Preparation method of high-temperature-resistant temperature response type expansion material

Abstract

The invention discloses a preparation method of a high-temperature-resistant temperature response type expansion material. The preparation method comprises the steps of preparation of a microsphere blank, primary coating of the microsphere blank and secondary coating of the microsphere blank. According to the preparation method, PI is adopted for coating the polyacrylonitrile-based expanded microspheres for the first time, the expansion point of the expanded microspheres is increased to the glass-transition temperature of polyimide by utilizing the supporting property of PI low-temperature plastic shaping and the temperature transition of a high-temperature and high-elastic state, the use temperature of the expanded microspheres is greatly increased, and temperature response type expansion is achieved; according to the invention, liquid silica gel is also adopted to carry out secondary coating on the expanded microspheres, so that the air tightness of the expanded microspheres is improved, and the liquid silica gel film is crosslinked with a silicone rubber matrix through hydrogen-containing silicone oil during vulcanization, so that the distribution uniformity of the expanded microspheres in the matrix is improved; a sealing product adopting the expansion microsphere has the advantages of high dimensional precision, high mechanical property, adaptability to a high-temperature sealing environment of 200-360 DEG C and the like.

Description

Technical Field

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

[0002] Expansion materials, especially thermoplastic microspheres, are widely used in fields such as sealing and foaming. Thermoplastic microspheres are hollow polymer microspheres composed of a thermoplastic polymer shell and internally sealed alkane gas, with an average diameter between 10 and 50 microns and a true density of 1000 to 1300 kg / m³. When the microspheres are heated, the gas pressure inside the shell increases, and at the same time, the thermoplastic shell gradually softens, causing the volume of the microspheres to expand; when the temperature drops, the shell of the microspheres hardens again, and the volume is correspondingly fixed. It should be noted that even slightly expanded microspheres can undergo secondary expansion when heated again.

[0003] However, the expansion temperature range of existing thermoplastic microspheres is usually between 80 and 200 °C. Under medium and low temperature conditions below 200 °C, such microspheres can maintain good heat resistance. But in a higher temperature environment, the shell of the microspheres faces the risk of leaking gas or liquid, and even cracking, which may not only cause local volume deformation of the matrix but also lead to a sharp decline in the sealing performance, further causing production accidents and bringing many troubles to related industries.

[0004] In the field of high-temperature sealing, traditional silicone rubber also has some deficiencies. During the high-temperature vulcanization 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 expansion microsphere materials (such as PAN-PAM substrates) is not suitable for high-temperature sealing scenarios (>200 °C), limiting their application scope. In high-temperature sealing application scenarios, a material that can overcome the vulcanization shrinkage of silicone rubber, improve the dimensional accuracy, and expand appropriately at high temperatures to enhance the sealing performance is needed. Summary of the Invention

[0005] The purpose of the present invention is to solve the deficiencies existing in the prior art, and to propose a preparation method of a high-temperature resistant temperature-responsive expansion material.

[0006] To achieve the above purpose, the present invention adopts the following technical solutions:

[0007] The present invention first proposes a preparation method of a high-temperature resistant temperature-responsive expansion material, including the following steps:

[0008] S1. Preparation of microsphere blanks:

[0009] Method according to Patent EP1964903B1 "Thermally Expandable Microspheres, Method for Producing the Same, and Use Thereof" -

[0010] S101, Preparation of the aqueous dispersion medium: Mix a dispersant, an emulsifier, sodium nitrite, sodium chloride, and water, and add hydrochloric acid to adjust the pH to 3.2 to prepare an aqueous dispersion medium;

[0011] S102, Preparation of the monomer mixture: Made by mixing a monomer, a blowing agent, and an initiator;

[0012] S103, Suspension polymerization: Mix the aqueous dispersion medium with the monomer mixture, heat at 60 °C for 15 h, continue to heat at 70 °C for 9 h, cool, and then filter to obtain the microsphere blank A;

[0013] S2, Primary coating of the microsphere blank:

[0014] S201, Amino modification of the microsphere blank: Mix the microsphere blank A, ethylenediamine, N-hydroxysuccinimide (NHS), and water, stir at high speed, react at 50 °C for 4 h, filter and wash to obtain the microsphere blank B with amino groups on the surface;

[0015] S202, Preparation of the polyamic acid solution:

[0016] Reference: Research on Biphenyl-Type Polyimide Precursor - Polyamic Acid, Zhou Haijun, Journal of Hebei Academy of Sciences, 23 - 3: 34 - 36 -

[0017] Put biphenyl dianhydride (BPDA) and diaminodiphenyl ether (ODA) into dimethyl sulfoxide (DMSO), react at 20 °C for 3 h to obtain the biphenyl-type polyamic acid solution C;

[0018] S203, Polyamic acid grafting reaction:

[0019] Put N-hydroxysuccinimide (NHS) into the polyamic acid solution obtained in S202, and the N-hydroxysuccinimide (NHS) accounts for 1% of the total weight of the system. Then continue to put the microsphere blank B with amino groups on the surface obtained in S201, and the microsphere blank B accounts for 40% of the total weight of the system. React at 50 °C for 4 - 8 h, filter to obtain the filtrate and the filter residue. The filtrate is the polyamic acid solution D, and the filter residue is the microsphere blank E with polyamic acid;

