Ultrathin silica gel foam as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of ultrathin silica gel foam, and particularly relates to ultrathin silica gel foam as well as a preparation method and application thereof. High-dosage hydroxyl silicone oil is adopted to provide sufficient reaction sites, and efficient micro-foaming is achieved; and meanwhile, by cooperating with composite powder compounded by flame-retardant, reinforcing and light-weight filler, foam hole combination and through hole formation are effectively inhibited, a foam hole structure with high closed-cell rate and uniform pore diameter is obtained, and the risks of die cutting chip falling and through hole water leakage are remarkably reduced. In addition, methyl phenyl silicone rubber is introduced, the steric hindrance effect of the methyl phenyl silicone rubber is utilized to further stabilize the foam structure, and the rebound resilience and high temperature resistance of the material are improved; and the mechanical property is enhanced by virtue of high-viscosity vinyl silicone oil, so that the balance between high resilience and controllable compression stress is realized. Through the synergistic effect of the components, the prepared silica gel foam has low density, high resilience, water resistance, weather resistance and buffering performance while meeting the ultra-thin requirement, and is suitable for being used as a waterproof sealing buffering material for electronic products.

Description

Technical Field

[0001] This application belongs to the field of ultra-thin silicone foam technology, and more specifically, relates to an ultra-thin silicone foam, its preparation method and application. Background Technology

[0002] As electronic products become thinner and lighter, their internal space becomes increasingly compact, and the gaps between components are also decreasing. This places stringent requirements on the foam materials used to fill them: while being ultra-thin (<1mm), they must also achieve uniform cell size, low density, lightweight, high water resistance, and excellent compression resilience to ensure that they can maintain dimensional stability and cushioning sealing function after long-term or repeated compression, thereby guaranteeing the product's service life and reliability.

[0003] Currently widely used polyurethane foam, IXPE foam, PP foam, and acrylic foam, while possessing good sealing, waterproofing, and cushioning properties, suffer from insufficient compression resilience and poor high-temperature resistance. Silicone foam exhibits excellent compression resilience and resistance to high and low temperatures, and is widely used in rail transportation and new energy battery fields. However, its thickness is typically difficult to control below 0.5mm, and it suffers from problems such as high density, poor cell uniformity, predominantly open-cell structure, and an excessively high proportion of through-cells, failing to meet the lightweight and waterproof sealing requirements of electronic products.

[0004] Patent document CN117683357A describes how adding organic foamed microspheres to a silicone rubber system can produce a good synergistic effect with the silicone rubber system, thereby obtaining flame-retardant silicone rubber foam with uniform foaming, good resilience and resistance to compression deformation, which can be used in new energy batteries and electronic devices. However, the preparation process of organic foamed microspheres is complicated and costly, and it is difficult to match the vulcanization temperature and the microsphere expansion temperature, making the process operation difficult.

[0005] Therefore, there is a need to develop a silicone foam that meets the basic requirements of ultra-thin electronic products, while also possessing low density, high resilience, excellent waterproofness, excellent high temperature resistance, and simple manufacturing process, making it suitable for large-scale mass production. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the purpose of this application is to provide an ultra-thin silicone foam, its preparation method and application, which aims to solve the technical problems of existing silicone foams being unable to balance low density, high resilience and high closed-cell rate at ultra-thin thickness (<1mm), and is not suitable as a waterproof sealing and cushioning protective material for electronic products.

[0007] To achieve the above objectives, in a first aspect, this application provides an ultra-thin silicone foam with a thickness of 0.4mm to 0.6mm and a density of 200kg / m³. 3 ~250kg / m 3The closed-cell rate is >60%, the average pore diameter is 50μm~150μm, and the raw materials used in its preparation include at least the following components: a) Methyl vinyl silicone rubber; b) Hydroxy silicone oil, wherein the mass ratio of the hydroxy silicone oil to the above-mentioned methyl vinyl silicone rubber is greater than 1:5; c) Vinyl silicone oil, wherein the viscosity of the vinyl silicone oil is not less than 60,000 mPa·s; d) Composite powder, which includes flame-retardant filler, reinforcing filler and lightweight filler; e) Methylphenyl silicone rubber.

[0008] Preferably, the viscosity of the vinyl silicone oil is 60,000 mPa·s to 200,000 mPa·s, and / or the mass percentage of vinyl in the vinyl silicone oil is 0.02% to 0.1%.

