A low-thermal expansion coefficient thermoplastic polyimide film and a method for preparing the same

Abstract

The application discloses a low-thermal-expansion-coefficient thermoplastic polyimide film, which is prepared by the following steps: firstly, preparing a polyamide acid solution by reacting a diamine monomer and a dianhydride monomer in a solvent; secondly, photo-crosslinking the polyamide acid solution under the action of a crosslinking agent and a photo-initiator; and thirdly, preparing the thermoplastic polyimide film by thermal imidization, wherein the diamine monomer at least includes a double-bond-containing diamine monomer. The thermoplastic polyimide film has a significantly improved crosslinking degree, and the ether bond, the thioether bond and the ester group are introduced into the system, so that the film has excellent size stability and mechanical properties while the good processability and the bonding performance of the film are ensured, and the film has a wide application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of polyimide films, in particular to a thermoplastic polyimide film with a low thermal expansion coefficient and a preparation method thereof. Background Art

[0002] Flexible copper-clad laminate (FCCL) is the primary material for flexible printed circuits (FPCs) used in the electronics, automotive, information technology, and various defense industries. FCCL is also the primary application area for polyimide film in China, accounting for approximately 60% of the market. Polyimide film is primarily used as an insulating base film and cover film. This enormous market demand has made TPI composite films for flexible copper-clad laminates a research hotspot.

[0003] Furthermore, as FPCs evolve towards higher performance, higher dimensional stability requirements are placed on thermoplastic polyimide-based films. A key parameter for high dimensional stability in polyimide films is a low coefficient of thermal expansion (CTE). Low CTE means that the thermal expansion coefficient of the PI film is as close as possible to that of copper, minimizing interfacial stress caused by the significant difference in thermal expansion coefficients between the two.

[0004] However, in order to make polyimide exhibit thermoplastic properties, researchers have introduced different functional groups into PI through molecular structure design to synthesize thermoplastic PI to improve PI's processability. The most effective method is to introduce flexible ether or thioether bonds, alkyl groups, asymmetric or non-coplanar structures into the PI molecular chain. The introduction of these parts helps to reduce the interaction between PI molecular chains, thereby giving PI good solubility and processability. However, while these molecular structures give PI good solubility and processability, they also greatly increase the thermal expansion coefficient of the film, thus limiting its application.

[0005] Therefore, finding a simple and improved preparation method to increase the cross-linking degree of polyimide is the key to obtaining thermoplastic polyimide films with low thermal expansion coefficient. Summary of the Invention

[0006] Based on the technical problems existing in the background technology, the present invention proposes a thermoplastic polyimide film with a low thermal expansion coefficient and a preparation method thereof.

[0007] The present invention provides a low thermal expansion coefficient thermoplastic polyimide film, which is prepared by photocrosslinking a polyamic acid solution obtained by reacting a diamine monomer with a dianhydride monomer in a solvent under the action of a crosslinking agent and a photoinitiator, and then thermally imidizing the solution.

[0008] Wherein, the diamine monomer is composed of the following components, calculated by molar percentage: 10% to 100% of a diamine monomer containing a double bond, and the remainder is a diamine monomer not containing a double bond; the diamine monomer containing a double bond is 3,3'-di(allyloxy)-[1,1'-biphenyl]-4,4'-diamine, 5,5'-(propane-2,2-diacyl)bis(2-(allyloxy)aniline, or a combination thereof.

[0009] Among them, the structure of 3,3'-bi(allyloxy)-[1,1'-biphenyl]-4,4'-diamine is as follows:

[0010]

[0011] The structure of 5,5'-(propane-2,2-diacyl)bis(2-(allyloxy)aniline is as follows:

[0012]

[0013] The synthetic routes of the above-mentioned 3,3'-bis(allyloxy)-[1,1'-biphenyl]-4,4'-diamine and 5,5'-(propane-2,2-diacyl)bis(2-(allyloxy)aniline are as follows:

[0014]

[0015] The preparation method of the diamine monomer containing no double bonds in the present invention is as follows:

