Preparation method of ethyl lactate-removed silicone sealant

Abstract

The present invention discloses a preparation method of an ethyl lactate-removing silicone sealant, belonging to the technical field of silicone sealants. The preparation method includes: preparing hydrophilic fillers, preparing hydrophobic fillers, and mixing materials; the preparation of hydrophilic fillers includes: primary coating and secondary coating; for the secondary coating, tetraethyl orthosilicate, hydrochloric acid aqueous solution, and primary-coated talc powder are mixed, stirred, centrifuged, the precipitate is collected, washed, and dried; the preparation of hydrophobic fillers includes: primary adsorption, secondary adsorption, and crosslinking; for the secondary adsorption, sodium stearate and water are mixed, stirred, primary-adsorbed silica is added, stirred, centrifuged, the precipitate is collected, washed, and dried; the ethyl lactate-removing silicone sealant prepared by the present invention is not easily formed with bubbles inside during curing at high temperature, has good fluidity, still has high strength after curing in a high-temperature and high-humidity environment, and at the same time, has high strength and transparency and a fast curing speed.

Description

Technical Field

[0001] The present invention relates to the technical field of silicone sealants, and particularly relates to a preparation method of an ethyl lactate - removing type silicone sealant. Background Art

[0002] Silicone sealant is an organosilicon polymer material that can cure at room temperature. It takes terminal - hydroxyl polydimethylsiloxane as the main component, supplemented with cross - linking agent, plasticizer, catalyst, coupling agent, and filler, and is mixed under vacuum conditions. Silicone sealant is in paste form at room temperature and will react with water molecules in the air during use to cure into a solid silicone rubber with a three - dimensional cross - linked network. According to different by - product types, silicone sealants are mainly divided into ketoxime - removing type silicone sealants, alcohol - removing type silicone sealants, acetone - removing type silicone sealants, acetic acid - removing type silicone sealants, ethyl lactate - removing type silicone sealants, etc. Currently, the silicone sealants on the market are mainly ketoxime - removing type silicone sealants and alcohol - removing type silicone sealants.

[0003] However, the ketoxime - removing type silicone sealant is corrosive to some materials during use, such as copper, zinc, polycarbonate, etc., and has a slight odor. Although the alcohol - removing type silicone sealant is non - corrosive, odorless, and has little environmental pollution during use, it has problems of slow curing speed and poor storage stability. The reason is that during the curing of the alcohol - removing type silicone sealant, the surface layer of the alcohol - removing type silicone sealant will quickly absorb water and cure, and then form a three - dimensional cross - linked network on the surface, affecting the further penetration of water, resulting in a slowdown in the deep - layer curing speed. During storage, the water and alcohol in the alcohol - removing type silicone sealant are extremely likely to react with the catalyst in the alcohol - removing type silicone sealant, resulting in poor storage stability.

[0004] The ethyl lactate - removing type silicone sealant has the advantages of fast curing speed, good storage stability, strong adhesion, high strength and transparency, non - corrosiveness, and no odor. It is a typical representative of high - end silicone sealants and has wide applications in the fields of national defense, construction, electronics, chemical industry, etc.

[0005] However, when the ethyl lactate - releasing silicone sealant is in use, the following problems exist: First, the ethyl lactate - releasing silicone sealant will release ethyl lactate during curing. Ethyl lactate is a colorless liquid with a slight odor and lower volatility than methanol and ethanol. When curing at high temperatures, due to the fast curing speed of the ethyl lactate - releasing silicone sealant, ethyl lactate cannot volatilize in time, and bubbles are easily formed inside, manifested as the problem of uneven surface of the cured ethyl lactate - releasing silicone sealant; Second, the ethyl lactate - releasing silicone sealant needs to use an ethyl lactate - type silane cross - linker during preparation. The molecular weight of the ethyl lactate - type silane cross - linker is relatively high, which will affect the fluidity of the ethyl lactate - releasing silicone sealant; Third, the ethyl lactate - type silane cross - linker contains an ester group, and the ester group is prone to hydrolysis. The higher the temperature, the faster the hydrolysis speed, resulting in the ethyl lactate - releasing silicone sealant being greatly affected by the environmental temperature and humidity during curing. The high - temperature and high - humidity environment will affect the strength of the cured ethyl lactate - releasing silicone sealant.

[0006] To address the above problems, the commonly used method at present is to add additives to the ethyl lactate - releasing silicone sealant. For example, adding fillers can improve the fluidity of the ethyl lactate - releasing silicone sealant and control the curing speed, thereby avoiding the bubble problem; adding dehydrating agents can avoid the influence of environmental temperature and humidity on the strength of the cured ethyl lactate - releasing silicone sealant. However, the fillers will affect the cross - link density of the cured ethyl lactate - releasing silicone sealant, further affecting the strength and transparency of the ethyl lactate - releasing silicone sealant. Therefore, the fillers need to be organically modified. Specifically, active groups are introduced on the surface of the fillers. The active groups can participate in the curing reaction of the ethyl lactate - releasing silicone sealant as active sites, forming a "sea - island" structure in the cured ethyl lactate - releasing silicone sealant, thereby improving the strength of the ethyl lactate - releasing silicone sealant. However, the active groups will further shorten the curing time of the ethyl lactate - releasing silicone sealant and exacerbate the bubble problem; the addition of dehydrating agents will affect the interaction between the ethyl lactate - releasing silicone sealant and water molecules during curing, further resulting in a slower curing speed.

