GB2585884A

GB2585884A - Threadlocking system

Info

Publication number: GB2585884A
Application number: GB1910371.2A
Authority: GB
Inventors: B Barnes Rory; Mullen David; Sweeney Nigel; Clarke Greg; Houlihan James
Original assignee: Henkel IP and Holding GmbH
Current assignee: Henkel IP and Holding GmbH
Priority date: 2019-07-19
Filing date: 2019-07-19
Publication date: 2021-01-27
Also published as: GB201910371D0

Abstract

A threadlocking system, comprising a threaded member having at least one threaded face, wherein the at least one threaded face comprises a first coating comprising an anaerobically curable (meth)acrylate composition, the composition comprising a nucleophilic curing agent, such as one or more of a hydrazine, a toluidine, a heterocyclic amine, or a triethanolamine, and wherein the first coating is coated by a second coating comprising a polycyanoacrylate film. The anaerobically curable (meth)acrylate composition, comprises a cure accelerator, such as n-butyl ferrocene. Also disclosed is a method of manufacturing the threaded member; and a method of assembling threaded members comprising matingly engaging a first threaded member and a second threaded member.

Description

THREADLOCKING SYSTEM

Field

[0001] The present invention relates to a threadlocking system including threaded parts and a dry-to-touch adhesive/sealing composition applied to said threaded part. The present invention also relates to a method of preparing a threaded part, and a method of assembling threaded parts. The present invention provides a threaded part with a dryto-touch coating applied to a threaded face thereof, the coating comprises a coated anaerobically curable composition. The threaded part can be conveniently handled, packed, transported and stored for an extended period, after which the anaerobically curable composition can be caused to cure at a selected time.

Brief Description of Related Technoloov

[0002] Threadlocking compositions are employed to lock and/or seal threaded parts such as nuts and bolts together in an interlocked state. Such threadlocking compositions significantly increase the torque required to break or turn the engaged threaded parts. Conventional threadlocking compositions oftentimes include co-reactive adhesive systems. With this type of threadlocking composition, two or more components are mixed before applying the resulting composition to the threaded engagement surface(s) of the fastener on which the components in the threadlocking composition react to cure. Examples of such co-reactive systems include epoxy resin adhesive compositions.

[0003] Liquid adhesive compositions have long been used in sealing and threadlocking applications and have become a standard part of assembly production as well as in the maintenance of machinery, tools and the like. Among the liquid adhesive compositions commonly used in these applications are anaerobic compositions. These compositions provide excellent threadlocking and sealing properties when cured. Anaerobically curable compositions which are applied as threadlocking compositions to threaded parts remain stable (in an uncured state), and thus in liquid form, until they are placed between interlocked threaded parts where they cure in the absence of oxygen.

[0004] Anaerobically curable compositions generally are well known. See e.g. R.D.

Rich, "Anaerobic Adhesives" in Handbook of Adhesive Technology, 29, 467-79, A. Pizzi and K.L. Mittal, eds., Marcel Dekker, Inc., New York (1994), and references cited therein. Their uses are legion and new applications continue to be developed.

[0005] Anaerobic adhesive systems are those which are stable in the presence of oxygen, but which polymerize in the absence of oxygen. Polymerization is initiated by the presence of free radicals, often generated from peroxy compounds. Anaerobic adhesive compositions are well known for their ability to remain in a liquid, unpolymerized state in the presence of oxygen and to cure to a solid state upon the exclusion of oxygen.

[0006] Oftentimes anaerobic adhesive systems comprise resin monomers terminated with polymerizable acrylate ester such as methacrylate, ethylacrylate and chloroacrylate esters [e.g., polyethylene glycol dimethacrylate and urethane-acrylates (e.g., U.S. Patent No. 3,425,988 (Gorman)] derived according to known urethane chemistry. Other ingredients typically present in anaerobically curable adhesive compositions include initiators, such as an organic hydroperoxide for example cumene hydroperoxide, tertiary butyl hydroperoxide and the like, accelerators to increase the rate at which the composition cures, and stabilizers such as quinone or hydroquinone, which are included to help prevent premature polymerization of the adhesive due to decomposition of peroxy compounds.

[0007] Desirable cure-inducing compositions to induce and accelerate anaerobic cure may include one or more of saccharin, toluidines, such as N,N-diethyl-p-toluidine ("DE-p-T") and N,N-dimethyl-o-toluidine ("DM-o-T"), and acetyl phenyl hydrazine ("APH") with maleic acid. See e.g. U.S. Patent Nos. 3,218,305 (Krieble), 4,180,640 (Melody), 4,287,330 (Rich) and 4,321,349 (Rich).

[0008] Saccharin and APH are used as standard cure accelerator components in anaerobic adhesive cure systems. Indeed, many of the LOCTITE®-brand anaerobic adhesive products currently available from Henkel Corporation use either saccharin alone or both saccharin and APH.

[0009] Anaerobically curable adhesive compositions also commonly include chelators such as ethylenediamine tetraacetic acid (EDTA) which are employed to sequester metal ions.

[0010] Compositions that are suitable for use in threadlocking applications are typically applied in a dry to touch form but with later stage anaerobic cure functionality.

[0011] In some cases the dry to touch form is achieved using a cure mechanism.

For example a first cure mechanism may form the dry to touch form so as to hold the composition in place on an article while a second cure mechanism is activated later to achieve threadlocking.

[0012] For example European Patent No. 0 077 659 (Thompson) describes a pre-applied polymerizable fluid for sealing and locking engineering parts. The composition has two mechanisms for curing and two curing reactions take place. The first mechanism is a UV light cure. An opacifier is dispersed in the fluid so that the fluid becomes substantially opaque to radiation. After the fluid is applied to the component it is exposed to UV radiation whereupon a coating is formed, creating a surface layer which is a dry, tack-free crust. The subcutaneous fluid is unaffected by the radiation and remains in a generally liquid state. When the component is threaded into another the surface layer breaks and the second polymerisation (such as a free radical polymerization) is initiated and the second cure reaction takes place once an anaerobic environment is established as the threaded components interlock. The second polymerization mechanism acts to lock the threads together. In Thompson, only a skin is formed in the first polymerization and the remainder of the composition remains fluid below the skin. There is a risk therefore that during handling of the coated engineering parts the skin may be disrupted and the fluid composition may leak out.

