Liquid silica gel foam with lasting and rapid resilience after hot pressing

Abstract

The invention belongs to the field of silica gel foam, and particularly relates to liquid silica gel foam with lasting and rapid rebound resilience after hot pressing. According to the liquid silica gel foam with lasting and rapid resilience after hot pressing, vinyl silicone oil with different viscosities is compounded, a proper amount of polyvinylsilicone oil is added, and the proportion of the vinyl silicone oil, the mixed hydroxyl silicone oil and the mixed hydrogen-containing silicone oil is regulated and controlled, so that the elasticity of the foam is improved; the liquid silica gel foam which is excellent in buffering performance and capable of rapidly rebounding and has no obvious damage on the surface after being subjected to hot pressing for multiple times at high temperature and high pressure is prepared according to the adding amount of the functional filler and the proportion of the fillers. When the liquid silica gel foam is used as a circuit board buffer material, scratches caused by hard contact between a heating plate and a laminated plate can be effectively avoided, and the service life of the heating plate and the service life of the laminated plate are prolonged.

Description

Technical Field

[0001] The present application belongs to the field of silicone foam, and more specifically, relates to a liquid silicone foam having long-lasting and rapid rebound properties after hot pressing. Background Art

[0002] The flexible circuit board industry typically uses solid silicone as a cushioning pad for PCB lamination. However, solid silicone lacks a cushioning function. During the PCB lamination process, when the laminate and the heating plate are thermally pressed together, the uneven copper foil on the laminate surface requires precise pressure control to reduce the risk of PCB damage. Furthermore, during the PCB lamination process, solid silicone can precipitate oil under high temperatures and pressure, potentially contaminating the circuit board and causing significant damage, making it unsafe and environmentally friendly.

[0003] Using liquid silicone foam instead of solid silicone can greatly improve product yield. However, the surface of existing liquid silicone foam will break after a few times of hot pressing, and it needs to be replaced frequently, which reduces production efficiency and increases production costs.

[0004] Therefore, it is necessary to provide a safe and environmentally friendly liquid silicone foam that has good cushioning and fast rebound properties, and at the same time has no obvious damage on the foam surface after undergoing multiple hot pressings under high temperature and high pressure. Summary of the Invention

[0005] In response to the defects of the existing technology, the purpose of this application is to provide a liquid silicone foam with long-lasting rapid rebound performance after hot pressing, aiming to solve the problems of the existing liquid silicone foam being damaged on the foam surface and having poor rapid rebound performance after a small number of hot pressing times (less than 10 times under the conditions of 180°C and 5MPa).

[0006] To achieve the above objectives, in a first aspect, the present application provides a liquid silicone foam having long-lasting and rapid rebound properties after hot pressing, wherein the raw materials for preparing the liquid silicone foam include the following components: a) Mixed vinyl silicone oil; b) mixed hydroxy silicone oil; c) Polyvinyl silicone oil; d) platinum catalyst; e) Mixed with hydrogenated silicone oil; f) inhibitors; g) functional fillers; The viscosity of the polyvinyl silicone oil is 1,000 mPa·s to 12,000 mPa·s, and the mass percentage of vinyl is 1.0% to 10.0%. The addition amount of the polyvinyl silicone oil is 0.5 wt% to 3 wt% of the total mass of the raw materials.

[0007] Preferably, the thickness of the liquid silicone foam is 2mm~10mm and the density is 330kg / m 3 ~ 650kg / m 3 , 25% compression stress is 60KPa~250KPa, tear strength is 1.4N / mm~2.5N / mm, stress relaxation ≤20%, elongation at break is 80%~150%, and Shore C hardness is 18~35.

[0008] Preferably, the liquid silicone foam can be reused at least 20 times during hot pressing, wherein the hot pressing conditions are: temperature ≤ 220° C., pressure ≤ 8 MPa.

[0009] Preferably, the mixed vinyl silicone oil includes vinyl silicone oil 1 and vinyl silicone oil 2; wherein, the viscosity of vinyl silicone oil 1 is 50,000 mPa·s~120,000 mPa·s, and the mass percentage of vinyl is 0.04%~0.10%; the viscosity of vinyl silicone oil 2 is 15,000 mPa·s~25,000 mPa·s, and the mass percentage of vinyl is 0.10%~0.16%.

[0010] Preferably, the mass ratio of the vinyl silicone oil 1 to the vinyl silicone oil 2 is (1-4):1.

[0011] Preferably, the functional filler includes a flame retardant filler and a reinforcing filler.

[0012] Preferably, the flame retardant filler comprises one or more of magnesium hydroxide, aluminum hydroxide, zinc borate, and modified montmorillonite, and has a median particle size of 1 μm to 50 μm. Further preferably, the flame retardant filler is added in an amount of 15 wt% to 25 wt% of the total mass of the raw materials.

[0013] Preferably, the reinforcing filler comprises one or more of white carbon black, hollow glass microspheres, silica powder, modified nano-calcium carbonate, wollastonite, and talc. Further preferably, the reinforcing filler is added in an amount of 15 wt% to 30 wt% of the total weight of the raw materials.

[0014] Preferably, the mixed hydroxy silicone oil comprises hydroxy silicone oil 1 and hydroxy silicone oil 2; wherein hydroxy silicone oil 1 has a viscosity of 5mPa·s to 100mPa·s and a hydroxyl content of 6% to 12% by weight; hydroxy silicone oil 2 has a viscosity of 5mPa·s to 100mPa·s and a hydroxyl content of 2% to 4% by weight. Preferably, the mass ratio of hydroxy silicone oil 1 to hydroxy silicone oil 2 is 1:(2-8).

