A fluorine-containing polyimide resin and an epoxy resin adhesive based thereon

Abstract

The application discloses a fluorine-containing polyimide resin and an epoxy resin adhesive based on the same, takes 2-trifluoromethyl-4,4'-diamino diphenyl ether containing-CF3 as raw material, optimizes the proportion of a dianhydride containing a flexible group and a dianhydride containing a rigid group, synthesizes the fluorine-containing polyimide resin, and then mixes the fluorine-containing polyimide resin with a tetrafunctional epoxy resin, a difunctional epoxy resin and a curing agent to obtain the epoxy resin adhesive. The fluorine-containing polyimide resin can improve the glass transition temperature of the adhesive, enhances the heat resistance of the adhesive, and because of containing-CF3, the solubility in the epoxy system is increased, the water absorption and the dielectric constant of the adhesive are reduced.

Description

Technical Field

[0001] This invention relates to a fluorinated polyimide resin and an epoxy resin adhesive based thereon, belonging to the field of polymer materials technology. Background Technology

[0002] With the rapid development of electronic technology, chip packaging density continues to rise in the electronics manufacturing industry. Components such as inductors generate a large amount of heat during operation, and their operating temperatures often exceed the limits that traditional epoxy resin adhesives can withstand. Ordinary epoxy resin adhesives soften rapidly and lose their adhesiveness when exposed to high temperatures, leading to serious problems such as inductor parameter drift and chip detachment. This significantly affects the stability and lifespan of electronic products, making it difficult to meet the requirements of miniaturized, high-performance, and high-reliability electronic products. Therefore, improving the temperature resistance of adhesives is urgently needed.

[0003] Polyimide resins with aromatic main chains are among the most widely used polymer resins in the electronics field due to their excellent heat resistance, electrical insulation, chemical resistance, and weather resistance. They are often physically blended with traditional epoxy adhesives. However, the rigid structure of polyimide results in strong intramolecular / intermolecular forces, leading to drawbacks such as poor solvent solubility and processing difficulties. Currently, a common strategy to increase solubility is to introduce a twisted, non-coplanar structure using spirofluorene, disrupting the symmetry of the molecular chains and increasing rotational resistance. However, the introduction of rigid fluorene reduces toughness. Chinese patent applications with publication numbers CN116574259A and CN114369243A, as well as the article "High performance imide oligomers and thermosets derived from 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride" (Polymer2023,281,126086), have reported the synthesis of polyimides using non-coplanar tortuous rigid fluorene structures. This results in polyimide resins exhibiting high solubility and high heat resistance after imidization. However, the rigid fluorene monomers used in these studies lead to high melt viscosity, poor processability, and insufficient toughness in the cured material due to the inherent rigidity of the monomer structure. Therefore, developing high-temperature resistant, high-toughness, and easily processable soluble polyimide resins is a pressing technical challenge. Summary of the Invention

[0004] To address the aforementioned problems in existing technologies, this invention provides a fluorinated polyimide resin and an epoxy resin adhesive based thereon. In the synthesis of the fluorinated polyimide resin, this invention uses 2-trifluoromethyl-4,4'-diaminodiphenyl ether containing -CF3 as a raw material, and optimizes the ratio of dianhydrides containing flexible groups and dianhydrides containing rigid groups. This not only overcomes the contradictions between heat resistance, solubility, and toughness in existing polyimide resins, but also reduces water absorption and dielectric constant to meet the needs of precision electronic applications.

[0005] To achieve its objectives, the present invention employs the following technical solution:

[0006] This invention first discloses a method for preparing fluorinated polyimide resin, comprising the following steps: 2-trifluoromethyl-4,4'-diaminodiphenyl ether is first added to a three-necked flask equipped with a rotor; under a nitrogen atmosphere, a solvent is added to completely dissolve the 2-trifluoromethyl-4,4'-diaminodiphenyl ether; then dianhydride is added, and a polycondensation reaction is carried out at room temperature; after reacting for 5-7 hours, triethylamine (catalyst) and acetic anhydride (dehydrating agent) are added; the reaction is carried out at room temperature for 0.5-1 hour, and then at 120-130°C for 6-8 hours; the reaction is then terminated, and after cooling, the resulting reaction solution is poured into a beaker containing ethanol and stirred; the resulting precipitate is dried to obtain the target product, fluorinated polyimide resin; wherein the ratio of 2-trifluoromethyl-4,4'-diaminodiphenyl ether, dianhydride, triethylamine, and acetic anhydride is 1 mol: 1 mol: 1.6-1.8 mL: 4.3-4.5 mL.

