Peelable seal film

(12) PATENT DESCRIPTION (19) PL (11) 206828 (13) B1 (21) Application number: 369926 (51) Int.Cl.

(22) Filing date: October 22, 2002 B32B 27/08 (2006.01)

B65D 65/40 (2006.01) (86) Date and number of the international application:

22.10.2002, PCT / EP02 / 011902 (87) International application publication date and number:

2003-05-30, WO03 / 043816

Heat-sealable coextruded multilayer packaging film, method of its production and application

<td></td><td>(73) The right holder of the patent: AMCOR FLEXIBLES TRANSPAC NV, Zaventem, BE</td>

<td>(30) Priority:</td><td></td>

<td>2001-11-20, EP, 01870249.8</td><td>(72) Inventor (s):</td>

<td>(43) Application was announced: 02.05.2005 BUP 09/05</td><td>TONY MALFAIT, Rollegem-Kapelle, BE PATRICK ROSSEAU, Grimbergen, BE ERIK BOGELS, Lanaken, BE LUC VEYS, Gent, BE</td>

<td>(45) The grant of the patent was announced: September 30, 2010 WUP 09/10</td><td>(74) Representative: item. stalemate. Sulima Sophia SULIMA GRABOWSKA SIERZPUTOWSKA PATENTS AND MARKS OFFICE TOWAROWYCH general partnership</td>

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Description of the invention

The subject of the invention is a heat-sealable coextruded multilayer packaging film, its production method and application. The foil creates a peelable heat seal, showing tampering attempts with low peel force.

In recent decades, various peelable / sealant connections have been developed for packaging films. For high-quality peelable film applications, the quality criteria are very demanding and the opening force should be much less than the internal cohesive strength of the peelable film with the substrate supporting the film to avoid delamination. Moreover, the peel strength should be achievable over a wide sealing temperature range, especially in fully automated packaging lines where sealing speed plays a very important role.

EP 0024270 of 1980 describes a sealable monolayer packaging film providing a peelable seal for a wide variety of packaging films. This document discloses a composition comprising an ethylene polymer, polystyrene and a styrene-butadiene-styrene or styrene-butadiene-styrene based thermoplastic elastomer in the form of a single layer heat sealable film with a variety of substrates such as polyethylene, polypropylene, polyester, polyvinyl chloride, polyamide, polyacrylonitrile and paper.

This type of peelable packaging film no longer meets the requirements of modern coextruded multilayer films, which include the inclusion of an oxygen barrier layer or tear free peelable film / paper joints, tamper evidence, wide cohesive peel-seal range, sterilizable radiation or ethylene oxide; and hot tack.

Particularly for medical applications, a tamper-evident peelable film is required with a cohesive failure mechanism when opening the package without the use of a zipper-type connection, fiber tearing or "angel hair" type strand. This means that the tear mark should be smooth and free from any visible tears. In addition, the film must be able to peel off a variety of substrates including polyester, polyvinyl chloride and polyamide.

In order to meet these criteria, the various incompatible polymers in the peelable blend composition must be thoroughly dispersed and homogenized during the extruder blending step. A high level of shear leading to fine dispersion can be achieved, for example, by mixing the ingredients in a twin screw extruder during premixing.

However, the problem with an off-line industrial mixing operation is mainly of an economic nature, and the high throughput capacity of modern mixing equipment, in the order of several tons / hour, requires large volumes of raw materials.

Large-scale operations at this stage inevitably limit the flexibility required for smaller orders, such as different custom-made peelable products. It was therefore desirable to find a solution to this problem without the need to invest in expensive in-line mixing equipment.

EP-A-00240270 discloses a packaging film suitable for laminating onto packaging substrates of articles to be sterilized according to US-A-6080456. Both documents do not disclose the use of uniformly branched LLDPE, such as in the final extrusion step in the process of the invention to adjust the peel force as shown below.

There was a need to develop a process for the production of a suitable peelable sealing film which additionally has an increased hot tack, by modifying the pre-mixed composition in the final extrusion step, in particular for use in high-quality packages with specially selected requirements. It was desired to develop a single bulk pre-blend base composition suitable for use as a final peelable sealant film precursor.

