Low-vacuum mass loss high electromagnetic shielding efficiency silicone rubber composite material and preparation method and application thereof

Abstract

This invention relates to a silicone rubber composite material with low vacuum mass loss and high electromagnetic shielding effectiveness, its preparation method, and its applications, belonging to the field of silicone rubber material technology. This invention improves upon existing mechanical blending methods by using mechanical blending to incorporate conductive fillers into the silicone rubber matrix: the silicone rubber masterbatch is pre-pressed into thin sheets and pre-treated with heat before mixing; the modified conductive filler and silicone rubber masterbatch are then kneaded and dispersed at high temperature; and post-treatment with heat is performed after vulcanization. The improved method for preparing the silicone rubber composite material effectively removes volatile substances from the silicone rubber. The resulting rubber composite material not only possesses excellent electromagnetic shielding effectiveness but also a low vacuum mass loss rate, showing promising application prospects in high vacuum applications.

Description

Technical Field

[0001] This invention relates to a silicone rubber material, and more specifically, to a silicone rubber composite material with low vacuum mass loss and high electromagnetic shielding effectiveness, its preparation method, and its application. Background Technology

[0002] Strong electromagnetic interference (EMI) can occur in highly integrated electronic instruments, severely affecting the normal operation of electronic systems and other equipment. To effectively prevent EMI, high-electromagnetic-shielding materials are typically used at connection points such as instrument hatches and cable connectors to achieve environmental sealing and EMI shielding. High-electromagnetic-shielding materials must possess high conductivity and / or high permeability and high EMI shielding effectiveness. Generally, an EMI shielding value <30 dB indicates poor EMI shielding effectiveness; an EMI shielding value between 30 and 60 dB indicates moderate EMI shielding effectiveness, suitable for general industrial or commercial electronic equipment; an EMI shielding value between 60 and 90 dB indicates good EMI shielding effectiveness, suitable for military instruments; and an EMI shielding value above 90 dB indicates excellent EMI shielding effectiveness, suitable for demanding, high-precision, and highly sensitive electronic equipment.

[0003] Silicone rubber possesses excellent resistance to high and low temperatures (-100℃~250℃), ozone, ultraviolet radiation, and vacuum thermal cycling, making it a promising candidate for various applications. Functionalization is achieved by mechanically blending the silicone rubber matrix with conductive (or magnetic) fillers, expanding its applications in electromagnetic shielding. Therefore, silicone rubber composites with high electromagnetic shielding effectiveness obtained by mechanically blending the silicone rubber matrix with conductive (or magnetic) fillers can be used for environmental sealing and electromagnetic shielding in high-vacuum equipment.

[0004] However, silicone rubber contains low-molecular-weight additives, impurities, and moisture during production, and it can absorb some gases during storage. When exposed to a high vacuum environment for extended periods, gas can escape from the material surface. The condensation of these small molecules can contaminate expensive equipment and devices. For example, in early NASA flights, oily residues of low-molecular-weight substances were observed in silicone materials used in spacecraft windows and other areas. These low-molecular-weight substances did not crosslink into the silicone polymer matrix and subsequently flowed out and deposited on cold surfaces. Furthermore, the sealed motor switch on Apollo 14 malfunctioned during flight because the room temperature vulcanized (RTV) silicone rubber used in operation released low-molecular-weight silicone compounds. These released compounds reacted with petroleum-based lubricants under the influence of the electric arc on the brushes, forming carbon particles, increasing brush marks and leading to motor failure. Therefore, based on these considerations, standard ASTM E595 requires materials used in high vacuum environments to be kept below 7 × 10⁻⁶ °C. -3After being placed in a Pa environment for 24 hours, the material's vacuum mass loss rate (TML) is ≤1% and CVCM is ≤0.1% to screen its use. However, under certain extreme conditions or for components near sensitive surfaces, ultra-low release silicone materials (TML ≤0.1%) are required to protect the cleanliness and safety of the instrument.

[0005] Wang Qiang et al. extracted vinyl silicone oil using solvent extraction and added 240 phr of silicon carbide to improve the thermal conductivity of silicone rubber. The resulting material had a thermal conductivity of 1.26 W / m·K and a vacuum mass loss rate of 0.27%. (Wang Qiang, Mao Yunzhong, Xu Jiangling et al. Development of space-level addition-type two-component thermally conductive silicone rubber [J]. Organosilicon Materials, 2015, 29(05):377-380.). Vinyl silicone oil is a raw material for preparing silicone rubber. This literature reduces the small molecules generated by extracting the raw material for preparing silicone rubber and adds silicon carbide to impart thermal conductivity to the material. This method of treating small molecules is relatively complex, and the vacuum mass loss rate of the prepared material cannot meet the requirements of ultra-low gas release organosilicon materials. In addition, this literature does not disclose whether this method can prepare silicone rubber with both low vacuum mass loss rate and high electromagnetic shielding effectiveness. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention employs mechanical blending to dope conductive fillers into a silicone rubber matrix, and improves upon existing methods for preparing silicone rubber through mechanical blending, thereby producing a silicone rubber composite material with low vacuum mass loss and high electromagnetic shielding effectiveness; thus providing a new preparation method for silicone rubber composite materials with low vacuum mass loss and high electromagnetic shielding effectiveness.

