GB1575666A - Method of bonding substrates with a resilient adhesive - Google Patents

Description

(54) METHOD OF BINDING SUBSTRATES WITH A RESILIENT ADHESIVE (71) We, SCHERING AKTIEN GESELLSCHAFT, a body corporate organised according to the laws of the Federal Republic of Germany, of Berlin and Bergkamen, Federal Republic of Germany, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to resilient adhesive substances based on polyurethane that can be hardened by means of atmospheric moisture.

Polyurethane systems in which the hardener components is not kept separate but is pre-mixed and which harden by means of moisture are known and have been used for coating and sealing compositions.

When they have been reacted, sealing compositions are very soft polymers which, although they may be very adhesive, do not bring about any appreciable cohesion of the contact surfaces. The requirement is, on the contrary, that such products have only slight restoring forces so that the varying extension-compression stress cannot destroy the adhesion or cohesion.

Compositions formulated in this manner are generally based on prepolymers, acting as binders, having free aromatic isocyanate groups. Also, combinations of such prepolymers, some of the free isocyanate groups of which may be masked, have been used recently with latent amine derivatives (e.g. German Auslegeschrift 1 719 121).

However, the sealing compositions formulated with these prepolymers are not suitable as adhesives since the only types of adhesive bond that can be produced withstand tensile forces of only about 2 to 12 kp/cm2, and, in addition, the hardening times are too long. Increases in binder and filler content do not improve formulations of this type since storage stability is thereby limited. Moreover, in the case of the direct action of isocyanate groups with atmospheric moisture, an undesirable bubble formation occurs as a result of the impeded diffusion of the cleaved carbon dioxide, and this can lead to defects in the adhesive bond.

In order to obtain improved adhesion a high cross-linkage density is also required, which necessitates the use of preponderantly branched prepolymers.

However, this increase in the crosslinkage density means that there is impeded diffusion of water vapour. Hence, after surface hardening, the rest of the composition is covered and only incomplete hardening of the system is achieved.

There is therefore a need for a polyurethane adhesive which hardens rapidly by means of moisture, has good storage stability and utilisable adhesive values, is not flawed by bubble formation in its adhesive layer and hardens through rapidly in spite of relatively high crosslinkage.

We have now found that good adhesive properties are shown by a composition, based on polyurethane, which is stable in the absence of water and which comprises (a) the addition product of (a) an OH-containing component comprising a linear or branched polyalkylene glycol with an average molecular weight in the range of from 200 to 10,000, preferably 400 to 6,000, and an an excess of a di- or poly-isocyanate, and (b) 1. the reaction product (enamine of (a) a cyclic secondary amine with (p) an aliphatic aldehyde or cyclic ketone, or (b) 2. the reaction product of (a) an enamine obtained by reacting a cyclic secondary amine, which, apart from the secondary amino group, has a further group capable of reacting with an isocyanate-especially a hydroxyl group-with an aliphatic aldehyde or cyclic ketone, and (p) a di- or poly-isocyanate, usually an aliphatic or cycloaliphatic di- or triisocyanate, especially a prepolymeric isocyanate according to (a).

A mixture of two or more of any of the components/reactants may be used.

The composition used in the process of the present invention will harden or cure in the presence of atmospheric or added moisture. Generally, therefore, the composition is substantially free from water and is suitable for storage under conditions of substantial exclusion of water.

If desired the composition may also contain (c) one or more additives known for addition to adhesive compositions, e.g. a customary filler, plasticiser, pigmerit or agent imparting adhesive properties, which are anhydrous or the water content of which is very low. These additives should not contain groups that react with isocyanates.

Applied to a suitable substrate, a highstrength resilient adhesive bond is formed substantially free of bubbles.

The present invention therefore provides a process for adhesively uniting two substrates which comprises applying to one or both substrates a composition specified above and allowing the composition to harden in contact with the substrates in the presence of water. The hardening may be brought about, for example, by water in the composition or applied thereto after application to the substate(s), and/or by atmospheric moisture.

The constituents (a) and (b) are preferably mixed in the stoichiometrical ratio of the (latent) amine groups and of the isocyanate groups.

The prepolymer component (a) comprises the addition product of an OH-group containing component, being a branched or linear polyalkylene oxide carrying hydroxyl groups, and an aliphatic, cycloaliphatic or aromatic di- or polyisocyanate.

