Positive photosensitive resin composition, method for producing photosensitive polyimide film

Abstract

The present application relates to the field of resin composition, and particularly relates to a positive photosensitive resin composition and a preparation method of a photosensitive polyimide film.The positive photosensitive resin composition provided by the present application comprises, by weight, 100 parts of alkali-soluble polyimide resin precursor, 1-50 parts of photosensitizer, 4-40 parts of thermal crosslinking agent and 100-1500 parts of solvent.The polyimide film prepared by the present application can meet the requirements of PDL and PNL of OLED devices, such as high heat resistance, low dielectric coefficient, chemical resistance and bending resistance, and can solve and eliminate the pixel shrinkage problem caused by Outgas.In addition, the polyimide film has excellent bending resistance and chemical resistance after reliability test, and can be widely used in the planarization layer and pixel definition layer of OLED display devices.

Description

Technical Field

[0001] This invention relates to the field of resin compositions, and more specifically to a positive photosensitive resin composition and a method for preparing a photosensitive polyimide film. Background Technology

[0002] With the development of science and technology, organic light-emitting diode (OLED) display technology is widely used in thin-film displays of electronic devices such as televisions, smartphones, and tablets. OLED devices consist of a thin-film transistor (TFT) driving circuit, a planarization layer, a first electrode, a pixel definition layer, a light-emitting layer, and a second electrode. They emit light by applying a voltage between the opposing first and second electrodes. The substrate materials for the planarization layer (PNL) and pixel definition layer (PDL) are mostly photosensitive resin compositions that can form patterns when irradiated with ultraviolet light. These photosensitive resin compositions, in addition to requiring high photosensitivity, high thermal stability, and bending resistance, also require high adhesion, chemical resistance, and a low dielectric constant, among other properties.

[0003] Polyimide is a special polymer resin with high thermal stability, high heat resistance, excellent mechanical properties, and insulation. Introducing photosensitizers into it yields photosensitive polyimide resin compositions (PSPI), which can simultaneously serve as both the PNL and PDL for OLED devices, improving device reliability and extending device lifespan. However, polyimide requires very high curing temperatures, often exceeding 300°C, while the operating temperature of OLED anode material indium tin oxide (ITO) requires the resin to be cured below 250°C. Furthermore, during high-temperature curing, a small amount of small molecules remain, which slowly volatilize during device use (outgas), thus reducing the lifespan of the OLED device. Traditional polyimides are mostly fully aromatic, with poor alkali solubility, limiting the resolution of the pattern formed during development. They are also prone to warping due to volume shrinkage after curing, and their compatibility and adhesion to the substrate need improvement. In addition, since PNL requires treatment with polar stripping solutions, the cured PSPI requires better chemical resistance. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a positive photosensitive resin composition and a method for preparing a photosensitive polyimide film, so as to reduce the curing temperature of PSPI and extend the service life of OLED. At the same time, the prepared polyimide film has excellent chemical resistance and bending resistance.

[0005] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a positive photosensitive resin composition comprising, by weight, the following raw materials: 100 parts of alkali-soluble polyimide resin precursor, 1-50 parts of photosensitizer, 4-40 parts of thermal crosslinking agent, and 100-1500 parts of solvent.

[0006] Furthermore, the average molecular weight of the alkali-soluble polyimide resin precursor is 5000~20000.

[0007] Furthermore, the alkali-soluble polyimide resin precursor is prepared from diamines with fluorine atoms, diamines with siloxane structures, aliphatic diamines, aromatic tetracarboxylic dianhydrides, end-capping agents, and alkylating agents as raw materials.

[0008] Furthermore, the preparation steps of the alkali-soluble polyimide resin precursor include: dissolving an aliphatic diamine, a diamine with a siloxane structure, or a diamine with a fluorine atom in a reaction solvent, then adding an aromatic tetracarboxylic dianhydride, stirring at 30-60°C for 1-5 hours, then adding a capping agent, continuing to stir at 30-60°C for 1-5 hours, then adding an alkylating agent dropwise and continuing the reaction for 1-3 hours to obtain a mixture, and separating the alkali-soluble polyimide resin precursor.

[0009] Furthermore, the specific implementation method for separating the alkali-soluble polyimide resin precursor is as follows: the obtained mixture is added to water to precipitate the solid, the solid is collected by vacuum filtration, and finally washed and dried.