[0009] Preferably, the vinyl content in the methyl vinyl silicone rubber is 0.1% to 0.2% by mass.

[0010] Preferably, the phenyl content in the above-mentioned methylphenyl silicone rubber is 0.5% to 1% by mass.

[0011] Preferably, the hydroxyl content of the hydroxyl group in the above-mentioned hydroxyl silicone oil is 0.5% to 1% by mass.

[0012] Preferably, the mass ratio of flame-retardant filler, reinforcing filler and lightweight filler in the above composite powder is (30~40):(16~20):(4~10).

[0013] More preferably, the flame-retardant filler includes one or more of modified hydrotalcite, modified aluminum hydroxide, and modified magnesium hydroxide; the reinforcing filler is one or more of nano-carbon powder, fumed silica, and nano-calcium carbonate; and the lightweight filler is one or more of hollow glass microspheres, expanded microspheres, and expanded phenolic microspheres.

[0014] Preferably, the raw materials for the preparation also include fumed silica, platinum catalyst, hydrogen-containing silicone oil, and inhibitor.

[0015] Preferably, in the above-mentioned raw materials, the mass ratio of methyl vinyl silicone rubber, vinyl silicone oil, methyl phenyl silicone rubber, fumed silica, hydroxyl silicone oil, platinum catalyst, hydrogen-containing silicone oil, inhibitor and composite powder is 200:(40~100):(10~20):(20~40):(100~200):(0.5~1):(30~50):(0.01~0.1):(50~70).

[0016] Preferably, the specific surface area of ​​the above-mentioned fumed silica is 200 m² / g.2 / g~350m 2 / g.

[0017] Preferably, the effective platinum content in the above-mentioned platinum catalyst is 3000ppm~5000ppm.

[0018] Preferably, the hydrogen content in the above-mentioned hydrogen-containing silicone oil is 1.4% to 1.6% by mass.

[0019] Preferably, the above-mentioned inhibitor is an alkynyl alcohol inhibitor.

[0020] Preferably, the above-mentioned raw materials further include additives. More preferably, the amount of the additives is 1 wt% to 5 wt% of the mass of the methyl vinyl silicone rubber.

[0021] Preferably, the ultra-thin silicone foam further includes a film attached to the ultra-thin silicone foam.

[0022] Preferably, the material of the film includes at least one of PET, PI, PE, and PP.

[0023] Preferably, the thickness of the film is 0.02 mm to 0.05 mm.

[0024] Secondly, this application provides a method for preparing the above-mentioned ultrathin silicone foam, comprising the following steps: S1. Mix a portion of the above-mentioned methyl vinyl silicone rubber, a portion of the above-mentioned vinyl silicone oil, a portion of the above-mentioned methyl phenyl silicone rubber, a portion of the above-mentioned fumed silica, a portion of the above-mentioned hydroxyl silicone oil, a portion of the above-mentioned composite powder and platinum catalyst to obtain component A; S2. Mix the remaining methyl vinyl silicone rubber, the remaining vinyl silicone oil, the remaining methyl phenyl silicone rubber, the remaining fumed silica, the remaining hydroxyl silicone oil, the remaining composite powder, the hydrogen-containing silicone oil, and the inhibitor to obtain component B. S3. Mix the above-mentioned component A and component B and apply the mixture onto a film, then perform a curing process to obtain the above-mentioned ultra-thin silicone foam.

[0025] Thirdly, this application provides a waterproof sealing and cushioning material for electronic products, which includes the aforementioned ultra-thin silicone foam.

[0026] In summary, the technical solutions conceived in this application have the following main technical advantages compared with the prior art: This application addresses the contradiction between thinning and increasing density in silicone foam by increasing the amount of hydroxyl silicone oil in the silicone foam formulation. This provides more reaction sites for efficient microfoaming, resulting in more bubble nuclei, thinner cell walls, and a higher expansion ratio. Simultaneously, the synergistic addition of a composite powder containing flame-retardant, reinforcing, and lightweight fillers acts as a bubble nucleating agent, inhibiting cell merging and through-cell formation through the synergistic effect between fillers. This achieves both thinness and low density while ensuring a uniform closed-cell structure, significantly reducing the risk of die-cutting chipping and through-cell leakage. Furthermore, the introduction of methylphenyl silicone rubber further synergistically inhibits bubble merging and stabilizes the cell structure through the steric hindrance of the phenyl groups, significantly improving the material's resilience and high-temperature resistance while maintaining low density and uniform cell size. Combined with the addition of high-viscosity vinyl silicone oil, whose high molecular weight silica chain enhances the mechanical strength of the system, the silicone foam exhibits both high resilience and controllable compressive stress, resulting in excellent cushioning performance. By combining the above adjustments, this application enables silicone foam to possess low density, high resilience, good water resistance, weather resistance, and cushioning properties while meeting the requirements of ultra-thin applications. Compared with existing ultra-thin silicone foams, it significantly reduces the difficulty of process operation and production costs, making it suitable for industrial mass production. Attached Figure Description

