Preparation method of insulating flat paper for high voltage grade

Abstract

The invention provides a preparation method of insulating flat paper for a high voltage grade, which belongs to the technical field of insulating product production and comprises the following steps: removing iron from slurry with the mass percentage concentration of 3-4%, adding the slurry into hydrochloric acid, stirring, washing until the mass percentage concentration is 3-4%, adding magnesium bicarbonate, stirring, and drying to obtain the insulating flat paper for the high voltage grade. The preparation method comprises the following steps: stirring, washing, deslagging, pulping and deironing, diluting to the mass percentage concentration of 0.3%-0.8%, purifying, carrying out jet molding at the linear velocity ratio of (1.1-1.7): 1 to obtain wet paper, controlling the gram weight of the wet paper to be 50-200gsm, carrying out vacuum suction dehydration and squeezing, drying to the dryness of 55-65% to form semi-wet paper, and squeezing and drying again to form the finished product flat paper. The use amount of hydrochloric acid is 0.5%-1.5% of the mass fraction of the slurry, and the addition amount of magnesium bicarbonate is 2%-2.5% of the mass fraction of the slurry, so that the technical problems that pure slurry is easily polluted and the phenomenon of breakdown caused by insufficient electric strength still occurs under high voltage in the existing flat paper preparation method are solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of the production of insulating products, and particularly relates to a preparation method of insulating flat paper for high voltage levels. Background Art

[0002] Flat cable paper, abbreviated as "flat paper", is mainly made of sulfate softwood pulp, and is formed by beating and then papermaking on a paper machine. It has high tear strength, breaking work and dynamic strength, and is used in fields such as oil-impregnated paper bushings, oil-immersed transformers, instrument transformers, and electromagnetic wires for transformers. In addition, flat paper can also be used as the wrinkling base paper for wrinkled cable paper.

[0003] At present, although electrical-grade pulp is selected in the manufacturing process of flat paper, impurities brought into the pulp by the wear of production equipment itself are not paid attention to during the production process, resulting in the pollution of pure pulp; in addition, although electrical-grade pulp meets the use of ordinary insulating paper, it still shows the phenomenon of being broken down due to insufficient electrical strength under high voltage and still needs further treatment to meet the production and manufacturing of flat paper; moreover, the existing manufacturing process is difficult to meet the insulation requirements of high voltage levels (100KV - 1000KV) in terms of quality indicators such as paper ash content, tightness, tensile strength, electrical strength and evenness.

[0004] Chinese Patent CN114657806B discloses a thickened insulating cardboard and its production method, which uses raw materials such as unbleached sulfate softwood pulp, polyethylene glycol, polyacrylamide, copolymer of acrylic acid-2-ethylhexyl ester and styrene, oxidized starch, tetrasodium pyrophosphate, formaldehyde, p-nitrophenol, waterproof film, fiberglass mesh cloth, fireproof mud, grid-shaped carbon fiber reinforcing rib plate and UV wear-resistant coating, etc. Through beating, hot pressing and multi-layer structure design, the strength and waterproof and fireproof performance of the cardboard are improved, but this preparation method only reduces conductive ions through reverse osmosis water purification, and there are still problems in the production process that impurities brought into the pulp by the wear of production equipment itself are not paid attention to, resulting in the pollution of pure pulp and the phenomenon of being broken down due to insufficient electrical strength under high voltage. Summary of the Invention

[0005] In order to overcome the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide a preparation method of insulating flat paper for high voltage levels, so as to solve the technical problems that the existing preparation method of flat paper is prone to cause the pollution of pure pulp and the phenomenon of being broken down due to insufficient electrical strength under high voltage.

[0006] To achieve the above purpose, the present invention adopts the following technical solutions:

[0007] The present invention provides a preparation method of insulating flat paper for high voltage levels, which includes adding the pulp with a mass percentage concentration of 3%-4% after iron removal into hydrochloric acid, stirring, washing until the mass percentage concentration is 3%-4%, then adding magnesium bicarbonate, stirring, washing, slag removal, refining and iron removal, diluting to a mass percentage concentration of 0.3%-0.8%, obtaining wet paper after purification by spraying molding at a linear speed of (1.1-1.7):1, controlling the grammage of the wet paper to be 50gsm-200gsm, dehydrating by vacuum suction and pressing, drying to a dryness of 55%-65% to form semi-wet paper, and forming the finished flat paper after re-pressing and drying; the dosage of hydrochloric acid is 0.5%-1.5% of the pulp mass fraction, and the addition amount of magnesium bicarbonate is 2%-2.5% of the pulp mass.

[0008] Further preferably, coniferous wood electrical grade sulfate pulp with an ash content <0.5% and reverse osmosis water are mixed to prepare a pulp with a mass percentage concentration of 6%-10%, and then disintegrated for ≥10 min, and diluted to a pulp with a mass percentage concentration of 3%-4% after iron removal.

[0009] Further preferably, the stirring time after adding hydrochloric acid is ≥45 min.

[0010] Further preferably, the stirring time after adding magnesium bicarbonate is ≥1 h.

[0011] Further preferably, refining to a beating degree of 25-35°SR.

