Method for preparing silicone rubber foam with high foaming ratio by efficiently inhibiting cell shrinkage

Abstract

The invention provides a method for preparing high-foaming-ratio silicone rubber foam by efficiently inhibiting cell shrinkage, which comprises the following steps: carrying out pre-treatment including banburying and standing on a composite base material comprising raw silicone rubber, and adding a rare metal catalyst to obtain a rubber compound; and then saturating the rubber compound under the supercritical CO2 process condition of 8-20MPa to complete the pre-crosslinking and saturation process, releasing the pressure to foam the rubber compound, continuously introducing CO2, maintaining the pressure in the kettle, heating, and performing post-crosslinking to obtain the high-foaming-ratio silicone rubber foam. According to the invention, a platinum-series rare metal catalyst is selected and utilized, so that the pre-crosslinking temperature of the rubber compound is close to the foaming temperature, and the saturation process of supercritical CO2 is completed during pre-crosslinking; a supercritical CO2 foaming process is improved, outward diffusion of CO2 in foam holes is slowed down by means of high-pressure CO2, fixation of the foam holes is accelerated by means of rapid post-crosslinking, and the purposes of stabilizing the foam hole structure and efficiently inhibiting shrinkage of the silicone rubber foam are achieved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of preparing silicone rubber foam by supercritical CO2 foaming method, and relates to a method for preparing high-foaming-ratio silicone rubber foam by efficiently inhibiting cell shrinkage. BACKGROUND

[0002] Flexible foams are widely used in medical machinery, electronics, construction and packaging due to their excellent mechanical properties, environmental adaptability and resilience. Among them, silicone rubber foam is efficiently used in new energy battery pack, aerospace and thermal insulation outer wall due to its excellent elasticity, chemical stability, good electrical insulation ability and excellent ultraviolet resistance, ozone resistance and flame resistance.

[0003] At present, silicone rubber foam is mainly prepared by chemical foaming method, and the balance between the crosslinking density of silicone rubber and the decomposition rate of chemical foaming agent must be finely controlled in the preparation process to make the strength of the matrix sufficient to maintain the formed cell structure. However, this balance is often difficult to achieve, usually resulting in too large matrix strength, foaming difficulty, or too small matrix strength, cell collapse or merging, so that the industrial silicone rubber foam has low foaming ratio (2-3 times), the cell is extremely uneven, and there is a problem of chemical foaming agent residue, performance degradation and application limitation.

[0004] Supercritical CO2 (ScCO2) foaming is a green, simple and efficient physical foaming technology, which has been widely used in the field of polymer foaming, mainly for the preparation of high-performance microcellular foams. However, the inventors found in the previous research that in the existing technology for preparing silicone rubber foam by supercritical CO2 foaming, there is also a balance problem between crosslinking and foaming. To solve the defects such as easy shrinkage and easy bubble merging of silicone rubber foam, some researchers proposed to use inorganic nano fillers with large aspect ratio such as carbon nanotubes as support, blend them with silicone rubber, and improve the strength of the silicone rubber matrix, so that after rapid pressure relief, it can effectively resist the shrinkage caused by the pressure difference between CO2 and air in the matrix (Tang, W.; Liao, X.; Shi, S., et al., Significantly Enhanced Porosity of Silicone Rubber Nanocomposite Foams via Cross-Linking Structure Regulation and Heterogeneous Nucleation by CNTs for Promising Ultralow-k Dielectrics. Industrial&Engineering Chemistry Research, 2022, 61, 38, 14251-14259). Some researchers also use fluorosilicone rubber which is compatible with silicone rubber to blend, improve the solubility and heterogeneous nucleation of supercritical CO2 in silicone rubber composite, and effectively inhibit the shrinkage of silicone rubber composite foam (Tang, W.; Wang, B.; Xu, R., et al., Promising Thermal Insulation Silicone Rubber Composite Foams with High Expansion Ratios via Fluorosilicone Rubber Blending and Cell Structure Design. Industrial&Engineering Chemistry Research, 2025, 64, 7, 4095-4104). However, the high aspect ratio inorganic nano fillers and polar rubbers used at present are high in cost, and increase the mixing process, making the overall foaming process more difficult and longer, which is not conducive to the actual industrial application.

[0005] Therefore, it is necessary to develop a preparation method which is simple, fast and efficient, easy to implement in industrialization, and can effectively inhibit the large shrinkage of silicone rubber foam caused by bubble merging and collapse during foaming, and obtain high expansion ratio. SUMMARY

[0006] The present application provides a method for preparing high foaming ratio silicone rubber foam by efficiently inhibiting cell shrinkage, which solves the problems in the prior art. On one hand, by selecting a platinum-based rare metal catalyst, the pre-crosslinking temperature of the rubber compound is close to the foaming temperature, and the saturation process of supercritical CO2 is completed at the same time of pre-crosslinking, which greatly improves the solubility and retention of the silicone rubber matrix to supercritical CO2, and significantly reduces the time required for pre-crosslinking of the rubber compound and CO2 saturation. On the other hand, by improving the supercritical CO2 foaming process, after rapid pressure relief to a specific pressure for foaming, CO2 is continuously introduced to maintain a high pressure in the autoclave, and post-crosslinking is completed with rapid heating. By virtue of high-pressure CO2, the diffusion of CO2 in the cell to the outside is slowed down, and the rapid post-crosslinking accelerates the fixation of the cell, so as to achieve the purposes of stabilizing the cell structure and efficiently inhibiting the shrinkage of silicone rubber foam.

