene diisocyanate.

[0088] In some embodiments, the polyfunctional isocyanate comprises a polyisocyanate that is a liquid at 25°C, either alone or in combination with minor amount of a polyisocyanate that is solid at 25°C. In other embodiments, such as when the polyol is an aliphatic polyol, the polyfunctional isocyanate could be a solid at 25°C.

[0089] In some embodiments, the polyfunctional isocyanate compound comprises an aliphatic isocyanate compound, such as hexamethylene diisocyanate. In other embodiments, the polyfunctional isocyanate compound comprises a ortho- or meta-aromatic isocyanate compound, such as 1,4 methylene diphenyl diisocyanate (MDI), m-tetramethylene diisocyanate (TMXDI), or mixtures thereof. Mixtures of aliphatic and aromatic polyfunctional isocyanate compounds are also possible.

[0090] The (meth)acrylate functionality of the (meth)acry late-containing polyurethane can be provided by including a suitable (meth)acrylate-containing alcohol or isocyanate in the polymerization reaction used to obtain the (meth)acrylate-containing polyurethane. In some embodiments, the (meth)acrylate-containing polyurethane is a linear polyurethane containing pendent acrylate groups. The (meth)acrylate-containing polyurethane can be present in an amount of from 10 wt% to 99 wt%, from 40 wt% to 97 wt%, from 70 wt% to 95 wt%, or in some embodiments less than, equal to, or greater than 10 wt%, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 96, 97, 98, or 99 wt% relative to the overall weight of the curable adhesive.

[0091] The polymer architecture above can be synthesized by reacting a compound comprising one or more hydroxy groups and one or more ethylenically unsaturated groups together with the aforementioned polyisocyanate and polyol components in a reactive mixture. In a preferred embodiment, the polyisocyanate is an aliphatic polyisocyanate and the polyol is an aromatic polyester polyol.

[0092] From the reactive mixture, the hydroxyl group reacts with the polyisocyanate component, incorporating ethylenically unsaturated groups into the polyurethane. In some embodiments, compound having a single hydroxyl group and a (meth)acrylate monomer having a single ethylenically unsaturated group can be used, such as hydroxyethyl acrylate (HEA). In some embodiments, an isocyanate group is bonded to the polyurethane polymer backbone and the opposing end of the diisocyanate is bonded to the hydroxyl group of the compound resulting in a terminal ethylenically unsaturated group.

[0093] In other embodiments, the (meth)acrylate-containing polyol includes at least two hydroxy groups and at least two ethylenically unsaturated groups, such as bisphenol A glycerolate dimethacrylate (Bis-GMA). In this embodiment, the compound reacts as a polyol and is thereby incorporated into the polyurethane backbone, where the ethylenically unsaturated groups are pendent with respect to the polyurethane backbone.

[0094] The one or more (meth)acry late-containing polyols can be present, independently, in an amount of from 0.1 wt% to 20 wt%, from 0.2 wt% to 10 wt%, from 0.5 wt% to 5 wt%, or in some embodimentsless than, equal to, or greater than 0.1 wt%, 0.2, 0.5, 1, 2, 2.5, 3, 4, 5, 7, 10, 11, 12, 15, 17, or 20 wt%, relative to the overall weight of the reactive mixture.

[0095] Various compounds comprising one or more hydroxy groups and one or more ethylenically unsaturated groups can be used during the preparation of the polyurethane. Such compound can be aliphatic or aromatic. Other representative compounds sold by Nagase ChemteX Corporation, Osaka, Japan include for example epoxy acrylate form 1,6 hexane diol, sold under the trade designation DA-212, or epoxy acrylate form 1,4 hexane diol, sold under the trade designation DA-214L.

[0096] The provided curable adhesive composition further incorporates one or more (meth) aery late monomers and / or (meth)acrylate-containing oligomers. These monomers and / or oligomers can be blended with the poly(meth)acrylate or (meth)acrylate-containing polyurethane to obtain a reactive mixture and eventually cured to form a crosslinked network at the time of bonding.

