WO1998049006A1

WO1998049006A1 - Multi-layered stretched hot-sealable polypropylene film with a polyketone gas barrier layer

Info

Publication number: WO1998049006A1
Application number: PCT/EP1998/002348
Authority: WO
Inventors: Bernd Sperlich; Rainer Brandt
Original assignee: Wolff Walsrode Ag
Priority date: 1997-04-30
Filing date: 1998-04-21
Publication date: 1998-11-05
Also published as: AU7527998A; CA2288158A1; EP0977665A1; DE19718199A1; BR9809372A

Abstract

The invention relates to a heat-sealable composite film with a biaxially stretched polypropylene base layer, a modified polyolefin adhesion-promoting layer, an ethylene and carbon monoxide copolymer gas barrier layer and an olefin polymer heat-seal layer. The base layer has optionally at least one monoaxially oriented layer combination on at least on one of its surfaces, comprising: A) an olefinic homo, co or terpolymer heat-sealable outer layer; B) a modified polyolefin adhesion-promoting layer; C) a one or more olefin or carbon monoxide (polyketone) gas barrier layer; D) a modified polyolefin adhesion-promoting layer and E) a polyethylene layer and an ethylene polymer with at least 3 wt. % ethylene. The base layer has optionally layer A, a combination of layers A-E, A-D or B and C on at least one of its surfaces.

Description

MULTI-LAYER, STRETCHED, HOT-SEALABLE POLYPROPYLENE FILM WITH POLYKF TON GAS BARRIER ru ^{L. if} t ^ji -

The present invention relates to a sealable, stretched multilayer film which, owing to its gas barrier properties, is particularly suitable as packaging film for goods which require low gas permeability and aroma protection.

The use of composite films made of polyolefins with a sealable layer of ethylene homo- or copolymers as packaging film has long been known. Attempts have also already been made to improve the gas permeability of such composite films by incorporating various polar barrier layer materials. In DE-A-

2,644,209 and EP 0 062 815 B1, the gas permeability is considerably reduced by incorporating a layer of saponified ethylene vinyl acetate. Saponified ethylene vinyl acetate has considerable disadvantages with regard to its processability. Due to the high metal adhesion and the low temperature stability, it often leads to polymeric deposits in the extruder and the extrusion die during extrusion.

In order to achieve a low gas permeability, the use of ethylene vinyl alcohol copolymers with a relatively high content of vinyl alcohol is necessary. This has the disadvantage that composite films made of PP and EVOH have only low stretchability and require relatively high stretching temperatures. A major disadvantage of barrier films with ethylene vinyl alcohol copolymers as the barrier layer is their low resistance to kink fracture, which is particularly difficult in the manufacture of tubular bags.

Polyamides as barrier materials have significantly poorer barrier properties, which are not sufficient for many applications.

It has therefore proven necessary to produce a multilayer, heat-sealable BOPP film which contains a barrier layer material which has a high oxygen barrier, is easy to process and leads to a high resistance to kink breakage of the film composite.

This problem is solved by a heat-sealable composite film made of a biaxially stretched polypropylene film as the base film, an adhesion promoter layer made of modified system polyolefin, a gas barrier layer of a copolymer of one or more olefins and carbon monoxide and a heat seal layer of olefin polymers, characterized in that the base film carries at least on one surface an optionally at least monoaxially oriented layer combination, which is composed of

A) a heat-sealable outer layer made of an olefinic homo-, co- or terpolymer;

B) an adhesion promoter layer made of modified polyolefin; C) a gas barrier layer made of a copolymer of one or more olefins and carbon monoxide (polyketone), in which the olefin (s) and carbon monoxide are incorporated in an alternating sequence;

D) an adhesion promoter layer made of modified polyolefin and

E) a layer of polyethylene an ethylene polymer with at least 3% by weight of ethylene,

the base film optionally carries a layer A, a layer combination A to E, A to D or B and C on at least one of its surfaces.

Optionally, layers A and B and / or D and E or the layers

B and C or C and D can be combined to form a layer by mixing the corresponding polymers.

The preferred feature is that the biaxially stretched and heat sealable polypropylene film made by a sequential process contains a gas barrier layer made from a copolymer of carbon monoxide and one or more olefinically unsaturated compounds. In principle, all monomers of this class of compounds can be considered as olefinically unsaturated compounds. Ethylene and C ₃ - to Cio-alkenes such as propylene, 1-butene, 2-butene, 1-pentene, 1-hexene, 1-octene, 1-nonen, 1-decene are preferred. Are particularly preferred

Ethylene and propylene. The barrier layer material preferably consists of a copolymer of 25 to 50 mol% of ethylene, 0-25 mol% of propylene and 50 mol% of carbon monoxide, the olefinically unsaturated compounds and carbon monoxide are incorporated alternately in the copolymer. The partial exchange of ethylene with higher olefins lowers the melting point and improves the stretchability of the copolymer.

