Preparation method and application of low-dielectric high-flame-retardant glass fiber cloth

Abstract

The invention discloses a preparation method and application of low-dielectric high-flame-retardant glass fiber cloth. The method comprises the following steps: mixing tetraethoxysilane, a phosphorus-containing silane coupling agent, a nitrogen-containing silane coupling agent, a template agent and a solvent, and carrying out ultrasonic pretreatment to obtain uniform and stable hybrid sol; enabling glass fiber cloth to be in full contact with the hybrid sol by adopting an ultrasonic-assisted impregnation process; and sequentially carrying out gelation and graded heat treatment to remove the template agent and stabilize the coating, and finally forming the phosphorus-nitrogen-silicon synergistic flame-retardant coating with a nano-porous structure on the surface of the glass fiber cloth. According to the preparation method, an ultrasonic field is coupled with a template agent, the nano-porous structure of the coating is accurately regulated and controlled, and a P-N-Si synergistic effect of a commercial monomer is utilized, so that the product has excellent low dielectric constant (Dklt; 2.8), a low dielectric loss (Dflt; 0.005) and a high flame retardancy (LOIgt; and the coating is uniform and firm, and is especially suitable for high-frequency and high-speed printed circuit board base materials.

Description

Technical Field

[0001] This invention belongs to the field of functional composite materials technology, specifically relating to a surface modification method for glass fiber cloth, and particularly to a method for preparing a nanoporous coating with both ultra-low dielectric constant and high flame retardancy using ultrasonic-assisted sol-gel technology, as well as the glass fiber cloth prepared by this method and its application in high-frequency and high-speed printed circuit boards. Background Technology

[0002] As an indispensable core reinforcing material for printed circuit boards (PCBs), fiberglass cloth's performance directly determines the mechanical strength, dimensional stability, heat resistance, and ultimately, the reliability of electrical performance of multilayer PCBs. With the rapid development of cutting-edge technologies such as 5G, artificial intelligence (AI), high-performance computing (HPC), and autonomous driving, signal transmission frequencies have entered the millimeter-wave band, placing unprecedented demands on PCB substrates for high-frequency, high-speed, low-transmission-loss, high-integration, and high-signal-integrity requirements. Against this backdrop, the dielectric properties of fiberglass cloth, as an insulating reinforcement—especially its dielectric constant (Dk) and dielectric loss factor (Df)—have become key factors affecting overall circuit transmission efficiency and latency. Traditional E-glass cloth (Dk≈6.0, Df≈0.002) can no longer meet the ultra-low transmission-loss requirements of next-generation communication and computing devices; therefore, developing new fiberglass cloths with even lower Dk and Df has become an urgent technological goal for the industry.

[0003] To effectively reduce the dielectric constant of glass fiber cloth, existing technologies mainly focus on surface functionalization modification, encompassing two main strategies: The first is constructing a porous silica coating, typically using a sol-gel method to form a SiO2 layer with nanoscale pores on the fiber surface. This strategy leverages the extremely low dielectric constant of air (Dk≈1) to significantly reduce the overall material's average polarizability, thereby lowering the Dk value without significantly altering the bulk composition of the glass fiber. The second strategy involves introducing low-polarity organic components, such as coating or impregnating the fibers with low-dielectric polymers like silicone resins, fluorinated polymers, or polyolefins. These materials, due to their low covalent bond polarizability in their molecular structure, inherently possess a low Dk value, which can improve dielectric properties to some extent.

[0004] However, while the aforementioned methods impart low dielectric properties to materials, they often inevitably introduce new performance shortcomings, particularly severely impairing the material's flame-retardant properties. Porous structures, due to their high specific surface area and air retention, tend to accelerate heat transfer to flammable materials, significantly increasing the risk of combustion. Furthermore, most low-polarity organic polymers are themselves flammable or combustible materials; their introduction further reduces the overall flame-retardant rating, making it difficult for the material to meet the stringent UL94 V-0 flame-retardant safety standard for electronic products. To compensate for the lack of flame-retardant performance, the industry currently typically uses post-addition of flame retardants, such as brominated flame retardants, phosphorus compounds, and metal hydroxides (e.g., aluminum hydroxide, magnesium hydroxide). However, these additives usually require large amounts to be effective, significantly increasing material density and severely degrading its dielectric properties (increasing Dk and Df values), reducing mechanical strength, impairing heat resistance and processing fluidity, creating an irreconcilable "functional contradiction." For example, adding a high amount of polar flame retardant will introduce more dipole polarization, resulting in a sharp increase in dielectric loss, which completely contradicts the original intention of low dielectric modification.

