GB1561180A - Nontacky coating and adhesive compositions - Google Patents

Description

(54) NONTACKY COATING AND ADHESIVE COMPOSITIONS (71) We, LOCTITE (IRELAND) LIMITED a body corporate organised under the laws of the Republic of Ireland of Kylemore Park North, Dublin 10, Ireland, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to nontacky coating and adhesive compositions.

Free radical curing compositions based on acrylate-type monomers, such as methylmethacrylate, among others, have long been known. Such compositions are typically initiated by organic peroxy compounds, e.g., benzoyl peroxide and methylethyl ketone peroxide, or by radiation-activated free radical generators such as benzophenone in combination with UV light. It has also been recognised that cure of such acrylate-type compositions is often inhibited to some extent by contact with oxygen, such as in atmosphere air. While this undesirable inhibiting effect can be overcome by various means, such as by application of heat, the need for surface curing at room temperature has not always been met. To facilitate handling, it is often desirable to obtain a dry-to-the-touch surface on the adhesive or coating even before any substantial cure has been effected.

More recently, the oxygen inhibition effect has been developed and commercially exploited in certain "anaerobic" curing adhesives and seal ants. These compositions depend on the exclusion of oxygen from the composition to allow curing to take place, usually between nonporous surfaces, as in threaded joints. These compositions remain liquid when in contact with an adequate concentration of oxygen, such as occurs in the atmosphere. In practice, this means that the compositions can be stored for long periods in thin-walled polyethylene containers or in the aerosol-type dispensers prepared as described in U.S.

Patent 3,736,260. Examples of these anerobic compositions have been described in detail in U.S. Patents 2,895,950; 3,218,305; 3,425,988; and 3,435,012, among others, as well as British Patent Specification 1,412,940. The compositions depend on the generation of free radicals, normally by a redox-type reaction catalysed by the metallic surfaces to which the compositions are applied in use, or by pre-applied primers. It has also been found that some of these compositions can be cured by exposing them to non-ionizing radiation, such as UV light: this is disclosed in French Patent 73.17729.

An anaerobic composition has as required elements a free radical polymerisable monomer (normally a mono-, di- or tri-acrylate or methacrylate) and a peroxy initiator or a photo-initiator, or both. It may include accelerators, such as amines and organic sulphimides. When such a composition is required to cure under irradiation such as UV, it must also include at least one photoinitiator or sensitiser such as benzoin methyl ether or one of the initiators described in Australian Patent 469,564. The composition may also include polymeric thickeners, colouring agents including those pigments used in reflective coatings, and plasticisers. Free radical stabilizers may also be required to balance the shelf life of the compositions against the speed of cure.These stabilisers are normally of the quinone type, and the preferred quinones are beta-naphthoquinone, 2-methoxy-1, 4-naphthoquinone, and p-benzoquinone. Other stabilisers are disclosed in U.S. Patent 3,043,820. Compatible plasticisers may optionally be used, the preferred plasticisers being selected from the group of polyester polymeric plasticisers described in U.S. Patent 3,794,610.

The anaerobic character of these compositions has made them suitable for such applications as threadlocking, the retaining of bearings on shafts, and other bonding and/or sealing applications wherein oxygen is excluded from the joint. However, the anaerobic character of the compositions has also caused considerable problems. In the first place, the liquid remaining outside the threaded joint or the bond line remains in the liquid or tacky state and never fully cures. This can cause serious problems when small parts are packed together for shipment purposes, as the parts can eventually stick together and become unusable. When conventional anaerobic compositions are used to bond decorative articles, the tacky surface outside the joint easily collects dust from the atmosphere and produces an unsightly and often dirty line adjacent to the bonds.When the compositions are used in very fine machinery, such as watches, any excess composition outside the joint which does not cure can flow into the working mechanism and cause moving parts to seize. An additional drawback has been the fact that, although the adhesives have excellent resistance to solvents and moisture and have good adhesion on a number of surfaces, they could never, because of their tacky outer surface, be used as coatings or potting materials for electronic parts.

Many methods are used today to reduce or abolish the inhibiting effect of atmospheric oxygen on the surface curing properties of acrylate-type compositions. It has been found that if irradiation-curable anaerobic curing compositions are exposed to ultraviolet light in the presence of inert gases such as nitrogen with the exclusion of oxygen, then tack-free surfaces can be obtained. It has also been found that certan types of monomers are less sensitive to inhibition by oxygen than others and these have been used to produce improved compositions. Another method involves the inclusion in the composition of waxes which exude to the surface as polymerisation proceeds and thereby form a barrier against inhibition of oxygen. However, this process is unsatisfactory since it leaves a waxy surface which often has to be removed by buffing or sanding before polishing.The wax in the material also reduces to some extent the adhesive properties of the cured compositions.

