CN113956668B

CN113956668B - Ultrahigh heat-resistant silicone rubber and preparation method thereof

Info

Publication number: CN113956668B
Application number: CN202111320798.4A
Authority: CN
Inventors: 吴超波; 高红凯; 韩田琛
Original assignee: Nanchang University; Jiangxi Bluestar Xinghuo Silicone Co Ltd
Current assignee: Nanchang University; Jiangxi Bluestar Xinghuo Silicone Co Ltd
Priority date: 2021-11-09
Filing date: 2021-11-09
Publication date: 2023-04-07
Anticipated expiration: 2041-11-09
Also published as: CN113956668A

Abstract

The present application relates to a heat-resistant silicone rubber composition comprising methyl vinyl silicone rubber, and 0.8 to 2.3 parts by weight of polysilazane and 1.55 to 2.5 parts by weight of iron-doped titanium dioxide, based on 100 parts by weight of methyl vinyl silicone rubber. The composition can maintain substantially unchanged hardness at 250 ℃ over 72 hours or more and at 300 ℃ or more over 24 hours or more, and has a variation of > 43% in tensile strength and elongation at break.

Description

Ultrahigh heat-resistant silicone rubber and preparation method thereof

Technical Field

The application relates to an ultrahigh heat-resistant silicone rubber, a preparation method thereof and a product prepared from the ultrahigh heat-resistant silicone rubber.

Background

Silicone rubbers have long been used, and in particular, methyl vinyl silicone rubber (which is also called vinyl silicone rubber, and is copolymerized from dimethylsiloxane and a small amount of vinyl siloxane) has been widely used because of its excellent heat aging resistance and mechanical properties.

However, methyl vinyl silicone rubbers can generally only be used at temperatures below 200 ℃. For these silicone rubbers, although the use temperature can be raised by adding a heat-resistant agent (e.g., lanthanum oxide, cerium oxide, iron oxide, etc.), the temperature in long-term use (e.g., over 72 hours) is usually also lower than 250 ℃, and temperatures of 300 ℃ or higher can be reached only in the case of short-term use (e.g., within 24 hours). If further improvement in heat resistance is required, particularly if it is desired to use the silicone rubber for a long period of time at a temperature exceeding 250 c, for example 300 c or higher, only the specific phenyl-or fluorine-containing silicone rubber, which is very expensive, can be used at present. In addition to being costly, silicone rubbers containing phenyl groups are generally not processable well, and the compounds are prone to softening and sticking, for example, on the rolls during two-roll sulfur mixing. As for the fluorine-containing silicone rubber, the processability is not good, but the Mooney viscosity of the rubber material is too high in contrast to the phenyl-containing silicone rubber, the processing difficulty is high during the sulfur adding and mixing, and the fluorine-containing silicone rubber is not easy to be uniformly mixed with other auxiliary agents such as a vulcanizing agent and the like. These drawbacks all contribute to the limitations of the use of the phenyl-or fluorine-containing silicone rubber.

In order to improve the heat resistance of the methyl vinyl silicone rubber, some attempts have been made in the prior art.

For example, CN112341823A provides a silicone rubber compound based on methyl vinyl silicone rubber crude rubber, wherein the heat resistance of the silicone rubber is improved by adding rice hull ash precipitated silica, among other things.

CN108342085a discloses a silicon compound that is claimed to be usable at 350 ℃ for a long period of time. The silicon rubber compound comprises 80-100 parts of methyl vinyl silicone rubber crude rubber, 8-12 parts of amine aryl end group polysiloxane, 0.3-0.5 part of hexamethyldisilazane, 35-40 parts of white carbon black, 1-3 parts of methyl phenyl diethoxy silane and 3-7 parts of hydroxyl silicone oil.

CN108587454A discloses a high temperature resistant, anti-aging and high-transparency organic silica gel. The silicone gum is based on 100 parts of methyl vinyl silicone rubber, wherein 40-80 parts of n-butyl terminated poly-bis-phenyl methyl silazane is specially added. According to the invention, the product has good heat resistance due to the specific ratio of phenyl to methyl in the added n-butyl terminated poly-bis-phenyl-methyl silazane.