[0005] Besides the performance contradictions, traditional modification methods—especially the sol-gel method—also have significant limitations at the process level. The gel coating prepared by this method is prone to cracking due to shrinkage stress during drying and heat treatment, leading to a disruption of coating continuity. Simultaneously, the viscosity and permeability of the sol are difficult to control precisely, resulting in uneven coating distribution on the fiber surface. Furthermore, within the dense glass fiber bundle, the sol cannot effectively penetrate and completely coat each monofilament. Consequently, the coating thickness and coverage differ significantly between the inner and outer layers of the fiber bundle, ultimately leading to a significant gradient distribution in the electrical, mechanical, and reliability properties of the modified glass cloth, failing to meet the stringent requirements of high-end applications for material uniformity and consistency.

[0006] Therefore, how to reduce the dielectric constant of glass fiber cloth while ensuring that its flame retardant properties are not compromised, and how to achieve uniform and firm coating on the fiber monofilament scale to avoid mutual constraints between various properties, has become a core technical challenge that urgently needs to be overcome in the current research and development of high-frequency substrate materials.

[0007] Developing a new generation of glass fiber cloth preparation technology that can synergistically optimize low dielectric properties, high flame retardancy, and excellent structural uniformity not only has important theoretical value but also has broad prospects for industrial application. Summary of the Invention

[0008] This invention aims to overcome the aforementioned deficiencies of the prior art and provide a method for preparing low-dielectric, high-flame-retardant glass fiber cloth. This method utilizes an ultrasonic-assisted process and an innovative blend of commercially available monomers to resolve the performance contradiction between low dielectric strength and high flame retardancy, while ensuring the uniformity and adhesion of the coating on the fiber surface.

[0009] The specific technical solution adopted by this invention is as follows:

[0010] A method for preparing a low-dielectric, high-flame-retardant glass fiber cloth includes the following steps:

[0011] S1. Sol preparation: Tetraethyl orthosilicate (TEOS), phosphorus-containing silane coupling agent, nitrogen-containing silane coupling agent, surfactant template agent, solvent, water and catalyst are mixed and ultrasonically treated to obtain a uniform and stable hybrid sol;

[0012] S2. Ultrasonic-assisted impregnation: The glass fiber cloth is impregnated in the hybrid sol obtained in step S1 with ultrasonic assistance;

[0013] S3. Gelation: Treat the impregnated glass fiber cloth at 60-100℃ for 10-60 minutes to gel the sol;

[0014] S4. Graded heat treatment: The gelled glass fiber cloth is first subjected to the removal of the template agent under an inert atmosphere; then it is heated for stabilization treatment and naturally cooled to room temperature, thus forming a nanoporous phosphorus-nitrogen-silicon synergistic flame retardant coating on the surface of the glass fiber cloth.

[0015] Preferably, in step S1, the phosphorus-containing silane coupling agent is diethylphosphonoethyltriethoxysilane or vinylbisphosphonate bis(2-chloroethyl) silane; the nitrogen-containing silane coupling agent is 3-(triethoxysilyl)propyl isocyanurate or N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane.

[0016] More preferably, in step S1, the phosphorus-containing silane coupling agent is diethylphosphorylethyltriethoxysilane; and the nitrogen-containing silane coupling agent is 3-(triethoxysilyl)propyl isocyanurate.

[0017] Preferably, in step S1, the molar ratio of each component is: TEOS:(phosphorus-containing silane coupling agent + nitrogen-containing silane coupling agent) = 1:(0.2~0.8); wherein the molar ratio of the phosphorus-containing silane coupling agent to the nitrogen-containing silane coupling agent is (1.5:1)~(3:1).

[0018] Preferably, in step S1, the surfactant template agent is cetyltrimethylammonium bromide (CTAB) or polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123), and its addition amount is 5% to 20% of the TEOS mass.

[0019] Preferably, in step S1, the solvent is ethanol or isopropanol; the catalyst is hydrochloric acid or nitric acid, and its amount is used to adjust the pH of the sol system to 2-4.

