A high dielectric strength bast fiber insulation paper and preparation method thereof

Abstract

The present invention provides a high-dielectric-strength bast fiber insulation paper and a preparation method thereof. The invention comprises the following steps: cutting bast fibers into bast segments of a preset length and soaking the segments in water to obtain pretreated bast segments; adding alkali and anthraquinone to the pretreated bast segments for treatment and steaming to obtain steamed pulp; performing enzyme treatment on the steamed pulp with pectinase, and washing the pulp several times after the enzyme treatment to obtain pectin-degraded bast fiber pulp; performing cold alkali extraction treatment on the pectin-degraded bast fiber pulp, and washing the pulp several times after the cold alkali extraction treatment to obtain cold alkali-treated pulp; performing pressure-free delamination and pressure beating on the cold alkali-treated pulp to obtain pulped pulp; purifying the pulped pulp with hydrochloric acid to obtain acid-treated pulp; treating the acid-treated pulp with magnesium bicarbonate to obtain acid-acid-treated pulp; and making paper with the acid-acid-treated pulp to obtain high-dielectric-strength bast fiber insulation paper.

Description

Technical Field

[0001] The present invention belongs to the field of electrical insulation materials, and in particular relates to high dielectric strength bast fiber insulation paper and a preparation method thereof. Background Art

[0002] Insulation paper is a critical insulating medium in the insulation systems of various power equipment, including transformer oil-based insulation paper, epoxy-impregnated paper for high-voltage bushings, and polypropylene laminated paper for oil-filled cables. Its performance and reliability are crucial to the safe operation of power transmission lines. Therefore, the design and preparation of electrical-grade insulation paper is a key technical issue in ensuring the stable operation of power equipment and the power grid.

[0003] Currently, my country still relies on imports for mid- to high-end insulation paper, and there is a high demand for insulation paper with excellent dielectric properties and aging resistance. Consequently, in recent years, my country has also been committed to exploring and researching high-performance electrical-grade insulation paper. Currently, insulation paper production primarily uses plant fibers, specifically perennial coniferous wood. However, with the dwindling availability of forest resources, timber extraction and export will gradually be restricted. Therefore, finding new and suitable plant fiber materials to replace wood in the production of insulation paper is crucial.

[0004] Among various fiber types, bast fiber has a large aspect ratio and good inter-fiber bonding, resulting in strong mechanical strength and excellent aging resistance. Bast paper made from it has a wide range of applications in cultural and creative industries, food packaging, and electronic devices. Although bast fiber paper has been produced for thousands of years, it has primarily been used for food packaging, cultural relic restoration, and writing paper. However, research on bast fiber paper as insulating paper has been limited, and its dielectric properties are still unclear. Summary of the Invention

[0005] The present invention aims to provide high-dielectric-strength bast fiber insulation paper and its preparation method to overcome the problems of the prior art. The present invention explores the preparation process for bast fiber insulation paper and invents the production of bast fiber insulation paper with uniform thickness. Testing of the breakdown field strength of the self-produced bast fiber insulation paper reveals that the bast fiber insulation paper produced in the present invention exhibits a high breakdown field strength, far exceeding the standard for transformer insulation paper.

[0006] The present invention is achieved through the following technical solutions:

[0007] A method for preparing high dielectric strength bast fiber insulation paper comprises the following steps:

[0008] 1) cutting bast fibers into bast segments of a preset length and soaking them in water to obtain pretreated bast segments;

[0009] 2) adding alkali and anthraquinone to the pretreated bast segment, treating the segment and steaming the segment to obtain a steamed pulp;

[0010] 3) treating the cooked pulp with pectinase, and washing the pulp several times after the enzymatic treatment to obtain a bast fiber pulp after degrading pectin;

[0011] 4) performing cold alkali extraction on the bast fiber pulp after the pectin degradation, and washing it several times after the cold alkali extraction to obtain a cold alkali treated pulp;

[0012] 5) performing pressure-free decomposition and pressure beating on the slurry after the cold alkali treatment to obtain a beating slurry;

[0013] 6) purifying the beating slurry with hydrochloric acid to obtain acid-treated slurry;

[0014] 7) treating the acid-treated slurry with magnesium bicarbonate to obtain acid salt-treated slurry;

[0015] 8) The pulp treated with acid salt is used for papermaking to obtain high dielectric strength bast fiber insulation paper.

