GB2037784A - Adhesives: activators - Google Patents

Abstract

Two part room temperature anaerobic curable adhesives based on (meth)acrylate monomers, comprise a peroxy compound and an activator derived from certain sodium salts of sulphuric acid esters of indigo or thioindigo dyestuffs. These activators are non-toxic and lead to reduced discolouration of the adhesive bond. The dyestuff is converted to the active form i.e. carbonyl group containing form by reaction with the peroxy compound. A typical active form of a leuco vat dyestuff and its reaction with hydroperoxide, is shown thus: <IMAGE>

Description

SPECIFICATION Adhesives : activators This invention is concerned with improvements in or relating to adhesives and activators therefor.

Various polymerisable compositions are known which are believed to cure or harden by free radical polymerisation of ethylenically unsaturated components thereof. In the field of polymerisable adhesives for example, reactive fluid adhesive compositions are known which cure at room temperature by addition polymerisation of monomeric components to provide adhesive bonds between surfaces of various different materials. Adhesive compositions intended to cure between opaque, impervious, or other materials to form an adhesive bond may comprise for example one or more polymerisable acrylate or methacrylate ester monomers, a source of free radicals for example a peroxide, hydroperoxide, per ester or per acid, and an activator for interaction with the source of free radicals to initiate polymerisation of the monomers at room temperature.The source of free radicals and the activator may be stored separated from each other prior to use of the adhesive, one of them being incorporated in admixture with the monomers during storage, so that one has an adhesive composition in two parts, which cures to form an adhesive bond when the two parts are brought together in absence of oxygen.

In one particularly convenient method of using reactive fluid adhesives, a part of the composition comprising the activator is applied to a surface to be bonded in the manner of a primer prior to the application of another part of the composition comprising the polymerisable monomers and source of free radicals. This method allows the use of the adhesive composition without the necessity to mix the two parts prior to application. The activator is conveniently one which can be used in non-stoichiometric quantities with respect to the monomers.

Whilst bonds formed in this way are highly useful, certain amine-aldehyde reaction products effective as activators are liquid materials having a certain degree of toxicity and offensive smell. In view of increasing opinion in favour of non-toxic materials, it is desirable to provide an adhesive composition comprising an activator system having a more acceptable level of toxicity and smell. In this context, one tends to consider use of solid materials as activators, but in adhesive work one also has to achieve a commercially accaptable level of technical performance which usually entails that the materials cannot be present in the bond in their solid form.Also, we have found that amine aldehyde reaction products heretofore preferred as activators have led to cured adhesive bonds which tgnd to discolour significantly under the influence of light. This tendency is regarded as a disadvantage in adhesive bonds which are visible, for example those between glass and other translucent or transparent materials.

One object of the present invention is to provide an improved adhesive composition comprising one or more polymerisable monomers comprising one or more acrylic or methacrylic acid residues per molecule, a source of free radicals, and an activator for co-operation with the source of free radicals to initiate polymerisation of the monomers.

We have now found that adhesive compositions which are curable at ambient temperature to form adhesive bonds between for example opaque, impervious, substrates without external application of heat, light or other radiation, may comprise polymerisable acrylic or methacrylic acid esters, a source of free radicals, and an activator comprising organic material which is easily derived from the readily available leuco sulphuric ester of an indigo or thioindigo dye.

Activators useful in the invention comprise an organic material comprising in its molecule a five membered ring including a sulphur or nitrogen atom which is linked to a substituted or unsubstituted aromatic ring system of the molecule and which is linked to a first carbon atom of the five membered ring which first carbon atom is linked to a second carbon atom of the five membered ring and to a third carbon atom which is not a member of the five membered ring but is a member of an aromatic or heterocyclic ring system, the structure being such that the C-C bond between the first and third carbon atoms is a single valency bond there being a substituent R, on the second carbon atom and a substituent R2 on a fourth carbon atom which is a member of the second mentioned aromatic or heterocyclic ring system linked to the third carbon atom, the substituents R1 and R2 and the organic material being such that the organic material is capable of conversion under adhesive bond-forming conditions in the presence of the source of free radicals to a diketo form in which R and R2 have each been converted to =0 and the C-C bond between the first and third carbon atoms has been converted to a double valency bond.

Formerly referred to as "indigosols", the leuco sulphuric esters are also referred to as "solubilized indigoid vat colours" and leuco vat dyestuffs; they are marketed as their sodium salts under various names including "Indigosol" and "Anthrasol".

