Preparation method of low-thermal expansion coefficient polyimide film and film

Abstract

The application discloses a preparation method of a low-thermal-expansion-coefficient polyimide film, and comprises the following steps: S1, configuring diamine, dianhydride and polar aprotic solvent, the molar ratio of the diamine and the dianhydride being 1:(0.95-1.05); adding the diamine into the polar aprotic solvent under nitrogen protection; S2, sequentially adding the dianhydride and a capping agent into the diamine solution, controlling the temperature and carrying out polycondensation reaction, controlling the viscosity of the reaction system to be 150-220 mPa.s, and filtering to obtain a polyamic acid solution; and S3, scraping the polyamic acid solution on a substrate, carrying out imidization treatment and drying to form a film, and obtaining a low-thermal-expansion-coefficient polyimide film product; the main component of the diamine is p-phenylenediamine and diaminobenzanilide, and the main component of the dianhydride is pyromellitic dianhydride. The obtained film has a thermal expansion coefficient similar to that of a copper foil and high tensile property. The application further discloses a polyimide film and a copper-clad plate comprising the polyimide film.

Description

Technical Field

[0001] This invention relates to the field of polyimide production technology, specifically to a method for preparing a polyimide film with a low coefficient of thermal expansion and the film itself. Background Technology

[0002] Polyimide refers to a class of polymers containing imide rings (-CO-NR-CO-) in their main chain. Its ingenious combination of electrical properties, high-temperature resistance, chemical resistance, and high strength and toughness makes it a key material in the flexible electronics and information industry. In products including copper-clad laminates, printed circuit boards, photosensitive films, solar panels, and display panels, the coefficient of thermal expansion of the material not only affects performance but is also a crucial parameter for structural design and process research.

[0003] As integrated circuits (ICs) evolve towards miniaturization and high-speed, high-frequency operation, higher performance requirements are being placed on adhesive-free flexible copper-clad laminates used in flip-chip film packaging. Polyimide (PI) films must possess high modulus, a suitable coefficient of thermal expansion, low hygroscopic expansion, and good dielectric properties. Therefore, developing polyimide films with a coefficient of thermal expansion compatible with copper foil and with a high degree of industrialization is one of the main research directions in the field of polyimide R&D. Summary of the Invention

[0004] One of the objectives of this invention is to overcome the deficiencies in the prior art and provide a method for preparing a polyimide film with a low coefficient of thermal expansion, wherein the resulting polyimide film has a coefficient of thermal expansion similar to that of copper foil and high tensile properties.

[0005] To achieve the above objectives, the technical solution of the present invention is: a method for preparing a polyimide film with a low coefficient of thermal expansion, comprising the following steps:

[0006] S1: Prepare a system with a solid content of 15% to 20% after the complete reaction of diamine and dianhydride, using diamine, dianhydride, and a polar aprotic solvent. The molar ratio of diamine to dianhydride is 1:(0.95 to 1.05). Add diamine to the polar aprotic solvent under nitrogen protection.

[0007] S2: Add dianhydride and end-capping agent to diamine solution in sequence, carry out temperature-controlled polycondensation reaction, control the viscosity of the reaction system to 150,000 to 220,000 mPa·s, and filter to obtain polyacrylic acid solution;

[0008] S3: The polyamide solution is coated onto the substrate, heated and kept at a high temperature for imidization treatment, and then dried to form a film, resulting in a polyimide film product with a low coefficient of thermal expansion.

[0009] The main components of the diamine are p-phenylenediamine and diaminobenzoyl aniline, and the main component of the dianhydride is pyromellitic dianhydride.

[0010] The preferred molar ratio of diamine to dianhydride is 1:1. Further, the dianhydride is pyromellitic dianhydride.

[0011] A preferred technical solution is that, based on a total molar percentage of 100% for the diamines, the molar percentage of p-phenylenediamine is 60%–86%, and the molar percentage of diaminobenzoyl aniline is 14%–40%. Further, the diamine is composed of p-phenylenediamine and diaminobenzoyl aniline, wherein the molar percentage of p-phenylenediamine is 75%–86%, and the molar percentage of diaminobenzoyl aniline is 14%–25%. Even further, the molar percentage of p-phenylenediamine is 78%–83%, and the molar percentage of diaminobenzoyl aniline is 17%–22%. Still further, the molar percentage of p-phenylenediamine is 80%, and the molar percentage of diaminobenzoyl aniline is 20%.

