POLYPROPYLENE COMPOSITION FOR HMS PP FOAM SHEET WITH BALANCED BENDING RESISTANCE

Abstract

The present invention relates to a polypropylene composition comprising —10 to 50 wt. % of recycled polypropylene (R-PP) and/or linear polypropylene (L-PP); —40 to 89.95 wt. % of a high melt strength polypropylene (HMS-PP) having an F30 melt strength of more than 25.0 cN and a v30 melt extensibility of more than 205 mm/s, wherein the F30 melt strength and the v30 melt extensibility are determined according to ISO 16790:2005; and —0.05 to 10 wt. % of a nucleating agent (NA); a foamed sheet formed from the polypropylene composition; an article comprising the foamed sheet and a process comprising the step of forming the polypropylene composition. Furthermore, the invention is further directed to the usage of the polypropylene composition for the formation of foamed sheets.

Claims

1. A polypropylene composition comprising: 10 to 50 wt. % of recycled polypropylene (R-PP) and/or linear polypropylene (L-PP); 40 to 89.95 wt. % of a high melt strength polypropylene (HMS-PP) having an F.sub.30 melt strength of more than 25.0 cN and a v.sub.30 melt extensibility of more than 205 mm/s, wherein the F.sub.30 melt strength and the v.sub.30 melt extensibility are determined according to ISO 16790:2005; and 0.05 to 10 wt. % of a nucleating agent (NA).

2. The polypropylene composition according to claim 1, wherein the recycled polypropylene (R-PP) and/or linear polypropylene (L-PP) has at least one of the following properties: a) an MFR, determined according to ISO 1133, at a temperature of 230° C. and under a load of 2.16 kg, of 3 to 25 g/10 min; b) an F30 melt strength of less than 25.0 cN, determined according to ISO 16790:2005.

3. The polypropylene composition according to claim 1, wherein the recycled polypropylene (R-PP) is a recycled polypropylene (Rec-PP) comprising at least 50 wt. % of recycled high melt strength polypropylene (HMS-PP).

4. The polypropylene composition according to claim 1, wherein the nucleating agent (NA) is talc.

5. A foamed sheet formed from the polypropylene composition according to claim 1.

6. The foamed sheet according to claim 5, having a thickness of 0.5 to 10 mm and/or a density of 150 to 250 kg/m.sup.3.

7. The foamed sheet according to claim 5, wherein the foamed sheet is covered by a cover layer (CL).

8. The foamed sheet according to claim 7, wherein the foamed sheet and the cover layer (CL) are directly adjacent.

9. An article comprising the foamed sheet according to claim 5.

10. A process comprising the following step a) producing a polypropylene composition comprising 10 to 50 wt. % of recycled polypropylene (R-PP) and/or linear polypropylene (L-PP); 40 to 89.95 wt. % of a high melt strength polypropylene (HMS-PP) having an F.sub.30 melt strength of more than 25.0 cN and a v.sub.30 melt extensibility of more than 205 mm/s, wherein the F.sub.30 melt strength and the v.sub.30 melt extensibility are determined according to ISO 16790:2005; and 0.05 to 10 wt. % of a nucleating agent (NA), whereby the recycled polypropylene (R-PP) and/or linear polypropylene (L-PP), the high melt strength polypropylene (HMS-PP) and the nucleating agent (NA) are simultaneously or consecutively combined and mixed in a mixing device.

11. The process according to claim 10, wherein the process further comprises the following step b) subsequent to step a) b) forming a foamed article comprising the step of foaming the polypropylene composition obtained in step a).

12. The process according to claim 11, wherein the process further comprises the following step c) subsequent to step b) c) forming a cup from the foamed article obtained after step b).

13. The process according to claim 11, wherein the recycled polypropylene (R-PP) is a recycled polypropylene (Rec-PP) and the process further comprises the following step d) subsequent to step c), if present, or step b): d) forming the recycled polypropylene (Rec-PP) using the polymer remains present after step b).

