CN111875806A - Application of Ziegler-Natta catalyst, method for preparing cable plant flexible joint and insulating layer thereof, and cable plant flexible joint - Google Patents

Abstract

The invention relates to an application of a Ziegler-Natta catalyst in copolymerization of crosslinked polyethylene and polypropylene, a method for preparing a cable plant flexible joint and an insulating layer thereof, and a method for preparing a cable plant flexible joint. The Ziegler-Natta catalyst can initiate the reaction of polyethylene and polypropylene to synthesize high molecular weight PE-b-PP copolymer, and can accurately control the length of the copolymerization block, so that the obtained copolymer has excellent mechanical properties.

Description

Application of Ziegler-Natta catalysts, preparation of flexible joints in cable factories and their insulating layers method, cable factory soft joint

technical field

The invention relates to the field of power cable accessories, in particular to the application of a Ziegler-Natta catalyst, a method for preparing a cable factory soft joint and an insulating layer thereof, and a cable factory soft joint.

Background technique

Extruded cables with cross-linked polyethylene (XLPE) as the main insulating material are widely used in power systems due to their simple structure, large transmission capacity, light weight, easy installation and maintenance, low processing and manufacturing costs, and stable operation. . Various types of cable accessories are required for electrical connection between cables and between cables and power primary equipment to optimize the insulation interface fit between cables and other components (including other cables) and evacuate the outer semi-conductive shield due to cable stripping The induced electric field stress concentration distortion. Cable accessories that interconnect between power cables are called cable splices or cable couplers.

Cable intermediate joints are divided into integral prefabricated, combined prefabricated and factory soft joints mainly made by cable factories or on-site according to their different structural forms. The main difference between the factory soft joint and the former two is that the factory soft joint mainly uses the same and close insulating materials and semi-conductive shielding materials as the cable body as structural materials, and its production process is also similar to the extrusion process of the cable body. The rear dimensions are nearly the same as the cable body.

In the production process of the factory soft joint of the existing cross-linked cable, the insulation layer is mainly welded by injection welding technology. From the tool, it mainly needs a melt injection extruder, which is almost the same as the core layer of the cable (within the outer shielding layer of the cable). Diameter coating mold, etc. Since the insulation material of the commonly used extruded cable is cross-linked polyethylene material, it is necessary to dope the cross-linking agent in the polyethylene insulating material to complete the cross-linking reaction when making the insulation of the soft joint, so as to finally form an insulating structure equivalent to the cable insulation. However, due to the difficulty in discharging the cross-linked by-products generated when the air inside the mold is covered and the insulation is restored and cross-linked, it is easy to form defects such as bubbles and impurities in the soft joint insulating material. During the injection molding process, the cable body and the injection material are in contact with each other. The material properties of the parts cannot be completely equal, resulting in a decrease in the insulation performance of the old and new insulation interface parts, which induces breakdown and damages the soft joints of the cable factory.

In traditional chemical materials, similar to cross-linked polyethylene materials, polypropylene materials also have the advantages of high dielectric strength, good insulating properties, good heat resistance, and equivalent mechanical strength. However, polyethylene and polypropylene, despite having similar hydrocarbon compositions, are incompatible with each other, resulting in an interface between cable insulation and intermediate flexible joints prepared with these two materials, respectively, in the conventional manner. In the end, insulation failure is caused by the breakdown of the interface along the surface.

SUMMARY OF THE INVENTION

Therefore, the technical problem to be solved by the present invention is to overcome the defect in the prior art that when using polyethylene and polypropylene to prepare factory soft joints, there is always an interface defect, so as to provide a Ziegler-Natta catalyst in polyethylene and polypropylene. Applications in polypropylene copolymerization.

The invention also provides a method for preparing the insulating layer of the soft joint of a cable factory.

The invention also provides a method for preparing a cable factory soft joint.

The invention also provides a cable factory soft joint.

Therefore, the present invention provides the application of a Ziegler-Natta catalyst in the copolymerization of cross-linked polyethylene and polypropylene.

