Curable compositions, cured compositions, and related method

Abstract

Curable compositions, cured compositions, articles containing the curable or cured compositions, and methods of making the cured compositions are provided. The curable compositions contain a (meth)acrylate-based polymer having pendant (meth)acryloyl groups, at least one monomer having a single ethylenically unsaturated group, a photoinitiator that includes an aminoketone-functional photoinitiator and a photosensitizer, and a thixotropic agent. At least one of the (meth)acrylate-based polymer or the monomer includes a nitrogen-containing functional group. A cured composition includes the polymerized product of the curable composition. A method of making a cured composition includes applying the curable composition to a surface of a substrate and exposing the curable composition to actinic radiation to form the cured composition. The method can be carried out in an atmosphere of air using a light emitting diode as a light source.

Description

[0001] CURABLE COMPOSITIONS, CURED COMPOSITIONS, AND RELATED METHOD

[0002] Cross-Reference to Related Application

[0003] This application claims priority to U.S. Provisional Application No. 63 / 640,094, filed April 29, 2024, the disclosure of which is incorporated by reference in its entirety herein.

[0004] Background

[0005] Some polymeric materials have been formed by applying a layer of a curable composition to the surface of a substrate. The curable composition can contain a pre-polymer (e.g., a syrup polymer) plus additional monomers and crosslinking agents. Cured compositions can be prepared by exposing the curable composition to actinic radiation such as ultraviolet and / or visible radiation. Such polymeric materials and processes are described in U.S. Patents 4,181,752 (Martens et al.), 4,330,590 (Vesley), 4,329,384 (Vesley et al.), 4,379,201 (Heilmann et al.), 5,506,279 (Babu et al.), 5,773,836 (Bennett et al.), and 5,773,485 (Bennett et al.). Some curable compositions have contained (meth)acrylate-based polymers with pendant (meth)acryloyl groups such as those described in U.S. Pat. Nos. 10,287,463 (Behling et al.) and 10,941,321 (Behling et al.), and U.S. Pat. Appl. Pub. No. 2014 / 0302313 (Suwa et al.). The resulting articles with a cured composition are often cut (e.g., die cut) or slit to a desired size and shape.

[0006] There is an increasing need for adhesive articles with small dimensions. Cutting small articles with a complex shape from a large adhesive article can be challenging. There is an increasing need for adhesive compositions that can be printed or dispensed to the desired size and shape. Various printable or dispensable adhesive compositions have been described in U.S. Patent Nos. 6,214,460 (Bluem et al.), 11,578,162 (Seth et al.), 11,655,403 (Volp et al.), 10,035,328 (Clapper et al.), 7,691,437 (Ellis et al.), and 9,890,304 (Yurt et al.), and U.S. Pat. Appl. Pub. No. 2018 / 0118982 (Campbell et al.).

[0007] Summary

[0008] Curable compositions, cured compositions, articles containing the curable or cured compositions, and method of making the curable and cured compositions are provided. The curable compositions contain a (meth)acrylate-based polymer having pendant (meth)acryloyl groups, at least one monomer having a single ethylenically unsaturated group, a photoinitiator, and a thixotropic agent. The curable compositions can be printed or dispensed, if desired, and the cured compositions are pressure-sensitive adhesives. In one aspect, the present disclosure provides a curable composition that contains (a) a (meth)acrylate-based polymer having pendant (meth)acryloyl groups and having a weight average molecular weight in a range of 25,000 to 400,000 Daltons, (b) at least one monomer having a single ethylenically unsaturated group, (c) a photoinitiator that includes an aminoketone -functional photoinitiator and a photosensitizer, and (d) a thixotropic agent including inorganic oxide particles. At least one of the (meth)acrylate-based polymer or at least one of the monomers includes a nitrogen-containing functional group.

[0009] In another aspect, a cured composition is provided that is a polymerized reaction product of the curable composition. The cured composition can be formed by exposing the curable composition to actinic radiation.

[0010] In another aspect, the present disclosure provides an article that includes a substrate and a curable composition on a surface of the substrate. The curable composition is the same as described above. The curable composition can be in a form of a continuous or discontinuous layer.

[0011] In another aspect, the present disclosure provides an article that includes a substrate and a cured composition on a surface of the substrate. The cured composition is the same as described above. The cured composition can be in a form of a continuous or discontinuous layer.

[0012] In another aspect, the present disclosure provides a method of making a cured composition. The method includes applying the curable composition described above to a surface of a substrate. The curable composition contains (a) a (meth)acrylate-based polymer having pendant (meth)acryloyl groups and having a weight average molecular weight in a range of 25,000 to 400,000 Daltons, (b) at least one monomer having a single ethylenically unsaturated group, (c) a photoinitiator that includes an aminoketone-functional photoinitiator and a photosensitizer, and (d) a thixotropic agent that includes inorganic oxide particles. The method further includes exposing the curable composition to actinic radiation to form the cured composition, in some embodiments, in an atmosphere of air using a light emitting diode as a light source. Applying can include positioning the curable composition in the form of a continuous or discontinuous layer.

[0013] Detailed Description

[0014] Curable compositions, cured compositions formed by exposing the curable compositions to actinic radiation (e.g., radiation in the ultraviolet and / or visible region of the electromagnetic spectrum), articles containing the curable or cured compositions, and methods of making the articles are provided. More particularly, the curable compositions contain a (meth)acrylate-based polymer having pendant (meth)acryloyl groups, at least one monomer having a single ethylenically unsaturated group, a photoinitiator that includes an aminoketone -functional photoinitiator and a photosensitizer, and a thixotropic agent comprising inorganic oxide particles. The cured compositions are formed by exposing the curable compositions to actinic radiation.

[0015] The term “actinic radiation” as used herein is electromagnetic radiation that is capable of initiating a chemical reaction and usually refers to radiation in the ultraviolet and / or visible region of the electromagnetic spectrum. The actinic radiation often has a wavelength of at least 100 nanometers (nm), 200 nm, 240 nm, 250 nm, 300 nm, 350 nm, or at least 365 nm and not more than 600 nm, 500 nm, 475 nm, 460 nm, or not more than 450 nm. The wavelength range can be, for example, from 100 to 500 nm, 200 to 500 nm, 240 to 500 nm, 240 to 475 nm, 240 to 460 nm, 250 to 500 nm, 250 to 475 nm, or 350 to 460 nm.

[0016] The curable compositions can be printed or dispensed, if desired. Printing or dispensing the curable composition onto a substrate can be advantageous in some applications because cutting (e.g., die-cutting) to get the desired size and shape is not needed. Die-cutting can add waste to the manufacturing process and can be challenging if the die-cut article has a complex shape and / or small size.

[0017] The terms “printed” or “dispensed” refer to different technologies used to apply a composition to a substrate. Dispensing typically implies that the composition being dispensed is forced through some sort of nozzle and / or tube before contacting the substrate. It also does not imply anything about patterning. Something being dispensed may or may not be in the form of a pattern. In some situations, a composition can be dispensed to simply fill a space like a groove, hole, cavity, plate, or slot. Printing often implies that the process of applying the composition to the substrate is done to form a self-standing pattern (i.e., the composition does not spread excessively on the substrate surface such that the pattern is destroyed or not apparent). Printing often includes moving-head printing (jetting or other nozzle-based printing), which are like the moving heads used for dispensing, in which the pattern is imparted by moving the printing head. However, printing also includes various static printing methods like flexographic printing, stencil printing, and screen printing, which are very dissimilar to dispensing. In these methods, the pattern is imparted by an existing pattern on the printing equipment.

[0018] The cured compositions are typically pressure-sensitive adhesives. The Pressure-Sensitive Tape Council defines pressure -sensitive adhesives (PSAs) as materials that possess the following properties: (1) aggressive and permanent tack, (2) adherence with no more than finger pressure, (3) sufficient ability to hold onto an adherend, and (4) sufficient cohesive strength to be removed cleanly from the adherend. Materials that have been found to function well as PSAs include polymers designed and formulated to exhibit the requisite viscoelastic properties resulting in a desired balance of tack, peel adhesion, and shear holding power. PSAs are characterized by being normally tacky at room temperature (e.g., 20 °C). Materials that are merely sticky or adhere to a surface do not constitute a PSA; the term PSA encompasses materials with additional viscoelastic properties. PSAs are adhesives that satisfy the Dahlquist criterion for tackiness at room temperature and typically exhibit adhesion, cohesion, compliance, and elasticity at room temperature. This criterion defines a pressure sensitive adhesive as an adhesive having a creep compliance of greater than 3 x 10’6cm2 / dyne as described in Handbook of Pressure Sensitive Adhesive Technology, Donatas Satas (Ed.), 2nd Edition, p. 172, Van Nostrand Reinhold, New York, NY, 1989. Alternatively, since modulus is, to a first approximation, the inverse of creep compliance, pressure sensitive adhesives may be defined as adhesives having a storage modulus of less than about 3 x 105N / m2.

[0019] The terms “a”, “an”, and “the” are used interchangeably with “at least one” to mean one or more of the elements being described.

[0020] The phrases "at least one of and "comprises at least one of followed by a list including the conjunction “or” refers to any one of the items in the list and any combination of two or more items in the list.

[0021] The term “and / or” means either or both. For example, “A and / or B” means only A, only B, or both A and B.

[0022] The terms “in a range of’ or “in the range of’ are used interchangeably to refer to all values within the range plus the endpoints of the range.

[0023] The terms “polymer” and “polymeric material” are used interchangeably and refer to materials formed by reacting one or more monomers. The terms include homopolymers, copolymers, and terpolymers. Likewise, the terms “polymerize” and “polymerizing” refer to the process of making a polymeric material that can be a homopolymer, copolymer, or terpolymer. The term “polymer” includes homopolymers or copolymers that may be formed in a miscible blend, e.g., by coextrusion or by reaction. The term “polymer” includes random, block, graft, and star polymers. The term “polymer” encompasses oligomers.

[0024] The term “monomer” refers to compounds having at least one ethylenically unsaturated group that can undergo free radical polymerization. In many embodiments, the ethylenically unsaturated group is a (meth)acryloyl group. The monomers can have any desired molecular weight. The term “monomeric unit” refers to a unit within a polymer that is derived from a monomer. As an example, the monomeric unit of 3 -hydroxypropyl acrylate (H2C=CH-(C=O)-OCH2CH2CH2OH) is where the asterisks (*) indicate the attachment site to another group such as another monomeric unit in the polymer.

[0025] The curable composition contains a (meth)acrylate-based polymer having pendant (meth)acryloyl groups. The term “(meth)acrylate-based polymer” refers to a polymeric material that is formed from multiple different monomers having (meth)acryloyl groups. At least 50 weight percent of the monomeric units in the (meth)acrylate-based polymer are derived from monomers having (meth)acryloyl groups. In some embodiments, at least 60 weight percent, at least 70 weight percent, at least 80 weight percent, at least 90 weight percent, at least 95 weight percent, at least 98 weight percent, at least 99 weight percent, or 100 weight percent of the monomeric units in the (meth)acrylate-based polymer are derived from monomers having (meth)acryloyl groups.

[0026] The term “(meth)acryloyl” refers to a group of formula CH2=CHR1-(CO)- where R1is hydrogen or methyl. The (meth)acryloyl group is a methacryloyl group when R1is methyl and an acryloyl group when R1is hydrogen. The (meth)acryloyl group is usually a (meth)acryloyloxy group of formula CH2=CHR1-(CO)-O- or (meth)acryloylamido group of formula CH2=CHR1-(CO)-NH-.

[0027] The (meth)acrylate-based polymer having pendant (meth)acryloyl groups is typically formed from another (meth)acrylate-based polymer that is referred to herein as the “precursor (meth)acrylate-based polymer”. The precursor (meth)acrylate-based polymer typically has pendant groups such as hydroxyl groups (-OH), carboxylic acid groups (-(CO)-OH), or anhydride groups (-(CO)-O-(CO-)) that can react with an unsaturated reagent compound to produce the (meth)acrylate-based polymer with pendant (meth)acryloyl groups. In many embodiments, the pendant groups in the precursor (meth)acrylate -based polymer are hydroxyl groups.

[0028] As used herein, the term “unsaturated reagent compound” refers to a compound having a (meth)acryloyl group plus a complementary group that can react with the pendant hydroxyl groups, pendant carboxylic acid groups, or pendant anhydride groups on the precursor (meth)acrylate-based polymer to prepare the (meth)acrylate-based polymer having pendant (meth)acryloyl groups.

[0029] The pendant (meth)acryloyl group is indirectly linked to the backbone of the (meth)acrylate-based polymer through a linking group. The pendant group is typically of formula CH2=CHR1-(CO)-Q-L- where L is the linking group, where Q is -O- or -NH-, and where R1is hydrogen or alkyl (e.g., methyl). The group L includes at least one alkylene, arylene, or combination thereof and can optionally further include -O-, -O(CO)-, -NH(CO)-, -NH-, or a combination thereof. Suitable alkylene groups (i.e., an alkylene is a divalent radical of an alkane) often have 1 to 10 carbon atoms, 1 to 6 carbon atoms, or 1 to 4 carbon atoms. Suitable arylene groups (i.e., an arylene is a divalent radical of a carbocyclic aromatic compound) often have 6 to 12 carbon atoms, 6 to 10 carbon atoms, or 6 carbon atoms. The arylene is often phenylene.

[0030] The precursor (meth)acrylate-based polymer is typically formed from a polymerizable composition that contains a monomer composition that includes (1) a first monomer that is a (hetero)alkyl (meth)acrylate (i.e., a (hetero)alkyl refers to a heteroalkyl, alkyl, or both) and (2) a second monomer having an ethylenically unsaturated group (e.g., a (meth)acryloyl group) and a functional group (i.e., a hydroxyl group, a carboxylic acid group, or an anhydride group). The (hetero)alkyl (meth)acrylate first monomers are selected to provide the desired modulus and glass transition temperature of the (meth)acrylate-based polymer having pendant (meth)acryloyl groups. The second monomers have a functional group that can react with the unsaturated reagent compound to provide pendant (meth)acryloyl groups. Typically, not all the functional groups from the second monomer are reacted with the unsaturated reagent compound. The remaining unreacted functional groups from the second monomer can facilitate adhesion of curable and / or cured compositions to a substrate.

