IE20010422A1 - Solvents for activator compositions for cyanoacrylate adhesives - Google Patents

Abstract

Solvents for activator compositions for cyanoacrylate adhesives are described. In particular, an activator composition for the accelerated hardening of cyanoacrylate adhesives is described, wherein the composition comprises a solution of one or more activators in a solvent mixture which comprises a volatile hydrocarbon and a cyclic ketone. A process for the accelerated bonding of substrates using cyanoacrylate adhesives is also described.

Description

SOLVENTS FOR ACTIVATOR COMPOSITION FOR CYANOACRYLATE ADHESIVES Solvents for activator compositions for cyanoacrylate adhesives are described. In particular, an activator composition for the accelerated hardening of cyanoacrylate adhesives is described, wherein the composition comprises a solution of one or more activators in a solvent mixture which comprises a volatile hydrocarbon and a cyclic ketone. A process for the accelarated bonding of substrates using cyanoacrylate adhesives is also described.

Field of the Invention This invention relates to solvents for activator compositions, particularly well suited for accelerating the hardening of cyanoacrylate adhesives. The invention also relates to novel mixtures of solvents and to the use of the activator compositions containing such solvents for the accelerated hardening of cyanoacrylate adhesives. The invention further relates to a l o process for the accelerated bonding of substrates using cyanoacrylate adhesives.

Brief Description of Related Technology Adhesive compositions based upon cyanoacrylate esters are well known and have found 15 extensive use, because of their rapid cure speed, excellent long-term bond strength, and applicability to a wide variety of substrates. They generally harden after only a few seconds, after which the joined parts exhibit at least a certain degree of initial strength.

It is known that certain cyanoacrylate adhesives typically harden by an anionic polymeri20 sation reaction. If the adhesive is applied in a relatively thick layer in the joint gap or relatively large amounts of adhesive are applied so that relatively large drops of adhesive protrude from between the parts to be joined, rapid hardening throughout may rarely be achieved.

Heretofore efforts have been made to accelerate the polymerisation for such applications by means of certain additives. Addition of accelerators directly to the adhesive formulation is possible to only a very limited extent, however, since substances having a basic or nucleophilic action, which would normally bring about a pronounced acceleration of the polymerisation of the cyanoacrylate adhesive, are generally used at the expense of the storage stability of such formulations.

OPEN TO PUBLIC INSPECTION UNDER SECTION 28 AND RULE 23 .........OF.. /iMsi -2Addition of such accelerators shortly before application of the adhesive results in virtually a two-component system. However, such method has the disadvantage that the working life is limited after the activator has been mixed in. In addition, with the small amounts of activator that are required, the necessary accuracy of metering and homogeneity of mixing are difficult to achieve. Moreover, use of such a two-component system is often seen as cumbersome to the end user, and sometimes only modestly improves the intended result.

Activators are also used in the form of a dilute solution which is either applied beforehand onto a substrate or part which is to be bonded, and/or is applied onto the adhesive where it is still liquid after the substrates have been joined. The solvents used for such dilute solutions of activators are generally low-boiling organic solvents, so that they may be readily evaporated, leaving the activator on the substrate/part or the adhesive.

Various types of activator composition are known for accelerating the hardening of cyanoacrylate (CA) adhesives, including amines such as N,N-dimethyl-p-toluidine. WO 0039229 Henkel KGaA describes organic compounds having the structural element -N=CS-S-C=N- which are useful as activators for accelerating the curing of CA adhesives if diluted in a solution.

Activator solutions are often applied by spraying. However there is a demand for activator solutions which can be applied in excess volumes (e.g. as drops) onto an adhesive already present on a substrate (e.g. in the form of a bead or fillet).

