Multi-layer, ethylene polymer-based films with high-density polyethylene based stiffening layer
View Patent ↗A multi-layer film for making pouches for containing flowable materials, said multi-layer film having generally five layers in order: inner sealant-layer, first interposed layer, the core layer, second interposed layer, and the outer sealant layer. All layers are ethylene-based. The combined thickness of the first and the second interposed layers is in the range of from about 10% to about 27% of the total thickness of said multi-layer film. Similarly, a combined thickness of the inner and the outer sealant-layers is in the range of from about 10% to about 27% of the total thickness of the multi-layer film. The interposed layers are of a high-density polyethylene that has a density of at least 0.950 g/cm. 3 and a melt-index of less than 1.05 dg/min.
1. A multi-layer film for making pouches for containing flowable materials, said multi-layer film comprising the following layers in order, from an at least one inner sealant-layer to an at least one outer sealant-layer: (A) said at least one inner sealant-layer comprising polyethylene that is selected from the group consisting of: (i) an at least one low-density ethylene-alpha-olefin copolymer, (ii) a blend of said at least one low-density ethylene-alpha-olefin copolymer and an at least one ethylene homopolymer, wherein said ethylene homopolymer is made in a high-pressure polymerization process; and (iii) a blend of said at least one low-density ethylene-alpha-olefin copolymer and an at least one ethylene copolymer, wherein said ethylene copolymer is made in a high-pressure polymerization process; (B) a first at least one interposed layer adjacent to said at least one inner sealant-layer, said first at least one interposed layer comprising: (i) an at least one high-density polyethylene, or a blend of said at least one high-density polyethylene and at least one ethylene-alpha-olefin copolymer; (ii) optionally, an ethylene homopolymer made in a high-pressure polymerization process; (iii) optionally, an ethylene copolymer made in a high pressure polymerization process; and (iv) optionally, a second ethylene-alpha-olefin copolymer that is not the same as said at least one ethylene-alpha-olefin copolymer in (B)(i); wherein the centerline of said first at least one interposed layer is closer to the centerline of said at least one inner sealant-layer than to the centerline of said multi-layer film; (C) at least one core layer, adjacent to said first at least one interposed layer, said at least one core layer comprising polyethylene that is selected from the group consisting of: (i) at least one low-density ethylene-alpha olefin copolymer, (ii) a blend of said at least one low-density ethylene-alpha-olefin copolymer and an at least one ethylene homopolymer, wherein said ethylene homopolymer is made in a high-pressure polymerization process; and (iii) a blend of said at least one low-density ethylene-alpha-olefin copolymer and an at least one ethylene copolymer, wherein said ethylene copolymer is made in a high-pressure polymerization process; (D) a second at least one interposed layer adjacent to said at least one core layer, said second at least one interposed layer comprising: (i) an at least one high-density polyethylene, or a blend of said at least one high-density polyethylene and at least one ethylene-alpha-olefin copolymer; (ii) optionally, an ethylene homopolymer made in a high-pressure polymerization process; (iii) optionally, an ethylene copolymer made in a high pressure polymerization process; and (iv) optionally, a second ethylene-alpha-olefin copolymer that is not the same as said at least one ethylene-alpha-olefin copolymer in (D)(i); wherein the centerline of said second at least one interposed layer is closer to the centerline of said at least one outer sealant-layer than to the centerline of said multi-layer film; and (E) said at least one outer sealant-layer, comprising polyethylene that is selected from the group consisting of: (i) an at least one low-density ethylene-alpha-olefin copolymer, (ii) a blend of said at least one low-density ethylene-alpha-olefin copolymer and an at least one ethylene homopolymer, wherein said ethylene homopolymer is made in a high-pressure polymerization process; and (iii) a blend of said at least one low-density ethylene-alpha-olefin copolymer and an at least one ethylene copolymer, wherein said ethylene copolymer is made in a high-pressure polymerization process; wherein said multi-layer film thickness is in the range of from about 35 microns to about 66 microns; wherein a combined thickness of said first at least one interposed layer and said second at least one interposed layer is in the range of from about 10% to about 27% of the total thickness of said multi-layer film; wherein a combined thickness of said inner sealant-layer and said outer sealant-layer is in the range of from about 10% to about 27% of the total thickness of said multi-layer film; and wherein said at least one high-density polyethylene in said first at least one interposed layer and said second at least one interposed layer has a density of at least of about 0.950 g/cm.sup.3 and a melt-index of less than 1.05 dg/min.