[0007] This invention improves upon existing methods for preparing silicone rubber through mechanical blending by the following steps: Before mixing, the silicone rubber masterbatch is pre-pressed into thin sheets, pre-treated with heat, and then the modified conductive filler and silicone rubber masterbatch are kneaded and dispersed at high temperature. After vulcanization, a post-treatment with heat is performed. This improved preparation method effectively removes volatile substances from the silicone rubber. The resulting silicone rubber composite material not only possesses excellent electromagnetic shielding performance but also exhibits a low vacuum mass loss rate, reducing the risk of damage to instruments and equipment due to the volatilization of small molecules during high-vacuum use.

[0008] One of the objectives of this invention is to provide a method for preparing a silicone rubber composite material with low vacuum mass loss and high electromagnetic shielding effectiveness.

[0009] The preparation method of the low vacuum mass loss high electromagnetic shielding effectiveness silicone rubber composite material includes:

[0010] 1) Pre-press the silicone rubber masterbatch into thin sheets to obtain silicone rubber masterbatch sheets;

[0011] 2) Pre-treat the silicone rubber masterbatch sheet by heating;

[0012] 3) The modified conductive filler and the preheated silicone rubber masterbatch sheet were kneaded and dispersed under closed conditions at high temperature to obtain the rubber compound;

[0013] 4) The rubber compound and additives are mixed to obtain a compounded rubber; the additives include vulcanizing agents and vulcanizing aids;

[0014] 5) Dehydrate and vulcanize the compounded rubber to obtain vulcanized rubber;

[0015] 6) The vulcanized rubber is heated and then treated to obtain the rubber composite material with low vacuum mass loss and high electromagnetic shielding effectiveness.

[0016] Step 1) The purpose of pre-compressing the silicone rubber masterbatch into thin sheets is to ensure that the small molecules of the silicone rubber masterbatch evaporate evenly and accelerate the evaporation efficiency during the heating pretreatment in step 2), thereby helping to reduce the vacuum mass loss rate of the product. The pre-compression pressure can be any pressure capable of compressing the rubber masterbatch into thin sheets, specifically 10-15 MPa.

[0017] Step 1) The smaller the thickness of the pre-pressed sheet, the better it is for reducing the vacuum mass loss rate of the prepared silicone rubber composite material, without significantly affecting the electromagnetic shielding effectiveness; however, too low a thickness will lead to a decrease in the amount of pre-treated adhesive per unit area, which is not conducive to large-scale industrial production. Taking all factors into consideration, the thickness of the silicone rubber masterbatch sheet can be 0.5-2 mm, preferably 1 mm.

[0018] Step 2) Pre-treat the silicone rubber masterbatch sheet by heating it. The purpose of this pre-treatment is to remove volatile small molecules from the silicone rubber masterbatch and reduce the vacuum mass loss rate of the prepared silicone rubber composite material. Increasing the pre-treatment temperature and time is beneficial for removing small molecules and reducing the vacuum mass loss rate of the silicone rubber composite material. However, excessively high pre-treatment temperatures can lead to the gradual loss of plasticizers during prolonged pre-treatment, affecting the processing performance of the silicone rubber. Furthermore, the removal of small molecules follows a trend of initial rapid removal followed by slower removal over time. While excessively increasing the treatment time may help reduce the vacuum mass loss rate, the reduction is very limited and increases the cost of industrialization. Therefore, the pre-treatment temperature is 60~120℃, and the treatment time is 1~5h; preferably, the temperature is 80~110℃, and the treatment time is 2~4h. In some embodiments of the present invention, the treatment temperature is 100℃, and the treatment time is 2h.

[0019] Step 3) The modified conductive filler and the pre-treated silicone rubber masterbatch sheet are kneaded and dispersed at high temperature under sealed conditions to obtain the rubber compound. This invention only kneads and disperses the masterbatch and modified conductive filler at high temperature; it involves kneading and dispersing a portion, not all, of the raw materials, and it is a high-temperature kneading and dispersion, not a room-temperature kneading and dispersion. Compared to the prior art where all raw materials are kneaded and dispersed together at room temperature, the kneading and dispersion method of this invention firstly allows for the simultaneous dispersion and removal of small rubber molecules during the high-temperature kneading and dispersion process, increasing the efficiency of small rubber molecule removal. Simultaneously, since other additives besides the modified conductive filler and masterbatch do not participate in the high-temperature kneading and dispersion, the degradation of other material properties due to high-temperature dispersion is avoided. Furthermore, kneading at high temperature is more conducive to the bonding between the conductive filler and the rubber, further improving the electromagnetic shielding effectiveness of the material. However, excessively high kneading temperatures can lead to a decrease in the tensile strength, elongation at break, conductivity, and electromagnetic shielding effectiveness of the silicone rubber composite material; indicating that excessively high kneading temperatures are also not conducive to preparing materials with excellent properties. Therefore, the temperature of the high-temperature kneading and dispersion is 120~150℃, preferably 130~150℃; the time of the high-temperature kneading and dispersion is 20~40min.

[0020] Step 4) Mix the rubber compound and additives to obtain a compound. The mixing can be performed using any existing mixing method for preparing silicone rubber.

