阅读说明：本技术 一种聚酰亚胺前体组合物、其制备方法及由其制造的聚酰亚胺基板 (Polyimide precursor composition, preparation method thereof and polyimide substrate manufactured by polyimide precursor composition ) 是由 黄仁焕 金周映 李翼祥 元东荣 林铉才 于 2018-06-25 设计创作，主要内容包括：本发明涉及一种聚酰亚胺前体组合物、其制备方法及由其制造的聚酰亚胺基板。所述聚酰亚胺前体组合物具有高固含量和低粘度,因此有利于制造基板并且具有优异的在室温下储存稳定性。另外,所述聚酰亚胺基板具有优异的耐热性和机械性能,因此适合用作显示基板。(The present invention relates to a polyimide precursor composition, a method for preparing the same, and a polyimide substrate manufactured therefrom. The polyimide precursor composition has a high solid content and a low viscosity, thus facilitating the manufacture of a substrate and having excellent storage stability at room temperature. In addition, the polyimide substrate has excellent heat resistance and mechanical properties, and thus is suitable for use as a display substrate.)

1. A polyimide precursor composition comprising:

a polyamic acid solution prepared from a polyamic acid composition comprising an aromatic dianhydride comprising 3,4,3',4' -biphenyltetracarboxylic dianhydride (BPDA) and an aromatic diamine comprising p-phenylenediamine (PPD);

an aromatic carboxylic acid having at least four carboxyl groups;

a tertiary amine curing agent; and

an antioxidant.

2. The polyimide precursor composition according to claim 1, wherein the aromatic dianhydride further comprises pyromellitic dianhydride (PMDA), 3,3',4,4' -benzophenonetetracarboxylic dianhydride (BTDA), 2,3,3',4' -biphenyltetracarboxylic dianhydride, 1H, 3H-naphtho [2,3-c:6,7-c ' ] difuran-1, 3,6, 8-tetraone 2,3,6, 7-naphthalenetetracarboxylic dianhydride, 1,4,5, 8-naphthalenetetracarboxylic dianhydride, 4,4' -oxydiphthalic anhydride, 4,4' -oxybis (2-benzofuran-1, 3-dione), 4- [ (1, 3-dioxo-1, 3-dihydro-2-benzofuran-5-yl) oxy ] -2-benzofuran-1, at least one of 3-dione and 5,5' -sulfonyl bis-1, 3-isobenzofurandione.

3. The polyimide precursor composition according to claim 2, wherein the additional aromatic dianhydride is contained in an amount of 0.1 to 70 moles per 100 moles of the aromatic diamine.

4. The polyimide precursor composition according to claim 1, wherein the aromatic carboxylic acid comprises at least one of pyromellitic acid (PMA), 3',4,4' -biphenyltetracarboxylic acid (BPTA), 1,2,3, 4-benzenetetracarboxylic acid, benzophenone-3, 3',4,4' -tetracarboxylic acid, pyrazinetetracarboxylic acid, 2,3,6, 7-naphthalenetetracarboxylic acid, and naphthalene-1, 4,5, 8-tetracarboxylic acid.

5. The polyimide precursor composition according to claim 1, wherein the polyamic acid composition comprises 1 to 8 moles of the aromatic carboxylic acid per 100 moles of the aromatic diamine.

6. The polyimide precursor composition of claim 1, wherein the tertiary amine curing agent comprises at least one of β -methylpyridine, isoquinoline, triethylenediamine, and pyridine.

7. The polyimide precursor composition of claim 6, wherein the tertiary amine curing agent comprises triethylenediamine and at least one of β -methylpyridine, isoquinoline, and pyridine.

8. The polyimide precursor composition according to claim 7, wherein the polyimide precursor composition comprises 0.1 to 2 moles of triethylenediamine per 100 moles of the polyamic acid.

9. The polyimide precursor composition according to claim 1, wherein the polyimide precursor composition comprises 1 to 8 moles of the aromatic carboxylic acid and 0.1 to 50 moles of the tertiary amine curing agent per 100 moles of the polyamic acid.

10. The polyimide precursor composition according to claim 1, wherein the temperature at which the antioxidant decomposes at 5 wt% is 400 ℃ or higher.

11. The polyimide precursor composition according to claim 10, wherein the antioxidant is at least one of a compound represented by formula 1, triethyl phosphate, and trimethyl phosphate,

wherein n is an integer of 0 to 4.

12. The polyimide precursor composition according to claim 1, wherein the polyimide precursor composition comprises 0.1 to 2 wt% of the antioxidant, based on the total weight of the polyimide precursor composition.