2. The multi-layer film as recited in claim 1 , wherein said multi-layer film thickness is in the range of from about 38 microns to about 63 microns.
3. The multi-layer film as recited in claim 1 , wherein said multi-layer film thickness is in the range of from about 44 microns to about 60 microns.
4. The multi-layer film as recited in claim 1 , wherein said multi-layer film thickness is in the range of from about 47 microns to about 59 microns.
5. The multi-layer film as recited in claim 1 , wherein said multi-layer film thickness is selected from the group consisting of about 45 microns, about 46 microns, about 47 microns, about 48 microns, about 49 microns, about 50 microns, about 51 microns, about 52 microns, about 53 microns, about 54 microns, about 55 microns, about 56 microns, about 57 microns and about 58 microns.
6. The multi-layer film as recited in claim 1 , wherein said at least one inner sealant-layer comprises: (i) from about 80 to about 98 parts by weight of said low-density copolymer of ethylene and an at least one C.sub.4-C.sub.10 alpha-olefin manufactured in a polymerization process using a single-site polymerization catalyst, with a density in the range of from about 0.909 to about 0.935 g/cm.sup.3 and a melt-index in the range of from about 0.5 to about 1.5, and (ii) from about 0 to about 15 parts by weight of an additional at least one low-density copolymer of ethylene and an at least one C.sub.4-C.sub.10 alpha-olefin, which is an ultra-low density copolymer of ethylene and at least one C.sub.4-C.sub.10 alpha-olefin manufactured in a polymerization process using a single-site polymerization catalyst, with a density in the range of from about 0.859 to about 0.888 g/cm.sup.3 and a melt-index in the range of from about 0.4 to about 0.6 dg/min.
7. The multi-layer film of claim 6 , wherein said low-density copolymer of ethylene and at least one C.sub.4-C.sub.10 alpha-olefin, or said at least one ultra-low density copolymer of ethylene and at least one C.sub.4-C.sub.10 alpha-olefin is selected from ethylene/butene-1 copolymers, ethylene/hexene-1 copolymers, ethylene/octene-1 copolymers, ethylene/octene-1/butene-1 terpolymers and ethylene/hexene-1/butene-1 terpolymers.
8. The multi-layer film as recited in claim 1 , wherein said at least one outer sealant-layer comprises: (i) from about 80 to about 98 parts by weight of said low-density copolymer of ethylene and an at least one C.sub.4-C.sub.10 alpha-olefin manufactured in a polymerization process using a single-site polymerization catalyst, with a density in the range of from about 0.909 to about 0.935 g/cm.sup.3 and a melt-index in the range of from about 0.5 to about 1.5 dg/min, and (ii) from about 0 to about 15 parts by weight of an additional at least one low-density copolymer of ethylene and an at least one C.sub.4-C.sub.10 alpha-olefin, which is an ultra-low density copolymer of ethylene and at least one C.sub.4-C.sub.10 alpha-olefin manufactured in a polymerization process using a single-site polymerization catalyst, with a density in the range of from about 0.859 to about 0.888 g/cm.sup.3 and a melt-index in the range of from about 0.4 to about 0.6 dg/min.