[0013] Similarly, European Patent No. 0 548 369 (Usami) describes a pre-applied adhesive composition for application to the threaded contact faces of a screw member such as a screw. The composition comprises a photo-hardening binder in which a secondary curable composition is dispersed. The secondary curable composition includes microencapsulated reactive monomer/activator/initiator.

[0014] International Patent Publication W02004/024841 A2 (Haller) describes curable compositions for application to a threaded article. The composition comprises a dispersion of components of a first cure mechanism comprising: (a) a (meth)acrylate functional monomer component; (b) a (meth)acrylate functional oligomer component; and (c) a photoinitiator component; and (ii) components of a second cure mechanism comprising: (e) an amine component; and (f) an encapsulated epoxy resin component; together with (iii) a thickener component. The photoinitiator component is suitable upon irradiation of the composition to achieve a first cure through the depth of the composition applied to a threaded article so that a binder matrix is formed with the components of the second cure mechanism dispersed through the matrix.

[0015] Though conventional anaerobic threadlockers have been and remain well-received in the marketplace, there are shortcomings for certain commercial applications that have been observed with the use of conventional liquid anaerobic threadlockers, as well as known non-flowable, thixotropic anaerobic-based threadlockers. For instance, oftentimes such compositions do not fully cure through large gaps. Also, because of their nature of anaerobic cure, portions of the adhesive which remain exposed to air once applied to the parts will have difficulty curing (absent a secondary cure mechanism that is triggered). Thus, external bondlines which remain exposed to air on a nut/bolt assembly oftentimes will remain liquid unless additional additives and cure measures are taken to ensure cure. As a result, liquid compositions at the external bondlines tend to migrate. In the case of conventional non-flowable compositions, which depend on the thixotropic and/or rheological properties of the composition for their non-flowability, these compositions will flow if the temperature to which they are exposed is high enough. Additionally, the resistance to solvents of cured products (that have portions which remain uncured, as noted above) may be poor, indicative of questionable integrity when environmental interaction occurs. This may lead to contamination problems and hazardous conditions for the surroundings.

[0016] U.S. Patent No. 9,181,457 (Attarwala) describes dry-to-the-touch compositions containing a polymeric matrix and a anaerobically curable component present within the polymeric matrix. In a particularly desirable form, the compositions are moisture curable. The compositions are non-flowable at high temperatures, and have an improved solvent resistance once cured. The compositions are useful as threadlocking compositions, and can be formulated as coatings on a carrier substrate, such as a tape, a string or a sheet.

[0017] British Patent No. 2,543,756 (Ledwith) describes a threadlocking composition comprising an anaerobically curable component and a curing component for curing the anaerobically curable component; wherein the composition is in flowable particulate form and has a melting point in the range 30-100 °C. The anaerobically curable component may comprise an anaerobically curable monomer and a resin component. The composition may be provided in at least two-part form. The anaerobically curable component is preferably provided in powder form. Preferably the resin component is selected from methacrylated polyurethane resins, novolac resins or higher methacrylated polyester resins. The anaerobically curable monomer preferably comprises at least one acrylate or methacrylate ester group. The composition is preferably solvent-free. Also disclosed is a method of threadlocking two threaded articles together comprising applying said composition to the threads of at least one article so as to fuse it by melting to the threads; subsequently, and optionally after cooling, threading the two articles together so as to initiate anaerobic cure of the threadlocking composition so as to chemically bond the two articles together. An article having said composition applied thereto is also disclosed.

[0018] Notwithstanding the state of the art, it would be desirable to provide alternative threadlocking systems, including threaded members comprising dry-to-touch threadlocking compositions, methods for forming such threaded members, and method for assembling such threaded members.

Summary

[0019] In one aspect, the present invention provides a threaded member comprising at least one threaded face, wherein said at least one threaded face comprises a first coating comprising an anaerobically curable (meth)acrylate composition, said composition comprising a nucleophilic curing agent, and wherein said first coating is itself coated by a second coating comprising a polycyanoacrylate film.

[0020] Suitably, the polycyanoacrylate film has a thickness in the range of from 5 pm to 150 pm, suitably in the range of from 10 pm to 100 pm, such as from 10 pm to 50 pm. Preferably, the polycyanoacrylate film is oxygen permeable.

[0021] Suitably, the second coating has a glass transition temperature in the range of from 90°C to 250°C, preferably the glass transition temperature is 120°C to 200°C.

[0022] The anaerobically curable (meth)acrylate composition may comprise a (meth)acrylate component in an amount of from about 10 to about 98% by weight based on the total weight of the anaerobically curable (meth)acrylate composition, such as in an amount of form about 60 to 98% by weight, based on the total weight of the anaerobically curable (meth)acrylate composition.

[0023] The nucleophilic curing agent may comprise an amine, amide, hydrazine, hydrazide, urea, imide, thiazole, benzothiazole, and/or sulfenamide. Suitably, the nucleophilic curing agent comprises 1-acetyl-2-phenylhydrazine, a toluidine, an indoline, an isoindoline, a quinoline, an isoquinoline, uric acid, caffeine, theophylline, theobromine, paraxanthine, dyphylline, xanthinol, a C5-C30 alkyl amine, an ethanolamine, a benzothiazole, a sulfenamide, an amidine. Preferably, the nucleophilic curing agent comprises 1-acetyl-2-phenylhydrazine, and or a toluidine.

[0024] Suitably, the nucleophilic curing agent is present in an amount of from about 0.001% to about 5% by weight based on the total weight of the anaerobically curable (meth)acrylate composition, preferably in an amount of from about 0.05 to about 1.75% by weight based on the total weight of the anaerobically curable (meth)acrylate composition, such as from 0.1 to about 1.0% by weight based on the total weight of the anaerobically curable (meth)acrylate composition.

[0025] The anaerobically curable (meth)acrylate composition may comprise an initiator of free radical polymerization, such as a peroxide.

