Production method of insulating paperboard

Abstract

The invention belongs to the technical field of production of insulating products, and discloses a production method of an insulating paperboard, which comprises the following steps: grinding pulp through a DD720 double-disc refiner, respectively adding a modified additive PDMS (Polydimethylsiloxane) emulsion and a phenyl silicone emulsion into the pulp, mixing with a cross-linking agent, adding a cross-linking agent, and uniformly stirring to obtain the insulating paperboard. Or adding a modified additive PDMS emulsion and a phenyl silicone emulsion into the slurry at the same time, and then mixing with a cross-linking agent; mechanically stirring the mixed pulp by a propeller, standing, and carrying out drifting purification, papermaking by a paper machine, multi-section hot pressing and cutting and shaping to obtain a finished paperboard. According to the insulating paperboard prepared by the production method, the electrical strength index value of an existing product in air can be improved by 30%-50%, so that the influence of aging damage to an insulating material caused by high-voltage, high-temperature and complex electromagnetic environments in the operation process of a transformer is reduced, the service life of the transformer is prolonged, and the safe operation performance of the transformer is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of insulating product production, and specifically relates to a method for producing insulating paperboard Background Art

[0002] With the rapid development of the power industry, the role of power transmission and distribution systems in modern society has become increasingly prominent. Large-scale, long-distance power transmission has become the norm, which has put forward higher requirements for the safety and stability of power transmission and transformation equipment. These development trends have all posed new challenges to the functionality and reliability of core power equipment such as transformers.

[0003] Transformers are indispensable equipment in power systems, and their performance is directly related to the efficiency and safety of power grid operation. Insulating materials, especially insulating paperboard, are key components inside transformers, and play an important role in electrical insulation and mechanical support. Their electrical strength and service life directly affect the operating stability and service life of transformers. However, traditional insulating paperboard is prone to problems such as reduced insulation performance, partial discharge, and even breakdown during long-term operation under high voltage, high temperature, and complex electromagnetic environments, resulting in increased transformer failure rates, increased maintenance costs, and even power grid safety accidents.

[0004] In addition, with the rapid development of the new energy electric vehicle industry, the popularity of high-power charging piles and high-performance motors has caused transformers to often operate at high loads, which has put forward higher requirements on the voltage resistance and aging performance of insulating materials. The electrical strength and durability of traditional insulating paperboard can no longer fully meet the needs of new power equipment. Especially under extreme working conditions, its service life is significantly shortened, which limits the overall performance improvement of the equipment. Existing methods include selecting high-quality fibers, increasing the tightness of paperboard or surface treatment processes, which have the problems of high cost, limited effect or large environmental impact. Therefore, the development of a new method that can significantly improve the electrical strength of insulating paperboard can not only extend the service life of insulating materials and reduce the maintenance cost of transformers, but also provide strong support for the technological progress and new energy development of the power industry. It has important practical significance and broad application prospects. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a method for producing insulating paperboard, wherein the insulating paperboard produced by the method can improve the electrical strength index value in the air of the existing product by 30% to 50%, thereby reducing the influence of aging damage on the insulating material caused by high voltage, high temperature and complex electromagnetic environment during the operation of the transformer, thereby improving the service life and safe operation performance of the transformer.

[0006] In order to solve the above technical problems, the technical solution of the present invention is:

[0007] A method for producing insulating paperboard comprises the following steps:

[0008] S1. Raw material selection: 100% unbleached kraft softwood pulp;

[0009] S2. Pulping (decomposing pulp): 3000 kg of 100% unbleached kraft softwood pulp is put into a hydraulic pulper, and 47000 kg of pure water is added. After soaking for 5 minutes, the pulper is turned on to decompress the pulp to a concentration of 5.5-6.5%. The decompressed pulp is pumped to the pre-grinding pulp tank and allowed to stand for 1-1.5 hours to allow the fibers to be fully stretched.

[0010] S3. Refining: The debonded pulp is removed by a high-concentration desander, and the concentration is adjusted to 4.35-4.65% by a BTG concentration meter (the BTG concentration meter adjusts the slurry concentration to an appropriate value online by adjusting the size of the pure water flow valve), and then enters the DD720 double-disc mill. The refining power is set to 545-575kW to knead the pulp fibers, cut, separate and broom them, and further optimize the fiber structure. The pulp is refined to a beating degree of 33-38°SR and a wet weight of 9-13g to obtain a milled pulp, which is pumped to a milled pulping tank;

[0011] S4. Adding modifying additives and crosslinking agents in proportion: Add modifying additives in proportion to the milled slurry, the modifying additives are PDMS (polydimethylsiloxane) emulsion and phenyl silicone emulsion, the two are used alone or simultaneously, wherein the addition ratio of PDMS emulsion with a solid content of 25% to 35% is 4.0 to 6.0% of the dry weight of the slurry; the addition ratio of phenyl silicone emulsion with a solid content of 20% to 40% is 1 to 3% of the dry weight of the slurry; both are added separately or simultaneously to the slurry tank, the propeller is turned on, and stirred for 15 minutes to form a hydrophobic layer in a coordinated manner to ensure that both are uniformly adsorbed on the fiber; then add the crosslinking agent TEOS (tetraethoxysilane) in a proportion of 0.5 to 2% of the total mass of the modifying additive; after mixing according to the above proportion, mechanical stirring is performed to ensure that the slurry and the additive are fully and evenly fused, and then the mixture is allowed to stand for 1 to 1.5 hours to allow the modifying additive to further react with the fiber and stably combine to form a uniform hydrophobic crosslinking layer, thereby significantly improving the electrical strength of the insulating paperboard in the air;

[0012] S5. Flow screening, filtration and purification: The modified and cross-linked milled pulp is concentrated to 2.4-2.6% by the material gate pump and BTG concentration adjustment meter, purified and screened by the first and third stage low-concentration desander, and then transported to the paper machine through the pressure screen;

[0013] S6. Papermaking, dehydration and forming: The pulp after concentration adjustment and purification passes through the paper machine headbox, breast roll, chopping board, chopping roll, vacuum water absorption box and other rectifying elements, net-loading device, dehydration, and then forms wet paper sheets on the forming net, and papermaking and forming; after double-layer lamination by the laminating roller, the moisture content of the wet paper sheets is maintained at 82-84%, and then enters the forming cylinder to continue winding and laminating. At the same time, it is pressed by the first, second and third support rollers to squeeze out the excess moisture of the wet paperboard, and the moisture content out of the forming cylinder is maintained at 68-70%. According to the requirements of each thickness, when the set number of process cycles is reached in advance, the conveying roller under the forming cylinder is started, and the knife of the forming cylinder is released to cut the wet paperboard, and it is transported to the pre-installation machine, installation machine and press machine along with the running dry net platform;

[0014] S7. Hot pressing of press: according to the thickness of each thickness of paperboard, set the pressure gradient and holding time of the process: after each laminating press is filled with wet paperboard, set the steam pressure to 230-320kpa, the pressing plate temperature to 130-144℃, the first holding pressure to 24-26MPa, the holding time to 8-350min, the second holding pressure to 8-22MPa, the holding time to 3-20min, the third holding pressure to 0-14MPa, the holding time to 2-10min, the fourth holding pressure to 0-6MPa, the holding time to 2-25min; after the pressing is completed, the unloading trolley enters the press, sucks the pressed paperboard with a suction cup, and transports it to the unloading platform to obtain the finished paperboard;

[0015] S8. Cut and shape the pressed dry cardboard according to the customer's order requirements using a vertical and horizontal saw to obtain the final product.

