A production process of nanofiber composite impregnated paper

Abstract

The application discloses a production process of a nanofiber composite impregnated paper in the papermaking industry and the composite material field, and comprises the following steps: wood pulp plates are disintegrated into paper pulp with a certain freeness, cationic polyacrylamide retention aid is added, stirring is performed, and then original paper is made by papermaking; the original paper is immersed in an impregnating solution containing phenolic resin, modified material and ethylene glycol, a certain linear pressure is applied to make the resin uniformly penetrate into the fiber layers; the impregnated wet paper sheet is dried in a hot air drying oven to a certain moisture content; and calendering treatment can be further performed to improve the surface smoothness of the paper. The modified material is prepared by dispersing nano silicon dioxide particles in deionized water, adding a dispersing agent, performing ultrasonic treatment, adding a silane coupling agent to react under temperature rising, adding wood pulp cellulose nanofilaments to stir and adsorb, and finally centrifugal washing, vacuum drying and grinding. The process enhances the interface combination of the nanofiber and the resin through the modified material, and improves the strength, water resistance and aging resistance of the impregnated paper.

Description

Technical Field

[0001] This invention relates to the fields of papermaking industry and composite materials technology, specifically to a production process for nanofiber composite impregnated paper. Background Technology

[0002] Traditional impregnated paper, as an important component of decorative materials, electronic substrates, and industrial filter media, has long been made primarily from plant fibers (such as wood pulp) through pulping, papermaking, resin impregnation, and post-processing. However, plant fibers themselves have inherent defects such as weak inter-fiber bonding, poor water resistance, and weak aging resistance. In particular, they are prone to absorbing water and swelling in humid environments, leading to delamination. Under high stress or long-term use, they are prone to blistering and cracking, making it difficult to meet the higher requirements of high-end fields for material strength, weather resistance, and functionality. For example, electronic substrates need to have low water absorption to ensure circuit stability, and industrial filter media need to maintain structural strength in high-humidity environments. The performance bottlenecks of traditional impregnated paper have gradually become a constraint on the development of related fields.

[0003] With the rise of nanomaterials, research on adding nanofibers (such as cellulose nanofibers and polyester nanofibers) to impregnated paper to enhance its performance has gradually increased. Nanofibers possess high specific surface area, high modulus, and strong interfacial bonding potential, and theoretically can improve the overall performance of impregnated paper by bridging inter-fiber voids and improving resin penetration uniformity. However, nanofibers have high surface energy and strong polarity, resulting in insufficient compatibility with traditional resin matrices (such as phenolic resins and epoxy resins). This can easily lead to uneven dispersion or interfacial debonding. Uneven dispersion can cause localized strength loss, while interfacial debonding weakens the synergistic load-bearing capacity of the resin and fibers, ultimately making it difficult to fully realize the reinforcing effect of nanofibers and limiting their application and promotion in high-end impregnated paper.

[0004] To address the aforementioned issues, existing technologies attempt to improve the compatibility between nanofibers and resins through surface modification. However, existing modification methods have certain limitations: some modification processes require complex equipment or high-temperature, high-pressure conditions, increasing production costs; some modifiers lack sufficient bonding strength with nanofibers and resins, potentially leading to performance degradation during long-term use; furthermore, modified nanofibers tend to agglomerate during impregnation, making uniform dispersion in the paper matrix difficult and resulting in limited improvement in paper performance. Therefore, developing a feasible nanofiber composite impregnated paper production technology that can effectively improve the interfacial bonding between nanofibers and resins while achieving uniform dispersion is of great significance for enhancing the overall performance of impregnated paper and expanding its application areas. Summary of the Invention

[0005] The purpose of this invention is to provide a production process for nanofiber composite impregnated paper, which solves the technical problems of traditional impregnated paper, such as weak bonding with plant fibers, poor water resistance, and weak aging resistance.

[0006] The present invention achieves the above objectives through the following technical solutions:

[0007] A manufacturing process for nanofiber composite impregnated paper includes the following steps:

[0008] S1, the wood pulp board is broken down into pulp with a freeness of 280-320mL by a pulper, cationic polyacrylamide retention aid is added, and the mixture is stirred to form the base paper;

[0009] S2, the base paper is immersed in an impregnation tank containing an impregnation solution, which consists of the following components: 80-90 parts of phenolic resin, 5-8 parts of modified material, and 5-10 parts of ethylene glycol. During the impregnation process, a linear pressure of 0.1-0.2 MPa is applied to make the resin evenly penetrate into the interlayer of the base paper.

