HMS PP FOAM SHEET WITH GOOD COMPRESSIVE STRENGTH AND RECOVERABILITY

Abstract

The present invention relates to a foamed sheet consisting of a polypropylene composition comprising at least 85 wt. %, e.g. from 85 to 99.5 wt.-%, of a high melt strength polypropylene (HMS-PP) and 0.5 to 15 wt. % of a nucleating agent (NA), wherein the foamed sheet has a thickness of below 0.5 mm or a thickness of 2.0 mm or more. The present invention further relates to a foamed material consisting of a polypropylene composition as well as the use of a polypropylene composition comprising at least 85 wt. %, e.g. from 85 to 99.5 wt.-%, of a high melt strength polypropylene (HMS-PP) and 0.5 to 15 wt. % of a nucleating agent (NA) for producing foamed material.

Claims

1. A foamed sheet consisting of a polypropylene composition comprising at least 85 wt. %, of a high melt strength polypropylene (HMS-PP) and 0.5 to 15 wt. % of a nucleating agent (NA), the foamed sheet having a thickness of below 0.5 mm or a thickness of 2.0 mm or more.

2. The foamed sheet according to claim 1, fulfilling the following relationship (I):
compressive strength at 25%/(foam density).sup.2>0.018 kPa/(kg/m.sup.3).sup.2   (I) wherein, compressive strength at 25% is the compressive strength determined according to ISO3386-1 at 25% without pre-compression cycles [0], in kPa foam density is the density of the foam determined according to ISO 845, in kg/m.sup.3.

3. The foamed sheet according to claim 1, fulfilling the following relationship (II):
compressive strength at 40%/(foam density).sup.2>0.020 kPa/(kg/m.sup.3).sup.2   (II) wherein, compressive strength at 40% is the compressive strength determined according to ISO3386-1 at 40% without pre-compression cycles [0], in kPa foam density is the density of the foam determined according to ISO 845, in kg/m.sup.3.

4. The foamed sheet according to claim 1, having a recoverability determined according to the method specified in the examples herein of at least 85%.

5. A foamed material consisting of a polypropylene composition and fulfilling the following relationships (I) and (II):
compressive strength at 25% compression/(foam density).sup.2>0.018 kPa/(kg/m.sup.3).sup.2   (I) wherein, compressive strength at 25% is the compressive strength determined according to ISO3386-1 at 25% without pre-compression cycles [0], in kPa foam density is the density of the foam determined according to ISO 845, in kg/m.sup.3;
compressive strength at 40%/(foam density).sup.2>0.020 kPa/(kg/m.sup.3)   (II) wherein, compressive strength at 40% is the compressive strength determined according to ISO3386-1 at 40% without pre-compression cycles [0], in kPa foam density is the density of the foam determined according to ISO 845, in kg/m.sup.3, and further having a recoverability determined according to the method specified in the examples herein of at least 85%.

6. The foamed material according to claim 5, being in the form of a foamed sheet, wherein the polypropylene composition comprises at least 85 wt. %, of a high melt strength polypropylene (HMS-PP) and 0.5 to 15 wt. % of a nucleating agent (NA) and the foamed sheet has a thickness of below 0.5 mm or a thickness of 2.0 mm or more.

7. The foamed sheet or foamed material according to claim 1, wherein the nucleating agent (NA) is talc.

8. The foamed sheet or foamed material according to claim 1, wherein the high melt strength polypropylene (HMS-PP) has an F.sub.30 melt strength of more than 25.0 cN and/or 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.

9. The foamed sheet or foamed material according to claim 1, having a density of 50 to 350 kg/m.sup.3.

10. The foamed sheet or foamed material according to claim 1, having a thickness of 0.1 to 0.5 mm or of 2.0 to 10 mm.

11. The foamed sheet or foamed material according to claim 1, wherein the entirety of polymeric parts present in the foamed sheet or foamed material consists of the high melt strength polypropylene (HMS-PP).

12. The foamed sheet or foamed material according to claim 1, being a packaging foam, insulating material or flooring underlay, sandwich composites with PP foam core layer.