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

[0021] S204, Polyimide film-forming reaction:

[0022] Immerse the wet microsphere green body E in a mixed solution of acetic anhydride and pyridine (volume ratio of acetic anhydride to pyridine is 1:1), stir at 500 r / min for 15 min, and obtain the surface-gelatinized microsphere green body F;

[0023] After diluting the polyamic acid solution D three times with dimethyl sulfoxide (DMSO), add the microsphere green body F, stir and react at 1500 r / min for 30 min, filter, and then wash successively with ethanol, dimethyl sulfoxide, and water to obtain the microsphere green body G coated with a polyimide wet gel film; further consume the dehydrating agent on the surface of the microsphere green body F and make the polyimide film dense;

[0024] S3, Secondary coating of the microsphere green body:

[0025] S301, Preparation of silicone rubber solution: Condensation-type one-component RTV silicone rubber (one-component room-temperature vulcanizing rubber 107 silicone rubber, Shenzhen Jipeng Silicon Fluoride Materials Co., Ltd.), ketoxime-type crosslinking agent (crosslinking agent LM43, German Nitration Group), catalyst (XYS-9092 type Kast platinum catalyst, Shenzhen Xinyongsheng New Materials Co., Ltd.) and n-hexane, stir under vacuum to obtain the silicone rubber solution H, which can be used immediately after mixing;

[0026] S302, Silicone rubber layer coating: Mix the microsphere green body G coated with a polyimide wet gel film obtained in S204 and the newly prepared silicone rubber solution H in a weight ratio of 1:10, stir and react at a high speed of 1000 r / min for 10 min, then fish out the microsphere green body G, put it into high-speed stirred pure water, react for 30 min, then take out the microsphere green body G, filter and dry at 50 °C with hot air, use the water in the polyimide wet gel film to promote crosslinking, and form a n-hexane / water heterogeneous film-forming condition, so as to carry out initial vulcanization on the surface of the microsphere green body G to form a silicone rubber layer, and obtain the microsphere finished product I with a silicone rubber layer coating.

[0027] Preferably, in the aqueous dispersion medium of S101, the weight ratio of the dispersant, emulsifier, sodium nitrite, sodium chloride, and water 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 is 78 mg KOH / g, Greenlink Chemical Technology Co., Ltd.).

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

[0029] Preferably, the specific operation of S103 is as follows: The aqueous dispersion medium and the monomer mixture are mixed by stirring with a homogenizer, so as to form tiny droplets of the monomer mixture in the aqueous dispersion medium. The aqueous dispersion medium containing the tiny droplets of the monomer mixture is charged into a polymerization tank (1.5 L) equipped with a stirrer, heated at 60 °C for 15 h using a water bath, and further heated at 70 °C for 9 h. After cooling, the slurry containing the generated heat-expandable microspheres is filtered, washed with water, and dried to obtain heat-expandable microsphere blanks A with an average particle size of 40 ± 0.5 μm.

[0030] Preferably, the weight ratio of microsphere blanks 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 2000 r / min. After the reaction, it is filtered, alternately washed with water and ethanol, reacted with ethylenediamine after carboxyl activation, and dried to obtain microsphere blanks B with amino groups on the surface.

[0031] Preferably, the specific operation of S2 is as follows: Biphenyl dianhydride (BPDA) and diaminodiphenyl ether (ODA) are put into dimethyl sulfoxide (DMSO) according to a molar ratio of 1.02:1. DMSO accounts for 80% of the total weight of the system, and the reaction is carried out at 20 °C for 3 h to obtain a polyamic acid solution C of the biphenyl type.

[0032] Preferably, the weight ratio of the condensation-type one-component RTV silicone rubber, ketoxime-based crosslinking agent, catalyst and n-hexane in S301 is 100:2.5 - 3:0.05 - 0.1:1000. It is secondarily coated by crosslinking into a film with low-molecular liquid silicone rubber, so that the direct compatibility between the microspheres and the silicone rubber or other rubber matrices is better. At the same time, the hydrogen-containing silicone oil can also crosslink and react with the silicone rubber coating layer, so that the microspheres are evenly distributed in the matrix and are not easy to fall off during application.

[0033] The present invention also proposes the application of the microsphere product I prepared by the foregoing preparation method in a silicone rubber sealing product, including the following steps:

[0034] A low-phenyl silicone rubber (with a molecular weight of 200,000 - 300,000, produced by Hubei Yamaide Biopharmaceutical Co., Ltd., which is made by introducing diphenylsiloxane linkages into the molecular chain of vinyl silicone rubber, and is a low-phenyl silicone rubber with a phenyl molar fraction of 0.05 - 0.10%), polytrifluoropropylmethylsiloxane (with a molecular weight of 110,000 - 150,000, and about 0.36% of vinylsiloxane is introduced into the molecular chain for copolymer modification to facilitate oxidative crosslinking, produced by Hubei Hengjingrui Chemical Co., Ltd.), modified nano-silica [produced by Hangzhou Hengge Nano Technology Co., Ltd., product number: HN-SP30N (amphiphilic), white powder fineness: 30 ± 5 nm, purity: 99.5%, specific surface area: 100 - 200 m 2 / g, the surface of the silica is modified with a silane coupling agent KH560, and it has amphiphilic properties, that is, it can be evenly dispersed in both aqueous and oily systems], hydrogen-containing silicone oil (with a hydrogen molar ratio of 3 - 7 mmol H / g of hydrogen-containing silicone oil, produced by Shandong Duoju Chemistry Co., Ltd.), catalyst (XYS-9092 type Kast platinum catalyst, produced by Shenzhen Xinyongsheng New Materials Co., Ltd.), antioxidant 1010 (BASF) and microsphere product I are kneaded at 10 - 30 °C. After kneading, they are put into a mold, and then vulcanized using a mid-infrared irradiation vulcanizing furnace to obtain a sealed product J containing microsphere product I.

