THERMOPLASTIC POLYMER COMPOSITION WITH REDUCED MIGRATION OF STABILISERS

Abstract

A thermoplastic polymer composition (A) leads to reduced migration of stabilisers or other ingredients (I), if it contains e.g. 50 to 90 wt. %, relative to the polymer composition (A), of a thermoplastic polymer (P), which has migration barrier properties, as well as at least one stabiliser component (S) and/or a further ingredient (I), wherein the following is true for the polymer composition (A): a) the glass transition temperature T.sub.g of the thermoplastic polymer (P) is greater than the use temperature; and b) the polymer-specific constant for polymers (Ap) of the thermoplastic polymer (P) is less than I; and c) the derived diffusion coefficient (Dp) of the thermoplastic polymer (P) for mineral oil is less than 10.sup.−12 cm.sup.2/s at 20° C.; and d) the morphology of the thermoplastic polymer (P) is either single-phase homogeneous, or two-phase heterogeneous.

Claims

1. A thermoplastic polymer composition (A) with reduced migration of stabilizers (S) and/or further ingredients (I), comprising at least 20 wt %, based on the polymer composition (A), of at least one thermoplastic polymer (P) which has migration barrier properties for stabilizers, and optionally at least 0.1 wt %, based on the polymer composition (A), of at least one stabilizer component (S) and/or at least 0.1 wt %, based on the polymer composition (A), of at least one further ingredient (I), where for the thermoplastic polymer composition (A): a) the glass transition temperature T.sub.g of the thermoplastic polymer (P) is above the service temperature, and b) the polymer-specific constant for polymers (A.sub.P) of the thermoplastic polymer (P) is less than 1, and c) the diffusion coefficient (D.sub.P), derived therefrom, of the thermoplastic polymer (P) for mineral oil is less than 10.sup.−12 cm.sup.2/s, at 20° C., and d) the morphology of the thermoplastic polymer (P) is either single-phase homogeneous, or two-phase heterogeneous, where, in the case of two-phase heterogeneous morphology of the thermoplastic polymer (P), the polymer component (Pp) having the higher Ap and the higher diffusion coefficient (D.sub.P) present as a discontinuous phase in particle form with a weight-average particle size (D) of 20 nm to 10 μm, is embedded in a polymer component (P.sub.m) of lower A.sub.P and lower diffusion coefficient (D.sub.P), where the morphology of the thermoplastic polymer (P) does not have a cocontinuous structure.

2. The thermoplastic polymer composition (A) with reduced migration as claimed in claim 1, characterized in that it contains 50 to 99.9 wt %, based on the polymer composition (A), of at least one thermoplastic polymer (P), and also at least 0.1 wt %, often 0.1 to 2.0 wt %, based on the polymer composition (A), of at least one stabilizer component (S) and/or at least 0.1 wt %, often 0.1 to 2.0 wt %, based on the polymer composition (A), of at least one further ingredient (I).

3. The thermoplastic polymer composition (A) with reduced migration as claimed in claim 1 or 2, characterized in that it comprises as thermoplastic polymer (P) a styrene-containing polymer having a glass transition temperature T.sub.g of at least 60° C., more particularly at least 70° C.

4. The thermoplastic polymer composition (A) with reduced migration as claimed in at least one of claims 1 to 3, characterized in that it comprises as thermoplastic polymer (P) a styrene-containing polymer component from the group consisting of polystyrene (PS), more particularly HIPS and GPPS, and also SBS copolymer/PS blends and SBC copolymer/PS blends.

5. The thermoplastic polymer composition (A) with reduced migration as claimed in at least one of claims 1 to 4, characterized in that it comprises as thermoplastic polymer (P) a polystyrene (PS) and also an SBS copolymer.

6. The thermoplastic polymer composition (A) with reduced migration as claimed in at least one of claims 1 to 5, characterized in that the thermoplastic polymer (P) comprises at least 50 wt % of polystyrene (PS) and also at least 10 wt % of SBS copolymer.

7. The thermoplastic polymer composition (A) with reduced migration as claimed in at least one of claims 1 to 6, characterized in that it comprises at least one stabilizer component (S) from the group consisting of antioxidants and light stabilizers, and/or comprises at least one further ingredient (I) from the group consisting of residue monomers and oligomers.

