Preparation method of polyimide film

Abstract

The invention relates to the technical field of polishing equipment, and provides a polyimide film preparation method, which comprises the following steps: by taking CBDA / BDA as dianhydride and ODA / DABA as diamine, reacting for 6-24 hours in a DMF (Dimethyl Formamide) solvent under the protection of nitrogen at 0-30 DEG C to synthesize a PAA solution; and carrying out gradient imidization after tape casting to prepare an initial PI film. According to the present invention, the alicyclic dianhydride (CBDA / BDA) is selected to replace the traditional aromatic dianhydride, such that the conjugated structure of the molecular chain is effectively cut off, and the formation of the charge transfer complex (CTC) causing the yellowing of the polyimide and the reduction of the light transmittance is fundamentally inhibited so as to achieve the high light transmittance (gt; 85%) and low chromaticity. Meanwhile, an optimized gradient imidization process (heat preservation at 80-350 DEG C in stages) is adopted, so that high-efficiency and complete conversion from polyamide acid (PAA) to polyimide (PI) is ensured, and the thermal stability (T5% gt; 500 DEG C).

Description

Technical Field

[0001] The present application relates to the technical field of polyimide film preparation, and in particular to a method for preparing a polyimide film. Background Art

[0002] The contents of this section merely provide background information related to this application and may not constitute prior art.

[0003] Polyimide (PI) films are widely used in aerospace, microelectronics, and other fields due to their excellent thermal stability, mechanical strength, and chemical inertness. However, traditional aromatic PI films (such as the PMDA-ODA system) suffer from severe absorption in the visible light region due to the presence of strong charge transfer complexes (CTCs) and conjugated chromophores in the main chain, resulting in a characteristic yellow-brown color (b* value > 40) and a transmittance of less than 60% at 400nm. This optical defect severely restricts their application in emerging fields such as flexible display cover panels and transparent circuit substrates.

[0004] To improve transparency, researchers introduced alicyclic dianhydride monomers (such as CBDA and BDA) to replace aromatic dianhydrides, inhibiting CTC formation by destroying the conjugated structure of the molecular chain. However, these alicyclic monomers have two major derivative problems due to the reduced molecular rigidity and lower molecular chain stacking density:

[0005] Deterioration of thermal stability: The thermal decomposition temperature of the alicyclic structure is generally lower than that of the aromatic ring, resulting in the film's 5% thermal weight loss temperature (T5%) dropping from >550°C of traditional PI to below 480°C;

[0006] Insufficient mechanical strength: The increased flexibility of the molecular chain causes a decrease in the elastic modulus, and the tensile strength is mostly lower than 90MPa, which makes it difficult to meet the mechanical load requirements during device processing. Summary of the Invention

[0007] In view of this, the purpose of this application is to provide a method for preparing a polyimide film. The method for preparing a polyimide film disclosed in this application can be achieved.

[0008] The purpose of the present application is achieved through the following technical solution: A method for preparing a polyimide film, characterized by comprising:

[0009] PAA solution was synthesized by using CBDA / BDA as dianhydride and ODA / DABA as diamine in DMF solvent at 0-30°C under nitrogen protection for 6-24 hours; after casting, the initial PI film was prepared by gradient imidization.

[0010] In some possible embodiments, the diamine dissolution comprises the following steps:

[0011] Step 11: Add DMF to a dry three-necked flask, turn on nitrogen protection, and maintain at 25°C;

[0012] Step 12: Add ODA and stir until completely dissolved;

[0013] Step 13: Add DABA and stir until it is completely dissolved to form a diamine solution.

[0014] In some possible embodiments, preparing the PAA solution includes the following steps:

[0015] Step 21: Cool the diamine solution to 0-5°C with ice salt solution;

[0016] Step 22: After mixing CBDA and BDA, divide the mixture into 4 equal parts and add them to the diamine solution in batches. After all the addition is completed, continue the reaction at 0-5°C for 12 hours to generate a PAA solution.

