Adhesive polyethylene composition
The present invention relates to an adhesive polyethylene composition comprising (A) from 60 to 90 wt % of a non-elastomeric polyethylene; (B) from 9.0 to 38 wt % of an ethylene based elastomer being a copolymer of ethylene and alpha-olefin comonomer units having from 4 to 12 carbon atoms; wherein onto component (A) or components (A) and (B) an acid grafting agent (C) has been grafted in an amount of from 0.01 to 3.0 wt %, all based on the total weight of the adhesive polyethylene composition, a multi-layer structure comprising said adhesive polyethylene composition and the use of said adhesive polyethylene composition for the production of a multi-layer structure.
1. An adhesive polyethylene composition comprising
(A) from 60 to 90 wt % of a non-elastomeric polyethylene;
(B) from 9.0 to 38 wt % of an ethylene based elastomer being a copolymer of ethylene and alpha-olefin comonomer units having from 4 to 12 carbon atoms, which has a density in the range of from 840 to 900 kg/m 3 ;
wherein onto components (A) and (B) an acid grafting agent (C) has been grafted in an amount of from 0.01 to 3.0 wt %, all based on the total weight of the adhesive polyethylene composition.
2. The adhesive polyethylene composition according to claim 1 , wherein the non-elastomeric polyethylene (A) is a copolymer of ethylene and one or more comonomer units selected from alpha-olefins having from 4 to 12 carbon atoms.
3. The adhesive polyethylene composition according to claim 1 , wherein the acid grafting agent (C) is selected from unsaturated carboxylic acids or derivatives thereof.
4. The adhesive polyethylene composition according to claim 1 , having a polydispersity index PDI (LS), being the ratio of Mw/Mn of from 1.5 to 4.5, determined by GPC-VISC-LS analysis.
5. The adhesive polyethylene composition according to claim 1 , having an elasticity index at a loss modulus G″=0.5 kPa EI(0.5 kPa) of from 75 to 320 Pa.
6. The adhesive polyethylene composition according to claim 1 , having only one peak in the GPC curve, which is defined below in the measurement methods as the concentration normalized LS 15 signal along the molecular weight of conventional GPC, obtained from the GPC-VISC-LS analysis.
7. The adhesive polyethylene composition according to claim 2 , wherein the non-elastomeric polyethylene (A) is a copolymer of ethylene and one single comonomer selected from alpha-olefins having from 4 to 12 carbon atoms.
8. The adhesive polyethylene composition according to claim 2 , wherein the non-elastomeric polyethylene (A) is a terpolymer of ethylene and two comonomers selected from alpha-olefins having from 4 to 12 carbon atoms.
9. The adhesive polyethylene composition according to claim 1 , obtained from a process comprising the steps of:
feeding components (A), (B) and (C) into an extruder into the feeding section of 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 the extruder in order to form the adhesive polyethylene composition; and
grafting components (A) and (B) with component (C) during the compounding step.
10. The adhesive polyethylene composition according to claim 9 , wherein the temperature of the second to the last control zone in the barrel section is maintained constant over all of these control zones with a total deviation of not more than 20° C.
11. The adhesive polyethylene composition according to claim 9 , 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.
12. A multi-layer structure comprising one layer comprising the adhesive polyethylene composition according to claim 1 .
13. The multi-layer structure according to claim 12 , being a three-layer coating of a metal pipe.
14. The multi-layer structure according to claim 12 , having a peel strength at 23° C. of at least 350 N/cm and/or a peel strength at 80° C. of at least 60 N/cm.