Polyamide-imide film and process for preparing the same

1. A polyamide-imide film, which comprises:

a polyamide-imide polymer formed by polymerizing a diamine compound, a dianhydride compound, and a dicarbonyl compound; and silica particles,

wherein the number of aggregates having an average diameter of 150 to 200 nm observed in a cross-section cut in the thickness direction of the polyamide-imide film is less than 0.5/μm 2 , and

wherein a ratio of an average particle diameter of secondary particles to an average particle diameter of primary particles of the silica particles is 1.2 to 3.0.

2. The polyamide-imide film of claim 1 , wherein the average particle size of primary particles of the silica particles is 10 to 40 nm, and

the average particle size of secondary particles of the silica particles is 30 to 80 nm.

3. The polyamide-imide film of claim 1 , wherein the content of the silica particles is 50 to 600 ppm based on the total weight of the polyamide-imide polymer.

4. The polyamide-imide film of claim 1 , wherein the number of aggregates having an average diameter of 150 to 200 nm observed in a cross-section cut in the thickness direction of the polyamide-imide film is 0 to 0.3/μm 2 .

5. The polyamide-imide film of claim 1 , wherein the diamine compound is represented by the following Formula 1,

the dianhydride compound is represented by the following Formula 2, and

the dicarbonyl compound is represented by the following Formula 3:

in the above Formulae 1 to 3,

E and J are each independently selected from a substituted or unsubstituted divalent C 6 -C 30 aliphatic cyclic group, a substituted or unsubstituted divalent C 4 -C 30 heteroaliphatic cyclic group, a substituted or unsubstituted divalent C 6 -C 30 aromatic cyclic group, a substituted or unsubstituted divalent C 4 -C 30 heteroaromatic cyclic group, a substituted or unsubstituted C 1 -C 30 alkylene group, a substituted or unsubstituted C 2 -C 30 alkenylene group, a substituted or unsubstituted C 2 -C 30 alkynylene group, —O—, —S—, —C(═O)—, —CH(OH)—, —S(═O) 2 —, —Si(CH 3 ) 2 —, —C(CH 3 ) 2 —, and —C(CF 3 ) 2 —,

e and j are each independently selected from integers of 1 to 5,

when e is 2 or more, then the 2 or more Es are the same as, or different from, each other,

when j is 2 or more, then the 2 or more Js are the same as, or different from, each other,

G is a substituted or unsubstituted tetravalent C 6 -C 30 aliphatic cyclic group, a substituted or unsubstituted tetravalent C 4 -C 30 heteroaliphatic cyclic group, a substituted or unsubstituted tetravalent C 6 -C 30 aromatic cyclic group, or a substituted or unsubstituted tetravalent C 4 -C 30 heteroaromatic cyclic group, wherein the aliphatic cyclic group, the heteroaliphatic cyclic group, the aromatic cyclic group, or the heteroaromatic cyclic group is present alone, bonded to each other to form a condensed ring, or bonded by a bonding group selected from a substituted or unsubstituted C 1 -C 30 alkylene group, a substituted or unsubstituted C 2 -C 30 alkenylene group, a substituted or unsubstituted C 2 -C 30 alkynylene group, —O—, —S—, —C(═O)—, —CH(OH)—, —S(═O) 2 —, —Si(CH 3 ) 2 —, —C(CH 3 ) 2 —, and —C(CF 3 ) 2 —, and

X is a halogen atom.

6. The polyamide-imide film of claim 1 , wherein the dianhydride compound is composed of a compound having a fluorine-containing substituent.

7. The polyamide-imide film of claim 1 , wherein the dicarbonyl compound comprises at least two dicarbonyl compounds different from each other.

8. The polyamide-imide film of claim 1 , wherein the polyamide-imide polymer comprises a repeat unit represented by the following Formula A and a repeat unit represented by the following Formula B:

wherein E, G, J, e, and j in the above Formulae A and B are as described in claim 5 .

9. The polyamide-imide film of claim 8 , wherein in the polyamide-imide polymer, the molar ratio of the repeat unit represented by the above Formula A to the repeat unit represented by the above Formula B is 10:90 to 25:75.

10. The polyamide-imide film of claim 1 , which, based on a thickness of 50 μm, has a modulus of 5.0 GPa or more, an elongation of 15% or more, a tensile strength of 15 kgf/mm 2 or more, and a haze of 2% or less.