14. A method comprising producing foamed sheets from the polypropylene composition according to claim 1, the foamed sheets fulfilling the following relationship (I):
bending resistance (MD)/bending resistance (CD)≤1.2  (I) wherein bending resistance (MD) is the bending resistance in machine direction measured according to SCAN P29:95, in mN; and bending resistance (CD) is the bending resistance in cross direction measured according to SCAN P29:95], in mN.

15. A method comprising producing foamed sheets from the polypropylene composition according to claim 1, the foamed sheets fulfilling the following relationship (II)
thermal conductivity at 100° C./thermal conductivity at 20° C. 1.5  (II) wherein thermal conductivity at 100° C. is the thermal conductivity of the foamed sheet at 100° C. determined according to ISO 1856:2000 in m.Math.K; and thermal conductivity at 20° C. is the thermal conductivity of the foamed sheet at 20° C. determined according to ISO 1856:2000 in m.Math.K.

Description

EXAMPLES

A. Measuring Methods

[0196] 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.

MFR

[0197] The MFR of the polypropylenes has been determined according to ISO 1133 under a load of 2.16 kg and at a temperature of 230° C.

Density of the Polymer

[0198] The Density was measured according to ISO 1183-1—method A (2004). Sample preparation is done by compression moulding in accordance with ISO 1872-2:2007.

Comonomer Content in Polypropylene

[0199] The comonomer content is determined by quantitative Fourier transform infrared spectroscopy (FTIR) after basic assignment calibrated via quantitative .sup.13C nuclear magnetic resonance (NMR) spectroscopy in a manner well known in the art. Thin films are pressed to a thickness of 250 μm and spectra recorded in transmission mode.

[0200] Specifically, the ethylene content of a polypropylene-co-ethylene copolymer is determined using the baseline corrected peak area of the quantitative bands found at 720-722 and 730-733 cm.sup.−1. Propylene-1-butene-copolymers were evaluated at 767 cm.sup.−1. Quantitative results are obtained based upon reference to the film thickness.

[0201] Melting temperature (T.sub.m) and heat of fusion (H.sub.f), crystallization temperature (T.sub.c) and heat of crystallization (H.sub.c): The melting temperature T.sub.m and crystallisation temperature T.sub.c were measured with a TA Instruments Q2000 differential scanning calorimetry device (DSC) according to ISO 11357/3 on 5 to 10 mg samples. Crystallisation and melting temperatures were obtained in a heat/cool/heat cycle with a scan rate of 10° C./min between 30° C. and 225° C. Melting and crystallisation temperatures were taken as the peaks of the endotherms and exotherms in the cooling cycle and the second heating cycle respectively.

[0202] MFR.sub.2 (230° C.) is measured according to ISO 1133 (230° C., 2.16 kg load).

F.sub.30 Melt Strength and v.sub.30 Melt Extensibility

[0203] The test described herein follows ISO 16790:2005.

[0204] The strain hardening behaviour is determined by the method as described in the article “Rheotens-Mastercurves and Drawability of Polymer Melts”, M. H. Wagner, Polymer Engineering and Science, Vol. 36, pages 925 to 935. The content of the document is included by reference. The strain hardening behaviour of polymers is analysed by Rheotens apparatus (product of Gottfert, Siemensstr.2, 74711 Buchen, Germany) in which a melt strand is elongated by drawing down with a defined acceleration.

[0205] The Rheotens experiment simulates industrial spinning and extrusion processes. In principle a melt is pressed or extruded through a round die and the resulting strand is hauled off. The stress on the extrudate is recorded, as a function of melt properties and measuring parameters (especially the ratio between output and haul-off speed, practically a measure for the extension rate). For the results presented below, the materials were extruded with a lab extruder HAAKE Polylab system and a gear pump with cylindrical die (L/D=6.0/2.0 mm). The gear pump was pre-adjusted to a strand extrusion rate of 5 mm/s, and the melt temperature was set to 200° C. The spinline length between die and Rheotens wheels was 80 mm. At the beginning of the experiment, the take-up speed of the Rheotens wheels was adjusted to the velocity of the extruded polymer strand (tensile force zero): Then the experiment was started by slowly increasing the take-up speed of the Rheotens wheels until the polymer filament breaks. The acceleration of the wheels was small enough so that the tensile force was measured under quasi-steady conditions. The acceleration of the melt strand drawn down is 120 mm/sect. The Rheotens was operated in combination with the PC program EXTENS. This is a real-time data-acquisition program, which displays and stores the measured data of tensile force and drawdown speed. The end points of the Rheotens curve (force versus pulley rotary speed) is taken as the F.sub.30 melt strength and drawability values.

