In-situ formed one-component addition-cured liquid silicone rubber and method for producing the same

Abstract

The application relates to the technical field of liquid silicone rubber, and particularly discloses in-situ forming single-component addition type liquid silicone rubber and a preparation method thereof. Base glue is prepared by kneading vinyl silicone oil, nano silicon dioxide and silicone resin, and then, additives such as a crosslinking agent, an adhesion promoter, a thixotropic agent, an inhibitor and a platinum gold catalyst are added in a proper proportion, and defoaming is carried out to obtain the silicone rubber, the preparation process is simple, the prepared silicone rubber product has single-component packaging, is convenient and simple to use, can be quickly cured at high temperature, no small molecules are released during the curing process, is efficient and environment-friendly. The silicone rubber cured at high temperature not only has excellent mechanical properties (tensile strength > 5 MP, elongation at break > 150%, compression set < 30% after long-term compression at high temperature), but also has good adhesion to an adhesive surface after high-temperature aging, has no adhesion to a sealing surface, and has good detachability.

Description

Technical Field

[0001] This invention belongs to the field of liquid silicone rubber technology, specifically relating to an in-situ molded one-component addition-curing liquid silicone rubber and its preparation method. Background Technology

[0002] Liquid silicone rubber (LSR) is a polymer material composed of polymers, crosslinking agents, and catalysts. Due to its unique structure, it combines the properties of inorganic and organic materials. It has basic properties such as low viscosity-temperature coefficient, high compressibility, and high flexibility at low temperatures. It also has excellent properties such as high and low temperature resistance, electrical insulation, oxidation stability, weather resistance, flame retardancy, water repellency, corrosion resistance, non-toxicity, odorlessness, and physiological inertness. It is widely used in aerospace, electronics, automotive, and high-end construction industries, and has been tested in harsh real-world environments.

[0003] Condensation-type liquid silicone rubber mainly comes in single-component and two-component products. Single-component condensation-type room temperature vulcanizing (room temperature curing) liquid silicone rubber has a long curing time. Under typical environmental conditions (temperature 25℃, relative humidity 60%), the curing depth and strength gradually reach the design target values ​​in about 3 weeks. Even with auxiliary conditions such as heating and humidification, its curing speed cannot be significantly increased. In contrast, two-component condensation-type room temperature vulcanizing liquid silicone rubber can significantly increase the curing speed, but it still requires at least 24 hours of curing time to fully achieve the design performance. Condensation-type room temperature vulcanizing liquid silicone rubber not only cannot adapt to the assembly efficiency of production lines, but its poor compression resilience and the release of low-molecular-weight substances during curing will also limit its application as an in-situ molding (in-situ molding refers to the process of first applying liquid sealant to flanges or other sealing surfaces, quickly curing it, and then assembling it to achieve single-sided bonding and double-sided compression sealing) sealing material. Addition-type liquid silicone rubber, due to its unique cross-linking curing mechanism, can achieve rapid curing upon heating, good compression resilience, and no low-molecular-weight release, making it more environmentally friendly. Two-component addition-cure silicone rubber requires the two components to be metered according to the specified ratio and then mixed evenly before it can be used. During the metering and mixing process, there are phenomena of uneven metering and uneven mixing, which seriously affects the stability of product performance, thereby affecting mechanical properties and compression set properties. In contrast, one-component addition-cure liquid silicone rubber is simpler and easier to use, without the need for complex proportioning and mixing operations. It can not only save packaging materials and reduce resource waste, but also has the advantages of easy storage and transportation, and convenient use. Therefore, one-component addition-cure liquid silicone rubber is the best choice for preparing in-situ molding sealing materials.

[0004] Conventional one-component addition-cured liquid silicone rubbers exhibit a highly saturated state due to the helical coiling of molecular chains and the shielding of the polarity of silicon-oxygen bonds by non-polar side groups. This results in low surface energy, poor wettability to various substrates, and a lack of reactive groups, leading to weak molecular forces and poor adhesion with the substrate. Currently, the simplest and most effective method is to add a silane coupling agent to the system. However, among conventional silane coupling agents, amino-based agents cause platinum catalyst deactivation, rendering them unusable; epoxy-based agents cannot participate in the crosslinking reaction, and after prolonged compression following sealant curing, they are prone to precipitation, which is detrimental to the long-term, safe, and stable operation of internal components; while acryloyloxy-based coupling agents can participate in the crosslinking reaction, they affect the curing speed and mechanical properties; and highly reactive methoxy or ethoxy groups in silane coupling agents cause the cured adhesive strip to continue reacting with the substrate surface after prolonged compression, resulting in adhesion and making non-destructive disassembly and repair impossible.

[0005] Existing in-situ molded one-component addition-cure liquid silicone rubbers generally suffer from large dimensional changes before and after high-temperature curing. Adding hydrophilic silica or organobentonite can improve this to some extent, but results in poor extrudability and noticeable particles, severely impacting dispensing speed and finished product yield. Commercially available liquid thixotropic additives, hydrogenated castor oil, and polyamide waxes, while effectively improving thixotropic effects, have poor compatibility with one-component addition-cure silicone rubbers, large dimensional changes before and after curing, and affect curing speed, failing to meet the requirements of good room-temperature extrudability and low dimensional changes before and after high-temperature curing. Therefore, it is essential to develop an in-situ molded one-component addition-cure liquid silicone rubber that not only exhibits excellent adhesion to metal substrates and low dimensional changes before and after curing, but also maintains good adhesion to bonding surfaces after high-temperature aging, while showing no adhesion to sealing surfaces and possessing good disassembly properties.

