Ammonium type ultra-small particle size peelable silica sol, and preparation method and application thereof

Abstract

The application provides an ammonium type ultra-small particle size peelable silica sol and a preparation method and application thereof. The silica sol is prepared by one-step hydrolysis and condensation reaction of hexa(ethylamino)disilane, a film forming agent, a release agent and a dispersing agent. The silica sol takes hexa(ethylamino)disilane as the only silicon source. In the hydrolysis process, ethylamine is released to form ammonium ions, provide an alkaline environment and act as a stabilizer. Meanwhile, the steric hindrance effect of the ethylamine controls the particle size in the ultra-small range of 2-7 nm. The film forming agent, the release agent and the dispersing agent are in-situ coated or bonded on the surface of the silica particles in the reaction process, and the synthesis of the silica sol, ammonium type stabilization, particle size control and peelable function are simultaneously completed by the one-step method. The silica sol has the pH response peelable function. The adhesion is moderate under neutral conditions to meet the temporary protection requirement. The adhesion is suddenly reduced under alkaline treatment to realize the whole piece peeling. The silica sol is suitable for the temporary protection in the fields of electronic components, automobile paint surfaces, optical elements and metal precision machining.

Description

Technical Field

[0001] This invention relates to the field of silica sol technology, specifically to ammonium-type ultra-small particle size exfoliable silica sol, its preparation method, and its application. Background Technology

[0002] Peelable temporary protective coatings are functional coatings that form a temporary protective film on the surface of a substrate during transportation, storage, or processing. After use, the protective film can be peeled off completely, restoring the substrate to its original state. These coatings have wide applications in electronics manufacturing, automotive paint protection, and precision machining.

[0003] Existing peelable temporary protective coatings are mainly divided into two categories: solvent-based and water-based. Solvent-based peelable coatings use organic solvents as a medium and have good peelability after film formation, but they have high VOC content, are flammable, and are not environmentally friendly, and are gradually being replaced by water-based systems. Water-based peelable coatings use water-based resins such as polyurethane and acrylic emulsions as film-forming substances, and are more environmentally friendly, but they have drawbacks such as poor water resistance, slow drying speed, easy breakage during peeling, and more residue. Although there have been reports in recent years of improving performance through nano-modification, such as using nano-silica to modify SBS resin to prepare peelable coatings, the system is still mainly composed of organic resins, with inorganic nanomaterials only used as additives.

[0004] Silica sol is an inorganic polymer colloidal solution with water as the dispersed phase. It possesses advantages such as large specific surface area, dense film formation, and good weather resistance, and is widely used in coating modification. Existing technologies for silica sol-based peelable coatings mainly include two methods: physical compounding and two-step modification compounding. The physical compounding method involves physically blending silica sol with organic resins such as polyurethane emulsions and acrylic emulsions, utilizing the organic resins to provide film-forming properties and peelability. For example, existing patent document CN106811075A discloses a peelable protective coating compounded from modified silica sol and polyurethane emulsion, where the silica sol accounts for only 5-10%, while the polyurethane emulsion accounts for as high as 60-80%. This method suffers from problems such as poor compatibility between silica sol and organic resins, poor storage stability, high organic component content in the coating leading to decreased weather resistance, and silica sol being used only as a filler without fully utilizing its inorganic properties.

[0005] The two-step modification and compounding method involves first synthesizing silica sol (mostly sodium-type), then surface modification using a silane coupling agent, and finally compounding with organic resins such as polyurethane. For example, existing patent document CN105153910A discloses a method for preparing a modified silica sol water-based peelable coating, which uses 3-aminopropyltriethoxysilane to modify alkaline silica sol and then compoundes it with a polyurethane emulsion. This method suffers from the problem of residual metal ions in sodium-type silica sol. Sodium ions affect the water resistance and electrochemical performance of the coating, and may cause ion contamination when used in electronic components. At the same time, the two-step process is complex, involving the synthesis and modification of silica sol, resulting in multiple steps, high energy consumption, poor batch stability, and a total reaction time that usually exceeds 6 hours. During the later modification, the silane coupling agent is mainly grafted onto the particle surface, making it difficult to achieve uniform distribution. In addition, peelability still depends on the organic components, and the peelability effect is greatly affected by the organic components. Moreover, the existing technology requires a dry film thickness of more than 0.1 mm to achieve complete peeling, resulting in high coating consumption.

[0006] Furthermore, existing methods for preparing silica sol mostly employ water glass acidification or ion exchange, resulting in silica sols that are predominantly sodium or potassium-type with particle sizes typically ranging from 20 to 100 nm, making it difficult to consistently obtain ultra-small particle sizes below 10 nm. Although there are reports of preparing high-purity silica sol by reacting high-purity silicon powder with ammonia, the particle size is still controlled at 25-35 nm, and it lacks peelable properties.

[0007] In summary, existing peelable temporary protective coatings suffer from several technical drawbacks, including complex preparation processes, separation of synthesis and functional assignment, high cost and low efficiency due to multiple steps, sodium-type silica sol leading to metal ion residue affecting electronic components and metal substrates, difficulty in stably preparing ultra-small particle size silica sol, reliance on organic resin compounding or post-modification for peelability, and high coating consumption due to strong correlation between peelability and coating thickness.

