IE83383B1 - Acrylic adhesive compositions - Google Patents

Description

ACRYLIC ADHESIVE COMPOSITIONS Technical Field This invention relates to acrylic adhesive compositions and particularly to the use in acrylic adhesive formulations of monomers or reactive diluents which have not previously been reported as useful in adhesive compositions. The invention is applicable to acrylic adhesive compositions with any appropriate cure system. The adhesive compositions find use as bonding agents, sealants, gasketing materials and potting compositions, for example.

Brief Description of Related Technology Numerous different acrylates and methacrylates are known as monomers in acrylic adhesive compositions. Frequently used monomers include hydroxy-containing [meth]acrylates, especially short—chain monoacrylate hydroxy (lower alkyl) methacrylatcs such as hydroxypropylmethacrylate (HPMA) and hydroxyethylmethacrylate (HEMA).

As used herein in relation to alkyl [meth]acrylates including hydroxyalkyl [meth]acrylates, the terms "short-chain" and "lower alkyl" mean having up to 5 carbon atoms in the alkyl group.

Short-chain monofunctional [meth]acrylates may be used alone as monomers but are often used with polyfunctional [meth]acrylate monomers and/or with [meth]acrylate-terminated prepolymers or resins. In particular, short-chain [meth]acrylates are often added to acrylic adhesive compositions at the formulation stage, as a reactive diluent or short-chain monomer to be present in addition to a [meth]acrylate-terminated prepolymer or resin. Hydroxy (lower alkyl) [meth]acrylates are typically used for this purpose.

However there are commercial concerns with the ongoing use of hydroxy (lower alkyl) methacrylates such as HPMA and HEMA. That is, methacrylates of this type have recently come under scrutiny by regulatory authorities and there appears to be a trend towards seeking heightened labelling requirements for compositions containing these compounds. This regulatory issue is causing manufacturers of acrylic adhesives to search for alternatives to HPMA and HEMA with a View to replacing at least a substantial portion of the hydroxy (lower alkyl) [meth]acrylate content with other compounds which do not have the same perceived concerns. Accordingly, it would be desirable to provide alternative monoacrylate [meth]acrylates which can provide compositions having adhesive properties that are at least comparable to similar formulations containing HPMA and HEMA, and whose use is not clouded by the regulatory perception discussed above.

The use of ketonyl [meth]acrylates in acrylic adhesive compositions has not previously been suggested. U.S. Patent No. 2, 376, 033 (Clifford) describes a method of producing keto esters of acrylic acids by reacting a metal salt of the acrylic acid with a halogen-substituted ketone. Compounds which may thus be prepared include acetyl methyl methacrylate (aeetonyl methacrylate), alpha acetyl ethyl methacrylate, propionyl methyl methacrylate, cyclohexanonyl methacrylate, methyl cyclohexanonyl methacrylate, 1—carbethoxy acetyl methyl methacrylate, and benzoyl methyl methacrylate. predicted.

Despite the state of the art, it would be desirable to provide acrylic adhesive compositions which display commercially acceptable cure properties and which yield bonds with good durability in high humidity environments. In general, it would be desirable to provide acrylic adhesive compositions using monoacrylate [meth]acrylates which can replace (at least in part) HPMA and/or HEMA while maintaining good cure properties and bond characteristics.

Summary of the Invention The present invention provides an adhesive formulation comprising: (i) a short chain polymerisable monoacrylate [meth]acry1ate ester‘, at least a substantial portion of which is a ketonyl [meth]acry1ate; optionally in combination with: (ii) a polymerisable [meth]acrylic monomer; and (iii) cure ingredients therefor.

In another aspect the invention provides an adhesive formulation comprising: (a) a polymerisable [methlacrylic monomer; (b) a reactive diluent capable of co-polymerising with the said monomer , at least a substantial portion of which is a ketonyl [meth]acrylate; and (C) cure ingredients for the monomer.

The term [meth]acrylate as used herein means acrylate or methacrylate.

It is an object of the present invention to reduce any content of free hydroxy (lower alkyl) methacrylate in the formulation to a level below that which would require labelling in a particular market. The term "a substantial portion" as used herein is to be interpreted in a manner consistent with this object. Suitably the term a "substantial portion" may indicate a proportion in the range from 10% to 100% by weight, desirably in the range from 40% to 100% by weight.

In the case where a ketonyl [meth]acrylate is used as a reactive diluent, the ketonyl [meth]acrylate desirably forms at least 80% by weight of the diluent, and more desirably 95~100% by weight of the diluent added to the monomer when making up the formulation.

Suitably, any remaining portion of the diluent is a conventional reactive diluent other than a monoacrylate hydroxy (lower alkyl) [meth]acrylate. Desirably the sole reactive diluent added to the monomer when making up the formulation is a ketonyl [meth]acrylate.

Most desirably, any content of hydroxy (lower alkyl) methacrylate does not exceed l% by weight of the total formulation.

The ketonyl [meth]acrylate not only acts as a reactive diluent but also serves as a satisfactory solvent for the cure ingredients and other additives (such for example as thickeners and stabilisers) in the formulation.

It has been found that adhesive compositions based on a ketonyl [meth]acrylate monomer have comparable adhesive properties and some improved humidity ageing characteristics as compared to similar adhesive compositions based on a conventional short—chain hydroxyalkyl [meth]acrylate monomer such as HPMA. No regulatory issues have arisen with regard to the ketonyl [meth]acrylates.

