MULTILAYER FILM FOR RECLOSABLE PET PACKAGING

Abstract

A multilayer film: an adhesive layer A: an extrudable hot-melt self-adhesive composition; a complexable thin layer B; and a heat-sealable and cleavable layer C of a linear copolyester C1 obtained by polycondensation of a composition of monomers: at least one diol (i), at least one compound (ii) chosen from terephthalic acid or a diester derivative and at least one compound (iii) chosen from an aromatic or aliphatic dicarboxylic acid or a diester or anhydride derivative;

the amounts of the monomers (i), (ii) and (iii) used in the polycondensation such that the softening temperature of C1 is below 190? C.

A process for producing the multilayer film by co-extrusion blow-molding.

A resealable packaging comprising a PET-based receptacle and a seal of said multilayer film, the heat-sealable and cleavable layer (C) of which is heat-sealed on the receptacle.

Claims

1. A multilayer film comprising: an adhesive layer A having a thickness ranging from 7 to 50 ?m and consisting of an extrudable hot-melt self-adhesive composition a which has a melt flow index (or MFI), measured for a temperature of 190? C. and a total weight of 2.16 kg, ranging from 0.01 to 200 g/10 minutes and which comprises, on the basis of the total weight of said composition a: from 40% to 70% by weight of a composition al of styrene block copolymers comprising at least one elastomer block, said composition al consisting, on the basis of its total weight: of 30% to 90% by weight of at least one diblock copolymer chosen from the group comprising SI, SBI, SIB, SB, SEB and SEP, and of 10% to 70% by weight of at least one triblock copolymer chosen from the group comprising SIS, SIBS, SBS, SEBS and SEPS; the total content of styrene units of said composition al ranging from 10% to 40% by weight on the basis of the total weight of al; and from 30% to 60% by weight of one or more tackifying resins a2 having a softening temperature of between 5 and 140? C.; a complexable thin layer B consisting of a thermoplastic b; and a heat-sealable and cleavable layer C; the layers B and C being linked to one another by the layer A; and said film being characterized in that the layer C consists of a composition c comprising, on the basis of the total weight of c, a content by weight of at least 95% of at least one linear copolyester C1 obtained by polycondensation of a composition m of monomers comprising: at least one diol (i), at least one compound (ii) chosen from terephthalic acid or a diester derivative thereof, optionally substituted with an alkyl radical, and at least one compound (iii) chosen from an aromatic or aliphatic dicarboxylic acid or a diester or anhydride derivative thereof; the amounts of the monomers (i), (ii) and (iii) used in the polycondensation being such that the softening temperature of C1 is below 190? C.

2. The multilayer film as claimed in claim 1, characterized in that the softening temperature of the linear copolyester C1 included in the constituent composition c of the heat-sealable and cleavable layer C is below 180? C. and preferably below 175? C.

3. The multilayer film as claimed in claim 1, characterized in that the linear copolyester C1 is obtained by polycondensation of a composition m consisting, on the basis of contents expressed as mol % per 100 mol of monomers, of: approximately 50% of diol (i), from 10% to 38% of compound (ii), and from 12% to 40% of compound (iii).

4. The multilayer film as claimed in claim 1, characterized in that ethylene glycol is used as diol (i).

5. The multilayer film as claimed in claim 1, characterized in that the constituent composition a of the layer A has a melt flow index ranging from 2 to 70 g/10 minutes.

6. The multilayer film as claimed in claim 1, characterized in that the composition al of styrene block copolymers included in the constituent composition a of the layer A consists of an SIS triblock copolymer and of an SI diblock copolymer.

7. The multilayer film as claimed in claim 1, characterized in that the resin(s) a2 included in the constituent composition a of the layer A are chosen from: (ii) resins obtained by hydrogenation, polymerization or copolymerization (with an aromatic hydrocarbon) of mixtures of unsaturated aliphatic hydrocarbons having approximately 5, 9 or 10 carbon atoms resulting from petroleum fractions; or (iii) terpene resins resulting from the polymerization of terpene hydrocarbons in the presence of Friedel-Crafts catalysts, which are optionally modified by the action of phenols.