[0006] Currently, the key to in-situ molding of one-component addition-curing liquid silicone rubber for sealing lies in solving the problems of adhesion, dimensional retention before and after high-temperature curing, and removability after high-temperature aging. To achieve good adhesion to the substrate, additional tackifiers are needed. While conventional tackifiers can effectively improve adhesion, they are prone to oil seepage and sticking after high-temperature aging. To achieve dimensional retention before and after high-temperature curing, additional thixotropic agents are needed. Although these can effectively improve thixotropic effects, they have poor extrudability or poor compatibility with the silicone matrix. One current method to solve these problems is to add low-activity thixotropic agents and tackifiers.

[0007] Chinese Patent Publication No. CN110387128 A discloses a self-adhesive one-component addition-cure silicone rubber and its preparation method. The method involves kneading vinyl silicone oil with nano-silica to obtain a paste, then adding appropriate proportions of crosslinking agents, tackifiers, polymerization inhibitors, and other additives, followed by degassing to obtain the final product. The preparation process is simple, and the resulting silicone rubber product combines the advantages of condensation-type and addition-cure silicone rubbers. It features single-component packaging, no release of small molecules during curing, no deep curing issues, rapid curing upon heating, and convenient, simple, and efficient use. More importantly, the appropriate proportions of the components enable it to exhibit excellent adhesion to various substrates, especially difficult-to-bond materials such as nickel, silver, gold, nylon 66, PVC, and PE, greatly expanding the application range of existing one-component addition-cure silicone rubbers. Its shortcomings are as follows: the tackifier is a polymer product of borate ester and silane coupling agent, which does not have active groups that can react with polymers or crosslinking agents. This will cause oil seepage after the cured adhesive strip is compressed at high temperature for a long time. In addition, the tackifier contains a large number of hydrolyzable active groups such as methoxy and ethoxy, which will cause the cured adhesive strip to continue to react with the substrate surface after long-term compression, resulting in adhesion and making it impossible to achieve non-destructive disassembly and repair.

[0008] Chinese Patent Publication No. CN 115521625 A discloses a low-temperature bonding, water-resistant two-component addition-cure silicone rubber and its preparation method. Component A consists of a base rubber, terminal vinyl silicone oil, reinforcing agent, and catalyst. Component B consists of a base rubber, terminal vinyl silicone oil, hydrogen-containing silicone oil, reinforcing agent, tackifier, water-resistant agent, and inhibitor. The base rubber consists of terminal vinyl silicone oil, fumed silica, silane treatment agent, and water. By adding a novel special tackifier and water-resistant agent, it can achieve rapid curing at a low temperature of 60℃ and form a strong bond with the substrate. The water-resistant agent containing long-chain phenyl silane has strong hydrophobicity, which can significantly improve water resistance; the bond strength does not decrease significantly after boiling. However, the drawback is that the two-component addition-cure silicone rubber requires the two components to be metered according to a specific ratio and then mixed evenly before use. During the metering and mixing process, uneven metering and mixing can occur, seriously affecting the stability of product performance and thus impacting mechanical properties and compression set properties.

[0009] Chinese Patent Publication No. CN110669344A discloses a one-component addition-type liquid silicone rubber and its preparation method, comprising the following raw materials: 20-50 parts by weight of low-viscosity vinyl silicone oil, the viscosity of which is 8000-12000 cs; high-viscosity vinyl silicone oil with a viscosity of 60000-80000 cs, the total amount of which is 70 parts by weight; 20-35 parts by weight of silica; 5-8 parts by weight of hexamethyldisilazane; 1-5 parts by weight of high-vinyl silicone oil, the vinyl content of which is 7%-10%; 1.5-2 parts by weight of water; 2-4 parts by weight of hydrogen-containing silicone oil; 0.2-0.5 parts by weight of platinum complex; and 0.02-0.08 parts by weight of 3-methyl-1-dodecyn-3-ol. Its drawbacks are: the surface energy of liquid silicone rubber without added tackifier is low after curing, resulting in poor adhesion to the substrate, and its storage period at 25°C is only 3 months.

[0010] Chinese Patent Publication No. CN102492391A discloses a one-component, strong-adhesion addition-cure silicone rubber encapsulant and its preparation method. The encapsulant comprises, by weight, 80-120 parts vinyl silicone oil, 5-20 parts vinyl silicone resin, 10-30 parts hydrogen-containing silicone oil, 1-3 parts organopolysiloxane tackifier, 1-3 parts silica, 1-5 parts titanium dioxide, 0.1-0.5 parts inhibitor, and 0.1-0.5 parts platinum catalyst. The preparation method involves first mixing the vinyl silicone oil, vinyl silicone resin, hydrogen-containing silicone oil, organopolysiloxane tackifier, silica, and titanium dioxide at high speed; then adding the inhibitor and mixing at high speed; finally adding the platinum catalyst and mixing at high speed, followed by discharging. The one-component addition-cure silicone rubber encapsulant prepared by this method achieves an adhesion strength of over 1.86 MPa between the encapsulant and the substrate (copper). Its shortcomings are: although the organopolysiloxane tackifier can participate in the hydrosilylation crosslinking reaction and can avoid the problem of long-term compression leakage to a limited extent, the thixotropic properties of the adhesive are poor after its addition, and the dimensional change rate is large before and after high-temperature curing. Summary of the Invention

[0011] In order to overcome the shortcomings and disadvantages of the existing technology, the primary objective of this invention is to provide a one-component addition-curing liquid silicone rubber for in-situ molding and sealing, which uses tackifiers and thixotropic agents and has a special structure.

