Ultraviolet curable pressure sensitive adhesive

Abstract

An ultraviolet (UV) curable pressure sensitive adhesive (PSA) having high cohesive strength and high moisture resistance is described. The PSA has versatile curing properties and can be cured by conventional mercury bulbs or UV LED lamps, and is particularly useful as a high performance adhesive tape. Furthermore, the PSA is suitable for wide temperature range processing, in particular from room temperature to 140 DEG C. Articles comprising the adhesives are also described.

Description

Technical Field

[0001] This invention relates to a pressure-sensitive adhesive (PSA) that can be cured by ultraviolet (UV) light. The PSA exhibits high cohesive strength, fast curing speed, and high coating weight. It also possesses a versatile curing profile and can be cured by conventional mercury lamps or UV LED lamps. The PSA is particularly suitable for use as a high-performance tape. Furthermore, the PSA is suitable for low-temperature processing, for example, from about 25°C to about 140°C. The invention also relates to articles comprising the PSA. Background Technology

[0002] Pressure-sensitive adhesives (PSA) are highly tacky, permanently sticky at room temperature, and adhere to surfaces by applying slight finger pressure. PSA compositions are typically applied to a variety of substrates, such as paper, fabrics, metals, and plastic films, and then transformed into many different products, such as pressure-sensitive tapes and labels. These pressure-sensitive adhesive products have a wide range of applications in many industries, including: fastening or sealing in the automotive industry, bandages or transdermal drug delivery systems in the pharmaceutical industry, and sealing, bonding, or labeling in the packaging industry. PSA can be formulated for application as a solution or melt adhesive.

[0003] Hot melt pressure-sensitive adhesives (HMPSAs) are compositions that combine the properties of hot melt adhesives with those of pressure-sensitive adhesives. Hot melt adhesives are solid or semi-solid at room temperature, melt at elevated temperatures to coat a substrate, and return to their solid form upon cooling. The combination of these properties provides a composition that melts at elevated temperatures and cools to form a permanently tacky solid coating that adheres upon contact. A good, viable HMPSA must exhibit high cohesive strength at room temperature, low shrinkage on the substrate, retention of pressure-sensitive properties during storage and use, and a relatively low fluid viscosity at typical coating temperatures (e.g., from about 80°C to about 180°C). While very low molecular weight polymers produce hot melt adhesives with sufficient flowability, the resulting adhesives lack cohesive strength. Very high molecular weight polymers produce better cohesive strength but are too viscous at common application temperatures to be easily coated onto the substrate. Therefore, they must be blended with a high proportion of low molecular weight oils or resins to reduce viscosity. The addition of low molecular weight oils or resins, in turn, reduces cohesive strength and heat resistance. To avoid these problems, polymers of medium molecular weight with various functional groups that undergo crosslinking reactions via heat or photochemical radiation have been prepared. In this way, the cohesiveness of acrylic PSAs can be improved through sufficient crosslinking. Acrylic polymers with epoxy functional groups are already known. Examples of such polymers are described in Japanese Patent Application No. 1186876. However, these polymers cannot be crosslinked under UV radiation and / or heat.

[0004] Japanese Patent Application No. 2008-208149 relates to acrylic copolymers using non-polymerizable oxetane compounds as polymerization media and reactive diluents. The polymerization is achieved using heat and / or X-ray irradiation to form an adhesive for flat panel displays.

[0005] Japanese Patent Applications No. 1994-0816 and No. 1996-060127 describe UV-curable acrylic polymers that require the addition of polyfunctional polyols and other hydroxyl functional groups to crosslink the polymer.

[0006] Japanese Patent Application No. JP 2003147311 relates to the use of photopolymerizable diacrylates. As a bifunctional acrylate, it is not well-suited for use in adhesives because it becomes partially cross-linked before being applied to a substrate.

[0007] U.S. Patent Nos. 8,796,350 and 9,469,794 describe UV-curable pressure-sensitive adhesives that can be applied at temperatures from 80 to 180°C, which may be unsuitable for heat-sensitive substrates and / or may shorten the adhesive’s pot life.

[0008] Therefore, there is a persistent and ongoing demand in the art for UV-curable acrylic adhesives that are hot-melt processable adhesives at low temperatures (e.g., from about room temperature to about 140°C) and can be cured with conventional mercury UV lamps or UV LED lamps at about 365 nm to about 405 nm. Furthermore, there is a significant need for improvements in rapid curing rates and dark curing, as well as increased coating weight. This invention addresses these needs by, for example, lowering the processability temperature and increasing the biocompatibility. Summary of the Invention

[0009] The inventors have surprisingly discovered that by including a silane co-catalyst (or its polymerized or oligomeric derivative) in the composition, a UV-curable acrylic pressure-sensitive adhesive that can be thermally melted at low temperatures can be prepared. The addition of a silane co-catalyst (or its polymerized or oligomeric derivative) to the UV-curable acrylic pressure-sensitive adhesive provides several benefits.

[0010] First, silane co-catalysts (or their polymerized or oligomeric derivatives) improve UV curing efficiency, especially for high-coat-weight adhesive films. Not wanting to be bound by theory, the inventors reason that it facilitates the transport of the superacid H₂. + This improves the mobility of the superacid catalyst within the binder matrix after UV irradiation and during the dark curing process. It is known in the art that trace amounts of moisture or OH- from alcohols... - The existence of H increases +The increased mobility enhances cationic curing efficiency. This is especially true when alkoxysilanes decompose in the presence of strong acids and moisture (either present in the binder or from air) to produce alcohols and silanol (SiOH) functional groups. The pKa of the silanol functional groups ranges from 5.0 to 14.0; compared to moisture or alcohols with pKas of approximately 15 to 18, this increases Hc. + migration rate.

[0011] A second benefit of silane cocatalysts (or their polymerization or oligomerization derivatives) is that they can act as adhesion promoters for substrates such as metals, glass, plastics, ceramics, etc.

[0012] A third benefit of silane cocatalysts (or their polymerization or oligomerization derivatives) is their function as a moisture scavenger. It is well known that excess moisture in adhesives or air is detrimental to cationic curing due to the leveling effect of water on superacids. In such cases, the adhesive cannot cure well. Many alkoxysilanes are known to act as moisture scavengers.

[0013] Another benefit of the presence of silane cocatalysts (or their polymerized or oligomeric derivatives) is the stabilization of the adhesive before UV curing at elevated temperatures, particularly above approximately 110°C. This improved thermal stability is likely due to a combination of effects: the silane cocatalysts (or their polymerized or oligomeric derivatives) (i) reduce the melt viscosity of the adhesive, (ii) remove moisture, and (iii) neutralize any strong acid impurities (pKa < 4.0) from the cationic photoinitiator. Typically, UV cationic hot melt adhesives are not thermally stable at elevated temperatures (e.g., above approximately 100°C) due to strong acid residues from acrylic monomers or acid impurities in the cationic photoinitiator, which triggers unwanted cationic crosslinking at temperatures above, for example, approximately 130°C.

[0014] In one aspect, the present invention relates to an acrylic pressure-sensitive adhesive (PSA) that is UV-curable. The PSA exhibits high cohesive strength, fast curing speed, and high coating weight, and is used in high-performance tapes.

[0015] In one embodiment, the UV-curable pressure-sensitive adhesive comprises: (A) An acrylic polymer prepared from at least one acrylic monomer having a reactive functional group selected from: alicyclic epoxides, vinyl ethers, ethylene oxide, oxetane, hydroxyl, silyl SiR3 (wherein each R is independently alkyl, aryl, aralkyl, alkoxy, aryloxy, acetoxy, oxime, alkenoxy, amino, amide, ester, H or halogen), benzophenone, and any combination of the foregoing groups; (B) co-catalyst; and (C) Cationic photoinitiator.

[0016] In another embodiment, the UV-curable pressure-sensitive adhesive comprises: (A) About 80% by weight to about 99.98% by weight of an acrylic polymer having at least one terminal or pendant reactive functional group selected from the following: alicyclic epoxides, vinyl ethers, ethylene oxide, oxetane, hydroxyl, silyl SiR3 (wherein each R is independently alkyl, aryl, aralkyl, alkoxy, aryloxy, acetoxy, oxime, alkenoxy, amino, amide, ester, H or halogen), benzophenone, and any combination of the foregoing groups; (B) From about 0.01% by weight to about 10% by weight of a cationic photoinitiator, a cationic and radical photoinitiator package, or a combination thereof; and (C) Approximately 0.01 wt% to approximately 10 wt% of silane co-catalyst; The total weight of the UV-curable pressure-sensitive adhesive is 100% by weight.

[0017] In one embodiment, the UV-curable pressure-sensitive adhesive has a viscosity of about 1,000 to about 100,000 cps at an application temperature (e.g., about 25°C to about 140°C). Attached Figure Description

[0018] Figure 1 The rheological comparisons of the adhesives in Examples 6, 7, and 8 are shown. Detailed Implementation

[0019] All references cited in this article are included in full through citation.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. In case of conflict, this document (including the definitions) shall prevail. Preferred methods and materials are described below, although methods and materials similar to or equivalent to those described herein may be used in the implementation or testing of this disclosure. The entire contents of all publications, patent applications, patents, and other references mentioned herein are incorporated herein by reference. The materials, methods, and examples disclosed herein are illustrative only and are not intended to be restrictive.

