Production process of nanofiber composite impregnated paper

Abstract

The invention discloses a production process of nanofiber composite impregnated paper in the fields of papermaking industry and composite materials, which comprises the following steps of: crushing a wood pulp board into paper pulp with certain freeness, adding a cationic polyacrylamide retention aid, stirring, and making raw paper; immersing the raw paper into an impregnation liquid containing phenolic resin, a modified material and ethylene glycol, and applying a certain linear pressure to enable the resin to uniformly permeate into fiber layers; drying the soaked wet paper sheet to a certain water content by a hot air drying box; and the surface smoothness of the paper can be improved through calendering treatment of a calender. Wherein the modified material is prepared by dispersing nano silicon dioxide particles in deionized water, adding a dispersing agent, performing ultrasonic treatment, heating, dropwise adding a silane coupling agent for reaction, adding wood pulp cellulose nano fibrils, stirring for adsorption, and finally performing centrifugal washing, vacuum drying and grinding. According to the process, the interface bonding of the nanofiber and the resin is enhanced through the modified material, and the strength, the water resistance and the aging resistance of the impregnated paper are improved.

Description

Technical Field

[0001] The present invention relates to the field of papermaking industry and composite material technology, and in particular to a production process of nanofiber composite impregnated paper. Background Art

[0002] Traditional impregnated paper, as an important component of decorative materials, electronic substrates and industrial filter materials, has long been made of plant fibers (such as wood pulp) as the main raw material, and is made 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 anti-aging properties. In particular, they are prone to water absorption and expansion in humid environments, leading to delamination. Under high stress or long-term use, they are prone to blistering and cracking. It is 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 materials need to maintain structural strength in high humidity environments. The performance bottleneck of traditional impregnated paper has gradually become a constraint on the development of related fields.

[0003] With the rise of nanomaterials, research on adding nanofibers (such as cellulose nanofibrils, polyester nanofibers, etc.) to impregnated paper to enhance performance has gradually increased. Nanofibers have high specific surface area, high modulus and strong interfacial bonding potential. In theory, they can improve the overall performance of impregnated paper by bridging the gaps between fibers and improving the uniformity of resin penetration. However, nanofibers have high surface energy and strong polarity, and are not compatible with traditional resin matrices (such as phenolic resins and epoxy resins), which can easily lead to uneven dispersion or interfacial debonding problems. Uneven dispersion will cause local strength loss, and interfacial debonding will weaken the collaborative load-bearing capacity of the resin and fiber. Ultimately, it is difficult to fully exert the reinforcing effect of nanofibers, limiting their application and promotion in high-end impregnated paper.

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

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

[0006] The present invention achieves the above-mentioned purpose through the following technical solutions:

[0007] A production process for nanofiber composite impregnated paper comprises the following steps:

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

[0009] S2, immersing the base paper in an impregnation tank containing an impregnation solution composed of the following components: 80-90 parts of phenolic resin, 5-8 parts of a modifying material, and 5-10 parts of ethylene glycol. During the impregnation process, a linear pressure of 0.1-0.2 MPa is applied to ensure that the resin evenly penetrates between the layers of the base paper.

[0010] S3, the wet paper sheets after impregnation 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 is purchased from Henan Qingshuiyuan Technology Co., Ltd.

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

[0013] According to a preferred embodiment of the present invention, the ethylene glycol is purchased from Yanshan Petrochemical Company of Sinopec.

[0014] According to a preferred embodiment of the present invention, the hot air drying oven is 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 minutes, and the basis weight of the base paper is 80-100g / m 2 .

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

[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 base paper is impregnated at a temperature of 50-60°C, and the impregnation time is 30-45 seconds.

[0018] In step S2 of the present invention, in the impregnation liquid, phenolic resin (solid content 50-55%) is used as the main binder, and the hydroxymethyl (-CH2OH) on its molecular chain undergoes a cross-linking reaction with the epoxy group 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 liquid and promote the uniform penetration of the resin into the fiber layers of the base paper.