[0017] In some possible embodiments, the initial PI film is prepared by gradient imidization after casting, comprising the following steps:

[0018] Step 3 includes the following steps:

[0019] Step 31: Filter the PAA solution through a filter;

[0020] Step 32: Coating on a glass substrate using a doctor blade casting machine;

[0021] Step 33: Immerse the film-coated substrate in 25°C deionized water for 10 seconds; lift the edge of the film with tweezers and peel it off slowly; and dry it in a vacuum oven at 60°C for 2 hours.

[0022] In some possible embodiments, an orthogonal test is conducted using the amount of DMF added, the temperature required for adding the second batch of mixed dianhydride, and the reaction time after all the dianhydride is added as key influencing factors.

[0023] In some possible embodiments, the amount of DMF added is 15% of the solid content.

[0024] In some possible embodiments, the temperature required for adding the second batch of mixed dianhydride is 25°C.

[0025] In some possible embodiments, the reaction time after all the dianhydride is added is 12 hours.

[0026] In some possible embodiments, 1-5 wt % POSS is incorporated into the PAA solution via ultrasonic dispersion, and the aggregation threshold is controlled to be ≤3%.

[0027] In some possible embodiments, the content of POSS is 3 wt %.

[0028] The technical solutions of the embodiments of the present application have at least the following advantages and beneficial effects:

[0029] By replacing traditional aromatic dianhydrides with alicyclic dianhydrides (CBDA / BDA), the conjugated structure of the molecular chain is effectively severed, fundamentally inhibiting the formation of charge transfer complexes (CTCs) that cause yellowing of polyimide and a decrease in transmittance, thereby achieving high transmittance (>85%) and low chroma. At the same time, an optimized gradient imidization process (staged insulation from 80°C to 350°C) ensures the efficient and complete conversion of polyamic acid (PAA) to polyimide (PI), significantly improving the thermal stability of the film (T5%>500°C). The rational combination of diamine components (ODA / DABA) balances the rigidity and flexibility of the molecular chain, providing the film with a good mechanical strength foundation (>100MPa).

[0030] Systematic orthogonal optimization of key variables in the polyamic acid synthesis process (solids content, reaction temperature, and reaction time) was conducted, precisely quantifying the previously broad empirical process window (e.g., 0-30°C reaction time of 6-24 hours) to precisely quantify (e.g., solids content 15%, temperature 25°C, reaction time 12 hours). This quantitative control effectively inhibits side reactions (e.g., hydrolysis of dianhydride), ensures the uniformity of PAA molecular weight and its distribution (narrow molecular weight distribution), and thus significantly improves the batch-to-batch stability and repeatability of the final PI film properties (especially tensile strength >100 MPa), laying a solid foundation for industrialization.

[0031] On the basic binary system, an innovative two-step modification strategy was introduced. First, a ternary copolymerization was carried out by a step-by-step feeding method (a rigid third monomer was added after pre-polymerization of the main monomer). Under the premise of maintaining good compatibility and optical properties of the molecular chain (transmittance>80%), the rigid chain segments were introduced in an orderly manner, which significantly improved the glass transition temperature (Tg increased by 10-20°C) and mechanical strength (increased by 10-20%) of the film. Secondly, nano-scale POSS particles were uniformly incorporated into the PAA solution through a precisely controlled ultrasonic dispersion process, and the doping amount was strictly controlled below the agglomeration threshold (≤3wt%). The cage-type siloxane structure of POSS effectively restricts the movement of polymer chain segments and enhances interfacial interactions at the nanoscale, thereby synergistically significantly improving the heat resistance (Tg↑25°C), mechanical strength (up to 130MPa) and thermal decomposition stability (TGA-MS confirmed the improvement) of the film with minimal loss of transmittance (such as 82% at 3wt%), achieving a multi-dimensional leapfrog enhancement of film performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 A schematic structural diagram of a polishing device provided in some embodiments of the present application; DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solutions and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with specific implementation methods. The same figure marks in the accompanying drawings represent the same components. It should be noted that the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the described embodiments of this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0034] Compared to the embodiments shown in the drawings, feasible embodiments within the scope of protection of the present application may have fewer components, other components not shown in the drawings, different components, differently arranged components, or differently connected components, etc. In addition, two or more components in the drawings may be implemented in a single component, or a single component shown in the drawings may be implemented as multiple separate components.