Gel Content

[0206] About 2 g of the polymer (m.sub.p) are weighted and put in a mesh of metal which is weighted (m.sub.p+m). The polymer in the mesh is extracted in a soxhlet apparatus with boiling xylene for 5 hours. The eluent is then replaced by fresh xylene and the boiling is continued for another hour. Subsequently, the mesh is dried and weighted again (m.sub.XHU+m). The mass of the xylene hot unsolubles (m.sub.XHU) obtained by the formula m.sub.XHU+m−m.sub.m=m.sub.XHU is put in relation to the weight of the polymer (m.sub.p) to obtain the fraction of xylene insolubles m.sub.XHU/m.sub.p.

Particle Size/Particle Size Distribution of the Polymer

[0207] A gradation test was performed on the polymer samples. The sieve analysis involved a nested column of sieves with wire mesh screen with the following sizes: >20 μm, >32 μm, >63 μm, >100 μm, >125 μm, >160 μm, >200 μm, >250 μm, >315 μm, >400 μm, >500 μm, >710 μm, >1 mm, >1.4 mm, >2 mm, >2.8 mm. The samples were poured into the top sieve which has the largest screen openings. Each lower sieve in the column has smaller openings than the one above (see sizes indicated above). At the base is the receiver. The column was placed in a mechanical shaker. The shaker shook the column. After the shaking was completed the material on each sieve was weighed. The weight of the sample of each sieve was then divided by the total weight to give a percentage retained on each sieve.

Particle Size of the Nucleating Agent

[0208] The median particle size d.sub.50 is calculated from the particle size distribution [mass percent] as determined by gravitational liquid sedimentation according to ISO 13317-3 using a Sedigraph 5100 (Micromeritics Corporation).

Density of the Foam

[0209] This has been measured using an analytical and semi-micro precision balance of Switzerland PRECISA Gravimetrics AG, Switzerland, the specific gravity balance (XS225A); test method: application of Archimedes, automatically calculate the density of the sample.

Cell Size Diameter of the Foam

[0210] The cell size diameter of the foam was determined using a light optical microscope of Taiwan CBS Stereoscopic microscope;

[0211] The testing method used is as follows:

1. Cut a strip of the foamed material along the cross direction (CD) and machine direction (MD).
2. Hold the foamed material with a flat clamp and use a razor blade to perform a fine shave.
3. Focus the microscope at 100× and adjust lighting onto the foamed material.
4. Perform length and width measurements of each unique cell in the CD and MD orientation and record values.
5. Count the number of measured unique cells and record the values.
6. Perform cell wall thickness measurements across 3-4 tangent lines to overall length of each unique cell in the CD and MD orientation and record the values.
7. Perform three overall strip thickness measurements starting from the bottom of the first measured cell group, to the middle of the cell group, to the top of the cell group.
8. Perform an overall length measurement starting from the lowest complete cell to the highest complete cell.
9. Move microscope visual field so the bottom of the most upper incomplete cell is touching the bottom of the screen.
10. Repeat steps 4-9 on each new unique cell until about 0.200″ to 0.800″ of the strip is measured. Ensure that the overall length and cell composition does not overlap. Each overall length measurement after the first measurement is taken from the top of the previous highest complete cell to the top of the current highest complete cell.

Surface Roughness of the Foam

[0212] This has been measured using the portable surface roughness tester, model SJ-310 of Mitutoyo, Japan. The surface roughness tester (also known as a profilometer) is a contact surface roughness tester. The roughness determination is fully automated and runs via the included software.

Bending Resistance

[0213] The bending resistances in machine and cross direction were determined according to the method SCAN P29:95 issued by the Scandinavian pulp, paper and board Testing committee.

