AU2005321269A1

AU2005321269A1 - Shrinkable multilayered film comprising a nitrocellulose layer of lacquer

Info

Publication number: AU2005321269A1
Application number: AU2005321269A
Authority: AU
Inventors: Walter Bernig; Jochen Dold
Original assignee: CFS Kempten GmbH
Current assignee: CFS Kempten GmbH
Priority date: 2004-12-27
Filing date: 2005-12-21
Publication date: 2006-07-06
Also published as: WO2006069949A2; DE102004063618A1; EP1833667A2; WO2006069949A3

Description

Certificate I, PAUL DAVID CHURCHILL CLARKE, B.A-, Dip. Voc. Tech., MITI, of Lodestar Translations, 21 Queens Road, Harrogate, North Yorkshire, HG2 OHA, do hereby certify that I am conversant with the English and German languages and am a competent translator thereof, and I further certify that to the best of my knowledge and belief the following translation is a true and correct translation made by me of PCT application no. WO 2006/069949 A2 in the name of CFS Kempten GmbH as published on 6th July 2006. Signed this 4t.h day of June 2007 PAUL DAVID CHURCHILL CLARKE G117014 WO 2006/069949 PCT/EP2005/057034 Shrinkable multilayer film with a nitrocellulose lacquer layer The present invention relates to a heat-shrinkable multilayer film comprising at least one support layer based on at least one thermoplastic polymer which preferably has 5 a melting point of < 170*C; at least one gas barrier layer and at least one heat sealing layer, wherein the entire surface of the support layer facing away from the gas barrier layer is covered with an external lacquer layer based on nitrocellulose, to the production thereof, to the use thereof as packaging material and to corresponding packages trade from the multilayer film according to the invention. 10 Heat-shrinkable multilayer films have found numerous useful applications for packaging fbodstuffs. When these films are used in such applications, the product to be packaged is enclosed by the multilayer film or introduced into a pouch made from such a multilayer film, the air is optionally removed from the interior of the 15 package and the package is then exposed to a source of heat, such that the multilayer film shrinks and adapts itself to the shape of the packaged product. Heat-shrinkable multilayer films preferably comprise a gas barrier layer, in particular an oxygen barrier layer, since the penetration of oxygen into a package 20 results in oxidative spoilage in many packaged products, in particular foodstuffs. It is additionally necessary for these films to have good seal strength, such that, even at elevated temperatures, such as shrinking temperatures, the packages produced from the film are resistant to delamination and do not lose their integrity. Moreover, heat shrinkable multilayer films should have good mechanical properties so that they 25 withstand the stresses arising during the production process and transport to the customer. For the purpose of selling packaged products to consumers, it is necessary for the heat-shrinkable films also to exhibit good optical properties which increase the 30 attractiveness of the package.

WO 2006/069949 PCT/EP2005/057034 -2 Multilayer films which meet these requirements are known from the prior art and are also commercially obtainable. One problem -n which arises in the production of packages from heat-shrinkable 5 multilayer films on known packaging machines, for example on horizontal or vertical, aul.omated packaging machines, in particular on pouch packaging machines is that, dun rig the production of the packages, in particular pouches, the individual packages simultaneously queuing for heat-sealing have often been introduced into the heat-seeling tool in overlapping manner and are not, as is necessary, present 10 there separate from one another. This means that the outer layers of the packages which are lying against one another in the overlapping area are also heat-sealed to one another. Such packaging pouches can be put to no further use, so giving rise to an amount of wastage. 15 It is already known from the prior art (WO 99/26783 and WO 00/26024) that this undesired joining together of packages in the overlapping area may be avoided by using a heat-shrinkable multilayer film with an outer layer made from polyamide. Restricting lhe support layer or outer layer to polyamide may also restrict the possible applications of the multilayer film, for example in the production of 20 packages, such that alternative solutions to the stated problem are desirable. The object of the present invention was accordingly to provide a heat-shrinkable multilayer film with which the problem of undesired adhesive bonding of'packages during heat-sealing in an optionally overlapping area of individual packages is 25 avoided, without its being necessary to restrict the material of the outer or support layer to polyamide. The object is achieved by the provision of the heat-shrinkable multilayer film according to the invention comprising at least one support layer a) based on at least one thermoplastic polymer, at least one gas barrier layer b) and at least one heat-sealing layer c), wherein the entire surface of the support layer a) 30 facing away from the gas barrier layer is covered with a preferably transparent, external laccuer layer d) based on nitrocellulose.

