Preparation method of high-temperature-resistant temperature-responsive expansion material

Abstract

The application discloses a preparation method of high-temperature-resistant temperature-responsive expansion material, which comprises the preparation of a microsphere blank, the first coating of the microsphere blank and the second coating of the microsphere blank. The polyacrylonitrile-based expansion microsphere is coated with PI for the first time, the support property of the PI low-temperature plastic is utilized to determine the temperature transformation of the high-temperature high-elastic state, the expansion point of the expansion microsphere is raised to the glass transition temperature of the polyimide, the use temperature of the expansion microsphere is greatly improved, and the temperature-responsive expansion is realized. The expansion microsphere is secondarily coated with liquid silica gel, the air tightness of the expansion microsphere is improved, and the liquid silica gel film is crosslinked with the silica rubber matrix by containing hydrogen silicone oil when vulcanized, so that the distribution uniformity of the expansion microsphere in the matrix is improved. The sealing product adopting the expansion microsphere has the advantages of high size precision, high mechanical property and adaptation to the high-temperature sealing environment of 200-360 DEG C.

Description

Technical Field

[0001] The present invention relates to the technical field of thermoplastic microsphere expansion materials, and in particular to a method for preparing a high-temperature resistant temperature-responsive expansion material. Background Art

[0002] Expandable materials, particularly thermoplastic microspheres, are widely used in sealing, foaming, and other fields. Thermoplastic microspheres are hollow polymer microspheres composed of a thermoplastic polymer shell and an encapsulated alkane gas. Their average diameter ranges from 10 to 50 microns, with a true density of 1,000 to 1,300 kilograms per cubic meter. When the microspheres are heated, the gas pressure within the shell increases, while the thermoplastic shell gradually softens, allowing the microspheres to expand. When the temperature drops, the shell hardens again, and the volume stabilizes. Notably, even slightly expanded microspheres can undergo a second expansion upon further heating.

[0003] However, the expansion temperature range of existing thermoplastic microspheres is typically between 80 and 200°C. At low to medium temperatures below 200°C, these microspheres maintain good heat resistance. However, at higher temperatures, the microsphere shells risk leaking gas or liquid, or even rupturing. This could not only cause localized volume deformation of the substrate but also lead to a sharp decrease in sealing performance, potentially causing production accidents and causing significant problems for the relevant industry.

[0004] In the field of high-temperature sealing, traditional silicone rubber also has some shortcomings. During the high-temperature vulcanization and cross-linking process, silicone rubber will shrink, resulting in a decrease in the dimensional accuracy of the sealing product and affecting the sealing effect. At the same time, the expansion temperature (120-130°C) of ordinary expandable microsphere materials (such as PAN-PAM substrate) is not suitable for high-temperature sealing scenarios (>200°C), which limits its application range. In high-temperature sealing applications, a material is needed that can overcome the shrinkage of silicone rubber during vulcanization, improve dimensional accuracy, and expand appropriately at high temperatures to enhance sealing. Summary of the Invention

[0005] The purpose of the present invention is to solve the shortcomings of the prior art and to propose a method for preparing a high-temperature resistant temperature-responsive expansion material.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] The present invention first proposes a method for preparing a high-temperature resistant temperature-responsive expansion material, comprising the following steps:

[0008] S1. Preparation of microsphere blanks:

[0009] According to the method of patent EP1964903B1 "heat-expandable microspheres, their preparation method and use"——

[0010] S101, preparing an aqueous dispersion medium: mixing a dispersant, an emulsifier, sodium nitrite, sodium chloride, and water, and adding hydrochloric acid to adjust the pH to 3.2, thereby preparing an aqueous dispersion medium;

[0011] S102, preparation of monomer mixture: mixing monomer, blowing agent and initiator;

[0012] S103, suspension polymerization: mixing the aqueous dispersion medium with the monomer mixture, heating at 60° C. for 15 h, then continuing to heat at 70° C. for 9 h, cooling, and filtering to obtain microsphere blank A;

[0013] S2. Primary coating of microsphere blanks:

[0014] S201, amine modification of microspheres: microspheres A, ethylenediamine, N-hydroxysuccinimide (NHS) and water were mixed, stirred at high speed, reacted at 50° C. for 4 h, filtered and washed to obtain microspheres B with amino groups on the surface;

[0015] S202, preparation of polyamic acid solution:

[0016] Reference: Research on biphenyl polyimide precursor - polyamic acid, Zhou Haijun, Journal of Hebei Academy of Sciences, 23-3: 34-36——

[0017] Biphenyl dianhydride (BPDA) and diaminodiphenyl ether (ODA) were added to dimethyl sulfoxide (DMSO) and reacted at 20°C for 3 hours to obtain a biphenyl-type polyamic acid solution C;

[0018] S203, polyamic acid grafting reaction:

[0019] N-hydroxysuccinimide (NHS) is added to the polyamic acid solution obtained in S202, and the N-hydroxysuccinimide (NHS) accounts for 1% of the total weight of the system. The microsphere blank B with amino groups on the surface obtained in S201 is further added, and the microsphere blank B accounts for 40% of the total weight of the system. The reaction is carried out at 50° C. for 4-8 hours, and the filtrate and filter residue are obtained. The filtrate is the polyamic acid solution D, and the filter residue is the microsphere blank E with polyamic acid.

[0020] Taking advantage of the good solubility of dimethyl sulfoxide (DMSO) with polymethacrylic acid (PMAA) and polyimide (PI), and its poor solubility with polymethacrylonitrile (PMAN), the excess carboxyl groups in the polyamic acid solution react with the surface amino groups of the microspheres after activation, so that the PI chains are embedded in the outer layer of the microspheres and form a film after reaching a certain thickness, thereby increasing the film density of the microsphere shell;

[0021] S204, polyimide film forming reaction:

[0022] The wet microsphere blank E was immersed in a mixed solution of acetic anhydride and pyridine (the volume ratio of acetic anhydride to pyridine was 1:1), and stirred at 500 r / min for 15 minutes to obtain a surface-gelled microsphere blank F.

