WO2013153501A1

WO2013153501A1 - Silicone rubber sealing glue used in medium and high voltage cable accessories and cable accessories

Info

Publication number: WO2013153501A1
Application number: PCT/IB2013/052794
Authority: WO
Inventors: Yugang LI; Peng Li; Lizhang Yang
Original assignee: Tyco Electronics Shanghai Co Ltd; Tyco Electronics UK Ltd
Current assignee: Tyco Electronics Shanghai Co Ltd; Tyco Electronics UK Ltd
Priority date: 2012-04-09
Filing date: 2013-04-08
Publication date: 2013-10-17
Anticipated expiration: 2014-10-09
Also published as: CN103361022A; CN103361022B

Description

SILICONE RUBBER SEALING GLUE USED IN MEDIUM

AND HIGH VOLTAGE CABLE ACCESSORIES AND CABLE ACCESSORIES

TECHNICAL FIELD

The present invention relates to power technical field. More particularly, it relates to silicone rubber sealing glue used in medium and high voltage cable accessories and cable accessories.

BACKGROUND OF THE INVENTION

Cable terminations and intermediate joints are important components in power transmission and transformation cable lines. The quality of connection between cable joints directly affects the reliability of the power transmission cable lines, and correspondingly the security and operation stability of the whole power transmission lines.

There are a variety of ways to achieve the protection of the cable joints in prior arts. For example, Chinese Patent ZL85109479.1 provides a cable accessory formed by a cable sealing glue in conjunction with a cold shrink sleeve to protect cable joints. The cable sealing glue may be used in conjunction with the cold shrink sleeve in two ways. One way is to first wind the sealing glue and filling glue onto the cable joint, then install the rubber body of the cold shrink sleeve to the outside of the sealing glue, filling glue and the cable insulation. This approach is complicated in installation, and has relatively high installing operation requirements. The other way is to prefabricate integrally the cable sealing glue and cold shrink sleeve. The sealing glue is filled in between the rubber body and the support tube of the cold shrink sleeve, and only the support tube needs to be removed at the time of installation. By this way the rubber body and the sealing glue is kept at the cable joint. This method is easy in installation, and has relatively lower installation requirements. However, cable accessories installed using the latter method has relatively poor weather resistance. After long storage and use, the mechanical strength of the rubber body of the shrink sleeve declines, and the rubber body becomes fragile and therefore is unable to protect the cable joint effectively.

SUMMARY OF THE INVENTION In prior arts, performance requirements are high for cable accessory with integral prefabrication of cable sealing glue and cold shrink sleeve. Firstly, the cable sealing glue is prefabricated between the rubber body of the cold shrink sleeve and the helically coiled support tube, which is subject to the contraction force of the rubber body after expansion. However sealing glue is required not to penetrate into the support tube under such contraction force during storage period (usually within three years), nor become dry or aging to lose their stickiness. Secondly, after cable accessories are installed to the cable joint, the sealing glue is still required to have certain plasticity value for filling the gaps at the cable joint and proofing water vapor and air in order to protect the cable joint. Thirdly, when installing the cable accessory and removing the support tube, the cable sealing glue needs to be adhered to the rubber body, and shall not move or break due to removal of the support tube, i.e. the adhesive force between the cable sealing glue and the support tube must be less than the adhesive force between the cable sealing glue and the rubber body as well as the sealing glue's own adhesive force. Fourthly, under low temperature conditions, even as low as minus 30 degrees, the cable sealing glue shall still maintain certain plasticity, and deformability and not brittle. Besides, the components of the cable sealing glue shall not penetrate into the rubber body and the support tube to affect the performance of the rubber body or the support tube.

The inventors discovered through repeated experiments, to meet the above performance requirements, the existing sealing glue of the cable accessory usually adds 10% (weight ratio) silicone oil (i.e. polyorganosiloxane) with a relatively small molecular weight and a relatively low viscosity. After long-term use, such silicone oil with a relatively small molecular weight will penetrate to the rubber body from the cable sealing glue and exude from outside of the rubber body. This will lead to a decline in the mechanical strength of the rubber body, thereby affecting the reliability of the cable accessory.

