GB2055109A

GB2055109A - Heat-curable epoxy resin adhesives

Info

Publication number: GB2055109A
Application number: GB8021655A
Authority: GB
Original assignee: TH Goldschmidt AG
Current assignee: Evonik Operations GmbH
Priority date: 1979-07-04
Filing date: 1980-07-02
Publication date: 1981-02-25
Also published as: DE2926945B2; DE2926945A1; IT1143160B; GB2055109B; DE2926945C3; FR2460985A1; IT8048650A0; FR2460985B1

Abstract

Heat-curable adhesive compositions, suitable for bonding brake linings to metallic supports, comprise, as active components, a) 30 to 90% by weight of one or more prepolymers selected from polyesterimides, polyamide-imides and polyhydantoins; b) 2 to 40% by weight of an epoxide resin and/or an epoxidised novolac resin; c) 0.1 to 20% by weight of curing agent, effective under curing conditions, for component b), d) 0 to 40% by weight of a heat- curable phenolformaldehyde resin having a softening point above 20 DEG C and e) 0 to 40% by weight of a copolymer obtained by copolymerisation of e1) 30 to 80% by weight of one or more (C1-8alkyl) esters of acrylic or methacrylic acid, e2) 5 to 25% by weight of acrylonitrile and/or methacrylonitrile, e3) 2 to 20% by weight of one or more omega -hydroxy-alkyl esters of acrylic or methacrylic acid having 1 to 5 carbon atoms in the alkyl radical, e4) 0 to 35% by weight of styrene and e5) 0 to 15% by weight of an olefinically unsaturated carboxylic acid, the amount of monomers e1) to e5) totalling 100% by weight and the amount of components a), b), c), d) and e) also totalling 100% by weight. s

Description

SPECIFICATION Heat-curable adhesives The present invention relates to heat-curable adhesive compositions and to the use of such adhesive compositions for bonding brake linings or brake lining compositions to metallic supports.

The bonding of brake linings or brake lining compositions to metallic supports, the brake shoes, is usually carried out by applying the adhesive in the form of an organic solution to the side of the metallic support facing the brake lining and, after the solvent has evaporated, pressing on an already moulded brake lining under hot conditions. The bonding temperatures in this process are generally 160 to 200 C, the compression time is generally 5 to 15 minutes and the applied pressure time is generally 0.5 to 1 N/mm2.

In the manufacture of brake pads for disc brakes, the abovementioned process is usually varied by not bonding pre-moulded brake linings to the metal support after applying the adhesive, but, instead, pressing onto the metal support brake lining compositions which have not yet been pre-compressed, compression and moulding of the brake lining composition taking place simultaneously with bonding to the metal support. The temperatures in this case are generally 160 to 180"C, the compression times are about 10 minutes, but the applied pressure is considerably higher and is usually 30 to 100 N/mm2. It is also customary to press the brake lining compositions on at a low temperature, for example 50,C, under applied pressures of up to 250 N/mm2 for a short time, for example 30 seconds.After moulding and compression, the resulting brake linings, which have been bonded onto the metallic support, are generally heat-treated at atmospheric pressure or under a slight applied pressure, for example 0.4 N/mm2, at 200 to 230 C for up to 15 hours.

The adhesives generally used are phenolic resins containing polyvinyl formal as the agent for imparting elasticity, or mixtures of adhesives consisting of phenolic resin and acrylonitrile/butadiene copolymers.

However, phenolic resins containing polyvinyl formal frequently produce bonds of low elasticity, after curing. A particular disadvantage of the phenolic resins containing acrylonitrile/butadiene copolymers is their high curing temperature of > 170 C.

Because of the stresses to which brake linings in drum brakes and brake pads in disc brakes are subjected, it is necessary, not least for reasons of safety, to set high requirements for an adhesive for bonding these.

The bond must be heat-resistant over a wide range of temperatures, that is to say from winter temperatures up to, for brief periods, high temperatures of about 350"C. The bond must be corrosion-resistant, that is to say the diffusion of water, and especially of aqueous salt solutions, into the bond must be prevented. The adhesive must also be resistant to oil and petrol. A particularly important requirement is that the adhesive should have high adhesion to the interfaces and that the cured adhesive should have sufficiently good cohesion. These adhesion or cohesion properties can be determined by exposing a bonded brake shoe to a shearing force acting in the direction of the bonded surface. In this pressure shearing test, the shearing force is increased until a fracture occurs. The fracture should, moreover, not take place in the bond, but in the brake lining.In order to simulate the temperature stresses which arise during braking, another test is carried out in which the brake shoe is heated at temperatures of 250 to 350"C for a prolonged time, for example 1 to 3 hours. After cooling, the cold shear strength should be virtually unchanged.

