Foamed blow molded article

Abstract

The invention is directed to a blow molded article. The article comprises at least three layers wherein layer A comprises polymer, layer B comprises a foam composition comprising high density polyethylene having a quotient of melt strength and apparent viscosity>2 cN/k.Pa.s and layer C comprises polymer wherein the layer comprising the foam composition is enclosed between two layers A and C and wherein the melt strength is determined as described in ISO 16790:2005 and the apparent viscosity is determined as described in ISO 11443:2014 and wherein the foam composition is produced with a physically blowing agent.

Claims

1. A blow molded article characterised in that the article comprises at least three layers wherein layer A comprises polymer, layer B comprises a foam composition comprising high density polyethylene having a quotient of melt strength and apparent viscosity >3 cN/k.Pa.s and ≤30 cN/k.Pa.s, layer C comprises polymer, wherein the layer comprising the foam composition is enclosed between two layers A and C and wherein the melt strength is determined as described in ISO 16790:2005 and the apparent viscosity is determined as described in ISO 11443:2014 and wherein the foam composition is produced with a physically blowing agent; and wherein the melt strength of the high density polyethylene is ≥10 cN; and wherein the foam composition comprising high density polyethylene has been obtained by physical foaming high density polyethylene with characteristics MI in the range between ≥0.01 and ≤0.9, density in the range between ≥930 and ≤985 kg/m.sup.3, a gel fraction less than 5%, which has been obtained by chain branching high density polyethylene with characteristics MI in the range between ≥7 and ≤100, and density in the range between ≥930 and ≤985 kg/m.sup.3, wherein chain branching is performed by irradiation.

2. Article according to claim 1 characterised in that the density of the high density polyethylene foam layer B ranges between ≥100 and ≤600 kg/m.sup.3.

3. Article according to claim 1 characterised in that the high density polyethylene foam composition has been obtained by physical foaming high density polyethylene with characteristics MI in the range between ≥0.1 and ≤0.9, density in the range between ≥935 and ≤970 kg/m.sup.3, a gel fraction less than 5%, which has been obtained by chain branching high density polyethylene with characteristics MI in the range between ≥10 and ≤100, and density in the range between ≥935 and ≤970 kg/m.sup.3.

4. Article according to claim 3 characterised in that the high density polyethylene foam composition has been obtained by physical foaming high density polyethylene with characteristics MI in the range between ≥0.1 and ≤0.9, density in the range between ≥940 and ≤970 kg/m.sup.3, a gel fraction less than 3%, which has been obtained by chain branching high density polyethylene with characteristics MI in the range between ≥12 and ≤50, and density in the range between ≥940 and ≤970 kg/m.sup.3.

5. Article according to claim 1 characterised in that the foam has more than 90% closed cells.

6. Article according to claim 1 characterised in that the polymer in layer A and the polymer in layer C is polyolefin.

7. Article according to claim 6 characterised in that the polyolefin is high density polyethylene.

8. Article according to claim 1 characterised in that the article contains three layers.

9. Article according to claim 8 characterised in that the blow molded article is a bottle, container, air duct or fuel tank.

10. The article of claim 1, wherein the foam composition is essentially free of residual chemical blowing agents.

11. The article of claim 10, wherein the foam composition is essentially free of reaction-by-products of chemical blowing agents.

12. The article of claim 1, wherein the foam composition is free of residual chemical blowing agents and reaction-by-products of chemical blowing agents.

13. The article of claim 1, wherein the foam composition comprises high density polyethylene having a quotient of melt strength and apparent viscosity >5 cN/k.Pa.s and ≤30 cN/k.Pa.s.

14. Bottle comprising at least three layers wherein layer A comprises polymer, layer B comprises a foam composition comprising high density polyethylene having a quotient of melt strength and apparent viscosity >3 cN/k.Pa.s and ≤30 cN/k.Pa.s, layer C comprises polymer, wherein the layer comprising the foam composition is enclosed between two layers A and C and wherein the melt strength is determined as described in ISO 16790:2005 and the apparent viscosity is determined as described in ISO 11443:2014 and wherein the foam composition is produced with a physically blowing agent; and wherein the melt strength of the high density polyethylene is ≥10 cN, and wherein the foam composition comprising high density polyethylene has been obtained by physical foaming high density polyethylene with characteristics MI in the range between ≥0.01 and ≤0.9, density in the range between ≥930 and ≤985 kg/m.sup.3, a gel fraction less than 5%, which has been obtained by chain branching high density polyethylene with characteristics MI in the range between ≥7 and ≤100, and density in the range between ≥930 and ≤985 kg/m.sup.3, wherein chain branching is performed by irradiation.

