DE102004063618A1 - Shrinkable multilayer film with a nitrocellulose lacquer layer - Google Patents

Abstract

The present invention relates to a heat-shrinkable multilayer 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, wherein the entire free surface of the carrier layer facing away from the gas barrier layer is covered with a lacquer layer based on nitrocellulose, their production, their use as packaging material and corresponding packaging of the multilayer film according to the invention.

Description

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

heat shrinkable Multilayer films have a variety of useful packaging applications found from food. This is when using this Foils enclosed the product to be packaged by the multilayer film or in a bag made of such a multilayer film, If necessary, remove the air from inside the packaging and the packaging subsequently a heat source exposed so that the multi-layer film shrinks and the Shape of the packaged good adapts.

Prefers have heat-shrinkable multilayer films a gas barrier layer, in particular an oxygen barrier layer, because of the penetration of oxygen into a package in many goods especially food, leads to oxidative spoilage. In addition, should These films have a good seal strength, so that the the film produced at elevated temperatures, as the shrink temperatures, are resistant to delamination and her integrity not lose. Furthermore should be heat shrinkable Multilayer films have good mechanical properties, so that she during the stress the production process and transportation to the customer.

For sale the packed goods At the consumers it is necessary that the heat-shrinkable films beyond that good optical properties possess the attractiveness of the packaging increase.

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

One Problem in the production of heat-shrinkable multilayer films on the known packaging machines, for example on horizontal as on vertical, automatically running packaging machines, In particular on bag packaging machines is that while the manufacture of packaging, in particular of bags, simultaneously often overlapping to seal individual packages introduced into the sealing tool and not, as necessary, separate from each other. this leads to to that in the overlapping Area the superimposed outer layers of the packaging also seal with each other. Such packaging bags can not More can be used, producing a lot of rejects becomes.

Out The prior art (WO 99/26783 and WO 00/26024) is already known to be this undesirable Connecting packages in the overlapping area by Use of a heat-shrinkable Multilayer film with an outer layer made of polyamide can be avoided. These restrictions the carrier or outer layer on polyamide may also have limited uses the multilayer film z. B. in the manufacture of packaging to lead, so that alternative solutions of the problem indicated are worth striving for.

The Object of the present invention, therefore, was a heat-shrinkable Multi-layer film available to face, with the problem of unwanted sticking of packaging while of the seal in a possibly overlapping Area is avoided and no restriction of the external or Carrier-layer material on polyamide is necessary.

The Task will be provided by the the heat-shrinkable invention Multilayer film 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, from the gas barrier layer facing away from the outer surface of the backing a) with a transparent lacquer layer d) based on nitrocellulose covered, solved.

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

When Lacquers based on nitrocellulose can use one-component or two-component coatings become. After applying the paint and removing solvents, preferably by means of vacuum, has the multilayer film according to the invention continue a smooth surface.

Prefers contains the paint used for applying a plasticizer. Suitable as plasticizers tricresyl phosphates, benzyl benzoates, tributyl phosphates, butyl acetylricinoleates, Glyceryl acetylricinoleates, 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.

Of the for application to the uncovered surface of the carrier layer a) varnish used contains preferably at least one organic, preferably slightly liquid solvent selected from the group comprising 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. Furthermore contains the paint preferably a curing catalyst.

Of the The lacquer used preferably has at least one acrylic resin component on.

The for application to the uncovered surface of the carrier layer a) preferably used paints therefore comprise a mixture of at least one Nitrocellulose and at least one acrylic resin, wherein the polymer components in a solvent solved or dispersed in a dispersing medium. Preferably they contain plasticizers. The paints are in the state of the art, for example in EP 06148-A1. The corresponding description is hereby incorporated by reference and is considered part of the present disclosure.

The dried lacquer layer d) preferably has 60 to 93 wt .-%, particularly preferably 73 to 85% by weight, of at least one nitrocellulose, 5 to 30%, more preferably 10 to at least 20%, at least an acrylic resin and 2 to 10%, more preferably 5 to 7%, plasticizer on, wherein the sum of the components always yields 100 wt .-%.