[0020] Preferably, the ultrasonic treatment conditions in step S1 are 20-40℃, ultrasonic frequency 25-80kHz, and power 100-500W for 10-60 minutes to obtain a uniform and stable hybrid sol.

[0021] Preferably, the ultrasonic-assisted impregnation conditions in step S2 are an ultrasonic frequency of 25-40kHz and a power of 50-300W.

[0022] Preferably, the immersion time in step S2 is 1-10 minutes;

[0023] Preferably, in step S2, the impregnated glass fiber cloth is treated at 60-100°C for 10-60 minutes to gel the sol.

[0024] Preferably, in step S4, the inert atmosphere is a nitrogen or argon atmosphere.

[0025] Preferably, the heating process in step S4 is as follows: first, the temperature is increased to 280-320°C at a rate of 2-5°C / min, and held for 30-120 minutes to remove the template agent; then, the temperature is increased to 380-420°C and held for 10-30 minutes for stabilization treatment, and then naturally cooled to room temperature, thus forming a nanoporous phosphorus-nitrogen-silicon synergistic flame-retardant coating on the surface of the glass fiber cloth.

[0026] A second aspect of the present invention provides a low-dielectric, high-flame-retardant glass fiber cloth obtained by the above-described preparation method.

[0027] A third aspect of the present invention provides the application of the above-mentioned low-dielectric, high-flame-retardant glass fiber cloth in the fabrication of high-frequency, high-speed printed circuit boards.

[0028] Beneficial effects

[0029] This invention successfully resolves the performance contradiction between low dielectric properties and high flame retardancy. Through molecular design, it selects commercially available phosphorus and nitrogen-containing silane coupling agents with specific structures. These coupling agents do not simply mix physically during the sol-gel process, but rather participate in the construction of an inorganic-organic hybrid network through hydrolysis and condensation reactions. The phosphorus-based component primarily plays a role in char formation and coverage in the condensed phase, while the nitrogen-based component and phosphorus-based component generate a highly efficient PN synergistic flame retardant effect, significantly improving the gas-phase flame retardant efficiency. This "structural" flame retardant design avoids the degradation of dielectric properties caused by adding traditional flame retardants, enabling the final product to simultaneously achieve excellent low dielectric properties and inherently high flame retardancy, overcoming a long-standing technical bottleneck in this field.

[0030] This invention creatively couples ultrasonic energy into the entire process of sol preparation and impregnation. In the sol preparation stage, the ultrasonic cavitation effect greatly promotes the hydrolysis and condensation of the precursor, forming a sol system with fine particle size, uniform distribution, and high stability. It also effectively reduces the number of terminal polar -Si-OH groups, laying the structural foundation for achieving low dielectric loss. In the impregnation stage, the microjets generated by ultrasonic cavitation strongly drive the sol to deeply penetrate into the dense glass fiber bundle, ensuring that the surface of each monofilament is uniformly coated. This completely solves problems such as uneven coating and interface defects caused by poor wetting, significantly enhancing the adhesion between the coating and the fiber matrix, and resulting in extremely high performance retention after friction testing.

[0031] The entire process of this invention primarily uses water and ethanol as solvents, avoiding the use and emission of large amounts of VOCs, thus meeting the requirements of green chemistry and clean production. All raw materials used are readily available commercial products, with controllable costs and stable sources. The ultrasonic treatment and graded heat treatment processes described are easily integrated and scaled up in existing fiberglass cloth processing production lines without requiring complex or expensive equipment modifications, therefore possessing extremely high industrialization value and market application prospects.

[0032] In summary, through ingenious material system design and innovative process flow, the glass fiber cloth product prepared by this invention has excellent comprehensive performance, meets the stringent requirements of next-generation high-frequency and high-speed communication technology for PCB substrate reinforcement materials, and has significant technical value and economic benefits. Detailed Implementation

[0033] To make the objectives and advantages of this invention clearer, the invention will be specifically described below with reference to embodiments. It should be understood that the following text is merely used to describe one or more specific embodiments of the invention and does not strictly limit the scope of protection specifically claimed by the invention.

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention. The test methods used in the following embodiments and comparative examples are as follows:

[0035] Dielectric constant (Dk) and dielectric loss (Df): Composite material samples prepared from treated glass fiber cloth were tested at a frequency of 10 GHz using a Keysight N5230C vector network analyzer via the stripline resonator method.

