FOAMED SHEET COMPRISING HIGH MELT STRENGTH POLYPROPYLENE

Abstract

The invention relates to a foamed sheet comprising a polymer composition comprising a high melt strength polypropylene wherein the high melt strength polypropylene has a melt strength?45 cN, preferably ?50 cN, more preferably ?55 cN, even more preferably ?60 cN, most preferably ?65 cN, wherein the melt strength is determined in accordance with ISO 16790:2005 at a temperature of 200? C., using a cylindrical capillary having a length of 20 mm and a width of 2 mm, a starting velocity v.sub.0 of 9.8 mm/s and an acceleration of 6 mm/s.sup.2.

Claims

1. Foamed sheet comprising a polymer composition comprising a high melt strength polypropylene wherein the high melt strength polypropylene has a melt strength?45 cN, or ?50 cN, or ?55 cN, or ?60 cN, or ?65 cN, wherein the melt strength is determined in accordance with ISO 16790:2005 at a temperature of 200? C., using a cylindrical capillary having a length of 20 mm and a width of 2 mm, a starting velocity v0 of 9.8 mm/s and an acceleration of 6 mm/s2.

2. Foamed sheet according to claim 1, wherein the melt strength of the high melt strength polypropylene is ?95 cN, or ?90 cN, or ?87 cN.

3. Foamed sheet according to claim 1, wherein the high melt strength polypropylene is chosen from the group of propylene homopolymers and propylene copolymers comprising moieties derived from propylene and one or more comonomers chosen from the group of ethylene and alpha-olefins with ?4 and ?12 carbon atoms.

4. Foamed sheet according to claim 1, wherein the high melt strength polypropylene has a melt flow rate?0.5 and ?8.0 g/10 min, or a melt flow rate?0.70 and ?5.0 g/10 min, or a melt flow rate?1.0 and ?4.0 g/10 min as determined in accordance with ASTM D1238 (2013) at a temperature of 230? C. under a load of 2.16 kg.

5. Foamed sheet according to claim 1, wherein the high melt strength polypropylene is prepared by a) irradiation of a polypropylene with at least one non-phenolic stabilizer, wherein the non-phenolic stabilizer is chosen from the group of hindered amines, wherein the irradiation is performed with ?2.0 and ?20 Megarad electron beam radiation in a reduced oxygen environment, wherein the amount of active oxygen is ?15% by volume with respect to the total volume of the reduced oxygen environment for a time sufficient for obtaining a long chain branched polypropylene and b) deactivation of the free radicals in the long chain branched polypropylene to form the high melt strength polypropylene.

6. Foamed sheet according to claim 1, wherein the high melt strength polypropylene is present in an amount ?10 wt % based on the polymer composition, wherein the high melt strength polypropylene is present in an amount ?10 wt % based on the polymer composition, or in an amount ?99.5 wt % based on the polymer composition.

7. Foamed sheet according to claim 1, wherein the polymer composition further comprises a further polypropylene.

8. Foamed sheet according to claim 1, wherein the polymer composition further comprises a nucleating agent, wherein the nucleating agent is present in an amount ?0.01 wt % and ?5.0 wt % based on the composition and/or wherein the nucleating agent is the nucleating agent is chosen from the group of talc, sodium bicarbonate, citric acid, azodicarbonamide and mixtures thereof.

9. Foamed sheet according to claim 1, wherein the polymer composition further comprises ?0.001 wt % and ?5.0 wt % additives based on the polymer composition.

10. Foamed sheet according to claim 1 wherein the polymer composition is present in the foamed sheet in an amount ?95 wt % based on the foamed sheet.

11. Foamed sheet according to claim 1, wherein the density of the foamed sheet is ?650 kg/m3 and ?20 kg/m3, wherein the density is determined according to ISO 845 (2006) and/or wherein the foamed sheet has an open cell content of ?15.0%, wherein the open cell content is determined according to ASTM D6226-10.

12. Foamed sheet according to claim 1, wherein the foamed sheet is prepared by a foam extrusion process.

13. Foamed sheet according to claim 1, wherein the polymer composition is present in the foamed sheet in an amount ?95 wt % based on the foamed sheet and/or wherein the amount of high melt strength polypropylene based on the polymer composition is ?15 wt %, ?20 wt %, ?25 wt %, or ?30 wt %, or ?40 wt %, or ?50 wt %, or ?60 wt %, or ?70 wt %, or ?80 wt %, or ?90 wt %.

14. Article comprising the foamed sheet of claim 1.

15. Process for the preparation of the foamed sheet of claim 1, comprising the sequential steps of: a) providing the polymer composition of claim 1 and b) adding a blowing agent to the polymer composition, wherein the blowing agent is added in an amount ?0.10 wt % and ?20 wt % based on the polymer composition and c) subjecting the mixture of the polymer composition and the blowing agent to a foaming process, and a foam extrusion process to form the foamed sheet and optionally d) stretching the foamed sheet in at least one direction.