The backing a) is preferably based on a thermoplastic polymer. Especially preferred is a thermoplastic polymer having a melting temperature <170 ° C, preferably <160 ° C, very particularly preferably from 110 ° C up to 150 ° C, having.

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 with a density <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. The thermoplastic polymers used preferably have a melting temperature of not more than 170 °, preferably less than 170 ° C., more preferably less than 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 common 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 the carrier layer a heat-shrinkable Multilayer film is advantageous because this thermoplastic blend has an excellent shrinkage behavior. Under usual Additives become anti-blocking agents, Antistatic agents and / or lubricants understood.

The backing a) preferably has a thickness of 3-50 microns, more preferably of 3-20 μm.

The Gas barrier layer b) is preferably based on at least one Polymer selected from the group comprising ethylene-vinyl alcohol copolymer, vinylidene chloride copolymer, Polyester and polyamide, preferably on a vinylidene chloride copolymer. The layer b) is preferably both for oxygen and for water vapor largely impermeable. This property preferably remains even when using the film at elevated temperatures maintained.

The Gas barrier layer b) preferably has a thickness of 2 to 15 microns, especially preferably from 3 to 10 μm, on.

The Sealing layer c) is preferably based on at least one polymer selected from the group comprising polyolefins and olefin copolymers. The for the preparation of the sealing layer c) polymers are used for Production of layers that come into contact with food allowed.

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

Especially the sealing layer c) is preferably based on m-PE, LDPE, LLDPE, ethylene copolymer or mixtures thereof.

The Sealing temperatures are preferably in the range of 100 ° C to 140 ° C.

The Sealing layer c) preferably has a thickness of 5-30 microns, especially preferably from 5 to 20 μm. The melting temperature of the sealing layer c) is preferably 90 to 140 ° C, especially preferably 95 ° C up to 130 ° C.

The Multilayer film may have additional layers based on at least a polymer selected from the group comprising polyolefins, olefin copolymers, polyester and polyamides.

Prefers the multilayer film can at least one adhesion promoter layer exhibit. The adhesion promoter layer can be between the carrier layer a) and the gas barrier layer b) and / or between the gas barrier layer b) and / or the sealing layer c) are present.

The Adhesive layer is based on a mixture of polyolefins and / or olefin copolymer, preferably selected from the group consisting of LDPE, HDPE, PP, ethylene-vinyl alcohol copolymer and / or ethylene-vinyl acetate copolymer.

The Adhesive layer preferably has a thickness of 5-50 microns, especially preferably from 5-15 μm.

The Thickness information is to be understood as the thickness of the respective layer of inventive multilayer film after a longitudinal and transverse orientation.

Prefers comprises the multilayer film at least one layer structure of successive Layers of a lacquer layer d), a carrier layer a), a primer layer, a gas barrier layer b), a primer layer and a sealant layer c).

Preferably Each layer of the multilayer film according to the invention may additionally contain conventional additives. and auxiliaries such as fillers, Colorants, antistatic Contain agents and stabilizers.

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

The Sealing layer c) can with the usual excipients as antistatics, lubricants and / or spacers are equipped.

The inventive multilayer film is preferably longitudinal in the machine direction in a ratio of 1: 3 to 1: 5 and across oriented to the machine direction in a ratio of 1: 3 to 1: 5. The multilayer film according to the invention is particularly preferably longitudinal in the machine direction in a relationship from 1: 3.5 to 1: 4.5 and cross machine direction in a ratio of 1: 3.5 to 1: 4.5 oriented.

The has inventive multilayer film preferably a shrinkage both in the longitudinal and in the transverse direction from 15 to 35% if they are for heated to a temperature of at least 85 ° C for at least 6 seconds become.

The inventive multilayer film is pasteurizable. Pasteurizing is in this Related to a method for preserving mostly liquid foods. In doing so, they will be up to a temperature of at most Heated to 100 ° C. The temperature varies by process and food high.

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

The Production of the Multilayer Film According to the Invention can after a blow, flat-film, coating, extrusion, Co-extrusion or a corresponding coating or lamination process take place, wherein the lacquer layer d) applied simultaneously or subsequently can be.

