A silicone rubber composition and a method for producing the same

Abstract

The application relates to the technical field of high polymer materials, and discloses a silicone rubber composition and a preparation method thereof, the silicone rubber composition comprising: 100 parts of methylphenyl vinyl silicone rubber crude rubber; 30-60 parts of fumed white carbon black; 4-10 parts of a structure control agent; 3-5 parts of phenyl silicone resin; 5-7 parts of platinum gold flame retardant; and 0.05-0.15 parts of nano zinc oxide; wherein the methylphenyl vinyl silicone rubber crude rubber is a base polymer, the proportions of the other components are based on the base polymer, the phenyl content of the methylphenyl vinyl silicone rubber crude rubber is 6-20%, the vinyl content is 0.05-2%, and the molecular weight is 0.6-0.75 million. Compared with the existing product, the silicone rubber composition adopts a new formula, the phenyl content is reduced, the cost is controlled, the flame retardation can reach the V0 level through testing, the light transmittance reaches 90%, the cost is low, and the product has good mechanical properties.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to a silicone rubber composition and its preparation method. Background Technology

[0002] Transparent flame-retardant silicone rubber possesses excellent optical properties, providing flame-retardant protection without affecting light transmission. This gives it a unique advantage in fields requiring transparency, such as electronic displays and optical instruments. While silicone rubber itself has some flame-retardant properties, flame retardants need to be added to enhance its flame-retardant performance to meet higher standards. By employing appropriate flame-retardant strategies, transparent flame-retardant silicone rubber can self-extinguish or delay combustion upon contact with a fire source, reducing the occurrence and spread of fires, thus providing crucial protection for the safe operation of precision equipment.

[0003] Among existing technical solutions, the main methods for improving the flame retardancy of silicone rubber include adding flame retardants, polymer modification, nanotechnology, and crosslinking technology. Specifically:

[0004] Adding flame retardants is a common method to improve the flame retardant properties of silicone rubber. Suitable flame retardants, such as halogenated, phosphorus-based, nitrogen-based, and inorganic flame retardants, can be selected and added to the silicone rubber through physical blending or chemical reaction. Different types of flame retardants have different flame retardant mechanisms and effects, and the selection must be based on specific application requirements.

[0005] Polymer modification involves surface modification of silicone rubber, which is also a method to improve its flame retardant properties. Surface treatment of silicone rubber with silane coupling agents can improve its compatibility and bonding with flame retardants, thereby enhancing the flame retardant effect. Modification of polymers, such as introducing phenyl groups, can also improve the flame retardant effect.

[0006] Nanotechnology enhances flame retardancy and transparency through nanofillers.

[0007] Crosslinking technology optimizes the crosslinking density and crosslinking network structure, which can improve the thermal stability and char-forming properties of materials, thereby enhancing their intrinsic flame retardant properties.

[0008] Patent application document CN103059574A describes a transparent flame-retardant silicone rubber made primarily from methylphenyl vinyl silicone rubber raw material with a phenyl content of 20-40%, compounded with reinforcing agents, vulcanizing agents, and structuring control agents. It also provides a transparent silicone mask for LED full-color screens that simultaneously satisfies the requirements of flame retardancy, transparency, and light transmittance. In principle, the higher the phenyl content, the better the flame retardant effect, but the cost also increases accordingly.

[0009] Patent application CN109504091A describes a low-smoke, high-transmittance flame-retardant silicone rubber, made primarily of methyl vinyl silicone rubber, with nano-aluminum hydroxide, nano-titanium dioxide, and fumed silica as fillers. Here, "high transmittance" refers to smoke transmittance; the ratio of light intensity transmitted through smoke to incident light intensity is related to smoke density and is primarily influenced by the smoke.

