Two-part adhesive composition and method of making a bonded article

Abstract

A two-part adhesive composition includes a first part comprising a crosslinker and a second part comprising a curing component for the crosslinker. At least one of the first part or the second part independently further comprise a rheology modifier. The first part has a first viscosity, and the second part has a second viscosity. The first viscosity and the second viscosity are each not more than 100 Pascal seconds when measured on a rheometer at a shear rate of 0.01 reciprocal second, and, in some embodiments, a ratio of the first viscosity to the second viscosity is in a range from 5:1 to 1:5 when measured on a rheometer at one or more shear rates of less than one reciprocal second. A method of making a bonded article using the two-part adhesive composition is also described.

Description

[0001] TWO-PART ADHESIVE COMPOSITION AND METHOD OF MAKING A BONDED ARTICLE

[0002] CROSS-REFERENCE TO RELATED APPLICATION

[0003] This application claims the benefit of U.S. Application No. 63 / 555,824, filed February 20, 2024, the disclosure of which is incorporated by reference in its entirety herein.

[0004] BACKGROUND

[0005] Adhesives are known to be useful for bonding one substrate to another, e.g., a metal to a metal, a metal to a plastic, a plastic to a plastic, a glass to a glass. Structural adhesives are attractive alternatives to mechanical joining methods, such as riveting or spot welding, because structural adhesives distribute load stresses over larger areas rather than concentrating such stresses at a few points.

[0006] In electric motors such as electric motors for cars, the motor core is made by laminating steel sheets. Usually, laminations are fastened by either mechanical interlocking or laser welding. Weaknesses of these methods may be the occurrence of iron losses due to electrical short-circuit in the laminated motor core or insufficient strength of the laminated core, especially when the steel sheets are relatively thin. To overcome these weaknesses, a lamination method using an adhesive was disclosed in Int. Pat. Appl. Pub. No. 2023 / 111722 (Koseki et al.).

[0007] Certain curable acrylic adhesive compositions are disclosed in U.S. Pat. Nos. 5,206,288 (Gosiewski), 5,863,989 (Taguchi), 6,852,801 (Briggs), 8,067,500 (Hisha), 10,392,532 (Doe), and 11,098,225 (Sasaki), U.S. Pat. Appl. Pub. No. 2019 / 0136102 (Hurlburt), Int. Pat. Appl. Pub. No. WO2021 / 051257 (Sun), European Pat. Appl. Pub. No. 4130179 (published February 8, 2023), and Japanese Pat. Appl. Pub. Nos. 2014088458 (published May 15, 2014) and 2003 / 165806 (published June 10, 2003.)

[0008] Two-part adhesive composition in which the two parts are proposed to have similar viscosities are described in U.S. Pat. Nos. 4,187,348 (Dearlove et al.), 4,724,892 (Schneider et al.), and 6,096,842 (Friese et al.), U.S. Pat. Appl. Pub. Nos. 2012 / 0301729 (Schmider et al.) and 2024 / 0010888 (Czaplicki et al.), and UK Pat. Appl. Pub. No. GB 2121811, published January 4, 1984.

[0009] SUMMARY

[0010] The present disclosure provides a composition useful, for example, as a structural adhesive. In some embodiments, the two-part adhesive composition described herein provides advantages due to the viscosities of the two adhesive parts. As shown in the Examples, below, the first part and the second part exhibit at least one of better co-diffusion, better curing, or better adhesive strength when cured when the first viscosity and the second viscosity are in these ranges. Beneficial co-diffusion of the two adhesive parts is visible upon combination without mixing, which can lead to a more rapid and complete polymerization of the adhesives. In some embodiments, adjusting the rheology with an impact modifier provides these advantages. In some embodiments, advantageously, improved adhesive performance is achieved with the two-part adhesive composition of the present disclosure as demonstrated by overlap shear (OLS) evaluations on steel substrates.

[0011] In one aspect, the present disclosure provides a two-part adhesive composition including a first part comprising a crosslinker and a second part comprising a curing component for the crosslinker. At least one of the first part or the second part independently further comprise a rheology modifier. The first part has a first viscosity, and the second part has a second viscosity. The first viscosity and the second viscosity are each not more than 100 Pascal seconds when measured on a rheometer at a shear rate of 0.01 reciprocal second, and a ratio of the first viscosity to the second viscosity is in a range from 5 : 1 to 1:5 when measured on a rheometer at a shear rate of less than one reciprocal second.

[0012] In another aspect, the present disclosure provides a two-part adhesive composition including a first part and a second part. The first part includes a crosslinker having two or more acrylate groups, methacrylate groups, or a combination thereof; a transition metal compound; and a quaternary ammonium salt. The second part includes a free-radical initiator comprising at least one of a peroxide initiator or a hydroperoxide initiator, a beta-dicarbonyl compound, and a non-reactive diluent. At least one of the first part or the second part independently further includes an impact modifier in an amount such that it is present in the two-part adhesive composition in a range from 2 weight percent to 25 weight percent, based on the total weight of the two-part composition. The first part has a first viscosity, and the second part has a second viscosity. The first viscosity and the second viscosity are each below 100 Pascal seconds when measured on a rheometer at a shear rate of 0.01 reciprocal second.

[0013] In another aspect, the present disclosure provides a method of making a bonded article. The method includes applying the first part and the second part of the two-part adhesive composition of any of the above aspects onto at least one of the first substrate or the second substrate without premixing the first part and the second part, adhering the first substrate and the second substrate using the two-part adhesive composition, and allowing the two-part adhesive composition to at least partially cure to make the bonded article.

[0014] In another aspect, the present disclosure provides an article bonded with the two-part composition disclosed herein and / or made by the method disclosed herein.

[0015] As used herein:

[0016] "alkyl group" and the prefix "alk-" have only C-C bonds and C-H bonds and are inclusive of both straight chain and branched chain groups and of cyclic groups. In some embodiments, alkyl groups have up to 30 carbons (in some embodiments, up to 20, 15, 12, 10, 8, 7, 6, or 5 carbons) unless otherwise specified. Cyclic groups can be monocyclic or polycyclic and, in some embodiments, have from 3 to 10 ring carbon atoms and other alkyl substituents; "Aryl" and “aromatic” as used herein include carbocyclic aromatic rings or ring systems, for example, having 1, 2, or 3 rings and optionally containing at least one heteroatom (e.g., O, S, or N) in the ring optionally substituted by up to five substituents including one or more alkyl groups having up to 4 carbon atoms (e.g., methyl or ethyl), alkoxy having up to 4 carbon atoms, halo (i.e., fluoro, chloro, bromo or iodo), hydroxy, or nitro groups, examples of which include phenyl, naphthyl, biphenyl, fluorenyl as well as furyl, thienyl, pyridyl, quinolinyl, isoquinolinyl, indolyl, isoindolyl, triazolyl, pyrrolyl, tetrazolyl, imidazolyl, pyrazolyl, oxazolyl, and thiazolyl; the term “acrylic” refers to both acrylic and methacrylic polymers, oligomers, and monomers;

[0017] “cure” refers to making polymer chains from one or more monomers; and the term "(meth)acryl" refers to acryl (also referred to in the art as acryloyl and acrylyl) and / or methacryl (also referred to in the art as methacryloyl and methacrylyl).

[0018] Terms such as "a", "an" and "the" are not intended to refer to only a singular entity but include the general class of which a specific example may be used for illustration. The terms "a", "an", and "the" are used interchangeably with the term "at least one".

[0019] The phrase "comprises at least one of followed by a list including the conjunction “or” refers to comprising any one of the items in the list and any combination of two or more items in the list. The phrase "at least one of followed by a list including the conjunction “or” refers to any one of the items in the list or any combination of two or more items in the list.

[0020] The term “crosslinker” refers to a molecule having at least two reactive functional groups. The molecule may be a monomer or polymer (including an oligomer). Both reactive functional groups react in the presence of the curing component to form a crosslinked network.

[0021] The term "crosslinking” refers to joining polymer chains together by covalent chemical bonds, usually via crosslinking molecules or groups, to form a network polymer. A crosslinked polymer is generally characterized by insolubility but may be swellable in the presence of an appropriate solvent. The term “crosslinked” includes partially crosslinked.

[0022] The term "polymer" refers to a molecule having a structure which includes the multiple repetition of units derived, actually or conceptually, from one or more monomers. The term “monomer” refers to a molecule of low relative molecular mass that can combine with others to form a polymer. The term “polymer” includes homopolymers and copolymers, as well as 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.

[0023] A “structural adhesive” means an adhesive that binds by irreversible cure. A structure adhesive typically bonds high strength materials (e.g., wood, composites, or metals) with a strength measured as stress at break (peak stress) using the overlap shear test described in the Examples herein, of at least 689 kPa (100 psi), at least 1379 kPa (200 psi), at least 3445 kPa (500 psi), or at least 6890 kPa (1000 psi).

[0024] All numerical ranges are inclusive of their endpoints and non-integral values between the endpoints unless otherwise stated (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc.). Features and advantages of the present disclosure will be further understood upon consideration of the detailed description as well as the appended claims.

[0025] DETAILED DESCRIPTION

[0026] The present disclosure provides a two-part adhesive composition. The first part of the two-part adhesive composition includes a crosslinker. The crosslinker can be an acrylate, a methacrylate, an epoxide, or a combination thereof. In some embodiments, the crosslinker has at least two acrylate groups, methacrylate groups, or a combination thereof. In some embodiments, both the first part and the second part of the two-part adhesive composition include a crosslinker. In some embodiments, the first part of the two-part adhesive composition includes a crosslinker having two or more acrylate groups, methacrylate groups, or a combination thereof, but the second part does not include such a crosslinker. In some embodiments, the first part of the two-part adhesive composition includes a crosslinker having two or more epoxide groups, but the second part does not include such a crosslinker.

[0027] Suitable crosslinkers having two or more acrylate groups, methacrylate groups, or a combination thereof include diacrylate esters of diols, such as ethylene glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, 1,3-propanediol diacrylate, 1,4-butanediol diacrylate, butane-l,3-diyl diacrylate, pentanediol diacrylate, hexanediol diacrylate (including 1,6- hexanediol diacrylate), heptanediol diacrylate, octanediol diacrylate, nonanediol diacrylate, decanediol diacrylate, 1,3-butylene glycol diacrylate, 1,4-cyclohexanediol diacrylate, cyclohexanedimethanol diacrylate, tricyclodecanedimethanol diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, polyethylene glycol (200) diacrylate, polyethylene glycol (400) diacrylate, polyethylene glycol (600) diacrylate, bis[l-(2-acryloxy)]-p-ethoxyphenyldimethylmethane, bis[l-(3-acryloxy-2-hydroxy)]-p- propoxyphenyldimethylmethane, caprolactone modified neopentyl glycol hydroxypivalate diacrylate, ethoxylated (10) bisphenol A diacrylate, ethoxylated (3) bisphenol A diacrylate, ethoxylated (4) bisphenol A diacrylate, ethoxylated bisphenol A diacrylate, alkoxylated cyclohexanedimethanol diacrylates, alkoxylated hexanediol diacrylate, neopentyl glycol diacrylate, alkoxylated neopentyl glycol diacrylate, hydroxypivalaldehyde modified trimethylolpropane diacrylate, dimethacrylates of any of the foregoing diacrylates, and combinations thereof.

[0028] Further suitable crosslinkers include polyacrylate esters of polyols, such as glycerol triacrylate, 1,2,4-butanetriol triacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, neopentyl glycol diacrylate, dipentaerythritol pentaacrylate, ethoxylated (20) trimethylolpropane triacrylate, ethoxylated (3) trimethylolpropane triacrylate, ethoxylated (6) trimethylolpropane triacrylate, ethoxylated (9) trimethylolpropane triacrylate, propoxylated (3) glyceryl triacrylate, propoxylated (3) trimethylolpropane triacrylate, propoxylated (5,5) glyceryl triacrylate, propoxylated (6) trimethylolpropane triacrylate, ditrimethylolpropane tetraacrylate, ethoxylated (4) pentaerythritol tetraacrylate, sorbitol hexaacrylate, caprolactone modified dipentaerythritol hexaacrylate, and tris(2 -hydroxyethyl) isocyanurate triacrylate, methacrylates of the foregoing acrylates, and combinations thereof. Further suitable crosslinkers include polyfunctional acrylate oligomers comprising two or more acrylate groups. The polyfunctional acrylate oligomer may be a urethane acrylate oligomer, an epoxy acrylate oligomer, a polyester acrylate, a polyether acrylate, a polyacrylic acrylate, a methacrylate of any of the foregoing acrylates, or a combination thereof. A difunctional (meth)acrylamide such as methylene bis(meth)acrylamide may also be useful.

