Cord having an improved adhesion promoting coating

1. A composite material comprising a cord embedded in a polymer material, said cord comprising a number of filaments twisted together, said cord being partially coated with an adhesion promoting coating configured to provide adhesion between said cord and said polymer material,

said cord comprising:

a core strand comprised of a plurality of core strand filaments, said core strand filaments being substantially free of said adhesion promoting coating; and

a plurality of peripheral strands arranged around said core strand, each of said peripheral strands being comprised of peripheral filaments and non-peripheral filaments, said peripheral filaments being coated with said adhesion promoting coating and said non-peripheral filaments being substantially free of said adhesion promoting coating,

said cord showing cross-sections in a plane perpendicular to an axis of said cord wherein two adjacent filaments define an interface zone, said interface zone being defined as a zone between adjacent filaments where a distance between said adjacent filaments is smallest,

said peripheral filaments having peripheral edges and non-peripheral edges, said peripheral edges of said peripheral filaments being defined as edges being part of an exterior surface of a peripheral strand and said non-peripheral edges of said peripheral filaments being defined as edges not being part of said exterior surface of said peripheral strand,

said peripheral edges of said peripheral filaments being coated with said adhesion promoting coating and said non-peripheral edges of said peripheral filaments being substantially free of said adhesion promoting coating,

said adhesion promoting coating having a thickness Tx at location x, the thickness Tx of said adhesion promoting coating in said interface zone of adjacent filaments is not higher than the thickness Tx of said adhesion promoting coating at a location of said exterior surface which is not in one of said interface zones of adjacent filaments,

said adhesion promoting coating comprising at least a first layer, said first layer comprising a silicon based coating, a titanium based coating, a zirconium based coating or a combination thereof, and

said first layer is an electrostatically-assisted-spray coating applied by electrostatically assisted spraying.

2. A composite material according to claim 1 , wherein three or more adjacent filaments in said cross-sections define a sub-structure, said sub-structure defining a void in the middle of said three or more filaments, said void being substantially free of said adhesion promoting coating.

3. A composite material according to claim 1 , wherein said silicon based coating is selected from the group consisting of silica based coatings and silane based coatings.

4. A composite material according to claim 1 , wherein said adhesion promoting coating further comprises a second layer, said second layer being deposited on said first layer and said second layer leaving said non-peripheral edges of said peripheral filaments substantially free of said adhesion promoting coating.

5. A composite material according to claim 4 , wherein said second layer of said adhesion promoting coating is selected from the group consisting of silane based coatings.

6. A composite material according to claim 5 , wherein said second layer is applied by electrostatically assisted spraying.

7. A composite material according to claim 1 , wherein said filaments are made of steel.

8. A composite material according to claim 2 , wherein said cord, said filaments, or a combination thereof are coated with a zinc or zinc alloy coating.

9. A method to manufacture a composite material as defined in claim 1 , said method comprising the steps of:

providing a cord, said cord comprising a core strand comprised of a plurality of core strand filaments, said core strand filaments being substantially free of adhesion promoting coating, and a plurality of peripheral strands arranged around said core strand, each of said peripheral strands being comprised of peripheral filaments and non-peripheral filaments, said peripheral filaments being coated with said adhesion promoting coating and said non-peripheral filaments being substantially free of said adhesion promoting coating, said cord showing cross-sections in a plane perpendicular to an axis of said cord, wherein two adjacent filaments define an interface zone, said interface zone being defined as the zone between adjacent filaments where the distance between said adjacent filaments is the smallest, said peripheral filaments having peripheral edges and non-peripheral edges, said peripheral edges of said peripheral filaments being defined as edges being part of an exterior surface of a peripheral strand and said non-peripheral edges of said peripheral filaments being defined as edges not being part of said exterior surface of said peripheral strand, and

applying on said cord a first layer of said adhesion promoting coating by electrostatically assisted spraying, said first layer comprising a silicon based coating, a titanium based coating, a zirconium based coating or a combination thereof, said adhesion promoting coating having a thickness Tx at location x,

wherein said peripheral edges of said peripheral filaments are coated with said adhesion promoting coating and said non-peripheral edges of said peripheral filaments are substantially free of said adhesion promoting coating, and

wherein the thickness Tx of said adhesion promoting coating in said interface zone of adjacent filaments is not higher than the thickness Tx of said adhesion promoting coating at a location of said peripheral edges which is not in an interface zone of adjacent filaments.

10. A method according to claim 9 , wherein said method comprises a further step of applying a second layer of an adhesion promoting coating on said first layer.

11. A composite material according to claim 1 , wherein the electrostatically assisted spraying comprises applying a static electricity charge to droplets of a spray of said first layer and an opposite charge to said cord such that the opposite charge of said cord attracts said droplets of said spray of said first layer directly to said peripheral edges of said peripheral filaments.

12. A composite material according to claim 1 , wherein a thickness of said adhesion promoting coating ranges from 5 nm to 5000 nm.

13. A composite material according to claim 1 , wherein said polymer material is selected from the group consisting of polyvinylchloride, polyurethane, polyethylene terephthalate, polypropylene, modified polypropylene and polyacrylate.

14. A composite material according to claim 1 , wherein said polymer material and said adhesion promoting coating are different materials.

15. A method according to claim 9 , wherein the electrostatically assisted spraying comprises applying a static electricity charge to droplets of a spray of said first layer and an opposite charge to said cord such that the opposite charge of said cord attracts said droplets of said spray of said first layer directly to said peripheral edges of said peripheral filaments.