[0010] Patent application CN114316605A discloses a method of obtaining transparent flame-retardant silicone rubber by adding 0.5-4 parts of platinum catalyst and 0.05-2 parts of flame-retardant synergist to silicone rubber. The flame-retardant synergist is a compound of base silicone rubber and flame-retardant material. The flame-retardant material is a phosphite, selected from one or more of tris(2,4-di-tert-butylphenyl) phosphite, bis(2,4-di-tert-butylphenol) pentaerythritol diphosphite, pentaerythritol dioctadecaphosphite, poly(dipropylene glycol) phenyl phosphite, triphenyl phosphite, and diphenyl isooctyl phosphite. This product can achieve a flame retardancy rating of V1, with a light transmittance of approximately 80%. Patent application CN111117187A discloses a high-transparency organosilicon flame-retardant polycarbonate material, in which the organosilicon flame retardant is polysilsesquioxane, used in an amount of 0.05-3 parts. This product achieves a V1 flame retardancy rating and a light transmittance of over 80%. However, silicone flame retardants are expensive and must be used in combination with traditional flame retardants, such as aluminum hydroxide, magnesium hydroxide, phosphorus-based, and nitrogen-based flame retardants, to achieve the desired effect. Although silicone can improve the melt strength of some materials, high addition levels may lead to: increased melt viscosity, making processing difficult; flow marks and surface roughness during injection molding or extrusion; poor mechanical properties, reducing the tensile and flexural strength of the material; affecting toughness and impact performance; unsuitability for applications with high mechanical performance requirements; and even poor long-term stability, making the material prone to aging.

[0011] In summary, existing technologies typically employ polymer modification, the addition of flame retardants, and nanofillers to obtain transparent flame-retardant silicone rubber. However, it is difficult to obtain transparent flame-retardant silicone rubber using traditional methods. The resulting silicone rubber may have poor flame retardancy, insufficient transparency, high cost, or poor mechanical properties, failing to meet market demands. Summary of the Invention

[0012] This invention provides a silicone rubber composition and its preparation method. The prepared silicone rubber can achieve a flame retardancy level of V0 and a light transmittance of 90%. It is low in cost and has good mechanical properties, thus solving the problems mentioned in the background art.

[0013] This invention provides the following technical solution: a silicone rubber composition comprising: 100 parts of methylphenyl vinyl silicone rubber raw rubber; 30-60 parts of fumed silica; 4-10 parts of a structure control agent; 3-5 parts of phenyl silicone resin; 5-7 parts of platinum flame retardant; and 0.05-0.15 parts of nano zinc oxide. The methylphenyl vinyl silicone rubber raw rubber is the base polymer, and the proportions of the other components are based on it. The methylphenyl vinyl silicone rubber raw rubber has a phenyl content of 6-20%, a vinyl content of 0.05-2%, and a molecular weight of 600,000-750,000. The platinum flame retardant is a compound of a platinum catalyst and a nitrogen-containing compound. Compared with existing products, this silicone rubber composition uses a new formulation, reducing the phenyl content and controlling costs. Testing shows that it can achieve a V0 flame retardancy rating, while maintaining a light transmittance of 90%. It is low-cost and has good mechanical properties.

[0014] As an optional embodiment of the silicone rubber composition described in this invention, the methyl phenyl vinyl silicone rubber raw rubber contains 6-10% phenyl groups, 0.1-1.5% vinyl groups, and has a molecular weight of 600,000-700,000. The base polymer is selected as methyl vinyl phenyl silicone rubber raw rubber. The introduction of phenyl groups enhances the rigidity of the molecular chain and the conjugation effect of the aromatic ring, further improving thermal stability, delaying main chain breakage, and making the decomposition process more inclined to form a continuous, dense ceramicized carbon layer. This carbon layer acts as a physical barrier, preventing heat transfer to the substrate, inhibiting the release of combustibles such as volatile small molecules, and isolating oxygen, thereby inhibiting the spread of combustion. Phenyl groups readily undergo carbonization reactions at high temperatures, forming a silicon-carbon-oxygen composite carbon layer, enhancing the graphitization degree and mechanical strength of the carbon layer. During the thermal decomposition of phenyl silicone rubber, carbon dioxide, water vapor, and a small amount of silicon-containing gases are mainly produced. These non-combustible gases can dilute the oxygen concentration and combustible gas concentration in the combustion zone, reducing the combustion reaction rate. Compared to ordinary silicone rubber, the introduction of low phenyl content increases the carbon content, generating more carbon dioxide during combustion, further enhancing the dilution effect. The synergistic effect of low phenyl content and siloxane chains can promote cross-linking, making the carbon layer more stable and less susceptible to damage from the gas flow generated during combustion, thereby enhancing the barrier effect.