[0036] Limiting Oxygen Index (LOI): Tested using an FTT oxygen index meter according to standard ASTM D2863.

[0037] UL94 Flame Retardant Rating: Tested using an FTT vertical flame tester on a 1.6 mm thick sample according to standard UL94.

[0038] Thermal decomposition temperature (Td5%): The temperature at which 5% weight loss occurs is measured using a TAQ50 thermogravimetric analyzer under N2 atmosphere at a heating rate of 10℃ / min.

[0039] Coating adhesion: The adhesion is evaluated by rubbing the coating surface 100 times with a standard cotton cloth under a certain pressure using a friction tester and measuring the rate of change of dielectric constant before and after friction.

[0040] Example 1

[0041] This embodiment provides a method for preparing low-dielectric, high-flame-retardant glass fiber cloth, the specific steps of which are as follows:

[0042] 1. Sol preparation: In a 250 mL three-necked flask, add 80 mL of anhydrous ethanol, 20 mL of deionized water (adjusted to pH 3.0 with dilute nitric acid), 10 mmol (2.08 g) of tetraethyl orthosilicate (TEOS), 3.0 mmol (0.89 g) of diethylphosphorylethyltriethoxysilane (P source), 1.5 mmol (0.59 g) of 3-(triethoxysilyl)propyl isocyanurate (N source), and 0.15 g of hexadecyltrimethylammonium bromide (CTAB). Incubate the mixture at 30 °C.

[0043] The mixture was mechanically stirred at 300 rpm for 30 minutes to induce preliminary hydrolysis. Subsequently, the flask was placed in an ultrasonic processor (operating frequency 40 kHz, rated power 300 W) and ultrasonically treated in a 30°C water bath for 30 minutes to obtain a uniform, transparent, and stable hybrid sol.

[0044] 2. Ultrasonic-assisted impregnation: Fix a 10cm×10cm piece of 106-type electronic-grade glass fiber cloth (commercially available) onto a fixture and completely immerse it in the above-mentioned sol. Turn on the ultrasonic cleaner (operating frequency 40kHz, power 150W) and impregnate for 5 minutes under ultrasonic field assistance to ensure that the sol fully penetrates into the fiber bundle.

[0045] 3. Gelation and aging: Remove the impregnated fiberglass cloth with tweezers, gently scrape off the excess sol on the surface with a flat scraper, then lay it flat on a polytetrafluoroethylene plate and transfer it to an 80°C forced-air drying oven for 30 minutes to complete the gelation and initial drying of the sol.

[0046] 4. Graded heat treatment: Place the gelled fiberglass cloth into a programmable temperature-controlled tube furnace and purge it with high-purity nitrogen gas (flow rate...).

[0047] A protective atmosphere of 200 mL / min was used. The temperature was programmed to rise to 300°C at a rate of 3°C / min and held at this temperature for 60 minutes to completely remove the CTAB template agent. Subsequently, the temperature was further increased to 400°C at a rate of 5°C / min and held for 20 minutes to further stabilize and densify the inorganic-organic hybrid network. After the treatment, the furnace was allowed to cool naturally to room temperature to obtain the low-dielectric, high-flame-retardant glass fiber cloth described in this invention.

[0048] Example 2

[0049] The difference between this embodiment and Example 1 is that the molar ratio of the phosphorus-containing silane coupling agent to the nitrogen-containing silane coupling agent is different in step 1. The remaining steps and parameters are exactly the same as in Example 1. The specific steps are as follows:

[0050] 1. Sol Preparation: In a 250 mL three-necked flask, 80 mL of anhydrous ethanol, 20 mL of deionized water (adjusted to pH 3.0 with dilute nitric acid), 10 mmol (2.08 g) of tetraethyl orthosilicate (TEOS), 2.4 mmol (0.71 g) of diethylphosphonylethyltriethoxysilane (P source), 2 mmol (0.79 g) of 3-(triethoxysilyl)propyl isocyanurate (N source), and 0.15 g of hexadecyltrimethylammonium bromide (CTAB) were added sequentially. The mixture was mechanically stirred at 300 rpm for 30 minutes at 30 °C to induce preliminary hydrolysis. Subsequently, the flask was placed in an ultrasonic processor (operating frequency 40 kHz, rated power 300 W) and ultrasonically treated in a 30 °C water bath for 30 minutes to obtain a homogeneous, transparent, and stable hybrid sol.