[0029] In some embodiments, the crosslinker is a cyclic crosslinker having two or more acrylate groups, methacrylate groups, or a combination thereof. Cyclic means that the crosslinker contains one or more aromatic or non-aromatic rings. Non-aromatic rings include carbocyclic rings and heterocyclic rings (that is, rings including N, O, or S as a member of the ring) of any size.

[0030] In some embodiments, the amount of the crosslinker present in the first part is 25 wt.%, 30 wt.%, or 35 wt.% and up to 65 wt.%, 60 wt.%, or 55 wt.%, based on the total weight of the first part. The amount of the crosslinker present in the first part may be 25 wt.% to 60 wt.%, 35 wt.% to 65 wt.%, 40 wt.% to 60 wt.%, or 45 wt.% to 55 wt.%, based on the total weight of the first part. These amounts may each be useful amounts of crosslinker in the second part, based on the total weight of the second part. In some embodiments, the second part is free of a crosslinker having two or more acrylate groups, methacrylate groups, or a combination thereof.

[0031] In some embodiments, the first part further includes a monofunctional monomer. In some embodiments, the monofunctional monomer is an acrylate or a methacrylate. A combination of monofunctional monomers can also be useful. In some embodiments, the first part includes acrylic monomer comprising a cyclic group, which may be a cycloalkyl group or a heterocylic group (that is, including N, O, or S as a member of the ring), may be aromatic or non-aromatic, and which may be a monocyclic ring or a polycyclic ring. The cyclic group can have up to 14, 12, or 10 carbon atoms. Such monomers can be useful, for example, for increasing the Tg of an adhesive made from the composition. Examples of suitable acrylic monomers comprising the cyclic group having up to 14, 12, or 10 carbon atoms include at least one of isobomyl acrylate, cyclohexyl acrylate, t-butylcyclohexyl acrylate, phenoxyethyl acrylate, benzyl acrylate, tetrahydrofurfuryl acrylate, dicyclopentanyl acrylate, dicyclopentadienyl acrylate, dihydrodicyclopentadienyl acrylate, methacrylates of the foregoing acrylates, and combinations thereof. In some embodiments, the acrylic monomer comprising the cyclic group having up to 14 or 12 carbon atoms comprises at least one of isobomyl acrylate or isobomyl methacrylate. Such monomers are available from a variety of commercial sources, for example, isobomyl acrylate available from Sartomer as SR506, or from Evonik Performance Materials GmbH as VISIOMER IBOA, isobomyl methacrylate available from Sartomer as SR423A or from Evonik Performance Materials GmbH under the trade name VISIOMER IBOMA, cyclohexyl methacrylate (available from Evonik Performance Materials GmbH as VISIOMER c-HMA), dicyclopentanyl methacrylate (available from Hitachi Chemical as FANCRYL FA-513M), isobomyl cyclohexyl methacrylate (available from Designer Molecules, Inc., San Diego, California, as product MM-304), and 4-t-butylcyclohexyl methacrylate (available from Miwon North America, Exton, Pennsylvania, as Miramer Ml 151). The acrylic monomer comprising a cyclic group having up to 14, 12, or 10 carbon atoms is present in the first part in an amount of at least 25 wt.%, 30 wt.%, or 35 wt.% and up to 65 wt.%, 60 wt.%, or 55 wt.%, based on the total weight of the first part. In some embodiments, the acrylic monomer comprising the cyclic group is present in an amount in a range from 30 wt.% to 60 wt.%, 35 wt.% to 65 wt.%, 40 wt.% to 60 wt.%, or 45 wt.% to 55 wt.%, based on the total weight of the first part. These amounts may each be useful amounts of crosslinker in the second part, based on the total weight of the second part. In some embodiments, the second part is free of a crosslinker having two or more acrylate groups, methacrylate groups, or a combination thereof.

[0032] In some embodiments, at least one of the first part or the second part of the two-part adhesive composition includes an additional acrylic monomer, such as any of those described below. In some embodiments, the first part of the two-part adhesive composition includes an additional acrylic monomer, but the second part does not include an additional acrylic monomer. The first part, the second part, or both may also be free of additional acrylic monomers. In some embodiments, the additional acrylic monomer is present in an amount of at least 5 wt.% and up to 25 wt.%, 20 wt.%, 15 wt.%, or 10 wt.%, based on the total weight of the first part or the second part, respectively. Examples of suitable additional acrylic monomers include at least one of an alkyl acrylate or methacrylate. The alkyl group of the alkyl acrylate or methacrylate may be straight-chained or branched and may have 1 to 14, 1 to 12, or 1 to 10 carbon atoms. The first part, the second part, or both may also be free of alkyl acrylate and methacrylate that are straight-chained or branched and have 1 to 14, 1 to 12, or 1 to 10 carbon atoms in the alkyl group. In some embodiments, the alkyl group is optionally substituted with hydroxyl and optionally interrupted by one or more ether linkages.

[0033] Examples of suitable additional acrylic monomers include 2-hydroxyethyl (meth)acrylate, 2- and 3 -hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, caprolactone mono(meth)acrylate, available under the trade designation “SR-495B” from Sartomer and other poly(e-caprolactone) mono[2- (meth)acryloxy ethyl] esters, poly(e-caprolactone) mono[2-acryloxy ethyl] esters, 2 -hydroxy-3 -alkyloxy (meth)acrylate, polyethylene glycol mono (meth)acrylates, alkoxylated lauryl (meth)acrylate, alkoxylated phenol (meth)acrylate, alkoxylated tetrahydrofurfuryl (meth)acrylate, cyclic trimethylolpropane formal (meth)acrylate, ethylene glycol methyl ether (meth)acrylate, ethoxylated nonyl phenol (meth)acrylate, isodecyl (meth)acrylate, isooctyl (meth)acrylate, octadecyl (meth)acrylate (stearyl (meth)acrylate), tridecyl (meth)acrylate, allyl (meth)acrylate, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, n-decyl (meth)acrylate, n-dodecyl (meth)acrylate, 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 2- or 3 -ethoxypropyl (meth)acrylate, 2-(2- ethoxyethoxy)ethyl acrylate, glycidyl (meth)acrylate, N-(2-(2-oxo-l- imidazolidinyl)ethyl)methacrylamide, and methacrylamidoethyl ethylene urea ("MAEEU") available from Solvay Specialty Polymers USA, LLC under the trade designation “SIPOMER WAM II”), and combinations thereof. Suitable additional acrylic monomers are available from a wide variety of commercial sources such as, for example, Sartomer Co., Exton, Pennsylvania, or can be made by known methods. The first part, the second part, or both may also be free of any of these monomers.

[0034] In some embodiments, the first part of the two-part adhesive composition includes an acrylic monomer comprising a carboxylic acid group. In some embodiments, both the first part and the second part of the two-part adhesive composition include an acrylic monomer comprising a carboxylic acid group. In some embodiments, the first part of the two-part adhesive composition includes an acrylic monomer comprising a carboxylic acid group, but the second part does not include an acrylic monomer comprising a carboxylic acid group. In some embodiments, neither the first part nor the second part includes an acrylic monomer comprising a carboxylic acid group. In first second part in an amount of 5 wt.% to 50 wt.%, 5 wt.% to 40 wt.%, or 5 wt.% to 15 wt.%, based on the total weight of the first part. These amounts may each be useful amounts of acrylic monomer comprising a carboxylic acid group in the second part, based on the total weight of the second part. Examples of suitable acrylic monomers comprising a carboxylic acid group include methacrylic acid, acrylic acid, ^-acryloyl oxyethyl hydrogen succinate and ^-methacryloyl oxyethyl hydrogen succinate. Many acrylic monomers comprising a carboxylic acid group are available from commercial sources, for example, methacrylic acid available from Evonik Performance Materials GmbH under the trade designation “VISIOMER GMAA” and >- methacryloyl oxyethyl hydrogen succinate available from Shin-Nakamura Co. Ltd., Arimoto, Japan, under the trade designation “NK ESTER SA”. In some embodiments, the acrylic monomer comprising a carboxylic acid group is at least one of acrylic acid or methacrylic acid. In some embodiments, the acrylic monomer comprising a carboxylic acid group is methacrylic acid.

[0035] Further free-radically polymerizable monomers may also be useful. Examples of suitable monofunctional (meth)acrylamides include N,N-dimethylacrylamide, N-vinylpyrrolidone, N- vinylcaprolactam, diacetone (meth)acrylamide, and (meth)acryloylmorpholine. Examples of suitable radically (co)polymerizable vinyl compounds include styrene, dialkyl phthalate, divinyl succinate, divinyl adipate, and divinyl phthalate.

[0036] In some embodiments, the first part of the two-part adhesive composition of the present disclosure further includes an acrylic monomer comprising a phosphate or phosphonate group. Such monomers can be useful, for example, for enhancing the adhesion to metal substrates. Useful acrylic monomer comprising a phosphate or phosphonate group include ethylene glycol methacrylate phosphate (available, for example, from Miwon North America, Exton, Pennsylvania, under the trade designations “MIRAMER SC 1400” and “MIRAMER SC1400A”, from Allnex, Alpharetta, GA, under the trade designation “EBACRYL 168”, and from Sartomer, King of Prussia, PA, under the trade designation “SR9054”) and phosphate esters of polypropylene glycol) monomethacrylate (available, for example, under the trade designation “SIPOMER PAM” from Solvay Novecare, Cranbury, NJ). Phosphates can have one or more than one acrylate or methacrylate group. Vinyl phosphonic acid may also be useful. In some embodiments, the first part of the two-part adhesive composition of the present disclosure further comprises an acrylic monomer comprising a phosphate group. The phosphonate- or phosphate- functionalized acrylic monomer can be present in the first part, for example, up to 5 wt.%, 4 wt.%, or 3 wt.%, based on the total weight of the first part. In some embodiments, the phosphonate- or phosphate- functionalized acrylic monomer is present in an amount of at least 0.01 wt.%, 0.05 wt.%, 0.5 wt.%, 1 wt.%, 1.5 wt.%, or 1.9 wt.%, based on the total weight of the first part. These amounts may each be useful amounts of crosslinker in the second part, based on the total weight of the second part. In some embodiments, the second part is free of an acrylic monomer comprising a phosphate or phosphonate group.

[0037] The second part of the two-part adhesive composition of the present disclosure includes a curing component for the crosslinker. In some embodiments, including embodiments in which the crosslinker has at least two acrylate functional groups, methacrylate functional groups or a combination thereof, the curing component comprises a free-radical initiator comprising at least one of a peroxide initiator or a hydroperoxide initiator. Peroxide initiators include carboxylic acid peroxyesters. Examples of free- radical initiators useful for practicing the present disclosure include cumene peroxide, cumene hydroperoxide, paramenthane hydroperoxide, tert-butyl hydroperoxide, tert-amyl hydroperoxide, diisopropylbenzene dihydroperoxide, methyl ethyl ketone peroxide, benzoyl peroxide, t-butyl peroxyacetate, and tert-butyl peroxybenzoate. Further examples of peroxyesters include carbonic - diisopropyl-peroxydiester, neodecanoic acid-tertiary-butyl-peroxyester, neodecanoic acid-tertiary-amyl- peroxyester, maleic acid-tertiary-butyl-monoperoxyester, 2-ethylhexanoic acid-tertiary-butyl-peroxyester, 2 -ethylhexanoic acid-tertiary-amyl-peroxyester, carbonic-monoisopropylester-monotertiary-butyl- peroxyester, carbonic-dicyclohexyl-peroxyester, carbonic dimyristyl-peroxyester, carbonic dicetyl peroxyester, carbonic-di(2-ethylhexyl)-peroxyester, carbonic-tertiary-butyl-peroxy-(2-ethylhexyl)ester or 3,5,5-trimethylhexanoic acid-tertiary-butyl-peroxyester, benzoic acid-tertiary-amyl-peroxyester, acetic acid-tertiary-butyl-peroxyester, carbonic -di(4-tertiary-butyl-cyclohexyl)-peroxyester, neodecanoic acid- cumene-peroxyester, pivalic acid-tertiary-amyl-peroxyester and pivalic acid tertiary-butyl-peroxyester. In some embodiments, the free-radical initiator is present in an amount from 0.5 wt.% to 20 wt.%, 1 wt.% to 15 wt.%, or 3 wt.% to 15 wt.%, based on the total weight of the second part.