[0007] To achieve the above-mentioned purposes, the present application is realized by adopting the technical scheme consisting of the following technical measures.

[0008] The present application provides a method for preparing high foaming ratio silicone rubber foam by efficiently inhibiting cell shrinkage, which solves the problems in the prior art. On one hand, by selecting a platinum-based rare metal catalyst, the pre-crosslinking temperature of the rubber compound is close to the foaming temperature, and the saturation process of supercritical CO2 is completed at the same time of pre-crosslinking, which greatly improves the solubility and retention of the silicone rubber matrix to supercritical CO2, and significantly reduces the time required for pre-crosslinking of the rubber compound and CO2 saturation. On the other hand, by improving the supercritical CO2 foaming process, after rapid pressure relief to a specific pressure for foaming, CO2 is continuously introduced to maintain a high pressure in the autoclave, and post-crosslinking is completed with rapid heating. By virtue of high-pressure CO2, the diffusion of CO2 in the cell to the outside is slowed down, and the rapid post-crosslinking accelerates the fixation of the cell, so as to achieve the purposes of stabilizing the cell structure and efficiently inhibiting the shrinkage of silicone rubber foam.

[0009] (1) After the composite base material including raw silicone rubber is pretreated by including mixing and standing, a rare metal catalyst is added and uniformly mixed to obtain a rubber compound;

[0010] The rare metal catalyst is any one of a platinum catalyst, a palladium catalyst, a ruthenium catalyst, and a rhodium catalyst.

[0011] (2) The rubber compound obtained in step (1) is placed in an autoclave, supercritical CO2 is introduced as a foaming agent, and the rubber compound is saturated under supercritical CO2 process conditions of 8-20 MPa and 40-70℃ for 15-30 min to complete the pre-crosslinking and saturation process;

[0012] After the time arrives, the autoclave is depressurized to 0.1 MPa, CO2 is continuously introduced after the rubber compound is foamed, the pressure in the autoclave is maintained at 2-18 MPa, then the temperature is raised to 150-200℃, and the post-crosslinking is completed after 10-30 min of heat preservation and pressure maintenance. After the time arrives, the autoclave is rapidly depressurized to obtain high foaming ratio silicone rubber foam.

[0013] In this text, the raw silicone rubber in step (1) is a conventional raw material for silicone rubber foam, and a person skilled in the art can select a suitable raw silicone rubber according to common knowledge or prior art, such as any one or combination of methyl vinyl silicone rubber, methyl phenyl vinyl silicone rubber, and poly(3,3,3-trifluoropropylmethyl)silicone rubber.

[0014] It should be noted that in the prior art, the in-situ pre-crosslinking temperature of the silicone rubber foam is high (usually 100-150℃) because high-temperature vulcanized silicone rubber is mainly used, which not only increases the movement degree of CO2, resulting in an increased CO2 diffusion rate and a decreased solubility in the rubber compound, but also increases the difficulty in controlling the pre-crosslinking degree of the silicone rubber. Meanwhile, the pre-crosslinking temperature is greatly different from the foaming temperature (40-70℃), which increases the time and process difficulty of reducing the temperature from the pre-crosslinking temperature to the foaming temperature.

[0015] One of the invention points of the present application is to select a platinum-based rare metal catalyst and a hydrogen-containing silicone oil and a silicone rubber crosslinking system, so that the pre-crosslinking temperature of the rubber compound is close to the foaming temperature, the pre-crosslinking and CO2 saturation processes are simultaneously performed, the solubility of the rubber compound to supercritical CO2 is improved, the time required for the pre-crosslinking and saturation processes is significantly reduced, and the process and operation difficulty are greatly simplified.

[0016] Based on the above invention point, in order to meet the technical purpose of the pre-crosslinking temperature being close to the foaming temperature, the addition amount of the rare metal catalyst in step (1) is 0.1-1wt% of the raw silicone rubber.