9. The multi-layer film of claim 8 , wherein said low-density copolymer of ethylene and at least one C.sub.4-C.sub.10 alpha-olefin, or said at least one ultra-low density copolymer of ethylene and at least one C.sub.4-C.sub.10 alpha-olefin is selected from ethylene/butene-1 copolymers, ethylene/hexene-1 copolymers, ethylene/octene-1 copolymers, ethylene/octene-1/butene-1 terpolymers and ethylene/hexene-1/butene-1 terpolymers.
10. The multi-layer film as recited in claim 1 , wherein said at least one inner sealant-layer further comprises from about 0 to about 15 parts by weight of said at least one ethylene homopolymer manufactured in a high pressure polymerization process or said at least one ethylene copolymer manufactured in a high pressure polymerization process, wherein said at least one ethylene homopolymer has a density in the range of from about 0.918 to about 0.923 g/cm.sup.3 and a melt-index in the range of from about 0.1 to 1.1 dg/min, and said at least one ethylene copolymer has a density in the range of from about 0.930 to about 0.960 g/cm.sup.3 and a melt-index in the range of from about 0.1 to about 10 dg/min.
11. The multi-layer film as recited in claim 1 , wherein said at least one outer sealant-layer further comprises from 0 to about 15 parts by weight of said at least one ethylene homopolymer manufactured in a high pressure polymerization process or said at least one ethylene copolymer manufactured in a high pressure polymerization process, wherein the ethylene homopolymer has a density in the range of from about 0.918 to about 0.923 g/cm.sup.3 and a melt-index in the range of from about 0.1 to 1.1 dg/min, and the ethylene copolymer has a density in the range of from about 0.930 to about 0.960 g/cm.sup.3 and a melt-index in the range of from about 0.1 to about 10 dg/min.
12. The multi-layer film as recited in claim 1 , wherein, in said first at least one interposed layer or in said at least second interposed layer: (i) said at least one high-density polyethylene is in the range of from about 78 to about 100 parts by weight of said first at least one interposed layer or of said second at least one interposed layer, wherein said at least one high-density polye-thylene that is manufactured in a polymerization process using a single-site polymerization catalyst or a Ziegler-Natta catalyst, wherein said at least one high-density polyethylene has a density greater than about 0.950 g/cm.sup.3 but less than about 0.970 g/cm.sup.3 and a melt-index in the range of from about 0.75 to about 10.5 dg/min, (ii) said at least one ethylene-alpha olefin copolymer is in the range from 0 to about 15 parts by weight of said first at least one interposed layer or of said second at least one interposed layer, wherein said at least one C.sub.4-C.sub.10 alpha-olefin is an ultra-low density copolymer of ethylene and at least one C.sub.4-C.sub.10 alpha-olefin manufactured in a polymerization process using a single-site polymerization catalyst, with a density in the range of from about 0.859 to about 0.905 g/cm.sup.3 and a melt-index in the range of from about 0.4 to about 1.1 dg/min, (iii) said at least one optional ethylene homopolymer or copolymer, manufactured in a high pressure polymerization process, is in the range of from about 0 parts to 15 parts by weight of said first at least one interposed layer or of said second at least on interposed layer, wherein the ethylene homopolymer has a density in the range of from about 0.918 to about 0.923 g/cm.sup.3 and a melt-index in the range of from about 0.1 to 1.1 dg/min, and the ethylene copolymer has a density in the range 0.930 to about 0.960 g/cm.sup.3 and a melt-index in the range of from about 0.1 to about 10 dg/min, and (iv) said at least one additional ethylene-alpha-olefin copolymer is in the range of from about 0 parts to 15 parts by weight, and can be manufactured in a polymerization process using either a single-site or Zeigler-Natta polymerization catalyst, wherein said copolymer has a density in the range of from about 0.909 to about 0.935 g/cm.sup.3 and a melt-index in the range of from about 0.5 to about 1.5 dg/min.
13. The multi-layer film of claim 12 , wherein said low-density copolymer of ethylene and at least one C.sub.4-C.sub.10 alpha-olefin, or said at least one ultra-low density copolymer of ethylene and at least one C.sub.4-C.sub.10 alpha-olefin is selected from ethylene/butene-1 copolymers, ethylene/hexene-1 copolymers, ethylene/octene-1 copolymers, ethylene/octene-1/butene-1 terpolymers and ethylene/hexene-1/butene-1 terpolymers.
