A nonwoven fabric based on high-temperature resistant ultra-high molecular weight polyethylene fiber and its preparation method

Abstract

This invention relates to the field of textile composite materials technology, and discloses a non-woven fabric based on high-temperature resistant ultra-high molecular weight polyethylene fiber and its preparation method. The method involves corona or plasma treatment of the polyethylene fiber, followed by the formation of an inorganic-organic hybrid coating layer on the fiber surface through a sol-gel hydrolysis-condensation reaction, consisting of a silicon-oxygen network and organosilane fragments. An aqueous polyurethane adhesive containing terminal hydroxyl polydimethylsiloxane fragments is prepared, combined with a blocked polyisocyanate crosslinking agent and hexagonal boron nitride with controlled particle size. This is coated into a unidirectional prepreg sheet, which is then stacked at 0° / 90° and hot-pressed to form the final product. This results in an interlayer bonding structure where the interface transition layer and the crosslinking adhesive work synergistically, improving molding consistency and reducing the risk of interlayer structure fluctuations and visible delamination under heat treatment conditions.

Description

Technical Field

[0001] This invention relates to the field of textile composite materials technology, specifically to a non-woven fabric based on high-temperature resistant ultra-high molecular weight polyethylene fiber and its preparation method. Background Technology

[0002] Non-woven fabrics are typically made by laying high-performance fibers parallel in the same direction to form unidirectional sheets, then cross-laying them at a set angle and combining them with a matrix material. They are characterized by regular structure, controllable mass per unit area, and ease of lamination and molding, and are widely used in protective, lightweight structural components, and composite laminates. Reinforcing materials, represented by ultra-high molecular weight polyethylene fibers, have become important candidates for non-woven fabric systems due to their low density, good chemical resistance, and strong processability.

[0003] In existing technologies, the preparation route for polyethylene nonwoven fabrics is mostly "fiber laying / sheet forming—adhesive application / coating—drying—orthogonal overlay—heat and pressure molding". One type uses epoxy resin or modified epoxy systems as the adhesive matrix, forming a composite nonwoven fabric through roller coating and hot pressing, or by coating polyethylene fibers in a modified epoxy resin solution and then laminating and pressing the fabric. Another type uses water-soluble polyurethane as a base, introducing polyvinylidene fluoride, initiators, glycidyl methacrylate, etc., to form an adhesive system, then coating ultra-high molecular weight polyethylene fibers with the adhesive and drying to obtain the nonwoven fabric. Under these routes, differences in the curing shrinkage, toughness, and heat resistance stability of the adhesive system can lead to differences in interlayer stress and deformation. Simultaneously, the chemical inertness of the ultra-high molecular weight polyethylene fiber surface and the limited number of effective bonding sites make the reliability of the fiber-matrix interface and the structural retention after long-term thermal aging easily affected by fluctuations in the material system and process window, thus limiting the application expansion of nonwoven fabrics under more stringent thermal conditions or lifespan requirements.

[0004] Therefore, it is necessary to propose a non-woven fabric material system and preparation route that meets the requirements of higher thermal conditions, so as to improve its structural stability and consistency under complex conditions. Summary of the Invention

[0005] The present invention aims to address the problems raised in the background art by providing a nonwoven fabric based on high-temperature resistant ultra-high molecular weight polyethylene fiber and its preparation method.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A nonwoven fabric based on high-temperature resistant ultra-high molecular weight polyethylene fiber includes at least two unidirectionally laid ultra-high molecular weight polyethylene fiber unidirectional layers and a resin matrix layer located between adjacent unidirectional layers. Each of the ultra-high molecular weight polyethylene fibers has an inorganic-organic hybrid coating layer on its outer surface, the inorganic-organic hybrid coating layer comprising a cross-linked structure composed of a silicon-oxygen network and organosilane fragments; The resin matrix layer is formed by curing an adhesive, which comprises, by weight, 100 parts of silicone-containing waterborne polyurethane, 3-25 parts of blocked polyisocyanate crosslinking agent, 1-15 parts of hexagonal boron nitride, 0.2-3 parts of aminosilane coupling agent, 0.01-1 parts of hindered phenolic antioxidant, and 0.1-2 parts of dispersant; In the non-woven fabric, the fiber directions of two adjacent unidirectional layers are arranged to cross each other.

[0007] Furthermore, the inorganic-organic hybrid coating layer is formed by a sol-gel hydrolysis-condensation reaction of tetraethoxysilane and aminopropyltriethoxysilane, and the thickness of the inorganic-organic hybrid coating layer is 50~500nm.

[0008] Furthermore, the ultra-high molecular weight polyethylene fiber has a molecular weight higher than 1 million, and the linear density of the ultra-high molecular weight polyethylene fiber is 400~1600 dtex.

[0009] Furthermore, the silicon-containing waterborne polyurethane comprises polycarbonate diol soft segments, diisocyanate hard segments, and hydroxyl-terminated polydimethylsiloxane segments, and the solid content of the silicon-containing waterborne polyurethane is 25~55wt%.

[0010] Furthermore, the D50 particle size of the hexagonal boron nitride is 0.3~5.0μm, and the adhesive is added after the surface of the hexagonal boron nitride has been silanized or hydroxylated.

[0011] Furthermore, the non-woven fabric has a [0 / 90]n-layer structure, where n is 2 to 16, and the areal density of each unidirectional layer is 20 to 120 g / m². 2 The coating amount of the adhesive is 8~35g / m². 2 .