The polypropylene of the core film is preferably an isotactic polypropylene with a density of 0.90 to 0.91 g / cm ³ and a melt flow index of 1 to 4 g / 10 min at 230 ° C / 2.16 kp / cm ² pressure (DIN 53 735).

Among the numerous materials used for sealable layers, the following are preferred:

- statistical propylene / ethylene copolymers

- statistical propylene / olefin (1) copolymers

- statistical propylene / ethylene / olefin terpolymers - mixtures of two or three of the above polymers.

A propylene / ethylene copolymer is particularly preferably characterized in that it contains 1.0 to 10% by weight of polyethylene. The density of the sealing layer polymer should preferably be in the range from 0.895 to 0.960 g / cm ³ and the crystallite melting point, depending on the type, in the range from 125 to 148 ° C.

In order to ensure good machinability of biaxially oriented polypropylene films, it is necessary to equip at least the sealing or cover layers with additives such as lubricants, antiblocking agents and antistatic agents.

Preferred antistatic agents are alkali alkane sulfonates, polyether-modified, ie ethoxylated and / or propoxylated, polydiorganosiloxanes (polydialkylsiloxanes, polyalkylphenylsiloxanes and the like) and / or the essentially straight-chain and saturated aliphatic, tertiary amines with an aliphatic radical, having 10 to 20 to 20 atoms which are substituted with ω-hydroxy (C 1 -C ₄ ) alkyl groups, N, N-bis (2-hydroxyethyl) alkylamines having 10 to 20 carbon atoms, preferably 12 to 18 carbon atoms, being particularly suitable in the alkyl radical . The effective amount of antistatic is in the range of 0.05 to 0.5% by weight. Glycerol monostearate is also suitable and is used in an amount of 0.03% to 0.5% by weight as an antistatic.

Suitable antiblocking agents are inorganic additives such as silicon dioxide, calcium carbonate, magnesium silicate, aluminum silicate, calcium phosphate and the like and / or incompatible organic polymers such as polyamides, polyacrylates, polymethacrylates, polyesters, polycarbonates and the like; preference is given to using polymethacrylates and silicon dioxide. The effective amount of antiblocking agent is in the range of 0.1 to 2% by weight, preferably 0.1 to 0.8% by weight. The average particle size is between 1 and 6 μm, in particular 2 and 5 μm, particles with a spherical shape being particularly suitable.

Lubricants are higher aliphatic acid amides, higher aliphatic acid esters, waxes and metal soaps as well as polydimethylsiloxanes. The effective amount of lubricant is in the range of 0.01 to 3% by weight, preferably 0.02 to 1% by weight. The addition of higher aliphatic acid amides in the range from 0.01 to 0.25% by weight is particularly suitable. A particularly suitable aliphatic acid amide is erucic acid amide. The addition of polydimethylsiloxanes in the range from 0.02 to 2% by weight is preferred, in particular polydimethylsiloxanes with a viscosity of

5000 to 1,000,000 mm ² / s.

Modified polyolefins are used to produce the adhesion promoter layer. These are preferably polyolefins with carboxyl groups, such as polypropylene or polyethylene, which contain copolymers of at least one monomer from the group of the α, β-monounsaturated dicarboxylic acids, such as maleic acid, fumaric acid, itaconic acid or their acid anhydrides, acid esters, acid amides and acid imides Ethylene with α, ß-monounsaturated carboxylic acids, such as acrylic acid, methacrylic acid and / or their metal salts (Zn, Na) and / or their alkyl (C 1 -C ₄ ) esters or corresponding graft polymers on polyolefins such as polyethylene or polypropylene or already Saponified copolymers described which have been graft-polymerized with a monomer of the abovementioned unsaturated acids. Particularly preferred are polyolefins such as polypropylene or copolymers of propylene and ethylene with a maximum of 1.0% by weight of grafted on α, β-monounsaturated dicarboxylic acid anhydride such as maleic anhydride or their saponified copolymers.

If the adhesion promoter polymer is incorporated either in the sealable layer A or in the gas barrier layer C, up to 40% by weight, preferably 25-30% by weight, based on layer-forming polymers, of the modified polyolefin are used to produce the corresponding polymers.

The invention further relates to packaging preferably for oxygen-sensitive foods made from the multilayer film according to the invention.