[0027] Figure 1 This is an electron microscope image of the cross-section of the ultrathin silicone foam prepared in Comparative Example 4 of this application; Figure 2 This is an electron microscope image of the cross-section of the ultrathin silicone foam prepared in Example 1 of this application. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0029] In the description of this application, it should be understood that the term "and / or" describes a relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. The symbol " / " in this document indicates that the related objects are in an "or" relationship; for example, A / B means A or B.

[0030] In the description of the embodiments in this application, the words "exemplary" or "for example" are used to indicate that they are examples, illustrations, or descriptions. Any embodiment or design that is described as "exemplary" or "for example" in the embodiments of this application should not be construed as being more preferred or advantageous than other embodiments or design options. Specifically, the use of the words "exemplary" or "for example" is intended to present the relevant concepts in a specific manner.

[0031] In the description of the embodiments in this application, unless otherwise stated, "multiple" means two or more.

[0032] This application provides an ultra-thin silicone foam with a thickness of 0.4mm~0.6mm and a density of 200kg / m³. 3 ~250kg / m 3 The closed-cell rate is >60%, and the average pore diameter is 50μm~150μm; the raw materials for preparing the above-mentioned ultrathin silicone foam include at least the following components: a) Methyl vinyl silicone rubber; b) Hydroxyl silicone oil; c) Vinyl silicone oil; d) Composite powder; e) Methylphenyl silicone rubber; The mass ratio of the above-mentioned hydroxyl silicone oil to the above-mentioned methyl vinyl silicone rubber is greater than 1:5; The viscosity of the aforementioned vinyl silicone oil is not less than 60,000 mPa·s; The aforementioned composite powder includes flame-retardant fillers, reinforcing fillers, and lightweight fillers.

[0033] This application addresses the contradiction between thinness and high density in silicone foam by adding a higher amount of hydroxyl silicone oil to the silicone foam formulation. This provides more reaction sites for micro-foaming, resulting in more bubble nuclei, thinner cell walls, and a higher foaming ratio. Simultaneously, the addition of a composite powder containing flame-retardant, reinforcing, and lightweight fillers, along with adjustments to the proportions of each filler, allows the composite powder to act as a bubble nucleating agent. Through the synergistic effect of the fillers, it inhibits cell coalescence and through-hole formation, effectively reducing cell coalescence. While maintaining thinness and low density, this ensures excellent closed-cell structure and uniform cell size, effectively avoiding the risks of chipping during die-cutting and leakage through through-holes. Furthermore, the addition of methylphenyl silicone rubber, through the steric hindrance effect of the phenyl groups, further synergistically inhibits bubble coalescence and locks in the bubbles, significantly improving resilience and high-temperature resistance while maintaining low density and a good cell structure. Simultaneously, by incorporating high-viscosity vinyl silicone oil into the system, the mechanical strength is enhanced through high-molecular-weight silica chain segments, enabling the silicone foam to maintain high resilience while also controlling compressive stress, resulting in excellent cushioning performance. Combining these effects, this application, while meeting the requirements for ultra-thin applications, also possesses low density, high resilience, water resistance, weather resistance, and cushioning performance. Compared to existing ultra-thin silicone foams, it significantly reduces the difficulty of foam processing and lowers production costs.

[0034] The vinyl silicone oil described in this application has a high viscosity. The inventors discovered through experiments that excessively low viscosity of the vinyl silicone oil leads to excessively high compressive stress and unbalanced resilience in the foam. In some embodiments, the viscosity of the vinyl silicone oil is 60,000 mPa·s to 200,000 mPa·s. In some embodiments, the vinyl content in the vinyl silicone oil is 0.02% to 0.1% by mass.