[0012] The preferred technical solution is that the diaminobenzoyl aniline is selected from one or two of 4,4'-diaminobenzoyl aniline and 3',4-diaminobenzoyl aniline, preferably 4,4'-diaminobenzoyl aniline.

[0013] The preferred technical solution is that the capping agent is phenylacetylene phthalic anhydride.

[0014] A preferred technical solution is that the molar ratio of the capping agent to the diamine is (0.03-0.1):1. Further, the molar ratio of the capping agent to the diamine is (0.05-0.1):1.

[0015] The preferred technical solution is that the temperature of the temperature-controlled polycondensation reaction in S2 is no more than 15°C, and further, the temperature-controlled polycondensation reaction is carried out under ice-water bath conditions.

[0016] The preferred technical solution is that the imidization treatment adopts a stepped heating method, wherein the temperature range of the stepped heating is 170 to 390°C, and the imidization treatment time is 7 to 20 minutes.

[0017] A preferred technical solution is that the starting temperature of the stepped heating is 175–185℃, the ending temperature is 370–385℃, the step heating range is 40–60℃, and the holding time after each stepped heating is 20–40 minutes. Furthermore, the stepped heating is as follows: starting temperature 175–185℃, holding for 35–40 minutes; heating to 215–225℃, holding for 20–25 minutes; heating to 275–285℃, holding for 20–25 minutes; heating to 325–335℃, holding for 35–40 minutes; heating to 375–385℃, holding for 35–40 minutes.

[0018] A second objective of this invention is to provide a film, which is a polyimide film, prepared by the above-described preparation method.

[0019] A third objective of this invention is to provide a flexible copper-clad laminate, comprising stacked copper foil and the aforementioned polyimide film.

[0020] The advantages and beneficial effects of this invention are as follows:

[0021] The present invention introduces amide bonds with a crankshaft structure into the rigid main chain of the low thermal expansion coefficient polyimide film, which not only provides a flexible structure for the main chain, but also disrupts the regularity of the molecular chain, making the molecular chain stacking loose, so that the thermal expansion coefficient is close to that of copper foil, making it suitable for flexible copper clad laminates.

[0022] The embedding of flexible segments can help improve the elongation at break of polyimide films;

[0023] By adjusting the content of diaminobenzoyl aniline in polyimide, the coefficient of thermal expansion can be changed within a certain range to match substrates with different coefficients of thermal expansion, including copper foil.

[0024] The addition of a preferred capping agent can significantly increase the molecular weight of polyimide and improve the tensile strength of the film. Detailed Implementation

[0025] The specific embodiments of the present invention will be further described below with reference to examples. These examples are only used to more clearly illustrate the technical solutions of the present invention and should not be construed as limiting the scope of protection of the present invention.

[0026] polar aprotic solvents

[0027] Polar aprotic solvents provide a solution environment for the reactions of diamines, dianhydrides, and capping agents. A range of solvents can be selected, including but not limited to highly polar dimethylacetamide, dimethylformamide, and dimethyl sulfoxide.

[0028] The capping agent can be selected from conventional bismaleimide, norbornene olefinic anhydride, or phenylethynyl phthalic anhydride, with phenylethynyl phthalic anhydride being preferred.

[0029] The dimethylacetamide, p-phenylenediamine, 4,4'-diaminobenzoyl aniline, 3',4-diaminobenzoyl aniline, pyromellitic dianhydride, phenylethynyl phthalic anhydride, and bismaleimide used in the examples are all commercially available products and are chemically pure.

[0030] Example

[0031] Example 1: The preparation method of polyimide includes the following steps:

[0032] S1: Add 500g of dimethylacetamide to an ice-water bath reaction vessel, purge with nitrogen for protection, add 0.2mol of p-phenylenediamine and 0.05mol of 4,4'-diaminobenzoylaniline under mechanical stirring, and add the diamine and dianhydride to a system with a solid content of 15% after the diamine and dianhydride have completely reacted. Stir for 10 minutes until the diamine is completely dissolved.