The polyalkylene oxide used may be obtained, for example, by the anionic polymerisation, copolymerisation, or block polymerisation of an alkylene oxide, e.g.

ethylene oxide, propylene oxide or butylene oxide, with a bi- or poly-functional alcohol, e.g. 1,4 - butanediol, 1,6 - hexanediol, glycerin, 1,1,1 - trimethylolpropane, 1,2,6 hexanetriol, pentaerythritol or sorbitol; or by the cationic polymerisation or copolymerisation of a cyclic ether, e.g.

tetrahydrofuran, ethylene oxide or propylene oxide, with an acidic catalyst, e.g.

borotrifluoride etherate; or by the polycondensation of a glycol, e.g. 1,6 hexanediol, in the presence of an acidic catalyst, e.g. p - toluenesulphonic acid. The linear or branched polyalkylene oxide carrying hydroxyl groups should have an average molecular weight of from 200 to 10,000, preferably 400 to 6,000 and may be used individually or in mixtures. Usually the polyalkylene oxide component is preponderantly branched.

Optionally, one or more other polymers containing hydroxyl groups may be used concomitantly, e.g. polyesterols, or polymers or copolymers of butadiene with terminal hydroxyl groups.

Suitable aliphatic and cylcoaliphatic diand tri-isocyanates are, e.g., 1,6 hexamethylene diisocyanate, 1 - methyl 2,4 - diisocyanatocyclohexane, 2,4,4 - trimethyl - 1,6 - diisocyanatohexane, isophorone, diisocyanate, N,N',N" - tri (6 - isocyanatohexyl)- biuret, and the addition product of 3 mol of isophorone diisocyanate and 1 mol of I, I, I trimethyloloropane.

Furthermore, an aromatic diisocyanate, such as, e.g., 2,4 - diisocyanatotoluene and 2,6 - diisocyanatotoluene, or a mixture of the two, may be used, and also 4,4'diisocyanatodiphenylmethane, naphthylene 1,5 - diisocyanate, m - xylene diisocyanate, triphenylmethane triisocyanate and the reaction product of 3 mol of 2,4 - diisocyanatotoluene and 1 mol of tri methylolprbpane.

For the production of the prepolymer isocyanate (a), the isocyanate component is used in excess. A ratio of isocyanate groups to hydroxyl groups of 1.8:1 to 2.2:1 is preferably chosen.

Usually, the polyalkylene oxide carrying free hydroxyl groups is reacted with the dior polyisocyanate at a temperature of approximately 700C in the presence of a suitable catalyst, e.g. triethylenediamine, dibutyltin dilaurate or tin(II) octoate.

The moisture-sensitive component (b) may be the condensation product of a heterocyclic secondary amine with an aliphatic aldehyde or aliphatic cyclic ketone.

It should be understood that the term "aliphatic" is used in a broad sense and includes a group with a cyclic carbon chain.

Thus, for example, an aldehyde with an aliphatic, a cycloaliphatic or cycloaliphaticaliphatic hydrocarbon radical may be used.

Similarly, the aliphatic cyclic ketone may contain, for example, both non-cyclic and cyclic hydrocarbon radicals, provided of course that the oxygen atom of the ketone group is bonded to a ring of carbon atom, i.e. the ketone group is part of a ring.

Generally these aliphatic compounds are saturated.

The cyclic amine is preferably: 1. A diamine of the general formula

in which R1 and R' may be the same or different and each represents a hydrogen atom, or a methyl group if the product is subsequently reacted with an aldehyde; 2. a diamine of the general formula

in which n=0, 1, 2, 3; or 3. an amine of the general formula

in which R represents a hydrogen atom or a methyl group.

Typical examples of the above-mentioned and other amines are: piperazine, 2 methylpiperazine, 2,5 - dimethylpiperazine, dipiperidine, 4,4' - dipiperidylpropane, N - (2 - aminoethyl) - piperazine, 1 - (2 - hydroxyethyl) - piperazine and 1 (2 - hydroxypropyl) - piperazine.

The amine may also be, for example, a polyaminoamide preparable by the condensation of a di- or poly-carboxylic acid with an excess amount of a secondary diamine.

