WO2008125539A1

WO2008125539A1 - Method of bonding aluminium substrates with anaerobic sealants to form a seal

Info

Publication number: WO2008125539A1
Application number: PCT/EP2008/054173
Authority: WO
Inventors: Peter Wrobel; Pat O'dwyer; David Condron
Original assignee: Loctite (R & D) Limited
Priority date: 2007-04-13
Filing date: 2008-04-07
Publication date: 2008-10-23
Also published as: IE20070270A1

Abstract

The invention relates to a method of providing a seal between an aluminium substrate and a second substrate, wherein the seal is exposed to engine fluids selected from oils and/or coolant mixtures at elevated temperatures in the range from 600C to 175°C. The method of the invention involves (a) applying to at least one of the substrates an anaerobic sealant composition made from (i) one or more polymerizable (meth)acrylate ester monomers, (ii) an anaerobic cure- inducing component, and (iii) 0.05 to 0.25 % by weight, based on the total composition, of an adhesion promoter comprising one or more phosphorus-containing compounds having the general formula (I), wherein: R1 is H, CH3 or C2H5, R2 is -CH2-C2H4TC3H6-, or -CH2-CH-(CH3)-, R3 is H, CH3 or C2H5, n is an integer from 1 to 10, and m is an integer from 1 to 3; (b) bringing the substrates together face-to-face with a gap between the faces in the range from 0.1 to 0.25 mm, in at least part of the total face-to-face area, and (c) allowing or enabling the composition to cure at substantially ambient temperature.

Description

Title

Method of Bonding Aluminium Substrates with Anaerobic Sealants to Form a Seal

Field of the Invention This invention relates to a method of bonding an aluminium substrate to another substrate to form a seal in an environment subject to elevated temperatures and exposure to fluids, particularly in an engine, suitably for the automotive industry. The invention also relates to the use of a selected adhesion promoter in anaerobic sealants for improved gasketting performance on an aluminium substrate in a working environment at prolonged elevated temperatures, while the seal is simultaneously exposed to fluids.

Backqroud Art

Anaerobic flange adhesives have commonly been used on steel substrates to form seals, for example in the form of gaskets, between flat metal faces. There is a recent trend in the automotive industry to use aluminium components instead of steel ones. As with steel flanges, in order to be commercially acceptable good adhesion between the anaerobic flange adhesive and the aluminium substrate (s) should be retained in the particular ageing conditions found in an engine.

Anaerobic flange adhesives are available which give good adhesion to steel and retain this adhesion after heat ageing at engine running temperatures in fluids such as oil and water/glycol mixtures, which would be encountered in an engine. However, on an aluminium substrate the initial adhesion of such adhesives is good but after heat ageing in the above-mentioned fluids the adhesion reduces sharply. There is therefore a need for an improvement in anaerobic sealant technology to overcome the problem.

Face-to-face joints between even carefully finished flat metal substrates have a so-called "zero gap" i.e. there is metal-to-metal contact in some areas (e.g. 25-35% of the total face-to-face area) while in other areas the gap is up to about 50 micrometres, more often in the range 10-40 micrometres, especially 20-30 micrometres. Anaerobic flange adhesives fill and seal this gap caused by the surface roughness. In addition, the automotive industry desires anaerobic flange adhesives to cure at ambient temperature. Zero gap conditions are achievable readily under laboratory testing conditions and fine control of the metal-to- metal face contact is manageable. However, under normal manufacturing conditions, zero gap environments could not be relied upon. In fact, oftentimes badly fitting faces may suffer from face-to-face gaps of in the region of 100 micrometres. Adhesion at such normal operating gap distances is often poor, and there is a need for provision of an anaerobic sealant that has optimized performance at these more usual gap distances.

It is of particular importance to provide anaerobic sealants that can perform well under combined conditions of high temperature and exposure to fluids at non-ideal gap conditions. U. S. Patent No. 4,044,044 (Saito) describes an anaerobic adhesive composition containing 0.05 to 20 parts by weight of phosphate esters of hydroxyacrylates per 100 parts by weight of polymerizable acrylic ester monomer. The compositions as described in the examples are cured at 120⁰C. There is no disclosure of use of the compositions on aluminium substrates and no teaching about the performance of the composition in the working environment of an engine.

U. S. Patent No. 4,322,509 (Zalucha) acknowledges the Saito patent but states that the addition of organophosphorus esters is accompanied by a significant increase in the time required for cure and, additionally, requires curing temperatures in excess of 100⁰C. The Zalucha'509 patent therefore proposes the addition of certain tertiary dimethylaryl amines to reduce the cure time and temperature, plus a carboxylated nitrile elastomer to substantially eliminate precipitation of amine phosphorous salts. One exemplary composition is said to be effective as an adhesive for non-ferrous materials such as galvanised steel and aluminium but the tests are conducted on steel lap strips with an uncontrolled glue line of approximately 0.02 to 0.05 mm. There is no teaching about performance of the compositions in the working environment of an engine, nor about gaps in the range from 0.1 to 0.5 mm.

