Activator Compositions for Cyanoacrylate Adhesives

(19) United States (12) Patent Application Publication (10) Pub. No.: US 2005/0000646 A1 Ryan et al. US 20050000646A1 (43) Pub. Date: Jan. 6, 2005 (54) ACTIVATOR COMPOSITIONS FOR CYANOCRYLATE ADHESIVES (76) Inventors: Bernard Ryan, Dublin (IE); Hanns Misiak, Dublin (IE); James Houlihan, Dublin (IE) Correspondence Address: Henkel Corporation Legal Department 1001 Trout Brook Crossing Rocky Hill, CT 06067 (US) (21) (22) (86) (30) Appl. No.: PCT Filed: PCT No.: Nov. 14, 2001 10/495,817 Nov. 13, 2002 PCT/ IE02/ 00157 Foreign Application Priority Data (IE) ...................................... .. S2001/0987 Publication Classification (51) Int. Cl.7 .............................. ..C09J 5/04; B01J 31/00 (52) U.S.Cl. ................. .. 156/314; 156/331.2; 156/331.6; 502/167 (57) ABSTRACT An activator composition for accelerating hardening and achieving cure-through-volume of cyanoacrylate adhesives) comprising; (a) one or more compounds selected from the group consisting of :(i) pyrazine; or a pyrazine derivative; said pyrazine derivative being pyrazine substituted with at least one electron-releasing group; (ii) pyridine N oxides substituted with at least one electron-releasing group; or (iii) 2,6 pyridines being pyridines substituted in the 2- and 6-positions by substituents, at least one of the substituents being electron-releasing provided that both substituents are not methyl; and (b) a volatile solvent carrier for the com- pound. US 2005/0000646 A1 ACTIVATOR COMPOSITIONS FOR CYANOCRYLATE ADHESIVES FIELD OF THE INVENTION [0001] This invention relates to activator compositions, particularly well suited for accelerating the hardening of cyanoacrylate adhesives. The invention further relates to a process for the accelerated bonding of substrates using cyanoacrylate adhesives. BRIEF DESCRIPTION OF RELATED TECHNOLOGY [0002] Adhesive compositions based upon cyanoacrylate esters are well known and have found 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. [0003] If the cyanoacrylate (CA) adhesive is convention- ally 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 the adhesive may rarely be achieved, i.e. cure-through-gap or cure- through-volume (CTV) performance may be unsatisfactory. [0004] With certain substrates, particularly substrates hav- ing acidic surfaces, such as wood or paper, the polymerisa- tion reaction may be retarded, often times to an unmanage- able extent. Moreover, unless the adhesive is gelled or rendered thixotropic by appropriate additives to confer such properties, the wood or paper substrates, due to their poros- ity, tend to draw the adhesive out of the joint gap by capillary action before hardening has taken place in the gap. [0005] Heretofore efforts have been made to accelerate the polymerisation of such CA adhesives by means of certain additives. Addition of accelerators directly to the adhesive formulation is possible to only a very limited extent, how- ever, since substances having a basic or nucleophilic action, which would normally bring about a pronounced accelera- tion of the polymerisation of the cyanoacrylate adhesive, are generally used, it is usually at the expense of the storage stability of such formulations. [0006] Addition of such accelerators shortly before appli- cation of the adhesive results in virtually a two-component (two-part) system—in other words the adhesive and the accelerator are stored apart—the accelerator would not normally be mixed with the adhesive for storage purposes. However, such method has the disadvantage that the work- ing 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 homoge- neity of mixing are difficult to achieve. Moreover, use of such a two-part system is often seen as cumbersome to the end user, and sometimes only modestly improves the intended result. [0007] Activators are also used in the form of a dilute solution which is either applied beforehand onto a substrate such as a part which is to be bonded, and/or is applied onto the adhesive where it is still liquid (before the adhesive has fully cured) after the substrates have been joined. The Jan. 6, 2005 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 and/or on the adhesive. [0008] Japanese Patent Application Nos. JP-A-62 022 877, JP-A-03 207 778 and JP-59-66471 propose the use of solutions of various amines in solution as accelerators for cyanoacrylate adhesives. U.S. Pat. No. 3,260,637 of von Bramer discloses the use of a range of organic amines (excluding primary amines) as accelerators for cyanoacry- late adhesives, particularly for use on metallic and non- metallic substrates. [0009] N,N-dimethyl-p-toluidine has been widely used as an accelerator for the accelerated hardening of cyanoacrylate adhesives. This chemical provides a short duration of the surface activation, which does not permit long waiting times between application of the accelerator solution beforehand to the substrates to be bonded and the subsequent bonding process. In addition, the use of N,N-dimethyl-p-toluidine