US 3449476 A
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U.S. Cl. 26428 Claim ABSTRACT OF THE DISCLOSURE The process for treating fibres produced from acrylonitrile polymers which contain from 85 to 97 percent by weight of acrylonitrile which comprises stretching the fibres to at least 5 times their initial length and quenching them immediately thereafter by bringing them to a temperature between about 30 C. and about 0 C. preferably in water. It is particularly preferred that the fibres are brought to a temperature of less than C.
This invention relates to the treatment of fibres produced from acrylonitrile polymers, and in particular to the treatment of fibres produced from acrylonitrile polymers containing from 85 percent to 97 percent by weight of acrylonitrile units.
Fibres produced from acrylonitrile polymers are stretched after spinning, and are commonly washed after stretching and subsequently dried. Irregularities in physical properties of the resulting fibres are sometimes noted, and there is some tendency to fibrillation, particularly with fibres of heavy denier, such as those larger than denier for example, and with the fibres which have been spun from polymer compositions containing certain additives including some flame-retarding additives.
According to this invention, a process for the treatment of fibres produced from acrylonitrile polymers containing from 85 percent to 97 percent by weight of acrylonitrile units comprises stretching the fibres in steam, and quenching the fibres immediately thereafter in a cooling bath at a temperature not greater than 30 C.
In the process of the invention, the fibres may be stretched in steam by conventional methods, for example in tubes fed with direct steam between rollers rotating at different speeds, and are preferably stretched to not less than five times their original length. After leaving the stretching tubes they are quenched immediately, i.e., with the minimum practicable delay, in a cooling bath at less than 30 C. The cooling bath preferably contains water, which may without disadvantage contain some dissolved alkali metal thiocyanate, through which the fibres are conducted, but it is also possible to quench the fibres by spraying water or other coolant on to them. Quenching may with advantage take place at lower temperatures than 30 C., and it may be found that the best results are United States Patent 0 obtained below 10 C., although it is not normally necessary to employ temperatures lower than 0 C.
It may be desired to wash the fibres after quenching, for example at 40 to 50 C. in water, whereafter they may be dried and subjected to further processing as desired.
The invention is illustrated by the following examples:
Example 1 An acrylonitrile copolymer containing 93 percent by weight of acrylonitrile units in solution in aqueous sodium thiocyanate was spun into fibres by coagulation with dilute aqueous sodium thiocyanate. The resulting fibres were stretched to eight times their initial length in steam between rollers, and were passed into a bath containing distilled water at 8 C., immediately upon leaving the last roller. They were then washed until they were substantially free from thiocyanate and dried. The fibres had a substantially uniform shrinkage of approximately 10 percent and showed no observable fibrillation either initially or on subsequent processing.
Example 2 A similar copolymer was spun and coagulated as in Example 1, and the fibres produced were stretched in steam to eight times their initial length, whereupon they were passed through a quenching spray of dilute sodium thiocyanate at 10 C., so that the temperature of the fibres was reduced to below 30 C. The resulting fibres, after drying, had similar properties to those produced by the process of Example 1.
1. In a process for the production of fibers from acrylonitrile polymers in which a polymer containing from to 97 percent by weight of acrylonitrile units is spun into an aqueous coagulating bath to form filaments, the improvement which consists essentially in removing said filaments from the bath, stretching said filaments in steam by at least 5 times their original length and immediately thereafter quenching the filaments by contact with a liquid bath consisting essentially of water, said liquid bath having a temperature between about 0 and 10 C., thereby to suppress the tendency of said filaments to fibrillate.
References Cited UNITED STATES PATENTS 2,558,731 7/1951 Cresswell 264-182 3,097,054 7/ 1963 Routson et a1. 264-182 FOREIGN PATENTS 887,008 l/1962 Great Britain.
JULIUS FROME, Primary Examiner. HERBERT M'INTZ, Assistant Examiner.
US. Cl. X.R.