[0021] As used herein, the term "alkyl" refers to a linear or branched hydrocarbon chain group consisting only of carbon and hydrogen atoms, without unsaturation, and connected to the remainder of the molecule by a single bond. Examples include, but are not limited to: methyl, ethyl, 1-propyl (n-propyl), 2-propyl (isopropyl), 1-butyl, 2-methyl-1-propyl (isobutyl), 2-butyl (sec-butyl), 2-dimethyl- 2-Propyl (tert-butyl), 1-pentyl (n-pentyl), 2-pentyl, 3-pentyl, 2-methyl-2-butyl, 3-methyl-2-butyl, 3-methyl-1-butyl, 2-methyl-1-butyl, 1-hexyl, 2-hexyl, 3-hexyl, 2-methyl-2-pentyl, 3-methyl-2-pentyl, 4-methyl-2-pentyl, 3-methyl-3-pentyl, 2-methyl-3-pentyl, 2,3-dimethyl-2-butyl, 3,3-dimethyl-2-butyl, n-heptyl, n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, n-pentadecanyl, n-hexadecyl, n-heptadecyl, n-octadecyl, n-nonadecanyl, and n-eicosyl. In some embodiments, the term alkyl refers to C10. 1-12 Alkyl (C 1-12 Hydrocarbons), for example, C 1-9 Alkyl (C 1-9 Hydrocarbons), or C 1-6 Alkyl (C 1-6 hydrocarbon).

[0022] As used herein, the term "aryl" refers to an aromatic hydrocarbon of 6 to 20 carbon atoms derived by removing hydrogen from the carbon atoms of a parent aromatic ring system. Typical aryl groups include, but are not limited to, monocyclic or bicyclic compounds derived from benzene, naphthalene, anthracene, biphenyl, etc.

[0023] As used herein, the term "alkoxy" refers to an alkoxy group having the formula –OR a The group, wherein R a Alkyl groups as defined above. Suitable C 1-6 Non-limiting examples of alkoxy groups include, for example, methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, sec-butoxy, tert-butoxy, pentoxy, and hexoxy.

[0024] As used in this article, the term aryloxy refers to an aryloxy group having the formula –OR b The group, wherein R b It is an aryl group as defined above.

[0025] As used in this article, the term acetoxy refers to the group -OC(O)CH3.

[0026] As used in this article, the term "oxime group" refers to the group -C(=N-OH)-R. c , where Rc It is hydrogen, or an alkyl or aryl group as defined above.

[0027] As used in this article, the term "olefinic group" refers to -OC(CH3)=CH2.

[0028] As used in this article, the term "amino" refers to -NR. d R e , where R d and R e Each is independently hydrogen, alkyl, or aryl as defined above.

[0029] As used herein, the term "amide" refers to the group -C(O)NR. f R g , where R f and R g Each is independently hydrogen, alkyl, or aryl as defined above.

[0030] As used herein, the term "ester" refers to a compound formed by the reaction between an acid and an alcohol and the elimination of water. Esters can be represented by the general formula RCOOR' (where R and R' are, for example, independently selected from alkyl and aryl groups).

[0031] As used in the specification and claims, the term "comprising" may include embodiments that are "composed of" and "substantially composed of". The terms "comprising", "including", "containing", "having", "having", "can / able / possibly", "contains", and variations thereof, as used herein, are intended as open-ended transitional phrases, terms, or words that require the presence of a specified ingredient / step and permit the presence of other ingredients / steps. However, such a description should be construed as also describing a composition or method as "composed of the listed ingredients / steps" and "substantially composed of the listed ingredients / steps", which permits only the specified ingredients / steps and any impurities that may arise therefrom, and excludes other ingredients / steps.

[0032] The numerical values ​​in the specification and claims of this application (particularly where they relate to polymers or polymer compositions) reflect average values ​​for compositions that may contain various polymers with different properties. Furthermore, unless otherwise stated, the numerical values ​​should be understood to include the same values ​​as when reduced to the same number of significant figures, and values ​​that differ from the stated values ​​by less than the experimental error of conventional measurement techniques of the type described in this application used to determine the values.

[0033] All ranges disclosed herein include the stated endpoints and are independently combinable (e.g., a range of “2 to 10” or “2-10” includes endpoints 2 and 10, as well as all intermediate values). The endpoints and any values ​​of the ranges disclosed herein are not limited to precise ranges or values; they are not precise enough to include values ​​that approximate these ranges and / or values. As used herein, approximate language can be applied to modify any quantitative representation that may vary without altering its underlying function. Thus, in some cases, a value modified by one or more terms (such as “about”) may not be limited to the specified precise value. In at least some cases, approximate language may correspond to the precision of the instrument used to measure the value. The modifier “about” should also be considered as disclosing a range defined by the absolute values ​​of the two endpoints. For example, the expression “about 2 to about 4” also discloses the range “2 to 4”. The term “about” can refer to ±10% of the indicated number. For example, “about 10%” can represent a range of 9% to 11%, and “about 1%” can mean 0.9% to 1.1%. Other meanings of “about” can be determined from the context (such as rounding), so for example, “about 1” can also mean 0.5 to 1.4.

[0034] As used herein, a polymer or oligomer refers to a macromolecule composed of monomer units equal to or greater than about two monomer units. The terms polymer, copolymer, and oligomer are used interchangeably herein.

[0035] As used herein, the terms “pressure-sensitive adhesive” and “PSA” are used interchangeably and refer to a viscoelastic material that adheres momentarily to most substrates by applying slight pressure and remains permanently tacky.

[0036] As used herein, the term “substantially free” means that the composition has less than about 1% by weight, for example less than about 0.5% by weight, less than about 0.4% by weight, less than about 0.3% by weight, less than about 0.2% by weight, less than about 0.1% by weight, or less than about 0.05% by weight, and preferably may not contain more than trace amounts of the specified component.

[0037] As used in this article, the term "no additional added component" means that the specified component is not intentionally added and may be present in trace amounts.

[0038] In one embodiment, the present invention relates to a pressure-sensitive adhesive that is UV-curable, comprising: (A) An acrylic polymer having one or more reactive terminal or side chain functional groups bonded to the acrylic polymer backbone (e.g., one or more reactive functional groups selected from: alicyclic epoxides, vinyl ethers, ethylene oxide, oxetane, hydroxyl, silyl-SiR3 (wherein each R is independently alkyl, aryl, aralkyl, alkoxy, aryloxy, acetoxy, oxime, alkenoxy, amino, amide, ester, H or halogen), benzophenone, and any combination of the foregoing groups; (B) co-catalyst; and (C) Cationic photoinitiator.

[0039] Acrylic polymers (A) having one or more reactive terminal or side-chain functional groups bonded to the acrylic polymer backbone undergo rapid cationic crosslinking catalyzed by the superacid generated by the decomposition of a cationic photoinitiator under UV irradiation. The initial rapid crosslinking provides the adhesive with initial strength, and the continued UV post-crosslinking (i.e., dark curing) over a wide range of application temperatures provides high cohesive strength and high adhesive properties.

[0040] Acrylic polymer (A) can be prepared by the following: (i) about 0.01% by weight to about 20% by weight of a first monomer having a reactive functional group selected from: alicyclic epoxides, vinyl ethers, ethylene oxide, oxetane, hydroxyl, silyl-SiR3 (wherein each R is independently alkyl, aryl, aralkyl, alkoxy, aryloxy, acetoxy, oxime, alkenoxy, amino, amide, ester, H or halogen), benzophenone, and mixtures of any of the foregoing groups; and (ii) about 80% by weight to about 99.99% by weight of a second acrylic monomer comprising: an acrylic or methacrylic acid derivative of the formula CH2=CH(R1)(COOR2), wherein R1 is H or CH3 and R2 is a linear, branched or cyclic C 1-24 Linear, branched, or cyclic C-shaped structures containing alkyl chains, or functional groups including ethoxy linkages, hydroxyl groups, or mixtures of the foregoing. 1-24 alkyl-aryl chains; and (iii) A third monomer, optionally present in about 0.1% to about 20% by weight, having a reactive silyl functional group -SiR3, wherein R is selected from (a) alkoxy, aryloxy, acetoxy, oxime, alkenoxy, amino, amide, ester, H, halogen, or combinations thereof, and (b) an acrylic monomer containing reactive benzophenone.

[0041] In one embodiment, the amount of the first monomer (i) is from about 0.01 to about 20 g per 100 g of acrylic polymer. In another embodiment, the amount of the first monomer (i) is from about 0.1 to about 10 g per 100 g of acrylic polymer.

[0042] In another embodiment, the acrylic polymer (A) is prepared by: (i) about 0.1% by weight to about 10% by weight of a first monomer having a reactive functional group selected from the following: alicyclic epoxides, vinyl ethers, ethylene oxide, oxetane, or a mixture of any of the foregoing groups; (ii) About 70% by weight to about 99.8% by weight of a second acrylic monomer comprising: an acrylic or methacrylic acid derivative of the formula CH2=CH(R1)(COOR2), wherein R1 is H or CH3 and R2 is selected from C 1-24 Alkyl chains, alkyl-aryl chains, and alkyl-aryl derivatives comprising functional groups including ethoxy linkages, hydroxyl groups, or mixtures of any of the foregoing groups; and (iii) about 0.1% by weight to about 20% by weight of a third monomer having a reactive silyl functional group -SiR3, wherein R is selected from (a) alkoxy, aryloxy, acetoxy, oxime, alkenoxy, amino, amide, ester, H, halogen, or combinations thereof, and (b) an acrylic monomer containing reactive benzophenone.

[0043] Suitable first monomers (i) of polymers (e.g., polymers capable of undergoing UV-activated cationic crosslinking and providing initial strength to adhesives) include, but are not limited to: vinyl or acrylic compounds of formula (1) containing cationic UV-reactive functional groups. (1) in R 1 It can be O, S, C=O, or linear, branched, or cyclic alkylene, oxyalkylene, or aryl; R 2 It can be linear, branched, or cyclic alkyl, alkoxy, aryl, H, halogen, C=O, or R connected by covalent bonds as a fused alicyclic ring. 1 Part of R 1 as a fused cycloaliphatic ringthrough a covalent bond connection); R 3 (CH2) n , where n is 0, 1, 2 or 3; X is an acrylate, a methacrylate, or contains a –W–Y group. W is O, S, amide, carbonate, carbamate, urea, siloxane, or a combination thereof, and Y is –R 4 –C(R 5 )=CH2, where R 4 Is it a linear or branched C? 2-10 Alkylene or C 2-10 oxyalkylene, arylene, or their derivatives, and R 5 It is H or CH3.

