Process for producing a polymer composition
Process for producing a polymer composition, a polymer composition obtainable by said process and the use of said polymer composition as adhesive polymer composition and for the production of a multilayer structure, such as a three-layer metal pipe coating, with improved peel strength.
1. 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.
2. The process according to claim 1 , wherein the extruder is a twin-screw extruder.
3. The process according to claim 1 , wherein temperature of the feeding section is in the range of from 20° C. to 70° C.
4. The process according to claim 1 , wherein the temperature increase of said two or more steps of increasing temperature is in the range of 5° C. to 30° C. for each step independently.
5. The process according to claim 1 , wherein a radical initiator (D) is fed into the extruder in order to initiate the grafting of component (A) or components (A) and (B) with component (C) and the radical initiator
(D) is selected from lauroyl peroxide, didecanoyl peroxide, tert-butylcumylperoxide, 2,5-bis(2-ethylhexanoylperoxy)-2,5-dimethylhexane, 2,5-bis(tert-butyl peroxy)-2,5-dimethylhexane, tert-butylcumylperoxide, tert-butylperoxypivalate, di(tert-butylperoxyisopropyl)benzene and mixtures thereof.
6. The process according to claim 1 , wherein component (A) is a copolymer of ethylene and one or more comonomer(s) selected from alpha-olefins having from 4 to 12 carbons atoms and has a density of from 900 kg/m 3 to 960 kg/m 3 and/or a melt flow rate MFR2 (190° C., 2.16 kg) of from 1.0 to 10.0 g/10 min before grafting.
7. The process according to claim 1 , wherein component (B) is selected from copolymers of ethylene with polar comonomer units.
8. The process according to claim 1 , wherein component (C) is selected from unsaturated carboxylic acids or derivatives thereof.
9. The process according to claim 1 , wherein components (A), (B) and (C) are fed in the following amounts of the total amount of components (A), (B) and (C) into the extruder:
from 60 to 90 wt % of component (A);
from 9.0 to 38 wt % of component (B); and
from 0.01 to 3.0 wt % of component (C).
10. A polymer composition obtainable from the process according to claim 1 .
11. The polymer composition according to claim 10 having a melt flow rate MFR 2 (190° C., 2.16 kg) of from 0.1 to 10.0 g/10 min and/or a density of from 900 kg/m 3 to 960 kg/m 3 .
12. The polymer composition according to claim 10 being an adhesive polymer composition.
13. The polymer composition according to claim 10 being in a multi-layer structure.
14. The polymer composition according to claim 13 being an adhesive composition in an adhesive layer in a three-layer metal pipe coating having a peel strength at 23° C. of at least 200 N/cm and/or a peel strength at 80° C. of at least 100 N/cm.