Liquid silicone rubber, and preparation method therefor and use thereof

Abstract

The present invention proposes a liquid silicone rubber, and a preparation method therefor and a use thereof. The liquid silicone rubber provided by the present invention comprises the following components or reaction products of the following components, in parts by mass: 100 parts of vinyl-terminated polydimethylsiloxane, 10-100 parts of a vinyl MQ silicone resin, 0.1-5 parts of an adhesion promoter, 40-200 parts of titanium dioxide, 1-15 parts of polymethylhydrosiloxane, and 0.001-0.5 parts of a reaction inhibitor; and based on the total mass of the liquid silicone rubber, the silicon hydroxyl content in the liquid silicone rubber is less than or equal to 0.07 wt%. The liquid silicone rubber or a cured product thereof according to the present invention has high reflectivity, low thixotropy, high fluidity, high heat resistance and storage stability and requires a relatively simple production process, and thus is suitable for industrial production.

Description

A liquid silicone rubber, its preparation method and application

[0001] Cross-references to related applications

[0002] This invention claims priority to Chinese Patent Application No. 202411446047.0, filed on October 16, 2024, entitled "A Silicone Rubber and a Method for Preparing the Same", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to the field of silicone rubber preparation, specifically to a liquid silicone rubber, its preparation method, and its application. Background Technology

[0004] Silicone rubber is widely used in electronic packaging due to its advantages such as high temperature resistance, good electrical insulation, aging resistance, and chemical stability. It is applied to critical components of electronic devices, including sealing, filling, heat insulation, and heat dissipation, providing crucial support for the performance and reliability of electronic products. When used in high-reliability ceramic-encapsulated LED white-wall packaging, a higher proportion of titanium dioxide is needed to achieve higher reflectivity, thereby increasing the brightness of the LED and preventing light leakage from the sides of the LED chips. Simultaneously, this silicone rubber needs to maintain a low thixotropic property to ensure that the silicone can fully fill the gaps between the chips and achieve better leveling, thus achieving the desired optical effects.

[0005] While adding a higher proportion of titanium dioxide to silicone rubber can improve reflectivity, it also increases the viscosity and thixotropy of the composition. Furthermore, in order to improve the adhesion strength between silicone rubber and substrates and chips, a certain proportion of adhesion promoters are often added during the preparation process. This also introduces some groups that improve thixotropy, thereby increasing the viscosity and thixotropy of the silicone rubber. This seriously affects the flowability of the silicone rubber, resulting in poor leveling in its application.

[0006] Chinese patent document CN110494473B discloses a dispensable chemical composition having a large amount of filler material and a low thixotropic index level. This invention controls the thixotropy of siloxane mixtures by selecting a suitable combination of compositions with specific molecular weight distributions and filler contents.

[0007] Chinese patent document CN117384586A discloses a low thixotropic de-alcoholized silicone sealant, its preparation method and application. The low thixotropic de-alcoholized silicone sealant of this invention has low thixotropy and good storage stability.

[0008] Addition-type silicone adhesives are easy to cure and do not produce small molecule substances. Adding a higher proportion of titanium dioxide can make them suitable for LED packaging with higher reflectivity requirements. However, this also results in higher viscosity and thixotropy, as well as poorer storage stability. Furthermore, in existing technologies, controlling the thixotropy of silicone rubber often sacrifices its high-temperature resistance or reflectivity, thus affecting the application performance of silicone rubber in high-temperature environments.

[0009] Therefore, there is a need in the existing technology for a silicone rubber with high reflectivity, low thixotropy, high fluidity and high temperature resistance, which has good storage stability and will be better applied in LED packaging. Summary of the Invention

[0010] To address the aforementioned problems in the prior art, this invention proposes a liquid silicone rubber, its preparation method, and its applications. The liquid silicone rubber of this invention exhibits excellent high-temperature resistance, UV resistance, and other aging resistance properties, while also possessing improved thixotropic properties.

[0011] In a first aspect, the present invention provides a liquid silicone rubber, which, by mass parts, comprises the following components or the reaction products of the following components: 100 parts vinyl-terminated polydimethylsiloxane; 10 to 100 parts vinyl MQ silicone resin; 0.1 to 5 parts adhesion promoter; 40 to 200 parts titanium dioxide; 1 to 15 parts polymethylhydrosiloxane; 0.001 to 0.5 parts reaction inhibitor;

[0012] Based on the total mass of the liquid silicone rubber, the content of silanol groups in the liquid silicone rubber is less than or equal to 0.07 wt%.

[0013] In this invention, the silanol content refers to the content of hydroxyl groups bonded to silicon.

[0014] This invention discovers that by controlling the silanol content in liquid silicone rubber, particularly the silanol content in vinyl-terminated polydimethylsiloxane and / or vinyl MQ silicone resin, a liquid silicone rubber with low thixotropy can be obtained. This allows for the addition of a large amount of titanium dioxide to improve its reflectivity, thus preparing a liquid silicone rubber with both low thixotropy and high reflectivity. Furthermore, the liquid silicone rubber of this invention, while exhibiting low thixotropy, also possesses excellent aging resistance.

[0015] In a specific embodiment of the present invention, the silanol content in the liquid silicone rubber is 0.001 wt% to 0.07 wt% based on the total mass of the liquid silicone rubber. For example, the silanol content in the liquid silicone rubber can be 0.001 wt%, 0.002 wt%, 0.005 wt%, 0.008 wt%, 0.01 wt%, 0.011 wt%, 0.012 wt%, 0.013 wt%, 0.014 wt%, 0.015 wt%, 0.018 wt%, 0.02 wt%, 0.025 wt%, 0.028 wt%, 0.03 wt%, 0.035 wt%, 0.04 wt%, 0.045 wt%, 0.05 wt%, 0.055 wt%, 0.06 wt%, 0.065 wt%, 0.07 wt%, or a range thereof, based on the total mass of the liquid silicone rubber. Preferably, the hydroxyl content in the liquid silicone rubber can be 0.001 wt% to 0.02 wt% based on the total mass of the liquid silicone rubber.

