Multiple layer polymer interlayers having a melt fractured surface

Abstract

The present invention provides multiple layer interlayers having a soft inner polymer layer and relatively stiff outer layers that can be laminated without unacceptable optical distortion and used in various multiple layer glass panel type applications. Multiple layer interlayers of the present invention have surface topography that is formed by controlling the melt fracture that occurs at the exposed surface of the interlayer, or individual layers of the multiple layer interlayer, during formation of the interlayer. By precisely controlling the surface topography of the interlayer, lamination of the interlayer with a rigid substrate does not lead to unacceptable optical distortion caused by the transfer of the surface topography through outer, stiffer layers into softer, internal layers of the interlayer.

1 . A low optical distortion polymer interlayer comprising:
 a first polymer layer comprising a plasticized thermoplastic polymer with a lower plasticizer content;   a second polymer layer comprising a plasticized thermoplastic polymer with a higher plasticizer content; and,   a third polymer layer comprising a plasticized thermoplastic polymer with a lower plasticizer content;   
       wherein said second polymer layer is disposed between said first polymer layer and said third polymer layer; 
       wherein the lower plasticizer content of the first and third plasticized thermoplastic layers each differ from the plasticizer content in the second plasticized thermoplastic layer by at least 20 phr by weight in plasticizer content, and 
       wherein both surfaces of said interlayer have been roughened by melt fracture to provide surfaces with an R Z  value of 25-60 and an R SM  value of less than 800, and when the interlayer is laminated between two sheets of glass, the laminate has a mottle grade of 3 or less. 
     
     
         2 . The interlayer of  claim 1 , wherein said first polymer layer, said second polymer layer, and said third polymer layer each comprise poly(vinyl butyral). 
     
     
         3 . The interlayer of  claim 1 , both surfaces of said interlayer have an R SM  value of less than 700. 
     
     
         4 . The interlayer of  claim 1 , wherein the laminate has a mottle grade of 2 or less. 
     
     
         5 . The interlayer of  claim 1  wherein said interlayer has no embossing. 
     
     
         6 . The interlayer of  claim 1  wherein the interlayer has a total thickness of 0.1 to 2.5 millimeters. 
     
     
         7 . The interlayer of  claim 1  wherein the lower plasticizer content of the first and third layers each differ from the plasticizer content in the second layer by at least 25 phr by weight in plasticizer content. 
     
     
         8 . The interlayer of  claim 2 , wherein the high plasticizer content in the second poly(vinyl butyral) layer comprises 40 to 90 phr by weight plasticizer, wherein the lower plasticizer content poly(vinyl butyral) layers differ from the high plasticizer content poly(vinyl butyral) layer by at least 20 phr by weight in plasticizer content, wherein both surfaces of said interlayer have an R z  of 25-50 microns and an R sm  of less than 700 microns. 
     
     
         9 . The interlayer of  claim 2 , wherein the high plasticizer content poly(vinyl butyral) layer comprises 50 to 80 phr by weight plasticizer, wherein the low plasticizer content poly(vinyl butyral) layers differ from the high plasticizer content poly(vinyl butyral) layer by at least 25 phr by weight in plasticizer content, wherein both surfaces of said interlayer have an R z  of 25-50 microns and an R sm  of less than 800 microns. 
     
     
         10 . The interlayer of  claim 1  wherein the first and third layers each have a tensile break stress at least 25 kilograms per square centimeter greater than the second layer. 
     
     
         11 .- 16 . (canceled) 
     
     
         17 . A multiple layer glass laminate comprising:
 i) A top glass layer;   ii) An interlayer; and   iii) A bottom glass layer   
       wherein the interlayer comprises,
 a first polymer layer comprising a plasticized thermoplastic polymer with a higher plasticizer content; 
 a second polymer layer comprising a plasticized thermoplastic polymer with a lower plasticizer content; and, 
 a third polymer layer comprising a plasticized thermoplastic polymer with a higher plasticizer content; 
 
       wherein said second polymer layer is disposed between said first polymer layer and said third polymer layer; 
       wherein the lower plasticizer content of the first and third plasticized thermoplastic layers each differ from the plasticizer content in the second a plasticized thermoplastic layer by at least 20 phr by weight in plasticizer content, and 
       wherein both surfaces of said interlayer have been roughened by melt fracture to provide surfaces with an R Z  value of 25-60 and an R SM  value of less than 800, and wherein the laminate has a mottle grade of 3 or less. 
     
     
         18 .- 22 . (canceled)