[0012] Further preferably, preliminary iron removal is carried out by a high-concentration iron remover, controlling the mass percentage concentration of the pulp to be 3%-4%.

[0013] Preferably, before adding magnesium bicarbonate, concentration and washing are carried out by a cylinder screen concentrator, and the washing water is papermaking recycled white water with a temperature exceeding 40°C; after adding magnesium bicarbonate, washing is carried out by a four-stage countercurrent drum displacement pulp washer, and the washing water is reverse osmosis water at 90-100°C.

[0014] Preferably, slag removal is carried out by a high-concentration screw slag remover at a mass percentage concentration of 3%-4%, and iron removal is carried out by a low-concentration iron remover to make the mass percentage concentration of the pulp 1%-4%.

[0015] Preferably, iron removal, slag removal, gas removal and screening purification are carried out through an iron removal and sand settling pan, a low-concentration slag remover, a degassing tank and a pressure screen, controlling the mass percentage concentration of the pulp to be 0.3%-1.2%.

[0016] Preferably, in vacuum suction dehydration, the vacuum degree is -5~-50 kpa; after three-roll pressing, stone-roll pressing and gloss pressing, the moisture is controlled to be 48%-50%.

[0017] Preferably, the drying temperature is 100°C - 130°C, and after drying to less than 6% moisture, a finished flat paper is formed.

[0018] Preferably, a semi-wet calender is used to press the semi-wet paper again, and the press line pressure is controlled at 30 - 50 KN / m.

[0019] The present invention also provides another method for preparing an insulating flat paper for high voltage levels, which includes adding a slurry with a mass percentage concentration of 3% - 4% to hydrochloric acid, stirring, washing until the mass percentage concentration is 3% - 4%, then adding magnesium bicarbonate, stirring, washing, removing slag and grinding to a beating degree of 25 - 35°SR and removing iron to obtain a mixed slurry; collecting production waste paper, shredding it to a mass percentage concentration of 3% - 4%, and then through iron removal, sieving, slag removal and defibering treatment to obtain a broke pulp with a beating degree of 30 - 40°SR; mixing the mixed slurry and the broke pulp in a mass ratio of (7 - 8):(3:2), diluting to a mass percentage concentration of 0.3% - 0.8% and purifying; through forming, vacuum suction dewatering, pressing and drying, an insulating flat paper for high voltage levels is obtained.

[0020] Preferably, the iron removal, sieving, slag removal and defibering treatments are completed through an iron remover, a pressure screen, a high-concentration screw slag remover and a defiberizer, so that the mass percentage concentration of the slurry is controlled at 0.3% - 1.2%.

[0021] Preferably, the mixed slurry is purified through an iron removal and sand settling pan, a low-concentration slag remover, a degassing tank and a pressure screen, so that the mass percentage concentration of the slurry is controlled at 0.3% - 1.2%.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The preparation method of the present invention treats free metal ions Na + , Ca 2+ with hydrochloric acid to reduce ash content, reduce conductive impurities and improve electrical strength; add magnesium bicarbonate to displace the sodium ions salified by carboxyl groups, reduce the free ion mobility, reduce the dielectric loss and increase the breakdown voltage, solving the technical problems that the existing flat paper preparation methods are prone to cause pollution of pure slurry and still have insufficient electrical strength and breakdown under high voltage. Alternately remove iron to remove equipment wear impurities and avoid metal pollution; set a pulp-to-wire speed ratio of (1.1 - 1.7):1 in the forming stage to optimize fiber interweaving, improve the longitudinal tensile strength, improve the paper evenness and reduce local electric field concentration; finally, enhance hydrogen bond binding through dewatering, make the structure dense and reduce air gaps to improve the insulation performance.

[0024] Furthermore, high temperatures of 90 - 100 °C enhance metal ion diffusion, improve countercurrent displacement efficiency, and further remove residual hydrochloric acid and metal salts; efficient concentration washing with white water above 40 °C reduces fiber loss and preheats the pulp to promote subsequent reactions.

[0025] Furthermore, large particle metal impurities such as iron filings are effectively removed at a high mass percentage concentration of 3% - 4%, and a low mass percentage concentration of 1% - 4% improves magnetic separation sensitivity, removes fine ferromagnetic particles, and reduces the risk of conductive channels.

[0026] Furthermore, iron is removed to eliminate inorganic impurities such as sand grains; slag is removed to eliminate light impurities; gas is removed to eliminate bubbles and avoid paper pinhole defects; screening is used to filter fiber bundles to ensure pulp uniformity and improve the mechanical strength of the paper.

[0027] Furthermore, vacuum suction dewatering reduces fiber loosening and prevents rewetting; in the press dewatering stage, first three-roll pressing is used. Taking advantage of the two pressure zones of the three rolls, the fibers are quickly dehydrated and combined, and the fibers are closely arranged to reduce the fluctuation of the dielectric constant. Then, stone roll pressing is carried out. Taking advantage of the weight of the stone roll, the fibers are subjected to greater force to dehydrate and form hydrogen bonds. After gloss pressing, the paper surface is smoothed and modified, making it easier to lose water by heating.

