Process for producing a fiber composite material having high gas barrier properties and interlaminar toughness

Abstract

This invention discloses a method for preparing a fiber composite material with high gas barrier properties and interlayer toughness, comprising the following steps: dissolving polyvinyl alcohol in deionized water and adding a boron-based modifier, then adding triethanolamine to adjust the pH and adding a zinc ion coordination agent to obtain a boron ester dynamically crosslinked polyvinyl alcohol solution; casting the above solution into a mold and drying it to obtain a core layer film; then adding a graphene oxide dispersion to the above solution and coating the new mixture onto the surface of the core layer film using a coating machine and drying it to obtain a core-shell structured composite film; modifying desizing basalt fiber cloth with a borane coupling agent and subjecting it to plasma treatment, then impregnating it with resin to obtain a prepreg; and then laying the prepreg and the composite film together and hot-pressing them to obtain a laminate. This invention achieves a three-dimensional synergistic enhancement of the interlayer toughness, gas barrier properties, and interface stability of the composite material by synergistically constructing a reversible crosslinking network through boron ester dynamic crosslinking and zinc ion coordination, combined with the directional arrangement and distribution of graphene oxide.

Description

Technical Field

[0001] This invention relates to the field of composite material technology, specifically to a method for preparing a fiber composite material with high gas barrier properties and interlaminar toughness, belonging to the field of fiber reinforced composite material technology. Background Technology

[0002] Basalt fiber bismaleimide composites hold an irreplaceable position in aerospace, high-end manufacturing, and other fields due to their excellent high-temperature resistance, mechanical properties, and thermal stability. However, this type of composite material has three shortcomings: First, the high crosslinking density and brittleness of bismaleimide resin after curing, coupled with the strong chemical inertness of the basalt fiber surface, result in weak bonding at the interlayer interfaces, leading to interlayer cracking and insufficient toughness under load. Second, the presence of micropores and interfacial gaps within the composite material allows gas molecules to easily diffuse and permeate, making it difficult to meet the high airtightness requirements for applications where it is used as an embedded reinforcement layer in pipes. Third, traditional modification methods often employ static covalent crosslinking, which can improve interfacial bonding in the short term but lacks stress relaxation, making it prone to interfacial damage after long-term use or impact.

[0003] Currently, there are three main technical approaches for modifying and optimizing the interlaminar properties and gas barrier properties of basalt fiber / bismaleimide resin composites. The first approach is to improve performance by directly modifying the bismaleimide resin matrix, for example, by adding flexible toughening agents or nano-barrier fillers to the resin. While the introduction of flexible toughening agents (such as amino-terminated polyethers and allyl compounds) can reduce the brittleness of the resin after curing and improve the interlaminar toughness of the composite, the compatibility between the toughening agent and the resin is limited. Excessive addition can lead to a significant decrease in the resin's heat resistance (glass transition temperature, thermal decomposition temperature), failing to meet the requirements of high-temperature operating conditions. On the other hand, when nano-barrier fillers such as graphene oxide and montmorillonite are directly mixed into the resin, although their layered structure can initially improve the barrier properties, the nano-fillers are prone to agglomeration, making it difficult to form a continuous barrier network in the resin. Furthermore, there is a lack of effective chemical bonding between the filler and the resin and fibers, and stress concentration points are easily formed at the interface, which in turn leads to a decrease in the mechanical properties of the composite. The second approach involves modifying the surface of basalt fibers, primarily through methods such as borane coupling agents, plasma etching, and nanoparticle coating. Borane coupling agents can introduce organic functional groups onto the fiber surface, enhancing the physical adsorption with resin. However, this interfacial bonding is mainly based on hydrogen bonds and van der Waals forces, resulting in low bonding strength. Long-term use or impact can easily lead to interfacial debonding. While plasma etching can create a rough structure and introduce active groups on the fiber surface through high-energy particle bombardment, the modification effect is time-sensitive, with active groups easily decaying during storage. Furthermore, it cannot construct a continuous interfacial layer on the fiber surface that combines toughening and barrier functions. Nanoparticle coating modification can improve interfacial bonding through particle bridging, but the uniformity of nanoparticle coating on the fiber surface is poor, easily leading to localized agglomeration and uneven internal properties of the composite material. Moreover, it only optimizes interfacial bonding and cannot create a synergistic enhancement effect on interlayer toughness and gas barrier properties.

