Process for producing mono-rotomoulded articles prepared from blends comprising polyethylene

Abstract

The present invention discloses a single layer rotomolded article prepared from a blend of polyethylene, functionalized polyolefin and one or more resins selected from polyetherester or saturated polyester or polycarbonate or polyamide.

Claims

1. A process for producing a mono-layer rotomoulded article comprising: rotomoulding a blend of: from 10 to 99.9 wt % of polyethylene; from 0.1 to 90 wt % of a polyether-block co-polyamide; and from 0 to 20 wt % of functionalised polyolefin.

2. The process of claim 1, wherein, prior to rotomoulding the blend, the blend is prepared by coextruding the polyethylene, the polyether-block co-polyamide, and optionally the functionalised polyolefin to obtain the blend in the form of pellets.

3. The process of claim 2, further comprising grinding the pellets into powder or micropellets prior to the rotomoulding.

4. The process of claim 1, wherein the blend is manually introduced during the moulding cycle.

5. The process of claim 1, wherein the blend is placed in a drop-box, and wherein the blend is released into the mould from the drop-box during the moulding cycle.

6. The process of claim 1, wherein the blend comprises: from 50 to 99.9 wt % of the polyethylene; from 0.1 to 50 wt % of the polyether-block co-polyamide; and from 0.5 to 20 wt % of the functionalised polyolefin, wherein the total of all components cannot exceed 100% of the blend.

7. The process of claim 1, wherein the blend comprises at least 75 wt % of a metallocene-produced polyethylene.

8. The process of claim 7, wherein the metallocene-produced polyethylene is produced in the presence of bis(tetrahydroindenyl) or bis(n-butyl-cyclopentadienyl).

9. The process of claim 1, wherein the functionalised polyolefin is a grafted polyethylene or an ionomer or a mixture thereof.

10. The process of claim 1, wherein the blend further comprises a minor component, wherein the minor component is selected from the group consisting of polyetherester, thermoplastic polyurethane and fluoropolymer.

11. The process of claim 10, wherein the minor component is a fluoropolymer, and wherein the fluoropolymer is a copolymer of vinylidene fluoride or a copolymer of vinylidene fluoride and hexafluoropropylene.

12. The process of claim 1, wherein the polyethylene exhibits a melt index ranging from 0.1 to 25 dg/min.

13. The process of claim 1, wherein the polyethylene exhibits a density ranging from 0.910 to 0.975 g/ml.

14. The process of claim 1, wherein the polyethylene exhibits bimodal or multimodal molecular weight distribution.

15. The process of claim 1, wherein the polyethylene exhibits a polydispersity ranging from 2 to 20.

Description

LIST OF FIGURES

(1) FIG. 1 represents the microstructure of a rotomoulded article prepared from a blend of 77 wt % of polyethylene, 3 wt % of graphted polyethylene and 20 wt % of Pebax 3533.

(2) FIG. 2 represents the microstructure of a rotomoulded article prepared from the same polyethylene as that used in the blend of FIG. 1, used alone.

(3) FIG. 3 represents the impact strength expressed in Newtons as a function of time expressed in ms, and where peak energy is marked by P. The deformation of the article as a function of time is also indicated on the graph.

EXAMPLES

(4) Several rotomoulded articles were prepared as follows.

(5) Different blends were prepared by coextrusion.

(6) They consisted of: 77 wt % of polyethylene produced with a metallocene catalyst system based on ethylene-bis-tetrahydro-indenyl zirconium dichloride and having a melt flow index MI2 of 4 dg/min and a density of 0.940 g/cm.sup.3; 3 wt % of grafted polyethylene represented by

(7) ##STR00001##
and having a melt flow index MI2 of 25 dg/min and a density of 0.940 g/cm.sup.3; and 20 wt % of Pebax 3533 having hydrophobic properties or of Pebax MH 1657 having hydrophilic properties.

(8) In another blend, the 3 wt % of grafted polyethylene were replaced by ionomer

(9) ##STR00002##

(10) The blends were produced either as micropellets or as powder obtained by grinding standard pellets.

(11) The Pebax that was used in the blend has a much lower Young's modulus than polyethylene and is a plasticiser.

(12) All test mouldings were carried out on the ROTOSPEED rotational moulding machine. It is a carrousel-style machine with offset arm, LPG burner arm with a burner capacity of 523 kW/hr, air fan cooling, and a maximum plate diameter of 1.5 m.

(13) An aluminum box mould was used to produce the test mouldings. The mould was equipped with a draft angle to facilitate demoulding and the bi-layer articles were prepared by the use of a drop box. The drop box was filled with the material needed for the first layer and then attached to the lid of the mould. A pneumatic ram in the drop box held the material in place until the required temperature was reached, the ram was then activated and the material was dropped in. That operation was repeated for each layer under the conditions described below.

(14) The moulding conditions for the trials were as follows: oven temperature: 300 C. peak internal air temperature (PIAT): 200 C. cooling medium: forced air preheated arm and mould cycle time: 20 minutes wall thickness of rotomoulded parts: 1.5 mm.

(15) The rotomoulded articles had an excellent homogeneity and the Pebax was perfectly dispersed into the finished article as can be seen on FIG. 1: this result is quite surprising as Pebax is known to be difficult to disperse. In addition, as can be seen on the same FIG. 1, the microstructure is very fine, much finer than that of typical polyethylene displayed on FIG. 2. This confers excellent mechanical properties to the finished articles.

(16) The impact properties of the rotomoulded articles were measured using the method of standard test ISO 6602-3 at a temperature of 40 C. and using a falling mass of 26.024 kg, a speed of the falling mass of 4.43 m/s and an impact energy of 255 J. All tests showed a ductile behaviour as can be seen on FIG. 3.