[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 the present invention, a linear pressure of 0.1-0.2 MPa is applied to ensure that the resin penetrates to a depth of more than 80% of the base paper thickness to ensure that the crosslinking reaction proceeds fully; drying (100-120° C.) solidifies the resin to form a stable crosslinked network; and calendering (80-90° C., 30-40 kN / m) compacts the paper through mechanical pressure, reduces surface porosity, improves smoothness (≥300 s), and promotes further bonding between the resin and the fiber.

[0021] According to a preferred embodiment of the present invention, the production process of the nanofiber composite impregnated paper further comprises: calendering treatment with a calender at a roller temperature of 80-90°C and a line pressure of 0.03-0.04 MPa to make the paper surface smoothness ≥300s.

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

[0023] A1, dispersing nano-silica particles in deionized water, adding a dispersant, and treating in an ultrasonic disperser to obtain a nano-silica dispersion;

[0024] A2, transferring the nano-silica dispersion to a reactor, raising the temperature to 60-70°C, and adding a silane coupling agent dropwise under stirring, wherein the mass ratio of the silane coupling agent to the nano-silica is 1:(5-8). After the addition is completed, the reaction is continued to allow the silane coupling agent to undergo a hydrolysis-condensation reaction on the surface of the nano-silica;

[0025] A3, adding wood pulp cellulose nanofibrils to the reactor, maintaining the temperature at 60-65°C and stirring to allow the modified nano-silica particles to adsorb on the surface of the cellulose nanofibrils;

[0026] A4. Finally, the mixture was centrifuged to remove the supernatant, and the precipitate was 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-silicon dioxide is purchased from Jiangsu Tianniao High-tech Co., Ltd.

[0028] According to a preferred embodiment of the present invention, the dispersant (sodium polyacrylate) is 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 nanofibrils are purchased from Shandong Sun Paper Co., Ltd.

[0032] According to a preferred embodiment of the present invention, the vacuum drying oven is purchased from Shanghai Yiheng Scientific Instrument 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 the present invention, nano-silica particles (particle size 50-100 nm) are stably dispersed in deionized water with a dispersant (such as sodium polyacrylate) to form a uniform colloid. The dispersant prevents nano-particle agglomeration through electrostatic repulsion. Ultrasonic dispersion (30-50 kHz, 30-35 min) further destroys the van der Waals forces between the particles, ensuring that the nano-silica exists in a monodisperse state in 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 after the dropwise addition is 1.5-2.5 hours.

[0036] In step A2 of the present invention, the temperature is raised to 60-70° C. and a silane coupling agent is added dropwise (at a mass ratio of 1:5-8 to the nano-silica). The epoxy group of the silane coupling agent (such as the epoxy group of γ-glycidyloxypropyltrimethoxysilane) undergoes a hydrolysis reaction in the presence of water to generate silanol (-Si-OH). The silanol reacts with the native silanol (-Si-OH) on the surface of the nano-silica through a condensation reaction (removing water molecules) to form a covalent bond, thereby grafting the silane coupling agent to the surface of the nano-silica. At the same time, the epoxy group (-COC-) of the silane coupling agent is exposed because it does not participate in the reaction, providing an active site for subsequent cross-linking.

[0037] According to a preferred embodiment of the present invention, in step A3, the length of the wood pulp cellulose nanofibrils 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 the present invention, wood pulp cellulose nanofibrils (length 1-3 μm, diameter 5-10 nm, solid content 1-1.5 wt%) are added. The surface of the wood pulp cellulose nanofibrils is rich in negatively charged hydroxyl groups (-OH). The hydroxyl groups are tightly combined with the positively charged areas on the surface of the modified nano-silica due to the protonation of epoxy groups through electrostatic attraction to form "nano-silica-cellulose" composite particles, thereby achieving uniform dispersion of the nanoparticles in the cellulose.

