Temperature-resistant low-compression-deformation foamed silica gel and preparation process thereof

Abstract

The invention relates to the technical field of silica gel high polymer materials, in particular to temperature-resistant low-compression-deformation foamed silica gel and a preparation process thereof. The problem that in the prior art, foamed silica gel is poor in high-temperature resilience performance is solved. The foamed silica gel is prepared from a component A and a component B through dynamic mixing and injection molding, wherein the basic sizing material adopts vinyl-terminated polydimethylsiloxane, vinyl-terminated polymethylphenyl siloxane and vinyl phenyl MQ silicon resin, and is matched with HMDS in-situ modified fumed silica to construct an enhanced network; a side chain fluorine-containing foam stabilizer and a liquid-phase cerium complex are introduced into the component B; a three-stage temperature control process of nucleation foaming, gel explosion and vulcanization after gradient high temperature is adopted. Through addition of the nano rigid particles and deep thermodynamic relaxation treatment, the problems of collapse and rebound failure of a closed pore structure of existing foamed silica gel at long-term high temperature are solved, and the foamed silica gel is suitable for heat-resistant sealing and buffer heat insulation of new energy batteries and precise electronic components.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of silica gel polymer materials, in particular to a temperature-resistant and low-compression-deformation foamed silica gel and a preparation process thereof. BACKGROUND

[0002] With the rapid development of new energy automobile power battery thermal management system, 5G communication base station sealing components and aerospace cushioning materials, the performance requirements of sealing materials have changed from pure normal temperature sealing to long-term reliability under extreme working conditions. Foamed silica gel becomes the first choice material due to its unique closed cell structure, excellent compression resilience and weather resistance. However, in the face of long-term high temperature and the need to maintain continuous resilience, the existing technology shows obvious limitations.

[0003] The current mainstream preparation process is based on an addition type liquid silicone rubber system. The dehydrogenation reaction of hydrogen-containing silicone oil and hydroxyl donors produces gas, and the addition reaction is used for crosslinking and curing. However, the existing technology still has the problem of being unable to balance performance. In order to improve the temperature resistance limit of ordinary methyl vinyl silicone rubber, the existing technology usually adds a large amount of cerium oxide, iron oxide and other metal oxides as heat-resistant agents or increases the crosslinking density. However, the addition of solid heat-resistant powder will destroy the flexibility of the siloxane main chain, increase the internal friction between the molecular chains, and cause the physical hysteresis of the material under compression to increase. At the same time, although the high crosslinking density improves the heat resistance, it makes the modulus of the foamed material too high, which causes brittle fracture or stress concentration under high compression ratio, thereby significantly increasing the compression permanent deformation rate.

[0004] In a high temperature environment, the methyl group of the side chain of silicone rubber is easily attacked by heat oxidation to form free radicals and initiate random chain scission or secondary crosslinking of the side chain. For foamed materials, the aging of this microstructure will directly lead to a decrease in the supporting force of the macroscopic cell wall. The existing foaming process is difficult to accurately control the rheological window matching of the bubble growth rate and the vulcanization rate of the rubber compound, often leading to uneven thickness of the cell wall or too high opening rate. Under the long-term action of high temperature and high pressure, the weak cell wall will undergo irreversible physical collapse and chemical bond rearrangement, resulting in the loss of resilience of the sealing element.

[0005] In summary, the existing technology improves the mechanical properties and high temperature resistance of the foamed silica gel through the modification process of the silicone rubber system. However, the existing technology still has the problem of poor high temperature resilience of the foamed silica gel, which limits the further application of the foamed silica gel material.

[0006] Therefore, a temperature-resistant and low-compression-deformation foamed silica gel and a preparation process thereof are proposed. SUMMARY

[0007] The present application aims to provide a kind of foamed silica gel with temperature resistance and low compression deformation and its preparation process.The foamed silica gel of the present application is prepared by dynamic mixing injection molding of A component and B component;Wherein base stock adopts end vinyl polydimethylsiloxane, end vinyl polymethylphenylsiloxane and vinyl phenyl MQ silicone resin, and constructs reinforcing network with HMDS in situ modified fumed white carbon black;Side chain fluorine-containing foam stabilizer and liquid phase cerium complex are introduced in B component;Three-stage temperature control process of nucleation foaming, burst gel and gradient high temperature post-curing is used.The present application solves the problems of existing foamed silica gel, such as collapse of closed structure and rebound failure under long-term high temperature, by nanometer rigid node and deep thermodynamic relaxation treatment, and is suitable for heat-resistant sealing and cushioning and heat insulation of new energy batteries and precision electronic components.

