The 3M Co. on Friday said it has acquired 52 percent of Cogent Inc. shares, but extended its tender offer as some of Cogent’s largest shareholders continue to hold out.

3M subsidiary Ventura Acquisition Corp. completed its $10.50-per-share cash tender offer for the Pasadena tech company with 46.4 million shares received by the end of the Thursday deadline. St. Paul, Minn.-based 3M extended the same offer until Oct. 22.

Cogent’s founder and chief executive, Ming Hsieh, tendered his nearly 39 percent stake in the company, which develops fingerprint identification systems. Three of Cogent’s largest shareholders did not tender, saying Cogent should have entertained other bids.

“When you get a 38 percent head start and you can barely make it past the halfway point, that’s not good,” Louis Meyer, an arbitrage expert with Oscar Gruss & Son, told Bloomberg News.

Even so, a Delaware judge on Tuesday against ruled against shareholders who favored a $12-a-share bid from NEC Corp., which Cogent said was not a firm offer and posed more anti-trust issues than 3M’s bid.

Cogent shares were down 5 cents, or less than a percent, to $10.49 in midday trading on the Nasdaq.