As a result of recent investigations into the harmful effects on health of asbestos fibres, especially those of small fibre dimensions, efforts are being made to replace the asbestos fibres which are usually added to brake lining compositions. Attempts have already been made to incorporate iron filings or sponge iron into the compositions instead of asbestos. However, brake lining compositions of this type have a higher heat conductivity, so that the heat exposure of the bond increases. There is, therefore, a requirement for brake lining adhesives which are highly heat-resistant.

A further desideratum is that it should be possible to process the adhesives without the use of an organic solvent. The adhesives should preferably be able to be processed in the form of an aqueous dispersion, a finely divided powder or a film. As a result of avoiding the use of organic solvents, processing conditions can be achieved which are particularly favourable in respect of effluent air and harmful substances. These problems of environmentally acceptable working conditions are assuming an increasingly more important aspect.

The present invention provides a heat-curable adhesive composition comprising, as active components a) 30 to 90% by weight of one or more prepolymers selected from polyesterimides, polyamide-imides and polyhydantoins; b) 2 to 40% by weight of an epoxide resin and/or an epoxidised novolac resin; c) 0.1 to 20% by weight of a curing agent, effective under curing conditions, for component b);; d) 0 to 40% by weight of a heat-curable phenolformaldehyde resin having a softening point above 20"C and e) 0 to 40% by weight of a copolymer obtained by copolymerisation of e1) 30 to 80% by weight of one or more alkyl esters of acrylic or methacrylic acid having 1 to 8 carbon atoms in the alkyl radical, e2) 5 to 25% by weight of acrylonitrile and/or methacrylonitrile, e3) 2 to 20% by weight of one or more -hydroxyalkyl esters of acrylic or methacrylic acid having 1 to 5 carbon atoms in the alkyl radical, e4) 0 to 35% by weight of styrene and e5) 0 to 15% by weight of an olefinically unsaturated carboxylic acid, the amount of monomers e1) toe5) totalling 100% by weight and the amount of components a), b), c), d) and e) also totalling 100% by weight.

If appropriate, the adhesive composition can also contain, in addition to the active components, customary additives, such as surface-active substances, anti-corrosion agents, fillers or pigments.

The adhesive according to the invention preferably contains: 40 to 80% by weight of component a), 5 to 30% by weight of component b), 0.2 to 10% by weight of component c), 2 to 30% by weight of component d) and 2 to 30% by weight of component e), which components must total 100% by weight.

Prepolymers which are polyester-imides, polyamide-imides or polyhydantoins are used as component a).

In this respect, pre-polymers within the meaning of the present invention are polymers which are soluble in a solvent and which are converted, under the influence of heat, into insoluble polymers of higher molecular weight.

Suitable polyester-imides are described for example in the journal "Kunststoffe", 61(1971), 46 etseq., and may be prepared from aromatic carboxylic acids or anhydrides thereof and aromatic amines. Examples of suitable polycarboxylic acids are trimellitic acid, pyromellitic acid and naphthalene-1,4,5,8-tetracarboxylic acid. Examples of suitable amines are 4,4'-diaminodiphenylmethane, p-phenylenediamine and paminobenzoic acid. The resulting imides may then be esterified with polyols, such as ethylene glycol, diethylene glycol or glycerol.The reaction can proceed, for example, according to the following specific

equation: 2 + H2NclJ2 7Th HOO J 2 47CH2 X NH2 o imide formation -H20 0 0 Ho3C/ C03ii o 0 Esterification with polyols HO-R-OH 2 2 0 CH2"o II 2 NIM O-R-O-Xt t\o-O-R-O . . .

0 The dimensional stability under heat of the polyester-imides can be improved by adding crosslinking agents, usually polycarboxylic acids or polyols, preferably with a symmetrical arrangement of the cross-linking groups, for example pyromellitic acid or tris-(2-hydroxyethyl) isocyanurate.

