High-transmittance colorless polyimide film and preparation method thereof

Abstract

The invention relates to the technical field of polyimide films, in particular to a high-transmittance colorless polyimide film and a preparation method thereof. The polyimide film is prepared from a mixture comprising dianhydride and diamine, and the molar ratio of dianhydride to diamine monomer is (0.9-1.1): 1. The polyimide film prepared by the invention has excellent light transmittance, tensile property and thermal stability, also has good processability, and can be widely applied to the field of flexible photoelectricity, especially flexible display.

Description

Technical Field

[0001] The invention relates to the technical field of polyimide films, and in particular to a colorless polyimide film with high transmittance and a preparation method thereof. Background Art

[0002] Polyimide polymer materials are well known for their outstanding thermal, electrical and mechanical properties, and are widely used in advanced technology fields such as microelectronics, aerospace and optical devices. Polyimide film can be used as a protective layer to reduce environmental damage to electronic devices, as a dielectric layer for device insulation, and as a substrate material for flexible circuit boards and liquid crystal films.

[0003] Traditional polyimide films are prone to forming intramolecular and inter-molecular charge transfer complexes, resulting in low transmittance and brown-yellow color of polyimide films, which severely limits the application of polyimide films in the optoelectronic field. In recent years, with the rapid development of the field of flexible optoelectronics, the development and commercialization of applications such as folding devices, bending devices, wearable devices, and transparent devices not only have strict requirements on the thermal and mechanical properties of polyimide materials, but also require good solubility to facilitate processing and molding. At the same time, polyimide materials are also required to be colorless and transparent. In addition, in order to reduce signal transmission delay, crosstalk and dielectric loss, and improve device performance, the insulating material between the conductive layers is required to have a low dielectric constant.

[0004] Patent application CN114605637A provides a low dielectric polyimide film, which introduces a fluorinated monomer and a low dielectric polyimide to prepare a polyimide matrix material layer, and then introduces fluorinated graphene nanosheets into the polyimide material layer to obtain a low dielectric polyimide film. However, fluorinated graphene nanosheets are expensive and difficult to prepare.

[0005] Patent application CN110922594A provides a kind of 10 -C 64 Aromatic or alicyclic tetravalent organic groups and C6-C 60 Although this patent can obtain a polyimide film with high light transmittance, solubility, excellent thermal and mechanical properties, the flexibility of the prepared polyimide film is poor due to the addition of a large amount of rigid aromatic structure, making it difficult to apply in the field of flexible optoelectronics. Summary of the invention

[0006] In order to overcome the shortcomings of the prior art, the present invention provides a polyimide film having excellent optical properties, mechanical properties, good solubility, good processing performance, and low dielectric constant, which can be widely used in the field of flexible optoelectronics.

[0007] The object of the present invention is achieved by providing a colorless polyimide film with high transmittance. The polyimide film is prepared from a mixture of dianhydride and diamine, wherein the molar ratio of the dianhydride to the diamine monomer is (0.9-1.1):1.

[0008] Preferably, the diamine is a mixture of an aromatic diamine having a fluorine atom and an ester group and a diamine containing a siloxane group, and the molar ratio thereof is (2.5-4):1.

[0009] Preferably, the polyimide film further comprises a polar aprotic solvent.

[0010] The present invention also provides a method for preparing the above-mentioned colorless polyimide film with high transmittance, which comprises the following steps:

[0011] S1. The aromatic diamine having a fluorine atom and an ester group and the diamine containing a siloxane group are mixed with a polar aprotic solvent and stirred to form a diamine solution;

[0012] S2. The dianhydride is added to the diamine solution in step S1 under stirring to form a polyamic acid solution by polycondensation reaction;

[0013] S3. The polyamic acid solution in step S2 is subjected to imidization reaction to obtain a polyimide film.

[0014] Preferably, the imidization reaction is to add a catalyst and a dehydrating agent to a polyamic acid solution, mix and stir evenly, and then evenly coat the solution on a glass plate, and complete the imidization reaction by a programmed temperature increase method. The dehydrating agent is an aliphatic anhydride.

[0015] Compared with the prior art, the present invention has the following significant features and positive effects:

[0016] 1. The present invention introduces ester-containing groups into the resin chain in the polyimide film, so that the secondary bond force between the main chain structure is enhanced, the orientation is enhanced, and the resin chain is more stable and compact, which is beneficial to improving the mechanical and thermal properties of the polyimide film. In addition, fluorine atoms can also increase the hydrophobicity and light transmittance of the polyimide film.