[0023] The polyamic acid solution D was diluted 3-fold with dimethyl sulfoxide (DMSO), and then added to the microspheres F. After stirring at 1500 r / min for 30 minutes, the mixture was filtered and washed with ethanol, dimethyl sulfoxide, and water in sequence to obtain microspheres G coated with a polyimide wet gel film. The dehydrating agent on the surface of the microspheres F was further consumed, and the polyimide film was made dense.

[0024] S3. Secondary coating of microsphere blank:

[0025] S301. Preparation of silicone rubber liquid: Condensation-type one-component RTV silicone rubber (one-component room temperature vulcanized rubber 107 silicone rubber, Shenzhen Jipeng Silicon Fluorine Materials Co., Ltd.), deketoxime-type crosslinker (crosslinker LM43, German Nitration Group), catalyst (XYS-9092 Custer platinum catalyst, Shenzhen Xinyongsheng New Materials Co., Ltd.) and n-hexane were stirred under vacuum to obtain silicone rubber liquid H, which was ready for use.

[0026] S302, silicone rubber layer coating: The microsphere blank G coated with the polyimide wet gel film obtained in S204 and the newly prepared silicone rubber liquid H are mixed in a weight ratio of 1:10, and reacted at a high speed of 1000 r / min for 10 minutes. Then, the microsphere blank G is removed and put into high-speed stirred pure water, reacted for 30 minutes, and then the microsphere blank G is taken out, filtered and dried with hot air at 50°C. The water in the polyimide wet gel film is used to promote crosslinking and form n-hexane / water heterogeneous film-forming conditions, thereby performing start-end vulcanization on the surface of the microsphere blank G to form a silicone rubber layer, thereby obtaining a microsphere finished product I coated with a silicone rubber layer.

[0027] Preferably, the weight ratio of the dispersant, emulsifier, sodium nitrite, sodium chloride and water in the aqueous dispersion medium of S101 is 100:4:0.3:443:1413, the dispersant is 20 wt% colloidal silica (HS-40 colloidal silica, Sigma-Aldrich), and the emulsifier is 50 wt% diethanolamine adipic acid condensation product (emulsifier ODEA, acid value of 78 mg KOH / g, Green Union Chemical Technology Co., Ltd.).

[0028] Preferably, the weight ratio of the monomer, the blowing agent and the initiator in the monomer mixture of S102 is 100:30:1, and the methacrylonitrile (MAN) and the methacrylic acid (MAA) in the monomer are formulated in a molar ratio of 1:1, the blowing agent is isooctane, and the initiator is 2,2'-azobisisobutyronitrile (AIBN).

[0029] Preferably, the specific operation of S103 is: mixing the aqueous dispersion medium and the monomer mixture by stirring with a homogenizer, thereby forming tiny droplets of the monomer mixture in the aqueous dispersion medium, charging the aqueous dispersion medium containing the tiny droplets of the monomer mixture into a polymerization tank (1.5L) with an agitator, heating at 60°C for 15h using a hot water bath, and further heating at 70°C for 9h after cooling, filtering the slurry containing the generated heat-foamable microspheres, washing with water, and drying to obtain a heat-foamable microsphere blank A with an average particle size of 40±0.5μm.

[0030] Preferably, the weight ratio of the microsphere blank A, ethylenediamine, N-hydroxysuccinimide and water in S201 is 10:2.0-2.5:0.2-0.3:100, the high-speed stirring speed is 2000r / min, and after the reaction, it is filtered, washed alternately with water and ethanol, activated by carboxyl groups and reacted with ethylenediamine, and dried to obtain the microsphere blank B with amino groups on the surface.

[0031] Preferably, the specific operation of S2 is: adding dimethyl sulfoxide (DMSO) to biphenyl dianhydride (BPDA) and diaminodiphenyl ether (ODA) in a molar ratio of 1.02:1, with DMSO accounting for 80% of the total weight of the system, and reacting at 20°C for 3h to obtain a biphenyl-type polyamic acid solution C.

[0032] Preferably, the weight ratio of the condensation-type single-component RTV silicone rubber, the deketoxime-type crosslinking agent, the catalyst and n-hexane in the S301 is 100:2.5-3:0.05-0.1:1000. The secondary coating is performed by cross-linking the low-molecular liquid silicone to form a film, so that the microspheres have better direct compatibility with the silicone rubber or other rubber matrix. At the same time, the hydrogen-containing silicone oil can also cross-link with the silicone coating layer, so that the microspheres are evenly distributed in the matrix during use and are not easy to fall off.

[0033] The present invention also proposes the use of the microsphere product I obtained by the above preparation method in silicone rubber sealing products, comprising the following steps:

[0034] Low-phenyl silicone rubber (molecular weight of 200,000-300,000, Hubei Yamade Biopharmaceutical Co., Ltd., which is made by introducing diphenylsiloxane chain segments into the molecular chain of vinyl silicone rubber, and the phenyl mole fraction is 0.05-0.10%), polytrifluoropropylmethylsiloxane (molecular weight of 110,000-150,000, and about 0.36% of vinylsiloxane is introduced into the molecular chain for copolymerization modification to facilitate oxidative cross-linking, Hubei Hengjingrui Chemical Co., Ltd.), and modified nano-silica [Hangzhou Hengge Nanotechnology Co., Ltd., product number: HN-SP30N (amphiphilic), white powder fineness: 30±5nm, purity: 99.5%, specific surface area: 100-200m 2 / g, the surface of silica is modified with silane coupling agent KH560, and the surface has amphiphilicity, that is, it can be uniformly dispersed in both aqueous and oily systems], hydrogen-containing silicone oil (hydrogen molar ratio of 3-7mmol H / g hydrogen-containing silicone oil, Shandong Poly Chemical Co., Ltd.), catalyst (XYS-9092 Custer platinum catalyst, Shenzhen Xinyongsheng New Materials Co., Ltd.), antioxidant 1010 (BASF) and microsphere finished product I are mixed at 10-30°C, put into a mold after mixing, and then vulcanized in a mid-infrared irradiation vulcanization furnace to obtain a sealing product J containing the microsphere finished product I.