[0038] In some embodiments of the two-part adhesive composition of the present disclosure, the curing component is a component of a redox initiating system. In some embodiments, the first part comprises a transition metal compound and a quaternary ammonium salt, and the second part comprises a betadicarbonyl compound as the curing component. In some embodiments, the first part comprises the betadicarbonyl compound, and the second part comprises the transition metal compound and the quaternary ammonium salt as the curing component.

[0039] Suitable transition metal compounds include transition metal complexes, especially salts of cobalt, manganese, copper, vanadium, and iron. When the metal salt is a copper compound, the salt may possess the general formula CuXn, where X is an organic and / or inorganic anion and n = 1 or 2. Examples of suitable copper salts include copper chloride, copper acetate, copper acetylacetonate, copper naphthenate, copper salicylate or complexes of copper with thiourea or ethylenediaminetetraacetic acid, and mixtures thereof. Further examples of suitable transition metal compounds include cobalt acetylacetonate, copper phthalocyanine, zinc acetylacetonate, iron acetylacetonate, titanium acetylacetonate, vanadium (III) acetylacetonate, vanadium (III) pentanedionate, vanadium (III) naphthenate, vanadium (IV) naphthenate, vanadyl oxalate, vanadium chloride, vanadium oxide, vanadium sulfate, vanadyl acetylacetonate. Vanadyl acetylacetonate is also known as “vanadium (IV) oxide bis (2,4-pentanedionate)”, “vanadium (IV)-oxy acetylacetonate”, and V0(acac)2. In some embodiments, the transition metal compound is present in an amount from 0.0005 wt.% to 2 wt.%, 0.05 wt.% to 1.5 wt.%, or 0. 1 wt.% to 1 wt.%, based on the total weight of the first part or the second part.

[0040] Suitable quaternary ammonium halides include those having four hydrocarbyl (e.g., alkyl, alkenyl, cycloalkyl, aralkyl, alkaryl, and / or aryl) groups. In some embodiments, the hydrocarbyl groups are independently selected from hydrocarbyl groups having from 1 to 18 carbon atoms, 1 to 12 carbon atoms, or 1 to 4 carbon atoms. Examples of suitable hydrocarbyl groups include methyl, ethyl, propyl, butyl, hexyl, octyl, dodecyl, hexadecyl, and octadecyl, benzyl, phenyl, tolyl, cyclohexyl, and methylcyclohexyl. Examples of suitable quaternary ammonium compounds include tetramethylammonium halides, tetraethylammonium halides, tetrapropylammonium halides, tetrabutylammonium halides, ethyltrimethylammonium halides, diethyldimethylammonium halides, trimethylbutylammonium halides, trioctylmethylammonium halides, and benzyltributylammonium halides. Any halide (e.g., F, Cl, Br, I) ion may be used in the quaternary ammonium halide. In some embodiments, the halide ion is chloride or bromide, in some embodiments, chloride. Any of the halides described above as examples may be a chloride. In some embodiments, the quaternary ammonium halide is trioctylmethylammonium chloride.

[0041] In some embodiments, the quaternary ammonium halide is present in an amount from 0.01 wt.% to 5 wt.% or 0.1 wt.% to 2 wt.%, based on the total weight of the first part or the second part.

[0042] Other reducing agents and / or accelerants may be useful in addition to or instead of the quaternary ammonium halide. In some embodiments, the first part or the second part includes a thiourea (e.g., pyridyl thiourea), an amine (e.g., primary amines, secondary amines, tertiary amines, pyridines such as 3,5-diethyl-l,2-dihydro-l-phenyl-2-propylpyridine, hydroxyethyl toluidine, N,N-dimethyl-4-toluidine, imidazoles, and quinolines), an aldehyde -amine condensate, or an acid chloride (e.g., sulfonyl chlorides such as p-toluene sulfonyl chloride, p-methoxy benzene sulfonyl chloride, 4,4’-oxybis(benzene sulfonyl chloride), and diacid chlorides). The first part or the second part may also be essentially free of any of these compounds. “Essentially free of’ in this context refers to an amount less than 0.05 wt.%, 0.01 wt.%, 0.005 wt.%, or 0.001 wt.% and includes 0 wt.%, based on the total weight of the first part and the second part.

[0043] The beta-dicarbonyl compound useful for practicing the present disclosure may be represented by the formula or may be a salt thereof, wherein: i

[0044] _ J, .

[0045] X1and X2independently represent a covalent bond, O, S, or , wherein each R4independently represents hydrogen or alkyl having from 1 to 18 carbon atoms,

[0046] R1and R2independently represent a hydrocarbyl or substituted hydrocarbyl group having from 1 to 18 carbon atoms,

[0047] R3represents hydrogen, or a hydrocarbyl or substituted hydrocarbyl group having from 1 to 18 carbon atoms, or taken together any two of R1, R2, or R3form a five-membered or six-membered ring.

[0048] In some embodiments, R1and R2each have from 1 to 12 carbon atoms, 1 to 8 carbon atoms, or 1 to 4 carbon atoms. Examples of suitable R1and R2groups include methyl, ethyl, isopropyl, n-propyl, butyl pentyl, hexyl, octyl, decyl, dodecyl, hexadecyl, and octadecyl. Generally, the nature of the substituents in the substituted hydrocarbyl groups (which may be mono-substituted or poly-substituted) is not particularly important, except that substituents that interfere with the radical polymerization should be used sparingly or excluded altogether. Examples of suitable substituted hydrocarbyl groups include hydroxyhydrocarbyl groups (e.g., hydroxyethyl and hydroxypropyl), alkoxyhydrocarbyl groups (e.g., methoxyethyl and methoxyethoxy), alkanoylhydrocarbyl groups (e.g., acetylethyl and benzoylethyl), haloalkyl groups (e.g., chloroethyl and dichloropropyl), and dialkylaminohydrocarbyl groups (e.g., dimethylaminopropyl and diethylaminoethyl).

[0049] In some embodiments, any two of R1, R2, and R3taken together form a five-membered or sixmembered ring. In these embodiments, two of R1, R2, and R3taken together may represent, for example, a divalent group selected from and combinations thereof, wherein each R4independently represents H or an alkyl group having from 1 to 18 carbon atoms (in some embodiments, 1 to 12 carbon atoms, 1 to 8 carbon atoms, or 1 to 4 carbon atoms), and y is 1, 2 or 3. For example, the beta-dicarbonyl compound may be 2,2-dimethyl-l,3-dioxane- 4, 6-dione (Meldrum’s acid). Examples of suitable R4groups include hydrogen, methyl, ethyl, isopropyl, n-propyl, butyl, pentyl, hexyl, octyl, decyl, dodecyl, hexadecyl, and octydecyl. Examples of divalent groups formed by two of R1, R2, and R3taken together -include alkylene, alkyleneoxy, oxycarbonyloxy, carbonylalkylene, alkylenecarbonyloxy, alkyleneoxycarbonyl, alkylene(alkyl)amino, and dialkylene (alkyl)amino. If R1and R2taken together form a 5-membered ring, then at least one of X1or X2is a covalent bond.

[0050] In some embodiments, R3has from 1 to 12 carbon atoms, 1 to 8 carbon atoms, or 1 to 4 carbon atoms. Examples of suitable R3groups include methyl, ethyl, isopropyl, n-propy, butyl, pentyl, hexyl, octyl, decyl, dodecyl, hexydecyl, phenyl, cyclohexyl, methylcyclohexyl, and octadecyl. Examples of substituted hydrocarbyl groups R3include -CH2C(=O)OR4wherein R4is as previously defined (e.g., R4may be H, methyl, ethyl, dodecyl, or octadecyl).

[0051] In some embodiments, the beta-dicarbonyl compound comprises barbituric acid (i.e., R3= H, both R4 wherein R4= H, and taken together R1and R2= carbonyl) or a derivative thereof (e.g., a 1,3 -dialkylbarbituric acid). Examples of suitable barbituric acid derivatives include 1,3,5- trimethylbarbituric acid, 1,3, 5 -triethylbarbituric acid, 1, 3 -dimethyl-5 -ethylbarbituric acid, 1,5- dimethylbarbituric acid, l-methyl-5 -ethylbarbituric acid, l-methyl-5 -propylbarbituric acid, 5- ethylbarbituric acid, 5 -propylbarbituric acid, 5 -butylbarbituric acid, l-benzyl-5 -phenylbarbituric acid, and 1 -cyclohexyl-5 -ethylbarbituric acid .

[0052] In some embodiments, the beta-dicarbonyl compound comprises a dialkyl 2-acetylsuccinate diester having from 8 to 14 carbon atoms, from 8 to 12 carbon atoms, or from 8 to 10 carbon atoms. The dialykl 2-acetylsuccinate diester may be substituted or unsubstituted. Examples include dimethyl 2- acetylsuccinate (dimethyl acetylsuccinate), diethyl 2-acetylsuccinate, and methyl ethyl 2-acetylsuccinate.

[0053] Useful salts of beta-dicarbonyl compounds include alkali metal (e.g., lithium, sodium, potassium, or cesium) salts; NHR salts; and primary, secondary, tertiary, and quaternary organoammonium salts, in some embodiments, having from 1 to 24 carbon atoms. Examples include tetrabutylammonium, dibenzyldimethylammonium, benzyltributylammonium, and tetraethylammonium salts.

[0054] In some embodiments, the beta-dicarbonyl compound is present in an amount from 0.05 wt.% to 20 wt.% or from 0. 1 wt.% to 10 wt.%, based on the total weight of the first part or second part.

[0055] In some embodiments, the first part of the two-part adhesive composition of the present disclosure includes a free-radical inhibitor. Examples of suitable free-radical inhibitors include benzoquinones, naphthoquinone, butylated hydroxytoluene (BHT), hydroquinone, p-methoxy hydroquinone (MEHQ), and combinations thereof. In some embodiments, the free-radical inhibitor is present in an amount from 0.025 wt.% to 1.0 wt.%, 0.05 wt.% to 0.5 wt.%, or 0.05 wt.% to 0.25 wt.%, based on the total weight of the first part. In some embodiments, a free-radical inhibitor is present in the second part. In some embodiments, the second part is free of a free-radical inhibitor. In some embodiments of the two-part adhesive composition of the present disclosure, the crosslinker comprises an epoxide, for example, comprising two or more oxirane rings. In some embodiments, the crosslinker includes a multifunctional epoxide comprising at least two oxirane rings and at least one of a cycloaliphatic or aromatic ring. A variety of multifunctional epoxides are useful in the first part of the two-part adhesive composition. A monomeric multifunctional epoxide may be a cycloalkylene, arylene, alkylarylene, arylalkylene, or alkylenearylalkylene having at least two epoxide groups, wherein any of the cycloalkylene, alkylarylene, arylalkylene, or alkylenearylalkylene are optionally interrupted by one or more ether (i.e., -O-), ester (i.e., -O-C(O)-), thioether (i.e., -S-), or amine (i.e., -NR1-) groups and optionally substituted by alkoxy, hydroxyl, oxo, or halogen (in some embodiments, chloro, bromo, or iodo). Cycloalkylene groups can include both ring carbon atoms and carbon atoms not in the ring. Useful monomeric multifunctional epoxides may be diepoxides or epoxides with more than 2 (in some embodiments, 3 or 4) oxirane rings. An epoxy resin may be prepared by chain-extending any of such multifunctional epoxides. It should be understood that the epoxy resin has reactive epoxide groups that can be cured, for example, using the photoinitiator that generates acid upon exposure to actinic radiation.