[0008] Therefore, it is necessary to propose an ultra-small particle size silica sol to meet the application requirements of peelable temporary protective coatings and overcome many shortcomings of existing technologies. Summary of the Invention

[0009] This invention proposes an ammonium-type ultra-small particle size silica sol that can be peeled off and its application, which solves the defects of existing technologies such as large particle size, poor stability and poor peelability.

[0010] The technical solution of this invention is implemented as follows:

[0011] The first aspect of the present invention is to provide an ammonium-type ultra-small particle size peelable silica sol, which is obtained by hydrolyzing hexa(ethylamino)disilane in an alcohol-water solvent, wherein the silica sol is added with additives, including a dispersant, a film-forming agent and a release agent; wherein the dispersant is a polymeric dispersant.

[0012] Furthermore, the silica nanoparticles in the silica sol have a particle size of 2-7 nm.

[0013] Furthermore, the silica sol is composed of, by weight, 100 parts of hexa(ethylamino)disilane, 10-50 parts of film-forming agent, 1-20 parts of release agent, and 5-30 parts of dispersant.

[0014] Furthermore, the alcohol is selected from one or more of methanol, ethanol, and isopropanol;

[0015] And / or, the dispersant is a polymeric ionic dispersant and / or a nonionic dispersant, selected from one or more of sodium polyacrylate, polycarboxylate, polyethylene glycol ether, and alkylphenol polyoxyethylene ether;

[0016] And / or, the film-forming agent is selected from one or more of polyvinyl alcohol, polyvinylpyrrolidone, polyethylene glycol, and hydroxyethyl cellulose;

[0017] And / or, the release agent is selected from one or more of fatty acid salts, fatty acid esters, silicone emulsions, and wax emulsions.

[0018] A second aspect of the present invention is to provide a method for preparing the silica sol described in the first aspect above, comprising the steps of: S1. Disperse hexa(ethylamino)disilane, film-forming agent, release agent and dispersant in an alcohol solvent to form a first mixture; S2. Mix water with an alcohol solvent to form a second mixture; S3. Under stirring conditions, the second mixture is mixed with the first mixture, and the reaction is carried out under stirring; S4. After the reaction is complete, remove part of the solvent to the target solid content to obtain ammonium-type ultra-small particle size silica sol.

[0019] Furthermore, in step S1, the dispersion process employs ultrasonic dispersion; and / or, in step S3, the reaction conditions are a reaction at 20-60°C for 60-240 min.

[0020] Further, in step S4, the solid content is 20-40 wt%.

[0021] A third aspect of the present invention is to provide a peelable protective coating comprising the silica sol described in the first aspect, or the silica sol prepared by the preparation method described in the second aspect.

[0022] A fourth aspect of the invention is to provide the application of the silica sol described in the first aspect, or the silica sol prepared by the preparation method described in the second aspect, in temporary protection, the application including but not limited to temporary protection of electronic components, automotive paint, optical components, or precision-machined metal products.

[0023] A fifth aspect of the present invention is to provide a temporary protection method comprising coating an ammonium-type ultra-small particle size silica sol onto a substrate surface and drying it at 40-80°C for 10-60 minutes to form a protective layer; wherein the ammonium-type ultra-small particle size sol is the silica sol described in the first aspect, or the silica sol prepared by the preparation method described in the second aspect.

[0024] Furthermore, the protective layer is treated with an alkaline solution at pH 9-12 during peeling.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] The ammonium-type ultra-small particle size silica sol described in this invention uses hexa(ethylamino)disilane as a silicon source. The molecule contains ethylamino groups, which release ethylamine during hydrolysis to form ammonium ions, acting as a stabilizer for the silica sol. Simultaneously, the ethylamino groups in its molecular structure have a moderate steric hindrance effect, effectively inhibiting the excessive growth of silica particles and controlling the particle size within the ultra-small range of 2-7 nm. Hexa(ethylamino)disilane simultaneously plays a triple role in the system as a silicon source, ammonium donor, and particle size control agent, resulting in an ultra-small particle size silica sol with pH-responsive exfoliation capabilities.

[0027] The ammonium-type ultra-small particle size silica sol described in this invention exhibits significantly superior film density compared to conventional silica sols due to its high specific surface area and dense film-forming properties resulting from its ultra-small particle size. Complete peeling can be achieved with a dry film thickness of only 0.02-0.04 mm, compared to the 0.1 mm or greater requirement of existing technologies, reducing coating consumption by more than 60%. Film-forming agents, release agents, and dispersants ensure that functional additives are uniformly coated or bonded to the surface of silica particles, forming a stable composite colloidal system. The film-forming agent ensures the continuity and mechanical strength of the coating during the protection period; the release agent forms a weak interface layer between the coating and the substrate to ensure integrity during peeling; and the dispersant stably disperses the silica particles to prevent agglomeration. The synergistic effect of these three agents results in moderate and stable adhesion of the coating during the protection period, and a sharp drop in adhesion when peeling is required, enabling complete peeling. This solves the problems of existing technologies where peelability depends on organic resin formulation and the peelability effect is unstable.