8. The thermoplastic polymer composition (A) with reduced migration as claimed in at least one of claims 1 to 7, characterized in that it contains 0.1 to 2.0 wt %, based on the polymer composition (A), of at least one stabilizer component (S), more particularly at least one antioxidant.

9. The thermoplastic polymer composition (A) with reduced migration as claimed in at least one of claims 1 to 8, characterized in that it contains 0.1 to 2.0 wt %, based on the polymer composition (A), of two different stabilizer components (S), and also optionally additionally at least one further ingredient.

10. A composite structure for packaging use, comprising at least two different layers, where at least one layer (S1) consists of a thermoplastic polymer composition (A) with reduced migration as claimed in at least one of claims 1 to 9.

11. The composite structure for packaging use as claimed in claim 10, comprising at least two different layers, where at least one layer (S1) consists largely of a thermoplastic polymer composition (A) of polystyrene (PS), SBS copolymer/PS blends and/or SBC copolymer/PS blends, and at least one further layer (S2) consists largely of a non-styrene-containing thermoplastic polymer composition (A2).

12. A process for producing a thermoplastic polymer composition (A) with reduced migration of stabilizers (S) and/or further ingredients (I), as claimed in any of claims 1 to 9, wherein at least one thermoplastic polymer (P) which has migration barrier properties is mixed with at least one stabilizer component (S) and also optionally further polymer additives.

13. The use of a thermoplastic polymer composition (A) with reduced migration of stabilizers (S) and/or further ingredients (I) as claimed in any of claims 1 to 9 for producing films, fibers or moldings.

14. The use of a composite structure as claimed in at least one of claims 10 and 11, comprising at least two different layers, wherein at least one layer (S1) consists of a thermoplastic polymer composition (A) with reduced migration, for providing packaging with enhanced resistance to delamination.

15. A process for producing a composite structure, comprising at least two different layers, where at least one layer (S1) consists of a thermoplastic polymer composition (A) with reduced migration as claimed in at least one of claims 1 to 9, by providing the layer (S1) and at least one further layer (S2) and also joining the at least two layers.

Description

EXAMPLES

[0146] To illustrate the technical advantages of the invention, the migration of three different additives was investigated:

[0147] (Antioxidant 1): Sumilizer GM (phenolic stabilizer from Sumitomo Chemical, JP) (2-tert-butyl-6-[(3-tert-butyl-2-hydroxy-5-methylphenyl)methyl]-4-methylphenyl prop-2-enoate);

[0148] (Antioxidant 2): TNPP (phosphite stabilizer)

[0149] (trisnonylphenyl) phosphite;

[0150] (Mineral Oil): commercial white oil (plasticizer, e.g., from Eni Oilproducts).

[0151] These following polymers were used:

[0152] SBS1: Styrolux 3G55 (INEOS Styrolution, Frankfurt), a coupled (star-shaped) SBS polymer with the following empirical composition:

[0153] 74% styrene/26% butadiene.

[0154] Polystyrene 158 (INEOS Styrolution, Frankfurt, standard PS with Vicat B/50 of 101° C. containing no white oil).

[0155] 2.5 wt % of mineral oil (white oil DAB 10); 0.25 wt % of antioxidant 1 (“Sumilizer GM”); and 0.4 wt % of antioxidant 2 (trisnonylphenyl phosphate (TNPP)) were added as stabilizers/ingredients during the melt processing.

[0156] SBS+PS

[0157] Additionally mixtures of the polymer component SBS1 with polystyrene 158 (INEOS Styrolution, Frankfurt, Standard-PS with Vicat B/50 of 101° C., containing no white oil) were prepared.

[0158] These mixtures were produced by mixing on a twin-screw extruder ZSK30 (Coperion) at a melt temperature of around 240° C.: [0159] SBS1+25% PS means: blend of 75 wt % of Styrolux 3G55 with 25 wt % of polystyrene 158 (stable morphology: 2-phase blend with lamellar/cylindrical structure); [0160] SBS1+50% PS means: blend of 50 wt % of Styrolux 3G55 with 50 wt % of polystyrene 158 (morphology consisting primarily of PS as homogeneous, continuous phase and polybutadiene-co-styrene as discontinuous phase, dispersed in particles, lamellae being visible in part); [0161] SBS1+75% PS means: blends of 25 wt % of Styrolux 3G55 with 75 wt % of polystyrene 158 (stable morphology with PS as homogeneous, continuous phase and polybutadiene-co-styrene as discontinuous phase, distributed in particles).