[0007] Therefore, for the ethyl lactate - releasing silicone sealant, the problems that need to be urgently solved at present are: avoiding the problem of easy formation of bubbles inside the cured ethyl lactate - releasing silicone sealant when curing at high temperatures; improving the fluidity of the ethyl lactate - releasing silicone sealant; avoiding the influence of high - temperature and high - humidity environment on the strength of the cured ethyl lactate - releasing silicone sealant; at the same time, ensuring the strength, transparency, and curing speed of the ethyl lactate - releasing silicone sealant. Summary of the Invention

[0008] In view of the deficiencies of the existing technology, the present invention provides a method for preparing an ethyl lactate-free silicone sealant. When the prepared ethyl lactate-free silicone sealant is cured at high temperature, bubbles are not easily formed inside, it has good fluidity, and still has high strength after curing in a high temperature and high humidity environment. At the same time, it has high strength and transparency, and a fast curing speed.

[0009] To solve the above technical problems, the technical solutions adopted by the present invention are as follows:

[0010] A method for preparing an ethyl lactate-free silicone sealant, comprising: preparing a hydrophilic filler, preparing a hydrophobic filler, and mixing.

[0011] The preparation of the hydrophilic filler includes: primary coating and secondary coating.

[0012] For the primary coating, chitosan and an acetic acid aqueous solution are added to a reaction device, the temperature of the reaction device is controlled to 30 - 50°C, the stirring speed is controlled to 60 - 120 rpm, stirred for 20 - 30 min, talcum powder is added, stirred for 3 - 4 h, then added to a centrifugal device, the centrifugal speed of the centrifugal device is controlled to 4000 - 5000 rpm, centrifuged for 10 - 15 min, the precipitate is collected, washed with deionized water, and dried at 120 - 140°C for 9 - 10 h to obtain primary-coated talcum powder.

[0013] In the primary coating, the dosage ratio of chitosan, acetic acid aqueous solution, and talcum powder is 38 - 42 g: 2000 - 2500 mL: 180 - 200 g.

[0014] The mass concentration of the acetic acid aqueous solution is 2 - 2.5%.

[0015] The particle size of the talcum powder is 800 mesh.

[0016] The molecular weight of the chitosan is 600,000, and the degree of deacetylation is 90%.

[0017] For the secondary coating, tetraethyl orthosilicate, hydrochloric acid aqueous solution, and primary-coated talcum powder are added to a reaction device, the temperature of the reaction device is controlled to 50 - 60°C, the stirring speed is controlled to 60 - 120 rpm, stirred for 2 - 2.5 h, then added to a centrifugal device, the centrifugal speed of the centrifugal device is controlled to 4000 - 5000 rpm, centrifuged for 10 - 15 min, the precipitate is collected, washed with deionized water, and dried at 120 - 140°C for 14 - 15 h to obtain the hydrophilic filler.

[0018] The dosage ratio of the talcum powder in the primary coating and tetraethyl orthosilicate and hydrochloric acid aqueous solution in the secondary coating is 180 - 200 g: 17 - 20 mL: 2000 - 2100 mL.

[0019] The mass concentration of the hydrochloric acid aqueous solution is 4-5%;

[0020] The preparation of the hydrophobic filler includes: primary adsorption, secondary adsorption, and crosslinking;

[0021] For the primary adsorption, chitosan and an acetic acid aqueous solution are added to a reaction device. The temperature of the reaction device is controlled to 30-50°C, the stirring speed is controlled to 60-120 rpm, and stirring is carried out for 20-30 min. Then, fumed silica is added and stirring is carried out for 3-4 h. It is added to a centrifugation device, the centrifugation speed of the centrifugation device is controlled to 12,000-13,000 rpm, and centrifugation is carried out for 18-20 min. The precipitate is collected, washed with deionized water, and dried at 120-140°C for 9-10 h to obtain fumed silica after primary adsorption;

[0022] In the primary adsorption, the dosage ratio of chitosan, acetic acid aqueous solution, and fumed silica is 38-42 g: 2000-2500 mL: 70-75 g;

[0023] The mass concentration of the acetic acid aqueous solution is 2-2.5%;

[0024] The particle size of the fumed silica is 40 nm;

[0025] The molecular weight of the chitosan is 600,000 and the degree of deacetylation is 90%;

[0026] For the secondary adsorption, sodium stearate and water are added to a reaction device. The temperature of the reaction device is controlled to 15-35°C, the stirring speed is controlled to 60-120 rpm, and stirring is carried out for 10-30 min. Then, fumed silica after primary adsorption is added and stirring is carried out for 3-4 h. It is added to a centrifugation device, the centrifugation speed of the centrifugation device is controlled to 12,000-13,000 rpm, and centrifugation is carried out for 18-20 min. The precipitate is collected, washed with deionized water, and dried at 120-140°C for 9-10 h to obtain fumed silica after secondary adsorption;