[0051] 2. Ultrasonic-assisted impregnation: Fix a 10cm×10cm piece of 106-type electronic-grade glass fiber cloth (commercially available) onto a fixture and completely immerse it in the above-mentioned sol. Turn on the ultrasonic cleaner (operating frequency 40kHz, power 150W) and impregnate for 5 minutes under ultrasonic field assistance to ensure that the sol fully penetrates into the fiber bundle.

[0052] 3. Gelation and aging: Remove the impregnated fiberglass cloth with tweezers, gently scrape off the excess sol on the surface with a flat scraper, then lay it flat on a polytetrafluoroethylene plate and transfer it to an 80°C forced-air drying oven for 30 minutes to complete the gelation and initial drying of the sol.

[0053] 4. Graded heat treatment: Place the gelled fiberglass cloth into a programmable temperature-controlled tube furnace and purge it with high-purity nitrogen gas (flow rate...).

[0054] A protective atmosphere of 200 mL / min was used. The temperature was programmed to rise to 300 °C at a rate of 3 °C / min and held at that temperature.

[0055] The CTAB template agent was completely removed after 60 minutes. Subsequently, the temperature was increased to 400°C at a rate of 5°C / min and held for 20 minutes to further stabilize and densify the inorganic-organic hybrid network. After treatment, the furnace was allowed to cool naturally to room temperature to obtain the low-dielectric, high-flame-retardant glass fiber cloth described in this invention.

[0056] Example 3

[0057] The difference between this embodiment and Example 1 is that the molar ratio of the phosphorus-containing silane coupling agent to the nitrogen-containing silane coupling agent is different in step 1. The remaining steps and parameters are exactly the same as in Example 1. The specific steps are as follows:

[0058] 1. Sol preparation: In a 250 mL three-necked flask, add 80 mL of anhydrous ethanol, 20 mL of deionized water (adjusted to pH 3.0 with dilute nitric acid), 10 mmol (2.08 g) of tetraethyl orthosilicate (TEOS), and 3.0 mmol (1.07 g) of sol in sequence.

[0059] Diethylphosphonoethyltriethoxysilane (P source), 1.2 mmol (0.47 g) of 3-(triethoxysilyl)propyl isocyanurate (N source), and 0.15 g of hexadecyltrimethylammonium bromide (CTAB). The mixture was incubated at 30 °C.

[0060] The mixture was mechanically stirred at 300 rpm for 30 minutes to induce preliminary hydrolysis. Subsequently, the flask was placed in an ultrasonic processor (operating frequency 40 kHz, rated power 300 W) and ultrasonically treated in a 30°C water bath for 30 minutes to obtain a uniform, transparent, and stable hybrid sol.

[0061] 2. Ultrasonic-assisted impregnation: Fix a 10cm×10cm piece of 106-type electronic-grade glass fiber cloth (commercially available) onto a fixture and completely immerse it in the above-mentioned sol. Turn on the ultrasonic cleaner (operating frequency 40kHz, power 150W) and impregnate for 5 minutes under ultrasonic field assistance to ensure that the sol fully penetrates into the fiber bundle.

[0062] 3. Gelation and aging: Remove the impregnated fiberglass cloth with tweezers, gently scrape off the excess sol on the surface with a flat scraper, then lay it flat on a polytetrafluoroethylene plate and transfer it to an 80°C forced-air drying oven for 30 minutes to complete the gelation and initial drying of the sol.

[0063] 4. Graded heat treatment: Place the gelled fiberglass cloth into a programmable temperature-controlled tube furnace and purge it with high-purity nitrogen gas (flow rate...).

[0064] A protective atmosphere of 200 mL / min was used. The temperature was programmed to rise to 300°C at a rate of 3°C / min and held at this temperature for 60 minutes to completely remove the CTAB template agent. Subsequently, the temperature was further increased to 400°C at a rate of 5°C / min and held for 20 minutes to further stabilize and densify the inorganic-organic hybrid network. After the treatment, the furnace was allowed to cool naturally to room temperature to obtain the low-dielectric, high-flame-retardant glass fiber cloth described in this invention.

