BACKGROUND

Field

[0001] The present invention relates to (meth)acrylate-based polymerizable compositions and adhesive systems prepared therefrom, which include an organoborane component. The inventive compositions and adhesive systems are particularly well suited for bonding applications, which involve at least one low energy bonding surface, for example, polyolefin surfaces, such as polyethylene and polypropylene.

Brief Description of Related Technology

[0002] Low energy surfaces such as polyolefins, e.g., polyethylene, polypropylene, polybutene, polyisoprene, and copolymers thereof, are well known to be difficult to bond to each other and to other surfaces using adhesive bonding technology since they have few active bonding sites available at the free surfaces. Low energy surfaces typically have surface energy values of less than 45 mJ/m ² , more typically less than 40 mJ/m ² , such as less than 35 mJ/m ² . Bonding low energy surfaces by surface pre-treatments such as flame treatments, plasma treatments, oxidation, sputter etching, corona discharge, or primer treatments with a high surface energy material is well known. Such treatments disrupt the bonds at the surface of the low energy material providing sites which are reactive and which can participate in bonding reactions with adhesive materials. However, such surface pre-treatments are usually undesirable, in that they add cost to the process, they are not particularly reproducible in their results, and the effect of the pre-treatments wears off with time so the pre- treated surfaces must be re-pre-treated if they are not bonded within a reasonable period of time.

[0003] The chemistry of organic boron compounds has been studied in detail

[see e.g. D. Barton and W. D. Olliis, "Comprehensive Organic Chemistry", Vol. 3, Part 14, Pergamon Press (1979) and H. C. Brown, Boranes in Organic Chemistry, Cornell University Press, Ithaca, N.Y. (1972)]. The use of organoboranes such as trialkylboranes including triethylborane and tributylborane for initiating and catalyzing the polymerization of vinyl monomers is well known. However, such organoborane compounds are known to be flammable in air so that the compounds and compositions containing them require special handling and the compositions have poor shelf stability [see e.g. U.S. Patent No. 3,236,823 (Jennes), and the Background section of U.S. Patent No. 5,935,711 (Pocius), at col. 2]

[0004] Certain alkylborane compounds and their use as initiators of polymerization are described in U.S. Patent Nos. 4,515,724, 4,638,092, 4,638,498, 4,676,858 and 4,921 ,921 , each to Ritter.

[0005] U.S. Patent Nos. 5,106,928, 5,143,884, 5,286,821 , 5,310,835 and

5,376,746, each disclose a two-part initiator system for acrylic adhesive compositions, in which the first part includes a reportedly stable organoborane amine complex and the second part includes a destabilizer or activator such as an organic acid or an aldehyde.

[0006] Japanese Patent Publication No. S48-18928 describes a method for adhering polyolefin or vinyl polymers using an adhesive obtained by adding trialkylboron to a vinyl monomer, with or without vinyl polymer. Examples of trialkylboron include triisopropylboron, tri-n-butylboron, tripropylboron and tri-tert- butylboron.

[0007] U.S. Patent No. 3,275,611 (Mottus) describes a process for polymerizing unsaturated monomers with a catalyst comprising an organoboron compound, a peroxygen compound and an amine complexing agent for the boron compound.

[0008] It is well known that the bonding of polyolefin substrates and other low surface energy substrates causes particular difficulties. Attempts have been made to overcome these difficulties by the extensive and expensive substrate surface preparation described above, or by priming the surface with a high surface energy primer. However, it is desired to develop adhesive compositions, which will bond low surface energy substrates without such surface preparation.

[0009] U.S. Patent No. 5,539,070 (Zharov), and U.S. Patent Nos. 5,616,796,

5,621 ,143, 5,681 ,910, 5,684,102, 5,686,544, 5,718,977, 5,795,657 and the '71 1 patent describe organoborane amine complexes which can be used in systems that initiate the polymerization of acrylic monomers in compositions useful for bonding low surface energy plastics substrates such as polyethylene, polypropylene and polytetrafluoroethylene.