[0015] Preferably, the mixed hydrogenated silicone oil comprises hydrogenated silicone oil 1 and hydrogenated silicone oil 2; wherein hydrogenated silicone oil 1 has a viscosity of 5 mPa·s to 200 mPa·s and a hydrogen content of 1.2% to 1.6% by weight; hydrogenated silicone oil 2 has a viscosity of 5 mPa·s to 200 mPa·s and a hydrogen content of 0.02% to 0.5% by weight. Preferably, the mass ratio of hydrogenated silicone oil 1 to hydrogenated silicone oil 2 is (2-5):1.

[0016] Preferably, the mass ratio of the mixed vinyl silicone oil, the mixed hydroxy silicone oil and the hydrogen-containing silicone oil 1 is (15-35):(1-3):1.

[0017] Preferably, the platinum catalyst is one or more of a tetrahydrofuran-coordinated platinum catalyst, an isopropyl alcohol-coordinated chloroplatinic acid catalyst, a chloroplatinic acid-diethyl phthalate complex solution, and a platinum complex containing a vinylsiloxane ligand. Preferably, the platinum catalyst is added in an amount of 0.1 wt% to 3 wt% of the total mass of the raw materials.

[0018] Preferably, the inhibitor is one or more of 2-methyl-3-alkyn-2-ol, 3-methyl-1-alkyn-3-ol, ethynylcyclohexanol, diallyl maleate, and diethyl fumarate. Preferably, the inhibitor is added in an amount of 0.01 wt% to 0.1 wt% of the total weight of the raw materials.

[0019] In a second aspect, the present application provides a method for preparing the above-mentioned liquid silicone foam, comprising the following steps: S1, mixing part of the mixed vinyl silicone oil, part of the polyvinyl silicone oil, part of the filler, the mixed hydroxy silicone oil and the catalyst to obtain a first material; S2, uniformly mixing the remaining mixed vinyl silicone oil, the remaining polyvinyl silicone oil, the remaining filler, the mixed hydrogenated silicone oil and the inhibitor to obtain a second material; S3. Mix the first material and the second material and apply them on the surface of the substrate, and perform low-temperature vulcanization and high-temperature vulcanization treatment in sequence to obtain the liquid silicone foam.

[0020] Preferably, in step S1 and step S2, the mixing speed is 300 r / min to 500 r / min, and the mixing time is 2 h to 5 h.

[0021] Preferably, in step S3, the temperature of the low-temperature vulcanization is 50°C to 90°C, and the time of the low-temperature vulcanization is 1 min to 10 min; the temperature of the high-temperature vulcanization is 150°C to 200°C, and the time of the high-temperature vulcanization is 10 min to 40 min.

[0022] In a third aspect, the present application provides the use of the above-mentioned liquid silicone foam or the liquid silicone foam prepared by the above-mentioned preparation method as a buffer material for a circuit board.

[0023] In general, the above technical solutions conceived by this application have the following technical advantages compared with the existing technologies: (1) The present application provides a liquid silicone foam having long-lasting rapid rebound performance after hot pressing. The liquid silicone foam is prepared by compounding vinyl silicone oils of different viscosities, adding a suitable amount of polyvinyl silicone oil, and regulating the ratio of vinyl silicone oil, mixed hydroxy silicone oil, and mixed hydrogen silicone oil, the amount of functional filler added, and the ratio between the fillers. The liquid silicone foam has excellent cushioning performance and rapid rebound function, and there is no obvious damage to the foam surface after multiple hot pressings under high temperature and high pressure. When the liquid silicone foam provided by the present application is used as a buffer material for a circuit board, it can effectively avoid scratches caused by hard contact between the heating plate and the laminate, thereby extending the service life of the heating plate and the laminate.

[0024] (2) The raw materials for preparing the liquid silicone foam of the present application are added with a suitable amount of polyvinyl silicone oil, and are compounded with mixed vinyl silicone oil of suitable viscosity and hydrogen-containing silicone oil of different hydrogen contents, so that when the vinyl silicone oil and hydrogen-containing silicone oil undergo a cross-linking reaction to form a three-dimensional network structure, plastic micro-regions with relatively high strength can be formed, which helps to improve the tear strength of the liquid silicone foam, delay the rupture process of the liquid silicone foam, and enhance the rapid rebound function of the liquid silicone foam.

[0025] (3) The raw materials for preparing the liquid silicone foam of the present application are added with reinforcing fillers of appropriate types and proportions, which can play a reinforcing role and at the same time block the thermal motion area of ​​the liquid silicone rubber foam molecular chains under high temperature and high pressure, inhibit the movement ability of the molecular chains, and effectively reduce stress relaxation, so that the liquid silicone foam still has good rebound performance after multiple hot pressing. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the structure of the hot pressing mold used in the hot pressing number test in the embodiment of the present application, wherein content (a) and content (b) are schematic diagrams of the upper mold plate and the lower mold plate of the hot pressing mold respectively; Figure 2 This is the appearance of the liquid silicone foam P2 prepared in Example 2 of the present application after hot pressing 38 times; Figure 3 This is the appearance of the liquid silicone foam D1 and D2 prepared in Comparative Examples 1 and 2 of the present application after hot pressing. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solutions and advantages of this application more clear, the following further describes this application in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0028] In the description of this application, it should be understood that the term "and / or" describes an association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. The symbol " / " herein indicates that the associated objects are in an "or" relationship, for example, A / B means either A or B.

