GB Patent 971356 - Improvements in or relating to bonding

Description

PATENT SPECIFICATION

NO DRAWINGS 971,356 //)"& 4 ' Date of Application and Filing Complete Specification Nov 1, 1962.

f w) Application made in Germany (No H 44027 I Vo/22 i) on Nov 2, 1961 No 41319/62.

/ Complete Specification Published Sept 30, 1964.

( Crown Copyright 1964.

Index at Acceptance:-C 3 B( 1 C 6, 1 C 9, 1 C 10, 1 C 12, l DIB, l Dl X, 1 D 2 A, 1 D 5, 1 N 4 H, 1 N 6 C, 1 N 6 J, 1 N 7, IN 15, 1 N 16 A); B 5 N( 2 F, 2 N 2, 2 N 4, 5 G 2, 5 G 10, 10 A, 10 B 2, 16 A, 16 B 2) International Classification:-C 08 g (B 29 d) COMPLETE SPECIFICATION

Improvements in or relating to bonding We HENKEL & CIE G m b H a German Company, of 67, Henkelstrasse, DuesseldorfHolthausen, 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: -

This invention relates to a process for bonding of elastomers to rigid substances, especially metals.

More particularly the invention relates to a process for bonding natural or synthetic elastomers to rigid substances, especially metals It is known that the bonding of highly elastic bodies to rigid bodies entails special problems, and previously only relatively few adhesives have been found which are suitable for this purpose.

It has already been proposed to use mixtures of diisocyanates and epoxide resins, prepared by condensation of epichlorhydrin with diphenylolpropane, for bonding of metals or plastics with metals In an attempt to bond elastomer and metal with such mixtures, the applicant did not obtain satisfactory results.

It has now been found that natural or synthetic elastomers may be satisfactorily bonded with rigid substances, especially with metals, if mixtures of organic isocyanates which contain more than one isocyanate group per molecule and certain epoxide resins are used as adhesives Epoxide resins which either contain no aromatic residues or if they do contain aromatic residues also contain aliphatic or cycloaliphatic residues with at least 8 members in the chain, are suitable.

lPrice 4 s 6 d l As examples of organic isocyanates which may be used as adhesives according to the invention may be mentioned:

phenylene diisocyanate, toluylene diisocyanate, diphenylmethane-4,4 '-diisocyanate, 45 diphenylene-4,4 '-diisocyanate, 3,3 '-dimethoxy-4,4 '-diphenylene diisocyanate (dianisidine diisocyanate), triphenylmethane triisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate and deca 50 methylene diisocyanate It is preferred to use isocyanates in which diisocyanate groups are linked to aromatic rings In some cases it is advantageous to use, instead of the isocyanates, their reaction products 55 which still contain at least 2 isocyanate groups in the molecule, e g the commercial reaction product of 1 mol of trimethylolpropane with 3 mol of toluylene.

diisocyanate 60 The epoxide resins for the process according to the invention are preferably prepared from aliphatic or cycloaliphatic di or polycarboxylic acids with more than 3 carbon atoms, or their salts, by reaction 65 with epichlorhydrin or other epihalohydrins, e.g by the process of British Patents Nos.

766,771 and 884,033.

Epoxide resins are particularly suitable which have been prepared from aliphatic 70 dicarboxylic acids with 4 to 10 carbon atoms, e g succinic acid, adipic acid, trimethyladipic acid or sebacic acid, or their salts, and epichlorhydrin according to the process of one of the above-named patents, 75 but the epoxide resins may also be prepared from those derivatives of the above acids which contain more than one free carboxyl group in the molecule, e g their acid esters 2 971,356 with polyhydric alcohols or with hydroxycarboxylic acids In this connection it has been found that when polyesters with acid terminal groups and with a molecular weight of about 2000 are used as starting substances, useful bonds are still obtained.

Suitable acid esters are prepared, for example, by reacting ethylene glycol, diethylene glycol, triethylene glycol, trimethylene glycol or hexamethylene glycol with 2 mol of succinic acid, adipic acid or sebacic acid or their anhydrides.

Furthermore, epoxide resins which are obtained by known methods from polyhydric alcohols by etherification with epichlorhydrin and subsequent splitting off of HC 1 are also suitable, for example, butanediol-1, 4 diglycide ether, butanediol-1,3 diglycide ether, hexanediol-l,6 diglycide ether, decanediol-1,10 diglycide ether, octadecanediol-l, 12 diglycide ether, 1,4-dimethylolcyclohexane diglycide ether and quinitoldiglycide ether.