However, there is still a need to further improve the heat resistance of methyl vinyl silicone rubber, especially under long-term use (e.g. use times of more than 72 hours).

Disclosure of Invention

Accordingly, a first aspect of the present application relates to a heat resistant silicone rubber, in particular based on methyl vinyl silicone rubber, which can maintain substantially unchanged hardness (e.g. hardness change in the range of 0-2%, even 0-1%) and a change in tensile strength and elongation at break of > -43%, preferably > -38% or > -35% over a period of 72 hours or more (e.g. 96 hours or more) at 250 ℃ and 24 hours or more (e.g. 48 hours or 72 hours or more) at 300 ℃ or more.

Such a heat-resistant silicone rubber comprises methyl vinyl silicone rubber and contains 0.8 to 2.3 parts by weight, such as preferably 0.9 to 2.1 parts by weight, of polysilazane and 1.55 to 2.5 parts by weight, such as 1.6 to 2.4 parts by weight, of iron-doped titanium dioxide, based on 100 parts by weight of methyl vinyl silicone rubber.

The inventors of the present application have found that the object of the invention as described above can be achieved if specific parts by weight of polysilazane and iron-doped titanium dioxide as defined above are added (advantageously in a physically mixed manner) to a methyl vinyl silicone rubber raw rubber or matrix.

A further aspect of the present application relates to a method of improving the heat resistance of silicone rubber, in particular based on methyl vinyl silicone rubber, comprising adding 0.8-2.3 parts by weight, such as preferably 0.9-2.1 parts by weight, of polysilazane and 1.55-2.5 parts by weight, such as 1.6-2.4 parts by weight, of iron-doped titanium dioxide to 100 parts by weight of methyl vinyl silicone rubber in a silicone rubber matrix.

Still another aspect of the present application relates to articles made from such heat resistant silicone rubbers.

Finally, the application relates to the use of a combination of polysilazane and iron-doped titanium dioxide for improving the heat resistance of methyl vinyl silicone rubber.

"methyl vinyl silicone rubber", also known as vinyl silicone rubber, can be made by copolymerizing dimethyl siloxane with a small amount of vinyl siloxane, wherein the vinyl content is generally in the range of 0.01 to 7.0mol%, such as 0.03%, 0.05%, 0.08%, 0.14%, 0.18%, 0.22%, 1.0%, 3.0%, 5.0% vinyl content. In the present application, one kind of methyl vinyl silicone rubber or a mixture of a plurality of kinds of methyl vinyl silicone rubbers having different vinyl contents may be used as the rubber base of the heat-resistant silicone rubber.

The methyl vinyl silicone rubber suitable for use herein is a polysiloxane elastomer generally having a main chain represented by the following formula (I):

wherein x and y are selected such that the molecular weight of the methyl vinyl silicone rubber or the silicone elastomer is in the range of 30 to 100 ten thousand and x and y are as definedThe units may be arranged in any sequence (e.g., random, statistical, or block, etc.), and denotes linkages at both ends of the backbone. Both ends of the main chain may be respectively substituted with a silyl group having a vinyl group such as a dimethylvinylsilyl group (-Si (CH) ₃ ) ₂ Vinyl) or a silyl group with a methyl group, e.g. a trimethylsilyl group (-Si (CH) ₃ ) ₃ ) And (4) end capping.

In a preferred embodiment, the vinyl content of the methyl vinyl silicone rubber is in the range of 0.02 to 2.0mol%, preferably 0.03 to 1.0%.

In a preferred embodiment, the molecular weight of the methyl vinyl silicone rubber ranges from 50 to 80 ten thousand, preferably from 55 to 70 ten thousand. The molecular weight of the silicone rubber is measured here using infrared spectroscopy, for example with reference to the standard GBT 28610-2012.