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

[0036] Preferably, the vulcanization is a two-stage vulcanization method. The parameters for the first-stage vulcanization are: 200 - 250 °C, time not exceeding 5 min; the parameters for the second-stage vulcanization are: temperature 150 - 200 °C, time 60 - 120 min. Through vulcanization at a slightly higher temperature for a short time for preliminary shaping, and then shaping and preservation at a slightly lower temperature for a long time, the final sealed product J has a higher dimensional accuracy.

[0037] Compared with the prior art, the beneficial effects of the present invention are:

[0038] 1. The present invention first uses PI to coat polyacrylonitrile-based expanded microspheres. By utilizing the support of PI low-temperature plastic shaping and the temperature transformation of high-temperature high-elastic state, the expansion point of the expanded microspheres is raised to the glass transition temperature of polyimide (≈270 °C), greatly increasing the use temperature of the expanded microspheres;

[0039] Moreover, it realizes temperature-responsive expansion: the expandable microspheres have only a small expansion when the temperature is lower than the glass transition temperature of polyimide (PI) (≈270 °C), which can inhibit the shrinkage of the silicone rubber matrix; when the temperature is higher than this temperature, PI transforms into a high-elastic state and has a large expansion under the secondary coating effect of the silicone rubber layer. By controlling the content of the microspheres, the sealed product can be appropriately expanded (≤5%) at high temperatures, such as making the O-ring fit the flange ring better and enhancing the sealing performance.

[0040] 2. To improve the compatibility between the PI-coated microspheres and the matrix rubber of the seal, the present invention also uses liquid silicone to perform secondary coating on the expandable microspheres. The liquid silicone film can also crosslink with the silicone rubber matrix through hydrogen-containing silicone oil during vulcanization, improving the uniformity of the distribution of the expandable microspheres in the matrix; it also further enhances the airtightness of the expandable microspheres, completely eliminating the risk of air leakage due to the pressure rupture of the wall material of the expandable microspheres at high temperatures.

[0041] 3. The sealed product using the expandable microspheres of the present invention has the following outstanding advantages:

[0042] 1) High dimensional accuracy: The addition of expandable microspheres can inhibit the vulcanization crosslinking shrinkage of the silicone rubber matrix, overcoming the volume shrinkage during the molding and vulcanization of the sealed product, thereby improving the dimensional accuracy. For example, the expansion rates in Examples 2, 4, and 5 are <0.4%, and the dimensional accuracy is higher.

[0043] 2) High mechanical properties: After adding expandable microspheres, under the condition that the temperature is lower than the glass transition temperature of PI, the compression deformation of the sealed product is significantly reduced, far lower than that of the existing silicone rubber; under the condition that the temperature is higher than this temperature, the fluorosilicon component and silica have a greater impact on the deformation. At the same time, with the addition of microspheres, the pressure resistance performance is improved, but too many microspheres will lead to the loss of elasticity and an increase in compression deformation, indicating that an appropriate amount of microspheres is beneficial for uniform distribution and further enhances the sealing effect.

[0044] 3) It can adapt to high-temperature sealing environments of 200 - 360 °C: The sealed product has an irreversible phase expansion at about 270 °C and a secondary reversible volume expansion at about 330 °C, enabling it to adapt to high-temperature sealing environments of ≤360 °C and meeting the sealing requirements at higher temperatures. Description of the Drawings

[0045] Figure 1 It is a diagram showing the influence of different microsphere contents of the present invention on the molding expansion rate of the silicone rubber-based sealed product;

[0046] Figure 2 It is a diagram showing the influence of different application temperatures of the present invention on the application expansion rate of the silicone rubber-based sealed product. Detailed Embodiments

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

[0048] I. Preparation of expandable microspheres:

[0049] 1. Preparation of microsphere blanks:

[0050] Preparation Example 1:

[0051] 1) Preparation of the aqueous dispersion medium: Mix a dispersant, an emulsifier, sodium nitrite, sodium chloride, and water in a weight ratio of 100:4:0.3:443:1413, and add hydrochloric acid to adjust the pH to 3.2 to prepare an aqueous dispersion medium. 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 78 mg KOH / g, Greenlink Chemical Technology Co., Ltd.);