Other methods involve the use of comparible compounds which are themselves reactive with oxygen in the presence of free radicals. In other cases the addition of chain transfer agents has been found to retard or eliminate the inhibiting effect of oxygen on polymerisation. None of these methods has proven fully satisfactory, however.

According to the present invention, there are provided anaerobic-curing compositions which, while stable in suitable oxygen-permeable containers, will nevertheless cure when unenclosed, even in the presence of oxygen. There is also provided a new method of excluding oxygen from unenclosed anaerobic-curing compositions so as to enable the compositions to cure. There is also provided a method of rendering non-tacky anaerobic systems, as well as general purpose acrylate-based systems, the surface cure of which is inhibited by oxygen.

It has now been found that by including in the curable monomeric system a selected dry polymeric substance and a volatile solvent these compositions can be made to cure tack-free. On evaporation, the solvent deposits a thin film of the polymeric substance on the exposed surface of the liquid composition. This substantially excludes atmospheric oxygen from contact with anaerobic-curing material, which accordingly cures to a hard, tack-free solid. When one of these compositions of the invention is applied to the threads of a standard bolt and a mating nut is then assembled on the bolt, the anaerobic composition cures in the threads to effect a locking action. The excess anaerobic composition outside the threads also cures to a tack-free coating, which effect is both new and useful.

More specifically, the invention provides an anaerobically curable adhesive or coating composition comprising in admixture: an anaerobically curable portion comprising: (a) at least one acrylate or methacrylate monomer; (b) an initiator of free radical polymerisation; and an additive portion comprising (c) an organic solvent compatible (as hereinafter defined) with the anaerobically curable portion which is not a monomer chosen for the anaerobically curable portion; (d) dissolved in the solvent 2 to 200 percent by weight of the anaerobically curable portion of an organic polymer having an average molecular weight of more than 10,000 and a glass transition temperature of at least 00C; ; whereby, upon evaporation of at least some of the solvent, the exposed surface of the composition becomes nontacky and substantially resistant to the passage of oxygen, such that the corresponding anaerobic portion thereof is permitted to cure.

The invention also provides a method of rendering nontacky an anaerobically curable adhesive or coating composition containing at least one anaerobicaly curable acrylate or methacrylate monomer and a free radical initiator comprising (1) adding to such composition an organic solvent compatible (as hereinafter defined) with the anaerobically curable composition which solvent is not a monomer chosen for the anaerobically curable composition and in which solvent is dissolved 2 to 200 percent by weight of the anaerobically curable portion composition of an organic polymer having an average molecular weight of more than 10,000 and a glass transition temperature of at least OOC, and (2) allowing at least a portion of the solvent to evaporate, thereby causing the exposed surface of the compositionn to become nontacky.

The invention also provides a method of excluding oxygen from an anaerobic curing composition.

As used herein, the term "nontacky" means that the exposed surface of the adhesive or sealant or coating composition is dry to the touch, not sticky, and does not adhere to contiguous exposed surfaces on similarly coated items in normal storage and handling.

Also as used herein, the term "compatible" means that the solvent must be miscible with the curable portion in the concentration used, must be readily removable from the system by evaporation, and any solvent residue after evaporation must have no significant adverse effect on the cure of the curable portion.

The invention provides an acrylate or methacrylate based anerobically curing composition which comprises, in addition to conventional ingredients, a film-forming quantity in the sense hereinbefore defined, of at least one organic polymeric substance. It is necessary that the polymeric substance have an average molecular weight of at least 10,000. The molecular weight may be as high as 3,000,000 or even higher, provided that the polymeric substance remains soluble in a compatible solvent and has a sufficiently high glass transition temperature, as discussed below. Preferably, the molecular weight range will be from 10,000 to 1,000,000, more preferably from 10,000 to 50,000. The polymeric substance should also have a glass transition temperature of at least 0 C, preferably from 20 to 1200C.

It has been found that this combination of molecular weight and glass transition temperature is characteristic of organic polymers which are typically soluble in common organic solvents and exude to the surface of the anaerobically curable composition upon evaporation of the solvent, thereby forming a nontacky, dry surface which is also resistant to the passage of oxygen. Suitable polymeric substances typically have a intrinisic viscosity of at least 0.2. Preferably, the polymeric substance is selected from the class which comprises polyalkylmethacrylates, polyacrylates, polyvinyl acetates, polyvinylidene chlorides, cellulose acetate butyrates and polyurethanes. The most preferred class of polymeric substances is the polyalkyl methacrylates, such as polymethyl methacrylate and poly (isobutyl) methacrylate.Other polymeric substances may also be used, provided they meet the above-mentioned molecular weight and glass transition temperature requirements, can be dissolved in a compatible solvent, and are capable of producing a nontacky surface upon evaporation of at least some of the solvent.