[0016] In this invention, in the term "vinyl MQ silicone resin", M represents the monofunctional siloxane unit R3SiO. 1 / 2 Q represents the tetrafunctional siloxane chain segment SiO. 4 / 2 Each of the three substituents R is independently selected from a hydrocarbon group, preferably a C1-C3 alkyl group or a C2-C5 alkenyl group. Examples of C1-C3 alkyl groups include, but are not limited to, methyl and ethyl groups. Examples of C2-C5 alkenyl groups include, but are not limited to, vinyl or allyl groups.

[0017] In this invention, the R values ​​between different segments in a vinyl MQ silicone resin can be the same or different, and the vinyl MQ silicone resin includes siloxane segments containing vinyl groups.

[0018] In a specific embodiment of the present invention, the silanol groups in the liquid silicone rubber mainly originate from vinyl MQ silicone resin and / or vinyl-terminated polydimethylsiloxane. Based on the total mass of vinyl MQ silicone resin and vinyl-terminated polydimethylsiloxane, the total silanol content in vinyl MQ silicone resin and vinyl-terminated polydimethylsiloxane is 0.001 wt% to 0.07 wt%. For example, based on the total mass of vinyl MQ silicone resin and vinyl-terminated polydimethylsiloxane, the silanol content in vinyl MQ silicone resin and vinyl-terminated polydimethylsiloxane can be 0.001 wt%, 0.002 wt%, 0.005 wt%, 0.008 wt%, 0.01 wt%, 0.011 wt%, 0.012 wt%, 0.013 wt%, 0.014 wt%, 0.015 wt%, 0.018 wt%, 0.02 wt%, 0.025 wt%, 0.028 wt%, 0.03 wt%, 0.035 wt%, 0.04 wt%, 0.045 wt%, 0.05 wt%, 0.055 wt%, 0.06 wt%, 0.065 wt%, 0.07 wt%, or a range thereof. Preferably, based on the total mass of vinyl MQ silicone resin and vinyl-terminated polydimethylsiloxane, the silanol content in vinyl MQ silicone resin and vinyl-terminated polydimethylsiloxane is 0.001 wt% to 0.03 wt%.

[0019] In a specific embodiment of the present invention, the silanol content in the vinyl MQ silicone resin is less than or equal to 0.05 wt%. For example, the silanol content in the vinyl MQ silicone resin can be 0.001 wt%, 0.002 wt%, 0.005 wt%, 0.008 wt%, 0.01 wt%, 0.011 wt%, 0.012 wt%, 0.013 wt%, 0.014 wt%, 0.015 wt%, 0.018 wt%, 0.02 wt%, 0.025 wt%, 0.03 wt%, 0.035 wt%, 0.04 wt%, 0.045 wt%, 0.05 wt%, or a range thereof. Preferably, the silanol content in the vinyl MQ silicone resin is 0.005 wt% to 0.05 wt%.

[0020] In a specific embodiment of the present invention, the silanol content in the vinyl-terminated polydimethylsiloxane is less than or equal to 0.05 wt%. For example, the silanol content in the vinyl-terminated polydimethylsiloxane is 0.001 wt%, 0.002 wt%, 0.005 wt%, 0.008 wt%, 0.01 wt%, 0.011 wt%, 0.012 wt%, 0.013 wt%, 0.014 wt%, 0.015 wt%, 0.018 wt%, 0.02 wt%, 0.025 wt%, 0.03 wt%, 0.035 wt%, 0.04 wt%, 0.045 wt%, 0.05 wt%, or a range thereof. Preferably, the silanol content in the vinyl-terminated polydimethylsiloxane is 0.005 wt% to 0.02 wt%.

[0021] The vinyl MQ silicone resin in this invention is a vinyl MQ silicone resin treated with silazane or chlorosilane. In this invention, by treating the vinyl MQ silicone resin with silazane or chlorosilane, the content of silanol groups in the vinyl MQ silicone resin can be reduced.

[0022] The steps for treating vinyl MQ silicone resin with silazane or chlorosilane include: mixing vinyl MQ silicone resin with a solvent, adding silazane or chlorosilane, heating under reflux, drying, pulverizing, and then obtaining vinyl MQ silicone resin treated with silazane or chlorosilane.

[0023] In a specific embodiment of the present invention, the temperature of the heating reflux is 140-145°C, and the time is 1-2 hours.

[0024] Specifically, xylene is used as a solvent in the heating and reflux process.

[0025] In a specific embodiment of the present invention, the amount of silazane or chlorosilane used is 5% to 10% of the mass of vinyl MQ silicone resin.

[0026] In a specific embodiment of the present invention, the vinyl content in the vinyl MQ silicone resin is 0.5–2 mmol / g. For example, the vinyl content in the vinyl MQ silicone resin can be 0.5 mmol / g, 0.6 mmol / g, 0.7 mmol / g, 0.8 mmol / g, 1 mmol / g, 1.2 mmol / g, 1.5 mmol / g, 1.7 mmol / g, 2 mmol / g, or a range thereof. Preferably, the vinyl content in the vinyl MQ silicone resin is 0.7–1.7 mmol / g.

[0027] The vinyl content in vinyl MQ silicone resin is generally determined based on the amount of material fed during synthesis. First, calculate the amount of substance containing the vinyl M-unit, and then divide it by the total mass of the MQ silicone resin to obtain the vinyl content of the vinyl MQ silicone resin, in mmol / g.

[0028] For example, in the synthesis of vinyl MQ silicone resin using the tetraethyl orthosilicate method, the vinyl content is calculated using hexamethyldisiloxane (x g), tetramethyldivinyldisiloxane (y g), and tetraethyl orthosilicate (z g) as follows: (y / 93) ÷ (x + y + z × 0.288), where 93 is half the molar mass of tetramethyldivinyldisiloxane, and 0.288 is the molar mass of SiO₂. 4 / 2 The mass fraction in tetraethyl orthosilicate is because the four ethoxy groups in tetraethyl orthosilicate will hydrolyze, and the Q-unit will only contain SiO. 4 / 2 .

[0029] The general method for detecting the vinyl content in vinyl MQ silicone resin is iodometric titration: excess iodine bromide reacts with vinyl in an addition reaction, then excess potassium iodide reacts with unreacted potassium bromide to produce elemental iodine, which is then titrated with sodium thiosulfate standard solution, and finally the vinyl content is calculated.

