CLAIMS
1. A resin composition which is configured such that, when the resin composition is formed into a resin composition film that has a thickness of. 3.0 (am after a heat treatment at a temperature within the range from 200 to 350°C, the resin composition film forms a heat-resistant resin film having a light transmittance of 50% or more at a wavelength of 365 to 436 nm before the heat treatment and having a light transmittance of 10% or less at a wavelength of 365 to 436 nm after the heat treatment.
2. The resin composition according to claim 1, wherein, when the resin composition is formed into a resin composition film having a thickness of 2.0 jam after a heat treatment at a temperature within the range from 200 to 350°C, the resin composition film forms a heat-resistant resin film having a light transmittance of 50% or more at a wavelength of 365 to 436 nm before the heat treatment and having a light transmittance of 5% or less at a wavelength of 350 to 460 nm after the heat treatment.
3. The resin composition according to claim 1 or 2, additionally containing a photo-acid generator and having positive-working photosensitivity.

4. A resin composition having positive-working photosensitivity and comprising (Al) a polyimide, a polybenzoxazole, a polyimide precursor or a polybenzoxazole precursor, (A3) a phenolic resin and/or a polyhydroxystyrene resin, (B) a thermally color-developing compound, (C) a photo-acid generator, and (D) a solvent, wherein the component (A3-) is contained in an amount of 5 to 50 parts by weight inclusive relative to 100 parts by weight of the component (Al) .
5 . A resin composition having positive-working photosensitivity and comprising (A2) a resin having such a backbone structure that two cyclic structures are bonded to a cyclic-structure-constituting quaternary carbon atom, (A3) a phenolic resin and/or a polyhydroxystyrene resin, (B) a thermally color-developing compound, (C) a photo-acid generator, and (D) a solvent, wherein the component (A3) is contained in an amount of 5 to 50 parts by weight inclusive relative to 100 parts by weight of the component (A2).
6. The resin composition according to claim 4 or 5, wherein the thermally color-developing compound (B) is a hydroxy-group-containing compound having a triarylmethane backbone.

7. The resin composition according to any one of claims 4 to 6, additionally containing (E) a dye and/or a pigment.
8. The resin composition according to any one of claims 4 to 7, additionally containing (F) a compound having 3 to 6
. thermally crosslinkable groups per molecule.
9. A resin composition having positive-working
photosensitivity and comprising (A) an alkali-soluble resin,
(I) a compound whose maximum absorption wavelength shifts by a heat treatment, (C) a photo-acid generator, and (D) a solvent.
10. The resin composition having positive-working photosensitivity according to claim 9, wherein the alkali-soluble resin (A) is a polyimide, a polybenzoxazole, a polyimide precursor or a polybenzoxazole precursor.
11. The resin composition having positive-working photosensitivity according to claim 9, wherein the alkali-soluble resin (A) comprises at least one alkali-soluble resin selected from: a resin having such a backbone structure that two cyclic structures are bonded to a
cyclic-structure-constituting quaternary carbon atom; and a phenolic resin and/or a polyhydroxystyrene resin.

12. The resin composition having positive-working photosensitivity according to any one of claims 9 to 11, wherein the compound (I) whose maximum absorption wavelength shifts by a heat treatment has a maximum absorption wavelength of 340 nm or more and less than 450 nm after a heat treatment.
13. The resin composition having positive-working photosensitivity according to any one of claims 9 to 12, wherein the compound (I) whose maximum absorption wavelength shifts by a heat treatment is a compound which has one or more phenolic hydroxyl groups and in which one, several or all of the phenolic hydroxyl groups are respectively protected by protecting groups.
14. The resin composition having positive-working photosensitivity according to claim 13, wherein the compound
(I) whose maximum absorption wavelength shifts by a heat treatment has one or more phenolic hydroxyl groups and each of the protecting groups which respectively protect one, several or all of the phenolic hydroxyl groups is a heat-labile group or an acid-labile group.
15. The resin composition having positive-working
photosensitivity according to claim 14, wherein the compound
(I) whose maximum absorption wavelength shifts by a heat

treatment has one or more phenolic hydroxy1 groups and a heat-labile group or an acid-labile group which protects each of one, several or all of the phenolic hydroxyl groups is represented by any one of general formula (8) to (11): [Chemical formula 16]

(in general formula (8) , R59 to R61 may be the same as one another or one or some of R59 to R61 may be different from the others, and independently represent a hydrogen atom or a monovalent hydrocarbon group having 1 or more carbon atoms; in general formula (9), n represents 0 or 1; in general formula (10), R62 represents a monovalent hydrocarbon group having 1 to 20 carbon atoms; and in general formula (11) , Z represents a hydrogen atom, a sulfur atom or -N (R63) -, R64 represents a monovalent hydrocarbon group having 1 to 20 carbon atoms, and R63 represents

a hydrogen atom or a monovalent hydrocarbon group having 1 to 20 carbon atoms).
16. The resin composition having positive-working photosensitivity according to any one of claims 9 to 15, wherein the compound (I) whose maximum absorption wavelength shifts by a heat treatment is a non-condensed polycyclic compound or a condensed polycyclic compound.
17 . The resin composition having positive-working photosensitivity according to any one of claims 9 to 16, wherein the compound (I) whose maximum absorption wavelength shifts by a heat treatment is a non-condensed polycyclic compound or a condensed polycyclic compound each having 2 to 8 inclusive of aromatic rings.
18. The resin composition having positive-working photosensitivity according to any one of claims 9 to 17, additionally containing (J) a compound which does not have an absorption maximum at a wavelength of 340 nm or more and less than 436 nm and has an absorption maximum at a wavelength of 436 to 750 nm inclusive.
19. The resin composition having positive-working photosensitivity according to any one of claims 9 to 18,

additionally containing (F) a compound having 3 to 6 thermally crosslinkable groups per molecule.
20. A method for producing a heat-resistant resin film, comprising the steps of: applying a resin composition as recited in any one of claims 1 to 19 onto a substrate to form a coating film; drying the coating film; exposing the dried photosensitive resin film to light; developing the light-exposed photosensitive resin film; and subjecting the developed photosensitive resin film to a heat treatment.
21. A method for producing a heat-resistant resin film, comprising the steps of: applying a resin composition as recited in any one of claims 1 to 19 onto a substrate using a slit nozzle to form a coating film; and drying the coating film under reduced pressure to form a photosensitive resin film.
22. A display device comprising a substrate, a first electrode which is formed on the substrate, an insulating layer which is formed on the first electrode in such a manner as to allow the first electrode to be partially exposed to light, and a second electrode which is provided opposed to the first electrode, wherein the insulating layer is a heat-resistant resin film produced by a production method as recited in claim 20 or 21.

23. A display device comprising a substrate on which thin film transistors (TFTs) are formed, a planarization film which is provided in such a manner as to cover projections and depressions on the substrate, and display elements which are provided on the planarization film, wherein the planarization film is a heat-resistant resin film produced by a production method as recited in claim 20 or 21.
24. A display device comprising a substrate on which oxide TFTs are formed as thin film transistors (TFTs) , a planarization film which is provided in such a manner as to cover projections and depressions on the substrate, and display elements which are provided on the planarization film, wherein the planarization film is a heat-resistant resin film produced by a production method as recited in claim 20 or 21.
25. The display device according to claim 23 or 24, wherein the degree of resolution of each of the display elements is 200 ppi or more.