[0028] The preparation method described in this invention employs a one-step synthesis process, in which hexa(ethylamino)disilane reacts with a film-forming agent, a release agent, and a dispersant in the same reaction system in a single step. This simultaneously completes silica sol synthesis, ammonium form stabilization, particle size control, and functional additive encapsulation. From raw materials to finished product, only one step is required, significantly simplifying the process, reducing production costs, and improving batch stability. Compared to the multi-step process of "synthesis + modification + compounding" in existing technologies, the process time of this invention is reduced by more than 50%, and energy consumption is reduced by more than 40%. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is an electron microscope image of the ammonium-type ultra-small particle size exfoliable silica sol described in one embodiment of the present invention. Detailed Implementation

[0031] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0032] This invention aims to solve the following technical problems existing in existing peelable temporary protective coatings and their preparation methods:

[0033] 1. Existing silica sol-based peelable coatings typically employ a multi-step process involving "silica sol synthesis + surface modification + organic resin compounding," which is complex, energy-intensive, and has low production efficiency. Furthermore, the multi-step operation makes it difficult to control batch stability.

[0034] 2. Most existing silica sols are sodium or potassium type, leaving residual metal ions (Na+). + K + It affects the water resistance and electrochemical properties of the coating. When used for the protection of electronic components, it may cause ion migration and circuit corrosion. When used on metal substrates, it is prone to flash rust problems.

[0035] 3. Existing methods for preparing silica sols are not able to stably obtain silica sols with particle sizes less than 7 nm. The silica sols obtained by conventional methods usually have particle sizes in the range of 10-100 nm, with small specific surface area and insufficient film density. To achieve peelability, a large coating thickness (usually >0.1 mm) is required, resulting in a large amount of coating consumption.

[0036] 4. The peelability of existing peelable silica sols relies on the addition of organic resins or complex surface modifications. The resulting coating has a high content of organic components, which affects the coating's weather resistance, chemical resistance, and long-term stability. Furthermore, the peelability is greatly affected by the organic components, making it difficult to achieve stable and controllable peelability.

[0037] 5. In the prior art, film-forming agents, release agents, dispersants and other additives are usually added after the synthesis of silica sol by physical blending. The lack of chemical bonding or uniform coating between the components leads to unstable coating performance and problems such as delamination and precipitation during storage.

[0038] To address the aforementioned technical problems, this invention provides a one-step synthesized ammonium-type ultra-small particle size exfoliable silica sol. The silica sol is prepared from raw materials comprising the following components via a one-step hydrolysis-condensation reaction: 100 parts by weight of hexa(ethylamino)disilane, 10-50 parts by weight of a film-forming agent, 1-20 parts by weight of a release agent, 5-30 parts by weight of a dispersant, 100-500 parts by weight of water, and 100-500 parts by weight of an alcohol solvent. The silica nanoparticles in the silica sol have a particle size of 2-7 nm, with ammonium ions acting as a stabilizer.

[0039] Hexa(ethylamino)disilane serves as the sole silicon source. Its molecule contains an ethylamino group, which releases ethylamine during hydrolysis, forming ammonium ions that act as a stabilizer for the silica sol. Simultaneously, the ethylamino group in its molecular structure provides a moderate steric hindrance effect, effectively inhibiting the excessive growth of silica particles and controlling the particle size within the ultra-small range of 2-7 nm. Hexa(ethylamino)disilane thus plays a triple role in the system: silicon source, ammonium donor, and particle size control agent.

[0040] The technical advantages of this invention stem from the following mechanism: First, the ethylamino group in the hexa(ethylamino)disilane molecule releases ethylamine during hydrolysis, forming ammonium ions (NH4+). + As a stabilizer for silica sol, it avoids the introduction of metal ions such as sodium and potassium, solving the problems of ion contamination and flash rust caused by residual metal ions in existing technologies. Simultaneously, the steric hindrance effect of ethylamino effectively inhibits the excessive growth of silica particles, ensuring stable particle size control within the ultra-small range of 2-7 nm and a specific surface area greater than 300 m². 2 / g, significantly improving film density, thus achieving a technological breakthrough where the dry film thickness is only 0.02-0.04mm, allowing for complete peeling and reducing coating consumption by more than 60%. Secondly, the ethylamine released by the hydrolysis of hexa(ethylamino)disilane provides an alkaline environment, catalyzing the hydrolysis-condensation reaction without the need for additional catalysts, making the system simpler and more environmentally friendly. Thirdly, the film-forming agent, release agent, and dispersant in situ coat or bond to the surface of the newly generated silica particles during the reaction, forming a stable composite colloidal system: the film-forming agent ensures the continuity and mechanical strength of the coating during the protection period, the release agent forms a weak interface layer between the coating and the substrate to ensure integrity during peeling, and the dispersant stably disperses the silica particles to prevent agglomeration and precipitation. The synergistic effect of these three agents results in moderate adhesion (1-5MPa) of the coating under pH 6-8 conditions, meeting temporary protection needs; and a sharp drop in adhesion to below 0.5MPa when treated with alkaline solutions at pH 9-12, achieving complete peeling without residue.