[0097] In some embodiments, the reactive mixture includes a urethane acrylate oligomer, such as sold under the trade designation CN983 by Arkema, Colombes, France. In other embodiments, the reactive mixture includes an ethoxylated triacrylate, such as sold under the trade designation SR415 by Arkema, Colombes, France. Both urethane acrylate oligomers and ethoxylated triacrylate can effectively function as crosslinkers, but the latter monomer is somewhat more hydrophilic and was found to improve haze performance after the cured adhesive is subjected to high temperature high humidity aging.

[0098] In some embodiments, the (methjacrylate-containing oligomers are comprised of a polyester-based urethane diacrylate oligomer. Suitable (methjacrylate-containing oligomers can have a homopolymer Tgof greater than 30°C, 40°C, or even 50°C.

[0099] Other monomers having multiple (methjacryloyl groups can be combined with a (methjacrylate copolymer or polyurethane with pendent (methjacrylate groups. These monomers can be added to adjust the crosslink density and increase the modulus of the cured (methjacrylate copolymer or polyurethane. These monomers can react with pendent (methjacryloyl groups of the curable (methjacrylate copolymer or polyurethane when exposed to ultraviolet or visible light radiation in the presence of a photoinitiator. If added, the amount of these monomers is typically in the range of 0 to 40 parts per hundred (pph) based on the weight of the curable (methjacrylate copolymer. For example, this amount can be less than, equal to, or greater than 1 pph, 2, 5, 10, 15, 20, 25, 30, 35, or 40 pph.

[0100] Exemplary monomers having two (methjacryloyl groups include bisphenol A diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylatfe, tetraethylene glycol diacrylate, tripropylene glycol diacrylate, polyethylene glycol diacrylate (e.g., commercially sold from Arkema under the trade designation SR-210, SR-252, and SR-603), polypropylene glycol diacrylate, ethoxylated (30) bisphenol A dsacrylaie (e.g., commercially sold from Arkema under the trade designation SR9038), polyethylene / polypropylene copolymer diacrylate, neopentylglycol hydroxypivalate diacrylate modified caprolactone, and polyurethane diacrylates (e.g., commercially sold by Arkema under the trade designation CN2920. CN9178, and CN983, and from Eternal Materials Co. Ltd. under trade designation ETERCURE 282).Exemplary monomers having three or four (meth)acryloyl groups include, but are not limited to, trimethylolpropane triacrylate (e.g., commercially sold under the trade designation TMPTA-N from Surface Specialties, Smyrna, GA and under the trade designation SR-351 from Sartomer, Exton, PA), ethoxylated trimethylolpropane triacrylate (e.g.g commercially sold under the trade designation SR 9035 from Sartomer), pentaerythritol triacrylate (e.g., commercially sold under the trade designation SR-444 from Sartomer), tris(2-hydroxyethylisocyanurate) triacrylate (commercially sold under the trade designation SR-368 from Sartomer), a mixture of pentaerythritol triacrylate and pentaerythritol tetraacrylate (e.g., commercially sold from Surface Specialties under the trade designation PETIA with an approximately 1 : 1 ratio of tetraacrylate to triacrylate, and under the trade designation PETA-K with an approximately 3:1 ratio of tetraacrylate to triacrylate), pentaerythritol tetraacrylate (e.g., commercially sold under the trade designation SR-295 from Sartomer), di-trimethylolpropane tetraacrylate (e.g., commercially sold under the trade designation SR-355 from Sartomer), and ethoxylated pentaerythritol tetraacrylate (e.g., commercially sold under the trade designation SR-494 from Sartomer). An exemplary crosslinker with five (meth)acryloyl groups includes, but is not limited to, dipentaerythritol pentaacrylate (e.g., commercially sold under the trade designation SR-399 from Sartomer).