[0016] (1) Protecting the amino group: using 2,2-bis(4-hydroxy-3-aminophenyl)propane (BAP), 3,3'-dihydroxybenzidine (HAP) or a combination thereof as raw materials and a mixture of deionized water and DMF as solvent, acetic anhydride is added dropwise to react to obtain intermediate 1, intermediate 2 or a combination thereof;

[0017] (2) Introduction of allyl group: Intermediate 1, Intermediate 2 or a combination thereof is used as raw material, acetone is used as solvent, a catalyst and allyl bromide are added to reflux reaction to obtain Intermediate 3, Intermediate 4 or a combination thereof;

[0018] (3) Deprotection of amino group: Intermediate 3, intermediate 4 or a combination thereof is used as raw material, ethanol is used as solvent, and sodium hydroxide solution is added to react to obtain 3,3'-di(allyloxy)-[1,1'-biphenyl]-4,4'-diamine, 5,5'-(propane-2,2-diacyl)bis(2-(allyloxy)aniline) or a combination thereof.

[0019] Among them, the structural formula of intermediate 1 is as follows:

[0020]

[0021] The structural formula of intermediate 2 is as follows:

[0022]

[0023] The structural formula of intermediate 3 is as follows:

[0024]

[0025] The structural formula of intermediate 4 is as follows:

[0026]

[0027] Preferably, in step (1), the solvent is prepared by mixing deionized water and DMF in a mass ratio of 1:2; the amount of acetic anhydride used is 200% to 400% of the molar fraction of the raw material;

[0028] Preferably, in step (2), the catalyst is potassium carbonate, the amount of the catalyst is 200% to 500% of the molar fraction of the raw material, and the amount of allyl bromide is 100% to 300% of the molar fraction of the raw material;

[0029] Preferably, in step (3), the mass fraction of sodium hydroxide is 5% to 25%.

[0030] Preferably, the molar amount of the cross-linking agent is 10% to 100% of the molar amount of the diamine monomer containing a double bond; and the cross-linking agent is pentaerythritol tetrakis(3-mercaptopropionate).

[0031] Among them, the structure of the cross-linking agent pentaerythritol tetrakis (3-mercaptopropionate) (PETMP) is as follows:

[0032]

[0033] Preferably, the molar amount of the photoinitiator is 1% to 30% of the molar amount of the crosslinker; and the photoinitiator is (2,4,6-trimethylbenzoyl) diphenylphosphine oxide.

[0034] The structure of the photoinitiator (2,4,6-trimethylbenzoyl) diphenylphosphine oxide is as follows:

[0035]

[0036] Preferably, the diamine monomer not containing a double bond is selected from at least one of p-phenylenediamine (PDA), 4,4'-diaminodiphenyl ether (ODA), 4,4'-diaminobenzanilide (DABA), 2,2'-dimethyl-1,1'diaminobiphenyl (MTD), 2,2'-bis(trifluoromethyl)-1,1'-biphenyl-4,4'-diamine (TFMB), 2,2'-bis[4-(4-aminophenoxyphenyl)]propane (BAPP), 1,3-bis(4'-aminophenoxy)benzene (TPE-R), 1,4-bis(4'-aminophenoxy)benzene (TPE-Q), and 4,4'-bis(4-aminophenoxy)biphenyl (BAPB).

[0037] Preferably, the dianhydride monomer is selected from at least one of terephthalic anhydride (PMDA), biphenyl dianhydride (BPDA), diphenyl ether dianhydride (ODPA), bisphenol A diether dianhydride (BPADA), ethylene glycol ditrimellitate anhydride (HQDPA), and ethylene glycol ditrimellitate anhydride (TMEG).

[0038] Preferably, the solvent is a polar aprotic solvent; preferably, the solvent is selected from at least one of N-methylpyrrolidone (NMP), N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), and dimethyl sulfoxide (DMSO).

[0039] Preferably, the molar ratio of the diamine monomer to the dianhydride monomer is 1:1.

[0040] Preferably, the solid content of the polyamic acid solution is 10% to 20%.

[0041] A method for preparing the low thermal expansion coefficient thermoplastic polyimide film comprises the following steps:

[0042] S1, adding diamine monomer and dianhydride monomer to a solvent for reaction to obtain a polyamic acid solution;

[0043] S2, adding a crosslinking agent and a photoinitiator to the polyamic acid solution, photocrosslinking, and degassing to obtain a precursor solution;

[0044] S3, coating, desolvating, and thermally imidizing the precursor solution to obtain a thermoplastic polyimide film with a low thermal expansion coefficient.