[0017] 2. The present invention uses a mixture of an aromatic diamine having a fluorine atom and an ester group and a diamine containing a siloxane group in a molar ratio of (2.5 to 4):1 to undergo a condensation reaction with a dianhydride having an alicyclic structure, thereby effectively improving the transparency and tensile properties of the polyimide film and the adhesion to the substrate, while also reducing the dielectric constant of the polyimide film.

[0018] 3. The present invention conducts polycondensation reaction of diamine and dianhydride in a polar aprotic solvent, which significantly increases the efficiency of the reaction of dianhydride and diamine, improves the conversion rate of reactants, and reduces the occurrence of side reactions.

[0019] 4. The present invention adopts aliphatic acid anhydride as a dehydrating agent, which can not only promote the complete imidization reaction and give the polyimide film the characteristics, but also the aliphatic acid anhydride can protect the residual terminal amino groups in the molecular chain, preventing the polyimide film from amino oxidation coloring in the high-temperature oven, thereby giving the polyimide film the characteristics of high light transmittance and low yellowness index.

[0020] 5. The polyimide film prepared by the present invention has excellent light transmittance, tensile properties and thermal stability, as well as good solubility and processing properties, and can be widely used in the field of flexible optoelectronics, especially flexible displays. DETAILED DESCRIPTION

[0021] The specific implementation methods of the present invention are further described in detail below in conjunction with the examples. In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. Unless otherwise expressly stated, throughout the specification and claims, the term "including" or its variations such as "comprising" or "including" will be understood to include the stated components and steps, without excluding the presence of other material components or steps.

[0022] In addition, in order to better illustrate the present invention, numerous specific details are given in the following detailed description.

[0023] Those skilled in the art will appreciate that the present invention can be implemented without certain specific details. In some embodiments, raw materials, methods, means, etc. that are well known to those skilled in the art are not described in detail in order to highlight the main purpose of the present invention.

[0024] The term "alkyl" in the context of the present invention is intended to denote in each case a straight-chain or branched alkyl group having generally 1 to 20 carbon atoms, frequently 1 to 6 carbon atoms, preferably 1 to 4 carbon atoms and in particular 1 to 3 carbon atoms.

[0025] The term "aryl" in the present invention refers to a monovalent monocyclic or bicyclic aromatic hydrocarbon group of 6 to 10 ring atoms, such as phenyl or naphthyl, preferably phenyl.

[0026] The term "dianhydride" in the present invention refers to dianhydrides including dianhydrides of aromatic structures and dianhydrides of alicyclic structures, preferably dianhydrides of alicyclic structures, such as hydrogenated pyromellitic dianhydride (HPMDA), norbornane-2-spiro-α-cyclopentanone-α'-spiro-2'-norbornane-5,5',6,6'-tetracarboxylic dianhydride (CPODA) and 1,2,3,4-cyclopentanetetracarboxylic dianhydride (CPDA), but is not limited thereto.

[0027] The invention discloses a colorless polyimide film with high transmittance. The polyimide film is prepared from a mixture of dianhydride and diamine, wherein the molar ratio of the dianhydride to the diamine monomer is (0.9-1.1):1.

[0028] Furthermore, the diamine is a mixture of an aromatic diamine having a fluorine atom and an ester group and a diamine containing a siloxane group, and the molar ratio thereof is (2.5-4):1.

[0029] Research has found that the present invention introduces fluorine atoms and ester-containing aromatic diamines into the resin chain of the polyimide film, which can not only improve the mechanical and thermal properties of the polyimide film, but also increase the hydrophobicity and light transmittance of the polyimide film.

[0030] At the same time, experimental results show that a mixture of aromatic diamines having fluorine atoms and ester groups and diamines containing siloxane groups undergoes a condensation reaction with alicyclic dianhydrides in a molar ratio of (2.5 to 4):1, which can effectively improve the transparency and tensile properties of the polyimide film and its adhesion to the substrate, while also reducing the dielectric constant of the polyimide film, which has a good technical effect. However, the corresponding effect will decrease outside the above molar ratio range.

[0031] Furthermore, the structure of the aromatic diamine having fluorine atoms and ester groups is as shown in formula (1):

[0032]

[0033] Wherein, Ar is an aryl group which is substituted with an alkyl group or not, and R1 and R2 are aryl groups containing a fluorine atom.

[0034] Preferably, Ar is a phenyl group which may be substituted with a C1-C4 alkyl group.

[0035] More preferably, the aromatic diamine having fluorine atoms and ester-containing groups includes at least one of Formula 1-1 to Formula 1-3.

[0036]

[0037] Formula 1-3.