Based on the above analysis, it is desirable to provide a cable sealing glue using in the protection of the cable accessory with good weather resistance and reliability.

To solve one or more of the above problems, silicone rubber sealing glue used in medium and high voltage cable accessories is provided according to one aspect of the present invention, comprising a) a first siloxane polymer containing a repeating unit represented by Formula (I): RaSiO(4-_a)/2, wherein group R is a substituted or unsubstituted group containing 1 to 20 carbon atoms, a is 0, 1 , 2 or 3, wherein the number-average molecular weight of the first siloxane polymer is 150000 to 900000 g/mol; b) a second siloxane polymer containing a unit represented by Formula (I), wherein kinematic viscosity of the second siloxane polymer is 5000 est to lOOMcst (100 million centistrok); and c) filler; wherein the filler accounts for more than 10% of the sealing glue in weight.

The present invention selects silicone polymers with relatively large molecular weights to adjust the plasticity value of the sealing glue. But because polymers have dispersion characteristics, silicone polymers with low molecular weights and small weight percentages are preferred. Pure silicone polymer of 5000cst and above will still swell silicone rubber body to different extents usually. But after blending with the filler, under aging test conditions, the swelling of the silicone oil to the rubber body is not observed. It is understood that the filler has the function of changing the viscosity of the sealing glue. As a result, if a small amount of silicone oil of less than 5000cst is added to the sealing glue, combined with appropriate filler, the silicone oil with a small molecular weight can still be made not to penetrate into the rubber body.

Optionally, silicone polymers with the kinematic viscosity of lower than 5000 est in the sealing glue account for less than 5% of the sealing glue in weight.

Optionally, silicone polymers with the kinematic viscosity of lower than 5000 est in the sealing glue account for less than 2% of the sealing glue in weight.

Optionally, the filler accounts for more than 20% of the sealing glue in weight. Optionally, the filler accounts for more than 40% of the sealing glue in weight.

Optionally, the kinematic viscosity of the second siloxane polymer is from lOOOOcst to 20000cst.

Optionally, the number-average molecular weight of the first siloxane polymer is from 600000 to 800000g/mol.

Optionally, the group R is selected from one or more of the following materials: alkyl halide, alkyl containing 1 to 8 carbon atoms, unsaturated group containing 2 to 8 carbon atoms or phenyl.

Optionally, the filler is selected from one or more of the following materials: fumed silica or precipitated silica, diatomaceous earth, calcium silicate, zirconium silicate, zeolites, powdered metal oxides, barium silicate, barium sulfate, calcium carbonate, calcium sulfate, polytetrafluoroethylene, hydrous metal oxides, quartz powder, organic silicone rosin powder or fiber.

Optionally, the filler is selected from one or more of the following materials: aluminium hydroxide, fumed silica or precipitated silica. Optionally, the weight ratio of the first siloxane polymer to the filler is from 20: 100 to 700: 100.

Optionally, the weight ratio of the first siloxane polymer to the filler is from 40: 100 to 300: 100.

Optionally, the weight ratio of the second siloxane polymer to the first siloxane polymer is from 0.05: 100 to 100: 100.

Optionally, the weight ratio of the second siloxane polymer to the first siloxane polymer is from 0.5: 100 to 30: 100.

Optionally, the plasticity value of the sealing glue is not less than 300, wherein the plasticity value of the sealing glue is tested based on GB/T 12828-2006 standards.

Optionally, the plasticity value of the sealing glue is from 350 to 750.

Optionally, the plasticity value of the sealing glue is from 450 to 550.

According to another aspect of the present invention, a cable accessory is also provided, including the rubber body, the support tube, and the sealing glue according to the previous aspects, wherein the sealing glue is filled in between the rubber body and the support tube, and the adhesive force between the sealing glue and the support tube is smaller than the adhesive force between the sealing glue and the rubber body as well as the sealing glue's own adhesive force.