[0045] In the present invention, the polyamic acid solution refers to a linear polymer solution containing free carboxyl groups and having an acid-amine structure as the main chain, which is formed by the condensation polymerization of dianhydride monomers and diamine monomers in a solvent. It is an intermediate product for the subsequent preparation of polyimide. The preparation method is a conventional method, for example, the following steps can be used: dissolving the diamine monomer in a solvent, and then adding the dianhydride monomer to react to obtain the polyamic acid solution.

[0046] Preferably, in S1, the reaction is carried out under a nitrogen atmosphere, the reaction temperature is room temperature, and the reaction time is 3 h to 10 h.

[0047] Preferably, in S2, the reaction is carried out under a nitrogen atmosphere, the reaction temperature is room temperature, and the reaction time is 0.5 h to 4 h.

[0048] Preferably, in S3, the desolvation condition is: treatment at 80°C to 150°C for 1 hour.

[0049] Preferably, in S3, the thermal imidization conditions are: treatment at 180°C to 220°C for 0.5h to 1.5h, treatment at 230°C to 280°C for 0.5h to 1.5h, and treatment at 300°C to 330°C for 0.5h to 1.5h.

[0050] The beneficial effects of the present invention are as follows:

[0051] To ensure easy processability and excellent solubility, conventional thermoplastic polyimide films often require the introduction of monomers containing flexible groups, such as alkyl, ether, thioether, and ester groups. However, these films often have high thermal expansion coefficients, which significantly limits their application in flexible printed circuits, flexible displays, and optical devices.

[0052] The present invention provides a thermoplastic polyimide film with a low thermal expansion coefficient and a preparation method thereof. The film is prepared using at least one diamine monomer or dianhydride monomer containing a double bond as a raw material in the presence of a crosslinker and a photoinitiator. In the present invention, an olefin is introduced into the thermoplastic polyimide system. The addition of the crosslinker and photoinitiator promotes crosslinking between the polymer backbones to form a crosslinked network, enhancing intermolecular interactions and restricting thermal motion of groups. This significantly reduces the film's thermal expansion coefficient while improving its mechanical properties. Furthermore, the addition of the double-bonded diamine monomer and crosslinker introduces ether bonds, thioether bonds, alkyl groups, and ester groups into the system, which also improves the film's adhesive properties to a certain extent. Furthermore, the degree of crosslinking can be controlled by adjusting the content of the olefin monomer, crosslinker, and light exposure time. The polyimide film prepared by the crosslinking method of the present invention has a significantly improved degree of crosslinking, maintaining good adhesiveness while exhibiting excellent dimensional stability and mechanical properties. This broadens the application of thermoplastic polyimide films and is expected to find promising applications in flexible printed circuits, flexible displays, and optical devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 Schematic diagram of the cross-linking reaction process and the formed cross-linking structure of the present invention. DETAILED DESCRIPTION

[0054] The technical solution of the present invention is described in detail below through specific embodiments.

[0055] Example 1

[0056] Preparation of low thermal expansion coefficient thermoplastic polyimide film:

[0057] S1. Under a nitrogen atmosphere, 3,3'-bi(allyloxy)-[1,1'-biphenyl]-4,4'-diamine and BAPP were added to DMAc and stirred until dissolved. BPDA was then added and the mixture was stirred at room temperature for 8 hours to obtain a polyamic acid solution with a solid content of 15%, wherein the molar ratio of 3,3'-bi(allyloxy)-[1,1'-biphenyl]-4,4'-diamine and BAPP was 1:1, and the ratio of the sum of the molar amounts of 3,3'-bi(allyloxy)-[1,1'-biphenyl]-4,4'-diamine and BAPP to the molar amount of BPDA was 1:1;