[0035] Unless otherwise defined, the technical or scientific terms used herein shall have the ordinary meaning understood by persons of ordinary skill in the field to which this application belongs. The words "first", "second" and similar terms used in the specification and claims of this application do not indicate any order, quantity or importance, but are only used to distinguish different components. Similarly, words such as "a" or "an" do not necessarily indicate a quantitative limitation. "Up", "down" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0036] Example 1: Preparation of basic film;

[0037] PAA solution was synthesized by using CBDA / BDA as dianhydride and ODA / DABA as diamine in DMF solvent under nitrogen protection at 0-30°C for 6-24h. After casting, the initial PI film was prepared by gradient imidization (80°C→350°C stepwise insulation).

[0038] The specific method is as follows:

[0039] Step 1: Diamine Dissolution:

[0040] Step 11: Add 700 g of DMF (N,N-dimethylformamide) to a dry three-necked flask, turn on nitrogen protection, and maintain 25°C.

[0041] Step 12: Add 100.8 g of ODA (4,4'-diaminodiphenyl ether) and stir at 200 rpm until completely dissolved;

[0042] Step 13: Add 36.9 g of DABA (3,3'-diaminodiphenyl sulfone) and stir at 200 rpm until completely dissolved to generate a diamine solution.

[0043] Step 2: Prepare PAA solution;

[0044] Step 21: Cool the diamine solution to 0-5°C with ice salt solution;

[0045] Step 22: 54.0 g of CBDA (cyclobutanetetracarboxylic dianhydride) and 48.0 g of BDA (butanetetracarboxylic dianhydride (BDA)) were mixed and divided into four equal portions;

[0046] Batch 1: Add 25.5 g of mixed dianhydride and stir at 150 rpm;

[0047] Batch 2: Add 25.5 g of mixed dianhydride and maintain 0-5°C;

[0048] Batch 3: Add 25.5 g of mixed dianhydride and monitor viscosity;

[0049] Batch 4: Add the remaining 25.5 g of mixed dianhydride;

[0050] After all the addition was completed, the reaction was continued at 0-5°C for 12 hours to generate a PAA solution.

[0051] Step 3: Filter the PAA solution to generate the initial PI membrane.

[0052] Step 3 includes the following steps:

[0053] Step 31: Filter the PAA solution through a 100-mesh stainless steel filter;

[0054] Step 32: Use a doctor blade tape casting machine to coat the glass substrate (pre-chromic acid cleaned)

[0055] Step 33: Immerse the film-coated substrate in 25°C deionized water for 10 seconds; lift the edge of the film with tweezers and peel it off slowly; and dry it in a vacuum oven at 60°C for 2 hours (vacuum degree -0.09 MPa).

[0056] Example 2: Setting key process parameters for optimization;

[0057] In step 1, the key process parameters are: the amount of DMF added, the temperature required when adding the second batch of mixed dianhydride, and the reaction time after all the dianhydride has been added.

[0058] To this end, this application sets up the following 9 groups of experiments:

[0059] Table 1: Experimental table group table:

[0060]

[0061]

[0062] Table 2: Experimental data table:

[0063]

[0064] Table 3: Range table of each data item;

[0065] factor K1 (level 1 mean) K2 (Level 2 Mean) K3 (Level 3 Mean) Range R A(solid content) (85+98+72) / 3＝85.0 (102+108+78) / 3＝96.0 (95+92+80) / 3＝89.0 96.0-85.0＝11.0 B (temperature) (85+102+95) / 3＝94.0 (98+108+92) / 3＝99.3 (72+78+80) / 3＝76.7 99.3-76.7＝22.6 C(time) (85+78+92) / 3＝85.0 (98+102+80) / 3＝93.3 (72+108+95) / 3＝91.7 93.3-85.0＝8.3

[0066] According to the above experimental data, we can know that:

[0067] The order of influence on strength is: temperature (B) > solid content (A) > time (C).

[0068] The optimal level combination: A2B2C2 (solid content 15%, temperature 25°C, time 12h).

[0069] The optimal polymerization conditions were determined by orthogonal test: solid content 15%, temperature 25°C, time 12h, which made the PAA molecular weight distribution uniform and the film tensile strength greater than 100MPa.