[0008] To achieve the above object, the present application provides the following technical scheme: The present application provides a preparation process of foamed silica gel with temperature resistance and low compression deformation, comprising the following steps: A component and B component are connected to feed pump, and feed pressure is set to 10-15MPa; they are delivered to dynamic mixer with cooling jacket (water temperature is kept at 20℃) by precision metering pump at 1:1 mass ratio; the rotation speed of dynamic mixer is set to 2000-3000rpm to ensure instantaneous uniform mixing without temperature rise; mixed stock is obtained; mixed stock is injected into preheated mold, and three-stage temperature control molding is carried out; nucleation foaming and burst static gel molding are carried out in mold, and then demolding is carried out; the obtained green bad is placed in oven for gradient post-curing; the oven is naturally cooled to room temperature; foamed silica gel is obtained; the temperature during nucleation foaming period is kept at 80-90℃, and the residence time is 3-5min; at this time, inhibitor effectively inhibits vinyl crosslinking, mainly carries out Si-H and -OH dehydrogenation reaction, and bubble nucleus grows uniformly under the protection of fluorine-containing foam stabilizer; the volume of stock expands to 3-4 times, and the viscosity increases moderately but does not gel; during burst gel period, the temperature is increased to 130-150℃ by heating, and the residence time is 5-8min; when the temperature breaks through the threshold of inhibitor, the addition reaction rate constant jumps exponentially, and the stock completes gel point mutation within 30s, physically locks bubble structure, and forms green bad; finally, gradient post-curing is carried out; the temperature is increased to 140-150℃ at a heating rate of 5℃ / min, and kept for 45-60min; then the temperature is increased to 180-190℃, and kept for 45-60min; then the temperature is increased to 200-230℃, and kept for 1.5-3h; during gradient temperature rising process, phenyl segment movement and network internal stress are promoted to release through thermal relaxation, network internal stress is eliminated, and the material is endowed with heat memory ability of resisting 200℃ compression.

[0009] Preferably, the preparation of A component includes the following steps: put 100 parts of base rubber into the mixing cylinder, open the circulating cooling water, control the temperature at 25-30°C, add 0.4-0.6 parts of platinum-divinyltetramethylsiloxane complex, first mix at low speed, revolution at 15 rpm, rotation at 20 rpm, mix for 10 min; then disperse at high speed, revolution at 25 rpm, rotation at 500-800 rpm, disperse for 30 min; keep the rotation speed, open the vacuum to-0.095 MPa, defoam for 15 min to obtain A component.

[0010] Preferably, the preparation of B component includes the following steps: use a double-planet vacuum mixer, put 100 parts of base rubber into the mixing cylinder, add 5-10 parts of vinyl silicone oil to adjust the viscosity, open the strong cooling to ensure that the temperature is always below 35°C to prevent the inhibitor from volatilizing or Si-H from activating; then add 1.2-2.2 parts of side-chain fluorine-containing foam stabilizer, 0.3-0.8 parts of liquid cerium heat-resistant agent, and 0.05-0.2 parts of inhibitor in sequence, disperse at medium speed, wherein the revolution speed is 20 rpm and the rotation speed is 300 rpm, mix for 20 min; then add 2-4 parts of terminal hydrogen silicone oil, 3.5-5.2 parts of side hydrogen silicone oil, and 2.2-4.5 parts of hydroxyl silicone oil, mix at high speed, defoam at low temperature to obtain B component, wherein the revolution speed is 30 rpm and the rotation speed is 600-900 rpm, mix for 30 min; defoam at-0.098 MPa vacuum and low speed, wherein the revolution speed is 10 rpm and the rotation speed is 5 rpm, defoam for 20 min.

[0011] Preferably, the preparation of the base glue includes the following steps: starting a double-shaft vacuum kneader, setting the stirring paddle speed to 20 rpm for the front paddle and 15 rpm for the back paddle, sequentially adding the formula amount of end-vinyl polydimethylsiloxane 40-50 parts, end-vinyl polymethylphenylsiloxane 15-20 parts and vinylphenyl MQ silicone resin 12-18 parts, mixing for 5-10 min to obtain a dissolved system; adding fumed white carbon black 20-25 parts in three equal portions to the dissolved system, and stirring at a speed of 25-35 rpm to ensure uniform mixing; then adding hydroxyl silicone oil 2-4 parts and hexamethyldisilazane 5-7.5 parts to obtain a reaction system; closing the cylinder cover of the reaction system, replacing the air with high-purity nitrogen for 3 times, adjusting the stirring paddle speed to medium speed, wherein the front paddle is 35 rpm and the back paddle is 25 rpm, mixing at room temperature for 30 min to preliminarily wet the material; then increasing the temperature to 170-180℃ at a rate of 2-3℃ / min, starting the vacuum pump, and vacuuming to a degree of -0.098 MPa or above, adjusting the stirring paddle speed to high speed, wherein the front paddle is 45-50 rpm and the back paddle is 30-35 rpm, maintaining high temperature, high vacuum and high speed shearing state for 3-5 h to obtain a modified system; this process needs to continuously remove the ammonia and water molecules generated during the reaction to ensure that the surface of the white carbon black is highly hydrophobically modified; cooling the modified system to below 80℃, releasing the vacuum, adding ultra-high molecular weight end-vinyl silicone oil 10-15 parts, and slowly mixing for 30 min, then grinding through a three-roll grinding machine (roller gap: 50 μm / 20 μm / 5 μm), and then filtering through a 300 mesh filter to obtain the base glue.