[0058] S2. Under a nitrogen atmosphere, a crosslinking agent PETMP and a photoinitiator (2,4,6-trimethylbenzoyl) diphenylphosphine oxide were added to the polyamic acid solution, and crosslinking was initiated by irradiation with an ultraviolet lamp (365 nm, 20 mW / cm2) for 10 min. The crosslinking reaction was then carried out at room temperature for 0.5 h. After the reaction was completed, vacuum degassing was performed to obtain a precursor solution, wherein the molar ratio of PETMP to 3,3'-di(allyloxy)-[1,1'-biphenyl]-4,4'-diamine was 0.1:1, and the molar ratio of (2,4,6-trimethylbenzoyl) diphenylphosphine oxide to PETMP was 0.2:1;

[0059] S3. The precursor solution is coated with a coating machine, and then placed in an imidization furnace for heating to remove the solvent and imidize. The heating program is as follows: 130°C for 1 hour, 200°C for 1 hour, 250°C for 1 hour, and 330°C for 1 hour to obtain a thermoplastic polyimide film with a low thermal expansion coefficient.

[0060] Example 2

[0061] Preparation of low thermal expansion coefficient thermoplastic polyimide film:

[0062] S1. Under a nitrogen atmosphere, 5,5'-(propane-2,2-diacyl)bis(2-(allyloxy)aniline) and BAPP were added to DMAc and stirred until dissolved. BPDA was then added and the mixture was stirred at room temperature for 8 hours to obtain a polyamic acid solution with a solid content of 15%, wherein the molar ratio of 5,5'-(propane-2,2-diacyl)bis(2-(allyloxy)aniline) and BAPP was 1:1, and the ratio of the sum of the molar amounts of 5,5'-(propane-2,2-diacyl)bis(2-(allyloxy)aniline) and BAPP to the molar amount of BPDA was 1:1;

[0063] S2. Under a nitrogen atmosphere, a crosslinking agent PETMP and a photoinitiator (2,4,6-trimethylbenzoyl) diphenylphosphine oxide were added to the polyamic acid solution, and crosslinking was initiated by irradiation with an ultraviolet lamp (365 nm, 20 mW / cm2) for 10 min. The crosslinking reaction was then carried out at room temperature for 0.5 h. After the reaction was completed, vacuum degassing was performed to obtain a precursor solution, wherein the molar ratio of PETMP to 3,3'-di(allyloxy)-[1,1'-biphenyl]-4,4'-diamine was 0.1:1, and the molar ratio of (2,4,6-trimethylbenzoyl) diphenylphosphine oxide to PETMP was 0.2:1;

[0064] S3. The precursor solution is coated with a coating machine, and then placed in an imidization furnace for heating to remove the solvent and imidize. The heating program is as follows: 130°C for 1 hour, 200°C for 1 hour, 250°C for 1 hour, and 330°C for 1 hour to obtain a thermoplastic polyimide film with a low thermal expansion coefficient.

[0065] Example 3

[0066] Preparation of low thermal expansion coefficient thermoplastic polyimide film:

[0067] S1. Under a nitrogen atmosphere, 3,3'-bi(allyloxy)-[1,1'-biphenyl]-4,4'-diamine was added to DMAc and stirred until dissolved, and then BPADA and BPDA were added. The mixture was stirred and reacted at room temperature for 8 hours to obtain a polyamic acid solution with a solid content of 15%, wherein the molar ratio of BPADA and BPDA was 1:1, and the ratio of the molar amount of 3,3'-bi(allyloxy)-[1,1'-biphenyl]-4,4'-diamine to the sum of the molar amounts of BPADA and BPDA was 1:1;

[0068] S2. Under a nitrogen atmosphere, a crosslinking agent PETMP and a photoinitiator (2,4,6-trimethylbenzoyl) diphenylphosphine oxide were added to the polyamic acid solution, and crosslinking was initiated by irradiation with an ultraviolet lamp (365 nm, 20 mW / cm2) for 10 min. The crosslinking reaction was then carried out at room temperature for 0.5 h. After the reaction was completed, vacuum degassing was performed to obtain a precursor solution, wherein the molar ratio of PETMP to 3,3'-di(allyloxy)-[1,1'-biphenyl]-4,4'-diamine was 0.1:1, and the molar ratio of (2,4,6-trimethylbenzoyl) diphenylphosphine oxide to PETMP was 0.2:1;

[0069] S3. The precursor solution is coated with a coating machine, and then placed in an imidization furnace for heating to remove the solvent and imidize. The heating program is as follows: 130°C for 1 hour, 200°C for 1 hour, 250°C for 1 hour, and 330°C for 1 hour to obtain a thermoplastic polyimide film with a low thermal expansion coefficient.