U. S. Patent No. 4,223,115 (Zalucha et al.) describes structural adhesive formulations for metal bonding in the transportation industry, for example in fabricating vehicle bodies. The formulations incorporate phosphorus-containing compounds and are said to increase the bonding of oily metals, especially steel, aluminium and copper. It is stated at column 13, lines 47 - 53, that the phosphorus containing compound will be present in an amount in the range from about 0.1 to about 20, preferably about 2 to 10 weight percent, based on the total weight of polymerizable adhesive composition, The working examples for one- part compositions are in the above preferred range. The gap shear strength tests are carried out according to ASTM D-1002. Use of the formulations for aluminium-aluminium metal bonding is described. However, these formulations are aerobic and are intended for fabricating vehicle body assemblies which are subject to quite different environments (such as saline and humid environments) as compared to vehicle engines. Test data at column 27 of the Zalucha '115 patent describe testing in gasoline, water and salt solutions, at room temperature.

There is no teaching about anaerobic sealants for sealing aluminium substrates in the working environment of an engine, cycling from low to high temperature repeatedly and with exposure to fluids such as oil and water/glycol mixtures. Reference is also directed to U. S. Patent No. 5,641,834 for other structural adhesive compositions incorporating the phosphorous-containing compounds.

U. S. Patent No. 4,647,638 (Yokoshima et al.) describes modified organophosphates for use in anaerobic adhesives, which are cured by irradiation with ultraviolet light, or by addition of an organic peroxide with heating to 120 C. There is no reference to aluminium substrates, gap distances or to flange sealing in auto engines.

International Application Publication No. WO 00/29456 (Loctite (R&D) Limited) describes a method of bonding an aluminium substrate and a second substrate to form a seal such as may be found in automotive engines at ambient temperature through use of an anaerobic adhesive, wherein the seal is exposed to engine type fluids at elevated temperatures and pressure. The method employs an organphosphate compound as adhesion promoter, wherein the promoter is present in an amount in a suitable range of 0.5 - 5 % by weight based on the total composition. Examples in the document show use of such an adhesion promoter at 0.9 - 5.0 % by weight. The seal adhesion strength was tested under simulated engine operating conditions after exposure to engine type fluids at high temperatures and under pressure for varying lengths of time. The document does not teach or indicate functionality at anything other than operation for surfaces under zero-gap conditions.

It would be desirable to provide an improved method of bonding an aluminium substrate to a second substrate under non-ideal working face-to-face gap conditions greater than zero- gap, to form a seal in engines with improved retention of adhesion after exposure to heat and fluids such as are encountered in the working environment of an engine. It would be particularly desirable to provide a sealing composition capable of forming durable seals while delivering high gap cure performance. While the invention is more specifically concerned with automobile engines, similar problems may be encountered in other types of engines and in other working environments where a seal between uneven metal surfaces is exposed to fluids, which have an adverse effect on the retention of adhesion at elevated temperatures.

It is desirable to provide an anaerobic flange sealant composition, which will show high adhesion on metals, particularly aluminium, after cure. It is desired that such adhesion be retained after environmental ageing in fluids at elevated temperatures at gaps of up to 0.125 mm. Such fluids include water/glycol and motor oil. High adhesion performance is also desirable on oiled substrates.

Summary of the Invention The present invention provides a method of providing a seal between an aluminium substrate and a second substrate, where the seal is exposed to engine fluids selected from oils and/or coolant mixtures at elevated temperatures in the range from 60° C to 175° C.

The method includes the steps of:

(a) applying to at least one of the substrates an anaerobic sealant composition comprising : (i) one or more polymerizable (meth) acrylate ester monomers, (ii) an anaerobic cure-inducing component, and

(iii) 0.05 to 0.25 % by weight, based on the total composition, of an adhesion promoter comprising one or more phosphorus-containing compounds having the general formula I

where R¹ Is ^ CH₃ Or C₂H₅

R² is -CH₂-, -C₂H₄-, -C₃H₆-, or -CH₂-CH-(CH₃)- R³ is H, CH₃ Or C₂H₅ n is an integer from 1 to 10, and m is an integer from 1 to 3,

(b) bringing the substrates together face-to-face with a gap between the faces in the range from 0.1 to 0.25 mm, in at least part of the total face-to-face area, and

(c) allowing or enabling the composition to cure at substantially ambient temperature.

Suitably R³ is H in at least one of the groups -OR³ and desirably is H in each of the groups- OR³. Suitably R¹ is CH₃.

In one aspect, the invention includes a method as defined above for providing a seal between an aluminium substrate and a second substrate in an engine, where the seal is exposed to engine fluids at engine operating temperatures (e. g. -30⁰C to + 150⁰C). Engine fluids include engine oils and water/glycol mixtures. The invention is particularly directed towards providing a seal between faces that have unevenly finished surfaces, one of which is suitably on a flange, for example forming part of an engine component, and the second of which is suitably on an external surface of another engine component such as the engine block. The unevenness of the faces means that zero gap contact is not achievable, typically, working gaps between the faces in the range from 0.1 to 0.25 mm, in at least part of the total face-to-face area, are encountered.