Preferably becomes the multilayer film according to the invention after the blown film co-extrusion process such as As described in US-A-3,456,044. there but it is also possible first only the carrier layer a) to extrude as a tube and the subsequent layers by to apply a coextrusion or any subcombination to extrude as tubular film and immediately afterwards with to extrude the remaining layers.

The Film may be corona and / or plasma treated prior to application of the paint to achieve better adhesion. Preferably, the application is carried out the lacquer layer d) on the film in a gravure printing plant.

Preferably, the application of the paint can preferably be done in line with the preferred coextrusion blown process. Especially preferred the paint is applied to the flattened tubular film by simultaneous application on both uncovered outer sides of the hose.

Of the applied paint can be dried by passing over the coated multilayer film in the drying channel at a temperature of 20 to 40 ° C, preferably at a temperature of 25-30 ° C, Air is blown and / or a vacuum to remove the organic solvent is created.

Preferably become one or all layers of the multilayer film according to the invention crosslinked before or after the orientation in order to increase their mechanical strength, preferably puncture resistance, to increase. The crosslinking is preferably carried out by the use of β radiation. The radiation source is an electron beam generator, the operating in a range of 150 kV to 300 kV. For irradiation Preferably, a dose of 60 kGy is used to reduce the total Film or just individual layers such as the outer layer to network.

The are polymers used for layer construction of the multilayer film commercially available and sufficiently described in the prior art. They usually become for producing the multilayer films according to the invention as pellets or granules, if necessary mixed in conventional mixing apparatus, and by melting preferably by means of extruders in the desired Brought final shape. As already mentioned, the production is after the Folienblascoextrusionsverfahren preferred extruder with Multiple nozzles are used, which ensure the formation of a multi-layered hose. The processing temperatures, especially in the extrusion, are The person skilled in the art is familiar with the provision of plastics generally indicated.

The Multilayer films according to the invention are suitable excellent for packaging goods, preferably food, especially preferred from perishable foods.

One Another object of the invention are therefore packaging from a Heat-shrinkable according to the invention Multilayer film, preferably for Foods, especially preferred for perishable foods.

Also are an object of the present invention pasteurizable Packaging of a tubular film according to the invention in the form of bags and the use of these packages for food packaging, preferably from perishable foods

The Packaging according to the invention can from the multilayer films according to the invention all known to those skilled packaging machines and manufactured filled be automatic, for example, horizontal or vertical current packaging machines or on bag packaging machines.

to Measurement of shrinkability a film according to the invention will be on the film sample to be tested a crosshair 10 × 10 cm recorded with a foil pen, with a beam in the Machine direction (md), d. H. Extrusion direction and the second Bars of the crosshairs drawn crosswise to the machine direction (cmd) becomes. The water bath, in which the film pattern is immersed for 6 sec has a temperature of 85 ° C.

To 6 sec, the pattern is taken, measured the shortening of the crosshair and the shortening for the respective direction as relation to initial length of the crosshairs in%.

example 1

By coextrusion blow molding a multilayer film was produced with the following structure:
A carrier layer of a mixture of 81 wt .-% LLDPE (Stamylex ^® 08026-F from DexPlastomers, Netherlands), 15 wt .-% of an ethylene-vinyl acetate copolymer with 12 mol% vinyl acetate units (Elvax ^® 3135X the company DuPont, USA) 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 -% of vinyl acetate units (Elvax 3165 ^® LG DuPont, USA), the layer had a thickness of 9 microns;
A gas barrier layer of a vinylidene chloride copolymer of vinylidene chloride and maleic acid (Ixan ^® PVS 815 Solvin, Belgium), which layer had a thickness of 6 microns;
An adhesive layer made of a mixture of 30 wt .-% of an ethylene-vinyl acetate copolymer having 12 mol% of vinyl acetate units (Elvax 3135X ^® from DuPont) and 70 wt .-% of an ethylene-vinyl acetate copolymer having 18 mol% vinyl acetate units (Elvax ^® 3165 LG), wherein the layer had a thickness of 15 microns;
A sealing layer of a mixture of 73% by weight of a copolymer of ethylene and an alpha-olefin (Affinity PF 1140G from Dow Plastics, USA); 24 wt .-% LLDPE (Stamylex ^® 08026-F DexPlastomers Company, the Netherlands) and 3% by weight of an antiblocking agent (Polybatch FSU 105E from A. Schulman, Inc., USA), the layer having a thickness of 14 μm.

