Multilayer polymer film and multipack made thereof

Abstract

A multilayer polymer film for multipacks is provided that includes at least two layers formed from polyester and additives, in which a first layer is porous and a second layer contains an inorganic filler. Multipacks thermoformed from the multilayer polymer film are equipped with snap incisions.

Claims

1. A multilayer polymer film with 2 to 10 layers, comprising a first layer consisting of 80 to 99.5% by weight of polyester and 0.5 to 20% by weight of additives, based on the total weight of the first layer, said first layer further comprising pores; a second layer bonded to a first surface of the first layer and consisting of 50 to 90% by weight of polyester and 10 to 50% by weight of additives, wherein 1 to 30% by weight of a first additive is selected from chalk, talc, mica, wollastonite, calcium carbonate, bentonite, kaolin, clay, titanium oxide and mixtures thereof, based on the total weight of the second layer.

2. The multilayer polymer film according to claim 1, wherein the multilayer polymer film has a thickness of 400 to 1200 m.

3. The multilayer polymer film according to claim 1, wherein the multilayer polymer film has a density of 1 to 1.4 g/cm.sup.3.

4. The multilayer polymer film according to claim 1, wherein the polyester of the first and second layer independently from each other are selected from polyethylene terephthalate and polyesters which consist of (i) 80 to 100 mol-% of a diacid residue component selected from terephthalic acid, naphthalene dicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, isophthalic acid and mixtures thereof and (ii) 80 to 100 mol-% of a diol residue component selected from diols containing 2 to 10 carbon atoms, and mixtures thereof and 0 to 20 mol-% of a modifying diol selected from 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, 1,4-cyclohexanedimethanol, 2,2,4-trimethyl-1,3-pentanediol, propylene glycol, 2,2,4,4-tetramethyl-1,3-cyclobutanediol, based on 100 mol-% diacid residues and, respectively 100 mol-% diol residues.

5. The multilayer polymer film according to claim 1, wherein the multilayer polymer film has a bending stiffness of 146.Math.t.sup.3 to 350.Math.t.sup.3 N/mm per 1 mm film width, wherein t is the thickness of the multilayer polymer film in units of mm.

6. The multilayer polymer film according to claim 1, wherein the ratio of thickness T1 of the first layer to thickness T2 of the second layer is in the range from 0.5T1/T24.

7. The multilayer polymer film according to claim 1, wherein the first and second layer independently from each other comprise 8 to 24% by weight of polyethylene and 0.1 to 2% by weight of ethylene vinyl acetate, based on the total weight of the first and, respectively the second layer.

8. The multilayer polymer film according to claim 1, wherein the first layer comprises 0.01 to 1% by weight of a foaming agent, based on the total weight of the first layer.

9. The multilayer polymer film according to claim 8, wherein the foaming agent is selected from carbon dioxide, sodium hydrogen carbonate and citric acid, nitrogen, azodicarbonamide, oxy-bis-benzene sulfonylhydrazide, toluene sulfonylhydrazide, benzene sulfonylhydrazide, toluene sulfonylsemicarbazide, 5-phenyltetrazole, di-nitroso pentamethylene tetramine and mixtures thereof.

10. The multilayer polymer film according to claim 1, wherein the multilayer polymer film comprises a third layer bonded to a second surface of the first layer opposite to the second layer, the third layer consisting of 90 to 99.5% by weight of polyester and 0.5 to 10% by weight of additives, based on the total weight of the third layer.

11. The multilayer polymer film according to claim 10, wherein the multilayer polymer film comprises a fourth layer bonded to a surface of the second layer opposite to the first layer, the fourth layer comprising 90 to 99.5% by weight of polyester and 0.5 to 10% by weight of additives, based on the total weight of the fourth layer.

12. The multilayer polymer film according to claim 10, wherein the third layer has a thickness of 4 to 60 m.

13. The multilayer polymer film according to claim 11, wherein the fourth layer has a thickness of 4 to 60 m.

14. A multipack comprising 2 to 40 containers thermoformed from the multilayer polymer film according to claim 10 and the first layer or the third layer of the multilayer polymer film constitute an upper surface of the multipack having concave portions.

15. The multipack according to claim 14, wherein the multipack comprises 1 to 40 snap incisions extending from the upper surface of the multipack into the multilayer polymer film to a depth D, wherein D1DD2, D1 extends to 80% of the thickness of the first layer and D2 extends to 50% of the thickness of the second layer.