[0010] S3, the impregnated wet paper sheets are dried in a hot air drying oven to a moisture content of 5-8%.

[0011] According to a preferred embodiment of the present invention, the cationic polyacrylamide was purchased from Henan Qingshuiyuan Technology Co., Ltd.

[0012] According to a preferred embodiment of the present invention, the phenolic resin was purchased from Shanghai Rongrong New Materials Technology Co., Ltd.

[0013] According to a preferred embodiment of the present invention, the ethylene glycol was purchased from Yanshan Petrochemical Branch of China Petroleum & Chemical Corporation.

[0014] According to a preferred embodiment of the present invention, the hot air drying oven was purchased from Changzhou Yibu Drying Equipment Co., Ltd.

[0015] According to a preferred embodiment of the present invention, in step S1, the cationic polyacrylamide accounts for 0.5-1% of the dry weight of the pulp; the stirring time is 10-20 min; and the basis weight of the base paper is 80-100 g / m³. 2 .

[0016] In step S1 of this invention, the base paper is made by breaking down wood pulp (freeness 280-320mL) and adding cationic polyacrylamide (0.5-1% of dry pulp weight). The cationic polyacrylamide improves the retention rate between fibers and enhances the basic strength of the paper through charge neutralization.

[0017] According to a preferred embodiment of the present invention, in step S2, the solid content of the phenolic resin is 50-55%, and the solid content of the modified material is 10-15%; the impregnation temperature of the base paper is 50-60°C, and the impregnation time is 30-45 seconds.

[0018] In step S2 of this invention, phenolic resin (solid content 50-55%) is used as the main binder in the impregnation solution. The hydroxymethyl (-CH2OH) groups on its molecular chain cross-link with the epoxy groups of the silane coupling agent in the modified material to form a three-dimensional network structure. Ethylene glycol (5-10 parts) is used as a diluent to reduce the viscosity of the impregnation solution and promote the uniform penetration of the resin into the interlayer of the base paper fibers.

[0019] According to a preferred embodiment of the present invention, in step S3, the drying temperature of the hot air drying oven is 100-120°C.

[0020] In step S3 of this invention, a linear pressure of 0.1-0.2 MPa is applied to allow the resin to penetrate to a depth of more than 80% of the original paper thickness, ensuring that the cross-linking reaction proceeds fully; drying (100-120℃) cures the resin and forms a stable cross-linking network; calendering (80-90℃, 30-40 kN / m) uses mechanical pressure to compact the paper, reducing surface porosity, improving smoothness (≥300s), and promoting further bonding between the resin and fibers.

[0021] According to a preferred embodiment of the present invention, the production process of the nanofiber composite impregnated paper further includes: calendering the paper by means of a calender with a roller temperature of 80-90°C and a linear pressure of 0.03-0.04MPa, so that the surface smoothness of the paper is ≥300s.

[0022] According to a preferred embodiment of the present invention, the modified material preparation step includes:

[0023] A1. Disperse nano-silica particles in deionized water, add a dispersant, and process in an ultrasonic disperser to obtain a nano-silica dispersion.

[0024] A2. Transfer the nano-silica dispersion to the reactor, heat it to 60-70℃, and add silane coupling agent dropwise under stirring conditions. The mass ratio of silane coupling agent to nano-silica is 1:(5-8). After the dropwise addition is completed, continue the reaction to allow the silane coupling agent to undergo a hydrolysis and condensation reaction on the surface of nano-silica.

[0025] A3. Add wood pulp cellulose nanofibers to the reactor, maintain the temperature at 60-65℃ and stir to mix, so that the modified nano silica particles are adsorbed on the surface of the cellulose nanofibers.

[0026] A4. Finally, the mixture is centrifuged to remove the supernatant. The precipitate is washed with deionized water, dried in a vacuum drying oven, and ground through a 100-mesh sieve.

[0027] According to a preferred embodiment of the present invention, the nano-silica was purchased from Jiangsu Tianniao High-Tech Co., Ltd.

[0028] According to a preferred embodiment of the present invention, the dispersant (sodium polyacrylate) was purchased from Henan Boyuan New Materials Co., Ltd.

[0029] According to a preferred embodiment of the present invention, the reactor was purchased from Jiangsu Yangyang Chemical Equipment Manufacturing Co., Ltd.