[0029] In the specification and claims of this application, the terms "first" and "second" and so on are used to distinguish different objects rather than to describe the specific order of objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features.

[0030] In the description of the embodiments of this application, words such as "exemplary" or "for example" are used to indicate examples, illustrations, or descriptions. Any embodiment or design described as "exemplary" or "for example" in the embodiments of this application should not be construed as being preferred or advantageous over other embodiments or designs. Rather, the use of words such as "exemplary" or "for example" is intended to present the relevant concepts in a concrete manner.

[0031] In the description of the embodiments of the present application, unless otherwise specified, “plurality” means two or more.

[0032] The stress relaxation of conventional liquid silicone foam is usually between 30% and 50%. After repeated compression under high temperature and high pressure, its rebound rate decays rapidly, making it unsuitable for use as a PCB board pressing cushion. Usually, the stress relaxation of liquid silicone foam is reduced by increasing the amount of hydrogenated silicone oil, raising the temperature of the vulcanization treatment, and extending the time of the vulcanization treatment. However, the toughness of the foam is significantly reduced, while the hardness is significantly increased. Based on this, the present application provides a liquid silicone foam with long-lasting compression rebound performance under high temperature and high pressure. The raw materials for preparing the liquid silicone foam include the following components: a) Mixed vinyl silicone oil; b) mixed hydroxy silicone oil; c) Polyvinyl silicone oil; d) platinum catalyst; e) Mixed with hydrogenated silicone oil; f) inhibitors; g) functional fillers; The viscosity of the polyvinyl silicone oil is 1,000 mPa·s to 12,000 mPa·s, and the mass percentage of vinyl is 1.0% to 10.0%. The addition amount of the polyvinyl silicone oil is 0.5 wt% to 3 wt% of the total mass of the raw materials.

[0033] This application can provide liquid silicone foam with a thickness of 2mm~10mm and a density of 330kg / m 3 ~650kg / m 3 .

[0034] In some embodiments, the 25% compressive stress of the liquid silicone foam is 60 KPa to 250 KPa, which has good cushioning performance and mechanical properties of rapid rebound after compression.

[0035] In some embodiments, the tear strength of the liquid silicone foam is 1.4 N / mm~2.5 N / mm. The higher the tear strength, the slower the rupture of the liquid silicone foam. The more times high temperature hot pressing is used.

[0036] In some embodiments, the stress relaxation of the liquid silicone foam is ≤20%, the stress relaxation is small, and the liquid silicone foam has long-lasting resilience after multiple compressions under high temperature and high pressure.

[0037] In some embodiments, the liquid silicone foam has an elongation at break of 80% to 150%, and has good toughness and conformability during use.

[0038] In some embodiments, the liquid silicone foam can be reused at least 20 times during hot pressing, wherein the hot pressing conditions are: temperature ≤ 220°C and pressure ≤ 8 MPa. In a preferred embodiment, the hot pressing temperature is 120°C to 200°C and the hot pressing pressure is 1.5 MPa to 6.0 MPa.

[0039] In some embodiments, the Shore C hardness of the liquid silicone foam is 18 to 35. If the Shore C hardness of the liquid silicone foam is lower than 18, the foam is easily compressed under high compressive stress, causing the heating plate to bottom out and damage the circuit board, and the foam completely loses its cushioning properties. If the Shore C hardness of the liquid silicone foam is higher than 35, the foam has poor cushioning properties under high compressive stress, and the foam surface is easily crushed.

[0040] In some embodiments, the mixed vinyl silicone oil includes vinyl silicone oil 1 and vinyl silicone oil 2; wherein, the viscosity of vinyl silicone oil 1 is 50,000mPa·s~120,000mPa·s, and the mass percentage of vinyl is 0.04%~0.10%; the viscosity of vinyl silicone oil 2 is 15,000mPa·s~25,000mPa·s, and the mass percentage of vinyl is 0.10%~0.16%. In some embodiments, the mass ratio of vinyl silicone oil 1 and vinyl silicone oil 2 is (1~4):1. In this application, the vinyl silicone oil is used as the main raw material for preparation and undergoes a cross-linking reaction with hydrogenated silicone oil to form a three-dimensional network structure. Among them, the vinyl silicone oil 1 with a larger viscosity has a large molecular weight, which can make the silicone foam have higher elasticity and a larger elongation at break, and the vinyl silicone oil 2 with a smaller viscosity has a small molecular weight, a high vinyl content, and a high cross-linking density, which can make the silicone foam have a higher tensile strength, and can reduce the viscosity of the system, which is beneficial for processing. In some embodiments, the amount of the vinyl silicone oil 1 is 25 wt% to 40 wt% of the total mass of the raw materials. It is understood that the vinyl silicone oil in this application can be purchased from companies selling chemical products such as Zhejiang Xin'an Chemical Group Co., Ltd., Shandong Dongyue Group Co., Ltd., Zhejiang Hesheng Silicon Industry Co., Ltd., Dow Corning Corporation, and Shin-Etsu Corporation.