[0012] The present invention also proposes a method for preparing the non-woven fabric, comprising: S1. Fiber pretreatment: Ultra-high molecular weight polyethylene fibers are subjected to corona treatment or plasma treatment, followed by dust removal and drying. S2. Coating layer formation: The pretreated ultra-high molecular weight polyethylene fiber is impregnated in a sol system containing tetraethoxysilane and aminopropyltriethoxysilane and hydrolyzed and condensed to form an inorganic-organic hybrid coating layer on the outer surface of the fiber. S3. Adhesive preparation: The silicone-containing waterborne polyurethane, blocked polyisocyanate crosslinking agent, hexagonal boron nitride, aminosilane coupling agent, hindered phenolic antioxidant and dispersant are mixed and dispersed according to solid content to obtain adhesive. S4. Coating and Sheet Formation: The adhesive is coated onto the ultra-high molecular weight polyethylene fiber and dried to obtain a unidirectional prepreg sheet; S5. Lamination and hot pressing: The multiple layers of the unidirectional prepreg are stacked in the cross fiber direction and then heated and pressed to cure, thus obtaining the non-woven fabric.

[0013] Furthermore, in S2, the pH of the sol system is 3-6, the molar ratio of tetraethoxysilane to aminopropyltriethoxysilane is (3-12):1, the impregnation time is 10-60s, and the condensation temperature is 20-60℃.

[0014] Furthermore, the drying temperature of S4 is 60~95℃ and the drying time is 20~180s, and the hot pressing temperature of S5 is 90~125℃, the hot pressing pressure is 5~20MPa, and the holding time is 10~40min.

[0015] Furthermore, the blocked polyisocyanate crosslinking agent is a trimer, biuret, or adduct derived from hexamethylene diisocyanate or isophorone diisocyanate, and uses caprolactam or methyl ethyl ketone oxime as the blocking agent, and the hydroxyl equivalent ratio of the blocked polyisocyanate crosslinking agent to the silicone-containing waterborne polyurethane is (0.6~1.2):1.

[0016] The present invention has the following beneficial effects: (1) By forming an inorganic-organic hybrid coating layer containing both silicon-oxygen network and organosilane fragments on the outer surface of the fiber after corona / plasma activation, the fiber surface is transformed from a single low-polarity interface into an interface layer with controllable polar groups and silicon-oxygen structure, thereby introducing a stable interface transition layer between the fiber and the adhesive, reducing the risk of discontinuous bonding caused by abrupt changes in interface components, and improving the consistency and repeatability of interlayer bonding. (2) In the adhesive system, waterborne polyurethane containing hydroxyl-terminated polydimethylsiloxane segments is used as the continuous phase, so that the segment composition of the adhesive forms an adjustable structure between the soft segments and the siloxane segments, and forms a compatibility matching relationship with the hybrid coating layer at the level of chemical groups and interfacial energy. This is beneficial to form a more continuous interfacial contact and a more uniform interfacial distribution during the coating and curing process, and reduces the interfacial defects caused by insufficient local wetting from the process perspective. (3) The present invention introduces a closed polyisocyanate crosslinking agent and triggers a crosslinking reaction within the hot-press curing window, so that the adhesive changes from a flowable state to a crosslinked network structure, thereby forming a more stable adhesive phase structure after the non-woven fabric layer is synthesized. This helps to suppress the interlayer structure fluctuation caused by adhesive phase softening, chain segment migration and interface stress concentration under high temperature conditions, and enhances the structural retention ability of the laminated structure during the heat treatment process. (4) The present invention introduces hexagonal boron nitride with controlled particle size into the adhesive and combines it with dispersion and coupling treatment, so that the inorganic filler is uniformly distributed in the adhesive phase at a controllable scale. This can provide stable inorganic phase support in the interface region and reduce the probability of local defects caused by filler agglomeration, thereby improving the uniformity of the interlayer structure and the consistency of molding. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the process for preparing the non-woven fabric of the present invention; Figure 2 This is a schematic diagram of the non-woven fabric laminate structure of the present invention. Detailed Implementation

[0018] The present invention will be further described below with reference to embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention; any equivalent substitutions or conventional adjustments made to the types, proportions, and process parameters of raw materials without departing from the technical features defined in the claims shall fall within the scope of protection of the present invention.

[0019] Terminology Explanation: The "non-woven fabric" described in this invention refers to a sheet material formed by cross-laminating at least two unidirectionally laid ultra-high molecular weight polyethylene fiber unidirectional layers, with a resin matrix layer sandwiched between adjacent unidirectional layers and cured. The "unidirectional layer" refers to a fiber layer formed by fibers arranged substantially parallel to each other and laid in the same direction within the layer; the "resin matrix layer" is formed by coating the fibers with an adhesive and then drying and hot-pressing to cure; "by solids content" refers to the non-volatile components in the adhesive that participate in curing and ultimately remain in the non-woven fabric, measured by mass parts. Water or low-boiling-point solvents are only used to adjust the construction viscosity and dispersion process and are not included in the mass parts of the solids content; "D50" refers to the particle size corresponding to a cumulative particle size distribution of 50%; "linear density" is the mass index per unit length of fiber, expressed using the industry-standard dtex unit.

[0020] Raw materials and equipment specifications: Ultra-high molecular weight polyethylene fibers can be made from continuous filaments or flat bundles with a molecular weight of over 1 million and a linear density of 400~1600 dtex. To ensure unidirectional laying stability, the fibers can be pre-treated with tension warping and dust removal.

