A sprayable thermally conductive silicone rubber and a method of making the same

Abstract

The application provides a sprayable heat-conducting silicone rubber and a preparation method thereof, and belongs to the technical field of heat-conducting materials. The preparation method is mixing component A and component B with a weight ratio of 98-102:1, and curing to obtain the sprayable heat-conducting silicone rubber. The raw materials for preparing the component A include methyl silicone rubber base glue, coupling agent prepolymer, processing stabilizer, thermal functional filler, reinforcing agent prepolymer and diluent. The raw materials for preparing the component B include crosslinking agent, catalyst and diluent. The sprayable heat-conducting silicone rubber has excellent heat-conducting performance and mechanical properties, is simple to operate, and can meet different production needs.

Description

Technical Field

[0001] This invention belongs to the field of thermal conductive materials technology, and particularly relates to a sprayable thermally conductive silicone rubber and its preparation method. Background Technology

[0002] Currently, my country's aerospace, electronics, and high-frequency communication technologies are developing rapidly. However, this rapid development has also brought about several challenges. For example, the increasing demand for high-performance and miniaturized key electronic devices in these fields leads to the generation and rapid accumulation of significant heat during operation. Research indicates that for electronic devices, a 2°C increase in temperature reduces reliability by 10%, while a 6°C increase in transformer winding temperature halves its expected lifespan. Therefore, high-performance thermal conductive materials have attracted widespread attention. Traditionally, thermal conductive materials in the market mainly fall into three categories: epoxy resin-based, acrylate-based, and silicone-based. The first two categories suffer from poor high-temperature resistance, require high-temperature curing, and have short storage times. The third category, silicone-based thermal conductive materials, has drawbacks such as high viscosity, large application thickness, reliance on scraping for application, and poor workability.

[0003] Therefore, it is necessary to develop a thermally conductive material that is easy to spray, has good thermal conductivity, good mechanical properties, and is simple to operate. Summary of the Invention

[0004] To address the above problems, this invention provides a sprayable thermally conductive silicone rubber and its preparation method.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A sprayable thermally conductive silicone rubber, wherein the raw materials for making the sprayable thermally conductive silicone rubber include component A and component B in a weight ratio of 98 to 102:1;

[0007] The raw materials used to make component A, by weight, include 100 parts of methyl silicone rubber base, 5-10 parts of coupling agent prepolymer, 2-5 parts of processing stabilizer, 50-200 parts of thermal functional filler, 3-10 parts of reinforcing agent prepolymer and 20-50 parts of diluent.

[0008] The raw materials for making component B, by weight, include 8 parts of crosslinking agent, 1.8 to 2.2 parts of catalyst and 2.8 to 3.2 parts of diluent.

[0009] Furthermore, the raw materials for preparing the coupling agent prepolymer include γ-glycidyl etheroxypropyltrimethoxysilane (KH560) and other coupling agents in a molar ratio of 3:1 to 5;

[0010] Other coupling agents are γ-aminopropyltriethoxysilane (KH550), 3-(2,3-epoxypropoxy)propylmethyldiethoxysilane (KH563), γ-mercaptopropyltriethoxysilane (KH580), or γ-mercaptopropyltrimethoxysilane (KH590).

[0011] Furthermore, the coupling agent prepolymer is prepared by mixing γ-glycidyl etheroxypropyltrimethoxysilane (KH560) and other coupling agents evenly, adding 2-6% of the total mass of the resulting mixture to an acidic solution, reacting at 30-60°C for 20-60 min, and then evacuating to -0.1 MPa to remove the acidic solution.

[0012] Among them, the acidic solution is an aqueous solution of acetic acid / hydrochloric acid with a pH of 4-6;

[0013] Coupling agents contain epoxy, mercapto, alkoxy, and amino groups. These groups not only improve the dispersibility of the powder in the adhesive, but more importantly, they improve the adhesion of the adhesive. KH560, as an essential component in the preparation of coupling agent prepolymers, contains epoxy and alkoxy groups. KH550 contains amino groups, and KH580 and KH590 both contain mercapto groups. After pretreatment to form prepolymers, the resulting coupling agent prepolymers not only have the addition of epoxy, mercapto, alkoxy, and amino groups, but also additional hydroxyl groups, resulting in a greater improvement in adhesion.

[0014] Furthermore, the raw materials for preparing the reinforcing agent prepolymer include a crosslinking agent prepolymer and a reinforcing filler in a weight ratio of 1:5;

[0015] The crosslinking agent prepolymer is made from tetraethyl orthosilicate and methyltriacetoxysilane or methyltrimethoxysilane in a weight ratio of 1:1.