[0070] Example 4

[0071] Preparation of low thermal expansion coefficient thermoplastic polyimide film:

[0072] S1. Under a nitrogen atmosphere, 5,5'-(propane-2,2-diacyl)bis(2-(allyloxy)aniline) was added to DMAc and stirred until dissolved, and then BPADA and BPDA were added. The mixture was stirred and reacted at room temperature for 8 hours to obtain a polyamic acid solution with a solid content of 15%, wherein the molar ratio of BPADA to BPDA was 1:1, and the ratio of the molar amount of 5,5'-(propane-2,2-diacyl)bis(2-(allyloxy)aniline) to the sum of the molar amounts of BPADA and BPDA was 1:1;

[0073] S2. Under a nitrogen atmosphere, a crosslinking agent PETMP and a photoinitiator (2,4,6-trimethylbenzoyl) diphenylphosphine oxide were added to the polyamic acid solution, and crosslinking was initiated by irradiation with an ultraviolet lamp (365 nm, 20 mW / cm2) for 10 min. The crosslinking reaction was then carried out at room temperature for 0.5 h. After the reaction was completed, vacuum degassing was performed to obtain a precursor solution, wherein the molar ratio of PETMP to 3,3'-di(allyloxy)-[1,1'-biphenyl]-4,4'-diamine was 0.1:1, and the molar ratio of (2,4,6-trimethylbenzoyl) diphenylphosphine oxide to PETMP was 0.2:1;

[0074] S3. The precursor solution is coated with a coating machine, and then placed in an imidization furnace for heating to remove the solvent and imidize. The heating program is as follows: 130°C for 1 hour, 200°C for 1 hour, 250°C for 1 hour, and 330°C for 1 hour to obtain a thermoplastic polyimide film with a low thermal expansion coefficient.

[0075] Comparative Example 1

[0076] Preparation of polyimide film:

[0077] S1. Under a nitrogen atmosphere, 3,3'-bi(allyloxy)-[1,1'-biphenyl]-4,4'-diamine and BAPP were added to DMAc and stirred until dissolved. BPDA was then added and the mixture was stirred at room temperature for 8 hours to obtain a polyamic acid solution with a solid content of 15%, wherein the molar ratio of 3,3'-bi(allyloxy)-[1,1'-biphenyl]-4,4'-diamine and BAPP was 1:1, and the ratio of the sum of the molar amounts of 3,3'-bi(allyloxy)-[1,1'-biphenyl]-4,4'-diamine and BAPP to the molar amount of BPDA was 1:1;

[0078] S2. The polyamic acid solution is vacuum degassed, then coated with a coating machine, and then placed in an imidization furnace for heating to remove the solvent and imidize. The heating program is as follows: 130°C for 1 hour, 200°C for 1 hour, 250°C for 1 hour, and 330°C for 1 hour to obtain a thermoplastic polyimide film.

[0079] Test example

[0080] The performance tests were performed on the films of Examples 1-4 and Comparative Example 1. The test results are shown in Table 1.

[0081] 1. Static Thermomechanical Analysis

[0082] 1. Experimental methods

[0083] Static thermomechanical analysis (TMA): American TA Instruments TMA Q400EM static thermomechanical analyzer (room temperature to 400 °C, 5 °C / min).

[0084] 2. Experimental results

[0085] As can be seen from Table 1, the thermal expansion coefficients of the thermoplastic polyimide films prepared in Examples 1-4 of the present invention at 400°C are 11-23 ppm / K, which are much lower than that of Comparative Example 1. This indicates that the dimensional stability of the thermoplastic polyimide films of the present invention is significantly improved, making them very suitable for flexible copper-clad laminate substrate materials.

