Curable adhesive

Abstract

A curable adhesive is provided. The curable adhesive comprises: a poly (meth) acrylate or a (meth) acrylate-containing polyurethane; one or more (meth) acrylate monomers and / or (meth) acrylate-containing oligomers; a radical initiator; and polyvinylpyrrolidone or a copolymer thereof. The inclusion of polyvinylpyrrolidone and certain reactive oligomers can result in both high adhesion modulus and excellent mechanical properties. Optical films coupled to the provided adhesive may also resist undesired flatness variations during assembly.

Description

Technical Field

[0001] Adhesive compositions and articles are provided. These adhesive compositions and articles can be used to bond optical films in electronic display applications. Background Technology

[0002] Specialized adhesives are used in the manufacture of electronic displays, such as those found in computer monitors, televisions, mobile phones, car dashboards, appliances, wearable devices, and other consumer devices. Some electronic displays are incorporated into flexible electronic displays, which can be attached to plastics, ultra-thin glass, or other flexible substrates. This capability greatly expands the functionality of electronic displays by allowing them to be integrated into non-planar objects, conform to desired designs, and bend flexibly during use, thus creating new applications.

[0003] These trends have increased the demand for adhesives, and particularly for optically clear adhesives (OCAs), to be used as assembly layers or gap-filling layers in electronic display assemblies. For example, OCA can be used to bond display modules to overlay lenses or sheets made of glass, PET, PC, PMMA, polyimide, PEN, or cyclic olefin copolymers. OCA can improve display performance by increasing brightness and contrast, while also providing structural support for the assembly.

[0004] Given the technical requirements of flexible display components, adhesives are needed that not only provide conventional performance properties such as optical clarity, adhesion, and durability, but also flexibility and recoverability, while avoiding defects and delamination. Summary of the Invention

[0005] For conventional adhesives (including pressure-sensitive adhesives), an increase in modulus is typically associated with certain desired effects, such as increased mechanical strength of the bond and improved peel and tensile adhesion. Additional technical benefits associated with increased modulus include improved die-cutting stability for conversion and storage, improved impact resistance and waviness control, and enhanced resistance to degassing under elevated humidity and temperature.

[0006] Modifications to increase the adhesive modulus without sacrificing other performance parameters, such as adhesion, have been explored, but many have not yet been successful. For example, the adhesive can be treated as a pressure-sensitive adhesive prior to curing to achieve good lamination and process control, and subsequently increased by adding reactive high glass transition temperatures (high Tg). gOligomers or monomers are used to increase modulus to form semi-adhesive or non-adhesive adhesive films. However, this approach often reduces initial adhesion strength, produces undesirable "sharkskin" peels from the release liner, and requires additional lamination steps to achieve adequate wetting of the adhesive onto the adherend. Such steps may include, for example, applying heat to close the bond. Matching these adhesives with release liners firmly coupled to the adhesive while providing a clean peel with the adhesive can also be a significant technical challenge.

[0007] These problems can be overcome using curable adhesives based on (meth)acrylate-containing polyurethanes, one or more (meth)acrylate monomers and / or (meth)acrylate-containing oligomers, free radical initiators, and polyvinylpyrrolidone (PVP) or copolymers thereof. Optionally, the curable adhesive may also contain silane tackifiers, such as 3-glycidoxypropyltrimethoxysilane. Without PVP, with high reactivity T... g Increasing the concentration of monomers and / or oligomers increases the modulus of the adhesive but decreases its mechanical properties (peel adhesion). By incorporating PVP and adjusting the amount of reactive monomers / oligomers, both high post-curing modulus and excellent adhesive properties can be achieved simultaneously. As an additional beneficial effect, due to this separation between modulus and adhesive properties, the optical film coupled to the adhesive can resist undesirable flatness variations during assembly. Once the film processing is complete, the provided adhesive can be cured to achieve high post-curing modulus while maintaining the flatness of the bonded optical film.

[0008] In a first aspect, a curable adhesive is provided. The curable adhesive comprises: poly(meth)acrylate or a polyurethane containing (meth)acrylate; one or more (meth)acrylate monomers and / or oligomers containing (meth)acrylate; a free radical initiator; and polyvinylpyrrolidone or a copolymer thereof.

[0009] In a second aspect, a method for preparing a curable adhesive is provided, the method comprising: providing a poly(meth)acrylate, or alternatively, reacting an aliphatic polyisocyanate with an aromatic polyester polyol to obtain a polyurethane containing (meth)acrylate; and mixing the poly(meth)acrylate or the polyurethane containing (meth)acrylate with one or more (meth)acrylate monomers and / or oligomers containing (meth)acrylate, a free radical initiator, an optional tackifier consisting of a silane tackifier, and polyvinylpyrrolidone or a copolymer thereof to obtain the curable adhesive.

[0010] In a third aspect, a method of making a bonded assembly is provided, the method comprising: positioning a curable adhesive between opposing major surfaces of a first adherend and a second adherend, wherein the free radical initiator comprises a photoinitiator; and exposing the curable adhesive to actinic radiation to obtain a cured adhesive, wherein the cured adhesive exhibits a tan d of 0.2 to 1 when tested at 70 °C and a frequency of 1 Hz, and exhibits a storage modulus of at least 500 kPa at ambient conditions.

[0011] In a fourth aspect, a bonded assembly is provided using the above method. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figures 1 to 4 is a front side view of an adhesive tape according to various example embodiments.

[0013] Reference signs that are repeated in the specification and drawings serve to identify like or similar features or elements in the present disclosure. It will be appreciated that those skilled in the art can devise many other modifications and embodiments that fall within the principles and scope of the present disclosure. The drawings can not be drawn to scale.

[0014] Definitions

[0015] As used herein: “Alkyl” refers to a monovalent radical of an alkane and includes straight chain, branched chain, cyclic and bicyclic alkyl radicals and combinations thereof, including both unsubstituted and substituted alkyl radicals. Unless stated otherwise, alkyl groups typically contain 1 to 30 carbon atoms. In some embodiments, 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 radicals 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, iso-butyl, t-butyl, iso-propyl, n-octyl, n-heptyl, ethylhexyl, cyclopentyl, cyclohexyl, cycloheptyl, adamantyl, and norbornyl.

[0016] “Allyl” refers to a functional group having the formula CH2=CH-CH2-.

[0017] “Ambient conditions” means at 21 °C and 101.3 kiloPascals.

[0018] “Ambient temperature” means 21 °C.

[0019] “Curable adhesive” refers to an adhesive that can be cured.

[0020] "Cured" refers to linking polymers together through covalent chemical bonds, typically via crosslinking of molecules or groups, to form a networked polymer. Thus, in the present disclosure, the terms "cured" and "crosslinked" can be used interchangeably. Cured or crosslinked polymers are typically characterized by insolubility, but can be swellable in the presence of a suitable solvent.

[0021] "Halogen" refers to a halogen atom or one or more halogen atoms, including a chlorine atom, a bromine atom, an iodine atom, and a fluorine atom or a fluorine substituent, a chlorine substituent, a bromine substituent, or an iodine substituent.

[0022] "(Meth)acrylate group" refers to a functional group that is an acrylate group of the formula CH2=CH-C(O)O- or a methacrylate group of the formula CH2=C(CH3)-C(O)O-.

[0023] Unless otherwise indicated, "molecular weight" refers to weight average molecular weight.

[0024] "Oligomer" refers to a molecule that contains at least two repeat units and has a molecular weight less than its entanglement molecular weight; unlike a polymer, such a molecule exhibits a significant change in properties when a single repeat unit is removed or added.