[0016] Preferably, the 100% unbleached kraft softwood pulp in step S1 is taken from mature wood from imported (Sweden, Russia) extremely cold regions. The fiber is long, low in thickness, thick in wall, and large in diameter. The fiber length is 2.5-4.5 mm, the wall thickness is 2.2-2.5 um, the fiber diameter is 0.025 mm-0.035 mm, the pulp ash content is extremely low at 0.2-0.3%, the ring crush index is 15-16 N.m / g, and the burst index is 6.5-7.5 kPa.m 2 / g, tensile index 70~85Nm / g, electrical conductivity 2~3mS / m; this wood pulp can significantly improve the insulation paperboard in terms of high purity, high electrical strength, high mechanical strength, heat resistance, aging resistance and other aspects.

[0017] Preferably, in step S2, the pulp is decomposed to a concentration of 6.0%, and the decomposed pulp is pumped to a pre-grinding pulp tank and allowed to stand for 1.5 hours; the pulp is decomposed by a D-type hydraulic pulper, and the pulper changes the streamline direction of the pulp so that the pulp contacts the rotor more quickly and more frequently, and the pulp fibers are decomposed quickly. In addition, a high-strength magnetic slag tank is provided inside the pulper to further improve the cleanliness of the pulp, lay a foundation for the subsequent synergistic effect of the pulp fibers and the modified additives not to be interfered by impurities, and thus improve the electrical strength of the paperboard in the air.

[0018] Preferably, in step S3, the BTG concentration meter is adjusted to 4.5%; the pulp is refined to a beating degree of 35°SR and a wet weight of 11 g.

[0019] DD720 double disc grinding has the following effects:

[0020] 1. The grinding efficiency is higher, the fiber length distribution is more uniform, and the fiber surface roughness is moderately increased. It provides a larger contact area and better bonding conditions for the penetration and adhesion of subsequent modified additives (PDMS, phenyl silicone, TEOS).

[0021] 2. Improving the uniformity of the slurry can optimize the slurry beating degree and fiber morphology according to the needs of the insulating paperboard. This uniformity directly reduces the possibility of electric field distortion inside the paperboard, laying the foundation for improving electrical strength.

[0022] 3. The double disc mill not only refines the fibers during the grinding process, but also produces a small amount of microfibrillation on the fiber surface, increasing the surface active sites (such as hydroxyl exposure), making the chemical bonding between the fiber and TEOS and the physical adsorption of PDM and phenyl silicone stronger, thereby improving the electrical strength while maintaining the mechanical properties of the paperboard.

[0023] Preferably, in the step S4, the addition ratio of the PDMS emulsion with a solid content of 30% is 5.0% of the dry weight of the slurry; the addition ratio of the phenyl silicone emulsion with a solid content of 30% is 2% of the dry weight of the slurry; the addition ratio of the crosslinking agent TEOS is 1% of the total mass of the modified additives; and the mixture is allowed to stand for 1.5 hours after mechanical stirring.

[0024] Furthermore, the phenyl silicone emulsion is a phenyl methyl polysiloxane emulsion, which has the following advantages:

[0025] 1. Excellent heat resistance and stability: Phenyl methyl polysiloxane contains phenyl (-C6H5) and methyl (-CH3) side chains. The introduction of phenyl significantly improves the thermal stability of the siloxane main chain (the decomposition temperature can reach above 300°C), so that it can still maintain structural integrity in the high temperature environment of high-load operation of the transformer, avoiding the degradation of insulation performance caused by aging, thereby enhancing electrical strength.

[0026] 2. Good emulsification and dispersibility: The compound has a moderate molecular weight and can be easily prepared into a stable aqueous emulsion through an emulsification process. When mixed with the slurry in the pulping tank, it can be evenly dispersed and adsorbed on the fiber surface, and cooperate with the PDMS emulsion to form a continuous hydrophobic layer, providing a uniform base for improving the electrical strength.

[0027] 3. Synergistic cross-linking with TEOS: The end group or side chain of phenylmethylpolysiloxane may contain a small amount of silanol (Si-OH), which can participate in cross-linking under the action of silanol generated by TEOS hydrolysis to form a denser network structure, further strengthen the combination of the modified layer and the fiber, and improve the breakdown voltage and electrical resistance.

[0028] The modified additive PDMS emulsion is based on the siloxane main chain (Si-O-Si) and a small amount of active silanol (Si-OH) it contains, and can react with TEOS during the curing process. TEOS generates silanol (Si-OH) under hydrolysis conditions, and then forms a three-dimensional cross-linked network through condensation reaction, providing structural stability for the insulating paperboard. The addition of phenyl methyl polysiloxane emulsion further enhances this cross-linking process: the phenyl (-C6H5) functional group and possible silanol (Si-OH) contained in its molecular structure can combine with the active sites generated by TEOS hydrolysis to form a more complex cross-linked structure. This synergistic cross-linking not only increases the cross-linking density, but also improves the thermal stability and antioxidant capacity of the cross-linking network through the rigid properties of the phenyl group. The introduction of phenyl silicone makes the cross-linking system more compact and durable, thereby effectively reducing the occurrence of partial discharge and improving the electrical strength of the paperboard.

[0029] Add PDMS emulsion and phenyl silicone emulsion into the slurry tank at the same time, turn on the propeller, stir for 15 minutes, and then add the crosslinking agent TEOS (tetraethoxysilane), rather than adding the first two in sequence. Adding the first two at the same time has the following advantages:

[0030] 1. Chemical compatibility and uniform dispersion: Both PDMS emulsion and phenyl silicone emulsion are siloxane-based aqueous emulsions with similar chemical structures and emulsification systems. Adding them together will not cause phase separation or agglomeration. Under the low shear and mild environment of the pulping tank, the two can be quickly and evenly dispersed in the slurry, adsorbed on the fiber surface and micropores together, forming a continuous and uniform hydrophobic substrate. This uniformity avoids the local concentration gradient that may be caused by sequential addition, ensures the overall consistency of the modified layer during subsequent TEOS cross-linking, and thus provides a guarantee for the stable improvement of electrical strength.

[0031] 2. Optimization of synergistic adsorption efficiency: When added simultaneously, the low surface tension and high permeability of PDMS and the heat resistance of phenyl silicone work simultaneously on the fiber surface. PDMS preferentially penetrates into the micropores of the fiber to form a hydrophobic barrier, while phenyl silicone enhances the surface heat resistance protection. The two synergistically cover the fiber, avoiding the reduced attachment efficiency of the later added emulsion due to competition for adsorption sites when added sequentially. The subsequent TEOS hydrolysis and cross-linking (forming Si-OC bonds and siloxane networks) further solidifies the substrate to form a composite modified structure. If one emulsion (such as PDMS) is added first, its hydrophobicity may partially repel the other (such as phenyl silicone) added later, affecting the overall modification effect, while adding them simultaneously maximizes the synergistic effect of the two.

