A colorless polyimide film with high fluorine content, high heat resistance, and low expansion, its preparation method, and its application.

Abstract

This invention discloses a colorless polyimide film with high fluorine content, high heat resistance, and low expansion, as well as its preparation method and applications. Specifically, a series of high-fluorine terphenyl dianhydride (structure I) and high-fluorine terphenyl diamine (structure II) are copolymerized (or homopolymerized), cast, and heat-treated to prepare CPI optical film materials with excellent properties. This type of CPI film exhibits excellent optical transparency, high glass transition temperature, high thermal decomposition temperature, low coefficient of thermal expansion, high mechanical properties, and low dielectric loss, making it highly suitable for applications in flexible displays, wearable devices, flexible batteries, and 5G high-frequency communications.

Description

Technical Field

[0001] This invention belongs to the field of optical thin films, specifically relating to a colorless polyimide thin film with high fluorine content, high heat resistance, and low expansion, as well as its preparation method and application. Background Technology

[0002] Compared to traditional electronic devices, novel flexible devices offer advantages such as thinness, flexibility, and wearability, demonstrating significant value in flexible displays, flexible batteries, and flexible high-frequency communications. The key to realizing flexible devices lies in the development of core flexible substrates, specifically including cover plates and substrates for flexible organic light-emitting diodes (OLEDs), substrates for thin-film solar cells (TFSCs), and flexible copper-clad laminates (FCCLs) for high-frequency communications. Taking key optical film materials for flexible OLEDs as an example, especially highly transparent and fold-resistant cover and substrate materials, current solutions primarily rely on ultra-thin optical glass (UTG). However, this cannot overcome its inherent drawbacks such as poor impact resistance, difficulty in processing and molding, and limited ability to achieve large sizes, severely restricting its application expansion. Based on the iterative development of flexible displays, colorless polyimide (CPI) with high heat resistance and high transparency is considered the optimal solution, specifically exhibiting: 1) high transmittance; 2) high colorlessness and low yellowness; 3) high thermodynamic stability, including high glass transition temperature, high thermal decomposition temperature, and dimensional thermal stability; 4) high strength, high modulus, and impact resistance; and 6) ease of molding and processing. Similarly, FCCLs used in high-frequency communication also have high requirements for the substrate's low dielectric properties, low thermal expansion, and high heat resistance, especially in terms of dielectric loss. The introduction of fluorinated aryl groups can significantly improve the thermal stability of CPI, particularly its thermal decomposition temperature. Trifluoromethyl, as a highly sterically hindered and electronegative substituent, can significantly improve the optical properties of CPI films while reducing their dielectric constant. Importantly, there are inherent contradictions among the various properties of demand-driven CPI films, such as high transparency, high heat resistance, and low expansion. Therefore, the challenge in designing highly applicable CPI films lies in achieving a balance and unity between high transparency, high colorlessness, low coefficient of thermal expansion, high mechanical properties, high thermal stability, and low dielectric properties, which fundamentally requires innovative development based on key molecular and chain structure designs.

[0003] Currently, almost none of the published or disclosed CPI films can simultaneously meet the aforementioned key properties, such as high heat resistance, high transparency, low expansion, and high toughness. This is the fundamental limitation restricting the application of CPI films in the field of flexible microelectronics. For example, CN115304915 A and Polymer, 2021, 218, 123488 disclose PI films with high glass transition temperatures (T0). g>390℃), low coefficient of thermal expansion (CTE<15ppm / K), but due to strong charge transfer (CT) within the macromolecular chains, it exhibits low transmittance and a high yellow index, failing to meet the stringent requirements of a novel flexible substrate with high transparency and low colorlessness. The PI films proposed in Polymers, 2021, 13(16), 2824, Polym. Chem., 2020, 11, 6009-6016, and Polym. Chem., 2017, 8, 6165-6172 meet the requirements of high transparency (T... 400 >80%), but its glass transition temperature is low (Tg<300℃), and its mechanical properties are particularly poor (σ). m <100MPa, Et<3GPa), it is difficult to meet the reliability and stability requirements of high-temperature processing and bending in flexible devices. Polym.Chem., 2021, 12(37), 5364-5376, Polymer, 2020, 206, 122889, etc., designed CPI films with amide structures that can maintain high transmittance (T<3GPa) at the same time. 550 It has a high glass transition temperature (Tg > 300℃) and low thermal expansion (CTE < 15ppm / K), but still exhibits poor mechanical properties (σ > 85%). m <200MPa, Et<4GPa). In summary, designing a CPI film that simultaneously meets multiple performance requirements and is truly applicable in practice remains a huge challenge, which is precisely the important significance and value of the present invention. Summary of the Invention