[0028] Furthermore, temperature-controlled drying avoids high-temperature carbonization of fibers, moderately dries to maintain flexibility, and at the same time ensures a low residual moisture content of <6%, reducing the risk of leakage current.

[0029] Furthermore, calendering is carried out when the paper is in a semi-dry state, making the paper surface denser, reducing surface burrs, evenly distributing the electric field, and increasing the breakdown voltage.

[0030] The present invention also provides another method for preparing insulating flat paper for high voltage levels. After the waste paper is subjected to iron removal, screening, slag removal, and beating, pollutants are removed and the fiber strength is retained; the mixed pulp and waste pulp are mixed at a mass ratio of (7 - 8):(2 - 3) to achieve resource recycling, while ensuring that the ash content ≤ 0.20%, balancing the electrical performance and economy; after forming, vacuum suction dewatering, pressing, and drying, insulating flat paper for high voltage levels is prepared to ensure the stable performance of the final product. Specific Embodiments

[0031] To enable those skilled in the art to understand the features and effects of the present invention, the following provides only a general description and definition of the terms and expressions mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used herein shall have the ordinary meaning understood by those skilled in the art for the present invention. In case of conflict, the definition in this specification shall prevail.

[0032] The theories or mechanisms described and disclosed herein, whether right or wrong, shall not limit the scope of the present invention in any way, that is, the content of the present invention can be implemented without being limited by any specific theory or mechanism.

[0033] In this article, all features defined in the form of numerical ranges or percentage ranges, such as numerical values, quantities, contents, and mass percentage concentrations, are only for the sake of brevity and convenience. Accordingly, the description of a numerical range or percentage range should be regarded as having covered and specifically disclosed all possible sub-ranges and individual numerical values within the range (including integers and fractions).

[0034] In this article, unless otherwise specified, terms such as "comprising", "including", "containing", "having", or similar terms cover the meanings of "consisting of" and "consisting essentially of". For example, "A comprises a" covers the meanings of "A comprises a and others" and "A consists only of a".

[0035] In this article, for the sake of concise description, all possible combinations of all technical features in each embodiment or example are not described. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each embodiment or example can be combined arbitrarily, and all possible combinations should be considered as the scope described in this specification.

[0036] The object of the present invention is achieved as follows: A preparation method of insulating flat paper for high voltage levels, with a product specification of 50 - 200 gsm and a vehicle speed of 70 - 100 m / min.

[0037] Scheme 1 includes the following steps:

[0038] Step 1: Add coniferous wood electrical grade kraft pulp (ash content less than 0.5%) to reverse osmosis water to a mass percentage concentration of 6% - 10%, and completely disintegrate it (time not less than 10 min);

[0039] Step 2: Preliminarily remove iron from the pulp obtained in Step 1 through a high - density iron remover, and then pump it to tank A with a stirrer and dilute it with reverse osmosis water to a mass percentage concentration of 3% - 4%; at the same time, add hydrochloric acid with a mass fraction of 0.5 - 1.5% and stir for more than 45 min.

[0040] Step 3: Concentrate and wash the pulp obtained in Step 2 through a cylinder screen concentrator. The washing water is white water recycled from papermaking at a temperature exceeding 40°C. Add reverse osmosis water to adjust the mass percentage concentration of the slurry to 3% - 4%. Subsequently, add magnesium bicarbonate, and the addition amount of magnesium bicarbonate is 2% - 2.5% of the mass of the coniferous wood electrical grade kraft pulp. Stir in tank B of the stirrer for more than 1 h, and wash it with a four - stage countercurrent drum displacement washer. The washing water is reverse osmosis hot water at 90 - 100°C.

[0041] Step 4: Remove impurities from the pulp obtained in Step 3 through a high-concentration screw slag remover, and then pump it to a double-disc refiner for refining until the beating degree reaches 25°-35°SR; then remove iron through a low-concentration iron remover and pump it into tank C for temporary storage.

[0042] Step 5: Dilute the pulp in Step 4 with reverse osmosis water to a mass percentage concentration of 0.3%-0.8%, and then purify the mixed pulp through an iron-removing sand settling pan, a low-concentration slag remover, a degassing tank, and a pressure screen.

[0043] Step 6: Pump the pulp in Step 5 into an isobaric pulp distributor, and use the isobaric pulp distributor to spray it evenly on a cylinder former. The ratio of the pulp spraying speed of the pulp distributor to the linear speed of the cylinder former is 1.1:1-1.7:1, and form it into wet paper. The pulp spraying amount of the pulp distributor controls the finished gram weight to be 50gsm-200gsm.

[0044] Step 7: Transfer the wet paper in Step 6 to a forming felt, and then dehydrate it through vacuum suction (the vacuum degree is -5~-50kpa). After passing through three-roll pressing, stone-roll pressing, and gloss pressing, send it into a drying cylinder and hot air for drying to a dryness of 55-65%, forming semi-wet paper.

[0045] Step 8: Send the semi-wet paper into a semi-wet calender for re-pressing, and then send it to a drying cylinder with a surface temperature of 100℃-130℃ for drying. After drying to a moisture content of less than 6%, form finished flat paper. The qualified flat paper is immediately wound, cut, and stored in the warehouse.

