IMPROVEMENTS IN AND RELATING TO ADHESIVES

(54) IMPROVEMENTS IN AND RELATING TO ADHESIVES (71) We, NIKOLAI NIKOLAEVICH TROFIMOV, prospekt Tsiolkovskogo, 49a, kv.45, VOLF SAMOILOVICH ETLIS, p;rov pekt Dzerzhinskogo, 4, kv.46, and DAVID AZRIELEVICH ARONOVICH, ulitsa Uritskogo, 8a, kv.25, all of Izerzhinsk, U.S.S.R., all citizens of the Union of Soviet Socialist Republics, 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 cyanoacrylate adhesive compositions. Cyanoacrylate adhesives are widely used for gluing glass, steel, brass, aluminium rubber, "Textolite" (registered Trade Mark), PVC, and other materials, in the aerospace industry, the manufacture of precision instruments, radio-electronics, the manufacture of electronic and optical instrutnents such as photographic cameras and transistor radios, in other branches of technology, and as an adhesive in medicine for soft and osseous tissues. Cyanoacrylate adhesives proposed hitherto have been derived from cyanoacrylates of formula CH2=C(CN)COOR, where R is an alkyl group containing 1-16 carbon atoms, or a cyclohexyl, phenyl, alkoxyalkyl, or some other group. These adhesives do not require solvents or hardening catalysts. They also do not require heat or elevated pressures during adhesion The 2 - cyanoacrylates polymerize rapidly in the presence of small amounts of moisture normally present on the surfaces being adhered, and the resulting polymer layer is very strong and durable. However, hitherto proposed 2 - cyano- acrylate - based adhesives are not sufficiently heat-resistant for some applications, and this is a serious limiting factor on their range of uses. For example, when exposed to temperatures in excess of 100" C., the adhesive joints lose much of their strength. As a result, the hitherto proposed adhesives cannot be used where the joints produced therefrom are subjected to operating conditions at temperatures above 100" C. In order to obtain increased temperature durability, it has been proposed hitherto to mix alkyl esters of 2 - cyaneacrylic acid, for example ethyl 2 - cyansacrylate or mimlres o ethyl 2 - cyanoacrylate and methyl 2 - cyans acrylate, with various additives such as di acrylyl or di - methacrylyl ester of a diol, for example ethylene, diethylene, triethylene, terraethylene or polyethylene glycols, an unsaturated phosphonate such as bi (methacrylyl hydrwg ethyl) - ,x - phenylvinyl - phosphonate, or a cyanurate derivative such as, for example, tris (acrylylhydroxyethyl) cyanurate or tri ( meth-- acrylyl hydroxyglycerine)cyanurate, or with an acrylate or methacrylate of a polyol such as, for example, trimethylol propane trimethacrylate. Typically, from 0.5 to 20 per cent by weight of the additive is added, based on the 2 - cyanoacrylate (see U.S. Patent No. 3,692,752). Hitherto proposed adhesive com positions can also contain 0.06 wt.% of hydroquinone and 0.001 wt.% of sulphur dioxide as a stabilizing agent. These hitherto proposed additives have better heat-resistance than the purely cyanb acrylate adhesives. Thus, for example, a shear strength in the range of 80 to 135 kgf/sq.cm has been obtained for steel plates adhered together and heated to a temperature of 1500 C for 60 min.In view of the fact that iustru ments intended to be used at elevated tempi peratures are usually required to have a design temperature margin of the order of 10 or 20 per cent, these hitherto proposed adhesive compositions can be used to join surfaces to gether which are rmrmally exposed to teme peratures in the range from 100 to 1200 C There are certain applications, however, where adhesive joints are required to be strong at temperatures in excess of 1200 C. Furthermore, hitherto proposed cyanow acrylate-based adhesive compositions have low initial tear strengths at 200 C (e.g. 1501250 kgf/sq.cm.) 24 hours after being adhered. According to the present invention there is provided a cyanoacrylate adhesive composition comprising a cyanoacrylate and from 2 to 20 per cent by weight of a compound of formula: EMI2.1 [wherein R is a group of formula (CH2) (where n is 1--4), EMI2.2 (where R' is an alkyl group), (where R" and R"' are alkyl groups), or (CH2)2-O[ (CH2)2 -Ojm(CH2)2 (where m is 0-2)] based on the weight of the cyanoacrylate. Adhesive