[0021] Tetraethoxysilane and aminopropyltriethoxysilane can be used as silicon and organosilane sources for the sol system; the solvent for the sol system can be a mixture of anhydrous ethanol and deionized water, and the acid catalyst can be glacial acetic acid or dilute hydrochloric acid to adjust the pH.

[0022] Silicon-containing waterborne polyurethane can be an aqueous dispersion containing polycarbonate diol soft segments, diisocyanate hard segments, and hydroxyl-terminated polydimethylsiloxane segments, with a solid content that can be controlled at 25-55% by mass.

[0023] The blocked polyisocyanate crosslinking agent can be a trimer, biuret or adduct with hexamethylene diisocyanate or isophorone diisocyanate as the isocyanate source, and caprolactam or methyl ethyl ketone oxime can be used as the blocking agent.

[0024] Hexagonal boron nitride can be selected as powder with a D50 of 0.3~5.0 micrometers, and after surface silanization or hydroxylation treatment, an adhesive is added.

[0025] The aminosilane coupling agent can be an aminopropylsilane; the hindered phenolic antioxidant can be 2,6-di-tert-butyl-p-cresol or pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]; the dispersant can be a polycarboxylate or phosphate ester dispersant.

[0026] Process equipment may include a corona treatment machine or an atmospheric pressure plasma treatment machine, an impregnation tank and traction roller assembly, a metering doctor blade / slit coating head, a hot air drying tunnel, and a flatbed hot press.

[0027] Overall process flow: S1. Fiber Pretreatment: Ultra-high molecular weight polyethylene (UHMWPE) fibers are introduced into the treatment zone under controlled tension for corona treatment or plasma treatment to enhance the activation of the fiber's outer surface. After treatment, oil-free compressed air or an electrostatic precipitator is used to remove floating dust, followed by short-term drying under hot air conditions at 40-70℃ to remove residual surface moisture and volatiles. Corona treatment can be performed at a power of 0.8-2.5 kW and a processing speed of 2-10 m / min; plasma treatment can be performed at a power of 50-200 W and a processing time of 5-30 seconds. These parameters can be adjusted according to the fiber bundle width and linear density.

[0028] S2. Coating Layer Formation: Prepare the sol system. Mix deionized water and ethanol at a mass ratio of 5:95 to 30:70, and add an acid catalyst to adjust the pH of the solution to 3-6. Under stirring, first add tetraethoxysilane, then add aminopropyltriethoxysilane, controlling the molar ratio of tetraethoxysilane to aminopropyltriethoxysilane at (3-12):1, and continue stirring for 10-40 minutes to complete the initial hydrolysis. Subsequently, pass the S1-treated fibers through the impregnation tank at a constant speed, controlling the impregnation time to 10-60 seconds. After exiting the tank, the liquid volume can be controlled using a squeezing roller or scraping structure, and condensation curing is carried out at 20-60℃ to form an inorganic-organic hybrid coating layer on the outer surface of the fibers. This coating layer is composed of a cross-linked structure consisting of a silicon-oxygen network and organosilane fragments: the silicon-oxygen network originates from the inorganic skeleton generated by the hydrolysis and condensation of tetraethoxysilane, and the organosilane fragments originate from the participation of aminopropyltriethoxysilane in condensation and grafting. By controlling the sol concentration, the amount of impregnation solution, and the condensation time, the coating thickness can be stabilized within the range of 50 to 500 nanometers; the thickness can be characterized by cross-sectional observation using transmission electron microscopy or by ellipsometric / atomic force microscopy.

[0029] S3. Adhesive Preparation: Weigh 100 parts by weight of silicone-containing waterborne polyurethane, 3-25 parts by weight of blocked polyisocyanate crosslinking agent, 1-15 parts by weight of hexagonal boron nitride, 0.2-3 parts by weight of aminosilane coupling agent, 0.01-1 parts by weight of hindered phenolic antioxidant, and 0.1-2 parts by weight of dispersant according to solid content. To reduce powder agglomeration, first dissolve / disperse the dispersant in part of the silicone-containing waterborne polyurethane, add hexagonal boron nitride and disperse using high-speed shearing or bead milling for 30-90 minutes to achieve the required fineness of the slurry; then add aminosilane coupling agent and hindered phenolic antioxidant and continue stirring for 10-30 minutes; finally, add blocked polyisocyanate crosslinking agent under low shear conditions and stir for 10-20 minutes to obtain the adhesive. The hydroxyl equivalent ratio of blocked polyisocyanate crosslinking agent to silicone-containing waterborne polyurethane can be controlled at (0.6-1.2):1 to match the deblocking and crosslinking reaction process under the subsequent hot pressing temperature window. The application viscosity of the adhesive can be adjusted by adding deionized water, and the added water is not included in the solid content.

[0030] S4. Coating and Sheet Formation: The ultra-high molecular weight polyethylene fibers with the coating layer formed in S2 are laid out unidirectionally. Combing, tension guiding, and yarn spreading structures can be used to ensure the fibers are parallel, straight, and form a continuous unidirectional fiber strip. Subsequently, the adhesive obtained in S3 is coated onto the fiber strip surface using blade coating, slot coating, or roller coating methods, allowing the adhesive to penetrate the fiber gaps and form a continuous coating on the fiber surface. The adhesive coating amount can be controlled at 8~35 g / m², and the unidirectional layer density can be controlled at 20~120 g / m². After coating, the fibers are dried in an oven at a temperature controlled at 60~95℃ for 20~180 seconds to remove moisture and obtain a unidirectional prepreg sheet. After drying, the prepreg sheet retains a certain degree of heat-melt fluidity to facilitate subsequent lamination and hot pressing for densification.

