Optical elements comprising a polyfluropolyether surface treatment

Abstract

The present invention relates to optical elements comprising fluorochemical surface treatments. The invention further relates to materials such as retroreflective sheetings, pavement markings and beaded projection screens comprising a binder and the surface treated optical elements. The fluorochemical surface treatment is substantially free of perfluoroalkyl groups having more than four carbon atoms. Preferably, the surface treatment is a polyfluoropolyether-based compound comprising at least one polar group or polar group-containing organic radical.

What is claimed is:  
     
         1 . An optical element having a surface treatment comprising a polyfluoropolyether compound having at least one polar group or polar group-containing organic radical.  
     
     
         2 . The optical element of  claim 1  wherein the polyfluoropolyether compound has the general formula R f -[X] y  wherein R f  is a monovalent or divalent perfluoropolyether group, X is a polar group or polar group-containing organic radical, and y ranges from 1 to 2.  
     
     
         3 . The optical element of  claim 2  wherein R f  comprises one or more repeating units selected from the group comprising —C n F 2n )—, —(C n F 2n O)—, —(CF(Z))—, —(CF(Z)O)—, —(CF(Z)C n F 2n O)—, —(C n F 2n CF(Z)O)—, —(CF 2 CF(Z)O)—, and combinations thereof; wherein the average n value ranges from 1 to 4 and Z is a perfluoroalkyl group, an oxygen-substituted perfluoroalkyl group, a perfluoroalkoxy group, or an oxygen-substituted perfluoroalkoxy group having 1 to about 4 carbon atoms and 1 to about 4 oxygen atoms.  
     
     
         4 . The optical element of  claim 2  wherein X is selected from the group comprising carboxylic acid, sulfonic acid, phosphonic acid, carboxylate salt, sulfonate, phosphonate, phosphate esters, ammonium salts, amine, amide, alkyl amide, alkyl aryl amide, imide, sulfonamide, hydroxymethyl, thiol, ester, silane, polyoxyalkyene, organic radicals substituted with one or more of said polar groups, and mixtures thereof.  
     
     
         5 . The optical element of  claim 2  wherein the polyfluoropolyether compound is selected from the group comprising the general formulas: 
 i) X—(CF 2 O(CF 2 O) m (C 2 F 4 O ) p CF 2 )—X;  
 ii) C 3 F 7 O(CF(CF 3 )C 2 O) p CF(CF 3 )—X; and  
 iii) X—CF 2 O(C 2 F 4 O) m CF 2 —X  
 wherein m and p each independently range from 0 to 50 with the proviso that m and p are not both 0 and X is a polar group or polar group-containing organic radical selected from the group comprising CONH(CH 2 ) 3 Si(OMe) 3 , CONH(R) wherein R is an alkyl radical having 1 to 8 carbon atoms, CONHCH 2 CH 2 Ph, CO 2 NH 4 , CH 2 NH 2 ,CO 2 H, CH 2 OH, CO 2 CH 3  and combinations thereof.  
 
     
     
         6 . The optical element of  claim 2  wherein the polyfluoropolyether compound has the general formula: 
 i) X—(CF 2 O(CF 2 O) m (C 2 F 4 O) p CF 2 )—X wherein X is CONH(CH 2 ) 3 Si(OMe 3 ; CO 2 H, CO 2 NH 4 , and mixtures thereof;  
 ii) C 3 F 7 O(CF(CF 3 )CF 2 O( p CF(CF 3 )—X wherein X is CO 2 H, CO 2 NH 4  and mixtures thereof,  
 wherein m ranges from 0 to 50 and p ranges from 0 to 50, with the proviso that m and p are not both 0.  
 
     
     
         7 . The optical element of  claim 1  wherein the number average molecular weight of the polyfluoropolyether compound ranges from about 400 to about 10,000 g/mole.  
     
     
         8 . The optical element of  claim 7  wherein the number average molecular weight of the polyfluoropolyether compound is greater than about 1000 g/mole.  
     
     
         9 . The optical element of  claim 7  wherein the number average molecular weight of the polyfluoropolyether compound is greater than about 2600 g/mole.,  
     
     
         10 . The optical element of  claim 7  wherein the number average molecular weight is less than about 8,000 g/mole.  
     