[0046] Scheme 2 includes the following steps:

[0047] Step 1: Add reverse osmosis water to needlewood electrical grade kraft pulp (ash content less than 0.5%) to a mass percentage concentration of 6%-10%, and completely disintegrate it (the time is not less than 10min);

[0048] Step 2: Conduct preliminary iron removal on the pulp obtained in Step 1 through a high-concentration iron remover, and then pump it into tank A with a stirrer and dilute it with reverse osmosis water to a mass percentage concentration of 3%-4%; at the same time, add hydrochloric acid with a mass fraction of 0.5-1.5% relative to the needlewood electrical grade kraft pulp and stir for more than 45min;

[0049] Step 3: Concentrate and wash the slurry obtained in Step 2 using a cylinder screen thickener. The washing water is white water recycled from papermaking at a temperature exceeding 40°C. Add reverse osmosis water to adjust the mass percentage concentration of the slurry to 3%-4%. Subsequently, add magnesium bicarbonate, with the addition amount of magnesium bicarbonate being 2%-2.5% of the mass of softwood electrical grade sulfate pulp. Stir in the tank B of the stirrer for more than 1 hour, and then wash using a four-stage countercurrent drum displacement pulp washer. The washing water is reverse osmosis hot water at 90-100°C;

[0050] Step 4: Remove impurities from the slurry obtained in Step 3 using a high-concentration screw slag remover, and then pump it to a double-disc refiner for refining until the beating degree reaches 25°-35°SR; then remove iron using a low-concentration iron remover and pump it into tank C for temporary storage;

[0051] Step 5: Collect all the waste paper generated during the production of flat paper for high voltage, add pure water to disintegrate and dilute it to a mass percentage concentration of 3%-4% to obtain broke pulp, and then obtain pure broke pulp with a beating degree of 30°-40°SR after passing through an iron remover, a pressure screen, a high-concentration screw slag remover, and a pulper;

[0052] Step 6: Mix the slurry obtained in Step 4 with the broke pulp in Step 5 at a ratio of 8:2 - 7:3 to obtain a mixed pulp;

[0053] Step 7: Add reverse osmosis water to dilute the mixed pulp in Step 6 to a mass percentage concentration of 0.3%-0.8%, and then purify the mixed pulp through an iron removal and sand settling tray, a low-concentration slag remover, a degassing tank, and a pressure screen;

[0054] Step 8: Pump the mixed pulp in Step 7 into an isobaric pulp distributor, and use the isobaric pulp distributor to uniformly spray the mixed pulp onto a cylinder former. The ratio of the spraying speed of the pulp in the pulp distributor to the linear speed of the cylinder former is 1.1-1.7:1, and form it into wet paper. Control the spraying amount of the pulp in the pulp distributor so that the finished grammage is 50gsm-200gsm;

[0055] Step 9: Transfer the wet paper in Step 8 onto a forming felt, and then dehydrate it through vacuum suction (the vacuum degree is -5~-50kpa). After passing through three-roll pressing, stone-roll pressing, and gloss pressing, send it into a dryer and hot air for drying to a dryness of 55-65% to form semi-wet paper;

[0056] Step 10: Send the semi-wet paper into a semi-wet calender for re-pressing, and then send it onto a dryer with a surface temperature of 100°C-130°C for drying. After drying to a moisture content of less than 6%, form the finished flat paper. The qualified flat paper is then wound, cut, and stored in the warehouse.

[0057] There are multiple metal impurity removal processes in the raw material treatment stage to ensure the quality of the finished product. Secondly, the pulp is treated with hydrochloric acid to eliminate a large amount of metal salts, significantly reducing the ash content of the pulp and improving the electrical properties of the paper. In this process, magnesium carbonate is used to convert the free carboxyl groups with greater ionization ability in the pulp after the reaction with hydrochloric acid into carboxylate salts, replacing the sodium ions in the pulp and further improving the electrical properties. In the papermaking forming stage, the mechanical properties and evenness of the paper are adjusted by using a cylinder former, a degassing tank, and controlling the pulp-to-wire speed ratio. After multiple adjustments, the process of the present invention is determined to meet the mechanical properties of high-voltage paper. In the pressing and dewatering stage, first, three-roll pressing is used to utilize the advantages of the three-roll two-pressure zone to quickly dehydrate and combine the fibers, making them tightly intertwined. Then, stone-roll pressing is carried out to utilize the weight advantage of the stone roll to make the fibers dehydrate under a greater force and form hydrogen bonds. After gloss pressing, the surface of the paper is smoothed, facilitating better heat loss and water evaporation. The heated paper undergoes semi-wet calendering to further improve the paper density and meet the requirements. Therefore, using this process can manufacture flat paper that meets the mechanical and electrical property requirements for 100KV - 1000KV applications.

[0058] The following specific embodiments are used to further illustrate the present invention. It should be understood that these embodiments are only used to illustrate the present invention and not 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 defined by the appended claims of this application.

[0059] Conventional instrument equipment in the art is used in the following embodiments. For the experimental methods without specific conditions noted in the following embodiments, they are usually carried out under conventional conditions or according to the conditions recommended by the manufacturer. Various raw materials are used in the following embodiments. Unless otherwise stated, commercially available products are used, and their specifications are conventional specifications in the art. In the specification of the present invention and the following embodiments, unless otherwise specified, "%" represents weight percentage, "parts" represents weight parts, and the ratio represents weight ratio.