[0010] Furthermore, the structural formula of the aliphatic diamine is represented by Formula 1: Formula 1 In Equation 1, m is an integer from 1 to 10.

[0011] Furthermore, the structural formula of the diamine having a siloxane structure is represented by Formula 2: Formula 2 In Formula 2, R1, R2, R3, and R4 are each independently a substituted or unsubstituted C1-C10 branched or straight-chain alkane, and R5 and R6 are each independently a substituted or unsubstituted C1-C10 branched or straight-chain alkylene.

[0012] Furthermore, the diamine having a siloxane structure comprises at least one of formulas 2-1 to 2-4: Equation 2-1 Equation 2-2 Equation 2-3 Equation 2-4.

[0013] Furthermore, the diamine containing fluorine atoms contains phenolic hydroxyl groups. Preferably, it is 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane. In this invention, by adding a diamine containing fluorine atoms, the high electronegativity of fluorine atoms can increase the light transmittance and hydrophobicity of the polyimide film. During development with an alkaline aqueous solution, it can impart hydrophobicity to the interface between the film and the substrate, inhibiting the penetration of the alkaline aqueous solution into the interface, and simultaneously reducing the dielectric constant of the system. However, excessive addition of fluorine atoms will reduce the adhesion between the polyimide film and the substrate, easily causing film warping. At the same time, the applicant has found that when the diamine containing fluorine atoms contains phenolic hydroxyl groups, it can effectively improve the photosensitivity and alkali solubility of the photosensitive resin.

[0014] Furthermore, the molar ratio of the diamine with fluorine atoms, the diamine with siloxane structure, and the aliphatic diamine is (12~20):1:(2~4).

[0015] Furthermore, the aromatic tetracarboxylic dianhydride is at least one of pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 3,3',4,4'-diphenylsulfone tetracarboxylic dianhydride, 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride, and 2,2'-bis(3,4-dicarboxylic acid)hexafluoropropane dianhydride.

[0016] Furthermore, the capping agent is at least one selected from 3-methylphthalic anhydride, 4-methylphthalic anhydride, phthalic anhydride, acetic anhydride, propionic anhydride, maleic anhydride, 3-methylaniline, aniline, 3-aminophenylacetylene, 3-aminophenol, 4-aminophenol, and 4-methylaniline.

[0017] Furthermore, the molar ratio of the aromatic tetracarboxylic dianhydride to the capping agent is (8~12):1.

[0018] The alkali-soluble polyimide resin precursor in this invention is formed by alkylation of polyamic acid. Polyamic acid is easily soluble in alkaline solutions, difficult to control, and not easy to store. Therefore, an alkylating agent can be added to the prepared polyimide resin precursor to convert the carboxyl groups in the polyamic acid into ester groups, thereby adjusting the dissolution rate of the polyimide resin precursor in alkaline solutions. Simultaneously, the introduction of ester groups reduces hygroscopic properties; however, excessive ester group content is detrimental to dissolution in alkaline solutions. In this invention, the molar ratio of the alkylating agent to the aromatic tetracarboxylic dianhydride is (1~3):1. The alkylating agent in this invention is at least one of N,N-dimethylformamide dimethyl acetal, N,N-dimethylformamide dibenzyl acetal, N,N-dimethylformamide diethyl acetal, N,N-dimethylacetamide dimethyl acetal, N,N-dimethylformamide dipropyl acetal, N,N-dimethylformamide dibutyl acetal, and N,N-dimethylacetamide diethyl acetal.

[0019] Furthermore, the reaction solvent is selected from at least one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, γ-butyrolactone, N-methylcaprolactam, and dimethyl sulfoxide.

[0020] Furthermore, the photosensitizer is a diazidonaphthoquinone compound, which is a compound obtained by combining a phenolic hydroxyl compound with a sulfonic acid compound of diazidonaphthoquinone.

[0021] More preferably, the molecular weight of the diazidonaphthoquinone compound is 350-1200.

[0022] In this invention, the photosensitizer is a mixture of 4-naphthoquinone diazidesulfonyl ester compound and 5-naphthoquinone diazidesulfonyl ester compound in a mass ratio of (0.3~3):1.

[0023] Further, the solvent is at least one of γ-butyrolactone, γ-valerolactone, δ-valerolactone, propylene glycol monomethyl ether, ethylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, propyl acetate, butyl acetate, isobutyl acetate, methyl butyl ketone, methyl isobutyl ketone, and methyl propyl ketone, preferably at least one of γ-valerolactone and propylene glycol monomethyl ether.

