Method for improving breakdown field strength and mechanical property of insulation paper by refilling hemicellulose and insulation paper

Abstract

The invention provides a method for improving breakdown field strength and mechanical performance of insulation paper by refilling hemicellulose and the insulation paper. The method comprises the following steps: pulping a plant fiber pulp board to obtain plant fiber pulp; preparing hemicellulose into a hemicellulose solution; adding the hemicellulose solution into the diluted plant fiber pulp, defibering and standing to obtain mixed pulp; and carrying out papermaking on the mixed slurry, and then carrying out hot-pressing smoothing treatment to obtain the insulation paper. The characteristics of the insulation paper are regulated and controlled by regulating and controlling the types and content of hemicelluloses in the insulation paper pulp, and reference is provided for preparation of the insulation paper pulp and the insulation paper.

Description

Technical Field

[0001] The invention belongs to the field of electrical insulation materials, and particularly relates to a method for improving the breakdown field strength and mechanical properties of insulation paper by backfilling hemicellulose, and the insulation paper. Background Art

[0002] Insulation paper is the primary insulating material for UHV transformers and bushings. It is used extensively in interturn insulation, interlayer insulation, oil gap stays, and corner rings. Therefore, the properties of insulation paper are a key factor affecting the performance of the main insulation system of power equipment, further impacting the safety of UHV equipment and even power transmission and transformation. Researching the properties of insulation paper and improving its performance are key technical issues.

[0003] Ultra-high voltage (UHV) equipment operates under complex conditions, particularly in UHVDC transmission projects. AC, DC, harmonic electrical stresses, and mechanical vibrations are present during operation. Therefore, the breakdown field strength and mechanical properties of oil-impregnated and rubber-impregnated paper, the primary insulation materials, are crucial. Currently, all insulation paper used in UHV equipment is made from unbleached softwood sulfate pulp. The main components of softwood fiber are cellulose, lignin, and hemicellulose. During the pulping process, most of the hemicellulose in the pulp material dissolves in the cooking liquor. The hemicellulose retained or adsorbed within the fibers significantly influences the properties of the cellulose fibers and the performance of the paper. In plant materials, hemicellulose often chemically bonds with lignin to form a lignin-carbohydrate complex (LCC). Therefore, during the pulping process, hemicellulose is lost in large quantities to the cooking liquor as delignification is removed. Quantitative separation and retention of hemicellulose is therefore challenging. However, it is readily possible to incorporate hemicellulose extracted from plant fibers into the pulp as a papermaking additive to improve the papermaking process and paper properties. Currently, the effect of hemicellulose as a papermaking additive backfilled into insulating paper pulp on the characteristics and electrical properties of insulating paper is unknown, especially the effect of hemicellulose on the composite properties, physical and chemical properties, interface properties and other properties of composite oil paper. Summary of the Invention

[0004] The present invention aims to provide a method and insulating paper for improving the breakdown field strength and mechanical properties by backfilling hemicellulose, thereby overcoming the problems of the prior art. By manipulating the type and content of hemicellulose in the insulating paper pulp, the present invention modulates the properties of the insulating paper, providing a reference for the preparation of insulating pulp and insulating paper.

[0005] The present invention is achieved through the following technical solutions:

[0006] A method for improving the breakdown field strength and mechanical properties of insulating paper by backfilling hemicellulose, comprising the following steps:

[0007] Step 1: taking a plant fiber pulp board and beating it to obtain a plant fiber slurry;

[0008] Step 2: preparing hemicellulose into a hemicellulose solution;

[0009] Step 3: adding the hemicellulose solution to the diluted plant fiber slurry, dispersing and allowing to stand to obtain a mixed slurry; the absolute dry mass of the plant fiber slurry accounts for 87-92 wt% of the absolute dry mass of the mixed slurry, and the absolute dry mass of the hemicellulose accounts for 8-13 wt% of the absolute dry mass of the mixed slurry;

[0010] Step 4: The mixed slurry is papered and then subjected to hot pressing and smoothing treatment to obtain insulating paper.

[0011] Furthermore, step 1 specifically includes: soaking the plant fiber pulp board, diluting and beating the pulp to obtain plant fiber pulp.

[0012] Furthermore, the plant fiber pulp board is soaked for 12 hours, diluted to a pulp concentration of 10% by mass, and then beaten to a beating degree of 50°SR.

