Adhesives and optically clear adhesives with high BIO-content

Abstract

Curable compositions comprising: a (meth)acrylate-functional polyurethane polymer that is the reaction product of a reaction mixture comprising: a polyisocyanate; a polyol; and a hydroxyl-reactive or isocyanate-reactive (meth)acrylate; at least one ethylenically unsaturated monomer having polar content that is a vinyl functional polar monomer or a (meth)acrylate represented by the formula CH2=CR1-(CO)-O-R2 wherein R1 is an H or a methyl group; (CO) is a carbonyl group C=O; R2 is an -R3-(X)p group or a polyether group; R3 is a linear or branched p+1 valent aliphatic group with at least two carbon atoms; X is a polar group comprising a hydroxyl group, a nitrogen-containing group, or an acid group; and p is an integer of 1 or greater; a menthyl (meth)acrylate represented by the structure OO R wherein R is an H or a methyl group; and an initiator and articles including the same.

Description

[0001] ADHESIVES AND OPTICALLY CLEAR ADHESIVES WITH HIGH BIO-CONTENT

[0002] SUMMARY

[0003] In one aspect, provided herein are curable compositions comprising: a (meth)acrylate-functional polyurethane polymer that is the reaction product of a reaction mixture comprising: a polyisocyanate; a polyol; and a hydroxyl-reactive or isocyanate-reactive (meth)acrylate; at least one ethylenically unsaturated monomer having polar content that is a vinyl functional polar monomer or a (meth)acrylate represented by the formula

[0004] CH2=CR1-(CO)-O-R2wherein R1is an H or a methyl group;

[0005] (CO) is a carbonyl group C=O;

[0006] R2is an -R3-(X)Pgroup or a polyether group;

[0007] R3is a linear or branched p+1 valent aliphatic group with at least two carbon atoms;

[0008] X is a polar group comprising a hydroxyl group, a nitrogen-containing group, or an acid group; and p is an integer of 1 or greater; a menthyl (meth)acrylate represented by the structure wherein R is an H or a methyl group; and an initiator.

[0009] In another aspect, provided are articles including such curable compositions.

[0010] As used herein: the term "alkyl group" and the prefix "alk-" have only C-C bonds and C-H bonds and are inclusive of both straight chain and branched chain groups and of cyclic groups. In some embodiments, alkyl groups have up to 30 carbons (in some embodiments, up to 20, 15, 12, 10, 8, 7, 6, or 5 carbons) unless otherwise specified. Cyclic groups can be monocyclic or polycyclic and, in some embodiments, have from 3 to 10 ring carbon atoms and other alkyl substituents; the term “acrylic” refers to both acrylic and methacrylic polymers, oligomers, and monomers; the term "directly bonded to" means bonded to through a single covalent bond; the term "free-radically polymerizable" means free-radically homopolymerizable and / or free radically copolymerizable (i.e., with a different monomer / oligomer); the term “bio-content” refers to the amount of biomass in a product, taking account of the four key components: carbon, hydrogen, oxygen and nitrogen; the bio-based content is expressed as a percentage of the overall weight of the product in question.

[0011] The term “biobased” refers to e.g., compositions that mainly consist of a substance (or substances) derived from living matter (biomass) and either occur naturally or are synthesized, or it may refer to products made by processes that use biomass. Following a strict definition, many common materials, such as paper, wood, and leather, can be referred to as biobased, but typically, the term refers to modem materials that have undergone more extensive processing. Materials from biomass sources include bulk chemicals, platform chemicals, solvents, polymers, and biocomposites (some materials may fall under more than one category).

[0012] The term “high bio-content” refers to e.g., compositions with at least 14% (in some embodiments 16, 18, 20, 22%) bio-content.

[0013] The term "(meth)acryl" refers to acryl (also referred to in the art as acryloyl and acrylyl) and / or methacryl (also referred to in the art as methacryloyl and methacrylyl).

[0014] Terms such as "a", "an" and "the" are not intended to refer to only a singular entity but include the general class of which a specific example may be used for illustration. The terms "a", "an", and "the" are used interchangeably with the term "at least one".

[0015] The phrase "comprises at least one of’ followed by a list refers to comprising any one of the items in the list and any combination of two or more items in the list. The phrase "at least one of’ followed by a list refers to any one of the items in the list or any combination of two or more items in the list.

[0016] The terms “cure” and “curable” refer to joining polymer chains together by covalent chemical bonds, usually via crosslinking molecules or groups, to form a network polymer.

[0017] 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.

[0018] All numerical ranges are inclusive of their endpoints and non-integral values between the endpoints unless otherwise stated (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 5).

[0019] Features and advantages of the present disclosure will be further understood upon consideration of the detailed description as well as the appended claims.