[0010] International Patent Publication No. WO 01/4431 1 also describes amine organoborane complex polymerization initiators in bonding compositions for low surface energy substrates. [0011] Tetraorganylborate salts of tetraalkylammonium, sodium or lithium are known as photoinitiators in photocurable compositions for imaging materials (see e.g. U.S. Patent Nos. 4,950,581 , 6,10,987 and 6,171 ,700). Tetraorganylborate salts do not however have a boron-hydrogen bond. The distinction between boron-hydrogen compounds, triorganylboranes and organoborate salts is well illustrated in D. Barton and W. D. Ollis, "Comprehensive Organic Chemistry", to which Chapters 14.2, 14.3 and 14.4 of Vol. 3 are devoted.

[0012] More recently, Loctite (R&D) Ltd. has designed and developed technology that is described in International Patent Publication Nos. WO 02/34851 , WO 02/34582 and WO 2003/089536 relating generally to polymerizable adhesive compositions with a free radically polymerizable component and an initiator system of an alkyl borohydride with either a metal or ammonium cation. These compositions also describe the use of aziridine components.

[0013] Henkel Corporation together with Loctite (R&D) Ltd. have designed and developed technology, which include a carrier to such polymerizable adhesive compositions so that the compositions have a flash point above 140 °F. See International Patent Publication No. WO 03/035703.

[0014] The use of aziridines generally however are under regulatory scrutiny, and thus labelling requirements are imposed, which may be an impediment to wide spread usage.

[0015] U.S. Patent Publication No. 2008/0090981 is directed to and claims the use of chlorosulfonated polyolefins and/or chlorinated polyolefins in combination with organosulfonyl halides in two-part organoborane:amine cured polymerisable compositions which accelerate cure speeds. However, non-chlorinated polyethylene and other common copolymers used as tougheners are not disclosed for use with organosulfonyl halides.

[0016] Despite the work of many in this general field of bonding low energy surfaces, there is a need for polymerizable compositions for bonding low surface energy substrates, such as polyolefins, and for end users to have a variety of such compositions which achieve that result through different technical strategies.

SUMMARY

[0017] In one aspect, the present invention provides a one-part photocurable composition comprising: (a) a (meth)acrylate component; (b) a Norrish type II photoinitiator; and

(c) an borane-amine component.

[0018] Suitably, borane-amine component is an organoborane.

[0019] The borane-amine component may be present in an amount of from about 1 wt% to about 15 wt% based on the total weight of the composition. For example an organoborane-amine component may be present in an amount of from about 1 wt% to about 15 wt% based on the total weight of the composition.

[0020] The borane-amine component may comprise a borane of the formula:

where independently each R is a hydrogen, a C1-C12 aliphatic, a C5-C20 aromatic group, or two or more of R may combine to form a ring structure.

[0021] Suitably, the borane-amine component comprises an organoborane of the formula:

where independently each R is a C1-C12 aliphatic, a C5-C20 aromatic group, or two or more of R may combine to form a ring structure, where each R is optionally substituted with one or more of C1-C3 alkyl or C1-C3 alkoxy, and where each R is optionally substituted with one or more hetereoatoms selected from S, N, O and P. Suitably, each R is optionally substituted with one or more heteroatoms selected from S or O.

[0022] For example, each R may independently be a C1-C12 alkyl or C1-C12 alkoxy optionally substituted with one or more heteroatoms selected from S, N, O and P.

[0023] The borane-amine component may comprise an organoborane such as a trialkyl organoborane.

[0024] The borane-amine component may comprises an amine of the formula:

where independently each R ¹ is hydrogen, a C1-C12 aliphatic, a C5-C20 aromatic group, or two or more of R ¹ may combine to form a ring structure. [0025] For example, each R ¹ may be a C1-C12 alkyl or C1-C12 alkoxy optionally substituted with one or more heteroatoms selected from S, N, O and P.