[0013] Furthermore, step 2 specifically includes: preparing hemicellulose into a hemicellulose solution with a mass concentration of 20 wt%.

[0014] Furthermore, the plant fiber pulp board is made of softwood pulp, hardwood pulp, grass pulp, straw pulp or bast pulp.

[0015] The hemicellulose is a mixture of one or more of xylose monosaccharide, mannose monosaccharide, polyxylose and polymannose.

[0016] Furthermore, step 3 specifically comprises: diluting the plant fiber slurry to a pulp concentration of 4%, deflaking for 15,000 revolutions, and then adding the hemicellulose solution to the diluted plant fiber slurry.

[0017] Furthermore, in step 3, the mixture is allowed to stand for 30 minutes after being dissipated at 10,000 revolutions.

[0018] Furthermore, step 4 specifically comprises: papermaking the mixed slurry to obtain a paper sample, vacuum drying the paper sample to obtain an insulating paper sample, and hot pressing and smoothing the insulating paper sample to obtain insulating paper.

[0019] Furthermore, the paper sample has a basis weight of 120 g / m 2 The temperature of the vacuum drying is 98°C and the vacuum degree is 1 bar, and the temperature of the hot pressing smoothing treatment is 105°C and the pressure is 15 MPa.

[0020] An insulating paper is prepared by adopting the above method.

[0021] Compared with the prior art, the present invention has the following beneficial technical effects:

[0022] The present invention selects an unbleached coniferous wood pulp as the base pulp, selects xylose monosaccharide, mannose monosaccharide, polyxylose, and polymannose, and after beating, mixes and returns the base pulp according to the single component and different types of hemicellulose, and finally obtains the insulating paper through papermaking, drying, and hot pressing. Due to the different molecular structures of different hemicelluloses, they have different effects on the inter-fiber bonding ability of the insulating paper, and also affect the composite properties between the insulating paper and the insulating oil in the transformer oil-paper insulation, ultimately improving the performance of the oil-paper insulation. The preparation of insulating pulp is a key technical link in the preparation of insulating paper. The present invention regulates the properties of the insulating paper by regulating the type and content of hemicellulose in the insulating pulp, providing a reference for the preparation of insulating pulp and insulating paper. DETAILED DESCRIPTION

[0023] The present invention is described in detail below:

[0024] Generally speaking, there are two main types of macromolecular hemicelluloses in plant fibers: polyxylose, whose main chain monosaccharide is mostly xylose, and polymannose, whose main chain monosaccharide is mostly mannose. Common plant substrates such as hardwood and bamboo contain more polyxylose hemicellulose, while coniferous wood contains a larger proportion of polymannose hemicellulose. Mannose monosaccharide has one more hydroxyl group than xylose monosaccharide. Currently, the effects of hemicellulose monosaccharides and polysaccharides on the performance of electrical insulation oil-paper as papermaking additives are unclear.

[0025] The present invention provides a method for improving the breakdown field strength and mechanical properties of needle insulation paper by backfilling hemicellulose as a papermaking auxiliary agent. It mainly provides a technical idea for using hemicellulose as a papermaking auxiliary agent to improve the dielectric strength, mechanical strength and aging resistance of oil paper insulation, as well as a formula for hemicellulose as a papermaking auxiliary agent.

[0026] In some embodiments, unbleached coniferous wood pulp is selected as the plant fiber pulp and is beaten using a PFI refiner to obtain a plant fiber pulp with a beating degree of 50° SR. It should be noted that the unbleached coniferous wood pulp listed here is merely an example of the pulp used in the embodiments of this application and does not constitute a limitation. In other embodiments, other plant fiber pulps such as hardwood pulp, grass pulp, straw pulp, and bast pulp may be used, and these are not listed here.

[0027] The plant fiber slurry obtained above is adjusted to a pulp concentration of 4wt%, and is deflaked by a deflaking machine for 15,000 revolutions. After that, a certain mass percentage of hemicellulose is weighed to prepare a hemicellulose solution with a concentration of 20wt%, which is poured into the diluted plant fiber slurry and deflaked for another 10,000 revolutions. The solution is then allowed to stand for 30 minutes to obtain a mixed slurry. The hemicellulose is a mixture of one or more of xylose monosaccharide, mannose monosaccharide, polyxylose, and polymannose; the absolute dry mass of the plant fiber slurry accounts for 87-92wt% of the absolute dry mass of the mixed slurry, and the absolute dry mass of the hemicellulose accounts for 8-13wt% of the absolute dry mass of the mixed slurry.