[0016] Furthermore, in step 1), the bast fibers are cut into 10-60 mm bast segments, and soaked in tap water with a liquid ratio of 1:10-1:50 and 50 g of absolute dry pulp for 1-2 hours, and the soaking is repeated twice to obtain pretreated bast segments.

[0017] Furthermore, in step 2), for every 50 grams of bast segment of absolute dry pulp mass, pure water is added at a liquid ratio of 1:5 to 1:50, and then sodium hydroxide is added at 5 to 30 g / L, and anthraquinone is added at 0.05 to 1 wt% of the absolute dry pulp mass. The cooking temperature is 110 to 160° C. and the cooking is kept warm for 1 to 4 hours.

[0018] Furthermore, in step 3), the cooking liquor is treated with pectinase in an amount of 5 to 50 wt% of the absolute dry pulp mass, and after the enzyme treatment reaction is completed, the cooking liquor is washed five times with purified water at room temperature.

[0019] Furthermore, in step 4), a sodium hydroxide solution with a concentration of 5-30 wt% of the absolute dry pulp mass is used for cold alkali treatment, with a liquid ratio of 1:10 to 1:30. After the cold alkali treatment, the pulp is washed twice with hot water at 50 to 70°C and then washed four times with pure water at room temperature.

[0020] Furthermore, in step 5), the pulp after cold alkali treatment is first deflaked by a deflaker for 3000-8000 revolutions, and then the pulp is placed in a slurry tank of a Wally beater, and the pulp concentration is adjusted to 1g / L. First, it is deflaked in the Wally beater without adding pressure to make the pulp evenly dispersed, and then a weight of 2000-4000 grams is added to apply pulping pressure for pulping. After the pulping is completed, the bast fiber is collected with a filter bag to obtain a pulped pulp.

[0021] Furthermore, in step 6), 2 to 10 wt% of the absolute dry mass of the pulped slurry is weighed and added to a sealed bag with hydrochloric acid, and the slurry concentration is adjusted to 2 to 8%. The slurry is fully kneaded to mix the slurry and the hydrochloric acid evenly and react for 1 to 2 hours. After the reaction is completed, the fibers are collected with a filter bag and the water is squeezed out. Subsequently, the slurry concentration is adjusted to 2 to 8 wt% with 60°C hot water and stirred for washing. Then, the slurry concentration is adjusted to 2 to 8 wt% with room temperature pure water and stirred for washing. The room temperature washing is repeated 4 times to obtain a treated slurry.

[0022] Furthermore, in step 7), 1 to 10 wt% of the absolute dry mass of the slurry after the primary treatment is weighed and added to a sealed bag. The slurry concentration is adjusted to 2 to 8 wt%, and the slurry is fully kneaded to mix the slurry and the magnesium salt evenly and react at room temperature. After the reaction is completed, the fiber is collected with a filter bag and the water is squeezed out. The slurry concentration is adjusted to 2 to 8 wt% with room temperature pure water, stirred and washed for 10 minutes, and the washing is repeated 5 times to obtain the slurry after the secondary treatment.

[0023] Furthermore, in step 8), the paper thickness is 100 to 200 g / m 2 The bast paper has a drying temperature and air pressure of 98°C and 1.0 bar during the papermaking process. A hot pressing process of 100-160°C and 10-20 MPa is selected to hot press the above-made bast paper for 20-60 minutes to obtain high dielectric strength bast fiber insulation paper.

[0024] A high dielectric strength bast fiber insulation paper is prepared by adopting the above preparation method.

[0025] Compared with the prior art, the present invention has the following beneficial technical effects:

