AU649641B2

AU649641B2 - Barrier film consisting of an alloy based on an ethylene-vinyl alcohol copolymer, its preparation, its use especially in packaging

Info

Publication number: AU649641B2
Application number: AU69355/91A
Authority: AU
Inventors: Richard Audry; Pierre Nogues
Original assignee: Atochem SA
Current assignee: Arkema France SA
Priority date: 1990-01-15
Filing date: 1991-01-14
Publication date: 1994-06-02
Anticipated expiration: 2011-01-14
Also published as: ES2085444T3; PT96475A; ZA91294B; CN1035680C; IL96911A; CN1121089A; FI103280B; CN1062278C; CA2034093A1; FI910184A0; IL96911A0; ATE135726T1; DK0441666T3; JPH04211443A; DE69118000D1; AU6935591A; FR2657070A1; FI103280B1; FI910184L; JPH0757834B2

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

la The present invention relates to the field of films and more particularly so-called barrier films which resist hot water and superheated steam and are intended for food packaging.

5 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 *0 1* e carbon dioxide and against odours.

Polymeric resins are employed for this purpose; these are known as barrier resins, which have gas .o..oo and water vapour permeability properties, that is to say 0 they are more or less permeable to gases and to water vapour.

The films generally consist of one or more 15 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 ethylene-vinyl alcohol (EVOH) copolymers, which are recognised as being excellent 2

S

CU

5

S..

*U..S

9o S055 U S S. C 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.

15 In these processes the packaging or the packaged food product is subjected to the action of hot water (85 0 C-100 0 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 121 0 C or even 135oC-1400C. 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 has been found that at the time of the sterilisation or under the effect of hot water, certain films, especially those based on EVOH, undergo degradation, 3 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, according to the present invention, which is characterised in that it consists wholly or partially of an alloy (or blend) comprising at least one ethylene-vinyl alcohol (EVOH) copolymer, at least one propylene polymer and at least one compatibilising agent.

According to the present invention there is provided a method of packaging food which method comprises packaging the food in a film which comprises a blend of at least one ethylene-vinyl alcohol (EVOH) copolymer, at least one propylene polymer and at least one compatibilising agent.

15 The film used according to the invention is generally 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: @sese 42.5% to 99.5% by weight of EVOH 42.5% to 0.4% by weight of propylene polymer 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 25 propylene polymer may be dispersed in the form of more or 3A less spherical nodules or of small cylindrical rods.

The adhesion between the phases is preferably ensured by a graft copolymer based on an cc-monoolefin referred to as a compatibility agent, whiLh is described in European Patent Application No. 0,342,066.

Among the compatibilising agents mentioned in the 0 0@ 0 IN:\IibR)00288:KEH 3a 3 ut I

*SO

S S 0

S*

S...r 4 European patent application mentioned as reference above, preference is given to the compatibilising agents of formula

AMXP:

AM denotes a backbone copolymer obtained by copolymer!.sing propylene and one or more 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 caprolactam, 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 desirably at least mol% and is preferably from 94 to 99.5 The molar 20 proportion of ethylene in the EVOH is desirably from 3 to and preferably from 10 to 50 The propylene polymer (hereafter referred to simply as "polypropylene") is a polymer consisting essentially of propylene units. It may contain quantities (generally 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 0 C 5 propylene copolymer with 0.5 to 30 mol% of ethylene, or a random copolymer of propylene and ethylene containing 0.1 to 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 generally in the form of 10 powder or granules, the preparation of t'ie blend/alloy can rO** 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.

Monolayer filmsAaccording to the invention will 15 generally consist wholly of the alloy.

Ce Osec Multilayer filmsconsist of at least one layer of alloy, the other layer or layers usually consisting of polyethylene polypropylene polyamide (PA), polyethylene terephthalate (PET) and polycarbonate (PC).

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

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

6 The following films may be mentioned as examples of use4 multilayer filmsAaccording to the invention: PP/alloy/PP PP/coextrusion binder/alloy PP/coextrusion binder/alloy/coextrusion binder/PP PA/alloy.

useo4 The filmsAaccording to the invention may be obtained by flat extrusion or by film blowing at temperatures of, say, 200 0 C to 260 0

C.

10 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 S 15 sheet of metal such as aluminium.

usa 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 20 subjected to superheated steam at temperatures of 100°C to 140 0 C at pressures 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.

used The films according to the invention consisting -7wholly or partially of the alloy can be used in the form of pouches, flexible envelopes, small tubs or pots.

The following Examples further illustrate the present invention.