[0031] S5. Lamination and Hot Pressing: Multiple unidirectional prepreg layers are stacked according to their cross-fiber directions, ensuring that the fiber directions of adjacent unidirectional layers intersect. A [0 / 90]n lamination structure can be used, where n is 2~16. After stacking, the layers are placed in a flatbed hot press, where a pressure of 5~20MPa is applied at 90~125℃ and held for 10~40 minutes. This allows the closed-cell polyisocyanate to gradually unblock within this temperature window and cross-link with the hydroxyl groups in the silicone-containing waterborne polyurethane. Simultaneously, the adhesive fully impregnates the fibers and fills the interlayer gaps under pressure, ultimately curing to form a resin matrix layer and completing the non-woven fabric molding. After hot pressing, the layers can be cooled to 40~60℃ under holding pressure before depressurization to reduce the probability of micropore formation caused by interlayer springback.

[0032] Surface treatment of hexagonal boron nitride: To meet the requirements of silanization or hydroxylation treatment of hexagonal boron nitride surface, any of the following methods can be used: Hydroxylation treatment: Add hexagonal boron nitride to a sodium hydroxide aqueous solution with a mass fraction of 2-5%, stir at 60-85℃ for 1-3 hours; after filtration, wash with deionized water until the filtrate is nearly neutral, and dry at 60-80℃ for 2-6 hours to obtain surface hydroxylated hexagonal boron nitride.

[0033] Silanization treatment: Hexagonal boron nitride is dispersed in an ethanol / water mixture (95 / 5 by volume), 0.5-3% by mass of a silane coupling agent is added, and the pH is adjusted to 4-6. The mixture is stirred at room temperature to 50°C for 1-4 hours. After filtration, washing, and drying, surface-silanized hexagonal boron nitride is obtained. The coupling agent used for silanization treatment can be an amino- or epoxy-containing silane to enhance its compatibility with the waterborne polyurethane dispersion.

[0034] Sources of silicone-containing waterborne polyurethane: Silicone-containing waterborne polyurethane can be directly selected from commercially available products; alternatively, it can be prepared using the following method: using polycarbonate diol as the soft segment raw material, hexamethylene diisocyanate or isophorone diisocyanate as the hard segment raw material, hydroxyl-terminated polydimethylsiloxane as the silicone-containing segment, introducing carboxyl-containing diol as the hydrophilic chain extender monomer, and after prepolymerization, neutralizing, dispersing, and chain extending to obtain a waterborne polyurethane dispersion; the solid content of the obtained dispersion can be controlled at 25~55% by mass, and a certain amount of hydroxyl groups that can react with blocked polyisocyanates are retained in the dispersion to meet the requirements of subsequent crosslinking and curing.

[0035] Example 1: Preparation of [0 / 90] 4-layer nonwoven fabric (n=4).

[0036] Ultra-high molecular weight polyethylene fiber filament bundles with a molecular weight higher than 1 million and a linear density of 1000 dtex were taken and subjected to corona treatment under controllable tension conditions (power 1.5kW, treatment speed 5m / min). After treatment, dust was removed by oil-free compressed air and dried under 60℃ hot air conditions for 60s.

[0037] Preparation of the sol-gel system: Ethanol and deionized water were mixed at a mass ratio of 90 / 10, and glacial acetic acid was added to adjust the pH of the solution to 4.6. Tetraethoxysilane was added first, followed by aminopropyltriethoxysilane, under stirring to achieve a molar ratio of 7:1. Stirring was continued for 25 minutes to complete the initial hydrolysis. The treated fibers were then impregnated for 30 seconds. After removal from the sol-gel, the liquid level was controlled using a squeezing roller, and the fibers were condensed and cured at 40°C for 30 minutes to form an inorganic-organic hybrid coating layer on the outer surface of the fibers.

[0038] Adhesive formulation (by solids content): 100 parts by weight of silicone-containing waterborne polyurethane (the silicone-containing waterborne polyurethane comprises polycarbonate diol soft segments, diisocyanate hard segments, and hydroxyl-terminated polydimethylsiloxane segments, with a solids content of 40 wt%), 12 parts by weight of blocked polyisocyanate crosslinking agent (using hexamethylene diisocyanate trimer as the isocyanate source and caprolactam blocking), 8 parts by weight of hexagonal boron nitride (D50=1.2μm, silanized), 1.0 part by weight of aminosilane coupling agent, 0.20 parts by weight of hindered phenolic antioxidant, and 0.50 parts by weight of dispersant. During preparation, the dispersant is first added to the silicone-containing waterborne polyurethane and stirred evenly. Hexagonal boron nitride is then added and dispersed at high speed for 60 minutes. Next, an aminosilane coupling agent and a hindered phenolic antioxidant are added and stirred for 15 minutes. Finally, a blocked polyisocyanate crosslinking agent is added under low shear conditions and stirred for 15 minutes. The application viscosity is adjusted to a coatable state with deionized water. The hydroxyl equivalent ratio of the blocked polyisocyanate crosslinking agent to the silicone-containing waterborne polyurethane is controlled at 0.90:1.