[0041] In some embodiments, the viscosity of the polyvinyl silicone oil is 1,000mPa·s~12,000mPa·s, preferably 2,000mPa·s~5,000mPa·s, and the mass percentage of vinyl is 1.0%~10.0%. In the present application, the polyvinyl silicone oil has vinyl groups at both ends and side chains, which can further improve the tear strength and crosslinking density of the liquid silicone foam during crosslinking, which is beneficial to enhancing the rapid rebound performance of the liquid silicone foam. In some embodiments, the amount of the polyvinyl silicone oil added is 0.5wt%~3wt% of the total mass of the raw materials prepared above. A certain amount of polyvinyl silicone oil added can effectively improve the tear strength of the liquid silicone foam and delay the process of liquid silicone foam rupture. The tear strength of the liquid silicone foam provided in this application is 1.4N / mm~2.5N / mm.

[0042] When the addition amount of polyvinyl silicone oil is too low, plastic micro-regions with higher strength cannot be formed, and the mechanical properties of the silicone foam are not significantly improved; when the addition amount of polyvinyl silicone oil is too high, the cross-linking points are too concentrated, and the tear strength growth of the liquid silicone foam tends to a constant value, but the elongation at break performance decreases rapidly, the hardness increases significantly, the toughness decreases, the foam becomes brittle, and it is easy to be crushed.

[0043] Hydroxyl silicone oil is used as a system foaming agent. It can react with the active group Si-H of hydrogenated silicone oil under the action of a catalyst to produce H2, so that the liquid silicone foam is foamed to form liquid silicone foam. In some embodiments, the mixed hydroxy silicone oil includes hydroxy silicone oil 1 and hydroxy silicone oil 2, wherein the viscosity of the hydroxy silicone oil 1 is 5mPa·s~100mPa·s, and the mass percentage of hydroxyl groups is 6%~12%; the viscosity of the hydroxy silicone oil 2 is 5mPa·s~100mPa·s, and the mass percentage of hydroxyl groups is 2%~4%; the mass ratio of hydroxy silicone oil 1 and hydroxy silicone oil 2 is 1:(2~8). By compounding hydroxy silicone oil 1 and hydroxy silicone oil 2, the liquid silicone foam has a higher elongation at break, more uniform pores, better mechanical properties, and better rebound performance. In some embodiments, the total amount of the hydroxy silicone oil 1 and hydroxy silicone oil 2 is 3wt%~7wt% of the total mass of the raw materials prepared above.

[0044] In some embodiments, the platinum catalyst is one or more of a platinum catalyst coordinated with tetrahydrofuran, a chloroplatinic acid catalyst coordinated with isopropyl alcohol, a chloroplatinic acid-diethyl phthalate complex solution, and a platinum complex containing a vinylsiloxane ligand.

[0045] In some embodiments, the amount of the platinum catalyst added is 0.1 wt% to 3 wt% of the total mass of the raw materials.

[0046] The hydrogen-containing silicone oil plays a cross-linking role in the system. Under the action of the catalyst, it reacts with the hydroxyl silicone oil to release H2 foaming, and reacts with the vinyl silicone oil for cross-linking and grafting to form the entire foam network structure. In some embodiments, the mixed hydrogen-containing silicone oil includes hydrogen-containing silicone oil 1 and hydrogen-containing silicone oil 2; wherein the viscosity of the hydrogen-containing silicone oil 1 is 5mPa·s~200mPa·s, and the mass percentage of hydrogen is 1.2%~1.6%; the viscosity of the hydrogen-containing silicone oil 2 is 5mPa·s~200mPa·s, and the mass percentage of hydrogen is 0.02%~0.5%; the mass ratio of hydrogen-containing silicone oil 1 to hydrogen-containing silicone oil 2 is (2~5):1. In this application, the side hydrogen contained in the molecular chain of the hydrogen-containing silicone oil 1 has high reactivity and more active sites, so that the liquid silicone foam has a high degree of cross-linking and better compression resilience; the molecular chain of the hydrogen-containing silicone oil 2 contains terminal hydrogen, which can play a chain extension role, so that the liquid silicone foam has better elongation at break. In some embodiments, the amount of the hydrogen-containing silicone oil 1 is 1.5 wt % to 3.2 wt % of the total mass of the raw materials.

[0047] In some embodiments, the inhibitor is one or more of 2-methyl-3-alkyn-2-ol, 3-methyl-1-alkyn-3-ol, ethynylcyclohexanol, diallyl maleate, and diethyl fumarate.

[0048] In some embodiments, the added amount of the above inhibitor is 0.01 wt% to 0.1 wt% of the total mass of the above raw materials.

[0049] In some embodiments, the mass ratio of the mixed vinyl silicone oil, the mixed hydroxyl silicone oil, and the hydrogen-containing silicone oil 1 is (15-35):(1-3):1. When the ratio of the mixed vinyl silicone oil to the hydrogen-containing silicone oil is too low, the crosslinking degree is too high, the silicone foam is brittle, and the tear strength is low; when the ratio is too high, the crosslinking reaction is incomplete, the crosslinking degree is low, the mechanical properties of the silicone foam are poor, and the stress relaxation is large. When the ratio of the mixed hydroxyl silicone oil to the mixed hydrogen-containing silicone oil is too low, the silicone foam has a low foaming degree, too high a density, high compressive stress, and poor cushioning performance; when the ratio is too high, the silicone foam foams too quickly and is prone to foaming.

