| 摘要 |
<p>THE INVENTION RELATES TO A POLYMER COMPRISING UNITS DERIVED FROM ETHYLENE, SAID POLYMER HAVING: A) A MELT INDEX OF FROM 0.05 TO 20 G/10 MIN AS DETERMINED BY ASTM-1238 CONDITION E; B) AT LEAST 10 PER 1000 C-ATOMS OF SHORT CHAIN BRANCHES, CONTAINING FIVE CARBON ATOMS OR LESS, AS DETERMINED BY C13 NMR, AND LESS THAN 3.5 MOL %, OF UNITS DERIVED FROM A COPOLYMERIZABLE ETHYLENICALLY UNSATURATED ESTER, C) A DENSITY OF FROM 0.90 TO 0.94 G/CM3, PREFERABLY 0.91 TO 0.935 G/CM3, ESPECIALLY 0.92 TO 0.93 G/CM3 AS DETERMINED BY ASTM D1505, AND D) A RELAXATION TIME AS DESCRIBED HEREIN OF AT LEAST 10 S. SUCH POLYMERS ARE OBTAINABLE BY POLYMERIZATION BY FREE RADICAL POLYMERIZATION USING A CHAIN TRANSFER AGENT THAT INCORPORATES INTO THE POLYMER CHAIN SUCH AS AN ALPHA-OLEFIN, PREFERABLY PROPYLENE, AS A CHAIN TRANSFER AGENT, PREFERABLY IN A TUBULAR REACTOR UNDER CIRCUN1STANCES TO FAVOR LCB FORMATION IN A DOWN STREAM PART OF THE TUBULAR REACTOR. THE POLYMER MAY BE USED FOR STRETCH HOOD FILM, PREFERABLY AS A BLOWN FILM COEXTRUDED TUBE COMPRISING: A) A CORE OF THE ABOVE POLYMER; AND B) A SKIN LAYER, ON EACH SIDE OF THE CORE WHICH MAY BE OF THE SAME OR DIFFERENT COMPOSITION, COMPRISING AT LEAST 60 WT % OF AN LLDPE HAVING DENSITY OF 0.91 TO 0.94 G/CM3 AS DETERMINED BY ASTM-D 1238 CONDITION E AND HEXANE EXTRACTABLES LESS THAN 1.5 WT %, SAID SKIN LAYER CONTAINING LESS THAN 7500 PPM OF ANTI-BLOCK PARTICULATES AND SAID FILM HAVING AN ELASTIC RECOVERY AFTER A 100 % STRETCH OF AT LEAST 40 % AND PROVIDING A NORMALIZED / HOLDING FORCE PER 100 UM THICKNESS PRE-STRETCH AT 85 % STRETCH AFTER AN INITIAL STRETCH OF 100 % OF AT LEAST 20 N/50 MM AT A DEFORMATION RATE OF LESS THAN 10 % OF THE STARTING LENGTH PER SECOND.</p> |