[0031] Examples of alkyl (meth)acrylate first monomers often have 1 to 32, 1 to 24, 1 to 20, 1 to 18, 1 to 12, 1 to 10, 1 to 8, or 1 to 4 carbon atoms. Suitable alky (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-pentyl (meth)acrylate, 2-methylbutyl (meth)acrylate, n- hexyl (meth)acrylate, cyclohexyl (meth)acrylate, 4-methyl-2-pentyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 2-methylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, 2- octyl (meth)acrylate, isononyl (meth)acrylate, isoamyl (meth)acrylate, isobomyl (meth)acrylate, n- decyl (meth)acrylate, isodecyl (meth)acrylate, 2-propylheptyl (meth)acrylate, isotridecyl (meth)acrylate, isostearyl (meth)acrylate, octadecyl (meth)acrylate, 2-octyldecyl (meth)acrylate, dodecyl (meth)acrylate, lauryl (meth)acrylate, and heptadecanyl (meth)acrylates. Some examples of branched alkyl (meth)acrylates are (meth)acrylic acid esters of Guerbet alcohols having 12 to 32 carbon atoms as described in U.S. Pat. No. 8,137,807 (Clapper et al.). Isomers and isomer mixtures of any of the alkyl (meth)acrylates can be used as described, for example, in U.S. Pat. No. 9,102,774 (Clapper et al.).

[0032] Suitable heteroalkyl (meth)acrylate first monomers include those having one or more ether linkages, which refers to an oxy group between two alkylene groups. That is, the heteroalkyl contains one or more oxygen heteroatoms. The heteroalkyl groups often have at least 2 carbon atoms, at least 3 carbon atoms, at least 4 carbon atoms, at least 6 carbon atoms, at least 10 carbon atoms and up to 40 or more carbon atoms, up to 30 carbon atoms, up to 20 carbon atoms, or up to 10 carbon atoms. One example is tetrahydrofuran (meth)acrylate. Other examples include alkoxylated alkyl (meth)acrylates such as ethoxyethoxyethyl (meth)acrylate, 2-methoxyethyl (meth)acrylate, and 2-ethoxyethyl (meth)acrylate; and poly(alkylene oxide) (meth)acrylates such as polyethylene oxide) (meth)acrylates and polypropylene oxide) (meth)acrylates. The poly(alkylene oxide) acrylates are often referred to as poly(alkylene glycol) (meth)acrylates. These monomers can have any suitable end group such as a hydroxyl group or an alkoxy group. For example, when the end group is a methoxy group, the monomer can be referred to as methoxy poly(ethylene glycol) (meth)acrylate. If the end group is a hydroxyl group, the monomer is classified as a second monomer having a functional hydroxyl group.

[0033] In some embodiments, at least some of the monomers used to form the precursor (meth)acrylate-based polymer are selected to be from renewable resources. For example, at least 25 weight percent, at least 30 weight percent, at least 35 weight percent, at least 40 weight percent, at least 45 weight percent, or at least 50 weight percent of the monomers used to form the precursor (meth)acrylate can be from renewable resources. The amounts are based on the total weight of monomers in the monomer composition used to form the precursor (meth)acrylate-based polymer. One such monomer is 2-octyl acrylate.

[0034] In some embodiments, the monomer composition in the polymerizable composition used to form the precursor (meth)acrylate-based polymer contains at least 50 weight percent, at least 55 weight percent, at least 60 weight percent, at least 65 weight percent, at least 70 weight percent, at least 75 weight percent, or at least 80 weight percent (hetero)alkyl (meth)acrylate. The monomer composition can contain up to 99.9 weight percent, up to 99.5 weight percent, up to 99 weight percent, up to 98 weight percent, up to 95 weight percent, up to 90 weight percent, up to 85 weight percent, up to 80 weight percent, up to 75 weight percent, up to 70 weight percent, up to 65 weight percent, or up to 60 weight percent (hetero)alkyl (meth)acrylate. In some embodiments, each of these weight percents refers to the amount of alkyl (meth)acrylate monomer units in the precursor (meth)acrylate-based polymer or (meth)acrylate-based polymer. The amounts are based on a total weight of monomers in the monomer composition used to form the precursor (meth)acrylate-based polymer or (meth)acrylate-based polymer. There can be a single or multiple (hetero)alkyl or alkyl (meth)acrylates in the monomer composition.

[0035] The second monomer included in the monomer composition used to form the precursor (meth)acrylate-based polymer has a (meth)acryloyl group and a functional group that reacts with the unsaturated reagent compound to provide pendant (meth)acryloyl groups. The functional group is typically a hydroxyl (-OH) and / or a carboxylic acid (-(CO)-OH) and / or an anhydride group (-(CO)-O-(CO)-). A combination of second monomers can be used.

[0036] Useful second monomers having a carboxylic acid group include (meth)acrylic acid, itaconic acid, fumaric acid, crotonic acid, citraconic acid, maleic acid, oleic acid, and B- carboxyethyl acrylate. Useful monomers having a hydroxyl group include, but are not limited to, hydroxyalkyl (meth)acrylates (e.g., 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3- hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate); hydroxyalkyl (meth)acrylamides (e.g., 2-hydroxyethyl (meth)acrylamide and 3 -hydroxypropyl (meth)acrylamide); and aryloxy substituted hydroxyalkyl (meth)acrylates (e.g., 2-hydroxy-2- phenoxypropyl (meth)acrylate). Additionally, hydroxyl functional monomers based on glycols derived from ethylene oxide or propylene oxide can also be used. These monomers typically have a hydroxyl equivalent weight of less than 400. The hydroxyl equivalent molecular weight is defined as the molecular weight of the monomeric compound divided by the number of hydroxyl groups in the monomer. Ethoxylated hydroxyethyl (meth)acrylate monomers are commercially available from Sartomer (Exton, PA, USA) under the trade designation CD570, CD571, and CD572. An example hydroxyl terminated polypropylene glycol acrylate is commercially available under the trade name BISOMER PPA 6 from Cognis, Germany.

[0037] Useful second monomers having an anhydride group include maleic anhydride and methacrylic acid anhydride.

[0038] The monomer composition used to form the precursor (meth)acrylate-based polymer often contains at least 0.1 weight percent, at least 0.2 weight percent, at least 0.3 weight percent, at least 0.5 weight percent, at least 1 weight percent, at least 2 weight percent, at least 3 weight percent, at least 5 weight percent, at least 10 weight percent, at least 15 weight percent, or at least 20 weight percent and up to 40 weight percent, up to 35 weight percent, up to 30 weight percent, up to 25 weight percent, up to 20 weight percent, up to 15 weight percent, up to 10 weight percent, or up to 5 weight percent of the second monomer. The amount of the second monomer is based on a total weight of monomers in the monomer composition used to form the precursor (meth)acrylate-based polymer. Multiple different second monomers can be included in the monomer composition.

[0039] Various optional monomers can be included in the monomer composition used to form the precursor (meth)acrylate-based polymer. Some optional (meth)acrylate monomers have an aromatic group. Examples include benzyl (meth)acrylate, 2-phenoxyethyl acrylate, 2- (phenylthio)ethyl acrylate, 2-phenylphenoxyethyl acrylate, 2-biphenylhexyl (meth)acrylate, and 2- (biphenyl)ethyl acrylate. Other optional monomers have a vinyl group that is not a (meth)acryloyl group. Examples include vinyl ethers, vinyl esters (e.g., vinyl acetate), olefinic monomers (e.g., ethylene, propylene, or butylene), styrene, and styrene derivatives (e.g., alpha-methyl styrene).

[0040] Still other optional monomers are nitrogen-containing monomers; in other words, they have a nitrogen-containing functional group. Suitable nitrogen-containing functional groups include a primary amido group, a secondary amido group, a tertiary amido group, a primary amino group, a secondary amino group, or a tertiary amino group. Nitrogen-containing monomers typically have an ethylenically unsaturated group and at least one of a primary amido group, a secondary amido group, a tertiary amido group, a primary amino group, a secondary amino group, or a tertiary amino group. Some examples of nitrogen-containing monomers are (meth)acrylamide, N-alkyl (meth)acrylamides, and N,N-dialkyl (meth)acrylamides. Examples of N-alkyl (meth)acrylamides and N,N-dialkyl (meth)acrylamides include N-methyl (meth)acrylamide, N-ethyl (meth)acrylamide, N,N-dimethyl (meth)acrylamide, and N,N-diethyl (meth)acrylamide, N-isopropyl (meth)acrylamide, and N-octyl (meth)acrylamide. Other nitrogencontaining monomers include various N,N -dialkylaminoalkyl (meth)acrylates and N,N- dialkylaminoalkyl (meth)acrylamides such as N,N-dimethyl aminoethyl (meth)acrylate, N,N- dimethylaminoethyl (meth)acrylamide, N,N-dimethylaminopropyl (meth)acrylate, N,N- dimethylaminopropyl (meth)acrylamide, N,N-diethylaminoethyl (meth)acrylate, N,N- diethylaminoethyl (meth)acrylamide, N,N-diethylaminopropyl (meth)acrylate, and N,N- diethylaminopropyl (meth)acrylamide. Other useful nitrogen-containing monomers include N- vinyl pyrrolidone, N-morpholino (meth)acrylate, diacetone (meth)acrylamide, and N-vinyl caprolactam. Still other useful nitrogen-containing monomers include N,N-dialkyl amine adducts of a di(meth)acrylate such as glycerol di(meth)acrylate, hexanediol di(meth)acrylate, triethylene glycol di(meth)acrylate, 1,3 -propanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,4- cyclohexanediol di(meth)acrylate, and polyethylene glycol di(meth)acrylates. Useful N-alkyl groups typically have up to 4, 3, or 2 carbon atoms including methyl, ethyl, propyl, and butyl groups.

[0041] Any of these optional monomers can be present in any desired amount, but typically the monomer composition contains 0 to 20 weight percent of the optional monomers. In some embodiments, the monomer composition contains less than 15 weight percent, less than 10 weight percent, or less than 5 weight percent of the optional monomers but can contain at least 1 weight percent, at least 2 weight percent, at least 3 weight percent, or at least 5 weight percent of the optional monomers. The amounts are based on a total weight of monomers in the monomer composition used to form the precursor (meth)acrylate -based polymer. Multiple optional monomers can be included in the monomer composition.

[0042] While nitrogen-containing monomer units are optional in the (meth)acrylate-based polymer, at least one of the (meth)acrylate-based polymer or the monomer includes a nitrogencontaining functional group. In some embodiments, the (meth)acrylate-based polymer and the monomer independently include a nitrogen-containing functional group. In some embodiments, the (meth)acrylate-based polymer includes a nitrogen-containing functional group. In some embodiments, the (meth)acrylate-based polymer comprises units of at least one of an N,N- dialkylaminoalkyl (meth)acrylate, an N,N-dialkyl amine adduct of a di(meth)acrylate, N-vinyl pyrrolidone, 2-N-morpholinoethyl(meth)acrylate, or N-vinyl caprolactam.

[0043] The precursor (meth)acrylate-based polymer typically is not crosslinked. Thus, the monomer composition used to form the precursor (meth)acrylate -based polymer typically is free or substantially free of a crosslinking monomer such as, for example, a crosslinking monomer having a plurality of (meth)acryloyl groups. As used herein, the term “substantially free” regarding the crosslinking monomer means that the monomer composition typically contains less than 0.5 weight percent, less than 0.4 weight percent, less than 0.3 weight percent, less than 0.2 weight percent, less than 0. 1 weight percent, less than 0.05 weight percent, less than 0.02 weight percent, or less than 0.01 weight percent of a crosslinking monomer. The weight percent values are based on the total weight of monomers in the monomer composition used to form the precursor (meth)acrylate-based polymer.

[0044] In some embodiments, the monomer composition used to prepare the precursor (meth)acrylate-based polymer contains 50 to 99.9, 60 to 99.5, 60 to 99, 60 to 95, 70 to 95, or 75 to 95 weight percent (hetero)alkyl (meth)acryiate monomers, 0.1 to 40, 0.5 to 40, 1 to 40, 5 to 40, 5 to 30, or 5 to 25 weight percent second monomers having an ethylenically unsaturated group and a functional group (i.e., a hydroxyl group, carboxylic acid group, or anhydride group) that reacts with the unsaturated reagent compound to provide pendant (meth)acryloyl groups, and 0 to 20, 0 to 15, or 0 to 10 weight percent optional monomers. Stated differently, the precursor (meth)acrylate polymer usually contains 50 to 99.9, 60 to 99.5, 60 to 99, 60 to 95, 70 to 95, or 75 to 95 weight percent monomeric units of (hetero)alkyl (meth)acrylate monomers, 0.1 to 40, 0.5 to 40, 1 to 40, 5 to 40, 5 to 30, or 5 to 25 weight percent monomeric units of second monomers having a hydroxyl group, carboxylic acid group, or anhydride group, and 0 to 20, 0 to 15, or 0 to 10 weight percent monomeric units of optional monomers. In some embodiments, the precursor (meth)acrylate polymer contains 50 to 99.9, 60 to 99.5, 60 to 99, 60 to 95, 70 to 95, or 75 to 95 weight percent monomeric units of (hetero)alkyl (meth)acrylate monomers, 0.1 to 40, 0.5 to 40, 1 to 40, 5 to 40, 5 to 30, or 5 to 25 weight percent monomeric units of second monomers having a hydroxyl group, and 0 to 20, 0 to 15, or 0 to 10 weight percent monomeric units of optional monomers, including those having a nitrogen-containing functional group. In some embodiments, the precursor (meth)acrylate polymer contains 50 to 99.9, 60 to 99.5, 60 to 99, 60 to 95, 70 to 95, or 75 to 95 weight percent monomeric units of alkyl (meth)acrylate monomers, 0. 1 to 40, 0.5 to 40, 1 to 40, 5 to 40, 5 to 30, or 5 to 25 weight percent monomeric units of second monomers having a hydroxyl group, and 0 to 20, 0 to 15, or 0 to 10 weight percent monomeric units of optional monomers, including those having a nitrogen-containing functional group. Chain-transfer agents are often included in the polymerizable composition to control the molecular weight of the precursor (meth)acrylate-based polymer. Examples of suitable chaintransfer agents include those selected from the group of carbon tetrabromide, hexabromoethane, bromotrichloromethane, 2-mercaptoethanol, tert-dodecylmercaptan, isooctylthioglycoate, 3- mercapto-l,2-propanediol, cumene, pentaerythritol tetrakis(3-mercapto butyrate) (available under the trade name KARENZ MT PEI from Showa Benko), ethylene glycol bisthioglycolate, and mixtures thereof Depending on the reactivity of the chain-transfer agent selected, the amount of chain transfer agent is often in a range of 0 to 5 weight percent based on the total weight of monomers in the polymerizable composition. In some embodiments, the amount of the chain transfer agent is at least 0.05 weight percent, at least 0.1 weight percent, at least 0.2 weight percent, at least 0.3 weight percent, or at least 0.5 weight percent and can be up to 4.5 weight percent, up to 4 weight percent, up to 3.5 weight percent, up to 3 weight percent, up to 2.5 weight percent, up to 2 weight percent, up to 1 .5 weight percent, or up to 1 weight percent. The weight percent values are based on the total weight of monomers in the monomer composition used to form the precursor (meth)acrylate-based polymer.

