Optical film, optical film manufacturing method, transparent substrate, image display device, and solar cell
View Patent ↗An optical film that is excellent not only in transparency and heat resistance but also in solubility in an organic solvent and linear thermal expansion coefficient. Also, a product or a member which meets high demands for heat resistance and low linear thermal expansion coefficient with the use of the optical film, more specifically a transparent substrate using the optical film, and an image display device and a solar cell including the optical film or the transparent substrate. The optical film contains a polyimide having a specific structure in which a repeating unit of a chain of a polymer has both an amide group and an imide group and the polymer has a fluorine atom. The polyimide is obtained by mixing a dehydrating agent and an imidizing agent with a polyamic acid solution so as to imidize the polyamic acid.
1. An optical film comprising a polyimide having a repeating unit n represented by the following formula (1):
where Af represents a bivalent organic group having an aromatic ring and a fluorine atom and B represents a bivalent organic group,
the optical film having a linear thermal expansion coefficient of 20 ppm/K or less.
2. The optical film according to claim 1 , wherein:
Af in the formula (1) is represented by the following formula (2):
where D represents a functional group selected from a single bond, a CR 2 group, a CO group, a SO 2 group, a SiR 2 group, an oxygen atom, and a sulfur atom, where R is identically or differently a hydrogen atom, a fluorine atom, an alkyl group having 1 to 20 carbon atoms, or an aryl group having 6 to 20 carbon atoms, the two Rs may form a ring with each other, and a hydrogen atom in the alkyl group and the aryl group may be substituted with a fluorine atom, and E represents a fluorine atom or an organic group which has a fluorine atom, m is an integer of 0 to 4, and 1 is an integer of 0 to 4.
3. The optical film according to claim 1 , wherein:
Af in the formula (1) is selected from the following formulas (3) and (4):
4. The optical film according to claim 1 , wherein B in the formula (1) has an aromatic ring and a fluorine atom.
5. The optical film according to claim 1 , wherein:
B in the formula (1) is represented by the following formula (2):
where D represents a functional group selected from a single bond, a CR 2 group, a CO group, a SO 2 group, a SiR 2 group, an oxygen atom, and a sulfur atom, where R is identically or differently a hydrogen atom, a fluorine atom, an alkyl group having 1 to 20 carbon atoms, or an aryl group having 6 to 20 carbon atoms, the two Rs may form a ring with each other, and a hydrogen atom in the alkyl group and the aryl group may be substituted with a fluorine atom, and E represents a fluorine atom or an organic group which has a fluorine atom, m is an integer of 0 to 4, and 1 is an integer of 0 to 4.
6. The optical film according to claim 1 , wherein B in the formula (1) is selected from the following formulas (3) and (4):
7. The optical film according to claim 1 , wherein the polyimide is obtainable by mixing a dehydrating agent and an imidizing agent with a polyamic acid so as to imidize the polyamic acid.
8. The optical film according to claim 1 , wherein the polyimide is soluble in an organic solvent.
9. The optical film according to claim 8 , wherein the organic solvent is at least one selected from amide type solvents, ketone type solvents, and ether type solvents.
10. The optical film according to claim 1 , wherein the optical film has total light transmittance of 85% or more.
11. The optical film according to claim 1 , wherein the optical film has transmittance of 10% or more at a wavelength of 400 nm.
12. The optical film according to claim 1 , wherein the optical film has glass transition temperature of 250° C. or more.
13. A method for producing an optical film as set forth in claim 1 , comprising the steps of:
(a) imidizing polyamic acid varnish, which is a mixture of a dehydrating agent, an imidizing agent, and a polyamic acid;
(b) mixing a poor solvent after the step (a) so as to obtain a solid product;
(c) dissolving the solid product in an organic solvent so as to obtain a solution; and
(d) applying the solution to a substrate after the step (c) so as to form a film.
14. A transparent substrate consisting of an optical film as set forth in claim 1 .
15. An image display device comprising an optical film as set forth in claim 1 .
16. A solar cell comprising an optical film as set forth in claim 1 .