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

[0053] 3) Suspension polymerization: Mix the aqueous dispersion medium with the monomer mixture by stirring with a homogenizer to form tiny droplets of the monomer mixture in the aqueous dispersion medium. Load the aqueous dispersion medium containing the tiny droplets of the monomer mixture into a polymerization tank (1.5 L) equipped with a stirrer, heat it at 60 °C for 15 h using a water bath, and further heat it at 70 °C for 9 h. After cooling, filter the slurry containing the produced heat-expandable microspheres, wash with water, and dry to obtain heat-expandable microsphere blanks A with an average particle size of 40 ± 0.5 μm;

[0054] 2. Coating treatment of expandable microspheres:

[0055] Preparation Example 2:

[0056] 1) Primary coating of microsphere blanks:

[0057] ①. Amino modification of microsphere blanks: The microsphere blanks A obtained in Preparation Example 1, ethylenediamine, N-hydroxysuccinimide (NHS), and water are in a weight ratio of 10:2.0:0.2:100, and are mixed with high-speed stirring and reacted at 50 °C for 4 h. After the reaction, filter, wash alternately with water and ethanol, react with ethylenediamine after carboxyl activation, and dry to obtain microsphere blanks B with amino groups on the surface;

[0058] ② Preparation of polyamic acid solution:

[0059] Biphenyl dianhydride (BPDA) and diaminodiphenyl ether (ODA) were added to dimethyl sulfoxide (DMSO) according to a molar ratio of 1.02:1. Dimethyl sulfoxide (DMSO) accounted for 80% of the total weight of the system. The reaction was carried out at 20 °C for 3 h to obtain a biphenyl-type polyamic acid solution C;

[0060] ③ Polyamic acid grafting reaction:

[0061] N-Hydroxysuccinimide (NHS) was added to the polyamic acid solution obtained in S202, and N-hydroxysuccinimide (NHS) accounted for 1% of the total weight of the system. Then, the microsphere blank B with amino groups on its surface obtained in S201 was added, and the microsphere blank B accounted for 40% of the total weight of the system. The reaction was carried out at 50 °C for 4 - 8 h. After filtration, the filtrate and the residue were obtained. The filtrate was the polyamic acid solution D, and the residue was the microsphere blank E with polyamic acid;

[0062] Utilizing the good solubility of dimethyl sulfoxide (DMSO) with polymethacrylic acid (PMAA) and polyimide (PI), and the poor solubility with polymethacrylonitrile (PMAN), through the excess carboxyl groups in the polyamic acid solution, after activation, the reaction was carried out with the amino groups on the surface of the microsphere blank, so that the PI chain was embedded and coated on the outer layer of the microsphere blank. After reaching a certain thickness, a film was formed, thereby increasing the film density of the outer shell of the microsphere blank;

[0063] ④ Polyimide 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). After stirring at 500 r / min for 15 min, the microsphere blank F with surface gelation was obtained;

[0065] After diluting the polyamic acid solution D with dimethyl sulfoxide (DMSO) by 3 times, the microsphere blank F was added. After stirring and reacting at 1500 r / min for 30 min, after filtration, it was washed successively with ethanol, dimethyl sulfoxide, and water to obtain the microsphere blank G coated with a polyimide wet gel film; further consuming the dehydrating agent on the surface of the microsphere blank F and making the polyimide film dense;

[0066] 2) Secondary coating of the microsphere blank:

[0067] ⑤ Preparation of silicone rubber solution: Condensation-type one-component RTV silicone rubber (one-component room-temperature vulcanizing rubber, 107 silicone rubber, Shenzhen Jipeng Silicon Fluoride Materials Co., Ltd.), ketoxime-type crosslinking agent (crosslinking agent LM43, German Nitrification Group), catalyst (XYS-9092 type Cast platinum catalyst, Shenzhen Xinyongsheng New Materials Co., Ltd.) and n-hexane are stirred under vacuum at a weight ratio of 100:2.5:0.05:1000 to obtain silicone rubber solution H, which is used immediately after mixing; the microspheres are secondarily coated by crosslinking low-molecular liquid silicone rubber into a film, so that the compatibility between the microspheres and the silicone rubber or other rubber matrixes is better. At the same time, the hydrogen-containing silicone oil can also crosslink with the silicone rubber coating layer, so that the microspheres are evenly distributed in the matrix during application and are not easy to fall off;

[0068] ⑥ Coating of silicone rubber layer: The microsphere blank G coated with polyimide wet gel film obtained in ④ and the newly prepared silicone rubber solution H are mixed at a weight ratio of 1:10, and stirred at a high speed of 1000 r / min for 10 min. Then, the microsphere blank G is fished out and put into pure water under high-speed stirring for 30 min. Then, the microsphere blank G is taken out, filtered and dried at 50 °C with hot air. The water in the polyimide wet gel film is used to promote crosslinking and form a n-hexane / water heterogeneous film-forming condition, so as to carry out initial vulcanization on the surface of the microsphere blank G to form a silicone rubber layer, and the microsphere finished product I coated with a silicone rubber layer is obtained.