13. A polyimide substrate prepared by coating, drying and curing the polyimide precursor composition according to any one of claims 1 to 12.

14. The polyimide substrate according to claim 13, wherein the drying and curing process comprises: drying at 20-120 ℃ for 5-60 minutes, heating to 450-500 ℃ at the rate of 1-8 ℃/minute, carrying out heat treatment at 450-500 ℃ for 30-60 minutes, and cooling to 20-120 ℃ at the rate of 1-8 ℃/minute.

15. The polyimide substrate according to claim 13, wherein the glass transition temperature is 400 to 500 ℃, the modulus is 6 to 12GPa, and the coefficient of thermal expansion at 50 to 400 ℃ is 1 to 8ppm/° C.

16. The polyimide substrate according to claim 13, wherein the polyimide substrate has a pyrolysis temperature of 550 to 620 ℃ at which 1 wt% of the polyimide substrate is decomposed and a light transmittance of 40 to 80% for light having a wavelength of 550nm, based on a substrate thickness of 10 μm.

17. A method of preparing a polyimide precursor composition comprising:

(1) mixing and reacting an aromatic dianhydride comprising 3,4,3',4' -biphenyltetracarboxylic dianhydride (BPDA) and an aromatic diamine comprising p-phenylenediamine (PPD) to prepare a polyamic acid solution;

(2) mixing the polyamic acid solution, the tertiary amine curing agent and the antioxidant to obtain a mixture;

(3) mixing the mixture with an aromatic carboxylic acid having at least four carboxyl groups.

18. The method of preparing a polyimide precursor composition according to claim 17, wherein the step (1) comprises: (1-1) mixing and reacting a reaction solvent, 3,4,3',4' -biphenyltetracarboxylic dianhydride, another aromatic dianhydride, and an aromatic diamine to prepare a first reactant having a viscosity of 100 to 10,000cP at 23 ℃;

(1-2) adding an aromatic dianhydride solution (having a solid content of 5 wt%) to the first reactant in portions so that the viscosity of the first reactant is 1,000-20,000 cP at 23 ℃, and reacting it to prepare a second reactant.

19. The method for preparing a polyimide precursor composition according to claim 17, wherein the step (1) is performed at 30 to 90 ℃, and the polyamic acid in the step (1) has a viscosity of 1,000 to 20,000cP at 23 ℃.

20. The method for preparing a polyimide precursor composition according to claim 17, wherein the step (2) is performed at 30 to 90 ℃ and the step (3) is performed at 30 to 90 ℃.

Technical Field

The present invention relates to a polyimide precursor composition, a method for preparing the same, and a polyimide substrate manufactured therefrom. The polyimide precursor composition has a high solid content and a low viscosity, thus facilitating the manufacture of a substrate and having excellent storage stability at room temperature. In addition, the polyimide substrate has excellent heat resistance and mechanical properties, and thus is suitable for use as a display substrate.

Background

In general, a Polyimide (PI) resin refers to a highly heat-resistant resin obtained by polymerizing an aromatic dianhydride with an aromatic diamine or an aromatic diisocyanate to produce a polyamic acid derivative, which is then subjected to ring closure and dehydration at high temperature to perform imidization. In addition, the polyimide resin is a highly heat-resistant resin that is insoluble and infusible. It has been widely used in various industries, for example, as an advanced heat-resistant material in the fields of automobiles, aviation and aerospace, and as an electronic material for dielectric coatings, dielectric films and electrode protective films of semiconductors and TFT-LCDs, due to its excellent characteristics in terms of thermal oxidation resistance, heat resistance, radiation resistance, low-temperature characteristics and chemical resistance (see korean patent No. 1472920).

In recent years, polyimide substrates having excellent optical, mechanical, and thermal properties have been developed by a simple method for forming a film from a polyimide resin (i.e., a polyimide precursor composition). It is known that in the preparation of polyimide precursor compositions, the molar ratio of aromatic dianhydride to aromatic amine is close to 1: 1, the molecular weight of the polyimide precursor composition is increased and the substrate obtained by thermochemical imidization will have better physical properties than if the ratio deviates from 1: 1. However, the higher the molecular weight of the polyimide precursor and the higher the solid content therein, the higher the viscosity of the polyimide precursor composition, which makes the polyimide precursor composition difficult to handle and difficult to prepare a substrate. In addition, the polyimide precursor composition having a high viscosity has low storage stability at room temperature. If the molecular weight of the polyimide precursor is low, the heat resistance and mechanical properties of the polyimide substrate prepared from the polyimide precursor may be poor. In addition, if the solid content of the polyimide precursor composition is low, there are problems in that a large amount of solvent must be removed from a substrate prepared therefrom and the manufacturing cost and time increase.