[0035] In some embodiments, the phenyl content in the methylphenyl silicone rubber is 0.5% to 1% by mass. For example, the phenyl content in the methylphenyl silicone rubber can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1% by mass. In some embodiments, the mass ratio of the methylvinyl silicone rubber to the methylphenyl silicone rubber is 200:(10-20).

[0036] In some embodiments, the mass percentage of hydroxyl groups in the hydroxyl silicone oil is 0.5% to 1%. For example, the mass percentage of hydroxyl groups in the hydroxyl silicone oil can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1%. The siloxane linkages in the hydroxyl silicone oil can improve the mechanical strength of silicone rubber, and the hydroxyl groups can provide Si-OH bonds, participating in crosslinking and foaming reactions. In some embodiments, the mass ratio of the methyl vinyl silicone rubber to the hydroxyl silicone oil is 200:(100~200).

[0037] In some embodiments, the composite powder includes flame-retardant filler, reinforcing filler, and lightweight filler. In some embodiments, the mass ratio of flame-retardant filler, reinforcing filler, and lightweight filler in the composite powder is (30~40):(16~20):(4~10). In some embodiments, the mass ratio of the methyl vinyl silicone rubber to the composite powder is 200:(50~70).

[0038] In some embodiments, the flame-retardant filler includes one or more of modified hydrotalcite, modified aluminum hydroxide, and modified magnesium hydroxide. In some embodiments, the modified hydrotalcite, modified aluminum hydroxide, and modified magnesium hydroxide are materials modified with a silane coupling agent (which may be, but is not limited to, aminosilane or vinylsilane), exhibiting good compatibility. In some embodiments, the average particle size of the flame-retardant filler is 1 μm to 10 μm.

[0039] In some embodiments, the reinforcing filler includes one or more of nano-carbon powder, silica, and nano-calcium carbonate. In some embodiments, the silica is fumed silica or precipitated silica. In some embodiments, the average particle size of the reinforcing filler is 0.1 μm to 5 μm.

[0040] In some embodiments, the lightweight filler comprises one or more of hollow glass microspheres, expanded microspheres, glass microspheres, and expanded phenolic microspheres. In some embodiments, the average particle size of the lightweight filler is 50 μm to 100 μm.

[0041] In some embodiments, the vinyl content in the methyl vinyl silicone rubber is 0.1% to 0.2% by mass.

[0042] In some embodiments, the raw materials for preparing the above-mentioned ultrathin silicone foam also include fumed silica, platinum catalyst, hydrogen-containing silicone oil, and inhibitors.

[0043] In some embodiments, the mass ratio of methyl vinyl silicone rubber, vinyl silicone oil, methyl phenyl silicone rubber, fumed silica, hydroxyl silicone oil, platinum catalyst, hydrogen-containing silicone oil, inhibitor, composite powder and additives in the above-mentioned raw materials is 200:(40~100):(10~20):(20~40):(100~200):(0.5~1):(30~50):(0.01~0.1):(50~70):(1~5).

[0044] In a preferred embodiment, the mass ratio of the methyl vinyl silicone rubber to the vinyl silicone oil is 200:(60~100), preferably 200:(80~100).

[0045] In some embodiments, the specific surface area of ​​the above-mentioned fumed silica is 200 m². 2 / g~350m 2 / g.

[0046] In some embodiments, the hydrogen content in the hydrogen-containing silicone oil is 1.4% to 1.6% by mass.

[0047] In some embodiments, the effective platinum content in the above-mentioned platinum catalyst is 3000ppm to 5000ppm. This application does not limit the specific type of platinum catalyst mentioned above; any platinum catalyst reported in the prior art may be used, such as, but not limited to, one or more of cassette catalyst and chloroplatinic acid.

[0048] In some embodiments, the above-mentioned inhibitor is an alkynyl alcohol inhibitor, which can inhibit the foaming reaction of hydroxyl silicone oil and hydrogen-containing silicone oil catalyzed by platinum catalyst. This application does not specifically limit the type of alkynyl alcohol inhibitor; any alkynyl alcohol inhibitor reported in the prior art is acceptable, such as, but not limited to, one or more of 1-ethynyl-1-cyclohexanol, 2-methyl-3-butynyl-2-ol, and 3-methyl-1-dodecyn-3-ol.

