LAMINATED STRUCTURE COMPRISING A NITRILE RESIN BARRIER LAYER, A TIE LAYER AND A POLYOLEFIN LAYER, AND COEXTRUSION PROCESS FOR MAKING SAID STRUCTURE

Abstract: A laminated structure comprising (I) a first outer layer composed of a nitrile barrier resin, (II) a second intermediate layer comprising a tie layer and (III) a third outer layer composed of a polyolefin, characterised in that the tie layer comprises a mixture of (1) a nitrile barrier resin (I) (2) a polyolefin, and (3) a halogenated polyolefin. The laminated structure is preferably prepared by a co-extrusion process.

Description: Title: TIE LAYER wOR CO-EXTRUDED ACHYSONITRILE - COPOLI'MRS. This invention relates to a mixture of a halogenated polyolefin, a nitrile barrier resin, optionally a polyurethane, and a polyolefin, and to the use of this mixture as a tie layer to adhere together a Co- extruded polyolefin and nitrile barrier resin. Composite structures composed of at least one layer of a polyolefin and at least one layer of a nitrile barrier resin have been prepared and are found to be useful for many purposes, primarily for packaging. Packages of such composites have excellent gas barrier properties, they are particularly good barriers to oxgen, carbon dioxide and water vapour, and they can be fabricated by heat sealing because of the excellent heat-sealing properties of polyolefins. The manufacture of such composites is not easy because of the lack of adhesion between the surfaces of the polyolefin and the nitrile barrier resin This lack of adhesion has in the past been improved b the use of an adhesive, corona-discharge treatment of the polyolefin surface, and other methods including the use of a tie layer composed of a blend of the polyolefin and the nitrilecontaining polymer as described in U.S. Patent No. 4,125,576. It is an object of the present invention to provide improved composite structures of polyolefins and nitrile barrier resins, by employing a polymeric mixture as a tie layer for adhering the polymer surfaces together. This invention therefore provides a laminated structure comprising (I) a first outer layer composed of a nitrile barrier resin, (II) a second intermediate layer comprising a tie layer and, (III) a third outer layer composed of a polyolefin characterised in that the layer comprises a mixture of (1) a nitrile barrier resin (I), (2) a polyolefin, and (3) a halogenated polyolefin. The proportions of the materials in the tie layer and the temperature at which the mixture is extruded affect both adhesion and viscosity control in the co-extrusion process. A significant advantage of the present invention is the fact that scrap material can be reground and used in the tie layer with some adjustment of the three essential components mentioned above. The polyolefins useful in the present invention include polyethylene, polypropylene, polybutylene, and interpolymers of two or more of ethylene, propylene, and the butylenes. Polyethylene includes both highand low- density polymer. The most preferred polyolefins are polyethylene and polypropylene. The halogenated polyolefins useful in this invention include halogenated polyethylene, halogenated polypropylene, halogenated polybutylene, and halogenated olefin copolymers. Preferred are chlorinated and brominated polyolefins and most preferred are chlorinated polyethylenes and chlorinated polypropylenes. The nitrile barrier resins useful in the present invention include those prepared by the polymerization of (A) from 60 to 900/o by weight of at least one nitrile having the structure EMI2.1 in which R represents hydrogen, a lower alkyl group having from 1 to 4 carbon atoms, or a halogen, (B) from 10 to 40f0 by weight based on the combined weight of (A) and (B) of (1) an ester having the structure EMI3.1 in which R1 represents hydrogen, an alkyl group having from 1 to 4 carbon atoms, or a halogen, and R2 represents an alkyl group having from 1 to 6 carbon atoms; (2) an alpha-olefin having the structure EMI3.2 in which Rl and R" which may be the same or different represent alkyl groups having from 1 to 7 carbon atoms; (3) methyl vinyl ether, ethyl vinyl ether, a propyl vinyl ether, or a butyl vinyl ether; (4) vinyl acetate; (5) styrene and/or (6) indene; in the presence of from 0 to 40 parts by weight of (C) a fllbbeim polymer of a conjugated diene monomer which is butadiene or isoprene and optionally a comonomer which is styrene, a nitrile monomer having the structure EMI3.3 in which R is as defined above or an ester haven the structure EMI3.4 in which R1 and R2 are as defined above, the rubbery polymer containing from 50 to 100% by weight of polymerized conjugated diene and from 0 to 50 by weight of comonomer. This invention is particularly applicable to the co-extrusion process. Two dissimilar thermoplastic polymer materials, i.e. a polyolefin and a nitrile barrier resin, are adhered together in the molten phase while being shaped by passage through a die. The tie layer is also in the molten state in the co-extrusion process and is also shaped by means of passing it through a die. In the co-extrusion process, the components of the tie layer are weighed, powder blended and fed into an extruder hopper