For the production of the moisturesensitive condensation products of the above-mentioned amines there may be used for example (a) an aldehyde of the general formula R-CHO IV wherein R represents a linear or branched hydrocarbon radical having from 3 to 13 carbon atoms, or (b) a cyclic ketone of the general formula

wherein R represents a tri- or tetramethylene group unsubstituted or substituted by one or ore alkyl radicals, any two or more of which may be the same or different.

Examples of suitable aldehydes and ketones are propionaldehyde, n butyraldehyde, isobutyraldehyde, diethylacetaldehyde, 2 - ethylhexanal, 3 methylbutanal, 2 - methylpentanal, isotridecylaldehyde, cyclopentanone, cyclohexanone, and isomeric trimethylcyclopentanones and trimethylcyclohexanones.

The condensation products may be produced, for example, in accordance with the method described in German Offenlegungsschrift 2 116 882 by the azeotropic removal of the reaction water.

If desired, the reaction product of an alkanolamine of the general formula III and an aldehyde or ketone of the general formulae IV or V may be added to a di- or polyisocyanate, for example in a ratio of isocyanate groups to hydroxyl groups of 1:1, (e.g. according to German Offenlegungsschrift 2 166 502).

In order to produce an adhesive for use in the process of the invention, the prepolymeric isocyanate (a) is mixed with the condensation product (b), preferably in the stoichiometrical ratio of isocyanate groups to the latent amino groups, and, if desired, with one or more additives.

The composition may also be prepared by (a) reacting (a) a hydoxy-containing component comprising a linear or branched polyalkylene glycol with an average molecular weight in the range of from 200 to 10,000 with (p) an excess of di- or polyisocyanate to form an isocyanate adduct (component (a)) and (b) 1. reacting (a) a cyclic secondary amine with (p) an aliphatic aldehyde or cyclic ketone or (b) 2.

(a) reacting a cyclic secondary amine which has a further functional group capable of reacting with an isocyanate with an aliphatic aldehyde or cyclic ketone, and (p) reacting this product with a di- or polyisocyanate, especially a prepolymeric isocyanate according to (a), to form an enamine as condensation product, and mixing components (a) and (b) and, if desired, one or more other additives.

The composition may be made up and applied in two parts each substantially free from water, wherein the first part comprises component (a) specified above and the second part comprises component (b) specified above.

The composition or two parts specified above may be in separate containers each substantially impermeable to water.

In addition, one or more fillers and/or auxiliaries may be added, such as, e.g., highly disperse silicic acids, carbon blacks, PVC powders, chalk, plasticisers, solvents, agents imparting adhesive properties and pigments. The addition of surface-active substances in particular, such as, for example, the highly disperse silicic acids and carbon blacks, can bring about an improvement in the adhesive values to be obtained. An agent imparting adhesive properties, e.g. y - aminopropyl triethoxysilane, glycidoxytriethoxysilane, or y - mercaptopropyl - triethoxysilane, is preferably added in a concentration of 0.1 to 1% by weight in order to achieve optimum adhesion. A silane may also be present as a pre-adduct with a di- or polyisocyanate. Furthermore, the surfaces to be joined adhesively may be pre-treated with a silane or silane pre-adduct.

Advantageously, the content of binder (i.e. isocyanate adduct (a) and enamine condensation product (b)) should be at least 20% by weight, preferably at least 30 / > by weight, of the total formulation (a), (b) and (c) and, especially advantageously, from 30 to 60 /" thereof.

The process of the present invention is suitable, in particular for the resilient adhesion of glass and/or metal, e.g. in windows, motor vehicles and aircraft.

Processing may be effected by means of pressure pumps from tanks via suitable metering devices or manually by means of commercial spray guns from aluminium cartridges.

The following Examples illustrate the invention.

Preparation of the Components Isocyanate adduct (prepolymer component) Example 1 30 g of dibutylin dilaurate were added, while stirring, to 3.5 kg of isophorone diisocyanate in a 50reactor having a stirrer and a nitrogen supply pipe. 25.75 kg of a branched polypropylene glycol (hydroxyl number approx. 35) were then added while stirring. The mixture was heated for 3 hours at 75"C. The reaction product had an isocyanate content of 2.2% Example 2 3.24 kg of 2,4 - toluylene diisocyanate and 3.3 g of dibutylin dilaurate were placed in a 501 reactor as in Example 1 and then 30 kg of a branched polypropylene glycol, as in Example 1, were added while stirring. the reaction mixture was kept at a temperature of 50"C for two hours. The reaction product had an isocyanate content of 2.3.