Optionally, the rubber body is prepared by catalyzed crosslinking with silicone rubber platinum compounds, the sealing glue is prepared by the first siloxane polymer containing unsaturated groups. Traces of platinum compounds in the rubber body can catalyze the crosslinking of the sealing glue contacted with the rubber body in long-term storage and usage. In this way, the sealing glue has a gradient structure, i.e. having a crosslinked structure near the rubber body, and gradually becoming a non-crosslinked structure away from the rubber body. The sealing glue with such a gradient structure can be reduced by one contact surface, thereby improving sealing performance.

Compared with prior arts, the second siloxane polymer molecule used in the sealing glue of the present invention is relatively big and is difficult to penetrate into the rubber body thereby exude from it. Therefore, performance of the rubber body, such as its mechanical properties and weather resistance, is not easily affected by the sealing glue, thereby prolonging the life of the rubber body and stabilizing the quality of protection for the cable headend.

The above and other features of the present invention will be clearly illustrated in the example sections below. BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features of the present invention will be more apparent through the following detailed description of the illustrated examples in conjunction with the appended drawings. The same or similar labels denote the same or similar parts in the appended drawings of the present invention.

Figure 1 illustrates cable accessory 100 according to an example of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

In the following specific description of the examplary embodiments, the attached drawings constituting part of the present invention will be referred to. The attacned drawings illustrate by way of example the particular examples which are able to achieve the present invention. The exemplary embodiments do not aim to exhaust all the examples of the present invention. It is understood that, under the premise of not departing from the scope of the present invention, other embodiments can be utilized and structural or logical changes can also be made. Therefore, the following specific description is not limiting, and the scope of the present invention is defined by the appended claims.

Figure 1 illustrates the cable accessory 100 of an example according to the present invention. The cable accessory 100 can be used for the protection of the cable terminal at the cable joints of medium and high voltage (e.g. lOkV) cable lines.

As shown in Figure 1, the cable accessory 100 includes the rubber body 101, the support tube 103 and the sealing glue 105, wherein the sealing glue 105 is filled in between the rubber body 101 and the support tube 103.

The support tube 103 of the cable accessory 100 is a hollow tubular, while the rubber body 101 is wrapped outside the support tube 103 and the sealing glue 105. Generally speaking, the diameter of the support tube 103 is larger than the diameter of the rubber body 101 in an expanded state, to make the rubber body 101 propped up by the support tube 103 and in an expanded state. When installing the cable accessory 100, the cable terminal at the cable joint is accommodated into the support tube 103. Thereafter, the support tube 103 is removed, while the rubber body 101 contracts correspondingly and compresses the sealing glue 105, making it bond closely to the cable joint. Specifically, the rubber body 101 can contain silicone rubber, for example, dimethyl silicone rubber, methyl vinyl silicone rubber, methyl phenyl vinyl silicone rubber, silicone fluoride, nitrile silicone rubber or the like. Silicone rubber has excellent properties of heat resistance, cold resistance, insulation property, ozone resistance, resistance to natural weather etc., and is particularly suitable for using as a protective portion of the cable joint. Preferably, the rubber body 101 is prepared by catalyzed crosslinking with silicone rubber platinum compounds.

The support tube 103 can contain polyolefm, such as polyethylene, polypropylene or blend materials thereof etc. Polyolefm is a good plastic material, and is able to be made into different shapes according to different practical application situations to meet the requirements during installation of the cable accessory 100. In practical applications, the support tube 103 can be made through helical coiling. When installing the cable accessory 100, the support tube 103 will be removed. Compared with the rubber body 101, the adhesive force between the support tube 103 employing polyolefm and the cable sealing glue 105 is less than the adhesive force between the rubber body 101 and the sealing glue 105 as well as the sealing glue 105's own adhesive force. This prevents the sealing glue 105 from being taken away or moved by the support tube 103 when installed, which results in the loss or broken of the sealing glue 105. Wherein, adhesive force denotes the bonding force between the molecules on the interface of the bonder and the object being bonded. The adhesive force can be measured with reference to the following test method: after pressing the sealing glue between the two planes of the rubber body and the support bar for a period of time, separate them vertically. If the sealing glue and the rubber body are attached together, the adhesive force between the sealing glue and the rubber body is greater than the adhesive force between the sealing glue and the support bar. In the present invention, the adhesive force of the sealing glue within itself shall also be greater than the adhesive force between it and the support bar, i.e. in the above test it cannot be partially attached to the rubber body while partially attached to the plane of the support bar.