[0038] Furthermore, the diamine containing a siloxane group may be selected from at least one of the following:

[0039]

[0040] Furthermore, the dianhydride includes a dianhydride of an alicyclic structure, and the dianhydride of the alicyclic structure is selected from at least one of hydrogenated pyromellitic dianhydride (HPMDA), norbornane-2-spiro-α-cyclopentanone-α'-spiro-2'-norbornane-5,5',6,6'-tetracarboxylic dianhydride (CPODA), and 1,2,3,4-cyclopentanetetracarboxylic dianhydride (CPDA).

[0041] Furthermore, the polyimide film also includes a polar aprotic solvent. Studies have shown that the present invention can achieve the excellent effect of increasing the efficiency of the reaction of dianhydride and diamine, improving the conversion rate of reactants, and reducing the generation of side reactions by polycondensing diamine and dianhydride in a polar aprotic solvent.

[0042] More preferably, the polar aprotic solvent is at least one of N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), and N,N-dimethylacetamide (DMAc).

[0043] A method for preparing a colorless polyimide film with high transmittance, the specific steps of which mainly include:

[0044] S1. The aromatic diamine having a fluorine atom and an ester group and the diamine containing a siloxane group are mixed with a polar aprotic solvent and stirred to form a diamine solution;

[0045] S2. The dianhydride is added to the diamine solution in step S1 under stirring to form a polyamic acid solution by polycondensation reaction;

[0046] S3. The polyamic acid solution in step S2 is subjected to imidization reaction to obtain a polyimide film.

[0047] Furthermore, the imidization reaction refers to adding a catalyst and a dehydrating agent into a polyamic acid solution, mixing and stirring the mixture evenly, and then coating the mixture evenly on a glass plate, and completing the imidization reaction by a programmed temperature increase method.

[0048] Furthermore, the catalyst is at least one of pyridine, quinoline, isoquinoline, imidazole and benzimidazole; and the added amount of the catalyst is 0.1-2% of the total mass of the diamine.

[0049] The dehydrating agent is an aliphatic anhydride, specifically at least one of acetic anhydride, trifluoroacetic anhydride or propionic anhydride.

[0050] Furthermore, the specific implementation of the programmed temperature is heating at 30-60° C. for 30-60 min, and then heating in a high temperature oven at 80-200° C. for 60-120 min.

[0051] Through research, it was found that the aliphatic anhydride of the present invention, as a dehydrating agent, can not only promote the complete imidization reaction and give the polyimide film the characteristics, but also the aliphatic anhydride can protect the residual terminal amino groups in the molecular chain, preventing the polyimide film from amino oxidation coloring in a high-temperature oven, thereby giving the polyimide film the characteristics of high light transmittance and low yellowness index.

[0052] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below in conjunction with embodiments.

[0053] Example 1, a method for preparing a colorless polyimide film with high transmittance, in a 500mL three-necked round-bottom flask reactor equipped with a stirrer, a thermometer and a nitrogen gas supply, 150mL of N-methylpyrrolidone, and then 12.36g of bis(2-fluoro-4-aminophenyl)terephthalate (Formula 1-2) (0.03mol) and 2.48g of 1,3-bis(3-aminopropyl)tetramethyldisiloxane (0.01 mol) was stirred evenly to obtain a clear diamine solution, and then 9.0 g of hydrogenated pyromellitic dianhydride (0.04 mol) was added to the clear diamine solution, and reacted at 20° C. for 10 h under nitrogen protection, and then 0.1484 g of pyridine and 0.5 g of acetic anhydride were added and mixed evenly to obtain a mixed solution, and the obtained mixed solution was cast onto a glass plate and heated at 30° C. for 50 min to remove the solvent, and then heated at 200° C. in a high-temperature oven for 100 min to complete imidization, and then the imidized film was peeled off from the glass plate to obtain a polyimide film, which was then used for performance testing. The structural formula of the bis(2-fluoro-4-aminophenyl)terephthalate is

[0054] The structural formula of the 1,3-bis(3-aminopropyl)tetramethyldisiloxane is