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

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

[0041] The present invention significantly improves the comprehensive performance of impregnated paper by optimizing the preparation of base paper, the impregnation process, and the addition of modified materials. Traditional impregnated paper is difficult to meet the requirements of high-end fields for material strength and stability due to its weak bonding between plant fibers, insufficient water resistance, and weak anti-aging performance. However, the present invention introduces modified materials to enhance the interface bonding between nanofibers and resins. The resulting impregnated paper has a significantly improved tensile strength compared to traditional products, a significantly reduced water absorption rate in humid environments, and can still maintain a high tensile strength retention rate after long-term wet and hot aging. This effectively solves the problems of delamination, blistering, and performance degradation of traditional products in humid and high-stress environments, and can be better applied to electronic substrates, industrial filter materials, and other scenarios with strict performance requirements.

[0042] The innovative design of the modified material is the core support for this performance improvement. Silane coupling agents are used to modify the surface of the nanoparticles, leveraging the chemical bonding between epoxy groups and the resin matrix to enhance the interfacial adhesion between the nanoparticles and the resin. Simultaneously, wood pulp cellulose nanofibrils act as a "bridge," evenly dispersing the modified nanoparticles in the resin through electrostatic adsorption, thus preventing nanoparticle agglomeration. This dual mechanism effectively improves the compatibility of the nanofibers with traditional resins, reduces interfacial debonding, and allows the resin to more evenly penetrate the fiber layers, forming a tighter three-dimensional reinforcement network, thereby comprehensively enhancing the structural stability and load-bearing capacity of the paper.

[0043] This process not only ensures performance improvement, but also takes into account production feasibility and economy. Conventional papermaking equipment is used in the steps of base paper making, impregnation and drying. The process conditions are mild and do not require a complex high-temperature and high-pressure environment. The preparation of modified materials is achieved through controllable steps such as dispersion, reaction, adsorption and post-treatment, which effectively reduces production energy consumption and costs. In addition, the calendering treatment further optimizes the surface smoothness of the paper and expands its application in the field of decorative materials that require high surface quality. In summary, the present invention provides a feasible solution for the large-scale production and application of high-end impregnated paper through the dual innovation of materials and processes. DETAILED DESCRIPTION

[0044] The following specific implementation methods are only used to further illustrate the present application and should not be understood as limiting the scope of protection of the present application. Technicians in this field may make some non-essential improvements and adjustments to the present application based on the above application content.