[0044] A suitable first monomer (i) is represented by structural formula (1A): Where R 1 = H or CH3 (1A).

[0045] Another compound used as the first monomer (i) is represented by structural formula (1B): (1B) Where R 2 = H or CH3.

[0046] Another compound used as the first monomer (i) is represented by structural formula (1C): (1C).

[0047] Another compound used as the first monomer (i) is represented by structural formula (1D): (1D).

[0048] Another compound used as the first monomer (i) is represented by structural formula (1E): (1E).

[0049] Another compound used as the first monomer (i) is represented by structural formula (1F): (1F).

[0050] Another compound used as the first monomer (i) is represented by structural formula (1G): (1G).

[0051] Another vinyl or acrylic compound used as the first monomer (i) is represented by the structural formula (1H): (1H) Where R 6= H or CH3.

[0052] Another compound used as the first monomer (i) is represented by structural formula (1I): (1I) Where R = H or CH3.

[0053] In another embodiment, the first monomer (i) is a vinyl or acrylic compound capable of undergoing either a rapid UV-activated cationic crosslinking reaction or a slow UV post-crosslinking reaction, and thus providing an adhesive with high-performance adhesive strength. Exemplary monomers include, but are not limited to: glycidyl methacrylate (GMA), 4-hydroxybutyl acrylate glycidyl ether (4-HBAGE), alicyclic epoxide monomers M100 and A400 (Daicel), TTA15 and TTA16 (Tetra), OXE-10 (Kowa), UVICURE S105 and S170, CD535 (Sartomer), and 4-vinyl-1-cyclohexene-1,2-epoxide (DOW). Another example of a suitable monomer has the formula (2A): (2A).

[0054] Acrylic monomers (ii) include monomers or mixtures derived from one or more of the following: CH2=CH(R) 1 (COOR) 2 ) of acrylic acid or methacrylic acid derivatives, wherein R 1 It is H or CH3 and R 2 C 1-24 Alkyl groups, C groups with aryl functional groups 1-24The alkyl chain, or the ethoxy linkage having a continuous repeating unit (wherein the repeating unit may be interrupted or capped by an aryl derivative and may contain a hydroxyl group), or R2 may be directly selected from aryl derivatives. Examples of acrylic monomers (ii) include, but are not limited to: methyl acrylate, ethyl acrylate, ethyl methacrylate, methyl methacrylate, n-butyl acrylate, n-butyl methacrylate, n-pentyl acrylate, n-hexyl acrylate, n-heptyl acrylate, and n-octyl acrylate, n-nonyl acrylate, lauryl methacrylate, cyclohexyl acrylate; branched (meth)acrylate isomers, such as isobutyl acrylate, isobutyl methacrylate; n-butyl methacrylate, 2-ethylhexyl acrylate, octadecyl methacrylate, and isooctyl acrylate, benzyl acrylate, ethoxylated nonylphenyl acrylate, 2-hydroxy-3-phenoxypropyl acrylate, phenoxyethyl acrylate, and mixtures of any of the foregoing. In one embodiment, the exemplary acrylic monomer (ii) is a monofunctional acrylate and does not include any diacrylate monomers and polyacrylate monomers.

[0055] The selection and relative amounts of the specific acrylic and vinyl monomers present in the acrylic polymers used in the preparation of the adhesives described herein depend on the desired end properties and intended end use of the adhesive. The selection of which acrylic and vinyl monomers to achieve the desired properties, and their relative amounts in the final composition, is within the scope of the expertise of a person skilled in the art.

[0056] In some embodiments of any of the UV-curable pressure-sensitive adhesives described herein, the acrylic polymer has a Tg value below about 10°C and a weight-average molecular weight (Mw) of about 1,000 to about 3,000,000 g / mol. Higher molecular weight acrylic polymers are desirable for achieving high cohesive strength and high performance in the UV-curable adhesive. A preferred weight-average molecular weight (Mw) for the acrylic polymer can be about 50,000 to about 2,000,000 g / mol, for example, about 200,000 to about 1,000,000 g / mol. For UV-curable pressure-sensitive adhesives that can be applied at room temperature, a preferred weight-average molecular weight (Mw) for the acrylic polymer is about 5,000 to about 500,000 g / mol, for example, about 10,000 to about 100,000 g / mol.

[0057] For the polymerization process, the first monomer (i) and the acrylic monomer (ii) are converted into an acrylic polymer or copolymer via free radical polymerization. During polymerization, the monomers are selected so that the resulting polymer can be used to prepare adhesives, and in particular, so that the resulting polymer possesses the pressure-sensitive adhesive properties according to Donatas Satas's *Handbook of Pressure Sensitive Adhesive Technology* (van Nostrand, NY 1989). For these applications, the glass transition temperature of the resulting polymer is below about 10°C, for example, below about 0°C.

[0058] In one embodiment, the acrylic polymer is substantially free of or contains no poly(meth)acrylates, polyols, or OH-functional groups, and the polymer remains substantially linear after polymerization.

[0059] In one embodiment, the matrix of the UV-curable pressure-sensitive adhesive comprises: (A) an acrylic polymer having reactive side-chain functional groups selected from the group consisting of alicyclic epoxides, vinyl ethers, ethylene oxide, oxetane, hydroxyl groups, silyl SiR3 (wherein each R is independently alkyl, aryl, aralkyl, alkoxy, aryloxy, acetoxy, oxime, alkenyloxy, amino, amide, ester, H, or halogen), benzophenone, and mixtures of any of the foregoing groups. The reactive functional groups of the polymer undergo a UV crosslinking reaction over a wide application temperature range in the presence of (B) a cationic photoinitiator or a combination of a cationic photoinitiator and a free radical photoinitiator to form a crosslinked network with high cohesive strength.

[0060] The UV-curable pressure-sensitive adhesive also contains a cationic photoinitiator (B). The primary function of the cationic photoinitiator is to initiate the crosslinking reaction of the acrylic polymer (A) upon UV irradiation. The cationic photoinitiator forms an excited state upon UV irradiation, which then decomposes to release cationic radicals. These cationic radicals react with solvents, water, or other hydrogen donors to produce protic acids, which are the active substances initiating the crosslinking reaction of the acrylic polymer (A). Radical reactive functional groups (e.g., (meth)acrylate C=C) react with the cationic radicals that decompose from the cationic photoinitiator upon UV irradiation. This reaction inhibits the formation of superacids. Preferably, the adhesive composition of the present invention is substantially free of or contains no radical reactive functional groups (e.g., mono- or poly(meth)acrylates) to avoid competition and interference between radical curing and cationic curing during UV irradiation.

[0061] Several cationic photoinitiators can be used to crosslink the acrylic polymer (A) of the present invention, including but not limited to iodonium and sulfonium salts. These substances include, for example, diaryliodonium salts, triarylsulfonium salts, dialkylphenylsulfonium salts, dialkyl(hydroxydialkylphenyl)sulfonium salts, and ferrocenium salts. The anions in these salts typically have low nucleophilic characteristics and include SbF6¯, PF6¯, AsF6¯, BF4¯, B(C6F5)4¯ or Ga(C6F5)4¯, PF n (Rf) 6-n Specific examples include, for example: Omnicat 320 from IGM (Omnicat is a cationic photoinitiator based on mixed triarylsulphonium hexaantimonates alts in 50% propylene carbonate), SPEEDCURE 937, SPEEDCURE 938, SPEEDCURE 939 from Sartomer (SPEEDCURE is 4,6-trimethylbenzoyl diphenylphosphine oxide), CPI-310B, CPI-200K, CPI-210S (CPI is a triarylsulphine salt type photoinitiator), and IK-1 (from San-Apro). Particularly useful cationic photoinitiators for use in this invention are soluble and LED-reactive sulfonate photoinitiators having structural formulas (6A) and (7A): (6A) Where R represents C3H7, C 12 H 25 And W is S, SO, SO2 or CO. (7A) Where R 1 and R 2 Each of the following is independently H, CH3, C2H5, C3H7, C 12 H 25 OCH3, OC2H5, OC3H7, or OC 12 H 25 .

[0062] These cationic photoinitiators have good solubility in the UV-curable pressure-sensitive adhesives of the present invention, promote efficient thick-film UV curing, and exhibit thermal stability before curing, resulting in an improved curing rate and a shortened dark curing time.

[0063] In another embodiment, the cationic photoinitiator of the UV-curable pressure-sensitive adhesive has the following structure: Where R represents C3H7, C12 H 25 And W is S, SO, SO2 or CO.

[0064] In addition to cationic photoinitiators, photosensitizers can be used as photoinitiator packages to improve crosslinking efficiency, particularly when using LED light sources in the UVA range of about 365 nm to about 405 nm to cure adhesives containing conventional UVB and UVC cationic photoinitiators. Examples of photosensitizers include, but are not limited to, thioxanthoxanone, 2-isopropylthioxanthoxanone (ITX), 2-chlorothioxanthoxanone, 2,4-diethyl-thioxanthoxanone (DETX), 1-chloro-4-propoxythioxanthoxanone (CPTX), anthraquinones, phenanthrenequinones, and camphorquinone.

[0065] The UV-curable pressure-sensitive adhesives described herein contain a silane cocatalyst (C). The silane cocatalyst, or its polymeric or oligomeric derivatives, acts as a stabilizer to stabilize the adhesive at elevated temperatures (above, for example, about 100°C), and simultaneously enhances the migration rate of superacidic protons in the cured adhesive matrix after UV irradiation. Another function of the silane, or its polymeric or oligomeric derivatives, is to promote adhesion to various substrates, such as metals, glass, plastics, and ceramics. Yet another function is that many of these silanes act as moisture scavengers.