[0030] According to a preferred embodiment of the present invention, the silane coupling agent (silane coupling agent KH560) was purchased from Hubei Xingfa Chemical Group Co., Ltd.

[0031] According to a preferred embodiment of the present invention, the wood pulp cellulose nanofibers were purchased from Shandong Sun Paper Co., Ltd.

[0032] According to a preferred embodiment of the present invention, the vacuum drying oven was purchased from Shanghai Yiheng Scientific Instruments Co., Ltd.

[0033] According to a preferred embodiment of the present invention, in step A1, the particle size of the nano-silica particles is 50-100 nm and the solid content is 30-35 wt%; the solid content of the dispersant is 0.5-1 wt%; the processing frequency in the ultrasonic disperser is 30-50 kHz and the processing time is 30-35 min.

[0034] In step A1 of this invention, nano-silica particles (particle size 50-100nm) are stably dispersed in deionized water with a dispersant (such as sodium polyacrylate) to form a uniform colloid. The dispersant prevents the nanoparticles from agglomerating through electrostatic repulsion. Ultrasonic dispersion (30-50kHz, 30-35min) further breaks down the van der Waals forces between the particles, ensuring that the nano-silica exists in a monodisperse state in the water.

[0035] According to a preferred embodiment of the present invention, in step A2, the stirring speed is 300-400 rpm, and the reaction time continues for 1.5-2.5 h after the addition is completed.

[0036] In step A2 of this invention, the temperature is raised to 60-70°C and a silane coupling agent (mass ratio of 1:5-8 to nano-silica) is added dropwise. The epoxy groups of the silane coupling agent (such as the epoxy groups of γ-glycidoxypropyltrimethoxysilane) undergo hydrolysis in the presence of water to generate silanol (-Si-OH). The silanol forms a covalent bond with the native silanol (-Si-OH) on the surface of nano-silica through a condensation reaction (removal of water molecules), grafting the silane coupling agent onto the surface of nano-silica. At the same time, the epoxy groups (-COC-) of the silane coupling agent are exposed because they do not participate in the reaction, providing active sites for subsequent crosslinking.

[0037] According to a preferred embodiment of the present invention, in step A3, the length of the wood pulp cellulose nanofibers is 1-3 μm, the diameter is 5-10 nm, and the solid content is 1-1.5 wt%; the stirring speed is 500-600 rpm, and the stirring time is 1-2 h.

[0038] In step A3 of this invention, wood pulp cellulose nanofibers (length 1-3 μm, diameter 5-10 nm, solid content 1-1.5 wt%) are added. Their surface is rich in negatively charged hydroxyl groups (-OH), which are tightly bonded to the positively charged regions on the surface of modified nano silica due to the protonation of epoxy groups through electrostatic attraction, forming "nano silica-cellulose" composite particles, thereby achieving uniform dispersion of nanoparticles in cellulose.

[0039] According to a preferred embodiment of the present invention, in step A4, the centrifugation speed of the mixture is 8000-9000 rpm, the centrifugation time is 10-15 min, and the precipitate is washed with deionized water 3-4 times; the drying temperature in the vacuum drying oven is 80-85℃, and the drying time is 12-14 h.

[0040] In step A4 of this invention, unreacted silane coupling agent and dispersant are removed by centrifugation (8000-9000 rpm, 10-15 min). The precipitate is washed with deionized water (3-4 times), dried in a vacuum drying oven (80-85℃, 12-14 h), and ground through a 100-mesh sieve to obtain a stable modified material with both epoxy groups and cellulose nanofibers on its surface. The beneficial effects of this invention are:

[0041] This invention significantly improves the overall performance of impregnated paper by optimizing the preparation of the base paper, the impregnation process, and the addition of modified materials. Traditional impregnated paper suffers from weak inter-fiber bonding, insufficient water resistance, and poor anti-aging properties, making it difficult to meet the strength and stability requirements of high-end applications. This invention, by introducing modified materials to enhance the interfacial bonding between nanofibers and resin, produces impregnated paper with significantly improved tensile strength compared to traditional products. It also exhibits significantly reduced water absorption in humid environments and maintains a high tensile strength retention rate even after long-term humid heat aging. This effectively solves the problems of delamination, blistering, and performance degradation of traditional products under humid and high-stress environments, making it better suited for applications with stringent performance requirements, such as electronic substrates and industrial filter materials.