[0056] Examples of cycloaliphatic multifunctional epoxides include 2-(3,4-epoxycyclohexyl-5,5-spiro-

[0057] 3.4-epoxy)cyclohexane-l,4-dioxane, bis(3,4-epoxycyclohexylmethyl)adipate, vinylcyclohexene oxide, 4- vinylepoxycyclohexane, bis(3,4-epoxy-6-methylcyclohexylmethyl)adipate, 3,4-epoxycyclohexylmethyl-

[0058] 3.4-epoxycyclohexanecarboxylate, 3,4-epoxy-6-methylcyclohexyl-3',4'-epoxy-6'- methylcyclohexanecarboxylate, methylenebis(3,4-epoxycyclohexane), dicyclopentadiene diepoxide, di(3,4-epoxy cyclohexylmethyl) ether of ethylene glycol, ethylenebis(3,4-epoxy cyclohexanecarboxylate), epoxyhexahydrodioctylphthalate, epoxyhexahydro-di-2-ethylhexyl phthalate, the diglycidyl ester of hexahydrophthalic acid, the diglycidyl ester of tetrahydrophthalic acid, bis(2,3-epoxycyclopentyl) ether,

[0059] 2.3 -epoxy cyclopentyl glycidyl ether, l,2-bis(2,3-epoxycyclopentyloxy)ethane, and hydantoin diepoxide. Other examples of useful multifunctional epoxides include glycidyl ethers of cycloaliphatic alcohols (e.g.,

[0060] 1.4-cyclohexanedimethanol, bis(4-hydroxycyclohexyl)methane or 2,2-bis(4-hydroxycyclohexyl)propane) . Combinations of any of these cycloaliphatic multifunctional epoxides can also be useful. In some embodiments, the cycloaliphatic multifunctional epoxide includes 3',4'-epoxycyclohexylmethyl 3,4- epoxy cyclohexanecarboxylate .

[0061] Epoxy compounds useful for the adhesive compositions according to the present disclosure include aromatic multifunctional epoxide resins (e.g., a chain-extended diepoxide or novolac epoxy resin having at least two epoxide groups) and aromatic monomeric multifunctional epoxides. A crosslinkable epoxy resin typically will have at least two epoxy end groups. The aromatic multifunctional epoxide typically contains at least one (in some embodiments, at least 2, in some embodiments, in a range from 1 to 4) aromatic ring that is optionally substituted by a halogen (e.g., fluoro, chloro, bromo, iodo), alkyl having 1 to 4 carbon atoms (e.g., methyl or ethyl), or hydroxyalkyl having 1 to 4 carbon atoms (e.g., hydroxymethyl). For epoxy resins containing two or more aromatic rings, the rings may be connected, for example, by an alkylene group having 1 to 4 carbon atoms that may be branched or straight-chained may optionally be substituted by halogen (e.g., fluoro, chloro, bromo, iodo).

[0062] Examples of aromatic multifunctional epoxides useful in the adhesive compositions disclosed herein include novolac epoxy resins (e.g., phenol novolacs, ortho-, meta-, or para-cresol novolacs or combinations thereof), bisphenol epoxy resins (e.g., bisphenol A, bisphenol F, halogenated bisphenol epoxies, and combinations thereof), resorcinol epoxy resins, tetrakis phenylolethane epoxy resins and combinations of any of these. Useful multifunctional epoxides include diglycidyl ethers of difunctional phenolic compounds (e.g., p,p’ -dihydroxydibenzyl, p,p'-dihydroxydiphenyl, p,p'-dihydroxyphenyl sulfone, p,p'-dihydroxybenzophenone, 2, 2'-dihydroxy- 1,1 -dinaphthylmethane, and the 2,2', 2,3', 2,4', 3,3', 3,4', and 4,4' isomers of dihydroxydiphenylmethane, dihydroxydiphenyldimethylmethane, dihydroxydiphenylethylmethylmethane, dihydroxydiphenylmethylpropylmethane, dihydroxydiphenylethylphenylmethane, dihydroxydiphenylpropylphenylmethane, dihydroxydiphenylbutylphenylmethane, dihydroxydiphenyltolylethane, dihydroxydiphenyltolylmethylmethane, dihydroxydiphenyldicyclohexylmethane, and dihydroxydiphenylcyclohexane) and the triglycidyl ether of tris-(hydroxyl phenyl) methane In some embodiments, the adhesive composition includes a bisphenol diglycidyl ether, wherein the bisphenol (i.e., -O-C6H5-CH2-C6H5-O-) may be unsubstituted (e.g., bisphenol F), or either of the phenyl rings or the methylene group may be substituted by one or more halogens (e.g., fluoro, chloro, bromo, iodo), methyl groups, trifluoromethyl groups, or hydroxymethyl groups. Examples of epoxy resins having amine groups include poly(N-glycidyl) compounds obtainable by dehydrochlorinating the reaction products of epichlorohydrin with amines containing at least two amine hydrogen atoms. Examples of these amines include aniline, bis(4-aminophenyl)methane, m-xylylenediamine or bis(4-methylaminophenyl)methane.

[0063] Examples of aromatic monomeric diepoxides useful in the adhesive compositions according to the present disclosure include the diglycidyl ethers of bisphenol A and bisphenol F and mixtures thereof. Bisphenol epoxy resins, for example, may be chain extended to have any desirable epoxy equivalent weight. Chain extending epoxy resins can be carried out by reacting a monomeric diepoxide, for example, with a bisphenol in the presence of a catalyst to make a linear polymer.

[0064] In some embodiments, the aromatic epoxy resin (e.g., either a bisphenol epoxy resin or a novolac epoxy resin) may have an epoxy equivalent weight of at least 150, 170, 200, or 225 grams per equivalent. In some embodiments, the aromatic epoxy resin may have an epoxy equivalent weight of up to 2000, 1500, or 1000 grams per equivalent. In some embodiments, the aromatic epoxy resin may have an epoxy equivalent weight in a range from 150 to 2000, 150 to 1000, or 170 to 900 grams per equivalent. Epoxy equivalent weights may be selected, for example, so that the epoxy resin may be used as a liquid or solid, as desired.

[0065] The first part of the two-part adhesive composition of the present disclosure can include two or more cycloaliphatic multifunctional epoxides, two or more aromatic multifunctional epoxides, or any combination of cycloaliphatic multifunctional epoxides and aromatic multifunctional epoxides. In some embodiments, the adhesive composition does not comprise an aromatic multifunctional epoxide or comprises less than 3, 2, or 1 percent by weight, based on the total weight of the adhesive composition of an aromatic multifunctional epoxide. Aromatic multifunctional epoxides that may be excluded from the adhesive composition may be any of those described above.

[0066] In some embodiments, the first part of the two-part adhesive composition of the present disclosure and / or useful in the method of the present disclosure includes an aliphatic compound comprising at least one oxirane ring, which typically comprises a straight-chain or branched aliphatic (i.e., non-aromatic) group. In some cases, such aliphatic compounds can be useful as reactive diluents that may help control the flow characteristics of the two-part adhesive composition. In some cases, such aliphatic compounds can provide flexibility to the cured epoxy. An aliphatic epoxy useful in the adhesive compositions of the present disclosure can include a branched or straight-chain alkylene group having 1 to 20 carbon atoms optionally interrupted with at least one -O- and optionally substituted by hydroxyl. In some embodiments, the aliphatic epoxy can include a poly(oxyalkylene) group having a plurality (x) of oxyalkylene groups, OR1, wherein each R1is independently C2 to C5 alkylene, in some embodiments, C2 to C3 alkylene, x is 2 to about 6, 2 to 5, 2 to 4, or 2 to 3. To become crosslinked into a network, useful aliphatic epoxies will typically have at least two oxirane rings. Examples of useful aliphatic compounds having at least two oxirane rings include glycidyl epoxy resins such as those based on diglycidyl ether compounds comprising one or more oxyalkylene units. Examples of these include resins made from ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, dipropylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, glycerol diglycidyl ether, glycerol triglycidyl ether, propanediol diglycidyl ether, butanediol diglycidyl ether, and hexanediol diglycidyl ether. Examples of useful epoxides having more than two epoxide groups include glycerol triglycidyl ether, and polyglycidyl ethers of 1,1,1 -trimethylolpropane, pentaerythritol, and sorbitol. Examples of multifunctional epoxides having thioether groups include di-S- glycidyl derivatives of dithiols (e.g., ethane- 1,2-dithiol or bis(4-mercaptomethylphenyl) ether). Other useful non-aromatic epoxy resins include a diglycidyl ether of neopentyl glycol, a triglycidyl ether of trimethylolpropane, a diglycidyl ether of 1,4-butanediol, and a reaction product of epichlorohydrin and n- butylamine.

[0067] Several multifunctional epoxides useful in the adhesive composition of the present disclosure and / or useful in the method of the present disclosure are commercially available. For example, several epoxy resins of various classes and epoxy equivalent weights are available from Dow Chemical Company, Midland, MI; Momentive Specialty Chemicals, Inc., Columbus, OH; Huntsman Advanced Materials, The Woodlands, TX; CVC Specialty Chemicals Inc. Akron, OH (acquired by Emerald Performance Materials); and Nan Ya Plastics Corporation, Taipei City, Taiwan. Examples of commercially available cycloaliphatic multifunctional epoxides include those obtained from Daicel ChemTech, Inc., Tokyo, Japan, under the trade designations “CELLOXIDE 2021 P”, “CELLOXIDE 2081”, “CELLOXIDE 2000”, and “CELLOXIDE 8010”, Shin-Etsu Chemical Co., Ltd., Tokyo, Japan, under the trade designation “KR470”, from Synasia, Inc., Metuchen, NJ, under the trade designation “SYNA EPOXY” in various grades, and from Hexion Specialty Chemicals GmbH, Columbus, Ohio, under the trade designation “HELOXY MODIFIER 107”. Examples of commercially available glycidyl ethers include diglycidylethers of bisphenol A (e.g. those available under the trade designations “EPON 828”, “EPON 1001”, “EPON 1310” and “EPON 1510” from Hexion Specialty Chemicals GmbH, Rosbach, Germany, those available under the trade designation “D.E.R.” from Dow Chemical Co. (e.g., D.E.R. 331, 332, and 334), those available under the trade designation “EPICLON” from Dainippon Ink and Chemicals, Inc. (e.g., EPICLON 840 and 850) and those available under the trade designation “YL- 980” from Japan Epoxy Resins Co., Ltd.); diglycidyl ethers of bisphenol F (e.g. those available under the trade designation “EPICLON” from Dainippon Ink and Chemicals, Inc. (e.g., “EPICLON 830”)); polyglycidyl ethers of novolac resins (e.g., novolac epoxy resins, such as those available under the trade designation “D.E.N.” from Dow Chemical Co. (e.g., D.E.N. 425, 431, and 438)); and flame retardant epoxy resins (e.g., “D.E.R. 580”, a brominated bisphenol type epoxy resin available from Dow Chemical Co.).

[0068] In some embodiments, the second part of the two-part adhesive composition of the present disclosure includes a multi-functional amine as a curing component for the epoxide crosslinker. Useful multi-functional amines may be aliphatic amines including at least two amino groups. In some embodiments, the multi-functional amine is a linear or branched alkylene polyamine. Useful alkylene polyamines include ethylene amines (e.g., ethylenediamine, diethylenetriamine, triethylenetetramine, etc.), higher alkylenediamines (e.g., hexamethylenediamine, methylpentamethylenediamine, and trimethylhexanediamine), and polyetheramines (e.g., polyoxyalkylene diamines such as poly oxypropylene diamines of various molecular weights and 4,7,10-trioxa-l,13-tridecane diamine).

[0069] The multi-functional amine may be an aromatic polyamine, in which the amino groups are bonded directly to the aromatic ring, or an arylalkylenyl polyamine, in which the amino groups are bonded to alkylene groups that are in turn bonded to the aromatic ring. The multi-functional amine may also contain two or more aromatic rings and at least two amino groups. In any of these embodiments, the aromatic ring can be unsubstituted or substituted by one or more halogens (e.g., fluoro, chloro, bromo, iodo), alkyl groups having 1 to 4 carbon atoms (e.g., methyl or ethyl), or hydroxyalkyl groups having 1 to 4 carbon atoms (e.g., hydroxymethyl). For amines containing two or more aromatic rings, the rings may be directly connected or connected, for example, by a branched or straight-chain alkylene group having 1 to 4 carbon atoms that may optionally be substituted by one or more halogens (e.g., fluoro, chloro, bromo, iodo), an oxygen, a sulfur, or a sulfone group. Examples of multi-functional amine that comprise at least two amino groups and at least one aromatic ring include phenylenediamine (e.g., meta-phenylenediamine or para-phenylenediamine), diethyl toluene diamine (e.g., in any of its isomeric forms), diamino toluene (e.g., 2,3-diaminotoluene and 3,4-diaminotoluene, and methyl-m-phenylenediamine), l,2-diamino-3,5- dimethylbenzene, 4,5-dimethyl-l,2-phenylenediamine, 2,4,6-trimethyl-m-phenylenediamine, 2, 3,5,6- tetramethyl-p-phenylenediamine, aminobenzylamines (e.g., 2-aminobenzylamine and 4- aminobenzylamine), ethylenedianiline, 2,2 ’-biphenyldiamine, diaminodiphenylmethane, diaminodiphenylsulfone, halogenated substituted pheneylene diamines (e.g., 4-chloro-l,3- diaminobenzene, 4-chloro-l,2-diaminobenzene, and 4-bromo-l,2-diaminobenzene), a xylylenediamine (e.g., ortho-xylylenediamine or meta-xylylenediamine), and 4-(2-aminoethyl)aniline.