[0035] Preferably, the weight ratio of the low-phenyl silicone rubber, polytrifluoropropylmethylsiloxane, modified nano-silica, hydrogenated silicone oil, catalyst, antioxidant 1010 and microsphere finished product I is 100:40-50:10-15:8-10:1-2:0.2-0.3. By blending fluorosilicone rubber and ultrafine silica, the high temperature resistance of the sealing product J is greatly improved, so that it can adapt to application environments of 300°C and above.

[0036] Preferably, the vulcanization is a two-stage vulcanization method, wherein the parameters of the first stage vulcanization are: 200-250°C, and the time does not exceed 5 minutes; the parameters of the second stage vulcanization are: temperature 150-200°C, and the time is 60-120 minutes; by vulcanizing at a slightly high temperature for a short time, a preliminary shape is produced, and then the shape is fixed and stored at a slightly low temperature for a long time, and the finally obtained sealing product has a high J dimensional accuracy.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] 1. This invention is the first to use PI to coat polyacrylonitrile-based expandable microspheres. Utilizing PI's low-temperature plastic shaping support and its high-temperature, high-elasticity temperature transition, the expansion point of the expandable microspheres is raised to the glass transition temperature of polyimide (≈270°C), significantly increasing the operating temperature of the expandable microspheres.

[0039] Moreover, temperature-responsive expansion is achieved: the expanding microspheres expand only slightly below the glass transition temperature of polyimide (PI) (≈270°C), which can inhibit the shrinkage of the silicone rubber matrix; above this temperature, PI is converted into a highly elastic state and expands significantly under the secondary coating of the silicone rubber layer. By controlling the microsphere content, the sealing product can expand appropriately at high temperatures (≤5%), such as making the O-ring fit more closely to the flange ring and enhancing the sealing performance.

[0040] 2. To improve the compatibility of the PI-coated microspheres with the sealant base rubber, the present invention also uses liquid silicone to perform a secondary coating on the expanded microspheres. During vulcanization, the liquid silicone film can also cross-link with the silicone rubber base through hydrogenated silicone oil, improving the uniformity of the distribution of the expanded microspheres in the base. This also further enhances the airtightness of the expanded microspheres, completely eliminating the risk of pressure-induced rupture and leakage of the expanded microsphere wall material at high temperatures.

[0041] 3. The sealing products using the expanded microspheres of the present invention have the following outstanding advantages:

[0042] 1) High dimensional accuracy: The addition of expandable microspheres can inhibit the shrinkage of the silicone rubber matrix during vulcanization and cross-linking, thus overcoming the volume shrinkage of the sealing product during molding and vulcanization, thereby improving dimensional accuracy. For example, the expansion rate of Examples 2, 4, and 5 is less than 0.4%, indicating higher dimensional accuracy.

[0043] 2) High Mechanical Properties: After adding expanded microspheres, the compression set of the sealing product is significantly reduced below the glass transition temperature of PI, far lower than that of existing silicone rubber. Above this temperature, the fluorosilicone component and silica have a greater impact on deformation. Furthermore, the addition of microspheres improves pressure resistance, but excessive microspheres can lead to a loss of elasticity and increased compression set. This suggests that an appropriate amount of microspheres facilitates uniform distribution, further enhancing the sealing effect.

[0044] 3) Adaptable to high temperature sealing environment of 200-360℃: The sealing product has an irreversible phase expansion at around 270℃ and a secondary reversible phase expansion at around 330℃, so that it can adapt to high temperature sealing environment of ≤360℃ and meet the sealing requirements at higher temperatures. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 This is a graph showing the effect of different microsphere contents on the molding expansion rate of silicone rubber-based sealing products of the present invention;

[0046] Figure 2 This is a diagram showing the influence of different application temperatures on the application expansion rate of the silicone rubber-based sealing product of the present invention. DETAILED DESCRIPTION

[0047] The technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the existing known technologies. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0048] 1. Preparation of expanded microspheres:

[0049] 1. Preparation of microsphere blanks:

[0050] Preparation Example 1:

[0051] 1) Preparation of an aqueous dispersion medium: A dispersant, an emulsifier, sodium nitrite, sodium chloride, and water were mixed in a weight ratio of 100:4:0.3:443:1413, and hydrochloric acid was added to adjust the pH to 3.2 to prepare an aqueous dispersion medium. The dispersant was 20 wt % colloidal silica (HS-40 colloidal silica, Sigma-Aldrich), and the emulsifier was 50 wt % diethanolamine adipic acid condensation product (emulsifier ODEA, acid value 78 mg KOH / g, Green Union Chemical Technology Co., Ltd.);

[0052] 2) Preparation of a monomer mixture: The monomer, blowing agent, and initiator are prepared in a weight ratio of 100:30:1, wherein the molar ratio of methacrylonitrile (MAN) and methacrylic acid (MAA) in the monomer is 1:1, the blowing agent is isooctane, and the initiator is 2,2'-azobisisobutyronitrile (AIBN);

[0053] 3) Suspension polymerization: The aqueous dispersion medium and the monomer mixture were mixed by stirring with a homogenizer to form small droplets of the monomer mixture in the aqueous dispersion medium. The aqueous dispersion medium containing the small droplets of the monomer mixture was charged into a polymerization tank (1.5 L) equipped with a stirrer, heated at 60° C. for 15 h using a hot water bath, and further heated at 70° C. for 9 h. After cooling, the slurry containing the generated heat-expandable microspheres was filtered, washed with water, and dried to obtain heat-expandable microsphere blanks A having an average particle size of 40±0.5 μm.