[0026] The initiator of free radical polymerization may be one or more selected from: cumene hydroperoxide ("CHP"), para-menthane hydroperoxide, t-butyl hydroperoxide ("TBH"), t-butyl perbenzoate, benzoyl peroxide, dibenzoyl peroxide, 1,3-bis(tbutylperoxyisopropyl)benzene, diacetyl peroxide, butyl 4,4-bis(t-butylperoxy)valerate, pchlorobenzoyl peroxide, t-butyl cumyl peroxide, t-butyl perbenzoate, di-t-butyl peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-di-t-butylperoxyhexane, 2,5-dimethyl-2,5-di-t-butylperoxyhex-3-yne, 4-methyl-2,2-di-t-butylperoxypentane, t-amyl hydroperoxide, 1,2,3,4-tetramethylbutyl hydroperoxide and combinations thereof [0027] The free radical cure inducing component may comprise an encapsulated peroxide.

[0028] The anaerobically curable (meth)acrylate composition may comprise a cure accelerator, such as one or more metallocenes, preferably a ferrocene, such as n-butyl ferrocene.

[0029] In another aspect, the present invention provides a method of manufacturing a threaded member comprising a threadlocking composition, comprising: providing at least one threaded member comprising at least one threaded face, applying to said at least one threaded face, an anaerobically curable (meth)acrylate composition, to form a first coating on said at least one threaded member, said composition comprising a nucleophilic curing agent; applying to said first coating a second coating comprising a polycyanoacrylate film.

[0030] Suitably, the step of applying a second coating comprising a polycyanoacrylate film comprises applying and curing a curable cyanoacrylate component to said first coating.

[0031] Advantageously, the cyanoacrylate component is cured by the nucleophilic curing agent present in the first coating.

[0032] Suitably, the curable cyanoacrylate component may be applied to the first coating using a carrier gas. The carrier gas may comprise nitrogen, argon or compressed air. Suitably, the carrier gas should dried, for example, the carrier gas may be dried by passing the gas through a desiccating agent.

[0033] The curable cyanoacrylate component may be applied to the first coating as an aerosol or mist. Advantageously, this facilitates accurate application of a specific amounts of cyanoacrylate and the formation of a specific thickness polycyanoacrylate film.

[0034] In another aspect, the present invention provides a method of assembling threaded members comprising: providing a first threaded member; providing a second threaded member capable of matingly engaging said first threaded member; at least one of said first and second threaded members comprising a first coating comprising an anaerobically curable (meth)acrylate composition, said composition comprising a nucleophilic curing agent, and wherein said first coating is itself coated by a second coating comprising a polycyanoacrylate film; matingly engaging said first and second threaded members and permitting the composition to anaerobically cure therebetween.

Brief Description of the Drawings

[0035] Embodiments of the invention will be described, by way of example only, with reference to the accompanying drawings in which: [0036] Figure 1 shows the torque strength assessment a threaded assembly formed using a threaded member according to the invention, and a comparative example formed using a threaded member coated with an anaerobically curable composition; [0037] Figure 2a is a cross-section of a threaded member coated with an anaerobically curable composition having a dry-to-touch outer coating as described in European Patent No. 0 077 659; Figure 2b is a cross-section of a threaded member according to the present invention.

Detailed Description

[0038] (Meth)acrylate monomers suitable for use as the (meth)acrylate component in the present invention may be selected from a wide variety of materials, such as those represented by H2C=CGCO2R8, where G may be hydrogen, halogen or alkyl groups having from 1 to about 4 carbon atoms, and R8 may be selected from alkyl, cycloalkyl, alkenyl, cycloalkenyl, alkaryl, alkaryl or aryl groups having from 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, carbonate, amine, amide, sulfur, sulfonate, sulfone and the like.

[0039] Additional (meth)acrylate monomers suitable for use herein include polyfunctional (meth)acrylate monomers, for example di-or tri-functional (meth)acrylates such as polyethylene glycol di(meth)acrylates, tetrahydrofuran (meth)acrylates and di(meth)acrylates, hydroxypropyl (meth)acrylate ("HPMA"), hexanediol di(meth)acrylate, trimethylol propane tri(meth)acrylates ("TMPTMA"), diethylene glycol dimethacrylate, triethylene glycol dimethacrylates ("TRIEGMA"), tetraethylene glycol di(meth)acrylates, dipropylene glycol di(meth)acrylates, di-(pentamethylene glycol) di(meth)acrylates, tetraethylene diglycol di(meth)acrylates, diglycerol tetra(meth)acrylates, tetramethylene di(meth)acrylates, ethylene di(meth)acrylates, neopentyl glycol di(meth)acrylates, and bisphenol-A mono and di(meth)acrylates, such as ethoxylated bisphenol-A (meth)acrylate ("EBIPMA"), and bisphenol-F mono and di(meth)acrylates, such as ethoxylated bisphenol-A (meth)acrylate.

[0040] For example the anaerobically curable component may include (as an anaerobically curable monomer) Bisphenol A dimethacrylate: 0 0

IJ

which has a melting point of approximately 72 to 74°C.

[0041] Still other (meth)acrylate monomers that may be used herein include silicone (meth)acrylate moieties ("SiMA"), such as those taught by and claimed in U.S. Patent No. 5,605,999 (Chu), incorporated herein by reference.

[0042] Other suitable monomers include polyacrylate esters represented by the formula R.4 o [ o 4 I II 11.

II

H2C=C-C-0 -[X-0]-C-C=CH2 where R4 is a radical selected from hydrogen, halogen or alkyl of from 1 to about 4 carbon atoms; q is an integer equal to at least 1, and preferably equal to from 1 to about 4; and X is an organic radical containing at least two carbon atoms and having a total bonding capacity of q plus 1. With regard to the upper limit for the number of carbon atoms in X, workable monomers exist at essentially any value. As a practical matter, however, a general upper limit is about 50 carbon atoms, such as desirably 30, and desirably about 20.

