EP0977664A1

EP0977664A1 - Metallizable bopp film with an outer polyketone layer

Info

Publication number: EP0977664A1
Application number: EP98920542A
Authority: EP
Inventors: Bernd Sperlich; Rainer Brandt
Original assignee: Wolff Walsrode AG
Current assignee: Dow Produktions und Vertriebs GmbH and Co oHG
Priority date: 1997-04-30
Filing date: 1998-04-21
Publication date: 2000-02-09
Also published as: AU7336198A; DE19718192A1; CA2287898A1; WO1998049007A1; BR9809371A

Abstract

The invention relates to a heat-sealable composite film comprising A) a base layer of preferably biaxially stretched polypropylene; B) an adhesion-promoting layer of modified polyolefin on at least one side of base layer (A); C) an outer layer of a copolymer consisting of one or several olefins and carbon monoxide (polyketone) located on the adhesion-promoting layer(s) (B).

Description

Metallizable BOPP film with polyketone outer layer

The invention relates to a multilayer, preferably biaxially stretched, heat-sealable, polypropylene film (BOPP film) which can be vaporized in a vacuum and has a good barrier action against water vapor, oxygen and aromas, and the process for

Production of the film. The film relating to the invention has a core layer made of polypropylene and an outer layer made of a copolymer of olefins and carbon monoxide as characteristic features.

Polypropylene films vapor-coated with metals or metal oxides are mostly used for packaging sensitive foods because of their good barrier properties against water vapor, oxygen, light and flavors. However, in addition to these functional properties, the look of the film plays a very important role. In addition, the film must also be able to be processed without problems on high-speed packaging machines.

Because of the flexibility of polypropylene films which are vapor-coated in a vacuum, a very high affinity of the metal or metal oxide for the film surface is important, which generally requires a corona pretreatment of the film surface. The barrier effect against water vapor, oxygen and aromas also depends crucially on the material of the outer layer onto which the metal or metal oxide is vapor-deposited.

It therefore turned out to be necessary to produce a BOPP film which can be vaporized in a vacuum and which has very good adhesion between the metal or metal oxide and the substrate surface to be vaporized and which has a significantly higher oxygen barrier.

This task is solved by a heat-sealable composite film, which is composed of A) a base layer made of biaxially stretched polypropylene;

B) an adhesion promoter layer made of modified polyolefin on at least one side of the base layer A;

C) an outer layer of a copolymer of one or more olefins and carbon monoxide (polyketone) on the adhesion promoter layer (s) B.

If necessary, layers A and B or B and C 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 produced by means of a sequential process has an outer layer which can be vaporized in a vacuum and is composed of a copolymer of carbon monoxide and one or more olefinically unsaturated compounds (polyketone). 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. Ethylene and propylene are particularly preferred. The outer layer which can be vaporized in vacuo 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 being 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 surface of polyketone can be evaporated in vacuo with an element or the oxides of the element of the first to fourth main or subgroup of the periodic table.

The polypropylene of the base layer A 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 / 21.6 N / cm ² pressure ( DIN 53 735)

Modified polyolefins are used to produce the adhesion promoter layer B. These are preferably polyolefins with carboxyl groups, such as polypropylene pylene or polyethylene, which contain at least one monomer from the group of the a, b-monounsaturated dicarboxylic acids, such as, for example, maleic acid, fumaric acid, itaconic acid or their acid anhydrides, acid esters, acid amides and acid imides, graft copolymers of ethylene with a, b-monounsaturated carboxylic acids , such as acrylic acid, methacrylic acid and / or their metal salts (Zn, Na) and / or their alkyl

(-C-C ₄ ) esters or corresponding graft polymers on polyolefins such as polyethylene or polypropylene or already described saponified copolymers which are graft-polymerized with a monomer of the above-mentioned unsaturated acids.

Particularly preferred are polyolefins such as polypropylene, polyethylene or copolymers of propylene or ethylene with a maximum of 1.0% by weight of grafted a, b-monounsaturated dicarboxylic acid anhydride such as maleic anhydride or their saponified copolymers.

If the adhesion promoter polymer either in the sealable layer A or in the

Gas barrier layer C incorporated, up to 40% by weight, preferably 25-30% by weight, based on the layer-forming polymers, of the modified polyolefin are used to produce the corresponding polymers.

The polypropylene base layer preferably carries a heat sealable layer on the

Base layer A, which is on the opposite side with respect to polyketone layer C.