[0024] Furthermore, the thermal crosslinking agent is a mixture of an epoxy compound containing a phosphazene ring and an alkoxymethyl compound, with a mass ratio of 1:(0.1~10).

[0025] Furthermore, the phosphazene-containing epoxy compound is named hexa-(3-methoxy-4-epoxymethylene)-phenoxy-cyclotriphosphazene, and its molecular structure is detailed in Formula 3: Formula 3.

[0026] Furthermore, the alkoxymethyl compound is 1,3,5-triazine-2,4,6-triene triazine hexamethylethanol.

[0027] During the research process, the applicant discovered that when diamines containing fluorine atoms contain phenolic hydroxyl groups, although they can effectively improve the photosensitivity and alkali solubility of photosensitive resins, the content of small molecule volatiles increases during the curing process of the photosensitive resin composition, which will adversely affect the lifespan of OLEDs. At the same time, the presence of diamines containing fluorine atoms and phenolic hydroxyl groups means that the pre-baked film still has a certain degree of solubility in alkaline developer in the unexposed area, which is not conducive to patterning. By adding a thermal crosslinking agent, the resin composition before exposure becomes almost insoluble in the unexposed area, reducing the film reduction caused by development and reducing the shrinkage rate after curing.

[0028] Through extensive research, the applicant has discovered that using a hexafunctional phosphazene ring-containing epoxy compound and the alkoxymethyl compound in a mass ratio of 1:(0.1~10) as a thermal crosslinking agent, the crosslinking reaction during high-temperature curing does not produce degassing due to curing, effectively reducing the content of small molecule volatiles (outgas). It also effectively improves the heat resistance, chemical resistance, and adhesion of the polyimide film, reducing curing warpage. Furthermore, compared to aromatic thermal crosslinking compounds, nitrogen-phosphorus heterocyclic compounds have very low absorption of short-wavelength exposure light sources, improving the photosensitivity of the photosensitizer. Compared to aliphatic compounds, the presence of nitrogen-phosphorus heterocyclic compounds provides excellent heat resistance. Furthermore, the hexafunctional epoxy group in hexa-(3-methoxy-4-epoxymethylene)-phenoxy-cyclotriphosphazene can undergo thermal crosslinking with the polymer below 200°C, and does not generate small molecules during crosslinking, i.e., does not experience volume shrinkage, thus enabling low-temperature curing and suppressing warping. On the other hand, hexa-(3-methoxy-4-epoxymethylene)-phenoxy-cyclotriphosphazene and 1,3,5-triazine-2,4,6-triene triazine-hexamethyl alcohol exhibit good compatibility. The introduction of heteroatoms such as N and P increases the interaction between the crosslinking agent molecules and the alkali-soluble polyimide resin precursor backbone, further enhancing the crosslinking effect. When the mass ratio of the hexafunctional phosphazene ring-containing epoxy compound to the alkoxymethyl compound is too high, the polyimide film prepared with it has poor bending resistance, which may also cause the cured film to warp and detach from the substrate. When the mass ratio is too low, the storage stability of the positive photosensitive resin composition is poor.

[0029] Furthermore, the positive photosensitive resin composition also includes a sensitizer and a surfactant.

[0030] Furthermore, the sensitizer is at least one of α,α,α'-tris(4-hydroxyphenyl)-1-ethyl-4-isopropylbenzene, 2,3,4-trihydroxybenzophenone, 2,3,4,4'-tetrahydroxybenzophenone, and 1-[1-(4-hydroxyphenyl)isopropyl]-4-[1,1-bis(4-hydroxyphenyl)ethyl]benzene.

[0031] Furthermore, the surfactant is an ester surfactant, specifically at least one of ethyl lactate and propylene glycol methyl ether acetate.

[0032] Secondly, the present invention provides a method for preparing a positive photosensitive resin composition, the main steps of which include: mixing an alkali-soluble polyimide resin precursor, a photosensitizer, a thermal crosslinking agent, a solvent, a sensitizer and a surfactant in the above-mentioned weight proportions to obtain the positive photosensitive resin composition.