[0060] Example 1

[0061] Step 1: Add softwood electrical grade kraft pulp with an ash content of less than 0.5% to reverse osmosis water to a mass percentage concentration of 6%, and disintegrate for 12 minutes.

[0062] Step 2: Initially remove iron from the pulp obtained in Step 1 through a high-concentration iron remover, and then pump it into a tank with a stirrer and dilute it with reverse osmosis water to a mass percentage concentration of 3%. At the same time, add hydrochloric acid with a mass fraction of 1% relative to the softwood electrical grade kraft pulp and stir for 60 minutes.

[0063] Step 3: Concentrate and wash the pulp obtained in Step 2 through a cylinder screen concentrator. The washing water is the recycled white water for papermaking at 40°C. Then, add magnesium bicarbonate and reverse osmosis water to adjust the pulp consistency to 4%. The addition amount of magnesium bicarbonate is 2% of the mass of the softwood electrical grade kraft pulp. Stir in the tank for 1 hour. Use a four-stage countercurrent drum displacement pulp washer, and the washing water is reverse osmosis hot water at 98°C;

[0064] Step 4: Remove impurities from the pulp obtained in Step 3 through a high-consistency screw cleaner at a mass percentage concentration of 3.5%. Then, pump it to a double-disc refiner for refining until the beating degree reaches 32°SR. Remove iron through a low-consistency iron remover to a mass percentage concentration of 2.5% and then pump it into the tank for temporary storage;

[0065] Step 5: Collect all the waste paper in the process of producing flat paper for high voltage. Then, add pure water to break it down and dilute it to a mass percentage concentration of 4% to obtain broke pulp. After passing through an iron remover, a pressure screen, a high-consistency screw cleaner, and a pulper, pure broke pulp with a beating degree of 35° is obtained;

[0066] Step 6: Mix 80% of the pulp obtained in Step 4 with 20% of the broke pulp in Step 5 to obtain a mixed pulp;

[0067] Step 7: Dilute the mixed pulp in Step 6 with reverse osmosis water to a mass percentage concentration of 0.3%. Then, purify and mix it through an iron removal and sand settling pan, a low-consistency cleaner, a degassing tank, and a pressure screen;

[0068] Step 8: Pump the mixed pulp in Step 7 into an isobaric pulp distributor, and use the isobaric pulp distributor to evenly spray the mixed pulp onto a cylinder former. The ratio of the spraying speed of the pulp in the distributor to the linear speed of the cylinder former is 1.38 to form wet paper. Control the spraying amount of the pulp in the distributor so that the finished grammage is 50 gsm;

[0069] Step 9: Transfer the wet paper in Step 8 to a forming felt, and then dehydrate it through vacuum suction with a vacuum degree of -38 kPa. After passing through three-roll pressing, stone-roll pressing, and gloss pressing, send it into a dryer and hot air for drying to a dryness of 55% to form semi-wet paper;

[0070] Step 10: Send the semi-wet paper into a semi-wet calender for re-pressing, and then send it onto a dryer with a surface temperature of 110°C for drying. After drying to a moisture content of 6%, form the finished flat paper. The qualified flat paper is immediately wound, slit, and stored in the warehouse.

[0071] Example 2

[0072] Step 1: Add purchased softwood electrical grade kraft pulp (ash content less than 0.5%) and reverse osmosis water to a mass percentage concentration of 10%, and completely break it down (time: 16 min);

[0073] Step 2: The slurry obtained in Step 1 is preliminarily de-ironed by a high-concentration iron remover, and then pumped into a tank with a stirrer and diluted to 4% mass percentage concentration with reverse osmosis water; meanwhile, hydrochloric acid with a mass fraction of 0.5% relative to softwood electrical grade kraft pulp is added thereto and stirred for 45 min;

[0074] Step 3: The slurry obtained in Step 2 is concentrated and washed by a cylinder screen concentrator. The washing water is white water recycled from papermaking at 45°C. Then, magnesium bicarbonate and reverse osmosis water are added to adjust the pulp concentration to 3%. The addition amount of magnesium bicarbonate is 2.5% of the mass of softwood electrical grade kraft pulp. Stir for 1 h in the tank, and use a four-stage countercurrent drum displacement pulp washer. The washing water is reverse osmosis hot water at 95°C;

[0075] Step 4: The slurry obtained in Step 3 is de-slagged by a high-concentration screw slag remover at a mass percentage concentration of 3.5%, and then pumped to a double-disc refiner for refining until the beating degree reaches 25°SR; after de-ironing by a low-concentration iron remover to a mass percentage concentration of 2.5%, it is pumped into a tank for temporary storage;

[0076] Step 5: All waste paper in the process of producing flat paper for high voltage is collected, and then added with pure water for pulping and diluted to 4% mass percentage concentration to obtain broke pulp. After passing through an iron remover, a pressure screen, a high-concentration screw slag remover, and a pulper, pure broke pulp with a beating degree of 40° is obtained;