[0012] A second objective of this invention is to provide a method for preparing the aforementioned one-component addition-curing liquid silicone rubber for in-situ molding and sealing.

[0013] The primary objective of this invention is achieved through the following technical solution:

[0014] An in-situ molded one-component addition-curing liquid silicone rubber, measured by mass parts, is made from raw materials comprising the following materials:

[0015]

[0016] The base material is made from raw materials comprising the following materials:

[0017] 65 parts vinyl silicone oil

[0018] 15-50 parts of fumed silica

[0019] 10-30 parts of silicone resin.

[0020] Preferably, the hydrogen-containing silicone oil is a bimethyl-terminated hydrogen-containing silicone oil with a hydrogen content of 0.36% to 1.6%. It is purchased and selected according to the required hydrogen content, and its structural formula is as follows:

[0021] g is a natural number between 15 and 100, and h is a natural number between 1 and 100. g being a natural number between 15 and 100 means that g can be any one of the following numbers: 15, 20, 30, 40, 50, 60, 70, 80, 90, or 100, or any other natural number between 15 and 100. Similarly, h being a natural number between 1 and 100 means that h can be any one of the following numbers: 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, or 100, or any other natural number between 1 and 100.

[0022] Preferably, the inhibitor is at least one selected from 3-methyl-1-dodecyn-3-ol, 3,7,11-trimethyldodecyn-3-ol, 3-methyl-1-butyn-3-ol, 1-ethynyl-1-cyclohexanol, and 3-phenyl-1-butyn-3-ol.

[0023] Preferably, the catalyst is a platinum-alkynyl complex, namely at least one of bis(1-ethynyl-1-cyclohexanol)bis(triphenylphosphine)platinum complex, bis(phenylacetylene)bis(triphenylphosphine)platinum complex, bis(alkynyloxysiloxane)bis(triphenylphosphine)platinum complex, and bis(3-methyl-1-butyn-3-ol)bis(triphenylphosphine)platinum complex, wherein the platinum content is 1000-3000 ppm.

[0024] Preferably, the vinyl silicone oil has a viscosity of 5000–20000 mPa·s at 25°C and a vinyl content of 0.05%–0.2%. It is purchased and selected according to the required vinyl content. The structural formula is as follows:

[0025] F is a natural number between 1 and 100; F being a natural number between 1 and 100 means that F can be any one of the numbers 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, or any other natural number between 1 and 100.

[0026] Preferably, the specific surface area of ​​the fumed silica is 200–400 m². 2 / g, Fumed silica includes hydrophilic fumed silica and hydrophobic fumed silica; hydrophobic fumed silica (such as fumed silica treated with hexamethyldisilazane) is preferred because adding too much hydrophilic fumed silica will result in a high viscosity of the liquid silicone rubber, which is not conducive to use. Hydrophobic fumed silica can be added at higher amounts without causing the rubber compound to become structured, which is beneficial for long-term storage stability. However, the amount of hydrophobic silica added should not be too much, so it is used in combination with silicone resin to meet good extrusion performance and mechanical properties.

[0027] Preferably, the silicone resin is phenyl vinyl MDQ silicone resin, with a viscosity of 500-1000 mPa·s at 25°C and a vinyl content of 0.4%-1%. It is purchased and selected according to the required vinyl content, and its general structural formula is: (Ph₂SiO)a(ViMe₂SiO). 0.5 )b(Me3SiO 0.5 )c(SiO2)d, where Ph is phenyl, Me is methyl, and Vi represents vinyl; the value of a ranges from 0.1 to 1; the value of b+c ranges from 0 to 0.1, and b>0; the value of d ranges from 0 to 0.8, and d>0; the value of a / d ranges from 1.6 to 2.5; and the value of (b+c) / d ranges from 1.6 to 2.5. Because organosilicon polymers have low cohesive energy density, they require reinforcing materials. The most common and widely used reinforcing filler is fumed silica or precipitated silica, but it also has a significant thickening effect on silicone rubber, leading to increased viscosity and affecting the practical application range of silicone rubber. Therefore, phenyl vinyl MDQ silicone resin, which has a structure similar to fumed silica and contains Q-linkers, is used for reinforcement. Phenyl vinyl MDQ silicone resin undergoes a hydrosilylation addition reaction with organosilicon polymers containing silane bonds (i.e., hydrogen-containing silicone oil) under the action of a catalyst, resulting in cross-linking and vulcanization. This significantly improves the cohesive energy density and heat resistance of organosilicon polymers, giving the cured silicone rubber better mechanical properties and compression resilience.

[0028] Tackifiers and their preparation methods:

[0029] A method for preparing a tackifier used in in-situ molded one-component addition-curing liquid silicone rubber includes the following steps:

[0030] (1) Stir tetramethylcyclotetrasiloxane (D4H) and catalyst evenly, add 2-epoxy-4-vinylcyclohexane (VCMX) and bisphenol A dielyl ether, and heat to 50℃~100℃ to react for 2h~5h;

[0031] (2) After cooling to room temperature, add activated carbon for adsorption for 8h to 24h, filter, and distill under reduced pressure to obtain the thickener.

[0032] The tackifier used in in-situ molded one-component addition-curing liquid silicone rubber has the following structure:

[0033] It is called product A.