14. The multi-layer film of claim 13 , wherein said low-density copolymer of ethylene and at least one C.sub.4-C.sub.10 alpha-olefin, or said at least one ultra-low density copolymer of ethylene and at least one C.sub.4-C.sub.10 alpha-olefin is selected from ethylene/butene-1 copolymers, ethylene/hexene-1 copolymers, ethylene/octene-1 copolymers, ethylene/octene-1/butene-1 terpolymers and ethylene/hexene-1/butene-1 terpolymers.
15. The multi-layer film as recited in claim 1 , wherein, in said at least one core layer: (i) said at least one low density ethylene-alpha olefin copolymer is in the range from 35 to about 85 parts by weight of said at least one core layer, and can be manufactured in a polymerization process using either a single-site or Zeigler-Natta polymerization catalyst, wherein said copolymer has a density in the range of from about 0.909 to about 0.935 g/cm.sup.3 and a melt-index in the range of from about 0.5 to about 1.5 dg/min; (ii) from 0 to about 15 parts by weight of an additional at least one low-density copolymer of ethylene and an at least one C.sub.4-C.sub.10 alpha-olefin, which is an ultra-low density copolymer of ethylene and at least one C.sub.4-C.sub.10 alpha-olefin manufactured in a polymerization process using a single-site polymerization catalyst, with a density in the range of from about 0.859 to about 0.905 g/cm.sup.3 and a melt-index in the range of from about 0.4 to about 1.1 dg/min; and (iii) said at least one low-density ethylene homopolymer or copolymer, made in a high pressure polymerization process, is in the range of from about 10 parts to 50 parts by weight of said at least one core layer, wherein the ethylene homopolymer has a density in the range of from about 0.918 to about 0.923 g/cm.sup.3 and a melt-index in the range of from about 0.1 to 1.1 dg/min, and the ethylene copolymer has a density in the range of from about 0.930 to about 0.960 g/cm.sup.3 and a melt-index in the range of from about 0.1 to about 10 dg/min.
16. The process for making pouches filled with a flowable material, using a vertical form, fill and seal apparatus, wherein each pouch is made from a flat web of film by the following steps: (I) forming a tubular film therefrom with a longitudinal seal and subsequently flattening said tubular film at a first position; (II) transversely heat-sealing said tubular film at the flattened position; (III) filling said tubular film with a predetermined quantity of flowable material above said first position; (IV) flattening said tubular film above the predetermined quantity of flowable material at a second position; and (V) transversely heat sealing said tubular film at said second position, wherein said pouches are made from a flat web of film made from a multi-layer film, comprising the following layers in order of an at least one inner sealant-layer to an at least one outer sealant-layer: (A) said at least one inner sealant-layer comprising polyethylene that is selected from the group consisting of: (i) an at least one low-density ethylene-alpha-olefin copolymer, (ii) a blend of said at least one low-density ethylene-alpha-olefin copolymer and an at least one ethylene homopolymer, wherein said ethylene homopolymer is made in a high-pressure polymerization process; and (iii) a blend of said at least one low-density ethylene-alpha-olefin copolymer and an at least one ethylene copolymer, wherein said ethylene copolymer is made in a high-pressure polymerization process; (B) a first at least one interposed layer adjacent to said at least one inner sealant-layer, said first at least one interposed layer comprising: (i) an at least one high-density polyethylene, or a blend of said at least one high-density polyethylene and at least one ethylene-alpha-olefin copolymer; (ii) optionally, an ethylene homopolymer made in a high-pressure polymerization process; (iii) optionally, an ethylene copolymer made in a high pressure polymerization process; and (iv) optionally, a second ethylene-alpha-olefin copolymer that is not the same as said at least one ethylene-alpha-olefin copolymer in (B)(i); wherein the centerline of said first at least one interposed layer is closer to the centerline of said at least one inner sealant-layer than to the centerline of said multi-layer film; (C) at least one core layer, adjacent to said first at least one interposed layer, said at least one core layer comprising