The concentration of the polymeric substance must be related to its solubility in the chosen volatile solvent so that the substance quickly solidifies as a surface film of solid polymer after a relatively small quantity of the solvent has evaporated. Accordingly, the said concentration is in the range of 2% to 200% by weight of the anaerobically curable portion (i.e. monomer plus initiator and accelerator, if any) of the composition. Preferably, the concentration of the polymeric substance will be in the range of 3 to 160% by weight of the anerobically curable portion of the composition. As a percentage of the total composition (i.e. anaerobically curable portion plus additive portion), the concentration of the polymeric substances will usually be in the range of 1.5 to 60%, preferably 2 to 30%.

Below 1.5% there will ordinarily not be sufficient polymeric substance present to produce a tack-free surface of low oxygen permeability. Above about 60% the viscosity and other properties of the liquid concentration may be undesirably altered and properties of the cured composition may be degraded.

The solvent used must be compatible (as defined above) with the ingredients of the anerobically curable composition, and must not be a monomer chosen for the anerobically curable composition. Chlorinated hydrocarbons are preferred. A second preferred class of solvents comprises "reactive" solvents, by which is meant that any solvent remaining in the composition after evaporation is able to copolymerise with the acrylate or methacrylate ingredients of the composition. Reactive solvents preferably are selected from the low molecular weight methacrylate esters, e.g., methyl methacrylate, butyl methacrylate, and isopropyl methacrylate. Compositions containing members of this class of solvents have the added advantage that voids and bubbles do not appear in the coating after aging.With nonreactive solvents (which continue to evaporate during and even after cure), voids and cavities can occur which may be unsightly and which can give rise to a coating having lower resistance to chemicals and to the environment than when the preferred copolymerising solvents mentioned above are used. The amount of solvent used will be a matter of routine experimentation, depending upon the solubility of the polymeric substance selected, the volatility of the solvent, the desired viscosity of the composition, and such other considerations as would be apparent to those skilled in the art. In general, the solvent concentraton is not critical and may range from 2 to 98% by weight of the total composition.

As has been indicated, the compositions of this invention are rendered nontacky while still in their uncured (or perhaps slightly cured) condition by evaporation of at least some portion of the solvent. Ideally, the solvent is entirely evaporated; however, this is not a necessity in all cases. The key requirement is that sufficient solvent be removed to cause deposition at the surface of the anaerobically curable composition of sufficient polymeric substance to cause the anaerobically curable composition to be nontacky. Thus, the exact amount of solvent which must be removed in any given composition is a matter of simple experimentation and will, of course, depend upon the particular ingredients used. The necessary evaporation may be allowed to occur naturally by the volatile nature of the solvent, or the rate of evaporation may be quickened by application of heat or vacuum.If all the solvent is not to be removed, obviously if must be sufficiently removed that the residue does not significantly interfere with the cure or properties of the composition. Of course, in the case of "reactive" solvents, it may be permissible, and even desirable, to leave a substantial quantity of the solvent behind for coreaction with the monomer or monomers.

The monomer used can be any of a wide variety of known, free radical curable acrylate and alkyl acrylate (e.g., methacrylate) types. Typical of such materials would be methylmethacrylate. Anaerobically curable compositions based on such monomers are polymerised through the action of known free radical generating initiators, such as benzoyl peroxide, methylethyl ketone peroxide, azobisisobutyronitrile, among others. Such initiators are activated by application of moderate heat, as is well known in the art.

Numerous ultraviolet-sensitive free radical generators are also well known for such monomer systems.

The preferred monomers for use in the present compositions are those normally associated with anerobic curing properties, as previously mentioned. One particularly useful class of monomers is that described in U.S. Patent 3,425,988, mentioned above.

These monomeric polyacrylate esters may be made in a variety of ways; however, the method which has proven most eminently suited involves the reaction of a monofunctionally substituted alkyl or aryl acrylate ester containing an active hydrogen atom on the functional substituent. This mono-functional, acrylate-terminated material is reacted with an organic polyisocyanate in suitable proportion so as to convert all of the isocyanate groups to urethane or ureido groups. The monofunctional alkyl and aryl acrylate esters are preferably the acrylates and methacrylates containing hydroxy and amino functional groups on the nonacrylate portion thereof.Acrylate esters suitable for use in this invention have the formula

wherein X is selected from -0- and

and wherein R is a hydrogen atom or an alkyl group of 1 to 7 carbon atoms; R1 is a hydrogen or a chlorine atom or a methyl or ethyl radical; and R2 is a divalent organic radical which is an alkylene radical with 1 to 8 carbon atoms, a phenylene or a naphthylene radical. These groups, upon proper reaction with a polyisocyanate, yield a sealant monomer of the following formula:

wherein Rl, R2 and X are as defined above; n is an integer from 2 to 6 inclusive; and B is an n-valent organic radical derived from an alkyl, alkenyl, cycloalkyl, aryl, aralkyl, alkaryl or heterocyclic radical either substituted or unsubstituted.