[0012] The application also provides a temperature-resistant and low-compression-deformation foamed silicone rubber, and the preparation raw materials of the foamed silicone rubber include end-vinyl polydimethylsiloxane, end-vinyl polymethylphenylsiloxane, vinylphenyl MQ silicone resin, fumed white carbon black, end-vinyl silicone oil, side-chain fluorine-containing foam stabilizer, liquid-phase cerium heat-resistant agent and hydroxyl silicone oil.

[0013] Compared with the prior art, the application has the following beneficial effects: 1. The application introduces side-chain fluorine-containing alkyl-modified polysiloxane as a foam stabilizer, which has extremely low surface energy, can quickly migrate to the gas-liquid interface and arrange in a direction, and form a high-strength monomolecular interface film; this dense interface film can effectively resist the curing effect, prevent small bubbles from merging and breaking, and cooperate with the precise locking of the foaming / gelation kinetics window by the inhibitor, so that the material can still maintain a relatively high closed cell rate at a low density, which is significantly better than the prior art, and ensures the uniformity and stability of the internal structure of the material.

[0014] 2、The application adopts hexamethyldisilazane to modify the fumed white carbon black in-situ at high temperature and vacuum in the base glue preparation stage, eliminates the active silicon hydroxyl on the surface of the white carbon black, converts it into hydrophobic methyl siloxyl, and prevents the combination of the filler and water molecules; not only excellent sealing capacity is given to the material, but also the decline of insulation performance caused by water vapor penetration is effectively prevented, and the electrical safety of sensitive devices such as battery packs is ensured.

[0015] 3、The application constructs a dual-mode network structure of long-chain entanglement and short-chain crosslinking, the vinyl silicone oil provides physical entanglement to dissipate stress and improve toughness; the short-chain silicone oil provides high crosslinking density to maintain hardness; at the same time, liquid phase cerium complex is adopted, and liquid phase additives are uniformly dispersed at a molecular level to eliminate microscopic stress concentration points caused by solid particles. The material can still achieve the perfect balance of lightweight and high toughness after foaming, and effectively resist mechanical damage during installation.

[0016] 4、The application introduces bulky phenyl side groups in the polymer main chain, the high steric effect of the phenyl group can effectively shield the attack of oxygen free radicals on the main chain, and improve the bond energy; in combination with the redox cycle of liquid phase cerium ions to capture free radicals, excellent heat resistance is shown, avoiding the risk of hardening, brittle cracking and failure of traditional materials under long-term high temperature, prolonging the service life of electronic equipment.

[0017] 5、The application introduces vinyl phenyl MQ resin as a nano-rigid pinning node to limit molecular chain slipping; and cooperates with the gradient post-vulcanization process, so that the high molecular chain segment completes the thermodynamic rearrangement and internal stress release in advance, and gives the material thermal memory capability. This makes the physical creep and chemical relaxation of the material under long-term compression conditions at 200 DEG C be reduced to the minimum, ensuring the persistent rebound sealing force of the sealing element in the whole life cycle. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 For Example 1, the high-temperature aging strength retention rate change diagram of Comparative Examples 5-9. DETAILED DESCRIPTION

[0019] The technical solutions in the embodiments of the application will be described below in detail with reference to the drawings of the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, not all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the application.