[0065] Comparative Example 1

[0066] The difference between this comparative example and Example 1 is that no ultrasonic treatment was applied during the sol preparation and impregnation processes; only mechanical stirring was used. The sol preparation stage involved mechanical stirring for 2 hours, and the impregnation stage involved silent impregnation for 10 minutes. The remaining steps and parameters were exactly the same as in Example 1, as detailed below:

[0067] 1. Sol preparation: In a 250 mL three-necked flask, add 80 mL of anhydrous ethanol, 20 mL of deionized water (adjusted to pH 3.0 with dilute nitric acid), 10 mmol (2.08 g) of tetraethyl orthosilicate (TEOS), and 3.0 mmol (0.89 g) of sodium ether.

[0068] Diethylphosphorylethyltriethoxysilane (P source), 1.5 mmol (0.59 g) 3-(triethoxysilyl)

[0069] Propyl isocyanurate (N source) and 0.15 g cetyltrimethylammonium bromide (CTAB). The mixture was mechanically stirred at 300 rpm for 30 minutes at 30 °C to achieve preliminary pre-hydrolysis. Subsequently, the flask was placed in an ultrasonic processor (operating frequency 40 kHz, rated power 300 W) and mechanically stirred in a 30 °C water bath for 2 hours to obtain a homogeneous, transparent, and stable hybrid sol.

[0070] 2. Ultrasonic-assisted impregnation: Fix a 10cm×10cm piece of 106-type electronic-grade glass fiber cloth (commercially available) onto the fixture and completely immerse it in the above-mentioned sol. Turn on the ultrasonic cleaner (operating frequency 40kHz, power 150W) and perform silent impregnation treatment for 10 minutes to ensure that the sol fully penetrates into the fiber bundle.

[0071] 3. Gelation and aging: Remove the impregnated fiberglass cloth with tweezers, gently scrape off the excess sol on the surface with a flat scraper, then lay it flat on a polytetrafluoroethylene plate and transfer it to an 80°C forced-air drying oven for 30 minutes to complete the gelation and initial drying of the sol.

[0072] 4. Graded heat treatment: Place the gelled fiberglass cloth into a programmable temperature-controlled tube furnace and purge it with high-purity nitrogen gas (flow rate...).

[0073] A protective atmosphere of 200 mL / min was used. The temperature was programmed to rise to 300 °C at a rate of 3 °C / min and held at that temperature.

[0074] The CTAB template agent was completely removed after 60 minutes. Subsequently, the temperature was increased to 400°C at a rate of 5°C / min and held for 20 minutes to further stabilize and densify the inorganic-organic hybrid network. After treatment, the furnace was allowed to cool naturally to room temperature to obtain low-dielectric-resistance flame-retardant glass fiber cloth.

[0075] Comparative Example 2

[0076] The difference between this comparative example and Example 1 is that no phosphorus- or nitrogen-containing silane coupling agents are added in step 1; only 10 mmol of TEOS is used to prepare pure silica sol. The remaining steps and parameters are exactly the same as in Example 1.

[0077] 1. Sol Preparation: In a 250 mL three-necked flask, add 80 mL of anhydrous ethanol, 20 mL of deionized water (adjusted to pH 3.0 with dilute nitric acid), 10 mmol (2.08 g) of tetraethyl orthosilicate (TEOS), and 0.15 g of cetyltrimethylammonium bromide (CTAB) sequentially. The mixture is mechanically stirred at 300 rpm for 30 minutes at 30 °C to allow for preliminary pre-hydrolysis. Subsequently, the flask is placed in an ultrasonic processor (operating frequency 40 kHz, rated power 300 W) and...

[0078] A uniform, transparent, and stable hybrid sol was obtained by ultrasonic treatment for 30 minutes in a 30℃ water bath.

[0079] 2. Ultrasonic-assisted impregnation: Fix a 10cm×10cm piece of 106-type electronic-grade glass fiber cloth (commercially available) onto a fixture and completely immerse it in the above-mentioned sol. Turn on the ultrasonic cleaner (operating frequency 40kHz, power 150W) and impregnate for 5 minutes under ultrasonic field assistance to ensure that the sol fully penetrates into the fiber bundle.

