Multi-layer blown film
A multi-layer blown polymer film comprising a core layer (CL) and at least one sealing layer (SL), said sealing layer(s) (SL) comprise(s) a propylene copolymer composition (P) having a comonomer content in the range of 3.0 to 8.0 wt.-%, the comonomers are C 5 to C 12 α-olefins, said propylene copolymer composition (P) comprises a polypropylene (A) and a polypropylene (B) in the weight ratio [(A)/(B)] of 20/80 to 80/20, wherein said polypropylene (A) has a comonomer content of equal or below 4.0 wt.-%, the comonomers are C 5 to C 12 α-olefins, and said propylene copolymer (B) has a comonomer content of 4.0 to 20.0 wt.-%, the comonomers are C 5 to C 12 α-olefins.
1. Process for producing a multi-layer blown polymer film comprising: providing a core layer (CL) being selected from the group consisting of polyvinyl alcohols, polyacrylates, polyamides, poly(ethylene terephthalate), polyolefins (PO) and mixtures thereof, a sealing layer (SL), and optionally an outer (OL), a further sealing layer (SL) or a metal layer (ML) wherein:
(a) the core layer (CL),
(a1) is coated on the one side with a propylene copolymer composition (P) obtaining a sealing layer (SL) and
(a2) optionally
(a2-i) is on the other side coated with a polyolefin (PO) obtaining an outer layer (OL), or
(a2-ii) is on the other side coated with a propylene copolymer composition (P) obtaining a second sealing layer (SL), or
(a2-iii) is on the other side metallized obtaining a metal layer (ML), wherein
(b) said propylene copolymer composition (P)
(b1) has a comonomer content in the range of 3.0 to 8.0 wt. %, the comonomer is C6 α-olefin,
(b2) comprises a polypropylene (A) and a polypropylene (B) in the weight ratio [(A)/(B)] of 35/65 to 50/50, wherein said polypropylene (A) is a propylene homopolymer (H-PP) or a propylene copolymer (C-A) having a comonomer content of below 4.0 wt. %, the comonomer is C6 α-olefin, said propylene copolymer (B) has a comonomer content of 4.0 to 20.0 wt. %, the comonomer is C6 α-olefin,
(b3) fulfills the ratio
MFR ( A )/MFR ( P )≤1.0
wherein MFR (A) is the melt flow rate MFR2 (230° C.) [g/10 min] measured according to ISO 1133 of the polypropylene (A), MFR (P) is the melt flow rate MFR2 (230° C.) [g/10 min] measured according to ISO 1133 of the propylene copolymer composition (P),
(b4) has a xylene soluble content (XCS) determined at 25° C. according to ISO 16152 of below 16.0 wt. %,
(b5) has a melting temperature Tm determined by differential scanning calorimetry (DSC) of at least 135° C.,
(b6) has a heat sealing initiation temperature (SIT) of equal or below 115° C.,
(b7) is free of any elastomeric polymer component, and wherein the film is not subjected to a stretching step,
and coextruding the polymer layers on a blown film line.
2. Process according to claim 1 , wherein the melts of the polymer for the core layer (CL), of the propylene copolymer composition (P) for the sealing layer (SL) and optionally of the polymer for the outer layer (OL) or for a further sealing layer (SL) are extruded through an annular die and blown into a tubular film by forming a bubble which is collapsed between nip rollers after solidification.
3. Process according to claim 1 , wherein the blown coextrusion is effected at a temperature in the range 160 to 240° C., and cooled by water or by blowing gas at a temperature of 10 to 50° C. to provide a frost line height of 0.5 to 8 times the diameter of the die.
4. Process according to claim 1 , wherein the blow up ratio is in the range from 1.5 to 4.
5. Process according to claim 1 , wherein the multi-layer film is corona-treated or flame-treated.
6. Process according to claim 1 , wherein the corona treatment or flame treatment is carried out by passing the film between two conductor elements serving as electrodes with high voltage.
7. Process according to claim 1 , wherein the corona treatment or flame treatment is carried out by passing the film between two conductor elements serving as electrodes with a high alternating voltage of about 10000 V and 10000 Hz.