[0028] In some embodiments, the mixed slurry obtained above was paper-coated into 120 g / m 2 The paper sample is vacuum dried to obtain an insulating paper sample, and the vacuum drying temperature is 98° C. and the vacuum degree is 1 bar.

[0029] In some embodiments, the prepared insulating paper sample is subjected to hot pressing and smoothing treatment using a flat plate vulcanizer at 105° C. and 15 MPa to obtain insulating paper.

[0030] Next, the insulating paper provided in the embodiments of the present application is introduced with examples in combination with the specific embodiment formula shown in Table 1.

[0031] Table 1 Example formulation

[0032]

[0033] By backfilling different types of hemicellulose into insulating paper pulp in different proportions and ratios, and comparing the tested mechanical properties of the insulating paper with the breakdown field strength of the oil-paper insulation, the optimal backfill formula was obtained.

[0034] 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.

[0035] Example 1

[0036] First, soak the commercial softwood pulp board for 12 hours, then use a PFI refiner to beat the fiber to a beating degree of 50°SR at a pulp consistency of 10%, then adjust the pulp consistency to 4%, and use a fiber defiberizer to defiber at 15,000 revolutions to fully disperse the fiber in the deionized water system.

[0037] Afterwards, mannose monosaccharide with a purity higher than 99.5% was weighed to prepare a mannose monosaccharide solution with a mass concentration of 20wt%, and the mannose monosaccharide solution was placed in the decomposed plant fiber pulp and mixed, and the pulp was decomposed again for 10,000 turns to fully mix the mannose monosaccharide and the pulp, and the mixture was allowed to stand for 30 minutes to obtain a mixed pulp, in which the absolute dry mass of the plant fiber pulp accounted for 90wt% of the absolute dry mass of the mixed pulp, and the absolute dry mass of the hemicellulose accounted for 10wt% of the absolute dry mass of the mixed pulp.

[0038] 120g / m2 paper was made by using Cathay paper machine under deionized water system. 2 The paper sample was vacuum dried at 98°C and 1 bar to obtain the insulating paper sample. Finally, the insulating paper was calendered at 105°C and 15MPa to obtain the final insulating paper.

[0039] The insulating paper filled with hemicellulose prepared in this example was placed in a vacuum drying oven at 105° C. for 48 hours to remove moisture, and then impregnated with the impurity- and water-removed Karamay KI50X insulating oil at 60° C. in a vacuum oven for 24 hours.

[0040] Example 2

[0041] First, soak the commercial softwood pulp board for 12 hours, then use a PFI refiner to beat the fiber to a beating degree of 50°SR at a pulp consistency of 10%, then adjust the pulp consistency to 4%, and use a fiber defiberizer to defiber at 15,000 revolutions to fully disperse the fiber in the deionized water system.

[0042] Afterwards, xylose monosaccharide with a purity higher than 99.5%, mannose monosaccharide with a purity higher than 99.5%, polyxylose with a purity higher than 99.5%, and polymannose with a purity higher than 99.5% were weighed and placed in the deflated plant fiber slurry and mixed. The pulp was deflated again for 10,000 turns to fully mix the mannose monosaccharide and the pulp, and the mixture was allowed to stand for 30 minutes to obtain a mixed slurry, in which the absolute dry mass of the plant fiber slurry accounted for 91wt% of the absolute dry mass of the mixed slurry, the absolute dry mass of xylose monosaccharide accounted for 4.5wt% of the absolute dry mass of the mixed slurry, the absolute dry mass of mannose monosaccharide accounted for 1.0wt% of the absolute dry mass of the mixed slurry, the absolute dry mass of polyxylose accounted for 1.5wt% of the absolute dry mass of the mixed slurry, and the absolute dry mass of polymannose accounted for 2.0wt% of the absolute dry mass of the mixed slurry.

[0043] The mixed slurry was papered using a Cathay paper machine under deionized water to produce 120g / m 2 The paper sample was vacuum dried at 98°C and 1 bar to obtain the insulating paper sample. Finally, the insulating paper was calendered at 105°C and 15MPa to obtain the final insulating paper.