[0025] "Weight average molecular weight" is a parameter that reflects the weight fraction of individual polymer chains in a polymer sample and is measured using known gel permeation chromatography (GPC) techniques. DETAILED DESCRIPTION

[0026] As used herein, the terms "preferred" and "preferably" refer to a description of embodiments described herein that, in some instances, can provide certain benefits. However, other embodiments can also be preferred under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful, and is not intended to exclude those other embodiments from the scope of the application.

[0027] As used herein and in the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a" or "the" component can include reference to one or more of the components known to one of ordinary skill in the art, and equivalents thereof. Additionally, the term "and / or" means one or all of the listed elements or combination of any two or more of the listed elements.

[0028] Notably, the terms "comprise" and variations thereof are not construed as having a limiting meaning. Further, "one," "a," or "the" as used herein, can be interpreted as "at least one" or "one or more." Also, relative terms such as "left," "right," "forward," "backward," "top," "bottom," "side," "upper," "lower," "horizontal," "vertical," and the like can be used herein and, if so, are taken from the perspective of the view observed in a particular drawing. These terms are used only to simplify description and not to limit the scope of the application in any way.

[0029] References throughout this specification to "one implementation," "certain implementations," "one or more implementations" or "implementation" mean that a particular feature, structure, material, or characteristic described in connection with the implementation is included in at least one implementation of the application. Thus, the appearances of the phrases, such as "in one or more implementations," "in certain implementations," "in one implementation," or "in an implementation" throughout this specification are not necessarily all referring to the same implementation of the application.

[0030] In various implementations, the provided adhesive compositions include: a poly(meth)acrylate or a (meth)acrylate-containing polyurethane; one or more (meth)acrylate monomers and (meth)acrylate-containing oligomers; a free radical initiator; a polyvinylpyrrolidone or a copolymer thereof, and optionally a silane adhesion promoter.

[0031] The poly(meth)acrylate typically includes an acrylic polymer, and need not be particularly limited. Useful poly(meth)acrylates can be homopolymerized or copolymerized (meth)acrylate alkyl ester monomers, such as (meth)acrylic acid alkyl esters containing alkyl groups including 4 to 18 carbon atoms.

[0032] To provide strong adhesion and / or flexibility to the fully cured adhesive and to obtain good wettability to the adherend, it can be beneficial for the poly(meth)acrylate to include polymerized units of one or more (meth)acrylic alkyl ester monomers whose corresponding homopolymer has a glass transition temperature of 25°C or less. Suitable (meth)acrylic alkyl esters can include, for example, n-butyl acrylate, isobutyl acrylate, isoamyl acrylate, hexyl acrylate, cyclohexyl acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, n-decyl (meth)acrylate, isodecyl (meth)acrylate, lauryl (meth)acrylate, isomyristyl (meth)acrylate, isocetyl (meth)acrylate, or isostearyl (meth)acrylate.

[0033] Alkyl (meth)acrylate monomers having alkyl groups of 4 to 18 carbon atoms, whose homopolymers have a glass transition temperature of 25°C or higher, can also be used in combination with any of the monomers described above. Examples of alkyl (meth)acrylates having alkyl groups of 4 to 18 carbon atoms include linear or branched alkyl (meth)acrylates such as t-butyl (meth)acrylate, n-butyl methacrylate, and isobutyl methacrylate, whose homopolymers have a glass transition temperature (T g ) of 25°C or higher; and alicyclic (meth)acrylates such as cyclohexyl methacrylate, 4-t-butylcyclohexyl (meth)acrylate, and isobornyl (meth)acrylate. Alkyl (meth)acrylate monomers having a higher T g associated with their homopolymers can be beneficial as these monomers can impart enhanced mechanical behavior in the cured adhesive to impart greater resistance to debonding.

[0034] Other alkyl (meth)acrylates that can be included in the poly(methacrylate) copolymers are classified as high T g monomers based on the glass transition temperature of the corresponding homopolymer. High T g monomers generally have a T g of 30°C or higher, 40°C or higher, or 50°C or higher (i.e., the T g of the homopolymer formed from the monomer is 30°C or higher, 40°C or higher, or 50°C or higher). Some suitable high T g monomers include, for example, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, sec-butyl methacrylate, t-butyl (meth)acrylate, cyclohexyl methacrylate, isobornyl (meth)acrylate, stearyl (meth)acrylate, and 3,3,5-trimethylcyclohexyl (meth)acrylate.

[0035] In some embodiments, it can be further advantageous for the poly(meth)acrylate to include polymerized units of one or more hydrophilic monomers whose homopolymers have a T g of 10°C or lower. These monomers can enable greater association with the substrate of interest, improved electrical properties and moisture management, or improved cohesive strength within the adhesive. Examples of hydrophilic monomers whose homopolymers have a T g of 10°C or lower.

[0036] Useful monomers include hydroxyalkyl acrylate having an alkyl group of 4 or fewer carbon atoms, and (meth)acrylic compounds having an oxyethylene group or an oxypropylene group, or a polyoxyethylene group or a polyoxypropylene group. Specific examples include, but are not limited to, 2-hydroxyethyl acrylate and hydroxypropyl acrylate. Among these, in view of imparting flexibility to the transparent adhesive sheet, a hydrophilic monomer is preferably one whose homopolymer has a glass transition temperature of 0°C or lower, and more preferably one whose homopolymer has a glass transition temperature of -5°C or lower, such as 2-hydroxyethyl acrylate or 2-hydroxypropyl acrylate. g Useful monomers include hydroxyalkyl acrylate having an alkyl group of 4 or fewer carbon atoms, and (meth)acrylic compounds having an oxyethylene group or an oxypropylene group, or a polyoxyethylene group or a polyoxypropylene group. Specific examples include, but are not limited to, 2-hydroxyethyl acrylate and hydroxypropyl acrylate. Among these, in view of imparting flexibility to the transparent adhesive sheet, a hydrophilic monomer is preferably one whose homopolymer has a glass transition temperature of 0°C or lower, and more preferably one whose homopolymer has a glass transition temperature of -5°C or lower, such as 2-hydroxyethyl acrylate or 2-hydroxypropyl acrylate.

[0037] In some embodiments, the (meth)acrylate polymer can include a non-hydroxy functional polar co-polymerizable monomer. Examples of suitable non-hydroxy functional polar co-polymerizable monomers include, but are not limited to: acrylic acid, methacrylic acid, itaconic acid, fumaric acid, ether functional monomers such as 2-ethoxyethyl (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-dimethyl acrylamide, N,N-diethyl acrylamide, N-vinyl pyrrolidone, and N-vinyl caprolactam. In some embodiments, the (meth)acrylate polymer can include between 0 and 25 parts by weight, particularly between 1 and 20 parts by weight, and more particularly between 1 and 15 parts by weight of the polar co-polymerizable monomer.

[0038] In some embodiments, the (meth)acrylate polymer can include a vinyl ester, and particularly a Ci to Cio vinyl ester. Examples of suitable vinyl esters that are commercially available include, but are not limited to: vinyl acetate, and VEOVA 9 or VEOVA 10 (available from Momentive Specialty Chemicals, New Smyrna Beach, Florida).

[0039] In some embodiments, the (meth)acrylate polymer can include a polar (meth)acrylate monomer. Examples of suitable polar (meth)acrylate monomers include, but are not limited to: hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, tetrahydrofurfuryl acrylate, acrylamide, N,N-dimethyl acrylamide, N-vinyl pyrrolidone, and acrylic acid.