[0020] BRIEF DESCRIPTION OF THE DRAWINGS

[0021] FIG. 1 is a graph showing the rheology data for Example 2 ("Ex-2") and Comparative Example ("CEx") of this disclosure. DETAILED DESCRIPTION

[0022] The present disclosure provides curable compositions including a (meth)acrylate-functional polyurethane polymer that is the reaction product of a reaction mixture comprising: a poly isocyanate; a polyol; and a hydroxyl-reactive or isocyanate-reactive (meth)acrylate; at least one ethylenically unsaturated monomer having polar content that is a vinyl functional polar monomer or a (meth)acrylate represented by the formula CH2=CR1-(CO)-O-R2wherein R1is an H or a methyl group;

[0023] (CO) is a carbonyl group C=O;

[0024] R2is an -R3-(X)Pgroup or a polyether group;

[0025] R3is a linear or branched p+1 valent aliphatic group with at least two carbon atoms;

[0026] X is a polar group comprising a hydroxyl group, a nitrogen-containing group, or an acid group; and p is an integer of 1 or greater; a menthyl (meth)acrylate represented by the structure wherein R is an H or a methyl group; and an initiator.

[0027] In some embodiments, the curable composition, upon curing in the form of a layer forms a pressure sensitive adhesive layer or a heat activated adhesive layer having a haze value of less than 1%, preferably less than 0.5%.

[0028] In some embodiments, the (meth)acrylate-functional polyurethane polymer is the reaction product of a reaction mixture comprising an aliphatic polyisocyanate, a polyol, and a hydroxyl-reactive or isocyanate-reactive (meth)acrylate.

[0029] In some embodiments, the (meth)acrylate-functional polyurethane polymer is the reaction product of a reaction mixture comprising a polyisocyanate, a polyester polyol, and a hydroxyl-reactive or isocyanate-reactive (meth)acrylate.

[0030] In some embodiments, the (meth)acrylate-functional polyurethane polymer has a number average molecular weight of at least 4000 grams / mole.

[0031] In some embodiments, the ethylenically unsaturated monomer having polar content is 2- hydroxyethyl (meth)acrylate. In some embodiments, the aliphatic polyisocyanate is represented by the formula (OCN-L)n- R4wherein R4is an n-valent aliphatic group;

[0032] L is single bond or an alkylene linking group; and n is an integer of at least 2.

[0033] In some embodiments, the polyester polyol is represented by the formula

[0034] (HO)m- R5wherein R5is an m-valent aliphatic group having a polyester linkage and m is an integer of at least 2.

[0035] In some embodiments, the polyester polyol is a dimerized fatty acid-based polyester polyol.

[0036] In some embodiments, the hydroxyl-reactive or isocyanate-reactive (meth)acrylate is represented by the formula

[0037] CH2=CR1-(CO)-O-R2-Z wherein R1is an H or a methyl group;

[0038] (CO) is a carbonyl group C=O;

[0039] R2is linear or branched alkylene group with at least 2 carbon atoms;

[0040] Z is a hydroxyl group or an isocyanate group.

[0041] In some preferred embodiments, the menthyl (meth)acrylate is L-menthyl (meth)acrylate.

[0042] In some embodiments, the menthyl (meth)acrylate is derived from L-menthol and in some preferred embodiments the menthyl (meth)acrylate is derived from biobased L-menthol.

[0043] In some embodiments, the curable composition may include at least one other free-radically polymerizable bio-based monomer such as, for example, ethyl (meth)acrylate, behenyl (meth)acrylate, stearyl (meth)acrylate, lauryl (meth)acrylate, 2-octyl (meth)acrylate, or combinations thereof.

[0044] In some embodiments, the composition may include, alone or in combination with other free- radical initiator(s) known to those of ordinary skill in the art, at least one photoinitiator that is activated by light, generally using an ultraviolet (“UV”) lamp, although other light sources such as LED lamps, Xe flashlamps, and lasers can also be used with the appropriate choice of photoinitiator. Useful photoinitiators include those known as useful for photocuring free-radically polyfunctional (meth)acrylates. Examples of suitable photoinitiators include benzoin and its derivatives such as alpha-methylbenzoin; alphaphenylbenzoin; alpha-allylbenzoin; alpha benzylbenzoin; benzoin ethers such as benzil dimethyl ketal (e.g., available as OMNIRAD BDK from IGM Resins USA Inc., St. Charles, Illinois), benzoin methyl ether, benzoin ethyl ether, benzoin n-butyl ether; acetophenone and its photoinitiator.

[0045] Other useful photoinitiators include the class of phosphine oxides. Preferred phosphine oxide photoinitiators with a functional wavelength range of about 365 nm to about 450 nm are acyl and bisacyl phosphine oxides. In a preferred embodiment, the photoinitiator initiates free radical polymerization of the composition when exposed to actinic radiation having a wavelength of from 365 nm to 450 nm. Commercially available phosphine oxide photoinitiators capable of free-radical initiation when irradiated at wavelength ranges of 365 nm to 450 nm include bis(2,4,6-trimethylbenzoyl)phenyl phosphine oxide (IRGACURE 819, Ciba Specialty Chemicals, Tarrytown, N.Y. or Omnirad 819 IGM Resins B.V. Waalwijk, Netherlands), (2,4,6-trimethylbenzoyl) diphenyl phosphine oxide (Omnirad TPO IGM Resins B.V. Waalwijk, Netherlands), bis(2,6-dimethoxybenzoyl)-(2,4,4-trimethylpentyl)phosphine oxide (CGI 403, Ciba Specialty Chemicals), a 25:75 mixture, by weight, of bis(2,6-dimethoxybenzoyl)-2,4,4- trimethylpentyl phosphine oxide and 2 -hydroxy -2 -methyl- 1-phenylpropan-l -one (IRGACURE 1700, Ciba Specialty Chemicals), a 1:1 mixture, by weight, of bis(2,4,6-trimethylbenzoyl)phenyl phosphine oxide and 2 -hydroxy -2 -methyl- 1 -phenylpropane- 1 -one (DAROCUR 4265, Ciba Specialty Chemicals), and ethyl 2,4,6-trimethylbenzylphenyl phosphinate (LUCIRIN LR8893X, BASF Corp., Charlotte, N.C.).