[0101] Advantageously, the curable adhesive composition further incorporates homopolymers or copolymers of substantially polar and high-Tgmonomeric units. In some preferred embodiments, the homopolymers or copolymers derive from polyvinylpyrrolidinone (PVP), sometimes referred to as povidone. PVP can be in the form of polyvinylpyrrolidinone homopolymer, polyvinylpyrrolidinone copolymer, or a combination thereof. Polyvinylpyrrolidinone is a non-ionic synthetic polymer composed of repeating 1 -vinyl-2 -pyrrolidone monomers. The repeat unit for PVP is represented by stmcture IV below:

[0102]

[0103] PVP is known for use in the pharmaceutical industry as a binder in tablet manufacturing and is soluble in water as well as in many organic solutions. This property is the result of hydrophilic and hydrophobic functional groups that can interact with varying solvents, with viscosity being largely unaffected by electrolytes. It was discovered, surprisingly, that the addition of PVP in the provided curable polyurethane-based or poly(meth)acry late-based adhesive compositions can yield a high adhesive modulus and substantially alleviate degradation of adhesive performance that normally occurs when the modulus of the adhesive composition is substantially increased upon curing.

[0104] PVP copolymers can include random and block copolymers of PVP. A useful PVP random copolymer is N-vinylpyrrolidone-co-vinyl acetate copolymer, also known as copovidone, and used widely as dry and wet binder in tablets in the pharmaceutical industry. Compared to povidone,copovidone is less hygroscopic and absorbs less water. Copolymers such as copovidone may also enable greater compatibility with the curable poly(meth)acrylate or curable polyurethane polymer.

[0105] The PVP or copolymer thereof can have a weight average molecular weight of from 1000 g / mol to 75,000 g / mol, from 1,500 g / mol to 60,000 g / mol, from 2,000 g / mol to 50,000 g / mol, or in some embodiments, less than, equal to, or greater than 1,000 g / mol; 1,500; 2,000; 5,000; 10,000; 20,000; 30,000; 40,000; 50,000; 60,000; 75,000; 100,000; 500,000, or 1,000,000 g / mol.

[0106] The PVP or copolymer thereof can be present in any suitable amount to obtain the desired adhesive modulus after curing. Typically, the amount of PVP or copolymer thereof is from 2 wt% to 30 wt%, from 5 wt% to 20 wt%, from 5 wt% to 15 wt%, or in some embodiments, less than, equal to, or greater than 2 wt%, 3, 4, 5, 7, 10, 12, 15, 17, 20, 25 or 30 wt%, relative to the overall weight of the curable adhesive.

[0107] The curable adhesive composition typically includes one or more free radical initiators enabling the curable adhesive composition to be cured.

[0108] In a preferred embodiment, the free radical initiator is a photoinitiator activated by actinic radiation. Useful photoinitiators include benzoin ethers such as benzoin methyl ether and benzoin isopropyl ether; substituted acetophenones such as 2, 2-dimethoxy -2 -phenylacetophenone photoinitiator, sold under the trade designation 1-651, sold by Merck KGaA, Darmstadt, Germany or ESACURE KB-1 photoinitiator, sold by Lehvoss Group, Hamburg, Germany, and dimethylhydroxyacetophenone; substituted a-ketols such as 2-methyl-2 -hydroxy propiophenone; aromatic sulfonyl chlorides such as 2-naphthalene-sulfonyl chloride; photoactive oximes such as l-phenyl-l,2-propanedione-2-(O-ethoxy-carbonyl)oxime; mono- or bis-acrylphosphine oxides sold under the trade designations IRGANOX 819 from BASF SE, Ludwigshafen, Germany or LUCIRIN TPO from Merck KGaA.

