CA1194664A

CA1194664A - Sealable multilayer films

Info

Publication number: CA1194664A
Application number: CA000400565A
Authority: CA
Inventors: Heinrich Rosenthal; Ingo Schinkel; Gunter Eger; Wolfgang Bair
Original assignee: Wolff Walsrode AG
Current assignee: Dow Produktions und Vertriebs GmbH and Co oHG
Priority date: 1981-04-08
Filing date: 1982-04-06
Publication date: 1985-10-08
Also published as: JPS57178747A; CS241505B2; NO820984L; MX160195A; DE3114171A1; ES8504420A1; FI77408C; FI77408B; EP0062815A3; KR830009935A; AU548004B2; AU8213982A; DK163082A; DD203013A5; US4400428A; DK161502C; ATE21857T1; PL235834A1; PL137578B1; JPH0249224B2

Abstract

ABSTRACT OF THE DISCLOSURE A composite film comprising a polypropylene basis film being laminated at least on one surface with a layer combination of a heat sealable layer with an addi-tive combination, an adhesion promotion layer, a gas-barrier layer, and an adhesion promotion layer and optionally a further heat sealable layer.

Description

i Sealable multilayer films~

This invention relates to a heat sealable, stretched multilayer film which, by virtue of its low permeability to gases, is particularly suitable for use as a packaging film for goods of the type which require minimal per-meability to gases and flavour or a high aroma retention.
The use of composite films of polyolefins with a sealable layer of ethylene homopolymers or of copclymers as a packaging film has been known for some time. Attempts have already been made to lower the permeability of these cornposite films to gases by adding a layer of hydrolysed ethylene/vinyl acetate copolymer. Thus, German Offenlegungsschrift No. 2,644,209 = GB-PS
1,567,189 describes a composite film of polypropylene, an adhesion-promoting layer of modified polyolefin, a layer of hydrolysed ethylene/vinyl acetate copolymer andr optionally a heat-sealable layer of polyolefins.
However, composite films of this type have the serious disadvantage that the unsatisfactory slippers pro-perties of this composite film at relatively high packaging speeds result in faulty seals, defective wrapping and deposites on parts of the packaging machines caused by abrasion.
With the composite films according to the invention, it is possible to obviate these disadvantages and to provide a packaging material which, by virtue of its remarkable .slippers properties and processibility on i~?' machines, is also suitable for high-speed packaging machines and, by virtue of its minimal permeability to gases, may be used in particular for perishable foods.
Accordingly, the present invention provides a heat-sealable composite film comprising a biaxially oriented polypropylene film as the base film and, on at least one surface thereof, a combination layer which comprises:
A) a heat-sealable outer layer of polyethylene or of an ethylene copolymer containing at least 3, preferably at least 4% by weight of ethylene;
B) an adhesion-promoting layer of modified polyolefin;
C) a gas-barrier layer of a hydrolysed ethylene/vinyl acetate copolymer containing from 50 to 80 mole percent of vinyl acetate units of which at leas~ 90% are hydrolysed;
D) an adhesion-promoting layer of modified polyolefin;
and E) a layer of polyethylene or of an ethylene copolymer containing at least 3, preferably at least 4% by weight of ethylene, layer A containing an additive combination comprising a) from 0.3 to 1% by weight, preferably 0.4-0.7, based on the sealable ~ layer, of a ]ong-chain aliphatic amine, b) from 0.1 to 0.7% by weight, preferably 0.15-0.50, based on the sealable layer, of a dispersed thermoplastic polymer which is incompatible with the polyethylene or ethylene copolymer and which has a softening point at most 50C below or above the softening point o~ the polyethylene or ethylene copolymer, and c) from 0.1 to 1.2% by weight, preferably 0.2-0.7, based on the seal-able layer, of a polydialkyl siloxane having a viscosity of 105 to 106 mPas at 20C.
The present invention also provides a package comprising material wrapped in a composite film as described above.
The base film may carry on one surface the combination layer and on the other surface a layer A, a layer combination A to E or B and C or one layer of a polymer mixture of the polymers of the layers B and C.
Each of the two layers A and B or D and E or B and C or C and D
can be combined into one single layer by mixing the corresponding polymers.
The polypropylene of the core film is preferably an isotactic polypropylene having a density of from 0.90 to 0.91 g/cc and a melt flow index of from 1 to ~ g/10 mins. at 230C/2.16 kp/cm2 pressure (as measured in accordance with DIN 53 735).
The heat sealable layer polymer consists of an ethylene homo- or co-polymer. A high-density polyethylene or statistical ethylene/propylene copolymers containing at least 4% by weight of ethylene, preferably 95% by weight of propylene and 5% by weight of ethylene, are preferably used.
The heat sealable layer polymer should preferably have a density in the range of from 0.895 to 0.960 g/cc, a melt flow index of from I to 7 g/10 mins at 190C/2.16 kp/cm2 pressure and a crystallite melting point, of from 125 to 148C (as measured under a polarisation microscope).