The area across which a gap in the range from 0.1 to 0.25mm may be encountered depends upon the surface roughness of one or both of the substrates and can be from at least 5 to 100%, particularly at least about 15%, in some cases it may be particularly at least about 25%, in other cases particularly at least about 45%, in other cases still, it may be at least about 65%, in some other cases it may be least about 85% of the total face-to- face area of the assembled substrates. In some particular cases, the area across which a gap in the range from 0.1 to 0.25mm may be encountered may be about 100% of the total face-to-face area. The gap between the faces may in some cases be in the range from 0.1 to 0.2 mm, particularly from 0.1 to 0.15 mm, especially from 0.12 to 0.13 mm, in particular about 0.125 mm.

In a particular aspect, the invention includes a method of providing a seal between an aluminium substrate and a second substrate in the cooling circuit of an engine, said seal being exposed to water/glycol mixtures at engine cooling-circuit temperatures (e. g. 80° to 130⁰C, especially 80° - 100⁰C).

In another aspect, the invention includes the use of one or more phosphorus containing compounds of the general formula I as defined above as an adhesion promoter in a flexible anaerobic sealant composition which is curable at substantially ambient temperature, for providing a seal between an aluminium substrate and a second substrate with a gap between the faces in the range from 0.1 to 0.25 mm, in at least part of the total face-to- face area, where the composition has the ability to retain adhesion on the aluminium substrate while exposed to fluids at elevated temperatures.

In a further aspect the invention includes an assembly of substrates having a seal provided by a method as defined above, in particular an assembly of an aluminium flange against a second substrate with a gap between the faces in the range from 0.1 to 0.25 mm, in at least part of the total face-to-face area. The invention also concerns an engine incorporating an assembly of substrates as defined above in this paragraph.

In a further aspect, the invention provides anaerobic formulations which show enhanced adhesion on aluminium in respect of both clean and oiled contacted surfaces with a gap between the faces in the range from 0.1 to 0.25 mm, in at least part of the total face-to- face area. The formulations and methods of the invention also give good adhesion at zero- gap. Furthermore, aluminum bonds made with formulations of the invention show good retention of adhesion after ageing in fluids such as water/glycol and oil at elevated temperatures.

In a particular aspect, the formulations of the invention are suitably based on an APH (acetyl phenyl hydrazine) cure system augmented by a number of adhesion promoters, in particular a small amount of phosphate methacrylate as defined above (previous anaerobic formulations based on APH and a higher percentage of phosphate methacrylate showed poorer performance and lack of cure through gap).

In another aspect, an oil tolerant monomer is suitably used in combination with (meth)acrylate functional resin(s). These formulations care particularly for flange sealing and could be most useful in difficult situations on aluminium flanges where standard products have problems. Oil tolerant monomers have a hydrophobic or oleophilic moiety, examples include isobornyl acrylate, isobornyl methacrylate, cyclohexyl methacrylate, tertiary butylcyclolhexyl methacrylate and phenoxyethyl methacrylate. The invention will now be more fully described by way of example and with reference to the accompanying drawing.

Brief Description of the Drawing One embodiment of the invention as applied to an automotive engine is illustrated in

Figure 1, which is a pictorial view of a water pump and part of an engine block aligned for assembly.

Figure 1: A water pump housing 1 of aluminium has a flange 2 which is also of aluminium and which has a flat face. An engine block 3 has an aperture 4 which is designed to communicate with a corresponding aperture on the face of the water pump (not shown). The area 5 of the surface of the engine defining the aperture 4 forms a flat face against which the face of the water pump is to be assembled face-to-face. Liquid sealant composition 6 in accordance with the invention is applied to the area 5 around the aperture 4 to form a gasket. During the course of assembly the water pump is brought against the engine block and is secured thereto by bolts 7. The sealant composition cures under anaerobic conditions created in the gap between the two substrates.

Detailed Description of the Invention

The present invention provides a method of providing a seal between an aluminium substrate and a second substrate, where the seal is exposed to engine fluids selected from oils and/or coolant mixtures at elevated temperatures in the range from 60° C to 175° C.

The method include the steps of:

(a) applying to at least one of the substrates an anaerobic sealant composition comprising : (i) one or more polymerizable (meth) acrylate ester monomers,

(ii) an anaerobic cure-inducing component, and (iii) 0.05 to 0.25 % by weight, based on the total composition, of an adhesion promoter comprising one or more phosphorus-containing compounds having the general formula I

where R¹ Is ^ CH₃ Or C₂H₅

Whereas conventional wisdom taught that the addition of organophosphorus esters required curing temperatures in excess of 100⁰C, the present inventors have found that in the situation where there is a face-to-face gap between the substrate faces in the range from 0.1 to 0.25 mm, the anaerobic compositions will cure at a satisfactory rate at or around ambient temperature (18-25°C, especially about 21°C).