Suitably the ketonyl [meth]acrylate may be of the formula: CH1 = C-—C————O _(cH2)n C —--R2 II o 0 wherein: R1 is H or C1-C5 alkyl, particularly C1-C2 alkyl; R2 is C1-C5 alkyl, cyclohexyl, phenyl, benzyl, or substituted derivatives of any of the foregoing; and n is 1-5.

In the definition of R2, "substituted derivatives" may be substituted or interrupted by oxygen, carbonyl or an ester group, particularly a C1-C5 alkyl ester group; or in the case of cyclohexyl, phenyl or benzyl, may be substituted with a C1-C5 alkyl group which may itself be optionally substituted or interrupted by oxygen, carbonyl or an ester group, particularly a C1-C5 alkyl ester group.

More suitably, 11 may be 1 or 2.

Most suitably, the ketonyl [meth] acrylate may be any of those described in U.S.

Patent No. 2, 376, 033 (Clifford) and listed in the acknowledgement of that document hereinabove. The contents of U.S. Patent No. 2, 376, 033 (Clifford), including the preparation methods described therein, are incorporated herein by reference.

Suitably, the cure ingredients may provide any desired acrylic cure system, including free radical, anaerobic, photo—activated, air-activated, moisture-activated and any combination of these cure systems. A heat—activated cure system may also be used but, desirably, the cure system does not require the application of external heat.

The conventional ingredients for acrylic adhesive compositions are well known to those skilled in the art and are described, for example, in GB 1 422 439.

In a certain aspect, the present invention provides an anaerobic adhesive composition comprising: (i) a polymerisable[meth]acrylic monomer selected from poly- and mono - functional [meth]acrylate esters and [meth]acrylate - terminated resins or prepolymers; (ii) a reactive diluent capable of co - polymerising with the monomer, at least a substantial portion of the diluent being a ketonyl [meth]acrylate; and (iii) ingredients for an anaerobic cure system for the monomer.

The invention further provides a method of bonding and/or sealing two substrates comprising applying an anaerobic adhesive composition as defined above to at least one substrate, and bringing the two substrates together so as to exclude oxygen from the composition, and allowing the composition to cure.

Anaerobic compositions generally contain an initiator such as peroxide, an accelerator such as an amine or organic sulfimide and a stabiliser.

In another aspect the invention provides a light-activated adhesive composition comprising: (i) a polymerisable[meth]acrylic monomer selected from poly- and mono - functional [mcth]acrylate esters and [meth]acrylate — terminated resins or prepolymersg (ii) a reactive diluent capable of co — polymerising with the monomer, at least a substantial portion of the diluent being a ketonyl [meth]acrylate; and (iii) ingredients for a light-activated cure system for the monomer.

The invention further provides a method of bonding and/or sealing two substrates comprising applying a light-activatable adhesive composition as defined above to at least one substrate, exposing the composition to light which activates the cure system, and bringing the two substrates together before or after the exposure to light.

Where the ketonyl [mcthlacrylate is used with another [methlacrylic monomer, the other [methlacrylic monomer may be any of the monomeric or telechelic [methlacrylates known in the field of adhesive and sealant compositions.

The other polymerizable [methlacrylate ester monomers (i) suitable for use in this invention include a wide variety of materials such as those given in U.S. Patent No. , 218,305 (Krieble), U.S. Patent No. 4, 417, 92 (Azevedo), U.S. Patent No. 4, 451, 615 (Charnock), U.S. Patent No. 5, 116, 558 (Wrobel et al.), and U.S. Patent No. 3, 996, 308 (Douek et al.), the contents of which are incorporated herein by reference.

One desirable class of polymerisable monomers is the poly- and mono-functional acrylate and methacrylate esters of the general formula: CH2:C(R)COOR1 (I) where R may be hydrogen, halogen or alkyl of 1 to about 4 carbon atoms, and R1 may be selected from alkyl, cycloalkyl, alkenyl, cycloalkenyl, alkaryl, aralkyl or aryl groups of 1 to about 16 carbon atoms, any of which may be optionally substituted or interrupted as the case may be with silane, silicon, oxygen, halogen, carbonyl, hydroxyl, ester, carboxylic acid, urea, urethane, carbamate, amine, amide, sulfur, sulonate, sulfone and the like.

More specific acrylate monomers particularly desirable for use herein include polyethylene glycol di—[mcth]acrylates, such as triethylene glycol di-methacrylate ("TRIEGMA"), dipropylene glycol di-[meth]acrylate, bisphenol-A di-[meth]acrylates, such as ethoxylatcd bisphenol-A methacrylate ("EB IPMA") and tetrahydrofuran [meth]acrylates and di-[meth]acrylates, hexanediol di-[meth]acrylate, trimethylol propane tri-[meth]acrylate, methyl [meth]acrylatc, cyclohexyl [meth]acrylate, 2- aminopropyl [meth]acrylate, an acrylate ester corresponding to the structure shown below: R o I II / C|‘—0 J C—C=CH2 P R n 3 (11) where R2 may be selected from hydrogen, alkyl of 1 to about 4 carbon atoms, hydroxyalkyl of 1 to about 4 carbon atoms or —-CH2-O-C —c|: =CH2 where R3 may be selected from hydrogen, halogen, and alkyl of 1 to about 4 carbon atoms; R4 may be selected from hydrogen, hydroxy and —CH2-O-C—C=CH2 m is an integer equal to at least 1, e.g., from 1 to about 8 or higher, for instance, from 1 to about 4; n is an integer equal to at least 1, e.g., 1 to about 20 or more; and p is 0 or 1.