[0045] 1. Implementation

[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 of about 200 m 2 / g), weigh 100g of the nano-silica powder and add it to a beaker, slowly inject deionized water into it and stir until it is completely dispersed to prepare a dispersion with a total volume of about 500mL (solid content of about 30%). Subsequently, 0.5wt% of dispersant (sodium polyacrylate, molecular weight of about 8000, mass of 2.5g) is added to the dispersion, and the beaker is placed in an ultrasonic disperser (model: KQ-600VDV, power 600W, frequency 40kHz), set the temperature to 30°C, and ultrasonicate for 30 minutes. During this period, the ultrasound is paused every 10 minutes and manually stirred once to ensure uniform dispersion, and finally a nano-silica dispersion is obtained. A2. Silane coupling agent modification: The above dispersion is transferred to a 500mL stainless steel reactor with a stirring device and a thermometer, stirring is started (speed 300rpm), and the temperature is raised to 65°C at a rate of 2°C / min and maintained constant. Weigh 5 g of the silane coupling agent KH560 (γ-glycidyloxypropyltrimethoxysilane, purity ≥98%) and slowly add it to the reactor at a rate of 1 mL per minute using a constant pressure dropping funnel, stirring continuously during the addition. After the addition is completed, continue the reaction for 2 hours, maintaining the temperature at 65°C. The reaction endpoint is confirmed by infrared spectroscopy to confirm that the silanol groups of the silane coupling agent are completely condensed with the hydroxyl groups on the surface of the nano-silica (the characteristic peak disappears). A3. Adsorption of cellulose nanofibrils: Weigh 10 g of wood pulp cellulose nanofibrils (the raw material is softwood pulp, obtained by high-pressure homogenization, length 1-3 μm, diameter 5-10 nm, solid content 1 wt%) and slowly add it to the above reactor. Maintain the temperature at 65°C and increase the stirring speed to 500 rpm. Continue stirring and mixing for 1 hour. Because the silane-modified nanosilica surface contains epoxy groups (positively charged), while the cellulose nanofibrils are rich in hydroxyl groups (negatively charged), the two are uniformly bonded through electrostatic adsorption, forming "nanosilica-cellulose" composite particles. A4. Post-treatment: Transfer the mixture to a centrifuge tube and centrifuge at 8500 rpm for 12 minutes (Eppendorf 5810R, relative centrifugal force approximately 15,000 × g). Remove the supernatant and collect the precipitate. Wash the precipitate three times with deionized water (200 mL of deionized water each wash, stirring for 5 minutes, and then centrifuging again) to ensure removal of unreacted silane coupling agent and dispersant. The precipitate is then transferred to a vacuum drying oven (DZF-6020, vacuum degree -0.08 MPa) and dried at 85°C for 13 hours to constant weight. Grind the mixture and pass it 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. Base papermaking: 1000g of absolutely dry softwood pulp board (raw material is radiata pine, fiber length 0.7-1.2mm, fine component content ≤20%) is selected and crushed to a freeness of 280mL (determined by the Canadian standard freeness method) by a pulper (model: VoithTwinFlo 300, power 550kW). A cationic polyacrylamide retention aid (molecular weight 500,000, charge density 30%, dosage 8g, accounting for 0.8% of the dry weight of the pulp) is added during the crushing process. After the crushing is completed, the pulp concentration is adjusted to 3%. The pulp was fed into a Fourdrinier paper machine (model: Valmet PrimeLine, wire speed 150m / min), evenly distributed to the forming wire through the headbox, dehydrated to a dryness of about 40% in the press section (line pressure 20kN / m), and then dried to a dryness of 92% in the drying section (drying cylinder temperature 120℃). Finally, it was made into base paper with a basis weight of 90g / m 2 (Thickness approximately 0.09mm). S2. Impregnation treatment: Prepare the impregnation solution: Weigh 85g (corresponding to 42.5g dry matter) of phenolic resin (model: 2123, viscosity 200-300mPa·s) with a solid content of 50%, 6g (corresponding to 0.6g dry matter) of modified material (solid content 10%), and 9g of ethylene glycol, add them to a beaker and stir to mix evenly (speed 200rpm, 5 minutes) to obtain an impregnation solution (phenolic resin accounts for 85%, modified material accounts for 6%, and ethylene glycol accounts for 9%). Pass the base paper roll (width 1m) through the impregnation tank (length 2m, stainless steel material, jacketed with hot water for insulation), control the impregnation temperature to 55°C, the impregnation time to 40 seconds (line speed 15m / min), and at the same time, apply a linear pressure of 0.15MPa at the entrance of the impregnation tank (controlled by a pressure sensor on the pressure roller) to ensure that the impregnation solution evenly penetrates the fiber layers of the base paper (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%) were placed in a hot air drying oven (Bühler LDT 500, width 1.2 m, air speed 5 m / s) and dried at 110°C for 12 minutes to a moisture content of 6% (as measured by a moisture meter). The sheets were then passed through a calender (Voith SuperCalender 88, 10 rollers, roller temperature 85°C, linear pressure 35 kN / m). After three calendering cycles, the paper achieved a surface smoothness of 320s (as measured by the Buick method), a thickness of 0.1 mm, and a tensile strength of ≥75 N / 15 mm in the longitudinal direction.

[0049] Example 2

[0050] The specific implementation method is the same as that of Example 1, except that the modified material is prepared (A1-A4): A1. Preparation of nano-silica dispersion: Take 100g of nano-silica particles with a particle size of 50-100nm (solid content 35wt%) and 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°C, add silane coupling agent dropwise (with a mass ratio of 1:5 to nano-silica, the mass of nano-silica is 35g, so the amount of silane coupling agent is 7g) while stirring at 350rpm, and react for 2.5 hours after the addition is completed. A3. Adsorption of Cellulose Nanofibrils: Add wood pulp cellulose nanofibrils (2 μm in length, 8 nm in diameter, 1.5 wt% solids content) and maintain stirring at 65°C for 1.5 hours (600 rpm) to form composite particles. A4. Post-treatment: Centrifuge at 8800 rpm for 14 minutes, wash three times, vacuum dry at 80°C for 12 hours, and grind through a 100-mesh sieve to obtain a modified material (15% solids content).