[0054] 2. Coating treatment of expanded microspheres:

[0055] Preparation Example 2:

[0056] 1) Primary coating of microsphere blanks:

[0057] ① Amino modification of the microspheres: The microspheres A obtained in Preparation Example 1, ethylenediamine, N-hydroxysuccinimide (NHS), and water were mixed in a weight ratio of 10:2.0:0.2:100 under high-speed stirring, reacted at 50°C for 4 hours, filtered after the reaction, washed alternately with water and ethanol, activated by carboxyl groups, reacted with ethylenediamine, and dried to obtain microspheres B with amino groups on the surface;

[0058] ② Preparation of polyamic acid solution:

[0059] Biphenyl dianhydride (BPDA) and diaminodiphenyl ether (ODA) were added into dimethyl sulfoxide (DMSO) at a molar ratio of 1.02:1, with dimethyl sulfoxide (DMSO) accounting for 80% of the total weight of the system, and reacted at 20°C for 3 hours to obtain a biphenyl-type polyamic acid solution C;

[0060] ③Polyamic acid grafting reaction:

[0061] N-hydroxysuccinimide (NHS) is added to the polyamic acid solution obtained in S202, and the N-hydroxysuccinimide (NHS) accounts for 1% of the total weight of the system. The microsphere blank B with amino groups on the surface obtained in S201 is further added, and the microsphere blank B accounts for 40% of the total weight of the system. The reaction is carried out at 50° C. for 4-8 hours, and the filtrate and filter residue are obtained. The filtrate is the polyamic acid solution D, and the filter residue is the microsphere blank E with polyamic acid.

[0062] Taking advantage of the good solubility of dimethyl sulfoxide (DMSO) with polymethacrylic acid (PMAA) and polyimide (PI), and its poor solubility with polymethacrylonitrile (PMAN), the excess carboxyl groups in the polyamic acid solution react with the surface amino groups of the microspheres after activation, so that the PI chains are embedded in the outer layer of the microspheres and form a film after reaching a certain thickness, thereby increasing the film density of the microsphere shell;

[0063] ④Polyimide film-forming reaction:

[0064] The wet microsphere blank E was immersed in a mixed solution of acetic anhydride and pyridine (the volume ratio of acetic anhydride to pyridine was 1:1), and stirred at 500 r / min for 15 minutes to obtain a surface-gelled microsphere blank F.

[0065] The polyamic acid solution D was diluted 3-fold with dimethyl sulfoxide (DMSO), and then added to the microspheres F. After stirring at 1500 r / min for 30 minutes, the mixture was filtered and washed with ethanol, dimethyl sulfoxide, and water in sequence to obtain microspheres G coated with a polyimide wet gel film. The dehydrating agent on the surface of the microspheres F was further consumed, and the polyimide film was made dense.

[0066] 2) Secondary coating of microsphere blanks:

[0067] ⑤ Preparation of silicone rubber liquid: Condensation type one-component RTV silicone rubber (one-component room temperature vulcanized rubber 107 silicone rubber, Shenzhen Jipeng Silicon Fluorine Materials Co., Ltd.), deketoxime type crosslinker (crosslinker LM43, German Nitration Group), catalyst (XYS-9092 Custer Platinum Catalyst, Shenzhen Xinyongsheng New Materials Co., Ltd.) and n-hexane are mixed in a weight ratio of 100:2.5:0.05:1000 under vacuum and stirred to obtain silicone rubber liquid H, which is ready for use. Secondary coating is performed by cross-linking low molecular liquid silicone to form a film, so that the microspheres have better direct compatibility with silicone rubber or other rubber matrices. At the same time, hydrogen-containing silicone oil can also cross-link with the silicone coating layer, so that the microspheres are evenly distributed in the matrix during application and are not easy to fall off.

[0068] ⑥ Silicone rubber layer coating: The microsphere blank G coated with the polyimide wet gel film obtained in ④ and the newly prepared silicone rubber liquid H in a weight ratio of 1:10 are mixed, and the mixture is stirred at a high speed of 1000 r / min for 10 minutes. The microsphere blank G is then removed and put into high-speed stirred pure water for reaction for 30 minutes. The microsphere blank G is then taken out, filtered, and dried with hot air at 50°C. The water in the polyimide wet gel film is used to promote crosslinking and form n-hexane / water heterogeneous film-forming conditions, thereby performing start-end vulcanization on the surface of the microsphere blank G to form a silicone rubber layer, thereby obtaining a microsphere finished product I coated with a silicone rubber layer.

[0069] Preparation Example 3:

[0070] 1) Primary coating of microsphere blanks:

[0071] ① Amino modification of the microspheres: The microspheres A obtained in Preparation Example 1, ethylenediamine, N-hydroxysuccinimide (NHS), and water were mixed in a weight ratio of 10:2.2:0.25:100 under high-speed stirring, reacted at 50°C for 4 hours, filtered after the reaction, washed alternately with water and ethanol, activated by carboxyl groups, reacted with ethylenediamine, and dried to obtain microspheres B with amino groups on the surface;

[0072] ② Preparation of polyamic acid solution:

[0073] Biphenyl dianhydride (BPDA) and diaminodiphenyl ether (ODA) were added into dimethyl sulfoxide (DMSO) at a molar ratio of 1.02:1, with dimethyl sulfoxide (DMSO) accounting for 80% of the total weight of the system, and reacted at 20°C for 3 hours to obtain a biphenyl-type polyamic acid solution C;

[0074] ③Polyamic acid grafting reaction:

[0075] N-hydroxysuccinimide (NHS) is added to the polyamic acid solution obtained in S202, and the N-hydroxysuccinimide (NHS) accounts for 1% of the total weight of the system. The microsphere blank B with amino groups on the surface obtained in S201 is further added, and the microsphere blank B accounts for 40% of the total weight of the system. The reaction is carried out at 50° C. for 4-8 hours, and the filtrate and filter residue are obtained. The filtrate is the polyamic acid solution D, and the filter residue is the microsphere blank E with polyamic acid.

