WO2006045896A1

WO2006045896A1 - Packing material

Info

Publication number: WO2006045896A1
Application number: PCT/FI2005/050372
Authority: WO
Inventors: Marjo-Riitta Myllymaa; Kyösti RIIHIKOSKI; Mikko Pellinen; Tomi Ruohomaa
Original assignee: Amcor Flexibles Finland Oy
Priority date: 2004-10-26
Filing date: 2005-10-25
Publication date: 2006-05-04
Also published as: FI20045400A; FI20045400A0

Abstract

The present invention relates to a packing material comprising a barrier layer and a peel layer containing polyolefin and inorganic filler, the adhesion of the layer to the attached layer being greater than its cohesion. The packing material comprises a peel layer having a grammage of at least 7 g/m2 and consisting substantially of polyolefin and inorganic filler, attached to the barrier layer directly or by means of one or more intermediate layers, whose organic component consists of polyolefin homopolymer.

Description

PACKING MATERIAL

The present invention relates to a packing material comprising a barrier layer and a peel layer containing polyolefin and inorganic filler, the adhesion of the layer to the attached layer being greater than its cohesion.

In general, layers formed by extrusion are based on weak adhesion between the different layers. Such compositions of multi-layered structures include, for example, Surlyn-HDPE-Surlyn (Surlyn is a trademark of DuPont; the product is a sodium salt of the copolymer of ethylene and methacrylic acid), and poly- butylene with some other materials (polybutylene is released from certain contact surfaces).

To improve the adhesion, a particular tack coat is generally needed, whose surface density is normally 2 to 3 g/m². Running such a small quantity nor¬ mally requires a separate screw in the extrusion machine, or a very low pro¬ duction rate.

Also, the peel layer and/or its adhesion plastics must be run in smaller quan- tities, i.e., with smaller screws, than normal coating plastics. The number of required screws is high, 4 to 5, and therefore, the structure cannot be pro¬ duced, for example, with a machine of 3 screws.

Publication US 5,145,737 discloses a material with an aluminum film, a poly- olefin-type layer, and a layer comprising HDPE, polypropylene or polyester, with a filler content of 15 to 50 wt-%. The polyolefin-type layer is modified to adhere to the other layers. The polymer layers are formed by extrusion.

Publication GB 2323812 discloses a material, in which a layer of polyamide, polycarbonate, polyester, paper, or metal used as a backing material is coated, by coextrusion, with a heat sealed layer and an intermediate layer (a layer that contains a filler and is torn when the package is opened) by apply¬ ing an adhesive between the intermediate layer and the backing material.

The packing ^'material according to the invention is characterized in that the packing material comprises a peel layer having a surface density of at least 7 g/m² and consisting of polyolefin and inorganic filler, that is attached to the barrier layer directly or by means of one or more intermediate layers, whose organic component consists of polyolefin homopolymer.

In the present application, adhesion refers to the capability of the material to adhere to its contact surface; cohesion refers to the internal cohesion of the material layer. Consequently, in practice, the packing material according to the invention is torn from the peel layer in such a way that a part of the layer is left on each side of the tear, because the cohesion of the layer is weaker than its adhesion to the adjacent layer/layers.

Advantages relating to different embodiments of the invention include:

No separate adhesion-improving layers are needed in the structure of the- packing material, but the peel layer can be attached to the other layers.

In the extrusion machine, only 1 or 2 screws are needed to form the peel layer, because no separate adhesion-improving layers are needed.

The capability of the peel layer to be torn off (peel properties) remains almost constant irrespective of variations in the surface density and composition of the peel layer.

The structure makes a high production rate possible when compared with a situation in which the surface density of the layer is low and/or the layer is provided between two layers.

The structure is simple: At best, the number of layers needed is two: the bar¬ rier layer and the peel layer directly attached to it.

The adhesion properties of the packing material remain substantially con¬ stant as a function of time; in other words, the packing material does not gradually come off the contact surface, to which it has been attached.

The material according to the invention can be used, for example, in food packages. The material according to the invention may form the inner surface of the food package, wherein the paper layer is outermost. For example, a cylindrical package can be closed with a cover piece that is heat sealed to the material according to the invention. When the package is opened by pulling the cover piece, the peel layer of the material according to the inven- tion is broken in such a way that a part of the layer is left on the cover piece. The inner surface of the package may be formed of a strip placed in a spiral shape, wherein it must be possible to join the edges of the strips to form a sealed package, preferably by heat sealing.