[0055] Example 2, a method for preparing a colorless polyimide film with high transmittance, in a 500mL three-necked round-bottom flask reactor equipped with a stirrer, a thermometer and a nitrogen gas supply, 150mL of N-methylpyrrolidone, and then 15.36g of bis(2-trifluoromethyl-4-aminophenyl)terephthalate (Formula 1-1) (0.03mol) and 3.04g of 1,3-bis(3-aminopropyl)tetraethyldisiloxane (0.01 mol) was stirred evenly to obtain a clear diamine solution, and then 9.0 g of hydrogenated pyromellitic dianhydride (0.04 mol) was added to the clear diamine solution, and reacted at 20° C. for 10 h under nitrogen protection, and then 0.1484 g of pyridine and 0.5 g of acetic anhydride were added and mixed evenly to obtain a mixed solution, and the obtained mixed solution was cast onto a glass plate and heated at 40° C. for 40 min to remove the solvent, and then heated at 180° C. in a high-temperature oven for 100 min to complete imidization, and then the imidized film was peeled off from the glass plate to obtain a polyimide film, which was then used for performance testing. The structural formula of the bis(2-trifluoromethyl-4-aminophenyl)terephthalate is The structural formula of the 1,3-bis(3-aminopropyl)tetraethyldisiloxane is

[0056] Example 3, a method for preparing a colorless polyimide film with high transmittance, in a 500mL three-necked round-bottom flask reactor equipped with a stirrer, a thermometer and a nitrogen gas supply, 150mL of N,N-dimethylformamide was added, followed by 20.48g of bis(2-trifluoromethyl-4-aminophenyl)terephthalate (Formula 1-1) (0.04mol) and 3.04g of 1,3-bis(3-aminopropyl)tetraethyldisiloxane (0.01 mol) was stirred evenly to obtain a clear diamine solution, and then 11.25 g of hydrogenated pyromellitic dianhydride (0.05 mol) was added to the clear diamine solution, and reacted at 20° C. for 10 h under nitrogen protection, and then 0.1484 g of pyridine and 0.5 g of acetic anhydride were added and mixed evenly to obtain a mixed solution, and the obtained mixed solution was cast onto a glass plate and heated at 60° C. for 30 min to remove the solvent, and then heated at 150° C. for 100 min in a high-temperature oven to complete imidization, and then the imidized film was peeled off from the glass plate to obtain a polyimide film, which was then used for performance testing. The structural formula of the bis(2-trifluoromethyl-4-aminophenyl)terephthalate is The structural formula of the 1,3-bis(3-aminopropyl)tetraethyldisiloxane is

[0057] Example 4, a method for preparing a colorless polyimide film with high transmittance, the preparation method is similar to that of Example 1, except that the structural formula of the terephthalate is

[0058] Example 5, a method for preparing a colorless polyimide film with high transmittance, the preparation method is referenced to Example 1, the difference being that the amount of bis(2-fluoro-4-aminophenyl)terephthalate (Formula 1-2) used is (0.025 mol), and the amount of 1,3-bis(3-aminopropyl)tetramethyldisiloxane used is 0.01 mol.

[0059] Example 6, a method for preparing a colorless polyimide film with high transmittance, the preparation method is referenced to Example 1, the difference being that the amount of bis(2-fluoro-4-aminophenyl)terephthalate (Formula 1-2) used is 0.04 mol, and the amount of 1,3-bis(3-aminopropyl)tetramethyldisiloxane used is 0.01 mol.

[0060] Example 7, a method for preparing a colorless polyimide film with high transmittance, the preparation method is referenced to Example 1, the difference being that the amount of bis(2-fluoro-4-aminophenyl)terephthalate (Formula 1-2) used is 0.02 mol, and the amount of 1,3-bis(3-aminopropyl)tetramethyldisiloxane used is 0.01 mol.

[0061] Example 8, a method for preparing a colorless polyimide film with high transmittance, the preparation method is referenced to Example 1, except that the amount of bis(2-fluoro-4-aminophenyl)terephthalate (Formula 1-2) used is 0.045 mol, and the amount of 1,3-bis(3-aminopropyl)tetramethyldisiloxane used is 0.01 mol.

[0062] Comparative Example 1:

[0063] The difference from Example 1 is that in Comparative Example 1, an equal amount of 1,3-bis(3-aminopropyl)tetramethyldisiloxane is replaced by bis(2-fluoro-4-aminophenyl)terephthalate.

[0064] Comparative Example 2:

[0065] Different from Example 1, in Comparative Example 2, an equal amount of bis(2-fluoro-4-aminophenyl)terephthalate was replaced by 1,3-bis(3-aminopropyl)tetramethyldisiloxane.

[0066] Comparative Example 3:

[0067] The difference from Example 1 is that the amount of the same substance is replaced with bis(2-fluoro-4-aminophenyl)terephthalate (Formula 1-2): Replace with

[0068] Comparative Example 4:

[0069] The difference from Example 1 is that the amount of the same substance is replaced with bis(2-fluoro-4-aminophenyl)terephthalate (Formula 1-2): Replace with

[0070] Comparative Example 5:

[0071] Different from Example 1, in Comparative Example 3, hydrogenated pyromellitic dianhydride is replaced with an equal amount of 3,3',4,4'-biphenyltetracarboxylic dianhydride.