Preferably, the heat resistant silicone rubber composition of the invention may comprise at least 80% by weight, preferably at least 90% by weight, more preferably at least 95% by weight or at least 98% by weight, especially 100% by weight, of methyl vinyl silicone rubber as the rubber or elastomer matrix in the composition. In other words, the heat-resistant silicone rubber composition of the invention is based on a methyl vinyl silicone rubber. In order to achieve heat resistance at higher temperatures, such as temperatures exceeding 250 ℃ or 300 ℃, phenyl-or fluorine-containing silicone rubbers, such as those having a Si-O-Si main chain and having fluoroalkyl and/or phenyl groups in side chains, and also polysiloxane compounds terminated with fluoroalkyl or phenyl groups, need not be added or may be added in very small amounts (such as not more than 5% by weight) to the methyl vinyl silicone rubber-based heat resistant silicone rubber according to the present invention. The fluorine-containing silicone rubber includes, for example, trifluoropropylmethylpolysiloxane. The phenyl-containing silicone rubber includes, for example, a polysiloxane containing a phenyl siloxane or methylphenyl siloxane unit in the main chain.

The polysilazane used in the heat-resistant silicone rubber composition of the present invention is a type of polymer having a main chain of-Si-N-. The backbone typically has hydrocarbyl substituents or hydrogens in the lateral direction. The polysilazanes of the invention are distinguished from simple silazane compounds or silazane monomeric compounds, the former havingAdvantageously having 5 or more than 5, such as 8 or more than 10, -Si-N-groups (e.g. -H) ₂ Si-NH-units or repeating units represented by the following structural formula (1).

In a preferred embodiment, the polysilazane has a structure represented by the following formula (1)

Wherein R1 and R2 are independently C1-C6 alkyl or C2-C6 alkenyl, such as methyl, ethyl, propyl, butyl, ethenyl or propenyl, etc.;

r3 is hydrogen or C1-C6 alkyl such as methyl, ethyl or propyl;

n is a number greater than or equal to 5, preferably greater than or equal to 10 or 15, for example from 10 to 30; and

* Represents a bond at both ends of the main chain.

The end-capping groups at both ends of the polysilazanes are well known to the person skilled in the art and, depending on the preparation method and starting materials, can be substituted, for example, by H, vinyl, hydroxy, methyl or NR ₂ -or SiR ₃ End-capping (where R represents H or a hydrocarbon group such as a hydrocarbon group having C1-C16 or C1-C12 or C1-C8, such as an alkyl group). The repeating units of the polysilazanes shown may be linear or cyclic.

In a preferred embodiment, the polysilazane may be selected from methyl, dimethyl polysilazane (CAS number 475645-84-2), polydimethylsilazane, methyl, methylvinyl polysilazane (CAS number 503590-70-3), perhydropolysilazane or its derivatives, and the like. Polysilazanes suitable for use in the present invention are themselves commercially available, for example as DURAZANE1800 from An Zhi.

The preparation of polysilazanes is known per se and can be obtained by small-molecule polymerization of silazane monomers. Suitable silazane monomer compounds are prepared by methods including the reaction of chlorosilanes with amines and the reaction of silazanes with butyllithium, by which either linear or cyclic silazanes are prepared. Alternatively, the polysilazane may be directly prepared by ammonolysis of a dialkyldihalosilane. The preparation of polysilazanes by ammonolysis can be referred to for example in US patent US6329487.

It has been found that the use of polysilazanes according to the invention leads to better heat resistance of the silicone rubber compared to conventional simple silazane compounds or monomers, in particular after 72 hours or more at 250 ℃ and 24 hours or more at 300 ℃, the initial mechanical properties remain good.

Iron-doped titanium dioxide must also be added to the heat-resistant silicone rubber composition of the present invention. The iron-doped titanium dioxide is a special structure formed by doping nano iron oxide with nano titanium dioxide, and is usually prepared in a powder form and used as a powder material. In the structure, part of iron ions in the iron oxide enter titanium dioxide crystal lattices as doping ions, so that a composite oxide of iron oxide coated titanium dioxide is formed.