[0016] The reinforcing filler is one or two of micron-sized hydrophobic calcium carbonate, hydrophobic calcium sulfate, and hydrophobic barium sulfate; the addition of the reinforcing filler can improve the mechanical properties of the rubber compound.

[0017] Furthermore, the preparation process of the crosslinking agent prepolymer is as follows:

[0018] Take tetraethyl orthosilicate and methyltriacetoxysilane / methyltrimethoxysilane in a weight ratio of 1:1 and mix them to obtain a crosslinking agent mixture;

[0019] Take an aqueous solution of acetic acid with a pH of 4-5, start stirring, raise the temperature to 60±2℃ for the first time, slowly add the crosslinking agent mixture dropwise, after the dropwise addition is complete, raise the temperature to 70±2℃ for the second time, continue stirring and react for more than 2 hours, cool to room temperature, and the crosslinking agent prepolymer is obtained.

[0020] The volume-to-weight ratio of the acetic acid aqueous solution to the crosslinking agent prepolymer is 1:20.

[0021] Furthermore, the reinforcing agent prepolymer is prepared by adding reinforcing filler to a processor, adding crosslinking agent prepolymer under stirring, treating at 160±2℃ and -0.03~-0.06MPa for 2~3h, and then removing residual low volatiles.

[0022] The reinforcing filler contained in the reinforcing agent prepolymer, which has been treated with cross-linking agent prepolymer, can improve its compatibility with the system.

[0023] Furthermore, the viscosity of the methyl silicone rubber base is at least one of 500 mPa·s, 1000 mPa·s, 2000 mPa·s, and 3000 mPa·s;

[0024] The processing stabilizer is diphenylsilanol or cyanoalkoxysilane, such as diphenyldihydroxysilane, γ-cyanopropyltriethoxysilane, β-cyanoethyltriethoxysilane or β-cyanoethylmethyldiethoxysilane; the processing stabilizer can slow down the sedimentation of the rubber compound and improve its stability.

[0025] The thermal functional filler is one or two of nano-sized aluminum nitride, silicon carbide, and silicon nitride; the function of the thermal functional filler is to improve the thermal conductivity of the adhesive.

[0026] The diluent is at least one of n-hexane, ethanol, tetrahydrofuran, octamethylpolytrimethylsiloxane, and methylpolytrimethylsiloxane; the diluent has good compatibility with the adhesive and can reduce the viscosity of the adhesive to meet the requirements for spraying.

[0027] The crosslinking agent is tetraethyl orthosilicate, methyltrimethoxysilane, or methyltriethoxysilane; after the crosslinking agent comes into contact with water in the air, it generates silanol groups, which can condense with the hydroxyl groups in methyl silicone rubber to form a crosslinking network;

[0028] The catalyst is an organotin or organobismuth, such as dibutyltin dilaurate or bismuth octyldecanoate.

[0029] Furthermore, component A is prepared by mixing methyl silicone rubber, coupling agent prepolymer, processing stabilizer and reinforcing agent prepolymer, adding thermal functional filler in batches, mixing evenly in a planetary mixer, heating to 110-130°C, opening a vacuum to -0.1MPa, heating and stirring under vacuum for 2-3 hours, then cooling to below 30°C, breaking the vacuum, adding diluent, stirring for 20-30 minutes, and discharging the material.

[0030] Furthermore, component B is prepared by mixing the crosslinking agent and catalyst evenly, adding a diluent, stirring for more than 5 minutes to achieve uniform mixing.

[0031] A method for preparing the above-mentioned sprayable thermally conductive silicone rubber, wherein the preparation method is to mix component A and component B to obtain the sprayable thermally conductive silicone rubber, which can then be sprayed and cured at room temperature or by heating.

[0032] Furthermore, mix component A and component B evenly, then degas for more than 30 minutes under a vacuum of ≥-0.09Mpa. Take it out, pour it into different molds, and cure it at room temperature or place it in an oven at 100-130℃. After curing, the sprayable thermally conductive silicone rubber is obtained.