The films according to the invention can be prepared using the customary processes such as lamination,

Coating or melt coextrusion can be produced. After the extrusion and the solidification of the thick film on the casting roll, the film is stretched in the running direction (lengthways) with a stretching ratio of 4/1 to 7/1 at a temperature of 120 ° C - 150 ° C. The stretch ratio in the transverse direction is preferably between 8/1 and 12/1 and the transverse stretching of the film is carried out at a temperature between 130 ° C. and 170 ° C. The subsequent heat setting is preferably carried out at 1 ° C - 40 ° C below the transverse stretching temperature. In order to ensure the affinity of the largely non-polar film surface for the printing inks, it is necessary to subject the film to a corona (spray) pretreatment. The atmospheric oxygen is stored in the form of carbonyl, epoxy, ether or alcohol groups on the film surface. Other methods of pretreating polypropylene films are flame, plasma and fluorine pretreatment. example

To produce a layer combination, 98.7% by weight of a propylene-ethylene copolymer with 4.5% by weight of ethylene had a density of 0.90 g / cm ³ with a melt index of 5 g / 10 min for layer A 230 ° C / 2.16 kp / cm ² and the crystalline melting point 140 ° C 0.5 wt .-% N, N-bis (2-hydroxyethyl) - (C ₁₂ -C ₁₆ ) alkylamine, 0, 3 wt .-% of a polydimethylsiloxane with a density of 0.985 g / cm ³ at 20 ° C. and a viscosity of 10 ⁶ m Pa s and 0.3 wt .-% silicon dioxide with an average particle size of 2.5 μm and incorporated with a modified polypropylene such as a saponified copolymer with 0.7% by weight of grafted maleic anhydride and a melt index of 5 g / 10 min at 250 ° C / 216 kp / cm ² for the adhesion promoter layers and an alternating carbon monoxide-ethylene copolymer (F. 220 ° C, MFI 6ml / 10min at 230 ° C / 2.16 kg) co-extruded for the gas barrier layer, according to conventional methods with the base film made of polypropylene with a density of 0.905 g / cm ³ , with which Melt index of 2 g / 10 min at 230 ° C / 2.16 kp / cm ² and that

Softening range of 160 to 166 ° C connected and stretched so that a composite film with a longitudinal stretching in the ratio 5: 1 and a transverse stretching in the ratio 10: 1 was obtained. The layer structure and the layer thicknesses are summarized in Table 1. The oxygen barrier of the composite film is 15 cm ³ / m ² d bar.

Table 1

Layer structure and layer thickness:

P E-Copo 1 μm

HV 0.5 μm

1 µm polyketone

HV 0.5 μm

PP 24 μm

HV 0.5 μm

1 µm polyketone

HV 0.5 μm

P / E-Copo 1 μm

Claims

claims

1) Heat-sealable composite film made of a biaxially stretched polypropylene film as the base film, an adhesion promoter layer made of modified polyolefin, a gas barrier layer made of a copolymer of ethylene and carbon monoxide and one

Heat seal layer made of olefin polymers, characterized in that the base film carries at least on one surface an optionally at least monoaxially oriented layer combination, which is composed of

A) a heat-sealable outer layer made of an olefinic homo-, co- or terpolymer;

B) an adhesion promoter layer made of modified polyolefin;

C) a gas barrier layer made of a copolymer of one or more olefins and carbon monoxide (polyketone); D) an adhesion promoter layer made of modified polyolefin and

2) composite film according to claim 1, characterized in that the gas barrier layer consists of a terpolymer of carbon monoxide, ethylene and propylene.

3) composite film according to claim 1, characterized in that carbon monoxide and the / the olefins are installed in an alternating sequence in the terpolymer of the gas barrier layer.

4) composite film according to claim 3, characterized in that the terpolymer consists of 50 mol% carbon monoxide, 25-24 mol% ethylene and 5-25 mol% propylene. 5) Composite film according to claim 1, characterized in that the layers A and B and / or D and E or the layers B and C or C and D are combined to form a layer by mixing the corresponding polymers.

6) Composite film according to at least one of the preceding claims, characterized in that at least the sealing or cover layers are equipped with additives such as lubricants, antiblocking agents and antistatic agents.

7) Composite film according to claim 1, characterized in that the layer B made of polypropylene or polyethylene with grafted units of maleic acid, fumaric acid, itaconic acid or their acid anhydrides, acid esters, acid amides and acid imides or copolymers of ethylene with acrylic acid, methacrylic acid, and / or their metal salts and / or their alky ^ d -estem or corresponding graft polymers.

8) Composite film according to claim 1, characterized in that the layer polymers A and E and / or B and D are identical.

9) composite film according to at least one of the preceding claims, characterized in that the layer combination by lamination or

Melt extruding is produced.

10) composite film according to at least one of the preceding claims, characterized in that it is flame, plasma or corona pretreated on the outer cover layers.

11) Packaging, preferably for food, made from composite films according to one of the preceding claims.