The iron oxide is typically the dried product of iron hydroxide, which is chemically prepared. The titanium dioxide can be prepared from commercial titanium dioxide, titanyl sulfate or metatitanic acid. The molar ratio of iron to titanium in the iron-doped titanium dioxide is typically 1:99-4:96, e.g., about 2:98.

in this structure, both the iron oxide and the titanium oxide are uniformly mixed on a nanometer scale, which is distinguished from the simple physical blending of ordinary titanium dioxide and iron oxide. This is because the doping blending of nano-iron oxide and gas phase method nano-titanium dioxide is never interrupted from the initial raw materials of titanium tetrachloride, iron tetrachloride to the final finished product in the synthesis process. Such iron-doped titanium dioxide is commercially available, for example, as PF2 commercial product from Evonik.

The inventors of the present application have found that the use of iron-doped titanium dioxide in the silicone rubber system of the present invention provides better heat resistance than other heat resistant fillers commonly used, such as iron oxide, titanium oxide or physical mixtures of the two, especially during exposure to heat at 250 ℃ for 72 hours or more and at 300 ℃ for 24 hours or more.

In a preferred embodiment of the invention, the silicone rubber composition does not contain other heat-resistant metal oxides, such as iron oxide, titanium oxide or a physical blend of the two, in particular. If used, they are present in an amount of not more than 1 part by weight, preferably not more than 0.5 part by weight, more preferably not more than 0.1 part by weight, based on 100 parts by weight of the methyl vinyl silicone rubber.

Further, the heat-resistant silicone rubber according to the present invention may preferably contain white carbon in addition to the methyl vinyl silicone rubber, polysilazane, and iron-doped titanium dioxide as described above. In an advantageous embodiment, the white carbon is used in an amount of 38 to 45 parts by weight, such as 40 to 44 parts by weight, relative to 100 parts by weight of methyl vinyl silicone rubber.

White carbon black is a generic name for powdered products of amorphous silicic acid and silicates, including precipitated silica, fumed silica, ultrafine silica gel, and the like. In a preferred embodiment herein, the white carbon black is selected from fumed silica. The white carbon black may generally have, for example, a primary particle size of about 3 to 50 nanometers and an aggregate particle size of about 150 to 400 nanometers. The silica suitable for use in the present invention (e.g., the preferred fumed silica) can be a single silica or a mixture of a plurality of silicas having different BET specific surface areas. They preferably have a diameter of, for example, 120 to 300m ² BET specific surface area/g, preferably 150 to 250m ² BET specific surface area/g, e.g. 150, 200 or 250m ² BET specific surface area in g. The white carbon black suitable for use in the present invention may be hydrophilic or hydrophobic, preferably hydrophilic. In the invention, the white carbon black can play a role in improving the mechanical property of the silicone rubber.

The surface of white carbon generally has hydroxyl groups, which may make it unfavorable for dispersion to cause processability problems of silicone rubber. Therefore, in a preferred embodiment of the present application, a surface-modifying substance for white carbon black is added. These surface-modifying substances are generally added in an amount of from 8% to 25% by weight, based on the white carbon. The modifying substance is selected from, for example, a hydroxypolysiloxane, a silazane compound such as hexamethyldisilazane or hexaphenylcyclotrisilazane, an alkylalkoxysilane monomer compound such as dimethyldiethoxysilane and dimethyldimethoxysilane, and the like. Preferably, the hydroxyl polysiloxane is added in an amount of 8-16% by weight of the white carbon black; the silazane compound or the alkyl alkoxy silane monomer compound may be added in an amount of about 15-25% by weight of the white carbon.

The hydroxyl polysiloxane is sometimes also referred to as a hydroxyl silicone oil, and generally has a main chain as shown in the following formula (II).

Wherein a and b may each independently represent a number from 1 to 15, such as from 3 to 12, from 1 to 10 or from 5 to 9 and the two units having a and b may be arranged in any sequence (e.g. random, statistical or block etc.),

r1, R2, R3 and R4 are independently of each other selected from C _1-6 An alkyl group;

and a bond at both ends of the main chain.

The end-capping groups at both ends of the main chain depend on the production raw materials and can be determined by the skilled person, for example both ends of the main chain can be individually end-capped with, for example, hydroxyl groups.

