Polyimide precursor solution and method for producing porous polyimide film

1. A polyimide precursor solution comprising:

a polyimide precursor;

a resin particle having 55% by weight or more of a structural unit derived from a styrene derivative; and

a mixed solvent containing a first organic solvent (S1) and a second organic solvent (S2),

wherein:

a content of the polyimide precursor in the polyimide precursor solution is 0.1% by weight or more and 40% by weight or less,

a volume ratio of the resin particle with respect to a total solid content of the polyimide precursor and the resin particle in the polyimide precursor solution is 20% or more and 80% or less, and

the polyimide precursor solution satisfies the following conditions (1) to (4),

condition (1): a weight ratio (S1/S2) of the first organic solvent (S1) to the second organic solvent (S2) is from 50/50 to 90/10,

condition (2): a Hansen solubility parameter (HSP) distance between the first organic solvent (S1) and the resin particle is 11 or more and less than 16,

condition (3): a HSP distance between the second organic solvent (S2) and the resin particle is 16 or more, and

condition (4): a HSP distance between the mixed solvent and the polyimide precursor is 12 or less.

2. The polyimide precursor solution according to claim 1 ,

wherein the polyimide precursor solution further satisfies the following conditions (12) to (14),

condition (12): a HSP distance between the first organic solvent (S1) and the resin particle is 11 or more and less than 16 and a HSP distance between the first organic solvent (S1) and the polyimide precursor is 11 or less,

condition (13): a HSP distance between the second organic solvent (S2) and the resin particle is 17 or more, and

condition (14): a HSP distance between the mixed solvent and the polyimide precursor is 11 or less.

3. The polyimide precursor solution according to claim 1 ,

wherein a boiling point of each of the first organic solvent (S1) and the second organic solvent (S2) is 150° C. or higher.

4. The polyimide precursor solution according to claim 1 ,

wherein a boiling point difference (absolute value) between the first organic solvent (S1) and the second organic solvent (S2) is 30° C. or lower.

5. The polyimide precursor solution according to claim 1 ,

wherein a boiling point difference (absolute value) between the first organic solvent (S1) and the second organic solvent (S2) is 20° C. or lower.

6. The polyimide precursor solution according to claim 1 ,

wherein the first organic solvent (S1) is at least one selected from the group consisting of dimethyl sulfoxide, γ-butyrolactone, ε-caprolactone, and furfuryl alcohol.

7. The polyimide precursor solution according to claim 1 ,

wherein the first organic solvent (S1) is dimethyl sulfoxide.

8. The polyimide precursor solution according to claim 1 ,

wherein the second organic solvent (S2) is at least one selected from the group consisting of ethylene glycol, diethylene glycol, propylene glycol, and dipropylene glycol.

9. The polyimide precursor solution according to claim 8 ,

wherein the second organic solvent (S2) is at least one selected from the group consisting of ethylene glycol and propylene glycol.

10. The polyimide precursor solution according to claim 1 ,

wherein a content of the second organic solvent (S2) with respect to the resin particle is 60% by weight or more.

11. The polyimide precursor solution according to claim 1 ,

wherein the resin particle has 70% by weight or more of the structural unit derived from the styrene derivative.

12. The polyimide precursor solution according to claim 1 , further comprising:

an anionic surfactant in an amount of 0.01% by weight or more and 3% by weight or less with respect to the resin particle.

13. The polyimide precursor solution according to claim 1 , further comprising:

0.2% by weight or more and 2% by weight or less of water with respect to the entire polyimide precursor solution.

14. A method for producing a porous polyimide film comprising:

forming a coating film by applying the polyimide precursor solution according to claim 1 on a substrate,

forming a dried film containing the polyimide precursor and the resin particle by drying the coating film, and

forming a polyimide film by heating the dried film to thereby imidize the polyimide precursor, wherein in forming the polyimide film, a treatment of removing the resin particle is included.

15. The polyimide precursor solution according to claim 1 , wherein the content of the polyimide precursor in the polyimide precursor solution is 0.5% by weight or more and 25% by weight or less.

16. The polyimide precursor solution according to claim 1 , wherein the content of the polyimide precursor in the polyimide precursor solution is 1% by weight or more and 20% by weight or less.

17. The polyimide precursor solution according to claim 1 , wherein the volume ratio of the resin particle with respect to the total solid content of the polyimide precursor and the resin particle in the polyimide precursor solution is 30% or more and 75% or less.

18. The polyimide precursor solution according to claim 1 , wherein a proportion of the resin particle in the polyimide precursor solution is greater than a proportion of the polyimide precursor in the polyimide precursor solution by volume.

19. The polyimide precursor solution according to claim 1 , wherein:

the content of the polyimide precursor in the polyimide precursor solution is 1% by weight or more and 40% by weight or less, and

a proportion of the resin particle in the polyimide precursor solution is greater than a proportion of the polyimide precursor in the polyimide precursor solution by volume.