Aliphatic hydrocarbons such as heptane are often used as the solvent for CA activators. However if the activator solution is applied onto a bead or fillet of CA adhesive which is already on a substrate (“post-application”), particularly if the solution is applied in excess volumes, a white “halo” may be formed on the substrate around the adhesive bead in the course of curing. Although the present invention is not limited by any theory, it is thought that the solvent heptane, which is substantially insoluble in the CA adhesive composition, dissolves small amounts of CA monomer and that some of the heptane phase (i.e. the activator solution with traces of CA monomer dissolved therein) runs off the adhesive bead onto the substrate. The traces of CA monomer then polymerise, and after evaporation of the solvent a thin layer of whitish amorphous material is left on the substrate around the adhesive bead, creating a “halo”. This is visually unattractive and is undesirable, particularly when the substrate is of a dark colour, such as black or dark shades of colours such as blue, red, brown or green, as well as transparent substrates like glass or polycarbonate, on which a whitish layer would be clearly visible. io While it may be possible to use a solvent which is miscible with the CA adhesive composition, so that the solvent would mix with the adhesive, a miscible solvent would likely make the adhesive composition undesirably soft and bulky. In addition the solvent in the adhesive composition would likely take a longer time to evaporate than n-heptane which remains as a separate phase. Miscible solvents such as acetone, ethyl acetate or acetylacetone also have a stronger odour than n-heptane, and they would be unappealing to the end user. If one or both substrates is of plastics materials, a solvent which is miscible in the adhesive composition (such as acetone, toluene etc.) would also likely attack the plastics material.

The present invention reduces the problem of the “halo” effect and provides activator solutions with different properties from the activator solutions used to date.

Summary of the Invention The present invention provides an activator composition for the accelerated hardening of cyanoacrylate adhesives, wherein the composition comprises 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” 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 adhesivemiscible 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 25% 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 75% 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. A substituted 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 cyclohexanone. Other examples include cyclobutanone, cyclopentanone, cycloheptanone and 2-methyl cyclopentanone. Examples -5of 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 hydrocarbon. Suitably, the volatile aliphatic hydrocarbon may have from 4 to 10 carbon atoms, particularly from 5 to 8 carbon atoms, and may be straight chain, branched or cyclic. One particular example of a suitable hydrocarbon is «-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 adhesive after application of the adhesive to a substrate.

In an activator composition for the accelerated hardening of cyanoacrylate adhesives, the activator may suitably comprise 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,Ndimethylbenzylamine, N-methylmorpholine and Ν,Ν-diethyltoluidine; amine compounds with a boiling point of between 50°C. and 250°C. such as triethylamine, diethylamine, butylamine, isopropyl amine, tributyl amine, Ν,Ν-dimethyl aniline, Ν,Νdiethyl aniline, N,N-dimethyl-p-toluidine, NjST-dimethyl-zw-toluidine, N,N-dimethyl-otoluidine, dimethyl benzyl amine, pyridine, picoline, vinyl pyridine, ethanolamine, propanolamine and ethylene diamine; organic compounds containing the structural element, -N=C-S-S-. 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, and mixtures of any of the foregoing with each other.

In the said organic compound containing the structural element -N=C-S-S-, the N=C double bond may optionally be part of an aromatic system, which may suitably be monocyclic, bicyclic or tricyclic. For example, the N=C double bond may suitably be part of an aromatic heterocyclic ring having one or more N hetero atoms in the ring, optionally with one or more other hetero atoms selected from S and O. The heterocyclic ring may be substituted.

Desirably the said organic compound contains the structural element -N=C-S-S-C=N-, in which case both the N=C double bond and the C=N double bond may optionally be part of aromatic systems as described above, suitably two similar aromatic systems. More desirably the said organic compound is selected from dibenzothiazyl disulfide, 6,6'dithiodinicotinic acid, 2,2'-dipyridyl disulfide, and bis(4-Z-butyl-l-isopropyl-2-imidazolyl) disulfide. Of course, combinations of these organic compounds may also be used. For further information see WO 0039229, the contents of which are incorporated herein by 0 reference.

Another class of activator comprises a member selected from the group consisting of pyridines, quinolines and pyrimidines substituted on the ring(s) with at least one electronwithdrawing group which decreases the base strength of the substituted compound compared to the corresponding unsubstituted compound.