Preferred activator compounds of the general class referred to include materials derived from the dyestuffs Anthrasol 04B, Anthrasolorange HR, Anthrasolgrau IBL, Anthrasolrosa IR extra, Anthrasolblau AGG, and Anthrasoldruckschwarz. Each of these dyestuffs can be regarded as characterised by a conjugated double bond system common to two ring systems one or both of which is a five membered heterocyclic ring including a nitrogen or sulphur atom. These preferred materials are further characterised in that the aforementioned heterocyclic or aromatic rings are each themselves linked through two carbon atoms of the ring to aromatic rings, at least one of which is a substituted aromatic ring or an element of a substituted ring system.These commercially available dyestuffs are believed to be in the form of the sodium salts of the sulphuric acid ester of their leuco form, and for the purposes of the present invention are converted into a form (hereinafter referred to as the active form) in which, in acidic medium (provided by the monomers) they are activators useful in the present invention. It is believed that in the active form the ester groups have been converted to hydroxyl groups, which are oxidizable in acid medium in the presence of a generator of free radicals for example a peroxide, to yield free radicals as shown schematically in Table 2 with respect to Anthrasol 04B.

The preferred activators are solids soluble to an acceptable extent in volatile organic solvent for application to a substrate. They are regarded as odourless, non-toxic materials, and in conjunction with acrylic and methacrylic acid ester monomers and a source of free radicals yield at room temperature adhesive bonds of good strength and performance between opaque impervious substrates of various materials. We have found that adhesive bonds formed with these activator compounds between translucent or transparent materials are also of good strength and performance. Whilst a pale colouring due to the dyestuff may be observed, the adhesive bonds do not become progressively discoloured under the influence of light to the same degree as bonds formed by use of activators based on aminealdehyde reaction products.

The source of free radicals and the activator are stored in separate containers prior to use.

Preferably the source of free radicals is included with the polymerisable monomers in a first or adhesive part of the adhesive composition together with inhibitors and stored in polyethylene bottles including a significant quantity of atmospheric oxygen in order to maintain stability of the first part. The activator is preferably stored as a solution in organic solvent to provide a second or activator composition part of the adhesive composition. Preferably the activator composition is stored in dark-coloured bottles or in a light impervious aerosol container.

As will be apparent, the activator composition is not required to be mixed in stoichiometric quantities with the adhesive part of the composition. In use, the activator composition and adhesive part of the composition may be mixed together just prior to use, or the activator composition may be applied to one or both substrates and the polymerisable composition subsequently applied to the activator on the substrate. The activator composition preferably comprises sufficient of an organic solvent so that the activator composition may be readily applied to the substrate, for example by brushing, to provide a very thin solid deposit after evaporation of the solvent. Alternatively, the activator composition may be packaged with a propellant in an aerosol container from which required quantities may be readily dispensed.Additional materials may be included in the activator composition as required, for example film forming polymeric material or liquid polymerisable monomer for example a methacrylate ester monomer for example 2-hydroxypropyl methacrylate or trimethylol propane trimethacrylåte or a mixture thereof, with a view to achieving the required deposit on the substrate.

The activator composition may conveniently comprise up to 5% by weight of the selected organic activator compound in organic solvent for example acetone or methanol. These activator compositions are effective in presence of a source of free radicals to bring about cure of polymerisable adhesive compositions comprising one or more ethylenically unsaturated compounds in adhesive bonds free from air. The time required to bring about setting of the composition is comparatively short, and may be reduced further by inclusion in the activator composition of certain sulphur-containing or transition metal compounds. By the expression "transition metal" where used herein we mean a metal which is capable of more than one stable valency state and which is capable of forming complexes notable examples of which are vanadium, chromium, manganese, iron, cobalt, nickel and copper.For rapid setting one may employ mixtrures of these materials for example a mixture of 0.1 to 1% S/o by weight of the solution of sulphur-containing compound and 0.05 to 0.5% by weight of the solution of transition metal compound. The preferred materials are soluble in commonly used organic solvents.

