Base film
The present application relates to a method for preparing a base film, a laminate or a polarizing film. The present application can provide an elongatable base film which simultaneously maintains elongation and recovery rates at proper levels and guarantees water resistance, and thus can be effectively applied in the preparation of, for example, a polarizing film. The present application can also provide a laminate using the film or a method for preparing a polarizing film using the base film. The base film can be effectively applied in the preparation of a polarizing film having an excellent function, such as polarization performance, while having a thickness of, for example, about 10 μm or less, about 8 μm or less, about 7 μm or less, about 6 μm or less, or about 5 μm or less.
1. A base film for elongation comprising a thermoplastic polyurethane which is a reaction product of a mixture comprising a polyol, a multivalent isocyanate and a chain extender,
wherein said multivalent isocyanate comprises a multivalent isocyanate having an aromatic core having 12 or more carbon atoms and a multivalent isocyanate having an aromatic core having less than 12 carbon atoms, and
wherein the base film satisfies the following Equation 1:
E/R≥ 5 [Equation 1]
wherein, E is an elongation rate (unit: %) of said base film measured at room temperature, and R is a recovery rate (unit: %), and said recovery rate is a value measured by substituting a longitudinal length (T) of the base film, which is measured after elongating a laminate prepared by attaching to one side of said base film tailored to have a width of 50 mm and a length of 100 mm a PVA film having the same width and length and a thickness of 30 μm in water (temperature: 60° C.) five times in the longitudinal direction, and then taking it out from water, peeling said PVA film off, and maintaining the base film at room temperature for 1 hour, into an equation “100×(T−A)/A,” where A is a longitudinal length of said base film before elongation,
wherein the ratio (C/D) of the weight (C) of the multivalent isocyanate having an aromatic core having 12 or more carbon atoms and the weight (D) of the multivalent isocyanate having an aromatic core having less than 12 carbon atoms is 5 to 30.
2. The base film for elongation according to claim 1 , wherein the chain extender comprises an aliphatic diol having 5 or more carbon atoms and an aliphatic diol having 4 or less carbon atoms.
3. The base film for elongation according to claim 2 , wherein the aliphatic diol having 4 or less carbon atoms is contained in a ratio of 30 parts by weight or less relative to 100 parts by weight of the polyol.
4. The base film for elongation according to claim 2 , wherein the ratio (A/B) of the weight (B) of the aliphatic diol having 5 or more carbon atoms and the weight (A) of the aliphatic diol having 4 or less carbon atoms is 1 or less.
5. The base film for elongation according to claim 1 , wherein the base film comprises inorganic particles.
6. The base film for elongation according to claim 5 , wherein the inorganic particles are talc or calcium carbonate.
7. The base film for elongation according to claim 5 , comprising 0.01 to 10 parts by weight of the inorganic particles relative to 100 parts by weight of the polyurethane.
8. The base film for elongation according to claim 1 , wherein the polyol is a polyester polyol.
9. The base film for elongation according to claim 1 , wherein the polyol comprises a first polyol having a weight average molecular weight of 1,500 or less and a second polyol having a weight average molecular weight of more than 1,500.
10. The base film for elongation according to claim 1 , wherein the polyol comprises a first polyol having a weight average molecular weight of 1,500 or less and a second polyol having a weight average molecular weight of more than 1,500, and said second polyol is contained in a ratio of 50 parts by weight to 200 parts by weight relative to 100 parts by weight of said first polyol.
11. The base film for elongation according to claim 1 , wherein the multivalent isocyanate having an aromatic core having 12 or more carbon atoms is contained in the mixture in an amount of at least 150 parts by weight relative to 100 parts by weight of the polyol.
12. The base film for elongation according to claim 1 , wherein the polyurethane has a weight average molecular weight in a range of 100,000 to 400,000.
13. The base film for elongation according to claim 1 , having an elongation rate in a range of 200% to 1500%.
14. The base film for elongation according to claim 1 , having a tensile strength in a range of 20 MPa to 200 MPa.
15. The base film for elongation according to claim 1 , having a yield point in a range of 10 MPa to 150 MPa.
16. The base film for elongation according to claim 1 , having an elastic limit in a range of 200 MPa to 1,000 MPa.
17. A laminate comprising the base film of claim 1 ; and a polarizing functional material layer formed on one or both sides of said base film.
18. A method for producing a polarizing film comprising elongating the laminate of claim 17 .