[0007] As a preferred embodiment, the solvent is at least one selected from anisole, m-cresol, N-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide.

[0008] As a preferred embodiment, the dianhydride is a mixture of a first dianhydride and a second dianhydride, wherein the first dianhydride is 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride, and the second dianhydride is at least one of 2,3,3',4'-biphenyl tetracarboxylic dianhydride and pyromellitic tetracarboxylic dianhydride, and the first dianhydride accounts for 50% to 100% of the total molar amount of the dianhydride.

[0009] As a preferred embodiment, the 2-trifluoromethyl-4,4'-diaminodiphenyl ether is prepared by the following steps:

[0010] Step 1: Add 22.56 g of 2-chloro-5-nitro-trifluorotoluene, 13.91 g of p-nitrophenol, 13.82 g of potassium carbonate and 100 mL of N,N'-dimethylformamide to a three-necked flask equipped with a rotor and a spherical condenser. Stir the mixture at 135–150 °C for 6–8 h under a nitrogen atmosphere. Pour the resulting reaction solution into distilled water to precipitate the product. Add an appropriate amount of hydrochloric acid to promote the precipitation of the product. Stir for 20–30 min. Filter and dry the precipitated solid. Recrystallize the solid with a mixture of ethanol and water to obtain 2-trifluoromethyl-4,4'-dinitrodiphenyl ether.

[0011] Step 2: Add 10 mmol of 2-trifluoromethyl-4,4'-dinitrodiphenyl ether, 0.25 g of wet palladium on carbon, and 100 mL of anhydrous ethanol to a three-necked flask. Stir and heat to 60-75 °C, then add 15 mL of 80% hydrazine monohydrate solution dropwise over 2 h, and then reflux for 7-8 h. Filter the resulting mixture to remove the wet palladium on carbon, then remove the ethanol by rotary evaporation, and then recrystallize with a mixture of ethanol and water to obtain 2-trifluoromethyl-4,4'-diaminodiphenyl ether.

[0012] The structural formula of the fluorinated polyimide resin prepared by the above preparation method is shown below:

[0013]

[0014] In the formula, x is the percentage of 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride in the total molar amount of dianhydride, y1 and y2 are the molar percentages of 2,3,3',4'-biphenyl tetracarboxylic dianhydride and pyromellitic tetracarboxylic dianhydride, respectively, and x+y1+y2=1.

[0015] The present invention also provides an epoxy resin adhesive, the raw materials of which include epoxy resin, curing agent and the fluorinated polyimide resin, wherein the epoxy resin is composed of tetrafunctional epoxy resin and difunctional epoxy resin in a mass ratio of 20% to 80%: 80% to 20%, the mass ratio of curing agent to epoxy resin is 6: 5 to 6, and the fluorinated polyimide resin accounts for 5% to 20% of the mass of epoxy resin.

[0016] As a preferred embodiment: the tetrafunctional epoxy resin is one of N,N,N',N'-tetraglycidyl-4,4'-diaminodiphenylmethane, N,N,N',N'-tetraglycidyl-4,4'-diaminodiphenyl ether, N,N,N',N'-tetraglycidyl-4,4'-diaminodiphenyl sulfone, and N,N,N',N'-tetraglycidyl-3,3'-dimethyl-4,4'-diaminodiphenylmethane; the difunctional epoxy resin is at least one of E-20 epoxy resin, E-44 epoxy resin, and E-51 epoxy resin. The curing agent is one of 4,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenylmethane, and m-phenylenediamine.