[0066] In this invention, any suitable silane (e.g., alkoxy and hydroxy functionalized silanes) and their polymeric or oligomeric derivatives may be used. Examples of silanes that may be used in this invention include, but are not limited to: C1-C 24 Alkyltrialkoxysilanes, (meth)acryloyloxypropyltrialkoxysilanes, chloropropylmethoxysilanes, vinyltrimethoxysilanes, vinyltriethoxysilanes, vinyltrimethoxyethoxysilanes, vinylbenzylpropyltrimethoxysilanes, aminopropyltrimethoxysilanes, vinyltriacetoxysilanes, glycidoxypropyltrialkoxysilanes, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilanes, mercaptopropylmethoxysilanes, 3-aminopropyltriethoxysilanes, aminomethyltrimethoxysilanes, aminomethyltriethoxysilanes, 3-aminopropylmethyldiethoxysilanes, and mixtures thereof, particularly preferred examples of silanes are vinyltrialkoxysilanes, C1-C 24 Alkyltrialkoxysilanes, (meth)acryloyloxypropyltrialkoxysilanes, glycidyloxypropyltrialkoxysilanes, (3,4-epoxycyclohexyl)ethyltrialkoxysilanes, and their oligomeric or polymeric derivatives, or mixtures of any of the foregoing substances.

[0067] Further examples of silanes (and their polymeric or oligomeric derivatives) include polymeric or oligomeric VTMO (vinyltrimethoxysilane) and VTEO (vinyltriethoxysilane), which are commercially available from Evonik as Dynasylan 6490 and Dynasylan 6498. Other examples of adhesive promoters that can be used in the present invention include, but are not limited to, hydrolyzable PDMS polymers or oligomers, such as PDMS (polydimethylsiloxane) terminated with trialkoxysilyl (meth)acrylate, dialkoxysilyl (meth)acrylate, or methacrylate groups.

[0068] In one embodiment, the UV-curable pressure-sensitive adhesive comprises: (i) about 80% by weight to about 99.98% by weight of an acrylic polymer having at least one side-chain reactive functional group selected from: alicyclic epoxides, vinyl ethers, ethylene oxide, oxetane, hydroxyl, silyl SiR3 (wherein each R is independently alkyl, aryl, aralkyl, alkoxy, aryloxy, acetoxy, oxime, alkenoxy, amino, amide, ester, H or halogen), benzophenone, and mixtures of any of the foregoing groups; (ii) about 0.01% by weight to about 10% by weight of a cationic photoinitiator, or a package of a cationic photoinitiator and a free radical photoinitiator; and (iii) about 0.01% by weight to about 10% by weight of a co-catalyst; The total weight of the UV-curable pressure-sensitive adhesive is 100% by weight.

[0069] Any of the UV-curable pressure-sensitive adhesives described herein optionally further comprises a reactive diluent. The reactive functional groups of both the polymer and the reactive diluent undergo a UV crosslinking reaction in the presence of (B) a cationic photoinitiator or a combination of a cationic photoinitiator and a free radical photoinitiator to form a crosslinked network with high cohesive strength over a wide application temperature range. The reactive diluent of the UV-curable pressure-sensitive adhesive can be a polymer, oligomer, or macromonomer containing at least one terminal or side-chain functional group selected from: alicyclic epoxides, ethylene oxide, oxetane, vinyl ethers, alicyclic epoxysilyl groups, or mixtures of any of the foregoing groups. The reactive diluent is substantially free of or contains no mono- or poly(meth)acrylates. The reactive diluent can have a weight-average molecular weight of about 100 to about 500,000 g / mol. In addition, the reactive diluent may be epoxy-functionalized soybean oil, epoxy-functionalized polybutadiene, epoxy-functionalized polyurethane, epoxy-functionalized polysiloxane, epoxy-functionalized polybutadiene, epoxy-functionalized polyisobutylene, epoxy-difunctionalized bisphenol A epoxy resin, epoxy-difunctionalized bisphenol F epoxy resin, epoxy-functionalized polyacrylate, epoxy-functionalized polyethylene glycol, epoxy-functionalized polypropylene glycol, epoxy-functionalized polyether, or a mixture of any of the foregoing substances.

[0070] A primary function of diluents is to reduce and control the viscosity of adhesives, enabling them to be coated at low temperatures. Low adhesive viscosity and low coating temperatures are always preferred for the thermal stability of adhesives, heat-sensitive substrates, and low energy consumption in LED curing and coating processes. However, non-reactive diluents typically impair the cohesive strength of adhesives. To achieve high cohesive strength and high performance in UV-curable adhesives, high molecular weight and high viscosity acrylic polymers are typically used. Reactive diluents in adhesive compositions reduce the viscosity to a coatable range of approximately 1,000 to 100,000 cps at approximately 25 to approximately 120°C, and more importantly, do not impair the cohesive strength of the adhesive after UV curing. Reactive diluents participate in cationic crosslinking reactions, thus increasing the crosslink density to enhance the cohesive strength of the adhesive. However, a controlled amount of epoxy functional groups must be used to balance the reactive diluent between the acrylic polymer and the reactive diluent to avoid over-crosslinking, which results in adhesive films with low peel strength, low tack, and poor wettability. Examples of commercially available reactive diluents include: CELLOXIDE 2021P, CELLOXIDE 8000, CELLOXIDE 2081, EHPE 3150, EPOLEAD GT401, EPOLEAD PB series, EPOFRIEND series (from Daicel Corp.); UVICURE S128, UVICURE S150, UVICURE S160 (from Sartomer); EPON 828, EPON 862 (from Hexicon Inc.); KF-8100, KF-8145, KF-12102, KEW-L2000, KET-L3000 (from Kolon Industries); and DER 335, 321, 324, 325, 326 liquid epoxy resins (from Olin). Epoxy); from Tetra's TTA20, TTA22, TTA26, TTA34, TTA60, TTA184, and TTA186. The reactive diluent can range from about 1% to about 50% by weight, based on the total weight of the UV-curable adhesive.

[0071] One specific embodiment of the reactive diluent is bio-based or derived from biological sources. Bio-based or biologically derived reactive diluents can be prepared by reacting renewable precursors such as vegetable oils, sugars, tannins, cashew nut shells, terpenes, rosin, and lignin. Examples of bio-based reactive diluents include vikoflex-7170 and epoxidized soybean oil. These diluents are compatible with the acrylic polymers described herein and also slow down the post-UV curing process and improve the wettability of the adhesive to the substrate through a longer shadowcure. This improvement in wettability and adhesion enhances the adhesive strength over a wide application temperature range with a SAFT value not exceeding approximately 200°C.

[0072] Any of the UV-curable pressure-sensitive adhesives described herein may optionally additionally include tackifiers, plasticizers, heat stabilizers, antioxidants, moisture scavengers, desiccants, solvents, or any combination of the foregoing.

[0073] Any of the UV-curable pressure-sensitive adhesives described herein may optionally additionally contain a tackifier, in an amount, for example, from about 1% to about 50% by weight of the adhesive, as is conventionally used in the preparation of PSAs. See, for example, *Handbook of Pressure Sensitive Adhesive Technology* by Donatas Satas (van Nostrand, 1989). Generally, any natural resin compatible with the corresponding acrylic polymer can be used. Non-limiting examples include: pinene resins, indene resins, rosin, terpene resins, terpene-phenolic resins, rosin resins, wood rosin, tall oil rosin, distilled rosin, hydrogenated rosin, dimerized rosin, polymerized rosin; and their disproportionated and esterified derivatives and salts, and combinations of any of the foregoing substances.

[0074] Other suitable tackifiers include, for example, aliphatic and aromatic hydrocarbon resins, hydrogenated hydrocarbon resins, and functionalized hydrocarbon resins. Non-limiting examples include aliphatic and aromatic hydrocarbon resins, C5 resins, and C9 resins. Any desired combination of any of these resins can be used to adjust the properties of the resulting PSA according to the desired final characteristics.

[0075] Specific examples of these tackifiers include: TECKROS R80H and R86 (from Teckrez Inc.); SYLVALITE RE 85GB (from Kraton); FORAL 85-E (from Eastman); WINGTACK Examples of tackifiers include CLEARTACK W85 (from Cray Valley); Kristalex 3085 (from Synthomer); and Lawter T90 (from Lawter). A preferred embodiment of the tackifier is a liquid tackifier, which can further reduce the viscosity of the adhesive. Examples include: polymerized C5 petroleum feed streams and polyterpenes such as WINGTACK 10 (from Cray Valley), ESCOREZ 2520 (from Exxon Mobil); and the liquid rosin ester tackifier SYLVALITE2038 (from Kraton).