[0044] The insulating paper filled with hemicellulose prepared in this example was placed in a vacuum drying oven at 105° C. for 48 hours to remove moisture, and then impregnated with the impurity- and water-removed Karamay KI50X insulating oil at 60° C. in a vacuum oven for 24 hours.

[0045] Example 3

[0046] First, soak the commercial softwood pulp board for 12 hours, then use a PFI refiner to beat the fiber to a beating degree of 50°SR at a pulp consistency of 10%, then adjust the pulp consistency to 4%, and use a fiber defiberizer to defiber at 15,000 revolutions to fully disperse the fiber in the deionized water system.

[0047] Afterwards, hemicellulose, including xylose monosaccharide with a purity higher than 99.5%, mannose monosaccharide with a purity higher than 99.5%, polyxylose with a purity higher than 99.5%, and polymannose with a purity higher than 99.5%, was weighed to prepare a hemicellulose solution with a mass concentration of 20wt%, and the hemicellulose solution was placed in the decomposed plant fiber pulp and mixed. The pulp was decomposed again for 10,000 turns to fully mix the hemicellulose and the pulp, and the mixture was allowed to stand for 30 minutes to obtain a mixed pulp, in which the absolute dry mass of the plant fiber pulp accounted for 92wt% of the absolute dry mass of the mixed pulp, the absolute dry mass of xylose monosaccharide accounted for 1.5wt% of the absolute dry mass of the mixed pulp, the absolute dry mass of mannose monosaccharide accounted for 4.0wt% of the absolute dry mass of the mixed pulp, the absolute dry mass of polyxylose accounted for 2.0wt% of the absolute dry mass of the mixed pulp, and the absolute dry mass of polymannose accounted for 0.5wt% of the absolute dry mass of the mixed pulp.

[0048] The mixed slurry was papered using a Cathay paper machine under deionized water to produce 120g / m 2 The paper sample was vacuum dried at 98°C and 1 bar to obtain the insulating paper sample. Finally, the insulating paper was calendered at 105°C and 15MPa to obtain the final insulating paper.

[0049] The insulating paper filled with hemicellulose prepared in this example was placed in a vacuum drying oven at 105° C. for 48 hours to remove moisture, and then impregnated with the impurity- and water-removed Karamay KI50X insulating oil at 60° C. in a vacuum oven for 24 hours.

[0050] Example 4

[0051] First, soak the commercial softwood pulp board for 12 hours, then use a PFI refiner to beat the fiber to a beating degree of 50°SR at a pulp consistency of 10%, then adjust the pulp consistency to 4%, and use a fiber defiberizer to defiber at 15,000 revolutions to fully disperse the fiber in the deionized water system.

[0052] Afterwards, hemicellulose, including xylose monosaccharide with a purity higher than 99.5%, mannose monosaccharide with a purity higher than 99.5%, polyxylose with a purity higher than 99.5%, and polymannose with a purity higher than 99.5%, was weighed to prepare a hemicellulose solution with a mass concentration of 20 wt%, and the hemicellulose solution was placed in the decomposed plant fiber pulp and mixed. The pulp was decomposed again for 10,000 turns to fully mix the hemicellulose and the pulp, and the mixture was allowed to stand for 30 minutes to obtain a mixed pulp, in which the absolute dry mass of the plant fiber pulp accounted for 88.5 wt% of the absolute dry mass of the mixed pulp, the absolute dry mass of xylose monosaccharide accounted for 1.5 wt% of the absolute dry mass of the mixed pulp, the absolute dry mass of mannose monosaccharide accounted for 1.0 wt% of the absolute dry mass of the mixed pulp, the absolute dry mass of polyxylose accounted for 2.5 wt% of the absolute dry mass of the mixed pulp, and the absolute dry mass of polymannose accounted for 6.5 wt% of the absolute dry mass of the mixed pulp.

[0053] The mixed slurry was papered using a Cathay paper machine under deionized water to produce 120g / m 2 The paper sample was vacuum dried at 98°C and 1 bar to obtain the insulating paper sample. Finally, the insulating paper was calendered at 105°C and 15MPa to obtain the final insulating paper.

[0054] The insulating paper filled with hemicellulose prepared in this example was placed in a vacuum drying oven at 105° C. for 48 hours to remove moisture, and then impregnated with the impurity- and water-removed Karamay KI50X insulating oil at 60° C. in a vacuum oven for 24 hours.