15. The bottle of claim 14, wherein layer B is a foam having more than 90% closed cells.

16. The bottle of claim 14, wherein a ratio between a thickness of the foam layer (B) and a total thickness of the bottle is between 0.4-0.9, and the polymer in layer (A) and layer (C) is each independently a high density polyethylene.

Description

EXAMPLES

(1) Electron beam irradiation of HDPE granules was carried out at using a 10 MeV Rhodotron. In order to improve the homogeneity of irradiation dose, HDPE was packed into bags of 600×450×100 mm.sup.3 containing 12.5 kg HDPE granules. The 100 mm thick bags were radiated with the target irradiation dose on two sides in order to further improve the homogeneity of the irradiation dose. The irradiated HDPE was characterized by the following measurements:

(2) The melt strength was measured according ISO 16790:2005 using a Göttfert Rheograph 6000 in combination with a Rheotens 71.97. The equipment specifications are: Oven diameter of 12 mm. Capillary 40/2 (I/d), length 40 mm, diameter 2 mm, entrance angle 180° (flat). Pressure transducer: max 200 bar.

(3) The test conditions were as follows: the rheograph was filled in less than one minute and the sample preheating time was 300 seconds. The measuring temperature was 190° C. The speed of the piston was 0.049 mm/s corresponding to a throughput of 5.5 mm.sup.3/s and apparent shear-rate of 7s.sup.−1. The drawing device (Rheotens 71.97) was operated at an acceleration of 1.2 mm/s.sup.2 and a velocity of 1.8 mm/s. The melt strength is expressed in cN.

(4) The apparent viscosity was measured according ISO11443:2014 using the Göttfert Rheograph 6000 and the test: conditions being described for the determination of the melt strength. The apparent viscosity is defined as the quotient of the apparent shear stress and the apparent shear rate being 7 s.sup.−1. The apparent shear stress is calculated from pressure drop [kPa] times the capillary diameter in mm divided by 4 times the length of the capillary in mm. The apparent shear rate (1/s) is calculated from the throughput (mm/s) divided by 6.28 times the Diameter (mm) to the power of 3. The apparent viscosity is usually expressed in kPa.s.

(5) The melt index was measured according IS01133-1:2011 at a temperature of 190° C. and at 2.16 kg.

(6) The density of the compression molded HDPE disks was measured at a temperature of 23° C. according to ISO1183-1:2012 after at least one day of conditioning.

(7) The gel content of irradiated polyethylene was determined according to ASTM D2765-11. The samples were extracted for 12 hours in o-xylene with 1% anti-oxidant. The xylene insoluble fraction was determined gravimetrically.

(8) SABIC HDPE type CC2056 with a melt index of 19.6 (190 C, 2.16 kg) is used as a raw material. Table 1 and Table 2 show characteristics of electron beam irradiated HDPE (HDPE I) as compared to the values for unmodified HDPE (HDPE A)

(9) TABLE-US-00001 TABLE 1 Characteristics of electron beam irradiated HDPE Irradiation dose Melt index Density Gel fraction HDPE resin kGy 90° C., 2.16 kg) kg/m.sup.3 % HDPE I 30 0.6 953 1.2 HDPE A 0 20 956 n.a.

(10) TABLE-US-00002 TABLE 2 Melt strength and apparent viscosity of electron beam irradiated HDPE Ratio between Melt Apparent melt strength and HDPE Irradiation strength viscosity apparent viscosity resin dosis kGy cN kPa .Math. s cN/kPa .Math. s HDPE I 30 21.7 3.3 6.6 HDPE A 0 0.3 0.4 0.7
Foam blow molding of modified and unmodified HDPE was carried out on a blow molding machine with three extruders in combination with a three-layer extrusion head and a dynamic mixer with gas dosing between the extruder and the extrusion head. The main extruder for the middle layer was a 60/25 D extruder and the extruders for the outer layers where a 30/25 D and a 25/25 D extruder. Multi-layer bottles have been produced with a volume of 100-200 ml. Talc was added as a nucleating agent. Nitrogen is used as physical blowing agent. Table 3 and Table 4 provide information with respect to additives and machine settings.

