WO2006069949A2

WO2006069949A2 - Shrinkable multilayered film comprising a nitrocellulose layer of lacquer

Info

Publication number: WO2006069949A2
Application number: PCT/EP2005/057034
Authority: WO
Inventors: Jochen Dold; Walter Bernig
Original assignee: Cfs Kempten Gmbh
Priority date: 2004-12-27
Filing date: 2005-12-21
Publication date: 2006-07-06
Also published as: WO2006069949A3; EP1833667A2; DE102004063618A1; AU2005321269A1

Abstract

The invention relates to a heat-shrinkable multilayered film comprising at least one carrier layer a) based on at least one thermoplastic polymer, at least one gas barrier layer, and at least one sealing layer. The entire free surface of the carrier layer opposing the gas barrier layer is covered with an outer layer of lacquer based on nitrocellulose. The invention also relates to the production of one such film, to the use thereof as a packaging material, and to corresponding packagings consisting of the inventive multilayered film.

Description

Shrinkable multilayer film with a nitrocellulose lacquer layer

The present invention relates to a heat-shrinkable multilayer film comprising at least one carrier layer based on at least one thermoplastic polymer, which preferably has a melting point <170 ° C; at least one gas barrier layer and at least one sealing layer, wherein the entire surface of the carrier layer facing away from the gas barrier layer is covered with an outer lacquer layer based on nitrocellulose, their production, their use as packaging material and corresponding packaging of the multilayer film according to the invention.

Heat-shrinkable multilayer films have found a variety of useful food packaging applications. When using these films, the material to be packaged is enclosed by the multilayer film or introduced into a bag made from such a multilayer film, if necessary the air is removed from the interior of the packaging and the packaging is then exposed to a heat source so that the multilayer film shrinks and conforms to the shape of the packaged good.

Heat-shrinkable multilayer films preferably have a gas barrier layer, in particular an oxygen barrier layer, since the penetration of oxygen into a package leads to oxidative spoilage in many packaged goods, in particular foods. In addition, these films must have good seal strength so that the packages made from the film are resistant to delamination even at elevated temperatures, such as shrink temperatures, and do not lose their integrity. In addition, heat-shrinkable multilayer films should have good mechanical properties to withstand the stresses during the production process and transport to the customer. For the sale of the packaged goods to consumers, it is necessary that the heat-shrinkable films also have good optical properties that increase the attractiveness of the packaging.

Multilayer films which meet these requirements are known from the prior art and are also available on the market.

A problem in the production of packages of heat-shrinkable multilayer films on the known packaging machines, for example, on horizontal or vertical, automatically running packaging machines, especially on bag packaging machines is that during the production of packaging, especially bags, the same time for sealing individual packages often overlapping introduced into the sealing tool and not, as necessary, there separated from each other. As a result, in the overlapping area, the superimposed outer layers of the packages are also sealed together. Such packaging bags can not be used any more, thereby producing a lot of waste.

It is already known from the prior art (WO 99/26783 and WO 00/26024) that this undesired bonding of packages in the overlapping region can be avoided by using a heat-shrinkable multilayer film with a polyamide outer layer. These restrictions of Trägerbzw. Outer layer on polyamide can also be limited to the possible uses of the multilayer film z. As in the manufacture of packaging, so that alternative solutions to the problem indicated are desirable.

The object of the present invention was therefore to provide a heat-shrinkable multilayer film, which avoids the problem of unwanted sticking of packaging during Siegeins in a possibly overlapping area of individual packaging, without any restriction of the external or Carrier layer material on polyamide is necessary. The object is achieved by providing the heat-shrinkable multilayer film according to the invention comprising at least one carrier layer a) based on at least one thermoplastic polymer, at least one gas barrier layer b) and at least one sealing layer c), wherein the entire external surface of the carrier layer facing away from the gas barrier layer a) is covered with a preferably transparent, outer lacquer layer d) based on nitrocellulose.

The amount of lacquer layer d) applied dry is preferably 0.1 to 6 g / m ² , more preferably 0.5 to 4 g / m ² surface of the carrier layer a).