[0045] A free radical initiator is typically used to form the precursor (meth)acry late -based polymer. The free radical initiator can be a photoinitator or a thermal initiator. Multiple photoinitiators or multiple thermal initiators can be used. The amount of the free radical initiator can influence the weight average molecular weight with larger amounts typically producing lower molecular weight polymeric materials. The amount of free radical initiator is usually at least 0.001 weight percent, at least 0.005 weight percent, at least 0.01 weight percent, at least 0.05 weight percent, or at least 0. 1 weight percent based on the total weight of monomers. The amount can be up to 5 weight percent, up to 4 weight percent, up to 3 weight percent, up to 2 weight percent, up to 1.5 weight percent, up to 1 weight percent, up to 0.5 weight percent, up to 0.3 weight percent, up to 0.2 weight percent, or up to 0.1 weight percent based on the total weight of monomers.

[0046] Suitable thermal initiators include various azo compound such as those commercially available under the trade designation VAZO from Chemours Co. (Wilmington, DE, USA) including VAZO 67, which is 2,2’ -azobis(2 -methylbutane nitrile), VAZO 64, which is 2,2’ - azobis(isobutyronitrile), VAZO 52, which is (2,2’-azobis(2,4-dimethylpentanenitrile), and VAZO 88, which is l,l’-azobis(cyclohexanecarbonitrile); various peroxides such as benzoyl peroxide, cyclohexane peroxide, lauroyl peroxide, di-tert-amyl peroxide, tert-butyl peroxy benzoate, di- cumyl peroxide, and peroxides commercially available from Atofina Chemical, Inc. (Philadelphia, PA, USA) underthe trade designation EUPERSOE (e.g., LUPERSOL 101, which is 2,5-bis(tert- butylperoxy)-2,5-dimethylhexane, and LUPERSOL 130, which is 2,5-dimethyl-2,5-di-(tert- butylperoxy) -3 -hexyne); various hydroperoxides such as tert-amyl hydroperoxide and tert-butyl hydroperoxide; and mixtures thereof.

[0047] In some embodiments, a photoinitiator is used to form the precursor (meth)acrylate-based polymer. Examples of suitable photoinitiators include benzoin ethers (e.g., benzoin methyl ether or benzoin isopropyl ether) and substituted benzoin ethers (e.g., anisoin methyl ether). Other examples of photoinitiators include substituted acetophenones such as 2,2-diethoxyacetophenone or 2, 2-dimethoxy-2 -phenylacetophenone, substituted alpha-ketols such as 2-methyl-2- hydroxypropiophenone, aromatic sulfonyl chlorides such as 2-naphthalenesulfonyl chloride, and photoactive oximes such as l-phenyl-l,2-propanedione-2-(O-ethoxycarbonyl)oxime. Other suitable photoinitiators include 1 -hydroxy cyclohexyl phenyl ketone, bis(2,4,6- trimethylbenzoyl)phenyl phosphine oxide, l-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-l- propane- 1 -one, 2 -benzyl -2 -dimethylamino- 1 -(4-morpholinophenyl)butanone, 2-methyl- 1-[4- (methylthio)phenyl]-2-morpholinopropan-l-one, and 2 -hydroxy-2 -methyl- 1 -phenyl propan- 1 -one.

[0048] The reaction of the polymerizable composition to form the precursor (meth)acrylate-based polymer can occur in the presence or absence of an organic solvent. If an organic solvent is included in the polymerizable composition, the amount is often selected to provide the desired viscosity. Examples of suitable organic solvents include methanol, tetrahydrofuran, ethanol, isopropanol, pentane, hexane, heptane, acetone, methyl ethyl ketone, methyl acetate, ethyl acetate, toluene, xylene, ethylene glycol alkyl ether, and mixtures thereof. In some embodiments, the polymerization occurs with little or no organic solvent present. That is, the polymerizable composition is free of organic solvent or contains a minimum amount of organic solvent. If used, the organic solvent is often present in amounts less than 10 weight percent, less than 5 weight percent, less than 4 weight percent, less than 3 weight percent, less than 2 weight percent, or less than 1 weight percent based on the total weight of the polymerizable composition.

[0049] The precursor (meth)acrylate-based polymer can be formed from the polymerizable composition using any suitable method. The polymerization can occur in a single step or in multiple steps. That is, all or a portion of the monomers and / or free radical initiator may be charged into a suitable reaction vessel and polymerized. For example, a polymerizable composition containing an organic solvent and a thermal initiator can be mixed and heated at an elevated temperature such as in a range of 50 °C to 100 °C for several hours.

[0050] In some embodiments, the precursor (meth)acrylate-based polymer is prepared using an adiabatic process as described, for example, in U.S. Patent Nos. 5,986,011 (Ellis et al.) and 5,637,646 (Ellis). In this polymerization method, the polymerizable composition, including at least one thermal initiator, is sealed in a reaction vessel. The contents are mixed and purged of oxygen and, if not already at induction temperature, then warmed to the induction temperature. The induction temperature, which is usually in the range of 40 °C to 75 °C, depends on various factors such as the monomers, the initiator, and the amount of the initiator used. The polymerization is performed under essentially adiabatic conditions with a peak reaction temperature in the range of 100 °C to 200 °C. Multiple reaction steps with optional cooling in between steps can be employed to increase polymerization conversion on each successive step and to control the molecular weight. Optionally, various reaction components can be added in multiple steps to control the properties (e.g., molecular weight, molecular weight distribution, and polymer composition) of the resulting polymeric material.

[0051] Various antioxidants and / or stabilizers such as hydroquinone monoethyl ether (p- methoxy phenol, MEHQ) and that available under the trade designation IRGANOX 1010 (pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate)) from BASF Corp. (Florham Park, NJ, USA) can be added to increase the temperature stability' of the polymeric material. If used, the antioxidant and / or stabilizer is typically added in a range of 0.01 weight percent to 1.0 weight percent based on a total weight of the total weight of monomers in the monomer composition used to form the precursor (nieth)acrylate-based polymer.

[0052] Once the precursor (meth)acrylate is prepared, it is reacted with the unsaturated reagent compound to provide the (meth)acrylate -based polymer having pendant (meth)acryloyl groups. The unsaturated reagent compound contains a (meth)acryloyl group and a complementary functional group that reacts with a pendant functional group of the precursor (meth)acrylate-based polymer, which is typically a hydroxyl group, a carboxylic acid group, or an anhydride group. Generally, the reaction is between nucleophilic and electrophilic functional groups that react by a ring opening, addition, or condensation reaction. When the functional group on the precursor (meth)acrylate-based polymer and the complementary functional group of the unsaturated reagent compound react, the resulting (meth)acrylate-based polymer will have pendant (meth)acryloyl groups.

[0053] When the pendant reactive functional group of the precursor(meth)acrylate-based polymer includes a hydroxyl group, the complementary functional group of the unsaturated reagent compound is typically a carboxylic acid, isocyanato, epoxy, or anhydride group. When the pendant reactive functional group of the precursor (meth)acrylate-based polymer includes a carboxylic acid group, the complementary functional group of the unsaturated reagent compound is typically a hydroxyl, amino, epoxy, isocyanato, aziridino, azetidino, or oxazolinyl group. When the pendant group of the precursor(meth)acrylate-based polymer includes an anhydride, the complementary functional group of the unsaturated reagent compound can be a hydroxyl or amino group. Precursor (meth)acrylate-based polymers having hydroxyl group may be useful in applications where the cured composition is used in articles having metal-containing components, for example, because hydroxyl groups may be less problematic in terms of corrosion than acidic groups or anhydride groups.

[0054] In some embodiments, the pendant (meth)acryloyl groups can be formed from the reaction between hydroxyl groups in the precursor (meth)acrylate -based polymer and isocyanatoethyl (meth)acrylate as the unsaturated reagent compound. In some embodiments, the pendant (meth)acryloyl groups can be formed from the reaction between carboxylic acids in the precursor (meth)acrylate-based polymer with glycidyl (meth)acrylate as the unsaturated reagent compound. In some embodiments, the pendant (meth)acryloyl group can be formed between anhydride groups in the precursor (meth)acrylate-based polymer and a hydroxyl functional monomer, such as 2- hydroxethyl (meth)acrylate, 3 -hydroxypropyl (meth)acrylate, or 2-hydroxyethyl (meth)acrylamide, as the unsaturated reagent compound.

[0055] In some embodiments, if the second monomer is a hydroxyalkyl (meth)acylate or a hydroxyalkyl (meth)acrylamide and the unsaturated reagent compound is an isocyanatoalkyl (meth)acrylate, the pendant (meth)acryloyl group is of formula -(CO)-O-L1-O-(CO)-NH-L2-Q-(CO)-C(R1)=CH2. The groups L1and L2are each independently an alkyl having 1 to 10 carbon atoms, 1 to 6 carbon atoms, 1 to 4 carbon atoms, or 2 to 4 carbon atoms. The group Q is -O- or -NH-. The group R1is hydrogen or methyl. If the second monomer is 3 -hydroxypropyl acrylate and the unsaturated reagent compound is isocyanatoethyl methacrylate, the pendant (meth)acryloyl groups are -(CO)-O-CH2CH2CH2-O-(CO)-NH-CH2CH2-O-(CO)-C(CH3)=CH2. This corresponds to the formula above where L1is propylene, L2is ethylene, and Q is -O-, and R1is methyl.

[0056] The reaction between the precursor (meth)acrylate-based polymer and the unsaturated reagent compound often occurs at room temperature or at elevated temperatures such as a temperature up to 150 °C or higher, up to 120 °C, up to 100 °C, up to 90 °C, up to 80 °C, up to 60 °C, or up to 40 °C. Further, this reaction can conveniently be carried out in the presence of some oxygen since oxygen can inhibit radical propagation. For example, the volume ratio of nitrogen to oxygen is often about 90: 10.

[0057] All or any fraction of the pendant reactive functional groups of the precursor (meth)acrylate-based polymer can be reacted with the unsaturated reagent compound. Up to 100, 95, 90, 85, 80, 75, 70, 60, 50, 40, 30, or up to 20 mole percent and at least 1, 2, 5, 7, 10, 12, 15, or at least 20 mole percent of the pendant reactive functional groups of the precursor (meth)acrylate- based polymer are reacted with the unsaturated reagent compound. The remaining pendant reactive functional groups after reaction with the unsaturated reagent compound often facilitate miscibility of the (meth)acrylate-based polymer having pendant (meth)acryloyl groups with other components of the curable composition. Further, the remaining pendant reactive functional groups can facilitate adhesion of the curable composition and final cured composition to a substrate.

[0058] In some embodiments, the (meth)acrylate-based polymer having pendant (meth)acryloyl groups contains at least 0.1 weight percent, at least 0.2 weight percent, at least 0.5 weight percent, at least 1 weight percent, at least 2 weight percent, or at least 5 weight percent and up to 10 weight percent, up to 8 weight percent, up to 6 weight percent, up to 5 weight percent, up to 4 weight percent, up to 2 weight percent, or up to 1 weight percent monomeric units having a pendant (meth)acryloyl group. For example, the amount of these monomeric units can be in a range of 0.1 to 10 weight percent, 0.5 to 10 weight percent, 1 to 10 weight percent, 0.1 to 5 weight percent, or 0.5 to 5 weight percent based on the weight of the (meth)acrylate-based polymer having pendant (meth)acryloyl groups.

[0059] There are usually 1 to 20 pendant (meth)acryloyl groups per chain on average. There can be at least 1, at least 2, at least 3, or at least 5 and up to 20, up to 16, up to 12, up to 10, up to 8, up to 6, or up to 5 pendant (meth)acryloyl groups per chain. If there are too many pendant groups, the cured composition may be too highly crosslinked to function well as a pressure-sensitive adhesive. If there are too few groups, however, the shear strength may be too low. The number of pendant groups that can be present is dependent on the overall composition of the curable composition. In some embodiments, as the weight average molecular weight of the polymer increases, there can be more pendant (meth)acryloyl groups per chain.

[0060] The number of pendant (meth)acryloyl groups can be calculated based on the weight average molecular weight of the precursor (meth)acrylate-based polymer in grams / mole (A), the weight fraction (i.e., weight percent divided by 100) of the monomeric unit having a pendant hydroxyl group, carboxylic acid group, or anhydride group in grams (B), the mole fraction of the monomeric units having a pendant hydroxyl group, carboxylic acid group, or anhydride group that is reacted with the unsaturated reagent compound (C), and the molecular weight of the monomeric unit having a pendant hydroxyl group, carboxylic acid group, or anhydride group in grams / mole (D). More specifically, the number of (meth)acryloyl groups per chain is equal to (A)(B)(C) (D) where (A), (B), (C), and (D) are defined above.