[0043] For example, X can be an organic radical of the formula: 0 0 El it -YI-OCZC-01'2 where each of Y1 and Y2 is an organic radical, such as a hydrocarbon group, containing at least 2 carbon atoms, and desirably from 2 to about 10 carbon atoms, and Z is an organic radical, preferably a hydrocarbon group, containing at least 1 carbon atom, and preferably from 2 to about 10 carbon atoms.

[0044] Other classes of useful monomers are the reaction products of di-or tri-alkylolamines (e.g., ethanolamines or propanolamines) with acrylic acids, such as are disclosed in French Pat. No. 1,581,361.

[0045] Examples of useful acrylic ester oligomers include those having the following general formula: H7C-C C 0 I '^5 R4 I C y C 0 C"-C=CHa K4 t.R5 1/412_6 i where R5 represents a radical selected from hydrogen, lower alkyl of from 1 to about 4 carbon atoms, hydroxy alkyl of from 1 to about 4 carbon atoms, or -CH2-0-C-C=CH2 R4 where IR' is a radical selected from hydrogen, halogen, or lower alkyl of from 1 to about 4 carbon atoms; 56 is a radical selected from hydrogen, hydroxyl, or 0 II -0-C-C=CH2 R4 m is an integer equal to at least 1, e.g., from 1 to about 15 or higher, and desirably from 1 to about 8; n is an integer equal to at least 1, e.g., 1 to about 40 or more, and desirably between about 2 and about 10, and p is 0 or 1.

[0046] Typical examples of acrylic ester oligomers corresponding to the above general formula include di-, tri-and tetraethyleneglycol dimethacrylate; di(pentamethyleneglycol)dimethacrylate; tetraethyleneglycol diacrylate; tetraethyleneglycol di(chloroacrylate); diglycerol diacrylate; diglycerol tetramethacrylate; butyleneglycol dimethacrylate; neopentylglycol diacrylate; and trimethylolpropane triacrylate.

[0047] While di-and other polyacrylate esters, and particularly the polyacrylate esters described in the preceding paragraphs, can be desirable, monofunctional acrylate esters (esters containing one acrylate group) also may be used. When dealing with monofunctional acrylate 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 halo polar groups. Typical examples of compounds within this category are cyclohexylmethacrylate, tetrahydrofurfuryl methacrylate, hydroxyethyl acrylate, hydroxypropyl methacrylate, tbutylaminoethyl methacrylate, cyanoethylacrylate, and chloroethyl methacrylate.

[0048] Another useful class of monomers is prepared by the reaction of a monofunctionally substituted alkyl or aryl acrylate ester containing an active hydrogen atom on the functional substituent. This monofunctional, acrylate-terminated material is reacted with an organic polyisocyanate in suitable proportions 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 or amino functional groups on the non-acrylate portion thereof. Acrylate esters suitable for use have the formula 117 ()

II

112C=C-C-0-0-X-11 Ry where X is selected from --0--and where R9 is selected from hydrogen or lower alkyl of 1 through 7 carbon atoms; R7 is selected from hydrogen, halogen (such as chlorine) or alkyl (such as methyl and ethyl radicals); and IR9 is a divalent organic radical selected from lower alkylene of 1 through 8 carbon atoms, phenylene and naphthylene. These groups upon proper reaction with a polyisocyanate, yield a monomer of the following general formula: [ R 0 0 i II it H2C=C-C-0-0-X-C-Nli, where n is an integer from 2 to about 6; B is a polyvalent organic radical selected from alkyl, alkenyl, cycloalkyl, cycloalkenyl, aryl, alkaryl, alkaryl and heterocyclic radicals both substituted and unsubstituted; and R7, R8 and X have the meanings given above.

[0049] Depending on the nature of B, these (meth)acrylate esters with urea or urethane linkages may have molecular weights placing them in the oligomer class (such as about 1,000 g/mol up to about 5,000 g/mol) or in the polymer class (such as about greater than 5,000 g/mol).

[0050] The anaerobically curable component may be chosen from at least one of epoxy (meth)acrylates, urethane (meth)acrylates, urethane di(meth)acrylates, alkyl (meth)acrylates, stearyl (meth)acrylates, isocyanurate (meth)acrylates, bisphenol-A(meth)acrylates, ethoxylated bisphenol-A-(meth)acrylates, bisphenol-F-(meth)acrylates, ethoxylated bisphenol-F-(meth)acrylates, bisphenol-A di(meth)acrylates, ethoxylated bisphenol-A-di(meth)acrylates, bisphenol-F-di(meth)acrylates, and ethoxylated bisphenol-F-di(meth)acrylates.

[0051] For example the anaerobically curable component may include (as an anaerobically curable monomer) diisocyanates capped with hydroxyethyl methacrylate (HEMA) such as:

LI

OtO HN 0.K.N which is hydroxyethyl methacrylate which has been reacted with isophorone diisocyanate (HEMA-IPDI-HEMA) -and has a melting point of about 72-74°C; or diXH N OJ ° 110 US,, N 0 which is hydroxyethyl methacrylate which has been reacted with dicyclohexylmethane 4,4'-diisocyanate (HEMA-HMDI-HEMA) -and has a melting point of about 75-85°C; or

N 0 0

which is hydroxyethyl methacrylate which has been reacted with 1,3-diisocyanatocyclohexane (HEMA-1,3-CHDI-HEMA ("RRT600" in the Examples below)) -and has a melting point of about 75-85°C; or °Y' 0 0 NH HN 0 0 0 which is glycerol dimethacrylate which has been reacted with 1,3-diisocyanatocyclohexane (Glycerol Dimethacrylate-6HXDI-Glycerol Dimethacrylate ("4RRT600" in the Examples below)) -and has a melting point in the range from about 75 to about 85°C.

[0052] The proportions in which the reactants may be combined can be varied somewhat; however, it is generally preferred to employ the reactants in chemically equivalent amounts up to a slight excess.

[0053] At least a portion of the (meth)acrylate component may be in the solid state at room temperature.

[0054] Of course, combinations of these (meth)acrylate monomers may also be used.