WO 2006/069949 PCT/EP2005/057034 The lacquer layer d) is applied in a dry amount of preferably 0.1 to 6 g/m_, particularly preferably 0.5 to 4 g/M_ of the surface of the support layer a). The lacquer used according to the invention may contain any grade of nitrocellulose 5 as the nitro::ellulose. This means that the lacquer may be based not only on A grade nitrocellulcses (nitrogen content 10.7%-11.35%), which are soluble in ethanol, and AM grade nitrocelluloses (nitrogen 11.3%-11.8%), which are only partially soluble in ethanol, but also on E grade nitrocelluloses (nitrogen content 11.8%-12.3%), which are rot soluble in ethanol but are soluble in esters, as are also the A and AM 10 grades, or mixtures. Nitrocelluloses of A grade with a viscosity (measured to ISO 14446) of 32 A-10 A, of AM grade with a viscosity (measured to ISO 14446) of 32 M to 25 M and/or of E grade with a viscosity of 32 E to 25 E may preferably be used, the viscosity being determined and stated to ISO 14446 (formerly DIN 53179) as follows. 15 The value sxted is the concentration of nitrocellulose (absolutely dry) which is necessary in order to obtain a viscosity of the solution of 375 to 425 mPa-s. The solvent is acetone with a water content of 5%. Viscosity is measured in a Hoppler falling ball viscosimeter at 20*C. Viscosity to ISO 14446 (sometimes also 20 designated 'standard" viscosity) is stated as a numerical value which is identical to the concentration of the nitrocellulose. Tf this numerical value is an integer, the nitrocellulose is designated as a "standard" grade. Depending on the solubility of the nitrocellulose in ethanol, the numerical values are followed by an A (A grade), M (M grade) o - F (1' grade). 25 The lacquer used for application optionally contains a plasticiser. Suitable plasticisers are tricresyl phosphates, benzyl benzoates, tributyl phosphates, butyl acetyl ricinaleates, glyceryl acetyl ricinoleates, dibutyl phthalates, dibutyl glycolates, diocryl phthalates, butyl stearates, triphenyl phosphates, triethyl citrates, 30 tributyl citrates, tributyl acetyl citrates, dibutyl tartrates, diisobutyl phthalates, diamyl phthalates, dioctyl sebacate and/or camphor.