Sulphur compounds for use in activator compositions according to the invention include for example organic thiols, organic disulphides and organic sulphur compounds including also nitrogen in their molecule. Suitable organic thiols (RSH) include dodecylmercaptan, octylmercaptan, phenyldimercaptan and thioglycolir, acid. Suitable organic disulphides (R-S-S-R') include phenyldisulphide.Suitable organic compounds also including nitrogen in their molecule include thioacetamide, tetra methylthiouramdisulphide, thiocarbanilide, thiourea, 1 -allylT2-thiourea, 2 mercaptothiazoline, 2-mercaptobenzothiazole and 2,5-dimercapto-l ,3,4-thiadiazole, Transitic;rl metal compounds for use in activator compositions according to the invention include compounds including the metal as a chelated compound for example with a ,B-diketone or ethylene or propylene diamine, or as a compound of an organic acid or alcohol for example naphenates (e.g. of cobalt, nickel, manganese), octoates (e.g. of copper), hexoates and propionates (e.g. of iron): Preferred materials are acetyl acetonates of vanadium, copper, cobalt and iron.

Polymerisable materials for use in adhesive compositions according to the invention comprise monomers polymerisable by free radical mechanism and preferably comprise one or more acrylate or methacrylate groups per molecule. These materials include the diacrylates and dimethacrylates of mono, di, tri and tetra ethylene glycol, tri methacrylates from trihydric alcohols for example trimethylol propane trimethacrylate, hydroxy and glycidyl terminated compounds of acrylic and methacrylic acid for example 2-hydroxypropyl methacrylate, hydroxyethyl methacrylate, glycidyl methacrylate and reaction products of these latter having preferably two or more acrylate or methacrylate terminal groups for example those derived from 2-hydroxy propyl methacrylate and pyromellitic acid dianhydride, and acrylates and methacrylates derived from epoxy resins, and mixtures thereof.Polymers, for example butadiene acrylonitrile, and polymethyl methacrylate may also be included in the adhesive part together with adhesion promoters, acrylic or methacrylic acid, and normal additives for adhesive compositions if desired.

Inhibitors (e.g. hydroquinone or 2,6,di-t-butyl-4-methyl-phenol) are included in the adhesive part to inhibit spurious polymerisation of the monomers.

Acrylates and methacrylates preferred for use in the adhesive compositions are tetraethylene glycol dimethacrylate, trimethylol propane trimethacrylate, 2-hydroxypropyl methacrylate, glycidylmethacrylate, and a diacrylate derived from an epoxy resin, and mixtures of two or more thereof.

The source of free radicals is maintained separated from the activator composition prior to polymerisation and is preferably incorporated in the first (adhesive) part of the composition. Suitable sources of free radicals include organic peroxides (including hydroperoxides) peresters and peracids.

Preferred materials are cumene hydroperoxide and 2,5-dimethyl-2,5-di-(t-butyl-peroxy)-hexane.

In order that the invention may become more clear, there now follows a description of examples of adhesive compositions according to the invention. It will of course be understood that these examples have been selected for description to illustrate the invention by way of example and not by way of limitation thereof.

Each of the example compositions referred to below was in two parts. A first or adhesive part comprised one or more polymerisable materials comprising one or more acrylate or methacrylate groups per molecule, and a source of free radicals. A second or activator composition part comprised an activator capable of co-operation with the source of free radicals (at the time of intimate contact between the two parts) when located between two impervious substrates with exclusion of oxygen to bring about curing of the adhesive to bond the substrates together without external application of heat or actinic radiation.

Example first parts of adhesive compositions fluid at 209C were made up using ingredients in amounts by weight as shown in Table I.

TABLE I

Example first part of adhesive Component 1 2 3 Tetraethylene glycol dimethacrylate 32 - - Trimethylol propane trimethyacrylate 20 15 30 2-Hydroxypropyl methacrylate 30 35 35 Diacrylate (A) derived from an epoxy resin -. 30.3 15.3 Glycidyl methacrylate - 3 3 Acrylic acid 10 7 7 Pyromellitic acid dianhydride - 1.5 1.5 Butadiene acrylonitrile rubber (B) 5 - - Butadieneaorylonitrilerubber(O) - 5 5 Cumene hydroperoxide 3 3 3 Hydroquinone 0.1 - - 2.6-di-t-butyl-4-methyl phenol - 0.2 -1 0.2 100.1 100.0 100.0 The diacrylate.(A) used was a reaction product of acrylic acid and an epoxy resin (from epichlorhydrin and bisPhenol A having an epoxide equivalent weight of 1 82 to 1 94 and a viscosity at 2 5 OC of 100 to 1 50 poise) in a molar ratio of 2:1.The reaction product is believed to comprise a significant amount of difunctional material comprising two functional acrylate groups per molecule.