[0004] In view of the key optical films in the background technology, especially those that simultaneously meet the requirements of high transparency, high heat resistance, low expansion, high mechanical properties, and low dielectric, this invention provides a colorless polyimide film with high fluorine content, high heat resistance, and low expansion, as well as its preparation method and application.

[0005] Specifically, a series of high-fluorine-content terphenyl dianhydrides (structures I-1 to I-16) and high-fluorine-content terphenyl diamines (structures II-1 to II-20) are copolymerized (or homopolymerized), cast, and heat-treated to prepare CPI optical film materials with excellent properties. These CPI films exhibit excellent optical transparency, high glass transition temperature, high thermal decomposition temperature, low coefficient of thermal expansion, high mechanical properties, and low dielectric loss. They can address the stability issues of flexible OLED devices during high-temperature evaporation fabrication, effectively replacing rigid glass substrates, and are thus widely used in flexible displays, wearable devices, thin-film batteries, and 5G high-frequency communications.

[0006] The primary objective of this invention is to provide a colorless polyimide film that meets multiple requirements, including high transparency, high heat resistance, low expansion, high mechanical properties, and low dielectric constant. Both the dianhydride and diamine portions adopt an aromatic structure containing fluorinated terphenyl. The CPI optical film material with excellent properties is prepared by copolymerization (or homopolymerization), casting, and heat treatment of highly fluorinated terphenyl dianhydride (structure I) and highly fluorinated terphenyl diamine (structure II).

[0007] A colorless polyimide film with high fluorine content, high heat resistance, and low expansion, characterized in that the general structural formula of polyimide is as follows:

[0008]

[0009] Wherein, X represents the residue of fluorinated terphenyl dianhydride, and Y represents the residue of fluorinated terphenyl diamine; R1 to R4 are independently selected from one or more of F and CF3; a to d are the number of groups in R1 to R4, respectively, where a takes the value 0 to 1, c takes the value 0 to 2, and b and d take the value 0 to 4; at the same time, a to b cannot both take the value 0 at the same time, and c to d cannot both take the value 0 at the same time.

[0010] Preferably, the fluorinated terphenyl dianhydride is one or more of the following structural formulas I-1 to I-16:

[0011]

[0012] Preferably, the fluorinated terphenyldiamine is one or more of the following structural formulas II-1 to II-20:

[0013]

[0014] Preferably, the glass transition temperature (Tg) of the colorless polyimide film with high fluorine content, high heat resistance, and low expansion is 343–381 °C, and the thermogravimetric temperature (Tg) corresponding to 5 wt% is... d5％ The temperature range is 568–575℃, and the coefficient of thermal expansion (CTE) is ≤12ppm / K.

[0015] Preferably, the optical transmittance T at 550 nm of the colorless polyimide film with high fluorine content, high heat resistance, and low expansion is... 550 ≥88.5%, with a yellow index (YI) value of 1.9 to 3.5.

[0016] Preferably, the colorless polyimide film with high fluorine content, high heat resistance, and low expansion has a tensile strength σm value of 271-348 MPa and a tensile modulus Et value of 4.5-6.3 GPa.

[0017] Preferably, the dielectric constant D of the colorless polyimide film with high fluorine content, high heat resistance, and low expansion at a high frequency of 10 GHz is...k Value 2.69~2.89, dielectric loss D f Values ​​range from 0.002 to 0.005.

[0018] The second objective of this invention is to provide a method for preparing a colorless polyimide film with high fluorine content, high heat resistance, and low expansion, as described in the first objective, specifically comprising the following steps:

[0019] (1) Fluorinated terphenyl dianhydride (I-1~I-16) and fluorinated terphenyl diamine (II-1~II-20) are homopolymerized / copolymerized to synthesize a polyimide (or polyamic acid precursor) solution;

[0020] (2) The polyimide (or polyamic acid precursor) solution described in step (2) is subjected to a certain film-forming process to obtain a colorless polyimide optical film.