The invention relates to a heat sealable coextruded multilayer packaging film peelable from a variety of substrates including polyethylene, polypropylene, polyester, polyvinyl chloride, polyamide, polyacrylonitrile and paper, comprising at least one peelable layer of a pre-blended precursor composition comprising:

- 80% by weight of an ethylene homo- and / or copolymer,

- 25% by weight of a styrene homo- and / or copolymer,

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- 20% by weight of thermoplastic elastomeric styrenebutadiene-styrene block copolymer, the film characterized in that the peelable layer further comprises 5 - 25% by weight, preferably 10 - 20% by weight, uniformly branched LLDPE as the peel strength modifying component of the peelable sealant layer .

The packaging film according to the invention is preferred in which the amount of the pre-blended precursor composition is 70-90% by weight of the total weight of the polymers present in the peelable layer.

The packaging film according to the invention is preferred which contains up to 4% by weight of processing aids selected from the group consisting of fluoro elastomers in the peelable layer.

The peelable layer in the coextruded multilayer film may be on the surface or within the multilayer system.

Preferably, the peelable layer in the coextruded multi-layer film constitutes at most 15% of the total thickness of the multi-layer film.

In particular, the peelable layer in the coextruded multilayer film constitutes 10% of the total thickness of the multilayer film.

The invention also relates to a process for the production of a sealable coextruded multilayer packaging film peelable from various substrates as defined above, characterized in that a precursor composition containing 50-80% by weight of ethylene homo- and / or copolymer, 15-25% by weight of homo- and / or or styrene copolymer, 5 - 20% by weight of thermoplastic elastomeric styrene-butadiene-styrene block copolymer, pre-mixed, in a first step, in an extruder with high shear and dispersing action, the premixed precursor composition is then extruded in a second step with a single screw extruder with the simultaneous addition of 5 - 25% by weight, preferably 10 - 20% by weight, of uniformly branched LLDPE as peel modifier component a peelable sealing layer.

Preferably, in the process according to the invention, the optical properties of the film surface are modified under the action of the external compressive force and the temperature during production.

The invention further relates to the use of a coextruded multi-layer packaging film peelable from various substrates as defined above for use in conjunction with paper.

The invention also relates to the use of a coextruded multilayer packaging film, peelable from various substrates, as defined above, containing HDPE as the ethylene polymer, for use in sterilized packages.

The invention also relates to the use of a coextruded multi-layer packaging film peelable from various substrates as defined above for use in tamper-evident packages.

The film obtained by the method of the invention is used as a peelable film from paper and in sterilized and tamper-evident packages.

It is particularly surprising and unexpected that large amounts, up to 25 wt% LLDPE, can be perfectly dispersed in the precursor composition in a single screw device in the second extrusion step. This confirms the excellent compatibility with the precursor composition.

During final extrusion, the pre-blended precursor composition can be quickly adapted to the specific requirements of the consumer by incorporating additional ingredients not present in the pre-blended composition. In this way, the peel strength and hot tack of the pre-blended precursor composition can be adjusted during the final film extrusion step without changing the composition of the pre-blend.

In particular, by mixing the uniformly branched LLDPE with the premixed precursor composition during film extrusion, lower or higher peel force and higher hot tack of the peelable sealant film can be provided without losing basic peel-seal properties such as obvious tampering, cohesive tearing, smooth tear mark, no need to use a zipper-type connection, tearing the fibers and the ability to peel from various substrates such as polyester, polyvinyl chloride, polyamide, polyacrylonitrile and paper.

The figures of the drawings are described below to illustrate the invention in more detail.

Fig. 1 shows the seal burst curve for a 50 μm coextruded composition (A), a composition containing 10% uniformly branched LLDPE (B), and a composition containing

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10% PB1 (C) as a function of the welding temperature on the abscissa. Sealing: the untreated tear-off sides are welded together.

Fig. 2 shows the seal break curve for a 50 µm coextruded composition (A), a composition containing 10% uniformly branched LLDPE (B), and a composition containing 10% PB1 (C) as a function of the seal temperature on the abscissa. Welding: corona treated tear side with 300 μm PVC as the peel back substrate.