Disclosure of Invention

Technical problem

Accordingly, it is an object of the present invention to provide a polyimide precursor composition having a high solid content and a low viscosity and excellent storage stability at room temperature.

In addition, another object of the present invention is to provide a polyimide substrate which has excellent heat resistance and mechanical properties and thus is suitable for use as a display substrate.

Technical scheme for solving technical problems

In order to achieve the above object, there is provided a polyimide precursor composition comprising:

a polyamic acid solution prepared from a polyamic acid composition, comprising an aromatic dianhydride comprising 3,4,3',4' -biphenyltetracarboxylic dianhydride (BPDA) and an aromatic diamine comprising p-phenylenediamine (PPD);

an aromatic carboxylic acid having at least four carboxyl groups;

a tertiary amine curing agent; and

an antioxidant.

To achieve another object, there is provided a polyimide substrate prepared by coating, drying and curing the polyimide precursor composition.

In addition, to achieve another object, there is provided a method of preparing a polyimide precursor composition comprising:

(1) mixing and reacting an aromatic dianhydride comprising 3,4,3',4' -biphenyltetracarboxylic dianhydride (BPDA) and an aromatic diamine comprising p-phenylenediamine (PPD) to prepare a polyamic acid solution;

(2) mixing the polyamic acid solution, the tertiary amine curing agent and the antioxidant to obtain a mixture;

(3) mixing the mixture with an aromatic carboxylic acid having at least four carboxyl groups.

The invention has the advantages of

The polyimide precursor composition of the present invention has a high solid content and a low viscosity, and is excellent in storage stability at room temperature. In addition, the polyimide substrate prepared from the composition is suitable for adhesion to glass or an inorganic layer in a heat treatment step during the manufacture of a display, and has excellent mechanical properties, heat resistance, and thermal dimensional stability.

Detailed Description

The polyimide precursor composition of the present invention comprises a polyamic acid solution prepared from a polyamic acid composition comprising an aromatic dianhydride comprising 3,4,3',4' -biphenyltetracarboxylic dianhydride (BPDA) and an aromatic diamine comprising p-phenylenediamine (PPD); an aromatic carboxylic acid having at least four carboxyl groups; a tertiary amine curing agent; and an antioxidant.

Polyamic acid solution

The polyamic acid solution is prepared from a polyamic acid composition comprising an aromatic dianhydride comprising 3,4,3',4' -biphenyltetracarboxylic dianhydride (BPDA) and an aromatic diamine comprising p-phenylenediamine (PPD).

The aromatic dianhydride comprises 3,4,3',4' -biphenyltetracarboxylic dianhydride (BPDA).

Further, the aromatic dianhydride may further comprise pyromellitic dianhydride (PMDA), 3,3',4,4' -benzophenonetetracarboxylic dianhydride (BTDA), 2,3,3',4' -biphenyltetracarboxylic dianhydride, 1H, 3H-naphtho [2,3-c:6,7-c ' ] difuran-1, 3,6, 8-tetraone 2,3,6, 7-naphthalenetetracarboxylic dianhydride, 1,4,5, 8-naphthalenetetracarboxylic dianhydride, 4,4' -oxydiphthalic anhydride, 4,4' -oxybis (2-benzofuran-1, 3-dione), 4- [ (1, 3-dioxo-1, 3-dihydro-2-benzofuran-5-yl) oxy ] -2-benzofuran-1, at least one of 3-dione and 5,5' -sulfonyl bis-1, 3-isobenzofurandione.

Specifically, the aromatic dianhydride may include 3,4,3',4' -biphenyltetracarboxylic dianhydride (BPDA), or may include 3,4,3',4' -biphenyltetracarboxylic dianhydride (BPDA) and pyromellitic dianhydride (PMDA). In addition, the aromatic dianhydride may include 3,4,3',4' -biphenyltetracarboxylic dianhydride (BPDA) and 3,3',4,4' -benzophenonetetracarboxylic dianhydride (BTDA), or may include 3,4,3',4' -biphenyltetracarboxylic dianhydride (BPDA), pyromellitic dianhydride (PMDA), and 3,3',4,4' -benzophenonetetracarboxylic dianhydride (BTDA).