[0021] Preferably, the molar ratio of the fluorinated terphenyl dianhydride to the fluorinated terphenyl diamine in step (1) is 1:(0.9-1.1).

[0022] Preferably, the homopolymerization / copolymerization reaction in step (1) is carried out in a one-step or two-step process.

[0023] More preferably, the one-step method involves the high-temperature polycondensation of fluorinated terphenyl dianhydride and fluorinated terphenyl diamine in a high-boiling-point solvent under an inert gas atmosphere, with or without a catalyst, to obtain a homogeneous and viscous polyimide solution. The catalyst is one or both of benzoic acid and isoquinoline, the high-boiling-point solvent is one or more of m-cresol, p-chlorophenol, and m-chlorophenol, the reaction temperature is 150–200°C, the reaction time is 5–36 h, and the inert atmosphere is one of nitrogen and argon.

[0024] More preferably, in the two-step method, under the protection of an inert gas, fluorinated terphenyl dianhydride and fluorinated terphenyl diamine are polycondensed at low temperature in an aprotic polar solvent to obtain a homogeneous and viscous polyamic acid solution. The aprotic polar solvent is one or more of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), and N-methylpyrrolidone (NMP). The reaction temperature is -10 to 50°C, the reaction time is 10 to 120 h, and the inert atmosphere is nitrogen or argon.

[0025] Preferably, the film-forming process in step (2) includes casting and heat treatment.

[0026] More preferably, the casting process includes one or more of the following: direct casting film formation, precision slot coating film formation, casting and stretching continuous film formation.

[0027] More preferably, the heat treatment process includes a desolvation process and an imidization process, the heating method is continuous heating or gradient heating, the temperature range is 20 to 450°C, and the high-temperature atmosphere is one of nitrogen, argon, or vacuum.

[0028] More preferably, the imidization includes thermal imidization or chemical imidization.

[0029] The third objective of this invention is to provide the application of a colorless polyimide film with high fluorine content, high heat resistance, and low expansion as described in the first objective in flexible displays, wearable devices, flexible batteries, and 5G high-frequency communication equipment.

[0030] A fourth objective of this invention is to provide a flexible display comprising a colorless polyimide film with high fluorine content, high heat resistance, and low expansion, as provided in the first objective of this invention.

[0031] The fifth objective of this invention is to provide a wearable device comprising a colorless polyimide film with high fluorine content, high heat resistance, and low expansion, as provided in the first objective of this invention.

[0032] The sixth objective of this invention is to provide a flexible battery, which includes a colorless polyimide film with high fluorine content, high heat resistance, and low expansion provided in the first objective of this invention.

[0033] The seventh objective of this invention is to provide a 5G high-frequency communication device, wherein the 5G high-frequency communication device includes a colorless polyimide film with high fluorine content, high heat resistance, and low expansion provided by the first objective of this invention.

[0034] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0035] The method for preparing CPI optical films provided by this invention produces CPI films that simultaneously meet the requirements of high transparency (T). 550 ≥88.5%, YI≤3.5), high heat resistance (Tg≥343℃, T d5％ ≥568℃), low expansion (CTE≤12ppm / K), high mechanical properties (σm≥271MPa, Et≥4.5GPa), low dielectric constant (D k As low as 2.69, D f With a temperature as low as 0.002, it can meet various needs, address the stability of flexible OLED devices in high-temperature evaporation preparation, effectively replace rigid glass substrates, and thus be widely used in flexible displays, wearable devices, thin-film batteries and 5G high-frequency communications.

[0036] In this invention, a high-fluorine-content monomer is used to prepare a CPI film. The introduction of a large number of fluorine-containing groups can suppress the CTC charge transfer effect within and between molecular chains, thereby effectively improving the transparency of the optical film and significantly reducing the yellowness of the film. On the other hand, a large number of low-polarity fluorine atoms help to reduce molecular polarity, weaken the response of molecular chain segments to electric fields, and thus reduce the dielectric constant and dielectric loss of the polymer, giving the film excellent dielectric properties. Attached Figure Description

[0037] Figure 1 The UV-Vis (optical transparency) curves of the CPI films prepared in Examples 1-2 are shown.