[0070] The multi-functional amine may comprise at least two amino groups and at least one cycloaliphatic ring. The amino groups may be bonded directly to the cycloaliphatic ring, or the amino groups may be bonded to straight-chain or branched alkylene groups that are in turn bonded to the cycloaliphatic ring. An amine curing agent may also contain two or more cycloaliphatic rings and at least two amino groups. In any of these embodiments, the cycloaliphatic ring can be unsubstituted or substituted by one or more halogens (e.g., fluoro, chloro, bromo, iodo), straight-chain or branched alkyl groups having 1 to 4 carbon atoms (e.g., methyl or ethyl), or hydroxyalkyl groups having 1 to 4 carbon atoms (e.g., hydroxymethyl). In any of these embodiments, the cycloaliphatic ring may be a carbocyclic ring, for example, including no heteroatoms such as sulfur or nitrogen. For amines containing two or more cycloaliphatic rings, the rings may be directly connected or connected, for example, by a branched or straight-chain alkylene group having 1 to 4 carbon atoms that may optionally be substituted by one or more halogens (e.g., fluoro, chloro, bromo, iodo), an oxygen, a sulfur, or a sulfone group. Examples of suitable amine curing agents that comprise at least two amino groups and at least one cycloaliphatic group are the fully or partially hydrogenated products of any of the amine curing agents that comprise at least two amino groups and at least one aromatic ring described above. For example, suitable amine curing agents include diaminocyclohexanes (e.g., 1,2-diaminocyclohexane or 1,4-diaminocyclohexane in their cis- or trans- forms) and 3-aminomethyl-3,5,5-trimethylcyclohexylamine (also called isophorone diamine).

[0071] Several multi-functional amines including at least two amino groups and at least one of an aromatic ring or a cycloaliphatic ring are available, for example, from Lonza, Basel, Switzerland, and Amberlite Corporation, Baton Rouge, LA. Other amine curing agents that may be useful include polyetheramines (e.g., polypropylene glycol diamines) available, for example, from Huntsman Chemical, The Woodlands, TX, under the trade designation “JEFF AMINE”.

[0072] The curing component for the epoxide can also include a catalyst or co-curing agent for the epoxide such as tertiary amines, imidazoles, ureas, and dicyandiamide.

[0073] In some embodiments, at least one of the first part or the second part of the two-part adhesive composition of the present disclosure includes a non-reactive diluent. In some embodiments, only the second part includes a non-reactive diluent. In some embodiments, only the first part includes a non- reactive diluent. In some embodiments, both parts include a non-reactive diluent. For the non-reactive diluent, any solvent (e.g., organic solvent) that does not react with the curing component may be useful. Suitable non-reactive diluent are paraffins such as liquid paraffins, mineral oil, hydrocarbons having six or more carbon atoms (e.g., petroleum naphtha), and ether acetates such as diethylene glycol monobutyl ether acetate. In some embodiments, the non-reactive diluent comprises at least one of a polyol or polyol ether independently having from 2 to 10 (in some embodiments, 2 to 9 or 2 to 8) carbon atoms. In some embodiments, the non-reactive diluent comprises a polyol. The term "polyol" refers to an organic molecule consisting of C, H, and O atoms connected one to another by C-H, C-C, C-O, O-H single bonds, and having at least two C-O-H groups. In some embodiments, useful polyols have 2 to 10, 2 to 8, or 2 to 6 carbon atoms. In some embodiments, the non-reactive diluent comprises a polyol ether or polyol ether ester. The term "polyol ether" refers to an organic molecule consisting of C, H, and O atoms connected one to another by C-H, C-C, C-O, O-H single bonds or C=C double bonds, and which is at least theoretically derivable by at least partial etherification of a polyol. In some embodiments, the polyol ether has at least one C-O-H group and at least one C-O-C linkage. In some embodiments, the polyol ether has at least two C-O-C linkages. Similarly, the term "polyol ether ester" refers to an organic molecule consisting of C, H, and O atoms connected one to another by C-H, C-C, C-O, O-H single bonds and C=O double bonds, and which is at least theoretically derivable by at least partial etherification and esterification of a polyol. In some embodiments, the polyol ether ester has one C-O-C(O)-C group and at least one C-O-C linkage. Useful polyol ethers and / or polyol ether esters may have from 3 to 10, 3 to 8, or from 5 to 8 carbon atoms. In some embodiments, the non-reactive diluent comprises at least one of 3-methoxy-3-methyl-l-butanol, 3 -methoxy-3 -methyl- 1 -butylacetate, diethylene glycol monoethyl ether, dipropylene glycol dimethyl ether, or dipropylene glycol monomethyl ether. In some embodiments, the non-reactive diluent comprises at least one polyol ether (e.g., glycol ethers (e.g., ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol dimethyl ether, propylene glycol monomethyl ether, 2-butoxyethanol, l-methoxy-2 -propanol, 3 -methoxy-3 -methyl - 1 -butanol, 2-phenoxyethanol, or those glycol ethers available under the trade designation "DOWANOL" from Dow Chemical Co., Midland, MI)).

[0074] Also, plasticizers such as plasticizers based on dipropylene glycol dibenzoate (e.g., Benzoflex 9- 88, available from Eastman Chemical Company, Kingsport, TN, USA) may be used as non-reactive diluents. Examples of suitable plasticizers include aliphatic and aromatic hydrocarbons, alkyl esters, alkyl ethers, aryl esters, and aryl ethers.

[0075] In some embodiments, the non-reactive diluent can migrate to the surface of the curable precursor to prevent oxygen inhibition of the polymerization of radically (co)polymerizable compounds of the two- part adhesive composition.

[0076] The amount of non-reactive diluent present in the first part or the second part may be up to 90 wt.%, 85 wt.%, or 80 wt.%, based on the total weight of the first part or the second part, respectively. In some embodiments, the amount of non-reactive diluent is at least 10 wt.%, 20 wt.%, 30 wt.%, 40 wt.%, or 50 wt.%, based on the total weight of the first part or the second part, respectively. The non-reactive diluent can be added to at least one of the first part or second part at any desirable time. The components including the non-reactive diluent can be stored for a period of time before applying the first part and second part, or at least one of the first part or the second part can be prepared and / or diluted with non- reactive diluent immediately prior to use.

[0077] At least one of the first part or the second part of the two-part adhesive composition of the present disclosure includes a rheology modifier. In some embodiments, only the first part includes a rheology modifier. In some embodiments, only the second part includes a rheology modifier. In some embodiments, both parts include a rheology modifier. In some embodiments, the rheology modifier independently comprises at least one of an impact modifier, a filler, or a thixotropic agent.

[0078] The amount of rheology modifier in the first part and the second part may be selected such that both the first part and the second part have a viscosity of not more than 100 Pascal seconds (Pa-s) when measured on a rheometer at a shear rate of 0.01 reciprocal second. In some embodiments, both the first part and the second part have viscosity of not more than 50 Pa-s, 40 Pa-s, 30 Pa-s, 20 Pa-s, 15 Pa-s, or 10 Pa-s when measured on a rheometer at a shear rate of 0.01 reciprocal second. In some embodiments, both the first part and the second part have viscosity of at least 0.001 Pa-s, 0.01 Pa-s, or 0.1 Pa-s when measured on a rheometer at a shear rate of 0.01 reciprocal second. In addition, in some embodiments, a ratio of the viscosity or the first part to the viscosity of the second part is in a range from 5 : 1 to 1 :5, 4: 1 to l:4, 3: l to l:3, 2.5: l to 1:2.5, or 2: l to 1:2 when measured on a rheometer at one or more shear rates of less than one reciprocal second, in some embodiments, at 0.01 reciprocal second. The test method in the Examples, below, is used to measure viscosity. As shown in the Examples, below, the first part and the second part exhibit at least one of better co-diffusion, better curing, or better adhesive strength when cured when the first viscosity and the second viscosity are in these ranges. These advantages are observed, for example, when the first part and the second part are not premixed before being applied to a substrate to be bonded. Shear rates of 0.01 1 / sec are representative of diffusion mixing in a static state with no forced flow. In contrast, shear rates up to about 1 1 / sec are characteristic of slow flow such as slow mechanical mixing, and shear rates above 10 1 / sec is the realm of dispensed flow, with exact shear rates dependent on flow rates and channel dimensions.

[0079] In some embodiments, at least one of the first part or the second part includes fumed silica, which is a thixotropic agent. In some embodiments, the fumed silica is present in the first part in an amount of 0.25 wt.% to 10 wt.%, 0.5 wt.% to 8 wt.%, or 1 wt.% to 7 wt.%, based on the total weight of the first part. If present in the second part, these amounts fumed silica may each be useful in the second part, based on the total weight of the second part. In some embodiments when at least one of the first part or the second part includes fumed silica, both the first part and the second part have viscosity of not more than 20 Pa-s, 15 Pa-s, or 10 Pa-s when measured on a rheometer at a shear rate of 0.01 reciprocal second.

[0080] In some embodiments, at least one of the first part or the second part includes an impact modifier. A variety of impact modifiers may be suitable as long as the impact modifier is a polymeric material having rubber elasticity at room temperature. Examples of elastomers suitable for as impact modifiers include various synthetic rubbers such as a methyl methacrylate-butadiene-styrene copolymer (MBS), an acrylonitrile-styrene-butadiene copolymer, a linear polyurethane, acrylonitrile -butadiene rubber, a styrene-butadiene rubber, a styrene-butadiene-styrene rubber, a polystyrene / EPDM (an ethylene / propylene / conjugated diene copolymer), a chloroprene rubber, a butadiene rubber, a thermoplastic elastomer, and natural rubber. The impact modifier may be a core-shell graft copolymer having a “rubbery” core and a “hard” shell. Examples of useful core-shell graft copolymers are those where “hard” monomers, such as styrene, acrylonitrile, or methyl methacrylate, are grafted onto a rubbery core made from polymers of “soft” or “elastomeric” monomers, such as butadiene or ethyl acrylate. Several core-shell graft copolymers are commercially available, including from the sources shown in the Examples, below. Useful thermoplastic elastomers include hard segments and soft segments. The soft segments and uncrystallized hard segments form an amorphous phase, and a portion of the hard segment crystallizes to form crystalline microdomains, which can function as physical crosslinking domains. Suitable thermoplastic elastomers include acrylic copolymers, in some embodiments, including poly(methyl methacrylate) (PMMA) hard segments such as a triblock copolymer of poly(methyl methacrylate)-poly(n-butyl (meth)acrylate)-poly(methyl methacrylate) triblock copolymer. In some embodiments, the thermoplastic elastomer is an ABA block copolymer elastomer where the A blocks are polystyrenic, and the B blocks are conjugated dienes (e.g., lower alkylene dienes). Other useful polymeric tougheners include epoxy-, hydroxy-, carboxyl- and amine-terminated acrylonitrile / butadiene elastomers such as those obtained from Huntsman Advanced Materials under the trade designation “HYPRO” (e.g., ETBN, HTBN, CTBN and ATBN grades) and carboxyl- and amine-terminated butadiene polymers such as those obtained from Huntsman Advanced Materials under the trade designation “HYPRO” (e.g., CTB grade). The amount of the impact modifier present in at least one of the first part or the second part may be 5 wt.% to 35 wt.%, 10 wt.% to 35 wt.%, or 15 wt.% to 30 wt.%, based on the total weight of the first part or the second part, respectively. In some embodiments, both the first part and the second part include an impact modifier.