Currently, the vast majority of polyethylene (PE) and polypropylene (PP) are produced using heterogeneous chromium and titanium catalysts. Heterophasic olefin polymerization catalysts have many active sites, each with individual differences in reactivity, resulting in polymers of varying molecular weight (MW), molecular weight distribution, and microstructure. In the case of polyethylene and polypropylene, these differences and phase separation inhibit interfacial adhesion and reduce the mechanical properties of melt blends. In order to solve the problem of compatibility between polypropylene and polyethylene, a Ziegler-Natta catalyst was found as a polymerization initiator to synthesize high molecular weight PE-b-PP copolymer, and the copolymerization block can be precisely controlled. length. The resulting block amorphous copolymer can act as an additive to increase the compatibility of polyethylene and polypropylene.

Further, the catalyst is TiCl ₄ -Al(C ₂ H ₅ ) ₃ and/or TiCl ₄ -Al(C ₂ H ₅ ) ₂ Cl.

The chemical reaction principle is shown below.

Alkylation:

TiCl ₄ +AlR ₃ →RTiCl ₃ +AlR ₂ Cl

TiCl ₄ +AlR ₂ Cl→RTiCl ₃ +AlRCl ₂

RTiCl ₃ +AlR ₃ →R ₂ TiCl ₂ +AlR ₂ Cl

Homolysis and reduction of alkyl titanium:

RTiCl ₃ →TiCl ₃ +R·

R ₂ TiCl ₂ →RTiCl ₂ +R·

TiCl ₄ +R·→TiCl ₃ +RCl

Free radical termination:

2R · → Coupling or disproportionation termination.

The present invention also provides a method for preparing an insulating layer of a soft joint in a cable factory, comprising the following steps:

S1, strip the XLPE insulating layer covering the conductor at the connection position of the factory soft joint into a slope and expose the inner semiconducting shielding layer and a section of conductor;

S2, connect the exposed conductor and restore the inner semiconducting shielding layer;

S3, winding the catalyst material tape made of Ziegler-Natta catalyst and polypropylene and/or polyethylene on the insulating layer of the slope;

S4, all the air at the insulating layer wound by the catalyst material tape is exhausted, and then the place is heated;

S5, extruding polypropylene into the insulating layer wound by the catalyst material tape to melt and copolymerize the polypropylene and the cross-linked polyethylene. After the reaction is completed, the temperature is lowered to make the reaction part turn into a solid state.

Further, the preparation method of the catalyst material tape is: mixing the Ziegler-Natta catalyst with polyethylene or polypropylene, and then extruding into the catalyst material tape.

Further, the included angle between the insulating layer of the slope and the conductor is 25-40°.

Further, before connecting the conductors, the exposed conductors are subjected to surface deoxidation and waterproofing treatment.

Further, in step S2, the inner semiconducting shielding layer is restored with a semiconducting shielding tape.

Further, before winding the catalyst material tape on the insulating layer of the slope, the step of grinding the insulating layer of the slope into a rough surface is also included.

Further, in step S4, the air is exhausted with inert gas or nitrogen, and the temperature is heated to 180°C to 240°C.

Further, in step S5, after the reaction part becomes solid, it continues to be in an inert gas or nitrogen environment for 24-36 hours.

The present invention also provides a method for preparing a cable factory soft joint, comprising the following steps:

According to the above method, the insulating layer of the soft joint of the cable factory is prepared;

Restore the outer semiconducting shielding layer;

Restore metal shield, buffer, outer jacket.

The present invention also provides the cable factory flexible joint prepared by the above method.

The technical scheme of the present invention has the following advantages:

1. Application of the Ziegler-Natta catalyst provided by the present invention in the copolymerization of polyethylene and polypropylene, the Ziegler-Natta catalyst can initiate the reaction of polyethylene and polypropylene to synthesize high molecular weight PE-b-PP copolymerization The length of the copolymerized block can be precisely controlled, and the obtained copolymer has excellent mechanical properties.