[0040] In some embodiments, the (meth)acrylate polymer can include a monofunctional non-vinyl (meth)acrylate monomer. Examples of suitable monofunctional non-vinyl (meth)acrylate monomers include, but are not limited to, N-vinylpyrrolidone, N-vinylcarbazole, vinyl acetate, and vinyl ether.

[0041] The poly(meth)acrylate can be a copolymer further comprising pendant vinyl groups, such as pendant acrylate groups, that can undergo further free radical addition. In one embodiment, the functionalized copolymer can be formed by first polymerizing a mixture of monomers including at least one (meth)acrylic (Ci-Cis) alkyl ester monomer and a hydroxyl-containing (meth)acrylate monomer. After polymerization, a portion of the pendant hydroxyl groups can be further converted to unsaturated pendant (meth)acrylate groups; In one embodiment, the unsaturated pendant groups can be grafted by reacting isocyanatoethyl (meth)acrylate with the hydroxyl groups of the copolymer. After heat treatment, the IEMs generate pendant unsaturated groups on the copolymer. Examples of commercially suitable isocyanatoethyl (meth)acrylate include 2-isocyanatoethyl acrylate and 2-isocyanatoethyl methacrylate sold under the trade names KARENZO OI and KARENZO MOI by Showa Denko, Toyko, Japan.

[0042] The (meth)acrylate-containing polyurethane can have a polyurethane backbone. Polyurethanes are generally prepared by reacting a polyisocyanate component with a polyol component.

[0043] The polyol component includes an aromatic and / or aliphatic polyester or polycaprolactone polyol that includes at least two hydroxyl end group. When the polyol has an average of two or three hydroxyl groups, it can be characterized as a diol or triol, respectively. In yet other embodiments, the polyol can include a mixture of one or more diols and one or more triols, wherein the average number of hydroxyl groups is greater than 2 but less than 3. Other polyols can have 4, 5, or 6 hydroxyl end groups.

[0044] The polyester polyol can be obtained, for example, by esterification reaction between the polyol component and an acid component. Examples of the acid component 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-1,4-cyclohexanedicarboxylic acid, 2-ethyl-1,4-cyclohexanedicarboxylic acid, terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 4,4'-biphenyldicarboxylic acid, and anhydrides thereof.

[0045] In some embodiments, the polyol component can be an aromatic polyester polyol. As known in the art, aromatic polyester polyols can be prepared by polymerizing an aromatic dicarboxylic acid with an aliphatic diol. In some embodiments, the aromatic dicarboxylic acid includes isophthalic acid or phthalic acid. The polyester polyol can optionally be prepared from some amount of other aromatic dicarboxylic acids, such as terephthalic acid. Optionally, the polyester polyol can be prepared from cycloaliphatic dicarboxylic acids, such as 1,3-cyclopentane dicarboxylic acid; 1,2-cyclohexane dicarboxylic acid; 1,4-cyclohexane dicarboxylic acid; or 2,5-norbornane dicarboxylic acid. These dicarboxylic acids are typically provided in the form of anhydrides.

[0046] The aliphatic diol used to make the aromatic or aliphatic (e.g., polyester or polycarbonate) polyol can include a linear 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-1,3-diol, 2,2-dimethyl-1,3- propanediol (neopentyl glycol), 2-ethyl-2-butyl-1,3-propanediol, 2-ethyl-2- isobutyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 2,2,4-trimethyl-1,6- hexanediol, and octadecanediol, among others. At least one of the aliphatic diols can include a linear or branched alkylene group comprising 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.

[0047] In some embodiments, the polyol can include a polycaprolactone polyol. Polycaprolactone polyols can be obtained by subjecting a cyclic ester monomer, such as ε-caprolactone or σ-valerolactone, to ring-opening polymerization. The polycaprolactone polyol comprises an alkylene group having 5 carbon atoms.

[0048] In some embodiments, the polyol component can include polycarbonate polyols such as obtained from the reaction of aliphatic diols (such as butanediol-(l,4) and / or hexanediol-(l,6)) with phosgene, a diaryl carbonate (such as diphenyl carbonate), or with a cyclic carbonate (such as ethylene carbonate or propylene carbonate). Polyester carbonates obtained from the aforementioned polyesters or polylactones with phosgene, a diaryl carbonate, or a cyclic carbonate are also suitable. The preparation of the polyester or polycarbonate polyols generally includes the use of at least one aliphatic diol as previously described. The alkylene groups of the aliphatic diols and the polyester or polycarbonate polyols can contain hydrophobic substituents (such as halogen substituents). One exemplary polycarbonate polyol is sold by Covestro AG under the trade name DESMOPHEN C2200.

[0049] In some embodiments, the polyol is prepared using a single aliphatic diol. In this embodiment, the aliphatic diol contains an alkylene group containing at least 4, 5, or 6 carbon atoms as previously described. Alternatively, the polyol can be prepared using two or more aliphatic diols, wherein at least one of such diols contains an alkylene group containing at least 4, at least 5, or at least 6 carbon atoms. When a mixture of aliphatic diols is used, at least 50 wt%, 60 wt%, 70 wt%, 80 wt%, 90 wt%, or 95 wt% of the total amount of diols is an alkylene group containing at least 4, 5, or 6 carbon atoms as previously described.

[0050] The polyol is generally a polymer. The polyol can have an equivalent weight (molecular weight per hydroxyl group) in the range of about 250 g / mol to about 30,000 g / mol. In some embodiments, the equivalent weight of the polyol is 500 g / mol to 30,000 g / mol, 2000 g / mol to 20,000 g / mol, 2000 g / mol to 10,000 g / mol, 2000 g / mol to 4000 g / mol, or in some embodiments, less than, equal to, or greater than 250 g / mol; 500 g / mol; 1000 g / mol; 2000 g / mol; 3000 g / mol; 3500 g / mol; 4000 g / mol; 5000 g / mol; 6000 g / mol; 7000 g / mol; 8000 g / mol; 10,000 g / mol; 20,000 g / mol; or 30,000 g / mol. For diols and triols, the typical molecular weight of the polyol can be twice or three times the aforementioned equivalent weight ranges, respectively. In some embodiments, the molecular weight of the polymeric polyol is less than 4000 g / mol, 3500 g / mol, or 3000 g / mol.

[0051] In some embodiments, the aliphatic polyester polyol comprises repeating units consisting of an alkylene group and a terminal ester group or more than one alkylene group bonded by way of ester linkages and terminal ester groups.

[0052] In other embodiments, the aliphatic polycarbonate polyol can comprise repeating units comprising an alkylene group and a terminal carbonate group or more than one alkylene group bonded by way of carbonate linkages and terminal carbonate groups.

[0053] In yet other embodiments, the aromatic polyester polyol can comprise polymerized units consisting of aromatic groups of a dicarboxylic acid bonded to alkylene groups of an aliphatic diol by ester linkages. In this embodiment, the molar ratio of six-membered rings to alkylene groups having at least 4, 5, or 6 carbon atoms can be about 1 : 1 and can range from about 1.5: 1 to 1 : 1.5.

[0054] In preferred embodiments, an aromatic polyester polyol is used, which can be obtained by reacting an aromatic ortho- or meta-dicarboxylic anhydride component with 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.

[0055] In some embodiments, the polyester polyol is prepared from isophthalic acid or phthalic acid and is represented by the following Structure I:

[0056] wherein R1is 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 in the ortho or meta position to the ring.