[0046] In some embodiments, the curable composition may include an additive, such as, for example, a silane adhesion promoter, a UV absorber, a tackifier, a rheological modifier, a radical stabilizer, a corrosion inhibitor, or combinations thereof.

[0047] In another aspect, provided herein are articles comprising: a substrate with a first major surface and a second major surface; and a pressure sensitive adhesive layer or heat activated adhesive layer disposed on at least a portion of the second major surface of the substrate, the pressure sensitive or heat activated adhesive layer being the reaction product of the curable composition of any one of the embodiments described above. In some embodiments, the substrate comprises an optically clear substrate comprising a polymeric film or a plate.

[0048] In some embodiments, the pressure sensitive adhesive layer has a thickness of from 10 micrometers to 1 millimeter. In some embodiments, the bio-content of the adhesive layer is at least 14% by weight.

[0049] In another aspect, the curable composition comprises at least one (methjacrylate-functional polyurethane polymer. The at least one (methjacrylate-functional polyurethane polymer is the reaction product of a reaction mixture comprising at least one aliphatic polyisocyanate, at least one polyester polyol, and a hydroxyl-functional or isocyanate-functional (methjacrylate. Each of these components of the reaction mixture are described in greater detail below.

[0050] Suitable (methjacrylate-functional polyurethane polymer(s) may include aromatic urethane acrylates, aliphatic urethane acrylates, aromatic / aliphatic urethane acrylates and combinations thereof. Many (methjacrylate-functional polyurethane polymer(s) are available commercially. Suitable examples of (methjacrylate-functional polyurethane polymer(s) may be obtained from Arkema, King of Prussia, Pennsylvania; SOLTECH LTD., Yangsan, South Korea, and; Nippon Soda Co. Ltd., Chiyoda, Japan, and; Dy max, Torrington, Connecticut, and Eternal Materials Co., Ltd Taiwan.

[0051] Typically, the polyurethane polymer is formed by forming a pre-polymer by reacting the at least one polyisocyanate and the at least one polyol. The pre-polymer is either isocyanate-functional or hydroxyl-functional depending upon the ratio of the at least one polyisocyanate, to the at least one polyol. The prepolymer is then end-capped by reacting with either a hydroxyl-functional or isocyanate-functional acrylate, methacrylate or combination thereof.

[0052] In some embodiments, the at least one aliphatic polyisocyanate is of Formula 1:

[0053] (OCN-L)„-A

[0054] Formula 1 where A is an n-valent aliphatic group, L is single bond or an alkylene linking group; n is an integer of 2 or greater.

[0055] Examples of diisocyanates include: aromatic diisocyanates (for example, 2,6-toluene diisocyanate; 2,5-toluene diisocyanate; 2,4-toluene diisocyanate; m-phenylene diisocyanate; p-phenylene diisocyanate; methylene bis(o-chlorophenyl diisocyanate); methylenediphenylene-4,4'-diisocyanate; polycarbodiimide- modified methylenediphenylene diisocyanate; (4,4'-diisocyanato-3,3',5,5'-tetraethyl) diphenylmethane; 4, 4'-diisocyanato-3, 3 '-dimethoxybiphenyl (o-dianisidine diisocyanate); 5-chloro-2,4-toluene diisocyanate; and l-chloromethyl-2,4-diisocyanato benzene), aromatic -aliphatic diisocyanates (for example, m-xylylene diisocyanate and tetramethyl-m-xylylene diisocyanate); aliphatic diisocyanates (for example, 1,4- diisocyanatobutane; 1,6-diisocyanatohexane; 2-methyl-l,5-pentamethylene diisocyanate; 1,12-dodecane diisocyanate); cycloaliphatic diisocyanates (for example, methylenedicyclohexylene-4,4'-diisocyanate; 3- isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (isophorone diisocyanate); 2,2,4-trimethylhexyl diisocyanate; l,4-cyclohexanebis(methylene isocyanate), l,3-bis(isocyanatomethyl)cyclohexane; and cyclohexylene-l,4-diisocyanate), polymeric or oligomeric compounds (for example, polyoxyalkylene, polyester, polybutadienyl, and the like) terminated by two isocyanate functional groups (for example, the diurethane of toluene-2,4-diisocyanate- terminated polypropylene oxide glycol); polyisocyanates commercially available under the trade designation MONDUR or DESMODUR (for example, DESMODUR XP7100 and DESMODUR 3300) from Covestro (Pittsburgh, PA); and combinations thereof.