An aromatic heterocyclic compound may suitably be monocyclic, bicyclic or tricyclic. The N hetero atoms(s) may be present in one or more of the rings. Two or more heterocyclic rings may be fused, or a heterocyclic ring may be fused to one or more carbocyclic rings. A -7heterocyclic ring may suitably be a 5- or 6-membered ring with one or two N-atoms in the ring.

Suitably the at least one electron-withdrawing group is selected from the group consisting of halo, CN, CF3, COOR, COR, OR, SR, CON^R2, NO2, SOR, SO2R3, SO3R3, PO(OR3)2 and optionally substituted C5-C2o aryl, wherein R, R1 and R2 (which may be the same or different) are H, optionally substituted Ci-Cio alkyl, or optionally substituted C6-C20 aryl, and R3 is optionally substituted Ci-Cio alkyl, or optionally substituted C6-C2o aryl.

For example, the electron-withdrawing group may be selected from the group consisting of halo, CN, COOR and COR^R, R1, R2 and R3 may suitably be optionally substituted C1-C5 alkyl, for example unsubstituted C1-C5 alkyl.

The criterion that the electron-withdrawing group decreases the base strength of the substituted compound compared to the corresponding unsubstituted compound may be determined by pKa measurement in water under standard conditions (e.g. 25°C and zero ionic strength) by conventional means or using a software package which calculates pKa of the base such as “ACD/pKa Calculator” available from Advanced Chemistry Development, 133 Richmond Street West, Suite 605, Toronto, ON N5H 2LS, Canada.

According to a particular aspect, the activator is selected from: pyridines having one or more electron-withdrawing groups in the 3-, 3,4- or 3,5- position in the ring, suitably 3^-dihalopyridines, such as 3^-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 in the ring, suitably a COOR or COR group, such as 2-acetyl pyridine, pyridines having an electron-withdrawing group in the 4-position in the ring, suitably 4nitropyridine, -,I !/ 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, and aromatic heterocyclic compounds which are substantially iso-electronic to any of the foregoing compounds.

An activator composition for the accelerated hardening of cyanoacrylate adhesives may suitably comprise 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, COR, OR, SR, CONR]R2, NO2, SOR, SO2R3, SO3R3, PO(OR3)2 and optionally substituted C6-C2o aryl, wherein R, R1 and R2 (which may be the same or different) are H, optionally substituted Ci-Cio alkyl, or optionally substituted C6-C2o aryl, and R3 is optionally substituted Ci-Cio alkyl, or optionally substituted C6-C2o aryl, mixtures of any of the foregoing with each other, and/or with N,N-dimethy]-p-toluidine, and mixtures of any of the foregoing and/or Ν,Ν-dimethyl-p-toluidine with an organic compound containing the structural element, -N=C-S-S-.

It is particularly desirable to use a mixture of activators in order to obtain a combination of properties, some at least of which would not be expected.

According to a special feature, an activator composition for the accelerated hardening of cyanoacrylate adhesives may suitably comprise a mixture of an aromatic heterocyclic compound as described above and an organic compound having the structural element, N=C-S-S-. According to a further feature, an activator composition for the accelerated hardening of cyanoacrylate adhesives may suitably comprise a mixture of a 3,5dihalopyridine and an organic compound having the structural element, -N=C-S-S-.

According to another feature, an activator composition may suitably comprise a mixture of: -9!C. t£= (A) 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 electron - withdrawing group which decreases the base strength of the substituted compound compared to the corresponding unsubstituted compound, Ν,Ν-dimethy\-p- toluidine, and mixtures of any of the foregoing, with (B) an organic compound containing the structural element, -N=C-S-S-. io According to another feature, an activator composition may suitably comprise a mixture of: (A) 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, COR, OR, SR, CONR’R2, NO2, SOR, SO2R3, SO3R3, PO(OR')2 and optionally substituted C6-C2o aryl, wherein R, R and R (which may be the same or different) are H, optionally substituted Ci-Cio alkyl, or optionally substituted Q-Cqo aryl, and R3 is optionally substituted Ci-Cio alkyl, or optionally substituted C6-C2o aryl, N ,N-dimethyl-p-toluidine, 0 and mixtures of any of the foregoing, with (B) an organic compound containing the structural element, -N=C-S-S-.