[0033] Thirdly, the present invention also provides a method for preparing a photosensitive polyimide film using the above-mentioned positive photosensitive resin composition, specifically comprising the following steps: S1, Coating: Applying the positive photosensitive resin composition to the substrate; S2. Preparation of pre-baked film: Drying at 60~150℃ to form a pre-baked film; S3. Exposure: The pre-baked film is exposed using an ultraviolet light source through a mask with a specific pattern; S4. Development: The exposed parts are washed away with a developing solution to obtain a patterned pre-baked film; S5. Heat curing treatment: The pre-baked film with the desired pattern is heat-treated at 150~250℃ to obtain the above-mentioned photosensitive polyimide film.

[0034] Finally, the present invention also provides the application of the above-mentioned photosensitive polyimide film in optoelectronic flat panel displays, semiconductor chip manufacturing and packaging, wherein the photosensitive polyimide film can be used as a planarization layer and pixel definition layer of OLED display devices.

[0035] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects: 1. The positive photosensitive resin composition provided by the present invention, through the selection and molecular weight control of the resin polymer monomers, enables the polyimide film prepared to meet the requirements of OLED devices such as high heat resistance, low dielectric constant, chemical resistance and bending resistance of PDL and PNL, thereby solving and eliminating the pixel shrinkage problem caused by Outgas.

[0036] 2. This invention uses a specific ratio of a hexafunctional phosphazene ring-containing epoxy compound and the alkoxymethyl compound as a thermal crosslinking agent to carry out a crosslinking reaction during high-temperature curing, thereby improving the patterning effect, reducing film loss caused by development, lowering the curing temperature, and also effectively improving the heat resistance, chemical resistance, and adhesion of the polyimide film, while reducing curing warpage.

[0037] 3. In the process of preparing alkali-soluble polyimide resin precursor, the present invention uses an esterification strategy of alkylating agent to free carboxyl groups and optimizes the combination of photosensitizer and crosslinking agent to effectively reduce curing temperature and achieve good photosensitivity, circular shape after development and low cone angle.

[0038] 4. The positive photosensitive resin composition provided by the present invention can be used to prepare polyimide films, which have excellent bending resistance and chemical resistance after reliability testing, and can be widely used as planarization layers and pixel definition layers in OLED display devices. Detailed Implementation

[0039] Exemplary embodiments will be described in detail below. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples of products consistent with some aspects of the invention as detailed in the appended claims.

[0040] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below with reference to embodiments.

[0041] Synthesis example 1 Synthesis of alkali-soluble polyimide resin precursor (A-1): Under a dry nitrogen stream, 29.3 g (0.08 mol) of 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (BAHF), 1.2 g (0.005 mol) of 1,3-bis(3-aminopropyl)tetramethyldisiloxane (Formula 2-1) (SiDA), and 15 g (0.015 mol) of polyethylene glycol diamine were dissolved in 200 mL of NMP. 21.8 g (0.1 mol) of pyromellitic anhydride was added to the solution, and the mixture was stirred at 40 °C for 2 h. Subsequently, 1.1 g (0.01 mol) of 3-aminophenol was added, and the mixture was stirred at 40 °C for another 2 h. 23.6 g (0.2 mol) of N,N-dimethylformamide dimethyl acetal (DFA) was dissolved in 20 mL of NMP solution and then added dropwise to the system. The mixture was stirred at 40 °C for 2 h. After the reaction was completed, the solution was added to 2L of ultrapure water, filtered to obtain polymer precipitate, washed three times with ultrapure water, and the obtained polymer solid was dried in a vacuum dryer at 80℃ for 48h to obtain alkali-soluble polyimide resin precursor (A-1).

[0042] Synthesis example 2 Synthesis of alkali-soluble polyimide resin precursor (A-2): The difference from Synthesis Example 1 is that the amount of 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (BAHF) added is 36.6 g (0.1 mol), and the amount of polyethylene glycol diamine added is 10 g (0.01 mol), finally yielding alkali-soluble polyimide resin precursor A-2.

[0043] Synthesis example 3 Synthesis of alkali-soluble polyimide resin precursor (A-3): The difference from Synthesis Example 1 is that 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane was replaced with an equal amount of 2,2-bis(4-aminophenyl)hexafluoropropane, ultimately yielding an alkali-soluble polyimide resin precursor (A-3).

[0044] Synthesis example 4 Synthesis of alkali-soluble polyimide resin precursor (A-4): The difference from Synthesis Example 1 is that 1,3-bis(3-aminopropyl)tetramethyldisiloxane (Formula 2-1) was replaced with an equal amount of polyethanol diamine, ultimately yielding an alkali-soluble polyimide resin precursor (A-4).