polyethylene that is selected from the group consisting of: (i) at least one low-density ethylene-alpha olefin copolymer, (ii) a blend of said at least one low-density ethylene-alpha-olefin copolymer and an at least one ethylene homopolymer, wherein said ethylene homopolymer is made in a high-pressure polymerization process; and (iii) a blend of said at least one low-density ethylene-alpha-olefin copolymer and an at least one ethylene copolymer, wherein said ethylene copolymer is made in a high-pressure polymerization process; (D) a second at least one interposed layer adjacent to said at least one core layer, said second at least one interposed layer comprising: (i) an at least one high-density polyethylene, or a blend of said at least one high-density polyethylene and at least one ethylene-alpha-olefin copolymer; (ii) optionally, an ethylene homopolymer made in a high-pressure polymerization process; (iii) optionally, an ethylene copolymer made in a high pressure polymerization process; and (iv) optionally, a second ethylene-alpha-olefin copolymer that is not the same as said at least one ethylene-alpha-olefin copolymer in (D)(i); wherein the centerline of said second at least one interposed layer is closer to the centerline of said at least one outer sealant-layer than to the centerline of said multi-layer film; and (E) said at least one outer sealant-layer, comprising polyethylene that is selected from the group consisting of: (i) an at least one low-density ethylene-alpha-olefin copolymer, (ii) a blend of said at least one low-density ethylene-alpha-olefin copolymer and an at least one ethylene homopolymer, wherein said ethylene homopolymer is made in a high-pressure polymerization process; and (iii) a blend of said at least one low-density ethylene-alpha-olefin copolymer and an at least one ethylene copolymer, wherein said ethylene copolymer is made in a high-pressure polymerization process; wherein said multi-layer film thickness is in the range of from about 35 microns to about 66 microns; wherein a combined thickness of said first at least one interposed layer and said second at least one interposed layer is in the range of from about 10% to about 27% of the total thickness of said multi-layer film; wherein a combined thickness of said inner sealant-layer and said outer sealant-layer is in the range of from about 10% to about 27% of the total thickness of said multi-layer film; and wherein said at least one high-density polyethylene in said first at least one interposed layer and said second at least one interposed layer has a density of at least of about 0.950 g/cm.sup.3 and a melt-index of less than 1.05 dg/min.
17. The process as recited in claim 16 , wherein said multi-layer film thickness is in the range of from about 38 microns to about 63 microns.
18. The process as recited in claim 16 , wherein said multi-layer film thickness is in the range of from about 44 microns to about 60 microns.
19. The process as recited in claim 16 , wherein said multi-layer film thickness is in the range of from about 47 microns to about 59 microns.
20. The process as recited in claim 16 , wherein said multi-layer film thickness is selected from the group consisting of about 45 microns, about 46 microns, 5 about 47 microns, about 48 microns, about 49 microns, about 50 microns, about 51 microns, about 52 microns, about 53 microns, about 54 microns, about 55 microns, about 56 microns, about 57 microns, and about 58 microns.
21. The process as recited in claim 16 , wherein said at least one inner sealant-layer comprises: (i) from about 80 to about 98 parts by weight of said low-density copolymer of ethylene and an at least one C.sub.4-C.sub.10 alpha-olefin manufactured in a polymerization process using a single-site polymerization catalyst, with a density in the range of from about 0.909 to 0.935 g/cm.sup.3 and a melt-index in the range of from about 0.5 to about 1.5, and (ii) from about 0 to about 15 parts by weight of an additional at least one low-density copolymer of ethylene and an at least one C.sub.4-C.sub.10 alpha-olefin, which is an ultra-low density copolymer of ethylene and at least one C.sub.4-C.sub.10 alpha-olefin manufactured in a polymerization process using a single-site polymerization catalyst, with a density in the range of from about 0.859 to about 0.888 g/cm.sup.3 and a melt-index in the range of from about 0.4 to about 0.6 dg/min.