[0030] In a specific embodiment of the present invention, the molar ratio (M / Q) of M to Q in the vinyl MQ silicone resin is 0.7 to 1.2. For example, the molar ratio of M to Q in the vinyl MQ silicone resin can be 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, or a range thereof. Preferably, the molar ratio of M to Q in the vinyl MQ silicone resin is 0.8 to 1.1.

[0031] The synthesis of vinyl MQ silicone resin is relatively stable. The molar ratio of M / Q is generally determined by the amount of raw materials fed. The molar ratio of M / Q can be obtained by calculating the amount of substance of M-chain segments and Q-chain segments.

[0032] For example, in the synthesis of vinyl MQ silicone resin using the tetraethyl orthosilicate method, the amount of substance of the M unit is the sum of the amount of substance of hexamethyldisiloxane and half the amount of substance of tetramethyldivinyldisiloxane, and the amount of substance of the Q unit is the amount of substance of tetraethyl orthosilicate.

[0033] In a specific embodiment of the present invention, the amount of vinyl MQ silicone resin can be 20 to 80 parts by weight.

[0034] This invention allows the prepared liquid silicone rubber to have suitable hardness, strength, and other properties after curing by adjusting the amount of vinyl MQ silicone resin added to the liquid silicone rubber and the vinyl content in the vinyl MQ silicone resin.

[0035] In a specific embodiment of the present invention, at a temperature of 25°C, the dynamic viscosity of the vinyl-terminated polydimethylsiloxane is 200–50000 mPa·s. For example, the dynamic viscosity of the vinyl-terminated polydimethylsiloxane can be 200 mPa·s, 300 mPa·s, 500 mPa·s, 800 mPa·s, 1000 mPa·s, 1500 mPa·s, 2000 mPa·s, 2500 mPa·s, 3000 mPa·s, 3500 mPa·s, 4000 mPa·s, 4… The dynamic viscosity of the vinyl-terminated polydimethylsiloxane is within the range of 500 mPa·s, 5000 mPa·s, 6000 mPa·s, 7000 mPa·s, 8000 mPa·s, 9000 mPa·s, 10000 mPa·s, 12000 mPa·s, 15000 mPa·s, 18000 mPa·s, 20000 mPa·s, 25000 mPa·s, 30000 mPa·s, 35000 mPa·s, 40000 mPa·s, 45000 mPa·s, 50000 mPa·s, or a combination thereof. Preferably, at a temperature of 25°C, the dynamic viscosity of the vinyl-terminated polydimethylsiloxane is 500–20000 mPa·s.

[0036] This invention controls the viscosity of the prepared liquid silicone rubber by limiting the viscosity of the vinyl-terminated polydimethylsiloxane.

[0037] In a specific embodiment of the present invention, the silane content of the polymethylhydrosiloxane is 0.6 wt% to 1.6 wt%. For example, the silane content of the polymethylhydrosiloxane is 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1.0 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, or a range thereof. Preferably, the silane content of the polymethylhydrosiloxane is 0.8 wt% to 1.4 wt%.

[0038] In this invention, the silane content refers to the content of hydrogen bonded to silicon.

[0039] This invention determines the amount of polymethylhydrosiloxane added and the silane content of polymethylhydrosiloxane based on the total vinyl content of vinyl-terminated polydimethylsiloxane and vinyl-terminated polydimethylsiloxane. This invention controls the molar ratio of silane to vinyl to be between 1.5 and 2.5 to ensure that the prepared liquid silicone rubber has suitable hardness after curing.

[0040] At a temperature of 25°C, the dynamic viscosity of polymethylhydrosiloxane is 5–30 mPa·s. For example, the dynamic viscosity of polymethylhydrosiloxane can be within the range of 5 mPa·s, 6 mPa·s, 8 mPa·s, 10 mPa·s, 12 mPa·s, 15 mPa·s, 18 mPa·s, 20 mPa·s, 22 mPa·s, 25 mPa·s, 28 mPa·s, 30 mPa·s, or combinations thereof. Preferably, the dynamic viscosity of polymethylhydrosiloxane is 8–30 mPa·s.

[0041] In a specific embodiment of the present invention, the amount of reaction inhibitor added can be 0.01 to 0.1 parts by weight. For example, the amount of reaction inhibitor added can be 0.01 parts, 0.02 parts, 0.03 parts, 0.04 parts, 0.05 parts, 0.06 parts, 0.08 parts, 0.1 parts, or a range thereof, by weight.

[0042] In a specific embodiment of the present invention, the reaction inhibitor is selected from at least one of phosphorus-containing compounds, nitrogen-containing compounds, vinylsilanes, alkynyl alcohols, and maleic esters.

[0043] Specifically, the phosphorus-containing compound is preferably triphenylphosphine.

[0044] The nitrogen-containing compound is preferably one or a combination of two or more of tributylamine, tetramethylethylenediamine, and benzotriazole.

[0045] Vinylsilane is preferably 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane.

[0046] The preferred alkynol compounds are one or a combination of two or more of 1-ethynylcyclohexanol, 3,5-dimethyl-1-hexyn-3-ol, and 3-methylbutynol.

[0047] Maleate esters are preferably dimethyl maleate.

[0048] Preferably, the reaction inhibitor is an alkynol compound.

[0049] More preferably, the reaction inhibitor is one or a combination of two or more of 1-ethynylcyclohexanol, 3,5-dimethyl-1-hexyn-3-ol, and 3-methylbutynol.

[0050] This invention, by limiting the amount and composition of the reaction inhibitor, enables the prepared liquid silicone rubber to have good operating time and storage stability.

[0051] In this invention, the amount of adhesion accelerator added is 0.5 to 2 parts by weight. If the amount of adhesion accelerator added is too small, it will affect the adhesion between the liquid silicone rubber and the substrate; if the amount added is too large, it will reduce the tensile strength of the liquid silicone rubber or its cured product.

[0052] In specific embodiments of the present invention, the adhesion promoter is selected from one or more of silane coupling agents or their semi-hydrolyzed derivatives. The addition of a silane coupling agent or its semi-hydrolyzed derivative as an adhesion promoter to the liquid silicone rubber of the present invention improves the adhesion between the liquid silicone rubber and the substrate. Therefore, the liquid silicone rubber provided by the present invention, in addition to having high reflectivity, low thixotropy, and high fluidity, also possesses excellent adhesion.

