Water-blocking powder, preparation method thereof, water-blocking tape and XLPE cable

Abstract

The present application relates to the field of cable power, in particular to a water-blocking powder, a preparation method thereof, a water-blocking tape and an XLPE cable. The present application provides a water-blocking powder, which comprises a composite of sodium polyacrylate and kaolin and ethyl cellulose coated on the surface of the composite. The water-blocking powder provided by the present application has an ethyl cellulose coating layer, which can be used in a water-blocking tape to fully exert the water-blocking performance of the water-blocking powder while avoiding the generation of poor conductive performance substances. Experiments show that, compared with the white powder at the contact position of the two kinds of water-blocking tapes and the trough of the corrugated aluminum sheath, the ordinary water-blocking tape has obvious white powder on the rough surface, the water-blocking tape has no white powder but small pieces of gel on the smooth surface, and the trough surface of the aluminum sheath has obvious corrosion marks; the water-blocking tape containing the water-blocking powder coated with ethyl cellulose has no white powder on the rough surface, no white powder on the smooth surface, and no corrosion marks on the trough surface of the aluminum sheath.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power cables, in particular to a water-blocking powder, a preparation method thereof, a water-blocking tape and an XLPE cable. BACKGROUND

[0002] With the continuous development of economic society, power cables are widely used in city network reconstruction due to their advantages such as beautifying the city, low failure rate, small occupied corridor, etc. Power cables are usually laid on the ground and are easily damaged by external forces such as municipal engineering, causing water intrusion. To prevent water trees from being generated due to the damp of cable insulation, semi-conductive buffer water-blocking tapes are often used as longitudinal water-blocking structures, and the water-blocking tapes are filled with water-blocking powder based on sodium polyacrylate, which can absorb 100 times its own mass of water due to its three-dimensional network structure. Figure 1 As shown in Figure 1 is a cross-sectional structure diagram of a high-voltage XLPE cable, which includes a conductor 1, a conductor shielding layer 2, an insulation layer 3, an insulation shielding layer 4, a water-blocking tape 5, an aluminum sheath 6 and an outer sheath 7. The water-blocking tape 5 is located between the insulation shielding layer 4 and the aluminum sheath 6, and plays a role in longitudinal water-blocking and mechanical buffering. Once water enters the cable, the water-blocking powder in the water-blocking tape 5 will swell from agglomerated water-absorbing to independent spherical shape, storing water inside and preventing further penetration into the deep part of the cable.

[0003] However, in recent years, several cable failures have occurred due to the ablation defects of the buffer layer, and white powder has been found to be generated at the contact position between the surface of the cable water-blocking tape and the aluminum sheath in several reconstruction projects. The industry analyzes that the white powder is generated by the chemical reaction of the water-blocking powder after it is swelled by moisture and contacts the aluminum sheath, which is one of the important reasons for the ablation defects of the buffer layer of the high-voltage cable. The white powder is a high-resistance substance, which is distributed on the surface of the water-blocking tape with originally good conductivity, causing field strength distortion and causing partial discharge of the water-blocking tape. Long-term discharge ablation causes insulation failure of the cable.

[0004] Currently, the water-blocking tape commonly used in the industry is a semi-conductive buffer water-blocking tape, which is composed of semi-conductive polyester fiber non-woven fabric, water-blocking powder, semi-conductive adhesive and semi-conductive fluffy cotton. When external water intrusion occurs, the water-blocking powder in the water-blocking tape will swell in volume after being swelled by moisture, and will react with the aluminum sheath trough through the small pores on the surface of the non-woven fabric and fluffy cotton, generating high-resistance white powder on the surface of the water-blocking tape, which is contrary to the original design idea of good electrical contact between the insulation shielding layer and the aluminum sheath.