[0041] In one embodiment, Figure 1 The morphology of the above-mentioned ammonium-type ultra-small particle size exfoliable silica sol particles at different magnification ratios is shown. The particle size distribution is in the ultra-small range of 2-7 nm, and the dispersion is good.

[0042] In a preferred embodiment, the film-forming agent is selected from one or more of polyvinyl alcohol, polyvinylpyrrolidone, polyethylene glycol, and hydroxyethyl cellulose, and is used to improve the film-forming properties and mechanical strength of the coating, ensuring that the coating remains intact and continuous during the protection period.

[0043] In a preferred embodiment, the release agent is selected from one or more of fatty acid salts, fatty acid esters, silicone emulsions, and wax emulsions, and is used to form a weak interface layer between the coating and the substrate, reduce the peeling force, and ensure that the coating can be peeled off in whole when needed.

[0044] In a preferred embodiment, the dispersant is selected from one or more of sodium polyacrylate, polycarboxylate, polyethylene glycol ether, and alkylphenol polyoxyethylene ether, and is used to stabilize and disperse the generated silica nanoparticles, prevent agglomeration and precipitation, and improve the storage stability of the coating.

[0045] In a preferred embodiment, the alcohol solvent is selected from one or more of methanol, ethanol, and isopropanol.

[0046] This invention also provides a method for preparing the above-mentioned ammonium-type ultra-small particle size exfoliable silica sol, comprising the following steps: (1) Dissolve hexa(ethylamino)disilane, film-forming agent, release agent and dispersant in an alcohol solvent to form a first mixture; (2) Mix water with an alcohol solvent to form a second mixture; (3) Under stirring conditions, the second mixture is mixed with the first mixture; (4) Continue stirring the reaction at 20-60℃ for 60-240 minutes; (5) After the reaction is complete, remove part of the solvent and adjust the solid content to 20-40% to obtain ammonium-type ultra-small particle size exfoliable silica sol.

[0047] In the above preparation method, hexa(ethylamino)disilane undergoes a hydrolysis-condensation reaction in the presence of water and alcohol solvents to generate silica nanoparticles. During the reaction, the ethylamine released from the hydrolysis of hexa(ethylamino)disilane provides an alkaline environment, catalyzing the hydrolysis-condensation reaction without the need for additional catalysts. Simultaneously, film-forming agents, release agents, and dispersants coat or bond to the surface of the newly generated silica particles in situ during the reaction, forming a stable composite colloidal system.

[0048] In a preferred embodiment, the specific operating conditions for dispersion in step (1) include ultrasonic dispersion for 20 to 40 minutes; the mixing conditions in step (2) are ultrasonic mixing for 10 to 20 minutes; and the specific operating conditions for stirring reaction in step (3) include stirring reaction at 500 to 1000 rpm at 20 to 60°C.

[0049] This invention also provides applications for the above-mentioned ammonium-type ultra-small particle size peelable silica sol, namely, its direct use as a peelable temporary protective coating without any subsequent compounding or modification. In use, the silica sol is directly sprayed, brushed, or dipped onto the substrate surface and dried at 40-80℃ for 10-60 minutes to form a transparent protective film with a dry film thickness of 0.02-0.08 mm. When it is necessary to remove the protective layer, it is sprayed or immersed in an alkaline solution (such as sodium carbonate solution) with a pH of 9-12. The protective film automatically peels off and can be completely removed without leaving any residue on the substrate surface.

[0050] The silica sol has a pH-responsive peelable function. Its mechanism is as follows: under neutral conditions (pH 6-8), the film-forming agent on the surface of the silica sol particles forms hydrogen bonds with the substrate surface, resulting in moderate adhesion (1-5 MPa) that meets the protection period requirements; when treated with alkaline solution (pH 9-12), the release agent plays a role, forming a weak interface layer at the interface between the coating and the substrate. At the same time, the dispersant assists the alkaline solution to penetrate, causing the adhesion to drop sharply to below 0.5 MPa, and the coating can be peeled off in whole.

[0051] Example 1

[0052] An ammonium-type ultra-small particle size peelable silica sol is provided, and the raw materials are weighed as follows: 100g of hexa(ethylamino)disilane, 25g of polyvinyl alcohol (film-forming agent), 8g of sodium stearate (release agent), 15g of sodium polyacrylate (dispersant), 200g of deionized water, and 200g of ethanol.

[0053] The preparation steps are as follows: 1) Dissolve hexa(ethylamino)disilane, polyvinyl alcohol, sodium stearate, and sodium polyacrylate in ethanol to form a first mixture; 2) Mix deionized water and ethanol to form a second mixture; 3) Under stirring conditions at room temperature, slowly add the second mixture to the first mixture dropwise over a period of about 40 minutes; (4) After the addition is complete, continue stirring at 40°C for 120 minutes. 4) After the reaction is complete, remove the ethanol by vacuum distillation at 50°C and concentrate to a solid content of 30% to obtain ammonium-type ultra-small particle size exfoliable silica sol.