13. A method comprising producing foamed material from a polypropylene composition comprising at least 85 wt. % of a high melt strength polypropylene (HMS-PP) and 0.5 to 15 wt. % of a nucleating agent (NA), the foamed material fulfilling the following relationships (I) and/or (II):
compressive strength at 25%/(foam density).sup.2>0.018 kPa/(kg/m.sup.3).sup.2   (I) wherein, compressive strength at 25% is the compressive strength determined according to ISO3386-1 at 25% without pre-compression cycles [0], in kPa foam density is the density of the foam determined according to ISO 845, in kg/m.sup.3
compressive strength at 40%/(foam density).sup.2>0.020 kPa/(kg/m.sup.3).sup.2   (I) wherein compressive strength at 40% is the compressive strength determined according to ISO3386-1 at 40% without pre-compression cycles [0], in kPa foam density is the density of the foam determined according to ISO 845, in kg/m.sup.3.

14. The method according to claim 13, wherein the foamed material has a recoverability determined according to the method specified in the examples herein of at least 85%.

15. The method according to claim 13, being a packaging foam, an insulating material or a flooring underlay, or a foam used in automotive.

Description

EXAMPLES

A. Measuring Methods

[0214] 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

[0215] 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

[0216] 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

[0217] The comonomer content is determined by quantitative Fourier transform infrared spectroscopy (FTIR) after basic assignment calibrated via quantitative .sup.13 C 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.

[0218] 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.

[0219] 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.

[0220] 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

[0221] The test described herein follows ISO 16790:2005.

[0222] 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 Sience, 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 Göttfert, Siemensstr.2, 74711 Buchen, Germany) in which a melt strand is elongated by drawing down with a defined acceleration.

[0223] 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/sec.sup.2. 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

[0224] 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

[0225] 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

[0226] 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

[0227] This has been measured according to ISO 845 using an analytical and semi-micro precision balance of Switzerland PRECISA Gravimetrics AG, Switzerland.

Cell Size Diameter of the Foam

[0228] The cell size diameter of the foam was determined using a light optical microscope of Tawain CBS Stereoscopic microscope;

[0229] The testing method used is as follows:

[0230] 1. Cut a strip of the foamed material along the cross direction (CD) and machine direction (MD).

[0231] 2. Hold the foamed material with a flat clamp and use a razor blade to perform a fine shave.

[0232] 3. Focus the microscope at 100× and adjust lighting onto the foamed material.

[0233] 4. Perform length and width measurements of each unique cell in the CD and MD orientation and record values.

[0234] 5. Count the number of measured unique cells and record the values.

[0235] 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.

[0236] 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.

[0237] 8. Perform an overall length measurement starting from the lowest complete cell to the highest complete cell.

[0238] 9. Move microscope visual field so the bottom of the most upper incomplete cell is touching the bottom of the screen.

[0239] 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

[0240] 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.

Compressive Strength

[0241] The compressive strengths at 25% and 40% are determined according to ISO3386-1 at 25% without pre-compression cycles [0].

Recoverability

[0242] The recoverability is determined on a 50×5 mm area specimen, which was cut and plied 6 layers high. The plied sample was measured for initial thickness and then compressed to 50% of its thickness under the Zwick Universal Testing Machine at a preload of 10N at a constant speed of 50 mm/min. The test was performed in normal lab environment set at 23+/−5° C. and 50+/−5% RH. The load was removed immediately and the sample allowed to recover for 5 minutes. The final thickness was then re-measured. The % recoverability was calculated by the following equation:

% recoverability=(final thickness×100)/initial thickness

Open Cell Content

[0243] The open cell content was determined according to ASTM D6226.

Tensile Strength and Elongation

[0244] The tensile strength and elongation in machine direction (MD) and cross direction (CD) was determined according to ISO 1798.

Flexural Force Maximum, Flexural Strain at Force Maximum, Flexural E-modulus, Flexural Toughness

[0245] The Flexural force maximum, flexural strain at force maximum, flexural E-modulus, flexural toughness in machine direction (MD) and cross direction (CD) was determined according to ISO 178.

Water Absorption

[0246] The water absorption (weight gain) was determined according to ASTM D1056.

Thermal Stability The thermal stability was determined by exposure to 70° C. for 24 hours according to ASTM D3575 suffix S.

Inventive Example 1 (IE1)

[0247] Preparation of a foamed sheet was carried out as follows: [0248] 1. dry-blending 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 A G (HMS-PP), and of talc in a weight ratio of Daploy™ WB140HMS/talc of 90:10; [0249] 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; [0250] 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; [0251] 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; [0252] 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 95.5 kg/m.sup.3 and a thickness of 3.0 mm.

Inventive Example 2 (IE2)

[0253] The procedure of inventive example 1 was repeated except that the density of the foamed sheet in step 5 was 200.6 kg/m.sup.3.

Inventive Example 3 (IE3)

[0254] The procedure of inventive example 1 was repeated except that the density of the foamed sheet in step 5 was 285.5 kg/m.sup.3.