[0020] The viscosity of the end-vinyl polydimethylsiloxane is 10000 mPa·s, the vinyl content is 0.16 mol%; the viscosity of the end-vinyl silicone oil is 5000000 mPa·s, which is in the form of raw rubber, the vinyl content is 0.08 mol%; the viscosity of the end-vinyl polymethylphenylsiloxane is 3000 mPa·s, the phenyl content is 15 mol%, and the vinyl content is 0.2 mol%; the MQ silicone resin is a vinyl phenyl MQ silicone resin, wherein M / Q is 0.7:1, the vinyl content is 2.5-3.5 wt%, and the phenyl content is 10-15 wt%; the fumed white carbon is a hydrophilic fumed white carbon, which is then subjected to in-situ modification treatment, and the specific surface area is 200±25 m² / g; the platinum catalyst is a platinum-divinyltetramethyldisiloxane complex, and the platinum content is 5000 ppm; the inhibitor is an ECH / DAM compound, wherein the mass ratio of 1-ethynyl-1-cyclohexanol (ECH) to diallyl maleate (DAM) is 1:1; the end-hydrogen silicone oil is an end-hydrogen polydimethylsiloxane, the viscosity is 500 mPa·s, and the hydrogen content is 0.08 wt%; the side-hydrogen silicone oil is a side-hydrogen polymethylhydrogen siloxane, the viscosity is 30 mPa·s, and the hydrogen content is 1.0 wt%; the hydroxyl silicone oil is an end-hydroxyl polydimethylsiloxane, the viscosity is 80 mPa·s, and the hydroxyl content is greater than 5.0 wt%; the side chain fluorine-containing foam stabilizer is a fluorine-modified polysiloxane, specifically a tridecafluorooctyl and polyether co-modified polymethylsiloxane, the viscosity is 500 mPa·s, the surface tension is 19 mN / m, the fluorine-containing side chain grafting rate is 15 mol%-20 mol%, and the polyether side chain grafting rate is 10 mol%-15 mol%; the liquid phase cerium heat-resistant agent is an organic cerium complex solution, anhydrous cerium iso-octanoate is dispersed in vinyl silicone oil, and hexamethyldisilazane is added as a stabilizing ligand, wherein the cerium content is 10-12%, and the solvent is vinyl silicone oil.

[0021] Please refer to Figure 1 The application provides a temperature-resistant and low-compression-deformation foamed silica gel and a preparation process thereof. Example 1 Start the double-shaft vacuum kneader, set the stirring paddle speed to 20 rpm for the front paddle and 15 rpm for the back paddle, and sequentially add the formula amount of end-vinyl polydimethylsiloxane 45 parts, end-vinyl polymethylphenylsiloxane 18 parts, and vinylphenyl MQ silicone resin 15 parts, mix for 8 min until the resin is initially dissolved to obtain a dissolution system; to the dissolution system, add fumed white carbon black 22 parts in three equal portions, with a stirring speed of 30 rpm to ensure uniform mixing; then add hydroxyl silicone oil 3 parts and hexamethyldisilazane 6 parts to obtain a reaction system; close the reaction system cylinder cover, replace the air with high-purity nitrogen for 3 times, adjust the stirring paddle speed to medium speed, with the front paddle at 35 rpm and the back paddle at 25 rpm, and mix at room temperature for 30 min to initially wet the material; then increase the temperature to 170°C at a rate of 2°C / min, start the vacuum pump, and vacuum to -0.098 MPa, adjust the stirring paddle speed to high speed, with the front paddle at 45 rpm and the back paddle at 35 rpm, and maintain high temperature, high vacuum, and high speed shearing for 4 h to obtain a modified system; this process needs to continuously remove the ammonia and water molecules generated during the reaction to ensure that the surface of the white carbon black is highly hydrophobically modified; cool the modified system to below 80°C, release the vacuum, add ultra-high molecular weight end-vinyl silicone oil 12 parts, and slowly mix for 30 min, then grind through a three-roll grinder (roller gap: 50 μm / 20 μm / 5 μm), and filter through a 300-mesh screen to obtain a base compound; Put the base compound 100 parts into the stirring cylinder, start the circulating cooling water, control the material temperature at 30°C, add platinum-divinyl tetramethyl disiloxane complex 0.5 parts, first mix at low speed, with revolution at 15 rpm and rotation at 20 rpm, mix for 10 min; then disperse at high speed, with revolution at 25 rpm and rotation at 600 rpm, disperse for 30 min; keep the speed, start the vacuum to -0.095 MPa, and defoam for 15 min to obtain component A; Use a double-planetary vacuum stirrer, put the weighed base compound 100 parts into the stirring cylinder, add vinyl silicone oil 8 parts to adjust the viscosity, start the strong cooling to ensure that the material temperature is always below 35°C; then sequentially add side-chain fluorine-containing foam stabilizer 1.8 parts, liquid cerium heat-resistant agent 0.5 parts, and inhibitor 0.1 parts, disperse at medium speed, with revolution speed at 20 rpm and rotation speed at 300 rpm, mix for 20 min; then add end-hydrogen silicone oil 3 parts, side-hydrogen silicone oil 4 parts, and hydroxyl silicone oil 3 parts, mix at high speed to defoam at low temperature to obtain component B, with revolution speed at 30 rpm and rotation speed at 800 rpm, mix for 30 min; defoam at low speed under -0.098 MPa vacuum, with revolution speed at 10 rpm and rotation speed at 5 rpm, for 20 min.