[0015] As an optional embodiment of the silicone rubber composition of the present invention, the phenyl silicone resin includes methylphenyl silicone resin and / or phenyl vinyl silicone grease. Preferably, the phenyl silicone resin is phenyl vinyl silicone resin, where the active groups Si-Vi on the resin can undergo co-crosslinking to form an interpenetrating network or semi-interpenetrating network structure, with a viscosity of 2000-20000 cP, a vinyl content of 0.5-5%, and a refractive index of 1.4560-1.5450. Preferably, the viscosity is 5000-20000 cP, and more preferably, the vinyl content is 0.5-3%. This viscosity range ensures good compatibility and processability between the resin and the methylphenyl vinyl silicone raw rubber, with moderate flowability, allowing for thorough and uniform mixing with the raw rubber and preventing phase separation. Low vinyl content results in too few active sites, preventing the resin from forming effective chemical bonds with the base rubber; excessively high content leads to overly dense crosslinking points, introducing significant internal stress, which can easily cause network breakage during high-temperature aging or long-term use, affecting service life. The refractive index is selected to achieve optimal matching with that of methylphenylvinyl silicone raw rubber, resulting in high transparency. It should be noted that phenyl silicone resin is a highly cross-linked, three-dimensional network polymer with a silicon-oxygen bond (Si-O) backbone and phenyl groups as side groups. Its addition not only enhances the flame retardancy of transparent phenyl silicone rubber, but in many cases, it is a more advanced and efficient method than simply adding traditional flame retardants, especially suitable for applications with high requirements for optical and mechanical properties. Its flame-retardant mechanism mainly manifests in the condensed phase. Under high temperature or flame conditions, the organic portion of the phenyl silicone resin decomposes into carbon sources, while the robust inorganic silicon-oxygen backbone (Si-O) is retained. These carbon sources react with the silicon-oxygen backbone at high temperatures, forming a silicon carbide or silicon-oxygen-carbon ceramic layer in situ. This ceramicized carbon layer is dense, robust, and not easily dispersed by flame gas flow, allowing it to function continuously.

[0016] As an optional embodiment of the silicone rubber composition described in this invention, the fumed silica has a specific surface area of ​​200-400 m² / g. A higher specific surface area results in higher transparency of the compound, and commercially available conventional grades are generally suitable. Theoretically, fumed silica with a higher specific surface area has a stronger light scattering suppression potential due to its smaller primary particle size, which helps improve the theoretical limit of transparency of the colloid. However, an excessively high specific surface area means extremely high particle surface energy and strong van der Waals forces, resulting in a very robust aggregate structure that is difficult to depolymerize and uniformly disperse in the silicone rubber matrix using conventional mechanical shearing processes. If fumed silica with a low specific surface area is used, its primary particle size is larger, which, although easy to disperse, cannot meet the requirements for high-transparency products.

[0017] As an optional embodiment of the silicone rubber composition of the present invention, the structure control agent is at least one selected from hydroxyl / alkoxy-containing silanes, hydroxyl / alkoxy-containing oligomeric siloxanes, compounds containing Si-N bonds, and diol compounds. Preferably, it is a compound of diphenylsilanediol, phenyltrimethoxysilane, and hydroxyl silicone oil.

[0018] As an optional embodiment of the silicone rubber composition described in this invention, the nano-zinc oxide has a particle size of 50-500 nm and a whiteness of over 90%. If the particle size of the nano-zinc oxide is too small, it is difficult to disperse and has a high cost; if the particle size is too large, it affects the transparency of the rubber compound. High whiteness is a direct external manifestation of high chemical purity and low metal impurity content, which is beneficial for improving flame retardancy and appearance. The platinum flame retardant includes: 2.5 parts of caster platinum catalyst, 2 parts of benzotriazole, and 100 parts of gas-phase compound, with a platinum content of 500 ppm. It should be noted that platinum complexes promote the rapid formation of the initial char layer in the polymer, but such char layers may have defects such as high porosity and easy breakage. Nano-zinc oxide, through reaction with platinum compounds, such as generating Zn-Pt-O composite oxides or physical filling, embeds itself into the char layer structure, enhancing the density and high-temperature resistance of the char layer and inhibiting the oxidation and volatilization of the char layer at high temperatures. By leveraging the catalytic char formation and free radical regulation capabilities of platinum, combined with the char formation enhancement, barrier, and smoke suppression properties of zinc oxide, a dual flame-retardant synergy is achieved in both the condensed and gas phases.