[0038] Figure 2 The TMA (thermal expansion coefficient) curves of the CPI films prepared in Examples 2-4 are shown.

[0039] Figure 3 The DMA (glass transition temperature) curves of the CPI films prepared in Examples 4-5 are shown. Detailed Implementation

[0040] The specific implementation of the present invention will be further described below with reference to the accompanying drawings and examples, but the implementation and protection of the present invention are not limited thereto. It should be noted that any processes not specifically described in detail below are those that can be implemented or understood by those skilled in the art by referring to the prior art. Reagents or instruments whose manufacturers are not specified are considered to be conventional products that can be purchased commercially.

[0041] Example 1

[0042] Under nitrogen protection, fluorinated terphenyl dianhydride (5.06 g, 10 mmol, Formula I-3), fluorinated terphenyl diamine (4.68 g, 10 mmol, Formula II-9), and N,N-dimethylacetamide (DMAc) (40 mL) were added to a 100 mL three-necked flask. After complete dissolution, the mixture was stirred at 25 °C for 80 h to obtain a viscous polyamic acid solution (intrinsic viscosity 2.531 dL / g). The solution was then precision slit-coated and imidized under nitrogen with a gradient temperature increase of 20-150-300 °C, followed by peeling to obtain a CPI film material.

[0043]

[0044] Example 2

[0045] Under argon protection, a fluorinated terphenyl dianhydride (3.07 g, 7 mmol, Formula I-1), a fluorinated terphenyl diamine 1 (4.32 g, 10 mmol, Formula II-8), another fluorinated terphenyl dianhydride (1.31 g, 3 mmol, Formula I-6), and N,N-dimethylformamide (DMF) (40 mL) were added to a 100 mL three-necked flask. After complete dissolution, the mixture was stirred at 35 °C for 24 h to obtain a viscous polyamic acid solution. Triethylamine (0.01 mol, 1.01 g) and acetic anhydride (0.015 mol, 1.53 g) were slowly added to this solution, and the mixture was stirred for 36 h to complete the chemical imidization process. Subsequently, the CPI solution with the corresponding structure was obtained by ethanol precipitation, drying, and DMF dissolution (solid content 15 wt%, intrinsic viscosity 2.414 dL / g, PI structure as shown below). Subsequently, the CPI solution was cast into a film, imidized under vacuum conditions with continuous heating from 20 to 250°C, and then peeled off to obtain the CPI film material.

[0046]

[0047] Example 3

[0048] Under argon protection, 5.06 g (10 mmol, Formula I-3), one fluorinated terphenyl diamine (1.06 g, 2 mmol, Formula II-12), another fluorinated terphenyl diamine (3.45 g, 8 mmol, Formula II-2), benzoic acid (0.24 g, 2 mmol), and m-cresol (40 mL) were added to a 150 mL three-necked flask. After complete dissolution, the mixture was heated to 180 °C and maintained for 24 h. Toluene was used to remove small molecule byproducts to promote polymerization and complete imidization. Then, a CPI solution with the corresponding structure (15 wt% solids, intrinsic viscosity 2.893 dL / g, PI structure as shown below) was obtained by methanol precipitation, drying, and dissolution with DM Ac. Subsequently, the CPI solution was poured onto a clean glass plate for direct casting to form a film, which was then continuously heated to 350 °C in an oven for imidization. The film was then peeled off to obtain the CPI film material.

[0049]

[0050] Example 4

[0051] Under nitrogen protection, 5.42 g, 10 mmol of fluorinated terphenyl dianhydride (Formula I-14), 0.93 g, 2 mmol of fluorinated terphenyl diamine (Formula II-10), 4.26 g, 8 mmol of another fluorinated terphenyl diamine (Formula II-12), and 40 mL of N-methylpyrrolidone (NMP) were added to a 100 mL three-necked flask. After complete dissolution, the mixture was stirred at 40 °C for 120 h to obtain a viscous polyamic acid solution (intrinsic viscosity 2.145 dL / g). This solution was cast into a film, heated directly to 400 °C under vacuum, and then peeled off to obtain a CPI film material.