[0027] The dosage ratio of the fumed silica in the primary adsorption, sodium stearate, and water in the secondary adsorption is 70-75 g: 80-90 g: 2000-2500 mL;

[0028] For the crosslinking, fumed silica after secondary adsorption and a glutaraldehyde aqueous solution are added to a reaction device. The temperature of the reaction device is controlled to 25-40°C, the stirring speed is controlled to 60-120 rpm, and stirring is carried out for 4-5 h. It is added to a centrifugation device, the centrifugation speed of the centrifugation device is controlled to 12,000-13,000 rpm, and centrifugation is carried out for 18-20 min. The precipitate is collected, washed with deionized water, and dried at 120-140°C for 14-15 h to obtain the hydrophobic filler;

[0029] The dosage ratio of the fumed silica in the primary adsorption to the aqueous glutaraldehyde solution in the crosslinking is 70 - 75 g : 1800 - 2000 mL;

[0030] The mass concentration of the aqueous glutaraldehyde solution is 4 - 5%;

[0031] For the mixing, high-viscosity α,ω-dihydroxypolydimethylsiloxane, low-viscosity α,ω-dihydroxypolydimethylsiloxane, hydrophilic filler, hydrophobic filler, and dimethyl silicone oil are added to a high-speed dispersion device. The vacuum degree of the high-speed dispersion device is controlled to 0.08 - 0.09 MPa, and the rotation speed is controlled to 900 - 1000 rpm. After high-speed dispersing for 50 - 60 min, ethyl lactate trimethylsilyl silane and ethyl lactate vinyl trisilane are added, and then high-speed dispersed for 30 - 40 min. Then, 3-glycidoxypropyltriethoxysilane, γ-aminopropyltriethoxysilane, and dibutyltin dilaurate are added, and high-speed dispersed for 50 - 60 min to obtain an ethyl lactate-free silicone sealant;

[0032] In the mixing material, the mass ratio of high-viscosity α,ω-dihydroxypolydimethylsiloxane, low-viscosity α,ω-dihydroxypolydimethylsiloxane, hydrophilic filler, hydrophobic filler, dimethyl silicone oil, ethyl lactate trimethylsilyl silane, ethyl lactate vinyl trisilane, 3-glycidoxypropyltriethoxysilane, γ-aminopropyltriethoxysilane, and dibutyltin dilaurate is 380 - 400 : 120 - 130 : 35 - 37 : 90 - 100 : 40 - 45 : 20 - 23 : 9 - 11 : 5 - 6 : 5 - 5.5 : 4 - 4.2;

[0033] The viscosity of the high-viscosity α,ω-dihydroxypolydimethylsiloxane at 25°C is 80000 mPa·s;

[0034] The viscosity of the low-viscosity α,ω-dihydroxypolydimethylsiloxane at 25°C is 20000 mPa·s;

[0035] The viscosity of the dimethyl silicone oil at 25°C is 500 mPa·s.

[0036] Compared with the prior art, the beneficial effects of the present invention are:

[0037] (1)Preparation method of ethyl lactate-removing silicone sealant of the present invention, including preparing hydrophilic filler, preparing hydrophobic filler, and mixing. Preparing hydrophilic filler includes primary coating and secondary coating. The primary coating is to mix an acetic acid aqueous solution of chitosan with talcum powder, and coat chitosan on the surface of talcum powder to obtain primary-coated talcum powder. The secondary coating is to mix silica sol with the primary-coated talcum powder, and react between the silica sol and the chitosan on the surface of the primary-coated talcum powder to form Si-O-C bonds, obtaining talcum powder with a complex of chitosan and silica on the surface. Before reacting with the silica sol, the hydroxyl groups of chitosan itself will form internal hydrogen bonds, reducing the hydrophilicity of chitosan. After reacting with the silica sol, the hydroxyl groups on the surface of the silica formed by the silica sol will break the internal hydrogen bonds of chitosan, increasing the hydrophilicity of chitosan. Therefore, hydrophilic filler is obtained. Preparing hydrophobic filler includes primary adsorption, secondary adsorption, and crosslinking. The primary adsorption is to mix an acetic acid aqueous solution of chitosan with fumed silica. Fumed silica has a high specific surface area and can adsorb chitosan to obtain primary-adsorbed fumed silica. The secondary adsorption is to mix an aqueous solution of sodium stearate with the primary-adsorbed fumed silica, and fix sodium stearate through the molecular chain entanglement between sodium stearate and chitosan and the intermolecular force between the two to obtain secondary-adsorbed fumed silica. Crosslinking is to treat the secondary-adsorbed fumed silica with an aqueous solution of glutaraldehyde, and crosslink between glutaraldehyde and chitosan to reduce the hydrophilicity of chitosan, obtaining fumed silica with crosslinked chitosan and sodium stearate coated on the surface, that is, hydrophobic filler. The hydrophilic filler can participate in crosslinking during curing. The complex of chitosan and silica on the surface has a high specific surface area and can adsorb and disperse the generated ethyl acetate, avoiding excessive release of ethyl acetate during curing at high temperature, aggregation and generation of bubbles. Moreover, compared with talcum powder, the hydrophilic filler is not easy to agglomerate and can also participate in the curing of the ethyl lactate-removing silicone sealant, thereby improving the fluidity, strength, transparency, and curing speed of the ethyl lactate-removing silicone sealant. When the ethyl lactate-removing silicone sealant polymerizes at high temperature and high humidity, the hydrophilic filler can play a certain water absorption role, thereby avoiding hydrolysis of the ester group caused by high temperature and high humidity, ensuring that the prepared ethyl lactate-removing silicone sealant still has high strength after curing in a high temperature and high humidity environment. The sodium stearate on the surface of the hydrophobic filler can improve the fluidity of the hydrophobic filler, avoid agglomeration, further improve the fluidity and transparency of the prepared ethyl lactate-removing silicone sealant, and can also participate in the curing of the ethyl lactate-removing silicone sealant, increasing the crosslinking density, thereby improving the strength and curing speed of the ethyl lactate-removing silicone sealant. When curing in a high temperature and high humidity environment, the hydrophobic filler can also adsorb and protect part of the ethyl lactate-removing silicone sealant, avoiding hydrolysis of this part of the ethyl lactate-removing silicone sealant. In addition, chitosan is used in the preparation of both hydrophilic filler and hydrophobic filler in the present invention. Chitosan raw materials are easily available and have low cost, thus reducing the production cost;

