CA1265395A

CA1265395A - Adhesive composition

Info

Publication number: CA1265395A
Application number: CA000474198A
Authority: CA
Inventors: Michael J. Read; Michael R. Read; Stephen J. Osborne; Geoffrey P. Hakes
Original assignee: Raychem Ltd
Current assignee: Raychem Ltd
Priority date: 1984-02-14
Filing date: 1985-02-13
Publication date: 1990-02-06
Anticipated expiration: 2007-02-06
Also published as: EP0223045A3; GB8403823D0; EP0223044B1; EP0223045B1; IL74335A; JPH08104854A; JPH07108966B2; KR850006218A; JPS60192775A; CA1281248C; ATE60078T1; ATE60619T1; EP0223044A3; IN164145B; EP0157478B1; KR950010937B1; US4935270A; EP0223044A2; IL74335A0; DE3581409D1

Abstract

ABSTRACT

Adhesive Composition Cohesive flexible curable adhesive coatings formed from a dispersion of first and second powdered curing components, preferably reactive at ambient temperatures, in a solution of a binder, the binder content being not more than 15%, preferably not more than 2.5% by weight of the dried composition. Also claimed are curable compositions having a specific advantageous reactive particle size distribution; specific epoxy-amine adduct curing agents; and specific polyalkylene oxide binders.

Description

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ADHESIVE COMPOSITION
This inven-tion relates to adhesive composi-tions and especially -to adhesive compositions that may be used with dimen-sionally heat-recoverable articles.
A divisional application has been filed, divided out of this parent application.
According to one aspect of -the divisional application there is provided a heat-curable adhesive coating on a heat-recoverable article, the coating comprising a mixture of substan-tially solid particles of a first reactive component with separatesubstantially solid particles of at least a second reactive component, the first and second reactive components being capable of reac-ting toge-ther to effect curing when the ar-ticle is heat-recovered, and the particles having a siæe distributlon in which not more than 40~ by weic~ht of the particles are less than 50 micrometers in size and substantially all the particles are less than 300 micrometers in size.
According to another aspect of -the divisional applica-tion there is provided a method of manufacturing a heat-curable adhesive coating on a heat-recoverable article, comprising (I) applying to a surface of -the article an adhesive coating compris-ing (a) a mixture of a first reactive component with separate substantially solid particles of at least a second reactive component, the first and second reactive components being capable o~ reacting together to ef~ect curing when the article is heat-recovered, and the particles having a size distribution in which not more than 40~ by weight of the particles are less than 50 micrometers in size and substantially all the particles are less than 300 micrometers in size, and (b) a binder, as a dispersion in ~a liquid which is substantially a non~solvent for the reactive components, and (II) removing the liquid from the dispersion.
A heal:-recoverable article is an article the dimensional configuration of which may be made substantially to change when subjected to heat treatment.

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~265395 - la -- 27065-105 Usually these articles recover, on heating, towards an original shape :Erom which they have previously been deformed but the term "heat-recoverable", as used herein, also includes an article which, on heating, adopts a new configuration, even lf i-t has not been previously deformed.
In t~eir most common -form, such articles comprise a heat-shrinkable sleeve made from a polymeric material exhibiting the property of elastic or plastic memory as described, for example, in U.S. Patents 2,027,962 3,086,242 and 3,597,372. As is made clear in, for example, U.S. Patent 2,027,962, the original dimensionally heat-stable form may be a transient form in a continuous process in which, for example, an extruded tube is expanded, whilst hot, to a dimensionally heat-unstable form but, in other applications, a preformed dimensionally heat-stable article is deformed to a dimensionally heat-unstahle form in a separate stage.