[0042] Innovative design of modified materials is the core support for performance improvement. This method utilizes silane coupling agents to modify the surface of nanoparticles, enhancing the interfacial bonding between nanoparticles and the resin matrix through the chemical bonding of epoxy groups. Simultaneously, wood pulp cellulose nanofibers act as a "bridge," uniformly dispersing the modified nanoparticles within the resin through electrostatic adsorption, thus preventing nanoparticle aggregation. This dual-action mechanism effectively improves the compatibility between nanofibers and traditional resins, reduces interfacial debonding, and allows the resin to penetrate more uniformly into the fiber layers, forming a denser three-dimensional reinforcing network, thereby comprehensively improving the structural stability and load-bearing capacity of the paper.

[0043] This process ensures performance improvement while also considering production feasibility and economy. The papermaking, impregnation, and drying steps all utilize conventional papermaking equipment, with mild process conditions and no need for complex high-temperature and high-pressure environments. The preparation of modified materials is achieved through controllable steps such as dispersion, reaction, adsorption, and post-treatment, effectively reducing production energy consumption and costs. Furthermore, calendering further optimizes the paper surface smoothness, expanding its application in decorative materials requiring high surface quality. In summary, this invention, through dual innovation in materials and processes, provides a feasible solution for the large-scale production and application of high-end impregnated paper. Detailed Implementation

[0044] The following detailed embodiments are only used to further illustrate this application and should not be construed as limiting the scope of protection of this application. Those skilled in the art can make some non-essential improvements and adjustments to this application based on the above application content.

[0045] I. Implementation Examples

[0046] Example 1

[0047] Preparation of modified materials (A1-A4): A1. Preparation of nano-silica dispersion: Spherical nano-silica particles with a particle size distribution of 50-100 nm (solid content 30 wt%, specific surface area approximately 200 m²) were selected. 2Weigh 100g of the nano-silica powder and add it to a beaker. Slowly pour in deionized water and stir until completely dispersed to prepare a dispersion with a total volume of about 500mL (solid content about 30%). Then add 0.5wt% of dispersant (sodium polyacrylate, molecular weight about 8000, mass 2.5g) to the dispersion. Place the beaker in an ultrasonic disperser (model: KQ-600VDV, power 600W, frequency 40kHz), set the temperature to 30℃, and sonicate for 30 minutes. During this period, pause the sonication every 10 minutes and stir manually once to ensure uniform dispersion. Finally, a nano-silica dispersion is obtained. A2. Silane coupling agent modification: Transfer the above dispersion to a 500mL stainless steel reactor equipped with a stirrer and thermometer. Turn on the stirrer (speed 300rpm) and heat to 65℃ at a rate of 2℃ / min and maintain a constant temperature. Weigh 5g of silane coupling agent KH560 (γ-glycidoxypropyltrimethoxysilane, purity ≥98%) and slowly add it dropwise to the reaction vessel at a rate of 1mL per minute through a constant pressure dropping funnel, stirring continuously during the addition. After the addition is complete, continue the reaction for 2 hours, maintaining the temperature at 65℃. The reaction endpoint is confirmed by infrared spectroscopy to be that the silanol groups of the silane coupling agent have completely condensed with the hydroxyl groups on the surface of nano-silica (characteristic peaks disappear). A3. Adsorbed cellulose nanofibers: Weigh 10g of wood pulp cellulose nanofibers (raw material is softwood pulp, obtained by high pressure homogenization, length 1-3μm, diameter 5-10nm, solid content 1wt%) and slowly add them to the above reaction vessel, maintaining the temperature at 65℃ and increasing the stirring speed to 500rpm, stirring and mixing continuously for 1 hour. Because the surface of silane-modified nano-silica has epoxy groups (positively charged), while the surface of cellulose nanofibers is rich in hydroxyl groups (negatively charged), the two are uniformly combined through electrostatic adsorption to form "nano-silica-cellulose" composite particles. A4. Post-treatment: The mixture was transferred to a centrifuge tube and centrifuged at 8500 rpm for 12 minutes (centrifuge model: Eppendorf 5810R, relative centrifugal force approximately 15000×g). After removing the supernatant, the precipitate was collected. The precipitate was washed three times with deionized water (200 mL of deionized water each time, stirred for 5 minutes, and then centrifuged again) to ensure the removal of unreacted silane coupling agent and dispersant. The precipitate was then transferred to a vacuum drying oven (model: DZF-6020, vacuum degree -0.08 MPa) and dried at 85°C for 13 hours until constant weight. After drying, it was ground and passed through a 100-mesh sieve (pore size approximately 0.15 mm) to obtain a modified material powder with uniform particle size.