[0017] In order to better illustrate the present application and provide a preferred technical solution for reference, in step (1), the rare metal catalyst is added to the composite base material including the raw silicone rubber after pre-treatment including mixing and standing, and mixed uniformly to obtain the rubber compound, and the preparation method is specifically as follows:

[0018] ①The raw silicone rubber, reinforcing agent and hydroxyl silicone oil are added to the internal mixer and mixed and treated at 80-150℃ and 30-80rad / min for 5-30min, after the time reaches, cooled to room temperature and then mixed and treated again at the above process conditions for 10-30min to obtain the pre-mixed rubber compound;

[0019] ②The pre-mixed rubber compound obtained in step ① and the rare metal catalyst are added to the internal mixer and mixed and treated at 20-50℃ and 30-80rad / min for 5-30min to obtain the silicone rubber composite A;

[0020] The pre-mixed rubber compound obtained in step ① and the hydrogen-containing silicone oil are added to the internal mixer and mixed and treated at 20-50℃ and 30-80rad / min for 5-30min to obtain the silicone rubber composite B;

[0021] ③The silicone rubber composite A and the silicone rubber composite B obtained in step ② are added to the internal mixer at room temperature and 30-80rad / min in a mass ratio of 1:(1-20) and mixed and treated for 5-30min, after the time reaches, cooled to room temperature and then mixed and treated again at the above process conditions for 10-20min to obtain the rubber compound.

[0022] In the above preferred technical solution, the reinforcing agent in step ① is any one or more of the conventional auxiliaries added in the preparation process of the silicone rubber foam material, such as fumed white carbon black, precipitated white carbon black. Generally, the amount of the reinforcing agent added is 10-50 wt% of the raw silicone rubber.

[0023] In the above preferred technical solution, the hydroxyl silicone oil in step ① is a conventional raw material in the preparation process of the silicone rubber foam material, and the amount of the hydroxyl silicone oil added is generally 1-10 wt% of the raw silicone rubber.

[0024] In the above preferred technical solution, the hydrogen-containing silicone oil in step ② is a conventional raw material in the preparation process of the silicone rubber foam material, and the amount of the hydrogen-containing silicone oil added is generally 1-10 wt% of the raw silicone rubber.

[0025] It should be noted that in the above preferred technical solution, in addition to the additional addition of rare metal catalyst, the raw material composition and preparation method of the rubber compound can be obtained from the prior art. Although only one preparation method of the rubber compound is described in the following examples, this does not mean the only designation or limitation of the rubber compound described in the present application. Based on the common knowledge in the technical field of the present application and the main purpose of simplifying the process steps, those skilled in the art can select the appropriate rubber compound preparation process and the way of mixing the rare metal catalyst.

[0026] It should be noted that in the prior art, the silicone rubber foamed by supercritical CO2 is usually post-crosslinked in an air environment at normal pressure (0.1 MPa), and there is a problem of rapid and large shrinkage of the silicone rubber foam, resulting in low foaming ratio and low porosity of the silicone rubber foam, and the function of regulating the pore structure is lost.

[0027] The second point of the present application is to improve the supercritical CO2 foaming process, adopt a high-pressure in-situ post-crosslinking strategy after foaming, maintain the pressure balance inside and outside the pores in the kettle during the post-crosslinking process by continuously feeding CO2 after pressure relief foaming, weaken the diffusion of CO2 to the outside of the silicone rubber matrix, and quickly heat to the post-crosslinking temperature to complete the in-situ post-crosslinking, fix the pore structure, so as to effectively inhibit the rapid shrinkage problem of the silicone rubber foam in the normal pressure environment, and greatly shorten the foaming period.

[0028] Through comparative experiments, it is found that based on the technical solution of the present application, the pressure in the adjustable in-situ post-crosslinking process can realize the regulation of the foaming ratio and the pore structure of the silicone rubber foam.

[0029] In one preferred technical solution, the step (2) is to put the rubber compound obtained in step (1) into an autoclave, and supercritical CO2 is used as a foaming agent to saturate the rubber compound under the process conditions of 10-12 MPa and 40-70 DEG C of supercritical CO2, and the pre-crosslinking and saturation process is completed by keeping the temperature and pressure for 15-30 min.

[0030] After the time arrives, the autoclave is depressurized to 0.1 MPa, CO2 is continuously fed after the rubber compound is foamed, the pressure in the autoclave is maintained at 2-10 MPa, then the temperature is raised to 150-200 DEG C, and the post-crosslinking is completed by keeping the temperature and pressure for 10-30 min, and after the time arrives, the pressure is rapidly released to obtain the high-foaming-ratio silicone rubber foam.

[0031] The high-foaming-ratio silicone rubber foam prepared by the method can be applied to the fields of packaging, insulation, cushioning, etc., such as building engineering, vehicle manufacturing, sports goods, etc.

[0032] The method has the following beneficial effects:

[0033] 1. The method for preparing the high-foaming-ratio silicone rubber foam provided by the application effectively inhibits the shrinkage of the cells, platinum-gold rare metal catalyst is selected for catalysis, hydrogen-containing silicone oil and a silicone rubber crosslinking system are used, the pre-crosslinking temperature of the rubber compound is close to the foaming temperature, the pre-crosslinking and the saturation are simultaneously performed, the solubility of supercritical CO2 in the silicone rubber matrix is effectively improved, and the time required for the pre-crosslinking and the saturation is significantly reduced.