[0049] To meet the requirements of different application environments, the raw materials for preparing the above-mentioned ultra-thin silicone foam also include additives to impart various properties to the foam. These additives include, but are not limited to, one or more of color pastes, antioxidants, and sensitizers. It is understood that this application does not limit the specific types of the aforementioned color pastes, antioxidants, and sensitizers, and those skilled in the art can select appropriate additives according to actual needs. In some embodiments, the amount of the above-mentioned additives is 1wt% to 5wt% of the mass of the above-mentioned methyl vinyl silicone rubber.

[0050] This application utilizes the synergistic effect of the components in the formulation to prepare ultrathin silicone foam with a 30% compressive stress ≥25KPa and a 70% compressive stress ≤700KPa.

[0051] In some embodiments, the compression set of the ultra-thin silicone foam, after being aged at 100°C for 22 hours under 50% compression, is less than 10%.

[0052] In some embodiments, the change rate of the 25% compressive stress of the above-mentioned ultra-thin silicone foam after aging at 200°C for 24 hours is <10%.

[0053] In some embodiments, the ultra-thin silicone foam described above has a UL94 flame retardancy rating of V0.

[0054] In some embodiments, the ultrathin silicone foam also includes a film attached to the ultrathin silicone foam.

[0055] In some embodiments, the material of the film includes at least one of PET, PI, PE, and PP.

[0056] In some embodiments, the thickness of the film is 0.02 mm to 0.05 mm.

[0057] On the other hand, this application also provides a method for preparing the above-mentioned ultrathin silicone foam, comprising the following steps: S1. Mix a portion of the above-mentioned methyl vinyl silicone rubber, a portion of the above-mentioned vinyl silicone oil, a portion of the above-mentioned methyl phenyl silicone rubber, a portion of the above-mentioned fumed silica, a portion of the above-mentioned hydroxyl silicone oil, a portion of the above-mentioned composite powder and platinum catalyst to obtain component A; S2. Mix the remaining methyl vinyl silicone rubber, the remaining vinyl silicone oil, the remaining methyl phenyl silicone rubber, the remaining fumed silica, the remaining hydroxyl silicone oil, the remaining composite powder, the hydrogen-containing silicone oil, and the inhibitor to obtain component B. S3. The mixture obtained by mixing the above-mentioned component A and component B is applied to the film and cured to obtain the above-mentioned ultra-thin silicone foam.

[0058] In some embodiments, the curing process described above includes the following steps: After mixing the above-mentioned components A and B, the mixture is applied to a non-peelable film. Then, a release film is placed on the upper surface of the mixture. Next, a low-temperature vulcanization treatment is performed, and then the release film is removed and a high-temperature vulcanization treatment is performed to obtain ultra-thin silicone foam.

[0059] It should be noted that this application does not limit the manner of “applying” mentioned above, such as, but not limited to, calendering coating, brush coating, dipping, spraying, roller coating, and doctor blade coating.

[0060] In some embodiments, the curing process described above involves first performing low-temperature vulcanization, followed by high-temperature vulcanization.

[0061] In some embodiments, the temperature for low-temperature vulcanization is 80°C to 90°C, and the vulcanization time is 5 min to 10 min. In some embodiments, the temperature for high-temperature vulcanization is 150°C to 180°C, and the vulcanization time is 10 min to 15 min.

[0062] This application also provides a waterproof sealing and cushioning material for electronic products, which includes the aforementioned ultra-thin silicone foam.

[0063] It should be understood that materials of the same or similar type, model, quality, properties, or function as the reagents and instruments used in the following embodiments can be used to implement this application. Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods. Unless otherwise specified, the materials and reagents used in the following embodiments are commercially available.

[0064] The following are examples and comparative examples: Example The components and their mass fractions of the ultrathin silicone foam provided in Example 1 of this application are shown in Table 1.

[0065] Table 1. Components and mass fractions of the ultrathin silicone foam provided in Example 1

[0066] Example 2 In the ultra-thin silicone foam provided in this embodiment, the mass fraction of hydroxyl silicone oil is 200 parts, and the mass percentage of hydroxyl groups is 1%. The other raw materials and their mass fractions are the same as in Example 1.

[0067] Example 3 In the ultra-thin silicone foam provided in this embodiment, the mass fraction of hydroxyl silicone oil is 100 parts, the mass fraction of composite powder is 70 parts (including 40 parts flame retardant filler, 20 parts reinforcing filler, and 10 parts lightweight filler), and the other raw materials and their mass fractions are the same as in Example 1.

[0068] Example 4 In the ultra-thin silicone foam provided in this embodiment, the mass fraction of methylphenyl silicone rubber is 20 parts, and the mass percentage of phenyl is 1%. The other raw materials and their mass fractions are the same as in Example 1.