[0021] Step 5) dehydration can be performed using any existing method for removing moisture from the rubber compound. Specifically, the rubber compound can be placed in a container containing a desiccant to remove moisture. The dehydration time can be 8-12 hours; the desiccant can be a molecular sieve desiccant. The molecular sieve desiccant can be any existing molecular sieve desiccant suitable for drying rubber compounds. In some embodiments of the present invention, a general-purpose molecular sieve desiccant is used, and drying is performed at room temperature for 8 hours.

[0022] The vulcanization in step 5) can be performed using any existing silicone rubber vulcanization process. Specifically, the vulcanization temperature can be 140~200℃, preferably 160~180℃; the vulcanization time can be 5~20min, preferably 6~15min. In some embodiments of the present invention, the vulcanization temperature is 170℃ and the vulcanization time is 10min.

[0023] Step 6) The purpose of heating the vulcanized rubber is to further remove volatile substances remaining in the prepared silicone rubber composite material and reduce its vacuum mass loss rate. Studies have found that lowering the post-treatment temperature is not conducive to a rapid reduction in the vacuum mass loss rate, while increasing the post-treatment temperature is beneficial for increasing electromagnetic shielding effectiveness. However, excessively high post-treatment temperatures can also lead to material degradation. Therefore, the chosen post-treatment temperature is 170~250℃, preferably 180~220℃. Research has also found that the removal of small molecules follows a trend of initial rapid reduction followed by slower reduction. While increasing the treatment time is beneficial for reducing the vacuum mass loss rate, excessively increasing the treatment time results in only a limited reduction in vacuum mass loss rate and increases industrialization costs. Furthermore, post-treatment initially improves the electromagnetic shielding effectiveness of the material, but there is no significant improvement later. Therefore, a reasonable treatment time is 2~8 hours, preferably 3~6 hours. In some embodiments of this invention, the post-treatment temperature is 200℃ and the treatment time is 4 hours.

[0024] The proportions of the silicone rubber masterbatch, vulcanizing agent, co-vulcanizing agent, and modified conductive filler can be those used in existing high electromagnetic shielding silicone rubber composites prepared by mechanical blending. To obtain a low vacuum mass loss high electromagnetic shielding silicone rubber composite with an SE value of 90 dB or higher, the weight parts of the silicone rubber masterbatch, vulcanizing agent, co-vulcanizing agent, and modified conductive filler are as follows:

[0025] 100 parts by weight of silicone rubber masterbatch;

[0026] 1-4 parts by weight of vulcanizing agent;

[0027] 1-3 parts by weight of vulcanizing agent;

[0028] 150-275 parts by weight of modified conductive filler.

[0029] The modified conductive filler is preferably used in an amount of 200-250 parts by weight per 100 parts by weight of silicone rubber masterbatch. In some embodiments of the present invention, the modified conductive filler is used in an amount of 225 parts by weight per 100 parts by weight of silicone rubber masterbatch. The resulting silicone rubber composite material with low vacuum mass loss and high electromagnetic shielding effectiveness has a higher SE value.

[0030] The silicone rubber masterbatch may be selected from at least one of methyl vinyl silicone rubber masterbatch, methyl vinyl phenyl silicone rubber masterbatch, methyl phenyl silicone rubber masterbatch, and fluorosilicone rubber masterbatch.

[0031] The vulcanizing agent may be at least one of dicumyl peroxide (DCP), 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane (DBPH) and 2,4-dichlorobenzoyl peroxide (DCBP).

[0032] The co-vulcanizing agent can be at least one of triallyl isocyanurate (TAIC) and triallyl cyanurate (TAC).

[0033] The modified conductive filler is obtained by modifying a conductive filler with a coupling agent. Preferably, the coupling agent is at least one selected from vinyltriethoxysilane, vinyltrimethoxysilane, γ-(2,3-epoxypropoxy)propyltrimethoxysilane, and 3-(methacryloyloxy)propyltrimethoxysilane. Preferably, the conductive filler is silver-plated aluminum powder with a particle size range of 30-100 μm. Preferably, the mass ratio of the conductive filler to the coupling agent is 75:1-9; more preferably, the mass ratio of the conductive filler to the coupling agent is 75:2-5.

[0034] The modified conductive filler is prepared by the following method: the conductive filler is dried at 100℃~150℃ for 1~5 hours, stirred and dispersed, and then a coupling agent is sprayed onto the surface of the conductive filler at 30~80℃. After standing for 5~10 minutes, the modified conductive filler is obtained. Preferably, the drying temperature is 110~130℃ and the spraying temperature is 40~60℃.

[0035] A second objective of this invention is to provide a low-vacuum-mass-loss, high-electromagnetic-shielding-effective rubber composite material. This low-vacuum-mass-loss, high-electromagnetic-shielding-effective silicone rubber composite material is prepared using the method described above.

[0036] The third objective of this invention is to provide an application of a low-vacuum-mass-loss, high-electromagnetic-shielding rubber composite material under vacuum conditions.

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

[0038] (1) Compared with existing methods for preparing low-vacuum mass loss silicone rubber, this invention effectively removes volatile substances from the rubber through a series of processes, including pre-pressing and heating the silicone rubber masterbatch before mixing, high-temperature kneading of the masterbatch and modified conductive filler, and post-heating treatment after vulcanization. The resulting rubber composite material not only has excellent electromagnetic shielding performance but also a low vacuum mass loss rate. This fills the gap in silicone rubber preparation methods that combine low vacuum mass loss rate and high electromagnetic shielding performance. The preparation method of this invention has a simple molding process, good processing performance, and broad application prospects in the high vacuum field.