[0048] Preparation of nanofiber composite impregnated paper (S1-S3): S1. Papermaking: 1000g of oven-dry softwood pulp board (raw material is radiata pine, fiber length 0.7-1.2mm, fine component content ≤20%) was selected and pulped to a freeness of 280mL (determined by Canadian standard freeness method) using a pulper (model: VoithTwinFlo 300, power 550kW). During the pulping process, cationic polyacrylamide retention aid (molecular weight 500,000, charge density 30%, dosage 8g, accounting for 0.8% of the dry weight of the pulp) was added. After pulping, the pulp concentration was adjusted to 3%. The pulp is fed into a fourdrinier paper machine (model: Valmet PrimeLine, wire speed 150m / min), where it is evenly distributed to the forming wire via the headbox. In the press section (linear pressure 20kN / m), it is dewatered to approximately 40% dryness, and then dried in the drying section (drying cylinder temperature 120℃) to 92% dryness, finally forming the base paper with a basis weight of 90g / m³. 2 (Thickness approximately 0.09mm). S2. Impregnation Treatment: Preparation of Impregnation Solution: Weigh 85g of phenolic resin (model: 2123, viscosity 200-300mPa·s) with a solid content of 50% (corresponding to 42.5g of dry matter), 6g of modified material (10% solid content) (corresponding to 0.6g of dry matter), and 9g of ethylene glycol. Add them to a beaker and stir until homogeneous (200rpm, 5 minutes) to obtain the impregnation solution (phenolic resin 85%, modified material 6%, ethylene glycol 9%). Pass the base paper roll (1m wide) through the impregnation tank (2m long, stainless steel, with hot water insulation in the jacket). Control the impregnation temperature at 55℃ and the impregnation time at 40 seconds (linear speed 15m / min). Simultaneously, apply a linear pressure of 0.15MPa at the inlet of the impregnation tank (controlled by a pressure roller sensor) to ensure that the impregnation solution penetrates evenly into the interlayer of the base paper fibers (penetration depth detection shows that the resin penetrates to 80% of the base paper thickness). S3. Drying and Calendering: The impregnated wet paper sheets (moisture content approximately 60%) are placed in a hot air drying oven (model: Bühler LDT 500, width 1.2m, air velocity 5m / s) and dried at 110℃ for 12 minutes until the moisture content reaches 6% (measured by a moisture meter). Subsequently, the paper is calendered three times (model: Voith SuperCalender 88, 10 rolls, roll temperature 85℃, linear pressure 35kN / m) to achieve a paper surface smoothness of 320s (measured by the Bühler method), a thickness of 0.1mm, and a tensile strength in the longitudinal direction ≥75N / 15mm.

[0049] Example 2

[0050] The specific implementation method is the same as in Example 1, except that the preparation of the modified material (A1-A4) is as follows: A1. Preparation of nano-silica dispersion: Take 100g of nano-silica particles with a particle size of 50-100nm (solid content 35wt%), add deionized water to prepare 400mL of dispersion (solid content 35%). Add 0.8wt% of dispersant (sodium polyacrylate, mass 3.2g), and treat with an ultrasonic disperser at a frequency of 50kHz for 35 minutes. A2. Silane coupling agent modification: Heat to 68℃, and add silane coupling agent dropwise under stirring at 350rpm (mass ratio of silane coupling agent to nano-silica is 1:5, the mass of nano-silica is 35g, so the amount of silane coupling agent is 7g). After the addition is complete, react for 2.5 hours. A3. Adsorbed cellulose nanofibers: Add wood pulp cellulose nanofibers (2μm in length, 8nm in diameter, 1.5wt% solid content), and mix at 65℃ for 1.5 hours (600rpm) to form composite particles. A4. Post-treatment: Centrifuge at 8800rpm for 14 minutes, wash 3 times, vacuum dry at 80℃ for 12 hours, and grind through a 100-mesh sieve to obtain the modified material (15% solid content).

