Activator Compositions for Cyanoacrylate Adhesives

US 6,995,227 B2 7 3,5-dihalopyridines, such as 3,5-dichloropyridine or 3,5- dibromopyridine, or 3-cyano pyridine, a lower alkyl 3,5- pyridine dicarboxylate, or a 5-halo nicotinic acid such as 5-bromo nicotinic acid, pyridines having an electron-withdrawing group in the 2 position on the ring, suitably a COOR or COR4 group, such as 2-acetyl pyridine, pyridines having an electron-withdrawing group in the 4-position on the ring, suitably 4-nitropyridine, pyrimidines having an electron-withdrawing group in the 4- or 5-position on the ring, suitably 4- or 5-halo pyrimidines, such as 4-bromopyrimidine or 5-bromopyrimidine, nitroquinolines, suitably 5-nitroquinoline, polyhalogenated quinolines, suitably 4,7- dihalo quinolines such as 4,7-dichloro quinoline, pyrazines having an electron-withdrawing group in the 2-position on the ring, suitably 2-methoxy pyrazine or 2-methylthio pyrazine. and aromatic heterocyclic compounds which are substan- tially iso-electronic to any of the foregoing compounds. According to one feature, the present invention provides an activator composition for the accelerated hardening of cyanoacrylate adhesives, wherein the activator comprises a member selected from the group consisting of: aromatic heterocyclic compounds having at least one N hetero atom in the ring(s) and substituted on the ring(s)with at least one substituent selected from the group consisting of halo, CN, CF3, COOR, COR4, OR, SR, CONR1R2, NO2, SOR, SOZR3, SO3R3, PO(OR3)2 and optionally substituted C5-C20 aryl, wherein R, R1, R2 and R4 (which may be the same or different) are H, optionally substituted C1-C10 alkyl, or optionally substituted C6-C20 aryl, and R3 is optionally substituted C1-C10 alkyl, or optionally substi- tuted C6-C20 aryl, mixtures of any of the foregoing with each other, and/or with N,N-dimethyl-p-toluidine, and mix- tures of any of the foregoing and/or N,N-dimethyl-p- toluidine with an organic compound containing the struc- tural element, —N=C—S—S—. According to a further aspect, the present invention includes the use of a composition as defined above for the accelerated hardening of a cyanoacrylate adhesive. The composition may be applied to a substrate before application of the cyanoacrylate adhesive thereto, and/or the composi- tion may be applied to the cyanoacrylate adhesive after application of the adhesive to a substrate. According to a further aspect, the present invention pro- vides an adhesive system comprising a cyanoacrylate adhe- sive together with a composition as defined above. Suitably, the composition as defined above is held separately from (i.e. does not contact) the adhesive prior to application on a substrate. According to another aspect, the present invention pro- vides a process for the bonding of substrates or parts, characterised by either of the following series of steps: (a) dispensing an activator composition as defined above onto at least one surface of the substrates or parts to be joined; (b) optionally exposing solvent or other liquid vehicle in the activator composition to air, optionally with heating or with the aid of a fan; (c) optionally holding the substrate or part having the activator composition thereon for a retention or ship- ping period, (d) applying a cyanoacrylate adhesive to at least one substrate or part; 10 15 20 25 30 35 40 45 50 55 60 65 8 (e) joining the substrates or parts, optionally with manual or mechanical fixing, and (f) optionally subsequently dispensing the activator com- position onto adhesive exposed from a joint gap; or (i) applying a cyanoacrylate adhesive onto at least one surface of the substrates or parts to be joined; (ii) joining the substrates or parts, optionally with manual or mechanical fixing; (iii) dispensing an activator composition as defined above onto the adhesive before or after the step of joining the substrates or parts, and (iv) optionally exposing solvent or other liquid vehicle in the activator composition to air, optionally with heating or with the aid of a fan. Suitably the retention or shipping period in step (c) may be in the range from several minutes to several days, for example from two minutes to forty-eight hours. Optionally the activator composition may be applied onto