Preferably, the hydroxyl polysiloxane is a hydroxyl terminated polydimethylsiloxane.

In addition to the above-described components, the heat-resistant silicone rubber of the present invention may further include the following additives: flame retardants such as ATH, pigments, other fillers such as quartz powder, electrically conductive fillers such as carbon nanotubes, thermally conductive fillers such as alumina, and the like. The total addition amount of these optionally added additives may be in the range of 0 to 100 parts by weight with respect to 100 parts by weight of the methyl vinyl silicone rubber. For example, 10 to 20 parts by weight of a flame retardant, 0.01 to 2 parts by weight of a pigment, 0 to 5 parts by weight of an electrically conductive filler, and/or 30 to 80 parts by weight of a thermally conductive filler may be used.

A second aspect of the present application relates to a method of improving the heat resistance of, in particular, a methyl vinyl silicone rubber-based silicone rubber, or a method of producing a methyl vinyl silicone rubber-based heat-resistant silicone rubber as described above. The method comprises the following steps: 0.8 to 2.3 parts by weight of polysilazane and 1.55 to 2.5 parts by weight of iron-doped titanium dioxide based on 100 parts by weight of methyl vinyl silicone rubber are added to the silicone rubber comprising the methyl vinyl silicone rubber.

Preferably, if white carbon black is used, the polysilazane and the iron-doped titanium dioxide are subsequently added after the white carbon black is added to the methyl vinyl silicone rubber and mixed uniformly.

Such additions include any mixing technique known in the art of silicone rubbers, and may be carried out, for example, in a kneader. The order of mixing or addition is not particularly limited as long as such mixing or addition facilitates the performance of the operation.

In an advantageous embodiment, the methylvinylsiloxane rubber can first be placed in a kneader, and subsequently at least part of the white carbon black and part or all of its modified substances can be added to the kneader. After being mixed evenly, the polysilazane and the iron-doped titanium dioxide are respectively added and mixed evenly. The combined materials may be subjected to elevated temperatures (e.g. elevated to 100-160 c) and vacuum (e.g. -0.05 to-0.1 MPa) before the polysilazane and iron-doped titanium dioxide are added. Preferably, the polysilazane and the iron-doped titanium dioxide may be added separately, for example after the polysilazane is added to the mixture and mixed for a period of time, the iron-doped titanium dioxide is added.

Still another aspect of the present application relates to articles made from such heat resistant silicone rubbers. Such articles include cables, particularly cables for new energy vehicles, seals, alloy molds, ovens, halogen lamp connectors, electric iron plugs and ignition coil jackets, and the like.

Examples

The present application is further described below with reference to examples. However, the present application is not limited to the following examples. In addition, the percentage data and the proportion of parts in the description of the present application are by weight unless explicitly stated otherwise.

Description of the raw materials

Preparation of Silicone rubber

The methyl vinyl silicone rubber mixtures of three different vinyl contents as shown in the above table were charged into the kneader as 100 parts by weight of raw rubber raw material. And (4) passivating the kneader by nitrogen. Then 12 parts by weight of white carbon black, 5 parts by weight of hydroxy silicone oil and possibly 1 part by weight of HMDZ are added into a kneader and mixed with the methyl vinyl silicone rubber for kneading, and after uniform mixing, the remaining 30 parts by weight of silicon dioxide are added into the kneader for 3 times and uniformly mixed. After all the silicon dioxide is uniformly mixed, gradually heating up, introducing nitrogen for protection in the whole process, heating up to 120 ℃, guan Danqi, starting to vacuumize, keeping for 1 hour, gradually heating up to 160 ℃ under the vacuum degree of-0.09 Mpa, then discharging vacuum, and introducing nitrogen. The resulting product was cooled to 50 ℃ and polysilazane and/or various additives shown in the table were added in the amounts shown in table 1 below and mixed for 20 minutes. Finally, the obtained rubber material is cooled to room temperature, discharged and filtered.