[0022] The A component and the B component are connected to a feed pump, the feed pressure is set to 15 MPa, and are conveyed to a dynamic mixer with a cooling jacket (the water temperature is kept at 20°C) by a precision metering pump at a mass ratio of 1:1, the rotation speed of the dynamic mixer is set to 3000 rpm, to ensure instantaneous and uniform mixing and no temperature rise, to obtain a mixed glue; the mixed glue is injected into a preheated mold, and is formed by three-stage temperature control, and is naturally cooled to room temperature in the oven, to obtain a foamed silicone; wherein the nucleation and foaming period is kept at 85°C for 4 min; then the explosive gelation period is passed, the temperature is increased to 140°C by heating, and the residence time is 6 min; finally, the gradient post-vulcanization is performed, the temperature is increased to 150°C at a heating rate of 5°C / min, and is kept for 60 min; the temperature is continuously increased to 180°C, and is kept for 60 min; and then the temperature is increased to 220°C, and is kept for 2 h.

[0023] Example 2-5 refers to the preparation method and parameter conditions of Example 1, and the differences are shown in Table 1.

[0024] Table 1 Parameter changes of Examples 1-5 Comparative Example 1 refers to Example 1, except that no fluorine-containing foam stabilizer is added, and an equal mass of ordinary polyether silicone oil is used, and the amounts of the other components remain unchanged.

[0025] Comparative Example 2 refers to Example 1, except that no ECH / DAM inhibitor is used, and the amounts of the other components remain unchanged.

[0026] Comparative Example 3 refers to Example 1, except that no 85°C nucleation and foaming is performed, and the mold is directly set to 140°C.

[0027] Comparative Example 4 refers to Example 1, except that no hydroxyl silicone oil is added, and the amounts of the other components remain unchanged.

[0028] Comparative Example 5 refers to Example 1, except that the Si-H / Vi molar ratio is adjusted to 3.5:1.

[0029] Comparative Example 6 refers to Example 1, except that solid cerium oxide is used instead of liquid cerium complex, and the molar amount of cerium elements remains unchanged.

[0030] Comparative Example 7 refers to Example 1, except that no ultra-high molecular weight vinyl-terminated silicone oil is added, and the amounts of the other components remain unchanged.

[0031] Comparative Example 8 refers to Example 1, except that no phenyl vinyl silicone oil is used, and the amounts of the other components remain unchanged.

[0032] Comparative Example 9 refers to Example 1, except that the Si-H / Vi molar ratio is adjusted to 9:1.

[0033] Comparative Example 10 Reference to Example 1, the difference is that no vinyl MQ silicone resin is added, and the amount of other components remains unchanged.

[0034] Comparative Example 11 Reference to Example 1, the difference is that the post-vulcanization process only goes through 150°C for 3h, and does not go through gradient high temperature.

[0035] Comparative Example 12 Reference to Example 1, the difference is that the highest temperature of the gradient post-vulcanization is reduced from 220°C to 180°C, and the rest remains unchanged.

[0036] Comparative Example 13 Reference to Example 1, the difference is that during the preparation of the base compound, only the fumed white carbon black is mixed at room temperature, and no 170°C vacuum treatment is performed.

[0037] Comparative Example 14 Reference to Example 1, the difference is that during the preparation of the base compound, no hydroxyl silicone oil and hexamethyl disilazane are added to modify the fumed white carbon black in situ, and the amount of other components remains unchanged.

[0038] Experimental Example 1 Basic Performance Test The foamed silica gels prepared in Examples 1-5 and Comparative Examples 1-5 were subjected to basic performance tests, wherein according to GB / T6343-2009, a standard cubic sample was cut and treated for 24h in a standard laboratory environment (23°C, 50%RH), and the mass and volume of the sample were accurately measured to test the apparent density; according to GB / T 10799-2020, a full-automatic true density analyzer was used to measure the volume of the sample to displace the gas, so as to calculate the percentage of the closed pore volume in the total volume, and the multipoint pressure regression method was used to correct the volume error caused by the sample compression; the higher the closed pore rate, the better the heat insulation, waterproof and rebound performance of the material; according to GB / T 8810-2005, the immersion method was used to test the water absorption rate, the sample was immersed in distilled water at a position 50mm below the liquid surface, and kept for 96h, then the surface water was removed, the mass change before and after immersion was measured, and the water absorption rate was calculated, the test used volume fraction; the test results are shown in Table 2.