[0034] 2. The method for preparing the high-foaming-ratio silicone rubber foam provided by the application effectively inhibits the shrinkage of the cells, the process of supercritical CO2 foaming is improved, CO2 is continuously fed after the foaming is completed, the pressure in the autoclave is balanced inside and outside the cells during the post-crosslinking process after the pressure is maintained to a specific pressure, the diffusion of CO2 to the outside of the silicone rubber matrix is weakened, the in-situ post-crosslinking is completed by rapidly raising the temperature to the post-crosslinking temperature, the cell structure is fixed, the shrinkage of the silicone rubber foam is effectively inhibited, and the foaming cycle is greatly shortened.

[0035] 3. The preparation method provided by the application can be directly applied to the preparation process of traditional silicone rubber foam, the pre-crosslinking, saturation foaming and post-crosslinking processes can be completed in the same device, and the process steps and operation are significantly simplified. DETAILED DESCRIPTION

[0036] Figure 1 The figure shows the parameter changes of the pressure, temperature and crosslinking density of the rubber compound in the autoclave in the process of step (2) of the preparation method.

[0037] Figure 2 The figure is a scanning electron microscope image of the high-foaming-ratio silicone rubber foam prepared in Example 1 of the application.

[0038] Figure 3 A cross-section scanning electron microscope image of the high expansion ratio silicone rubber foam prepared in Example 2 of the present application.

[0039] Figure 4 A cross-section scanning electron microscope image of the high expansion ratio silicone rubber foam prepared in Example 3 of the present application.

[0040] Figure 5 A cross-section scanning electron microscope image of the high expansion ratio silicone rubber foam prepared in Example 4 of the present application.

[0041] Figure 6 A cross-section scanning electron microscope image of the silicone rubber foam prepared in Comparative Example 1 of the present application.

[0042] Figure 7 A comparison bar chart of the expansion ratios of the silicone rubber foams prepared in Examples 1-4 and Comparative Example 1 of the present application. In the horizontal axis, 0 MPa corresponds to Comparative Example 1, 2 MPa corresponds to Example 4, 4 MPa corresponds to Example 3, 6 MPa corresponds to Example 2, and 8 MPa corresponds to Example 1.

[0043] Figure 8 A comparison line graph of the cell densities of the silicone rubber foams prepared in Examples 1-4 and Comparative Example 1 of the present application. In the horizontal axis, 0 MPa corresponds to Comparative Example 1, 2 MPa corresponds to Example 4, 4 MPa corresponds to Example 3, 6 MPa corresponds to Example 2, and 8 MPa corresponds to Example 1.

[0044] Figure 9 A comparison photograph of the silicone rubber foams prepared in Examples 1-4 and Comparative Example 1 of the present application. In the horizontal axis, 0 MPa corresponds to Comparative Example 1, 2 MPa corresponds to Example 4, 4 MPa corresponds to Example 3, 6 MPa corresponds to Example 2, and 8 MPa corresponds to Example 1. DETAILED DESCRIPTION

[0045] For a further understanding of the present application, preferred embodiments thereof will be described in conjunction with examples, it is to be understood, however, that this description is made only by way of example and is not intended to limit the scope of the application. Those skilled in the art can make appropriate modifications to the process parameters with reference to the contents described herein. It is particularly pointed out that all such similar alterations and modifications that are apparent to those with ordinary skill in the art are considered within the scope of the present application. The methods and applications of the present application have been described by preferred embodiments, and the relevant personnel can obviously make modifications or appropriate changes and combinations to the methods and applications described herein without departing from the content, spirit and scope of the present application, to realize and apply the present application technology. Although it is believed that the following terms are well understood by those skilled in the art, the following definitions are set forth to facilitate the understanding of the subject matter disclosed herein.

[0046] The present application provides a method for preparing high-foaming-ratio silicone rubber foam by efficiently inhibiting cell shrinkage, mainly comprising the following steps:

[0047] (1) After the composite base material including raw silicone rubber is pretreated by including mixing and standing, a rare metal catalyst is added and uniformly mixed to obtain a mixed rubber;

[0048] Among them, the rare metal catalyst is any one of platinum catalyst, palladium catalyst, ruthenium catalyst, rhodium catalyst;

[0049] (2) The mixed rubber obtained in step (1) is placed in an autoclave, supercritical CO2 is introduced as a foaming agent, and the mixed rubber is saturated under supercritical CO2 process conditions of 8-20 MPa and 40-70℃ for 15-30 min to complete the pre-crosslinking and saturation process;

[0050] After the time arrives, the autoclave is depressurized to 0.1 MPa, CO2 is continuously introduced after the mixed rubber is foamed, the pressure in the autoclave is maintained at 2-18 MPa, and then the temperature is raised to 150-200℃, and the pressure is maintained for 10-30 min to complete the post-crosslinking, and after the time arrives, the pressure is quickly released to obtain high-foaming-ratio silicone rubber foam.