On the flattened film tube a multi-layer coating based on nitrocellulose (Haptobond ^® CT 120 from Sun Chemical, Germany) was applied to both sides in a gravure press evenly order. The excess paint was stripped with a squeegee after the rotating screen roller had rotated out of the paint tray. There was 1 g / m ² paint, each applied to the free surface of the outer 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 bagged on a packaging machine processed. The committee was lying at most 2% of the bags during the Sealing process overlapping lay.

Comparative example

To The coextrusion blown process was a multilayered film with the same Construction, as described in Example 1, prepared.

On The flattened multilayer film tube was on the free surfaces no paint applied.

The Multilayer film was bagged on a packaging machine processed. The committee was lying at 95% of the bags during overlapping of the seal lay.

Claims (22)

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 uncovered surface of the carrier layer a) facing away from the gas barrier layer b) is coated with a lacquer layer d ) is covered based on nitrocellulose. Multilayer film according to claim 1, characterized in that that the thermoplastic polymer has a melting temperature of maximum as 170 ° C, preferably from 110 ° C up to 160 ° C, having. Multilayer film according to claim 1 or 2, characterized in that the amount of lacquer layer d) applied is dry 0.1 to 6 g / m ² , preferably 0.5 to 4 g / m ² . Multilayer film according to one of claims 1 to 3, characterized in that the lacquer layer d) at least one Contains plasticizer. Multilayer film according to one of claims 1 and 3, characterized in that the carrier layer a) on at least a thermoplastic polymer selected from the group comprising polyamides, Copolyamides, polyolefins and olefin copolymers based. 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. Multilayer film according to one of claims 1 to 6, characterized in that the gas barrier layer b) on at least a polymer selected from the group comprising ethylene-vinyl alcohol copolymer, vinylidene chloride copolymer, polyester and polyamide, preferably on a vinylidene chloride copolymer, based. Multilayer film according to one of claims 1 to 7, characterized in that the sealing layer c) on at least a polymer selected from the group is based on polyolefins and olefin copolymers. Multilayer film according to claim 8, characterized in that in that the sealing layer c) is selected from at least one polyolefin the group comprising polyethylene (m-PE), high density polyethylene (HDPE), low density polyethylene (LDPE), linear polyethylene low density (LLDPE), ethylene copolymer, polypropylene (PP) and Propylene copolymer is. Multilayer film according to claim 9, characterized in that that the sealing layer c) on m-PE, ethylene copolymer, LLDPE, LDPE or their mixture is based. Multilayer film according to one or more of Claims 1 to 10, characterized that it comprises further layers based on at least one polymer selected from the group comprising polyolefins, olefin copolymers, polyesters and polyamides. Multilayer film according to one of claims 1 to 11, characterized in that the multilayer film at least having a primer layer. Multilayer film according to claim 12 comprising at least a 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). Multilayer film according to one of claims 1 to 13, characterized in that the multilayer film along the Machine direction in a ratio from 1: 3 to 1: 5 and cross machine direction in a ratio of 1: 3 to 1: 5 oriented. Multilayer film according to one of claims 1 to 14, characterized in that the multilayer film pasteurizable is. Multilayer film according to one of claims 1 to 15, characterized in that the multilayer film as a tubular film is present. Method for producing a multilayer film according to one the claims 1 to 16, characterized in that the multilayer film after a blown, flat-film, Coating, extrusion, co-extrusion or a corresponding coating or laminating process, preferably a blown film coextrusion process, and simultaneously or subsequently the lacquer of the lacquer layer d) and the solvent content Will get removed. Method according to claim 17, characterized; that the application of the paint with the help a gravure printing system takes place. Use of a multilayer film according to a the claims 1 to 16 for the packaging of goods, preferably of foods, more preferably of perishable ones Food. Packaging of a multilayer film according to a the claims 1 to 16, preferably for food, especially preferred for perishable food. Packaging of a tubular film according to claim 16th Packaging according to claim 21 for packaging food, preferably perishable Food.