[0039] The coated fibers are spread out and laid unidirectionally to form unidirectional layers, with the areal density of each unidirectional layer controlled at 60 g / m². 2 Slot coating was used to achieve an adhesive coating amount of 18 g / m². 2 The unidirectional prepreg was dried at 80°C for 90 seconds to obtain a unidirectional prepreg. Eight layers of unidirectional prepreg were stacked alternately at 0° / 90° to form a [0 / 90] 4-layer structure. The prepreg was placed in a hot press and held at 110°C and 12MPa for 25 minutes. After cooling to 50°C, the prepreg was demolded to obtain the nonwoven fabric.

[0040] Example 2: Preparation of [0 / 90] 8-layer nonwoven fabric (n=8).

[0041] Ultra-high molecular weight polyethylene fiber filament bundles with a molecular weight higher than 1 million and a linear density of 1550 dtex were taken and subjected to plasma treatment (power 180W, treatment time 20s) under controllable tension. After treatment, oil-free compressed air was used for dust removal, and the fibers were dried under 65℃ hot air conditions for 80s.

[0042] Preparation of the sol-gel system: Ethanol and deionized water were mixed at a mass ratio of 75 / 25, and glacial acetic acid was added to adjust the pH of the solution to 5.8. Tetraethoxysilane was added first, followed by aminopropyltriethoxysilane, under stirring to achieve a molar ratio of 11:1. Stirring was continued for 35 minutes to complete the initial hydrolysis. The treated fibers were then impregnated for 55 seconds. After removal from the sol-gel, the liquid level was controlled using a squeezing roller, and the fibers were condensed and cured at 58°C for 20 minutes to form an inorganic-organic hybrid coating layer on the outer surface of the fibers.

[0043] Adhesive formulation (by solids content): 100 parts by weight of silicone-containing waterborne polyurethane (the silicone-containing waterborne polyurethane comprises polycarbonate diol soft segments, diisocyanate hard segments, and hydroxyl-terminated polydimethylsiloxane segments, with a solids content of 53 wt%), 23 parts by weight of blocked polyisocyanate crosslinking agent (using isophorone diisocyanate biuret as the isocyanate source and methyl ethyl ketone oxime blocking), 14 parts by weight of hexagonal boron nitride (D50=0.40 μm, hydroxylated), 2.60 parts by weight of aminosilane coupling agent, 0.80 parts by weight of hindered phenolic antioxidant, and 1.70 parts by weight of dispersant. In the preparation process, the dispersant is first added to the silicone-containing waterborne polyurethane and stirred evenly. Hexagonal boron nitride is then added and dispersed using a bead mill or high-speed mill for 90 minutes. Next, an aminosilane coupling agent and a hindered phenolic antioxidant are added and stirred for 20 minutes. Finally, a blocked polyisocyanate crosslinking agent is added under low shear conditions and stirred for 15 minutes. The application viscosity is adjusted to a coatable state with deionized water. The hydroxyl equivalent ratio of the blocked polyisocyanate crosslinking agent to the silicone-containing waterborne polyurethane is controlled at 1.15:1.

[0044] The coated fibers are spread out and laid unidirectionally to form unidirectional layers, with the areal density of each unidirectional layer controlled at 100 g / m². 2 Slot coating was used to achieve an adhesive coating amount of 30 g / m². 2 The unidirectional prepreg was dried at 93℃ for 40s to obtain a unidirectional prepreg. Sixteen layers of unidirectional prepreg were stacked alternately at 0° / 90° to form an 8-layer [0 / 90] composite structure. The prepreg was placed in a hot press and held at 123℃ and 18MPa for 12min. After cooling to 55℃, the prepreg was demolded to obtain the nonwoven fabric.

[0045] Example 3: Preparation of [0 / 90] 2-layer nonwoven fabric (n=2).

[0046] Ultra-high molecular weight polyethylene fiber filament bundles with a molecular weight higher than 1 million and a linear density of 450 dtex were taken and subjected to corona treatment under controllable tension (power 0.9 kW, treatment speed 8 m / min). After treatment, oil-free compressed air was used for dust removal, and the fibers were dried in hot air at 55℃ for 120 s.

[0047] Preparation of the sol-gel system: Ethanol and deionized water were mixed at a mass ratio of 95 / 5, and glacial acetic acid was added to adjust the pH of the solution to 3.2. Tetraethoxysilane was added first, followed by aminopropyltriethoxysilane, under stirring to achieve a molar ratio of 3.5:1. Stirring was continued for 15 minutes to complete the initial hydrolysis. The treated fibers were then impregnated for 12 seconds. After removal from the sol-gel, the liquid level was controlled using a squeezing roller, and the fibers were condensed and cured at 22°C for 45 minutes to form an inorganic-organic hybrid coating layer on the outer surface of the fibers.

