Thermoplastic compositions suitable for use in films

Abstract

The invention relates to a linear low density polyethylene composition comprising a linear low density polyethylene having a melt flow index of 1.5-2.5, a phenolic antioxidant, a processing stabilizer and ZnO, wherein the composition is free or substantially free of tris(nonylphenyl) phosphite (TNPP).

Claims

1. A linear low density polyethylene composition comprising a linear low density polyethylene having a melt flow index of 1.5-2.5, a phenolic antioxidant, a processing stabilizer and ZnO, wherein the composition is free or substantially free of tris(nonylphenyl) phosphite (TNPP), wherein a weight ratio between the phenolic antioxidant and the processing stabilizer is from 2:1 to 3:1, and wherein a weight ratio between the phenolic antioxidant and the ZnO is from 2:1 to 3:1.

2. The composition according to claim 1, wherein the linear low density polyethylene has a density of from 917 to 920 kg/m.sup.3 according to ISO1183.

3. The composition according to claim 1, wherein the total amount of the phenolic antioxidant, the processing stabilizer and ZnO is 1300 ppm to 4000 ppm based on the composition.

4. The composition according to claim 1, wherein the phenolic antioxidant is a compound represented by general formula (I): ##STR00024## in which R.sub.1 is C.sub.1-C.sub.4 alkyl, n is 1, 2, 3 or 4, X is methylene, ##STR00025## Y is hydrogen or NH; and, if n is 1, X is ##STR00026## where Y is attached to R.sub.2, and R.sub.2 is C.sub.1-C.sub.25 alkyl; and, if n is 2, X is ##STR00027## where Y is attached to R.sub.2, and R.sub.2 is C.sub.2-C.sub.12 alkylene, C.sub.4-C.sub.12 alkylene interrupted by oxygen or sulfur; or, if Y is NH, R.sub.2 is additionally a direct bond; and, if n is 3, X is methylene or ##STR00028## where the ethylene group is attached to R.sub.2, and R.sub.2 is ##STR00029## and if n is 4, X is ##STR00030## where Y is attached to R.sub.2, and R.sub.2 is C.sub.4-C.sub.10 alkanetetrayl.

5. The composition according to claim 1, wherein the processing stabilizer is at least one compound of the group of the organic phosphites or phosphonites of the formulae II to VIII excluding tris(nonylphenyl) phosphite ##STR00031## in which the indices are integral and n is 2, 3 or 4; p is 1 or 2; q is 2 or 3; r is 4 to 12; y is 1, 2 or 3; and z is 1 to 6; A, if n is 2, is C.sub.2-C.sub.18 alkylene; C.sub.2-C.sub.12 alkylene interrupted by oxygen, sulfur or NR.sub.4; a radical of the formula ##STR00032## or phenylene; A, if n is 3, is a radical of the formula C.sub.rH.sub.2r-1; A, if n is 4, is ##STR00033## A has the meaning of A if n is 2; B is a direct bond, CH.sub.2, CHR.sub.4, CR.sub.1R.sub.4, sulfur or C.sub.5-C.sub.7 cycloalkylidene, or cyclohexylidene substituted by from 1 to 4 C.sub.1-C.sub.4 alkyl radicals in position 3, 4 and/or 5; D, if p is 1, is methyl and, if p is 2, is CH.sub.2OCH.sub.2; E, if y is 1, is C.sub.1-C.sub.18 alkyl, OR.sub.1 or halogen; E, if y is 2, is O-A-O, E, if y is 3, is a radical of the formula R.sub.4C(CH.sub.2O).sub.3 or N(CH.sub.2CH.sub.2O).sub.3; Q is the radical of an at least z-valent alcohol or phenol, this radical being attached via the oxygen atom to the phosphorus atom; R.sub.1, R.sub.2 and R.sub.3 independently of one another are unsubstituted or halogen, COOR.sub.4, CN or CONR.sub.4R.sub.4-substituted C.sub.1-C.sub.18 alkyl; C.sub.2-C.sub.18 alkyl interrupted by oxygen, sulfur or NR.sub.4; C.sub.7-C.sub.9 phenylalkyl; C.sub.5-C.sub.12 cycloalkyl, phenyl or naphthyl; naphthyl or phenyl substituted by halogen, 1 to 3 alkyl radicals or alkoxy radicals having in total 1 to 18 carbon atoms or by C.sub.7-C.sub.9 phenylalkyl; or are a radical of the formula ##STR00034## in which m is an integer from the range 3 to 6; R.sub.4 is hydrogen, C.sub.1-C.sub.18 alkyl, C.sub.5-C.sub.12 cycloalkyl or C.sub.7-C.sub.9 phenylalkyl, R.sub.5 and R.sub.6 independently of one another are hydrogen, C.sub.1-C.sub.8 alkyl or C.sub.5-C.sub.6 cycloalkyl, R.sub.7 and R.sub.8, if q is 2, independently of one another are C.sub.1-C.sub.4 alkyl or together are a 2,3-dehydropentamethylene radical; and R.sub.7 and R.sub.8, if q is 3, are methyl; R.sub.14 is hydrogen, C.sub.1-C.sub.9 alkyl or cyclohexyl, R.sub.15 is hydrogen or methyl and, if two or more radicals R.sub.14 and R.sub.15 are present, these radicals are identical or different, X and Y are each a direct bond or oxygen, Z is a direct bond, methylene, C(R.sub.16).sub.2 or sulfur, and R.sub.16 is C.sub.1-C.sub.8 alkyl.

6. The composition according to claim 1, wherein the amount of the phenolic antioxidant is 700-2000 ppm based on the composition.

7. The composition according to claim 1, wherein the amount of the processing stabilizer is 300-1000 ppm based on the composition.