[0056] Of these, particularly advantageous diisocyanates include aliphatic diisocyanates. Aliphatic diisocyanates were generally observed to provide superior weatherability compared with their aromatic counterparts. Particularly preferred species include dicyclohexylmethane diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, tetramethylxylene diisocyanate (TMXDI), l,4-cyclohexanebis(methylene isocyanate), l,3-bis(isocyanatomethyl)cyclohexane, 2-methyl-l,5-pentamethylene diisocyanate, 1,12-dodecane diisocyanate, along with copolymers and mixtures thereof. In select embodiments, the diisocyanate includes at least one ring in its structure, i.e., comprises a cyclic structure.

[0057] In some embodiments, the at least one aliphatic poly isocyanate of Formula 1 comprises a diisocyanate where A is an alkylene group with at least 6 carbon atoms, L is single bond, and n is an integer of 2.

[0058] Examples of particularly suitable polyisocyanates include the liquid cycloaliphatic di-isocyanates commercially available from Covestro of Leverkusen, Germany under the trade name “DESMODUR” such as DESMODUR W, DESMODUR H, DESMODUR I, or from Evonik Corporation of Theodore, AL under the trade name “VESTANAT” such as VESTANAT TMDI (a mixture of 2,2,4- and 2,4,4-trimethyl- hexamethylene di-isocyanate), VESTANAT IPDI, or from Vencorex Chemicals of Freeport, TX such as hexamethylene diisocyanate and isophorone diisocyanate.

[0059] Polyols used in polyurethane synthesis include, for example, polyester polyols, polyether polyols, polycaprolactone polyols, polycarbonate polyols, polyolefin polyols, fatty acid dimer diols, and copolymers and mixtures thereof. Examples of suitable polyols include materials commercially available under the trade designation DESMOPHEN from Covestro LLC (Pittsburgh, PA). The polyols can be polyester polyols (for example, DESMOPHEN CHOO, C1200, 850, and 1700 or available under the trade designation FOMREZ from Lanxess AG (Cologne, Germany)) or SREPANPOL from Stepan Company (Northfield, IL); polyether polyols (for example, DESMOPHEN 1262BD, 1110BD, 1111BD or materials commercially available under the trade designation KURARAY P-500, P-1010, P-2010, P-3010, P-4010, P-5010, P-6010, P-2011, P-520, P-1020, P-2020, P-1012, P-2012, P-530, P-2030, and P-2050 from Kuraray (Tokyo, Japan)); polycaprolactone polyols such as, for example, caprolactone polyols available under the trade designation CAPA from Ingevity (North Charleston, SC) (for example, CAPA 2043, 2054, 2100, 2121, 2200, 2201, 2200A, 2200D, 2100A, 3031, 3091, and 3051); polycarbonate polyols (for example, polycarbonate polyols available under the trade designations PC-1122, PC-1167, and PC-1733 from Picassian Polymers (Boston, MA), under the trade designation DESMOPHEN C2102, 2202, C XP 2716, C XP 2613 from Covestro LLC, and under the trade designation KURARAY C-590, C-1090, C- 2090, and C-3090 from Kuraray); polyolefin polyols (for example polyolefin polyols available from Nippon Soda Co., LTD under the trade designation NISSO-PB).

[0060] The reaction mixture also comprises at least one polyester polyol. In some embodiments, the at least one polyester polyol is of Formula 2:

[0061] (HO)m-B

[0062] Formula 2 where B is an m-valent aliphatic group with at least one polyester linkage, and m is an integer of 2 or greater.

[0063] In some embodiments, the at least one polyester polyol of Formula 2 comprises a polyester diol of at least 500 molecular weight where B is a di-valent aliphatic group with at least one polyester linkage, m is an integer of 2.

[0064] In some embodiments, the polyester diol is prepared from the condensation reaction of a di-acid and a diol, where at least one of the di-acid and the diol comprise an alkylene group with at least 12 carbon atoms. In some embodiments, it may be desirable that the alkylene group with at least 12 carbon atoms be a branched alkylene group.

[0065] Examples of particularly suitable polyester polyols include the dimerized fatty acid-based polyester polyols from Cargill, Minneapolis MN under the trade name “PRIPLAST” such as PRIPLAST 3196, PRIPLAST 3190, PRIPLAST 3238, PRIPLAST 3187, PRIPLAST 3188, PRIPLAST 3186, PRIPLAST 1838, PRIPLAST 3172, PRIPLAST 3197, PRIPLAST 3286 and PRIPLAST 3293, and combinations thereof.

[0066] In some embodiments, it may be desirable to include a polyol of Formula 7:

[0067] D-((E-OH)-Y)a

[0068] Formula 7 where D is an a-valent aromatic, aliphatic, or alkylene oxide group, E is an alkylene oxide linking group, Y is a (meth)acrylate group, and a is an integer of 2 or greater. An advantage of including this type of monomer is that the (meth)acrylate group is already attached to the polyol and thus does not need to react with a compound of Formula 3 as described below.

[0069] Examples of suitable compounds of Formula 7 are the DENACOL ACRYLATE materials commercially available from Nagase ChemteX Corporation as DA-911, DA-920, DA-931, DA-212, DA- 214, DA-250, DA-721, and DM-201.

[0070] Typically, if used, the polyol of Formula 7 is a minor component of the reaction mixture and additional polyols as described above, are also present in the reaction mixture.

