IL96911A

IL96911A - Barrier film consisting of an alloy based on an ethylene-vinyl alcohol copolymer, its preparation and its use

Info

Publication number: IL96911A
Application number: IL9691191A
Authority: IL
Original assignee: Atochem
Priority date: 1990-01-15
Filing date: 1991-01-09
Publication date: 1994-12-29
Also published as: CA2034093C; NO910153D0; KR910014436A; FI910184A0; FI910184A; JPH0757834B2; EP0441666B1; ATE135726T1; GR3020026T3; CN1035680C; FR2657070A1; CA2034093A1; IL96911A0; FI103280B; KR0165125B1; ES2085444T3; ZA91294B; FI103280B1; CN1062278C; EP0441666A3

Abstract

Barrier films consisting wholly or partially of an alloy based on an ethylene-vinyl alcohol copolymer, a polypropylene and a compatibilising agent. These films have an improved resistance to hot water and to superheated steam and can be employed for packaging and especially for the packaging of foodstuffs.

Description

i>> 3 > i-^!? >nH iw ~ιο>>ιο·> i>j> oomnn ΑΪΟΟ nvyn ooin onp Barrier film consisting of an alloy based on an ethylene- vinyl alcohol copolymer, its prepartion, and its use ATOCHEM C: 82479 BARRIER FILM CONSISTING OF AN ALLOY BASED ON AN ETHYLENE-VI YL ALCOHOL COPOLYMER, ITS PREPARATION, ITS USE ESPECIALLY IN PACKAGING * * * * * * * * * The present invention relates to the field of films and more particularly that of so-called barrier films resisting hot water and superheated steam and intended for food packaging.

To ensure preservation of food products it is necessary to ensure not only protection against dust but also against moisture, against some gases such as oxygen and carbon dioxide and against odours.

Polymeric resins are employed for this purpose, which are known as barrier resins, which have gas and water vapour permeability properties, that is to say which are more or less permeable to gases and to water vapour.

The films generally consist of one or more layers consisting of polymers which are impervious to gases and of polymers which are impervious to water vapour.

Thus, when permeability to oxygen must be low, use is made of polymers whose barrier properties in respect of this gas are very high, such as, for example, ethylene-vinyl alcohol (EVOH) copolymers, which are recognised as being excellent materials in this respect.

If a sufficient protection against water vapour is to be obtained, a barrier layer consisting of polyolefins such as polypropylene is employed.

Since the requirements of imperviousness to gases and to water vapour vary from one form of packaging to another and from one food product to another, the films employed may consist of one or more polymer layers which have different gas and water vapour permeability properties.

To improve the quality of "fresh" food products and to increase their preservation time, the food products must be packaged aseptically.

Many processes exist for this purpose. For example, pasteurisation and sterilisation may be mentioned.

In these processes the packaging - or the packaged food product - is subjected to the action of hot water (85eC-100°C) or to the action of superheated steam for periods ranging from a few seconds to several hours. For example, in the case of sterilisation the temperature reaches 121eC or even 135°C-140eC. It is then necessary for the packaging consisting of a film which has one or more barrier layers to withstand mechanically the combined action of water and of temperature, as well as the pressures, which may reach 3 to 4 bars.

It is found that at the time of the sterilisation or under the effect of hot water, certain films, especially those based on EVOH, undergo degradation, which is seen as creasing of the affected layer or even a total delamination of the multilayer film.

A film which has an improved resistance to hot water and to superheated steam has now been found, which is characterised in that it consists wholly or partially of an alloy comprising at least one ethylene-vinyl alcohol (EVOH) copolymer, at least one polypropylene and at least one compatibilising agent.

The film according to the invention is characterised in that the alloy contains at least 30 % by weight of EVOH. Among these films preference will be given to those made from alloys comprising: - 42.5 % to 99.5 % by weight of EVOH - 42.5 % to 0.4 % by weight of polypropylene - 0.1 % to 15 % by weight of compatibilising agent.

The EVOH composition of the alloy is characterised by the fact that the matrix or dispersing phase is EVOH. The polypropylene is dispersed in the form of more or less spherical nodules or of small cylindrical rods.

