Shrink films comprising PA 6/6,6

Abstract

The present invention relates to a process for producing a polymer film (P) comprising a polyamide composition (PC) by extruding the polyamide composition (PC) through an annular die and then stretching the tube thus obtained by blowing in air. The present invention further relates to the polymer film (P) obtainable by the process of the invention and to a process for packaging foodstuffs with the polymer film (P).

Claims

1. A process for producing a polymer film (P) comprising a polyamide composition (PC), wherein the polyamide composition (PC) comprises nylon-6/6,6 and polyamide oligomers and where it is possible to extract in the range from 5% to 25% by weight, based on the total weight of the polyamide composition (PC), of polyamide oligomers from the polyamide composition (PC) according to ISO 6427: 2013, the process comprising: i) providing the polyamide composition (PC) in molten form in a first extruder, ii) extruding the polyamide composition (PC) provided in i) in molten form from the first extruder through an annular die to obtain a tube comprising the polyamide composition (PC) in molten form, iii) cooling the tube comprising the polyamide composition (PC) in molten form obtained in ii) in a water bath to a first temperature (T.sub.1), which solidifies the polyamide composition (PC) to obtain a first tubular film comprising the polyamide composition (PC), iv) heating the first tubular film obtained in iii) to a second temperature (T.sub.2) to obtain a heated first tubular film comprising the polyamide composition (PC), v) blowing air into the heated first tubular film obtained in iv), which stretches the heated first tubular film widthwise, and where the heated first tubular film is cooled to a third temperature (T.sub.3) to obtain the polymer film (P) comprising the polyamide composition (PC).

2. The process according to claim 1, wherein the polymer film (P) comprises in the range from 0.1% to 80% by weight, based on the total weight of the polymer film (P), of the polyamide composition (PC).

3. The process according to claim 1 wherein the nylon-6/6,6 comprises in the range from 70% to 78% by weight of nylon-6 units and in the range from 22% to 30% by weight of nylon-6,6 units, based in each case on the total weight of the nylon-6/6,6.

4. The process according to claim 1, wherein the polyamide composition (PC) has a melting temperature (T.sub.M(PC)) in the range from 178 to 187° C.

5. The process according to claim 1, wherein the tube obtained in ii) has a thickness in the range from 10 μm to 1 mm.

6. The process according to claim 1, wherein the first temperature (T.sub.1) in iii) is in the range from 5 to 60° C.

7. The process according to claim 1, wherein the polyamide composition (PC) has a glass transition temperature (T.sub.G(PC)) and a melting temperature (T.sub.M(PC)), and the second temperature (T.sub.2) in step iv) is above the glass transition temperature (T.sub.G(PC)) and below the melting temperature (T.sub.M(PC)) of the polyamide composition (PC).

8. The process according to claim 1, wherein the tube comprising the polyamide composition (PC), during the cooling in iii), is guided through a first roll system, which stretches the tube lengthwise.

9. The process according to claim 8, wherein the heated first tubular film comprising the polyamide composition (PC), during the blowing-in of air in v), is guided through a second roll system, which stretches the heated first tubular film lengthwise.

10. The process according to claim 9, wherein, after v), the process further comprises the following: vi) guiding the polymer film (P) obtained in v) over at least one third roll, vii) heating the polymer film (P) obtained in v) to a fourth temperature (T.sub.4) which is above the glass transition temperature (T.sub.G(PC)) of the polyamide composition (PC) to obtain a heated polymer film (P), viii) guiding the heated polymer film (P) obtained in vii) over at least one fourth roll to obtain the polymer film (P), where the heated polymer film (P), between vii) and viii), during viii) and/or after viii), is cooled to a fifth temperature (T.sub.5) which is below the glass transition temperature (T.sub.G(PC)) of the polyamide composition (PC).

11. The process according to claim 1, wherein the polymer film (P) has a thickness ≥0.1 μm and <1 mm.

12. A polymer film (P) obtained by a process according to claim 1.

13. A process for packaging foodstuffs, comprising: a) providing a foodstuff encased by at least one polymer film (P) according to claim 12, where the at least one polymer film (P) has a provision temperature (T.sub.B), b) heating the at least one polymer film (P) to a shrink temperature (T.sub.S), which shrinks the at least one polymer film (P) to obtain a foodstuff encased by the at least one shrunk polymer film (P).