[0034] Optionally, in the preparation method of the tackifier, the molar ratio of D4H, catalyst, 2-epoxy-4-vinylcyclohexane (VCMX), and bisphenol A dielyl ether is (100-200):1:(100-200).

[0035] (50~100), the preferred molar ratio is (120~160):1:(120~160):(60~80).

[0036] Preferably, in the method for preparing the thickener, the catalyst in step (1) is at least one of chloroplatinic acid and Karstedt platinum catalyst.

[0037] Thixotropic agents and their preparation methods:

[0038] A method for preparing a thixotropic agent used in in-situ molded one-component addition-curing liquid silicone rubber includes the following steps:

[0039] (1) Stir the hydrogen-containing polydimethylsiloxane and catalyst evenly, add auxiliary agent 1, and heat to 50℃~100℃ to react for 2h~5h;

[0040] (2) After cooling to room temperature, add activated carbon for adsorption for 8-24 hours, filter, and distill under reduced pressure to obtain the thixotropic agent.

[0041] In the preparation method of the thixotropic agent, the hydrogen-containing polydimethylsiloxane in step (1) is at least one of single-ended hydrogen-containing polydimethylsiloxane, double-ended hydrogen-containing polydimethylsiloxane, side-ended hydrogen-containing polydimethylsiloxane, or end-side hydrogen-containing polydimethylsiloxane.

[0042] In the preparation method of the thixotropic agent, the auxiliary agent 1 in step (1) is at least one of 1,2-epoxy-4-vinylcyclohexane (VCMX), allyl glycidyl ether (AGE), and dodecene.

[0043] Preferably, when the auxiliary agent 1 is 2-epoxy-4-vinylcyclohexane (VCMX) and the hydrogen-containing polydimethylsiloxane is a side-hydrogen-containing polydimethylsiloxane, the prepared thixotropic agent has the following structure:

[0044] This is called product B, where p is a natural number between 1 and 100, n is a natural number between 1 and 100, and m is a natural number between 1 and 100. p, m, and n can be any natural number such as 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, or other natural numbers between 1 and 100;

[0045] Optionally, in the preparation method of the thixotropic agent, the molar ratio of hydrogen-containing polydimethylsiloxane, catalyst and auxiliary 1 is (100-150):1:(20-50), preferably (110-120):1:(30-40).

[0046] Preferably, in the method for preparing the thixotropic agent, the catalyst in step (1) is at least one of chloroplatinic acid and Karstedt platinum catalyst.

[0047] Small molecule thixotropic agents have a siloxane backbone, which has good compatibility with liquid silicone rubber. This facilitates the formation of hydrogen bonds between the epoxy groups on the thixotropic agent and the hydroxyl groups on the hydrophobic fumed silica (such as hexamethyldisilazane-treated silica) used as a reinforcing filler in the base rubber, thus better exerting the thixotropic effect.

[0048] In this invention, room temperature usually refers to a temperature in the range of 20 to 35°C, which varies naturally with the environment.

[0049] The second objective of this invention is achieved through the following technical solution:

[0050] A method for preparing an in-situ molded one-component addition-curing liquid silicone rubber, the method comprising the following steps:

[0051] (1) Preparation of base material:

[0052] 65 parts by weight of vinyl silicone oil, 15-50 parts by weight of fumed silica and 10-30 parts by weight of silicone resin are stirred in a vacuum kneader for 30-120 min, heated to 120℃-200℃, and then de-blended under a vacuum of -0.08 to -0.1 MPa for 60-180 min. After dilution, cooling and grinding, the base material is obtained.

[0053] (2) Preparation of in-situ molded one-component addition-curing liquid silicone rubber:

[0054] 100 parts by weight of base material and 2-8 parts by weight of hydrogen-containing silicone oil are added to a planetary mixer equipped with a cooling and high-speed dispersion device. The mixture is stirred for 15-20 minutes at a high-speed dispersion of 300-600 r / min, a low-speed stirring of 30-60 r / min, and a vacuum of -0.08 to -0.1 MPa. 1-5 parts by weight of tackifier and 1-5 parts by weight of thixotropic agent are added. The mixture is stirred for 10-30 minutes at a high-speed dispersion of 500-1000 r / min and a low-speed stirring of 40-80 r / min. 0.05-1 parts by weight of inhibitor and 0.1-1 parts by weight of catalyst are added. The mixture is stirred for 5-15 minutes at a high-speed dispersion of 300-600 r / min, a low-speed stirring of 30-60 r / min, and a vacuum of -0.08 to -0.1 MPa. The mixture is then discharged, sealed, and stored to obtain a one-component addition-cured liquid silicone rubber for in-situ molding and sealing.