[0051] Preparation of nanofiber composite impregnated paper (S1-S3): S1. Base paper making: 1000g of absolute dry wood pulp board was crushed to a pulp with a freeness of 300mL, 10g of cationic polyacrylamide (1% of pulp dry weight) was added, stirred for 20 minutes, and papered into a basis weight of 100g / m 2 Base paper. S2. Impregnation: The impregnation solution consists of 88g of phenolic resin (50% solids), 8g of modified material (15% solids), and 10g of ethylene glycol, for a total mass of 106g. Impregnation temperature: 60°C, time: 45 seconds, linear pressure: 0.2 MPa. S3. Drying and calendering: Drying temperature: 120°C, to a moisture content of 5%; calendering roll temperature: 90°C, linear pressure: 40 kN / m, surface smoothness: 350 seconds.

[0052] Example 3

[0053] The specific implementation method is the same as that of Example 1, except that the modified material is prepared (A1-A4): A1. Preparation of nano-silica dispersion: 100g of nano-silica particles with a particle size of 50-100nm (solid content 32wt%) is added to deionized water to prepare 350mL of dispersion (solid content 32%). 0.6wt% of dispersant (sodium polyacrylate, mass 2.1g) is added and treated with an ultrasonic disperser at a frequency of 45kHz for 32 minutes. A2. Silane coupling agent modification: The temperature is raised to 62°C, and the silane coupling agent (with a mass ratio of 1:7 to nano-silica, the mass of nano-silica is 32g, so the amount of silane coupling agent is 4.57g) is added dropwise while stirring at 380rpm and the reaction is allowed to react for 1.5 hours. A3. Adsorption of Cellulose Nanofibrils: Add wood pulp cellulose nanofibrils (length 1.5 μm, diameter 6 nm, solids content 1.2 wt%) and maintain stirring at 62°C (550 rpm) for 1.2 hours to form composite particles. A4. Post-treatment: Centrifuge at 8200 rpm for 13 minutes, wash four times, vacuum dry at 82°C for 13 hours, and grind through a 100-mesh sieve to obtain a modified material (solids content 12%).

[0054] Preparation of nanofiber composite impregnated paper (S1-S3): S1. Base papermaking: 1000g of absolute dry wood pulp board was crushed to a pulp with a freeness of 320mL, 10g of cationic polyacrylamide (1% of the pulp dry weight) was added, stirred for 20 minutes, and papered into a quantitative 80g / m 2 Base paper. S2. Impregnation: The impregnation solution consists of 80g of phenolic resin (55% solids), 5g of modified material (10% solids), and 5g of ethylene glycol, for a total mass of 90g. Impregnation temperature: 50°C, time: 30 seconds, linear pressure: 0.1 MPa. S3. Drying and calendering: Drying temperature: 100°C, to a moisture content of 8%; calendering roll temperature: 80°C, linear pressure: 30 kN / m, surface smoothness: 310 seconds.

[0055] Comparative Example 1

[0056] The specific implementation method is the same as that of Example 1, except that the modified material is not added. Preparation of nanofiber composite impregnated paper: except that the modified material is not added to the impregnation liquid, the other steps are the same as those of Example 1. The impregnation liquid composition is phenolic resin (solid content 50%) 85g, ethylene glycol 9g, total mass 94g. The base paper weight is 90g / m 2 , dipping temperature 55°C, time 40 seconds, line pressure 0.15 MPa, drying temperature 110°C, calendering treatment is the same as Example 1.