[0109] Preferred photoinitiators are photoactive compounds that undergo a Norrish I cleavage to generate free radicals that can initiate by addition to the acrylic double bonds. The photoinitiator can be added to the mixture to be coated after the polymer has been formed. Exemplary polymerizable photoinitiators are described, for example, in U.S. Patent Nos. 5,902,836 and 5,506,279 (Gaddam et al.).

[0110] Thermal free radical initiators are also possible, for which activation occurs through the application of heat rather than through exposure to actinic radiation. Such initiators include, but are not limited to, azo, peroxide, persulfate, and redox initiators, and combinations thereof. Further options and associated advantages relating to free radical thermal and photopolymerization techniques are described in U.S. Patent Nos. 4,654,233 (Grant et al.); 4,855,184 (Klun et al.); and 6,224,949 (Wright et al.).

[0111] Free radical initiators can be present in an amount of from 0.1 wt% to 5 wt%, or in some embodiments, less than, equal to, or greater than 0.1 wt%, 0.2, 0.5, 1, 2, 3, 4, or 5 wt%, based on the overall weight of the uncured composition.

[0112] For improved adhesive performance, adhesion promoting additives, such as silanes and titanates can be incorporated therein. Such additives can promote adhesion between the adhesive and the substrates, such as the glass and cellulose triacetate of a liquid crystal display (LCD) by coupling to thesilanol, hydroxyl, or other reactive groups in the substrate. The silanes and titanates may have only alkoxy substitution on the silicon or titanium atom connected to an adhesive copolymerizable or interactive group. Alternatively, the silanes and titanates may have both alkyl and alkoxy substitution on the silicon or titanium atom connected to an adhesive copolymerizable or interactive group.

[0113] The adhesive copolymerizable group is generally an acrylate or methacrylate group, but vinyl and allyl groups may also be used. Alternatively, the silanes or titanates may also react with functional groups in the adhesive, such as a hydroxyalkyl (meth)acrylate. In addition, the silane or titanate may have one or more group providing strong interaction with the adhesive matrix. Examples of this strong interaction include hydrogen bonding, ionic interaction, and acid-base interaction. An example of a preferred silane is (3-glycidyloxypropyl)trimethoxysilane.

[0114] In some embodiments, a silane adhesion promoter is present in an amount of from 0.02 wt% to 1 wt%, from 0.04 wt% to 0.5 wt%, or in some embodiments less than, equal to, or greater than 0.02, 0.04, 0.05, 0.1, 0.2, 0.5, 1, 2, or 5 wt%, relative to the overall weight of the curable adhesive.

[0115] In a preferred method of making the curable adhesive, an aliphatic polyisocyanate is reacted with an aromatic polyester polyol to obtain a (meth)acry late-containing polyurethane in a common solvent, as appropriate. Suitable solvents for the reactive components can include ethyl acetate and methyl ethyl ketone. The (meth)acrylate-containing polyurethane can then be mixed with one or more (meth)acrylate monomers and / or (meth)acrylate-containing oligomers, a free radical initiator, an adhesion promoter comprised of a silane adhesion promoter, and polyvinylpyrrolidone or similar copolymer thereof. As explained previously, a poly (meth)acrylate can be substituted for the (meth)acry late-containing polyurethane above, where the poly(meth)acrylate can include unsaturated pendent groups to facilitate further crosslinking in the cured adhesive.

[0116] Where a solvent is used, the solution can be cast onto a surface and then the solvent removed through a separate drying step at elevated temperatures to obtain a uniform curable adhesive layer.

[0117] Related curable adhesives are described in International Appl. No. PCT / IB2024 / 058296, filed August 26, 2024.