[0076] ④Polyimide film-forming reaction:

[0077] The wet microsphere blank E was immersed in a mixed solution of acetic anhydride and pyridine (the volume ratio of acetic anhydride to pyridine was 1:1), and stirred at 500 r / min for 15 minutes to obtain a surface-gelled microsphere blank F.

[0078] The polyamic acid solution D was diluted 3 times with dimethyl sulfoxide (DMSO), and then added to the microsphere blank F. After stirring at 1500 r / min for 30 minutes, the solution was filtered and washed with ethanol, dimethyl sulfoxide, and water in sequence to obtain the microsphere blank G coated with the polyimide wet gel film.

[0079] 2) Secondary coating of microsphere blanks:

[0080] ⑤ Preparation of silicone rubber liquid: Condensation type one-component RTV silicone rubber (one-component room temperature vulcanized rubber 107 silicone rubber, Shenzhen Jipeng Silicon Fluorine Material Co., Ltd.), deketoxime type crosslinker (crosslinker LM43, German Nitration Group), catalyst (XYS-9092 Custer platinum catalyst, Shenzhen Xinyongsheng New Materials Co., Ltd.) and n-hexane are mixed in a weight ratio of 100:2.8:0.08:1000 under vacuum and stirred to obtain silicone rubber liquid H, which is ready for use;

[0081] ⑥ Silicone rubber layer coating: The microsphere blank G coated with the polyimide wet gel film obtained in ④ and the newly prepared silicone rubber liquid H in a weight ratio of 1:10 are mixed, and the mixture is stirred at a high speed of 1000 r / min for 10 minutes. Then, the microsphere blank G is removed and put into high-speed stirred pure water. The reaction is carried out for 30 minutes. Then, the microsphere blank G is taken out, filtered, and dried with hot air at 50°C to obtain the finished microsphere I coated with a silicone rubber layer.

[0082] Preparation Example 4:

[0083] 1) Primary coating of microsphere blanks:

[0084] ① Amino modification of the microspheres: The microspheres A obtained in Preparation Example 1, ethylenediamine, N-hydroxysuccinimide (NHS), and water were mixed in a weight ratio of 10:2.5:0.3:100 under high-speed stirring, reacted at 50°C for 4 hours, filtered after the reaction, washed alternately with water and ethanol, activated by carboxyl groups, reacted with ethylenediamine, and dried to obtain microspheres B with amino groups on the surface;

[0085] ② Preparation of polyamic acid solution:

[0086] Biphenyl dianhydride (BPDA) and diaminodiphenyl ether (ODA) were added into dimethyl sulfoxide (DMSO) at a molar ratio of 1.02:1, with dimethyl sulfoxide (DMSO) accounting for 80% of the total weight of the system, and reacted at 20°C for 3 hours to obtain a biphenyl-type polyamic acid solution C;

[0087] ③Polyamic acid grafting reaction:

[0088] N-hydroxysuccinimide (NHS) is added to the polyamic acid solution obtained in S202, and the N-hydroxysuccinimide (NHS) accounts for 1% of the total weight of the system. The microsphere blank B with amino groups on the surface obtained in S201 is further added, and the microsphere blank B accounts for 40% of the total weight of the system. The reaction is carried out at 50° C. for 4-8 hours, and the filtrate and filter residue are obtained. The filtrate is the polyamic acid solution D, and the filter residue is the microsphere blank E with polyamic acid.

[0089] ④Polyimide film-forming reaction:

[0090] The wet microsphere blank E was immersed in a mixed solution of acetic anhydride and pyridine (the volume ratio of acetic anhydride to pyridine was 1:1), and stirred at 500 r / min for 15 minutes to obtain a surface-gelled microsphere blank F.

[0091] The polyamic acid solution D was diluted 3-fold with dimethyl sulfoxide (DMSO), and then added to the microspheres F. After stirring at 1500 r / min for 30 minutes, the mixture was filtered and washed with ethanol, dimethyl sulfoxide, and water in sequence to obtain microspheres G coated with a polyimide wet gel film. The dehydrating agent on the surface of the microspheres F was further consumed, and the polyimide film was made dense.

[0092] 2) Secondary coating of microsphere blanks:

[0093] ⑤ Preparation of silicone rubber liquid: Condensation type one-component RTV silicone rubber (one-component room temperature vulcanized rubber 107 silicone rubber, Shenzhen Jipeng Silicon Fluorine Material Co., Ltd.), deketoxime type crosslinker (crosslinker LM43, German Nitration Group), catalyst (XYS-9092 Custer platinum catalyst, Shenzhen Xinyongsheng New Materials Co., Ltd.) and n-hexane are mixed in a weight ratio of 100:3:0.1:1000 under vacuum and stirred to obtain silicone rubber liquid H, which is ready for use;

[0094] ⑥ Silicone rubber layer coating: The microsphere blank G coated with the polyimide wet gel film obtained in ④ and the newly prepared silicone rubber liquid H in a weight ratio of 1:10 are mixed, and the mixture is stirred at a high speed of 1000 r / min for 10 minutes. Then, the microsphere blank G is removed and put into high-speed stirred pure water. The reaction is carried out for 30 minutes. Then, the microsphere blank G is taken out, filtered, and dried with hot air at 50°C to obtain the finished microsphere I coated with a silicone rubber layer.