Thermal Conductivity

[0214] The thermal conductivities of the foamed sheet at 20° C. and at 100° C. were determined according to ISO 1856:2000.

Inventive Example 1 (IE1)

Preparation of a Foamed Sheet

[0215] 1. dry-blending of 750 kg of Daploy™ WB140HMS (MFR.sub.2 (230° C.) measured according to ISO 1133 of 2.1 g/10 min; F.sub.30 melt strength, determined according to ISO 16790:2005 of 36 cN; v.sub.30 melt extensibility, determined according to ISO 16790:2005 of 230 mm/s of Borealis AG (HMS-PP), 248 kg of recycled polypropylene (MFR.sub.2 (230° C.) measured according to ISO 1133 of 5.8 g/10 min; F.sub.30 melt strength, determined according to ISO 16790:2005 of 16.9 cN; v.sub.30 melt extensibility, determined according to ISO 16790:2005 of 270 mm/s) which is obtained by recycling the foamed sheet prepared in a previous production process performed as the present process and 2 kg of talc; [0216] 2. feeding the blend obtained in the 1.sup.st step into a 1.sup.st single screw extruder of Pitac Taiwan (screw diameter 90 mm; L/D ratio 26). The extruder is operated at a temperature of 200° C. (5 heating zones: 150° C.; 200° C.; 200° C.; 200° C.; 200° C.) so as to melt the polymer; [0217] 3. injecting of 3 wt % liquid butane (as blowing agent), based on the total weight of the blend, in the last section of the 1.sup.st single screw extruder obtaining thereby a molten blend; [0218] 4. passing the molten blend through a 2.sup.nd single screw extruder of Pitac Taiwan (screw diameter 120 mm; L/D ratio 34) thereby cooling down the molten blend to 160° C. at the end of the 2.sup.nd single screw extruder; [0219] 5. passing the molten blend of the 4.sup.th step through an extruding die placed at the end of the 2.sup.nd extruder; when exiting the extruder the molten blend is exposed to a pressure drop into atmospheric pressure by the sudden pressure drop the blowing agent in the molten blend expands and thereby accomplishes foaming resulting in a foamed structure; subsequently the foamed structure is cooled at cooling-drums with temperature below 100° C. thereby obtaining a foam sheet having a density of 200 kg/m.sup.3 and a thickness of 0.8 mm; [0220] 6. thereafter the foam sheet and a 20 μm thick BOPP film are passed through an in-line extruding laminating unit of YC Group Taiwan to laminate the foamed sheet on the BOPP film obtaining thereby a 2 layer sheet.

Inventive Example 2 (IE2)

[0221] The procedure of inventive example 1 was repeated except that the thickness of the foamed sheet in step 5 was 1.0 mm.

Comparative Example 1 (CE1)

[0222] Cupforma Natura™ PE from Stora Enso (Standard LDPE laminated carton cup)

[0223] The results of the inventive examples IE1 and IE2 as well as of the comparative example CE1 are set out in the following table 1.

TABLE-US-00003 TABLE 1 results of the inventive and comparative examples IE1 IE2 CE1 Sheet thickness mm 0.8 1.0 0.4 Foam density kg/m3 200 200 — Sheet grammage g/m2 230 260 275 Thickness of LDPE coating μm — — 10 Thickness of BOPP coating μm 25 25 — machine direction (MD) mN 200 270 290 cross direction (CD) mN 190 340 130 Surface roughness foam side μm 4.7 4.3 n.m Surface roughness BOPP side μm 1.2 1.63 n.m Thermal conductivity at 20° C. W/(m .Math. K) 0.032 0.036 0.072 Thermal conductivity at 100° C. W/(m .Math. K) 0.036 0.036 0.122

[0224] As can be seen from the above, the inventive composition leads to foamed sheets with balanced bending resistance in machine direction and cross direction enables simplified cup production as blanks can be used in every direction. Moreover, the foamed sheets have excellent thermal insulation properties which are not temperature dependent.

[0225] The produced sheet were used in cup production after cutting using standard paper cup machine (Eagle 1000S ACE Pack Korea) with a heating element modification in order to form the cup rim.