Epoxide resins may also be used which contain aromatic residues but in this case it is necessary that aliphatic or cycloaliphatic residues with at least 8 members should be present in the molecule in addition to the aromatic rings It is not necessary for the aliphatic chains to consist wholly of carbon atoms, and they may be interrupted by hetero-atoms A suitable epoxide resin which, besides aromatic residues, contains relatively long aliphatic chains, can be prepared, for example, by the process of the above-mentioned British Patent No 884,033 from a reaction product from I mol of ricinoleic acid and 1 mol of phthalic anhydride Other examples of suitable starting substances are the acid ester prepared from castor oil and phthalic anhydride or the reaction product from 2 mol of phthalic anhydride and a dimeric fatty alcohol.

The most suitable mixing proportions of the said isocyanates and epoxide resins are when the ratio of epoxide groups to isocyanate groups is in the range 1:1 to 1: 5, and is preferably 1:3.

The action of the adhesives according to the invention can be further improved when fillers with a large surface, e g soot, are added to them, preferably in an amount of 1 to 10 % by weight In this way the resistance to peeling of the rubber-metal bonds is considerably improved.

The applicant has found that a further improvement of the bonds prepared with the mixtures according to the invention can be attained by addition of 1 to 10 %, preferably 2 to 5 % by weight, of maleic anhydride.

The adhesive mixture according to the invention is used either as such or in the form of solutions Inert organic solvents such as toluene, xylene, methylene chloride, dioxan, acetone, methyl ethyl ketone and cyclohexanone may be used as solvents.

The application of the adhesive mixtures according to the invention is carried out by pressing together with light pressure the surfaces to be bonded, after the application of the adhesive to one or both of the sur 70 faces, possibly after evaporation of the solvent The hardening of the adhesive is then effected, preferably at elevated temperature between 60 and 180-C, and in particular at 120 to 160 C The hardening time 75 depends, among other things, on the temperature used At a hardening temperature of 160 C, it may amount to 10 to 30 minutes, according to the composition of the adhesive 80 The applicant has further found that the hardening of the adhesives can be accelerated by a number of catalysts, e g by quaternary ammonium compounds such as tetramethylammonium bromide or tetra 85 ethylammonium bromide.

Other suitable accelerators are sulphonium salts, e g diethylmethylsulphonium bromide, diphenylmethylsulphonium bromide or hydroxyphenyldimethylsulphonium chloride 90 The acceleration of the hardening by sulphonium compounds was not previously known.

The bonds produced by the process according to the invention, especially those 95 of natural or synthetic rubber to metals, have outstanding tenacity and resistance to flexing and peeling They are very stable towards chemical attack, e g against the permanent action of hot water A special advantage of 100 the process according to the invention is to be seen in that, with the adhesive mixtures described, metals may be combined with already vulcanised rubber elastomers, while the majority of the known metal-rubber ad 105 hesives can only be used with simultaneous vulcanisation of the rubber.

When not otherwise indicated, the following test materials were used for the tests described in the following examples: 110 (a) Strips of aluminium sheet of size x 20 x 2 mm, the surface of which had been rubbed with emery and then degreased with methylene dichloride, (b) Strips of vulcanised rubber-elastomers, 115 which had a tensile strength of 25 to 40 kg/cm 2 and dimensions of 100 X 20 x 2 mm, which had been degreased with toluene and roughened with fine sandpaper on the surfaces to be treated with adhesive 120 These test materials were glued on an overlapping surface of 20 X 10 mm During the hardening a pressure of 0 '05 kg/cm 2 was exerted.

EXAMPLE 1 125

An acid ester was prepared from 1 mol of castor oil and 3 mol of phthalic anhydride An epoxide resin which had an epoxide oxygen content of 2 '6 % was obtained from this ester according to Example 130 971,356 97,5 3 6 of the British Patent No 884,033 by reaction with epichlorhydrin in the presence of an ion exchanger 3 G of this resin and 1.5 g of dianisidine diisocyanate were mixed with 2 cc of ethyl acetate at a temperature of 40 to 50 C The homogeneous mixture was applied in a thin layer to the metal and rubber surfaces to be bonded After minutes the surfaces coated with the adhesive were pressed together and heated for 2 hours at 120 C under load The bond produced in this way had a very good tenacity and resistance to peeling.

EXAMPLE 2

3 G of the epoxide resin used in Example 1 were dissolved at 60 C in 29 g of a 75 % solution of the reaction product from 3 mol of toluylene diisocyanate and 1 mol of trimethylolpropane in ethyl acetate The metal and rubber surfaces to be bonded were painted with this solution and after pressing were heated at 120 C for two hours under load.

A bond of high tensile strength and resistance to peeling was obtained.