8. The composition according to claim 1, wherein the amount of ZnO is 300-1000 ppm based on the composition.

9. A polyethylene composition comprising the LLDPE composition according to claim 1 and a low density polyethylene or a plastomer.

10. A multi-layer film comprising a layer comprising the LLDPE composition according to claim 1.

11. The film according to claim 10, wherein the film is a film of five layers prepared by blown film co-extrusion process comprising, in the following order, a) a layer comprising 85-99 wt % of the LLDPE composition and 1-15 wt % of LDPE, b) a first tie layer, c) an oxygen barrier layer, d) a second tie layer, and e) a layer comprising 85-99 wt % of the LLDPE composition and 1-15 wt % of LDPE.

12. The film according to claim 10, wherein the film is a film of three layers prepared by casting comprising, in the following order, A) a cling layer comprising 90-99 wt % of the LLDPE composition and 1-10 wt % of the plastomer, wherein the sum of the LLDPE composition and plastomer is 95-100 wt %, B) a layer comprising 60-100 wt % of the LLDPE composition, and C) a layer consisting of the LLDPE composition.

13. Food packaging comprising the LLDPE composition of claim 1.

14. A method for making a shrink film, the method comprising subjecting the LLDPE composition according to claim 1 to a blown film co-extrusion process.

15. A method for making a stretch film by casting the LLDPE composition according to claim 1.

16. The composition according to claim 1, wherein the phenolic antioxidant is represented by the formula (Ib) ##STR00035## and the processing stabilizer is tris(2,4-di-tert-butylphenyl) phosphite.

17. A linear low density polyethylene composition comprising a linear low density polyethylene having a melt flow index of 1.5-2.5, a phenolic antioxidant, a processing stabilizer and ZnO, wherein the composition is free or substantially free of tris(nonylphenyl) phosphite (TNPP), wherein the amount of the phenolic antioxidant is 900-1100 ppm, the amount of the processing stabilizer is 450-550 ppm, and the amount of the ZnO is 450-550 ppm, each based on the composition, wherein a weight ratio between the phenolic antioxidant and the processing stabilizer is from 2:1 to 2.4:1, and wherein a weight ration between the phenolic antioxidant and the ZnO is from 2:1 to 2.4:1.

18. A multi-layer film comprising a layer comprising the polyethylene composition according to claim 9.

19. Food packaging comprising the polyethylene composition according to claim 9.

Description

EXAMPLES

(1) LLDPE composition 1 was prepared by melt-mixing an LLDPE powder having a density of 918 kg/m.sup.3 and a melt flow index (ISO1133, 2.16 kg/190 C.) of 2.0 g/10 minutes with additives as shown in Table 1 in a twin screw extruder. The LLDPE composition and the LLDPE powder have the same melt flow index.

(2) LLDPE compositions 2-4 were prepared in a similar manner except that the LLDPE powder used for the preparation has different MFI and the additives used are different, as shown in Table 1.

(3) TABLE-US-00001 TABLE 1 LLDPE melt flow density composition index stabilizing additives (kg/m3) LLDPE1 2.0 Irganox 1076 1000 ppm 918 Irgafos 168 500 ppm ZnO 500 ppm LLDPE2 1.0 Irganox 1076 800 ppm 918 Irgafos 168 200 ppm Zinc stearate 500 ppm LLDPE3 2.0 Irganox 1076 1500 ppm 918 Trinonylphenylphosphite (TNPP) 500 ppm ZnO 900 ppm LLDPE4 3.0 Irganox 1076 1500 ppm 918 Trinonylphenylphosphite (TNPP) 500 ppm ZnO 900 ppm

(4) LLDPE1 is an LLDPE composition according to the invention.

(5) LLDPE2, LLDPE3, LLDPE4 are comparative examples

(6) The melt flow index was determined by ISO1133:2011 (190 C./2.16 kg).

(7) The density was determined by ISO1183.

(8) LLDPE1 has an MFI suitable for a blown film co-extrusion process and a casting process.

(9) LLDPE2 has an MFI suitable for a blown film co-extrusion process but not for a casting process.

(10) The oxidative-induction time (OIT) tests were performed for LLDPE1 and LLDPE2 at 210 C. according to a method based on ISO11357-6, PlasticsDifferential scanning calorimetry (DSC)Part 6: Determination of oxidation induction time (isothermal OIT).

(11) According to the results of the OIT tests, the thermal stability of LLDPE1 is much higher than LLDPE2. The OIT was measured to be 42 minutes for LLDPE1 and less than 3 minutes for LLDPE2. The high thermal stability of LLDPE1 indicates that LLDPE1 can be processed better than LLDPE2 at the high temperature that is especially required for blown film co-extrusion process. Also, the deposits for an LLDPE1 film may be less than for an LLDPE2 film prepared using blown film co-extrusion process. Hence, LLDPE1 is very suitable for preparing a blown film.

(12) LLDPE3 and LLDPE4 comprise TNPP and therefore LLDPE1 is more suitable for food packaging applications than LLDPE3 and LLDPE4 since TNPP is a substance suspected to have a health affect. LLDPE3 and LLDPE4 are made using the same stabilizing additives. Monolayer films of 20 m were prepared by a casting process at 270 C. using LLDPE3 and LLDPE4. Puncture resistance was measured by ASTM D5748-95 and tear strength was measured by ISO6383-2. Puncture resistance and tear strength were higher for the film made from LLDPE3 than the film made from LLDPE4. LLDPE composition made from an LLDPE having a MFI of 2.0 was found to have a higher puncture resistance and tear strength than LLDPE composition made from an LLDPE having a MFI of 3.0.