2. The method for preparing the insulating layer of a cable factory soft joint provided by the present invention uses a Ziegler-Natta catalyst to copolymerize a polypropylene material and a polyethylene material in a molten state, which can effectively eliminate the old and new insulation in the production process of the factory soft joint The interface between the materials directly improves the success rate and reliability of the factory soft joint production, and achieves the purpose of realizing all the functions of the factory soft joint without using cross-linking reaction. Because the polyethylene main material does not need exhaust during the melting recovery process, only a small amount of exhaust or impurity removal is available in the copolymerization area with the polypropylene material, which can greatly shorten the production time of soft joints in power cable factories and greatly improve Factory soft joint reliability.

3. The method for preparing the insulating layer of a soft joint in a cable factory provided by the present invention utilizes the method of winding an insulating material base tape containing a catalyst to precisely place the catalyst for the copolymerization reaction of polypropylene and polyethylene to the position where the copolymerization reaction is required. The original cross-linked polyethylene is de-cross-linked, and the copolymerization reaction is completed with polypropylene under the action of a catalyst, and the obtained integral joint no longer contains an obvious interface between polyethylene and polypropylene, so as to achieve the effect of restoring the overall cable body.

4. The method for preparing the insulating layer of the flexible joint of a cable factory provided by the present invention also includes deoxidizing and waterproofing the exposed conductors on the surface before connecting the conductors, so that impurities can be contained as little as possible when restoring the conductor connections, preventing future damage due to Poor contact of conductors or decreased electrical conductivity at the conductor joints leads to the problem of heating of the conductor joints, which can effectively ensure the reliability of the conductor connection; grinding the insulating layer of the slope into a rough surface can increase the contact between it and the catalyst material tape. It is more conducive to the fusion between the catalyst material band and the cross-linked polyethylene in the reaction process, and promotes the reaction to proceed.

5. In the method for preparing the insulating layer of a flexible joint of a cable factory provided by the present invention, the temperature in step S4 is heated to 180° C. to 240° C., which is the suitable melt polymerization reaction temperature of polypropylene and cross-linked polyethylene, and is within this temperature range. It can ensure the formation of high molecular weight PE-b-PP copolymer.

6. In the method for preparing the insulating layer of a cable factory flexible joint provided by the present invention, after the reaction part becomes solid, the reaction part is kept in an inert gas environment for 24-36 hours, which can ensure that the impurities generated in the melt copolymerization process are completely discharged.

7. The flexible joint prepared by the method for preparing a cable factory flexible joint provided by the present invention can be applied to various voltage levels and has nothing to do with the AC or DC properties of the power system.

Description of drawings

In order to illustrate the specific embodiments of the present invention or the technical solutions in the prior art more clearly, the following briefly introduces the accompanying drawings that need to be used in the description of the specific embodiments or the prior art. Obviously, the accompanying drawings in the following description The drawings are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings without creative efforts.

1 is a cross-sectional view of a cable in Embodiment 1 of the present invention;

Fig. 2 is the structural representation of the cable after step 3) processing in embodiment 1 of the present invention;

3 is a schematic structural diagram of the cable after the conductors are connected in step 5) of Embodiment 1 of the present invention;

4 is a schematic diagram of the cable structure after restoring the inner semiconducting shielding layer in step 6) of Embodiment 1 of the present invention;

5 is a schematic diagram of the cable structure after forming a new insulating layer in step 13) of Embodiment 1 of the present invention.

Reference number:

1. Conductor; 2. Inner semiconductor shielding layer; 3. XLPE insulating layer; 4. Outer semiconductor shielding layer; 5. Metal shielding layer; 6. Buffer layer; 7. Outer sheath; 8. Semi-conductive shielding tape 9. Polypropylene insulating layer.

Detailed ways

The following examples are provided for a better understanding of the present invention, and are not limited to the best embodiments, and do not limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by combining with the features of other prior art shall fall within the protection scope of the present invention.

If the specific experimental steps or conditions are not indicated in the examples, it can be carried out according to the operations or conditions of the conventional experimental steps described in the literature in this field. The reagents or instruments used without the manufacturer's indication are all conventional reagent products that can be obtained from the market.