[0033] S2: Add 0.25 mol of pyromellitic dianhydride in 5 portions, with an 8-minute interval between each addition. After the addition is complete, add 0.025 mol of the end-capping agent bismaleimide and continue stirring for 12 hours. After the reaction is complete, a reddish-brown viscous solution (polyacrylic acid solution) will be formed. The temperature of the polycondensation reaction system should be controlled below 15℃.

[0034] S3: The polyacrylic acid solution is filtered through a sand core funnel and then degassed under vacuum to fully relax the molecular chains;

[0035] S4: Coat a uniformly thick polyamic acid liquid film onto a clean and smooth glass plate, place the glass plate in an oven to dry, and obtain a glass plate carrying a dry polyamic acid film.

[0036] S5: Place the glass plate carrying the dried polyamic acid film into a muffle furnace for controlled stepwise imidization: rapidly heat from room temperature to 180℃ and hold for 40 min; then heat to 220℃ and hold for 20 min; heat to 280℃ and hold for 20 min; heat to 330℃ and hold for 40 min; heat to 380℃ and hold for 40 min) to obtain a polyimide film with dimensions of 45cm*15cm and a thickness of approximately 50μm.

[0037] Examples 1-6 were prepared according to the table below, using diamine and dianhydride as raw materials for polyimide synthesis. Based on the same solid content of the system after the reaction, the amount of dimethylacetamide added was adjusted according to the mass of diamine and dianhydride added. The preparation method and process parameters were the same. The viscosity of the polyacrylic acid solution after the S2 polycondensation reaction was in the range of 150,000 to 220,000 mPa·s. The thickness of the liquid film coating was adjusted according to the viscosity to obtain a polyimide film of approximately the same thickness.

[0038]

[0039] Example 6

[0040] The process parameters for S1-S4 in Example 6 are the same as those in Example 1. S2 in Example 6 is as follows: 0.25 mol of pyromellitic dianhydride is added in 5 portions, with an 8-minute interval between each addition. After the addition is complete, 0.025 mol of the capping agent bismaleimide is added, and stirring is continued for 12 hours. After the reaction is complete, a viscous solution is formed, and the temperature of the reaction mixture is below 15°C.

[0041] Examples 7-8

[0042] The polyimide preparation methods in Examples 7 and 8 are the same as those in Example 1, with the difference being the control of the imidization temperature at S4:

[0043] Example 7: A glass plate carrying a dry PAA film was placed in a muffle furnace for imidization by controlled step temperature rise: the temperature was rapidly increased from room temperature to 75°C and held for 60 min; the temperature was increased to 110°C and held for 30 min; the temperature was increased to 180°C and held for 30 min; the temperature was increased to 260°C and held for 30 min; the temperature was increased to 360°C and held for 30 min.

[0044] Example 8: The polyamide solution was coated on a heated plate at 100°C and pre-dried for 10 min. Then it was placed in a muffle furnace for imidization by controlled step temperature increase: 130°C for 120 min, 220°C for 60 min, 300°C for 60 min, and 400°C for 60 min.

[0045] The polyimide films prepared in the examples were subjected to the following tests (10 samples, average value):

[0046] 1. Determine the elongation at break and tensile strength of polyimide film according to ASTM D882 standard;

[0047] 2. Using a static mechanical analyzer, according to ASTM D696, under a nitrogen atmosphere, apply a load of 50 mN and measure the coefficient of thermal expansion in the temperature range of 50 to 200 °C at a heating rate of 10 °C / min.

[0048] The test results for the elongation at break, coefficient of thermal expansion, and film strength of the polyimide film are shown in the table below:

[0049] Tensile strength / MPa Elongation at break / % Coefficient of thermal expansion / ppm / k Example 1 197 65 17.5 Example 2 203 67 18.4 Example 3 212 68 19.7 Example 4 188 70 22.3 Example 5 191 64 18.7 Example 6 179 65 17.3 Example 7 188 56 21.9 Example 8 185 53 22.5

[0050] Examples 1-5 serve as a control for the component content in the diamine. Examples 1-3, while having a thermal expansion coefficient close to that of copper foil (18 ppm / K), exhibit higher tensile strength and elongation at break. Both 4,4'-diaminobenzoyl aniline and 3',4-diaminobenzoyl aniline possess amide bonds with a crankshaft structure in their molecular structures. Introducing these amide bonds, as flexible structures, into the rigid polyimide backbone is beneficial for improving the tensile strength and elongation at break of the polyimide film. The introduction of an appropriate amount of flexible structure into the molecular chain disrupts its regularity, making the molecular chain packing looser, thus increasing the thermal expansion coefficient of the polyimide film.