[0026] Suitably, the borane-amine component is an organoborane-amine component and is selected from triethylborane-1 ,3-diaminopropane, tributylborane-3- methoxypropylamine, and triethylborane diethylenetriamine.

[0027] The methacrylate component may be a (meth)acrylate monomer having the formula:

H ₂ C=CGC0 ₂ R ¹ ,

where G may be hydrogen, halogen or alkyl groups having from 1 to about 4 carbon atoms, and R ¹ may be selected from alkyl, cycloalkyl, alkenyl, cycloalkenyl, alkaryl, aralkyl or aryl groups having from 1 to about 16 carbon atoms, any of which may be optionally substituted or interrupted as the case may be with silane, silicon, oxygen, halogen, carbonyl, hydroxyl, ester, carboxylic acid, urea, urethane, polyurethane, carbonate, amine, amide, sulfur, sulfonate, and sulfone.

[0028] Suitably, the type II photoinitiator is selected from benzophenone, chlorobenzophenone, methyl-benzophenone, dimethylamino benzopheone, 4,4’- bis(dimethylamino)benzophenone, 5-dibenzosuberenone, xanthone, benzil, anthraquinone, 2-(hydroxymethyl)anthraquinone, 2-methylanthraquinone, and coumarin.

[0029] The one-part photocurable composition may further comprise a toughener. The toughener may for example be selected from styrene-isoprene-styrene (SIS), styrene-butadiene-styrene (SBS), styrene-isobutylene styrene (SIBS), styrene-b- ethylene/butylene-b-styrene (SEBS), and/or styrene-b-ethylene/propylene-b-styrene (SEPS). The toughener may be present in an amount of from about 1 wt% to about 20 wt% based on the total weight of the composition.

[0030] In one aspect, the one-part photocurable composition comprises:

(a) a (meth)acrylate component;

(b) a Norrish type II photoinitiator; and

(c) a borane-amine component; wherein the borane-amine component is an orgnoborane-amine component and is present in an amount of from about 2 wt% to about 8 wt% based on the total weight of the composition; wherein the orgnoborane-amine component comprises a trialkyl borane and an amine of the formula:

where independently each R ¹ is hydrogen, a C1-C12 aliphatic, a C5-C20 aromatic group, or two or more of R ¹ may combine to form a ring structure; and wherein the type II photoinitiator is selected from the group consisting of

benzophenone, chlorobenzophenone, methyl-benzophenone, dimethylamino benzopheone, 4,4’-bis(dimethylamino)benzophenone, 5-dibenzosuberenone, xanthone, benzil, anthraquinone, 2-(hydroxymethyl)anthraquinone, 2- methylanthraquinone, and coumarin.

[0031] Also provided herein is a method of bonding together two substrates comprising the steps of applying the photocurable one-part composition according to any preceding claim to at least one of the substrates, mating together the substrates and exposing the photocurable composition to radiation in the electromagnetic spectrum having a wavelength in the range of from 200 nm to 700 nm (full UVA/is range) more preferably 200 nm to 400 nm (UV range) for a time sufficient to effect cure of the composition. For example, the photocurable composition may be exposed to radiation in the electromagnetic spectrum having a wavelength in the range of from 200 nm to 700 nm, more preferably 200 nm to 400 nm from a light source which is within 1 metre thereof, for example within 30 cm thereof. The duration of the exposure may be from about 0.1 seconds to about 360 minutes, such as from about 0.5 seconds to about

180 minutes, for example from about 0.5 seconds to about 30 minutes, including from about 1 second to about 15 minutes, suitably, for a time period of less than about 240 seconds.

[0032] Suitably, one or both substrates are plastic or glass substrates. For example one or both substrates may be a polyolefin, such as polypropylene, polyethylene, polybutylene, polyisoprene, polymethylpentene and copolymers thereof. Suitably, at least one of the substrates is transmissive to UV radiation. One or more of the substrates may be transparent.