[0057] In some embodiments, n is no greater than 25, 20, 15, or 10. When the aromatic polyester polyol comprises 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. In addition, such aromatic polyester polyols tend to be amorphous viscous liquids at 25°C. In some embodiments, the viscosity of the aromatic polyester polyol at 80°C is less than 10,000 cP or even less than 5,000 cP.

[0058] Aromatic polyester polyols derived from phthalic acid are commercially sold by Stepan Co. under the trade name STEPANPOL. These can be represented, for example, by the following Structure II:

[0059] wherein R1and n have any of the values described above.

[0060] When the aromatic polyester polyol is derived from isophthalic acid, the polyester polyol can be represented by the following structure III:

[0061] wherein R1and n have any of the values described above.

[0062] The polyisocyanate component can be any of a variety of polyfunctional isocyanate compounds. Examples of such polyfunctional isocyanate compounds include polyfunctional aliphatic isocyanate compounds, polyfunctional aliphatic cyclic isocyanate compounds, and polyfunctional aromatic isocyanate compounds. Examples of 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.

[0063] 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 toluene diisocyanate, hydrogenated tetramethyl xylene diisocyanate, a partially bio-based aliphatic isocyanate polymer sold under the trade designation TOLONATE X FLO 100 by Vencorex US, Inc., Freeport, TX, and a bio-based polyfunctional aliphatic cyclic isocyanate such as 2-heptyl-3,4-bis(9- isocyanatononyl)-l-pentylcyclohexane sold under the trade designation DDI 1410 by BASF Corporation.

[0064] Examples of polyfunctional aromatic isocyanate compounds include phenylene diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 2,2'-diphenylmethane diisocyanate, 4,4'- diphenylmethane diisocyanate, 4,4'-toluidine diisocyanate, 4,4'-diphenylether diisocyanate, 4,4'- diphenyl diisocyanate, 1,5-naphthyl diisocyanate, and xylylene diisocyanate.

[0065] In some embodiments, the polyfunctional isocyanate includes a polyisocyanate that is liquid alone at 25 °C or in combination with a small amount of polyisocyanate that is solid at 25 °C. In other embodiments, such as when the polyol is an aliphatic polyol, the polyfunctional isocyanate can be solid at 25 °C.

[0066] In some embodiments, the polyfunctional isocyanate compound includes an aliphatic isocyanate compound, such as hexamethylene diisocyanate. In other embodiments, the polyfunctional isocyanate compound includes a para-aromatic isocyanate compound or a meta-aromatic isocyanate compound, such as 1,4-methylene diphenyl diisocyanate (MDI), meta-tetramethylxylene diisocyanate (TMXDI), or mixtures thereof. Mixtures of aliphatic polyfunctional isocyanate compounds and aromatic polyfunctional isocyanate compounds are also possible.

[0067] The (meth)acrylate functionality of the (meth)acrylate-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 pendant acrylate groups. The (meth)acrylate-containing polyurethane can be present in an amount of 10 wt% to 99 wt%, 40 wt% to 97 wt%, 70 wt% to 95 wt%, or, in some embodiments, less than, equal to, or greater than 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, 65 wt%, 70 wt%, 75 wt%, 80 wt%, 85 wt%, 90 wt%, 95 wt%, 96 wt%, 97 wt%, 98 wt%, or 99 wt%, relative to the total weight of the curable adhesive.

[0068] The above polymer structure can be synthesized by reacting a compound containing one or more hydroxyl groups and one or more olefinically unsaturated groups with the above polyisocyanate and polyol components in the reactive mixture. In preferred embodiments, the polyisocyanate is an aliphatic polyisocyanate and the polyol is an aromatic polyester polyol.

[0069] From the reactive mixture, the hydroxyl groups react with the polyisocyanate component, thereby incorporating the olefinically unsaturated groups into the polyurethane. In some embodiments, a compound having a single hydroxyl group and a (meth)acrylate monomer having a single olefinically unsaturated group, such as hydroxyethyl acrylate (HEA), can be used. In some embodiments, the isocyanate groups are bonded to the polyurethane polymer backbone and the opposite ends of the diisocyanate are bonded to the hydroxyl groups of the compound, thereby creating terminal olefinically unsaturated groups.

[0070] In other embodiments, the (meth)acrylate-containing polyols include at least two hydroxyl groups and at least two ethylenically unsaturated groups, such as bisphenol A glyceryl dimethacrylate (Bis-GMA). In this embodiment, the compound reacts as a polyol and is thereby incorporated into the polyurethane backbone, with the ethylenically unsaturated groups being pendant to the polyurethane backbone.

[0071] The one or more (meth)acrylate-containing polyols can independently be present in an amount of 0.1 wt% to 20 wt%, 0.2 wt% to 10 wt%, 0.5 wt% to 5 wt%, or in some embodiments, less than, equal to, or greater than 0.1 wt%, 0.2 wt%, 0.5 wt%, 1 wt%, 2 wt%, 2.5 wt%, 3 wt%, 4 wt%, 5 wt%, 7 wt%, 10 wt%, 11 wt%, 12 wt%, 15 wt%, 17 wt%, or 20 wt%, relative to the total weight of the reactive mixture.

[0072] Various compounds comprising one or more hydroxyl groups and one or more ethylenically unsaturated groups can be used during the preparation of the polyurethane. Such compounds can be aliphatic or aromatic. Other representative compounds sold by Nagase ChemteX Corporation, Osaka, Japan include, for example, 1,6-hexanediol in the form of an epoxy acrylate sold under the trade name DA-212, or 1,4-hexanediol in the form of an epoxy acrylate sold under the trade name DA-214L.

[0073] The provided curable adhesive compositions also incorporate one or more (meth)acrylate 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 ultimately cured to form a crosslinked network upon bonding.

[0074] In some embodiments, the reactive mixture includes a urethane acrylate oligomer, such as sold under the trade name CN983 by Arkema, Colombes, France. In other embodiments, the reactive mixture includes an ethoxylated triacrylate, such as sold under the trade name SR415 by Arkema, Colombes, France. Both the urethane acrylate oligomer and the ethoxylated triacrylate are effective for use as crosslinkers, but the latter monomer is slightly more hydrophilic and is found to improve haze performance after the cured adhesive is subjected to high temperature high humidity aging.

[0075] In some embodiments, the (meth)acrylate-containing oligomer consists of polyester-based urethane diacrylate oligomers. Suitable homopolymers of (meth)acrylate-containing oligomers T g may be greater than 30°C, 40°C, or even 50°C.

[0076] Other monomers having multiple (meth)acryl groups can be combined with the (meth)acrylate copolymer or polyurethane having pendant (meth)acrylate groups. These monomers can be added to adjust the crosslinking density and increase the modulus of the cured (meth)acrylate copolymer or polyurethane. These monomers can react with the pendant (meth)acryl groups of the curable (meth)acrylate 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 parts per hundred ("pph") to 40 pph, based on the weight of the curable (meth)acrylate copolymer. For example, the amount can be less than, equal to, or greater than 1 pph, 2 pph, 5 pph, 10 pph, 15 pph, 20 pph, 25 pph, 30 pph, 35 pph, or 40 pph.

[0077] Exemplary monomers having two (meth)acryl groups include bisphenol A diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, tripropylene glycol diacrylate, polyethylene glycol diacrylate (e.g., commercially available under the trade designation SR-210, SR-252, and SR-603 from Arkema Inc.), polypropylene glycol diacrylate, ethoxylated (30) bisphenol A diacrylate (e.g., commercially available under the trade designation SR9038 from Arkema Inc.), polyethylene / polypropylene copolymer diacrylate, neopentyl glycol hydroxypivalate diacrylate-modified caprolactone, and polyurethane diacrylate (e.g., commercially available under the trade designations CN2920, CN9178, and CN983 from Arkema Inc., and under the trade designation ETERCURE 282 from Eternal Materials Co. Ltd.).