[0039] Table 2 Test Results of Examples and Comparative Examples According to the results of Table 2, the foamed silica gel prepared in the comparative example has obvious differences in basic performance compared with the examples; Example 1 exhibits excellent comprehensive structural performance, with moderate density and extremely high closed cell rate, proving that the rheological window under the regulation of fluorine-containing blowing stabilizer and inhibitor matches well; in Example 5, due to the low amount of fluorine-containing blowing stabilizer, the gas-liquid interface film strength is insufficient, leading to partial co-blowing and a slight decrease in closed cell rate; in Comparative Example 1, ordinary polyether silicone oil is used, which usually has a surface tension higher than 20 mN / m, and cannot effectively reduce the surface energy of the polysiloxane matrix, while the fluorine-containing blowing stabilizer has extremely low surface tension and can form a closely arranged monomolecular film at the gas-liquid interface; lacking this interface film, the gas in the small bubbles between the bubbles diffuses to the large bubbles, leading to the disappearance of small bubbles, the merging and rupture of large bubbles, the formation of connected pore structure, and the loss of waterproof ability; in Comparative Example 2, the formation of foamed silica gel depends on the matching of the competition rate of foaming reaction and crosslinking reaction, without the addition of inhibitor (ECH / DAM), the platinum catalyst shows high activity at room temperature or in the initial stage of heating, leading to a much larger addition reaction rate constant than the dehydrogenation reaction rate constant, and the viscosity of the glue rises sharply and reaches the gel point before a large amount of gas is generated, the high modulus crosslinking network binds the gas, preventing the gas from expanding and opening the glue, and finally forming a solid dead glue containing a small amount of micro-bubbles; according to the results of Comparative Example 4, the gas source of the addition-type foamed silica gel comes from the dehydrogenation reaction of Si-H and Si-OH under platinum catalysis, and the removal of hydroxyl silicone oil, a key proton donor, only addition reaction of vinyl and hydrogen-containing silicone oil exists in the system, which cannot produce hydrogen, and the cured product is a dense solid elastomer without any foaming structure; the 85°C nucleation period set in the examples is to allow the bubble nucleus to grow uniformly at low viscosity, while in Comparative Example 3, the direct entry into a high-temperature environment of 140°C causes the gas production rate of the decomposed hydroxyl silicone oil to increase explosively, and the gas pressure increases instantaneously, at this time the crosslinking network of the glue has not established enough strength to withstand the internal pressure, leading to the bubble wall being broken by the gas flow and forming a string hole and open hole structure; at the same time, the large difference in vulcanization rate caused by the severe thermal shock leads to skin separation phenomenon, affecting the overall performance; in Comparative Example 5, the foaming process not only requires gas expansion, but also requires the polymer matrix to provide sufficient modulus to support the bubble wall, when the Si-H / Vi molar ratio is reduced to 3.5:1, the crosslinking density of the system is insufficient, and in the late foaming stage, the internal pressure of the bubble decreases with the decrease of temperature, and the modulus of the matrix is insufficient to resist the shrinkage force of atmospheric pressure and surface tension, and the bubble will physically collapse, leading to product shrinkage, increased density, and distorted bubble shape.

[0040] Experimental Example 2 Mechanical Properties and Aging Resistance Test The foamed silica gels prepared from Examples 1-5 and Comparative Examples 5-9 were subjected to mechanical property testing, and were subjected to a high-temperature heat aging process to test the high-temperature resistance of the foamed silica gels; the tensile strength and elongation at break of the foamed silica gels were tested according to GB / T 528-2009, the foamed silica gels were cut into standard dumbbell-shaped samples, the samples were conditioned for 24 h in a standard laboratory environment (23°C, 50% RH), and a universal material testing machine was used to test the samples at a tensile rate of 500 mm / min, and the maximum stress and corresponding elongation at break of the samples were recorded; the tensile strength of the samples after aging was determined according to GB / T 3512-2014, the aging conditions were set to 200°C x 168 h to simulate long-term high-temperature working conditions, and the tensile strength retention rate of the samples after aging was calculated; the test results are shown in Table 3; wherein the strength retention rate changes of Examples 1, Comparative Examples 5-9 are shown in Figure 1