The sealing glue 105 comprises:

a) a first siloxane polymer containing a repeating unit represented by Formula (I): RaSiO(4-a)/2, wherein group R is a substituted or unsubstituted group containing 1 to 20 carbon atoms, a is 0, 1, 2 or 3, wherein the number-average molecular weight of the first siloxane polymer is from 150000 to 900000 g/mol;

b) a second siloxane polymer containing a unit represented by Formula (I), wherein kinematic viscosity of the second siloxane polymer is from 5000 est to lOOMcst at 25 degrees Celsius; and

c) filler; wherein the filler accounts for more than 10% of sealing glue 105 in weight. Preferably, the fillers account for more than 20% of the sealing glue in weight; more preferably, the fillers account for more than 40% of the sealing glue in weight.

The kinematic viscosity refers to the ratio of the dynamic viscosity of fluid to density p of the fluid under the same temperature. GB/T265-1988 standards can be referred to for testing method of the kinematic viscosity. The kinematic viscosities in the current text are all measured at 25 degrees Celsius. In addition, the number-average molecular weight means the average molecular weight calculated according to the number of molecules.

The first siloxane polymer in the sealing glue 105 has good electrical insulation properties. After mixed up with the filler, it is able to ensure the sealing glue 105 possess certain degree of hardness and plasticity value, so as to meet with the requirements of non- penetration into the support tube slit and protection of the cable headend. However, the kinematic viscosity of the second siloxane polymer in the sealing glue 105 is relatively small; thus, it can improve the plasticity value of the sealing glue 105 to meet with the requirements for the installation and operatinal use of the cable accessory 100. It is understood that, in practical applications, the number-average molecular weight of the second siloxane polymer is generally less than the number-average molecular weight of the first siloxane polymer. In some examples, the number-average molecular weight of the first siloxane polymer is from 600000 to 800000g/mol.

Compared with the sealing glue in prior arts, the second siloxane polymer molecule used in the sealing glue 105 is relatively big, and the second siloxane polymer is difficult to penetrate into the rubber body 101 and exude from the rubber body 101 after installation. Therefore, the performance of the rubber body 101, such as its mechanical properties and weather resistance, is not easily affected by the sealing glue 105, and can thus prolong the life of the rubber body 101 and stabilize the quality of protection for the cable headend. In some examples, the kinematic viscosity of the second siloxane polymer is from lOOOOcst to 20000cst.

In some examples, group R is selected from one or more of the following materials: alkyl halide or alkyl containing 1 to 8 carbon atoms. Alkyl halide is for example chloralkane or hydrofluoroalkane; while alkyl containing 1 to 8 carbon atoms is for example methyl or ethyl. In other examples, group R is selected from unsaturated group containing 2 to 8 carbon atoms or phenyl. Unsaturated group containing 2 to 8 carbon atoms is for example vinyl. Preferably, the sealing glue 105 is prepared by the first siloxane polymer containing unsaturated groups, and the rubber body 101 is prepated by catalyzed crosslinking with silicone rubber platinum compounds. The platinum compounds in the rubber body 101 can catalyze the crosslinking of the sealing glue 105 contacted with the rubber body 101 in long- term storage and usage. In this way, the sealing glue 105 transfers to a gradient structure, i.e. having a crosslinked structure near the rubber body 101, and gradually becoming a non- crosslinked structure away from the rubber body. The sealing glue 101 with such a gradient structure can be reduced by one contact surface, thereby improving the sealing performance.