14. The process according to claim 13, wherein the shrink temperature (T.sub.S) in b) is in the range from 50 to 150° C.

15. The process according to claim 13, wherein the shrink temperature (T.sub.S) in b) is above the glass transition temperature (T.sub.G(PC)) of the polyamide composition (PC) present in the at least one polymer film (P).

16. The process according to claim 1, wherein the polymer film (P) is a multilayer film.

Description

EXAMPLES

(1) The properties of the polymer films and of the components present were determined as follows:

(2) The viscosity number (VN.sub.(PC)) of the polyamide composition (PC) was determined in a 0.5% by weight solution in 96% by weight sulfuric acid at 25° C. according to EN ISO 307:2007+Amd 1:2013.

(3) The glass transition temperature (T.sub.G) and melting temperature (T.sub.M) both of the polyamide composition (PC) and of the further polymers (FP) were determined according to ISO 11357-1:2009, ISO 11357-2: 2013 and ISO 11357-3: 2011. For this purpose, two heating runs were conducted and the glass transition temperature (T.sub.G) and melting temperature (T.sub.M) were each ascertained from the second heating run.

(4) The density of the polyamide composition (PC) and of the further polymers (FP) was determined by the gas pycnometer method according to EN ISO 1183-3:1999.

(5) To determine the proportion of nylon-6,6 in the nylon-6/6,6, the polyamide composition (PC) was hydrolyzed in dilute hydrochloric acid (20%). This protonates the units derives from hexamethylenediamine, with the chloride ion from the hydrochloric acid forming the counterion. By means of ion exchanger, this chloride ion was then exchanged for a hydroxide ion with release of hexamethylenediamine. By titration with 0.1 molar hydrochloric acid, the hexamethylenediamine concentration is then determined, from which the proportion of nylon-6,6 in the nylon-6/6,6 can be calculated.

(6) The proportion of polyamide oligomers that can be extracted from the polyamide composition (PC) was determined according to ISO 6427:2013 in methanol.

(7) The area stretching ratio was reported as the product of the stretching ratios in extrusion direction (MD) and at right angles thereto (TD). For this purpose, the first tubular film, prior to step v), was guided through a conveying roll system and the polymer film (P), during step v), was guided through a second roll system with a higher roll speed than the conveying roll system, such that it was stretched lengthwise. The stretching ratio in MD was read off from the roll speeds of the conveying roll system (prior to stretching) and the second roll system (after stretching); the stretching ratio in TD was determined with a slide gauge on the inflated tube.

(8) Hot shrinkage was determined in water at 90° C. First, a specimen of length 30 cm of the tube, directly after stretching, was cut by guiding it through a second roll system in step v). This tube was laid flat and cut open at the bent edges, and one side was discarded. A 10 cm*10 cm square was drawn on the remaining side of the tube. The lateral edges were each drawn parallel to extrusion direction (MD) or at right angles thereto (TD), and the individual centimeters between 0 and 10 cm were each marked individually. This marked film was then immediately immersed into water at 90° C. for 5 min. After the water bath, the edge lengths of the square were determined again and shrinkage values in MD and TD were thus obtained in each case from the difference between the originally drawn 10 cm minus the length present after shrinkage.

(9) The modulus of elasticity of the polymer films was determined according to ISO 527-3:1995.

(10) Tear propagation resistance was determined according to Elmendorf, DIN ISO 6383-2:2004 in extrusion direction (MD) and at right angles thereto (TD). The polymer films were conditioned under standard climatic conditions for non-tropical countries according to DIN EN ISO 291:2008.

(11) The area-based specific migration of the monomers present in the polyamide composition was determined in Simulant C of DIN EN 1186-5:2002 at 60° C. for 10 days. This was used to calculate the contents-based specific migration according to EU 10/2011.

(12) The impact resistance (dart drop) of the monofilms was determined according to DIN ISO 7765-2:1994 with 5 specimens at a relative air humidity of 50% (50% RH), with reporting of the fracture energy in the present case.

