Aqueous polymer blend composition

Abstract

An aqueous polymer blend composition containing particles of a first polymer and particles of a second polymer with preferred molecular weight ranges is provided. Coatings prepared from the aqueous polymer blend composition may be employed as coatings which have water whitening resistance and provide resistance to efflorescence to cementitious substrates, such as roof tiles. A method of preparing a coated cementitious substrate with the aqueous polymer blend composition and an article containing the coated cementitious substrate are also provided.

We claim:  
     
         1 . An aqueous polymer blend composition comprising: 
 a) particles of a first polymer; and    b) particles of a second polymer;    wherein said first polymer has a weight average molecular weight of 250,000 or greater; wherein said second polymer has a weight average molecular weight of 150,000 or less; wherein said particles of said second polymer have an average diameter in the range of 20 nm to 350 nm; wherein the glass transition temperature of said first polymer and the glass transition temperature of said second polymer have substantially the same value;    wherein the weight ratio of said first polymer to said second polymer is in the range of 1:3 to 3:1; and wherein the average glass transition temperature of said first polymer and said second polymer is in the range of 15° C. to 50° C.    
     
     
         2 . The aqueous polymer blend composition according to  claim 1  wherein the difference in said glass transition temperature of said first polymer and said glass transition temperature of said second polymer is 5° C. or less.  
     
     
         3 . The aqueous polymer blend composition according to  claim 1  wherein said particles of said first polymer have an average diameter in the range of 60 nm to 170 nm.  
     
     
         4 . The aqueous polymer blend composition according to  claim 3  wherein said particles of said second polymer have an average diameter in the range of 60 nm to 170 nm.  
     
     
         5 . A method for providing a coated cementitious substrate comprising the steps of: 
 a) preparing an aqueous polymer blend composition comprising: 
 i) particles of a first polymer; and  
 ii) particles of a second polymer;  
 wherein said first polymer has a weight average molecular weight of 250,000 or greater; wherein said second polymer has a weight average molecular weight of 150,000 or less; wherein said particles of said second polymer have an average diameter in the range of 20 nm to 350 nm; wherein the glass transition temperature of said first polymer and the glass transition temperature of said second polymer have substantially the same value; wherein the weight ratio of said first polymer to said second polymer is in the range of 1:3 to 3:1; and wherein the average glass transition temperature of said first polymer and said second polymer is in the range of 15° C. to 50° C.;  
   b) applying said aqueous polymer blend composition onto a green cementitious substrate to form a coated green cementitious substrate; and    c) curing or allowing to cure said coated green cementitious substrate to form said coated cementitious substrate.    
     
     
         6 . The method according to  claim 5  wherein the difference in said glass transition temperature of said first polymer and said glass transition temperature of said second polymer is 5° C. or less.  
     
     
         7 . The method according to  claim 5  wherein said particles of said first polymer have an average diameter in the range of 60 nm to 170 nm.  
     
     
         8 . The method according to  claim 7  wherein said particles of said first polymer have an average diameter in the range of 60 nm to 170 nm.  
     
     
         9 . An article comprising a coated cementitious substrate comprising: 
 a) a cementitious substrate; and    b) a coating formed from an aqueous polymer blend composition comprising: 
 i) particles of a first polymer; and  
 ii) particles of a second polymer;  
 wherein said first polymer has a weight average molecular weight of 250,000 or greater; wherein said second polymer has a weight average molecular weight of 150,000 or less; wherein said particles of said second polymer have an average diameter in the range of 20 nm to 350 nm; wherein the glass transition temperature of said first polymer and the glass transition temperature of said second polymer have substantially the same value; wherein the weight ratio of said first polymer to said second polymer is in the range of 1:3 to 3:1; and wherein the average glass transition temperature of said first polymer and said second polymer is in the range of 15° C. to 50° C.  
   
     
     
         10 . The article according to  claim 9  wherein said particles of said first polymer have an average diameter in the range of 60 nm to 170 nm.