[0032] The modified additives are added to the pulping tank after grinding rather than the pulping process. During the pulping process, the mechanical shear force is large, which will cause some of the initial cross-linked products of the emulsion and TEOS to be destroyed, affecting the final cross-linking efficiency. After the pulping is completed, the fiber has formed a relatively stable form, and the conditions in the pulping tank are milder. PDMS and phenyl silicone can be uniformly adsorbed on the fiber surface and fiber gaps in the pulping tank, and the hydrolysis and cross-linking reaction of TEOS can also occur more controllably, ensuring the integrity of the cross-linked network.

[0033] Preferably, in step S5, the BTG concentration adjuster adjusts the slurry concentration to 2.5% to meet the requirements of the subsequent molding process. This concentration not only ensures the fluidity of the slurry, but also provides a suitable medium environment for the stable combination of the modified additives (PDMS, phenyl silicone and TEOS) and the fibers. Subsequently, the adjusted slurry is purified and screened through a primary and three-stage low-concentration desander to effectively remove sand, coarse fiber clusters and other impurities in the slurry, thereby improving the cleanliness and uniformity of the slurry. Finally, the purified slurry is further finely filtered through a pressure screen, and the purified slurry is transported to a paper machine for molding. This step ensures that the synergistic effect of the fibers and the modified additives in the slurry is not disturbed by impurities through precise concentration control and multi-stage purification, while optimizing the uniformity of fiber distribution. The clean slurry allows the hydrophobic layer of PDMS and phenyl silicone and the cross-linked network of TEOS to be completely retained, avoiding the formation of local defects or electric field concentration points, thereby further improving the electrical strength and withstand voltage stability of the insulating paperboard.

[0034] Preferably, in step S6, the slurry is dehydrated by a rectifying element and a dehydrating element to form a wet paper sheet, the combination of the modified additive (PDMS, phenyl silicone and TEOS) and the fiber is further stabilized in a wet state, the hydrophobic cross-linked structure is initially solidified, and then multi-stage pressing and dehydration are performed to ensure that the modified additive is evenly distributed in the fiber network, avoiding electric field defects caused by uneven moisture, thereby providing a uniform substrate for subsequent hot pressing curing, and further improving the electrical strength of the insulating paperboard.

[0035] Preferably, the pressure and holding time required for paperboards of different thicknesses in step S7 are shown in Table 1:

[0036] Table 1 Pressure and holding time required for different thickness of paperboard

[0037]

[0038]

[0039] The hot pressing process ensures that the moisture inside the wet paperboard is gradually volatilized, the cross-linking reaction of TEOS is completely cured, and the hydrophobic layer of PDMS and phenyl silicone is tightly attached to the fiber surface. The hot pressing process uses gradient pressure and high temperature curing to form a dense insulating structure between the modified additives and the fiber, which significantly improves the breakdown voltage and heat resistance stability of the paperboard.

[0040] Preferably, in step S8, the longitudinal and transverse saws perform precise cutting according to the size and specifications required by the order. This process ensures that the edges of the cardboard are smooth, avoids cutting damage to the modified layer, and retains its excellent electrical insulation properties.

[0041] Due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0042] The present invention makes full use of the synergistic effect of the modified additive PDMS emulsion, phenyl silicone emulsion and cross-linking agent TEOS by scientifically proportioning and uniformly mixing them with the slurry in a slurry tank, thereby significantly improving the electrical strength of the insulating paperboard. Among them, PDMS emulsion can enhance the hydrophobicity and flexibility of the fiber surface. With its low surface tension and permeability, its siloxane chain segments penetrate into the micropores and gaps of the fiber to form a hydrophobic barrier, effectively blocking the intrusion of water and reducing the risk of moisture-induced conductivity pathways and partial discharge; phenyl silicone emulsion, due to its introduction of benzene ring structure, further enhances the heat resistance and anti-aging properties of the paperboard by physical adsorption on the fiber surface, so that the hydrophobic layer can remain stable under high temperature and high voltage environment, avoiding the degradation of insulation performance caused by fiber aging; TEOS, as a cross-linking agent, hydrolyzes in the wet slurry to generate silanol (Si-OH), forms Si-OC chemical bonds with the hydroxyl groups on the fiber surface, and cross-links with the silanols of PDMS and phenyl silicone to construct a dense organic-inorganic hybrid network. The cross-linking effect of TEOS "locks" the molecular network of PDMS and phenyl silicone in the paperboard substrate. This cross-linked structure not only strengthens the combination of the fiber and the modified layer, but also improves the mechanical strength and electrical stability of the overall structure.

[0043] Under the synergistic effect of the three, the insulation paperboard forms a composite modified structure with hydrophobicity, heat resistance and cross-linking strength, which increases the electrical strength of the insulation paperboard in the air by 30% to 50%. This improves the performance of the insulation paperboard, provides high-performance insulation material support for high-voltage power transmission and new energy equipment, and has significant economic benefits and application value. DETAILED DESCRIPTION

[0044] The technical solution of the present invention is further described below in conjunction with embodiments:

[0045] Example 1: Production of 1.0 mm cardboard

[0046] S1. Raw material selection

[0047] Pure imported 100% unbleached sulfate softwood pulp (Swedish electronic grade Aspartame pulp, Russian electronic grade EKB pulp), fiber length 3.5mm, wall thickness 2.5um, fiber diameter 0.03mm, ash content 0.25%, conductivity 3.0mS / m.

[0048] S2, pulping (dispersing pulp)

[0049] 3000kg of pure imported 100% unbleached kraft softwood pulp (mixed with aspartame and EKB in a mass ratio of 6:4, i.e., 1800kg aspartame + 1200kg EKB) was put into a D-type hydraulic pulper, and 47000kg of pure water with a conductivity of less than 18uS / cm was added to make the mixed pulp concentration at 6%. After soaking for 5 minutes, the D-type hydraulic pulper was turned on to decompose the pulp sheet into fibers, and then the pulp pump was turned on to pump it into the pre-grinding pool and allowed to stand for 1.5 hours to allow the fibers to fully swell in the pure water environment.

[0050] S3, refining

[0051] The deflated pulp is removed from impurities by a high-concentration desander, and the concentration is adjusted to 4.5% by a BTG concentration meter. It then enters the DD 720 double-disc mill, and the refining power is set to 550W to knead, cut, separate, and broom the pulp fibers to further optimize the fiber structure. The pulp is refined to a beating degree of 35°SR and a wet weight of 11g, and then pumped to the post-grinding pulp pool.

[0052] S4. The slurry in the pulping tank is mixed with the modified additives in a specific proportion.

[0053] The modified additive PDMS emulsion, with a solid content of 30%, is added at a ratio of 5% of the dry weight of the slurry, i.e. 135kg; the phenyl silicone emulsion, with a solid content of 30%, is added at a ratio of 2% of the dry weight of the slurry, i.e. 54kg. Both are added to the slurry tank at the same time, the propeller is turned on, and stirred for 15 minutes, and then the crosslinking agent TEOS (tetraethoxysilane) is added; the crosslinking agent TEOS is 1% of the total weight of the modified additive, i.e. 1.89kg. After the addition is completed, the propeller is started and mechanical stirring is performed until the slurry and the additive are fully and evenly fused, and then left to stand for 1.5 hours to allow the modified additive to further react with the fiber and stably combine to form a uniform and consistent hydrophobic crosslinking layer.