[0118] In some embodiments, the first curable adhesive layer 120 has a tan delta of at least 1, 1.05, 1.1, 1.15, 1.2, 1.25, or 1.3 for a frequency of 1 Hz and for at least a first temperature below, and within 35 deg. C of, a glass transition temperature of the polymeric optical film (or the first temperature can be in another range described elsewhere herein). In some such embodiments, or in other embodiments, upon curing the first curable adhesive layer to form a cured adhesive layer, the cured adhesive layer has a tan delta of less than 0.8, 0.7, 0.6, 0.55, or 0.5 at the first temperature and at 1 Hz. In some such embodiments, or in other embodiments, the real part of the shear modulus of the first curable adhesive layer 120 at the first temperature and at 1 Hz is no more than about 300, 250, 200, 150, 100, 50, 45, 40, 35, 30, or 25 kPa. In some such embodiments, or in other embodiments, the first curable adhesive layer 120 has a refractive index in a range of 1.48 to 1.58 at a wavelength in a range of about 400 nm to about 700 nm. For example, in some embodiments, the first curable adhesive layer 120 has a refractive index ina range of 1.50 to 1.55 at a wavelength of about 633 nm. The second curable adhesive layer 125 may have any of the properties (e.g., tan delta, shear modulus, refractive index) described for the first curable adhesive layer 120.

[0119] In some embodiments, the first curable adhesive layer 120 comprises (meth)acrylate-containing polyurethane. In some embodiments, the polyurethane has an intrinsic viscosity (IV) in methyl ethyl ketone (MEK) in a range of 0.4 to 0.65 dl / g at room temperature (e.g., 25 deg. C). In some embodiments, the first curable adhesive layer 120 comprises polyvinylpyrrolidone or a copolymer thereof. In some embodiments, the first curable adhesive layer 120 comprises a poly(meth)acrylate or (meth)acrylate-containing polyurethane; one or more (meth)acrylate monomers, one or more (meth)acry late-containing oligomers, or both; a free radical initiator; and polyvinylpyrrolidone or a copolymer thereof.

[0120] The composition of the second curable adhesive layer 125 may be as described for the first curable adhesive layer 120. The composition of the second curable adhesive layer 125 may be the same or different from the composition of the first curable adhesive layer 120.

[0121] In some embodiments, an optical assembly 105 includes first and second adhesive layers 120 and 125 disposed between, and bonding together, the polymeric multilayer optical film 110 and the respective first and second substrates 130 and 135. In some embodiments, each of the first and second adhesive layers comprises a cured product of a curable adhesive, where the curable adhesive comprises a poly(meth)acrylate or (meth)acrylate-containing polyurethane; one or more (meth)acrylate monomers, one or more (meth)acrylate-containing oligomers, or both; a free radical initiator; and polyvinylpyrrolidone or a copolymer thereof.

[0122] In some embodiments, an optical assembly 100, 105 includes a first substrate 130; a polymeric optical film 110; and a first adhesive layer 120 disposed between, and bonding together, the polymeric optical film 110 and the first substrate 130. In some embodiments, for at least one major surface (e.g., 112, 114, 112', 114') of the polymeric optical film 110, the major surface has a mean slope error of less than 100, 90, 80, 70, 60, 55, 50, 45, 42, 40, 49, 38, 37, 36, 35 microradians. The mean slope error is a mean of a slope magnitude error determined from a surface profile of the major surface filtered with a bandpass Fourier filter that can have band edge wavelengths of about 0.2 mm and about 5 mm, for example, or the band edge wavelengths can be in ranges described elsewhere herein. In some embodiments, the first adhesive layer 120 comprises a cured product of a curable adhesive, where the curable adhesive comprises a poly(meth)acrylate or (methjacrylate-containing polyurethane; one or more (methjacrylate monomers, one or more (methjacrylate-containing oligomers, or both; a free radical initiator; and polyvinylpyrrolidone or a copolymer thereof. In some embodiments, the optical assembly 105 further includes a second substrate 135 disposed on an opposite side of the polymeric optical film 110 from the first substrate 130; and a second adhesive layer 125 disposed between, and bonding together, the polymeric optical film 110 and the second substrate 135. The second adhesive layer 125 can be as described for the first adhesive layer 120.EXAMPLES