[0004] The third approach involves introducing intercalation films between the composite material layers to improve interlayer performance through interfacial bridging. This is currently considered a feasible and effective technical direction in scientific research. Existing intercalation films are mainly divided into two categories: pure organic films (such as polyvinyl alcohol and polyimide films) and inorganic-organic composite films (such as polyvinyl alcohol / graphene oxide composite films). Pure organic films can improve interlayer toughness through the stretching and slippage of flexible segments, but they lack a dense microstructure and have generally poor gas barrier properties. Inorganic-organic composite films can optimize barrier properties through the layered structure of inorganic fillers, but traditional composite methods mostly use static physical mixing. Polyvinyl alcohol and graphene oxide are only bonded by hydrogen bonds, resulting in weak interfacial interactions and easy phase separation, which leads to a decrease in the mechanical properties of the film itself. More importantly, existing intercalated films lack strong chemical bonding with basalt fibers and bismaleimide resins, and interlayer connections are only achieved through physical bonding. The interfacial bonding strength is low, and the film-fiber / resin interface delamination is prone to occur under load. This not only fails to exert the synergistic effect of toughening and barrier, but may also become a weak point in the performance of the composite material.

[0005] However, the current technology for preparing and applying intercalated films of basalt fiber bismaleimide resin composites still faces many unresolved issues. For example, traditional polyvinyl alcohol / graphene oxide composite films are formed by simple ultrasonic dispersion followed by casting. The graphene oxide sheets tend to stack randomly, making it difficult to form a directional and dense barrier network. Furthermore, the film surface lacks active groups that can react with the fiber and resin, resulting in poor interfacial compatibility. Some technologies enhance the molecular interactions within the film by introducing static covalent bonds (such as crosslinking of epoxy groups and amino groups), but the static crosslinked network lacks stress relaxation capabilities and is prone to rigid fracture under load, failing to effectively absorb energy. Other technologies use high-temperature crosslinking processes to prepare composite films, which not only leads to the degradation of polyvinyl alcohol segments, affecting film toughness, but also increases production costs under high-temperature conditions and exhibits poor heat resistance compatibility with basalt fibers.

[0006] Based on this, this invention proposes a technical solution for constructing polyvinyl alcohol / graphene oxide intercalated films through the synergistic construction of boron ester dynamic crosslinking and zinc ion coordination, and applies it to the interlayer modification of basalt fiber bismaleimide resin composites. Compared with existing intercalated film technologies, the boron ester dynamic crosslinking network can achieve stress relaxation and energy absorption through bond breaking and recombination, while the graphene oxide forms a dense barrier layer through directional alignment. Simultaneously, the boron-based active groups can form a strong chemical bond with the pretreated basalt fiber and bismaleimide resin, ultimately achieving a synergistic breakthrough in the interlayer toughness, gas barrier properties, and interfacial stability of the composite material. Therefore, this invention aims to provide a method for preparing fiber composite materials with high gas barrier properties and interlayer toughness to overcome the shortcomings of existing technologies. Summary of the Invention

[0007] The present invention mainly overcomes the shortcomings of the prior art and provides a method for preparing fiber composite materials with high gas barrier properties and interlayer toughness. Through the structural design and process optimization of the dynamic cross-linked intercalated composite film, the interlayer toughness, gas barrier properties and high temperature resistance are synergistically improved.

[0008] The technical solution provided by this invention to solve the above-mentioned technical problems is: a method for preparing a fiber composite material with high gas barrier properties and interlaminar toughness, and the method thereof, comprising the following steps:

[0009] S1. Polyvinyl alcohol is dissolved in deionized water and boron-based modifier is added. Then, triethanolamine is used to adjust the pH and zinc ion ligand is added to obtain a boron ester dynamically crosslinked polyvinyl alcohol solution.

[0010] S2. The boron ester dynamically cross-linked polyvinyl alcohol solution in S1 is cast into a polytetrafluoroethylene mold to obtain a core layer film;

[0011] S3. The boron ester dynamically cross-linked polyvinyl alcohol solution and graphene oxide dispersion in S1 are mixed and ultrasonically dispersed, and then coated onto the surface of the core layer film using a slit-type doctor blade to form a shell layer, thus obtaining a core-shell structured composite film.