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- 2 - RK232 In the production of heat-recoverable articles the polymeric material may be cross-linked at any stage in the production of the article that will enhance the desired dimensional recoverability One manner of producing a heat-recoverable article comprises shaping the polymeric material into the desired heat-stable form. subsequently cross-linking the polymeric material heating the article to a temperature above the crystalline melting point or for amorphous mater-ials the softening point. as the case may be of thepolymer. deforming the article and cooling the article whilst in the deformed state so that the deformed state of the article is retained. In use- since the deformed state of the article is heat-unstable. application of heat will cause the article to assume its original heat-stable shape~

In other articles as described. for example in British Patent 1.440-524. an elastomeric member such as an outer tubular member is held in a stretched state by a second member- such as an inner tubular member which. upon heating weakens and thus allows the elasto-meric member to recover~

Heat-recoverable articles are often used in applications in which they are required to be coated ~ith an adhesive~ In certain applications such art-icles are required to be used with curable adhe~ives in order that the bonds so formed will exhibit good performance at high temperatures and/or under high loads~ One example of such an application is where hollow heat-recoverable moulded articles having one or more outlets ~often called end-caps~ boots. transitions . . . .

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- 3 - 27065-105 or udders) are used to enclose various parts of cable harnesses.
Until recently it had not been possible to pre-coat such articles with a heat-curable adhesive that would cure when the article was recovered because the relatively low recovery temperatures of the articles, e.g. about 100 to 130~ and the relatively short recovery times, e.g. up to 2 minutes, were incompatible with an adhesive that would have an acceptably long c;torage life, and so it was necessary to coat the articles with a two-component curable adhesive immediately prior to installation.
Recently~ i-t has been proposed in U.K. Patent Specifica-tion No. 2,104t800A, the disclosure of which is incorporated here-in by reference, that heat-recoverable articles may be coated with a heat-curable adhesive in which the reactive components are in the form o~ separate particles that are mixed to~ether. It has been observed that such adhesives exhibit a synergistic increase in rate of cure when used with a heat-recoverable article, which enables them to cure sufficiently rapidly when the article is recovered and ye-t have an acceptably long storage life.
Although the coated ar-ticles so formed work well in practice it has been found that the functional performance of the adhesives may be considerably improved.
According to one aspect, the invention of the divisional application provides a heat-curable adhesive composition which comprises a plurality of reactive components that will react together to cure the adhesive composition, the r ~
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- 4 - RK232 components existing separately from one another in the form of solid particles that are mixed together and which will fuse when heated the particles havinq a size distribution in which not more than 40%. prefer-ably not more than 35% and especially not more than 30%by weight of the particles are less than 50 micrometres in size and substantially all the particles- that is to say at least 90% and especially at least 95% by weight.
are less than 300 micrometres in size.

Preferably not more than 60%- more preferably not more than 50% and especially not more than 40% by weight of the particles are less than 75 micrometres in size. and preferably not more than 70% especially not more than 60~ by weight of the particles are less than 100 micrometres in size. The preferred particle size distributions are those in which the particles have a weight average particle size in the range of from 75 to 125 micrometres.