[0050] In some embodiments, the functional filler includes a flame retardant filler and a reinforcing filler.

[0051] In some embodiments, the flame retardant filler includes one or more of magnesium hydroxide, aluminum hydroxide, zinc borate, and modified montmorillonite, and the median particle size of the flame retardant filler is 1 μm to 50 μm.

[0052] In some embodiments, the added amount of the flame retardant filler is 15 wt% to 25 wt% of the total mass of the raw materials.

[0053] In some embodiments, the reinforcing filler includes one or more of white carbon black, hollow glass microspheres, silica powder, modified nano-calcium carbonate, wollastonite, and talc.

[0054] The reinforcing filler of the right type and the right proportion can play a reinforcing role, and at the same time block the thermal motion area of ​​the liquid silicone rubber foam molecular chain under high temperature and high pressure, inhibit the movement ability of the molecular chain, reduce stress relaxation, and make the silicone foam still have good rebound performance after multiple hot pressing. In a preferred embodiment, the above-mentioned reinforcing filler includes white carbon black, modified nano calcium carbonate and wollastonite. In some embodiments, the above-mentioned white carbon black is fumed white carbon black or precipitated white carbon black, and its surface area is 150m 2 / g~400m 2 / g. The above-mentioned modified nano-calcium carbonate has good compatibility and can significantly improve the mechanical properties of liquid silicone foam such as elongation and tear strength. Wollastonite is calcium silicate, which has good wear resistance and compression resistance. In some embodiments, the addition amount of the above-mentioned reinforcing filler is 15wt%~30wt% of the total mass of the above-mentioned preparation raw materials. Among them, the mass ratio of modified nano-calcium carbonate and wollastonite is (1~4):1. When the modified nano-calcium carbonate is excessive, the viscosity-increasing effect of the modified nano-calcium carbonate is obvious, the processing performance is difficult, and the tear strength of the silicone foam will be significantly reduced. When the proportion of wollastonite is excessive, the silicone foam is significantly hardened and the elongation at break will be significantly reduced.

[0055] On the other hand, the present application provides a method for preparing the above-mentioned liquid silicone foam, comprising the following steps: S1, mixing part of the mixed vinyl silicone oil, part of the polyvinyl silicone oil, part of the filler, the mixed hydroxy silicone oil and the catalyst to obtain a first material; S2, mixing the remaining mixed vinyl silicone oil, the remaining polyvinyl silicone oil, the remaining filler, the mixed hydrogenated silicone oil and the inhibitor to obtain a second material; S3. Mix the first material and the second material and apply them on the surface of the substrate, and perform low-temperature vulcanization and high-temperature vulcanization treatment in sequence to obtain the liquid silicone foam.

[0056] In some embodiments, in step S1 and step S2, the mixing speed is 300 rpm to 500 rpm, and the mixing time is 2 h to 5 h.

[0057] In some embodiments, in step S3, the temperature of the low-temperature vulcanization is 50°C to 90°C, and the time of the low-temperature vulcanization is 1 min to 10 min; the temperature of the high-temperature vulcanization is 150°C to 200°C, and the time of the high-temperature vulcanization is 10 min to 40 min.

[0058] The present application also provides the use of the above-mentioned liquid silicone foam or the liquid silicone foam prepared by the above-mentioned preparation method as a buffer material for a circuit board.

[0059] It should be understood that materials of the same or similar type, model, quality, properties, or functions as the reagents and instruments used in the following examples can be used to implement this application. The experimental methods used in the following examples are all conventional methods unless otherwise specified. The materials, reagents, etc. used in the following examples, unless otherwise specified, can all be obtained from commercial sources.

[0060] The following are examples and comparative examples: Example 1 This embodiment provides a liquid silicone foam (denoted as P1) having long-lasting rapid rebound performance after hot pressing. The raw material composition and mass fraction thereof are shown in Table 1. The preparation method includes the following steps: S1. Prepare the first material According to the raw material composition and mass fractions of the first material shown in Table 1, the mixed vinyl silicone oil, polyvinyl silicone oil, mixed hydroxy silicone oil, platinum catalyst, flame retardant filler and reinforcing filler were uniformly mixed in a disperser at a mixing speed of 500 r / min and a mixing time of 2 h to obtain the first material.

[0061] S2. Preparation of the second material According to the raw material composition and mass fraction of the second material shown in Table 1, the mixed vinyl silicone oil, polyvinyl silicone oil, mixed hydrogen silicone oil, inhibitor, flame retardant filler and reinforcing filler were uniformly mixed in a disperser at a mixing speed of 500 r / min and a mixing time of 2.5 h to obtain the second material.

[0062] S3. Preparation of liquid silicone foam The first material and the second material are mixed evenly at a mixing speed of 450 r / min, and then the mixed material is immediately coated on a PET film, baked and vulcanized at 50°C for 10 minutes, and then transferred to 150°C for baking and vulcanization for 25 minutes to obtain liquid silicone foam.

[0063] Example 2 This embodiment provides a liquid silicone foam (denoted as P2) having long-lasting rapid rebound performance after hot pressing. The raw material composition and mass fraction thereof are shown in Table 1. The preparation method includes the following steps: S1. Prepare the first material According to the raw material composition and mass fractions of the first material shown in Table 1, the mixed vinyl silicone oil, polyvinyl silicone oil, mixed hydroxy silicone oil, platinum catalyst, flame retardant filler and reinforcing filler were uniformly mixed in a disperser at a mixing speed of 300 r / min and a mixing time of 5 h to obtain the first material.