in some countries oftentimes involves rigorous regulatory labelling requirements. [0010] Basicity of an accelerator substance is not a suffi- cient criterion for identifying solutions which are acceptable in practice in terms of application technology. Many sub- stances, such as alkylamines, 1,2-di-(4-pyridyl-ethane), 4,4‘- dipyridyl disulfide, 3-(3-hydroxypropyl)pyridine, 1,2-bis- (diphenylphosphino)-ethane, pyridazine, methylpyridazine or 4,4‘-dipyridyl, are so basic or nucleophilic that sponta- neous superficial hardening takes place at the adhesive interface (shock hardening) before the activator is able to initiate polymerisation throughout the liquid adhesive (usu- ally a drop or layer) by dispersion processes such as by convection and diffusion. The result is that an often cloudy polymerisation occurs at the surface only. With other com- pounds, such as oxazoles, the basicity is evidently too low, and the hardening is often too slow for practical purposes. [0011] German Patent DE-A-22 61 261 proposes accel- erator substances containing the structural element —N=C—S—, including 2,4-dimethylthiazole. U.S. Pat. Nos. 5,567,266 (Liu) and U.S. Pat. No. 5,643,982 (Liu) describe accelerator compositions comprising amine com- pounds. EP 0 822 242 and U.S. Pat. No. 5,749,956 (Fisher et al.) describe non-ozone depleting non-flammable co- solvent useful for carrying inter alia accelerators. [0012] European Patent Publication No. 0 271 675 A2 of Three Bond Co. Ltd. describes a primer for CA adhesive for use in bonding non-polar or highly crystallized resins such as polyolefins, polyethyleneterephthalates, nylons, fluorine- containing resins, soft PVC films and the like which are notorious as being ordinarily difficult to bond. The primer comprises (A) a compound selected from the group consist- ing of benzene ring compounds having aldehyde groups and nitrogen or oxygen atom-containing heterocyclic com- pounds having aldehyde groups (such as 2-pyridine car- boxylaldehyde, 2,6-pyridine carboxylaldehyde and pyrrole 2-carboxylaldehyde), and (B) an organic amine compound. The EP ’675 publication states that in bonding non-polar or highly crystallized resins using a CA adhesive the primer instantaneously exhibits a high bonding strength at ambient temperature by simply applying such primer onto a surface of one of the resins, applying the CA adhesive onto a surface US 2005/0000646 A1 of the other resin and bringing both surfaces into contact with each other, thus achieving “zero gap” and an instanta- neous high bonding strength. [0013] British Patent Specification No. 1 230 560 of International Chemical Company Limited (ICC) describes CA adhesive compositions containing certain substituted heterocyclic compounds as accelerators. The compositions may be presented in a two-part form, the first part compris- ing the CA adhesive and the second part comprising at least one of the substituted heterocyclic compounds, preferably in solution in an organic solvent. In the compositions in which the heterocyclic compound is an iminoethylene-substituted triazine or pyrimido-pyrimidine, the heterocyclic compound is invariably present in one part of a two-part composition because iminoethylene-substituted triazines and pyrimido- pyrimidines accelerate the polymerisation so rapidly they must be kept apart from the CA composition before use. [0014] Japanese Patent Abstract Publication No. 62018485 of Alpha Giken KK also describes a primer for a CA adhesive and is not concerned with an activator for good CTV performance. [0015] Activator solutions are often applied by spraying. 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). [0016] Aliphatic hydrocarbons such as heptane are often used as a carrier for CA activators. [0017] Notwithstanding the state-of-the-art, it would be desirable to provide new activators and combinations thereof with different physical properties from the activator substances than those known heretofore. In addition, it would be desirable for such activators to have a pronounced accelerating action on the cyanoacrylate adhesive and low volatility. Such physical properties will allow for the appli- cation of the activators either onto the substrate to be bonded prior to application of the cyanoacrylate adhesive or after application of the cyanoacrylate adhesive onto the substrate to be bonded as an overspray. It would also be desirable to find chemicals useful as activators for cyanoacrylate adhe- sives which are subject to regulatory labelling requirements less rigorous than those currently in place for N,N-dimethyl- p-toluidine. SUMMARY OF THE INVENTION [0018] According to one aspect, the present invention provides a composition (in particular suitable for use as an accelerator composition for CTV of cyanoacrylate adhe- sives) comprising: [0019] (a) one or more compounds selected from the group consisting of: [0020] pyrazine; or a pyrazine derivative; [0021] said pyrazine derivative being pyrazine substituted with at least one electron-releasing gI'O1lp; [0022] (ii) pyridine