[0048] Adhesive formulation (by solids content): 100 parts by weight of silicone-containing waterborne polyurethane (the silicone-containing waterborne polyurethane comprises polycarbonate diol soft segments, diisocyanate hard segments, and hydroxyl-terminated polydimethylsiloxane segments, with a solids content of 28 wt%), 4 parts by weight of blocked polyisocyanate crosslinking agent (using hexamethylene diisocyanate adduct as the isocyanate source and caprolactam blocking), 2 parts by weight of hexagonal boron nitride (D50=3.8μm, silanized), 0.25 parts by weight of aminosilane coupling agent, 0.03 parts by weight of hindered phenolic antioxidant, and 0.15 parts by weight of dispersant. During preparation, the dispersant is first added to the silicone-containing waterborne polyurethane and stirred evenly. Hexagonal boron nitride is then added and dispersed at high speed for 45 minutes. Next, an aminosilane coupling agent and a hindered phenolic antioxidant are added and stirred for 15 minutes. Finally, a blocked polyisocyanate crosslinking agent is added under low shear conditions and stirred for 10 minutes. The application viscosity is adjusted to a coatable state with deionized water. The hydroxyl equivalent ratio of the blocked polyisocyanate crosslinking agent to the silicone-containing waterborne polyurethane is controlled at 0.65:1.

[0049] The coated fibers are spread out and laid unidirectionally to form unidirectional layers, with the areal density of each unidirectional layer controlled at 25 g / m². 2 Slot coating was used to achieve an adhesive coating amount of 10 g / m². 2 The unidirectional prepreg was dried at 62℃ for 170s to obtain a unidirectional prepreg. Four layers of unidirectional prepreg were stacked alternately at 0° / 90° to form a [0 / 90] 2-layer structure. The prepreg was placed in a hot press and held at 92℃ and 6MPa for 35min. After cooling to 45℃, the prepreg was demolded to obtain the nonwoven fabric.

[0050] Comparative Example 1: The S2 coating layer formation step was not performed; that is, the fibers were directly introduced into S3 after only undergoing corona treatment, dust removal and drying as in Example 1. The remaining steps (S3 adhesive formulation and preparation sequence, S4 sheeting conditions, S5 [0 / 90]4 stacking and hot pressing conditions) were performed as in Example 1 to obtain the non-woven fabric sample of Comparative Example 1.

[0051] Comparative Example 2: Perform S1 and S2 according to Example 1; the difference is that no blocked polyisocyanate crosslinking agent is added to the adhesive in S3, and the remaining components and solid content by weight are the same as in Example 1; S4 and S5 are both performed according to Example 1 to obtain the non-woven fabric sample of Comparative Example 2.

[0052] Comparative Example 3: S1 and S2 were performed according to Example 1; the difference was that hexagonal boron nitride in S3 was selected as powder with D50=8.0μm, and the amount added was still set according to the solid content mass fraction of Example 1. The other components and preparation order were the same as in Example 1. S4 and S5 were performed according to Example 1 to obtain the non-woven fabric sample of Comparative Example 3.

[0053] Comparative Example 4: S1 and S2 were performed according to Example 1; the difference was that in S3, the adhesive system was replaced with an epoxy / amine curing system, which was prepared by mixing 100 parts by weight of epoxy resin, 25 parts by weight of diaminodiphenylmethane, and 0.5 parts by weight of polysiloxane defoamer; S4 and S5 (unidirectional lay-up method, coating amount, drying conditions, [0 / 90]4 overlay and hot pressing conditions) were performed according to Example 1 to obtain the non-woven fabric sample of Comparative Example 4.

[0054] Comparative Example 5: Perform S1 and S2 according to Example 1; the difference is that in S3, the adhesive system is replaced with a water-soluble polyurethane-glycidyl methacrylate-initiator premixed system and further mixed with polyvinylidene fluoride to obtain an adhesive system, and the other components are not added; the replaced adhesive system is prepared by premixing water-soluble polyurethane 100, glycidyl methacrylate 5, and initiator 0.5 by mass and then dispersing it with polyvinylidene fluoride 10; S4 and S5 are both performed according to Example 1 to obtain the non-woven fabric sample of Comparative Example 5.

[0055] Comparative Example 6: Perform S1 and S2 according to Example 1; the difference is that in S3, "silicone-containing waterborne polyurethane" is replaced with "waterborne polyurethane dispersion without terminal hydroxyl polydimethylsiloxane fragments", and its solid content is adjusted to 40 wt% to be consistent with the construction diameter of Example 1; except for the above substitution, the solid content of the blocked polyisocyanate crosslinking agent, hexagonal boron nitride, aminosilane coupling agent, hindered phenolic antioxidant and dispersant and the preparation order are all performed according to Example 1, and the hydroxyl equivalent ratio of crosslinking agent to waterborne polyurethane is controlled according to the diameter of Example 1; S4 and S5 are both performed according to Example 1, and the non-woven fabric sample of Comparative Example 6 is obtained.

[0056] Comparative Example 7: Perform S1, S3, S4 and S5 according to Example 1; the difference is that in the S2 coating layer formation step, only tetraethoxysilane is used for hydrolysis and condensation to form the coating layer, and aminopropyltriethoxysilane is not added, so that the coating layer contains only a silicon-oxygen network and does not contain organosilane fragments; except for not adding aminopropyltriethoxysilane, the other conditions in S2 are performed according to Example 1, and the non-woven fabric sample of Comparative Example 7 is obtained.

[0057] Performance testing method: To standardize the testing approach, all samples (Examples 1-3, Comparative Examples 1-7) were prepared and cut using a uniform laminated structure and sheet construction method, i.e., the laminated structure was [0 / 90]8, and the density of each unidirectional layer was 60 g / m³. 2 The adhesive coating amount is 20g / m 2Except for the differences in the composition / process of the S2 coating layer or the adhesive system / components of the S3 group, the other materials and process steps are performed according to the description of the corresponding examples or comparative examples.