[0052]

[0053] Example 5

[0054] Under nitrogen protection, fluorinated terphenyl dianhydride (45.6 g, 100 mmol, Formula I-2), a fluorinated terphenyl diamine (32.8 g, 70 mmol, Formula II-6), another fluorinated terphenyl diamine (13.9 g, 30 mmol, Formula II-18), and dimethyl sulfoxide (DMSO) (400 mL) were added to a 1000 mL three-necked flask. After complete dissolution, the mixture was mechanically stirred at 10 °C for 60 h to obtain a viscous polyamic acid solution (intrinsic viscosity 2.237 dL / g). This solution was cast into a film, and then imidized under vacuum by gradually increasing the temperature from 50 °C to 450 °C at a rate of 20 °C / min. The resulting CPI film material was then obtained by peeling.

[0055]

[0056] The performance of the CPI films obtained in Examples 1-5 was tested, and the results are shown in Table 1. The intrinsic viscosity was measured using an Ubbelohde viscometer at 30°C. The polymer (PAA or PI) concentration was 0.5 g / dL, and the average value was taken from three measurements to reflect the molecular weight of the polymer. The glass transition temperature (Tg) of the CPI film is also shown. g The temperature was measured by DMA, and the characterization instrument was a TA Q800. The heating rate was 3℃ / min, and the atmosphere was nitrogen. The 5wt% thermal decomposition temperature (T) was measured by DMA. d5％ The CPI film's optical transparency was measured using TGA, with a TAQ50 instrument, a heating rate of 10℃ / min, and a nitrogen atmosphere. The optical transparency of the CPI film was measured using UV-Vis, with a Shimadzu 3600Plus instrument, ranging from 200 to 800 nm. Yellowness (YI) and haze were measured using a thin film colorimeter, with a HunterLab instrument and a D65 light source. The dielectric properties of the CPI film (dielectric constant D) were also measured. k Dielectric loss D fThe values ​​were measured by a vector network analyzer, characterized by an Agilent N5244A at a frequency of 10 GHz in resonant cavity mode.

[0057] Table 1

[0058]

[0059] The above data indicate that the T of the CPI film prepared by this invention is... g The value is 343~381℃, T d5％ The value is 568–575℃, and the CTE is 7–12 ppm / K; meanwhile, the optical transmittance T 550 The value is 88.5%–89.8%, and the yellow index (YI) value is 1.9–3.5; in terms of mechanical properties, the σm value is 271–348 MPa, and the Et value is 4.5–6.3 GPa; the dielectric properties at a high frequency of 10 GHz are D k Values ​​2.69–2.89, D f Values ​​range from 0.002 to 0.005.

[0060] Figure 1 The UV-Vis curves of the CPI films prepared in Examples 1 and 2 reflect their high optical transparency at wavelengths of 400-800 nm. Figure 3 The TMA curves of the CPI films prepared in Examples 2-4 are shown, and the slope of the curves reflects their ultra-low coefficient of thermal expansion (CTE) values. Figure 3 The DMA curves of the CPI films prepared in Examples 4 and 5 are shown, where the peak value of tanδ reflects its high glass transition temperature Tg value.

[0061] As can be seen from the above, the method for preparing high-fluorine-content aromatic diamine, high-fluorine-content aromatic dianhydride, and CPI optical film provided by the present invention simultaneously satisfies the requirements of high transparency (T). 550 ≥88.5%, YI≤3.5), high heat resistance (T d5％ ≥568℃), low expansion (CTE≤12ppm / K), high mechanical properties (σm≥271MPa, E t≥4.5GPa), low dielectric constant (D k As low as 2.69, D f With a thickness as low as 0.002, it can meet various needs, address the stability of flexible OLED devices in high-temperature processes, effectively replace ultra-thin glass substrates, and be widely used in flexible displays, wearable devices, thin-film batteries, and 5G high-frequency communications.