[0033] Advantageously, the compositions of the present invention are particularly useful for bonding low energy surfaces such as polyolefins. DETAILED DESCRIPTION

(Meth)Acrylate Monomer Component

[0034] The (meth)acrylate monomer component may comprise at least one

(meth)acrylate ester selected from beta-carboxy ethyl acrylate, isobornyl acrylate, n- octyl acrylate, n-decyl acrylate, cyclohexyl acrylate, tetrahydrofurfuryl acrylate, 2- ethylhexyl acrylate, ethoxyethoxyethyl acrylate, ethoxylated phenyl monoacrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, isooctyl acrylate, n-butyl acrylate, neopentyl glycol diacrylate, ethylene glycol diacrylate, diethylene glycol diacrylate, dipropylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, 1 ,6-hexane diol diacrylate, tripropylene glycol diacrylate, glycerol triacrylate, trimethylol propane diacrylate, trimethylol propane triacrylate, pentaerythritol tetraacrylate, phenoxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, cyclohexyl methacrylate, glycerol mono- methacrylate, glycerol 1 ,3-dimethacrylate, trimethyl cyclohexyl methacrylate, methyl triglycol methacrylate, isobornyl methacrylate trimethylolpropane trimethacrylate, neopentyl glycol dimethacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, 1 ,6-hexanediol dimethacrylate, hydroxybutyl methacrylate, tetrahydrofurfuryl methacrylate, cyclohexyl methacrylate, phenoxyethyl methacrylate, and poly(ethylene glycol) methacrylate. [0035] Suitably, the (meth)acrylate monomer component comprises at least one

(meth)acrylate component selected from isobornyl acrylate, tetrahydrofurfuryl acrylate, 2-carboxyethyl acrylate, di(ethylene glycol) ethyl ether acrylate and a diacrylate ester.

[0036] One or more suitable (meth)acrylates may be chosen from among polyfunctional (meth)acrylates, such as, but not limited to, di-or tri-functional (meth)acrylates like polyethylene glycol di(meth)acrylates, tetrahydrofuran

(meth)acrylates and di(meth)acrylates, hydroxypropyl (meth)acrylate (“HPMA”), hexanediol di(meth)acrylate, trimethylol propane tri(meth)acrylate (“TMPTMA”), diethylene glycol dimethacrylate, triethylene glycol dimethacrylate (“TRIEGMA”), tetraethylene glycol dimethacrylate, dipropylene glycol dimethacrylate, di- (pentamethylene glycol) dimethacrylate, tetraethylene diglycol diacrylate, diglycerol tetramethacrylate, tetramethylene dimethacrylate, ethylene dimethacrylate, neopentyl glycol diacrylate, trimethylol propane triacrylate and bisphenol-A mono and di(meth)acrylates, such as ethoxylated bisphenol-A (meth)acrylate ("EBIPMA"), and bisphenol-F mono and di(meth)acrylates, such as ethoxylated bisphenol-F (meth)acrylate.

[0037] For example the anaerobically curable component may include

Bisphenol A dimethacrylate:

[0038] Still other (meth)acrylates that may be suitable for use herein are silicone (meth)acrylate moieties ("SiMA"), such as those taught by and claimed in U.S. Patent No. 5,605,999 (Chu), the disclosure of which is hereby expressly incorporated herein by reference. [0039] Other suitable materials may be chosen from polyacrylate esters represented by the formula: where R ⁴ is a radical selected from hydrogen, halogen or alkyl of from 1 to about 4 carbon atoms; q is an integer equal to at least 1 , and preferably equal to from 1 to about 4; and X is an organic radical containing at least two carbon atoms and having a total bonding capacity of q plus 1. With regard to the upper limit for the number of carbon atoms in X, workable monomers exist at essentially any value. As a practical matter, however, a general upper limit is about 50 carbon atoms, such as desirably about 30, and desirably about 20. [0040] For example, X can be an organic radical of the formula: o o

— Y , ¹ — OC ¹¹ ZC ¹¹ — OY^ where each of Y ¹ and Y ² is an organic radical, such as a hydrocarbon group, containing at least 2 carbon atoms, and desirably from 2 to about 10 carbon atoms, and Z is an organic radical, preferably a hydrocarbon group, containing at least 1 carbon atom, and preferably from 2 to about 10 carbon atoms. Other materials may be chosen from the reaction products of di- or tri-alkylolamines (e.g., ethanolamines or propanolamines) with acrylic acids, such as are disclosed in French Pat. No. 1 ,581 ,361.