Component a) of the additive combination is a long-chain aliphatic tertiary amine which may optionally be mono-unsaturated, preferably a tertiary amine of which the aliphatic radical has a C-chain length of from C12 to C18 and which is substituted ~y two hydroxy-alkyl-(C1 C4)-groups. N,N-bis-(~-hydroxyethyl)-C12-C16-alkylamines are particularly preferred.
The thermoplastic polymer which is incom-patible with the sealing polymer should have a softening point at most 50C below or above the softening point of the sealing polymer and should be dispersed in the sealing polymer, its particle size being from 0.01 to 4 ~m and preferably from 0.1 to 2 ~m. Dispersion of the incompatible polymer in the sealing polymer is carried out by standard known methods. Preferred incompatible polymers are thermoplastic resins, such as high density, high molecular polyethylene (softening point preferably about 129C), ethylene~methacrylic acid copolymers (90 to 99C), polylauric lactamide (180C), acrylo-nitrile/butadiene/methacrylate copolymers ~0CJ, and ethylene/vinyl alcohol copolymers ~85C).
Ethylene/methacrylic acid copolymers which may be completely or partly present in the form of alkali salts, metal or alkaline earth metal, preferably Zn-salts, or polylauric lactamide are particularly preferred.
The polydialkyl siloxane used as addi~ive component (c3 should have a viscosity of 105 to 106 mPa.s/
preferably a viscosity o~ at least 106mPas at 20~.
It is particularly preferred to use polydimethyl siloxane.

- s -The gas-barrier layer preferably consists of an ethylene/vinyl acetate copolymer which consists of from 50 to 80 mole percent and more preferably of from 60 to 75 mole percent of vinyl acetate units of which at least 90 ~ and preferably more than 95 % are hydrolysed.
The polymer generally has an intrinsic viscosity, as measured in a solvent mixture of 85 ~ by weight of phenol and 15 % by weight of water, of preferably from 0.07 to 0.17 l/g and more preferably from 0.09 to 0.15 l/g.
Modified polyolefins are used fox producing the adhesion-promoting layer. The polyolefins in question are preferably polyolefins containing carboxyl groups such as, for example, polypropylene or polyethylene containing grafted unit s of at least one monomer from the group comprising ~,B-mono-unsaturated dicarboxylic acids such as, for example, maleic acid, fumaric acid, itaconic acid or their anhydrides, acid esters, acid amides and acid imides; copolymers of ethylene with acrylic acid and/or methacr~lic ~cid and/or their metal salts (Zn, Na) and/or their C1-C4-alkyl esters, or saponified copoly-mers which are grafted with above mentioned acid mono-mers.
Grafted products are preferably used.
It is particular preferred to use polyolefins, such as polypropylene or copolymers of propylene and ethylene, containing at most 1.0 % by weight of grafted units of oC,B-mono-unsaturated dicarboxylic acid anhydrides, such as maleic acid anhydride~ and their ~aponified copolymers.
If the adhesion-promoting polymer is incorporated either in the sealable layer A or in the gas barrier layer C, up to 40 % by weight and preferably from 25 to 30 % by weight of the modified polyolefin, based on layer-forming polymers, are used for producing the polymer mixture.
By using the combination of additives according to the invention, it is possible to produce mul~ilayer films having very good S~i~Di~.~ properties combined with good machine processibility. It is also possible to use the film without the usual electrical treatment which is known to have an adverse effect upon the slipping pro-perties of the film. Neither is there any sign of scratching or hazing of the film such as occurs when known lubricants based on inorganic powders are used.
Surprisingly, the affinity of the film for adhesives, for example for the purpose of applying a tear-open strip, is also not adversely af~ected, although this has to be expected in view of the use of polyalkyl siloxanes as additives.
Accordingly, it had not been expected that the required improvement over known multilayer films would be obtained with the combination of additives according to the invention, especially, since even the use of know~ lubricants such as, for example, saturated or unsaturated fatty acid amides and relatively high molecular weight substituted fatty acid amides having melting points of from 70 to 150C, such as for example erucic acid amide, oleic acid amide, alkyl-di-fatty acid amides or N,N-polyethoxylated fatty acid amides, does not ensure adequate slipability on high-speed packaging machines.