The adhesion between the phases is preferably ensured by a graft copolymer based on an a-monoolefin called a compatibilising agent, which is described in European Patent Application published on 15.09.1989. under No. 0,342,066 and whose content is incorporated by reference in the present document.

Among the compatibilising agents mentioned in the European patent application mentioned as reference above, preference will be given to the compatibilising agents of formula AMXP: - AM denotes a backbone copolymer obtained by copolymerising propylene and a-olefins, - X is chosen from the group consisting of citraconic anhydride, fumaric acid, mesaconic acid, the anhydride of 3-allylsuccinic acid and maleic anhydride, - P denotes a polyamide oligomer derived from caprolactarn, 11-aminoundecanoic acid or dodecalactam.

The EVOH is a copolymer consisting essentially of ethylene and vinyl alcohol units and may contain small quantities of other monomer units, in particular of vinyl ester units. These copolymers may be obtained by saponification or partial or complete alcoholysis of ethylene-vinyl ester copolymer. Among the vinyl esters, vinyl acetate is the preferred monomer. The degree of saponification or of alcoholysis is at least 90 mol% and is preferably between 94 and 99.5 %. The molar proportion of ethylene in the EVOH is in the range from 3 to 75 % and preferably from 10 to 50 %.

The polypropylene is a polymer consisting essentially of propylene units. It may contain quantities (not exceeding 40 mol%) of another monomer .... unit, in particular ethylene and/or one or more a-olefins containing 4 to 6 carbon atoms . In particular, a homopolypropylene or a block propylene copolymer with 0.5 to 30 mol% of ethylene, or a random copolymer of propylene and ethylene containing 0.1 to 30 mol% of ethylene is employed.

Small quantities of other compounds of the stabiliser, antistatic agent or lubricant type and other polymeric compounds may be optionally added to three main constituents, which are EVOH, polypropylene and the compatibilising agent.

Since the constituents are in the form of powder or granules, the preparation of the alloy can be carried out in solution or in the molten state by means of a conversion machine of the single-screw or counter-or corotative twin-screw extruder type or a roll mill.

The monolayer films according to the invention consist wholly of alloy.

The multilayer films consist of at least one layer of alloy, the other layer or layers consisting of polymers chosen from the group consisting especially of polyethylene (PE), polypropylene (PP), polyamide (PA), polyethylene terephthalate (PET) and polycarbonate (PC).

A coextrusion binder, which ensures better adhesion between the layers must be employed in the case of some polymers.

In the multilayer films according to the invention the alloy layer may be external or internal.

The following films may be mentioned as examples of multilayer films according to the invention: - PP/alloy/PP - PP/coextrusion binder/alloy - PP/coextrusion binder/alloy/coextrusion binder/PP - PA/alloy.

The films according to the invention may be obtained by flat extrusion or by film blowing at temperatures of between 200°C and 260 C.

Apart from the coextrusion techniques using a flat die or an annular die, the films in accordance with the invention can be processed by techniques such as extrusion coating and extrusion lamination, the latter technique making it possible, for example, to combine a film and a sheet of metal such as aluminium.

The films according to the invention which are produced from the alloy exhibit an improved resistance to hot water and to superheated steam.

Thus, the single-layer or multilayer films subjected to superheated steam at temperatures of between 100°C and 140°C at pressures ranging from 1 to 4 bars, retain their transparency and have a virtually intact surface appearance, whereas the same films consisting wholly or partially of EVOH become opaque and are striated, distorted or delaminated.

The films according to the invention consisting wholly or partially of the alloy can be used in the production of various packagings and most particularly they can be employed for the manufacture of pouches, flexible envelopes, small tubs, pots, etc. for food packaging.

The films in accordance with the invention can also be employed for the manufacture of membranes employed in the medical field, in techniques such as haemodialysis or plasmapheresis.

The following examples illustrate the invention.