Condensation product (enamine) Example 3 1,000 g of benzene and 1,790 g of anhydrous piperazine were placed in a 10 1 flask having a stirrer, a reflux condenser with a water separator, a nitrogen supply pipe and a vacuum connection. 200 mg of formic acid were then added and 3,170 g of isobutyraldehyde were slowly added through a dropping funnel, the temperature rising to approximately 600 C. The mixture was then heated until water separation at the water separator was complete. The excess solvent and the aldehyde were then distilled off in vacuo. The viscous residue had a content of blocked amine corresponding to 560 mg KOH/g.

Example 4 172.1 g of anhydrous piperazine and 140 ml of xylene were added to 570 g of a dimerised tall oil fatty acid having a content of dimeric fatty acid of 96). After the addition of 0.6 g of phosphoric acid the mixture was heated under reflux for three hours. A water separator was then interposed and the product was heated for a further 9 hours under reflux, the sump temperature rising to approximately 1700C.

After determining the free amine content of the mixture, the equivalent quantity of 3,3,5 - trimethylcyclcohexanone, and also an excess of a further 20%, were added. 0.6 g of formic acid were then added and the mixture was heated for a further 14 hours in the water separator. During this time the sump temperature rose to approximately 175"C. A water yield of approximately 90 /O of the theoretical yield was obtained. The solvent and the excess ketone were drawn off in vacuo until a temperature of 1700C was reached. The highly viscous yellowish reaction product had a content of tertiary amine groups (enamine groups) corresponding to 108 mg KOH/g.

Example 5 (a) 800 g of 1 - (2 - hydroxyethyl)piperazine were heated under nitrogen using a water separator with 443 g of isobutyraldehyde and 400 ml of toluene until an approximately quantitative yield of water was obtained (approximately 110 g).

The duration of the reaction was approximately 8 to 13 hours. The solvent was drawn off and the residue was distilled in vacuo. The distillate had a nitrogen content of 15.18 and was sufficiently pure for further processing.

(b) 6,754 g of a trifunctional polypropylene glycol having a hydroxyl number of 35.6 were mixed with 746 g of toluolylene - 2,4 - diisocyanate (2,4 - diisocyanatoluene) and heated while stirring, for two hours at 700C and for a further hour at 800 C. The reaction product had an isocyanate content of 2.6% by weight.

(c) 870 g of the enamine produced under (a) and containing hydroxyl groups were then stirred into the product (b) which had been cooled to room temperature.

Preparation of Adhesive Compositions Example 6 1,310 g of the isocyanate adduct produced in Example 1 were mixed in a planetary mixer with 150 g of disperse silicic acid, 820 g of dioctyl phthalate, 386 g of toluene and 1,000 g of flame soot and worked in thoroughly. 72.4 g of the hardening agent produced in Example 3 were then added and likewise worked in thoroughly. After degassing, the adhesive was placed in commercial single-constituent aluminium cartridges. The binder content of the product was 37%.

Two steel sheets were cleaned with a 1% solution of V - aminopropyltriethoxysilane in ethanol and then stuck together by means of a layer of the adhesive 3 mm thick. After storage for three weeks at 230C and 50% air humidity the tensile shear strength was measured and found to be 41 kp/cm2.

In the case of two glass plates likewise cleaned with a solution of y - aminopropyltriethoxysilane, the following values were found for a 1.5 cm thick adhesive joint after three weeks' storage in a normal climate: Tensile, test according to DIN 52455: elongation at break 220% at 22.6 kp/cm2.

Hardening behaviour of the adhesive: skin formation in a normal climate after approximately 60 minutes bubble-free hardening.

Example 7 In a planetary mixer, 1,310 g of the isocyanate adduct produced in Example 2 were mixed with 400 g of highly disperse silicic acid and 820 g of dioctyl phthalate, 1,008 g of PVC powder and 390 g of petroleum spirit and worked in thoroughly.

72.5 g of the enamine produced under Example 3 were then added and worked in for a further 10 minutes and degassing was effected briefly in vacuo. The product was placed in aluminium cartridges. The skin formation time was 15 minutes. The product hardened through, free of bubbles.