[0038] (2)The preparation method of the ethyl lactate - removed silicone sealant of the present invention. When the prepared ethyl lactate - removed silicone sealant cures at high temperature, bubbles are not easily formed inside.

[0039] (3)The preparation method of the ethyl lactate - removed silicone sealant of the present invention. The prepared ethyl lactate - removed silicone sealant has good fluidity, and the extrusion time is 2.5 - 2.7 s.

[0040] (4)The preparation method of the ethyl lactate - removed silicone sealant of the present invention. The prepared ethyl lactate - removed silicone sealant has high strength. When cured and tested in an environment with a temperature of 23°C and a relative humidity of 50%, the tensile strength is 2.15 - 2.26 MPa, and the elongation at break is 491 - 514%.

[0041] (5)The preparation method of the ethyl lactate - removed silicone sealant of the present invention. The prepared ethyl lactate - removed silicone sealant has high transparency and is colorless and transparent in appearance.

[0042] (6)The preparation method of the ethyl lactate - removed silicone sealant of the present invention. The prepared ethyl lactate - removed silicone sealant has a fast curing speed. The surface - drying time is 14 - 17 min, and the curing speed is 3.21 - 3.32 mm / 24 h.

[0043] (7)The preparation method of the ethyl lactate - removed silicone sealant of the present invention. The prepared ethyl lactate - removed silicone sealant still has high strength after curing in a high - temperature and high - humidity environment. After curing in an environment with a temperature of 50°C and a relative humidity of 80%, when tested in an environment with a temperature of 23°C and a relative humidity of 50%, the tensile strength is 2.12 - 2.27 MPa, and the elongation at break is 485 - 498%. Detailed Embodiments

[0044] In order to have a clearer understanding of the technical features, objectives, and effects of the present invention, the detailed embodiments of the present invention are now described.

[0045] In Examples 1 - 3 and Comparative Examples 1 - 2, the particle size of the talcum powder used is 800 mesh, and the particle size of the fumed silica used is 40 nm.

[0046] The molecular weight of the chitosan used is 600,000, and the degree of deacetylation is 90%.

[0047] Example 1

[0048] A preparation method of an ethyl lactate - removed silicone sealant is as follows:

[0049] 1. Prepare hydrophilic filler:

[0050] (1)Primary coating: Add 38 g of chitosan and 2000 mL of aqueous acetic acid solution to the reaction device. Control the temperature of the reaction device at 30 °C, the stirring speed at 60 rpm, stir for 20 min, add 180 g of talcum powder, stir for 3 h, add it to the centrifugation device, control the centrifugation speed of the centrifugation device at 4000 rpm, centrifuge for 10 min, collect the precipitate, wash it with deionized water, and dry it at 120 °C for 9 h to obtain primary-coated talcum powder;

[0051] The mass concentration of the aqueous acetic acid solution is 2%;

[0052] (2)Secondary coating: Add 17 mL of tetraethyl orthosilicate, 2000 mL of aqueous hydrochloric acid solution, and all the primary-coated talcum powder obtained in the primary coating step of step (1) to the reaction device. Control the temperature of the reaction device at 50 °C, the stirring speed at 60 rpm, stir for 2 h, add it to the centrifugation device, control the centrifugation speed of the centrifugation device at 4000 rpm, centrifuge for 10 min, collect the precipitate, wash it with deionized water, and dry it at 120 °C for 14 h to obtain a hydrophilic filler;

[0053] The mass concentration of the aqueous hydrochloric acid solution is 4%;

[0054] 2. Preparation of hydrophobic filler:

[0055] (1)Primary adsorption: Add 38 g of chitosan and 2000 mL of aqueous acetic acid solution to the reaction device. Control the temperature of the reaction device at 30 °C, the stirring speed at 60 rpm, stir for 20 min, add 70 g of fumed silica, stir for 3 h, add it to the centrifugation device, control the centrifugation speed of the centrifugation device at 12000 rpm, centrifuge for 18 min, collect the precipitate, wash it with deionized water, and dry it at 120 °C for 9 h to obtain primary-adsorbed silica;

[0056] The mass concentration of the aqueous acetic acid solution is 2%;

[0057] (2)Secondary adsorption: Add 80 g of sodium stearate and 2000 mL of water to the reaction device. Control the temperature of the reaction device at 15 °C, the stirring speed at 60 rpm, stir for 10 min, add all the primary-adsorbed silica obtained in the primary adsorption step of step (1), stir for 3 h, add it to the centrifugation device, control the centrifugation speed of the centrifugation device at 12000 rpm, centrifuge for 18 min, collect the precipitate, wash it with deionized water, and dry it at 120 °C for 9 h to obtain secondary-adsorbed silica;

[0058] (3) Crosslinking: Add all the secondary adsorbed silica white carbon obtained in the secondary adsorption step in (2) and 1800 mL of glutaraldehyde aqueous solution into the reaction device. Control the temperature of the reaction device at 25 °C, the stirring speed at 60 rpm, stir for 4 h, add it to the centrifugal device, control the centrifugal speed of the centrifugal device at 12,000 rpm, centrifuge for 18 min, collect the precipitate, wash it with deionized water, and dry it at 120 °C for 14 h to obtain a hydrophobic filler;

[0059] The mass concentration of the glutaraldehyde aqueous solution is 4%;

[0060] 3. Mixing: Add 380 g of high-viscosity α,ω-dihydroxypolydimethylsiloxane, 120 g of low-viscosity α,ω-dihydroxypolydimethylsiloxane, 35 g of hydrophilic filler, 90 g of hydrophobic filler, and 40 g of dimethyl silicone oil into the high-speed dispersion device. Control the vacuum degree of the high-speed dispersion device at 0.08 MPa, the rotation speed at 900 rpm, disperse at high speed for 50 min, add 20 g of ethyl lactate methyl silane and 9 g of ethyl lactate vinyl silane, disperse at high speed for 30 min, add 5 g of 3-glycidoxypropyltriethoxysilane, 5 g of γ-aminopropyltriethoxysilane, and 4 g of dibutyltin dilaurate, and disperse at high speed for 50 min to obtain an ethyl lactate-free silicone sealant;

[0061] The viscosity of the high-viscosity α,ω-dihydroxypolydimethylsiloxane at 25 °C is 80,000 mPa·s;

[0062] The viscosity of the low-viscosity α,ω-dihydroxypolydimethylsiloxane at 25 °C is 20,000 mPa·s;

[0063] The viscosity of the dimethyl silicone oil at 25 °C is 500 mPa·s.

[0064] Example 2

[0065] A preparation method of an ethyl lactate-free silicone sealant, specifically:

[0066] 1. Preparation of hydrophilic filler:

[0067] (1) Primary coating: Add 40 g of chitosan and 2200 mL of acetic acid aqueous solution into the reaction device. Control the temperature of the reaction device at 40 °C, the stirring speed at 100 rpm, stir for 25 min, add 190 g of talcum powder, stir for 3.5 h, add it to the centrifugal device, control the centrifugal speed of the centrifugal device at 4500 rpm, centrifuge for 15 min, collect the precipitate, wash it with deionized water, and dry it at 130 °C for 9.5 h to obtain primary-coated talcum powder;

[0068] The mass concentration of the acetic acid aqueous solution is 2.5%;

[0069] (2) Secondary coating: Add 18 mL of tetraethyl orthosilicate, 20 - 50 mL of hydrochloric acid aqueous solution, and all the first - coated talc powder obtained in the first - coating step of step (1) into the reaction device. Control the temperature of the reaction device to 55 °C, control the stirring speed to 100 rpm, stir for 2.5 h, add it into the centrifugal device, control the centrifugal speed of the centrifugal device to 4500 rpm, centrifuge for 15 min, collect the precipitate, wash it with deionized water, and dry it at 130 °C for 14.5 h to obtain a hydrophilic filler;

[0070] The mass concentration of the hydrochloric acid aqueous solution is 4.5%;

[0071] 2. Preparation of hydrophobic filler:

[0072] (1) Primary adsorption: Add 40 g of chitosan and 2200 mL of acetic acid aqueous solution into the reaction device. Control the temperature of the reaction device to 40 °C, control the stirring speed to 100 rpm, stir for 25 min, add 72 g of fumed silica, stir for 3.5 h, add it into the centrifugal device, control the centrifugal speed of the centrifugal device to 13000 rpm, centrifuge for 20 min, collect the precipitate, wash it with deionized water, and dry it at 130 °C for 9.5 h to obtain primary - adsorbed fumed silica;

[0073] The mass concentration of the acetic acid aqueous solution is 2.5%;

