Low-loss high-transparency polyimide film and preparation method thereof

Abstract

The invention relates to the technical field of film materials, and particularly discloses a low-loss high-light-transmission polyimide film and a preparation method thereof.The low-loss high-light-transmission polyimide film is prepared through a polymerization reaction of a fluorine-containing diamine monomer and a fluorine-containing dianhydride monomer, the molar ratio of a C-F bond to a C-H bond in the molecular structure of the low-loss high-light-transmission polyimide film ranges from 13: 1 to 20: 1, the light transmittance of the low-loss high-light-transmission polyimide film at the wave band of 1300-1550 nm ranges from 90% to 95%, and the light loss coefficient of the low-loss high-light-transmission polyimide film ranges from 0.2 dB / cm to 0.3 dB / cm; through the specific combination of the fluorine-containing diamine monomer and the fluorine-containing dianhydride monomer and the high molar ratio setting of a C-F bond and a C-H bond, the molecular polarity of the polyimide film is remarkably reduced, and the light scattering and absorption loss are reduced, so that the high light transmission and low light loss characteristics of the film in the wave band of 1300-1550 nm are realized, and the film has a wide application prospect. Through the combination of the gradient heating imidization process and the high vacuum annealing treatment, the molecular chain arrangement and internal stress distribution of the film are effectively controlled, and the compactness and uniformity of the film are improved, so that the film has higher glass transition temperature and lower thermal expansion coefficient, and the dimensional stability requirement in a high-temperature environment is met.

Description

Technical Field

[0001] The present invention belongs to the technical field of thin film materials, and in particular relates to a low-loss and high-transmittance polyimide film and a preparation method thereof. Background Art

[0002] With the rapid development of optical communication technology, the requirements for optical materials are becoming increasingly stringent, especially in high-speed, long-distance optical transmission systems. The light transmittance and optical loss performance of the material have become key factors determining the performance of the system. Polyimide film, as a high-performance organic polymer material, has been widely used in electronics, aerospace, and microelectronics packaging due to its excellent mechanical properties, thermal stability, and chemical stability. However, traditional polyimide film still cannot meet the high-performance material requirements of modern optical communication technology in terms of optical performance, especially transmittance and optical loss coefficient.

[0003] Specifically, traditional polyimide films are mostly made by polymerization of non-fluorinated diamine monomers and dianhydride monomers. C-H bonds dominate their molecular structure, while the CF bond content is extremely low or even non-existent. This molecular structure characteristic results in the film having a low transmittance in the important optical communication band of 1300-1550nm, usually only reaching 70%-80%. At the same time, the optical loss coefficient is high, ranging from 0.5-1.0dB / cm. High optical loss not only limits the transmission distance of optical signals, but also increases the energy consumption and cost of the system, posing an obstacle to the further development of optical communication technology. In addition, the preparation process of traditional polyimide films mostly adopts a one-step high-temperature imidization, and the annealing treatment conditions are simple, which often leads to uneven stress distribution inside the film and disordered arrangement of the molecular chains, further affecting the optical properties and thermal stability of the film, so it needs to be improved. Summary of the Invention

[0004] The object of the present invention is to provide a low-loss and high-transmittance polyimide film and a preparation method thereof, so as to solve the problems raised in the above background technology.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] Low-loss, high-transmittance polyimide film is made by the polymerization reaction of fluorinated diamine monomers and fluorinated dianhydride monomers. The molar ratio of CF bonds to CH bonds in its molecular structure is 13:1 to 20:1. The transmittance in the 1300-1550nm band is 90%-95%, and the optical loss coefficient is 0.2-0.3dB / cm.

[0007] Preferably, the fluorine-containing diamine monomer is a mixture of 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane and 4,4'-(hexafluoroisopropylidene)diphthalic anhydride derivative diamine, with a mixing molar ratio of 1:1 to 1:2.

[0008] Preferably, the fluorine-containing dianhydride monomer is a mixture of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride and 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, with a mixing molar ratio of 2:1.

[0009] Preferably, the glass transition temperature is 300-320° C., the thermal expansion coefficient is 15-20 ppm / ° C., and the refractive index is 1.52-1.62@1550 nm when the film thickness is 5-50 μm.