Tensile shear strength on steel: 32.8 kp/cm2 (3 mm thick adhesive joint; 3 weeks' storage under normal conditions, agent imparting adhesive properties=silane).

Tensile test on glass according to DIN 18540 (agent imparting adhesive properties=silane): elongation at break 38.3% at 17.3 kp/cm2.

Example 8 Example of a transparent adhesive composition: 676 g of the isocyanate adduct produced in Example 1 were premixed thoroughly in a planetary mixer with 400 g of highly disperse hydrophobic silicic acid (dry!) and 560 g of dioctyl phthalate. 630 g of the hardening product produced in Example 5 were then added and worked in. After degassing in vacuo, aluminium cartridges were filled with the product.

Two steel sheets which had been pretreated with a 1% solution of y aminopropyltriethoxysilane in ethanol were stuck together at a distance of 3 mm from one another. After 3 weeks' storage under normal conditions, the tensile shear strength was measured and was found to be 24.8 kp/cm2.

The tensile strength according to DIN 18540 for two glass plates stuck together at a distance of 1.5 cm and likewise pretreated with silane was 26 kp/cm2 at 280% elongation after 3 weeks' storage under normal conditions.

Example 9 540 g of the isocyanate adduct produced in Example 1, 300 g of highly disperse hydrophobic silicic acid (dry), 450 g of dioctyl phthalate and 500 g of PVC powder were mixed together thoroughly in a planetary mixer. 145 g of the product produced in Example 4 were added and worked in. The product was degassed by the brief application of a vacuum and then immediately placed in aluminium cartridges. The binder content was 31%.

Two steel sheets were cleaned with a 1% solution of y - aminopropyltriethoxysilane in ethanol and then stuck together at a distance of 3 mm from one another. The tensile shear strength was determined after 3 weeks' storage in a normal climate and was 32.1 kp/cm2.

WHAT WE CLAIM IS: 1. A process for adhering two substrates, which comprises applying to one or both substrates an adhesive composition which comprises (a) the addition product of (a) a hydroxyl-containing component comprising a linear or branched polyalkylene glycol with an average molecular weight in the range of from 200 to 10,000 and (p) an excess of di- or poly-isocyanate, and

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

Claims (31)

**WARNING** start of CLMS field may overlap end of DESC **. of toluolylene - 2,4 - diisocyanate (2,4 - diisocyanatoluene) and heated while stirring, for two hours at 700C and for a further hour at 800 C. The reaction product had an isocyanate content of 2.6% by weight. (c) 870 g of the enamine produced under (a) and containing hydroxyl groups were then stirred into the product (b) which had been cooled to room temperature. Preparation of Adhesive Compositions Example 6 1,310 g of the isocyanate adduct produced in Example 1 were mixed in a planetary mixer with 150 g of disperse silicic acid, 820 g of dioctyl phthalate, 386 g of toluene and 1,000 g of flame soot and worked in thoroughly. 72.4 g of the hardening agent produced in Example 3 were then added and likewise worked in thoroughly. After degassing, the adhesive was placed in commercial single-constituent aluminium cartridges. The binder content of the product was 37%. Two steel sheets were cleaned with a 1% solution of V - aminopropyltriethoxysilane in ethanol and then stuck together by means of a layer of the adhesive 3 mm thick. After storage for three weeks at 230C and 50% air humidity the tensile shear strength was measured and found to be 41 kp/cm2. In the case of two glass plates likewise cleaned with a solution of y - aminopropyltriethoxysilane, the following values were found for a 1.5 cm thick adhesive joint after three weeks' storage in a normal climate: Tensile, test according to DIN 52455: elongation at break 220% at 22.6 kp/cm2. Hardening behaviour of the adhesive: skin formation in a normal climate after approximately 60 minutes bubble-free hardening. Example 7 In a planetary mixer, 1,310 g of the isocyanate adduct produced in Example 2 were mixed with 400 g of highly disperse silicic acid and 820 g of dioctyl phthalate, 1,008 g of PVC powder and 390 g of petroleum spirit and worked in thoroughly. 72.5 g of the enamine produced under Example 3 were then added and worked in for a further 10 minutes and degassing was effected briefly in vacuo. The product was placed in aluminium cartridges. The skin formation time was 15 minutes. The product hardened through, free of bubbles. Tensile shear strength on steel: 32.8 kp/cm2 (3 mm thick adhesive joint; 3 weeks' storage under normal conditions, agent imparting adhesive properties=silane). Tensile test on glass according to DIN 18540 (agent imparting adhesive properties=silane): elongation at break 38.3% at 17.3 kp/cm2. Example 8 Example of a transparent adhesive composition: 676 g of the isocyanate adduct produced in Example 1 were premixed thoroughly in a planetary mixer with 400 g of highly disperse hydrophobic silicic acid (dry!) and 560 g of dioctyl phthalate. 630 g of the hardening product produced in Example 5 were then added and worked in. After degassing in vacuo, aluminium cartridges were filled with the product. Two steel sheets which had been pretreated with a 1% solution of y aminopropyltriethoxysilane in ethanol were stuck together at a distance of 3 mm from one another. After 3 weeks' storage under normal conditions, the tensile shear strength was measured and was found to be 24.8 kp/cm2. The tensile strength according to DIN 18540 for two glass plates stuck together at a distance of 1.5 cm and likewise pretreated with silane was 26 kp/cm2 at 280% elongation after 3 weeks' storage under normal conditions. Example 9 540 g of the isocyanate adduct produced in Example 1, 300 g of highly disperse hydrophobic silicic acid (dry), 450 g of dioctyl phthalate and 500 g of PVC powder were mixed together thoroughly in a planetary mixer. 145 g of the product produced in Example 4 were added and worked in. The product was degassed by the brief application of a vacuum and then immediately placed in aluminium cartridges. The binder content was 31%. Two steel sheets were cleaned with a 1% solution of y - aminopropyltriethoxysilane in ethanol and then stuck together at a distance of 3 mm from one another. The tensile shear strength was determined after 3 weeks' storage in a normal climate and was 32.1 kp/cm2. WHAT WE CLAIM IS:

1. A process for adhering two substrates, which comprises applying to one or both substrates an adhesive composition which comprises (a) the addition product of (a) a hydroxyl-containing component comprising a linear or branched polyalkylene glycol with an average molecular weight in the range of from 200 to 10,000 and (p) an excess of di- or poly-isocyanate, and

(b) 1. the reaction product (enamine) of (a) a cyclic secondary amine with (p) an aliphatic aldehyde or cyclic ketone, or

2. the reaction product of (a) an enamine obtained by reacting a cyclic secondary amine, which, apart from the secondary amino group, has a further group capable of reacting with an isocyanate with an aliphatic aldehyde or cyclic ketone, and (p) a di- or poly-isocyanate, and allowing the composition to harden in .the presence of water and in contact with both substrates.

2. A process as claimed in claim 1, wherein the composition applied is substantially free from water.

3. A process as claimed in claim 1 or claim 2, wherein the polyalkylene glycol has an average molecular weight in the range of from 400 to 600.

4. A process as claimed in any one of claims 1 to 3, wherein the polyalkylene glycol is branched.

5. A process as claimed in any one of claims 1 to 4, wherein the hydroxylcontaining component includes a polyesterol or a butadiene polymer or copolymer having terminal hydroxyl groups.

6. A process as claimed in any one of claims 1 to 5, wherein the isocyanate component (p) of the addition product (a) is 1,6 - hexamethylene diisocyanate, 1 - methyl - 2,4 - diisocyanatocyclohexane, 2,4,4 - trimethyl - 1,6 - diisocyanatohexane, isophorone diisocyanate, N,N',N" tri - (6 - isocyanatohexyl)- biuret, the addition product of 3 mol of isophorone diisocyanate and 1 mol of 1,1,1 trimethylolpropane, 2,4 - diisocyanatotoluene, 2,6 - diisocyanatotoluene, 4,4' diisocyanatodiphenylmethane, naphthylene 1,5 - diisocyanate, m - xylylene diisocyanate, triphenylmethane triisocyanate or the reaction product of 3 mol of 2,4 - diisocyanatotoluene and 1 mol of trimethylolpropane.

7. A process as claimed in any one of claims 1 to 5, wherein the hydroxylcontaining component and isocyanate are reacted together to form the addition product (a) in a ratio of isocyanate to hydroxyl groups of from 1.8:1 to 2.2:1.

8. A process as claimed in claim 1 or claim 2, wherein the addition product (a) is substantially as described in Example 1 or Example 2 herein.