[0051] In this text, the raw silicone rubber in step (1) is a conventional raw material for silicone rubber foam, and those skilled in the art can select appropriate raw silicone rubber according to common knowledge or prior art. In one embodiment, for example, any one or combination of methyl vinyl silicone rubber, methyl phenyl vinyl silicone rubber and poly(3,3,3-trifluoropropylmethyl)silicone rubber.

[0052] It should be noted that in the prior art, the silicone rubber foam mainly uses high temperature vulcanized silicone rubber, and the in-situ pre-crosslinking temperature thereof is high (usually 100-150℃), which not only increases the movement degree of CO2, resulting in an increased CO2 diffusion rate and a decreased solubility in the mixing rubber, but also increases the difficulty in controlling the pre-crosslinking degree of the silicone rubber. Meanwhile, the pre-crosslinking temperature is greatly different from the foaming temperature (40-70℃), which increases the time and process difficulty from the pre-crosslinking temperature to the foaming temperature.

[0053] One of the invention points of the present application is to select platinum-based rare metal catalysts, hydrogen-containing silicone oil and silicone rubber crosslinking systems, so that the pre-crosslinking temperature of the mixing rubber is close to the foaming temperature, the pre-crosslinking and CO2 saturation processes are carried out at the same time, the solubility of the mixing rubber to supercritical CO2 is improved, the time required for pre-crosslinking and saturation is significantly reduced, and the process and operation difficulty are greatly simplified.

[0054] Based on the above invention point, in order to meet the technical purpose of the pre-crosslinking temperature being close to the foaming temperature, in one embodiment, the addition amount of the rare metal catalyst in step (1) is 0.1-1wt% of the raw silicone rubber, for example, 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1wt% or any range or point value therebetween.

[0055] In order to better illustrate the present application and provide a preferred embodiment for reference, in step (1), the composite base material including the raw silicone rubber is pre-processed by including mixing and standing, the rare metal catalyst is added, and the mixture is uniformly mixed to obtain the mixing rubber, and the preparation method is specifically as follows:

[0056] ①The raw silicone rubber, reinforcing agent and hydroxyl silicone oil are added to the internal mixer and mixed and processed at 80-150℃ and 30-80rad / min for 5-30min, after the time reaches, the temperature is cooled to room temperature, and then the above process conditions are returned to mixing for 10-30min to obtain the pre-mixing rubber;

[0057] ②The pre-mixing rubber obtained in step ① and the rare metal catalyst are added to the internal mixer and mixed and processed at 20-50℃ and 30-80rad / min for 5-30min to obtain the silicone rubber composite A;

[0058] The pre-mixing rubber obtained in step ① and the hydrogen-containing silicone oil are added to the internal mixer and mixed and processed at 20-50℃ and 30-80rad / min for 5-30min to obtain the silicone rubber composite B;

[0059] ③ The silicone rubber compound A and silicone rubber compound B obtained in step ② are added into a mixing mill in a mass ratio of 1 : (1-20) under room temperature and process conditions of 30-80 rad / min, and mixing and processing are carried out for 5-30 min. After the time reaches, the mixing mill is cooled to room temperature, and then re-mixing is carried out under the above process conditions for 10-20 min to obtain a mixed rubber.

[0060] In the above preferred embodiments, the reinforcing agent in step ① is any one or more of the conventional additives in the preparation process of the silicone rubber foam material, such as fumed white carbon black, precipitated white carbon black, etc. Generally, the amount of the reinforcing agent added is 10-50 wt% of the raw rubber, such as 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, or any range or point value between them.

[0061] In the above preferred embodiments, the hydroxyl silicone oil in step ① is a conventional raw material in the preparation process of the silicone rubber foam material, and the amount of the hydroxyl silicone oil added is generally 1-10 wt% of the raw rubber, such as 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, or any range or point value between them.

[0062] In the above preferred embodiments, the hydrogen-containing silicone oil in step ② is a conventional raw material in the preparation process of the silicone rubber foam material, and the amount of the hydrogen-containing silicone oil added is generally 1-10 wt% of the raw rubber, such as 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, or any range or point value between them.

[0063] It should be noted that in the above preferred technical solutions, in addition to the additional addition of rare metal catalyst, the raw material composition and preparation method of the mixed rubber can be obtained by referring to the prior art. Although only one preparation method of the mixed rubber is described in the following examples, this does not mean the unique designation or limitation of the mixed rubber described in the present application. Based on the common knowledge in the technical field of the present application, and based on the main idea of simplifying the process steps, the person skilled in the art can select the appropriate mixed rubber preparation process and the way of mixing the rare metal catalyst.

[0064] It should be noted that in the prior art, the silicone rubber foamed by supercritical CO2 is usually post-crosslinked in an air environment under normal pressure (0.1 MPa), and there is a problem of rapid and large shrinkage of the silicone rubber foam, which leads to low foaming ratio and low porosity of the silicone rubber foam, and the function of regulating the pore structure is lost.