[0071] In some embodiments, it is desirable that the functionality of the pre-polymer formed by the reaction of a polyisocyanate and polyol have a functionality of less than 2. It is well understood that the reaction of a diol and a diisocyanate forms a linear difunctional prepolymer. To form a prepolymer with a functionality of less than 2, at least some of the reactants have a functionality of less than 2. In some of the embodiments, the reaction mixture comprises at least some reactants that are monofunctional such that the average functionality of the prepolymer is greater than 1 and less than 2. This prepolymer upon reaction with the (meth)acrylate-functional compound described below forms the (meth)acrylate-functional polyurethane. Therefore, in these embodiments, the (meth)acrylate-functional polyurethane polymer has a functionality of greater than 1 and less than 2.

[0072] Examples of suitable monofunctional reactants are described by Formula 8:

[0073] Z-L-K

[0074] Formula 8 where K is an aliphatic group, L is single bond or an alkylene linking group, and Z is a hydroxyl group or an isocyanate group.

[0075] The reaction mixture also comprises at least one acrylate, methacrylate, or a combination thereof of Formula 3 :

[0076] CH2=CR1-(CO)-O-R2-Z

[0077] Formula 3 where R1is an H or a methyl group, (CO) is a carbonyl group C=O, R2is a linear or branched alkylene group with at least 2 carbon atoms, and Z is an isocyanate-reactive group or hydroxyl-reactive group. Examples of isocyanate-reactive groups include hydroxyl groups, acid groups, and amino groups. Examples of hydroxyl-reactive groups include isocyanates, carboxylic acid groups, and anhydrides. Typically, the Z groups are isocyanates or hydroxyl groups.

[0078] As described above, the choice of whether the Z group is a hydroxyl group or an isocyanate group depends upon the relative ratio of the polyisocyanate and polyol components described above. If the polyisocyanate is present in excess so that the growing polymer is isocyanate-functional, the acrylate or methacrylate is hydroxyl-functional (i.e. reactive with isocyanate groups). If the polyester polyol is present in excess so that the growing polymer is polyol-functional, the acrylate or methacrylate is isocyanate- functional (i.e. reactive with hydroxyl groups).

[0079] The choice of whether the component is an acrylate, methacrylate or a combination thereof depends upon the desired properties of the polyurethane polymer. Because acrylates and methacrylates react at different rates, the functionality of the polyurethane polymer provides a handle for controlling the ultimate properties of the formed adhesive layer.

[0080] In some embodiments, the at least one acrylate, methacrylate, or a combination thereof of Formula 3 is a hydroxyl-functional (meth)acrylate where R1is an H or a methyl group, (CO) is a carbonyl group C=O, R2is linear or branched alkylene group with at least 2 carbon atoms, and Z is a hydroxyl group.

[0081] Examples of particularly suitable hydroxyl-functional (meth)acrylates include HEA (2 -hydroxyethyl acrylate), HEMA (2 -hydroxy ethyl ethyl methacrylate), HPA (hydroxypropyl acrylate), HPMA (hydroxypropyl methacrylate), HBA (4-hydroxybutyl acrylate), and HBMA (4 -hydroxybutyl methacrylate).

[0082] The kinetics of the polymerization between the polyisocyanate and polyol species is typically accelerated with the help of a suitable catalyst. In exemplary embodiments, the (meth)acrylate-functional polyurethane polymer is prepared using any of a wide variety of known urethane catalysts, including dibutyltin dilaurate, dibutyltin diacetate, stannous octoate, triethylene diamine, zirconium catalysts, and bismuth catalysts.

[0083] In some embodiments, the at least one (meth)acrylate-functional polyurethane polymer has a number average molecular weight of at least 4000 grams / mole.

[0084] In some embodiments, the ethylenically unsaturated monomer having polar content is an acrylic monomer and can comprise a hydroxyl group. The acrylic monomer comprising the hydroxyl group can be useful, for example, for providing the composition with improved adhesion to a variety of plastics, in some embodiments, polyamides, acrylonitrile butadiene styrene (ABS), polycarbonate (PC), PC / ABS blends, polyvinyl chloride (PVC), poly(methyl) methacrylate (PMMA). Examples of suitable acrylic monomers comprising a hydroxyl group include 2 -hydroxy ethyl acrylate, 2 -hydroxy ethyl methacrylate, 2- and 3- hydroxypropyl acrylate, 2- and 3-hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, caprolactone mono(meth)acrylate, available under the trade designation “SR-495B” from Sartomer and other poly(e-caprolactone) mono[2- (meth)acryloxy ethyl] esters, poly(e-caprolactone) mono[2-acryloxy ethyl] esters, 2-hydroxy-3 -alkyloxy methacrylate, 2 -hydroxy -3 -alkyloxy acrylate, and polyethylene glycol mono acrylates and methacrylates. Many acrylic monomers comprising a hydroxyl group are available from commercial sources, for example, 2-hydroxyethyl methacrylate (available from Evonik Performance Materials GmbH as VISIOMER HEMA 97 and HEMA 98), hydroxypropyl methacrylate (available from Evonik Performance Materials GmbH as VISIOMER HPMA 97 and HPMA 98).