In its simplest form, the packing material consists of a barrier layer and a peel layer attached to it. The barrier layer refers to a layer with a low permeability to oxygen and water vapour. Normally, a low permeability to oxygen is not higher than 3 ml/m², preferably not higher than 0.5 ml/m². A low permeability to water vapour is normally not higher than 3 g/m²/d (75% RH/ 25°C), pref- erably not higher than 0.5 g/m²/d. The material -of the barrier layer may be a metallized polymer layer, such as metallized polyester, or a layer of metal, such as aluminum. In addition to the above-mentioned materials, any mate¬ rial is feasible that has corresponding' properties of permeability to oxygen and water vapour.

The peel layer is attached directly to the barrier layer, without a layer to improve the adhesion between the layers. The peel layer is formed by extru¬ sion onto the surface of the barrier layer. The peel layer comprises 5 to 50 wt-% of an inorganic substance, such as talc, and 50 to 95 wt-T of polyolefin homopolymer, such as low-density polyethylene (LDPE). The surface density of the peel layer is at least 7 g/m².

Normally, the packing material comprises at least the following layers:

- a paper layer as the outermost layer of the material, - a polyolefin layer, such as a polyethylene layer, attached to the paper layer,

- a metallized polymer layer, such as a metallized polyester layer or a metallized oriented polypropylene layer, attached to the polyolefin layer in such a way that the metallization is on the side of the polymer layer, and - a peel layer attached to the metallized polymer layer in such a way that the attachment is made on the polymer side, and the peel layer comprises 5 to 50 wt-% of inorganic filler, preferably 12 to 30 wt-% of the inorganic filler, and 50 to 95 wt-% of polyolefin, such as poly- ethylene, preferably 70 to 88 wt-% of the polyolefin, such as polyethyl¬ ene. The polyethylene normally consists of LDPE.

The inorganic filler may be any known inorganic filler, such as talc, calcium carbonate, titanium dioxide, or barium or magnesium sulphate. The filler must be approved for use in food products, it must be mixable with polyolefin, resistant to extrusion temperatures and such it does not cause damage to the extruder when being run through the same.

Polyolefins include, for example, polyethylene (LDPE, LLDPE, HDPE), poly- propylene, polybutylene, and polymethyl pentene, .

Instead of a metallized polymer layer it is possible to use a metal film, such as an aluminum film or a copper film. . . v .

The material according to the invention is made in such a way that the paper layer and the metallized polymer layer are combined with a polyolefin layer extruded between the above-mentioned layers. Furthermore, a peel layer is extruded onto the surface of the metallized polymer layer.

The material of the peel layer is well adhesive to, for example, an aluminum film, polyamide, polyester and paper without a need for pre-treatment of the surfaces before the extrusion of the peel layer onto them. The peel layer is made a relatively thick layer with a surface density exceeding 5 g/m², nor¬ mally at least 7 g/m², even at least 10 g/m².

A useful commercial product to be used in the peel layer is CC7209 (Borealis A/S, Denmark) containing 30 wt-% of inorganic filler and LDPE (polyethylene homopolymer). In addition to the inorganic filler, no additives are included in the LDPE. The inorganic filler is talc. The adhesion to other surfaces is provided by carrying out the extrusion at a high temperature, and^'the material to be extruded has a higher surface energy than the LDPE without a filler. The adhesion is also improved by the roughness of the surface, caused by the filler. To reduce the content of the inorganic filler, CC7209 can be used in a blend with LDPE containing no inorganic filler. The temperature used for extruding CC7209 is 300 to 330⁰C. Even though high temperatures are used in the processing, no problems of taste or smell are caused in the material, which is important in the case of food packages.

Consequently, the substantial composition of the peel layer is polyolefin homopolymer and inorganic filler, but in addition to the above-mentioned substances, the peel layer may contain a maximum of 1 wt-% of an auxiliary agent, such as a friction-reducing agent. The friction-reducing agent may consist of, for example, various waxes or wax-like substances. As disclosed above, the substantial composition refers, in this application, to the fact that a possible addition of an auxiliary agent does not change the properties of the peel layer with respect to the functionality of the peel layer described in this application.

Structures, with which very advantageous properties have been achieved, include:

1. Paper + LDPE + metallized PET such that the metallized layer is towards the paper layer + 15 wt-% of inorganic filler, 85 wt-% of LDPE + HDPE + 15 wt-% of inorganic filler, 85 wt-% of LDPE.

In this alternative, the layer containing inorganic filler and polyethylene and coming against the polyester layer is used as a tack coat, wherein the quan¬ tity to be extruded is at least 7 g/m². Onto the tack coat, an HDPE layer is extruded to improve the grease resistance of the material. Onto the HDPE layer, a peel layer is extruded, comprising inorganic filler and polyethylene and having a surface density of at least 7 g/m².