[0086] 2. Mechanical properties test

[0087] 1. Experimental methods

[0088] An INSTRON 5567 universal strength testing machine was used with a tensile rate of 5 mm / min and a test temperature of room temperature (approximately 23°C). The initial fixture span was approximately 20 mm, and the sample dimensions were approximately 0.025 mm thick, 15 mm wide, and 100 mm long.

[0089] 2. Experimental results

[0090] As can be seen from Table 1, the tensile strength of the thermoplastic polyimide film prepared in the present invention is greater than 190 MPa, and the elastic modulus is as high as 4939 to 5713 MPa. Both the tensile strength and the elastic modulus are higher than those in Comparative Example 1, indicating that the polyimide film of the present invention has improved mechanical properties while improving dimensional stability.

[0091] 3. Peel strength test

[0092] 1. Experimental methods

[0093] An INSTRON 5567 universal strength testing machine was used. The tensile rate was 5 mm / min and the test temperature was room temperature (approximately 23°C). The film and copper foil were hot pressed and then subjected to a 180° peel tensile test. The data was processed as follows:

[0094]

[0095] LM=Minimum load

[0096] WS = measured width of the peel strip

[0097] 2. Experimental results

[0098] As can be seen from Table 1, the peel strength of the thermoplastic polyimide film prepared in the present invention is greater than 16 N / cm, which is higher than that of Comparative Example 1, indicating that the polyimide film of the present invention has improved dimensional stability and bonding performance.

[0099] Table 1

[0100]

[0101]

[0102] In summary, the present invention, under the action of a crosslinking agent and a photoinitiator, produces a thermoplastic polyimide film with a significantly improved degree of crosslinking. This thermoplastic polyimide film has excellent dimensional stability, mechanical properties, and adhesion, and has broad application prospects.

[0103] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for preparing a low thermal expansion coefficient thermoplastic polyimide film, characterized in that: The steps include: S1, adding diamine monomer and dianhydride monomer to a solvent for reaction to obtain a polyamic acid solution with a solid content of 10% to 20%; S2, adding a crosslinking agent and a photoinitiator to the polyamic acid solution, photocrosslinking, and degassing to obtain a precursor solution; S3, coating, desolvating, and thermally imidizing the precursor solution to obtain a thermoplastic polyimide film with a low thermal expansion coefficient; Wherein, the diamine monomer is composed of the following components, based on molar percentage: 10% to 100% of a diamine monomer containing a double bond, and the remainder is a diamine monomer not containing a double bond; the diamine monomer containing a double bond is 3,3'-di(allyloxy)-[1,1'-biphenyl]-4,4'-diamine, 5,5'-(propane-2,2-diacyl)bis(2-(allyloxy)aniline, or a combination thereof; the diamine monomer not containing a double bond is selected from 2,2'-bis[4-(4-aminophenoxyphenyl)]propane; The dianhydride monomer is selected from at least one of biphenyl dianhydride and bisphenol A diether dianhydride; The molar amount of the cross-linking agent is 10% of the molar amount of the diamine monomer containing a double bond; the cross-linking agent is pentaerythritol tetrakis(3-mercaptopropionate); The molar amount of the photoinitiator is 20% of the molar amount of the crosslinker; the photoinitiator is (2,4,6-trimethylbenzoyl) diphenylphosphine oxide.

2. The method for preparing a thermoplastic polyimide film having a high thermal expansion coefficient according to claim 1, wherein: In S1, the reaction is carried out under a nitrogen atmosphere, at room temperature, and for 3 to 10 hours.

3. The method for preparing a thermoplastic polyimide film with a high thermal expansion coefficient according to claim 1, wherein: In S2, the reaction is carried out under a nitrogen atmosphere, the reaction temperature is room temperature, and the reaction time is 0.5h~4h.

4. The method for preparing a thermoplastic polyimide film with a high thermal expansion coefficient according to claim 1, wherein: In S3, the desolvation condition is: treatment at 80°C~150°C for 1 hour.

5. The method for preparing a thermoplastic polyimide film with a high thermal expansion coefficient according to claim 1, wherein: In S3, the thermal imidization conditions are: treatment at 180°C-220°C for 0.5h-1.5h, treatment at 230°C-280°C for 0.5h-1.5h, and treatment at 300-330°C for 0.5h-1.5h.

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