[0061] Alternatively, the number of pendant (meth)acryloyl groups can be calculated based on the weight average molecular weight of the precursor (meth)acrylate-based polymer in grams / mole (A), the moles of unsaturated reagent compound reacted with the precursor (meth)acrylate-based polymer (E), and the amount in grams of the precursor (meth)acrylate-based polymer treated with the unsaturated reagent compound (F). More specifically, the number of (meth)acryloyl groups per chain is equal to (A)(E) (F) where (A), (E), and (F) are defined above. In some embodiments, the (meth)acrylate-based polymer having pendant (meth)acryloyl groups contains 50 to 99.9, 60 to 99, 60 to 98, 60 to 95, 70 to 95, or 75 to 95 weight percent monomeric units of a (hetero)alkyl (meth)acrylate, 0.1 to 10, 0.5 to 10, or 0.5 to 5 weight percent monomeric units having a pendant (meth)acryloyl group, and 0 to 40, 1 to 40, 5 to less than 40, or 1 to less than 40 weight percent monomeric units of a monomer having a pendant hydroxyl group, amino group, or anhydride group, and 0 to 20, 0 to 15, or 0 to 10 weight percent monomeric units derived from optional monomers as described above. In some embodiments, the (meth)acrylate- based polymer having pendant (meth)acryloyl groups contains 50 to 99.9, 60 to 99, 60 to 98, 60 to 95, 70 to 95, or 75 to 95 weight percent monomeric units of an alkyl (meth)acrylate, 0. 1 to 10, 0.5 to 10, or 0.5 to 5 weight percent monomeric units having a pendant (meth)acryloyl group, and 0 to 40, 1 to 40, 5 to less than 40, or 1 to less than 40 weight percent monomeric units of a monomer having a pendant hydroxyl group, amino group, or anhydride group, and 0 to 20, 0 to 15, or 0 to 10 weight percent monomeric units derived from optional monomers as described above. The amounts are based on a total weight of the (meth)acrylate-based polymer having pendant (meth)acryloyl groups.

[0062] The (meth)acrylate-based polymer having pendant (meth)acryloyl groups typically has a weight average molecular weight in a range of 25,000 Daltons to 400,000 Daltons. The weight average molecular weight is typically determined by gel permeation chromatography as described in the Examples. If the weight average molecular weight of the (meth)acrylate-based polymer having pendant (meth)acryloyl groups is less than 25,000 Daltons, the overlap shear strength of the final cured composition may be unacceptably low. If the weight average molecular weight of the (meth)acrylate-based polymer having pendant (meth)acryloyl groups is too high, however, the viscosity of the curable composition may be unacceptably high. The weight average molecular weight of the (meth)acrylate-based polymer having pendant (meth)acryloyl groups is often at least 30,000 Daltons, at least 35,000 Daltons, at least 40,000 Daltons, at least 50,000 Daltons, at least 60,000 Daltons, at least 80,000 Daltons, at least 100,000 Daltons and can be up to 400,000 Daltons, up to 375,000 Daltons, up to 350,000 Daltons, up to 325,000 Daltons, up to 300,000 Daltons, up to 275,000 Daltons, up to 250,000 Daltons, up to 200,000 Daltons, up to 175,000 Daltons, up to 150,000 Daltons, up to 125,000 Daltons, or up to 100,000 Daltons. In some embodiments, the weight average molecular weight is in a range of 35,000 to 400,000 Daltons, 50,000 to 400,000 Daltons, 35,00 to 350,000 Daltons, 50,000 to 350,000 Daltons, 35,000 to 300,000 Daltons, 50,000 to 300,000 Daltons, 35,000 to 250,000 Daltons, 50,000 to 250,000 Daltons, 35,000 to 200,000 Daltons, 50,000 to 200,000 Daltons, 35,000 to 100,000 Daltons, 50,000 to 100,000 Daltons, 35,000 to 80,000 Daltons, or 40,000 to 80,000 Daltons. The glass transition temperature of the precursor (meth)acrylate-based polymer and / or the (meth)acrylate-based polymer having pendant (meth)acryloyl groups can be determined using the Fox equation based on the amount and identity of the monomeric units.

[0063] 1 / Tg mix= S Wi / Tg i

[0064] In this equation, Tgmixrefers to the glass transition temperature of the mixture of components used to form the polymer, which refers to the overall glass transition temperature of the precursor (meth)acrylate-based polymer or (meth)acrylate-based polymer having pendant (meth)acryloyl groups. Tgi is the glass transition temperature of each component i, (i.e., each component is a different monomeric unit in the copolymer) and Wiis the mass fraction of each component i. The glass transition temperature of each component (i.e., monomer) is the glass transition temperature of a homopolymer formed from that monomer. Both Tgi and Tgmixare in degrees Kelvin for purposes of the Fox equation but are often reported in degrees Celsius. Further information about the Fox equation and its use can be found in various reference texts for polymeric materials such as, for example, Hiemenz and Lodge, Polymer Chemistry. Second Edition. 2007, pp. 492-495. Tables of glass transition temperatures for homopolymers are available from various suppliers of monomer such as, for example, Sigma-Aldrich, Polyscience, and BASF. In some embodiments, the glass transition temperature of the precursor (meth)acrylate-based polymer as well as the glass transition temperature of the (meth)acrylate-based polymer having pendant (meth)acryloyl groups are no greater than 10 °C, no greater than 0 °C, no greater than -10 °C, or no greater than -20 °C but are usually greater than -60 °C, -50 °C, or -40 °C.

[0065] The curable composition can include multiple (meth)acrylate-based polymers that differ in weight average molecular weight and / or glass transition temperature and / or number of (meth)acryloyl groups per chain.

[0066] The curable composition typically contains 30 to 90 weight percent of the (meth)acrylate- based polymer having pendant (meth)acryloyl groups based on the total weight of the curable composition. If the amount is greater than 90 weight percent, the curable composition may be too viscous for application by printing or dispensing. If the amount is less than 30 weight percent, however, the curable composition may spread undesirably when printed or dispensed. The amount of the (meth)acrylate-based polymer having pendant (meth)acryloyl groups can be at least 35 weight percent, at least 40 weight percent, at least 45 weight percent, at least 50 weight percent, at least 55 weight percent, at least 60 weight percent, at least 65 weight percent, at least 70 weight percent, or at least 75 weight percent and up to 90 weight percent, up to 85 weight percent, up to 80 weight percent, or to up to 75 weight percent. In some embodiments, the amount of the (meth)acrylate-based polymer having pendant (meth)acryloyl groups is in a range of 40 to 90 weight percent, 40 to 85 weight percent, 40 to 80 weight percent, 40 to 75 weight percent, 40 to 70 weight percent, 40 to 60 weight percent, 50 to 75 weight percent, 50 to 80 weight percent, 50 to 85 weight percent, 50 to 90 weight percent, 60 to 75 weight percent, 60 to 80 weight percent, 60 to 85 weight percent, or 60 to 90 weight percent. The amounts are based on a total weight of the curable composition.

[0067] The curable composition also contains a monomer having a single ethylenically unsaturated group. Any of the monomers having a single ethylenically unsaturated group that were described above for use in preparation of the precursor (meth)acrylate-based polymer can be used. The ethylenically unsaturated group is often a (meth)acryloyl group. The monomer having a single ethylenically unsaturated group can function as a diluent for the (meth)acrylate-based polymer having pendant (meth)acryloyl groups. The monomer is typically selected so that it is miscible with the polymeric material in the curable composition. The monomer can be used to adjust the viscosity of the curable composition for ease of printing and / or dispensing. Conveniently, the monomer can be useful for adjusting viscosity rather than adding an organic solvent or for minimizing the amount of organic solvent that is added.

[0068] In some embodiments, the monomer is added after preparation of the precursor (meth)acrylate-based polymer but before reaction of the precursor (meth)acrylate-based polymer with the unsaturated reagent compound. Because the reaction with the unsaturated reagent compound often occurs at an elevated temperature, monomers that will not evaporate during this reaction may be useful. In some embodiments, the monomer has a boiling point of at least 60 °C, 70 °C, 80 °C, or at least 90 °C.

[0069] In some embodiments, the monomer added is a (hetero)alkyl (meth)acrylate or an alkyl (meth)acrylate. Suitable examples include various branched alkyl (meth)acrylate (e.g., 2- ethylhexyl (meth)acylate, isooctyl (meth)acrylate, and 2-octyl acrylate) or cyclic alkyl (meth)acrylates such as isobomyl (meth)acrylate, 3,3,5-trimethylcyclohexyl (meth)acrylate, cyclohexyl (meth)acrylate, and 4-tert-butylcylcohexyl (meth)acrylate.

[0070] While a nitrogen-containing monomer is optional in curable composition, at least one of the (meth)acrylate-based polymer or the monomer includes a nitrogen-containing functional group. In some embodiments, the (meth)acrylate-based polymer and the monomer independently include a nitrogen-containing functional group. In some embodiments, the monomer includes a nitrogencontaining functional group. In some embodiments, the monomer comprises at least one of an N,N-dialkylaminoalkyl (meth)acrylate, an N,N-dialkyl amine adduct of a di(meth)acrylate, N- vinyl pyrrolidone, 2,N-morpholinoethyl(meth)acrylate, or N-vinyl caprolactam.

[0071] In some embodiments, the amount of the monomer having a single ethylenically unsaturated group in the curable composition is in a range of 10 to 70 weight percent. If the amount is less than 10 weight percent, the viscosity of the curable composition may be too high for printing and / or dispensing. On the other hand, if the amount is greater than 70 weight percent, there may be an insufficient amount of the polymeric material present, and the viscosity may be unacceptably low. In some embodiments, the amount of monomer can be at least 15 weight percent, at least 20 weight percent, at least 25 weight percent, at least 30 weight percent and up to 70 weight percent, up to 65 weight percent, up to 60 weight percent, up to 55 weight percent, up to 50 weight percent, up to 45 weight percent, up to 40 weight percent, up to 35 weight percent, up to 30 weight percent, or up to 25 weight percent. In some embodiments, the amount of monomer is in a range of 10 to 65 weight percent, 10 to 60 weight percent, 10 to 55 weight percent, 10 to 50 weight percent, 10 to 45 weight percent, 10 to 40 weight percent, 20 to 60 weight percent, 20 to 55 weight percent, 20 to 50 weight percent, 20 to 40 weight percent, 30 to 60 weight percent, or 40 to 60 weight percent. The amounts are based on the total weight of the curable composition.

[0072] In some embodiments, at least 25 weight percent of the monomers having a single ethylenically unsaturated group in the curable composition are based on renewable resources. The amount is based on the total weight of monomers having a single ethylenically unsaturated group. The amount can be at least 30 weight percent, at least 35 weight percent, at least 40 weight percent, at least 50 weight percent and up to 100 weight percent, up to 90 weight percent, up to 80 weight percent, up to 70 weight percent, up to 60 weight percent, or up to 50 weight percent.

[0073] Crosslinking monomers optionally can be added to the curable composition. Crosslinking monomers have at least two ethylenically unsaturated groups, which are typically (meth)acryloyl groups. These monomers can be added, for example, to increase the overlap shear strength of the cured composition.

[0074] Examples of crosslinking monomers with two (meth)acryloyl groups include glycerol di(meth)acrylate, hexanediol di(meth)acrylate, triethylene glycol di(meth)acrylate, 1,3 -propanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,4-cyclohexanediol di(meth)acrylate, urethane di(meth)acrylate, and polyethylene glycol di(meth)acrylates. Examples of crosslinking monomers with three (meth)acryloyl groups include glycerol tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, 1,2,4-butanetriol tri(meth)acrylate, and pentaerythritol tri(meth)acrylate. Examples of crosslinking monomers with four or more (meth)acryloyl groups include pentaerythritol tetra(meth)acrylate and sorbitol hexa(meth)acrylate.

[0075] In some embodiments, the amount of the optional crosslinking monomers is in a range of 0 to 5 weight percent based on a total weight of the curable composition. In some embodiments, there is at least 0.01 weight percent, at least 0.05, at least 0.1 weight percent, at least 0.5 weight percent, or at least 1 weight percent and up to 5 weight percent, up to 4 weight percent, up to 3 weight percent, up to 2 weight percent, or up to 1 weight percent of a crosslinking monomer. In some embodiments, the amount of the optional crosslinking monomer is in a range of 0.01 to 5 weight percent, 0.05 to 5 weight percent, 0.05 to 2 weight percent, 0.05 to 1 weight percent, 0. 1 to 5 weight percent, 0 to 1 weight percent, or 0.5 to 1 weight percent based on the total weight of the curable composition. In some embodiments, the curable composition is free of the optional crosslinking monomers.

[0076] In some embodiments, at least 25 weight percent of the monomers used to form the (meth)acrylate-based polymer having pendant (meth)acryloyl groups and / or the monomers having a single ethylenically unsaturated group in the curable composition are from a renewable resource. This amount can be at least 30 weight percent, at least 35 weight percent, at least 40 weight percent, at least 45 weight percent, or at least 50 weight percent based on the total weight of the curable composition.

[0077] The curable composition of the present disclosure includes a photoinitiator, generally a free-radical photoinitiator. The photoinitiator comprises an aminoketone-functional photoinitiator and a photosensitizer. A free radical photoinitiator is useful for initiating curing of the curable composition. The ethylenically unsaturated groups (e.g., (meth)acryloyl groups) in the monomer and the (meth)acrylate-based polymer undergo free radical polymerization.

[0078] Examples of suitable aminoketone-functional photoinitiators include amino-substituted aromatic ketones such as alkylamino acetophenones (e.g., 2-benzyl-2-dimethylamino-l-(4- morpholinophenyl)butanone and 2-methyl-l-[4-(methylthio)phenyl]-2-morpholinopropan-l-one, which are both commercially available, for example, from IGM Resins, Charlotte, NC, under the trade designation “OMNICURE”.

[0079] The amount of the amino-ketone functional photoinitiator can be in a range of 0.1 to 10 weight percent based on a total weight of the curable composition. The amount of the aminoketone functional photoinitiator can impact the speed of the curing (i.e., polymerization) reaction. In some embodiments, the amount of the amino-ketone functional photoinitiator is at least 0.2 weight percent, at least 0.5 weight percent, at least 1 weight percent, at least 2 weight percent, or at least 3 weight percent and up to 10 weight percent, up to 8 weight percent, up to 6 weight percent, or up to 5 weight percent. In some embodiments, the amount of the amino-ketone functional photoinitiator is in a range of 0.5 to 10 weight percent, 1 to 10 weight percent, 2 to 10 weight percent, 0.5 to 8 weight percent, 1 to 8 weight percent, 1 to 6 weight percent, 1 to 4 weight percent, 2 to 4 weight percent, or 1 to 3 weight percent.

