Ceramifiable silicone rubber with gradient structure and preparation method and application thereof

Abstract

The application discloses a kind of ceramicized silicone rubber with gradient structure and its preparation method and application, it is related to the technical field of silicone rubber composite material, the ceramicized silicone rubber includes silicone rubber and porcelain filler, the content of porcelain filler is gradient distribution along the thickness direction of silicone rubber;Under flame impact, the ceramicized silicone rubber described in the application forms the gradient structure that porcelainizing strength gradually reduces from fire surface to backfire surface, the hard ceramic shell of this structure surface can block the impact of external flame;After internal silicone rubber absorbs heat and is heated and decomposed, porous structure with weak porcelainizing strength and no strength is formed, this special porous structure can isolate the transmission of heat, under the continuous impact of 1200 DEG C flame temperature, backfire surface can still maintain the partial softness of silicone rubber within 30min.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of silicone rubber composite materials, in particular to a ceramicized silicone rubber with gradient structure and a preparation method and application thereof. BACKGROUND

[0002] Ceramifiable polymers have become a hot topic in the development of thermal protection materials in the fields of aerospace, electronics, and shipping because the products after ceramicization have excellent high-temperature resistance, ablation resistance, and flame resistance. Among them, silicone rubber with a silicone structure as the main chain has become one of the ideal substrates for ceramifiable polymers because of its excellent high and low temperature resistance, chemical stability, weather resistance, and high residual weight.

[0003] Traditional ceramicized silicone rubber takes high ceramic strength as the primary requirement. In existing silicone rubber ceramifiable technology, a large amount of low-melting-point glass powder or ceramic powder is introduced to promote the mass transfer process and crystal formation process at high temperatures, thereby reducing the ceramicization temperature and forming a single-layer silicone rubber protective layer. This structure can resist the impact of flames, but it is not as good as a multi-layer silicone rubber composite material in terms of heat insulation. Most multi-layer silicone rubber composite materials are composed of two or more layers of materials stacked together (for example, multiple types of silicone rubber are processed and then bonded together), which is a complex process. SUMMARY

[0004] The technical problem to be solved by the present application is to provide a ceramicized silicone rubber with a gradient structure and a preparation method thereof. The gradient distribution of ceramic filler and heat insulation filler in the silicone rubber improves the fire resistance and heat insulation performance of the ceramicized silicone rubber.

[0005] The technical problem to be solved by the present application is solved by the following technical solution:

[0006] The first object of the present application is to provide a ceramicized silicone rubber with a gradient structure, which comprises silicone rubber and ceramic filler, and the content of the ceramic filler is gradiently distributed along the thickness direction of the silicone rubber.

[0007] The second object of the present application is to provide a preparation method of a ceramicized silicone rubber with a gradient structure, which comprises the following steps:

[0008] (1) uniformly mix vinyl silicone oil, catalyst, coupling agent, and filler to obtain base glue A;

[0009] (2) uniformly mix the remaining vinyl silicone oil, hydrogen-containing silicone oil, inhibitor, coupling agent, and filler to obtain base glue B;

[0010] (3) uniformly mix base glue A and base glue B to obtain liquid silicone rubber;

[0011] (4) Pouring the liquid silicone rubber into the mold cavity, standing to make the filler settle and / or float;

[0012] (5) Vulcanizing the silicone rubber after standing to obtain the ceramicized silicone rubber with gradient structure.

[0013] A third object of the present application is to provide the use of the ceramicized silicone rubber with gradient structure in thermal protection materials.

[0014] The present application has the following advantages:

[0015] 1. The preparation method of the ceramicized silicone rubber realizes the one-piece forming of the ceramicized silicone rubber with gradient structure, and has the characteristics of simple process and easy operation compared with the conventional multi-layer composite structure.

[0016] 2. At room temperature, the ceramicized silicone rubber has excellent elasticity, softness, flame retardancy, electrical properties, high and low temperature resistance, oil resistance, and water resistance, etc., as well as ordinary rubber and thermoplastic elastomers.