The filler contained in the sealing glue 105 is selected from one or more of the following materials: fumed silica or precipitated silica, diatomaceous earth, calcium silicate, zirconium silicate, zeolites, powdered metal oxides (e.g. alumina, ferric oxide or zinc oxide etc.), barium silicate, barium sulfate, calcium carbonate, calcium sulfate, polytetrafluoroethylene, hydrous metal oxides (e.g. aluminum hydroxide, magnesium hydroxide or zinc hydroxide etc.), quartz powder, organic silicone rosin powder or fiber (e.g. glass fibers carbon fibers or synthetic polymer fibers etc.). Preferably, the filler is selected from one or more of the following materials: aluminium hydroxide, fumed silica or precipitated silica.

As mentioned above, the plasticity value of sealing glue 105 has an important impact on performance of the cable accessory 100. If the plasticity value of the sealing glue 105 is too low, then the sealing glue 105 is easily deformed, and will penetrate from slits or side portion of the support tube 103. In some examples, the plasticity value of the sealing glue 105 is no less than 300; preferably, the plasticity value of the sealing glue 105 is in the range of 350 to 750; more preferably, the plasticity value of the sealing glue 105 is in the range of 450 to 550, wherein the plasticity value of the sealing glue 105 is tested based on GB/T 12828-2006 standards.

It is understood that the ratio of different components in the sealing glue 105 will also affect the elasticity value of the sealing glue 105. The elasticity value of the sealing glue 105 can be adjusted by adding fillers with different ratios. Optionally, the weight ratio of the first siloxane polymer to the filler is from 20: 100 to 700: 100. Preferably, the weight ratio of the first siloxane polymer to the filler is from 40: 100 to 300: 100. Optionally, the weight ratio of the second siloxane polymer to the first siloxane polymer is from 0.05: 100 to 100: 100. Preferably, the weight ratio of the second siloxane polymer to the first siloxane polymer is from 0.5: 100 to 30: 100.

In some examples, the sealing glue 105 can also contain other types of additives, such as pigments, stabilizers, or the like, wherein the stabilizer comprises metal oxide in transition state or fatty acid salts, such as iron octylate, cerium octylate, propoxy titanium compound, transition metal silane acid salt, iron oxide, titanium oxide, cerium oxide or cerium hydroxide.

In the cable accessory 100 shown in Figure 1 , the rubber body 101 also contains a stress cone 107. After installing the cable accessory 100 onto the cable, the stress cone 107 is overlapped to the fracture of the semiconductor layer outside the cable. It enables the power lines originally concentrated on the fracture of the semiconductor layer to distribute uniformly along the geometry of the stress cone 107, thereby improves the electric field distribution, reduces the possibility of generating corona and ensures the operation life of the cable. It is understood that in other examples, the cable accessory 100 may also contain a stress tube or other structures suitable for improving the distribution of electric field at the fracture of the semiconductor layer of the cable.

In practical applications, the sealing glue 105 can be prepared by kneading or other methods suitable for mixing solid powder and liquid. In some examples, different weight ratios of the first siloxane compound, the second siloxane compound and the filler can be added to the internal mixer, and these materials are kneaded to obtain the sealing glue 105. Optionally, the the kneading step is carried out in the internal mixer of 25 degrees Celsius to 150 degrees Celsius, and the kneading time is from 1 to 2 hours.

Example 1

Select polydimethylsiloxane with a number-average molecular weight of about 600000 g/mol and a kinematic viscosity of about 10000 est as the second siloxane polymer, and select fumed silica and aluminum hydroxide powder as the filler.

Add 100 parts of the first siloxane polymer into the 150 degrees Celsius internal mixer for kneading, and add 220 parts of 600 mesh aluminum hydroxide powder and 20 parts of fumed silica as well as 2 parts of the second siloxane polymers and knead for 1 hour, cooling to sheets. Thereafter, the strip-shaped sealing glue is extruded through the double- stick open mill, calenderstack or extruder. The strip-shaped sealing glue can be further cut to sizes to fit with the rubber body and the support tube of the cable accessory for usage.

