DE19962114B4 - release film - Google Patents

Abstract

Multi-layer release film (1) for labels with at least a first core layer (1.2) made of polypropylene and two cover layers (1.1; 1.3) made of polyethylene arranged on one side of the core layer, the single or the core layers together being thicker than each of the cover layers and are coextruded, and in which at least one of the cover layers (1.1, 1.3) has an adhesion-reducing coating, preferably based on stearic acid, amides, waxes, silicone, silicone compounds or fluorinated polyolefins, characterized in that the cover and core layers (1.2, 1.2, 1.3), undrawn and unoriented and that the thickness of the core layer (1.2) is 5 to 20 times the respective thickness of a cover layer (1.1, 1.3).

Description

The invention relates to a multi-layer release film for labels, with at least a first core layer made of polypropylene and two cover layers arranged on one side of the core layer Polyethylene, the only or the core layers together being thicker are as each of the facings and are coextruded, and at the at least one of the cover layers has an adhesion-reducing coating, preferably based on stearic acid, amides, waxes, Silicone, silicone compounds or fluorinated polyolefins.

Such a release film, also referred to as a separating layer support, is from the DE 195 48 2 65 A1 known. According to this document, the release liner has a flat base substrate made of plastic, which has a release layer on one side that separates against a pressure sensitive adhesive. The base substrate consists of a stretched thermoplastic polyolefin film with a polymer surface coating. The separating layer support is produced, for example, by coextrusion.

By stretching it becomes in known rigidity brought into the polyolefin film. With the known release film there is a monaxial or biaxial stretching in the ratio 1 : 10 to 1:20. Stretching requires another one Operation. It makes a mass product more expensive, like a release film is considerable.

According to the state of the art as a release film also substrates made of paper, oriented polyesters, etc. used which is coated with silicone compounds to reduce adhesion are. A release paper with an adhesion reducing coating is through the process from the European Patent 0 190 354 B1 known.

On the release film are usually one Adhesive layer and a label film applied. The entire network from release film, Adhesive layer and label film are punched out. The waste is taken as a lead frame. It is important that the label film is easy to punch, so a clean cut is possible. In return, the release film but provide enough resistance to punch through completely the release liner safe to avoid.

When donating, i.e. when applying of the label on the container to be labeled or the like, the release film deflected with a small bending radius at a large angle, whereby the label section detaches from the release film. The release film must be so stiff that the label and release film be separated safely when donating. A release film that is too flexible could entrained by the adhesive label when donating and overstretched by it be so that interference in Machine run can occur.

Known release films also have high thermal resistance in order to cure the high thermal load during curing Silicon compound and sufficiently resistant when applying adhesive his.

A disadvantage of known ones release films from paper that for the illustrated Processing properties a relatively large thickness is necessary. On The main disadvantage of cellulose-containing substrates is the extremely large surface roughness and absorbency, causing large amounts of silicone compounds needed be a thin, continuously smooth surface coating to accomplish. Here are the costs of using silicone compounds disproportionately high as a coating across from those of the substrate of the release film.

Show known release films on plastic basis has a lower surface roughness, which means less material for the non-stick coating needed is, however, the known release films are based on films from the the aforementioned expensive raw materials.

Since a release film is only an aid for processing labels after the application the label section is useless and must be disposed of is also the recyclability important. However, recycling is known release films due to the inhomogeneous Composition difficult to carry out.

It is therefore the object of the present invention an inexpensive release film to create, which has a high temperature resistance and the one has such stiffness that a good processability in labeling systems is guaranteed. The adhesive layer side Surface must be adequate Have separation effect to when dispensing the label sections to ensure, that itself the label from the release liner solves and exactly on the container can be placed. The release film should also have sufficient resistance to the punching knife have to trim the label film; cutting the release film must sure be prevented.

The above tasks will be according to the invention solved with a multi-layer release film of the type mentioned above, in which the cover and core layers are undrawn and disoriented and the thickness of the core layer 5 times to 20 times the respective thickness of a cover layer.

An advantage of the release film according to the invention is that it is produced exclusively from undrawn polyolefins, that is to say from inexpensive bulk plastics. The symmetrical structure ensures that the curl of the release film is prevented during processing, so that the release film lies flat during processing. It is also advantageous that the plastics of the cover and core layers can be coextruded with one another as blown or cast film.

Due to the core layer made of polypropylene, the in proportion to the cover layers has a significantly greater strength, is a high temperature resistance and a high mechanical resistance to the punch knives. The cover layers made of polyethylene have a low roughness on and are good by the used as a non-stick coating Silicone compounds wettable, so that only small amounts thereof are needed a coating with a good release effect compared to the Manufacture label adhesives.

By choosing a polyolefin for the top layers is already a surface given with a very low specific surface energy. The top layers made of polyethylene are insufficiently wettable and have poor adhesive properties, what with a release film are good prerequisites for achieving a high separation effect.

To have a good inner bond in the release film To manufacture, it is favorable in this embodiment that few steps between the anti-adhesive top layer and the core layer a coextruded adhesive layer is arranged.