Suitable polyamide-imides can be obtained, for example, in accordance with German Patent Specification 1,266,427, German Auslegeschrift 1,770,202 or German Offenlegungsschrift 2,443,576 from aromatic polvcarboxvlic acid anhydrides, generally tr mellitic anhydride, and polyisocyanates:

o ) \.cO 15O0C n | ll 0 + n R catalysts (for }iOOc i1co exainpie acids) + XN-R | + 2nC02 a Polyisocyanates containing isocyanurate groups or partially blocked polyisocyanates can also be present in this synthesis.

Suitable polyhydantoins can be obtained by reacting glycine derivatives, for example bisglycine esters, with aliphatic, cycloaliphatic or aromatic, polyfunctional isocyanates or partially polymerised isocyanates, for example in accordance with German Patent Specification 1,570,552 following the specific equation shown below::

a NH-CH -C-OCII NCO 140 - 28O0C go 140 < 2800C 280 C catalysts (tertiary amines) Y Y (tertiary amines) CH2 + 2 CH2 NH-CH -C-OCI1 NCO 3 N < Cl 12 CH2 + 2 CH3 0J I Qi 2 - ' " The abovementioned prepolymers a) are soluble, for example, in N-methylpyrrolidone, phenol and cresols, benzyl alcohol or y-butyrolactone. In the solvent-free state they can be ground to give fine powders and dispersed in water.

In the cured state, the prepolymers a) are heat resistant substances. However, they have no adhesion, or and inadequate adhesion, to brake lining compositions and are therefore unsuitable in this form as adhesives.

It has been found, however, that, surprisingly, their adhesion is increased to such an extent by the modifying action of components b), d) and e) that they can be employed with particular advantage for bonding brake linings and that high heat-resistance is retained.

Component b) is an epoxide resin and/or an epoxidised novolac resin. Suitable epoxide resins are the epoxides of polyunsaturated hydrocarbons, glycidyl ethers of polyhydric alcohols and phenols and glycidyl ethers of polyglycols or polyesters. The epoxidised novolac resins are suitably glycidyl ethers of condensation products of monohydric or polyhydric phenols or homologues thereof with formaldehyde, the condensation products generally being obtained in an acid medium.

Component c) is a curing agent, for component b). The curing agent must be "effective under hot conditions" which means that the curing agents do not become effective while the adhesives are stored, but only at curing temperatures (temperatures of use). Examples of suitable curing agents are polybasic organic carboxylic acids or anhydrides thereof, for example maleic anhydride, phthalic anhydride, tetrahydrophthalic anhydride, trimellitic anhydride or pyromellitic dianhydride.

It is also possible for curing to be effected in a manner which is in itself known by means of amines as component c). Aromatic polyamines, for example m-phenylenediamine, m-xylylenediamine, 4,4'-diamino- diphenylmethane, 4,4'-diaminodiphenyl sulphone or benzidine, are particularly suitable for this purpose. In addition, dicyandiamide is suitable. It is also possible to use dicyandiamides which are substituted by alkyl or aryl groups or adducts of dicyandiamide with less than equivalent amounts, in respect of reactive groups, of epoxide resins.

Component d) is a heat-curable phenol-formaldehyde resin. It can for example, be a resol resin having a phenol/formaldehyde molar ratio of 1 1 to 1 : 2 or a mixture of a novolac having a phenol/formaldehyde molar ratio of 1: 0.5 to 1: 0.8 and hexamethylene-tetramine, in a weight ratio of 85:15 to 95: 5. The phenol can be wholly or partially replaced by its homologues, such as cresol. The preparation of resins of this type is known in the art and is described, for example, in the book "Phenoplaste" ("Phanoplasts") by Bachmann/Mijller, (VEB Deutscher Verlag für Grundstoffindustrie, Leipzig 1973).The resin should be solid at room temperature, that is to say it should have a softening point above 20"C, and should preferably be capable of being ground to give as fine a powder as possible.

Component e) is an acrylic copolymer, which may be prepared in solution or in emulsion in a manner which is in itself known. Alkyl esters of acrylic or methacrylic acid having 1 to 8 carbon atoms in the alkyl radical or mixtures thereof are used as monomer e1). Examples of suitable monomers e1) are ethyl acrylate, butyl acrylate, butyl methacrylate, methyl acrylate and methyl methacrylate. However, higher alkyl esters containing up to 8 carbon atoms in the alkyl radical, such as, ethylhexyl acrylate, are also suitable.