[0017] 3. Under flame impact, the ceramicized silicone rubber forms a gradient structure with gradually decreasing ceramic strength from the fire-facing surface to the backfire surface. The hard ceramic shell on the surface can block the impact of external flames. The internal silicone rubber absorbs heat and decomposes to form a porous structure with weak ceramic strength and no strength. This special porous structure can isolate the transfer of heat. Under the continuous impact of 1200℃ flame temperature, the backfire surface can still maintain part of the softness of the silicone rubber within 30 minutes.

[0018] 4. Under uniform high temperature environment, such as calcination in a 600℃ muffle furnace for 30 minutes, the ceramicized silicone rubber forms a gradient structure with a hard ceramic shell on the outside and a powder structure with no strength on the inside. This structure also has excellent heat insulation effect. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 The figure shows the settling of the filler in the liquid silicone rubber. The spherical mark represents the heat insulation filler, and the rest represents the ceramic filler. DETAILED DESCRIPTION

[0020] In order to make the technical means, creative features, purposes and effects realized by the present application easy to understand, the present application is further described below in combination with specific examples and drawings.

[0021] The present application provides a ceramicized silicone rubber with gradient structure, which comprises silicone rubber and ceramic filler, and the content of the ceramic filler is distributed in a gradient along the thickness direction of the silicone rubber.

[0022] To further improve the heat insulation effect of the ceramicized silicone rubber, the ceramicized silicone rubber further comprises a heat insulation filler, and the content of the heat insulation filler is inversely gradient-distributed relative to the ceramic-forming filler.

[0023] The application provides a preparation method of the ceramicized silicone rubber with a gradient structure, comprising the following steps:

[0024] (1) uniformly mixing vinyl silicone oil, a catalyst, a coupling agent and a filler to obtain base glue A;

[0025] (2) uniformly mixing residual vinyl silicone oil, hydrogen-containing silicone oil, an inhibitor, a coupling agent and a filler to obtain base glue B;

[0026] (3) uniformly mixing the base glue A and the base glue B to obtain liquid silicone rubber;

[0027] (4) pouring the liquid silicone rubber into a mold cavity, and standing to make the filler settle and / or float;

[0028] (5) vulcanizing the silicone rubber after standing to obtain the ceramicized silicone rubber with a gradient structure.

[0029] Further, the weight ratio of the vinyl silicone oil, the hydrogen-containing silicone oil, the filler, the coupling agent, the catalyst and the inhibitor in the liquid silicone rubber is (20-120) : (2-10) : (10-80) : (0.5-3.5) : (0.1-1) : (0.05-1). Wherein, the amount of the coupling agent and the filler is respectively calculated based on the total amount of the two in the base glue A and the base glue B.

[0030] Further, the mixing is vacuum mixing, the mixing time is 0.5-2h, and the vacuum degree is-0.08-0.1MPa. A double-planetary mixer can be used to prepare the base glue A, the base glue B and the liquid silicone rubber, and the pressure is released after the materials are uniformly mixed.

[0031] Further, the standing time is 0.5-6h. By controlling the standing time, the filler moves upward or downward in the liquid silicone rubber to form a gradient structure.

[0032] Further, the vulcanization temperature is 120-180℃, the pressure is 12-15MPa, and the time is 5-20min. By vulcanization, the linear molecular structure is converted into a network structure, so as to improve the physical and chemical properties of the silicone rubber.

[0033] Further, the filler is a ceramic-forming filler and / or a heat insulation filler.

[0034] As a preferred technical solution, the specific gravity of the porcelain-forming filler is greater than that of the liquid silicone rubber. The porcelain-forming filler includes, but is not limited to, at least one of calcium carbonate, talcum powder, wollastonite, mica, magnesium hydroxide, aluminum hydroxide, kaolin, halloysite, low-melting-point glass powder, boron nitride, aluminum nitride, silicon nitride, silicon carbide, aluminum oxide, zinc oxide, magnesium oxide, titanium dioxide, calcite, and silicon carbide.

[0035] As a preferred technical solution, the specific gravity of the heat-insulating filler is less than that of the liquid silicone rubber. The heat-insulating filler includes, but is not limited to, at least one of hollow glass microbeads and aluminum oxide hollow spheres.

