Method for treating a substrate

Abstract

A method for treating a substrate is described. In accordance with one aspect, the method includes applying a polymer coating to a substrate, and bringing the polymer coating into contact with a heated surface in a pressure nip while the coating is still in a wet state. Optionally the polymer coating may include a crosslinkable material, and a crosslinking agent may be used to promote crosslinking. The polymer coating replicates the heated surface. A product produced in accordance with the described method is also disclosed. The product is characterized by having subsurface voids within the coating.

1 . A process for treating a substrate, comprising: 
 applying to the substrate a wet film of an aqueous polymer solution,    bringing the film into contact with a heated surface in a nip,    the nip having a nip dwell time, a nip local pressure, and a nip average pressure, whereby during a first portion of the nip dwell time the nip local pressure increases and the film undergoes heating with substantially no vapor formation, and during a second portion of the nip dwell time the nip local pressure decreases and the aqueous polymer solution boils and forms voids that remain in the film, and    at least partially drying the film.    
     
     
         2 . The process of  claim 1 , wherein the nip dwell time is between about 0.5 milliseconds and about 5 milliseconds.  
     
     
         3 . The process of  claim 1 , wherein the nip average pressure is between about 70 psi and about 700 psi.  
     
     
         4 . The process of  claim 1 , wherein the heated surface is at a temperature above about 150° C.  
     
     
         5 . The process of  claim 1 , wherein the heated surface temperature is above the saturation temperature of water at the nip average pressure.  
     
     
         6 . The process of  claim 1 , wherein the heated surface temperature is between about 30° C. and 70° C. above the saturation temperature of water at the nip average pressure.  
     
     
         7 . A process for treating a substrate, comprising: 
 applying to the substrate a first coating of an aqueous polymer solution as a wet film,    wherein the first coating includes a water soluble polymer and a release agent,    bringing the film into contact with a heated surface in a nip,    the nip having a nip dwell time, a nip local pressure, and a nip average pressure, whereby during a first portion of the nip dwell time the nip local pressure increases and the film undergoes heating with substantially no vapor formation, and during a second portion of the nip dwell time the nip local pressure decreases and the aqueous polymer solution boils and forms voids that remain in the film, and    at least partially drying the film.    
     
     
         8 . The process of  claim 6 , wherein the nip dwell time is between about 0.5 milliseconds and about 5 milliseconds.  
     
     
         9 . The process of  claim 6 , wherein the nip average pressure is between about 70 psi and about 700 psi  
     
     
         10 . The process of  claim 6 , wherein the nip average pressure is between about 150 psi and about 550 psi.  
     
     
         11 . The process of  claim 6 , wherein the heated surface is at a temperature above about 150° C.  
     
     
         12 . The process of  claim 6 , wherein the heated surface temperature is above the saturation temperature of water at the nip average pressure.  
     
     
         13 . The process of  claim 6 , wherein the heated surface temperature is between about 30° C. and 70° C. above the saturation temperature of water at the nip average pressure.  
     
     
         14 . The process of  claim 6 , wherein the aqueous polymer solution contains essentially no elastomeric material.  
     
     
         15 . The process of  claim 6 , wherein the substrate includes at least one of cellulose, paper, paperboard, fabric, fibrous material, porous material, porous film, or polylactic acid.  
     
     
         16 . The process of  claim 6 , wherein the first coating includes by dry weight at least about 60% water soluble polymer and up to 10% release agent.  
     
     
         17 . The process of  claim 6 , wherein the first coating includes at least one of starch, waxy maize, protein, polyvinyl alcohol, casein, gelatin, soybean protein, and alginate.  
     
     
         18 . The process of  claim 6 , further comprising the application of a second coating after at least partially drying the film.  
     
     
         19 . The process of  claim 6 , wherein the substrate comprises a web.  
     
     
         20 . The process of  claim 6 , wherein the substrate comprises a sheet.  
     
     
         21 . A process for treating a substrate, comprising: 
 applying to the substrate a first coating of an aqueous polymer solution as a wet film,    bringing the film into contact for less than about 3 seconds with a heated surface having a temperature above about 150° C.,    wherein the contact comprises a nipped contact with the heated surface    wherein the nipped contact has a nip local pressure associated therewith,    wherein the nipped contact comprises a first duration during which the nip local pressure increases and the film undergoes heating with substantially no vapor formation, and a second duration during which the nip local pressure decreases and the aqueous polymer solution boils and forms voids that remain in the film.    
     
     
         22 . The process of  claim 21 , wherein the first coating includes a water soluble polymer.  
     
