NL plans to spin off its chemical business.

NL Industries’ board approved the plan at the same time that it rejected as inadequate the $723-million takeover bid by Dallas financier Harold C. Simmons, who has launched a tender offer of $15.25 a share for NL. Simmons, who with affiliates already owns 20.4% of NL’s 60 million common shares outstanding, said he will seek a court ruling blocking NL’s spinoff plan. Simmons also said his tender offer for NL remains in place.