[0077] Step 6: 70% of the slurry obtained in Step 4 is mixed with 30% of the broke pulp in Step 5 to obtain a mixed pulp;

[0078] Step 7: The mixed pulp in Step 6 is diluted with reverse osmosis water to a mass percentage concentration of 0.5%. Subsequently, the mixed pulp is purified by an iron removal and sand settling pan, a low-concentration slag remover, a degassing tank, and a pressure screen;

[0079] Step 8: The mixed pulp in Step 7 is pumped into an isobaric pulp distributor, and the mixed pulp is evenly sprayed on a cylinder former by the isobaric pulp distributor. The ratio of the spraying speed of the pulp in the distributor to the linear speed of the cylinder former is 1.1, and it is formed into wet paper. The spraying amount of the pulp in the distributor is controlled so that the finished product gram weight is 75 gsm;

[0080] Step 9: The wet paper in Step 8 is transferred to a forming felt, and then dehydrated by vacuum suction (vacuum degree is -45 kPa). After passing through three-roll pressing, stone-roll pressing, and gloss pressing, it is sent into a drying cylinder and hot air for drying to a dryness of 58% to form semi-wet paper;

[0081] Step 10: Feed the semi-wet paper into a semi-wet calender for re-pressing, and then feed it onto a dryer with a surface temperature of 115 °C for drying. After drying to 6% moisture content, finished flat paper is formed. The flat paper meeting the quality requirements is then wound, slit, and stored in the warehouse.

[0082] Example 3

[0083] Step 1: Add needlewood electrical grade sulfate pulp with an ash content of less than 0.5% to reverse osmosis water to a mass percentage concentration of 8%, and disintegrate for 14 minutes.

[0084] Step 2: Preliminarily remove iron from the pulp obtained in Step 1 through a high-concentration iron remover, and then pump it into a tank with a stirrer and dilute it with reverse osmosis water to a mass percentage concentration of 3%. At the same time, add hydrochloric acid with a mass fraction of 1.5% relative to the needlewood electrical grade sulfate pulp and stir for 45 minutes.

[0085] Step 3: Concentrate and wash the pulp obtained in Step 2 through a cylinder screen concentrator. The washing water is papermaking recycled white water at 43 °C. Then add magnesium bicarbonate and reverse osmosis water to adjust the pulp consistency to 3.5%. The addition amount of magnesium bicarbonate is 2.5% of the mass of the needlewood electrical grade sulfate pulp. Stir in the tank for 1 hour, and use a four-stage countercurrent drum displacement pulp washer. The washing water is reverse osmosis hot water at 95 °C.

[0086] Step 4: Remove slag from the pulp obtained in Step 3 through a high-concentration screw slag remover at a mass percentage concentration of 3.5%, and then pump it to a double-disc refiner for refining until the beating degree reaches 35 °SR. Remove iron through a low-concentration iron remover to a mass percentage concentration of 2.5%, and then pump it into a tank for temporary storage.

[0087] Step 5: Dilute the pulp obtained in Step 4 with reverse osmosis water to a mass percentage concentration of 0.35%, and then purify the mixed pulp through an iron-removing sand trap, a low-concentration slag remover, a degassing tank, and a pressure screen.

[0088] Step 6: Pump the mixed pulp in Step 5 into an isobaric pulp distributor, and use the isobaric pulp distributor to evenly spray the mixed pulp onto a cylinder former. The ratio of the spraying speed of the pulp in the distributor to the linear speed of the cylinder former is 1.7, and form it into wet paper. Control the spraying amount of the pulp in the distributor so that the finished grammage is 125 gsm.

[0089] Step 7: Transfer the wet paper in Step 6 to a forming felt, and then dehydrate it through vacuum suction (vacuum degree is -50 kPa). After passing through three-roll pressing, stone-roll pressing, and gloss pressing, send it into a dryer and hot air for drying to 60% dryness to form semi-wet paper.

[0090] Step 8: Feed the semi-wet paper into a semi-wet calender for further pressing, and then feed it onto a drying cylinder with a surface temperature of 115 °C for drying. After drying to 6% moisture content, the finished flat paper is formed. The flat paper meeting the quality requirements is then wound, slit, and stored in the warehouse.

[0091] The indicators of the above Examples 1-3 are as follows in the table

[0092]

[0093]

[0094] As can be seen from the above table, the electrical strength in Examples 1-3 is ≥16.5 KV / mm, the dielectric loss tangent (tgδ) ≤0.16%, meeting the insulation requirements for high voltage levels of 100-1000 KV. Hydrochloric acid deionization makes the ash content ≤0.2%, and the replacement of sodium ions by magnesium bicarbonate makes the conductivity of the water extract ≤1.6 mS / m. The two work together to reduce the risk of conductive channels; Tensile strength: 4.2-10.0 KN / m longitudinally and 2.2-4.6 KN / m transversely, superior to conventional insulating paper (longitudinally ≤8 KN / m). Multi-stage pressing (three-roll + stone roll + gloss pressing) enhances hydrogen bond binding, and semi-wet calendering improves the density (0.96-1.01 g / cm 3 ); The air permeability ≤0.18 μm / (Pa·s), and the pH value of the water extract is 6.5-6.8, indicating uniform fiber distribution and no local defects, avoiding electric field concentration breakdown.