[0085] Compositions of the present disclosure can also include other monofunctional free-radically polymerizable monomers. Examples of useful monomers include 2-phenoxyethyl (meth)acrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate, alkoxylated lauryl (meth)acrylate, alkoxylated phenol (meth)acrylate, alkoxylated tetrahydrofurfuryl (meth)acrylate, caprolactone (meth)acrylate, cyclic trimethylolpropane formal (meth)acrylate, ethylene glycol methyl ether (meth)acrylate, ethoxylated nonyl phenol (meth)acrylate, isodecyl (meth)acrylate, isooctyl (meth)acrylate, octadecyl (meth)acrylate (stearyl (meth)acrylate), tetrahydrofurfuryl (meth)acrylate, tridecyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, allyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, n- decyl (meth)acrylate, n-dodecyl (meth)acrylate, and combinations thereof.

[0086] Objects and advantages of this disclosure are further illustrated by the following non-limiting examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to unduly limit this disclosure.

[0087] EXAMPLES

[0088] Unless otherwise noted or readily apparent from the context, all parts, percentages, ratios, etc. in the Examples and the rest of the specification are by weight.

[0089] Methods

[0090] Method for Determining Polyurethane Molecular Weight: The molecular weight distribution of the compounds was characterized using gel permeation chromatography (GPC). The GPC instrumentation, which was obtained from Waters Corporation (Milford, Mass., USA), included a high pressure liquid chromatography pump (Model 1515HPLC), an auto-sampler (Model 717), a UV detector (Model 2487), and a refractive index detector (Model 2410). The chromatograph was equipped with two 5 micrometer PL gel MIXED-D columns available from Varian Inc. (Palo Alto, Calif., USA). Samples of polymeric solutions were prepared by dissolving dried polymer samples in tetrahydrofuran at a concentration of 1.0 percent (weight / volume) and filtering through a 0.2 micrometer polytetrafluoroethylene filter that is available from VWR International (West Chester, Pa., USA). The resulting samples were injected into the GPC and eluted at a rate of 1 mL per min. through the columns maintained at 35° C. The system was calibrated with polystyrene standards using a linear least squares analysis to establish a standard calibration curve.

[0091] Haze and Transmission Test: Transmission measurements were made using an ULTRASCANPRO Spectrophotometer (HunterLab, Reston, VA) in transmission mode. For measured samples, a 0.1 mm thick coated adhesive layer between release-coated carrier liners (Liner- l / Liner-2, as described in the Examples below) was cut to approximately 5 cm width by 10 cm length. One of the carrier liners was removed and the sample was laminated to a clear piece of 1 mm thick LCD glass (Swift Glass, Elmira Heights, New York). The second carrier liner was removed, and the sample was placed in the ULTRASCANPRO Spectrophotometer to measure transmission and haze through the glass / OCA assembly.

[0092] 180° Peel on Glass Test: This peel adhesion test is similar to the test method described in ASTM D 3330- 90, substituting a glass substrate for the stainless steel substrate described in the test. The cured adhesive samples were first laminated onto a 2 mil (51 micrometer) primed PET backing (3 SAB from Mitsubishi). They were then slit into 1 cm strips and rolled onto glass substrates with a Cheminstruments HR-100 roller. The test specimens were allowed to condition in a CTH room for 18 h prior to peel adhesion analysis with a 6 cm / min peel rate at a 180° peel angle using a IMass SP-2000 peel tester.

[0093] Dynamic Mechanical Analysis Test: 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 was placed between the probes of a DHR parallel plate rheometer (TA Instruments, New Castle, DE). A temperature scan was performed by ramping from -50°C to 100°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 Tg of the material was also determined as the peak in the Tan delta vs. temperature profile.

[0094] Synthesis of L-menthyl acrylate ("L-MTA"): All quantities were calculated relative to the amount of L-menthol. To a 1 L round bottom flask was added L-menthol (500 g, 3.20 mol, 1.00 eq.), acrylic acid (277 g, 3.84 mol, 1.20 eq.), phenothiazine (1.00 g, 2000 ppm), furfural (1.00 g, 2000 ppm), p-toluenesulfonic acid (pTSA, 5.75 g, 1.15 wt%), and cyclohexane (75.0 g, 15.0 wt%). The flask was equipped with a 30 cm Vigreux column and a Dean-Stark head that was filled with cyclohexane containing 50 ppm of furfural. The separated water was collected every 30 min to Ih throughout the complete reaction. First, the mixture was heated to 120 °C and reacted for Ih, where tO is marked by the start of reflux from the Dean-Stark head. Next, the setpoint was increased to 140 °C, and the mixture was allowed to react for 5.5 h. Finally, the temperature was increased to 150 °C for another 2.5 h, after which the mixture was cooled to room temperature. The conversion was determined via 1H-NMR and was found to be typically >98%.

[0095] The Dean-Stark head was replaced with a Claisen head and a distilling condenser. Vacuum was applied and the crude was heated to 80 °C for Ih. An ultimate vacuum of 5 mmHg was obtained. Next, the batch was heated from 115 °C to 135 °C to collect 545 g of the desired product (95-97°C at 5 mmHg), to which 10 mg of MEHQ (18 ppm) was added. A clear change in refractive index compared to lower boiling compounds can be observed when L-MTA is being distilled. The purity was determined to be >98 wt% via 1H-NMR.

