HK1069149B - Peelable seal film - Google Patents

Description

Peelable sealing film

Technical Field

The present invention relates to a multilayer heat sealable coextruded film which produces a peelable and tamper evident seal with low peel forces, and in particular to a package comprising said film. The invention also discloses a preparation method of the peelable sealing film.

Background

Over the last several decades, various packaging films have been developed that are peel/seal combinations. For high quality release film applications, these quality criteria are very selective, and the breaking force should be well below the internal adhesion of the release film and the substrate supporting the film to avoid delamination. And the peel strength must be operable over a large heat seal temperature window, especially for fully automated packaging lines where sealing speed is an important factor.

Document EP0024270 describes in 1980 a heat-sealable packaging monolayer film which can produce a peelable seal to various packaging films. This document discloses a composition comprising an ethylene polymer, polystyrene, and a styrene-butadiene-styrene or styrene-butadiene-styrene based thermoplastic elastomer heat sealed as a single layer film to a variety of substrates including polyethylene, polypropylene, polyester, polyvinyl chloride, polyamide, polyacrylonitrile, and paper.

Such packaging release films no longer meet the requirements of modern coextruded multilayer films, which need to include the following properties: oxygen barrier or tear free and peelable film/paper combinations, tamper evident, large adhesive peel-seal windows, sterilizability and thermal adhesion of radiation or ethylene oxide.

In particular, for pharmaceutical use, it is desirable that the release film tampers significantly, must undergo a mechanism of failure to bond during package opening, and has no serrations, fiber tears, or edge fuzzing. This means that the peel mark should be smooth and free of any macroscopic damage. Moreover, the film is peelable on various substrates including polyester, polyvinyl chloride and polyamide.

To meet these criteria, it is necessary to highly disperse and homogenize the incompatible different polymers in the peel mix composition during the extrusion mixing step. High levels of shear leading to high dispersion can be achieved, for example, by mixing the components in a twin screw extruder in a premixing section.

However, the problem with industrial off-line mixing operations is mainly economical and the high output speeds (several tons per hour) of practical mixing machines require large volumes.

The large scale operation of this step inevitably limits the flexibility required for smaller scales, for example, for each particular tailored release product. The challenge of the present invention is therefore to find a solution to this problem which does not require the investment of expensive on-line mixing equipment.

EP- ｃA-00240270 discloses ｃA packaging film suitable for lamination on ｃA carrier for packaging of articles which must be sterilised according to US- ｃA-6,080,456. Neither of these documents discloses the use of a homogeneously branched LLDPE and/or polybutene-1 for the final extrusion step of the present invention to fine tune the peel force as presented in the following description.

Disclosure of Invention

Object of the Invention

The present invention aims to provide a process for the preparation of tailor-made peelable sealing films which finally have improved hot tack by improving the premix formulation in the final extrusion step and which are especially useful for high quality packaging applications with very selective criteria.

Summary of The Invention

The present invention relates to a heat-sealable coextruded multilayer packaging film peelable on a variety of substrates including polyethylene, polypropylene, polyester, polyvinyl chloride, polyamide, polyacrylonitrile and paper, comprising at least one peelable layer derived from a pre-mixed precursor formulation containing 50-80% by weight of ethylene homo-and/or copolymer, 15-25% by weight of styrene homo-and/or copolymer, 5-20% by weight of a thermoplastic elastomeric styrene-butadiene-styrene block copolymer, characterized in that the peel force in said peelable sealing film prepared from said pre-mixed precursor is improved by adding 5-25, and preferably 10-20% by weight of a homogeneously branched LLDPE to said precursor in the final extrusion step.

A key aspect of the present invention is that the pre-mixed precursor formulation comprises 70-90% by weight relative to the total weight of the polymers in the peelable layer. The total weight of the film in the peelable layer contains up to 4% by weight of processing additives selected from fluoroelastomers.

Another key aspect of the invention is that the release layer in the coextruded multilayer film may be located on the surface or within the multilayer composite when used for multilayer composite release and the thickness of the release layer is up to 15% of the total thickness of the multilayer film.

Use of the coextruded peelable multilayer sealing film of the invention comprising HDPE as the ethylene polymer for sterilizable packaging applications.

The packaging of the heat-sealable coextruded multilayer packaging film of the invention.