16. Use of the foamed sheet of claim 1 for the preparation of an article.

Description

EXAMPLES

Methods Used:

Melt Flow Rate

[0064] The melt flow rate of the polymers was determined in accordance with ASTM D1238 (2013) at a temperature of 230? C. (MFR.sub.230) under a load of 2.16 kg.

Melt Strength

[0065] Melt strength was measured according to ISO standard 16790:2005. Melt strength is defined as the maximum (draw-down) force (in cN) by which a molten thread can be drawn before it breaks, e.g. during a Rheotens measurement. Measurements were done on a G?ttfert Rheograph 6000 at a temperature of 200? C. with a setup like shown in FIG. 1 of ISO standard 16790:2005. The rheometer has an oven with a diameter of 12 mm. A capillary of 20 mm length and 2 mm width was used. The entrance angle of the capillary was 180? (flat). The piston in the rheometer moved with a velocity of 0.272 mm/s to obtain an exit velocity v0, of 9.8 mm/s. After filling the rheometer, the melt was held in the rheometer for 5 minutes, to stabilize the temperature and fully melt the polymer. The strand that exits the capillary was drawn with a Rheotens 11 from Goettfert with an acceleration of 6 mm/s.sup.2 until breakage occurred. The distance between the exit of the capillary and the uptake wheels of the Rheotens II (=draw length) was 100 mm.

[0066] The pressure required to push the melted polymer through the capillary, the maximum drawing force (=Melt strength) and the maximum draw ratio at breakage were recorded.

Flexural-Modulus

[0067] The flexural-modulus of samples of the foamed sheets was determined with a three-point bending test according to ISO1209-2 Rigid cellular plasticsDetermination of flexural properties, using a testing speed of 20 mm/min. Samples having a span of 60 mm and a width of 20 mm were cut from the foamed sheets. The samples were cut in the machine direction (MD, extrusion direction) and in the transverse direction (TD, direction perpendicular to the extrusion direction and perpendicular to the thickness direction), such that the thickness of the foamed sheet (as indicated in Table 2) was maintained. As used herein, thickness direction is the size of the foamed sheet with the smallest dimension. Flexural modulus average is the average of the flexural modulus MD and the flexural modulus TD.

Foam Density

[0068] Density of the foam (kg/m.sup.3) is the apparent overall density and was determined according to ISO 845:2006.

Thickness and Width

[0069] Thickness and width of the foamed sheets were determined without applying pressure to the sheets.

Open Cell Content

[0070] The open cell content was determined by using a Quantachrome Pentapyc 5200e gas pycnometer using a method based on ASTM D6226-10. The volume from the external dimensions of the sample was determined by using the Archimedes' principle by immersing the sample in water. It was assumed that the uptake of water by the sample can be neglected. After drying the sample from adhering water, the sample volume (V.sub.SPEC) was determined by the pycnometer according ASTM D6226-10 at different pressures.

[0071] All applied pressures were below 0.1 bar to minimize compression of the foam.

[00001]$V_{\mathrm{SPEC}}=V_{\mathrm{CHAMBER}}-V_{\mathrm{EXP}}/\left[\frac{P_1}{P_2}-1\right]$

[0072] Where: [0073] V.sub.SPEC=Volume Sample [0074] V.sub.CHAMBER=Volume sample chamber [0075] V.sub.EXP=Expansion volume

[0076] The sample volume of the foam was plotted against the applied pressures (0.090 bar; 0.075 bar, 0.060 bar, 0.045 bar, 0.035 bar, 0.020 bar and 0.010 bar). A straight line was fit through the measurement points, using linear regression. The interception of the linear regression line with the Y-axis at p=0 bar is the volume (V.sub.SPEC_0) used in equation below.

[0077] The open cell content V.sub.open (%) was calculated using the following formula:

[00002]$O_V=\left[\left(V-V_{\mathrm{SPEC}\_0}\right)/V\right]*100$

[0078] Where: [0079] O.sub.v=open cell content [%] [0080] V=Geometric volume [0081] V.sub.SPEC_0=Volume sample interpolated to a pressure of 0 bar

Materials Used:

[0082] PP-UMS1 is a long chain branched propylene homopolymer which is commercially available from SABIC as SABIC? PPUMS 561P as of 18 Feb. 2021 without confidentiality restrictions, having a melt flow rate MFR.sub.230 of 2.5 g/10 min and a melt strength of 71 cN. SABIC? PPUMS 561P has a VOC-value as measured in accordance with VDA278 (2011-10) within 7 days of its production of 10.9 ?g/g. SABIC? PPUMS 561P has a FOG-value as measured in accordance with VDA278 (2011-10) within 7 days of its production of 56.4 ?g/g.

[0083] PP-HMS is a long chain branched propylene homopolymer which is commercially available from Borealis as Daploy? WB140HMS. It has a melt flow rate of MFR.sub.230 of 2.2 g/10 min and a melt strength of 42 cN.

[0084] PP-UMS2 is an experimental long chain branched propylene homopolymer having a melt flow rate MFR.sub.230 of 0.23 g/10 min and a melt strength of 62 cN. This PP-UMS2 is prepared as described in WO2009/003930A1, sample 11 (Polymer B) with 0.05 pph Genox EP.