[0095] Example 4

[0096] Step 1: Add needlewood electrical grade sulfate pulp with an ash content of less than 0.5% to reverse osmosis water to a mass percentage concentration of 8%, and disintegrate for 15 min;

[0097] Step 2: After preliminarily removing iron from the pulp obtained in Step 1 through a high-concentration iron remover, pump it to a tank with a stirrer and dilute it to a mass percentage concentration of 4% with reverse osmosis water; at the same time, add hydrochloric acid with a mass fraction of 1.2% relative to the needlewood electrical grade sulfate pulp and stir for 50 min;

[0098] Step 3: Concentrate and wash the pulp obtained in Step 2 through a cylinder screen concentrator. The washing water is papermaking recycled white water at 45 °C. Then add magnesium bicarbonate and reverse osmosis water to adjust the pulp concentration to 3.5%. The addition amount of magnesium bicarbonate is 2.3% of the mass of the needlewood electrical grade sulfate pulp, stir in the tank for 1 h, and use a four-stage countercurrent drum displacement pulp washer. The washing water is reverse osmosis hot water at 95 °C;

[0099] Step 4: Remove impurities from the pulp obtained in Step 3 using a high-consistency screw cleaner at a mass percentage concentration of 3%, and then pump it to a double-disc refiner for refining until the beating degree reaches 30° SR; remove iron using a low-consistency iron remover until the mass percentage concentration is 1%, and then pump it into a tank for temporary storage;

[0100] Step 5: Collect all the waste paper generated during the production of flat paper for high-voltage use, add pure water to it for pulping and dilution to a mass percentage concentration of 4% to obtain broke pulp, and then obtain pure broke pulp with a beating degree of 35° after passing through an iron remover, a pressure screen, a high-consistency screw cleaner, and a pulper;

[0101] Step 6: Mix 80% of the pulp obtained in Step 4 with 20% of the broke pulp obtained in Step 5 to obtain a mixed pulp;

[0102] Step 7: Dilute the mixed pulp obtained in Step 6 with reverse osmosis water to a mass percentage concentration of 0.8%, and then purify the mixed pulp through an iron removal and sand settling pan, a low-consistency cleaner, a degassing tank, and a pressure screen;

[0103] Step 8: Pump the mixed pulp obtained in Step 7 into an isobaric pulp distributor, and use the isobaric pulp distributor to uniformly spray the mixed pulp onto a cylinder former. The ratio of the spraying speed of the pulp in the distributor to the linear speed of the cylinder former is 1.2, and form it into wet paper. The spraying amount of the pulp in the distributor is controlled to make the finished product grammage 200 gsm;

[0104] Step 9: Transfer the wet paper obtained in Step 8 onto a forming felt, and then dehydrate it through vacuum suction with a vacuum degree of -5 kPa. After passing through three-roll pressing, stone-roll pressing, and gloss pressing, send it into a dryer and hot air for drying to a dryness of 65% to form semi-wet paper;

[0105] Step 10: Send the semi-wet paper into a semi-wet calender for re-pressing, and then send it onto a dryer with a surface temperature of 100°C for drying. After drying to a moisture content of 6%, form the finished flat paper. The flat paper meeting the quality requirements is then wound, slit, and stored in the warehouse.

[0106] Example 5

[0107] Step 1: Add softwood electrical grade kraft pulp with an ash content of less than 0.5% to reverse osmosis water to a mass percentage concentration of 9%, and disintegrate for 12 minutes;

[0108] Step 2: Conduct preliminary iron removal on the pulp obtained in Step 1 using a high-consistency iron remover, and then pump it into a tank with a stirrer and dilute it to a mass percentage concentration of 4% with reverse osmosis water; at the same time, add hydrochloric acid with a mass fraction of 0.8% relative to the softwood electrical grade kraft pulp and stir for 55 minutes;

[0109] Step 3: Concentrate and wash the slurry obtained in Step 2 through a cylinder screen concentrator. The washing water is the recycled white water for papermaking at 42°C. Then, add magnesium bicarbonate and reverse osmosis water to adjust the pulp consistency to 3%. The addition amount of magnesium bicarbonate is 2.5% of the mass of the softwood electrical grade kraft pulp. Stir in the tank for 1.2 h. Use a four-stage countercurrent drum displacement pulp washer, and the washing water is reverse osmosis hot water at 98°C;

[0110] Step 4: Remove impurities from the slurry obtained in Step 3 through a high-consistency screw cleaner at a mass concentration of 4%. Then, pump it to a double-disc refiner for refining until the beating degree reaches 28°SR; Remove iron through a low-consistency iron remover until the mass concentration is 4%, and then pump it into the tank for temporary storage;

[0111] Step 5: Collect all the waste paper during the production of flat paper for high voltage. Then, add pure water to disintegrate and dilute it to a mass concentration of 4% to obtain broke pulp. After passing through an iron remover, a pressure screen, a high-consistency screw cleaner, and a pulper, obtain pure broke pulp with a beating degree of 35°;

[0112] Step 6: Mix 80% of the slurry obtained in Step 4 with 20% of the broke pulp in Step 5 to obtain a mixed pulp;