[0026] The present invention cuts bast fibers into bast segments of a specific length to facilitate sufficient cooking, and then soaks the prepared material in water for a certain period of time to complete the pretreatment process. A certain amount of alkali and anthraquinone are added to the pretreated bast segments for treatment and cooking. The addition of alkali accelerates the degradation and removal of lignin, hemicellulose, and pectin, and at the same time, anthraquinone can hinder the cellulose peeling reaction and thus improve the pulp yield. Pectinase is added to the pulp after cooking to degrade the pectin present in large quantities in the bast, thereby removing the negative effects of pectin on the subsequent pulping process and dielectric properties. The bast fiber pulp after the pectin is degraded is then subjected to cold alkali treatment (cold alkali extraction) to proceed. One step removes components such as lignin, pectin, and hemicellulose, and then the above-mentioned obtained slurry is pressure-free decomposition and pressure-pulping respectively. The obtained slurry contains more ash, mainly metal ions such as iron and calcium. A small amount of iron ions will also be introduced during the beating process. Therefore, the present invention uses hydrochloric acid to treat the obtained slurry to reduce the metal ion content in the slurry. The sodium ions introduced into the slurry due to alkali treatment are removed by adding magnesium bicarbonate and replacing sodium ions with magnesium ions, while neutralizing hydrogen ions. Based on the above operation, the paper-coated bast insulation paper has a higher dielectric strength, which provides new possibilities for the research and development of electrical insulation paper. In addition, the price of bast fiber is low, which reduces the production cost of insulating paper, and using annual bast fiber as raw material instead of perennial coniferous wood raw material helps the country save wood, reduce production costs, and promote low-carbon environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. The following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0028] Figure 1 Surface SEM images of bast fiber insulation paper prepared in Example 3, where (a) 100 μm scale, (b) 50 μm scale, (c) 14.3 μm scale, and (d) 3.33 μm scale;

[0029] Figure 2 Graph of the real and imaginary parts of the dielectric constant of bast fiber insulation paper in Example 3;

[0030] Figure 3 Weibull distribution diagram of AC and DC breakdown field strength of bast fiber insulation paper in Example 3. DETAILED DESCRIPTION

[0031] The present invention is described in detail below:

[0032] The present invention provides a method for preparing high dielectric strength bast fiber insulation paper, comprising the following steps:

[0033] Step 1: Cut the bast fibers into 10-60 mm bast segments and soak them in tap water with a liquid ratio of 1:10-1:50 for 1-2 hours using 50 g of absolute dry pulp (absolutely dry). Repeat the above pretreatment process twice.

[0034] Step 2: Place 50 grams of bast segments (absolute dry weight) in a single cooking pot. Add purified water at a liquid ratio of 1:5 to 1:50, then add 5 to 30 grams / liter of sodium hydroxide (0.05 to 1 weight percent anthraquinone, based on the absolute dry weight). Cook at a temperature of 110 to 160°C for 1 to 4 hours.

[0035] Step 3: Pectin contained in bast fibers has a negative effect on the pulping process and paper quality. Therefore, the present invention uses 5-50 wt% pectinase on an absolute dry weight basis to enzymatically treat the cooking liquor. After the enzymatic treatment reaction is completed, the cooking liquor is washed five times with room temperature purified water.

[0036] Step 4: Treat with 5-30 wt% sodium hydroxide solution at a ratio of 1:10 to 1:30. After the cold alkali treatment, wash twice with 50-70°C hot water and then four times with room temperature purified water.

[0037] Step 5: First, deflagrate the slurry using a deflaker at 3,000-8,000 revolutions. Then, place the slurry in the trough of a Wally beater and adjust the slurry concentration to 1g / L. Initially, deflagrate the slurry in the Wally beater without applying pressure to ensure uniform dispersion. Then, add a weight of 2,000-4,000 grams to apply beating pressure and continue beating. After beating, collect the bast fibers in a filter bag for later use.

[0038] Step 6: Weigh 2-10 wt% of the absolute dry weight of the above slurry with hydrochloric acid and add it to a sealed bag. Adjust the slurry concentration to 2-8 wt%. Knead thoroughly to mix the slurry and hydrochloric acid evenly and react for 1-2 hours. After the reaction is complete, collect the fibers in a filter bag and squeeze out the water. Then, adjust the slurry concentration to 2-8 wt% with 60°C hot water and stir and wash. Then, adjust the slurry concentration to 2-8 wt% with room temperature purified water and stir and wash. Repeat the room temperature washing four times before bagging for later use.

[0039] Step 7: Weigh 1-10 wt% of the above slurry's absolute dry weight of magnesium bicarbonate and add it to a sealed bag. Adjust the slurry concentration to 2-8 wt%. Knead thoroughly to mix the slurry and magnesium salt evenly and react at room temperature. After the reaction is complete, collect the fibers in a filter bag and squeeze out the water. Adjust the slurry concentration to 2-8 wt% with room temperature purified water, stir and wash for 10 minutes, repeat the washing process 5 times, and finally bag for later use.

[0040] Step 8: The weight of the paper is 100-200g / m 2 For bast paper, the drying temperature and air pressure during papermaking are 98°C and 1.0 bar.