Examples of suitable monomers e3) are hydroxyethyl methacrylate, hydroxypropyl methacrylate and hydroxybutyl acrylate. Examples of suitable monomers e5) are acrylic acid, methacrylic acid and itaconic acid.

The adhesive compositions of the invention are preferably used in the absence of a solvent. From the point of view of application technology, it is particularly easy to use an aqueous dispersion. These dispersions may be prepared by dispersing component b), namely the epoxide resin and/or the epoxidised novolac resin, in water, using dispersing auxiliarieslagents, for example anionic surface-active agents, such as alkyl sulphates, alkyl polyglycol ether-sulphates, alkylaryl polyglycol ether-sulphates, alkyl sulphonates, alkylaryl sulphonates or sulphonates of polycarboxylic acid esters; nonionic surface-active agents, such as alkyl polyglycol ethers, alkylaryl polyglycoi ethers or ethoxylated fatty acids; fatty acid amides; fatty acid esters; fatty amines or fatty alcohols; or polymeric substances having a protective colloid action, such as vinyl polymers (polyvinyl alcohol or polyvinylpyrrolidone), acrylic polymers containing carboxyl, carboxamide or sulphonic acid groups attached laterally, polycarboxylic acids, polyethers (for example, block copolymers formed from ethylene oxide and propylene oxide), polyimines, alginates, guarflour, pectins, dextrins, gum arabic, carboxymethylcellulose, methylcellulose, hydroxyethylcellulose or hydroxypropyicellulose or inorganic polymers, such as montmorillonite, polysilicic acids or zeolites.

The prepolymers (component a)) can be finely ground and made into a paste with the aid of the above-mentioned dispersing agents.

The curing agent (component c)) can be made into a paste in a similar manner to component a).

The phenol-formaldehyde resin (component d)) can similarly be made into a paste with the aid of the dispersing agents or can be prepared direct in a disperse form in a manner which is in itself known. Suitable processes are described, for example, in German Auslegeschrift 2,235,439, U.S. Patent Specification 4,026,848 and German Offenlegungssch rift 2,804,362.

The acrylic copolymer (component e)) can be prepared by emulsion polymerisation and can be used direct in this form.

It has proved particularly appropriate first to mix component b) and, if present, component e) with one another and to stirthe remaining components a), c) and, if present, d) into the resulting dispersion.

The resulting dispersions can then be applied in a thin layer to the surfaces of the components to be bonded. The water is then allowed to evaporate and the components to be bonded are then pressed together while being warmed to temperatures above 170" and up to 250 C.

The preparation of an adhesive in powder form is also easy. In most cases components a) to d) are in a pulverulent form. The desired polymer can be precipitated from the dispersion of acrylic copolymers (component e)) and can be dried and ground. The individual powders can then be mixed, if necessary with further grinding, for example in a ball mill. Preferably the powder adhesive has an average particle size of not more than 250 mm.

If it is desired to prepare sheetlike adhesives, it has proved particularly suitable to impregnate or to coat supports such as glass fibre mats with the paste dispersion of the adhesive according to the invention and to dry the product. The resulting adhesive films are then generally cut into sizes appropriate to the application or can be used direct from the roll.

The adhesive can also contain customary additives. The dispersing agents used in the preparation of the aqueous dispersions already mentioned may be incorporated as surface-active substances. It is also possible to add to aqueous preparations of the adhesives, anti-corrosion agents, such as alkali metal nitrites, thiourea derivatives, heterocyclic compounds containing sulphur and/or nitrogen (for example 2mercaptobenzthiazole, quinoline or thiazole derivatives), secondary amines, sulphoxides, fatty acid derivatives (for example oleic acid diethanolamide or N-lauroylsarcosine), sulphonic acid derivatives, abietic acid polyglycol esters or alkylamine polyglycol ethers. Further usual additives are fillers and pigments, such as barium sulphate, titanium dioxide or carbon black. If the adhesives of the invention are to be used in an aqueous phase, it can, in some circumstances, be appropriate to add anti-foaming agents. If the viscosity of the aqueous preparation of an adhesive according to the invention is too low, its viscosity can be adjusted by adding customary organic or inorganic thickeners.

Although the bonding of brake linings has been mentioned as the main field of application for the adhesives of the invention, they are, however, also suitable for bonding, for example, metals, such as aluminium, steel or steel alloys to one another or metals to heat-resistant plastics.