[0045] Synthesis example 5 Synthesis of 4-naphthoquinone diazidosulfonyl ester compound (B-1) Under a nitrogen atmosphere, 20.23 g (0.05 mol) of 1,1,2-tris(3,5-dimethyl-4-hydroxyphenyl)propane, 36.27 g (0.135 mol) of 4-naphthoquinone azidosulfonyl chloride, and 450 g of 1,4-dioxane were added to a reaction flask. The mixture was heated to 30 °C, and a mixture of 14.19 g (0.14 mol) of triethylamine and 45 g of 1,4-dioxane was slowly added dropwise. After the addition was complete, the temperature was raised to 35 °C, and the reaction was allowed to proceed for 4 h. After the reaction was complete, the triethylamine salt was removed by filtration. The filtrate was added dropwise to deionized water, and a solid precipitated. The solid was then dried in a vacuum oven to obtain the 4-naphthoquinone azidosulfonyl ester compound (B-1).

[0046] Synthesis example 6 Synthesis of 5-naphthoquinone diazidosulfonyl ester compound (B-2) Under a nitrogen atmosphere, 15.3 g of 1,1,1-tris(4-hydroxyphenyl)ethane and 41 g of 5-diazidonaphthoquinone sulfonyl chloride were dissolved in 1,4-dioxane. The mixture was heated to 30 °C, and 7.4 g of triethylamine and 50 g of 1,4-dioxane were mixed and added dropwise to the reaction solution. The system temperature was maintained at 30 °C ± 2 °C, and the reaction was carried out for 2 h. After the reaction was completed, the triethylamine salt was removed by filtration. The filtrate was added dropwise to deionized water, and a solid precipitated. The solid was dried in a vacuum oven to obtain the 5-naphthoquinone diazidosulfonyl ester compound (B-2).

[0047] Synthesis Example 7 Synthesis of hexa-(3-methoxy-4-epoxymethylene)-phenoxy-cyclotriphosphazene In a nitrogen atmosphere, 90.0 g (0.55 mol) of eugenol was dissolved in 500 mL of dioxane. 5 g of TBAB was added as a phase transfer catalyst, and the mixture was stirred at room temperature for 30 min. Then, 22.0 g (0.55 mol) of NaOH was added, and the mixture was heated to 40 °C and stirred for 3 h. Finally, 30.0 g of HCCP (0.086 mol) was dissolved in 150 mL of dioxane and slowly added dropwise to the reaction mixture. The mixture was heated to 70 °C and stirred continuously for 48 h. After the reaction was complete, the mixture was cooled to room temperature, and the dioxane was removed by rotary evaporation. The resulting viscous product was dissolved in dichloromethane, repeatedly washed with ultrapure water, and dried over anhydrous sodium sulfate. The solvent was removed by rotary evaporation to obtain the first product, hexa-(3-methoxy-4-allyl)-phenoxy-cyclotriphosphazene.

[0048] 50 g (0.045 mol) of the product from the first step was dissolved in 750 mL of dichloromethane. This solution was then slowly added dropwise to a suspension of 80 g of 85% m-CPBA in 800 mL of dichloromethane, and the mixture was stirred for 96 h. After the reaction was complete, the filtrate was filtered and washed with a saturated aqueous solution of sodium thiosulfate, sodium bicarbonate, and distilled water. The solution was dried over anhydrous sodium sulfate and the solvent was removed by rotary evaporation to obtain hexa-(3-methoxy-4-epoxymethylene)-phenoxy-cyclotriphosphazene.

[0049] The abbreviations of the components used in the examples and comparative examples are explained below.

[0050] (A) Alkali-soluble polyimide resin precursors: (A-1) Alkali-soluble polyimide resin precursors prepared in Synthesis Example 1; (A-2) Alkali-soluble polyimide resin precursors prepared in Synthesis Example 2; (A-3) Alkali-soluble polyimide resin precursors prepared in Synthesis Example 3; (A-4) Alkali-soluble polyimide resin precursors prepared in Synthesis Example 4.

[0051] (B) Photosensitizers: (B-1) 4-naphthoquinone diazidesulfonyl ester compound prepared in Synthesis Example 5; (B-2) 5-naphthoquinone diazidesulfonyl ester compound prepared in Synthesis Example 6.

[0052] (C) Thermal crosslinking agents: (C-1) Hexa-(3-methoxy-4-epoxymethylene)-phenoxy-cyclotriphosphazene prepared in Synthesis Example 7; (C-2) 1,3,5-triazine-2,4,6-triene triazine hexamethyl alcohol (CAS No.: 531-18-0).