[0017] The preparation method of the epoxy resin adhesive of the present invention is as follows: fluorinated polyimide resin is added to a solvent and mechanically stirred until clear and transparent, then epoxy resin and curing agent are added and mixed and mechanically stirred until clear and transparent, then poured into a mold, and the solvent is removed by vacuum degassing, reduced pressure distillation and curing to obtain epoxy resin adhesive.

[0018] As a preferred embodiment, the vacuum degassing temperature is 60-85℃ and the time is 2-3 hours; the vacuum distillation temperature is 80-90℃ and the time is 1-2 hours; and the curing temperature is 120-180℃ and the curing time is 2-4 hours.

[0019] Compared with existing technologies, the beneficial effects of this invention are reflected in:

[0020] 1. In the synthesis of fluorinated polyimide resin, this invention optimizes the ratio of rigid dianhydride to flexible dianhydride, which not only enables the synthesized fluorinated polyimide resin to have excellent solubility in epoxy resin adhesive systems, but also improves its heat resistance without reducing the toughness of the adhesive, preventing the adhesive from softening and losing its stickiness at high temperatures, thus protecting the stability of electronic products and extending their lifespan.

[0021] 2. In the synthesis of fluorinated polyimide resin, this invention uses 2-trifluoromethyl-4,4'-diaminodiphenyl ether containing -CF3 as a raw material. When applied to epoxy adhesives, it can not only increase solubility and reduce the water absorption rate of the adhesive to prevent electronic products from failing due to moisture, but also reduce the dielectric constant to protect the stable transmission of electrical signals.

[0022] 3. The epoxy resin adhesive of the present invention uses a synergistic combination of tetrafunctional and difunctional epoxy resins, which can improve heat resistance while avoiding damage to mechanical properties compared with a single epoxy resin system.

[0023] 4. The adhesive of the present invention has a simple preparation process and stable performance, meeting the high standard requirements of electronic products such as inductors and electronic packaging. Attached Figure Description

[0024] Figure 1 The 2-trifluoromethyl-4,4'-diaminodiphenyl ether synthesized in the embodiments of the present invention 1 H NMR spectrum.

[0025] Figure 2 These are DSC diagrams of the adhesives obtained in various embodiments of the present invention;

[0026] Figure 3 The dielectric constant diagrams of the adhesives obtained in various embodiments of the present invention are shown.

[0027] Figure 4 The diagram shows the mechanical properties of the adhesives obtained in various embodiments of the present invention. Detailed Implementation

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments improved or modified by those skilled in the art are within the scope of protection of the present invention. It should be understood that the embodiments of the present invention are only used to illustrate the technical achievements of the present invention, and are not intended to limit the scope of protection of the present invention. Unless otherwise specified, the methods used in the embodiments are conventional methods.

[0029] Example 1

[0030] This embodiment prepares fluorinated polyimide resin and epoxy resin adhesive based thereon according to the following steps:

[0031] Step 1: Synthesis of 2-trifluoromethyl-4,4'-diaminodiphenyl ether

[0032] 22.56 g of 2-chloro-5-nitro-trifluorotoluene, 13.91 g of p-nitrophenol, 13.82 g of potassium carbonate, and 100 mL of N,N'-dimethylformamide were added to a three-necked flask equipped with a rotor and a spherical condenser. The mixture was stirred at 150 °C for 6 h under a nitrogen atmosphere. The resulting reaction solution was poured into distilled water to precipitate the product. An appropriate amount of hydrochloric acid was added to promote the precipitation of the product. The mixture was stirred for 30 min. The precipitated solid was filtered, dried, and recrystallized from a mixture of ethanol and water (volume ratio of 6:4) to obtain 2-trifluoromethyl-4,4'-dinitrodiphenyl ether.

[0033] 10 mmol (3.28 g) of 2-trifluoromethyl-4,4'-dinitrodiphenyl ether, 0.25 g of wet palladium on carbon (10% Pd / C), and 100 mL of anhydrous ethanol were added to a three-necked flask. The mixture was stirred and heated to 75 °C. Then, 15 mL of 80% hydrazine monohydrate solution was added dropwise over 2 h, followed by reflux for 8 h. The resulting mixture was filtered to remove the wet palladium on carbon, and then the ethanol was removed by rotary evaporation. Recrystallization was performed using a mixture of ethanol and water (volume ratio 6:4) to obtain 2-trifluoromethyl-4,4'-diaminodiphenyl ether. 1 HNMR spectrum as follows Figure 1 As shown.