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. - 10According to a further aspect, the present invention provides an adhesive system comprising a cyanoacrylate adhesive 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 provides 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 as defined above onto the adhesive before or after the step of joining the substrates or parts, and (iv) optionally exposing the solvent mixture in the activator 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.

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 Ci-Cio 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 substituted 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, CONR’R2, NO2, SOR, SO2R3, 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 C0-C20 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 substituted for example with optionally substituted C1-C10 alkyl, optionally substituted Cj-Cio alkoxy, optionally substituted C1-C10 alkoxyalkyl, halo, CN, CF3, COOR, COR, OR, SR, CONR’R2, NO2, SOR, SO2R3, 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 RR1 and R2 (which may be the same or different) are H, optionally substituted Cj-Cio alkyl, or optionally substituted C6-C2o aryl, and R (which may be the same or different) is optionally substituted C1-C10 alkyl, or optionally substituted Cg-C2o aryl.

Desirably, an activator composition comprises an amount of activator effective to accelerate hardening of a cyanoacrylate 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. - 12When 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 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 having 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 heterocyclic compound and about 0.01% to about 5% by weight of the said organic io compound, more particularly about 0.05% to about 1%, of the said organic compound, based on the total weight of the activator composition.

Various conventional organic solvents are suitable as the hydrocarbon solvent (in the solvent mixture) for the activators) 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. 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 «-heptane, «-hexane, «-pentane, octane, cyclohexane, cyclopentane, 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.

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, inhibitors of free-radical polymerisation, inhibitors of anionic polymerisation and, optionally, conventional auxiliary substances employed in such adhesive systems, like thickening agents or dyes.. -13 The cyanoacrylic acid esters used in the adhesives are in the main one or more esters of 2cyanoacrylic acid. Such esters correspond to the following general formula: H2C=C(CN)-CO-O-R4.

In that formula, R4 represents an alkyl, alkenyl, cycloalkyl, aryl, alkoxyalkyl, aralkyl or haloalkyl or other suitable group, especially a methyl, ethyl, «-propyl, isopropyl, «-butyl, isobutyl, pentyl, hexyl, allyl, methallyl, crotyl, propargyl, cyclohexyl, benzyl, phenyl, cresyl, 2-chloroethyl, 3-chloropropyl, 2-chlorobutyl, tiifluoroethyl, 2-methoxyethyl, 310 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 Al, p. 240, Veriag Chemie Weinheim (1985) and U.S. Patent Nos. 3,254,111 and 3,654,340. Preferred monomers are the allyl, methoxyethyl, ethoxyethyl, methyl, ethyl, propyl, isopropyl or butyl esters of 2-cyanoacrylic acid. The monocyanoacrylic acid esters represent the largest proportion by weight of the polymerisable 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 o 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,pmethoxyphenol, 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 methacrylate copolymers, acrylic rubber, cellulose derivatives, polyvinyl acetate or ,1 I - 14polyalphacyanoacrylate. 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 polydialkylsiloxanes.

The cyanoacrylate adhesives according to the present invention may also contain io 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, Ci-Cio alkyl esters of dibasic acids, especially of sebacic acid, phthalic acid or malonic acid. Other plasticisers are diary 1 ethers and polyurethanes and the like. Furthermore, the adhesive preparations according to the present invention may also contain colorings, pigments, aromatic o substances, extenders and the like, as well as fluorescing additives. Reference is directed to U.S.Patent Nos. 5,749,.956 (Fisher et al.), 4,869,772 (McDonnell et al.) and 5,314,562 (McDonnell et al.), the contents of which are incorporated herein by reference.

The activator solutions 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 particularly plastics substrates. In all cases, the advantage of the solutions is particularly evident on dark-coloured substrates.