The butadiene acrylonitrile rubber (B) used was Perbunan N3807NS supplied by Bayer AG. The butadiene acrylonitrile rubber (C) used was Hycar 1 401 H80 supplied by Goodrich Company.

These first parts of adhesive compositions were made up by dissolving the rubber in a mixture of the di- and tri-methacrylate monomers, the 2-hydroxypropyl methacrylate and the inhibitor. The rubber (C) can be dissolved in this mixture directly at 750C. The rubber (B) however must first be dissolved in methylene chloride and this solution mixed with the mixture of di- and tri-methyacrylate monomers, 2 hydroxypropyl methacrylate and inhibitor, and then the methylene chloride removed under vacuum. The pyromellitic acid dianhydride was added to the mixture including the rubber and this mixture heated to 8O0C for two hours in order to obtain a reaction product from the dianhydride and 2-hydroxypropyl methacrylate molecules.Finally, after the mixture had cooled to room temperature, the glycidyl methacrylate, acrylic acid, and cumene hydroperoxide, were added.

Various example activator compositions were made up by dissolving various leuco vat dyestuffs supplied under the name Anthrasol in methanol as solvent. The precipitate formed (presumed to be sodium sulphate) was filtered off and the remaining solution, including the active form, used in the foilowing tests. Structural formulae believed to show the active form of these dyestuff materials in the solution, and an oxidized form of the active form produced in reaction with a hydroperoxide to yield free radicals and water are shown in Tables 2 and 3.It will be apparent that each of these active forms consists of an organic material comprising in its molecule a five membered ring including a sulphur or nitrogen atom which is linked to a substituted or unsubstituted aromatic ring system of the molecule and which is linked to a first carbon atom of the five membered ring which first carbon atom is linked to a second carbon atom of the five membered ring and to a third carbon atom which is not a member of the five membered ring but is a member of an aromatic or heterocyclic ring system, the structure being such that the C-C bond between the first and third carbon atoms is a single valency bond there being a substituent R1 on the second carbon atom and a substituent R2 on a fourth carbon atom which is a member of the second mentioned aromatic or heterocyclic ring system linked to the third carbon atom, the substituents R, and R2 and the organic material being such that the organic material is capable of conversion under adhesive bond-forming conditions in the presence of the source of free radicals to a diketo form in which R1 and R2 have each been converted to =0 and the C-C bond between the first and third carbon atoms has been converted to a double valency bond. In Tables 2 to 8, the active forms I to VI are derived from Anthrasol materials as follows: Active form No. Derived from Anthrasol 04B II Anthrasolorange HR Ill Anthrasolgrau lBL IV Anthrasolrosa IR Extra V Anthrasol Blau AGG VI Anthrasoldruckschwarz IGR In Examples 1 to 4 the solutions were made up using 1% by weight in the soiution of the selected Anthrasol materials.In the solutions of Examples 2, 0.5% by weight of selected organic sulphur compounds were used in addition to the Anthrasol materials. In the solutions of Example 3, 0. 1% by weight of transition metal compound were used in addition to the Anthrasol material. In the solutions of Example 4, 0.5% by weight organic sulphur compound and 0.1% by weight of a transition metal compound, were used in addition to the Anthrasol material. Ingredients of the activator compositionsare shown in Tables 4, 5,6 and 7.

EXAMPLES 1,2,3 AND 4 The setting time of various adhesive-activator combinations at standard room temperature (230C + 20C) and humidity of about 50% was determined on glass plate substrates. The glass was solvent wiped, and a thin layer of the activator applied to one of the surfaces to be bonded and the solvent allowed to evaporate. Example 1 of the example first parts of adhesive was applied as a thin layer and the glass plates pressed together in partially overlapping relation with the adhesive between them and with air excluded from the adhesive compositions by pressing the substrate firmly together.

The bonds were tested by pulling the glass plates apart by hand. When this could no longer be done, the adhesive was regarded as set. The shortest time after which the bonds could not be opened manually was recorded as the setting time. The results are shown in Tables 4, 5, 6 and 7 below. It was observed that the time within which the activators retained their activating ability after application to the surface was of the order of two hours.