[0076] Any of the UV-curable pressure-sensitive adhesives described herein may optionally additionally include a heat stabilizer (e.g., a stabilizer to slow tackifier oxidation and minimize color change due to temperature variations) or an antioxidant. Examples of heat stabilizers and antioxidants that may be used include high molecular weight hindered phenols and polyfunctional phenols (e.g., sulfur- and phosphorus-containing phenols). Hindered phenols are well known to those skilled in the art and can be characterized as phenolic compounds that also contain sterically bulky groups closely adjacent to the phenolic hydroxyl group. Any known heat stabilizer may be suitable. Preferred heat stabilizer categories include, but are not limited to: phenolic antioxidants, alkylated monophenols, alkylthiomethylphenols, hydroquinone, alkylated hydroquinone, tocopherol, hydroxylated thiodiphenyl ethers, alkylene bisphenols, O-, N- and S-benzyl compounds, hydroxybenzyl malonates, aromatic hydroxybenzyl compounds, triazine compounds, amine antioxidants, arylamines, diarylamines, polyarylamines, acetaminophens, oxalamide, metal deactivators, phosphites, phosphonites, benzylphosphonates, ascorbic acid (vitamin C), hydroxylamine, nitrones, thiosynergists, benzofuranones, indolinones, and mixtures thereof. Examples of commercially available stabilizers include, for example: IRGANOX 1010, IRGANOX 1520, IRGANOX 1726, EVERNOX 1726, IRGANOX 565, IRGANOX 3114, EVERNOX 10 (IRGANOX and EVERNOX are major phenolic antioxidant stabilizers), IRGASTAB FS301 (IRGASTAB is a blend of oxidized bis(hydrogenated tallow alkyl)amines), TINUVIN 123, TINUVIN 292, TINUVIN 5100, TINUVIN 249, TINUVIN 770 (TINUVIN is an amine stabilizer based on amino-ether functional groups), BHT (butylated hydroxytoluene), and 4-MEHQ (4-methoxyphenol, from Sigma Aldrich).

[0077] The use of a heat stabilizer is optional and may not be preferred in some cases. When a heat stabilizer is used, it may be present at a level of about 0.001 g to about 0.5 g based on a total of 100 g of adhesive.

[0078] In another embodiment of any of the UV-curable pressure-sensitive adhesives described herein, a desiccant may be used to improve the moisture barrier properties of the adhesive. Suitable fillers with desiccant properties (referred to as desiccant fillers) may include any substance that provides a suitable moisture removal rate, capability, and residual moisture level (the minimum moisture level at which the desiccant can actively remove moisture) to meet the permissible moisture levels of a particular electronic device. Desiccant fillers are capable of reacting with or adsorbing water and / or water vapor. A representative list of such desiccants can be found, for example, in Dean, J. Lange's Handbook of Chemistry, 1999, McGraw Hill, Inc., New York, NY, pp. 11.5. When a desiccant is used as a moisture remover, it may be present at a level of approximately 0.001% by weight to approximately 0.5% by weight, based on the total weight of the adhesive.

[0079] Any of the UV-curable pressure-sensitive adhesives described herein may also contain additional additives (e.g., plasticizers and fillers), all of which are conventionally used in the preparation of PSAs. Any desired combination of these or other additives may be used to adjust the properties (e.g., viscosity and rheology) of the resulting adhesive according to the desired final characteristics, as known to those skilled in the art.

[0080] In addition, one or more plasticizers or non-reactive diluents (such as low molecular weight acrylic polymers, phthalates, whale plasticizers, mineral oils, or plasticizer resins) can be added to UV-curable pressure-sensitive adhesives to adjust the viscosity, wettability, and rheology of the adhesive before and after curing.

[0081] The UV-curable pressure-sensitive adhesives described herein can be approximately 100% solids, or in hot-melt, warm-melt, or room-temperature liquid form. The adhesives can have a Brinell viscosity of approximately 1,000 to 1,000,000 cps at coating temperatures (typically from approximately 25 to approximately 140°C), for example, a Brinell viscosity of approximately 1,000 to approximately 100,000 cps at approximately 25°C to approximately 120°C. Such a viscosity range allows the adhesive to be coated into a film. The film thickness is in the range of approximately 25 µm to approximately 250 µm (e.g., from approximately 50 µm to approximately 150 µm).

[0082] As is known to those skilled in the art, acrylic polymers can be prepared using well-known free radical polymerization techniques in a batch or continuous process in solution, as an emulsion, or in a bulk polymerization procedure. The polymer and the uncured adhesive can then be combined to form a pure adhesive by removing the solvent, latex coagulation, or melt processing of the pure polymer.

[0083] The polymerization can be carried out in the presence of one or more organic solvents and / or in the presence of water. Suitable organic solvents or solvent mixtures include, for example: alkanes, such as hexane, heptane, octane, isooctane, and cyclohexane; aromatic hydrocarbons, such as benzene, toluene, and xylene; esters, such as ethyl acetate, propyl acetate, butyl acetate, and heptyl acetate; halogenated hydrocarbons, such as chlorobenzene; alkanols, such as methanol, ethanol, isopropanol, ethylene glycol, and ethylene glycol monomethyl ether; ethers, such as diethyl ether and dibutyl ether; ketones, such as acetone and methyl ethyl ketone; or mixtures of any of the foregoing.

[0084] In one embodiment of the method, the polymerization reaction is carried out in ethyl acetate solvent with AIBN (2,2'-azobis(2-methylpropionitrile)), AMBN (2,2'-azobis(methylbutyronitrile)), or Luperox as a free radical initiator. ® The procedure is carried out in the presence of LP dilauroyl peroxide initiator.

[0085] In another embodiment of the method, the polymerization reaction is carried out in a binary solvent system of ethyl acetate and isopropanol in the presence of free radical initiators AIBN, AMBN, or Luperox LP.

[0086] The acrylic polymers prepared for the UV-curable pressure-sensitive adhesives of the present invention typically have an average molecular weight (M) of about 1,000 to about 3,000,000 g / mol—for example, about 5,000 to about 500,000 g / mol. w The molecular weight can be determined by gel permeation chromatography (GPC) or matrix-assisted laser desorption / ionization mass spectrometry (MALDI-MS).

[0087] For formulation and use in the UV-curable pressure-sensitive adhesive of the present invention, the acrylic polymer is substantially free of solvents (e.g., organic solvents). Any solvents used in the preparation of the acrylic polymer and the formulation of the UV-curable adhesive may be removed in a reaction vessel or vacuum mixer prior to coating. However, the UV-curable pressure-sensitive adhesive may also be formulated as a solvent-based or water-based adhesive and used to make an adhesive film, and then the solvent or water may be removed subsequently by drying the adhesive film.

[0088] The UV-curable pressure-sensitive adhesive according to any of the embodiments described herein is substantially free of or contains no free radical reactive functional groups to avoid competition and interference between free radical curing and cationic curing during UV irradiation. Free radical reactive functional groups (e.g., (meth)acrylate C=C) react with cationic free radical fragments decomposed from cationic photoinitiators upon UV irradiation, which can inhibit the formation of superacids. Such free radical curable components are, for example, mono- or poly(meth)acrylates.

[0089] In another aspect, the present invention relates to articles comprising a UV-curable pressure-sensitive adhesive according to any of the embodiments described herein. The articles may be in the form of, for example, tapes, labels, graphics, or coatings. Applying the UV-curable pressure-sensitive adhesive to the articles can be achieved using any conventional means, such as roll coating, slotted-orifice coating, spray coating, curtain coating, or extrusion coating. Non-limiting examples of substrates include films, tapes, sheets, boards, foams, etc. These substrates may be made of materials such as paper, fabrics, metal foils, glass, plastics (e.g., polyester, polyethylene, polypropylene, biaxially oriented polypropylene (BOPP), and polyvinyl chloride), nonwoven fibers, metals, foils, glass, natural rubber, synthetic rubber, wood, plywood, and cement. If the coated substrate is used in the form of a self-rolling roll, a release coating is typically applied to the back of the substrate to prevent the adhesive from adhering to the opposite side of the substrate. If the substrate is coated with adhesive on both sides and rolled, a peelable paper or other means is laid on the adhesive on one side to prevent the adhesive from adhering to the adhesive on the other side. In some implementations, the second substrate can be applied directly to the adhesive.

[0090] In some articles with pressure-sensitive adhesives, the adhesive is applied to the backing or substrate before crosslinking. The adhesive is typically formulated to have sufficient coatable viscosity in a temperature range of about 25 to about 180°C.

[0091] The UV-curable pressure-sensitive adhesive of the present invention has a melt viscosity of about 1,000 to about 100,000 cps at an application temperature of about 25°C to about 140°C. The presence of a reactive diluent reduces the viscosity of the adhesive, thereby allowing application at a lower application temperature of about 25°C to about 120°C. The lower application temperature is particularly preferred for heat-sensitive substrates, including electronic devices.

[0092] Pressure-sensitive adhesive films can be formed by applying pure adhesive to a release liner (e.g., silicone-coated paper or plastic film), and then, after UV light irradiation, removing the adhesive from the release liner and using it as a linerless film to be laminated and transferred to a target substrate. The UV-curable pressure-sensitive adhesives described herein can be crosslinked in air by UV light irradiation in the range of about 200 to about 500 nm (e.g., about 280 to about 400 nm), depending on the cationic photoinitiator present in the adhesive composition. Irradiation can be performed immediately, for example, immediately after the adhesive film is applied. A nitrogen layer can also be used during the coating and curing process to isolate moisture.

[0093] The adhesive composition can be irradiated with UV light for a period of time sufficient to transform a low-cohesion composition into a higher-modulus viscoelastic adhesive. The exact length of UV exposure or dose depends on the type and intensity of the UV light, the cationic photoinitiator, the amount of acrylic polymer and adhesive composition, the thickness of the adhesive film, environmental factors (such as relative humidity and temperature), and the distance between the radiation source and the adhesive film. The dose or length of UV exposure can be controlled by the linear velocity. It may be appropriate to adapt the lamp output to the linear velocity or to partially shield the strip to reduce its thermal load on the heat-sensitive substrate. The adhesive composition can also be irradiated with UV light at elevated temperatures of about 50°C to about 150°C, where the heating source is from the UV lamp itself or an added infrared lamp or oven. UV curing at high temperatures accelerates the curing rate and avoids the influence of humidity on the UV post-curing process.

