A lightweight high-strength honeycomb core and a method for preparing the same

Abstract

The application relates to the technical field of high-performance composite materials, in particular to a light-weight high-strength honeycomb core material and a preparation method thereof. The composite paper base of the honeycomb core material comprises, in percentage by mass, 40-70% of p-aramid short-cut fibers, 10-40% of polyimide short-cut fibers and 15-30% of p-aramid fibrids.

Description

Technical Field

[0001] This invention relates to the field of high-performance composite materials technology, specifically to a lightweight, high-strength honeycomb core material and its preparation method. Background Technology

[0002] With the rapid development of the aviation industry and the continuous improvement of aircraft passenger capacity, range, and speed, higher demands are being placed on the performance of aircraft materials. The application of lightweight, high-strength materials is particularly important in aircraft design. Currently, a certain type of passenger aircraft widely uses aramid paper honeycomb sandwich composite materials in the wing-fuselage fairing, directly reducing weight by approximately 30%. Therefore, research on lightweight honeycomb sandwich composite materials based on aramid paper, and the development of honeycomb design and fabrication processes that balance lightweighting with excellent mechanical properties, are urgently needed to provide key material support and technological reserves for the next generation of aircraft.

[0003] Aramid paper honeycomb possesses excellent properties such as high specific strength, specific modulus, low dielectric constant, good weather resistance, and flame retardancy, making it a core material for aircraft honeycomb sandwich composite structures. It is widely used in secondary load-bearing structures of the airframe, cabin components, and radar radomes. Currently, the lowest density of aramid paper honeycomb used in aircraft is 48 kg / m³, which is insufficient to meet the further weight reduction requirements of new, multi-functional aircraft.

[0004] Aramid paper honeycomb is one of the best lightweight structural core materials available today, widely used in the aerospace industry. Among them, honeycomb core materials made from para-aramid (such as PPTA and aramid 1414) have the highest specific strength and specific modulus. However, pure para-aramid paper has some inherent drawbacks that limit its adoption in more cost-sensitive and diverse fields: (1) High brittleness and poor process adaptability: Para-aramid molecular chains are extremely rigid, resulting in a hard and brittle texture after papermaking. During the key processes of coating, stacking and stretching in honeycomb manufacturing, micro-cracks are easily generated, leading to node cracking and low yield.

[0005] (2) Poor resin wettability: The surface of para-aramid is chemically inert and has weak adhesion to the impregnating resin, which affects the final node strength and compressibility of the honeycomb.

[0006] (3) High cost: High-performance para-aramid paper is mostly imported and is expensive. Summary of the Invention

[0007] Purpose of the invention: This invention provides a lightweight, high-strength honeycomb core material and its preparation method to meet the requirements of weight reduction and mechanical properties of honeycomb core materials for civil aircraft.

[0008] Technical solution: A lightweight, high-strength honeycomb core material, wherein the composite paper base used in the honeycomb core material comprises, by weight percentage: 40%–70% para-aramid chopped fibers; 10%–40% polyimide chopped fibers; and 15%–30% para-aramid precipitated fibers.

[0009] Furthermore, the composite paper base also includes, by mass percentage, 10% meta-aramid precipitated fibers.

[0010] A method for preparing a lightweight, high-strength honeycomb core material, the method comprising: S1, Determine the fiber raw materials for the composite paper base: by mass percentage, para-aramid chopped fibers: 40%–70%; polyimide chopped fibers: 10%–40%; para-aramid precipitated fibers: 15%–30%; S2, the fiber raw materials are added into the hydrapulper in proportion to form a uniform mixed pulp; S3, the paper is printed to obtain a wet paper sheet; S4. The wet paper sheet is dried and calendered on a high-temperature hot press: the hot pressing temperature is increased in a gradient: 200-250℃ in the first zone, 250-300℃ in the second zone, and 300-330℃ in the third zone; the linear pressure is 60-150 kN / m; and the machine speed is 5-15m / min. S5: Apply adhesive to the composite paper base; S6, using a staggered lamination method to laminate and press the composite paper base, so that the adhesive strip is cured to form a strong node, thus producing a honeycomb laminated board; S7, cutting, stretching and shaping to obtain bare honeycomb; S8 is used to impregnate and cure bare honeycomb to obtain honeycomb core material.