The present invention will now be illustrated in greater detail. - 15 EXAMPLES In the Examples, the following abbreviations and terms are used: DCP = 3,5-dichloro pyridine, DPDS = 2,2'-dipyridyl disulfide, DMPT = N,N-dimethyl-/?-toluidine, Heptane = n-heptane THF = tetrahydrofuran 7455 = Loctite 7455 (activator) io Main ingredients of adhesive compositions used in the examples: Loctite 401: (also called 401 herein) is a low viscosity, fast curing, single component ethyl cyanoacrylate adhesive (see for example U.S. Patent No. 4,695,615).

Loctite 401: ethylcyanoacrylate; acidic stabilizer against anionic polymerization; antioxidant against radical polymerization; polymer thickening agent; curing accelerator (see for example EP-A-0151521 and EP-A-0259016).

Loctite 406: ethylcyanoacrylate; acidic stabilizer against anionic polymerization; o antioxidant against radical polymerization; polymer thickening agent; adhesion promoter.

Loctite 407: ethylcyanoacrylate; acidic stabilizer against anionic polymerization; antioxidant against radical polymerization; polymer thickening agent; adhesion promoter (see for example WO 8200829 Al).

Loctite 410: ethylcyanoacrylate; acidic stabilizer against anionic polymerization; antioxidant against radical polymerization; polymer thickening agent; adhesion promoter; silica; toughening agent (see for example WO 8302450 Al) Loctite 431: ethylcyanoacrylate; acidic stabilizer against anionic polymerization; ‘‘y £, I. - 16antioxidant against radical polymerization; polymer thickening agent; curing accelerator.

Loctite 460: methoxyethyl cyanoacrylate; acidic stabilizer against anionic 5 polymerization; antioxidant against radical polymerization; polymer thickening agent.

Loctite LID-3693: ethylcyanoacrylate + n-buty Icy anoacrylate; acidic stabilizer against anionic polymerization; antioxidant against radical polymerization; polymer ι o thickening agent; plasticizer (ester type); curing accelerator.

Loctite LID-3692: the same as LID-3693 except that it is of higher viscosity.

Sicomet 5195: ethylcyanoacrylate; acidic stabilizer against anionic polymerization; antioxidant against radical polymerization; polymer thickening agent Loctite 7455 is a single component surface activator based on DMPT in heptane.

Loctite is a trade mark. The above Loctite products are commercially available from Loctite Corporation, Rocky Hill, Conn., USA or Loctite (Ireland) Limited, Dublin 24, Ireland. The above Sicomet product is available from Sichel-Werke GmbH, Sichelstrasse 1,30453 Hanover, Germany.

Permabond CS A activator is commercially available from National Starch & Chemical Company, 10 Finderne Avenue, Bridgewater, N.J., USA.

ABS = acrylonitrile-butadiene-styrene terpolymer PMMA = polymethylmethacrylate The concentration of activator in an activator solution is expressed as % by weight based on the amount of solvent. The concentration of cyclohexanone is expressed as % by weight based on the total amount of solvent, the remainder being «-heptane. Ζ .η - 17Example 1 Four drops of CA-adhesive were placed as a bead or fillet on a sheet of black ABSplastic, then a large excess , (6 drops), of CA-activator solution was added on top of the bead. The adhesive was left to cure without application of a second substrate. After evaporation of the solvent, the specimens were judged. The results are shown in the following table.

In case of post application of large quantities of zi-heptane based CA-activators on top of CA-beads or fillets, the cured adhesive is often surrounded by a white area (white halo). See Nrs. 1; 2; 3; 5; 7; 9; 11.

A few percent of cyclohexanone added to the activator formulations successfully combats this effect. See Nrs. 4; 6; 8; 10; 13; 14.

It seems that addition of 3 % cyclohexanone is beneficial but not sufficient to obtain the full effect; see Nr. 12., but in the case of 5% and 7% (see Nrs. 13; 14) no white halo formation is observed (except: a slight whitening still remains in the case of adhesive o Loctite 407, which is a slow curing adhesive and which in the batch tested had a low reactivity).