[0094] Actinic light from any source can be used on the adhesive, provided that the source provides an effective amount of UV radiation. Suitable UV light sources include, for example, carbon arc lamps, mercury vapor arc lamps, fluorescent lamps with special UV-emitting phosphors, electronic flash lamps, and lasers of specific wavelengths, UV LEDs, or any combination thereof. Preferred lamps are: electrodeless microwave-powered lamps from Fusion Systems; or commercially available high-pressure or medium-pressure mercury (H and / or D) lamps with an output, for example, from about 80 W / cm to about 240 W / cm. Preferred UV light is high-intensity LEDs having wavelengths of about 365 nm, about 385 nm, about 395 nm, about 405 nm, or any combination thereof. The adhesive compositions described herein generally exhibit their greatest sensitivity to wavelengths in the ultraviolet region from about 280 nm to about 400 nm.

[0095] The adhesives described herein can be used to bond a first substrate to a second substrate. Suitable substrates include, but are not limited to, paper, plastics, glass, plastic-coated glass, wood, cement, metal, and foil. The adhesive can be applied in an amount sufficient to allow the substrates to be bonded together to adhere, by a variety of methods, including, for example, coating or spraying. The adhesive-coated substrate can be irradiated before or after bonding. Because the crosslinking reaction begins immediately upon UV irradiation but may not be completed even after several days, there is time for bonding to occur immediately after irradiation but before gelation. Sometimes, bonding is performed before UV irradiation to obtain optimal wetting and adhesion.

[0096] The pressure-sensitive adhesives described herein can be advantageously used in the manufacture of adhesive articles, including but not limited to industrial tapes and transfer films. Tapes can be single-sided or double-sided tapes, and films can be supported or unsupported backing films. In one embodiment, the adhesive article comprises an adhesive described herein coated on at least one main surface of a backing having first and second main surfaces. Suitable backing substrates include, but are not limited to, foams, metals, paper, fabrics, and polymers (e.g., polypropylene, polyamide, polyester, polyethylene terephthalate, and mixtures of any of the foregoing). The adhesive can be present on one or both surfaces of the backing. When the adhesive is coated on both surfaces of the backing, the adhesive coatings can be the same or different.

[0097] In one embodiment, the invention also relates to a UV-curable pressure-sensitive adhesive according to any of the embodiments described herein, wherein the adhesive has an application temperature of about 40°C to about 200°C, and wherein the adhesive is stable such that the viscosity of the adhesive changes by no more than about 15% over about 24 hours.

[0098] In one embodiment, the invention also relates to a UV-curable pressure-sensitive adhesive according to any of the embodiments described herein, wherein the adhesive has a viscosity of about 5,000 cps to about 200,000 cps at an application temperature of about 25°C to about 140°C.

[0099] In one embodiment, the invention also relates to a UV-curable pressure-sensitive adhesive according to any of the embodiments described herein, wherein the adhesive is stable for about 48 hours at a temperature below about 140°C.

[0100] The table below provides additional exemplary parameters for any of the adhesives described herein.

[0101] The following embodiments are provided to further describe the invention in detail. These embodiments illustrate preferred modes currently contemplated for carrying out the invention and are intended to be illustrative rather than limiting.

[0102] Example Test the adhesive and its properties according to the following test procedures or the methods described below.

[0103] Viscosity Viscosity was measured using a Brookfield DV-I viscometer. For testing, 11 g samples were used with a No. 27 spindle at a speed of 2 to 4 rpm at a temperature of 110 to 140 °C.

[0104] Preparation of adhesive coating Using desktop Chemsultants ® A hot melt laminator was used to prepare the adhesive coating. The adhesive was heated to 110-120°C and coated onto a 2 mil (51 μm) thick silicone-coated PET insulating pad. The adhesive on the PET pad was irradiated at a certain linear velocity to achieve the necessary UV dose. The UV light source was an H-bulb (Fusion Systems) or Heraeus 365 nm LED lamp. The film was then laminated and transferred to a polyethylene terephthalate (PET) substrate (Mylar). ® (DuPont), and condition at 23°C and 50% relative humidity, unless otherwise specified.

[0105] UV dose UV dose was measured and recorded using EIT Power Puck II.

[0106] Shear adhesion Shear adhesion was measured using a modified procedure A, PSTC-107, as described below. All test samples of acrylic polymers were subjected to UV irradiation according to the procedure described above. Shear adhesion was measured under a 1 kg shear load applied over a ½'' × 1'' area after immersion in the test plate for 15 minutes. All tests were conducted at 23°C and 50% relative humidity. Failure times were recorded.

[0107] Loop Tack Circular fast-adhesion was measured according to test method B, PSTC-16, as modified below. A circular fast-adhesion tester was used for the measurement. All test samples of acrylic polymers were subjected to UV irradiation according to the procedure described above. The adhesive was applied to a 2 mil PET film backing, and the sample strip size was 6'' × 1''.

[0108] Peel adhesion According to the following modified Test Method A, PSTC-101 measures the peel adhesion between the substrate and the adherend at 180°. All test samples for acrylic polymers were subjected to UV irradiation according to the procedure described above. Peel strength was measured after immersion in a stainless steel sheet for 15 minutes.

[0109] Shear Adhesion Failure Temperature (SAFT) Three 1” × 3” samples were cut from each cured sample in the machine coating direction. SAFT plates (mirror steel) were cleaned with ethyl acetate. The samples were adhered to the steel plate until they overlapped with the scribe lines, ensuring contact between the 1” × 1” square adhesive and the test plate. The test area was rubbed with a straight-edged wooden applicator to ensure good contact between the plate and the test sample. The samples were placed in a test oven at room temperature. The heating program was started, and a 1 kg shear load was applied when the temperature reached 40°C. The oven temperature was ramped up to 200°C at 0.5°C / min, and the shear-bonded failure temperature (SAFT) was recorded.

[0110] Example 1 (Comparative Example) A four-necked 1L round-bottom polymerization flask is equipped with a thermometer connected to a temperature control device, a condenser, a top-mounted mechanical stirrer, two feeding funnels, and a nitrogen inlet / outlet. The apparatus is purged with nitrogen for 15 minutes. A mixture of the following monomers is prepared: 2-ethylhexyl acrylate (468.00 g), methyl acrylate (428.94 g), and 1-acrylomethyl-3,4-cyclohexene epoxide (3.06 g). 675.00 g of the monomer mixture is added to one funnel. 2,2'-azobis(2-methylpropionitrile) initiator (AIBN, 3.60 g) and ethyl acetate (100 mL) are added to the other funnel. The remaining monomer mixture (225.00 g), AIBN initiator (1.20 g), and ethyl acetate (750 mL) are added to the polymerization flask. The mixture was heated to vigorous reflux and maintained for 15 minutes. Then, the monomer mixture in the funnel was continuously added at a constant rate over 2 hours. Simultaneously, the initiator solution in the funnel was continuously added at a constant rate over 3 hours. After the initiator solution was completely added, the mixture was stirred under reflux for another 3 hours. An acrylic polymer with a weight-average molecular weight (Mw) of 277,000 g / mol and a polydispersity index (PDI) of 6.5, as determined by gel permeation chromatography (GPC), was obtained. The polymerization solution was cooled to 60°C. TECKROS R86 (185.00 g), Epon 828 (121.00 g), and Omnicat 320 (6.00 g) were added and thoroughly mixed for 30 minutes. A UV-curable pressure-sensitive adhesive (PSA 1) with a viscosity (Bruchwegian) of 74,000 cps at 110°C was obtained.

[0111] Example 2 A four-necked 1L round-bottom polymerization flask is equipped with a thermometer connected to a temperature control device, a condenser, a top-mounted mechanical stirrer, two feeding funnels, and a nitrogen inlet / outlet. The apparatus is purged with nitrogen for 15 minutes. A mixture of the following monomers is prepared: 2-ethylhexyl acrylate (468.00 g), methyl acrylate (428.94 g), and 1-acryloylmethyl-3,4-cyclohexene epoxide (3.06 g). 675.00 g of the monomer mixture is loaded into one funnel. The initiator (AIBN, 3.60 g) and ethyl acetate (100 mL) are loaded into the other funnel. The remaining monomer mixture (225.00 g), initiator AIBN (1.20 g), and ethyl acetate (750 mL) are loaded into the polymerization flask. The mixture is heated to vigorous reflux and maintained for 15 minutes. Then, the monomer mixture in the funnels is continuously added at a constant rate over 2 hours. Simultaneously, the initiator solution in the funnels is continuously added at a constant rate over 3 hours. After the initiator solution was completely added, the mixture was stirred under reflux for another 3 hours. An acrylic polymer with a weight-average molecular weight (Mw) of 277,000 g / mol and a PDI of 6.5, as determined by GPC, was obtained. The polymerization solution was cooled to 60°C. TECKROS R86 (185.00 g), Epon 828 (121.00 g), Omnicat 320 (6.00 g), and 1% vinyltrimethoxysilane (VTMO, 6.00 g) were added and thoroughly mixed for 30 minutes. A UV-curable pressure-sensitive adhesive (PSA 2) with a viscosity (Buchner) of 68,000 cps at 110°C was obtained.

[0112] Example 3 The UV-curable pressure-sensitive adhesives of Examples 1 and 2 were coated onto 2 mil polyethylene terephthalate (PET) films at 110 to 120°C to achieve thicknesses of 50 gsm and 100 gsm (grams per square meter), respectively, and then passed through a FusionH lamp at 2 mJ / cm². 2 Curing was performed using a UV-C dosage per gsm. The properties of the PSA were tested on stainless steel plates according to the PSTC method for shear and SAFT. The resulting properties are shown in Table 1. As can be seen from Table 1, by adding VTMO (Example 2), the UV-curable pressure sensitive material exhibits a lower melt viscosity and less viscosity change over time at 110°C, thus making it more thermally stable for hot-melt coating processes. Furthermore, cohesive strength and high-temperature adhesive strength are significantly improved.