8. The multilayer film as claimed in claim 1, characterized in that the constituent composition a of the layer A comprises: from 50% to 70% of the composition al of styrene block copolymers; and from 30% to 50% of tackifying resin a2.

9. The multilayer film as claimed in claim 1, characterized in that it also comprises a tie layer D, connecting the layer A to the layer B, and/or a tie layer E, connecting the layer A to the layer C.

10. The multilayer film as claimed in claim 1, characterized in that the thickness of the layer A ranges from 8 to 25 ?m.

11. A process for producing the multilayer film as defined in claim 1, characterized in that it comprises the co-extrusion of the hot-melt self-adhesive composition a and of the compositions b and c, at a temperature of between 150? C. and 200? C.

12. The production process as claimed in claim 11, characterized in that the co-extrusion is carried out by blow-molding.

13. The production process as claimed in claim 11, characterized in that it comprises: (i) the introduction, into separate extruders, of constituent compositions and materials of the layers A, B, C, and where appropriate D and E, in the form of granules having a size of between 1 and 10 mm, then (ii) the conversion by heating of said granules to the viscous liquid state, then (iii) the passing of the corresponding streams through an extrusion head comprising a set of coplanar and concentric annular dies, each brought to a temperature below 200? C., so as to form a tubular bubble comprising several layers, in which the order of the layers corresponds to that desired for the final film, then (iv) the radial expansion and the drawing of the bubble, then (v) the cooling of said bubble.

14. The production process as claimed in claim 13, characterized in that the extrusion head used in step (iii) is a monoblock extrusion head, in which the annular dies are brought to one and the same temperature below 200? C.

15. A resealable packaging comprising: a PET-based receptacle which consists either of amorphous PET or of a bilayer system of amorphous PET and of semicrystalline PET, said receptacle having a flat bottom and a perimeter in the form of a flat band, and a seal consisting of the multilayer film as defined in claim 1, the heat-sealable and cleavable layer (C) of which is heat-sealed on the perimeter of the receptacle, in contact with amorphous PET.

Description

EXAMPLE A

(Reference): Extrudable Hot-Melt Self-Adhesive Composition

[0171] A composition consisting, on the basis of % weight/weight, of 59.5% of Kraton? D1113BT, 25% of Escorez ? 1310 LC, 15% of Dercolyte? S115 and 0.5% of Irganox? 1010 is prepared, in the form of a viscous liquid, by simply mixing the ingredients at 160? C. by means of a twin-screw extruder.

[0172] An MFI of 57 g/10 minutes is measured.

EXAMPLE B

(Reference): Three-Layer Film BAC Comprising a Layer A Consisting of the Composition of Example A and a Heat-Sealable and Cleavable Layer C Consisting of LDPE:

[0173] This three-layer film is produced by means of a continuously operating co-extrusion bubble blowing pilot-scale device equipped with a monoblock extrusion head brought to a temperature of 190? C., in which device 3 extruders are fed in the following way: [0174] one is fed with the composition of example A, and [0175] the other two are fed with low-density polyethylene (or LDPE); the 3 compositions being in the form of granules having a size of approximately 4 mm.

[0176] The process parameters are adjusted so as to produce a three-layer film consisting: [0177] as layer A, of a layer with a thickness of 15 ?m consisting of the extrudable hot-melt self-adhesive composition of example A, [0178] as complexable thin layer B, of a layer with a thickness of 30 ?m consisting of LDPE; [0179] as heat-sealable and cleavable layer C, of a layer with a thickness of 15 ?m also consisting of LDPE.

[0180] Among the parameters usually set, mention may made of a degree of radial expansion of the bubble equal to 3, a drawing speed of 7 m/minute and an overall throughput of 11 kg/hour.

[0181] The three-layer film thus obtained has a total thickness of 60 ?m and a length of 50 m and is packaged in the form of a reel with a machine width of 250 mm.

[0182] It is subjected to tests B.1. and B.2. described below.