[0041] Table 3 Test results of examples and comparative examples ​According to the results of Table 3, the mechanical properties of the foamed silica gel prepared in the comparative examples are obviously different from those of the examples; Example 1 builds a rigid-flexible dual-mode network by compounding long and short chain vinyl silicone oil and enhancing MQ resin, showing excellent initial strength and toughness, and its aging retention rate is close to 90%, proving that liquid cerium and phenyl groups effectively inhibit the thermal oxidation process; in Comparative Example 5, when the Si-H / Vi ratio is too low, the number of crosslinking points formed in the system is severely insufficient, and a continuous and dense three-dimensional network structure cannot be formed, resulting in extremely low modulus and a soft and sticky material that cannot effectively resist external stretching; under high-temperature aging, the sparse network structure lacks thermal stability and is prone to thermal depolymerization of the main chain, resulting in further loss of strength; in Comparative Example 9, too high a crosslinker dosage results in too small a molecular weight between crosslinking points, and the network is too tightly bound, resulting in a material that exhibits extreme brittleness; in addition, a large number of active Si-H groups remain in the system, which will continue to oxidize and crosslink or react with other groups in a high-temperature oxygen environment, causing the material to further harden and become brittle during the aging process, resulting in the generation of microcracks inside and a significant decline in macroscopic mechanical properties; in Comparative Example 6, cerium oxide is an effective heat-resistant additive, but the compatibility of solid micron-sized powder in the silicone matrix is poor, and the interfacial bonding force between the solid particles and the rubber matrix is weak during stretching, becoming a micro stress concentration point that induces the propagation of crazes and cracks, thereby reducing the initial strength; at the same time, the specific surface area of the solid powder is much smaller than that of the liquid-phase molecular-level dispersed cerium complex, resulting in lower efficiency in capturing free radicals and reducing the heat-resistant protective effect; the vinyl silicone oil in Example 1 acts as a physical entanglement point in the crosslinked network, and the long-chain molecules can undergo large conformational changes and slip when stressed, dissipating a large amount of deformation energy and imparting high toughness to the material; Comparative Example 7 lacks this component, and the network is mainly composed of short-chain chemical crosslinking, lacking the toughening mechanism of physical entanglement, resulting in brittle fracture of the material during stretching and a significant decrease in elongation; as can be seen from Comparative Example 8, the methyl side chains of ordinary methyl vinyl silicone rubber are extremely susceptible to attack by oxygen radicals at high temperatures, resulting in oxidative crosslinking or main chain rupture; the phenyl group has a large steric hindrance effect and a high resonance energy, effectively shielding the attack of oxygen on the main chain and increasing the bond energy.

[0042] Experimental Example 3: Elasticity performance test The foamed silica gels prepared from Examples 1-5 and Comparative Examples 8-14 were compressed to 50% of the original thickness, and kept at 25°C for 24 hours, and then the thickness was measured after 30 minutes of recovery. The foamed silica gels were compressed to 50% of the original thickness, and kept at 200°C for 24 hours, and then the thickness was measured after 30 minutes of recovery at standard temperature and humidity. The permanent compression set at room temperature and the permanent compression set at high temperature were calculated. The foamed silica gels were compressed to 25% of the original thickness, and kept at constant deformation, and then the stress retention rate after 1000 hours was recorded by continuously monitoring the rebound force at 150°C. The test results are shown in Table 4.

[0043] Table 4 Test results of examples and comparative examples According to the results of Table 4, the foamed silica gel prepared in the comparative examples has obvious difference in elastic performance compared with the examples; Example 1 exhibits excellent room temperature resilience and excellent high temperature deformation resistance, confirming the synergistic effectiveness of nano-pinning and gradient heat treatment technology; the phenyl group in the polysiloxane side chain plays a key role in thermal shielding and steric rigidity, and in Comparative Example 8, the lack of phenyl group, the heat resistance limit of methyl vinyl silicone rubber is usually around 180°C, under the high temperature compression condition of 200°C, the main chain is oxidized and rearranged, this chemical level structural damage is irreversible, directly leading to the loss of the thermodynamic driving force of the material to restore the original shape; in Comparative Example 9, due to the excessive active Si-H groups remaining in the system, under compression, in a high temperature environment, these groups will undergo secondary crosslinking reaction with residual vinyl or moisture in the air, this newly generated crosslinking bond in the deformed state will lock the shape after compression, when the external force is removed, the newly established network balance hinders the material to restore the original shape, resulting in reduced resilience; the MQ resin acts as a nano-scale physical crosslinking node and rigid reinforcing phase in the formula, at high temperature, the molecular chain movement of the polydimethylsiloxane soft segment is extremely violent, and is prone to slip between molecular chains, the absence of MQ resin, the rubber network cannot maintain the stability of the topological structure under high temperature and high pressure, leading to permanent collapse on the macro level; as can be seen from the results of Comparative Examples 11-12, at this temperature, the orientation of the phenyl chain segment and the internal stress of the network cannot be relaxed, when the test temperature rises to 200°C, the material inside undergoes intense thermal relaxation and secondary crystallization and rearrangement, superimposed with external compression stress, resulting in significant plastic deformation of the material during the test; although 180°C exhausts most of the chemical active groups, it is still lower than the test working condition of 200°C; materials that have not undergone heat memory treatment above 200°C are still in the thermodynamic instability zone at 200°C, and will continue to undergo physical creep; further proving the necessity of the gradient post-treatment process in Example 1; in Comparative Example 13, the white carbon black surface without high temperature in-situ modification contains a large number of active silicon hydroxyl groups, which can form weak hydrogen bonds with the molecular chains of silicone rubber, and in the compression process, these physical bonding points are destroyed, and in the compressed state, new weak bonds can be formed, hindering the resilience of the molecular chain; as can be seen from the results of Comparative Example 14, incomplete surface treatment or no surface treatment can lead to uneven dispersion of the filler, and the air and stress concentration points wrapped inside the agglomerates increase the deformation, and at the same time affect the processing process.