WO 2006/069949 PCT/EP2005/057034 -4 Depending on the solubility of the nitrocellulose, the lacquer used for application onto the uncovered surface of the support layer a) preferably contains at least one organic, preferably mobile, solvent selected from the group comprising ethyl acetate, n-butyl acetate, methyl acetate, n-amyl acetate, methyl isobutyl ketone, 5 methyl ethyl ketone, ethanol, propanol, isopropanol, n-butanol, toluene, heptane, isopropyl a:etate and hexane. The lacquer may optionally contain a curing catalyst. The lacquer used may optionally comprise at least one acrylic resin component or alkyd resin component as a further polymer component. 10 The lacquers preferably used for application onto the uncovered surface ofthe support layer a) are based on at least one nitrocellulose, which may assume a form dissolved ir a suitable solvent or dispersed in a dispersion medium. The nitrocellulose preferably assumes dissolved form. Suitable lacquers are described in 15 the prior art, for example in EP 061348-Al. The corresponding description is hereby introduced as a reference and is deemed to be part of the present disclosure. The support layer a) is preferably based on a thermoplastic polymer. A thermoplastic polymer which exhibits a melting temperature of < 170'C, preferably 20 of < 160*C, very particularly preferably of 1 10"C to 150*C, is particularly preferred. The support layer a) is preferably based on at least one thermoplastic polymer selected from the group comprising polyarnides. copolyamides, polyolefins and olefin capolymers. The support layer (T) is particularly preferably based on an 25 aliphatic polyamide or copolyamide, a polyethylene, very particularly preferably polyethylene with a density of < 0.92 g/cm , a polypropylene (PP), an ethylene copolymer, very particularly preferably an ethylene/vinyl acetate copolymer and/or a propylene copolymer. Suitable aliphatic polyamides are in particular polyamide 6 and the copcolyamides thereof: The thermoplastic polymers used preferably exhibit a 30 melting ternerature of at most 170"C, preferably of less than 170*C, particularly preferably o F less than 160*C. The support layer a) is very particularly preferably based on a mixture of 70 to 90 wt.% of linear low density polyethylene (LLDPE), 10 WO 2006/069949 PCTI/EP2005/057034 -5 to 30 wt.% of ethylene/vinyl acetate copolymer and optionally up to 5 wt.% of conventional additives, in each case relative to the total weight of the support layer. Using this mixture of LLDPE and ethylene/vinyl aceLate copolymer to produce the 5 support layer of a heat-shrinkable multilayer film is advantageous as this thermoplas-ic mixture exhibits excellent shrinkage behaviour. Conventional additives are taken to mean antiblocking agents, antistatic agents and/or slip agents. The support layer a) preferably has a thickness of 3-50 prm, particularly preferably of 10 3-20 pm. The gas barrier layer b) is preferably based on at least one polymer selected from the group comprising ethylene/vinyl alcohol copolymer (EVOI I), vinylidene chloride copolymer, polyester and polyamide, preferably on a vinylidene chloride copolymer. 15 Layer b) is preferably largely impermeable to both oxygen and water vapour. This property is preferably also maintained even if the film is used at elevated temperatures. The gas barber layer b) preferably has a thickness of 2 to 15 tm, particularly 20 preferably cf 3 to 10 lm. The heat-sealing layer c) is preferably based on at least one polymer selected from the group comprising polyolefins and olefin copolymers. The polymers used for the production of the heat-scaling layer c) are those approved for the production of 25 layers which come into contact with foodstuffs. In a preferred embodiment, the heat-sealing layer c) is based on at least one polyolelin selected from the group comprising m-polyethylene (m-PB), high density polyethylene (HDPF), low density polyethylene (LDPE), Iinear low density 30 polyethylene (LJLDPE), ethylene copolymers, polypropylenes and propylene copolymers.

WO 2006/069949 PCT/EP2005/057034 -6 The heat-sealing layer c) is particularly preferably based on m-PE, LDPE, LLDPE, ethylene copolymer or mixtures thereof. The polymer selected as the heat-sealing layer polymer is preferably a polymer whose melting or softening temperature is at least I 0 0 C, preferably at least 25*C lower than the melting or softening temperature 5 of the nitrocellulose layer d). (leat-sealing temperatures preferably lie in the range from 1 00 0 C to 140*C. The heat-scaling layer c) preferably has a thickness of 5-30 pm, particularly 10 preferably of 5-20 pim. The melting temperature of the heat-scaling layer c) is preferably from 90 to 140*C, particularly preferably 95*C to 130"C. The multilayer film may comprise further layers based on at least one polymer selected from the group comprising polyolelins, olefin copolymers, polyesters and 15 polyanides, The multilayer film may preferably comprise at least one coupling agent layer. The coupling agent layer may be located between the support layer a) and the gas barrier layer b) and/or between the gas barrier layer b) and the heat-sealing layer c) 20 The coupling agent layer is preferably based on a mixture of at least one polyolefin and/or olefh copolymer, which optionally comprises grafted malcic anhydride units, preferably at least one polymer selected from the group comprising LDPE, HDP, PP, ethylene/vinyl alcohol copolymer and ethylene/vinyl acetate copolymer. 25 A coupling agent layer may preferably have a thickness of 5-50 pm, particularly preferably of 5-15 Inm. The stated thicknesses are taken to be the thickness of the particular layer of the 30 multilayer film according to the invention after having undergone lengthwise and transverse orientation.