[0058] (1) Heat treatment conditions: After cutting each group of non-woven fabrics into samples of the specified size, they were conditioned for 24 hours at (23±2)℃ and (50±5)% relative humidity. Then, a portion of the samples were placed in a (115±2)℃ forced-air oven for 168 hours for testing the "mechanical and interlayer bonding retention rate before and after heat treatment". Another portion of the samples were placed in a (115±2)℃ forced-air oven for 800 hours for recording the "appearance and delamination / bubbling area". After heat treatment, the samples were placed at (23±2)℃ for 2 hours before subsequent tests.

[0059] (2) Interlayer peel strength test: The sample was cut into strips of (200±5)mm×(25±0.5)mm. During the stacking and hot pressing stage, a polytetrafluoroethylene film of (50±5)mm in length and (25±0.5)mm in width was pre-placed at one end of the sample as a pre-crack. After curing, a peelable end was formed. A tensile testing machine was used to perform a 180° peel test at a speed of (100±10)mm / min. The average load of the stable peel section was recorded and converted into peel strength, with the unit being N / 25mm. Five parallel samples were taken from each group, and the mean and standard deviation were taken.

[0060] (3) Short beam shear strength test: The sample was cut into a rectangular strip of (20±0.2)mm×(6±0.2)mm with the same thickness as the original fabric. The three-point bending short beam method was used for loading. The span was set at (4±0.1) times the sample thickness, and the loading rate was (1.0±0.1)mm / min. The failure load was recorded and the short beam shear strength was calculated in MPa. Five parallel samples were taken from each group, and the mean and standard deviation were taken.

[0061] (4) High-temperature creep test: The sample was cut into strips of (50±1)mm×(10±0.5)mm. A constant surface pressure of (0.5±0.02)MPa was applied in an environmental chamber at (115±2)℃ and maintained for 2h. The length direction strain at 2h was recorded as creep strain, in units of %; 3 parallel samples were taken for each group, and the mean and standard deviation were taken.

[0062] (5) Appearance and delamination area record after high temperature treatment: Take photos of the front and back of the sample after treatment at (115±2)℃ for 800h. Use the image threshold method to count the proportion of the visible area of ​​blistering / whitening / delamination to the whole effective area as the delamination area ratio (%). Take 3 parallel samples for each group and take the mean and standard deviation.

[0063] The performance test results are shown in Table 1: Table 1 Performance Test Results

[0064] Based on the data in Table 1, we can analyze and conclude that: (1) In Table 1, the peel strength of Example 1 at 180°C at room temperature was 9.2 N / 25 mm, which was higher than that of Comparative Example 1 (6.1 N / 25 mm). After heat treatment at 115°C for 168 hours, the peel strength of Example 1 was 7.8 N / 25 mm, while that of Comparative Example 1 was 3.8 N / 25 mm, with corresponding retention rates of 84.8% and 62.3%, respectively. Meanwhile, the delamination area ratio of Example 1 was 0.9%, lower than that of Comparative Example 1 (5.8%). Under conditions of further changes in the coating composition, the peel strength of Comparative Example 7 after heat treatment was 5.4 N / 25 mm, with a retention rate of 69.2% and a delamination area ratio of 2.6%, both lower than those of the Example group. This indicates that under the same laminated structure and test aperture, the inorganic-organic hybrid coating layer of "silicon-oxygen network + organosilicon fragments" exhibits a higher level of peel strength retention after heat treatment, and a lower visible delamination area after long-term high-temperature treatment.

[0065] (2) Under the condition that the coating layer and the other components are consistent, compared with Comparative Example 2, the 180° peel strength after heat treatment in Example 1 was 7.8 N / 25 mm and 3.1 N / 25 mm, respectively, and the short beam shear strength was 29.5 MPa and 13.5 MPa, respectively; at the same time, the creep deformation was 0.42% and 1.05%, respectively, and the delamination area ratio was 0.9% and 7.6%, respectively. This shows that under the curing window and test aperture of this application, when the crosslinking agent is missing, the interlayer strength index and appearance stability index decrease more after heat treatment, accompanied by higher creep deformation; when a closed polyisocyanate crosslinking system is introduced, the corresponding numerical levels of the above indexes are more stable.

[0066] (3) The peel strength of Comparative Example 3 at room temperature and after heat treatment was 6.8 N / 25 mm and 4.5 N / 25 mm, respectively. The short beam shear strength decreased from 26.0 MPa to 18.0 MPa, the creep deformation became 0.80%, and the delamination area ratio was 4.6%. The corresponding values ​​for Example 1 were 9.2 / 7.8 N / 25 mm, 34.0 / 29.5 MPa, 0.42%, and 0.9%. Under the same conditions, the interlaminar strength and appearance stability of the sample with particle size exceeding the window were generally lower than those of the Example group after heat treatment, and the creep deformation was also larger.

[0067] (4) Comparative Example 6 had a peel strength of 4.7 N / 25 mm after heat treatment, a retention rate of 62.7%, a creep rate of 0.78%, and a delamination area ratio of 3.8%; Example 1 had corresponding values ​​of 7.8 N / 25 mm, 84.8%, 0.42%, and 0.9%. When the coating layer and crosslinking system are consistent, it shows that when a silicone-containing waterborne polyurethane system is used, the peel strength retention rate after heat treatment is higher, the creep rate is smaller, and the delamination area ratio is lower.