Example 1 which follows describes adhesives according to the invention and their preparation. Example 2 illustrates in greater detail the use, in accordance with the invention, of the adhesives for bonding brake linings. Test results in line with actual practice are also quoted.

EXAMPLE 1 Preparation of the adhesives according to the invention 1. Raw materials 1.1 Prepolymers a) The commercially available polyester-imide used contains trimellitic anhydride, 4,4'diaminodiphenylmethane, ethylene glycol and glycerol as the basis and tris-(2-hydroxyethyl) isocyanurate as the crosslinking component.

The commercially available polyamide-imides used were obtained by reacting trimellitic an hydride with stoichiometric amounts of diphenylmethane-4,4'-diisocyanate (polyamide-imide No. 1) or with a mixture of diphenylmethane-4,4'-diisocyanate and hexamethylene-1,6-diisocyanate in a ratio by weight of 2 1 (polyamide-imide No. 2).

The commercially available polyhydantoin No. 1 used is synthesised on a basis of diphenylmethane-4,4'diisocyanate and N,N'-bis-ethoxycarbonylmethyl-4,4'-diaminodiphenylmethane, while the polyhydantoin No. 2 is synthesised on a basis of 2,4-toluylene diisocyanate and N,N-bis-ethoxycarbonylmethyl-4,4'diaminodiphenylmethane.

The prepolymers mentioned are used either in a finely ground powder form or as 30 to 45% w/v solutions, examples of suitable solvents being N-methylpyrrolidone, dimethylformamide, N,N-dimethylacetamide, y-butyrolactone, benzyl alcohol and dimethyl sulphoxide.

Further diiution can also be effected by adding, to a limited extent, ketones, such as acetone or methyl ethyl ketone, aromatic compounds, such as toluene orxylene, esters, such as ethyl acetate or butyl acetate, and partially etherified glycols, for example methylglycol or ethylglycol.

1.2 Epoxide resins b) The commercially available epoxide resins b 1) to b 3) used have been formed by subjecting ephichlorohydrin to a condensation reaction with bisphenol A and have the following epoxide equivalents: epoxide resin b 1) approx. 180 g/equivalent (liquid and emulsifiable) epoxide resin b 2) approx. 700 g/equivalent (solid and grindable) epoxide resin b 3) approx. 950 g/equivalent (solid and grindable) Epoxide resin b 4) is a commercially available epoxy novolac resin having an epoxide equivalent of 190 g/equivalent.

1.3 Curing agents c) The chemical composition of the curing agents c) employed can be seen from Table 1.

1.4 Phenol-formaldehyde resins d) Phenol-formaldehyde resin d 1) is a resol resin and is prepared in a known manner by subjecting 141 g of phenol and 114 g of 37% w/v aqueous formaldehyde solution to a condensation reaction at 80"C in the presence of 1.7 g of sodium hydroxide. The condensation reaction is continued until the phenolic resin has a softening point of 85 C after being suitably worked up. After separating off the aqueous phase and removing the residual water by drying under reduced pressure, the resin is either dissolved in organic solvents, as described under 1.1, or is finely ground.

Phenol-formaldehyde resin d 2) consists of a novolac/hexamethylenetetramine mixture with a novolac content of 90% by weight. The novolac is prepared in a known manner by subjecting 235 g of phenol and 142 g of 37% w/v aqueous formaldehyde solution to a condensation reaction in the presence of small quantities of sulphuric acid by heating under reflux for 2 to 3 hours. After separating off the water and drying and comminuting the product, the hexamethylenetetramine is added in the ratio by weight indicated and the mixture is finely ground. The resin is either dissolved in organic solvents as above or is used in powder form.

1.5 Acrylic copolymers e) The copolymers e) are prepared either by solution polymerisation or by emulsion polymerisation.

In the case of solution polymerisation, the monomers e1) to e5) are reacted by conventional solution polymerisation in a solvent mixture consisting of 50% by weight of toluene, 30% by weight of acetone and 20% by weight of ethanol, at 70 to 80"C with the addition of 0.3 to 0.8% by weight of azodiisobutyronitrile and 0.3% of n-dodecylmercaptan. The solvent is evaporated and the copolymer is dissolved in the solvents mentioned under 1.1. The solids content in the copolymer solution is about 40% by weight. The chemical composition of the individual copolymers e) can be seen from Table 1.