[0044] Although embodiments of the present application have been shown and described, it is to be understood that various modifications, substitutions, replacements and changes can be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A process for preparing temperature-resistant, low-compression-deformation foamed silicone, characterized in that, Includes the following steps: Components A and B are fed to a dynamic mixer at a mass ratio and stirred to obtain a mixed rubber compound. The mixed rubber compound is injected into a preheated mold and formed by three-stage temperature control, then cooled to room temperature in the furnace to obtain the foamed silicone. Component A is obtained by degassing a mixture of base rubber compound and platinum catalyst. Component B is obtained by degassing a mixture of base rubber compound, vinyl silicone oil, side-chain fluorinated foam stabilizer, liquid-phase cerium heat resistant agent, terminal hydrogen silicone oil, side-hydrogen silicone oil, and hydroxyl silicone oil. The base rubber compound is obtained by stepwise mixing of terminal vinyl polydimethylsiloxane, terminal vinyl polymethylphenylsiloxane, vinyl phenyl MQ silicone resin, fumed silica, and terminal vinyl silicone oil.

2. The preparation process of a temperature-resistant, low-compression-deformation foamed silicone according to claim 1, characterized in that, The preparation of component A includes the following steps: the base adhesive is put into a mixing tank, the material temperature is controlled, the platinum catalyst is added, the mixture is mixed and dispersed, and the component A is obtained by vacuum degassing.

3. The preparation process of a temperature-resistant, low-compression-deformation foamed silicone according to claim 1, characterized in that, The preparation of component B includes the following steps: the base adhesive is put into a mixing tank, the vinyl silicone oil is added, and the mixture is stirred and the temperature is controlled; then the side-chain fluorinated foam stabilizer, the liquid-phase cerium heat resistant agent and the inhibitor are added in sequence, and the mixture is stirred and mixed; then the terminal hydrogen silicone oil, the side hydrogen silicone oil and the hydroxyl silicone oil are added, the mixture is stirred and mixed, and the mixture is degassed under vacuum to obtain component B.

4. The preparation process of a temperature-resistant, low-compression-deformation foamed silicone according to claim 1, characterized in that, The preparation of the base adhesive includes the following steps: starting a biaxial vacuum kneader, sequentially adding the terminal vinyl polydimethylsiloxane, the terminal vinyl polymethylphenylsiloxane, and the vinylphenyl MQ silicone resin, and mixing and dissolving to obtain a solution system; adding the fumed silica to the solution system and mixing evenly; then adding hydroxyl silicone oil and hexamethyldisilazane to obtain a reaction system; replacing the reaction system with nitrogen and mixing to obtain a modified system; then adding the terminal vinyl silicone oil, mixing and grinding, and filtering to obtain the base adhesive.

5. The preparation process of a temperature-resistant, low-compression-deformation foamed silicone according to claim 1, characterized in that, The three-stage temperature-controlled molding includes a nucleation and foaming stage, a burst gelation stage, and a gradient post-vulcanization; wherein the temperature of the nucleation and foaming stage is 80-90℃; and the temperature of the burst gelation stage is 130-150℃.

6. The preparation process of a temperature-resistant, low-compression-deformation foamed silicone according to claim 5, characterized in that, The gradient post-vulcanization includes the following steps: first, raise the temperature to 140-150℃ and hold for 45-60 minutes; then raise the temperature to 180-190℃ and hold for 45-60 minutes; finally, raise the temperature to 200-230℃ and hold for 1.5-3 hours.

7. A temperature-resistant, low-compression-deformation foamed silicone, characterized in that, The foamed silicone is obtained by the preparation process described in any one of claims 1-6; the raw materials for preparing the foamed silicone include vinyl-terminated polydimethylsiloxane, vinyl-terminated polymethylphenylsiloxane, vinylphenyl MQ silicone resin, fumed silica, vinyl-terminated silicone oil, side-chain fluorinated foam stabilizer, liquid-phase cerium heat resistant agent and hydroxyl silicone oil.

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