[0010] A method for preparing a low-loss and high-transmittance polyimide film comprises the following steps:

[0011] S1. Under nitrogen protection, dissolving the fluorinated diamine monomer in N-methylpyrrolidone to form a solution with a concentration of 15 wt%;

[0012] S2, adding fluorinated dianhydride monomer in a molar amount 1-1.05 times that of diamine monomer in batches, controlling the reaction temperature at 5°C to carry out prepolymerization for 3 hours;

[0013] S3, heating to 25°C and continuing the reaction for 18 hours to obtain a polyamic acid solution;

[0014] S4, after the polyamic acid solution is cast into a film, imidization is performed by a gradient temperature method: 80°C for 1 hour, 150°C for 1 hour, 250°C for 2 hours, and 300°C for 1 hour;

[0015] S5, in 10 -3 Annealing was performed under a Pa vacuum environment at a temperature of 300°C for 3 hours.

[0016] Preferably, the water content of N-methylpyrrolidone in step S1 is 30-50 ppm.

[0017] Preferably, the imidization process in step S4 is carried out in a dry nitrogen atmosphere with a nitrogen dew point of -70°C to -80°C.

[0018] Preferably, the heating rate of the post-annealing treatment in step S5 is 3°C / min, and the cooling rate is 2°C / min.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] (1) Through the specific combination of fluorinated diamine monomers and fluorinated dianhydride monomers and the high molar ratio of CF bonds to CH bonds, the molecular polarity of the polyimide film is significantly reduced, and the light scattering and absorption losses are reduced, thereby achieving high transmittance and low light loss characteristics of the film in the 1300-1550nm band, making it more suitable for precision optical devices and optical communications.

[0021] (2) By combining the gradient temperature imidization process with high vacuum annealing treatment, the molecular chain arrangement and internal stress distribution of the film are effectively controlled, and the density and uniformity of the film are improved, so that it has a higher glass transition temperature and a lower thermal expansion coefficient, meeting the dimensional stability requirements in high temperature environments.

[0022] (3) By optimizing the solvent water content and the precise control settings of the reaction temperature conditions, the sufficiency and stability of the polymerization reaction are ensured, and the occurrence of side reactions is avoided, thereby obtaining a polyimide film with excellent mechanical properties and surface flatness, which is suitable for the high-quality film formation requirements of flexible electronics and display devices.

[0023] (4) Through the imidization process in a dry nitrogen atmosphere and the annealing process setting at a specific heating rate, the residual solvent and bubbles in the film are further eliminated, and the defect density is reduced, so that its refractive index is stable and the optical properties are consistent, providing a reliable material basis for optical coatings and sensors. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a raw material flow chart of the present invention;

[0025] Figure 2 It is a preparation flow chart of the present invention. DETAILED DESCRIPTION

[0026] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0027] Example 1:

[0028] See also Figure 1 and Figure 2 As shown, the preparation method of low-loss and high-transmittance polyimide film, raw material preparation:

[0029] Fluorinated diamine monomer:

[0030] 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (6FAP);

[0031] 4,4'-(Hexafluoroisopropylidene)diphthalic anhydride derivative diamine (6FDA-DA);

[0032] Molar ratio: 6FAP:6FDA-DA=1:1.5.

[0033] Fluorinated dianhydride monomer:

[0034] 4,4'-(Hexafluoroisopropylidene)diphthalic anhydride (6FDA);

[0035] 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6F-DA);

[0036] Molar ratio: 6FDA:6F-DA=2:1.

[0037] Solvent: N-methylpyrrolidone (NMP), water content ≤40ppm.

[0038] Preparation of polyamic acid (PAA) solution:

[0039] Under nitrogen protection, 15 g of NMP was added to the dry reactor.

[0040] 6FAP (2.00 g, 5.0 mmol) and 6FDA-DA (2.85 g, 7.5 mmol) were added and stirred until completely dissolved.

[0041] The reaction temperature was controlled at 5±1°C, and 6FDA (4.44 g, 10.0 mmol) and 6F-DA (1.11 g, 2.5 mmol) were added in batches, and the reaction was maintained for 3 hours.

[0042] The temperature was raised to 25±1° C., and the reaction was continued with stirring for 18 hours to obtain a transparent and viscous polyamic acid (PAA) solution.

[0043] Film formation and imidization:

[0044] The PAA solution was cast on a clean glass substrate, and the wet film thickness was controlled to be 100 μm.

[0045] Gradient temperature rise was used for imidization: 80°C / 1 hour (solvent removal), 150°C / 1 hour (preliminary imidization), 250°C / 2 hours (complete imidization), and 300°C / 1 hour (high temperature curing).

