Polyimide film for graphite sheet, graphite sheet prepared by using the same and method for preparing graphite sheet

1. A polyimide film prepared from a precursor composition containing a polyamic acid and an organic solvent and having a value of the following Formula 1 less than 0.4:

(first FWHM−second FWHM)/(first FWHM+second FWHM)   Formula 1

wherein, when a diffraction peak of (010) plane according to XRD analysis of the polyimide film is in the form of a single peak, the first FWHM (full width at half maximum) indicates a FWHM of the single peak; and when the diffraction peak of (010) plane is in the form of a plurality of single peaks or in the form of a plurality of single peaks overlapped with each other, the first FWHM indicates an average of individual FWHMs of the single peaks, and

when a diffraction peak of (102) plane according to XRD analysis of the polyimide film is in the form of a single peak, the second FWHM indicates a FWHM of the single peak; and when the diffraction peak of (102) plane is in the form of a plurality of single peaks or in the form of a plurality of single peaks overlapped with each other, the second FWHM indicates an average of individual FWHMs of the single peaks,

wherein the precursor composition satisfies the following conditions (a) to (c):

(a) a viscosity of the precursor composition is from 55,000 cP to 900,000 cP;

(b) a heat treatment temperature for heating and drying the precursor composition after casting the precursor composition is from 150 degrees C. to 200 degrees C.; and

(c) a film intermediate derived from the precursor composition is stretched in at least one of a machine direction.

2. The polyimide film of claim 1 , wherein the polyamic acid is contained in an amount 15 to 20% by weight based on the total weight of the precursor composition.

3. The polyimide film of claim 1 , wherein the film intermediate is stretched so that the polyimide film has a thickness of 20 to 125 micrometers.

4. The polyimide film of claim 1 , wherein a stretching ratio in the at least one of the machine direction and the transverse direction is +3% or more and +25% or less.

5. The polyimide film of claim 1 , wherein the polyamic acid is prepared by polymerization of dianhydride monomers and diamine monomers.

6. The polyimide film of claim 1 , wherein the first FWHM is 35 degrees or more and 80 degrees or less, and the second FWHM is 43% or more and 92% or less of the first FWHM.

7. The polyimide film of claim 1 , wherein the value of Formula 1 is 0.01 or more and 0.37 or less.

8. A method for preparing a graphite sheet, comprising:

preparing a polyimide film having a value of the following Formula 1 less than 0.4;

carbonizing the polyimide film; and

obtaining a graphite sheet by graphitizing the carbonized polyimide film,

wherein the graphite sheet has a thermal conductivity of 1400 W/m·K or more:

(first FWHM−second FWHM)/(first FWHM+second FWHM)   Formula 1

wherein, when a diffraction peak of (010) plane according to XRD analysis of the polyimide film is in the form of a single peak, the first FWHM (full width at half maximum) indicates a FWHM of the single peak; and when the diffraction peak of (010) plane is in the form of a plurality of single peaks or in the form of a plurality of single peaks overlapped with each other, the first FWHM indicates an average of individual FWHMs of the single peaks, and when a diffraction peak of (102) plane according to XRD analysis of the polyimide film is in the form of a single peak, the second FWHM indicates a FWHM of the single peak; and when the diffraction peak of (102) plane is in the form of a plurality of single peaks or in the form of a plurality of single peaks overlapped with each other, the second FWHM indicates an average of individual FWHMs of the single peaks, wherein the preparation of a polyimide film satisfies the following process conditions (a) to (c):

(a) a viscosity of a precursor composition containing a polyamic acid and an organic solvent is from 55,000 cP to 900,000 cP;

(b) a heat treatment for heating and drying the precursor composition after casting the precursor composition is conducted at a temperature of from 150 degrees C. to 200 degrees C.; and

(c) a film intermediate prepared by the heat treatment is stretched at least once to obtain the polyimide film.

9. The method for preparing a graphite sheet of claim 8 , wherein the preparation of a polyimide film includes:

preparing a precursor composition under the process condition (a);

forming a film intermediate by heat-treating the precursor composition under the process condition (b); and

stretching the film intermediate in at least one of a machine direction and a transverse direction under the process condition (c).

10. The method for preparing a graphite sheet of claim 9 , wherein the film intermediate is stretched so that the polyimide film has a thickness of 20 to 125 micrometers.

11. The method for preparing a graphite sheet of claim 10 , wherein the film intermediate is stretched at a temperature of 20 degrees C. to 40 degrees C.

12. The method for preparing a graphite sheet of claim 9 , wherein the film intermediate is stretched at a stretching ratio of +3% or more and +25% or less in at least one of the machine direction and the transverse direction.

13. The method for preparing a graphite sheet of claim 9 , wherein the precursor composition is prepared by mixing the polyamic acid in an amount of 15 to 20% by weight and the organic solvent in an amount of 80 to 85% by weight based on the total weight of the precursor composition.

14. The method for preparing a graphite sheet of claim 9 , wherein the polyamic acid is prepared by polymerization of dianhydride monomers and diamine monomers.

15. The method for preparing a graphite sheet of claim 8 , wherein the first FWHM is 35 degrees or more and 80 degrees or less, and the second FWHM is 43% or more and 92% or less of the first FWHM.

16. The method for preparing a graphite sheet of claim 8 , wherein the value of Formula 1 is 0.01 or more and 0.37 or less.

17. The method for preparing a graphite sheet of claim 8 , wherein the polyimide film is carbonized by heat-treating the polyimide film at a temperature of 1,000 degrees C. to 1,500 degrees C.

18. The method for preparing a graphite sheet of claim 8 , wherein the carbonized polyimide film is graphitized by heat-treating the carbonized polyimide film at a temperature of 2,500 degrees C. to 3,000 degrees C.