     
         23 . The process of  claim 21 , wherein the first coating contains a release agent.  
     
     
         24 . The process of  claim 21 , wherein the first coating contains essentially no elastomeric material.  
     
     
         25 . The process of  claim 21 , wherein the aqueous polymer solution comprises at least about 60% water soluble polymer by dry weight, and up to 10% release agent by dry weight.  
     
     
         26 . The process of  claim 21 , wherein the nipped contact has a dwell time and the dwell time is between about 0.5 milliseconds to about 5 milliseconds,  
     
     
         27 . The process of  claim 21 , wherein the nipped contact has a nip average pressure associated therewith, wherein the nip average pressure is between about 70 psi to about 700 psi.  
     
     
         28 . The process of  claim 21 , wherein the first coating includes a surface and at least 50% of the first coating surface has subsurface voids having a transverse dimension of at least 5 microns.  
     
     
         29 . The process of  claim 21 , further comprising at least partially drying the film.  
     
     
         30 . The process of  claim 21 , wherein the first coating includes a surface with a Sheffield Smoothness of less than about 300 units.  
     
     
         31 . The process of  claim 21 , wherein the first coating includes a surface with a Sheffield Smoothness of less than about 150 units.  
     
     
         32 . The process of  claim 21 , wherein the substrate is a cellulosic substrate.  
     
     
         33 . An apparatus for treating a web substrate, comprising: 
 an applicator for applying to the substrate an aqueous coating as a wet film,    a drum having a diameter between about 24 inches and about 84 inches,    a press roll forming a nip with the drum,    wherein the web substrate travels through the nip at a speed between about 300 fpm and about 3000 fpm,    wherein the nip provides a dwell time between about 0.5 milliseconds and 5 milliseconds, and    an energy source for maintaining the drum temperature above the boiling point of the aqueous coating.    
     
     
         34 . The apparatus of  claim 33 , wherein the nip provides a nip average pressure between about 70 psi and about 700 psi.  
     
     
         35 . The apparatus of  claim 33  wherein the hot drum has a diameter between about 60 inches and about 72 inches.  
     
     
         36 . The apparatus of  claim 33  wherein the web substrate travels through the nip at a speed between about 600 fpm and about 2000 fpm.  
     
     
         37 . The apparatus of  claim 33  wherein the press roll has a diameter between about 12 inches and about 72 inches.  
     
     
         38 . The apparatus of  claim 33  wherein the press roll has a diameter between about 24 inches and about 48 inches.  
     
     
         39 . An apparatus for treating a web substrate, comprising: 
 an applicator for applying to the substrate an aqueous coating as a wet film,    a drum having a diameter between about 24 inches and about 84 inches,    a belted shoe device forming a nip with the drum,    wherein the web substrate travels through the nip at a speed between about 300 fpm and about 3000 fpm,    wherein the nip provides a dwell time between about 0.5 milliseconds and about 20 milliseconds, and    an energy source for maintaining the drum temperature above the boiling point of the aqueous coating.    
     
     
         40 . The apparatus of  claim 39 , wherein the nip provides a nip average pressure between about 70 psi and about 700 psi.  
     
     
         41 . The apparatus of  claim 39  wherein the hot drum has a diameter between about 60 inches and about 72 inches.  
     
     
         42 . The apparatus of  claim 39 , wherein the web substrate travels through the nip at a speed between about 600 fpm and about 2000 fpm.  
     
     
         43 . The apparatus of  claim 39 , wherein the nip length in the direction of substrate travel is between about 0.1 inches and about 3 inches.  
     
     
         44 . A process for treating a substrate, comprising: 
 applying to the substrate a wet film of an aqueous polymer solution;    heating the film under a first pressure with substantially no vapor formation; and    reducing the first pressure so that the aqueous polymer solution boils and forms voids that remain in the film.    
     
     
         45 . The process of  claim 44 , wherein the film is heated by contact with a heated surface.  
     
     
         46 . The process of  claim 45 , wherein the heated surface is at a temperature above about 150° C.  
     
     
         47 . The process of  claim 44 , further comprising at least partly drying the film.  
     
     
         48 . The process of  claim 44 , wherein heating the film under a first pressure, and reducing the first pressure, occur at least partly in a pressure nip.  
     
     
         49 . The process of  claim 48 , wherein the pressure nip is characterized by a nip average pressure between about 70 psi and about 700 psi.  
     
     
         50 . The process of  claim 48  wherein pressure nip has a nip dwell time between about 0.5 milliseconds and about 5 milliseconds.  
     