[0081] As shown in the Examples, below, some of the best overlap shear values were obtained when the viscosities of the first part and the second part matched, and the total amount of impact modifier in the two-part adhesive composition (combined first and second parts) was at least 5 wt.% or greater than 5 wt.% and less than 30 wt.%, 25 wt.%, 20 wt%, or 15 wt.%. In some embodiments in which the amount of impact modifier is in these ranges, the ratio of the first viscosity to the second viscosity need not be in a range from 5 : 1 to 1 : 5 as long that both the first viscosity and the second viscosity are not more than 100 Pascal seconds (Pa-s) when measured on a rheometer at a shear rate of 0.01 reciprocal second.

[0082] In some embodiments, at least one of the first part or the second part of the two-part adhesive composition of the present disclosure may include other components useful, for example, in adhesive compositions. For example, at least one of the first part or the second part can include at least one of tackifiers, corrosion inhibitors, UV stabilizers, hindered amine light stabilizers (e.g., 2, 2,6,6- tetramethylpiperidine-N-oxyl and 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl), antioxidants, flame retardants, dyes, pigments (e.g., ferric oxide, brick dust, carbon black, and titanium oxide), reinforcing agents (e.g., silica, magnesium sulfate, calcium sulfate, and beryllium aluminum silicate), clays such as bentonite, surface-modified clays, other suitable filler (e.g., glass beads, talc, and calcium metasilicate), dispersing agents, wetting agents, waxes, adhesion promoters (e.g., silane coupling agents), antistatic agents, thermally and / or electrically conductive particles, foaming agents, and hollow polymeric or ceramic microspheres (e.g., glass bubbles). In some embodiments, at least one of the first part or the second part of the two-part adhesive composition of the present disclosure includes a filler. Examples of fillers useful for some embodiments of the two-part composition of the present disclosure include at least one of a micro-fibrillated polyethylene, a fumed silica, a talc, a wollastonite, an aluminosilicate clay (e.g., halloysite), phlogopite mica, calcium carbonate, kaolin clay, metal oxides (e.g., barium oxide, calcium oxide, magnesium oxide, zirconium oxide, titanium oxide, zinc oxide), nanoparticle fillers (e.g., nanosilica, nanozirconia). These components may be present in at least one of the first part or the second part in any suitable amount. The first part, the second part, or both may also be free of any of these components. In some embodiment, at least one of the first part or the second part includes a pigment, which may be any of those described above. Useful levels of pigment include up to 2 wt.%, 1.5 wt.%, 1 wt.%, or 0.5 wt.%, based on the total weight of the first part or the second part.

[0083] In one aspect, the present disclosure provides a two-part adhesive composition comprising a first part comprising a crosslinker having two or more acrylate groups, methacrylate groups, or a combination thereof, a transition metal compound, and optionally, a quaternary ammonium salt; and a second part comprising a free-radical initiator comprising at least one of a peroxide initiator or a hydroperoxide initiator, a beta-dicarbonyl compound, and a non-reactive diluent, wherein the first part and the second part independently further comprise an impact modifier, wherein the first part has a first viscosity and the second part has a second viscosity, wherein the first viscosity and the second viscosity are each below 100 Pascal seconds when measured on a rheometer at a shear rate of 0.01 reciprocal second. The crosslinker, transition metal compound, quaternary ammonium salt, free-radical initiator, beta-dicarbonyl compound, non-reactive diluent, impact modifier, first and second viscosities, and viscosity ratios may be any of those described above in any of their embodiments. The two-part adhesive composition comprises the impact modifier in a total amount in a range from 2 weight percent to 25 weight percent, based on the total weight of the two-part adhesive composition.

[0084] In some embodiments of this aspect of the two-part adhesive composition, the crosslinker having two or more acrylate groups, methacrylate groups, or a combination thereof includes an aromatic or nonaromatic ring. Examples include 1,4-cyclohexanediol diacrylate, cyclohexanedimethanol diacrylate, tricyclodecanedimethanol diacrylate, tris(2 -hydroxyethyl) isocyanurate triacrylate, methacrylates of the foregoing acrylates, and combinations thereof. In some embodiments, the first part further includes a monfunctional monomer having a methacrylate group or an acrylate group and at least one of an aromatic or non-aromatic ring. Examples include each of the monomers used in the Examples. In some embodiments, there is no crosslinker or monofunctional monomer in the second part.

[0085] The first part and the second part can be located in any suitable system or kit for containing and dispensing the first part and the second part. The system can be suited for large-scale industrial applications or small-scale applications. Either system can include first and second chambers for holding the respective first part and second part. The chambers can be sized for any application and formed from plastic, metal, or any other suitable material.

[0086] To facilitate movement of the first part and the second part, the system can include elements such as one or more plunger or one or more pumps. The one or more plungers can be useful for systems that are handheld. In these embodiments, a user can push one or two plungers, between at least a first and a second position, to force the first part and the second part through the system. If there is one plunger, then the first part and the second part can be dispensed at a predetermined volume or weight ratio. Pumps can be useful in industrial applications where large volumes or a continuous supply of the first part and the second part are dispensed. These systems can include one or more pumps that are in fluid communication with the first and second chambers.

[0087] Compositions of the present disclosure may be used, for example, to bond a first substrate to a second substrate to provide a bonded article. Thus, the present disclosure provides a method of making a bonded article. The method includes applying the first part and the second part of the two-part adhesive composition disclosed herein onto at least one of the first substrate or the second substrate without premixing the first part and the second part, adhering the first substrate and the second substrate using the two-part adhesive composition, and allowing the two-part adhesive composition to at least partially cure to make the bonded article. In some embodiments, the applying comprises applying the first part on at least a portion of a contact surface of the first substrate and applying the second part on at least a portion of a contact surface of the second substrate. In some embodiments, the adhering comprises contacting the first part on the contact surface of the first substrate with the second part on the contact surface of the second substrate. This may be repeated successively to result in more than one bonded lamination and achieve a lamination of desired height from many layers of substrates (e.g., steel).

[0088] The first and the second part of the two-part adhesive composition may be applied on the contact surface of the first or second substrate, respectively, by using any suitable conventional coating process technology. In some embodiments, the applying comprises at least one of spraying, droplet application, coating, or roll-to-roll process. One of such processes can be used to apply the first part, and another such process can be used to apply the second part. The weight ratio of the amount of the first part to the amount of the second part applied on the contact surface of the first and second substrates may be from 20: 1 to 1 : 1. In some embodiments, the weight ratio of the amount of the first part to the amount of the second part is from 15: 1 to 5: 1, from 12: 1 to 8: 1, or about 10: 1.

[0089] The curing does not start until the first and second part of the two-part adhesive composition are brought together, and upon mating, the two parts of the two-part adhesive composition are mixed spontaneously by diffusion and are cured. The two-part adhesive composition can be cured substantially uniformly without any physically mixing process.

[0090] After at least partial curing, a crosslinked composition is generally obtained, and if sufficiently cured, it may be suitable for use as a structural adhesive to bond two adherends. In such use, the composition is typically sandwiched between the adherends and at least partially cured; for example, sufficient to achieve at least a desired level of bond strength.

[0091] While it is not practical to enumerate a particular curing temperature suitable for all situations, generally suitable temperatures are in a range from about 23 °C to about 200 °C. In some embodiments, advantageously, the two-part adhesive composition can be cured at room temperature (e.g., 23 °C to 25 °C), for at least 60 minutes, 90 minutes, 120 minutes, 6 hours, 12 hours, 24 hours, 48 hours, or 72 hours for example, to at least partially cure the composition.

[0092] Many types of substrates may be bonded with the two-particle adhesive composition of the present disclosure such as metal (e.g., stainless steel or aluminum), glass (e.g., which may be coated with indium tin oxide), a polymer (e.g., a plastic, rubber, thermoplastic elastomer, or thermoset), or a composite. A composite material may be made from any two or more constituent materials with different physical or chemical properties. When the constituents are combined to make a composite, a material having characteristics different from the individual components is typically achieved. Some examples of useful composites include fiber-reinforced polymers (e.g., carbon fiber reinforced epoxies and glass- reinforced plastic), metal matrix compositions, and ceramic matrix composites. Useful polymeric substrates that can be bonded include polymers such as acrylonitrile butadiene styrene (ABS), polycarbonate (PC), PC / ABS blends, polyvinyl chloride (PVC), polyester, polyurethane (PUR), thermoplastic elastomers (TPE), polystyrene, poly(methyl) methacrylate (PMMA), polyvinyl chloride (PVC), and combinations thereof. The substrate may also include a metal coating on such polymers. The composition of the present disclosure can be useful, for example, for bonding electronic articles and automotive and aerospace components.

[0093] In some embodiments, steel substrates are coated with an insulation coating. Electrical steel coatings are pigmented coatings that insulate steel sheets of motors and generators. To ensure the efficiency of motors or generators, a material that can be magnetized and demagnetized is needed. The insulation coating may have both an organic component and an inorganic component, for example, it may be an organic coating filled with an inorganic filler.

[0094] In an aspect of the present disclosure, surface treatment of a steel substrate having an insulation coating is used to improve the bonding of an adhesive to the coated substrate. In some embodiments, the surface treatment is a plasma treatment (e.g., air, nitrogen, or argon) or a corona treatment, for example. In some embodiments, the adhesive is an anaerobically cured two-part adhesive. In some embodiments, the adhesive is an anaerobically cured two-part acrylic adhesive. In some embodiments, the two-part adhesive composition of the present disclosure is useful for bonding the coated steel substrates. Useful plasma treatments include open air plasma, which can be generated by a Plasmatreat FG5001, “OPENAIR PLASMA” generator and an RD1004 rotary jet using the conditions of a 5-millimeter height, a speed of 5 meters per minute, a voltage of 284 volts and a current of 7.5 ampules. As shown in the Examples below, plasma treatment of coated steel substrate can improve the overlap sheer strength of an adhesive. The adhesive strength (overlap shear strength, OLS) of the cured composition after a curing time of at least 48 hours at room temperature (23 °C) may be at least 2 MPa, or at least 3 MPa, or at least 4 MPa, or at least 5 MPa, when measured according to the test method described in the Examples, below. The curing time may be adjusted as desired depending on the targeted applications and manufacturing requirements.

[0095] The cured composition of the present disclosure or made by the process disclosed herein may have an overlap shear strength (OLS) in a range from 2.0 to 10.0 MPa, or from 2.0 to 8.0 MPa at room temperature (23 °C), when measured according to the test method described in the experimental section.

[0096] The cured composition of the present disclosure or made by the process disclosed herein may have an overlap shear strength (OLS) of at least 1.0 MPa, at least 1.5 MPa, at least 2.0 MPa, at least 3.0 MPa, in a range from 1.0 to 5.0 MPa, or from 2.0 to 5.0 MPa at 180 °C, when measured according to the test method described in the experimental section.

[0097] Some Embodiments of the Disclosure

[0098] In a first embodiment, the present disclosure provides a two-part adhesive composition comprising a first part comprising a crosslinker and a second part comprising a curing component for the crosslinker wherein at least one of the first part or the second part independently further comprise a rheology modifier, wherein the first part has a first viscosity and the second part has a second viscosity, wherein the first viscosity and the second viscosity are each not more than 100 Pascal seconds when measured on a rheometer at a shear rate of 0.01 reciprocal second, and wherein a ratio of the first viscosity to the second viscosity is in a range from 5: 1 to 1:5 when measured on a rheometer at at least one shear rate of less than one reciprocal second. In a second embodiment, the present disclosure provides the two-part adhesive composition of the first embodiment, wherein the crosslinker is an acrylate, a methacrylate, an epoxide, or a combination thereof. In a third embodiment, the present disclosure provides the two-part adhesive composition of the first or second embodiment, wherein the crosslinker has at least two acrylate functional groups, methacrylate functional groups, or a combination thereof. In a fourth embodiment, the present disclosure provides the two-part adhesive composition of the third embodiment, wherein the crosslinker comprises one or more aromatic or non-aromatic rings and at least two acrylate functional groups, methacrylate functional groups, or a combination thereof. In a fifth embodiment, the present disclosure provides the two-part adhesive composition of any one of the first to fourth embodiments, wherein the first part further comprises a monofunctional monomer. In a sixth embodiment, the present disclosure provides the two-part adhesive composition of the fifth embodiment, wherein the monofunctional monomer comprises one or more aromatic or non-aromatic rings and an acrylate or methacrylate functional group. In a seventh embodiment, the present disclosure provides the two-part adhesive composition of any one of the first to sixth embodiments, wherein the second part further comprises a non-reactive diluent. In an eighth embodiment, the present disclosure provides the two-part adhesive composition of any one of the first to seventh embodiments, wherein the curing component comprises a free-radical initiator comprising at least one of a peroxide initiator or a hydroperoxide initiator. In a ninth embodiment, the present disclosure provides the two-part adhesive composition of any one of the first to eighth embodiments, wherein curing component is a component of a redox initiating system. In a tenth embodiment, the present disclosure provides the two-part adhesive composition of any one of the first to ninth embodiments, wherein either the first part comprises a transition metal compound and a quaternary ammonium salt, and the second part comprises a betadicarbonyl compound as the curing component, or the first part comprises the beta-dicarbonyl compound and the second part comprises the transition metal compound and the quaternary ammonium salt as the curing component.