[0080] As used herein, a photosensitizer may be understood to be a compound having an absorption spectrum that overlaps or closely matches the emission spectrum of the radiation source to be used and that can improve the overall quantum yield by means of, for example, energy transfer or electron transfer to other component(s) of the composition (e.g., the aminoketone- functional photoinitiator). Useful photosensitizers include aromatic ketones (e.g., substituted or unsubstituted benzophenones, substituted or unsubstituted thioxanthones, substituted or unsubstituted anthraquinones, and combinations thereof), dyes (e.g., oxazines, acridines, phenazines, rhodamines, and combinations thereof), 3 -acylcoumarins (e.g., substituted and unsubstituted 3 -benzoylcoumarins and substituted and unsubstituted 3 -naphthoylcoumarins, and combinations thereof), anthracenes (e.g., substituted and unsubstituted anthracenes), 3-(2- benzothiazolyl)-7-(diethylamino)coumarin (coumarin 6), 10-acetyl-2,3,6,7-tetrahydro-lH,5H,l lH- [l]benzopyrano[6,7,8-ij]quinolizin-l l-one (coumarin 521), other carbonyl compounds (e.g., camphorquinone, 4-phenylacetophenone, benzil, and xanthone, and combinations thereof), and combinations thereof. In some embodiments, the photosensitizer has an absorbance in the blue light range. In some embodiments, the photosensitizer is camphorquinone. In some embodiments, the photosensitizer has an absorbance in a range from 350 nm to 375 nm. In some embodiments, the photosensitizer is 2-isopropyl thioxanthone. In some embodiments, the photosensitizer has an absorbance in a range from 390 nm to 420 nm. In some embodiments, the photosensitizer is an anthraquinone. In some embodiments, the photoinitiator comprises 2-methyl-l-[4- (methylthio)phenyl]-2-morpholinopropan-l-one and 2-isopropyl thioxanthone.

[0081] The amount of photosensitizer can vary, depending upon, for example, its nature, the nature of other componcnt(s) of the curable composition, and the particular curing conditions. For example, amounts ranging from about 0.1 weight percent to about 10 weight percent can be useful for some applications. In some embodiments, the photosensitizer is included in the curing composition in an amount from 0.5 percent to 7.5 percent by weight, 1 percent to 7.5 percent by weight, or 1 percent to 5 percent by weight, based on the total weight of the curable composition.

[0082] In some embodiments, the photoinitiator further comprises an acyl phosphine oxide or acyl phosphinate photoinitiator. Acyl phosphine oxide and acyl phosphinate photoinitiators typically can be activated when exposed to actinic radiation in a range of 365 to 460 nm or 365 to 400 nm. Such photoinitiators are particularly effective for curing throughout a layer of the curable composition when exposed to light sources that emit actinic radiation. More specifically, the acyl phosphine oxide compounds often are transformed after activation by exposure to actinic radiation into a species that absorbs less of the actinic radiation (i.e., the compounds experience photobleaching). This can allow the actinic radiation to penetrate further into a layer of the curable composition. Furthermore, polymeric materials formed using these photoinitiators are often colorless.

[0083] In some embodiments, the acyl phosphine oxide photoinitiator is a compound such as those described, for example, in U.S. Pat. No. 4,737,593 (Ellrich et al.). The acyl phosphine oxides can be represented by Formula (I) or (II).

[0084] (I) (II)

[0085] In Formulas (I) and (II), each R2is independently a linear or branched alkyl having 1 to 18 carbon atoms, a cycloalkyl having 5 to 6 ring members (i.e., cyclopentyl and cyclohexyl), a substituted cycloalkyl, an aryl (e.g., phenyl, biphenyl, and naphthyl), a substituted aryl, or a heterocyclic ring with 5 or 6 ring members and having one or more sulfur, nitrogen, or oxygen heteroatoms. In some embodiments of Formulas (I) and (III), one R2can be alkoxy having 1 to 18, 1 to 12, 1 to 8, or 1 to 4 carbon atoms. Suitable substituents for substituted aryl and substituted cycloalkyl groups include halo groups (e.g., F, Cl, Br, and I), alkyl groups (e.g., alkyl groups with 1 to 10 carbon atoms, 1 to 6 carbon atoms, or 1 to 4 carbon atoms), and alkoxy groups (e.g., alkoxy groups with 1 to 10 carbon atoms, 1 to 6 carbon atoms, or 1 to 4 carbon atoms).

[0086] Each R3in Formulas (I) and (II) and each R4in Formula (I) is independently a cycloalkyl having 5 to 6 ring members (i.e., cyclopentyl and cyclohexyl), a substituted cycloalkyl, an aryl (e.g., phenyl, biphenyl, and naphthyl), a substituted aryl, or a heterocyclic ring having one or more sulfur, nitrogen, or oxygen heteroatoms and having 5 or 6 ring members. Suitable substituents for substituted aryl and substituted cycloalkyl groups include those described above in connection with R2. Groups R3and R4in Formula (I) can combine to form a ring that contains 4 to 10 carbon atoms that can optionally be substituted with one or more alkyl groups (e.g., 1 to 6 alkyl groups).

[0087] The acyl phosphine oxides represented by Formulas (I) and (II) usually have at least one aromatic group. In some embodiments, the acyl phosphine is represented by Formula (I) where R2is aryl, R3is an aryl substituted with an alkyl or alkoxy, and R4is an aryl substituted with an alkyl or alkoxy. In some particular embodiments, the acyl phosphine is bis(2,4,6- trimethylbenzoyl)phenyl phosphine oxide, which is commercially available under the trade designation OMNICURE 819 from IGM Resins.

[0088] In some embodiments, the acyl phosphine oxide is represented by Formula (II) where each R2is any aryl and R3is an aryl substituted with an alkyl or alkoxy. For example, the acyl phosphine oxide can be diphenyl(2,4,6-trimethylbenzoyl) phosphine oxide, which is commercially available under the trade designation TPO from Millipore Sigma (formerly Sigma Aldrich), St. Louis, MO, USA. In some embodiments, the acyl phosphine oxide is represented by Formula (II) where a first R2is an aryl, a second R2is an alkyl, and R3is an aryl substituted with an alkyl. In some embodiments, the acyl phosphine oxide is represented by Formula (II) where a first R2is an aryl, a second R2is an alkoxy, and R3is an aryl substituted with an alkyl. For example, the acyl phosphine can be ethyl(2,4,6-trimethylbenzoyl)phenyl phosphinate, which is commercially available under the trade designation TPO-L from Lambson, Wetherby, West Yorkshire, England.

[0089] In some embodiments, the total amount of the photoinitiator is often in a range of 0.1 to 10 weight percent based on a total weight of the curable composition. The amount of the photoinitiator can impact the speed of the curing (i.e., polymerization) reaction. In some embodiments, the total amount of photoinitiator is at least 0.2 weight percent, at least 0.5 weight percent, at least 1 weight percent, at least 2 weight percent, or at least 3 weight percent and up to 10 weight percent, up to 8 weight percent, up to 6 weight percent, or up to 5 weight percent. In some embodiments, the total amount of photoinitiator is in a range of 0.5 to 10 weight percent, 1 to 10 weight percent, 2 to 10 weight percent, 0.5 to 8 weight percent, 1 to 8 weight percent, 1 to 6 weight percent, 2 to 8 weight percent, 2 to 6 weight percent, or 4 to 6 weight percent.

[0090] If the photoinitiator includes an amino-functional photoinitiator and an acyl phosphine oxide photoinitiator, the photoinitiator often includes at least 10 weight percent, at least 15 weight percent, at least 20 weight percent, or at least 25 weight percent of each photoinitiator based on the total weight of photoinitiator. In some embodiments, the photoinitiator contains 10 to 90 weight percent of the amino-functional photoinitiator and 10 to 90 weight percent of the acyl phosphine oxide photoinitiator, 20 to 80 weight percent of the amino-functional photoinitiator and 20 to 80 weight percent of the acyl phosphine oxide photoinitiator, 25 to 75 weight percent of the aminofunctional photoinitiator and 25 to 75 weight percent of the acyl phosphine oxide photoinitiator, 50 to 90 weight percent of the amino-functional photoinitiator and 10 to 50 weight percent of the acyl phosphine oxide photoinitiator, or 50 to 75 weight percent of the amino-functional photoinitiator and 25 to 50 weight percent of the acyl phosphine oxide photoinitiator.

[0091] Other photoinitiators can be used in addition to the amino-functional photoinitiator, the photosensitizer, and the optional acyl phosphine oxide photoinitiator although it is not required. Examples of additional photoinitiators include methyl benzoylformate and aromatic ketones. Examples of aromatic ketones include benzophenone, acetophenone, substituted acetophenones such as 2,2-diethoxyacetophenone and 2, 2-dimethoxy-2 -phenylacetophenone, a bezoin ether such as benzoin methyl ether, benzoin ethyl ether, or benzoin isopropyl ether, a substituted benzoin ether such as anisoin methyl ether, and a substituted alpha-ketol such as -methyl-2- hydroxypropiophenone. Other aromatic ketones include 1 -hydroxy cyclohexyl phenyl ketone and 1 -[4-(2-hydroxyethoxy)phenyl] -2-hydroxy-2-methyl- 1 -propane- 1 -one, 2 -hydroxy-2 -methyl- 1 - phenyl propan-l-one. Polymeric photoinitiators having a desired activation group (e.g., an acyl phosphine oxide group, an aromatic ketone group, or a phenylglyoxylate group) can also be useful.

[0092] The curable composition further includes a thixotropic agent. The thixotropic agent contains inorganic oxide particles that are optionally treated with a surface modification agent. The thixotropic agent is useful, for example, for adjusting the viscosity of the curable composition. For example, the thixotropic agent is added to facilitate printing or dispensing of the curable composition.

[0093] Any inorganic oxide particles that function as a thixotropic agent can be used. As used herein, a composition is thixotropic if the viscosity decreases when the composition is subjected to a shearing stress over a given time with subsequent recovery or partial recovery of viscosity when the shearing stress is decreased or removed. The advantage of the thixotropic behavior is that the composition can be dispensed or printed more easily. For example, the curable composition can have decreased viscosity during dispensing or printing, but the viscosity can increase significantly after being dispersed or printed. The increased viscosity can keep the printed or dispensed composition from spreading undesirably.

[0094] The selection of the thixotropic inorganic oxide particles is often based on the final use and performance requirements of the cured composition. In some instances, the selection can be based on the desired color, light transmission, and haze of the cured composition. The inorganic oxide particles are often silicon oxide (e.g., silica), zirconium oxide, titanium oxide, aluminum oxide, clay, or boron nitride. The average diameter of the inorganic oxide particles is often selected so that the particles do not settle from the composition under normal gravitational forces. The average diameter is often no greater than 500 nm, no greater than 400 nm, no greater than 300 nm, no greater than 200 nm, or no greater than 100 nm. The average diameter is often at least 10 nm, at least 20 nm, at least 50 nm, or at least 100 nm. The average diameter can be determined using techniques such as electron microscopy based on image analysis of at least several hundred particles.

[0095] In some embodiments, the inorganic oxide is a silicon oxide such as, for example, fumed silica. Examples of suitable fumed silicas include those available under the trade designation AEROSIL from Evonik Industries, under the trade designations CAB-O-SIL and CAB-O-SPERSE from Cabot Corporation, and under the trade designation HDK (e.g., HDK Hl 8, which is a fumed silica that has been surface treated with a hydrophobic surface modifier) from Wacker Chemie AG. In some embodiments, the inorganic oxide is fumed aluminum oxide such as those available, for example, under the trade designation AEROXIDE from Evonik Industries. In some embodiments, the inorganic oxide is clay such as those available under the trade designation GARAMITE from Southern Clay Products.

[0096] Suitable inorganic oxide particles include those that have been treated with a surface modification agent to increase compatibility with the polymerized and polymerizable composition. The surface modification agent can be hydrophobic or hydrophilic. Examples of suitable surface modification agents include silanes, siloxanes, carboxylic acids, and phosphonic acids. In some embodiments, an inorganic oxide particle with a hydrophobic surface modification is used as the thixotropic agent, which may be useful, for example, to enhance compatibility with the monomers in the curable composition.

[0097] Examples of suitable surface treatment agents for inorganic oxide particles include various silanes with at least one hydrolyzable group such as alkoxy groups and with at least one alkyl group having 1 to 20 carbon atoms. The hydrolyzable alkoxy group often has 1 to 4 carbon atoms, 1 to 3 carbon atoms, or 1 to 2 carbon atoms. There can be 1 to 3 alkoxy groups and 1 to 3 alkyl groups with the sum of the alkoxy and alkyl groups being equal to 4. Stated differently, the silane can be represented by formula Si(R5)t(R6)4-t where the variable t is equal to 1, 2, or 3, R5is an alkoxy, and R6is an alkyl. A mixture of silanes can be used. For example, a mixture of a first silane having an alkyl group with 10 to 20 carbon atoms and a second silane having an alkyl group with 1 to 9 carbon atoms can be used. A combination of short and long chains tends to increase the overall coverage of the inorganic oxide particles with the hydrophobic groups.

[0098] The thixotropic agent is usually either inorganic oxide particles or surface modified inorganic oxide particles. Such thixotropic agents often contain 50 to 100 weight percent inorganic oxide particles and 0 to 50 weight percent surface treatment. In some embodiments, the thixotropic agent is at least 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or at least 99 weight percent inorganic oxide particles with the remainder being the surface treatment. The amounts are based on the total weight of the thixotropic agent.

[0099] In some embodiments, the amount of the thixotropic agent is in a range of 1 to 15 weight percent based on a total weight of the curable composition. If the amount of the thixotropic agent is less than 1 weight percent, the curable composition may not be thixotropic, and the viscosity may be too low (i.e., the composition may be too runny after being dispensed or printed). If the amount is greater than 15 weight percent, however, the viscosity may be too high, and the inorganic oxide particles may settle out or form a particle network, particularly if they are not miscible with the other components of the curable composition. In some embodiments, the amount of the thixotropic agent is at least 1 weight percent, at least 2 weight percent, at least 3 weight percent, or at least 5 weight percent and up to 15 weight percent, up to 12 weight percent, up to 10 weight percent, up to 8 weight percent, up to 6 weight percent, or up to 5 weight percent, based on the total weight of the curable composition.