[0054] S5, Stream screening, filtration, purification

[0055] The evenly mixed and consistent post-grinding pulp is adjusted to 2.5% by the material gate pump and BTG concentration adjuster. The adjusted pulp is purified and screened by the first-stage and three-stage low-concentration desander to effectively remove sand, coarse fiber clusters and other impurities in the pulp, improve the cleanliness and uniformity of the pulp, and finally, it is further finely filtered through the pressure screen and the purified pulp is transported to the paper machine for forming.

[0056] S6, paper machine making, dehydration, forming

[0057] After concentration adjustment and purification, the pulp passes through the paper machine headbox, breast roll, chopping board, chopping roll, vacuum water absorption box and other rectifying elements, net-loading device, dehydration, and then forms wet paper sheets on the forming net and forms paper. After double-layer compounding by the compounding roller, the moisture content of the wet paper sheet is ensured to be 83%, and the combination of the modified additives (PDMS, phenyl silicone and TEOS) and the fiber is further stabilized in the wet state, and then enters the forming cylinder to continue winding and compounding. At the same time, it is pressed by the first, second and third rollers to squeeze out the excess moisture of the wet paperboard, and the hydrophobic cross-linking structure is initially solidified to ensure that the moisture content out of the forming cylinder is 69%, and the modified additives are evenly distributed in the fiber network. According to the 1.0mm thickness requirement, when the set number of process cycles is reached, the conveying roller under the forming cylinder is started, the knife of the forming cylinder is released, the wet paperboard is cut, and it is transported to the pre-installation machine, installation machine, and press machine along with the running dry net platform.

[0058] S7, hot pressing

[0059] After all layers of the press are filled with wet cardboard, click the boost button, and the boost pump, pressure-maintaining pump, and energy storage pump will start to provide hydraulic oil to the main cylinder, causing the main cylinder to rise quickly. After the press pressure reaches 3.0MPa after the board is closed, when the pressure of the energy storage tank drops to 2.0MPa, the energy storage pump participates in the energy storage tank to store energy. When the energy storage reaches 3.3MPa, the energy storage pump stops. The boost pump and the pressure-maintaining pump continue to participate in the press pressure boost until the press pressure reaches the process requirement of 24MPa. The boost pump stops and the pressure-maintaining pump participates in the pressure maintenance. When the pressure is lower than 23.5MPa, the pressure-maintaining pump starts to replenish the pressure. The whole boost time is controlled at 1.5min, and the energy storage pump participates in the energy storage time for 5min. When the pressure of the first stage of the press reaches 24MPa, the pressure holding time is 8min. After reaching the specified pressure holding time, the unloading valve will be automatically opened and the pressure of the second stage of the press will drop to 8MPa. The unloading valve will be closed and the pressure holding time will be 3min. The other three and four stages are similar (1.0mm does not have three and four stages of pressure holding). After the whole pressure holding time is over, the press starts, and the dry cardboard is sucked out by the unloading trolley and transported to the unloading platform to obtain the finished cardboard.

[0060] S8. The finished cardboards in the rough board area are selected and then accurately cut, packaged and stored according to the size and specifications required by the order using a longitudinal and transverse saw to obtain the final product.

[0061] Example 2: Production of 1.0 mm cardboard 2

[0062] The solid content of the PDMS emulsion in Example 1 was adjusted to 25%, the corresponding addition ratio of the PDMS emulsion was adjusted to 6%, the corresponding addition amount of TEOS was 2.16 kg, and the other process conditions were the same as in Example 1.

[0063] Example 3: Production of 1.0 mm cardboard 3

[0064] The solid content of the PDMS emulsion in Example 1 was adjusted to 35%, the corresponding addition ratio of the PDMS emulsion was adjusted to 4.3%, the corresponding addition amount of TEOS was 1.701 kg, and the other process conditions were the same as in Example 1.

[0065] The 1.0 mm paperboard produced in the above embodiment was sampled and pre-treated according to the national standard GB / T 19264.2-2013 Electrical Pressed Paperboard and Thin Paperboard Part 2 Test Method, and the index of electrical strength in air was tested according to the test method in the above standard (three groups of parallel samples were taken for each embodiment, and the test data were averaged, the same below), and the data were recorded and summarized, as shown in Table 2:

[0066] Table 2 Test data of products of Examples 1 to 3:

[0067]

[0068] Conclusion: According to the test data of the products produced in Examples 1 to 3: Under the premise of meeting the requirements of GB / T19264.3-2013 Electrical Pressed Paper and Thin Paperboard Part 3: Pressed Paperboard B.3.1A Type Paperboard for electrical properties and mechanical properties such as electrical strength in the air and tensile strength, the PDMS emulsion solid content is 30% and the addition ratio is 5%, which is the best addition ratio, and the final product has the best electrical strength in the air.

[0069] Example 4: Production of 1.0 mm cardboard

[0070] The solid content of the phenyl silicone emulsion in Example 1 was adjusted to 20%, the corresponding emulsion addition ratio was adjusted to 3%, the corresponding addition amount of TEOS was 2.16 kg, and the other process conditions were the same as in Example 1.

[0071] Example 5: Production of 1.0 mm cardboard

[0072] The solid content of the phenyl silicone emulsion in Example 1 was adjusted to 40%, the corresponding emulsion addition ratio was adjusted to 1.5%, the corresponding addition amount of TEOS was 1.755 kg, and the other process conditions were the same as in Example 1.

[0073] The 1.0 mm paperboard products obtained in Examples 1, 4 and 5 were sampled and pre-treated according to the national standard GB / T19264.2-2013 Electrical Pressed Paperboard and Thin Paperboard Part 2 Test Method, and the electrical strength index in the air was tested according to the test method in the above standard. The data were recorded and summarized, and compared with the data of the product in Example 1, as shown in Table 3:

[0074] Table 3 Test data of products of Examples 1, 4 and 5

[0075]

[0076] Conclusion: According to the test data of the products of Examples 1, 4 and 5: Under the premise of meeting the electrical properties and mechanical properties requirements of GB / T19264.3-2013 Electrical Pressed Paper and Thin Paperboard Part 3 Pressed Paperboard B.3.1A Type Paperboard in the air, such as electrical strength and tensile strength, the phenyl silicone emulsion solid content is 30% and the addition ratio is 2%, which is the best addition ratio, and the final product has the best electrical strength in the air.

[0077] Example 6: Production of 1.0 mm cardboard

[0078] The addition ratio of the cross-linking agent TEOS in Example 1 was adjusted to 0.5%, and the other process conditions were the same as in Example 1.

[0079] Example 7: Production of 1.0 mm cardboard

[0080] The addition ratio of the cross-linking agent TEOS in Example 1 was adjusted to 1.5%, and the other process conditions were the same as in Example 1.

[0081] Example 8: Production of 1.0 mm cardboard 8

[0082] The addition ratio of the cross-linking agent TEOS in Example 1 was adjusted to 2.0%, and the other process conditions were the same as in Example 1.