Of course, combinations of these [meth]acrylate monomers may also be used.

The [meth]acrylate monomers should desirably be present in the compositions within the range of from about 1% by weight to about 60% by weight, more desirably from about 5% by weight to about 50% by weight, such as from about 10% by weight to about 40% by weight, based on the total composition.

The polymerizable [meth]acrylate ester monomers suitably include a [meth]acrylate-terminated prepolymer in addition to a poly- or mono functional [rneth]acrylate ester.

Other preferred acrylate ester monomers are urethane - acrylates as known to the art and disclosed, for example in U.S. Patent No. 3, 425, 988 Gorman e_t a_l. or U.S.

Patent No. 4, 533, 446 Conway e_ta_l. the contents of which are incorporated herein by reference. Suitable monomers include those selected from the class consisting of urethane acrylates having the general formula: (CH2:C(R5)COOR6OCONH-)2R7 (111) wherein R5 is H, CH3, CZHS or C1; R6 is (r) a C1,, hydroxyalkylene or aminoalkylene group, (ii) a C16 alkylamino C1_3 alkylenc, a hydroxyphenylene, aminophenylene, hydroxynaphthylene or aminonaphthylene optionally substituted by a C1_3 alkyl, C" alkylamino or di—C1_3 alkylamino group; and R7 is CH0 alkylene, alkenylene, or cycloalkylene, C640 arylene, alkarylene, aralkylene, alkyloxyalkylene or aryloxyarylene optionally substituted by 1-4 halogen atoms or by 1-3 amino or mono— or di—C1_3 alkylamino or C1_3 alkoxy groups; or said acrylates having the general formula: (CH2:C(R5)COOR°OCON(H)R7N(H)COX-)nR8 (IV) wherein R5, R6 and R7 have the meanings given above; R8 is the non-functional residue of a polyamine or a polyhydric alcohol having at least 11 primary or secondary amino or hydroxy groups respectively; X is O or NR9 where R9 is H or a C1_7 alkyl group; and n is an integer from 2 to 20.

Copolymers or mixtures of monomers disclosed herein with other compatible monomers are also contemplated.

The anaerobic cure system useful in the present invention includes a variety of ingredients such as one or more initiators of polymerization and one or more accelerators of polymerization. lnitiators of free-radical polymerization useful in the instant composition include peroxides, hydroperoxides, peresters, and peracids. Desirably the initiator is a peroxide such as benzoyl peroxide or a hydroperoxide such as cumene hydroperoxide. Such initiators are generally present in the sealant composition in the amounts of about 0.1% to about 5% by weight of the composition, and desirably about 0.1% to about 2.0% by weight.

Commonly known accelerators of polymerization include amines (including amine oxides, sulfonamides, and triazines) and sulfimides. Tertiary amines, such as N,N-dimethyl-p-toluidine, N,N-dimethyl-o-toluidine, N,N-diethyl-p—toluidine and/or N,N-diethyl-o—toluidine, and sulfimides such as 3-oxo-2, 3-dihydrobenz—[d]isothiazole— , 1—dioxide, commonly known as saccharin, are particularly useful as are acetyl phenylhydrazine and maleic acid. Two or more of these materials may be used in combination. Of course, other materials known to induce anaerobic cure may also be included or substituted therefor. See for example Loctite U.S. Patent Nos. 3, 218, 305 (Krieble), 4, 180, 640 (Melody), 4, 287, 330 (Rich) and 4, 321,349 (Rich). Other suitable accelerators are organometallic compounds, preferably organometallic polymers containing a metallocene moiety such as a ferrocene moiety. Suitable metallocenes in related compositions are disclosed more fully in U.S. Patent No. 3, 855, 040. The accelerators are preferably added to the monomer in amounts of about 0.1% to about 2.5% by weight of the composition. Other metallo—containing materials which are non—polymeric have also been found to be effective.

Inhibitors and chelators, well recognised in the art for imparting stability to polymerizable compositions and for scavenging free radicals, are recommended. Those inhibitors useful in the present composition are usually selected from the group consisting of hydroquinones, benzoquinones, naphthoquinones, phenanthraquinones, anthraquinones, and substituted compounds of any of these. Naphthoquinone and anthraquinone are particularly suitable. Among the chelators which may be optionally present in the adhesive composition are the beta-diketones, ethylenediamine tetraacetic acid (EDTA) and the sodium salt of EDTA. Both the inhibitors and chelators may be effectively employed in levels of about 0.1 to about 1% by weight of the monomer, without adversely affecting the speed of cure of the polymerizable adhesive/sealant composition.

Photoinitiators enhance the rapidity of the curing process when photocurable compositions are exposed to electromagnetic radiation.