[0012] S4. Desizing basalt fiber cloth is modified with a boron coupling agent and subjected to plasma treatment before being impregnated with resin to obtain a prepreg.

[0013] S5. The prepreg in S4 is then laid layer by layer with the core-shell structure composite film in S3 and hot-pressed to obtain basalt fiber composite material.

[0014] A further technical solution is that the boron-based modifier is at least one of 3-aminophenylboronic acid, 4-carboxyphenylboronic acid, or tributyl borate; and the zinc ion coordinating agent is one of zinc acetate, zinc nitrate, or zinc chloride.

[0015] A further technical solution is that, in step S1, the mass ratio of polyvinyl alcohol, boron-based modifier, and zinc ion ligand is 100:10:3, the pH is adjusted to 7.5, and 750 ml of deionized water is used.

[0016] A further technical solution is that, in step S3, the concentration of the graphene oxide dispersion is 2.5 mg / mL; the ultrasonic dispersion power is 350 W for 70 min; and the ultrasonic vibration sieve with 5 μm apertures is used for dispersion for 40 min.

[0017] Further advancements include core layer construction: using a polyvinyl alcohol / zinc ion coordination system as the core layer material, a dense substrate is formed through casting and pre-drying. Shell layer coating: using a graphene oxide / boron ester crosslinking system as the shell layer material, a slit-scalpel is used to coat the core layer film surface, controlling the ratio of coating thickness to core layer thickness to ensure complete shell coating of the core layer; gradient drying synergy: low-temperature pre-drying (50℃) fixes the core layer morphology, preventing subsequent high-temperature shrinkage; then medium-temperature drying (60℃) promotes the directional alignment of graphene oxide sheets in the shell layer, and ultrasonic vibration sieve dispersion ensures the graphene oxide sheets are parallel to the film surface; finally, high-temperature drying (70℃) strengthens the coordination crosslinking of boron ester bonds with zinc ions in the core layer, resulting in a core-shell composite film.

[0018] A further technical solution is to use fibers with a diameter of 11 μm and an areal density of 220 g / m² in step S4. 2 The basalt fiber cloth was soaked in a 2.5% borane coupling agent solution at room temperature for 55 minutes and dried at 135°C for 3.5 hours. Then it was placed in a plasma device and a mixed gas of argon and carbon dioxide in a volume ratio of 3:1 was introduced at a power of 550W for 18 minutes. The resin used in step S4 was a diphenyl ether type bismaleimide and allyl phenolic resin in a mass ratio of 8:2. The fiber fabric was heated and melt-impregnated at 95°C to obtain a prepreg.

[0019] A further technical solution is that in step S5, the layers are laid in the order of prepreg-core-shell composite film-prepreg, with a total of 12 layers of prepreg and 11 layers of core-shell composite film; and cured by a three-gradient heating process with hot pressing temperature of 130℃-190℃ and time of 1.5h-3.5h, and hot pressing pressure of 15MPa.

[0020] The molding method involved in this patent is not limited to hot pressing.

[0021] The second technical problem to be solved by the present invention is to provide a method for preparing a fiber composite material with high gas barrier properties and interlaminar toughness prepared by the above method.

[0022] The present invention has the following beneficial effects:

[0023] (1) The present invention adopts a multi-modification method to improve the interlayer toughness and interface stability of the composite material by using the synergistic effect of dynamic crosslinking of boron ester and pretreatment of polyvinyl alcohol / graphene oxide with borane. The dynamic crosslinking network of boron ester can achieve stress relaxation and energy absorption through bond breaking and recombination, which greatly improves the interlayer shear and interlayer toughness of the composite material, inhibits interlayer cracking and crack propagation, and the interlayer shear performance can still be maintained under high temperature and long-term action, so that the composite material has no risk of debonding during long-term use.