[0078] Exemplary monomers having three or four (meth)acryloyl groups include, but are not limited to, trimethylolpropane triacrylate (e.g., commercially marketed under the trade designation TMPTA-N by Surface Specialties, Smyrna, GA, and under the trade designation SR-351 by Sartomer, Exton, PA), ethoxylated trimethylolpropane triacrylate (e.g., commercially marketed under the trade designation SR9035 by Sartomer), pentaerythritol triacrylate (e.g., commercially marketed under the trade designation SR-444 by Sartomer), tris(2-hydroxyethyl isocyanurate) triacrylate (e.g., commercially marketed under the trade designation SR-368 by Sartomer), a mixture of pentaerythritol triacrylate and pentaerythritol tetraacrylate (e.g., commercially marketed under the trade designation PETIA (tetraacrylate to triacrylate ratio of about 1 : 1) and under the trade designation PETA-K (tetraacrylate to triacrylate ratio of about 3: 1) by Surface Specialties), pentaerythritol tetraacrylate (e.g., commercially marketed under the trade designation SR-295 by Sartomer), di-trimethylolpropane tetraacrylate (e.g., commercially marketed under the trade designation SR-355 by Sartomer), and ethoxylated pentaerythritol tetraacrylate (e.g., commercially marketed under the trade designation SR-494 by Sartomer). Exemplary crosslinkers having five (meth)acryloyl groups include, but are not limited to, bis-pentaerythritol pentaacrylate (e.g., commercially marketed under the trade designation SR-399 by Sartomer).

[0079] Advantageously, the curable adhesive composition also incorporates a substantially polar and high T g homopolymers or copolymers of monomeric units. In preferred embodiments, the homopolymers or copolymers are derived from polyvinylpyrrolidone (PVP), sometimes referred to as povidone. The PVP can be in the form of a polyvinylpyrrolidone homopolymer, a polyvinylpyrrolidone copolymer, or a combination thereof. Polyvinylpyrrolidone is a non-ionic synthetic polymer consisting of repeating 1 -vinyl-2-pyrrolidone monomers. The repeating unit of PVP is represented by the following Structure IV:

[0080] PVP is known in the pharmaceutical industry as a binder in tablet manufacture and is capable of dissolving in water as well as many organic solutions. This property is a result of hydrophilic and hydrophobic functional groups that can interact with different solvents, where the viscosity is largely unaffected by electrolytes. Surprisingly, it was found that the addition of PVP in the provided curable polyurethane or poly(meth)acrylate based adhesive compositions can result in high adhesive modulus and substantially mitigate the degradation of adhesive performance that typically occurs when the modulus of the adhesive composition increases significantly upon curing.

[0081] PVP copolymers can include random and block copolymers of PVP. A useful random copolymer of PVP is N-vinylpyrrolidone-co-vinyl acetate copolymer, also known as copovidone, and is widely used in the pharmaceutical industry as a dry and wet binder in tablets. Copovidone has a lower hygroscopicity and absorbs less water compared to povidone. Copolymers such as copovidone can also achieve greater compatibility with curable poly(meth)acrylate or curable polyurethane polymers.

[0082] The weight average molecular weight of the PVP or copolymer thereof can be from 1,000 g / mol to 75,000 g / mol, 1,500 g / mol to 60,000 g / mol, 2,000 to 50,000 g / mol, or in some embodiments, less than, equal to, or greater than 1,000 g / mol; 1,500 g / mol; 2,000 g / mol; 5,000 g / mol; 10,000 g / mol; 20,000 g / mol; 30,000 g / mol; 40,000 g / mol; 50,000 g / mol; 60,000 g / mol; 75,000 g / mol; 100,000 g / mol; 500,000 g / mol; or 1,000,000 g / mol.

[0083] The PVP or copolymer thereof can be present in any suitable amount to achieve a desired adhesive modulus after curing. Typically, the amount of PVP or copolymer thereof is from 2 wt% to 30 wt%, 5 wt% to 20 wt%, 5 wt% to 15 wt%, or in some embodiments, less than, equal to, or greater than 2 wt%, 3 wt%, 4 wt%, 5 wt%, 7 wt%, 10 wt%, 12 wt%, 15 wt%, 17 wt%, 20 wt%, 25 wt%, or 30 wt%, relative to the total weight of the curable adhesive.

[0084] Advantageously, the introduction of carboxylic acid functionality into the polymer chain enables hydrogen bonding between the PVP / PVP vinyl acrylate and the polyurethane component. This hydrogen bonding can have the effect of providing a physical crosslink (also referred to as a “thermodynamic crosslink”) between polymer chains, thereby increasing the storage modulus at the pre-cured state, particularly at elevated temperatures.

[0085] In certain applications, the increased storage modulus can be a key benefit. Examples include three-dimensional lamination and thermoforming lamination, which typically require handling of uncured adhesive at elevated temperatures. Operations can include lamination, clean release from release liners, and die cutting. Uncured adhesives also need to have flow properties to sufficiently wet curved surfaces, while maintaining their dimensional stability until they are fully cured. Physical crosslinking can help provide an adhesive solution that achieves the foregoing benefits while retaining high adhesion and high modulus performance properties after curing.

[0086] In some embodiments, the reactive mixture further comprises a carboxylic acid containing polyol. An example of a useful carboxylic acid containing polyol is dimethylol propionic acid. When the reactive mixture is polymerized, the resulting copolymer has carboxylic acid groups along the polymer backbone. This can induce hydrogen bonding between the PVP groups and the acid to the polymer chain, as exemplified below:

[0087] Given the desired degree of physical crosslinking, the carboxylic acid containing polyol can be present in an amount that provides a suitable concentration of acid functionality on the copolymer backbone. This amount can be 0.1 wt% to 20 wt%, 0.2 wt% to 10 wt%, 0.5 wt% to 5 wt%, or, in some embodiments, less than, equal to, or greater than 0.1 wt%, 0.2 wt%, 0.5 wt%, 1 wt%, 2 wt%, 2.5 wt%, 3 wt%, 4 wt%, 5 wt%, 7 wt%, 10 wt%, 11 wt%, 12 wt%, 15 wt%, 17 wt%, or 20 wt%, relative to the total weight of the reactive mixture.

[0088] The curable adhesive composition comprises one or more free radical initiators that enable the curable adhesive composition to be cured.

[0089] In preferred embodiments, the free radical initiator is a photoinitiator that is 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 name I-651 by Merck KGaA, Darmstadt, Germany) or ESACURE KB-1 photoinitiator (sold by the Levoss Group, Hamburg, Germany), and dimethylhydroxyacetophenone; substituted alpha-ketols such as 2-methyl-2-hydroxypropiophenone; aromatic sulfonyl chlorides such as 2-naphthalene-sulfonyl chloride; photosensitive oximes such as 1-phenyl-1,2-propanedione-2-(O-ethoxy-carbonyl)oxime; mono- or bis-acryloyl phosphine oxides sold under the trade name IRGANOX 819 by BASF SE, Ludwigshafen, Germany or under the trade name LUCIRIN TPO by Merck KGaA.

[0090] Preferred photoinitiators are photoactive compounds that undergo Norrish I cleavage to generate radicals that can initiate by addition to the double bond of an acrylic. 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 No. 5,902,836 and U.S. Patent No. 5,506,279 (Gaddam et al.).