[0033] The viscosity range of the sprayable thermally conductive silicone rubber is 40–300 mPa·s, which is not limited by the shape of the device and can be used in any scenario. It is easy to operate and can be cured quickly at room temperature, which can meet the bonding requirements on metal substrates. It also has good adhesion to silicone rubber substrates and can meet the process requirements of thin-layer coating on silicone substrates. The cured sprayable thermally conductive silicone rubber has a hardness of 30–60A, tear strength of 10–20 N / mm, elongation at break of 150–200%, tensile strength of 6–12 MPa, and thermal conductivity of 0.7–4 W / (m·K). Detailed Implementation

[0034] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Those skilled in the art can make similar extensions without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0035] Example 1: A pretreatment method for coupling agents

[0036] This embodiment is a pretreatment method for coupling agents, specifically including the following steps:

[0037] γ-glycidyl etheroxypropyltrimethoxysilane (KH560) and other coupling agents were mixed in a molar ratio of 3:1 to 5. After thorough mixing, 2 to 7% (by mass) of an acidic solution was added to the mixture. The mixture was reacted at 30 to 60°C for 20 to 60 minutes. Then, the mixture was evacuated to -0.1 MPa to remove the acidic solution, yielding the coupling agent prepolymer. The acidic solution was an aqueous solution of acetic acid / hydrochloric acid with a pH of 4 to 6.

[0038] Other coupling agents are γ-aminopropyltriethoxysilane (KH550), 3-(2,3-epoxypropoxy)propylmethyldiethoxysilane (KH563), γ-mercaptopropyltriethoxysilane (KH580), or γ-mercaptopropyltrimethoxysilane (KH590).

[0039] The specific raw materials, process parameters, and the numbering of the resulting coupling agent prepolymer in the pretreatment method of this embodiment are as follows:

[0040] Table 1. Summary of parameters during the pretreatment process of each coupling agent.

[0041]

[0042] Among them, KH560 is γ-glycidoxypropyltrimethoxysilane, KH550 is γ-aminopropyltriethoxysilane, KH563 is 3-(2,3-epoxypropoxy)propylmethyldiethoxysilane, KH580 is γ-mercaptopropyltriethoxysilane, and KH590 is γ-mercaptopropyltrimethoxysilane.

[0043] The amount of acidic solution added is the ratio of the weight of the acidic solution added to the total weight of the resulting mixture.

[0044] Meanwhile, it can be seen that when the amount of KH560 and other coupling agents exceeds a specific molar ratio, the resulting coupling agent prepolymer exhibits a gel state and cannot be used.

[0045] Example 2: A method for synthesizing a reinforcing agent prepolymer

[0046] Take tetraethyl orthosilicate and methyltriacetoxysilane / methyltrimethoxysilane in a weight ratio of 1:1 and mix them to obtain a crosslinking agent mixture.

[0047] Water and acetic acid were added to the reactor, resulting in an acetic acid aqueous solution with a pH of 4–5. Stirring was started, and the temperature was raised to 60±2℃ for the first time. The crosslinking agent mixture was slowly added dropwise. After the addition was complete, the temperature was raised to 70±2℃ for the second time, and the reaction was continued with stirring for at least 2 hours. The mixture was then cooled to room temperature to obtain the crosslinking agent prepolymer. The volume-to-weight ratio of the acetic acid aqueous solution to the crosslinking agent prepolymer was 1:20.

[0048] The reinforcing filler was added to the processor, and the crosslinking agent prepolymer was added under stirring. The mixture was treated at 160±2℃ and -0.03 to -0.06 MPa for 2 to 3 hours. Then, the residual low-volatile substances were removed to obtain the reinforcing agent prepolymer. The weight ratio of the crosslinking agent prepolymer to the reinforcing filler was 1:5.

[0049] In this embodiment, the specific raw materials, process parameters, and the numbering of the resulting reinforcing agent prepolymer in the synthesis method of the reinforcing agent prepolymer are as follows:

[0050] Table 2. Summary of parameters during the synthesis of prepolymers of various reinforcing agents

[0051]

[0052] Example 3: A method for preparing sprayable thermally conductive silicone rubber

[0053] A sprayable thermally conductive silicone rubber, wherein the raw materials for making the sprayable thermally conductive silicone rubber include component A and component B in a weight ratio of 98 to 102:1;

[0054] When using, mix components A and B at a weight ratio of 98–102:1, apply by spraying, and cure at room temperature or with heat.

[0055] The raw materials used to make component A, by weight, include 100 parts methyl silicone rubber, 5-10 parts coupling agent prepolymer, 2-5 parts processing stabilizer, 50-200 parts thermal functional filler, 3-10 parts reinforcing agent prepolymer and 20-50 parts diluent.