As used herein the terms "acrylate" and "polyacrylate" include the methyl, ethyl and halogen homologues thereof.

The hydroxy- and amine-containing materials suitable for use in the preparation of the above monomeric products are exemplified by but not limited to such materials as hydroxy ethyl acrylate, hydroxy ethyl methacrylate, amino ethyl methacrylate, 3-hydroxy propyl methacrylate, amino propyl meth-acrylate, hydroxy hexyl acrylate, t-butylaminoethyl methacrylate and hydroxy octyl methacrylate.

Illustrative of the polyisocyanates employed are, among others, toluene diisocyanate, 4,4'-diphenyl diisocyanate, 4,4'-diphenylene methane diisocyanate, dianisidine diisocyanate, 1,5-naphthalene diisocyanate, 4,4'-diphenyl ether diisocyanate, p-phenylene diisocyanate, trimethylene diisocyanate, tetra-methylene diisocyanate, hexamethylene diisocyanate, ethylene diisocyanate, cyclohexylene diisocyanate, nonamethylene diisocyanate, octadecamethylene diisocyanate, 2-chloropropane diisocyanate, 2,2'-diethylether diisocyanate, 3-(dimethylamine) pentane diisocyanate, tetrachlorophenylene diisocyanate, 1,4-3-heptene diisocyanate and transvinylene diisocyanate.Still other polyisocyanates that may be used are the higher molecular weight polyisocyanates obtained by reacting polyamines containing terminal, primary and secondary amine groups or polyhydric alcohols, for example, the alkane and alkene polyols such as glycerol, 1,2,6-hexanethanol, 1,5pentanediol, ethylene glycol, polyethylene glycol, bisphenol-A and 4,4'-dihydroxyphenyldimethylmethane substituted bisphenol-A, with an excess of any of the above-described isocyanates. These higher molecular weight urethane or ureide polyisocyanates may be represented by the formula:

wherein B, X and n have the meanings set forth above and R3 is an alkylene, alkenylene, cycloalkylene, arylene, aralkvlene or alkarylene radical of 2 to 20 carbon atoms.

Preferred organic polyisocyanates comprise the higher alkenyl diisocyanates, the cycloalkenyl diisocyanates and the aromatic diisocyanates containing more than 8 carbon atoms and preferably from 15 to 30 carbon atoms, such as, for example. octamethylene diisocyanate, durene diisocyanate, 4,4'-diphenyl diisocyanate, and the higher molecular weight polyisocyanate reaction products mentioned hereinbefore.

Further detail may be obtained by reference to U.S. Patent 3,425,988.

Other useful monomers are the polyacrylate esters represented by the formula

wherein R4 is a hydrogen or a halogen atom or an alkyl group of from 1 to 4 carbon atoms; p is an integer equal to at least 1. and preferably equal to from 1 to 4; and M is an organic radical containing at least two carbon atoms and having a total bonding capacity of p plus 1.

With regard to the upper limit for the number of carbon atoms in M, workable monomers exist at essentially any value. As a practical matter, however, a general upper limit is about 50 carbon atoms, preferably 30, and most preferably 20. For example, M can be an organic radical of the formula

wherein each of Y1 and Y iS an organic radical, preferably a hydrocarbon group, containing at least 2 carbon atoms, and preferably from 2 to 10 carbon atoms, and Z is an organic radical, preferably a hydrocarbon group, containing at least 1 carbon atom, and preferably from 2 to 10 carbon atoms.

Other classes of useful polyacrylate ester monomers are the reaction products of di- or tri-alkylolamines (e.g., ethanolamines or propanolamines) with acrylic acids, such as are disclosed in French Patent No. 1,581,361.

Still other useful monomers are polyacrylate esters which have the following formula:

wherein R5 represents a hydrogen atom, a lower alkyl radical of from 1 to 4 carbon atoms, a hydroxy alkyl radical of from 1 to 4 carbon atoms, or a radical of the formula

where R4 is as defined above; R6 is a hydrogen atom, a hydroxyl group or a radical of the formula

q is an integer equal to at least 1, e.g., from 1 to 15 or higher, and preferably from 1 to 8 inclusive; s is an integer equal to at least 1, e.g., 1 to 40 or more, and preferably from 2 to 10; and r is 0 or 1.

Typical examples of polyacrylate esters corresponding to the above formula are di-, triand tetraethyleneglycol dimethacrylate, di(pentamethyleneglycol) dimethacrylate, tetraethyleneglycol diacrylate, tetraethyleneglycol di(chloro-acrylate), diglycerol diacrylate, diglycerol tetramethacrylate, butyleneglycol dimethacrylate, neopentylglycol diacrylate, and trimethylolpropane triacrylate.