Possible is also an embodiment at least the core layer with mineral fillers like chalk, lime or talc is. The advantage here is that the thermal resistance and mechanical strength of the core layer further improved and at the same time an improvement in economy through material savings is achieved on the relatively thick core layer.

The invention is implemented with further advantageous embodiments explained in more detail using examples and the drawing. The figures of the drawing demonstrate:

1a a schematic representation of a combination of release film, adhesive layer and label film,

1b the release film with adhesive labels after punching and removing the lead frame in a schematic representation and

2 a further embodiment of a release film in a schematic sectional view.

In 1a is a composite for labeling, e.g. B. of packaging.

example 1

• – Die Deckschichten 1.1, 1.3 bestehen aus Polyethylen hoher Dichte (HDPE) mit einer Dichte p von 0,930 bis 0,960 g/cm³, und einem Schmelzindex MFI (DIN 53735, Prüfbedingungen 190°C/2,16 kg) von 0,5 bis 7g/10 min, vorzugsweise 0,2 bis 2 g/10 min, und haben eine Dicke von 3 bis 10μm.
• – Die Kernschicht 1.2 besteht aus Polypropylen mit einem Schmelzindex MFI (DIN 53735, Prüfbedingungen 190°C/2,16 kg) von 0,2 bis 4 g/10 min, vorzugsweise 0,2 bis 2 g/10 min.
• – Die Ablösefolie 1 weist eine Gesamtdicke von 20 bis 100μm, vorzugsweise 30 bis 70 μm auf.
• – Der Schmelzpunkt der Kernschicht ist größer als 155°C.

The release film 1 is produced as a three-layer coextrudate as a blown film and has the following properties:

• - The top layers 1.1 . 1.3 consist of high density polyethylene (HDPE) with a density p of 0.930 to 0.960 g / cm ³ , and a melt index MFI (DIN 53735, test conditions 190 ° C / 2.16 kg) of 0.5 to 7 g / 10 min, preferably 0.2 to 2 g / 10 min, and have a thickness of 3 to 10 μm.
• - The core layer 1.2 consists of polypropylene with a melt index MFI (DIN 53735, test conditions 190 ° C / 2.16 kg) of 0.2 to 4 g / 10 min, preferably 0.2 to 2 g / 10 min.
• - The release film 1 has a total thickness of 20 to 100 μm, preferably 30 to 70 μm.
• - The melting point of the core layer is greater than 155 ° C.

On one of the top layers 1.1 . 1.3 the release film 1 a silicone compound is applied as a non-stick coating. Due to the very low surface roughness 1.1 . 1.3 only a small amount is required to produce an even, full-surface coating.

The silicone compounds are cured with the application of heat at about 160 ° C. Because of the relationship to the surface layers 1.1 . 1.3 thick core layer 1.2 polypropylene provides sufficient heat resistance for the release film at these temperatures.

After the silicone compounds have hardened, an adhesive layer is applied 2 applied. This can be a hot melt adhesive or an adhesive that is present in an aqueous or solvent-containing dispersion, for example ethylene vinyl alcohol (EVAc). On the adhesive layer 2 then becomes an already printed label film 3 concealed.

Along the in the 1a Contour shown as dashed line 5 becomes the label sheet 3 trimmed, creating label sections 4 be worked out. The trimming is done using die cutters, which are the label film 3 have to penetrate. Since it is hardly technically possible, the punch knives only go into the adhesive layer 2 Allow penetration, it must be accepted that the knives also somewhat in the surface of the release film 1 penetration. The release film according to the invention 1 provides the punch knife with sufficient mechanical resistance to prevent cutting of the release film. The tear-off surface of the release film of the invention is also prevented from tearing due to the multilayer structure and the material properties of the layers.

The area of the label film 3 outside the label sections 4 is taken as a coherent lead frame. Is received in 1b shown release film 1 with a large number of label sections arranged one behind the other 4 , The release film is fed to an automatic dispenser where the labels are removed slice 4 detached and applied to packaging, etc.

In 2 is another embodiment of a release liner 1 shown. The plastic is the core layer 1.2 with mineral filler particles 6 , for example chalk, lime or talc. The filler content is 2 to 20% by weight, preferably 10% by weight. The filler particles 6 increase the mechanical resistance to the punching tools. At the same time, they set the thermal conductivity in the core layer 1.2 which increases the melting point.

The plastics of the top layers 1.1 . 1.3 are mixed with an adhesion-reducing additive, preferably based on stearic acid, amides, waxes, silicone, silicone compounds or fluorinated polyolefins, so that the surfaces of the cover layers are poorly wettable without additional additives, which results in a good release effect compared to a label adhesive.