[0074] (2) Secondary adsorption: Add 85 g of sodium stearate and 2200 mL of water into the reaction device. Control the temperature of the reaction device to 25 °C, control the stirring speed to 100 rpm, stir for 20 min, add all the primary - adsorbed fumed silica obtained in the primary - adsorption step of step (1), stir for 3.5 h, add it into the centrifugal device, control the centrifugal speed of the centrifugal device to 13000 rpm, centrifuge for 20 min, collect the precipitate, wash it with deionized water, and dry it at 130 °C for 9.5 h to obtain secondary - adsorbed fumed silica;

[0075] (3) Cross - linking: Add all the secondary - adsorbed fumed silica obtained in the secondary - adsorption step of step (2) and 1900 mL of glutaraldehyde aqueous solution into the reaction device. Control the temperature of the reaction device to 30 °C, control the stirring speed to 100 rpm, stir for 4.5 h, add it into the centrifugal device, control the centrifugal speed of the centrifugal device to 13000 rpm, centrifuge for 20 min, collect the precipitate, wash it with deionized water, and dry it at 130 °C for 14.5 h to obtain a hydrophobic filler;

[0076] The mass concentration of the glutaraldehyde aqueous solution is 5%;

[0077] 3. Mixing: Add 390 g of high-viscosity α,ω-dihydroxypolydimethylsiloxane, 125 g of low-viscosity α,ω-dihydroxypolydimethylsiloxane, 36 g of hydrophilic filler, 95 g of hydrophobic filler, and 42 g of dimethyl silicone oil into a high-speed dispersion device. Control the vacuum degree of the high-speed dispersion device to 0.09 MPa and the rotation speed to 1000 rpm. Disperse at high speed for 55 min. Then add 22 g of ethyl tri(lactate) silane and 10 g of vinyl tri(lactate) silane, and disperse at high speed for 35 min. Next, add 5.5 g of 3-glycidoxypropyltriethoxysilane, 5.2 g of γ-aminopropyltriethoxysilane, and 4.1 g of dibutyltin dilaurate, and disperse at high speed for 55 min to obtain an ethyl lactate-free silicone sealant;

[0078] The viscosity of the high-viscosity α,ω-dihydroxypolydimethylsiloxane at 25 °C is 80000 mPa·s;

[0079] The viscosity of the low-viscosity α,ω-dihydroxypolydimethylsiloxane at 25 °C is 20000 mPa·s;

[0080] The viscosity of the dimethyl silicone oil at 25 °C is 500 mPa·s.

[0081] Example 3

[0082] A preparation method of an ethyl lactate-free silicone sealant, specifically:

[0083] 1. Preparation of hydrophilic filler:

[0084] (1) Primary coating: Add 42 g of chitosan and 2500 mL of acetic acid aqueous solution into a reaction device. Control the temperature of the reaction device to 50 °C and the stirring speed to 120 rpm. Stir for 30 min, then add 200 g of talc powder and stir for 4 h. Transfer to a centrifugation device, control the centrifugation speed of the centrifugation device to 5000 rpm, and centrifuge for 15 min. Collect the precipitate, wash it with deionized water, and dry it at 140 °C for 10 h to obtain primary-coated talc powder;

[0085] The mass concentration of the acetic acid aqueous solution is 2.5%;

[0086] (2) Secondary coating: Add 20 mL of tetraethyl orthosilicate, 2100 mL of hydrochloric acid aqueous solution, and all the primary-coated talc powder obtained in the primary coating step (1) into a reaction device. Control the temperature of the reaction device to 60 °C and the stirring speed to 120 rpm. Stir for 2.5 h. Transfer to a centrifugation device, control the centrifugation speed of the centrifugation device to 5000 rpm, and centrifuge for 15 min. Collect the precipitate, wash it with deionized water, and dry it at 140 °C for 15 h to obtain the hydrophilic filler;

[0087] The mass concentration of the hydrochloric acid aqueous solution is 5%;

[0088] 2. Preparation of hydrophobic filler:

[0089] (1) Primary adsorption: Add 42 g of chitosan and 2500 mL of acetic acid aqueous solution to the reaction device, control the temperature of the reaction device to 50 °C, control the stirring speed to 120 rpm, stir for 30 min, add 75 g of fumed silica, stir for 4 h, add to the centrifugation device, control the centrifugation speed of the centrifugation device to 13000 rpm, centrifuge for 20 min, collect the precipitate, wash with deionized water, and dry at 140 °C for 10 h to obtain primary adsorption fumed silica;

[0090] The mass concentration of the acetic acid aqueous solution is 2.5%;

[0091] (2) Secondary adsorption: Add 90 g of sodium stearate and 2500 mL of water to the reaction device, control the temperature of the reaction device to 35 °C, control the stirring speed to 120 rpm, stir for 30 min, add all the primary adsorption fumed silica obtained in the primary adsorption step of (1), stir for 4 h, add to the centrifugation device, control the centrifugation speed of the centrifugation device to 13000 rpm, centrifuge for 20 min, collect the precipitate, wash with deionized water, and dry at 140 °C for 10 h to obtain secondary adsorption fumed silica;

[0092] (3) Crosslinking: Add all the secondary adsorption fumed silica obtained in the secondary adsorption step of (2) and 2000 mL of glutaraldehyde aqueous solution to the reaction device, control the temperature of the reaction device to 40 °C, control the stirring speed to 120 rpm, stir for 5 h, add to the centrifugation device, control the centrifugation speed of the centrifugation device to 13000 rpm, centrifuge for 20 min, collect the precipitate, wash with deionized water, and dry at 140 °C for 15 h to obtain hydrophobic filler;