[0162] The respective morphology was determined on the basis of ultramicrotome thin-layer sections contrasted using RuO.sub.4, by means of a conventional scanning electron microscope at a magnification of 100 000 to 1.

[0163] Implementation of the migration measurements:

[0164] The use of oil as a fat simulant is less suitable owing to technical difficulties with analysis, and also 95% ethanol and also isooctane are less instructive as fat simulants, owing to high levels of interaction with the polymer matrix. Aqueous simulants are difficult because of the very low solubility of the additives.

[0165] For this reason, migration cells were used into which polymer films were clamped that consisted of the following polymer compositions: [0166] “SBS1”, [0167] “SBS+25% PS” [0168] “SBS+50% PS” and [0169] “SBS+75% PS”
each with a thickness of 1 mm (tab 3) and in each case between 2 polyethylene films (LDPE) 0.5 mm thick. The blank migration values with polyethylene (LDPE) were determined. Following extraction with diethyl ether, the amounts of migrated substances (after the times and temperatures indicated in tab. 3a) were determined by means of FID gas chromatography:

TABLE-US-00003 TABLE 3 Instrument parameters: Column: DB1ht, 30 m, ID 0.25 mm, film 0.1 μm Carrier gas/flow: helium; 1.6 ml/min; 35 cm/sec Injector: split/splitless; 320° C. Injection: 1 μm splitless Detector: FID; 320° C. Temperature program: 60° C. (2 min) 20° C./min 320° C.

[0170] The results of the kinetic measurements of the migration (at 40-70° C., in μg/dm2) of the ingredients in SBS and SBS+25% PS and of the further blends according to the invention (SBS+50 and +75% PS) are shown in table 3a.

[0171] The diffusion coefficients D.sub.P, were ascertained from the migration values for the respective polymer matrix and the corresponding migrant, and were used to determine the migration properties with the aid of equation (1).

TABLE-US-00004 TABLE 3a Antioxidant 1 Antioxidant 2 Mineral oil M = 394 M = 689 M = 515 Temp. 40° 60° 70° 40° 60° 70° 40° 60° 70° C. C. C. C. C. C. C. C. C. SBS 1 0.26 0.56 0.76 0.26 1.86 2.47 25.2 74.1 64.0 +25% 0.51 0.29 47.6 PS +50% 0.15 <0.1 9.5 PS +75% <0.01 <0.1 <2 PS

[0172] The diffusion coefficients Dp were ascertained from the migration values for the respective polymer matrix and the corresponding migrants, and were used to calculate the Ap values, by means of equation 2; see

TABLE-US-00005 TABLE 3b Antioxidant 1 Antioxidant 2 Mineral oil M = 394 M = 689 M = 515 Temp. 40° 60°  70°  40° 60°  70° 40° 60° 70° C. C. C. C. C. C. SBS 1 5.0 5.0 5.1 4.5 5.5 6.0 9.0 10.3 8.9 +25% 3.2 6.2 7.0 PS +50% 0.5 n.d. 4.5 PS +75% <−2   <0   <2 PS n.d. was not determined

[0173] The mineral oil causes the discontinuous polymeric soft phase to swell and in the boundary region leads from a discontinuous (particulate) morphology in accordance with the invention to a partly lamellar morphology, which is accompanied by adverse technical effects. This is apparent, for example, from the compositions with 50 wt % of polystyrene and 50 wt % of Styrolux 3G55 as polymer components.

[0174] It was found that on transition from a (cocontinuous) structure of the polymer to the discontinuous particulate structure used in the case of the composition (A) according to the invention, there are distinct reductions both in the migration values and in the A.sub.P polymer-specific parameters. This demonstrates that the barrier effect of the polymer composition is increased, so that the polymer composition (A) with reduced migration of stabilizers (or ingredients) in accordance with the invention procures a significant technical advantage.

[0175] This is utilized among other things in order to produce packaging with a composite structure having two different layers, layer (S1) of a thermoplastic mixture of 25 wt % of styrene-butadiene-styrene copolymer and 75% of PS, and a further layer (S2) composed of non-styrene-containing thermoplastic, more particularly polyurethane or PET.