[0011] Furthermore, S2 specifically refers to: The fiber raw materials are added into a hydrapulper in proportion and dispersed in weakly alkaline water with a pH of 7.5 to 9.5 to form a uniform mixed pulp with a pulp concentration of 0.1% to 0.5%.

[0012] Furthermore, S3 specifically refers to: using an inclined wire paper machine to form the mixed pulp into shape, and after pressing and dewatering, obtaining a wet paper sheet.

[0013] Furthermore, in S4, the hot pressing temperature adopts a gradient increase: 200-250℃ in the first zone, 250-300℃ in the second zone, and 300-330℃ in the third zone; the linear pressure is 60-150 kN / m; and the vehicle speed is 5-15 m / min.

[0014] Furthermore, S5 specifically includes: Before applying the adhesive, the epoxy-modified phenolic resin needs to be diluted to a certain viscosity. According to the specifications of the honeycomb core material, the adhesive is applied to the composite paper base. The width of the adhesive strip is 2mm to 4mm.

[0015] Furthermore, S7 specifically includes: According to the specifications of the honeycomb core material, the honeycomb laminate is cut and stretched according to the usage height using a paper cutter. After the grid size meets the requirements, the honeycomb is shaped.

[0016] Furthermore, in S8, the core impregnation resin is one or both of low molecular weight epoxy resin and phenolic resin.

[0017] Furthermore, in S8, the curing curve is as follows: hold at 80-100℃ for 30 minutes, then gradually increase the temperature to 150℃ and 180℃ and hold for 1-2 hours respectively.

[0018] Beneficial effects: This invention uses paper-based materials prepared from para-aramid fibers and polyimide fibers, and epoxy-modified phenolic resin as the core adhesive. The honeycomb core material prepared by impregnating the core with phenolic resin has the characteristics of being lightweight, high-strength, high-toughness, and having excellent processability. It can meet the usage requirements of integrated structural / transmission functions such as radar radomes, and will significantly improve the transmission frequency domain and angular domain of radar radomes.

[0019] (1) Synergistic reinforcement and excellent performance: Para-aramid fibers provide a foundation for extremely high strength and modulus. The introduction of polyimide fibers, like "micro-ligaments," effectively improves the brittleness of pure aramid paper with its excellent flexibility and toughness, reduces crack generation during honeycomb manufacturing and subsequent processing, and improves the yield. At the same time, the high strength and temperature resistance of polyimide fibers themselves ensure that the mechanical and thermal properties of the composite material do not decrease.

[0020] (2) Improved processability: The flexibility and toughness of the composite paper base are improved, making it more resistant to mechanical stress during coating, lamination and stretching, reducing the risk of defects such as node cracking and S-shaped holes, and making the process window wider and more suitable for large-scale civilian production.

[0021] (3) Optimize interfacial bonding: The compatibility of polyimide fibers with precipitated fibers and impregnating resins may be better than that of para-aramid fibers, which helps to form stronger fiber-fiber interfaces and fiber-resin interfaces, thereby significantly improving the node strength and overall mechanical properties of the honeycomb, such as planar compressive strength and shear strength.

[0022] (4) Balanced cost: By using some domestically produced polyimide fiber and para-aramid fiber composite, the dependence on imported para-aramid paper can be effectively reduced while maintaining excellent performance, making the overall cost more competitive and conducive to promotion in the civilian market. Detailed Implementation

[0023] Polyimide (PI) fiber is another high-performance organic fiber that not only possesses excellent high-temperature resistance, flame retardancy, and high specific strength comparable to para-aramid, but also exhibits better UV aging resistance and flexibility. Currently, there are no reports of mature technologies for compounding polyimide fibers with para-aramid fibers at the paper-based stage for the preparation of lightweight, high-strength honeycomb for civilian use.

[0024] This application combines polyimide fibers and para-aramid fibers in the paper-based stage, overcoming the shortcomings of the prior art, and provides a lightweight, high-strength, high-toughness, relatively low-cost, and excellent processability polyimide-aramid composite paper-based honeycomb core material and its preparation method.

[0025] The lightweight and high-strength honeycomb core material provided in this application comprises, by weight percentage: 40%–70% para-aramid chopped fiber; 10%–40% polyimide chopped fiber; and 15%–30% para-aramid precipitated fiber.

[0026] In one possible embodiment, the composite paper base further includes, by weight percentage, 10% meta-aramid precipitated fibers.