[0064] S2. Preparation of the second material According to the raw material composition and mass fraction of the second material shown in Table 1, the mixed vinyl silicone oil, polyvinyl silicone oil, mixed hydrogen silicone oil, inhibitor, flame retardant filler and reinforcing filler were uniformly mixed in a disperser at a mixing speed of 300 r / min and a mixing time of 5 h to obtain the second material.

[0065] S3. Preparation of liquid silicone foam The first material and the second material were mixed evenly at a mixing speed of 400 r / min, and then the mixed material was immediately coated on a PET film, baked and vulcanized at 80°C for 3 minutes, and then transferred to 150°C for baking and vulcanization for 25 minutes to obtain liquid silicone foam.

[0066] Examples 3 to 9 The liquid silicone foams (denoted as P3 to P9) with long-lasting and rapid rebound properties after hot pressing provided in Examples 3 to 9 of the present application have raw material compositions and mass fractions as shown in Table 1, and the preparation method is the same as that in Example 2.

[0067]

[0068] The specific parameter information of the above raw materials is as follows: The average viscosity of vinyl silicone oil 1 is 100,000 mPa·s, and the mass percentage of vinyl is 0.1%; The average viscosity of vinyl silicone oil 2 is 20,000 mPa·s, and the mass percentage of vinyl is 0.15%; The average viscosity of the polyvinyl silicone oil is 2,000 mPa·s, and the mass percentage of vinyl is 8%; The viscosity of hydroxy silicone oil 1 is 30 mPa·s, and the mass percentage of hydroxyl groups is 8%; The viscosity of hydroxy silicone oil 2 is 38 mPa·s, and the mass percentage of hydroxyl group is 3.5%; The platinum catalyst is a chloroplatinic acid catalyst coordinated with isopropyl alcohol; Hydrogenated silicone oil 1 is a methyl-terminated side-chain hydrogenated silicone oil with a viscosity of 20 mPa·s and a hydrogen mass percentage of 1.6%; Hydrogenated silicone oil 2 is a hydrogen-terminated low-hydrogen silicone oil with a viscosity of 260 mPa·s and a hydrogen mass percentage of 0.2%; The median particle size of aluminum hydroxide and magnesium hydroxide is 20 μm; Silica is fumed silica with a specific surface area of ​​300m 2 / g; Modified calcium carbonate is surface-modified nano calcium carbonate treated with stearic acid and has good compatibility; The aspect ratio of wollastonite is 15~20.

[0069] Comparative Examples 1 to 7 The raw material compositions and weight fractions of the liquid silicone foams provided in Comparative Examples 1 to 7 of the present application (denoted as D1 to D7) are shown in Table 2. The raw materials used are the same as those in Example 1. The preparation method of the liquid silicone foam provided in Comparative Example 1 is the same as that in Example 1, and the preparation methods of the liquid silicone foams provided in Comparative Examples 2 to 7 are the same as those in Example 2.

[0070]

[0071] The performance of the liquid silicone foam prepared in the above examples and comparative examples was tested, and the testing method was as follows: a) Thickness, density, and 25% compressive stress test: The thickness, density and 25% compressive stress of each liquid silicone foam sample were tested according to standard ASTM D 1056.

[0072] b) Tensile strength test The tensile strength of each liquid silicone foam specimen was tested according to standard ASTM D 412.

[0073] c) Elongation at break test The elongation at break of each liquid silicone foam specimen was tested according to standard ASTM D 412.

[0074] d) Tear strength test The tear strength of each liquid silicone foam sample was tested according to the standard GB / T 529-2008, Determination of tear strength of vulcanized rubber or thermoplastic rubber.

[0075] e) Rebound rate test The initial thickness of the liquid silicone foam sample tested at the standard test temperature is T1. The cut sample is placed between the upper and lower molds. The mold is placed in the middle of the hot press plate of a flat vulcanizer with a pre-set temperature of 180°C. The pressure is increased to 2.5MPa and maintained for 1 hour. The sample is then taken out and allowed to stand at room temperature for 5 minutes. The thickness of the foam is tested at the standard test temperature and recorded as T2. The rebound rate is calculated according to the formula Rebound rate = (T2 / T1) × 100%. A rebound rate greater than 99% is considered qualified. The qualified rebound rate test is a prerequisite for the hot press test. If the rebound rate test is qualified, the subsequent hot press test is carried out; if the rebound rate test fails, the hot press test number is recorded as zero.

[0076] f) Compression stress relaxation test The compressive stress relaxation R of each liquid silicone foam sample was tested according to the standard GB / T 1685-2008 Determination of compressive stress relaxation of vulcanized rubber or thermoplastic at room temperature and high temperature. t Specifically, the liquid silicone foam is compressed by 25% at standard laboratory temperature. The initial compressive stress tested after 30 minutes of compression is recorded as F0. Then the test liquid silicone foam is compressed by 50% at a temperature of 150℃. The compressive stress tested after 168 hours of compression is recorded as F t , (F0-F t ) / F0 is the compressive stress relaxation R t .

[0077] g) Hardness (Shore C) test The hardness (Shore C) of each liquid silicone foam specimen was tested according to ASTM D 2240.