[0041] Suitable oligomers with (meth)acrylate functionality may also be used. Examples of such (meth)acrylate-functionalized oligomers include those having the following general formula:

where R ⁵ represents a radical selected from hydrogen, alkyl of from 1 to about 4 carbon atoms, hydroxy alkyl of from 1 to about 4 carbon atoms, or where R ⁴ is a radical selected from hydrogen, halogen, or alkyl of from 1 to about 4 carbon atoms; R ⁶ is a radical selected from hydrogen, hydroxyl, or m is an integer equal to at least 1 , e.g., from 1 to about 15 or higher, and desirably from 1 to about 8; n is an integer equal to at least 1 , e.g., 1 to about 40 or more, and desirably between about 2 and about 10; and p is 0 or 1.

[0042] Typical examples of acrylic ester oligomers corresponding to the above general formula include di-, tri- and tetraethyleneglycol dimethacrylate; di(pentamethyleneglycol)dimethacrylate; tetraethyleneglycol diacrylate; tetraethyleneglycol di(chloroacrylate); diglycerol diacrylate; diglycerol tetramethacrylate; butyleneglycol dimethacrylate; neopentylglycol diacrylate; and trimethylolpropane triacrylate. [0043] While di- and other polyacrylate esters, and particularly the polyacrylate esters described in the preceding paragraphs, can be desirable, monofunctional acrylate esters (esters containing one acrylate group) also may be used.

[0044] Suitable compounds can be chosen from among are cyclohexylmethacrylate, tetrahydrofurfuryl methacrylate, hydroxyethyl acrylate, hydroxypropyl methacrylate, t-butylaminoethyl methacrylate, cyanoethylacrylate, and chloroethyl methacrylate.

[0045] Another useful class of materials are the reaction product of

(meth)acrylate-functionalized, hydroxyl- or amino-containing materials and polyisocyanate in suitable proportions so as to convert all of the isocyanate groups to urethane or ureido groups, respectively.

[0046] The so-formed (meth)acrylate urethane or urea esters may contain hydroxy or amino functional groups on the non-acrylate portion thereof. (Meth)acrylate esters suitable for use may be chosen from among those of the formula where X is selected from --0-- and where R ⁹ is selected from hydrogen or lower alkyl of 1 through 7 carbon atoms; R ⁷ is selected from hydrogen, halogen (such as chlorine) or alkyl (such as methyl and ethyl radicals); and R ⁸ is a divalent organic radical selected from alkylene of 1 through 8 carbon atoms, phenylene and naphthylene.

[0047] These groups upon proper reaction with a polyisocyanate, yield a monomer of the following general formula: where n is an integer from 2 to about 6; B is a polyvalent organic radical selected from alkyl, alkenyl, cycloalkyl, cycloalkenyl, aryl, alkaryl, alkaryl and heterocyclic radicals both substituted and unsubstituted, and combinations thereof; and R ⁷ , R ⁸ and X have the meanings given above. [0048] Depending on the nature of B, these (meth)acrylate esters with urea or urethane linkages may have molecular weights placing them in the oligomer class (such as about 1 ,000 g/mol up to about 5,000 g/mol) or in the polymer class (such as about greater than 5,000 g/mol).

[0049] Other unsaturated reactive monomers and oligomers such as styrenes, maleimides, vinyl ethers, allyls, allyl ethers and those mentioned in US6844080B1 (Kneafsey et al.) can be used. Vinyl resins as mentioned in US6433091 (Xia) can also be used. Methacrylate or acrylate monomers containing these unsaturated reactive groups can also be used.