[0055] Working principle of the invention:

[0056] The one-component addition-type liquid silicone rubber for in-situ molding and sealing described in this invention utilizes the hydrosilylation addition reaction between phenyl vinyl MDQ silicone resin and a silicone polymer containing silane bonds under the action of a catalyst to achieve crosslinking and vulcanization. This significantly improves the cohesive energy density and heat resistance of the silicone polymer, resulting in cured silicone rubber with better mechanical properties and compression resilience. Therefore, both are chosen for use in combination. A hydrogen-containing cyclic siloxane tackifier with epoxy and benzene ring groups was designed and synthesized. This tackifier not only has good compatibility with the silicone matrix, but also allows Si-H to participate in the crosslinking reaction, introducing epoxy and benzene ring groups into the main chain. The epoxy groups have low activity at room temperature, but can react with the surface active groups of the substrate to form a strong adhesive effect when heated at high temperatures. After high-temperature curing, the one-component addition-type liquid silicone rubber with this tackifier exhibits a highly saturated state due to the helical coiling of the molecular chain segments and the shielding of the polarity of the epoxy groups and silane bonds by the non-polar benzene ring macromolecules and side groups. This results in low surface energy and weak molecular forces between the molecule and the substrate, thus avoiding oil seepage and adhesion during long-term compression. Adding hydrophobic fumed silica can improve mechanical properties, but excessive addition can lead to significant thickening of silicone rubber and increased viscosity, affecting its practical applications. This invention designs and synthesizes a hydrogen-containing polydimethylsiloxane (thixotropic agent) with epoxy groups in its side chains. The thixotropic agent relies on the numerous oxygen atoms on the epoxy groups to form stable hydrogen bonds with the hydrophobic fumed silica, which acts as a reinforcing agent. This results in a thixotropic effect without affecting extrudability. Furthermore, the introduction of siloxane segments into the thixotropic agent structure increases its compatibility with the organosilicon matrix, thus enhancing its thixotropic effect. It also effectively avoids the risk of incompatibility and leakage between the thixotropic agent and the adhesive system, solving the problems of large dimensional changes and poor extrudability in single-component addition-cured sealants.

[0057] Planetary mixers contain a high-speed dispersion disc (high-speed mixing) and a shear mixing disc (low-speed mixing). Performing high-speed mixing and dispersion first, followed by low-speed mixing, can achieve better dispersion results.

[0058] In this invention, the term "de-lowering" refers to the removal of small molecules.

[0059] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0060] (1) The one-component addition-curing liquid silicone rubber for in-situ molding and sealing prepared by the present invention has good mechanical properties (tensile strength > 5 MPa, elongation at break > 150%), good adhesion to metal substrates (AL-AL shear strength > 2 MPa) and excellent compression resilience (compression permanent deformation rate < 30% after 25% compression and aging at 150°C for 1000 h).

[0061] (2) A multifunctional hydrogen-containing cyclic tackifier was designed and synthesized. This tackifier reacts with the main resin, introducing epoxy siloxanes and benzene rings into the sealant. This alters the surface polarity of the sealant, improving its wettability to the substrate and thus enhancing its adhesive performance. Simultaneously, the tackifier itself does not contain alkoxy groups, reducing the amount of hydrolyzable alkoxy groups within the colloid and preventing subsequent re-adhesion. Test results show a high anti-adhesion rating because alkoxy groups continue to react in the later stages of adhesive curing, preventing re-adhesion. The one-component addition-curing liquid silicone rubber for in-situ molding and sealing prepared using this tackifier solves the technical problems of poor adhesion to the substrate and compression sealing adhesion when added to one-component addition-curing liquid silicone rubber using conventional coupling agents and commercially available tackifiers.

[0062] (3) By designing and synthesizing an epoxy group grafted polymethylhydrosiloxane thixotropic agent, it not only has good compatibility with silicone rubber system, but can also participate in cross-linking reaction to prevent exudation. The one-component addition-type liquid silicone rubber for in-situ molding and sealing prepared with this thixotropic agent not only has good room temperature extrudability, but also has excellent thixotropic properties at high temperature. The test results show that the dimensional change before and after high temperature curing is small, which solves the contradiction between the poor room temperature extrudability of addition-type silicone rubber and the dimensional change during the high temperature curing process. Attached Figure Description

[0063] Figure 1 This is the reaction equation for the preparation of the thickener.

[0064] Figure 2 This is the reaction equation for the preparation of thixotropic agents.

[0065] Figure 3 It is a standard fixture for applying adhesive.

[0066] Figure 4 This is a schematic diagram illustrating the interaction between thixotropic agents and silica. Detailed Implementation

[0067] The present invention will be specifically described below through embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments based on the content of the present invention.

[0068] The preparation method of the thickener described in Example 1 is as follows:

[0069] In a three-necked flask equipped with a thermometer, condenser, and mechanical stirrer, 0.3 mol of tetramethylcyclotetrasiloxane (D4H) and 0.002 mol of Castrol platinum catalyst (5000 ppm) were added and stirred for 15 min. Then, 0.3 mol of 2-epoxy-4-vinylcyclohexane (VCMX) and 0.14 mol of bisphenol A dielyl ether were added, and the mixture was heated to 80 °C and reacted for 3 h. After cooling to room temperature, activated carbon was added for adsorption for 24 h. The mixture was then filtered and distilled under reduced pressure to obtain product A. The reaction equation is as follows. Figure 1 As shown.

[0070] The preparation method of the thixotropic agent described in Example 1 is as follows:

[0071] In a three-necked flask equipped with a thermometer, condenser, and mechanical stirrer, 0.115 mol of hydrogen-containing polydimethylsiloxane with a hydrogen content of 1.2% and 0.001 mol of Castel platinum catalyst (5000 ppm) were added and stirred for 15 min. Then, 0.035 mol of 1,2-epoxy-4-vinylcyclohexane (VCMX) was added and the temperature was raised to 90 °C and reacted for 2 h. After cooling to room temperature, activated carbon was added for adsorption for 24 h. The mixture was then filtered and distilled under reduced pressure to obtain product B.

[0072] The reaction equation is as follows Figure 2 As shown, Figure 2 The values ​​of t and m are determined by the hydrogen content of the hydrogen-containing silicone oil.