[0036] As shown in FIG. 1, during the standing process of the liquid silicone rubber, the porcelain-forming filler moves downward and the heat-insulating filler moves upward due to the difference in specific gravity between the porcelain-forming filler and the liquid silicone rubber and between the heat-insulating filler and the liquid silicone rubber, so that the prepared ceramicized silicone rubber has a gradient structure. Figure 1 As shown in FIG. 1, during the standing process of the liquid silicone rubber, the porcelain-forming filler moves downward and the heat-insulating filler moves upward due to the difference in specific gravity between the porcelain-forming filler and the liquid silicone rubber and between the heat-insulating filler and the liquid silicone rubber, so that the prepared ceramicized silicone rubber has a gradient structure.

[0037] Further, the vinyl silicone oil is composed of vinyl silicone oil I with a kinematic viscosity of 500-1000 mPa·s and vinyl silicone oil II with a kinematic viscosity of 10000-30000 mPa·s; and the mass ratio of the vinyl silicone oil I to the vinyl silicone oil II is (20-50) : (50-100).

[0038] Further, the hydrogen-containing silicone oil is selected from at least one of side hydrogen-containing silicone oil and end hydrogen-containing silicone oil. The hydrogen content of the side hydrogen-containing silicone oil is 0.1-1.5%, and the hydrogen content of the end hydrogen-containing silicone oil is 0.06-1.2%.

[0039] Further, the coupling agent includes, but is not limited to, at least one of a silane coupling agent and a titanate coupling agent. The coupling agent promotes the dispersion of the filler in the silicone rubber.

[0040] Further, the catalyst includes, but is not limited to, at least one of a platinum catalyst and an organic tin catalyst. The catalyst accelerates the reaction rate and promotes the formation of a stable silicone rubber skeleton structure.

[0041] Further, the inhibitor includes, but is not limited to, at least one of a vinyl ring compound and an alkyne alcohol.

[0042] The application provides application of the ceramicized silicone rubber with the gradient structure in thermal protection materials.

[0043] Performance test method of ceramicized silicone rubber:

[0044] Thermal insulation performance test: cut a 3mm thick sample into a 6mm wide strip, place the sample in a muffle furnace, heat at a rate of 5℃ / min, and keep it at 600℃ for 45min, then take out the sample after natural cooling, and test the bending strength of the sample according to GB / T6569-2006 "Fine Ceramic Bending Strength Test Standard" using an electronic universal testing machine.

[0045] Ceramic performance test: cut a 4mm thick sample into 5 strips with a width of 6mm, place the strips in a muffle furnace, heat at a rate of 5℃ / min, and keep it at 600℃ for 45min, then take out the sample after natural cooling, and test the bending strength of the sample according to GB / T6569-2006 "Fine Ceramic Bending Strength Test Standard" using an electronic universal testing machine.

[0046] Example 1

[0047] Table 1

[0048]

[0049] The ceramicized silicone rubber was prepared according to the type and amount of raw materials in Table 1, and the specific preparation steps were as follows:

[0050] (1) 30 parts of vinyl silicone oil I with a viscosity of 500mPa·s, 25.03 parts of vinyl silicone oil II with a viscosity of 10000mPa·s, 0.18 parts of chloroplatinic acid, 0.75 parts of silane coupling agent KH560, 35 parts of aluminum hydroxide and 40 parts of wollastonite were sequentially added into a double planetary mixer, vacuum mixed for 60min, the vacuum degree was-0.08MPa, and then the pressure was released to obtain base glue A.

[0051] (2) 1.52 parts of hydrogen-containing silicone oil with a hydrogen content of 0.81%, 0.09 parts of 1-ethynylcyclohexanol, 54.97 parts of vinyl silicone oil II with a viscosity of 10000mPa·s, 0.75 parts of silane coupling agent KH560, 15 parts of hollow glass microbeads and 54 parts of calcite were sequentially added into a double planetary mixer, vacuum mixed for 60min, the vacuum degree was-0.08MPa, and then the pressure was released to obtain base glue B.