The lacquer used according to the invention can contain as nitrocellulose any type of nitrocellulose. This means that both nitrocelluloses of the A type (nitrogen content 10.7% - 1 1, 35%), which are soluble in ethanol, AM type nitrocelluloses (nitrogen 1 1, 3% - 1 1, 8%), the are only partially soluble in ethanol, as well as nitrocelluloses of E-type (nitrogen content 1 1, 8% - 12.3%), which are not ethanol but as well as the A-types or AM-types are soluble in esters, or by Mixtures can serve as a paint base. Preferably, A-type nitrocelluloses having a viscosity (measured to ISO 14446) of 32A-10A, of the AM type having a viscosity (measured to ISO 14446) of 32M to 25M and / or of the E-type with a Viscosity of 32 E to 25 E are used. The viscosity according to ISO 14446 (formerly DIN 53179) is determined and indicated as follows:

The concentration is given in nitrocellulose (atro), which is necessary to obtain a viscosity of the solution of 375 to 425 mPas. Solvent is acetone with a water content of 5%. The viscosity in a Hoppler falling ball viscometer at 20 ⁰ C. is 14446 (also sometimes referred to as a standard viscosity) The viscosity measured according to ISO is given as a numerical value, which is identical to the concentration of the nitrocellulose. If this numerical value is an integer, then the nitrocellulose is referred to as a so-called standard type. Depending on the solubility of the nitrocellulose in ethanol, an A (A-type), M (M-type) or E (E-type) is set after the numerical values. Possibly. The paint used for application contains a plasticizer. Suitable plasticizers are tricresyl phosphates, benzyl benzoates, tributyl phosphates, butylacetyl ricinoleates, glyceryl acetyl ricinoleates, dibutyl phthalates, dibutyl glycolates, dioctyl phthalates, butyl stearates, triphenyl phosphates, triethyl citrates, tributyl citrates, tributyl acetyl citrates, dibutyl tartrates, diisobutyl phthalates, diamyl phthalates, dioctyl sebacate and / or camphor.

Depending on the solubility of the nitrocellulose, the lacquer used for application to the uncovered surface of the carrier layer a) preferably contains at least one organic, preferably slightly liquid solvent selected from the group consisting of ethyl acetate, n-butyl acetate, methyl acetate, n-amyl acetate, methyl isobutyl ketone, methyl ethyl ketone, ethanol , Propanol, isopropanol, n-butanol, toluene, heptane, isopropyl acetate and hexane. Possibly. the paint may contain a curing catalyst.

The lacquer used may optionally have, as further polymer component, at least one acrylic resin component or alkyd resin component.

The lacquers preferably used for application to the uncovered surface of the carrier layer a) are based on at least one nitrocellulose, which may be dissolved in a suitable solvent or dispersed in a dispersing medium. Preferably, the nitrocellulose is dissolved. Suitable paints are described in the prior art, for example in EP 061348-A1. The corresponding description is hereby incorporated by reference and is considered part of the present disclosure.

The backing layer a) is preferably based on a thermoplastic polymer. Particularly preferred is a thermoplastic polymer which has a melting temperature <170 ° C, preferably <160 ° C, most preferably from 1 10 ° C to 150O.

The backing layer a) is preferably based on at least one thermoplastic polymer selected from the group comprising polyamides, copolyamides, polyolefins and olefin copolymers. Particularly preferably, the carrier layer a) is based on an aliphatic polyamide or copolyamide, a Polyethylene, very particularly preferably polyethylene having a density of <0.92 g / cm ³ , a polypropylene (PP), an ethylene copolymer, very particularly preferably an ethylene-vinyl acetate copolymer and / or a propylene copolymer. Polyamide 6 and its copolyamides are particularly suitable as aliphatic polyamides. Exhibit The used thermoplastic polymers preferably have a melt temperature of at most 170 °, preferably less than 170 ⁰ C, particularly preferably of less 160 °. Most preferably, the carrier layer a) based on a mixture of 70 to 90 wt .-% linear low density polyethylene (LLDPE), 10 to 30 wt .-% ethylene-vinyl acetate copolymer and optionally up to 5 wt .-% more usual Additives, in each case based on the total weight of the carrier layer

The use of this mixture of LLDPE and ethylene-vinyl acetate copolymers for the production of the carrier layer of a heat-shrinkable multilayer film is advantageous because this thermoplastic mixture has an excellent shrinkage behavior. Conventional additives are understood to be anti-blocking agents, antistatic agents and / or lubricants.

The carrier layer a) preferably has a thickness of 3 to 50 μm, more preferably 3 to 20 μm.

The gas barrier layer b) is preferably based on at least one polymer selected from the group consisting of ethylene-vinyl alcohol copolymer, Vinylidenchlohd copolymer, polyester and polyamide, preferably on a vinylidene chloride copolymer. The layer b) is preferably substantially impermeable to both oxygen and water vapor. This property is preferably maintained even when using the film at elevated temperatures.

The gas barrier layer b) preferably has a thickness of 2 to 15 μm, more preferably of 3 to 10 μm.

The 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 preparation of the sealing layer c) are permitted for the production of layers which come into contact with foodstuffs.