[0051] Preparation of nanofiber composite impregnated paper (S1-S3): S1. Papermaking: Take 1000g of oven-dry wood pulp board, break it down to 300mL of free pulp, add 10g of cationic polyacrylamide (1% of dry pulp weight), stir for 20 minutes, and form paper with a basis weight of 100g / m³. 2 The base paper. S2. Impregnation treatment: The impregnation solution consists of 88g of phenolic resin (50% solid content), 8g of modified material (15% solid content), and 10g of ethylene glycol, for a total mass of 106g. Impregnation temperature is 60℃, time is 45 seconds, and linear pressure is 0.2MPa. S3. Drying and calendering: Drying temperature is 120℃ until the moisture content is 5%; calendering roller temperature is 90℃, linear pressure is 40kN / m, and surface smoothness is achieved in 350s.

[0052] Example 3

[0053] The specific implementation method is the same as in Example 1, except that the preparation of the modified material (A1-A4) is as follows: A1. Preparation of nano-silica dispersion: Take 100g of nano-silica particles with a particle size of 50-100nm (solid content 32wt%), add deionized water to prepare 350mL of dispersion (solid content 32%). Add 0.6wt% of dispersant (sodium polyacrylate, mass 2.1g), and treat with an ultrasonic disperser at a frequency of 45kHz for 32 minutes. A2. Silane coupling agent modification: Heat to 62℃, and add silane coupling agent dropwise under stirring at 380rpm (mass ratio of silane coupling agent to nano-silica is 1:7, the mass of nano-silica is 32g, so the amount of silane coupling agent is 4.57g), and react for 1.5 hours. A3. Adsorbed cellulose nanofibers: Wood pulp cellulose nanofibers (length 1.5 μm, diameter 6 nm, solid content 1.2 wt%) were added and stirred at 62℃ for 1.2 hours (550 rpm) to form composite particles. A4. Post-treatment: The mixture was centrifuged at 8200 rpm for 13 minutes, washed 4 times, vacuum dried at 82℃ for 13 hours, and ground through a 100-mesh sieve to obtain the modified material (solid content 12%).

[0054] Preparation of nanofiber composite impregnated paper (S1-S3): S1. Papermaking: Take 1000g of oven-dry wood pulp board, break it down to 320mL of free pulp, add 10g of cationic polyacrylamide (1% of dry pulp weight), stir for 20 minutes, and form paper with a basis weight of 80g / m³. 2 The base paper. S2. Impregnation treatment: The impregnation solution consists of 80g of phenolic resin (55% solid content), 5g of modified material (10% solid content), and 5g of ethylene glycol, for a total mass of 90g. Impregnation temperature is 50℃, time is 30 seconds, and linear pressure is 0.1MPa. S3. Drying and calendering: Drying temperature is 100℃ until the moisture content is 8%; calendering roller temperature is 80℃, linear pressure is 30kN / m, and surface smoothness is 310s.

[0055] Comparative Example 1

[0056] The specific implementation method is the same as in Example 1, except that the preparation of the modified material is not included. The preparation of the nanofiber composite impregnated paper is the same as in Example 1, except that no modified material is added to the impregnation solution. The impregnation solution consists of 85g of phenolic resin (50% solid content) and 9g of ethylene glycol, with a total mass of 94g. The basis weight of the base paper is 90g / m³. 2 The immersion temperature was 55°C, the time was 40 seconds, the linear pressure was 0.15 MPa, the drying temperature was 110°C, and the calendering treatment was the same as in Example 1.

[0057] Comparative Example 2

[0058] The specific implementation method is the same as in Example 1, except that the modified material preparation is as follows: step A2 is omitted (silane coupling agent is not added), and the nano-silica dispersion (30% solid content) is directly mixed with wood pulp cellulose nanofibers (1-3μm, 5-10nm, 1wt% solid content) by stirring (500rpm, 1 hour). The subsequent centrifugation, washing, and drying steps are the same as in Example 1. The amount of modified material used in the impregnation solution is 6g (10% solid content), and the other steps are the same as in Example 1. The preparation of nanofiber composite impregnated paper is the same as in Example 1.

[0059] Comparative Example 3

[0060] The specific implementation method is the same as in Example 1, except that the preparation of the nanofiber composite impregnated paper is as follows: except that no linear pressure (0 MPa) is applied during the impregnation process, the other steps are the same as in Example 1. The impregnation solution consists of 85g of phenolic resin (50% solid content), 6g of modified material (10% solid content), and 9g of ethylene glycol. The impregnation temperature is 55°C, the time is 40 seconds, the drying temperature is 110°C, and the calendering treatment is the same as in Example 1.