[0069] Example 5 In the ultra-thin silicone foam provided in this embodiment, the mass fraction of vinyl silicone oil is 50 parts and the viscosity is 60,000 mPa·s. The other raw materials and their mass fractions are the same as in Example 1.

[0070] Comparative Example 1 The ultra-thin silicone foam provided in this comparative example does not contain methyl phenyl silicone rubber, and the other raw materials and their mass fractions are the same as in Example 1.

[0071] Comparative Example 2 In the ultra-thin silicone foam provided in this comparative example, the viscosity of the vinyl silicone oil is 5000 mPa·s, and the mass percentage of vinyl is 1.2%. The other raw materials and their mass percentages are the same as in Example 1.

[0072] Comparative Example 3 In the ultra-thin silicone foam provided in this comparative example, the mass fraction of hydroxyl silicone oil is 40 parts, and the mass percentage of hydroxyl groups is 0.4%. The other raw materials and their mass fractions are the same as in Example 1.

[0073] Comparative Example 4 The ultra-thin silicone foam provided in this comparative example does not contain any composite powder, and the other raw materials and their mass proportions are the same as in Example 1.

[0074] Comparative Example 5 In the ultra-thin silicone foam provided in this comparative example, the composite powder consists of only 30 parts flame-retardant filler and 16 parts reinforcing filler, with no lightweight filler. The other raw materials and their mass fractions are the same as in Example 1.

[0075] The preparation method of the above-mentioned ultrathin silicone foam includes the following steps: S1. Preparation of component A: Mix 50% by mass of methyl vinyl silicone rubber, vinyl silicone oil, methyl phenyl silicone rubber, fumed silica, hydroxyl silicone oil, composite powder, all platinum catalyst, and all additives in a kneader at room temperature for 1 hour to obtain component A. S2. Preparation of component B: The remaining methyl vinyl silicone rubber, vinyl silicone oil, methyl phenyl silicone rubber, fumed silica, hydroxyl silicone oil, composite powder, all hydrogen-containing silicone oil, and all inhibitors are kneaded in a kneader at room temperature for 1 hour to obtain component B. S3. Preparation of silicone foam sheet: Mix the above components A and B to obtain a composition. Coat the composition onto a non-release PET black film (thickness of 0.025 mm). Then, place a transparent release film on the lower surface of the non-release PET black film to prevent wrinkles. Cover the upper surface of the composition with a transparent release film. Then, perform low-temperature vulcanization at 100°C for 5 minutes. Then, remove the upper and lower transparent release films and perform high-temperature vulcanization at 150°C for 15 minutes. Roll up to obtain silicone foam sheet, i.e., ultra-thin silicone foam.

[0076] The performance of the ultrathin silicone foams prepared in Examples 1-5 and Comparative Examples 1-5 was tested using the following methods: (1) Total thickness of foam: measured using a micrometer in accordance with the standard GB / T6342.

[0077] (2) Foam density: The density was measured using a density balance with an accuracy of 1 mg, in accordance with the standard GB / T 6343 2009.

[0078] (3) Foam closed-cell rate: Use a scanning electron microscope (S3400 scanning electron microscope, magnification 1000 times) to observe the cross-section of the foamed sheet, determine whether the cell walls are connected, and calculate the closed-cell rate = (number of cells with independent closed-cell structure / total number of cells) × 100%.

[0079] (4) Average cell diameter of foam: Cut a square sample with a size of 50mm×50mm from the foamed sheet, immerse it in liquid nitrogen for 1 minute, cut it with a blade, take a magnified photo of the cross section using a digital microscope, measure the diameter of all cells on the 5mm long cut surface, and take the arithmetic mean of the cell diameters as the average cell diameter.

[0080] (5) Compressive stress: The 30% compressive stress and 70% compressive stress of the foamed sheet were determined according to the standard ASTM D1056.

[0081] (6) Compression set: 50mm×50mm×thickness foam sheets were stacked to a thickness of d0. The stacked sample was then clamped between two SUS 304 steel plates, compressed, and fixed to achieve 50% compression. The sample was then placed at 100℃ for 22 hours. The sample was then released from the compressed state at room temperature and allowed to stand at room temperature for 24 hours. The thickness d1 was measured, and the compression set was calculated as [(d0-d1) / d0]×100%.