compositions in accordance with the invention can be used at temperatures irx excess of 1200 C. 2 - Cyaneacrylates can be polymized anionically. Bifunctional compounds of formula' I present when adhering surfaces with 2cyanoacrylates copolymerize with the 2cyanoacrylates under the effect of surface moisture to form three-dimensional cross- linked structures. The result is that the soten; ing temperature of the resulting joint is higher than for a joint formed from the cyanoacrylate alone, which indicates a rise in the heat-resis- tance of the joint. The compounds of formula I are preferably present in an amount of from 5 to 10 per cent by weight based on the weight of cyanoacrylate in the composition. A steel to steel adhesive joint produced using an adhesive composition in accordance with the invention was heated at a temperature of 1500 C for 60 minutes, and the tear strength was in the range from 240 to 320 kgf/sq.cm. At 1700 C., the tear strength was within the range of 120 to 250 kgf/sq.cm. Simultaneously, a high initial strength was achieved Thus, for example, after adhering at 200 C. for 24 hours, a tear strength of 250 to 300 kgf/sq.cm. was observed. Furthermore, cyanoacrylate adhesives modified by the presence of a compound of formula I are usually more resistant to organic solvents and to water than hitherto proposed cyan acrylate adhesives. We have not found the compounds of formula I to reduce the storability of 2 - cyans acrylate adhesives. The adhesives have been found to be stable for 6 months, like hitherto proposed cyanoacrylate adhesives. The setting times for adhesives which have been modified in accordance with the invention are generally in the range of from 5 to 125 seconds, depending on the kinds of materials being adhered. The production of an adhesive in accordance with the invention can be effected as follows:- A compound of formula I is added at the date of 2 to 20 wt.% to a cyanoacrylate adhesive, preferably containing a polymerizat tion inhibitor, and a stabilizer, and optionally a thickening agent and a plasticizer. The resultant mixture is agitated until a homogeneous colourless mobile composition is formed This is an adhesive composition in accordance with the invention, and it is ready for use. The compounds of formula I are cross- linking agents, and their effect depends upon the two end groups of the di-ester, namely the EMI2.3 groups. The viscosity of adhesive compositions in accordance with the invention can be varied by the addition of a thickening agent for example poly-methyl methacrylate, a polycyanoacrylate or poly-vinyl acetate. Various plasticizers can also be included in the compositions, for example dibutyl phthalate or triphenyl phosphate. Adhesive compositions in accordance with the invention can be stabilized with a variety of anionic Of radical polymerization inhibitors, such as, for example, sulphur dioxide or hydro- quinine. The compounds of formula I can be prepared by known methods (see U.S. Patent No. 3,316,227), for example by reacting acrolein with a dicyanoacetate of a diol in an organic solvent at a temperature of from 10 to 300 C, and in the presence of a catalyst The following Examples are given by way of illustration only:- Example 1. 5 gm of ethylene glycol di - 2 - cyanopenta2,4 - dienoate were added to 95 gm: of an ethyl 2 - cyanoacrylate adhesive containing 0.001 am of sulphur dioxide and 0.03 gm of hydroquinone. The resultant mixture was agitated to form a homogeneous colourless mobile adhesive composition. Example 2. An adhesive composition was prepared in a manner similar to that described in Example 1, except that 10 gm of diethylene glycol di2 - cyanopenta - 2,4 - dienoate were added to 90 gm of the ethyl - 2 - cyanoacrylate. Example 3. An adhesive composition was prepared in a manner similar to that described in Example 1, except that 5 gm of trimethylene glycol di2 - cyanopenta - 2,4 - dienoate were added to 95 gm of the ethyl 2 - cyanoacrylate. Example 4. An adhesive composition was prepared in a manner similar to that described in Example 1, except that 5 gin of the propylene 1,2- glycol di - 2 - cyanopenta - 2,4 - dienoate were added to 95 gm of the ethyl 2 - cyanoacrylate. Example 5. An adhesive composition was