In another aspect of the invention, a method of making a heat-sealable peelable coextruded multilayer packaging film is disclosed, characterized by a first step of pre-blending in a high shear and dispersive extrusion apparatus a peelable layer precursor formulation comprising: 50-80% by weight of an ethylene homopolymer and/or copolymer; 15 to 25% by weight of a styrene homopolymer or/and copolymer; 5-20% by weight of a thermoplastic elastomeric styrene-butadiene-styrene block copolymer; the pre-blended precursor formulation is then extruded in a second step through a single screw extrusion device while adding the homogeneously branched LLDPE to improve the peel force and thermal adhesion of the packaging film.

It was particularly surprising and unexpected that more than 25% by weight of LLDPE could be dispersed into the precursor formulation in a single screw apparatus in the second extrusion step. This confirms the preferred compatibility with the precursor formulation.

It is yet another aspect of the present invention to optically increase the surface area of the film during processing by applying external kneading forces and temperatures.

The films obtained according to the invention can be used for peeling off from paper and for packaging applications which are sterilizable and tamper evident.

Drawings

FIG. 1 represents a graph of the peel seal curves of a 50 μm coextruded formulation (A) and a formulation (B) containing 10% homogeneously branched LLDPE and a formulation (C) containing 10% PB1, relative to the sealing temperature on the abscissa. Sealing: against its own untreated release surface.

FIG. 2 represents a graph of the peel seal curves of a 50 μm coextruded formulation (A), a formulation (B) containing 10% homogeneously branched LLDPE and a formulation (C) containing 10% PB1, relative to the sealing temperature on the abscissa. Sealing: relative to a corona treated release surface of 300 μmPVC as the release layer carrier.

FIG. 3 represents the thermal bonding curves of a 50 μm coextruded formulation (A) and a formulation (B) containing 10% of a homogeneously branched LLDPE.

FIG. 4 represents the effect of adding homogeneously branched LLDPE (B) and PB-1(C) on the peel force of a 50 μm coextruded precursor formulation. Sealing at 140 ℃: against its own untreated release surface.

Detailed Description

The idea of the present invention is to develop a standard premix formulation that can be mixed in large volumes and used as precursor for the final peelable sealing film.

The particular formulation can be quickly tuned to the specific consumer's requirements by adding other components not present in the pre-blend formulation at the time of final film extrusion. In this way, the peel force and thermal adhesion of the pre-mixed precursor formulation can be adjusted during the final film extrusion step without changing the composition of the mixture that must be pre-extruded.

More specifically, by blending homogeneously branched LLDPE directly into the pre-mix precursor formulation during film extrusion, the peel seal film can be made to have lower and higher peel forces and higher hot tack without losing the necessary peel-seal properties such as tamper evident, bond fracture, smooth peel traces, absence of tooth-like and fiber tear and peelability on various substrates including polyester, polyvinyl chloride, polyamide, polyacrylonitrile and paper.

Detailed Description

Description of the preferred embodiments of the invention

The various formulations were extruded and tested according to the conditions described below. Conventional film single screw extrusion equipment was unable to uniformly disperse the precursor described in formulation a. This step must therefore be carried out in a compounding extrusion apparatus, for example a twin-screw extrusion apparatus. It was unexpected that LLDPE and PB-1 could be homogenized in the second single screw extrusion step.

Formulation A

This formulation is an example of a pre-mix precursor formulation:

62% polyethylene (LDPE)

20% Polystyrene (PS)

13% of styrene-butadiene-styrene (SBS)

2.5% fluoroelastomer-or Polymer-based masterbatch

2.5% of an antioxidant-based masterbatch

Examples of precursor formulation materials

LDPE

Escorene LD150BW(Exxon Mobil，ρ＝0.923，MI＝0.923)、Lacqtène(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 < 0.5, butadiene/styrene 69/31), Finaprene 417(Atofina, MI 1.7, butadiene/styrene 71/29).

Fluoroelastomer or polymer-based master batches

Ampacet 10562-A (PE-carrier)

Schulman AMF 705 (PE-vector)

Antioxidant-based masterbatch

Ampacet 10886 (PE-carrier)

Schulman A025 (PE-carrier)

In a second step, the formulation is fed into a single screw film coextrusion apparatus. The following formulations (B and C) relate only to the peelable layers of the coextruded multilayer composite.