[0050] Of course, combinations of these (meth)acrylates and other monomers may also be used.

[0051] Desirably the anaerobically curable component comprises at least one acrylate or methacrylate ester group.

[0052] Desirably the anaerobically curable component comprises is chosen from at least one of epoxy (meth)acrylates, urethane (meth)acrylates, urethane di(meth)acrylates, alkyl (meth)acrylates, stearyl (meth)acrylates, isocyanurate (meth)acrylates, bisphenol-A-(meth)acrylates, ethoxylated bisphenol-A-(meth)acrylates, bisphenol-F-(meth)acrylates, ethoxylated bisphenol-F-(meth)acrylates, bisphenol-A di(meth)acrylates, ethoxylated bisphenol-A-di(meth)acrylates, bisphenol-F- di(meth)acrylates, and ethoxylated bisphenol-F-di(meth)acrylates. [0053] The (meth)acrylate monomer component may be present in an amount of from about 10 wt% to about 80 wt% based on the total amount of photocurable compostion, suitably, the (meth)acrylate monomer component is present in an amount of from about 20 wt% to about about 55 wt%, desirably from about 25 wt% to about 50 wt%, such as from about 30 wt% to about 45 wt% based on the total weight of photocurable acrylate composition.

Borane-amine component [0054] The borane-amine component may be present in an amount of from about 1 wt% to about 15 wt% based on the total weight of the composition. For example, the borane-amine component may be present in an amount of from about 2 wt% to about 8 wt%, such as from about 3 wt% to about 6 wt% based on the total weight of the composition. Suitably, the borane-amine component is an organoborane- amine component which is present in an amount of from about 2 wt% to about 8 wt%.

[0055] As outlined above, the borane-amine component may comprise an organoborane of the formula:

where independently each R is a C1-C12 aliphatic, a C5-C20 aromatic group, or two or more of R may combine to form a ring structure, and where each R is optionally substituted with one or more heteroatoms selected from S, N, O and P.

[0056] Suitably, R may be C1-C12 alkyl. For example, each R may be independently selected from methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl and isomers thereof.

[0057] The borane-amine component may comprise an amine of the formula:

where independently each R ¹ is hydrogen, a C1-C12 aliphatic, a C5-C20 aromatic group, or two or more of R ¹ may combine to form a ring structure. [0058] Suitably, one or more or each R ¹ is a C1-C12 alkyl optionally substituted with a C1-C6 alkyl or a C1-C6 alkoxy. For example each R ¹ may be independently selected from methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl and isomers thereof.

[0059] The borane-amine component may be an organoborane amine complex of the formula: where each R is C ₁ -C ₁₀ alkyl or phenyl, each R may optionally be substituted with one or more C ₁ -C ₃ alkyl or C ₁ -C ₆ alkoxy, and each R may optionally be substituted with one or more heteroatoms selected from O, S and N, each R ¹ is hydrogen, or C ₁ -C ₁₀ alkyl which may optionally be substituted with one or more C ₁ -C ₃ alkyl or C ₁ -C ₆ alkoxy, or each R ¹ may be

where each R ² is hydrogen or C1-C10 alkyl, m is 2 to 10 and n is 1 to 6.

[0060] The alkyl groups mentioned throughout may be straight chained or branch chained.

[0061] Suitably, the R ¹ or R ² groups will be hydrogen or C ₁ -C ₄ alkyl, m will be 2 or 3 and n will be 1 or 2. [0062] For example, the amine of the borane-amine component may be propylamine, dipropylamine, 2-methoxypropylamine, 3-methoxypropylamine, 1 ,3- diaminopropane, ethylamine, diethylamine, 2-methoxyethylamine, butylamine, dibutylamine, 4-methoxybutylamine, n-octylamine, 1 ,6-diaminohexane, diethylenetriamine, dipropylene diamine, ammonia, and 1 ,2-diaminopropane. [0063] Preferred borane-amine components include tri-n-butylborane-3- methoxypropylamine complex, triethylborane-1 ,3-diaminopropane complex or combinations thereof. [0064] Suitably, the borane-amine component may comprise an organoborane selected from tri-n-octylborane, tridodecylborane, triethylborane, tri-n-butylborane and tri-secbutylborane; and the amine component may be selected from 1 ,3- propanediamine, 1 ,6-hexanediamine, methoxypropylamine, diethylenetriamine, isophorone diamine, aminomethyltrimethoxysilane, 3-aminopropyl trimethoxysilane, aminomethyltriethoxysilane, 3-aminopropyltriethoxysilane, 2-