TABLE 2

STRUCTURAL FORMULAE O-S03Nh H ANTHRASOW G4B B > N/ \\C4E Q ACTIVE FORM I B i Br ANIHD4SB B 191\ H l [H+] R ROOH OKIBIZEb 0C11\/II FRDM | C=C t| t2RO ANTHRASOL O4B < 8 ~ s b o TABLE 3

SrRucroR4L FORMULAE Acrid FORM Na OH OH O O 0 I I Q' OC2Hy Hi20 o +2R-tE20 mii OH OH C: :0 e \/C + +ic.+2 U20 rv CH jH PH CHJ CU9 O P Ct S t2R-O-t2 CL TABLE 3 (CONT'D.)

TABLE 4 Results of Example 1 - setting time

Activator containing active form No. Setting time 1 to 1% hours II 1 to 1 hours Ill 1 to 1t/2 hours IV 1 to 1 hours V | 1 to 11/2 hours VI | 50 minutes TABLE 5 Results of Example 2 - setting time

Active form No.

Sulphur-containing compound l III V Vl Dodecylmercaptan 50 min. 25 min. 90 min. 30 min.

Thioglycolicacid 3 min. 4 min. 10 min.7 min, Tetramethyl thiuramdisulphide 6 hours 6 hours 6 hours 6 hours Thiocarbanilide 15 min. 15 min. 15 min. 15 min.

Allylthiourea 4.5 min. 3.5 min. 2.5 min. 5 min.

2,5-dimercapto 1,2,4-thiadiazol 16 min. 11 min. 23 min. 21 min.

2-mercapto benzthiazol 2 hours 1 hour 2 hours 1 hours TABLE 6 Results of Example 3 - setting time

Transition Metal Compound Va(III) Cu(II) acetylacetonate acetyl acetonate 0.1% in methanol 0.1% in methanol Active form: I 11 min. 75 min.

III 14 min. 30 min.

V 9 min. 70 min.

VI 7 min. 28 min.

TABLE 7 Results of Example 4 - setting time

Organic sulphur compound and transition metal compound 0.5% 0.5% 0.5% allyl-thiourea thioglycolic acid thiocarbanilide +0.1% +0.1% +0.1% +0.1% +0.1% +0.1% Active form Va-AcAc Cu-AcAc Va-AcAc Cu-AcAc Va-AcAc Cu-AcAc I 20 sec. 11/4 min. 30 sec. 13 min. 45 sec. 1 min.

III 20 sec. 11/4 min. 30 sec. 15 min. 45 sec. 1 min.

V. 20 sec. 1 min. 30 sec. 13 min. 45 sec. 2 min.

VI 20 sec. 1 min. 30 sec. 11 min. 45 sec. 1 min. (Va-AcAc means Vanadium III a acetyl acetonate) (Cu-AcAc means Copper II acetylacetonate) From the results of Examples 1 to 4 it can be seen that a setting time of less than two hours at room temperature of the first example part 1 of adhesive and activator combination can be achieved with the selected dyestuff derivatives. Further it can be seen that setting times at room temperature can be reduced by inclusion of selected sulphur compounds or transition metal compounds alone or in combination. Thus by appropriate selection of materials, setting times at room temperature of a few seconds or several minutes or even hours may be achieved.

It should be noted that the setting times were measured on glass substrates in order that the comparison between various combinations of adhesive part and activator part should not be unduly influenced by possible catalytic effect of the substrate surface on the curing reaction. In practice, these adhesive compositions are required to be capable of use to give satisfactory adhesive bonds by curing at room temperature in bonds using any of a variety of substrate materials some of which (e.g. steel, copper, brass and stainless steel) are likely to have a significant effect in reducing the setting time and some of which (e.g. chromium, zinc and tin) are likely to have less effect or even no significant effect (e.g. pvc) on the setting time.

A further factor requiring consideration is the desirability for the adhesive compositions to be capable of use and performance with various impervious, opaque or transparent materials without additional use of externally applied heat, light or other curing treatment under a variety of normal ambient temperature conditions ranging at least from about 50C to 300 C.

EXAMPLE 5 In order to examine the strength of adhesive bonds formed using adhesive compositions according to the invention, the second and third example first parts of adhesive were used in conjunction with two selected activator compositions to bond various substrates at standard room conditions (230C + 20C, and about 50% RH). The amounts of ingredients used in the selected activator compositions are shown in Table 8 in parts by weight.