[0083] The 1.0 mm paperboard products obtained in Examples 1, 6 to 8 were sampled and pre-treated according to the national standard GB / T19264.2-2013 Electrical Pressed Paperboard and Thin Paperboard Part 2 Test Method, and the electrical strength index in the air was tested according to the test method in the above standard, and the data were recorded and summarized, as shown in Table 4:

[0084] Table 4 Test data of the products of Examples 1, 6 to 8:

[0085]

[0086]

[0087] Conclusion: According to the test data of Examples 1, 6 to 8: Under the premise of meeting the electrical properties and mechanical properties requirements of GB / T19264.3-2013 Electrical Paperboard and Thin Paperboard Part 3 Paperboard B.3.1A Type Paperboard in the air, such as electrical strength and tensile strength, the TEOS addition ratio is 1% which is the best addition ratio, and the final product has the best electrical strength in the air.

[0088] Example 9: Production of 1.0 mm cardboard

[0089] In Example 1, no phenyl silicone emulsion was added, the corresponding amount of TEOS added was 1.35 kg, and the other process conditions were the same as in Example 1.

[0090] The 1.0 mm paperboard products obtained in the tests of Example 1 and Example 9 were sampled and pre-treated according to the test method of Part 2 of the national standard GB / T19264.2-2013 Electrical Pressed Paperboard and Thin Paperboard, and the index of electrical strength in air was tested according to the test method in the above standard. The data were recorded and summarized, and compared with the data of the product in Example 1, as shown in Table 5:

[0091] Table 5 Test data of the products of Example 1 and 9:

[0092]

[0093] Conclusion: According to the test data of the products of Examples 1 and 9, under the premise of meeting the requirements of electrical properties and mechanical properties such as electrical strength and tensile strength in air of type A paperboard in Part 3 of GB / T 19264.3-2013 Electrical pressboard and thin paperboard, the electrical strength in air of the final product obtained by adding phenyl silicone emulsion is the best. This is because: phenyl silicone is an organic silicon compound with phenyl functional groups. Compared with pure PDMS, it has higher thermal stability and oxidation resistance, and also has potential advantages in electrical insulation performance. It can further enhance the high temperature aging resistance and electrical strength of the material, especially in the application scenarios of transformer high load operation or extreme environment. The synergistic effect of this additive may enable the insulating paperboard to maintain more stable performance in long-term use. Phenyl silicone and PDMS emulsion belong to silicone compounds and have similar chemical structure basis, so it is not easy to phase separate or react adversely when mixed. In addition, TEOS, as a cross-linking agent, can cross-link with phenyl silicone and silanol (Si-OH) in PDMS through hydrolysis condensation reaction, further forming a denser network structure and improving the mechanical strength and insulation properties of the overall material.

[0094] Example 10: Production of 1.0 mm paperboard

[0095] In Example 1, no PDMS emulsion was added, the corresponding amount of TEOS added was 0.54 kg, and the other process conditions were the same as in Example 1.

[0096] The 1.0 mm paperboard products obtained in the tests of Example 1 and Example 10 were sampled and pre-treated according to the test method of Part 2 of the national standard GB / T19264.2-2013 Electrical Pressed Paperboard and Thin Paperboard, and the index of electrical strength in air was tested according to the test method in the above standard. The data were recorded and summarized, and compared with the data of the product in Example 1, as shown in Table 6:

[0097] Table 6 Test data of the products of Examples 1 and 10:

[0098]

[0099]

[0100] Conclusion: According to the test data of the products of Examples 1 and 10, under the premise of meeting the electrical properties and mechanical performance index requirements of GB / T 19264.3-2013 Electrical Pressed Paper and Thin Paperboard Part 3 Pressed Paperboard B.3.1A Type Paperboard in the air, such as electrical strength and tensile strength, the final product obtained by adding PDMS emulsion has the best electrical strength in the air. This is because: PDMS emulsion, with its low surface tension and high permeability, can penetrate into the micropores of the fiber to form a uniform hydrophobic barrier, effectively blocking the intrusion of water, and reducing the risk of moisture-induced conduction paths and partial discharge. Although phenyl silicone emulsion provides heat resistance, it has a high viscosity (poor fluidity compared to PDMS) and insufficient permeability, making it difficult to fully cover the fiber surface and internal micropores. The cross-linking effect of TEOS alone cannot make up for the lack of hydrophobicity. The experimental group has weak hydrophobicity and is easy to penetrate with water, resulting in limited improvement in breakdown voltage.

[0101] Example 11: Production of 1.0 mm cardboard

[0102] The adding position of PDMS emulsion, phenyl silicone emulsion and crosslinking agent TEOS in Example 1 was changed to before the mill, that is, in the pulper, and the other process conditions were the same as those in Example 1.

[0103] The 1.0 mm paperboard product obtained in the experiment of Example 11 was sampled and pre-treated according to the test method of GB / T 19264.2-2013 Electrical Pressed Paperboard and Thin Paperboard Part 2, and the index of electrical strength in air was tested according to the test method in the above standard. The data was recorded and summarized, and compared with the data of the product in Example 1, as shown in Table 7 below:

[0104] Table 7 Test data of the products of Example 1 and 11:

[0105]

[0106]

[0107] Conclusion: According to the test data of the products of Examples 1 and 11, under the premise of meeting the electrical and mechanical performance index requirements of GB / T 19264.3-2013 Electrical pressboard and thin paperboard Part 3: Pressboard B.3.1A type paperboard in the air, such as electrical strength and tensile strength, the electrical strength of the final product added to the pulping chest after grinding is the best. This is because:

[0108] 1. The pulping process uses high shear mechanical action and high moisture environment to disperse the raw materials into dispersed fiber slurry. Under this condition, the emulsification system of PDMS emulsion and phenyl silicone emulsion may be demulsified due to strong turbulence and shear force, resulting in coagulation or loss of silicone components, reducing its hydrophobicity and heat resistance modification effect. Similarly, TEOS may be hydrolyzed prematurely and polymerized into uneven siloxane particles under high moisture and uncontrollable pH environment in the pulping stage, which cannot effectively combine with the fiber. After the slurry in the pulping tank is refined by the DD 720 double disc mill, it is in a low shear and low turbulence state, providing a gentle mixing environment for additives. This condition ensures that the dispersibility of the emulsion and the controllable hydrolysis of TEOS are retained, thereby maximizing its modification efficiency.

[0109] 2. The fibers in the pulping stage have not been refined yet, and there are many fiber bundles. The surface roughness and active sites (such as hydroxyl groups) are not exposed enough, making it difficult for additives to penetrate or adhere effectively. Most of them may be dispersed in the water instead of acting on the fiber surface, resulting in poor modification effect. In contrast, the pulp after refining is treated with a double-disc mill, and the fibers have been fully dispersed and microfibrillated, with increased exposure of surface hydroxyl groups and richer microporous structure. At this time, when the modified additives are added to the pulping tank, PDMS and phenyl silicone can be more evenly adsorbed on the fiber surface and penetrate into the interior, and the silanol groups of TEOS form stable Si-OC chemical bonds with the fiber hydroxyl groups. This optimized combination makes the hydrophobic layer and the cross-linked network more uniform and dense, significantly reduces the risk of moisture penetration and partial discharge, and directly improves the electrical strength of the paperboard.