[0039] (2) The low vacuum mass loss, high conductivity electromagnetic shielding rubber composite material prepared by this invention has a low vacuum mass loss rate (TML) of ≤0.1% compared to the standard TML ≤1%. In a vacuum environment, the amount of gas released is relatively small, effectively reducing the impact of volatile gases on space exploration equipment. It can be used in certain extreme conditions or components near sensitive surfaces. Simultaneously, the material has an SE ≥90dB in the 100MHz~1200MHz band, effectively preventing electromagnetic interference and ensuring the normal operation of the equipment. Detailed Implementation

[0040] The present invention will now be described in detail with reference to specific 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. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0041] The silicone rubber masterbatch, vulcanizing agent, co-vulcanizing agent, conductive filler, coupling agent and molecular sieve desiccant used are all commercially available products.

[0042] Example 1

[0043] A silicone rubber composite material with low vacuum mass loss and high conductivity electromagnetic shielding effectiveness is prepared by the following steps.

[0044] Step 1, Heat Pretreatment: The silicone rubber masterbatch is pre-compressed into a 1mm sheet under a pressure of 15 MPa, and then pre-treated at 100℃ for 2 hours. The silicone rubber masterbatch used is methyl vinyl silicone rubber masterbatch.

[0045] Step 2, Modification: The conductive filler was dried at 125℃ for 1 hour, then added to a beaker and dispersed with stirring. The coupling agent was sprayed onto the surface of the conductive filler at 40℃ in a small amount to ensure uniform coating. After standing for 6 minutes, the modified conductive filler was obtained. The conductive filler was silver-plated aluminum powder with a particle size range of 30~100μm, and the coupling agent was vinyltriethoxysilane (A151). The mass ratio of the conductive filler to the coupling agent was 75:2.

[0046] Step 3, kneading: The pretreated silicone rubber masterbatch and modified conductive filler are placed in a close-fitting kneader for high-temperature kneading and dispersion. The modified conductive filler is added in multiple batches. The high-temperature kneading and dispersion temperature is 140℃ and the dispersion time is 25 minutes.

[0047] Step 4, mixing: Add vulcanizing agent and vulcanizing aid to the kneaded rubber compound in a two-roll mill and mix 5 times to obtain the compounded rubber; the mixing temperature is 25℃.

[0048] Step 5, Dehydration: Place the compounded rubber in a container containing a general-purpose molecular sieve desiccant at room temperature to further remove moisture. The dehydration time is 8 hours.

[0049] Step 6, vulcanization: The dehydrated compound obtained in step 5 is vulcanized at a temperature of 160℃ for 15 minutes to obtain vulcanized rubber.

[0050] Step 7, post-heating treatment: The vulcanized rubber obtained in step 6 is subjected to post-heating treatment at a temperature of 200℃ for 4 hours.

[0051] in,

[0052] Silicone rubber masterbatch: 100g

[0053] Vulcanizing agent DCP: 1g

[0054] TAIC (a vulcanizing agent): 2g

[0055] Modified conductive filler: 225g.

[0056] Example 2

[0057] A low-vacuum-mass-loss, high-conductivity electromagnetic shielding silicone rubber composite material was prepared according to the preparation method and conditions of Example 1, including heat pretreatment, modification, kneading, mixing, vulcanization, dehydration, and post-heat treatment. The difference between this example and Example 1 is that the silicone rubber masterbatch was pre-pressed into a 2mm sheet during the heat pretreatment step.

[0058] in:

[0059] Silicone rubber masterbatch: 100g

[0060] Vulcanizing agent DCP: 1g

[0061] TAIC (a vulcanizing agent): 2g

[0062] Modified conductive filler: 225g.

[0063] Example 3

[0064] A low-vacuum mass loss, high-conductivity electromagnetic shielding silicone rubber composite material was prepared according to the preparation method and conditions of Example 1, including heat pretreatment, modification, kneading, mixing, vulcanization, dehydration, and post-heat treatment. The difference between this example and Example 1 is that the silicone rubber masterbatch was pre-pressed into a 0.5 mm sheet during the heat pretreatment step.

[0065] in:

[0066] Silicone rubber masterbatch: 100g

[0067] Vulcanizing agent DCP: 1g

[0068] TAIC (a vulcanizing agent): 2g

[0069] Modified conductive filler: 225g.

[0070] Example 4

[0071] A low-vacuum mass loss, high-conductivity electromagnetic shielding silicone rubber composite material was prepared according to the preparation method and conditions of Example 1, including heat pretreatment, modification, mixing, vulcanization, dehydration, and heat posttreatment.

[0072] in:

[0073] Silicone rubber masterbatch: 100g

[0074] Vulcanizing agent DCP: 1g

[0075] TAIC (a vulcanizing agent): 2g

[0076] Modified conductive filler: 175g.

[0077] Example 5

[0078] A low-vacuum mass loss, high-conductivity electromagnetic shielding silicone rubber composite material was prepared according to the preparation method and conditions of Example 1, including heat pretreatment, modification, mixing, vulcanization, dehydration, and heat posttreatment.