It has been observed that the correct choice of particle size distribution is important in determining whether or not the adhesive will exhibit the required high temperature performance properties. For examPle the German Military V.G. Specification No. 95343 part 14. for testing harness systems. issued by the ~undes-amt fur Wehrtechnik und Beschaffung includes a sta~icload test in which the bonds between the harness components are subjected to a 5 kg force load at 100C
for 4 hours without failing or without shearing by more than 5 mm. It had been considered that particulate curable adhesives having the finest particle size distributions commensurate with adequate stora~e stability would exhibit the best performance on ., , , :... . ..
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- 5 - 27065-105 the basis that the finer the particles the greater their surface area/volume ratio and the more intimate their mixing would be, and indeed thi.s belief was borne out when the adhesives were tested using conventional lap-shear test methods. However, surprisingly it has been observed that although lap-shear values improve as the adhesive particle size i5 reduced, such adhesives fail the V.G.
static load test completely and that only those adhesives having relatively coarse particles according to this aspect of the inven-tion pass the test. The reason why -this is so is not known.
Heat-curable adhesives which may be suitable for the present invention include, those described in British Patent Application 2104800.
According to one aspect of the invention of the presen-t parent application there is provided a heat-curable adhesive coat-ing on a sub.strate, the coat;.ng comprising (a) a mixture of sub-stantially solid particles of a Eirst reactive component with separate substantially solid particles of at least a second reactive component and (b) a water-soluble polymeric binder having substantially no free hydroxyl groups, the first and second reactive components being present in the coating as substantially unreacted separate particles capable of reacting together to effect curing when the coating is heated to the curing tempera-ture.
According to a ~urther aspect of the invention of the present parent application there is provided a method oE manufac-turing a heat-curable adhesive coating on a substrate, comprising tI) applying to a surface of the substrate an adhesive coating comprising (a) a mixture of substantially solid particles of a first reactive component with separate substantially solid particles of at least a second reactive comæonent and (b) a water- :
soluble polymeric binder having substantially no free hydroxyl groups, the first and second reactive components being present in the coating as substantially unreacted separate particles capable of reacting together to effect curing when the coating is heated . ,' , . . . .
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- 5a - 27065-105 to the curing -temperature, as a dispersion in a liquid which is subs-tantially a non-solvent for the reactive components, and (II) removing the liquid.
Preferred reactive components are -those which are capable of reacting together at ambien-t temperatures, e.g. when forced into intimate contact by shear ~orces or when dissolved in a mutual solvent.
Preferably one of the reactive components is a thermo-plastic epoxy resin, for example an epoxy resin based on a bisphenol A or an epoxy novolak resin, in which case the other reactive component may comprise a carboxylic acid, phenolic resin, anhydride or isocyanate or a material having reactive amine groups. Preferably the adhesive is based on a thermoplastic epoxy resin as one reactive component and a material containing reactive amine groups as the or at least one other reactive component. The material containing free amine groups m~y be a polyamide, Eor example one that is used convenkionally as a hot-melt adhesive.
These polyamides are characterized by the fact that their amide linkages are separated by an average of at least fifteen carbon atoms and have amorphous structures in contrast with the more highly crystalline, fibre forming polyamides such as nylon 6 or nylon 6.6. The polyamides preerably have an amine number of at least 5, the upper limit for the amine number being determined by the fact that as the amine number increases -the polyamides become liquid at lower temperatures.
Alternatively or in addition the or at least one mater-ial having reactive amine groups is one based on a polymer that is the same as or similar to that on which the epoxy resin is based.
For example, and preferably, the or at least one material contain-ing reactive amine groups is an adduct o the epoxy resin that isused with a compound containing reactive amine groups, preferably with an aliphatic diamine or triamine and especially with ethylene diamine or ethylene triamine.

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- 6 - 27065-105 It has been found that the use of an epoxy-amine com-pound adduct as the o-ther reactive component or one of the other reac-tive components can significantly improve the cure rate of the adhesive in relation to its storage life, thereby per~itting the storage life of the adhesive or the cured properties thereof to be improved or allowing greater freedom to alter the adhesive in order to op-timise i-ts other properties. Thus, the heat-curable adhesive composition, comprises a plurality of reactive components that will react together to cure the adhesive co~position, the reactive components existing separately from one another in the form of particles which are mixed together and which will fuse when heated, at leas-t one : -iS39~
~ 7 ~ RK232 of the reactive components being a thermoplastic epoxyresin and the or at least one other reactive component being an adduct of the epoxy resin with a comPound containing reactive amine groups.

The adduct may. if desired. be used as the sole reactive component that contains reactive amine groups although it is preferred for the adduct to be present in combination with at least one other reactive amine group such as a thermoplastic polyamide for example to improve flexibility of the adhesive. Preferably the adhesive contains from 30 to 90% and especially from 40 to 80% by weight adduct based on the total weight of the adduct and other reactive amine group containing components.

Chemical curing accelerators may also be present in the adhesive- either blended with one of the reac-tive components or as separate particles. Examples of accelerators include dimethylaminopyridine- tris ~dimethylaminomethyl) phenol. tin octoate imidazole or imidazole derivatives such as salts. substituted imidazoles or metal complexes thereof.