If the copolymers e) are prepared by emulsion polymerisation, a polymer dispersion is prepared at 85"C, in the course of approx. 6 hours, in a known manner in accordance with the emulsion feed process from: 1,000 g of the monomers e) toe5) 1,000 g of water 2.5 g of potassium peroxydisulphate 2.0 g of sodium lauryl sulphate.

The solids content of the polymer dispersion is about 50% by weight. The chemical composition of the copolymers e) can be seen from Table 1.

2. Preparation of the adhesives The preparation of the adhesives in organic solvents, in an aqueous phase, in the form of adhesive films and in powder form is described below. The quantities of the individual components used can be seen from Table 1. They relate in each case to quantities of solids.

2.1 Solutions ofadhesives Solutions of adhesives are prepared by mixing, while stirring, the solutions of the prepolymers a), the epoxide resins b), the curing agents c) and, if appropriate, the phenol-formaldehyde resins d) and also the acrylic copolymers e) which have been prepared by solution polymerisation, until a solution is obtained. The solvents mentioned under 1.1 are added to dilute the adhesive and to adjust the viscosity as desired. Dilution is possible to a limited extent with aromatic compounds, such as xylene or toluene, ketones, such as acetone or methyl ethyl ketone, or partially etherified glycols, such as methylglycol, ethylglycol or diethylene glycol monomethyl ether.

2.2 Aqueous dispersions ofadhesives Aqueous dispersions of adhesives are prepared by making into a paste, in water, with the aid of a high-speed stirring disc (Dissolver), the finely ground prepolymers a), the curing agents c) and, if appropriate, the phenol-formaldehyde resin d), with the addition of 4.5% by weight of a mixture of surface-active agents consisting of 60% by weight of a nonylphenol polyglycol ether, 30% by weight of an ethoxylated sorbitan monooleate and 10% by weight of a sorbitan monooleate. The solids content of the paste is approx. 60% by weight. It is also possible to make the individual components into pastes separately.

A 50 per cent by weight emulsion of the epoxide resin b 1) is prepared in the customary manner after adding 3% of nonylphenol polyethylene glycol ether. The paste is now added to the epoxide resin emulsion, while stirring. If desired, the polymer dispersion of the acrylic copolymer e), in which the same quantity of the mixture of surface-active agents described above has previously been dissolved, is also added, while stirring. Small amounts of commrecially available, preferably silicone-free anti-foaming agents can be added in order to keep the formation of foam within bounds during the preparation of the pastes and during mixing with the epoxide resin emulsion and the polymer dispersion. If required, the viscosity of the dispersions of adhesives can be adjusted by means of organic or inorganic thickeners which are in themselves known. The thickeners are stirred in subsequently.

2.3 Adhesive films Adhesive films are prepared by impregnating and coating a glass fibre mat having a weight per unit area of 25 g/m2 with the dispersions of adhesives described under 2.2. After the water has been evaporated at approx. 130"C, the weight per unit area of the adhesive films should be approx. 180 g/m2.

24 Adhesive powders The finely ground components a) to e) are mixed in a powder mixer to give a homogeneous mixture which is used as the adhesive.

The acrylic copolymers e) are obtained in powder form by precipitating the copolymer from the polymer dispersion by adding methanol or ethanol, washing the precipitate with water and drying and grinding it.