[0046] The imidization process was carried out under a nitrogen atmosphere (dew point ≤ -70 °C).

[0047] Annealing treatment:

[0048] The film was placed in a high vacuum (10 -3 Pa) annealing furnace.

[0049] The temperature was raised to 300°C at 3°C / min and maintained for 3 hours.

[0050] The temperature was lowered to room temperature at a rate of 2°C / min to obtain a polyimide film with a thickness of 25±2 μm.

[0051] Example 2:

[0052] See also Figure 1 and Figure 2 As shown, the preparation method of low-loss and high-transmittance polyimide film, raw material preparation:

[0053] Fluorinated diamine monomer:

[0054] 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (6FAP);

[0055] 3,3'-diamino-4,4'-difluorodiphenyl ether (TFDB);

[0056] Molar ratio: 6FAP:TFDB=1:1.

[0057] Fluorinated dianhydride monomer:

[0058] 4,4'-(Hexafluoroisopropylidene)diphthalic anhydride (6FDA);

[0059] Perfluorocyclobutane dianhydride (PFCBDA);

[0060] Molar ratio: 6FDA:PFCBDA=3:1.

[0061] Solvent: γ-butyrolactone (GBL), water content ≤30ppm.

[0062] Preparation of polyamic acid (PAA) solution:

[0063] Under nitrogen protection, 15 g of GBL was added to the dry reactor.

[0064] 6FAP (2.00 g, 5.0 mmol) and TFDB (1.66 g, 5.0 mmol) were added and stirred until completely dissolved.

[0065] The reaction temperature was controlled at 0±1°C, and 6FDA (4.44 g, 10.0 mmol) and PFCBDA (0.74 g, 2.5 mmol) were added in batches, and the reaction was maintained for 4 hours.

[0066] The temperature was raised to 30±1° C. and the reaction was continued with stirring for 24 hours to obtain a transparent and viscous polyamic acid solution.

[0067] Film formation and imidization

[0068] The PAA solution was spin-coated on a silicon wafer substrate (rotation speed 1500 rpm, time 30 s) with a wet film thickness of 80 μm.

[0069] The imidization was carried out by gradient temperature increase (nitrogen dew point ≤ -75°C): 80°C / 1 hour, 180°C / 1 hour, 260°C / 2 hours, and 320°C / 1 hour.

[0070] Annealing treatment:

[0071] Place the film at 10 -3 The temperature was raised to 320°C at a rate of 5°C / min in a Pa vacuum and maintained for 2 hours.

[0072] The temperature was lowered at 3°C / min to obtain a polyimide film with a thickness of 20±1 μm.

[0073] Comparative Example:

[0074] Description of the Prior Art: Traditional polyimide films are typically produced through the polymerization reaction of non-fluorinated diamine monomers (such as 4,4'-diaminodiphenyl ether, ODA) and non-fluorinated dianhydride monomers (such as pyromellitic dianhydride, PMDA). Their molecular structure primarily consists of C-H bonds, with very low or even non-existent C-F bonds. Such films exhibit low transmittance in the 1300-1550nm band (typically 70%-80%) and high optical loss coefficient (0.5-1.0 dB / cm). Furthermore, they have a glass transition temperature of 250-280°C, a thermal expansion coefficient of 30-50 ppm / °C, and a refractive index of 1.65-1.75 at 1550nm. Preparation methods typically utilize a one-step high-temperature imidization process (e.g., directly heating to 300°C), and relatively simple annealing conditions (normal pressure or low vacuum).

[0075] Existing technology preparation method:

[0076] Raw materials preparation:

[0077] Diamine monomer: 4,4'-diaminodiphenyl ether (ODA);

[0078] Dianhydride monomer: pyromellitic dianhydride (PMDA);

[0079] Solvent: N-methylpyrrolidone (NMP), water content ≤100ppm.

[0080] Preparation of polyamic acid (PAA) solution:

[0081] Under nitrogen protection, ODA (2.00 g, 10.0 mmol) was dissolved in 15 g NMP;

[0082] PMDA (2.18 g, 10.0 mmol) was added in batches, the reaction temperature was controlled at 25° C., and the reaction was stirred for 24 hours to obtain a viscous PAA solution.