L~

The present inventlon also relates to the use of the inventive film composites as a packaging material for foods sensitive to oxygen.
The additives may be incorporated in the sealing layer polymer by mixiny and the multilayer film may be produced by standard methods, such as lamination or melt extrusion.
It is advantageous to add the additives directly to the sea]ing layer polymer because this eliminates the need for a complicated additive/masterbatch tech-nique.
It is also advantageous to apply the layer combi-nation to the base film separately from the production of the polypropylene film in a later step.
Biaxial stretching may be carried out by any of the usual stretching techniques. Longitudinal stretching is preferably carried out in a ratio of from 5:1 to 7:1 whilst transverse stretching is preferably carrled out in a ratio of from 7:1 to 10:1.
In the inventive film composite, the polypropylene base film should preferably have a thickness of from 20 to 50 ~m and the layer combination should preferably have a thickness of from 2 to 6 ~m and more preferably from 3.5 to 5 ~m, the sealing layer having a thickness of from 0.8 to 2 ~m, preferably of 1 ~m, the adhesion-promoting layer a thickness of from 0.1 to 1 ~m, pre-ferably from 0.4 to 0.6 ~m, and the gas-barrier layer a thickness of from 0.2 to 1.2 ~m, preferably from 0.6 to 0.8 ~m.
The layers B and D and A and E are preferably identical.

Test Methods The packaging process is assessed by crlteria stipulated by the machine operator, such as throughput, wrapping and absence of deposites. Providing there are no disturbances relating to these criteria during packaging at relatively high speeds, the film may be regarded as satisfactory. Even an occasional distur~ance means that the film is unsuitable. It is presupposed that distur~
~ances may be ruled out by optimally setting up the packaging machine before the trial.
In the context of the invention, the sealing strength is understood to be that force which is required to split a seal seam produced under controlled conditions (50 N/cm /0.5 sec, 130C, smooth sealing jaws~. Sealing strength is expressed in Newtons (N) and is based on a 15 mm wide test strip.
The antistatic behaviour of a film is assessed by the ash test. The ash test is carried out after the film has been charged to a certain ex-tent (by rubbing three times in one direction using a woollen cloth~.
The film is regarded as being sufficiently antistatic if it does not attract cigarette ash from a distance of 3 cm.
Permeability to oxygen is measured in accordance with DIN 53 380. Hazing is measured in accordance with ASTM D 1003-52 and coefficient of friction in accor-dance with DIN 53 375.
EX~MPLE 1 To produce a layer combination, 0.5 ~ by weight of N,N-bis-(2-hydroxyethyl)-(C12 C16)-alkylamine, WW 5~07 0.5 ~ by weight of an ethylene/methacrylic acid copoly-mer, in which some of the carboxyl groups are present in the form of Zn salts and which has a melt index of 5 g/10 mins at 190C/1 kp/cm2 and a melting point of 99C, and 0.3 % by weight of a polydimethyl siloxane having a density of 0.985 g/cc at 20C and a viscosity of 106 mPa.s at 20C were incorporated into 98.7 % by weight of a propylene-ethylene copolymer containing 4.5 9O by weight of ethylene and having a density of 0.90 g/cc, a melt index of 5 g/10 mins at 230C/2.16 kp/
cm and a crystallite melting point of 140C for layer A and co-extruded with a modified polypropylene, l~ke saponified copolymer, containing 0.7 % by weight of grafted maleic acid anhydride, with a melt index of 5 g/10 mins at 250C/2.16 kp/cm2j for the adhesion-promoting layers and an ethylene/vinyl acetate copoly-mer containing 55 mole percent of vinyl acetate units, of which 96 % are hydrolysed, for the gas-barrier layer and the above-mentioned propylene/ethylene copo-lymer for the layer E, combined with the base film of polypropylene having a density of 0.905 g/cc, a melt index of 2 g/10 mins at 230C/2.16 kp/cm2 and a softening range of 160 to 166C by standard methods and stretched in such a way that a composite f~lm stretched in a ratio of 5:1 in the longitudinal direction and in a ratio of 10:1 in the transverse direction was obtained.
The layer structure and the properties of the completed film are shown in the following Tables.
EX~MPLE 2 To produce a layer combination, 0.5 ~ by weight of N,N-bis-(2-hydroxyethyl)-(C12-C16)-alkylamine, 0.2 %
by weight of polylauric lactamid having a density of 1.01 g/cc, a viscosity number (according to DIN 53 729) of ww 520?