While di- and other polyacrylate esters (and particularly the polyacrylate esters described in the preceding paragraphs) have been found particularly desirable, monoacrylate esters also may be used. When dealing with monoacrylate esters, it is highly preferable to use an ester which has a relatively polar alcoholic moiety. Such materials are less volatile than low molecular weight alkyl esters and, more important, the polar group tends to provide intermolecular attraction during and after cure, thus producing more desirable cure properties, as well as a more durable sealant or adhesive. Most preferably the polar group is selected from labile hydrogen, heterocyclic ring, hydroxy, amino, cyano, and halogen polar groups.Typical examples of compounds within this category are cyclohexyl-methacrylate tetrahydrofurfuryl methacrylate, hydroxyethyl acrylate, hydroxypropyl methacrylate, t-butylaminoethyl methacrylate, cyanoethylacrylate, and chloroethyl methacrylate.

Anaerobic compositions based on such monoacrylates are described more fully in U.S.

Patent 3,435,012.

Still other useful class of monomers is that disclosed by U.S. Patent 3,944,521. These monomers have the formula

wherein the aromatic groups are substituted or unsubstituted benzene rings or other aromatic groups; R9 and R are hydrogen, alkyl, aryl, hydroxyalkyl groups, or halogen; and R7 and R8 are

wherein x is an integer from 1 to 20 and preferably 1 to 5, and R11, R12 and R13 are hydrogen, alkyl, alkoxy groups, or halogen.

Examples of aromatic groups other than benzene are naphthalene, anthracene and other polynuclear groups. The alkyl groups may be methyl, ethyl and other primary, secondary or tertiary alkyl groups and the hydroxyalkyl groups, for example, hydroxyethyl. The preferred halogen is chlorine.

A preferred monomer of this class is the dimethacrylate of propoxylated bisphenol-A, the number of propoxyl residues in the chain being preferably 1 to 5; others are propoxylated bisphenol-C dimethacrylate, ethoxylated bisphenol-A dimethacrylate, and ethoxylated bisphenol-A diacrylate.

As indicated above, the anaerobic compositions are discussed herein are prepared by mixing a peroxy initiator with one or more acrylate esters as described above. While certain peroxides (generally dialkyl peroxides) have been disclosed as useful initiators in, e.g., U.S.

Patents 3,419,512 and 3,479,246, the hydroperoxides are far superior and constitute a highly preferred embodiment.

The real benefit of the nonhydroperoxide initiators is as co-initiators with the hydroperoxides to make the cure properties of the anaerobic composition more universal.

Hydrogenperoxide may be used, but the most desirable polymerisation initiators are the organic hydroperoxides. Included within this definition are materials such as organic peroxides or organic peresters which decompose or hydrolyse to form organic hydroperoxides in situ. Examples of such peroxides and peresters are cyclohexyl and hydroxycyclohexyl peroxide and t-butyl perbenzoate, respectively.

While the nature of the organic hydroperoxides is not critical to the broad concept of this invention, the general class of hydroperoxides can be represented by the formula R14OOH, wherein R14 generally is a hydrocarbon group containing up to 18 carbon atoms, and referably is an alkyl, aryl or aralkyl hydrocarbon group containing from 3 to 12 carbon atoms. Naturally R can contain any substituent or linkage, hydrocarbon or otherwise, which does not affect the hydroperoxide adversely for the purpose disclosed herein.Typical examples of such organic hydroperoxides are cumene hydroperoxide, tertiary butyl hydroperoxide, methylethylketone hydroperoxide, and hydroperoxides formed by oxygenation of various hydrocarbons such as methylbutene, cetane, and cyclohexene, and various ketones and ethers, including certain compounds represented by formula 5, above.

The organic hydroperoxide initiators can be used within wide ranges, e.g., up to 20% by weight of the composition. Mostly commonly, however, they comprise no more than 10 percent by weight of the composition since above that level adverse effects on the strength and durability of the cured composition may be experienced. While in some instances lower amounts can be used, 0.1% by weight of the composition is a common lower limit.

Preferably the hydroperoxide initiator comprises from 0.1% to 5% by weight of the composition.

Common additives for or anaerobic compositions are latent polymerisation accelerators, compounds which do not of themselves initiate cure, but which accelerate the cure once it has been started by the polymerisation initiator. it should be noted that large numbers of polymerisation accelerators are known in the art, and the broad concept of this invention is intended to encompass any polymerisation accelerator which can be incorporated in the anerobic composition without destroying the essential characteristics of such composition.

Among the earliest of the polymerisation accelerators used in anaerobic compositions were amines. The most commonly used are tertiary amines such as tributylamine and triethylamine. Essentially the entire class of tertiary amines can be used in such compositions, and the class may be broadly represented by the formula NR15R16R17 wherein each of Rips, R16 and R17 is a hydrocarbon group containing up to ten carbon atoms. Naturally, the hydrocarbon groups can contain any substituent or linkage which does not adversely affect the ability of the amine to perform its intended function.