WO 2006/069949 PCT/EP2005/057034 -7 The multilayer film preferably comprises at least one layer structure with successive layers of a lacquer layer d), a support layer a), a coupling agent layer, a gas barrier layer b), a coupling agent layer and a heat-sealing layer c). 5 Each layer of the multilayer film according to the invention may preferably additionally contain conventional additives and auxiliary substances such as fillers, dyes, pigments, antistatic agents and/or stabilisers. The multileyer film according to the invention may be printed, wherein at least one 10 layer of the multilayer film may be printed or coloured by the addition of additives such as orgmic or inorganic dyes and pigments. The heat-sealing layer c) may preferably be provided with conventional auxiliary substances such as antistatic agents, slip agents and/or spacers. 15 The multilayer film according to the invention is preferably oriented lengthwise in machine direction in a ratio of 1:3 to 1:5 and transversely to machine direction in a ratio of 1:3 to 1:5. The multilayer film according to the invention is particularly preferably oriented lengthwise in machine direction in a ratio of 1:3.5 to 1:4.5 and 20 transversely to machine direction in a ratio of 1:3.5 to 1:4.5. The multilayer film according to the invention preferably exhibits shrinkability in both the lengthwise and transverse direction of 15 to 35%, when it is heated for at least 6 seconds to a temperature of at least 85"C. 25 The multilayer film according to the invention is pasteurisable. Pasteurisation in this connection is a process for preserving usually liquid foodstuffs which involves briefly heating the packaged foodstuff to a temperature of at most 100*C. The temperature varies depending on the process and foodstuff. 30 The multilayer film according to the invention may be produced by a blowing, flat film, coating, extrusion, coextrusion or a corresponding coating or laminating WO 2006/06949 PCT/EP2005/057034 -8g process, it being possible to apply the lacquer layer d) simultaneously or subsequently The multilhyer film according to the invention is preferably produced by the blown 5 film coextr-ision process, as is described for example in US-A-3,456,044. It is, however, also possible, initially to extrude only the support layer a) as a tube and to apply the subsequent layers by coextrusion or to extrude any desired sub combinatio i as a tubular film and immediately thereafter to extrude it with the remaining iyers. 10 The multilayer film preferably assumes the form of a tubular film, the innermost layer of wh..ch forms the heat-sealing layer c). The film may be corona- or plasma-treated prior to application of the lacquer in 15 order to achieve better adhesion. The lacquer layer d) is preferably applied onto the film in a gravure printing press. The lacquer may preferably be applied in line after the preferred coextrusion blowing process for the tubular film. The lacquer is particularly preferably applied 20 onto the collapsed tubular film by simultaneous application onto both uncovered outer sides of the tube. The applied lacquer may be dried by blowing air over the coated multilayer film in the drying tunnel at a temperature of 20 to 40*C, preferably at a temperature of 25-30 0 C, and/or by applying a vacuum to remove the organic solvent. The surface of the multilayer film lacquer coated in this manner is 25 furthermore smooth. One or all the layers of the multilayer film according to the invention may optionally be crosslinked before or after orientation in order to increase the mechanical strength, preferably puncture resistance, thereof. Crosslinking preferably proceeds 30 by using _ radiation. An electron beam generator operating in a range from 150 kV to 300 kV is used as the irradiation source. A dose of 60 kGy is preferably provided WO 2006/069949 PCT/EP2005/057034 -9 for irradiation in order to crosslink the entire film or also only individual layers, such as for example the support layer. The polymers used for the layer structure of the multilayer film are commercially 5 obtainable and described sufficiently in the prior art. In order to produce the multilayer Iilms according to the invention, they are conventionally mixed in the form of pellets or granules so far as is necessary in conventional mixers and further processed by melting preferably with the assistance of extruders. As has already been explained, production by the blown film coextrusion