- Tests 1 to 5 a) Five compositions are produced with the aid of a corotative twin-screw extruder with the following proportions of the constituents: - EVOH: 99.3 % hydrolysed ethylene-vinyl acetate copolymer containing 32 mol% of ethylene with a melt index of 3.2 g/10 minutes measured at 210CC under 2.16 kg, - PP: random ethylene-propylene copolymer containing 3 % by weight of ethylene of MI 2 g/10 minutes, measured at 230°C under 2.16 kg, - compatibilising agent: graft copolymer as shown in Table I, prepared according to Example 1 of European Patent Application No. 0, 342,066. - In this table: A is a unit derived from propylene M is a unit derived from ethylene X is a unit derived from maleic anhydride P is a caprolactam oligomer of molecular mass 2,700, determined by potentiometric determination of the end amine functional groups. b) These compositions are then extruded in the form of a 20-μΐη thick film by means of a single-screw extruder at a temperature ranging from 210QC to 230°C.

These films are inspected using a scanning electron microscopy (SE ) after cryogenic fracture. (see Table I) .

Because of the orientation due to the film extrusion, the disperse phase is i the form of small rods which are oriented in the extrusion direction: the size of the small rods is measured on the fractures after dissolving the disperse phase in xylene.

The assessment of the adhesion between phases is made qualitatively on the fractures.

TABLE I COMPOSITION OF THE ALLOY SEM INSPECTION (% by weight) OF THE ALLOY AS 20-μπι THICK FILM TESTS EVOH PP COMPATIBILI - SING AGENT 1 com85 15 0 The PP is distriparative buted in the EVOH matrix in the form of small cylindrical rods from 0.7 to 5 m in cross- section. No adhesion between phases. 2 com80.75 14.25 663 136 The PP is distriparative Xo.65 : 4 buted in the EVOH matrix EVOH cont. in the form of small - 29 mol% 5 cylindrical rods from of ethy0.5 to 3 m in cross- lene : 1 section. A weak adhesion exists between phases. 3 80.75 14.25 663 136Χ2.β1 The PP is distributed in the EVOH matrix in the ^0.87 : 5 form of small cylindrical rods from 0.1 to 2 μιη in cross-section. A strong adhesion exists between phases. 4 85.5 9.5 ^663^136^2.91 The PP is distributed in P0.87 : 5 the form of the EVOH matrix in small cylindrical rods from 0.05 to 1. 5 /in in cross- section. A strong adhesion exists between phases . 5 com9.5 85.5 6e3M136X2.g1 The EVOH is distributed parative in the PP matrix in the ^0.87 : 5 form of small cylindrical rods from.0.1 to 2 μιη in cross-section. A strong adhesion exists between phases. c) Hot water resistance of single-layer films 1) Film composition - Example 1 (Comparative) Composition of the single-layer film: 100 % of ethylene-vinyl alcohol copolymer containing 32 % of ethylene (melt index: 3.2 g/10 minutes, measured at 210 °C under 2.16 kg) - Example 2 Composition of the single-layer film according to the invention: 100 % of the alloy which has the following composition by weight: EVOH of Example 1: 80.75 % PP: random ethylene-propylene copolymer containing 3 % of ethylene (Mis 10-230°C/2.16 kg): 14.25 % compatibilising agent Α^Μ^Χ-, 91P087: 5 % - Example 3 (Comparative) Composition of the single-layer film: 100 % of ethylene-vinyl alcohol copolymer containing 44 mol% of ethylene (MI: 3.5-210/2.16 kg).

- Example 4 Composition of the single-layer film according to the invention: 100 % of the alloy which has the following weight composition: EVOH of Example 3 : 80.75 % polypropylene of Example 2 : 14.25 % compatibilising agent of Example 2 : 5 % - Example 5 Film which has the composition of the film of Example 2, but obtained by blow extrusion. 2) Conditions of the hot water behaviour tests The films are stretched in a transparency frame and are then immersed for 30 minutes in a bath of distilled water at constant temperature and gently stirred using a bar magnet .

- Assessment of the results At the end of the test, film appearance and transparency are assessed according to the following arbitrary classification: Appearance; A : unchanged Transparency B : streaked from 1: unchanged C : creased to D : holed 4: opaque Thus a film which is unchanged in appearance and opaque will be classified as A4.

The results are listed in Table II TABLE II The single-layer films according to the invention - Examples 2 , 4 and 5 - exhibit a better behaviour towards hot water than the single-layer films based on EVOH - Examples 1 and 3. The best results are obtained with the alloy based on EVOH containing 32 mol% of ethylene (Example 5) . d) Superheated steam f sterilisation) resistance 1) Film composition - Example 6 (Comparative^ Composition of the single-layer film: as Example 1.

