Background of the invention Various materials for providing oxygen barriers for products sensitive to oxidation are mown, including ethylene vinyl alcohol (EVOH), amorphous nylon, semicrystalline polyamide 6 and polyacrylonitrile.

For packaging liquid or semi-liquid materials that are sensitive to oxidation, water barrier properties are also needed. C.f. EP 0241 819, which discloses a laminate using nylon as a barrier; EP 0293 098, which discloses a multilayer structure with EVOH and low density polyethylene (LDPE) coated on board. More recently, EP 0520 767 discloses the use of amorphous nylon as a non-foil composite laminate. In all of these cases, water vapor transmission is below 10 g/m2d due to a relatively thick polyethylene seal layer.

In soft cheese packaging the right balance of an oxygen barrier and a moisture barrier is given by a cellulosic film laminate to paper. In this case, the water vapor transmission is between 400 and 630 g/m2d at 38 "C and 90'/o relative humidity (RH), while the oxygen permeability is below 10 cc/m2d atm.

Summarv of the invention The present invention provides a flexible or semi-flexible packaging material with an oxygen barrier between 10 and 100 cc/m2d atm and a water vapor barrier between 100 and 1000 g/m2d at 380C and 90% relative humidity comprising (a) a layer of paper having a weight between 20 and 400 g/m2, (b) a layer of ethylene copolymer or grafted ethylene copolymer having a weight between 1 and 5 g/m2 adjacent to layer (a), and (c) a layer of nylon comprising between 5 and 100 weight % of amorphous nylon and 0 and 95 weight % semicrystalline polyamide 6 having a weight between 10 and 30 g/m2 adjacent to layer (b). This packaging material is particularly useful for packaging dairy products, such as cheese, butter and margarine.

The packaging material may be made by means known in the art such as by coextrusion coating or lamination of coextruded film onto paper.

Detailed description of the invention As used herein, the following terms have the meanings given below.

'Flexible packaging material' means packaging sheet material suitable for wrapping goods, e.g. the aforementioned dairy products. 'Semi-flexible packaging material'

means packaging material having a somewhat higher resistance to flex, typically having a board (e.g. cardboard) as paper layer (a). Semi-flexible packaging material may be thermoformed, as known in the art, to form desired shapes, such as trays.

'Oxygen barrier' measures the rate at which oxygen passes through the packaging material of the present invention, and is between 10 and 100 cc/m2d atm measured according to ASTM D 3985.

'Water vapor barrier' measures the rate at which water vapor passes through the packaging material of the present invention, and is between 100 and 1000 g/m2d at 38"C and 90% relative humidity.

Paper layer (a) can be any type of paper typically used in the packaging industry, flexible or semi-flexible, and having a weight between 20 and 400 git2. This weight governs the degree of flexibility of the paper. Paper, being a very porous material, does not control the oxygen or water vapor barrier properties of the packaging material of the present invention.

The ethylene copolymer of layer (b) can be ethylene vinyl acetate, ethylene-ethyl acrylate, ethylene-methyl acrylate or ethylene butyl acrylate, an ethylene-acid copolymer or its corresponding ionomer.

The ethylene-acid copolymers are copolymers of ethylene and a, -ethylenically- unsaturated C3-C8 carboxylic acid have the acid moiety present in an amount of 1 to about 25, (preferably 6 to 9) wt. % of the copolymer. The preferred acid moieties are methacrylic acid and acrylic acid.

The ethylene-acid copolymers can also be E/X/Y copolymers where E is ethylene; X is a softening comonomer and Y is the a, -ethylenically-unsaturated C3-C carboxylic acid, particularly acrylic or methycrylic acid. By "softening", it is meant that the polymer is made less crystalline. Suitable "softening comonomers (X) are monomers selected from alkyl acrylate, and alkyl methacrylate, wherein the alkyl groups have from 1 - 12 carbon atoms which, when present, may be up to 25 (preferably up to 15, most preferably up to 10) wt. % of the ethylene-acid copolymer.