[0083] Film formation and imidization:

[0084] The PAA solution was cast on a glass substrate with a wet film thickness of 100 μm;

[0085] The temperature was directly raised to 300° C. for imidization and maintained for 2 hours (no gradient temperature increase process).

[0086] Annealing treatment:

[0087] Under normal pressure, the temperature was raised to 280° C. at a rate of 5° C. / min, maintained for 2 hours, and naturally cooled to room temperature to obtain a polyimide film with a thickness of about 25 μm.

[0088] Performance comparison table:

[0089]

[0090] Comparative Conclusion

[0091] Optical properties: The films of Examples 1 and 2 significantly improve light transmittance (90%-95% vs. 70%-80%) and reduce light loss coefficient (0.2-0.3dB / cm vs. 0.5-1.0dB / cm) due to their fluorine-containing structure (high CF bond ratio).

[0092] The existing technology lacks CF bonds and has high molecular polarity, resulting in large light scattering and absorption losses.

[0093] Thermal performance: The fluorine-containing structure makes the embodiment have a higher glass transition temperature (300-320°C vs. 250-280°C) and a lower thermal expansion coefficient (15-20ppm / °C vs. 30-50ppm / °C), making it more suitable for high-temperature applications.

[0094] Preparation process: The existing technology uses a simple one-step imidization and normal pressure annealing, which leads to uneven internal stress in the film and poor performance stability;

[0095] In Examples 1 and 2, the uniformity and density of the thin film are significantly improved by gradient heating and high vacuum annealing.

[0096] Summary: This application solves the problems of poor light transmittance, high loss, and insufficient thermal stability of traditional polyimide films by selecting fluorine-containing monomers and optimizing the process. It is suitable for high-end fields such as optical communications and flexible displays.

[0097] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. Low-loss and high-transmittance polyimide film, characterized in that: It is prepared by polymerization of fluorinated diamine monomers and fluorinated dianhydride monomers. The molar ratio of CF bonds to CH bonds in its molecular structure is 13:1 to 20:

1. The transmittance in the 1300-1550nm band is 90%-95%, and the optical loss coefficient is 0.2-0.3dB / cm.

2. The low-loss, high-transmittance polyimide film according to claim 1, wherein: The fluorine-containing diamine monomer is a mixture of 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane and 4,4'-(hexafluoroisopropylidene)diphthalic anhydride derivative diamine, with a mixing molar ratio of 1:1 to 1:

2.

3. The low-loss and high-transmittance polyimide film according to claim 1, wherein: The fluorine-containing dianhydride monomer is a mixture of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride and 2,2-bis(3,4-dicarboxylic acid phenyl)hexafluoropropane dianhydride, with a mixing molar ratio of 2:

1.

4. The low-loss, high-transmittance polyimide film according to claim 1, wherein: The glass transition temperature is 300-320° C., the thermal expansion coefficient is 15-20 ppm / ° C., and the refractive index is 1.52-1.62@1550 nm when the film thickness is 5-50 μm.

5. A method for preparing a low-loss, high-transmittance polyimide film, applicable to the low-loss, high-transmittance polyimide film according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1. Under nitrogen protection, dissolving the fluorinated diamine monomer in N-methylpyrrolidone to form a solution with a concentration of 15 wt%; S2, adding fluorinated dianhydride monomer in a molar amount 1-1.05 times that of diamine monomer in batches, controlling the reaction temperature at 5°C to carry out prepolymerization for 3 hours; S3, heating to 25°C and continuing the reaction for 18 hours to obtain a polyamic acid solution; S4, after the polyamic acid solution is cast into a film, imidization is performed by a gradient temperature method: 80°C for 1 hour, 150°C for 1 hour, 250°C for 2 hours, and 300°C for 1 hour; S5, in 10 -3 Annealing was performed under a Pa vacuum environment at a temperature of 300°C for 3 hours.

6. The method for preparing a low-loss and high-transmittance polyimide film according to claim 5, wherein: The water content of N-methylpyrrolidone in step S1 is 30-50 ppm.

7. The method for preparing a low-loss and high-transmittance polyimide film according to claim 5, wherein: The imidization process in step S4 is carried out in a dry nitrogen atmosphere with a nitrogen dew point of -70°C to -80°C.

8. The method for preparing a low-loss and high-transmittance polyimide film according to claim 5, wherein: The heating rate of the post-annealing treatment in step S5 is 3°C / min, and the cooling rate is 2°C / min.

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