Comparative Example 1 (CE1)

[0255] A foamed sheet of polyethylene was prepared as follows: [0256] 1. dry-blending of LD 1925 AS of Tasnee (LDPE), Plastron GMS 50 of Plastron SAS (GMS) and of talc in a weight ratio of LDPE/GMS/talc of 95:3:2; [0257] 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 185° C. (5 heating zones: 150° C.; 165° C.; 175° C.; 185° C.; 185° C.) so as to melt the polymer; [0258] 3. injecting of 8 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; [0259] 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 100° C. at the end of the 2.sup.nd single screw extruder; [0260] 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 30.6 kg/m.sup.3 and a thickness of 13 mm.

Comparative Example 2 (CE2)

[0261] The procedure of comparative example 1 was repeated except that the sheet thickness was 3 mm and the density of the foamed material was 14.4 kg/m.sup.3.

Comparative Example 3 (CE3)

[0262] A foamed sheet of polystyrene was prepared as follows: [0263] 1. dry-blending of Styrolution PS 168 N/L of Ineos (GPPS), and of talc in a weight ratio of Styrolution PS 168 N/L/talc of 98:2; [0264] 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; [0265] 3. injecting of 8 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; [0266] 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 110° C. at the end of the 2.sup.nd single screw extruder; [0267] 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 52.6 kg/m.sup.3 and a thickness of 3 mm.

Comparative Example 4 (CE4)

[0268] The procedure of comparative example 3 was repeated except that the sheet thickness was 5 mm and the density of the foamed material was 72.2 kg/m.sup.3.

[0269] The results for inventive examples IE1, IE2 and IE3 as well as comparative examples CE1, CE2, CE3 and CE4 are shown in the following table 1.

TABLE-US-00001 TABLE 1 results of the inventive and comparative examples HMS-PP foam PE foam PS foam unit IE1 IE2 IE3 CE1 CE2 CE3 CE4 sheet thickness mm 3 3 3 13 3 3 5 foam density kg/m.sup.3 95.5 200.6 285.5 30.6 14.4 52.6 72.2 open cell content % 25.5 7.6 9.9 41.3 79.6 2.7 80.7 tensile strength (MD) kPa 1804 3906 5122 322 352 1362 1581 tensile strength (CD) kPa 1513 4507 7202 208 166 1362 949 elongation (MD) % 33 21 19 107 81 3 3 elongation (CD) % 15 8 8 99 54 4 3 compressive strength at 25% kPa 214 873 1734 32.7 19.5 220.8 422.2 compressive strength at 40% kPa 338 1142 2282 56.4 51.4 275.5 546.3 Recoverability % 93.8 91.8 89.9 98.7 97.2 84.1 59.9 Flexural force max.(MD) N 5.7 12 14.7 7.8 0.1 6.3 19.7 Flexural force max. (CD) N 5 22 28.9 4.8 0 5.7 12.7 Flexural strain at force max.(MD) mm 17.2 20.3 20.4 22.5 23.5 8.6 6.4 Flexural strain at force max. (CD) mm 10.5 17.7 21.2 24.7 20.7 9.4 10.6 Flexural E-modulus (MD) MPa 79.7 182.2 230.4 2.2 2.1 121.3 121.1 Flexural E-modulus (CD) MPa 102.8 312.2 437.4 1.2 0.3 90 51.9 flexural toughness (MD) % 88 97 95 99.5 91.2 3 3 flexural toughness (CD) % 73 81 97 99.8 70.5 0.9 0.3 water absorption % 19.3 n.m. n.m. n.m. 126.1 7.7 761.3 change in length % −0.1 n.m. n.m. n.m. 0.3 −0.4 −0.1 change in width % −0.3 n.m. n.m. n.m. −4.0 −0.4 0.0 change in thickness % 3.9 n.m. n.m. n.m. −0.6 −0.2 −1.1 n.m. = not measured As can be seen from table 1 above, the inventive HMS-PP foam samples show excellent load bearing capacity which is comparable with the load bearing capacity of PS foams, expressed by comparable tensile strength and compressive strength. Furthermore, all samples have densities typically achieved for the corresponding kind of foam prepared. However, PS-foams have low recoverability whereas the HMS-PP foam of the present invention shows excellent recoverability, which is comparable with the PE foam. However, PE-foams do not have the load bearing capacity (measured as a compressive strength or tensile strength) of the foam of the present invention (or PS-foams). Thus, the HMS-PP foams of the present invention have a unique combination of properties.