[0099] In an eleventh embodiment, the present disclosure provides a two-part adhesive composition comprising a first part comprising a crosslinker having two or more acrylate groups, methacrylate groups, or a combination thereof and a transition metal compound and a second part comprising a free-radical initiator comprising at least one of a peroxide initiator or a hydroperoxide initiator, a beta-dicarbonyl compound, and a non-reactive diluent, wherein at least one of the first part or the second part independently further comprise a rheology modifier, wherein the first part has a first viscosity and the second part has a second viscosity, wherein the first viscosity and the second viscosity are each below 100 Pascal seconds when measured on a rheometer at a shear rate of 0.01 reciprocal second, and wherein a ratio of the first viscosity to the second viscosity is in a range from 5: 1 to 1:5 when measured on a rheometer at one or more shear rates of less than one reciprocal second. In a twelfth embodiment, the present disclosure provides the two-part adhesive composition of any one of the first to eleventh embodiments, wherein the rheology modifier independently comprises at least one of an impact modifier, a filler, or a thixotropic agent. In a thirteenth embodiment, the present disclosure provides the two-part adhesive composition of any one of the first to twelfth embodiments, wherein the rheology modifier comprises fumed silica. In a fourteenth embodiment, the present disclosure provides the two-part adhesive composition of the thirteenth embodiment, wherein the first viscosity and the second viscosity are each below 10 Pascal seconds when measured on a rheometer at a shear rate of 0.01 reciprocal second. In a fifteenth embodiment, the present disclosure provides the two-part adhesive composition of any one of the first to twelfth embodiments, wherein the rheology modifier is independently an impact modifier. In a sixteenth embodiment, the present disclosure provides the two-part adhesive composition of the fifteenth embodiment, wherein both the first part and the second part comprise the impact modifier. In a seventeenth embodiment, the present disclosure provides a two-part adhesive composition comprising: a first part comprising: a crosslinker having two or more acrylate groups, methacrylate groups, or a combination thereof; and a transition metal compound; and a second part comprising: a free- radical initiator comprising at least one of a peroxide initiator or a hydroperoxide initiator; a betadicarbonyl compound; and a non-reactive diluent, wherein at least one of the first part or the second part independently further comprises an impact modifier, wherein the first part has a first viscosity and the second part has a second viscosity, wherein the first viscosity and the second viscosity are each below 100 Pascal seconds when measured on a rheometer at a shear rate of 0.01 reciprocal second, and wherein the two-part adhesive composition comprises the impact modifier in a total amount in a range from 2 weight percent to 25 weight percent, based on the total weight of the two-part composition. In an eighteenth embodiment, the present disclosure provides the two-part adhesive composition of the fifteenth or sixteenth or seventeenth embodiment, wherein the impact modifier is a methylmethacrylate-butadiene- styrene core-shell toughening agent. In a nineteenth embodiment, the present disclosure provides the two-part adhesive composition of any one of the first to eighteenth embodiments, wherein the transition metal compound is a vanadium compound or a copper compound. In a twentieth embodiment, the present disclosure provides the two-part adhesive composition of any one of the first to nineteenth embodiments, wherein the beta-dicarbonyl compound comprises at least one of a substituted or unsubstituted barbituric acid, a dialkyl 2-acetylsuccinate diester having from 8 to 14 carbon atoms, or dimedone. In a twenty-first embodiment, the present disclosure provides the two-part adhesive composition of any one of the first to twentieth embodiments, wherein the first part further comprises a monofiinctional acrylate or methacrylate. In a twenty-second embodiment, the present disclosure provides the two-part adhesive composition of the twenty-first embodiment, wherein the monofiinctional acrylate comprises an aromatic or non-aromatic ring. In a twenty-third embodiment, the present disclosure provides the two-part adhesive composition of the twenty-first or twenty-second embodiment, wherein a ratio of the crosslinker to the monofiinctional acrylate or methacrylate is 1.1 : 1 to 1 : 1. 1. In a twenty-fourth embodiment, the present disclosure provides the two-part adhesive composition of any one of the first to twenty-third embodiments, wherein the first part further comprises a monomer comprising at least one of a phosphate, phosphonate, or silane functional group. In a twenty-fifth embodiment, the present disclosure provides the two-part adhesive composition of any one of the first to twenty-fourth embodiments, wherein the first part further comprises a free-radical inhibitor. In a twenty-sixth embodiment, the present disclosure provides the two-part adhesive composition of any one of the first to twenty-fifth embodiments, wherein at least one of the first part or the second part further comprises at least one of a dye or pigment.

[0100] In a twenty-seventh embodiment, the present disclosure provides a method of making a bonded article comprising a first substrate and a second substrate, the method comprising applying the first part and the second part of the two-part adhesive composition of any one of the first to twenty-sixth embodiments to at least one of the first substrate or the second substrate without premixing the first part and the second part, adhering the first substrate and the second substrate using the two-part adhesive composition, and allowing the adhesive to at least partially cure to make the bonded article. In a twentyeighth embodiment, the present disclosure provides the method of the twenty-seventh embodiment, wherein the applying comprises: applying the first part on at least a portion of a contact surface of the first substrate and applying the second part on at least a portion of a contact surface of the second substrate, and wherein the adhering comprises contacting the first part on the contact surface of the first substrate with the second part on the contact surface of the second substrate. In a twenty-ninth embodiment, the present disclosure provides the method of the twenty-seventh embodiment, wherein the applying step comprises: applying the first part and the second part successively on at least a portion of a contact surface of the first substrate to form an adhesive on the first substrate, and wherein the adhering step comprises contacting the adhesive on the contact surface of the first substrate with the second substrate. In a thirtieth embodiment, the present disclosure provides the method of any one of the twenty-seventh to twenty-ninth embodiments, wherein at least one of the first substrate or the second substrate comprises at least one of metal, glass, a polymer, or a composite. In a thirty-first embodiment, the present disclosure provides the method of any one of the twenty-seventh to thirtieth embodiments, wherein at least one of the first substrate or the second substrate comprises steel with an insulation coating. In a thirty-second embodiment, the present disclosure provides the method of the thirty-first embodiment, wherein the insulation coating has an organic component and an inorganic component. In a thirty-third embodiment, the present disclosure provides the method of the thirty-first or thirty-second embodiment, the method further comprising plasma treating or corona treating the insulation coating on the steel substrate. In a thirty-fourth embodiment, the present disclosure provides an article made by the method of any one of the twenty-seventh to thirty-third embodiments.

[0101] In a thirty-fifth embodiment, the present disclosure provides a method of making a bonded article comprising a first substrate and a second substrate, wherein at least one of the first substrate or the second substrate is a steel substrate having an insulation coating, the method comprising plasma treating or corona treating the insulation coating on the steel substate, applying an adhesive composition to at least one of the first substrate or the second substrate, adhering the first substrate and the second substrate using the adhesive, and allowing the adhesive to at least partially cure to make the bonded article.

[0102] Objects and advantages of this disclosure are further illustrated by the following non-limiting examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to unduly limit this disclosure.

[0103] EXAMPLES

[0104] Unless otherwise noted, all parts, percentages, ratios, etc. in the Examples and the rest of the specification are by weight. The following abbreviations are used in this section: in = inches, g = grams, kg = kilogram, lb = pound, kN = kilo Newtons, N = Newtons, Ibr = pound force, min = minutes, s = seconds, °C = degrees Celsius, °F = degrees Fahrenheit, Hz = hertz, J = Joules, ° = degree angle, cm = centimeters, mm = millimeters, psi = pounds per square inch, and rpm = revolutions per minute. Table 1 : Materials List

[0105] Te st Methods

[0106] Overlap Shear (OLS) Test The overlap shear strength testing of examples was conducted using either SPCC-SB cold rolled steel plates (available from Test Piece Co., Ltd., Kanagawa, Japan having dimensions 1.6 mm x 25 mm x 100 mm) or using non-grain oriented electrical steel with ASTM A976 Class C5 coating (part number 5236N2 containing an ASTM A976 C5 coating available from McMaster-Carr, Elmhurst, IL, and cut to dimensions of 0.005 in x 1 in x 4 in). The test coupons were wiped with isopropyl alcohol to remove grease and / or particle contaminant from the surface. The area of overlap between two plates was 25 mm x 12.5 mm in the case of SPCC-SB or 1 in x 0.5 in in the case of electrical steel with insulation coating. Approximately 40 mg of an Adhesive Precursor Composition - Part B (i.e., of the first part of a curable precursor of an adhesive composition) was dispersed on the surface of a first plate in the overlap area and then a thin layer of approximately 8 mg of Adhesive Precursor Composition - Part A (i.e., of the second part of a curable precursor of an adhesive composition) was coated on the surface of a second plate in the overlap area. The two regions of the plates with adhesive precursors on them were then brought into contact with each other so that the Part A composition was in contact with the Part B composition. Two binder clips were used to hold the two plates together. The adhesive precursor composition between the plates was allowed to cure for two to three days at room temperature, forming an overlap shear sample specimen. Overlap shear strength testing was conducted using a conventional tensile testing machine (Material Test Systems Insight Universal Test System model 820-030-EL / 0045, MTS Systems Corporation, Eden Prairie, MN) with a 6,744 lb (30 kN) load cell by mounting the opposed plate ends of the overlap shear sample specimen in the clamps of the tensile testing machines and then applying a shear force to the specimen via a clamp extension rate of 5 mm / min. The peak stress values (MPa) are reported as an average of three test specimens.

[0107] Rheological Test (Viscosity)

[0108] Testing was performed using a Discovery HR-30 rheometer (TA Instruments, New Castle, Delaware, US), operated using the TRIOS software. A 40-mm diameter parallel plate was used as the upper fixture. Temperature was controlled at 23 °C using a water-cooled Peltier plate as the lower measurement stage. Fluid was dispensed on the lower plate by pipette, and the gap between the plates was set to 0.325 mm. Excess fluid was trimmed from the edges of the plate and then the gap was set to 0.300 mm. Temperature was equilibrated for 2 minutes, followed by a pre-shearing at 10.0 1 / s for 30 seconds and 1 minute of equilibration. A flow sweep measurement was performed at shear rates of 0.01 1 / sec to 1000 1 / sec, sweeping logarithmically at 5 points per decade. At each shear rate, the flow was equilibrated for 10 seconds and then viscosity was averaged over the next 75 seconds before moving to the next higher shear rate.

[0109] General Mixing Procedure

[0110] In the following first part and second part preparations, mixing was carried out in a polypropylene mixing cup (from FlackTek, Inc., Landrum, SC, USA). The cup was closed with a polypropylene lid and the mixture was high shear mixed at ambient temperature and pressure using a SPEEDMIXER (Hauschild SpeedMixer inc., Dallas, Texas, USA). This mixing is referred to herein as being “speedmixed”. First Part Preparations

[0111] Preparation 1

[0112] VaAcAc (0.27 g), AP (0.46 g), BnMA (2.29 g), TOMAC (0.10 g), MEHQ (0.03 g), and 4-OH- TEMPO (0.01 g) were placed in a mixing cup and speedmixed at 3500 rpm for two minutes. TCDDMDA (11.14 g) was added to the mixing cup and the resultant mixture was speedmixed at 3500 rpm for two minutes. MBS-1 (5.51 g) was added to the mixing cup and the resultant mixture was speedmixed for several one-minute cycles at 3500 rpm, allowing the mixture to cool to room temperature between cycles.