Such materials include, but are not limited to, photoinitiators available commercially from Ciba Specialty Chemicals, Tarrytown, New York under the "IRGACURE" and "DAROCUR" tradenames, specifically "IRGACURE" 184 (1- hydroxyeyclohexyl phenyl ketone), 907 (2-methyl[4-(methylthio)phenyl] morpholino propanone), 369 (2-benzylnn N,N-dimethylamino(4- morpholinophenyl)—1—butanone), 500 (the combination of 1-hydroxy cyclohexyl phenyl ketone and benzophenone), 651 (2,2-dimethoxyphenyl acetophenone), 1700 (the combination of bis(2,6-dimethoxybenzoyl—2,4—,4—trimethyl pentyl phosphine oxide and 2-hydroxymethylphenyl-propanone), 819 (bis(2,4,6-trimethyl benzoyl) phenyl phosphine oxide) and "DAROCUR" 1173 (2-hydroxy—2-methylphenylpropane) and 4265 (the combination of 2,4,6-trimethylbenzoyldiphenyl-phosphine oxide and 2- hydroxy 2—methyl—1-phenyl—propan—1—one); photoinitiators available commercially from Union Carbide Chemicals and Plastics Co. Inc., Danbury, Connecticut under the "CYRACURE" tradename, such as "CYRACURE" UVI-6974 (mixed triaryl sulfonium hexafluoroantimonate salts) and UVI-6990 (mixed triaryl sulfonium hexafluorophosphate salts); and the visible light [blue] photoinitiators, dl- camphorquinone and "IRGACURE" 784DC. Of course, combinations of these materials may also be employed herein.

Photoinitiators particularly suitable for use herein include ultraviolet photoinitiators, such as 2,2—dimethoxy—2-phenyl acetophenone (gg, "IRGACURE" 651), and 2-hydroxy—2—methyl—1—phenylpropane (gg_., "DAROCUR" 1173) and the ultraviolet/visible photoinitiator combination of bis(2,6-dimethoxybenzoyl-2,4-,4- trimethylpentyl) phosphine oxide and 2-hydroxy-2—methyl—1—phenyl~propan—1—one (gg_., "IRGACURE" 1700), as well as the visible photoinitiator bis(h5 -2,4-cyclopentadien—1— yl)—bis[2,6-dit1uoro—3—(1H-pyrrolyl)phenyl]titanium (e_.g;, "IRGACURE" 784DC).

According to another certain aspect, the present invention provides an air- activatable adhesive composition comprising: a). at least one free—radically polymerisable monomer wherein all or a substantial part of the monomer content is a ketonyl [meth]acrylate, and b). an activator system for effective polymerisation of the free-radically polymerisable monomer, said activator system comprising at least one auto- oxidisable compound, with the proviso that the composition does not contain a peroxide, or a peroxide precursor which produces peroxide in the absence of air or any ingredient which is a significant source of radicals in the absence of air.

In the air—activatab1e composition as defined above, the presence of a weak acid is also generally preferred. The composition will also generally comprise one or more soluble ionic salts, particularly metal salts.

The auto-oxidisable compound may suitably be any of those described in EP—A— O,502,733 or EP-A- f), 611, 813 or their US equivalents, the contents of which are incorporated herein by reference. A particularly desirable auto-oxidisable compound is a dihydropyridine having a general formula selected from 11: R7 R1 R7 R1 R7 R R R5 R6 1 R6 l 2 R5 1 R2 R \R2 R5 4R3 R3 R4 R4 3 i’) (ii) (iii) ||:l7 I137 R1 Fl R R1 R2 R5 R2 R5 \R3 R4 3 R4 UV) (V) II where: R1 to R7, which may be the same or different, are independently selected from hydrogen, hydrocarbyl and heterohydroearbyl groups, silyl groups, and substituted derivatives of any of the foregoing, and any two of the groups R1 to R-1 may together form a mono- or polycyclic ring structure, which may optionally be a fused ring structure, and which in turn may be substituted, provided that none of the groups R1 to R7 is a group which is known to interfere with polymerisation, and that in the case of 1,4—dihydropyridines of formula II (iv) the groups R2 and R5 at the 3- and 5-positions are not both electron—withdrawing groups.

For the auto-oxidisable compound (b), 1,4-dihydropyridines of formula II (iv) and 1,2—dihydropyridines of formula II (V) are preferred, the 1,2-dihydropyridines being most preferred. R7 in the compounds of formula II (iv) or II (V) is preferably other than hydrogen, and more preferably is an electron-donating group. In the case of 1,4-dihydropyridines of formula II (iv) the groups R2 and R5 at the 3- and 5-positions must not both be electron-withdrawing groups such as ester, acid, ketone, amide or nitrile groups because such substituents would render the 1,4-dihydropyridine stable to air oxidation. Other 1,4-dihydropyridines including the parent 1,4-dihydropyridine react rapidly in air [N.C. Cook and EJ. Lyons, J. Amer. Chem. Soc., 87, 3238 (1965)].

The term "hydrocarbyl" as used herein includes: (i) straight chain or branched linear or alicyclic aliphatic groups including alkyl, alkenyl and alkynyl, preferably containing from 1 to 20, more preferably from 1 to 10, most preferably from 1 to 5 carbon atoms; and alkylene and alkenylene groups forming part of a ring structure and which preferably contains from 3 to , more preferably 5 to 20 carbon atoms; (ii) aromatic groups including aryl, alkaryl and aralkyl groups, preferably containing 6 to 20 carbon atoms, more preferably 6 to 10 carbon atoms, and optionally having a fused ring structure.

The term "heterohydrocarbyl" as used herein includes hydrocarbyl groups as described above interrupted by one or more hetero atoms selected from oxygen, nitrogen or sulphur.