[0053] Preferably, examples of the adhesion promoters in this invention include, but are not limited to, one or more combinations of vinyltrimethoxysilane, vinyltriethoxysilane, 3-(2,3-epoxypropoxy)propyltrimethoxysilane, 3-(2,3-epoxypropoxy)propyltriethoxysilane, acryloyloxypropyltrimethoxysilane, acryloyloxypropyltriethoxysilane, methacryloxypropyltrimethoxysilane, methacryloxypropyltriethoxysilane, mercaptopropyltrimethoxysilane, mercaptopropyltriethoxysilane, isocyanate-propyltrimethoxysilane, isocyanate-propyltriethoxysilane, or combinations of hydrolysis or hemihydrolysis products of the above adhesion promoters.

[0054] More preferably, the adhesion promoter is one or a combination of two or more of vinyltrimethoxysilane, vinyltriethoxysilane, acryloyloxypropyltrimethoxysilane, acryloyloxypropyltriethoxysilane, methacryloyloxypropyltrimethoxysilane, or a combination of the hydrolysis or semi-hydrolysis products of the above adhesion promoters.

[0055] In this invention, the amount of titanium dioxide added is 50 to 150 parts by weight. If too little titanium dioxide is added, the reflectivity of the prepared liquid silicone rubber will be low, thus affecting the brightness of the encapsulated LED light. Conversely, if too much titanium dioxide is added, the viscosity of the prepared liquid silicone rubber will be high, which is not conducive to practical use. For example, the amount of titanium dioxide added can be 50 parts, 80 parts, 100 parts, 120 parts, 150 parts by weight, or a range thereof.

[0056] Examples of titanium dioxide in this invention include, but are not limited to, Chemours R103, R104, R960, KRONOS2220, KRONOS2222, Ishihara R-930, R-980, and other titanium dioxide of similar specifications.

[0057] In a specific embodiment of the present invention, the liquid silicone rubber comprises, by weight parts, the following components or the reaction products of the following components: 100 parts vinyl-terminated polydimethylsiloxane; 20-80 parts vinyl MQ silicone resin; 0.5-2 parts adhesion promoter; 50-150 parts titanium dioxide; 4-15 parts polymethylhydrosiloxane; and 0.01-0.5 parts reaction inhibitor.

[0058] In a specific embodiment of the present invention, the temperature is 25°C and the shear rate is 20s. -1 At this temperature, the shear viscosity of liquid silicone rubber is 3000–5500 mPa·s; at 25°C, the ratio of shear rates is 1 s⁻¹. -1 / 10s -1 At that time, the thixotropic index of the liquid silicone rubber was 1.0 to 1.5; under a wavelength of 450 nm, the reflectivity of the cured liquid silicone rubber product was greater than or equal to 98%, preferably 98% to 99.95%.

[0059] Preferably, the temperature is 25°C and the shear rate is 20s. -1 At that time, the shear viscosity of liquid silicone rubber can be 3000 mPa·s, 3500 mPa·s, 4000 mPa·s, 4500 mPa·s, 5000 mPa·s, or 5500 mPa·s.

[0060] Preferably, at a temperature of 25°C, the ratio of shear rates is 1 s. -1 / 10s -1 At that time, the thixotropic index of liquid silicone rubber was 1.0, 1.1, 1.2, 1.3, 1.4, and 1.5.

[0061] Preferably, the reflectance of the liquid silicone rubber cured product is 98%, 98.3%, 98.5%, 99%, 99.3%, 99.5%, 99.8%, and 99.95% under a wavelength of 450 nm.

[0062] In a second aspect, the present invention provides a method for preparing liquid silicone rubber according to the first aspect of the present invention, comprising the following steps: in the presence of a catalyst, mixing a mixture of vinyl-terminated polydimethylsiloxane and vinyl MQ silicone resin, an adhesion promoter, titanium dioxide, polymethylhydrosiloxane, and a reaction inhibitor to obtain liquid silicone rubber, wherein the vinyl MQ silicone resin is a vinyl MQ silicone resin treated with silazane or chlorosilane.

[0063] In a specific embodiment of the present invention, the step of treating vinyl MQ silicone resin with silazane or chlorosilane includes: mixing vinyl MQ silicone resin with a solvent, adding silazane or chlorosilane, heating under reflux, drying, pulverizing, and then obtaining vinyl MQ silicone resin treated with silazane or chlorosilane.

[0064] In a specific embodiment of the present invention, the temperature of the heating reflux is 140-145°C, and the time is 1-2 hours.

[0065] Specifically, xylene is used as a solvent in the heating and reflux process.

[0066] In a specific embodiment of the present invention, the amount of silazane or chlorosilane used is 5% to 10% of the mass of vinyl MQ silicone resin.

[0067] In a specific embodiment of the present invention, the catalyst contains any one of the noble metals platinum, rhodium, and palladium.

[0068] Preferably, the catalyst is selected from any one of platinum complexes, rhodium complexes, and palladium complexes.

[0069] Preferably, the platinum complex is selected from any one of platinum-olefin complexes, platinum-vinylsiloxane complexes, platinum-vinylsilane complexes, platinum-ketone complexes, and platinum-phosphine complexes.

[0070] Preferably, the rhodium complex is selected from any one of rhodium-phosphine complexes and rhodium-sulfur compound complexes;

[0071] Preferably, the palladium complex is a palladium-phosphine complex.

[0072] More preferably, the catalyst is a complex of platinum and vinylsiloxane.

[0073] Specifically, the catalyst is a cassiterite catalyst.