[0070] Step 3: POSS nanohybrid enhancement

[0071] 1-5 wt% POSS (octaaminopropyl POSS) was added to the PAA solution by ultrasonic dispersion (400W, 30min), and the aggregation threshold was controlled to be ≤3%;

[0072] The transmittance of the hybrid film remains at 82% at a doping content of 3wt%, Tg↑25℃, and the tensile strength reaches 130MPa. TGA-MS confirms that the thermal decomposition temperature is increased.

[0073] Specifically: Prepare a PAA solution (15% solids content, CBDA / BDA-ODA / DABA, reaction time 12 h at 25°C) using the optimized process from Step 2; intrinsic viscosity η = 1.65-1.70 dL / g. Mix 100 g of PAA solution (containing 15 g solids) with 3.0 g of POSS / NMP dispersion (containing 0.09 g POSS). Calculate the actual doping level: 0.09 g POSS / (15 g PAA + 0.09 g POSS) × 100% = 0.6 wt%.

[0074] The POSS was pretreated as follows before use: OAPS-POSS was dried in a vacuum oven at 80°C for 24 h (vacuum degree -0.1 MPa); 3.0 g of dry POSS (target doping amount 3 wt%) was weighed and 97 g of NMP was added;

[0075] Stir magnetically (500 rpm) for 30 minutes to obtain a primary dispersion. Immerse the probe into the dispersion (depth 15 mm);

[0076] Start ultrasound and pause every 5 minutes to scrape particles off the wall of the cup.

[0077] Table 4: Performance test after adding POSS nanoparticles;

[0078]

[0079] The above are merely preferred embodiments of the present application and are not intended to limit the present application. Those skilled in the art will readily appreciate that various modifications and variations are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. A method for preparing a polyimide film, characterized in that: include: PAA solution was synthesized by using CBDA / BDA as dianhydride and ODA / DABA as diamine in DMF solvent at 0-30°C under nitrogen protection for 6-24 hours; after casting, the initial PI film was prepared by gradient imidization.

2. The method for preparing a polyimide film according to claim 1, wherein: Diamine dissolution includes the following steps: Step 11: Add DMF to a dry three-necked flask, turn on nitrogen protection, and maintain at 25°C; Step 12: Add ODA and stir until completely dissolved; Step 13: Add DABA and stir until it is completely dissolved to form a diamine solution.

3. The method for preparing a polyimide film according to claim 1, wherein: The preparation of PAA solution includes the following steps: Step 21: Cool the diamine solution to 0-5°C with ice salt solution; Step 22: After mixing CBDA and BDA, divide the mixture into 4 equal parts and add them to the diamine solution in batches. After all the addition is completed, continue the reaction at 0-5°C for 12 hours to generate a PAA solution.

4. The method for preparing a polyimide film according to claim 3, wherein: The initial PI film is prepared by gradient imidization after casting, including the following steps: Step 3 includes the following steps: Step 31: Filter the PAA solution through a filter; Step 32: Coating on a glass substrate using a doctor blade casting machine; Step 33: Immerse the film-coated substrate in 25°C deionized water for 10 seconds; lift the edge of the film with tweezers and peel it off slowly; and dry it in a vacuum oven at 60°C for 2 hours.

5. The method for preparing a polyimide film according to any one of claims 1 to 4, characterized in that: An orthogonal experiment was conducted with the amount of DMF added, the temperature required for adding the second batch of mixed dianhydride, and the reaction time after all the dianhydride was added as key influencing factors.

6. The method for preparing a polyimide film according to claim 5, wherein: The amount of DMF added was 15% solid content.

7. The method for preparing a polyimide film according to claim 5, wherein: The desired temperature for adding the second batch of mixed dianhydride was 25°C.

8. The method for preparing a polyimide film according to claim 5, wherein: The reaction time after all the dianhydride was added was 12 h.

9. The method for preparing a polyimide film according to claim 1, wherein: 1-5 wt% POSS was incorporated into PAA solution by ultrasonic dispersion, and the aggregation threshold was controlled to be ≤3%.

10. The method for preparing a polyimide film according to claim 9, wherein: The content of POSS was 3 wt%.

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