Type II photoinitiator system and method for crosslinking silicone compositions

1. A silicone composition C that is crosslinkable by exposure to radiation with a wavelength between 200 nm and 450 nm, comprises:

at least one radical photoinitiator A;

at least one co-initiator B chosen from compounds comprising at least one hydrogen atom bonded to a silicon atom; and

at least one organopolysiloxane D comprising at least one (meth)acrylate group;

wherein the co-initiator B comprises at least 0.05 mole of functions Si—H per 100 g of co-initiator B; and

the ratio between the number of moles of radical photoinitiator A and the number of moles of Si—H functions of co-initiator B is greater than or equal to 0.5.

2. The composition C according to claim 1 , wherein the co-initiator B comprises at least one siloxane bond and at least one hydrogen atom bonded to a silicon atom.

3. The composition according to claim 1 , wherein the co-initiator B is chosen from organohydrogenpolysiloxanes.

4. The composition C according to claim 1 , wherein the co-initiator B comprises at least 0.08 moles of Si—H functions per 100 g of co-initiator B.

5. The composition C according to claim 1 , wherein the radical photoinitiator A is selected from the group consisting of benzophenone and its derivatives, thioxanthone and its derivatives, anthraquinone and its derivatives, the esters of benzoyl formate, camphorquinone, benzil, phenanthrenequinone, coumarins and cetocoumarins, and mixtures thereof.

6. The composition C according to claim 1 , wherein the radical photoinitiator A is benzophenone.

7. The composition C according to claim 1 , wherein the organopolysiloxane D comprises:

a1) at least one unit of formula (I) below:

R a Z b SiO (4−a−b)/2   (I)

in which:

the symbols R, which are identical or different, each represent a linear or branched C 1 -C 18 alkyl group, a C 6 -C 12 aryl or aralkyl group, optionally substituted, preferably with halogen atoms, or an alkoxy —OR 4 radical; wherein R 4 is a hydrogen atom or a hydrocarbon radical comprising from 1 to 10 carbon atoms,

the symbols Z are monovalent radicals of formula -y-(Y′)n in which:

y represents a linear or branched C 1 -C 18 alkylene polyvalent radical optionally extended by bivalent oxyalkylene or C 1 -C 4 polyoxyalkylene radicals optionally substituted by a hydroxyl radical,

Y′ represents a monovalent alkenylcarbonyloxy radical, and

n is 1, 2 or 3, and

a is an integer equal to 0, 1 or 2, b is an integer equal to 1 or 2 and the sum a+b=1, 2 or 3; and

a2) optionally units of the following formula (II):

R a SiO (4−a)/2   (II)

in which:

the symbols R, which are identical or different, each represent a linear or branched C 1 -C 18 alkyl group, a C 6 -C 12 aryl or aralkyl group, optionally substituted, preferably with halogen atoms, and

a is an integer equal to 0, 1, 2 or 3.

8. The composition C according to claim 1 , wherein the ratio between the number of moles of radical photoinitiator A and the number of moles of Si—H functions of co-initiator B is between 0.5 and 20.

9. The composition C according to claim 1 , wherein the concentration of Si—H functions is less than or equal to 0.01 mol per 100 g of composition C.

10. The composition C according to claim 1 , wherein the concentration of radical photoinitiator A is between 0.0003 and 0.015 mole per 100 g of composition C.

11. A silicone elastomer obtained by crosslinking a composition C according to claim 1 .

12. A method for preparing silicone films with non-stick properties, comprising a step of crosslinking a composition C according to claim 1 .

13. The method according to claim 12 , wherein the crosslinking step is carried out under an air or inert atmosphere.

14. The method according to claim 12 , wherein the crosslinking step is carried out by exposure to radiation with a wavelength between 200 nm and 450 nm.

15. The method for preparing a coating on a substrate, comprising the steps of:

the application of a composition C on a substrate according to claim 1 , and

the crosslinking of the composition by exposure to radiation with a wavelength between 200 nm and 450 nm.

16. A coated substrate obtainable by the method according to claim 15 .

17. The composition C according to claim 1 , wherein the concentration of Si—H functions is between 0.0002 and 0.01 mol per 100 g of composition C.

18. The composition C according to claim 1 , wherein the ratio between the number of moles of radical photoinitiator A and the number of moles of Si—H functions of co-initiator B is between 1 and 10.