[0005] The existing water-blocking tape not only has the function of preventing moisture, but also needs to consider the mechanical buffering effect, so the function of fluffy cotton cannot be replaced, and the surface of the water-blocking tape will inevitably have a porous structure. The water-blocking powder swelled in volume after being swelled by moisture can contact the aluminum sheath trough through the pores on the surface of the water-blocking tape, and react to generate white powder mainly composed of high-resistance NaHCO3, Na2CO3 and Al2O3, etc. The formation principle of these white powders is as follows:

[0006] The water-blocking powder processing process based on sodium polyacrylate is polymerization of acrylic monomer to generate polyacrylic acid, and the pH of the reaction solution is adjusted to 6-9 by adding sodium hydroxide, and white powder sodium polyacrylate is obtained by drying. Therefore, the water-blocking powder is usually alkaline. When OH - After absorbing CO2 in the air, CO3 2- (less CO2) or HCO3 - (excessive CO2) is formed by combining with Na + The possible chemical reaction process is as follows: when the CO2 concentration is low, CO2+2OH - =CO3 2- +H2O or CO3 2- +2Na + =Na2CO3 two reactions; when the CO2 concentration is high, CO2+OH - =HCO3 - or HCO3 - +Na + =NaHCO3 two reactions. This process is irreversible, and once the high-resistance substance is formed, it will not disappear on its own, resulting in distortion of the field strength at the position of the insulating shielding layer-aluminum sheath due to the presence of white powder, and continuous degradation under the action of long-term discharge ablation to form weak points of insulation, eventually leading to insulation breakdown. SUMMARY

[0007] Therefore, the technical problem to be solved by the present application is to provide a water-blocking powder and a preparation method thereof, a water-blocking tape and an XLPE cable. The water-blocking powder provided by the present application has an ethyl cellulose coating, which can be used in a water-blocking tape to fully play the water-blocking performance of the water-blocking powder while avoiding the generation of poor conductive performance substances.

[0008] The present application provides a water-blocking powder, which comprises a composite of sodium polyacrylate and kaolin and an ethyl cellulose coating on the surface of the composite.

[0009] The water-blocking powder provided by the present application comprises a composite of sodium polyacrylate and kaolin, which are common water-blocking powder components known to those skilled in the art. The water-blocking powder provided by the present application further comprises ethyl cellulose coated on the surface of the composite. The present application encapsulates the water-blocking powder with porous ethyl cellulose. Once the water-blocking tape is wet, water molecules can be absorbed by the common water-blocking powder components in the interior through the porous structure of the ethyl cellulose, preventing further migration and diffusion of water. Meanwhile, the ethyl cellulose, which is insoluble in water and not sensitive to alkaline and weak acid, can effectively isolate the wet and expanded water-blocking powder from the trough part of the aluminum sheath, avoiding the electrochemical reaction between the water-blocking powder and aluminum to generate white powder. The content of the ethyl cellulose can be adjusted according to the requirements of the production unit for moisture control in the cable laying environment. In some embodiments of the present application, the mass ratio of the sodium polyacrylate, kaolin and the ethyl cellulose is (80-130):(10-20):(20-40). In some embodiments of the present application, the particle size of the water-blocking powder is 100-150 μm.

[0010] The water-blocking powder provided by the present application, when applied to the water-blocking layer of the water-blocking tape with ethyl cellulose coated on the surface of the common water-blocking powder, can fully absorb water when the cable is wet, and the water-blocking tape plays a role in longitudinal water-blocking. Meanwhile, the ethyl cellulose coating, as a substance that is insoluble in water and not reactive, can avoid contact between the internal water-blocking powder components and the trough of the aluminum sheath, thereby preventing the occurrence of local white powder that causes poor electrical contact. Furthermore, the ethyl cellulose coating can prevent the local field distortion of the cable insulation shielding layer-aluminum sheath caused by the white powder.

[0011] The present application also provides a preparation method of the above water-blocking powder, comprising: heating and mixing a composite of sodium polyacrylate and kaolin, ethyl cellulose and an organic solvent to obtain the water-blocking powder. Specifically, the present application heats and mixes the ethyl cellulose and the organic solvent, and simultaneously stirs while adding the composite of sodium polyacrylate and kaolin thereto, until the organic solvent volatilizes and disappears, to obtain the water-blocking powder. In some embodiments of the present application, a certain amount of ethyl cellulose and an organic solvent are placed in a container, and heated and mixed uniformly by mechanical stirring until a homogeneous transparent solution is formed. The stirring is continued while adding the composite of sodium polyacrylate and kaolin, and the organic solvent is allowed to volatilize and disappear sufficiently to obtain the water-blocking powder.