EXAMPLE 3

3 G of the epoxide resin described in Example 1 were triturated at room temperature with 2-2 g of dianisidine diisocyanate, 0-2 g of maleic anhydride and 1 cc of methylene dichloride to a brushable paste A small amount of this paste was applied in a thin layer to the prepared metal and rubber surfaces After pressing, the test materials were heated at 120 C.

for two hours under load A bond of such great strength was formed that both in the tensile and peeling tests fracture of the rubber took place.

5 Bonded samples which had been prepared according to the foregoing Example and 5 further samples which were produced in the same way but using only 1-5 g of dianisidine diisocyanate, were exposed for 240 hours to the action of distilled water at 70 C At the end of this experiment, no change in the tensile strength and peeling resistance of the metal-rubber bonds could be ascertained.

EXAMPLE 4

3 G of the epoxide resin described in Example 1, 1-5 g of dianisidine diisocyanate, 3 cc of xylene and 0 '1 g of hydroxyphenyldimethylsulphonium c h 1 o r i d e were triturated to a homogeneous mixture.

Samples of this mixture were applied in a thin layer to the surfaces to be bonded.

After pressing, one hour's heating at C under load was sufficient to produce very hard layers of adhesive which gave a rubber-metal bond of great strength.

EXAMPLE 5

An acid ester was prepared in known way from 1 mol of dimerised fatty alcohol (prepared by dimerisation of unsaturated 65 fatty acids of chain length C 18 and subsequent reduction) and 2 mol of phthalic anhydride An epoxide resin, which had an epoxide oxygen content of 2-65 %, was obtained from this acid ester by the pro 70 cess of the British Patent No 884,033 by reaction with epichlorhydrin in the presence of an ion exchanger 3 G of this epoxide resin were triturated with 2-2 g of dianisidine diisocyanate with addition of 75 2 cc of xylene The prepared rubber and metal strips were coated with a small quantity of this mixture After evaporating the solvent, the coated surfaces were pressed together and heated at 120 C for 80 2 hours under load Rubber-metal bonds were obtained of especially high tensile strength.

EXAMPLE 6

An epoxide resin was prepared accord 85 ing to Example 40 of the British Patent No 884,033 by reacting dimeric fatty acids with epichlorhydrin in the presence of an ion exchanger 3 G of this resin, 2-65 g.

of dianisidine diisocyanate and 2-5 to 3 cc 90 of xylene were mixed at 50 C, a homogeneous solution being formed This solution was applied in a thin layer to the surfaces to be bonded After 20 minutes, the test materials were pressed together 95 and heated at 120 C for 2 hours under load A rubber-metal bond of very good tensile strength and peeling resistance was formed.

EXAMPLE 7

3 G of the epoxide resin used in Example 1 were triturated to a fluid paste with 2 '2 g of dianisidine diisocyanate, 0-2 g of maleic anhydride and 0-52 g of commercial finely divided soot (High 105 Abrasion Furnace, subsequently denoted as HAF-soot) The prepared sample materials were coated with a thin layer of this paste, then pressed and heated at 120 C for 2 hours under load After this the patch of 110 adhesive had such great strength that both in the tension test and in the peeling test, fracture of the rubber took place.

EXAMPLE 8

3 G of the epoxide resin described in 115 Example 6, 1-56 g of toluylene diisocyanate, 0-2 g of maleic anhydride and 0 '46 g of HAF-soot were triturated to a homogeneous mixture When this mixture was used according to Example 7, 120 fracture of the rubber in the vicinity of the adhesive patch took place both under tension and under peeling strain.

971,356 971,356 EXAMPLE 9

An epoxide resin which had an epoxide oxygen content of 4-4 % was prepared according to Example 17 of British Patent No 884,033 from an acid ester obtained by reacting triethylene glycol and phthalic anhydride in the molar ratio 1:2, and epichlorhydrin, in the presence of an ion exchanger 3 G of this resin were mixed with 2-15 g of toluylene diisocyanate, 0-2 g.

of maleic anhydride and 0-52 g of HAFsoot to give a suspension When this adhesive was used according to Example 7, rubber-metal bonds were obtained which at high peeling and tensile stresses only separated with removal of the surface of the rubber.

EXAMPLE 10

An epoxide resin, which had an epoxide oxygen content of 4-2 %, was prepared according to Example 30 of British Patent No 884,033 from an acid ester obtained by reaction of triethylene glycol with 2 mol of adipic anhydride, and epichlorhydrin, in the presence of an ion exchanger 3 G of this resin were triturated with 2-05 g of toluylene diisocyanate, 0-2 g of maleic anhydride and 0-5 g of HAF-soot to give a suspension On application of this adhesive according to Example 7, again both in the tension and peeling tests, fracture of the rubber but not the adhesive layer was observed.