TABLE 8

Example activator compositions Component (a) (b) Anthrasol Blau AGG 1.5 1.5 2-hydroxypropyl methacrylate it .5 3.0 Trimethylol propane tri- 1.5 methacrylate Allyl thiourea 1.5 1.5 Vanadium (lV) oxide-acetyl acetonate 0.3 Acetyl acetone 0.3 Methanol 93.4 94.0 100.0 100.0 These activator compositions were made by dissolving the Anthrasol Blau AGG in the methanol, with agitation and then allowing the mixture to stand at room temperature for 2 hours, The precipitate was removed, and then the remaining components were added to the solution with stirring. The solutions were charged into dark coloured glass bottles having a screw cap witb a brush fixed to the inside of the cap.

The setting time on glass at room temperature was determined with many samples in the manner set out above, using the second and third example first parts of adhesive together with example activator compositions (a) and (b). The ranges of results are shown in Table 11.

Sample bonds were prepared and subjected to tests to determine tensile shear strength, peel strength and impact strength of the bonds. The sample bonds were prepared in the following way, using substrate materials prepared as shown in Table 9. Pairs of coupons of the prepared substrates 100 mm x 25.4 mm were brushed with the activator solution and allowed to dry, the solution leaving a thin layer of activator compound on each coupon weighing about 5 to 10 mg per square centimeter. The example first part was applied to one only of the coupons, and the pair of coupons aligned and pressed together to exclude air and to provide an overlap of 12.7 mm with the adhesive between the, overlapped portions in a layer approximately 0.1 mm thick.

Tensile shear strength of sample bonds was determined at 230C (in Newtons per square millimeter) 24 hours after forming the sample bonds: the bonds being aged at 230C. An Instron machine set to tear the bonds apart at 1 mm per minute was used. The force required is recorded in Table 10.

Peel strength of sample bonds aged at 230C for 24 hours was determined at 230C using a 900 peel angle and a separation rate of 30 mm per minute. The force required to initiate separation of the bonds is recorded in Table 11 as "initial", and the force required to continue separation of the bonds is recorded in Table 11 as "peel".

Impact strength of sample bonds was determined at 230C by an impact pendulum according to ASTM-D 950--72. The overlapping area was one square inch. The samples were aged for 24 hours at 230C before testing. The results are shown in N.cm/cm2 in Table 11.

For many purposes in adhesive work tensile shear strength results of about 4 N/mm2 or more are regarded as satisfactory, and it will be observed from Table 9 that values of this order can be achieved using adhesive compositions according to the present invention with several different materials appropriately prepared for bonding. The peel and impact test results show the adhesive compositions of the present invention are likely to be satisfactory for many purposes.

TABLE 9 Example 5 Surfaces and preparation treatments Substrate No. Material and treatment 1 Mild steel; degreased and sand blasted.

2 Mild steel; oily surface untreated.

3 Mild steel; rinsed with acetone and dried.

4 Aluminium; sand blasted.

5 Aluminium; pickled and dried.

6 Aluminium; rinsed with acetone and dried.

7 Brass; sand blasted.

8 Brass; rinsed with acetone and dried.

9 Chromium plated steel; sand blasted 10 Chromium plated steel; rinsed with acetone and dried.

11 Cadmium plated steel; rinsed with acetone and dried.

12 Stainless steel; rinsed with acetone and dried.

13 Tin plated steel; rinsed with acetone and dried; 14 Zinc plated steel; sand blasted, 15 Zinc plated steel; rinsed with acetone, and dried.

16 Copper; sand blasted.

17 Copper; rinsed with acetone and dried.

18 PVC; solvent wiped.

19 Glass; solvent wiped.

TABLE 10 Example 5 - Tensile shear strength (N/mm2)

Example Example first activator Substrate No.

part of comadhesive position 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 2 a 8.18 10.0 21.4 5.07 16.3 7.5 6.0 6.88 11.7 14.9 9.74 9.5 5.8 9.1 0.76 0.68 4.93 3 a 7.63 11.2 2.11 4.84 2.6 6.82 6.0 5.45 5.6 0.91 0.93 3.13 TABLE 11 Example 5 - Setting time. Peel Strength. Impact Strength.