[0053] (D) Sensitizer: α,α,α'-tris(4-hydroxyphenyl)-1-ethyl-4-isopropylbenzene (CAS No.: 110726-28-8). (E) Surfactant: Ethyl lactate (CAS No.: 97-64-3).

[0054] (F) Solvents: (F-1) γ-Butyrolactone (CAS No.: 96-48-0); (F-2) Propylene glycol monomethyl ether (CAS No.: 107-98-2).

[0055] Example 1 Under a nitrogen atmosphere, 20g of alkali-soluble polyimide resin precursor (A-1), 2g of 4-naphthoquinone diazidosulfonyl ester compound prepared in Synthesis Example 5 (B-1), 1g of 5-naphthoquinone diazidosulfonyl ester compound prepared in Synthesis Example 6 (B-2), 3g of hexa-(3-methoxy-4-epoxymethylene)-phenoxy-cyclotriphosphazene prepared in Synthesis Example 7 (C-1), 3g of 1,3,5-triazine-2,4,6-triene triazine hexamethyl alcohol, and 3g of α,α,α'-tris(4-hydroxyphenyl)-1-ethyl-4-isopropylbenzene were added to a mixed solvent of 60g of γ-butyrolactone and 60g of propylene glycol monomethyl ether. The mixture was stirred at 25°C until completely dissolved and reacted for 6 hours. The reaction solution was filtered through a 0.02μm filter to obtain a positive photosensitive resin composition (S-1).

[0056] This embodiment also provides a process for preparing a polyimide film, the steps of which include: S1, coating: the above-obtained positive photosensitive resin composition (S-1) is coated onto a glass substrate using a spin coating method; S2, pre-baking film preparation: drying at 120°C for 2 min to obtain a pre-baked film with a thickness of approximately 12 μm; S3, exposure: exposing the pre-baked film to a photomask using a 365 nm mercury lamp; S4, development: dissolving the exposed portion using a 2.38% tetramethylammonium hydroxide developer to obtain a pre-baked film with a specific pattern; S5, heat curing: heat-treating the patterned pre-baked film at 250°C for 1 h, followed by cooling to obtain the polyimide film (M-1).

[0057] Example 2 Under a nitrogen atmosphere, 20 g of alkali-soluble polyimide resin precursor (A-1), 2 g of 4-naphthoquinone diazidosulfonyl ester compound prepared in Synthesis Example 5 (B-1), 1 g of 5-naphthoquinone diazidosulfonyl ester compound prepared in Synthesis Example 6, 5 g of hexa-(3-methoxy-4-epoxymethylene)-phenoxy-cyclotriphosphazene prepared in Synthesis Example 7 (C-1), 0.5 g of 1,3,5-triazine-2,4,6-triene triazine hexamethyl alcohol, and 3 g of α,α,α'-tris(4-hydroxyphenyl)-1-ethyl-4-isocumene were added to a mixed solvent of 40 g of γ-butyrolactone and 60 g of propylene glycol monomethyl ether. The mixture was stirred at 25 °C until completely dissolved and reacted for 6 h. The reaction solution was filtered through a 0.02 μm filter to obtain a positive photosensitive resin composition (S-2).

[0058] The specific implementation method for preparing the polyimide film in this embodiment is the same as in Example 1. A polyimide film (M-2) was obtained.

[0059] Example 3 Under a nitrogen atmosphere, 20 g of alkali-soluble polyimide resin precursor (A-1), 3 g of 4-naphthoquinone diazidosulfonyl ester compound prepared in Synthesis Example 5 (B-1), 1 g of 5-naphthoquinone diazidosulfonyl ester compound prepared in Synthesis Example 6, 0.5 g of hexa-(3-methoxy-4-epoxymethylene)-phenoxy-cyclotriphosphazene (C-1) prepared in Synthesis Example 7, 5 g of 1,3,5-triazine-2,4,6-triene triazine hexamethyl alcohol, and 3 g of α,α,α'-tris(4-hydroxyphenyl)-1-ethyl-4-isocumene were added to a mixed solvent of 60 g of γ-butyrolactone and 70 g of propylene glycol monomethyl ether. The mixture was stirred at 25 °C until completely dissolved and reacted for 6 h. The reaction solution was filtered through a 0.02 μm filter to obtain a positive photosensitive resin composition (S-3).