[0027] A method for preparing a lightweight, high-strength honeycomb core material includes: Step 1, fiber raw material ratio for composite paper base: by mass percentage, para-aramid chopped fiber: 40%–70%; polyimide chopped fiber: 10%–40%; para-aramid precipitated fiber: 15%–30%. Optionally, up to 10% of the total mass of meta-aramid precipitated fibers may be added as an auxiliary binder.

[0028] Step 2, Pulp preparation: The above-mentioned fiber raw materials are put into a hydrapulper in proportion and dispersed in weakly alkaline water with a pH of 7.5 to 9.5 to form a uniform mixed pulp with a pulp concentration of 0.1% to 0.5%.

[0029] Step 3, papermaking: The mixed pulp is formed using an inclined wire papermaking machine, and after pressing and dewatering, a wet paper sheet is obtained.

[0030] Step 4, High-Temperature Hot Pressing: The wet paper sheets are dried and calendered on a high-temperature hot press. The hot pressing temperature is increased in a gradient: Zone 1 200–250℃, Zone 2 250–300℃, Zone 3 300–330℃; the linear pressure is 60–150 kN / m; and the machine speed is 5–15 m / min. This process melts the para-aramid fibers, firmly bonding the high-strength para-aramid and polyimide fibers together to form a dense, smooth composite paper base.

[0031] Step 5: Glue preparation: Before applying the glue, the epoxy-modified phenolic resin needs to be diluted to a certain viscosity. According to the specifications of the honeycomb core material, the glue is applied to the composite paper base. The width of the glue strip is 2mm to 4mm.

[0032] Step 6, Lamination and Curing: The composite paper base is laminated using a staggered lamination method and pressed under certain temperature and pressure to cure the adhesive strips and form strong nodes, thus producing a honeycomb laminated board.

[0033] Step 7, Slitting, Stretching and Shaping: According to the specifications of the honeycomb core material, the honeycomb laminate is cut according to the usage height using a paper cutter, and then stretched under the set stretching process conditions. After the grid size meets the requirements, it is fixed on the tooling for honeycomb shaping.

[0034] Step 8, Impregnation and Curing: The stretched honeycomb core is impregnated in a resin solution (such as low molecular weight epoxy resin, phenolic resin, or a mixture thereof). The resin content is precisely controlled by adjusting the impregnation time, pulling speed, and resin viscosity (preferably, the resin content of the honeycomb core material is controlled between 25% and 50% (by weight)). Subsequently, curing is carried out in a programmed temperature curing oven. The curing profile is as follows: hold at 80–100°C for 30 minutes to evaporate the solvent, then gradually increase the temperature to 150°C and 180°C and hold for 1–2 hours respectively to ensure complete curing.

[0035] Example 1: Step 1: Preparation of composite paper base: Take 50% para-aramid short chopped fiber (6mm in length), 30% polyimide short chopped fiber (5mm in length), and 20% para-aramid precipitated fiber. After decomposition, inclined wire papermaking, and gradient hot pressing (250℃ / 280℃ / 310℃, linear pressure 100kN / m), a composite paper with a basis weight of 80g / m² is obtained.

[0036] Step 2: Honeycomb Preparation: Epoxy-modified phenolic resin core strips are coated onto the composite paper, with a strip width of 2 mm. After stacking 100 layers, the mixture is pressed at 120℃ and 0.5 MPa for 60 minutes. Following this, it is stretched and shaped at 180℃. It is then impregnated in a 40% solids content phenolic resin ethanol solution, controlling the final resin content to 40% (by weight). Finally, it is cured according to the specified procedure, and sliced ​​to obtain a honeycomb core material with a density of 48 kg / m³ (cell side length 2 mm).

[0037] Example 2: Step 1: Preparation of composite paper base: Take 60% para-aramid short chopped fiber, 15% polyimide short chopped fiber, and 25% para-aramid precipitated fiber to prepare a composite paper with a basis weight of 100 g / m².

[0038] Step 2: The subsequent honeycomb preparation process is the same as in Example 1. By controlling the amount of adhesive applied, a honeycomb core material with a cell side length of 2mm and a density of 56kg / m3 is finally obtained.

[0039] Comparative example: Honeycomb core material was prepared using pure para-aramid paper (imported, basis weight 80 g / m²) under the same process conditions.

