PAPERBOARD PLANS BID TO ACQUIRE BELKIN <Paperboard Industries Corp> said it planned to make an unconditional 21 dlr a share cash offer for <Belkin Inc>'s 7.6 mln common and 2.3 mln non-voting shares. Paperboard said Balaclava Enterprises Ltd, owned by Morris Belkin, agreed to tender 98.2 pct of Belkin's common shares. It added that in case of a competing offer of more than 23 dlrs, it had the right to match it. If it did not match the offer, Balaclava could accept the competing bid. The two companies manufacture linerboard and boxboard from recycled fibre. Their combined revenues are about 500 mln dlrs.