[0069] Preparation Example 3:

[0070] 1) Primary coating of microsphere blank:

[0071] ① Amine modification of microsphere blank: The microsphere blank A obtained in Preparation Example 1, ethylenediamine, N-hydroxysuccinimide (NHS) and water are mixed at a weight ratio of 10:2.2:0.25:100, stirred at a high speed, reacted at 50 °C for 4 h, filtered after the reaction, washed alternately with water and ethanol, reacted with ethylenediamine after carboxyl activation, and dried to obtain a microsphere blank B with amine groups on the surface;

[0072] ② Preparation of polyamic acid solution:

[0073] Biphenyl dianhydride (BPDA) and diaminodiphenyl ether (ODA) are put into dimethyl sulfoxide (DMSO) at a molar ratio of 1.02:1. Dimethyl sulfoxide (DMSO) accounts for 80% of the total weight of the system, and the reaction is carried out at 20 °C for 3 h to obtain a biphenyl-type polyamic acid solution C;

[0074] ③ Polyamic acid grafting reaction:

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

[0076] ④ Polyimide film-forming reaction:

[0077] The wet microsphere blank E is immersed in a mixed solution of acetic anhydride and pyridine (the volume ratio of acetic anhydride to pyridine is 1:1). After stirring at 500 r / min for 15 min, the surface-gelatinized microsphere blank F is obtained;

[0078] The polyamic acid solution D is diluted 3 times with dimethyl sulfoxide (DMSO), and then the microsphere blank F is added. After stirring and reacting at 1500 r / min for 30 min, after filtration, it is washed successively with ethanol, dimethyl sulfoxide, and water to obtain the microsphere blank G coated with a polyimide wet gel film;

[0079] 2) Secondary coating of the microsphere blank:

[0080] ⑤ Preparation of silicone rubber solution: Condensation-type one-component RTV silicone rubber (one-component room-temperature vulcanizing rubber 107 silicone rubber, Shenzhen Jipeng Silicon Fluoride Materials Co., Ltd.), ketoxime-type crosslinking agent (crosslinking agent LM43, German Nitration Group), catalyst (XYS-9092 type Kast platinum catalyst, Shenzhen Xinyongsheng New Materials Co., Ltd.) and n-hexane are mixed in a weight ratio of 100:2.8:0.08:1000 and stirred under vacuum to obtain the silicone rubber solution H, which is used immediately after mixing;

[0081] ⑥ Coating with a silicone rubber layer: The microsphere blank G coated with a polyimide wet gel film obtained in ④ and the newly prepared silicone rubber solution H in ⑤ are mixed in a weight ratio of 1:10. After high-speed stirring and reacting at 1000 r / min for 10 min, then the microsphere blank G is fished out and put into high-speed stirred pure water for reaction for 30 min. Then, the microsphere blank G is taken out, filtered, and dried with hot air at 50 °C to obtain the microsphere finished product I coated with a silicone rubber layer.

[0082] Preparation Example 4:

[0083] 1) Primary coating of the microsphere blank:

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

[0085] ② Preparation of polyamic acid solution:

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

[0087] ③ Polyamic acid grafting reaction:

[0088] N-hydroxysuccinimide (NHS) was added to the polyamic acid solution obtained in S202, and N-hydroxysuccinimide (NHS) accounted for 1% of the total weight of the system. Then, the microsphere green body B with amino groups on the surface obtained in S201 was added, and the microsphere green body B accounted for 40% of the total weight of the system. The reaction was carried out at 50 °C for 4 - 8 h. After filtration, the filtrate and the residue were obtained. The filtrate was polyamic acid solution D, and the residue was the microsphere green body E with polyamic acid;

[0089] ④ Polyimide film-forming reaction:

[0090] The wet microsphere green body E was immersed in a mixed solution of acetic anhydride and pyridine (the volume ratio of acetic anhydride to pyridine was 1:1), stirred at 500 r / min for 15 min to obtain a microsphere green body F with surface gelation;

[0091] After diluting polyamic acid solution D with dimethyl sulfoxide (DMSO) by 3 times, the microsphere green body F was added, stirred and reacted at 1500 r / min for 30 min, filtered, and washed successively with ethanol, dimethyl sulfoxide, and water to obtain a microsphere green body G coated with a polyimide wet gel film; further consume the dehydrating agent on the surface of the microsphere green body F and make the polyimide film dense;

[0092] 2) Secondary coating of the microsphere green body:

[0093] ⑤ Preparation of silicone rubber solution: Condensation-type one-component RTV silicone rubber (one-component room temperature vulcanizing rubber 107 silicone rubber, Shenzhen Jipeng Silicon Fluoride Materials Co., Ltd.), ketoxime-type crosslinking agent (crosslinking agent LM43, German Nitration Group), catalyst (XYS-9092 type Kast platinum catalyst, Shenzhen Xinyongsheng New Materials Co., Ltd.) and n-hexane were mixed at a weight ratio of 100:3:0.1:1000, stirred under vacuum to obtain silicone rubber solution H, which was used immediately after mixing;

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

[0095] Comparative Preparation Example 1:

[0096] 1) Primary coating of microsphere blank:

[0097] ① Amine modification of microsphere blank: The microsphere blank A obtained in Preparation Example 1, ethylenediamine, N-hydroxysuccinimide (NHS) and water are mixed at a weight ratio of 10:2.2:0.25:100, stirred and mixed at a high speed, and reacted at 50 °C for 4 h. After the reaction, it is filtered, washed alternately with water and ethanol, reacted with ethylenediamine after carboxyl activation, and dried to obtain the microsphere blank B with amine groups on the surface;