[0057] Comparative Example 2

[0058] The specific implementation method is the same as that of Example 1, except that, in the preparation of the modified material, step A2 is omitted (no silane coupling agent is added), and the nanosilica dispersion (30% solid content) and wood pulp cellulose nanofibrils (1-3 μm, 5-10 nm, 1 wt% solid content) are directly stirred and mixed (500 rpm for 1 hour). The subsequent centrifugation, washing, and drying steps are the same as those of Example 1. The amount of modified material used in the impregnation solution is 6 g (10% solid content), and the other steps are the same as those of Example 1. Preparation of nanofiber composite impregnated paper: The same as in Example 1.

[0059] Comparative Example 3

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

[0061] 2. Performance Testing

[0062] The nanofiber composite impregnated paper prepared by the preparation process of the above examples 1-3 and comparative examples 1-3 was tested for performance according to the following method

[0063] 1. Quantitative test: According to GB / T 451.2-2023 "Paper and board - Determination of quantitative weight". Take an area of 100cm 2 The sample (accurate to 0.01g) was dried to constant weight and weighed to calculate the mass per unit area (g / m 2 ).

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

[0065] 3. Smoothness test: According to GB / T 456-2002, "Paper and paperboard - Determination of smoothness (Buick method)", use a Buick smoothness tester (model: L&W smoothness tester). Place the sample on the test platform, apply a certain pressure (about 100kPa), and measure the air leakage time (s).

[0066] 4. Tensile Strength Test: According to GB / T 453-2002, "Paper and paperboard—Determination of tensile strength (constant rate of tension)." Use an electronic tensile testing machine (Instron 5967), with a specimen size of 25 mm x 150 mm and a tensile speed of 50 mm / min. Record the maximum load (N) at break and calculate the tensile strength (N / 15 mm). Wet Tensile Strength Test: Immerse the specimen in 23°C deionized water for 1 minute. Remove and remove with filter paper to remove surface moisture. Test as described above.

[0067] 5. Water Absorption Test: According to GB / T 1543-2007, "Determination of Water Absorption of Paper and Paperboard (Cobble Method)", weigh 10g of the dry sample (m0), spread it flat on absorbent paper, cover it with absorbent paper of the same mass, apply pressure (10kPa) for 30 seconds, remove it, and weigh the total mass (m1). Water Absorption = (m1 - m0) / m0 × 100%.

[0068] 6. Moisture and heat aging resistance test: According to GB / T 24849-2010, "Determination of moisture and heat aging resistance," place the sample in a constant temperature and humidity chamber (model: ESPECSH-241) at 100°C and 80% relative humidity for 500 hours. After removal, measure the tensile strength after aging using the tensile strength test method. Retention rate = (post-aging strength / initial strength) × 100%.

[0069] 7. Test results:

[0070] Table 1: Test results of various embodiments and comparative examples

[0071]

[0072] As can be seen from Table 1, Examples 1-3 of the present invention effectively solve the technical problems of weak plant fiber bonding, poor water resistance, and weak aging resistance of traditional impregnated paper by optimizing the interface bonding between plant fibers and nanofibers and precisely controlling the process parameters. The specific analysis is as follows: Traditional impregnated paper has a loose structure and is easy to delaminate due to weak bonding between plant fibers. However, Examples 1-3 add a modified material (silane-modified nano-silica-cellulose composite particles) to form a chemical crosslink with the phenolic resin by using the epoxy group of the silane coupling agent. At the same time, the cellulose nanofibrils are adsorbed on the surface of the nano-silica by electrostatic action, forming a three-dimensional reinforced network of "nanoparticles-cellulose-resin", which significantly enhances the bonding between fibers. The tensile strength (68-80N / 15mm) is increased by more than 36% compared to the comparative example (50-58N / 15mm), and the wet tensile strength (11-13N / 15mm) is increased by 30%-50% compared to the comparative example (8-9N / 15mm), effectively solving the structural instability problem caused by weak plant fiber bonding. Traditional impregnated paper has poor water resistance due to plant fibers, and is prone to water absorption, swelling, and delamination in humid environments. However, the nano-silica particles (particle size 50-100nm) in the modified materials of Examples 1-3 fill the fiber gaps, forming a dense structure. At the same time, the epoxy groups of the silane coupling agent cross-link with the resin to reduce the water penetration path. The water absorption rate (0.7-0.9%) is reduced by 40%-50% compared with the control example (1.3-1.5%), significantly improving water resistance. Traditional impregnated paper is prone to aging and cracking in long-term humid and hot environments due to debonding at the plant fiber and resin interface. However, the modified materials of Examples 1-3 enhance the interfacial bonding stability through the chemical cross-linking of the silane coupling agent and the resin. After 500 hours of aging, the tensile strength retention rate (85-90%) is increased by 13%-25% compared with the control example (65-72%), effectively delaying the performance degradation caused by aging. Comparative Example 1 (no modified material) lacks an interface reinforcement mechanism, resulting in the lowest tensile strength, wet tensile strength, and aging retention rate, and the highest water absorption rate, continuing the performance defects of traditional impregnated paper. Comparative Example 2 (unmodified nanosilica) does not use a silane coupling agent, resulting in weak adsorption of nanoparticles to cellulose and uneven dispersion, resulting in inferior performance. Comparative Example 3 (no pressure) has uneven resin penetration and loose interface bonding, resulting in slightly better performance than the previous two but still weaker than the examples. In summary, the examples systematically address the core issues of traditional impregnated paper through modified materials and process optimization, achieving significant performance improvements.