Performance testing

The silicone rubber prepared as described above was subsequently subjected to a performance test as follows:

hardness (shore a): testing in accordance with DIN ISO 48-4

Tensile strength: testing according to ISO 37 type 1

Elongation at break: testing according to ISO 37 type 1

Tear strength: testing was performed according to ASTM D624B

Wherein, before the silicone rubber is tested, the prepared sample is first subjected to a primary vulcanization at 170 ℃ for 10min and then to a secondary vulcanization at 200 ℃ for 4h, and then the hardness, tensile strength, elongation at break and tear strength values of the sample are measured in accordance with the standards as described above.

Thereafter, the samples were divided into two batches, one batch was aged at 250 ℃ for 72hrs and the other batch was aged at 300 ℃ for 24 hrs. The samples were then removed to measure their rate of change of hardness, tensile strength and elongation at break.

The change rate is a percentage value of the difference between the hardness, tensile strength and elongation at break before and after aging and the initial hardness, tensile strength and elongation at break before aging.

The results are shown in Table 2.

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As shown in tables 1 and 2, when the iron-doped titanium dioxide and polysilazane are added in the required ranges, the hardness and mechanical properties of the product such as tensile strength and elongation at break and the rate of change under long high-temperature load are optimum. If the iron-doped titanium dioxide is used in an amount of less than 1.55 parts by weight, poor heat resistance of the silicone rubber may result; on the other hand, if it is more than 2.5 parts by weight, the effect is not so much changed and is not remarkable, which leads to an increase in cost. As for polysilazane, when the amount thereof is less than 0.8 part by weight, a good heat-resistant effect is not obtained, which makes the heat resistance of the rubber compound insufficient; when the amount of polysilazane is more than 2.3 parts by weight, initial elongation at break and tear resistance of the product are poor although the rate of change after long-term aging at high temperature and heat resistance are good.

Claims

1. A heat-resistant silicone rubber composition comprising at least 80% by weight of methyl vinyl silicone rubber as a rubber or elastomer matrix in the composition, and comprising 0.8 to 2.3 parts by weight of polysilazane and 1.55 to 2.5 parts by weight of iron-doped titanium dioxide, based on 100 parts by weight of methyl vinyl silicone rubber;

wherein the polysilazane has a structure represented by the following formula (1):

wherein R1 and R2 are independently C1-C6 alkyl or C2-C6 alkenyl;

r3 is hydrogen or C1-C6 alkyl;

n is a number greater than or equal to 5; and

* Represents a bond at both ends of the main chain.

2. The heat-resistant silicone rubber composition according to claim 1, wherein the vinyl content of the methyl vinyl silicone rubber is in the range of 0.01 to 7.0 mol%.

3. The heat-resistant silicone rubber composition according to claim 1, wherein the vinyl content of the methyl vinyl silicone rubber is in the range of 0.02 to 2.0 mol%.

4. The heat-resistant silicone rubber composition according to claim 1, wherein the vinyl content of the methyl vinyl silicone rubber is in the range of 0.03 to 1.0 mol%.

5. The heat resistant silicone rubber composition according to any one of the preceding claims 1 to 4, characterized in that it comprises at least 90 wt.% of methyl vinyl silicone rubber as rubber or elastomer matrix in the composition.

6. The heat resistant silicone rubber composition according to any one of the preceding claims 1 to 4, characterized in that it comprises at least 95 wt.% of methyl vinyl silicone rubber as rubber or elastomer matrix in the composition.

7. The heat resistant silicone rubber composition according to any one of the preceding claims 1 to 4, characterized in that it comprises at least 98 wt.% of methyl vinyl silicone rubber as rubber or elastomer matrix in the composition.

8. The heat-resistant silicone rubber composition according to any one of the preceding claims 1 to 4, characterized in that it comprises 100% by weight of methyl vinyl silicone rubber as the rubber or elastomer matrix in the composition.

9. The heat-resistant silicone rubber composition according to any one of claims 1 to 4, characterized in that the heat-resistant silicone rubber composition comprises not more than 5 wt.% of a phenyl-or fluorine-containing silicone rubber.