Specific ethylene-acid copolymers include ethylene/acrylic acid, ethylene/methacrylic acid, ethylene/acrylic acid/n-butyl acrylate, ethylene/methacrylic acid/n-butyl acrylate, ethylene/methacrylic acid/iso-butyl acrylate, ethylene/acrylic acid/iso-butyl acrylate, ethylene/methacrylic acid/n-butyl methacrylate, ethylene/acriylic acid/methyl methacrylate, ethylene/acrylic acid/methyl acrylate, ethylene/methacrylic acid/methyl acrylate, ethylene/methacrylic acid/methyl methacrylate, and ethylene/acrylic acid/n- butyl methacrylate.

Corresponding ionomers of the ethylene-acid copolymers are formed by partially neutralizing the acid moiety. The acid moiety is partially neutralized with monovalent and/or bivalent metal cations such as lithium, sodium*, potassium, magnesium, calcium, barium, lead, tin, zinc* or aluminum (*= preferred), or a combination of such

cations. The mole percent of acid neutralized is up to about 70 %, preferably 30 to 50 %.

Ionomers can be made by processes well known in the art (cf. U.S. Pat. No. 3,262,272 to Rees, for example).

The graft of the ethylene copolymer will be maleic anhydride, typically in an amount between 0.1 and 3 weight %. Grafting can be carried out using techniques known in the art.

Optionally, layer (b) may further comprise up to 40 weight % of a copolyether ester, a copolyether amide or a polyurethane thermoplastic. Suitable copolyether esters are available under the name HytrelO from the DuPont Company; suitable copolyether amides are available under the name PebaxO from Elf Atochem.

Layer (b) will be applied to paper layer (a) at a weight between 1 and 5 g/m2 to assure the desired oxygen and water vapor barrier levels of the present invention are met.

Suitable ethylene copolymers for use in layer (b) are the BynelO and Surlyn(g families of resins, both available from the DuPont Company.

Nylon layer (c) can contain pure amorphous nylon or can be a blend of between 5 and 100 weight % of amorphous nylon and 0 and 95 weight % semicrystalline polyamide 6.

The term "amorphous polyamide" is well known to those skilled in the art, "Amorphous polyamide", as used herein, refers to those polyamides which are lacking in crystallinity as shown by the lack of an endotherm crystalline melting peak in a Differential Scanning Calorimeter ("DSC") measurement (ASTM D-3417), 10 "C/minute.

Examples of the amorphous polyamides that can be used include those amorphous polymers prepared from the following diamines: Hexamethylenediamine, 2- methylpentamethylenediamine, 2,2,4-trimethylhexamethylenediamine, 2,4,4- trimethylhexamethylenediamine, bis-(4-aminocyclohexyl)methane, 2,2-bis(4- aminocyclohexyl)isopropylidine, 1 4-diaminocyclohexane, 1,3 -diaminocyclohexane, meta-xylylenediamine, 1,5-diaminopentane, 1,4-diaminobutane, 1,3-diaminopropane, 2-ethyldiaminobutane, 1 ,4-diaminomeThylcyclohexane, p-xylylenediamine, m-phenylenediamine, p-phenylenediamine, and alkyl substituted m-pehnylenediamine and p-phenylenediamine.

Examples of polyamides that can be used include those amorphous polymers prepared from the following diacarboxylic acids: isophthalic acid, terephthalic acid, alkyl substituted iso- and terephthalic acid, adipic acid, sebacic acid, butane dicarboxylic acid, and the like.

Specific examples of amorphous polyamides which are suitable for this invention include: hexamethylenediamine isophthalamide, hexamethylenediamine isophthalamide/terephthalamide, copolymers of hexamethylene diamine and 2-

methylpentamethylenediame with iso-or terephthalic acids, or mixtures of these acids.