[0073] The above-described embodiments merely illustrate several implementations of the present invention. 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 a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, and all such variations and improvements fall within the scope of protection of the present invention.

Claims

1. A production process for nanofiber composite impregnated paper, characterized in that: The following steps are involved: S1, the wood pulp board is crushed into pulp with a freeness of 280-320 mL by a pulper, a cationic polyacrylamide retention aid is added, and the pulp is stirred to form a base paper; S2, immersing the base paper in an impregnation tank containing an impregnation solution composed of the following components: 80-90 parts of phenolic resin, 5-8 parts of a modifying material, and 5-10 parts of ethylene glycol. During the impregnation process, a linear pressure of 0.1-0.2 MPa is applied to ensure that the resin evenly penetrates between the layers of the base paper. S3, the wet paper sheets after impregnation are dried in a hot air drying oven to a moisture content of 5-8%.

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 minutes, and the basis weight of the base paper is 80-100g / m 2 .

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 base paper is impregnated at a temperature of 50-60° C., and the impregnation time is 30-45 seconds.

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°C.

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 further comprises: calendering treatment with a calender at a roller temperature of 80-90° C. and a line pressure of 0.03-0.04 MPa to ensure that the paper surface smoothness is ≥300s.

6. The production process of nanofiber composite impregnated paper according to any one of claims 1 to 5, characterized in that: The modified material preparation step comprises: A1, dispersing nano-silica particles in deionized water, adding a dispersant, and treating in an ultrasonic disperser to obtain a nano-silica dispersion; A2, transfer the nano-silica dispersion to a reactor, raise the temperature to 60-70°C, and add a silane coupling agent dropwise under stirring, wherein the mass ratio of the silane coupling agent to the nano-silica is 1:(5-8), and continue the reaction after the addition is completed; A3, adding wood pulp cellulose nanofibrils into a reactor, maintaining the temperature at 60-65°C and stirring to obtain a mixed solution; A4. Finally, the mixture was centrifuged to remove the supernatant, and the precipitate was washed with deionized water, dried in a vacuum drying oven, and ground through a 100-mesh sieve.

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

8. The production process of nanofiber composite impregnated paper according to claim 6, characterized in that: In step A2, the stirring speed is 300-400 rpm, and the reaction time after the dropwise addition is continued is 1.5-2.5 hours.

9. The production process of nanofiber composite impregnated paper according to claim 6, characterized in that: In step A3, the length of the wood pulp cellulose nanofibrils 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.

10. The production process of nanofiber composite impregnated paper according to claim 6, characterized in that: In step A4, the mixed solution is centrifuged at a speed of 8000-9000 rpm for 10-15 min, and the precipitate is washed 3-4 times with deionized water; the drying temperature in the vacuum drying oven is 80-85° C. for 12-14 h.

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