N oxides substituted with at least one electron-releasing group; or [0023] (iii) 2,6 pyridines being pyridines substi- tuted in the 2-and 6-positions by substituents, at Jan. 6, 2005 least one of the substituents being electron-releas- ing provided that both substituents are not methyl; and [0024] (b) a volatile solvent carrier for the com- pound. [0025] In the groups to (iii) above (the groups to (iii) are used for convenience and mixtures of compounds within a designated group and/or between groups is encompassed by the use of the phrase “at least one”) the electron releasing effect of the substituent is measured relative to hydrogen— in other words a substituent which is considered more electron-releasing than a hydrogen substituent is desired. Usually the electron-releasing effect would be manifested in a net increase in the base strength of the substituted com- pound compared to the corresponding Substituted com- pound. Such a net increase in the base strength of the substituted compound compared to the corresponding unsubstituted compound is desirable for all compounds of groups to (iii) above. [0026] This base strength effect is particularly desirable for the substituted pyrazines of group and the pyridine N-oxides of group (ii). [0027] A net increase in the base strength of the substi- tuted compound compared to the corresponding unsubsti- tuted compound is seen as desirable also for the 2,6 pyridines of group (iii). In the group (iii) compounds the proximity of the substituents of these compounds to the N atom of the heterocycle also has an effect on the nucleophi- licity of the (N atom) of the compounds which is thought to occur due to steric hindrance effects. In this respect it is desirable that the compounds of group (iii) are not substi- tuted in both the 2-and 6-position by methyl. The present inventors have found that such substitution (for example in lutidine-2,6-dimethyl pyridine) results in a compound which is too reactive toward cyanoacrylate (both substituents being electron-releasing and together not providing sufficient steric hindrance) and does not achieve the desirable effects set out above. Accordingly at least one of the substituents in the 2-or 6-positions should not be methyl and desirably at least one of those substituents is more sterically hindering toward the N atom of the heterocycle than a methyl group. It may be that both substituents are each more sterically hindering than a methyl group would be in the 2-and 6-positions. [0028] The compounds of groups to (iii) may be additionally substituted with one or more other groups such as one or more electron-withdrawing and/or electron-releas- ing groups and/or groups that are neither electron-withdraw- ing nor electron-releasing. Overall it is desirable that the net effect of all substituents is to increase the base strength of the substituted compound as compared to the unsubstituted one. [0029] In the case of pyrazines where there are two N heteroatoms it is desirable that each N heteroatom is steri- cally hindered each desirably by two N heteroatom adjacent groups particularly where there are two electron-releasing groups. Desirably both groups are electron-releasing groups. In this respect N heteroatom adjacent position is used to mean the substituent is on a carbon atom of the heterocycle which is directly bonded to a N heteroatom of the hetero- cycle. [0030] In the case of pyridine, the substituent(s) is (are) desirably sufficiently bulky to decrease the nucleophilicity US 2005/0000646 A1 of the N heteroatom(s) of the heterocycle. In other words the substituents should be such as to make the compound less reactive (as accelerator) toward a cyanoacrylate adhesive. Less reactive is used herein in the comparative sense against the parent pyridine compound. [0031] Preferably the electron releasing substituent(s) are selected from one or more of straight chain, branched chain, or cyclic (each optionally substituted) alkyl groups particu- larly where there are two electron-releasing . Typically up to 40 carbon atoms may be present in the substituent though this upper limit is not seen as critical in at least as so far as electron-releasing effects are to be considered. Typical sub- stituents such as methyl, ethyl, propyl (in particular n-propyl or iso propyl), butyl (in particular n-butyl, iso butyl, tert butyl), pentyl such as n-pentyl or cyclopentyl, or hexyl such as cyclohexyl may be employed. [0032] These chains may themselves be further substituted (provided that the substitution results in an electron-releas- ing substituent). The additional substituent(s) may be one or more substituents selected from the group consisting of: [0033] halo, CR=CR1R2, CF3, CCI3, OC(O)R, COOR, COR, OR, SR, CONR1R2, NO2, NO3, SOR, SO2NR2, NRSOZR, SOZR3, SO3R3, PO(OR3)2 and optionally substituted C6-C20 aryl, , or aryloxy, CSOR3, COONR32, NRCOOR, NRCOR, N=N— R3, OOR3, SSR3, OC(O)OR3, N(OR3)2, P(OR3)2, SOR3, OSR3, wherein R, R1 and R2 (which may be the same or different) are H, optionally substituted C1-C103al.l