and continuously passed from the hopper to the extruder where they are mixed, heated to a melt, and extruded between two outside layers of extruded polyolefin and nitrile barrier resin The three shaped melt streams of polymer are combined using a co-extrusion adapter and die in a one-step in-line manufacturing operation. This permits the component layers to flow together to form the desired multilayer structure. The tie layer can be extruded within a temperature range of 150 to 2350 C. The tie layer melt should preferably be extruded at a temperature of from 200 to 2100C for best results. The proportions of the three essential components in the tie layer can be varied widely from nearly all halogenated polyolefin to nearly all polyolefin with minor amounts of the nitrile barrier resin. A weight ratio of from 2:1:1 to 5:1:1 of halogenated polyolefin: nitrile barrier resin:polyolefin is preferred. A particularly good tie layer was obtained with a 4:1:1 weight ratio mixture, with 1 part of polyurethane included. This mixture, when used to tie a nitrile barrier resin to polyethylene, had a peel strength of 980 g per linear centimetre (5.5 pounds per linear inch) and excellent viscosity control. The halogenated polyolefin was a suspension polymerized high density polyethylene resin which was chlorinated to an extent of Ó* by weight. The polyethylene and polyurethane were standard low density polyethylene and extrudable polyurethane, In making the composite co-extruded structures of this invention, the pressure in the die may reach as high as 350 kg per sq.cm. (5zoo psi). A normal pressure is about 175 kg per sq.cm. (2500 psi). The halogenated polyolefins useful in this invention may contain cross-linking agents such as a peroxide. Although this invention includes the use of halogenated polymers of many types in the tie layer, the halogenated polyolefins are preferred. The invention is further illustrated in the following examples wherein the amounts of ingredients are expressed in parts by weight unless other TiS.e indicated. In the examples, the composite sheets were prepared using a co-extrusion adapter which was of conventional feed block design. Three extruders fed this multiple inlet heated block. The three, still separate, melt streams were aligned in the direction of the outlet and fed into a converging plate which directs the flow into the single manifold and die. At the point of entry into the die, the melts flow into contact and distribute to the contour of the die. Example 1 mixture of (1) a high nitile barrier resin prepared by copolymerization of 75 parts by weight of acrylonitrile and 25 parts by weight of methyl acrylate in the presence of 10 parts by weight of a rubbery copolymer ot. butadiene and acrylonitrile according to U.S. Patent No. 3,426,102, (2) a low density polyethylene having a melt index of 0.25 and density of 0.919, and (3) a chlorinated low density polyethylene having 360to chlorine by weight and a viscosity of 17 centipoises in which the weight ratio of 1:1:4 was prepared by powder blending the three components by adding each component to a can and mixing with a steel rod. The mixture was placed in a Brabender extrusion apparatus and was melt extruded into a co-extrusion adapter at 2000C. At the same time, some resin (1) and some resin (2) were also independently and simultaneously extruded in a co extrusion adapter. The three co-extruded materials were passed through a 6-inch sheet die at 2050C where the melts were allowed to flow freely in a laminar form and the mixture of resins served as a tie layer between sheets of resins (1) and (2). The resulting laminated sheet was found to be very uniform with about 27-mil thickness. The peel strength as measured by an Instron ASTM +1876 (1971 Part 6) apparatus using a 1800 peel on a 2.54 cm. (1 inch) wide sample approximately 15 cm. (6 inches) long. The peel strength as determined at both 5 cm.-and 25 cm.-per-minute rates from edge to edge of the laminate was found to be 446 g per linear centimetre (2.5 pounds per linear inch). Example 2 Example 1 was repeated with the variation that there was included in the tie layer mixture a polyurethane (Q-thane, marketed by X.J. Quinn) and the weight ratio of halogenated polyethylene:nitrile barrier resin:polyolefin:polyurethane was :1:1:1. A composite sheet which had a peel strength of 996 g per linear centimetre (5.58 pounds per linear inch) was produced. Example 3 Example 1 was repeated using only resins (1) and (2) with no tie layer to produce a product outside the scope of this invention which showed no measurable peel strength between the co-extruded layers of resins (1) and (2). Example 4 Example 1 was repeated except that only resin (S) (chlorinated polyethylene) was used as the tie layer to produce a co-estruded composite outside the scope of the present invention having a peel strength of only 267 g per linear centimetre (1.50 pounds per linear inch). Example 5 Example 1 was repeated except that resin (3) was excluded from the tie layer to produce a composite sheet which was outside the scope of this invention having a peel strength of only about 90 g per linear centimetre (0.5 pounds per linear inch).