TABLE 1 Adhesive formulations Formu- Form of Prepolymer a) Epoxide Curing agent c) Phenollation adhesive parts by weight resin b) parts by weight formalde No. parts by hyde resin weight d) parts by weight 1 solution 70 of polyamide- 21 of 1.3 of pyromellitic 7.7 of imide 1) b 3) dianhydride dl) 2 solution 73 of polyester-imide 15 of 3.8 of 4,4'-diamino b 4) diphenylmethane 3 aqueous 68 of polyhydantoin 17 of 5.6of4,4'-diamino- dis- 2) b 1) diphenyl sulphone persion 4 aqueous 63 of polyamide- 21 of 7.1 of4,4'-diamino- 8.9 of dis- imide 2) b 1) diphenyl suiphone d 2) persion 5 aqueous 65 of polyhydantoin 14 of 3.1 of benzidine 6.9 of dis- 1) bl) d2) persion 6 adhesive 66 of polyester-imide 15 of 5.0of4,4'-diamino- film b 1) diphenyl sulphone 7 adhesive 77 of polyamide-imide 20.7 2.3 of dicyandiamide film 1) ofbl) 8 adhesive 68ofpolyhydantoin2) 17 of 3.9of4,4'-diamino- 11.1 of film b1) diphenylmethane d 2) 9 adhesive 72 of polyamide- 11.2 0.8 of pyromellitic 16of powder imide 1) of b 2) dianydride d 2) 10 adhesive 69 of polyester-imide 16.1 2.9 of endomethylene- powder of b 2) tetrahydrophthalic anhydride 11 adhesive 66ofpolyhydantoin2) 10.4 0.6 of 4,4'-diamino- 12of powder of b 3) diphenyl sulphone d 2) 12 adhesive 73 of polyester-imide 9.8 of 0.2 of dicyandiamide 8 of powder b 3) dl) TABLE 1 - continuation Formu- Acrylic copolymer e) lation Composition in % by weight Parts by Type of polymerisation No. Weight 1 - - - ; 2 50 of ethyl acrylate e1) 8.2 solution polymerisation 20 of butyl acrylate e,) 15 of acrylonitrile e2) 5 of hydroxyethyl methacrylate e3) 10 of styrene e4) 3 22 of methyl methacrylate e1) 9.4 emulsion polymerisation 53 of butyl acrylate e) 5 of acrylonitrile e2) 3 of hydroxyethyl methacrylate e3) 17 of styrene e4) 4 - 5 31 of methyl methacrylate e1) 11 emulsion polymerisation 35 of ethyl acrylate e) 13 of ethylhexyl acrylate e1) 8 of acrylonitrile e2) 9 of hydroxyethyl methacrylate e3) 4 of methacrylic acid es) 6 38 of ethyl acrylate e1) 14 emulsion polymerisation 40 of butyl acrylate e1) 5 of acrylonitrile e2) 4 of hydroxyethyl methacrylate e3) 13 of styrene) e4) 7 - 8 - g 10 40 of methyl methacrylate e1) 12 emulsion polymerisation 35 of ethyl acrylate e1) 16 of acrylonitrile e2) 7 of hydroxyethyl methacrylate e3) 2 of methacrylic acid eS) 11 45 of methyl methacrylate et) 11 emulsion polymerisation 20 of butyl acrylate e1) 15 of acrylonitrile e2) 6 of hydroxyethyl methacrylate e3) 14 of styrene e4) 12 49 of methyl methacrylate e1) 9 emulsion polymerisation 19 of ethyl acrylate e) 22 of acrylonitrile e2) 9 of hydroxyethyl methacrylate e2) 2 of acrylic acid e5) EXAMPLE 2 The bonding and technological testing of bonded friction lining compositions for disc brakes Two different friction lining compositions are employed for testing the adhesives. Friction lining composition A, which is processed by the so-cailed cold compression-moulding process, contains asbestos, nitrile rubber as a binder, brass filings, barium sulphate and graphite. After blasting the surface with particles of grey cast iron, sufficient adhesive is applied to the side of the steel shoes which is to be bonded, to leave remaining, after the solvent or the water has been evaporated at approx. 100"C, an adhesive film approx. 25 um thick. If an adhesive film is used, the adhesive film alone is placed on the steel shoe, after the latter has been blasted. If adhesive powders are used, the steel support is warmed to 100"C and is then sprinkled uniformly with a quantity of 30 to 40 g/m2 of adhesive powders.In the course thereof, the powders sinter on the hot metal surface. The friction lining composition A, which has not been pre-compressed, is now pressed in a mould onto the adhesive side of the steel shoe at 40 to 60"C, for 30 seconds, under a pressure of 50 N/mm2. The friction lining is cured by subsequently subjecting the samples to heat-treatment under a pressure of 0.4 N/mm2, in the following programme: 1 hourat100 C 1 hourat130 C 1 houratl600C 2 hours at 200"C 8 hours at 230"C The other friction lining composition used, B, which is processed under hot conditions, contains steel wool, phenolic resin as a binder, graphite, kieselguhr and barium sulphate.In processing this friction lining composition, a thin layer of asbestos-containing friction lining composition, of composition similar to that described above, is sprinkled beforehand onto the steel shoe, which has been provided with adhesive, and the friction lining composition B is then pressed on at 170"C, for 8 minutes, under a pressure of 35 N/mm2.

Fresh air is admitted several times during the first one-third of the pressing operation. The friction lining is cured further by subsequently subjecting the samples to heat-treatment under a pressure of 0.4 N/mm in the following programme: 1 hourat160 C 1 houratl800C 10 hours at 220"C.