parts prior to their shipping, forwarding or delivery to an end-user, cus- tomer or contractor. The present invention includes a bonded assembly of substrates or parts bonded by a process as defined above. The present invention also includes as an article of com- merce a substrate or part having a composition as defined above applied thereto. According to another aspect, the present invention pro- vides an activator composition for the accelerated hardening of cyanoacrylate adhesives, wherein the composition com- prises a solution of one or more activators in a solvent mixture which comprises a volatile hydrocarbon and a cyclic ketone. Cyclic ketones as co-solvents have shown better results in reducing the “halo effect” discussed above than linear ketones such as acetone, butanone, pentanone, hexanone, 4-methyl-2-pentanone, or octanone; than cyclic ethers such as dioxane or tetrahydrofuran; or than adhesive- miscible solvents such as ethyl acetate. Suitably, the cyclic ketone is present in an amount of up to about 15%, especially up to about 12%, particularly up to about 10%, by weight of the solvent mixture. If an amount substantially greater than 10%, and particularly greater than 15% is used, there may be a risk that a plastic substrate will be attacked. Desirably, the cyclic ketone is present in an amount of at least about 2.5% by weight of the solvent mixture. Below this amount the reduction in the “halo effect” may not be sufficient for full visual satisfaction. Preferably, the cyclic ketone is present in an amount of at least about 3% by weight of the solvent mixture. At or above this level the presence of cyclic ketone is seen to be beneficial. Desirably, the cyclic ketone is present in an amount in the range of 3% to 7.5% by weight of the solvent mixture, particularly an amount in the range of 4% to 7% by weight of the solvent mixture. A cyclic ketone may suitably be monocyclic or bicyclic. Suitably the cyclic ketone is an optionally-substituted cyclic ketone, desirably an alicyclic ketone, having 3-10 carbon atoms in the ring. Asubstituted cyclic ketone may be mono- or di-substituted on the ring with C1-C5 alkyl, more particularly C1-C2 alkyl. One particular example of suitable cyclic ketone is cyclo- hexanone. Other examples include cyclobutanone, cyclopentanone, cycloheptanone and 2-methyl cyclopen- tanone. Examples of bicyclic ketones include 2-norbomanone, bicyclo[3.2.1]octan-2-one and bicyclo [2.2.2] octanone. Desirably, the volatile hydrocarbon is an aliphatic hydro- carbon. Suitably, the volatile aliphatic hydrocarbon may have from 4 to 10 carbon atoms, particularly from 5 to 8 US 6,995,227 B2 9 carbon atoms, and may be straight chain, branched or cyclic. One particular example of a suitable hydrocarbon is n-heptane. In one aspect, the present invention relates to use of an activator composition as defined above for the accelerated hardening of a cyanoacrylate adhesive, particularly when the activator composition is applied to the cyanoacrylate adhe- sive after application of the adhesive to a substrate. In an activator composition for the accelerated hardening of cyanoacrylate adhesives, the activator may suitably com- prise a member selected from the group consisting of: organic amines including: lower fatty amines, aromatic amines, dimethylamine and the like; aliphatic, alicyclic and, especially, tertiary aromatic amines; such as N,N- dimethylbenzylamine, N-methylmorpholine and N,N- diethyltoluidine; amine compounds with a boiling point of between 50° C. and 250° C. such as triethylamine, diethylamine, butylamine, isopropyl amine, tributyl amine, N,N-dimethyl aniline, N,N-diethyl aniline, N,N-dimethyl-p-toluidine, N,N-dimethyl-m-toluidine, N,N-dimethylo-toluidine, dim- ethyl benzyl amine, pyridine, picoline, vinyl pyridine, ethanolamine, propanolamine and ethylene diamine; organic compounds containing the structural element, —N=C—S—S— (as described above). aromatic heterocyclic compounds having at least one N hetero atom in the ring(s) and substituted on the ring(s)with at least one electron-withdrawing group which decreases the base strength of the substituted compound compared to the corresponding unsubstituted compound (as described above), and mixtures of any of the foregoing with each