Web transport apparatus and solution casting process

Abstract

A pin tentering apparatus as web transport apparatus includes a tentering mechanism for transporting self-supporting cast film by retaining web edge portions of the cast film. A gas flow device blows evaporative gas to the cast film being transported, to float the cast film. A static pressure adjuster lowers static pressure of the evaporative gas to a web middle portion with respect to a web width direction of the cast film, to regularize distribution of the static pressure in the web width direction. In the gas flow device, a blower duct introduces the evaporative gas. A nozzle plate is positioned at a front end of the duct, and has nozzles which blow the evaporative gas. Preferably, the static pressure adjuster includes an exhaust device, disposed to face the web middle portion between the plural nozzles, for exhausting the evaporative gas.

1 . A web transport apparatus comprising:
 a transport mechanism for transporting web by retaining web edge portions of said web;   a gas flow device for blowing gaseous medium to said web being transported, to float said web; and   a static pressure adjuster for lowering static pressure of said gaseous medium to a web middle portion of said web with respect to a web width direction thereof, to regularize distribution of said static pressure in said web width direction.   
   
   
       2 . A web transport apparatus as defined in  claim 1 , wherein said gas flow device includes:
 a duct for introducing said gaseous medium; and   a nozzle plate, positioned at a front end of said duct, having a nozzle, for blowing said gaseous medium through said nozzle.   
   
   
       3 . A web transport apparatus as defined in  claim 2 , wherein said static pressure adjuster limits said distribution of said static pressure to a value equal to or more than −200% and equal to or less than +200% per unit area of said web. 
   
   
       4 . A web transport apparatus as defined in  claim 3 , wherein said gaseous medium is evaporative gas, and said transport mechanism is constituted by a tentering mechanism. 
   
   
       5 . A web transport apparatus as defined in  claim 3 , wherein said static pressure adjuster controls a flow rate of said gaseous medium in said gas flow device with respect to said web width direction. 
   
   
       6 . A web transport apparatus as defined in  claim 3 , wherein said nozzle is constituted by plural nozzles;
 said static pressure adjuster includes an exhaust device, disposed to face said web middle portion between said plural nozzles, for exhausting said gaseous medium.   
   
   
       7 . A web transport apparatus as defined in  claim 6 , wherein said exhaust device is so constructed that a flow rate of exhausting said gaseous medium is variable. 
   
   
       5 . A web transport apparatus as defined in  claim 6 , wherein said plural nozzles include:
 a first nozzle group of nozzles opposed to said web edge portions; and   a second nozzle group of nozzles, opposed to said web middle portion, and offset from said exhaust device.   
   
   
       9 . A web transport apparatus as defined in  claim 3 , wherein said static pressure adjuster includes a recess, formed in said nozzle plate, and opposed to said web middle portion. 
   
   
       10 . A web transport apparatus as defined in  claim 3 , wherein said nozzle is constituted by plural nozzles including:
 a first nozzle group of nozzles opposed to said web edge portions;   a second nozzle group of nozzles, opposed to said web middle portion, for operating at a smaller flow rate of said gaseous medium than a flow rate of said gaseous medium of said first nozzle group, to constitute said static pressure adjuster.   
   
   
       11 . A web transport apparatus as defined in  claim 10 , wherein said duct includes:
 a first duct section for introducing said gaseous medium to said first nozzle group;   a second duct section for introducing said gaseous medium to said second nozzle group;   said static pressure adjuster controls said duct by setting said flow rate smaller for said second duct section than for said first duct section.   
   
   
       12 . A web transport apparatus as defined in  claim 10 , wherein a total aperture area of said second nozzle group is smaller than a total aperture area of said first nozzle group. 
   
   
       13 . A web transport apparatus as defined in  claim 10 , wherein a number of said nozzles in said second nozzle group is smaller than a number of said nozzles in said first nozzle group. 
   
   
       14 . A web transport apparatus as defined in  claim 3 , wherein said nozzle plate is constituted by plural nozzle plates, arranged in a transport direction of said web at a regular interval, disposed respectively to extend in said web width direction, for blowing said gaseous medium;
 said static pressure adjuster includes a movable plate portion disposed between said nozzle plates, a distance of said movable plate portion from said web being variable.   
   
   
       15 . A web transport apparatus as defined in  claim 14 , wherein said movable plate portion is set farther from said web than said nozzle plates. 
   
   
       16 . A web transport apparatus as defined in  claim 14 , further comprising an exhaust device, disposed through said movable plate portion, for exhausting said gaseous medium. 
   
   
       17 . A web transport apparatus as defined in  claim 3 , wherein said transport mechanism includes:
 first and second tenter pin groups, disposed to face respectively said web edge portions, respectively including plural tenter pins for piecing said web edge portions;   a moving device for endlessly moving said first and second tenter pin groups along said web edge portions, to transport said web.   
   
   
       18 . A web transport apparatus as defined in  claim 17 , wherein said web is cast film, formed by casting cellulose ester solution containing cellulose ester and solvent, and having a self-supporting property. 
   
   
       19 . A web transport apparatus as defined in  claim 18 , wherein content of said solvent contained in said cast film is equal to or more than 130 wt. %. 
   
   
       20 . A solution casting process comprising steps of:
 casting cellulose ester solution on to an endlessly traveling support, to form cast film;   stripping said cast film from said support;   transporting said cast film by retaining web edge portions of said cast film;   blowing gaseous medium to said cast film being transport for flotation; and   lowering static pressure of said gaseous medium to a web middle portion of said cast film with respect to a web width direction thereof, to regularize distribution of said static pressure in said web width direction.