[0012] In some embodiments of the present application, the mass ratio of the sodium polyacrylate and kaolin composite, ethyl cellulose and organic solvent is (10-20):(1-2):(60-120), preferably 17:1.5:81.5. In some embodiments of the present application, the temperature of the mixing is 55-65°C, preferably 60°C. In some embodiments of the present application, the organic solvent is selected from at least one of anhydrous ethanol, methanol or dichloromethane, preferably anhydrous ethanol.

[0013] In the present application, the preparation method of the sodium polyacrylate and kaolin composite comprises: reacting acrylic acid, sodium lignosulfonate, urea and kaolin under the action of an initiator and a crosslinking agent to obtain a sodium polyacrylate and kaolin composite. Specifically, the acrylic acid, sodium lignosulfonate, urea and kaolin are subjected to a composite reaction under the action of an initiator and a crosslinking agent, and a water-blocking powder is prepared through processes such as neutralization of acrylic acid, initiation treatment, ultrasonic reaction, dehydration, drying and crushing. In some embodiments of the present application, the initiator is selected from water-soluble persulfates, specifically any one of potassium persulfate or sodium persulfate; the crosslinking agent is selected from any one of dimethyl glycol acrylate, ethylene glycol diacrylate or propylene glycol diacrylate. In some embodiments of the present application, the mass ratio of the acrylic acid:sodium lignosulfonate:urea:kaolin:initiator:crosslinking agent is (80-130):(20-40):(10-30):(10-20):(1-2):(0.3-0.7), preferably 110:30:20:10:1:0.5. In some embodiments of the present application, the temperature of the composite reaction is 55-65°C; the time of the composite reaction is 3-4h.

[0014] The present application also provides a water-blocking tape, comprising a substrate, a water-blocking layer adhered to the substrate and a water-absorbing layer compounded on the water-blocking layer; the water-blocking layer is composed of the water-blocking powder described above or the water-blocking powder prepared by the preparation method described above.

[0015] The water-blocking tape provided by the present application comprises a substrate; in one embodiment, the thickness of the substrate is 0.1-0.2mm. The water-blocking tape provided by the present application further comprises a water-blocking layer adhered to the substrate; specifically, an adhesive layer is arranged between the water-blocking layer and the substrate, and the water-blocking layer is adhered to the substrate through the adhesive layer; in one embodiment, the thickness of the water-blocking layer is 0.1-0.2mm; the thickness of the adhesive layer is 0.1-0.2mm. The water-blocking tape provided by the present application further comprises a water-absorbing layer compounded on the water-blocking layer, and the thickness of the water-absorbing layer is 1.0-1.5mm.

[0016] In some embodiments of the present application, the water-blocking tape provided by the present application specifically comprises a semi-conductive polyester fiber non-woven fabric base, an adhesive layer coated on the non-woven fabric, a water-blocking layer dispersedly adhered on the adhesive layer, and a semi-conductive fluffy cotton water-absorbing layer compounded on the water-blocking layer. In some embodiments of the present application, the thickness of the water-blocking tape is 1.3 mm to 2.1 mm. As shown in Figure 1 , Figure 1 Fig. 1 is a schematic diagram of the cross-sectional structure of the water-blocking tape of the high-voltage XLPE cable containing the water-blocking powder coated with ethyl cellulose according to the present application, Figure 1 which comprises semi-conductive fluffy cotton 51, the water-blocking powder 52 according to the present application, semi-conductive adhesive 53, and semi-conductive polyester fiber non-woven fabric 54.

[0017] In the present application, the preparation method of the water-blocking tape comprises the following steps: immersing the inner surface of the base in semi-conductive adhesive, dispersing the water-blocking powder according to the present application on the inner surface of the base, and compounding the water-absorbing layer on the water-blocking powder to obtain the water-blocking tape. In some embodiments of the present application, the preparation method of the water-blocking tape comprises the following steps: immersing the inner surface of the semi-conductive polyester fiber non-woven fabric in semi-conductive adhesive; using a tape drawing device to pull the semi-conductive polyester fiber non-woven fabric, immersing the side of the non-woven fabric with semi-conductive adhesive in the water-blocking powder tank according to the present application at a uniform speed, so that the water-blocking powder is uniformly dispersed on the non-woven fabric; compounding and rolling the semi-conductive fluffy cotton and the side of the semi-conductive polyester fiber non-woven fabric with semi-conductive adhesive to obtain the high-voltage XLPE cable water-blocking tape, and cutting the tape into appropriate width by a slitting machine for packaging.