other. According to one aspect, the present invention includes the use of an activator composition as defined above for the accelerated hardening of a cyanoacrylate adhesive. The composition may be applied to a substrate before application of the cyanoacrylate adhesive thereto, but more suitably the composition is applied to the cyanoacrylate adhesive after application of the adhesive to a substrate. According to a further aspect, the present invention pro- vides an adhesive system comprising a cyanoacrylate adhe- sive together with an activator composition as defined above. Suitably, the activator composition as defined above is held separately from the adhesive prior to application on a substrate. According to another aspect, the present invention pro- vides a process for the bonding of substrates or parts, characterised by the following series of steps: (i) applying a cyanoacrylate adhesive onto at least one surface of the substrates or parts to be joined; (ii) joining the substrates or parts, optionally with manual or mechanical fixing; (iii) dispensing an activator composition comprising a solution of one or more activators in a solvent mixture which comprises a volatile hydrocarbon and a cyclic ketone onto the adhesive before or after the step of joining the substrates or parts, and (iv) optionally exposing the solvent mixture in the acti- vator composition to air, optionally with heating or with the aid of a fan. The process of the invention is particularly advantageous when at least one of the substrates has a surface of a dark colour or is transparent and/or at least one of the substrates is of a plastics material. However the invention is also useful with substrates of other materials such as cardboard, paper, or wood, particularly if the surface is of a dark colour. The present invention includes a bonded assembly of substrates or parts bonded by a process as defined above. 10 15 20 25 30 35 40 45 50 55 60 65 10 Desirably, an activator composition comprises an amount of activator effective to accelerate hardening of a cyanoacry- late adhesive, the activator being carried in a suitable solvent mixture in accordance with the invention. The solutions of the activator(s) may suitably contain the activator compound(s) in concentrations of from 0.01 to 10 g per 100 ml of solvent mixture; for example, from 0.05 to 5 g of activator substance are dissolved per 100 ml of solvent mixture. Various conventional organic solvents are suitable as the hydrocarbon solvent (in the solvent mixture) for the activator(s) according to this aspect of the present invention, provided they have a sufficiently high volatility. Desirably, the boiling point of the solvent is below about 120° C., suitably below about 100° C., at ambient pressure. Although aromatic solvents such as toluene or xylene may be used, the hydrocarbon solvent is desirably an aliphatic hydrocarbon. Suitable solvents include specialized boiling point gasolines, but especially n-heptane, n-hexane, n-pentane, octane, cyclohexane, cydopentane, methyl cyclopentane, methyl cyclohexane and isomers of them like isooctane, methylhexanes, methylpentanes, 2,2-dimethyl butane (neohexane), or mixtures thereof, as well as petroleum benzines and ligroin. DETAILED DESCRIPTION OF THE INVENTION An alkyl group may be straight-chained or branched and may be unsaturated, i.e. the term alkyl as used herein includes alkenyl and alkynyl. A C1—C10 alkyl group may for example be a C1-C5 alkyl group. A lower alkyl group may suitably be a C1-C5 alkyl group. An aryl group includes phenyl and naphthyl groups, either of which may be sub- stituted with an alkyl group, more particularly a lower alkyl group. Halo includes chloro, bromo, fluoro and iodo, as well as pseudohalo-radicals such as CN, SCN, OCN, NCO, NCS. An optionally substituted alkyl, alkoxy or aryl group may be substituted with a substituent selected from the group consisting of halo, CN, CF3, COOR, COR, OR, SR, CONR1R2, NO2, SOR, SOZR3, SO3R3, PO(OR3)2 and optionally substituted C6—C20 aryl, wherein R, R1 and R2 (which may be the same or different) are H, optionally substituted C1—C10 alkyl, or optionally substituted C6—C20 aryl, and R3 is optionally substituted C1—C10 alkyl, or optionally substituted C6—C2O aryl. In an organic compound