(13) The following components were used:

(14) Polyamide Compositions: P-1 Nylon-6 from BASF SE®, sold under the Ultramid B40L brand name, with 1.03% by weight of extractable polyamide oligomers. The viscosity number (VN) was 250 mL/g, the glass transition temperature (T.sub.G) 57° C., the melting temperature (T.sub.M) 220° C. and the density 1.15 g/mL. P-2 Copolymer of nylon-6 and nylon-6,6 (nylon-6/6,6) from BASF SE®, sold under the Ultramid C40L brand name, with a nylon-6,6 level of 16.8 and 2.43% by weight of extractable polyamide oligomers. The viscosity number (VN) was 250 mL/g, the glass transition temperature (T.sub.G) 53° C., the melting temperature (T.sub.M) 188° C. and the density 1.143 g/mL. P-3 Copolymer of nylon-6 and nylon-6,6 (nylon-6/6,6) with a nylon-6,6 level of 22.6, prepared according to WO 2010/066769 A2, and 18.33% by weight of extractable polyamide oligomers with a number-average molecular weight of 1760 g/mol. The viscosity number (VN) was 213 mL/g, the glass transition temperature (T.sub.G) 58° C., the melting temperature (T.sub.M) 183° C. and the density 1.14 g/mL. P-4 Copolymer of nylon-6 and nylon-6,6 (nylon-6/6,6) with a nylon-6,6 level of 24.6, prepared according to WO 2010/066769 A2, and 20.7% by weight of extractable polyamide oligomers with a number-average molecular weight of 9020 g/mol. The viscosity number (VN) was 209 mL/g, the glass transition temperature (T.sub.G) 57° C., the melting temperature (T.sub.M) 181.5° C. and the density 1.14 g/mL.

(15) Further Polymers (FP): FP-1 Linear low-density polyethylene (LLDPE) from BOREALIS®, sold under the STAMYLEX 08-026F brand name, with an MFR (melt flow rate) (190° C./2.16 kg) of 2.2 g/10 min according to ISO 1133 and a density of 0.910 g/cm.sup.3 according to ISO 1183. FP-2 Ultralow-density linear polyethylene (ULDPE) from DOW®, sold under the DOW ATTANE 4102G brand name, with an MVI (melt flow index) (190° C./2.16 kg) of 1 g/10 min according to ISO 1133 and a density of 0.905 g/cm.sup.3 according to ASTM D792. FP-3 Antiblock masterbatch from Schulman®, sold under the Polybatch FSU 105 E brand name, with a density of 0.98 g/cm.sup.3 according to ISO 1183, Method A. FP-4 Anhydride-modified linear low-density polyethylene (LLDPE) from Mitsubishi Chemical®, sold under the MODIC M603E brand name, with an MFR (melt flow rate) (190° C./21.2 N) of 1.9 g/cm.sup.3 according to ISO 1133 and a density of 0.91 g/cm.sup.3 according to ISO 1183, Method A. FP-5 Low-density polyethylene (LDPE) from LyondellBasell®, sold under the Lupolen 2420 F brand name, with an MFR (melt flow rate) (190° C./2.16 kg) of 0.75 g/10 min. FP-6 Anhydride-modified linear low-density polyethylene (LLDPE) from DuPont®, sold under the Bynel 4104 brand name, with an MFR (melt flow rate) (190° C./2.16 kg) of 1.1 g/10 min. FP-7 A poly(ethylene-vinyl alcohol) (EVOH) from Kuraray®, sold under the EVAL F171B brand name, with an MFR (melt flow rate) (210° C./2.16 kg) of 1.8 g/10 min and an ethylene level of 32 mol %.

(16) Production of Multilayer Films for Determination of Area Stretching Ratio and Hot Shrinkage:

(17) Production of 5-Layer Primary Tubes:

(18) For production of the primary tubes, a 5-layer tubular film system from PLAMEX® with a die head diameter of 80 mm was used. 4 extruders were used, which had a diameter of 50 mm (extruders A, B, C, D). Extruder A was laden with 67% FP-1, 30% FP-2 and 3% FP-3 and gave the outer layer. Extruder B was laden in each case with 100% polyamide composition and produced the middle layer. Extruder C was laden with 65% FP-1, 30% FP-2 and 5% FP-3 and gave the inner layer. Extruder D was laden with 100% FP-4 and gave the adhesion promoter layers. Between extruder D and die head there was a “Y” adapter, such that extruder D melted the material for two layers.

(19) A primary tube of thickness 500 μm was produced. The layer sequence resulted from the compositions present in the extruders; the sequence of the extruders was as follows: C, D, B, D, A, and the following layer thicknesses were obtained from the respective extruders: extruder C 100 μm, D 37.5 μm each, B 225 μm and A 100 μm. The respective layer thickness was established via the respective extruder throughput.

(20) The primary tubes were wound up and stored for one day before further processing.