[0098] ② Preparation of polyamic acid solution:

[0099] Biphenyl dianhydride (BPDA) and diaminodiphenyl ether (ODA) are put into dimethyl sulfoxide (DMSO) at a molar ratio of 1.02:1. Dimethyl sulfoxide (DMSO) accounts for 80% of the total weight of the system, and the reaction is carried out at 20 °C for 3 h to obtain the biphenyl-type polyamic acid solution C;

[0100] ③ Polyamic acid grafting reaction:

[0101] N-hydroxysuccinimide (NHS) is put into the polyamic acid solution obtained in S202, and N-hydroxysuccinimide (NHS) accounts for 1% of the total weight of the system. Then, the microsphere blank B with amine groups on the surface obtained in S201 is 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 h. After filtration, the filtrate and the 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] ④ Polyimide film-forming reaction:

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

[0104] After diluting the polyamic acid solution D three times with dimethyl sulfoxide (DMSO), the microsphere blank F was added, and after stirring and reacting at 1500 r / min for 30 min, it was filtered, and then washed successively with ethanol, dimethyl sulfoxide, and water to obtain the microsphere blank G coated with a polyimide wet gel film. After drying this microsphere blank G, it directly replaced the microsphere product I in Preparation Example 3 and was used as an expanding microsphere additive for the sealing product, and the difference in the effect after use from Preparation Example 3 was observed.

[0105] II. Preparation of the sealing product containing expanding microspheres:

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

[0107] Low phenyl silicone rubber (molecular weight 200,000 - 300,000, Hubei Yamaide Biopharmaceutical Co., Ltd., which is made by introducing diphenylsiloxane chain segments into the molecular chain of vinyl silicone rubber and has a phenyl molar fraction of 0.05 - 0.10% low phenyl silicone rubber), polytrifluoropropylmethylsiloxane (molecular weight 110,000 - 150,000, and about 0.36% of vinylsiloxane is introduced into the molecular chain for copolymerization modification to facilitate oxidative crosslinking, Hubei Hengjingrui Chemical Co., Ltd.), modified nano-silica [Hangzhou Hengge Nano Technology Co., Ltd., product number: HN-SP30N (amphiphilic), white powder fineness: 30 ± 5 nm, purity: 99.5%, specific surface area: 100 - 200 m 2 / g, the surface of silica was modified with silane coupling agent KH560, and it has amphiphilicity, that is, it can be evenly dispersed in both aqueous and oily systems], hydrogen-containing silicone oil (hydrogen-containing molar ratio of 3 - 7 mmol H / g hydrogen-containing silicone oil, Shandong Duopoly Chemical Co., Ltd.), catalyst (XYS-9092 type Karstedt platinum catalyst, Shenzhen Xinyongsheng New Materials Co., Ltd.), antioxidant 1010 (BASF) and the microsphere product I were kneaded at a weight ratio of 100:40 - 50:10 - 15:8 - 10:1 - 2:0.2 - 0.3:3 - 6 at 10 - 30 °C, put into a mold to obtain a sealing blank, after demolding the sealing blank, a two-stage vulcanization method was carried out using a mid-infrared irradiation vulcanization furnace to obtain a sealing product J containing the microsphere product I; the parameters of the first-stage vulcanization were: 200 - 250 °C, time not exceeding 5 min; the parameters of the second-stage vulcanization were: temperature 150 - 200 °C, time 60 - 120 min; through vulcanization at a slightly higher temperature for a short time, preliminary shaping was generated, and then through vulcanization at a slightly lower temperature for a long time for shaping and preservation, and finally the obtained sealing product J had a higher dimensional accuracy in vulcanization.

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

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

[0110]

[0111] It should be noted that for Comparative Example 9 in Table 1, the uncoated microsphere blank A was directly used, which expanded violently during the vulcanization process. At the same time, the experimenter was reminded to pay attention to safety. It can be used for foamed rubber products, but the present invention did not conduct further research; while Comparative Example 8 used a single layer of PI wrapping, and the volume expansion during vulcanization was larger than that of Example 2 (for Example 2, it was -0.11%, that is, it shrank by 0.11%, while for Comparative Example 8, it was +0.25%, that is, it expanded by 0.25%). Considering the special PI film prepared from polyamic acid as the precursor in the present invention, the sealing performance may be challenged to a certain extent, but the main sealing structure of the PI film should not be damaged.

[0112] III. Influence of expanded microspheres on the performance of sealing products:

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

[0114] According to the vulcanization process of existing ordinary silicone rubber, the cross-linking process of heat vulcanization often results in volume shrinkage, which seriously challenges the dimensional accuracy. The present invention attempts to use a temperature-sensitive expanded microsphere material to overcome this point. However, existing expanded microspheres generally use a PAN-PAM (acrylonitrile and acrylamide copolymerization) substrate, and its expansion point temperature is generally 120 - 130 °C, which is not suitable for high-temperature sealing application scenarios above 200 °C. Therefore, PI coating is used to limit its movement. In an environment below its glass transition temperature (≈270 °C), PI is a glassy plastic and has a shaping effect, with only a small expansion at <200 °C. This small expansion can appropriately inhibit the vulcanization 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 transforms into a high elastic state, and under the secondary coating effect of the liquid silicone rubber film, it has a relatively large expansion rate. Controlling its content can cause the sealing product to have an appropriate high-temperature expansion (should be ≤5%), such as making the O-ring fit more closely to the flange ring of the sealed tank mouth, improving the sealing performance, that is, forming a temperature-responsive expansion material with the glass transition temperature of the PI film as the node (i.e., Figure 1 the inflection point in the middle broken line, Tg≈270 °C).