[0052] (3) Mix base glue A and base glue B under a vacuum degree of-0.08MPa for 30min, and then release the pressure to obtain liquid silicone rubber.

[0053] (4) Pour the liquid silicone rubber into the mold cavity and let it stand for 0.5h.

[0054] (5) Place the silicone rubber after standing in a flat vulcanizing machine with a temperature of 150℃ and a pressure of 15MPa, heat vulcanize for 10min, and obtain a ceramicized silicone rubber with a gradient structure.

[0055] Examples 2~3 and Comparative Examples 1~2

[0056] The method of Example 1 was followed, except that the standing time of the liquid silicone rubber in step (4) was adjusted, as shown in Table 2.

[0057] Table 2

[0058]

[0059] As can be seen from Table 2, Examples 1~3 and Comparative Examples 1~2 have different standing times of the liquid silicone rubber, resulting in different distributions of the heat-insulating filler and the ceramic-forming filler in the silicone rubber, and thus forming ceramicized silicone rubbers with different gradient structures. At different flame spraying times, the back temperatures of the silicone rubber samples of Example 2 and Example 3 after continuous flame spraying are significantly lower than those of Example 1, Comparative Example 1 and Comparative Example 2, indicating that they have better heat-insulating effects. This is because the standing time of Examples 2 and 3 is appropriate, making the fillers reasonably distributed. At 1200℃, the bottom layer of the filler sedimentation is selected as the fire surface, and after the silicone rubber sample is sprayed, a ceramic structure with gradient changes is formed. The surface ceramic layer endows the silicone rubber with flame impact resistance, and the internal silicone rubber is decomposed to form a porous structure with weak ceramic strength or no strength, which can hinder the transfer of heat and thus play a heat-insulating role. Example 1 and Comparative Example 2 have insufficient standing time, and after the liquid silicone rubber is heated and vulcanized, the silica residues produced by decomposition at high temperature environment and the inorganic fillers undergo eutectic reaction, finally forming a uniform ceramic body with certain strength, and heat is more easily conducted through the ceramic body, so the heat-insulating effect is poor. Comparative Example 1 extends the standing time of the liquid silicone rubber to 8h, and the heat-insulating filler and the ceramic-forming filler are layered to form a non-gradient change structure, and the distribution of the fillers becomes unreasonable, which may result in the over-concentration of the heat-insulating filler in the upper layer, while the heat-insulating filler in the middle and bottom layers is too little, so that heat is more easily transferred through the bottom and middle layers, thus reducing the overall fire-resistant and heat-insulating performance. Therefore, the standing time needs to be accurately controlled to balance the filler sedimentation / floatation and crosslinked structure, and a standing time of 3~6h can form an ideal gradient structure, which can significantly improve the fire-resistant and heat-insulating performance of the material while ensuring the integrity of the ablation sheet, and provides a key process parameter for the practical application of the ceramicized silicone rubber.

[0060] Examples 4~5 and Comparative Examples 3~4

[0061] The method of Example 2 was followed, except that the composition and amount of the heat-insulating filler and the ceramic-forming filler were adjusted, as shown in Table 3.

[0062] Table 3

[0063]

[0064] As can be seen from Table 3, Examples 2, 4 and 5 can exhibit better thermal insulation performance by adjusting the composition and amount of the thermal insulation filler and the porcelain-forming filler. The back temperature of Example 4 after spraying for 5 min, 15 min and 30 min is significantly lower than that of Example 2, indicating that the alumina hollow sphere has better thermal insulation performance due to its higher thermal stability and lower thermal conductivity. The back temperature of Example 5 is between that of Example 2 and Example 4, indicating that the mixed filler balances the thermal insulation and porcelain-forming performance through synergistic effect. Comparative Example 3 uses aluminum hydroxide as the porcelain-forming filler. Aluminum hydroxide starts to decompose and release bound water when heated to about 230°C, which slows down the combustion of the polymer due to the endothermic dehydration process, thus the back temperature of the silicone rubber sample measured after spraying for 5 min is lower. Since the ablation product has no strength, it cannot support the continuous impact of the flame and breaks, so the back temperature after spraying for 15 min and 30 min is high. Comparative Example 4 has a solid fiber filler (wollastonite) and lacks the thermal insulation capacity of the hollow structure, so the heat is directly conducted to the back layer, resulting in a higher back temperature.

