Composition

1. A coating layer containing a particulate coating composition, the particulate coating composition comprising:

(i) at least one polyester polymer present in the particulate coating composition in an amount of from 30% wt % to 80 wt % of the particulate coating composition;

(ii) at least one hardener present in the particulate coating composition in an amount of from 30% wt % to 80 wt % of the particulate coating composition;

(iii) at least one metallic pigment present in the particulate coating composition in an amount of at least 0.1 wt % of the particulate coating composition, wherein said metallic pigment comprises metal in elemental form or as an ahoy and is not a metal salt; and

(iv) at least one polyorganosiloxane

wherein the coating layer is a single layer coating or a top coat.

2. A coating layer as claimed in claim 1 , wherein said metallic pigment is corrodible.

3. A coating layer as claimed in claim 1 , wherein said metallic pigment comprises Al or Sn.

4. A coating layer as claimed in claim 1 , wherein said polyorganosiloxane has a softening temperature of at least 40° C.

5. A coating layer as claimed in claim 1 , wherein said polyorganosiloxane comprises OH and/or OR substituents, wherein R is C 1-24 alkyl or C 6-24 aryl.

6. A coating layer as claimed in claim 1 , wherein said polyorganosiloxane comprises 1.0-15 wt % of OH groups, based on the total weight of the polyorganosiloxane.

7. A coating layer claimed in claim 1 , wherein said polyorganosiloxane comprises a repeat unit of formula (I):

wherein

each R 1 is independently a monovalent organic group;

each X is independently OH, OR′ or O—;

each R′ is independently C 1-24 alkyl or C 6-24 aryl; and

a is 0 or 1.

8. A coating layer claimed in claim 1 , wherein said polyorganosiloxane is of the general formula (III):

M m D n T o Q p   (III)

wherein

M is a terminal group of the general formula (IIIa)

R 3 R 4 R 5 SiO 1/2   (IIIa),

is a Bifunctional group of the general formula (IIIb)

R 6 R 7 SiO 2/2   (IIIb),

T is a trifunctional group of the general formula (IIIc)

R 8 SiO 3/2   (IIIc),

Q is a unit of the general formula SiO 4/2 ,

where each of R 3 , R 4 , R 5 , R 6 , R 7 and R 8 is independently selected from a monovalent organic group, a hydroxyl group or an alkoxy group comprising 1 to 10 C, wherein no more than 75% of all of the groups are hydroxyl or alkoxy,

m is an integer 0-20,

n is an integer 0-1000,

is an integer 0-30,

p is an integer 0-20, and

m+n+o+p is an integer which is at least 2.

9. A coating layer as claimed in claim 1 , wherein said polyorganosiloxane is a silsesquioxane.

10. A coating layer as claimed in claim 1 , further comprising a silane, a metal phosphate, a metal borate and/or an amino alcohol.

11. A coating layer as claimed in claim 10 , comprising an amino alcohol.

12. A coating layer as claimed in claim 11 , wherein said amino alcohol has one amine group and 2 or more hydroxyl groups.

13. A coating layer as claimed in claim 10 , comprising a metal phosphate.

14. A coating layer as claimed in claim 13 , wherein said metal phosphate is an ortho-phosphate.

15. A kit comprising:

(i) a first container containing at least one polyester polymer, at least one hardener, and at least one polyorganosiloxane;

(ii) a second container containing at least 0.1 wt % of said at least one metallic pigment, based on the total weight of contents of the containers of the kit, wherein said metallic pigment comprises metal in elemental form or as an alloy and is not a metal salt; and

(iii) instructions for mixing the at least one polyester polymer, at least one hardener, at least one polyorganosiloxane and at least one metallic pigment to form a single coating layer or a top coat containing a particulate coating composition, wherein

the at least one polyester polymer is present in the particulate coating composition in an amount of from 30% wt % to 80 wt % of the particulate coating composition;

the at least one hardener is present in the particulate coating composition in an amount of from 30% to 80 wt % of the particulate coating composition; and

the at least one metallic pigment is present in the particulate coating composition in an amount of at least 0.1 wt % of the particulate coating composition.

16. A process for preparing a coating layer as claimed in claim 1 , comprising:

(i) blending the at least one polyester polymer, the at least one hardener, and the least one polyorganosiloxane to form a mixture;

(ii) extruding said mixture to form particles; and

(iii) adding the at least one metallic pigment to the particles.

17. A substrate coated with a single layer coating or a top coat as claimed in claim 1 .

18. A coating layer as claimed in claim 1 , wherein the particulate coating composition is a powder coating composition.