[0074] In specific embodiments of the present invention, the amount of catalyst, based on the precious metal in the catalyst, such as platinum, is 0.1 to 100 ppm of the total mass of the liquid silicone rubber. For example, the amount of catalyst, based on the precious metal in the catalyst, is within the range of 0.1 ppm, 0.2 ppm, 0.5 ppm, 0.8 ppm, 1 ppm, 1.5 ppm, 2 ppm, 2.5 ppm, 3 ppm, 3.5 ppm, 4 ppm, 4.5 ppm, 5 ppm, 6 ppm, 7 ppm, 8 ppm, 9 ppm, 10 ppm, 12 ppm, 15 ppm, 18 ppm, 20 ppm, 25 ppm, 30 ppm, 35 ppm, 40 ppm, 45 ppm, 50 ppm, 60 ppm, 70 ppm, 80 ppm, 90 ppm, 100 ppm, or a combination thereof, based on the total mass of the liquid silicone rubber. Preferably, the amount of catalyst, based on the precious metal in the catalyst, such as platinum, is 0.5 to 50 ppm of the total mass of the liquid silicone rubber.

[0075] Insufficient catalyst addition affects the curing of liquid silicone rubber, while excessive addition leads to yellowing of the cured product, thereby reducing the reflectivity of the cured liquid silicone rubber product.

[0076] In a specific embodiment of the present invention, the mixture of vinyl-terminated polydimethylsiloxane and vinyl MQ silicone resin is prepared by mixing vinyl-terminated polydimethylsiloxane and vinyl MQ silicone resin at 40-100°C for 0.5-1 hour.

[0077] Preferably, the mixture of vinyl-terminated polydimethylsiloxane and vinyl MQ silicone resin, adhesive accelerator, titanium dioxide, polymethylhydrosiloxane, and reaction inhibitor is mixed for 0.5 to 1 hour.

[0078] Thirdly, the present invention provides an application of liquid silicone rubber prepared by the preparation method provided in the first aspect of the present invention or the second aspect of the present invention in automotive-grade high-reflectivity LED packaging.

[0079] In this invention, "high reflectivity" in high reflectivity LED packaging refers to the reflectivity of the LED packaging material reaching over 90%, for example 90-99.8%, when measured with a spectrophotometer at a wavelength of 450nm.

[0080] Specifically, the liquid silicone rubber of this invention is centrifuged and degassed using a vacuum planetary mixer, then coated onto a substrate with the chip fixed on it. After the silicone rubber is leveled, it is cured at 150°C for 3 hours. After cutting, automotive-grade LED beads suitable for high reflectivity requirements can be obtained.

[0081] Fourthly, an LED bead includes a cured product of liquid silicone rubber provided in the first aspect of the present invention or a cured product of liquid silicone rubber prepared by the preparation method provided in the second aspect of the present invention.

[0082] An LED lamp bead includes: a chip, a bracket, a wire, a die bond adhesive, and an encapsulation material. The encapsulation material includes a cured product of liquid silicone rubber provided in the first aspect of the present invention or a cured product of liquid silicone rubber prepared by the preparation method provided in the second aspect of the present invention.

[0083] In this invention, the defined dosage, unless otherwise specified, generally refers to parts by weight.

[0084] Compared with the prior art, the present invention has the following beneficial effects.

[0085] The liquid silicone rubber or its cured product of the present invention has high reflectivity, low thixotropy, high fluidity, high heat resistance and UV resistance.

[0086] This invention provides a method for preparing liquid silicone rubber, which enables the prepared liquid silicone rubber or its cured product to have excellent heat resistance and UV resistance while ensuring high reflectivity, low thixotropy, and high fluidity. Detailed Implementation

[0087] The present invention will be further described below with reference to specific embodiments, but this does not constitute any limitation on the present invention.

[0088] All raw materials used in the embodiments of this invention are commercially available.

[0089] Vinyl MQ silicone treatment

[0090] MQ1: A vinyl MQ silicone resin with an M / Q (molecular ratio of M to Q) of 0.8, a vinyl content of 1.0 mmol / g, a silanol content of 0.36 wt%, and a number average molecular weight of 5600 was treated with silazane. The treatment method was as follows: 100 g of the above vinyl MQ silicone resin was first dissolved in 100 mL of xylene in a three-necked flask to form a solution. Then, hexamethyldisilazane, which was 10% of the mass of the above MQ silicone resin, was added dropwise to the solution. The solution was heated to 140 °C and refluxed at 140 °C for 1 hour to allow the residual silanol in the vinyl MQ silicone resin to react fully with the silazane. Then, it was directly dried into powder in a centrifugal spray dryer with an inlet temperature of 140 °C. The silanol content was measured to be 0.03 wt%.

[0091] MQ2, a vinyl MQ silicone resin with an M / Q (molecular ratio of M to Q) of 1.0, a vinyl content of 1.5 mmol / g, a silanol content of 0.51 wt%, and a number average molecular weight of 3200, was treated with silazane. The treatment method was as follows: 100 g of the above vinyl MQ silicone resin was first dissolved in 100 mL of xylene in a three-necked flask to form a solution. Then, hexamethyldisilazane, at 10% of the mass of the above MQ silicone resin, was added dropwise to the solution. The solution was heated to 140 °C and refluxed at 140 °C for 1 hour to allow the residual silanol in the vinyl MQ silicone resin to react fully with the silazane. Then, it was directly dried into powder in a centrifugal spray dryer with an inlet temperature of 140 °C. The silanol content was measured to be 0.04 wt%.

[0092] MQ3 is a vinyl MQ silicone resin with an M / Q ratio of 0.8, a vinyl content of 1.0 mmol / g, a silanol content of 0.36 wt%, and a number average molecular weight of 5600, which is untreated MQ1.

[0093] The method for testing the mass content of silanol groups in this invention is as follows:

[0094] First, hydroxyl silicone oil is silanized with phenyldimethylchlorosilane to obtain a crude standard sample. Then, the crude sample is separated by column chromatography to obtain a pure standard sample. Next, the standard sample is analyzed by GPC-UV and 1H NMR to calculate the phenyl content. Then, a series of concentration standard samples are prepared and analyzed by GPC-UV. A standard working curve is constructed by comparing peak area with phenyl concentration. Finally, the processed sample, including the processed vinyl MQ silicone resin or the processed terminal vinyl polymethylsiloxane, is dissolved in n-hexane, and phenyldimethylchlorosilane is added and reacted fully at room temperature. After filtration, GPC-UV analysis is performed directly, and the silanol content is calculated from the standard curve.

[0095] Vi-PDMS1, a vinyl-terminated polydimethylsiloxane, has a dynamic viscosity of 1000 mPa·s and a silanol content of 0.02 wt%.