     
         11 . The optical element of  claim 1  wherein the percent float in heptane is at least about 90%.  
     
     
         12 . An optical element having a surface treatment comprising a fluorochemical compound at a concentration of less than about 100 ppm wherein the percent float in heptane is at least about 90%.  
     
     
         13 . An optical element having a surface treatment comprising a fluorochemical compound having the general formula (C n F 2n+1 )—X wherein n ranges from 1 to 3 and X is a polar group or polar group-containing organic radical.  
     
     
         14 . An optical element having a surface treatment comprising a fluorochemical compound having the general formula (C n F 2n+1 )—X wherein n ranges from 1 to 4 and X is a polar group or polar group-containing organic radical; and wherein said compound is free of heavy metals and transition metals.  
     
     
         15 . The optical element of  claim 14  wherein X is selected from the group comprising sulfonic acids and salts thereof; sulfonamides, sulfonimides and salts thereof; amides, silanes and mixtures thereof.  
     
     
         16 . A method of coating optical elements comprising the steps of: 
 a) providing an aqueous surface treatment comprising at least one fluorocarbon compound wherein said compound is free of perfluoroalkyl groups having more than four carbon atoms; and    b) coating optical elements with said composition; and    c) drying, said composition.    
     
     
         17 . The method of  claim 16  wherein said fluorocarbon compound has the general formula (C n F 2n+1 )—X wherein n ranges from 1 to 4, m ranges from 0 to 4, and X is a polar group or polar group-containing organic radical.  
     
     
         18 . The method of  claim 16  wherein said aqueous composition is substantially free of heavy metals and transition metals.  
     
     
         19 . The method of  claim 16  wherein said aqueous composition comprises up to about 30 wt-% of a cosolvent with respect to the total weight of the solution.  
     
     
         20 . A pavement marking comprising a liquid binder and a multitude of the optical elements of  claim 1 .  
     
     
         21 . A pavement marking comprising a liquid binder and a multitude of the optical elements of  claim 13 .  
     
     
         22 . A pavement marking comprising a liquid binder and a multitude of the optical elements of  claim 14 .  
     
     
         23 . The pavement marking of  claim 20  wherein the optical elements are embedded in the binder at a depth of about 40-70% of their diameters.  
     
     
         24 . The pavement marking of  claim 21  wherein the optical elements are embedded in the binder at a depth of about 40-70% of their diameters.  
     
     
         25 . The pavement marking of  claim 22  wherein the optical elements are embedded in the binder at a depth of about 40-70% of their diameters.  
     
     
         26 . A reflective sheeting comprising: 
 a) a top coat layer having an exposed surface;    b) a binder layer disposed on the exposed surface of the top coat layer;    c) a multitude of the optical elements of  claim 1  disposed on the binder layer;    d) a space coat layer disposed on the binder layer; and    e) a reflective layer disposed on the space coat layer.    
     
     
         27 . A reflective sheeting comprising: 
 a) a top coat layer having an exposed surface;    b) a binder layer disposed on the exposed surface of the top coat layer;    c) a multitude of the optical elements of  claim 13  disposed on the binder layer;    d) a space coat layer disposed on the binder layer; and    e) a reflective layer disposed on the space coat layer.    
     
     
         28 . A reflective sheeting comprising: 
 a) a top coat layer having an exposed surface;    b) a binder layer disposed on the exposed surface of the top coat layer;    c) a multitude of the optical elements of  claim 14  disposed on the binder layer;    d) a space coat layer disposed on the binder layer; and    e) a reflective layer disposed on the space coat layer.    
     
     
         29 . The reflective sheeting of  claim 26  wherein the optical elements are embedded in the binder at a depth of about 40-70% of their diameters.  
     
     
         30 . The reflective sheeting of  claim 27  wherein the optical elements are embedded in the binder at a depth of about 40-70% of their diameters.  
     
     
         31 . The reflective sheeting of  claim 28  wherein the optical elements are embedded in the binder at a depth of about 40-70% of their diameters.