A pressure shearing test is then carried out on the cooled samples without subjecting them to any further load and also after 2 hours storage at 3500C (heat test) and cooling again to 20"C. In this test, the shearing force required to prise off the brake linings is determined and the appearance of the fracture is assessed in respect of failure of cohesion in the brake lining. The test results obtained are listed in Table 2.

For comparison, two adhesives of the prior art, based on phenol-formaldehyde resin and polyvinyl formal or nitrile rubber, are given at the end of the Table.

TABLE 2 Pressure shearing test on disc brake linings Adhesive Not subjected to heat After heat test formula- Pressure Appearance Pressure Appearance tion No. shear of fracture shear of fracture strength strength N/mm2 %CF3 Nimm2 %CF3 Friction lining composition A 1 3.8 95 3.4 90 3 3.9 100 3.5 90 4 3.7 95 3.6 90 5 3.5 95 3.2 90 6 3.9 100 3.5 95 7 4.3 100 4.0 90 10 4.1 90 4.0 85 11 3.9 95 3.7 80 12 3.8 100 3.4 90 Comparison adhesives It 3.5 90 0.9 15 112) 3.4 85 1.2 30 Friction lining composition B 1 7.1 100 6.7 90 2 6.8 95 6.4 90 3 7.2 95 7.0 85 4 7.0 95 6.6 85 5 7.1 90 6.5 90 7 7.8 100 7.1 95 8 7.9 95 7.2 90 9 6.9 95 6.5 90 10 6.8 90 6.5 85 11 6.7 90 6.2 90 Comparison adhesives 6.4 6.4 80 1.2 25 112) 6.1 90 1.1 30 1) Adhesive made from phenol-formaldehyde resin/polyvinyl formal 2) Adhesive made from phenol-formaldehyde resin/nitrile rubber 3) CF = cohesion failure

Claims

1. A heat-curable adhesive composition comprising, as active components, a) 30 to 90% by weight of one or more prepolymers selected from polyesterimides, polyamide--imides and polyhydantoins; b) 2 to 40% by weight of an epoxide resin andror an epoxidised novolac resin;; c) 0.1 to 20% by weight of a curing agent, effective under curing conditions, for component b), d) O to 40% by weight of a heat-curable phenolformaldehyde resin having a softening point above 20"C and e) O to 40% by weight of a copolymer obtained by copolymerisation of e1) 30 to 80% by weight of one or more alkyl esters of acrylic or methacrylic acid having 1 to 8 carbon atoms in the alkyl radical, e2) 5 to 25% by weight of acrylonitrile and/or methacrylonitrile, e3) 2 to 20% by weight of one or more o-hydrnxy-aIkyl esters of acrylic or methacrylic acid having 1 to 5 carbon atoms in the alkyl radical, e4) 0 to 35% by weight of styrene and e5) O to 15% by weight of an olefinically unsaturated carboxylic acid, the amount of monomers e1) to es) totalling 100% by weight and the amount of components a), b), c), d) and e) also totalling 100% by weight.

2. A composition according to Claim 1 which contains 40 to 80% by weight of component a), 5 to 30% by weight of component b), 0.2 to 10% by weight of component c), 2 to 30% by weight of component d) and 2 to 30% by weight of component e), the amount of components a), b), c), d) and e) totalling 100% by weight.

3. A composition according to claim 1 or 2, in the form of an aqueous dispersion.

4. A composition according to claim 1 to 2, in the form of finely divided powder.

5. A composition according to claim 4, in the form of a powder having an average particle size of not more than 250 cm.

6. A composition according to claim 1 or 2, in the form of a film having a support, the support being coated and/or impregnated with the composition.

7. A composition according to claim 6, in which the support is a glass fibre mat.

8. A composition according to any one of the preceding claims which also contains one or more surface active substances, anti-corrosion agents, fillers and/or pigments.

9. A composition according to claim 1 substantially as hereinbefore described with reference to Example 1.

10. A composition according to claim 1 in which components a), b), c), d) and e) are said components specifically identified herein.

11. A method of bonding a brake lining or brake lining composition to a metallic support which comprises applying, as adhesive, a composition as claimed in any one of the preceding claims.

12. A method according to claim 11 substantiallty as hereinbefore described with reference to Example 2.