[0079] in:

[0080] Silicone rubber masterbatch: 100g

[0081] Vulcanizing agent DBPH: 2g

[0082] TAC (tandem vulcanizing agent): 3g

[0083] Modified conductive filler: 275g.

[0084] Example 6

[0085] A silicone rubber composite material with low vacuum mass loss and high conductivity electromagnetic shielding effectiveness is prepared by the following steps:

[0086] Step 1, Heat Pretreatment: The silicone rubber masterbatch is pre-compressed into a 1mm sheet under a pressure of 15 MPa, and then pre-treated at 100℃ for 1 hour. The silicone rubber masterbatch used is methyl vinyl silicone rubber masterbatch.

[0087] Step 2, Modification: The conductive filler was dried at 110℃ for 5 hours, then added to a beaker and dispersed with stirring. At 40℃, a coupling agent was sprayed onto the surface of the conductive filler in a small amount to ensure uniform coating. After standing for 10 minutes, the modified conductive filler was obtained. The conductive filler was silver-plated aluminum powder with a particle size range of 30~100μm, and the coupling agent was vinyltriethoxysilane (A151). The mass ratio of the conductive filler to the coupling agent was 75:2.

[0088] Step 3, kneading: The pretreated silicone rubber masterbatch and modified conductive filler are placed in a close-fitting kneader for high-temperature kneading and dispersion. The modified conductive filler is added in multiple batches. The high-temperature kneading and dispersion temperature is 120℃ and the dispersion time is 40 minutes.

[0089] Step 4, Mixing: Add vulcanizing agent and co-vulcanizing agent to the kneaded rubber compound in a two-roll mill, and mix multiple times to obtain the compounded rubber; the mixing temperature is 25℃.

[0090] Step 5, Dehydration: Place the compounded rubber in a container containing a general-purpose molecular sieve desiccant at room temperature to further remove moisture. The dehydration time is 8 hours.

[0091] Step 6, vulcanization: The dehydrated compound obtained in step 5 is vulcanized at a temperature of 140℃ for 20 minutes to obtain vulcanized rubber.

[0092] Step 7, post-heating treatment: The vulcanized rubber obtained in step 6 is subjected to post-heating treatment at a temperature of 180℃ for 8 hours.

[0093] in,

[0094] Silicone rubber masterbatch: 100g

[0095] Vulcanizing agent DBPH: 1g

[0096] TAC (tandem vulcanizing agent): 2g

[0097] Modified conductive filler: 225g.

[0098] Example 7

[0099] A silicone rubber composite material with low vacuum mass loss and high conductivity electromagnetic shielding effectiveness is prepared by the following steps:

[0100] Step 1, Heat Pretreatment: The silicone rubber masterbatch is pre-compressed into a 1mm sheet under a pressure of 15 MPa, and then pre-treated at 80℃ for 4 hours. The silicone rubber masterbatch used is methyl vinyl silicone rubber masterbatch.

[0101] Step 2, Modification: The conductive filler was dried at 130℃ for 1 hour, then added to a beaker and dispersed with stirring. The coupling agent was sprayed onto the surface of the conductive filler in a small amount at 60℃ to uniformly coat the surface. After standing for 5 minutes, the modified conductive filler was obtained. The conductive filler was silver-plated aluminum powder with a particle size range of 30~100μm, and the coupling agent was vinyltriethoxysilane (A151). The mass ratio of the conductive filler to the coupling agent was 75:5.

[0102] Step 3, kneading: The pretreated silicone rubber masterbatch and modified conductive filler are placed in a close-fitting kneader for high-temperature kneading and dispersion. The modified conductive filler is added in multiple batches. The high-temperature kneading and dispersion temperature is 150℃ and the dispersion time is 20min.

[0103] Step 4, Mixing: Add vulcanizing agent and co-vulcanizing agent to the kneaded rubber compound in a two-roll mill, and mix multiple times to obtain the compounded rubber; the mixing temperature is 25℃.

[0104] Step 5, Dehydration: Place the compounded rubber in a container containing a general-purpose molecular sieve desiccant at room temperature to further remove moisture. The dehydration time is 12 hours.

[0105] Step 6, vulcanization: The dehydrated compound obtained in step 5 is vulcanized at a temperature of 200℃ for 5 minutes to obtain vulcanized rubber.

[0106] Step 7, post-heating treatment: The vulcanized rubber obtained in step 6 is subjected to post-heating treatment at a temperature of 220℃ for 2 hours.

[0107] in,

[0108] Silicone rubber masterbatch: 100g

[0109] Vulcanizing agent DCBP: 1g

[0110] TAC (tandem vulcanizing agent): 2g

[0111] Modified conductive filler: 225g.

[0112] Comparative Example 1

[0113] A silicone rubber composite material was modified, kneaded, mixed, vulcanized, dehydrated, and subjected to heat treatment according to the preparation method and conditions of Example 1. The difference between this example and Example 1 is that the heat pretreatment step was omitted.

[0114] in:

[0115] Silicone rubber masterbatch: 100g

[0116] Vulcanizing agent DCP: 1g

[0117] TAIC (a vulcanizing agent): 2g

[0118] Modified conductive filler: 225g.