[0080] 3. Gelation and aging: Remove the impregnated fiberglass cloth with tweezers, gently scrape off the excess sol on the surface with a flat scraper, then lay it flat on a polytetrafluoroethylene plate and transfer it to an 80°C forced-air drying oven for 30 minutes to complete the gelation and initial drying of the sol.

[0081] 4. Graded heat treatment: Place the gelled fiberglass cloth into a programmable temperature-controlled tube furnace and purge it with high-purity nitrogen gas (flow rate...).

[0082] A protective atmosphere of 200 mL / min was used. The temperature was programmed to rise to 300°C at a rate of 3°C / min and held at this temperature for 60 minutes to completely remove the CTAB template agent. Subsequently, the temperature was further increased to 400°C at a rate of 5°C / min and held for 20 minutes to further stabilize and densify the inorganic-organic hybrid network. After the treatment, the furnace was allowed to cool naturally to room temperature to obtain the low-dielectric, high-flame-retardant glass fiber cloth described in this invention.

[0083] Comparative Example 3

[0084] The difference between this comparative example and Example 1 lies in the graded heat treatment regime in step 4. The gelled sample was directly heated to 400°C at a rate of 5°C / min in air and held for 60 minutes. The remaining steps and parameters were exactly the same as in Example 1.

[0085] 1. Sol preparation: In a 250 mL three-necked flask, add 80 mL of anhydrous ethanol, 20 mL of deionized water (adjusted to pH 3.0 with dilute nitric acid), 10 mmol (2.08 g) of tetraethyl orthosilicate (TEOS), and 3.0 mmol (0.89 g) of sodium ether.

[0086] Diethylphosphonoethyltriethoxysilane (P source), 1.5 mmol (0.59 g) of 3-(triethoxysilyl)propyl isocyanurate (N source), and 0.15 g of hexadecyltrimethylammonium bromide (CTAB). The mixture was incubated at 30°C.

[0087] The mixture was mechanically stirred at 300 rpm for 30 minutes to induce preliminary hydrolysis. Subsequently, the flask was placed in an ultrasonic processor (operating frequency 40 kHz, rated power 300 W) and ultrasonically treated in a 30°C water bath for 30 minutes to obtain a uniform, transparent, and stable hybrid sol.

[0088] 2. Ultrasonic-assisted impregnation: Fix a 10cm×10cm piece of 106-type electronic-grade glass fiber cloth (commercially available) onto a fixture and completely immerse it in the above-mentioned sol. Turn on the ultrasonic cleaner (operating frequency 40kHz, power 150W) and impregnate for 5 minutes under ultrasonic field assistance to ensure that the sol fully penetrates into the fiber bundle.

[0089] 3. Gelation and aging: Remove the impregnated fiberglass cloth with tweezers, gently scrape off the excess sol on the surface with a flat scraper, then lay it flat on a polytetrafluoroethylene plate and transfer it to an 80°C forced-air drying oven for 30 minutes to complete the gelation and initial drying of the sol.

[0090] 4. Graded heat treatment: The gelled fiberglass cloth is heated to 400℃ in air at a rate of 5℃ / min and then...

[0091] Keep warm for 60 minutes. After processing, allow to cool naturally to room temperature to obtain low dielectric and high flame retardant fiberglass cloth.

[0092] Performance test results

[0093] The performance of the products obtained in Examples 1-3 and Comparative Examples 1-3 was tested, and the results are shown in the table below:

[0094]

[0095] Results Analysis

[0096] Example 1 employed an ultrasonic-assisted process, while Comparative Example 1 did not. Test results showed that ultrasonic treatment significantly reduced the dielectric constant and loss of the product (Dk decreased from 3.10 to 2.75, and Df decreased from 0.0075 to 0.0042), and substantially improved the coating's adhesion (the rate of change of Dk after friction decreased from 15.3% to 2.1%). This demonstrates that ultrasonic treatment plays a crucial role in obtaining a coating with low dielectric loss and strong adhesion. SEM observation revealed that the coating in Example 1 was continuous and uniform, while the coating in Comparative Example 1 exhibited obvious cracks and discontinuous areas.

[0097] Comparative Example 2, without the addition of P and N flame-retardant components, exhibited the best dielectric properties (Dk = 2.65), but its flame retardancy was completely unsuccessful (LOI only 21%, UL94 flammability). In contrast, Example 1 achieved a leap in flame retardancy from "flammable" to "flame-retardant (V-0 rating)" with only a slight sacrifice in dielectric properties, demonstrating the successful construction of the PN-Si synergistic flame-retardant system.