[0065] The ablation piece integrity reflects the structural stability of the material at high temperature. The ablation pieces of Examples 2, 4 and 5 remain intact and have moderate porcelain-forming strength, mainly due to the melting of the porcelain-forming filler (such as calcite, calcium carbonate, low-melting-point glass powder) to form a dense ceramic layer at high temperature, combined with the thermal insulation skeleton of the hollow sphere, forming a stable composite structure, achieving a balance between thermal insulation and mechanical properties. Comparative Example 3 has no porcelain-forming strength after ablation, because aluminum hydroxide decomposes to produce a large amount of water vapor, and there is no ceramic layer formed by the porcelain-forming filler to seal the pores, resulting in structural collapse. Comparative Example 4 has the highest bending strength and the ablation piece remains intact, because it relies on the high mechanical strength of wollastonite fiber support structure and does not break. In summary, optimizing the ratio of thermal insulation filler and porcelain-forming filler is the key to balancing the thermal insulation, mechanical strength and high-temperature durability of the material.

[0066] Examples 6-7 and Comparative Examples 5-6

[0067] According to the method of Example 2, except that the viscosity of the vinyl silicone oil was adjusted, as shown in Table 4.

[0068] Table 4

[0069]

[0070] As can be seen from Table 4, the back temperature of the examples is lower and the back temperature of the comparative examples is higher due to the different viscosities of the liquid silicone rubber. With the extension of the spray-burning time, the back temperature shows an upward trend. The viscosity of the liquid silicone rubber directly affects the sedimentation rate of the heat insulation filler (such as hollow glass microbeads) and the porcelain-forming filler (such as aluminum hydroxide, wollastonite), and then determines the uniformity of the distribution of the filler in the system and the formation effect of the gradient structure. The system of Comparative Example 5 uses low-viscosity vinyl silicone oil, and the silicone oil has strong fluidity, and the filler has fast sedimentation / floating speed, which leads to the excessive concentration of the filler at one end and the uneven distribution of the filler in the middle layer and the surface layer. When spray-burning, the surface layer lacks sufficient porcelain-forming filler support, and the formed ceramic layer is loose and insufficient in thickness, which cannot effectively block heat transfer, and the back temperature rises rapidly. The following reasons cause the cracks in the ablation sheet and the low measured bending strength: (1) The short molecular chain of the low-viscosity vinyl silicone oil has a small number of crosslinking points, and the network structure formed is loose, and the network is easy to break at high temperature, which causes cracks; (2) The uneven sedimentation of the filler weakens the interfacial bonding force in the material, reduces the bending strength, and easily causes cracks; (3) The uneven distribution of the filler in the system leads to the uneven network of local high crosslinking density and local low crosslinking density formed by the concentrated crosslinking reaction in the resin-rich region. This structural defect reduces the overall strength of the material, and cracks are easily generated under stress concentration during ablation. In Examples 2, 6, and 7, the medium-viscosity vinyl silicone oil is used, and when the viscosity is moderate, the filler has a proper sedimentation / floating rate, and a relatively uniform gradient distribution is formed: the surface layer is rich in porcelain-forming filler, which melts to form a dense ceramic layer at high temperature to resist flame impact; the middle layer and the back surface are distributed with heat insulation fillers to build a porous structure to hinder heat conduction. In Comparative Example 6, high-viscosity vinyl silicone oil is used, and the high viscosity leads to the almost no sedimentation of the filler within 3h, and the system tends to be uniformly distributed, although the stratification defect of the filler is avoided, but the gradient structure of the “surface layer porcelainization-internal layer insulation” synergistic effect is lacking, and heat is conducted through the dense structure, and the back temperature is higher. However, the uniformly distributed porcelain-forming filler forms a continuous skeleton after crosslinking, which helps to significantly improve the bending strength. In summary, the viscosity of the vinyl silicone oil needs to be matched with the sedimentation behavior of the filler and the crosslinking density to prepare a ceramicized silicone rubber with excellent heat insulation, structural stability, and mechanical strength.