The elevated temperatures to which the seal is exposed may be in the range from 60⁰C to 175°C. The seal may also be exposed to temperatures below 60⁰C, down to -30⁰C in some climatic conditions. Cycling of temperatures from 5°C to 150⁰C is frequent. Under working engine conditions, seals may have to withstand pressures up to about 6 bar, particularly up to about 4 bar.

The fluids to which the seal is exposed include fluids which are known to degrade adhesion on metals. The fluids include oils and hydroxy-containing materials such as engine coolant mixtures.

One or both of the substrates may suitably be a flange, more particularly a flange at a joint between components in an engine assembly. The second substrate may be of aluminium or may be of another material on which anaerobic sealants are effective, such as iron, steel and other metals.

The polymerizable (meth) acrylate ester monomers (i) useful in this invention include a wide variety of materials such as those given in U. S. Patent No. 3,218,305 (Krieble), U. S. Patent No. 4,417,92 (Azevedo), U. S. Patent No. 4,451,615 (Chamock), 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)COOR' (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- (meth) acrylates, such as Methylene glycol di-methacrylate, dipropylene glycol di- (meth) acrylate, bisphenol-A di- (meth) acrylates, such as ethoxylated bisphenol-A methacrylate ("EBIPMA") and tetrahydrofuran (meth) acrylates and di- (meth) acrylates, hydroxypropyl (meth) acrylate, hexanediol di (meth) acrylate, trimethylol propane tri- (meth) acrylate, 2-hydroxyethyl (meth) acrylate, methyl (meth) acrylate, cyclohexyl (meth) acrylate, isobomyl (meth) acrylate, phenoxyethyl methacrylate, 2-aminopropyl (meth) acrylate, an acrylate ester corresponding to the structure shown below:

H₂C

where R² may be selected from hydrogen, alkyl of 1 to about 4 carbon atoms, hydroxyalkyl of 1 to about 4 carbon atoms or

R³ may be selected from hydrogen, halogen, and alkyl of 1 to about 4 carbon atoms; R⁴ may be selected from hydrogen, hydroxy and

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 polymerizable (meth)acrylate ester monomers suitably include a (meth)acrylate- terminated prepolymer in addition to a poly-or mono functional (meth) acrylate ester.

Other preferred acrylate ester monomers are those selected from the class consisting of urethane acrylates having the general formula : (CH²=C(ΪV^li)COOR^ήOCONH-)-₁R^'7 (HI)

wherein R⁵ is H, CH₃, C₂H₅ or Cl; R⁵ is (i) a Ci_-8 hydroxyalkylene or aminoalkylene group, (ii) a Ci_-6 alkylamino Ci_-8 alkylene, a hydroxyphenylene, aminophenylene, hydroxynaphthylene or aminonaphthylene optionally substituted by a Ci_-3 alkyl, Ci_-3 alkylamino or di-Ci_-3 alkylamino group; and R⁷ is C₂-₂₀ alkylene, alkenylene, or cycloalkylene, C₆-₄₀ arylene, alkarylene, aralkylene, alkyloxyalkylene or aryloxyarylene optionally substituted by 1-4 halogen atoms or by 1-3 amino or mono-or di-Ci_-3 alkylamino Or Ci_-3 alkoxy groups; or said acrylates having the general formula :

{CH₂=C(R⁵)COOR⁶OCON(H)R⁷N'(H)COX-)_BR⁸ (IV)

wherein R⁵, R⁵ and R⁷ have the meanings given above; R⁸ is the non-functional residue of a polyamine or a polyhydric alcohol having at least n primary or secondary amino or hydroxy groups respectively; X is O or NR⁹ where R⁹ is H or a Ci_-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-inducing component (ii) 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.

Initiators 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] isothiazolel,l- 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.

Block resins such as described in Loctite International Patent Application No, PCT/US/98/00862 (Woods) and U. S. Patent No. 4, 295, 909 (Baccei) may suitably be used in the composition. Block resins are, for example, polybutadiene-based polymer resins formed by linking two "pre-polymers" which are subsequently capped with an acrylate (e,g, polybutadiene diols and their acrylonitrile copolymers with e.g. methacrylate-capped aromatic diisocyanates). Such pre-polmers can be produced from hydroxyl-terminated butadiene nitrile co-polymers (HTBNs). HTBNs may be used to form block pre-polymer resins in accordance with the teaching of the '909 patent, such as by chemically-linking two "pre-polymers" which are subsequently "capped" with acrylate or methacrylate functionality. In this way, a "flexible" polymeric butadiene polyol segment of relatively low molecular weight is reacted with a molar excess of "rigid" diisocyanate, such as toluene diisocyanate or methylene diisocyanate, thereby forming urethane linkages. Thus, the resin structures include a central flexible low glass transition linear polymer which is chemically linked to relatively short rigid segments, located at either end of the linear polymer through urethane groups and capped with acrylate or methacrylate groups. The term "rigid" segment as used herein with respect to block resins includes a segment or segments containing aromatic, heterocyclic-or cycloaliphatic rings, with multiple segments joined by e by a minimum number of carbon atoms(e.g., 1 to 2, if linear, or 1 to about 6, if branched) such that there is little or no flexing of the segments. The term "flexible" segment as used herein with respect to block resins includes a segment of primarily linear aliphatic moieties containing internal unsaturation, with pendant functional groups, such as aromatic, heterocyclic, cycloaliphatic, and the like, as well as branching, also incorporated therein, provided no substantial interference exists with the flexible nature of the linear portion. By selection of appropriate flexible and rigid segments, the material properties of the cured resins may be optimized for adhesive applications. And in order to ensure rapid and complete incorporation of the flexible segment into the urethane polymer, it is desirable for the terminal hydroxyl groups of the HTBN to be primary, rather than secondary or tertiary.