In a preferred embodiment, the sealing layer c) is based on at least one polyolefin selected from the group consisting of m-polyethylene (m-PE), high density polyethylene (HDPE), low density polyethylene (LDPE), linear low density polyethylene (LLDPE), ethylene copolymers , Polypropylenes and propylene copolymers.

The sealing layer c) is particularly preferably based on m-PE, LDPE, LLDPE, ethylene copolymer or mixtures thereof. The preferred sealing layer polymer used is a polymer whose melting or softening temperature is at least 10 ^° C., preferably at least 25 ^° C. lower than the melting or softening temperature of the nitrocellulose layer d).

The sealing temperatures are preferably in the range of 100 ° C to 14O ⁰ C.

The sealing layer c) preferably has a thickness of 5 to 30 μm, particularly preferably 5 to 20 μm. The melting temperature of the sealing layer c) is preferably 90 to 140O, more preferably 95 ⁰ C to 130 ° C.

The multilayer film may comprise further layers based on at least one polymer selected from the group comprising polyolefins, olefin copolymers, polyesters and polyamides.

The multilayer film may preferably have at least one adhesion promoter layer. The adhesion promoter layer may be present between the carrier layer a) and the gas barrier layer b) and / or between the gas barrier layer b) and the sealing layer c).

The adhesion promoter layer is preferably based on a mixture of at least one polyolefin and / or olefin copolymer which optionally has grafted maleic anhydride units, preferably at least one polymer selected from the group comprising LDPE, HDPE, PP, ethylene-vinyl alcohol copolymer and ethylene-vinyl acetate copolymer.

An adhesion promoter layer may preferably have a thickness of 5 to 50 μm, particularly preferably 5 to 15 μm.

The thickness specifications are understood to mean the thickness of the respective layer of the multilayer film according to the invention after a longitudinal and transverse orientation has taken place.

The multilayer film preferably comprises at least one layer structure comprising successive layers of a lacquer layer d), a carrier layer a), a primer layer, a gas barrier layer b), a primer layer and a sealing layer c).

Each layer of the multilayer film according to the invention may additionally contain customary additives and auxiliary substances such as fillers, dyes, pigments, antistatic agents and / or stabilizers.

The multilayer film according to the invention can be printed, wherein at least one layer of the multilayer film can be printed or dyed by the addition of additives such as organic or inorganic dyes and pigments.

Preferably, the sealing layer c) can be equipped with the usual excipients such as antistatic agents, lubricants and / or spacers.

The multilayer film according to the invention is preferably oriented longitudinally in the machine direction in a ratio of 1: 3 to 1: 5 and transversely to the machine direction in a ratio of 1: 3 to 1: 5. Particularly preferably, the multilayer film according to the invention is oriented longitudinally in the machine direction in a ratio of 1: 3.5 to 1: 4.5 and transversely to the machine direction in a ratio of 1: 3.5 to 1: 4.5. The multilayer film of the present invention preferably has a shrinkability in both the longitudinal and transverse directions of 15 to 35% when heated to a temperature of at least 85 ° C for at least 6 seconds.

The multilayer film according to the invention can be pasteurized. In this context, pasteurization is a process for preserving mostly liquid foods. The packaged food is briefly heated up to a maximum temperature of 100 ⁰ C. The temperature varies depending on the process and food.

The multilayer film according to the invention can be produced by a blown, flat film, coating, extrusion, coextrusion or a corresponding coating or laminating method, wherein the lacquer layer d) can be applied simultaneously or subsequently.

Preferably, the multilayer film according to the invention after the blown film co-extrusion process such. As described in LJS-A-3, 456.044. However, it is also possible initially to extrude only the backing layer a) as a tube and to apply the subsequent layers by coextrusion or to extrude any subcombination as a tubular film and then to extrude it directly with the remaining layers.

The multilayer film is preferably in the form of a tubular film whose innermost layer forms the sealing layer c).

The film may be corona and / or plasma treated prior to application of the paint for better adhesion. Preferably, the paint layer d) is applied to the film in a gravure press.

Preferably, the application of the paint can preferably be carried out in line according to the preferred co-extrusion blown process of the tubular film. Particularly preferably, the paint is applied to the flattened tubular film by simultaneous application to both uncovered outer sides of the hose. The applied paint can 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 to 30 ° C., and / or applying a vacuum to remove the organic solvents The painted surface of the multilayer film is still smooth.