Despite cyclohexanone’s pronounced solvent properties towards several plastics (e.g. ABS) the mixtures mentioned in the table were not found to cause swelling of the plastic (neither the black ABS, nor PMMA). -18Table 1 Nr. Activator Solution Loctite 401 Loctite 407 Loctite 410 Loctite 431 Loctite 460 LoctiteLID 3693 Sicomet 5195 1 Loctite 7455 hhh hhh hh hhh N h hh 2 Permabond CSA activator h hh h hh N hhh N 3 1 % DMPT in n-heptane hhh hhh hh hhh N h hhh 4 1 % DMPT in n-heptane/5 % cyclohexanone ... ... N N ... ... N 5 0.4 % DPDS in n-heptane hhh hhh hh hh h hh hhh 6 0.4 % DPDS in n-heptane/5 % cyclohexanone ... ... N N — ... N 7 15 %35-DCP in n-heptane hhh hhh hh hhh N hh hh -8 1.5 % 3,5-DCP in n-heptane/5 % cyclohexanone ... ... N N ... ... N 9 0.95 % DMPT; 0.09 %DPDS in n-heptane hhh hhh hh hh h hh hhh 10 0.95 % DMPT, 0.09 % DPDS in n-heptane/5 % cyclohexanone N hh ... N N N N 11 1.5 % 3,5-DCP, 0.09 %DPDS in n-heptane hhh hhh hh hhh N h h 12 1.5 % 3,5-DCP, 0.09 % DPDS in n-heptane/3 % cyclohexanone hh hh hh h N h h 13 15 % 3,5-DCP, 0.09 %DPDS in n-heptane/5 % cyclohexanone h h N N N N N 14 15 % 3,5-DCP, 0.09% DPDS in n-heptane/7 % cyclohexanone N h N N N N N Legend: h hh hhh slight white halo white halo very strong white halo no halo no data evaluated -19Example 2 Tests with other co-solvents like ethylacetate or acetone instead of cyclohexanone do not result in an attenuation of the white halo: The tests were carried out in the same way as mentioned above in Example 1. Formulations based on «-heptane; concentration of co-solvent as percent by weight of the solvent mixture as mentioned in left column. io Table 2 Co-Solvent Concentration Co-Solvent Loctite 401 Loctite 431 Loctite LID-3692 Sicomet 5195 3 % Ethyl acetate h hh hh hhh 5 % Ethyl acetate hhh hhh hh hhh 7 % Ethyl acetate hhh hhh h hhh 3 % Acetone hh hhh hh hhh 5 % Acetone hhh hhh hh hhh 7% Acetone hh hh hh hh Example 3 Further tests were conducted to compare cyclic ketones with linear ketones and cyclic ethers. As shown in Table 3, the results show that the cyclic ketones are effective in attenuating the white halo whereas the linear ketones and cyclic ethers tested are not.