The plasticity value of the sealing glue obtained by the above method is tested based on GB/T 12828-2006 standards, and the plasticity value of this sealing glue is 560. In this standard, the plasticity value is defined as: under specified temperature and time and after withstanding a pressure of 49 N ,a result multiplied by 100 of the height value represented by millimeter of a cylindrical specimen with an initial height of 10 mm and a volume of 2 cm². The temperature and time of the assay of the present invention is 70 degrees Celsius and 3 minutes.

Further, assemble the sealing glue, the support tube and the rubber body into the cable accessory, and conduct an aging test to this cable accessory. The test conditions of the aging test are: the cable accessory is placed under the environmental condition of a temperature of 60 degrees Celsius and a humidity of 10% to 50% for 10 weeks. After the aging test ended, the support tube of the cable accessory is removed, and the outer surface of the rubber body of the cable accessory is visually observed. The outer surface is relatively flat and no oily droplets or likewise liquid is found exuded; and there is no exudation of the sealing glue also inside the support tube. Simultaneously as a control, the aging test is also conducted on the cable accessory in prior arts. After the test ended, the support tube of the cable accessory is removed, and exudation of large quantities of oily substance and oil contaminates are visually observed on the outer surface of the rubber body of the cable accessory in prior arts. In addition, after the aging test, the support tube is removed from inside of the rubber body to observe whether there is sealing glue penetrating into the slit of the support tube. The surface of the support tube is clean and there is also no sealing glue residue in the slit through visual observation. This indicates that the adhesive force between the sealing glue and the support tube is smaller than the adhesive force between the sealing glue and the rubber body, and installation requirements of the cable accessory can be satisfied.

In addition, the cable accessory is installed to the cable joint, and a group of tests is conducted for electrical safety performance of the cable and its connectors. The group of tests includes immersion thermal cycling test and AC voltage withstand test, wherein the experimental conditions of the immersion thermal cycling test are: immersion in water for lm, conductor temperature of 95 to 100 degrees Celsius, and 8 hours per cycle wherein heating consists 5 hours and cooling consists 3 hours; the experimental conditions of the AC voltage withstand test are: a 39kV test voltage, test time of 5 minutes; and the experimental result is that the cable accessory does not breakdown or flashover, which complies with the technical requirements of the experiment. The experimental results show that after completion of 10 water immersion heating/cooling cycles, electrical breakdown problem of the cable accessory does not occur. It can be seen that the sealing glue and the cable accessory employing such sealing glue can provide good protection for the cable joint. This also increases safety during use of cables. Example 2

Select number-average molecular weight to be about 600000 g/mol and kinematic viscosity to be 10000 est, and select fumed silica and aluminum hydroxide powder as the filler.

Add 100 parts of the first siloxane polymer to the 150 degrees Celsius internal mixer to knead, and add 220 parts of 600 mesh aluminum hydroxide powder and 15 parts of fumed silica as well as 2 parts of the second siloxane polymers and knead for 1 hour, cooling to sheets. Thereafter, the strip-shaped sealing glue is extruded through the double-stick open mill, calenderstack or extruder. The strip-shaped sealing glue can be further cut to sizes to fit with the rubber body and the support tube of the cable accessory for usage.

The plasticity value of the sealing glue obtained by the above method is tested based on GB/T 12828-2006 standards, and the tested plasticity value of this sealing glue is 400.

Further, assemble the sealing glue, the support tube and the rubber body into the cable accessory, and conduct an aging test to this cable accessory. After the aging test ended, the support tube of the cable accessory is removed, and the outer surface of the rubber body of the cable accessory is visually observed. No oily droplets or likewise liquid is found exuded; and there is no exudation of the sealing glue also inside the support tube.

In addition, the cable accessory is installed to the cable joint, and a group of immersion thermal cycling test and AC voltage withstand test is conducted for the electrical safety performance of the cable and its connectors. The cable accessory also passes the immersion thermal cycling test and AC voltage withstand test.

Example 3

Select number-average molecular weight to be about 400000 g/mol and kinematic viscosity to be 10000 est, and select fumed silica as the filler.