• – eine erste Deckschicht 1.1
• – eine erste Haftvermittlerschicht 7.1
• – eine Kernschicht 1.2
• – eine zweite Haftvermittlerschicht 7.2
• – eine zweite Deckschicht 1.3

To the inner cohesion between the anti-adhesive top layers 1.1 . 1.3 and the core layer 1.2 In this embodiment, it is advantageous to coextrude a five-layer composite with adhesion promoter layers, the following sequence of layers resulting:

• - a first top layer 1.1
• - a first layer of adhesion promoter 7.1
• - a core layer 1.2
• - a second layer of adhesion promoter 7.2
• - a second top layer 1.3

The adhesion promoter layers 7.1 . 7.2 preferably have a thickness of 5 to 8 μm.

Example 2

• – Außenschichten jeweils eine 5 μm dicke Folie aus LLDPE mit einer Dichte von 0,935 g/cm³ und einem MFI von 2g/10 min bei 190°C und 21,6 N gemessen, bei denen der im Zugversuch ermittelte Elastizitätsmodul 700 N/mm² betrug;
• – die Kernschicht bestand aus hochisotaktischem Polypropylen, mit einem Schmelzpunkt von 163°C, einen im Zugversuch ermittelten Elastizitätsmodul von 1600 N/mm² und einem Schmelzindex von 5g/10 m, gemessen bei 210°C und 21,6 N/mm².

On a 3-layer blown film coextrusion line, a 50 μm thick film with the structure:

• - Outer layers each measured a 5 μm thick film of LLDPE with a density of 0.935 g / cm ³ and an MFI of 2g / 10 min at 190 ° C and 21.6 N, in which the elastic modulus determined in the tensile test was 700 N / mm ² scam;
• - The core layer consisted of highly isotactic polypropylene, with a melting point of 163 ° C, a tensile modulus of 1600 N / mm ² and a melt index of 5g / 10 m, measured at 210 ° C and 21.6 N / mm ² .

The film was tube-extruded, wherein the inner side of the tube has been corona treated so that an improved Wettability of 46 mN / m was reached. Then was the film on the treated side is coated with UV-curing silicone.

Example 3

Similar to Example 2, a 60 μm thick film was produced in which the outer layers were 10 μm thick and made of a mixture (blend) of metallocene LLDPE with a density of 0.918 g / cm ³ ; Melt index MFI 2.5 and an LDPE, density 0.932, melt index MFI 3.0. The core layer, 40 μm thick, consisted of a mixture of 70% by weight polypropylene homopolymer, melt index MFI 1, and 30% by weight polypropylene, random copolymer with ethylene, melt index MFI 1.

The coextruded film was then like in Example 2 corona treated and siliconized.

Example 4

In a manner analogous to that in Example 3, a 75 μm thick film could be extruded. The outer layers consisted of 5 μm thick metallocenes LLDPE, which was modified with octene. The density was 0.926 g / cm3, the melt index MFI 0.9. The core layer with a thickness of 65 μm consisted of a polypropylene homopolymer with a melt index MFI 1 and a density of 0.95 g / cm ³ . Its modulus of elasticity, measured in tensile tests, was 1450 N / mm ² .

Summary: Through the invention a release film provided that for the processability in automatic dispensing systems suitable mechanical Has properties and through the use of polyolefins as starting material as well as minimizing or even doing without enables a significant cost reduction on silicone coatings.

Claims (6)

Multi-layer release film ( 1 ) for labels with at least a first core layer ( 1.2 ) made of polypropylene and two cover layers arranged on one side of the core layer ( 1.1 ; 1.3 ) made of polyethylene, the single or the core layers together being thicker than each of the outer layers and being coextruded, and in which at least one of the outer layers ( 1.1 . 1.3 ) has an adhesion-reducing coating, preferably based on stearic acid, amides, waxes, silicone, silicone compounds or fluorinated polyolefins, characterized in that the top and core layers ( 1.2 . 1.2 . 1.3 ), undrawn and unoriented and that the thickness of the core layer ( 1.2 ) 5 to 20 times the thickness of a top layer ( 1.1 . 1.3 ) is. Multi-layer release film ( 1 ) according to claim 1, characterized in that - the cover layers ( 1.1 . 1.3 ) have a thickness of 3 to 10μm and best of a polyethylene hen which has a modulus of elasticity of 100 to 700 N / mm ² determined in the tensile test, and - that the core layer ( 1.2 ) consists of polypropylene, which has a modulus of elasticity of 1100 to 1800 N / mm ² determined in the tensile test. Multi-layer release film according to Claim 1 or 2, characterized in that a coextruded adhesion promoter layer (at least between the top layer which is provided with an adhesion-reducing agent and the core layer) ( 7.1 . 7.2 ) is arranged. Multi-layer release film ( 1 ) according to claim 3, characterized in that the adhesion promoter layer ( 7.1 . 7.2 ) has a thickness of 5 to 8 μm. Multi-layer release film ( 1 ) according to one of claims 1 to 4, characterized in that at least the core layer ( 1.2 ) is filled with mineral fillers such as chalk, lime or talc. Multi-layer release film ( 1 ) according to claim 5, characterized in that the proportion of fillers in the core layer ( 1.2 ) Is 2 to 20% by weight, preferably 10% by weight.