[0055] Example 5

[0056] First, soak the commercial softwood pulp board for 12 hours, then use a PFI refiner to beat the fiber to a beating degree of 50°SR at a pulp consistency of 10%, then adjust the pulp consistency to 4%, and use a fiber defiberizer to defiber at 15,000 revolutions to fully disperse the fiber in the deionized water system.

[0057] Afterwards, hemicellulose, including xylose monosaccharide with a purity higher than 99.5%, mannose monosaccharide with a purity higher than 99.5%, polyxylose with a purity higher than 99.5%, and polymannose with a purity higher than 99.5%, was weighed to prepare a hemicellulose solution with a mass concentration of 20 wt%, and the hemicellulose solution was placed in the decomposed plant fiber pulp and mixed. The pulp was decomposed again for 10,000 turns to fully mix the hemicellulose and the pulp, and the mixture was allowed to stand for 30 minutes to obtain a mixed pulp, in which the absolute dry mass of the plant fiber pulp accounted for 88 wt% of the absolute dry mass of the mixed pulp, the absolute dry mass of xylose monosaccharide accounted for 4.0 wt% of the absolute dry mass of the mixed pulp, the absolute dry mass of mannose monosaccharide accounted for 4.0 wt% of the absolute dry mass of the mixed pulp, the absolute dry mass of polyxylose accounted for 1.0 wt% of the absolute dry mass of the mixed pulp, and the absolute dry mass of polymannose accounted for 3.0 wt% of the absolute dry mass of the mixed pulp.

[0058] The mixed slurry was papered using a Cathay paper machine under deionized water to produce 120g / m 2 The paper sample was vacuum dried at 98°C and 1 bar to obtain the insulating paper sample. Finally, the insulating paper was calendered at 105°C and 15MPa to obtain the final insulating paper.

[0059] The insulating paper filled with hemicellulose prepared in this example was placed in a vacuum drying oven at 105° C. for 48 hours to remove moisture, and then impregnated with the impurity- and water-removed Karamay KI50X insulating oil at 60° C. in a vacuum oven for 24 hours.

[0060] Example 6

[0061] First, soak the commercial softwood pulp board for 12 hours, then use a PFI refiner to beat the fiber to a beating degree of 50°SR at a pulp consistency of 10%, then adjust the pulp consistency to 4%, and use a fiber defiberizer to defiber at 15,000 revolutions to fully disperse the fiber in the deionized water system.

[0062] Afterwards, hemicellulose, including xylose monosaccharide with a purity higher than 99.5%, mannose monosaccharide with a purity higher than 99.5%, polyxylose with a purity higher than 99.5%, and polymannose with a purity higher than 99.5%, was weighed to prepare a hemicellulose solution with a mass concentration of 20wt%, and the hemicellulose solution was placed in the decomposed plant fiber pulp and mixed. The pulp was decomposed again for 10,000 turns to fully mix the hemicellulose and the pulp, and the mixture was allowed to stand for 30 minutes to obtain a mixed pulp, in which the absolute dry mass of the plant fiber pulp accounted for 87wt% of the absolute dry mass of the mixed pulp, the absolute dry mass of xylose monosaccharide accounted for 2.5wt% of the absolute dry mass of the mixed pulp, the absolute dry mass of mannose monosaccharide accounted for 2.5wt% of the absolute dry mass of the mixed pulp, the absolute dry mass of polyxylose accounted for 4.0wt% of the absolute dry mass of the mixed pulp, and the absolute dry mass of polymannose accounted for 4.0wt% of the absolute dry mass of the mixed pulp.

[0063] The mixed slurry was papered using a Cathay paper machine under deionized water to produce 120g / m 2 The paper sample was vacuum dried at 98°C and 1 bar to obtain the insulating paper sample. Finally, the insulating paper was calendered at 105°C and 15MPa to obtain the final insulating paper.

[0064] The insulating paper filled with hemicellulose prepared in this example was placed in a vacuum drying oven at 105° C. for 48 hours to remove moisture, and then impregnated with the impurity- and water-removed Karamay KI50X insulating oil at 60° C. in a vacuum oven for 24 hours.

[0065] Example 7

[0066] First, soak the commercial softwood pulp board for 12 hours, then use a PFI refiner to beat the fiber to a beating degree of 50°SR at a pulp consistency of 10%, then adjust the pulp consistency to 4%, and use a fiber defiberizer to defiber at 15,000 revolutions to fully disperse the fiber in the deionized water system.

