CONDUCTIVE PLASTIC PRODUCT

Abstract

An electrically conductive plastic product is made via rotational moulding. The product comprises a plastic matrix; and a network of conductive fibers of discrete length embedded in the plastic matrix. The conductive fibers are metal fibers. The network of conductive fibers provides electrical conductivity to the plastic product. The average length of the conductive fibers is at least 3 mm.

Claims

1. Electrically conductive plastic product made via rotational moulding, comprising a plastic matrix; and a network of conductive fibers of discrete length embedded in the plastic matrix for providing electrical conductivity to the plastic product, wherein the conductive fibers are metal fibers; and wherein the average length of the conductive fibers is at least 3 mm.

2. Electrically conductive plastic product as in claim 1, wherein the average length of the conductive fibers is less than 25 mm.

3. Electrically conductive plastic product as in claim 1, wherein the plastic matrix is a thermoplastic matrix.

4. Electrically conductive plastics product as in claim 1, wherein the metal fibers are metal fibers out of a ferrous alloy, or are metal fibers out of a non-ferrous metal or alloy.

5. Electrically conductive plastic product as in claim 1, wherein the metal fibers have a cross section, wherein the cross section has two neighbouring straight lined sides with an included angle of less than 90° and one or more irregularly shaped curved sides.

6. Electrically conductive plastic product as in claim 1, wherein the metal fibers have a kidney or a banana shaped cross section.

7. Electrically conductive plastic product as in claim 1, wherein the metal fibers have an equivalent diameter less than 100 μm.

8. Electrically conductive plastic product as in claim 1, wherein the metal fibers have a length over equivalent diameter ratio of less than 300.

9. Electrically conductive plastic product as in claim 1, wherein the weight percentage of the conductive fibers in the plastic product is between 0.1 and 20%.

10. Mixture for use in rotational moulding of electrically conductive plastic products, wherein the mixture comprises a solid dispersion of conductive fibers of discrete length in a plastic powder; wherein the conductive fibers are metal fibers; and wherein the conductive fibers have an average length of at least 3 mm.

11. Mixture as in claim 10, wherein the weight percentage of the conductive fibers in the mixture is between 0.1 and 20%.

12. Method for producing an electrically conductive plastic product made via rotational moulding as in claim 1, comprising the steps of providing a mixture as in claim 10; introducing the mixture in a mould; performing a rotational moulding operation with the mould to convert the mixture into an electrically conductive plastic product.

13. Method as in claim 12, wherein the weight percentage of the conductive fibers in the mixture is between 0.1 and 20%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] FIG. 1 shows the cross section of a metal fiber that can be used in the invention.

[0034] FIG. 2 shows the cross section of an alternative metal fiber than can be used in the invention.

[0035] FIG. 3 shows the cross section of an electrically conductive plastic product according to the first aspect of the invention.

MODE(S) FOR CARRYING OUT THE INVENTION

[0036] In order to make samples, machined aluminium fibers of 65 μm equivalent diameter and 5.5 mm length have been made. Alternative machined aluminium fibers of 35 μm equivalent diameter and 3 mm length have been made. Such fibers have a cross section as is shown in FIG. 1. The cross section 100 has two neighbouring straight lined sides 110, 120 with an included angle less than 90° and one or more irregularly shaped curved sides 130. The fibers had been made according to the method as described in WO2014/048738A1.

[0037] An alternative kind of metal fibers that can be used, are metal fibers extracted from the melt, having a kidney or banana cross sectional shape 200, as shown in FIG. 2.

[0038] The machined aluminium fibers have been mixed with polyethylene powder, in the weight ratios of 5%, 10% and 17% of fibers to the total weight of the mixture of plastic powder and fibers. Thereby, a solid dispersion of the aluminium fibers in the polyethylene powder has been obtained. The mixture has been made with standard blending equipment used in the rotomoulding industry to mix powder additives with the thermoplastic powder.

[0039] Plastics products have been made by means of rotational moulding, using these mixtures. FIG. 3 shows the cross section 300 of boxes that have been made using rotational moulding. The products made had a wall thickness T of 4 mm. In the walls 340 of the box, a network of conductive fibers 350 of discrete length is embedded in the plastic matrix. The network of conductive fibers is created on the one hand thanks to the solid dispersion of conductive fibers and powder in the mixture, and on the other hand thanks to the rotational moulding process. The electrical conductivity has been measured on the outer surface of the plastic product. To this end, two circular probes with 5 mm diameter were used. One point on the plastic product was used as reference, and the electrical resistance was measured at several points on the outer surface of the plastic product relative to the reference point. The test results showed that the rotomoulded plastic products made had good conductivity levels (order of magnitude 10.sup.7 Ohm for the 5% fiber weight ratio sample; order of magnitude 10.sup.3-10.sup.4 Ohm for the 10% fiber weight ratio sample; order of magnitude 10.sup.3 Ohm for the 17% fiber weight ratio sample), such that for all samples excellent protection against electrical discharge (ESD) is obtained.