Example 1

A method for preparing a cable factory soft joint, comprising the following steps:

1) Fully mix the Ziegler-Natta catalyst TiCl ₄ -Al(C ₂ H ₅ ) ₃ (granular) and polyethylene in a mass ratio of 1:1, and use a unidirectional pultrusion method on a flat extruder A catalyst material tape having a width of about 4 cm and a thickness of about 2 mm was prepared.

2) Heating and aligning the connection position of the factory soft joint of the extruded insulated power cable. The cross-section of the cable is shown in Figure 1, including conductor 1, inner semiconductor shielding layer 2, XLPE insulating layer 3, outer semiconductor shielding layer 4, metal shielding layer 5, buffer layer 6 and outer sheath 7;

3) Remove part of the outer sheath 7, buffer layer 6, metal shielding layer 5, outer semiconducting shielding layer 4, XLPE insulating layer 3 and inner semiconducting shielding layer 2 from the straightened cable until a section of conductor 1 is exposed , and use a stripping tool to strip the cross-linked polyethylene insulation layer 3 into a slope with an angle of 35° to the conductor, and expose a 20mm inner semi-conductive shielding layer (commonly known as making cable core soft joint pencil head), after this treatment The cross-section of the cable is shown in Figure 2 (only part of the structure is marked in the figure);

4) grinding the cross-linked polyethylene insulating layer 3 of the slope into a rough surface;

5) Deoxidize and waterproof the exposed conductor 1 on the surface, connect the exposed conductor 1 in the two cables with bolts, and treat the connected conductor 1 until the surface is smooth and free of burrs. The cable after connection is shown in the figure. 3 shown;

6) Use the semiconducting shielding tape 8 that is consistent with the material of the inner semiconducting shielding layer 2 to restore the inner semiconducting shielding layer 2, and the cable after restoring the inner semiconducting shielding layer 2 is shown in Figure 4;

7) Use the catalyst material tape to wrap around the sloped cross-linked polyethylene insulating layer 3 on both sides. When wrapping, start from the bottom of the slope surface, and the catalyst material tape at the back is overlapped with the half width of the material tape at the front. Winding until it reaches the top of the slope. At this time, there should be no residual air gaps or air bubbles on the winding contact surface;

8) Fix the factory soft joint mold on the connected cable, place the factory soft joint connection position in the middle of the factory soft joint mold, close the factory soft joint mold, connect the nitrogen closed loop, and pass 2 atmospheres of nitrogen gas, Make sure that the factory soft joint is connected to the insulation recovery position, that is, the air at the insulation layer wrapped by the catalyst material tape is completely exhausted;

9) Heat the cable connection section where the mold is located to 210°C;

10) Use a small extruder to extrude polypropylene at 210 °C into the factory soft joint mold until the polypropylene is discharged from the gas outlet of the factory soft joint mold, and maintain the temperature in the factory soft joint mold at 210 °C;

11) wait for 2 hours to complete the melt copolymerization of polypropylene and cross-linked polyethylene;

12) After the melting reaction is completed, it is naturally cooled to normal temperature, and after the reaction part becomes solid, continue to wait for 30 hours;

13) Remove the factory soft joint mold, treat the surface of the newly extruded insulating material to the required surface cleanliness, and wipe the surface of the insulating material with alcohol cloth and other materials. The treated cable is shown in Figure 5 (only the part is marked in the figure). structure), including the newly formed polypropylene insulating layer 9, and the contact part of the polypropylene insulating layer 9 and the cross-linked polyethylene insulating layer 3 is a copolymerized polyethylene-polypropylene copolymer;

14) Use the semiconductive shielding tape to restore the outer semiconductive shielding layer 4;

15) Restore the metal shielding layer 5, buffer layer 6 and outer sheath 7 of the cable.

Plane the prepared factory soft joint in the direction of the vertical conductor, and observe that there is no slash boundary between the old and new insulating materials in the contact part of the original cross-linked polyethylene insulating layer of the cable and the newly formed polypropylene insulating layer, which is completely realized. Interface-free transition between the cross-linked polyethylene material of the cable body and the polypropylene insulating material of the intermediate joint.