[0100] In some embodiments, the curable composition contains 30 to 90, 40 to 90, 30 to 80, 40 to 80, 40 to 70, or 40 to 60 weight percent of the (meth)acrylate-based polymer having pendant (meth)acryloyl groups, 10 to 70, 10 to 60, 20 to 70, 20 to 60, 30 to 60, or 40 to 60 weight percent monomers having a single ethylenically unsaturated group, 0. 1 to 10 or 1 to 10 weight percent photoinitiator, and 1 to 15, 1 to 10, or 1 to 5 weight percent thixotropic agent based on a total weight of the curable composition.

[0101] If desired, tackifiers can be added to the curable composition used to form pressuresensitive adhesives compositions. Suitable tackifying resins include rosin resins such as rosin acids and their derivatives (e.g., rosin esters); terpene resins such as polyterpenes (e.g., alpha pinene-based resins, beta pinene-based resins, and limonene -based resins) and aromatic-modified polyterpene resins (e.g., phenol modified polyterpene resins); coumarone -indene resins; and petroleum -based hydrocarbon resins such as C5 -based hydrocarbon resins, C9-based hydrocarbon resins, C5 / C9-based hydrocarbon resins, and dicyclopentadiene-based resins. These tackifying resins, if added, can be hydrogenated to lower their color contribution to the pressure-sensitive adhesive composition. Combinations of various tackifiers can be used, if desired. Any desired amount of tackifier can be used depending on the use of the pressure-sensitive adhesive. In some embodiments, the amount of tackifier is in a range of 0 to 100 parts per 100 parts of the polymeric material (e.g., the polymeric material usually includes the (meth)acrylate-based polymer having pendant (meth)acryloyl groups plus the monomers included in the curable composition). For example, the amount of the tackifier can be 0 to 80 parts, 0 to 60 parts, 0 to 40 parts, or 0 to 20 parts per 100 parts of the (meth)acrylate-based polymer having pendant (meth)acryloyl groups along with the monomer.

[0102] Other optional components can be included in the curable composition as described above. Examples of optional components include pigments, dyes, colorants, defoamers, surfactants, scents, antistatic agents, electrically conductive particles, thermally conductive particles, nanoparticles, thickeners, fibers, processing aids, and expandable microspheres. Any suitable amount of these optional components can be used such as 0 to 20 parts per 100 parts of the polymeric material. For example, the amount of any optional component can be 0 to 15 parts, 0 to 10 parts, 0 to 5 parts, 0 to 3 parts, 0 to 2 parts, or 0 to 1 part per 100 parts of the polymeric material.

[0103] Further, if desired, an organic solvent can be added to control the viscosity of the curable composition. In some embodiments, no organic solvent (i.e., the curable composition is free of organic solvent) or only a minimum amount of the organic solvent is added. The amount of organic solvent can be up to 60 weight percent or even higher based on a total weight of the curable composition. The amount of organic solvent can be up to 50 weight percent, up to 40 weight percent, up to 30 weight percent, up to 20 weight percent, up to 10 weight percent, or up to 5 weight percent. In some embodiments, it is desirable to keep the content of organic solvent as low as possible. In some embodiments, the amount of organic solvent is not more than 4, 3, 2, 1, 0.5, or 0. 1 weight percent, based on the total weight of the curable composition. Any organic solvent used in the curable composition is typically removed at the completion of the curing (i.e., polymerization) reaction. Suitable organic solvents include, but are not limited to, methanol, tetrahydrofuran, ethanol, isopropanol, heptane, acetone, methyl ethyl ketone, methyl acetate, ethyl acetate, toluene, xylene, and ethylene glycol alkyl ether. Those solvents can be used alone or as mixtures thereof.

[0104] In some embodiments, the curable composition is free of an epoxy resin or substantially free of an epoxy resin. As used herein with reference to the epoxy resin, “substantially free” means that the curable composition contains less than 1 weight percent, less than 0.5 weight percent, less than 0.2 weight percent, less than 0.1 weight percent, less than 0.05 weight percent, less than 0.02 weight percent, or less than 0.01 weight percent epoxy resin based on the total weight of the curable composition.

[0105] Cured compositions can be prepared by exposing the curable composition described above in any of its embodiments to actinic radiation. To form a cured composition, the curable composition is often applied to a substrate and then exposed to actinic radiation. Any suitable substrate can be used. Accordingly, the present disclosure provides an article that includes a substrate and a curable composition positioned on a surface of the substrate, and the present disclosure provides an article that includes a substrate and a cured composition positioned on a surface of the substrate. The curable composition can be positioned in any desired pattern, as a discontinuous layer, or as a continuous layer. Patterns can be regular or irregular and of any desired size, shape, or design. The curable composition can be positioned on or adjacent to any suitable substrate. The curable composition layer can contact the substrate or be separated from the substrate by another layer, for example, a primer layer. The cured composition is a cured (i.e., polymerized) reaction product of any of the curable compositions described above. The cured composition layer can contact the substrate or be separated from the substrate by another layer, for example, a primer layer. The cured composition can be in a form of a continuous or discontinuous layer and can have any desired pattern.

[0106] The curable composition can be positioned on a surface of the substrate using any suitable process such as flow coating, dip coating, spray coating, knife coating, die coating, extrusion, printing, or dispensing. Once positioned on a surface of the substrate, the curable composition is exposed to actinic radiation to react the curable composition and form the cured composition.

[0107] In some embodiments, the curable composition is printed or dispensed onto a surface of the substrate. In some embodiments, the curable composition can be printed or dispensed into a pattern on a surface of the substrate. To be printed or dispensed, the viscosity of the curable composition depends on several variables such as the amount of the (meth)acrylate-based polymer having pendant (meth)acryloyl groups, the weight average molecular weight of this polymer, the amount of the monomer having a single ethylenically unsaturated group, the amount of the thixotropic agent, and the amount of any optional organic solvent. As the molecular weight of the polymeric material increases, a lower amount of the polymeric material will be needed. Further, as the weight average molecular weight of the polymeric material increases, the likelihood of undesirable stringing of the curable composition upon printing or dispensing can increase. As the weight average molecular weight of the polymeric material decreases, however, larger amounts can be used before the viscosity of the curable composition becomes unacceptably high.

[0108] For use in printing or dispensing applications, the curable composition often has a Trouton’s ratio in a range of 3 to 25 at a rate (i.e., extensional rate) of 1000 sec1. The Trouton’s ratio is the extensional viscosity divided by the shear viscosity. If the Trouton’s ratio is greater than 25 (i.e., if the extensional viscosity is too high relative to the shear viscosity), the curable composition has an increased tendency towards stringing upon printing or dispensing. That is, the curable composition may be too elastic in nature and stringing can result that can cause poor pattern quality or strings of curable composition landing on substrate in areas not intended. In some embodiments, the Trouton’s ratio is at least 4, at least 5, at least 6, at least 8, or at least 10 and can be up to 25, up to 22, up to 20, up to 18, up to 16, up to 15, up to 14, or up to 12. In some embodiments, the Trouton’s ratio is in a range of 3 to 20, 3 to 15, 3 to 10, 5 to 25, 5 to 20, 5 to 15, 10 to 25, or 10 to 20.

[0109] Printing or dispensing the curable composition advantageously eliminates the need to die cut the cured composition layer to get the desired size and shape. Die cutting can create undesirable waste because the trimmed material often needs to be discarded. Additionally, some soft or compliant cured composition layers may be difficult to cleanly die cut in that they may deform or flow when die cut.

[0110] The substrate can be flexible or inflexible and can be formed from a polymeric material, glass or ceramic material, metal, or combination thereof. Some substrates are polymeric films such as those prepared from polyolefins (e.g., polyethylene, polypropylene, or copolymers thereof), polyurethanes, polyvinyl acetates, polyvinyl chlorides, polyesters (polyethylene terephthalate or polyethylene naphthalate), polycarbonates, polymethyl(meth)acrylates (PMMA), ethylene-vinyl acetate copolymers, and cellulosic materials (e.g., cellulose acetate, cellulose triacetate, and ethyl cellulose). Other substrates are metal foils, nonwoven materials (e.g., paper, cloth, nonwoven scrims), and foams (e.g., polyacrylic, polyethylene, polyurethane, neoprene). For some substrates, it may be desirable to treat the surface to improve adhesion to the curable composition, cured composition, or both. Examples of such treatments include application of primer layers, surface modification (e.g., corona treatment or surface abrasion), and combinations thereof. In some embodiments, the substrate is a release liner. Release liners typically have low affinity for the curable composition and / or cured composition. Examples of release liners can be paper release liners (e.g., polymer coated Kraft paper) and polymeric films. Some release liners are coated with an outer layer of a release agent such as a silicone-containing material or a fluorocarbon-containing material. In some embodiments, the release liner comprises at least one of a polyester film, polyethylene film, polypropylene film, polyolefin coated polymer film, polyolefin coated paper, acrylic coated polymer film, and polymer coated kraft paper. The polyolefin coated film or paper may be polyethylene coated film or paper.

[0111] The curable composition can be positioned next to a substrate using a roll-to-roll process. That is, the substrate can be moved from a first roll to a second roll in a continuous process. As the substrate moves between the first roll and the second roll, it can be coated with the curable composition. Such a substrate can be regarded as being a web and the web is often a polymeric material (e.g., a polymeric film) such as those described above. The polymeric web can be unrolled from a first roll, coated with the curable composition, exposed to actinic radiation for crosslinking, and then rolled onto the second roll.

[0112] The curable composition can have any desired thickness that can be effectively cured when exposed to actinic radiation. In some embodiments, the curable composition coating has a thickness no greater than 20 mils (500 micrometers), no greater than 10 mils (250 micrometers), no greater than 5 mils (125 micrometers), no greater than 4 mils (100 micrometers), no greater than 3 mils (75 micrometers), or no greater than 2 mils (50 micrometers). The thickness is often at least 0.5 mils (12.5 micrometers) or at least 1 mil (25 micrometers). For example, the thickness of the curable composition can be in the range of 0.5 mils (2.5 micrometers) to 20 mils (500 micrometers), in the range of 0.5 mils (5 micrometers) to 10 mils (250 micrometers), in the range of 0.5 mils (12.5 micrometers) to 5 mils (125 micrometers), in the range of 1 mil (25 micrometers) to 3 mils (75 micrometers), or in the range of 1 mil (25 micrometers) to 2 mils (50 micrometers).

[0113] The cured composition typically is elastomeric and, in some embodiments, is a pressuresensitive adhesive. Thus, articles having a substrate and a pressure-sensitive adhesive layer on or adjacent to the substrate are provided. The pressure-sensitive adhesive layer can be continuous or patterned. The substrate can be selected depending on the specific application. For example, the substrate can be a sheeting material and the resulting article can provide decorative graphics or can be a reflective product. In other examples, the substrate can be label stock (the resulting article is a label with an adhesive layer), a tape backing (the resulting article is an adhesive tape), or a foam.

[0114] In some embodiments, the substrate is a release liner, and the resulting article can be an adhesive transfer tape. The adhesive transfer tape can be used to transfer the pressure -sensitive adhesive layer to another substrate or surface. Other substrates and surfaces include a panel (e.g., a metal panel such as an automotive panel), a glass window, or a component of an electronic display.

[0115] In some embodiments of the article of the present disclosure, the article is a single-sided adhesive tape with the cured composition attached to a single side of the tape backing. In some embodiments, the article is a double-sided adhesive tape with a pressure -sensitive adhesive layer on both major surfaces of the tape backing. At least one of the two pressure -sensitive adhesive layers is the cured composition described above. Double-sided adhesive tapes are often carried on a release liner.

[0116] A variety of light sources of various wavelengths are useful for making the cured composition. The curable composition can be exposed to actinic radiation in a range of 250 nm to 475 nm. Ultraviolet light sources can be of various types. Low light intensity lights such as black lights generally provide intensities ranging from 0.1 or 0.5 mW / cm2(milliWatts per square centimeter) to 10 mW / cm2(as measured in accordance with procedures approved by the United States National Institute of Standards and Technology as, for example, with a UVIMAP UM 365 L-S radiometer manufactured by Electronic Instrumentation & Technology, Inc., in Sterling, VA). High light intensity sources generally provide intensities greater than 100, 500 or 1000 mW / cm2or greater. In some embodiments, high intensity light sources provide intensities up to 1, 10, or 20 W / cm2. Examples of useful light sources include light emitting diodes (LEDs), black lights, medium pressure mercury lamps, higher intensity light sources as available from Heraeus UV Systems Inc., and combinations thereof. The exposure time for curing can vary depending on the intensity of the light source(s) used. Further, the wavelength of the light can affect curing because longer wavelengths tend to pass further into the curable composition.

[0117] In some embodiments, the light source is a light emitting diode (LED). In some embodiments, the light emitting diode emits light in a wavelength range of 350 nm to 460 nm or in a wavelength range from 365 nm to 460 nm. Many commonly used LED light sources for use in the ultraviolet region of the electromagnetic spectrum emit light in a range of 365 nm to 460 nm. Commonly used LED light sources typically do not emit light in a range of 240 nm to 300 nm. Other UV light sources that are not light emitting diodes tend to emit over a broader wavelength range.

[0118] U.S. Pat. No. 11,578,162 (Seth et al.) teaches that when an LED light source is used to cure a curable composition including a (meth)acrylate -based polymer having pendant (meth)acryloyl groups and having a weight average molecular weight in a range of 25,000 to 400,000 Daltons, a monomer having a single ethylenically unsaturated group, a photoinitiator comprising an acyl phosphine oxide, and a thixotropic agent comprising inorganic oxide particles, curing can be performed under an inert atmosphere, and a second photoinitiator (e.g., that absorbs in a wavelength range of 240 nm to 300 nm) may not be useful. To achieve an inert atmosphere, nitrogen can be used to displace oxygen such that the oxygen levels are less than 200 ppm, less than 100 ppm, or less than 50 ppm during curing. U.S. Pat. No. 11,578,162 (Seth et al.) further teaches that in the inert atmosphere, the curable composition can typically be effectively cured through the entire thickness. If the curing reaction occurs in air (i.e., in an ambient atmosphere), however, the major surface of the resulting pressure-sensitive adhesive layer opposite the release liner (e.g., the exposed surface) may not be sufficiently cured. Alternatively, if the major surface of the resulting pressure-sensitive adhesive layer opposite the release liner is sufficiently cured in air, the major surface of the resulting pressure-sensitive adhesive layer adjacent to the release liner may be over cured. Shorter wavelengths (such as those in a wavelength range of 240 nm to 300 nm) are said to be effective at curing the outer surface of the curable composition opposite the release liner (and nearer to the light source), but LED light sources typically do not emit light in this wavelength range.