Formulation B

This is an improvement towards increased peel force and better hot tack.

Article B ═ article a +5 to 25% by weight of homogeneously branched LLDPE. Examples of such LLDPEs are: exact 0203(Dex Plastomers, ρ ═ 0.902, MI ═ 3.0), Exact 2518 CB (ExxonMobil, ρ ═ 0.918, MI ═ 2.5), Evolue SP2020(Mitsui, ρ ═ 0.916, MI ═ 1.5), mPact D143 (phils Petroleum (ρ ═ 0.916, MI ═ 1.3)

Formulation C

This is an improvement towards reducing the peel force. Product C is product a + 5-25% polybutene-1. Examples of such polybutene-1 are:

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

the test peel forces observed on these extruded films depend on the measurement conditions, and therefore it is necessary to compare them with each other under the same test conditions. This is the reason why recipes A, B and C appear on the same graph.

Sealing conditions for the test

The sealing curve, the relative peel and the peel to 300 μm PVC were performed with a Kopp sealer. The upper jaw was heated and the lower jaw containing rubber with a hardness of shore a60 was at room temperature. The sealing was carried out at a pressure of 2bar with a residence time of 1 second. The peel force was measured at a 90 ° peel angle. The 50 μm film was laminated against 19 μm opet prior to peel seal testing to avoid elastic effects, which gave better than realistic results.

Measurement of Hot tack

The hot tack was measured using a DTC hot tack tester. The 50 μm film was laminated against 19 μm OPET and sealed under a pressure of 5bar for 0.5 seconds. The heated jaw was opened after sealing for 0.1 seconds.

The optical quality of the peelable film can be improved by applying different kneading forces or temperatures during the extrusion step.

Claims (13)

1. A heat sealable coextruded multilayer packaging film which is peelable on a variety of substrates including polyethylene, polypropylene, polyester, polyvinyl chloride, polyamide, polyacrylonitrile and paper, the film comprising at least one peelable layer from a pre-mixed precursor formulation comprising:

50-80% by weight of ethylene homopolymer and/or copolymer

15 to 25% by weight of a styrene homopolymer or/and copolymer

5 to 20% by weight of a thermoplastic elastomeric styrene-butadiene-styrene block copolymer

Characterised in that the peelable layer further comprises 5 to 25% by weight of a homogeneously branched LLDPE in order to improve the peel force in the peelable sealing film.

2. The packaging film as claimed in claim 1, characterized in that the homogeneously branched LLDPE in the peelable layer is present in an amount of 10 to 20% by weight.

3. The packaging film according to claim 1, characterized in that the amount of the pre-blended precursor formulation is 70 to 90% by weight relative to the total weight of the polymers in the peelable layer.

4. Packaging film according to any of claims 1 to 3, characterized in that the film contains 4% by weight of processing additives selected from fluoroelastomers in the peelable layer.

5. The packaging film according to claim 1, characterized in that the release layer in the coextruded multilayer film is located on the surface or in the interior of the multilayer composite.

6. The packaging film according to claim 4, characterized in that the thickness of the release layer in the coextruded multilayer film amounts to a maximum of 15% of the total thickness of the multilayer film.

7. The packaging film according to claim 4, characterized in that the thickness of the release layer in the coextruded multilayer film is 10% of the total thickness of the multilayer film.

8. A process for the preparation of a heat-sealable and peelable coextruded multilayer packaging film, characterized in that in a first step a peelable layer precursor formulation as claimed in claim 1 is pre-blended in a high shear and dispersive extrusion device, and then in a second step the pre-blended precursor formulation is extruded through a single screw extrusion device, while adding a homogeneously branched LLDPE to improve the peel force and hot tack of the packaging film.

9. The method according to claim 8, characterized in that the surface area of the film is optically modified during processing by applying external kneading forces and temperatures.

10. Use of the coextruded peelable multilayer sealing film according to claim 1 for peeling off a facing paper.

11. Use of a coextruded peelable multilayer sealing film comprising HDPE as the ethylene polymer of claim 1 for sterilizable packaging applications.

12. Use of the coextruded peelable multilayer sealing film according to claim 1 for tamper evident packaging applications.

13. A package comprising a film according to any one of claims 1 to 7.