[0065] The second point of the present application is to improve the supercritical CO2 foaming process. A high-pressure in-situ post-crosslinking strategy is adopted after foaming. CO2 is continuously introduced to maintain the pressure balance between the inside and outside of the cell in the kettle during the post-crosslinking process after pressure relief foaming, which weakens the diffusion of CO2 to the outside of the silicone rubber matrix, and at the same time, the temperature is quickly raised to the post-crosslinking temperature to complete the in-situ post-crosslinking and fix the cell structure, so as to effectively inhibit the rapid shrinkage of the silicone rubber foam in the normal pressure environment and greatly shorten the foaming period.

[0066] It is found through comparative experiments that, based on the technical scheme of the present application, the foaming ratio and cell structure of the silicone rubber foam can be controlled through the controllable pressure in the in-situ post-crosslinking process.

[0067] In one embodiment, in step (2), the rubber compound obtained in step (1) is placed in an autoclave, supercritical CO2 is introduced as a foaming agent, and the rubber compound is saturated under supercritical CO2 process conditions of 8-20 MPa and 40-70°C, and the pre-crosslinking and saturation process is completed by maintaining the temperature and pressure for 15-30 min. The 8-20 MPa can be 8 MPa, 9 MPa, 10 MPa, 11 MPa, 12 MPa, 13 MPa, 14 MPa, 15 MPa, 16 MPa, 17 MPa, 18 MPa, 19 MPa, 20 MPa, or any range or point value therebetween.

[0068] In a preferred embodiment, in step (2), the rubber compound obtained in step (1) is placed in an autoclave, supercritical CO2 is introduced as a foaming agent, and the rubber compound is saturated under supercritical CO2 process conditions of 10-12 MPa and 40-70°C, and the pre-crosslinking and saturation process is completed by maintaining the temperature and pressure for 15-30 min.

[0069] After the time elapses, the autoclave is depressurized to 0.1 MPa, CO2 is continuously introduced after the rubber compound is foamed, the pressure in the kettle is maintained at 2-18 MPa, then the temperature is raised to 150-200°C, and the post-crosslinking is completed by maintaining the temperature and pressure for 10-30 min. After the time elapses, the pressure is quickly released to obtain a high-foaming-ratio silicone rubber foam.

[0070] The high-foaming-ratio silicone rubber foam prepared by the present application can be applied in the fields of packaging, insulation, cushioning, etc., such as construction engineering, vehicle manufacturing, sports goods, etc.

[0071] The present application will be further explained in detail below with reference to the examples. However, those skilled in the art should understand that these examples are provided only for illustrative purposes, and are not intended to limit the present application.

[0072] Example

[0073] The embodiments of the present application will be described in detail below with examples, but those skilled in the art will understand that the following examples are only for illustration of the present application and should not be regarded as limiting the scope of the present application. The specific conditions are not specified in the examples, which are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used are not specified by the manufacturer, which are all conventional products that can be obtained by purchase. The present application should not be interpreted as being limited to the specific examples described.

[0074] 1. Raw materials

[0075] Methyl vinyl silicone rubber, provided by Guangdong Baimi Silicone Fluorine New Material Co., Ltd.;

[0076] Meteor white carbon black, provided by Guangdong Baimi Silicone Fluorine New Material Co., Ltd.;

[0077] Hydroxyl silicone oil, provided by Guangdong Baimi Silicone Fluorine New Material Co., Ltd.;

[0078] Hydrogen-containing silicone oil, provided by Guangdong Baimi Silicone Fluorine New Material Co., Ltd.;

[0079] Platinum catalyst, provided by Guangdong Baimi Silicone Fluorine New Material Co., Ltd.;

[0080] Carbon dioxide (purity 99%), Chengdu Xuyuan Gas Co., Ltd.

[0081] 2. Preparation method

[0082] (1) After the composite base material including raw silicone rubber is pretreated by including mixing and standing, platinum catalyst is added and uniformly mixed to obtain a mixed rubber;

[0083] Specifically:

[0084] ① 100 g of methyl vinyl silicone rubber, 30 g of meteor white carbon black, and 4 g of hydroxyl silicone oil were added to a mixing mill and mixed and treated at 120°C and 50 rad / min for 10 min. After the time reached, it was cooled to room temperature and then returned to the mixing mill and mixed and treated at the above process conditions for 10 min to obtain a premixed rubber;

[0085] ② 100 g of the premixed rubber obtained in step ① and 0.3 g of platinum catalyst were added to a mixing mill and mixed and treated at 30°C and 50 rad / min for 10 min to obtain a silicone rubber composite A;

[0086] 100 g of the premixed rubber obtained in step ① and 3 g of hydrogen-containing silicone oil were added to a mixing mill and mixed and treated at 30°C and 50 rad / min for 10 min to obtain a silicone rubber composite B;

[0087] ③The silicone rubber compound A and the silicone rubber compound B obtained in step 2 are added into a mixer in a mass ratio of 1:5, and mixed at room temperature and a process condition of 50 rad / min for 10 min. After the time reaches, the mixer is cooled to room temperature, and then mixed again under the above process condition for 20 min to obtain a mixed rubber;