[0054] Product performance characterization

[0055] Transmission electron microscopy (TEM) revealed that the silica nanoparticles were spherical, uniformly dispersed, and showed no aggregation, with an average particle size of 4.5 nm. Dynamic light scattering (DLS) analysis showed an average particle size of 5.2 nm, a polydispersity index (PDI) of 0.08, and a narrow particle size distribution. The pH value was 8.6. The solid content was determined to be 29.8% by drying and weighing. Ion chromatography showed an ammonium content of 0.42 mmol / g, sodium ion content below 5 ppm, and potassium ion content below 3 ppm. After standing at room temperature for 6 months, no precipitation or thickening was observed, indicating good storage stability.

[0056] Peelability performance test

[0057] The silica sol was directly sprayed onto the glass plate surface and dried at 60°C for 30 minutes to form a transparent protective film with a dry film thickness of approximately 0.03 mm. Adhesion was tested using a pull-off test at pH 7.0, and the adhesion was measured to be 2.8 MPa. After immersing in a sodium carbonate solution at pH 10 for 2 minutes, the edges of the protective film automatically peeled off, allowing it to be peeled off entirely without residue on the substrate surface.

[0058] PCB application testing

[0059] The aforementioned silica sol was sprayed onto the PCB board pad area and dried at 60°C for 30 minutes to form a protective film. After a reflow soldering process (peak temperature 250°C), the protective film remained intact. Immersion in a pH=10 sodium carbonate solution resulted in the complete peeling of the protective film, leaving no residue on the pad surface, and the solderability test was passed.

[0060] Example 2

[0061] An ammonium-type ultra-small particle size peelable silica sol is provided, and the raw materials are weighed as follows: 100g of hexa(ethylamino)disilane, 15g of polyvinyl alcohol (film-forming agent), 5g of stearic acid (release agent), 10g of sodium polyacrylate (dispersant), 200g of deionized water, and 200g of ethanol. The preparation steps are the same as in Example 1.

[0062] Product performance: The average particle size observed under transmission electron microscopy is 6.2 nm, the average particle size under dynamic light scattering is 6.8 nm, PDI=0.09, pH value is 8.8, and solid content is 29.5%. The adhesion is 2.5 MPa under neutral conditions and 0.08 MPa after alkaline treatment. It can be peeled off in whole sheets without leaving any substrate residue.

[0063] Example 3

[0064] An ammonium-type, ultra-small particle size, peelable silica sol is provided, with the following raw materials weighed as follows: 100g hexa(ethylamino)disilane, 20g polyvinylpyrrolidone (film-forming agent), 10g Shin-Etsu B-1000N silicone emulsion (release agent), 15g Dow Chemical ACUMER 9400 polycarboxylate (dispersant), 200g deionized water, and 200g ethanol. The preparation steps are the same as in Example 1.

[0065] Product performance: The average particle size observed under transmission electron microscopy is 4.8 nm, the average particle size under dynamic light scattering is 5.5 nm, PDI=0.07, pH value is 9.1, and solid content is 30.2%. The adhesion is 2.9 MPa under neutral conditions and 0.04 MPa after alkaline treatment. It can be peeled off in one piece without leaving any substrate residue.

[0066] Example 4

[0067] An ammonium-type ultra-small particle size peelable silica sol is provided, and the raw materials are weighed as follows: 100g of hexa(ethylamino)disilane, 30g of polyethylene glycol (film-forming agent), 8g of BASF WE-6 wax emulsion (release agent), 20g of polyethylene glycol ether (dispersant), 200g of deionized water, and 200g of ethanol. The preparation steps are the same as in Example 1.

[0068] Product performance: The average particle size observed under transmission electron microscopy is 5.5 nm, the average particle size under dynamic light scattering is 6.1 nm, PDI=0.10, pH value is 8.7, and solid content is 28.9%. The adhesion is 2.3 MPa under neutral conditions and 0.10 MPa after alkaline treatment. It can be peeled off in one piece without leaving any substrate residue.

[0069] Example 5

[0070] An ammonium-type, ultra-small particle size, peelable silica sol is provided, with the following raw materials weighed as follows: 100g hexa(ethylamino)disilane, 25g hydroxyethyl cellulose (film-forming agent), 12g LOXIOL®112 (release agent) from Emery Oleochemicals, 12g alkylphenol polyoxyethylene ether (dispersant), 200g deionized water, and 200g ethanol. The preparation steps are the same as in Example 1.

[0071] Product performance: The average particle size observed under transmission electron microscopy is 4.2 nm, the average particle size under dynamic light scattering is 4.9 nm, PDI=0.08, pH value is 9.2, and solid content is 30.5%. The adhesion is 3.0 MPa under neutral conditions and 0.03 MPa after alkaline treatment. It can be peeled off in whole pieces without leaving any substrate residue.

[0072] Example 6

[0073] The effect of reaction temperature on product performance was investigated. Reactions were carried out at 20°C, 30°C, 40°C, 50°C, and 60°C, respectively, using the same raw material ratio as in Example 1, with other conditions remaining constant.