One or all layers of the multilayer film according to the invention may optionally be crosslinked before or after the orientation in order to increase their mechanical strength, preferably puncture resistance. The crosslinking is preferably carried out by the use of .beta.-radiation. The irradiation source is an electron beam generator operating in a range of 150 kV to 300 kV. For irradiation, a dose of 60 kGy is preferably used to crosslink the entire film or just individual layers such as the carrier layer.

The polymers used for layer construction of the multilayer film are commercially available and sufficiently described in the prior art. They are usually mixed in the production of multilayer films according to the invention as pellets or granules, if necessary, in conventional mixing apparatus and brought by melting, preferably by means of extruders in the desired final shape. As already mentioned, production by the blown film coextrusion method is preferred, with extruders having multiple nozzles being used, which ensure the formation of a multilayered tube. The processing temperatures, especially in the extrusion, are known in the art and are generally indicated with the provision of the plastics.

The multilayer films according to the invention are outstandingly suitable for packaging goods, preferably foods, particularly preferably perishable foods.

A further subject of the invention is therefore packaging made of a heat-shrinkable multilayer film according to the invention, preferably for foodstuffs, particularly preferably for perishable foodstuffs. Also an object of the present invention are pasteurizable packages of a tubular film according to the invention in the form of bags and the use of these packages for packaging food, preferably perishable foods

The packagings according to the invention can be produced and filled from the multilayer films according to the invention on the packaging machines known to the person skilled in the art, for example on horizontal or on vertical, automatically running packaging machines such as, for example, bag packaging machines.

Examples

To measure the shrinkability of a film according to the invention, a reticle 10 × 10 cm is recorded on the film sample to be tested with a film pen, a beam in the machine direction (MD), d. H. Extrusion direction and the second bar of the crosshairs transverse to the machine direction (cmd) is drawn. The water bath, in which the film pattern is immersed for 6 sec, has a temperature of 85 "C.

After 6 sec, the pattern is taken, the shortening of the cross hairs measured and the shortening for the respective direction as a ratio to the initial length of the reticle in% indicated.

example 1

By coextrusion blow molding a multilayer film was produced with the following layer structure:

A backing layer a) from a mixture of 81% by weight LLDPE (Stamylex® 08026-F from DexPlastomers, Netherlands), 15% by weight of an ethylene-vinyl acetate copolymer with 12 mole% vinyl acetate units (Elvax® 3135X DuPont, U.S.A.) and 4% by weight of an antiblock agent, the layer having a thickness of 10 μm;

A primer layer of a mixture of 30 wt .-% of an ethylene-vinyl acetate copolymer with 12 mol% vinyl acetate units (Elvax® 3135X from DuPont, USA) and 70 wt .-% of an ethylene-vinyl acetate copolymer with 18 mol % Vinyl acetate units (Elvax 3165® LG from DuPont, USA), the layer having a thickness of 9 μm;

A gas barrier layer b) of a vinylidene chloride copolymer of vinylidene chloride and maleic acid (Ixan® PVS 815 from Solvin, Belgium), the layer having a thickness of 6 μm; An adhesion promoter layer comprising a mixture of 30% by weight of an ethylene-vinyl acetate copolymer with 12 mol% of vinyl acetate units (Elvax® 3135X from DuPont) and 70% by weight of an ethylene-vinyl acetate copolymer having 18 mol%

O%, vinyl acetate units (Elvax 3165® LG), the layer having a thickness of 15 μm;

A sealing layer c) of a mixture of 73% by weight of a copolymer of ethylene and an alpha-olefin (Affinity PF 1 140G from Dow Plastics, USA); 24% by weight of LLDPE (Stamylex® 08026-F from DexPlastomers, Netherlands) and 3% by weight of an antiblocking agent (Polybatch FSLJ 105E from A. Schulman, Inc., USA), the layer having a thickness of 14 μm would have.

On the flattened multilayer film tube, a uniform application of a lacquer based on a nitrocellulose (Haptobond® CT 120 from SunChemical, Germany) was applied on both sides in a gravure press. The excess paint was stripped with a squeegee after the rotating screen roller had rotated out of the paint tray. The paint was applied in an amount of 1 g / m ² free surface on the entire support layer. The flattened multilayer film tube was passed through the gravure press at a speed between 55 and 100 m / min and coated on both sides. Subsequently, the paint was dried at a temperature of 30 ° C in a drying tunnel.

The measurement of the shrinkability of the thus coated with varnish, oriented multilayer film was carried out by the method mentioned above and was in each case

cmd: 40% md: 32%

The multilayer film was processed into bags on a packaging machine. The Committee had a maximum of 2% of the number of bags produced that overlapped during the sealing process. Comparative example

After the co-extrusion blown process, a multilayer film having the same structure as described in Example 1 was prepared.