[0116] Referring to Figure 1 , it should be noted first that Figure 1 the expansion rate calculation during the forming process in n is calculated by the following formula: (d m ) / d m , d m is the thickness of the sealed blank obtained after demolding after being kneaded and filled into the mold, d nis the thickness of the sealed product J obtained after vulcanization. Comparing Comparative Examples 3-7 with Examples 2, 4-6 in sequence, as the content of expandable microspheres increases, the shrinkage of the molded and vulcanized volume is gradually overcome. Among them, Examples 2, 4, and 5 have lower expansion rates (<0.4%), and thus higher dimensional accuracy.

[0117] 2. Influence of temperature on the expansion rate of silicone rubber-based sealed products:

[0118] Referring to Figure 2 , it should be noted that Figure 2 the thermal application expansion rate in t is defined as follows: The sealed product J is made into a block-shaped specimen with a length of 30 cm, a width of 10 cm, and a thickness of 5 cm according to the process of Example 2, and the expansion test is carried out at a certain temperature. At a fixed temperature, the thickness of the specimen is measured every 10 s. The thermal application 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 corresponding to time t, and d o is the initial thickness of the sample. The final thickness is recorded at the time point when the thickness is basically unchanged.

[0119] It can be seen from Figure 2 that the sealed product has a sudden change in the first expansion rate at about 270°C. The first time 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 is cured into a plastic form and has a shaping effect on the microspheres; there is a second sudden change in the expansion rate at about 330°C. The second expansion amplitude is smaller and is the volume expansion caused by the stretching of the Si-O main chain of the silicone rubber body when heated. The secondary expansion is a reversible expansion and contraction at ≤400°C, but it is also beneficial for the sealing conditions at higher temperatures, proving that the product of the present invention can adapt to the sealing environment at any temperature ≤360°C (required to be > the Tg temperature of the silicone rubber body), and undergoes a first temperature-sensitive irreversible phase expansion near 270°C and a second temperature-sensitive reversible volume expansion near 330°C to meet the higher sealing requirements for high-temperature gas overflow.

[0120] 3. Mechanical properties of the sealed product:

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

[0122] And refer to this method to test the compression set at 250°C and 350°C: Keep the sealed sample at the specified temperature (250°C or 350°C) and at a low compression rate (10%, making the sample thickness 10% smaller) 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] The specific properties are shown in Table 2 below:

[0124] Table 2. Mechanical properties of the sealing product containing expandable microspheres

[0125]

[0126] As can be seen from Table 2, comparing Examples 1-3, below the Tg condition, the addition of microspheres may be beneficial to improving the structural toughness, significantly reducing the compression deformation, far lower than the strength and toughness of the existing silicone rubber (the compression set at 25°C is generally not less than 10%); above the Tg condition, the fluorosilicon component and silica have a greater impact on the deformation, making the compression deformation change irregularly;

[0127] And comparing Comparative Examples 3-7, Examples 4-6 with Example 2, with the addition of microspheres, the pressure resistance performance increases significantly, but too many microspheres cause the loss of elasticity and more compression deformation, indicating that there may be aggregation of microspheres, which is not conducive to the uniform distribution of the blowing agent.

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

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

[0130] Comparing Comparative Example 8 with Example 2, the microspheres without silicone rubber coating may have poor compatibility, resulting in differences in tensile and compression properties.

[0131] The above data prove that adding expandable microspheres to the silicone rubber matrix can make the compression deformation of the rubber smaller while ensuring the basic mechanical properties, and at the same time meet a certain expansion under high-temperature sealing. Therefore, the present invention is suitable for high-temperature sealing products at 200-360°C and can maintain a highly sealed state with expansion at high temperatures for a long time.

[0132] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and should be covered by the protection scope of the present invention.