[0123] Materials

[0124]

[0125] Mean Slope Error (MSE) Measurement

[0126] Surface profile was measured as follows. A 4-D ACCUFIZ Fizeau interferometer using a 633 nm wavelength laser with the polarization aligned with the block state of the reflective polarizer was used to measure surface profile. The surface profile was filtered with a Fourier filter 250 having band edge wavelengths W1 and W2 of 0.2 mm and 5 mm. At each point of the filtered surface profile, slope was calculated along two orthogonal in-plane directions and the slope magnitude at the point was calculated as the square root of the sum of the squares of slopes in the two directions. The magnitude of the slope was averaged over the measured area to determine MSE.

[0127] Curable Adhesive Adhl

[0128] Polyurethane polymers were prepared as follows. To a resin reaction vessel equipped with a mechanical stirrer, a condenser, and an air inlet, 200 g of Polyol, 17.26 g of HDI, 1.1 g of Bis-GMA, 0.02 g of BHT, 0.11 g of DBTDA and 50 g of MEK were added. The solution was heated up to 75°C while stirring. The temperature was maintained at 75±2° C until the NCO was disappeared under FT-IR. During the reaction, a total 170 g of MEK was added to dilute the viscosity of the system. The clear PU solution of 50% by weight was obtained with an IV of 0.47.

[0129] A curable adhesive formulation was prepared by adding the polyurethane polymers at 81.2% by weight (as 50% in MEK), CN983 at 8.12% by weight (as 50% in MEK), SR415 at 1.62% by weight,TPO at 0.91% parts by weight, KBM 403 at 0.05% by weight, PVP-VA at 8.12% by weight, and MEK to dilute the final composition to 50% solids by weight to an 8 oz amber jar and roller mixing for at least 8 hours until the formulation was fully homogeneous.

[0130] Curable Adhesive Adhl was prepared by coating the curable adhesive formulation using a knife coater to control the coating caliper. The coating was dried at ambient temperature for 10 min and then 70°C for 15 min.

[0131] Dynamic mechanical analysis was used to probe the modulus as a function of temperature as well as to determine the glass transition temperature (Tg) of the material. An 8-mm diameter by approximately 1-mm thick disk of laminated assembly layers (stack of layers of the adhesive having a total thickness of approximately 1 mm) was placed between the probes of a DHR parallel plate rheometer (TA Instruments, New Castle, DE). A temperature scan was performed by ramping from -45°C to 150°C at 3°C / minute. During this ramp, the samples was oscillated at a frequency of 1 Hz and a strain of approximately 0.4%. The shear storage modulus (G'), loss modulus (G") and tan delta was recorded at select temperatures during this scan. The Tgof the material was also determined as the peak in the tan delta vs. temperature profile. The tan delta at 90 deg. C was 1.24 before curing and 0.529 after 3J ultraviolet (UV) curing. The shear storage modulus at 90 deg. C was 36 kPa before curing and 152 kPa after curing.

[0132] Example 1

[0133] A multilayer optical film reflective polarizer (IQP-E available from 3M Company, St. Paul, MN) was laminated to a smooth surface (MSE of about 10 microradians) of a glass layer with a layer of the curable adhesive Adhl. The resulting assembly was annealed at 85 to 95 deg. C for 15 to 25 min. The MSE of a major surface of the reflective polarizer corresponding the red optical repeat units of the reflective polarizer was measured through the glass layer and from the air side before and after annealing. Various samples were tested. The MSE was about the same (within about 2 microradians) when measured through the glass layer (B side) and from the air side (A side). Before annealing, the MSE was roughly 140 microradians, and after annealing, the MSE was in a range of about 50 to 80 microradians. Results are shown in FIG. 7 which is a box and whisker plot indicating the variation in the MSE between samples.