containing the structural element —N=C—S—S—, in which the N=C double bond is part of a heterocyclic ring, the heterocyclic ring may be substi- tuted for example with optionally substituted C1—C10 alkyl, optionally substituted C1—C1O alkoxy, optionally substituted C1—C10 alkoxyalkyl, halo, CN, CF3, COOR, COR, OR, SR, CONR1R2, NO2, SOR, SOZR3, SO3R3, PO(OR3)2 and optionally substituted C6—C20 aryl or aryloxy, CSOR3, COONR32, NRCOOR, N=N—R3, OOR3, SSR3, OOCOR3, NOR32, ON(COR3)2, S-aryl, NR32, SH, OH, SiR33, Si(OR3)3, OSiR33, OSi(OR3)3, B(OR3)2, P(OR3)2, SOR3, OSR3, wherein R,R1 and R2 (which may be the same or different) are H, optionally substituted C1—C1O alkyl, or optionally substituted C6—C2O aryl, and R3 (which may be the same or different) is optionally substituted C1—C10 alkyl, or optionally substituted C5—C20 aryl. Desirably, an activator composition comprises an amount of activator effective to accelerate hardening of a cyanoacry- late adhesive, the activator being carried in a suitable vehicle. Suitably the activator composition is an activator solution of the activator in a solvent. Alternatively the composition US 6,995,227 B2 11 may be a dispersion of the activator in a suitable vehicle, particularly a liquid vehicle. Desirably, the activator(s) are dissolved in readily volatile organic solvents, such as hydrocarbons, carboxylic acid esters, ketones, ethers or halogenated hydrocarbons and carbonic acid esters or acetals or ketals. The solutions of the activator(s) may suitably contain the activator compound(s) in concentrations of from 0.01 to 10 g per 100 ml of solvent; for example, from 0.05 to 5 g of activator substance are dissolved per 100 ml of solvent. When the activator composition contains a mixture of two activator compounds, the respective amounts of the activator compounds may vary and are only limited by respective amounts which will no longer be effective for the desired combination of properties. More particularly, when the activator composition contains a mixture of an aromatic heterocyclic compound substituted with at least one electron-withdrawing group and an organic compound hav- ing the structural element —N=C—S—S—, the activator compounds may suitably be present in amounts of about 0.1% to about 10% by weight of the said aromatic hetero- cyclic compound and about 0.01% to about 5% by weight of the said organic compound, more particularly about 0.05% to about 1%, of the said organic compound (c), based on the total weight of the activator composition. Various conventional organic solvents are suitable as solvents for the activator(s) according to the present invention, provided they have a sufficiently high volatility. Desirably, the boiling point of the solvent is below about 120° C., suitably below about 100° C., at ambient pressure. Suitable solvents include specialized boiling point gasolines, but especially n-heptane, n-bromopropane, alcohols, for example isopropyl alcohol, alkyl esters of lower carboxylic acids, for example ethyl acetate, isopropyl acetate, butyl acetate, ketones, such as acetone, methyl isobutyl ketone and methyl ethyl ketone. Also suitable are ether solvents, ether esters or cyclic ethers, such as, especially, tetrahydro- furan. In the case of sparingly soluble activators, chlorinated hydrocarbons, such as dichloromethane or trichloromethane (chloroform), may also be used. The activator compositions according to the present invention are suitable for the accelerated hardening of conventional cyanoacrylate adhesives which contain as the fundamental constituent one or more cyanoacrylic acid esters, suitably with inhibitors of free-radical polymerisation, inhibitors of anionic polymerisation and, optionally, conventional auxiliary substances employed in such adhesive systems, like fluorescence markers. The cyanoacrylic acid esters used in the adhesives are in the main one or more esters of 2-cyanoacrylic acid. Such esters correspond to the following general formula: H2C:C(CN)—CO—O—R5. In that formula, R5 represents an alkyl, alkenyl, cycloalkyl, aryl, alkoxyalkyl, aralkyl or haloalkyl or other suitable group, especially a methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, pentyl, hexyl, allyl, methallyl, crotyl, propargyl, cyclohexyl, benzyl, phenyl, cresyl, 