[0074] The results showed that stable silica sols with particle sizes of 2-7 nm could be obtained within a reaction temperature range of 20-60℃. Specifically, a reaction at 20℃ required 240 minutes to achieve complete conversion, yielding a product particle size of 6.5 nm; a reaction at 40℃ required 120 minutes, yielding a product particle size of 4.5 nm; and a reaction at 60℃ required 60 minutes, yielding a product particle size of 3.8 nm. Considering both reaction efficiency and particle size control, a reaction temperature of 40-50℃ was optimal.

[0075] Example 7

[0076] The effect of different types of alcohol solvents on product performance was investigated. Methanol, ethanol, and isopropanol were used as solvents, and the reactions were carried out according to the raw material ratios and preparation steps of Example 1.

[0077] The results showed that stable silica sols could be obtained from all three solvents. Ethanol produced the smallest particle size (4.5 nm) and the best dispersibility. Methanol had a slightly faster reaction rate but a slightly larger particle size (5.8 nm). Isopropanol produced a slightly slower reaction rate but a moderate particle size (5.2 nm). Considering all factors, ethanol was the preferred solvent.

[0078] Comparative Example 1 (without film-forming agent)

[0079] Weigh the following raw materials according to the following weights: 100g hexa(ethylamino)disilane, 8g sodium stearate (release agent), 15g sodium polyacrylate (dispersant), 200g deionized water, and 200g ethanol. The preparation steps are the same as in Example 1.

[0080] During the reaction, the product showed no obvious abnormalities. When the resulting silica sol was sprayed onto a glass plate surface and dried at 60°C for 30 minutes, the coating became powdery after drying and failed to form a continuous protective film, making adhesion testing impossible. This indicates that the lack of a film-forming agent resulted in poor film-forming properties, failing to meet temporary protection requirements.

[0081] Comparative Example 2 (without release agent)

[0082] Weigh the following raw materials according to the specified weights: 100g hexa(ethylamino)disilane, 25g polyvinyl alcohol (film-forming agent), 15g sodium polyacrylate (dispersant), 200g deionized water, and 200g ethanol. The preparation steps are the same as in Example 1.

[0083] Product performance: Transmission electron microscopy revealed an average particle size of 4.8 nm, while dynamic light scattering showed an average particle size of 5.5 nm. Adhesion was 3.5 MPa under neutral conditions and 2.8 MPa after alkaline treatment, failing to peel off completely, resulting in coating fragmentation and residue. This indicates that the lack of a release agent led to excessively strong bonding between the coating and the substrate interface, preventing the coating from achieving its peelable function.

[0084] Comparative Example 3 (without dispersant)

[0085] Weigh the following raw materials according to the specified weights: 100g hexa(ethylamino)disilane, 25g polyvinyl alcohol (film-forming agent), 8g sodium stearate (release agent), 200g deionized water, and 200g ethanol. The preparation steps are the same as in Example 1.

[0086] During the reaction, the reaction solution gradually became turbid, and a significant precipitate appeared after the reaction was completed. After the obtained product was allowed to stand for 24 hours, it showed layering and precipitation, and a stable colloid could not be obtained. This indicates that the lack of dispersant led to the agglomeration and precipitation of silica particles, rendering the product unusable.

[0087] Comparative Example 4 (Two-step method – prior art)

[0088] Referring to the method in existing patent document CN104725948A, sodium-type silica sol is first prepared: water glass ( 100g of a sodium silicate sol (25% content, modulus 3.2) was diluted with 200g of deionized water and passed through a cation exchange resin column to obtain a silicic acid solution. The pH was adjusted to 9.0 with sodium hydroxide, and the solution was heated under reflux at 90°C for 4 hours to obtain a sodium silicate sol with a particle size of approximately 20nm. Surface modification was then performed: 100g of the sodium silicate sol was mixed with 5g of 3-aminopropyltriethoxysilane and stirred at 60°C for 2 hours to obtain a modified silicate sol. Finally, 50g of the modified silicate sol was mixed with 50g of polyurethane emulsion and stirred until homogeneous to obtain a peelable coating.

[0089] The obtained coating was sprayed onto the surface of a glass plate and dried at 60°C for 60 minutes, resulting in a dry film thickness of approximately 0.12 mm. Under neutral conditions, the adhesion was 2.2 MPa; after alkaline treatment, the adhesion decreased to 1.8 MPa, making complete peeling impossible. Ion chromatography determined the sodium ion content to be 150 ppm. Storage stability testing showed that stratification occurred after one month of standing at room temperature. This indicates that the existing two-step process is complex, has a long reaction time (over 6 hours in total), and the resulting product contains residual metal ions, exhibits poor peelability, and suffers from poor storage stability.

[0090] Comparative Example 5 (Comparison of different particle sizes)

[0091] Following the raw material ratio of Example 1, silica sols with different particle sizes were prepared by changing the reaction conditions, and the effect of particle size on peelability was investigated. By controlling the reaction temperature and reaction time, silica sols with particle sizes of 2-7 nm (Example 1), 8-12 nm, 13-18 nm, and 19-25 nm were prepared, respectively.