A number of inert components may be incorporated in the compositions as long as they do not adversely affect the increase in rate or level of cure of the adhesive composition. Also it is preferred if they do not adversely affect the storage life of the adhesive~
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Inert components that may be incorporated in the adhesive include plasti~isers such as phthalates or rosln esters. thermoplastic or thermosetting polymers.

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cured or uncured rubbers inorganic materials to modi-Ey the proper-ties of the uncured or cured adhesive such as reinforcing fillers, reinforcing fibres or microspheres, or tackifiers and the like.
The other components, whether organic or inorganic, may be in any appropriate physical form, for example they may be in the form of powder, flake or fibres, or they may be compounded with one or more of the reactive components, and are preferably present in an amount o-f from 5 to 50 percent by weight based on the total weight of the composition.
Electrically conductive fillers. e.g. metal flakes may be incorporated in the adhesive to provide electrical continuity, e.g. when the adhesives are used to seal parts of an electro-magnetically shielded electrical wiring harness, as discussed hereinafter.
Preferably the adhesive compositions contain a polymeric binder in order to prevent the adhesive crumbling oE the surEace to which it is applled be~ore it is cured. This is a particular problem when using particulate adhesives that are applied to heat-recoverable articles since the heat-recoverable articles, which will usually be in an expanded configuration, are generally easily deformable and are usually subjected to various degrees of mechan-ical abuse in storage. It has surprisingly been Eound that useful degrees of cbhesion can be achieved wit'nout unacceptahly affecting the curing performance~
~ hus, a cohesive flexible substantially solid heat-curable adhesive coating is formed from a mixture of substantially solid particles of a first reactive component with separate sub-stantially solid particles of at least a second reactive component ~ in a solution of not more than 15% by weight, based on the total dry weight of the coating, of a binder, the binder solution solvent being substantially a non-solvent or the first and second reactive components which are present in the dry coating as sub-stantially unreacted separate particles capable of reacting together to effect curing when the coating is heated to the cur~ng ~::

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~2~53~i - 9 ~ 27065-105 temperature. Preferab:Ly the binder content will be less than 10 more preferably less than 5~, and even more preferably less than 2.5%, and preEerably at least 1% by weight. It will be understood that re~erences to "substantially solid" particles exclude liquid filled microcapsules and are intended to mean particles which are substantially non-flowable (to render the coating storage stable) at the intended maximum storage temperature.
It is preferable to apply the adhesive onto the article by forming a dispersion of the reactive components in a non-solvent, either spraying or dip-coating the adhesive, in which case -the binder should be soluble in the non-solvent, and then removing the non-solvent by evaporation. The preferred binders Eor use with the adhesive are unsubstitu-ted or substituted poly~
alkylene oxides that are soluble in water and water~solub:Le poly-vinyl acetate polyrners having substantially no ~ree hydroxyl groups. ~he preferred b;nders are t~e polyalkylene. oxides and especially polyethylene oxide. It has been found that most solvents with the e~ception of water, water based solvents and light aliphatic solvents such as hexane, solubilise one or other of the reactive components at least to some extent and so are unsuitable, while those binders that were considered for use with acceptable non-aqueous solvents lead to unacceptably poor cured adhesives. When water is used as a non-solvent for the dispersion the al]cylene oxide and vinyl acetate polymers mentioned above produced adhesives having the best properties although it is envisaged that some other water-soluble polymers having subs-tan-tially no ~ree hydroxyl groups may be suitable. Whatever polymer is used for the binder, it is pre~erred that it be thermoplastic having a melting or softening point no higher than 20C above the highest melting or softening point of the reactive components and preferably no higher than the highest melting or softening point of the reactive components, in order to ensure that the binder melts completely when the adhesive is cured. When the adhesive is used in conjunction with a heat~recoverable article~ the binder 1 .