[0113] Table 1—Effect of VTMO on film thickness

[0114] Example 4 A four-necked 1L round-bottom polymerization flask is equipped with a thermometer connected to a temperature control device, a condenser, a top-mounted mechanical stirrer, two feeding funnels, and a nitrogen inlet / outlet. The apparatus is purged with nitrogen for 15 minutes. A mixture of the following monomers is prepared: 2-ethylhexyl acrylate (500.00 g), methyl acrylate (396.85 g), and 1-acryloylmethyl-3,4-cyclohexene epoxide (3.15 g). 675.00 g of the monomer mixture is loaded into one funnel. The initiator (AIBN, 4.00 g) and ethyl acetate (100 mL) are loaded into the other funnel. The remaining monomer mixture (225.00 g), initiator AIBN (0.80 g), and ethyl acetate (800 mL) are loaded into the polymerization flask. The mixture is heated to vigorous reflux and held for 15 minutes. The monomer mixture in the funnels is then continuously added at a constant rate over 2 hours. Simultaneously, the initiator solution in the funnels is continuously added at a constant rate over 3 hours. After the initiator solution was completely added, the mixture was stirred under reflux for 3 hours. An acrylic polymer with a weight-average molecular weight (Mw) of 206,000 g / mol and a PDI of 6.8, as determined by GPC, was obtained. The polymerization solution was cooled to 60°C. TECKROS R86 (200.00 g) and Epon 828 (120.00 g) were added, and the mixture was thoroughly mixed for 30 minutes. After removing ethyl acetate under vacuum at 60–120°C, Omnicat 320 (6.00 g) and VTMO (13.00 g) were added, and the mixture was thoroughly mixed for 30 minutes. A UV-curable pressure-sensitive adhesive with a viscosity (Burlman) of 66,000 cps at 110°C was obtained. PSA exhibits excellent thermal stability at high temperatures, as shown in Table 2.

[0115] Table 2—Comparison of Melt Viscosities

[0116] Example 5 The UV-curable pressure-sensitive adhesive of Example 4 was coated onto a 2 mil PET film at 110 to 120°C to a thickness of 120 gsm, and then passed through a Fusion H lamp at 240 mJ / cm². 2UV-C dose curing was performed. Some of the adhesive films were also aged immediately after UV curing in a humidity chamber at 35°C and 95% relative humidity. The properties of the PSA were tested on stainless steel plates according to the PSTC method for shear and SAFT. With the addition of VTMO (Example 4), the UV-curable pressure-sensitive material exhibited good cohesive and adhesive strength, and high-temperature adhesive strength, with all failure modes being the desired adhesive failure. However, without VTMO, as in Example 1, all failure modes for shear, SAFT, peel, and tack were cohesive failures. Compared to Example 1 under the same humidity conditions, the PSA film retained its PSA properties even after conditioning under high humidity conditions immediately after UV curing. The resulting PSA properties are shown in Table 3.

[0117] Table 3—Comparison of Post-Cure Status

[0118] Example 6 The 2-liter reactor was equipped with an anchor stirrer, a condenser, and two automatic syringe pumps. Injection pump 1 was filled with a monomer solution of methyl acrylate (87.6 g), 2-ethylhexyl acrylate (97.9 g), 3,4-epoxycyclohexyl methacrylate (2.07 g), and ethyl acetate (32.5 g). Injection pump 2 was filled with an initiator solution of AIBN (1.14 g) and ethyl acetate (60 g). The reactor was purged with nitrogen for 15 minutes. Then, methyl acrylate (29.2 g), 2-ethylhexyl acrylate (32.6 g), AIBN (0.16 g), 3,4-epoxycyclohexyl methacrylate (0.69 g), and ethyl acetate (217.5 g) were added to the reactor. The reaction system was heated to reflux and held for 15 minutes. Then, the monomer solution was continuously added at a constant rate through injection pump 1 over 3 hours. Simultaneously, the initiator solution was continuously added at a constant rate through injection pump 2 over 3 hours. After addition, the mixture was stirred under reflux for 3 hours. At completion, the reaction solvent and any volatile substances were removed under vacuum and reflux temperature. The resulting polymer was cooled to room temperature under nitrogen. Photoinitiator Omnicat 320 (0.05 wt%) was added and mixed for 30 minutes. The final product was coated onto a 2-mil thick polyester film to produce a 1-mil thick dry adhesive, using 20 mJ / cm². 2 The material was cured under UV-C, and then its pressure-sensitive adhesive properties were tested. See Table 4.

[0119] Example 7 The 2-liter reactor was equipped with an anchor stirrer, a condenser, and two automatic syringe pumps. Injection pump 1 was filled with a monomer solution of methyl acrylate (87.6 g), 2-ethylhexyl acrylate (97.9 g), 3,4-epoxycyclohexyl methacrylate (1.13 g), 3-methacryloyloxypropyltrimethoxysilane (0.94 g), and ethyl acetate (32.5 g). Injection pump 2 was filled with an initiator solution of AIBN (1.14 g) and ethyl acetate (60 g). The reactor was purged with nitrogen for 15 minutes. Then, methyl acrylate (29.2 g), 2-ethylhexyl acrylate (32.6 g), AIBN (0.16 g), 3,4-epoxycyclohexyl methacrylate (0.38 g), 3-methacryloyloxypropyltrimethoxysilane (0.31 g), and ethyl acetate (217.5 g) were added to the reactor. The reaction system was heated to reflux and maintained for 15 minutes. Then, the monomer solution was continuously added at a constant rate through syringe pump 1 over 3 hours. Simultaneously, the initiator solution was continuously added at a constant rate through syringe pump 2 over 3 hours. After addition, the mixture was stirred under reflux for another 3 hours. Upon completion, the reaction solvent and any volatile substances were removed under vacuum and reflux temperature. The resulting polymer was cooled to room temperature under nitrogen. Photoinitiator Omnicat 320 (0.05 wt%) was added and mixed for 30 minutes. The final product was coated onto a 2-mil thick polyester film to produce a 1-mil thick dry binder, using 20 mJ / cm². 2 The material was cured with UVC, and then its pressure-sensitive adhesive properties were tested. See Table 4.

[0120] Example 8 Example 6 (80 g) was mixed with ethyl acetate (80 g) at room temperature until completely dissolved. Then, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane (0.4 g) was added to the mixture and mixed at room temperature for 30 minutes. The final product was coated onto a 2-mil thick polyester film to produce a 1-mil thick dry adhesive, using 20 mJ / cm². 2 The adhesives were cured under UV-C and then their pressure-sensitive adhesive properties were tested. The shear properties of the adhesives in Examples 6, 7, and 8 are shown in Table 4. A comparison of the rheological properties of the adhesives in Examples 6, 7, and 8 is shown in... Figure 1 middle.

[0121] Table 4—Shear properties of the adhesives in Examples 6, 7 and 8

[0122] Example 9 A four-necked 1L round-bottom polymerization flask is equipped with a thermometer connected to a temperature control device, a condenser, a top-mounted mechanical stirrer, two feeding funnels, and a nitrogen inlet / outlet. The apparatus is purged with nitrogen for 15 minutes. A mixture of the following monomers is prepared: methyl acrylate (30 g), 2-ethylhexyl acrylate (100 g), benzyl acrylate (20 g), and 1-acryloylmethyl-3,4-cyclohexene epoxide (1.2 g). 112 g of the monomer mixture is loaded into one funnel. The initiator (AIBN, 0.1 g) and ethyl acetate (45 mL) are loaded into the other funnel. The remaining monomer mixture (38 g), initiator AIBN (0.2 g), and ethyl acetate (40 mL) are loaded into the polymerization flask. The mixture is heated to vigorous reflux and maintained for 15 minutes. Then, the monomer mixture in the funnels is continuously added at a constant rate over 2.5 hours. Simultaneously, the initiator solution in the funnels is continuously added at a constant rate over 3 hours. After the initiator solution was completely added, the mixture was stirred under reflux for another 2 hours. A short-half-life initiator, 0.75 g of t-amyl peroxypivalate peroxide and 25 mL of ethyl acetate were loaded into an initiator funnel and then added to the polymerization flask over 1 hour to reduce residual monomer. After removing the ethyl acetate under vacuum at 120 °C, acrylic binder I was obtained with a weight-average molecular weight (Mw) of 130,000 g / mol (GPC), a PDI of 3, and a viscosity of 50,000 cps at 120 °C (Buchner's standard).

[0123] Example 10 A four-necked 1L round-bottom polymerization flask is equipped with a thermometer connected to a temperature control device, a condenser, a top-mounted mechanical stirrer, two feeding funnels, and a nitrogen inlet / outlet. The apparatus is purged with nitrogen for 15 minutes. A mixture of the following monomers is prepared: methyl acrylate (40 g), 2-ethylhexyl acrylate (100 g), 2-hydroxy-3-phenoxypropyl acrylate (10 g), and 1-acryloylmethyl-3,4-cyclohexene epoxide (1.5 g). 112 g of the monomer mixture is loaded into one funnel. The initiator (AIBN, 0.1 g) and ethyl acetate (45 mL) are loaded into the other funnel. The remaining monomer mixture (38 g), initiator AIBN (0.2 g), and ethyl acetate (40 mL) are loaded into the polymerization flask. The mixture is heated to vigorous reflux and held for 15 minutes. Then, the monomer mixture in the funnels is continuously added at a constant rate over 3 hours. Simultaneously, the initiator solution in the funnels is continuously added at a constant rate over 3 hours. After the initiator solution was completely added, the mixture was stirred under reflux for another 2 hours. A short-half-life initiator, tert-amyl peroxypentanoate peroxide (0.75 g), and ethyl acetate (25 mL) were loaded into an initiator funnel and then added to the polymerization flask over 1 hour to reduce residual monomer. After removing the ethyl acetate under vacuum at 120 °C, acrylic binder II was obtained with a weight-average molecular weight (Mw) of 130,000 g / mol (GPC), a PDI of 3, and a viscosity of 60,000 cps at 120 °C (Buchner's standard).