[0073] The preparation method of the thixotropic agent described in Example 2 is as follows:

[0074] In a three-necked flask equipped with a thermometer, condenser, and mechanical stirrer, 0.110 mol of hydrogen-containing polydimethylsiloxane with a hydrogen content of 1.2% and 0.001 mol of caster platinum catalyst (5000 ppm) were added and stirred for 15 min. Then, 0.038 mol of allyl glycidyl ether (AGE) was added and the temperature was raised to 90 °C and reacted for 2 h. After cooling to room temperature, activated carbon was added for adsorption for 24 h. The product B1 was obtained by filtration and vacuum distillation.

[0075] The preparation method of the thixotropic agent described in Example 3 is as follows:

[0076] In a three-necked flask equipped with a thermometer, condenser, and mechanical stirrer, 0.120 mol of hydrogen-containing polydimethylsiloxane with a hydrogen content of 1.2% and 0.001 mol of caster platinum catalyst (5000 ppm) were added and stirred for 15 min. Then, 0.030 mol of dodecene was added and the temperature was raised to 90 °C and reacted for 2 h. After cooling to room temperature, activated carbon was added for adsorption for 24 h. The product was then filtered and distilled under reduced pressure to obtain product B2.

[0077] Example 1:

[0078] 65 parts by weight of vinyl silicone oil with a viscosity of 10000 mPa·s at 25°C and a specific surface area of ​​300 m² will be used. 2 15 parts by weight of hydrophobic fumed silica and 15 parts by weight of phenyl vinyl MDQ silicone resin with a vinyl content of 0.58% were added to a vacuum kneader and stirred for 30 min. The mixture was then heated to 120°C and stirred for 60 min. After de-blending at 160°C and a vacuum degree of -0.08 MPa for 120 min, the mixture was diluted, cooled, and ground to obtain the base material.

[0079] Three parts by mass of a hydrogen-containing silicone oil with a hydrogen content of 0.75% and 100 parts by mass of a base material were added to a planetary mixer. The mixture was stirred for 15 minutes under high-speed dispersion at 500 rpm, low-speed stirring at 50 rpm, and a vacuum of -0.08 MPa (the stirring conditions for the following examples and comparative examples are the same as in Example 1). Then, one part by mass of each of product A and product B were added. The mixture was stirred for 20 minutes under high-speed dispersion at 750 rpm and low-speed stirring at 60 rpm. Then, 0.15 parts by mass of bis(1-ethynyl-1-cyclohexanol)bis(triphenylphosphine)platinum complex (platinum content 3000 ppm) and 0.05 parts by mass of 1-ethynyl-1-cyclohexanol were added. The mixture was stirred for 15 minutes under high-speed dispersion at 400 rpm, low-speed stirring at 45 rpm, and a vacuum of -0.099 MPa. The mixture was then discharged, sealed, and stored to obtain a one-component addition-cured liquid silicone rubber for in-situ molding and sealing, which was labeled as finished product C1.

[0080] Example 2:

[0081] The preparation process is similar to that of Example 1, except that product B in Example 1 is replaced with an equal amount of product B1, which is labeled as finished product C2.

[0082] Example 3:

[0083] The preparation process is similar to that of Example 1, except that product B in Example 1 is replaced with an equal amount of product B2, which is labeled as finished product C3.

[0084] Example 4:

[0085] The preparation process is similar to that of Example 1, except that the silicone resin in Example 1 is replaced with an equal mass of phenyl vinyl MDQ silicone resin with a vinyl content of 0.45% and 2.6 parts by mass of side-hydrogen silicone oil with a hydrogen content of 0.75%, which is labeled as finished product C4.

[0086] Example 5:

[0087] The preparation process is similar to that of Example 1, except that the silicone resin in Example 1 is replaced with an equal mass of phenyl vinyl MDQ silicone resin with a vinyl content of 0.66% and 3.5 parts by mass of side-hydrogen silicone oil with a hydrogen content of 0.75%, which is labeled as finished product C5.

[0088] Example 6:

[0089] The preparation process is similar to that of Example 1, except that 3 parts by mass of the side-containing hydrogen silicone oil with a hydrogen content of 0.75% in Example 1 are replaced with 2 parts by mass of the side-containing hydrogen silicone oil with a hydrogen content of 1.2%, and it is labeled as finished product C6.

[0090] Comparative Example 1:

[0091] 65 parts by weight of vinyl silicone oil with a viscosity of 10000 mPa·s at 25°C and a specific surface area of ​​300 m² will be used. 2 15 parts by weight of hydrophobic fumed silica and 15 parts by weight of phenyl vinyl MDQ silicone resin with a vinyl content of 0.58% were added to a vacuum kneader and stirred for 30 minutes. The mixture was then heated to 120°C and stirred for 60 minutes. After stirring under vacuum at 160°C and a vacuum degree of -0.08 MPa for 120 minutes, the mixture was diluted, cooled, and ground to obtain the base material.

