Heat-curable powder coating composition

Abstract

The invention relates to a one component heat curable powder coating composition system for being cured at a temperature from 60 to 130° C. comprising: a thermal initiation system and a resin system, wherein the reactivity of the thermal initiation system is such that the thermal initiation system provides a geltime between 2.5 and 1000 minutes at 60° C. in butane diol-dimethacrylate as measured according to DIN 16945 using 1 wt % of the thermal initiation system in 99 wt % of butane diol-dimethacrylate, wherein the amount of thermal initiation system is chosen such that when the powder coating composition is applied to a substrate and cured at a temperature of 130° C. for 20 minutes, the coating resists at least 50 acetone double rubs, wherein the resin system comprises a resin and a co-crosslinker, wherein the resin contains reactive unsaturations and wherein said reactive unsaturations are carbon carbon double bonds connected directly to an electron withdrawing group, wherein the co-crosslinker is chosen from methacrylates, vinyl esters, vinyl ethers, vinyl amides, alkyne ethers, alkyne esters, alkyne amides, alkyne amines, propargyl ethers, propargyl ethers, propargyl esters, itaconates, enamines and mixtures thereof, wherein the weight per unsaturation in the resin system is between 100 and 1000 g/mole as determined using 1 H NMR.

1 . Heat curable powder coating composition suitable for being cured at a temperature from 60 to 130° C. comprising:
 a thermal initiation system and a resin system 
 wherein the reactivity of the thermal initiation system is such that the thermal initiation system provides a geltime between 2.5 and 1000 minutes at 60° C. in butane diol-dimethacrylate as measured according to DIN 16945 using 1 wt % of the thermal initiation system in 99 wt % of butane diol-dimethacrylate 
 wherein the amount of thermal initiation system is chosen such that when the powder coating composition is applied to a substrate and cured at a temperature of 130° C. for 20 minutes, the resulting coating resists at least 50 acetone double rubs 
 wherein the resin system comprises a resin and a co-crosslinker 
 wherein the resin contains reactive unsaturations and wherein said reactive unsaturations are carbon carbon double bonds connected directly to an electron withdrawing group 
 wherein the co-crosslinker is chosen from the group of acrylates, methacrylates, vinylesters, vinylethers, vinyl amides, alkyn ethers, alkyn esters, alkyn amides, alkyn amines, propargyl ethers, propargyl esters, itaconates, enamines and mixtures thereof 
 wherein the weight per unsaturation in the resin system is between 100 and 1000 g/mole as determined using  1 H NMR and 
 wherein the powder coating composition is a one component system. 
 
     
     
         2 . Composition according to  claim 1 , wherein the geltime provided by the thermal initiation system is at least 6 minutes. 
     
     
         3 . Composition according to  claim 1 , wherein the thermal initiation system comprises a peroxide. 
     
     
         4 . Composition according to  claim 1 , wherein the thermal initiation system comprises hydroquinones or catechols. 
     
     
         5 . Composition according to  claim 1 , wherein the resin is a polyester. 
     
     
         6 . Composition according to  claim 1 , wherein the co-crosslinker is chosen from the group of vinylethers, vinylesters, methacrylates, acrylates, itaconates and mixtures thereof. 
     
     
         7 . Composition according to  claim 1 , wherein the weight per unsaturation of the co-crosslinker is lower than 630 g/mole and/or wherein the weight per unsaturation of the resin is less than 1150 g/mole. 
     
     
         8 . Composition according to  claim 1 , wherein the resin and the co-crosslinker are the same. 
     
     
         9 . Composition according to  claim 1 , wherein the resin is a polyester based on fumaric acid, wherein the co-crosslinker is a vinylether and wherein the thermal initiation system comprises a perdicarbonate, preferably di(4-t-butylcyclohexyl)peroxydicarbonate or dimyristyl peroxydicarbonate and a hydroquinone, preferably tert-butylhydroquinone or
 2,3,5-trimethylhydroquinone.   
     
     
         10 . Composition according to  claim 1 , wherein the resin is a polyester based on fumaric acid, wherein the co-crosslinker is a vinylether and wherein the thermal initiator is benzoyl peroxide. 
     
     
         11 . Process for the preparation of a powder coating composition according to  claim 1  comprising the steps of:
 a. mixing the components of the powder coating composition to obtain a premix 
 b. heating the premix to obtain an extrudate 
 c. cooling down the extrudate to obtain a solidified extrudate and 
 d. breaking the solidified extrudate into smaller particles to obtain the powder coating composition. 
 
     
     
         12 . Process for coating a substrate comprising the following steps:
 1) applying a powder coating composition according to  claim 1  to a substrate to obtain a coated substrate   2) heating the coated substrate.   
     
     
         13 . Substrate that is fully or partially coated with a powder coating composition according to  claim 1 . 
     
     
         14 . Use of a powder coating composition of  claim 1  to coat a heat-sensitive substrate. 
     
     
         15 . Use according to  claim 14 , wherein the heat-sensitive substrate is wood.