[0134] Example 2

[0135] A multilayer optical film reflective polarizer (IQP-E available from 3M Company, St. Paul, MN) was laminated to smooth surfaces (MSE of about 10 microradians) of glass layers on opposite sides of the reflective polarizer with a layer of the curable adhesive Adhl between the reflective polarizer and each glass layer. The resulting assembly was annealed at 85 to 95 deg. C for 15 to 25 min. The MSE of a major surface of the reflective polarizer corresponding to the optical repeat units of the reflective polarizer reflecting red light was measured through each glass layer before and after annealing. Varioussamples were tested. Before annealing, the MSE was approximately 80 microradians, and after annealing, the MSE was in a range of about 35 to 45 microradians. Results are shown in FIG. 7 which is a box and whisker plot indicating the variation in the MSE between samples.

[0136] Terms such as “about” will be understood in the context in which they are used and described in the present description by one of ordinary skill in the art. If the use of “about” as applied to quantities expressing feature sizes, amounts, and physical properties is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description, “about” will be understood to mean within 10 percent of the specified value. A quantity given as about a specified value can be precisely the specified value. For example, if it is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description, a quantity having a value of about 1 , means that the quantity has a value between 0.9 and 1.1, and that the value could be 1.

[0137] Terms such as “substantially” will be understood in the context in which they are used and described in the present description by one of ordinary skill in the art. If the use of “substantially” with reference to a property or characteristic is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description and when it would be clear to one of ordinary skill in the art what is meant by an opposite of that property or characteristic, the term “substantially” will be understood to mean that the property or characteristic is exhibited to a greater extent than the opposite of that property or characteristic is exhibited.

[0138] All references, patents, and patent applications referenced in the foregoing are hereby incorporated herein by reference in their entirety in a consistent manner. In the event of inconsistencies or contradictions between portions of the incorporated references and this application, the information in the preceding description shall control.

[0139] Descriptions for elements in figures should be understood to apply equally to corresponding elements in other figures, unless indicated otherwise. Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and / or equivalent implementations can be substituted for the specific embodiments shown and described without departing from the scope of the present disclosure. This application is intended to cover any adaptations, or variations, or combinations of the specific embodiments discussed herein. Therefore, it is intended that this disclosure be limited only by the claims and the equivalents thereof.

Claims

What is claimed is:

1. An optical stack comprising a polymeric optical film disposed on a first curable adhesive layer, the polymeric optical film comprising a first major surface having a mean slope error of greater than about 60 microradians, the first curable adhesive layer having a tan delta of at least 1 for a frequency of 1 Hz and for at least a first temperature below, and within 35 deg. C of, a glass transition temperature of the polymeric optical film, the tan delta being a ratio of imaginary to real parts of shear modulus, such that when the optical stack is heated at the first temperature for at least 10 min, the mean slope error is reduced by at least 10 percent,wherein mean slope is a mean of a slope magnitude error determined from a surface profile of the first major surface filtered with a same bandpass Fourier filter having band edge wavelengths of W1 and W2, 0.1 mm < W1 < 0.3 mm, 2W1 < W2 < 10 mm.

2. The optical stack of claim 1 wherein W1 is about 0.2 mm and W2 is about 5 mm.

3. The optical stack of claim 1, wherein the first curable adhesive layer comprises (methjacry late-containing polyurethane.

4. The optical stack of claim 1, wherein the first curable adhesive layer comprises polyvinylpyrrolidone or a copolymer thereof.

5. The optical stack of claim 1, wherein the real part of the shear modulus of the first curable adhesive layer at the first temperature and at 1 Hz is no more than about 300 kPa.

6. The optical stack of claim 1 further comprising a second curable adhesive layer disposed on the polymeric optical film opposite the first curable adhesive layer.

7. The optical stack of claim 6, wherein the first major surface of the polymeric optical film faces the first curable adhesive layer and the polymeric optical film has an opposite second major surface facing the second curable adhesive layer, the second major surface having a mean slope error of greater than about 60 microradians, such that when the optical stack is heated at the first temperature for at least 10 min, the mean slope error of the second major surface is reduced by at least 10 percent.