[0060] The specific implementation method for preparing the polyimide film in this embodiment is the same as in Example 1. A polyimide film (M-3) was obtained.

[0061] Example 4 The difference from Example 1 is that the alkali-soluble polyimide resin precursor (A-1) is replaced with an equal mass of alkali-soluble polyimide resin precursor (A-2) to obtain a positive photosensitive resin composition (S-4) and a polyimide film (M-4).

[0062] Comparative Example 1 The difference from Example 1 is that in Comparative Example 1, the alkali-soluble polyimide resin precursor (A-1) was replaced with an equal mass of alkali-soluble polyimide resin precursor (A-3) to obtain a positive photosensitive resin composition (S-5) and a polyimide film (M-5).

[0063] Comparative Example 2 Unlike Example 1, in Comparative Example 2, the alkali-soluble polyimide resin precursor (A-1) was replaced with an equal mass of alkali-soluble polyimide resin precursor (A-4) to obtain a positive photosensitive resin composition (S-6) and a polyimide film (M-6).

[0064] Comparative Example 3 Unlike Example 1, in Comparative Example 3, the hexa-(3-methoxy-4-epoxymethylene)-phenoxy-cyclotriphosphazene prepared in Synthesis Example 5 was replaced with an equal mass of 1,3,5-triazine-2,4,6-triene triazine hexamethyl alcohol in the preparation of the positive photosensitive resin composition; that is, the hexa-(3-methoxy-4-epoxymethylene)-phenoxy-cyclotriphosphazene prepared in Synthesis Example 5 was not added. A positive photosensitive resin composition (S-7) and a polyimide film (M-7) were obtained.

[0065] Comparative Example 4 Unlike Example 1, in Comparative Example 4, 1,3,5-triazine-2,4,6-triene triazine hexamethyl alcohol was replaced with an equal mass of hexa-(3-methoxy-4-epoxymethylene)-phenoxy-cyclotriphosphazene prepared in Synthetic Example 5 in the preparation of the positive photosensitive resin composition; that is, 1,3,5-triazine-2,4,6-triene triazine hexamethyl alcohol was not added. Positive photosensitive resin composition (S-8) and polyimide film (M-8) were obtained.

[0066] Comparative Example 5 Unlike Example 1, in Comparative Example 4, the 4-naphthoquinone diazidesulfonyl ester compound prepared in Synthetic Example 5 was replaced with an equal mass of the 5-naphthoquinone diazidesulfonyl ester compound prepared in Synthetic Example 6 in the preparation of the positive photosensitive resin composition; that is, 3 g of the 5-naphthoquinone diazidesulfonyl ester compound was added. A positive photosensitive resin composition (S-9) and a polyimide film (M-9) were obtained.

[0067] Performance testing: 1. Sensitivity Evaluation: The pre-baked film was exposed using the i-line (365nm) of an exposure machine. After exposure, development was performed using a developing device with a 2.38% tetramethylammonium hydroxide aqueous solution as the developing solution. This process was repeated twice. The film was then washed with purified water, dried, and the lowest exposure value at which the exposed portion completely dissolved was taken as the sensitivity. Sensitivity values ​​above 300 mJ / cm² were considered acceptable. 2 Considered poor, rated C; value between 200 and 300 mJ / cm³ 2 Within the acceptable range, it is considered good and rated B; values ​​below 200 mJ / cm³ are considered good. 2 It is considered better and is rated A.

[0068] 2. Outgas test: The polyimide film was heated at 300℃ for 60 min. The residual small molecules that overflowed from the film were adsorbed by a gas adsorbent. The residual small molecules were desorbed for 10 min. At the same time, the gas chromatography-mass spectrometry (GC-MS) was used to test and analyze the residual small molecules that overflowed from the film sample and calculate the content of residual small molecules.

[0069] 3. Bending Resistance: A 50mm × 10mm × 2μm polyimide film was bent 180° along a 25mm longitudinal line and held for 30 seconds. After 30 seconds, the bent polyimide film was opened, and the bent portion along the 25mm longitudinal line on the surface of the cured film was observed using an FPD inspection microscope to evaluate the appearance changes of the cured film surface. The bending test was conducted within a radius of curvature of 0.1–1.0mm, and the minimum radius of curvature at which no appearance changes such as cracks appeared on the polyimide film surface was recorded.

