Polyvinyl alcohol film, and polarizing film and polarizing plate using the same
View Patent ↗The present invention provides a polyvinyl alcohol film which has a width of 3 m or more, an in-plane retardation value of 30 nm or less and a fluctuation of in-plane retardation value of 15 nm or less.
1. A polyvinyl alcohol film,
wherein the film has a width of 3 m or more,
the film has in-plane retardation values of 30 nm or less obtained at measuring points placed at one cm intervals in a width direction across an entire width of the film,
the film has a fluctuation of the in-plane retardation values of 15 nm or less among the in-plane retardation values obtained at the measuring points, and
the film has a thickness in a range from 30 to 70 μM prior to being subjected to a stretching treatment for producing a polarizing film.
2. The polyvinyl alcohol film according to claim 1 , which is used as a raw film of a polarizing film.
3. The polyvinyl alcohol film according to claim 1 , wherein the polyvinyl alcohol film has light transmittance of 90% or higher.
4. The polyvinyl alcohol film according to claim 1 , wherein a complete dissolution temperature in water of the polyvinyl alcohol film is 65° C. or higher.
5. A polarizing film, which is formed of the polyvinyl alcohol film according to claim 1 .
6. A polarizing plate comprising the polarizing film according to claim 5 and a protective film provided on at least one surface of the polarizing film.
7. A process for producing a polyvinyl alcohol film, comprising:
a step of forming a film by a casting method; and
a step of thermally treating the film by a plurality of hot rolls each having a surface temperature of 40° C. or higher,
wherein a contact time at any one in-plane point of the film with each of the hot rolls is from 1 to 6 seconds in the step of the thermal treatment,
the polyvinyl alcohol film has a width of 3 m or more,
the film has in-plane retardation values of 30 nm or less obtained at measuring points placed at one cm intervals in a width direction across an entire width of the film,
the film has a fluctuation of the in-plane retardation values of 15 nm or less among the in-plane retardation values obtained at the measuring points, and
the film has a thickness in a range from 30 to 70 μm prior to being subjected to a stretching treatment for producing a polarizing film.
8. The process for producing a polyvinyl alcohol film according to claim 7 , wherein a sum of the contact time at any one in-plane point of the film with each of the hot rolls is from 30 to 100 seconds.
9. The process for producing a polyvinyl alcohol film according to claim 7 , wherein a diameter of all of the hot rolls is from 150 to 500 mm.