[0096] Two batches of distilled L-MTA (545 g and 550 g) were combined and washed with 220 g of a 2% aqueous sodium hydroxide solution. The organic phase was then washed with 220 g of deionized water until the aqueous phase was neutral (three times). The obtained slightly turbid organic phase was finally filtered over a filter paper to obtain clear L-MTA (1083 g, 80.1% yield). The purity was determined to be >98 wt% via 1H-NMR and GC. 19 mg of MEHQ was added (18 ppm expected). Via standard QC tests, the presence of 19 ppm MEHQ, 0.3 ppm phenothiazine, and 0.173% water was determined. No residual furfural was detected in the sample. L-MTA (C13H22O2 molecular weight 210.32) made from bio-based L- menthol (C10H20O molecular weight 156.27 g / mol) has a bio-content of 73.8% (i.e., 73.8% = 100% x (molecular weight of C10H19O / molecular weight of C13H22O2T)).

[0097] Synthesis of DL-menthyl acrylate ("DL-MTA"):

[0098] All quantities were calculated relative to the amount of DL-menthol. To a 1 L round bottom flask was added DL-menthol (500 g, 3.20 mol, 1.00 eq.), acrylic acid (277 g, 3.84 mol, 1.20 eq.), phenothiazine (1.00 g, 2000 ppm), furfural (1.00 g, 2000 ppm), p-toluenesulfonic acid (pTSA, 5.75 g, 1.15 wt%), and cyclohexane (75.0 g, 15.0 wt%). The flask was equipped with a 30 cm Vigreux column and a Dean-Stark head that was filled with cyclohexane containing 50 ppm of furfural. The separated water was collected every 30min to Ih throughout the complete reaction. First, the mixture was heated to 120 °C and reacted for Ih, where 10 is marked by the start of reflux from the Dean-Stark head. Next, the setpoint was increased to 140 °C, and the mixture was allowed to react for 5.5 h. Finally, the temperature was increased to 150 °C for another 2.5 h, after which the mixture was cooled to room temperature. The conversion was determined via 1H-NMR and was found to be >98%.

[0099] The Dean-Stark head was replaced with a Claisen head and a distilling condenser. Vacuum was applied and the crude was heated to 80 °C for Ih. An ultimate vacuum of 5 mmHg was obtained. Next, the batch was heated from 115 °C to 135 °C to collect 5425 g of the desired product (95-97°C at 5 mmHg), to which 10 mg of MEHQ (18 ppm) was added. A clear change in refractive index compared to lower boiling compounds can be observed when DL-MTA is being distilled. The purity was determined to be >98 wt% via 1H-NMR.

[0100] Two batches of distilled DL-MTA (both 542 g) were combined and washed with 220 g of a 2% aqueous sodium hydroxide solution. The organic phase was then washed with 220 g of deionized water until the aqueous phase was neutral (three times). The obtained slightly turbid organic phase was finally filtered over a filter paper to obtain clear DL-MTA (1076 g, 80.0% yield). The purity was determined to be 98.7 wt% via 1H-NMR. 20 mg of MEHQ was added (19 ppm expected). Via standard QC tests, the presence of 21 ppm MEHQ, 0.2 ppm phenothiazine, and 0.160% water was determined. No residual furfural was detected in the sample.

[0101] Synthesis of polyurethane (meth)acrylate ("PU"):

[0102] To a resin reaction vessel equipped with a mechanical stirrer, a condenser, and an air inlet, 205.6 gram (g) of Polyol, 15.77 g of DI, 0.22 g of BC, 0.08 g of BHT 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 content reached the theoretical NCO value, which was determined by utilizing a standard dibutylamine back titration method. Upon obtaining the theoretical NCO value, the polyurethane was then end capped by adding 2.88 g of HEMA. During the reaction, an additional 50 g of MEK was added to dilute the viscosity of the system. After the reaction was completed, 224 g of 2EHA was added, followed by the evaporation of MEK through a Rotavapor to obtain a polyurethane (meth)acrylate (PU) (Mn = 6300 obtained from GPC) in 2EHA with a weight ratio of 1 : 1. Polyol PRIPL AST 3196 has ~82% of bio-based content; and the final PU (1: 1 weight ratio between polyurethane and 2-EHA) has ~38% of bio-based content.

[0103] Formulations for Optically Clear Adhesives and Test Results for Comparative Example ("CEx") and Examples 1 and 2

[0104] All curable formulations were prepared by adding the PU (as a 1: 1 weight ratio with 2-EHA as described in ‘Synthesis of polyurethane (meth)acrylate ("PU")’), monomers, and photoinitiators in weight percent ratios as shown in Table 1. All materials were mixed together in an 8 oz amber jar and roller mixed for at least 8 hours at room temperature until the formulations were fully homogeneous. Table 1. Optically Clear Adhesive Formulations

[0105] The resulting adhesive formulations were coated between two release liners (Liner- 1 and Liner-2 from SKC Haas) using a knife coater to control the coating caliper (4 mil). The adhesive samples were cured under 405nm UV-LED light with a total dose of 2000 mJ / cm2.