16. The multilayer polymer film according to claim 4, wherein the diol containing 2 to 10 carbon atoms is ethylene glycol.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0082] FIG. 1-3 are schematics of multilayer films of the present invention;

[0083] FIG. 4 shows a perspective view of a multipack made from the inventive film;

[0084] FIG. 5-8 show details of snap incisions in the multipack of the present invention;

[0085] FIG. 9 shows the geometry of the setup for measuring the bending stiffness of the inventive film.

DETAILED DESCRIPTION

[0086] FIG. 1 shows a multilayer polymer film 10 according to the present invention comprising a first layer 1 and a second layer 2.

[0087] FIG. 2 shows a multilayer polymer film 11 according to the present invention comprising a first layer 1, a second layer 2 and a third layer 3.

[0088] FIG. 3 shows a multilayer polymer film 13 according to the present invention comprising a first layer 1, a second layer 2, a third layer 3 and a fourth layer 4.

[0089] The inventive multilayer polymer film may consist of three layers, i.e. the first and second layer plus either the third or fourth layer. In particular the multilayer polymer film may consist of layers 1, 2 and 3 or layers 1, 2 and 4.

[0090] FIG. 4 shows a perspective view of an exemplary multipack 30 thermoformed from the multilayer polymer film of the present invention. The multipack 30 comprises six containers 31. Preferably, containers 31 are arranged in a periodic pattern of parallel rows and columns. An upper surface 32 of the multipack 30 comprises concave portions, the shape of which corresponds to the shape of containers 31. Preferably, the upper surface 32 is formed by the first layer or the third layer of the multilayer polymer film of the present invention. The upper surface 32 of multipack 30 further comprises incisions 33 and 34. Preferably, incisions 33 and 34 are located symmetrically halfway between adjacent rows and columns of containers 31.

[0091] FIG. 5 schematically shows details of incisions 33 and 34 in the upper surface 32 of a multipack thermoformed from a film according to the present invention, wherein said film comprises a first layer 21 and a second layer 22, corresponding to layer 1 and, respectively layer 2 of FIG. 1. In FIG. 5 the thickness of the first layer 21 is designated by reference sign T1. Incisions 33 and 34 extend from the upper surface 32 into the first layer 21 down to depth D. Preferably, depth D is equal or larger than 60% of T1, i.e. D0.6T1, and more preferably equal or larger than 80% of T1, i.e. D0.8T1.

[0092] Similarly to FIG. 5, FIG. 6 shows incisions 33 and 34 with depth D in the upper surface 32 of a multipack thermoformed from a film according to the present invention, wherein said film comprises a first layer 21 and a second layer 22, corresponding to layer 1 and, respectively layer 2 of FIG. 1. Layer 21 and 22 have thickness T1 and, respectively T2. Incisions 33 and 34 extend through the first layer 21 into the second layer 22, preferably down to a depth D which corresponds to less or equal to 50% of thickness T2 of second layer 22, i.e. DT1+0.5T2.

[0093] With reference to FIGS. 5 and 6, the depth D of incisions 33 and 34 is preferably bounded according to the following relation

0.6T1DT1+0.5T2

and more preferably, according to the relation

0.8T1DT1+0.5T2

[0094] Similarly to FIGS. 5 and 6, FIGS. 7 and 8 show incisions 33 and 34 with depth D in the upper surface 32 of a multipack thermoformed from a film according to the present invention, wherein said film comprises a first layer 21, a second layer 22 and a third layer 23, corresponding to layer 1, respectively layer 2 and, respectively layer 3 of FIGS. 2 and 3. Layer 21, 22 and 23 have thickness T1, respectively T2 and, respectively T3.

[0095] FIG. 7 shows incisions 33 and 34 extending through the third layer 23 into the first layer 21, preferably down to a depth D which corresponds to at least 60% of thickness T1 of first layer 21, i.e. DT3+0.6T1, and more preferably at least 80% of thickness T1, i.e. DT3+0.8T1.

[0096] FIG. 8 shows incisions 33 and 34 extending through the third and first layer 23 and 21 into the second layer 22, preferably down to a depth D which is less or equal to 50% of thickness T2 of second layer 22, i.e. DT3+T1+0.5T2.

