Polypropylene Compound with Improved Optical Property and Gel Level

Abstract

Composition for producing films with low amount of gels and good haze, wherein said composition comprises a polypropylene and a high density polyethylene powder.

Claims

1. Composition comprising (a) at least 85 parts per weight (ppw) based on 100 ppw of the composition of a polypropylene (PP), and (b) not more than 15 parts per weight (ppw) based on 100 ppw of the composition of a high density polyethylene (HDPE), wherein said high density polyethylene (HDPE) has particle top cut d.sub.90 of below 1000 μm.

2. Composition according to claim 1, wherein the composition is obtained by mixing said polypropylene (PP) with said high density polyethylene (HDPE).

3. Composition obtained by mixing (a) at least 85 parts per weight (ppw) based on 100 ppw of the composition of a polypropylene (PP), and (b) not more than 15 parts per weight (ppw) based on 100 ppw of the composition of a high density polyethylene (HDPE), wherein said high density polyethylene (HDPE) has particle top cut d.sub.90 of below 1000 μm.

4. Composition according to claim 3, wherein the mixing is a dry- or melt-mixing.

5. Composition according to claim 1, wherein the high density polyethylene (HDPE) has a median particle size d.sub.50 of below 800 μm.

6. Composition according to claim 1, wherein the high density polyethylene (HDPE) has (a) a melting temperature (T.sub.m) in the range of 120 to 150° C.; and/or (b) a melt flow rate MFR.sub.2 (190° C., 2.16 kg) in the range of 10 to 30 g/10 min; and/or (c) a density of at least 930 kg/m.sup.3.

7. Composition according to claim 1, wherein the polypropylene (PP) is a random propylene copolymer having a comonomer content in the range of 0.5 to 6.0 mol %.

8. Composition according to claim 1, wherein the polypropylene (PP) has (a) a melt flow rate MFR2 (230° C.) measured according to ISO 1133 from 5 to 15 g/10 min; and/or (b) a xylene cold soluble (XCS) fraction in the range of 1.0 to 6.0 wt.-%.

9. Composition according to claim 1 being free of slip agent(s).

10. Film made from a composition according to claim 1.

11. Film according to claim 10, wherein said film has (a) haze of below 5.0% measured on a 50 μm cast film according to ASTM D1003-00; and/or (b) a gel index of less than 30.

12. Film according to claim 10, wherein the film is a cast film or blown film wherein, optionally, said film is metallized.

13. Process for producing a composition wherein (a) at least 85 parts per weight (ppw) based on 100 ppw of the composition of a polypropylene (PP), and (b) not more than 15 parts per weight (ppw) based on 100 ppw of the composition of a high density polyethylene (HDPE), are mixed, wherein said high density polyethylene (HDPE) has particle top cut d.sub.90 of below 1000 μm.

14. Process according to claim 13, wherein the high density polyethylene (HDPE) has a median particle size d.sub.50 of below 800 μm.

15. Process for producing a film by feeding a composition according to claim 1 to a cast film line or blown film line and subsequently obtaining a film.

16. Process according to claim 13, wherein (a) and (b) are dry- or melt-mixed.

17. Process for lowering the gel index of a film, comprising producing a film from a composition comprising a high density polyethylene (HDPE) having a particle top cut d.sub.90 of below 1000 μm and a polypropylene.

18. Process according to claim 17, wherein the gel index of a film produced using the composition comprising the high density polyethylene (HDPE) and the polypropylene is lower compared to the gel index of a film (film 2) made under the same conditions using the same composition except that the high density polyethylene (HDPE) is replaced by the same amount by weight of the polypropylene.

19. Process according to claim 17, wherein (a) the high density polyethylene (HDPE) has a median particle size d.sub.50 of below 800 μm; and/or (b) the propylene is a polypropylene (PP) is a random propylene copolymer having a comonomer content in the range of 0.5 to 6.0 mol %; and/or (c) the composition is free of slip agent(s).

20. Process according to claim 17, wherein the composition comprises (a) at least 85 parts per weight (ppw) based on 100 ppw of the composition of a polypropylene (PP), and (b) not more than 15 parts per weight (ppw) based on 100 ppw of the composition of a high density polyethylene (HDPE), wherein said high density polyethylene (HDPE) has particle top cut d.sub.90 of below 1000 μm.

Description

EXAMPLES

[0141] The following definitions of terms and determination methods apply for the above general description of the invention as well as to the below examples unless otherwise defined.