The polyamic acid composition may include additional aromatic dianhydride in an amount of 0.1 to 70 moles per 100 moles of the aromatic diamine. Specifically, the polyamic acid composition may include 2 to 65 moles of additional aromatic dianhydride per 100 moles of the aromatic diamine. More specifically, the polyamic acid composition may include 42 to 99 moles of BPDA and 0.1 to 57 moles of PMDA, or 92 to 99 moles of BPDA per 100 moles of the diamine.

In addition, the polyamic acid composition may include 0.1 to 5 moles or 0.1 to 3 moles of BTDA per 100 moles of the diamine.

In order to improve heat resistance, thermal dimensional stability and modulus, 0.8 to 1.0 mole of p-phenylenediamine is used per 1.0 mole of the total aromatic diamine. Para-phenylenediamine is a monomer having linearity compared with other aromatic diamines such as diaminophenyl ether, and has the advantage of reducing the coefficient of thermal expansion of the film produced.

The aromatic diamine may contain at least one of diaminophenyl ether, o-phenylenediamine, m-phenylenediamine, 2, 6-diaminopyridine, 4 '-diaminodiphenyl sulfone, 2- (4-aminophenyl-1H-benzoxazol-5-amine, 2- (4-aminophenyl) -5-aminobenzimidazole, 6-amino-2-p-aminophenylbenzoxazole and 4,4' -diamino-p-terphenyl in addition to p-phenylenediamine.

The polyamic acid composition may further include a reaction solvent in addition to the aromatic dianhydride and the aromatic diamine. The reaction solvent may be an amide based aprotic solvent. Specifically, the reaction solvent may be at least one of N, N '-Dimethylformamide (DMF), N' -dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), acetonitrile, Tetrahydrofuran (THF), 3-methylphenol (m-cresol), 1,3, 3-Tetramethylurea (TMU), dimethyl sulfoxide (DMSO), and γ -butyrolactone.

The polyamic acid solution is prepared from the polyamic acid composition. Specifically, the polyamic acid solution may be prepared by reacting the polyamic acid composition. The reaction can be carried out at 30-90 ℃.

The polyamic acid solution can have a viscosity of 1,000 to 20,000cP at 23 ℃. Specifically, the viscosity of the polyamic acid solution at 23 ℃ may be 2,000 to 10,000 cP.

The weight average molecular weight of the polyamic acid solution may be 10,000 to 200,000 or 15,000 to 150,000.

Aromatic carboxylic acids

The aromatic carboxylic acid has at least four carboxyl groups. It functions to improve heat resistance, thermal dimensional stability and mechanical properties while reducing the viscosity of the polyamic acid solution thus prepared. Specifically, the aromatic carboxylic acid may be an aromatic carboxylic acid having four carboxyl groups.

More specifically, the aromatic carboxylic acid may include at least one of pyromellitic acid (PMA), 3',4,4' -biphenyltetracarboxylic acid (BPTA), 1,2,3, 4-benzenetetracarboxylic acid, benzophenone-3, 3',4,4' -tetracarboxylic acid, pyrazinetetracarboxylic acid, 2,3,6, 7-naphthalenetetracarboxylic acid and naphthalene-1, 4,5, 8-tetracarboxylic acid. More specifically, the aromatic carboxylic acid may include at least one of pyromellitic acid and 3,3',4,4' -biphenyltetracarboxylic acid. More specifically, the aromatic carboxylic acid may comprise pyromellitic acid or 3,3',4,4' -biphenyltetracarboxylic acid.

The polyamic acid composition may include 1 to 8 moles of the aromatic carboxylic acid per 100 moles of the aromatic diamine. Specifically, the polyimide precursor composition may include 1 to 7 moles or 1 to 6 moles of the aromatic carboxylic acid per 100 moles of the polyamic acid.

Tertiary amine curing agent

The tertiary amine curing agent may comprise at least one of β -methylpyridine, isoquinoline, triethylenediamine, and pyridine, in particular, the tertiary amine curing agent may comprise triethylenediamine and at least one of β -methylpyridine, isoquinoline, and pyridine the function of triethylenediamine is to enable curing of the polyimide precursor composition at low temperatures and to improve the heat resistance of the resulting substrate.

The polyimide precursor composition may include 0.1 to 50 moles of the tertiary amine curing agent per 100 moles of the polyamic acid, specifically, 0.1 to 2 moles of triethylenediamine per 100 moles of the polyamic acid, and more specifically, 0.1 to 2 moles of triethylenediamine and 5 to 50 moles of at least one of β -methylpyridine, isoquinoline, and pyridine per 100 moles of the polyamic acid.