[0097] With reference to FIGS. 7 and 8, the depth D of incisions 33 and 34 is preferably bounded according to the following relation

T3+0.6T1DT3+T1+0.5T2

and more preferably, according to the relation

T3+0.8T1DT3+T1+0.5T2

[0098] Despite not being shown in FIGS. 4, 5, 6, 7 and 8, the multipack 30 of the present invention may also comprise a lid film sealed onto contiguous planar strips of the multipack 30 extending between adjacent container rows and columns. Preferably, said lid film consists of a sealable single-layer or multilayer polymer film equipped with a metal coating and one or more print layers. Regardless of whether or not the inventive multipack 30 comprises a lid film, the above stated bounds for the depth D of snap incisions 33, 34 with respect to the upper surface 32 of multipack 30, formed by the first layer 21 or third layer 23 of the inventive multilayer polymer film, are implemented.

[0099] FIG. 9 shows a perspective schematic of the geometry for measurement of bending stiffness according to DIN 53350. A film sample 10 having width W is fixated at one end by a clamp 50. At distance L from clamp 50 the free standing end of film sample 10 is deflected in a direction perpendicular to the nominal film sample plane defined by clamp 50. In the present invention distance L, is also designated as bending length L.

[0100] The perpendicular deflection is designated by reference sign x and the corresponding deflection angle by , wherein =tan.sup.1(x/L). The deflection of film 10 is effected by an electronic actuator (not shown in FIG. 9) equipped with a load cell and a position transducer for measuring the bending force and corresponding deflection x. The bending stiffness S is defined as the ratio of bending moment M to curvature , i.e. S=M/, wherein curvature is the inverse of the bending radius R, i.e. =1/R. For small angular deflection 7 degree (i.e. 0.122 radian) the bending stiffness S can be approximated according to the formula S=F.Math.L.sup.3/(3.Math.x), wherein F designates the bending force.

[0101] In the present invention the bending stiffness is preferably measured using an automated instrument, such as 2-Point Bending Tester from Zwick Roell.

[0102] In the invention the bending stiffness S is stated in physical units of [N.Math.mm.sup.2 per 1 mm film width]. The physical bending stiffness of a film having a width of W in units of [mm] is then given by WS. In scientific and technical literature, it is also common to state bending stiffness in width normalized units of [N.Math.mm]. The physical bending stiffness of a film having a width normalized bending stiffness and a width of W in units of [mm], is then calculated as Wmm. Aside from differing units the numerical values of physical bending stiffness S [N.Math.mm.sup.2 per 1 mm film width] and width normalized bending stiffness [N.Math.mm] are identical.

Inventive Example

[0103] A four-layer polymer film according to the present invention of type C/A/B/C was prepared using three extruders and a feedblock/die designed for overlay of four melt streams. The thickness and material composition of the four layers are listed beneath.

TABLE-US-00001 TABLE 1 Composition of inventive example film Layer Layer no./type thickness.sup. Layer material 3/C 20 m 96.5 wt-% APET RAMAPET.sup. N180/ 0.5 wt-% antiblock agent (wax + SiO.sub.2 Sukano T dc S479)/3 wt-% masterbatch color (PET + white pigment) 1/A 265 m 97.5 wt-% BPET.sup./2 wt-% masterbatch white (25 wt-% LDPE + 75 wt-% TiO.sub.2)/ 0.5 wt-% foaming agent (NaHCO.sub.3 + citric acid + nucleating agent) 2/B 395 m 68 wt-% BPET.sup./30 wt-% masterbatch chalk (20 wt-% PPH + 80 wt-% CaCO.sub.3 particle size < 5 m)/2 wt-% masterbatch white (25 wt-% LDPE + 75 wt-% TiO.sub.2) 4/C 20 m 96.5 wt-% APET RAMAPET.sup. N180/ 0.5 wt-% antiblock agent (wax + SiO.sub.2 Sukano T dc S479)/3 wt-% masterbatch color (PET + white pigment) .sup.nominal layer thickness based on amount and density of the respective layer material; .sup.RAMAPET N180 having intrinsic viscosity of 0.8 dl/g; .sup.BPET consisting of 85 wt-% PET (50 wt-% post consume recycled PET + 50 wt-% APET RAMAPET N180), 13 wt-% LDPE with melt flow rate of 3 to 8 g/min and 2 wt-% ethylene vinyl acetate.