[0056] The preparation method of component A is as follows: methyl silicone rubber, coupling agent prepolymer, processing stabilizer and reinforcing agent prepolymer are stirred and mixed evenly, and then thermal functional filler is added in batches. The mixture is mixed evenly in a planetary power mixer, heated to 110-130℃, and vacuumed to -0.1MPa. The mixture is heated and stirred under vacuum for 2-3 hours, then cooled to below 30℃, the vacuum is broken, diluent is added, and the mixture is stirred for 20-30 minutes. After discharge, the mixture is sealed and stored to obtain component A.

[0057] The raw materials for making component B, by weight, include 8 parts of crosslinking agent, 1.8 to 2.2 parts of catalyst and 2.8 to 3.2 parts of diluent.

[0058] The preparation method of component B is to mix the crosslinking agent and catalyst evenly, add the diluent, stir for more than 5 minutes to mix evenly, and then seal and store the mixture after discharge to obtain component B.

[0059] The specific preparation method of a sprayable thermally conductive silicone rubber in this embodiment is as follows:

[0060] Preparation of S1 and A components

[0061] Take 90 kg of methyl silicone rubber with a viscosity of 2000 mPa·s, 10 kg of methyl silicone rubber with a viscosity of 500 mPa·s, 5 kg of coupling agent prepolymer C05, 3 kg of diphenyl dihydroxysilane and 5 kg of reinforcing agent prepolymer D05, and stir them evenly. Then add 120 kg of silicon nitride in batches (in this example, it is added in 5 batches) and mix them evenly in a planetary power mixer. At the same time, heat to 120°C, turn on the vacuum to -0.1 MPa, heat and stir under vacuum for 2.5 h, then cool to 25°C, break the vacuum, add 30 kg of n-hexane and 8 kg of octamethyl polytrisiloxane, stir for 25 min, discharge and seal for storage to obtain component A.

[0062] Preparation of S2 and B components

[0063] Take 8 kg of tetraethyl orthosilicate and 2 kg of bismuth octanoate, mix them evenly, add 3 kg of n-hexane, stir for more than 5 minutes to mix evenly, discharge the material and seal it for storage to obtain component B.

[0064] S3. Preparation of Sprayable Thermally Conductive Silicone Rubber

[0065] Mix components A and B evenly at a weight ratio of 100:1, then degas for at least 30 minutes under a vacuum of ≥-0.09 MPa. Remove the mixture, pour it into different molds, and cure at room temperature. Once cured, the resulting thermally conductive sprayable silicone rubber is obtained. Alternatively, it can be cured in an oven at 100–130°C.

[0066] The resulting sprayable thermally conductive silicone rubber has a viscosity of 107 mPa·s, a hardness of 42A, a thermal conductivity of 3.2 W / (m·k), a tear strength of 13 N / mm, a tensile strength of 10.2 MPa, an elongation at break of 180%, a 180° peel force of 3.3 N / 25 mm on iron sheets, and a 180° peel force of 3.7 N / 25 mm on aluminum sheets.

[0067] The viscosity was tested according to GB / T 15357-2014, "Determination of viscosity and flow properties of liquid products by rotational viscometer for surfactants and detergents".

[0068] Hardness was tested according to GB / T531.1-2008, "Test method for indentation hardness of vulcanized rubber or thermoplastic rubber - Part 1".

[0069] The thermal conductivity was tested according to GB / T 31134.2-2014, "Silicone Rubber Thermally Conductive Curing Adhesives for Electronic Components".

[0070] Hardness, elongation at break and tensile strength were tested in accordance with GB / T 528-2009 "Determination of tensile stress-strain properties of vulcanized rubber or thermoplastic rubber".

[0071] Tear strength was tested according to GB / T 529-2008, "Determination of tear strength of vulcanized rubber or thermoplastic rubber (trouser-shaped, right-angled and crescent-shaped specimens)".

[0072] The 180° peel strength was tested according to GB / T 2792-2014, "Test Method for Peel Strength of Adhesive Tapes".

[0073] Examples 4-10: Preparation methods of sprayable thermally conductive silicone rubber

[0074] Examples 4-10 are methods for preparing sprayable thermally conductive silicone rubber. Their steps are basically the same as in Example 3, differing only in the amount of raw materials and process parameters. See Tables 3-4 for details.

[0075] Table 3. Summary of process parameters in Examples 4-8

[0076]

[0077]

[0078] Table 4. Summary of process parameters in Examples 9-10

[0079]

[0080]

[0081] The contents of other parts of Examples 4 to 10 are the same as those of Example 3, and will not be repeated here.