[0024] (2) The basalt fiber composite material prepared by the present invention increases the gas barrier properties of the composite material while increasing the mechanical properties. The composite material is formed by layering the modified film intercalation between the fabrics. After ultrasonic vibration dispersion, the graphene oxide is oriented and the sheet-brick structure of the graphene oxide is used to block and extend the passage path of gas molecules to improve the gas barrier properties. At the same time, it can also be used as a nanoparticle reinforcing material to improve the mechanical properties of the composite material. Attached Figure Description

[0025] Figure 1 This is a flowchart illustrating the preparation process of the present invention;

[0026] Figure 2 Thermogravimetric analysis diagram of the composite thin film;

[0027] Figure 3 The diagram shows the gas barrier properties of different intercalated basalt fiber composite materials.

[0028] Figure 4 A and Figure 4 B shows the scanning electron microscope images of the fiber-resin interface bonding and the modified fiber, respectively.

[0029] Figure 5 Graphs showing the bending properties of composite materials with different intercalated basalt fibers;

[0030] Figure 6 The energy release rate diagram for the type II fracture toughness of different intercalated basalt fiber composite materials; Detailed Implementation

[0031] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0032] Example 1

[0033] like Figure 1 As shown, a fiber composite material with high gas barrier properties and interlaminar toughness according to the present invention is prepared by the following steps:

[0034] Step 1: Dissolve 100g of polyvinyl alcohol in 750mL of deionized water, stir at 95℃ to dissolve, add 10g of 3-aminophenylboronic acid, adjust the pH to 7.5 with triethanolamine, keep the reaction at 80℃ for 5h, add 3g of zinc acetate, stir at 55℃ for 1.5h, cool to room temperature to obtain a boron ester dynamically crosslinked polyvinyl alcohol solution with a mass concentration of 13%.

[0035] Step 2: (1) Core layer preparation: Take 50g of boron ester dynamic cross-linked polyvinyl alcohol solution (containing zinc ion coordination system) prepared by S1 process, cast it into a 200mm×200mm polytetrafluoroethylene mold, place it in a vacuum drying oven, and pre-dry it at 50℃ and vacuum degree -0.09MPa for 4h to form a core layer substrate with a thickness of 12μm; (2) Shell coating: Take 25g of graphene oxide dispersion with a concentration of 2.5mg / mL (deionized water to ethylene glycol volume ratio 6:1), mix it with 75g of boron ester dynamic cross-linked polyvinyl alcohol solution (graphene oxide / boron ester cross-linked polyvinyl alcohol solution). The mixture (with a mass ratio of 25:75) was ultrasonically dispersed at 45 kHz and 350 W for 70 min, and then dispersed again through an ultrasonic vibrating screen with 5 μm sieve openings for 40 min. The mixture was then coated onto the core substrate surface using a slit-type scraper at a coating speed of 0.3 m / min to form a shell layer with a thickness of 23 μm. The mold with the coated shell layer was placed in a vacuum drying oven and dried at 60 °C and a vacuum of -0.09 MPa for 4 h. The temperature was then raised to 70 °C and the vacuum was kept constant for 3 h. After cooling to room temperature, the mold was demolded to obtain a core-shell intercalated film with a total thickness of 35 μm.

[0036] Step 3: Immerse the desized basalt fiber cloth (basalt fiber is obtained by soaking in acetone at 80℃ for 24h) in a 2.5% borane coupling agent solution, soak at room temperature for 55min, and dry at 135℃ for 3.5h; then place it in a plasma device, introduce a mixture of argon and carbon dioxide gas (volume ratio 3:1), power 550W, and process for 18min;

[0037] Step 4: Mix diphenyl ether type bismaleimide and allyl phenolic resin at a mass ratio of 8:2, and heat at 95°C to melt and impregnate the fiber fabric to obtain a prepreg. Use the hot melt impregnation method to impregnate the pretreated basalt fiber fabric with resin, and control the resin content of the fiber to be 58% to obtain basalt fiber prepreg.

[0038] Step 5: Lay out 12 layers of prepreg and 11 layers of core-shell composite film in the order of prepreg-core-shell composite film; place in a vacuum hot press mold, preheat to 85℃ under a vacuum of -0.09MPa and hold for 30 minutes, then cure using a three-gradient heating process of 130℃-190℃ and 1.5h-3.5h, with a hot pressing pressure of 15MPa; after cooling to room temperature, demold to obtain the composite material sheet.

[0039] The composite film obtained in Example 1 through casting and drying was subjected to thermogravimetric analysis, and the results are as follows: Figure 2 As shown.