- Example 7 Composition of the single-layer film: as Example 2. 2) - Conditions of the superheated steam behaviour tests The tests carried out at a temperature equal to or higher than 100 eC were performed in an autoclave.

The films, stretched in a stainless steel frame (5 x 5 cm), are arranged in the autoclave and subjected for 30 minutes to the test conditions which may take place either in saturated steam or in superheated water.

In the case where the test is carried out using superheated water the water, is preheated in a storage vessel adjoining the autoclave and is then quickly introduced into the autoclave by means of a device designed for this purpose.

In the case of the tests carried out with superheated steam the pressures range from 1 to 3 bars.

- Assessments of the results The arbitrary classification mentioned above in the case of the hot water behaviour tests is employed.

Results - Temperature of the superheated steam: 120eC - Example 6 fComparative) D4 - Example 7 Bl e) Resistance of three-laver films to superheated steam 1) Film composition Three-layer films whose composition and thicknesses are listed in Table III are obtained by blow coextrusion.

In this table, copolymer X denotes a coextrusion binder (propylene-ethylene copolymer grafted with maleic anhydride) .

These tests were carried out on a three-layer blow coextrusion equipment. 2) Coextrusion conditions - Extruder 1 (copolymer X) temperature: 210eC - 230°C screw speed: 132 rev/min - Extruder 2 (copolymer X) temperature: 210eC - 230eC screw speed: 122 rev/min - Extruder 3 (alloy or EVOH) temperature: 210°C - 230eC - Die: diameter : 150 mm blow ratio : 8.12 temperature : 220°C - Draw speed: 8.83 m/min The results are collated in Table IV.

TABLE IV f) Resistance of five-layer films to superheated steam 1) Film composition Five-layer films whose composition and thicknesses are collated in Table V are obtained by flat coextrusion.

TABLE V Coextrusion conditions These tests were carried out on a five-layer coextrusion equipment.

- Extruder (PP) temperature: 200°C - 245°C - Extruder (coextrusion binder) temperature: 220eC - 245 °C - Extruder (EVOH or alloy) temperature: 215 eC - 245"C - Die gaps 0.7 mm, width 2 m temperature: 2500C The results are collated in Table VI.

TABLE VI

Claims

9691 1 / 2 - 1 8 - Claims:

1. A polymer alloy comprising (a) an oxygen-barrier effective amount of at least one ethylene-vinyl alcohol (EVOH) copolymer; (b) a water vapor-barrier effective amount of at least one polypropylene, and (c) a compatibilizing amount of at least compatabilizing agent therefore comprising a graft copolymer having the formula AMXP in which AM comprises a propylene/ -olefin backbone copolymer, X comprises a citraconic anhydride, fumaric acid, mesaconic acid, 3-allysuccinic acid anhydride or maleic anhydride structural unit, and P comprises a polyamide oligomer of caprolactam, 11,-aminoundecanoic acid or dodecalactam.

2. Film according to Claim 1, characterised in that the alloy comprises at least 30 % by weight of EVOH.

3. Film according to Claim 1 or 2, characterised in that the alloy comprises : - 42.5 % to 99.5 ¾ by weight of EVOH - 0.2 % to 42.5 % by weight of polypropylene " 0.1 % to 15 % by weight of ccmpatibilising agent.

4. Film according to any one of Claims 1 to 3, characterised in that the molar proportion of ethylene in the EVOH is in the range 3 % to 75 % and preferably from 10 % to 50 %.

5. Multilayer film comprising at least one layer 96911/3 - 19 - consisting of an alloy such as described in Claim 1.

6. * Multilayer film according to Claim 5> in which the other layer or layers consist of polymers chosen from the group consisting of polyethylene, polypropylene, polyamide, polyethylene terephthalate and polycarbonate.

7. A film according to any one of Claims 1 to 6, for use as packaging material. 8· A film for the use according to Claim 7 , for packaging foodstuffs. 9· Materials and articles packaged by means of the film according to any one of Claims 1 to 6. For the Applicants, DR