[0142] Particle Size:

[0143] Throughout the present document, the “particle size” of a filler material or other particulate material is described by its distribution of particle sizes. The value d.sub.x represents the diameter relative to which x % by volume of the particles have diameters less than d.sub.x. The d.sub.50 value is thus the volume determined medium particle size, i.e. 50% of the total volume of all particles results from particles smaller than this particle size. For the purpose of the present invention the particle size is specified as volume determined particle size d.sub.50 unless indicated otherwise. The same applies for the d.sub.90, d.sub.10 and SPAN ((D.sub.90-D.sub.10)/D.sub.50) values. For determining the volume determined medium particle size d.sub.50, top cut d.sub.90 and d.sub.10 a Mastersizer 2000 or Mastersizer 3000 from the company Malvern Instruments Ltd., Great Britain, using the Fraunhofer light scattering model is used. The weight determined particle size distribution may correspond to the volume determined particle size if the density of all the particles is equal.

[0144] Transparency, haze and clarity were determined according to ASTM D1003-00 on 60×60×1 mm.sup.3 plaques injection molded in line with EN ISO 1873-2 using a melt temperature of 200° C. and on cast films of 50 μm thickness produced on a monolayer cast film line with a melt temperature of 220° C. and a chill roll temperature of 20° C.

[0145] OCS Gel Index

[0146] 1. Apparatus

[0147] The apparatus consists of a laboratory extruder ME 25/5800 V3 with five heating zones, an adapter and a 150 mm broad die. The follow-on unit encompasses a chillroll CR-9, diameter 140 mm, including Haake C40P heating- and cooling device (15 to 90° C.), a line scan camera FS-5/4096 Pixel (dynamical digital converting of gray scale images) and a wind-up unit with automatic tension control up to 10 N.

[0148] 2. Material-Specific Settings for Film-Manufacturing

[0149] The temperature setting for the heating zones at cylinder and die is classified for polypropylene according to MFR-ranges in six groups: [0150] Group 1: MFR-range 0.2-0.5 g/10 min (230° C./2.16 kg), temperatures 240(feed)/260/270/280/290/290/290° C. [0151] Group 2: MFR-range 0.5 to 1.0 g/10 min (230° C./2.16 kg), temperatures 220(feed)/240/255/270/270/270° C. [0152] Group 3: MFR-range of greater than 1.0 to 2.0 g/10 min (230° C./2.16 kg), temperatures 190(feed)/210/225/240/240/240° C. [0153] Group 4: MFR-range of greater than 2.0 to 4.5 g/10 min (230° C./2.16 kg), temperatures 190(feed)/205/220/230/230/230° C. [0154] Group 5: MFR-range of greater than 4.5 to 8.0 g/10 min (230° C./2.16 kg), temperatures 190(feed)/205/215/220/220/220° C. [0155] Group 6: MFR of greater than 8.0 g/10 min (230° C./2.16 kg), temperatures 180(feed)/195/210/220/220/220° C.

[0156] Preset Parameters:

TABLE-US-00001 Rotational speed (screw): 20 rpm Haul-off speed:  2 m/min; The film thickness is 50+/−5 μm

[0157] 3. Measurement

[0158] After fulfilment of the following parameters: In case of similar materials ca. 60 min running-in period, in case of highly diverging materials ca. 120 min.

[0159] Goal: Adjustment of a homogenous film at constant melt pressure and melt temperature. The measuring area is standardised at 5 m.sup.2. The measurement itself is terminated automatically when the area is accomplished. The report will be printed simultaneously.

[0160] 4. Analysis

[0161] The number of found defects is, referring 1/m.sup.2, class-divided according to size and multiplied with the mass factor, adding up to the gelindex.

TABLE-US-00002 Size class 1  100-300 μm mass factor × 0.1 Size class 2  301-600 μm mass factor × 1.0 Size class 3 601-1000 μm mass factor × 5.0 Size class 4    >1000 μm mass factor × 10

Example

[0162]

TABLE-US-00003 17 defects size class 1  × 0.1 = 1.7 5 defects size class 2  × 1.0 = 5.0 2 defects size class 3  × 5.0 = 10.0 0 defects size class 4 × 10.0 = 0 gelindex = 16.7

[0163] The Ink test was performed according to ISO 8296

[0164] The Melt Flow Rate (MFR) was determined according to ISO 1133.

[0165] The xylene cold solubles (XCS, wt.-%): Content of xylene cold solubles (XCS) is determined at 25° C. according ISO 16152; first edition; 2005-07-01.

[0166] Melting temperature Tm, crystallization temperature Tc: measured with Mettler TA820 differential scanning calorimetry (DSC) on 5 to 10 mg samples. DSC is run according to ISO 11357/part 3/method C2 in a heat/cool/heat cycle with a scan rate of 10° C./min in the temperature range of +23 to +210° C. Crystallization temperature and enthalpy are determined from the cooling step, while melting temperature and melting enthalpy are determined from the second heating step.

