CA2288158A1

CA2288158A1 - Multi-layered stretched hot-sealable polypropylene film with a polyketone gas barrier layer

Info

Publication number: CA2288158A1
Application number: CA002288158A
Authority: CA
Inventors: Bernd Sperlich; Rainer Brandt
Original assignee: Individual
Current assignee: Dow Produktions und Vertriebs GmbH and Co oHG
Priority date: 1997-04-30
Filing date: 1998-04-21
Publication date: 1998-11-05
Also published as: WO1998049006A1; BR9809372A; EP0977665A1; DE19718199A1; AU7527998A

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

WW 5486-Foreign / Br/Kr/W6N02.03.1998 FILE, PAN-ttd THIS AMENA~.r' TES T~AN~~A'~p~~a Multilayer, drawn, heat-sealable polypropylene film The present invention relates to a sealable drawn multilayer film which, on account of its gas barrier properties, is suitable especially as a packaging film for goods that require low gas permeability and flavour protection.
The use of composite films of polyolefins with a sealable layer of ethylene homo- or co-polymers as packaging films 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 B 1, the gas permeability is reduced considerably by the incorporation of a layer of hydro-lysed ethylene vinylacetate. However, ethylene vinylacetate has considerable disad-vantages as regards its processability. As a result of the high degree of metal adhe-sion and the low temperature stability, polymeric deposits in the extruder and the extrusion die are frequently obtained-on extrusion. In order to achieve low gas per-meability it is necessary to use ethylene-vinyl alcohol copolymers having a rela-tively high vinyl alcohol content. The disadvantage is that composite films of PP and EVOH exhibit only a low degree of drawability and require relatively high draw temperatures. A fundamental disadvantage of barrier films containing ethylene-vinyl alcohol copolymers as the barrier layer is their low resistance to breaking when folded, which presents difficulties especially in the production of bags in tube form.
Polyamides as barrier layer materials exhibit markedly poorer barrier properties which are not satisfactory for many applications.
Accordingly, it has proved necessary to manufacture a multilayer, heat-sealable BOPP film containing a barrier layer material which exhibits a high oxygen barrier, is easy to process and results in a film composite having a high resistance to break-ing when folded.