The fully-prepared monomeric block prepolymers may be represented by:

where R³ may be hydrogen, halides, (e.g., chlorine) and alkyl groups (e.g., methyl and ethyl); and R⁴ may be lower alkyl groups, such as linear, branched or cyclic groups having 1 to about 8 carbon atoms, phenylene and naphthalene; A is a polyisocyanate linkage; D is an aromatic, heterocyclic or cycloaliphatic polyol or polyamine group (e.g., a diol of a cycloaliphatic compound); Z is a polymeric or copolymeric polyol or poly radical of butadiene, the latter having a degree of polymerization of from about 5 to about 150 and at least about 70 % of the polybutadiene portion of the 1,4-configuration; z is an integer corresponding to the valency of Z; d is either 0 or 1; and i is 0 when d is 0, and otherwise is one less than the number of reactive hydrogen atoms of D. An asterisk indicates a urethane (-NH-COO-) or ureide (-NH-CO-NH-) linkage. The block pre-polymer resins cure to a hard, tough resin, using any of a wide variety of known free radical initiators, which may be activated by redox, thermal or photo-initiated mechanisms.

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.

In one embodiment the adhesion promoter (iii) is a mixture of at least two phosphorus- containing compounds having the general formula I as defined above, in one of which m is 1 and in the other of which m is 2, i.e. a mixture of a bis (hydroxyalkyl (meth) acrylate) acid phosphate and a hydroxyalkyl (meth) acrylate acid phosphate. A minor proportion of a compound of general formula I in which m is 3 may also be present e.g. in an amount up to about 10% by weight of the adhesion promoter. A commercially available adhesion promoter comprises (at least to the extent of up to about 80% by weight of the promoter) a combination of bis (2-hydroxyethyl methacrylate) acid phosphate and 2-hydroxyethyl methacrylate acid phosphate, as described in U. S. Patent Nos. 4,044,044 (Saito) and 4,647,638 (Yokoshima et al.). Such a promoter may also have a minor proportion (e. g. up to about 20% by weight) of other ingredients such as up to about 10% by weight of tris (2-hydroxyethyl methacrylate) acid phosphate and/or up to about 10% by weight of phosphoric acid.

The adhesion promoter is suitably used in an amount of 0.05 - 0.25% by weight based on the total composition. Desirably the promoter is used in an amount of 0.05 - 0.1% by weight based on the total composition. At a level less than 1% the amount of adhesion promoter is sufficiently small to satisfy product labelling requirements. Suitable weight ranges of ingredients in the composition used in the invention are as follows:

Component Compositional Range %

(Meth)acrylate resins 20 to 40%

(Meth)acrylate Monomers 35 to 65%

Curatives and Stabilisers 5 to 10%

Thickeners and Colourants 5 to 25%

Phosphomethacrylate ester based adhesion promoter 0.05 to 0.25%

Thickeners, plasticizers, pigments, dyes, diluents, fillers, and other agents common in the art can be employed in any reasonable manner to produce desired functional characteristics, providing they do not significantly interfere with polymerization of the monomer.

Modes for Carrying Out the Invention

The invention is illustrated in the following non-limiting examples, in which all parts are parts by weight.

Example 1

The following abbreviations are used : RT = room temperature NQ = naphthoquinone EDTA = ethylenediamine tetra acetic acid HEMA = 2-Hydroxyethyl methacrylate APH = Acetyl Phenyl Hydrazine PTFE = Polytetrafluoroethylene CHP = Cumene Hydroperoxide

Ebecryl 168 is a methacrylate modified acidic adhesion promoter which is designed as a modifier for ultraviolet and electron beam (EB) curable coatings on metals. It is commercially available from UCB s.a. Chemical Sector, B-1620 Drogenbos, Belgium.