[0041] Step 9: Using a flat-plate hot press, hot-press the bast paper for 20 to 60 minutes at 100 to 160° C. and 10 to 20 MPa, to obtain the bast insulation paper prepared in the present invention.

[0042] The bast fibers of the present invention include but are not limited to bark fibers such as sandalwood bark, mulberry bark, goose bark, three-leaf bark, and cotton stalk bark; and hemp fibers such as kenaf, flax, green hemp, jute, and hemp.

[0043] The bast fiber insulation paper prepared by the present invention is obtained through the above steps. The negative impact of pectin on the beating process and dielectric properties is reduced by an enzyme treatment process. Through specific chemical reaction processes such as alkali treatment, acid treatment, and acid salt treatment, the amount of chemical reagents, reaction time, and treatment temperature are strictly controlled to reduce the content of components such as lignin, hemicellulose, and ash in the slurry, so that the paper-coated bast insulation paper has a higher dielectric strength, providing new possibilities for the research and development of electrical insulation paper. The pulping rate of bast fiber is higher, which greatly improves the utilization rate of raw materials compared to wood pulp, and the price of bast fiber is low, which reduces the production cost of insulation paper. The process of the present invention uses bast fiber, which is abundant in my country's resources, as raw material instead of perennial coniferous wood, which helps the country save wood and reduce production costs.

[0044] The following examples describe the embodiments of the present invention in detail. These examples are preferred embodiments of the present invention and are not intended to limit the scope of the present invention. In the following examples, the methods and experimental equipment used are conventional methods and instruments unless otherwise specified. In the following examples, several representative bast fibers from the above bast fibers are used for detailed description.

[0045] Example 1

[0046] This embodiment 1 provides a method for preparing high dielectric strength sandalwood fiber insulation paper, comprising the following steps:

[0047] Step 1: Cut the sandalwood bark into 10mm segments and soak them in tap water with a ratio of 50g absolute dry pulp (absolutely dry) and a liquid ratio of 1:10 for 2 hours. Repeat the above pretreatment process twice.

[0048] Step 2: Place 50 grams of sandalwood bark segments (absolute dry mass) in a single cooking pot. Add purified water at a liquid ratio of 1:5, followed by 5 grams / liter of sodium hydroxide and 0.05 weight percent anthraquinone (absolute dry mass). Cook at 110°C for 4 hours.

[0049] Step 3: The pectin contained in the sandalwood bark fiber has a negative effect on the pulping process and the paper quality. Therefore, the present invention uses 5 wt% pectinase on the absolute dry weight to treat the cooking liquid. After the enzyme treatment reaction is completed, it is washed with room temperature purified water five times.

[0050] Step 4: Treat with 5 wt% sodium hydroxide solution at a ratio of 1:10. After the cold alkali treatment, wash twice with 50°C hot water and then four times with room temperature purified water.

[0051] Step 5: First, deflagrate the slurry using a deflaker at 3,000 revolutions. Then, place the slurry in the slurry tank of a Wally beater and adjust the slurry concentration to 1g / L. Initially, deflagrate the slurry in the Wally beater without applying pressure to ensure uniform dispersion. Then, add a 2,000-gram weight to apply beating pressure and continue beating. After beating, collect the sandalwood bark fibers in a filter bag for later use.

[0052] Step 6: Weigh 2% hydrochloric acid (2% by weight of the absolute dry weight) of the slurry and add it to a sealed bag. Adjust the slurry concentration to 2% by weight. Knead thoroughly to ensure the slurry and hydrochloric acid mix evenly and react for 2 hours. After the reaction is complete, collect the fibers in a filter bag and squeeze out the water. Then, adjust the slurry concentration to 2% by weight with 60°C hot water and stir and wash. Then, adjust the slurry concentration to 2% by weight with room temperature purified water and stir and wash. Repeat the room temperature washing process four times before bagging.

[0053] Step 7: Weigh 1 wt% of the above slurry's absolute dry weight of magnesium bicarbonate and add it to a sealed bag. Adjust the slurry concentration to 2 wt%. Knead thoroughly to mix the slurry and magnesium salt evenly and react at room temperature. After the reaction is complete, collect the fibers in a filter bag and squeeze out the water. Adjust the slurry concentration to 2 wt% with room temperature purified water and stir and wash for 10 minutes. Repeat the washing process 5 times before bagging.