WW 5486-Foreign That object is achieved by a heat-sealable composite film consisting of a biaxially drawn polypropylene film as the base film, an adhesion promoter layer of modified polyolefin, a gas barner layer of a copolymer of one or more olefins and carbon monoxide, and a heat-sealing layer of olefin polymers, characterised in that the base film carries at least on one surface a layer combination which is optionally oriented at least monoaxially and is composed of A) a heat-sealable outer layer of an olefinic homo-, co- or ter-polymer;
B) an adhesion promoter layer of modified polyolefin;
C) a gas barrier layer of a copolymer of one or more olefins and carbon monox-- ide (polyketone), in which the olefins) and the carbon monoxide are incor-porated in an alternating sequence;
D) an adhesion promoter layer of modified polyolefin; and E) a layer of polyethylene or an ethylene polymer containing at least 3 wt.%
ethylene, the base film carrying on at least one of its surfaces optionally a layer A, a layer combination A to E, A to D or B and C.
The layers A and B andlor D and E or the layers B and C or C and D can optionally be combined to form one layer by mixing the corresponding polymers.
The preferred feature is that the biaxially drawn, heat-sealable polypropylene film produced by means of a sequential process contains a gas barrier layer of a copoly-mer of carbon monoxide and one or more olefinically unsaturated compounds.
There come into consideration as olefinically unsaturated compounds in principle all monomers of that class of compounds. Preference is given to ethylene and C3-to C,o-alkenes, such as, for example, propylene. 1-butene, 2-butene, 1-pentene, 1-hexene, 1-octene, 1-nonene, 1-decene. Special preference is given to ethylene and propylene. The barrier layer material preferably consists of a copolymer of from WW 5486-Foreign 25to 50 mol % ethylene. from 0 to 25 mol % propylene and 50 mol % carbon mon-oxide, the olefinically unsaturated compounds and the carbon monoxide being in-corporated alternately into the copolymer. By replacing some of the ethylene by higher olefins, the melting point falls and the drawability of the copolymer is im-proved.
The polypropylene of the core film is preferably an isotactic polypropylene having a density of from 0.90 to 0.91 g/cm' and a melt flow index of from 1 to 4 g/10 min. at 230°C/2.16 kp/cmz pressure (DIN ~3 735).
- Of the numerous materials used for sealable layers, the following are preferably em-ployed:
- random propylene/ethylene copolymers I S - random propylene/olefin (1) copolymers - random propylene/ethylene/olefin terpolymers - mixtures of two or three of the above polymers.
Special preference is given to a propylene/ethylene copolymer which is characterised in that it contains from 1.0 to 10 wt.% polyethylene. The density of the sealing layer polymer is preferably to be in the range of from 0.895 to 0.960 g/cm3 and the crys-tallite melting point, depending on the type, is to be in the range of from 125 to 148°C.
In order to ensure that biaxially oriented polypropylene films run well on the ma-chine, it is necessary to provide at least the sealing or cover layers with additives, such as lubricants, antiblocking agents and antistatics.
Preferred antistatics are alkali alkanesulfonates, polyether-modified, that is to say ethoxylated and/or propoxylated, polydiorganosiloxanes (polydialkylsiloxanes, poly-WW 5486-Foreign alkylphenylsiloxanes and the like) and/or the substantially straight-chained and satu-rated aliphatic tertiary amines which contain an aliphatic radical having from 10 to 20 carbon atoms and are substituted by w-hydroxy-(C,-C4)-alkyl groups, there being especially suitable N,N-bis(2-hydroxyethyl)alkylamines having from 10 to 20 car-bon atoms, preferably from 12 to 18 carbon atoms, in the alkyl moiety. The effective amount of antistatic is in the range of from 0.05 to 0.5~ wt.%. In addition, glycerine monostearate is suitable and is used as an antistatic in an amount of from 0.03 to 0.5 wt.%.
Suitable antiblocking agents are inorganic additives, such as silicon dioxide, calcium - carbonate, magnesium silicate, aluminium silicate, calcium phosphate and the like, and/or incompatible organic polymers, such as polyamides, polyacrylates, polymethacrylates, polyesters, polycarbonates and the like. with polymethacrylates and silicon dioxide preferably being used. The effective amount of antiblocking I ~ agent is in the range of from 0.1 to 2 wt.%, preferably from 0.1 to 0.8 wt.%. The mean particle size is from 1 to 6 pm, especially from 2 to 5 pm, particles having a spherical shape being especially 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 from 0.01 to 3 wt.%, preferably from 0.02 to 1 wt.%. The addition of higher aliphatic acid amides in the range of from 0.01 to 0.25 wt.% is especially suitable. An especially suitable aliphatic acid amide is erucic acid amide.
The addi-tion of polydimethylsiloxanes is preferred in the range of from 0.02 to 2 wt.%, espe-2~ dally polydimethylsiloxanes having a viscosity of from 5000 to I 000 000 mm'/s.
In order to produce the adhesion promoter layer, modified polyolefins are used.
These are preferably polyolefins containing carboxyl groups, such as, for example, polypropylene or polyethylene, which contain grafted on with at least one monomer from the group of the a,(3-monounsaturated dicarboxylic acids, such as, for example, WW 5486-Foreign malefic acid, fumaric acid, itaconic acid or their acid anhydrides, acid esters, acid amides and acid imides, copolymers of ethylene with a,,(3-monounsaturated carbox-ylic acids, such as acrylic acid, methacrylic acid and/or their metal salts (Zn, Na) and/or their (C,-C4)-alkyl esters, or corresponding graft polymers on polyolefins such as polyethylene or polypropylene, or already described hydrolysed mixed polymers, which are graft-polymerised with a monomer of the above-mentioned un-saturated acids.
Special preference is given to polyolefins, such as polypropylene, or copolymers of propylene and ethylene with not more than I.0 wt.% of grafted-on a,~3-mono-- unsaturated dicarboxylic acid anhydride, such as malefic anhydride. or their hydro-lysed mixed polymers.
If the adhesion promoter polymer is incorporated either in the sealable layer A or in the gas barrier layer C, up to 40 wt.%, preferably from 25 to 30 wt.%, based on layer-forming polymers, of the modified polyolefin are used for the preparation of the corresponding polymers.
The invention also provides packaging, especially for oxygen-sensitive foodstuffs, produced from the multilayer film according to the invention.
The films according to the invention can be produced by conventional processes such as lamination, coating or melt co-extrusion. After extrusion and solidification of the thick film on the casting roller, the film is drawn in the direction of movement (longitudinally) with a draw quotient of from 4/1 to 7/1 at a temperature of from 120°C to 150°C. The draw ratio in the transverse direction is preferably from 8/1 to I 2/ I , and transverse drawing of the film is carried out at a temperature of from 130°C to 170°C. Subsequent heat setting is preferably carried out at from 1 °C to 40°C below the transverse-drawing temperature. In order to ensure that the largely non-polar film surface has affinity for the printing inks, it is necessary to subject the WW.5486-Foreign film to corona (spray) pretreatment, in which atmospheric oxygen is deposited on the surface of the film in the form of carbonyl, epoxide, ether or alcohol groups.
Other methods of pretreating polypropylene films are flame, plasma and fluorine pretreatment.
J
Example For the production of a layer combination, 0.5 wt.% of N,N-bis(2-hydroxyethyl)-(C,z-C,6)-alkylamine, 0.3 wt.% of a polydimethylsiloxane having a density of 0.985 g/cm3 at 20°C and a viscosity of 106 mPa s, and 0.3 wt.% of silicon dioxide having a mean particle size of 2.5 pm were incorporated, for layer A, into 98.7 wt.%
of a propylene-ethylene copolymer containing 4.5 wt.% ethylene and having a den-sity of 0.90 g/cm3, a melt index of 5 g/10 min. at 230°C/2.16 kp/cm' and a crystallite melting point of 140°C;-the mixture was co-extruded with a modified polypropylene 1 ~ such as a hydrolysed mixed polymer containing 0.7 wt.% of grafted-on malefic anhy-dride and having a melt index of ~ g/10 min. at 250°C/216 kp/cm' for the adhesion promoter layers and an alternating carbon monoxide-ethylene copolymer (m.p.
220°C, MFI 6 ml/10 min. at 230°C/2.16 kg) for the gas barrier layer, was bonded by conventional processes with the base film of polypropylene having a density of 0.905 g/cm3, a melt index of 2 g/10 min. at 230°C/2.16 kp/cm'- and a softening range of from 160 to 166°C, and was drawn so that a composite film having longitudinal drawing in a ratio of ~:l and transverse drawing in a ratio of 10:1 was obtained. The layer structure and the layer thicknesses are summarised in Table 1. The oxygen bar-rier of the composite film is 1 ~ cm'/m' d bar.