Claims

1. A preparation method of a high-temperature resistant temperature-responsive expansion material, characterized in that, It includes the following steps: S1. Preparation of microsphere blanks: S101. Preparation of aqueous dispersion medium: Mix a dispersant, an emulsifier, sodium nitrite, sodium chloride and water, and add hydrochloric acid to adjust the pH to 3.2 to prepare an aqueous dispersion medium; S102. Preparation of monomer mixture: It is made by mixing monomers, a foaming agent and an initiator; S103. Suspension polymerization: Mix the aqueous dispersion medium with the monomer mixture, heat at 60 °C for 15 h, continue to heat at 70 °C for 9 h, cool, and then filter to obtain microsphere blank A; S2. Primary coating of microsphere blanks: S201. Amino modification of microsphere blanks: Mix microsphere blank A, ethylenediamine, N-hydroxysuccinimide and water, stir at high speed, react at 50 °C for 4 h, filter and wash to obtain microsphere blank B with amino groups on the surface; S202. Preparation of polyamic acid solution: Put biphenyl dianhydride and diaminodiphenyl ether into dimethyl sulfoxide, react at 20 °C for 3 h to obtain a biphenyl-type polyamic acid solution C; S203. Polyamic acid grafting reaction: Put N-hydroxysuccinimide into the polyamic acid solution obtained in S202, and the N-hydroxysuccinimide accounts for 1% of the total weight of the system. Then put microsphere blank B with amino groups on the surface obtained in S201, and the microsphere blank B accounts for 40% of the total weight of the system. React at 50 °C for 4 - 8 h, filter to obtain a filtrate and a filter residue. The filtrate is polyamic acid solution D, and the filter residue is microsphere blank E with polyamic acid; S204. Polyimide film-forming reaction: Soak the wet microsphere blank E in a mixed solution of acetic anhydride and pyridine, stir at 500 r / min for 15 min to obtain microsphere blank F with surface gelation; Dilute polyamic acid solution D with dimethyl sulfoxide by 3 times, put in microsphere blank F, stir and react at 1500 r / min for 30 min, filter, and then wash successively with ethanol, dimethyl sulfoxide and water to obtain microsphere blank G coated with a polyimide wet gel film; S3. Secondary coating of microsphere blanks: S301. Preparation of silicone rubber solution: Condensation-type one-component RTV silicone rubber, a ketoxime-type crosslinking agent, a catalyst and n-hexane are stirred under vacuum to obtain silicone rubber solution H; S302. Coating with a silicone rubber layer: Mix microsphere blank G coated with a polyimide wet gel film obtained in S204 and the newly prepared silicone rubber solution H in a weight ratio of 1:10, stir and react at 1000 r / min for 10 min, then fish out microsphere blank G and put it into vigorously stirred pure water, react for 30 min; then take out microsphere blank G, filter and dry at 50 °C with hot air to obtain microsphere finished product I coated with a silicone rubber layer.

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

3. The preparation method of a high-temperature resistant temperature-responsive expansion material according to claim 1, characterized in that, The weight ratio of monomer, blowing agent and initiator in the monomer mixture of S102 is 100:30:1, and in the monomer, methacrylonitrile and methacrylic acid are prepared according to a molar ratio of 1:

1. The blowing agent is isooctane, and the initiator is 2,2'-azobisisobutyronitrile.

4. The preparation method of a high-temperature resistant temperature-responsive expansion material according to claim 1, characterized in that, The specific operation of S103 is as follows: The aqueous dispersion medium and the monomer mixture are mixed by stirring with a homogenizer, so as to form tiny droplets of the monomer mixture in the aqueous dispersion medium. The aqueous dispersion medium containing the tiny droplets of the monomer mixture is charged into a polymerization tank equipped with a stirrer, heated in a water bath at 60 °C for 15 h, and further heated at 70 °C for 9 h. After cooling, the slurry containing the generated heat-expandable microspheres is filtered, washed with water, and dried to obtain a heat-expandable microsphere blank A with an average particle size of 40 ± 0.5 μm.

5. The preparation method of a high-temperature resistant temperature-responsive expansion material according to claim 1, characterized in that, In S201, the weight ratio of 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. After the reaction, it is filtered, washed alternately with water and ethanol, reacted with ethylenediamine after carboxyl activation, and dried to obtain a microsphere blank B with amino groups on the surface.

6. The preparation method of a high-temperature resistant temperature-responsive expansion material according to claim 1, characterized in that, The specific operation of S2 is as follows: Diphenyl dianhydride and diaminodiphenyl ether are put into dimethyl sulfoxide according to a molar ratio of 1.02:

1. Dimethyl sulfoxide accounts for 80% of the total weight of the system, and the reaction is carried out at 20 °C for 3 h to obtain a biphenyl-type polyamic acid solution C.

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

8. Use of the microsphere finished product I prepared by the preparation method according to any one of claims 1-7 in a silicone rubber sealing product, characterized in that, It includes the following steps: Mix low phenyl silicone rubber, polytrifluoropropylmethylsiloxane, modified nano-silica, hydrogen-containing silicone oil, catalyst, antioxidant 1010 and microsphere finished product I at 10 - 30 °C, put the mixture into a mold after mixing, and then vulcanize it with a mid-infrared irradiation vulcanizing furnace to obtain a sealed product J containing microsphere finished product I.

9. Use of the finished microsphere I according to claim 8 in a silicone rubber sealing product, characterized in that, The weight ratio of the low phenyl silicone rubber, polytrifluoropropylmethylsiloxane, modified nano-silica, hydrogen-containing silicone oil, catalyst, antioxidant 1010 and microsphere finished product I is 100:40 - 50:10 - 15:8 - 10:1 - 2:0.2 - 0.

3.

10. Use of the finished microspheres I according to claim 8 in a silicone rubber sealing product, characterized in that, The vulcanization is a two-stage vulcanization method. The parameters of the first-stage vulcanization are: 200 - 250 °C, and the time does not exceed 5 min; the parameters of the second-stage vulcanization are: the temperature is 150 - 200 °C, and the time is 60 - 120 min.

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