[0096] Vi-PDMS2, a vinyl-terminated polydimethylsiloxane, has a dynamic viscosity of 3000 mPa·s and a silanol content of 0.02 wt%.

[0097] Vi-PDMS3, a vinyl-terminated polydimethylsiloxane, has a dynamic viscosity of 5000 mPa·s and a silanol content of 0.02 wt%.

[0098] PMHS, polymethylhydrosiloxane, has a hydrogen content of 1.2 wt% and a dynamic viscosity of 20 mPa·s.

[0099] Titanium dioxide, rutile titanium dioxide prepared by the chlorination process, Chemours R-104.

[0100] The catalyst used is a caster catalyst with a platinum content of 0.5 wt%, manufactured by Shanghai Vivo Chemical Co., Ltd.

[0101] Test methods

[0102] (1) Shear viscosity, thixotropic index

[0103] After the prepared liquid silicone rubber was stirred evenly and degassed under vacuum, its properties at a shear rate of 1 s⁻¹ were measured using an MCR92 rheometer at 25°C. -1 10s -1 and 20s -1 The shear viscosity at 20s is taken as the value. -1 The data at that time is the shear viscosity of the sample, 1s. -1 / 10s -1 The data represents the thixotropic index of the sample.

[0104] (2) Hardness

[0105] After vacuum degassing the prepared liquid silicone rubber, it was poured into a 20×15×10mm PTFE mold and cured at 150℃ for 3 hours to form a 10mm thick sample. The hardness of the cured sample was measured using a Shore A rubber hardness tester according to the test method specified in the national standard GB / T 531.1-2008.

[0106] (3) Tensile strength and elongation at break

[0107] After the prepared liquid silicone rubber was stirred evenly and degassed under vacuum, it was poured into a 65×55×1mm PTFE mold and cured at 150℃ for 3 hours to form a 1mm thick sample. According to the test method specified in the national standard GB / T 528-2009, the cured sample was cut into specimens of the specified size, and the tensile strength and elongation at break of the specimens were determined using a universal testing machine.

[0108] (4) Reflectivity

[0109] First, the liquid silicone rubber was cured at 150℃ for 3 hours to form a 1mm thick sample, and then its reflectance at a wavelength of 450nm was measured using a spectrophotometer.

[0110] Example 1

[0111] 15 parts by weight of MQ1 and 100 parts by weight of Vi-PDMS3 were added to a beaker and heated to 100°C. The mixture was then mechanically stirred at 100 rpm for 1 hour. Next, 100 parts by weight of titanium dioxide, 4 parts by weight of PMHS, 2 parts by weight of the adhesion promoter 3-(2,3-epoxypropoxy)propyltriethoxysilane, 0.1 parts by weight of the reaction inhibitor 1-ethynylcyclohexanol, and 7 ppm (based on platinum mass) of Castrol catalyst (based on the total mass of the liquid silicone rubber raw materials) were added. After manual stirring for 10 minutes, the mixture was ground three times using a three-roll mill at a feed roller gap of 30 μm, a discharge roller gap of 10 μm, and a roller speed of 200 rpm. Vacuum degassing was then performed to obtain liquid silicone rubber. The silanol content in the liquid silicone rubber was measured to be 0.011 wt%. The prepared liquid silicone rubber was cured by heating at 150°C for 3 hours to obtain cured silicone rubber.

[0112] Example 2

[0113] 30 parts by weight of MQ1 and 100 parts by weight of Vi-PDMS1 were added to a beaker and heated to 100°C. The mixture was then mechanically stirred at 100 rpm for 1 hour. Next, 100 parts by weight of titanium dioxide, 7 parts by weight of PMHS, 2 parts by weight of the adhesion promoter 3-(2,3-epoxypropoxy)propyltriethoxysilane, 0.1 parts by weight of the reaction inhibitor 1-ethynylcyclohexanol, and 7 ppm (based on platinum mass) of Castrol catalyst (based on the total mass of the liquid silicone rubber raw materials) were added. After manual stirring for 10 minutes, the mixture was ground three times using a three-roll mill at a feed roller gap of 30 μm, a discharge roller gap of 10 μm, and a roller speed of 200 rpm. Vacuum degassing was then performed to obtain liquid silicone rubber. The silanol content in the liquid silicone rubber was measured to be 0.012 wt%. The prepared liquid silicone rubber was cured by heating at 150°C for 3 hours to obtain cured silicone rubber.

[0114] Example 3

[0115] 50 parts by weight of MQ2 and 100 parts by weight of Vi-PDMS2 were added to a beaker and heated to 100°C. The mixture was then mechanically stirred at 100 rpm for 1 hour. Next, 100 parts by weight of titanium dioxide, 14 parts by weight of PMHS, 2 parts by weight of the adhesion promoter 3-(2,3-epoxypropoxy)propyltriethoxysilane, 0.1 parts by weight of the reaction inhibitor 1-ethynylcyclohexanol, and 7 ppm (based on platinum mass) of Castrol catalyst (based on the total mass of the liquid silicone rubber raw materials) were added. After manual stirring for 10 minutes, the mixture was ground three times using a three-roll mill at a feed roller gap of 30 μm, a discharge roller gap of 10 μm, and a roller speed of 200 rpm. Vacuum degassing was then performed to obtain liquid silicone rubber. The silanol content in the liquid silicone rubber was measured to be 0.015 wt%. The prepared liquid silicone rubber was cured by heating at 150°C for 3 hours to obtain cured silicone rubber.

[0116] Comparative Example 1

[0117] 15 parts by weight of MQ3 and 100 parts by weight of Vi-PDMS3 were added to a beaker and heated to 100°C. The mixture was then mechanically stirred at 100 rpm for 1 hour. Next, 100 parts by weight of titanium dioxide, 4 parts by weight of PMHS, 2 parts by weight of the adhesion promoter 3-(2,3-epoxypropoxy)propyltriethoxysilane, 0.1 parts by weight of the reaction inhibitor 1-ethynylcyclohexanol, and 7 ppm (based on platinum mass) of Castrol catalyst (based on the total mass of the liquid silicone rubber raw materials) were added. After manual stirring for 10 minutes, the mixture was ground three times using a three-roll mill at a feed roller gap of 30 μm, a discharge roller gap of 10 μm, and a roller speed of 200 rpm. Vacuum degassing was then performed to obtain liquid silicone rubber. The silanol content in the liquid silicone rubber was measured to be 0.03 wt%. The prepared liquid silicone rubber was cured by heating at 150°C for 3 hours to obtain cured silicone rubber.