[0085] Talc is TALCOLIN PP70+ which is a propylene homopolymer masterbatch with 70 wt % of talc (d50 of 9 ?m), which is commercially available from JM Polymers.

[0086] Blowing agent is isobutane.

Preparation of the Foamed Sheets

[0087] The preparation of the foamed sheets was performed on a 30 mm double screw foam extruder from Theysohn having a length over diameter ratio (l/d) of 40. This extruder consists of nine electrical heating zones equipped with water cooling followed by a cooling section, static mixer and a die. For CE5, it is expected that the temperature in front of the cooling section increases by approximately 5? C. relative to the experiments with PP-UMS1. Isobutane was added as a physical blowing agent in an amount of 2.5 wt % based on the composition of Table 1 and introduced in the polymer melt in the 8.sup.th zone of the extruder. A slit die adjustable in thickness was used for the production of the foamed sheets. The die pressure was adapted by adjusting the thickness of the slit die such that the pressure at the die was 50 bar. A slit die having a width of 35 mm was used.

[0088] The foamed sheets were then stretched in machine direction at the draw ratio indicated in Table 2 using a double belt drawing unit. The thus obtained sheets were then cooled in a water cooled calibration unit to fix the dimensions of the prepared foamed sheets. The draw ratio was adjusted by adjusting the speed of the double belt unit to the exit speed of the foam at free expansion. At a draw ratio of 1, the exit speed of the foam at free expansion (v.sub.exit) equals the speed of the double-belt unit (v.sub.line-speed).

[0089] Table 1 reports the polymer compositions, the foaming extrusion conditions and results.

CONCLUSION

[0090] As can be seen from Table 1, when preparing foamed sheets in accordance with the invention, a higher flexural modulus average is obtained. The flexural modulus average is a measure for the overall bending stiffness.

[0091] The foamed sheets of the invention (containing a polymer composition based on a high melt strength polypropylene having a melt strength?45 cN (E1-E4) show a higher overall bending stiffness than those sheets containing a polymer composition based on a high melt strength polypropylene having a melt strength<45 cN (CE1-CE4).

[0092] Therefore, the foamed sheets of the invention can be used for applications requiring a higher overall bending stiffness. For applications requiring the same overall bending stiffness, it is possible to use foamed sheets of the invention that are thinner and/or sheets that have a lower foam density. This so-called down-gauging is advantageous from an environmental point of view in terms of carbon footprint (less material and less transport costs and energy) as well as from an economical (cost) perspective.

[0093] Furthermore, foamed sheets of the invention prepared from a high melt strength polypropylene having a melt flow rate?1.0 and ?4.0 g/10 min, preferably ?1.5 and ?4.0 g/10 min as determined in accordance with ASTM D1238 (2013) at a temperature of 230? C. under a load of 2.16 kg will lead to a better surface appearance of the sheets (see examples E1-E4) as compared to sheets prepared from a high melt strength polypropylene having a melt flow rate of <1.0 g/10 min (see CE5 having a melt flow rate of 0.23 g/10 min).

[0094] Another advantage of the use of a high melt strength polypropylene composition having a melt flow rate?0.5 and ?8.0 g/10 min, preferably a melt flow rate?0.70 and ?5.0 g/10 min, more preferably a melt flow rate?1.0 and ?4.0 g/10 min, most preferably a melt flow rate?1.5 and ?4.0 g/10 min as determined in accordance with ASTM D1238 (2013) at a temperature of 230? C. under a load of 2.16 kg is that the extruder can be operated at a lower temperature as compared to CE5 where the temperature in front of the cooling section is expected to increase by approximately 5? C. as compared to E1-E4 and CE1-CE4. In commercial foam extruders, this increase of temperature is undesired as this limits the maximum throughput.

TABLE-US-00001 TABLE 1 polymer compositions used, foaming conditions and results E1 E2 E3 E4 CE1 CE2 CE3 CE4 CE5 composition PP-UMS1 wt % 97.9 97.9 97.9 97.9 PP-HMS wt % 97.9 97.9 97.9 97.9 PP-UMS2 wt % 97.9 talc wt % 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 conditions die pressure bar 50 50 50 50 50 50 50 50 50 draw ratio 1 1.31 1.63 1.95 1 1.34 1.66 1.95 1 line speed m/min 7.5 9.9 12.3 14.7 7.3 9.8 12.2 14.3 5 results density kg/m.sup.3 100 100 100 100 100 100 100 100 100 thickness mm 2.3 2.0 1.9 1.6 2.5 2.2 1.9 1.8 2.5 width mm 112 91 79 74 95 83 77 71 95 flexural modulus MPa 88 106 142 159 90 120 135 163 MD flexural modulus MPa 54 50 36 45 42 30 27 21 TD flexural modulus MPa 71 78 92 104 66 75 82 93 average surface + + + + + + + + ? appearance +: surface of the sheets was smooth ?: surface of the sheets expected to be uneven