[0055] The (meth)acrylate component can comprise from about 10 to about 98% by weight of the composition, such as from about 20 to about 95%, from about 25 to about 90%, or about 30 to about 85%, for example about 35 to about 80%, or from about 40 to about 75%, such as from about 60 to about 75% by weight, based on the total weight of the composition. Suitably, the (meth)acrylate component is present in an amount of from about 60 to about 98% by weight based on the total weight of the anaerobically curable (meth)acrylate composition.

[0056] Additional components have in the past been included in traditional anaerobic adhesives to alter the physical properties of either the formulation or the reaction products thereof. For instance, one or more of maleimide components, thermal resistance-conferring co reactants, diluent components reactive at elevated temperature conditions, mono-or poly-hydroxyalkanes, polymeric plasticizers, and chelators (see U.S. Patent No. 6,391,993, incorporated herein by reference) may be included to modify the physical property and/or cure profile of the formulation and/or the strength or temperature resistance of the cured adhesive.

[0057] When used, the maleimide, co-reactant, reactive diluent, plasticizer, and/or mono-or poly-hydroxyalkanes may be present in an amount within the range of about 1% to about 30% by weight, based on the total weight of the composition.

[0058] The anaerobically curable (meth)acrylate composition may include other conventional components such as one or more of the following free radical initiators, free radical accelerators, inhibitor of free radical generation as well as metal catalysts such as iron and copper.

[0059] Suitably, the anaerobically curable (meth)acrylate composition comprises one or more initiators of free radical polymerization. Metal catalysts may also be used.

[0060] A number of well-known initiators of free radical polymerization are typically incorporated into anaerobic curable compositions including, without limitation, hydroperoxides, such as cumene hydroperoxide ("CHP"), para-menthane hydroperoxide, t-butyl hydroperoxide ("TBH") and t-butyl perbenzoate. Other peroxides include benzoyl peroxide, dibenzoyl peroxide, 1,3-bis(t-butylperoxyisopropyl)benzene, diacetyl peroxide, butyl 4,4-bis(t-butylperoxy)valerate, p-chlorobenzoyl peroxide, t-butyl cumyl peroxide, t-butyl perbenzoate, di-t-butyl peroxide, dicumyl peroxide, 2,5-dimethy1-2,5-di-t-butylperoxyhexane, 2,5-dimethyl-2,5-di-t-butyl-peroxyhex-3-yne, 4-methyl-2,2-di-t-butylperoxypentane, t-amyl hydroperoxide, 1,2,3,4-tetramethylbutyl hydroperoxide and combinations thereof.

[0061] Encapsulated peroxides may also be used. For instance, encapsulated benzoyl peroxides may be used. Encapsulated benzoyl peroxide having a particle size of 200 pm, commercially available from Japan Capsular Products is one particularly useful material. Others with particle sizes in the 100 pm range are also desirable. Other than Japan Capsular Products, commercial sources of encapsulated benzoyl peroxides include Lipo Technologies Inc. and RT Dodge.

[0062] Such peroxides are typically employed in the present invention in the range of from about 0.1 to about 10% by weight, based on the total weight of the composition, with about 1 to about 5% by weight being desirable.

[0063] As noted, conventional accelerators of free radical polymerization are typically of the hydrazine variety (e.q. APH), as disclosed in U.S. Patent Nos. 4,287,350 (Rich) and 4,321,349 (Rich). Maleic acid is usually added to APH-containing anaerobic cure inducing composition. The compositions of the invention suitably may comprise such accelerators of free radical polymerization.

[0064] Co-accelerators of free radical polymerization may also be used in the compositions of the present invention including, without limitation, organic amides and imides, such as benzoic sulfimide (also known as saccharin) (see U.S. Patent No. 4,324,349).

[0065] The accelerators (or co-accelerators) may be used in amounts of about 0.1 to about 5% by weight, such as about 1 to about 2% by weight, based on the total weight of the composition.

[0066] Stabilizers and inhibitors (such as phenols including hydroquinone and quinones) may also be employed to control and prevent premature peroxide decomposition and polymerization of the composition of the present invention [0067] Chelating agents [such as the tetrasodium salt of ethylenediamine tetraacetic acid ("EDTA")] may be used to trap trace amounts of metal contaminants. When used, chelating agents may ordinarily be present in the compositions in an amount from about 0.001% by weight to about 0.1% by weight, based on the total weight of the composition.

[0068] Other additives such as plasticizers, fillers, toughening agents (such as elastomers and rubbers) and other well-known additives may be incorporated therein where the art-skilled believes it would be desirable to do so.

[0069] It will be appreciated that the anaerobically curable (meth)acrylate compositions can include non-reactive species including resins. Such components do not participate in an anaerobic cure reaction. They are unreactive. Such components may however become part of the cure product having been incorporated therein during the curing of other components. Examples of such non-reactive species include: fumed silica, polyethylene, PTFE, mica, polyamide wax, titanium dioxide, and barium sulphate.

[0070] The nucleophilic curing agent may for example be selected from an amine, amide, hydrazine, hydrazide, urea, imide, thiazole, benzothiazole, and/or sulfenamide.

[0071] Suitably, the nucleophilic curing agent is a hydrazine, such as 1-acety1-2- phenylhydrazine, a toluidine, such as N,N-Dimethyl para toluidine, N,N-diethyl para toluidine, N,N-diethanol para toluidine, N,N-dimethyl ortho toluidine, N,N-dimethyl meta toluidine, or a heterocyclic amine, such as indoline, 2-methylindoline, isoindoline, indole, 1,2,3,4-tetrahydroquinoline, 3-methyl-1,2,3,4-tetrahydro-quinoline, 2-methy1-1,2,3,4- tetrahydroquinoline, 1,2,3,4-tetrahydroquinoline 4 carboxylic acid, 1234-tetrahydroisoquinoline, uric acid, caffeine, theophylline, theobromine, paraxanthine, dyphylline, and/or xanthinol, a 04-C60 alkyl amine, e.g. tributyl amine, or tallow amines, ethanolaimes, such as n-ethanolamine, diethanolamine, and/or triethanolamine, a sulfenamide, and/or an amidine, such as 1,5-diazabicyclo[4.3.0]non-5-ene, 1,8-diazabicyclo[5.4.0]undec-7-ene, and/or 1,5,7-triazabicyclo[4.4.0]dec-5-ene.