The term "substituted" or "substituted derivative" as used herein includes the appropriate group substituted with one or more oxygen, nitrogen, sulphur or halogen atoms or atom-containing moieties, or with one or more hydrocarbyl, heterohydrocarbyl or silyl groups, which in turn may be substituted with one or more oxygen, nitrogen, sulphur or halogen atoms or atom-containing moieties. Preferably R1 to R7 and/or the substitucnts on the ring formed by any two of the R1 to R7 groups are hydrogen or methyl, ethyl, propyl, butyl, phenyl, benzyl, amide or trimethyl silyl groups. Halogen may be chlorine, bromine, fluorine or iodine.

Another group of autoxcs having the structure I in EP-A—0,502,733 includes partially reduced diazines, more particularly dihydropyridazines, dihydropyrimidines and dihydropyrazines.

Other auto-oxidisable compounds which may be used include those described in EP—A—0,356,875, German Specification Nos. 3,829,461, 4,123,194 and 4,330,354 and the compounds described in our Irish patent application no. 980775 and International patent application no. PCT/IE99/00095 entitled AUTO—OXlDATION SYSTEMS FOR AIR-ACTIVATABLE POLYMERISABLE, the contents of which, and of their U.S. equivalent, are incorporated herein by reference.

Preferred soluble ionic salts for inclusion in the air-activatable adhesive composition are metal salts of the type generally used in oil drying technology. The metals should have several valency states and suitable metal salts are those of multivalent metals, especially transition metals. The metal ions are preferably present in their low valency state. The metal salt must be at least partially soluble in the composition, and may be present in the composition in an effective amount which is generally in a range of between about 1 and about 1,000 parts per million, particularly about 1 to 300 ppm, more particularly about 30 to 200 ppm.

The choice of metal may have a velocity determining effect on initiation of polymerisation because of a temperature dependence of the metal component in the process. Iron, cobalt, manganese and vanadium are highly active at room temperature.

In addition, compounds of these metals can be mixed with one or more other metallic components such as lead, cerium, copper, calcium, barium, zinc and/or zirconium.

Metal naphthenates or metal acetyl acetonates are generally soluble in the composition, but other salts or organometallics may be used if they are sufficiently soluble.

The auto—oxidisable compound will generally be present in an effective amount for effecting polymerisation of the composition upon exposure to atmospheric oxygen.

Such effective amount is generally within the range of from about 0.1 to about 20%, suitably from about 0.1 to about 10%, more suitably about 0.5 to about 5%, based on the weight of the polymerisable composition.

The weak acid, when required for the air-activatable adhesive composition, is an acid other than a mineral acid. The pKa of the weak acid normally is no lower than about 0.5 with the preferred limit being about 0.9. The upper limit is approximately , more desirably 11.5. However, carboxylic acids which have a pKa of up to about , desirably 6 or 7 are particularly suitable.

The carboxylie acids may contain one or more carboxyl groups, suitably 1 to 4 and more particularly 1 or 2 carboxyl groups. Suitable aliphatic carboxylic acids are CH8 and desirably CH0 monocarboxylic acids.

The choice of the acid depends to a large extent on the auto-oxidisable material being used. Suitable acids may be monobasic or polybasic. Typical but not limiting examples of suitable acids are fonnic acid, acetic acid, propionic acid, maleic acid, malic acid, fumaric acid, acrylic acid and copolymers thereof, methacrylic acid and copolymers thereof, pyruvic acid, itatonic acid, nadic acid, benzoic acid, phthalic acids, cinnamic acid, trichloroacetic acid and saccharin. The effective amount of the acid is generally Within the range from about 0.1 to about 20%, suitably from about 0.1 to about 10%, more desirably from about 0.5 to about 5% based on the weight of the polymerisable composition.

A masked carboxylic acid compound hydrolyzable on contact with moisture, such as an acid anhydride, may be used. Attention is directed to EP-A-0 356 875 or its U.S. equivalent, the contents of which are incorporated herein by reference.

Peroxides, or peroxide percursors which produce peroxide in the absence of air, or any ingredient which is a significant source of radicals in the absence of air, should not be included in the air—activatable compositions, so that polymerisation of the free- radically polymerisable monomer does not commence until it is exposed to oxygen.

The air-activatable compositions of the present invention may suitably comprise 0.1 to 20% by weight of the auto-oxidisable compound, 0.1% to 20% by weight of the weak acid (if present) and at least 10% by weight of the free-radically polymerisable monomer, optionally with the ionic salt, thickeners, fillers, pigments, reducing agents and/or stabilisers, the total constituents adding up to 100%.

The invention also provides a method of bonding two substrates comprising applying an air-activatable adhesive composition as defined above to at least one substrate, exposing the composition to oxygen for sufficient time to activate polymerization, and bringing the two substrates together. Typically at least about 1 minute, but desirably at least about 2 minutes exposure to air would be suitable.

Furthermore, the invention provides a method of forming a polymer, for example in topical coatings, encapsulation, moulding and the like, comprising exposing to oxygen for sufficient time to activate polymerization a composition as defined above.

Typically at least about 1 minute, but desirably at least about 2 minutes exposure to air would be suitable.