[0070] 4. High temperature resistance: A polyimide film with dimensions of 50mm×10mm×2μm was stored at 90℃ for 100h, and then a bending resistance test was conducted. The minimum radius of curvature at which no appearance changes such as cracks appeared on the surface of the polyimide film was recorded.

[0071] 5. Chemical resistance: Five samples of the prepared polyimide film were immersed in N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), N,N-dimethylacetamide (DMAC), 10% hydrochloric acid aqueous solution, and 10% NaOH aqueous solution, respectively, for 150 min. Then, the etched polyimide film samples were taken out, washed twice with pure water, and dried. The film thickness of the polyimide film after etching was measured using a film thickness gauge. The film thickness difference was used as an evaluation of the chemical resistance of the polyimide film.

[0072] The performance test results of the polyimide film are shown in Tables 1 and 2: Table 1 As can be seen from the results in Table 1, the polyimide film prepared by this invention can meet the requirements of high heat resistance, low dielectric constant, chemical resistance and bending resistance of OLED devices such as PDL and PNL.

[0073] Table 2 As can be seen from the results in Table 2, the polyimide film prepared by this invention has excellent chemical resistance and can be widely used as a planarization layer and pixel definition layer in OLED display devices.

[0074] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention.

[0075] It should be understood that the present invention is not limited to the content already described above, and various modifications and changes can be made without departing from its scope. The scope of the present invention is limited only by the appended claims.

Claims

1. A positive photosensitive resin composition, characterized in that, By weight, it includes the following raw materials: 100 parts of alkali-soluble polyimide resin precursor, 1-50 parts of photosensitizer, 4-40 parts of thermal crosslinking agent, and 100-1500 parts of solvent. The thermal crosslinking agent is a mixture of an epoxy compound containing a phosphazene ring and an alkoxymethyl compound, with a mass ratio of 1:(0.1~10); the epoxy compound containing the phosphazene ring is hexa-(3-methoxy-4-epoxymethylene)-phenoxy-cyclotriphosphazene, and its molecular structure is shown in Formula 3: Formula 3.

2. The positive photosensitive resin composition according to claim 1, characterized in that, The average molecular weight of the alkali-soluble polyimide resin precursor is 5000~20000.

3. The positive photosensitive resin composition according to claim 1, characterized in that, The preparation steps of the alkali-soluble polyimide resin precursor include: First, aliphatic diamines, diamines with siloxane structures, and diamines with fluorine atoms are dissolved in a reaction solvent. Then, aromatic tetracarboxylic dianhydride is added, and the mixture is stirred at 30-60°C for 1-5 hours. Next, an end-capping agent is added, and the mixture is stirred at 30-60°C for another 1-5 hours. Then, an alkylating agent is added dropwise, and the reaction continues for 1-3 hours to obtain a mixture. The alkali-soluble polyimide resin precursor is then separated.

4. The positive photosensitive resin composition according to claim 3, characterized in that, The molar ratio of the diamine with fluorine atoms, the diamine with siloxane structure, and the aliphatic diamine is (12~20):1:(2~4).

5. The positive photosensitive resin composition according to claim 1, characterized in that, The photosensitizer is a mixture of 4-naphthoquinone diazidesulfonyl ester compound and 5-naphthoquinone diazidesulfonyl ester compound, with a mass ratio of (0.3~3):

1.

6. The positive photosensitive resin composition according to claim 1, characterized in that, The solvent is at least one of γ-butyrolactone, γ-valerolactone, δ-valerolactone, propylene glycol monomethyl ether, ethylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, propyl acetate, butyl acetate, isobutyl acetate, methyl butyl ketone, methyl isobutyl ketone, and methyl propyl ketone.

7. The positive photosensitive resin composition according to claim 1, characterized in that, It also includes sensitizers and surfactants.

8. A method for preparing a photosensitive polyimide film, characterized in that, The preparation process using the positive photosensitive resin composition according to any one of claims 1-7 specifically includes the following steps: S1, Coating: Applying the positive photosensitive resin composition to the substrate; S2. Preparation of pre-baked film: Drying at 60~150℃ to form a pre-baked film; S3. Exposure: The pre-baked film is exposed using an ultraviolet light source through a mask with a specific pattern; S4. Development: The exposed parts are washed away with a developing solution to obtain a patterned pre-baked film; S5. Heat curing treatment: The pre-baked film with the desired pattern is heat-treated at 150~250℃ to obtain a photosensitive polyimide film.

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