Improvements in and relating to the bonding of rubber to viscose rayon yarns

In the production of viscose rayon yarns having an improved adhesion to rubber, a main viscose stream is delivered to a spinning machine comprising a number of jets immersed in an aqueous coagulating bath and supplied with individual viscose streams branching off from the main stream, and there is injected into the main stream, just before it reaches the spinning machine, an aqueous caustic soda solution of an incompletely condensed heat-hardenable resorcinol-formaldehyde resin having a resorcinol/formaldehyde molar ratio of 1:1:3-3.5 and a resorcinol/caustic soda molar ratio of 1:1.0-3.5. The resin content of the solution is preferably 5-15 per cent. by weight and that of the finished yarn 0.5-3 per cent. by weight based on the dry weight of the yarn. When the injector unit and/or the feed pipes associated therewith are made of iron or of a ferrous alloy subject to corrosion in contact with viscose, the resorcinol/caustic soda molar ratio should be 1:1.5-3.5, to prevent gelling of the viscose-resin solution mixture. In an example, resorcinol is dissolved in an aqueous solution of sodium hydroxide and a 37 per cent. aqueous solution of formaldehyde is added (with cooling) to give a solution containing 9 per cent. of resorcinol, 3.68 of formaldehyde, and 6.56 of sodium hydroxide. After standing for 8 hours at 20 DEG C. the solution is injected as described in Specification 290,693, [Class 15 (ii)], into a stream of a mature viscose containing 7.4 per cent. cellulose and 6.5 sodium hydroxide as it is being delivered to a spinning machine, and the mixture is extruded to form threads, which are then stretched as described in Specification 467,500. The yarn is washed free from acid but not given an alkaline desulphurizing treatment. The injection ratio of resin solution to viscose is 1:99, giving about 1.5 per cent. resin on the dry weight of the yarn. The yarn is more flexible than yarn treated with similar resinous compositions after it has been spun. Specifications 477,380 and 582,210 also are referred to.