Tests 1 to 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 210 0 C under 2.16 kg, PP: random ethylene-propylene copolymer containing 3% by weight of ethylene of MI 2 g/10 minutes, measured at 15 230 0 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: 20 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-pm thick film by means of a singlescrew extruder at a temperature ranging from 210 0 C to 230°C.

These films are inspected using a scanning 10 electron microscopy (SEM) after cryogenic fracture.

S* (see Table I).

Because of the orientation due to the film s extrusion, the disperse phase is in the form of small rods which are oriented in the extrusion direction: the size of the small rods is measured on the fractures 6/ after dissolving the disperse phase in xylene.

The assessment of the adhesion between phases 6' is made qualitatively on the fractures.

a l 9 TABLE I COMPOSITION OF THE ALLOY SEM INSPECTION by weight) OF THE ALLOY AS 20-pm THICK FILM TESTS EVOH PP COMPATIBILI- SING AGENT 1 comparative 6e@ C *e 6o *6 C

C

S.

C@o 1 e@ CCl *0 o Cooo 2 comparative 85 80.75 80.75 85.5 9.5 15 14.25 14.25 9.5 85.5

A

66 3

MI

3 6 X0. 65 4 EVOH cont.

29 mol% of ethylene: 1

A

66 3

M

1 35

X

2 91 PO. 67 5 A663MI36X2.91 PO. 87 5

A

86 3

M

136

X

2 .91 The PP is distributed in the EVOH matrix in the form of small cylindrical rods from 0.7 to 5 pm in crosssection. No adhesion between phases.

The PP is distributed in the EVOH matrix in the form of small cylindrical rods from 0.5 to 3 pm in crosssection. A weak adhesion exists between phases.

The PP is distributed in the EVOH matrix in the form of small cylindrical rods from 0.1 to 2 Am in cross-section. A strong adhesion exists between phases.

The PP is distributed in the form of the EVOH matrix in small cylindrical rods from 0.05 to 1. 5 pm in crosssection. A strong adhesion exists between phases.

The EVOH is distributed in the PP matrix in the form of small cylindrical rods from 0.1 to 2 pm in cross-section. A strong adhesion exists between phases.

comparative

PO.

87 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

C

10 according to the invention: 100 of the alloy which has S* C the following composition by weight: EVOH of Example 1: 80.75 i e.

PP: random ethylene-propylene copolymer containing 3 of ethylene (MI: 10-230 0 C/2.16 kg): 14.25 S 15 compatibilising agent Ag 63 Mi 36 Xz.

91

P

087 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).

20 Example 4 Composition of the single-layer film according to the invention: 100 of the alloy which has the following weight composition: 11 EVOH of Example 3 80.75 polypropylene of Example 2 14.25 compatibilising agent of Example 2 5 Example Film which has the composition of the film of Example 2, but obtained by blow extrusion.

2) Conditions of the hot water behaviour tests 6 *e "The films are stretched in a transparency frame 10 and are then immersed for 30 minutes in a bath of distilled S* water at constant temperature and gently stirred using a bar 0 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 0 B streaked from 1: unchanged C creased to 20 D holed 4: opaque Thus a film which is unchanged in appearance and I opaque will be classified as A4.

12 The results are listed in Tabl.e II *b 0 0 *00 0 00 0 S so. 0 S. 00 0 0 0 *5*0

OS

*0 0 0e 0 5004 Water temperature under 1 bar) 80 0 C 90 0 C 9 5 0

C

1 (Comparative) Al D4 D4 2 Al B3 C3 3 (Comparative) Al Al D4 4 Al A2 B2 5 IAI 'Al A2 0 000000 0004 00 is.

**S

000000 *0 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 EVON containing 32 mol% of ethylene (Example 13 d) Superheated steam (sterilisation) resistance 1) Film composition Example 6 (Comparative) Composition of the single-layer film: as Oxample 1.

Example 7 Composition of the single-layer film: as Example 2.

war 0 0 a 00 00 0t a a a. a *a 0 *r S a a *0 a a t S 10 2) Conditions of the superheated steam behaviour tests The tests carried out at a temperature equal to or higher than 100 0 C were performed in an autoclave.

The films, stretched in a stainless steel frame (5 x 5 cm), are arranged in the autoclave and 15 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.

14 Results Temperature of the superheated steam: 120*C Example 6 (Compara~iy2.) D4 Example 7 B1 e) Resistance of three-layver films to superheated steam me em S *0O em 10 *0 0.

0 0 0 'mm'

CO

*6 0

OC

0 0 1) Film comosition Three-layer films whose composition and thicknesses are listed in Table III are obtained by blow coextrus ion.

COMPOSITION 8 9 Layer I. copolymer X 40 pm 40 pim Layer 2 EVOH of Example 3 10 jam Layer 2 alloy of Example 2 10 pm Layer 3 copolymer X 40 ur, 40 pam

C

0 moe em 0 0061 00 0@ 0 0 *3.