     
         51 . The process of  claim 49 , wherein heating the film is by contact with a heated surface having a temperature between about 30° C. and 70° C. above the saturation temperature of water at the nip average pressure.  
     
     
         52 . A process for treating a substrate, comprising: 
 applying to the substrate a first coating of an aqueous polymer solution as a wet film;    wherein the first coating includes a water soluble polymer and a release agent,    heating the film under a first pressure with substantially no vapor formation; and    reducing the first pressure so that the aqueous polymer solution boils and forms voids that remain in the film.    
     
     
         53 . The process of  claim 52 , further comprising at least partly drying the film.  
     
     
         54 . The process of  claim 52 , wherein the film is heated by contact with a heated surface.  
     
     
         55 . The process of  claim 54 , wherein the heated surface is at a temperature above about 150° C.  
     
     
         56 . The process of  claim 55 , wherein heating the film under a first pressure, and reducing the first pressure, occur at least partly in a pressure nip.  
     
     
         57 . The process of  claim 56 , wherein the pressure nip is characterized by a nip average pressure between about 70 psi and about 700 psi.  
     
     
         58 . The process of  claim 57 , wherein the pressure nip is characterized by a nip average pressure between about 150 psi and about 550 psi.  
     
     
         59 . The process of  claim 58  wherein pressure nip has a nip dwell time between about 0.5 milliseconds and about 5 milliseconds.  
     
     
         60 . The process of  claim 56 , wherein the heated surface temperature is above the saturation temperature of water at the average nip pressure.  
     
     
         61 . The process of  claim 56 , wherein heating the film is by contact with a heated surface having a temperature between about 30° C. and 70° C. above the saturation temperature of water at the nip average pressure.  
     
     
         62 . The process of  claim 44 , wherein the aqueous polymer solution contains essentially no elastomeric material.  
     
     
         63 . The process of  claim 44 , wherein the substrate includes at least one of cellulose, paper, paperboard, fabric, fibrous material, porous material, porous film, or polylactic acid.  
     
     
         64 . The process of  claim 44 , wherein the first coating includes by dry weight at least about 60% water soluble polymer and up to 10% release agent.  
     
     
         65 . The process of  claim 44 , wherein the first coating includes at least one of starch, waxy maize, protein, polyvinyl alcohol, casein, gelatin, soybean protein, and alginate.  
     
     
         66 . The process of  claim 44 , further comprising the application of a second coating after at least partially drying the film.  
     
     
         67 . The process of  claim 44 , wherein the substrate comprises a web.  
     
     
         68 . The process of  claim 44 , wherein the substrate comprises a sheet.  
     
     
         69 . A process for treating a substrate, comprising: 
 applying to the substrate a first coating of an aqueous polymer solution as a wet film, bringing the film into contact for less than about 3 seconds with a heated surface having a temperature above about 150° C., 
 wherein the contact comprises a nipped contact with the heated surface, heating the film under a first pressure with substantially no vapor formation; and  
 reducing the first pressure so that the aqueous polymer solution boils and forms voids that remain in the film.  
   
     
     
         70 . The process of  claim 69 , wherein the first coating includes a water soluble polymer.  
     
     
         71 . The process of  claim 69 , wherein the aqueous polymer solution contains a release agent.  
     
     
         72 . The process of  claim 69 , wherein the first coating contains essentially no elastomeric material.  
     
     
         73 . The process of  claim 69 , wherein the nipped contact has a nip average pressure associated therewith, wherein the nip average pressure is between about 70 psi to about 700 psi.  
     
     
         74 . The process of  claim 69 , further comprising at least partially drying the film.  
     
     
         75 . The process of  claim 69 , wherein the nipped contact with a heated surface comprises a nip dwell time between about 0.5 milliseconds to about 5 milliseconds.  
     
     
         76 . The process of  claim 69 , wherein the first coating includes a surface and at least 50% of the first coating surface has subsurface voids having a transverse dimension of at least 5 microns.  
     
     
         77 . The process of  claim 69 , wherein the first coating includes a surface with a Sheffield Smoothness of less than about 300 units.  
     
     
         78 . The process of  claim 69 , wherein the first coating includes a surface with a Sheffield Smoothness of less than about 150 units.  
     
     
         79 . The process of  claim 69 , wherein the substrate is a cellulosic substrate.  
     
     
         80 . The process of  claim 69 , wherein the aqueous polymer solution comprises at least about 60% water soluble polymer by dry weight, and up to 10% release agent by dry weight.