B767 CAPT REPORTS PLASTIC FUMES AND FAINT VIBRATION 90 MINUTES INTO FLIGHT. AT 2:30 INTO FLT VIBRATION RETURNS AND RECIRC FAN INOP LIGHT ILLUMINATES. FUMES RETURN MUCH STRONGER AND FLIGHT DIVERTS.

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I WAS THE CAPT WITH 2 FO'S. DURING FLT AT TKOF AND 1:30 A FLT ATTENDANT CALLED TO RPT A SMELL/FUME OF MELTING PLASTIC. SHORTLY AFTER THE CALL THE FO ON BREAK CALLED TO COME INTO THE COCKPIT TO RPT A VIBRATION IN BUSINESS CLASS WITH THE SAME MELTING PLASTIC SMELL. JUST PRIOR TO ALL OF THIS THE FO WHO WAS ACTING AS PF AND MYSELF NOTED A LOUD HUMMING NOISE IN THE RADOME AREA BUT NO SMELL OR FUMES. I DIRECTED THE FLT ATTENDANTS TO CHK THE GALLEY AREAS AND OVENS FOR ANY POSSIBLE SOURCES FOR THE SMELL. THE ORIGIN OF THE SMELL WAS INDISCERNIBLE AND WITHIN A FEW MINS HAD DISSIPATED WITH NO OTHER INDICATIONS. THE NOISE AND VIBRATION REMAINED WITH NO OTHER INDICATIONS OF ANYTHING ABNORMAL. THE OTHER PLTS AND I DISCUSSED ANY POSSIBLE DIFFERENCES BTWN THE B757 VERSUS B767 NORMAL NOISES AND COULDN'T ARRIVE AT A CONSENSUS OF ANY ACFT DIFFERENCES THAT COULD BE THE CAUSE. WITH NO SMELL REMAINING AND THE VIBRATION BECOMING VIRTUALLY NEGLIGIBLE AND NO OTHER INDICATIONS OF AN ABNORMALITY I ASKED THE OTHER PLTS AND THE FLT ATTENDANTS IF THEY HAD ANY CONCERNS WITH THE CONTINUATION OF THE FLT WITH THE FLT ATTENDANTS READ ON THE PAX AND THE CONSENSUS WAS TO PROCEED. THIS DECISION OCCURRED APPROX TKOF AND 2:00. AT TKOF AND 2:30 A MORE PRONOUNCED NOISE WITH VIBRATION OCCURRED IN THE RADOME AREA WITH AN INOP LIGHT ILLUMINATING IN THE L RECIRC FAN ACCOMPANIED WITH THE ASSOCIATED EICAS MESSAGE. THE FO AND I REFED AND ACCOMPLISHED THE QRH PROC FOR THE L RECIRC FAN INOP LIGHT EICAS WHICH REQUIRED NO ACTION BY THE CREW INFO ONLY. ALMOST SIMULTANEOUSLY WITH THE COMPLETION OF THE QRH PROC THE FLT ATTENDANTS CALLED TO RPT THE SMELL HAD RETURNED AND STATED THE SMELL WAS MUCH WORSE THAN BEFORE AND THAT IT HAD MORE OF AN ACRID; ELECTRICAL SMELL WHICH WAS THEN FOLLOWED WITH A HAZE FORMING IN THE AFT CABIN AND IT IS MOVING FORWARD. AT THIS POINT THE FO AND I DONNED OUR OXYGEN MASKS AND ESTABLISHED COMS IN THE COCKPIT. I DIRECTED HIM TO FLY AND HANDLE THE ATC COMS. THE RELIEF FO CALLED AND STATED THE VIBRATION WAS APPARENT IN BUSINESS CLASS AGAIN ONLY WORSE THAN BEFORE. I ASKED HER TO RETURN TO THE COCKPIT TO ASSIST IN THE SITUATION. AT THIS TIME WE REQUESTED RADAR VECTORS TO TURN AWAY FROM NAT. THE FO AS PF CONTINUED WHILE THE RELIEF FO AND I ACCOMPLISHED THE SMOKE OR FIRE OR FUMES CHKLIST IN THE QRH WHILE SIMULTANEOUSLY COORDINATING WITH THE DISPATCHER VIA ACARS FOR A DIVERT TO THE NEAREST SUITABLE AIRFIELD FOR THE SITUATION WE WERE IN. FROM THE GEOGRAPHIC POS WE WERE AT; ZZZZ WAS THE NEAREST SUITABLE AIRFIELD WITH THE SITUATION AT THAT POINT WORSENING WITH THE HAZE INCREASING AS RPTED BY THE FLT ATTENDANT IN THE AFT CABIN. AS WE WERE ACCOMPLISHING THE QRH PROC FOR SMOKE OR FIRE OR FUMES AND IN THE DSCNT; THE FLT ATTENDANT ADDITIONALLY RPTED A WORSENING OF THE SMELL IN THE CABIN. ONLY AFTER THE QRH STEP TO TURN OFF THE L RECIRCULATION FAN SWITCH DID THE FLT ATTENDANT RPT THAT IT SEEMED TO BE IMPROVING BUT WAS STILL PRESENT. I HAD THE FO CONTINUE AS THE PF WHILE THE RELIEF FO AND I COMPLETED THE QRH TO THE POINT THAT THE FLT ATTENDANT SAID THE HAZE WAS STARTING TO LESSEN AND THE SMELL WAS DIMINISHING. AT APPROX 18000 FT THE SMELL WAS NO LONGER EVIDENT IN THE COCKPIT AND WE ALL REMOVED THE OXYGEN MASKS. WE DECLARED AN EMER AND CONTINUED THE DSCNT AND LNDG WITH ACCOMPLISHMENT OF ALL NORMAL CHKLISTS. AFTER CONSULTING THE QRH; I ELECTED TO NOT DUMP FUEL SO THAT WE COULD LAND AS SOON AS POSSIBLE. I HAD THE FO ACCOMPLISH THE DSCNT; APCH AND LNDG VIA A VISUAL APCH TO RWY XX. REF TO THE ACFT'S LNDG DISTANCE CHART INDICATED A LNDG DISTANCE OF 5400 FT. WE CONDUCTED THE VISUAL APCH TO RWY XX WITH THE BC/LOC AS A BACK UP AS THE LONGER RWY WAS CLOSED. I CONDUCTED THE PM DUTIES AND CONTINUED TO MONITOR THE SITUATION IN THE CABIN WITH THE RELIEF FO AND THE LEAD FLT ATTENDANT AS WELL AS COORDINATE WITH THE TWR AND EMER PERSONNEL FOR THE POST LNDG INSPECTION. LNDG WAS UNEVENTFUL. AFTERWARD; FO NOTED THAT IT WAS DIFFICULT TO COMMUNICATE WHILE WEARING THE OXYGEN MASK. THERE IS ONLY LISTENING CAPABILITY AT THIS JUMPSEAT; WITH NO PLACE TO PLUG IN THE MIKE CORD. THIS MEANS THE RELIEF PLT HAS NO WAY TO COMMUNICATE WITH OTHER PLTS; FLT ATTENDANTS; OR OUTSIDE AGENCIES WITHOUT REMOVING THE OXYGEN MASK FIRST AND FROM THE OTHER JUMPSEAT IT IS DIFFICULT TO SEE THE PANELS OR OUT THE WINDOWS; AND NEARLY IMPOSSIBLE TO REACH THE INTERPHONE HANDSET.