Claims: CLAIMS 1. A laminated structure comprising (1) a first outer layer composed of a nitrile barrier resin, (II) a second intermediate layer comprising a tie layer and (III) a third outer layer composed of a polyolefin characterised in that the layer comprises a mixture of (1) a nitrile barrier resin ( (2) a polyolefin, and (3) a halogenated polyolefin. 2. A structure as claimed in claim 1 characterised in that the nitrile barrier resin (1) is one prepared by the polymerization of (A) from 60 to 90 ,-c by weight of at least one nitrile having the structure EMI8.1 in which R represents hydrogen, a lower alkyl group halting from 1 to 4 carbon atoms, or a halogen, (B) from 10 to 40% by weight based on the combined weight of (A) and (B) of (1) an ester having the structure EMI8.2 in which R1 represents hydrogen, and alkyl group having from 1 to 4 carbon atoms, or a halogen, and R2 represents an alkyl group having from 1 to 6 carbon atoms; ; (2) an alpha-olefin having the structure EMI8.3 in which Rt and R" which may be the same or different represent alkyl groups having from I to 7 carbon atoms; (3) methyl vinyl ether, ethyl vinyl ether, a propyl vinyl ether or a butyl vinyl ether, (4) vinyl acetate, (5) styrene, and (6) indene, in the presence of from 0 to 40 parts by weight of (C) a rubbery polymer of a conjugated diene monomer which is butadiene or isoprene and optionally a comonomer which is styrene, a nitrile monomer having the structure EMI9.1 in which R is as defined above, and an ester having the structure EMI9.2 in which R1 and R2 are as defined above, the rubbery polymer containing from 50 to 1009c by weight of polymerized conjugated diene and from 0 to 50 by weight of comonomer. 3. A structure as claimed in claim 1 or claim 2 characterised in that the polyolefin is polyethylene, polypropylene, polybutylene, and/or an interpolymer of two or more of ethylene, propylene, and the butylenes. 4. A structure as claimed in any of claims 1 to 3 characterised in that the halogenated polyolefin is halogenated polyethylene, halogenated polypropylene, and/or halogenated polybutylene. 5. A structure as claimed in any of claims 1 to 4 characterised in that (A) is acrylonitrile, (B) is methyl acrylate, and (C) is a butadiene-acrylonitrile rubbery polymer. 6. A co-extrusion process for the production of a laminated structure characterised in that there are adhered together in the molten phase at a temperature in the range of 150 to 2350C and passed through a shaping die to form a laminate. (I) a first outer layer composed of a nitrile barrier resin, (II) a second intermediate layer comprising a mixture of (1) a nitrile barrier resin (I). (2) a polyolefin, and (3) a halogenated polyolefin, and (III) a third outer layer composed of a polyolefin. 7. A process as claimed in claim 6 characterised in that the nitrile barrier resin (I) is one prepared by the polymerization of (A) from 60 to 90 by weight of at least one nitrile having the structure EMI10.1 in which R represents hydrogen5 a lower alkyl group having from 1 to 4 carbon atoms or a halogen, (B) from 10 to 40 by weight based on the combined weight of (A) and (B) of (1) an ester having the structure EMI10.2 in which R1 represents hydrogen, an alkyl group having from 1 to 4 carbon atoms, or a halogen, and R2 represents an alkyl group having from 1 to 6 carbon atoms; (2) an alpha-olefin having the structure EMI10.3 in which R' and R" which may be the same or different represent aDzçlgroups having from 1 to 7 carbon atoms; ; (3) methyl vinyl ether, ethyl vinyl ether, a propyl vinyl ether, or a butyl vinyl ether; (4) vinyl acetate; (5) styrene, and (6) indene; in the presence of from 0 to 40 parts by weight of (C) a rubbery polymer of a conjugated diene monomer which is butadiene or isoprene and optionally a comonomer which is styrene, a nitrile monomer having the structure EMI11.1 in which It is as defined above, and an ester having the structure EMI11.2 in which R1 and R2 are as defined above, the rubbery polymer containing from 50 to 100 by weight of polymerized conjugated diene and from 0 to 50 by weight of comonomer. 8. A process as claimed in claim 6 or claim 7 characterised in that the polyolefin is polyethylene, polypropylene, polybutylene, and/or an interpolymer of two or more of ethylene, propylene, and the butylenes. 9. A process as claimed in any of claims 6 to S characterised in that the halogenated polyolefin is halogenated polyethylene, halogenated polypropylene, and/or halogenated polybutylene. 10. A process as claimed in any of claims 6 to 9 characterised in that (A) is acrylonitrile, (B) is methyl acrylate, and (C) is a butadiene-acrylonitrile rubbery polymer.

Inventors: GERRY, FRANK SCOTT, WIGGINS, WAYNE THOMAS
Applicants: THE STANDARD OIL COMPANY
Application year: 1980
Main classification: B32B27
IPC codes: B32B27, B65D65