[0113] Step 7: Dilute the mixed pulp in Step 6 with reverse osmosis water to a mass concentration of 0.6%. Then, purify the mixed pulp through an iron removal and sand settling pan, a low-consistency cleaner, a degassing tank, and a pressure screen to a mass concentration of 0.5%;

[0114] Step 8: Pump the mixed pulp in Step 7 into an isobaric pulp distributor. Use the isobaric pulp distributor to evenly spray the mixed pulp on a cylinder former. The ratio of the spraying speed of the pulp in the distributor to the linear speed of the cylinder former is 1.5, and form it into wet paper. Control the spraying amount of the pulp in the distributor so that the finished grammage is 150 gsm;

[0115] Step 9: Transfer the wet paper in Step 8 to a forming felt, and then dehydrate it through vacuum suction. The vacuum degree is -25 kPa. After passing through a three-roll press, a stone roll press, and a calender press, send it into a dryer and hot air for drying to 60% dryness to form semi-wet paper;

[0116] Step 10: Send the semi-wet paper into a semi-wet calender for re-pressing, and then send it to a dryer with a surface temperature of 130°C for drying. After drying to 6% moisture, form the finished flat paper. The flat paper that meets the quality requirements is immediately wound, slit, and stored in the warehouse.

[0117] The above content is only to illustrate the technical idea of the present invention and cannot be used to limit the protection scope of the present invention. Any modification made on the basis of the technical solution according to the technical idea proposed by the present invention falls within the protection scope of the claims of the present invention.

Claims

1. A preparation method of insulating flat paper for high voltage levels, characterized in that, It includes adding the slurry with a mass percentage concentration of 3%-4% after iron removal into hydrochloric acid, stirring and washing it until the mass percentage concentration is 3%-4%, then adding magnesium bicarbonate. After stirring, washing, slag removal, pulping and iron removal, it is diluted to a mass percentage concentration of 0.3%-0.8%. After purification, it is spray-formed at a linear speed ratio of (1.1-1.7):1 to obtain wet paper. The grammage of the wet paper is controlled to be 50 gsm-200 gsm. After vacuum suction dewatering and pressing, it is dried to a dryness of 55%-65% to form semi-wet paper. After being pressed and dried again, finished flat paper is formed; the dosage of hydrochloric acid is 0.5%-1.5% of the mass fraction of the slurry, and the addition amount of magnesium bicarbonate is 2%-2.5% of the mass of the slurry.

2. The preparation method of an insulating flat paper for high voltage levels according to claim 1, characterized in that, Concentrating and washing are carried out before adding magnesium bicarbonate, and the washing water is the recycled white water for papermaking above 40°C; after adding magnesium bicarbonate, washing is carried out, and the washing water is the reverse osmosis water at 90-100°C.

3. The preparation method of an insulating flat paper for high voltage levels according to claim 1, characterized in that, Slag removal is carried out at a mass percentage concentration of 3%-4%, and then iron removal is carried out to make the mass percentage concentration of the slurry 1%-4%.

4. The preparation method of an insulating flat paper for high voltage level according to claim 1, characterized in that, After iron removal, slag removal, degassing and sieving purification, the mass percentage concentration of the slurry is controlled at 0.3%-1.2%.

5. The preparation method of an insulating flat paper for high voltage levels according to claim 1, characterized in that, In vacuum suction dewatering, the vacuum degree is -5~-50 kpa; after pressing, the moisture is controlled at 48%-50%.

6. The preparation method of an insulating flat paper for high voltage levels according to claim 1, characterized in that, The drying temperature is 100°C-130°C, and after drying to a moisture content of less than 6%, finished flat paper is formed.

7. The preparation method of an insulating flat paper for high voltage levels according to claim 1, characterized in that, The semi-wet paper is pressed again, and the pressing line pressure is controlled at 30-50 KN / m.

8. A preparation method of insulating flat paper for high voltage levels, characterized in that, It includes adding the slurry with a mass percentage concentration of 3%-4% into hydrochloric acid, stirring and washing it until the mass percentage concentration is 3%-4%, then adding magnesium bicarbonate. After stirring, washing, slag removal and pulping to a beating degree of 25-35°SR and iron removal, a mixed slurry is prepared; collecting production waste paper, shredding it to a mass percentage concentration of 3%-4% and then through iron removal, sieving, slag removal and defibering, a broke pulp with a beating degree of 30-40°SR is prepared; mixing the mixed slurry and the broke pulp according to the mass ratio of (7-8):(2-3), diluting it to a mass percentage concentration of 0.3%-0.8% and purifying it; after forming, vacuum suction dewatering, pressing and drying, insulating flat paper for high voltage grades is prepared.

9. The preparation method of an insulating flat paper for high voltage levels according to claim 8, characterized in that, Through iron removal, sieving, slag removal and defibering treatment, the mass percentage concentration of the slurry is controlled at 0.3%-1.2%.

10. The preparation method of an insulating flat paper for high voltage levels according to claim 8, characterized in that, After iron removal, slag removal, degassing and sieving purification, the mass percentage concentration of the slurry is controlled at 0.3%-1.2%.

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