(trimethoxysilylethyl)pyridine, aminopropylsilanetriol, 3-(m- aminophenoxy)propyltrimethoxysilane, 3-aminopropyldiisopropylmethoxysilane, aminophenyltrimethoxysilane, 3-aminopropyltris(methoxy ethoxy)silane, N-(2- aminoethyl)aminomethyltrimethoxysilane, N-(2-aminoethyl)-3- aminopropyltrimethoxysilane, N-(6-aminohexyl)aminomethyltrimethoxysilane,

N-(2-aminoethyl)-11 -aminoundecyltrimethoxysilane,

(aminoethylaminomethyl)phenethyltrimethoxysilane, N-(2-aminoethyl)-3- aminopropylmethyldimethoxysilane,

N-(2-aminoethyl)-3-aminoisobutylmethyldimethoxysilane.

Photoinitiator

[0065] A free radical photoinitiator initiates the polymerization of monomers when exposed to actinic radiation by the formation of a free radical. Photoinitiators are frequently used in UV-curable compositions, such as in photocurable adhesives or in UV-curable inkjet inks.

[0066] Two types of free radical photoinitiators can be distinguished. A Norrish

Type I initiator is an initiator which cleaves after excitation, yielding the initiating radical immediately. A Norrish Type ll-initiator is a photoinitiator which is activated by actinic radiation and forms free radicals by hydrogen abstraction from a second compound that becomes the actual initiating free radical. This second compound is called a co initiator or polymerization synergist.

[0067] Examples of suitable Norrish Type II photoinitiators are aromatic ketones such as benzophenone, xanthone, derivatives of benzophenone (e.g. chlorobenzophenone), blends of benzophenone and benzophenone derivatives (e.g. Photocure 81 , a 50/50 blend of 4-methyl-benzophenone and benzophenone), Michler's

Ketone, Ethyl Michler's Ketone, thioxanthone and other xanthone derivatives like Quantacure ITX (isopropyl thioxanthone), 5-dibenzosuberenone, benzil, anthraquinones (e.g. 2-ethyl anthraquinone), coumarin, and the like. Chemical derivatives and combinations thereof may also be used.

[0068] The Norrish Type II photoinitiator may be present in an amount of from 1 wt% to about 40 wt% based on the total weight of the one-part photocurable acrylate composition.

[0069] Suitably, the photoinitiator is present in an amount of from about 10 wt% to about 25 wt% based on the total weight of the composition.

Toughener

[0070] Some embodiments of the present invention may comprise a toughener component. Examples of toughener components include synthetic rubbers, such as acrylonitrile/butadiene rubber (NBR rubber), a polyurethane, styrene/butadiene rubber, styrene/butadiene/methacrylate rubber, chloroprene rubber or butadiene rubber, a natural rubber, a styrene thermoplastic elastomer such as styrene/polybutadiene/styrene synthetic rubber, a polyacrylate or polymethacrylate elastomer, a methacrylate/acrylate block co-polymer or an olefin thermoplastic elastomer such as polystyrene/EPDM (an ethylene/propylene/conjugated diene co polymer) synthetic rubber. Chlorinated and chlorosulfonated polyethylene elastomers can also be used. The toughener component can also be a mixture or dispersion of these types of materials. [0071] The toughener component can be present in an amount from about 5 to about 50% weight percentage based on the total weight of the composition, desirably in an amount from about 10 to about 30% weight percentage based on the total weight of the composition. Examples