Formulations 1 and 2 are APH-based formulations of anaerobic sealants. Both formulations contain 0.1 % w/w phosphate methacrylate. The formulations 1 and 2, differ in the type of oligomer resin used in the composition. Details of the compositions are presented in Table 1 below. Table 1: Composition Details for Formulations 1 and 2:

Component Formulation 1 Formulation 2

% w/w % w/w

HEMA 8.00 8.00

Isobornyl Methacrylate 14.45 14.45

Phenoxyethyl methacrylate 29.45 29.45

Urethane acrylate oligomer 26.03 0.00

Block resin I 0.00 26.03

Naphthaquinone Stabiliser 0.25 0.25

EDTA Stabiliser 0.65 0.65

Phosphonic acid based stabilizer 0.65 0.65

Saccharin 0.75 0.75

APH 0.76 0.76

Acrylic acid 1.00 1.00

Phosphate Methacrylate (Ebecryl 168) 0.10 0.10

Methacryloxyethyl succinate 1.00 1.00

Polyethylene powder 6.50 6.50

PTFE Powder 2.50 2.50

Fluorescent agent 0.99 0.99

CHP 1.48 1.48

Fumed Silica 5.44 5.44

Total 100.0 100.00

The adhesion performance of the exemplary formulations was tested under conditions simulating zero-gap and face-to-face gap of 0.125 mm across 100% of the face-to-face area, which was achieved by putting spacers between the lap shears. Cure time was twenty-four hours at room temperature for all test subjects.

The first set of tests comparatively examines the adhesion performance of the formulations on dry lap shears at zero-gap and at a face-to-face gap of 0.125 mm, with the performance by two standard products.

The second set of tests comparatively examines the adhesion performance of the formulation on oiled lap shears at zero-gap and at a face-to-face gap of 0.125 mm, with the performance by two standard products under identical cure and oiling conditions.

The third set of tests comparatively examines the adhesion performance of the formulation on dry lap shears at zero-gap and at a face-to-face gap of 0.125 mm, where the lap shears are subsequently exposed to a mixture of water/glycol at 120⁰C for a period of 24 hours, with the performance by two standard products under identical cure and oiling conditions.

The fourth set of tests comparatively examines the adhesion performance of the formulation on oiled lap shears at zero-gap and at a face-to-face gap of 0.125 mm, where the lap shears are subsequently exposed to a mixture of water/glycol at 120⁰C for a period of 24 hours, with the performance by two standard products under identical cure and oiling conditions.

Adhesion performance was assessed using standard aluminium lap shear tests, details of which are provided below. All lap shear tests were carried out at room temperature. The performance data is presented in Table 2 below. Two standard flange sealants were used for comparative purposes. 5450 and 518 sealants do not use the phosphate methacrylate adhesion promotion system.

Table 2: Comparative Testing Performance

Test Formulation 1 Formulation 2 5450 518

24hr RT cure; 0 gap 11.4 15 .5 3.2 2.9

24hr RT cure; 0.125mm gap 10.6 5. 7 0.7 1.0

24hr RT cure; oiled; 0 gap 8.9 12 .8 _ 2.6

24hr RT cure; oiled at 0.125 mm gap 6.1 5. 2 - 0.0

24hr RT cure then 24 hr in

7.5 12 .2 0.0 3.1 water/glycol at 120⁰C; 0 gap 24hr RT cure then 24 hr in water/glycol at 120⁰C at 0.125mm 3.2 6. 1 0.0 0 gap

24hr RT cure then 24 hr in _{fi 1 1} . _. n water/glycol at 120°C; oiled; 0 gap ^'

24hr RT cure then 24 hr in water/glycol at 120⁰C at 0.125mm 3.3 10.6 - 0 gap; oiled

(a) All results are in Mpa.

(b) Oiled means that lapshears are solvent wiped and re-oiled with 10% solution of 5W30 oil in heptane. Solvent was subsequently dried to leave oil coating.

(c) Products 518 and 5450 are standard anaerobic flange sealant products.

Typical compositional details of products 518 and 5450 are given in the Table 3 below.

Table 3: Compositional Details of Products 518 and 5450

Ingredient Parts by Weight 518 5450

(Meth)acrylate terminated

60 urethane polyesters to 100 10 to 40

(Meth)acrylate Monomers 10 to 30 45 to 70 l-aceto-2-phenyl hydrazine 0.1 to 1.0 0.1 to 1.0

Cumene Hydroperoxide 1 to 5 1 to 5

Silica 5 to 10 1 to 5

Acrylic acid 1 to 5

Formulations 1 and 2 according to the invention use two different resin materials which leads to different basic adhesive strengths at zero gap on Aluminium flanges and also to different strength retention values after heat ageing. However, the basic effects are the same. The oil tolerance of both Formulations is good. The strength behaviour after ageing immersed in water/glycol at 120⁰C is particularly good for these Formulations, particularly when compared to 518 and 5450. It can be noted that Formulation 1 retains a lower absolute strength value than Formulation 2 and this may be useful when it is necessary to easily disassemble sealed components. Example 2

Example 2 shows the effect of the addition of larger concentrations of phosphate methacrylate adhesion promoter on adhesion performance. Formulation 1 was initially tested and the level of the phosphate methacrylate was incrementally increased while the level of the other ingredients of Formulation 1 was maintained. Tests were executed at gap distances of zero-gap, 0.125 mm gap and 0.25 mm gap. In order to investigate the reliability of the seal over time. The test subjects were re-examined after a period of four weeks. The results are presented in Table 4 below.

