Partly crystalline propylene polymerisate composition for production of biaxial-stretched polypropylene films

Abstract

The present invention relates to a semicrystalline propylene polymer composition prepared by polymerizing propylene, ethylene and/or C 4 -C 18 -1-alkenes, where at least 50 mol % of the monomer units present stem from the polymerization of propylene and at least 20% by weight of the propylene polymer composition is the result of a polymerization using metallocene catalysts, with a melting point TM of from 65 to 170° C., where the semicrystalline propylene polymer composition can be broken down into from 65 to 85% by weight of a principal component A, from 10 to 35% by weight of an ancillary component B and from 0 to 25% by weight of an ancillary component C, and where the proportions of components A, B and C are determined by carrying out TREF (temperature rising elution fractionation) in which that fraction of the propylene polymer composition which is soluble in xylene at (T M /2)+7.5° C. is firstly dissolved and separated off and then, as the temperature rises, at all of the higher temperatures 70° C., 75° C., 80° C., 85° C., 90° C., 94° C., 98° C., 102° C., 107° C., 112° C., 117° C., 122° C. and 125° C., the fractions soluble within the temperature range between this elution temperature and the preceding elution temperature are eluted, and the principal component A is formed by all of the fractions which are eluted at above (T M /2)+7.5° C. and have an average molar mass M N [sic] (number average)≧120,000 g/mol, the ancillary component B is formed by the fraction which is eluted at (T M /2)+7.5° C., and the ancillary component C is formed by all of the fractions which are eluted at above (T M /2)+7.5° C. and have an average molar mass M n (number average)<120,000 g/mol. A process for preparing the semicrystalline propylene polymer composition is also described, as are the use of the semicrystalline propylene polymer composition for producing films, fibers or moldings, and the films, fibers and moldings made from this composition.

We claim:  
     
         1 . A semicrystalline propylene polymer composition obtainable by polymerizing propylene, ethylene and/or C 4 -C 18 -1-alkenes using metallocene catalysts, where at least 50 mol % of the resultant monomer units stem from the polymerization of propylene, 
 with a melting point T M  of from 65 to 170° C.,    where the melting point T M  is measured in ° C. by differential scanning calorimetry (DSC) to ISO 3146 by heating a previously melted specimen at a heating rate of 20° C./min, and is the maximum of the resultant curve,    where the semicrystalline propylene polymer composition can be broken down into    from 65 to 85% by weight of a principal component A,    from 10 to 35% by weight of an ancillary component B and    from 0 to 25% by weight of an ancillary component C,    where the proportions of components A, B and C are determined by carrying out TREF (temperature rising elution fractionation) in which the polymers are firstly dissolved in boiling xylene and the solution is then cooled at a cooling rate of 10° C./h to 25° C., and then, as the temperature rises, that fraction of the propylene polymer composition which is soluble in xylene at (T M /2)+7.5° C. is firstly dissolved and separated off from the remaining solid, and then, as the temperature rises, at all of the higher temperatures 70° C., 75° C., 80° C., 85° C., 90° C., 94° C., 98° C., 102° C., 107° C., 112° C., 117° C., 122° C. and 125° C., the fractions soluble within the temperature range between this elution temperature and the preceding elution temperature are eluted, and the fractions taken into consideration during the evaluation which follows are those whose proportion by weight is at least 1% by weight of the initial weight of the propylene polymer composition, and gel permeation chromatography (GPC) at 145° C. in 1,2,4-trichlorobenzene is used to measure the molar mass distribution of all of the fractions to be taken into consideration,    and the principal component A is formed by all of the fractions which are to be taken into consideration and are eluted at above (T M /2)+7.5° C. and have an average molar mass M N  (number average)≧120,000 g/mol,    the ancillary component B is formed by the fraction which is eluted at (T M /2)+7.5° C., and    the ancillary component C is formed by all of the fractions which are to be taken into consideration and are eluted at above (T M /2)+7.5° C. and have an average molar mass MN (number average)<120,000 g/mol.    
     
     
         2 . A semicrystalline propylene polymer composition as claimed in  claim 1 , where at least 85 mol % of the monomer units present stem from polymerization of propylene.  
     
     
         3 . A semicrystalline propylene polymer composition as claimed in  claim 1  or  2 , which was prepared by homopolymerization of propylene or by copolymerization of propylene and ethylene.  
     
     
         4 . A semicrystalline propylene polymer composition as claimed in any of  claims 1  to  3 , where the metallocene used comprised at least one compound selected from the group consisting of 
 dimethylsilanediylbis(2-methylindenyl)zirconium dichloride,  
 dimethylsilanediylbis(2-methylbenz[e]indenyl)]zirconium dichloride,  
 dimethylsilanediylbis(2-methyl-4-phenylindenyl)zirconium dichloride,  
 dimethylsilanediylbis(2-methyl-4[4′-tert-butylphenyl]-indenyl)zirconium dichloride,  
 dimethylsilanediylbis(2-ethyl-4[4′-tert-butylphenyl]-indenyl)zirconium dichloride,  
 dimethylsilanediylbis(2-propyl-4[4′-tert-butylphenyl]-indenyl)zirconium dichloride and  
 dimethylsilanediyl(2-isopropyl-4[4′-tert-butylphenyl]-indenyl)(2-methyl-4[4′-tert-butylphenyl]indenyl)-zirconium dichloride.  
 
     
     
         5 . A semicrystalline propylene polymer composition as claimed in any of  claims 1  to  4 , where the melting point T M  is from 135 to 165° C.  
     
     
         6 . A process for preparing the semicrystalline propylene polymer composition as claimed in any of  claims 1  to  5 , which comprises using a catalyst system comprising at least two metallocene compounds and polymerizing in a single reactor.  
     
     
         7 . A process for preparing the semicrystalline propylene polymer composition as claimed in any of  claims 1  to  5 , which comprises using a catalyst system with only one metallocene compound and polymerizing in a reactor cascade composed of at least two reactors.  
     
     
         8 . The use of the semicrystalline propylene polymer composition as claimed in any of  claims 1  to  5  for producing films, fibers or moldings.  
     
     
         9 . A film, a fiber or a molding comprising a semicrystalline propylene polymer composition as claimed in any of  claims 1  to  5 .  
     
     
         10 . A biaxially stretched film made from the semicrystalline propylene polymer composition as claimed in any of  claims 1  to  5  and having a longitudinal stretching ratio of at least 1:3 and a transverse stretching ratio of at least 1:5.