Polycarbonate films prepared by coating methods

Abstract

A method of film fabrication is taught that uses a coating and drying apparatus to fabricate resin films suitable for optical applications. In particular, polycarbonate films are prepared by simultaneous application of multiple liquid layers to a moving carrier substrate. After solvent removal, the polycarbonate films are peeled from the sacrificial carrier substrate. Polycarbonate films prepared by the current invention exhibit good dimensional stability and low birefringence.

What is claimed is:  
     
         1 . A coating method for forming a polycarbonate film comprising the steps of: 
 (a) applying a liquid polycarbonate/solvent mixture onto a moving, discontinuous carrier substrate; and    (b) drying the liquid polycarbonate/solvent mixture to substantially remove the solvent yielding a composite of a polycarbonate film adhered to the discontinuous carrier substrate, the polycarbonate film being releasably adhered to the discontinuous carrier substrate thereby allowing the polycarbonate film to be peeled from the discontinuous carrier substrate.    
     
     
         2 . A coating method as recited in  claim 1  wherein: 
 the liquid polycarbonate/solvent mixture is applied using slide bead coating die with a multi-layer composite being formed on a slide surface thereof.  
 
     
     
         3 . A coating method as recited in  claim 2  wherein: 
 the viscosity of each liquid layer of the multi-layer composite is less than 5000 cp.  
 
     
     
         4 . A coating method as recited in  claim 1  wherein: 
 the carrier substrate is polyethylene terephthalate.  
 
     
     
         5 . A coating method as recited in  claim 1  wherein: 
 the carrier substrate has a subbing layer applied to the coated surface.  
 
     
     
         6 . A coating method as recited in  claim 2  wherein: 
 an uppermost layer of the multi-layer composite contains a surfactant.  
 
     
     
         7 . A coating method as recited in  claim 1  wherein: 
 the first drying section is operated at a temperature between 25 and 95° C.  
 
     
     
         8 . A coating method as recited in  claim 1  further comprising the step of: 
 winding the composite into at least one roll before the polycarbonate sheet is peeled from the discontinuous carrier substrate.  
 
     
     
         9 . A coating method as recited in  claim 1  further comprising the steps of: 
 (a) separating the polycarbonate film from the carrier substrate immediately after the drying step; and  
 (b) winding the polycarbonate film into at least one roll.  
 
     
     
         10 . A coating method as recited in  claim 8  further comprising the step of: 
 (a) unwinding at least a portion of at least one roll of the composite; and  
 (b) separating the polycarbonate film from the carrier substrate.  
 
     
     
         11 . A coating method as recited in  claim 1  wherein: 
 the polycarbonate film is adhered to the carrier substrate with an adhesive strength of less than about 250 N/m.  
 
     
     
         12 . A coating method as recited in  claim 9  further comprising the step of: 
 reducing residual solvent in the polycarbonate film to less than 10% by weight prior to the separating step.  
 
     
     
         13 . A coating method as recited in  claim 10  further comprising the step of: 
 reducing residual solvent in the polycarbonate film to less than 10% by weight prior to the separating step.  
 
     
     
         14 . A coating method as recited in  claim 8  further comprising the step of: 
 delivering the composite to a user of the polycarbonate film, the carrier substrate acting as a protective support for the polycarbonate film prior to the polycarbonate film being separated from the substrate carrier.  
 
     
     
         15 . A coating method as recited in  claim 1  further comprising the step of: 
 including a plasticizer in the liquid polycarbonate/solvent mixture.  
 
     
     
         16 . A coating method as recited in  claim 1  wherein: 
 the polycarbonate film has an in-plane retardation of less than 20 nm.  
 
     
     
         17 . A coating method as recited in  claim 1  wherein: 
 the polycarbonate film has an in-plane retardation of less than 10 nm.  
 
     
     
         18 . A coating method as recited in  claim 1  wherein: 
 the polycarbonate film has an in-plane retardation of less than 5.0 nm.  
 
     
     
         19 . A coating method as recited in  claim 1  further comprising the step of: 
 applying at least one additional polycarbonate layer to the composite after the drying step.  
 
     
     
         20 . A coating method as recited in  claim 1  wherein: 
 the polycarbonate film has a thickness in the range of 1 to 500 μm.  
 
     
     
         21 . A composite film comprising: 
 a polycarbonate film coated on a discontinuous carrier substrate, the polycarbonate film having a thickness in the range of from about 1 to about 500 μm, the polycarbonate film having an in-plane retardation that is less than 20 nm, the polycarbonate film being adhered to the carrier substrate with an adhesive strength of less than about 250 N/m.    
     
     
         22 . A composite film as recited in  claim 21  wherein: 
 the polycarbonate film has an in-plane retardation that is less than 10 nm.  
 
     
     
         23 . A composite film as recited in  claim 21  wherein: 
 the polycarbonate film has an in-plane retardation that is less than 5.0 nm.  
 