[0095] Comparative Preparation Example 1:

[0096] 1) Primary coating of microsphere blanks:

[0097] ① Amino modification of the microspheres: The microspheres A obtained in Preparation Example 1, ethylenediamine, N-hydroxysuccinimide (NHS), and water were mixed in a weight ratio of 10:2.2:0.25:100 under high-speed stirring, reacted at 50°C for 4 hours, filtered after the reaction, washed alternately with water and ethanol, activated by carboxyl groups, reacted with ethylenediamine, and dried to obtain microspheres B with amino groups on the surface;

[0098] ② Preparation of polyamic acid solution:

[0099] Biphenyl dianhydride (BPDA) and diaminodiphenyl ether (ODA) were added into dimethyl sulfoxide (DMSO) at a molar ratio of 1.02:1, with dimethyl sulfoxide (DMSO) accounting for 80% of the total weight of the system, and reacted at 20°C for 3 hours to obtain a biphenyl-type polyamic acid solution C;

[0100] ③Polyamic acid grafting reaction:

[0101] N-hydroxysuccinimide (NHS) is added to the polyamic acid solution obtained in S202, and the N-hydroxysuccinimide (NHS) accounts for 1% of the total weight of the system. The microsphere blank B with amino groups on the surface obtained in S201 is further added, and the microsphere blank B accounts for 40% of the total weight of the system. The reaction is carried out at 50° C. for 4-8 hours, and the filtrate and filter residue are obtained. The filtrate is the polyamic acid solution D, and the filter residue is the microsphere blank E with polyamic acid.

[0102] ④Polyimide film-forming reaction:

[0103] The wet microsphere blank E was immersed in a mixed solution of acetic anhydride and pyridine (the volume ratio of acetic anhydride to pyridine was 1:1), and stirred at 500 r / min for 15 minutes to obtain a surface-gelled microsphere blank F.

[0104] After polyamic acid solution D was diluted 3 times with dimethyl sulfoxide (DMSO), microsphere blank F was added and stirred at 1500 r / min for 30 min. After filtration, it was washed with ethanol, dimethyl sulfoxide and water in sequence to obtain microsphere blank G coated with polyimide wet gel film. After drying, the microsphere blank G directly replaced the microsphere finished product I of Preparation Example 3 and was used as an expandable microsphere additive for sealing products. The difference between the effect after use and Preparation Example 3 was observed.

[0105] 2. Preparation of Sealing Products Containing Expanded Microspheres:

[0106] The application process of microsphere finished product I in silicone rubber sealing products is as follows:

[0107] Low-phenyl silicone rubber (molecular weight of 200,000-300,000, Hubei Yamade Biopharmaceutical Co., Ltd., which is made by introducing diphenylsiloxane chain segments into the molecular chain of vinyl silicone rubber, and the phenyl mole fraction is 0.05-0.10%), polytrifluoropropylmethylsiloxane (molecular weight of 110,000-150,000, and about 0.36% of vinylsiloxane is introduced into the molecular chain for copolymerization modification to facilitate oxidative cross-linking, Hubei Hengjingrui Chemical Co., Ltd.), and modified nano-silica [Hangzhou Hengge Nanotechnology Co., Ltd., product number: HN-SP30N (amphiphilic), white powder fineness: 30±5nm, purity: 99.5%, specific surface area: 100-200m 2 / g, the surface of silicon dioxide is modified by silane coupling agent KH560, and the surface has amphiphilicity, that is, it can be evenly dispersed in both aqueous and oily systems], hydrogenated silicone oil (hydrogen molar ratio of 3-7mmol The product I is prepared by mixing a mixture of H / g hydrogen-containing silicone oil (Shandong Polychemical Co., Ltd.), a catalyst (XYS-9092 Custer platinum catalyst, Shenzhen Xinyongsheng New Materials Co., Ltd.), an antioxidant 1010 (BASF), and a microsphere product I in a weight ratio of 100:40-50:10-15:8-10:1-2:0.2-0.3:3-6 at 10-30° C. and placing the mixture into a mold to obtain a sealing body. After demolding the sealing body, the sealing body is subjected to a two-stage vulcanization process in a mid-infrared irradiation vulcanization furnace to obtain a sealing product J containing the microsphere product I. The first stage vulcanization parameters are: 200-250° C., and the time is no more than 5 minutes. The second stage vulcanization parameters are: temperature 150-200° C., and the time is 60-120 minutes. The initial shaping is achieved by short-term vulcanization at a slightly high temperature, and the shaping is then preserved for a long time at a slightly low temperature. Finally, the obtained sealing product J is vulcanized with high dimensional accuracy.

[0108] The formula of each sealing product J is shown in Table 1 below:

[0109] Table 1. Formulations of silicone rubber-based sealing products

[0110]

[0111] It should be noted that Comparative Example 9 in Table 1 directly uses the uncoated microsphere blank A, which expands violently during the vulcanization process, and reminds the experimenter to pay attention to safety. It can be used for foam rubber products, but the present invention has not been further studied; while Comparative Example 8 uses a single layer of PI for wrapping, and the volume expansion during the vulcanization process is greater than that of Example 2 (Example 2 is -0.11%, that is, it shrinks by 0.11%, while Comparative Example 8 is +0.25%, that is, it expands by 0.25%). Considering the special PI film prepared with polyamic acid as a precursor in the present invention, the sealing performance may be subject to certain challenges, but the sealing main structure of the PI film should not be damaged.

[0112] 3. The impact of expanded microspheres on the performance of sealing products:

[0113] 1. Effect of microsphere content on the molding expansion rate of silicone rubber-based sealing products:

[0114] According to the existing vulcanization process of ordinary silicone rubber, the cross-linking process of hot vulcanization often results in volume shrinkage, which in turn poses a serious challenge to dimensional accuracy. The present invention attempts to overcome this problem by using a temperature-sensitive expandable microsphere material. However, existing expandable microspheres generally use a PAN-PAM (acrylonitrile and acrylamide copolymer) substrate, whose expansion point temperature is generally 120-130°C, which is not suitable for high-temperature sealing applications above 200°C. Therefore, PI is used for coating to limit its movement. In an environment below its glass transition temperature (≈270°C), PI is a glassy plastic with a shaping effect. It only expands slightly at <200°C. This small expansion can appropriately suppress the vulcanization and cross-linking shrinkage of the silicone rubber matrix, thereby improving the dimensional accuracy of the sealing product.