[0118] Comparative Example 2

[0119] 30 parts by weight of MQ3, 2 parts by weight of octyltrimethoxysilane, and 100 parts by weight of Vi-PDMS1 were added to a beaker. The mixture was heated to 100°C and mechanically stirred at 100 rpm for 1 hour. Then, 100 parts by weight of titanium dioxide, 7 parts by weight of PMHS, 2 parts by weight of the adhesion promoter 3-(2,3-epoxypropoxy)propyltriethoxysilane, 0.1 parts by weight of the reaction inhibitor 1-ethynylcyclohexanol, and 7 ppm (based on platinum mass) of Castrol catalyst (based on the total mass of the liquid silicone rubber raw materials) were added. After manual stirring for 10 minutes, the mixture was ground three times using a three-roll mill at a feed roller gap of 30 μm, a discharge roller gap of 10 μm, and a roller speed of 200 rpm. Vacuum degassing was then performed to obtain liquid silicone rubber. The silanol content in the liquid silicone rubber was measured to be 0.05 wt%. The prepared liquid silicone rubber was cured by heating at 150°C for 3 hours to obtain cured silicone rubber.

[0120] Comparative Example 3

[0121] 30 parts by weight of MQ3, 2 parts by weight of dodecyltrimethoxysilane, and 100 parts by weight of Vi-PDMS1 were added to a beaker. The mixture was heated to 100°C and mechanically stirred at 100 rpm for 1 hour. Then, 100 parts by weight of titanium dioxide, 7 parts by weight of PMHS, 2 parts by weight of the adhesion promoter 3-(2,3-epoxypropoxy)propyltriethoxysilane, 0.1 parts by weight of the reaction inhibitor 1-ethynylcyclohexanol, and 7 ppm (based on platinum mass) of Castrol catalyst (based on the total mass of the liquid silicone rubber raw materials) were added. After manual stirring for 10 minutes, the mixture was ground three times using a three-roll mill at a feed roller gap of 30 μm, a discharge roller gap of 10 μm, and a roller speed of 200 rpm. Vacuum degassing was then performed to obtain liquid silicone rubber. The silanol content in the liquid silicone rubber was measured to be 0.05 wt%. The prepared liquid silicone rubber was cured by heating at 150°C for 3 hours to obtain cured silicone rubber.

[0122] The performance of Examples 1-3 and Comparative Examples 1-3 was tested according to the test method. The results are shown in Table 1.

[0123] Table 1. Performance test results of the liquid silicone rubber and its cured products prepared in Examples 1-3 and Comparative Examples 1-3.

[0124] Compared to Example 1, the liquid silicone rubber prepared in Comparative Example 1 was prepared without silazane or chlorosilane treatment of the vinyl MQ silicone resin used in its preparation process, resulting in a higher silanol content in the vinyl silicone resin. Compared to Example 2, the silicone resin prepared in Comparative Example 2 was also prepared without silazane or chlorosilane treatment of the vinyl MQ silicone resin used in its preparation process, resulting in a higher silanol content in the vinyl silicone resin. Additionally, octyltrimethoxysilane was added to the liquid silicone rubber. Compared to Example 2, the silicone rubber prepared in Comparative Example 3 was also prepared without silazane or chlorosilane treatment of the vinyl MQ silicone resin used in its preparation process, resulting in a higher silanol content in the vinyl silicone resin. Additionally, dodecyltrimethoxysilane was added to the liquid silicone rubber.

[0125] As can be seen from the data in Table 1, the liquid silicone rubbers prepared by treating vinyl MQ silicone resin with silazane in Examples 1 to 3 have low shear viscosity and thixotropy before curing. In contrast, the untreated vinyl MQ silicone resin in Comparative Example 1 has more silanol groups on its surface, which makes the liquid silicone rubber prepared under hydrogen bonding have higher shear viscosity and thixotropy before curing and poorer fluidity.

[0126] Because the liquid silicone rubber prepared by this invention contains a high proportion of titanium dioxide, the cured product of the prepared liquid silicone rubber has a reflectivity of more than 98% before aging, and has excellent light reflection performance.

[0127] After aging at 200°C for 1000 hours, the reflectivity of the cured liquid silicone rubber products prepared in Examples 1-3 decreased slightly to 97%. Although the liquid silicone rubbers with added octyltrimethoxysilane and dodecyltrimethoxysilane in Comparative Examples 2 and 3 also exhibited relatively good low viscosity and low thixotropy, after aging at 200°C for 1000 hours, the cured liquid silicone rubber products prepared by this method showed obvious yellowing, and the reflectivity also decreased significantly.

[0128] After 1000 hours of aging under 313nm UV, the reflectance of the liquid silicone rubber cured products prepared in Examples 1-3 showed almost no change. However, in Comparative Examples 2 and 3, the reflectance of the liquid silicone rubber with added octyltrimethoxysilane and dodecyltrimethoxysilane decreased significantly. This indicates that alkylsilanes have poor UV resistance, while the cured products of liquid silicone rubber prepared from vinyl MQ silicone resin treated with silazane have strong UV resistance.

[0129] Furthermore, the samples prepared from the above-mentioned liquid silicone rubber for hardness measurement were aged at 200°C for 1000 hours. The cured products of the liquid silicone rubber prepared in Examples 1 to 3 showed a slight increase in Shore A hardness of 3 to 5, with minimal hardness change. However, in Comparative Examples 2 and 3, the cured products of the liquid silicone rubber with added octyltrimethoxysilane and dodecyltrimethoxysilane components showed a significant increase in Shore A hardness of more than 20, indicating poor high-temperature resistance.

[0130] The liquid silicone rubber or its cured product of the present invention exhibits high reflectivity, low thixotropy, and high fluidity, as well as high heat resistance and UV aging resistance. While the liquid silicone rubber or its cured product prepared by the methods in Comparative Examples 2 and 3 also possess high reflectivity, low thixotropy, and high fluidity, their resistance to high temperatures and ultraviolet radiation is poor.