The above—described air—activatable compositions are stable when prepared in the absence of air. Exposure to air results in the polymerisation of the composition, the polymerisation being sustained in the presence or absence of air once the initial exposure to air has taken place. Typically, the exposure to air should be for at least about 5 seconds, preferably not less than 30 seconds, more preferably 1 to 5 minutes.

The air - activatable composition may be agitated during its exposure to oxygen to accelerate activation by introducing oxygen into the composition. The purpose of agitation is to increase the surface area of the composition exposed to the oxygen. For example, the composition may be applied to a substrate in finely divided form e.g. by spraying or in the form of a foam. The composition may be packaged in and/or dispensed from a container having a nozzle which entrains air as the composition is dispensed e.g. an aerosol container or pump-action aspirator. In addition, or alternatively, the composition may be agitated on the substrate e.g. by stirring.

Agitation of the composition also improves cure-through-volume (CT V) in a layer having significant depth.

The invention further provides an air - activatable composition as described above packaged in an aerosol container or pump-action aspirator.

General When any of the compositions of the invention are prepared with reactive diluents which are capable of copolymerising with the monomer(s), the concentration of such diluents should preferably be less than 60%, for example 40 to 10%, by weight of the composition.

The balance of the composition comprises the monomer together with other additives known to the art which may be employed as needed and at concentrations known in the art. One or more stabilisers, including polymerisation inhibitors such as those of the quinone or hydroquinone type and/or chelating agents, may suitably be used. Inhibitors are used in an amount sufficient to prevent premature polymerisation of the composition.

The composition may optionally further comprise reducing agents, thickeners, fillers and pigments.

Suitable reducing agents may be, but are not limited to, acetylphenylhydrazine, tetramethylthiourea or thiocaprolactam.

Polymeric thickeners may be present in the compositions in a minor amount, up to about 50%, and may be thickeners such as a polymer or prepolymer of low or high molecular weight. Suitable polymeric thickeners are a commercially available methacrylate polymer sold by E.I. du Pont de Nemours and Company, under the trademark Elvacite or by Rohm and Haas under the Trade Mark Ryloid, as well as styrene-methyl methacrylate co-polymers and polybisphenol A maleate (sold by ICI Americas Inc. under the trademark Atlac). It is also possible to add inert filling materials such as finely divided silica, fumed silica (treated or untreated), [Q U] montmorillonite, clay, bentonite and the like. The use of micronized silica would result in a paste—like thixotropic composition.

Additionally, it is conventional to include in adhesive formulations certain "inert" fillers such as wood flour, glass fibres, cotton linters, mica, alumina, silica and the like to modify viscosity, improve impact resistance and for other purposes. Such fillers could be incorporated in the formulations of the present invention. Small percentages of silane monomers could also be added to increase moisture resistance, as well as to enhance bonding of an adhesive to glass and similar surfaces. Other substances such as dyes, fire retarders, stabilizers such as quinones and hydroquinones, thixotropes, plasticizers, antioxidants, and the like may also be included, although such additives may often be furnished in the principal ingredients, making their separate introduction unnecessary.

A primer of a kind known in the art may be used on one or both surfaces, if desired. A copper based primer is preferred.

The invention is illustrated further in the following non—limiting examples.

Example 1 describes anaerobic adhesive formulations having acetonyl methacrylate as a reactive diluent. Examples 2-5 describe air-activated compositions which illustrate one aspect of the invention but also show more generally that satisfactory adhesive properties are retained, and in some respects enhanced, when hydroxypropyl methacrylate is replaced wholly or partially by acetonyl methacrylate in an adhesive composition. Aeetonyl methacrylate was prepared following the method described in U.S. Patent No. 2, 376, 033 (Clifford).

Examples Example 1 Acetonyl methacrylate was employed as a replacement for HPMA as the reactive diluent in a conventional peroxide-initiated anaerobic acrylic adhesive formulation, and tested under a Variety of conditions. The monomer was a polyurethane methacrylate resin as used in conventional formulations and as described for example in US Patent No. 4, 018, 851. It should be noted that such resins may contain a small residue of HPMA which is in excess of the amount which was required for capping the polyurethane backbone. Such residual HPMA was not replaced by acetonyl methacrylate. However the content of residual HPMA in the resin can be monitored so that it does not exceed a certain percentage by weight (e.g. 1% by weight) of the total formulation.

Two formulations were made up as follows: Formulation A Formulation B Polyurethane methacrylate resin 73.7g 73.7g Hydroxypropyl methacrylate (Diluent) 14.5g — Acetonyl methacrylate (Diluent) — 14.5g Acrylic acid 6.0g 6.0g Saccharin 1.0g 1.0g Cumene hydroperoxide 2.0g 2.0g Other ingredients (accelerator, stabiliser, 3.0g 3.0g chelating agent, dye) Each formulation was tested as an anaerobic adhesive and also as a primer- activated adhesive, using conventional testing procedures well known to those skilled in the art.

The test results are presented in the following table, in which the following abbreviations are used: RT = room temperature: Min = minutes: h = hours Primer N is a copper-containing primer which is Commercially available from Loetite Corporation: Test Compressive Shear (Degreased Pins/Collars) Tensile Shear (Degreased Mild Steel Laps) Compressive Shear (Degreased Pins/Collars) Tensile Shear (Degreascd Mild Steel Laps) Conditions RT Cure, 15 Min.