Table 4: Effect on Cure of Addition of Phosphate Methacrylate Adhesion Promoters to Formulation 1

Gap Distance Formulation 1 + 0.4 % (Total 0.5 + 0.9 % (Total 1.0

%) %)

Initial 4 weeks Initial 4 weeks Initial 4 weeks

0 Gap 11.0 10.8 12.7 10.2 11.4 1.0

0.125 mm Gap 8.5 8.6 7.5 3.0 1.8 0.2

0.25 mm Gap 4.7 4.3 3.4 2.9 1.8 0

All results are 24 hour RT cure on solvent wiped aluminium lap shears, values are in Mpa

The data shows that at lower levels of phosphate methacrylate concentrations, there is a significantly higher adhesion performance than formulations with higher concentrations where experimental face-to-face contact is in the range of from 0.1 to 0.25 mm.

Initially the addition of progressively higher amounts of the phosphate methacrylate adhesion promoter (PMA) does not affect the overall strength achieved in a 0 gap situation. However, two effects can be seen.

(a) On addition of the higher level of PMA (0.9%) a significant reduction in strength at gap is seen initially which in itself is a negative point.

(b) As the formulation ages at RT the strength performance of the formulations with higher levels of PMA decreases significantly at gap and even at zero gap for the 0.9% addition. This is particularly important as it suggests a poorer shelf life performance for the formulations with higher levels of PMA. The much better situation is seen in Formulation 1 where there is no significant loss in strength performance seen over time. Example 3

To investigate the effect of the seal under elevated temperature and pressure conditions subject to exposure to motor oil or water/glycol.

Seal Testing of Anaerobic Formulations Test procedure

The product under testing is applied to one of the flanges (aluminium surface). 0.1mm thick steel shims are placed in the product. A mating flange is placed on top of product and the test rig bolted together. The test rig is then filled with test fluid (motor oil or water/glycol) and product is allowed to cure for 24 hrs at RT.

The test rig is then pressurized at appropriate pressure for test and placed in an oven at appropriate temperature. After 7 days in the oven at pressure and temperature the test rig is allowed to cool and pressure is released. Fluid is removed from the test rig and then the test rig is pressurized with air and immersed in a tank of water for 10 minutes.

A leak is indicated by air bubbles escaping from the sealing area of the flange.

Table 5: Results of Seal Testing

-. .... 0.1% Phosphate 0.9% Phosphate

Conditions » M_•e_t.■h_acry Vla .t.e . M.e.t.■h_acry ϊla _*t.e

Fluid : motor oil

Temperature: 150⁰C No Leaks Leaks

Pressure: 4 bar

Fluid : water/glycol

Temperature: 120⁰C No Leaks Leaks

Pressure: 2 bar

Notes:

1. Water/glycol is a 50 :50 mixture of water and antifreeze (commercial grade)

2. Each test has been carried out at least 2 times, with the same result

Conclusions

Overall, the data show that reliable adhesion can be achieved and maintained using formulations containing phosphate methacrylate concentrations of below 0.25 %w/w on aluminium parts, including those with oiled surfaces and where there are small gaps (up to 0.25 mm). Adhesion can be retained after immersion in automotive fluids such as water/glycol and motor oil at elevated temperatures. The effect is observable directly after initial cure and persists after an accelerated ageing period of at least four weeks. Such formulations are superior to existing products, since adhesion under these conditions cannot be maintained using products such 5450 and 518.

Claims

:iaim<

1. A method of providing a seal between an aluminium substrate and a second substrate, said seal being exposed to enginefluids selected from oils and/or coolant mixtures at elevated temperatures in the range from 60⁰C to 175°C, wherein the method includes the steps of:

(a) applying to at least one of the substrates an anaerobic sealant composition comprising :

(i) one or more polymerizable (meth)acrylate ester monomers,

(ii) an anaerobic cure-inducing component, and

wherein :

R¹ is H, CH₃ Or C₂H₅

R² is -CH₂-, -C₂H₄-, -C₃H₆-, or -CH₂-CH-(CH₃)-

R³ is H, CH₃ Or C₂H₅ n is an integer from 1 to 10, and m is an integer from 1 to 3,

2. A method according to claim 1 wherein the area across which a gap in the range from 0.1 to 0.25mm is encountered is from at least 5 to 100% of the total face-to-face area of the assembled substrates.

3. A method according to claim 2 wherein the said area of is at least about 65% of the total face-to-face area of the assembled substrates.

4. A method according to any proceeding claim wherein the gap between the faces is in the range from 0.1 to 0.2 mm.

5. A method according to claim 4 wherein the gap between the faces is in the range from 0.12 to 0.13 mm.

6. A method according to claim 1 wherein the adhesion promoter comprises a combination of at least two phosphorus-containing compounds having the general formula I, in one of which m is 1 and in the other of which m is 2.

7. A method according to claim 1 wherein the adhesion promoter comprises compounds of the formula I in which R¹ is CH₃ and R³ is H.