[0131] Through the above embodiments, the present invention effectively overcomes the problem of performance degradation of traditional silicone rubber under high temperature and ultraviolet irradiation environments, improves the stability and durability of silicone rubber, and provides a new solution for the application of silicone rubber in high temperature and outdoor environments. Because the liquid silicone rubber or its cured product prepared by the present invention has high reflectivity, low thixotropy, high fluidity, and excellent storage stability, the liquid silicone rubber can be applied to high-power LED packaging with high reflectivity requirements, and its excellent leveling and durability are suitable for industrial production.

[0132] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A liquid silicone rubber, characterized by, Based on parts by mass, the liquid silicone rubber comprises the following components or the reaction products of the following components: 100 parts vinyl-terminated polydimethylsiloxane; 10-100 parts vinyl MQ silicone resin; 0.1 to 5 parts of adhesion accelerator; 40–200 parts titanium dioxide; 1 to 15 parts polymethylhydrosiloxane; 0.001–0.5 parts of reaction inhibitor; Based on the total mass of the liquid silicone rubber, the silanol content in the liquid silicone rubber is less than or equal to 0.07 wt%.

2. The liquid silicone rubber according to claim 1, characterized in that Based on parts by mass, the liquid silicone rubber comprises the following components or the reaction products of the following components: 100 parts vinyl-terminated polydimethylsiloxane; 20-80 parts vinyl MQ silicone resin; 0.5 to 2 parts of adhesion accelerator; 50-150 parts titanium dioxide; 4 to 15 parts polymethylhydrosiloxane; 0.01 to 0.5 parts of reaction inhibitor.

3. The liquid silicone rubber according to claim 1 or 2, characterized in that, At a shear rate of 20 s -1 At that time, the shear viscosity of the liquid silicone rubber was 3000–5500 mPa·s; and the ratio of shear rate was 1 s. -1 / 10s -1 When the liquid silicone rubber has a thixotropic index of 1.0 to 1.5, and the reflectivity of the cured liquid silicone rubber product is greater than or equal to 98% under a wavelength of 450 nm, preferably 98% to 99.95%.

4. The liquid silicone rubber according to any one of claims 1 to 3, characterized in that Based on the total mass of the liquid silicone rubber, the silanol content in the liquid silicone rubber is 0.001 wt% to 0.07 wt%, preferably 0.001 wt% to 0.02 wt%. And / or, based on the total mass of vinyl MQ silicone resin and vinyl-terminated polydimethylsiloxane, the total silanol content in vinyl MQ silicone resin and vinyl-terminated polydimethylsiloxane is 0.001 wt% to 0.07 wt%, preferably 0.001 wt% to 0.03 wt%. And / or, the silanol content in the vinyl MQ silicone resin is less than or equal to 0.05 wt%, preferably 0.005 wt% to 0.05 wt%; And / or, the silanol content in the vinyl-terminated polydimethylsiloxane is less than or equal to 0.05 wt%, preferably 0.005 wt% to 0.02 wt%.

5. The liquid silicone rubber according to any one of claims 1 to 4, characterized in that, The vinyl content in vinyl MQ silicone resin is 0.5–2 mmol / g, preferably 0.7–1.7 mmol / g; And / or, the molar ratio of M to Q in vinyl MQ silicone resin is 0.7 to 1.2, preferably 0.8 to 1.1; And / or, the dynamic viscosity of the vinyl-terminated polydimethylsiloxane is 200–50000 mPa·s, preferably 500–20000 mPa·s; And / or, the polymethylhydrosiloxane has a silane content of 0.6 wt% to 1.6 wt%, preferably 0.8 wt% to 1.4 wt%; And / or, the dynamic viscosity of the polymethylhydrosiloxane is 5–30 mPa·s, preferably 8–30 mPa·s.

6. The liquid silicone rubber according to any one of claims 1 to 5, characterized in that, The reaction inhibitor is selected from at least one of phosphorus-containing compounds, nitrogen-containing compounds, vinylsilanes, alkynols, and maleic esters. And / or, the adhesion promoter is selected from one or more of silane coupling agents or silane coupling agent semi-hydrolysates.

7. A process for the preparation of the liquid silicone rubber according to any one of claims 1 to 6, characterized in that, The process includes the following steps: in the presence of a catalyst, a mixture of vinyl-terminated polydimethylsiloxane and vinyl MQ silicone resin, an adhesion promoter, titanium dioxide, polymethylhydrosiloxane, and a reaction inhibitor are mixed to obtain the liquid silicone rubber, wherein the vinyl MQ silicone resin is a vinyl MQ silicone resin treated with silazane or chlorosilane.

8. The preparation method according to claim 7, characterized in that, The catalyst contains any one of the noble metals platinum, rhodium, and palladium.

9. The production method according to claim 7 or 8, characterized by, The steps of treating vinyl MQ silicone resin with silazane or chlorosilane include: mixing vinyl MQ silicone resin with a solvent, adding silazane or chlorosilane, heating under reflux, and drying to obtain vinyl MQ silicone resin treated with silazane or chlorosilane; the temperature of heating under reflux is 140-145°C, and the time is 1-2 hours; the amount of silazane or chlorosilane used is 5%-10% of the mass of vinyl MQ silicone resin. And / or, the catalyst is selected from any one of platinum complexes, rhodium complexes, and palladium complexes; And / or, the amount of catalyst used is, and the content of precious metals in the catalyst is 0.1 to 100 ppm of the total mass of liquid silicone rubber.

10. The method of any one of claims 7 to 9, wherein the method further comprises, The mixture of vinyl-terminated polydimethylsiloxane and vinyl MQ silicone resin is obtained by mixing vinyl-terminated polydimethylsiloxane and vinyl MQ silicone resin at 40–100°C for 0.5–1 hour.

11. An LED lamp, characterized in that The LED beads comprise the liquid silicone rubber cured product as described in any one of claims 1 to 6 or the liquid silicone rubber cured product prepared by the preparation method described in any one of claims 7 to 10.

12. The application of the liquid silicone rubber according to any one of claims 1 to 6 or the liquid silicone rubber prepared by the preparation method according to any one of claims 7 to 10 in LED packaging.

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