RT Cure 24 h RT 18h RT 18 h, Primer N on one side RT 18 h, Primer N on two sides RT 13 days RT 22 days :50 Water/Glycol 13 days at 87°C 50:50 Water/Glycol 22 days at 87°C RT 22 days :50 Water/Glycol 13 days at 87 0C 50:50 Water/Glycol 22 days at 87"C Bond Strength (MPa) .6 5 .2 29 27 29 27 26 30 23 26 9 13 4 11 The table above shows that formulation B containing acetonyl methacrylate showed similar room temperature performance and "durability" to formulation A and an overall superior humidity ageing performance in a water/glycol mixture at elevated temperature.

Light—activated acrylic adhesive formulations are also made up in which acetonyl methacrylate is used as the reactive diluent in place of HPMA and the monomer and other ingredients are conventional, as known to the person skilled in the art. Radiation activatable anaerobic adhesive formulations are prepared by mixing the following ingredients together in the following weight percentages: C D Monomer A 23.3 23.3 Monomer B 50.7 50.7 Hydroxypropyl methacrylatc 20.5 - Acetonyl methacrylate - 20.5 Diphcnyliodonium hexafluorophosphate 2.87 2.87 Ferrocene 0.944 0.944 Cumenc hydroperoxide 1.64 1.64 Monomer A is a urethane-acrylate reaction product of toluene diisocyanate and the hydroxypolyoxypropylene derivative of trimethylolpropane (commercially available under the trademark Pluracol TP 2450) having unreacted isocyanate functionality capped with hydroxyethl methacrylate.

Monomer B is urethane-acrylate prepared by reacting two moles of toluene diisocyanate with 1 mole of hydrogenated bisphenol A, diluting the reaction mixture with methyl methacrylate and further reacting it with two moles of hydroxyethyl methacrylate in the manner disclosed in Example V of U.S. Pat No. 3,425,988.

Pairs of mild steel grit blasted lapshears, 2 centimetres wide are coated on one face with the adhesive composition C and D and irradiated at 700 ll W/cmz (measured to LII at 365 nm) for a time interval which is different for each of seven groups of pairs. The coated surfaces of each pair are firmly placed in contact 45 seconds after cessation of irradiation, to give in each case a half inch overlap in the length direction of the lapshears for an adhesive bond to develop. The bonds are left for 24 hours at room temperature to cure. The bond strengths are measured in the tensile shear mode, using conventional tensile testing equipment. The results for Formulation C are quoted in US Patent No 4,533,446 (Conway gt a_l_.). Based on the results in the examples of this application, it is expected that comparable bond strengths are obtained for Formulation Example 2 An air-activatable adhesive composition comprising: acetonyl methacrylate 4.25g methacrylic acid 0.25g 0.1% Ferric acetylacetonate in hydroxypropyl methacrylate 0.25g N—phenyl—2 propyl-3, 5-diethyl-1, 2—dihydropyridine O.25g was prepared under anaerobic conditions and activated in air for 2 and 4 minutes giving bond strengths of 20 MPa on mild steel test specimens after 24 hours. Identical bond assemblies aged at 87°C in water/glycol for 7 days gave bond strengths of 7-10 MPa.

Similarly prepared formulations, having hydroxypropyl methacrylate (HPMA) as the monomer, gave zero strengths following ageing under these same conditions.

Example 3 An adhesive formulation (A) was prepared by formulating in the proportions outlined in the table below, acetonyl methacrylate, methacrylic acid and Fe(III) acetylacetonate. This formulation was then added to a 25 ml aluminium tube and exposed to a steady stream of inert gas such as nitrogen through a syringe needle for at least two minutes. N—phenyl—2 propyl-3,5-diethyl-1,2—dihydropyridine was added to the formulation under the inert atmosphere. The aluminium tube was then sealed by crimping, thus trapping inert gas in the head space above the formulation. The aluminium tube was shaken for 10 - 20 seconds to ensure thorough mixing of the formulation components. A similar formulation (B) was prepared comprising hydroxypropyl methacrylate. The compositions of the formulations are as follows: Formulation A Formulation B Acetonyl methacrylate 8.5g -- Hydroxypropyl methacrylate -- 8.5g Methacrylic acid 0.5g 0.5g .1 % Fe(III) Acetylacetonate oil in 0.5g 0.5g Hydroxypropyl methacrylate N—phenyl—2 propyl-3,5—diethyl—1,2- 0.5g 0.5g dihydropyridine The adhesive compositions were tested as follows; samples of the adhesive were squeezed from the aluminium tube and spread onto mild steel test-pieces (100 x 25mm - 4 x 1 inches) to form a film of approximately 0.1 mm in depth and exposed to air for a measured interval (hereafter referred to as the open time). Following the open time the mild steel test-pieces were brought together to form an adhesive joint with 12.5mm - 0.5 inch overlap. The bond strengths for bonds assembled using the above procedure and allowed to cure for 24 hours were tested according to ASTM - D1002 and are presented in the table below.

Formulation (A) Formulation (B) Open Times Shear Strengths Shear Strengths /Minutes MPa MPa 2 21 14 4 20.3 14 Similar sets of bond assemblies were aged in 50:50 water/glycol solutions at 87"C for seven days, removed, and allowed to cool and tested to give the following results.

Formulation (A) Formulation (B) Open Times Shear Strengths Shear Strengths /Minutes MP3 MP3 2 7 0 4 7 O The assemblies prepared from formulation (B) had lost all bond strengths.