I 6 4 2 2 -20Table 3 Nr. Activator Loctite401 Loctite 406 Loctite 480 Sicomet 5195 1 1 % DMPT n-heptane /12 % 1,4-dioxan hhh hhh hh hh 2 1 % DMPT n-heptane /12% THF hhh hhh hh hh 3 1 % DMPT n-heptane 16 % butanone hh hhh h hh 4 1 % DMPT n-heptane /12 % butanone hhh hhh hh hh 5 1 % DMPT n-heptane /16 % butanone hhh hhh hh hhh 6 1 % DMPT n-heptane / 3 % 3-pentanone hhh hhh hh hh 7 1 % DMPT n-heptane / 6 % 3-pentanone hhh hhh hhh hh 8 1 % DMPT n-heptane / 8 % 3-pentanone hhh hhh hh hhh 9 1 % DMPT n-heptane / 6 % 2-hexanone hh hh hh h 10 1 % DMPT n-heptane 16 % 4-methyl-2pentanone hhh hh h hh 11 1 % DMPT n-heptane /12 % 4-methyl-2pentanone hhh hhh hhh hh 12 1 % DMPT n-heptane /16 % 4-methyl-2pentanone hhh hhh hhh hh 13 1 % DMPT n-heptane / 6 % 3-octanone hh hhh hh hh 14 1 % DMPT n-heptane /12 % cyclobutanone N N N N 15 1 % DMPT n-heptane / 3 % cyclopentanone hh hhh h hh 16 1 % DMPT n-heptane / 6 % cyclopentanone N h N N 17 1 % DMPT n-heptane /12 % cyclopentanone hh hhh N hh 18 1 % DMPT n-heptane / 3 % cycloheptanone N h N N 19 1 % DMPT n-heptane / 6 % cycloheptanone N N N N 20 1 % DMPT n-heptane / 8 % cycloheptanone N N N N 21 1 % DMPT n-heptane / 6 % 2-methyl cyclopentanone h N N N 22 1 % DMPT n-heptane /12 % 2-methyl cyclopentanone N h h N 23 1.5 % 3,5-DCP, 0.09 % DPDS n-heptane /12% 1,4-dioxan hhh hhh hh hh 24 1.5% 3,5-DCP, 0.09% DPDS n-heptane/12% THF hhh hhh h hh 25 1.5% 3,5-DCP, 0.09% DPDS n-heptane / 6 % butanone hhh hhh hh hh 26 1.5% 3,5-DCP, 0.09% DPDS n-heptane /12 % butanone hh hhh hh hh 27 1.5% 3,5-DCP, 0.09% DPDS n-heptane /16 % butanone hhh hhh h hhh 28 1.5% 3,5-DCP, 0.09% DPDS n-heptane / 3 % 3-pentanone hhh hhh hh hh 29 1.5% 3,5-DCP, 0.09% DPDS n-heptane / 6 % 3-pentanone hh hhh hh hh 30 1.5% 3,5-DCP, 0.09% DPDS n-heptane / 8 % 3-pentanone hhh hhh h hhh 31 1.5% 3,5-DCP, 0.09% DPDS n-heptane / 6 % 2-hexanone hh hhh h h 32 1.5% 3,5-DCP, 0.09% DPDS n-heptane / 6 % 4-methyl-2pentanone hhh hhh h h 33 1.5% 3,5-DCP, 0.09% DPDS n-heptane /12 % 4-methyl-2pentanone hhh hhh h hh 34 1.5% 3,5-DCP, 0.09% DPDS n-heptane /16 % 4-methyl-2pentanone hh hhh hh hh 35 1.5% 3,5-DCP, 0.09% DPDS n-heptane / 6 % 3-octanone hhh . hhh h hh 36 1.5% 3,5-DCP, 0.09% DPDS n-heptane /12 % cyclobutanone N N N N 37 1.5 % 3,5-DCP, 0.09 % DPDS n-heptane / 3 % cyclopentanone hh hh h h 38 1.5% 3,5-DCP, 0.09% DPDS n-heptane / 6 % cyclopentanone N h N N 39 1.5 % 3,5-DCP, 0.09% DPDS n-heptane/12% cyclopentanone hh hhh h h 40 1.5 % 3,5-DCP, 0.09% DPDS n-heptane / 3 % cycloheptanone h N N N 41 1.5 % 3,5-DCP, 0.09% DPDS n-heptane / 6 % cycloheptanone N h N N 42 1.5% 3,5-DCP, 0.09% DPDS n-heptane / 8 % cycloheptanone N N N N 43 1.5% 3,5-DCP, 0.09% DPDS n-heptane / 6 % 2-methyl cyclopentanone N N N N 44 1.5% 3,5-DCP, 0.09% DPDS n-heptane /12 % 2-methyl cyclopentanone hh hhh N N Legend: h slight white halo hh white halo hhh very strong white halo N no halo ___ no data evaluated Comparative tests described above are carried out using commercially-available adhesive compositions but the individual nature of these adhesive compositions is not essential to the disclosure of the invention. The behaviour of activator solutions is to be compared within each test in relation to a particular adhesive composition and not from test to test in different adhesive compositions.