Add 125 parts of the first siloxane polymer to the 150 degrees Celsius internal mixer to knead, and add 25 parts of fumed silica as well as 5 parts of the second siloxane polymers and knead for 2 hours, cooling to sheets. Thereafter, the strip-shaped sealing glue is extruded through the double-stick open mill, calenderstack or extruder. The strip-shaped sealing glue can be further cut to sizes to fit with the rubber body and the support tubeof the cable accessory for usage.

Assemble the sealing glue, the support tube and the rubber body into the cable accessory, and conduct an aging test to this cable accessory. After the aging test ended, the support tube of the cable accessory is removed, and the outer surface of the rubber body of the cable accessory is visually observed. No oily droplets or likewise liquid is found exuded; and there is no exudation of the sealing glue also inside the support tube.

Example 4

Select number-average molecular weight to be about 400000 g/mol and a kinematic viscosity to be 10000 est, and select precipitated silica as the filler.

Add 125 parts of the first siloxane polymer to the 150 degrees Celsius internal mixer to knead, and add 45 parts of precipitated silica as well as 1 part of the second siloxane polymers and knead for 1 hour, cooling to sheets. Thereafter, the strip-shaped sealing glue is extruded through the double-stick open mill, calenderstack or extruder. The strip-shaped sealing glue can be further cut to sizes to fit with the rubber body and the support tube of the cable accessory for usage.

Example 5

Select number-average molecular weight to be about 400000 g/mol and kinematic viscosity to be 10000 est, and select fumed silica and aluminum hydroxide powder as the filler.

Add 125 parts of the first siloxane polymer to the 150 degrees Celsius internal mixer to knead, and add 10 parts of fumed silica and 280 parts of aluminum hydroxide powder as well as 0.5 part of the second siloxane polymers and knead for 1 hour, cooling to sheets. Thereafter, the strip-shaped sealing glue is extruded through the double-stick open mill, calenderstack or extruder. The strip-shaped sealing glue can be further cut to sizes to fit with the rubber body and the support tube of the cable accessory for usage.

Assemble the sealing glue, the support tube and the rubber body into the cable accessory, and conduct an aging test to this cable accessory. After the aging test ended, the support tube of the cable accessory is removed, and the outer surface of the rubber body of the cable accessory is visually observed, No oily droplets or likewise liquid is found exuded; and there is no exudation of the sealing glue also inside the support tube. Example 6

Select number-average molecular weight to be about 400000 g/mol and kinematic viscosity to be 10000 est, and select polytetrafluoroethylene as the filler.

Add 125 parts of the first siloxane polymer to the 150 degrees Celsius internal mixer to knead, and add 60 parts of the polytetrafluoroethylene as well as 0.5 part of the polydimethylsiloxane and knead for 2 hours, cooling to sheets. Thereafter, the strip-shaped sealing glue is extruded through the double-stick open mill, calenderstack or extruder. The strip-shaped sealing glue can be further cut to sizes to fit with the rubber body and the support tube of the cable accessory for usage.

It can be seen that, compared with prior arts, the second siloxane polymer molecule used in the sealing glue of the present invention is relatively big and is difficult to penetrate into the rubber body thereby exuded from it. Therefore, performance of the rubber body, such as its mechanical properties and weather resistance, is not easily affected by the sealing glue, thereby prolonging the life of the rubber body and stabilizing the quality of protection for the cable headend.

Although the present invention is illustrated and described in detail in the appended drawings and the foregoing description, it should be considered that such illustration and description is illustrative and exemplary, rather than restrictive; the present invention is not limited to the above embodiments.

Those ordinarily skilled in the art can understand and implement other changes of the disclosed embodiments through studying the description, the disclosure and the appended drawings and the appended claims. In the claims, the wording "comprising" does not exclude other elements and steps, and the wording "an" does not exclude a plurality. In practical applications of the invention, a part may perform functions of multiple technical features recited in the claims. Any reference labels in the appended drawings in the claims shall not be construed as limiting the scope.