[0106] The cured samples were tested according to the test methods described above, and their test results were summarized in Table 2. Compositions including menthyl acrylates demonstrate good haze (<1%) and peel values similar to compositions including IBOA.

[0107] Table 2. Test Results for Examples

[0108] Rheology Data:

[0109] DMA curves (storage modulus G’ and Tan delta) of CEx and Example 2 ("Ex -2") are shown in FIG. 1 and Table 2 summarized Tg and 25 °C G’. Compared to IBOA-comprising compositions, L-MTA- and DL-MTA-comprising compositions show slightly lower Tg and lower storage modulus.

[0110] The combination of PU and bio-derived L-menthyl (meth)acrylate as high-Tg monomer can provide optically clear adhesives with ~37.6% bio-content.

[0111] All cited references, patents, and patent applications in the above application for letters patent are herein incorporated 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. The preceding description, given in order to enable one of ordinary skill in the art to practice the claimed disclosure, is not to be construed as limiting the scope of the disclosure, which is defined by the claims and all equivalents thereto.

Claims

What is claimed is:

1. A curable composition comprising: a (meth)acrylate-functional polyurethane polymer that is the reaction product of a reaction mixture comprising: a poly isocyanate; a polyol; and a hydroxyl-reactive or isocyanate-reactive (meth)acrylate; at least one ethylenically unsaturated monomer having polar content that is a vinyl functional polar monomer or a (meth)acrylate represented by the formulaCH2=CR1-(CO)-O-R2wherein R1is an H or a methyl group;(CO) is a carbonyl group C=O;R2is an -R3-(X)Pgroup or a polyether group;R3is a linear or branched p+1 valent aliphatic group with at least two carbon atoms;X is a polar group comprising a hydroxyl group, a nitrogen-containing group, or an acid group; and p is an integer of 1 or greater; a menthyl (meth)acrylate represented by the structurewherein R is an H or a methyl group; and an initiator.

2. The curable composition of claim 1, wherein the curable composition, upon curing in the form of a layer forms a pressure sensitive adhesive layer or a heat activated adhesive layer having a haze value of less than 1%, preferably less than 0.5%.

3. The curable composition of claim 1, wherein the (meth)acry late-functional polyurethane polymer is the reaction product of a reaction mixture comprising an aliphatic polyisocyanate, a polyol, and a hydroxylreactive or isocyanate-reactive (meth)acrylate.

4. The curable composition of claim 1, wherein the (meth)acrylate-functional polyurethane polymer is the reaction product of a reaction mixture comprising a polyisocyanate, a polyester polyol, and a hydroxylreactive or isocyanate-reactive (meth)acrylate.

5. The curable composition of claim 1, wherein the (meth)acrylate-functional polyurethane polymer has a number average molecular weight of at least 4000 grams / mole.

6. The curable composition of claim 1, wherein the ethylenically unsaturated monomer having polar content is 2 -hydroxy ethyl (meth)acrylate.

7. The curable composition of claim 1, wherein the polyisocyanate is represented by the formula(OCN-L)n- R4wherein R4is an n-valent aliphatic group,L is single bond or an alkylene linking group; and n is an integer of at least 2.

8. The curable composition of claim 1, wherein the polyol is represented by the formula(HO)m- R5wherein R5is an m-valent aliphatic group having a polyester linkage and m is an integer of at least 2.

9. The curable composition of claim 8, wherein the polyester polyol is a dimerized fatty acid-based polyester polyol.

10. The curable composition of claim 1, wherein the hydroxyl-reactive or isocyanate-reactive (meth)acrylate is represented by the formulaCH2=CR1-(CO)-O-R2-Z wherein R1is an H or a methyl group;(CO) is a carbonyl group C=O;R2is linear or branched alkylene group with at least 2 carbon atoms;Z is a hydroxyl group or an isocyanate group.

11. The curable composition of claim 1, wherein the menthyl (meth)acrylate is L-menthyl (meth)acrylate.

12. The curable composition of claim 1, wherein the menthyl (meth)acrylate is derived from L- menthol.

13. The curable composition of claim 11, wherein the menthyl (meth)acrylate is derived from biobased L-menthol.

14. The curable composition of claim 1, wherein the initiator comprises a photoinitiator.

15. The curable composition of claim 1, further comprising at least one other free-radically polymerizable bio-based monomer.

16. An article comprising: a substrate with a first major surface and a second major surface; and a pressure sensitive adhesive layer or heat activated adhesive layer disposed on at least a portion of the second major surface of the substrate, the pressure sensitive or heat activated adhesive layer being the reaction product of the curable composition of any one of claims 1 to 15.

17. The article of claim 16, wherein the substrate comprises an optically clear substrate comprising a polymeric film or a plate.

18. The article of claim 16, further comprising a silane adhesion promoter, a UV absorber, a tackifier, a rheological modifier, a radical stabilizer, a corrosion inhibitor, or combinations thereof.

19. The article of claim 16, wherein the pressure sensitive adhesive layer has a thickness of from 10 micrometers to 1 millimeter.

20. The article of claim 16, wherein the bio-content of the adhesive layer is at least 14% by weight.

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