[0088] (2) The mixed rubber obtained in step (1) is placed into an autoclave, and supercritical CO2 is introduced as a foaming agent. The mixed rubber is saturated under a process condition of 10 MPa and 50°C for 30 min to complete the pre-crosslinking and saturation process;

[0089] After the time reaches, the autoclave is depressurized to 0.1 MPa, and the mixed rubber is foamed. Then, CO2 is continuously introduced to maintain the pressure in the autoclave at 2-18 MPa, and then the temperature is increased to 200°C. After 30 min of heat preservation and pressure maintenance, the post-crosslinking is completed. After the time reaches, the pressure is rapidly released to obtain a high-foaming-ratio silicone rubber foam.

[0090] For convenience of testing, the product is taken out after cooling, and the density thereof is measured. The product is immersed in liquid nitrogen for 5 min, and the cross section thereof is analyzed by a scanning electron microscope.

[0091] 3. Test method

[0092] Analysis test method: drainage method for density analysis, field emission scanning electron microscope analysis.

[0093] The density of the silicone rubber foam material sample is measured by the Archimedes drainage method. In the method, m0 is the mass of the sample in air, m1 is the mass of the sample in water and a density bottle, m2 is the mass of the density bottle filled with water, and ρ waler is the density of water. The calculation formula is as follows:

[0094] ρ = [m0 / (m2 + m0 - m1)]ρ waler

[0095] The cross section of the silicone rubber foam material sample is analyzed by a field emission scanning electron microscope (SEM) to explore the cell size and cell density of the silicone rubber foam material sample under different process conditions. The analysis instrument is a JSM-5900LV scanning electron microscope of Japan Electron Corporation. The cell size and cell size distribution in the SEM picture are analyzed by the Nano Measure software independently developed by the applicant. The cell density (N f ) is calculated by using the following formula. n is the number of cells in the SEM microscope picture, A is the area (cm 2 ) of the SEM microscope picture, ρ0 is the density (1.16 g / cm 3 ) of the sample before foaming, and ρ f is the density of the completely crosslinked sample after foaming.

[0096] N f = (n / A) 3 / 2 (ρ0 / ρ f )

[0097] Example 1

[0098] In this example, the mixing gum was foamed in step (2) of the above-mentioned “2. Preparation method” procedure, and CO2was continuously introduced to maintain the pressure in the autoclave at 8 MPa, i.e., the in-situ post-crosslinking process pressure was 8 MPa. Finally, a high-foaming-ratio silicone rubber foam was prepared and used as a sample for testing.

[0099] Example 2

[0100] In this example, the mixing gum was foamed in step (2) of the above-mentioned “2. Preparation method” procedure, and CO2was continuously introduced to maintain the pressure in the autoclave at 6 MPa, i.e., the in-situ post-crosslinking process pressure was 6 MPa. Finally, a high-foaming-ratio silicone rubber foam was prepared and used as a sample for testing.

[0101] Example 3

[0102] In this example, the mixing gum was foamed in step (2) of the above-mentioned “2. Preparation method” procedure, and CO2was continuously introduced to maintain the pressure in the autoclave at 4 MPa, i.e., the in-situ post-crosslinking process pressure was 4 MPa. Finally, a high-foaming-ratio silicone rubber foam was prepared and used as a sample for testing.

[0103] Example 4

[0104] In this example, the mixing gum was foamed in step (2) of the above-mentioned “2. Preparation method” procedure, and CO2was continuously introduced to maintain the pressure in the autoclave at 2 MPa, i.e., the in-situ post-crosslinking process pressure was 2 MPa. Finally, a high-foaming-ratio silicone rubber foam was prepared and used as a sample for testing.

[0105] Comparative Example 1

[0106] Comparative Example 1 was prepared according to the above-mentioned “2. Preparation method” procedure, but step (2) was replaced by the following procedure to prepare a silicone rubber foam by a conventional supercritical CO2method:

[0107] (2) The mixing gum obtained in step (1) was placed in an autoclave, and supercritical CO2was introduced as a foaming agent. The mixing gum was saturated under supercritical CO2process conditions of 10 MPa and 50°C, and the pre-crosslinking and saturation processes were completed by keeping the temperature and pressure for 30 min;

[0108] After the time elapsed, the pressure was rapidly released to atmospheric pressure (0.1 MPa), and then the autoclave was heated to 200°C and kept for 1 h to prepare a silicone rubber foam, which was used as a comparative sample for testing.

[0109] 4. Test Results

[0110] The samples prepared in Examples 1 to 4 and Comparative Example 1 were tested according to the above “3. Test Method”. The test results are as follows: Figures 2-8 shown.