[0018] The specific preparation method of the semi-conductive polyester fiber non-woven fabric comprises the following steps: mixing and stirring conductive carbon black, methyl acrylate, butyl acrylate, polyester grade ethylene glycol, and water in an aqueous solution to obtain semi-conductive adhesive; wherein the mass ratio of each substance is conductive carbon black: methyl acrylate: butyl acrylate: polyester grade ethylene glycol: water = 5: (0.5-1.5): (0.5-1.5): (2.5-3.5): 10.

[0019] The present application also provides an XLPE cable, which comprises a conductor, an insulation layer, a water-blocking tape, and a sheath from inside to outside; the water-blocking tape is the water-blocking tape described above. In some embodiments of the present application, the XLPE cable comprises a conductor, a conductor shielding layer, an insulation layer, an insulation shielding layer, a water-blocking tape, an aluminum sheath, and an outer sheath from inside to outside. As shown in Figure 2 , Figure 2 Fig. 2 is a schematic diagram of the cross-sectional structure of the high-voltage XLPE cable, Figure 2The high-voltage XLPE cable comprises a conductor 1, a conductor shielding layer 2, an insulation layer 3, an insulation shielding layer 4, a water-blocking tape 5, an aluminum sheath 6 and an outer sheath 7. The water-blocking tape 5 is located between the insulation shielding layer 4 and the aluminum sheath 6 and plays a role in longitudinal water blocking and mechanical buffering; once water enters the cable, the water-blocking powder component in the water-blocking tape 5 is expanded from the agglomerated water-absorbing state into a spherical state independent of each other, stores water in the interior and prevents further penetration of water into the deep part of the cable; at the same time, the ethyl cellulose coating avoids the contact between the internal water-blocking powder component and the aluminum sheath valley, thereby avoiding the generation of local white powder caused by poor electrical contact and further avoiding the local field strength distortion of the cable insulation shielding layer-aluminum sheath.

[0020] The application provides a water-blocking powder comprising a composite of sodium polyacrylate and kaolin and ethyl cellulose coated on the surface of the composite. The water-blocking powder provided by the application has an ethyl cellulose coating and can be used in a water-blocking tape to fully play the water-blocking performance of the water-blocking powder while avoiding the generation of poor conductive performance substances. Experiments show that, compared with the white powder at the contact position of the ordinary water-blocking tape and the corrugated aluminum sheath valley, the rough surface of the ordinary water-blocking tape has obvious white powder, the smooth surface of the water-blocking tape has no white powder but has small pieces of gel, and the surface of the aluminum sheath valley has obvious corrosion marks; the rough surface of the water-blocking tape containing the ethyl cellulose coated water-blocking powder has no white powder, the smooth surface of the water-blocking tape has no white powder, and the surface of the aluminum sheath valley has no corrosion marks. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 It is a cross-sectional structure schematic diagram of the high-voltage XLPE cable water-blocking tape containing the ethyl cellulose coated water-blocking powder of the application;

[0022] Figure 2 It is a cross-sectional structure schematic diagram of the high-voltage XLPE cable;

[0023] Figure 3 It is a preparation flowchart of the high-voltage XLPE cable water-blocking tape containing the ethyl cellulose coated water-blocking powder of the application;

[0024] Figure 4 It is a water injection test schematic diagram of the water-blocking tape;

[0025] Figure 5 It is a schematic diagram of the white powder generation of the ordinary water-blocking tape and the corrugated aluminum sheath valley contact on the rough surface of the water-blocking tape;

[0026] Figure 6 It is a schematic diagram of the white powder generation of the ordinary water-blocking tape and the corrugated aluminum sheath valley contact on the smooth surface of the water-blocking tape;

[0027] Figure 7 It is a schematic diagram of the influence of the ordinary water-blocking tape and the corrugated aluminum sheath valley contact on the surface of the aluminum sheath valley;

[0028] Figure 8A schematic diagram showing the white powder generation on the rough surface of a water-blocking tape containing ethyl cellulose water-blocking powder in contact with the trough of a wrinkled aluminum sheath.

