Process for producing a polymer composition

A process for producing a polymer composition comprising

• (A) a non-elastomeric polyethylene,
• (B) an elastomer, which is selected from copolymers of ethylene with polar comonomer units, polyolefin plastomers, polyolefin elastomers, olefin block copolymers or mixtures thereof, and
• (C) an acid grafting agent, comprising the steps of:
• feeding components (A), (B) and (C) into an extruder comprising a feeding section, a barrel section and a die plate, wherein the barrel section of the extruder downstream of the feeding section and upstream of the die plate is divided into a plurality of control zones, and the first control zone represents the first control zone within the barrel section downstream of the feeding zone in which the fed component(s) (A) and/or (B) start(s) to melt;
• compounding the components (A) and (B) in order to form the polymer composition;
• and
• grafting component (A) or components (A) and (B) with component (C) during the compounding step;
• wherein the process further comprises the step of
• independently controlling the temperature of each control zone of the plurality of control zones of the barrel section of the extruder as such that
• a) the temperature in the first control zone of the barrel section downstream of the feeding section is in the range of from higher than 85° C. to 180° C.,
• b) the temperature of the control zones of the barrel section from the first control zone of the barrel section downstream the feeding section to the control zone in the middle of the barrel section is increased over the length of the barrel section in two or more steps so that the temperature of the control zone in the middle of the barrel section is from 105% to 145% of the temperature in the first control zone of the barrel section downstream of the feeding section;
• and
• c) the temperature of the control zones of the barrel section from control zone in the middle of the barrel section to the control zone of the barrel section directly upstream of the die plate in maintained at the same temperature or increased to a temperature
• of not more than 120% of the temperature of the control zone in the middle of the barrel section,
• wherein the polymer composition has two distinct peaks and a valley between the peaks in the GPC curve and a Z value, determined from the areas below the two peaks of the GPC curve, of at least −1.0, wherein the Z-value is determined according to formula (I)
• Z=s/Abs(B−A) (I)
• wherein
• Abs (B−A) is the absolute value of (B−A);
• A=the area, between the tangent parallel to the MW axis going through log M (Min) and the LS15 signal, from log M of 5.1 to log M value where the LS signal is minimum log M (Min), in the log M range between 5.1 and 6;
• B=the area, between the tangent parallel to the MW axis going through log M (Min) and the LS15 signal, from log M (Min) to the point where the LS signal is crossed again;
• and
• s is the slope between the two peaks of the GPC curve, defined at log M of 5.1 and 6,
• wherein the GPC curve is defined as the concentration normalized LS15 signal obtained from GPC-VISC-LS analysis.