[0067] Afterwards, hemicellulose, including xylose monosaccharide with a purity higher than 99.5%, mannose monosaccharide with a purity higher than 99.5%, polyxylose with a purity higher than 99.5%, and polymannose with a purity higher than 99.5%, was weighed to prepare a hemicellulose solution with a mass concentration of 20wt%, and the hemicellulose solution was placed in the decomposed plant fiber pulp and mixed, and the pulp was decomposed again for 10,000 turns to fully mix the hemicellulose and the pulp, and the mixture was allowed to stand for 30 minutes to obtain a mixed pulp, in which the absolute dry mass of the plant fiber pulp accounted for 91wt% of the absolute dry mass of the mixed pulp, the absolute dry mass of xylose monosaccharide accounted for 1.0wt% of the absolute dry mass of the mixed pulp, the absolute dry mass of mannose monosaccharide accounted for 3.5wt% of the absolute dry mass of the mixed pulp, the absolute dry mass of polyxylose accounted for 1.0wt% of the absolute dry mass of the mixed pulp, and the absolute dry mass of polymannose accounted for 3.5wt% of the absolute dry mass of the mixed pulp.

[0068] The mixed slurry was papered using a Cathay paper machine under deionized water to produce 120g / m 2 The paper sample was vacuum dried at 98°C and 1 bar to obtain the insulating paper sample. Finally, the insulating paper was calendered at 105°C and 15MPa to obtain the final insulating paper.

[0069] The insulating paper filled with hemicellulose prepared in this example was placed in a vacuum drying oven at 105° C. for 48 hours to remove moisture, and then impregnated with the impurity- and water-removed Karamay KI50X insulating oil at 60° C. in a vacuum oven for 24 hours.

[0070] Example 8

[0071] First, soak the commercial softwood pulp board for 12 hours, then use a PFI refiner to beat the fiber to a beating degree of 50°SR at a pulp consistency of 10%, then adjust the pulp consistency to 4%, and use a fiber defiberizer to defiber at 15,000 revolutions to fully disperse the fiber in the deionized water system.

[0072] Afterwards, hemicellulose, including xylose monosaccharide with a purity higher than 99.5%, mannose monosaccharide with a purity higher than 99.5%, polyxylose with a purity higher than 99.5%, and polymannose with a purity higher than 99.5%, was weighed to prepare a hemicellulose solution with a mass concentration of 20wt%, and the hemicellulose solution was placed in the decomposed plant fiber pulp and mixed, and the pulp was decomposed again for 10,000 turns to fully mix the hemicellulose and the pulp, and the mixture was allowed to stand for 30 minutes to obtain a mixed pulp, in which the absolute dry mass of the plant fiber pulp accounted for 90wt% of the absolute dry mass of the mixed pulp, the absolute dry mass of xylose monosaccharide accounted for 2.5wt% of the absolute dry mass of the mixed pulp, the absolute dry mass of mannose monosaccharide accounted for 2.5wt% of the absolute dry mass of the mixed pulp, the absolute dry mass of polyxylose accounted for 2.5wt% of the absolute dry mass of the mixed pulp, and the absolute dry mass of polymannose accounted for 2.5wt% of the absolute dry mass of the mixed pulp.

[0073] The mixed slurry was papered using a Cathay paper machine under deionized water to produce 120g / m 2 The paper sample was vacuum dried at 98°C and 1 bar to obtain the insulating paper sample. Finally, the insulating paper was calendered at 105°C and 15MPa to obtain the final insulating paper.

[0074] The insulating paper filled with hemicellulose prepared in this example was placed in a vacuum drying oven at 105° C. for 48 hours to remove moisture, and then impregnated with the impurity- and water-removed Karamay KI50X insulating oil at 60° C. in a vacuum oven for 24 hours.

[0075] Comparative Example

[0076] First, soak the commercial softwood pulp board for 12 hours, then use a PFI refiner to beat the fiber to a beating degree of 50°SR at a pulp consistency of 10%, then adjust the pulp consistency to 4%, and use a fiber defiberizer to defiber at 15,000 revolutions to fully disperse the fiber in the deionized water system.

[0077] Based on the pulp obtained above, a 120 g / m2 paper was made by using a Cathay paper machine under a deionized water system. 2 The paper sample was vacuum dried at 98°C and 1 bar, and calendered at 105°C and 15 MPa to obtain a comparison paper sample.