22. The process of claim 21 , wherein said low-density copolymer of ethylene and at least one C.sub.4-C.sub.10 alpha-olefin, or said at least one ultra-low density copolymer of ethylene and at least one C.sub.4-C.sub.10 alpha-olefin is selected from ethylene/butene-1 copolymers, ethylene/hexene-1 copolymers, ethylene/octene-1 copolymers, ethylene/octene-1/butene-1 terpolymers and ethylene/hexene-1/butene-1 terpolymers.
23. The process as recited in claim 16 , wherein said at least one outer sealant-layer comprises: (i) from about 80 to about 98 parts by weight of said low-density copolymer of ethylene and an at least one C.sub.4-C.sub.10 alpha-olefin manufactured in a polymerization process using a single-site polymerization catalyst, with a density in the range of from about 0.909 to about 0.935 g/cm.sup.3 and a melt-index in the range of from about 0.5 to about 1.5, and (ii) from about 0 to about 15 parts by weight of an additional at least one low-density copolymer of ethylene and an at least one C.sub.4-C10 alpha-olefin, which is an ultra-low density copolymer of ethylene and at least one C.sub.4-C.sub.10 alpha-olefin manufactured in a polymerization process using a single-site polymerization catalyst, with a density in the range of from about 0.859 to about 0.888 g/cm.sup.3 and a melt-index in the range of from about 0.4 to about 0.6 dg/min.
24. The process of claim 23 , wherein said low-density copolymer of ethylene and at least one C.sub.4-C.sub.10 alpha-olefin, or said at least one ultra-low density copolymer of ethylene and at least one C.sub.4-C.sub.10 alpha-olefin is selected from ethylene/butene-1 copolymers, ethylene/hexene-1 copolymers, ethylene/octene-1 copolymers, ethylene/octene-1/butene-1 terpolymers and ethylene/hexene-1/butene-1 terpolymers.
25. The process as recited in claim 16 , wherein said at least one inner sealant-layer further comprises from about 0 parts to about 15 parts by weight of said at least one low-density ethylene homopolymer with a density in the range of from about 0.918 to about 0.923 g/cm.sup.3 and a melt-index in the range of from about 0.1 to about 1.1 dg/min.
26. The process as recited in claim 16 , wherein said at least one inner sealant-layer further comprises from 0 to about 15 parts by weight of said ethylene copolymer with a density in the range 0.930-0.960 g/cm.sup.3 and a melt-index in the range of from about 0.1 to 10 dg/min.
27. The process as recited in claim 16 , wherein said at least one outer sealant-layer further comprises from 0 to 15 parts by weight of said at least one low-density ethylene homopolymer with a density in the range of from about 0.918 to about 0.923 g/cm.sup.3 and a melt-index in the range of from about 0.1 to about 1.1 dg/min.
28. The process as recited in claim 16 , wherein said at least one outer sealant-layer further comprises from 0 to about 15 parts by weight of said ethylene copolymer with a density in the range 0.930-0.960 g/cm.sup.3 and a melt-index in the range of from about 0.1 to 10 dg/min.