[0072] Suitably, the nucleophilic curing agent may induce cure of one or more cyanoacrylate monomers which polymerise to form the polycyanoacrylate film, as well as functioning as a cure inducing component and/or accelerator for free radical polymerization of the anaerobically curable (meth)acrylate composition, i.e. the nucleophilic curing agent may be a bifunctional curing agent, which facilitates cure of one or more cyanoacrylate components which form the polycyanoacrylate film, in addition to curing the anaerobically curable (meth)acrylate composition, when said composition is exposed to anaerobic conditions.

[0073] The polycyanoacrylate film is formed by curing a curable cyanoacrylate component, i.e. the polycyanoacrylate film is the cure product of curing a curable cyanoacrylate component.

[0074] The cyanoacrylate component includes one or more cyanoacrylate monomers, such as those represented by H2C=C(CN)-COOR, where R is selected from C1.15 alkyl, C2.15 alkoxyalkyl, C3.15cycloalkyl, 02.15alkenyl, C7.15 aralkyl, Ce.is aryl, C3.15ally1 and C3.15 haloalkyl groups. Desirably, the cyanoacrylate monomer is selected from methyl cyanoacrylate, ethyl-2-cyanoacrylate, propyl cyanoacrylates, butyl cyanoacrylates (such as n-butyl-2-cyanoacrylate), octyl cyanoacrylates, ally! cyanoacrylate, R-methoxyethyl cyanoacrylate and combinations thereof. A particularly desirable cyanoacrylate monomer is ethyl-2-cyanoacrylate ("EGA").

[0075] The cyanoacrylate component may be a cyanoacrylate composition comprising one or more cyanoacrylate monomers, such as those specified above.

[0076] Suitably, the cyanoacrylate composition may comprise one or more stabilizers. The stabilizer may include one or more free radical stabilizers and anionic stabilizers, each of the identity and amount of which are well known to those of ordinary skill in the art. See e.g. U.S. Patent Nos. 5,530,037 and 6,607,632, the disclosures of each of which are hereby incorporated herein by reference.

[0077] The polycyanoacrylate film which forms the second coating, which is applied to the anaerobically curable (meth)acrylate composition suitably has a thickness of from 5 pm to 150 pm, for example from 10 pm to 100 pm, such as from 10 pm to 50 pm. Preferably, the polycyanoacrylate film is oxygen permeable.

[0078] Advantageously, an oxygen permeable polycyanoacrylate film, such as a polycyanoacrylate film having a thickness in the range of from 5 pm to 150 pm, may be used to coat an anaerobically curable (meth)acrylate composition wherein the initiator for the anaerobically curable (meth)acrylate composition is not encapsulated in microcapsule form i.e. encapsulation is not required. Notwithstanding the foregoing, such an oxygen permeable polycyanoacrylate film having said thickness may also suitably be used to coat an anaerobically curable (meth)acrylate composition comprising an initiator which is encapsulated.

[0079] Surprisingly, cure of the cyanoacrylate monomer on the first coating comprising the anaerobically curable (meth)acrylate composition occurs without deleteriously affecting the performance of the anaerobically curable (meth)acrylate composition.

[0080] As outlined above, the cyanoacrylate monomer may be applied to the first coating using a carrier gas. For example, cyanoacrylate monomer may be heated to form a cyanoacrylate vapour, which is then employed to coat the threaded member to which the first coating is applied, thereby forming the second coating on said first coating. The carrier gas may for example be nitrogen, argon, or compressed air, other inert gases would be equally suitable. Suitably, the carrier gas is dried to such an extent that its moisture content will not deleteriously impact the formation of the polycyanoacrylate film i.e. the carrier gas is dried, for example, by passing it through/over a desiccating agent, prior to employing it to carry cyanoacrylate monomer vapour. The person skilled in the art knows suitable means for drying the carrier gas. Suitably, the carrier gas has a moisture content of 1% or less by volume, more suitably, 0.5% or less by volume, preferably 0.1% or less by volume.

[0081] The method of present invention has significant advantages over prior art methods for forming dry to touch coatings of anaerobically curable compositions on threaded substrates, such as nuts and bolts. For example, some prior art methods for forming dry to touch anaerobically curable coatings on threaded substrates involve heating threaded substrates to which an anaerobically curable composition was applied in an aqueous formulation, to remove the water content from the aqueous formulation. This is a costly and energy intensive process. In contrast, the method of the present invention provides a low cost method for forming a dry to touch coating comprising an anaerobically curable (meth)acrylate composition coated on a threaded member. In particular, the step of applying a polycyanoacrylate film on the first coating using a carrier gas, such nitrogen, has significant advantages over prior art methods for forming such dry to touch coatings. For example, the dry to touch coating described in European Patent No. 0 077 659 (Thompson) which involves radiative cure and shadow effects can deleteriously impact such radiative cure systems. Furthermore, in the method of Thompson, a single layer of anaerobically curable adhesive composition is applied to the threaded member, and part of this layer is then converted to a dry to touch film through radiative cure, with deep cure through volume being prevented by the presence of the opacifier. As a consequence the amount of anaerobically curable adhesive which remains in the threaded face of the threaded member, is reduced in comparison to that which was applied. In contrast, in the present invention, the polycyanoacrylate film is applied to the first coating comprising the anaerobically curable (meth)acrylate composition, thus none of the anaerobically curable adhesive is expended in the formation of a dry to touch film, as is the case in the method of Thompson. This is illustrated in Figures 2a and 2b. In Figure 2a the dry to touch crust or skin (6) is formed from the outer layer of anaerobically curable composition 2 applied to the bolt 1. In contrast, in the present invention a polycyanoacrylate film is applied on the outer surface of the first coating of anaerobically curable (meth)acrylate composition, thus as seen in Figure 2b, the polycyanoacrylate film anchors on the crest of the threads 8, and none of the anaerobically curable composition applied to the threaded face of the threaded member is exhausted in order to form said film.