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should have a melting or softening point no higher than the recovery temperature of the article and preferably no higher than 20C below the recovery temperature of the article, whatever the melting point of the reactive components may be.
Thus, a heat-curable adhesive composition comprises:
(a) a plurality of reactlve components -that will react together to cure the adhesive composition, the componen-ts existing separately from one another in the form of solid particles which are ~ .
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Preferably the binder is present in the adhesive compositions only to relatively low levels. for example up to 15% by weight. more preferably up to 10% by weight and especially up to 5% by weight. based on the total weight of the adhesive composition. in order that the binder does not adversely affect the cured proper-ties of the adhesive. It has been found that even though the quantity of binder used is generally signif-icantly below the quantities used in the prior art. the uncured adhesive does not show any unacceptable tenaen-~cy to crumble off the article during storage. Prefer-ably the binder is present in quantities of at least 0.1%, more preferably at least 0.2% and especially at least 0.5% by weigh~. the optimum binder level being about 2% by weight. based on the total weight of the adhesive composition.

In addition. the use of relatively low quantities of binder reduces the adverse affect that binders generally have on the performance of the adhesives and.
in particular, on their high temperature performance.

PreEerably the adhesive composition is as des-cribed above~

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The adhesive compositions are particularly useful as latent curing adhesives for dimensionally heat-recoverable ar-ticles in view of their good s-torage life and their relatively rapid cure rate during recovery of the article. In order to maxi-mise the cure rate of t'ne adhesive, it is pre~erred that the or each reactive component has a melting or softening point that is no higher than 20C below the recovery temperature of the article.
Preferred articles with which the adhesives are used include open-ended hollow articles which are, for example, used for enclosing parts of electrical harness and the like, although the adhesives may be used with other heat-recoverable articles and, if desired, with articles that are not heat-recoverable. Such articles, which are often termed end-caps, boots, transi-tions or udders, depending on the number of outlets, are preferably coated with the adhesive on their internal surface in the region oE the or each outlet, but not in the centraL region. This may be achieved by applying the adhes:ive by a dip-coating method in which the outlet o the article is dipped in an aqueous dispersion of the adhesive, or if possible a dispersion in another non-solvent, and the water or other non-solvent is allowed to evaporate off.
The Eollowing Examples illustrate -the invention of both this parent and the divisional application.
Examples I to 3 A heat-curable adhesive composition was formed based on the following composition:

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1~ I I Trade nameI Parts by weiqht I Epoxy resin I Epikote 1001 1 100 (Ex Shell ) 2 (cure agent) I Pol~emide I Macromelt 6071 1 25 1 ¦ (Ex Henkel ) I Epoxydiamine adduct ¦ EDA 870 (Ex 1 75 I Anchor Chemi- I
I cals I Aluminosilicate filler I 1 20 I Carbon black l l 2 3 (flexibilizer) I Acid/Ethylene/vinyl I CXA 2002 1 10 ¦ acetate terpol~mer ¦ ~Ex du Pont) 4 (binder) I Polyethylene o~:ide ¦ Pol~x 1 2 4 I (Ex Union 1 I Carbide Component 2 was formed by melt blending and then grinding on a fanbeater mill at room temperature until the desired particle size distribution is reached by adjusting the grinding conditions. Component 1 was 20 also ground on a fan beater mill in the same manner as component 2. Component 3 was cryogenically ground. and components 1. 2 and 3 were then tumble blended.
Component 4 was dissolved in a quanti'cy of water equal to the total weight of the other components to form a 25 2% solut Lon to which was added the powdered components 2 and 3 to form an aqueous dispersion of the com-plete adhesive.

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~2653g5 This dispersion was applied to a standard Raychem 202K153 boot formed from Raychem -25 material by a dip-coating method and the adhesive was dried in air at room temperature for 6 hours followed by dryin~
under vacuum at room temperature for a further 7 hours The resulting adhesive thickness was 0.6 to 0 7 mm The boot was recovered about a cable and the adhesive joint was tested by means of the static load test at 100C specified in the V.G. Specification No.
10 95343 part 14 as well as by the lap shear test accord-ing to A.S.T.~. D 1002 In the static load test.
the cable and boot are subjected to a 5 kg load at 100C for 4 hours and the length that the cable had pulled out of the boot or the time to failure of the bond is recorded. For those bonds in which the cable had not been pulled out of boot. the strength of the resulting bond is then measured at room temperature.
The results are shown in Table I for three adhesives that had differing particle size distributions~ The 2Q particle size distributions of the adhesives are given in Table II.

