Cross-linkable silicone composition for the production of non-stick coatings for flexible substrates and an attachment-promoting additive contained in said composition
The invention relates to cross-linkable or cross-linked silicone compositions that can be used, in particular, to form a non-stick water-repellent coating for flexible substrates, for example paper or similar, in the form of natural or synthetic polymer films.
1. A silicone composition A comprising a silicone base B capable of cross-linking or hardening by polyaddition, wherein said silicone composition comprises at least one cross-linking and attachment-promoting additive X comprising at least one polyorganosiloxane C consisting of the siloxyl units (I.1) to (I.3) having formulae:
Y
a
Z
b
1
SiO
4
-
(
a
+
b
)
2
(
I
.1
)
Z
c
2
SiO
4
-
c
2
(
I
.2
)
H
d
Z
e
3
SiO
4
-
(
d
+
e
)
2
(
I
.3
)
in which:
a=1 or 2, b=0, 1 or 2 and a+b=1, 2 or 3;
c=1, 2 or 3
d=1 or 2, e=0, 1 or 2 and d+e=1, 2 or 3
Y independently represents an epoxyfunctional hydrocarbon group;
Z 1 , Z 2 and Z 3 represent, independently of each other, a monovalent hydrocarbon group selected from the group consisting of alkyl groups having from 1 to 8 carbon atoms inclusive and aryl groups
said polyorganosiloxane C comprising, per molecule, at least one siloxyl unit (I.1) bearing epoxyfunctional hydrocarbon groups and at least three siloxyl units (I.3) bearing hydrogenosiloxyl groups, and
the content of siloxyl units (I.1) is less than or equal to 100 mmol per 100 g of polyorganosiloxane C.
2. The silicone composition A as claimed in claim 1 , wherein the content of siloxyl units (I.3) is less than or equal to 1.6 mol per 100 g of polyorganosiloxane C.
3. The silicone composition A as claimed in claim 1 , wherein a number N1 of siloxyl units (I.1) bearing epoxyfunctional hydrocarbon groups and a number N3 of siloxyl units (I.3) satisfy the following conditions:
1≦N1≦10, and
3≦N3≦20.
4. The silicone composition A as claimed in claim 1 , wherein the total number N of siloxyl units (I.1), (I.2) and (I.3) of the polyorganosiloxane C is from 3 to 25 inclusive.
5. The silicone composition A as claimed in claim 1 wherein said attachment-promoting additive X is a clear and homogeneous mixture which comprises, relative to the total weight of the additive X:
from 1 to 100 parts by weight of at least one polyorganosiloxane C, and
from 99 to 0 parts by weight of at least one cross-linking silicone oil D comprising per molecule at least three hydrogen atoms bonded to silicon.
6. The silicone composition A as claimed claim 1 , wherein said silicone base B comprises:
(A) at least one alkenylated polyorganosiloxane E comprising at least two siloxyl units (I.4) comprising formula:
W
a
Z
b
SiO
4
-
(
a
+
b
)
2
(
I
.4
)
in which:
a=1 or 2, b=0, 1 or 2 and a+b=1, 2 or 3;
W independently represents an alkenyl group and
Z independently represents a monovalent hydrocarbon group having from 1 to 30 carbon atoms,
(B) optionally at least one cross-linking silicone oil D′ comprising per molecule at least three hydrogen atoms bonded to silicon,
(C) at least one polyaddition catalyst F;
(D) optionally at least one cross-linking inhibitor G;
(E) optionally an adhesion modulating system H;
(F) optionally at least one diluent I;
(G) optionally at least one anti-misting additive J,
(H) optionally at least one polyorganosiloxane resin K, and
(I) optionally at least one nonfunctionalized polyorganosiloxane L having siloxyl units (I.5) of formula:
Z
a
1
SiO
4
-
a
2
(
I
.5
)
in which:
a=0, 1, 2 or 3,
Z 1 independently represents a monovalent hydrocarbon group having from 1 to 30 carbon atoms.
7. The silicone composition A as claimed in claim 1 , wherein the siloxyl unit (I.1), Y is selected from the group consisting of the groups (R-1) to (R-4) having formulae:
8. The silicone composition A as claimed in claim 7 , wherein in said siloxyl unit (I.1) Y is the group (R-4) having formula:
9. The silicone composition A as claimed in claim 1 , wherein quantities of constituents are such that a ≡SiH/≡SiAlkenyl molar ratio is from 1 to 7, with:
[SiH]=total number of mol of siloxyl units comprising a hydrogen atom bonded to silicon, and
[SiAlkenyl]=total number of mol of siloxyl units comprising an alkenyl radical bonded to silicon.
10. The silicone composition A as claimed in claim 1 , wherein the polyorganosiloxane C has a viscosity at 25° C. from 5 to 100 mPa·s.
11. A silicone elastomer which is obtained by the cross-linking and/or hardening of the silicone composition A according to claim 1 .
12. A process for producing a non-stick and water-repellent coating on a substrate, wherein said process comprises applying on at least one face of said substrate at least one layer of the silicone composition A as claimed in claim 1 , and ensuring said layer cross-links, optionally by activating said layer by heating.
13. A substrate comprising at least one non-stick and water-repellent coating obtained according to the process as described in claim 12 .
14. The substrate as claimed in claim 13 , wherein said substrate is a flexible substrate selected from the group consisting of paper, a polymer film of the polyolefin, polypropylene, polyethylene or polyester type, and a polymer film for protecting the adhesive face of a self adhesive or pressure-sensitive adhesive element.
15. A substrate comprising at least one non-stick and water-repellent coating obtained from a silicone composition A as claimed in claim 1 .
16. The silicone composition A as claimed in claim 1 , wherein Y independently represents an alkyl glycidyl ether; a linear, branched and/or cyclic epoxyalkyl; a linear, branched and/or cyclic epoxyalkenyl; or a carboxylic acid glycidyl ester.
17. The silicone composition A as claimed in claim 1 , wherein Z 1 , Z 2 and Z 3 , independently of each other are selected from the group consisting of a methyl, ethyl, propyl, 3,3,3-trifluoropropyl, ylyl, tolyl and phenyl radical.
18. The silicone composition A as claimed in claim 1 , wherein the content of siloxyl units (I.1) is from 20 to 80 mmol per 100 g of polyorganosiloxanes C.
19. The silicone composition A as claimed in claim 1 , wherein the content of siloxyl units (I.3) is from 0.1 to 1.5 mol per 100 g of polyorganosiloxane C.
20. The silicone composition A as claimed in claim 1 , which is free of solvent.