[0124] Example 11 The polymer prepared in Example 9 was formulated with the following substances: 20% of the epoxy-functionalized diluent Epon828, 0.1% of 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane, 0.1% of oligomeric 3-glycidoxypropyltrimethoxysilane, and 0.05% of Irganox 1726 (from BASF). In addition, 0.5% of Omnicat 320 and 0.75% of isopropylthioxanthone were added. The resulting hot melt adhesive had a viscosity of 35,000 cps at 110°C and exhibited excellent stability. The viscosity remained unchanged at 110°C for 72 hours. The adhesive was coated onto silicone paper to 100 gsm and tested with 2000 mJ / cm² from a 365 nm LED. 2 UV-A radiation was applied. The adhesive was tested after lamination (transfer) with 50 µm PET foil and a conditioning period of 24 hours at room temperature and 50% relative humidity. Adhesive properties are shown in Table 5. Peel values ​​are given after 24 hours.

[0125] Table 5—Press-sensitive properties of Example 11

Claims

1. A UV-curable pressure-sensitive adhesive comprising: (A) About 80% by weight to about 99.98% by weight of an acrylic polymer having at least one terminal or side-chain reactive functional group selected from: alicyclic epoxides, vinyl ethers, ethylene oxide, oxetane, hydroxyl, silyl SiR3 (wherein each R is independently alkyl, aryl, aralkyl, alkoxy, aryloxy, acetoxy, oxime, alkenoxy, amino, amide, ester, H or halogen), benzophenone, and any combination of the foregoing groups; (B) From about 0.01% by weight to about 10% by weight of a cationic photoinitiator, or a package of a cationic photoinitiator and a free radical photoinitiator; and (C) about 0.01% by weight to about 10% by weight of co-catalysts and stabilizers.

2. The adhesive of claim 1, wherein the adhesive has a viscosity of about 1,000 to about 100,000 cps at a coating temperature of about 25°C to about 140°C.

3. The adhesive of claim 1, wherein the acrylic polymer (A) is prepared from the following substances: (i) about 0.01% by weight to about 20% by weight of a first monomer having a reactive functional group selected from: alicyclic epoxides, vinyl ethers, ethylene oxide, oxetane, hydroxyl, silyl SiR3 (wherein each R is independently alkyl, aryl, aralkyl, alkoxy, aryloxy, acetoxy, oxime, alkenoxy, amino, amide, ester, H or halogen), benzophenone, or any combination of the foregoing groups; and (ii) about 80% by weight to about 99.99% by weight of a second acrylic monomer comprising: an acrylic or methacrylic acid derivative of the formula CH2=CH(R1)(COOR2), wherein R1 is H or CH3 and R2 is selected from C 1-24 Alkyl-aryl derivatives of functional groups including alkyl chains, alkyl-aryl chains, and alkyl-aryl derivatives containing ethoxy linkage groups, hydroxyl groups, or mixtures of any of the aforementioned groups.

4. The adhesive of claim 1, wherein the acrylic polymer (A) is prepared from the following substances: (i) about 0.1% by weight to about 10% by weight of a first monomer having a reactive functional group selected from the following: alicyclic epoxides, vinyl ethers, ethylene oxide, oxetane, or a mixture of any of the foregoing groups; (ii) about 70% by weight to about 99.8% by weight of a second acrylic monomer comprising: an acrylic or methacrylic acid derivative of the formula CH2=CH(R1)(COOR2), wherein R1 is H or CH3 and R2 is selected from C 1-24 Alkyl chains, alkyl-aryl chains, and alkyl-aryl derivatives comprising functional groups including ethoxy linkages, hydroxyl groups, or mixtures of any of the foregoing groups; and (iii) about 0.1% by weight to about 20% by weight of a third monomer having a reactive silyl functional group -SiR3, wherein R is selected from (a) alkoxy, aryloxy, acetoxy, oxime, alkenoxy, amino, amide, ester, H, halogen, or combinations thereof, and (b) an acrylic monomer containing reactive benzophenone.

5. The adhesive according to any one of claims 2 to 4, wherein the acrylic polymer has (a) a Tg value of less than about 10°C and (b) a weight-average molecular weight (Mw) of about 1,000 to about 1,000,000 g / mol.

6. The adhesive according to any one of claims 2 to 4, wherein (i) the first monomer is an alicyclic epoxide having the following formula: in: R 1 It can be O, S, C=O, linear, branched or cyclic alkylene, oxoalkylene, or aryl; R 2 It can be linear, branched, or cyclic alkyl, alkoxy, aryl, H, halogen, C=O, or R connected by covalent bonds as a fused alicyclic ring. 1 Part of; R 3 (CH2) n , where n is 0, 1, 2 or 3; X is an acrylate or a methacrylate, or contains a –W–Y group; W is O, S, amide, carbonate, carbamate, urea, siloxane, or a combination thereof; and Y is –R 4 –C(R 5 )=CH2, where R 4 Is it a linear or branched C? 2-10 Alkylene, C 2-10 Oxyalkylene, C=O, arylene or their derivatives, and R 5 It is H or CH3.

7. The adhesive of claim 6, wherein the alicyclic epoxide has the following formula: Where R 2 = H or CH3, ， ， ， ， Where R = H or CH3 Where R 1 = H or CH3, Or a mixture of any of the aforementioned types.

8. The adhesive according to any one of claims 2 to 4, wherein the second acrylic monomer is methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, methyl acrylate, methyl methacrylate, tert-octylacrylamide, hydroxyethyl acrylate, acrylic acid, hydroxypropyl acrylate, hydroxypropyl methacrylate, or a mixture of any of the foregoing substances.

9. The adhesive of claim 4, wherein the third monomer is 3-methacryloyloxypropyltrimethoxysilane, 3-[diethoxy(methyl)silyl]propyl methacrylate, benzophenone methacrylate, or a mixture of any of the foregoing substances.

10. The adhesive of claim 4, wherein the third monomer is 3-methacryloyloxypropyltrimethoxysilane, 3-[diethoxy(methyl)silyl]propyl methacrylate, or a mixture of any of the foregoing substances.

11. The adhesive of claim 1, wherein the cationic photoinitiator is a sulfonium salt or an iodonium salt.

12. The adhesive of claim 11, wherein the cationic photoinitiator has a structure Where R represents C3H7, C 12 H 25 W represents S, SO, SO2, or CO.

13. The adhesive of claim 1, wherein the cationic photoinitiator is: Where R 1 and R 2 Each of the following is independently H, CH3, C2H5, C3H7, C 12 H 25 OCH3, OC2H5, OC3H7, or OC 12 H 25 .

14. The adhesive of claim 1, wherein the photoinitiator package is a mixture of a cationic photoinitiator and a free radical photosensitizer selected from the group consisting of thioxanthone, 2-isopropylthioxanthone, 2-chlorothioxanthone, 2,4-diethyl-thioxanthone, 1-chloro-4-propoxythioxanthone, and any combination thereof.

15. The adhesive of claim 14, wherein the ratio of the cationic photoinitiator to the free radical photosensitizer is from about 0.1 to about 10.

16. The adhesive of claim 1, wherein the co-catalyst is a silane, or an oligomer or polymeric derivative thereof.

17. The adhesive of claim 16, wherein the co-catalyst is an alkoxy-functionalized silane, an epoxy-functionalized silane, a (meth)acrylic acid-functionalized silane, or an oligomeric or polymeric derivative thereof, or a mixture of any of the foregoing substances.

18. The adhesive of claim 17, wherein the co-catalyst is vinyltrialkoxysilane, C3-C 24 Alkyltrialkoxysilane, (meth)acryloyloxypropyltrialkoxysilane, glycidoxypropyltrialkoxysilane, (3,4-epoxycyclohexyl)ethyltrialkoxysilane, or their oligomeric or polymeric derivatives, or mixtures of any of the foregoing substances.

19. The adhesive of claim 18, wherein the co-catalyst is vinyltrimethoxysilane, vinyltriethoxysilane, glycidoxypropyltrimethoxysilane, glycidoxypropyltriethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane, or oligomer or polymeric derivatives thereof, or a mixture of any of the foregoing substances.

20. The adhesive of claim 1, further comprising a reactive diluent of a polymer, oligomer, or macromonomer, said polymer, oligomer, or macromonomer containing at least one terminal or side-chain reactive functional group selected from: alicyclic epoxides, ethylene oxide, oxetane, vinyl ethers, hydroxyl groups, silyl SiR3 (wherein each R is independently alkyl, aryl, aralkyl, alkoxy, aryloxy, acetoxy, oxime, alkenoxy, amino, amide, ester, H, or halogen), benzophenone, and any combination of the foregoing groups.

21. The adhesive of claim 20, wherein the reactive diluent has a weight-average molecular weight of about 100 to about 500,000 g / mol.

22. The adhesive of claim 20, wherein the reactive diluent is epoxy-functionalized soybean oil, epoxy-functionalized polybutadiene, epoxy-functionalized polyurethane, epoxy-functionalized polysiloxane, epoxy-functionalized polyisobutylene, epoxy-difunctionalized bisphenol A epoxy resin, epoxy-difunctionalized bisphenol F epoxy resin, epoxy-functionalized polyacrylate, epoxy-functionalized polyethylene glycol, epoxy-functionalized polypropylene glycol, epoxy-functionalized polyether, or a mixture of any of the foregoing substances.

23. The adhesive of claim 1, further comprising a tackifier, a heat stabilizer, a moisture scavenger, or any combination thereof.

24. The adhesive of claim 1, wherein the adhesive is substantially free of organic solvents.

25. An article comprising the UV-curable pressure-sensitive adhesive as described in any one of claims 1 to 24.

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