[0111] exist Figures 2-5 It can be found that the samples have good pore structures under different pressure differences. The pore sizes of the samples in Examples 1 to 4 are 131.8 μm to 338.3 μm, and the pore density is 3.15×10 5 ~1.03×10 7 cells / cm 3 . And in Figure 6 In the corresponding comparative example 1 sample, the phenomenon of cell collapse can be clearly observed. Figure 7 、 8 It can be found that the foaming ratio and pore density of silicone rubber foam can be controlled by adjusting the pressure difference.

[0112] Among them, the most striking is the sample prepared in Example 1, whose foaming ratio can reach up to 6.7 times, which is 36.7% higher than the foaming ratio (4.9 times) of silicone rubber foam prepared by supercritical CO2 foaming reported in the current literature (Key factors for regulation of cell morphology in supercritical CO2 rapid depressurization foaming silicone rubber process, The Journal of Supercritical Fluids, 202, 2023, 106036). Compared with the foaming ratio (4.1 times) of the silicone rubber foam prepared in Comparative Example 1, it is increased by 63.4%, and the comprehensive performance is also excellent.

[0113] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for preparing high expansion ratio silicone rubber foam by effectively suppressing cell shrinkage, characterized in that The main steps include: (1) adding a rare metal catalyst to a composite base material including raw silicone rubber after pretreatment including mixing and standing, and mixing uniformly to obtain a rubber compound; Wherein, the rare metal catalyst is any one of a platinum catalyst, a palladium catalyst, a ruthenium catalyst, and a rhodium catalyst; (2) placing the rubber mix obtained in step (1) into an autoclave, introducing supercritical CO2 as a foaming agent, saturating the rubber mix under supercritical CO2 process conditions of 8-20 MPa and 40-70° C., and maintaining the temperature and pressure for 15-30 minutes to complete the pre-crosslinking and saturation process; After the time is up, the autoclave is depressurized to 0.1MPa. After the rubber mix is ​​foamed, CO2 is continuously introduced to maintain the pressure in the autoclave at 2-18MPa. The temperature is then raised to 150-200°C and kept warm for 10-30 minutes. After post-crosslinking is completed, the pressure is quickly released after the time is up to obtain a silicone rubber foam with a high foaming ratio.

2. The method according to claim 1, wherein: The silicone rubber raw rubber includes any one or more of methyl vinyl silicone rubber, methyl phenyl vinyl silicone rubber and poly (3,3,3-trifluoropropyl methyl) silicone rubber.

3. The method according to claim 1, wherein: The amount of the rare metal catalyst added in step (1) is 0.1 to 1 wt % of the raw silicone rubber.

4. The method according to claim 1, wherein: In step (1), the composite base material including the silicone rubber raw rubber is subjected to pretreatment including mixing and standing, and then a rare metal catalyst is added and mixed uniformly to obtain a rubber compound. The preparation method thereof is specifically as follows: ① Add the silicone rubber, reinforcing agent and hydroxy silicone oil into an internal mixer and mix them under the process conditions of 80-150℃ and 30-80rad / min for 5-30min. After the time is up, cool to room temperature and then remix under the above process conditions for 10-30min to obtain a premixed rubber; ② The premix obtained in step ① and the rare metal catalyst are added to an internal mixer and mixed at 20-50° C. and 30-80 rad / min for 5-30 minutes to obtain a silicone rubber compound A; The premix obtained in step ① and the hydrogenated silicone oil are added to an internal mixer and mixed at 20-50° C. and 30-80 rad / min for 5-30 min to obtain a silicone rubber compound B; ③ The silicone rubber compound A and the silicone rubber compound B obtained in step ② are added to an internal mixer in a mass ratio of 1: (1 to 20) and mixed at room temperature and 30 to 80 rad / min for 5 to 30 minutes. After the time is up, the mixture is cooled to room temperature and then re-mixed under the above process conditions for 10 to 20 minutes to obtain a mixed rubber.

5. The method according to claim 4, characterized in that: The reinforcing agent in step ① includes any one or more of fumed silica and precipitated silica.

6. The method according to claim 1, wherein: The step (2) is to place the rubber mix obtained in the step (1) into an autoclave, introduce supercritical CO2 as a foaming agent, saturate the rubber mix under supercritical CO2 process conditions of 10-12 MPa and 40-70°C, and maintain the temperature and pressure for 15-30 minutes to complete the pre-crosslinking and saturation process; After the time is up, the autoclave is depressurized to 0.1MPa. After the rubber mix is ​​foamed, CO2 is continuously introduced to maintain the pressure in the autoclave at 2-10MPa. The temperature is then raised to 150-200°C and kept warm for 10-30 minutes. After post-crosslinking is completed, the pressure is quickly released after the time is up to obtain a silicone rubber foam with a high foaming ratio.

7. The high expansion ratio silicone rubber foam prepared by the method for preparing high expansion ratio silicone rubber foam by efficiently suppressing cell shrinkage as claimed in claim 1.

8. Use of the high expansion ratio silicone rubber foam according to claim 7 in the fields of construction engineering, vehicle manufacturing, and sporting goods.

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