[0054] Step 8: Copy the weight to 100g / m 2 The drying temperature and air pressure during the papermaking process of sandalwood paper are 98℃ and 1.0bar.

[0055] Step 9: Using a flat-plate hot press, select a hot pressing process of 100° C. and 20 MPa to hot press the above-copied sandalwood paper for 60 minutes, and finally obtain the sandalwood insulation paper prepared by the present invention.

[0056] Performance testing: The sandalwood fiber insulation paper prepared in Example 1 was placed in a 105°C oven for 48 hours to remove moisture. The paper was then vacuum-impregnated in insulating mineral oil for 24 hours to produce an oil-impregnated paper sample. The AC and DC breakdown field strengths of the oil-impregnated paper were tested. The DC breakdown field strength of the oil-impregnated paper was 245.26 kV / mm, and the AC breakdown field strength was 98.43 kV / mm.

[0057] Example 2

[0058] This embodiment 2 provides a method for preparing high dielectric strength kenaf fiber insulation paper, comprising the following steps:

[0059] Step 1: Cut the kenaf raw material into 30mm kenaf segments and soak them in tap water with a ratio of 50g absolute dry pulp (absolutely dry) and 1:20 liquid ratio for 1.5 hours. Repeat the above pretreatment process twice.

[0060] Step 2: Place 50 grams of kenaf segments (absolute dry weight) in a single cooking pot. Add purified water at a liquid ratio of 1:15, followed by 10 grams / liter of sodium hydroxide and 0.2 weight percent of anthraquinone (absolute dry weight). Cook at 120°C for 3 hours.

[0061] Step 3: Since pectin contained in kenaf fiber has a negative effect on the pulping process and paper quality, the present invention uses 15 wt% pectinase to treat the cooking liquor. After the enzyme treatment reaction, the cooking liquor is washed five times with room temperature purified water.

[0062] Step 4: Treat with 15 wt% sodium hydroxide solution at a ratio of 1:15. After the cold alkali treatment, wash twice with 55°C hot water and then four times with room temperature purified water.

[0063] Step 5: First, deflagrate the slurry using a deflaker at 5,000 revolutions. Then, place the slurry in the trough of a Wally beater and adjust the slurry concentration to 1g / L. Initially, deflagrate the slurry in the Wally beater without applying pressure to ensure uniform dispersion. Then, add a 3,000-gram weight to apply beating pressure and continue beating. After beating, collect the kenaf fibers in a filter bag for later use.

[0064] Step 6: Weigh 5% hydrochloric acid (5% by weight of the absolute dry weight) of the slurry and add it to a sealed bag. Adjust the slurry concentration to 4% by weight. Knead thoroughly to ensure the slurry and hydrochloric acid are evenly mixed and react for 1.5 hours. After the reaction is complete, collect the fibers in a filter bag and squeeze out the water. Then, adjust the slurry concentration to 4% by weight with 60°C hot water and stir and wash. Then, adjust the slurry concentration to 4% by weight with room temperature purified water and stir and wash. Repeat the room temperature washing process four times before bagging.

[0065] Step 7: Weigh 4 wt% of the above slurry's absolute dry weight of magnesium bicarbonate and add it to a sealed bag. Adjust the slurry concentration to 4 wt%. Knead thoroughly to mix the slurry and magnesium salt evenly and react at room temperature. After the reaction is complete, collect the fibers in a filter bag and squeeze out the water. Adjust the slurry concentration to 4 wt% with room temperature purified water and stir and wash for 10 minutes. Repeat the washing process 5 times before bagging.

[0066] Step 8: The weight of the paper is 120g / m 2The drying temperature and pressure during the papermaking process of kenaf paper are 98℃ and 1.0 bar.

[0067] Step 9: Using a flat-plate hot press, the kenaf paper is hot-pressed for 40 minutes at 120° C. and 17 MPa to obtain the kenaf insulating paper prepared by the present invention.

[0068] Performance testing: The kenaf fiber insulation paper prepared in Example 2 was placed in a 105°C oven for 48 hours to remove moisture. The paper was then vacuum-impregnated in insulating mineral oil for 24 hours to produce an oil-impregnated paper sample. The AC and DC breakdown field strengths of the oil-impregnated paper were tested. The DC breakdown field strength of the oil-impregnated paper was 250.35 kV / mm, and the AC breakdown field strength was 99.68 kV / mm.