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Ex~mple I Particle 100C lap shear V~G. static load test ¦ size strength N(25mm) (100 C) strength and pullout I of passes time to failure of I failures 1 I Coarse 140 5 passes mean pullout = 1mm I mean strength - 453N
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2 ¦ Medium 250 1 pass I pullout = 1mm I strength - 360N
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1 2 failures failure time 1~5 hr I and 1 hr 15 3 I Fine 300 All fail within 10 minutes TABLE II

Weight percentage of particles less than-:
Example ¦ 50 um 75 um 100 um150 um 300 um 2 1 ~8 61 81 95 100 , ` .

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~539~i Examples 4 to 7 An adhesive composition was prepared according to Example 1 with the exception that the curing agent (component 2) was formed from a blend of two polyamides (80 parts Macromelt 6071 and 20 parts Versamid 140j.
and that the binder content was varied between 0 and 4~. The adhesive was applied to a -25 Raychem moulded part as an aqueous dispersion and dried and then used to form a bond between it and either a cable having a Raychem DR-~5 jacket or an adaptor, The room temper-ature peel strength was measured according to V.G.
95343 part 14 Section 2.2 and 2.3. The results are shown in table III from which it can be seen that the cable peel strength increases considerably for small quantities of polyethylene oxide binder. In addition~
the moulded parts were subject to a further test before being recovered onto the cable in which they were squeezed to 75% of their original ~iameter in one direction and then rotated through 120 about their axis before being squeezed again. None of the adhesive was observed to fall off the part in any instance in which the binder level was between 1 and 4~.

Examples 8 to 10 (comparison) Examples 5 to 7 were repeated with the exception that the binder was a styrene-isoprene-styrene rubber and the adhesive dispersion was formed in hexane as the non-solvent. The results for the cable peel and adaptor peel strength are also shown in table III and show that the rubber based binder gave significantly inferior performance.

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TABLE III

Example Binder content Cable peel Adaptor peel (weight %) ~N) (N) 4 (ccmparison) 0 63 132

7 4 111 150

8 (oo~ison) 1 25 20

9 (comparison) 2 40 43 1010 (oomparison) 4 29 38 _ amples 11 and 12 In order to demonstrate the improved storaqe stability and curing of the adhesive formulations that contain an adduct. the following two adhesive formu-lations were prepared by the method described inExample 1 Example I Components Parts by weiqht I

I (1) Epoxy ~pikote 1001 100 Il I
¦ (2) Cure agent Polyamide - Macromelt 6071 50 I adduct - EDA 870 50 I
I (3) Plexibiliser CXA 2002 20 :
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Epoxy Epikote 1001 100 I
¦ (2) Cure agent Polyamide Macromelt 6071 80 12 I P~lyamide Versamid 14020 : ¦ (3) Flexibiliser CXA 2002 20 : :

, ~2~5395i The minimum viscosity of the adhesives with respect to time were measured at 100C using a Ferranti-Shirley Viscometer both when fresh and after a few weeks storage at ambient temperature.

For Example 11 the minimum viscosity on heating reduced from 900 poise when fresh to 464 poise after 10 weeks at 40C whereas for Example 12 the minimum viscosity increased from 260 poise when fresh to 1125 poise after 12 weeks storage at 40C. indicating that the adduct did not cure to any si~nificant extent on storage whereas the polyamide based one did.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PRIVILEGE OR PROPERTY IS CLAIMED ARE DEFINED AS
FOLLOWS:

1. A heat-curable adhesive coating on a substrate, the coating comprising (a) a mixture of substantially solid particles of a first reactive component with separate substantially solid particles of at least a second reactive component and (b) a water-soluble poly-meric binder having substantially no free hydroxyl groups, the first and second reactive components being present in the coating as substantially unreacted separate particles capable of reacting together to effect curing when the coating is heated to the curing temperature.