Example 2

A method for preparing a cable factory soft joint, comprising the following steps:

1) Mix the Ziegler-Natta catalyst TiCl ₄ -Al(C ₂ H ₅ ) ₂ Cl (granular) and polypropylene in a ratio of 1:1, and prepare by unidirectional pultrusion on a flat extruder A catalyst material belt with a width of about 4 cm and a thickness of about 2 mm was obtained.

2) Heating and straightening the connection position of the factory soft joint of the extruded insulated power cable;

3) Remove part of the outer sheath, buffer layer, metal shielding layer, outer semiconducting shielding layer, XLPE insulating layer and inner semiconducting shielding layer of the straightened cable until a section of conductor is exposed, and use a peeling tool to remove the insulating layer. It is stripped to a slope with an included angle of 25° to the conductor, and a 20mm inner semi-conductive shielding layer is exposed (commonly known as the pencil head of the cable core soft joint);

4) Grind the cross-linked polyethylene insulating layer of the slope to a rough surface;

5) Deoxidize and waterproof the exposed conductors on the surface, connect the exposed conductors in the two cables by welding, and treat the connected conductors until the surface is smooth and free of burrs;

6) Use the semiconductive shielding tape that is consistent with the material of the inner semiconductive shielding layer to restore the inner semiconducting shielding layer;

7) Use the catalyst material tape to wrap around the sloped cross-linked polyethylene insulating layer on both sides. When wrapping, start from the bottom of the slope surface, and the latter catalyst material tape is overlapped with half the width of the front material tape, and then wound in turn. , until the winding reaches the top of the slope, at this time, there should be no residual air gaps or air bubbles on the winding contact surface;

8) Fix the factory soft joint mold on the connected cable, place the factory soft joint connection position in the middle of the factory soft joint mold, close the factory soft joint mold, connect the nitrogen closed loop, and pass 2 atmospheres of nitrogen gas, Make sure that the factory soft joint is connected to the insulation recovery position, that is, the air at the insulation layer wrapped by the catalyst material tape is completely exhausted;

9) Heat the cable connection section where the mold is located to 180°C;

10) Use a small extruder to extrude polypropylene at 180 °C into the factory soft joint mold until the polypropylene is discharged from the gas outlet of the factory soft joint mold, and maintain the temperature in the factory soft joint mold at 180 °C;

11) wait for 2 hours to complete the melt copolymerization of polypropylene and cross-linked polyethylene;

12) After the melting reaction is completed, it is naturally cooled to normal temperature, and after the reaction part becomes solid, continue to wait for 24 hours;

13) Remove the factory soft joint mold, treat the surface of the newly extruded insulating material to the required surface cleanliness, and use alcohol cloth and other materials to clean the surface of the insulating material. The cable soft joint after this treatment includes the newly formed polypropylene insulating layer , the contact part of the polypropylene insulating layer and the cross-linked polyethylene insulating layer is a copolymerized polyethylene-polypropylene copolymer;

14) Use semiconducting shielding tape to restore the outer semiconducting shielding layer;

15) Restore the metal shielding layer, buffer layer and outer sheath of the cable.

Plane the prepared factory soft joint in the direction of the vertical conductor, and observe that there is no slash boundary between the old and new insulating materials in the contact part of the original cross-linked polyethylene insulating layer of the cable and the newly formed polypropylene insulating layer, which is completely realized. Interface-free transition between the cross-linked polyethylene material of the cable body and the polypropylene insulating material of the intermediate joint.

Example 3

A method for preparing a cable factory soft joint, comprising the following steps:

1) Mix the Ziegler-Natta catalyst TiCl ₄ -Al(C ₂ H ₅ ) ₂ Cl (granular) and polypropylene in a ratio of 1:1, and prepare by unidirectional pultrusion on a flat extruder A catalyst material belt having a width of about 4 cm and a thickness of about 2 mm was obtained.