(11) TABLE-US-00003 TABLE 3 Nucleating agent and blowing agent. Commercial name Chemical name Master batch Schulman Talc 50% in LDPE Nucleating PBHFPE50T agent N.sub.2 Nitrogen — Blowing agent

(12) TABLE-US-00004 TABLE 4 Machine settings for blow molding foaming. Example Example Comparative Parameter Unit I II Example A Layer A HDPE Type HDPE I HDPE I HDPE A Layer B HDPE type HDPE I HDPE I HDPE A Talc weight 4 8 8 (masterbatch) % Nitrogen weight 0.23 0.34 0.23 % Layer C HDPE Type HDPE I HDPE I HDPE A Extruder Throughput kg/h 7.2 7.2 3.6 Temperature ° C. 225 225 225 Die Entrance ° C. 135 135 140 Temperature Exit ° C. 120 120 145 Temperature Mold Temperature ° C Ambient Ambient Ambient Cycle time s 12 12 12
The total density of the foam blow molded samples was determined by the immersion method, also referred to as Archimedes method. The density is expressed in kg/m.sup.3. The density of the foamed core was calculated using the following equation:

(13) $\mathrm{density}\mathrm{of}\mathrm{foam}\mathrm{core}=\frac{\mathrm{total}\mathrm{density}-\left(\mathrm{fraction}\mathrm{skin}\times \mathrm{density}\mathrm{skin}\right)}{1-\mathrm{fraction}\mathrm{skin}}$
Total density is density of the three layer foam blow molded bottle (skins+core), The density of skin is assumed to be similar to the density of compact HDPE being 950 kg/m.sup.3.

(14) The open cell content was determined using a gas pycnometer. Samples of the foam blow molded bottles were taken being 5-10 gram in weight. The volume changes were measured at different nitrogen pressures. The open cell content was determined by extrapolation to atmospheric pressure,

(15) The cellular morphology of the HDPE foams was visualized using scanning electron microscopy. Each sample was frozen with liquid nitrogen and fractured. The fractured surface was made conductive by sputtering deposition of gold and observed using a Jeol JSM-820 operating at 20 kV. The microstructure of the materials has been studied in one plane (machine direction, thickness direction). Three micrographs were taken with a magnification of ×30. The cell size was calculated using an image processing tool based on the software Image J. The fraction skin is defined as the quotient of the thickness of the two skins and the total thickness.

(16) The flexural properties of the foam blow molded samples were determined using ISO 178:2010 as a guideline. Five tests per sample were conducted,

(17) A sample width of 10 mm and a length of 80 mm was used, Following testing conditions were applied:

(18) TABLE-US-00005 Support distance 50.65 mm Testing speed 2 mm/min Modulus between 0.05 and 0.25% strain Temperature 23° C.

(19) The flexural rigidity (F) is defined as the product of the modulus (E) by the moment of inertia (I). The moment of inertia (I=width×thickness.sup.3/12) is influenced by the construction of the specific test specimen, whereas the modulus is a material property. In order to compare samples correctly, the thickness used to determine the moment of inertia (I) is corrected for the weight of the bottle assuming a linear relationship between the weight of the bottle and its thickness. The flexural rigidity (F) is calculated using the following formula:

(20) $\mathrm{Flexural}\mathrm{rigidity}\left(E.I\right)=\mathrm{flexural}\mathrm{modulus}\left(E\right)\times \frac{\mathrm{width}\times {\mathrm{thickness}}^3}{12}$

(21) TABLE-US-00006 TABLE 5 Structural and mechanical properties of three layer foam blow molded bottles with a weight of 13 gram as well as a compact bottle with the same weight Example Example Comparative Compact Parameter Unit I II Example A bottle Total density kg/m.sup.3 513 491 779 950 Density foam kg/m.sup.3 421 432 714 n.a. layer Open cell % 3 4 64 n.a. content Cell size μm 115 88 69 n.a. Foam thickness/ 0.83 0.88 0.72 n.a. Total thickness Thickness μm 0.89 1.09 0.59 0.47 Flexural N/mm.sup.2 554 376 773 1023 modulus Flexural N .Math. mm.sup.2 327 406 133 89 rigidity (E.I)