Example 4.

Adhesive compositions comprising the components outlined in the following table were prepared using the procedures outlined in the previous example.

Formulation Acetonyl methacrylate 23g I-lydroxypropyl methacrylate 20g % polymethyl methacrylate in methyl 42g methacrylate Methacrylic acid 5g .1 % Fe(IlI) acetylacetonate oil in 5g hydroxypropyl methacrylate N-phenyl-2 propyl-3,5-diethyl—1,2— 5g dihydropyridine The adhesive formulation was tested as in the previous example giving the following results: Open Times Formulation /Minutes Shear Strengths MPa 2 18 4 19 Similar tests on polyvinyl chloride test pieces gave the following results: Open Times Formulation /Minutes Shear Strengths MPa 2 2 4 1 .8 Example 5.

Adhesive compositions comprising the components outlined in the following table were prepared using the procedures outlined in the previous examples.

Formulation A Acetonyl methacrylate 42.5g % polymethyl methacrylate in methyl 42.5g methacrylatc Methacrylic acid 5g 0.1 % Fe(lII) acetylacetonatc oil in 5g hydroxypropyl methacrylate N-phenyl—2 propyl-3,5—diethyl-1,2- 5g dihydropyridine The adhesive formulation was tested as in the previous examples giving the following results with mild steel substrates: Open Times Formulation /Minutes Shear Strengths MPa 2 20 4 21 Similar sets of bond assemblies were aged in 50:50 water/glycol solutions at 87C for 96 hours, removed, and allowed to cool and tested to give the following results.

Open Times Formulation /Minutes Shear Strengths MPa 2 10 4 8 Similar tests on polyvinyl chloride test pieces gave the following results: Open Times Formulation /Minutes Shear Strengths MPa 2 2 4 2 .3

Claims (1)

1. Claims 1 . An adhesive formulation comprising: (i) a short chain polymerisable monoacrylate [meth]acrylate ester, at least a substantial portion of which is a ketonyl [meth]acrylate, optionally in combination with: (ii) a polymerisable [meth]acrylic monomer; and (iii) cure ingredients therefor. An adhesive formulation comprising: (a) a polymerisable [methjacrylic monomer; (b) a reactive diluent capable of co—polymerising with the said monomer, at least a substantial portion of the diluent being a ketonyl [meth]acrylate; and (c) cure ingredients for the monomer. A formulation according to claim 1 or 2 wherein the substantial portion is a proportion in the range from 10 to 100% by weight. A formulation according to claim 3 wherein the substantial portion is a proportion in the range from 40% to 100% by weight. A formulation according to claim 2 wherein the ketonyl [meth]acrylate forms at least 80% by weight of the reactive diluent. A formulation according to claim 5 wherein the ketonyl [meth]acrylate forms 95 to 100% by weight ofthe diluent. A formulation according to claims 2, 5 or 6 wherein any remaining portion of the diluent is a conventional diluent other than a hydroxy (lower alkyl) [meth]acrylate. A formulation according to any of claims 2 or 5-7 wherein the sole reactive diluent which has been added to the monomer when making up the formulation is a ketonyl [meth]acrylate. A formulation according to any of the preceding claims wherein any content of free hydroxy (lower alkyl) rnethacrylate does not exceed 1% by weight of the total formulation. 10. A formulation according to any of claims 2 to 9 which is an anaerobic adhesive composition wherein at least part of the monomer content comprises a [meth]acry1ate—terminated resin or prepolymer. l I. A formulation according to any of the preceding claims wherein the ketonyl [meth]acrylate is of the formula: 11 CH: : C": W-""0 "(CH2)n R2 1 O 0 wherein: R1 is H or C1-C5 alkyl, particularly C1-C3 alkyl;Rg is C1-C5 alkyl, cyclohexyl, phenyl, benzyl, or substituted derivatives of any of the foregoing; and n is 1-5. 12. A formulation according to claim 11 wherein R1 and R2 are both C1-C3 alkyl. 13. A formulation according to claim 12 wherein the ketonyl [meth]acr_vlate is acetonyl methacrylate. 14. Use of a ketonyl [meth]acrylate as a replacement for at least a substantial portion of the content of hydroxy (lower alkyl) methacrylate in an acrylic adhesive composition. 15. Use according to claim 14 wherein any remaining content of free hydroxy (lower alkyl) methacrylate does not exceed 1% by weight of the total composition. 16. Use according to claim 14 or 15 wherein the ketonyl [meth]acrylate is as defined in any of claims 11-13. A method of preparing an acrylic adhesive composition which conventionally would contain a hydroxy (lower alkyl) methacrylate, wherein at least a substantial portion of the hydroxy (lower alkyl) methacrylate content is replaced by a ketonyl [meth]acrylate. A method according to claim 17 wherein any remaining content of free hydroxy (lower alkyl) methacrylate does not exceed 1% by weight of the total composition. A method according to claims 17 or 18 wherein the ketonyl [meth]acrylatc is as defined in any of claims 11-13. A method of bonding and/or sealing two substrates comprising applying an adhesive formulation according to any of claims 1 to 13 to at least one substrate, bringing the two substrates together, and allowing the composition to cure. Substrates bonded by a method according to claim 20 and/or by use of a formulation according to any of claims 1 to 13 and/or a composition prepared by a method according to any of claims 17 - 19. Tomkins & Co.