[0113] Preparation 2.1 to 2.5

[0114] THEITA (6.88 g), TCDDMDA (4.09 g), and BnMA (0.57 g) were placed in a mixing cup and speedmixed at 3500 rpm for several two-minute cycles until the TCDDMDA was completely dissolved. IBOMA (8.02 g) was added to the mixing cup and the resultant mixture was speedmixed at 3500 rpm for two minutes. AO (0.05 g) and silica, for Preparations 2. 1 to 2.4, were added to the mixing cup and the resultant mixture was speedmixed for several one-minute cycles at 3500 rpm. The amount of silica used in Preparations 2.1 to 2.5 were 0.44 g, 0.33 g, 0.22 g, 0.11 g, and 0 g, respectively.

[0115] Preparation 1 (1.00 g) was mixed with Preparations 2.1 to 2.5 in the amounts provided in Table 2, below. The preparations were placed in a mixing cup and speedmixed at 3500 rpm for several one-minute cycles to provide FP 1 to FP 5.

[0116] Table 2.

[0117] Second Part Preparation

[0118] DMAS (2.50 g), DEGMBEA (21.12 g), and silica (for SP 1 to SP 3) were placed in a mixing cup and speedmixed at 3500 rpm for several one-minute cycles. CHP (1.38 g) was added to the mixing cup and the resultant mixture was speedmixed at 2000 rpm for one minute. The amount of silica used in Preparations SP 1 to SP 4 were 1.77 g, 0.88 g, 0.44 g, 0 g, respectively.

[0119] Small drops of the first and second parts were combined without mixing. The various combinations were then visually observed. In Table 3, below, poor co-diffusion indicated that the separate first and second parts were visible for extended time periods before curing. “Not as poor” combinations exhibited slightly improved co-diffusion relative to the poor combinations. In combinations referred to as “good” or “best”, there was little or no ability, respectively, to observe the separate parts. Table 3.

[0120] Viscosities of FP 1 to FP 5 and SP 1 to SP 4 were measured using the test method described above. The results are shown in Table 4, below. The viscosities are reported in Pa-s.

[0121] Table 4. Viscosity of FP 1 to FP 5 and SP 1 to SP 4

[0122] *Value measured was below the detection limit of the rheometer.

[0123] FTIR (Nicolet IR iS50 spectrometer from Nicolet Thermo Fisher Scientific Inc., Waltham, MA, USA) was used to quantify differences in curing rate and efficiency for two-part formulations of varying viscosities. 30 mg of FP 1 was placed on a glass slide (25 mm x 75 mm, precleaned microscope slide from Fisher Scientific, Pittsburgh, PA), and 6 mg of SP 4 was placed on a glass cover slip (22 mm x 22 mm microscope cover glass from Fisher Scientific, Pittsburgh, PA). The glass slide and cover slip were joined together to combine the formulations without mixing to simulate contact bonding. The bonded sample was immediately placed in the FTIR chamber, and the conversion of acrylic monomers was followed for 20 minutes by measuring the disappearance of the acrylate / methacrylate absorbance overtone peak measured from 6145-6185 cm-1. This disappearance was translated into a % conversion value. The monomer conversion at 20 minutes was about 20%. When SP 2 and FP 4 were combined in a similar experiment, the monomer conversion at 20 minutes was about 75%. First Part 6 (FP 6), 15% MBS

[0124] VaAcAc (0.04 g), phosphate (0.40 g), and MEHQ (0.04 g) were placed in a mixing cup and speedmixed at 3500 rpm for two minutes. DCPM (11.16 g) and THFMA (5.00 g) were added to the mixing cup and the resultant mixture was speedmixed at 3500 rpm for two minutes. MBS-2 (6.00 g) was added to the mixing cup in three separate batches and the mixture was speedmixed several one-minute cycles at 3500 rpm after each batch addition, allowing the mixture to cool to room temperature after each round of mixing. Once the MBS-2 appeared to be fully dissolved in the mixture, THFMA (6.16 g), THEITA (11.16 g), and TOMAC (0.04 g) were added to the mixing cup and the resultant mixture was speedmixed for several one- minute cycles at 3500 rpm until the THEITA was completely dissolved.

[0125] First Part 7 (FP 7), 0% MBS

[0126] VaAcAc (0.04 g), phosphate (0.40 g), and MEHQ (0.04 g) were placed in a mixing cup and speedmixed at 3500 rpm for two minutes. DCPM (13.16 g) and THFMA (7.00 g) were added to the mixing cup and the resultant mixture was speedmixed at 3500 rpm for two minutes. THFMA (6.16 g), THEITA (13.16 g), and TOMAC (0.04 g) were added to the mixing cup and the resultant mixture was speedmixed for several one-minute cycles at 3500 rpm until the THEITA was completely dissolved.

[0127] First Part 8 (FP 8), 5% MBS

[0128] A mixture of FP 7 (4.0 g) and FP 6 (2.0 g) were placed in a mixing cup and speedmixed at 3500 rpm for two minutes.

[0129] First Part 9 (FP 9), 10% MBS

[0130] A mixture of FP 7 (2.0 g) and FP 6 (4.0 g) were placed in a mixing cup and speedmixed at 3500 rpm for two minutes.

[0131] Second Part 5 (SP 5), 30% MBS

[0132] DMAS (1.00 g), DEGMBEA (5.00 g), and MBS-2 (3.00 g) were placed in a mixing cup and speedmixed at 3500 rpm for two minutes. CHP (1.00 g) was added, and the resultant mixture was speedmixed at 2000 rpm for two minutes.

[0133] Second Part 6 (SP 6), 0% MBS

[0134] DMAS (1.00 g) and DEGMBEA (8.00 g) were placed in a mixing cup and speedmixed at 3500 rpm for two minutes. CHP (1.00 g) was added, and the resultant mixture was speedmixed at 2000 rpm for two minutes. Second Part 7 (SP 7), 10% MBS

[0135] A mixture of SP 6 (4.0 g) and SP 5 (2.0 g) were placed in a mixing cup and speedmixed at 2000 rpm for one minute.

[0136] Second Part 8 (SP 8), 20% MBS

[0137] A mixture of SP 6 (2.0 g) and SP 5 (4.0 g) were placed in a mixing cup and speedmixed at 2000 rpm for one minute.

[0138] Small drops of the first and second parts were combined without mixing. The various combinations were then visually observed. In Table 5, below, co-diffusion was rated on a scale of 1 to 4, with 1 being worst and 4 being best.

[0139] Table 5.

[0140] Viscosities of FP 6 to FP 9 and SP 5 to SP 8 were measured using the test method described above. The results are shown in Table 6, below. The viscosities are reported in Pa-s.

[0141] Table 6.

[0142] First Parts and Second Parts were mixed in a 5: 1 ratio. Overlap Shear evaluations on cold rolled steel were carried out according to the test method described above. The results are given in Table 7, below. Table 7.

[0143] The First Parts and Second Parts were mixed in a 5: 1 ratio. Overlap Shear evaluations on e-steel were carried out according to the test method described above. The area under the stress v strain curve was integrated to give average toughness. E-steel substrates were then first plasma treated by a Plasmatreat FG5001, “OPENAIR PLASMA” generator and an RD1004 rotary jet using the conditions of a 5-millimeter height, a speed of 5 meters per minute, a voltage of 284 volts, and a current of 7.5 ampules. Overlap Shear evaluations were carried out using the test method described above. The results are shown in Table 8, below.

[0144] Table 8.

[0145] Second Parts 9 to 13 The second parts shown in Table 9, below, were prepared by combining the appropriate amounts of TTD amine and silica in a 10-gram DAC mixing cup and speedmixing at 2000 rpms for 1 minute. Table 9.

[0146] Co-diffusion was tested through combination of the epoxy materials with the amine formulations and visual inspection of results. Specifically, approximately 50 mg of each epoxy was added via pipette to approximately 100 mg of each of SP 9 to SP 13 without physical / mechanical mixing of the two. Each cell in the chart below qualitatively describes how effectively co-diffusion had taken place at 5 minutes after combination. The ratings as described in Table 3, above, are used in Table 10, below.

[0147] Table 10.

[0148] The preceding description, given in order to enable one of ordinary skill in the art to practice the claimed disclosure, is not to be construed as limiting the scope of the disclosure, which is defined by the claims and all equivalents thereto.

Claims

What is claimed is:

1. A two-part adhesive composition comprising: a first part comprising a crosslinker; and a second part comprising a curing component for the crosslinker, wherein at least one of the first part or the second part independently further comprise a rheology modifier, wherein the first part has a first viscosity and the second part has a second viscosity, wherein the first viscosity and the second viscosity are each not more than 100 Pascal seconds when measured on a rheometer at a shear rate of 0.01 reciprocal second, and wherein a ratio of the first viscosity to the second viscosity is in a range from 5: 1 to 1:5 when measured on a rheometer at one or more shear rates of less than one reciprocal second.

2. The two-part adhesive composition of claim 1, wherein the crosslinker is an acrylate, a methacrylate, an epoxide, or a combination thereof.

3. The two-part adhesive composition of claim 1 or 2, wherein the crosslinker has at least two acrylate functional groups, methacrylate functional groups, or a combination thereof.

4. The two-part adhesive composition of any one of claims 1 to 3, wherein the first part further comprises a monofunctional monomer.

5. The two-part adhesive composition of any one of claims 1 to 4, wherein the second part further comprises a non-reactive diluent.

6. The two-part adhesive composition of any one of claims 1 to 5, wherein the curing component comprises a free-radical initiator comprising at least one of a peroxide initiator or a hydroperoxide initiator.

7. The two-part adhesive composition of any one of claims 1 to 6, wherein curing component is a component of a redox initiating system.

8. The two-part adhesive composition of any one of claims 1 to 7, wherein either the first part comprises a transition metal compound and a quaternary ammonium salt, and the second part comprises a beta-dicarbonyl compound as the curing component; or the first part comprises the beta-dicarbonyl compound and the second part comprises the transition metal compound and the quaternary ammonium salt as the curing component.

9. The two-part adhesive composition of any one of claims 1 to 8, wherein the rheology modifier independently comprises at least one of an impact modifier, a filler, or a thixotropic agent.

10. A two-part adhesive composition comprising: a first part comprising: a crosslinker having two or more acrylate groups, methacrylate groups, or a combination thereof; and a transition metal compound; and a second part comprising: a free-radical initiator comprising at least one of a peroxide initiator or a hydroperoxide initiator; a beta-dicarbonyl compound; and a non-reactive diluent, wherein at least one of the first part or the second part independently further comprises an impact modifier, wherein the first part has a first viscosity and the second part has a second viscosity, wherein the first viscosity and the second viscosity are each below 100 Pascal seconds when measured on a rheometer at a shear rate of 0.01 reciprocal second, and wherein the two-part adhesive composition comprises the impact modifier in a total amount in a range from 2 weight percent to 25 weight percent, based on the total weight of the two-part composition.

11. The two-part adhesive composition of claim 10, wherein the first part further comprises a quaternary ammonium salt.

12. The two-part adhesive composition of any one of claims 8 to 11, wherein the transition metal compound is a vanadium compound or a copper compound, and wherein the beta-dicarbonyl compound comprises at least one of a substituted or unsubstituted barbituric acid, a dialkyl 2-acetylsuccinate diester having from 8 to 14 carbon atoms, or dimedone.

13. The two-part adhesive composition of any one of claims 1 to 12, wherein the first part further comprises a monofiinctional acrylate or methacrylate.

14. The two-part adhesive composition of any one of claims 1 to 13, wherein the first part further comprises a monomer comprising at least one of a phosphate, phosphonate, or silane functional group.

15. A method of making a bonded article comprising a first substrate and a second substrate, the method comprising:applying the first part and the second part of the two-part adhesive composition of any one of claims 1 to 14 onto at least one of the first substrate or the second substrate without premixing the first part and the second part; adhering the first substrate and the second substrate using the two-part adhesive composition; and allowing the two-part adhesive composition to at least partially cure to make the bonded article.

16. The method of claim 15, wherein at least one of the first substrate or the second substrate comprises steel with an insulation coating, wherein the insulation coating has an organic component and an inorganic component, the method further comprising at least one of plasma treating or corona treating the insulation coating on the steel substrate.

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