8. A method according to claim 6 wherein the adhesion promoter comprises a combination of bis (2-hydroxyethyl methacrylate) acid phosphate and 2-hydroxyethyl methacrylate acid phosphate, optionally with the addition of tris (2-hydroxyethyl methacrylate) acid phosphate.

9. A method according to claim 1 wherein the adhesion promoter is used in an amount of 0.05-0.1 % by weight based on the total composition.

10. A method according to claim 1 wherein the anaerobic cure-inducing component includes a polymerization initiator selected from peroxides, hydroperoxides, peresters and peracids.

11. A method according to claim 10 wherein the initiator is benzoyl peroxide or cumene hydroperoxide.

12. A method according to claim 10 or 11 wherein the initiator is present in the sealant composition in an amount of about 0.1 % to about 15%, preferably about 0.1 % to about 2.0%, by weight of the composition.

13. A method according to claim 1, wherein the (meth) acrylate ester monomer comprises a member with the structure, H₂C=CRCO₂R¹, wherein 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, sulfonate, and sulfone.

14. A method according to claim 1 wherein the anaerobic cure-inducing component includes a polymerization accelerator selected from saccharin, a toluidine, acetyl phenylhydrazine and maleic acid.

15. A method according to claim 1 of providing a seal between an aluminium substrate and a second substrate with a gap between the faces in the range from 0.1 to 0.25 mm, in at least part of the total face-to-face area, in an engine, said seal being exposed to engine fluids at engine operating temperatures.

16. A method according to claim 14 wherein the fluids include oil and/or water/glycol mixtures.

17. A method according to claim 1 of providing a seal between an aluminium substrate and a second substrate with a gap between the faces in the range from 0.1 to 0.25 mm, in at least part of the total face-to-face area, in the cooling circuit of an engine, said seal being exposed to water/glycol mixtures at engine-operating temperatures.

18. Use of one or more phosphorus-containing compounds of the general formula I as defined in claim 1 as an adhesion promoter in an amount of 0.05 to 0.25 % by weight in an anaerobic sealant composition which is curable at substantially ambient temperature, for providing a seal between an aluminium substrate and a second substrate with a gap between the faces in the range from 0.1 to 0.25 mm, in at least part of the total face-to- face area, said composition having the ability to retain adhesion on the aluminium substrate while exposed to fluids at elevated temperatures.

19. A method according to claim 18 wherein the area across which a gap in the range from 0.1 to 0.25mm is encountered is from at least 5 to 100% of the total face-to-face area of the assembled substrates.

20. A method according to claim 19 wherein the said area of is at least about 65% of the total face-to-face area of the assembled substrates.

21. A method according to any one of claims 18 - 20 wherein the gap between the faces is in the range from 0.1 to 0.2 mm.

22. A method according to claim 21 wherein the gap between the faces is in the range from 0.12 to 0.13 mm.

23. Use according to claim 18 wherein the adhesion promoter comprises a combination of at least two phosphorous-containing compounds, having the general formula I, in one of which m is 1 and in the second of which m is 2.

24. Use according to claim 18 wherein the adhesion promoter comprises compounds of the formula I in which R¹ is CH₃ and R³ is H.

25. Use according to claim 23 wherein the adhesion promoter comprises a combination of at least bis (2-hydroxyethyl methacrylate) acid phosphate and 2 hydroxyethyl methacrylate acid phosphate.

26. Use according to claim 18 wherein the adhesion promoter is used in an amount of 0.05 - 0.1 % by weight based on the total composition.

27. Use according to claim 18 for providing a seal between an aluminium substrate and a second substrate with a gap between the faces in the range from 0.1 to 0.25 mm, in at least part of the total face-to-face area, in an engine, said seal being exposed to engine fluids at engine operating temperatures.

28. Use according to claim 18 for providing a seal between an aluminium substrate and a second substrate with a gap between the faces in the range from 0.1 to 0.25 mm, in at least part of the total face-to-face area, in the cooling circuit of an engine, said seal being exposed to water/glycol mixtures at engine-operating temperatures.

29. An assembly of substrates together face-to-face with a gap between the faces in the range from 0.1 to 0.25 mm, in at least part of the total face-to-face area,, having a seal provided by a method according to claim 1.

30. An assembly according to claim 29 of an aluminium flange against a second substrate.

31. An engine incorporating an assembly of substrates according to claim 29 or 30.

32. A method of providing a seal between an aluminium substrate and a second substrate with a gap between the faces in the range from 0.1 to 0.25 mm, said seal having the ability to retain adhesion on the aluminium substrate while exposed to fluids at elevated temperatures in the range from 60⁰C to 175°C, wherein the method includes the steps of:

(i) one or more polymerizable (meth)acrylate ester monomers,

(ii) an anaerobic cure-inducing component, and

wherein :

R¹ is H, CH₃ Or C₂H₅

R² is -CH₂-, -C₂H₄-, -C₃H₆-, or -CH₂-CH-(CH₃)-

TOMKINS & CO