[0082] (7) Flame retardant performance: The flame retardancy of the foamed sheet is tested according to standard UL94.

[0083] (8) Temperature resistance: The foamed sheet was placed in a hot air aging test chamber at 200℃ for 24 hours. The change rate of 25% compressive stress of the foam before and after the hot air aging treatment was tested.

[0084] (9) Waterproof performance: The foamed sheet was treated with double-sided adhesive, and then a window frame-shaped sample with a width of 1mm was punched using a die with an inner frame size of 43mm×33.5mm and an outer frame size of 45mm×35.5mm. The sample was placed on a polycarbonate board, and spacers were placed on the outside of the sample to achieve 25% compression. The sheet that would change color after absorbing water was placed in the middle of the sample, and a polycarbonate board was placed on top of the sample. That is, the sample was clamped between two polycarbonate boards and fixed with bolts to achieve a compression rate of 25%, and the sheet that would change color after absorbing water was placed in the middle of the sample. The waterproof performance was evaluated by observing the water immersion state inside the sample. The evaluation criteria were: if there was no leakage after 60 minutes, the waterproof effect was excellent and it was judged as A; if there was no leakage within 30 minutes, and leakage occurred between 30 and 60 minutes, the waterproof effect was good and it was judged as B; if there was leakage within 30 minutes, the waterproof effect was poor and it was judged as C.

[0085] (10) Shedding performance: In a Class 1000 cleanroom, the foamed sheet die-cut parts are placed on a dust-free glass slide and left to stand for 24 hours. The surface of the glass slide is observed using a high-power microscope (100x). The number of debris with a diameter > 5μm is counted. The cleanliness standard for the electronics industry is: the number of debris with a diameter > 5μm is ≤ 3 pieces / piece.

[0086] The performance test results of the ultrathin silicone foams prepared in Examples 1-5 and Comparative Examples 1-5 are shown in Tables 2 and 3, respectively.

[0087] Table 2. Performance of the ultrathin silicone foams prepared in Examples 1-5

[0088] Table 3. Performance of the ultrathin silicone foams prepared in Comparative Examples 1-5

[0089] As can be seen from Tables 2 and 3, compared with the examples, when methyl phenyl silicone rubber was not added to the silicone foam components (Comparative Example 1), the viscosity of the vinyl silicone oil was too low (Comparative Example 2), and the amount of hydroxyl silicone oil was too small (Comparative Example 3), the silicone foam produced could not meet the requirements of ultra-thin application, while also having low density, moderate compressive stress, and small compression set. It did not meet the requirements of lightweight foam, cushioning performance, and high resilience, and was not suitable for precision electronic products.

[0090] Comparative Example 4, based on Comparative Example 3, only added a higher amount of hydroxyl silicone oil without adding composite powder. The resulting ultra-thin silicone foam had a lower density but a larger average cell diameter. Figure 1The low closed-cell rate resulted in a low waterproof rating for the foam, and significant die-cutting debris was a major concern. The likely cause is the presence of a large amount of hydroxyl silicone oil dispersed in components A and B. This high proportion of hydroxyl silicone oil creates numerous reaction sites, which, while increasing the foaming ratio and reducing the foam density, easily leads to a large number of through-cell structures, thus increasing the risk of leakage and die-cutting debris. Comparative Example 5, based on the silicone foam components of Comparative Example 4, only added flame-retardant and reinforcing fillers, without adding lightweight fillers. While this improved the flame-retardant properties, reduced the average pore size, increased the closed-cell rate, and improved waterproofing and die-cutting debris, the increased foam density and compressive stress also made it unsuitable for precision electronic products.

[0091] This application, through formula optimization and under simplified process conditions, effectively solves the problem of synergistic achievement of low thickness, low density, and high resilience in silicone foam. It achieves this by adding a higher amount of hydroxyl silicone oil, introducing a composite powder containing flame-retardant fillers, reinforcing fillers, and lightweight fillers to form a synergistic nucleation system, controlling the proportions between fillers, and compounding with phenyl vinyl silicone rubber, high-viscosity vinyl silicone oil, and other components. Through the synergistic effect of these components, it achieves efficient foaming and reduces foam density while effectively stabilizing the cell structure, inhibiting bubble coalescence and through-cell formation, and significantly improving the closed-cell rate and cell structure uniformity. This results in ultra-thin (<1mm), low-density (200~250kg / m³) silicone foam. 3 Under these conditions, a bubble structure with uniform bubble size and high closed-cell ratio is formed. Figure 2 This effectively avoids the risks of die-cutting chips and water leakage through through holes. Simultaneously, through the synergistic effect of the steric hindrance of the phenyl vinyl silicone rubber and the polymer chain reinforcement of the high-viscosity vinyl silicone oil, excellent high resilience, softness, and controllable compressive stress (30% compressive stress ≥25kPa, 70% compressive stress ≤700kPa) are achieved while maintaining good high-temperature resistance. This meets the requirements of precision electronic products for thinness, lightweight, high cushioning, and high reliability, providing a suitable waterproof sealing and cushioning protection material for precision electronic products.