[0040] Figure 2The curve results show that the film initially begins to slowly lose weight due to the evaporation of the crystal water. When the temperature reaches 275℃, the composite film begins to thermally decompose, indicating that the thermal stability of the entire film is greatly improved after the boron ester crosslinking treatment.

[0041] Figure 3 This study revealed the gas barrier properties of basalt fiber composites with different composite film intercalations. It can be seen that the gas barrier properties of the composites were significantly improved after composite film intercalation optimization. Specifically, during the ultrasonic vibration sieve dispersion process, the graphene oxide sheets were oriented to form a continuous and dense barrier layer, thus extending the gas molecule permeation path. Simultaneously, the boron ester bonds and zinc ion coordination formed a three-dimensional network, causing the polyvinyl alcohol molecular chains to pack tightly, reducing internal porosity. Furthermore, the strong chemical bonding between the fiber, film, and resin through the three-dimensional network also eliminated interfacial gaps, significantly improving gas barrier properties.

[0042] The microstructure of the composite board and modified basalt fiber from Example 1 was observed, and the results are as follows: Figure 4 A and Figure 4 As shown in B.

[0043] Figure 4 A and Figure 4 B reveals the microstructure of the composite plate and the modified basalt fiber. Figure 4 A clearly shows that a strong chemical bond is formed between the resin, film, and fiber fabric, with the resin extensively coating the fiber to enhance the interfacial bonding force. Figure 4 B shows that the roughness of the basalt fiber modified with borane coupling agent is significantly improved. At the same time, Zn metal particles with angular distribution are also attached to the borane coupling agent, proving that the modification was successful and the film and resin are well bonded.

[0044] The basalt fiber composite material prepared in Example 1 was subjected to a uniaxial bending test, and the results are as follows: Figure 5 As shown.

[0045] Figure 5 This study reveals that thin-film intercalation can improve the flexural strength and flexural modulus of unintercalated basalt fiber composites. Specifically, after borane-plasma composite pretreatment, active sites such as boron hydroxyl groups are introduced onto the surface of the basalt fibers. These sites form a chemical complement to the boron ester crosslinking network in the intercalated film, enhancing the interfacial bonding between the fiber and the matrix and effectively transferring stress from the matrix to the fiber. Simultaneously, the dynamically crosslinked boron ester intercalated film possesses both rigidity and toughness, forming an elastic bridging structure between the composite layers. Under bending stress, the film can disperse stress through its own deformation, inhibiting crack propagation. Furthermore, the rigidity of the graphene oxide sheets enhances the film's load-bearing capacity, synergistically strengthening the overall flexural strength of the composite, thus improving its mechanical properties.

[0046] The basalt fiber composite material prepared in Example 1 was subjected to an end-notch bending test, and the results are as follows: Figure 6 As shown.

[0047] Figure 6 The study revealed the energy release rate trend of basalt fiber composites in type II fracture toughness, showing that the energy release rate of the composite film reinforced by dynamic crosslinking of boron ester is significantly higher than that of the previous two materials. Utilizing the flexible characteristics of polyvinyl alcohol molecular chains, deformation occurs under interlaminar stress to dissipate energy and alleviate stress concentration, while simultaneously forming a dual toughening mechanism in conjunction with the dynamic crosslinking network. Furthermore, strong interfacial bonding ensures effective stress transfer between layers, resulting in more uniform interlaminar stress and thus significantly improving the interlaminar toughness of the composite material.

[0048] The above description is not intended to limit the present invention in any way. Although the present invention has been disclosed through the above embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing a fiber composite material with high gas barrier properties and interlaminar toughness, characterized in that, Includes the following steps: S1. Polyvinyl alcohol is dissolved in deionized water and a boron-based modifier is added. The mass ratio of polyvinyl alcohol to boron-based modifier is 100:

10. After adjusting the pH with triethanolamine, a zinc ion complexing agent is added. The mass ratio of polyvinyl alcohol, boron-based modifier and zinc ion complexing agent is 100:10:3, to obtain a boron ester dynamically crosslinked polyvinyl alcohol solution. S2. The boron ester dynamically cross-linked polyvinyl alcohol solution in S1 is cast into a polytetrafluoroethylene mold to obtain a core layer film; S3. The boron ester dynamically cross-linked polyvinyl alcohol solution and graphene oxide dispersion in S1 are mixed and ultrasonically dispersed, and then coated onto the surface of the core layer film using a slit-type doctor blade to form a shell layer, thus obtaining a core-shell structured composite film. S4. Desizing basalt fiber cloth is modified with a boron coupling agent and subjected to plasma treatment before being impregnated with resin to obtain a prepreg. S5. The prepreg in S4 is then laid layer by layer with the core-shell structure composite film in S3 and hot-pressed to obtain basalt fiber composite material.