     
     
         24 . A composite film as recited in  claim 21  wherein: 
 the polycarbonate film is adhered to the carrier substrate with an adhesive strength of at least about 0.3 N/m.  
 
     
     
         25 . A composite film as recited in  claim 21  wherein: 
 the polycarbonate film is peelable from the carrier substrate.  
 
     
     
         26 . A composite film as recited in  claim 21  wherein: 
 the polycarbonate film is a multi-layer composite.  
 
     
     
         27 . A composite film as recited in  claim 26  wherein: 
 at least a top layer of the multi-layer composite includes a surfactant therein.  
 
     
     
         28 . A composite film as recited in  claim 21  wherein: 
 a plasticizer is incorporated in the polycarbonate film.  
 
     
     
         29 . A polycarbonate film made by the method of  claim 1  wherein: 
 the in-plane retardation is less than 20 nm.  
 
     
     
         30 . A polycarbonate film comprising: 
 a layer of polycarbonate formed by a coating operation, the polycarbonate film having a thickness in the range of from about 1 to about 500 μm, the polycarbonate film having an in-plane retardation that is less than 20 nm.    
     
     
         31 . A polycarbonate film as recited in  claim 30  further comprising: 
 a plasticizer incorporated in the polycarbonate film.  
 
     
     
         32 . A polycarbonate film as recited in  claim 30  wherein: 
 the polycarbonate film having an in-plane retardation that is less than 10 nm.  
 
     
     
         33 . A polycarbonate film as recited in  claim 30  wherein: 
 the polycarbonate film having an in-plane retardation that is less than 5.0 nm.  
 
     
     
         34 . A coating method as recited in  claim 1  further comprising the step of: 
 using the polycarbonate film to form a light polarizer.  
 
     
     
         35 . A display device including a polycarbonate film therein made by the method of  claim 1 .  
     
     
         36 . A polycarbonate film comprising: 
 a layer of polycarbonate formed by a coating operation, the polycarbonate film having an in-plane retardation that is less than about 20 nm.    
     
     
         37 . A polycarbonate film as recited in  claim 36  wherein: 
 the polycarbonate film having an in-plane retardation that is less than 10 nm.  
 
     
     
         38 . A polycarbonate film as recited in  claim 36  wherein: 
 the polycarbonate film having an in-plane retardation that is less than 5.0 nm.  
 
     
     
         39 . A composite film as recited in  claim 26  wherein: 
 only a top layer of the multi-layer composite includes a surfactant therein.  
 
     
     
         40 . A composite film as recited in  claim 26  wherein: 
 at least a top layer of the multi-layer composite includes a fluorinated surfactant therein.  
 
     
     
         41 . A coating method as recited in  claim 2  wherein: 
 an uppermost layer of the multi-layer composite contains a fluorinated surfactant.  
 
     
     
         42 . A coating method as recited in  claim 2  wherein: 
 an uppermost layer of the multi-layer composite contains a polysiloxane surfactant.  
 
     
     
         43 . An electronic display device having view screen comprising: 
 a polycarbonate film having an in-plane retardation that is less than about 10 nm.    
     
     
         44 . An electronic display device as recited in  claim 43  wherein: 
 the polycarbonate film having an in-plane retardation that is less than about 5 nm.  
 
     
     
         45 . An polycarbonate film comprising: 
 a coated layer of polycarbonate having an in-plane retardation that is less than about 20 nm.    
     
     
         46 . A coating method as recited in  claim 7  wherein: 
 the drying step is initially performed at a temperature in the range of from about 25° C. to less than 95° C.  
 
     
     
         47 . A coating method as recited in  claim 7  wherein: 
 the drying step is initially performed at a temperature in the range of from about 30° C. to about 60° C.  
 
     
     
         48 . A coating method as recited in  claim 7  wherein: 
 the drying step is initially performed at a temperature in the range of from about 30° C. to about 50° C.  
 
     
     
         49 . An electronic display device as recited in  claim 43  wherein: 
 the polycarbonate film has a light transmittance of at least about 85 percent and a haze value of less than about 1.0 percent.  
 
     
     
         50 . A polycarbonate film as recited in  claim 45  wherein: 
 the coated layer of polycarbonate has a light transmittance of at least about 85 percent and a haze value of less than about 1.0 percent.  
 
     
     
         51 . A coating method as recited in  claim 1  wherein: 
 the optical resin film has a light transmittance of at least about 85 percent and a haze value of less than about 1.0 percent.  
 
     
     
         52 . A coating method as recited in  claim 1  wherein: 
 the optical resin film has an average surface roughness of less than about 100 nm.  
 
     
     
         53 . A coating method as recited in  claim 1  wherein: 
 the optical resin film has an average surface roughness of less than about 50 nm.  
 
     
     
         54 . A coating method as recited in  claim 1  wherein: 
 the optical resin film has an average surface roughness of not more than about 1 nm.