8. An optical assembly, comprising:first and second substrates;a polymeric multilayer optical film disposed between the first and second substrates and comprising a plurality of optical repeat units numbering at least 10 in total, each optical repeat unitcomprising at least two polymeric layers, each layer of each optical repeat unit having an average thickness less than about 500 nm; andfirst and second adhesive layers disposed between, and bonding together, the polymeric multilayer optical film and the respective first and second substrates,wherein for at least one major surface of the polymeric multilayer optical film, the major surface has a mean slope error of no more than about 45 microradians, the mean slope error being a mean of a slope magnitude error determined from a surface profile of the major surface filtered with a bandpass Fourier filter having band edge wavelengths of about 0.2 mm and about 5 mm.

9. The optical assembly of claim 8, wherein the first adhesive layer is substantially perminately bonded to the polymeric multilayer optical film and releasably bonded to the first substrate.

10. The optical assembly of claim 8, wherein the first adhesive layer is substantially perminately bonded to each of the polymeric multilayer optical film and the first substrate.

11. The optical assembly of claim 8, wherein each of the first and second adhesive layers comprises a cured product of a curable adhesive, the curable adhesive comprising:a poly(meth)acrylate or (methjacrylate-containing polyurethane;one or more (methjacrylate monomers, one or more (methjacrylate-containing oligomers, or both;a free radical initiator; andpolyvinylpyrrolidone or a copolymer thereof.

12. An optical assembly, comprising:a first substrate;a polymeric optical film; anda first adhesive layer disposed between, and bonding together, the polymeric optical film and the first substrate,wherein for at least one major surface of the polymeric optical film, the major surface has a mean slope error of less than 100 microradians, the mean slope error being a mean of a slope magnitude error determined from a surface profile of the major surface filtered with a bandpass Fourier filter having band edge wavelengths of W1 and W2, 0.1 mm < W1 < 0.3 mm, 2W1 < W2 < 10 mm, andwherein the first adhesive layer comprises a cured product of a curable adhesive, the curable adhesive comprising:a poly(meth)acrylate or (methjacrylate-containing polyurethane;one or more (methjacrylate monomers, one or more (methjacrylate-containing oligomers, or both;a free radical initiator; andpolyvinylpyrrolidone or a copolymer thereof.

13. The optical assembly of claim 12 further comprising:a second substrate disposed on an opposite side of the polymeric optical film from the first substrate; anda second adhesive layer disposed between, and bonding together, the polymeric optical film and the second substrate.

14. A method of reducing a mean slope error of at least a first major surface of a polymeric optical film, the method comprising:forming an optical stack by disposing a first curable adhesive layer on the polymeric optical film and disposing a first substrate on the first curable adhesive layer opposite the polymeric optical film, the polymeric optical film having a glass transition temperature Tg, the first curable adhesive layer having a tan delta of at least 1 for a frequency of 1 Hz and for at least a first temperature Tl, Tg - 35 deg. C < T1 < Tg, the tan delta being a ratio of imaginary to real parts of shear modulus; andannealing the optical stack at the first temperature for at least 10 minutes, the annealing reducing the mean slope error of the first major surface of the polymeric optical film by at least 10 percent, mean slope error being a mean of a slope magnitude error determined from a surface profile of the first major surface filtered with a same bandpass Fourier filter having band edge wavelengths of W1 and W2, 0.1 mm < W1 < 0.3 mm, 2W1 < W2 < 10 mm.

15. The method of claim 14, wherein the polymeric optical film comprises a plurality of optical repeat units numbering at least 10 in total, each optical repeat unit comprising at least two polymeric layers, each layer of each optical repeat unit having an average thickness less than about 500 nm, the first major surface being an outermost major surface of the plurality of optical repeat units.

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