[0167] Materials:

[0168] UNEX HDPE T1 supplied by Dakota nv, Belgium, which is a high density polyethylene in form of a powder having a melting temperature T.sub.m of 130° C., a melt flow rate MFR.sub.2 of 20 g/10 min (190° C./2.16 kg), a density of about 940 kg/m.sup.3, a d50 of 401.6, a d90 of 712.3, a d10 of 187.9 and a SPAN of 1.31.

[0169] MG9601, supplied by Borealis, in a form of pellets, which is a high density polyethylene having a density of 960 kg/m.sup.3, a melt flow rate MFR.sub.2 of 31 g/10 min (190° C./2.16 kg), and a particle size d.sub.50 of more than 1 mm.

[0170] Polypropylene (PP)

[0171] The catalyst used in the polymerization processes of the examples was the catalyst as prepared in Example 8 of WO 2004/029112A1 (see pages 22-23), except that diethylaluminium chloride was used as an aluminium compound instead of triethylaluminium.

[0172] An external donor, dicyclopentyldimethoxy silane, has been used. The ratio of aluminium to donor was 7.5. Polypropylene has been copolymerized with ethylene in a pilot bimodal multireactor system for polymerization mode consisting of a pre-polymerization, a loop reactor and a gas reactor, with a catalyst of the above-described system and under the following polymerization conditions (Table 1). Technical features of the copolymer obtained are listed in Table 2.

TABLE-US-00004 TABLE 1 Polymerization conditions of random copolymer of propylene (PP) Example PP Total prod (kg/h) 60 Prepoly Temperature (° C.) 30 Pressure (bar) 55 Donor (g/t) 35 H2 feed (g/h) 2.5 C2 feed (g/h) 300 Loop Reactor Temp (° C.) 70 Prod (kg/h) 25 Pressure (bar) 55 C2-content (wt-%) 2 C2/production rate (kg/t) 22 C2 feed (g/h) 350 H2/C3 in Loop (mol/kmol) 4 MFR (230° C.) 8 Gas Reactor C2/C3 (mol/kmol) 14 C2-content (wt-%) 2 H2/C3 (mol/kmol) 40 MFR (230° C.) 8 Temperature (° C.) 85 Pressure (bar) 21 Split (%) 55

[0173] In Table 1, “H2/C3 (mol/kmol)” means the feed ratio of H2/C3, and “C2/C3 mol/kmol” means the feed ratio of C2/C3. The volume of pre-polymerization reactor is very small, and production rate is much less than that in loop reactor and gas reactor. In this case, R-PP1 means the sum of copolymers as produced in pre-polymerization reactor and loop reactor, and R-PP2 means the fraction as produced in gas reactor.

[0174] The technical features of the final copolymer product are listed in Table 2.

TABLE-US-00005 TABLE 2 Technical features of the random copolymer of propylene (PP) PP C.sub.2 [wt.-%] 2 MFR.sub.2 [g/10 min] 8.0 XS [wt.-%] 3.5

[0175] After polymerization, the copolymer had been pelletized in an extruder. The formulation contained regular additives such as a normal acid scavenger (e.g. Ca stearate), antioxidants (e.g. Irganox 1010, Irgafos 168), and anti-blocking agents (e.g. synthetic silica) at a total amount of 0.45 wt %.

[0176] CE1:

[0177] 100 wt. % PP thus prepared was extruded together in a cast machine to form a monolayer cast film with a thickness of 50 μm.

[0178] CE2:

[0179] 96 wt. % of PP thus prepared was co-extruded together with 4 wt. % MG9601 (in pellet form) in a cast machine to form a monolayer cast film with a thickness of 50 μm.

[0180] IE1

[0181] 96 wt. % of PP prepared above was co-extruded together with 4 wt. % cryogenically grounded UNEX HDPE T1 in a cast machine to form a monolayer cast film with a thickness of 50 μm.

TABLE-US-00006 TABLE 3 Test results Ink test Gel index Day 7 Day 14 Day 21 Haze CE1 16 38 36 36 1.4 CE2 61 38 36 36 3.5 IE1 8 38 36 36 3.1

[0182] The use of high density polyethylene (HDPE) which has the inventive particle size only slightly affects the optical properties while significantly improving the gel index. The use of a high density polyethylene (HDPE) powder results in a reduced haze versus the use of high density polyethylene (HDPE) pellets, i.e. a high density polyethylene (HDPE) with a particle size, e.g. d.sub.50 value, above the claimed range. Moreover, the Corona retention is maintained at the same level.