Test B.1.: Measurement of the Force of the First Opening by T-Peeling, at 23? C., of the Three-Layer Film Previously Heat-Welded on a PET/PE Complex:

[0183] A sample in the form of a rectangular sheet with A4 format (21?29.7 cm) is cut out from the three-layer film previously obtained.

[0184] The external face of the complexable layer B of this sample is: [0185] in a first step, subjected to a corona surface treatment (by means of a plasma), then [0186] in a second step, complexed (in other words laminated) on a PET film having a thickness of 23 ?m by means of a polyurethane-based solvent-based adhesive and using a coating device of the Mayer bar type.

[0187] The rectangular sheet is then placed under pressure for 24 h.

[0188] Rectangular test specimens E1 that are 10 cm long and 2 cm wide are then cut from this rectangular sheet.

[0189] Rectangular test specimens E2 that are 10 cm long and 2 cm wide are, moreover, cut from a rigid block consisting of a sheet of PET having a thickness of approximately 200 ?m, covered with a layer of PE.

[0190] The 2 test specimens E1 and E2 are then placed facing one another, in such a way that the heat-sealable and cleavable layer of E1 is in contact with the layer of PE of E2.

[0191] Partial sealing is then carried out using two heating clamping jaws at 130? C. applied under a pressure of 6 bar for 1 second, so as to obtain a sealed region of rectangular shape (8 cm in length and 1 cm in width). Said sealed region is placed in the lengthwise direction and in contact with one of the small sides of the rectangular test specimens E1 and E2 thus joined, in order to leave on the other small side of said test specimens a band of film approximately 2 cm in length originating from E1, that is free and not sealed on the end of the rigid plate of E2 located opposite.

[0192] The band of free film of E1 and the end of the rigid plate of E2 are attached to two holding devices (known as jaws) respectively connected to a stationary part and a movable part of a tensile testing device, which are located on a vertical axis. This tensile testing device is a dynamometer.

[0193] While a drive mechanism imparts a uniform rate of 300 mm/minute to the movable part, resulting in the peeling of the two sealed test specimens E1 and E2, the ends gradually move along a vertical axis with the formation of an angle of 180?. A force sensor connected to said movable part measures the force withstood by the test specimen thus held. The measurement is carried out in a climate-controlled room maintained at a temperature of 23? C. The force obtained is shown in table 1.

Test B.2. Measurement of the Force of the Second Opening by T-Peeling, at 23? C., of the Three-Layer Film Heat-Welded on a PET/PE Complex:

[0194] The 2 parts of the preceding test specimen are, after peeling, repositioned facing one another and brought into contact manually. They are then subjected to a pressure exerted by means of a roller with a weight of 2 kg, with which a to-and-fro movement is carried out in a direction parallel to the length of the test specimen.

[0195] A tensile test specimen is thus obtained which is identical in shape to that prepared for the preceding peeling test, which is then repeated.

[0196] The force obtained is shown in table 1.

EXAMPLE 1

Three-Layer Film Bac Comprising a Layer A Consisting of the Composition of Example A and a Heat-Sealable and Cleavable Layer C according to the Invention

[0197] First of all, an amorphous linear copolyester C1 is prepared according to the 3-step procedure indicated below, said copolyester having been obtained by means of a reaction for polycondensation of a composition m of monomers which consists, on the basis of the total number of moles of monomers, of: [0198] 50 mol % of monoethylene glycol, [0199] 30 mol % of dimethyl terephthalate, and [0200] 20 mol % of isophthalic acid.

[0201] 1st Step:

[0202] 100 g of monoethylene glycol (1.61 mol), 291 g of dimethyl terephthalate (1.5 mol) and 0.19 g of titanium-based catalyst (of formula Ti(nBuO).sub.4) and 0.05 g of zinc-based catalyst (zinc acetate) are placed in a 1-liter closed reaction vessel equipped with a stirrer, with a distillation column, with heating means and with a thermometer and connected to a vacuum pump. The assembly is heated from ambient temperature to 190? C. for 5 hours in order to eliminate the methanol formed.