A steel sheet was bonded to a natural rubber-styrene-butadiene-elastomer with the same adhesive The tensile strength of this bond in the peeling test (ASTM test No D 429-56-T, Method B) at an angle of amounted to 42 kg/inch When a steel sheet was bonded to a neoprene elastomer, under the same conditions a tensile strength of 60 kg/inch was obtained.

EXAMPLE 11

3 G of the epoxide resin described in Example 10, 3-48 g of dianisidine diisocyanate, 0-2 g of maleic anhydride and 0-65 g of HAF-soot were triturated with 4 cc of xylene to a mobile suspension.

When rubber was bonded to aluminium or iron by means of this adhesive, bonds of such great strength were obtained that, on tension and peeling tests, a smooth fracture in the rubber took place.

Under the same conditions, steel sheet was bonded to a natural rubber-styrenebutadiene elastomer These bonds showed a tensile strength of 44 kg/inch in the peeling test (ASTM test No D 429-56-T, Method B) at an angle of 45 When steel was bonded to a neoprene elastomer, a tensile strength of 55 kg/inch was found under the same conditions.

EX Am PLE 12 3 G of the epoxide resin described in Example I were triturated with 2-6 g of 4,4 '-diphenyhnethane diisocyanate, 0-2 g.

of maleic anhydride, 0-56 g of HAF-soot and 3 cc of xylene to give a suspension.

The metal and rubber surfaces to be bonded were coated with this suspension and after pressing were heated at 120 C for 2 hours.

A metal-rubber bond of especially high tensile and peeling strength was obtained.

EXAMPLE 13

3 G of the epoxide resin described in Example 6 were triturated with 12-8 g of a 20 % solution of 4,4 ',4 "-triphenylmethanetriisocyanate in methylene dichloride, 0-2 g.

of maleic anhydride and 0-55 g of HAFsoot until homogeneous The adhesive mixture formed was applied to the test material in a thin layer After evaporation of the solvent and pressing and hardening for 2 hours at 120 C rubber-metal bonds of great strength were obtained.

EXAMPLE 14

A commercial polyester with terminal hydroxyl groups, which was prepared from adipic acid and ethylene glycol and had a molecular weight of about 2000, was first o 90 reacted in known way with 1 mol of adipic anhydride to each hydroxyl equivalent The polyester with terminal carboxy groups obtained in this way was converted into an epoxide resin, which had an epoxide 95 oxygen content of 1-32 %, by the process of British Patent No 884,033 by boiling for 6 hours with 20 times its amount by weight of epichlorhydrin in the presence of an ion exchanger 3 G of this resin were tri 100 turated to a paste with 1-11 g of dianisidine diisocyanate, 0-2 g of maleic anhydride, 0-4 g of HAF-soot and 1 cc of xylene The surfaces to be bonded were thinly coated with this paste After evaporation of the 105 solvent, pressing and hardening for 2 hours at 120 C, rubber-metal bonds of very good tensile strength were again obtained.

EXAMPLE 15

An ester with terminal hydroxyl groups 110 was prepared in known way from 1 mol of adipic acid and 2 mol of thiodiglycol and 2 mol of adipic anhydride were subsequently added on The ester-dicarboxylic acid obtained in this way was converted into an 115 epoxide resin, wnhich had an epoxide oxygen content of 3-3 %, by reacting with 20 times its amount by weight of epichlorhydrin in the presence of an ion exchanger according to the process of British Patent No 884,033 120 3 G of this resin were triturated to a suspension with 2-75 g of dianisidine diisocyanate, 0-2 g of maleic anhydride, 0-6 g of HAF-soot and 0-5 cc of xylene.

971,356 The surfaces to be bonded were coated with this mixture and pressed together 20 minutes after the coating The bond was then hardened at 160 'C for 20 minutes.

The rubber-metal bond obtained was again of high tensile and peeling strength.

EXAMPLE 16

An epoxide resin, which had an epoxide oxygen content of 7 %, was prepared similarly to the Examples 10 and 11 of British Patent No 884,033 by reacting adipic acid with epichlorhydrin in the presence of an ion exchanger 3 G of this resin were triturated to a suspension with 58 g of dianisidine diisocyanate, 0-2 g of maleic anhydride, 0-88 g of HAF-soot and 2 cc.

of xylene On application of this adhesive according to Example 15, rubber-metal bonds of such great strength were obtained that both in the tension and the peeling test fracture of the rubber took place.