[0115] In an environment above its glass transition temperature, PI is converted into a highly elastic state and has a relatively large expansion rate under the secondary coating of the liquid silicone film. Controlling its content can make the sealing product produce appropriate high-temperature expansion (should be ≤5%), such as making the O-ring fit more closely to the flange ring of the sealing tank mouth, improving the sealing performance, that is, forming a node with the glass transition temperature of the PI film (i.e. Figure 1 The inflection point in the middle broken line, Tg≈270℃) is a temperature-responsive expansion material.

[0116] Reference Figure 1 , first of all, it should be noted that Figure 1 The expansion rate during the molding process is calculated by the following formula: (d n -d m ) / d m , d m It is the thickness of the sealing body obtained after the mixture is filled into the mold and demoulded. nis the thickness of the sealing product J obtained after vulcanization. From comparative examples 3-7, and examples 2, and examples 4-6, it can be seen that with the increase of the content of expanded microspheres, the shrinkage of the molding vulcanization volume is gradually overcome. Among them, the expansion rate of example 2, example 4 and example 5 is relatively low (<0.4%), and thus the dimensional accuracy is higher.

[0117] 2. The influence of temperature on the expansion rate of silicone rubber-based sealing products:

[0118] Reference Figure 2 , it should be noted that Figure 2 The thermal expansion rate in the above formula is: according to the process of Example 2, the sealing product J is made into a block sample with a length of 30 cm, a width of 10 cm, and a thickness of 5 cm. The expansion test is carried out at a certain temperature. At a fixed temperature, the thickness of the sample is tested every 10 seconds. The thermal expansion rate after use is calculated according to the following formula: (d t -d o ) / d o , where d t is the thickness of the sample at time t, d o The initial thickness of the sample is recorded at the time point when the thickness remains basically unchanged, and the final thickness is recorded.

[0119] Depend on Figure 2 It can be seen that the sealing product has a sudden change in expansion rate at around 270°C. The first is the expansion of the microspheres themselves caused by the phase change of PI, and this expansion is irreversible. The reason is that below Tg, PI solidifies into a plastic form, which has a shaping effect on the microspheres; there is a second sudden change in expansion rate at around 330°C. The second expansion amplitude is smaller, which is the volume expansion caused by the thermal extension of the Si-O main chain of the silicone rubber body. The secondary expansion is reversible expansion and contraction at ≤400°C, but it is also beneficial to sealing conditions at higher temperatures. It proves that the product of the present invention can adapt to sealing environments of any temperature ≤360°C (needs to be greater than the Tg temperature of the silicone rubber body), and undergoes a temperature-sensitive irreversible phase expansion near 270°C and a secondary temperature-sensitive reversible volume expansion near 330°C to meet the higher sealing requirements of high-temperature gas overflow.

[0120] 3. Mechanical properties of sealing products:

[0121] Tensile properties: According to the experimental method specified in "GB / T528-2009 Vulcanized rubber or thermoplastic rubber - Determination of tensile stress-strain properties", the tensile strength and elongation at break are tested. Compression test: According to the experimental method specified in "GB / T7759.1-2015 Vulcanized rubber or thermoplastic rubber - Determination of compression set Part 1: At room temperature and elevated temperature", the compression set of the sample is tested at 25°C and 100°C respectively;

[0122] Refer to this method to test the compression set at 250℃ and 350℃: keep the sealing sample at the specified temperature (250℃ or 350℃) and at a low compression rate (10%, so that the sample thickness is reduced by 10%) for 24 hours, remove the pressure, and then measure the thickness change of the sample before and after compression, and calculate the percentage of compression set.

[0123] Specific performance is shown in Table 2 below:

[0124] Table 2. Mechanical properties of sealing products containing expanded microspheres

[0125]

[0126] As shown in Table 2, when comparing Examples 1-3, the addition of microspheres may help improve structural toughness and significantly reduce compression set below Tg, far below the strength and toughness of existing silicone rubber (compression set at 25°C is generally not less than 10%). Above Tg, the fluorosilicone component and silica have a greater impact on deformation, causing the compression set to vary irregularly.

[0127] And by comparing Comparative Examples 3-7, Examples 4-6 and Example 2, with the addition of microspheres, the pressure resistance is greatly improved, but too many microspheres cause loss of elasticity and more compression deformation, indicating that the microspheres may have aggregated, which is not conducive to the uniform distribution of the expansion agent.

[0128] Comparing Comparative Example 1 with Example 2, the addition of fluorosilicone components leads to an all-round improvement in elasticity, thermal stability and pressure resistance;

[0129] Comparative Example 2 Compared with Example 2, the addition of silicon dioxide leads to a decrease in elasticity, but improves thermal stability and pressure resistance;

[0130] Comparing Comparative Example 8 with Example 2, it is possible that the microspheres without silicone rubber coating have poor compatibility, resulting in differences in tensile and compressive properties.

[0131] The above data proves that by adding expandable microspheres to the silicone rubber matrix, the compression deformation of the rubber can be reduced while ensuring basic mechanical properties, while also meeting a certain expansion requirement under high-temperature sealing. Therefore, the present invention is suitable for high-temperature sealing products of 200-360°C and can maintain a highly expanded and sealed state at high temperatures for a long time.