[0110] Example 12: Production of 1.0 mm cardboard

[0111] The PDMS emulsion and phenyl silicone emulsion in Example 1 were added into the slurry tank one by one in sequence, and the other process conditions were the same as in Example 1.

[0112] Example 13: Production of 1.0 mm cardboard

[0113] The phenyl silicone emulsion and PDMS emulsion in Example 1 were added into the slurry tank one by one in sequence, and the other process conditions were the same as in Example 1.

[0114] The 1.0 mm paperboard products obtained in the tests of Examples 12 and 13 were sampled and pre-treated according to the test method of Part 2 of the national standard GB / T19264.2-2013 Electrical Pressed Paperboard and Thin Paperboard, and the index of electrical strength in air was tested according to the test method in the above standard. The data were recorded and summarized, and compared with the data of the product in Example 1, as shown in Table 8:

[0115] Table 8 Test data of the products of Examples 1, 12 and 13:

[0116]

[0117] Conclusion: According to the test data of the products of Examples 1, 12 and 13, under the premise of meeting the electrical and mechanical performance index requirements of GB / T19264.3-2013 Electrical Pressed Paper and Thin Paperboard Part 3 Pressed Paperboard B.3.1A Type Paperboard in the air, such as electrical strength and tensile strength, the PDMS emulsion and phenyl silicone emulsion are added to the slurry at the same time, and the electrical strength of the final product in the air is the best. This is because:

[0118] 1. Chemical compatibility and uniform dispersion: Both PDMS emulsion and phenyl silicone emulsion are siloxane-based aqueous emulsions with similar chemical structures and emulsification systems (usually nonionic or anionic emulsifiers are used). Adding them simultaneously will not cause phase separation or agglomeration. In the low shear environment of the pulping tank, the two can be quickly and evenly dispersed in the slurry, and adsorbed on the fiber surface and micropores together to form a continuous and uniform hydrophobic substrate. This uniformity avoids the local concentration gradient that may be caused by sequential addition, ensuring the overall consistency of the modified layer during subsequent TEOS cross-linking, thereby providing a guarantee for the stable improvement of electrical strength.

[0119] 2. Optimization of synergistic adsorption efficiency: The low surface tension and high permeability of PDMS and the heat resistance of phenyl silicone (phenyl enhances thermal stability) are added simultaneously on the fiber surface to work synchronously. PDMS preferentially penetrates into the fiber micropores to form a hydrophobic barrier, while phenyl silicone enhances the surface heat resistance protection. The two synergistically cover the fiber, avoiding the reduction of the attachment efficiency of the later added emulsion due to competition for adsorption sites when added sequentially. The subsequent TEOS hydrolysis and cross-linking further solidifies this substrate to form a composite modified structure. If one emulsion (such as PDMS) is added first, its hydrophobicity may partially repel the other one (such as phenyl silicone) added later, affecting the overall modification effect, while adding them at the same time maximizes the synergistic effect of the two.

[0120] Example 14: Production of 1.5 mm cardboard

[0121] S1-S5: Same as in Example 1.

[0122] S6, paper machine making, dehydration, forming

[0123] After concentration adjustment and purification, the pulp passes through the paper machine headbox, breast roll, chopping board, chopping roll, vacuum water absorption box and other rectifying elements, net-loading device, dehydration, and then forms wet paper sheets on the forming net and forms paper. After double-layer compounding by the compounding roller, the moisture content of the wet paper sheet is ensured to be 83%, and the combination of the modified additives (PDMS, phenyl silicone and TEOS) and the fiber is further stabilized in the wet state, and then enters the forming cylinder to continue winding and compounding. At the same time, it is pressed by the first, second and third rollers to squeeze out the excess moisture of the wet paperboard, and the hydrophobic cross-linking structure is initially solidified to ensure that the moisture content out of the forming cylinder is 69%, and the modified additives are evenly distributed in the fiber network. According to the 1.5mm thickness requirement, when the set number of process cycles is reached, the conveying roller under the forming cylinder is started, the knife of the forming cylinder is released, the wet paperboard is cut, and it is transported to the pre-installation machine, installation machine, and press machine along with the running dry net platform.

[0124] S7, hot pressing

[0125] The holding pressure and holding time of each section of the 1.5 mm press are shown in Table 1, and the remaining processes are in accordance with Example 1.

[0126] S8. The process is the same as in Example 1.

[0127] Example 15: Production of 2.0 mm paperboard

[0128] S1-S5: Same as in the first embodiment.

[0129] S6, paper machine making, dehydration, forming

[0130] After concentration adjustment and purification, the pulp passes through the paper machine headbox, breast roll, chopping board, chopping roll, vacuum water absorption box and other rectifying elements, net-loading device, dehydration, and then forms wet paper sheets on the forming net and forms paper. After double-layer compounding by the compounding roller, the moisture content of the wet paper sheet is ensured to be 83%, and the combination of the modified additives (PDMS, phenyl silicone and TEOS) and the fiber is further stabilized in the wet state, and then enters the forming cylinder to continue winding and compounding. At the same time, it is pressed by the first, second and third rollers to squeeze out the excess moisture of the wet paperboard, and the hydrophobic cross-linking structure is initially solidified to ensure that the moisture content out of the forming cylinder is 69%, and the modified additives are evenly distributed in the fiber network. According to the 2.0mm thickness requirement, when the set number of process cycles is reached, the conveying roller under the forming cylinder is started, the knife of the forming cylinder is released, the wet paperboard is cut, and it is transported to the pre-installation machine, installation machine, and press machine along with the running dry net platform.

[0131] S7, hot pressing

[0132] The holding pressure and holding time of each section of the 2.0 mm press are shown in Table 1, and the remaining processes are in accordance with Example 1.

[0133] S8. The process is the same as in Example 1.

[0134] Example 16: Production of 3.0 mm cardboard

[0135] S1-S5: Same as in the first embodiment.

[0136] S6, paper machine making, dehydration, forming

[0137] After concentration adjustment and purification, the pulp passes through the paper machine headbox, breast roll, chopping board, chopping roll, vacuum water absorption box and other rectifying elements, net-loading device, dehydration, and then forms wet paper sheets on the forming net and forms paper. After double-layer compounding by the compounding roller, the moisture content of the wet paper sheet is ensured to be 83%, and the combination of the modified additives (PDMS, phenyl silicone and TEOS) and the fiber is further stabilized in the wet state, and then enters the forming cylinder to continue winding and compounding. At the same time, it is pressed by the first, second and third rollers to squeeze out the excess moisture of the wet paperboard, and the hydrophobic cross-linking structure is initially solidified to ensure that the moisture content out of the forming cylinder is 69%, and the modified additives are evenly distributed in the fiber network. According to the 3.0mm thickness requirement, when the set number of process cycles is reached, the conveying roller under the forming cylinder is started, the knife of the forming cylinder is released, the wet paperboard is cut, and it is transported to the pre-installation machine, installation machine, and press machine along with the running dry net platform.

[0138] S7, hot pressing

[0139] The holding pressure and holding time of each section of the 3.0 mm press are shown in Table 1, and the remaining processes are in accordance with Example 1.