2. Paper + LDPE + metallized PET such that the metallized layer is towards the paper layer + 15 wt-% of inorganic filler, 85 wt-% of LDPE + HDPE 30 wt-% of inorganic filler, 70 wt-% of LDPE. This alternative differs from the material of the alternative 1 in that the peel layer contains more inorganic filler.

3. Paper + LDPE + metallized PET such that the metallized layer is towards 5 the paper layer + 15 wt-% of inorganic filler, 85 wt-% of LDPE + 30 wt-% of inorganic filler, 70 wt-% of LDPE + LDPE heat-sealable at a low temperature.

This alternative differs from the alternative 2 in that there is no HDPE layer, and the outermost extruded layer is LDPE which is heat-sealable at a low 10 temperature.

4. Paper + LDPE + metallized PET such that the metallized layer is towards the paper layer + 15 wt-% of inorganic filler, 85 wt-% of LDPE + LDPE heat- sealable at a low temperature.

,15

In this alternative, the peel layer comprising inorganic filler and polyethylene is extruded onto a metallized polyester layer, and LDPE that is heat sealable at a low temperature is extruded onto the peel layer.

20 In the above-mentioned four samples, the raw materials may be as follows:

The grammage of the paper layer is normally more than 30 g/m², for example 50 g/m².

25 The thickness of the metallized polyester layer is 12 μm; a suitable quality is, for example, High Barrier 3530 (Toray, Japan).

A 12 g/m² polyethylene layer is extruded between the paper layer and the metallized polyester layer. 30

A 30 g/m² peel layer is extruded on the polyester side of the metallized poly¬ ester layer, to contain 15 wt-% of inorganic filler and 85 wt-% of polyolefin.

35 Example. Table 1. Properties of a reference sample and samples according to the invention.

Sample 1 : paper/ LDPE/ metallized PET/ LDPE (reference sample)

Sample 2: paper/ LDPE/ metallized PET/ 15 wt-% of filler, 85 wt-% of LDPE

(sample according to the invention)

Sample 3: paper/ LDPE/ metallized PET/ 30 wt-% of filler, 70 wt-% of LDPE/

HDPE/ 15 wt-% of filler, 85 wt-% of LDPE (sample according to the invention)

1 ) Heat-seal strength was measured as adhesion of the material against itself (a layer comprising LDPE heat-sealed against itself).

2) The adhesion of the coating to the back refers to the adhesion of the polyolefin-containing layer to the polyester side of the metallized poly- ester layer.

3) The adhesion of the coating after the sealing refers to the same thing as in point 2), but measured after the sealing.

The results show that in the samples 2 and 3 according to the invention, the adhesion was good between the polyester surface of the metallized polyester layer and the layer formed onto the polyester surface, whereas it was not sufficient in the reference sample 1. Furthermore, the results show that the samples 2 and 3 are sealed tightly to the other contact surface and there are no problems with the adhesion of the coating after the sealing of the samples 2 and -3; on the other hand, the adhesion of the coating of the sample 1 is clearly reduced after the sealing.

The invention is not restricted to the description above, but it may vary within the scope of the claims.

Claims

Claims:

1. A packing material comprising a barrier layer and a peel layer comprising polyolefin and inorganic filler, the adhesion of the layer to a layer attached to it being greater than its cohesion, characterized in that the packing material comprises a peel layer having a surface density of at least 7 g/m² and consisting essentially of polyolefin and the inorganic filler, attached to the barrier layer directly or by means of one or more intermediate layers whose organic component consists of polyolefin homopolymer.

2. The packing material according to claim 1 , characterized in that an intermediate layer is provided between the barrier layer and the peel layer, comprising of polyolefin homopolymer and inorganic filler.

3. The packing material according' to claim 2, characterized in that further¬ more, a layer consisting of a high-density polyethylene (HDPE) is provided between the barrier layer and the peel layer, being in contact with the peel layer. . ^.. .

4. The packing material according to any of the preceding claims, charac¬ terized in that a heat-sealable layer is provided on the outer surface of the peel layer.

5. The packing material according to any of the preceding claims, charac- terized in that the barrier layer is a metal layer or a metallized polymer layer.

6. The packing material according to claim 5, characterized in that the met¬ allized polymer layer is a metallized polyester or a metallized oriented poly¬ propylene (OPP).

7. The packing material according to any of the preceding claims, charac¬ terized in that the peel layer comprises 5 to 50 wt-% of inorganic filler and 50 to 95 wt-% of a low-density polyethylene (LDPE).

8. The packing material according claim 7, characterized in that the peel layer comprises 12 to 30 wt-% of inorganic filler and 70 to 88 wt-% of a low- density polyethylene (LDPE).

9. The packing material according to any of the preceding claims, character¬ ized in that a paper layer is provided on the second side of the packing mate¬ rial.