[0078] h) Flame retardant performance test The flame retardancy of each liquid silicone rubber sample was tested according to the vertical combustion method of the UL 94-2016 standard.

[0079] i) Hot pressing test The cut sample is placed between the upper and lower templates of the hot pressing mold with a size of 200mm×200mm. The upper template structure of the hot pressing mold is as follows: Figure 1As shown in content (a), the gray shadow surface is the convex surface, and the height of the protruding mold panel is 3mm; the lower template structure of the hot pressing mold is as follows Figure 1 As shown in content (b), the white surface is concave, and the depth of the recess into the mold panel is 3mm. Set the temperature of the flatbed vulcanizer to 180°C and the pressure to 5MPa. When the temperature reaches the set value, place the hot press mold in the center of the hot press platen of the vulcanizer. Start the flatbed vulcanizer and maintain hot pressing for 30 minutes. Release the pressure, remove the mold while wearing protective gloves, and place it in the center of the cold press platen. Start the flatbed vulcanizer and chiller. Maintain cold pressing for 8 minutes. Release the pressure, remove the hot press mold, and disassemble the hot press mold. Observe the surface condition of the foam at the concave and convex surfaces of the hot press mold: ① Whether the foam surface is peeling, ② Whether the foam is flakes, and ③ Whether there are obvious cracks on the foam surface. If all three of the above criteria are negative, repeat the above steps until the foam meets any of the three criteria. Stop the simulation and record the number of simulations until any of the three criteria are met. This is the number of hot pressing times.

[0080] The performance test results of the liquid silicone foams (P1-P9) prepared in Examples 1-9 and the liquid silicone foams (D1-D7) prepared in Comparative Examples 1-7 are shown in Tables 3, 4, Figure 2 、 Figure 3 shown.

[0081]

[0082]

[0083] Compared with the examples, the viscosity of the mixed vinyl silicone oil in Comparative Example 1 is too low, wherein the amount of high-viscosity vinyl silicone oil (vinyl silicone oil 1) is too low, and the amount of low-viscosity vinyl silicone oil (vinyl silicone oil 3) is too much; the amount of polyvinyl silicone oil added in Comparative Example 2 is more than the amount of polyvinyl silicone oil added in the examples; the total amount of functional fillers (including flame retardant fillers and reinforcing fillers) added in Comparative Example 3 is too low; the ratio of hydroxy silicone oil and hydrogen-containing silicone oil in Comparative Example 4 is too high; the ratio of wollastonite and modified calcium carbonate in the reinforcing filler of Comparative Example 5 is too high; the ratio of wollastonite and modified nano-calcium carbonate in the reinforcing filler of Comparative Example 6 is too low; and the amount of hydroxy silicone oil and hydrogen-containing silicone oil added in Comparative Example 7 is excessive. The performance test results show that although the compression stress relaxation of the foam of Comparative Example 1 is low, its density and compression stress are both high, and its cushioning performance is deteriorated; in addition, the elongation at break of the foam of Comparative Example 1 is low, and the number of times the foam is used under high-temperature hot pressing is small. The damage of foam D1 after 8 hot pressings is as shown in FIG. Figure 3 The tear strength of the foam in Comparative Example 2 is improved, but the elongation at break is significantly lower than that in the embodiment. The foam is hard and brittle, and the number of times it is used under high temperature hot pressing is small. The damage of foam D2 after 7 hot pressings is as shown in the figure. Figure 3As shown. The flame retardant performance of the foam in Comparative Example 3 deteriorates, and the stress relaxation is high, and the number of uses under high temperature hot pressing does not meet the requirements. Although the elongation at break of the foam in Comparative Example 4 is high, its 25% compressive stress is low, and its resilience is poor and rebound is slow, making it unsuitable for use as a PCB board pressure buffer. The hardness of the foam in Comparative Example 5 increases, and the elongation at break decreases significantly, and the number of uses under high temperature hot pressing is small. The tear strength of the foam in Comparative Example 6 is low, and the number of uses under high temperature hot pressing does not meet the requirements. The compressive stress and tear strength of the foam in Comparative Example 7 are both low. Under high temperature hot pressing, the low-density and low-compressive stress foam is easily compressed, and the heating plate will touch the bottom and damage the circuit board, causing the foam to completely lose its buffering performance.

[0084] In summary, the present application controls the tear strength of liquid silicone foam to be between 1.4N / mm and 2.5N / mm, the stress relaxation is less than or equal to 20%, the elongation at break is 80% to 150%, and it can rebound quickly under high temperature and hot pressing and can be used multiple times (such as Figure 2 (as shown) and meets UL94 vertical combustion V0 requirements. Furthermore, the 25% compressive stress is 60kPa to 250kPa, making it suitable for use as a PCB press cushion.

[0085] It is easy for those skilled in the art to understand that the above is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A liquid silicone foam with long-lasting and rapid rebound performance after hot pressing, characterized in that: The raw materials for preparing the liquid silicone foam include the following components: a) Mixed vinyl silicone oil; b) mixed hydroxy silicone oil; c) Polyvinyl silicone oil; d) platinum catalyst; e) Mixed with hydrogenated silicone oil; f) inhibitors; g) functional fillers; The viscosity of the polyvinyl silicone oil is 1,000 mPa·s to 12,000 mPa·s, and the mass percentage of vinyl is 1.0% to 10.0%. The addition amount of the polyvinyl silicone oil is 0.5 wt% to 3 wt% of the total mass of the raw materials.

