Wikipedia:

Following the sale of One Times Square by the Times, the zipper was operated on an inconsistent basis by various news outlets, and was shut off entirely between 1961 to 1965, and 1977 to 1986.

It was a mean, needless renovation - in retrospect. At the time it was no doubt a sign of revitalization. Allied Chemical no longer exists under that name - the firm, founded in 1920, eventually bought Minneapolis-originated Honeywell and took its name.