Antioxidant agent

The antioxidant functions to reduce the reactivity of amide groups in the polyimide precursor composition, thereby preventing oxidation due to the reactivity of the amide groups in a heat treatment during the preparation of a substrate.

The temperature for decomposing 5 wt% of the antioxidant is 400 ℃ or above or 400-480 ℃. Specifically, the antioxidant may be at least one of a compound represented by formula 1, triethyl phosphate, and trimethyl phosphate.

[ formula 1]

In the above formula 1, n is an integer of 0 to 4.

More specifically, the antioxidant may be triphenyl phosphate (TPP) where n is 0 or a mixture of compounds where n is an integer of 1 to 4 (CAS 1003300-73-9).

The polyimide precursor composition may include 0.1 to 2 wt% of the antioxidant, based on the total weight of the polyimide precursor composition. Specifically, the polyimide precursor composition may include 0.2 to 1.5 wt% or 0.2 to 1 wt% of the antioxidant, based on the total weight of the polyimide precursor composition.

Polyimide substrate

The polyimide substrate of the present invention is prepared by coating, drying and curing the above polyimide precursor composition. Specifically, the polyimide substrate is prepared by coating the above polyimide precursor composition on a support substrate, drying and curing, and then peeling it off.

The support substrate may be a glass substrate, a metal plate, a wafer, or the like.

The drying temperature and drying time of the drying and curing may be adjusted according to the thickness of the coated polyimide precursor composition. For example, the drying and curing process may comprise: drying at 20-120 ℃ for 5-60 minutes, heating to 450-500 ℃ at the rate of 1-8 ℃/minute, carrying out heat treatment at 450-500 ℃ for 30-60 minutes, and cooling to 20-120 ℃ at the rate of 1-8 ℃/minute.

The polyimide substrate has a glass transition temperature of 400 to 500 ℃, a modulus of 6 to 12GPa, and a coefficient of thermal expansion of 1 to 8 ppm/DEG C at 50 to 400 ℃. Specifically, the polyimide substrate has a glass transition temperature of 420 to 480 ℃, a modulus of 6 to 11GPa, and a coefficient of thermal expansion of 2 to 8 ppm/DEG C at 50 to 400 ℃.

The pyrolysis temperature at which the polyimide substrate is decomposed by 1 wt% may be 550 to 620 ℃ and the light transmittance for light having a wavelength of 550nm may be 40 to 80%, based on a substrate thickness of 10 μm. Specifically, the pyrolysis temperature at which the polyimide substrate is decomposed by 1 wt% may be 550 to 600 ℃, and the light transmittance for light having a wavelength of 550nm may be 50 to 75%, based on a substrate thickness of 10 μm.

The tensile strength of the polyimide substrate can be 200-500 MPa, the peel strength can be 0.01-10N/cm, and the decomposition time for decomposing 1 wt% at 480 ℃ can be 1-12 hours. Specifically, the tensile strength of the polyimide substrate can be 250-460 MPa, the peel strength can be 0.5-5N/cm, and the decomposition time for decomposing 1 wt% at 480 ℃ can be 2-10 hours.

The average thickness of the polyimide substrate may be 3 to 30 μm.

Method for preparing polyimide precursor composition

The method for preparing a polyimide precursor composition according to the present invention comprises:

(1) mixing and reacting an aromatic dianhydride comprising 3,4,3',4' -biphenyltetracarboxylic dianhydride (BPDA) and an aromatic diamine comprising p-phenylenediamine (PPD) to prepare a polyamic acid solution;

(2) mixing the polyamic acid solution, the tertiary amine curing agent and the antioxidant to obtain a mixture; and

(3) mixing the mixture with an aromatic carboxylic acid having at least four carboxyl groups.

Step (1)

In this step, a polyamic acid solution is prepared by mixing and reacting an aromatic dianhydride comprising 3,4,3',4' -biphenyltetracarboxylic dianhydride (BPDA) and an aromatic diamine comprising p-phenylenediamine (PPD).

The step (1) can be carried out at 30-90 ℃.