Fig. 3 shows the hot tack curves of 50 µm of coextruded composition (A) and composition (B) containing 10% uniformly branched LLDPE.

Fig. 4 shows the effect of the addition of uniformly branched LLDPE (B) and PB-1 (C) on the peel force of 50 µm of the coextruded precursor composition. Sealing at 140 ° C: the untreated tear-off sides are welded together.

A preferred embodiment of the invention is described below.

Various compositions were extruded and tested under the conditions described below. Conventional single screw film extruder cannot disperse evenly the precursor referred to as composition A. Therefore, this step has to be carried out with a mixing extruder, e.g. a twin screw extruder. Surprisingly, LLDPE and PB-1 can be introduced uniformly in the second step using a single screw extruder.

Composition A

This composition is an example of a pre-blended precursor composition:

62% polyethylene (LDPE)

20% polystyrene (PS)

13% styrene-butadiene-styrene copolymer (SBS)

2.5% fluoro elastomer or polymer based masterbatch

2.5% antioxidant based masterbatch

Examples of raw materials for a precursor composition

LDPE

Escorene LD150BW (Exxon Mobil, ρ (density) = 0.923, MI (melt index) = 0.923), Lacqtene (Atofina, ρ = 0.923, MI = 0.3), Novex LD5307AA (BP Chemicals, ρ = 0.921, MI = 0.7).

PS

Lacqrene 1240 (Atofina, MI = 2), Lacqrene 1320 (MI = 3.5).

SBS

Finaprene 411 (Atofina, MI &lt;0.5, butadiene / styrene 69/31),

Finaprene 417 (Atofina, MI = 1.7, butadiene / styrene 71/29).

Fluorine elastomer or polymer based masterbatch

Ampacet 10562-A (PE - carrier)

Schulman AMF 705 (PE - carrier)

Antioxidant based masterbatch

Ampacet10886 (PE - carrier)

Schulman AO 25 (PE - carrier)

This composition was introduced in a second step into a single screw film coextrusion device. The following compositions (B and C) relate only to the peelable layer of the coextruded multilayer composite film.

Composition B

This is a modification that increases the peel strength and better hot tack.

Composition B = Composition A + 5 - 25 wt.% uniformly branched LLDPE. Examples of such LLDPEs include:

Exact 0203 (Dex Plastomers, ρ = 0.902, MI = 3.0), Exceed 2518 CB (Exxon Mobil, ρ = 0.918, MI = 2.5), Evolue SP2020 (Mitsui, ρ = 0.916, MI = 1.5) , mPact D143 (Phillips Petroleum (ρ = 0.916, MI = 1.3)

Composition C

It is a modification by which a reduction in the detachment force is achieved.

Composition C = Composition A + 5 - 25% polybutene-1.

Examples of such polybutene-1 are:

PB8340 (Basell, ρ = 0.908, MI = 4.0), PB8310 (Basell, ρ = 0.895, MI = 3.0), Tafmer BL3110 (Mitsui, ρ = 0.910, MI = 1.0), Tafmer BL4000 (Mitsui , ρ = 0.915, MI = 1.8)

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The experimentally determined peel force values ​​for the extruded films depend on the measuring conditions and should therefore be compared under the same experimental conditions. It is for this reason that the results for compositions A, B and C are shown in the same graphs.

Experimental welding conditions

The welds and tear-off layers with a tear-off layer and with 300 μm PVC were made using a Kopp welding machine. The upper jaw was heated and the lower one made of 60 Shore A rubber was at room temperature. Welding was performed at a pressure of 0.2 MPa with a contact time of 1 s. The peel force was measured at a peel angle of 90 °. Prior to the tear test of the 50 µm seal, the films were laminated to the 19 µm OPET film to eliminate elastic effects, providing better results compared to reality.

Hot tack measurements

The hot tack was measured with a hot tack DTC. 50 μm films were laminated with 19 μm OPET films and sealed for 0.5 s at a pressure of 0.5 MPa. Heated jaws were opened for 0.1 s after welding.

The optical properties of the peelable film can be modified during the embossing step by exposure to different values ​​of the compressive force and the temperature.