process is preferred, 10 wherein extruders with multiple dies ensuring the formation of a multilayer tube are used. Processing temperatures, in particular during extrusion, are known to the person skilled in the art and are generally stated on supply of the plastics. The multilayer films according to the invention are extremely well suited to the 15 packaging cf products, preferably of foodstuffs, particularly preferably of perishable foodstuffs. The present invention accordingly also provides packages made from the heat shrinkable raultilayer film according to the invention, preferably for foodstuffs, 20 particularly preferably for perishable foodstuffs. The present invention likewise provides pasteurisable packages made from a tubular film according to the invention in the form of pouches and the use of these packages for packaging foodstuffs, preferably perishable foodstuffs. 25 The packages according to the invention may be produced from the multilayer films according to the invention and filled on packaging machines known to a person skilled in the art, for example on horizontal or on vertical, automated packaging machines, such as for example pouch packaging machines. 30 WO 2006/069949 PCT/EP2005/057034 - 10 Examples The shrinkability of a film according to the invention is measured by drawing a 1010 cm hairline cross on the film sample to be tested with a film pen, one bar of 5 the cross being drawn in machine direction (md), i.e. extrusion direction, and the second bar of the hairline in cross-machine direction (cmd). The water bath, in which the film sample is immersed for 6 see, has a temperature of 85*C. After 6 sec. the sample is removed, the shortening of the hairline cross is measured 10 and the shortening in each direction is stated in percent as a ratio to the initial length of the hairline cross. Example 1 15 A multilayc r film with the following layer structure was produced by a coextrusion blowing process: A support layer a) made from a mixture of 81 wt.% of LLDPF (Stamylex@ 08026-F from DexPlastomers, Netherlands), 15 wt.% of an ethylene/vinyl acetate copolymer 20 having 12 mol% vinyl acetate units (Elvax@ 3135X from DuPont, USA) and 4 wt.% of an antiblocking agent, the layer having a thickness of 10 pm; A coupling agent layer made from a mixture of 30 wt.% of an ethylene/vinyl acetate copolymer having 12 mol% vinyl acetate units (Elvax@ 3135X from DuPont, USA) 25 and 70 wt.h of an ethylene/vinyl acetate copolymer having 18 mol% vinyl acetate units (Elvax 3165@ LG from DuPont, USA), the layer having a thickness of 9 pm; A gas barrier layer b) made from a vinylidene chloride copolymer of vinylidene chloride anc maleic acid (Ixan@ PVS 815 from Solvin, Belgium), the layer having a 30 thickness of 6 [im; WO 2006/069949 PCT/EP2005/057034 - 11 A coupling agent layer made from a mixture of 30 wt.% of an ethylene/vinyl acetate copolymer having 12 mol% vinyl acetate units (Elvax@ 3135X from DuPont) and 70 wt.% of an ethylene/vinyl acetate copolymer having 18 mol% vinyl acetate units (Filvax 316.5 LG), the layer having a thickness of 15 pm; 5 A heat-sealing layer c) made from a mixture of 73 wt.% of a copolymer of ethylene and an alpha-olefin (Affinity PF 1 140G from Dow Plastics, USA); 24 wt.% of LLDPE (Stamylex@ 08026-F from DexPlastomers, Netherlands) and 3 wt.% of an antiblocking agent (Polybatch FSLJ 105E from A. Schulman, Inc., USA), the layer 10 having a thickness of 14 pm. A uniform application of a lacquer based on a nitrocellulose (Haptobond@ CT 120 from SunChemical, Germany) was applied in a gravure printing press onto both sides of the collapsed multilayer film tube. Excess lacquer was removed with a 15 coating knife after the rotating screen roll had turned out of the lacquer trough. The lacquer was applied onto the entire support layer in an amount of I g/m of free surface. The collapsed multilayer film tube was then passed through the gravure printing press at a speed of between 55 and 100 m/min and, in so doing, coated on both sides. The lacquer was then dried in the drying tunnel at a temperature of 30*C, 20 The shrinkability of the oriented multilayer film coated in this manner with lacquer was measured in accordance with the above-stated method and amounted in each case to: 25 cmd: 40% md: 32% The multilayer film was converted into pouches on a packaging machine. Wastage was at most 2% of the number ofpouches produced which were overlapping during 30 of the heat-sealing operation.