In the step (1), the polyamic acid solution may be obtained by reacting the reaction solvent, 3,4,3',4' -biphenyltetracarboxylic dianhydride, another aromatic dianhydride, and an aromatic diamine, or by mixing and reacting 3,4,3',4' -biphenyltetracarboxylic dianhydride, another aromatic dianhydride, and an aromatic diamine. Specifically, the step (1) may include (1-1) mixing and reacting a reaction solvent, 3,4,3',4' -biphenyltetracarboxylic dianhydride, additional aromatic dianhydride, and aromatic diamine to prepare a first reactant having a viscosity of 100 to 10,000cP at 23 ℃; and (1-2) adding an aromatic dianhydride solution (solid content of 5 wt%) to the first reactant in divided portions so that the viscosity of the first reactant is 1,000-20,000 cP at 23 ℃, and reacting to obtain a second reactant.

The additional aromatic dianhydride may be pyromellitic dianhydride (PMDA), 3,3',4,4' -benzophenonetetracarboxylic dianhydride (BTDA), 2,3,3',4' -biphenyltetracarboxylic dianhydride, 1H, 3H-naphtho [2,3-c:6,7-c ' ] difuran-1, 3,6, 8-tetraone 2,3,6, 7-naphthalenetetracarboxylic dianhydride, 1,4,5, 8-naphthalenetetracarboxylic dianhydride, 4,4' -oxydiphthalic anhydride, 4,4' -oxybis (2-benzofuran-1, 3-dione), 4- [ (1, 3-dioxo-1, 3-dihydro-2-benzofuran-5-yl) oxy ] -2-benzofuran-1, at least one of 3-dione and 5,5' -sulfonyl bis-1, 3-isobenzofurandione.

The reaction solvent may be an amide based aprotic solvent. Specifically, the reaction solvent may be at least one of N, N '-dimethylformamide, N' -dimethylacetamide, and N-methylpyrrolidone (NMP).

The first reactant can be obtained by mixing 100 moles of an aromatic diamine, 42 to 99 moles of BPDA and 0.1 to 57 moles of another aromatic dianhydride, or 100 moles of an aromatic diamine and 92 to 99 moles of BPDA, and reacting the mixture at 30 to 90 ℃.

The second reactant may be prepared by adding an additional aromatic dianhydride solution in an amount of 0.1 to 57 moles per 100 moles of the aromatic diamine to the first reactant in divided portions, and then reacting the resultant at 30 to 90 ℃. In addition, the second reactant may be prepared by adding 42 to 99 moles of BPDA per 100 moles of the aromatic diamine to the first reactant, reacting the resultant at 30 to 90 ℃, and then adding a small amount of additional aromatic dianhydride solution in portions to adjust the viscosity of the resultant at 23 ℃ to 1,000 to 20,000 cP.

The solid content of the additional aromatic dianhydride solution may be 1-10 wt% or 2-8 wt%. The solvent of the additional aromatic dianhydride solution may be the same as the reaction solvent.

The additional aromatic dianhydride solution may be added at intervals of 10 to 30 minutes. Further, the second reactant may be stirred while adding the pyromellitic dianhydride solution.

The viscosity of the polyamic acid solution at 23 ℃ may be 1,000-20,000 cP. Specifically, the viscosity of the polyamic acid solution at 23 ℃ may be 2,000-10,000 cP.

Step (2)

In this step, the polyamic acid solution, the tertiary amine curing agent, and the antioxidant are mixed to obtain a mixture.

The type of the tertiary amine curing agent and the antioxidant is the same as defined in the polyimide precursor composition.

The step (2) can be carried out at 30-90 ℃. Specifically, the step (2) can be carried out at 40-80 ℃.

The tertiary amine curing agent may be used in an amount of 0.1 to 50 moles per 100 moles of the polyamic acid, and specifically, the tertiary amine curing agent may include 5 to 50 moles of pyridine, β -methylpyridine, or isoquinoline, and 0.1 to 2 moles of triethylenediamine per 100 moles of the polyamic acid.

The antioxidant may be used in an amount of 0.1 to 2 wt% based on the total weight of the polyimide precursor composition. Specifically, the antioxidant may be used in an amount of 0.2 to 1 wt% based on the total weight of the polyimide precursor composition.

Step (3)

In this step, the mixture is mixed with an aromatic carboxylic acid having at least four carboxyl groups

The step (3) can be carried out at 30-90 ℃. Specifically, the step (3) can be carried out at 40-80 ℃.

The aromatic carboxylic acid may be used in an amount of 1 to 8 moles per 100 moles of the aromatic diamine. Specifically, the aromatic carboxylic acid may be used in an amount of 1 to 6 moles per 100 moles of the aromatic diamine.

The present invention is explained in detail by the following examples. The following examples are intended to further illustrate the invention. The scope of the invention is not limited in this respect.