[0068] (5) Comparative Example 4, after heat treatment, had a peel strength of 4.0 N / 25 mm, a short beam shear strength of 16.0 MPa, a creep rate of 0.92%, and a delamination area ratio of 6.5%; Comparative Example 5 had corresponding values ​​of 4.9 N / 25 mm, 19.5 MPa, 0.74%, and 3.4%. In contrast, Example 1, after heat treatment, had a peel strength of 7.8 N / 25 mm, a short beam shear strength of 29.5 MPa, a creep rate of 0.42%, and a delamination area ratio of 0.9%.

[0069] (6) After heat treatment, Example 2 showed a peel strength of 8.9 N / 25 mm, a creep rate of 0.36%, and a delamination area ratio of 0.6%, which were generally better than Examples 1 and 3. After heat treatment, Example 3 showed a peel strength of 6.2 N / 25 mm, a short beam shear strength of 25.5 MPa, and a delamination area ratio of 1.6%, which were lower than Example 2 but still higher than the comparative examples (such as Comparative Example 1) with key features removed. This indicates that within the defined sol parameters, sheet drying, and hot pressing window, variations in the formulation and process combination can lead to differences in performance indicators.

[0070] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A non-woven fabric based on high-temperature resistant ultra-high molecular weight polyethylene fiber, characterized in that, It includes at least two unidirectionally laid ultra-high molecular weight polyethylene fiber unidirectional layers and a resin matrix layer located between adjacent unidirectional layers. Each of the ultra-high molecular weight polyethylene fibers has an inorganic-organic hybrid coating layer on its outer surface, the inorganic-organic hybrid coating layer comprising a cross-linked structure composed of a silicon-oxygen network and organosilane fragments; The resin matrix layer is formed by curing an adhesive, which comprises, by weight, 100 parts of silicone-containing waterborne polyurethane, 3-25 parts of blocked polyisocyanate crosslinking agent, 1-15 parts of hexagonal boron nitride, 0.2-3 parts of aminosilane coupling agent, 0.01-1 parts of hindered phenolic antioxidant, and 0.1-2 parts of dispersant; In the non-woven fabric, the fiber directions of two adjacent unidirectional layers are arranged to cross each other.

2. The non-woven fabric according to claim 1, characterized in that, The inorganic-organic hybrid coating layer is formed by a sol-gel hydrolysis-condensation reaction of tetraethoxysilane and aminopropyltriethoxysilane, and the thickness of the inorganic-organic hybrid coating layer is 50~500nm.

3. The non-woven fabric according to claim 1, characterized in that, The ultra-high molecular weight polyethylene fiber has a molecular weight higher than 1 million and a linear density of 400~1600 dtex.

4. The non-woven fabric according to claim 1, characterized in that, The silicon-containing waterborne polyurethane comprises a polycarbonate diol soft segment, a diisocyanate hard segment, and a hydroxyl-terminated polydimethylsiloxane segment, wherein the solid content of the silicon-containing waterborne polyurethane is 25-55 wt%.

5. The non-woven fabric according to claim 1, characterized in that, The hexagonal boron nitride has a D50 particle size of 0.3~5.0μm, and the adhesive is added after the surface of the hexagonal boron nitride has been silanized or hydroxylated.

6. The non-woven fabric according to claim 1, characterized in that, The non-woven fabric has a [0 / 90]n-layer structure, where n is 2 to 16, and the areal density of each unidirectional layer is 20 to 120 g / m². 2 The coating amount of the adhesive is 8~35g / m². 2 .

7. A method for preparing the non-woven fabric of claim 1, characterized in that, include: S1. Fiber pretreatment: Ultra-high molecular weight polyethylene fibers are subjected to corona treatment or plasma treatment, followed by dust removal and drying. S2. Coating layer formation: The pretreated ultra-high molecular weight polyethylene fiber is impregnated in a sol system containing tetraethoxysilane and aminopropyltriethoxysilane and hydrolyzed and condensed to form an inorganic-organic hybrid coating layer on the outer surface of the fiber. S3. Adhesive preparation: The silicone-containing waterborne polyurethane, blocked polyisocyanate crosslinking agent, hexagonal boron nitride, aminosilane coupling agent, hindered phenolic antioxidant and dispersant are mixed and dispersed according to solid content to obtain adhesive. S4. Coating and Sheet Formation: The adhesive is coated onto the ultra-high molecular weight polyethylene fiber and dried to obtain a unidirectional prepreg sheet; S5. Lamination and hot pressing: The multiple layers of the unidirectional prepreg are stacked in the cross fiber direction and then heated and pressed to cure, thus obtaining the non-woven fabric.

8. The method according to claim 7, characterized in that, The pH of the sol system in S2 is 3-6, the molar ratio of tetraethoxysilane to aminopropyltriethoxysilane is (3-12):1, the impregnation time is 10-60s, and the condensation temperature is 20-60℃.

9. The method according to claim 7, characterized in that, The drying temperature of S4 is 60~95℃ and the drying time is 20~180s, and the hot pressing temperature of S5 is 90~125℃, the hot pressing pressure is 5~20MPa, and the holding time is 10~40min.

10. The method according to claim 7, characterized in that, The blocked polyisocyanate crosslinking agent is a trimer, biuret, or adduct with hexamethylene diisocyanate or isophorone diisocyanate as the isocyanate source, and caprolactam or methyl ethyl ketone oxime is used as the blocking agent. The hydroxyl equivalent ratio of the blocked polyisocyanate crosslinking agent to the silicone-containing waterborne polyurethane is (0.6~1.2):1.

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