Preferably, each of R15, R16 and R17 is an alkyl, aryl or aralkyl group containing up to 8 carbon atoms The N,N-dialkyl aryl amines are particularly effective tertiary amines. Typical amines within this class may be represented by the following general formula:

wherein E represents a carbocyclic aromatic nucleus which is a phenyl or naphthyl 18 and R19 are hydrocarbon groups contaning up to 10 carbon atoms, and preferably are lower alkyl radicals of 1 to 4 carbon atoms; t is 0 or an integer from 1 to 5 inclusive; R20 is a hydrocarbon group containing up to 5 carbon atoms, and preferably is an alkyl or alkoxy radical of 1 to 4 carbon atoms inclusive, provided that when an R20 radical is in the ortho position, t is greater than 1.

Primary and secondary amines also can be used as accelerators in the anaerobic compositions of this invention. Particularly good primary and secondary amines are the primary and secondary alkyl amines, most particularly those wherein each alkyl group contains up to 10 carbon atoms. A separate and highly preferred class of secondary amines has been found to be the class of heterocyclic secondary amines, particularly heterocyclic secondary amines containing up to 20 carbon atoms, It also is preferred to use those amines wherein the heterocyclic ring is hydrogenated. Typical of such compounds are pyrrolidine, piperazine and 1,2,3,4-tetrahydroquinoline.

Another highly successful class of accelerators is the organic sulphimides, i.e., organic compounds which contain the group

Because of the extreme effectiveness of the sulphimides as accelerators for anaerobic compositions, compositions containing sulphimides constitute a highly preferred embodiment of the invention disclosed herein. While the broad class of organic sulphimides can be used successfully, the sulphimides most commonly used can be represented by the formula

wherein each of R21 and R22 is a hydrocarbon group containing up to ten carbon atoms, and preferably up to six carbon atoms. Naturally R i and R22 can contain any linkage or substituent which does not adversely affect the sulphimide for its intended use in the anaerobic composition.Further, R21 and R22 can be united to bond the sulphimide group in a heterocyclic ring, or a polynuclear heterocyclic ring system. Of the organic sulphimides, benzoic sulphimide has been found to be the most preferable.

An even more highly preferred composition is that which contains a sulphimide, particularly benzoic sulphimide, in combination with either a heterocyclic secondary amine or a tertiary N,N-dialkyl aryl amine, both of which are described above. For an expanded discussion of this type of system, reference is made to U.S. Patent 3,218,305.

Other less active accelerators can be used in the compositions of this invention. Typical examples of such accelerators are succinimide, phthalamide and formamide.

Routine testing will easily determine the optimum amount of accelerator which can be incorporated in a given anaerobic composition. However, the following general guidelines may be used. With regard to tertiary amines, large amounts may be used if desired, up to 8 percent by weight of the composition, or higher. However, little if any additional benefit is obtained above about 5 percent. Most preferably these tertiary amine accelerators are used at from 1 percent to 4 percent by weight of the anaerobic composition. The succinimide, phthalamide and formamide accelerators also can be used in significant amounts, up to 8 percent by weight of the composition, or higher, and preferably from 1 percent to 5 percent by weight. The sulphimide and heterocyclic secondary amine accelerators generally are used at less than 4 percent by weight of the anaerobic composition.In the special case where a sulphimide is used in combination with a heterocyclic secondary amine or an N,N-dialkyl arylamine, the total of the two accelerators preferably does not exceed 4 percent by weight of the anaerobic composition, and either component does not exceed 3 percent by weight.

Other ingredients can be used in the anaerobic compositions useful to this invention, and in its preferred aspects polymerisation inhibitors are included to offer protection against spurious polymerisation prior to the time of intended use. The quinones have been found to be a particularly effective class of polymerisation inhibitors, and can be used herein.

Examples of such quinones are beta-naphthoquinone, 2-methoxy-1, 4-naphthoquinone, and p-benzoquinone. Compositions containing such inhibitors are described more fully in U.S. Patent 3,043,820, mentioned above.

Other typical functional ingredients which can be used if desired to impart commercially desirable properties to the composition are thickeners, dyes, adhesive agents, thixotropic agents, and plasticisers, especially those polyester plasticisers described in U.S. Patent 3,794,610.

Such functional materials can be used in such combination and proportions as desired, provided they do not adversely affect the nature and essential properties of the composition. While exceptions may exist in some cases, these materials in toto generally do not comprise more than 50% by weight of the total composition, and preferably not more than 20% by weight of the composition. The above-described anaerobic compositions generally can be prepared by the use of any conventional mixing techniques. Certain other ingredients which may desirably be added may not possess ready solubility, and if such additives are used (e.g., silica), it may be desirable to use high-shear mixing.

The following examples illustrate, but do not limit, the invention.

EXAMPLE 1 This example shows comparative data for normal anaerobic curing compositions compared with compositions of the invention.