[0019] A method for preparing a silicone rubber composition, comprising:

[0020] Step 1: Add the raw methyl phenyl vinyl silicone rubber, structure control agent, phenyl silicone resin, and nano zinc oxide to the kneader according to the specified ratio;

[0021] Step 2: Add the fumed silica to the kneader in 3-10 batches, mixing thoroughly after each addition;

[0022] Step 3: Heat the kneader to 130-150℃, vacuum to <-0.07Mpa, and knead for 1-3 hours;

[0023] Step 4: Cool to room temperature, add platinum flame retardant, mix well and discharge to obtain silicone rubber composition.

[0024] The present invention has the following beneficial effects: The silicone rubber composition prepared in this application has been tested and found to achieve a flame retardancy rating of V0 and a light transmittance of up to 90% under the condition of a material thickness of 3 mm. It also has good overall performance in terms of mechanical properties. The use of methyl vinyl phenyl silicone rubber raw rubber with low phenyl content reduces costs and successfully overcomes the technical problem of balancing transparency, flame retardancy, mechanical properties and cost in silicone rubber materials. It is particularly suitable for fields with stringent requirements for safety and optical performance, such as LED packaging, optical sensors, and flexible display materials. Attached Figure Description

[0025] Figure 1 This is a photograph of the silicone rubber composition prepared in Example 1 of this application after combustion;

[0026] Figure 2 This is a SEM image of the silicone rubber composition prepared in Example 1 of this application. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] This application provides a silicone rubber composition and a method for preparing the same, and provides examples of five silicone rubber compositions with different ratios, as well as comparative examples of five silicone rubber compositions with different ratios in the example section. The component ratios and test results of the specific examples and comparative examples are shown in Table 1:

[0029] Table 1

[0030] .

[0031] It should be noted that the preparation methods of Examples 1-5 and Comparative Examples 1-5 are the same, and the specific preparation process is as follows;

[0032] Step 1: Add all components of the formula except for fumed silica and platinum flame retardant into the vacuum kneader according to the specified ratio;

[0033] Step 2: Add the fumed silica from the formula to the vacuum kneader in 7 batches, mixing thoroughly after each addition;

[0034] Step 3: Heat the vacuum kneader to 140℃, evacuate to -0.08Mpa, and knead for 2 hours;

[0035] Step 4: Cool to room temperature, add the platinum flame retardant from the formula, mix well, knead for 30 minutes, and then discharge to obtain the silicone rubber compositions corresponding to Examples 1-5 and Comparative Examples 1-5.

[0036] It should also be noted that the performance test conditions and standards for Examples 1-5 and Comparative Examples 1-5 are as follows:

[0037] The vulcanization conditions are as follows: add 1.0% of the product weight of bis(2,5) vulcanizing agent, first stage vulcanization at 170℃ for 10 min, and second stage vulcanization at 200℃ for 2 hr.

[0038] Hardness test standard: GB / T531, tensile strength test standard: GB / T528, tear strength test standard: GB / T529, light transmittance test standard: GB / T2410, 1mm sheet test, flame retardant test standard: GB / T10707.

[0039] Based on the test results of Examples 1-5 and Comparative Examples 1-5 above, it can be seen that:

[0040] 1. First, comparing Examples 1-5, the silicone rubber compositions prepared in Examples 1-5 meet the requirement of achieving V0 flame retardancy, and the light transmittance is all above 80%, even reaching 90%. They have good flame retardancy and transparency, and good physical properties, which can meet the application requirements of optics, electronics, and electrical appliances.

[0041] 2. The difference between Example 1 and Example 5 lies in the difference in the phenyl content in the methyl phenyl vinyl silicone rubber raw rubber. Example 5 has a higher phenyl content, which significantly improves the light transmittance. However, as the phenyl content increases, the material cost also increases.