1 o 250 and a melting range of 176 to 180C, and 0.3 %
by weight of a polydimethyl siloxane having a density of 0.985 g/cc at 20C and a viscosity of 106 mPa.s at 20C were incorporated into 99.0 % by weight of a pro-pylene/ethylene copolymer containing 4.5 ~ by weight of ethylene and having a density of 0.90 g/cc, a melt index of 5 g/10 mins at 230C/2.16 kp/cm2 and a crystallite melting point of 140C for layer A, co-extruded and com-bined by standard methods with the base film a polypropy-lene having a density of O.90S g/cc, a melt index of 2 g/
10 mins at 230C/2.16 kp/cm2 and a softening range of 160 to 166C, followed by stretching in such a way that a composite film stretched in a ratio of 5:1 in the longitudinal direction and in a ratio of 10:1 in the transverse direction was obtained.
The layer structure and properties of the finished film are shown in the following Tables.

.
To produce a layer combination, 0.5 % by weight of N,N-bis-(2-hydroxyethyl)-(C12-C16)-alkylamine, 0.5 %
by weight of an ethylene/methacrylic acid copolymer, in which the carboxyl groups are partly present in the form of ~n-salts and which has a density of 5 g/10 mins at 190C/1 kp/cm and a melting point of 99C, and 0.7 % by weight of a polydimethyl siloxane having a density of 0.985 g/cc at 20C and a viscosity of 106 mPa.s at 20C were incorporated into 98.3 % by weight of a propylene/ethylene copolymer containing 4.5 % by weight of ethylene and having a density of 0.90 g/cc, ~ 5207 a melt index of 5 g/10 mins at 230C/2.16 kp/cm2 and a crystallite melting point of 140C for layer A, and co-extruded with a modified propylene/ethylene copolymer, like a saponified copolymer, containing 0.5 ~ by weight of grafted maleic acid anhydride, with a melt index of 10 g/10 mins at 250C/2.16 kp/cm2 for the adhesion-promoting layers and an ethylene/vinyl acetate copolymer containing 55 mole percent of vinyl acetate units, of which 96 ~ are hydrolysed for the gas-barrier layer and the above-mentioned propylene/ethylene copolymer for layer E, united by standard methods with the base film of polypropylene having a density of 0.905 g/cc, a melt index of 2 g/10 mins at 230C/2.16 kp/cm2 and a softening range of 160 to 166C, and stretched in such a way that a composite film stretched in a ratio of 5:1 in the longitudinal direction and in a ratio of 10:1 in the transverse dixection was obtained.
The layer structure and properties of the finished film are shown in the following Tables.

Ta~le_l Example l Comparison Example 2 Example 3 Example l S
Layer P/E-copo l P/E-copo l P/E-copo 1 P/E-co~o 1 structure AP 0.5 AP 0.5 PP 25 AP 0.5 and layer EVAL l EVAL l P/E CGpO 1 EVAL
thickness AP 0.5 AP 0~5 AP 0.5 (~m) P/E-copo l P/E-copo l PP 25 PP 25 P/E-copo l P/E-copo l P/E-copo 1 PP 25 P/E-copo l EVAL

P/E
Total thickness (~m) 30 30 27 33 Additives in the sealing layer (~ by weight) Aliphat. amine 005 0.2 0.5 0.5 Ethylene/meth-acrylic acid copol~mer 0.5 - - O.S
Polylauric lactam ~ - 0.2

2~ Polydimethyl ~ siloxane 0.3 - 0.3 0.7 Erucic acid amide - 0.3 - ~
P/E-copo = propylene/ethylene copolymer AP = modified polyole~ines with poly ~ ctional.groups EVAL = hydrolysed ethylene/vinyl acetate copolymer PP = polypropylene ~W 5~07 Tab Example l Comparison Example Example Example l 2 3 Film properties Coefficient of friction film/film 0.30 0.48 0.30 0.27 Coefricient of friction film/metal 0.20 0.35 0.20 0.17 Haze (~) 2~8 2.8 2.5 3.0 Seal strength (N/15 m~.) 5 5 5 5 02-~ermeability (cm /m2.d.bar) 20 20 lOOO
Antistatic behaviour adequate inadeq- adequate aequate uate Behavicur in very unsati- very very packaging machine good sfactory good good To produce a layer ~ombination, 0.2 % by weight of N,N-bis-(2-hydroxyethyl-(C12-C16)-alkylamine and 0.3 ~ by weight of erucic acid amide were incorporated into 99.5 %
by weight of a propylene/ethylene copolymer containing 4.5 %
by weight of ethylene and having a density of 0.90 g/cc, a melt index of 5 g/10 mins at 230C/2.16 kp/cm2 and a crystallite melting point of 140C for layer A, co-extruded with a modified polypropylene,-a saponified copolymer, containing 0.7 ~ by weight of grafted maleic acid anyhdride, with a melt index of 5 g/1~ mins at 250C/2.16 kp/cm2rfor -the adhesion-promoting layers and an ethylene/vinyl acetate copolymer containing 55 mole percent of vinyl acetate units, of which 96 ~ are hydrolysed, for the gas-barrier layer and the above-mentioned propylene/ethylene copolymer for layer E, united by standard methods with the base film of polypropylene having a density of 0.905 g/cc, a melt index of 2 g/
10 mins at 230C/2.16 kp/cm2 and a softening range of 160 to 166~C, and stretched in such a way that a composite film stretched into a ratio of 5:1 in the longitudinal direction and in a ratio of 10:1 in the transverse direction was c~tained.
The layer structure and properties of the finished film are shown in -the above Tables.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