[0034] Step 2: Synthesize fluorinated polyimide resin

[0035] In a three-necked flask equipped with a rotor, 1 mol of 2-trifluoromethyl-4,4'-diaminodiphenyl ether was first added. Under a nitrogen atmosphere, 18 mL of DMAc was added to completely dissolve the 2-trifluoromethyl-4,4'-diaminodiphenyl ether. Then, 1 mol of 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride was added, and the reaction was carried out at room temperature. After 6 hours of reaction, 1.6 mL of triethylamine and 4.3 mL of acetic anhydride were added, and the reaction was carried out at room temperature for 30 minutes, followed by a reaction at 120°C for 6 hours. The reaction was then terminated, and after cooling, the resulting reaction solution was poured into a beaker containing ethanol and stirred. The resulting precipitate was then dried under vacuum at 60°C to obtain the target product, fluorinated polyimide resin, denoted as PIs-1.

[0036] Step 3: Synthesize epoxy resin adhesive

[0037] Add 0.15g of fluorinated polyimide resin to DMA C The solution was mechanically stirred until clear and transparent. Then, 1.5g of N,N,N',N'-tetraglycidyl-4,4'-diaminodiphenylmethane, 1.5g of E-51 epoxy resin, and 2.55g of curing agent 4,4'-diaminodiphenylmethane were added, mixed, and mechanically stirred until the solution was clear and transparent. The resulting mixture was poured into a mold and degassed in a vacuum oven at 85°C for 2 hours, followed by vacuum distillation at 85°C for 1 hour, then cured at 140°C for 2 hours and 180°C for 2 hours to obtain the epoxy resin adhesive, denoted as PIs / EP-1.

[0038] Example 2

[0039] In this embodiment, the fluorinated polyimide resin and epoxy resin adhesive were synthesized using the same method as in Example 1. The only difference was that the amount of PIs-1 added in step 3 was 0.3g, and the resulting adhesive was denoted as PIs / EP-2.

[0040] Example 3

[0041] In this embodiment, fluorinated polyimide resin and epoxy resin adhesive were synthesized using the same method as in Example 2. The only difference was that 1 mol of 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride in step 2 was replaced with 0.5 mol of 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride and 0.5 mol of pyromellitic tetracarboxylic dianhydride. The resulting polyimide resin was designated PIs-2, and the resulting adhesive was designated PIs / EP-3.

[0042] Comparative Example 1

[0043] This comparative example synthesizes fluorinated polyimide resin using the same method as in Example 1, except that 1 mol of 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride in step 2 is replaced with 1 mol of 2,3,3',4'-biphenyl tetracarboxylic dianhydride. The resulting fluorinated polyimide resin is denoted as PIs-3.

[0044] Comparative Example 2

[0045] This comparative example synthesizes fluorinated polyimide resin using the same method as in Example 1, except that in step 2, 1 mol of 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride is replaced with 0.75 mol of 2,3,3',4'-biphenyl tetracarboxylic dianhydride and 0.25 mol of 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride. The resulting fluorinated polyimide resin is denoted as PIs-4.

[0046] Comparative Example 3

[0047] Mix 3g of E-51 epoxy resin and 2.55g of curing agent 4,4'-diaminodiphenylmethane and mechanically stir until the solution is clear and transparent. Pour the resulting mixture into a mold, degas at 85°C for 2 hours in a vacuum oven, distill under reduced pressure at 85°C for 1 hour, then cure at 140°C for 2 hours and 180°C for 2 hours to obtain the epoxy resin adhesive, denoted as E1.

[0048] Comparative Example 4

[0049] 1.5g of N,N,N',N'-tetraglycidyl-4,4'-diaminodiphenylmethane, 1.5g of E-51 epoxy resin, and 2.55g of curing agent 4,4'-diaminodiphenylmethane were mixed and mechanically stirred until the solution was clear and transparent. The resulting mixture was poured into a mold and degassed in a vacuum oven at 85°C for 2 hours, followed by vacuum distillation at 85°C for 1 hour, then cured at 140°C for 2 hours and 180°C for 2 hours to obtain the epoxy resin adhesive, denoted as EP1.