WW 5486-Foreign Table 1 Layer structure and l ayer thickness:

P/E copolymer 1 ~m adhesion promoter 0.5 ~m polyketone 1 pm adhesion promoter 0.5 ~m PP 24 pm adhesion promoter 0.5 p.m polyketone 1 p.m adhesion promoter 0.5 p.m - P/E copolymer 1 pm

Claims

claims

1. Heat-sealable composite film consisting of a biaxially drawn polypropylene film as the base film, characterised in that the base film carries at least on one surface a layer combination composed of A) a heat-sealable outer layer of an olefinic homo-, co- or ter-polymer;
B) an adhesion promoter layer of modified polyolefin;
C) a gas barrier layer of a copolymer of one or more olefins and carbon monoxide (polyketone), in which the olefin(s) and the carbon monoxide are incorporated in an alternating sequence;
D) an adhesion promoter layer of modified polyolefin.

2. Composite film according to claim 1, characterised in that the layer combination A) to D) has on the outer surface of layer D) an additional layer E) of polyethylene or a polyethylene polymer containing at least 3 wt.% ethylene.

3. Composite film according to claim 1 or 2, characterised in that the layer combination A) to D) or A) to E) is drawn at least monoaxially.

4. Composite film according to any one of claims 1 to 3, characterised in that the gas barrier layer consists of a terpolymer of carbon monoxide, ethylene and propylene.

5. Composite film according to claim 4, characterised in that the terpolymer consists of 50 mol % carbon monoxide, from 25 to 50 mol % ethylene and from 0 to 25 mol % propylene.

6. Composite film according to claim 1, characterised 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 one layer by mixing the corresponding polymers.

7. Composite film according to at least one of the preceding claims, characterised in that at least the sealing or cover layers are provided with additives, such as lubricants, antiblocking agents and antistatics.

8. Composite film according to claim 1, characterised in that layer B consists of polypropylene or polyethylene 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 (C1-C4)-alkyl esters, or corresponding graft polymers.

9. Composite film according to claim 1 or 2, characterised in that the layer polymers A and E and/or B and D are identical.

10. Composite film according to at least one of the preceding claims, characterised in that the layer combination is produced by lamination or melt extrusion.

11. Composite film according to at least one of the preceding claims, characterised in that its outer cover layers are flame-, plasma- or corona-pretreated.

12. Packaging, especially for foodstuffs, produced from composite films according to any one of the preceding claims.