0 0 TABLE III In this table, copolymer X denotes a coextrusion binder (propylene-ethylene copolymer grafted with maleic anhydride).

P.

a S.

C B

C.

10 B* CC

S

5655

SU

.6 t.

a These tests were carried out on a three-layer blow coextrus ion equipment.

2) Coextrusion conditions Extruder 1 (copolymer X) temperdture: 210 0 C 230 0

C

screw speed: 132 rev/min Extruder 2 (copolymer X) temperature: 210aC 230 0

C

screw speed: 122 rev/mmn Extruder 3 (alloy or EVOH) temperature: 210 0 C 230 0

C

Die: diameter :150 mm blow ratio :8.12 temperature :220 0

C

Draw speed: 8.83 rn/mmn The results are collated in Table IV.

Temperature of the superheated steam 120 0 C 1 33 0C

EXMPLES

8 A4 A4 9 A2 A3 TABLE IV f) Resistance of five-layer films to sup-erheated

S

*0e~e* C 0 a *4 S 54*54

S

a. S.

9~ Ce.

S

*46. CC

I

0 u 16 steam 1) Film composition Five-layer films whose composition and thicknesses are collated in Table V are obtained by flat coextrusion.

a a a a i~ aS @4 4 a a a a a S. ha a ma...

EXAMPLESII

LAYER 10 11 12

COMPOSITION

Layer 1: PP 75 Am 50 pm 50 pm Layer 2: coextrusion binder 20 pm 10 pm 10 pA Layer 3: alloy of Example 2 20 pm 10 pm Layer 3: EVOH cont. 38 mol% of ethylene 10 AM Layer 4: coextrusion binder 20 pm 10 pm 10 pAM Layer 5: PP 75 pm 50 pM 50 pm a N S @4 .S a aaaq a @4 a. a a 5515 @4 a a. Sa p Sq..

a *4544 a TABLE V 2) Coextrusion conditions 44 o -e coextrus ion These tests were carried out on a five-layer equipment.

Extruder (PP) temperature: 200 0 C 245*C Extruder (coextrusion binder) temperature: 220 0 C 245 0

C

Extruder (EVOH or alloy) temperature: 215 0 C 245 0

C

II.

S

I

S IS b I S b~I 4

S.

I S a I 11(4 p II Ip I

IS

I SIll '11114 4

SSSI

It IA P

S

111115

S

SIll

S

WIll

I

1511 I I I 10 Die gap: 0.7 mm, width 2 m temperature: 250 0

C

The results are collated in Table VI.

TABLE VI

Claims

1. A method of packaging food which'method comprises packaging the food in a film which comprises a blend of at least one ethylene-vinyl alcohol (EVOH) copolymer, at least one propylene polymer and at least one compatibilising agent.

2. A method according to claim 1 in which the blend comprises at least 30% by weight of EVOH.

3. A method according to claim 1 or 2 in which the blend comprises:

42.5% to 99.5% by weight of EVOH 0.2% to 42.5% by weight of propylene polymer 0.1% to 15% by weight of compatibilising agent. 4. A method according to any one of claims 1 to 3 in which the compatibilising agent is a graft copolymer of formula AMXP in which: AM denotes units of a backbone copolymer obtained by copolymerising propylene and one or more a-olefins, X denotes units derived from citraconic anhydride, 20 fumaric acid, mesaconic acid, the anhydride of 3- allylsuccinic acid or maleic anhydride, and P denotes units of a polyamide oligomer derived from caprolactam, 11-aminoundecanoic acid or dodecalactam. 5. A method according to any one of claims 1 to 4 in which the molar proportion of ethylene in the EVOH is from 3% to .O 19 6. A method according to claim 5 in which the molar proportion of ethylene in the EVOH is from 10% to 7. A method of packaging food which'comprises packaging the food in a multilayer film comprising at least one layer which is a film as defined in any one of claims 1 to 6. 8. A method according to claim 7 in which the other layer or layers of the film consist of polyethylene, polypropylene, polyamide, polyethylene terephthalate or polycarbonate. 9. A method according to any one of claims 1 to 8 which further comprises subjecting the packaged food to the action of water at 85 0 C to 100 0 C or of superheated steam. 10. A method according to claim 1 or 7 wherein S; 15 the film used is substantially as described in any one of Examples 2, 4, 5 and 7 to 12. 11. Food whenever packaged by the method claimed in any one of claims 1 to Soo Dated 5 April, 1994 Atochem •oeo Patent Attorneys for the Applicant/Nominated Person SPRUSON FERGUSON *o