On the free surfaces of the support layer a) of the flattened multilayer film tube no paint was applied.

The multilayer film was processed into bags on a packaging machine. The committee was 95% of the number of bags that overlapped during the winnings.

Claims

claims:

1 . Heat-shrinkable multilayer film comprising at least the following layers

a) a carrier layer based on at least one thermoplastic polymer,

b) a gas barrier layer and

c) a sealing layer,

characterized in that the entire, from the gas barrier layer b) facing away from uncovered surface of the carrier layer a) is covered with an outer lacquer layer d) based on nitrocellulose.

2. multilayer film according to claim 1, characterized in that the thermoplastic polymer of the carrier layer has a melting temperature of at most 170 ⁰ C, preferably from 1 10 ⁰ C to 160 ° C.

3. multilayer film according to claim 1 or 2, characterized in that the amount of the applied lacquer layer d) is dry 0.1 to 6 g / m ² , preferably 0.5 to 4 g / m ² free surface of the support layer a).

4. multilayer film according to one of claims 1 to 3, characterized in that the lacquer layer d) on at least one nitrocellulose of the A-type with a viscosity (according to ISO 14446) of 32 A - 10 A, AM type with a viscosity ( according to ISO 14446) of 32 M to 25 M and / or of the E-type with a viscosity of 32 E to 25 E.

5. Multilayer film according to one of claims 1 and 4, characterized in that the carrier layer a) is based on at least one thermoplastic polymer selected from the group comprising polyamides, copolyamides, polyolefins and olefin copolymers.

6. multilayer film according to claim 5, characterized in that the carrier layer a) on a polyamide 6, an aliphatic copolyamide, a polyethylene, preferably polyethylene having a density of less than 0.92 g / cm ³ , a polypropylene, an ethylene copolymer, preferably an ethylene-vinyl acetate copolymer and / or a propylene copolymer based.

7. Multilayer film according to one of claims 1 to 6, characterized in that the gas barrier layer b) is based on at least one polymer selected from the group consisting of ethylene-vinyl alcohol copolymer, vinylidene chloride copolymer, polyester and polyamide, preferably on a vinylidene chloride copolymer ,

8. Multilayer film according to one of claims 1 to 7, characterized in that the sealing layer c) is based on at least one polymer selected from the group comprising polyolefins and olefin copolymers.

9. multilayer film according to claim 8, characterized in that the sealing layer c) on at least one polyolefin selected from the group comprising polyethylene (m-PE), high density polyethylene (HDPE), low density polyethylene (LDPE), linear low density polyethylene ( LLDPE), ethylene copolymer, polypropylene (PP) and propylene copolymer.

10. Multilayer film according to claim 9, characterized in that the sealing layer c) is based on m-PE, ethylene copolymer, LLDPE, LDPE or a mixture thereof.

1 1. Multilayer film according to one or more of claims 1 to 10, characterized in that it comprises further layers based on at least one thermoplastic polymer selected from the group comprising polyolefins, olefin copolymers, polyesters and polyamides.

12. Multilayer film according to one of claims 1 to 1 1, characterized in that the multilayer film has at least one adhesion promoter layer.

13. Multilayer film according to claim 12 comprising at least one layer structure

a lacquer layer d), a carrier layer a), a primer layer, a gas barrier layer b), a primer layer and a sealing layer c).

14. Multilayer film according to one of claims 1 to 13, characterized in that the multilayer film is oriented along the machine direction in a ratio of 1: 3 to 1: 5 and transversely to the machine direction in a ratio of 1: 3 to 1: 5.

15. Multilayer film according to one of claims 1 to 14, characterized in that the multilayer film is pasteurizable.

16. Multilayer film according to one of claims 1 to 15, characterized in that the multilayer film is present as a tubular film.

17. A process for producing a multilayer film according to any one of claims 1 to 16, characterized in that the multilayer film according to a blown, flat-film, coating, extrusion, co-extrusion or a corresponding coating or lamination process , preferably a blown film coextrusion process, prepared and simultaneously or subsequently the nitrocellulose lacquer is applied as lacquer layer d) and the solvent fraction is removed.

18. The method according to claim 17, characterized in that the application of the paint takes place by means of a gravure printing system.

19. Use of a multilayer film according to one of claims 1 to 16 for the packaging of goods, preferably of foods, particularly preferably of perishable foods.

20. Packaging of a multilayer film according to one of claims 1 to 16, preferably for food, particularly preferably perishable food.

21. Packaging of a tubular film according to claim 16.

22. Bag packaging according to claim 21 for packaging food, preferably perishable food.