[0061] II. Performance Testing

[0062] The nanofiber composite impregnated papers prepared using the above-described preparation processes of Examples 1-3 and Comparative Examples 1-3 were subjected to performance testing according to the following methods.

[0063] 1. Basis weight test: Performed according to GB / T 451.2-2023 "Determination of basis weight of paper and paperboard". Take a sample with an area of ​​100 cm². 2 The sample (accurate to 0.01 g) was dried to constant weight and then weighed. The mass per unit area (g / m²) was calculated. 2 ).

[0064] 2. Thickness test: According to GB / T 451.3-2002 "Determination of thickness of paper and paperboard". Using a thickness gauge (model: L&W thickness gauge), take 10 evenly distributed points on the sample, measure the thickness (mm), and take the average value.

[0065] 3. Smoothness Test: According to GB / T 456-2002 "Determination of Smoothness of Paper and Paperboard (Beck Method)". Using a Beck smoothness tester (model: L&W smoothness tester), place the sample on the test platform, apply a certain pressure (approximately 100 kPa), and measure the air leakage time (s).

[0066] 4. Tensile Strength Test: According to GB / T 453-2002 "Determination of Tensile Strength of Paper and Paperboard (Constant Rate Tensile Method)". Use an electronic tensile testing machine (model: Instron5967), with a sample size of 25mm × 150mm, a tensile speed of 50mm / min, record the maximum load (N) at break, and calculate the tensile strength (N / 15mm). Wet Tensile Strength Test: Immerse the sample in 23℃ deionized water for 1 minute, remove it, absorb the surface moisture with filter paper, and test according to the above method.

[0067] 5. Water Absorption Test: According to GB / T1543-2007 "Determination of Water Absorption of Paper and Paperboard (Cobb Method)". Weigh 10g of dry sample (m0), spread it evenly on absorbent paper, cover with the same mass of absorbent paper, apply pressure (10kPa) for 30 seconds, remove and weigh the total mass (m1). Water absorption rate = (m1-m0) / m0×100%.

[0068] 6. Damp heat aging resistance test: According to GB / T24849-2010 "Determination of damp heat aging resistance". Place the sample in a constant temperature and humidity chamber (model: ESPECSH-241) and place it in an environment of 100℃ and 80% relative humidity for 500 hours. After removal, determine the tensile strength after aging according to the tensile strength test method. Retention rate = (strength after aging / initial strength) × 100%.

[0069] 7. Test Results:

[0070] Table 1: Test results of each embodiment and comparative example

[0071]

[0072] As shown in Table 1, Examples 1-3 of this invention effectively solved the technical problems of traditional impregnated paper, such as weak bonding between plant fibers, poor water resistance, and weak aging resistance, through optimization of the interface between plant fibers and nanofibers and precise control of process parameters. Specifically, traditional impregnated paper suffers from a loose structure and easy delamination due to weak bonding between plant fibers. Examples 1-3, by adding modified materials (silane-modified nano-silica-cellulose composite particles), utilize the epoxy groups of the silane coupling agent to form chemical cross-links with phenolic resin. Simultaneously, cellulose nanofibers are adsorbed onto the surface of nano-silica through electrostatic interaction, forming a three-dimensional reinforcing network of "nanoparticles-cellulose-resin," significantly enhancing the bonding between fibers. This results in a 36% or more increase in tensile strength (68-80 N / 15 mm) compared to the comparative example (50-58 N / 15 mm), and a 30%-50% increase in wet tensile strength (11-13 N / 15 mm) compared to the comparative example (8-9 N / 15 mm), effectively solving the structural instability problem caused by weak bonding between plant fibers. Traditional impregnated paper is prone to absorbing water and swelling in humid environments due to the poor water resistance of plant fibers. However, the modified materials in Examples 1-3 contain nano-silica particles (50-100nm in diameter) that fill the fiber gaps, forming a dense structure. Simultaneously, the epoxy groups of the silane coupling agent cross-link with the resin, reducing water permeation pathways. The water absorption rate (0.7-0.9%) is 40%-50% lower than the comparative example (1.3-1.5%), significantly improving water resistance. Traditional impregnated paper is also prone to aging and cracking under long-term humid and hot conditions due to the debonding of the plant fiber and resin interface. The modified materials in Examples 1-3, through the chemical cross-linking of the silane coupling agent with the resin, enhance interfacial bonding stability. After 500 hours of aging, the tensile strength retention rate (85-90%) is 13%-25% higher than the comparative example (65-72%), effectively delaying performance degradation caused by aging. Comparative Example 1 (unmodified material) lacks an interfacial reinforcement mechanism, resulting in the lowest tensile strength, wet tensile strength, and aging retention rate, while exhibiting the highest water absorption rate, thus perpetuating the performance defects of traditional impregnated paper. Comparative Example 2 (unmodified nano-silica) lacks a silane coupling agent, leading to weak adsorption of nanoparticles and cellulose, uneven dispersion, and thus inferior performance. Comparative Example 3 (no pressure) exhibits slightly better performance than the previous two but still weaker than the examples due to uneven resin penetration and weak interfacial bonding. In summary, the examples systematically solved the core problems of traditional impregnated paper through material modification and process optimization, achieving a significant performance improvement.