prepared in a manner similar to that described in Example 1, except that 5 gin of 2,2 - dimethyl - pro pylene - 1,3 - diol di - 2 - cyanopenta - 2,4 dienoate were added to 95 gm of the ethyl 2cyanoacrylate. Example 6. An adhesive composition was prepared in a manner similar to that described in Example 1, except that 10 gm of triethylene glycol di2 - cyanopenta - 2,4 - dienoate were added to 90 gm of the ethyl 2 - cyanoacrylate. Example 7. An adhesive composition was prepared in a manner similar to that described in Example 1, except that 5 gm of ethylene glycol di - 2 cyanopienta - 2,4 - dienoate were added to 95 gin of butyl 2 - cyanoacrylate. Example 8. An adhesive composition was prepared in a manner similar to that described in Example 1, except that 3 gin of a thickening agent [poly - (ethyl cyanoacrylate)], and 10 gin of diethylene glycol di - 2 - cyanopenta - 2,4 dienoate were added to 90 gin of the ethyl 2 - cyanoacrylate. Example 9. An adhesive composition was prepared in a manner similar to that described in Example 1, except that 5 gm of ethylene glycol di - 2 cyaropenta - 2,4 - dienoate were added to 95 gm of ethoixyethyl 2 - cyanoacrylate. The tear strengths of the various eaampli- fled adhesives at different temperatures are given in Tables 1 and 2. TABLE 1 EMI4.1 Tear yy Tear strength, kgf./sq.cm. Adhered Adhesives Materials 20 C. 100 C. 150 C. 170 C. 200 C. Example 1 steel-steel 300 420 320 250 100 Example 1 brass-brass 285 350 300 200 Example 2 steel-steel 260 300 240 170 90 Example 2 brass-brass 240 290 230 160 Example 3 steel-steel 240 300 340 220 92 Example 3 brass-brass- 220 260 290 190 Example 4 steel-steel 300 400 330 225 Example 5 steel-steel 275 350 310 230 Example 6 steel-steel 250 290 240 160 Example 7 steel-steel 270 320 240 120 Example 8 steel-steel 240 240 190 - - Example 9 steel-steel 220 250 280 - - ethylcyano acrylate steel-steel 190 140 100 30 0 Adhesive (for the sake of comparison) brass-brass 190 130 50 30 0 The tear strengths were determined by a known method in which glued specimens were left for 24 hours at room temperature, then heated for an hour to various temperatures (from 100 to 200 C), and thereafter cooled and tested for resistance to a uniform direct pull at room temperature. TABLE 2 EMI4.2 Tear strength, kgt/sq.cm. Adhered Adhesives Materials 80 C 100 C 120 C 150 C 170 C 200 C Example 1 steel-steel 300 270 250 170 60 20 Example 7 steel-steel 260 190 - 100 50 - The tear strengths were determined by a known method in which glued specimens were left for 24 hours at room temperature, then heated for an hour at various elevated temperatures, and thereafter tested for resistance to a uniform direct pull at the respective elevated temperatures. The stability of the adhesive composition in accordance with the invention produced in Example 1, to various liquids is illustrated in Table 3. TABLE 3 EMI5.1 Tear strength, kgf/sq.cm. Preheating the Without preheating specimen for Solvent the specimen 1 hour at 100 C Toluene 340 430 Acetone 280 240 Water 280 280 No Solvent 350 430 The tear strengths in Table 3 were determined in the following way: specimens glued together by the adhesive were left for 24 hours at room temperature. Thereafter, they were preheated for 1 hour at 1000 C., or not preheated, and immersed in various liquids for 24 hours at room tempeza- ture. They were then tested for resistance to a uniform direct pull at room temperature. WHAT WE CLAIM IS: 1. A cyanoacrylate adhesive composition comprising a cyanoacrylate and from 2 to 20 percent by weight of a compound of formula: EMI5.2 [wherein R is a group of formula (CH2)- (where n is 1-4), EMI5.3 (where R' is an alkyl group), (where R" and R"' are alkyl groups), or (CII2)2[(CH)2 -O-]-(CH2)2 (where mis 0-2)] based on the weight of the cyanoacrylate. 2. An adhesive composition as claimed in claim 1, which contains from 5 to 10 per cent by weight of the compound of formula I, based on the cyanoacrylate. 3. A cyanoacrylate adhesive composition as claimed in claim 1, substantially as herein described. 4. A cyanoacrylate adhesive composition as claimed in claim 1, substantially as herein des- cribed with reference to any of the Examples. **WARNING** end of DESC field may overlap start of CLMS **.