[0104] The thickness, density, bending stiffness, oxygen permeability (OTR) and water vapor permeability (WVTR) of the thus obtained four-layer polymer film were measured according to the methods recited in Table 4 and following results obtained:

TABLE-US-00002 TABLE 2 Inventive example film properties thickness 695 m density 1.28 g .Math. cm.sup.3 bending stiffness 104.7 N .Math. mm.sup.2 per 1 mm width oxygen permeability 7.4 cm.sup.3/(m.sup.2 .Math. day .Math. atm) water vapor permeability 1.61 g/(m.sup.2 .Math. day)

Comparative Example

[0105] A commercially available white polystyrene film for thermoforming of multipacks was tested using the same measurement methods and conditions as in the inventive example. For thickness, density, oxygen permeability and water vapor permeability of the white polystyrene film the following results were obtained:

TABLE-US-00003 TABLE 3 Comparative example film properties thickness 840 m density 1.09 g .Math. cm.sup.3 bending stiffness 141.7 N .Math. mm.sup.2 per 1 mm width oxygen permeability 220.0 cm.sup.3/(m.sup.2 .Math. day .Math. atm) water vapor permeability 3.80 g/(m.sup.2 .Math. day)

[0106] The bending stiffness S of a film consisting of a homogeneous material is proportional to the elastic modulus E multiplied by the third power of the film thickness t, i.e. SE.Math.t.sup.3. In order to compare the bending stiffness of the inventive and comparative example films on a thickness, respectively material adjusted basis the bending stiffness of the comparative example film is multiplied by a factor of (695 m/840 m).sup.3=0.57. Accordingly, for the thickness adjusted bending stiffness of the comparative example film a value of 0.57141.7 N.Math.mm.sup.2=80.26 N.Math.mm.sup.2 per 1 mm film width is obtained. Thus, the thickness/material adjusted bending stiffness of the inventive film example is 30% larger than that of the comparative polystyrene film.

[0107] Similarly, in order to compare the oxygen permeability (OTR) and the water vapor permeability (WVTR) of the inventive and comparative film examples on a thickness/material adjusted basis, the respective values of the comparative film example are multiplied by a factor of 840 m/695 m=1.21. Accordingly, for the comparative polystyrene film thickness/material adjusted values of 265.9 cm.sup.3/(m.sup.2.Math.day.Math.atm) for OTR and 4.59 g/(m.sup.2.Math.day) for WVTR are obtained. These values are larger by factors of 35.9 and, respectively 2.9 than the OTR and WVTR of the inventive film example.

[0108] The above results show that the inventive film has favorable properties compared to conventional polystyrene film.

[0109] Measurement Methods

[0110] The physical properties of the inventive film and additives are measured according to the following methods:

TABLE-US-00004 TABLE 4 Measurement methods Film property Method Total film thickness DIN 53370:2006 Layer thickness Optical and electron microscope imaging of film section Density DIN EN ISO 1183:2005 Elastic modulus/ DIN EN ISO 527:2012 Tensile modulus Bending stiffness DIN 53350 at a bending length of 100 mm using a film sample with 160 mm length, 30 mm width. Oxygen permeability/ DIN 53380-3:1998 Oxygen transmission rate at 23 C. and < 0.1% relative humidity. (OTR) Water vapor permeability/ DIN EN ISO 15106-2:2005 Water vapor transmission at 38 C. and 90% relative humidity. rate (WVTR) Powder particle size, Electron microsope imaging of more than equivalent diameter 1000 particles in combination with software based image analysis; Light scattering using Horiba LA-300 laser diffraction particle size distribution analyzer for particle sizes from 0.01 to 5000 m. Intrinsic viscosity DIN EN ISO 1628-5:1998 Melt flow rate DIN EN ISO 1133.2012 at 190 C. using a load of 2.16 kg and a standard nozzle having diameter of 2.095 mm and length of 8 mm.

[0111] In Table 4 and throughout the present invention the term equivalent diameter designates the diameter of an equivalent spherical particle having the same chemical composition and areal section (electron microscope imaging) or scattering intensity (laser diffraction) as the examined particle. In practice the areal section or scattering intensity of each examined (irregularly shaped) particle is assigned to a spherical particle having a diameter commensurate with the measured signal.

[0112] In order to obtain representative values for the density and elastic modulus (tensile modulus) of individual layers of the inventive multilayer film, in particular the first and second layer, homogeneous films i.e. single layer films were prepared from the polymer compound of the respective layer using the same machine settings, such as extruder torque, extruder slit width, extruder slit height and temperature profile as those used for the manufacture of the inventive multilayer film. The density and tensile modulus (elastic modulus) of a single layer film prepared in such manner are then measured according to DIN EN ISO 1183:2005 and, respectively DIN EN ISO 527:2012 and assigned to the layer of an inventive multilayer film prepared from the same compound under the same process conditions.