The following materials are preferably used for the sealable layer:

- 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 and a propylene / ethylene / butene terpolymer are particularly preferred. The density of the sealant polymer should be preferably 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, i.e. H. ethoxylated and / or propoxylated polydiorganosiloxanes and / or the essentially straight-chain and saturated aliphatic, tertiary amines with an aliphatic

Rest with 10 to 20 carbon atoms, which are substituted with ω-hydroxy (-C-C) alkyl groups, where N, N-bis (2-hydroxyethyl) alkylamines with 10 to 20 carbon atoms, preferably 12 to 18 carbon atoms , are particularly suitable in the alkyl radical. The effective amount of antistatic is in the range of 0.05 to 0.5% by weight. Furthermore, glycerol monostearate is suitable and is used in an amount of

0.03% to 0.5 wt .-% used 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 methacrylates 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 is in the range of 0.02 to 2 % By weight is preferred, in particular polydimethylsiloxanes with a viscosity of 5000 to 1,000,000 mm 7s.

The films according to the invention can be produced by the customary processes such as lamination, coating or melt coextrusion. 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.

example

To produce a 4-layer film, an alternating copolymer of ethylene and carbon monoxide (polyketone) (mp: 220 ° C., volume flow index: 6 ml / 10 min at 240 ° C./2, 16 kg) was saponified with a modified polypropylene Copolymers of 0.7% by weight of grafted-on maleic anhydride and a melt index of 5 g / 10 min at 250 ° C / 21.6 N / cm ² for the adhesion promoter layer and co-extruded according to conventional methods with the base film made of polypropylene with a density of 0.905 g / cm ³ , the melt index 3 g / 10 min (230 ° C / 21.6 N / cm ² ) and the softening range from 160 to 166 ° C and stretched, the base layer on the other hand with respect to the polyketone a coextruded, heat-sealable Layer of a propylene / ethylene / butene terpolymer, which contains 2500 ppm of silicon dioxide as an antiblocking agent. In this way, a composite film with a longitudinal stretching ratio of 5: 1 and a transverse stretching ratio of 10: 1 was obtained.

The total film thickness was 20 μm. The layer thickness of the polyketone, the adhesion promoter and the terpolymer was 1 μm in each case. The film was metallized with aluminum in a vacuum on the polyketone side. The water vapor permeability of the metallized film was 0.27 g / m ² d at 38 ° C. and 90% relative air humidity. The oxygen permeability of the metallized film was 3 cm ³ / m ² d bar.

Measuring method

Determination of water vapor permeability (Wddu:

The water vapor permeability was determined in accordance with DIN 53122, part 2, at 38 ° C. and 90% relative air humidity difference.

Determination of oxygen permeability (Xb-Du ^' ):

The oxygen permeability was determined according to DIN 53380, Part 3, at 23 ° C and 0% relative humidity.

Claims

claims

1. Heat-sealable composite film, which is composed of

A) a base layer of preferably biaxially stretched polypropylene;

C) an outer layer made of a copolymer, which consists of one or more olefins and carbon monoxide (polyketone) and is located on the adhesion promoter layer (s) B.

2) composite film according to claim 1, characterized in that the layers A and B or B and C are combined to form a layer by mixing the corresponding polymers.

3) Composite film according to at least one of the preceding claims, characterized in that carbon monoxide and the olefin (s) are incorporated in an alternating sequence in the terpolymer of the outer layer C.

4) Composite film according to claim 3, characterized in that the terpolymer consists of 50 mol% carbon monoxide, 25 to 45 mol% ethylene and 5 to 25 mol% propylene.

5) composite film according to at least one of the preceding claims, characterized in that the outer layer C consists of a terpolymer of carbon monoxide, ethylene and propylene.

6) Composite film according to claim 1, characterized in that the layer B from a homo- or copolymer of propylene or ethylene with grafted-on 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 alkyl (C ₁ -C) esters or corresponding graft polymers.

7) composite film according to at least one of the preceding claims, characterized in that there is a heat-sealable layer on the base layer A.

8) Composite film according to claim 6, characterized in that the heat-sealable layer is a propylene / ethylene copolymer or a propylene ethylene / butene terpolymer.

9) 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.

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

1 1) Composite film according to at least one of the preceding claims, characterized in that the outer layer C is evaporated in vacuo with an element or the oxides of the element of the first to fourth main or subgroup of the periodic table.

12) composite film according to at least one of the preceding claims, characterized in that the layer combination is produced by lamination or melt extrusion.

13) Use of the film according to at least one of the preceding claims as a solo film or composite film component for packaging purposes.