Silicone Release Coating Compositions

• US 20100255205A1
• Filed: 08/02/2007
• Published: 10/07/2010
• Est. Priority Date: 08/14/2006
• Status: Active Grant

• Current Assignee: Dow Silicones Corporation (Dow, Inc.)
• Original Assignee: Dow, Inc.
• Inventors: Thibaut, Marc, Rich, David, Cray, Stephen, Habimana, Jean De La Croix
• Granted Patent: US 9,562,149 B2
• Time in Patent Office: Days
• US Class Current: 427/386
• CPC Class Codes: C08K 5/541 containing oxygen
• CPC Class Codes: C08L 83/00 Compositions of macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon only; Compositions of derivatives of such polymers
• CPC Class Codes: C08L 83/04 Polysiloxanes
• CPC Class Codes: C08L 83/06 containing silicon bound to oxygen-containing groups C08L83/12 takes precedence
• CPC Class Codes: C09D 183/06 containing silicon bound to oxygen-containing groups C09D183/12 takes precedence

Abstract

A release coating composition is prepared comprising a polyorganosiloxane (A) having alkenyl groups, a crosslinking agent (B) having organohydrogensiloxane groups, a catalyst for the hydrosilylation reaction between (A) and (B), and an anchorage additive for enhancing the adhesion of the composition to a polymer film substrate. The anchorage additive is the reaction product of a fluid polyorganosiloxane (C) containing at least one alkenyl group and at least one silanol group with a hydrolysable silane (D) containing at least one epoxide group. The curable silicone release coating composition can be applied to a substrate known as a ‘liner’ retaining a label, which liner can for example be paper or a polymer film, and cured.

Claims

1. A release coating composition comprising a polyorganosiloxane (A) having alkenyl groups, a crosslinking agent (B) having organohydrogensiloxane groups, a catalyst for the hydrosilylation reaction between (A) and (B), and an anchorage additive for enhancing the adhesion of the composition to a polymer film substrate, characterised in that the anchorage additive is the reaction product of a fluid polyorganosiloxane (C) containing at least one alkenyl group and at least one silanol group with a hydrolysable silane (D) containing at least one epoxide group.

2. A release coating composition according to claim 1, characterised in that the polyorganosiloxane (C) has a degree of polymerisation of at 4 to 50 siloxane units.

3. A release coating composition according to claim 1, characterised in that the polyorganosiloxane (C) is a polydiorganosiloxane having terminal silanol groups.

4. A release coating composition according to claim 3, characterised in that the polyorganosiloxane (C) is a copolymer of methylvinylsiloxane units and dimethylsiloxane units.

5. A release coating composition according to claim 1, characterised in that the silane (D) comprises an (epoxy-substituted alkyl) di or trialkoxy silane.

6. A release coating composition according to claim 1, characterised in that the epoxide groups in the silane (D) are present as glycidyl groups.

7. A release coating composition according to claim 1, characterised in that the epoxide groups in the silane (D) are epoxycyclohexyl groups.

8. A release coating composition according to claim 1, characterised in that the fluid polyorganosiloxane (C) and hydrolysable silane (D) are reacted in a weight ratio in the range 10:

90 to 90;

10.

9. A release coating composition according to claim 1, characterised in that the anchorage additive is the reaction product of the polyorganosiloxane (C), the silane (D) and a di(hydrocarbyl)dialkoxysilane in which each hydrocarbyl group is selected from alkyl and alkenyl groups.

10. A release coating composition according to claim 1, characterised in that the polyorganosiloxane (A) is a branched siloxane comprising one or more Q units of the formula (SiO_4/2), from 15 to 995 D units of the formula R^b2SiO2_/2 and M units of the formula R^aR^b₂SiO_1/2, wherein the R^a and R^b substituents are selected from alkyl and alkenyl groups having 1 to 6 carbon atoms, at least three R^a substituents in the branched siloxane being alkenyl units.

11. A release coating composition according to claim 1, characterised in that the composition further contains a cure inhibitor selected from ethylenically or aromatically unsaturated amides, acetylenic compounds, ethylenically unsaturated isocyanates, olefinic siloxanes, unsaturated hydrocarbon diesters, conjugated ene-ynes, hydroperoxides, nitriles and diaziridines.

12. A release coating composition according to claim 1, characterised in that the anchorage additive is present at 0.5 to 10% by weight of the release coating composition.

15. A release coating composition according to claim 2, characterised in that the polyorganosiloxane (C) is a polydiorganosiloxane having terminal silanol groups.

16. A release coating composition according to claim 15, characterised in that the polyorganosiloxane (C) is a copolymer of methylvinylsiloxane units and dimethylsiloxane units.

17. A release coating composition according to claim 2, characterised in that the silane (D) comprises an (epoxy-substituted alkyl) di or trialkoxy silane.

18. A release coating composition according to claim 2, characterised in that the epoxide groups in the silane (D) are present as glycidyl groups.

19. A release coating composition according to claim 2, characterised in that the epoxide groups in the silane (D) are epoxycyclohexyl groups.

13. A process for providing a release coating to a polymer film comprising applying to the polymer film a composition comprising a polyorganosiloxane (A) having alkenyl groups, a crosslinking agent (B) having organohydrogensiloxane groups, a catalyst for the hydrosilylation reaction between (A) and (B) and an anchorage additive for enhancing the adhesion of the composition to the polymer film and heating the coated film to cure the release coating, characterised in that the anchorage additive is the reaction product of a fluid polyorganosiloxane (C) containing at least one alkenyl group and at least one silanol group with a hydrolysable silane (D) containing at least one epoxide group.

14. (canceled)