[0051] Example 4 has a larger coefficient of thermal expansion; the elongation at break increases, but the tensile strength decreases; this is due to the polyimide molecular space becoming too loose after the proportion of flexible monomers is increased.

[0052] The tensile strength of Example 5 was lower than that of Example 1, indicating that the polyimide molecular chains synthesized by 4,4'-diaminobenzoyl aniline had a higher degree of regularity in packing compared to 3',4-diaminobenzoyl aniline.

[0053] In Example 6, conventional bismaleimide was used as the end-capping agent, indicating that phenylethynyl phthalic anhydride helps to improve the strength of the polyimide film obtained in Example 1.

[0054] Examples 7 and 8 employ a stepped heating method different from Example 1. In Example 7, the high-temperature section heats up too quickly and has a short holding time, while in Example 8, the high-temperature section reaches an even higher temperature. Test results show that, based on the polyamic acid obtained from the diamine and dianhydride polycondensation reaction in Example 1, the preferred stepped heating process of Example 1, with appropriately extended holding times in the low and high temperature sections, results in a moderate evaporation rate of solvent and water vapor on the polyamic acid film surface, which is beneficial for forming a polyimide film with better mechanical strength, and also results in a shorter overall imidization time. Heating rates that are too fast or too slow are detrimental to the formation of the film's crystalline structure, thus affecting the coefficient of thermal expansion.

[0055] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles 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 method for preparing a polyimide film with a low coefficient of thermal expansion, comprising the following steps: S1: Prepare a system with a solid content of 15% to 20% after the complete reaction of diamine and dianhydride, using diamine, dianhydride, and a polar aprotic solvent. The molar ratio of diamine to dianhydride is 1:(0.95 to 1.05). Add diamine to the polar aprotic solvent under nitrogen protection. S2: Add dianhydride and end-capping agent to diamine solution in sequence, carry out temperature-controlled polycondensation reaction, control the viscosity of the reaction system to 150,000 to 220,000 mPa·s, and filter to obtain polyacrylic acid solution; S3: The polyamide solution is coated onto the substrate, heated and kept at a high temperature for imidization treatment, and then dried to form a film, resulting in a polyimide film product with a low coefficient of thermal expansion. The diamine is characterized in that its main components are p-phenylenediamine and diaminobenzoylaniline, and its main component is pyromellitic dianhydride. Based on a total molar percentage of 100% diamines, the molar percentage of p-phenylenediamine is 60%–86%, the molar percentage of diaminobenzoyl aniline is 14%–40%, and the end-capping agent is phenylethynyl phthalic anhydride; the molar ratio of the end-capping agent to the diamine is (0.03–0.1):1; The imidization treatment employs a stepped heating process, with an initial temperature of 175–185°C, an ending temperature of 370–385°C, a step heating range of 40–60°C, and a holding time of 20–40 minutes after each step heating.

2. The method for preparing a low thermal expansion coefficient polyimide film according to claim 1, characterized in that, The diaminobenzoyl aniline is selected from one or both of 4,4'-diaminobenzoyl aniline and 3',4-diaminobenzoyl aniline.

3. The method for preparing a low thermal expansion coefficient polyimide film according to claim 1, characterized in that, The molar ratio of the capping agent to the diamine is (0.03–0.1):

1.

4. The method for preparing a low thermal expansion coefficient polyimide film according to claim 1, characterized in that, The temperature of the S2 temperature-controlled polycondensation reaction is no more than 15℃.

5. A thin film, characterized in that, It is a polyimide film, prepared by the preparation method according to any one of claims 1 to 4.

6. A flexible copper-clad laminate, characterized in that, It includes stacked copper foil and the polyimide film of claim 5.

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