[0069] Example 3

[0070] This embodiment 3 provides a method for preparing high dielectric strength mulberry fiber insulation paper, comprising the following steps:

[0071] Step 1: Cut the mulberry bark into 40mm segments and soak them in tap water with a ratio of 1:40 for 2 hours using 50g of absolute dry pulp. Repeat the above pretreatment process twice.

[0072] Step 2: Place 50 grams of mulberry bark segments (absolute dry mass) in a single cooking pot. Add purified water at a liquid ratio of 1:35, then add 20 grams / liter of sodium hydroxide (0.5 wt% anthraquinone based on the absolute dry mass). Cook at 140°C for 2 hours.

[0073] Step 3: The pectin contained in the mulberry fiber has a negative effect on the pulping process and the paper quality. Therefore, the present invention uses 35 wt% of pectinase on the absolute dry weight to treat the cooking liquid. After the enzyme treatment reaction is completed, it is washed with room temperature purified water five times.

[0074] Step 4: Treat with 20 wt% sodium hydroxide solution at a ratio of 1:20. After the cold alkali treatment, wash twice with 65°C hot water and then four times with room temperature purified water.

[0075] Step 5: First, deflagrate the slurry using a deflaker at 6,500 revolutions per minute. Then, place the slurry in the trough of a Wally beater and adjust the slurry concentration to 1 g / L. Initially, deflake the slurry in the Wally beater without applying pressure to ensure uniform dispersion. Then, add a 3,500-gram weight to apply beating pressure and continue beating. After beating, collect the bast fibers in a filter bag for later use.

[0076] Step 6: Weigh 7% hydrochloric acid (7% by weight of the absolute dry weight of the slurry) into a sealed bag and adjust the slurry concentration to 6% by weight. Knead thoroughly to ensure the slurry and hydrochloric acid are evenly mixed and react for 1-2 hours. After the reaction is complete, collect the fibers in a filter bag and squeeze out the water. Then, adjust the slurry concentration to 6% by weight with 60°C hot water and stir and wash. Then, adjust the slurry concentration to 6% by weight with room temperature purified water and stir and wash. Repeat the room temperature washing process four times before bagging.

[0077] Step 7: Weigh 8 wt% of the above slurry's absolute dry weight of magnesium bicarbonate and add it to a sealed bag. Adjust the slurry concentration to 6 wt%. Knead thoroughly to mix the slurry and magnesium salt evenly and react at room temperature. After the reaction is complete, collect the fibers in a filter bag and squeeze out the water. Adjust the slurry concentration to 6 wt% with room temperature purified water and stir and wash for 10 minutes. Repeat the washing process 5 times before bagging for later use.

[0078] Step 8: The weight of the paper is 150g / m 2 The drying temperature and air pressure during the papermaking process are 98°C and 1.0 bar.

[0079] Step 9: Using a flat-plate hot press, select a hot pressing process of 140° C. and 13 MPa to hot press the mulberry paper for 30 minutes, and finally obtain the mulberry insulation paper prepared by the present invention.

[0080] Performance testing: The mulberry fiber insulation paper prepared in Example 3 was placed in a 105°C oven for 48 hours to remove moisture. The paper was then vacuum-impregnated in insulating mineral oil for 24 hours to produce an oil-impregnated paper sample. The AC and DC breakdown field strengths of the oil-impregnated paper were tested. The DC breakdown field strength of the oil-impregnated paper was 254.92 kV / mm, and the AC breakdown field strength was 101.94 kV / mm.

[0081] Depend on Figure 1 It can be seen that the mulberry fiber insulation paper in this embodiment has a smaller width and a higher degree of fibrilization, which enables better bonding between the fibers.

[0082] Depend on Figure 2 It can be seen that the relative dielectric constant of the mulberry fiber oil-impregnated paper in this embodiment at room temperature is between 3.0 and 3.5, which is at a normal level; and the dielectric loss is relatively low, and the dielectric loss at an operating frequency of 50 Hz is 2×10 -2 Around, at a lower level.

[0083] Depend on Figure 3 It can be seen that the mulberry fiber oil-impregnated paper of this embodiment has an AC / DC breakdown field strength of 254.92 kV / mm at room temperature and an AC breakdown field strength of 101.94 kV / mm, which shows a relatively high breakdown field strength.