[0098] Comparative Example 3 underwent heat treatment in an air atmosphere, which resulted in the oxidation and decomposition of the P and N flame-retardant components at high temperatures, leading to a decrease in flame-retardant efficiency (LOI dropped to 28%, UL94 V-1). In contrast, Example 1 employed a staged heat treatment under nitrogen protection, which effectively protected the flame-retardant components and maintained its high flame-retardant efficiency (LOI = 32.5%, V-0), demonstrating the necessity of this heat treatment process.

[0099] In summary, this invention, through the synergistic effect of specific component design (PN-Si system), innovative ultrasonic-assisted process, and precise graded heat treatment, successfully prepared a low-dielectric, high-flame-retardant glass fiber cloth with excellent comprehensive performance. The embodiments described are merely illustrative; any common variations and substitutions made by those skilled in the art within the scope of this invention should be included within the protection scope of this invention.

Claims

1. A method for preparing a low-dielectric, high-flame-retardant glass fiber cloth, characterized in that, Includes the following steps: S1. Sol preparation: Tetraethyl orthosilicate (TEOS), phosphorus-containing silane coupling agent, nitrogen-containing silane coupling agent, surfactant template agent, solvent, water and catalyst are mixed and ultrasonically treated for 10-60 minutes at 20-40℃ and ultrasonic frequency of 25-80kHz and power of 100-500W to obtain a uniform and stable hybrid sol. S2. Ultrasonic-assisted impregnation: The glass fiber cloth is impregnated in the hybrid sol obtained in step S1, and ultrasonic-assisted impregnation is carried out under the conditions of ultrasonic frequency 25-40kHz and power 50-300W for 1-10 minutes. S3. Gelation: Treat the impregnated glass fiber cloth at 60-100℃ for 10-60 minutes to gel the sol; S4. Graded heat treatment: The gelled glass fiber cloth is first heated to 280-320℃ at a rate of 2-5℃ / min under an inert atmosphere and held for 30-120 minutes to remove the template agent; then the temperature is further increased to 380-420℃ and held for 10-30 minutes for stabilization treatment, and then naturally cooled to room temperature, thus forming a nanoporous phosphorus-nitrogen-silicon synergistic flame retardant coating on the surface of the glass fiber cloth.

2. The method for preparing a low-dielectric, high-flame-retardant glass fiber cloth according to claim 1, characterized in that, In step S1, the phosphorus-containing silane coupling agent is diethylphosphonyl ethyltriethoxysilane or vinyl bisphosphonate bis(2-chloroethyl) ester silane; the nitrogen-containing silane coupling agent is 3-(triethoxysilyl)propyl isocyanurate or N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane.

3. The method for preparing a low-dielectric, high-flame-retardant glass fiber cloth according to claim 1, characterized in that, In step S1, the molar ratio of each component is: TEOS:(phosphorus-containing silane coupling agent + nitrogen-containing silane coupling agent) = 1:(0.2~0.8); wherein the molar ratio of the phosphorus-containing silane coupling agent to the nitrogen-containing silane coupling agent is (1.5:1)~(3:1).

4. The method for preparing a low-dielectric, high-flame-retardant glass fiber cloth according to claim 1, characterized in that, In step S1, the surfactant template agent is cetyltrimethylammonium bromide (CTAB) or polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123), and its addition amount is 5% to 20% of the TEOS mass.

5. The method for preparing a low-dielectric, high-flame-retardant glass fiber cloth according to claim 1, characterized in that, In step S1, the solvent is ethanol or isopropanol; the catalyst is hydrochloric acid or nitric acid, and its amount is used to adjust the pH of the sol system to 2-4.

6. The method for preparing a low-dielectric, high-flame-retardant glass fiber cloth according to claim 1, characterized in that, In step S4, the inert atmosphere is a nitrogen or argon atmosphere.

7. A low-dielectric, high-flame-retardant glass fiber cloth prepared by the method described in any one of claims 1 to 6.

8. The application of the low dielectric and high flame retardant glass fiber cloth of claim 7 in the preparation of high frequency and high speed printed circuit boards.

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