[0093] The mass concentration of the glutaraldehyde aqueous solution is 5%;

[0094] 3. Mixing: Add 400 g of high-viscosity α,ω-dihydroxypolydimethylsiloxane, 130 g of low-viscosity α,ω-dihydroxypolydimethylsiloxane, 37 g of hydrophilic filler, 100 g of hydrophobic filler, and 45 g of dimethyl silicone oil to the high-speed dispersion device, control the vacuum degree of the high-speed dispersion device to 0.09 MPa, control the rotation speed to 1000 rpm, disperse at high speed for 60 min, add 23 g of methyltri(lactate ethyl)silane and 11 g of vinyltri(lactate ethyl)silane, disperse at high speed for 40 min, add 6 g of 3-glycidoxypropyltriethoxysilane, 5.5 g of γ-aminopropyltriethoxysilane, and 4.2 g of dibutyltin dilaurate, and disperse at high speed for 60 min to obtain ethyl lactate-free silicone sealant;

[0095] The viscosity of the high-viscosity α,ω-dihydroxypolydimethylsiloxane at 25 °C is 80,000 mPa·s;

[0096] The viscosity of the low-viscosity α,ω-dihydroxypolydimethylsiloxane at 25 °C is 20,000 mPa·s;

[0097] The viscosity of the dimethyl silicone oil at 25 °C is 500 mPa·s.

[0098] Comparative Example 1

[0099] This comparative example is based on the preparation method of the ethyl lactate-removing silicone sealant in Example 2, omitting the first step of preparing the hydrophilic filler, and in the third step of the mixing step, using talc with a particle size of 800 mesh to replace the addition of the hydrophilic filler in equal mass.

[0100] Comparative Example 2

[0101] This comparative example is based on the preparation method of the ethyl lactate-removing silicone sealant in Example 2, omitting the second step of preparing the hydrophobic filler, and in the third step of the mixing step, using fumed silica with a particle size of 40 mesh to replace the addition of the hydrophobic filler in equal mass.

[0102] Performance Test 1

[0103] The ethyl lactate-removing silicone sealants prepared in Examples 1-3 and Comparative Examples 1-2 were cured in an environment with a temperature of 50 °C and a relative humidity of 50%. After complete curing, observe whether there are bubbles inside and whether there are problems of unevenness on the surface. The observation results are as follows:

[0104]

[0105] It can be seen from the above results that only the ethyl lactate-removing silicone sealant prepared in Comparative Example 1 has bubbles inside and unevenness on the surface when cured at high temperature, indicating that the addition of the hydrophilic filler can avoid the generation of internal bubbles when cured at high temperature. Further, it can also avoid the problem of unevenness on the surface when cured at high temperature.

[0106] Performance Test 2

[0107] The extrudability, tensile strength, elongation at break, appearance, surface dry time, and curing speed of the ethyl lactate-removing silicone sealants prepared in Examples 1-3 and Comparative Examples 1-2 were tested. When curing the test specimens and testing the tensile strength and elongation at break, they were all carried out in an environment with a temperature of 23 °C and a relative humidity of 50%. The test results are as follows:

[0108]

[0109] It can be seen from the above results that the extrusion property, tensile strength, elongation at break, appearance, surface drying time, and curing speed of the ethyl lactate-free silicone sealant prepared in Comparative Example 1 and Comparative Example 2 are all inferior to those of the ethyl lactate-free silicone sealant prepared in Example 2, indicating that the addition of hydrophilic fillers and hydrophobic fillers can improve the extrusion property, tensile strength, elongation at break, appearance, surface drying time, and curing speed of the prepared ethyl lactate-free silicone sealant.

[0110] Performance Test 3

[0111] The tensile strength and elongation at break of the ethyl lactate-free silicone sealants prepared in Examples 1-3 and Comparative Examples 1-2 were tested. When curing the test specimens, it was carried out in an environment with a temperature of 50 °C and a relative humidity of 80%. When testing the test specimens, it was carried out in an environment with a temperature of 23 °C and a relative humidity of 50%. The test results are as follows:

[0112]

[0113] After comparing the above results with those of Performance Test 1, it can be seen that compared with the ethyl lactate-free silicone sealant prepared in Example 2, the strength and elongation at break of the ethyl lactate-free silicone sealants prepared in Comparative Example 1 and Comparative Example 2 have decreased significantly after curing in a high-temperature and high-humidity environment, indicating that the addition of hydrophilic fillers and hydrophobic fillers can improve the strength and elongation at break of the prepared ethyl lactate-free silicone sealant after curing in a high-temperature and high-humidity environment.