[0084] Example 4

[0085] This embodiment 4 provides a method for preparing high dielectric strength mulberry fiber insulation paper, comprising the following steps:

[0086] Step 1: Cut the bark raw material into 60mm bark segments and soak them in tap water with a ratio of 50g absolute dry pulp (absolutely dry) and a liquid ratio of 1:50 for 1 hour. Repeat the above pretreatment process twice.

[0087] Step 2: Place 50 grams of the absolute dry mass of the bark segments in a single cooking pot. Add purified water at a liquid ratio of 1:50, then add 30 grams / liter of sodium hydroxide (1 wt% of the absolute dry mass) and anthraquinone. Cook at 160°C for 1 hour.

[0088] Step 3: The pectin contained in the bark fiber has a negative effect on the pulping process and the paper quality. Therefore, the present invention uses 50 wt% of pectinase on the absolute dry weight to treat the cooking liquid. After the enzyme treatment reaction is completed, it is washed with room temperature purified water five times.

[0089] Step 4: Treat with 30 wt% sodium hydroxide solution at a ratio of 1:30. After the cold alkali treatment, wash twice with 70°C hot water and then four times with room temperature purified water.

[0090] Step 5: First, deflagrate the slurry using a deflaker at 8,000 revolutions per minute. Then, place the slurry in the slurry tank of a Wally beater and adjust the slurry concentration to 1 g / L. Initially, deflagrate the slurry in the Wally beater without applying pressure to ensure uniform dispersion. Then, add a 4,000-gram weight to apply beating pressure and continue beating. After beating, collect the bark fibers in a filter bag for later use.

[0091] Step 6: Weigh 10% of the absolute dry weight of the slurry in hydrochloric acid and add it to a sealed bag. Adjust the slurry concentration to 8% by weight. Knead thoroughly to mix the slurry and hydrochloric acid, and allow to react for 2 hours. After the reaction is complete, collect the fibers in a filter bag and squeeze out the water. Then, adjust the slurry concentration to 8% by weight with 60°C hot water and stir and wash. Then, adjust the slurry concentration to 8% by weight with room temperature purified water and stir and wash. Repeat the room temperature washing process four times before bagging.

[0092] Step 7: Weigh 10 wt% of the absolute dry weight of the above slurry and add magnesium bicarbonate to a sealed bag. Adjust the slurry concentration to 8%. Knead thoroughly to mix the slurry and magnesium salt evenly and react at room temperature. After the reaction is complete, collect the fibers with a filter bag and squeeze out the water. Adjust the slurry concentration to 8 wt% with room temperature purified water and stir and wash for 10 minutes. Repeat the washing process 5 times before bagging.

[0093] Step 8: Copy the weight to 200g / m 2 The drying temperature and air pressure during the papermaking process of the mulberry paper are 98°C and 1.0 bar.

[0094] Step 9: Using a flat-plate hot press, select a hot pressing process of 160° C. and 10 MPa to hot press the above-written mulberry paper for 20 minutes, and finally obtain the mulberry insulation paper prepared by the present invention.

[0095] Performance testing: The mulberry fiber insulation paper prepared in Example 4 was placed in a 105°C oven for 48 hours to remove moisture. The paper was then vacuum-impregnated in insulating mineral oil for 24 hours to produce an oil-impregnated paper sample. The AC and DC breakdown field strengths of the oil-impregnated paper were tested. The DC breakdown field strength of the oil-impregnated paper was 240.58 kV / mm, and the AC breakdown field strength was 92.36 kV / mm.

[0096] Although the present invention has been disclosed above in terms of preferred embodiments, it is not intended to limit the present invention. Anyone familiar with this technology can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the definition of the claims.

Claims

1. A method for preparing high dielectric strength bast fiber insulation paper, characterized in that: The following steps are involved: 1) cutting bast fibers into bast segments of a preset length and soaking them in water to obtain pretreated bast segments; 2) adding alkali and anthraquinone to the pretreated bast segment and steaming the bast segment to obtain a steamed pulp; 3) treating the cooked pulp with pectinase, and washing it several times after the enzymatic treatment to obtain a bast fiber pulp with degraded pectin; 4) performing cold alkali extraction on the bast fiber pulp after the pectin degradation, and washing it several times after the cold alkali extraction to obtain a cold alkali treated pulp; 5) performing pressure-free decompression and pressure beating on the slurry after the cold alkali treatment to obtain a beaten slurry; 6) Purifying the beaten pulp with hydrochloric acid to obtain acid-treated pulp; 7) treating the acid-treated slurry with magnesium bicarbonate to obtain acid salt-treated slurry; 8) Use the acid-treated pulp to make paper to obtain high dielectric strength bast fiber insulation paper.

