Patent ID: 8826636

Claim:
A multifilament aramid yarn which has been subjected to a process of heating the yarn in at least two process steps, the process of heating comprising: in a first step, heating the yarn at a temperature of from 200 to 360° C. at a tension of at least 0.2 cN/dtex; and then in a second step, heating the yarn at a temperature of from 370 to 500° C. at a tension of less than 1 cN/dtex, wherein the tension in the first process step is higher than the tension in the second process step, wherein the heat processed multifilamaent aramid yarn: has a tenacity of at least 2500 mN/tex and a sulfur content of at least 0.1 wt %; and comprises a copolymer obtained from a mixture of monomers comprising DAPBI, an aromatic para-diamine, and an aromatic para-diacid, wherein at least 12.5 mole % of the monomers is DAPBI, and less than 20 mole % of the monomers is Cl-PPD.