Ethylene resin packaging films

Abstract

The present invention provides a packaging film which exhibits excellent mechanical strength properties such as high dart impact strength with retaining properties of transparency and film surface smoothness. The ethylene resin packaging film comprises an ethylene/α-olefin copolymer having the following properties: the density is in the range of 0.918 to 0.935 g/cm 3 ; the melt flow rate (MFR) at 190° C. under a load of 2.16 kg is in the range of 0.05 to 1.0 g/10 min; the decane-soluble component fraction (W) at room temperature and the density (d) satisfy the relation W<80×exp(−100(d−0.88))+0.1; the flow index (FI), which is defined as a shear rate at which the shear stress of said copolymer in a molten state at 190° C. reaches 2.4×10 6 dyne/cm 2 , and MFR satisfy the relation FI>75×MFR; and the melt tension (MT) at 190° C. and MFR satisfy the relation MT>2.2×MFR −0.84 .

What is claimed is:  
     
         1 . An ethylene resin packaging film comprising an ethylene/α-olefin copolymer (A) which is a copolymer obtained by copolymerizing ethylene and an α-olefin of 6 to 20 carbon atoms in the presence of an olefin polymerization catalyst comprising (a) a compound of a transition metal of Group IV of the periodic table, said compound (a) containing a ligand having cyclopentadienyl skeleton, and (b) an organoaluminum oxy-compound, and which has the following properties: 
 (i) the density is in the range of 0.918 to 0.935 g/cm 3 ,  
 (ii) the melt flow rate (MFR (g/10 min)) at 190° C. under a load of 2.16 kg is in the range of 0.05 to 2.0 g/10 min,  
 (iii) the decane-soluble component fraction (W (% by weight) at room temperature and the density (d (g/cm 3 )) satisfy the following relation  
   W< 80 ×exp (−100( d− 0.88))+0.1,  
 (iv) the flow index (FI (l/sec)), which is defined as a shear rate at which the shear stress of said copolymer in a molten state at 190° C. reaches 2.4×10 6  dyne/cm 2 , and the melt flow rate (MFR (g/10 min)) satisfy the following relation  
   FI> 75 ×MFR , and  
 (v) the melt tension (MT (g)) at 190° C. and the melt flow rate (MFR (g/10 min)) satisfy the following relation  
   MT> 2.2 ×MFR   −0.84 .  
 
     
     
         2 . The ethylene resin packaging film as claimed in  claim 1 , wherein the ethylene/α-olefin copolymer (A) further has the following property: 
 the mean value (B1) of the numbers of branches on the higher molecular weight side, as determined by GPC-IR, and the mean value (B2) of the numbers of branches on the lower molecular weight side, as determined by GPC-IR, satisfy the following relation  
 B1≧B2.  
 
     
     