[0029] Figure 9 A schematic diagram showing the formation of white powder on the smooth surface of a water-blocking tape containing ethyl cellulose water-blocking powder in contact with the trough of a wrinkled aluminum sheath.

[0030] Figure 10 This is a schematic diagram showing the effect of a water-blocking tape containing ethyl cellulose water-blocking powder in contact with the troughs of a wrinkled aluminum sheath on the surface of the troughs of the aluminum sheath. Detailed Implementation

[0031] This invention discloses a water-blocking powder and its preparation method, a water-blocking tape, and an XLPE cable. Those skilled in the art can refer to the content of this document and appropriately modify the process parameters to achieve the desired results. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in this invention. The methods and applications of this invention have been described through preferred embodiments, and those skilled in the art can clearly modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit, and scope of this invention to realize and apply the technology of this invention.

[0032] like Figure 3 As shown, Figure 3 This is a flowchart illustrating the preparation process of the high-voltage XLPE cable water-blocking tape containing coated ethyl cellulose water-blocking powder according to the present invention; the present invention is based on... Figure 3 The water-blocking tape described in this invention is prepared in steps S1 to S6 of the preparation flowchart shown.

[0033] The present invention will be further described below with reference to the embodiments:

[0034] Example 1

[0035] Conductive carbon black is mixed with methyl acrylate, butyl acrylate, polyester-grade ethylene glycol and water in a ratio of 5:0.5:0.5:2.5:10 to obtain a semi-conductive adhesive, which is then applied to the surface of a semi-conductive polyester fiber nonwoven fabric.

[0036] Acrylic acid, sodium lignosulfonate, urea, kaolin, potassium persulfate, and ethylene glycol diacrylate were reacted in a mass ratio of 110:30:20:10:1:0.5 at a reaction temperature of 60°C for 3 hours. The composite of sodium polyacrylate and kaolin was prepared by processes including acrylic acid neutralization, initiation treatment, ultrasonic reaction, dehydration, drying, and crushing.

[0037] The compound of sodium polyacrylate and kaolin, ethyl cellulose and anhydrous ethanol are uniformly mechanically stirred at a temperature of 60°C in a ratio of 17:1.5:81.5 until the anhydrous ethanol is fully volatilized and disappears, and a water-blocking powder coated with ethyl cellulose is obtained.

[0038] The semi-conductive polyester fiber non-woven fabric is pulled by a tape laying device, and the side of the non-woven fabric with the semi-conductive adhesive is parallelly immersed into a tank containing the water-blocking powder coated with ethyl cellulose, and is pulled at a uniform speed so that the water-blocking powder is uniformly dispersed on the non-woven fabric. The semi-conductive bulk cotton and the side of the semi-conductive polyester fiber non-woven fabric with the semi-conductive adhesive are compounded and rolled into a high-voltage XLPE cable water-blocking tape, and the water-blocking tape is dried. The water-blocking tape is cut into a size of 150mm x 80mm x 1.5mm, and the corrugated aluminum sheath is cut into equal lengths. After a certain amount of water is injected into the water-blocking tape by a syringe, the water-blocking tape is observed for 30 days to record whether there is white powder on the rough surface and the smooth surface of the water-blocking tape and whether there are corrosion marks at the contact position of the aluminum sheath. If Figure 4 , Figure 4 it is shown that the water-blocking tape with the water-blocking powder coated with ethyl cellulose has no white powder on the rough surface and the smooth surface of the water-blocking tape and no corrosion marks at the contact position of the aluminum sheath.

[0039] Comparative Example 1

[0040] The water-blocking tape with the water-blocking powder coated with ethyl cellulose is replaced by a common water-blocking tape with the water-blocking powder without ethyl cellulose, and the water injection test of Example 1 is repeated, that is, a certain amount of water is injected into the water-blocking tape by a syringe, and the water-blocking tape is observed for 14 days to record whether there is white powder on the rough surface and the smooth surface of the water-blocking tape and whether there are corrosion marks at the contact position of the aluminum sheath.

