AN EMB145 FLT CREW FAILED TO RETRIEVE THEIR CLRNC UNTIL AFTER TKOF.

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I REQUESTED A PDC CLRNC FROM THE ACARS SYS FOR A FLT FROM ORD TO MEM. I REQUESTED THE CLRNC ABOUT 2 MINS EARLIER THAN THE USUAL 30 MINS PRIOR TO DEP TIME. RECEIVED MESSAGE BACK THAT THE CLRNC WAS NOT AVAILABLE AND TO CONTACT CLRNC VIA VOICE. SINCE I WAS TOO EARLY FOR THE REQUEST I DELAYED AND THOUGHT I WOULD REQUEST IT AGAIN VIA THE ACARS SYS CLOSER TO DEP TIME. WE THEN PROCEEDED TO TAXI FOR DEP AND WE NEVER RECEIVED THE CLRNC. WE PROCEEDED TO TAKE OFF. ON THE INITIAL CLB; TWR TOLD US TO RESET OUR XPONDER TO THE CORRECT CODE. WE ENTERED THE CORRECT CODE AND THEN VECTORED AND CLRED TO OUR FIRST FIX. AFTER REACHING A NON-STERILE ALT I PROCEEDED TO LOOK FOR THE PRINTED COPY OF THE CLRNC AND THAT IS WHEN IT OCCURRED TO ME THAT I NEVER RECEIVED THE CLRNC. I NOTIFIED THE CAPT WHO ASKED THE DEP CTL TO VERIFY OUR CLRNC; WHICH; WAS AS FILED BY DISPATCH. CONTRIBUTING FACTORS: NEW SECURITY PROCS HAD PUT AN EXCESS LOAD ON ALL EMPLOYEES. BOTH THE GATE AGENT AND NEW FLT ATTENDANT WERE COMING TO THE COCKPIT WITH THEIR VARIOUS QUESTIONS WHILE THE CAPT HAD TO LEAVE THE COCKPIT TO VERIFY SECURITY CLRNC WITH DISPATCH VIA THE TELEPHONE. CORRECTIVE ACTIONS: I NOW RESET THE XPONDER TO SQUAWK 1200 AS PART OF MY PREFLT FLOW AS AN INDICATOR THAT I HAVE NOT RECEIVED A CLRNC. SO WHEN I SET THE XPONDER TO TA/RA ON THE BEFORE TKOF CHKLIST I WILL NOTICE THE CODE WAS NOT ENTERED AND THE CLRNC WAS NOT RECEIVED BEFORE LEAVING THE GND.