[0092] The results show that for silica sol with a particle size in the range of 2-7 nm, a dry film thickness of 0.03 mm is sufficient for complete peeling; for particle sizes in the range of 8-12 nm, a dry film thickness of 0.06 mm is required; for particle sizes in the range of 13-18 nm, a dry film thickness of 0.10 mm is required; and for particle sizes in the range of 19-25 nm, even a dry film thickness of 0.12 mm is insufficient for complete peeling, and the coating becomes brittle. This indicates that ultra-small particle size (2-7 nm) is a key factor in achieving peelable thin layers.

[0093] Comparative Example 6 (using unsubstituent silicon source)

[0094] Weigh the following raw materials by weight: 100g tetraethoxysilane (TEOS), 25g polyvinyl alcohol (film-forming agent), 8g sodium stearate (release agent), 15g sodium polyacrylate (dispersant), 200g deionized water, and 200g ethanol. The preparation steps are the same as in Example 1.

[0095] During the reaction, the reaction rate was extremely slow. After stirring at room temperature for 4 hours, the reaction system remained a clear and transparent liquid with no obvious silica sol formation. Adding 5g of ammonia (28%) as a catalyst initiated the reaction, resulting in an opalescent appearance. Continuing the reaction for another 2 hours yielded silica sol. Spraying the obtained silica sol onto a glass plate surface and drying at 60℃ for 30 minutes resulted in a white, opaque coating with poor film-forming properties; cracks appeared even at a dry film thickness of 0.08mm. The adhesion was 1.2MPa under neutral conditions and 0.9MPa after alkaline treatment, making complete peeling impossible.

[0096] Comparative Example 7 (using monosubstituted aminosilanes)

[0097] Weigh the following raw materials according to the following weights: 100g of 3-aminopropyltriethoxysilane (APTES), 25g of polyvinyl alcohol (film-forming agent), 8g of sodium stearate (release agent), 15g of sodium polyacrylate (dispersant), 200g of deionized water, and 200g of ethanol. The preparation steps are the same as in Example 1.

[0098] During the reaction, APTES hydrolyzes rapidly, causing the reaction solution to quickly become turbid and exhibiting significant exothermic activity. After the reaction is complete, the product is translucent, and precipitation occurs after standing for 24 hours. The resulting silica sol is sprayed onto a glass plate surface and dried at 60°C for 30 minutes. The coating is translucent, with moderate film-forming properties; fine cracks appear when the dry film thickness is 0.05 mm. The adhesion is 2.2 MPa under neutral conditions, but only 1.5 MPa after alkaline treatment; the coating crumbles and cannot be peeled off completely.

[0099] Comparative Example 8 (using disilane substituted with monoethylamino)

[0100] Weigh the following raw materials by weight: 100g mono(ethylamino)disilane, 25g polyvinyl alcohol (film-forming agent), 8g sodium stearate (release agent), 15g sodium polyacrylate (dispersant), 200g deionized water, and 200g ethanol. The preparation steps are the same as in Example 1.

[0101] During the reaction, the reaction rate was moderate, and the product was translucent with no obvious precipitation. The obtained silica sol was sprayed onto a glass plate surface and dried at 60°C for 30 minutes. The coating was translucent, and fine cracks appeared when the dry film thickness was 0.06 mm. The adhesion was 2.0 MPa under neutral conditions and 0.8 MPa after alkaline treatment. The coating partially fractured, and the peel integrity was poor (peel area approximately 60%).

[0102] The performance and test results of the above embodiments and comparative examples are summarized in Table 1.

[0103] As can be seen from Examples 1-5, this invention uses hexa(ethylamino)disilane as the sole silicon source, combined with film-forming agents, release agents, and dispersants, to synthesize silica sols via a one-step method. The resulting silica sols exhibit particle sizes ranging from 2-7 nm, with narrow particle size distribution, uniform dispersion, and good storage stability. These silica sols can be directly used as peelable temporary protective coatings. Under neutral conditions, their adhesion is moderate (2.3-3.0 MPa), meeting the protection period requirements. After alkaline treatment, the adhesion drops sharply to below 0.10 MPa, allowing for complete peeling without substrate residue.

[0104] As can be seen from Comparative Examples 1-3, film-forming agents, release agents, and dispersants are all indispensable. The absence of a film-forming agent prevents film formation; the absence of a release agent prevents the coating from being peeled off; and the absence of a dispersant leads to particle aggregation and precipitation. The synergistic effect of these three components is key to achieving good film formation and peelability.

[0105] As can be seen from Comparative Example 4, the existing two-step process is complex, has a long reaction time, and the resulting product contains metal ion residues, has poor peelability, and poor storage stability, which are obviously inferior to the one-step method of this invention.

[0106] As can be seen from Comparative Example 5, particle size is a crucial factor affecting peelability. This invention controls the particle size within an ultra-small range of 2-7 nm, which is key to achieving thin-layer peelability. Compared to conventional particle size silica sol, ultra-small particle size silica sol has a larger specific surface area and higher surface activity, resulting in a denser film. Complete peeling can be achieved with thinner coating thicknesses, significantly reducing coating consumption.