Claims

Claims:

1. Silicone rubber sealing glue used in medium and high voltage cable accessories, characterized in that it comprises:

a first siloxane polymer containing a repeating unit represented by Formula (I):

RaSiO(4-_a)/2, wherein group R is a substituted or unsubstituted group containing 1 to 20 carbon atoms, a is 0, 1, 2 or 3, and wherein number-average molecular weight of said first siloxane polymer is 150000 to 900000g/mol;

a second siloxane polymer containing a unit represented by the Formula (I), wherein kinematic viscosity of said second siloxane polymer is from 5000cst to lOOMcst; and filler;

wherein said filler accounts for more than 10% of said sealing glue in weight.

2. The sealing glue according to claim 1, characterized in that said filler accounts for more than 20% of said sealing glue in weight.

3. The sealing glue according to claim 2, characterized in that said filler accounts for more than 40% of said sealing glue in weight. 4. The sealing glue according to claim 1, characterized in that siloxane polymer contained in said sealing glue with kinematic viscosity lower than 5000cst accounts for less than 10%) of said sealing glue in weight.

5. The sealing glue according to claim 4, characterized in that said siloxane polymer contained in said sealing glue with kinematic viscosity lower than 5000cst accounts for less than 5%> of said sealing glue in weight.

6. The sealing glue according to claim 5, characterized in that said siloxane polymer contained in said sealing glue with kinematic viscosity lower than 5000cst accounts for less than 2%> of said sealing glue in weight.

7. The sealing glue according to claim 1, characterized in that the kinematic viscosity of said second siloxane polymer is from lOOOOcst to 20000cst. 8. The sealing glue according to claim 1, characterized in that the number-average molecular weight of said first siloxane polymer is from 600000 to 800000g/mol.

The sealing glue according to claim 1 , characterized in that said group R is selected one or more of the following materials: alkyl halide, alkyl containing 1 to 8 carbon atoms, unsaturated group containing 2 to 8 carbon atoms or phenyl.

10. The sealing glue according to claim 1, characterized in that said filler comprises one or more of the following materials: fumed silica or precipitated silica, diatomaceous earth, calcium silicate, zirconium silicate, zeolites, powdered metal oxides, barium silicate, barium sulfate, calcium carbonate, calcium sulfate, polytetrafluoroethylene, hydrous metal oxides, quartz powder, organic silicone rosin powder or fiber.

11. The sealing glue according to claim 10, characterized in that said filler is selected from one or more of the following materials: aluminium hydroxide, fumed silica or precipitated silica.

12. The sealing glue according to claim 1, characterized in that the weight ratio of said first siloxane polymer to said filler is from 20: 100 to 700: 100.

13. The sealing glue according to claim 12, characterized in that the weight ratio of said first siloxane polymer to said filler is from 40: 100 to 300: 100.

14. The sealing glue according to claim 1, characterized in that the weight ratio of said second siloxane polymer to said first siloxane polymer is from 0.05 :100 to 100: 100.

15. The sealing glue according to claim 14, characterized in that the weight ratio of said second siloxane polymer to said first siloxane polymer is from 0.5 :100 to 30: 100. 16. The sealing glue according to claim 1, characterized in that the plasticity value of said sealing glue is not less than 300, wherein said plasticity value of said sealing glue is tested based on GB/T 12828-2006 standards.

17. The sealing glue according to claim 16, characterized in that the plasticity value of said sealing glue is from 350 to 750.

18. The sealing glue according to claim 17, characterized in that the plasticity value of said sealing glue is from 450 to 550. 19. A cable accessory, characterized in that it comprises a rubber body, a support tube, and the sealing glue according to any one of claims 1 to 18, wherein said sealing glue is filled between said rubber body and said support tube, and adhesive force between said sealing glue and said support tube is smaller than that between said sealing glue and said rubber body as well as said sealing glue's own adhesive force.

20. The cable accessory according to claim 19, characterized in that said rubber body prepared by catalyzed cross-linking with silicone rubber platinum compounds, and said sealing glue is prepared by a first siloxane polymer containing unsaturated groups.