[0073] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A production process for nanofiber composite impregnated paper, characterized in that, Includes the following steps: S1, the wood pulp board is broken down into pulp with a freeness of 280-320mL by a pulper, cationic polyacrylamide retention aid is added, and the mixture is stirred to form the base paper; S2, the base paper is immersed in an impregnation tank containing an impregnation solution, which consists of the following components: 80-90 parts of phenolic resin, 5-8 parts of modified material, and 5-10 parts of ethylene glycol. During the impregnation process, a linear pressure of 0.1-0.2 MPa is applied to make the resin evenly penetrate into the interlayer of the base paper. S3, the impregnated wet paper sheets are dried in a hot air drying oven to a moisture content of 5-8%; The modified material preparation steps include: A1. Disperse nano-silica particles in deionized water, add a dispersant, and process in an ultrasonic disperser to obtain a nano-silica dispersion. A2. Transfer the nano-silica dispersion to a reaction vessel, heat to 60-70℃, and add the silane coupling agent γ-glycidoxypropyltrimethoxysilane dropwise under stirring. The mass ratio of the silane coupling agent to the nano-silica is 1:(5-8). After the dropwise addition is complete, continue the reaction. A3. Add wood pulp cellulose nanofibers to the reactor and stir to obtain a mixture while maintaining the temperature at 60-65℃. A4. Finally, the mixture is centrifuged to remove the supernatant. The precipitate is washed with deionized water, dried in a vacuum drying oven, and ground through a 100-mesh sieve.

2. The production process of nanofiber composite impregnated paper according to claim 1, characterized in that, In step S1, the cationic polyacrylamide accounts for 0.5-1% of the dry weight of the pulp; the stirring time is 10-20 min; and the basis weight of the base paper is 80-100 g / m².

3. The production process of nanofiber composite impregnated paper according to claim 1, characterized in that, In step S2, the solid content of the phenolic resin is 50-55%, and the solid content of the modified material is 10-15%; the impregnation temperature of the base paper is 50-60℃, and the impregnation time is 30-45s.

4. The production process of nanofiber composite impregnated paper according to claim 1, characterized in that, In step S3, the drying temperature of the hot air drying oven is 100-120℃.

5. The production process of nanofiber composite impregnated paper according to claim 1, characterized in that, The production process of the nanofiber composite impregnated paper also includes: calendering the paper surface with a calender at a roller temperature of 80-90℃ and a linear pressure of 0.03-0.04MPa to achieve a smoothness of ≥300s.

6. The production process of nanofiber composite impregnated paper according to claim 1, characterized in that, In step A1, the particle size of the nano-silica particles is 50-100nm, the solid content of the nano-silica dispersion is 30-35wt%, the solid content of the dispersant is 0.5-1wt%, the processing frequency of the ultrasonic disperser is 30-50kHz, and the processing time is 30-35min.

7. The production process of nanofiber composite impregnated paper according to claim 1, characterized in that, In step A2, the stirring speed is 300-400 rpm, and the reaction time continues for 1.5-2.5 hours after the addition is completed.

8. The production process of nanofiber composite impregnated paper according to claim 1, characterized in that, In step A3, the wood pulp cellulose nanofibers have a length of 1-3 μm, a diameter of 5-10 nm, and a solid content of 1-1.5 wt%; the stirring speed is 500-600 rpm, and the stirring time is 1-2 h.

9. The production process of nanofiber composite impregnated paper according to claim 1, characterized in that, In step A4, the mixture is centrifuged at 8000-9000 rpm for 10-15 min, and the precipitate is washed with deionized water 3-4 times. The drying temperature in the vacuum drying oven is 80-85℃, and the drying time is 12-14 h.

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