[0062] The above description is only a preferred embodiment of the present invention. For those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A colorless polyimide film with high fluorine content, high heat resistance, and low expansion, characterized in that, Polyimide is prepared from fluorinated terphenyl dianhydride and fluorinated terphenyl diamine; The fluorinated terphenyl dianhydride is one or more of the following structural formulas I-1 to I-16: ； The fluorinated triphenylenediamine is one or more of the following structural formulas II-1 to II-20: 。 2. The colorless polyimide film with high fluorine content, high heat resistance, and low expansion according to claim 1, characterized in that, The glass transition temperature of the colorless polyimide film with high fluorine content, high heat resistance, and low expansion. T g is 343~381°C, and the thermogravimetric temperature corresponding to 5wt% is... T d5% The temperature range is 568~575 °C, and the coefficient of thermal expansion (CTE) is ≤ 12 ppm / K. The optical transmittance at 550 nm of the colorless polyimide film with high fluorine content, high heat resistance, and low expansion is [not specified]. T 550 ≥ 88.5%, yellowness index (YI) value 1.9~3.5; the tensile strength of the colorless polyimide film with high fluorine content, high heat resistance, and low expansion is... σ m value is 271~348 MPa, tensile modulus E The t-value is 4.5~6.3 GPa; the dielectric constant of the colorless polyimide film with high fluorine content, high heat resistance, and low expansion at a high frequency of 10 GHz is... D k Value 2.69~2.89, dielectric loss D f Values ​​range from 0.002 to 0.

005.

3. The method for preparing a colorless polyimide film with high fluorine content, high heat resistance, and low expansion as described in any one of claims 1-2, specifically includes the following steps: (1) Fluorinated terphenyl dianhydride I-1~I-16 reacts with fluorinated terphenyl diamine II-1~II-20 to synthesize polyimide or polyamic acid precursor solutions; (2) The polyimide or polyamic acid precursor solution described in step (1) is used in a film-forming process to obtain a colorless polyimide film with high fluorine content, high heat resistance, and low expansion. The molar ratio of fluorinated terphenyl dianhydride to fluorinated terphenyl diamine in step (1) is 1:(0.9~1.1); The reaction described in step (1) can be carried out in one step or two steps.

4. The method for preparing a colorless polyimide film with high fluorine content, high heat resistance, and low expansion according to claim 3, characterized in that, The one-step method involves polycondensation of fluorinated terphenyl dianhydride and fluorinated terphenyl diamine in a high-boiling-point solvent under an inert gas atmosphere, with or without a catalyst, to obtain a homogeneous and viscous polyimide solution. The catalyst is one or two of benzoic acid and isoquinoline, the high-boiling-point solvent is one or more of m-cresol, p-chlorophenol, and m-chlorophenol, the reaction temperature is 150-200 °C, the reaction time is 5-36 h, and the inert atmosphere is one of nitrogen and argon. The two-step method involves the condensation polymerization of fluorinated terphenyl dianhydride and fluorinated terphenyl diamine in an aprotic polar solvent under inert gas protection to obtain a homogeneous and viscous polyamic acid solution. The aprotic polar solvent is... N,N -Dimethylformamide, N,N -Dimethylacetamide, dimethyl sulfoxide, N The reaction is carried out at one or more of the following: -10 ~ 50 °C, for a reaction time of 10 ~ 120 h, and under an inert atmosphere of either nitrogen or argon.

5. The method for preparing a colorless polyimide film with high fluorine content, high heat resistance, and low expansion according to claim 3, characterized in that, The film-forming process in step (2) includes casting and heat treatment; the casting process includes one or more of direct casting, precision slot coating, casting and stretching continuous film formation; the heat treatment includes continuous heating and gradient heating, with a temperature range of 20~450 °C.

6. The application of a colorless polyimide film with high fluorine content, high heat resistance, and low expansion as described in any one of claims 1-2 in flexible displays, wearable devices, flexible batteries, and 5G high-frequency communication equipment.

7. A flexible display, characterized in that, Includes a colorless polyimide film with high fluorine content, high heat resistance, and low expansion as described in any one of claims 1-2.

8. A wearable device, characterized in that, Includes a colorless polyimide film with high fluorine content, high heat resistance, and low expansion as described in any one of claims 1-2.

9. A flexible battery, characterized in that, Includes a colorless polyimide film with high fluorine content, high heat resistance, and low expansion as described in any one of claims 1-2.

10. A 5G high-frequency communication device, characterized in that, Includes a colorless polyimide film with high fluorine content, high heat resistance, and low expansion as described in any one of claims 1-2.

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