9. A process as claimed in any one of claims 1 to 8, wherein the aldehyde or ketone is a compound of the general formula R-CHO wherein R represents a linear or branched hydrocarbon radical having from 3 to 13 carbon atoms or a compound of the general formula

wherein R represents a tri- or tetramethylene group which is unsubstituted or substituted by one or more alkyl radicals, any two or more of which may be the same or different.

10. A process as claimed in claim 9, wherein the aldehyde or ketone is propionaldehyde, n - butyraldehyde, isobutyraldehyde, diethylacetaldehyde, 2 ethylhexanal, 3 - methylbutanal, 2 methylpentanal, isotridecylaldehyde, cyclopentanone, cyclohexanone or one of the isomeric trimethylcyclopentanones or trimethylcyclohexanones.

11. A process as claimed in any one of claims 1 to 10, wherein the amine is a polyaminoamide or a compound of the general formula

in which R1 and R2 represent hydrogen atoms or, when the enamine is formed from an aldehyde, one or both of them may also represent a methyl group, or a compound of the general formula

in which n represents'0, 1, 2 or 3, or

in which R prepresents a hydrogen atom or a methyl group.

12. A process as claimed in any one of claims I to 11, wherein the amine is piperazine, 2 - methylpiperazine, 2,5 dimethylpiperazine, dipiperidine, 4,4' dipiperidylpropane, N - (2 - aminoethyl) piperazine, 1 - (2 - hydroxyethyl) piperazine or 1 - (2 - hydroxypropyl) piperazine.

13. A process as claimed in any one of claims 1 to 12, wherein component (b) is the reaction product of an isocyanate and an enamine obtained from an amine with a hydroxyl group.

14. A process as claimed in any one of claims 1 to 13, wherein component (b) is the reaction product of the enamine and an aliphatic or cycloaliphatic isocyanate.

15. A process as claimed in any one of claims 1 to 13, wherein component (b) is the reaction product of the enamine and an isocyanate as specified in claim 6.

16. A process as claimed in any one of claims 1 to 13, wherein component (b) is the reaction product of an enamine (2a) and the addition product of (a') a hydroxyl-containing component comprising a linear or branched polyalkylene glycol with an average molecular weight in the range of from 200 to 10,000 and (P') a di- or poly-isocyanate.

17. A process as claimed in claim 16, wherein the addition product of the hydroxyl-containing component and the isocyanate is as specified in any one of claims 3 to 8.

18. A process as claimed in any one of claims 1 to 8, wherein component (b) is substantially as described in any one of Examples 3 to 5 herein.

19. A process as claimed in any one of claims 1 to 18, wherein the composition comprises components (a) and (b) in substantially stoichiometric ratio.

20. A process as claimed in any one of claims 1 to 19, wherein the composition contains a filler, plasticiser, pigment, surfactant, solvent or agent imparting adhesive properties or a mixture of two or more such additives.

21. A process as claimed in claim 20, wherein components (a) and (b) are at least 20% by weight of the composition.

22. A process as claimed in claim 21, wherein components (a) and (b) are at least 30 /n by weight of the composition.

23. A process as claimed in claim 22, wherein components (a) and (b) are from 30 to 60 /n by weight of the composition.

24. A process as claimed in any one of claims 20 to 23, wherein the composition contains carbon black, PVC powder, highly disperse hydrophobic silicic acid (dry), a silane, a silane isocyanate pre-adduct or dioctyl phthalate.

25. A process as claimed in any one of claims 20 to 24, wherein the composition contains from 0.1 to 1% by weight of an agent imparting adhesive properties.

26. A process as claimed in claim 1, wherein the composition is substantially as described in any one of the Examples 6 to 9 herein.

27. A process as claimed in any one of claims 1 to 25, wherein the composition is made up and applied in two parts wherein the first part comprises component (a) and the second part comprises component (b).

28. A process as claimed in any one of claims 1 to 27, wherein the composition is allowed to harden under the action of atmospheric moisture.

29. A process as claimed in any one of claims 1 to 28, wherein the substrates comprise glass and/or metal.

30. A process as claimed in claim 1, carried out substantially as described in any one of the Examples 6 to 9 herein.

31. Two substrates which have been adhered together by a process as claimed in any one of claims 1 to 30.