Peel Strength Example Example Setting Time Substrate No. 3 Impact Strength first part activator Substrate No. 19 (N/30mm) Substrate No. 1 of adhesive composition (seconds) Initial Peel (N.cm/cm2) 2 a 10 to 20 15.3 2.9 77 2 b 90 to 180 3 a 10 to 20 4.9 2.5 29 3 b 90 to 180

Claims (14)

1. An adhesive composition in two parts comprising one or more polymerisable materials comprising one or more acrylate or methacrylate groups per molecule, a source of free radicals comprising an organic peroxide, hydroperoxide, perester or peracid, and an activator for co-operation with the source of free radicals to initiate addition polymerisation of the polymerisable materials, the activator comprising an organic material comprising in its molecule a five membered ring including a sulphur or nitrogen atom which is linked to a substituted or unsubstituted aromatic ring system of the molecule and which is linked to a first carbon atom of the five membered ring which first carbon atom is linked to a second carbon atom of the five membered ring and to a third carbon atom which is not a member of the five membered ring but is a member of an aromatic or heterocyclic ring system, the structure being such that the C-C bond between the first and third carbon atoms is a single valency bond there being a substituent R, on the second carbon atom and a substituent R2 on a fourth carbon atom which is a member of the second mentioned aromatic or heterocyclic ring system linked to the third carbon atom, the substituents R, and R2 and the organic material being such that the organic material is capable of conversion under adhesive bond-forming conditions in the presence of the source of free radicals to a diketo form in which R, and R2 have each been converted to =0 and the C-C bond between the first and third carbon atoms has been converted to a double valency bond, the composition being such that on intimate contact between the parts of the composition located between two inpervious substrates with exclusion of air from the adhesive composition, the adhesive composition becomes cured to adhesively bond the substrates together.

2. A composition according to claim 1 wherein the activator comprises an oxidizable organic material substantially as hereinbefore described with reference to any one of the active forms shown in Table 2 or Table 3.

3. An adhesive composition according to either one of claims 1 and 2 wherein the activator also comprises a sulphur containing compound or a transition metal compound or a mixture thereof.

4. An adhesive composition according to claim 3 wherein the sulphur ccntaining compound comprises an organic thiol, disuiphide or compound containing also nitrogen in its molecule.

5. An adhesive composition according to claim 3 wherein the metal compound comprises vanadium (III) acetonyl acetonate, copper (II) acetonyl acetonate, or vanadium (IV) oxide-acetyl acetonate.

6. An adhesive composition according to any one of the preceding claims wherein a first pert of the composition comprises polymerisable material and the source of free radicals, and a second part of the composition comprises the activator.

7.,An adhesive composition according to claim 6 wherein the second part is in the form of a solution in volatile organic solvent.

8. An adhesive composition according to claim 7 wherein the second part also comprises a polymerisable methacrylate ester monomer.

9. An adhesive composition according to claim 8 wherein the polymerisable methacrylate ester monomer comprises 2-hydroxypropyl methacrylate or trimethylol propane trimethacrylate or a mixture thereof.

10. An adhesive composition according to any one of the preceding claims wherein said one or more polymerisable materials comprises tetraethylene glycol dimethacrylate, trimethylol propane trimethacrylate, 2-hydroxypropyl methacrylate, glycidyl methacrylate, a diacrylate derived from an epoxy resin or mixtures of two or more thereof.

11. An adhesive composition according to either one of claims 6 and 11 wherein the first part of the composition is prepared from polymerisable monomers including 2-hydroxypropyl methacrylate in admixture with an amount of pyromellitic acid dianhydride.

12. An adhesive composition according to either one of claims 6 and 11 wherein the first part also comprises acrylic acid, and the source of free radicals comprises cumene hydroperoxide.

1 3. An adhesive composition according to any one of the preceding claims also comprising a butadiene-acrylonitrile copolymer.

14. An adhesive composition according to claim 1 comprising an activator substantially as described with reference to any one of the activator compositions hereinbefore described with respect to the Examples.

1 5. An adhesive composition according to claim 14 comprising an adhesive part substantially as described with reference to any one of the example first adhesive parts hereinbefore described.

1 6. A method of adhesively bonding two air-impervious substrates at ambient temperature which comprises procuring two substrates having suitably prepared surfaces, appiying to the surface of one or both of the substrates an activator composition which is a solution of an activator as hereinbefore specified in any one of claims 1 to 5, 7 to 9, and 14, allowing the composition to dry, applying to one of the surfaces a part of an adhesive composition comprising one or more polymerisable materials comprising one of more acrylate or methacrylate groups per molecule, a source of free radicals comprising an organic peroxide, hydroperoxide, perester or peracid, pressing the substrates together with the compositions in intimate contact with exclusion of air and allowing polymerisation of the polymerisable materials to form an adhesive bond between the surfaces.