[0107] As can be seen from Comparative Examples 6-8, the number of ethylamino substituents has a decisive influence on the particle size control and peelability of silica sol: the silica source with zero ethylamino substituents (Comparative Example 6, tetraethoxysilane) lacks autocatalytic ability and requires the addition of an additional catalyst to carry out the hydrolysis-condensation reaction. Furthermore, the resulting product has a large particle size (45 nm), a wide distribution, poor film-forming properties, and cannot achieve peelability. With the increase of the number of ethylamino substituents, the silica sol particle size gradually decreases: the monosubstituted (Comparative Examples 7 and 8) particle size is approximately 12-18 nm, while the hexasubstituted (Example 1) particle size is only 4.5 nm. This indicates that the steric hindrance effect of ethylamino is a key factor in inhibiting the excessive growth of silica particles; the more substituents, the stronger the steric hindrance effect, and the more precise the particle size control. Smaller particle sizes result in denser films, and a more significant decrease in adhesion after alkali treatment. The silica sol (particle size 4.5 nm) prepared by hexa(ethylamino)disilane of this invention has an adhesion as low as 0.05 MPa after alkali treatment, which is much lower than that of monosubstituted (0.8-1.5 MPa). It has the best peeling effect and can achieve peeling without residue on the whole piece.

[0108] In summary, this invention achieves a one-step synthesis of ammonium-type ultra-small particle size peelable silica sol using hexa(ethylamino)disilane as the silicon source. Leveraging the autocatalytic ability and multiple steric hindrance effects brought by its multifunctional ethylamino structure (six ethylamino substituents), it simultaneously imparts pH-responsive peelable functionality to the ultra-small particle size silica sol, demonstrating significant inventiveness and technological advancement. The process is simple, catalyst-free, and leaves no metal ion residue, allowing it to be directly used as a peelable temporary protective coating. Compared to the multi-step process of "synthesis + modification + compounding" in existing technologies, the one-step process significantly simplifies the production process, shortens reaction time, reduces energy consumption and cost, and improves batch stability. The resulting silica sol can be directly used as a peelable temporary protective coating, particularly suitable for temporary protection of electronic components, automotive paint, optical components, and precision metal processing, exhibiting broad application prospects and commercial value.

[0109] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An ammonium-type ultra-small particle size exfoliable silica sol, characterized in that, It is obtained by hydrolyzing hexa(ethylamino)disilane in an alcohol-water solvent. The silica sol contains additives, including dispersants, film-forming agents and release agents; the dispersant is a polymeric dispersant.

2. The silica sol according to claim 1, characterized in that, The silica nanoparticles in the silica sol have a particle size of 2-7 nm.

3. The silica sol according to claim 1, characterized in that, The silica sol is composed of, by weight, 100 parts hexa(ethylamino)disilane, 10-50 parts film-forming agent, 1-20 parts release agent, and 5-30 parts dispersant.

4. The silica sol according to claim 1, characterized in that, The alcohol is selected from one or more of methanol, ethanol, and isopropanol; And / or, the dispersant is selected from one or more of sodium polyacrylate, polycarboxylate, polyethylene glycol ether, and alkylphenol polyoxyethylene ether; And / or, the film-forming agent is selected from one or more of polyvinyl alcohol, polyvinylpyrrolidone, polyethylene glycol, and hydroxyethyl cellulose; And / or, the release agent is selected from one or more of fatty acid salts, fatty acid esters, silicone emulsions, and wax emulsions.

5. The method for preparing silica sol according to any one of claims 1-4, characterized in that, step include: S1. Disperse hexa(ethylamino)disilane, film-forming agent, release agent and dispersant in an alcohol solvent to form a first mixture; S2. Mix water with an alcohol solvent to form a second mixture; S3. Under stirring conditions, the second mixture is mixed with the first mixture, and the reaction is carried out under stirring; S4. After the reaction is complete, remove part of the solvent to the target solid content to obtain ammonium-type ultra-small particle size silica sol.

6. The preparation method according to claim 5, characterized in that, In step S1, the dispersion process employs ultrasonic dispersion; and / or, in step S3, the reaction conditions are a reaction at 20-60℃ for 60-240 min.

7. The preparation method according to claim 5, characterized in that, In step S4, the solid content is 20-40 wt%.

8. A peelable protective coating, characterized in that, The silica sol comprising any one of claims 1-4, or silica sol prepared by any one of claims 5-7.

9. The application of the silica sol according to any one of claims 1-4, or the silica sol prepared by any one of claims 5-7, in temporary protection, the application including temporary protection of electronic components, automotive paint, optical components, or precision-machined metal products.

10. A temporary protection method, characterized in that, The method includes coating an ammonium-type ultra-small particle size silica sol onto the surface of a substrate and drying it at 40-80°C for 10-60 minutes to form a protective layer; wherein the ammonium-type ultra-small particle size sol is the silica sol described in any one of claims 1-4, or the silica sol prepared by the preparation method described in any one of claims 5-7.

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