[0140] S8. The process is the same as in the first embodiment.

[0141] Example 17: Production of 4.0 mm paperboard

[0142] S1-S5: Same as in the first embodiment.

[0143] S6, paper machine making, dehydration, forming

[0144] After concentration adjustment and purification, the pulp passes through the paper machine headbox, breast roll, chopping board, chopping roll, vacuum water absorption box and other rectifying elements, net-loading device, dehydration, and then forms wet paper sheets on the forming net and forms paper. After double-layer compounding by the compounding roller, the moisture content of the wet paper sheet is ensured to be 83%, and the combination of the modified additives (PDMS, phenyl silicone and TEOS) and the fiber is further stabilized in the wet state, and then enters the forming cylinder to continue winding and compounding. At the same time, it is pressed by the first, second and third rollers to squeeze out the excess moisture of the wet paperboard, and the hydrophobic cross-linking structure is initially solidified to ensure that the moisture content out of the forming cylinder is 69%, and the modified additives are evenly distributed in the fiber network. According to the 4.0mm thickness requirement, when the set number of process cycles is reached, the conveying roller under the forming cylinder is started, the knife of the forming cylinder is released, the wet paperboard is cut, and it is transported to the pre-installation machine, installation machine, and press machine along with the running dry net platform.

[0145] S7, hot pressing

[0146] The holding pressure and holding time of each section of the 4.0 mm press are shown in Table 1, and the remaining processes are in accordance with Example 1.

[0147] S8. The process is the same as in the first embodiment.

[0148] Example 18: Production of 5.0 mm paperboard

[0149] S1-S5: Same as in the first embodiment.

[0150] S6, paper machine making, dehydration, forming

[0151] After concentration adjustment and purification, the pulp passes through the paper machine headbox, breast roll, chopping board, chopping roll, vacuum water absorption box and other rectifying elements, net-loading device, dehydration, and forms wet paper sheets on the forming net and forms paper. After double-layer compounding by the compounding roller, the moisture content of the wet paper sheet is ensured to be 83%, and the combination of the modified additives (PDMS, phenyl silicone and TEOS) and the fiber is further stabilized in the wet state, and then enters the forming cylinder to continue winding and compounding. At the same time, it is pressed by the first, second and third rollers to squeeze out the excess moisture of the wet paperboard, and the hydrophobic cross-linking structure is initially solidified to ensure that the moisture content out of the forming cylinder is 69%, and the modified additives are evenly distributed in the fiber network. According to the 5.0mm thickness requirement, when the set number of process cycles is reached, the conveying roller under the forming cylinder is started, the knife of the forming cylinder is released, the wet paperboard is cut, and it is transported to the pre-installation machine, installation machine, and press machine along with the running dry net platform.

[0152] S7, hot pressing

[0153] The holding pressure and holding time of each section of the 4.0 mm press are shown in Table 1, and the remaining processes are in accordance with Example 1.

[0154] S8. The process is the same as in the first embodiment.

[0155] Example 19: Production of 6.0 mm paperboard

[0156] S1-S5: Same as in the first embodiment.

[0157] S6, paper machine making, dehydration, forming

[0158] After concentration adjustment and purification, the pulp passes through the paper machine headbox, breast roll, chopping board, chopping roll, vacuum water absorption box and other rectifying elements, net-loading device, dehydration, and forms wet paper sheets on the forming net and forms paper. After double-layer compounding by the compounding roller, the moisture content of the wet paper sheet is ensured to be 83%, and the combination of the modified additives (PDMS, phenyl silicone and TEOS) and the fiber is further stabilized in the wet state, and then enters the forming cylinder to continue winding and compounding. At the same time, it is pressed by the first, second and third rollers to squeeze out the excess moisture of the wet paperboard, and the hydrophobic cross-linking structure is initially solidified to ensure that the moisture content out of the forming cylinder is 69%, and the modified additives are evenly distributed in the fiber network. According to the 6.0mm thickness requirement, when the set number of process cycles is reached, the conveying roller under the forming cylinder is started, the knife of the forming cylinder is released, the wet paperboard is cut, and it is transported to the pre-installation machine, installation machine, and press machine along with the running dry net platform.

[0159] S7, hot pressing

[0160] The holding pressure and holding time of each section of the 6.0 mm press are shown in Table 1, and the remaining processes are in accordance with Example 1.

[0161] S8. The process is the same as in Example 1.

[0162] Example 20: Production of 7.0 mm paperboard

[0163] S1-S5: Same as in the first embodiment.

[0164] S6, paper machine making, dehydration, forming

[0165] After concentration adjustment and purification, the pulp passes through the paper machine headbox, breast roll, chopping board, chopping roll, vacuum water absorption box and other rectifying elements, net-loading device, dehydration, and then forms wet paper sheets on the forming net and forms paper. After double-layer compounding by the compounding roller, the moisture content of the wet paper sheet is ensured to be 83%, and the combination of the modified additives (PDMS, phenyl silicone and TEOS) and the fiber is further stabilized in the wet state, and then enters the forming cylinder to continue winding and compounding. At the same time, it is pressed by the first, second and third rollers to squeeze out the excess moisture of the wet paperboard, and the hydrophobic cross-linking structure is initially solidified to ensure that the moisture content out of the forming cylinder is 69%, and the modified additives are evenly distributed in the fiber network. According to the 7.0mm thickness requirement, when the set number of process cycles is reached, the conveying roller under the forming cylinder is started, the knife of the forming cylinder is released, the wet paperboard is cut, and it is transported to the pre-installation machine, installation machine, and press machine along with the running dry net platform.

[0166] S7, hot pressing

[0167] The holding pressure and holding time of each section of the 7.0 mm press are shown in Table 1, and the remaining processes are in accordance with Example 1.

[0168] S8. The process is the same as in Example 1.

[0169] Example 21: Production of 8.0 mm paperboard

[0170] S1-S5: Same as in the first embodiment.

[0171] S6, paper machine making, dehydration, forming

[0172] After concentration adjustment and purification, the pulp passes through the paper machine headbox, breast roll, chopping board, chopping roll, vacuum water absorption box and other rectifying elements, net-loading device, dehydration, and forms wet paper sheets on the forming net and forms paper. After double-layer compounding by the compounding roller, the moisture content of the wet paper sheet is ensured to be 83%, and the combination of the modified additives (PDMS, phenyl silicone and TEOS) and the fiber is further stabilized in the wet state, and then enters the forming cylinder to continue winding and compounding. At the same time, it is pressed by the first, second and third rollers to squeeze out the excess moisture of the wet paperboard, and the hydrophobic cross-linking structure is initially solidified to ensure that the moisture content out of the forming cylinder is 69%, and the modified additives are evenly distributed in the fiber network. According to the 8.0mm thickness requirement, when the set number of process cycles is reached, the conveying roller under the forming cylinder is started, the knife of the forming cylinder is released, the wet paperboard is cut, and it is transported to the pre-installation machine, installation machine, and press machine along with the running dry net platform.

[0173] S7, hot pressing

[0174] The holding pressure and holding time of each section of the 8.0 mm press are shown in Table 1, and the remaining processes are in accordance with Example 1.