[0072] The photocurable acrylate composition may have the following components, said components may be mixed together to form the photocurable acrylate composition:

EXAMPLE 1

[0073] The following formulation was prepared:

[0074] The composition of example 1 was employed to bond the following substrates, and load at bond failure strengths are also specified:

[0075] The composition of example 1 was applied to an end region of a lap shear having the following dimensions 2.54 cm X 10.16 cm X 0.3 cm (width X length X thickness), the composition was applied as a drop or a globule onto the centre of the end region of the lap shear; a second lap shear was mated with the first lap shear to form an overlap joint of length 1.27 cm said overlap joint having an area of 3.23 cm ² . When the two lap shears were mated the drop or globule of adhesive was squeezes in the overlapping area creating a thin layer of adhesive between the lap shear specimen. The composition was exposed to UV radiation, through the lap shear, from a 375 nm LED light source at 900 mW/cm ² for 60 seconds to cure the adhesive. Bonding was carried out at room temperature. The bonded specimens were tested 1 day after curing of the adhesive joints. To test the bonded specimen were placed in the grips of a calibrated Hounsfield tensile testing machine and pulled to failure at a rate of 2 mm per minute. [0076] All testing was carried out in accordance with ASTM D3163: Strength properties of adhesively bonded rigid plastic lap-shear joints in shear by tension loading and in accordance with ISO 4587: Adhesives - determination of tensile lap shear strength of high strength adhesive bonds.

EXAMPLE 2

[0077] The following formulation was prepared:

[0078] The composition of example 2 employed to bond the following substrates, and load at bond failure strengths are also specified:

[0079] The composition of example 2 was tested in the same manner as outlined above for example 1.

EXAMPLE 3

[0080] The following formulation was prepared:

[0081] The composition of example 3 was employed to bond the following substrates, and load at load at bond failure strengths are also specified:

[0082] The composition of example 3 was tested in the same manner as outlined above for example 1.

EXAMPLE 4

[0083] The following formulation was prepared:

[0084] The composition of example 3 was employed to bond the following substrates, and load at load at bond failure strengths are also specified:

[0085] The composition of example 3 was tested in the same manner as outlined above for example 1. COMPARATIVE EXAMPLE

[0086] The following formulation was prepared:

[0087] The composition of the comparative example was employed to bond the following substrates, and load at load at bond failure strengths are also specified:

[0088] The composition of the comparative example was tested in the same manner as outlined above for example 1. The comparative example does not comprise an organoborane-amine component and cannot effect bonding between polypropylene and glass.

[0089] Advantageously, when the photocurable composition of the present invention is exposed to radiation in the electromagnetic spectrum having a wavelength in the range of from 200 nm to 700 nm, the absorption of such radiation by a type II photoinitiator leads to the generation of an excited electron state in the photointiator that will react with the borane-amine component by abstracting a hydrogen from the amine component, which in turn leads to the release of the borane component (i.e. decomplexation of the borane from the borane-amine component). The borane component can then oxidise leading to the generation of highly reactive radical species which can abstract a hydrogen from low energy surfaces such as a polyolefin surface. The resulting radical species on the low energy surface can react with the (meth)acrylate leading to grafting of polymerised (meth)acrylate with the low energy surface.

[0090] In contrast, Norrish type I photoinitiators would lead to polymerisation of the (meth)acrylate monomer, without grafting to a low energy surface occurring. [0091] While (meth)acrylate compositions comprising borohydride species have demonstrated utility in bonding low energy surfaces in two-part compositions, borohydride species have not been successfully employed to form one-part (meth)acrylate adhesive compositions.

[0092] Advantageously, the compositions of the present invention are particularly useful for bonding two or more substrates, wherein at least one of said substrates is a polyolefin substrate.

[0093] The words “comprises/comprising” and the words “having/including” when used herein with reference to the present invention are used to specify the presence of stated features, integers, steps or components but do not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

[0094] It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.