Monomer I used in this Example has the formula

in which (PR) represents the propylene triol oligomer devoid of its three hydroxyl groups.

A general process for preparing Monomer I, aong others, is given in British Patent Specification 1,430,422.

Compositions A, B, and C were made up by simple admixture of the following ingredients in the proportions given: Parts by Weight A B C 1. Monomer I - 95 2. Ethoxylated bisphenol-A diacrylate - - 95 3. Benzoin isobutyl ether 4 4 4 4. Cumene hydroperoxide 1 1 1 5. Poly(methylmethacrylate) 19 - 6. Methylmethacrylate 77 - Total weight prepared 140g 10g 50g Ingredient 5 is the polymeric substance used in the invention It has an intrinsic viscosity in chloroform at 250C between 2.5 and 3.0 and is supplied by Imperial Chemical Industries, Limited under the product reference CA-603. Ingredient 6 is the volatile solvent; it is a reactive solvent in the sense described above. Ingredient 3 is a photoinitiator which reacts to UV-irradiation by releasing free radicals. Ingredient 4 is a peroxy catalyst, which forms free radicals.Ingredients 1 and 2 are polymerisable monomers in the sense current in the art, which can polymerise to form the anaerobically cured adhesive or coating composition.

It will be seen that compositions B and C are conventional, each requiring the addition of a portion of composition A to convert it into a composition of the invention.

Compositions A (90g) and B (log) were thoroughly mixed to yield composition D of the invention. Composition A (50g) and C (50g) were thoroughly mixed to yield composition E of the invention.

Each of composition B and C (or the prior art) and D and E (of the invention) was tested as follows. A thin film of the composition was spread over a microscope slide and exposed to a Philips MB/U ("Phillips" is a Registered Trade Mark) 400-watt ultraviolet lamp at a distance of 10cm.

All the compositions were converted to hard solids B and D in 2 minutes, C and E in 1 minute.

The prior art compositions B and C retained greasy or tacky surfaces, which remained thus even after several hours, whereas the compositions D and E of the invention became dry to the touch within 30 seconds of exposure to the lamp, and remained dry indefinitely thereafter.

EXAMPLE 2 Compositions F and G were made up by simple admixture of the following ingredients in the proportions given: Parts by Weight F G Ethoxylated bisphenol-A diacrylate 95 Cumene Hydroperoxide 4.5 3.5 Tributyl amine 0.5 0.5 Poly(methylmethacrylate) - 19 Methylmethacrylate - 77 Total Weight prepared 25g 75g Composition F was thoroughly mixed with composition G to make composition H.

Bonds were made by applying adhesive to a grit blasted flat surface of mild steel.

Another surface of steel was placed over the first and the two clamped together with a spring clamp. This was done using composition H and also composition F.

After 5 hours the clamps were removed and the metal parts were found to be strongly bonded together. The excess adhesive outside the bond made with composition F was wet to the touch. The excess adhesive outside the bond was made with composition H was dry to the touch.

EXAMPLE 3 Compositions J and K were made up as shown below: Parts by Weight J K 1. Poly(methyl,n-butylmethacrylate) (Elvacite 2013 - DuPont, the word "Elvacite" being a Registered Trade Mark 31 2. Ethylene glycol dimethacrylate 69 3. Monomer II 45.0 4. Monomer I 20.6 5. Hydroxypropylmethacrylate 28.6 6. Acrylic Acid 2.8 7. Tributyl amine 0.3 8. Cumene hydroperoxide 2.6 Monomer I is as defined above. Monomer II has the formula

A general process for preparing Monomer II is given in British Patent Specification 1,430,422, above cited.

To 90 parts by weight of formulation K were added 10 parts of J to form, after mixing, formulation L.

Thin films of formulations K and L were spread over glass surfaces (microscope slides) and heated in an oven at 105"C for twenty minutes. They then were cooled to a temperature of 35"C. At that temperature the surface of formulation K was tacky, that of formulation L was not.

WHAT WE CLAIM IS: 1. An anaerobically curable adhesive or coating composition comprising in admixture: an anaerobically curable portion comprising (a) at least one acrylate or methacrylate monomer; (b) an initiator of free radical polymerication; and an additive portion comprising (c) an organic solvent compatible (as hereinbefore defined) with the anaerobically curable portion which is not a monomer chosen for the anaerobically curable portion; (d) dissolved in the solvent 2 to 200% by weight of the anaerobically curable portion of an organic polymer having an average molecular weight of more than 10,000 and a glass transition temperature of at least OOC; ; whereby upon evaporation of at least some of the solvent the exposed surface of the composition becomes nontacky and substantially resistant to the passage of oxygen, such that the corresponding anaerobic portion thereof is permitted to cure.