[0175] S8. The process is the same as in Example 1.

[0176] Comparative Example Production of Prior Art Paperboard

[0177] The preparation processes of Examples 1 and 14 to 21 were respectively set with corresponding prior arts as controls. The prior arts did not have the S4 step in Examples 1 and 14 to 21, did not add modifying additives, and only performed conventional process treatment on the slurry. The other steps were the same as the corresponding steps of Examples 1 and 14 to 21 to obtain corresponding products.

[0178] The products obtained in Examples 1, 14 to 21 and the 1.0-8.0 mm paperboard samples produced by the prior art were sampled and pre-treated according to the national standard GB / T 19264.2-2013 Electrical Pressed Paperboard and Thin Paperboard Part 2 Test Method, and the electrical strength index in the air was tested according to the test method in the above standard, and the data were recorded and summarized, as shown in Table 9 below:

[0179] Table 9 Test data of the products of Examples 1, 14 to 21 and their corresponding prior art products:

[0180]

[0181]

[0182]

[0183] Conclusion: According to the comparative test data of the products of Examples 1, 14 to 21 and the corresponding products produced by the prior art, the requirements of the electrical properties and mechanical properties of GB / T 19264.3-2013 Electrical pressboard and thin paperboard Part 3 Pressboard B.3.1A type paperboard in the air, such as electrical strength and tensile strength, are met. That is, the produced paperboard can increase the existing value of the electrical strength index in the air by 30% to 50%, providing an innovative solution for the industry. In the future, the long-term stability and environmental impact of additives can be further studied to promote industrial application.

[0184] It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope limited by the appended claims of the application.

Claims

1. A method for producing insulating paperboard, characterized in that: The following steps are involved: S1. Raw material selection: 100% unbleached kraft softwood pulp; S2. Pulping: 3000 kg of 100% unbleached kraft softwood pulp is put into a hydraulic pulper, and 47000 kg of pure water is added. After soaking for 5 minutes, the pulper is turned on to de-pulp the pulp to a concentration of 5.5-6.5%. The de-pulped pulp is pumped to the pre-grinding pulp tank and allowed to stand for 1-1.5 hours to allow the fibers to be fully stretched. S3. Refining: The debonded pulp is removed by a high-concentration desander, and the concentration is adjusted to 4.35-4.65% by a BTG concentration meter. It enters the DD720 double-disc mill, and the refining power is set to 545-575kW to knead, cut, separate and broom the pulp fibers to further optimize the fiber structure. The pulp is refined to a beating degree of 33-38°SR and a wet weight of 9-13g to obtain a milled pulp, which is pumped to a post-milling pulping tank; S4. Adding modifying additives and crosslinking agents in proportion: Adding modifying additives in proportion to the milled slurry, the modifying additives are PDMS emulsion and phenyl silicone emulsion, the two are used alone or simultaneously, wherein the addition ratio of PDMS emulsion with a solid content of 25% to 35% is 4.0 to 6.0% of the dry weight of the slurry; the addition ratio of phenyl silicone emulsion with a solid content of 20% to 40% is 1 to 3% of the dry weight of the slurry; both are added separately or simultaneously to the slurry tank, the propeller is turned on, and stirred for 15 minutes to form a hydrophobic layer in a coordinated manner to ensure that both are uniformly adsorbed on the fiber; then add the crosslinking agent TEOS, the addition ratio is 0.5 to 2% of the total mass of the modifying additive; after mixing according to the above ratio, mechanical stirring is performed to ensure that the slurry and the additive are fully and evenly fused, and then allowed to stand for 1 to 1.5 hours to allow the modifying additive to further react with the fiber and stably combine to form a uniform hydrophobic crosslinking layer, thereby significantly improving the electrical strength of the insulating paperboard in the air; S5. Flow screening, filtration and purification: The modified and cross-linked milled pulp is concentrated to 2.4-2.6% by the material gate pump and BTG concentration adjustment meter, purified and screened by the first and third stage low-concentration desander, and then transported to the paper machine through the pressure screen; S6. Papermaking, dehydration and forming: The pulp after concentration adjustment and purification passes through the paper machine headbox, breast roll, chopping board, chopping roll, vacuum water absorption box and other rectifying elements, net-loading device, dehydration, and then forms wet paper sheets on the forming net, and papermaking and forming; after double-layer lamination by the laminating roller, the moisture content of the wet paper sheets is maintained at 82-84%, and then enters the forming cylinder to continue winding and laminating. At the same time, it is pressed by the first, second and third support rollers to squeeze out the excess moisture of the wet paperboard, and the moisture content out of the forming cylinder is maintained at 68-70%. According to the requirements of each thickness, when the set number of process cycles is reached in advance, the conveying roller under the forming cylinder is started, and the knife of the forming cylinder is released to cut the wet paperboard, and it is transported to the pre-installation machine, installation machine and press machine along with the running dry net platform; S7. Hot pressing of press: according to the thickness of each thickness of paperboard, set the pressure gradient and holding time of the process: after each laminating press is filled with wet paperboard, set the steam pressure to 230-320kpa, the pressing plate temperature to 130-144℃, the first holding pressure to 24-26MPa, the holding time to 8-350min, the second holding pressure to 8-22MPa, the holding time to 3-20min, the third holding pressure to 0-14MPa, the holding time to 2-10min, the fourth holding pressure to 0-6MPa, the holding time to 2-25min; after the pressing is completed, the unloading trolley enters the press, sucks the pressed paperboard with a suction cup, and transports it to the unloading platform to obtain the finished paperboard; S8. Cut and shape the pressed dry cardboard according to the customer's order requirements using a vertical and horizontal saw to obtain the final product.

2. The method for producing insulating paperboard according to claim 1, characterized in that: The 100% unbleached kraft softwood pulp in step S1 is taken from mature wood in the extremely cold regions of Sweden and Russia.

3. The method for producing insulating paperboard according to claim 1, characterized in that: In the step S2, the slurry is decomposed to a concentration of 6.0%, and the decomposed slurry is pumped to a pre-grinding pulp tank and allowed to stand for 1.5 hours.

4. The method for producing insulating paperboard according to claim 1, characterized in that: In the step S3, the BTG concentration is adjusted to 4.5% by a concentration meter; the pulp is refined to a beating degree of 35°SR and a wet weight of 11 g.

5. The method for producing insulating paperboard according to claim 1, characterized in that: In the step S4, the addition ratio of the PDMS emulsion with a solid content of 30% is 5.0% of the dry weight of the slurry; the addition ratio of the phenyl silicone emulsion with a solid content of 30% is 2% of the dry weight of the slurry; the addition ratio of the crosslinking agent TEOS is 1% of the total mass of the modified additives; and the mixture is allowed to stand for 1.5 hours after mechanical stirring.

6. The method for producing insulating paperboard according to claim 1, characterized in that: The phenyl silicone emulsion in step S4 is phenyl methyl polysiloxane emulsion.

7. The method for producing insulating paperboard according to claim 1, characterized in that: In step S5, the BTG concentration meter adjusts the slurry concentration to 2.5%.

8. The method for producing insulating paperboard according to claim 1, characterized in that: The pressure and holding time required for paperboards of different thicknesses in step S7.

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