[0072] Performance Test 1:

[0073] 1. Optical properties: The transmittance, yellowness index and haze of the polyimide film in the visible light range of 400nm to 700nm were measured by UV spectrophotometer.

[0074] 2. Mechanical properties: Use an electronic universal testing machine (Shimadzu AG-X plus) to test the tensile strength and elongation at break. Test conditions: test speed 5 mm / min, sample size 10 mm*15 mm*20 μm, test gauge length: 50 mm, extensometer gauge length 20 mm.

[0075] 3. Dielectric constant: obtained by using the cavity resonance method at a frequency of 10 GHz. Performance test results: The performance test results of the polyimide film of the embodiment and the comparative example are shown in Table 1.

[0076] 4. Hydrophobicity: Use SDC-100 hydrophilicity and hydrophobicity test water drop angle contact angle meter. The film sample is immersed in pure water and dried in vacuum at 40° to constant weight. Then, deionized water is used for contact angle test. The average value of 0s and 1s is selected as the contact angle value of the film material.

[0077] 5. Thermal stability: Use differential scanning calorimeter DSC-600, test conditions: heating and cooling rate 10℃ / min.

[0078] Table 1 Optical properties, mechanical properties and dielectric constant data

[0079]

[0080]

[0081] Table 2 Hydrophobicity of polyimide film

[0082]

[0083]

[0084] Table 3 Thermal stability

[0085]

Claims

1. A colorless polyimide film with high transmittance, characterized in that: The polyimide film is prepared from a mixture of dianhydride and diamine, wherein the molar ratio of the dianhydride to diamine monomers is (0.9-1.1):1, and the diamine is a mixture of an aromatic diamine having a fluorine atom and an ester group and a diamine containing a siloxane group, wherein the molar ratio is (2.5-4):

1.

2. A colorless polyimide film with high transmittance according to claim 1, characterized in that: The structure of the aromatic diamine having fluorine atoms and ester groups is as shown in formula (1): Wherein, Ar is an optionally substituted aryl group, and R1 and R2 are aryl groups containing fluorine atoms.

3. A colorless polyimide film with high transmittance according to claim 1 or 2, characterized in that: The aromatic diamine having fluorine atoms and ester groups is selected from one or more of Formula 1-1 to Formula 1-3, 4. A colorless polyimide film with high transmittance according to claim 1, characterized in that: The diamine containing a siloxane group is selected from one or more of the following compounds:

5. A colorless polyimide film with high transmittance according to claim 1, characterized in that: The dianhydride includes a dianhydride of an alicyclic structure, and the dianhydride of the alicyclic structure is selected from at least one of hydrogenated pyromellitic acid dianhydride (HPMDA), norbornane-2-spiro-α-cyclopentanone-α'-spiro-2'-norbornane-5,5',6,6'-tetracarboxylic dianhydride (CPODA), and 1,2,3,4-cyclopentanetetracarboxylic dianhydride (CPDA).

6. A colorless polyimide film with high transmittance according to claim 1, characterized in that The polyimide film also includes a polar aprotic solvent.

7. A method for preparing a colorless polyimide film with high transmittance according to any one of claims 1 to 6, characterized in that: The method comprises the following steps: S1. The aromatic diamine having a fluorine atom and an ester group and the diamine containing a siloxane group are mixed with a polar aprotic solvent and stirred to form a diamine solution; S2. The dianhydride is added to the diamine solution in step S1 under stirring to form a polyamic acid solution by polycondensation reaction; S3. The polyamic acid solution in step S2 is subjected to imidization reaction to obtain a polyimide film.

8. The method for preparing a colorless polyimide film with high transmittance according to claim 7, characterized in that: The imidization reaction refers to adding a catalyst and a dehydrating agent into a polyamic acid solution, mixing and stirring the mixture evenly, and then coating the mixture evenly on a glass plate, and completing the imidization reaction by a programmed temperature increase method.

9. The method for preparing a colorless polyimide film with high transmittance according to claim 7, characterized in that: The catalyst is at least one of pyridine, quinoline, isoquinoline, imidazole and benzimidazole; the added amount of the catalyst is 0.1-2% of the total mass of the diamine.

10. The method for preparing a colorless polyimide film with high transmittance according to claim 7, characterized in that: The dehydrating agent is an aliphatic anhydride, specifically at least one of acetic anhydride, trifluoroacetic anhydride or propionic anhydride.

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