[0091] Thermal free radical initiators are also possible, whose activation occurs by the application of heat rather than by exposure to actinic radiation. Such initiators include, but are not limited to, azo, peroxide, persulfate, and redox initiators, and combinations thereof. Additional options and related benefits associated with thermal and photopolymerization techniques are described in U.S. Patent No. 4,654,233 (Grant et al.); U.S. Patent No. 4,855,184 (Klun et al.); and U.S. Patent No. 6,224,949 (Wright et al.).

[0092] The free radical initiator can be present in an amount of 0.1 wt% to 5 wt%, or in some embodiments, less than, equal to, or greater than 0.1 wt%, 0.2 wt%, 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, or 5 wt%, based on the total weight of the uncured composition.

[0093] To improve adhesive performance, adhesion promoting additives such as silanes and titanates can be incorporated therein. Such additives can promote adhesion between the adhesive and a substrate by coupling to silanol, hydroxyl, or other reactive groups in the substrate, such as the glass of a liquid crystal display (LCD) and cellulose triacetate. Silanes and titanates can have only alkoxy substitution on the silicon or titanium atom attached to the adhesive copolymerizable group or interaction group. Alternatively, silanes and titanates can have both alkyl and alkoxy substitution on the silicon or titanium atom attached to the adhesive copolymerizable group or interaction group.

[0094] The adhesive copolymerizable group can generally be an acrylate or methacrylate group, although vinyl and allyl groups can also be used. Alternatively, the silane or titanate can also react with a functional group in the adhesive, such as a (meth)acrylic acid hydroxyalkyl ester. In addition, the silane or titanate can have one or more groups that provide strong interactions with the adhesive matrix. Examples of such strong interactions include hydrogen bonding, ionic interactions, and acid-base interactions. An example of a preferred silane is (3-glycidyloxypropyl)trimethoxysilane.

[0095] In some embodiments, the silane adhesion promoter is present in an amount of 0.02 wt% to 1 wt%, 0.04 wt% to 0.5 wt%, or, in some embodiments, less than, equal to, or greater than 0.02 wt%, 0.04 wt%, 0.05 wt%, 0.1 wt%, 0.2 wt%, 0.5 wt%, 1 wt%, 2 wt%, or 5 wt%, relative to the total weight of the curable adhesive.

[0096] In a preferred method of making the curable adhesive, an aliphatic polyisocyanate is reacted with an aromatic polyester polyol to obtain a (meth)acrylate-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 consisting of a silane adhesion promoter, and a polyvinylpyrrolidone or similar copolymer thereof. As previously explained, the poly(meth)acrylate can replace the above-described (meth)acrylate-containing polyurethane, where the poly(meth)acrylate can include unsaturated pendant groups to promote further crosslinking in the cured adhesive.

[0097] In cases where a solvent is used, the solution can be cast onto a release surface and subsequently the solvent removed by a separate drying step at elevated temperature to obtain a uniform curable adhesive film.

[0098] Figures 1 to 3An exemplary transfer adhesive incorporating the provided adhesive composition is shown. The tape adhesive according to one exemplary embodiment is illustrated in Figure 1 is exemplified in FIG. 1 and is hereinafter referred to by the numeral 100. The tape adhesive 100 is embodied in a primary layer 102 comprised of an adhesive composition as described herein and has opposing first and second major surfaces 104, 106. Advantageously, the primary layer 102 provides resistance to mechanical waviness while retaining high impact performance. The provided adhesive can be optically clear both before and after curing, with a haze value of less than 2% after curing.

[0099] Figure 2 A tape adhesive assembly 150 representing a bonded assembly is shown. The assembly 150 includes the tape adhesive 100 comprised of the primary layer 102, which features are as described above. The assembly 150 further includes a pair of release substrates 152, 154 disposed on each of the respective opposing major surfaces 104, 106 of the primary layer 102. In some embodiments, the primary layer 102 directly contacts both release substrates 152, 154, thereby serving to adhesively couple these release substrates 152, 154 to one another. Useful release substrates are known in the art and can include, for example, a liner comprised of silicone-coated polyester or silicone-coated paper. Alternatively, the primary layer 102 can be coated onto a functional film along one of its major surfaces, with a release substrate disposed on its opposing major surface. Useful functional films can be made of polyethylene terephthalate, polyimide, cyclic olefin polymer (COP), multilayer optical film (MOF), or polarizing film.

[0100] Figure 3 A tape adhesive 200 according to yet another embodiment is shown, which has similarities in construction to the tape adhesive 100, with the difference being that a pair of secondary layers 210, 210' are interposed between the primary layer 202 and the release substrates 252, 254, as shown. The secondary layers 210, 210' can serve as skin layers made of an acrylic OCA containing a lower weight fraction of PVP or copolymer thereof relative to the PVP or copolymer thereof of the primary layer 202.

[0101] Figure 4A bonded assembly is shown in which a pair of adhesive layers 302, 302' are disposed on opposite major surfaces of a quarter waveplate 360, thereby bonding the quarter waveplate 360 to a lens layer 362 on one side and to a reflective polarizer 364 on its opposite side. The reflective polarizer 364 substantially reflects light having a first polarization state and substantially transmits light having a second, orthogonal polarization state. The material that can be used for the lens layer 362 is not particularly limited, although the layer is typically made of glass or a hard polymer such as a cyclic olefin copolymer or polycarbonate. The pair of adhesive layers 302, 302' have the properties of the provided adhesives as shown and described herein.

[0102] Bonded assembly 300 is an example of an optical stack used in a display device. Details regarding the operation of the optical stack are described elsewhere, for example in U.S. Patent No. 11,630,290 (Yun et al.), U.S. Patent Publication No. 2020 / 0319388 (Ambur et al.), and International Patent Publication Nos. WO 2023 / 111739 (Le et al.) and WO 2022 / 043791 (Haag et al.).

[0103] In preferred embodiments, one or both of secondary layers 210, 210' include PVP or copolymer thereof in an amount of zero or substantially zero. A potential advantage of this embodiment is to maintain high room temperature tack, which can be beneficial for certain applications. Another potential advantage is the possibility of introducing greater flow at the surface, which can improve adhesive wet-out of the substrate or topographical features such as ink steps, if present. Other advantages can include the possibility of isolating certain functionalities such as UV blocking to a particular layer.

[0104] More generally, a bonded assembly can be prepared by disposing a curable adhesive between opposite major surfaces of a first adherend and a second adherend, wherein the free radical initiator comprises a photo-initiator; and exposing the curable adhesive to actinic radiation to obtain a cured adhesive.

[0105] Before curing, the curable adhesive can exhibit a tan delta of 0.5 to 3, 0.5 to 2, or in some embodiments, less than, equal to, or greater than 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.5, 1.7, 2, 2.5, or 3 when tested at 70 °C and a frequency of 1 Hz to provide the adhesive with suitable flow properties. After curing, the adhesive can exhibit a tan delta of 0.2 to 1, 0.2 to 0.6, 0.2 to 0.5, or in some embodiments, less than, equal to, or greater than 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or 1 when tested at 70 °C and a frequency of 1 Hz. In various embodiments, the cured adhesive exhibits a storage modulus of at least 500 kPa at ambient conditions.

[0106] Examples

[0107] The objects and advantages of the disclosure will be further illustrated by the following non-limiting examples, but the specific materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to unduly limit this disclosure.