[0050] The solubility properties of the fluorinated polyimide resins obtained in the above embodiments and comparative examples in different solvent systems are shown in Table 1. In the table, √ represents complete dissolution, ○ represents partial dissolution, and × represents no dissolution.

[0051] Table 1

[0052]

[0053] As can be seen from Table 1, when the molar ratio of flexible dianhydride is not less than 50%, the resulting fluorinated polyimide resin has excellent solubility in a variety of solvents.

[0054] Figure 2 The images show the DSC diagrams of the adhesives obtained in each embodiment. Comparing adhesives PIs / EP-1 and PIs / EP-2, it can be seen that the heat resistance (Tg) gradually increases with the increase of the fluorinated polyimide resin content, from 175°C to 185°C. Comparing adhesives PIs / EP-2 and PIs / EP-3, it can be seen that as the rigidity content of the fluorinated polyimide resin continuously increases, its heat resistance continuously improves, with Tg increasing from 185°C to 193°C. Comparing E1 and EP1, it can be seen that the addition of tetrafunctional epoxy resin increases the crosslinking density of the adhesive, causing Tg to increase from 148°C to 166°C.

[0055] Figure 3 The diagram shows the dielectric constants of the adhesives obtained in each embodiment. A comparison reveals that the adhesive with added fluorinated polyimide resin, due to the presence of -CF3 in its structure, exhibits a lower dielectric constant. When the PIs-2 content reaches 10%, the dielectric constant at high frequencies decreases by 31.4%.

[0056] Figure 4 The figures show the mechanical properties of the adhesives obtained in each embodiment. Comparing adhesive E1 with PIs / EP-1 and PIs / EP-2, it can be seen that the mechanical properties increase continuously with the increase of flexible groups, from 60 MPa to 82 MPa. Comparing adhesive E1 with PIs / EP-1, PIs / EP-2, and PIs / EP-3, it can be seen that when a rigid structure is introduced into the fluorinated polyimide resin system, its mechanical properties will decrease, but are still improved compared to the adhesive without fluorinated polyimide resin.

[0057] Table 2 shows the water absorption rate of the adhesives obtained in each embodiment. The test method is as follows: the cured resin sample is made into a disc with a diameter of 2.0 cm and a thickness of 2 mm, and dried in a 60℃ oven for 8 hours. The sample is weighed using an analytical balance and recorded as m0. Then, the sample is placed in deionized water at room temperature for 24 hours, and the surface moisture is wiped off. The mass is recorded as m1. The formula for calculating the water absorption rate is:

[0058] Table 2

[0059] sample Water absorption rate (%) E1 1.21 PIs / EP-1 0.89 PIs / EP-2 0.71 PIs / EP-3 0.64

[0060] As can be seen from Table 2, the addition of fluorinated polyimide resin can significantly reduce the water absorption rate.

[0061] The above are merely exemplary embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a fluorinated polyimide resin, characterized in that, Includes the following steps: In a three-necked flask equipped with a rotor, 2-trifluoromethyl-4,4'-diaminodiphenyl ether is first added. Under a nitrogen atmosphere, a solvent is added to completely dissolve the 2-trifluoromethyl-4,4'-diaminodiphenyl ether. Then, dianhydride is added, and a polycondensation reaction is carried out at room temperature. After reacting for 5-7 hours, triethylamine (catalyst) and acetic anhydride (dehydrating agent) are added, and the reaction is carried out at room temperature for 0.5-1 hour. Then, the reaction is carried out at 120-130°C for 6-8 hours. The reaction is then terminated, and after cooling, the resulting reaction solution is poured into ethanol and stirred. The resulting precipitate is dried to obtain the target product, fluorinated polyimide. The amine resin contains 2-trifluoromethyl-4,4'-diaminodiphenyl ether, dianhydride, triethylamine, and acetic anhydride in a ratio of 1 mol: 1 mol: 1.6~1.8 mL: 4.3~4.5 mL. The dianhydride is a primary dianhydride or a mixture of a primary dianhydride and a secondary dianhydride. The primary dianhydride is 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride, and the secondary dianhydride is at least one of 2,3,3',4'-biphenyltetracarboxylic dianhydride and pyromellitic dianhydride. The primary dianhydride accounts for 50%~100% of the total molar amount of the dianhydride.