[0119] Comparative Example 2

[0120] A silicone rubber composite material was prepared according to the preparation method and conditions of Example 1, including heat pretreatment, modification, mixing, vulcanization, dehydration, and post-heat treatment. Compared with Example 1, in this example, before the mixing step, the silicone rubber masterbatch, modified conductive filler, vulcanizing agent DCP, and vulcanizing agent TAIC were placed in a kneader for kneading and dispersion at room temperature (25°C), and the dispersion time was the same as in Example 1.

[0121] in,

[0122] Silicone rubber masterbatch: 100g

[0123] Vulcanizing agent DCP: 1g

[0124] TAIC (a vulcanizing agent): 2g

[0125] Modified conductive filler: 225g.

[0126] Comparative Example 3

[0127] A silicone rubber composite material was prepared according to the preparation method and conditions of Example 1, including heat pretreatment, modification, kneading, mixing, vulcanization, dehydration, and post-heat treatment. Compared with Example 1, the kneading temperature in this example was 200°C, and the dispersion time was the same as in Example 1.

[0128] in,

[0129] Silicone rubber masterbatch: 100g

[0130] Vulcanizing agent DCP: 1g

[0131] TAIC (a vulcanizing agent): 2g

[0132] Modified conductive filler: 225g.

[0133] Comparative Example 4

[0134] A rubber composite material, the raw material composition and mass are as follows:

[0135] Silicone rubber masterbatch: 100g

[0136] Vulcanizing agent DCP: 1g

[0137] TAC (tandem vulcanizing agent): 2g

[0138] Modified conductive filler: 225g;

[0139] The preparation method is as follows:

[0140] Step 1: Dry modification of the conductive filler is carried out by adding coupling agent dropwise to the conductive filler and then shaking it evenly to coat the surface of the conductive filler with coupling agent.

[0141] Step 2: Place the silicone rubber masterbatch and the modified conductive filler in a two-roll mill, add vulcanizing agent and vulcanizing agent, mix at 25°C 5 times to obtain the compound, and let it stand for 8 hours.

[0142] Step 3: The compound obtained in Step 2 is vulcanized at a vulcanization temperature of 160℃ for 15 minutes to obtain vulcanized rubber.

[0143] Step 4: Heat the vulcanized rubber obtained in Step 3 at a temperature of 200℃ for 4 hours.

[0144] Comparative Example 5

[0145] A rubber composite material, the raw material composition and mass fractions of which are as follows:

[0146] Silicone rubber masterbatch: 100g

[0147] Vulcanizing agent DCP: 1g

[0148] TAC (tandem vulcanizing agent): 2g

[0149] Modified conductive filler: 225g;

[0150] The preparation method is as follows:

[0151] Step 1: The conductive filler is modified by wet method. The conductive filler is dispersed in anhydrous ethanol and ultrasonically vibrated. Then, it is ultrasonically stirred for 30 minutes under water bath heating. The coupling agent is then added dropwise to the solution and ultrasonically stirred for 1 hour. The solvent in the solution is then evaporated to dryness, the powder is collected, and then repeatedly filtered and washed with tetrahydrofuran in a vacuum filter. Finally, it is dried and pulverized in an oven at 80°C.

[0152] Step 2: Place the silicone rubber masterbatch and the modified conductive filler in a two-roll mill, add vulcanizing agent and vulcanizing agent, mix at 25°C 5 times to obtain the compound, and let it stand for 8 hours.

[0153] Step 3: The compound obtained in Step 2 is vulcanized at a vulcanization temperature of 160℃ for 15 minutes to obtain vulcanized rubber.

[0154] Step 4: Heat the vulcanized rubber obtained in Step 3 at a temperature of 200℃ for 4 hours.

[0155] The silicone rubber composite materials prepared in Examples 1-7 and Comparative Examples 1-5 were tested.

[0156] Thermogravimetric analysis: The silicone rubber was tested using a thermogravimetric analyzer under a nitrogen atmosphere, with the temperature increased from room temperature to 300°C at a rate of 10°C / min. The mass loss rate of the rubber was obtained, which indirectly reflects the volatility of the material.

[0157] Conductivity Testing: Following GB / T 31838.2-2019 standard, the conductivity of the rubber was tested using a four-probe resistance meter (model HPS-2661) from Changzhou Haierpa Electronic Technology Co., Ltd. Five areas were randomly selected on the surface of the prepared rubber sample for measurement. Readings were taken after the values ​​stabilized. The average value was determined and then input into the specific software of the four-probe resistance meter, along with the input dimensions, to correct the data. The data obtained directly from the four-probe resistance meter is the volume resistivity of the material (ρ). v The unit is mΩ•cm. The conductivity (σ) is the reciprocal of the volume resistivity, and the unit is S / m. The calculation formula is shown in (1-1):

[0158] σ= Equation (1-1)

[0159] Electromagnetic shielding effectiveness test: The shielding effectiveness of rubber in an electric field of 100~1200MHz was tested according to GB / T 30142-2013 standard using a flange coaxial device of model DR-S02 from Beijing Dingrong Shichuang Technology Co., Ltd., connected to a vector network analyzer of model E5063A from Beijing Dingrong Shichuang Technology Co., Ltd.