[0071] The above shows and describes the basic principles and main features of the present application and the advantages of the present application. Those skilled in the art should understand that the present application is not limited to the above examples, and the above examples and descriptions in the specification are only to illustrate the principles of the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the claimed present application. The scope of protection of the present application is defined by the appended claims and their equivalents.

Claims

1. A ceramic silicone rubber with a gradient structure, characterized in that: The preparation method of the ceramic silicone rubber comprises the following steps: (1) Vinyl silicone oil, a catalyst, a coupling agent, and a filler are uniformly mixed to obtain a base rubber A; (2) uniformly mixing the remaining vinyl silicone oil, hydrogenated silicone oil, inhibitor, coupling agent, and filler to obtain base rubber B; (3) mixing base rubber A and base rubber B to obtain liquid silicone rubber; (4) Pour liquid silicone rubber into the mold cavity and allow it to settle and / or float; (5) vulcanizing the silicone rubber after standing to obtain a ceramic silicone rubber with a gradient structure; The fillers are ceramic fillers and thermal insulation fillers; the content of the ceramic fillers is distributed in a gradient along the thickness direction of the silicone rubber; the content of the thermal insulation fillers is distributed in an opposite gradient relative to the ceramic fillers; The standing time is 0.5 to 6 hours; The ceramic filler is selected from at least two of calcium carbonate, talc, wollastonite, mica, magnesium hydroxide, aluminum hydroxide, kaolin, halloysite, low-melting-point glass powder, boron nitride, aluminum nitride, silicon nitride, silicon carbide, aluminum oxide, zinc oxide, magnesium oxide, titanium dioxide, calcite, and silicon carbide; The vinyl silicone oil consists of vinyl silicone oil I with a kinematic viscosity of 500-1000 mPa·s and vinyl silicone oil II with a kinematic viscosity of 10000-30000 mPa·s.

2. The ceramic silicone rubber with a gradient structure according to claim 1, characterized in that: The weight ratio of vinyl silicone oil, hydrogenated silicone oil, filler, coupling agent, catalyst and inhibitor in the liquid silicone rubber is (20-120): (2-10): (10-80): (0.5-3.5): (0.1-1): (0.05-1).

3. The ceramic silicone rubber with a gradient structure according to claim 1, characterized in that: The mixing is vacuum mixing, the mixing time is 0.5 to 2 hours, and the vacuum degree is -0.08 to -0.1 MPa; The vulcanization temperature is 120-180° C., the pressure is 12-15 MPa, and the time is 5-20 minutes.

4. The ceramic silicone rubber with a gradient structure according to claim 1, characterized in that: The specific gravity of the porcelain-forming filler is greater than that of liquid silicone rubber; The specific gravity of the thermal insulation filler is smaller than that of liquid silicone rubber.

5. The ceramic silicone rubber with a gradient structure according to claim 4, characterized in that: The heat-insulating filler is selected from at least one of hollow glass microspheres and hollow alumina spheres.

6. The ceramic silicone rubber with a gradient structure according to claim 1, characterized in that: The mass ratio of the vinyl silicone oil I to the vinyl silicone oil II is (20-50): (50-100); The hydrogen-containing silicone oil is selected from at least one of side hydrogen-containing silicone oil and end hydrogen-containing silicone oil; The hydrogen content of the side hydrogen-containing silicone oil is 0.1-1.5%; the hydrogen content of the end hydrogen-containing silicone oil is 0.06-1.2%; The coupling agent is selected from at least one of a silane coupling agent and a titanate coupling agent; The catalyst is a platinum catalyst; The inhibitor is selected from at least one of vinyl ring body and 1-ethynyl cyclohexanol.

7. Use of the ceramic silicone rubber with a gradient structure according to any one of claims 1 to 6 in thermal protection materials.

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