[0132] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for preparing a high-temperature resistant temperature-responsive expansion material, characterized in that: The following steps are involved: S1. Preparation of microsphere blanks: S101, preparing an aqueous dispersion medium: mixing a dispersant, an emulsifier, sodium nitrite, sodium chloride, and water, and adding hydrochloric acid to adjust the pH to 3.2, thereby preparing an aqueous dispersion medium; S102. Preparation of a monomer mixture: The monomer, the blowing agent, and the initiator are mixed, wherein the weight ratio of the monomer, the blowing agent, and the initiator is 100:30:1, and the methacrylonitrile and the methacrylic acid in the monomer are prepared in a molar ratio of 1:1, the blowing agent is isooctane, and the initiator is 2,2'-azobisisobutyronitrile; S103, suspension polymerization: mixing the aqueous dispersion medium with the monomer mixture, heating at 60° C. for 15 h, then continuing to heat at 70° C. for 9 h, cooling, and filtering to obtain microsphere blank A; S2. Primary coating of microsphere blanks: S201, amine modification of microspheres: microspheres A, ethylenediamine, N-hydroxysuccinimide and water were mixed, stirred at high speed, reacted at 50°C for 4 hours, filtered and washed to obtain microspheres B with amino groups on the surface; S202, preparation of polyamic acid solution: Add biphenyl dianhydride and diaminodiphenyl ether into dimethyl sulfoxide and react at 20°C for 3 hours to obtain a biphenyl-type polyamic acid solution C; S203, polyamic acid grafting reaction: N-hydroxysuccinimide is added to the polyamic acid solution obtained in S202, and the N-hydroxysuccinimide accounts for 1% of the total weight of the system. The microsphere blank B with amino groups on the surface obtained in S201 is further added, and the microsphere blank B accounts for 40% of the total weight of the system. The reaction is carried out at 50° C. for 4-8 hours, and the filtrate and filter residue are obtained. The filtrate is polyamic acid solution D, and the filter residue is microsphere blank E with polyamic acid. S204, polyimide film forming reaction: The wet microsphere blank E was immersed in a mixed solution of acetic anhydride and pyridine, and stirred at 500 r / min for 15 minutes to obtain a surface-gelled microsphere blank F; The polyamic acid solution D was diluted 3 times with dimethyl sulfoxide, and then added to the microsphere blank F. After stirring at 1500 r / min for 30 minutes, it was filtered and washed with ethanol, dimethyl sulfoxide, and water in sequence to obtain the microsphere blank G coated with the polyimide wet gel film; S3. Secondary coating of microsphere blank: S301, preparation of silicone rubber liquid: condensation type one-component RTV silicone rubber, deketoxime type crosslinking agent, catalyst and n-hexane are stirred under vacuum to obtain silicone rubber liquid H; S302, silicone rubber layer coating: The microsphere blank G coated with the polyimide wet gel film obtained in S204 and the newly prepared silicone rubber liquid H are mixed in a weight ratio of 1:10, and reacted at a high speed of 1000 r / min for 10 minutes. Then, the microsphere blank G is removed and put into high-speed stirred pure water and reacted for 30 minutes; then, the microsphere blank G is taken out, filtered, and dried with hot air at 50°C to obtain a microsphere finished product I coated with a silicone rubber layer.

2. The method for preparing a high-temperature resistant temperature-responsive expansion material according to claim 1, characterized in that: The weight ratio of the dispersant, emulsifier, sodium nitrite, sodium chloride and water in the aqueous dispersion medium of S101 is 100:4:0.3:443:1413, the dispersant is 20 wt% colloidal silica, and the emulsifier is 50 wt% diethanolamine adipic acid condensation product.

3. The method for preparing a high-temperature resistant temperature-responsive expansion material according to claim 1, characterized in that: The specific operation of S103 is as follows: mixing the aqueous dispersion medium and the monomer mixture by stirring with a homogenizer, thereby forming tiny droplets of the monomer mixture in the aqueous dispersion medium, charging the aqueous dispersion medium containing the tiny droplets of the monomer mixture into a polymerization tank equipped with an agitator, heating at 60° C. for 15 hours using a hot water bath, and further heating at 70° C. for 9 hours, and after cooling, filtering the slurry containing the generated heat-foamable microspheres, washing with water, and drying to obtain heat-foamable microsphere blanks A having an average particle size of 40±0.5 μm.

4. The method for preparing a high-temperature resistant temperature-responsive expansion material according to claim 1, characterized in that: In the S201, the weight ratio of the microsphere blank A, ethylenediamine, N-hydroxysuccinimide and water is 10:2.0-2.5:0.2-0.3:100, the high-speed stirring speed is 2000 r / min, and after the reaction, it is filtered, washed alternately with water and ethanol, activated by carboxyl groups, and reacted with ethylenediamine. After drying, a microsphere blank B with amino groups on the surface is obtained.

5. The method for preparing a high-temperature resistant temperature-responsive expansion material according to claim 1, characterized in that: The specific operation of S2 is: adding dimethyl sulfoxide to biphenyl dianhydride and diaminodiphenyl ether at a molar ratio of 1.02:1, with dimethyl sulfoxide accounting for 80% of the total weight of the system, and reacting at 20° C. for 3 hours to obtain a biphenyl-type polyamic acid solution C.

6. The method for preparing a high-temperature resistant temperature-responsive expansion material according to claim 1, characterized in that: The weight ratio of the condensation-type single-component RTV silicone rubber, the deketoxime-type crosslinking agent, the catalyst and n-hexane in the S301 is 100:2.5-3:0.05-0.1:1000.

7. Use of the microsphere product I obtained by the preparation method according to any one of claims 1 to 6 in silicone rubber sealing products, characterized in that: The following steps are involved: Low-phenyl silicone rubber, polytrifluoropropylmethylsiloxane, modified nano-silica, hydrogen-containing silicone oil, a catalyst, an antioxidant 1010, and a microsphere finished product I are mixed at 10-30° C., wherein the weight ratio of the low-phenyl silicone rubber, polytrifluoropropylmethylsiloxane, modified nano-silica, hydrogen-containing silicone oil, the catalyst, the antioxidant 1010, and the microsphere finished product I is 100:40-50:10-15:8-10:1-2:0.2-0.3:3-6. After mixing, the mixture is placed in a mold and then vulcanized in a mid-infrared irradiation vulcanization furnace to obtain a sealing product J containing the microsphere finished product I.

8. The use of the microsphere product I according to claim 7 in silicone rubber sealing products, characterized in that: The vulcanization is a two-stage vulcanization method, wherein the parameters of the first stage vulcanization are: 200-250° C., and the time is no more than 5 minutes; the parameters of the second stage vulcanization are: temperature 150-200° C., and the time is 60-120 minutes.

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