Although the invention has been described above, many modifications and equivalents thereof will be clear to those persons of ordinary skill in the art and are intended to be covered hereby, the true spirit and scope of the invention being defined by the claims.

Claims (21)

Claims:

1. An activator composition for the accelerated hardening of cyanoacrylate adhesives, wherein the composition comprises a solution of one or more 5 activators in a solvent mixture which comprises a volatile hydrocarbon and a cyclic ketone.

2. A composition according to claim 1 wherein the cyclic ketone is present in an amount of up to about 15%, particularly up to about 10%, by weight of the l o solvent mixture.

3. A composition according to claim 2 wherein the cyclic ketone is present in an amount of at least about 25% by weight of the solvent mixture.

4. A composition according to claim 3 wherein the cyclic ketone is present in an amount of at least about 3% by weight of the solvent mixture.

5. A composition according to claim 1 wherein the cyclic ketone is present in an amount in the range of 3% to 75% by weight of the solvent mixture.

6. A composition according to claim 5 wherein the cyclic ketone is present in an amount in the range of 4% to 7% by weight of the solvent mixture.

7. A composition according to any preceding claim wherein the cyclic ketone is 2 5 monocyclic or bicyciic.

8. A composition according to any preceding claim wherein the cyclic ketone is an optionally-substituted cyclic ketone having 3-10 carbon atoms per ring. -249. A composition according to claim 8 wherein the cyclic ketone is mono- or disubstituted on the ring with C1-C5 alkyl.

9. 10. A composition according to any preceding claim wherein the cyclic ketone is 5 an alicyclic ketone.

10. 11. A composition according to any preceding claim wherein the volatile hydrocarbon is an aliphatic hydrocarbon. 10

11. 12. A composition according to claim 11 wherein the volatile aliphatic hydrocarbon is «-heptane.

12. 13. A composition according to any preceding claim wherein the activator is 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 Ν,Ν-dimethylbenzylamine, N-methylmorpholine and N,N-diethyItoluidine; amine compounds with a boiling point of between 50°C. and 250°C. such as triethylamine, diethylamine, butylamine, isopropylamine, tributyl amine, Ν,Ν-dimethyl aniline, Ν,Ν-diethyl aniline, N,N-dimethyl-p-toluidine, Ν,Νdimethyl-/n-toluidine, Ν,Ν-dimethyl-o-toluidine, dimethyl benzyl amine, 25 pyridine, picoline, vinyl pyridine, ethanolamine, propanolamine and ethylene diamine; organic compounds containing the structural element, -N=C-S-S-; (1 ·>Ύ. Τ ϋ -25 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, and mixtures of any of the foregoing with each other.

13. 14. A composition according to any preceding claim wherein the composition comprises a mixture of two or more activators.

14. 15. A composition according to claim 14 wherein the composition comprises a mixture of: (A) 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 electron - withdrawing group which decreases the base strength of the substituted compound compared to the corresponding unsubstituted compound, Ν,Ν-dimethyl-p-toluidine, and mixtures of any of the foregoing, with (B) an organic compound containing the structural element, -N=C-S-S-.

15. 16. Use of an activator composition according to any of the preceding claims for the accelerated hardening of a cyanoacrylate adhesive.

16. 17. Use according to claim 16 wherein the activator composition is applied to the cyanoacrylate adhesive after application of the adhesive to a substrate.

17. 18. A process for the bonding of substrates or parts, characterised by the following series of steps: -2610 (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 the solvent mixture in the activator composition to air, optionally with heating or with the aid of a fan.

18. 19. A process according to claim 18 wherein at least one of the substrates or parts has a surface of a dark colour, or is transparent.

19. 20. A process according to claim 18 or 19 wherein at least one of the substrates 15 or parts is of a plastics material.

20.

21. A bonded assembly of substrates or parts bonded by a process according to any of claims 18-20.