2. The method for preparing fluorinated polyimide resin according to claim 1, characterized in that, The solvent is at least one selected from anisole, m-cresol, N-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide.

3. The method for preparing fluorinated polyimide resin according to claim 1, characterized in that, The 2-trifluoromethyl-4,4'-diaminodiphenyl ether is prepared according to the following steps: Step 1: Add 22.56 g of 2-chloro-5-nitro-trifluorotoluene, 13.91 g of p-nitrophenol, 13.82 g of potassium carbonate and 100 mL of N,N-dimethylformamide to a three-necked flask equipped with a rotor and a spherical condenser. Stir the mixture at 135-150 °C for 6-8 h under a nitrogen atmosphere. Pour the resulting reaction solution into distilled water to precipitate the product. Add an appropriate amount of hydrochloric acid to promote the precipitation of the product. Stir for 20-30 min. Filter and dry the precipitated solid. Recrystallize the solid with a mixture of ethanol and water to obtain 2-trifluoromethyl-4,4'-dinitrodiphenyl ether. Step 2: Add 10 mmol of 2-trifluoromethyl-4,4'-dinitrodiphenyl ether, 0.25 g of wet palladium on carbon, and 100 mL of anhydrous ethanol to a three-necked flask. Stir and heat to 60-75 °C, then add 15 mL of 80% hydrazine monohydrate solution dropwise over 2 h, and then reflux for 7-8 h. Filter the resulting mixture to remove the wet palladium on carbon, then remove the ethanol by rotary evaporation, and then recrystallize with a mixture of ethanol and water to obtain 2-trifluoromethyl-4,4'-diaminodiphenyl ether.

4. A fluorinated polyimide resin prepared by the preparation method according to any one of claims 1 to 3.

5. An epoxy resin adhesive, characterized in that, The raw materials include epoxy resin, curing agent, and the fluorinated polyimide resin as described in claim 4, wherein the epoxy resin is composed of tetrafunctional epoxy resin and difunctional epoxy resin in a mass ratio of 20%~80%:80%~20%, the mass ratio of curing agent to epoxy resin is 6:5~6, and the fluorinated polyimide resin accounts for 5%~20% of the mass of epoxy resin.

6. The epoxy resin adhesive according to claim 5, characterized in that: The tetrafunctional epoxy resin is one of N,N,N',N'-tetraglycidyl-4,4'-diaminodiphenylmethane, N,N,N',N'-tetraglycidyl-4,4'-diaminodiphenyl ether, N,N,N',N'-tetraglycidyl-4,4'-diaminodiphenyl sulfone, and N,N,N',N'-tetraglycidyl-3,3'-dimethyl-4,4'-diaminodiphenylmethane; the difunctional epoxy resin is at least one of E-20 epoxy resin, E-44 epoxy resin, and E-51 epoxy resin.

7. The epoxy resin adhesive according to claim 5, characterized in that: The curing agent is one of 4,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenylmethane, and m-phenylenediamine.

8. A method for preparing the epoxy resin adhesive according to any one of claims 5 to 7, characterized in that: Fluorinated polyimide resin is added to a solvent and mechanically stirred until clear and transparent. Then epoxy resin and curing agent are added and mixed and mechanically stirred until clear and transparent. The mixture is then poured into a mold, degassed under vacuum, distilled under reduced pressure to remove the solvent, and cured to obtain epoxy resin adhesive.

9. The preparation method according to claim 8, characterized in that: The vacuum degassing temperature is 60~85℃ and the time is 2~3h; the vacuum distillation temperature is 80~90℃ and the time is 1~2h; the curing temperature is 120~180℃ and the curing time is 2~4h.

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