2. The method for preparing a fiber composite material with high gas barrier properties and interlaminar toughness according to claim 1, characterized in that, The boron-based modifier in S1 is at least one of 3-aminophenylboronic acid, 4-carboxyphenylboronic acid, or tributyl borate.

3. The method for preparing a fiber composite material with high gas barrier properties and interlaminar toughness according to claim 1, characterized in that, The zinc ion coordinating agent in S1 is one of zinc acetate, zinc nitrate, or zinc chloride.

4. The method for preparing a fiber composite material with high gas barrier properties and interlaminar toughness according to claim 1, characterized in that, In step S1, the mass ratio of polyvinyl alcohol, boron-based modifier, and zinc ion ligand is 100:10:

3.

5. The method for preparing a fiber composite material with high gas barrier properties and interlaminar toughness according to claim 1, characterized in that... In step S3, the composite film has a core-shell structure, with the core layer being a polyvinyl alcohol / zinc ion coordination system and the shell layer being a graphene oxide / boron ester crosslinking system, and the graphene oxide sheet orientation degree being ≥85%.

6. The method for preparing a fiber composite material with high gas barrier properties and interlaminar toughness according to claim 1, characterized in that, The formation process of the core-shell composite film in S3 is a staged casting and gradient drying process; Core layer preparation: 50g of the boron ester dynamic crosslinked polyvinyl alcohol solution prepared by the S1 process in claim 1 is cast into a 200mm×200mm polytetrafluoroethylene mold and pre-dried at 50℃ and vacuum degree -0.09MPa for 4h to form a core layer substrate with a thickness of 12μm; Shell layer coating: 25g of graphene oxide dispersion with a concentration of 2.5mg / mL is mixed with 75g of the boron ester dynamic crosslinked polyvinyl alcohol solution in S1, and ultrasonically dispersed at 45kHz and 350W for 70min, and then dispersed through an ultrasonic vibrating screen with 5μm sieve holes for 40min; The mixture was coated onto the surface of the core layer film using a slit-type doctor blade at a coating speed of 0.3 m / min, forming a shell layer with a thickness of 23 μm. The mold with the coated shell layer was placed in a vacuum drying oven and dried at 60℃ and a vacuum of -0.09 MPa for 4 h. Then, the temperature was raised to 70℃ and the vacuum was kept constant for 3 h. After cooling to room temperature, the mold was demolded to obtain a core-shell composite film with a total thickness of 35 μm.

7. The method for preparing a fiber composite material with high gas barrier properties and interlaminar toughness according to claim 1, characterized in that, The mass concentration of the boron ester dynamically crosslinked polyvinyl alcohol solution in S1 is 13%.

8. The method for preparing a fiber composite material with high gas barrier properties and interlaminar toughness according to claim 1, characterized in that, In step S4, the basalt fiber cloth is soaked in a 2.5% borane coupling agent solution at room temperature for 55 minutes and dried at 135°C for 3.5 hours. Then it is placed in a plasma device, and a mixture of argon and carbon dioxide gas is introduced with a volume ratio of argon to carbon dioxide of 3:1 and a power of 550W for 18 minutes. The resin used in step S4 is a diphenyl ether type bismaleimide and an allyl phenolic resin with a mass ratio of 8:

2. The fiber fabric is then heated and melt-impregnated at 95°C to obtain a prepreg.

9. The method for preparing a fiber composite material with high gas barrier properties and interlaminar toughness according to claim 1, characterized in that, In step S5, the layers are laid in the order of prepreg-core-shell composite film-prepreg, for a total of 12 layers of prepreg and 11 layers of core-shell composite film; the film is cured by a three-gradient heating process with hot pressing temperature of 130℃-190℃ and time of 1.5h-3.5h, and hot pressing pressure of 15MPa.

Images