[0040] Performance testing: The performance of the honeycomb core materials obtained in the above embodiments and comparative examples was tested, and the results are shown in the table below:

[0041] Test results show that the polyimide-aramid composite paper-based honeycomb core material prepared by this invention has significantly better key mechanical properties (compressive strength and shear strength) than traditional pure aramid paper honeycomb at the same density, while the yield is greatly improved, fully demonstrating the technical advantages of this invention.

[0042] The above detailed embodiments are a description of the present invention. It should not be considered that the specific embodiments of the present invention are limited to these descriptions. For those skilled in the art, several simple deductions and substitutions can be made without departing from the concept of the present invention, and all of these should be considered to fall within the protection scope of the present invention.

Claims

1. A lightweight, high-strength honeycomb core material, characterized in that, The composite paper base used in the honeycomb core material comprises, by weight percentage: 40%–70% para-aramid chopped fiber; 10%–40% polyimide chopped fiber; and 15%–30% para-aramid precipitated fiber.

2. The lightweight, high-strength honeycomb core material according to claim 1, characterized in that, The composite paper base also includes, by weight percentage: 10% of the total weight of meta-aramid precipitated fibers.

3. A method for preparing a lightweight, high-strength honeycomb core material, characterized in that, The method is used to prepare the lightweight, high-strength honeycomb core material according to claim 1 or 2, and the method includes: S1, Determine the fiber raw materials for the composite paper base: by mass percentage, para-aramid chopped fibers: 40%–70%; polyimide chopped fibers: 10%–40%; para-aramid precipitated fibers: 15%–30%; S2, the fiber raw materials are added into the hydrapulper in proportion to form a uniform mixed pulp; S3, the paper is printed to obtain a wet paper sheet; S4. The wet paper sheet is dried and calendered on a high-temperature hot press: the hot pressing temperature is increased in a gradient: 200-250℃ in the first zone, 250-300℃ in the second zone, and 300-330℃ in the third zone; the linear pressure is 60-150 kN / m; and the machine speed is 5-15 m / min. S5: Apply adhesive to the composite paper base; S6, using a staggered lamination method to laminate and press the composite paper base, so that the adhesive strip is cured to form a strong node, thus producing a honeycomb laminated board; S7, cutting, stretching and shaping to obtain bare honeycomb; S8 is used to impregnate and cure bare honeycomb to obtain honeycomb core material.

4. The method for preparing lightweight high-strength honeycomb core material according to claim 3, characterized in that, S2, specifically: The fiber raw materials are added into a hydrapulper in proportion and dispersed in weakly alkaline water with a pH of 7.5 to 9.5 to form a uniform mixed pulp with a pulp concentration of 0.1% to 0.5%.

5. The method for preparing lightweight high-strength honeycomb core material according to claim 3, characterized in that, S3, specifically, involves using an inclined wire paper machine to form the mixed pulp into a sheet, which is then pressed and dewatered to obtain a wet paper sheet.

6. The method for preparing lightweight high-strength honeycomb core material according to claim 3, characterized in that, In S4, the hot pressing temperature adopts a gradient increase: Zone 1 200~250℃, Zone 2 250~300℃, Zone 3 300~330℃; the linear pressure is 60~150 kN / m; the vehicle speed is 5~15 m / min.

7. The method for preparing lightweight high-strength honeycomb core material according to claim 3, characterized in that, S5: Specifically includes: Before applying the adhesive, the epoxy-modified phenolic resin needs to be diluted to a certain viscosity. According to the specifications of the honeycomb core material, the adhesive is applied to the composite paper base. The width of the adhesive strip is 2mm to 4mm.

8. The method for preparing lightweight high-strength honeycomb core material according to claim 3, characterized in that, S7, specifically includes: According to the specifications of the honeycomb core material, the honeycomb laminate is cut and stretched according to the usage height using a paper cutter. After the grid size meets the requirements, the honeycomb is shaped.

9. The method for preparing lightweight high-strength honeycomb core material according to claim 3, characterized in that, In S8, the core impregnation resin is one or both of low molecular weight epoxy resin and phenolic resin.

10. The method for preparing lightweight high-strength honeycomb core material according to claim 3, characterized in that, In S8, the curing curve is as follows: hold at 80-100℃ for 30 minutes, then gradually increase the temperature to 150℃ and 180℃ and hold for 1-2 hours respectively.

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