(21) Production of Shrink Films:

(22) The primary tubes were unwound using a roll system and heated to 70° C.+/−5° C. In the startup process, there was subsequently dynamic introduction of air into the tube up to the stretch point, i.e. the maximum stretch. If the tube had been inflated, it was laid flat in a further roll system and stretched in machine direction, since the speed of the second roll system was higher than that of the first roll system. After the further roll system, samples were taken for the shrinkage measurements.

(23) The components used and the results from the measurement of the area stretching ratio and hot shrinkage are reported in table 1:

(24) TABLE-US-00001 TABLE 1 C1 I2 I3 Component P-2 P-3 P-4 Area stretching ratio 11.2 12.6 14.65 Shrinkage (MD) 50% 52% 53% Shrinkage (TD) 50% 52% 55%

(25) While the tube comprising the polyamide composition P-2 inflated abruptly over and above a particular pressure, inflation was much more gentle with the polyamide compositions P-3 and P-4. In the case of polyamide composition P-2, there was therefore an increased incidence of bubble explosions on startup since the pressure was too high, and the startup was much more time-consuming for that reason.

(26) Production of Multilayer Films in a Blowing Process for Determination of Modulus of Elasticity and Tear Propagation Resistance

(27) Multilayer films comprising four different materials were produced in a 7-layer blown film system from Collin® with a die head diameter of 180 mm. Of the 7 extruders, 6 had a diameter of 30 mm and one a diameter of 45 mm. The multilayer films obtained had a thickness of 100 μm and the layers a layer thickness of 15/14/14/14/14/15 μm. The extruders of the blown film system were supplied with the components in accordance with the structure of the multilayer films specified in table 2. Table 2 also states the properties of the multilayer films produced.

(28) TABLE-US-00002 TABLE 2 C4 C5 I6 I7 Structure FP-5 // FP-5 // FP-5 // FP-5 // FP-6 // FP-6 // FP-6 // FP-6 // P-1 // P-2 // P-3 // P-4 // FP-7 // FP-7 // FP-7 // FP-7 // P-1 // P-2 // P-3 // P-4 // FP-6 // FP-6 // FP-6 // FP-6 // FP-5 FP-5 FP-5 FP-5 Modulus of [MPa] 990 824 798 682 elasticity (MD) Modulus of [MPa] 966 784 770 618 elasticity (TD) Tear [mN] 1932 3080 8972 6804 propagation (8N (8N (32N (32N resistance pendulum) pendulum) pendulum) pendulum) (MD) Tear [mN] 2276 6124 9201 11058 propagation (8N (8N (32N (32N resistance pendulum) pendulum) pendulum) pendulum) (TD)

(29) Production of Monolayer Films in a Casting Process for Measurement of Specific Migration for Foodstuff Applications:

(30) A monofilm of P-4 was produced in a cast film system from Weber® with a die head diameter of 150 mm. The extruder had a diameter of 30 mm. The throughput was 5 kg/h. The monofilm produced had a thickness of 50 μm and was wound directly after the chill roll. The results of the area-based and contents-based specific migration are reported in table 3.

(31) TABLE-US-00003 TABLE 3 Hexamethylene- Adipic Caprolactam diamine acid Area-based [mg/dm.sup.2] 2.56 <detection 1.5 migration limit Contents-based [mg/kg] 15.34 <detection 9.0 migration limit

(32) Production of Monolayer Blown Films for Determination of Puncture Energy and Modulus of Elasticity:

(33) Monofilms were produced in a 7-layer blown film system from Collin® having a die head diameter of 180 mm. Of the 7 extruders, 6 had a diameter of 30 mm (extruders B, C, D, E, F, G) and one a diameter of 45 mm (extruder A). The melt from extruder A was on the inside in the bubble; the melt from extruder G was on the outside. The sequence of layers, from the inside outward, was A, B, C, D, E, F, G. The monofilms produced had a thickness of 100 μm and the layers a layer thickness of 15/14/14/14/14/14/15 μm in the monofilms. All the extruders were laden with the same component. The films were slit open before being wound up.

(34) The components used and the properties of the monofilms are reported in table 4.

(35) TABLE-US-00004 TABLE 4 C8 C9 I10 I11 Component P-1 P-2 P-3 P-4 Modulus of [MPa] 666 484 391 338 elasticity (MD) Modulus of [MPa] 678 457 402 267 elasticity (TD) Dart drop [N*mm] 2.7 4.3 4.5 5.8