l. A heat-sealable composite film comprising a biaxially orientated polypropylene film as a base film and, on at least one surface thereof, a combination layer which comprises:
(A) a heat-sealable outer layer of polyethylene or of an ethylene copolymer containing at least 3% by weight of ethylene;
(B) an adhesion-promoting layer of modified polyolefin;
(C) a gas-barrier layer of hydrolysed ethylene/vinyl acetate copolymer containing from 50 to 80 mole percent of vinyl acetate units of which at least 90% are hydrolyzed;
(D) an adhesion-promoting layer of modified polyolefin;
and (E) a layer of polyethylene or of an ethylene copolymer containing at least 3% by weight of ethylene;
each of the two layers A and B or D and E or layers B and C or C and D are combinable into one single layer by mixing the corresponding polymers;
layer A containing an additive combination comprising a) from 0.3 to 1% by weight, based on the sealable layer, of a long-chain aliphatic amine, b) from 0.1 to 0.7% by weight, based on the sealable layer, of a dispersed thermoplastic polymer which is incompatible with the polyethylene or ethylene copolymer and which has a softening point at most 50°C below or above the softening point of the polyethylene or ethylene copolymer, and c) from 0.1 to 1.2% by weight, based on the sealable layer, of a polydialkyl siloxane having a viscosity of 105 to 106 mPas at 20°C.
2. A composite film as claimed in claim 1, wherein the base film carries on one surface the combination layer and on the other surface a layer A, a layer combination A to E or B and C or one layer of polymer mixture of the polymers of the layers B and C.
3. A composite film as claimed in Claim 1, wherein component (a) is a tertiary amine having a C12-C18 aliphatic radical and two hydroxyalkyl-(C1-C4)-groups.
4. A composite film as claimed in claim 3, wherein component (a) is N,N-bis-(2-hydroxyethyl)-C12-C16-alkylamines.
5. A composite film as claimed in Claim 1, wherein component (b) is an ethylene/methacrylic acid copolymer.
6. A composite film as claimed in claim 5, wherein component (b) is at least partly in the form of a moiety selected from the group consisting of a metal salt and polylauric lactamide.
7. A composite film as claimed in Claim 1, wherein the modified polyolefin of layer B is a polypropylene or polyethylene containing grafted unit of ?,B -mono-unsaturated dicarboxylic acids.
8. A composite film as claimed in Claim 7, wherein the modified polyolefin is a polypropylene or polyethylene containing grafted unit of maleic acid or maleic acid anhydride.
9. A composite film as claimed in Claim 1, wherein the polymer of layer C is a hydrolysed ethylene/vinyl acetate copolymer containing from 60 to 75 mole percent vinyl acetate units of which more than 95% are hydrolysed.
10. A composite film as claimed in Claim 1 or 2, wherein layer B and layer D are identical.
11. A composite film as claimed in Claim 1 or 2, wherein layer A and E are identical.
12. A composite film as claimed in Claim 1 or 2, wherein the combination layer is at least monoaxially oriented.
13. A composite film as claimed in claim 1 or 2, wherein component (c) is polydimethyl siloxane.
14. A composite film as claimed in claim 1, 2 or 3, wherein at least one of the pairs of:
(i) layers (A) and (B), (ii) layers (D) and (E), (iii) layers (B) and (C), and (iv) layers (C) and (D), are combined into one single layer by mixing the corresponding polymers.
15. A composite film as claimed in claim 5, 7 or 9, wherein at least one of the pairs of:
(i) layers (A) and (B), (ii) layers (D) and (E), (iii) layers (B) and (C), and (iv) layers (C) and (D), are combined into one single layer by mixing the corresponding polymers.
16. A package comprising material wrapped in a composite film as claimed in Claim 1.

A package as claimed in Claim 16, wherein the wrapped material is a foodstuff.