WO 2006/069949 PCT/EP20051057034 - 12 Comparative Example Using the cocxtrusion blowing process, a multilayer film was produced having the same strul ure as described in Example 1. 5 No lacquer was applied onto the free surfaces of the support layer a) of the collapsed multilayer im tube. The multilkyer film was converted into pouches on a packaging machine. Wastage 10 was 95% of the number of pouches which were overlapping during the heat-scaling operation.

Claims

1. A heat-shrinkable multilayer film comprising at least the following layers 5 a) a support layer based on at least one thermoplastic polymer, b) a gas barrier layer and c) a heat-scaling layer, 10 characterised in that the entire surface of the support layer a) facing away from the gas barrier layer b) is covered with an external lacquer layer d) based on nitrocellulose. 15

2. A rr ultilayer film according to claim 1, characterised in that the thermoplastic polymer of the support layer exhibits a melting temperature of at most 170*C, preferably of I 10*C to 160*C.

3. A multilayer film according to claim 1 or claim 2, characterised in that the 20 quantity of the applied dry lacquer layer d) amounts to 0.1 to 6 g/m_, preferably 0.5 to 4 g/m of free surface of the support layer a).

4. A multilayer fitn according to any one of claims I to 3, characterised in that the lacquer layer d) is based on at least one nitrocellulose of A grade with a 25 viscosity (to ISO 14446) of 32 A-i 0 A, of AM grade with a viscosity (to ISO 14446) of 32 M to 25 M and/or of E grade with a viscosity of 32 E to 25 E.

5. A multilayer film according to one of claims I and 4, characterised in that the support layer a) is based on at least one thermoplastic polymer selected 30 fron- the group comprising polyamides, copolyamides, polyolefins and olefin copclymers. WO 2006/06)949 PCT/EP2005/057034 - 14

6. A multilayer film according to claim 5, characterised in that the support layer a) i; based on a polyamide 6, an aliphatic copolyamide, a polyethylene, preferably polyethylene with a density of less than 0.92 g/cm_, a polypropylene, an ethylene copolymer, preferably an ethylene/vinyl acetate 5 cop lymer and/or a propylene copolymer.

7. A multilayer film according to any one of claims I to 6, characterised in that the gas barrier layer b) is based on at least one polymer selected from the group comprising ethylene/vinyl alcohol copolymer, vinylidene chloride 10 copolymer, polyester and polyamide, preferably on a vinylidene chloride copolymer.

8. A rrultilayer film according to any one of claims 1 to 7, characterised in that the heat-sealing layer c) is based on at least one polymer selected from the 15 group comprising polyolefins and olefin copolymers.

9. A multilayer film according to claim 8, characterised in that the heat-scaling layer c) is based on at least one polyolefin selected from the group comprising polyethylene (m-PE), high density polyethylene (HDPE), low 20 den5 ity polyethylene (LDPE), linear low density polyethylene (LLDPE), ethylene copolymer, polypropylene (PP) and propylene copolymer.

10. A multilayer film according to claim 9, characterised in that the heat-sealing laye: c) is based on m-PE, ethylene copolymer, LLDPE, LDPE or mixtures 25 thereof.

11. A multilayer film according to one or more of claims I to 10, characterised in that it comprises further layers based on at least one thermoplastic polymer selected from the group comprising polyolefms, olefin copolymers, 30 polyesters and polyamides. WO 2006/069949 PCT/EP2005/057034 - 15

12. A niultilayer film according to any one of claims I to 11, characterised in thai the multilayer film comprises at least one coupling agent layer.

13. A multilayer film according to claim 12 comprising at least one layer 5 structure of a la::quer layer d), a support layer a), a coupling agent layer, 10 a ggs barrier layer b), a coupling agent layer and a he at-sealing laycr c).

14. A multilayer film according to any one of claims I to 13, characterised in 15 that the multilayer film is oriented lengthwise to machine direction in a ratio of 1:3 to 1:5 and transversely to machine direction in a ratio of 1:3 to 1:5.

15. A multilayer film according to any one of claims I to 14, characterised in that the multilayer film is pasteurisable. 20

16. A multilayer film according to any one of claims 1 to 15, characterised in that the multilayer film assumes the form of a tubular film.

17. A process for the production of a multilayer film according to any one of 25 claims I to 16, characterised in that the multilayer film is produced by a blowing, flat film, coating, extrusion, coextrusion or a corresponding coating or lamination process, preferably a blown film coextrusion process and the nitrocellulose lacquer is applied simultaneously or subsequently as lacquer layer d) and the solvent fraction is removed. 30

18. A process according to claim 17, characterised in that the lacquer is applied with, the assistance of a gravure printing press. WO 2006/069949 PCT/EP2005/057034 -16

19. Use of a multilayer film according to any one of claims 1 to 16 for packaging products, preferably foodstuffs, particularly preferably perishable foodstuffs. 5

20. A package made from a multilayer film according to any one of claims I to 16, preferably for foodstuffs, particularly preferably for perishable foodstuffs.

21. A package made from a tubular film according to claim 16. 10

22. A pouch package according to claim 21 for packaging foodstuffs, preferably perishable foodstuffs. WO 2006/064949 PCT/EP2005/057034 - 17 Translator's comment (Page & lir.e number relates to the original) p.15, claim 9, final line: "ist" has been assumed to be in error for "basiert", c.f. claims 6-8 and also claim 10 and accordingly translated as "is based".