[0114] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing ethyl lactate-free silicone sealant, characterized in that: include: preparing hydrophilic fillers, preparing hydrophobic fillers, and mixing; The preparation of the hydrophilic filler comprises: primary coating and secondary coating; The first-stage coating comprises adding talcum powder to the protonated chitosan solution, stirring, centrifuging, collecting the precipitate, washing, and drying to obtain the first-stage coated talcum powder; The secondary coating comprises mixing ethyl orthosilicate, hydrochloric acid aqueous solution and primary coated talc, stirring at 50-60° C., centrifuging, collecting the precipitate, washing and drying to obtain a hydrophilic filler; The preparation of the hydrophobic filler comprises: primary adsorption, secondary adsorption, and cross-linking; The first-stage adsorption comprises adding fumed silica to the protonated chitosan solution, stirring, centrifuging, collecting the precipitate, washing, and drying to obtain first-stage adsorbed silica; The secondary adsorption comprises mixing sodium stearate and water, stirring at 15-35° C., adding primary adsorption white carbon black, stirring, centrifuging, collecting precipitates, washing, and drying to obtain secondary adsorption white carbon black; The cross-linking comprises mixing the secondary adsorbed white carbon black and the glutaraldehyde aqueous solution, stirring at 25-40° C., centrifuging, collecting the precipitate, washing, and drying to obtain a hydrophobic filler; The mixed material comprises the following steps: mixing high-viscosity α,ω-dihydroxy polydimethylsiloxane, low-viscosity α,ω-dihydroxy polydimethylsiloxane, hydrophilic filler, hydrophobic filler and dimethyl silicone oil, and then dispersing the mixture at high speed for 50-60 minutes under a vacuum degree of 0.08-0.09 MPa; adding methyl triethyl lactate silane and vinyl triethyl lactate silane, and dispersing the mixture at high speed for 30-40 minutes; and adding 3-glycidyloxypropyl triethoxysilane, γ-aminopropyl triethoxysilane and dibutyltin dilaurate, and dispersing the mixture at high speed for 50-60 minutes to obtain a de-ethyl lactate type silicone sealant.

2. The method for preparing the ethyl lactate-free silicone sealant according to claim 1, characterized in that: In the primary coating, the protonated chitosan solution is prepared by mixing chitosan and acetic acid aqueous solution and stirring at 30-50°C; In the preparation of the protonated chitosan solution, the ratio of chitosan to acetic acid aqueous solution is 38-42 g: 2000-2500 mL; The molecular weight of the chitosan is 600,000 and the degree of deacetylation is 90%; The mass concentration of the acetic acid aqueous solution is 2-2.5%; The mass ratio of talc to chitosan in the protonated chitosan solution is 180-200:38-42; The particle size of the talcum powder is 800 meshes.

3. The method for preparing the ethyl lactate-free silicone sealant according to claim 1, characterized in that: The dosage ratio of talc in the primary coating and ethyl orthosilicate and hydrochloric acid aqueous solution in the secondary coating is 180-200 g: 17-20 mL: 2000-2100 mL; The mass concentration of the hydrochloric acid aqueous solution is 4-5%.

4. The method for preparing the ethyl lactate-free silicone sealant according to claim 1, characterized in that: In the primary adsorption, the protonated chitosan solution is prepared by mixing chitosan and an acetic acid aqueous solution and stirring at 30-50°C; In the preparation of the protonated chitosan solution, the ratio of chitosan to acetic acid aqueous solution is 38-42 g: 2000-2500 mL; The molecular weight of the chitosan is 600,000 and the degree of deacetylation is 90%; The mass concentration of the acetic acid aqueous solution is 2-2.5%; The mass ratio of fumed silica to chitosan in the protonated chitosan solution is 70-75:38-42; The particle size of the fumed silica is 40 nm.

5. The method for preparing the ethyl lactate-free silicone sealant according to claim 1, characterized in that: The usage ratio of the fumed silica in the primary adsorption to the sodium stearate and water in the secondary adsorption is 70-75g:80-90g:2000-2500mL.

6. The method for preparing the ethyl lactate-free silicone sealant according to claim 1, characterized in that: The amount ratio of the fumed silica in the primary adsorption to the glutaraldehyde aqueous solution in the crosslinking is 70-75 g: 1800-2000 mL; The mass concentration of the glutaraldehyde aqueous solution is 4-5%.

7. The method for preparing the ethyl lactate-free silicone sealant according to claim 1, characterized in that: In the mixture, the mass ratio of high viscosity α,ω-dihydroxy polydimethylsiloxane, low viscosity α,ω-dihydroxy polydimethylsiloxane, hydrophilic filler, hydrophobic filler, dimethyl silicone oil, methyl triethyl lactate silane, vinyl triethyl lactate silane, 3-glycidyloxypropyl triethoxysilane, γ-aminopropyl triethoxysilane and dibutyltin dilaurate is 380-400:120-130:35-37:90-100:40-45:20-23:9-11:5-6:5-5.5:4-4.

2.

8. The method for preparing the ethyl lactate-free silicone sealant according to claim 1, characterized in that: In the mixture, the viscosity of the high-viscosity α,ω-dihydroxy polydimethylsiloxane at 25° C. is 80,000 mPa·s; The viscosity of the low-viscosity α,ω-dihydroxy polydimethylsiloxane at 25° C. is 20000 mPa·s; The viscosity of the dimethyl silicone oil at 25° C. is 500 mPa·s.

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