Polyamides based on hexamethylenediamine iso/terephthalamide containing high levels of terephthalic acid moiety may also be useful provided a second diamine such as 2-methyldiaminopentane is incorporated to produce a processible amorphous polymer.

The above amorphous polyamides may contain as comonomers minor amounts of lactam species such as caprolactam or lauryl lactam, even though polymers based on these monomers alone are not amorphous. The important feature is that the polyamide as a whole must be amorphous. Thus small amounts of these comonomers may be incorporated as long as they do not impart crystallinity to the polyamide. In addition, up to about 10 weight % of a liquid or solid plasticizer such as glycerol, sorbital, mannitol, or aromatic sulfonamide compounds (such as Santicizer 88 from Monsanto) may be included with the amorphous polyamide.

A suitable amorphous polyamide for use in the present invention is available from the DuPont Company under the tradename SELARPA.

The term "semicrystalline polyamide 6" is well known to those skilled in the art.

Semicrystalline polyamide 6 suitable for this invention are generally prepared from lactams or amino acids or from condensation of diamines such as hexamethylene diamine with dibasic acids such as sebacic acid. Copolymers and terpolymers of these polyamides are also included. A suitable semicrystalline polyamide 6 for use in the present invention is Durethang) B29, available from Bayer.

Layer (c) will be applied to paper layer (b) at a weight between 10 and 30 g/m2 to assure the desired oxygen and water vapor barrier levels of the present invention are met.

This packaging material is particularly useful for packaging dairy products, such as cheese, butter and margarine. It will be typically be produced by coextrusion coating of layers (b) and (c) onto layer (a), or by lamination of extruded or coextruded layers (b) and (c) onto layer (a). Optionally, the so prepared packaging material can be subsequently thermoformed into a desired shape, such as a tray.

Example 1 Layer (b) of BynelB 21E533 (an anhydride modified ethylene acrylate resin from DuPont) is coextruded with layer (c) of various blend of SelarB PA 3426 (an amorphous nylon from DuPont) and DurethanB B29 (a semicrystalline polyamide 6 from Bayer) and coated on paper.

The nylon blend is introduced into a 3.5" extruder with barrel temperatures set at 240, 280, 280, 280 and 280 "C. The BynelB 21E533 is introduced in 2.5" extruder with barrel temperatures set at 180, 220, 250, 270, 280 "C. Feed bloc and die temperatures are set at 2800C.

The 800 mm wide die is 150 mm (air gap) above the nip where it coats the paper. The paper is corona treated and run at the line speed of 200 m/min. The final so produced structure is: paper // The BynelQ) 21E533 // Selart) PA3426+Durethan) B29 40 g/m2 2 g/m2 12 g/m The following water transmission (38°C, 90% RH) and oxygen permeability (room temperature) is measured (% given by weight): Example water oxygen g/ m2d cc/ m2d atm 1.1 80% Selar(g) PA3426 + 20% DurethanO B29 400 32 1.2 50% " + 50% " 500 35 1.3 20% " + 80% " 800 43 The last two structures are particularly well suited for soft cheese packaging.

Example 2 Example 1 is repeated except that Surlynt) AD2 is substituted for BynelB 21E533.

SurlynO AD2 (2 g/m2) is coextruded with the blend 80 weight % SelarB PA3426 + 20 weight % DurethanO B29 (12 g/m2). The oxygen permeability is the same as in Example 1.1. Water permeability lowers to 250 g/m2d.

This structure when extruded on a glossy chill-roll has a very glossy appearance.

Together with the dead-foil, it can be used for candy and butter wrapping.

Example 3 Example 2 is repeated except that the paper layer is replaced with board having a weight of 200 g/m2. The board can be thermoformed to produce trays or lidding.

Example 4 Example 1 is repeated except that the 70 wt. % BynelO 21E533 and 30 wt % HytrelB 3548 is substituted for Bynelt 21E533.