Crosslinking agent for a silicone composition which can be crosslinked at low temperature based on a hydrogenated silicone oil comprising Si-H units at the chain end and in the chain

Abstract

The invention relates to crosslinkable or crosslinked silicone compositions capable of being used to form a water-repellent and release coating for a flexible support made of paper or of polymer, in particular a heat-sensitive flexible support. These compositions are of the type of those comprising crosslinking polyorganosiloxanes carrying SiH units and unsaturated, preferably vinylated, polyorganosiloxanes capable of reacting with the crosslinking agent by polyaddition in the presence of platinum to form the release crosslinked coating on the flexible support. The targeted aim is to make possible the instantaneous crosslinking at low temperature (85-90° C.) of such silicone compositions coated on flexible supports at a very high speed. To achieve this aim, the invention provides for the use of specific crosslinking agents composed of POSs hydrogenated at the chain end and in the chain. The invention also relates to the silicone compositions of solvent-free type or of emulsion type comprising the Si-Vi POS, the SiH POS crosslinking agent α,ω-bis(hydrodimethylsiloxyl)poly(hydromethyl)-(dimethyl)siloxane, and the platinum catalyst, inter alia. Applications: release silicone coatings obtained by crosslinking/polyaddition for heat-sensitive flexible supports, for example polymeric films made of polyethylene.

1 . A crosslinking agent used to prepare a water-repellent and release coating for a fibrous or nonfibrous support comprising: 
 at least one silicone oil:    comprising at least one hydrogenated (preferably linear) PolyOrganoSiloxane (POS) exhibiting, per molecule, at least three hydrogen atoms bonded to silicon atoms, and having the following mean linear formula:      M α M′ β D γ D′ δ     with M=(R 1 ) 3 SiO 1/2      M′=H a (R 1 ) b SiO 1/2 , a+b=3, a=1, 2 or 3,    b=0 to 3    D=(R 2 ) 2 SiO 2/2      D′=HR 3 SiO 2/2      0≦α≦2    0<β≦2    0<γ   0<δ   and with:    0<γ/δ;    15≦(β/δ)×1000≦150;    the POS or POSs of higher viscosity of the said composition having a dynamic viscosity η at 25° C. of less than or equal to 1500 mPa.s.    
     
     
         2 . The crosslinking agent according to  claim 1 , wherein the support to be coated is made of a heat-sensitive material, comprising polyethylene and/or polypropylene and/or polyester and/or poly(vinyl chloride) and/or from thermally printable flexible supports.  
     
     
         3 . The crosslinking agent according to  claim 1 , wherein, for the crosslinking of the coating, the support is placed at a temperature of less than or equal to 110° C.  
     
     
         4 . The crosslinking agent according to  claim 1 , wherein the silicone composition is a mixture formed of: 
 (I.1) at least one POS exhibiting, per molecule, at least two alkenyl groups bonded to silicon atoms,    (I.2) at least one crosslinking ≡SiH POS as defined above,    (II) at least one catalyst (II) comprising at least one metal belonging to the platinum group.    
     
     
         5 . The crosslinking agent according to  claim 4 , wherein the crosslinking POS exhibits an ≡SiH/≡Si-alkenyl (Vi) molar ratio such that:  
         1.0≦≡SiH/≡Si-alkenyl (Vi)≦4  preferably  1.4≦≡SiH/≡Si-alkenyl (Vi)≦3.  
     
     
         6 . The crosslinking agent according to  claim 5 , wherein the POS (I.1) is a product comprising units of formula:  
       
         
           
             
               
                 
                   
                     
                       W 
                       a 
                     
                     ⁢ 
                     
                       Z 
                       b 
                     
                     ⁢ 
                     SiO 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       
                         4 
                         - 
                         
                           ( 
                           
                             a 
                             + 
                             b 
                           
                           ) 
                         
                       
                       2 
                     
                   
                 
                 
                   
                     ( 
                     
                       I 
                       ⁢ 
                       .1 
                     
                     ) 
                   
                 
               
             
           
         
       
       in which: 
 W is an alkenyl group,  
 Z is a monovalent hydrocarbonaceous group which has no unfavourable effect on the activity of the catalyst and which is selected from alkyl groups having from 1 to 8 carbon atoms inclusive, and from aryl groups,  
 a is 1 or 2, b is 0, 1 or 2 and a+b is between 1 and 3.  
 
     
     
         7 . The crosslinking agent according to  claim 1 , wherein the release crosslinkable silicone composition comprises: 
 at least one adhesion-adjusting system,    and/or at least one agent for inhibiting hydrosilylation.    
     
     
         8 . The crosslinking agent according to  claim 1 , wherein the POS (I.1) is a blocked linear polydiorganosiloxane comprising “Si-alkenyl” functional groups, exhibiting a viscosity of the order of 100 to 1000 mPa.s and a level of alkenyl functional groups La, expressed as equivalent number of alkenyl functional groups per 100 g of oil, of:  
         0.010≦La.  
     
     
         9 . The crosslinking agent according to  claim 1 , wherein the oil used as the crosslinking agent comprises at least one POS comprising ≡SiH functional groups (I.2) and exhibits a viscosity of the order of 5 to 150 mPa.s.  
     
     
         10 . The crosslinking agent according to  claim 1 , wherein the composition is provided in the form of an aqueous emulsion/dispersion.  
     
     
         11 . Silicone composition capable of crosslinking by polyaddition to form a water-repellent and release coating for a fibrous or nonfibrous support, wherein: 
 the composition comprises:    (I.1) at least one POS exhibiting, per molecule, at least two alkenyl groups (preferably C 2 -C 6  alkenyl groups) bonded to silicon atoms,    (I.2) at least one silicone oil:    comprising at least one hydrogenated linear PolyOrganoSiloxane (POS) exhibiting, per molecule, at least three hydrogen atoms bonded to silicon atoms,    and having the following mean linear formula:      M α M′ βD   γ D′ δ     with M=(R 1 ) 3 SiO 1/2      M′=H a (R 1 ) b SiO 1/2 , a+b=3, a=l, 2 or 3,    b=0 to 3    D=(R 2 ) 2 SiO 2/2      D′=HR 3 SiO 2/2      0≦α≦2    0<β≦2    0<γ   0<δ   and with:    0<γ/δ;    15≦(β/δ)×1000≦150;    at least one catalyst (II) comprising at least one metal belonging to the platinum group;    and in that the POS or POSs of higher viscosity which it comprises has (have) a dynamic viscosity η at 25° C. of less than or equal to 1500 mPa.s.    
     
     
         12 . Support which comprises at least one release coating obtained from the composition according to  claim 11.