2) Heating and straightening the connection position of the factory soft joint of the extruded insulated power cable;

3) Remove part of the outer sheath, buffer layer, metal shielding layer, outer semiconducting shielding layer, cross-linked polyethylene insulating layer and semiconducting shielding layer of the straightened cable until a section of conductor is exposed, and the insulating layer is stripped with a stripping tool It is a slope with an included angle of 45° with the conductor, and exposes a 20mm inner semi-conductive shielding layer (commonly known as making a cable core soft joint pencil head);

4) Grind the cross-linked polyethylene insulating layer of the slope to a rough surface;

5) Deoxidize and waterproof the exposed conductors on the surface, connect the exposed conductors in the two cables by welding, and treat the connected conductors until the surface is smooth and free of burrs;

6) Use the semiconductive shielding tape that is consistent with the material of the inner semiconductive shielding layer to restore the inner semiconducting shielding layer;

7) Use the catalyst material tape to wrap around the sloped cross-linked polyethylene insulating layer on both sides. When wrapping, start from the bottom of the slope surface, and the latter catalyst material tape is overlapped with half the width of the front material tape, and then wound in turn. , until the winding reaches the top of the slope, at this time, there should be no residual air gaps or air bubbles on the winding contact surface;

8) Fix the factory soft joint mold on the connected cable, place the factory soft joint connection position in the middle of the factory soft joint mold, close the factory soft joint mold, connect the nitrogen closed loop, and pass 2 atmospheres of nitrogen gas, Make sure that the factory soft joint is connected to the insulation recovery position, that is, the air at the insulation layer wrapped by the catalyst material tape is completely exhausted;

9) Heat the cable connection section where the mold is located to 240°C;

10) Use a small extruder to extrude polypropylene at 240°C into the factory soft joint mold until the polypropylene is discharged from the gas outlet of the factory soft joint mold, and maintain the temperature in the factory soft joint mold at 240°C;

11) wait for 2 hours to complete the melt copolymerization of polypropylene and cross-linked polyethylene;

12) After the melting reaction is completed, it is naturally cooled to normal temperature, and after the reaction part becomes solid, continue to wait for 36 hours;

13) Remove the factory soft joint mold, treat the surface of the newly extruded insulating material to the required surface cleanliness, and use alcohol cloth and other materials to clean the surface of the insulating material. The cable soft joint after this treatment includes the newly formed polypropylene insulating layer , the contact part of the polypropylene insulating layer and the cross-linked polyethylene insulating layer is a copolymerized polyethylene-polypropylene copolymer;

14) Use semiconducting shielding tape to restore the outer semiconducting shielding layer;

15) Restore the metal shielding layer, buffer layer and outer sheath of the cable.

Plane the prepared factory soft joint in the direction of the vertical conductor, and observe that there is no slash boundary between the old and new insulating materials in the contact part of the original cross-linked polyethylene insulating layer of the cable and the newly formed polypropylene insulating layer, which is completely realized. Interface-free transition between the cross-linked polyethylene material of the cable body and the polypropylene insulating material of the intermediate joint.

Example 4

A polypropylene film with a thickness of 0.5 mm and a diameter of 150 mm was prepared using polypropylene particles at 160 °C;

Mixing polyethylene particles with TiCl ₄ -Al(C ₂ H ₅ ) ₃ (granular) in a mass ratio of 1:1 to prepare a catalyst film with a thickness of 0.5 mm and a diameter of 150 mm at 170° C.;

A polyethylene film with a thickness of 0.5mm and a diameter of 150mm was prepared at 160°C using polyethylene particles;

The polypropylene film, polyethylene film and catalyst film were superimposed together in the order of polyethylene (bottom)-catalyst (middle)-polypropylene (top). room temperature.

Comparative Example 1

The polypropylene film and the polyethylene film were prepared according to the method of Example 4, and the polypropylene film and the polyethylene film were stacked together in the order of polyethylene (bottom)-polypropylene (top), and were bonded by thermocompression at 180°C, After holding for 2 hours, it was cooled to room temperature.