[0092] Three parts by mass of a hydrogen-containing silicone oil with a hydrogen content of 0.75% and 100 parts by mass of a base material were added to a three-dimensional high-speed disperser. The mixture was stirred for 15 minutes under high-speed dispersion at 500 r / min, low-speed stirring at 50 r / min, and a vacuum of -0.08 MPa (the stirring conditions for the following examples and comparative examples are the same as in Example 1). Then, 0.15 parts by mass of a bis(1-ethynyl-1-cyclohexanol)bis(triphenylphosphine)platinum complex (platinum content 3000 ppm) and 0.05 parts by mass of 1-ethynyl-1-cyclohexanol were added. The mixture was stirred for 15 minutes under high-speed dispersion at 400 r / min, low-speed stirring at 45 r / min, and a vacuum of -0.099 MPa. The mixture was then discharged, sealed, and stored to obtain a one-component addition-type liquid silicone rubber, which was labeled as the finished product C7.

[0093] Comparative Example 2:

[0094] The preparation process is similar to that of Comparative Example 1, except that phenyl vinyl MDQ is replaced by vinyl silicone oil with a viscosity of 10000 mpa·s at 25°C and 2 parts by mass of hydrogen-containing silicone oil with a hydrogen content of 0.75%, which is labeled as finished product C8.

[0095] Comparative Example 3:

[0096] The preparation process is similar to that of Case 1, except that product A is not added and is labeled as finished product C9.

[0097] Comparative Example 4:

[0098] The preparation process is similar to that of Case 1, except that product A is replaced with a commercially available thickener and labeled as finished product C10.

[0099] Performance testing

[0100] a. Adhesion and mechanical property testing

[0101] The above-mentioned finished products C1-C9 were prepared according to GB / T 7124-2008 and GB / T 528-2009 standards, and cured in a 150℃ forced-air drying oven for 30 min. After being removed and left at room temperature for 2 h, shear strength (test substrate was 3003 aluminum), tensile strength and elongation at break were tested. The test results are shown in Table 1:

[0102] Table 1 Comparison of mechanical properties of the embodiments and comparative examples

[0103] Product Number Shear strength, MPa Tensile strength, MPa Elongation at break, % C1 3.6 5.2 300 C2 3.52 5.3 290 C3 3.5 5.1 290 C4 3.3 4.6 320 C5 3.5 5.8 260 C6 3.8 5.6 230 C7 0.6 4.7 320 C8 0.58 4.2 360 C9 1.2 4.9 300 C10 2.0 4.8 270

[0104] Compared with Example 1, Examples 2 and 3 used different thixotropic agents, and the resulting liquid silicone rubbers all had high shear strength, tensile strength and elongation at break, indicating that the liquid silicone rubbers of Examples 1 to 3 have good adhesive properties.

[0105] Compared to Example 1, Example 4 shows a decrease in the vinyl content of the phenyl vinyl MDQ silicone resin and a decrease in the amount of hydrogen-containing silicone oil. Compared to Example 1, Example 5 shows an increase in the vinyl content of the phenyl vinyl MDQ silicone resin and an increase in the amount of hydrogen-containing silicone oil. The changes in mechanical properties among the three examples are not significantly different, indicating that the vinyl content and amount of hydrogen-containing silicone oil in the phenyl vinyl MDQ silicone resin can be adjusted within a certain range. Compared to C5, C6 shows improved shear strength and tensile strength, but a decreased elongation at break.

[0106] Compared to Example 1, the hydrogen content of the hydrogen-containing silicone oil in Example 6 was increased, but the dosage was reduced. It still yielded an adhesive with high shear strength and tensile strength, but the elongation at break decreased to some extent. This indicates that the hydrogen content and dosage of the hydrogen-containing silicone oil can be adjusted within a certain range of total hydrogen content.

[0107] Compared with Example 1, Comparative Examples 1 and 2 did not use tackifiers and thixotropic agents, so their shear strength was very poor, indicating poor bonding performance.

[0108] Compared to Example 1, Comparative Example 3 did not use an tackifier, and therefore had very poor shear strength, indicating poor adhesion performance. Compared to Comparative Example 1, Comparative Example 3 used a thixotropic agent, and therefore its adhesion performance was improved.

[0109] b. Dimensional change rate and high temperature anti-adhesion test

[0110] The above-mentioned finished products C1-C9 were coated onto the test samples using an adhesive coating device. Figure 3 On the standard fixture shown, the width of the adhesive strip is (3±0.5) mm and the height is (2.0±0.2) mm. After curing in a 150℃ forced-air drying oven for 30 minutes, the dimensional change rate is tested. Then, the fixture is covered with the top cover and the screws are tightened with a torque screwdriver. The torque requirement is between 1.5 and 5.0 NM. After aging in a 110℃ forced-air drying oven for 1000 hours, the anti-adhesion performance is tested according to GB / T 23982-2009. The test results are shown in Table 2.

[0111] Table 2 Comparison of dimensional change rate and high-temperature anti-adhesion test results for the examples and comparative examples

[0112]

[0113]

[0114] As shown in Tables 1 and 2, the shear strength of the liquid silicone rubber after adding product A is greater than 3 MPa, and the anti-adhesion grade can reach A0. This indicates that the liquid silicone rubber has good adhesion and good disassembly properties. This is mainly because Si-H in product A can participate in the crosslinking reaction to introduce epoxy and benzene ring groups into the main chain. The epoxy groups have low activity at room temperature, but can react with the active groups on the substrate surface to form a strong adhesive effect when heated at high temperature. After high-temperature curing, due to the helical coiling of the molecular chain segments and the non-polar benzene ring macromolecules and side groups shielding the polarity of the epoxy groups and silicon-oxygen bonds, the entire molecule is in a highly saturated state, showing a low surface energy and low molecular force between the molecule and the substrate. The thixotropic agent is weak, thus avoiding oil seepage and adhesion during long-term compression, thereby achieving excellent anti-adhesion effect. After high-temperature curing, the dimensional change rate of thixotropic agents B and B1 is within 5%, and after high-temperature curing, the dimensional change rate of thixotropic agent B2 is within 20%. Without thixotropic agents, the dimensional change rate after high-temperature curing is relatively large, exceeding 20%. This is mainly because B and B1 introduce more epoxy groups into their structures. Due to the strong electronegativity of oxygen atoms, the numerous oxygen atoms on the epoxy groups form stable hydrogen bonds with the reinforcing silica in the system, thus producing a thixotropic effect. Simultaneously, the introduction of siloxane segments into the structure increases the compatibility of the thixotropic agent with the silicone oil-based polymer, further enhancing the thixotropic effect. The thixotropic effect produced by the thixotropic agent is as follows: Figure 4 As shown.