[0108] All parts, percentages, ratios, etc. in the examples and the rest of the specification are by weight, unless otherwise indicated. Solvents and other reagents were obtained from Millipore Sigma Company; Burlington, MA, unless otherwise specified. The following abbreviations are used: nm = nanometer; mm = millimeter; cm = centimeter; in = inch; Hz = hertz; min = minute; h = hour; mJ = millijoule.

[0109] Materials

[0110] The materials used in the examples are provided in Table 1 below.

[0111]

[0112] Test Methods

[0113] Peel test, 25°C and 85°C

[0114] This 180° peel adhesion test is similar to the test method described in ASTM A 3330-90, except that a glass substrate is used in place of the stainless steel substrate described in the test method.

[0115] The coated adhesive samples were first laminated to a 2 mil (51 micron) primed PET backing (3SAB from Mitsubishi). They were then cut into 1 cm strips and rolled onto a glass substrate using a Cheminstruments HR-100 roll. The test samples were then autoclaved and tested for 85°C peel adhesion using a 3J / cm 2 D bulb cure. Prior to peel adhesion analysis, the test samples were allowed to acclimate in the CTH chamber for 18 h. For 25°C testing, an IMass SP-2000 peel tester was utilized using a 6 cm / min peel rate at a 180° peel angle. For 85°C testing, the samples were allowed to dwell at 85°C in an Instron environmental chamber for at least 15 minutes and analyzed using an Instron load frame and environmental chamber at a 6 cm / min peel rate at a 180° peel angle.

[0116] Dynamic mechanical analysis (DMA)

[0117] Dynamic mechanical analysis was used to probe the modulus as a function of temperature and to determine the glass transition temperature (T g ) of the material. A 8 mm diameter x approximately 1 mm thick disc of the laminated assembly was placed between the probes of a DHR parallel plate rheometer (TA Instruments, New Castle, DE). A temperature sweep was performed by ramping from -45°C to 150°C at 3°C / minute. During this ramp, the sample 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 were recorded at selected temperatures during the sweep. The T g g was also determined as the peak in the tan delta versus temperature curve.

[0118] Haze test

[0119] Haze determination was performed using a HunterLab Ultrascan Pro spectrophotometer in transmission mode. One of the carrier liners was removed and the sample was laminated to a piece of clear 0.7 mm thick LCD glass (Swift Glass, Elmira Heights, New York). The sample was placed in the Ultrascan Pro spectrophotometer to determine the transmission and haze % through the OCA / glass assembly.

[0120] Polyurethane (PU) preparation

[0121] To a resin reaction vessel equipped with a mechanical stirrer, condenser, and air inlet, 200 g of polyol, 17.26 g of DI, 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 °C ± 2 °C until the NCO signal disappeared under FT-IR spectroscopy. During the reaction, a total of 170 g of MEK was added to dilute the viscosity of the system. A 50 wt% clear PU solution was obtained with an intrinsic viscosity (IV) of 0.47.

[0122] Low IV polyurethane (PU-low IV) preparation

[0123] To a resin reaction vessel equipped with a mechanical stirrer, condenser, and air inlet, 200.43 grams (g) of polyol, 17.02 g of DI, 0.55 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 °C ± 2 °C until the isocyanate peak disappeared under FT-IR spectroscopy. During the reaction, a total of 125 g of MEK was added to dilute the viscosity of the system. A 56 wt% clear PU solution was obtained with an IV of 0.40.

[0124] Polyurethane with 0.2 acid functionality (PU-0.2 acid) preparation

[0125] To a resin reaction vessel equipped with a mechanical stirrer, condenser, and air inlet, 200.98 grams (g) of polyol, 19.32 g of DI, 1.1 g of Bis-GMA, 0.44 g of DMPA, 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 °C ± 2 °C until the isocyanate peak disappeared under FT-IR spectroscopy. During the reaction, about 172 g of MEK was added to dilute the viscosity of the system. A 50 wt% clear PU solution was obtained with an IV of 0.46.

[0126] Polyurethane with 0.5 acid functionality (PU-0.5 acid) preparation

[0127] Add 200 grams (g) of polyol, 20.37 g of DI, 1.1 g of Bis-GMA, 1.11 g of DMPA, 0.02 g of BHT, 0.11 g of DBTDA, and 50 g of MEK to a resin reaction vessel equipped with a mechanical stirrer, condenser, and air inlet. Heat the solution to up to 75 °C while stirring. Maintain the temperature at 75 °C ± 2 °C until the isocyanate peak disappears under FT-IR spectroscopy. During the reaction, add about 172 g of MEK to dilute the viscosity of the system. Obtain a clear PU solution at 50 wt% with an IV of 0.48.

[0128] Comparative examples CE-1 to CE-2 and examples EX-1 to EX-6

[0129] Preparation of curable formulations

[0130] All curable formulations were prepared by adding polyurethane polymer (as 50% in MEK), (meth)acrylate functionalized oligomer, polyvinylpyrrolidone based oligomer or copolymer, tackifier, and photoinitiator (in wt%) as shown in Table 2. Typically, all materials were mixed together in an 8 oz amber jar and roll mixed for at least 8 h until the formulation was completely homogeneous.

[0131] Preparation of adhesive coating

[0132] The adhesive formulation was first coated on Liner-2 using a knife coater to control the coating thickness. The coating was dried at ambient temperature for 10 min and subsequently dried at 70 °C for 15 min before laminating Liner-1 on the dried adhesive.

[0133] The samples were tested according to the test methods described above and their data are summarized in Table 2. Comparing CE-2 with CE-1, more urethane diacrylate oligomer CN983 increased G' but decreased peel at 25 °C. When comparing EX-1 with CE-1, using PVP oligomer increased both G' and peel at 25 °C. In the case of using different molecular weight PVP oligomers (EX-2, EX-3, and EX-4), higher molecular weight was observed to increase both G' and peel at 25 °C. EX-5 using PVP-VA copolymer resulted in the highest peel at 25 °C. EX-6 using lower IV PU showed higher 70 °C tan delta before 3J UV cure, indicating better flowability of the curable adhesive.

[0134] Preparations PE-1 to PE-5

[0135] A series of prep adhesive solutions were prepared using the formulations shown in Table 3. In Table 3 below, adhesive solutions were prepared by adding the indicated amounts of acrylic monomers together with the indicated amounts of solvent EtOAC, thermal initiator (Vazo 52), and chain transfer agent (PE1) into a glass container. After sparging the solution with nitrogen for 3 minutes, the container was sealed and heated to 60°C for 16 hours, then heated to 65°C for 4 hours. The container was opened and B8108 and IEM were added as indicated in Table 3 below. The container was resealed and heated at 60°C for 12 hours.