2. A composition as claimed in claim 1 wherein the initiator is a UV initiator.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (14)

**WARNING** start of CLMS field may overlap end of DESC **. Composition F was thoroughly mixed with composition G to make composition H. Bonds were made by applying adhesive to a grit blasted flat surface of mild steel. Another surface of steel was placed over the first and the two clamped together with a spring clamp. This was done using composition H and also composition F. After 5 hours the clamps were removed and the metal parts were found to be strongly bonded together. The excess adhesive outside the bond made with composition F was wet to the touch. The excess adhesive outside the bond was made with composition H was dry to the touch. EXAMPLE 3 Compositions J and K were made up as shown below: Parts by Weight J K 1. Poly(methyl,n-butylmethacrylate) (Elvacite 2013 - DuPont, the word "Elvacite" being a Registered Trade Mark 31 2. Ethylene glycol dimethacrylate 69 3. Monomer II 45.0 4. Monomer I 20.6 5. Hydroxypropylmethacrylate 28.6 6. Acrylic Acid 2.8 7. Tributyl amine 0.3 8. Cumene hydroperoxide 2.6 Monomer I is as defined above. Monomer II has the formula A general process for preparing Monomer II is given in British Patent Specification 1,430,422, above cited. To 90 parts by weight of formulation K were added 10 parts of J to form, after mixing, formulation L. Thin films of formulations K and L were spread over glass surfaces (microscope slides) and heated in an oven at 105"C for twenty minutes. They then were cooled to a temperature of 35"C. At that temperature the surface of formulation K was tacky, that of formulation L was not. WHAT WE CLAIM IS:

1. An anaerobically curable adhesive or coating composition comprising in admixture: an anaerobically curable portion comprising (a) at least one acrylate or methacrylate monomer; (b) an initiator of free radical polymerication; and an additive portion comprising (c) an organic solvent compatible (as hereinbefore defined) with the anaerobically curable portion which is not a monomer chosen for the anaerobically curable portion; (d) dissolved in the solvent 2 to 200% by weight of the anaerobically curable portion of an organic polymer having an average molecular weight of more than 10,000 and a glass transition temperature of at least OOC;; whereby upon evaporation of at least some of the solvent the exposed surface of the composition becomes nontacky and substantially resistant to the passage of oxygen, such that the corresponding anaerobic portion thereof is permitted to cure.

2. A composition as claimed in claim 1 wherein the initiator is a UV initiator.

3. A composition as claimed in claim 1 wherein the initiator is an organic peroxide.

4. A composition as claimed in any of claims 1 to 3 wherein the solvent is a chlorinated hydrocarbon.

5. A composition as claimed in any of claims 1 to 3 wherein the solvent is a reactive solvent (as hereinbefore defined).

6. A composition as claimed in any of claims 1 to 5 wherein the organic polymer is a polyacrylate or a polyalkylmethacrylate.

7. An anaerobically curable adhesive or coating composition comprising in admixture; an anaerobically curable portion comprising (a) at least one acrylate or methacrylate monomer; (b) an organic hydroperoxide or perester initiator of free radical polymerisation; and an additive portion comprising (c) an organic solvent compatible (as hereinbefore defined) with the anaerobically curable portion, which is not a monomer chosen for the anaerobically curable portion; (d) dissolved in the solvent 2 to 200% by weight of the anaerobically curable portion of an organic polymer having an average molecular weight of more than 10,000 and a glass transition temperature of at least OOC;; whereby upon evaporation of at least some of the solvent the exposed surface of the composition becomes nontacky and substantially resistant to the passage of oxygen, such that the corresponding anaerobic portion thereof is permitted to cure.

8. A composition as claimed in claim 7 wherein the initiator is cumene hydroperoxide.

9. A composition as claimed in claim 7 or 8 which contains in addition a UV initiator.

10. A composition as claimed in any of claims 7 to 9 wherein the solvent is a chlorinated hydrocarbon.

11. A composition as claimed in any of claims 7 to 9 wherein the solvent is a reactive solvent (as hereinbefore defined).

12. A composition as claimed in any of claims 7 to 11 wherein the organic polymer is a polyacrylate or a polyalkylmethacrylate.

13. An anaerobically curable adhesive or coating composition including an organic polymer having an average molecular weight of more than 10,000 and a glass transition temperature of at least 0 C substantially as described with particular reference to any of the Examples excluding the comparative material.

14. A method of rendering nontacky an anaerobically curable adhesive or coating composition containing at least one anaerobically curable acrylate or methacrylate monomer and a free radical initiator comprising (1) adding to such composition an organic solvent compatible (as hereinbefore defined) with the anaerobically curable composition which solvent is not a monomer chosen for the anaerobically curable composition and in which solvent is dissolved 2 to 200% by weight of the composition of an organic polymer having an average molecular weight of more than 10,000 and a glass transition temperature of at least 0 C and (2) allowing at least a portion of the solvent to evaporate, thereby causing the exposed surface of the composition to become nontacky.