[0082] Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A sprayable thermally conductive silicone rubber, characterized in that, The raw materials for making the sprayable thermally conductive silicone rubber include component A and component B in a weight ratio of 98~102:1; The raw materials used to make component A, by weight, include 100 parts of methyl silicone rubber base, 5-10 parts of coupling agent prepolymer, 2-5 parts of processing stabilizer, 50-200 parts of thermal functional filler, 3-10 parts of reinforcing agent prepolymer and 20-50 parts of diluent. By weight, the raw materials for making component B include 8 parts crosslinking agent, 1.8 to 2.2 parts catalyst and 2.8 to 3.2 parts diluent; The raw materials for preparing the coupling agent prepolymer include γ-glycidoxypropyltrimethoxysilane and other coupling agents in a molar ratio of 3:1 to 5; the other coupling agents are γ-aminopropyltriethoxysilane, 3-(2,3-epoxypropoxy)propylmethyldiethoxysilane, γ-mercaptopropyltriethoxysilane or γ-mercaptopropyltrimethoxysilane; The raw materials for preparing the reinforcing agent prepolymer include a crosslinking agent prepolymer and a reinforcing filler in a weight ratio of 1:5; wherein, the crosslinking agent prepolymer is prepared from tetraethyl orthosilicate and methyltriacetoxysilane or methyltrimethoxysilane in a weight ratio of 1:1; the reinforcing filler is one or two of micron-sized hydrophobic calcium carbonate, hydrophobic calcium sulfate, and hydrophobic barium sulfate; The reinforcing agent prepolymer is prepared by taking reinforcing filler, adding crosslinking agent prepolymer, and treating it at 160±2℃ and -0.03~-0.06MPa for 2~3h.

2. The sprayable thermally conductive silicone rubber according to claim 1, characterized in that, The coupling agent prepolymer is prepared by mixing γ-glycidyl etheroxypropyltrimethoxysilane and other coupling agents evenly, adding an acidic solution, reacting, and then removing the acidic solution under vacuum. The acidic solution is an aqueous solution of acetic acid / hydrochloric acid with a pH of 4-6.

3. The sprayable thermally conductive silicone rubber according to claim 1, characterized in that, The preparation process of the crosslinking agent prepolymer is as follows: Take tetraethyl orthosilicate and methyltriacetoxysilane or methyltrimethoxysilane in a weight ratio of 1:1 and mix them to obtain a crosslinking agent mixture; Take an aqueous solution of acetic acid with a pH of 4-5, heat it to 60±2℃ for the first time, slowly add the crosslinking agent mixture dropwise, after the addition is complete, heat it to 70±2℃ for the second time, react for more than 2 hours, and cool it to room temperature to obtain the crosslinking agent prepolymer. The volume-to-weight ratio of the acetic acid aqueous solution to the crosslinking agent prepolymer is 1:

20.

4. The sprayable thermally conductive silicone rubber according to claim 3, characterized in that, The viscosity of the methyl silicone rubber base is at least one of 500 mPa·s, 1000 mPa·s, 2000 mPa·s, and 3000 mPa·s; The processing stabilizer is diphenylsilanol or cyanoalkoxysilane; The thermally functional filler is one or two of nano-sized aluminum nitride, silicon carbide, and silicon nitride; The diluent is at least one of n-hexane, ethanol, tetrahydrofuran, octamethylpolytrisiloxane, and methylpolytrimethylsiloxane; The crosslinking agent is tetraethyl orthosilicate, methyltrimethoxysilane, or methyltriethoxysilane; The catalyst is an organotin or organobismuth.

5. The sprayable thermally conductive silicone rubber according to claim 3, characterized in that, Component A is prepared by mixing methyl silicone rubber, coupling agent prepolymer, processing stabilizer and reinforcing agent prepolymer, adding thermal functional filler in batches, mixing evenly, heating to 110~130℃, opening vacuum to -0.1MPa, heating and stirring under vacuum for 2~3 hours, then cooling to below 30℃, breaking vacuum, adding diluent.

6. The sprayable thermally conductive silicone rubber according to claim 3, characterized in that, Component B is prepared by mixing the crosslinking agent and catalyst evenly, adding a diluent, and mixing thoroughly.

7. A method for preparing a sprayable thermally conductive silicone rubber according to any one of claims 1-6, characterized in that, The preparation method is to mix component A and component B to obtain the sprayable thermally conductive silicone rubber, and then perform spraying application.

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