2. The method for preparing high dielectric strength bast fiber insulation paper according to claim 1, wherein: In step 1), the bast fibers are cut into 10-60 mm bast segments, and soaked in tap water with a liquid ratio of 1:10-1:50 and 50 g of absolute dry pulp for 1-2 hours, and the soaking is repeated twice to obtain pretreated bast segments.

3. The method for preparing high dielectric strength bast fiber insulation paper according to claim 1, wherein: In step 2), for every 50 grams of bast segment of absolute dry pulp, pure water is added at a liquid ratio of 1:5 to 1:50, then sodium hydroxide is added at a rate of 5 to 30 g / L, and anthraquinone is added at a rate of 0.05 to 1 wt% of the absolute dry pulp mass. The cooking temperature is 110 to 160 °C, and the cooking is carried out at this temperature for 1 to 4 hours.

4. The method for preparing high dielectric strength bast fiber insulation paper according to claim 1, characterized in that: In step 3), the cooking liquor is treated with pectinase at a concentration of 5 to 50 wt% by weight of the absolute dry pulp, and the cooked liquor is washed five times with purified water at room temperature after the enzyme treatment reaction is completed.

5. The method for preparing high dielectric strength bast fiber insulation paper according to claim 1, wherein: In step 4), cold alkali treatment is performed using a sodium hydroxide solution with a concentration of 5-30 wt% of the absolute dry pulp mass, with a liquid ratio of 1:10-1:

30. After the cold alkali treatment, the pulp is washed twice with hot water at 50-70°C and then washed four times with pure water at room temperature.

6. The method for preparing high dielectric strength bast fiber insulation paper according to claim 1, wherein: In step 5), the pulp treated with cold alkali is first deflaked by a deflaker for 3000-8000 revolutions, and then the pulp is placed in a slurry tank of a Wally beater, and the pulp concentration is adjusted to 1 g / L. First, the pulp is deflaked in the Wally beater without applying pressure to make the pulp evenly dispersed, and then a weight of 2000-4000 grams is added to apply beating pressure for beating. After the beating is completed, the bast fiber is collected with a filter bag to obtain a beating pulp.

7. The method for preparing high dielectric strength bast fiber insulation paper according to claim 1, characterized in that: In step 6), 2-10 wt% of the absolute dry mass of the pulped slurry is weighed and added to a sealed bag, and the slurry concentration is adjusted to 2-8%. The slurry is fully kneaded to mix the slurry and the hydrochloric acid evenly and react for 1-2 hours. After the reaction is completed, the fibers are collected with a filter bag and the water is squeezed out. Subsequently, the slurry concentration is adjusted to 2-8 wt% with 60°C hot water and stirred for washing. Then, the slurry concentration is adjusted to 2-8 wt% with room temperature pure water and stirred for washing. The room temperature washing is repeated 4 times to obtain a treated slurry.

8. The method for preparing high dielectric strength bast fiber insulation paper according to claim 7, characterized in that: In step 7), 1-10 wt% of the absolute dry mass of the slurry after the primary treatment is weighed and added to a sealed bag. The slurry concentration is adjusted to 2-8 wt%, and the slurry is fully kneaded to mix the slurry and the magnesium salt evenly and react at room temperature. After the reaction is completed, the fibers are collected with a filter bag and the water is squeezed out. The slurry concentration is adjusted to 2-8 wt% with pure water at room temperature, and stirred and washed for 10 minutes. The washing is repeated 5 times to obtain the slurry after the secondary treatment.

9. The method for preparing high dielectric strength bast fiber insulation paper according to claim 1, wherein: In step 8), the paper weight is 100~200 g / m 2 The bast paper is prepared, and the drying temperature and air pressure during the papermaking process are 98°C and 1.0 bar. A hot pressing process of 100~160°C and 10~20 MPa is selected to hot press the above-made bast paper for 20~60 minutes to obtain high dielectric strength bast fiber insulation paper.

10. A high dielectric strength bast fiber insulation paper, prepared by the preparation method according to any one of claims 1 to 9.

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