Experimental example

A tensile test was carried out on the bonded films prepared in Example 4 and Comparative Example 1, and the test method was as follows:

Take the bonded film, use a sharp sheet blade to lightly cut small slits with a length of 1 cm and a depth of 1 cm along the bonding interface at the edge, and perforate the corresponding positions on the cut film into two pieces, respectively. Use "T"-shaped hooks to pass through the holes from the inside to the outside, the beams of the "T"-shaped hooks are stuck on the holes, and the two hooks are fixed on the upper and lower clamps of the tensile tester. Check that there is no damage such as cracks at the piercing position.

Use a tensile tester to slowly stretch the two hooks and slowly tear apart the two bonded films. The tensile force was recorded. Repeat the test 3 times.

Experimental results:

The tear tensile force of the adhesive film of Comparative Example 1 was 0.9-1.1 N.

The tensile force of the adhesive poly film of Example 4 is 5-8N.

Obviously, the above-mentioned embodiments are only examples for clear description, and are not intended to limit the implementation manner. For those of ordinary skill in the art, changes or modifications in other different forms can also be made on the basis of the above description. There is no need and cannot be exhaustive of all implementations here. And the obvious changes or changes derived from this are still within the protection scope of the present invention.

Claims (12)

1. Application of a Ziegler-Natta catalyst in the copolymerization of cross-linked polyethylene and polypropylene. 2. the application of Ziegler-Natta catalyst according to claim 1 in polyethylene and polypropylene copolymerization, it is characterized in that, described catalyst is TiCl ₄ -Al(C ₂ H ₅ ) ₃ and/or TiCl _{4 -} Al( _{C2H5 )} 2Cl. 3. a method for preparing the insulating layer of a soft joint in a cable factory, is characterized in that, comprises the following steps: S1, strip the XLPE insulating layer covering the conductor at the connection position of the factory soft joint into a slope and expose the inner semiconducting shielding layer and a section of conductor; S2, connect the exposed conductor and restore the inner semiconducting shielding layer; S3, winding the catalyst material tape made of Ziegler-Natta catalyst and polypropylene and/or polyethylene on the insulating layer of the slope; S4, all the air at the insulating layer wound by the catalyst material tape is exhausted, and then the place is heated; S5, extruding polypropylene into the insulating layer wound by the catalyst material tape to melt and copolymerize the polypropylene and the cross-linked polyethylene. After the reaction is completed, the temperature is lowered to make the reaction part turn into a solid state. 4. The method for preparing an insulating layer of a soft joint in a cable factory according to claim 3, wherein the preparation method of the catalyst material tape is: mixing the Ziegler-Natta catalyst with polyethylene or polypropylene, and then extruding into a catalyst material belt. 5. The method for preparing an insulating layer of a flexible joint in a cable factory according to claim 3 or 4, wherein the angle between the insulating layer on the slope and the conductor is 25-40°. 6. The method for preparing an insulating layer of a flexible joint in a cable factory according to any one of claims 3-5, characterized in that, before connecting the conductors, it further comprises deoxidizing and waterproofing the exposed conductors on the surface. 7. The method for preparing an insulating layer of a flexible joint in a cable factory according to any one of claims 3-6, wherein in step S2, the inner semiconducting shielding layer is restored with a semiconducting shielding tape. 8. The method for preparing an insulating layer of a flexible joint in a cable factory according to any one of claims 3-7, characterized in that, before winding the catalyst material tape on the insulating layer of the slope, it also comprises insulating the slope of the slope. The step of sanding the layer to a rough surface. 9 . The method according to claim 3 , wherein in step S4 , the air is exhausted with inert gas or nitrogen, and the temperature is heated to 180° C. to 240° C. 10 . 10. The method for preparing an insulating layer of a flexible joint in a cable factory according to any one of claims 3-9, wherein in step S5, after the reaction part becomes solid, it continues to be in an inert gas or nitrogen environment 24-36 Hour. 11. A method for preparing a cable factory soft joint, characterized in that, comprising the following steps: According to the method described in any one of the claims 3-10, prepare the insulating layer of the flexible joint of the cable factory; Restore the outer semiconducting shielding layer; Restore metal shield, buffer, outer jacket. 12. A cable factory flexible joint prepared by the method of claim 11.

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