2. The liquid silicone foam according to claim 1, characterized in that The thickness of the liquid silicone foam is 2mm~10mm and the density is 330kg / m 3 ~650kg / m 3 , 25% compression stress is 60KPa~250KPa, tear strength is 1.4N / mm~2.5N / mm, stress relaxation ≤20%, elongation at break is 80%~150%, and Shore C hardness is 18~35; The liquid silicone foam can be reused at least 20 times during hot pressing, wherein the hot pressing conditions are: temperature ≤ 220° C., and pressure ≤ 8 MPa.

3. The liquid silicone foam according to claim 1, characterized in that The mixed vinyl silicone oil includes vinyl silicone oil 1 and vinyl silicone oil 2; The viscosity of the vinyl silicone oil 1 is 50,000 mPa·s to 120,000 mPa·s, and the mass percentage of vinyl is 0.04% to 0.10%; the viscosity of the vinyl silicone oil 2 is 15,000 mPa·s to 25,000 mPa·s, and the mass percentage of vinyl is 0.10% to 0.16%; The mass ratio of the vinyl silicone oil 1 to the vinyl silicone oil 2 is (1-4):

1.

4. The liquid silicone foam according to claim 1, characterized in that The functional filler includes a flame retardant filler and a reinforcing filler; the flame retardant filler includes one or more of magnesium hydroxide, aluminum hydroxide, zinc borate and modified montmorillonite, and the median particle size of the flame retardant filler is 1 μm to 50 μm; the reinforcing filler includes one or more of white carbon black, hollow glass microspheres, silica powder, modified nano calcium carbonate, wollastonite and talc; Preferably, the added amount of the flame retardant filler is 15wt%~25wt% of the total mass of the raw materials; the added amount of the reinforcing filler is 15wt%~30wt% of the total mass of the raw materials.

5. The liquid silicone foam according to claim 2, characterized in that: The mixed hydroxy silicone oil includes hydroxy silicone oil 1 and hydroxy silicone oil 2; the mass ratio of the hydroxy silicone oil 1 to the hydroxy silicone oil 2 is 1:(2-8); the viscosity of the hydroxy silicone oil 1 is 5mPa·s-100mPa·s, and the mass percentage of hydroxyl groups is 6%-12%; the viscosity of the hydroxy silicone oil 2 is 5mPa·s-100mPa·s, and the mass percentage of hydroxyl groups is 2%-4%; and / or, The mixed hydrogen-containing silicone oil includes hydrogen-containing silicone oil 1 and hydrogen-containing silicone oil 2; the mass ratio of the hydrogen-containing silicone oil 1 to the hydrogen-containing silicone oil 2 is (2-5):1; the viscosity of the hydrogen-containing silicone oil 1 is 5 mPa·s-200 mPa·s, and the mass percentage of hydrogen is 1.2%-1.6%; the viscosity of the hydrogen-containing silicone oil 2 is 5 mPa·s-200 mPa·s, and the mass percentage of hydrogen is 0.02%-0.5%.

6. The liquid silicone foam according to claim 5, characterized in that: The mass ratio of the mixed vinyl silicone oil, the mixed hydroxy silicone oil and the hydrogen-containing silicone oil 1 is (15-35):(1-3):

1.

7. The liquid silicone foam according to claim 1, characterized in that The platinum catalyst is one or more of a platinum catalyst coordinated with tetrahydrofuran, a chloroplatinic acid catalyst coordinated with isopropyl alcohol, a chloroplatinic acid-diethyl phthalate complex solution, and a platinum complex containing a vinylsiloxane ligand, and the amount of the platinum catalyst added is 0.1 wt% to 3 wt% of the total mass of the raw materials; and / or, The inhibitor is one or more of 2-methyl-3-alkyn-2-ol, 3-methyl-1-alkyn-3-ol, ethynylcyclohexanol, diallyl maleate, and diethyl fumarate, and the added amount of the inhibitor is 0.01 wt% to 0.1 wt% of the total mass of the raw materials.

8. A method for preparing the liquid silicone foam according to any one of claims 1 to 7, characterized in that: The steps include: S1, mixing part of the mixed vinyl silicone oil, part of the polyvinyl silicone oil, part of the filler, the mixed hydroxy silicone oil and the catalyst to obtain a first material; S2, uniformly mixing the remaining mixed vinyl silicone oil, the remaining polyvinyl silicone oil, the remaining filler, the mixed hydrogenated silicone oil and the inhibitor to obtain a second material; S3. Mix the first material and the second material and apply them on the surface of the substrate, and perform low-temperature vulcanization and high-temperature vulcanization treatment in sequence to obtain the liquid silicone foam.

9. The preparation method according to claim 8, characterized in that In step S1 and step S2, the mixing speed is 300 rpm to 500 rpm, and the mixing time is 2 h to 5 h; and / or, In step S3, the temperature of the low-temperature vulcanization is 50°C to 90°C, and the time of the low-temperature vulcanization is 1 min to 10 min; the temperature of the high-temperature vulcanization is 150°C to 200°C, and the time of the high-temperature vulcanization is 10 min to 40 min.

10. Use of the liquid silicone foam according to any one of claims 1 to 7 or the liquid silicone foam prepared by the preparation method according to claim 8 or 9 as a buffer material for a circuit board.

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