[0078] The comparative paper sample prepared in the comparative example was placed in a vacuum drying oven at 105°C for 48 hours to remove moisture, and then impregnated with the Karamay KI50X insulating oil that had been decontaminated and dehydrated under vacuum and 60°C conditions for 24 hours.

[0079] Table 2 Performance test results

[0080]

[0081] Table 2 shows a feasible technical route for backfilling hemicellulose to improve the insulation breakdown strength of plant fiber insulation paper and oil-impregnated paper. Through the hemicellulose backfilling route and hemicellulose formulation designed in this application, the AC breakdown strength of softwood fiber insulation paper and oil-impregnated paper can be increased by 3.8-9.1%, the DC breakdown strength can be increased by 10.8-21.6%, and the tensile strength of dry paper can be increased by 29.7-50.8%. The hemicellulose backfilling technology route and backfilling formulation proposed in this application have important guiding significance for the manufacture of transformer paper.

[0082] 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 improving the breakdown field strength and mechanical properties of insulating paper by backfilling hemicellulose, characterized in that: The following steps are involved: Step 1: taking a plant fiber pulp board and beating it to obtain a plant fiber slurry; Step 2: preparing hemicellulose into a hemicellulose solution; Step 3: adding the hemicellulose solution to the diluted plant fiber slurry, dispersing and standing to obtain a mixed slurry; the absolute dry mass of the plant fiber slurry accounts for 87-92wt% of the absolute dry mass of the mixed slurry, and the absolute dry mass of the hemicellulose accounts for 8-13wt% of the absolute dry mass of the mixed slurry; Step 4: Papermaking the mixed slurry, and then hot pressing and smoothing it to obtain insulating paper.

2. The method for improving the breakdown field strength and mechanical properties of insulating paper by backfilling hemicellulose according to claim 1, characterized in that: Step 1 specifically comprises: soaking the plant fiber pulp board, diluting and beating the pulp to obtain the plant fiber slurry.

3. The method for improving the breakdown field strength and mechanical properties of insulating paper by backfilling hemicellulose according to claim 2, characterized in that: The plant fiber pulp was soaked for 12 h, diluted to a pulp concentration of 10%, and then beaten to a beating degree of 50°SR.

4. The method for improving the breakdown field strength and mechanical properties of insulating paper by backfilling hemicellulose according to claim 1, characterized in that: Step 2 is specifically as follows: preparing hemicellulose into a hemicellulose solution with a mass concentration of 20 wt%.

5. The method for improving the breakdown field strength and mechanical properties of insulating paper by backfilling hemicellulose according to claim 1, characterized in that: The plant fiber pulp board is a coniferous wood pulp board, a broadleaf wood pulp board, a grass plant pulp board, a grass pulp board or a bast pulp board; The hemicellulose is a mixture of one or more of xylose monosaccharide, mannose monosaccharide, polyxylose and polymannose.

6. The method of improving the breakdown field strength and mechanical properties of insulating paper by backfilling hemicellulose according to claim 1, characterized in that: Step 3 is specifically as follows: diluting the plant fiber slurry to a slurry concentration of 4%, deflaking for 15,000 revolutions, and then adding the hemicellulose solution to the diluted plant fiber slurry.

7. The method for improving the breakdown field strength and mechanical properties of insulating paper by backfilling hemicellulose according to claim 1, characterized in that: In step 3, spin at 10,000 rpm and let stand for 30 minutes.

8. The method for improving the breakdown field strength and mechanical properties of insulating paper by backfilling hemicellulose according to claim 1, characterized in that: Step 4 specifically comprises: papermaking the mixed slurry to obtain a paper sample, vacuum drying the paper sample to obtain an insulating paper sample, and hot pressing and smoothing the insulating paper sample to obtain insulating paper.

9. The method for improving the breakdown field strength and mechanical properties of insulating paper by backfilling hemicellulose according to claim 8, characterized in that: The basis weight of the paper sample is 120 g / m 2 The temperature of the vacuum drying is 98 °C and the vacuum degree is 1 bar, and the temperature of the hot pressing smoothing treatment is 105 °C and the pressure is 15 MPa.

10. An insulating paper, characterized in that: The method according to any one of claims 1 to 9 is used to prepare the product.

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