2. A coating according to claim 1, comprising not more than 5% by weight, of the binder.

3. A coating according to claim 2, comprising not more than 2.5% by weight of the binder.

4. A coating according to claim 3, comprising at least 1% by weight of the binder.

5. A coating according to claim 1, carried on a flexible substrate.

6. A coating according to claim 5, wherein the substrate is a heat-recoverable polymeric article capable of being recovered around an object with the adhesive coating between the polymeric article and the object.

7. A coating according to claim 6, wherein the substrate is a hollow article with at least one opening to the exterior and has the adhesive coating on the inner surface thereof in the region of an opening.

8. A coating according to claim 6, wherein a reac-tive component has a melting or softening point no higher than 20°C below the recovery temperature of the article.

9. A coating according to claim 1, wherein the par-ticles of the first reactive component are connected to those of the second reactive component substantially only by the binder.

10. A coating according to claim 1, wherein the reac-tive component particles have a size distributuion in which not more than 40% by weight of the particles are less than 50 micrometers in size and substantially all the particles are less than 300 micrometers in size.

11. A coating according to claim 1, wherein one of the reactive components is a thermoplastic epoxy resin.

12. A coating according to claim, 11 wherein the or at least one other reactive component is a material having reactive amine groups

13. A coating according to claim 11, wherein the or at least one other reactive component is an adduct of the epoxy resin with a material having reactive amine groups.

14. A coating according to claim 12 or 13, wherein the material having reactive amine groups is a polyamide.

15. A coating according to claim 12 or 13, wherein the material having reactive amine groups is ethylene diamine or ethylene triamine.

16. Acoating according to claim 1, wherein the par-ticles have a size distribution in which not more than 30% by weight of the particles are less than 50 micro-metres in size.

17. A coating according to claim 1, wherein not morethan 60% by weight of the particles are less than 75 micrometres in size.

18. A coatingt according to claim 17, wherein not more than 50% by weight of the particles are less than 75 micrometres in size.

19. A coating according to claim 1, wherein the par-ticles have a weight average particle size in the range of from 75 to 125 micrometres.

20. A coating according to claim 1, wherein the first and second reactive components are capable of reacting together when brought into reactive contact at ambient temperatures.

21. A coating according to claim 1, wherein electri-cally conductive solid particles are incorporated to render the cured coating electrically conductive.

22. A coating according to claim 1, wherein the binder comprises a polyvinyl acetate.

23. A coating according claim 1, wherein the binder comprises a substituted or unsubstituted polyalkylene oxide.

24. A coating according to claim 23, wherein the binder comprises polyethylene oxide.

25. A coating according to claim 1, wherein the poly-meric binder is present in an amount of up to 15% by weight, based on the total dry weight of the coating.

26. A coating according to claim 1, wherein the binder is present in an amount of from 0.5 to 5% by weight, based on the total dry weight of the coating.

27. A method of manufacturing a heat-curable adhesive coating on a substrate, comprising (I) applying to a surface of the substrate an adhesive coating comprising (a) a mixture of substantially solid particles of a first reactive component with separate substantially solid particles of at least a second reactive component and (b) a water-soluble polymeric binder having substantially no free hydroxyl groups, the first and second reactive components being present in the coating as substantially unreacted separate particles capable of reacting together to effect curing when the coating is heated to the curing temperature, as a dispersion in a liquid which is substantially a non-solvent for the reactive components, and (II) removing the liquid.

28. A method according to claim 27, wherein the par-ticles of the first reactive component are freely moveable in the dispersion relative to the particles of the second reactive component, so as to produce a coating wherein the particles of the first reactive component are connected to those of the second reactive component substantially only by the binder.

29. A method according to claim 27, wherein the adhesive coating is applied to the surface of the substrate from an aqueous dispersion.

30. A method according to claim 27, wherein the adhesive coating is applied to the surface of the substrate by dip-coating.