[0119] Advantageously, and unexpectedly, the curable composition of the present disclosure can be cured with an LED light source in an ambient atmosphere (e.g., air). While U.S. Pat. No. 11,578,162 (Seth et al.) teaches that a combination of a first photoinitiator that is an acyl phosphine oxide compound and a second photoinitiator that is activated at shorter wavelengths (e.g., in a wavelength range of 240 nm to 300 nm) can effectively cure a curable composition in either an inert atmosphere or in an ambient atmosphere, the Examples below demonstrate that with an LED light source, the curable composition of the present disclosure is more effectively cured than a composition cured with a combination of an acyl phosphine oxide and methyl benzoylformate. The curable composition of the present disclosure can provide one of the following advantages when it is cured using an LED light source in an ambient atmosphere. l)The extent of curing is relatively uniform throughout the thickness of the pressure-sensitive adhesive layer so that the peel adhesive strength of each major surface towards a given substrate (e.g., stainless steel) varies by no more than 30 percent, no more than 20 percent, no more than 15 percent, no more than 10 percent, or no more than 5 percent. 2) The pressure-sensitive adhesive has a shear strength that is at least 10,000 minutes when adhered to stainless steel, in some advantageous embodiments, on each major surface.

[0120] In view of the advantages provided by the curable composition, the present disclosure provides a method of making a cured composition. The method includes applying the curable composition to a surface of a substrate and exposing the curable composition to actinic radiation in an atmosphere of air using a light emitting diode as a light source to form the cured composition. However, the curable composition may also be cured in an inert atmosphere (e.g., nitrogen atmosphere) using a different light source (e.g., any of those described above) if desired. The cured composition and article of the present disclosure and / or made by the method of the present disclosure, for example, an adhesive transfer tape, a single-sided adhesive tape, or a double-sided adhesive tape, may be useful for adhering to a variety of surfaces or adhering a variety of surfaces together. In some embodiments, at least one of the surfaces comprises at least one of metal (e.g., steel, stainless steel, or aluminum), glass (e.g., which may be coated with indium tin oxide, for example,), a polymer (e.g., a thermoplastic, rubber, thermoplastic elastomer, or thermoset), paper, a painted surface, a nonwoven or woven fabric, or a composite (e.g., fiber- reinforced polymers such as carbon fiber reinforced epoxies and glass-reinforced plastic, metal matrix compositions, and ceramic matrix composites). The material of the surface may be found throughout the adherend, or the surface may include a different material from the bulk of the adherend (e.g., a metal coating on a polymer). At least one of the surfaces may include polymers such as polyolefins (e.g., polypropylene, polyethylene, high density polyethylene, blends of polypropylene), polyamide 6 (PA6), acrylonitrile butadiene styrene (ABS), polycarbonate (PC), PC / ABS blends, polyvinyl chloride (PVC), polyamide (PA), polyurethane (PUR), thermoplastic elastomers (TPE), polyoxymethylene (POM), polystyrene, polyester (e.g., polyethylene terephthalate), poly(methyl) methacrylate (PMMA), and combinations thereof. Thus, the cured composition and article of the present disclosure may be useful for low-surface-energy surfaces such as polypropylene, polyethylene [e.g., high density polyethylene (HDPE), low density polyethylene (LDPE), and liner low density polyethylene (LLDPE)], and blends and copolymers thereof (e.g., polypropylene blended with ethylene propylene diene terpolymer (EPDM) and thermoplastic polyolefins (TPO)) and medium-surface-energy surfaces such as PA6, ABS, PC / ABS blends, PC, PVC, PUR, TPE, POM, polystyrene, and PMMA.

[0121] Various embodiments are provided that include a curable composition, a cured composition, articles, and methods of making articles.

[0122] In a first embodiment, the present disclosure provides a curable composition comprising a (meth)acrylate-based polymer having pendant (meth)acryloyl groups and having a weight average molecular weight in a range of 25,000 to 400,000 Daltons, a monomer having a single ethylenically unsaturated group, a photoinitiator comprising an aminoketone-functional photoinitiator and a photosensitizer, and a thixotropic agent comprising inorganic oxide particles, wherein at least one of the (meth)acrylate-based polymer or the monomer includes a nitrogencontaining functional group. In a second embodiment, the present disclosure provides the curable composition of the first embodiment, wherein the curable composition is free of an epoxy resin or substantially free of an epoxy resin. In a third embodiment, the present disclosure provides the curable composition of the first or second embodiment, wherein the (meth)acrylate-based polymer having pendant (meth)acryloyl groups further comprises monomeric units having a pendant hydroxyl group. In a fourth embodiment, the present disclosure provides the curable composition of any one of the first to third embodiments, wherein the (meth)acrylate-based polymer having pendant (meth)acryloyl group comprises 50 to 99.9 weight percent monomeric units of an alkyl (meth)acrylate, 0.1 to 10 weight percent monomeric units having a pendant (meth)acryloyl group, 0 to 40 weight percent monomeric units having a pendant hydroxyl group, amino group, amido group, or anhydride group, based on a total weight of the (meth)acrylate-based polymer having pendant (meth)acryloyl groups. In a fifth embodiment, the present disclosure provides the curable composition of any one of the first to fourth embodiments, wherein the (meth)acrylate-based polymer having pendant (meth)acryloyl group comprises 60 to 98 weight percent monomeric units of an alkyl (meth)acrylate, 0.5 to 5 weight percent monomeric units having a pendant (meth)acryloyl group, 5 to less than 40 weight percent monomeric units having a pendant hydroxyl group, amino group, amido group, or anhydride group. In a sixth embodiment, the present disclosure provides the curable composition of any one of the first to fifth embodiments, wherein the (meth)acrylate -based polymer comprises units of at least one of an N,N-dialkylaminoalkyl (meth)acrylate, an N,N-dialkyl amine adduct of a di(meth)acrylate, N-vinyl pyrrolidone, 2-N- morpholinoethyl(meth)acrylate, or N-vinyl caprolactam. In a seventh embodiment, the present disclosure provides the curable composition of any one of the first to sixth embodiments, wherein the (meth)acrylate -based polymer having pendant (meth)acryloyl groups has 1 to 20 pendant (meth)acryloyl groups per chain on average. In an eighth embodiment, the present disclosure provides the curable composition of any one of the first to seventh embodiments, wherein the (meth)acylate -based polymer has a weight average molecular weight in a range of 35,000 to 100,000 Daltons or in a range of 40,000 to 80,000 Daltons.

[0123] In a ninth embodiment, the present disclosure provides the curable composition of any one of the first to eighth embodiments, wherein the (meth)acrylate-based polymer having pendant (meth)acryloyl groups is a reaction product of a precursor (meth)acrylate-based polymer having pendant hydroxyl groups, pendant carboxylic acid groups, or pendant anhydride groups and an unsaturated reagent compound having a (meth)acryloyl group plus a complementary group that is capable of reacting with the pendant hydroxyl groups, pendant carboxylic groups, or pendant anhydride groups. In a tenth embodiment, the present disclosure provides the curable composition of the ninth embodiment, wherein the precursor (meth)acrylate-based polymer has pendant hydroxyl groups and the unsaturated reagent compound has a complementary group that is a carboxylic acid group, isocyanato group, epoxy group, or anhydride group. In an eleventh embodiment, the present disclosure provides the curable composition of the tenth embodiment, wherein the unsaturated reagent compound is isocyanatoethyl (meth)acrylate. In a twelfth embodiment, the present disclosure provides the curable composition of the tenth embodiment, wherein the unsaturated reagent compound is glycidyl (meth)acrylate.

[0124] In a thirteenth embodiment, the present disclosure provides the curable composition of any one of the first to twelfth embodiments, wherein the monomer comprises at least one of an N,N- dialkylaminoalkyl (meth)acrylate, an N,N-dialkyl amine adduct of a di(meth)acrylate, N-vinyl pyrrolidone, 2-N-morpholinoethyl(meth)acrylate, or N-vinyl caprolactam. In a fourteenth embodiment, the present disclosure provides the curable composition of any one of the first to thirteenth embodiments, wherein the monomer comprises at least one of 2-ethylhexyl (meth)acylate, isooctyl (meth)acrylate, 2-octyl acrylate, isobomyl (meth)acrylate, 3,3,5- trimethylcyclohexyl (meth)acrylate, cyclohexyl (meth)acrylate, or 4-tert-butylcylcohexyl (meth)acrylate. In a fifteenth embodiment, the present disclosure provides the curable composition of any one of the first to fourteenth embodiments, wherein the monomer having the single ethylenically unsaturated group has a boiling point of at least 60 °C or at least 80 °C.

[0125] In a sixteenth embodiment, the present disclosure provides the curable composition of any one of the first to fifteenth embodiments, wherein at least one of the photoinitiator or the photosensitizer absorbs wavelengths of light in a range from 350 nm to 460 nm. In a seventeenth embodiment, the present disclosure provides the curable composition of any one of the first to sixteenth embodiments, wherein the photoinitiator comprises 2-methyl-l-[4-(methylthio)phenyl]- 2-morpholinopropan-l-one and 2-isopropyl thioxanthone. In an eighteenth embodiment, the present disclosure provides the curable composition of any one of the first to seventeenth embodiments, wherein the photoinitiator further comprises an acyl phosphine oxide or acyl phosphinate photoinitiator. In a nineteenth embodiment, the present disclosure provides the curable composition of the eighteenth embodiment, wherein the acyl phosphine oxide or acyl phosphinate has an aromatic group. In a twentieth embodiment, the present disclosure provides the curable composition of the nineteenth embodiment, wherein the acyl phosphine oxide comprises bis(2,4,6-trimethylbenzoyl) phenylphosphine oxide.

[0126] In a twenty-first embodiment, the present disclosure provides the curable composition of any one of the first to twentieth embodiments, wherein the thixotropic agent comprises silica. In a twenty-second embodiment, the present disclosure provides the curable composition of any one of the first to twentieth embodiments, wherein the thixotropic agent comprises a surface -modified inorganic oxide. In a twenty-third embodiment, the present disclosure provides the curable composition of any one of the first to twenty-second embodiments, wherein the thixotropic agent is hydrophobic.

[0127] In a twenty-fourth embodiment, the present disclosure provides the curable composition of any one of the first to twenty-third embodiments, wherein the curable composition comprises the (meth)acrylate-based polymer having pendant (meth)acryloyl groups in an amount from 30 to 90 weight percent, 40 to 90 weight percent, 40 to 80 weight percent, or 40 to 70 weight percent; the monomers having a single ethylenically unsaturated group in an amount from 10 to 70 weight percent, 10 to 60 weight percent, 20 to 60 weight percent, or 30 to 60 weight percent; the photoinitiator in an amount from 0.1 to 10 weight percent; and the thixotropic agent in an amount from 1 to 15 weight percent or 1 to 10 weight percent, based on a total weight of the curable composition. In a twenty-fifth embodiment, the present disclosure provides the curable composition of any one of the first to twenty-fourth embodiments, wherein the curable composition is printable or dispensable.

[0128] In a twenty-sixth embodiment, the present disclosure provides a cured composition comprising a polymerized product of the curable composition of any one of the first to twenty-fifth embodiments. In a twenty-seventh embodiment, the present disclosure provides the cured composition of the twenty-sixth embodiment, wherein the cured composition is formed by exposing the curable composition to actinic radiation. In a twenty-eighth embodiment, the present disclosure provides the cured composition of the twenty-sixth or twenty-seventh embodiment, wherein the cured composition is a pressure-sensitive adhesive. In a twenty-ninth embodiment, the present disclosure provides an article comprising a substrate and the cured composition of any one of the twenty-sixth to twenty-eighth embodiments on a surface of the substrate. In a thirtieth embodiment, the present disclosure provides the article of the twenty-ninth embodiment, wherein the substrate is a release liner. In a thirty-first embodiment, the present disclosure provides the article of the twenty-ninth or thirtieth embodiment, wherein the substrate is a polymeric film. In a thirty-second embodiment, the present disclosure provides the article of any one of the twentyninth to thirty-first embodiments, wherein the cured composition is in a form of a continuous layer. In a thirty-third embodiment, the present disclosure provides the article of any one of the twentyninth to thirty-first embodiments, wherein the cured composition is discontinuous on the surface of the substrate. In a thirty-fourth embodiment, the present disclosure provides the article of any one of the twenty-ninth to thirty-third embodiments, wherein the article is an adhesive tape or an adhesive transfer tape.

[0129] In a thirty-fifth embodiment, the present disclosure provides a method of making a cured composition, the method comprises applying the curable composition of any one of the first to twenty-fifth embodiments to a surface of a substrate and exposing the curable composition to actinic radiation to form the cured composition. In a thirty-sixth embodiment, the present disclosure provides the method of the thirty-fifth embodiment, wherein the cured composition is a polymerized reaction product of the curable composition. In a thirty-seventh embodiment, the present disclosure provides the method of the thirty-fifth or thirty-sixth embodiment, wherein the cured composition is a pressure-sensitive adhesive. In a thirty-eighth embodiment, the present disclosure provides the method of any one of the thirty-fifth to thirty-seventh embodiments, wherein applying comprises printing or dispensing the curable composition. In a thirty-ninth embodiment, the present disclosure provides the method of any one of the thirty-fifth to thirtyeighth embodiments, wherein applying comprises screen printing or stencil printing. In a fortieth embodiment, the present disclosure provides the method of any one of the thirty-fifth to thirtyninth embodiments, wherein exposing the curable composition to actinic radiation comprises using a light emitting diode as a light source. In a forty-first embodiment, the present disclosure provides the method of the fortieth embodiment, wherein the light emitting diode emits light with a wavelength range of 350 nm to 460 nm. In a forty-second embodiment, the present disclosure provides the method of any one of the thirty-fifth to forty-first embodiments, wherein exposing the curable composition to actinic radiation is carried out in an ambient atmosphere (i.e., in an atmosphere of air).