2-chloroethyl, 3-chloropropyl, 2-chlorobutyl, trifluoroethyl, 2-methoxyethyl, 3-methoxybutyl or 2-ethoxyethyl group. The above-mentioned cyanoacrylates are known to a person skilled in the art of adhesives, see Ullmann’s Encyclopaedia of Industrial Chemistry, Volume A1, p. 240, Verlag Chemie Weinheim (1985) and U.S. Pat. Nos. 3,254,111 and 3,654, 340. Preferred monomers are the allyl, methoxyethyl, ethoxyethyl, methyl, ethyl, propyl, isopropyl or butyl esters 10 15 20 25 30 35 40 45 50 55 60 65 12 of 2-cyanoacrylic acid. The monocyanoacrylic acid esters represent the largest proportion by weight of the polymer- isable monomers in the adhesive. The mentioned cyanoacrylic acid esters may suitably be present in the adhesives in amounts of from 99.99 to 90 wt. %. Preference is given to cyanoacrylic acid esters the alcohol radical of which is derived from alcohols having from 1 to 10 carbon atoms, which may also be cyclic, branched or perfluorinated. The cyanoacrylate adhesives according to the present invention may also contain an inhibitor of free-radical polymerisation. Such inhibitors are, for example, hydroquinone, p-methoxyphenol, but also sterically- hindered phenols, phenothiazine and the like. The cyanoacrylate adhesives according to the present invention may also contain thickeners as further auxiliary substances. That is desirable especially when there are to be bonded porous materials which otherwise readily absorb the low viscosity adhesive. Many types of polymer may be used as thickeners, such as polymethyl methacrylate, other meth- acrylate copolymers, acrylic rubber, cellulose derivatives, polyvinyl acetate or polyalphacyanoacrylate. A usual amount of thickener is generally about 10 wt. % or less, based on the total adhesive. In addition to or instead of the thickeners, the cyanoacrylate adhesives according to the present invention may also contain Reinforcing agents. Examples of such reinforcing agents are acrylic elastomers, acrylonitrile copolymers, elastomers or fluoroelastomers. Moreover, inorganic additives may also be used, for example silicates, thixotropic agents having a large surface area, which may be coated with polydi-alkylsiloxanes. The cyanoacrylate adhesives according to the present invention may also contain substances for increasing the thermal stability thereof. There may be used for that purpose, for example, the sulfur compounds mentioned in European Patent specification No. 579 476. In addition to or instead of the mentioned additives, the cyanoacrylate adhesives according to the present invention may also contain plasticisers. These serve to protect the resulting adhesive bond from brittleness. Such plasticisers are, for example, C1—C1O alkyl esters of dibasic acids, especially of sebacic acid, phthalic acid or malonic acid. Other plasticisers are diaryl ethers and polyurethanes and the like. Furthermore, the adhesive preparations according to the present invention may also contain colorings, pigments, aromatic substances, extenders and the like, as well as fluorescing additives. Reference is directed to U.S. Pat. No. 5,749,956 (Fisher et al.), U.S. Pat. No. 4,869,772 (McDonnell et al.) and U.S. Pat. No. 5,314,562 (McDonnell et al.), the contents of which are incorporated herein by reference. The activator compositions of the present invention are intended to be used with a wide variety of both metallic and non-metallic substrates, including substrates having acidic surfaces such as wood and paper or cardboard, and plastics substrates. In the aspect of the invention using a cyclic ketone as a co-solvent, the advantage of the activator solutions of the invention is particularly evident on dark-coloured substrates. The present invention will now be illustrated in greater detail. EXAMPLES In the Examples, the following abbreviations and terms are used: US 6,995,227 B2 13 DCP = 3,5-dichloro pyridine, NQ = 5-nitro quinoline DPDS = 2,2’-dipyridyl disulfide, DBP = 3,5-dibromo pyridine, DCQ = 4,7-dichloro quinoline, disulfide, NBP = n-bromopropane, CT V = cure through volume THF = tetrahydrofuran DMPT = N,N-dimethyl-p-toluidine, Heptane = n-heptane, CNP = 3-Cyano Pyridine uo< E 23% qouaomaoo 22% E Q; uo< E 2325 qofiooaoo 22% E Q; o2=2:so-uo< afi u23w2m 00020000200 2230 02 $_ 00000000-