[0160] Mechanical property testing: The tensile strength (σ) of the rubber specimen was tested according to GB / T 528-2009 standard using a universal tensile testing machine (model AI-7000S1) manufactured by High-Speed ​​Rail Monitoring Instruments (Dongguan) Co., Ltd. b / MPa), elongation at break (ε b Mechanical properties such as ( / %) were tested.

[0161] Hardness Testing: The hardness of the rubber was tested using an LAC-J Shore A hardness tester manufactured by Beijing Ruida Yuchen Instrument Co., Ltd., according to GB / T 531.1-2008 "Test Methods for Indentation Hardness of Vulcanized Rubber or Thermoplastic Rubber Part 1: Shore Hardness Tester Method (Shore Hardness)". Cut rubber strips were stacked together, approximately 6-8 mm thick, and the indenter was quickly pressed down, with the integer value read within 3 seconds.

[0162] Vacuum mass loss rate (TML) test: The vacuum mass loss rate (TML) of rubber is tested according to the QJ 1558B-2016 standard.

[0163] TML= ×100%……Equation (1-2)

[0164] S I —Initial mass of the small box containing the sample

[0165] S F —The final mass of the small box containing the sample.

[0166] B—The weight of the small box.

[0167] A—Mass of the sample carrier.

[0168] Collected volatile organic compounds (CVCM) test: Test the volatile organic compounds collected by the rubber according to the standard QJ 1558B-2016;

[0169] CVCM= ×100%……Equation (1-3)

[0170] C F —The initial mass of the collection plate,

[0171] C I —The final quality of the collection plate.

[0172] Water vapor reabsorption (WVR) test: The water vapor reabsorption of rubber is tested according to the QJ 1558B-2016 standard;

[0173] WVR= ×100%……Equation (1-4)

[0174] S F’ —The mass of the sample box containing the sample after it has been stored in a constant temperature and humidity chamber for 24 hours.

[0175] The test results are shown in Tables 1 and 2; among them, the performance of the silicone rubber composite materials prepared in Examples 6 and 7 is comparable to that in Example 1. "-" in Tables 1 and 2 indicates that no test was conducted.

[0176] Table 1

[0177]

[0178] Table 2

[0179]

[0180] Based on the experimental data in Table 1, comparing the performance of the silicone rubber composites prepared in Examples 1, 2, and 3, it can be concluded that: as the pre-compression thickness decreases, it further reduces the volatility of the material (increases the thermogravimetric value). However, too low a pre-compression thickness leads to a significant reduction in the amount of pretreated adhesive per unit area, affecting the material preparation efficiency. Therefore, 1 mm is preferred as the pre-compression thickness of the silicone rubber masterbatch. Compared to the silicone rubber composites prepared in Examples 1 and 4, the silicone rubber composite prepared in Example 5 shows a significant decrease in thermogravimetric value and elongation at break, and a significant increase in tensile strength, hardness, conductivity, and electromagnetic shielding effectiveness. This indicates that with the increase of modified conductive filler, the electromagnetic shielding effectiveness and conductivity of the rubber increase. Simultaneously, the gradually decreasing thermogravimetric value indicates a gradual decrease in the volatility of the material, while the hardness of the rubber also gradually increases. Therefore, considering comprehensive performance, selecting an appropriate amount of conductive filler can both reduce the volatility of the material and improve its electromagnetic shielding effectiveness.

[0181] According to the experimental data in Table 2, compared with the silicone rubber composite material prepared in Comparative Example 1 without heat pretreatment, the thermogravimetric value Δm of the silicone rubber composite material prepared in Example 1 was significantly lower; it can be seen that heat pretreatment of the silicone rubber masterbatch effectively reduced the volatility of the material. Compared with the room temperature kneading of Comparative Example 2 at 25℃, the thermogravimetric value and TML value of the silicone rubber composite material prepared by high temperature kneading in Example 1 were significantly lower, while the electrical conductivity and electromagnetic shielding effectiveness were somewhat increased. This indicates that the high temperature kneading process of some raw materials in this invention is beneficial for dispersing and removing small rubber molecules during the mixing process, which increases the efficiency of removing small rubber molecules. At the same time, kneading at high temperature is more conducive to the bonding of conductive fillers and rubber, further improving the electromagnetic shielding effectiveness of the material. Compared with the kneading of Comparative Example 3 at 200℃, the tensile strength, elongation at break, electrical conductivity, and electromagnetic shielding effectiveness of the silicone rubber composite material prepared in Example 1 were somewhat increased, indicating that excessively high kneading temperature is also not conducive to preparing materials with excellent properties. Compared to Comparative Example 4, the silicone rubber composite material prepared by the process in Example 1 showed significantly lower thermogravimetric values, TML, CVCM, and WVR, while its electrical conductivity and electromagnetic shielding effectiveness increased to some extent. This indicates that this process effectively reduces the volatility and vacuum mass loss rate of the material compared to traditional conductive adhesive preparation processes. Compared to Comparative Example 5, although the electrical conductivity and electromagnetic shielding effectiveness of the silicone rubber composite material prepared by the process in Example 1 were not as good as those in Comparative Example 5, its thermogravimetric values, TML, CVCM, and WVR were significantly lower. This suggests that although the traditional wet-process modification of conductive fillers produces conductive adhesives with superior electrical conductivity and electromagnetic shielding effectiveness, the introduction of a large amount of solvent during the modification of the conductive filler can easily lead to an increase in the volatility of the material.