[0092] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. An ultra-thin silicone foam, characterized in that, Its thickness is 0.4mm~0.6mm, and its density is 200kg / m³. 3 ~250kg / m 3 The closed-cell rate is >60%, and the average pore diameter is 50μm~150μm; the raw materials for preparing the ultrathin silicone foam include at least the following components: a) Methyl vinyl silicone rubber; b) Hydroxy silicone oil, wherein the mass ratio of the hydroxy silicone oil to the methyl vinyl silicone rubber is greater than 1:5; c) Vinyl silicone oil, wherein the viscosity of the vinyl silicone oil is not less than 60,000 mPa·s; d) Composite powder, wherein the composite powder includes flame-retardant filler, reinforcing filler and lightweight filler; e) Methylphenyl silicone rubber.

2. The ultra-thin silicone foam according to claim 1, characterized in that, The vinyl silicone oil has a viscosity of 60,000 mPa·s to 200,000 mPa·s, and / or the vinyl content in the vinyl silicone oil is 0.02% to 0.1% by mass.

3. The ultra-thin silicone foam according to claim 1, characterized in that, The mass ratio of flame-retardant filler, reinforcing filler, and lightweight filler in the composite powder is (30~40):(16~20):(4~10); and / or, The methylphenyl silicone rubber contains 0.5% to 1% phenyl by mass; and / or, The hydroxyl silicone oil contains 0.5% to 1% hydroxyl groups by mass; and / or, The methyl vinyl silicone rubber contains 0.1% to 0.2% vinyl by mass.

4. The ultra-thin silicone foam according to any one of claims 1 to 3, characterized in that, The raw materials for preparation also include fumed silica, platinum catalyst, hydrogen-containing silicone oil, and inhibitors.

5. The ultra-thin silicone foam according to claim 4, characterized in that, The mass ratio of the raw materials used in the preparation is 200:(40~100):(10~20):(20~40):(100~200):(0.5~1):(30~50):(0.01~0.1):(50~70).

6. The ultra-thin silicone foam according to claim 4, characterized in that, The raw materials used in the preparation also include additives; the amount of the additives is 1 wt% to 5 wt% of the mass of the methyl vinyl silicone rubber.

7. The ultra-thin silicone foam according to claim 1, characterized in that, It also includes a film attached to the ultra-thin silicone foam; The film is made of at least one of PET, PI, PE, and PP. The thickness of the film is 0.02mm to 0.05mm.

8. A method for preparing ultrathin silicone foam as described in any one of claims 4 to 6, characterized in that, Includes the following steps: S1. Mix a portion of the methyl vinyl silicone rubber, a portion of the vinyl silicone oil, a portion of the methyl phenyl silicone rubber, a portion of the fumed silica, a portion of the hydroxyl silicone oil, a portion of the composite powder, and the platinum catalyst to obtain component A; S2. Mix the remaining methyl vinyl silicone rubber, the remaining vinyl silicone oil, the remaining methyl phenyl silicone rubber, the remaining fumed silica, the remaining hydroxyl silicone oil, the remaining composite powder, the hydrogen-containing silicone oil, and the inhibitor to obtain component B. S3. Mix the components A and B and apply the mixture onto a film, then cure it to obtain the ultra-thin silicone foam.

9. The preparation method according to claim 8, characterized in that, The curing process involves first performing low-temperature vulcanization, followed by high-temperature vulcanization. The temperature for low-temperature vulcanization shown is 80℃~90℃, and the vulcanization time is 5min~10min; The high-temperature vulcanization temperature is 150℃~180℃, and the high-temperature vulcanization time is 10min~15min.

10. A waterproof sealing and cushioning material for electronic products, characterized in that, Includes the ultrathin silicone foam as described in any one of claims 1 to 7.

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