[0082] Figure 2a shows a bolt 1 having a coating of polymerisable fluid 2 applied on a threaded portion of the bolt. The fluid 2 comprises an acrylic monomer composition comprising a microencapsulated peroxide initiator (not shown). An opacifier 3 is dispersed throughout the fluid 2. A dry-to-touch skin 6 having a depth X, which is in the range of from 0.01 mm to 0.1 mm is formed by exposing the polymerisable fluid 2 to radiation from an ultra violet source which impinges on the surface 5 of the coating. Due to the presence of the opacifier, the radiation only penetrates the polymerisable fluid 2 to a depth X, thereby precluding the polymerisation of the entirety of the polymerisable fluid 2.

[0083] Figure 2b shows a threaded member in accordance with the present invention. Polycyanoacrylate film 701 forms a dry-to-touch second coating 702 anchored on the crests 801 of the threaded bolt 101, and which coats (i.e. encapsulates) the first coating 202 of anaerobically curable (meth)acrylate composition 201. Advantageously, the presence of the second coating 702 comprising the polycyanoacrylate film 701 does not diminish the amount of anaerobically curable composition 201 on the thread which forms the threadlocking cured composition when a threaded assembly is formed using the threaded member of the present invention.

[0084] Advantageously, the cyanoacrylate monomer cures effectively on the surface of the first coating comprising the anaerobically curable (meth)acrylate composition, to form a hard polycyanoacrylate film which encapsulates the anaerobically curable (meth)acrylate composition. A significant advantage of the present invention, is that the cyanoacrylate cure occurs under sufficiently mild conditions that mixing of the cyanoacrylate with the anaerobically curable (meth)acrylate composition does not occur, for example, cure can occur at room temperature, and there is no negative impact on the performance of said anaerobically curable (meth)acrylate composition (see Figure 1). A further advantage of the polycyanoacrylate film is its hardness/robustness. The encapsulation by the polycyanoacrylate film of the anaerobically curable (meth)acrylate composition is sufficiently robust to enable handling, storage and transport of the coated threaded members, thus making such coated threaded members useful in an industrial and commercial context. This represents a marked improvement on the threaded members of Thompson, whose dry-to-touch crust or skin was not sufficiently robust to withstand handling, packaging, storage and transport, and which suffered from leakage of the anaerobically curable composition due to cracks occurring in the crust or skin encapsulating said composition. Furthermore, the method of the present invention enables the formation of a polycyanoacrylate film of varying thickness which coats the first coating comprising the anaerobically curable (meth)acrylate composition. Thus the method of the present invention enables the formation of a thicker dry to touch coating layer, which coats the anaerobically curable composition, than can be formed for example via the methodology described in Thompson. Advantageously, the method of the present invention does not require conversion of a portion of the anaerobically curable composition which is applied to the threaded member into a dry to touch coating, thus the quantity of anaerobically curable composition applied to the threaded member in the method of the present invention is not diminished in order to facilitate the formation of a dry to touch coating on the anaerobically curable composition. Moreover, when a carrier gas or aerosol is used in the method of the invention, the thickness of the polycyanoacrylate film can be built up, to form a polycyanoacrylate film of a suitable thickness and robustness for a given application, for example, certain applications may require the dry to touch coating to be more robust than others. As outlined in Figure 2b, a further advantage of the present invention is the slight increase in prevail strength observed when disassembling a threaded nut and bolt assembly as described herein, as a consequence of the polycyanoacrylate particles which are formed between the threads when the polycyanoacrylate film is broken during assembly of the nut and bolt assembly.

Examples

[0085] An anaerobically curable composition as defined in Table 1 was prepared.

Table 1

Component Amount (wt%) Ethoxylated bisphenol A dimethacrylate 92.94 Maleic acid 0.1 n-butylferrocene 0.06 Butyl hydroxytoluene 0.1 Triethanolamine 1.3 Fumed silica 1.5 Microencapsulated benzoyl peroxide 4.0

Example 1

[0086] The components of table 1 were mixed to form an anaerobically curable paste. The anaerobically curable paste was applied as a paste to the threaded face of a degreased black oxide bolt. To a three-neck round bottom flask equipped with a thermometer, a nitrogen line and a stirrer was added a curable cyanoacrylate composition, specifically Loctite® 401 -which comprises ethyl cyanoacrylate. The cyanoacrylate composition was heated to 65°C. The bolt to which the anaerobically curable paste was applied, was rotatably held over an open neck of said three-neck round bottom flask containing the cyanoacrylate composition. Nitrogen gas was bubbled through the cyanoacrylate composition. The bolt was rotated continuously over the open neck of the flask. Cyanoacrylate vapour was carried by the nitrogen stream from the round bottom flask through the open neck of the flask and into contact with the rotating bolt. Upon exposure to the anaerobically curable paste on the rotating bolt, the cyanoacrylate vapour polymerised to form a dry to touch polycyanoacrylate film. The bolt to which the first coating comprising the anaerobically curable composition and the second coating comprising the polycyanoacrylate film was applied was left to stand at room temperature for 1 hour.

Comparative Example 1 [0087] The components of table 1 were mixed to form an anaerobically curable paste. The anaerobically curable paste was applied as a paste to the threaded face of a degreased black oxide bolt.

Torque Strength Assessment [0088] Appropriately sized degreased lock nuts were used to form nut and bolt assemblies with the coated bolt from Example 1 and that from Comparative Example 1. The threaded members employed were black oxide nuts and bolts. The effect of the polycyanoacrylate coating on the efficacy of the anaerobic is shown in Figure 1. Break and prevail strengths were assessed for the threaded assemblies in accordance with ISO 10964.

[0089] The break strength for both the coated bolt from Example 1 and that from Comparative Example 1 were almost identical, whereas the prevail strength for the anaerobic on the bolt from Example 1 was slightly higher than that for Comparative Example 1.