[0041] The white powder at the contact position of the corrugated aluminum sheath valley of the two kinds of water-blocking tapes is compared. As Figures 5 to 7 shown, Figure 5 a diagram showing the generation of white powder on the rough surface of the common water-blocking tape contacted with the corrugated aluminum sheath valley, Figure 6 a diagram showing the generation of white powder on the smooth surface of the common water-blocking tape contacted with the corrugated aluminum sheath valley, Figure 7 a diagram showing the influence of the corrugated aluminum sheath valley surface contacted with the common water-blocking tape; it can be seen that Figures 5 to 7 the rough surface of the common water-blocking tape has obvious white powder, the smooth surface of the water-blocking tape has no white powder but has small pieces of gel, and the corrugated aluminum sheath valley surface has obvious corrosion marks.

[0042] As Figures 8 to 10 shown, Figure 8 a diagram showing the generation of white powder on the rough surface of the water-blocking tape with the water-blocking powder coated with ethyl cellulose contacted with the corrugated aluminum sheath valley, Figure 9 a diagram showing the generation of white powder on the smooth surface of the water-blocking tape with the water-blocking powder coated with ethyl cellulose contacted with the corrugated aluminum sheath valley, Figure 10The schematic diagram of the influence of the water-blocking tape containing water-blocking powder coated with ethyl cellulose contacting with the valley surface of the corrugated aluminum sheath is shown in the figure; and Figures 8 to 10 It can be seen that the water-blocking tape containing water-blocking powder coated with ethyl cellulose has no white powder on the rough surface, no white powder on the smooth surface, and no corrosion marks on the valley surface of the aluminum sheath.

[0043] The above is only the preferred specific embodiment of the present application, but the protection scope of the present application is not limited to this. Any person skilled in the art can make equivalent replacement or change according to the technical scheme and the inventive concept of the present application within the technical range disclosed by the present application, which should be covered in the protection scope of the present application.

Claims

1. A water-blocking powder applied to an aluminum-sheathed cable, characterized by, It comprises a composite of sodium polyacrylate and kaolin and ethyl cellulose coated on the surface of the composite; The mass ratio of the sodium polyacrylate, kaolin and ethyl cellulose is (80-130):(10-20):(20-40); The water-blocking powder is prepared by the following method: The ethyl cellulose and organic solvent are heated and mixed, and the composite of sodium polyacrylate and kaolin is added thereto while stirring until the organic solvent volatilizes and disappears, to obtain the water-blocking powder.

2. The water-blocking powder according to claim 1, characterized by, The particle size of the water-blocking powder is 100-150 μm.

3. A method for the preparation of a water-blocking powder to be applied to a cable comprising an aluminium sheath, characterized in that, It comprises: The ethyl cellulose and organic solvent are heated and mixed, and the composite of sodium polyacrylate and kaolin is added thereto while stirring until the organic solvent volatilizes and disappears, to obtain the water-blocking powder. The mass ratio of the composite, ethyl cellulose and organic solvent is (10-20):(1-2):(60-120).

4. The production method according to claim 3, characterized by, The temperature of the mixing is 55-65°C.

5. A water-blocking tape applied to an aluminum-sheathed cable, characterized by It comprises a substrate, a water-blocking layer adhered to the substrate and a water-absorbing layer compounded on the water-blocking layer. The water-blocking layer is composed of the water-blocking powder of any one of claims 1-2 or the water-blocking powder prepared by the preparation method of any one of claims 3-4.

6. A waterstop according to claim 5, characterised in that The thickness of the water-blocking layer is 0.1-0.2 mm.

7. The waterstop of claim 5, wherein, It specifically comprises a semi-conductive polyester fiber non-woven fabric, an adhesive layer coated on the non-woven fabric, a water-blocking layer dispersedly adhered to the adhesive layer and a semi-conductive fluffy cotton compounded on the water-blocking layer.

8. An XLPE cable characterised in that, It comprises a conductor, an insulating layer, a water-blocking tape and a sheath in order from inside to outside; The water-blocking tape is the water-blocking tape of any one of claims 5-7.

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