[0136]

[0137] Comparative example CE-3 and examples EX-7, EX-8

[0138] Polymer solutions of PVP2 (Mw ~ 2500 g / mol) were added to base polymers PE-3 and PE-4 in the amounts indicated in Table 4 below along with 15 pph of CN983, 0.4 pph of photoinitiator I651, and 0.1 pph of silane KBM403, and mixed for at least 12 h. The samples were coated and tested for both DMA and peel as described above. The properties listed below represent 3 J / cm w ~2500g / mol) to base polymers PE-3 and PE-4 in the amounts indicated in Table 4 below along with 15 pph of CN983, 0.4 pph of photoinitiator I651, and 0.1 pph of silane KBM403, and mixed for at least 12 h. The samples were coated and tested for both DMA and peel as described above. The properties listed below represent 3 J / cm 2 ~2,500 g / mol) to base polymers PE-3 and PE-4 in the amounts indicated in Table 4 below along with 15 pph of CN983, 0.4 pph of photoinitiator I651, and 0.1 pph of silane KBM403, and mixed for at least 12 h. The samples were coated and tested for both DMA and peel as described above. The properties listed below represent 3 J / cm w ~2,500g / mol) to base polymers PE-3 and PE-4 in the amounts indicated in Table 4 below along with 15 pph of CN983, 0.4 pph of photoinitiator I651, and 0.1 pph of silane KBM403, and mixed for at least 12 h. The samples were coated and tested for both DMA and peel as described above. The properties listed below represent 3 J / cm

[0139]

[0140] Comparative examples CE-4 and CE-5 and examples EX-9 to EX-12

[0141] Polymer solutions of PVP and PVP copolymers of different molecular weights were added to base polymer PE-4 or PE-5 as indicated in Table 5 in the amounts indicated along with 15 pph of CN983, 0.4 pph of photoinitiator I-651, and 0.1 pph of silane KBM403 to make compositions of EX-9 to EX-12, CE-4, and CE-5. These components were mixed for at least 12 h. The samples were coated and tested for both DMA and peel as described above. The properties listed below represent 3 J / cm 2 UVA irradiated samples.

[0142] Likewise, the trend of increasing modulus at 25°C and increased peel at 25°C and 85°C was observed with the addition of PVP or PVP copolymer components. In particular, PVP1 at 10,000 g / mol and PVP-VA at 50,000 g / mol showed both high modulus and high adhesion compared to the comparative examples and other examples listed in Table 5. The control adhesive, which indicated no addition of PVP or PVP copolymer, when tested for modulus at 25°C and 85°C.

[0143]

[0144] Comparative examples CE-6, CE-7, CE-8, CE-9 and examples EX-13, EX-14

[0145] Preparation of curable formulations

[0146] All curable formulations were prepared by adding amounts of polyurethane polymer (50% in MEK), (meth)acrylate functionalized oligomer, polyvinylpyrrolidone based oligomer or copolymer, tackifier, and photoinitiator (in weight %) as shown in Table 6. All materials were mixed together in an 8 oz amber jar and mixed for at least 8 h until the formulation was uniform.

[0147] Preparation of adhesive coating

[0148] First, the adhesive formulation was coated on Liner-2 using a knife coater to control the coating thickness. The coating was dried at ambient temperature for 10 min and subsequently heated to 70°C for 15 min, then Liner-1 was laminated to the dried adhesive.

[0149] As outlined in Table 7, comparing EX-13 (acid containing PU + PVP) to CE-6 (no acid in PU, no PVP) and CE-7 (no acid in PU, with PVP), it was observed that the acid groups significantly increased the 85°C G' before and after curing, indicating strong hydrogen bonding between the acid containing PU and PVP oligomers.

[0150] When comparing EX-14 (acid containing PU + PVP) to CE-8 (PU without acid, with PVP), EX-14 shows a significant decrease in tan delta at 70°C before and after cure and a significant increase in G' at 85°C before and after cure, indicating an interaction between the acid containing PU and the PVP oligomer. Comparing EX-14 (acid containing PU + PVP) to CE-9 (acid containing PU, no PVP), the former shows a decrease in tan delta at 70°C before cure and an increase in G' at 85°C. When comparing EX-14 to CE-9, the addition of PVP results in almost a doubling of G' at 25°C after cure, while also showing a significantly improved peel performance.

[0151]

[0152] All cited references, patents and patent applications referenced in the granted patent applications above are incorporated herein by reference in their entirety. In the event of an inconsistency between the incorporated references and the present application, the information in the foregoing description shall prevail. The foregoing description of the present disclosure is not intended to be limiting of the scope of the disclosure, which is defined solely by the claims, and equivalents thereof.

Claims

1. A curable adhesive comprising: a poly(meth)acrylate or (meth)acrylate-containing polyurethane; one or more (meth)acrylate monomers and / or (meth)acrylate-containing oligomers; a free radical initiator; and a polyvinylpyrrolidone or copolymer thereof.

2. The curable adhesive of claim 1, further comprising a silane adhesion promoter, optionally comprising 3-glycidyloxypropyltrimethoxysilane.

3. The curable adhesive of claim 1 or 2, wherein the (meth)acrylate-containing polyurethane is a linear polyurethane containing pendant acrylate groups.

4. The curable adhesive of any one of claims 1 to 3, wherein the poly(meth)acrylate comprises pendant acrylate groups.

5. The curable adhesive of any one of claims 1 to 4, wherein the free radical initiator comprises a photoinitiator.

6. The curable adhesive of any one of claims 1 to 5, wherein the (meth)acrylate- containing polyurethane is derived from a reactive mixture comprising: an aliphatic polyisocyanate; and an aromatic polyester polyol.

7. The curable adhesive of claim 6, wherein the aromatic polyester polyol is derived from phthalic acid.

8. The curable adhesive of claim 6 or 7, wherein the reactive mixture further comprises bisphenol A glyceryl dimethacrylate.

9. The curable adhesive of any one of claims 6 to 8, wherein the reactive mixture further comprises a carboxylic acid-containing polyol.

10. The curable adhesive of claim 9, wherein the carboxylic acid-containing polyol comprises dimethylolpropionic acid.

11. The curable adhesive of any one of claims 1 to 10, wherein the one or more (meth)acrylate monomers and / or (meth)acrylate-containing oligomers comprise ethoxylated trimethylolpropane triacrylate.

12. The curable adhesive of any one of claims 1 to 11, wherein the one or more (meth)acrylate monomers and / or (meth)acrylate-containing oligomers comprise urethane acrylate oligomers.

13. The curable adhesive of claim 12, wherein the urethane acrylate oligomers comprise polyester-based urethane diacrylate oligomers.

14. The curable adhesive of any one of claims 1 to 13, wherein the homopolymer T of the (meth)acrylate-containing oligomer is greater than 50 °C. g greater than 50 °C.

15. The curable adhesive of any one of claims 1 to 14, wherein the polyvinylpyrrolidone or copolymer thereof comprises a polyvinylpyrrolidone homopolymer.

16. The curable adhesive of any one of claims 1 to 15, wherein the polyvinylpyrrolidone or copolymer thereof comprises an N-vinylpyrrolidone-co-vinyl acetate copolymer.

17. The curable adhesive of any one of claims 1 to 16, wherein the polyvinylpyrrolidone or copolymer thereof is present in an amount of 2 to 30 weight percent relative to the total weight of the curable adhesive.

18. The curable adhesive of any one of claims 1 to 17, wherein the curable adhesive exhibits a tan delta of 0.5 to 2 at 70 °C.

19. The curable adhesive of any one of claims 1 to 18, wherein the adhesive is optically clear having a haze value of less than 2%.

20. A method of making a curable adhesive, the method comprising: providing a poly(meth)acrylate, or, alternatively, reacting an aliphatic polyisocyanate with an aromatic polyester polyol to obtain a (meth)acrylate-containing polyurethane; and combining 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, an optional adhesion promoter consisting of a silane adhesion promoter, and a polyvinylpyrrolidone or copolymer thereof to obtain the curable adhesive.

21. A method of making a bonded assembly, the method comprising: placing the curable adhesive of any one of claims 1 to 19 between opposing major surfaces of a first adherend and a second adherend, wherein the free radical initiator comprises a photoinitiator; and exposing the curable adhesive to actinic radiation to obtain a cured adhesive, wherein the cured adhesive exhibits a tan delta of 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.

22. A bonded assembly made using the method of claim 21, wherein the first adherend or the second adherend comprises a multilayer optical film.

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