[0203] 2nd Step:

[0204] 70 g of monoethylene glycol (1.13 mol) and 166 g of isophthalic acid (1 mol) are then placed, at 190? C., in the 1st-step reaction vessel under nitrogen flushing. The polycondensation reaction is continued for 5 hours from 190? C. to 230? C. in order to eliminate the water formed. The progression of the reaction is monitored by measuring the acid number AN expressed in mg KOH/g.

[0205] 3rd Step:

[0206] The reaction mixture of the 2nd step is brought to a temperature of 250? C. under a pressure of approximately 2 mbar for 10 hours in order to increase the molecular weight.

[0207] The amorphous linear copolyester C1 obtained has a molecular weight Mw of 35 kDa. Its softening temperature is 175? C.

[0208] The copolyester C1 thus obtained is made into granules having a size of approximately 4 mm after extrusion, and is used as constituent material of the layer C of the three-layer film BAC.

[0209] By reproducing the process of example B, and in particular by bringing the temperature of the monoblock extrusion head to the same temperature of 190? C., a three-layer film BAC is produced which consists: [0210] as layer A, of a layer with a thickness of 15 ?m consisting of the extrudable hot-melt self-adhesive composition of example A, [0211] as complexable thin layer B, of a layer with a thickness of 30 ?m consisting of LDPE; [0212] as heat-sealable and cleavable layer C, of a layer having a thickness of 8 ?m also consisting of the amorphous linear copolyester C1 prepared as indicated above.

[0213] The three-layer film thus obtained has a total thickness of 53 ?m and a length of 50 m and is packaged in the form of a reel with a machine width of 250 mm.

[0214] Tests B.1. and B.2. of example B are then repeated using, as rigid plate for producing the test specimens E2, a plate consisting exclusively of a sheet of amorphous PET, having a width of approximately 200 ?m (not covered with a layer of PE).

[0215] The forces obtained are shown in table 1.

TABLE-US-00001 TABLE 1 Example B (reference) Example 1 Example 2 Constitutive material of the PET/PE PET PET rigid plate of the test specimen E2 mentioned in test B1 Force of the 1st opening 4.0 5.4 5 (N/cm) Force of the 2nd opening 1.2 2 1.1 (N/cm)

EXAMPLE 2

Three-Layer Film BAC Comprising a Layer A Consisting of the Composition of Example A and a Heat-Sealable and Cleavable Layer C according to the Invention

[0216] First of all, an amorphous linear copolyester C1 is prepared according to the 2-step procedure indicated below, said copolyester having been obtained by means of a reaction for polycondensation of a composition m of monomers which consists, on the basis of the total number of moles of monomers, of: [0217] 50 mol % of monoethylene glycol, [0218] 30 mol % of terephthalic acid, and [0219] 20 mol % of azelaic acid.

[0220] 1st Step:

[0221] 100 g of monoethylene glycol (1.61 mol), 142 g of terephthalic acid (0.85 mol), 107 g of azelaic acid (0.57 mol) and 0.0011 g of titanium-based catalyst (of formula Ti 2-EtHexO).sub.4) and 0.04 g of germanium-based catalyst (germanium dioxide) are placed in a 1-liter closed reaction vessel equipped with a stirrer, with a distillation column, with heating means and with a thermometer and connected to a vacuum pump. The assembly is heated from 170? C. to 230? C. for 5 hours in order to eliminate the water formed.

[0222] The progression of the reaction is monitored by measuring the acid number AN expressed in mg KOH/g.

[0223] 2nd Step:

[0224] The reaction mixture of the 1st step is brought to a temperature of 250? C. under a pressure of approximately 2 mbar for 10 hours in order to increase the molecular weight.

[0225] The amorphous linear copolyester C1 obtained has a molecular weight Mw of 75 kDa. Its softening temperature is 150? C.

[0226] Example 1 is then repeated with the amorphous linear copolyester C1 thus obtained.

[0227] The forces obtained at the end of tests B.1. and B.2. are shown in table 1.

[0228] It is thus noted that the three-layer films of examples 1 and 2, that can be produced by co-extrusion at a temperature of 190? C., exhibit, after heat-sealing on a PET support, properties of easy opening and substantially hermetic resealing properties that are of the same level as the reference three-layer film of example B that was heat-sealed on a PE layer.