10. The heat-resistant silicone rubber composition according to any one of claims 1 to 4, characterized in that the heat-resistant silicone rubber composition does not contain a phenyl-containing or fluorine-containing silicone rubber.

11. Heat-resistant silicone rubber composition according to claim 1, characterized in that R1, R2 are independently of one another methyl, ethyl, propyl, butyl, vinyl or propenyl.

12. The heat-resistant silicone rubber composition according to claim 1, wherein R3 is a methyl group, an ethyl group, or a propyl group.

13. The heat-resistant silicone rubber composition according to claim 1, characterized in that n is a number of 10 or more.

14. The heat-resistant silicone rubber composition according to claim 1, characterized in that n is a number of 15 or more.

15. The heat-resistant silicone rubber composition according to claim 1, characterized in that n is a number from 10 to 30.

16. The heat resistant silicone rubber composition according to any one of the preceding claims 1 to 4, characterized in that the polysilazane is selected from methyl having a CAS number of 475645-84-2, dimethyl polysilazane, polydimethylsilazane, methyl having a CAS number of 503590-70-3, methyl vinyl polysilazane, perhydropolysilazane or derivatives thereof.

17. The heat-resistant silicone rubber composition according to any one of claims 1 to 4, characterized in that the composition further comprises 38 to 45 parts by weight of white carbon black based on 100 parts by weight of the methyl vinyl silicone rubber.

18. The heat-resistant silicone rubber composition according to claim 17, characterized in that the white carbon black is fumed silica.

19. Heat-resistant silicone rubber composition according to claim 17, characterized in that white carbon black is hydrophilic fumed silica.

20. The heat-resistant silicone rubber composition according to claim 17, wherein the white carbon black is surface-modified with a surface-modifying substance, the surface-modifying substance being added in an amount of 8% to 25% based on the weight of the white carbon black.

21. The heat-resistant silicone rubber composition according to claim 20, wherein the modifying substance is selected from the group consisting of a hydroxyl polysiloxane, a silazane compound, and an alkylalkoxysilane monomer compound.

22. The heat-resistant silicone rubber composition according to claim 21, wherein the silazane compound is hexamethyldisilazane or hexaphenylcyclotrisilazane.

23. The heat-resistant silicone rubber composition according to claim 21, wherein the alkylalkoxysilane monomer compound is dimethyldiethoxysilane or dimethyldimethoxysilane.

24. A method of preparing the heat resistant silicone rubber composition according to any one of claims 1-23, comprising adding 0.8-2.3 parts by weight of polysilazane and 1.55-2.5 parts by weight of iron-doped titanium dioxide, based on 100 parts by weight of methyl vinyl silicone rubber, to a silicone rubber matrix comprising methyl vinyl silicone rubber.

25. The method according to claim 24, characterized in that white carbon black is also added and after adding white carbon black to the methyl vinyl silicone rubber and mixing homogeneously, polysilazane and iron-doped titanium dioxide are subsequently added.

26. An article made from the heat resistant silicone rubber composition according to any one of claims 1-23.

27. The article of claim 26 comprising cables, seals, alloy molds, ovens, halogen lamp connectors, electric iron plugs and ignition coil sheaths.

28. The article of claim 27, wherein the cable is a cable for a new energy automobile.

29. Use of a combination of polysilazane and iron-doped titanium dioxide for improving the heat resistance of a methyl vinyl silicone rubber, wherein 0.8 to 2.3 parts by weight of polysilazane and 1.55 to 2.5 parts by weight of iron-doped titanium dioxide based on 100 parts by weight of methyl vinyl silicone rubber are added to a silicone rubber matrix comprising methyl vinyl silicone rubber;

wherein the silicone rubber matrix comprises at least 80% by weight of a methyl vinyl silicone rubber and the polysilazane has a structure represented by the following formula (1):

wherein R1 and R2 are independently C1-C6 alkyl or C2-C6 alkenyl;

r3 is hydrogen or C1-C6 alkyl;

n is a number greater than or equal to 5; and

* Represents a bond at both ends of the main chain.