[0090] Advantageously, the anaerobically curable adhesive which formed the first coating on the bolt from Example 1 was not deleteriously affected by the presence of the polycyanoacrylate coating. Surprisingly, when measuring the break and prevail strengths, the prevail strength of the polycyanoacrylate coated anaerobic was higher than that of Comparative Example 1. Without being bound by theory, it is thought that the brittle nature of the hard polycyanoacrylate film once shattered by assembling the nut and bolt assembly, results in crushed polycyanoacrylate particles which become incorporated in the anaerobically curable composition, and upon cure in the resulting cured composition. Once break strength of the cured anaerobic adhesive composition is overcome, these particles or shards increase the frictional forces between the bolt and nut, thereby increasing the prevail strength for removing the nut from the bolt.

[0091] The words "comprises/comprising" and the words "having/including" when used herein with reference to the present invention are used to specify the presence of stated features, integers, steps or components but do not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

[0092] It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.

Claims

Claims A threaded member comprising at least one threaded face, wherein said at least one threaded face comprises a first coating comprising an anaerobically curable (meth)acrylate composition, said composition comprising a nucleophilic curing agent, and wherein said first coating is itself coated by a second coating comprising a polycyanoacrylate film.
The threaded member according to claim 1, wherein said oxygen permeable polycyanoacrylate film has a thickness in the range of from 5 pm to 150 pm, suitably in the range of from 10 pm to 100 pm, such as from 10 pm to 50 pm.
The threaded member according to any preceding claim, wherein the anaerobically curable (meth)acrylate composition comprises a (meth)acrylate component in an amount of from about 10 to about 98% by weight based on the total weight of the anaerobically curable (meth)acrylate composition, such as in an amount of form about 60 to 98% by weight, based on the total weight of the anaerobically curable (meth)acrylate composition.
The threaded member according to any preceding claim, wherein the nucleophilic curing agent is one or more of a hydrazine, a toluidine, a heterocyclic amine, a 04-C60 alkyl amine, a triethanolamine, a sulfenamide and an amidine, or combinations thereof.
The threaded member according to any preceding claim, wherein the nucleophilic curing agent is one or more selected from the group consisting of 1-acetyl-2-phenylhydrazine, such as N,N-Dimethyl para toluidine, N,N-diethyl para toluidine, N,N-diethanol para toluidine, N,N-dimethyl ortho toluidine, N,Ndimethyl meta toluidine, indoline, 2-methylindoline, isoindoline, indole, 1,2,3,4-tetrahydroquinoline, 3-methyl-1,2,3,4-tetrahydro-quinoline, 2-methyl-1,2,3,4- tetrahydroquinoline, 1,2,3,4-tetrahydroquinoline 4 carboxylic acid, 1234- tetrahydroisoquinoline, uric acid, caffeine, theophylline, theobromine, paraxanthine, dyphylline, xanthinol, tributyl amine, a tallow amine, n- ethanolamine, diethanolamine, triethanolamine, a sulfenamide, 1,5-diazabicyclo[4.3.0]non-5-ene, 1,8-diazabicyclo[5.4.0]undec-7-ene, and 1,5,7-triazabicyclo[4.4.0]clec-5-ene.
6. The threaded member according to any preceding claim, wherein the nucleophilic curing agent is present in an amount of from about 0.001% to about 5% by weight based on the total weight of the anaerobically curable (meth)acrylate composition, preferably in an amount of from about 0.05 to about 1.75% by weight based on the total weight of the anaerobically curable (meth)acrylate composition, such as from 0.1 to about 1.0% by weight based on the total weight of the anaerobically curable (meth)acrylate composition.
The threaded member according to any preceding claim, wherein the anaerobically curable (meth)acrylate composition comprises an initiator of free radical polymerization, such as a peroxide.
The threaded member according to claim 7, wherein the initiator of free radical polymerization is one or more selected from the group consisting of: cumene hydroperoxide ("CHP"), para-menthane hydroperoxide, t-butyl hydroperoxide ("TBH"), t-butyl perbenzoate, benzoyl peroxide, dibenzoyl peroxide, 1,3-bis(tbutylperoxyisopropyl)benzene, diacetyl peroxide, butyl 4,4-bis(tbutylperoxy)valerate, p-chlorobenzoyl peroxide, t-butyl cumyl peroxide, t-butyl perbenzoate, di-t-butyl peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-di-tbutylperoxyhexane, 2,5-dimethyl-2,5-di-t-butyl-peroxyhex-3-yne, 4-methy1-2,2-di-t-butylperoxypentane, t-amyl hydroperoxide, 1,2,3,4-tetramethylbutyl hydroperoxide and combinations thereof.
The threaded member according to claim 7 or 8, wherein the free radical cure inducing component comprises an encapsulated peroxide.
10. The threaded member according to any preceding claim, wherein the anaerobically curable (meth)acrylate composition comprises a cure accelerator.
11. The threaded member according to claim 10, wherein the cure accelerator comprises one or more metallocenes, such as ferrocene, suitably, n-butyl ferrocene.
12. A method of manufacturing a threaded member comprising a threadlocking composition, comprising: a. providing at least one threaded member comprising at least one threaded face, b. applying to said at least one threaded face, an anaerobically curable (meth)acrylate composition to form a first coating on said at least one threaded member, said composition comprising a nucleophilic curing agent; c. applying to said first coating a second coating comprising a polycyanoacrylate film.
13. The method according to claim 12, wherein the step of applying a second coating comprising a polycyanoacrylate film comprises applying and curing a curable cyanoacrylate component to said first coating.
14. The method according to claims 12 or 13, wherein the curable cyanoacrylate component is applied to the first coating using a carrier gas.
15. The method according to claim 14, wherein the carrier gas is selected from nitrogen, argon and compressed air, or combinations thereof.
16. The method according to any one of claims 12 to 15, wherein the curable cyanoacrylate component is applied to the first coating as an aerosol or mist.
17. A method of assembling threaded members comprising: (a) providing a first threaded member; (b) providing a second threaded member capable of matingly engaging said first threaded member; at least one of said first and second threaded members comprising a first coating comprising an anaerobically curable (meth)acrylate composition, said composition comprising a nucleophilic curing agent, and wherein said first coating is itself coated by a second coating comprising a polycyanoacrylate film; matingly engaging said first and second threaded members and permitting the composition to anaerobically cure therebetween.