[0130] In a forty-third embodiment, the present disclosure provides the method of any one of the thirty-fifth to forty-second embodiments, wherein the substrate is a release liner. In a forty-fourth embodiment, the present disclosure provides the method of any one of the thirty-fifth to forty-third embodiments, wherein the substrate is a polymeric film. In a forty-fifth embodiment, the present disclosure provides the method of any one of the thirty-fifth to forty-fourth embodiments, wherein the cured composition is in a form of a continuous layer. In a forty-sixth embodiment, the present disclosure provides the method of any one of the thirty-fifth to forty-fifth embodiments, wherein the cured composition is discontinuous on the surface of the substrate. In a forty-seventh embodiment, the present disclosure provides the method of any one of the thirty-fifth to forty-sixth embodiments, wherein the cured composition is an adhesive transfer tape. In a forty-eighth embodiment, the present disclosure provides the method of any one of the thirty-fifth to fortyseventh embodiments, wherein the substrate is a release liner and the cured composition is a pressure-sensitive adhesive having a first major surface adjacent to the release liner and a second major surface opposite the release liner, the first major surface having a peel strength within 30, 20, or 10 percent of a peel strength of the second major surface. In a forty-ninth embodiment, the present disclosure provides the method of any one of the thirty-fifth to forty-eighth embodiments, wherein the substrate is a release liner and the cured composition is a pressure-sensitive adhesive having a first major surface adjacent to the release liner and a second major surface opposite the release liner, the first major surface and the second surface have a shear adhesive strength of at least 10,000 minutes when adhered to stainless steel. In a fiftieth embodiment, the present disclosure provides the method of the forty-ninth embodiment, wherein the first major surface has a shear adhesive strength within 30, 20, or 10 percent of the shear adhesive strength of the second major surface.

[0131] Examples

[0132] The materials with their sources were as listed in Table 1. Unless otherwise indicated, all materials were purchased from commercial sources and used as received.

[0133] Table 1. Materials List EXPERIMENTAL METHODS

[0134] Capillary Rheometry for Trouton ’s Ratio Measurements

[0135] Capillary rheometry was used for measurements of shear viscosity at rates up to 20000 sec1, and for measurements of the steady-state extensional viscosity based on contraction flow through an orifice. A Rosand RH-7 twin-bore capillary rheometer (Malvern Instruments Ltd, Malvern, Worcestershire, United Kingdom) was used with a 30-mm length, 1-mm diameter, and 90 degree entrance angle die in the first bore and a 1-mm diameter, 90 degree entrance angle orifice in the second bore. Pressure drop was recorded independently across each die. A Bagley correction was applied to account for entrance pressure effects. A Rabinowitz correction was applied to account for shear thinning effects, which tend to result in true shear rates which are greater than the shear rate predicted for a Newtonian fluid. Extensional rate and extensional viscosity were determined according to Cogswell’s analysis, using the entrance pressures determined by the Bagley correction. Cogswell’s analysis is described in greater detail in the article “Converging Flow of Polymer Melts in Extrusion Dies” (F. N. Cogswell, Polymer Engineering and Science, lanuary 1972, 12, pp. 64-73). Trouton’s Ratio is typically defined as the ratio of extensional viscosity to shear viscosity at the same rate.

[0136] Molecular Weight Determination

[0137] (Meth)acrylate-based polymers having multiple pendant (meth)acryloyl groups were evaluated for their molecular weights using gel permeation chromatography (GPC). The compositions were dissolved in tetrahydrofuran at a concentration of 0.5 percent (weight / volume) and passed through a 0.45 micrometer polytetrafluoroethylene filter. Samples of the resulting solution were analyzed using an Agilent Systems (Santa Clara, CA, USA) GPC unit equipped with one Agilent Mixed-D and one Mixed-B columns (7.8 mm x 300 mm) at 40 °C (obtained from Agilent Systems) and Agilent 1260 Refractive Index Detector. After injection, samples were eluted at 1 milliliter / minute. Calibration was carried out using polystyrene standards. The weight average molecular weight (Mw) was determined and reported in Daltons (Da).

[0138] Functionality

[0139] Functionality (i.e., number of pendant (meth)acryloyl groups per polymer chain) of curable compositions of Examples 1-2 was calculated using the equation:

[0140] F= (A)(E) ^ (F) wherein:

[0141] (A) is the average molecular weight of the precursor (meth)acrylate-based polymer in grams / mole; (E) is the moles of unsaturated reagent compound reacted with the precursor (meth)acrylate based polymer; and

[0142] (F) is the amount in grams of the precursor (meth)acry late -based polymer treated with the unsaturated reagent compound.

[0143] Peel Adhesion Strength

[0144] Peel adhesion strength was measured at room temperature (between 23 and 25°C) and 50% relative humidity (RH) using an IMASS Model 2000 Slip / Peel Tester (Instrumentors Incorporated, Strongsville, OH). A stainless-steel substrate was cleaned with 1 wash of acetone, 3 washes of heptane, and dried prior to testing. The adhesive surface of Cured Controls 1 and 2 and Example 1 were laminated to a 51 micrometers (0.002 inches) thick polyester fdm to give a test specimen. The test specimen measuring 1.0 inch (2.54 centimeters) wide by approximately 3 inches (15.2 centimeters) long was applied to the cleaned steel substrate. The prepared samples were dwelled at 23°C / 50% RH (relative humidity) for 15 minutes before testing. A 2-kilogram rubber roller was rolled over the length of the test specimen two times in each direction to ensure intimate contact with the substrate surface. The free end of the tape test specimen was doubled back at an angle of 180 degrees and attached to the testing arm. The substrate was attached to the moveable platen on the instrument. The peel test was run at a constant rate of 12 inches / minute (30.5 cm / min) for 6 seconds and the peel force was obtained by averaging the last five seconds of data. The average peel force for the test specimen was recorded in ounces (oz) per inch (0.004 N / cm).

[0145] Shear Adhesion Strength

[0146] Shear adhesion strengths were measured at 70 °C as follows. Stainless steel (SS) panels were cleaned with one wash of acetone, 3 washes of heptane and dried prior to testing. Samples of Cured Controls 1 and 2 and Example 1 measuring 1 inch (2.54 cm) wide and between 2.5 and 3 inches (6.3 and 7.6 cm) long were cut, then centered on the cleaned panels and adhered to one end such that tape overlapped the panel by 1 inch (2.54 cm) in the lengthwise direction. The tape sample was then rolled down two times in each direction using a 4.5-pound (2 -kg) rubber roller. The prepared samples were dwelled at 23 °C / 50% RH (relative humidity) for 24 hours before testing. The tape / test panel assembly was then suspended in a stand and tilted at an angle of 2 degrees from vertical to ensure a shear force. A 500-gram weight was hung from the free end of the tape sample. The time, in minutes, for the tape to fall from the panel was recorded. The test was terminated if failure had not occurred in 10000 minutes and the result recorded as “10000”. PREPARATIONS

[0147] PREPARATION OF PRECURSOR ACRYLATE POLYMERS A and B

[0148] Precursor Acrylate Polymers A and B used in the control and Examples 1 and 2 were prepared by two-step bulk polymerization as generally described in U.S. Patent No. 5,986,011 (Ellis). In the first step of polymerization, the reactor was charged with ingredients and amounts shown in Table 2, wherein monomer amounts are expressed in weight percent, and the other ingredients were added in parts per hundred of the monomer composition. The reactor was sealed and purged of oxygen and then held at approximately 0.5 bar nitrogen pressure. The reaction mixture was heated to 60 °C and the reaction proceeded adiabatically, producing First Reaction Products A and B.

[0149] Table 2, First step of polymerization

[0150] When the adiabatic reaction temperature peaked (indication that the reaction was complete), the First Reaction Product was cooled to below 40 °C to initiate the second step of the polymerization. Additional ingredients were added to the First Reaction Product as shown in Table 3, below. The term “pph” means parts per hundred (grams added for every 100 grams of the monomers used). The reactor was re-sealed, purged of oxygen and pressurized at 0.5 bar nitrogen pressure. The reaction mixture was heated to 60 °C and the reaction proceeded adiabatically to produce acrylate polymers.

[0151] Table 3 , Second step of polymerization

[0152] PREPARATION OF (METH)ACRYLATE-BASED POLYMERS (AP 1 and 2) (Meth)acrylate-based polymer having multiple pendant (meth)acryloyl groups (AP 1 and 2) were prepared by reacting Precursor Acrylate Polymers A and B with isocyanatoethyl methacrylate (IEM) at 110 °C for 6 to 10 hours under a nitrogen / oxygen 90 / 10 atmosphere in the amounts shown in Table 4, below, wherein IEM amounts are expressed in parts per hundred of acrylate polymer. Molecular weight and functionality (average number of (meth)acryloyl groups per chain) of (meth)acrylate-based polymer having multiple pendant (meth)acryloyl groups (AP 1 and 2) were measured and calculated following the procedures previously described. The results are reported in Table 4, below.

[0153] CONTROLS 1 and 2 and EXAMPLE 1 : Curable Compositions

[0154] Curable compositions of Controls 1 and 2 and Example 1 were prepared by mixing (Meth)acrylate-based polymers AP 1 and 2 with the materials shown in Table 5, below, wherein the amounts are expressed in weight percent (%). The mixing was carried out at room temperature (about 23 °C) until the composition was homogeneous.

[0155] Table 5 , Curable Composition Examples

[0156] CURED CONTROLS and EXAMPLE 1

[0157] Curable compositions of Controls 1 and 2 and Example 1 were coated onto the silicone side of the PET release liner at a coating thickness of 50 microns (about 2 mils) and subjected to ultraviolet (UV) irradiation at room temperature. Coated samples were prepared in duplicates, and each sample cured using LED lights (XP-9, peak wavelength 365 nm, commercially available from Baldwin AMS Spectral UV, river Falls, WI, USA).

[0158] Radiometers were used determine radiant power of the light sources, which was then used to calculate total energy of exposure (Target UV total). Target UV total for the LED light source was measured with a first radiometer (model LED-R L365 LEDCURE, from EIT of Leesburg, VA, USA). Curing was carried out in ambient air.

[0159] The adhesive properties of the resulting cured composition were determined by measuring the adhesive properties on both sides of the cured composition, the front side (adhesive exposed side, FS) and on the back side (adhesive adjacent to the release liner, BS). Specifically, peel adhesion and shear strength were tested, using the test methods described above. Results are shown in Table 6, below, wherein caliper of the samples was approximately 2 mils (50 microns). Table 6, Shear and adhesion to stainless steel of Cured Controls 1 and 2 and Example 1

[0160] Those having skill in the art will appreciate that many changes may be made to the details of the above-described embodiments and implementations without departing from the underlying principles thereof. The scope of the present disclosure should, therefore, be determined only by the following claims.

Claims

What is claimed is:

1. A curable composition comprising: a (meth)acrylate-based polymer having multiple pendant (meth)acryloyl groups, the (meth)acrylate-based polymer having a weight average molecular weight in a range of 25,000 to 400,000 Daltons; a monomer having a single ethylenically unsaturated group; a photoinitiator comprising an aminoketone-functional photoinitiator and a photosensitizer; a thixotropic agent comprising inorganic oxide particles, wherein at least one of the (meth)acrylate-based polymer or the monomer includes a nitrogencontaining functional group.

2. The curable composition of claim 1, wherein the curable composition is free of an epoxy resin or substantially free of an epoxy resin.

3. The curable composition of claim 1 or 2, wherein the (meth)acrylate-based polymer having multiple pendant (meth)acryloyl groups further comprises monomeric units having pendant hydroxy groups.

4. The curable composition of any one of claims 1 to 3, wherein at least one of the photoinitiator or the photosensitizer absorbs wavelengths of light in a range from 350 nanometers to 460 nanometers.

5. The curable composition of any one of claims 1 to 4, wherein the photoinitiator comprises 2-methyl-l-[4-(methylthio)phenyl]-2-morpholinopropan-l-one and 2-isopropyl thioxanthone.

6. The curable composition of any one of claims 1 to 5, wherein the photoinitiator further comprises an acyl phosphine oxide or acyl phosphinate photoinitiator.

7. The curable composition of any one of claims 1 to 6, wherein the (meth)acrylate-based polymer comprises units of at least one of an N,N -dialkylaminoalkyl (meth)acrylate, an N,N- dialkyl amine adduct of a di(methacrylate), N-vinyl pyrrolidone, 2-N- morpholinoethyl(meth)acrylate, or N-vinyl caprolactam.

8. The curable composition of any one of claims 1 to 7, wherein the monomer comprises at least one of an N,N-dialkylaminoalkyl (meth)acrylate, an N,N-dialkyl amine adduct of a di(methacrylate), N-vinyl pyrrolidone, 2-N-morpholinoethyl(meth)acrylate, or N-vinyl caprolactam.

9. The curable composition of any one of claims 1 to 8, wherein the (meth)acrylate-based polymer having pendant (meth)acryloyl groups comprises 50 to 99.9 weight percent monomeric units of an alkyl (meth)acrylate, 0.1 to 10 weight percent monomeric units having a pendant (meth)acryloyl group, and 0 to 40 weight percent monomeric units having a pendant hydroxyl group, amino group, amido group, or anhydride group.

10. The curable composition of any one of claims 1 to 9, wherein the curable composition comprises 30 to 90 weight percent of the (meth)acrylate-based polymer having pendant (meth)acryloyl groups, 10 to 70 weight percent of the monomer having a single ethylenically unsaturated group, 0. 1 to 10 weight percent of the photoinitiator, and 1 to 15 weight percent of the thixotropic agent, based on a total weight of the curable composition.

11. A cured composition comprising the polymerized product of the curable composition of any one of claims 1 to 10, wherein the cured composition is a pressure -sensitive adhesive.

12. A method of making a cured composition, the method comprising: applying the curable composition of any one of claims 1 to 10 to a surface of a substrate; and exposing the curable composition to actinic radiation in an atmosphere of air using a light emitting diode as a light source to form the cured composition.

13. The method of claim 12, wherein applying comprises at least one of printing or dispensing.

14. The method of claim 12 or 13, wherein the light emitting diode emits light in a wavelength range of 350 to 460 nanometers.

15. An article comprising: a substrate; and the cured composition of claim 11 on a surface of the substrate.

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