[0115] c. Compression permanent deformation performance test

[0116] The above-mentioned finished products C1-C9 were extruded into a polytetrafluoroethylene mold with a cavity thickness of (2.1±0.1) mm, cured in a 150℃ forced-air drying oven for 30 min, and left at room temperature for 2 h. The samples were then removed and cut into test pieces with a diameter of (13±0.5) mm and a thickness of (2.1±0.1) mm using a cutting machine. Three test pieces were stacked to form type B test pieces as specified in GB / T7759.1-2015. The compression set was tested according to GB / T 7759.1-2015 standard. The test conditions were: aging temperature 150℃, compression ratio 25%, and aging time 1000 h. The test results are shown in Table 3.

[0117] Table 3 Comparison of compression set rate tests in the examples and comparative examples.

[0118] Product Number Compression permanent deformation rate C1 23％ C2 26％ C3 28％ C4 29％ C5 23％ C6 22％ C7 27％ C8 32％ C9 25％ C10 30％

[0119] Compared to Comparative Example 1, Comparative Example 2 did not use phenyl vinyl MDQ silicone resin. As shown in Table 3, the compression set of Comparative Example 2 was higher than that of Comparative Example 1. Adding phenyl vinyl MDQ silicone resin effectively improved the mechanical properties and compression set of liquid silicone rubber. Even after aging at 150℃ for 1000 hours, the compression set remained below 30%. This is mainly because phenyl vinyl MDQ silicone resin significantly improves the cohesive energy density and heat resistance of organosilicon polymers. Furthermore, due to the steric rigidity of the benzene ring and the dense crosslinking points of the polyvinyl functional groups in the silicone resin, the cured silicone rubber exhibits good mechanical properties and compression resilience, thus endowing the liquid silicone rubber with excellent compression set performance.

[0120] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. An in-situ molded one-component addition-curing liquid silicone rubber, characterized in that, The preparation method is as follows: 65 parts by weight of vinyl silicone oil with a viscosity of 10000 mPa·s at 25°C and a specific surface area of ​​300 m² will be used. 2 15 parts by weight of hydrophobic fumed silica and 15 parts by weight of phenyl vinyl MDQ silicone resin with a vinyl content of 0.58% were added to a vacuum kneader and stirred for 30 min. The mixture was then heated to 120°C and stirred for 60 min. After de-blending at 160°C and a vacuum degree of -0.08 MPa for 120 min, the mixture was diluted, cooled, and ground to obtain the base material. Two parts by mass of a hydrogen-containing silicone oil with a hydrogen content of 1.2% and 100 parts by mass of a base material were added to a planetary mixer. The mixture was stirred for 15 min under high-speed dispersion at 500 r / min, low-speed stirring at 50 r / min, and vacuum of -0.08 MPa. Then, one part by mass each of a thixotropic agent and a tackifier were added. The mixture was stirred for 20 min under high-speed dispersion at 750 r / min and low-speed stirring at 60 r / min. Finally, 0.15 parts by mass of a bis(1-ethynyl-1-cyclohexanol)bis(triphenylphosphine)platinum complex and 0.05 parts by mass of 1-ethynyl-1-cyclohexanol were added. The mixture was stirred for 15 min under high-speed dispersion at 400 r / min, low-speed stirring at 45 r / min, and vacuum of -0.099 MPa. The mixture was then discharged, sealed, and stored to obtain a one-component addition-curing liquid silicone rubber for in-situ molding and sealing. The method for preparing the thixotropic agent includes the following steps: In a three-necked flask equipped with a thermometer, condenser, and mechanical stirrer, 0.115 mol of hydrogen-containing polydimethylsiloxane with a hydrogen content of 1.2% and 0.001 mol of caster platinum catalyst were added and stirred for 15 min. Then, 0.035 mol of 1,2-epoxy-4-vinylcyclohexane was added and the temperature was raised to 90 °C and reacted for 2 h. After cooling to room temperature, activated carbon was added for adsorption for 24 h. The mixture was then filtered and distilled under reduced pressure to obtain the thixotropic agent. The preparation method of the thickener includes the following steps: In a three-necked flask equipped with a thermometer, condenser, and mechanical stirrer, 0.3 mol of tetramethylcyclotetrasiloxane and 0.002 mol of Castel platinum catalyst were added and stirred for 15 min. Then, 0.3 mol of 2-epoxy-4-vinylcyclohexane and 0.14 mol of bisphenol A dielyl ether were added and the mixture was heated to 80 °C and reacted for 3 h. After cooling to room temperature, activated carbon was added and adsorbed for 24 h. The mixture was then filtered and distilled under reduced pressure to obtain a thickener.

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