[0042] 3. Compared with Examples 1 and 4, Examples 1 and 3 show better light transmittance. This is mainly attributed to the higher specific surface area of ​​fumed silica, which can more effectively reduce the scattering of visible light, thereby improving the transparency of the composite material. However, when the amount of nano-zinc oxide added is high, its particle size distribution and agglomeration tendency lead to enhanced light scattering, resulting in increased haze and adversely affecting the overall optical performance.

[0043] 4. Compared with Example 1, Comparative Example 1 uses methyl vinyl silicone rubber raw material, and the flame retardancy of the prepared silicone rubber cannot meet the V0 requirement. This indicates that the silicone rubber prepared using methyl phenyl vinyl silicone rubber raw material has better flame retardancy.

[0044] 5. Compared with Example 1, Comparative Example 2 reduced the amount of platinum flame retardant used, and the prepared silicone rubber could not meet the flame retardant V0 requirement, indicating that the platinum flame retardant of this application has a significant effect on improving flame retardant performance.

[0045] 6. Compared with Example 1, Comparative Example 3 added an excessive amount of nano zinc oxide. Although the flame retardancy met the V0 level, it could not meet the transparency requirements.

[0046] 7. Compared with Example 1, Comparative Example 4, without the addition of phenyl silicone resin and phenyl silane treatment agent, although the flame retardancy rating of the prepared silicone rubber can reach V0 level, the total burning time of the 5 samples is prolonged and the transparency is slightly reduced, indicating that phenyl silicone resin and phenyl silane treatment agent have a significant effect on improving transparency.

[0047] 8. Compared with Example 1, Comparative Example 5 uses methyl vinyl phenyl silicone rubber raw material with 4% phenyl content. The prepared silicone rubber has a flame retardancy rating of V1 and a slight decrease in transparency.

[0048] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0049] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A silicone rubber composition, characterized in that, By weight, it includes: 100 parts of raw methyl phenyl vinyl silicone rubber; 30-60 parts of fumed silica; 4-10 parts of structure control agent; 3-5 parts of phenyl silicone resin; 5-7 parts platinum flame retardant; 0.05-0.15 parts of nano zinc oxide; The base polymer is methyl phenyl vinyl silicone rubber raw rubber, and the proportions of the other components are based on it. The phenyl content of the methyl phenyl vinyl silicone rubber raw rubber is 6-20%, the vinyl content is 0.05-2%, and the molecular weight is 600,000-750,000. The phenyl silicone resin is phenyl vinyl silicone resin with a viscosity of 2000-20000 cP, a vinyl content of 0.5-5%, and a refractive index of 1.4560-1.5450. The structure control agent includes at least one of diphenylsilanediol or phenyltrimethoxysilane. The platinum flame retardant is prepared from the following raw materials: 2.5 parts platinum catalyst, 2 parts benzotriazole, and 100 parts gas phase compound, with a platinum content of 500 ppm.

2. The silicone rubber composition according to claim 1, characterized in that: The specific surface area of ​​fumed silica is 200-400 m² / g.

3. The silicone rubber composition according to claim 1, characterized in that: The particle size of nano zinc oxide is 50-500nm, and its whiteness is over 90%.

4. The silicone rubber composition according to claim 1, characterized in that: The phenyl content of methyl phenyl vinyl silicone rubber raw rubber is 6-10%, the vinyl content is 0.1-1.5%, and the molecular weight is 600,000-700,000.

5. The silicone rubber composition according to claim 1, characterized in that: The viscosity of phenyl vinyl silicone resin is 5000-20000 cP, and the vinyl content is 0.5-3%.

6. A method for preparing a silicone rubber composition, used to prepare the silicone rubber composition as described in any one of claims 1-5, characterized in that: include: Step 1: Add the raw methyl phenyl vinyl silicone rubber, structure control agent, phenyl silicone resin, and nano zinc oxide into the kneader according to the specified ratio; Step 2: Add the fumed silica to the kneader in 3-10 batches, mixing thoroughly after each addition; Step 3: Heat the kneader to 130-150℃, vacuum to <-0.07Mpa, and knead for 1-3 hours; Step 4: Cool to room temperature, add platinum flame retardant, mix well and discharge to obtain silicone rubber composition.

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