[0182] The vacuum release performance of the silicone rubber composite material prepared in Example 1 was tested, revealing that its TML value could reach as low as 0.06%, CVCM as low as 0.01%, and WVR as low as 0.02%, meeting the requirement of TML ≤ 0.1% for low vacuum mass loss. The electromagnetic shielding effectiveness of the prepared silicone rubber composite material in the 100MHz~1200MHz band was tested, showing an electromagnetic shielding effectiveness of 90~110dB, indicating that this material possesses excellent electromagnetic shielding performance. Therefore, the silicone rubber composite material prepared in this invention has significant application prospects in the field of electromagnetic shielding under high vacuum conditions.

Claims

1. A method for preparing a low-vacuum mass-loss high electromagnetic shielding effectiveness silicone rubber composite material, characterized in that, The preparation method includes: 1) Pre-press the silicone rubber masterbatch into thin sheets to obtain silicone rubber masterbatch sheets; 2) The silicone rubber masterbatch sheet is subjected to heat pretreatment; the heat pretreatment temperature is 60~120℃; 3) The modified conductive filler and the preheated silicone rubber masterbatch sheet are kneaded and dispersed under closed conditions at high temperature to obtain the rubber compound; the temperature of the high-temperature kneading and dispersion is 120~150℃. 4) The rubber compound and additives are mixed to obtain a compounded rubber; the additives include vulcanizing agents and vulcanizing aids; 5) Dehydrate and vulcanize the compounded rubber to obtain vulcanized rubber; 6) The vulcanized rubber is heated and then treated to obtain the low vacuum mass loss and high electromagnetic shielding efficiency silicone rubber composite material.

2. The preparation method according to claim 1, characterized in that, The pre-compression pressure is 10-15 MPa; or / and, The thickness of the silicone rubber masterbatch sheet is 0.5-2 mm.

3. The production method according to claim 1, wherein The heating pretreatment temperature is 80~110℃.

4. The production method according to claim 1, wherein The heating pretreatment process takes 1 to 5 hours.

5. The production method according to claim 1, wherein The heating pretreatment process takes 2 to 4 hours.

6. The production method according to claim 1, wherein The high-temperature kneading and dispersion temperature is 130~150℃; the high-temperature kneading and dispersion time is 20~40min.

7. The production method according to claim 1, wherein The dehydration refers to removing moisture from the compound by placing it in a container containing a desiccant; or / and, The vulcanization temperature is 140~200℃; the vulcanization time is 5~20min; or / and, The temperature of the post-heating treatment is 170~250℃, and the time is 2~8h.

8. The preparation method according to claim 7, characterized in that, The dehydration time is 8-12 hours; the desiccant is a molecular sieve desiccant; or / and, The vulcanization temperature is 160~180℃; the vulcanization time is 6~15min; or / and, The temperature of the post-heating treatment is 180~220℃, and the time is 3~6h.

9. The production method according to claim 1, wherein The weight proportions of the silicone rubber masterbatch, vulcanizing agent, co-vulcanizing agent, and modified conductive filler are as follows: 100 parts by weight of silicone rubber masterbatch; 1-4 parts by weight of vulcanizing agent; 1-3 parts by weight of vulcanizing agent; 150-275 parts by weight of modified conductive filler.

10. The production method according to claim 9, wherein 200-250 parts by weight of modified conductive filler.

11. The preparation method according to claim 1, characterized in that, The silicone rubber masterbatch is selected from at least one of methyl vinyl silicone rubber masterbatch, methyl vinyl phenyl silicone rubber masterbatch, methyl phenyl silicone rubber masterbatch, and fluorosilicone rubber masterbatch; The vulcanizing agent is at least one of dicumyl peroxide, 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane and 2,4-dichlorobenzoyl peroxide. The co-vulcanizing agent is at least one of triallyl isocyanurate and triallyl cyanurate; The modified conductive filler is obtained by modifying the conductive filler with a coupling agent.

12. The preparation method according to claim 11, characterized in that, The coupling agent is at least one selected from vinyltriethoxysilane, vinyltrimethoxysilane, γ-(2,3-epoxypropoxy)propyltrimethoxysilane, and 3-(methacryloyloxy)propyltrimethoxysilane; or / and, The conductive filler is silver-plated aluminum powder with a particle size range of 30~100μm; or / and, The mass ratio of the conductive filler to the coupling agent is 75:1~9.

13. The production method according to claim 11, wherein The mass ratio of the conductive filler to the coupling agent is 75:2~5.

14. The production method according to claim 11, wherein The modified conductive filler is prepared by the following method: the conductive filler is dried at 100℃~150℃ for 1~5h, stirred and dispersed, and then the coupling agent is sprayed onto the surface of the conductive filler at 30~80℃. After standing for 5~10min, the modified conductive filler is obtained.

15. The preparation method according to claim 14, characterized in that, The drying temperature is 110~130℃, and the spraying temperature is 40~60℃.

16. A silicone rubber composite material with low vacuum mass loss and high electromagnetic shielding effectiveness, characterized in that, It is prepared by the preparation method described in any one of claims 1-15.

17. The application of a low-vacuum mass loss, high electromagnetic shielding effectiveness silicone rubber composite material as described in claim 16 under vacuum conditions.

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