29. The process as recited in claim 16 , wherein, in said first at least one interposed layer and/or in said second at least one interposed layer: (i) said at least one high-density polyethylene is in the range of from about 78 to about 100 parts by weight of said first at least one interposed layer or of said second at least one interposed layer, wherein said at least one high-density polyethylene that is manufactured in a polymerization process using a single-site polymerization catalyst or a Ziegler-Natta catalyst, wherein said at least one high-density polyethylene has a density greater than 0.950 g/cm.sup.3 and a melt-index in the range of from about 0.75 to about 1.05 dg/min, (ii) said at least one ethylene-alpha olefin copolymer is in the range from 0 to about 15 parts by weight of said first at least one interposed layer or of said second at least one interposed layer, wherein said at least one C.sub.4-C.sub.10 alpha-olefin is an ultra-low density copolymer of ethylene and at least one C.sub.4-C.sub.10 alpha-olefin manufactured in a polymerization process using a single-site polymerization catalyst, with a density in the range of from about 0.859 to about 0.905 g/cm.sup.3 and a melt-index in the range of from about 0.4 to about 1.1 dg/min, (iii) said at least one optional ethylene homopolymer or copolymer, manufactured in a high pressure polymerization process, is in the range of from about 0 parts to 15 parts by weight of said first at least one interposed layer or of said second at least on interposed layer, wherein the ethylene homopolymer has a density in the range of from about 0.918 to about 0.923 g/cm.sup.3 and a melt-index in the range of from about 0.1 to 1.1 dg/min, and the ethylene copolymer has a density in the range 0.930 to about 0.960 g/cm.sup.3 and a melt-index in the range of from about 0.1 to about 10 dg/min, and (iv) said at least one additional ethylene-alpha-olefin copolymer is in the range of from about 0 parts to 15 parts by weight, and can be manufactured in a polymerization process using either a single-site or Zeigler-Natta polymerization catalyst, wherein said copolymer has a density in the range of from about 0.909 to about 0.935 g/cm.sup.3 and a melt-index in the range of from about 0.5 to about 1.5 dg/min.
30. The process as recited in claim 29 , wherein said low-density copolymer of ethylene and at least one C.sub.4-C.sub.10 alpha-olefin, or said at least one ultra-low density copolymer of ethylene and at least one C.sub.4-C.sub.10 alpha-olefin is selected from ethylene/butene-1 copolymers, ethylene/hexene-1 copolymers, ethylene/octene-1 copolymers, ethylene/octene-1/butene-1 terpolymers and ethylene/hexene-1/butene-1 terpolymers.
31. The process as recited in claim 16 , wherein, in said at least one core layer: (i) said at least one low density ethylene-alpha olefin copolymer is in the range from 35 to about 85 parts by weight of said at least one core layer, and can be manufactured in a polymerization process using either a single-site or Zeigler-Natta polymerization catalyst, wherein said copolymer has a density in the range of from about 0.909 to about 0.935 g/cm.sup.3 and a melt-index in the range of from about 0.5 to about 1.5 dg/min; (ii) from 0 to about 15 parts by weight of an additional at least one low-density copolymer of ethylene and an at least one C.sub.4-C.sub.10 alpha-olefin, which is an ultra-low density copolymer of ethylene and at least one C.sub.4-C.sub.10 alpha-olefin manufactured in a polymerization process using a single-site polymerization catalyst, with a density in the range of from about 0.859 to about 0.905 g/cm.sup.3 and a melt-index in the range of from about 0.4 to about 1.1 dg/min; and (iii) said at least one low-density ethylene homopolymer or copolymer, made in a high pressure polymerization process, is in the range of from about 10 parts to 50 parts by weight of said at least one core layer, wherein the ethylene homopolymer has a density in the range of from about 0.918 to about 0.923 g/cm.sup.3 and a melt-index in the range of from about 0.1 to 1.1 dg/min, and the ethylene copolymer has a density in the range of from about 0.930 to about 0.960 g/cm.sup.3 and a melt-index in the range of from about 0.1 to about 10 dg/min.
32. The process of claim 31 , wherein said low-density copolymer of ethylene and at least one C.sub.4-C.sub.10 alpha-olefin, or said at least one ultra-low density copolymer of ethylene and at least one C.sub.4-C.sub.10 alpha-olefin is selected from ethylene/butene-1 copolymers, ethylene/hexene-1 copolymers, ethylene/octene-1 copolymers, ethylene/octene-1/butene-1 terpolymers and ethylene/hexene-1/butene-1 terpolymers.