         3 . An ethylene resin packaging film comprising an ethylene/α-olefin copolymer composition (B) which comprises: 
 (I) 50 to 99 parts by weight of an ethylene/α-olefin copolymer (a-1), and  
 (II) 1 to 50 parts by weight of high-density polyethylene (b-1),  
 wherein the ethylene/α-olefin copolymer (a-1) is a copolymer obtained by copolymerizing ethylene and an α-olefin of 6 to 20 carbon atoms in the presence of an olefin polymerization catalyst comprising (a) a compound of a transition metal of Group IV of the periodic table, said compound (a) containing a ligand having cyclopentadienyl skeleton, and (b) an organoaluminum oxy-compound, and has the following properties: 
 (i) the density is in the range of 0.900 to 0.935 g/cm 3 ,  
 (ii) the melt flow rate (MFR (g/10 min)) at 190° C. under a load of 2.16 kg is in the range of 0.01 to 1.0 g/10 min,  
 (iii) the decane-soluble component fraction (W (% by weight)) at room temperature and the density (d (g/cm 3 )) satisfy the following relation  
   W< 80 ×exp (−100( d− 0.88))+0.1,  
 (iv) the flow index (FI (l/sec)), which is defined as a shear rate at which the shear stress of said copolymer in a molten state at 190° C. reaches 2.4×10 6  dyne/cm 2 , and the melt flow rate (MFR (g/10 min)) satisfy the following relation  
   FI> 75 ×MFR,    
 (v) the melt tension (MT (g)) at 190° C. and the melt flow rate (MFR (g/10 min)) satisfy the following relation  
   MT> 2.2 ×MFR   −0.84 , and  
 (vi) the temperature (Tm (° C.)) at the maximum peak position in an endothermic curve of said copolymer (a-1), as measured by a differential scanning calorimeter (DSC), and the density (d) satisfy the following relation  
   Tm< 400 d− 250;  
 and  
 the high-density polyethylene (b-1) is ethylene homopolymer or ethylene/α-olefin copolymer obtained by copolymerizing ethylene and an α-olefin of 3 to 20 carbon atoms, which has the following properties: 
 (i) the density is in the range of 0.935 to 0.975 g/cm 3 , and  
 (ii) the melt flow rate (MFR (g/10 min)) at 190° C. under a load of 2.16 kg is in the range of 0.1 to 100 g/min.  
 
 
 
     
     
         4 . The ethylene resin packaging film as claimed in any one of  claims 1  to  3 , which has: 
 (A) a Young's modulus of not less than 4,000 kg/cm 2 , and  
 (B) a dart impact strength of not less than 55 kg/cm.  
 
     
     
         5 . An ethylene resin packaging film comprising an ethylene/α-olefin copolymer composition (C) which comprises: 
 (I) 1 to 50 parts by weight of an ethylene/α-olefin copolymer (a-2), and  
 (II) 50 to 99 parts by weight of an ethylene copolymer (b-2),  
 wherein the ethylene/α-olefin copolymer (a-2) is a copolymer obtained by copolymerizing ethylene and an α-olefin of 4 to 12 carbon atoms in the presence of an olefin polymerization catalyst comprising (a) a compound of a transition metal of Group IV of the periodic table, said compound (a) containing a ligand having cyclopentadienyl skeleton, and (b) an organoaluminum oxy-compound, and has the following properties:  
 (i) the density is in the range of 0.880 to 0.925 g/cm 3 ,  
 (ii) the melt flow rate (MFR (g/10 min)) at 190° C. under a load of 2.16 kg is in the range of 0.01 to 5.0 g/10 min,  
 (iii) the decane-soluble component fraction (W (% by weight)) at room temperature and the density (d (g/cm 3 )) satisfy the following relation  
   W< 80 ×exp (−100( d− 0.88))+0.1,  
 (iv) the flow index (FI (l/sec)), which is defined as a shear rate at which the shear stress of said copolymer in a molten state at 190° C. reaches 2.4×10 6  dyne/cm 2 , and the melt flow rate (MFR (g/10 min)) satisfy the following relation  
   FI> 75 ×MFR,  and  
 (v) the melt tension (MT (g)) at 190° C. and the melt flow rate (MFR (g/10 min)) satisfy the following relation  
   MT> 2.2 ×MFR   −0.84 ;  
 and  
 the ethylene copolymer (b-2) is a copolymer obtained by copolymerizing ethylene and an α-olefin of 4 to 10 carbon atoms and has the following properties:  
 (i) the density is in the range of 0.920 to 0.945 g/cm 3 ,  
 (ii) the melt flow rate (MFR (g/10 min)) at 190° C. under a load of 2.16 kg is in the range of 0.1 to 10 g/10 min, and  
 (iii) the ratio of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn), Mw/Mn, is in the range of 3 to 6.  
 
     
     
         6 . The ethylene resin packaging film as claimed in  claim 5 , which has: 
 (B) a dart impact strength of not less than 250 kg/cm, and    (C) an Elmendorf tear strength of not less than 60 kg/cm in the machine direction.